Recent studies have indicated that nickel gallium alloys can be effective for the catalytic hydrogenation of CO2 to methanol. To simplify the characterization of NiGa catalysts, we are developing model systems using NiGa thin films. We prepared NiGa thin films by RF magnetron sputtering using an equiatomic alloy target, followed by annealing in ultrahigh vacuum. The resulting films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). AFM data showed that the film roughness and the grain size increased significantly as the film was annealed above 700 oC. The XRD patterns indicated that Ni-Ga thin films were nanocrystalline as deposited and then converted to the Ni13Ga9 phase after annealing above 500 oC. XPS was used to determine chemical and thermal stabilities by monitoring changes in Ni 2p, Ga 2p, and O 1s spectra. It was found that surface segregation of gallium and oxygen occurred after annealing up to 600 oC, resulting in the formation of a Ga2O3 layer on the NiGa surface. For anneals above 600 oC, the Ga2O3 XPS signal was reduced in intensity due to desorption of Ga2O3 from the NiGa surface.
The ability to control the size and shape of porous materials is of considerable interest, where controllably modulating pore size may allow trapping and releasing molecules in the pores. MIL-53(Al) is a flexible metal organic framework (MOF) material with large breathing effect, which may be useful for these applications. In this study, MIL-53(Al) was successfully synthesized by a microwave reactor. To grow thin film MIL-53(Al), a Au surface was treated with an organic self-assembled monolayer (SAM). Isolated MIL-53(Al) particles were formed on the SAM-functionalized Au substrate by using the mother solution from the MW-assisted growth of MIL-53(Al). These thin films were studied by AFM, XRD and Raman spectroscopy.
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