Abstract
Despite the application potential of nickel tungstate (NiWO4) in heterogeneous catalysis, humidity and gas sensing, etc, its surfaces have essentially remained unexplored. In this work, NiWO4 nanoparticles and films with the wolframite structure have been grown via a solid-state reaction of (WO3)(3) clusters and a NiO(100) film on a Ni(110) crystal surface and characterized by a variety of experimental techniques, including x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM) and x-ray diffraction (XRD), combined with ab-initio density functional theory (DFT) calculations.
NiWO4 grows initially as three-dimensional (3D) crystalline nanoparticles displaying mainly two crystalline facets vicinal to the (100) surface, which merge with increasing the (WO3)(3) coverage into a quasi-continuous epitaxial film. The DFT results provide an account of the energetics of NiWO4 low index surfaces and highlight the role of faceting in the stabilization of extended polar (100) terraces.
These combined experimental and theoretical results show that interaction with a metal substrate and vertical confinement may stabilize oxide nano-objects with high energy facets, able to enhance their reactivity.