IMAGING AND MODIFICATION OF AU(111) MONATOMIC STEPS WITH ATOMIC-FORCE MICROSCOPY

AFM images of Au(111) films on mica substrates show crystallite plateaus averaging 230 nm across and separated by ca. 20-nm-deep valleys. Images obtained at relatively low (approximately 20 nN) tip-sample forces reveal well-defined monatomic-high (0.24 nm) terraces on top of individual crystallites. At high tip-sample force (approximately 200 nN), scanning the AFM tip results in selective removal of Au atoms at and near monatomic terrace edges. Generation of monolayer-deep pits as small as 12 x 12 nm was observed; however, no such deformations were observed in regions void of defects. In order to compare our observations with those of other researchers, a model is presented for estimation of the AFM tip dimension from high-resolution step profiles of the monatomic terrace edges. The analysis gave a tip radius of curvature of 43 nm, from which further calculation of tip-sample pressures employing Hertzian and Johnson-Kendall-Roberts theories was possible. The results suggest that the contact mechanics of the Au surface are a function of defect density within and near the tip-sample contact area.