高温超导衬底大尺寸LaAlO_3单晶体生长研究

铝酸镧(LaAlO3)单晶是超导研究领域使用最普遍的单晶体之一,详细介绍了采用下称重,CZ法(Czo-chralski)生长大尺寸(Φ80mm)LaAlO3单晶的工艺条件,并对影响晶体质量的主要因素进行了分析、讨论,给出了解决晶体质量问题的手段和有效途径。     

The study of the influence of uniaxial stress on impurity complexes in silicon

The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed γ –γ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.     

Improving the material quality of silicon ingots by aluminum gettering during crystal growth

We present a method for the purification of silicon ingots during the crystallization process that reduces significantly the width of the low charge carrier lifetime region at the ingot top. The back‐diffusion of impurities from the ingot top is suppressed by adding a small amount of pure aluminum into the silicon melt right at the end of the solidification. We study the aluminum gettering effect by instrumental neutron activation analysis (INAA) and Fe_i imaging. Furthermore, we present a model for aluminum gettering of Fe in the silicon ingot that is in agreement with literature data for aluminum gettering at lower temperature. The distribution of iron in the ingots with and without aluminum is fairly well predicted by a combination of this model with a model for Fe contamination from the crucible system. A simulation with varying Al content exhibits further potential for an increased yield of silicon wafers with high charge carrier lifetime. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

单晶合金激光熔凝过程中晶向对单晶完整性的影响

运用几何模型对单晶合金激光熔凝过程中激光扫描方向与[100]方向夹角ξ变化时熔池内的枝晶生长方向和速度进行了计算,研究了ξ增大时不同晶向区域的分布变化规律.发现随着ξ的增大, 0]区域增大,[010]区域减小,且熔池两边不同部分速度差别增强.根据速度变化规律,构造出了熔池不同部位的过冷区域变化图,说明了可能出现新晶粒的趋势变化,并与实验结果进行了比较,揭示了在晶向不同的交界区域产生新晶粒的内在机理. 关键词： 单晶合金 激光熔凝 晶向 组成过冷     

Localized bifurcations and defect instabilities in the convection of a nematic liquid crystal

The stationary and the time-dependent homogeneous ordered states in convection may both become unstable against localized perturbations. Defects are then created and they may contribute to the disorganization of the homogeneous state. We present an experimental study of defects in some homogeneous stationary structures as well as in the traveling-wave states of convection of a nematic liquid crystal. We show that the core of the defects is a germ of the unstable state and it can become unstable under the external stress. Then, either fully homogeneous states with the symmetry of the core, or complex disordered states can develop from the local instability of defects in processes quite similar to displacive transitions in solids. Some of the main features are qualitatively similar to numerical simulations of an appropriate Landau-Ginzburg equation.     

籽晶尺寸对宝石级金刚石单晶生长的影响

本文在国产六面顶压机上,在5.6 GPa, 1250—1450℃的高压高温条件下,分别选用边长0.8, 1.5和2.2 mm三种尺寸的籽晶,系统开展了Ib型宝石级金刚石单晶的生长研究.文中系统考察了籽晶尺寸对宝石级金刚石单晶生长的影响.首先,考察了籽晶尺寸变化对宝石级金刚石单晶裂晶问题带来的影响.研究得到了籽晶尺寸变大,裂晶出现概率增加的晶体生长规律.其次,在25 h的生长时间内,考察了上述三种尺寸籽晶生长金刚石单晶时,生长时间与单晶极限生长速度的关系.得到了选用大尺寸籽晶,可以提高优质单晶合成效率、降低合成成本的研究结论.借助扫描电子显微镜和光学显微镜,对三种尺寸籽晶生长金刚石单晶的表面形貌进行了标定.最后,傅里叶微区红外测试,对三种尺寸籽晶生长宝石级金刚石单晶的N杂质含量进行了表征.研究得到了选用大尺寸籽晶实现快速生长金刚石的同时,晶体的N杂质含量会随之升高的晶体生长规律.     

掺杂剂对重掺n型直拉硅片的氧化诱生层错生长的影响

对比研究了电阻率几乎相同的重掺锑和重掺磷直拉硅片的氧化诱生层错(OSF)的生长, 以揭示掺杂剂对重掺n型直拉硅片的OSF生长的影响. 研究表明: 在相同的热氧化条件下, 重掺锑直拉硅片的OSF的长度大于重掺磷硅片的. 基于密度泛函理论的第一性原理计算结果表明: 与磷原子相比, 锑原子是更有效的空位俘获中心, 从而抑制空位与自间隙硅原子的复合. 因此, 在经历相同的热氧化时, 氧化产生的自间隙硅原子与空位复合后所剩余的数量在重掺锑硅片中的更多, 从而导致OSF更长.     

点缺陷二维光子晶体波导的出射光集束

光子晶体器件在高密度集成光通信中有广泛的应用,为解决光子晶体波导出射光场的空间控制,采用时域有限差分法分析光子晶体波导结构的缺陷传播特性,提出基于点缺陷优化波导结构,通过在波导出射口两侧加上点缺陷,出射光方向性有显著提高,实现三点光源干涉系统的光集束。模拟结果表明缺陷态越靠近能带结构中央,共振腔的耦合效率越高;相反,缺陷态越靠近能带结构边缘位置,则共振腔耦合效率越低,因此,选取禁带区域四分之一处对应的点缺陷,可以有效实现波导出射的光集束。     

点缺陷二维光子晶体波导的出射光集束

光子晶体器件在高密度集成光通信中有广泛的应用,为解决光子晶体波导出射光场的空间控制,采用时域有限差分法分析光子晶体波导结构的缺陷传播特性,提出基于点缺陷优化波导结构,通过在波导出射口两侧加上点缺陷,出射光方向性有显著提高,实现三点光源干涉系统的光集束。模拟结果表明缺陷态越靠近能带结构中央,共振腔的耦合效率越高;相反,缺陷态越靠近能带结构边缘位置,则共振腔耦合效率越低,因此,选取禁带区域四分之一处对应的点缺陷,可以有效实现波导出射的光集束。     

点缺陷阵列对声子晶体波导定向辐射性能的影响

将点缺陷阵列应用于声子晶体波导,提出一种具有高定向辐射性能的复合声子晶体波导. 基于有限元法的数值分析表明,附加到声子晶体波导表面的点缺陷阵列可激发出作为次级声源的谐振模. 谐振模辐射的声波与波导出射端口直接辐射的声波相互干涉,可以使声子晶体波导的法向辐射声压提高161.21%、发散角减小85.35%. 当点缺陷的数目增大到一定程度后,波导的定向辐射性能不再有明显的改善. 该研究为改善波导的定向辐射性能提供了一种新方法. 关键词： 声子晶体波导 点缺陷 谐振模 定向辐射     

温度对Ib型和IIa型金刚石大单晶(100)表面特征的影响

本文在5.6 GPa, 1250–1340 ℃的条件下, 利用温度梯度法, 以FeNiMnCo 合金为触媒, 沿籽晶的(100)晶面成功合成了不同晶形的优质Ib型和IIa型金刚石大单晶. 利用激光拉曼附件显微镜, 分别对上述不同温度下合成的两类金刚石样品上表面(100)面的中心区域及棱角区域进行观察分析. 研究发现, Ib型和IIa型金刚石大单晶(100)晶面上从中心到棱角处黑色纹路的分布逐渐变黑变密集; 另外, 随着金刚石合成温度的升高, Ib型金刚石大单晶(100)面上黑色纹路由稀疏逐渐变稠密, 而IIa型金刚石大单晶的黑色纹路较为稀疏; Ib型金刚石大单晶的形貌特征表现为从低温晶体的不规则分布过渡到中温、高温晶体的典型树枝状分布. IIa型金刚石大单晶(100)面特征随温度变化规律与Ib型的类似. 这两类金刚石大单晶表面特征的差异可能是由于IIa 型金刚石具有比Ib型更小的生长速度和更少的氮含量. 最后, 对两类塔状金刚石大单晶进行拉曼光谱测试分析, 结果表明IIa型金刚石大单晶的品质较Ib型金刚石大单晶好.     

分子动力学研究表面缺陷对硅纳米线杨氏模量的影响

硅纳米线因受量子尺寸效应与表面效应的影响而具有奇特的力、电及其耦合特性,成为了纳米电子器件的核心构件.然而在硅纳米线的制备过程中,表面产生缺陷不可避免.因此本文采用分子动力学方法着重研究了表面缺陷浓度对不同横截面形状(正方形、六角形和三角形)的[110]晶向和[111]晶向硅纳米线杨氏模量的影响.研究结果表明,当硅纳米线仅有单一表面缺陷时,不同晶向硅纳米线的杨氏模量均随表面缺陷浓度增加而迅速单调减小.当表面缺陷浓度为10%时,杨氏模量的减小幅度在10%-20%之间,减小幅度的差异与硅纳米线的晶向以及横截面形状密切相关.当存在多个表面缺陷时,杨氏模量随着缺陷浓度的增加表现出了不同程度的波动趋势.三角形截面硅纳米线的杨氏模量波动幅度最大,正方形截面的波动较小,即表面缺陷分布的不同对正方形截面硅纳米线的杨氏模量影响较小,这表明表面缺陷的影响与其分布及硅纳米线的横截面形状密切相关.通过与实验结果对比,本文的研究结果揭示了表面缺陷是导致硅纳米线杨氏模量实验值变小的重要因素,因此在表征硅纳米线的力学性能时,需要考虑表面缺陷的影响.     

Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

The growth and shrinkage of interstitial clusters on {113} planes were investigated in electron irradiated Czochralski grown silicon (Cz-Si), floating-zone silicon (Fz-Si), and impurity-doped Fz-Si (HT-Fz-Si) using a high voltage electron microscope. In Fz-Si, {113} interstitial clusters were formed only near the beam incident surface after a long incubation period, and shrank on subsequent irradiation from the backside of the specimen. In Cz-Si and HT-Fz-Si, {113} interstitial clusters nucleated uniformly throughout the specimen without incubation, and began to shrink under prolonged irradiation at higher electron beam intensity. At lower beam intensity, however, the {113} interstitial cluster grew stably. These results demonstrate that the {113} interstitial cluster cannot grow without a continuous supply of impurities during electron irradiation. Detailed kinetics of {113} interstitial cluster growth and shrinkage in silicon, including the effects of impurities, are proposed. Then, experimental results are analyzed using rate equations based on these kinetics.     

直拉硅单晶生长过程中工艺参数对相变界面形态的影响

为改善晶体相变界面形态,提高晶体品质,提出了一种融合浸入边界法（immersed boundary method,IBM）和格子Boltzmann法（lattice Boltzmann method,LBM）的二维轴对称浸入边界热格子Boltzmann模型来研究直拉法硅单晶生长中的相变问题.将相变界面视为浸没边界,用拉格朗日节点显式追踪相变界面;用LBM求解熔体中的流场和温度分布;用有限差分法求解晶体中的温度分布.实现了基于IB-LBM的动边界晶体生长过程研究.得到了不同晶体生长工艺参数作用下的相变界面,并用相变界面位置偏差绝对值的均值和偏差的标准差来衡量界面的平坦度,得到平坦相变界面对应工艺参数的调整方法.研究表明,相变过程与晶体提拉速度、晶体旋转参数和坩埚旋转参数的相互作用有关,合理地配置晶体旋转参数和坩埚旋转参数的比值,能够得到平坦的相变界面.     

Fabrication and growth rate estimation of PrBa2Cu3O7−δ single crystal by the modified top seeded crystal pulling method

Recently, we succeeded in fabricating single crystals of PrBa₂Cu₃O_7−δ by a modified top seeded crystal pulling method called the SRL-CP (Solute Rich Liquid-Crystal Pulling) method. Y₂O₃ and MgO polycrystalline crucibles and a MgO single crystal crucible were used to grow the single crystals. The crystal growth temperature was set in the range of 968°C to 972°C. The grown crystals were identified as PrBa₂Cu₃O_7−δ by X-ray diffraction. In the case of using Y₂O₃ crucibles the composition of the grown crystals was Y_xPr_1−xBa₂Cu₃O_7−δ (0.48 < x < 0.57) and in the case of using MgO crucibles a relatively small amount of Mg contamination to the grown crystals occurred at a typical concentration of approximately 1 at.% of the sum of cations. According to the crystal growth model of the SRL-CP method [1–5], a maximum growth rate of 1.7 × 10⁻⁵ cm/s was calculated with the aid of the phase diagram studies we reported earlier [6]. This value is reasonably in agreement with the experimental results.     

单晶金刚石边缘表面倾斜角度对同质外延生长的影响

利用微波等离子体化学气相沉积法,对单晶金刚石(100)晶面边缘进行精细切割抛光处理,形成偏离(100)晶面不同角度的倾斜面,在CH_4/H_2反应气体中进行同质外延生长,研究单晶金刚石边缘不同角度倾斜面对边缘金刚石外延生长的影响.实验结果表明,边缘倾斜面角度对边缘的单晶外延生长质量有影响,随着单晶金刚石边缘倾斜面角度的增大,边缘多晶金刚石数量先减少后增多,在倾斜角3.8°时边缘呈现完整的单晶外延生长特性.分析认为,边缘不同角度的倾斜面会改变周围电场强度和等离子体密度,导致到达衬底表面的含碳前驱物发生改变,倾斜面台阶表面的含碳前驱物浓度低于能形成层状台阶生长的临界浓度是减弱单晶金刚石生长过程中边缘效应的主要原因.     

Crack growth on the basal plane in single crystal zinc: experiments and computations

Crack propagation on the basal planes in zinc was examined by means of in situ fracture testing of pre-cracked single crystals, with specific attention paid to the fracture mechanism. During quasistatic loading, crack propagation occurred in short bursts of dynamic crack extension followed by periods of arrests, the latter accompanied by plastic deformation and blunting of the crack-tip. In situ observations confirmed nucleation and propagation of microcracks on parallel basal planes and plastic deformation and failure of the linking ligaments. Pre-existing twins in the crack path serve as potent crack arrestors. The crystallographic orientation of the crack growth direction on the basal plane was found to influence both the fracture load as well as the deformation at the crack-tip, producing fracture surfaces of noticeably different appearances. Finite element analysis incorporating crystal plasticity was used to identify dominant slip systems and the stress distribution around the crack-tip in plane stress and plane strain. The computational results are helpful in rationalizing the experimental observations including the mechanism of crack propagation, the orientation dependence of crack-tip plasticity and the fracture surface morphology.     

Hydrogen-related defect creation at the Si(100)–SiO2interface of metal-oxide-semiconductor field effect transistors during hot electron stress

We explore the hydrogen-related microstructures involved in hot electron defect creation at the Si(100)–SiO₂interface of metal-oxide-semiconductor field effect transistors. Based on the energetics of hydrogen desorption from the interface between silicon and silicon-dioxide, we argue that the hard threshold for hydrogen-related degradation may be considerably lower than the previously assumed value of 3.6 eV. Also, hydrogen atoms released from Si–H bonds at the interface by hot electron stress are trapped in bulk silicon near the interface.     

苝四甲酸二酐有机单晶纳米结构的制备及形成机理的研究

在分子束外延(MBE)系统中, 利用物理气相沉积(PVD)的方法在阳极氧化铝(AAO)模板上制备了有机 染料分子苝四甲酸二酐(PTCDA)的不同纳米结构; 并使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、 高分辨透射电子显微镜(HRTEM)以及选区电子衍射(SAED)技术进行了系统的研究. 结果发现, 当衬底温度(T_s)为330 ℃时得到的是纳米丝、针、带以及棒; T_s为280 ℃, 230 ℃, 180 ℃时得到的主要是纳米棒, 并且纳米棒的长度随T_s的降低而变短; T_s为50 ℃时只能得到连续的PTCDA薄膜. HRTEM以及SAED结果证实了纳米针与棒为单晶. 依据SEM结果, 提出纳米结构的生成主要受T_s以及衬底表面曲率的影响.