Paper & Patents

Inspired by the controversy over tensile deformation modes of single-crystalline 〈110〉/{111} Au nanowires, we investigated the dependency of the deformation mode on diameters of nanowires using the molecular dynamics technique. A new criterion for assessing the preferred deformation mode—slip or twin propagation—of nanowires as a function of nanowire diameter is presented. The results demonstrate the size-dependent transition, from superplastic deformation mediated by twin propagation to the rupture by localized slips in deformed region as the nanowire diameter decreases. Moreover, the criterion was successfully applied to explain the superplastic deformation of Cu nanowires.

The effects of oxygen vacancies on the atomic and electronic structures in crystalline Zn2SnO4 were examined by ab-initio calculations using screened hybrid density functional. The formation energy and the electronic structure indicated that the neutral oxygen vacancy was stable in the n-type region with forming deep level in the bandgap. The ionization energy of oxygen vacancy was calculated to be around 2.0 eV, which can be excited by visible photon energy. The atomic movements and the Bader charge analyses around the neutral oxygen vacancy showed that Sn played a dominant role in changing the electronic properties by forming the pair of Sn2+-VO0, which was accompanied by the reduction of the charge state of Sn due to its multiple oxidation states. On the contrary, the electronic state of Zn hardly changed despite of its more predominant atomic shifts than Sn around the oxygen vacancy.

Catalysts in commercial proton exchange membrane fuel cells must be optimized for activity and cost, but improvements are hampered for Pt nanoparticles by low activity resulting from extensive OH adsorption. A model system clearly elucidating the impact of OH coverage on Pt nanoparticles was therefore developed. Using first principles calculations, free energies due to changing OH coverage in the oxygen reduction reaction were predicted as functions of electrode potential and local surface structure. Free energy contour plots that considered surface OH coverage were developed. Therefrom, we theoretically predicted the optimum range of operating potentials, yielding design guidelines for catalytic surfaces.

The creep properties of an 18Cr9Ni3CuNbVN austenitic stainless steel have been investigated at temperatures ranging from 923 to 1,073 K and stresses from 120 to 250 MPa. The rupture lives ranged from 10 to 20,105 hours. The stress dependence of the minimum creep rate obeyed a power law, with stress exponents ranging from 6 to 8.6. The activation energy was determined to be 460 to 485 kJ/mol/K. The microstructural evolution during the creep test was investigated. The V-rich Z-phase and metallic Cu precipitates began to precipitate in the middle of the creep deformation, resulting in an increase of the creep strength, while only Nb-based MX precipitates were present from the beginning of the high-temperature creep test.

The grain-refinement mechanisms involved during the deposition of diamond films by direct-current plasma assisted chemical vapor deposition (DC-PACVD) were investigated as a function of the inter-electrode electric field (IEEF). As IEEF was increased from 260 to 940 V cm À1 , the local electron temperatures near the growth front increased strongly; as a result, a strong grain refinement occurred ultimately yielding ultrananocrys-talline diamond films (UNCD). Such observations were attributed to novel features of the DC-PACVD, including the electron-stimulated desorption (ESD) of the hydro-gen-terminated moieties located at the surface, and the consequently enhanced generation of bi-radical sites at the growing diamond surface.

A close encounter with reality on core-shell catalysts for fuel cells: the outstanding significance of the work is (i) suggestion of a computational methodology to design a specific combination of core and shell materials in terms of both the activity and the durability, (ii) development of a novel facile synthesis of core-shell/C electrocatalysts, and (iii) experimental validation of the design and synthesis of the core-shell/C catalysts and their performance as well as long-term stability.