缺陷对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和缺陷石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,本征石墨烯中,钠原子的最佳吸附位置为H位,缺陷石墨烯中,钠原子的最佳吸附位置为T_D位.缺陷石墨烯对钠原子的吸附能是-4.423 eV,约为本征石墨烯对钠原子吸附能的2.5倍;钠原子与缺陷石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没有发生轨道杂化现象.缺陷石墨烯能够吸附10个钠原子,与本征石墨烯相比显著提高.因此,缺陷石墨烯有望成为一种潜在的储钠材料.     

Kinetic modelling of the H2---O2 reaction on Pd and of its influence on the hydrogen response of a hydrogen sensitive Pd metal-oxide-semiconductor device

We have established a model for the water forming reaction on Pd in the temperature range 350–475 K. Importantly, the model takes into account the possibility that hydrogen may absorb and adsorb at interface sites on supported Pd catalysts. It is shown that already at modest conditions interface adsorption may significantly affect reaction rates. The model may also be used to quantify the response of a hydrogen sensitive Pd-MOS device during hydrogen sensing in oxygen. In the case of Pd supported on SiO₂, the concentration of interface sites is so low that interface hydrogen adsorption will have only a minor influence on a catalytic reaction. The fact that a Pd-MOS device may be used as a very sensitive hydrogen detector at atmospheric oxygen conditions, despite a steric oxygen blocking of hydrogen dissociation sites, is predicted by the model.     

掺杂硅烯吸附CO分子的第一性原理研究

硅烯具有独特的电子、光学、热学、力学以及量子特性,在电子器件、电极材料、储氢材料、催化剂和气体传感器等领域有巨大的潜在应用价值.本文采用基于密度泛函理论的第一性原理计算方法,利用Materials Studio软件中的CASTEP程序包对硅烯与CO分子之间的吸附行为进行了研究.重点研究了硅烯掺杂方式、CO分子吸附构型及硅烯空位缺陷浓度对CO分子吸附的影响,研究结果表明：1)空位缺陷硅烯对CO分子的吸附能力最强;2)碳原子垂直朝向空位缺陷硅烯更有利于CO分子的吸附;3)硅烯对CO分子的吸附能力随其空位浓度的增加显著增强;4)空位硅烯向CO分子转移电荷,电荷转移量与二者的吸附作用强弱呈正相关.该研究可为硅烯基CO气体传感器的设计提供理论指导.     

纳米尺度下Si/Ge界面应力释放机制的分子动力学研究

采用分子动力学方法研究了纳米尺度下硅(Si)基锗(Ge)结构的Si/Ge界面应力分布特征,以及点缺陷层在应力释放过程中的作用机制.结果表明:在纳米尺度下, Si/Ge界面应力分布曲线与Ge尺寸密切相关,界面应力下降速度与Ge尺寸存在近似的线性递减关系;同时,在Si/Ge界面处增加一个富含空位缺陷的缓冲层,可显著改变Si/Ge界面应力分布,在此基础上对比分析了点缺陷在纯Ge结构内部引起应力变化与缺陷密度的关系,缺陷层的引入和缺陷密度的增加可加速界面应力的释放.参考对Si/Ge界面结构的研究结果,可在Si基纯Ge薄膜生长过程中引入缺陷层,并对其结构进行设计,降低界面应力水平,进而降低界面处产生位错缺陷的概率,提高Si基Ge薄膜质量,这一思想在研究报道的Si基Ge膜低温缓冲层生长方法中初步得到了证实.     

Interface delocalization in the three-dimensional Ising model

The interface delocalization in the three-dimensional Ising model is studied by real-space renormalization group methods. The first-order cumulant expansion approximation is used. Defect free energies for a boundary plane of defects and an internal plane of defects are calculated in the whole temperature region. The phase diagrams are also obtained. The method and the model analyzed may give a correct phase diagram only in the regime of continuous interface delocalization. The interface delocalization is obtained for the boundary defect and also for the internal defect if the systems on two sides of the internal defect plane have a different degree of order. The delocalization transition does not occur in the case of the internal defect plane between two equally ordered systems.     

Probing interfacial dynamics of water in confined nanoporous systems by NMRD

The confined dynamics of water molecules inside a pore involves an intermittence between adsorption steps near the interface and surface diffusion and excursions in the pore network. Depending on the strength of the interaction in the layer(s) close to the surface and the dynamical confinement of the distal bulk liquid, exchange dynamics can vary significantly. The average time spent in the surface proximal region (also called the adsorption layer) between a first entry and a consecutive exit allows estimating the level of ‘nanowettablity’ of water. As shown in several seminal works, NMRD is an efficient experimental method to follow such intermittent dynamics close to an interface. In this paper, the intermittent dynamics of a confined fluid inside nanoporous materials is discussed. Special attention is devoted to the interplay between bulk diffusion, adsorption and surface diffusion on curved pore interfaces. Considering the nano or meso length scale confinement of the pore network, an analytical model for calculating the inter-dipolar spin–lattice relaxation dispersion curves is proposed. In the low-frequency regime (50?KHz–100?MHz), this model is successfully compared with numerical simulations performed using a 3D-off lattice reconstruction of Vycor glass. Comparison with experimental data available in the literature is finally discussed.     

Total Internal Reflection Fluorescence Spectroscopy for Investigating the Adsorption of a Porphyrin at the Glass/Water Interface in the Presence of a Cationic Surfactant Below the Critical Micelle Concentration

Total internal reflection fluorescence (TIRF) spectroscopy was used to investigate the adsorption behavior of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) at the glass/water interface in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) far below the critical micelle concentration. The adsorption model of TPPS at the glass/water interface in the presence of low concentration of CTAB was proposed, which was different from the adsorption of TPPS in the presence of micelles of CTAB at the glass/water interface. TPPS and CTAB did not form stable complex at the interface in dilute system. The interfacial species of TPPS were analyzed by comparing the spectra of TPPS at the glass/water interface and in the aqueous phase. The influences of the TPPS concentration, the CTAB concentration, and the pH values on the interfacial fluorescence spectra and intensities were studied. It was demonstrated that electrostatic interaction and hydrophobicity performed an important role on the adsorption of TPPS in the presence of CTAB. The different effects of TPPS concentration on the adsorption behaviour of TPPS at different pH were observed for the first time. It was found that the adsorption isotherms of TPPS at glass/water interface could fit Freundlich equation at pH 7.1.     

Coupled Soliton States and Localization of Cnoidal Waves at the Interface of Nonlinear and Linear Media

Contact effects at the interface of linear and nonlinear media are studied. The problem of different stationary states in two-level system with different parameters of the dispersion relation is considered. A model that employs the nonlinear Shrödinger equation is used to show coupled states of solitons, localization of waves on one side of a defect, and transformation of nonlinear wave into linear wave upon transition through interface for the system under study due to variation in energy. Dispersion relations that determine the energies of such states are derived.     

MoO_3/Si界面区钼掺杂非晶氧化硅层形成的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,通过模拟MoO_3/Si界面反应,研究了MoO_x薄膜沉积中原子、分子的吸附、扩散和成核过程,从原子尺度阐明了缓冲层钼掺杂非晶氧化硅(a-SiO_x(Mo))物质的形成和机理.结果表明,在1500 K温度下, MoO_3/Si界面区由Mo, O, Si三种原子混合,可形成新的稳定的物相.热蒸发沉积初始时, MoO_3中的两个O原子和Si成键更加稳定,同时伴随着电子从Si到O的转移,钝化了硅表面的悬挂键. MoO_3中氧空位的形成能小于SiO_2中氧空位的形成能,使得O原子容易从MoO_3中迁移至Si衬底一侧,从而形成氧化硅层;替位缺陷中, Si替位MoO_3中的Mo的形成能远远大于Mo替位SiO_2中的Si的形成能,使得Mo容易掺杂进入氧化硅中.因此,在晶硅(100)面上沉积MoO_3薄膜时, MoO_3中的O原子先与Si成键,形成氧化硅层,随后部分Mo原子替位氧化硅中的Si原子,最终形成含有钼掺杂的非晶氧化硅层.     

掺杂对金属-MoS_2界面性质调制的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,计算了卤族元素掺杂对金属-MoS_2界面性质的影响,包括缺陷形成能、电子能带结构、差分电荷密度以及电荷布居分布.计算结果表明:卤族元素原子倾向于占据单层MoS_2表面的S原子位置;对于单层MoS_2而言,卤族元素的掺杂将在禁带中引入杂质能级以及导致费米能级位置的移动.对于金属-MoS_2界面体系,结合Schottky-Mott模型,证明了卤族元素的掺杂可以有效地调制金属-MoS_2界面间的肖特基势垒高度.发现F和Cl原子的掺杂将会降低体系的肖特基势垒高度.相比之下,Br和I原子的掺杂却增大了体系的肖特基势垒高度.通过差分电荷密度和布居分布的分析,阐明了肖特基势垒高度的被调制是因为电荷转移形成的界面偶极矩的作用导致.研究结果解释了相关实验现象,并给二维材料的器件化应用提供了调节手段.     

Numerical analysis of CdS-CIGS interface configuration on the performances of Cu(In,Ga)Se2 solar cells

One dimension solar Cell Simulation package (SCAPS) is used to analyze the impact of the CdS-CIGS interface configuration on the performances of CIGS solar cells. We simulated the current-voltage characteristic of two models of the cell: one with a donor type defect (OVC model) and the other with acceptor type defect (P+ model) at the CdS-CIGS interface. The advantages and disadvantages of these CIGS surface configuration on the electrical parameters were discussed according to their thicknesses, defect density and carrier lifetime. The simulation results show that the model with the P+ layer has poor performance when its thickness and defect density increase, due to a huge distortion on the J-V characteristic. On the other hand, the OVC layer plays a fundamental role in the performance of CIGS solar cells. Better performances are obtained with the OVC model when the density of donor defect is in the range 10¹³ - 10¹⁵ cm⁻³, the charge carriers lifetime in the range 0.02 - 1 ns, and the thickness of the OVC layer in the range 200 - 400 nm.     

Hydrogen adsorption of the [0 0 1] diamond surface

A slab model employing a tight binding scheme is used to study changes in the electronic structure of hydrogen on a [0 0 1] diamond surface. We suggest that the valence band tailing observed in photoemission studies of the [1 1 1] surface reflects a range of atomic relaxations due to the presence of hydrogen which in turn effects the dispersion of the surface defect levels throughout the band structure. Electronic structure well into the bulk is affected by the surface adsorption of hydrogen and is far different from that of the perfect surface.     

表面活性剂浓度对球形气泡界面和尾流的影响

发展了一种研究气泡界面污染程度的数值模型,并用其对流场中不同表面活性剂浓度下、上浮气泡的界面参量和周围流场进行了模拟研究。该模型假设吸附于气泡界面的表面活性剂分布在毗邻气液界面的薄吸附层中,且气泡界面上表面活性剂的吸附与解吸过程也发生于此;界面切应力为界面浓度的函数。研究发现:气泡界面的流动性会因表面活性剂的吸附而降低,该现象会增大气泡周围流域中切向速度在界面法向上的变化量,从而对界面性质和周围流场产生影响;由于对流的作用和吸附-解吸动态平衡的存在,气泡前部界面不完全干净,且受污染界面的流动性也不完全为零。     

Electronic States in Quantum Wells with Interface Defects

Effects of ilr terface defects on electronic states in quan tum wells (Q Ws) are investigated theoretically by introducing a coordinate transformation that transforms QWs with defective interfaces to those with planar interfaces plus an effective potential associated with interface defects. The interface defects are idealized as a cylindrical hollow protruding into the barrier materials on one of the interfaces. Electronic ground state energies are calculated variationally aa functions of the defect lateral sizes. For GaA8-Ga_1-zAl_zAs Q WS with the well width d less than 150 Å, the changes in electronic energies due to interface defects will produce sizable effects on optical experiments, such as broadenings of excitation spectra of Q We. But our calculation predicts smaller spectrum broadenings than those predicated by the previous theory for the same interface disorder.     

The secondary X-ray fluorescence and absorption near the interface of multi-material: Case of EDS microanalysis

A simple model is proposed to take into account secondary X-ray fluorescence and absorption effects near the interface. This model is based on the investigation of the shape change of the first derivative equation that can fit the sigmoidal EDS profile obtained when a high vacuum electron beam passes through the interface of two adjacent materials. The contribution of the photoelectric absorption of primary X-rays (characteristic and Bremsstrahlung) and the secondary fluorescence on the degradation of the X-ray spatial resolution can be easily quantified. The close agreement between the simulated (Monte Carlo simulation using the Casino software) and the experimental data serves to assess the reliability of this developed model.     

Smoothing Effect of Quenched Disorder on Polymer Depinning Transitions

We consider general disordered models of pinning of directed polymers on a defect line. This class contains in particular the (1+1)-dimensional interface wetting model, the disordered Poland–Scheraga model of DNA denaturation and other (1+d)-dimensional polymers in interaction with flat interfaces. We consider also the case of copolymers with adsorption at a selective interface. Under quite general conditions, these models are known to have a (de)localization transition at some critical line in the phase diagram. In this work we prove in particular that, as soon as disorder is present, the transition is at least of second order, in the sense that the free energy is differentiable at the critical line, so that the order parameter vanishes continuously at the transition. On the other hand, it is known that the corresponding non-disordered models can have a first order (de)localization transition, with a discontinuous first derivative. Our result shows therefore that the presence of the disorder has really a smoothing effect on the transition. The relation with the predictions based on the Harris criterion is discussed.     

氧在硅表面上吸附的晶向关系

利用AES和同步辐射光电子谱,在圆柱状的Si单晶样品上研究了氧表面吸附的晶向关系。结果表明:在350K曝氧²L时,总吸附量的晶向关系比较弱,并可利用台阶的增强吸附来解释;随着曝氧量的增加(～10L),氧原子首先从(111)面进入体内,从而支持Si(111)-(7×7)再构是属于“缺陷”类模型的结论。 关键词：     

Mathematical simulation of the plastic deformation of crystalline materials with a nanodispersed hardening phase

The effect of the scale characteristics of a nanodispersed hardening phase on the strain hardening and evolution of the defect subsystem in materials with an fcc matrix has been studied with the use of a mathematical model including differential balance equations for the components of the strain defective subsystem. The two-stage character of evolution of the strain defect subsystem and the possibility of plastic shearing in dispersion-hardened materials due to either the motion of individual dislocations or the generation of numerous dislocations in the shear band were taken into consideration. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 25–32, November, 2007.     

表面增强拉曼散射光谱的应用进展

表面增强拉曼光谱是一种非常有效的探测界面特性和分子间相互作用、表征表面分子吸附行为和分子结构的工具。已成为灵敏度最高的研究界面效应的技术之一,最大范围地应用于研究吸附分子在表面的取向及吸附行为、吸附界面表面状态、生物大分子的界面取向及构型、构象和结构分析;SERS技术也逐渐成为表面科学和电化学领域有力的研究手段,并已在痕量分析乃至单分子检测、化学及工业、环境科学、生物医学体系、纳米材料以及传感器等方面的研究中得到了广泛应用,甚至出现了拉曼技术与其他技术的联用。文章综述了近几年来表面增强拉曼散射作为一种光谱技术在这些应用领域的研究进展以及潜在应用价值;并简单介绍了作者所在实验室的相关工作,特别是富勒烯和碳纳米管材料等领域的一些探讨与研究。     

改性石墨烯SO_2气敏性质的第一性原理研究

为了寻求高灵敏度的石墨烯基的SO_2气体传感器,本文采用基于密度泛函理论的第一性原理方法,研究纯净石墨烯(PG)、单空位缺陷(SVG)、SW缺陷(SWG)、Mn掺杂修饰的石墨烯(Mn-PG)及掺杂和缺陷共修饰的石墨烯(Mn-SVG和Mn-SWG)对SO_2分子的吸附特性.研究表明:PG和SWG对SO_2分子的吸附作用较弱,对SO_2分子不具有敏感性;SO_2分子在SVG表面的吸附能够有效调控其电子结构的变化,使其由金属性转变为半金属性,但其吸附能较低(0.636 eV);结合了Mn掺杂和SV缺陷的Mn-SVG基底尽管增大了与SO_2分子相互作用,但未能引起该体系电子结构和磁性的明显改变;相比之下,SO_2分子在Mn-PG和Mn-SWG基底上具有较强的吸附稳定性;同时,该分子吸附可诱发Mn-PG和Mn-SWG体系磁矩的急剧降低和电导率的显著变化,故可作为探测和清除环境中SO_2分子理想材料.该研究为设计新型石墨烯气体传感器提供理论参考.