蓝宝石单晶窗口材料空间粒子辐照效应研究

蓝宝石单晶(α-Al2O3)窗口材料服役于空间环境中将不可避免地受到各种不同射线及离子流的辐照作用,影响其使用性能.本文研究了蓝宝石单晶经不同剂量质子流、电子流以及综合流辐照后其表面粗糙度、透过率以及面形精度等光学性能和结构的变化.实验表明空间粒子辐照使蓝宝石表面粗糙度增大且具有剂量效应,其中综合流对表面粗糙度影响最大,质子次之,电子影响最小;UV-Vis-VIR及FTIR测试实验表明空间粒子辐照使蓝宝石透过率下降,在紫外波段下降最明显,且在不同波段范围内不同辐照粒子种类对蓝宝石单晶透过率的影响程度也不同;粒子辐照对面形精度的影响不明显.     

以乙醇为氧源生长ZnO薄膜中温度对光谱影响的研究

本文探索了以乙醇为氧源通过MOCVD方法生长ZnO薄膜的方法,着重研究了该实验中生长温度对薄膜发光光谱的影响.我们分别在350℃、370℃、380℃、400℃和420℃温度下生长了ZnO薄膜,并对其发光光谱进行了研究.结果表明适当地提高生长温度可以使近带边发光峰蓝移,但温度过高,使得峰位红移并展宽.在380℃的生长条件下得到了较好的光谱.370℃条件下还出现了474nm的发光峰,经退火后此峰消失.     

元素级ZnS高温性能研究

作为一种重要的中长波红外窗口材料,元素级ZnS具有良好的光学性能和力学性能。目前,高超声速飞行器的发展迫切需要开展元素级ZnS红外窗口的高温性能研究。本文研究了不同温度下元素级ZnS的高温性能,结果表明,元素级ZnS的辐射率随着波长增大而增加,且同一波长下随温度的升高而增加,500℃时,在3～5.5μm平均法向光谱辐射率小于0.05,7～10.5μm平均法向光谱辐射率小于0.10。在2～9.5μm,温度对透过率影响并不大,在9.5μm后,随着温度的升高,透过率明显降低。折射率、热光系数和线膨胀系数随温度的升高而增大。温度对弯曲强度几乎无影响,弹性模量随温度升高而降低,800℃时的弹性模量与室温下的相比下降约30%。     

高效大功率LED用蓝宝石图形衬底的制备

首先在蓝宝石衬底上旋涂PMMA/copolymer双层胶,然后再进行电子束光刻处理,随后溅射铝膜,并结合剥离技术,从而制备图形化金属铝膜;最后再采用两步热处理法,使图形铝膜发生固相外延反应.在此过程中,侧重于电子束光刻和高温热处理的工艺优化研究.SEM测试结果表明,图形化铝膜在450℃低温氧化热处理24h后,其图形形貌没有发生明显改变;在温度低于1200℃的高温热处理1h后,图形仍然存在.HRXRD分析表明,图形化铝膜在450℃低温热处理24h后再在1000℃高温热处理1h,可在蓝宝石衬底上形成氧化铝外延薄膜;并且相比于基片,氧化铝外延薄膜的结晶质量还有所提高.本方法成功实现了高效大功率用LED蓝宝石图形衬底的制备.     

湿法腐蚀制备蓝宝石图形衬底的研究

利用湿法腐蚀方法,制备出图形化蓝宝石衬底(PSS).在相同的腐蚀时间下,研究腐蚀液温度对腐蚀蓝宝石表面形貌和外延后GaN材料的影响.扫描电镜(SEM)测试结果表明:随着腐蚀液温度的增加,图形的深度增加.腐蚀后图形阵列排布整齐,所有图形都方向一致,这与蓝宝石本身晶体性质有关.腐蚀液温度对外延后GaN的影响也比较大,随着腐蚀液温度的增加,(002)半峰宽逐渐增加,光致发光谱(PL)发光强度逐渐增加.管芯结果表明,LED管芯的光强也逐渐增加.     

化学浴沉积法制备ZnS薄膜的结构及可见-近红外光谱特性研究

采用化学水浴法,以ZnSO4、柠檬酸钠、NH3·H2O、SC(NH2)2为反应物,在玻璃衬底上制备了ZnS薄膜,采用XRD、SEM、分光光度计、台阶仪等手段研究了水浴温度、沉积时间、pH值等条件对ZnS薄膜的晶体结构、表面形貌、光学性能的影响.结果表明,ZnS薄膜经退火后出现明显特征衍射峰,为闪锌矿结构,可见光范围内平均透过率均大于80;.经过工艺优化,在水浴温度为80℃、沉积时间为1h、pH=10条件下沉积的ZnS薄膜表面均匀致密,可见光范围内平均透过率为89.6;,光学带隙为3.82 eV,适合做铜铟镓硒和铜锌锡硫薄膜太阳电池的缓冲层.     

利用辐射加热炉进行蓝宝石及其它高温氧化物的热物理和光学性能的研究

本文描述了一种特大的实验装置-辐射加热炉,获得了蓝宝石和其它高温氧化物在固相、液相时的光学、热学和物理性能.该装置和相应的技术使得在高于3500K温度下研究这些材料的粘度、熔点、热导率、发射率和吸收系数成为可能,并以此得到了高温下蓝宝石的分子热传导系数,以及不同降温速率下蓝宝石的过冷情况.此外,介绍了一种复合氧化物材料MgO-Al2O3-HfO在宽波段范围内的反射率.本文所给出的数据对于从事晶体和高温陶瓷方面研究的专家学者将很有用处.     

热处理温度对Na2O-K2O-ZnO-SiO2微晶玻璃析晶行为和性能的影响

以P2O5为形核剂制备了Na2O-K2O-ZnO-SiO2 (NKZS)透明微晶玻璃,研究了热处理温度对NKZS微晶玻璃的析晶行为、可见-近红外透过率和抗弯强度的影响.结果表明,在NKZS玻璃中,表面析晶和体积析晶同时存在.热处理温度低于750℃时,NKZS微晶玻璃表面析晶较显著,抗弯强度随热处理温度的升高而明显增强,可见-近红外透过率随热处理温度变化较小;温度高于750 ℃时,主要为体积析晶,其力学性能和可见-近红外透过率随热处理温度升高急剧降低.     

反式二苯乙烯(TSB)的溶液法晶体生长

本文观测了TSB在苯甲醚等有机溶剂中的结晶习性,测定了相应的溶解度曲线和亚稳区.采用溶液降温法在50~30 ℃的温度范围内进行晶体生长,获得透明度好的厘米级TSB晶体.通过对所得晶体进行X射线粉末衍射、紫外-近红外透过光谱、吸收光谱和紫外荧光光谱等测试,表明:本实验使用的不同生长溶剂对TSB晶体结构不会产生影响,所得晶体在410~1000 nm波长范围内透过率不低于80;,而在200~360 nm范围内有吸收,在波长为272.8 nm的激发光作用下,得到较强的荧光峰,峰位为386 nm.     

溶胶-凝胶法制备ZnO薄膜及其微结构特性研究

采用溶胶-凝胶法(Sol-Gel)制备氧化锌(ZnO)薄膜,研究镀膜层数和退火温度对ZnO薄膜晶体结构、光谱性质及表面形貌的影响.X射线衍射谱测试表明,退火温度为600℃、镀膜层数为10层时制备样品的晶粒尺寸最大,结晶度最好.紫外-可见透过谱发现,样品退火后其透过率曲线变得陡直,光学带隙随退火温度升高而逐渐减小.光致发光谱测试显示,ZnO薄膜的发光谱包含388 nm和394 nm附近的两个主要发光峰,分别对应于本征发射和缺陷发射,其强度随退火温度升高呈现相反的变化.原子力显微照片则显示了随退火温度的升高制备样品表面晶粒的分布趋于均匀而致密.     

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.     

Luminescence of crystals of divalent tungstates

Crystals of divalent tungstates are characterized by two main luminescence spectral ranges: a short-wavelength (blue) luminescence band in the range 390–420 nm and a group (often two groups) of longer wavelength (green) bands in the range 480–520 nm. For crystals of calcium, strontium, barium, cadmium, magnesium, zinc, and lead tungstates, it is shown that the wavelength corresponding to the maximum of the blue luminescence band (λ_max) correlates with the melting temperature (T_m) of these compounds. The position of the blue luminescence band is the same (in the range 510–530 nm) for crystals with different divalent cations. Annealing in vacuum and electron irradiation decrease the intensity of both blue and green luminescence bands but do not change the ratio of their maximum intensities. This circumstance suggests that vacancies serve as luminescence quenchers to a greater extent rather than facilitate the formation of emission centers responsible for a particular luminescence band.