气液界面微观结构研究的一种实验新方法（英文）

许多物理、化学和生物过程发生于气液界面,且受到局域微观结构的深远影响.不同于液体的体相,分子取向是界面处微观结构突出的不对称特征之一.本文综述了电子碰撞时间延迟质谱方法和近期取得的进展.利用这个崭新的方法,不仅可以侦测得到利用小角度X射线或中子散射以及振动和频光谱方法获得的界面微观结构,同时也提供了一种研究气液界面处电子驱动化学反应的实验方案.     

硬脂酸单分子膜上电沉积Ag膜的研究

通过电沉积方法 ,以气 /液界面上形成的硬脂酸单分子膜为模板诱导沉积金属银膜 .考察了镀液 pH值、单分子膜表面压及沉积电位对银膜形貌及结构的影响 .实验发现 ,酸性镀液的气 /液界面上形成的单分子膜不能诱导沉积银 ,而在中性和碱性镀液的气 /液界面上可以诱导银膜的生长 .当单分子膜处于液态或固态时 ,气 /液界面有银膜形成 ;液态单分子膜上的银膜生长速度较快 ,且银膜的结构一致 .随着电极电位的升高 ,银膜沉积的速度加快 ,呈环状向外生长的圆形银膜逐渐变得不规则 .将不同实验条件下的银膜转移出来 ,采用扫描电镜 (SEM )、透射电镜 (TEM )对银膜的结构与形貌进行了表征 .研究表明 ,银首先在单分子膜上异相成核 ,由八面体构型逐渐发展成星型 ,最终在气 /液界面形成具有松枝状微观结构的光亮银膜 .     

添加正辛醇的溴化锂水溶液汽液界面微观形态

采用分子动力学方法研究303 K时,添加正辛醇(1-octanol)的溴化锂水溶液汽液界面的微观形态、密度分布和结构性质.模拟结果表明: Li+、Br在汽液界面处解吸;正辛醇分子吸附在汽液界面并在界面处优势取向;醇分子的亲水基会尽可能多地趋向水分子,二者在界面处以氢键相互作用.同时,在非平衡条件下,采用分子动力学方法模拟了添加或未添加正辛醇的溴化锂水溶液吸收水蒸气的动态过程,发现在短时间内,部分水蒸气分子吸附在汽液界面处或到达溶液内部.     

不同组分厚度比的LaMnO3/SrTiO3异质界面电子结构和磁性的第一性原理研究

基于密度泛函理论的第一性原理计算, 研究了(LaMnO₃)_n/(SrTiO₃)_m(LMO/STO)异质界面的离子弛豫、电子结构和磁性质. 研究表明, 不同组分厚度比及界面类型时, 离子弛豫程度各不相同, 并且界面处的电子性质受此影响较大. 对于n型界面, 当LMO的厚度达到6个单胞层后, 电子会从LMO转移到STO, 转移的电子占据界面层Ti原子的3d电子轨道, 界面处出现二维电子气. 对于n型界面(LMO)_n/(STO)₂, 随着LMO厚度数n的增加, 由离子弛豫造成的结构畸变减小, 而界面处Ti原子周围电子的态密度和自旋极化却增大, 表明高厚度比的n型界面有利于产生高迁移率的二维电子气和自旋极化. 而对于p型(LMO)₂/(STO)₈界面, 在STO一侧基本没有结构畸变, 界面处无电子转移和自旋极化现象. 通过计算平均静电势发现n型和p型界面处的势差大小相差2 eV, 解释了p型界面不容易发生电荷转移的原因.     

广义等温等压系综-分子动力学模拟全原子水的气液共存形貌

探测相变过程中瞬时共存相的形貌等特征对理解其微观机制十分重要.本文应用广义等温等压系综-分子动力学模拟方法,研究全原子水模型的气液两相平衡及相变的中间过程.研究发现,此广义系综方法能够通过持续降温,连续地历经从气态、气液共存到液态的整个相变过程,通过持续升温历经其相反过程,而不会发生标准正则系综中的过饱和热滞现象.该方法不需要使用副本交换等增强抽样方法,因此可以用于较大体系的研究,多个独立的模拟即能获得整个气态液态区的平衡性质及共存相特征.本文还提出了计算气液共存界面面积的新方法,给出了水的气液共存界面形状随温度、压强的变化规律.结果表明,低压时水的气液共存界面因其较大的表面张力而接近球面,符合经典成核理论的描述,但随着压强升高接近其临界压强时,气态和液态的差别减小,界面的表面张力变小,界面形状变为无规则的枝杈结构,表现为二阶相变特征.     

Sr掺杂对La_(1-x)Sr_xMnO_3/LaAlO_3/SrTiO_3界面电子结构的影响

采用基于密度泛函理论的第一性原理计算方法,系统地研究了La_(1-x)Sr_xMnO_3层中Sr的掺杂方式和掺杂量对4La_(1-x)Sr_xMnO_3/3LaAlO_3/4SrTiO_3(LSMO/LAO/STO)异质结构原子和电子结构的影响.结果表明:对于相同的Sr掺杂量,掺杂方式的差异对体系电子结构的影响微弱,不会导致体系发生金属-绝缘体转变;掺杂量的不同对体系电子结构有着显著的影响,当Sr的掺杂量较少时,LAO/STO界面处存在着准二维电子气,当Sr的掺杂量高于1/3时,LAO/STO界面处准二维电子气消失.我们相信,Sr的引入以及通过Sr掺杂量的改变可以对LSMO覆盖层极化进行调控,这也是导致体系LAO/STO界面处金属-绝缘体转变的可能原因,进一步为极化灾变机制导致的界面处电子重构提供了证据.     

气液段塞流气弹区相界面结构理论研究

根据气液段塞流气弹区相界面结构特征将气弹分为气弹头、气弹体、水跃面和气弹尾四部分,并根据各自的流动和界面结构特征分别进行模化,建立了描述不同倾角的圆管内气液段塞流气弹区相界面结构的一维理论模型.该模型的计算结果表明气液混合Froude数、管道倾角和气弹长度显著影响气液段塞流气弹区相界面结构,计算与实验结果吻合良好.     

微尺度驻停气泡柔性气-液界面抗流体剪切能力

在微流控系统中,稳定、可控的柔性气-液界面可实现声流体颗粒富集、微纳操作、快速气-液反应等各种实际物理和生化应用.微流道内气-液界面的抗流体剪切能力对于增强微尺度下气-液界面的可控性具有十分重要的意义.为此,文章研究了具有高稳定性、高可控性、可阵列化的微尺度驻停气泡现象.利用嵌入局部裂隙的微流道以及与之平行的气体流道,可对驻停气泡的生成和形态进行有效调节,并利用其可控的气-液界面实现多种功能化应用.在此基础上,文章进一步研究柔性可控气-液界面的抗流体剪切能力,对形态变化中的气-液界面受力进行分析,利用仿真和实验手段研究不同状态下气-液界面的形状特征,研究不同的液体驱动压力、裂隙尺寸以及裂隙形状对气-液界面抗剪切能力的影响,并将界面的曲率半径作为气泡驻留与否的判定依据.文章对驻停气泡柔性气-液界面抗流体剪切能力的研究有助于优化其控制方法,增强其控制稳定性并拓展其潜在应用场合.      

模型二元有序合金固液界面结构的分子动力学研究

采用分子动力学方法,研究了模型二元有序合金体系的平衡界面结构和界面处原子的扩散行为.计算结果表明,该二元有序合金的固液界面属于光滑界面.由于固体中同时存在结构和化学有序,从而导致界面处的原子结构与单质以及异质固液界面的结构明显不同.在界面法向方向上,粒子数密度呈复杂的波动行为,并延伸到液体中约30 (A).对界面层的二维结构分析表明,固液转变层部分原子形成了二维固体团簇.从固体到液体,扩散系数从零逐渐增加到一个饱和值.在界面处附近,平行于界面方向的扩散系数明显比垂直于界面方向的大.     

疏水表面蒸发液滴下气液界面形态演化研究

研究蒸发液滴下气液界面的形态演化可为换热表面性能改进提供指导。本文以单个微槽及槽内液滴下气液界面为研究对象,运用能量分析法确定了疏水微槽表面放置液滴下气液界面的初始形态,提出了蒸发液滴上下气液界面同步演变理论,并利用该理论对液滴下气液界面失稳的原因、条件及下气液界面曲率的变化规律进行了探讨。结果表明,放置在疏水微槽表面上的液滴,其初始下气液界面与槽壁形成的微观接触角会介于0和本征接触角之间,在形态上呈现为曲率圆。当蒸发液滴下气液界面与槽壁形成的微观接触角大于一定数值后,会引发液滴下气液界面失稳,失稳后的液滴下气液界面形态受槽壁与水平面夹角的影响较大。     

微通道内反应流体粘性指进的数值研究

采用格子Boltzmann方法数值模拟化学反应中混溶流体在微通道中的粘性指进现象.模拟采用单浓度变量的双稳态化学反应模型,重点研究指进的形态位置随化学反应速率和稳态浓度参数（即无化学反应发生的界面浓度）的变化.结果表明：随着反应速率的增加,指进界面变薄;而稳态浓度参数的变化则影响反应区的分布以及反应速率,导致指进形态以及位置的改变,甚至出现指尖液滴分离.     

Single-point imaging of vulcanized boundary in rubber

A single-point imaging-based method for broad-line analysis is presented. The technique is used for obtaining spectroscopic information of a two-component covulcanized rubber sample. A new noninvasive procedure allows for the discrimination of natural rubber and poly(styrene-cobutadiene) rubber components, resulting in chemical and mechanical characterization of the sample interface. On the basis of the space-resolved chemical shift weighted measurements a sharp interface of thickness less than 200 um was found. Spin-spin relaxation weighted profiles show a wider interface, with a gradual cross-link density change extended to about 500 μm over the natural-rubber component.     

低覆盖度的Au/GaN(0001)界面的同步辐射研究

利用同步辐射光电子能谱研究了低覆盖度Au在GaN(0001)表面的初始生长模式,肖特基势垒高 度以及界面的电子结构.结果表明，Au沉积初始阶段有界面的化学反应,随后呈三维岛状生长 .由光电子能谱实验确定的肖特基势垒高度为14 eV. 通过对界面价带谱和Au 4f芯能级谱 的分析,确定了界面化学反应的存在.利用线性缀加平面波方法计算了GaN(0001)和Au的价带 态密度并分析了化学反应产生的机理,认为在初始阶段界面形成了Au_Ga合金. 关键词： 同步辐射 光电子能谱 Au/GaN欧姆接触 态密度     

Construction of a Linux based chemical and biological information system

A chemical and biological information system with a Web-based easy-to-use interface and corresponding databases has been developed. The constructed system incorporates all chemical, numerical and textual data related to the chemical compounds, including numerical biological screen results. Users can search the database by traditional textual/numerical and/or substructure or similarity queries through the web interface. To build our chemical database management system, we utilized existing IT components such as ORACLE or Tripos SYBYL for database management and Zope application server for the web interface. We chose Linux as the main platform, however, almost every component can be used under various operating systems.     

Theoretical study of the magnetic moments and anisotropy energy of CoRh nanoparticles

The role of size, structure and chemical order on the magnetic moments and magnetic anisotropy energy (MAE) of CoRh nanoparticles are studied in the framework of a self-consistent real-space tight-binding method. Our results show that a Rh core in a geometry having a large surface/volume ratio and with Co–Rh mixing at the interface is the most likely chemical arrangement. A local analysis reveals that the orbital and spin moments at the Co–Rh interface are largely responsible for the increase of the magnetic moments and magnetic anisotropy. Moreover, the local moments induced at the Rh atoms, which amount to about 20% of the moment per Co atom [ μ_Rh = (0.2–0.3) μ_B] and the orbital moments of Co atoms play a crucial role on the interpretation of experiment. The results are discussed in the context of the interplay between chemical order and magnetic properties.     

Standardless XPS method for determining the chemical composition of multiphase compounds and its application to studies of InP plasma oxide nanofilms

A modified version of x-ray photoelectron spectroscopy (XPS) is proposed for analysis of the phase chemical composition of substances. In contrast to the well-known XPS method of Siegbahn, the proposed version is standardless and permits determination of the chemical composition of complex multiphase compounds with high accuracy and reliability. In addition to the chemical composition, the method yields the core-level binding energies of atoms in the chemical phases of a studied compound, which have had to be determined in separate experiments on reference samples. The main idea underlying the proposed approach consists in self-consistent unfolding of photoelectron lines of two or more elements. The binding energies act as fitting parameters in this decomposition. The requirement that the contents of like chemical phases derived from the decomposition of spectra of two or more elements be identical makes the solution of the problem unique. This method was used to study the chemical composition of nanofilms of the InP plasma oxide containing several chemical phases. It is shown that, in order to improve the quality of a film and of the interface, the oxidizable surface should be enriched by phosphorus.     

Interfaces analysis of the HfO2/SiO2/Si structure

The physical and chemical properties of the HfO₂/SiO₂/Si stack have been analyzed using cross-section HR TEM, XPS, IR-spectroscopy and ellipsometry. HfO₂ films were deposited by the MO CVD method using as precursors the tetrakis 2,2,6,6 tetramethyl-3,5 heptanedionate hafnium—Hf(dpm)₄ and dicyclopentadienil-hafnium-bis-diethylamide—Сp₂Hf(N(C₂H₅)₂)₂.The amorphous interface layer (IL) between HfO₂ and silicon native oxide has been observed by the HRTEM method. The interface layer comprises hafnium silicate with a smooth varying of chemical composition through the IL thickness. The interface layer formation occurs both during HfO₂ synthesis, and at the annealing of the HfO₂/SiO₂/Si stack. It was concluded from the XPS, and the IR-spectroscopy that the hafnium silicate formation occurs via a solid-state reaction at the HfO₂/SiO₂ interface, and its chemical structure depends on the thickness of the SiO₂ underlayer.     

Photoemission study of SrTiO<Subscript>3</Subscript> surface layers instability upon metal deposition

In this work we study the Pt/SrTiO₃ (STO) interface system using X-ray photoelectron spectroscopy (XPS). The polycrystalline Pt layers with a thickness of about 2–3 nm are deposited by sputtering and thermal evaporation methods on STO(100) single crystals with two different type of terminations. We propose and show local conductivity (LC) measurements as a good method to check whether such very thin metal layers are continuous. The XPS data show that both methods of Pt deposition lead to changes of the chemical composition of the crystal surface layers, and such chemical instability should be taken into consideration when studying the physical properties of a metal–insulator interface. PACS 68.35.-p; 68.35.Dy; 73.40.Ns; 79.60.-i; 81.07.–b     

Stress-Assisted Reaction at a Solid-Fluid Interface

On the interface between a solid and a fluid, a reaction can occur in which atoms either leave the solid to join the fluid, or leave the fluid to join the solid. If the solid is in addition subject to a mechanical load, two outcomes may be expected. The reaction may proceed uniformly, so that the interface remains flat as the solid recedes or extends. Alternatively, the reaction may cause the interface to roughen and develop sharp cracks, leading to fracture. This paper reviews the current understanding of the subject. The solid-fluid is a thermodynamic system: the solid is in elastic equilibrium with the mechanical load, but not in chemical equilibrium with the fluid. Thermodynamic forces that drive the interfacial reaction include chemical energy difference between the solid and the fluid, elastic energy stored in the solid, and interfacial energy. The reaction is taken to be thermally activated. A kinetic law is adopted in which the stress affects both the activation energy and the driving force of the interface reaction. A linear perturbation analysis identifies the stability condition, which differs substantially from the well known stability condition based on the driving force alone. Large perturbations are examined by assuming that the interface varies as a family of cycloids, from slight waviness to sharp cracks. An analytic elasticity solution is used to compute the stress field in the solid, and a variational method to evolve the shape of the interface.     

Interface states study of intrinsic amorphous silicon for crystalline silicon surface passivation in HIT solar cell

Intrinsic hydrogenated amorphous silicon(a-Si:H) film is deposited on n-type crystalline silicon(c-Si) wafer by hotwire chemical vapor deposition(HWCVD) to analyze the amorphous/crystalline heterointerface passivation properties.The minority carrier lifetime of symmetric heterostructure is measured by using Sinton Consulting WCT-120 lifetime tester system,and a simple method of determining the interface state density(D_(it)) from lifetime measurement is proposed.The interface state density(D_(it)) measurement is also performed by using deep-level transient spectroscopy(DLTS) to prove the validity of the simple method.The microstructures and hydrogen bonding configurations of a-Si:H films with different hydrogen dilutions are investigated by using spectroscopic ellipsometry(SE) and Fourier transform infrared spectroscopy(FTIR) respectively.Lower values of interface state density(D_(it)) are obtained by using a-Si:H film with more uniform,compact microstructures and fewer bulk defects on crystalline silicon deposited by HWCVD.