FRICTION FORCE MICROSCOPY OF AGBR CRYSTALS - AG(0) RODS AND ADSORBED GELATIN FILMS

Friction force microscopy was performed on the (111) surface of soluti on-grown AgBr crystals before and after deposition of gelatin films. I mages of the initial surface identify the dissimilar chemical nature o f the AgBr and rod-shaped crystallites which grow along the (110) fami ly of crystal directions during imaging and are attributed to Ag0. Por es in gelatin films on AgBr and on highly-oriented pyrolytic graphite are seen to extend to the substrate, based on a reduced frictional for ce sensed at the bottom of the pores. The images also distinguish fric tional contributions of ''physical'' versus chemical origin. The forme r are manifest as variations in image contrast seen at subnanometer-sc ale steps in AgBr(111) and at the edges of the Ag0 crystallites and th e gelatin pores and reflect additional cantilever torsion at these loc ations. The quantitative dependence of this effect on the size and sha pe of surface asperities is discussed, and an expression is derived wh ich relates cantilever torsion to both chemical and physical component s of friction.