氨气流量对富硅SiNx薄膜结构及其光学特性的影响

采用等离子体增强化学气相沉积技术,以NH3、SiH4和N2为反应气体制备富硅-氮化硅薄膜.在优化了其它沉积参数条件下,研究氨气流量对富硅-氮化硅薄膜的结构和光学性质的影响.利用傅立叶变换红外光谱、紫外可见光谱和X射线衍射谱分析了薄膜的键合情况、带隙结构.结果表明,随着NH3流量的增大,薄膜中的Si-N键和N-H键增强,Si-H键减小并向高波数方向移动,薄膜逐渐由非晶SiNx相向小晶粒Si3 N4相转变.同时随着NH3流量的增大,薄膜的光学带隙逐渐展宽,微观结构的有序度降低.XRD图谱分析表明薄膜内的平均晶粒尺寸也随着氨气流量的增加而在逐渐增大.结合以上结果分析,适当增加NH3流量有助于薄膜由非晶SiNx向包含小晶粒的Si3 N4转变.     

Cu掺杂硅量子点的电子结构和光学性质

采用基于密度泛函理论的第一性原理的方法,对Cu掺杂H钝化硅量子点的形成能、态密度、磁性和光学性质进行了计算,考虑了Cu占据硅量子点替代和间隙的不同位置.结果表明:Cu趋向占据硅量子点表面的六角形间隙位置.Cu掺杂硅量子点引入了杂质能级,带隙变窄.由于Cu的d态p态和Si的p态耦合,导致Cu替代掺杂硅量子点具有铁磁性,且在低能区出现了一个较强的吸收峰.     

衬底温度对氢化非晶硅薄膜特性的影响

采用等离子增强化学气相沉积(PECVD)系统,以乙硅烷和氢气为气源,石英玻璃和单晶硅片为衬底制备了氢化非晶硅(a-Si∶ H)薄膜.采用扫描电子显微镜、X-射线衍射仪、台阶仪、紫外可见分光光度计、傅里叶变换红外光谱仪和电子能谱仪等分别表征了a-Si∶H薄膜的表面形貌、结晶特性、沉积速率,光学带隙,键合结构和Si化合态等特性.结果表明:随着衬底温度的增加,a-Si∶H薄膜表面的颗粒尺寸减小,均匀性增加,沉积速率则逐渐降低;衬底温度从80℃增加到130℃时,光学带隙显著增加,而在130℃至230℃范围内,光学带隙基本不随衬底温度变化;以SiH键对应的伸缩振动的相对峰强度逐渐增加,而以SiH2或(SiH2)n键对应的伸缩振动的相对强度逐渐减小;a-Si∶H薄膜中Si0+态的相对含量增加.因此,衬底温度大于130℃有利于制备优质a-Si∶H薄膜,230℃是沉积a-Si∶H薄膜的最佳衬底温度.     

氢钝化对低温沉积nc-SiOx/SiO2多层薄膜发光特性影响机制研究

采用等离子体增强化学气相沉积技术实现了nc-SiOx/SiO2多层结构薄膜在220℃的低温沉积,并对其450℃N2+ H2形成气体退火前后的微结构及其发光特性进行了研究.结果表明,直接沉积的纳米硅多层薄膜未观察到较明显的室温发光,而形成气体退火后样品出现峰值位于780 nm附近较强的光致发光,归因于活性氢能有效钝化纳米硅表面悬键,提高了材料的发光强度.结合瞬态发光谱分析,采用量子限制-发光中心模型可以合理解释纳米硅多层结构的发光特性.     

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.     

H2流量对直流磁控溅射制备a-Si∶H薄膜微观结构及光学性能的影响

采用直流磁控溅射法在不同H2流量的条件下制备了a-Si∶H薄膜,研究了H2流量对薄膜微观结构以及光学性能的影响.结果表明:随H2流量的增加,a-Si∶H薄膜的沉积速率有所下降,但其原子排列的有序度上升,并出现了细小的纳米晶粒,使得薄膜的无序结构得到了一定改善.同时,薄膜的光学性能也表现出明显变化,其中透过率持续上升,而光学带隙则呈现出先增大后减小的趋势.最终得到制备a-Si∶H薄膜的最优H2流量为15 sccm.     

B掺杂对平面结构MOCVD-ZnO薄膜性能的影响

本文研究了B2H6掺杂流量(B掺杂)对平面结构MOCVD-ZnO薄膜的微观结构和光电性能影响.XRD、SEM和AFM测试的研究结果表明,玻璃衬底上制备的ZnO薄膜具有(002)峰择优取向的平面结构,B掺杂使薄膜的球状晶粒尺寸变小,10 sccm流量时晶粒尺寸为～15 nm.ZnO:B薄膜的最小电阻率为5.7×10-3Ω·cm.生长的ZnO薄膜(厚度d=1150 nm)在400～900 nm范围的透过率为82;～97;,且随着B2H6掺杂流量增大,光学吸收边呈现蓝移(即光学带隙Eg展宽)现象.     

衬底温度对含硅量子点的SiCx薄膜结构及其光学特性的影响

采用磁控共溅射沉积法,以Si靶和SiC靶为靶材,单晶Si(100)和石英为衬底,在不同衬底温度下沉积了富硅SiCx薄膜.在氮气氛下于1100 ℃退火,得到包含硅量子点的SiCx薄膜.采用傅立叶变换红外吸收光谱、拉曼光谱、掠入射X射线衍射和吸收谱对退火后的SiCx薄膜进行了表征.结果表明:当衬底温度从室温(25℃)升至300℃时,薄膜的晶化率增至71.3;,硅量子点尺寸增至8.9 nm,而光学带隙则减至2.42 eV;随着衬底温度进一步升高,薄膜的晶化率降至63.1;,硅量子点尺寸减小至7.3 nm,而光学带隙却增加至2.57 eV;当衬底温度从室温(25℃)升至400℃时,薄膜的吸收系数呈先增大后减小趋势.在本实验条件下,最佳衬底温度为300℃.     

基底温度对c-Si(100)面生长a-Si∶H薄膜结构特性影响的分子动力学模拟研究

运用分子动力学方法模拟了不同基底温度下在硅(100)表面沉积生长氢化非晶硅薄膜的过程.Si-H体系的原子间相互作用采用Murty-Tersoff势计算.结果得到:随着基底温度的升高,a-Si∶H薄膜表面粗糙度降低,内部致密度提高,H原子、Si-H键和悬挂键密度均减少.进一步分析发现,粗糙度和致密度随基底温度变化的原因是基底温度升高增大了表面原子的扩散能力;而H原子和Si-H键等含量随基底温度升高而下降是因为高温下Si-H弱键更易断键导致.悬挂键密度随基底温度升高而降低则主要是由于内部原子的晶化率增大引起.     

反应溅射法制备高透明导电ZnO薄膜的研究

利用Zn/ZnO复合靶材,通过射频磁控溅射技术,在衬底温度为150℃时分别在Ar+O2和Ar+H2的混合气氛中制备ZnO薄膜,通过干涉显微镜、XRD、Hall效应测试仪、紫外-可见分光光度计研究了O2和H2流量对薄膜结构及透明导电性能的影响.结果发现,薄膜厚度随O2流量增加而明显增加而随H2流量增加呈下降趋势.只有通入合适流量的O2或H2,薄膜才能保持(002)择优取向、较高的结晶度以及较小的压应力,同时在薄膜中形成高浓度Vo和/或Hi等缺陷,因此有效降低ZnO薄膜的电阻率,并保持高的透光率,从而改善ZnO薄膜透明导电性能.当前研究中,当O2和H2流量分别为0.4 sccm和2.0 sccm时,得到的最低电阻率分别为6.33×10-3和2.51×10-3Ω·cm,平均透光率均大约为81.5;,相应的最高品质因子分别为1.04×10-3和1.29×10-3 Ω-1.     

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.