Previous abstract
Next abstract
Session A6 - Chemical Sensitivity in Scanning Probe Microscopy.
MIXED session, Monday morning, March 18
Room 260, America's Center
The role of a liquid medium in regulating adhesive forces in scanning force microscopy measurements is investigated. We have measured the adhesive forces between chemically tailored organic surfaces in three prototypical solvents - water, ethanol, and n-hexadecane (HD), comparing our results to the forces due to the macroscopic work of adhesion. Interfacial forces between like chemically functionalized (S(CH_2)_nX)/Au, where X= CH_3, OCH_3, CO_2CH_3, CONH_2, CO_2H, and OH) cantilever tips and surfaces in water scale directly with the work due to solvent exclusion: Contacts between hydrophobic surfaces result in significantly larger adhesive forces than do hydrophilic contacts. The range of these adhesive forces decreases when the solvent is changed from water to either ethanol or HD, consistent with the reduced work of solvent exclusion. These results show that chemical contrast in scanning force microscopy may be enhanced by choice of tip modification and liquid medium. This chemical contrast is exploited in scanning force measurements of several block copolymer samples.