分子束外延ZnSe/GaAs材料的拉曼散射研究

用分子束外延(MBE)技术，在GaAa(100)衬底上生长了厚度从0．045μm到1．4μm的ZnSe薄膜。通过室温拉曼光谱的测量对ZnSe薄膜纵光学声子(Longitudinal-opticalphonon)的谱形进行了分析。用拉曼散射的空间相关模型定量分析了一级拉曼散射的型间相关长度与晶体质量之间的关系，结果表明ZnSe外延层的晶体质量随着外延层厚度的减薄是渐渐退化的，这是由于界面失配位错引入外延层所致，理论分析与实验结果相吻合。     

GaAs-InP异质材料的结构特性和光学特性研究

我们在低压金属有机汽相沉积(MOCVD)设备上采用两步升温法与金属有机源流量周期调制生长界面过渡层方法制备出GaAs-InP材料,并对此进行了X-射线衍射、低温光致发光谱(PL)和Raman谱分析,结果表明,GaAs外延层的位错密度低于用两步升温法得到的GaAs材料,PL谱峰较强,GaAs的特征激子峰和杂质相关的激子峰同时被测到。Raman谱PL谱的峰移表明GaAs外延层处于(100)双轴伸张应力下,应力大小随温度变化是由于GaAs、InP之间的热膨胀系数不同。     

发射层厚度对反射式GaAs光电阴极性能的影响

通过求解扩散方程,推导了含有后界面复合速率的反射式GaAs光电阴极量子效率公式,并利用MBE在GaAs (100)衬底上外延生长了发射层厚度分别为1.6 μm、2.0 μm和2.6 μm,掺杂浓度为1×1019cm－3的三个反射式GaAs阴极样品,进行了激活实验.实验结果显示:随着发射层厚度的增加,阴极的长波量子效率和灵敏度都有所提高,而这种提高与阴极电子扩散长度的增长有关.同时,理论仿真研究发现,当后界面复合速率小于或等于105cm/s时,阴极发射层有一个最佳厚度,此时阴极灵敏度最高.后界面复合速率对阴极灵敏度在发射层厚度较小时影响较大,而随着厚度的增大阴极灵敏度最终趋于稳定.     

三元混晶四层系统的表面和界面声子极化激元

运用改进的无规元素等位移模型和玻恩-黄近似,结合电磁场的麦克斯韦方程和边界条件,研究了真空/极性二元晶体薄膜/极性三元混晶薄膜/极性二元晶体衬底四层系统的表面和界面声子极化激元.以AlxGa1-xAs/GaAs和ZnxCd1-xSe/ZnSe为例,获得了表面和界面声子极化激元模的色散关系以及表面模和界面模的频率随混晶组分和薄膜厚度的变化关系.结果表明,三元混晶四层异质结系统中存在七支表面和界面声子极化激元模,且这七支表面模和界面模的频率随混晶组分和薄膜厚度呈非线性变化,三元混晶的"单模"和"双模"性也在色散曲线中得到了很好的体现.     

发射层厚度对透射式GaAs光电阴极表面光电压谱的影响

通过求解一维稳态少子扩散方程,推导了含有后界面复合速率和发射层厚度的透射式GaAs光电阴极表面光电压谱理论方程.通过对发射层厚度分别为1.6 μm和2.0 μm,掺杂浓度为1×1019 cm－3的GaAs透射式阴极样品测试,理论曲线和实验曲线基本一致.通过引入表面光电压谱积分灵敏度公式,仿真探讨了表面光电压谱在一定体材料参量条件下,积分灵敏度受发射层厚度的影响|发现在体材料参量一定条件下,透射式GaAs光电阴极具有最佳厚度,同时最佳厚度受后界面复合速率的影响更大,同时GaAlAs窗口层也能很好降低发射层后界面复合速率.     

气相外延GaN的拉曼散射

测量了在蓝宝石衬底上气相外延生长GaN的拉曼散射谱.除观察到已被确认的两个E2,一个A1(TO)和一个E1(TO)声于振动以外,在734±3cm-1处观察到一个散射峰且从实验上确认其为GaN的纵向光学声子模E1(LO).而且发现其强度与外延层晶体质量密切相关.A1(TO)和高频E2散射峰相对强度变化显示不同生长条件引起的外延层质量的变化.     

GaAs/Ge的MOCVD生长研究

用常压MOCVD在Ge衬底上外延生长了GaAs单晶层,研究了GaAs和6e的极性与非极性材料异质外延生长,获得了质量优良的GaAs/Ge外延片,GaAs外延层X射线双晶衍射回摆曲线半高宽达16弧秒.10K下PL谱半峰宽为7meV.讨论了极性与非极性外延的界面反相畴问题和GaAs-Ge界面的Ga、Ge原子互扩散问题.     

在(100)GaAs衬底上低温液相外延晶格匹配的In1-xGaxAs1-yPy层及其特性研究

介绍一种低温液相外延技术,可在650℃在GaAs衬底上生长晶格匹配和组份可重复的In1-xGaxAs1-yPy层。给出对外延层进行场发射扫描电镜观察、电子探针、X光双晶衍射、俄歇电子谱和光荧光测量得到的结果。结果表明外延层具有平坦的异质结界面和良好的晶体特性。同时研究了异质结界面的粗糙度和组份梯度变化区域的宽度和晶格失配率的关系。     

基于MOCVD三步生长的GaAs/Si外延技术EI北大核心CSCD

在硅(Si)上外延生长高质量的砷化镓(GaAs)薄膜是实现硅基光源单片集成的关键因素。但是,Si材料与GaAs材料之间较大的晶格失配、热失配等问题对获得高质量的GaAs薄膜造成了严重影响。本文利用金属有机化学气相沉积(MOCVD)技术开展Si基GaAs生长研究。通过采用三步生长法,运用低温成核层、高温GaAs层与循环热退火等结合的方式,进一步降低Si基GaAs材料的表面粗糙度和穿透位错密度。并利用X射线衍射(XRD)ω-2θ扫描追踪采用不同方法生长的样品中残余应力的变化。最终,在GaAs低温成核层生长时间62 min(生长厚度约25 nm)时,采用三步生长、循环热退火等结合的方式获得GaAs(004)XRD摇摆曲线峰值半高宽(FWHM)为401″、缺陷密度为6.8×10^(7) cm^(-2)、5μm×5μm区域表面粗糙度为6.71 nm的GaAs外延材料,在材料中表现出张应力。     

GaSb/GaAs复合应力缓冲层上自组装InAs量子点的生长

研究了GaSb/GaAs复合应力缓冲层上自组装生长的InAs量子点.在2ML GaSb/1ML GaAs复合应力缓冲层上获得了高密度的、沿［100］方向择优分布量子点.随着复合应力缓冲层中GaAs层厚度的不同,量子点的密度可以在1.2×10¹⁰cm^-2和8×10¹⁰cm^-2进行调控.适当增加GaAs层的厚度至5ML,量子点的发光波长红移了约25nm,室温下PL光谱波长接近1300nm. 关键词： 自组装量子点 分子束外延 Ⅲ-Ⅴ族化合物半导体     

Spectroscopic study of BixEu1−xVO4 and BiyGd1−yVO4 mixed oxides

The mixed oxides Bi_xEu_1−xVO₄ and Bi_yGd_1−yVO₄ crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s² of Bi³⁺ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the Bi_xEu_1−xVO₄ spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu³⁺ ion. The broad absorption shift in BiLnVO₄ (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO₄ lattice, is ascribed to charge transfer processes in a Bi-VO₄ center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi³⁺. The concept of an internal pressure of Bi³⁺ ions is also used to explain the broad A-band shifts.     

单异硫氰基3∶1不对称酞菁锌的光谱性质研究

测定了三种含异硫氰基3∶1不对称酞菁锌配合物(RO)₆(NCS)PcZn(Ⅱ)(R=n-C₄H₉; n-C₅H₁₁; n-C₁₀H₂₁)在五种有机溶剂中的电子吸收光谱,研究了取代基和溶剂对吸收光谱的影响和规律。同时测定它们在有机溶剂中的荧光发射光谱,研究了外部取代基、溶剂和浓度对最大发射波长及荧光强度的影响规律,发现此类配合物具有特定的荧光效应,有望成为光动力诊断和治疗的有效光敏剂。     

多铁材料Bi1-xCaxFeO3的介电、铁磁特性和高温磁相变

采用溶胶凝胶法制备Bi_1-xCa_xFeO₃ (x=0, 0.05, 0.1, 0.15, 0.2)陶瓷样品. X衍射图谱表明所有样品的主衍射峰均与纯相BiFeO₃相符合且具有良好的晶体结构. 随着x的增大, Bi_1-xCa_xFeO₃样品的主衍射峰由双峰(104)与(110) 逐渐重叠为单峰(110), 当x ≥0.15时, 样品呈现正方晶系结构; 扫描电镜形貌分析可知, 晶粒由原来的0.5 μm逐渐增大到2 μm. Bi_1-xCa_xFeO₃样品介电常数和介电损耗随着x 的增加先增大而后减小. 当f=1 kHz, Bi_0.9Ca_0.1FeO₃ 的介电常数达到最大值, 是BiFeO₃的7.5倍, 而Bi_0.8Ca_0.2FeO₃的介电常数达到最小值, 仅仅是BiFeO₃的十分之一. Bi_1-xCa_xFeO₃样品所呈现的介电特性是由偶极子取向极化和空间电荷限制电流两种极化机理共同作用的结果. 随着Ca²⁺ 的引入, BiFeO₃ 样品的铁磁性显著提高. X射线光电子能谱图表明Fe²⁺和Fe³⁺ 共存于Bi_1-xCa_xFeO₃ 样品中, Fe²⁺/Fe³⁺比例随着Ca²⁺ 掺杂量的增加而增大, 证明Ca²⁺掺杂增加了Fe²⁺的含量, 增强BiFeO₃的铁磁特性. 从M-T曲线观察到BiFeO₃样品在878 K附近发生铁磁相变, 示差扫描量热法测试再次证明BiFeO₃ 在878 K发生相变. Ca²⁺掺杂使BiFeO₃样品的T_N略有变化而T_M基本不变, 其主要原因是Fe-O-Fe反铁磁超交换作用的强弱和磁结构相对稳定.     

MAGNETIC FIELD EFFECT OF THE EUROPIUM a8S7/2-z6P7/2 LINES

The magnetic field effect of a⁸S_7/2-z⁶P_7/2 lines of ¹⁵¹Eu and ¹⁵³Eu in magnetic fields up to 66.7 mT has been studied by using laser atomic beam spectroscopy. The Zeeman level structures of the europium a⁸S_7/2 and z⁶P_7/2 states in magnetic fields were discussed. The location and intensity of the measured Zeeman transition lines were found in good agreement with the theoretical results.     

铀在Nd_2Zr_2O_7烧绿石中的固溶量及重离子辐照效应

Nd_2Zr_2O_7烧绿石因其稳定的物理化学性质和辐照稳定性可以作为高放废物中锕系核素的固化基材.通过溶胶凝胶—喷雾热解—高温烧结方法制备了含铀的Nd_2Zr_2O_7烧绿石固化体;开展了Nd_2Zr_2O_7和Nd_(1.9)U_(0.1)Zr_2O_7固化体的重离子辐照实验,辐照剂量为1 dpa和3 dpa;利用X射线衍射和Raman光谱对固化体结构进行了分析.研究发现铀在Nd_2Zr_2O_7烧绿石体系的固溶量仅为10 at%,高价态铀掺杂导致固化体结构向无序化转变.重离子辐照实验表明, Nd_2Zr_2O_7烧绿石基材具有较高的抗辐照稳定性;而Nd_(1.9)U_(0.1)Zr_2O_7在较低辐照剂量下,固化体烧绿石体系结构破坏,重离子辐照诱导固化体结构转变为更加无序化的萤石结构.低固溶量和抗辐照能力减弱主要是由于锕系核素烧绿石固化体的结构无序化所致.     

Magnetic alignment in nominally non-magnetic hexagonal metal hydrides: NMR

Powders of three hexagonal metal-hydrides or -deuterides are found to align in 4.4–8.3 T magnetic fields used for NMR. The field-alignment is unexpected, since all three systems have very small susceptibilities, as demonstrated by sharp NMR lines. The extent of alignment runs from nearly complete to barely detectable in ZrBe₂(H,D)_x, LuD₃, and YD₃, respectively. The preferred alignment direction in ZrBe₂(H,D)_x is with the crystallites’ c-axis perpendicular to B, while the c-axis and B tend to be parallel in LuD₃ and YD₃. The susceptibilities χ_|| and χ are determined from bulk magnetization measurements in aligned ZrBe₂H_1.4 powder. The alignment must be considered for proper analysis of NMR spectra in these and related materials.     

Magnetic and structural investigations on substituted Pr2Co17-xTx systems (T= Fe, Mn, Cr, Cu and Al)

Magnetic and structural characteristics of Pr₂Co₁₇-based ternaries, in which Co is partly replaced by other transition elements, namely Fe, Mn, Cr, Cu and Al, have been investigated. The objective of the work was to explore the possibility of enhancing the anisotropy of Pr₂Co₁₇ to the point that it would be useful for permanent magnet fabrication. X-ray diffraction indicates that all the systems studied occur in the rhombohedral Th₂Zn₁₇ structure. The cell constants increase as Fe, Mn, etc., are introduced in the system, which indicates that substitution occurs in the Co sublattice. The Curie temperatures, T_c, decrease monotonically with increasing x in the order Fe < Cu < Mn < Al < Cr. The saturation magnetization, M_s, increases with increasing x for the Fe system with x 8. For x #62; 8 in the Pr₂Co_17-xFe_x system and in all other ternary systems st died, M_s decreases with x, the magnitude of the effect being in the order Cr #62; Al #62; Mn #62; Cu. The rate of decrease is larger than that expected as a simple dilution except for the systems containing Cu. Significant modification of the anisotropy characteristics of Pr₂Co₁₇ is observed upon substitution. The planar anisotropy of Pr₂Co₁₇ becomes uniaxial with Fe (x 4) and Mn (x 2) substitutions. With Cr and Al substitutions, the plane-seeking tendency of Pr₂Co₁₇ is significantly weakened.     

中性和阳离子丁酮团簇的结构及稳定性的理论研究

使用密度泛函B3LYP方法,在6-31G*和6-311+G**基组水平上计算中性和阳离子丁酮团簇(CH_3COC_2H_5)_n和(CH_3COC_2H_5)_n~+(n 7)的稳定结构,并比较不同尺寸团簇之间的相对稳定性.中性和阳离子丁酮团簇的结构具有相似性:n=3—7时,组成团簇的丁酮的平均几何参数基本相同,单环结构最稳定;随着团簇尺寸的增加,双环结构的稳定性逐渐上升.通过平均结合能、一阶差分能、HOMO-LUMO能隙等计算分析可知:在所研究的各种尺寸团簇中,(CH_3COC_2H_5)_3是最稳定的中性团簇,与实验中的最强峰对应;(CH_3COC_2H_5)_4~+是最稳定的阳离子团簇.通过电离能计算得到丁酮分子的垂直电离能为9.535 eV与实验值相符,同时证明中性和阳离子丁酮二元团簇的结构变化较大.研究结果为实验中丁酮团簇碎片离子的形成机理提供一定的理论依据,并且为进一步研究酮类分子团簇的生长规律提供有价值的信息.     

Continuous photoluminescence, time resolved photoluminescence and optically detected magnetic resonance measurements of PbI2 nanometer-sized particles, embedded in SiO2 films

The nanometer sized particles of PbI₂ were embedded in SiO₂ films. X-ray diffraction and the TEM pictures showed the preservation of the bulk layered structure and symmetry. The PL spectrum of the nano-particles exhibited a pronounced blue shift of the exciton band due to quantum size effect. The Lead Iodide represents an exceptionally small exciton Bohr radius (a_B = 19 Å) and a special case in which m_e m_h. The prepared samples contained particles with mean radii, a, in the range a_B < a < 3a_B. Within this limit (with m_e m_h), the experimental results suggest that the electron is localized nearly at the center of the particle, enabling the hole to move around it. Thus, the size confinement permits the creation of an acceptor-like exciton. The PL spectrum revealed additional states, associated with stoichiometric defects either at the interior or surface sites of the nano-particles. These defects act either as donor or acceptor states. The dynamics of the various recombination processes has been investigated by measuring the time resolved PL spectra. The results show a multiexponential behavior of the various recombination emission bands, indicating the occurrence of trapping and detrapping processes. Analysis of these results suggests that the existence of surface states give rise to these complex radiative decay processes. The correlation between donor-acceptor recombination emission bands in the aforementioned samples and lattice imperfections was examined, utilizing optically detected magnetic resonance (ODMR) spectroscopy. The results identified the following imperfection sites: an acceptor site associated with an isotropic Lead vacancy defect, [V⁻]_pb²⁺ and a donor site, associated with an anisotropic Iodine vacancy, [V⁰]_Iodine.     

Ln1−xSrxCoO3(Ln = Sm, Dy) for the electrode of solid oxide fuel cells

The perovskite-type oxides were synthesized in the series of Ln_1−xSr_xCoO₃(Ln = Sm, Dy). The formation of solid solutions in Dy_{1 − x}Sr_xCoO₃ was limited, compared with that in Sm_{1 − x}Sr_xCoO₃. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm_0.7Sr_0.3CoO₃. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO₃ at 900 °C after 96 h. However, no reaction product between SmCoO₃ and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO₃ shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples.