空位缺陷对β-AgVO_3电子结构和光吸收性能的影响

基于密度泛函的第一性原理研究了Ag空位、O空位和Ag-O双空位对β-AgVO_3的电子结构及光学性质的影响.采用广义梯度近似平面波超软赝势GGA+U方法,对不同缺陷体系的形成能、能带结构、电子态密度、差分电荷密度和吸收光谱进行了计算和分析.通过比较不同Ag空位和O空位的形成能,确定了β-AgVO_3中主要形成Ag3空位和O1空位,并且Ag空位较O空位更容易形成.Ag3空位和O1空位的存在都使得β-AgVO_3带隙有一定程度的减小;Ag3空位使β-AgVO_3呈现p-型半导体性质,而O1空位和Ag3-O1双空位使β-AgVO_3呈现n-型半导体性质.Ag3和O1空位对晶体在可见光范围内的光吸收影响较小.     

Cu_2O纳米线激子精细结构光谱分析

基于显微拉曼光谱仪研究比较单根与多根Cu_2O纳米线荧光光谱特性,通过详细分析显微荧光谱线信息,研究制备得到的Cu_2O纳米线的精细结构。单根Cu_2O纳米线表现出高能激子发射及其高阶声子辅助的光学跃迁谱线。     

氧化钨纳米线气敏传感器的制备及其室温NO_2敏感特性

纳米结构的氧化钨有高比表面积和气体吸附能力,在气体传感器领域得到了广泛研究.本文采用磁控溅射金属钨薄膜和两步热氧化工艺在二氧化硅衬底上生长出氧化钨纳米线.通过改变第二步氧化温度,研究退火温度对氧化钨纳米线气敏特性的影响.采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱分析仪和透射射电子显微镜表征材料的微观特性和晶体结构,利用静态配气法测试气敏性能.研究结果表明,经过退火处理后氧化钨纳米线密度略微降低,300℃比400℃退火后的氧化钨结晶性差,对应的表面态含量多,有利于室温气体敏感性.测试NO_2的气敏性能,经过对比得出300℃退火温度下制备的氧化钨纳米线在室温下表现出较很好的气敏响应,对6 ppm(1 ppm=10~(-6))NO_2达到2.5,对检测极限0.5 ppm NO_2响应达1.37.氧化钨纳米线在室温下表现出反常的P型响应,是因为氧化钨纳米线表面被氧气吸附形成反型层,空穴取代电子成为主要载流子所致.     

NiFe2O4纳米线阵列的制备与磁性

在氧化铝模板的纳米孔洞中, 用电化学的方法沉积铁镍合金纳米线，经过550℃30h氧化处理 , 成功制备出 NiFe2O4纳米线阵列. 分别用扫描电子显微镜 (SEM) 、透射电 子显微镜 (TEM) 、x射线衍射仪 (XRD) 和振动样品磁场计 (VSM) 对样品的形貌、晶体结构 和磁学性质进行了表征测试. SEM和TEM观察结果显示氧化铝模板的孔洞分布均匀，孔心距约 为110nm; 纳米线的直径约为70nm. XRD显示纳米线阵列的物相结构为NiFe2O4; VSM测试结果表明，NiFe2O4纳米线阵列膜的易磁化方向垂直于膜面. 当垂直 磁化时磁滞回线的矩形比约为05，矫顽力为41×103A/m，比氧化处理前的铁镍合金 纳米线阵列都有显著提高. 关键词： 纳米线 Ni Fe2O4 矫顽力     

Mg12O12纳米线掺杂3过渡金属元素的第一性原理计算研究

基于密度泛函第一性原理计算,系统研究了Mg12O12笼状团簇组装一维纳米线及其掺杂3d族元素体系的几何结构与电子结构。结果表明：Mg12O12团簇组装一维纳米线为非磁性半导体,带隙值为3.16 eV;掺杂Sc和V后,体系由半导体转变为金属;掺杂Ti、Cr、Mn、Fe、Co、Ni、Cu后体系仍然保持半导体特性、但带隙值明显减小,而掺杂Zn时带隙值变化不大;掺杂V、Cr、Mn、Fe、Co、Ni、Cu后纳米线具有磁性。     

Electrodeposition and magnetic properties of Ni nanowire arrays on anodic aluminum oxide/Ti/Si substrate

Ni nanowire arrays with different diameters have now been extended to directly fabricate in porous anodic alumina oxide (AAO) templates on Ti/Si substrate by direct current (DC) electrodeposition. An aluminum film is firstly sputter-deposited on a silicon substrate coated with a 300 nm Ti film. AAO/Ti/Si substrate is synthesized by a two-step electrochemical anodization of the aluminum film on the Ti/Si substrate and then used as template to grow Ni nanowire arrays with different diameters. The coercivity and the squareness in parallel direction of Ni nanowires with about 10 nm diameters are 664 Oe and 0.90, respectively. The Ni nanowire arrays fabricated on AAO/Ti/Si substrates should lead to practical applications in ultrahigh-density magnetic storage devices because of the excellent properties.     

Mn掺杂ZnO纳米线磁性质的第一性原理研究

本文采用第一性原理方法系统研究了Mn原子单掺杂和双掺杂ZnO纳米线的稳定性和磁性质.所有掺杂纳米线的束缚能都为负值,表明掺杂增强了纳米线的稳定性.表面掺杂纳米线显示了直接带隙半导体特性,而中间掺杂纳米线显示了间接带隙半导体特性.纳米线的总磁矩主要来源于Mn原子3d轨道的贡献.由于杂化,相邻的O原子和Zn原子也产生了少量自旋.在超原胞内,Mn原子和O原子磁矩平行排列,表明它们之间是铁磁耦合.     

单根SnO_2纳米线器件的电输运性能及其机理研究

为探究常态环境下氧空位对单根SnO_2纳米线电输运性能的影响,采用化学气相沉积法合成了SnO_2纳米线,通过光刻微加工技术构筑了Au/单根SnO_2纳米线/Au二端纳米器件.将单根SnO_2纳米器件进行氢化处理,测试其在空气与真空中的伏安特性曲线,发现单根SnO_2纳米线在空气和真空环境中呈现异常不同的电输运特性:在空气中,加偏压注入电子会使通过纳米器件的电流减小,Au电极与SnO_2纳米线之间的接触势垒增大;抽真空后,在偏压的影响下,通过纳米器件的电流增大,Au/SnO_2交界面的接触方式由肖特基接触转变成欧姆接触.实验分析表明,影响单根SnO_2纳米线电输运特性行为的因素与纳米线表面的氧原子吸附与脱吸附所引起的氧空位浓度的变化有关.为进一步分析氧空位浓度变化的作用,利用第一性原理计算方法计算了氧空位浓度对SnO_2纳米线电输运性能的影响,通过分析体系的能带结构、态密度及Au/SnO_2接触界面的I-V曲线和透射谱,发现随着氧空位浓度的增大,SnO_2纳米线的带隙变小.同时,氧空位缺陷使Au/SnO_2接触界面处电子透射率增大,体系电输运能力变强.该研究结果将为集成纳米功能器件的设计提供一种新思路.     

Effects of vacancy defects and axial strain on thermal conductivity of silicon nanowires: A reverse nonequilibrium molecular dynamics simulation

Thermal conductivity of silicon nanowires (SiNWs) is evaluated using the reverse nonequilibrium molecular dynamics simulation. The Stillinger–Weber (SW) and Tersoff interatomic potentials are employed to simulate thermal conductivity of SiNWs. In this work, the influence of random vacancy defects, axial strain, temperature and length on thermal conductivity and effective mean free path of SiNWs is investigated. It is found that by raising the percent of random vacancy defects, thermal conductivity of SiNWs decreases linearly for the results obtained form SW potential and nonlinearly for those obtained from Tersoff interatomic potential. Dependence of the thermal conductivity on axial strain is also studied. Results show that thermal conductivity increases as compressive strain increases and decreases as tensile strain increases. Influence of temperature is also predicted. It is found that the thermal conductivity of SiNWs decreases with increasing the mean temperature. Most of the simulations are performed for 4 UC×4 UC×40 UC silicon nanowires using ssp boundary condition.     

Study of titanium adsorption on perfect and defected BC3 nanotubes using density functional theory

Density functional theory calculations were used to study the titanium (Ti) adsorption on perfect and defected (4, 0) BC₃ nanotubes, considering Stone–Wales and vacancy defects. The binding energy values for these nanotubes were larger than the corresponding values for carbon nanotubes. The charge transfer from the Ti atom to nanotube was observed for all systems studied. The most exothermic binding process occurred for the Ti adsorption on a native V_B defect, which showed minimum structural deformation with respect to a perfect BC₃ tube. In the case of a nanotube with a reconstructed carbon vacancy, the adsorption of Ti generated a half-metallic anti-ferromagnet. The results obtained in this paper are relevant for spintronics and hydrogen adsorption applications.     

金红石型TiO_2中四种点缺陷态研究

利用第一性原理计算方法研究了金红石型TiO_2中四种缺陷的电子态.这四种缺陷包括氧空位(O_v)、钛空位(Ti_V)、钛间隙(Ti_S)以及氧空位O_v与钛间隙态Ti_S共存态.氧空位的存在导致禁带内施主缺陷能级较浅,而深施主能级与Ti间隙态有关.预测了氧空位更倾向于与钛间隙结合,主要通过钛间隙态的3d电子部分转移到近邻近氧空位的部分形成O_V-Ti_S对缺陷.具有O_v、Ti_S或O_V-Ti_S缺陷的体系都出现间隙态,促进体系出现红外吸收.     

Uncovering the internal structure of five-fold twinned nanowires through 3D electron diffraction mapping

Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement. Although both of metallic and semiconductor five-fold twinned nanostructures show inhomogeneity in their cross-sectional strain distribution, the evident strain concentration at twin boundaries in the semiconductor systems has been found in contrast to the metallic systems. Naturally, a problem is raised how the chemical bonding characteristics of various five-fold twinned nanosystems affects their strain-relieving defect structures. Here using three-dimensional(3 D)electron diffraction mapping methodology, the intrinsic strain and the strain-relieving defects in a pentagonal Ag nanowire and a star-shaped boron carbide nanowire, both of them have basically equal radial twin-plane width about 30 nm, are nondestructively characterized. The non-uniform strain and defect distribution between the five single crystalline segments are found in both of the five-fold twinned nanowires. Diffraction intensity fine structure analysis for the boron carbide five-fold twinned nanowire indicates the presence of high-density of planar defects which are responsible for the accommodation of the intrinsic angular excess. However, for the Ag five-fold twinned nanowire, the star-disclination strain field is still present, although is partially relieved by the formation of localized stacking fault layers accompanied by partial dislocations.Energetic analysis suggests that the variety in the strain-relaxation ways for the two types of five-fold twinned nanowires could be ascribed to the large difference in shear modulus between the soft noble metal Ag and the superhard covalent compound boron carbide.     

不同气氛下SiOx纳米线的制备及形貌、红外、光致发光研究

以N₂/H₂、N₂或NH₃为载气,利用碳辅助化学气相沉积法,常压1140℃下在石英衬底上制备了大量直径为20—300 nm,长数百微米的非晶SiO_x纳米线.制备得到的纳米线具有高度定向生长的特性.利用透射电子显微镜、扫描电子显微镜及电子能谱对SiO_x纳米线的形貌及组分进行了分析,Si与O原子之比为1∶18.傅里叶红外吸收谱显示了非晶氧化硅的三个特征峰（482,806和1095 cm^-1）及1132 cm^-1无序氧化硅结构的强吸收峰.SiO_x纳米线光致发光光谱（PL）在440 nm（283 eV）处具有较强的荧光峰;N₂为载气生长的SiO_x纳米线的PL峰强比NH₃为载气生长的SiO_x纳米线峰强大四个数量级. 关键词： x纳米线')" href="#">SiO_x纳米线 碳辅助化学气相沉积法 傅里叶红外吸收 光致发光     

Ferromagnetism of V-doped ZnO nanowires

The geometry structures,electronic structures,and magnetic properties of Zn46V2O48 nanowires are studied by density functional theory(DFT) calculations.We find that the ferromagnetic(FM) coupling is more stable for six configurations of Zn46V2O48 nanowires,and is mediated by neighboring O as evidenced from the strong hybridization of V 3d and O 2p states,exhibiting strong spin polarization.The spin polarization is found to be 100% in the Zn46V2O48 nanowires,which confirms that it is a half-metallic ferromagnet and very suitable for the injection of the spin carriers,which shows that Zn46V2O48 nanowire is one of the ideal materials to realize spin electronic devices.At the same time,the magnetic coupling mechanisms of Zn46V2O48 nanowires are analyzed with V 3d and O 2p orbitals and their magnetic moments mainly come from the contributions of the unpaired electrons of V 3d orbitals.The above results provide a theoretical basis for the preparation of 3d transition metal-doped ZnO nanowire materials.     

Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

Formation energies of native defects and Pr impurities in orthorhombic CaTiO₃ are explored using the first-principles calculations. The Ca vacancy (V_Ca), Ti vacancy (V_Ti) and Ca antisite (Ca_Ti) are found to be energetically preferable. The Ti antisite (Ti_Ca) and O vacancy (V_O) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO₃, Pr substituting for Ca (Pr_Ca) is likely to form under condition A in which CaTiO₃ is in equilibrium with CaO and O₂. Under condition B (TiO₂, CaTiO₃ and O₂ are in equilibrium), Pr_Ti defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO₃ are coincided with several different defects in Pr-doped CaTiO₃ reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca_1−xV_Ca(x/2)Pr_xTiO₃ is not the best for efficient red photoluminescence, which is realized via the experimental measurements.     

X-ray photoelectron spectroscopy study of disordering in Gd2(Ti1-xZrx)2O7 pyrochlores

The dramatic increases in ionic conductivity in Gd2(Ti1-xZrx)2O7 solid solution are related to disordering on the cation and anion lattices. Disordering in Gd2(Ti1-xZrx)2O7 was characterized using x-ray photoelectron spectroscopy (XPS). As Zr substitutes for Ti in Gd2Ti2O7 to form Gd2(Ti1-xZrx)2O7 (0.25 < x < or =0.75), the corresponding O 1s XPS spectrum merges into a single symmetric peak. This confirms that the cation antisite disorder occurs simultaneously with anion disorder. Furthermore, the O 1s XPS spectrum of Gd2Zr2O7 experimentally suggests the formation of a split vacancy.     

Bandgap engineering of GaxZn1–xO nanowire arrays for wavelength‐tunable light‐emitting diodes

Wavelength‐tunable light‐emitting diodes (LEDs) of Ga_xZn_1–xO nanowire arrays are demonstrated by a simple modified chemical vapor deposition heteroepitaxial growth on p‐GaN substrate. As a gallium atom has similar electronegativity and ion radius to a zinc atom, high‐level Ga‐doped Ga_xZn_1–xO nanowire arrays have been fabricated. As the x value gradually increases from 0 to 0.66, the near‐band‐edge emission peak of Ga_xZn_1–xO nanowires shows a significant shift from 378 nm (3.28 eV) to 418 nm (2.96 eV) in room‐temperature photoluminescence (PL) measurement. Importantly, the electroluminescence (EL) emission of Ga_xZn_1–xO nanowire arrays LED continuously shifts with a wider range (∼100 nm), from the ultraviolet (382 nm) to the visible (480 nm) spectral region. The presented work demonstrates the possibility of bandgap engineering of low‐dimensional ZnO nanowires by gallium doping and the potential application for wavelength‐tunable LEDs.     

Modelling self-ordering behaviour on Ag covered Pt vicinal surfaces

We use computer simulation to explore the formation process of a monolayer of Ag on a stepped Pt(111) substrate and the formation of 3D Pt nanostructures on an Ag covered (111) and (100) Pt substrate. We show that broken lines of Pt nanostructures are preferred at the step edges on the (111) substrate while continuous lines of Pt nanowires are preferred at the step edge on the (100) substrate. This different behaviour is due to the exposed front facet of the nanostructures running along the step, specifically for the (100) stepped substrate a nanowire grown on the step edge has a stable (111) exposed front facet, whereas a nanowire grown on the (111) substrate would have an unstable (100) front facet (depending on the direction of the step). For the Pt nanowires grown on the (100) substrate we show how arriving Pt dimers (and monomers) preferentially move up off the Ag substrate onto the nanowire's (111) facet where they undergo fast diffusion. We also show that these Pt dimers (and monomers) move up and down the nanowire's facet until a vacancy or defect is encountered.     

Template preparation of Pt nanowire array electrode on Ti/Si substrate for methanol electro-oxidation

Platinum (Pt) nanowire array electrode is obtained by dc electrodeposition of Pt into the pores of anodic aluminum oxide (AAO) template on Ti/Si substrate. Transmission electron microscope (TEM) examination shows all the nanowires have uniform diameter of about 30 nm. The brush shapes Pt nanowire array electrode can be seen clearly by field emission scanning electron microscope (FESEM). Pt nanowire array electrode gives the X-ray diffraction (XRD) pattern of face-centered cubic (fcc) crystal structure. The electro-oxidation of methanol on this electrode is investigated at room temperature by cyclic voltammetry. The results demonstrated that the Pt nanowire array electrode will have good potential applications in portable power sources.