Formation of bcc-Ni thin film on GaAs(100) substrate and phase transformation from bcc to fcc

Ni thin films are prepared on GaAs(100) single-crystal substrates at room temperature by using an ultra-high vacuum radio-frequency magnetron sputtering system. The growth behavior and the crystallographic properties are studied by in-situ refection highenergy electron diffraction and pole-figure X-ray diffraction. In an early stage of film growth, a metastable bcc Ni(100) single-crystal film is formed on GaAs(100) substrate, where the bcc structure is stabilized through hetero-epitaxial growth. With increasing the film thickness, fcc crystals coexist with the bcc(100) crystal. High-resolution cross-sectional transmission electron microscopy shows that the film consists of a mixture of bcc and fcc crystals and that a large number of planar faults exist parallel to the fcc(111) close-packed plane. The results indicate that the bcc structure starts to transform into fcc structure through atomic displacement parallel to the bcc{110} close-packed planes.