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.     

低温下单根ZnO纳米带电学性质的研究

用化学气相沉积法在硅衬底上合成了宽1 μm左右、长数十微米的ZnO纳米带. 采用微栅模板法得到单根ZnO纳米带半导体器件, 由I-V特性曲线测得室温下ZnO纳米带电阻约3 MΩ, 电阻率约0.4 Ω·cm. 研究了在20–280 K温度范围内单根ZnO纳米带电阻随温度的变化. 结果表明: 在不同温度区间内电阻随温度变化趋势明显不同, 存在两种不同的输运机制. 在130–280 K较高的温度范围内, 单根ZnO纳米带电子输运机制符合热激活输运机制, 随着温度继续降低(< 130 K), 近邻跳跃传导为主导输运机制. 关键词： ZnO 纳米带 低温 输运机制     

巴基球C60内嵌原子(Li,Na,K,Rb,Cs;F,Cl,Br,I)的稳定存在位置及其复合物的几何与电子结构

本文用量子化学EHMO/ASED方法对巴基球C60内嵌原子(A=Li,Na,K,Rb,Cs;F,Cl,Br,I)进行了计算。结果表明除Li、Na外,其它元素当置于C60笼中心附近时,复合物能量最低,最稳定;对于内嵌Li、Na原子的巴基球(Li@C60)及(Na@C60),当Li、Na位于围绕中心的一个球壳层(r～1.5A)内时最稳定。     

Ge(112)-(4×1)-In表面重构的原子结构

用扫描隧道显微镜(STM)研究了亚单层In原子引起的Ge(112)-(4×1)-In表面重构.结合随偏压极性不同而显著不同的STM图象和相应的“原子图象”,为这个重构提出了一个原子结构模型,供进一步研究参考.其中,In原子的吸附位置与它在Si(112)表面的吸附位置一致,但与Al原子和Ga原子在Si(112)表面的吸附位置不同.这个吸附位置的不同主要是由In原子较长的共价键键长引起的 关键词： 表面结构 In Ge 扫描隧道显微镜(STM)     

Cu台阶面多层弛豫的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法对Cu(311),(511),(331)和(221)四个高指数台阶表面的弛豫结构和弛豫后表面各层的电子特性进行了系统研究.发现四个台阶面的层间弛豫规律依次为-+-…,--+-…,--+-…和---+-…,与其平台-阶梯n(hkl)×(uvw)的表示法2(100)×(111),3(100)×(111),3(111)×(111)和4(111)×(111)中的原子排数n相关,即     

3D hopping conduction in SnO2 nanobelts

The temperature dependence of the electrical transport of an individual tin oxide nanobelt was measured in darkness from 400 to 5 K. We found four intrinsic electrical transport mechanisms through the nanobelt. It starts with thermally activated conduction between 400 K and 314 K, followed by nearest‐neighbor hopping conduction between 268 K and 115 K and variable range hopping conduction below 58 K, with a crossover from the 3D Mott to the 3D Efros–Shklovskii regime at 16 K. We claim that this sequence reveals the three‐dimensional nature of the electrical transport in the SnO₂ nanobelts, even though they are expected to behave as one‐dimensional systems. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cu(100) (2×22)R45°-O的表面结构与电子态的密度泛函研究

用第一性原理的总能计算研究了Cu(100))面的表面结构、弛豫以及氧原子的(2×22)吸附状 态.计算给出了Cu(100) (2×22)R45°-O吸附表面的结构参数，并得到了上述结构下氧吸附 的Cu(100)表面氧原子和各层Cu原子的电子态密度.计算得到的吸附表面功函数为4.58 eV ，与清洁Cu(100)表面功函数(～4.53 eV)几乎相同.吸附氧原子与最外层铜原子之间的垂直 距离约为0.02 nm，其能带结构体现出一定的金属性，同时由于Cu-O的杂化作用在费米能以 下约6.4 eV附近出现了局域的表面态.可以认为，在Cu(100) (2×22)R45°的氧吸附表面结 构下，吸附氧原子和衬底之间的结合主要来源于表面最外层铜原子与氧原子的相互作用. 关键词： Cu(100)(2×22)R45°-O表面 缺列再构 表面电子态     

Co chemisorption on PtCu surfaces II. (1 × 1)-CO/Pt0.98Cu0.02(110)

The chemisorption of CO on the Pt atoms of an initially (1 × 3) reconstructed Pt_0.98Cu_0.02(110) surface at ~ 373 K can lead to the formation of a (1 × 1) surface. Comparisons are made with (1 × 3)-CO surfaces formed by CO exposures at 293 or 155 K. Thermal desorption shows that the (1 × 1)-CO surface has an enhanced population of high temperature CO peak ( ~ 543 K) from Pt sites. The CO-induced structural conversion also leads to a decrease in the subsequent CO uptake on the low temperature Pt sites and on the Pt-Cu “mixed” sites, with a concomitant increase in adsorption on the Cu-like sites. Such a reduction in the number of the Pt-Cu “ mixed” sites is also reflected in the CO-induced changes of the Cu 3d-derived states and the $\text{Cu 2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core levels. A dynamic interplay between chemisorption and surface structure is thus demonstrated.     

Preparation and NO_2-gas sensing property of individual β-Ga_2O_3 nanobelt

Monoclinic gallium oxide (β-Ga_2O_3) nanobelts are synthesized from gallium and oxygen by thermal evaporation in an argon atmosphere and their NO_2 sensing properties are studied at room temperature.Electron microscopy studies show that the nanobelts have breadths ranging from 30 to 50 nm and lengths up to tens of micrometers.Both the x-ray diffraction (XRD) and the selected are electron diffraction (SAED) examinations indicate that β-Ga_2O_3 nanobelts have grown into single crystals.Room temperature NO_2 sensing tests show that the current of individual β-Ga_2O_3 nanobelt decreases quickly,and then gently when the NO_2 concentration increases from low to high.It is caused by the NO_2 molecule chemisorption and desorption processes in the surface of β-Ga_2O_3 nanobelt.     

A Cu(1 1 1)(√3×√3)R30°-Sb structure by impact collision ion-scattering spectroscopy

We have investigated the structures of Cu(1 1 1)(√3×√3)R30°-Sb using time of flight-impact collision ion-scattering spectroscopy. The experimental data and computer simulations support a structural model for the Cu(1 1 1)(√3×√3)R30°-Sb structure in which Sb atoms displace up to 1/3 of the first layer of Cu atoms and incorporate them into the first Cu layer with the Sb atoms displaced outward 0.40 Å with respect to the first-layer Cu atoms. The outermost first layer of Sb and Cu atoms shift from fcc- to hcp-hollow sites (only the top layer of Sb and Cu atoms occupies hcp hollow sites).     

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℃.     

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg     

Oxidation of a ZnS nanobelt into a ZnO nanotwin belt or double single-crystalline ZnO nanobelts

Single-crystalline wurtzite ZnS nanobelts are synthesized by the vapor phase transport (VPT) process. When oxidized, a single-crystalline ZnS nanobelt turns into a ZnO nanotwin belt containing two twinning parts with a sharp and clear edge, which is a (0001) twinning plane parallel to and running through the length direction. The two twinning parts in a ZnO nanotwin belt have the same crystalline direction, [0001], along their width, and the and crystalline directions along the length direction. On some ZnO nanobelts, nanovoids appear along the twinning planes and when those nanovoids connect with each other, one original ZnS nanobelt can divide into two single-crystalline ZnO nanobelts with quite clear edges.     

Mechanism of Cu transport along clean Si surfaces

Cu diffusion along clean Si(111), (110) and (100) surfaces are investigated by Auger electron spectroscopy and low energy electron diffraction. The effective diffusion coefficients of copper are measured in the temperature range from 500 to 650°C. It is shown that the Cu transport along silicon surface occurs by the diffusion of Cu atoms through Si bulk and the segregation of Cu atoms to the surface during the diffusion process. It is found that the segregation coefficients of Cu to silicon surface during the diffusion process depend on surface orientation.     

Electronic structure of Ge(111)-(2 × 1) surface in the presence of doping atoms. Ab initio analysis of STM data

We present the result of ab initio modeling of the Ge(111)-(2 × 1) surface electronic structure in the presence of donor doping atom at certain position in the surface bilayer of (2 × 1) reconstruction. We briefly compare these results with the data of experimental low temperature STM investigations. Ab initio calculations demonstrate that doping atom strongly disturbs local electronic structure. The separate state, most probably split off conduction band, appears in the bandgap. Surface LDOS reveals spatial oscillations in vicinity of foreign atom. We also show that the spatial extent of non-negligible inter-atomic interaction between neighboring donor atoms is not less than 70 Å.     

Soft ZnSe nanobelts: Characterization and feasibility for assembling tubular ZnSe nanostructures

Soft ZnSe nanobelts were synthesized by taking Triton X-100 as the template surfactant in a microemulsion. Orderly alternating grooves and bulges on the surface of the nanobelts were first observed via TEM images, and potentially divide a nanobelt into quantum wire bundles. We found that the as-prepared nanobelts show remarkable varied photon scattering and optical properties. A tubular ZnSe structure was successfully obtained with extra treatment. This is an important phenomenon because that the regular folded nanobelts should help us to understand the plastic mechanical properties in a nanoscale assembled tubular structure of nanomaterials and modulate the optical properties of semiconductors.     

Electrical and photocatalytic properties of Na2Ti6O13 nanobelts prepared by molten salt synthesis

Single-crystalline Na₂Ti₆O₁₃ nanobelts were prepared on large-scale by molten salt synthesis at 825 °C for 3 h. The obtained nanobelts have typical width of less than 200 nm and thickness of 10-30 nm, and length up to 10 μm. The growth direction of the nanobelts was determined to be along [0 1 0]. Electrical transport property of an individual nanobelt was measured at room temperature and ambient atmosphere, and results showed that the nanobelts are semiconductor. Na₂Ti₆O₁₃ nanobelts exhibited good photocatalytic efficiency for the degradation of RhB under UV irradiation.     

Surfactant properties of cesium in molecular beam epitaxy of GaAs(100)

The experimental and ab initio investigations of the effect of a decrease in the binding energy of surface arsenic atoms under the cesium adsorption on an As-stabilized GaAs(001)-(2 × 4) surface have been performed. The cesium-induced redistribution of the charge on the surface atoms reduces the electron density in the As-Ga bond of the upper layer of the GaAs(001) surface; thus, the As-Ga binding energy decreases and, as a result, the diffusion activation energy, as well as the arsenic atom desorption, decreases. An increase in the diffusion coefficient of surface atoms, along with the property of Cs to segregate on the surface of a growing semiconductor film, makes it possible to use cesium as a surfactant in the low-temperature growth of GaAs by molecular beam epitaxy.     

Multilayer relaxation of fcc metals (001) surface: A modified embedded atom method study

The (001) surface multilayer relaxation results calculated by the modified embedded atom method (MEAM) show that Ni, Al, Rh and Ir (001) surface are ‘anomalous’ outward relaxation, while Cu, Ag, Au, Pd, Pt and Pb (001) surface are inward relaxation. For the inward relaxation metals, the relaxation between the first two layers increase for the 3d, 4d and 5d metals at the same column in the periodic table, successively. The expansion (contraction) between the first two layers at fcc (001) surfaces is accompanied by the decrease (increase) in the electronic density at the lattice of the first two layers. The surface energies results show that the surface energies decrease for all fcc (001) surfaces due to relaxation, whereas the changes not more than 5%.