A low energy electron diffraction study of the (100), (110) and (111) surfaces of gold

Abstract

The technique of low energy electron diffraction has been used to determine the structure of (100), (110) and (111) surfaces of single crystals of gold. Following short periods of argon ion bombardment, 1 × 1 bulk type structures are generated on all three surfaces. Subsequent low temperature annealing or extended ion bombardment, without annealing, results in the formation of the anomalous structures, (100) 5 × 1 and (110) 1 × 2; no change is observed in the (111) surface structure. The anomalous structures were observed to transform reversibly as follows: 5×1 ⇄ 800°C 1×1(100) 1×2 ⇄ 600°C 1×1(110) Based on the assumption that these structures arise from the interaction of an impurity with the gold substrate, a surface dislocation model is proposed that qualitatively accounts for the superperiodic character of these structures. A theory which invokes impurity layer roughening (disordering) is advanced to account for the reversible transformations. Evidence is presented that suggests that the impurity is derived from the bulk of the crystals and is brought to the surface by a combination of selective sputtering, volume and surface diffusion processes. A second type of impurity structure, resulting in “ring” type diffraction features for all three orientations, is observed after extended high temperature annealing in vacuum. Results describing the thermal desorption of impurities from electropolished surfaces of gold are also presented.