氮气氛中高温退火对ZnO薄膜发光性质的影响

以二乙基锌和水汽分别作为锌源和氧源,用LP-MOCVD方法在p型Si(100)衬底上生长了单一取向的ZnO薄膜。对得到的样品在氮气气氛中进行高温热处理,退火温度分别为900,1000,1100℃。利用室温PL谱、XRD、AFM、XPS等方法对样品的性质进行了研究。研究表明:(1)随着退火温度的升高,样品的结晶性质也逐渐提高,从表面形貌观察到晶粒尺寸逐渐增大;(2)当退火温度从900℃升高至1000℃时,样品的光致发光谱中可见光波段的发光强度有所减弱,而紫外波段的发光强度明显增强;当退火温度升高至1100℃时,可见光波段的发光几乎完全被抑制,而紫外波段的发光强度急剧增强。分析认为,高温退火改善晶体结晶质量的同时调制了样品的Zn/O比,氮气气氛下的热处理使得样品内的氧原子逸出,来自受主缺陷OZn的可见发射随温度升高逐渐减弱,而当退火温度达到1000℃以上时样品成为富锌状态,此时与施主缺陷Zni有关的紫外发射急剧增强。     

离子注入及后退火方法制备SiO2基质中镶嵌ZnO纳米粒子的结构和光学性质

利用离子注入及后退火方法在光学纯的石英基片中注入3×1017cm-2剂量的Zn离子,然后在不同的退火条件下制备了高质量的镶嵌在SiO2基质中的ZnO纳米粒子.X射线衍射光谱的实验结果表明在氧气气氛、700℃退火温度和2小时退火时间条件下,得到了(002)择优取向镶嵌在SiO2基质中的ZnO纳米粒子;而在700℃退火温度、N2和O2气氛下顺次退火1小时,得到了比上述条件(002)择优取向更好的ZnO纳米粒子.室温下对用上述两种条件制备的镶嵌在SiO2基质中的ZnO纳米粒子观察到了自由激子吸收峰.室温光致发光谱中观察到了ZnO纳米粒子位于3.29eV处的强紫外发射,紫外发射强度与深能级发光强度之比为40,紫外发射峰的半高宽为96meV,晶体质量类似于分子束外延方法生长的ZnO.在低温(77K)光致发光谱中,较强的自由激子的紫外发光峰仍然存在.     

热处理温度对ZnO：Al薄膜性能的影响

利用溶胶-凝胶技术在玻璃衬底上制备了ZnO:Al薄膜,表征了薄膜的结构、光透过和光致发光特性,探讨了热处理温度对薄膜晶体结构和光学性质的影响.结果表明,在热分解温度400 ℃和退火温度600 ℃时,ZnO:Al薄膜的C轴择优取向明显,透过率较高.在热处理温度400 ℃情况下,激发波长340 nm的光致发光谱中有三个发光中心,紫外发光强度随退火温度的升高先升高后下降,500 ℃时发光强度最强.其它两个发光峰的强度随退火温度的升高而降低甚至消失.激发波长不同,ZnO:Al薄膜的发光中心和强度均发生变化.     

热处理温度对ZnO∶Al薄膜性能的影响

利用溶胶-凝胶技术在玻璃衬底上制备了ZnO∶Al薄膜,表征了薄膜的结构、光透过和光致发光特性,探讨了热处理温度对薄膜晶体结构和光学性质的影响.结果表明,在热分解温度400 ℃和退火温度600 ℃时,ZnO∶Al薄膜的C轴择优取向明显,透过率较高.在热处理温度400 ℃情况下,激发波长340 nm的光致发光谱中有三个发光中心,紫外发光强度随退火温度的升高先升高后下降,500 ℃时发光强度最强.其它两个发光峰的强度随退火温度的升高而降低甚至消失.激发波长不同,ZnO∶Al薄膜的发光中心和强度均发生变化.     

聚氧化乙烯表面修饰对ZnO光学性质的影响

利用聚氧化乙烯(PEO)对ZnO表面进行修饰,研究有机包覆对ZnO光学性质的影响。用吸收光谱和光致发光光谱来表征和研究PEO包覆对ZnO纳米粒子光学性质的影响。吸收光谱结果表明随着ZnO薄膜中PEO含量的增加,激子吸收峰逐渐向低能侧方向移动。光致发光光谱是由紫外发射和与氧空位有关的深能级缺陷发光组成,且随着ZnO薄膜中PEO含量的增加,紫外发射与深能级发光强度之比逐渐增大,当ZnO薄膜中的PEO达到最大值时,其比值为31．5,远远大于纯ZnO薄膜的紫外发射与深能级发光强度之比1．04。由此可见,ZnO被PEO包覆后,提高了紫外发光效率,改善了ZnO薄膜的质量。     

ZnO/Zn界面对纳米ZnO薄膜光学性质的影响

采用氧等离子体辅助电子束蒸发金属Zn后低温退火的方法制备纳米ZnO薄膜。利用X射线衍射(XRD)谱、拉曼(Raman)谱、X射线光电子能谱(XPS)以及光致发光(PL)谱等手段,分析了退火温度及ZnO/Zn界面对样品的结构和发光性质的影响。Raman结果表明随着退火温度的升高,界面模式(Es)振动减弱并向低波数方向移动。当退火温度为400℃时,界面振动消失,Zn全部转化成具有六方纤锌矿结构的ZnO,得到化学配比的纳米ZnO薄膜。PL谱表明,经400℃退火处理的样品紫外发射最强,发光性质最好。     

稀土Tb3+掺杂纳米ZnO的发光性质

ZnO是一种优良的直接宽带隙半导体发光材料(Eg=3.4 eV),具有优异的晶格、光学和电学性质,稀土离子掺杂浓度和热处理温度对ZnO∶Re3 纳米晶发光强度、峰位变化等光学性质具有重要影响.利用溶胶-凝胶法(Sol-Gel),在不同退火温度下,制备了不同浓度的ZnO∶Tb3 纳米晶.室温下,测量了样品的X射线衍射谱(XRD)、光致发光谱(PL)和激发谱(PLE).观察到纳米ZnO基质在520 nm附近宽的绿光可见发射和稀土Tb3 在485,544,584和620 nm附近的特征发射.通过ZnO基质可见发射强度和稀土Tb3 特征发射强度随Tb3 掺杂浓度、退火温度的变化关系,获得了5D4→7F5跃迁的绿色主发射峰最强的样品制备工艺参数,其退火温度为600℃、掺杂浓度为4 at%;给出了稀土Tb3 的激发态5D4→7F6(485 nm),5D4→7F5(544 nm)和5D4→7F4(584 nm)的发射机制;证实了稀土Tb3 与纳米ZnO基质之间存在双向能量传递.     

纳米ZnO和ZnO∶Eu3+的表面效应及发光特性

纳米ZnO, ZnO:Eu3+及其添加覆盖层样品的光谱性质表明,表面有机物覆盖层具有改善发射光谱, 增强基质与Eu3+间能量传递的良好效果. 通过比较不同温度(60,800℃)处理的ZnO:Eu3+发光强度, 发现了小尺度(纳米)颗粒的特殊发光行为.     

热处理参数对溶胶-凝胶法制备氧化锌薄膜特性的影响

采用溶胶-凝胶旋涂法在Si(111)衬底上生长了ZnO薄膜，并用荧光光谱、原子力显微镜和XRD对ZnO薄膜样品进行了分析.结果表明，溶胶-凝胶旋涂法制备的ZnO薄膜为纤锌矿结构，其c轴取向程度与热处理温度有很大的关系.当热处理温度小于550℃时，氧化锌薄膜在室温下均有较强的紫外带边发射峰，而可见波段的发射很弱；当热处理温度高于550℃时，可见波段发射明显增强.对经过不同时间热处理的ZnO薄膜样品分析表明，氧化锌薄膜的荧光特性及表面形貌与热处理时间也有很大关系，时间过短可见波段的发射较强，但时间过长会导致晶 关键词： ZnO薄膜 光致发光     

沉淀法制备In/ZnO纳米粉及其发光特性

采用沉淀法制备In/ZnO纳米粉,通过XRD和光致发光谱等分析手段,详细讨论了不同In掺杂浓度、煅烧温度、反应物配比,以及沉淀剂种类对In/ZnO纳米粉微结构及光致发光特性的影响。实验结果表明,随着In掺杂浓度的增加,In/ZnO纳米粉的结晶性能和紫外发光强度因杂质缺陷的增多而逐渐减弱;同时观察到该发光峰位从389nm红移至419nm,这可能是由于施主能级和导带的合并,以及杂质能级的潜在波动因素的影响所致。当煅烧温度从500℃升至600℃时,晶粒尺寸逐渐变大,紫外发射强度也因结晶性的增强而逐渐增大;当温度继续升高至800℃时,结晶性的进一步提高导致紫外发射强度增强,同时由于温度的升高使得ZnO晶格中离子动能变大而更易于产生氧空位,从而导致525nm绿光发射也大大增强;当温度升高至1 000℃时,紫外发射强度由于过多的氧空位而被极大抑制,此时525nm绿光发射成为了发光主成份。随着反应物NH4HCO3/Zn(NO3)2摩尔比的增加,由于反应速率的加快,使得In/ZnO纳米粉晶粒变小,紫外发光强度下降。沉淀剂种类(NH4HCO3或NaOH)对前驱体粉末的结晶性能有着显著的影响,但对最终纳米粉产物的发光性能影响不大。     

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.