The interaction of oxygen with Ni−Cr(100) alloy surfaces is studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to observe the initial steps of oxidation and formation of the alloy−oxide interface. The progression of oxidation was observed for Ni(100) and Ni−Cr(100) thin films including Ni−8 wt % Cr(100) and Ni−12 wt % Cr(100), which were grown on MgO(100) in situ. These surfaces were exposed to between 1 and 150 L O 2 at 500 °C, and additional annealing steps were performed at 500 and 600 °C. Each oxidation and annealing step was studied with STM and STS, and differential conductance maps delivered spatially resolved information on doping and band gap distributions. Initial NiO nucleation and growth begins along the step edges of the Ni−Cr alloy accompanied by the formation of small oxide particles on the terraces. The incubation period known in oxidation of Ni( 100) is absent on Ni−Cr alloy surfaces illustrating the significant changes in surface chemistry triggered by Cr-alloying.Step edge faceting is initiated by oxide decoration along the step edges and is expressed as moirépatterns in the STM images. The surface oxide can be characterized by NiONi(6 × 7) and NiO−Ni(7 × 8) coincidence lattices, which have a cube-on-cube epitaxial relationship. Small patches of NiO are susceptible to reduction during annealing; however, additional oxide coverage stabilizes the NiO. NiO regions are interspersed with areas covered predominantly with a novel cross-type reconstruction, which is interpreted tentatively as a Cr-rich, phase-separated region. Statistical analysis of the geometric features of the surface oxide including step edge heights, and NiO wedge angles illustrates the layer-by-layer growth mode of NiO in this pre-Cabrera−Mott regime, and the restructuring of the alloy−oxide interface during the oxidation process. This experimental approach has offered greater insight into the progression of oxide growth in Ni−Cr thin films and underscores the dramatic impact of alloying on oxidation process in the pre-Cabrera−Mott regime.

Quantum confinement in small metal clusters leads to a bunching of states into electronic shells reminiscent of shells in atoms, enabling the classification of clusters as superatoms.

The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCu, VAg, and VAu (x = 3-14) clusters were examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and that at small sizes some of the valence electrons of vanadium are localized on vanadium, while at larger sizes the 3d orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium atom. A molecular orbital analysis reveals that in planar clusters the delocalization of the 3d orbital of vanadium is enhanced when surrounded by gold due to enhanced 6s-5d hybridization. Once the clusters become three-dimensional, this hybridization is reduced, and copper most readily delocalizes the vanadium's valence electrons. By understanding these unique features, greater insight is offered into the role of a host material's electronic structure in determining the bonding characteristics and stability of localized spin magnetic moments in quantum confined systems.