温度梯度溶液生长法制备x=0.2的Cd1-xZnxTe晶体及性能研究

利用温度梯度溶液生长法(TGSG)在较低生长温度下制备了掺Al和掺In的x=0.2的Cd1-xZnxTe晶体,晶体起始生长温度约为1223K,温度梯度为20～30K/cm,坩埚的下降速度为1mm/h。采用红外显微镜、傅里叶红外光谱仪、扫描电镜能谱仪(SEM/EDS)和I-V测试分别研究了晶体中的Te夹杂相、红外透过率、Zn组分分布和电阻率。结果显示CdZnTe晶锭初始生长区、稳定生长区的Te夹杂相密度分别为8.3×103、9.2×103/cm-2,比垂直布里奇曼法生长的晶体低约1个数量级,红外透过率分别为61%、60%。Al掺杂CdZnTe晶体的电阻率为1.05×106Ω.cm,而In掺杂CdZnTe晶体的电阻率为7.85×109Ω.cm。晶锭初始生长区和稳定生长区的Zn组分径向分布均匀。     

ACRT技术对大尺寸ZnTe晶体溶液法制备及其性能影响

太赫兹(Terahertz,THz)技术在工业无损检测、科学研究和军事领域发挥着越来越重要的作用。作为太赫兹产生和探测最常用的电光晶体材料,ZnTe晶体在生长中依然面临众多挑战。为了制备大尺寸、均匀性好、高性能的ZnTe单晶,本研究在温度梯度溶液法生长ZnTe晶体过程中引入坩埚旋转加速技术,制备具有高结晶质量的ZnTe晶体。模拟计算得到不同坩埚旋转速度下生长界面处对流场和溶质分布,研究了坩埚旋转对晶体生长过程中的固液界面稳定性和晶体内Te夹杂分布的影响规律,证明坩埚旋转加速技术可以有效地促进熔体流动,改善溶质传质能力,稳定溶液法晶体生长的固液界面,不仅避免出现尾部混合相区,也减少了ZnTe晶体内Te夹杂相的数量并减小其尺寸。通过进一步优化坩埚旋转参数,制备出具有较高结晶质量的大尺寸ZnTe晶体(?60 mm)。同时,得益于晶体良好的均匀性,晶体对太赫兹的高响应区域超过90%,边缘效应小,满足太赫兹成像要求。研究表明,引入坩埚旋转加速技术为制备大尺寸ZnTe基电光晶体提供了新的思路。     

Cd/Zn气氛退火过程中CdZnTe晶体内Te夹杂的迁移研究

通过红外透过成像研究了Cd/Zn气氛退火过程中Cd0.9Zn0.1Te∶In晶体内Te夹杂的密度及尺寸分布的演变。结果发现,Cd/Zn气氛退火前,晶体中的Te夹杂密度分布比较均匀;退火后,晶体高温端近表面区域的Te夹杂密度较退火前提高了1个数量级,而晶体内部的Te夹杂密度则较退火前降低了1个数量级,且其密度沿温度梯度方向逐渐增加。退火前,晶体表面和内部的Te夹杂的直径主要分布在1~25μm;退火后,在晶体表面,直径45μm的Te夹杂密度显著增大;而在晶体内部,直径5μm和25μm的Te夹杂密度显著增大。导致这些现象的原因是退火过程中,Te夹杂沿着温度梯度方向不断向晶体表面迁移,在迁移过程中尺寸相近的Te夹杂通过合并长大,尺寸相差较大的Te夹杂则以Ostwald熟化方式长大,并使小尺寸的Te夹杂更小。但由于熟化不充分,在Ostwald熟化长大过程中留下了很多尺寸5μm的Te夹杂颗粒。     

坩埚中自由空间量对Bridgman法生长的CdZnTe晶体缺陷的影响

采用Bridgman法生长CdZnTe晶体.分别采用红外透过显微镜和正电子湮灭寿命谱仪研究了CdZnTe晶体中的Te夹杂相、Cd空位等缺陷与坩埚中的自由空间量大小的关系. 结果表明: 随着坩埚自由空间量的减小, 晶体中Te夹杂相密度从6.67×10⁴/cm²降低到2.36×10³/cm², 且Te夹杂相尺寸减小; 晶体的正电子平均寿命值随着坩埚自由空间量的减小从325.4 ps降低到323.4 ps, 表明晶体的Cd空位浓度及微结构缺陷减少; 晶体的红外透过率和电阻率则随着坩埚自由空间量的减小大幅提高, 进一步表明坩埚中自由空间量的减小能够有效地降低晶体中的缺陷浓度.     

Cd0.9Mn0.1Te晶体生长及其缺陷分析

采用Bridgman法和ACRT-B法生长了两根Cd0.9Mn0.1Te晶锭(简称CMT-B和CMT-A).采用光学金相显微镜和扫描电镜研究了这两种方法生长的晶体中出现的各种缺陷,并分析了其形成机理.采用JEOL-733电子探针测定了两根晶锭中Mn的分布.对比CMT-B和CMT-A两根晶锭,发现ACRT所产生的对流可提高Cd0.9Mn0.1Te晶体的结晶质量.     

溶剂熔区移动法生长Cd_(0.9)Zn_(0.1)Te晶体的工艺优化研究

为了解决Cd_(0.9)Zn_(0.1)Te(CZT)晶体生长温度高、单晶率低、成分不均匀等问题,采用溶剂熔区移动法(THM)在优化工艺参数下生长了掺In的CZT晶体,在优化晶体的生长温度、固液界面处的温度梯度、原位退火过程等生长条件后,生长出直径为45 mm的低Te夹杂浓度、高电阻率、高透过率、均匀的高质量CZT晶体。X射线衍射结果显示,晶体的结晶性较好、Zn成分轴向偏析小。红外透过光谱测试结果显示,晶体内部的杂质、缺陷水平相对较少,晶体整体的红外透过率在60%左右。紫外-可见光吸收光谱测试结果也进一步表明,晶体的均匀性良好。采用红外显微镜对晶体内部的Te夹杂形貌及其尺寸进行观察,结果表明Te夹杂的尺寸主要分布在0~10μm之间。采用直流稳态光电导技术测得电子的迁移率寿命积约为8×10~(-4) cm~2/V。     

Cd0.9Mn0.1Te晶体生长及其缺陷分析

采用Bridgman法和ACRT－B法生长了两根Cd0.9Mn0.1Te晶锭（简称CMT－B和CMT－A）。采用光学金相显微镜和扫描电镜研究了这两种方法生长的晶体中出现的各种缺陷,并分析了其形成机理。采用JEOL－733电子探针测定了两根晶锭中Mn的分布。对比CMT－B和CMT－A两根晶锭,发现ACRT所产生的对流可提高Cd0.9Mn0.1Te晶体的结晶质量。     

Bridgman法生长的MnxCd1-xIn2Te4晶体相形成规律和物理性能研究

采用Bridgman法生长了x为0.1,0.22和0.4的四元稀磁半导体化合物MnxCd1-xIn2Te4晶体.研究了三根晶体中相的形貌、结构、成分和Mn0.1Cd0.9In2Te4晶体中各组元沿轴向和径向的成分分布.晶体生长初始端的组织为α+β+β1,随着生长的进行,形成β相的单相区.在晶锭末端,形成In2Te3类面心立方结构化合物.组分x增大后,MnxCd1-xIn2Te4晶体的吸收边向短波方向移动,禁带宽度则线性增大.磁化率测量结果表明:晶体在高温区的x-1-T曲线服从居里-外斯定律,在低温区(<50K)则表现出顺磁增强现象.     

溶剂熔区移动法生长Cd0.9Zn0.1Te晶体的工艺优化研

为了解决Cd_0.9Zn_0.1Te(CZT)晶体生长温度高、单晶率低、成分不均匀等问题, 采用溶剂熔区移动法(THM)在优化工艺参数下生长了掺In的CZT晶体, 在优化晶体的生长温度、固液界面处的温度梯度、原位退火过程等生长条件后, 生长出直径为45 mm的低Te夹杂浓度、高电阻率、高透过率、均匀的高质量CZT晶体。 X射线衍射结果显示, 晶体的结晶性较好、Zn成分轴向偏析小。红外透过光谱测试结果显示, 晶体内部的杂质、缺陷水平相对较少, 晶体整体的红外透过率在60%左右。紫外-可见光吸收光谱测试结果也进一步表明, 晶体的均匀性良好。采用红外显微镜对晶体内部的Te夹杂形貌及其尺寸进行观察, 结果表明Te夹杂的尺寸主要分布在0~10 μm之间。采用直流稳态光电导技术测得电子的迁移率寿命积约为8×10^-4 cm²/V。     

温度梯度溶液法生长ZnTe晶体时生长界面的优化设计

为了优化用温度梯度溶液法(TGSG)生长ZnTe晶体时的生长界面,设计了一种由莫来石圆筒及其内部的圆柱形石墨芯组成的安瓿支撑结构。用有限元的方法数值模拟了这种支撑结构对生长过程中各种传输现象及生长界面形貌的影响。模拟结果显示,晶体生长开始时,溶液内存在上下两个顺时针方向的涡流。随后,靠近生长界面的涡流很快消失,远离生长界面的涡流逐渐缩小,并向溶液顶部移动。生长界面前的对流消失后,ZnTe溶质以扩散形式向生长界面传输。生长界面最开始为凸界面,待生长至晶锭总长度的1/3处时转为平直界面,之后转为凹界面。生长界面深度始终明显小于未采用本支撑结构时的生长界面,也没有出现生长界面的分段现象。这样的生长界面将有利于提高ZnTe晶体的单晶率及结晶质量。     

Mechanistic consideration of ZnTe microspheres formation in a PVP-contained polyol system via hot injection method

Zinc telluride (ZnTe) microspheres have been synthesized in a polyol system with adding various amount of poly(N-vinyl-2-pyrrolidone) (PVP, K-90) at 200 °C via a hot injection method. The smallest sized ZnTe microspheres obtained in this study had an average size of 634 nm through reaction for 48 h using 518 mg of PVP. A retrospective study was conducted to evaluate the formation process of ZnTe microspheres by conducting experiments from 0.2 h to 48 h. Nucleation and growth of ZnTe at the tips of Te rods in a PVP-contained polyol system were observed in sample reacted less than 1 h. More ZnTe microspheres and less Te rods were observed when the reaction was proceeded for longer time, suggesting that Te rods were the sacrificial template for the growth of ZnTe. Amount of PVP is the key factor of controlling dimensions of Te rods formed at the initial stage as well as the sizes of ZnTe microspheres by influencing the nucleation and growth rate of ZnTe. The obtained ZnTe microspheres at 48 h consisted of voids, which were originated by the detachment of ZnTe microspheres from Te rods after their growth.     

高温导热绝缘涂料

以环氧改性有机硅树脂为基体, 氮化硅、 氧化铝混合填料为导热粒子制备了导热绝缘涂料。研究了涂料力学性能、 热导率、 电绝缘性、 热稳定性等性能。结果表明: 在填料质量分数40％及较佳的氧化铝与氮化硅质量比时, 涂层拉伸强度为8.02MPa, 断裂延伸率为1.27％, 附着力达到572.2N · cm-2, 热导率高达1.25W · (m · K)-1, 介电常数5.7, 体、 表电阻率分别为3×1013Ω · cm与4.3×1013Ω, 可长期在200℃下使用。与不使用导热填料的环氧改性有机硅树脂涂层相比具有较高的传热能力。      

Effects of gradient heat treatment on Te-rich CdZnTe crystal

The gradient heat treatment was performed on Te-rich CZT crystal grown by the vertical Bridgman (VB) method, which was under the temperature of 1073 K and the temperature gradient of 2 K/mm and the velocity of 1.8 mm/h. IR transmission, IR microscope, I-V curves and glow discharge mass spectrometry (GDMS) revealed that Te inclusions moved towards the last-to-freeze region in CZT ingot, which proved that the gradient heat treatment has the possibility to purify the CZT ingot. Finally, after the gradient heat treatment, the resistivity of the CZT ingot was enhanced, and the IR transmittance was also improved.     

Cu/ABS复合导电梯度功能材料的制备和性能

借助HAAKE转矩流变仪,采用熔融共混法制备了一系列Cu粉含量不同的Cu/丙烯腈-丁二烯-苯乙烯共聚物(ABS)复合材料,采用多层叠压法制备了内部Cu粉含量逐渐变化的板状Cu/ABS复合导电梯度功能材料,并对其结构和性能进行了表征。结果表明,所制备导电梯度功能材料的性能与均质复合材料存在很大差异。电性能测试结果显示,随着Cu粉含量沿板材厚度方向的梯度增加,其导电性能发生逾渗转变,体积电阻率从一侧的1016Ω.cm降低到另一侧的105Ω.cm。弯曲性能测试表明,富含ABS树脂的一侧表现出较高的弯曲强度,仅比纯ABS的弯曲强度低6%;而富含填料的另一侧则表现出较高的模量,比纯ABS高约20%。实验证明,将导电复合材料做成梯度结构可以兼顾材料的导电性能和力学性能。     

Distribution of Te inclusions in a CdZnTe wafer and their effects on the electrical properties of fabricated devices

We quantified the size and concentration of Te inclusions along the lateral- and the growth-directions of a ∼6 mm-thick wafer cut axially along the center of a CdZnTe ingot. We fabricated devices, selecting samples from the center slice outward in both directions, and then tested their response to incident X-rays. We employed, in concert, an automated IR transmission microscopic system and a highly collimated synchrotron X-ray source that allowed us to acquire and correlate comprehensive information on Te inclusions and other defects to assess the material factors limiting the performance of CdZnTe detectors.     

Magnetocrystalline anisotropy of zinc-blende CrTe (001) surface: A first-principles study

By using the highly precise all-election full potential linearized augmented plane-wave method based on density functional theory within the generalized gradient approximation, we investigated magnetocrystalline anisotropy and magnetism of zinc-blende CrTe (001) surface. We observed that both of the Cr- and Te-terminated zinc-blende CrTe (001) surfaces maintain the half-metallicity by analyzing the density of states. The magnitudes of the calculated magnetic moments for the Cr(S) and Cr(S-1) atoms are calculated to be 3.92 and 3.16 μ_B for the Cr- and Te-terminated surfaces, respectively. The Te atoms show significantly induced negative spin polarizations of 0.13-0.30 μ_B. The spin orientations at the Te-terminated (Cr-terminated) surfaces were found to be in-plane (out-of-plane) regardless of its thickness. Since a Te-terminated surface is known as to be more stable than a Cr-terminated one, our result is consistent with an experiment which observed in-plane magnetic anisotropy at a CrTe (001) surface.     

Composition Distribution in the MnxCd1-xIn2Te4 Ingot Grown by ACRT-B Method

MnxCd1-xIn2Te4 (x=0.1) ingot was successfully grown by the modified Bridgman technique, which applied the accelerated crucible rotation technique (ACRT) in Bridgman process, or briefly ACRT-B. The growth interface profile shape and the composition distribution in the MnxCd1-xIn2Te4 (x=0.1) ingot were analyzed. Even though the stoichiometric composition was synthesized in the original ingot, the composition has been redistributed during the ACRT-B growth process. Mn and Cd contents decrease while In increases along the longitudinal axis. The partition ratios of solutes Mn, Cd and In at the growth interface are evaluated by a mathematical method based on the experimental data, which are found to be 1.286, 1.926 and 0.729 in α phase growth process, and 1.120, 1.055 and 0.985 in β phase growth process, respectively. In the radial direction,Mn and Cd contents increase while In decreases with the distance from the centerline of the ingot.     

气相生长碳纤维增强水泥基复合材料的制备及性能

研究了脱油沥青(De-oiled asphalt)基气相生长碳纤维(VGCFs)增强水泥基复合材料的制备方法及其性能。以脱油沥青作原料,采用化学气相沉积法(CVD)制备出气相生长碳纤维,以此纤维制备水泥基功能复合材料。结果表明:低含量VGCFs的碳纤维增强水泥基复合材料具有良好的抗压强度和导电性能,在VGCFs的掺量由0增至0.6 %范围内,随着VGCFs掺量的增加,碳纤维增强水泥基复合材料的电阻率下降,抗压强度提高。当VGCFs为0.4 %时,VGCFs水泥基复合材料电阻率降低2个数量级,从3.25 ×105 Ω·cm 降为1.49 ×103 Ω· cm ,抗压强度提高28.8 %,为最佳掺量。