Ag掺杂对TiO_2性质影响的第一性原理研究

采用Ag原子对锐钛矿型TiO2半导体进行掺杂,利用基于密度泛函理论的第一性原理研究了Ag掺杂TiO2的晶体结构和能带结构.计算表明,Ag掺杂导致TiO2电子局域能级的出现及禁带变窄,从而导致吸收光谱红移.同时对Ag、Cu这两种同族原子进行掺杂比较,结果证明,用Ag原子对锐钛矿型TiO2进行掺杂在提高光催化性能方面效果更好.     

新鲜多孔硅(001)表面结构与电子特性理论研究

在周期边界条件下的k空间中,采用基于密度泛函理论的广义梯度近似(GGA)平面波超软赝势法,建立H12S i31几何模型来对表面主要被H覆盖的新鲜多孔硅(Porous S ilicon,PS)(001)表面最外层的S i—H键的几何结构和电子特性进行初步的理论研究.计算得到氢化PS(001)表面几何结构S i—H键长为0.148 nm、H—S i—H键角为106°,并通过原子布居数、电子密度图分析得到氢化PS表面原子的电子特性.     

金红石TiO2(011)表面的理论研究进展

基于密度泛函理论 (DFT) 的第一性原理 (First-principles) 计算方法,就金红石TiO₂(011)表面在理论方面的研究进展做了介绍.首先,通过阐述研究金红石TiO₂(011)表面的必要性和实验在其结构方面的研究进展,介绍了金红石TiO₂(011)表面的电子结构和光学性质,指出并验证了该表面对可见光有较强的响应能力.随后,介绍了金红石TiO₂(011)表面的缺陷和杂质,指出吸附H原子和形成O缺陷后还能显著增强其在红外区的红外吸收.在此基础上,不仅从理论上提供了一些传统实验所无法提及的数据资料,还弥补了相关实验在微观领域研究中的不足.最后,就目前金红石TiO₂(011)表面研究中存在的问题做了展望,指出金红石TiO₂(011)表面各种表面现象的微观本质是未来研究的重点内容.     

应用低能正电子衍射对Si(111)-(2×1)表面结构的分析

对Si(111) (2× 1)表面 7个非等价垂直入射衍射束的自动张量低能正电子衍射强度的分析的结果表明 ,该表面偏向于改进的π键链模型 ,但得到的可靠性因子不如其它化合物半导体表面结构分析时小 ,本文对其可能的原因进行了较详细的分析。     

The structure and chemistry of the TiO(2)-rich surface of SrTiO(3) (001)

Oxide surfaces are important for applications in catalysis and thin film growth. An important frontier in solid-state inorganic chemistry is the prediction of the surface structure of an oxide. Comparatively little is known about atomic arrangements at oxide surfaces at present, and there has been considerable discussion concerning the forces that control such arrangements. For instance, one model suggests that the dominant factor is a reduction of Coulomb forces; another favours minimization of 'dangling bonds' by charge transfer to states below the Fermi energy. The surface structure and properties of SrTiO(3)--a standard model for oxides with a perovskite structure--have been studied extensively. Here we report a solution of the 2 x 1 SrTiO(3) (001) surface structure obtained through a combination of high-resolution electron microscopy and theoretical direct methods. Our results indicate that surface rearrangement of TiO(6-x) units into edge-sharing blocks determines the SrO-deficient surface structure of SrTiO(3). We suggest that this structural concept can be extended to perovskite surfaces in general.     

First-principles investigation on initial stage of 2H-SiC(001) surface oxidation

We present comprehensive first-principles calculations on the initial stages of SiC oxidation by atomic oxygen on the 2H-SiC(001) surface. In order to study the kinetics of oxygen incorporation at the 2H-SiC(001) surface, we investigated adsorption and diffusion of oxygen atoms and SiO₂ nucleation. The adsorption sites, corresponding to the local minima of the potential energy surface (PES) for isolated adatoms, were identified through a comparative study of the adatom binding energy at different locations. We found that the Bridge (siloxane) site is preferred over other adsorption sites. There is no energy barrier at 0K for oxygen insertion into this site. The diffusion energy barriers that the adatom has to overcome when jumping between two adsorption sites were calculated. The premises of silica nucleation were investigated by calculating the modifications of the oxygen atom binding energy due to the interaction with neighboring adatoms. Supported by Snecma Propulsion Solide (Contract FPR No. 0539298A), Natural Science Foundation of China (Grant No 50802076) and Flying Star Program of Northwestern Polytechnical University of China     

Au原子在H-Si（001）表面扩散的研究

本文用第一原理总能理论研究了金属Au在H-Si(001)表面的吸附与扩散。计算表明,Au原子的吸附不能打破Si二聚体键,其稳定吸附位置处于一个Si二聚体的中部;同时还给出了Au原子处于其它位置时的能量以及相对于Si(001)表面的高度,分析了Au原子在H-Si(001)表面的可能扩散路径。     

第一性原理计算锐钛矿（101）面的电子结构

采用基于密度泛函理论的平面波赝势方法计算了锐钛矿（101）表面的电子结构．首先对锐钛矿完整（101）表面模型进行结构优化,在此基础上计算了电子结构,得到了能带结构和态密度等数据．结果分析表明表面的电子结构与体相基本相同,在完整表面上没有出现表面态,驰豫后完整的锐钛矿（101）表面是稳定的,表面价带主要由O2p组成,导带主要由Ti3d组成,表面导带态密度变窄导致表面能隙比体相能隙略增大．通过表面原子局域态密度和Mulliken净电荷的分析,推测O2c、O3c、Ti5c可能是活性位置．     

Imaging the atomic arrangements on the high-temperature reconstructed alpha-Al2O3(0001) surface.

Alumina is a technologically important oxide crystal because of its use as a catalyst and as a substrate for microelectronic applications. A precise knowledge of its surface atomic structure is a prerequisite for understanding and controlling the physical processes involved in many of its applications. Here we use a dynamic scanning force microscopy technique to image directly the atomic structure of the high-temperature phase of the alpha-Al2O3(0001) surface. Evidence for a surface reconstruction appears as a grid of protrusions that represent a rhombic unit cell, and we confirm that the arrangement of atoms is in the form of surface domains with hexagonal atomic order at the centre and disorder at the periphery. We show that, on exposing the surface to water and hydrogen, this surface structure is important in the formation of hydroxide clusters. These clusters appear as a regular pattern of rings that can be explained by self-organization processes involving cluster-surface and cluster-cluster interactions. Alumina has long been regarded as the definitive test for atomic-resolution force microscopy of insulators so the whole class of insulating oxides should now open for direct atomic-scale surface investigations.     

低能粒子轰击(001)2×1表面重构金刚石的计算机模拟

利用Tersoff势和分子动力学方法研究了初始动能为500eV的硼原子注入金刚石的微观行为.结果表明:硼注入后产生温度为5000K的热峰,其寿命为0.18ps;同时产生了半径为0.45nm的局部非晶化区域,三重配位原子数占该区域原子数的7%.硼原子以B〈110〉分裂间隙的形式存在于金刚石结构中.     

铅盐PbS(001)表面几何结构特性

用第一性原理方法计算了铅盐PbS的体晶格常数和 （001） 表面的几何结构,计算结果表明铅盐 （001）表面几何结构具有弛豫和褶皱的特性,为铅盐的广泛应用提供了理论参考数据.     

Zr 掺杂对锐钛矿型TiO2 电子结构和光学性质的影响

本文采用密度泛函理论的平面波超软赝势方法研究了Zr 掺杂对锐钛矿型TiO₂ 电子结构和光学性质的影响, 计算了Zr 掺杂前后锐钛矿型TiO₂ 的电子态密度分布、能带结构、光吸收系数等性质, 定性地分析了掺杂前后电子结构和光学性质的变化. 研究结果表明: Zr 掺杂锐钛矿型TiO₂, 导致带隙减小, 掺杂后在360~400nm 附近的光吸收系数增大, TiO₂ 的吸收带产生红移, 增强了TiO₂ 的光催化活性, 理论与实验结果 一致.     

二氧化钛的有机表面改性研究

采用有机改性处理二氧化钛,首先对表面改性剂进行了筛选,然后对改性剂浓度、改性剂用量、改性时间、改性温度等工艺条件进行正交实验,得到最佳改性方案。     

吡啶在Mo-Mo_2C(001)表面吸附的密度泛函理论研究

以量子化学理论为基础,以周期性平板模型为模拟表面,采用GGA/RPBE方法研究了吡啶分子在Mo_2C(001)表面的吸附特性.研究结果表明吡啶分子在Mo-Mo2C(001)表面上存在两种稳定的吸附构型:平行吸附和垂直吸附.其最稳定吸附构型为平行吸附.吸附能、几何结构参数及Mulliken电荷布局分析表明吡啶分子平行吸附情况下其环状结构受到了较大的影响,在后续的加氢过程中更为有利.而在垂直吸附情况下,吡啶分子在吸附前后的形变较小.     

Zr（0001）初始氧化的表面结构变化

LEED和XPS实验观察到了Zr(0001)初始氧化的表面结构变化,多重散射理论分析结构表明,Zr(0001)表面的初始氧化形成的(2×2)表面结构,为表面FCC重构的underlayer的C(B) A(C)BAB的结构形式,并存在纵向的原子的Relaxation,使Zr原子移向O原子,计算的最佳模型中的位移量为d_(11)=0.005nm,d_(22)=0.005 nm。     

A study on poly (N-vinyl-2-pyrrolidone) covalently bonded NiTi surface for inhibiting protein adsorption

Near equiatomic NiTi alloys have been extensively applied as biomaterials owing to its unique shape memory effect, superelasticity and biocompatibility. It has been demonstrated that surfaces capable of preventing plasma protein adsorption could reduce the reactivity of biomaterials with human blood. This motivated a lot of researches on the surface modification of NiTi alloy. In the present work, following heat and alkaline treatment and silanization by trichlorovinylsilane (TCVS), coating of poly (N-vinyl-2-pyrrolidone) (PVP) was produced on the NiTi alloy by gamma ray induced chemical bonding. The structures and properties of modified NiTi were characterized and in vitro biocompatibility of plasma protein adsorption was investigated. The results indicated that heat treatment at 823 K for 1 h could result in the formation of a protective TiO2 layer with “Ni-free” zone on NiTi surface. It was found that PVP was covalently bonded on NiTi surface to create a hydrophilic layer for inhibiting protein adsorption on the surface. The present work offers a green approach to introduce a bioorganic surface on metal and other polymeric or inorganic substrates by gamma irradiation.     

Real-space imaging of an orbital Kondo resonance on the Cr(001) surface

The Kondo effect is usually connected with the interaction between a localized spin moment and itinerant electrons. This interaction leads to the formation of a narrow resonance at the Fermi level, which is called the Abrikosov-Suhl or Kondo resonance. Scanning tunnelling microscopy is an ideal technique for real-space investigations of complicated electronic structures and many-body phenomena, such as the formation of the Kondo resonance or d-wave pairing in high-T(c) superconductors. Theory has predicted that similar, Kondo-like many-electron resonances are possible for scattering centres with orbital instead of spin degrees of freedom--the quadruple momenta in uranium-based compounds or two-level systems in metallic glasses are examples of such 'pseudo-Kondo' scattering centres. Here we present evidence for the orbital Kondo resonance on a transition-metal surface. Investigations of an atomically clean Cr(001) surface at low temperature using scanning tunnelling microscopy reveal a very narrow resonance at 26 meV above the Fermi level, and enable us to visualize the orbital character of the corresponding state. The experimental data, together with many-body calculations, demonstrate that the observed resonance is an orbital Kondo resonance formed by two degenerate d(xz), d(yz) surface states.     

CoSi2（001）表面的第一原理计算

基于广义梯度近似的从头算平面波超软赝势方法,考虑了CoSi2（001）面的Si和Co两种终止表面。结果表明表面能较低的Si终止表面比Co终止表面稳定。但是,由于差距不大,这两种终止表面可以共同存在。两种不同终止表面第1层原子与第2层原子弛豫后的间距都变小,Si终止表面的表面四层间距弛豫量略大于Co终止表面。