大尺寸电阻加热式碳化硅晶体生长热场设计与优化

大尺寸低缺陷碳化硅(SiC)单晶体是功率器件和射频(RF)器件的重要基础材料,物理气相传输(physical vapor transport, PVT)法是目前生长大尺寸SiC单晶体的主要方法。获得大尺寸高品质晶体的核心是通过调节组分、温度、压力实现气相组分在晶体生长界面均匀定向结晶,同时尽可能减小晶体的热应力。本文对电阻加热式8英寸(1英寸=2.54 cm)碳化硅大尺寸晶体生长系统展开热场设计研究。首先建立描述碳化硅原料受热分解热质输运及其多孔结构演变、系统热输运的物理和数学模型,进而使用数值模拟方法研究加热器位置、加热器功率和辐射孔径对温度分布的影响及其规律,并优化热场结构。数值模拟结果显示,通过优化散热孔形状、保温棉的结构等设计参数,电阻加热式大尺寸晶体生长系统在晶锭厚度变化、多孔介质原料消耗的情况下均能达到较低的晶体横向温度梯度和较高的纵向温度梯度。     

FeS2多晶薄膜电子结构的实验研究

用磁控溅射方法制各纯Fe薄膜,并硫化合成FeS2.采用同步辐射X射线近边吸收谱与X射线光电子能谱研究了薄膜的电子结构.结果表明,合成的FeS2薄膜,在费米能级附近,有较强的Fe 3d态密度存在,同时,在价带谱中2-10eV处有强度较大的S 3p态密度存在;Fe的3d轨道在八面体配位场作用下分别为t2g和eg轨道,实验中由Fe的吸收谱计算得到两分裂能级之差为2.1eV;实验测得FeS2价带结构中导带宽度约为2.4eV,导带上方仍存在第二能隙,其宽度约为2.8eV.     

Synthesis, Crystal Structure, Fluorescent and Thermal Properties of Sodium Tridecafluorodizirconate Na_5Zr_2F_(13) Compound

1 INTRODUCTION Considerable research effort on the heavy metal fluoride glasses like barium, zirconium fluoride and a series of rare-earth fluorozirconate compounds du- ring the last two decades was initiated by the broad optical transmission window of these glasses and thereby the potential for ultralow-loss optical fi- bers[1~10]. The fluorozirconate of alkali metals was first reported in 1938[11], and most of the sodium and potassium fluorozirconates were reported amongthe 1940s and 19…     

Theoretical Studies on the Si（001）-SiO2 Interface Structure

1 INTRODUCTION Silicon and its alloy have been widely applied in such fields as electronic industry, high-temperature structural ceramics, etc. In addition, the researches on silicon and its relevant materials greatly promote the rapid development of modern optics and infor- mation technology. Therefore, more and more at- tention is focused on the structure of silicon, oxide of silicon and the interfaces between silicon and metal or nonmetal. As an ideal passive film on the Si surface, S…     

Synthesis, Crystal Structure and Electrochemical Properties of a Novel Phenothiazine Derivative

A new compound 1,1‘-bis(3-pyridyl)-propylene(3,7-diformyl-N-ethylphenothiazinyl)ketone (C30H23N3O2S, Mr = 489.4) has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction method. The crystal is of orthorhombic, space group Ima2 with a = 27.491 (5), b = 11.942(2), c = 7.389(2) A, V = 2425.8(7) A^3, Z = 8, Dc =1.340 g/cm^3,μ = 0,167 mm ^1, F(000) = 1024, the final R = 0.0363 and wR = 0.0869 for 2054 unique reflections with Rint = 0.0254. The structural determination shows that the molecule assumes a butterfly configuration with nearly planar wings. In addition, the electrochemical study indicates that there is a high electronic delocalization in the molecule.     

Hydrothermal Synthesis and Crystal Structure of a Novel Isophthalate-bridged Copper(II) Polymer with Two-dimensional Network Structure: [Cu_2(phen)(ipt)_2]_(2n)·nH_2O (ipt = isophthalate, phen = 1,10-phenanthroline)

1 INTRODUCTION donor due to the presence of the protonated carboxyl group; (d) it can form short bridges via one car- Coordination polymers are of great interest due to boxylato end or long bridges via the benzene ring[7]. their physical properties and potential applications in We believe that coordination functionality of isoph- functional materials[1~3]. Aromatic polycarboxylic acids thalate can lead to interesting structures. In this com- such as 1,2,4,5-benzenetetracarboxylic acid[4],…     

室温离子液体FeCl3-BPC体系的研究

利用差示扫描量热法(DSC)建立了无水三氯化铁和氯化正丁基吡啶(BPC)二元体系相图. 依据相图, FeCl₃和BPC形成室温离子液体的窗口是x＝0.26～0.58; 室温离子液体的深度是80 ℃. 利用UHF/6-31G^*对FeCl₃, FeCl₄^－, Fe₂Cl₇^－等配合物的几何结构、键长、能量和Raman频率进行优化, 从头算和Raman光谱证实了相图中FeCl₃摩尔分数x＝0.50处有稳定化合物存在, FeCl₄^－是主要阴离子; x＝0.67处, FeCl₄^－, Fe₂Cl₇^－是主要阴离子.     

新铌酸盐Ba5NdTi3Nb7O30的合成与介电性能

The New Niobate Ba₅NdTi₃Nb₇O₃₀ was synthesized by solid state reaction at 1250℃ for 48h. The crystal structure and dielectric properties of Ba₅NdTi₃Nb₇O₃₀ were determined by X-ray powder diffraction and dielectric measurements. The results show that Ba₅NdTi₃Nb₇O₃₀ belongs to ferroelectric phase of tetragonal tungsten bronze structure at room temperature with unit cell parameters: a=1.24424(4)nm, c=0.39476(2)nm, calculated density 5.719g·cm^-3. Ba₅NdTi₃Nb₇O₃₀ belongs to relaxor ferroelectrics. The phase transition temperature (T_c) of Ba₅NdTi₃Nb₇O₃₀ from ferroelectric to paraelectric is found to shift toward higher temperature side at higher fre-quency, and T_c is 90℃ at 1kHz. At room temperature, the dielectric constant (ε_r) and dielectric loss of Ba₅NdTi₃Nb₇O₃₀ decrease with the increase of frequency, and Ba₅NdTi₃Nb₇O₃₀ ceramic have high dielectric constant 489 at 1kHz.