Abstract
Dark pits of a monolayer depth were observed on the Au(111) surfaces by STM in ambient. Similar results were observed also in other redox experiments on the same surface. Our experiments confirmed that the formation of these dark pits is related to the ambient environment. Suppose the formation of the dark pits is a consequence of redox process, there would exist unknown mechanism by which gold is oxidized in the ambient environment. However, we could not exclude the possibility that their formation is due to contamination. In our studies, oxidation of Au(111) surface was carried out by exposing the surface to ionized oxygen which was produced by leaking oxygen gas through a hot filament. From AES and LEED results, oxygen was confirmed to stay at the top few layers. Although the surface is rough, atomic steps could be observed in STM images. The surface was annealed to 473 K followed by STM observation. From the change of surface morphology, the place exchange mechanism is the most probable model responsible for the oxidation of gold surface. The field-gradient-induced diffusion was applied to interpret the tip-induced diffusion observed on the Au(111) surface. In this observation, tiny islands and craters on the terraces and finger-like structure formed at step edges were elongated along <1 –1 0> direction. The <1 –1 0> is the direction along which the surface stress on Au(111) is released.