催化剂辅助化学气相沉积法制备InN纳米线

采用催化剂辅助化学气相沉积法,通过固-液-气(V-L-S)机理控制在硅衬底上制备了高质量的InN纳米线。利用FESEM、XRD、HRTEM对制备的InN纳米线的表面形貌和结构进行了表征。分析表明合成的InN纳米线为标准的六方纤锌矿结构,纳米线沿[102]方向生长。室温PL光谱表明,制备的InN纳米线在1580nm(0.78eV)处存在很强的无缺陷的带边发射,与六方纤锌矿结构InN单晶发射峰位置一致,表现出良好的光电性能。

GaAs纳米线阵列太阳能电池的设计与优化

为了得到纳米线阵列太阳能电池的最优转换效率,通过仿真计算对GaAs轴向pin结纳米线阵列进行了结构优化.首先利用三维有限时域差分法分析了GaAs纳米线阵列的光吸收特性,并对其直径、密度等结构参量进行优化,优化后的GaAs纳米线阵列的光吸收率可达87.4%.在此基础上,利用Sentaurus软件包中的电学仿真模块分析了电池的电学性能,并根据光生载流子在纳米线中的分布,对轴向pin结结构进行优化,最终优化过的太阳能电池功率转换效率可达到17.6%.分析结果表明,通过钝化处理以降低GaAs纳米线的表面复合速率,可显著提升电池的功率转换效率,而通过减小纳米线顶端高掺杂区域的体积,可减少载流子复合损耗,从而提高电池效率.该研究可为制作高性能的纳米线太阳能电池提供参考.

硫化物钝化对InAs纳米线光学特性的影响

针对InAs纳米线表面氧化造成的发光效率低的问题,采用十八硫醇和硫化铵钝化了由化学气相沉积设备生长的闪锌矿结构的InAs纳米线。对硫化物钝化前后的InAs纳米线进行温度依赖的光致发光光谱测试。实验结果表明,十八硫醇和硫化铵钝化的InAs纳米线在25 K温度下的发光效率与未钝化的InAs纳米线相比分别提高了~ 6倍和~7倍,此外,可以在室温下探测到硫化铵钝化的InAs纳米线的光致发光,这为未来基于InAs纳米线的中红外纳米光子器件提供了可能性。

弯曲应变下单根GaAs纳米线的电学性能的原位透射电子显微镜研究

在透射电子显微镜下,对单根GaAs纳米线实施了原位弯曲变形并获得了其弯曲变形下的电输运性能特性。本研究中,利用扫描透射探针系统和电子束诱导碳沉积技术,选取了单根GaAs纳米线并将纳米线两端与两根钨针尖连接固定。控制可移动的钨针尖,使GaAs纳米线发生弯曲变形同时获得相应的电流-电压曲线。有限元分析表明当纳米线的两端都固定时,纳米线同时承受了压缩应变和拉伸应变,其中压缩应变分布更为广泛。随着变形增加,GaAs纳米线的电导率增加了55%,这可能归因于弯曲变形下压缩与拉伸应变对GaAs纳米线能带结构的共同作用。

一维硒化亚铜的合成及其电催化二氧化碳还原性能的研究

硒化亚铜具有多重氧化态和高导电性等优点,被电催化研究者所青睐。本文采用水合肼还原法制备了硒化亚铜(Cu_(2-x)Se)纳米材料,并对其进行物理化学性质及电化学性能进行了表征。结果表明,Cu_(2-x)Se纳米催化剂相比于铜纳米颗粒,有效地提高了催化剂CO_(2)RR的性能。直径约为10 nm的硒化亚铜纳米线(Cu_(2-x)Se NWs)具有最优的电催化CO_(2)还原性能,在-1.09 V vs.RHE电势下,表现出94.2%的甲酸法拉第效率(FEHCOOH)和20 h运行稳定性。这种通过Se的引入及催化剂结构控制提高其电催化活性的策略,对于开发廉价高效的电催化剂具有重要意义。

Low Temperature Synthesis and Optical Properties of ZnO Nanowires

ZnO nanowire arrays are fabricated on anodized aluminum oxide templates with electric field-assisted electrochemical technology. Transmission electron microscopy results indicate that the nanowires are straight and uniform. X-ray diffraction patterns indicate that the nanowires are highly oriented. The result of selected area electron diffraction suggests that the nanowires are single crystals. The photoluminescence spectrum presents a broad-band luminescence in the region of 350-650nm. The effect of the assisted transverse electric field on the growth process of ZnO nanowires is also discussed.

Characterization of SiC nanowires prepared on C/C composite without catalyst by CVD

SiC nanowires were prepared on C/C composite surface without catalyst by chemical vapor deposition（CVD） using CH3 SiCl3 as precursor.SEM images of the CVD-product reveal that some long nanowires have grown to tens of micrometers with some gathered as a ball.Some short nanowires agglomerate like chestnut shell with many thorns accompanied by some deposited nano-particles.XRD,Raman-spectrum and FTIR patterns indicate that the product is a typical β-SiC.TEM images show that the nanowires have a wide diameter range from 10 to 100 nm,and some thin nanowires are bonded to the thick one by amorphous CVD-SiC.A SiC branch generates from an amorphous section of a thick one with an angle of 70° between them,which is consistent with the [111] axis stacking angle of the crystal.SAED and fast Fourier transform（FFT） patterns reveal that the nanowires can grow along with different axes,and the bamboo-nodes section is full of stacking faults and twin crystal.The twisted SiC lattice planes reveal that the screw dislocation growth is the main mechanism for the CVD-SiC nanowires.

Hydrothermal Synthesis and Efficient Visible Light Photocatalytic Properties of InVO4 Hierarchical Microspheres and InVO4 Nanowires

In this work, InVO4 hierarchical microspheres and InVO4 nanowires were successfully synthesized by a facile hydrothermal method. Field emission scanning electron microscopy showed that InVO4 crystals can be fabricated in different morphologies by simply manipulating the reuction parameters of hydrothermal process. The as-prepared InVO4 photocatalysts exhibited higher photocatalytic activities in the degradation of rhodamine B under visible-light irradiation （λ〉420 nm） compared with commercial P25 TiO2. Furthermore, the as-synthesized InVO4 hierarchical microspheres showed higher photocatalytic activity than that of InVO4 nanowires. Up to 100% Rh B （3 μmol/L） was decolorized after visible-light irradiation for 40 min. In addition, the reason for the difference in the photocatalytic activities for InVO4 hierarchical microspheres and InVO4 nanowires was studied based on their structures and morphologies.

Fabrication and Growth Mechanism of Bamboo-structured Boron Nitride Nanotubes with Thorn-Like Morphology

Bamboo-structured boron nitride （BN） nanotubes with thorn-like morphology were synthe-sized by thermal chemical reaction using amorphous boron powders and NiO nanoparticles as precursors under the flow of NH3 at 1100 oC. The structural and morphological charac-teristics of BN nanotubes were investigated by X-ray diraction and transmission electron microscopy. The results showed that the thorn-like nanostructures attaching to the stems of bamboo-structured BN nanotubes were the hexagonal BN nano akes. Based on the diffu-sion of solid B and vapor B2O2, a possible growth mechanism of these novel thorn-like BN nanotubes was primarily proposed.

A binder-free, flexible cathode for rechargeable Na-O_2 batteries

Rechargeable Na-O2 batteries have attracted significant attention as energy storage devices owing to their theoretically high energy storage capacity and the natural abundance of sodium. However, practical applications of this type of battery still suffer from low specific capability, poor cycle sta- bility, instable electrolytes, and unstable polymer binders. Herein, we report a facile method of synthesizing binder free and flexible cathodes with C0304 nanowire arrays vertically grown onto carbon textiles. When employed as a cathode for Na-O2 batteries, this cathode exhibits superior performance, including a reduction of charge overpotential, high specific capacity （4687 mAh/g）, and cycle stability up to 62 cycles. These enhanced performance can be attributed to the synergistic effect of the porosity and catalytic activity of the C0304 nanowire catalyst.

Distance-Dependent Long-Range Electron Transfer in Protein:a Case Study of Photosynthetic Bacterial Light-Harvesting Antenna Complex LH2 Assembled on TiO 2 Nanoparticle by Femto-Second Time-Resolved Spectroscopy

The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by alpha- and beta-apoprotein helices. The alpha- and beta-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 run (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.

Preparation and photoelectric properties of Ho^(3+)-doped titanium dioxide nanowire downconversion photoanode

Ho^3＋-doped titanium dioxide（TiO2：Ho^3＋） downconversion（DC） nanowires were synthesized through a simple hydrothermal method followed by a subsequent calcination process after being immersed in Ho（NO3）3 aqueous solution. Moreover, TiO2：Ho^3＋ nanowires（HTNWs） were used as the photoanode in dye-sensitized solar cells（DSSCs） to investigate their photoelectric properties. Scanning electron microscopy（SEM） and X-ray diffraction（XRD） were used to characterize the morphology and structure of the material, respectively. The photofluorescence and ultraviolet-visible absorption spectra of HTNWs reveal a DC from the near and middle ultraviolet light to visible light which matches the strong absorbed region of the N719 dye. Compared with the pure TNW photoanode, HTNWs DC photoanodes show greater photovoltaic efficiency. The photovoltaic conversion efficiency（η） of the DSSCs with HTNWs photoanode doped with 4% Ho2O3（mass fraction） is two times that with pure TNW photoanode. This enhancement could be attributed to HTNWs which could extend the spectral response range of DSSCs to the near and middle ultraviolet region and increase the short-circuit current density（Jsc） of DSSCs, thus leading to the enhancement of photovoltaic conversion efficiency.

Synthesis and Photocatalytic Activity of One-dimensional ZnO-Zn2SnO4 Mixed Oxide Nanowires

Mixed oxide photocatalysts, ZnO-Zn2SnO4 （ZnO-ZTO） nanowires with different sizes were prepared by a simple thermal evaporation method. The ZnO-ZTO nanowires were characterized with a scanning electron microscope, X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectrom- eter, and X-ray photoelectron spectra. The photocatalytic activity of the ZnO-ZTO mixed nanowires were studied by observing the photodegradation behaviors of methyl orange aqueous solution. The results suggest that the ZnO-ZTO mixed oxide nanowires have a higher photocatalytic activity than pure ZnO and Zn2SnO4 nanowires. The photocatalyst concentration in the solution distinctly affects the degradation rate, and our results show that higher photodegradation efficiency can be achieved with a smaller amount of ZnO-ZTO nanowire catalyst, as compared to the pure ZnO and ZTO nanowires. Moreover, the photocatalytic activity can also be enhanced by reducing the average diameter of the nanowires. The activity of pure ZnO and ZTO nanowires are also enhanced by physically mixing them. These results can be explained by the synergism between the two semiconductors.

Preparation and Characterization of Amorphous Silicon Oxide Nanowires

Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO). Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that the silicon nanowires are smooth. Selected area electron diffraction (SAED) shows that the silicon nanowires are amorphous and en-ergy-dispersive X-ray spectroscopy (EDS) indicates that the nanowires have the composition of Si and O elements in an atomic ratio of 1:2,their composition approximates that of SiO2. SiO is considered to be used as a Si sources to produce SiNWs. We conclude that the growth mechanism is closely related to the defect structure and silicon monoxide followed by growth through an oxide-assisted vapor-solid reaction.

Preparation of Al2O3 nanowires on 7YSZ thermal barrier coatings against CMAS corrosion

The commonly-employed material for thermal barrier coatings(TBCs)is 7 wt.%Y2O3 ZrO2(7YSZ),generally deposited by electron beam-physical vapor deposition(EB-PVD).Due to the increasing demand for higher operating temperature in aero-derivative gas turbines,a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs,which is induced by the microstructure degradation,sintering and spallation after the deposition of infiltrated siliceous mineral(consisting of calcium magnesium aluminum silicate(CaO MgO Al2O3 SiO2,i.e.,CMAS)).A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present.The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs,followed by performing vacuum heat treatment of the Al-deposited TBCs.During the heat treatment,the molten Al reacted with ZrO2 to formα-Al2O3 overlay that effectively hindered CMAS infiltration.Moreover,the Al film could evaporate and re-nucleate,leading to the generation of Al2O3 nanowires,which further restrained the moving of molten CMAS.

In situ growth of minimal Ir-incorporated CoxNi1-xO nanowire arrays on Ni foam with improved electrocatalytic activity for overall water splitting

Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen.Here,earth-abundant CoxNi1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting.Minimal Ir-incorporated CoxNi1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam(NF)as both the substrate and source of Ni.The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent CoxNi1-xO nanowire arrays.As a result,for a minimal Ir content,as low as 0.57 wt%,the obtained Ir-CoxNi1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm?2 in 1 mol L–1 KOH.When used as bifunctional electrodes in water splitting,the current density of 10 mA cm–2 was obtained at a low cell voltage of 1.55 V.Density functional theory calculations revealed that the Ir-doped CoxNi1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy,which contributed to the improved electrocatalytic activity.The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.

Formation of GaN Nanowires by Ammoniating Ga_2O_3 Films Deposited on Oxidized Al Layers on Si Substrate

Large quantities of gallium nitride(GaN) nanowires have been prepared via ammoniating the Ga2O3 films deposited on the oxidized aluminum layer at 950 ℃ in a quartz tube. The nanowires have been confirmed as crystalline wurtzite GaN by X-ray diffraction, X-ray photoelectron spectrometry scanning electron microscope and selected-area electron diffraction. Transmission electron microscope(TEM) and scanning electron microscopy(SEM) reveal that the nanowires are amorphous and irregular, with diameters ranging from 30 nm to 80 nm and lengths up to tens of microns. Selected-area electron diffraction indicates that the nanowire with the hexagonal wurtzite structure is the single crystalline. The growth mechanism is discussed briefly.

Superior activity of Rh1/ZnO single-atom catalyst for CO oxidation

CO oxidation is of great importance in both fundamental study and industrial application.Supported noble metal catalysts are highly active for CO oxidation but suffer from the scarcity and high cost.Single-atom catalysts(SACs)can maximize the metal atom efficiency.Herein,ZnO nanowire(ZnO-nw)supported Rh,Au,and Pt SACs were successfully developed to investigate their CO oxidation performance.Interestingly,it was found that Rh1/ZnO-nw showed much higher activity than the other noble metals which are usually regarded as good candidates for CO oxidation.In addition,the Rh SAC possessed high stability in high-temperature CO oxidation under simulated conditions in the presence of water and hydrocarbons.The high activity and stability make Rh1/ZnO-nw promising for practical applications,especially in the automotive exhaust emission control.Theoretical calculations indicate that the CO oxidation proceeds via the Mars-van Krevelen mechanism and the lowest barrier for the rate-limiting O2 dissociation at a surface oxygen vacancy site is a key factor in determining the observed highest activity of Rh1/ZnO-nw amongst the studied SACs.

Molecular dynamics analysis on bending mechanical behavior of alumina nanowires at different loading rates

The molecular dynamics(MD)model ofα-Al_(2)O_(3) nanowires in bending is established by using LAMMPS to calculate the atomic stress and strain at different loading rates in order to study the effect of loading rate on the bending mechanical behaviors of theα-Al_(2)O_(3) nanowires.Research results show that the maximum surface stress−rotation angle curves ofα-Al_(2)O_(3) nanowires at different loading rates are all divided into three stages of elastic deformation,plastic deformation and failure,where the elastic limit point can be determined by the curve symmetry during loading and unloading cycle.The loading rate has great influence on the plastic deformation but little on the elastic modulus ofα-Al_(2)O_(3) nanowires.When the loading rate is increased,the plastic deformation stage is shortened and the material is easier to fail in brittle fracture.Therefore,the elastic limit and the strength limit(determined by the direct and indirect MD simulation methods)are closer to each other.The MD simulation result ofα-Al_(2)O_(3) nanowires is verified to be valid by the good agreement with the improved loop test results.The direct MD method becomes an effective way to determine the elastic limit and the strength limit of nanoscale whiskers failed in brittle or ductile fracture at arbitrary loading rate.

First-Principles Study of Ultrathin Molybdenum Sulfides Nanowires:Electronic and Catalytic Hydrogen Evolution Properties

Molybdenum sulfides nanomaterials, such as one-dimensional (1D) nanotubes, nanoribbons, and two-dimensional (2D) nanosheets, have attracted intensive research interests for their novel electronic, optical, and catalytic properties. On the basis of first-principles calculation, here, we report a new series of 1D ultrathin molybdenum sulfides nanowires, including Mo2S6、Mo3S6 and Mo6S10 nanowires. Our results demonstrate that these ultrathin nanowires are both thermal and lattices dynamically stable, confirmed with the calculated phonon spectrum and Born-Oppenheimer molecular dynamic simulation at the temperature up to 600 K. The calculated elastic constant is 21.33, 103.22, and 163.00 eV/■ for Mo2S6, Mo3S6, and Mo6S10 nanowires, respectively. Mo2S6 and Mo3S6 nanowires are semiconductors with band gap of 1.55 and 0.46 eV, while Mo6S10 nanowires is metal, implying their potential applications in electronics and optoelectronics. In particular, ultrathin molybdenum sulfides nanowires can be used as catalysts for hydrogen evolution reaction. The calculated Gibbs free energy change for hydrogen evolution is about -0.05 eV for Mo2S6 nanowire, comparable with those of Pt and H-MoS2. The prediction of these 1D molybdenum sulfides nanowires may enrich the 1D family molybdenum sulfides and make a supplement to understand the high performance of hydrogen evolution reaction in transition-metal dichalcogenides.