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From the perspectives of bond energy theory, the bond–order–length–strength correlation mechanism, and the core–surface configuration for nanomaterials, a physics-based model, free of any adjustable parameters and simultaneously considering the coupling effects of surface orientation, temperature, and size on the vacancy formation energy of metal materials is developed. To confirm our present model, the temperature-dependent vacancy formation energies of six face-centered cubic metals and the size-dependent vacancy formation energies of gold particles are predicted, which are in reasonable agreement with the simulation results. In particular, the model can provide a convenient method to predict the temperature-dependent vacancy formation energy of nanomaterials with different surface orientations, and also can provide a new method to study the structural relaxation. The study shows that the size effect on the vacancy formation energy depends on the stronger bond energy in the surface layers compared with those in the core interior, and the temperature-dependent vacancy formation energy arises from cohesive energy weakening, with the opposite trend to that induced by size reduction. [ABSTRACT FROM AUTHOR]

The geometric and electronic structures of scandium carbonitride endofullerene Sc3CN@C2n (2n = 68, 78, 80, 82, and 84) and Sc(Y)NC@C76 have been systematically investigated to identify the preferred position of internal C and N atoms by density functional theory (DFT) calculations combined with statistical mechanics treatments. The CN bond orientation can generally be inferred from the molecule stability and electronic configuration. It is found that Sc3CN@C2n molecules have the most stable structure with C atom locating at the center of Sc3CN cluster. The CN bond has trivalent form of [CN]3− and connects with adjacent three Sc atoms tightly. However, in Sc(Y)NC@C76 with [NC]−, the N atom always resides in the center of the whole molecule. In addition, the stability of Sc3CN@C2n has been further compared in terms of the organization of the corresponding molecular energy level. The structural differences between Sc3CN@C2n and Sc3NC@C2n are highlighted by their respected infrared spectra. [ABSTRACT FROM AUTHOR]

The surface orientation of metal nanoparticles is critical to their physical and chemical properties. This study aims on the understanding of the effect of surface orientation as well as heterogeneous epitaxy of metal nanoparticles at an interface between two materials with a large lattice mismatch. Silver nanoparticles of different diameters were grown on arrays of calcium fluoride (CaF2) nanorods using oblique angle deposition as a model system for this study. Scanning electron microscopy and transmission electron microscopy (TEM) imaging were used to verify that the nanoparticles were selectively grown on the desired {111} facets of the nanorod tips. Using selected area diffraction and dark field imaging in TEM, it was shown that the nanoparticles were grown at a (111) orientation at the CaF2 interface with large lattice strains. Thus biaxially textured CaF2 nanorod arrays can be used as a catalytic support. [ABSTRACT FROM AUTHOR]

Self-catalysed and self-organized GaN nanowires were grown on c-, a-, m- and r-plane sapphire by metal-organic vapour phase epitaxy. In dependence on the crystallographic orientation of the sapphire substrate, vertical, tilted and in-plane GaN nanowires were achieved. The nanowire orientation is visualized by scanning electron microscopy and analysed by x-ray diffraction. The influence of the sapphire nitridation step on the nanowire formation is investigated. Spatially and spectrally resolved cathodoluminescence studies are carried out on the GaN nanowires to analyse the influence of the GaN nanowire orientation as well as the presence of both N- and Ga-polar sections in a single nanowire on the optical properties. [ABSTRACT FROM AUTHOR]