Potential Induced Structural Transformations of the Au(100) and Au(111) Surfaces

摘要

Work has concentrated on the use of emersed Au(111) films evaporated on cleaved mica, analogous to the Ag(111) films used in other GID studies. We have studied these Au(111) films using the dame LEEDUHV apparatus as in our previous studies of Au(111) crystals, and supplemented these with GID (grazing incidence x-ray diffraction) analysis of emersed Au(111) films with thru-air transfer to a two-circle diffractometer on beamline VI at SSRL. In-situ studies using GID with a new four-circle diffractometer on beamline VI ar SSRL are scheduled for the spring running or SSRL. The ex-situ analyses by LEED and GID of the (1 )times) 1) )yield) (5 )times) 20) transformation were in reasonable agreement with one another, and the results qualitatively similar to the results for Au(100), i.e. the reconstructed ( sqrt 3 )times) 22) surface was observed only with emersion from K sup + and Cs sup + electrolytes, and not from pure acids, but the ( sqrt 3 )times) 22) was observed at much more anodic potentials of emersion than for the )100)-(5 )times) 20). Both of the reconstructions on Au(111) and (100) represent a contraction of the Au-Au bond length for the Au-Au bond length for the Au atoms in surface layer, 4% and 6.5%. Anions on the emersed surface stabilize the (1 )times) 1) structure and possibly cause an as yet unobserved expansion in the Au-Au surface atom bond length. Charge density waves (solitonsreverse arrow produced by ion (cation or anion) adsorption appear to be the driving force for the (111)-(1 )times) 1) in equilibrium ( sqrt 3 )times) 22) and (100)-(1 )times) 1) )rightleftharpoons) (5 )times) 20) surface phase transitions.