Influence of fcc Underlayer Facet on Microstructure of Co Thin Film

Co epitaxial thin films are prepared on (111)-oriented fcc-Au and fcc-Ag underlayers with island-like surfaces consisting of wide top (111) terraces surrounded by narrow side {111} and {100} facets by using an ultrahigh vacuum molecular beam epitaxy system. The influences of side facet of underlayer on crystallographic properties are investigated by pole figure X-ray diffraction and cross-sectional transmission electron microscopy. fcc-Co crystals grow epitaxially not only on top Au(111) terraces, but also on side Au{111} facets, involving stacking faults along the directions normal to the top Au(111) terraces and the side Au{111} facets, respectively. hcp-Co crystals are also formed on side Au{100} facets, where the c -axis of hcp-Co crystals is parallel to the side Au{100} facets. On the contrary, hcp-Co crystals grow epitaxially on top Ag(111) terraces and side Ag{111} facets, whereas fcc-Co crystals are formed on side Ag{100} terraces. As the surface roughness of underlayer increases, the Co film growth on the side facet is promoted. It is demonstrated that surface roughness reduction of underlayer is important in the preparation of well-oriented magnetic thin films.