The atomic and electronic structures of Au/ TiO 2 ͑110͒ systems have been investigated theoretically based on the density-functional theory. We have examined Au adsorption on three types of TiO 2 ͑110͒ surfaces with different stoichiometry and defects; the stoichiometric surface, the surface formed by removing bridgingoxygen atoms (Ti-rich surface), and the surface formed by removing sixfold Ti and bridging-oxygen atoms (O-rich surface). For the stoichiometric surface, the stable site for the Au adatom is the hollow site surrounded by one bridging-oxygen and two in-plane oxygen atoms or the on-top site above the fivefold Ti atom. For the Ti-rich surface, the bridging site between fourfold Ti atoms along the [001] direction is the most stable. For the O-rich surface, the vacant site formed by removing a sixfold Ti atom is the most stable. The adhesive energies between the Au layer and the TiO 2 surface for the nonstoichiometric surfaces are much larger than that for the stoichiometric surface. The charge transfer between the Au adatom and the substrate is negligible for the stoichiometric surface, in accordance with its smaller adhesive energy. The electron transfer occurs from the sixfold Ti atom to the Au atom for the Ti-rich surface, while from the Au atom to the in-plane and inner oxygen atoms for the O-rich surface. Significant orbital hybridization between Au and O or Ti is also observed for the nonstoichiometric surfaces. It can be said that the TiO 2 surface conditions such as defects or nonstoichiometry strongly affect the adsorption energy and the electronic structure of the Au adlayer. This point should be closely related to the catalytic property of the Au/ TiO 2 system.

The molecular orientation effect of a liquid crystalline (LC) epoxy resin (LCER) on thermal conductivity was investigated, with the thermal conductivity depending on the surface free energy of amorphous soda–lime–silica glass substrate surfaces modified using physical surface treatments. The LC epoxy monomer was revealed to form a smectic A (SmA) phase with homeotropic alignments on the surfaces of substrates that possess high surface free energies of 71.3 and 72.7 mN m –1 , but forming a planar alignment on the surface of a substrate that possesses a relatively low surface free energy of 46.3 mN m –1 . The optical microscopy observations and the X-ray analyses revealed that the LC epoxy monomer also induced a homeotropically aligned SmA structure due to cross-linking with a curing agent on the high-free-energy surface. The orientational order parameter of the resulting homeotropic SmA structure was calculated from the grazing incidence small-angle X-ray scattering patterns to be 0.73–0.75. The thermal conductivity of the cross-linked LCER forming a homeotropically aligned SmA structure was also estimated to be 2.0 and 5.8 W m –1 K –1 for the average and maximum in the direction of the Sm layer normal. The value of the thermal conductivity was remarkable among the thermosetting polymers and ceramic glass, and the LCER could be applied for high-thermal-conductive adhesives and packaging materials in electrical and electronic devices.

No abstract

The atomic and electronic structure of the ͓0001͔/(1 2 3 0) ⌺ϭ7 symmetric tilt boundary in ZnO has been investigated by an ab initio plane-wave pseudopotential method within the local-density approximation. Two types of equilibrium geometries are obtained with similar boundary energies. Atomic arrangement is largely reconstructed to vanish dangling bonds in one configuration, whereas the other shows small bond distortion but has dangling bonds at the boundary core. The balance between the energies for deforming atomic arrangements and vanishing dangling bonds should be significant in determining the boundary energies. The electronic structure of the grain boundaries is discussed with a special interest in the relationship with the bond disorder. Owing to the bond distortion and/or the presence of the dangling bonds, localized states form mainly at the lower valence band and the bottom of the upper valence band. On the other hand, the electronic states in the vicinity of the band gap are not significantly affected by the bond disorder. Deep electronic states are not generated in the band gap even for the configuration with dangling bonds. This behavior can be generally explained by the band structure intrinsic to ZnO.