Near infrared photoluminescence from Yb,Al Co-implanted SiO2 films on silicon

Intense room-temperature near infrared (NIR) photoluminescence (980 nm and 1032 nm) is observed from Yb,Al co-implanted SiO2 films on silicon. The optical transitions occur between the F-2(5/2) and F-2(7/2) levels of Yb3+ in SiO2. The additional Al-implantation into SiO2 films can effectively improve the concentration quenching effect of Yb3+ in SiO2. Photoluminescence exitation sprectroscopy shows that the NIR photoluminescence is due to the non-radiative energy transfer from Al-implantation-induced non-bridging oxygen hole defects in SiO2 to Yb3+ in the Yb-related luminescent complexes. It is believed that the defect-mediated luminscence of rare-earth ions in SiO2 is very effective.

Crack control in GaN grown on silicon (111) using In doped low-temperature AlGaN interlayer by metalorganic chemical vapor deposition

The effects of In doped low-temperature (LT) AlGaN interlayer on the properties of GaN/Si(111) by MOCVD have been investigated. Using In doping LT-interlayer can decrease the stress sufficiently for avoiding crack formation in a thick (2.0 mu m) GaN layer. Significant improvement in the crystal and optical properties of GaN layer is also achieved. In doping is observed to reduce the stress in AlGaN interlayer measured by high-resolution X-ray diffraction (HRXRD). It can provide more compressive stress to counteract tensile stress and reduce crack density in subsequent GaN layer. Moreover, as a surfactant, indium is observed to cause an enhanced PL intensity and the narrowed linewidths of PL and XRD spectra for the LT-interlayer. Additionally, the crystal quality of GaN layer is found to be dependent on the growth parameters of underneath In-doped LT-AlGaN interlayer. The optimal parameters, such as TMIn flow rate, TMAl flow rates and thickness, are achieved to obtain nearly 2.0 mu m thick crack free GaN film with advanced optical and crystal properties. (c) 2005 Elsevier B.V. All rights reserved.

Structure and visible luminescence of ZnO nanoparticles

ZnO nanoparticles were synthesized in ethanolic solution using a sol-gel method. The structural and optical properties were investigated by X-ray diffraction, transmission electron microscopy, UV absorption, and photoluminescence. After annealing at 200 degrees C, the particle size is increased and the peak of defect luminescence in the visible region is changed. A yellow emission was observed in the as-prepared sample and a green emission in the annealed sample. The change of the visible emission is related to oxygen defects. Annealing in the absence of oxygen would increase oxygen vacancies. (c) 2006 Elsevier Ltd. All rights reserved.

Synthesis and structures of morphology-controlled ZnO nano- and microcrystals

Zinc oxide flower-like bunches were directly synthesized on indium-doped tin oxide (ITO) glass substrates through a simple chemical bath deposition process. By adjusting precursor concentration, other morphologies ( spindles and rods) were also obtained. All of them are hexagonal and single crystalline in nature and grow along the [ 0001] crystallographic direction. The possible growth mechanisms for these nano- and microcrystals were proposed. It was revealed that both the inherent highly anisotropic structure of ZnO and the precursor concentration play crucial roles in determining final morphologies of the products. In addition, vibrational properties of ZnO crystals with different morphologies were investigated by Raman spectroscopy.

Aluminium doping induced enhancement of p-d coupling in ZnO

Valence-band type Auger lines in Al doped and undoped ZnO were comparatively studied with the corresponding core level x-ray photoelectron spectrography (XPS) spectra as references. Then the shift trend of energy levels in the valence band was that p and p-s-d states move upwards but e and p-d states downwards with increasing Al concentration. The decreased energy of the Zn 3d state is larger than the increased energy of the 0 2p state, indicating the lowering of total energy. This may indicate that Al doping could induce the enhancement of p-d coupling in ZnO, which originates from stronger Al-O hybridization. The shifts of these states and the mechanism were confirmed by valence band XPS spectra and 0 K-edge x-ray absorption spectrography (XAS) spectra. Finally, some previously reported phenomena are explained based on the Al doping induced enhancement of p-d coupling.

Temperature dependence of the formation of nano-scale indium clusters in InAlGaN alloys on Si(111) substrates

The temperature dependence of the formation of nano-scale indium clusters in InAlGaN quaternary alloys, which are grown by metalorganic chemical vapour deposition on GaN/Si(111) epilayers, is investigated. Firm evidence is provided to support the existence of phase separation, or nano-scale In-rich clusters, by the combined results of high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction (HRXRD) and micro-Raman spectra. The results of HRXRD and Raman spectra indicate that the degree of phase separation is strong and the number of In clusters in the InAlGaN layers on silicon substrate is higher at lower growth temperatures than that at higher growth temperatures, which limits the In and Al incorporated into the InAlGaN quaternary alloys. The detailed mechanism of luminescence in this system is studied by low temperature photoluminescence (LT-PL). We conclude that the ultraviolet (UV) emission observed in the quaternary InAlGaN alloys arises from the matrix of a random alloy, and the second emission peak in the blue-green region results from the nano-scale indium clusters.

Synthesis and temperature-dependent near-band-edge emission of chain-like Mg-doped ZnO nanoparticles

Chain-like Mg-doped ZnO nanoparticles were prepared using a wet chemical method combined with subsequent heat treatment. The blueshifted near-band-edge emission of the doped ZnO sample with respect to the undoped one was investigated by temperature-dependent photoluminescence. Based on the energy shift of the free-exciton transition, a band gap enlargement of similar to 83 meV was estimated, which seems to result in the equivalent shift of the bound-exciton transition. At 50 K, the transformation from the donor-acceptor-pair to free-to-acceptor emissions was observed for both the undoped and doped samples. The results show that Mg doping leads to the decrease of the acceptor binding energy. (c) 2006 American Institute of Physics.

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.

Structure and visible luminescence of ZnO nanoparticles

ZnO nanoparticles were synthesized in ethanolic solution using a sol-gel method. The structural and optical properties were investigated by X-ray diffraction, transmission electron microscopy, UV absorption, and photoluminescence. After annealing at 200 degrees C, the particle size is increased and the peak of defect luminescence in the visible region is changed. A yellow emission was observed in the as-prepared sample and a green emission in the annealed sample. The change of the visible emission is related to oxygen defects. Annealing in the absence of oxygen would increase oxygen vacancies. (c) 2006 Elsevier Ltd. All rights reserved.

Magnetoresistance in a nominally undoped InGaN thin film

The magnetotransport properties of a nominally undoped InGaN thin film grown by metal-organic chemical vapor deposition were investigated. Resistivity was measured under a magnetic field up to 5 T over the temperature range of 3 to 298 K. The film exhibits a negative magnetoresistance at low temperatures. Its magnitude decreases with increasing temperature, and turns to be positive for temperatures above 100 K. The negative component was described by a model proposed by Khosla and Fischer for spin scattering of carriers in an impurity band. The positive part was attributed to the effect of Lorentz force on the carrier motion. Agreement between the model and the data is presented.

后向无关联性的本地验证撤销群签名研究

数字签名，是密码理论的一个重要分支，在身份认证等方面举足轻重。但随着电子商务、电子政务等业务的不断展开，在多用户参与的应用环境中显得捉襟见肘。群数字签名应运而生，主要特点是保护了签名者的匿名性。 群签名撤销研究的两个主要方向：设计算量小的撤销成员算法，以及保证成员被撤销之前签名的匿名性和无关联性。目前主要有基于撤销列表（RL）和证据的撤销算法是两类主流算法，前者更适用于移动环境中。因此，在网络化、信化的今天，基于撤销列表的群签名的研究显得弥足重要。 本地验证撤销（VLR），是目前效率最高的一种基于撤销列表的方法。后向无关联性（BU），是指当成员即使在某个时段被撤销，以前的签名仍然保持匿名性。本论文主要工作，是对有群签名方案的分析和BU-VLR方案的设计，主要有以下几个方面： 1. 2007年IEEE Transactions on Vehicular Technology上的一个方案，建立在2004年Boneh等在 CRYPTO的群签名方案。本论文指出，方案使得同一成员的签名具有关联性，导致在VLR安全模型下方案不具有匿名性。 2. 分析的另外两个群签名方案，都是方案设计者在设计签名算法时由于设计不当，使得同一成员的签名具有关联性，从而导致方案在相应的安全模型下不具有匿名性。 3. 对一种基于身份的群签名方案，有文献曾对该签名方案做过分析，在本论文将给出另外一种方法来证明方案不具有匿名性。 4. 分析指出了一种新型群签名方案，其本身是建立在一个错误的签名方案之上，因而该方案不过是空中楼阁。此外，方案还存在其他缺陷。 5.构造了一个BU-VLR群签名方案，具有较短的签名长度和较低的运算量。利用k叉树扩展了方案以减少RL的数据量。最后，对2007年IEICE中一个BU-VLR方案加以改进，签名长度为原来的77.8%，运算量不变。 6.设计的第二个方案，针对现有BU-VLR方案中存在的缺陷，使得到的方案公钥长度不再与成员个数相关；撤销上的数据不再随着时间段的更新而更新，而只是在列表需要更新的时间段更新。 7.在q-SDH假设和困难性假设较强的XDH假设下，构造了一个BU-VLR群签名方案，性能上优于目前最高效的VLR方案，即BS04方案。

稀土催化剂合成窄分子量分布聚异戊二烯的研究

本论文利用传统的稀土催化剂组成，探讨了稀土催化剂的配制方式，配制出稳定的均相催化剂；深入探讨了影响聚异戊二烯分子结构的因素，合成了高顺式、高分子量、窄分子量分布且具有与天然橡胶相似的拉伸结晶特点的聚合物；讨论了催化剂活性中心的形成机理；均相催化剂用于丁二烯-异戊二烯共聚合可制备窄分子量分布的无规共聚物。 1. NdCl3•3iPrOH/MMAO催化体系：可在较低的MMAO (Al/Nd < 40)用量下，高收率地合成高的顺式-1,4含量(> 96%)、非常高的分子量(Mn > 100×104)、相当窄的分子量分布(Mw/Mn < 2.0)的聚异戊二烯。与烷基铝助催化剂如Al(i-Bu)3和Al(i-Bu)2H相比，在顺-1,4含量相同的情况下，MMAO体系所得聚合物的分子量最高，分子量分布最窄。催化剂形成配位阳离子性质的活性中心。 2. Nd(vers)3/Al(i-Bu)2H/Al(i-Bu)2Cl催化体系：可在适当的陈化条件下配制出稳定的均相催化剂，该均相催化剂可在较低的Al/Nd用量(Al/Nd = 10)和催化剂用量([Nd] = 0.20 mM)下，高收率(> 80%)地合成高顺式-1,4含量(> 96%)、高分子量(Mn > 50×104)、窄分子量分布(Mw/Mn < 3.0)的聚合物。均相催化剂的活性中心为配位阳离子性质的单活性中心。 3. Nd(vers)3/MMAO/Al(i-Bu)2H/Al(i-Bu)2Cl催化体系：在相当低的MMAO用量(Al/Nd = 10，总铝量Al/Nd = 20)下，仍具有高的催化活性，所得聚合物的分子量较高(Mn 52.4×104)，分子量分布较窄(Mw/Mn < 3.0)，顺-1,4结构含量可达96%。通过调节Al(i-Bu)2H和MMAO用量可以控制聚合物的分子量及分子量分布。 4. Nd(vers)3/Al(i-Bu)3/Al(i-Bu)2Cl催化体系：用Al(i-Bu)3代替Al(i-Bu)2H作助催化剂，可在各种加料方式下高收率地获得高顺-1,4含量(96%)、非常高分子量(Mn > 100×104)、窄分子量分布(Mw/Mn < 3.0)的聚异戊二烯，且所得异戊橡胶在高顺-1,4含量(96%)、高分子量(Mn ≥ 90×104)、窄分子量分布(Mw/Mn ≤ 2.1)时存在拉伸结晶现象，性能接近甚至超过天然橡胶。 5. Nd(vers)3/AlR3(Al(i-Bu)2H, Al(i-Bu)3)/Al(i-Bu)2Cl催化体系在一定条件下，可获得高顺式-1,4含量(丁二烯和异戊二烯的顺-1,4含量均可达99.9%)、高分子量(Mn > 50×104)、窄分子量分布(Mw/Mn < 3.0)的丁二烯-异戊二烯共聚物。只是用Al(i-Bu)3作助催化剂时，均相和非均相催化剂均可得到高顺式、更高分子量(Mn > 100×104)、更窄分子量分布(Mw/Mn < 1.8)的共聚物。两单体的竞聚率为：对于Al(i-Bu)2H体系，rBD = 0.923，rIP = 0.612；对于Al(i-Bu)3体系，rBD = 1.02，rIP = 0.919。表明聚合物为无规共聚物。

铁系催化马来酸酐与烯类单体的共聚

马来酸酐（MAn）与烯类单体的共聚物应用于许多工业领域，这些工业生产都以自由基聚合为主，但自由基聚合的定向性差、分子量分布宽。ZieglarNatta催化剂用于烯烃的聚合可得到结构规整的、分子量分布窄的聚合物，但所采用的中心原子一般都是前过渡金属，这类催化剂在催化烯烃与极性单体共聚的时候催化效率较低，而在烯烃中插入极性单体可改善聚烯烃的性质，扩大其应用范围。本论文采用以后过渡金属铁为中心原子的乙酞丙酮铁（Fe（acac）_3）和三异丁基铝（Al（i-Bu）_3）组成的双组分催化体系催化马来酸酐与烯类单体茵香脑（ANE）、降冰片烯（NBE）及异戊二烯（Ip）的共聚合反应。实验结果表明，在该催化体系中，马来酸酐与烯类单体共聚合反应的机理可初步认为是配位共聚合机理。马来酸酐与茵香脑共聚合反应的适宜条件为：苯为溶剂，n（Al）／n（Fe）＝8，c(M)＝2.8mol／L，c（Fe）＝1.7×10~(-2)mol/L，n(MAn)／n(ANE)＝1，80℃，6h。在该反应条件下，反应收率为77.0％；聚合反应对单体浓度呈一级关系，表观活化能为31.0 KJ／mol；得到的共聚物是交替的，其中马来酸酐的摩尔含量为45.6％（IR、NMR），共聚物的重均分子量为2.28*10~4分子量分布为2.32（GPC）。马来酸酐与降冰片烯共聚合反应的适宜条件为：二氧六环为溶剂，70℃，n（Al）/n（Fe）＝14，n（CCl_4）／n(Fe)=20,n(M)/n(Fe)＝100，n（MAn）／n（NBE）＝1,12h收率为85.4％；CC14的加入可大幅度提高反应的收率，但分子量却大大降低，虽然共聚物的分子量较小（M_W=2713），但具有较好的溶解性，分子量‘分布为1.31，共聚物中不含CCl_4部分。马来酸酐与异戊二烯共聚合反应的适宜条件为：甲苯与二氧六环的混合溶剂（T／D＝2/5），n（MAn)／n（Ip）＝1，n（Al）／n（Fe）=8，c（M）= 4.1mol／L，c（Fe）＝5.8×l0~(-3) mol／L，20℃，2h，收率78.3％。在该条件下得到的共聚物中马来酸酐的摩尔含量为53.1％（元素分析），并发生部分交联，不溶于有机溶剂中，而采用极性溶剂如二氧六环时，所得共聚物能微溶于四氢吠喃中。综上所述，铁系催化体系催化马来酸酐与烯类单体的共聚合反应可得到产率高、分子量分布较小、具有一定交替度的共聚物。

ZnO基稀磁半导体的制备与性质研究

本论文利用溶胶一凝胶法和水热法制备了不同离子（Eu~3＋，Sm~3＋，Mn~2＋，Fe~3＋，Co~2＋，Ni~2＋）作为磁性杂质的ZnO基稀磁半导体，并系统地研究了材料的薄膜、粉末和纳米结构的结晶特性、结构形态和光、电、磁性质。溶胶一凝胶法制备的薄膜的晶体为c轴取向生长的六方纤维锌矿结构。薄膜的取向生长受烧结气氛、烧结温度和掺杂离子浓度的影响，其中烧结气氛是影响薄膜取向生长的最直接、最显著因素。随着烧结气氛中氧含量的减小，薄膜的沿c轴生长的趋势加强。此外，烧结温度的提高也增强薄膜沿c轴生长的趋势，但掺杂离子浓度的增加却抑制薄膜的c轴取向生长特性。通过薄膜表面形态的研究发现，在空气中烧结的薄膜由立方晶粒构成，而在真空中烧结的样品则由不规则的片状晶粒组成。组成薄膜的多晶颗粒粒径小于10Onm，15层薄膜的膜厚为357-366nm。掺杂离子在薄膜中均匀分布，成膜过程不改变掺杂离子（Eu3+，Sm3＋，Mn2+，Fe3＋，Co2＋，Ni2＋）和基质离子（Zn2+和O2-）的价态。 不同Eu3+掺杂浓度的ZnO薄膜样品的吸收光谱的吸收边出现在363nm和368nm之间，对应半导体材料的禁带宽度Eg=3.42～3.40ev。由于Eu3＋改变了薄膜的表面性质，Zn1-xEux（0.005≤x≤0.15）薄膜在可见光区出现了一系列干涉带。Zn1-xTMxO薄膜的吸收光谱的吸收边位置出现在356nm-369nm，对应半导体的禁带宽度为3.34-3.46eV，在可见光区发现了Co2＋的电子的d-d跃迁引起的吸收带。随着掺杂浓度的增加，薄膜的透光率逐渐减小。Zn1-xCoxO薄膜在近紫外与可见光区的透光率都在60％以上，Zn1-xEuxO薄膜的透光率则高达90％。在Zn1-xEuxO薄膜的激发发射光谱中，以613nm作为监控波长，激发光谱除了检测到Eu3＋的7F→5D能级的吸收跃迁外，还检测到最大值位于378nm附近的ZnO的吸收带。以394nm为激发波长，发射光谱检测到Eu3+的5D0→7FJ（J＝1，2，3，4）跃迁。以zno的带隙能量378nm作为激发波长进行激发，检测到Eu3+的5D0→7F2跃迁，说明基质zno和E矿十之间存在能量交换。薄膜磁性测试在4-400K温度范围内进行，发现在此温度范围内Zn0.9Eu0.1O薄膜表现居里一外斯顺磁性；在低温区，存在磁性增强现象。zno．gCoo．IO薄膜在23oK以下表现为铁磁性，200K的M-H曲线显示薄膜的剩磁（Br）约为0．21em侧g，矫顽力（Hc）约为327Oe。但Zn0.9Mn0.1O，Zn0.9Ni0.1O，Zn0.9Co0.1O薄膜的磁性测试则显示在80K以上三种薄膜均表现为顺磁性。Zn0.9Eu0.1O薄膜的电阻呈现典型的半导体性质，在ZT的磁场下，薄膜在110K获得最大14.53％的磁阻率。Zn1-xTMxO薄膜的电阻也表现典型的半导体特性，实验研究了薄膜在不同掺杂离子浓度、外加磁场以及温度条件下的磁阻性质。粉末样品中磁性离子的掺杂浓度均小于薄膜样品。Co，Fe，Ni，Mn掺杂的Zn1-xTMxO粉末在80以上均为顺磁性。在Co2＋掺杂的粉末样品中没有发现类似于薄膜样品的铁磁性，说明DMS的磁性与制备条件关系密切。实验证明了利用sol-gel方法，Zno：TM稀磁半导体能够有效地组装在MCM-41和AAO的孔道内。ZnO:TM材料组装进在MCM-41孔道后，不改变孔道的六方结构但使孔径变小。随着组装次数的增加，MCM-41的孔径和孔容累进减小。组装在AAo模板孔道内的材料呈单分散纳米颗粒状态，颗粒粒径小于loonm。组装材料的磁性测试显示：组装在MCM-41内的Zn0.9Co0.1O材料在80K-30OK呈现超顺磁性。而Mn，Fe，Ni掺杂的Zno在此温度范围内表现顺磁性。组装在AAO内的ZnO:TM(TM=Mn，Fe，Co，Ni）材料在SOK-30OK温度范围内都呈现顺磁性。在水热法合成ZnO:A（A＝Bu，Sm，co）纳米粒子的过程中，发现反应温度、压力、时间和溶液浓度等因素只影响Znl．xCoxO纳米粒子的的产量，而溶液的酸度却影响产物的形貌。控制溶液的酸度，可以控制产物的形貌从粒状向棒状转变。当溶液的PH＝5时，在甲醇：水体系中可以水热合成规则的棒状ZnO：RE（RE=Eu，Sm）纳米晶。所得到的Zn0.98Co0.02O纳米晶在80K呈超顺磁行为，而ZnO：RE（RE＝Eu，Sm）纳米晶在80K则表现较弱的顺磁性。 实验通过控制水热条件，制备了一种新型结构的柠檬酸锌晶体。由于利用了水热反应的非平衡合成条件，所得到的晶体的层状结构不同于目前已知的所有柠檬酸配合物的离散型分子结构。单晶衍射结果表明：化合物是一个由八面体和一个非对称单元交替相连构成的二维层状结构。