A comparison between contactless electroreflectance and photoreflectance spectra from n-doped GaAs on a semi-insulating GaAs substrate

Contactless electroreflectance (CER) and photoreflectance (PR) measurements have been performed on samples with the structure of an n-doped GaAs epitaxial layer on a semi- insulating GaAs substrate. Modulated reflectance signals from the n-GaAs surface and those from the n-GaAs/SI-GaAs interface are superposed in PR spectra. For the case of CER measurement, however, Franz-Keldysh oscillations (FKOs) from the interface, which are observed in PR spectra, cannot be detected. This discrepancy is attributed to different modulation mechanisms of CER and PR. In CER experiments, the electric field modulation cannot be added to the interfacial electric field because of the effective screening by the fast response of carriers across the interface. FKOs from the interface without any perturbation by the surface signals are extracted by subtracting CER spectra from PR spectra.

Crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth

The crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth (ELO) on sapphire (0001) substrates was investigated by using double crystal X-ray diffraction (DC-XRD). It was found that ELO GaN stripes bent towards the SiNx mask in the direction perpendicular to seeding lines. Each side of GaN (0002) peak in DC-XRD rocking curves was a broad peak related with the crystallographic tilt. This broad peak split into two peaks (denoted as A and B), and peak B disappeared gradually when the mask began to be removed by selective etching. Only narrow peak A remained when the SiNx mask was removed completely. A model based on these results has been developed to show that there are two factors responsible for the crystallographic tilt: One is the non-uniformity elastic deformation caused by the interphase force between the ELO GaN layer and the SiNx mask. The other is the plastic deformation, which is attributed to the change of the threading dislocations (TDs)-from vertical in the window regions to the lateral in the regions over the mask.

Thermoluminescence of ZnS nanoparticles

The thermoluminescence (TL) of ZnS nanoparticles is reported. The TL intensity increases as the particle size is decreased. The consistency of the size dependence of the TL with that of the surface fluorescence indicates that the TL may be related to the surface states. TL may be caused by the recombination of carriers released from the surface states or defect sites by heating. Smaller particles have higher surface/volume ratio and more surface states, therefore contain more accessible carriers for TL. Besides, the carrier recombination rate increases upon decreasing size due to the increase of the overlap between the electron and hole wave functions. These two effects may make the TL increase upon decreasing size of the particles. The appearance of TL prior to any radiation reveals that trapped carriers have pre-existed. The investigation of TL may provide some useful information about the surface states that may explain the size dependence of the surface fluorescence. (C) 1997 American Institute of Physics.

实用化1730nm波段掩埋结构半导体激光器的研制

报道了应用于医疗器械的InP基1730nm波段半导体激光器．外延片采用低压金属有机物化学气相沉积法（MOCVD）生长，有源区为5个周期的InGaAs量子阱层和InGaAsP垒层．器件采用pnpn结限制掩埋结构，有源区脊宽2μm、腔长300μm．室温下腔面镀膜后激光器管芯的阈值电流为18±5mA，8mW输出功率时的工作电流为60±5mA．采用TO封装后，100mA工作电流下激光器的输出功率大于5mW，输出波长为1732±10nm，高温恒流加速老化筛选实验表明，器件具有长期工作的可靠性，满足实用化要求。

Bimolecular quadruplexes and their transitions to higher-order molecular structures detected by ESI-FTICR-MS

Four individual quadruplexes, which are self-assembled in ammonium acetate solution from telomeric sequences of closely related DNA strands - d(G(4)T(4)G(4)), d(G(3)T(4)G(4)), d(G(3)T(4)G(3)), and d(G(4)T(4)G(3)) - have been detected in the gas phase using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). The bimolecular quadruplexes associate with the same number of NH4+ in the gas phase as NMR shows that they do in solution. The quadruplex structures formed in solution are maintained in the gas phase. Furthermore, the mass spectra show that the bimolecular quadruplexes generated by the strands d(G(3)T(4)G(3)) and d(G(4)T(4)G(3)) are unstable, being converted into trimolecular and tetramolecular structures with increasing concentrations of NH4+ in the solution. Circular dichroism (CD) spectra reveal structural changes during the process of strand stoichiometric transitions, in which the relative orientation of strands in the quadruplexes changes from an antiparallel to a parallel arrangement. Such changes were observed for the strand d(G(4)T(4)G(3)), but not for the strand d(G(3)T(4)G(3)). The present work provides a significant insight into the formation of various DNA quadruplexes, especially the higher-order species.

Synthesis and structure of molybdenum-citrato cluster mu(2)-S bridge

A new molybdenum-citrato cluster containing [Mo2O2(mu-S)(2)(C6H5O7)(C6H4O7)](5-) anion was synthesized and characterized by elemental analysis, IR, UV-Vis spectra, XPS and X-ray diffraction. The parameters of the crystal structure of the compound are monoclinic, space group P2(1)/c, a = 2. 376 6(5) nm, b = 1. 327 4(3) nm, c = 2. 247 1(5) nm, beta = 118. 21 degrees, V = 6. 247(2) nm(3), Z = 8, D-c = 2. 128 g/cm(3), F(000) = 3 984, mu = 1 694 cm(-1), R = 0. 083 1 and R-2,R-w = 0. 154 9. The anion is binuclear molybdenum-citrato complex with mu(2)-S bridge. Each molybdenum atom pocesesses a distorted octahedral struture, which is coordinated with a terminal oxygen, two sulfur atoms, three oxygen atoms of hydroxyl, alpha-carboxylate, beta-carboxylate from citrate.

含柠檬酸配体的钼硫簇合物的合成与晶体结构的测定

合成了含有Mo—S簇阴离子 [Mo2 O2 ( μ S) 2 (C6H5O7) (C6H4 O7) ]5-柠檬酸簇合物 ,并通过元素分析、红外光谱、紫外 可见光谱和X射线光电子能谱对配合物进行了表征 ,用X射线衍射法测定了该化合物的晶体结构 .结果表明 ,该簇合物属于单斜晶系 ,空间群P2 1/c,a =2 3 766( 5)nm ,b =1 3 2 74 ( 3 )nm ,c =2 2 4 71 ( 5)nm ,α=γ =90°,β=1 1 8 2 1°,V =6 2 4 7( 2 )nm3 ,Z =8,一致性因子R =0 0 83 1 ,R2 ,w=0 1 536.该簇合物阴离子中每一个Mo原子都采取扭曲的八面体结构 ,柠檬酸通过羟基、α 羧基、一个 β 羧基与Mo配位 .晶体结构表明在一个结晶学上不对称的结构单元内有两个结晶学上独立的分子.

Magnetic microsphere and its use in biochemical separation and analysis

Magnetic microsphere comprises a magnetically responsive metal or metal oxide core surrounded by a polymer shell with active groups. Nowadays, methods of directly coating polymer, monomer polymerazation, impregnation, extrusion and biological synthesis are generally used to prepare magnetic particles. This kind of superparamagnetic microspheres can be attached to chemical, biochemical and biological substances by their active groups, then applying a magnetic field to separate from the media. Preparation and utilization of magnetic microspheres in immunoassay, nucleic acid hybrization assay, gene sequencing, cell isolation, enzyme immoblization, receptor isolation and other Gelds are reviewed with 44 references in this paper. Also, the further development is outlooked.

磁微球及其在生化分离分析中的应用

磁微球是以金属或金属氧化物为核,外面包被带有活性基团物质的一种新型生物分离材料.目前制备磁微球的方法有包埋法、聚合法、浸渍法、挤压法和生物合成法等.这种微球通过其活性基团与化学、生化和生物物质连接后,利用其顺磁性外加一定磁场可实现与介质分离.本文全面地介绍了磁微球的制备,详尽评述了其在免疫分析、核酸杂交分析、基因测序、细胞分离、酶的固定、受体分离等各个领域的应用.

胆红素系列氧化过程中的自催化现象

胆红素系列氧化过程中的自催化现象牛建军，董绍俊（中国科学院长春应用化学研究所电分析化学开放研究实验室，长春，１３００２２）关键词胆红素；胆汁红紫素；电催化氧化胆红素（ＢＲ）曾一度被认为是一种毒害性物质，因为它是导致黄疸病和核黄疸的主要原因［１，２］。...