Photoluminescence study of InAs/GaAs self-organized quantum dots with bimodal size distribution

We have investigated the temperature dependence of the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy image for uncapped sample. The power-dependent PL study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. Due to lacking of the couple between quantum dots, an unusual temperature dependence of the linewidth and peak energy of the dot ensemble photoluminescence has not been observed. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 mu m at room temperature.

Nanostructure in the p-layer and its impacts on amorphous silicon solar cells

The open circuit voltage (V-oc) of n-i-p type hydrogenated amorphous silicon (a-Si:H) solar cells has been examined by means of experimental and numerical modeling. The i- and p-layer limitations on V-oc are separated and the emphasis is to identify the impact of different kinds of p-layers. Hydrogenated protocrystalline, nanocrystalline and microcrystalline silicon p-layers were prepared and characterized using Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), optical transmittance and activation energy of dark-conductivity. The n-i-p a-Si:H solar cells incorporated with these p-layers were comparatively investigated, which demonstrated a wide variation of V-oc from 1.042 V to 0.369 V, under identical i- and n-layer conditions. It is found that the nanocrystalline silicon (nc-Si:H) p-layer with a certain nanocrystalline volume fraction leads to a higher V-oc. The optimum p-layer material for n-i-p type a-Si:H solar cells is not found at the onset of the transition between the amorphous to mixed phases, nor is it associated with a microcrystalline material with a large grain size and a high volume fraction of crystalline phase. (c) 2006 Elsevier B.V. All rights reserved.

人工柠条灌丛林下草地植物群落特征研究

以宁夏固原上黄东山封育的人工柠条(Caragana korshinskii Kom.)灌丛林下草地为研究对象,并以设置在其周围的放牧地天然草地作为对照,采用样线法进行群落调查,分析二者群落数量特征和地上生物量变化,以期为退化草地植被恢复提供理论依据。结果表明:上黄东山封育后的人工柠条灌丛林下草地群落物种数较放牧地显著增加,封育区本氏针茅(Stipa bungeana Trin.)的优势地位明显加强,重要值远大于放牧地;人工灌丛林下草地与放牧地的相似性系数为0.585,表明二者的相似程度不高,人工种植的柠条对群落的结构影响较大,能够改善草地群落的小生境,为新物种出现提供良好的环境;物种丰富度指数和多样性指数(Shannon-winner指数)均表现为人工灌丛林下草地显著高于放牧地(P<0.05),而均匀度指数则相反(P<0.01);人工柠条灌丛林下草地地上生物量鲜重极显著高于放牧地(P<0.01)。

聚合物载体缩硫醛大环螯合剂的合成和选择络合汞的性能以及做为高分子汞解毒促排药物的动物实验

在我国某些地区，汞的污染已达到十分严重的程度。如，第二松花江吉林市下游江段，江水总汞含量和鱼体含汞量已能和日本严重汞污染的水俣湾相比。在化学工业，仪表工业中，汞中毒列为严重性占第二位的职业病。因此，汞的污染防治已是急待解决的问题。各种含硫螯合剂可应用于含汞污水处理及汞中毒的治疗。Nyssen等1976年合成了一种缩聚型的缩硫醛大环螯合树脂，作者希望它能成为汞中毒的口服解毒药物。这种产物对Hg~(++)和CH_3Hg~+表现了极强的选择络合性能。但是由于其交联结构不利于Hg~(++)深入树脂内部，因此络合容量太低，仅为2毫克Hg~(++)/克。为了提高其络合能力并进而得到一种水溶性产物，我们合成了二种新的高分子缩硫醛大环螯合剂；其一，以聚苯乙烯为载体的缩硫醛大环螯合剂（简写为PS-S）。其二，以右旋糖苷为载体的缩硫醛大环螯合剂（简写为D-S）。前者做为螯合树脂表现了对Hg~(++)极强的选择络合能力，并且络合容量比缩聚型产物高十倍以上（达30-60毫克Hg~(++)/克）。后者经动物实验证明是一种无毒而有效的高分子汞解毒药。（一）PS-S的合成和络合性能1）醛基的引入采用了不同交联度的凝胶型聚苯乙烯（PS）树脂及不同孔径和表面的大孔型PS树脂做为骨架材料，并采用了二种不同的方法在PS上联结醛基。2）PS-S的合成采用了一系列巯基化合物与PS-CHO反应合成PS-S。例如，用乙二醇二巯基乙酸酯与PS-CHO反应，其它采用的巯基化合物还有：丁二醇二巯基乙酸酯、季戊四醇四巯基乙酸酯、乙硫醇、巯基乙酸、巯基乙酸乙酯等。同一骨架材料的上述各产物的静态Hg~(++)络合容量基本相同，可是含硫环的大小对络合容量影响不大。3）缩硫醛化产物模型化合物的研究合成了几种小分子缩硫醛化产物，对它们进行了MS、NMR谱分析，从以上三种不同类型的缩硫醛化产物本身及其对Hg~(++)作用物的稳定性比较，以第二类大环型产物稳定性最好。4）不同骨架结构的PS-S络合性能比较对不同交联度的凝胶型PS树脂为骨架的PS-S树脂，及不同孔经和比表面积的大孔型PS树脂为骨架的PS-S树脂，分别测定了对Hg~(++)的络合容量，结果表明：大孔型PS-S树脂络合容量最高。当其孔径在100-1000埃，比表面积100米~2/克时，静态络合容量可达65毫克Hg~(++)/克。5）大孔PS-S树脂络合性能的研究①研究了不同测定方法下（静态法、动态法、饱和法），不同测定条件（如树脂用量、Hg~(++)溶液浓度等）对产物络合容量测定的影响。在PS-S装柱反复络合洗脱十次后，树脂络合容量不下降。②不同PH测定PS-S络合容量表明：中性条件下对Hg~(++)络合容量较高。某些有机溶剂（如乙醇、二氧六环）加入Hg~(++)水溶液有利于络合容量的提高。而某些有机溶剂（如丙酮、乙酸）的添加却降低了树脂络合容量。③大孔PS-S树脂对不同金属离子(Pb~(++)、Co~(++)、Cd~(++)、Ca~(++)、Zn~(++))络合容量的测定表明：大孔PS-S树脂对Hg~(++)的络合容量比上述其它金属离子高几十倍到近千倍。（二）D-S的合成与性能研究了介质、温度、时间、反应物用量等条件对反应结果的影响，反应所用Dextran分子量31600，生成的D-CHO含醛基量0.66毫克当量/克。生成的D-S含硫量3.5～6%，分子量约3600。（三）PS-S和D-S对汞中毒巯基酶的解毒实验生物体汞中毒的一个重要毒理是汞使巯基酶中毒，我们采用了PS-S和D-S来对汞中毒的巯基酶-脲酶解毒，使失活的脲酶重新恢复活力，模拟药物在生物体内的解毒过程。实验表明：PS-S和D-S的解毒能力比相同重量的离子交换树脂、巯基树脂、巯基棉等都要强。而且很少量的PS-S和D-S就能使脲酶100%的恢复活力。不同用量的PS-S和D-S使汞中毒脉酶恢复活力的试验显示了良好的线性关系，尤其是D-S，它几乎等当量地（每二个硫原子络合一个汞原子）使汞中毒脲酶恢复活力。（四）D-S的汞解毒及代谢促排过程的同位素示踪试验1）当给小白鼠静脉注射极限注射量（达1毫升/只鼠）的6%D-S水溶液时未发生受试动物的死亡，即LD_(50) > 4000毫克/公斤体重，说明D-S是无毒的。同时病理镜检表明动物肝肾此时无异常。2）分别对10只小白鼠静注致死量的Hg~(++)，对其中一组注射D-S（0.2毫升/只）一次，结果3小时后对照组动物全部死亡时，给药组尚存活6只。D-S表面了对受试动物良好的保护作用。病理镜检表明D-S使肾脏的汞中毒病变有所缓解。3）用同位素~(125)I标记D-S，研究了口服，静注D-S在小白鼠体内的代谢情况。试验得到了D-S经静注，口服二种途径在小白鼠体内血、肝、肾、脾等主要脏器中的经时代谢曲线。六小时后D-S大部分代谢出体外，12天后全部代谢出体外。并进而得到了二种不同给药方式的药物代谢动力学方程。D-S口服为：C_血=0.1 (e~(-0.00183t)-e~(-0.01t))符合于一级吸收过程的单室模型 D-S静注为：C_血=0.384 e~(-0.645t) + 0.074 e~(-0.08t) + 0.042~(-0.00464t)符合于快速静注下的三室模型。4）采用~(203)Hg做了D-S口服、静注给药时对Hg~(++)的促排作用的实验，得到了二种给药方式下Hg~(++) 在小白鼠血、肝、肾、脑及全身的促排代谢经时曲线。实验表明D-S对汞有明显促排作用，其中口报组效果更好。D-S促排与代谢同位素示踪试验数据之间表现了有趣的相关性，有助于我们解释D-S对汞促排的机制。动物实验表明：D-S可能成为一种临床使用的副作用小的汞中毒解毒促排新药。

苄基环戊二烯基和茚基稀土二氯化物的合成与结构

本文通过元素分析，红外光谱、水解产物质谱、核磁共振、热失重分析及x-光单晶衍射分析，确认合成了下述两种新型稀土金属有机配合物。并对它们结构特点进行了研究和讨论。(1) ErCl_3 + C_6H_5CH_2C_5H_4Na → (THF) C_6H_5CH_2C_5H_4ErCl_2·3THF + NaCl; (2)GuCl_3·nTHF + C_9H_7K → (THF) C_9H_7GuCl_2·3THF + Kcl; 在第一种配合物的合成中，讨论了苄基环戊二烯与无水氯化稀土反应的条件。并首次成功的合成了苄基环戊二烯基稀土配合物。对于第二种化合物的合成，采取了与文献不同的反应条件及合成方式。提高了产物收率并第一次得到了茚基稀土二氯化物的单晶结构表征。上述两类配合物均对空气、水汽敏感，均可溶于四氢呋喃溶剂中，难以溶解在汽油等烷烃溶剂中。其中C_6H_5CH_2C_5H_4ErCl_2·3THF在DME·Et_2O甲苯等溶剂中也有较为良好的溶解性。在C_6H_5CH_2C_5H_4ErCl_2·3THF的红外光谱中，1600cm~(-1)、1490cm~(-1)和1450cm~(-1)为苯环骨架振动吸收峰，700cm~(-1)为取代苯环的面外弯曲振动吸收峰，2980cm~(-1)，2880cm~(-1)为CH_2的振动吸收峰，1600cm~(-1)、1040cm~(-1)和860cm~(-1)为环戊二烯基的特征吸收峰，1060cm~(-1)、910cm~(-1)为四氢呋喃分子的特征吸收峰，460cm~(-1)为Ln-Cl键的特征吸收峰。其分子结构见图I，晶体为单斜晶系，空间群为P21/n、晶胞参数a = 11.622A. b = 10.281A, c = 26.040A. β = 86.65°、V = 3106.09A、E = 4L。最终端离因子R = 0.050。中心离子Er~(3+)处于八面体中心，配位数为8。化合物C_9H_(17)GdCl_2·3THF的红外光谱中，出现的四氢呋喃分子特征峰为1050cm~(-1), 900cm~(-1)。茚基特征峰为845cm~(-1)和1020cm~(-1)；GuCl键吸收峰为460cm~(-1)，热失重分析表明，配合物分子中含有三个四氢呋喃分子。单晶结构见图II，单晶属单斜晶系，P21空间群，晶胞参数a = 10.468A, b = 11.888A, c = 11.854A, β = 108.46°, D = 1399.3A~3。最后一改性因子R = 0.042。平均键长Gd-C（环）为2.739，Gd-O为2.444A，两个Gd-Cl键长分别为2.583A和2.721A，夹角Cl(1)-Gd-Cl(2)为158.0°。比较所得两个配合物，它们具有相同的化学组成形式，单晶结构也非常相似。在苄基环戊二烯基化合物结构中Cl(1)-Er-Cl(2)夹角为156.3°，而C_9H_7GdCl_2·3THF中相应角度为158.0°，前者较后者小的不到两度，这可能与取代环戊二烯基的空间位阻小大有关。

取代环戊二烯基稀土有机氯化物的合成及其反应

本文通过无水LnCl_3(Ln = Pr.Nd.Gd)与两倍摩尔的叔丁基环戊二烯基碱金属盐在THF中60－80℃反应，分离到一类新的二（叔丁基环戊二烯基）稀土氯化物（T-DuCp）_2 2net.nTHF (Ln = Pr,Nd,n = 2 Ln = Gd,n = 1)，对它们进行了元素分析。红外光谱及水鲜色质谱的表征。对于配合物（t-BuCp）_2PrCl·2THF的单晶，测定了它的晶体结构，晶体层单斜晶系P21/C空间群，晶胞参数为：a = 15.080 b = 8.855 c = 21.196A, β = 110.34°V = 2653.9A~3 δ = 4，结构分析表明此配合物是一中性的单分子配合物。最后的R = Rw = 0.058平均Pr-C.2.81 Pr-Cent 2.53A, Pr-Cl及Rr-O键长分别为2.72与2.62A。本文通过Lnel_3(Ln = Nd.Pr.Ga)与等摩尔的叔丁基环戊二烯基碱金属盐在THF中60－80℃反应，分离到一类中性的单(叔丁基环戊二烯基)稀土二氯化物，并对它们进行了元素分析，红外光谱及水鲜色质谱的表征。本文通过轻稀土元素La,Pr的三氯化物与带基钠以1:2摩尔比在THF中70－80℃反应，分离到了二带基轻稀土氯化物（CaH_7）_2LaCl.2THF及[(CqH_7)_2PrCl.THF]_2。并且对此二配合物进行了元素分析。红外光谱及水鲜色质谱的表征。对于[(CuH_7)_2PrCl.TH]_2配合物，测定了它的晶体结构，这是第一个得到结构表征的茚基稀土氯化物，晶体层于单斜晶系，P_(21)/C空间群，晶胞参数为a = 7.808 b = 17.796 c = 14.070A β = 93.97°v = 1950.31A. E = 2最后的R = 0.045. Rw = 0.039结构分析表明此配合物以中性的二聚体形式存在。平均的Pr-C.2.81 Pr-Cent 2.53. Pr-Cl.2.84H Pr-O钻长2.54A。为了进一步研究不同配体对配合物结构的影响，我们还研究了Gael_3与Nae_5Mes以1:1摩尔比在THF中的反应，分离到了两种配合物[(NaTHF)(C_5MesGd.THF)_2Cl_5]_2.6THF(I)及L_5Me_5GdCl2.3THF(II)并且对配合物（I），测定了它的晶体结构，晶体层于三斜晶系。Pi空间群。晶胞参数a = 12.183 b = 13.638 c = 17.883A, α = 110.38 β = 94.04 γ = 99.44°, V = 2721.20A, E = 1。结构分析表明，此配合物是一种以两个Na原子通过THF中的O原子而桥联的金层有机配合物，在结构上有十分新颖的特点。在此配合物分子中含有四个Gd原子及二个Na原子，Na及Gd间以Cl桥键相联结，Gd-Gd_2 = 4.033 Gdll-Na = 2.818A。最后的R = 0.04M Rw = 0.042。本文还对（t-BuCp）_2P_2Cl.2THF与NaH及LiAlH4的反应进行了初步的研究，分离到（t-Bucp）_2PrH.2THF及(t-Bucp)_2P_2RIH_4.3THF两种新的氢化物，并且对它们进行了元素分析，红外光谱的表征，对于它们水鲜产物的气相分中的H_2，用气相色谱法进行了定性表征。

GROWTH OF GASB AND GAASSB IN THE SINGLE-PHASE REGION BY MOVPE

GaSb layers are grown on GaSb substrates; the effects of input partial pressure of trimethylantimony and the V/III ratio are studied. A model of the MOVPE phase diagram for the growth of GaSb and GaAsxSb1-x is developed which assumes thermodynamic equilibrium to be established at the solid-vapor interface.

Kinetics and transport model for the chemical vapor epitaxy of GexSi1-x

A numerical model that combines mass transport and surface kinetics was applied, for the first time, to the chemical vapor epitaxy of GexSi1-x. The temperature, velocity and concentration fields were calculated from the conservation equations for energy, momentum and species coupled with the boundary conditions on the growth surface which were determined by surface kinetics. The deposition rates of Si and Ge were assumed to be limited, respectively, by surface kinetics and mass transport. A theoretical relation between the initial conditions and the Ge composition in the solid was established. The calculated growth rate as well as the Ge composition in the solid and its dependence on growth temperature agree well with experimental data.

PROCESS OF PHOTOLUMINESCENCE AND PHOTOSTIMULATED LUMINESCENCE IN BAFBR-EU PHOSPHORS

The photoluminescence (PL) and photostimulated luminescence (PSL) of BaFBr: Eu phosphors are reported. In the photoluminescence of BaFBr:Eu, the emission of Eu2+, e-h recombination and Eu3+ have been observed, while in the photostimulated luminescence only the emission of Eu2+ was observed. This phenomenon may be explained well by the suggestion of a two-hand model for the host emission in which the host emission energy may transfer to Eu2+ difference of excitation in those two processes results in different transfer rates which makes the PL and PSL emission different.

HIGH-PRESSURE STUDY OF GAMMA-X MIXING IN INAS/GAAS QUANTUM DOTS

We have measured low-temperature photoluminescence spectra of InAs quantum dots embedded in a GaAs crystalline matrix under hydrostatic pressures up to 7 GPa. Below 4.2 GPa the spectra are dominated by the Gamma-like electron-heavy hole (HH) exciton transition in the InAs dots. Above 4.2 GPa the spectra show two X-related luminescence bands which are attributed to the indirect type-I transition between X(Xy) and HH states of the dots and the type-II transition from X states in GaAs to InAs HH states, respectively. In the Gamma-X crossover regime we find evidence for a pronounced mixing interaction between InAs Gamma-like and GaAs X-like states. The corresponding interaction potential is estimated to be 9 meV.

Low -temperature preparation of ZnO films on Si substrates by MOCVD

ZnO films were deposited on Si（100） substrates at 300℃ by metal - organic chemical vapor deposition（MOCVD）. The effect of different ratios of DEZn to N2O on crystal quality was analyzed. It is found that the optimum ratio of DEZn to N2O is 2.1. And in this optimum growth condition, X - ray diffraction （XRD） and scanning probe morphology （SPM） images indicate that the films grow along the c - axis orientation. ZnO film exhibits a strong UV optical absorption near 388 nm. And the optical absorbance is close to zero,that indicates nearly 100% optical transparence. Photoluminescence （PL） spectrum shows only strong near - band - edge emissions with little or no deep - level emission related to defects. The full - width at half - maximum （FWHM） of the ultraviolet emission peak is 80meV. The results indicate that better crystal quality can be obtained.