J. Schoiswohl

Vanadium oxide nanostructures: from zero- to three-dimensional

A fluid and elastomer device for isolating dynamic loading between members connected to the device, the fluid and elastomer device comprising: an inner member that defines a compliance chamber; an outer member that defines an outer housing chamber; an elastomeric element flexibly interconnecting said inner member relative to said outer member; a passageway located in the compliance chamber and flow connecting the compliance chamber with a primary working chamber; a secondary compliance member joined to the passageway in the compliance chamber; a volume compensator located in the housing chamber the volume compensator comprising spring means, piston member at one spring end and a diaphragm member that overlies the piston; a member located between the compliance and housing chambers, the member being moveable with the outer housing, the moveable member in combination with the diaphragm defining a compensator chamber; and a volume of working fluid in said chambers and passageway.

The metal–insulator transition in V2O3(0001) thin films: surface termination effects

Epitaxially grown V2O3(0001) thin films have been prepared with different surface terminations, as evidenced by atomically resolved scanning tunnelling microscopy and high-resolution electron energy loss spectroscopy (HREELS) phonon spectra. The spectral changes observed in valence band photoemission spectra and HREELS on cooling the V2O3 samples from 300 to 100 K have been associated with the metal–insulator transition (MIT) in the bulk of the V2O3 film. The reconstructed surface regions per se do not display the MIT, but affect the MIT signature observed with surface sensitive techniques, depending on the thickness of the reconstructions. Whereas the thermodynamically stable (1 × 1) vanadyl V = O surface termination allows the observation in photoemission and HREELS of a clear signature of the MIT, the latter is screened on a surface formed by V = O defect structures. Doping of the surface with small amounts of adsorbed water restores reversibly the MIT spectral fingerprints. These observations are discussed in terms of the different geometrical and electronic structures of the different surface terminations.

Reactivity of V2O3(0001) surfaces: molecular vs dissociative adsorption of water

The adsorption of water on V2O3(0001) surfaces has been investigated by thermal desorption spectroscopy, high-resolution electron energy loss spectroscopy, and X-ray photoelectron spectroscopy with use of synchrotron radiation. The V2O3(0001) surfaces have been generated in epitaxial thin film form on a Rh(111) substrate with three different surface terminations according to the particular preparation conditions. The stable surface in thermodynamic equilibrium with the bulk is formed by a vanadyl (VO) (1x1) surface layer, but an oxygen-rich (radical3xradical3)R30 degrees reconstruction can be prepared under a higher chemical potential of oxygen (microO), whereas a V-terminated surface consisting of a vanadium surface layer requires a low microO, which can be achieved experimentally by the deposition of V atoms onto the (1x1) VO surface. The latter two surfaces have been used to model, in a controlled way, oxygen and vanadium containing defect centres on V2O3. On the (1x1) V=O and (radical3xradical3)R30 degrees surfaces, which expose only oxygen surface sites, the experimental results indicate consistently that the molecular adsorption of water provides the predominant adsorption channel. In contrast, on the V-terminated (1/radical3x1/radical3)R30 degrees surface the dissociation of water and the formation of surface hydroxyl species at 100 K is readily observed. Besides the dissociative adsorption a molecular adsorption channel exists also on the V-terminated V2O3(0001) surface, so that the water monolayer consists of both OH and molecular H2O species. The V surface layer on V2O3 is very reactive and is reoxidised by adsorbed water at 250 K, yielding surface vanadyl species. The results of this study indicate that V surface centres are necessary for the dissociation of water on V2O3 surfaces.