Structure Characterization of Fe, Co, and Ni Thin Films Epitaxially Grown on GaAs(111) Substrate

Abstract

Fe, Co, and Ni films of 40 nm thickness are prepared on GaAs(111) single-crystal substrates at room temperature by using a radio-frequency magnetron sputtering system. The film growth behavior and the crystallographic properties are investigated by in-situ reflection high-energy electron diffraction and pole-figure X-ray diffraction. bcc single-crystals of (111) orientation are formed on the substrates for all the film materials, though the bcc structure is metastable for Co and Ni materials. The metastable structure is stabilized through hetero-epitaxial growth. Fe films possess bcc structure for the investigated thickness range. On the contrary, the bcc-Co and the bcc-Ni crystals, respectively, start to transform into hcp and fcc structures, as the thickness is increased beyond 2 nm. The phase transformations occur through atomic displacements from the close-packed planes of bcc(11 _ 0), bcc(1 _ 01), and bcc(011 _ ), which are perpendicular to the substrate surface, to hcp(0001) and fcc(111) close-packed planes. The crystallographic orientation relationships of hcp and fcc crystals with respect to bcc crystal are similar to the Kurdjumov-Sachs relationship.