STM study of Bi-on-Cu(100)

摘要

Scanning tunneling microscopy (STM) has been used to study the various possible structures of adsorbed Bi on the Cu(100) surface, after equilibration at a temperature of 520 K. All of the structures previously identified by X-ray diffraction (lattice gas, c(2 × 2), c(92~(1/2) × 2~(1/2))R45°, and p(10 × 10), in order of increasing Bi-coverage) were found to be present on a single sample produced by diffusing Bi onto the Cu(100) surface from a 3-d source. By investigating the possible coexistence of various pairs of phases, it was demonstrated that the c(2 × 2) phase transforms to the c(92~(1/2) × 2~(1/2))R45°phase by a first order transition, whereas the transition from c(92~(1/2) × 2~(1/2))R45° to p( 10 × 10) is continuous. In addition, the structure of surface steps was studied as a function of Bi-coverage. The results showed that the presence of Bi changes the nature of the step-step interactions at the Cu(100) surface from repulsive to attractive. The attractive step-step interactions transform any small deviations from the nominal (100) orientation of the Cu substrate into (310) microfacets. When compared with the known equilibrium crystal shape (ECS) of Bi-saturated Cu, the observed microfaceting may imply that the ECS of Cu-Bi alloys is temperature dependent.