坩埚材料对生长CdSiP2晶体表面的影响研究

针对CdSiP2晶体生长过程中,晶体表面与石英坩埚内壁严重粘连甚至开裂的问题,研究了柔性氮化硼(PBN)内衬坩埚生长CdSiP2晶体的新工艺.运用X射线能量色散谱仪(EDS)和X射线光电子能谱仪(XPS)分别对两种坩埚材料生长的CdSiP2晶体表面元素成分和化学状态进行测试发现,采用石英坩埚生长的CdSiP2晶体表面主要组分元素为33.31;的Si和65.63;的O,晶体表面Si 2p的结合能为103.2 eV,与文献中SiO2的Si 2p结合能一致.进一步的分析表明,高温CdSiP2熔体离解产物与石英材料反应生成SiO2界面层是导致晶体严重粘连,甚至开裂成碎块的重要原因;采用柔性氮化硼(PBN)内衬坩埚能有效解决晶体与器壁的粘连,生长的CdSiP2晶体完整较好,表面层各组分元素含量接近CdSiP2理论化学配比1:1:2,质量较高.     

温度对SiO2表面上磁控溅射制备Ge纳米点的生长模式和尺寸的影响

采用磁控溅射技术在SiO2/Si(100)表面上制备了一系列不同生长温度的Ge纳米点样品.原子力显微镜(AFM)的实验结果表明:不同衬底温度下Ge纳米点在SiO2薄膜上的生长模式和尺寸分布有所不同.当衬底生长温度达到500 ℃时,SiO2开始与Ge原子发生化学反应,并形成"Ge纳米点的Si窗口".在此温度条件下,外延生长实验可获得尺寸均匀且密度高达3.2×1010 cm-2的Ge纳米点.     

氧化硅中纳米晶硅薄膜的低温沉积及其键合特性研究

以Ar和H2为溅射气体,采用Si和SiO2双靶活性溅射技术实现了镶嵌纳米晶硅(nc-Si)的富硅氧化硅(SiOx)薄膜的300℃低温生长,并分析了氢气掺入对薄膜微观结构及键合特性的影响.结果表明,氢气流量比的增加导致纳米硅粒子尺寸增加,而生长速率逐渐减小.薄膜中Si-O键合结构以Si(O4)键为主,随H2流量比的增加,Si-O4-nSin(n=0,1)键密度减小,Si-O4-nSin(n=2,3)和SiH2键密度持续增加,而所对应Si-H键密度呈现先减小后增加趋势,该结果可解释为等离子体内氢原子对反应前驱物中氧的去除效应增强和氢原子与表面氧的解吸附反应几率的增加.     

负离子配位多面体生长基元与晶体表面结构(Ⅰ)水晶(SiO2),闪锌矿(ZnS),碘化镉(CdI2)

本文用负离子配位多面体生长基元理论模型研究了水晶(SiO2)、闪锌矿(ZnS)和碘化镉(CdI2)晶体表面结构的形成,指出晶体的表面结构是负离子配位多面体在晶体表面的迭合轨迹,把晶体的表面结构与内部结构由表及里的有机联系起来.     

SiO2纳米线/纳米颗粒复合结构的制备及光致发光性能研究

采用热蒸发法制备了非晶SiO2纳米线/纳米颗粒复合结构,确定了非晶SiO2纳米线、微米颗粒及SiO2纳米线/纳米颗粒复合结构生长的工艺条件,并利用XRD、SEM、Raman、PL光谱等技术手段分析表征样品.实验结果表明,在不同的沉积温度范围内,生长样品的形貌和结构不同;SiO2纳米线/纳米颗粒复合结构的发光区与Si衬底明显不同,主要集中在黄绿光范围.     

水热合成硅酸锌纳米粉体及其形成机理的研究

以醋酸锌为锌源、正硅酸乙酯为硅源水热合成硅酸锌(Zn2 SiO4)晶体.研究了反应时间、温度、pH以及不同的反应溶剂对Zn2 SiO4晶体生长的影响.采用X射线衍射仪(XRD)分析样品物相,扫描电镜(SEM)和透射电镜(TEM)对样品晶粒聚集成球的过程在结构和形貌上进行表征.利用Johnson-Mehl-Avrami (JMA)方程对Zn2 SiO4晶体进行生长动力学分析.结果表明:随着温度升高与反应时间的延长,球状Zn2SiO4不断长大,结晶性能逐渐增强.水热合成的Zn2 SiO4晶体Avrami指数n145℃=0.55、n165℃=0.60、n205℃=0.71、n185℃=0.85,表明晶体的形成有从扩散机制向成核机制转变的趋势.     

不同衬底表面上大晶粒多晶Si薄膜的制备

利用高频感应加热化学气相沉积(HFCVD)工艺,以H2稀释的SiH4作为反应气体源,分别在n-(111)Si衬底上常规热生长的SiO2层、织构的SiO2层和纳米晶粒多晶Si薄膜表面上,制备了具有均匀分布的大晶粒多晶Si膜.采用扫描电子显微镜(SEM)和X射线衍射(XRD)等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸、密度分布与择优取向等结构特征.结果表明,多晶Si膜中Si晶粒的尺寸大小和密度分布不仅与衬底温度、SiH4浓度与反应气压等工艺参数有关,而且强烈依赖于衬底的表面状态.本实验获得的最好的薄膜中,Si晶粒平均尺寸约为2.3 μm,密度分布约为3.8×107/cm2.对薄膜的沉积机理分析表明,衬底表面上Si原子基团的吸附、迁移、成核与融合等热力学过程支配着大晶粒多晶Si膜的生长.     

热壁外延制备InAs/Si(211)薄膜及其电学性能研究

采用热壁外延(Hot Wall Epitaxy,HWE)沉积系统在单晶Si(211)衬底表面制备了InAs薄膜,研究了不同生长温度(300℃、350℃、400℃、450℃和500℃)对薄膜材料结构及其电学性能的影响.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)、霍尔(Hall)测试等,对InAs/Si(211)薄膜的晶体结构、表面形貌及电学参数进行了测试分析.结果表明:采用HWE技术在Si(211)衬底表面成功制备了InAs薄膜,薄膜具有闪锌矿结构并沿(111)方向择优生长.随着生长温度从300℃升高到500℃,全峰半高宽(FWHM)先减小后增大,生长温度为400℃时薄膜的晶粒尺寸最大为73.4 nm,载流子浓度达到1022 cm-3,霍尔迁移率数值约为102 cm2/(V·s),说明优化生长温度能够降低InAs薄膜的缺陷复合,使薄膜结晶质量和电学性能得到提高.SEM及AFM的测试结果显示由于较高的晶格失配及Si衬底斜切面(211)的特殊取向,在Si(211)衬底上生长的InAs薄膜主要为三维层加岛状(S-K)生长模式,表面粗糙度(Ra)随温度的升高先减小后增大,400℃时薄膜的平均表面粗糙度Ra为48.37 nm.     

沉积温度对热蒸发法制备SiO2一维纳米材料的影响

利用热蒸发法在N型硅片表面成功制备出大面积SiO2纳米线和SiO2纳米棒结构.采用X射线粉末衍射(XRD),扫描电子显微镜(SEM),X射线能量色散谱(EDX),拉曼光谱(RS)和光致发光(PL)对合成的产物进行了表征.结果表明,用此方法生长的SiO2纳米材料,其结构和形貌与生长参数关系密切,随着沉积温度降低纳米线长度变短,最后呈现出棒状结构.此外,还研究了SiO2纳米结构独特的光学性质.该研究对改善光电子半导体器件的性能应用具有重要意义.     

Zn2+掺杂高岭石基纳米TiO2光催化材料的表面特性研究

基于高岭石表面是以Si-O键为主的亲水表面且具有巨大比表面积,易于复合光催化优异的TiO2膜.以高岭石为基材,溶胶-凝胶法制备了具有光催化活性的Zn2掺杂TiO2/高岭石复合光材料.采用XRD、FrIR、Raman、XPS等技术对材料的晶体结构、分子结构、表面元素组成及化学态、纳米TiO2晶体膜的覆盖面积进行表征分析.结果表明:Ti-O与高岭石结构的Si-O发生化学键合,在高岭石表面形成Si-O-Ti键合的纳米TiO2晶体膜,占高岭石表面积的91.35;.掺杂的Zn2只是在TiO2晶体表面复合氧化成红锌矿,而不能进入TiO2晶格.物理化学复合增加了基材高岭石表面晶体缺陷,有利于TiO2晶体表面光生载流子的增生和传输.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.