硼掺杂金刚石薄膜研究

硼掺杂是改善金刚石薄膜电阻率的有效手段,被认为是将金刚石薄膜用于制备电化学电极的途径.本文通过CVD法在单晶硅片上制得掺硼金刚石薄膜(BDD),并采用四点探针、扫描电镜、激光拉曼和电化学工作站对之进行检测,发现随着硼掺入量的增加,薄膜电阻率逐渐降低,重掺杂时可达2.0×10-3Ω·cm.同时金刚石薄膜的固有质量出现恶化,表现为金刚石晶粒的碎化以及拉曼观察到的薄膜内应力的增加和非金刚石峰的出现.对薄膜电极进行电化学测量发现BDD电极在酸性溶液中具有非常宽的电位窗口和高的阳极极化电位,且背景电流极低.     

高温高压金刚石衬底上的同质外延生长研究

在自主研发的小功率微波等离子体化学气相沉积(MPCVD)装置上利用高温高压(HPHT)单晶金刚石片为衬底进行了金刚石同质外延生长的研究.研究了甲烷浓度、工作气压对金刚石生长速率的影响.测量了金刚石外延 生长过程中等离子体的发射光谱,利用扫描电子显微镜(SEM)和数码相机对生长前后金刚石的形貌进行了表征,利用激光拉曼光谱对金刚石的质量进行了分析.结果表明:一定程度内,适当升高工作气压和甲烷浓度能够有效提高金刚石的生长速率;在外延生长过程会产生过多的丘状体,导致许多金刚石颗粒的产生,影响其生长时间和质量,通过生长、刻蚀相结合的方法能够有效延长生长时间,改善生长形貌;外延生长出的金刚石的激光拉曼图谱中金刚石1332 cm-1特征峰明显、尖锐,荧光背底低,非金刚石相特征峰较低.     

预处理对超纳米金刚石薄膜表面质量的影响

本文研究了金刚石粉手工研磨及超声波震荡两种预处理方法对硅片衬底及超纳米金刚石膜表面粗糙度和形貌的影响,利用表面轮廓仪、X射线衍射分析(XRD)、激光拉曼、场发射扫描电子显微镜(FE-SEM)对衬底及超纳米金刚石膜进行表征.结果表明,由于衬底轮廓的遗传特性,手工研磨的硅片上沉积的超纳米金刚石膜表面粗糙度远高于超声震荡的硅片上沉积的超纳米金刚石膜.     

直流等离子体喷射CVD技术制备自支撑金刚石膜的新结构和新形貌

采用30kW高功率直流等离子体喷射CVD技术制备了自支撑金刚石膜的新型结构,通过使甲烷与氢气的浓度比随沉积时间变化的方法,制备了两层、三层和四层结构.扫描电镜结果显示所制备的层结构是由柱状晶和非常细晶粒组成的,而拉曼谱结果表明这层细晶粒具有纳米金刚石的激光散射特征.在甲烷与氢气的浓度比超过15;的沉积条件下,我们发现一种新形貌,这种形貌是由具有非常好的刻面的晶粒构成的.     

细胞色素c在硼掺杂金刚石电极上的电化学特性研究

采用直流电弧等离子体喷射设备制备掺硼金刚石(BDD)电极.并用扫描电镜及拉曼光谱分析了薄膜的表面形貌及薄膜品质,测试结果表明,掺硼金刚石薄膜表面结构排列紧密.使用BDD电极研究细胞色素c的直接电化学特性,结果表明在磷酸盐缓冲液中细胞色素c(Cytc)在BDD电极上呈现一对峰形较好的氧化还原峰,峰电流与扫速的平方根呈线性关系,且与细胞色素c浓度在5～50μmol·L-范围内近似呈线性关系.     

[100]定向织构生长金刚石薄膜的红外光学性能研究

采用微波等离子增强化学气相沉积法在(100)镜面抛光的硅片衬底上实现了金刚石薄片[100]定向织构生长.并用扫描电子显微镜、拉曼散射和傅立叶红外光谱仪分析测试了不同工艺得到的金刚石薄片的表面形貌、组成结构和红外性能.结果表明:负偏压辅助定向成核和氢的等离子刻蚀不仅促进了金刚石薄膜的定向织构生长,而且还能刻蚀成核期的非金刚石成分.从而提高了金刚石薄片的红外光透过特性.     

自支撑金刚石厚膜表面外延掺硼金刚石薄膜研究

采用微波等离子体化学气相沉积技术(MPCVD),在抛光厚度0.5 mm的高热导率自支撑金刚石厚膜表面沉积厚度10 μm掺硼金刚石薄膜,通过热导率测试仪、扫描电子显微镜、激光拉曼光谱、X射线光电子能谱以及四探针仪等测试手段对材料的热导率、形貌及微观质量、表面键合状态及导电性能等进行分析.结果表明,优化工艺后在自支撑金刚石厚膜表面外延形成了质量优异,结合力佳的掺硼金刚石薄膜,其电阻率最低为1.7 ×102 Ω·cm.同时,鉴于界面同质外延特性以及大尺寸晶粒特点,整体材料的热导率可高达1750 W/(m·K),显示这种层状复合材料良好的整体导热性能及表面导电性能.     

面向微机械应用的CVD金刚石微齿轮的制备

以电感耦合等离子体(ICP)刻蚀工艺制备单晶硅微齿轮陈列模具,采用热丝法化学气相沉积(HFCVD)制备出结构精细的金刚石微齿轮,其齿顶圆直径约1.55 mm、齿轮厚度10μm.应用扫描电镜分别观察了ICP刻蚀的硅微齿轮模具及CVD金刚石微齿轮,表明齿轮微结构形貌精细,金刚石微齿轮较好地复制了硅微细结构;Raman光谱分析表明微齿轮的金刚石质量较高.此工艺可以实现金刚石薄膜的精细图形化,为面向微机械应用的金刚石器件的经济批量制备提供了一种途径.     

纳米金刚石薄膜的掺杂、表/界面调控及性能研究

本文综述了近年来国内外研究者在纳米金刚石薄膜的掺杂、导电性能、场发射性能和电化学性能等方面的工作,涉及化学气相沉积法制备n型纳米金刚石薄膜,离子注入掺杂纳米金刚石晶粒提高薄膜的n型导电性能,金属离子注入制备场发射性能良好的纳米金刚石薄膜,低剂量离子注入和晶粒表面氧终止态获得高迁移率n型电导,纳米金刚石/石墨烯复合结构的调控对其电学及电化学性能的影响,以及硼掺杂金刚石薄膜电极的微结构和电化学性能研究等。综合分析发现,晶粒掺杂和表界面协同调控可以提升薄膜的电学性能、场发射性能及电化学性能,为纳米金刚石薄膜在纳米电子器件、电化学电极等领域的应用提供了理论基础。     

界面对热沉用金刚石-Cu复合材料热导率的影响

用特殊粉末冶金技术制备了金刚石-Cu复合材料.用SEM、拉曼光谱、EDS分析了复合材料的界面状态,用激光闪光法测量复合材料常温下的热导率.结果表明:在最佳工艺参数下,复合材料热导率可达570W·m-1·K-1;烧结时添加适量的钴可极大促进金刚石与铜之间的粘结;钴向金刚石中的扩散及其在铜熔液中的固溶,使金刚石与铜之间形成过渡层;过渡层可增强金刚石与铜基体过渡界面的相容性,降低界面热阻;金刚石骨架的形成有助于获得超高热导率.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

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...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

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.     

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.     

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.     

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.     

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.