H. T. Chu

Rearrangement of Au(111) surface as a result of scanning with scanning tunneling/atomic force microscopes

Rearrangements of monolayer islands on the (111) surface of Au films, grown epitaxially on mica substrates, are observed as a result of continuous scanning with either a scanning tunneling microscope (STM) or an atomic force microscope (AFM) under ambient conditions. With the STM, a contiguous monolayer as large as 150×150 nm2 can be moved from atop to the edges of underlying terrace in about an hour of continuous scanning at a rate of 2.0 μm/s. In general, islands coalesce, vacancies fill, and terrace edges become straighter as a result of the tip scanning over the Au surface. Crystal defects such as screw dislocations, however, are not modified appreciably with scanning, although rearrangements are seen in regions near the defects. Similar effects are observed with an AFM scanning, but to a lesser extent, and only on freshly grown films.

Epitaxial growth of ultrathin films of bismuth: an atomic force microscopy study

Abstract Ultrathin films of bismuth have been grown epitaxially onto mica substrates by vapor deposition and atomic force microscopy has been used to image the growth surface to determine optimum conditions for fabricating films having the least variations in thickness and largest possible grain size. The films always grow from three-dimensional islands which coalesce to form crystallites with their trigonal axis perpendicular to the mica surface. Crystallites as large micrometers squared with monatomic stepped topology and an rms surface roughness on the order of 1.0 nm have been observed. For mica substrates, it has been found that cleavage conditions, substrate preheating, substrate temperature during deposition. Bi deposition rate, and annealing temperature all affect nucleation and growth of Bi films.

Crystallographic structure and defects in epitaxial bismuth films grown on mica

Abstract Atomic force microscopy is used to image the surface relief of epitaxial Bi films grown on mica substrates. Monatomic terrace steps are readily resolved, which provide detailed information on crystal growth and defect structures. The films grow from the coalescence of isolated three-dimensional islands, however, each island grows layer-by-layer. The islands are triangular in shape and when they coalesce to form a continuous film, their structures are either in-phase, and consequently large crystallites are formed, or they are out-of-phase and defect structures are formed. The most common defects observed are twinning and stacking faults. Images showing the microscopic details of stacking faults, twinning, and grain boundaries are observed as a result of islands coalescing to form a continuous film.