Scanning tunneling microscopy of the local atomic structure of two-dimensional gold and silver islands on graphite

Small, two-dimensional islands of silver and gold formed in situ by evaporation onto graphite cleaved in ultrahigh vacuum are imaged atom by atom with a scanning tunneling microscope. These islands contain ordered regions of roughly 50 atoms in rectangular lattices, incommensurate with the substrate lattice, that are not close packed as in the bulk fcc structure. In one series of images, the shorter lattice spacing remained constant at 2.35 0.15 A whereas the longer decreased from 4.05 0.1 to 3.50.1 A over a period of roughly 10 min.