Comparison of Nanoscaled and Bulk NiO Structural and Environmental Characteristics by XRD, XAFS, and XPS

NiO has been analyzed by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) analysis, and X-ray photoelectron spectroscopy (XPS) for bulk-scale and nanosized polycrystalline samples. XAFS indicates that the 5- and 25-nm NiO materials show bulk-like structural properties, with the exception of a lattice contraction, relative to the bulk material, and exhibit the anticipated decrease in average coordination numbers typically observed for nanoparticle systems. Carefully calibrated high-resolution XRD measurements confirm the lattice contraction for the nanoparticles. XPS also indicates the surface of NiO is comparable across the size scale for both binding energies and characteristic Ni 2p satellite structure. Detailed examination of the Ni 2p and O 1s regions reveals that hydroxylation upon prolonged exposure to the ambient causes a noticeable change in the Ni 2p peak shape that could be misinterpreted as an artifact of particle size.