Microstructure of hcp-Ni(11̄00)/bcc-Cr(211) Bi-layer Film Grown on MgO(110) Substrate

A Ni epitaxial film with hcp(1100) single-crystal structure is obtained on a Cr(211) underlayer hetero-epitaxially grown on an MgO(110) single-crystal substrate in an early stage of film growth by ultra high vacuum rf magnetron sputtering. Reflection high energy electron diffraction (RHEED) observation indicates that the metastable hcp-Ni crystal tends to transform into more stable fcc crystal with increasing the film thickness. The crystallographic orientation relationship between the hcp and the fcc crystals is determined by RHEED and - scan X-ray diffraction. High-resolution transmission electron microscopy shows that the hcp and the fcc crystals exist separately on the Cr underlayer. The lattice constants of hcp-Ni crystal are determined from X-ray diffraction analysis as a=0.249 nm, c=0.415 nm, and c/a=1.67.