Gold Nanobelt Reorientation by Molecular Dynamics Simulation

The embedded atom method is used to study the structure stability of gold nanobelt. The Au nanobelts have a rectangular cross-section with （100） orientation along the x^-,γ- and z-axes. Free surfaces are used along the x- and y-directions, and periodic boundary condition is used along z-direction. The simulation is performed at different temperatures and cross-section sizes. Our results show that the structure stability of the Au nanobelts depends on the nanobelt size, initial orientation, boundary conditions and temperature. A critical temperature exists for Au nanobelts to transform from initial （100） nanobelt to final （110） nanobelt. The mechanism of the reorientation is the slip and spread of dislocation through the nanobelt under compressive stress caused by tensile surface-stress components.     

Surface Structure of Large Synthetic Diamonds by High Temperature and High Pressure

With NiMnCo and FeCoNi alloys as solvent metals, large single-crystal diamonds of about 3mm across are grown by temperature gradient method （TGM） under high temperature and high pressure （HPHT）. Although both {100} and {111} surfaces are developed by a layer growth mechanism, some different characteristic patterns are seen clearly on the different surfaces, no matter whether NiMnCo or FeCoNi alloys are taken as the solvent metals. For {100} surface, it seems to have been melted or etched greatly, no dendritic patterns to be found, and only a large number of growth hillocks are dispersed net-likely; while for {111} surface, it often seems to be more smooth-faced, no etched or melted traces are present even when a lot of depressed trigonal growth layers. This distinct difference between {111} and {100} surfaces is considered to be related to the difference of surface-atom distribution of different surfaces, and {111} surfaces should be more difficult to be etched and more steady than {100} surfaces.     

Controllable synthesis of ultrathin vanadium oxide nanobelts via an EDTA-mediated hydrothermal process

Ultrathin VO_2 nanobelts with rough alignment features are prepared on the induction layer-coated substrates by an ethylenediaminetetraacetic acid(EDTA)-mediated hydrothermal process. EDTA acts as a chelating reagent and capping agent to facilitate the one-dimensional(1D) preferential growth of ultrathin VO_2 nanobelts with high crystallinities and good uniformities. The annealed induction layer and concentration of EDTA are found to play crucial roles in the formation of aligned and ultrathin nanobelts. Variation in EDTA concentration can change the VO_2 morphology of ultrathin nanobelts into that of thick nanoplates. Mild annealing of ultrathin VO_2 nanobelts at 350℃ in air results in the formation of V_2O_5 nanobelts with a nearly unchanged ultrathin structure. The nucleation and growth mechanism involved in the formations of nanobelts and nanoplates are proposed. The ethanol gas sensing properties of the V_2O_5 nanobelt networks-based sensor are investigated in a temperature range from 100℃ to 300℃ over ethanol concentrations ranging from 3 ppm to 500 ppm.The results indicate that the V_2O_5 nanobelt network sensor exhibits high sensitivity, good reversibility, and fast responserecovery characteristics with an optimal working temperature of 250℃.     

Production of ZnO Nanobelts and Meso-Scale Study of Mechanical Properties

We investigate a peculiar phenomenon by processing ZnO nanobelts with an atomic force microscope （AFM）. In the contact mode of AFM, peculiar bending occurs in meso-scale when the nanobelt is applied with force in lateral direction. We study the mechanical properties of ZnO nanobelts under the influence of small size effect, with finite element analysis and mathematical analysis by means of Matlab. Based on this abnormal effect, a novel measuring method is proposed, which allows the surface morphology and surface properties to be characterized at the same time.     

Orientation dependence of structural transition in fcc Al driven under uniaxial compression by atomistic simulations

By molecular dynamics simulations employing an embedded atom method potential,we have investigated structural transformations in single crystal Al caused by uniaxial strain loading along the [001],[011] and [111] directions. We find that the structural transition is strongly dependent on the crystal orientations. The entire structure phase transition only occurs when loading along the [001] direction,and the increased amplitude of temperature for [001] loading is evidently lower than that for other orientations. The morphology evolutions of the structural transition for [011] and [111] loadings are analysed in detail. The results indicate that only 20% of atoms transit to the hcp phase for [011] and [111] loadings,and the appearance of the hcp phase is due to the partial dislocation moving forward on {111} fcc family. For [011] loading,the hcp phase grows to form laminar morphology in four planes,which belong to the {111} fcc family; while for [111] loading,the hcp phase grows into a laminar structure in three planes,which belong to the {111} fcc family except for the (111) plane. In addition,the phase transition is evaluated by using the radial distribution functions.     

Grow Large High-Quality Diamonds with Different Seed Surfaces

Large high-quality type Ib diamond crystals have been grown with different seed surfaces by temperature gradient method at 5.5 CPa, 1500-1600K, with NiMnCo alloy as the metal solvent. Compared with {100} as the growth surface, the growth region of large high-quality diamond crystals with {111} as the growth surface at a higher growth rate shifts markedly from lower temperatures （suitable for {100}-facet growth） to higher temperatures （suitable for {111}-facet growth）. However, regardless of different growth surfaces, {100} or {111}, the grown crystals of sheet-shaped shape are most difflcult for metal inclusions to be trapped into, and whether or not matched growth between the seed surfaces and the growth temperatures determines the crystal shapes. In view of the growth rates, large high-quality diamond crystals of sheet-shaped shapes can be grown at a growth rate of above 2.5 mg/h, while the growth rate of large high-quality diamond crystals should not be beyond 1.5 mg/h for tower-shaped crystals.     

Electron Backscattered Diffraction of Transgranular Crack Propagation in Soft Steel

We consider the crack propagation in a soft steel sheet during the formation. The drawability is considered in relation with the structural anisotropy, the mechanical behaviour is related to both the grain morphology and the texture. The structure heterogeneity could lead to the apparition of micro-cracks. The results show the texture effect on the crack propagation and on the crack arrest in soft steel during the formation. The EBSD technique allows to show that the adjustment of the grain orientation from the initial main component {111}（112） towards the deformation orientation {111}（110） incites a trans-granular crack through a grain with initial {111}（112） orientation in a globally ductile material. It is the presence of grains with {111}（110） orientation which permits the closing of micro-cracks.     

Study on Synthesis and Gas Sensitivity of SnO2 Nanobelts

Tin dioxide （SnO2 ） nanobelts have been successfully synthesized in bulk quantity by the CVD process based on the thermal evaporation of tin powders. The x-ray diffraction analysis indicates that the nanobelts are the tetragonal futile structure of SnO2. Scanning electron microscopy and transmission electron microscopy observations reveal that the nanobelts are uniform. The selected-area electron diffraction analysis demonstrates that the nanobelts are single crystals. The energy dispersive x-ray analysis of the nanobelt shows that the nanobelts are composed of Sn and O, Gas-sensing components have been manufactured with prepared SnO2 nanobelts. Their performance indicates that SnO2 nanobelts have high sensitivity and selectivity to liquefied petroleum gas with fairly good response-recovery characteristic and stability at 220℃.     

Atomistic simulation of kink structure on edge dislocation in bcc iron

Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 （111）{011} and 1/2 （111）{112} edge dislocations （EDs） in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 （111）{011} and 1/2 （111）{112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively （b is the magnitude of the Burgers vector）. The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.     

Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

The transition energies and electric dipole （El） transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac-Fock （MCDF） method. In the calculations, the contributions from Breit interaction and quantum electrodynamics （QED） effects （vacuum polarization and self-energy）, as well as nu- clear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1＋ to Np6＋ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.