Molecular dynamics simulation of atomic force microscopy: imaging single-atom vacancies on Ag(001) and Pt(001)

In a growing number of examples, the atomic force microscope (AFM) has demo nstrated an ability to provide genuine atomic-resolution images of single c rystal surfaces by resolving atomic-sized surface features. However, to dat e, all such examples have either used ionic or covalent crystal samples; me tals are notably absent from the list of materials yielding true atomic res olution. This study has used molecular dynamics simulation to study the int eraction of a single-atom Ag tip with Ag(001) and Pt(001) surfaces in order to address the question of whether or not atomic-resolution AFM imaging of metal surfaces is likely to be feasible, and under what conditions. Using a constant force imaging procedure, a narrow window of imaging forces betwe en 1 and 3 nN (attractive) was identified in which genuine atomic resolutio n was achieved without tip-induced disruption of the surface structure, For ces outside this range caused rearrangement of surface atoms or penetration of the tip into the surface. These findings suggest that severe experiment al conditions are required to image metal surfaces with AFM at atomic resol ution. (C) 1999 Elsevier Science B.V. All rights reserved.