Deposition and characterization of nickel gallium thin films

Recent studies have indicated that nickel gallium alloys can be effective catalysts for the hydrogenation of CO2 to methanol. To simplify the characterization of NiGa catalysts, the authors are developing model systems using sputter deposited NiGa thin films. The NiGa thin films used in this study were deposited using an equimolar alloy target and annealed in ultrahigh vacuum. Atomic force microscopy (AFM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) were used to characterize the NiGa films before and after annealing. AFM results showed that film roughness and grain size significantly increased as the film was annealed above 700 °C. XRD patterns indicated that NiGa thin films were nanocrystalline as deposited and then transitioned to the Ni13Ga9 phase after annealing above 500 °C. XPS results indicated that gallium and oxygen segregated to the surface after annealing up to 600 °C, and formed a surface Ga2O3 layer. For anneals above 600 °C, the Ga2O3 XPS signal was reduced in intens...