Strain-induced metal to semiconductor transition in ultra-small diameter single-wall carbon nanotubes

Under a large tensile strain near fracture limit, the band structures of single-wall carbon nanotubes (SWCNTs) with diameter less than 0.5 nm begin a metal to semiconductor transition and these ultra-small SWCNTs can normally maintain their metallicities. The band gap behavior of these SWCNTs intrinsically originates from the long axial direct bond lengths and the severe curvature. The gap opening comes mainly from the transfer of pπ electrons. And the localized π and σ states can result in a lower electrical conductivity. This band gap behavior suggests that it has potential to find applications in nano-electromechanical system.     

单轴〈111〉应力硅价带结构计算

基于k·p微扰法计算了单轴〈111〉应力作用下硅的价带结构, 并与未受应力时体硅的价带结构进行了比较. 给出了单轴〈111〉应力作用下硅价带顶处能级的移动、分裂以及空穴有效质量的变化情况. 计算所得未受应力作用时硅价带顶处重空穴带、轻空穴带有效质量与相关文献报道体硅有效质量结果一致. 拓展了单轴应力硅器件导电沟道应力与晶向的选择范围,给出的硅价带顶处重空穴带、轻空穴带能级间的分裂值和有效质量随应力的变化关系可为单轴〈111〉应力硅其他物理参数的计算提供参考. 关键词： 单轴应力硅 k·p法')" href="#">k·p法 价带结构     

沉积温度对Cu_2O薄膜生长过程及光电性能的影响(英文)

以硫酸铜为铜源,采用一步化学浴沉积法制备出了晶粒尺寸可调的纳米晶Cu2O薄膜。通过X射线衍射、扫描电镜和紫外可见分光光度法研究了沉积温度对薄膜晶体结构、成核密度、晶粒尺寸、薄膜厚度和光电性能的影响。结果表明,当在60~90℃范围内调节温度时,能够很好地控制晶粒尺寸、薄膜厚度,并将禁带宽度控制在33~51 nm、392~556 nm和2.47~2.61 eV范围内;随着晶粒尺寸的减小,紫外可见光谱的吸收边有明显的蓝移。此外还对薄膜的生长过程,成核密度和颗粒尺寸变化的机理进行了讨论。     

Density functional theory study of p‐chloroaniline adsorption on Pd surfaces and clusters

The adsorption mode of aromatic molecules on transition metal surfaces plays a key role in their catalytic transformation. In this study, by means of density functional theory calculations, we systematically investigate the adsorption of p‐chloroaniline on a series of Pd surfaces, including stepped surfaces, flat surfaces, and clusters. The adsorption energies of p‐chloroaniline on these substrates [Pd(221), Pd(211), Pd(111), Pd(100), Pd₁₃‐icosahedral, Pd₁₃‐cubo‐octahedron, Pd₅₅] are ?1.90, ?2.13, ?1.70, ?2.11, ?2.53, ?2.65, ?2.23 eV, respectively. Benzene ring is adsorpted on catalyst rather than amine group in p‐chloroaniline molecular. A very good linear relationship is further found between the adsorption energies of p‐chloroaniline and the d‐band center of both Pd surfaces and clusters. The lower of d‐band center of Pd models, the stronger adsorption of p‐chloroaniline on catalysts. In addition, the frontier molecular orbital and density of states analysis explain the adsorption energy sequence: cluster Pd₁₃ > stepped Pd(221) surface > flat Pd(111) surface. © 2014 Wiley Periodicals, Inc.     

新型1,3,4-噁二唑衍生物的合成与性质研究

研制高效载流子传输材料是提高有机电致发光器件性能的关键. 采用对酯对二酰氯(5)与含不同链长烷氧取代基的苯甲酰肼(2)缩合制备了一系列腰接羧基1,3,4-噁二唑衍生物, 即1,4-二[5-(4-烷氧基苯)-1,3,4-噁二唑基]-2,5-二羧基苯(7; 烷氧基＝OCnH2n＋1; n＝8, 12, 16), 并采用UV-vis吸收和荧光光谱对合成物进行了表征. 结果表明: 7的分子结构中羧基的横向引入, 对化合物的光物理性质和能带结构产生较大影响. 这些噁二唑化合物的LUMO及HOMO值分别介于－3.62与－3.58 eV之间及－6.94与－6.90 eV之间, 说明它们可能具有良好的电子传输性.     

Theoretical Study on the Structural and Electronic Properties of Thiocarbamide Hydrochloride

In the present paper, the electronic band structure, density of states （DOS）, and projected density of states （PDOS） analysis of thiocarbamide hydrochloride are reported. Calculations of the electronic properties have been carried out on the basis of fully self-consistent pseudopotential method using DFT. The results show that near the Fermi level, more prominent densities of states are seen between -8 eV and -6 eV in the valence band mainly due to the Cl-3p, N-2p and S-3p orbitals.     

二维相关分析中参考谱的选择对分离重叠峰的影响

二维相关光谱是一项将光谱强度看作两个独立的光谱变量的函数的技术, 它是由动态光谱经过数学转化后得到的. 在扰动过程中, 动态光谱等于实际测得的光谱减去参考谱, 参考谱的选择是任意的, 甚至可以为0, 但是在实际应用时, 人们逐渐发现参考谱的选择会对二维相关光谱产生一定的影响. 本篇文章采用模拟的方法, 建立光谱模型, 光谱强度按e指数形式单调变化, 比较以平均谱为参考谱和不设参考谱得到的二维相关光谱图, 分析它们的区别, 在不同参考谱条件下, 利用二维相关光谱分离重叠峰, 得到的结果也不相同, 将两种条件综合利用可以得到更多更正确的信息.     

球磨法制备异质结型光催化剂ZnO/Bi_4Ti_3O_(12)及催化性能

本文用水作为分散介质,掺杂一定量的ZnO于Bi_4Ti_3O_(12)中,采用高能球磨法制备了异质结型光催化剂ZnO/Bi_4Ti_3O_(12).利用UV-Vis、XRD、SEM和PL等仪器对样品进行了分析与表征.以375 W中压汞灯为光源,通过对亚甲基蓝的氧化来研究其光催化活性.结果表明,对于光氧化亚甲基蓝(MB),异质结型光催化剂ZnO/Bi_4Ti_3O_(12)光催化活性高于钛酸铋的光催化活性.当ZnO的掺杂量分别是0.0和0.5wt.%,异质结型光催化剂ZnO/Bi_4Ti_3O_(12)对亚甲基蓝光氧化率分别达到50.2和80.3 %.     

单壁碳纳米管的轴向能带工程

单壁碳纳米管具有优异的电子学特性,是制备新一代高性能集成电路的重要材料.碳纳米管芯片之路存在诸多挑战,包括直径和手性的控制生长方法、金属性和半导体性单壁碳纳米管的分离方法、器件加工与集成方法等.这些课题从本质上讲大多属于化学问题,因此碳纳米管芯片研究为化学家们提供了新的机遇与挑战.过去10年来,我们围绕单壁碳纳米管的轴向能带工程这一研究思路,开展了一系列碳纳米管芯片的基础探索工作,发展了若干有效的单壁碳纳米管局域能带的调控方法,包括温度阶跃生长法、脉冲供料生长法、基底调控法以及形变调控法等.本文系统地阐述了这些局域能带调控方法,为使读者对该领域的研究进展有一个较为全面的了解,文中对其他课题组开展的代表性工作也给予了综述性介绍.     

Microwave absorbing properties of Fe3O4–poly(3, 4‐ethylenedioxythiophene) hybrids in low‐frequency band

A facile method is proposed to obtain microwave absorbing materials (MAMs), which possess strong microwave absorption properties in low‐frequency range. By simply mechanical mixing, the obtained Fe₃O₄–poly (3,4‐ethylenedioxythiophene) (PEDOT) hybrids exhibit more excellent microwave absorbing properties than that of Fe₃O₄ or PEDOT individually. The analysis on the microwave absorbing properties of the Fe₃O₄–PEDOT hybrids indicates that the excellent microwave absorbing properties are ascribed to several factors, like the dielectric loss, the interface polarization, eddy current effect, natural ferromagnetic resonance, and the impedance as well as the thickness of the coating. The Fe₃O₄–PEDOT hybrids with appropriate mass ratios of PEDOT to Fe₃O₄ (represented by (PEDOT)/(Fe₃O₄)) show superior microwave absorbing property at low frequency. When the thickness is 4 mm, the reflection loss of the sample reached ?15.8 dB at 3.2 GHz with (PEDOT)/(Fe₃O₄) of 3 and ?31.4 dB at 4.5 GHz with (PEDOT)/(Fe₃O₄) of 2, respectively. The obtained Fe₃O₄–PEDOT MAMs will have a promising application in the practical industry and commerce affairs. Copyright © 2013 John Wiley & Sons, Ltd.