Electrochemical Au deposition on stepped Si(1 1 1)-H surfaces: 3D versus 2D growth studied by AFM and X-ray diffraction

In order to grow magnetic layers on silicon substrates, a non-magnetic buffer layer is often needed to avoid silicide formation and to reproduce the perpendicular magnetic anisotropy obtained on metal single crystals, as in the case of Co on Au(1 1 1) and Pt(1 1 1). In this context, we have studied the electrochemical growth of Au buffer layers, and show that it is possible to obtain different film morphologies on hydrogen-terminated vicinal Si(1 1 1) surfaces by varying the electrochemical deposition parameters and solution composition. Two different morphologies have been obtained as observed by atomic force microscopy: continuous 2D Au films (chloride solution at pH 4), and films consisting in flat top 3D Au islands decorating the Si(1 1 1) step edges (cyanide solution at pH 14). X-ray diffraction measurements reveal that the gold layer and islands have Au(1 1 1) orientation and are in epitaxy with the Si(1 1 1) surface. In the case of islands, the lateral facets have also Au(1 1 1) orientation. Results are discussed within a model in which the breaking of the Si-H surface bonds plays a major role in the Au nucleation and growth mechanisms.