杂质和缺陷对SiC单晶导热性能的影响

目前关于SiC单晶室温的导热性能,以及导热特性随温度的变化方面的研究报道还存在较大的差异,有关SiC单晶热导率的研究主要是沿c轴<0001>晶向或者垂直于c轴的某一晶向进行的,无法有效地解释热导率的各向异性.本文研究了4H-SiC和6H-SiC单晶<1100>,<1120>,<0001>三个不同晶向上热导率以及其随温度...     

Graphene/ZrO2复合陶瓷材料的热导性能研究

采用3Y-ZrO2粉体和石墨烯(Graphene)为原料,利用放电等离子体烧结技术(SPS),烧结制备了Graphene/ZrO2复合陶瓷材料.利用SEM、HRTEM、XRD、激光热导仪等研究了烧结温度和石墨烯含量对Graphene/ZrO2复合陶瓷材料的显微结构、物相和热传导性能的影响.研究结果表明,引入石墨烯不但可以抑制ZrO2晶粒的生长,而且对复合材料的热传导性有着显著的影响;相对于单相ZrO2陶瓷,随着石墨烯的引入, Graphene/ZrO2复合陶瓷材料扩散系数反而降低,其原因可以归结于三个方面:首先,石墨烯含量比较低(0.5~1.5wt;),其次,石墨烯与ZrO晶粒界面处产生的强声子散射作用导致热导下降,最后是Graphene/ZrO2复合陶瓷材料没有完全致密.     

氮化硼,碳化硅和锗纳米管的导热与拉伸力学特性研究

采用Tersoff势的分子动力学方法,分析了单壁氮化硼,碳化硅和锗纳米管的导热系数与轴向拉伸特性;进而根据模拟结果,讨论了直径、温度等因素对三种纳米管导热性的影响,以及三种纳米管之间导热性及拉伸性能的差异.研究结果表明:各单壁纳米管的导热系数均随温度的升高以及直径的增大而降低;温度相同时,氮化硼管的导热系数最大,而碳化硅和锗管的导热系数相当;三种纳米管中,锗管的抗变形与抗载荷能力最小,氮化硼管的抗变形能力最大,而氮化硼、碳化硅管的抗载荷能力相当.     

基于第一性原理的单层WS2热输运特性研究

二维WS₂是一种层状过渡金属硫化物,因其具有特殊的层状结构、可调带隙及稳定的物理化学性质而备受关注。结合玻尔兹曼输运方程(BTE)和密度泛函理论(DFT),利用第一性原理研究了单层WS₂声子的输运特性,分析了声子的谐性效应和非谐性效应对WS₂晶格热导率的影响机理,计算了其声子的临界平均自由程,提出通过调整阻断频率的方法来调控WS₂的晶格热导率。研究结果表明：单层WS₂在300 K时的本征晶格热导率为149.12 W/(m·K),且随温度的升高而降低;从各声子支对总热导率的贡献来看,声学声子支起主要作用,特别是纵向声学(longitudinal acoustic, LA)声子支对单层WS₂热导率的贡献百分比最大(44.28%);单层WS₂声学声子支和光学声子支之间的较大带隙(声光学声子支之间无散射)导致其具有较高的晶格热导率。本文研究可为基于单层WS₂纳米电子器件的设计和改进提供借鉴和理论指导。     

Stabilization of color conversion process of various colors in glass production

A new color conversion process has been proposed for minimizing the glass defect occurring during the color conversion caused by the glass flow turbulence in glass melting furnace. Glass flow turbulence is caused by the variation of bottom furnace temperature and also due to the change of high temperature thermal conductivity of glasses. Iron oxide was examined as an additive to control the high temperature conductivity of glasses. The effect of iron oxide on the high temperature thermal conductivity was examined. Based on these results, optimum content of iron oxide needed to keep the high temperature conductivity constant between the glasses of different colors was determined. Finally color coordinate of glasses which contained estimated optimum iron oxide content was also examined to check if it can be used as a panel of cathode ray tube.     

Investigation of the Thermal Conductivity Terbium Gallium and Terbium Scandium Aluminum Garnet Crystals

The thermal conductivity of terbium gallium and terbium scandium aluminum garnet crystals has been studied by the method of steady-state longitudinal heat flow in the temperature range of 50?300 K. The effect of the impurity composition of terbium gallium garnet crystals and the formula composition of terbium scandium aluminum garnet crystals on their thermal conductivity is shown.

     

Investigations of the crystal growth of PbMoO4 by the Czochralski method

The thermal conditions at the liquid/solid interface are characterized by temperature measurements in the melt and on the growing crystal with 〈001〉-seed orientation. The thermal boundary layer was determined, from which the relation of effective thermal conductivity of the liquid and solid phase was found to be λ_l,eff/λ_s,eff = 0.25. The liquid/solid interface is extremly convex towards the melt and has a conical shape. When the crystal diameter reaches a certain value the cone was truncated with the formation of a facet in the centre. This typical interface shape is mainly the result of a difference between the effective thermal conductivity of melt and crystal.     

SiC/Al复合材料的热导率研究

用无压浸渗法制备了高导热的SiC/Al电子封装材料.采用光学显微镜、X射线衍射仪、扫描电镜和激光热导仪对复合材料导热率、晶体结构和微观形貌进行了分析,研究了SiC颗粒大小、形状、体积分数、基体中Mg的含量和预氧化等参数对SiC/Al复合材料的导热率的影响.结果表明,选择适当的原料参数和工艺参数可制得导热率高达172.27 W/(m·k)的SiC/Al复合材料,满足电子封装材料的要求.     

坩埚下降法中各向热异性坩埚热场的数值模拟

本文对不同坩埚热物性组合时计算得到的结果进行了比较.对各向异性坩埚而言,纵向导热系数应该优先选择较小的材料;也可选择具有与晶体和熔体的导热系数相当导热系数的材料.横向导热系数则越大越有利于晶体生长.复合坩埚两种坩埚材料的导热系数最好不要相差太大.     

高功率MPCVD金刚石膜透波窗口材料制备研究

使用自行研制的椭球谐振腔式MPCVD装置,以H2-CH4为气源,在沉积功率8 kW条件下,对大面积金刚石膜透波窗口材料进行了制备研究.分别使用扫描电镜、Raman、分光光谱仪、热导率测试仪和空腔谐振法对金刚石膜的表面形貌、品质、光透过率、热导率和微波复介电常数等进行了表征及测试.实验结果表明,使用自行研制的椭球谐振腔式MPCVD装置,能够满足较高功率下高品质金刚石膜的快速沉积;抛光后的自支撑金刚石膜具有高的光学透过率和热导率,在23 ～ 36 GHz频率范围内微波介电损耗小于1×10-4,有着良好的微波介电性能,是较为理想的透波窗口材料.     

Thermal conductivity and specific heat of tellerium-based chalcogenide glasses

The specific heat and thermal conductivity of tellerium-based chalcogenide glasses are reported, together with their glass transition and synthesizing temperatures. The thermal conductivity has been measured in the temperature range between 100 and 500 K while the specific heat was determined at temperatures between 373 and 600 K. Below the glass transition temperature, both physical parameters were observed to be temperature independent.     

Bas晶体生长研究进展

立方砷化硼(BAs)为间接带隙、闪锌矿结构的Ⅲ-Ⅴ族化合物半导体材料.理论分析预测BAs具有仅次于金刚石的超高热导率,在电子器件散热领域表现出广阔应用前景,成为当前的研究热点.近年来立方BAs单晶材料的制备取得突破性进展,采用化学气相传输法(CVT)合成了毫米尺寸的高质量单晶,室温下热导率高达1300 W·m-1·K-...     

Statistical considerations on electronic behavior of the gap states in amorphous semiconductors

The equilibrium distribution functions of the gap states taking into account the effective intrasite electronic correlation energy have been employed to discuss the electronic behaviors of amorphous semiconductors, especially to interpret the temperature dependence of dc and ac conductivity and also the effect of foreign impurity atoms on the conductivity in chalcogenide glasses. The dc conductivity of thermal activation type has been explained without assuming a negligible density of states near the Fermi level, and the gradual decrease in activation energy of conductivity with increasing impurity concentration, even in melt-quenched chalcogenide glasses, has been deduced.     

金刚石衬底上GaN HEMT沟道温度建模:各向异性且非均匀热导率的影响

为了改善GaN HEMT的自热效应,集成高热导率的金刚石衬底有助于增强器件有源区的热量耗散。然而,化学气相淀积(CVD)生长的多晶金刚石(PCD)具有柱状晶粒结构,导致了各向异性的材料热导率,且其热导率值与生长厚度有关。为此,通过建模金刚石生长过程中晶粒尺寸的演变过程,计算了金刚石沿面内和截面方向的热导率。基于该PCD热导率模型,利用计入材料非线性热导率的GaN器件热阻解析模型,计算得到了GaN HEMT沟道温度的波动范围,并分析了其与器件结构(栅长、栅宽、栅间距、衬底厚度)和功耗的依赖关系。最后,通过与有限元(FEM)仿真结果对比,分区域提取了GaN HEMT器件中PCD衬底的有效热导率,分别为260~310 W/(m·K)和1 250~1 450 W/(m·K)。本文的计算为预测金刚石衬底上GaN HEMT器件的沟道温度提供了快速、有效的方法。     

A molecular dynamics study of the thermal conductivity of nanoporous silica aerogel,obtained through negative pressure rupturing

In this study, classical molecular dynamics with the well-known van Beest, Kramer and van Santen potential are used for the first time to investigate the solid thermal conductivity of silica aerogel. Aerogel samples at various densities are obtained through negative pressure rupturing of dense silica samples, and reverse non-equilibrium molecular dynamics is employed to determine the thermal conductivity at each density. Results indicate that a power-law fit of the thermal conductivity obtained varies almost linearly with density, where decreasing density and increasing porosity led to an almost linear decrease in thermal conductivity. This is reflective of the trend observed in experimental bulk sintered silica aerogel. The results also showed that the thermal conductivity is of the same order of magnitude as bulk sintered aerogel. The power-law fit of the results also accurately reflected the variation found in bulk sintered aerogel.     

Thermal conductivity of FeS2 pyrite crystals in the temperature range 50–300 K

The thermal conductivity of two single-crystal samples of pyrite FeS₂ are investigated by the method of stationary longitudinal heat flux in the temperature range 50–300 K. The low electrical conductivity of the crystals with a small impurity content causes an identical value of experimental lattice thermal conductivity. The temperature dependence of the phonon mean free path is established.     

Bridgman法晶体生长的热物性各向同性坩埚的选择

本文对不同坩埚热物性组合时计算得到的结果进行了比较.对各向同性坩埚而言,应该优先选择具有与晶体和熔体的导热系数相当导热系数的材料,也可选择导热系数较大的材料.在强度允许的情况下,减小坩埚壁厚对晶体生长有利.     

Thermal properties of vitreous silica with He impurities

The specific heat and thermal conductivity of vitreous silica (Suprasil W) doped with He at 420°C and 200 bar has been measured at low temperatures (0.5 K to 8 K). While with respect to an undoped sample the specific heat shows an excess contribution which varies as T^1.7, no effect of doping on the thermal conductivity is observed. This shows that the coupling to phonons of the excitations introduced by He doping is weak compared to that of intrinsic low energy excitations common to glasses. The excess specific heat can be attributed to excitations of He atoms in cavities.     

Surface Conductivity of Bi,Ga, In,and Sb Nanocrystals Condensed on Glassy Carbon Substrates

Crystallography Reports - The conductivity of Bi, Ga, In, and Sb nanocrystals deposited onto glassy carbon substrates by thermal evaporation at effect of laser irradiation at room temperature has...     

用于晶体生长的氮化铝保温材料的研究

在不添加任何添加剂的情况下,采用氮化铝粉体作高温气相法生长氮化铝晶体的保温材料.实验结果表明:氮化铝保温材料具有耐高温、对钨坩埚材料没有损伤、使用寿命长、不易在晶体中引入杂质等优点,是一种优良的高温保温材料.与目前常用的石墨保温材料相比较,氮化铝存在热导率相对较高、在高温过程中会少量升华污染炉腔等缺点,在使用中要采取一定的对策,以消除其不利影响.