VARIATION OF THE MORPHOLOGY OF SILVER SURFACES BY THERMAL AND CATALYTIC ETCHING

The structural and morphological variations of the surfaces of polycrystalline silver foils upon heating in ultra-high vacuum (UHV) or in reacting gases related to methanol oxidation have been investigated using scanning electron microscopy (SEM) and reflection high-energy electron diffraction (RHEED). Thermal etching under UHV conditions with and without net evaporation of silver atoms results in two distinct restructural features: the formation of surface hill-and-valley structures including low-index faces, and the preferential development of (012) facets. In the presence of an oxygen atmosphere, as well as for conditions of methanol oxidation, a strong surface facetting occurs, depending on the composition and temperature. Flat facets, terrace-and-step structures, pits, as well as combinations thereof, may be formed, and the underlying mechanisms are qualitatively discussed on the basis of the related chemical processes and thermodynamic principles.