Session NP01 - Poster Session IV.
POSTER session, Tuesday evening, March 23
Exhibit Hall, GWCC

[NP01.01] Production of oxygen anions in the K-shell photoionization of CO

High-resolution measurements of the photofragmentation of CO in the vicinity of the C and O K edges is reported. In particular, the production of O- has been observed near both edges. Although negative ions have been seen previously in low-resolution core-hole measurements, the new results, with vibrational resolution, should be valuable for comparison to detailed spectroscopic calculations. Furthermore, there is evidence for post-collision interaction effects in cation and anion yields just above the K-edges.

[NP01.02] High-Energy Valence Photoionization of Argon: Effect of Interaction with 3s Photoionization Channels

Electron time-of-flight measurements on argon in the photon energy range 600-850 eV were analyzed to determine the anisotropy parameter \beta and the ratio of the intensities of the 3p and 3s lines. Our measurements confirm the finding that the independent particle model is inadequate to explain photoionization of nl (l>0) electrons even at energies well above the ionization threshold.

[NP01.03] Beyond the Dipole Approxiamtion: Angular - Distribution Effects in the 1s Photoemission from Small Molecules

Over the past two decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Our experiments on the 1s inner shells of small molecules at relatively low photon energies (<1000 eV) show strong non-dipole effects. They are significant and measurable at energies close to threshold, in conflict with a common assumption that the dipole approximation is valid for photon energies below 1 keV. The effect is attributed on basis of concomitant theoretical analysis to the displacement of the 1s charge distributions from the molecular center of mass, providing a much larger effective charge distribution of molecular dimensions consequent of rotational averaging over which the phase of the incident radiation can vary significantly.

[NP01.04] Post Collision-Interaction Effects in H_2S

Ion time-of-flight mass spectroscopy was used to study the relaxation dynamics of H_2S following photoexcitation in the vicinity of the S-K threshold (\approx2.5 keV). The data was analyzed to obtain quantitative observations of molecular fragmentation mediated by the post-collision interaction between a photoelectron and an Auger electron.

[NP01.05] Resonant Auger studies in Kr 3d3/2,5/2-1np states using angle-resolved electron imaging spectroscopy

An extensive and detailed mapping of the resonant Auger decay of all the photoexcited 3d3/2,5/2-1np states in Kr has been performed using angle resolved two-dimensional photoelectron spectroscopy at the Advanced Light Source. This has allowed us to obtain angular distributions, spectator and shake probabilities for the Kr 3d-1np --> 4s-14p-1(1P)mp + e- (n = 5-9, m = 5-11) resonance Auger decays. The results show that the spectator-core coupling is strong at lower n (n = 5,6) but it lessens for higher n, with a shake-up of m = n+1 preferred. The observed trend is in good agreement with the previous experimental and theoretical spectator and shake probabilities for these transitions and also with the analogous decay to the 4s24p4mp states (Aksela et al. [1]). However, no prior angular distribution measurements for the Kr 3d-1np -->4s-14p-1(1P)mp + e- (n = 5-9, m = 5-11) resonant Auger decay has been reported. These are found to also show similar behavior to the decay to the 4s24p4mp states.

[1] H. Aksela, M. Kivilompolo, E. Nmmiste, and S. Aksela Phys. Rev. Lett. 25, 4970 (1997).

[NP01.06] First spin-resolved gas-phase studies at the ALS

One way to accomplish a so-called complete photoionization or Auger electron emission experiment is to use circularly polarized radiation to determine the spin polarization vector of the outgoing electrons. The new EPU beamline of the ALS will deliver highly circularly polarized light in the important photon energy range of 100-1000 eV. To perform spin-resolved gas-phase experiments, we have developed a new apparatus consisting of a time-of-flight electron energy analyzer combined with a retarding field Mott detector. In a first investigation, we have measured the spin polarization of the Xe 5p^-1\enspace ^2P_1/2,3/2 and 4d^-1\enspace ^2D_3/2,5/2 photolines parallel to the photon beam. The measurements were performed with linearly polarized light. Our main objective for the near future is to study the spin polarization of photo- and Auger electrons of atomic and molecular gas-phase targets after photoionization with circularly polarized radiation.

[NP01.07] Rotationally resolved spectra of the 3p \; ^1\Sigma^+_g gerade Rydberg state of acetylene.

Although the gerade Rydberg states of acetylene (C_2H_2) are of interest to many, information on these states has remained limited due to their predissociative character and the prohibitive selection rules for their excitation from the ground state. By using a two-color resonantly-enhanced, multiphoton ionization (REMPI) technique however, the gerade Rydberg states may be probed in a state-selective manner that allows the observation of their rovibronic structure. As part of an ongoing study of the gerade Rydberg states in acetylene, the rotational structure of the ^1\Sigma^+_g component of the 3p state, the lowest member of the gerade Rydberg complex, has been investigated. Analysis of the rotationally resolved spectra corresponding to transitions from the V^3_0 K^1_0 vibrational level of the intermediate \widetilde A \; ^1A_u electronic state to the 0^0 vibrational level of the 3p \; ^1\Sigma^+_g Rydberg state yields rotational constants and information on the geometry of the \widetilde X \; ^2 \Pi_u ground electronic state of the C_2H_2^+ ion. Several unexpected features are observed in the spectra and the possible implications of these observations on the assumed linear geometry of the state will be discussed.

[NP01.08] Multi-channel B-spline based K-matrix approach

A multi-channel B-spline based K-matrix approach for the multiple continua is presented as an extension of the B-spline based configuration interaction approach (BSCI) for a single ionization channel. [1] Applications to photoionization of He to multiple continua from the ground and bound excited states will be presented. Results of our calculation agree well with other existing theoretical and experimental results.

This work is supported by the NSF.

[1] T. N. Chang, in "Many-body Theory of Atomic Structure and Photoionization", edited by T. N. Chang (World Scientific, Singapore, 1993), p. 213

[NP01.09] Photoabsorption of Mg above the 3p threshold

We present the results of a joint experimental and theoretical study of the autoionization structures of Mg atom at energies above the 3p~^2P threshold. The absolute photoabsorption cross sections are determined by measuring the light attenuation through a heatpipe using the synchrotron radiation. [1] The observed spectra are compared with the theoretical spectra using a B-spline based multi-channel K-matrix approach. In particular, the "hidden" 3d4p~^1P resonance missing from the observed Mg ground state photoabsorption spectrum is analyzed in detail. Theoretical spectra from bound excited states will also be presented.

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This work is supported in part by the NSC in Taiwan and the NSF in the US.

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[1] C. C. Chu, H. S. Fung, H. H. Wu, and T. S. Yih, J. Phys. B31, 3843 (1998).

[NP01.10] Observation of the 3snd ^1D to the 3png ^1F Autoionization Resonances in Mg

Intense ultranarrow resonances have been observed in the photoionization of Mg from the excited 3snd ^1D states to the doubly-excited 3png ^1F autoionization states using stepwise laser excitation and time-of-flight mass spectrometry detection. These resonances are the result of the 3pg configuration series interacting with the 3pd configuration series and mixing substantially with the 3sf ^1F continuum, acquiring a large strength for the normally weak 3snd-3png transition. Comparison of the measured line positions and transition widths with results derived from the B-spline-based configuration interaction calculations are presented(T.N. Chang and X. Tang, Phys. Rev. A 38), 1258 (1988); T.K. Fang, Atomic Photoionization dominated by doubly excited resonances, Ph. D Thesis, USC, 1997..

[NP01.11] Photoionization of Multiply-Charged Positive Ions using an ECR Ion Source and Synchrotron Radiation.

Experimental data on the interaction of the electromagnetic radiation with ions are very scarce, because of the experimental difficulties to confine a plama of highly-charged ions in a small volume for a long enough period of time. A new experimental set-up has been built to study photoionization processes in multiply-charged ions using synchrotron radiation emitted from the SU6 undulator of the Super-ACO storage ring in Orsay. Ions are produced in a permanent-magnet 10 Ghz-ECR ion source, then a Wien filter allow us to select the ionic species to be studied. After deflection by an electrostatic quadrupole, the ion beam is merged with the monochromatic photon beam. The ions which are produced in the interaction of the photon beam with the incident ion beam are analyzed by ionic spectrometry. The characteristics of the experiment will be described and preliminary results will be presented at the conference.

[NP01.12] A variable matter wave beam splitter

We demonstrate a robust variable beam splitter for Ne atoms based on a modified scheme of stimulated Raman adiabatic passage (STIRAP) in the form of a tripod linkage. A pump laser couples the initially populated level (the metastable J = 0 state) to an intermediate one. Two Stokes radiation fields (same frequency but different circular polarizations) couple the intermediate state to the m = + 1 and m = - 1 states of the J = 2 level.

The interaction with both Stokes fields begins earlier than the interaction with the pump field. When the time dependence of the Stokes interactions is idential, the splitting ratio is 50:50. The splitting ratio can be controlled by the time delay between the interaction of one Stokes field relative to the other. The features of this variable beam splitter, and its robustness, are determined by the controlled nonadiabatic couplings between the two dark states of the systems.

[NP01.13] Single Ionization of He and H^- by Compton Scattering.

The differential cross section per unit energy tranfer for single ionization of He and H^- is calculated and compared to the corresponding Compton cross section by one and two free electrons. The incoming photon energy varies from 6 to 40 KeV. For the initial state we use fully correlated configuration-interaction type wave functions expanded in terms of Sturmian functions, using as many as 35 terms. For the final state we use uncorrelated wave functions. Our results show that the He cross section is comparable to the cross section by two free electrons, while the H^- cross section is between the cross section for one and two free electrons. Our results are in a range of energy transfer larger than the atomic threshold, and extending a little beyond the binary encounter limit. Near threshold only a few partial waves contribute in contrast to higher energy transfer where many partial waves contribute, unlike photoannhilation.

[NP01.14] Quantitative Measurements of Dynamic Partitioning of Angular Momentum of Valence Electrons During the Autoionizion of Ar^**

We have produced the autoionizing states Rydberg states \3p^4[^1S]4s\^2S-np of Ar^** using linearly polarized light of high resolution at the Advanced Light Source Synchrotron. For this state the angular momentum and any resulting magnetic substate distributions (alignment) reside entirely in the outer np Rydberg electron, with the ^2S core being spherically symmetric. In this case the np electron is in an m =0 state since it is formed with linearly polarized light. By measuring the polarized fluorescence of the Ar^+\3p^4[^3P]4p\^2D^O(J=5/2) state that is formed in the autoionization process, we have determined the alignment of A(J) of the J=5/2 state. Using standard angular momentum recoupling procedures(K.W. McLaughlin, et. al., Phys. Rev. Lett. 81), 289 (1998)., we have determined the alignments A(L) of the L=1 core and A(\ell) of the 4p electron. Our results indicate a significant redistribution of the angular momentum that originally resided in only the np electron to angular momentum of the 3p and 4p electrons, as well as the free electron.

[NP01.15] Analysis of 2l2l^\prime n^\prime \primel^\prime \prime resonances in the photoionization of 1s^22p excited Lithium

Total and partial cross sections for photoionization of the 1s^22p ^2P^o lithium excited state have been calculated using the R-matrix code. We decomposed the total and partial cross section into its component SL\pi final states to determine the resonance positions. In addition we used the eigenphase derivative technique (QB method) to obtain 19 series of 2l2l^\prime n^\prime \primel^\prime \prime resonance positions and effective quantum numbers, n = n-\mu_n for n as high as 22. We found a number of series perturbations among the resonances. The strong resonances and resonance series without perturbations converge to a constant quantum defect quickly; these include 2s2p(^1P)np ^2S^e, 2p^2(^1S)ns ^2S^e, 2s2p(^1P)np ^2P^e, 2s2p(^1P)np ^2D^e. The strong resonances are found to perturb the weak ones. For example, the weak 2s^2(^1S)7d ^2D^e resonance is perturbed by the stronger 2s2p(^3P)4p ^2D^e so that the quantum defect for the 2s^2(^1S)7d ^2D^e does not follow the rest of series. Further this weak resonance has ``borrowed'' a bit of the oscillator strength of the strong one, making it more stronger than the other members of the series. Similarly 2s^2(^1S)10s ^2S^e is perturbated by the strong ``neighbor'' 2s2p(^3P)4p ^2S^e. Owing to these strong perturbations, the quantum defect for weaker series converge only for very high n.

[NP01.16] Inner-shell Photoabsorption of X-Rays by Atomic Carbon and Nitrogen

Cross sections for inner-shell photoabsorption by atomic carbon and nitrogen, are being calculated with multi-configuration target wave functions using the R-matrix approach in the soft x-ray energy range. Various direct and Auger auto-ionizing processes contributing to the cross sections are analyzed and discussed. In the vicinity of the carbon and nitrogen K-edges the theoretical cross section results show a wealth of structure. Analogous calculations for atomic oxygen showed good agreement with recent synchrotron measurements (B M McLaughlin and K P Kirby J. Phys. B. 31), 4991 (1998).. For carbon and nitrogen, little experimental data is available, but accuracies similar to those for oxygen are expected and comparisons are made whenever possible.

[NP01.17] Comparison of the Photoelectron Angular Distributions of C^-, Si^-, and Ge^- at Visible Photon Wavelengths

The photoelectron angular distributions of C^-, Si^-, and Ge^- have been measured at discrete visible photon wavelengths. The measurements were performed at the University of Nevada, Reno. Negative ion beams of carbon, silicon, and germanium were extracted from a cesium-sputter negative ion source, and mass analyzed using a 90^\circ bending magnet. The negative ion beam of interest was then crossed at 90^\circ with a photon beam from a cw 25-Watt Ar^+ laser. The photon beam was linearly polarized (\geq10^5:1) and the polarization vector was rotated with respect to the photoelectron collection direction with a double Fresnel rhomb. The resulting photoelectrons were energy analyzed with a 160^\circ spherical-sector spectrometer. Photoelectron yields, Y(\theta), were collected at discrete angles and then fit to the function Y(\theta) \propto \frac\sigma4\pi (1 + \beta P_2 (\cos\theta)) to determine the asymmetry parameter, \beta. The spectral dependence of the photoelectron asymmetry parameters of C^-, Si^-, and Ge^- are compared to each other and fit to a straightforward model of the asymmetry parameter for photodetachment of p-electrons(D. Hanstorp et al.), Phys. Rev. A 40, 670 (1989)..

[NP01.18] Measurement of the Electron Affinities of Indium and Thallium

The electron affinities of indium and thallium were measured in separate experiments using the laser-photodetachment electron spectroscopy technique. The measurements were performed at the University of Nevada, Reno. Negative ion beams of both indium and thallium were extracted from a cesium-sputter negative ion source, and mass analyzed using a 90^\circ bending magnet. The negative ion beam of interest was then crossed at 90^\circ with a photon beam from a cw 25-Watt Ar^+ laser. The resulting photoelectrons were energy analyzed with a 160^\circ spherical-sector spectrometer. The electron affinity of In(^2P_1/2) was determined(W. W. Williams et al.), Phys. Rev. A 58, 3582 (1998). to be 0.404\pm0.009 eV and the electron affinity of thallium was determined to be 0.377\pm0.013 eV. The fine-structure splittings in the ground states of the negative ions were also determined. The experimental measurements will be compared to several recent theoretical predictions.

[NP01.19] Identification of Two-Electron Resonances in He^- (1s2s2p ^4P^o) Photodetachment

We present eigenchannel R-matrix results for He^- photodetachment partial cross sections in the energy region above the n=4 thresholds, stimulated by recent measurements of the He(1s3p ^3P) partial cross section in which a large number of unidentified resonances are found(I. Yu. Kiyan, U. Berzinsh, D. Hanstorp and D.J. Pegg, Phys. Rev. Lett. 81), 2874 (1998).. Since the energy region considered is much lower than the 1s excitation energy, we treat He^- as a quasi two-electron system. Owing to the three final state channels which contribute to the He(1s3p ^3P) partial cross section, it is difficult for experiment to identify the resonances. Our calculations give good overall agreement with the experimental measurements. We also identify all resonance structures and demonstrate their effects on the partial cross sections, even though many of them are not well resolved in the measurements. Propensity rules for populating certain doubly-excited states are discussed, as well as the induced polarization model proposed in the experimental paper^1. Work supported in part by the U.S. Department of Energy, Division of Chemical Sciences, Office of Science under Grant No. DE-FG03-96ER14646.

[NP01.20] Progress Toward a Sympathetically-cooled Positron Plasma

We plan to use laser-cooled ^9Be^+ ions to trap and sympathetically cool positrons in a cylindrical Penning trap. High energy positorns from a Na^22 source pass through a ^9Be^+ plasma before striking a Cu(111) single crystal moderator. As the positrons pass back through the plasma, axial momentum can be converted to perpendicular momentum and the positrons can be temporarily trapped. The positrons can then cool by cyclotron radiation and sympathetic cooling with the cold ^9Be^+ and become permanently trapped. Estimates of the trapping efficiency will be discussed. We have been able to trap \sim 1 mm long, \sim 10^10 cm^-3 ^9Be^+ which we think will be useful for traping positrons. In this experiment we have also observed non-sheroidal plasma shapes due to deviations from a quadratic trapping potential. These deviations become pronounced when a plasma is axialy thin (radial size is much larger then axial thickness). The measured plasma shapes will be compared with a global thermal equlibrium computation. (R.L. Spencer, BYU, private comunications)

[NP01.21] Mode Studies of Laser-Cooled Be^+ Ion Plasmas in a Penning Trap.

We trap up to 10^6 Be^+ ions in a Penning trap and utilize laser cooling to reduce the ion temperature to less than 5 mK. In this regime, the ions are an excellent experimental realization of the one-component plasma (OCP). The plasma shape is spheroidal and analytic solutions exist for all of the modes.(D. H. E. Dubin Phys. Rev. Lett.,) 66 2076 (1991). We non-destructively measure the plasma shape from the ion fluorescence induced by the cooling laser. Plasma modes are excited with sinusoidally time-varying potentials applied to the trap electrodes, and imaged by changes in the ion resonance fluorescence produced by Doppler shifts from the coherent velocities of the mode. A comparison with theory of measurements of mode eigenfunctions and frequencies shows good agreement. The damping of the modes can be measured by sweeping the frequency of the perturbation through a mode frequency, while measuring the mode's resultant amplitude and phase. Preliminary measurments show damping rates consistent with the rates of viscous damping seen in simulations; the scaling of the damping with temperature and particle number will be presented.

[NP01.22] Resonance Fluorescence of Two Closely Spaced Trapped Ions

The distance between two trapped ions can be on the scale of a wavelength of the atomic transition. This opens a relatively new regime of quantum optics, in which the properties of the resonance fluorescence can be measurably modified. For example, super- and sub-radiance(R.H. Dicke, Phys. Rev. \textbf93), 99 (1954). has been demonstrated in two barium ions confined in a spherical Paul trap(R.G. DeVoe and R.G. Brewer, Phys. Rev. Lett. \textbf76), 2049 (1996).. With two strontium ions tightly confined in a linear Paul trap, this effect can be made more pronounced. Also, the dependence of the transition frequency on ion spacing(Th. Richter, Optica Acta \textbf30), 1769 (1983). may be measured, and population transfer between two ions(H. Dehmelt, X. Zhao, N. Yu, and W. Nagourney, Proc. Natl. Acad. Sci. USA \textbf93), 6861 (1996). may be demonstrated. In the process of setting up these experiments, other experiments may be done in a less tightly confining trap. I will describe progress in the developement of the laser system and ion trap construction for these experiments.

[NP01.23] Velocity-Resonant Precession

We have measured Velocity Selective Resonances (vsr)(S-Q. Shang et al. Phys. Rev. Lett. 65), 317, (1990) that are narrower than the few-recoil widths expected from sub-Doppler laser cooling theory(P. van der Straten et al., Phys. Rev. A47), 4160, (1993). Consider a circularly polarized standing wave with \veck-vectors along \hatz, and a B-field along \hatx. Atoms with M_J = J at the standing wave node (no excitation), that travel a distance \lambda/2 in one Larmor precession time, arrive at the antinode with M_J = -J where excitation by the strong light field is minimized by the small Clebsch-Gordan coefficent. This speed is v = ømega_z/2k \equiv v_vsr, exactly the condition for vsr. Just like dark states, atoms with v = v_vsr experience a minimal excitation rate, so they undergo less momentum diffusion, and thus collect in a narrow range of velocities. Atoms with speeds v \neq v_vsr scatter light preferentially from one beam or the other and thus experience a force pushing them toward v_vsr. Thus the Zeeman coherences among ground state sublevels produce quasi-dark states (related to ground state quantum beats). This interpretation is supported by calculations of the lifetimes of the quasi-dark states and by QMCWF calculations. These permit analysis of the cooling dynamics as well as of the steady state, and also identification of magnetic dipole autocorrelation functions.

[NP01.24] Precise Measurements of the Bichromatic Force

The limit on the magnitude of radiative forces of \hbar k \gamma/2 imposed by the spontaneous decay rate \gamma of the excited state can be overcome by coherent control of the momentum exchange between atoms and the light field. This can be implemented with light beams containing two frequencies in the form of rectification of the dipole force, but its velocity range is limited to \sim \gamma/k. Recently there has been a demonstration of beam slowing by the very strong bichromatic force whose velocity range is limited only by laser power(J. Söding et. al, Phys. Rev. Lett. 78), 1420 (1997). We have made precise measurements of this bichromatic force by deflecting a thermal beam of Rb atoms. We used a standing wave of circularly polarized light whose components had carefully chosen relative phases, amplitudes, and frequency differences. Our results show its extremely large magnitude and velocity range, and also show that its velocity dependence near the edge of the range is suitable for atomic beam slowing and laser cooling. Our measurements have corroborated various models and calculations of this bichromatic force in great detail.

[NP01.25] Dipole-force atom traps using Laguerre-Gaussian modes of diode lasers

Bose-Einstein condensation (BEC) in weekly-interacting gasses may lead to important advances in atomic physics: better atom interferometers, more accurate and precise atomic clocks, and highly improved probes of atomic interactions. There is also considerable interest in BEC as a laboratory to study phenomena that might give new insights into strongly interacting systems such as superfluids and superconductors. A major step towards the realization of this goal is the creation and study of vortices and persistent currents, effects not yet observed in atomic gas condensates. We will present progress towards developing a new set of optical atom traps by transforming the Gaussian output mode of a diode laser into various Laguerre-Gaussian (LG) propagation modes using diffraction gratings. These modes exhibit the distinguishing characteristic of a note in the center of the intensity profile cross-section. Higher order LG modes have multiple radial nodes, allowing a wide variety of trap potential geometries. This can open the door to create effectively 1D and 2D confining potentials as well as toroidal traps that will allow new studies of BEC including the creation and stabilization of vortices and persistent currents.

[NP01.26] Atom Guiding by a Dark Hollow Laser Beam

A dark hollow laser beam(DHB) is generated by properly collimating the output beam of the LP_01 mode guided in the hollow-core optical fiber. The rubidium atoms are magneto-optically cooled and trapped, and then loaded into a blue-detuned DHB which propagates upwards and overlaps with atomic molasses. A near-resonant weak repumping beam is also added upwards. If the transverse kinetic energy of an atom is smaller than the optical potential of the blue-detuned DHB, the atom is reflected and guided along the DHB. We have observed the dependence of the flux of guided atoms on the detuning and intensity of DHB at a position 12 cm below the MOT. The cold guided atoms in the DHB will be directly coupled into the HOF without using a lens to enhance the phase space density of cold atoms inside the hollow-core fiber.

[NP01.27] Novel Atomic Funneling into a Hollow Optical Fiber

We have produced a continuous cold atomic beam from the magneto-optical trap in the simple pyramidal hollow mirror system and coupled it into a hollow-core optical fiber. To make the coupling efficiency higher, we use a novel atomic funnel with the dark hollow beam directly produced by the hollow-core optical fiber. We combine two LP_11 modes having node lines and polarization orthogonal to each other, so that the resulting mode has no nodes and can be used for efficient funneling atoms into the hollow optical fiber. The guided atoms will be used for atom lithography with a submicron-sized hollow-core optical fiber.

[NP01.28] Magneto-Optical Trap for On-line Fr Spectroscopy

We have constructed a second generation magneto-optical trap for on-line capture of radioactive francium at the Stony Brook Superconducting LINAC. We produce francium isotopes via the ^16,18O(^197Au,xn) or ^19F(^198Pt,xn) reactions, in the target room of the accelerator. We then extract and transport the activity using electrostatic optics to a different room where we neutralize and capture the atoms in a Magneto-Optical trap (MOT). Tests with Rb show greater than 90 percent transport efficiency, and we have delivered over 3 \times 10^6 Fr/sec to a Faraday cup in front of the trap. We are currently characterizing the MOT with a beam of stable Rb ions that follow the same path as that of the Fr. This new trap will function as the accumulating trap to fill a purely optical trap for further studies with Fr. The new possibility of working next to the Fr atoms, in contrast with our previous situation where we worked remotely, will permit direct optimization of the traps without remote control of the experiments. This work is supported by the NSF and REU supplements from the NSF.

[NP01.29] Compact Cold Atom Clock for Space Applications

Highly stable atomic frequency standards are of increasing importance for a variety of space applications, ranging from communication to navigation and time transfer to tests of fundamental science. We present a new design for a compact Cs beam atomic clock suitable for space applications and featuring a cold atomic beam source based on a single beam, conical mirror MOT with a hole at the apex to produce a low velocity high flux atomic beam. This cold atomic beam is then used in a laser-pumped Ramsey clock, with the clock signal derived from either a microwave C-field or alternatively by Raman resonance between the Ramsey fields. In order to reduce light shifts from the MOT light, the atomic beam is deflected and transversely cooled upon exiting the MOT's conical reflector. Initial numerical estimates indicate that a short term Allan varaince of \sigma_y(\tau)\approx3\times10^-14\tau^-1/2 should be achievable with this design. We will present our experimental progress towards a working frequency standard.

[NP01.30] Progress Towards Creating a Quantum Degenerate Fermionic System with Radioactive Rb Isotopes

Progress in trapping large numbers of radioactive ^82Rb atoms (\tau_1/2 ^[1] has opened up the possibility of studying quantum degenerate systems with fermionic Rb isotopes. Theoretical calculations indicate that the scattering length of ^84Rb/^87Rb and ^86Rb/^87Rb are large and positive, a desirable condition to achieve Fermi degeneracy through sympathetic cooling of ^84,86Rb (\tau_1/2 days, respectively) with evaporative cooled ^87Rb atoms. Recently, we have demonstrated the simultaneous trapping of ^85Rb and ^87Rb atoms in a TOP trap constructed for a beta-asymmetry measurement of polarized ^82Rb. The latest progress and plans in trapping a mixture of ^84, 86Rb/^87Rb for quantum degeneracy studies will be reported.

[1] R. Guckert, et al. PRA 58 R1637 (1998).

[NP01.31] GLACE: A Technology Demonstration Experiment for Laser Cooled Atomic Clocks in Space

We have been developing a laser-cooling apparatus for flight on the International Space Station (ISS), with the intention of demonstrating linewidths on the cesium clock transition narrower than can be realized on the ground. GLACE (the Glovebox Laser-cooled Atomic Clock Experiment) is scheduled for launch on Utilization Flight 3 (UF3) in 2002, and will be mounted in the ISS Glovebox platform for an anticipated 2--3 week run. Core technologies for this and other LCAP missions are being developed at JPL. Significant technical challenges in developing a space qualifiable laser cooling apparatus include reducing the volume, mass, and power requirements, while increasing the ruggedness and reliability in order to both withstand typical launch conditions and achieve several months of unattended operation. This work was performed at the Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration.

[NP01.32] Generation of a cold atom beam from a pyramidal magneto-optical trap

We have built an atomic beam source utilizing a simple and robust design based on the pyramidal trap geometry of Kim et al.\ (Opt.\ Lett.\ 22, 117 (1997)). Our design allows use of a single large diameter (\le20 cm) laser beam to obtain large capture rates of atoms from a background vapor. A small (1~mm diameter) hole in the retro-optic at the apex of the pyramid provides an extraction column for the atoms. We have operated the apparatus both as a magneto-optical trap (using an auxiliary plug laser beam), and as a cold atomic beam source.

The characterization of this large pyramidal beam source will be reported, including an investigation of scaling to very large (10--20cm) high power (1~W) laser beams which should allow significant improvements in atomic beam flux.

[NP01.33] Improved Loading and Lifetimes in a Far-Off Resonance Trap

We have confined large samples of Rb in deep far-off resonance traps (FORT's). Enhanced loading is achieved by using a magneto-optical trap (MOT) to cool atoms as they enter the FORT. We have investigated the dependencies of this cooling process on laser power and frequency, and characterized the trap temperatures and densities using both fluorescence and absorption imaging. In addition, intensity stabilization of the trap laser has been used to substantially increase the trap lifetime in certain regimes. These large FORT samples are transferred into a circularly-polarized FORT, described elsewhere at this meeting.

[NP01.34] Magnetostatic control of atoms near surfaces

We have demonstrated that a suitably magnetized surface can be used to retroreflect cold atoms. The evolution of an 18 \mu K cloud of ^85Rb atoms bouncing freely on a horizontal concave atom mirror was imaged directly up to the 14th bounce. Initially compact, the cloud is alternately collimated (odd bounces) and brought back to a focus (even bounces) when dropped from a height R/4 (R is the radius of curvature). An external uniform magnetic field added to the sinusoidal mirror field causes a corrugated potential from which the atoms bounce with increased angular spread. Varying the external field allowed us to control the shape of the reflected cloud. Magnetic surfaces can support the atoms against gravity. Additional electrostatic forces might then be used to manipulate the atoms in a horizontal plane.

[NP01.35] Experiments with single ytterbium ions

Trapped ions are now widely used in generating frequency standards, studying fundamental physics, and implementing quantum computation. In this proceeding, we report our initial experimental results with single trapped Yb^+ ions. We have observed resolved micromotion-sideband spectrum in an allowed transition and demonstrated that it can be conveniently used in micromotion reduction. In addition, we have made lifetime measurements in the both 4f^145d metastable states. Experimental design and progress toward cavity QED using the trapped ions will also be discussed.

[NP01.36] Two-atom dark states in electromagnetic cavities

We study the center-of-mass motion of two two-level atoms coupled to a single mode of an electromagnetic resonator. For the basic case of one atom being initially excited and the cavity mode in the vacuum state the atomic time evolution is found to be dominated by the appearance of quasi-dark states. These states, in which the initial excitation is stored in the internal atomic degrees of freedom and which possess a very small spread in momentum, are almost immune against photon loss from the cavity. We present an analysis of these states within and beyond the Raman-Nath approximation of atom optics.

[NP01.37] Radiative Properties of Confined Fermi Gases

We study the radiative behavior of a system of confined degenerate fermionic atoms. Using density matrix methods, we investigate the influence of quantum statistics on radiative lifetimes and the anisotropy of spontaneous emission profiles (Th. Busch et al. cond-mat/9805037 May 1998), including re-absorption of radiation within the trap.

[NP01.38] Linewidth of a single-atom laser

We investigate the linewidth of a single-atom laser. The system of interest is a single four-level atom, essentially stationary in an optical cavity. In previous work on this system (Y. Mu and C. Savage, Phys. Rev. A. 46, 5944 (1992).), (B. Jones, S. Ghose, P. Rice, and L. M. Pedrotti, submitted to Phys. Rev. A.).it has been shown that as \beta is increased, the photon statistics of this system has three regimes. For small \beta (less than 0.1) we have super-thermal light for all pump rates. As \beta increases to around 0.2 we find a peak in the photon number variance vs. pump, but this peak is much smaller and wider than in many-atom lasers with smaller \beta values. Finally, increasing \beta above 0.3 results in the emission of amplitude squeezed light.

We have calculated the output spectrum of our system in these different regimes. We find that the linewidth does not narrow with increase in pump strength in the low \beta regime. In the moderate \beta, semiclassical regime, there is a decrease in the linewidth with pump, along the lines of the usual Schawlow-Townes relation. In the high \beta regime, where the light is amplitude squeezed, we find that the linewidth decreases with pump, but is above the Schawlow-Townes limit.

[NP01.39] Laser-Generated Surface Acoustic Pulses: Nonlinear Elastic Properties and Adhesion Studies

Nanosecond surface acoustic wave (SAW) pulses excited by a focused laser beam in solid materials were investigated. The nonlinear transformation of these pulses is connected with the nonlinear elastic moduli of the material. The possibility to solve the inverse problem of the determination of the nonlinear moduli from the measurements of the observed waveforms is demonstrated. Another aspect of the surface interaction, namely extremely high surface accelerations produced by the SAW pulses is also being studied. The detachment of small particles residing on the surface due to the inertial force is examined. The nonlinear transformation of the excited SAW pulses results in an increase of the surface acceleration and contributes to the detachment process extending it to very small particle dimensions. It is shown that the adhesion of fine particles with dimensions as small as 50 nm can be investigated.

[NP01.40] Silicon Microlithography Using Metastable Argon Atoms

We have investigated the use of an intense Ar(^3P_0,2) metastable beam to pattern Si(100) surfaces. The Ar(^3P_0,2) flux at the sample was \sim2\times10^11 atoms sec^-1 cm^-2. Two different approaches to patterning were studied. In the first, a hydrogen-passivated Si(100) surface was exposed to the beam, in the presence of a small partial pressure of O_2, using a 2000 line/inch grid as a mask. The hydrogen-passivation layer is removed in those areas exposed to the beam, allowing formation of an oxide layer. Immersion in a KOH solution then selectively etches the hydrogen-passivated regions, producing an image of the grid on the Si surface. In the second approach, a siloxane self-assembled monolayer (SAM) was first grown on the Si surface and then exposed to the beam through the grid. Metastable atom impact damages the SAM permitting pattern transfer through subsequent plasma and chemical etching. Because intense Ar(^3P_0,2) metastable beams can be manipulated and focused using optical fields, the present techniques could be used to produce structures on Si(100) surfaces without the need for physical masks and with the potential for massively parallel fabrication.

[NP01.41] Investigation ino the ionic diffusion of Rb & Na ions in sulfonated polystyrene

In the study we have investigated the diffusion of Rb ions verses the diffusion of polymer chains in sulfonated PS (Psssa). The following bi-layer samples were investigated: 1)psssaRb / psssaNa, 2)psssa / psssaRb 3)psssa / psssaNa with a 0.45% level of sulfonation. Both layers are approximately 1000A thick and unless noted have a sulfonation level of 3.4%. Samples were annealed at a temperature of 150C to 170C at times of 4hrs to 36hrs. The samples were examined by Secondary Ion Mass Spectrometry. This revealed that the segmental fluctuation of the polymer resulted in rapid diffusion of the Rb ions relative to the translational diffusion of the polymer chains. The purpose of this study is to obtain a comparison of the diffusion rates of sulfonated polystyrene, with and without ions, to the the rates of normal polystyrene. We compared the results to reptation models modified to account for ionic interactions.

This work is supported by the NSF, (MRSEC DMR-9732230) and the DOE(SG02-93-ER45481)

[NP01.42] Heavy Ion Irradiation of Solids: Projectile Charge and Target Dependence of Electron Emission between 0^o and 180^o

Motivated by the recent observation of narrow electron jets (``spikes'') emitted along the ion beam axis in forward and backward directions we measured for Fluorine ions of 1.5~AMeV the complete angular distribution of electron emission from 0 eV up to 4000~eV (beyond the maximum of the ``Binary Encounter'' electron peak) as a function of the projectile charge state (q = 5+, screened, and 9+, bare) and the target nuclear charge Z (two extreme cases: carbon, Z = 6, and Gold, Z = 79). In particular, the low energy part of the angular distribution was investigated in a high resolution run (0-50 eV). Results on the charge state, target material and angular dependence of low energy ``cascade'' electrons, Auger electrons, electrons from collective excitation (plasmons) will be presented. The evolution of the electron emission characteristics along the beam axis with the angular resolution of the spectrometer will be presented confirming the existence of the jet like electron spikes. The relevance of the experimental cross sections for electron emission for model calculations in radiobiology (linear energy transfer LET) and energy deposition and track formation in solids will be discussed.

[NP01.43] A new experiment for studying ion-beam interactions with frozen-gas targets.

We have recently constructed a new experiment at East Carolina University to study the interactions of ion beams with thin films of frozen gases. The experimental arrangements were initially developed at Pacific Northwest National Laboratory, where electron emission from collisions of fast protons with carbon foils were measured.(C.G. Drexler and R.D. DuBois, Phys.~Rev.~A \underline53), 1630 (1996). The experimental apparatus consists of a cyrogenically cooled target housed in a magnetically shielded ultra-high vacuum chamber. Gases introduced into the chamber condense on a cold copper foil target. Electrons emitted from the frozen-gas target are energy analyzed by a time-of-flight spectrometer that can be rotated around the target. Absolute electron-emission yields, differential in energy and angle, can be measured down to electron energies of 0.1 eV. For these systems, the electron yields are determined not only by the primary collision interactions, but also by the transport of the electrons through the bulk and the interaction of the electrons with the surface. Preliminary measurements for 10-50 keV protons will be presented, and potential applications, including the detection of ions sputtered from surfaces, will be discussed.

[NP01.44] Calculation of charge transfer between an atomic projectile and a metal surface

The formation of atomic resonances during the interaction of an atomic particle with a metal surface allows under certain conditions resonant charge transfer to occur between the two participants. Due to the finite velocity of the ion approaching and leaving the surface, the dynamic charge transfer process is determined by the non-adiabatic coupling between these resonances as well as with electronic states of the surface band structure.

Based on accurate resonance data, we present in this work results of our calculations for the charge transfer in a model system consisting of a hydrogen atom and an aluminium surface.

Work supported by US DOE, Office of Basic Energy Sciences, Division of Chemical Sciences, under contract No.\ DE-AC05-96OR22464 with Lockheed Martin Energy Research, Inc.\ and the Austrian Science Foundation.

[NP01.45] Calculation of dynamic charge transfer between an atomic projectile and an ionic crystal surface (H on MgO(100))

Lately, the charge state evolution of projectiles in low energy (E\leq 10\,keV) collisions with insulating surfaces of ionic crystals has been studied extensively.

A high negative ion yield from neutral H, O, and F projectiles was observed experimentally on alkali-halide surfaces [C. Auth et~al., Phys.\ Rev.\ Lett. 75, 2292 (1995); Phys.\ Rev.\ A 57, 351 (1998)] and explained theoretically by charge transfer via binary encounters (BE) of the projectile with the lattice anions [A.~G. Borisov, V. Sidis, Phys.\ Rev.\ B 56, 10628 (1997)]. Collisions of such projectiles with a MgO(100) surface yield, similar to alkali-halide targets, also a large negative ion fraction [S. Ustaze et~al., Phys.\ Rev.\ Lett. 79, 3526 (1997)].

The efficient negative ion production is of interest for the design of low-flux negative ion beam sources, and in space research for the construction of neutral particle detectors. Moreover, most chemical reactions on surfaces involve an electron transfer, so it is desirable to understand this process.

In this paper, we present our theoretical results for the negative ion production from H projectiles during slow (E\leq 100\,eV) collisions with a MgO(100) surface using the BE model for the charge transfer.

Work supported by the European Union under contract No.\ ERBFMBICT971983.

[NP01.46] Broadening of hydrogenic levels near thin metallic films

We evaluate the width of resonantly broadened hydrogenic levels in the vicinity of thin metallic films in first--order perturbation theory. We calculate the electronic states of the film as eigenstates of a Jennings-type (LDA) potential. In order to include hybridization effects, we represent the hydrogenic levels in a parabolic (Stark) basis. The widths show characteristic, sawtooth shaped, oscillations as the film thickness is varied between 0.5 and 3 nm. These oscillations are related to threshold effects in the onset of resonant capture into a particular hydrogenic level. We analyze the influence of these quantum size effects on measurable parameters, such as electron capture probabilities of slow incident hydrogenic ions.

[NP01.47] New Close Coupling Approach for Ion-Surface Interactions

Within a two-center close-coupling expansion, we rewrite the time- dependent Schrödinger equation for an active electron interacting with a slowly moving projectile and a metal surface as a system of coupled equations and solve this system numerically. In contrast to other close-coupling approaches (e.g. Ref.~(P. Kürpick, U. Thumm and U. Wille, Phys. Rev. A 56, 543 (1997); \hspace*0.065in)P. Kürpick and U. Thumm, Phys. Rev. A 58, 2174 (1998).), we fully discretize the active electrons motion in the metal subspace along the surface normal by using a discrete sum of Weyl wave packets (G. Schiwietz, Phys. Rev. A 42, 296 (1990) and refs. therein.). For the H/Al system, we provide level shifts, transition rates for atom-metal transitions, the time evolution of the atomic and metallic population amplitudes, and excitation rates for one-electron transitions in the substrate.

[NP01.48] Patterning Surfaces with Highly Charged Ions

We present results which demonstrate masked ion beam lithography using highly charged ions. An electron beam ion trap was used to deliver a continuous ion beam current of approximately 10 pA of Xe44+ onto a silicon wafer coated with one of two materials: (1) a commercial lithographic resist (PMMA, 400 nm thick) and (2) an ultrathin self assembled monolayer (<2 nm thick). The resists were covered with stencil masks with rectangular openings ranging from approximately 1 micrometers to 12 micrometers in width. Subsequent to exposure, the resists were developed and then imaged using atomic force microscopy (AFM), scanning electron microscopy, and optical microscopy. The results of these studies show effective patterning with edge resolutions of 100 nm or better, apparently limited by the commercial masks rather than fundamentals of the ion exposure process itself. For PMMA exposed to low doses, it was possible to observe single ion impact sites (24 nm diameter). Results of ongoing work involving the direct modification (no chemical development) of HOPG surfaces with Xe23+ and Xe44+ will also be reported.

[NP01.49] \itAb Initio Single and Multiple Scattering EXAFS Debye-Waller factors: Applications to medium and large size molecules

This paper describes recent results using our approach to calculating self-consistently single (SS) and multiple-scattering (MS) Debye-Waller factors (DWF) on medium and large size molecular structures. The calculation of MS DWF, together with the Feff7 program allows us to simulate ab-initio EXAFS spectra for a given temperature systems with no adjustable parameters. In our first report(N. Dimakis and G. Bunker, Phys. Rev. B58), 2467 (1998). we calculate ab-initio and semi-empirically SS and MS DWF for small molecules using Raman, infrared and EXAFS spectra. Lately, we calculate DWFs for Zn tetrahedral imidasol, an active site of a metaloprotein that contains thirty two atoms using the semiempirical MNDO Hamiltonian. Unfortunately the semiempirical Hamiltonians, although much faster than the ab-initio Density Functional Theory (DFT), would not provide accurate results for any molecule tested. In this report we test various samples using EXAFS spectra. Our approach takes advantage of commercially available molecular orbital programs. We have written additional programs which, using normal mode calculations, calculate the MS paths, and transparently interface with Feff7 to produce the EXAFS spectra. Results are in very good agreement with experimental EXAFS data tested.

[NP01.50] X rays emitted by implanted Ar atoms

Argon atoms were implanted in various solid targets (metals, semiconductors and insulators) at depths of the order of 1000 Åand K ionized with photons of energy slightly higher than the Ar K shell binding energy at the Advanced Light Source of the Lawrence Berkeley National Laboratory. The subsequent fluorescence of the Ar atoms was observed with a very high resolution SiLi detector. These fluorescence spectra have been compared to those emitted following the excitation of Ar atoms in a gas cell. The K\alpha lines of implanted Ar have been found shifted down in energy by about 2 eV for most targets, with respect to those of gas phase Ar, while the relative intensity of the K\beta and K\alpha lines is similar in gas and solid targets. A possible explanation involving coupling of ion levels with the solid will be discussed.

[NP01.51] Measurement of Pressure Broadening and Shift for Hg 254-nm line by N_2

We have performed a measurement of the collisional broadening and shift of the 254-nm line of Hg by N_2 for pressures below 400 Torr. We used the 500 mW output of a commercial MOPA single-mode laser at 1016 nm which is first doubled to 508 nm using a KNbO_3 crystal then doubled again using a BBO crystal, both in external enhancement cavities. This system produces over 100 \muW at 254 nm, and can be easily tuned over tens of GHz. The transmission through two vapor cells (one containing natural mercury and one containing natural mercury plus 40-400 Torr of N_2) as well as the laser intensity were monitored simultaneously while the laser was scanned. The well-known isotope shifts and hyperfine structures of natural mercury were used to calibrate the frequency scale. Our preliminary results are \Delta\nu_S = -(2.533 \pm 0.011) MHz/Torr for the shift and \Delta\nu_B = (8.996 \pm 0.028) MHz/Torr for the broadening (statistical uncertainty only); these represent a substantial improvement over earlier work. The measurements are motivated by ongoing time-reversal symmetry measurements at the University of Washington.

[NP01.52] Experimental benchmarks of the relative 2p-3d ^\, 1\!P_1, ^\, 3\!D_1 excitation cross sections in neon-like ions

The n=3\rightarrow2 \space^\, 1\!P_1 and ^\, 3\!D_1 resonance and intercombination lines are two of the strongest spectral features exhibited by neon-like ions making them prime diagnostic candidates. However, a study of theoretical predictions of the relative cross sections of these two transitions reveals a wide variation, rendering this diagnostic unreliable. For example, in the case of Fe XVII, the calculated ratio varies between 2.7 and 4.7. To provide benchmarks for calculations we have done a systematic study of the intercombination to resonance line ratio for ions along the neon-like iso-electronic sequence between Cr^14+ and Kr^26+. Our measurements employed the Electron Beam Ion Trap facility under conditions where the only line formation processes are electron impact excitation followed by radiative cascades. The measurements, thus, provide a clean platform for evaluating the accuracy of theoretical atomic data. We have compared our measured ratios with those predicted by a distorted wave calculation. Our comparison shows a systematic difference between theory and experiment of approximately 30%. This discrepancy clearly demonstrates the limits of approximations which are present in many calculations.

[NP01.53] All-optical triple-resonance excitation of singlet nf Rydberg states of molecular hydrogen

We have efficiently excited singlet nf Rydberg states of molecular hydrogen using a triply-resonant process driven by vuv and visible tunable pulsed lasers. The first excitation step uses vuv light near 111 nm to excite specific rotational states of the B (v"=0) state. The vuv light is produced through a non-resonant four-wave mixing process in a phase-matched mixture of krypton and argon gas. A second laser operating near 460 nm then further excites the molecules to selected rotational and vibrational levels of several possible ns, nd intermediate states, including the G,K (v'=0 and 1) and several other 3d\lambda electronically excited states. A third, near-infrared tunable dye laser finally excites the molecules into high principle quantum number p and f states. Both ion production due to pulsed field ionization and photoionized dissociation products are monitored in the experiment. The Rydberg spectra show relative intensity effects due to both the choice of intermediate state and the excited state dynamics.

[NP01.54] Nuclear Structures Predicted by the Checker Board Model

The Checker Board Model (CBM) explains many aspects of the nucleus. The CBM predicts that the de Broglie wavelength of the up quark in the proton equals the circumference of the proton, just like the Bohr model of the atom, only 100,000 times smaller. It is one of the few models that uses quarks to explain the strong force. It can explain a wide variety of structures: halo nuclei, linear alpha chains, and the more stable structures. It predicts that Fe 56 will be the most stable nuclei. It can predict the binding energy of a nucleus based upon the number of nearest neighbor sites (1,2,3,or 4). The CBM model therefore supports the 1979 Tamagaki's two dimensional ordered states model. Since the two protons (and neutrons) in the alpha particle have opposite spin orientations, the magnetic flux couples between these two, making the paired structure more stable. One addition item in support of this model: the mass difference between the two excited states of the pi meson (Phi(1020) and W(782)) is 237.47 +- .13 MeV, making this value almost the same, considering uncertainty, as the predicted mass of the up quark in the CBM model (237.31 MeV). These two excited pi meson states are significant since they both have all the same quantum numbers.

[NP01.55] Checker Board Model

The Checker Board Model (CBM) is a new model of the nucleus that proposes that the protons and neutrons form a checker board pattern in the nucleus. This model assumes the two up quarks in the proton revolve around the down (dn) quark which is located in the center of the proton. Similarly the two dn quarks revolve around the up quark in the center of the neutron. This model assumes that the strong nuclear force is generated primarily from the close approach of the up quarks in the proton and the dn quarks in the neutron. CBM assumes the same frequency of revolution of quarks in the proton and neutron. This assumed structure plus the magnetic moments and masses of the proton and neutron, plus the binding energy difference of He(3) vs. H(3) gives some predictions of the size of the proton and neutron and the rest mass of the up and dn quarks and their speeds inside the proton and neutron. Avg radius proton = 0.519406 fm. Avg radius neutron = 0.6079394 fm. Rest mass up quark = 237.31 MeV. Rest mass dn quark = 42.392 MeV. Velocity up quarks in the proton = 0.848123 c. Velocity dn quarks in the neutron = 0.992685 c. Period of revolution = 1.283533 X10-23 seconds. Notice the de Broglie wavelength of the up quarks in the proton are equal to the circumference of their orbit in the proton.

[NP01.56] A "Zero Space" Theory

The term "Zero Space" describes the idea that every point in our local universe is occupied by the same field existing in two diffrent states or phases: a matter state and a "space" state. The matter state as "Condensed Space" and space is simply the free state of matter. A theory is discussed which describes the development of the matter state from the basefield, the micro structure of the basefield (The fabric of space time), and the relation of the field to light.

[NP01.57] The Kaon Angular Distributions for \Lambda and \Sigma^0 Electroproduction at CLAS

The electroproduction of kaons on protons has been studied with the CLAS spectrometer at Jefferson Laboratory as part of experiment 93-030.

The K^+ Y final states were selected by identifying the charged kaon with momentum and time of flight measurements, and then using the p(e,e'K^+) missing mass to select the recoiling hyperon.

From the data collected thus far with electron beam energies of 2.445 GeV and 4.045 GeV, the hyperon production spectra span a range of W from threshold to 2.5 GeV, Q^2 from 0.5 to 2.5 (GeV/c)^2, and most notably cover the full angular range in the hadronic center of mass frame.

The preliminary kaon angular distributions for K^+ \Lambda and K^+ \Sigma^0 final states as a function of Q^2 and W will be shown.

It will be seen that the \Lambda and \Sigma^0 angular distributions are markedly different in given ranges of W and Q^2.

[NP01.58] Determination of Nitrogen Concentration in Metallic Lithium

At the University of Massachusetts Lowell Van de Graaff accelerator, neutrons are generated by bombarding thick metallic lithium targets with a 4-MeV proton beam. Lithium is purchased in the form of 2.25-gram ingots encased in sealed copper cartridges. Purchasing circumstances led us to acquire a 4-year supply of these cartridges. On occasion, this "aged" lithium was used, and a reduced neutron yield was obtained. Since nitrogen is the most abundant element in air, a contamination of lithium by nitrogen was considered, and a (p,\gamma) experiment was performed to determine the nitrogen concentration. We describe the experimental setup and show results.

[NP01.59] Fiber-Based Neutron Spectrometer

PNNL has developed scintillating fibers that are sensitive to thermal neutrons. Because these fibers are thin, they present an enabling technology for several applications, including highly efficient neutron spectroscopy. The underlying concept is to arrange the fibers in an array of layers separated by moderating and absorbing materials whose characteristics have been chosen to optimize the desired bandwidth and resolution. Monte Carlo experiments have been performed to characterize the conceptual design and to determine concept’s value as a tool for research and other applications. These results will be reported.

[NP01.60] Solar cell array for nuclear spectroscopy with YRAST Ball

Solar cells present a simple and cost-effective alternative for the detection of heavy-ions in nuclear spectroscopy experiments. Here we present an array of eight 1cm\times1 cm large solar cells, which was used in conjunction with the YRAST Ball array at the Wright Nuclear Structure Laboratory at Yale University. The cells were used for fission detection, fission suppression and the detection of inelastically scattered beam in various experiments. Their use in a Coulomb excitation experiment on ^154Sm enabled the measurement of the level lifetime with the Doppler-shift Attenuation Method (DSAM) of the first excited 0^+ state, which was found to be a \beta-vibrational excitation of the ground-state. We will present data on the performance of the cells, future developments of the array and some physics results of the YRAST Ball experiments.

[NP01.61] An Integrating Low-Energy Positron Spectrometer

The production of low-energy positrons from beta decay sources is important for a variety of applications, including surface studies and trapping of positrons for symmetry studies and attempts to produce anti-hydrogen. Positrons for these purposes come at energies of hundreds of keV from a radioactive source such as 22Na, and then are degraded and/or moderated in a solid. We have developed an integrating low-energy spectrometer specifically to enable us to inspect the low-energy tail of a degraded positron spectrum. This device uses a nearly solenoidal magnetic field to transport only the low energy positrons to a counting region where annihilation gamma rays are counted using coincidence techniques. The spectrometer is integrating in the sense that it accepts all low energy positrons with a transverse momentum below a cutoff determined by collimation and the magnetic field strength. Because no effort is made to do momentum determination within this momentum window, it is possible to create a device with nearly 2 pi acceptance solid angle. The longitudinal component of momentum can be inferred with a variable repelling voltage on the annihilation surface. We will present details of the design and construction of this device and the results from early tests.

[NP01.62] Electron Deuteron Elastic Scattering in a Simple NN Potential with Excluded Spurious States: Non-relativistic Calculations.

Simple analytic forms for the NN potential are useful for many nuclear physics applications. We present a new version of a simple NN potential which excludes the Pauli forbidden state coming from the short-range attractive part of the interaction. Parameters of np interaction have been chosen via a fit to the deuteron binding energy and the np scattering threshold behavior. The wave function of the potential has a node in the S wave and no node in the D wave. We find that our results reproduce all deuteron properties and are in good agreement with previous np results of NN Nijmegen-potential calculations below 350~MeV as well as the recent VPIamp;SU PWA determinations below 500~MeV. The observables form factors A(Q^2) and B(Q), and the tensor polarizations T_10, T_20, T_21, and T_22, for ed elastic scattering are calculated over the kinematic range that is probed in Jefferson Lab measurements.

[NP01.63] Revisit to Gamow Factor

The conventional Gamow factor is valid for free-moving incident particles only. For resonance penetration via the lattice confined ions the penetration factor of the Coulomb barrier is \theta^-1, while the Gamow factor is \theta^-2. This theory answers Professor J.R. Huizenga's challenge of three miracles. The basic assumption(a (d+d) resonant state with a life-time of 3 hours) is checked by the experiment data, and prediction is made for the future test in material science.

[NP01.64] The strong interaction shift in kaonic deuterium

High precision measurements of kaonic hydrogen x-rays and also, for the first time, of kaonic deuterium are under way within the DEAR (DA\Phi NE Exotic Atom Research) project using the e^+ e^- storage ring at Frascati. The values of the strong interaction 1s level shift and width in kaonic deuterium cannot be simply predicted by relating them, via the Deser formula, to the K^-d scattering length because the latter is not known experimentally. It cannot be obtained, moreover by adding the K^-p and K^-n scattering lengths but involves the solution of a complicated multi-channel three-body problem. We give results of calculations of the kaonic deuterium strong interaction shift and width using (N\barK,\, Y\pi) interaction which fits the available low-energy scattering data. The K^-d 1s shift comes out negative and both the shift and the width are estimated to be about 1\,KeV. The 2p level width is predicted to be at least four orders of magnitude smaller than the 1s width. This information is of importance for the planned experiment as it indicates that most of the kaons should reach the lowest 1s level.

[NP01.65] The pion-nucleus interaction and pionic atoms

We have derived a relativistic impulse approximation to calculate the relativistic DKP pion-nucleus optical potentials, using the Duffin-Kemmer-Petiau (DKP) wave equation. These potentials use the time-like vector and scalar nuclear densities and relativistic pion-nucleon scattering amplitudes as input. The off-shell effects in pionic atoms result in different predictions by the DKP and Klein-Gordon equations (which predict the same effects on-shell).

We give a systematic comparative analysis of our DKP relativistic pion-nuclear optical potential with all other previously proposed relativistic models, and with all the non-relativistic models available in the literature. We compare these models by looking at their respective prescriptions for the real and absorptive, S-wave and P-wave, isoscalar and isovector, pieces of the pion-nuclear optical potentials.

We compare with experimental strong interaction level shifts and widths in pionic atoms over the whole of the periodic table using the DKP equation with our DKP pion-nucleus potentials.

[NP01.66] A Toy Model for the Spatial Arrangement of Nucleons in Nuclei

It is not known how nucleons are spatially arranged in nuclei. This work proposes a toy model for the arrangement of nucleons in nuclei which agrees with the experimental data on dipole and quadrupole moments. With the model we are able to explain the absence of A=5 nuclei and the strange instability of ^8Be.

[NP01.67] Proton Induced Fission Cross Sections for Heavy Nuclei in the 200 - 1000 MeV Energy Range

An accurate determination of the total fission cross sections of ^natPb, ^209Bi, ^232Th, ^233U, ^235U, ^238U, ^237Np, and ^239Pu induced by 0.2 to 1 GeV protons that are needed in nuclear waste transmutation studies and other nuclear physics applications of current interest is made in 100 MeV increments at an external beam position of the Gatchina 1-GeV proton synchrocyclotron. The beam intensity at that position is up to 1 \muA but is decreased for this experiment to 10^5 to 10^6 s^-1 so that it can be measured with a scintillation counter telescope, and the beam spot size varies from 1 to 2 cm^2. The targets range in thickness from 0.3 to 0.5 mg/cm^2. The fission fragments are detected in coincidence by two parallel plate avalanche counters located in front and in back of the target at a short distance from it, so that the solid angle acceptance for fission products is nearly 4\pi. The registration efficiency is about 100%. With this setup, fission cross sections of several target nuclei at 1 GeV were determined in previous work with an accuracy of better than 10% (see, e.g., L. M. Andonenko et al. J. Part. and Nuclei, 18, 289 (1987)).

[NP01.68] Charge Symmetry Violation in Pion Scattering from Light Nuclei

The theoretical and experimental status of charge symmetry violation (CSV) in the scattering of pions from deuterium and trinucleons is discussed. While not very noticeable in the pion-deuterium case, CSV seems to be more pronounced for the pion-trinucleon system. We present a theoretical formalism for CSV in terms of single- and double-scattering terms with Delta-mass splitting taken into account. Our theoretical results will be compared with the available experimental data.

This work was supported in part by the George Washington University Center for Nuclear Studies Visiting Scholar Program and the Russian grant for Basic Research N~98--02--17618.

[NP01.69] Hydrogen-like Atoms from Ultrarelativistic Nuclear Collisions

The number of hydrogen-like atoms produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider using the sudden approximation of Baym et al. As first suggested by Schwartz, a simultaneous measurement of the hydrogen and hadron spectra will allow an inference of the electron or muon spectra at low momentum where a direct experimental measurement is not feasible.

[NP01.70] Photo-Production of the Delta with current quark masses

The proton and Delta are three quarks assumed solely in the (1/2^+)^3 configuration, with angular momenta coupled to 1/2 and 3/2 respectively. The three body Dirac equation is solved with hypercentral linear and quadratic confining potentials, including all 8 components of the composite three quark wave function. With small quark masses, this model reproduces the proton and delta energies, the proton rms size, axial charge, and magnetic moment. The lower components of the one quark wave function are (1/2^-). These components have the orbital angular momentum needed for the E2 photo-production amplitude not to vanish, and contribute over 40 percent to the normalization. These are neglected in constituent quark calculations. With all 8 component wave functions, the E2/M1 ratio is mostly given by the first terms of -j_2(kr)/2j_1(kr)=-0.05. Assigning anomalous magnetic moments to quarks, the proton magnetic moment and the M1 photo-production amplitude can be simultaneously reproduced with a quark mass of order 1 MeV. About 20 percent of the M1 amplitude then comes from the quark anomalous magnetic moment interaction.

[NP01.71] Experiments with Laser Trapped Radioactive ^21Na

A laser trap for radioactive ^21Na (t_1/2 = 22 seconds) atoms has been constructed on-line at the 88'' cyclotron at LBNL. It is to be used to improve current beta decay measurements such as the parity violating asymmetry of spin-polarized nuclei and the electron-neutrino correlation. Our current focus is on recoil ion detection. Inside the trapping chamber we are installing a microsphere plate about 8 centimeters below the trapped atom cloud. Electric field rings will apply a constant electric field of about 500V/cm over the region from the trap center to the plate. When a ^21Na atom in the trap beta decays the daughter ion is accelerated into the microsphere plate and detected. Coincidence detection of both the ion and the beta from the decay will reduce our current background levels by discriminating against background from the vacuum chamber walls, allowing beta decay measurements to be made. The beta is detected with a plastic scintillator above the trap. The time between the essentially immediate hit of the upward going beta and the arrival of the accelerated ion at the microsphere plate gives information on their relative emission directions. From the timing information the beta-neutrino correlation can be extracted. For ^21Na the beta-neutrino correlation is mainly sensitive to possible scalar contributions to the weak interaction.

[NP01.72] The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary Studies of the Nova Outburst

The observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One of the more important sources of uncertainty is the nuclear reaction data used as input for the evolutionary calculations. A recent paper by Starrfield, Truran, Wiescher amp; Sparks (1998) has demonstrated that changes in the reaction rate library used within a nova simulation have significant effects, not just on the production of individual isotopes (which can change by an order of magnitude), but on global observables such as the peak luminosity and the amount of mass ejected. We will present preliminary results of systematic analyses of the impact of reaction rate uncertainties on nova nucleosynthesis. While the primary goal of our studies is to discern the extent to which theory is discrepant from observations, we will also determine the relative importance of changes in individual reaction rates and provide guidance in the selection of reactions for further experimental study.

[NP01.73] Polarized Parity Violating Electron Scattering in ^3He and ^3H

We obtain the asymmetry,A, for a range of incident electron energies from 0.5 GeV to 6.0 GeV for elastic scattering on ^3He and ^3H. We also obtain the corresponding figures of merit. We show that the asymmetry for these nuclei have substantial structure. We also show that contributions from the weak strange quark current induce large changes in the asymmetry in the region of the first maximas and minimas which might be measureable under favorable circumstances. We also discus the relationship between the two reactions considered here and show that measurements of both at the same q^2 would enable the weak current form factors to be determined at energies not otherwise available.

[NP01.74] The Deuteron Binding Energy and the Neutron Mass

A new value for the deuteron binding energy of S(d) = 2.38817007(42) \times 10^-3 u is reported based on an absolute wavelength determination of the 2.2 MeV n-p capture gamma-ray using a crystal diffraction spectrometer. A previous crystal diffraction measurement of the deuteron binding energy has an uncertainty 5 times larger than this result. A new more precise value for the neutron mass m_n = 1.00866491637(82) u is obtained by summing this binding energy and the ^2H - ^1H mass difference. The uncertainty of the neutron mass has been reduced by \approx 2.5 and the uncertainty contributions are 0.42 \times 10^-9 u and 0.71 \times 10^-9 u from the binding energy and mass spectroscopic measurements, respectively.

[NP01.75] The Fundamental Constants and the Inertial Field

The constants, G, c, h, and e can be derived from one natural constant, tav, the inertial constant, (herein \heartsuit due to no LaTeX support for tav) in light of an expanding inertial field (quantum vacuum) of variable inertial density, \rho. Particles are 3D waves, not points. G, B and E fields are density fluctuations propagating from particle motion. Functionally, where r, m, ømega, \gamma and \alpha are customary:

m = f(\rho), r = f(m) = \heartsuit/m, \heartsuit = \gamma(-m^2) dr/dm (also = 1/\gamma (-r^2) dm/dr), ømega = g(r) = c/r = g(f(m)) = mc/\heartsuit, c = 1/\gamma (-r^2) dømega/dr = \heartsuit dømega/dm, h = 2\pi \heartsuit^2 dømega/dm, e^2 = -4\pi\epsilon_0\alpha(\heartsuit 1/\gamma^2r^4)dømega^2/dr^2 = -4\pi\epsilon_0\alpha(\heartsuit^3)dømega^2/dm^2 (= -\alpha\prime\heartsuit^2dømega^2, where \epsilon_0 = dm^2/\heartsuit and \alpha\prime = 4\pi/\alpha \approx 1/(2\pi\surd3)), e =i\alpha\prime^1/2\heartsuitdømega, G = [(r_a^2/\heartsuit)^2/(\pi/3)] r_a^2 dømega^2, (where r_a = avg nucleon radii, dømega\rightarrow0) = [(r_a^2 /\heartsuit)^2/(\pi/3)] \heartsuit dømega^2 (-1/\gamma)(dr/dm),

And

P = -\heartsuitr dømega/dr = (\heartsuit^2\gamma/r) dømega/dm, E = (\heartsuit^2 r) (dømega/dm)( dømega/dr) = (1/\gamma \heartsuit r^3) dømega^2/dr^2, Schrodinger’s: E = (\heartsuitr^2/2) dømega^2/(dr^2 /n^2 ) = (n^2/2) (\gamma \heartsuit/ r) (-1/\gamma r^2 dømega/dr )^2, Gravitation, where n_m and n_d = qty of fundamental units: F_g = [(n_m1n_m2)/(4\pin_d^2/12)][h^2/4m^2L^2] = [(M_1M_2)/d^2] [(r_a^2/\heartsuit)^2/(\pi/3)] \heartsuit dømega^2 (-1/\gamma)(dr/dm). Inertial constant: \heartsuit = \hbar/c = 3.517672286e-43 kg-m. The Quanta (dømega/dm = constant): Momentum-\heartsuitdømega, Force-\heartsuitdømega^2, Action(\hbar)-\heartsuit^2 dømega/dm, Energy-\heartsuit^2 (dømega/dm) dømega. Strong and weak interactions and electron/neutron mass ratio can be derived in light of the above, given geometric constraints.

[NP01.76] Frequency Stabilization of rf-Pumped Me-Ne/^127I_2 Laser

For practical realization (mise en pratique) of definition of metre as the length which light pass in vacuum during 1/299792458 sec Comité International des Poids et Mesures in 1997 recommended twelve standard wavelengths. The wavelengths of He-Ne laser stabilized by saturation absorption ^127I_2 molecule are very important for practical application. The very first He-Ne lasers have been pumped by longitudinal rf-discharge. Due to essential imperfections these lasers were replaced by lasers pumped by dc-discharge. Now the He-Ne lasers pumped by transversal rf-discharge are developed. There are some advantages of these lasers, main of them is lower amplitude noise level (3-4 times comparing to dc-pumping). We study the frequency stability of rf-pumped He-Ne/I_2 laser (632,8 nm). It was showed that the frequency stability of rf-pumped He-Ne/I_2 lasers is higher then one of lasers pumped by dc-discharge. The frequency unstability of rf-pumped He-Ne/I_2 lasers is 2.8\cdot 10 ^-12 at the average time 10 sec. The comparision of rf-pumped laser with iodine stabilized dc- pumped He-Ne laser of State Primery Length Standard of Ukraine were performed. The averaged frequency difference over d,e,f,g absorption components of the iodine molecular transition 11-5, R(127) was \nu_rf - \nu_dc = 1.2 kHz, standard deviation 3.2 kHz.

[NP01.77] Hyperfine Structure Measurements of the 4d2D3/2,5/2 Levels of Gallium 69 and 71

We have determined the hyperfine structure of the 4d2D3/2,5/2 levels of 69,71Ga. The 4p2P3/2 - 4d2D3/2 (294.50 nm) and 4p2P3/2 - 4d2D5/2 (294.45 nm) transitions were studied by laser induced fluorescence in an atomic Ga beam. The hyperfine B constants for the 4d states are determined for the first time. The A constants are measured with a greater accuracy and are found to have the opposite sign from literature values. Improved values of the isotope shifts of both transitions are reported. The relevance of this work to the optical manipulation of gallium will also be discussed.

[NP01.78] ^133Cs (I=7/2) 6^2P_3/2 Hyperfine Structure Measurements

The experimentally studied hyperfine structure (HFS) can be compared with the results from Hartree-Fock and many-body perturbation theories which are important to interpretation of parity nonconservation (PNC) in atomic systems. The HFS of ^133Cs 6^2P_3/2 level is being intensively investigated. It may be possible to determine the magnetic octupole interaction contribution to HFS energy (frequency) differences by measuring the splittings with an accuracy of 1kHz or better. We propose to lock two frequency stabilized 852nm diode lasers to two different HFS levels of 6^2S_1/2-6^2P_3/2 transition and mix their frequencies with a photodiode to determine the frequency difference between the HFS levels. To obtain a Doppler-free spectrum the laser beam will cross a collimated thermal atomic beam at a right angle. In this case the spectrum is Doppler-free with natural linewidth of the transition (5MHz).

[NP01.79] Laser-induced continuum structure in He*

We report the observation of laser-induced continuum structure (LICS) in

the photoionization of helium out of the metastable singlet state. The same region of the continuum is reached from the 2s and 4s states by 294 nm and 1064 nm radiation, respectively. We observe in this otherwise unstructured continuum a strong and spectrally sharp resonance (the narrowest being 0.6 GHz), showing both enhanced and diminished ionization (by as much as 70%). The latter is due to population trapping associated with LICS. We also show the effect of dynamic Stark shifts upon the LICS profiles. A theoretical

model gives quantitative agreement with the experimental results for a wide range of intensities.

[NP01.80] Enhanced chaotic positron accumulation by sequenced resonant kicks

We report on improvements to the Michigan positron accumulator resulting from an understanding of the chaotic nature of the long term trapping mechanism [1]. In the previous incarnation, a brute-force method was used to give the positrons large radial kicks each time they execute an axial orbit. In the improved version the chaotic action of a synchronized series of small kicks efficiently transfers the positrons to low-loss orbits where they accumulate for later extraction.

[1]B. Ghaffari and R.S. Conti Phys. Rev. Lett., 75 3118 (1995)

[NP01.81] What we have learned from restricting the use of calculators in general physics

Over the past several years, I have restricted the use of calculators in my college-level, non-calculus, general physics courses. The goal was to improve the ability of students to handle the arithmetic and algebraic requirements of the class. Student resistance is significant at the beginning of the semester, but diminishes with time. What has been revealed, however, is an inherent weakness in performing calculations by many of our students, including some who have taken high school calculus. This is evidenced by the type of arithmetical errors made on the simplest of problems, and it suggests that an over-dependence on calculators has robbed our students of fundamental computational skills that, in turn, may limit mathematical reasoning.

[NP01.82] The effect of arithmetic skills on success in general physics

Freshman students at our college must take a mathematics placement examination which also serves as a diagnostic tool. A comparison of performance on the arithmetic section of the test, with grades in our non-calculus, general physics classes, demonstrates the correlation between an understanding of arithmetic operations, and, success with physics, regardless of the number and the level of the high school courses that have been successfully completed

[NP01.83] Atmosphere, Weather, and Baseball: Does the Ball Really Fly Farther at Denver's Coors Field?

From its inauguration in 1995, Coors Field has gained national notoriety as a launching pad of historic proportions. Over the 1995- 1997 seasons, the Denver ball park led all major league parks in total home runs and home runs per at bat -- both by a very wide margin. Most observers, physicists and baseball people alike, assume that more home runs are hit at Coors Field due to the effect of low air density at higher elevations; compared to the league average adjusted for the actual elevation of each ball park, the ball should travel 9.3 percent farther in Denver. Our research tested this assumption through an analysis of fly ball distance data for all National League ballparks for the years 1995-1997. Our results show that the ball travels only 6.5 percent farther at Coors Field compared to the average for all other National League ball parks. When this comparison is adjusted to reflect actual field dimensions, the difference is just 2.8 percent. In order to explain these unexpected results, we set up two weather monitoring stations inside Coors Field during the 1997 season. Measurements taken included temperature, relative humidity, barometric pressure, and wind as recorded by equipment that provides three-dimensional modeling of air flow. The initial results of our micro-meteorological analysis indicate that of the measured variables, wind -- especially the vertical component -- is most strongly correlated with shorter fly ball distances in Coors Field. We have constructed a computer model which permits a variation in air density and wind velocity as well as the launch speed and angle for the trajectory of fly balls.

[NP01.84] Using a Synchrotron Light Source to Probe Brain Mechanisms

This paper suggests that synchrotron light activates polarized brain cells which, because of membrane polaribility can receive light.

It explains how Synchrotron radiation can penetrate and activate brain cells and thus serve as an excellent probe of brain mechanism.

Wavelengths within the broad range of Synchrotron Light have the same dimensions as molecules, atoms, and solids in brain cells, and with the correct polarization can allow the light to pass through brain membranes, rather than be absorbed.

This theory describes how outer influences can effect intellectual thought processes and brain activity because Superlattices and the geometry of brain membrane surfaces permit coherent quantum transmission.

[NP01.85] An Automatic Impedance Measurement System for Detecting Superconducting Transitions via Magnetic Screening

Using a microcomputer with an A/D and D/A interface board, we have developed an automatic impedance meter for detecting the critical temperature of superconductor ceramics. The superconductive sample is introduced in a coil and the set is placed in a simple cryostat. Our system measures the temperature of the sample using a commercial integrated circuit sensor and can change the sample temperature in steps of 0.5K from 77K to 350K. It can also calculate the coil's impedance generating a sinusoidal signal applied over the coil and measuring the current and the voltage of the coil. The impedance is composed of a real component (related to the resistance) and an imaginary component (related to the reactance). The coil's reactance change dramatically at the phase transition of the sample and from this change we can determine the critical temperature. All the process is controlled by software based on LabVIEW. This is a good and inexpensive apparatus for general demonstration of superconductor transitions and it is also useful to introduce undergraduate students to the basic research.

[NP01.86] Development of Laboratories to Supplement Moore's IUPP-Based "Six Ideas" at Smith College: I. Mechanics and Thermodynamics

In this pair of poster papers we present a series of laboratories developed at Smith College to be used with Thomas A. Moore's "Six Ideas That Shaped Physics" model. We discuss several pedagogical issues, such as balancing minilabs and project labs, correlation of labs with class topics, and evaluation of students' lab work. The first semester laboratories deal entirely with mechanics and are well integrated with the course material. We make extensive use of sonar rangers, as well as camcorders and freeze-frame VCR's for video data acquisition and qualitative analysis. We will demonstrate video analysis of projectile motion of extended objects, momentum conservation in collisions, and energy conservation in oscillating spring systems. Similar techniques can be used for more extensive investigations, e.g., filming apparent weight changes during an elevator ride and determining the total distance traveled. We also discuss a series of thermodynamics minilabs and illustrate the counting-of-microstates software used in conjunction with the course.

[NP01.87] Development of Laboratories to Supplement Moore's IUPP-Based "Six Ideas" at Smith College: II. Electricity, Magnetism, Waves, and Optics

The second semester laboratories focus on electrical fields and circuit analysis, a series of minilabs on magnetic phenomena, and quite extensive investigations of waves and interference and diffraction phenomena. The lab topics are less well correlated with course material than in the first semester, due to the large amount of time devoted in class to electricity and magnetism and the relatively brief treatment of waves and optics (in Unit Q). We use lab work to explore some material not covered in the course; this also helps to better synchronize lectures and laboratories. For example, we spend 1-2 lab periods on geometrical optics; a set of minilabs on standing waves; and a set of minilabs exploring forced oscillations and resonance in a variety of physical systems. We also spend one lab period having students assemble the components of an open-bore He-Ne laser and having them explore its transverse mode patterns. We will demonstrate this apparatus and discuss more extensive investigations which can be done with the laser.

[NP01.88] Educational Computer Program for Accurate Visualization of Electron Transport in Noble Gases

The transport of electrons in noble gases under the influence of an electric field was the subject of recent research work using a tri-dimensional Monte Carlo technique with a set of accurate integral and differential cross-sections, leading to results (drift velocities, diffusion coefficients, electroluminescence yields, etc) in very good agreement with experiments [1]. In the present work we apply these techniques to the development of an educational computer program that allows the accurate visualization of detailed movement of individual electrons in a noble gas (xenon) under variable conditions of pressure and electric field intensity. The Fortran program running on Linux in a portable Pentium computer will be demonstrated. It allows the student to visualize in the display the electrons drifting in the gas and to study the physics of the processes involved.

[1] T.H.V.T.Dias and F.P. Santos, A.D. Stauffer, C.A.N. Conde, Monte Carlo simulation of x-ray absorption and electron drift in gaseous xenon, Phys. Rev. A, 48 (1993), 2887.

[NP01.89] ESFERAS: Radiation Hydrodynamics Through a web-based computer experimentation

It is the purpose of this poster to present an application, ESFERAS, oriented to understand better the of general relativistic stellar collapse through computational experimentation. This algebraic-numeric-visual web based environment is to intended to provide undergraduate and graduate students with some physical insight of very complex phenomena closely related to research topics.

ESFERAS is based on a general method proposed by L. Herrera, and Collaborators (L. Herrera, J. Jiménez and G. Ruggeri Phys. Rev. D 22, 2305 (1980)). Besides regularity conditions, models are only restricted by a heuristic assumption relating density, pressure and radial matter velocity. This ansatz, guided by very solid physical principles, reduces the problem of solving Einstein Equations to a numerical integration of a system of ordinary differential equations for quantities evaluated at the surfaces (shocks and/or boundaries).

Through a library of models, the user can visualized several collapsing configurations. It is also possible to select the corresponding field equations regarding the fluid to be consider and in two limits for the radiation transport: free streaming out and diffusion. As possible fluids, the system have: isotropic, anisotropic, viscous, and charged, and any combination of them. New models can be worked out using algebraic modules written in REDUCE or MAPLEV which allows the user to calculate and to write down subroutines starting from a ``seed'' static equation of state.

[NP01.90] Computational Physics: a Course, a Book, and Web Tutorials

A university level course in Computational Physics has been developed, a book based on this course (Computational Physics, Problem Solving with Computers, Wiley) has been published, and an extensive collection of multimedia, interactive Web tutorials which complement and extend the book have been developed. This part of an experiment in academic--commercial publishing in which Wiley publishes a traditional book while we maintain links to free Web tutorials.

A table of contents for all these materials with links to the Web materials is at www.physics.orst.edu/\~\mboxrubin/CPbook/. A description of the course and it setup is at http://goophy.physics.orst.edu/\~\mboxph465/.

The educational material is in the form of individual projects which follow a problem-solving paradigm for a very wide class of problems employing physical, mathematical, and computational techniques. As a consequence of having to interact with the material, it becomes part of the personal experience of the students.

The Web materials were developed by the Physics group of NACSE (an NSF Metacenter Regional Alliance). Some are directly related to the course, while others are more general, dealing deal with visualizations, HPC library use, PVM, and, Coping with Unix. Our emphasis is to exploit Web technology to better teach about and improve the use of HPC resources in science.

[NP01.91] Developing Interesting Interactive Exercises as a Supplement to First-Year Physics Lectures

We have developed several interactive Macintosh-based exercises to supplement lecture material on a variety of topics in our first-year calculus and non-calculus physics courses. We describe the exercise construction process and present sample screens from two of the exercises.

[NP01.92] Physics - Concepts and Models: A Web-based Physics Learning and Teaching Tool.

Physics - Concepts and Models: A Web-based Physics Learning and Teaching Tool.

We present an overview of Physics - Concepts and Models (PCAM). PCAM is aimed at helping students understand physics concepts, starting from student "alternative conceptions". PCAM gets students to test and modify their understanding of physics in a constructivist manner by taking advantage of the computer medium's strength that makes interactive simulations possible. The program is Web-based and written in Java and HTML which allows it to be platform-independent and customizable. Instructors are able to select and order the material or add new material as needed for a given course or in-class presentations. The intuitive navigation system will automatically display such re-arrangements to the users. By being able to customize the software, instructors will find it easier to integrate it into their courses. At the same time, students will appreciate having software arranged by their instructor.

The PCAM project is funded by the Province of Alberta through a Learning Enhancement Envelope grant.

[NP01.93] A Universal Physics Modeling Environment in Java

Computer simulations of physical processes have long provided scientists with valuable insights into their field of study. Its benefits in science education, however, are still masked by the complicated and counterintuitive handling of the necessary numerical algorithms. Although computer animations successfully allow for the interactive illustration of a specific topic, arbitrary experiments with various physical objects are mostly impracticable. On the other hand, our teaching experience shows that it is especially such unrestricted and creative examination of new concepts that greatly boosts the motivation of students and improves their learning results. In order to provide such unrestricted experiments in our TeleTeaching and HomeLearning scenarios, we developed a universal physics modeling environment in Java. Here students can freely combine predefined physical objects like springs, ropes, charged spheres and observe the resulting physical effects. Furthermore they can easily define new objects, e.g. a magnet, by describing the physical interactions without having to know the mathematics underlying the simulation.

[NP01.94] Assessment of In-Service Workshops on Students' Learning

Moorhead State University has conducted in-service Sharing Science workshops for nearly a decade to improve teachers' knowledge with the goal of better student achievement in physical sciences. The workshops were assessed by participants for instructional effectiveness each year. Additionally, an assessment project was initiated last year to measure students' learning at all levels in one school district in rural Minnesota. The assessment procedure consisted of interviews with teachers, a questionairre completed by teachers, and a set of tests taken by their students. The tests were designed to assess specific analytical skills along with content knowledge. This presentation focuses on the kinds of tests that were designed and why, and the results which are not as conclusive as anticipated. Based on experiences from the first set of data, the tests were redesigned and are being administered again. Included in the presentation is the progress to-date and a discussion of what has been learned.

[NP01.95] Teaching Fundamental Physics Concepts through Tricky Problems

In this presentation, I will discuss the use of unusual, Olympiad-style problems in teaching certain fundamental, yet frequently overlooked concepts, such as: Physics Models vs. Physical Reality; Frames of Reference and Relativity of Motion; Omnipresence of Simple Harmonic Motion. Most of the problems are taken from my book "Challenging Problems for Physics", which I have been using with my AP Physics classes for several years. In addition, I hope to make my colleagues aware of the necessity to use non-conventional, creative problems in classroom teaching. Problem-solving can be made more enjoyable and instructive if these "braintwisters" become regular at classroom discussions.

[NP01.96] The Earth's Rotational Period and the Origin of Species

All organisms (bacteria, plants, fungi, and animals) appear to have an internal biological clock which governs circadian rhythms. This clock is an internal mechanism which measures time in the living organism independent of environmental cues. The clock of each species has its own daily cycle length which is close to, but not exactly, 24 hours. It has been suggested that different species with the same daily cycle length may have descended from a common ancestor. An alternative explantion may be that these species originated approximately at the same time, not necessaily from a common ancestor. More specifically, we hypothesize in this paper that the internal daily cycle length of each species was determined (excluding gene mutations) at the time the species originated and its value corresponds to the earth's rotational period at that time -- a period which is increasing by about 22 microseconds per year. For example, under this hypothesis, squirrels, which have a 23 hour biological clock, originated 164 million years ago and plants with 22 hour biological clocks originated 316 million years ago.

[NP01.97] High Zeeman Field Narrowing of the NMR Peaks of Spin 1/2 Nuclei Coupled to Quadrupolar Nuclei: ^31P NMR Widths as a Probe of the RbH_2PO_4(x)-NH_4 H_2PO_4(1-x) Proton Glass

The understanding of the microscopic origin of the electric analog of the spin glass behavior by a random mixture of a single crystal of a ferroelectric and an antiferroelectric lattice is one of the areas of active research in phase transitions. In particular, this opens up a new area in solid state physics wherein one can compare the fundamental similairities and differences between a behavior of the magnetic dipoles versus electric dipoles. It has been well established that in a certain composition range, the mixed crystals of the RbH_2PO_4 (RDP) and NH_4H_2PO_4 (ADP) exhibit a spin glass behavior, but the details of the underlying mechanism are still not fully understood. In order to obtain new clues to this phenomenon, we have initiated a systematic study of the utility of the high field NMR techniques. We have carried out ^31P NMR measurements on a series of R_xA_1-xDP compositions. It is found that compared to Zeeman field at 7T, those at 14T yield improved NMR resolution in the case of the Rb dominated compositions. This opens up a new avenue for studying these proton glasses. The possible cause of this high field-induced NMR line-narrowing will be discussed, together with the interpretation of the data in terms of the spin glass mechanism.

[NP01.98] Miniaturized High Resolution Thermometer for use in Earth-Orbiting Low-Temperature Physics Experiments

We present performance data on a prototype of a miniaturized High Resolution Thermometer (mHRT) to be used in upcoming flight experiments, such as Critical Dynamics in Microgravity (DYNAMX). This mHRT utilizes a magnetic alloy as its sensing element, and has a mass of approximately 4 grams. The design is optimized to minimize the effects of cosmic radiation once on orbit, and to withstand mechanical launch loads. On earth, one such thermometer has demonstrated 0.4 nK/\sqrtHz noise with a time constant of less than one second, and a drift rate of less than 80 fK/s.

[NP01.99] Trapped positrons for materials analysis

Significant progress has been made in accumulating large numbers of room-temperature positrons in a Penning trap (e.g., >10^8 e^+ in a few minutes from a radioactive source and rare-gas moderator).(R.G. Greaves and C.M. Surko, Phys. Plasmas 4), 1528 (1997). These collections of positrons are useful for a variety of scientific and technological applications. For example, by releasing the trapped positrons in a controlled manner, it is possible to form a beam with a very narrow energy spread (< 20~meV).(S.J. Gilbert et al.), App. Phys. Lett. 70, 1944 (1997); C. Kurz et al., Nucl. Instr. Meth. B143, 188 (1998). While this beam is magnetized in the Penning trap, it should also be possible to extract the positrons from the field, remoderate, focus, and bunch them to create a state-of-the-art pulsed electrostatic beam. The capture efficiency of the trap is remarkably high (>30%) and losses in the trap are small (annihilation time >60 s), so that high e^+ throughput can be obtained. We discuss the creation and potential uses of such beams for materials analysis techniques now existing and under development.

[NP01.100] Positron and Positronium Annihilation in Natural Opals: Novel Approaches to Analysis

Natural opal samples have been examined by use of the Positron Annihilation Techniques: Lifetime (LT) and Doppler Broadening Spectroscopy (DBS). Additionally all solid samples have been examined under the Scanning Electron Microscope. Opal samples were in different maturation stages, amorphous and powdered: Opal - A, partly crystallized: Opal-CT , Opal-VV from Virgin Valley, quartz altered from opal sample (Q-O) and completely crystallized Quartz Aventurine (Quartz-Av) sample. In all opal samples two long lifetimes with the values: 2 ns and 10-50 ns were detected with the intensities of 10-17have been attributed to the pick-off otho-positronium annihilation in crystals of cristobalite and tridymite (2 ns) and in the three-dimensional tektosilicate framework structure (10-50 ns). By use of the DBS quotient analysis as well as the derivative analysis the distinction between the self para-positronium annihilation (dominant process in opal samples) and valence electron annihilation (dominant process in rocks with low microporosity) has been detected. From the lifetime values we were able to calculate the average size of the micropores, their distribution and correlate the positron annihilation parameters with the stage of maturation of opals from the early amorphous stage through the formation of cristobalite and tridymite crystals to the completely crystallized quartz structure.

[NP01.101] Micromachined Tip with Subwavelength Metal Aperture for NSOM and SPM Application

Micromachining of a nanoscale Si tip for near field scanning optical microscopy(NSOM) and scanning force microscopy(SFM) has been described. Various micromachining methods have been performed in order to have a metal aperture with radius less than ¥ë/2. Apertures provided with less than ¥ë/2 and hollow tips would provide a suitable probes for both NSOM and SFM. The nanosize (10nm>)Si tips were fabricated.A silicon nitride and a metal layer have been deposited on the Si-tip.The procedures such as field evaporation and PR removal technique have been performed in order to get a subwavelength aperture on the tip suitable for NSOM and SPM.

[NP01.102] A Digital Correlation Spectrometer for Plasma Research

Combining the correlation spectrometer concept with modern digital techniques has resulted in a novel grating spectrometer with unique advantages for measurements in noisy plasma systems and in discharges with intense continuum background. The instrument, dubbed an "active" spectrometer, incorporates digital control of an oscillating component (a mirror) and phase-locked digital recording of the intensity profile within the narrow spectral domain defined by the mirror oscillation. Flexible choice of oscillation frequency permits measurement in a quiet region of the noise spectrum. Reference waveforms acquired with the same instrument can be stored and later used to deconvolute a more complex spectrum. The use of multiple detector/slit combinations along a Rowland circle makes the spectrometer sensitive to specific atomic elements. Application of the active spectrometer to a partial pressure diagnostic on a tokamak fusion device illustrates some of the unique characteristics of this invention.

[NP01.103] Diffuse x-ray scattering from sputtered multilayers at large in-plane Q's

Synchrotron x-ray studies of the diffuse scattering for both correlated and uncorrelated roughness were obtained for length scales down to 5 nm. The data require a logarithmic interface roughness correlation function.

[NP01.104] Neutron three-axis spectrometry with focusing monochromators and position sensitive detection

Bent perfect crystals show promise in neutron three-axis spectrometry with position sensitive detection (PSD). Usual sequential scans may be replaced by simultaneous PSD scans along any given direction in the scattering (hømega,Q) plane. The direction is controlled by the curvature of the analyzer crystal. In focusing instruments with thin silicon wafers the achievable resolution, expressed in angular terms, is of about 0.03 deg. In conventional three-axis instruments this would require Sollers of about 1 minute of arc divergence. The corresponding resolutions in energy transfer are in the 10 to 100 microeV range. PSD spatial resolutions of about 0.2 mm will be required, though, to achieve such resolutions. With PSD analysis a new kind of focusing exists, that allows the thickness of the analyzer crystal to be increased with gains in intensity at no loss of resolution. Experimental results are presented, confirming that under the right conditions a multilamella analyzer looks like a single bent wafer, the individual curves of many wafers having been put together. Were not for this possibility, usual sequential and simultaneous PSD scans would have been equivalent as to the rate of data collection. Because of it, an intensity gain by the number of lamellae (15-20) is achievable. This is in addition to the intensity gain from "normal" focusing, which our recent experiments (Physica B 241-243, 1998, 216-218) have shown to range from 10 to more than 100. Supported by DOE grant FG02-96ER45599.

[NP01.105] The scales of fluctuations in stochastic media which produce Doppler--like Wolf shifts

The rate of fluctuations and the magnitude of the spatial correlations required to generate Doppler--like Wolf shifts of spectral lines on scattering from stochastic media are considered for a class of model media.

[NP01.106] Comparison between Kinematical and Dynamical Calculations of Rocking RHEED Intensities

Kinematical and dynamical calculations are two important tools for the quantitative analysis of RHEED intensities. Dynamical models are considered to be generally superior to kinematical ones when performing RHEED rocking curve analyses. However, several recent studies have reported the successful use of this latter approach for surface structure determination. In our research, numerical methods are being developed for both kinematical and dynamical calculations of RHEED intensities. Comparison is made between these two methods based on their application to several well-known reconstructed surface systems, including the clean Si(111)-(7\times7) and Si(100)-(2\times1) surfaces. Critera for selecting the appropriate method are proposed.

[NP01.107] Instrumentation for Precise Energy- and Angle-Resolved Secondary Electron Emission Measurements

The production of secondary electrons (SE) by energetic electron or ion bombardment involves multiple events including electron-electron and electron-lattice scattering. To date, the details of the mechanisms for SE production and emission are not well understood, and few accurate cross section measurements are available. Current instrumentation developed at USU has been used to measure the energy-angle resolved double differential SE cross section of elemental metals. Samples are bombarded with <20 eV to 30 keV electrons. For energy-resolved measurements, a hemispherical retarding-field analyzer is employed. A custom retarding-field Faraday cup detector, rotatable about sample position, measures the energy-angle resolved cross section. Details of instrumentation, experimental methods, and characteristic data will be presented. This work is supported by grants from the AFOSR/DURIP Program and the NASA/SEE Program.

[NP01.108] Implementation of a Lock-in Amplifier with a PC

An inexpensive Lock-in Amplifier is designed and characterized based on the half-flash A/D converter ADC0820 and a PC. The hardware of the amplifier consists of a computer card with two ADC0820 ICs that sample both the modulated signal and the reference one. The modulated signal passes trough filtering and amplifying stages before entering the A/D converter. The software acquires the data by simulating Chevyshev and Butterworth low-pass filters that constitute the output of the Lock-in Amplifier. The results of thermal characterization of materials like Candelilla wax, titanium oxides, etc., by open cell photoacoustic spectroscopy and Newton's law of cooling techniques are compared using this amplifier and the SR510 Lock-in Amplifier from Stanford Research Systems.

[NP01.109] Wavelet Analysis in an Optical Computer

The objective of this research is to design, construct, and test a simple optical computer, followed by an analysis of the signals generated using both Fourier Transform analysis and Integral Wavelet Transform (IWT) analysis. In order to study the spectral behavior of an analog signal from its Fourier transform, full knowledge of the signal (in the time-domain to be analyzed) must be acquired. This knowledge includes future information of the signal. In addition, if a signal is altered in the small neighborhood of some time instant, the entire spectrum is affected. Hence, in applications such as the analysis of non-stationary signals and in real-time signal processing, the use of a Fourier transform alone is inadequate. The use of IWT analysis allows room for a dilation (compression) parameter that widens (narrows) the time-frequency window according to the signal frequencies as needed. The IWT of a function simultaneously localizes the function and its Fourier transform with this zoom-in/zoom-out capability. We analyze the signals of the optical computer using both Fourier transforms and Integral Wavelet Transforms to illustrate the relative strengths and weaknesses of each method in analyzing an analog signal. This research is relevant to applications such as real-time diagnostic imaging and fiber-optic communications.

[NP01.110] Combined molecular dynamics and finite element method technique as applied to laser induced pressure w ave propagation

Analysis of a variety of dynamic phenomena requires simultaneous resolution of both atomistic and continuum length scales. A computational technique based on a combination of molecular dynamics technique and finite element method allows one to find balance between the necessary level of detail and computational cost. This technique has been implemented and tested on the propagation of a pressure wave induced by laser irradiation of organic solids. The strength of this combined approach is that a pressure wave can be transported over micron dimensions without losing the essential characteristics of the wave profile. The effect of the transition from molecular resolution in the molecular dynamics region to more coarse grid in the finite element region on the wave profile is discussed. This computational approach can be useful in cases where a detailed molecular-level analysis is necessary in localized regions which are spatially separated from each other whereas continuum mechanics and thermodynamics is sufficient in the rest of the system. In the field of laser ablation this approach can be applied to study back spallation, acoustic desorption, or laser ablation/damage of heterogeneous systems with spatially localized absorbers.

[NP01.111] A Di- Central Event Plane

A certain descriptive and simple quality is derived in the spheric basis of 4-space and how it scales. It is in general terms. As volume doubles, length increases by lesser factor \,^3\!\surd\,2\,, halving being inverse. Observers are at a one-way outward moving surface in respect to proper-time, origin in every direction and reference frame radio-polar. So the complementary proximate one-half of space is, given the outer radius as C and D observing distance\,, C=\left(1\:-\;^3\!\surd\;\frac12\right)D\;.A di- central event plane between halves divides space in two parts.\vspace.95mm A primary difference is it being \:\frac2^3\!\surd\,2\: later to one-half of linear age. The radius reflected at the observer's origin in \:C\,^3 defines a partial space in the one above, but it is unknown if it follows for there being any special importance to it.

[NP01.112] An algebraic characterization of singular quasi - bi - Hamiltonian systems

We prove an algebraic criterion which characterize singular quasi - bi - hamiltonian structures constructed on the lines of a general, and simple, new formal procedure proposed by the authors. This procedure shows that for the definition of a quasi-bi-hamiltonian system the requirement of non-singular Poisson tensors, contained in the original definition by Brouzet et al., is inessential. Besides, it is shown, incidentally, that one method of constructing Poisson tensors available in the literature, is a particular case of the treatment proposed in this work.

[NP01.113] Nonlinear Charge Distribution and Quantum Capacitance Microscopy

We report a general and gauge invariant theory for nonlinear DC transport in the coherent quantum regime. It is applied to investigate the nonlinear charge distribution and nonlinear electrochemical capacitance for conductors which are coupled capacitively. We derived an exact expression for the electrochemical capacitance-voltage curve in a generic form. This result suggests a quantum scanning capacitance microscopy at the nano-scale: by inverting the capacitance-voltage expression one is able to measure the local spectral function of a nano-system.

[NP01.114] Lie symmetries of classical field theories

We consider systems of nonlinear partial differential equations describing classical field theories. A Lie symmetry of such a system is a transformation of the independent and dependent variables that leaves the solution set invariant and belongs to a local Lie group. The general method of finding Lie symmetries is to apply the appropriate prolongation of the symmetry generators to the equations and set the resulting expressions to zero wherever the original system of equations holds. We have applied the method to several types of equations, with or without the help of symbolic packages. In particular, we have considered the full or self-dual Yang-Mills equations, Einstein's equations in N dimensions, and the equations describing an electromagnetic field coupled to a complex scalar field or a two-dimensional spinor. Results obtained in all these cases will be reviewed and discussed.

[NP01.115] Transient effects in time-dependent resonant tunneling

We consider an analytic solution to the time-dependent Schroedinger equation with the initial condition of a cut off wave to investigate the time evolution of tunneling in double-barrier resonant structures. Our approach involves the S-matrix poles and resonant (Gamow) states of the problem. At resonance energy we study the buildup time of the probability density along the internal region of the structure and the formation of the propagating transmitted solution. At long times we compare the transmitted wavefront with the propagating wavefront for the free case and obtain a delay time of the same order of magnitude as obtained in the stationary-phase treatment.

Ref. G. Garcia-Calderon and A. Rubio, Phys. Rev. A 55, 3361 (1997).

[NP01.116] Topological and Nontopological Solitons in Ordered Systems

The dynamics of the systems which are described by the order parameter taking values on the sphere is examined. There are two types of solitons (domain walls) whose existence is due to two different machanisms of the soliton’s size fixing (topological and nontopological). We consider a situation when topological and nontopological (higher order gradient) terms, breaking respectively the degeneracy of the equilibrium state and the scale invariance, are present in the free energy of the system. For the angle \phi of the planar configuration of the unit-vector order parameter we find the equation of motion \phi_tt=\phi_xx*(1+a\phi^2_x)+b*\phi_xxxx-d*sin(\phi), where x and t are nondimensional space-time variables; a, b and d are parameters of the model. This equation is novel. It has soliton solutions which combine the properties of both topological and nontopological solitons. The stability of solitons and their propagation are studied. For definite choice of parameters or space-time scales the equation goes over to the different particular equations, e.g., sine-Gordon, modified Korteweg-de Vries and other ones. We show that in the A-phase of superfluid ^3He the conditions for creating the nontopological spin solitons (d = 0) may be realized in the presence of magnetic field. Other physical applications are discussed. We are also able to take into account in the equation the \phi_t-type dissipative term.

[NP01.117] Electron Propagator in a 3-D Saddle Point Potential in the Presence of Electric and Magnetic Fields

The nonrelativistic retarded Schrödinger Green's function is derived

for electron motion in a 3-D saddle point potential subject to a time dependent electric field and a constant uniform magnetic field. The saddle point potential considered here is of the form V(x_\perp,x_\parallel)=\frac12 m_\parallelømega_\parallel^2 x_\parallel^2-\frac12m_\perpømega_\perp^2 x_\perp^2, and the electric field is oriented arbitrarily with respect to the magnetic field. Schwinger's operator of motion equation method is employed to obtain a closed form expression for the electron propagator.

[NP01.118] Results of the Michelson-Morley Experiment In View of Rutherford's Discovery of the Incredible Emptiness of Atoms.

Atomic bodies consist of nothing but nuclear praticles, very far apart from one another. In atomic bodies, distaces between the nuclei of neighboring atoms are up to 10^5 times the radii of the nuclei. If the nucleus is represented by a node of a network made of 0.1 mm thin nylon threads, then the next thread and node of the net should be a 10 m away. Such a network can move undisturbly through normal gases and liquids (even with schools of birds of herring), without making winds or currents in them (but wavelets around the nodes). Our vacuum space contains electron and positrons which, too, are far apart frome one another. The nuclear particles constituting an atomic body can move through the network of electrons and positrons in space, creating in it real EM waves of de Broglie wavelength, but no winds or currents. EM radiation, once emitted into this carrying space, propagates with a velocity c that depends on the conditions in it, not on the already forgotten velocity of the emitter. Atomic bodies, including the earth and ourselves are not dense and continuous, as perceived, and do not buldoze the electron positron network in space. (M.Simhony, The Epola Space, 1990, 160 pp, and, The Story of Matter and Space, 1998, 70 pp (available from the author). Also, M.Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994 (292 pp).)

[NP01.119] Electronic structure of silicon based clathrate

Recently, silicon based clathrates draw much attention with discovery of superconductivity in the silicon based clathrate that is Si_20 based materials alkali (Na) and Alkaline-earth (Ba) atoms locate in the silicon cluster cage. For further finding of new superconductors and additional characters, it is essential to study bonding character of this materials. The first principle norm-conserving pseudopotential with a planewave basis set and supercell approximation employ the silicon based clathrate that an aluminum atom locates in the silicon cluster cage. We calculate the second derivatives of charge density with respect to position to clarify covalent bonding strength among atoms in the clathrates. We discuss the bonding character differences between silicon - silicon and silicon - aluminum.

[NP01.120] Special Points for (GaAs)/(Ge_2) Semiconductor Superlattices

The special point method has been used for many years to do electronic structure calculation of solids. Here we obtain and discuss the special points for performing integrals over the Brillouin Zone of (GaAs)/(Ge_2) Superlattices. If the period of the Superlattice is taken properly the number of special points can be greatly reduced, thus making the calculations much faster.

[NP01.121] Meter-Scale Model of a Scanning Force Microscopy Cantilever Operating at High Frequencies

Scanning Force Microscopes (SFM) provide microscopic information of surface morphology. At each point on the surface, it is also possible to measure a force-separation curve, which provides chemical information of the region. In order to obtain that kind of curve, the sample is approached towards the tip and the tip deflection, due to changing tip-sample forces, is recorded. Then, for each separation, the tip deflection is multiplied by the cantilever's spring constant to obtain the desired force. Lately, the SFM community has recognized the importance of allowing the cantilever to move fast in order to make movies of biomolecules. Fast motion implies excitation of higher vibrational modes in the cantilever. Thus, the force is no more obtained via Hooke's law. We present results on how to properly analyze the high frequency data to extract the force. In addition, we have built a large-scale model of the cantilever for educational purposes. This project is supported by NSF grant number DMR-9872689

[NP01.122] A scheme to improve the quality of pseudopotential and to reconstruct all-electron wave functions

The norm-conserving pseudopotential method has been used in calculations of electronic structures of a wide range of materials and systems. We propose a method to improve the quality of the pseudopotential by improving the matching of higher orders of energy derivative of wave functions' logarithmic derivative at the cut-off radius. By direct modification to the pseudopotential is applied to minimize the error of logarithmic derivative over a certain energy range. We were able to improve the quality of the standard norm-conserving pseudopotential. The energy derivative are calculated from differential equations derived directly from Schrödinger's equation. For heavy atoms, the energy derivative for all-electron wave functions are calculated using spin-averaged Dirac equation. Results for simple atoms as well as heavy atoms will be presented. The same approach also give us the suitable localized functions to reconstruct the all-electron valence wave functions. Use the core-orthogonalization scheme, the all-electron wave functions of Li and Si were reconstructed from the pseudo wave functions.

[NP01.123] Accurate and Efficient Perturbation Theory by Matrix Inversion

An approach to time-independent perturbation theory is developed which has significant advantages over the traditional Rayleigh-Schroedinger method. With this new approach, energies and wavefunctions corresponding to perturbations of arbitrary strength acting on either degenerate or non-degenerate systems can be efficinetly recovered via a conceptually straightforward matrix-inversion scheme. Tedious summations are eliminated, and no integrals beyond those appearing in first-order perturbation theory need be computed.

[NP01.124] Electronic band structure of CaCuO_2 and SrCuO_2

The discovery of high-temperature oxide superconductors stimulates much interest in low-dimensional spin systems. By means of band calculations within both the local-spin-density approximation (LSDA) and the on-site Coulomb correlation U correction (LSDA+U), we have investigated the electronic structure of the Cu^2+ spin=1/2 antiferromagnetic insulators, the two-dimensional (2D) CaCuO_2 and the 1D SrCuO_2. The LSDA calculations show that strongly orbital-dependent exchange splittings open an insulating gap in SrCuO_2, which is in contrast to the metallic solution for CaCuO_2 due to the enhanced p-d hybridization in the 2D CuO_2 plane. While the U correction to the local Cu 3d orbitals in both the cuprates leads to an insulating state in agreement with the experimental results.

[NP01.125] Selective Resonant Tunneling and Damp-Matching

The resonant quantum tunneling current through the barrier between two wells may be maximized when the damp (absorption) in one well matches the barrier parameters. The maximum resonant tunneling current is much greater than the conventional expectation by a large factor of \theta (\theta ^-2 is the conventional barrier tunneling factor). Thus, the resonant tunneling would select not only the right energy level, but also the right damping. In other word, when the barrier is thick and high the damp-matching would select only the energy level which has a long life-time . The implication of this resonant tunneling model would be discussed in quantum spin tunneling and nuclear physics

[NP01.126] Self-Consistent Calculation for the Interface Between the Semiconductor and Vacuum

We apply the density-functional theory to calculate the junction characteristics between the semiconductor and vacuum. We obtain the self-consistent solution of the charge distribution around the interface. The zero-temperature form of the exchange-correlation potential which corrected by Sham for semiconductor is used, but full account is taken through the Fermi distribution function of the finite-temperature occupancy effects. We also apply the effective mass approximation to the Schroedinger equation in our method. The electronic structure and potential for the interface are reported. Our calculations for the semiconductor with the conduction electron densities r=24, 36, and 48 a.u.

[NP01.127] Tight-Binding in Diamond Structure Materials: Bulk Phases and Phonons

The NRL-developed tight-binding method(M. J. Mehl and D. A. Papaconstantopoulos, Phys. Rev. B) 54, 4519 (1996) has recently been extended to Carbon (in both sp^2 and sp^3-bonded phases) using only s and p orbitals, and to Si, using s, p, and d orbitals.(D. A. Papaconstantopoulos, M. J. Mehl, S. C. Erwin, and M. R. Pederson, MRS Proceedings) 491, (1998). We have now improved the parametrization of Si by fitting to the experimental electronic band gap, and developed parameters for Germanium, also fitted to the observed band gap. Here we look at the relative stability of the bulk structures of all three elements. Using the tight-binding formalism and the DoD-TBMD program, we can directly determine the dynamical matrix of the diamond structure of each element. From this we determine the phonon spectra. If time permits, we will also determine the thermal expansion parameter for all three elements.

[NP01.128] ^7Li nuclear magnetic resonance relaxation measurements on LiMPSA + [2.2.2] Cryptand

^7Li nuclear spin-lattice relaxation and spin-spin relaxation measurements have been performed on the amorphous electrolyte system consisting of Lithium N-(3-methoxypropyl)trifluoromethanesulfonamide salt added to a [2.2.2] cryptand. The cryptand's enhancement of the cationic mobility and thus the ionic conductivity is discussed. The relaxation data fits well to a single correlation time model for the spectral density of the lithium ionic motion. A single activation energy and attempt frequency have been measured for the lithium ion motion using the spin-lattice relaxation data. Comparison of these measurements to motion parameters extracted from an electronic structure calculation of the cryptate's electrostatic potential is discussed. This work is supported by the NSF-MRSEC program through the Materials Research Center at Northwestern University, grant DMR-9357506.

[NP01.129] Finite Size Scaling method for the Stability of Atomic and Molecular Ion

Phase transitions at absolute zero temperature can take place as some parameter in the Hamiltonian of the system is varied. For such transitions, crossing the phase boundary means that the quantum ground state changes in some fundamental way. For the Hamiltonian of N-electron atoms, this parameter is taken to be the nuclear charge. As the nuclear charge reaches a critical point, the quantum ground state changes its characters from being bound to being degenerate or absorbed by a continuum. We describe finite Size Scaling method to calculate the critical nuclear charge for which an atom can bind an extra electron to form a stable negative ion. The method can be generalized to calculate other critical phenomena in atomic and molecuar system.

[NP01.130] Stability of one-electron bond in a strong magnetic field

Stability in a system Z_A Z_B e^- consisting of two nuclear centers with charges Z_A, Z_B and one electron is studied as a function of q=\fracZ_AZ_B and magnetic field B. Our results are based on fully numerical approach and variational calculations. Critical charge parameters separating the regime of stable and unstable binding energies are calculated as a function of the magnetic field. Results show that the stable binding region 0 < Z_A \leq 1.236 in the free field becomes smaller as B increases. For q=1, the critical magnetic field B_c=0.94 a.u. corresponds to a critical charge Z_c=0.86 where the molecular binding energy equals to zero. Stability is also studied for different values of the parameter q. The stability scenario of states in a strong megnatic field are not restricted to one-electron systems, but can be expected also to be of relevance for more general situations of atoms and molecules.

[NP01.131] Exact Exchange-Correlation Energy Functional for a System of Spinless Fermions

We obtain an explicit exact expression for the exchange-correlation energy functional E_xc[\rho] for systems of harmonically interacting spinless fermions. The construction of E_xc[\rho] is made possible by a mapping procedure that exploits its universal property. We denonstrate the procedure and discuss its implications for the Coulomb interaction.

[NP01.132] A time-dependent quantum mechanical model of photoexcitation in conjugated polymers

We treat photoexcitation in conjugated polymers as the creation of a particle-hole pair, and model these quasiparticles using a formally exact time-dependent wavepacket treatment. The polymer lattice is treated as a set of classical oscillators interacting with the quantum particles. The model, which permits exciton- and polaron-like states, allows us to examine the role of the lattice with respect to ultrafast spectroscopic observables such as the time-dependent Stokes shift (exciton-polaron formation energy) and the nature of vibrational coupling between the dipole-allowed 1Bu singlet state and the lowest lying triplet excited electronic state.

[NP01.133] A generalized Lagrangian approach for excited state molecular dynamics in the random phase approximation.

This paper reviews our efforts towards developing methods to do molecular dynamics in electronically excited systems using a first principles description of the forces. Our method is based upon a Lagrangian treatment of the electronic excited state energy functional which depends parametrically upon the classical positions of the nuclei. Working within the random phase approximation, we derive coupled equations of motion for the electronic amplitudes (for both the ground and excited state orbitals) and the nuclear coordinates. Model calculations on linear polyenes will be presented and we discuss the advantages and disadvantages of our methods.

[NP01.134] Lennard-Jones as a Model for Argon and Test of Extended RG Calculations

Pressure isotherms for argon measured at temperatures somewhat below and above the critical point, for densities from 5% to somewhat more than twice that at the critical point(A. Michels, J. M. Levelt, and W. DeGraaff, Physica 24), 659 (1958)., together with a model Lennard-Jones intermolecular potential, have been used to test features of an extended renormalization group (ERG) theory for fluids.(J. A. White and S. Zhang, J. Chem Phys. 99), 2012 (1993); 103, 1922 (1995); and Int. J. Thermophys (in press). In particular, in addition to choices for the Lennard-Jones model parameters sigma and epsilon, theoretical ERG predictions of nonuniversal thermal quantities depend also on the choice made for the ratio of edge of averaging volume to current fluctuation wavelength in the renormalization procedure and in addition somewhat upon the precise value chosen for smallest fluctuation wavelength considered (generally taken to be between about three and five times the "sigma" of the model). Results will be discussed in relation to the question "To what extent could the ERG procedure have been relied upon to make a priori predictions for argon?"

[NP01.135] Spatial de-orientation lifetimes for upper Stark state selected beams of CH_3F, CH_3Cl, CH_3Br and CH_3I in field-free space.

The mean lifetimes for spatial scrambling or deorientation of upper Stark state (KM_J<0) selected beams of CH_3F, CH_3Cl, CH_3Br and CH_3I in field free conditions have been measured. Supersonic beams were quantum state selected in a hexapole inhomogeneous electric field and directed through a uniform electric field maintained between a pair of parallel field plates before focusing through a second hexapole field to a quadrupole mass spectrometer detector. Orientation effects were measured via the effect of the uniform field on the beam signal. The beam signal at the detector was shown to remain constant for uniform field strengths greater than approximately 3~Vcm^-1. A drop in signal of around 40% was observed when the field strength was switched from >3~Vcm^-1 to zero field due to spatial scrambling of the molecular dipoles and subsequent loss of lower Stark states (KM_J<0) and partial loss of KM_J=0 states, which previously would have remained in upper Stark states, in the B field. Mean scrambling lifetimes were measured by subjecting the molecular beam to field free conditions for increasing time periods and measuring the effect on the beam attenuation. The mean deorientation lifetimes for CH_3F, CH_3Cl, CH_3Br and CH_3I were found to be 277, 257, 241 and 238~\mus respectively. These lifetimes are consistent with the observation of asymmetry effects previously reported for collisions of electrons with oriented molecules in experiments where the orienting field was switched to zero prior to electron impact ionization(Aitken et al), J. Chem. Phys., 1994, 101, 11074 Aitken et al, Int. J. Mass Spectrom. Ion Processes, 1995, 149/150, 297.

[NP01.136] Studies of electron - molecule collisions using crossed beams and ion imaging.

A crossed molecular beam machine has been constructed to investigate collisions between electrons and spatially oriented symmetric top molecules. Supersonic beams of neat and seeded symmetric top molecules, such as CH_3F, are quantum state selected and spatially oriented using a combination of inhomogeneous and homogeneous electric fields. The molecular beam is crossed with an energy selected pulsed electron beam and the products of ionization detected using an ion imaging system. This allows product angular differential cross sections and velocity distributions to be determined.

[NP01.137] Molecular Dynamics Simulations of Drift Tubes Experiments

The transport properties of ions drifting through neutral atomic gases under the influence of the uniform electrostatic field are studied by molecular dynamics simulations. For representative system, NO^+ in He, the drift velocities, effective temperatures and ionic diffusion coefficients in the direction parallel and perpendicular to the applied field have been obtained, and the comparison with the experimental and theoretical results on the same system have been performed. The good agreement between the results establishes the validity and accuracy of the method and enables us to pursue the analysis. In particular the velocity and angular momentum correlations functions, translational and rotational energy distributions, orientation and alignment parameters have been obtained for NO^+ and other model systems in order to probe the sensitivity of these properties on different geometries, interaction potentials and charge distributions. Furthermore the assumption that the different isomeric structures can be distinguished on the ground of their mobility alone have been investigated.

[NP01.138] Ab initio studies of the Na^+--N_2 and Na^+--O_2 ion--molecule complexes.

Long-lived Na^+--N_2 ion--molecule complexes have been implicated in the chemistry of meteoritic sodium in Earth's upper atmosphere. Accurate estimates of the lifetime of these complexes require knowledge of the Na^+--N_2 potential surface. We present a global (rigid rotor) ab initio potential surface for Na^+--N_2, computed at the MP4 level using large correlation-consistent basis sets. We compare the long-range behavior of this ab initio surface with that of a model surface based on electrostatic and induction contributions. We also compare the Na^+--N_2 and Na^+--O_2 interactions. The Na^+--N_2 complex is more strongly bound than the Na^+--O_2 complex, and has a much more anisotropic potential surface.

[NP01.139] Rotational excitation of CH^+ in collisions with He.

Far-infrared emissions attributed to pure rotational (j \rightarrow j-1) transitions of CH^+ have recently been detected from the direction of planetary nebula NGC 7027. The CH^+ ions are rotationally hot, with significant population in rotational levels up to j = 6. Collisions between CH^+ and H, H_2, or He could populate these rotational levels. We present a CCSD(T) ab initio potential surface for He + CH^+ collisions and use this surface to compute rate constants for the production of rotationally excited CH^+.

[NP01.140] Peculiar non-adiabatic effects in the photoelectron spectrum of allene (1,2-propadiene)

The synchrotron photoelectron spectra (PES) of allene (C3H4) at 20-120eV photon energies have been obtained at the ALS beamline 10.0.1. The study reveals, for the first time, additional structure around the 12.7eV binding energy peak which has been observed previously [Chem Phys Lett 287,61(1998)]. The additional structure confirms the previous theoretical interpretation that the very low intensity PES peaks around 12.7eV result from peculiar non-adiabatic effects or strong vibronic coupling (Jahn-Teller-like) between at least two electronic states --- one of which is a correlation state.

[NP01.141] Experimental Studies of the simplest fluxional anion, methide, CH_3-

Anions exhibit an enhanced sensitivity to electron correlation effects, and thus are good systems for studying electron correlation. CH3- does not have a fixed structure but instead exhibits an inversion motion, similar to the motion in the isoelectronic neutral NH3. The inversion frequency in CH3- is expected to be very sensitive to the details of the potential, including electron correlation effects. Theoretical calculations variously predict that electron correlation will either increase^2 or decrease^3 the tunnelling rate, depending on the theoretical approach. Methide has a small (0.08 eV) electron affinity and vibrationally excited states are expected to autodetach. Methide is thus a good candidate for autodetachment spectroscopy. There is little experimental data on this simple system and none at high resolution. Production of adequate beams of CH3- is experimentally challenging. Progress will be reported in our studies of methide.

[2]. D. S. Marynick and D. A. Dixon, Proc. Natl. Acad. Sci U. S. A. 74, 410-413 (1977). [3]. F. Driessler et al., Theo. Chim. Acta (Berlin) 30, 315-326 (1973); C. E. Dykstra et al., J. Chem. Phys. 67, 4071 (1977).

[NP01.142] A Scaling Method for Computing Scattering Between Atomic Helium Beams

We describe a scaling method for calculating the scattering between and within beams of helium atoms. The number of atoms N in the beams is reduced by a large scaling factor \lambda while the collision cross-section is increased by \lambda. This leaves the rate of scattering for each particle unchanged. As an example of the method, we predict the outcome of a low temperature atomic beam experiment designed to measure the ^4\!He--^4\!He atomic scattering cross-section \sigma at low energies. Because of the existence of a very weakly bound dimer, the low energy cross-section is expected to be unusually large, \sim 1.83 \times 10^5~ÅIn the simulation N/\lambda is small enough for the trajectories of all the scaled atoms to be calculated numerically. The simulation shows that the experiment is quite practicable. The proposed apparatus is just over 20~cm long, and a few centimeters wide, small enough to fit in a dilution refrigerator. The heaters and bolometers are assumed to be similar to those used in previous low temperature scattering experiments. We show that, using low intensity beams, the cross-section can be measured as a function of the relative velocity v_r. By fitting \sigma (v_r) one can determine the scattering length and effective range of the interaction. We also predict that, at high intensity, the two beams coalesce into a single beam.

[NP01.143] Molecular Detachment Spectroscopy of Triplet He_2^* on Helium Nanodroplet Surfaces

Metastable excitations produced in a beam of helium nanodroplets by electron bombardment evolve into triplet He_2^* molecules bound on the droplet's surface. Absorption of an infrared photon can lead to the detachment of a molecule. When a detached metastable molecule hits the walls surrounding the beam it releases an electron which can be counted. We will describe the spectral dependence of this effect in the region of the c^3\Sigma^+_g \leftarrow a^3\Sigma^+_u transition of the free molecule. We observe very sharp but highly structured spectral lines, which carry detailed information about the molecule and its unusual rotational distribution, about its interaction with the helium surface, and about the dynamics of the underlying droplet.

[NP01.144] Mechanical Properties of Poly(ethylene oxide)/Poly(L-lactide)/Compatibilizer Ternary Blend

Diblock and triblock copolymers of poly(ethylene glycol)(PEG) and poly(L-lactide)(PLLA) were used as the compatibilizer for the biodegradable PEO/PLLA (60/40) blend. Poly(vinyl acetate)(PVAc) was used as another compatibilizer for the same blend. Overall mechanical properties of the PEO/PLLA blends were enhanced only marginally, when diblock and triblock PEG-PLLA copolymers were utilized, because the molecular weights of the PEG-PLLA block copolymers were shorter than that of individual homopolymers comprising the blend. When PVAc was added to the PEO/PLLA blend, the spherulitic growth rate of PLLA in the blend decreased and the characteristic crystalline features of the PLLA spherulite became less obvious. Tensile properties were affected greatly by the method of blend preparation and the annealing time. As long as the effect of quenching was suppressed, PVAc was found to be entrapped inside the PLLA spherulites, resulting in an increase in the toughness of the crystalline PEO/PLLA blend.

[NP01.145] Observation of Boson Peaks by Inelastic Neutron Scattering In Polyolefins

Inelastic neutron scattering was used to probe the nature of the boson peak in atactic poly-propylene (aPP), head-to-head polypropylene (hhPP), polyisobutylene (PIB) and a 1/1 volume ratio hhPP/PIB blend. Atactic polypropylene is among the most "fragile" of glass formers and was found to have a shoulder rather than the distinctive peak exhibited by hhPP at an equivalent displacement from the glass transition. This appears to be due to both an increased density of states for aPP at the the lowest temperature measured (15 K) and the more rapid development with temperature of a fast process. The difference in the boson peak behavior suggests that the fragilities of hhPP and aPP are quite different. For the three pure, chemically similar polymers the position of the boson peak can be correlated with the glass transition temperature, the cohesive energy density and the characteristic ratio. In general this is not the case for chemically dissimilar molecules. PIB is miscible with hhPP but not aPP and the dynamics generating the boson peak in the blend appear to be intermediate between those of the pure components.

[NP01.146] Designing High-performance Fibers with Improved Compressive Strength

Significant progress has been reported in improving the compressive strength of high performance polymeric fibers via the introduction of crosslinks or bi-directional hydrogen bonding. In order to quantify the effect of the latter on the compression behavior of rigid-rod polymers, we are investigating systems (i) void of hydrogen bonding, (ii) with one-dimensional hydrogen bonding, and (iii) with two- dimensional hydrogen bonding. Moreover, ab initio calculations are being employed to study the affect of intra vs. intermolecular hydrogen bond formation on compressive strength. In a previous study on the effects of crosslinking, an anisotropic residual stress was found to form on crosslinking in MePBZT fiber. We are currently pursuing approaches to measure and, if possible, eliminate the development of stresses on crosslinking. Results of these studies will be presented.

[NP01.147] Physical Aging Behavior of Substituted Poly(p-Phenylenes)

The effect of varying the molecular structure on the physical aging behavior of poly(p-phenylenes) substituted with benzoyl and 4-phenoxybenzoyl groups and a copolymer of benzoyl-1,4-phenylene and 1,3-phenylene has been investigated by studying their volumetric and enthalpic relaxation behavior. The 4-phenoxybenzoyl substituted polymer was shown to have the largest volumetric relaxation rate. Master curves from the the volumetric and the enthalpic relaxation data have been prepared. The shift factors obtained can be fit to the WLF equation, and agree well with shift factors previously obtained from master curves generated by dynamic mechanical data. The times to reach equilibrium as well as the relative approach to equilibrium as measured by the two methods will be discussed for the three polymers, and in turn compared to that obtained for other polymers.

[NP01.148] Droplet size hysteresis and coalescence kinetics in immiscible polymer blends

Shear-induced droplet breakup and coalescence in binary polymer blends was investigated by optical microscopy during simple shearing. The steady-state droplet size was investigated as a function of shear rate, and the kinetics of droplet-size evolution was monitored after either a step up or step down in shear rate, which produced droplet breakup or coalescence, respectively. In each of four blend systems, the steady state size produced by coalescence was equal to that produced by breakup. Therefore, no permanent hysteresis was observed. However, a significant temporary hysteresis occurs, because of the relatively slow kinetics of coalescence. The amount of strain required to achieve steady state was investigated as a function of the composition of the system and of the shear-rate step-down ratio. Coalescence requires two events: droplet collision and drainage of the matrix fluid film between them. For gentle collisions, i.e. large step-down ratio, the probability of film drainage is unity and the kinetics of droplet collision can be measured independently. The authors gratefully acknowledge the financial support of the Goodyear Tire and Rubber Co., GE plastics, and NSF grant #CTS-9731502.

[NP01.149] The Relevance of Modeling Amorphous State Waxd Scattering to the Phase Morphology and Melting in Branched, Metallocene Polyethylenes

Waxd and DSC analyses were performed on a wide range of branched polyethylenes. Waxd liquid scattering in the melt in the region of the low angle amorphous halo revealed a temperature dependent fraction and a temperature independent fraction. The liquid state is modeled in such a way to semi-quantitatively represent inter- and intra-molecular scattering, based on literature references in studies designed to resolve this dependency. Properly defined, the liquid fraction is shown to be 5-8% greater than that from empirical fitting and, for the first time, permits the interfacial content to be revealed by Waxd for polyethylenes. When combined with temperature resolved Waxd lattice studies and DSC, the phase analysis permit a quantitative description of the real melting points. A large portion of the melting endotherm, in highly branched systems, is associated with annealing and cannot be fully correlated with the crystals. As such, it is suggested to result from a large 'tethered' liquid like fraction.

[NP01.150] Electrospinning of polyethylene oxide solution

In the electrospinning process, electrostatic force is used to spin ultra thin fibers. Parameters that control this process include the volume flow rate of the solution, applied voltage, jet current, jet diameter, jet velocity, concentration of the solution and the electrical field. The jet was projected upwards from a droplet sitting on the top of a 3 mm diameter glass tube. The feed rate of poly(ethylene oxide) solution into the droplet was set at particular values and the electric field was adjusted to give a quasi-stable jet, that is a jet which carried solution away from the droplet at the feed rate. When the feed rate did not equal the flow rate of the jet out of the droplet, the shape and the volume of the droplet changed and the jet became unstable. Jet oscillation, jet vibration and the formation of multiple jets were observed and recorded with a video camera. At high feed rates and high applied voltages, a single jet is very unstable and multiple jets are formed. The relationship between jet current and electric field intensity was measured. Increasing the electric field increased both jet diameter and jet velocity and hence the volume flow rate of the jet. Data on the shape of the jet are compared to theoretical predictions.

[NP01.151] Secondary Crystal Melting in Ethylene-Methacrylic Acid Ionomers

The detailed structure of ethylene-methacrylic acid (\emphE/MAA) ionomers, which contain both polyethylene (\emphPE) crystallites and ionic aggregates, remains a subject of debate. DSC heating thermograms of annealed or slow-cooled \emphE/MAA ionomers typically show two endotherms. The higher-temperature endotherm (\sim90^oC) is universally attributed to the melting of primary \emphPE crystallites. The origin of the lower-temperature endotherm (\sim50^oC) is less clear; it has been suggested that this endotherm arises from an order-disorder transition within the ionic aggregates. We have studied the structural changes occurring on heating in several \emphE/MAA ionomers by simultaneous SAXS/WAXS/DSC. The \emphPE (110) reflection in the WAXS data decreases modestly but monotonically on heating through the low-T endotherm. More significantly, the intensity of the principal SAXS peak (\emphq\approx0.5nm^-1) increases significantly on heating through the low-T endotherm, then decreases as the primary \emphPE crystals melt at the high-T endotherm. We thus attribute the observed low-T endotherm to the melting of very small secondary crystals which form between the primary \emphPE crystallites on annealing or slow cooling. When these secondary crystals melt, the electron density difference between the primary \emphPE crystallites and the interlamellar regions (which contain the ionic aggregates) increases, increasing the intensity of the SAXS peak.

[NP01.152] Solid-State Complexes of Branched Poly(ethyleneimine) and Dodecyl Benzene Sulfonic Acid: Self-Assembled Structure and Thermal Properties

Supramolecular structure and thermal properties of the solid-state complexes of a highly branched poly(ethyleneimine)(PEI) and dedecyl benzene sulfonic acid(DBSA) surfactant (surf) have been investigated. Polarized optical microscopy and small-angle X-ray scattering (SAXS) revealed the presences of mesomorphic phases and microphase-separated lamellar morphology consisting of alternating polymer and surf layers. The ordered supramolecular structure was observed over a wide composition range. Consequently, the high branching level of PEI chains did not undermine the ordered packing of alkyl tails in the complexes. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. The glass transition temperature of PEI was raised by complexation. Complexation with DBSA also enhanced the thermal stability of PEI, where the thermal decomposition temperature can be raised by as many as 50 C.

[NP01.153] Effects of Pendent Chain and Backbone Lengths on the High Temperature Dielectric Spectra of Tyrosine-Derived Biopolymers

In this work we present a comparative study of the high temperature dielectric spectra in a series of four tyrosine-derived polycarbonates and four tyrosine-derived polyarylates. The pendent chain of the polycarbonates was varied in steps of two methylene groups from two to eight carbons. The number of methylene groups of the polyarylates backbone was increased in steps of two from two to eight carbons. The Thermally Stimulated Depolarization Current (TSDC) technique was used to obtain the high temperature dielectric spectra. Each spectrum shows a very intense and sharp current peak, A peak, indicative of the glass transition relaxation of the polymer. The analysis and comparison of the observed relaxations provided correlations with pendent chain and backbone lengths. A linear relationship was obtained between the temperature of the current maxima of the A peak and the number of methylene groups. The results found suggested that the effect of methylene groups on polymer mobility and packing efficiency was independent of the position of the methylene groups within the polymer molecule. Concerning the polarization built up for the A peak, six methylene groups were found to be the threshold for an introduction of an extra effect in polymer structure.

[NP01.154] Ellipsometric Determination of the Glass Transition in Thin Polymer Films

A spectroscopic ellispometer equipped with a hot stage was used to investigate thermal transitions of thin (.1-1 micron) and ultrathin (less then100 nm) polymer films. The glass transition was determined by identifying inflection points in the temperature dependent behavior of the ellispometeric parameters (\Delta and \Psi). This work parallels prior efforts by Keddie (1994) where he used an ellispometric technique to show substrate and thickness dependencies for the glass transition temperature in polymer films. The present study focuses on understanding the thermal transitions observed in both \Delta and \Psi as a function of the heating and cooling rate. The possibility of dewetting was investigated at elevated temperatures. Understanding the ellipsometric technique for random coil polymers has produced a sensitive tool for studying films for specialized applications such as concentrated polymer solutions of optically active dyes. Keddie, et al (1994) Europhys. Lett., 1, 59. Beaucage, et al (1993) J. Polymer Science: B Polymer Physics, 31,319.

[NP01.155] Controlled Dewetting in Confined Geometries via Photo Patterned Ultra Thin Capping Layers

Polystyrene dewetting represents an area of intense scientific interest. Optical and atomic force microscopy provide convenient ways to characterize this process. In this study, thin films of polystyrene are spin-coated on rigorously cleaned hydrophilic silicon wafers. These wafers are then covered with ultra-thin capping layers of isopentylcellulose cinnamate by the Langmuir-Blodgett technique. The thickness of the photo cross-linkable capping layers can be controlled in increments of 10 ÅIn the non cross-linked regions, dewetting is initiated upon annealing. Cross-linking the capping layer has profound effects on the rate of dewetting. This difference has been exploited to photo pattern the surface. Non cross-linked regions undergo rapid dewetting which effectively confines the regions underneath the cross-linked capping layer. This leads to a wide variety of dewetting patterns that depend on both the size and shape of the cross-linked region.

[NP01.156] Adhesion to Rough Surfaces

The effect of surface roughness on adhesion has been examined by the JKR method. Artificially roughened substrate surfaces were prepared by thermal evaporation of pure calcium fluoride (CaF_2) onto silicone wafers. Root-mean-square roughness of the substrates was found to vary from 25Åto 125Åwith the CaF_2 thickness. Hemispherical lenses of cross-linked hydroxyl-terminated poly(dimethylsiloxane) (PDMS) were subject to loading and unloading on the substrates. The adhesion values obtained by fitting the JKR model to loading data were decreased with increasing roughness of the substrates and only 45Årms roughness is sufficient to reduce the adhesion to a very small fraction of its value for smooth surface.

[NP01.157] Determination Of Three Dimensional Refractive Indices And Absorption Coefficients For Anisotropic Polymer Films By Prism Waveguide Coupling

A Metricon PC-2010 prism waveguide coupler has been used to obtain the three dimensional refractive indices of oriented free standing polymer films (1) (2), but the mode equations used neglect the effects of air gaps and polymer film absorption. General mode equations are developed here, which consider the effects of air gap between both the prism and the polymer film as well as absorption of the polymer film. Levenberg-Marquardt algorithms implemented by Optimization TOOLBOX for MATLAB® was used to extract the three- dimensional refractive indices, three dimensional absorption coefficients, and the thickness of polymer film by fitting the effective refractive indices of modes measured by the Metricon PC-2010. As an example, two polymer films, spin coated PPV (polyphenylenevinylene) and cast PMDA-ODA polyimide, are analyzed. The three-dimensional refractive indices, three dimensional absorption coefficients and the film thickness are obtained. The in-plane absorption coefficients and the thickness agreed with those obtained from independently measured UV-VIS-NIR transmission spectra.

(1) Hardaker, S.S., Moghazy, S., Cha, C.Y. and R. J. Samuels, J Polym Sci Part B, 31, 1951 (1993).

(2) C. Cha , S. Hardaker, R. Gregory and R. Samuels , Synth. Met., 84 , 743 (1997).

[NP01.158] Converse Electrostriction in Polymers and Composites

Electrostriction is the fundamental mechanism of electromechanical coupling in all insulator materials. The evaluation of electrostrictive properties of low permittivity dielectrics requires extremely sensitive instrumentation. In the present work, the electrostriction coefficients of several polymers were measured by a converse method. A dynamic compressometer was specifically designed to resolve fractional changes in capacitance on the order of 10^-6 caused by in-phase cyclic uniaxial stresses on the samples. Measurements were done at room temperature with an electrical frequency of 1kHz and a mechanical frequency of 0.4Hz. We found negative electrostriction coefficients for the polymers tested. Trends in the electrostriction coefficients with the structure and the presence of additives in the resins were identified. Moreover we checked that the corrected electrostriction coefficient Q of polypropylene was independent of the electrical frequency in the range 500Hz-100kHz. Using these new data, along with widely accepted data on other materials, the linear relationship between electrostriction coefficient (Q) and the ratio of elastic compliance and the dielectric constant (s/K) was obtained. This relationship leads to an effective way to predict the electrostriction coefficient in dielectric materials. This study was supported through National Science Foundation grant DMR-9634101.

[NP01.159] Local and Global Dynamics in Polyethylene and Polypropylene Melts by ^13C NMR

We report ^13C NMR T_1, T_1\rho and NOE measurements of atactic polypropylene (PP) and polyethylene (PE) melts as a function of Larmor frequency and temperature. We found that the data taken on PP discriminated decisively against two commonly used bimodal distribution functions, the DLM and modified logX^2. A trimodal distribution function was required to describe the dynamics, with the third component placed between the fast and slow components of the modified logX^2 distribution. Compared to PP, PE has a very pronounced long time tail in the orientation correlation function for C-H bond vectors and the local motions are more anisotropic. We hypothesized the difference to be caused by the lack of side groups on PE which allows C-H vectors to keep some memory of their initial orientation even after many conformational transitions occur. T_1\rho provides the upper and lower limit for the integral of the full correlation function.

[NP01.160] Chain Motion in Polyethylene and Related Systems

The rate of the 180^o flip motion, which leads to the crystalline \alpha relaxation in polyethylene, was determined from 280 to 360 K by solid-state NMR that observes the reorientation of C-C bonds. The activation energy is (93 \pm 10) kJ/mol, consistent with dielectric and dynamic mechanical relaxation. In contrast, in 1,22-docosanediol which has a similar crystal lattice as polyethylene but a different crystal surface structure, a solid-solid phase transition is found at T_r=93^oC. Static ^1H and ^13C NMR show that below T_r the chains have no (or slow if any) large-amplitude mobility, while above T_r they rotate freely. ^1H NMR shows that throughout the transition, neighboring regions of the emerging rotator phase are separated by > 100 nm and the mobility of the chains in both phases remains unchanged, consistent with the nucleation and growth model. As in several n-alkanes and ultradrawn polyethylene fibers, a liquid-like phase of 1% - 5% was observed in the diol well below the melting point. Its possible association with grain boundaries is under investigation. A polyethylene- like crystalline component was found in several soil samples. Based on the Thomson-Gibbs relation, the melting behavior observed by NMR yields crystallite thicknesses of 3-4 nm.

[NP01.161] Morphology and Properties of Extrusion Cast Elastomeric Films

The effects of processing and additives on the structure and properties of two SBS thermoplastic elastomers, are reported. The initial materials contained either 15 wt.diblock copolymer(trade name Kraton D1102, Shell Co., 28 wt.The pellets were extruded by using a single-screw extruder and wound on a quench roll under minimal tension. SAXS results indicate that the morphology of the hard segment (PS) domains in D4150 is hexagonally packed cylinders, i. e. similar to that of the equilibrium structures. It was concluded that the processing oil promotes a rapid microphase separation and ordering. In contrast, the morphology of the extruded specimen D1102 appears to be similar to the fluctuation- induced disordered structures [1]. Annealing at 145 C and slow cooling did not lead to equilibrium ordering of the PS domains. It appears that low molecular weight diblock copolymer inhibits phase segregation and ordering. [1] See for example N. Sakamoto, T. Hashimoto, Macromol. 31, 3815 (1998).

[NP01.162] Analysis of Molecular Parameters Governing Phase Separation in Polyurethanes

It is well established that polyurethanes phase separate into hard domains coexisting with a phase of hard segments dispersed in a soft matrix. However, previous studies have shown that the interaction energy is negative, indicating that phase mixing is enthalpically favorable. Theoretical work has shown that the driving force for phase separation comes from the orientational entropy associated with the chain rigidity of the hard blocks. The implication is that chain length is crucial in determining the phase separated morphology in polyurethanes. Our current research has focused on a chemically crosslinked polyurea urethane system consisting of an aromatic urea hard segment and a polyether soft segment. We detached the hard segments from the soft segments and used MALDI Mass Spec to characterize the chain lengths of the rigid blocks. We have found that the distribution of chain lengths is quite broad, ranging from 3 to greater than 8 repeat units in a system that theoretically has an average of 4 or 6 repeat units. The impact of hard segment length on morphology and mechanical properties will be addressed.

[NP01.163] Response Saturation in the Analysis of Synthetic Polymers by MALDI

Matrix-assisted laser desorption/ionization (MALDI) is one of the most successful mass spectrometric techniques developed to date for the analysis of large and thermally labile molecules. For synthetic polymers, MALDI can yield quantitative information, such as a description of the molecular weight distribution, as well as qualitative information about end groups and repeat units. Accurate quantitative measurements require an equimolar response, or at least a predictable variation in response, for all sample species in the mass range over which the polymer sample is distributed. There are both instrumental and sample-related factors that can influence the relative response of sample species. Some sample-related factors may influence the dispersion of polymer molecules throughout the matrix and so affect the degree of matrix-isolation achieved and whether there is any size-based order to it. To probe this, we examine the influence of polymer loading and matrix choice on the responses of low molecular weight poly(ethylene glycol) and poly(styrene) samples.

[NP01.164] The Hydrogen-Hydrogen Inter-molecular Structure of Polyethylene in the Melt

The model-free inter-molecular HH distribution function for PE is extracted from wide-angle (NDIS) and small-angle neutron difference scattering experiments at 428 K, and compared to MD simulations. The inter-molecular HH structure function was obtained without recourse to intra-molecular structure models, and is interpreted on three length scales: 1) the correlation hole which depends on the radius of gyration of the molecule, 2) chain-chain packing, and 3) local HH inter-molecular correlations. These results are significant because they demonstrate that the HH inter-molecular correlation function is useful for studying inter-molecular polymer structure, which has been shown to underpin phase behavior in polyolefin blends.

[NP01.165] Surface Initiated Living Cationic Polymerization of 2-Oxazolines on Gold Nanoparticles

Based on our synthetic concept of preparing dense polymer brushes on planar gold substrates, in which self-assembled monolayers (SAM) of terminal functionalized thiols were used to initiate living cationic ring-opening polymerization [1] we prepared a series of analog reactions using functionalized gold nanoparticles as starting materials. End-functionalized self-assembled monolayers (SAMs) were used to initiate living cationic polymerization reaction directly on the particle interface ('grafting from technique'). In this manner, dense poly(N-propionylethylenimine) (PPEI) polymer brushes of amphiphilic nature as well as Poly(2-phenyloxazoline)[2] were prepared in a 'one-pot multi-step' reaction. ER FTIR spectroscopy confirms the successful polymerization reaction as well as the introduction of terminal functional group. The resulting gold/polymer-nanocomposite was found to be very stable. The combination of a 'grafting from reaction' resulting in preorganized polymer 'brush-type' layers of linear macromolecules and the introduction of a terminal mesogene, providing further order based on the hydrophilic/lipophilic balance (HLB), offers the possibility to create significantly thicker layers responding to environmental stimuli in a well-defined fashion. This strategy provides a facile way for the preparation of dense functional polymer brushes for applications in biotechnology and the development of sensor devices. [1] R. Jordan, A. Ulman : J. Am. Chem. Soc. 120 (1998) 243-247. [2] Y. Chou, A.Ulman, R. Jordan: in preparation.

[NP01.166] Atomistic Modeling of Liquid Crystalline Phases

Recently many molecular dynamics (MD) studies of thermotropic liquid crystals have been carried out using atomistic models. These models allow for a detailed description of the molecular structure and are essential for a quantitative study of liquid crystalline properties, which are very sensitive to the molecular details. The aim of the current study is to investigate the effect of the system size (which often limits such calculations) and the shape of the periodic cell on the evolution of the mesophase during the MD simulation. We have focused on 4-n-pentyl-4'-cyanobiphenyl (5CB) in the nematic phase. The equilibration time required for the evolution of the mesophase was also estimated for different initial conditions.

[NP01.167] Healing of Sheared Confined Films Following Large-Amplitude Deformation

Polydimethylsiloxane (PDMS) chains of variable molecular weight were confined between mica sheets in a surface forces apparatus modified for the application of shear. The film thickness was of order 5 nm. First the films were deformed for 30 min at constant shear rate by the application of force impulses with triangular waveforms. The resulting nonequilibrium surface structure was probed by the subsequent application of small-amplitude sinusoidal shear, and the measurement of the in-phase (elastic) and out-of-phase (dissipative) components of the resulting deflection. It emerged that the films healed over times lasting of order several hours. Immediately following the strong shear the dissipative response exceeded the elastic response, but following the cessation of strong shear the elastic response grew more quickly with elapsed time than the dissipative response. The kinetics of these processes could be described as proportional to the square root of elapsed time -- suggesting that the healing process stemmed from the interdiffusion of two initially-distinct sheared layers.

[NP01.168] Diffusive Transport in and Development of Polymer Membranes for Immunoisolation

The encapsulation and implantation of living cells for the treatment of disease, such as diabetes via an implantable membrane device containing insulin-secreting tissue, is an exciting biotechnology. A major challenge is membrane development which permits passage of O2, glucose and insulin yet excludes large immune factors causing graft rejection. Membrane development and characterization for immunoisolation was studied. A multi-station diffusion test system was designed and characterized for boundary layer effects. Diffusion of vitamin B12, myoglobin, albumin, IgG and dextran were measured by Taylor dispersion. Multi-solute test methods were used with polydisperse dextran and biological markers. Membranes were made from cellulose acetate, cuprammonium cellulose, and poly(ethylene-co-vinyl alcohol) and their diffusive permeabilities measured. Small-solute permeability was achieved, but low permeability to larger solutes was not, likely due to a small number of large pores determining large-solute transport.

[NP01.169] A Monte Carlo Simulation of Polyethylene Melts between Two Attractive Plates, with Pulling of the Plates.

The dynamics of C120 and C60 polyethylene melts between two attractive plates, with pulling of both plates at various speeds, has been studied by using a Monte Carlo simulation on a high coordination lattice [1]. At each pulling speed, C120 and C60 showed quite different density profiles in such a way that the faster pulling resulted in the higher density in the middle region between the plates. It was also found that the dependence of the density on the speed was much more prominent in the case of C120, which can be considered to be close to entangled system. The total attractive energy between the plates and chains increased rapidly at the faster pulling, while it remained constant at the slowest pulling. This dependence is in accordance with the experiment of elongational viscosity on polyethylene melt [2]. These results have been analysed in terms of three main processes during the pulling, attachment/detachment of chains on the plates, chain relaxation, and development of entanglement.

Supported by NSF grant DMR 95-23278.

1. Rapold, R. F.; Mattice, W. L. J. Chem. Soc. Faraday Trans. 1995, 91, 2435

2. Meissner, J. Rheol. Acta 1971, 10, 230

[NP01.170] Local and Electronic Structure of Vitamin B12: X-ray Fluorescence Measurements

The results of fluorescence measurements of Co L2,3 and F Ka X-ray emission spectra (XES) from vitamin B12 are presented. The data are compared with spectra of reference samples: Co, CoO, LiCoO2, CoF2 and AlF3. A single crystal of vitamin B12 was obtained by adding KF to a water solution of cobalamin. According to X-ray diffraction measurements, this crystal is an octahedral Co complex with five coordination sites occupied by a large macrocycles (corrins) and the sixth by either OH or F ligand. The analysis of the emission spectra shows that Co-F bonds are formed indicating that fluorine is the sixth ligand of this compound. The Oxidation State of Co ion is found to be Co3+.

[NP01.171] Experimental and molecular modeling study of polyelectrolyte gels

Polymeric gels (PGs) are ubiquitous and versatile materials with applications ranging from the oil to the medical industries. The development of improved PGs resulted in PGs of more complex constitution and new chemical composition. These efforts have been led by random screening of materials. The structure and conformation of the polymer chain control the PGs properties. Another approach towards improved PGs proceeds through the study of PGs structural features. In absence of experimental structural information modeling techniques can be used to describe structural details of PGs. Various techniques have to be applied, in order to fully characterize the structure of PGs. In this work swelling and shrinking of PGs are studied using molecular modeling and experimental techniques. PGs show a significant volume variation with changes in the external solution composition, the temperature, osmotic pressure, or electrical field. Gels of acrylic acid (AA) were synthesized and characterized for this study. The swelling of the gel was measured at different crosslinker contents and for different pH values. Structural correlations for these processes were established using molecular modeling studies. These studies included molecular dynamic simulations using as a model a crosslinker molecule (N, N'- Methylenebisacrylamide) having bounded to each of its four extremes segments constituted by eight monomer units each. Periodic boundary conditions with explicit water molecules were used to complete the model. This model was used to study the monomer-solvent interaction along the polymer chain. An extension of this study using alternative modeling techniques will also be presented.

[NP01.172] Incorporation of Polyelectrolyte Complexes into Multilayer Assemblies

The sequential adsorption of molecular layers of polyelectrolyte onto charged substrates has been established as a promising route to the fabrication of stable thin film multilayer structures. The thickness of each layer deposited can be controlled by varying the adsorption parameters, but only to an upper limit of approximately 100 Angstroms. Beyond this thickness limit one requires alternative techniques for incorporating layers of polyelectrolyte into multilayer structures. Here we report the use of soluble complexes of polycation and weakly-charged polyanion, which can be readily adsorbed onto the surface of multilayer structures from dilute solution to yield stable and uniform layers in the thickness regime of 100 to 1000 Angstroms. Solution properties of the complexes were studied by light scattering and compared with the properties of the adsorbed layers, as studied by ellipsometry and neutron reflectivity.

[NP01.173] Comprehensive Study of Conformational, Thermodynamic and Rheological Properties of Binary and Ternary Polymer Solutions

In going from the dilute to the semidilute regime, the progressive coil overlapping gives rise to a gradual screening of both hydrodynamic and excluded volume interactions, while at the same time making topological interactions among different chains possible.

These effects strongly affect all properties of the solutions, and in recent years, different theoretical approaches based in renormalization group theories have been developed to account for them. However, a simultaneous analysis, including static and dynamic properties is not yet available.

In this work, we present a comprehensive study of conformational, thermodynamic and rheological properties of semidilute polymer solutions in good solvent. The description of our experimental data is made combining the de Gennes's reptation model with Schafer's RG results. This analysis allows to take into account the polydispersity influence and can be extended to the interpretation of properties of ternary an quaternary polymer solutions.

[NP01.174] A Simple Relation for the Solubility of Gases in Polymers

The polymer reference interaction site model theory is applied to gas solubility in polyethylene-like polymers. With a few simplifications, the single site type model can be extended to other polymers. Using only the monomer structure and some gas solute properties, reasonable predictions of the gas solubility of various polymers can be made. The resulting predictions are compared with experimental data and the simplified solubility equation is compared to the Flory-Huggins form.

[NP01.175] Thermal enhancement of AFM phase contrast for imaging diblock copolymer morphologies

Atomic Force Microscopy (AFM) has become a standard tool for imaging the microphase separated morphologies of block copolymers. Particularly useful in this endeavor is so called "phase" imaging, which elucidates local elasticity differences in the sample surface. At room temperature, phase imaging some block copolymer morphologies can be problematic. If each of the block components is below its glass transition temperature, there may be little or no elasticity difference between them. Accordingly, there will be little contrast in the phase image, and little morphological information will be conveyed. Recently, we have developed a simple scheme for dramatically increasing the phase contrast in AFM micrographs of polystyrene-b-(n-alkyl methacrylate) diblock copolymers. At room temperature, both block components are below their glass transition. By heating these materials to a point between the glass transition temperatures of polystyrene and the methacrylate block, the latter becomes rubbery while the f ormer remains glassy. Thus, an elasticity difference between the block domains has been created, which imparts added contrast to the phase imaging, adding remarkable detail to the resulting AFM micrographs.

[NP01.176] Structure Formation in Polymer Blends in an Electric Field

When a droplet from one phase of a phase separated solution of two immiscible homopolymers is injected in the matrix of the other phase and a homogeneous electric field is applied, the droplet can deform either parallel or perpendicular to the electric field direction. The direction of the deformation has been predicted by Taylor(Taylor,~G.~I. \textitProc.\ R.\ Soc.\ Lond.\ A) \textbf1966, \textsl291, 159-166. and Torza et al.(Torza,~S.;\ \ Cox,~R.~G.;\ \ Mason,~S.~G. \textitPhil.\ Trans.\ R.\ Soc.\ Lond.) \textbf1971, \textsl269, 295-319. in terms of the Leaky Dielectric Model (LDM). The LDM has been extended to accurately predict large deformations, as commonly observed in polymer-polymer-solvent systems. An approximate solution has been obtained in spheroidal coordinates. To test the extended theory, experiments with different systems have been conducted and comparison with theory was done using uncertainty analysis. (Supported by NSF, DMR-9521265)

[NP01.177] Determination of the Optical Refractive Index of PS Thin Films

To calculate the optical refractive index of thin film, we used X-ray reflectometer and optical ellipsometry. We used X-ray reflectivity to measure the exact thickness of ps films and ellipsometry to calculate the optical refractive index. Thin film coatings are commonly used to optically match the refractive index of lenses and minimize reflections in optical components. Consequently it is of interest to know whether the refraction index of a polymer is affected by film thickness and processing method. We therefore studied monodisperse polystyrene films after spin coating from toluene solution onto Si wafers before and after annealing. The thickness of thin films studied ranged from 30 to 1000Åand the Mw ranged from 90 to 2650k. The results show that prior to annealing, the index of refraction is a parabolic function of film thickness, with a maximum at 1000ÅThe minimum value measured 1.3 at 30Åand the bulk value was achieved only for films thicker than 2000ÅNo significant dependence on Mw was detected. The index of refraction of the annealed film was much less sensitive to thickness and averaged Nu=1.59. Larger deviations were detected for blue light than red light. These results are interpreted in term of internal strain in the spin coated film, which relax upon annealing.

[NP01.178] Phase Structure and Dynamics of Crown-Ether-Based Polyrotaxanes

Solid-state NMR was used to examine structure and dynamics of crown-ether-based polyrotaxanes. For poly[(acrylonitrile)_n-rotaxa-(60-crown-20)_x] with x/n = 0.01, the crown was found to be phase-separated, amorphous, and highly mobile (albeit showing the presence of more than one dynamic environment) at room temperature. Dipolar magnetization transfer experiments revealed typical smallest diameters of 6 to 8 nm for the 60-crown-20 domains, with interfacial regions of 2 to 4 nm. The interface was attributed to crown segments in contact with PAN as required by the threaded architecture; a physical blend of PAN and 60-crown-20 was phase-separated with a sharper interface than the polyrotaxane. The NMR long periods compared favorably with electron-density correlation lengths from SAXS data. Linear aliphatic polyurethane-rotaxanes were synthesized with 36-crown-12. For this system, new loss peaks appeared in the dynamic mechanical spectrum (DMS) as compared to the unthreaded backbone. Interpretation regarding the molecular origin of the loss processes was provided by comparing DMS with solid-state NMR and dielectric spectroscopy.

[NP01.179] Effects of Solution Concentration and Spinning Voltage on Electrospun Poly(ethylene oxide) Nanofiber Textiles

Electrospinning is a process which uses an electric field applied to a polymer solution to produce continuous fibers with diameters in the 10-500 nanometer range. The technique is experiencing a resurgence in popularity due to the recent commercial success of nanofibers in textile and filtration applications. Although it is well established that electrospinning produces nanofibers, very little information is available relating processing variables to the quality of electrospun fibers. In this study, the effects of two such variables, solution concentration and spinning voltage, on the properties of electrospun poly(ethylene oxide) nanofiber textiles have been explored. The defect density in fiber mats is found to be strongly coupled with spinning voltage. A power law relation has been found between solution concentration and fiber size, and a bimodal distribution in fiber diameters has been observed above a critical lower concentration limit. The phenomena has been correlated to similar behavior observed in electrospray processing of droplets.

[NP01.180] The Roles of Diffusion and Chain Transfer in Determining the Strength of the Gel Effect in Free Radical Polymerization

Recent studies reveal that the gel effect (autoacceleration) in bulk methyl methacrylate radical polymerization is unrelated to entanglements and instead is dominated by diffusion-controlled termination of the shortest radicals present in great number. Here we show that as the polymer concentration dependence of chain diffusion is a function of chain length, the strength of the gel effect is also a function of the molecular weight of the polymer produced, and we extend our model to molecular weight determination. We also compare the gel effect response among alkyl methacrylates. As alkyl length increases, the gel effect weakens. Modeling of butyl and lauryl methacrylate reactions reveal that, even if termination were dominated by the concentration dependence of monomer diffusion, this would be too strong an effect to explain the autoacceleration. Styrene exhibits similar behavior. We explain these weak gel effect systems based on a combination of diffusion-controlled termination mitigated by the role of chain transfer (resulting in retardation of the reaction) in the longer alkyl methacrylate and styrene systems.

[NP01.181] Stability of Thin Film Nanocomposites of Polymers and Organically Modified Layered Silicates

The stability of thin film nanocomposites comprised of organically modified layered silicates (OLS) and OLS/polystyrene-b-polymethylmethacrylate (PS-b-PMMA) was examined using atomic force microscopy. The lateral homogeniety of the OLS/polystyrene-b-polymethylmethacrylate was readily disrupted above the glass transition temperature. Notably, the block copolymer chains were self assembled in the vicinity of the OLS structures while diblock chains on the substrate in regions away from the OLSs became unstable and locally dewet the substrate. In the absence of the OLS structures, the block copolymers remain self assembled on the substrate. The kinetics of the dewetting of the copolymer were determined to be logarithmic.

[NP01.182] Aggregation effects on the photophysics of tetrathienylene vinylene

The photophysics of tetrathienylene vinylene (4TV) have been studied by absorption, electroabsorption, photoinduced absorption and optically detected magnetic resonance (ODMR). Blends of 4TV in PMMA can be thermally processed so that an isolated or a strongly aggregated state is produced. The absorption spectrum of the isolated state has a 0-0 transition at 2.55 eV with clear structure. Aggregation results in Davydov splitting and new absorption peaks are seen at 2.28 and 3.48 eV. The ODMR magnitude increases linearly with excitation power and also increases with the 4TV concentration. We conclude that recombination is monomolecular and that intermolecular interactions signficantly affect photoexcitation dynamics and yield.

[NP01.183] Entropic Elasticity of Single Macromolecules of Wheat Gluten Protein Measured by Atomic Force Microscopy

High molecular weight (HMW) wheat gluten proteins play an important role in the viscoelasticity and baking of dough. One part of the central repetitive domain of this protein was subcloned (denoted dB1) and found to exist in a \beta-spiral structure, \sim15 nm in length and \sim1.5 nm in diameter(Van Dijk, et. al, Protein Science, 1997, 6, 649). Here we have used the technique of single molecule force spectroscopy (SMFS) to study the mechanical denaturation and the entropic elasticity of single chains of dB1. The protein was fixed covalently by one chain end to a substrate and then tethered to an atomic force microscope Si_3N_4 probe tip via non-specific, physisorption interactions. Upon retraction of the probe tip from the surface, continuous, attractive peaks in the force versus distance profiles are frequently observed due to the entropic resistance of uncoiling of the individual chains. These peaks could be fit, for all chain bridging lengths, to the (inextensible) freely-jointed chain (FJC) model. From these datafits a statistical segment length of 0.5 nm was obtained, suggesting incomplete denaturation and a significant portion of H-bonded \beta-turns still in tact.

[NP01.184] Study of the viscosity peak of polyelectrolytes in low ionic strength aqueous solutions

Polyelectrolytes are polymers that develop a high charge in solution. They include examples of technical interest (such as xanthan, a very stiff polyelectrolyte used as a thickener in food and other products) as well as biological interest (such as hyaluronan, a flexible polyelectrolyte found in, for example, connective tissue and the eye). Viscometry is a powerful polymer characterization technique, but extraction of polymer characteristics is frequently model dependent. Thus, it is of interest to experimentally constrain theories that model the viscosity of dilute polymer solutions in terms of the properties of the polymer molecules. It has long been known that the reduced viscosity of polyelectrolytes in low ionic strength solution presents a peak as a function of concentration (Fuoss, R. M., and U. P. Strauss, J. Polym. Sci., 3, 246, 602 (1948)). Some models seek to explain this in terms of interactions of the polyelectrolyte molecules with other charges. Other theories explain the peak in terms of changes in the conformation of the polyelectrolyte. We present measurements of the viscosity of a very stiff polyelectrolyte (xanthan, with a persistance length of about 1500 Å(Norwood, D. P., Mustapha Benmouna, and Wayne. F. Reed, Macromolecules, 29, 4293-4304 (1996)) at very low added salt. The stiffness of xanthan minimizes conformation changes, permitting an investigation of the differences between the various models.

[NP01.185] Thermoreversible Gelation of Aqueous Poly(vinyl alcohol) Solutions

As an aqueous poly(vinyl alcohol) solution is cooled near and below room temperature, the solution slowly phase separates. If the polymer molecular weight and concentration are sufficiently large, the result of phase separation is a gel. A gel of similar modulus and pore size can be created more rapidly if the same solution is quenched below the freezing point of water and then thawed. Additional freeze/thaw cycles increase the modulus. To understand gelation and gel microstructure, we have used small angle X-ray and light scattering, solid-state NMR, cryogenic TEM, DSC, and optical microscopy. We believe that the formation of small, 5-10 nm crystallites induces solidification, with several percent of polymer segments involved; this percentage rises with aging or thermal cycling. Crystallite crosslinks are separated by approximately 20 to 40 nm on a random mesh with intervening amorphous segments. Ice crystallization and spinodal-like phase separation before gelation may superimpose larger, micron-sized microstructural features on the gel.

[NP01.186] Transport Tensors for a Wormlike Chain

The transport tensors (translational diffusion and rotational diffusion) for wormlike chains have been computed by averaging over a large Hagerman-Zimm ensemble of rigid linear bead shapes (statistical precision to .2/100). The calculations were done as a function of both axial ratio (number of beads) and the number of persistence lengths in the chain. The hydrodynamic calculations have been carried out with a high precision program which takes into account translation-rotation coupling and the rotation-rotation terms between pairs of beads, and other bead effects on the self diffusion terms.(R. Goldstein, J. Chem.Phys. 83,2390 (1985)) The inclusion of this type of terms permits the accurate calculation of tensors even for the completely straight bead array. The tensors are represented by interpolation formulas for axial ratios up to 100, and contour length to persistence length ratio up to 10. These tensors are useful in interpreting experiments such as electric birefringence, dynamic light scattering and fluorescence polarization anisotropy that are sensitive to the dynamics of the wormlike chain. They are also useful in the study of simulations carried out with bead representations of wormlike chains.

[NP01.187] Phase Behavior and Unusual Macroscale Order in Styrene/n-Alkyl Methacrylate Diblock Copolymers

In an attempt to identify the molecular origin of the lower critical ordering transition (LCOT) in polystyrene-block-poly n-butyl methacrylate, the phase behavior of copolymers formed from styrene and a homologous series of n-alkyl methacrylates was investigated. It was found that the thermodynamic compatibility between the two blocks and the resulting phase behavior strongly depend on the degree of branching of the methacrylate block. This same structural parameter also seems to influence the viscoelastic properties of the copolymers and their tendency to align under external flow fields when in the ordered state. In fact, abnormally large degrees of alignment of the lamellar microdomains were observed in some symmetric copolymers after processing steps as trivial as compression molding. This strong tendency to align under minor stresses or strain fields appears extremely advantageous from an engineering standpoint, as it could yield a host of new materials in which macroscopic alignment and directional properties can be induced via standard polymer processing steps. The possible origins of such behavior and its implications from a processing standpoint will be discussed.

[NP01.188] Molecular Dynamics Simulation of Poly Vinylidene Floride (PVDF)

We present a new ab initio based force-field for molecular dynamics simulations of poly(vinylidene floride), PVDF. It was obtained using Hartree-Fock geometries (D95**) and MP2 energies (D95+**) of four molecular compounds: 1,1,1,3,3 -- pentafluorobutane, 2 molecular dimers -- 1,1,1,3,3,5,5,5-octofluoro- and 2,2,4,4-tetrafluoropentane, and a molecular trimer -- 2,2,4,4,6,6-hexafluoroheptane. The conformational energy contours reveal that the -CF_2-CH_2-CF_2-CH_2- torsion is split in both the trans and gauche states and has a lowest energy state at gauche (~65^o). These conformational characteristics are fully represented by a six-state rotational isometric state (RIS) model comprised of all six possible states, located at the split energy minima. Preliminary molecular dynamics simulations of amorphous PVDF were performed at temperatures higher than melting point (439 K) and yield PVT and conformational properties with available experimental data.

[NP01.189] Gibbs-DiMarzio Theory for the Tg Behavior of Polymer Thin Films

Changes in the glass transition temperature (Tg) for very thin polymer films have been measured using a wide range of experimental techniques. The polymer Tg has been observed to increase or decrease depending upon whether or not the film is supported on a solid substrate and the nature of the interaction between the polymer and the substrate. To date, few theoretical approaches have been undertaken to complement the extensive experimental effort. In this work, the Gibbs-DiMarzio criterion of a vanishing configurational entropy at Tg for polymers is adapted for the thin film geometry. The configurational statistics are evaluated using a self-consistent mean field model. The effect of the polymer chain length, bending energy, and surface interaction energy on the calculated Tg and the polymer configurations within the film will be presented and discussed in relation to data from recent X-ray and neutron reflectivity experiments.

[NP01.190] The Effects of Surface Interactions on Phase Segregation

The effects of the surface interactions on the phase segregation of Polystyrene(PS)/ Poly(methyl methacrylate)(PMMA) was studied. Film of symmetric blends of PS(Mw=90k) and PMMA (Mw=27k) were spun cast onto Au, Co, Si and patterned substrates. The samples were analyzed using both Scanning Transmission X-ray Microscope (STXM) and Scanning Force Microscopy. The patterned surfaces were made by printing Au,Co and Sistructures approx. 300Åhigh with a specific wave vector onto a silicon wafer. The results on the flat surface show that the morphology is determined by the polymer which wets the surface. On the patterned surface the extent of phase segregation can be controlled by the wave vector of the pattern. This may be a potential mechanism in phase stabilizing polymer blend film on surface. Acknowlegement:We appreciate the support of the National Science Foundation Polymer Program(DMR9316157), the Department of Energy(DE-FG02-93ER45481), and the MRSEC program of the National Science Foundation(DMR9632525)

[NP01.191] Self Assembly of Islands/Holes in Diblock Copolymer Films Under the Influence of a Confinement Layer with a Thickness Gradient

We cast symmetric poly(styrene-b-2vinylpyridine) (PS-PVP) diblock copolymer thin films on Si which form lamellae oriented parallel to the substrate surface, with equilibrium thicknesses 1.5 L_0, 2.5 L_0, etc. where L_0 is the lamellar period. We investigate films of initial thickness 2.0 L_0, which form bicontinuous structures of domains with either 1.5 or 2.5 L_0 thickness after annealing. Preannealing such films under a \sim 100 nm thick confinement layer of a third, glassy polymer restricts island/hole formation and causes the chains in the lamellae to stretch. If there is a thickness gradient in the confinement layer, however, we observe a grating structure after a final anneal with no confinement that consists of alternating stripes of PS-PVP film thickness 1.5L_0 and 2.5L_0. The stripes of this grating are perpendicular to the gradient of the confining film thickness, indicating that stripe orientation results from the stiffness anisotropy of the confining film.

[NP01.192] Optical Properties of Carbon Nanotube-PMMA Composites

Carbon Nanotube-PMMA (Polymethal Methacrylate) composites have been formed though a new dispersion process. This process utilizes surfactant separation of nanotubes and ultrasonic mixing to achieve near ideal dispersion of tubes within the polymer matrix. We will present recent results on the optical properties of such composites which include broad band optical limiting and nonlinear optical scattering due to nanotube alignment. Further, we demonstrate the fabrication of optical fibers and fiber coatings from this material and the result of nanotube alignment in fiber mode structure.

[NP01.193] Excited State Study of Thiophene, Cyclopentadiene and Fulvene Based Polymers

Excitation energies of polythiophene, polycyclopentadiene and polyfulvene and their cyano-bridged derivatives are analyzed with the use of model compounds. We employ ab initio, configuration interaction (singles) approach (CIS) with 3-21G* and 6-31G* basis sets to investigate excited state (singlets) energies and structures of stable thiophene, cyclopentadiene, fulvene and their cyano-bridged oligomers (monomers to octamers). The results of CIS/3-21G* calculations predict substantial structural changes in the backbones of (aromatic or quinoid) oligomers in comparison to their ground state geometries. For small oligomers, these changes are sensitive to the size of the oligomer. Trends in structures, especially as related to bond alternation, will be discussed extensively. In agreement with previous studies, this investigation gives strong theoretical evidence that the cyano substituted compounds have considerably smaller intrinsic band gaps then their respective unsubstituted parents.

[NP01.194] Correlation of the scope of sub- \mathbfT_g molecular motion with the ductility of polymers based on SBI

Main chain sub- \mathrmT_g molecular motion is strongly correlated with the toughness of polymeric materials. Chair-boat-chair (CBC) transitions of cyclohexane rings (C rings) in the polymer chain can enhance cooperative molecular motions and thus improve mechanical proerties. The \textitextent to which C ring CBC transitions can enhance the cooperative motion is not known. In order to answer this question, we incorporate a unique monomer SBI into polymer chains. The chemical structure of SBI (3,3,3',3'-tetramethyl-1,1'-spirobiindane) differs significantly from that of bisphenol-A. The phenyl rings in SBI are locked, eliminating rotational degrees of freedom and thus providing a unique probe. Polymers with different structural lengths between consecutive SBI units have been synthesized. DMA, Positron Annihilation Lifetime Spectroscopy (PALS), and mechanical tests have been used to characterize these polymers. The results show that the cooperative motion of C rings and BPA can make inherently brittle SBI polycarbonate ductile. This cannot be achieved with CBC transitions alone. The results suggest that in order for the polymers to yield, cooperative motion involving at least a couple of structural units may be necessary. Work supported by the AFOSR (grant F49620-98-1-0158).

[NP01.195] Secondary Crystallization Kinetics of Poly ether ether ketone

The multiple melting behavior of poly[ether ether ketone] (PEEK) has been investigated in detail. Specifically, we have studied the effects of heating rate, crystallization time and temperature on the evolution of the high and low endotherms recorded subsequent to isothermal crystallization, from the melt or from the glass. Our results indicate that PEEK behaves in a very similar fashion to polycarbonate, and to some extent to ethylene copolymers (i.e. the multiple melting behavior is due to the melting of separate population of crystals, lamellar and fringed micellar). We also showed that, secondary crystallization whether occurring subsequent to cold or to melt crystallization is characterized by a unique mechanism. Secondary crystallization leads to a shift of the material relaxation spectrum to longer times as a result of increased constraints in the remaining amorphous fraction. Correlations between the upward shift of the low endotherm and the glass transition temperature with increase in crystallization time provides strong support to our speculation that the upward shift of the low endotherm location is associated with a steady decrease in the configurational entropy of the remaining amorphous fraction during secondary crystallization.

[NP01.196] Investigation of the Nanofibrils of Silk Fibers

Silk from Bombyx mori as well as other silks have been investigated using Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM). A range of morphological features including nanofibrils, bundles of nanofibrils and a layered structure with a cross angle between nanofibrils in different layers was observed for all silks. The average width of the fibrils is about 110-190 nm. While there is no correlation between the size of silk fiber and the size of fibrils from different species of silkworm, there is a correlation along the length of the single fiber in the cocoon for a given silk. The cross angle is in the range of 30-50 degrees. A simplified computer calculation method has been used to obtain the possible angles which minimize the interaction energy of packing between beta sheets of silk. Wide angle X-ray diffraction (WAXD) measurements are used in an attempt to determine the fraction of fibrils at different cross angles. All the results are qualitatively consistent with the hypothesis of fibril formation by crystal nucleation and orientation by epitaxy.

[NP01.197] Study of structural & morphological changes of polypropylene fibers during deformation by WAXD/SAXS

The solid state deformation of fibers by drawing leads to a considerable enhancement of their mechanical properties in the elongation direction. This improvement of the macroscopic properties has a close relationship with the change of the structure and morphology in the fibers. Further more, the processes of fibers such as drawing and heat treatment are dynamic, during which structure and morphology are changing continuously. Therefore it is important to study these changes of fibers in real time during deformation. Wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) is the most important technology to do the on-line characterization of these changes[1,2]. In this work, an industrial prototype drawing machine is placed into the X3a2 beam line of NSLS to do the on-line WAXD/SAXS determinations of the polypropylene fibers at different drawing conditions. Here we present the high quality two-dimentional WAXD/SAXS image patterns of deformed fibers. A comprehensive analysis software (XDPP) is used to obtain a quantitative result of the structural and morphological changes of the fibers. The results show that the drawing ratio has more effects on the structural and morphological changes of fibers than the drawing temperature and the drawing speed.

References: [1] Chappel, F.; Culpin, M.; Gosden, R. amp; Tranter, T. J. Appl. Chem. 1964, 14,12 [2] Haberkorn, H.; Hahn, k.; Breuer, H.; Dorrer, H.D. amp; Matthies, P. J. Appl. Polym. Sci. 1993, 47, 1551-1579

[NP01.198] Effect of compositional fluctuations on the cure kinetics of network polymers

Network polymers are produced by curing two or more multifunctional reactive monomers in order to form a three-dimensional network. A basic assumption in the analysis of cure kinetics of the system is that its composition is homogeneous; hence, concentrations of the reactants do not vary across the system. With this assumption, reaction order obtained from the analysis of the cure kinetics should be of elementary order. However, contrary to the model, experimental data always resulted in fractional order kinetics. The assumption of homogeneous composition is correct for as long as the system is capable of large scale mixing. However, as the reaction proceeds the formation of the network will hinder the large scale mixing permitting only mixing in local region, which may be sufficiently small that fluctuations in local monomer composition are significant. A model that incorporates the effect of local composition fluctuations in a mesoscopic domain after the cessation of macroscopic mixing has been developed to explain the fractional kinetic reaction order obtained by traditional analysis. The model shows that although the reactions are elementary, the local compositional fluctuation could result in an overall fractional kinetic reaction order.

[NP01.199] Epitaxial crystallization of triblock copolymers onto benzoic acid

Epitaxial crystallization of polyethylene blocks (PE)in ethylene-b-(ethylene-alt-propylene)-b-ethylene (PE/PEP/PE) and styrene-b-(ethylene-alt-propylene)-b-ethylene (PS/PEP/PE) triblock copolymers has been achieved on benzoic acid crystal substrate. The epitaxial relationship is similar to that obtained for the polyethylene homopolymer. For both copolymers uniplanar textures characterized by crystalline lamellae standing edge-on on the substrate are obtained. Electron diffraction patterns indicate that the polymer chains lie flat on the substrate surface, with the chain axis parallel to the a axis of benzoic acid. For the PE/PEP/PE copolymer the pattern correspond to the bc section of the reciprocal lattice of PE, the (100) plane of PE being in contact with the (001) plane of benzoic acid. Lamellar twisting, in particular rotation around the b axis, accounts for the presence of 1kl and 2kl reflections in addition to the expected 0kl ones. For the PS/PEP/PE copolymer the electron diffraction pattern corresponds to a fiber-like pattern, indicating rotation around the c axis as a result of lamellar twisting.

[NP01.200] Characterization of low-dielectric poly--silsesquioxanes with Positron Annihilation Lifetime Spectroscopy

As the scale of microelectronic devices is decreased, the dielectric constant of insulating materials becomes a major contributor to RC delay times. Poly-silsesquioxane (poly-SSQ) films, (with dielectric constants k \leq 3) are being explored as possible replacements SiO_2 (k \approx 4). Little is known about the basic structure of poly-SSQs even in bulk form. As low-dielectric thin films, structure studies are hampered by a lack of submicron film probes. Positron Annihilation Lifetime Spectroscopy (PALS) has been applied to study several types of poly-SSQ including octaglycidyl-SSQ (OG-SSQ) epoxy and methyl-SSQ. Source-based PALS studies of OG-SSQ epoxy confirm a structure consisting of 5~Å\ rigid cubes embedded in a more flexible crosslinked network. Beam-based PALS has also been applied to characterize submicron OG-SSQ epoxy films and methyl-SSQ films which are thought to form ladder structures. This work is supported by National Science Foundation grant ECS-9732804 and National Institute of Health grant 5-P50-DE09296-08.

[NP01.201] Bridges vs. Loops in Ordered Triblocks: Dielectric Spectroscopy and Computer Simulations

Dielectric relaxation spectroscopy and computer simulations have been used to probe the bridge fraction in ordered symmetric B-A-B triblock copolymers. The separation of loop- and bridge-contribution to the dielectric relaxation of a PS-PI-PS triblock having symmetrically inverted dipoles along the middle block is significantly affected by sample preparation/annealing, which may affect not only the bridge fraction but even more both bridge and loop dynamics. Computer simulations lead to the conclusion that at equilibrium the contribution of loops is almost twice that of bridges with both, however, having similar relaxation rates. The total intensity is much larger than for the respective diblocks, which agrees with the data for the annealed triblocks. The static information from the simulations agree with theory and with the data resulting in bridge fractions of 0.50-0.37. The dynamics of loops and bridges are found not very different from that of the diblocks in disagreement with the observation on the annealed systems.

[NP01.202] Molecular Modeling of Polyhedral Oligomeric Silsesquioxanes (POSS) Based Polymers

The study of structure- property relationships in polymers based on Polyhedral Oligomeric Silsesquioxane (POSS) is a subject of ongoing research. Co-polymerization of POSS macromers into conventional polymers can lead to dramatic changes in properties, such as the glass transition temperature, mechanical, and transport properties. The large variety of functionalities that can be incorporated on the POSS macromers lend themselves to tailoring property/application specific polymers. Ab initio and semi-empirical methods have been used to aid in the development of force field parameters to describe these molecules for use in performing molecular mechanics and dynamics (MD) simulations. POSS macromers having methy, cylcopentyl or cyclohexyl substituents have been investigated in various geometries. The behavior of free individuals, linear tethers of various lengths, and four-arm star tethered macromers have been examined. The results of vacuum and bulk phase MD simulations indicate that the substituents serve dual roles of affecting persistent interaction between macromers while at the same time disrupting any ordered association.

[NP01.203] Phase I/II Crystals of Poly(p-oxybenzoate): Effects of Substrate and Polymerization Conditions

The phase I/II crystal structure ratio of thin film melt polymerized PpOBA^a is affected by the substrate; base treatment of glass and mica results in II while acid treatment of mica (not glass) enhances I and also reduces the development of epitaxially polymerized/crystallized^b phase I polymer. In bulk melt polymerization II is nearly absent unless T_p is greater than 300^oC (i.e. T_k-m). The changes are attributed to a substrate nucleating effect. For solution polymerization effects of T_p, t_p and concentration on I/II and morphology are shown. The morphology of the phases (and T_k-m) can not be distinguished, with II appearing to contribute to coherence of the discs and whisker-discs observed for certain solution conditions. T_k-m, however, depends strongly on the morphology, whiskers having T_k-m 30-40 ^oC greater than the discs, a T_k-m that is retained through several heating-cooling cycles. ^a. F. Rybnikar, et al., Macromol. Chem. Phys., 195, 81 (1994). ^b. F. Rybnikar et al., J. Polym. Sci., Polym. Phys. Ed., 35, 1807, (1997).

[NP01.204] Time-Domain Spectroscopy Analysis of the Amorphous Phase in Semicrystalline Polycarbonate

The amorphous state of bisphenol-A polycarbonate was examined by time-domain dielectric spectroscopy as a function of crystallization time over a frequency range of 1x10^-4 Hz to 1x10^4 Hz. The dielectric measurements were performed in the temperature range around the glass transition temperature. Dielectric studies were performed on a series of samples, which were partially melted and recrystallized so as to investigate the influence of "secondary crystallinity" on the alpha relaxation, thereby probing the effect of crystalline constraints on cooperative motions in the amorphous fraction. Analysis of the relaxation behavior was performed by fitting the loss max frequency data to the Vogel-Fulcher-Hesse-Tammann and Arrhenius equations. Fits to the Havriliak-Negami equation were performed with careful consideration of the conclusions made by two of us in a recent paper: C.R. Snyder and F.I. Mopsik, J. Appl. Phys., 84 (8), 4421 (1998).

[NP01.205] Patterning of Self-Assembled Monolayers (SAMs) Using Synchrotron X-ray Radiation

The use of X-ray lithography to pattern self-assembled monolayers was investigated as a means to create surfaces with regions of different chemical functionality. Our long-term goal is to use advanced lithographic techniques to pattern regions with dimensions less than 100 nm. SAMs were prepared by the chemisorption of organotrichlorosilanes on SiO_x substrates, and were exposed to synchrotron X-ray radiation through a mask. Patterns of various shapes and lateral dimensions (0.2 to 50 \mum) were transferred from the X-ray mask to the SAM surface over large areas. The SAMs remained intact on the surface for doses as high as 3000 mJ/cm^2. When SAMs of octadecyltrichlorosilane were exposed in the presence air, the contact angle of water monotonically decreased with dose from 110º to 25º, and XPS data revealed the presence CHO and OH groups on the surface of the SAMs. Patterned SAMs were imaged with condensation figures and lateral force microscopy.

[NP01.206] Sub-nanometer Defects near Polymer Surfaces Studied by Positron Annihilation

Sub-nanometer defects (free volumes and holes) near the surface of polymeric systems have been measured by using Doppler broadening of positron annihilation radiation and positron annihilation lifetime spectroscopy coupled with a mono-energy positron beam. The positron annihilation results show the applicability of using positron annihilation spectroscopy to probe physical properties near the surface of polymers and to study degradation of polymeric coating systems under UV irradiation.

Supported by AFOSR and NSF. H. Cao et al, J. Phys. Condens. Matter 10, 1(1998).

[NP01.207] Diffusion in Porous Systems With Binding: Exact Results

Our recently developed lattice model of particle diffusion in porous media can be extended to account for the presence of attractive particle-medium interactions. This algorithm is a very powerful numerical method, because it has the flexibility to include such interactions while still providing us with exact results in a much more efficient manner than the widely used Monte-Carlo simulations. We assign a negative local potential energy to each of the sites adjacent to an obstacle, and we use periodic boundary conditions. The study of the effect of attractive interactions on the reduced diffusion coefficient can be applied to various problems including: affinity electrophoresis, chiral separations, diffusion of colloidal particles in gels and polymer solutions, and the diffusion of proteins on cell membranes. The interplay between obstruction and enthalpic effects can lead to very interesting phenomena, especially for fractal media.

[NP01.208] Effect of Hydrogen Bonding on Translational and Rotational Probe Molecule Dynamics in Polymers

The influence of hydrogen bonding on translational and rotational diffusion of small molecule probes differing in structure only by one probe having an S atom in place of an NH group on the second have been studied in polymers using second harmonic generation and fluorescence nonradiative energy transfer. Near Tg, the dynamics of the two probes are nearly identical in polystyrene which does not promote hydrogen bonding. However, in poly(isobutyl methacrylate), which accommodates hydrogen bonding with the NH group, rotational and translational diffusion are typically an order of magnitude or more slower for the probe which can hydrogen bond. Translational diffusion of both probes may be represented by Vrentas-Duda free volume theory, taking into account the energy of interaction due to hydrogen bonding. However, rotational diffusion cannot be adequately accounted for by simple activation energy effects due to hydrogen bonding. This may be due to an increase in the size scale of local cooperativity involved in probe rotation for hydrogen bonding systems.

[NP01.209] Preparation of Poly(styrene-co-methyl methacrylate) Multiblock Copolymers via Atom Transfer Radical Polymerization

The synthesis of multiblock copolymers is difficult with conventional synthetic techniques. These difficulties arise from the inability of one monomer to initiate the polymerization of the other monomer. This common limitation is observed with polystyrene and poly(methyl methacrylate) copolymers. Atom transfer radical polymerization is a method that may prove useful in the preparation of multiblock copolymers. This technique has been used to synthesize triblock copolymers of styrene (S) and methyl methacrylate (MMA) using phenoxybenzene-4'4' disulfonyl chloride with a copper(I) chloride/ bipyridine complex as the initiator. To monitor the kinetics, the molecular weights of periodically removed samples were monitored by size exclusion chromatography. Results indicate that the addition of MMA onto S is more efficient than the addition of S onto MMA. Further investigations will expand this study to a larger number of blocks and also examine the effect of heterogeneous verses homogeneous initiation on the synthesis of multiblock copolymers.

[NP01.210] Biological Hydroxiapatite coatings by Pulsed Electron Beam Deposition

Thin films of biologic hydroxiapatite were deposited on titanium and silicon substrates. The source was human teeth, previously cut in a slice, polished, and heated in air at 150 degree for 3 hours to remove excess water. A plasma discharge in oxygen at 1 Pa generates an electron pulse, which is accelerated at 15-16 KeV onto an area of 1 mm2 on the target. The discharge lasts for about 100 ns, leading to nearly stoichiometric ablation of the target material. SEM micrographs of the films revealed a rough surface with grains up to 1 micrometer. The thickness was determined by profilometry, after defining a step and etching with HNO3, giving an average value of 280 nm, with minimum thickness of 120 nm, maximum of 682, and a rms. roughness of 110 nm. The film composition was analyzed by x-ray photoemission spectrometry. Preliminary dissolution experiments in the ultrasonic bath indicate dissolution in deionized water only at the thinnest regions of the films.

[NP01.211] The Work of Adhesion of Polymer/Wall Interfaces and the Onset of Wall Slip

The interfacial characteristics of a variety of polymer/wall interfaces were measured by using the sessile drop method in order to calculate the work of adhesion. Polymers included linear low-density- as well as high-density- polyethylenes, while wall substrates included clean stainless steel and modified stainless steel by applying two different fluoropolymers in order to alter its surface energy. A linear correlation is found between the critical shear stress for the onset of slip and the work of adhesion of the corresponding polymer/wall interface, in agreement with the earlier predictions, which are used to interpret the experimental results. It is suggested that small deviations from the no-slip boundary condition in the case of polymer melts flow are due to a stress induced chain detachment / desorption of polymer chains from the wall.

[NP01.212] Self Diffusion of a Semiflexible Polymer Measured Across the Lyotropic Liquid Crystalline Phase Boundary

The self diffusion of fluorescently tagged poly(benzylglutamate), a helical, semiflexible synthetic homopolypeptide, has been measured in isotropic and cholesteric liquid crystalline solutions by pattern fluorescence photobleaching recovery. On the isotropic side of the sharp ISO-LC phase boundary, the rodlike polymers assume all possible orientations in a three-dimensional space, becoming enmeshed. In liquid crystalline solutions, as first shown by Robinson (Trans.Faraday Soc., 52, 571-592, 1956), spontaneous alignment of the cholesteric screw axis parallel to the optical (z) axis of the instrument produces small monodomains in which parallel rodlike polymers are organized into planes. Each horizontal plane is twisted slightly compared to its neighbors. Over the thickness of the sample, the rodlike polymers assume all possible orientations in this two-dimensional space. Despite the small size of the monodomains, it was possible to determine the self diffusion coefficient of the semiflexible rods, orientationally averaged in two dimensions. Crossing the sharp ISO-LC phase boundary corresponds to the sudden release of any putative topological constraints active in the isotropic phase, and produced a modest but significant increase in diffusion. A relationship developed by Hess, Frenkel and Allen (Mol.Phys., 74(4), 765-774) is used to show that diffusion perpendicular to the rod axis is about 10 times slower than diffusion parallel to the rod axis in the liquid crystalline phase. In dilute solution, the comparable number would be 2. The perpendicular diffusion had decreased to about 8% of its initial value in dilute, isotropic solution. The parallel diffusion decreased to about 40% of its initial value.

[NP01.213] Deformation of Ionic Hydrogels Under Electric Fields

Previously, we had found a reversible gel bending phenomenon of a partially sulfonated (50~% sulfonation) triblock copolymer gel of styrene-ethylene/butylene-styrene (S-SEBS) in low DC electric fields(DHPP abstracts, APS meeting, March 1997). However, the life-time of the gel in the experiments was limited by the lack of chemical crosslinks in the network. Therefore, a series of crosslinked S-SEBS gels were prepared by gamma irradiation. The bending behavior of the crosslinked gels in electrolyte solutions was qualitatively similar to that of previous studied S-SEBS gels. Quantitative analysis of the bending of crosslinked S-SEBS gels as function of gel crosslink density, electrolyte cation size and concentration will be reported. In addition, the bending of a partially sulfonated crosslinked PS gel will also be discussed. By studying the bending kinetics, we tentatively believe that the bending is due to differential swelling between the two sides of the gel strip. The mobility of the cations in the system is the key to this electromechanical response. This work was supported by ONR and NSF (Grand No. DMR-9521265.)

[NP01.214] Heat Capacity Anomaly in Succinonitrile and Water

The heat capacity at constant pressure has been measured in the near-critical, binary fluid mixture succinonitrile and water. Our adiabatic calorimeter used a computer-based data acquisition and control system and determined the heat capacity in the one- and two-phase regions from multiple runs within five degrees of the critical temperature (329K). The anomaly in the heat capacity can be characterized by a simple scaling relationship using the critical exponent alpha as 0.11. The resulting amplitudes allow universal relationships to be tested. Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the ACS, for support of this research.

[NP01.215] Effect on the dielectric relaxations of substitutions in the mesogenic unit and the flexible spacer of main chain liquid crystal polyesters

The asymmetrical substitutions either in the tetramethylene spacer and/or in the mesogenic unit of a main chain thermotropic liquid crystal polyester, has important consequences on the dielectric relaxations studied here by Thermally Stimulated Depolarization Currents (TSDC). By comparing the TSDC spectra given by the four polymers the effect of the chlorine substitution in the external rings of the mesogenic unit slightly affects the position of the low temperature relaxation modes but reverts the relative intensity of the peaks forming this multicomponent band, favoring the most energetic one. The addition of the methyl groups in the flexible spacer enhances the intermediate relaxation. The different modes as temperature increases are assigned to the localized reorientations of the COO peripheral groups, and to the internal COO for the two higher modes. The \alpha-transition is shifted to higher temperatures in presence of methylene substituents which reduce considerably the molecular chain mobility, and its high intensity shows the absence of crystalline order. In the presence of Cl substituents the relaxation times for the cooperative motions which originate the \alpha-mode, shows a wider distribution attributed to the multiphase character of these materials.

[NP01.216] Adhesion at Model Polymer Interfaces

We investigated the structure-strength relations for model interfaces containing selectively deuterated polymers, and polymer-solid interfaces with controlled number of sticker groups adhering to surfaces of known receptor site density. The interface structure was determined by Neutron Reflectivity, DSIMS, XPS and AFM. The fracture energy G, was determined by the J-Integral methods applied to the deformation zone containing the interface at the crack tip. Time dependent weld structure results were obtained which confirmed the reptation dynamics model proposed by P.-G. DeGennes. New vector percolation models of adhesion were developed and found to be the key to relating structure to strength of the weak boundary layer observed for polymer-solid interfaces.

[NP01.217] Relaxation Dynamics of Polymer Chains in Rubbed Thin Films Probed Using Linear and Nonlinear Optical Techniques

Rubbing of polymer surfaces is used in aligning liquid crystals in the manufacturing of displays. It has been shown to induce orientation of the surface chains along the direction of rubbing which is lost on heating close to the glass transition temperature of the polymer, Tg. The mechanism of this disorientation and how it is influenced by the structure of the polymer chain is poorly understood. We have employed a sensitive birefringence and sum frequency generation to probe the dynamics of this reorientation process in polystyrene (PS), polymethylmethacrylate (PMMA), and polyimides (PI) systems. Since the side group in PS dominates the birefringence, this offers an opportunity to understand the influence of side group motion on the surface dynamics. For the case of lightly rubbed PS upon heating at a rate of 1K/min, the birefringence begins to decrease at 70oC and reaches zero at 100oC. This is reminiscent of the motion associated with the Tg and in qualitative agreement with previous studies using NEXAFS. The influence of the film thickness on the dynamics of surface reorientation and consequently the influence on Tg, will be discussed.

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