Epitaxial growth of (1Â 1Â 0) and (1Â 1Â 1) SmAl2 films: Deposition temperature dependence of the growth direction

The epitaxial growth of (1 1 0) and (1 1 1) SmAl2 thin films has been achieved on (1 1 0)Nb∥(1 1 2¯ 0) sapphire by molecular beam epitaxy. The successful fabrication of this compound as thin films is the first and promising step towards the growth of thin films of the ternary compound Sm1−xGdxAl2, a zero magnetization ferromagnet of high interest for magnetic nanodevices. We report especially on the influence of the deposition temperature on the growth direction of SmAl2: in-situ RHEED analysis and ex situ large angle X-ray scattering experiments show that the growth direction evolves from [1 1 1] to [1 1 0] when the deposition temperature increases from 510 to 620 °C. The (1 1 0) films stabilized at higher temperature present twins rotated by 70° about the surface normal, whereas the (1 1 1) films are twin-free single domains. Results are correlated to the film morphology at the beginning of growth, observed by AFM, which depends also significantly on the deposition temperature. The strains measured parallel to the growth direction depend slightly on the film thickness and are larger than those expected from the substrate thermal contraction after deposition.