RESUMO
Experimental conductivity measurements made during highly stable tensile deformation of Au nanowires show a rich variety of behaviors, including noninteger quantum conductance plateaus, transitions, and slopes. Using tight binding conductance calculations on simulated nanowires previously deformed using density functional theory, we demonstrate that all of these phenomena arise from structural transitions between deeply metastable ordered atomic configurations that self-organize during tensile deformation.
RESUMO
Using scanning tunneling microscopy and infrared reflection absorption spectroscopy we have observed that the alpha-Fe2O3(0001) surface exhibits ferryl (Fe=O) groups, which may coexist with domains of the Fe-terminated surface. We therefore fully support ab initio calculations recently reported in the literature [W. Bergmeyer, H. Schweiger, and E. Wimmer, Phys. Rev. B 69, 195409 (2004)]. The close similarity to the results on the (0001) surfaces of Cr2O3 and V2O3 strongly suggests that the M=O termination under certain oxygen pressure conditions is the most stable for the close-packed surfaces of transition metal oxides with the corundum structure.
RESUMO
We report that calculating the Gibbs free energy of the alpha-Al2O3 (0001) surfaces in equilibrium with a realistic environment containing both oxygen and hydrogen species is essential for obtaining theoretical predictions consistent with experimental observations. Using density-functional theory we find that even under conditions of high oxygen partial pressure the metal-terminated surface is surprisingly stable. An oxygen-terminated alpha-Al2O3 (0001) surface becomes stable only if hydrogen is present on the surface. In addition, including hydrogen on the surface resolves discrepancies between previous theoretical work and experimental results with respect to the magnitude and direction of surface relaxations.
