Structure of Vanadium Oxide (V2O3) Grown on Cu3Au(100)

The epitaxial growth of vanadium oxide (V2O3) has been investigated by scanning tunneling microscopy (STM), low energy ion back-scattering (ISS) and low energy electron diffraction (LEED). Direct evaporation of vanadium onto metal surfaces (Cu, Au or Cu3Au) gives rise to massive surface alloying. The attempt to oxidize the vanadium film by consequent oxygen exposure leads to the formation of rough VO x films of poor quality and mixed valency. A new way of oxide formation has been developed by preoxidation of a Cu3Au substrate, which acts positively in two ways since it prevents completely alloy formation and also forces strong surface wetting of the vanadium oxide. As a result, two-dimensional layer growth of good quality has been achieved. Depending on the preoxygen content at Cu3Au(100), the amount of V deposition and annealing temperature, different epitaxial layers of vanadium oxides can be prepared. In particular, the surface structure of V2O3(0001) was investigated. The surface structure appears completely different from the half layer metal termination at Cr2O3(0001). Specifically, the full vanadium layer stabilized by one third of an oxygen layer located in pseudo bridge positions close to regular oxygen positions of a next layer. Close to defects the full vanadium layer appears also without oxygen stabilization.

An Investigation of the Effects of Layer Thickness on the Fracture Behavior of Layered NiAl/V Composites

The effects of vanadium layer thickness (100, 200 and 400 μm) on the resistance-curve behavior of NiAl/V, microlaminates are examined in this paper. The fracture resistance of the NiAl microlaminates reinforced with 20 vol.% of vanadium layers is shown to increase with increasing vanadium layer thickness. The improved fracture toughness (from an NiAl matrix toughness of 6˜.6MPam to a steady-state toughness of 1˜5MPam obtained from finite element analysis) is associated with crack bridging and the interactions of cracks with vanadium layers. The reinitiation of cracks in adjacent NiAl layers is modeled using finite element methods and the reinitiation is shown to occur as a result of strain concentrations at the interface between the adjacent NiAl layers and vanadium layers. The deviation of the reinitiated cracks from the pure mode I direction is shown to occur in the direction of maximum shear strain. Toughening due to crack bridging is also modeled using large-scale bridging models. The intrinsic toughness levels of the microlaminates are also inferred by extrapolating the large scale bridging models to arbitrarily large specimen widths. The extrapolations also show that the small-scale bridging intrinsic toughness increases with increasing vanadium layer thickness.