The origin of faceting of ultraflat gold films epitaxially grown on mica

A two-step deposition process for the formation of atomically flat gold films on mica is developed. The process starts with a high deposition rate followed by a 1:100 reduced rate. Using this combination a completely wetting of mica by gold resulting in a two-dimensional growth mode and finally extremely flat gold films with large terraces are achieved. Additionally hexagonal faceting of the gold films on mica is observed at moderate temperatures which can be related to the relaxation of stress caused by different thermal coefficients of expansion of mica and gold. The stress release leads to the generation of misfit dislocations that glide along the (1 0 0) planes producing facets on the surface. Annealing experiments in a UHV-STM and thermogravimetry point to the inset of intensified hexagonal faceting due to the starting decomposition of mica at elevated temperatures.