溶剂效应对DCM发光特性的影响

有机发光二极管利用有机半导体光电功能材料的电致发光效应,具有许多优异性能,是新一代有发展前途的平板显示器件及光源。有机发光材料的光电特性、光物理、光化学过程直接决定了有机发光二极管的性能。利用荧光光谱方法观察典型高效有机小分子激光染料DCM在不同溶剂中的发光特性,研究其与溶剂分子的相互作用,即溶剂效应对其发光特性的影响。结果表明DCM溶液的荧光光谱中心波长随溶剂极性增大而红移,相对发光强度基本上随溶剂极性增大。同时,还观察了不同浓度DCM溶液的发光特性,研究DCM分子间相互作用导致的浓度猝灭效应,结果表明DCM溶液浓度为10^-6mol／L时,DCM溶液相对发光强度最大。     

花状的氧化锌纳米结构的制备及其光学性能

以氢氧化钠和六水合硝酸锌为反应物,在未使用任何表面活性剂的简单反应体系中制得了玫瑰花状ZnO纳米结构,采用X射线衍射(XRD)、扫描电子显微镜(SEM)和室温荧光光谱对产物的晶体结构、形貌和发光性质进行了表征和分析.测试结果表明,所得产物为六方纤锌矿结构ZnO纳米材料,产物结晶完整,尺寸较均匀.这种简单水热法制备的ZnO纳米材料仅在384nm处具有一个较强的紫外发光峰,而在黄绿区几乎没有发光峰,进一步证明了所得样品结晶良好,没有缺陷和空位.以上结果表明所制备的氧化锌纳米材料具有优异的紫外光发射能力.     

Synthesis and Solvent Polarity-Sensitive Photoluminescent Property of 4-Phenylethynyl-4'-Dimethylaminochalcone

以4-溴-4'-二甲氨基查尔酮和苯乙炔为原料,通过Sonogashira钯催化偶联反应合成了4-苯乙炔基-4'-二甲氨基查尔酮,并通过红外光谱和核磁共振氢谱对其结构进行了表征.进一步研究了4-苯乙炔基-4’-二甲氨基查尔酮在不同极性的溶剂中的紫外可见吸收光谱和荧光光谱,结果表明该化合物具有极性敏感的发光特性.     

聚乙烯亚胺对氧化锌纳米阵列形貌的影响

采用化学沉淀法,以硝酸锌和六次亚甲基四胺的水溶液为生长溶液,在涂覆氧化锌晶种层的玻璃衬底上制备了定向生长的氧化锌纳米棒阵列,并研究了添加剂聚乙烯亚胺的浓度对氧化锌纳米棒形貌和结构的影响。X射线衍射和场发射扫描电镜的结果表明,合成的氧化锌纳米棒阵列较为均匀致密,具有六方纤锌矿结构,且有沿(002)晶面择优生长的特性;随着聚乙烯亚胺浓度的增加,氧化锌纳米棒的直径减小,直径分布趋于均匀,且氧化锌纳米棒的形貌也从锥状转变为柱状结构;另外,聚乙烯亚胺的加入对氧化锌的生长速度具有抑制作用,当聚乙烯亚胺的浓度增加至0.012 mol·L-1时,无氧化锌阵列生长。对氧化锌纳米棒阵列进行了拉曼光谱表征,结果表明,随着溶液中聚乙烯亚胺浓度的增加,氧化锌纳米棒的氧空位缺陷减少。最后,对聚乙烯亚胺浓度对氧化锌纳米阵列影响的机理进行了探讨。     

网络状表面结构纳米氧化锌的发光特性

为研究表面形貌对微纳结构氧化锌晶体光学特性的影响,利用气相传输法制备了一种具有特殊表面结构的纳米氧化锌颗粒状样品.应用X射线衍射谱、电子能量散射谱和扫描电镜等对样品结构和形貌进行了分析,结果表明样品具有三种层次结构组成的网络状表面形貌|室温下以波长355 nm激光激发样品,观察到紫外峰明显被抑制的发光谱.基于样品表面周期性微结构,用时域有限差分法和严格耦合波分析法对样品发光谱特性及成因进行仿真研究.结果表明,发光谱中紫外峰的被削弱与材料能级结构无关,其形成机理缘于样品表面类蝴蝶翅膀表面微结构,类似于光子晶体表面结构颜色.     

水热法制备形貌可控的ZnMoO4微晶及其光致发光性能

以Zn(Ac)2和(NH4)6Mo7O24.4H2O为原料,分别以CTAB、SDS、PVP-K30作为辅助剂,采用水热法合成了不同形貌和结构的ZnMoO4微晶。使用X射线衍射(XRD)、扫描电镜(SEM)及光致发光光谱(PL)等分析手段对所得材料的结构、形貌及发光性能进行了分析和表征。测试结果表明:通过改变辅助剂的种类、用量和反应时间可以合成形貌可控的ZnMoO4微晶,不同形貌的样品发光强度不同,但发射中心均在565 nm左右。     

多孔ZnO微米球的制备及其优异的丙酮敏感特性

以六水合硝酸锌、尿素为原料,以六亚甲基四胺为表面活性剂,利用水热法合成了多孔氧化锌微米球.通过X射线衍射仪、扫描电子显微镜和吸附仪对样品的结构、形貌、比表面积和孔径进行了表征.利用所得多孔微米球氧化锌制备了气敏元件,并对其气敏特性进行了测试.结果表明:在280℃的工作温度下,表面多孔氧化锌微米球气敏元件对50 ppm的丙酮气体的灵敏度为26.8,响应时间和恢复时间分别约为4 s和10 s,并具有良好的选择性.     

电场条件下氧化锌结晶特性及极化产物的拉曼光谱分析

开展高压电场调控纳米材料结构形貌和性能研究在功能材料领域具有重要的理论和实际意义.本文在高压电场条件下合成了氧化锌纳米粉体,并对粉末试片进行了后期电场极化处理,研究了电场对氧化锌的结构形貌、点缺陷、拉曼光谱的影响.以X射线衍射仪(XRD)、扫描电镜(SEM)和拉曼光谱仪对产物的结构形貌、拉曼位移、缺陷分布等进行了表征.结果表明,高压电场条件下氧化锌的完全晶化时间和温度比未施加电场时明显延长和升高,直流电场能够显著促进前驱物中氧化锌的形核,并降低晶化速度.不同电场强度下氧化锌具有不同的显微形貌.纳米氧化锌粉末试片在直流电场中极化后,其阴极面和阳极面的拉曼光谱表现出明显的差异.有明显漏电电流的情况下,阳极面在1050 cm~(–1)处的二级光学声子模A_1(LO)的强度显著提高,且拉曼强度I_1=438 cm~(–1)和I_2=1050 cm~(–1)的比值与极化电场的场强呈线性关系.当调转试片正反面进行二次极化时,原来在阳极面尖锐的1050 cm~(–1)峰经过阴极极化而消失.阳极面1050 cm~(–1)拉曼峰的锐化与氧化锌晶粒内的缺陷重新分布和双肖脱基势垒有关.     

有序ZnO纳米阵列的制备及其光学特性

纳米球刻蚀技术和磁控溅射方法在普通玻璃衬底上制备有序氧化锌(ZnO)纳米阵列。利用扫描电子显微镜对样品表面形貌进行了观测,并对样品进行荧光(PL)光谱测试。结果表明,相比于普通ZnO薄膜,ZnO纳米阵列的有序结构可以提高在紫外区域的发光性能,减少蓝绿光的发射缺陷。研究了不同ZnO纳米阵列粒径大小和不同ZnO纳米阵列的厚度对其光学性质的影响。溅射时间30min的有序ZnO纳米阵列样品的质量和结晶状态较好,随着聚苯乙烯(PS)纳米球粒径的减小,样品吸收峰和荧光光谱均发生"蓝移"。     

高温热处理a面AlN表面形貌演变机理

非极性a面AlN(a-AlN)能够从根本上解决极性AlN引起的量子限制斯塔克效应问题,是提升AlGaN发光器件效率的有效途径。但是,非极性AlN生长面临更大的挑战,目前难以实现低缺陷密度、高平整表面的非极性a-AlN。高温热处理是一种提高AlN质量的有效方法,但在热处理过程中,非极性a-AlN的表面形貌演变的物理机理尚不明确,直接影响了a-AlN表面改善与质量提升。本研究通过对a-AlN薄膜在不同条件下进行高温热处理,对样品的表面形貌演变过程进行了表征与分析,并结合第一性原理计算,揭示了高温热处理对非极性a-AlN表面的影响及其物理机理。结果表明,在高温热处理过程中Al、N原子更趋向于从a面与m面分解,而在c面吸附,使得a-AlN样品表面在高温热处理过程中出现了沿c轴方向的高取向性条纹原子台阶形貌,进而提高a-AlN材料质量。本研究为实现高质量非极性a-AlN材料及紫外发光器件提供了重要基础。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.