Gold-induced faceting on a Si(001) vicinal surface: Spot-profile-analyzing LEED and reflection-electron-microscopy study

Au-induced faceting on a 4° off Si(001) vicinal surface at temperatures between 750 and 880 °C was studied by in situ high-resolution low-energy electron diffraction and ultrahigh vacuum reflection electron microscopy. The formation of an Au-induced incommensurate $5\times 3.2$ reconstruction on (001) terraces triggers the transformation of the initial regular step train of the vicinal surface into a “hill-and-valley” structure composed of very wide (001) terraces and step bands. With further increasing Au coverage the step bands transform to well-ordered (119) facets, which also exhibit the Au-induced reconstruction. For adsorption temperatures below 800 °C the transformation to the well-ordered (119) facet is kinetically hindered: an irregular mixture of (115), (117), and (119) facets is observed. The (001) terraces and facets are alternately arranged to form a hill-and-valley structure with an average period of ∼400 nm and terrace lengths of more than several hundreds of μm. Driving force for the large-scale morphological transformation into the hill-and-valley structure is the decrease of surface free energy of the (001) and the (119) surface due to the formation of Au-induced reconstruction on (119) facets as well as on (001) areas.