Influence of in-situ substrate temperature on anisotropic behaviour of glancing angle grown nickel nanocolumns

In this work, we report magnetic and optical anisotropies in tilted nickel (Ni) nanocolumns and their dependencies on the film growth conditions. The Ni nanocolumns were prepared using electron beam evaporation technique in conjunction with glancing angle deposition methodology. The film depositions were performed at various in-situ substrate temperatures viz. 30 °C, 150 °C, 250 °C and 300 °C. An increase in material density with in-situ substrate temperature due to the thermal diffusion mediated coalescence of neighbouring grains was observed. The results were further corroborated with the alterations in surface morphology of the films. The modification in tilt angle of the Ni nanocolumns was also observed with in-situ substrate heating due to the non-ballistic growth approach. The presence of uniaxial optical anisotropy was established in the films deposited at low substrate temperatures (< 250 °C) using generalized ellipsometry (GE). However, the uniaxial optical anisotropy was found to be negligible for the high temperature deposited films due to thermal diffusion effect. SQUID measurements were performed for quantification of magnetic anisotropy in the films. The estimated magnetic anisotropy energy confirmed low substrate temperature deposited films to be more anisotropic as compared to others. Magnetic coercivity of the films showed film porosity dependent changes in the field values. Overall, the present investigation demonstrates anisotropic behaviour of nanocolumnar nickel thin films for non-ballistic glancing angle deposition.