Role of a buried ultrathin amorphous interlayer on the growth of Co films on different metal substrates

Abstract

Thin films of different metals M (M=Ti, Zr, Hf, Nb, Fe, and Ni) of thickness around 10 nm are deposited on Si(100) substrates and a ∼30 nm Co film is deposited on these metal films using the magnetron sputtering method. Cross-sectional transmission electron microscopy (XTEM) shows the presence of a ∼2 nm buried ultrathin amorphous interlayer at the interface between the Co layer and the M layers (M=Ti, Zr, Hf, and Nb). X-ray reflectivity is used to determine the electron density of this buried ultrathin amorphous interlayer. X-ray diffraction (XRD) is used to determine the crystalline quality of the deposited Co film on these various metal film substrates. The XRD peaks of Co(111) and Co(222) are observed when Ti, Zr, Hf, and Nb are used as substrates. Pole figure measurements confirm that the Co film is highly textured on such metallic substrates. On the other hand no characteristic XRD peaks of cobalt are observed when Ni and Fe are used as the substrate, however, XTEM shows the presence of the Co film on those substrates. Theoretically, the heat of mixing (−ΔH) has been calculated for Co–M systems. The local temperature rise is estimated using the average heat capacity and the calculated heat of mixing of the amorphous interface compound (Co3M). The local temperature rise due to the amorphous phase formation and hence better mobility of the further deposited metal atoms is the cause of highly textured Co thin films on such metal substrates.