Effects of fcc Noble Metal Underlayer and Substrate Temperature on the Formation of Ni(111) Epitaxial Thin Films

Ni(111)_fcc epitaxial thin films were prepared on fee noble metal, X [X = Cu, Au, Ag], underlayers hetero-epitaxially grown on MgO(111) substrates by ultra-high vacuum molecular beam epitaxy. The microstructure and the lattice strain of Ni epitaxial films are influenced by the underlayer material and the substrate temperature. Ni films formed on Cu and Au underlayers are strained, which is interpreted to be caused by atomic mixing around the interface. The atomic mixing is enhanced with increasing the substrate temperature. On the contrary, Ni films with small strain are formed on Ag underlayers. The small film strain is possibly due to formation of sharp Ni/Ag interface resulting from immiscibility of the two elements and introduction of misfit dislocations. It is also shown that parts of Ag atoms segregate from the underlayer to the surface during Ni deposition and Ag(111)_fcc crystal is coexisting with Ni(111)_fcc crystal in the surface layer.