LB薄膜的线性电光效应

本文用电光微分表面等离子激元光谱研究芪盐单分子层LB薄膜在不同光波长处(488nm,633nm和832nm)的电光响应.指出这是一种十分有效,简便的评估厚度小于100nm超薄膜非线性光学特性的实验技术.     

不同厚度溅射Ag膜的微结构及光学常数研究

用直流溅射法在室温Si基片上制备了4．9nm-189.0nm范围内不同厚度的Ag薄膜，并用X射线衍射及反射式椭偏光谱技术对薄膜的微结构和光学常数进行了测试分析。结构分析表明：制备的Ag膜均呈多晶状态，晶体结构仍为面心立方；随膜厚增加薄膜的平均晶粒心潮6．3nm逐渐增大到14．5nm；薄膜晶格常数均比标准值（0．40862nm)稍小，随膜厚增加，薄膜晶格常数由0．40585nm增大到0.40779nm。250nm-830nm光频范围椭偏光谱测量结果表明：与Johnson的厚Ag膜数据相比，我们制备的Ag薄膜光学折射率n总体上均增大，消光系数k变化复杂；在厚度为4．9nm-83.7nm范围内，实验薄膜的光学常数与Johnson数据差别很大，厚度小于33．3nm的实验薄膜k谱线中出现吸收峰，峰位由460nm红移至690nm处，且其对应的峰宽逐渐宽化；当膜厚达到约189nm时，实验薄膜与Johnson光学常数数据已基本趋于一致。     

对硅片上自组装生长的Pentacene薄膜生长机制及其结晶相态的研究

采用热蒸发的方法在硅片衬底上自组装生长的Pentacene薄膜,薄膜在80℃温度下经2 h恒温真空热处理,通过原子力显微镜(AFM)对Pentacene薄膜表面形貌及其生长机制进行研究.结果得到,在硅片上生长的Pentacene薄膜足以台阶岛状结构生长,其岛状直径约为100 nm.且Pentacene分子以垂直于衬底的方向生长,台阶岛状结构中每个台阶的平均高度约为1.54 nnl·s-1,与Pentacene分子的沿长轴方向的长度相近.从Pentacene薄膜的XRD图谱中可以看出,薄膜在形成的过程中会因条件的不同而形成不同的结晶相,分别为薄膜相和三斜体相,且薄膜的结晶相将随着薄膜厚度的增加向三斜体相转变,其临界厚度为80和150 nm,当薄膜大于150 nm时,薄膜的三斜体相占主导地位,而当Pentacene薄膜的厚度小于80 nm时,Pentacene薄膜呈薄膜相存在.     

基于铝浸润层的超薄银透明导电薄膜研究北大核心CSCD

超薄银薄膜具有高柔韧性和优良的光电性能,是用于透明导电电极的潜在材料。通过电阻热蒸发技术以金属铝作为浸润层制备超薄银透明导电薄膜。引入铝浸润层降低银薄膜的阈值厚度,使银薄膜在K9玻璃基底上以尽可能低的厚度达到连续。对不同厚度铝浸润层上银薄膜方块电阻进行测试,经SEM图像验证后得出,1 nm铝浸润层对银薄膜具有较好的浸润效果。随后采用相同的工艺在1 nm铝浸润层上制备了不同厚度的银薄膜,透过率和方阻测试结果表明,1 nm铝浸润层上制备的10 nm银薄膜方阻值可达到13Ω/,其在0.4μm~2.5μm波段内透过率可达到50%以上。     

近红外波段锑基铋掺杂薄膜厚度对光学常数与光学带隙的影响

采用磁控溅射法制备了不同厚度的锑基铋掺杂薄膜,用X射线衍射(XRD)和透射电子显微镜(TEM)研究了薄膜结构随厚度的变化。利用椭圆偏振法测定了样品薄膜在近红外波段的光学常数与光学带隙,研究了膜厚对样品薄膜光学常数和光学带隙的影响。结果表明,膜厚从7 nm增加至100 nm时,其结构由非晶态转变为晶态。在950～2200 nm波段,不同厚度薄膜样品的折射率在4.6～8.9范围,消光系数在0.6～5.8范围,光学带隙在0.32～0.16 eV范围。随着膜厚的增加,薄膜的折射率和光学带隙减小,而消光系数升高;光学常数在膜厚50 nm时存在临界值,其原因是临界值前后薄膜微观结构变化不同。     

厚度诱导的YBa2Cu3O7-δ超导薄膜剩余应力及临界电流变化

本文通过脉冲激光沉积法制备了不同厚度(80nm、320nm、1000nm和2000nm)的YBa2Cu3O7-δ(YBCO)超导薄膜,对它们的剩余应力和临界电流特性进行了对比研究.通过系列的激光显微Raman光谱和磁化曲线测量分别获得了薄膜剩余应力和磁化临界电流密度(Jc)对薄膜厚度的依赖关系.结果显示超导薄膜内剩余应力越小,Jc越高.对于中等厚度的薄膜样品(320nm和1000nm),其膜内剩余应力较小,同时由其特征的磁通匹配场大小推知在该厚度范围内的样品具有较高的线性缺陷密度,从而显示出较高的Jc值.     

溶胶-凝胶法制备Si基ZnO薄膜的光伏特性

用溶胶-凝胶法在P型半导体Si（100）基片上生长了具有六角晶形的ZnO薄膜。SEM和XRD显示,C轴择优取向性明显,薄膜生长质量较好。ZnO薄膜的光致发光谱不仅有384.2nm的紫外波峰（FWHM=20.3nm）,而且还有649.2nm的红光波峰（FWHM=214nm）,两峰相对高度比为0.934。用波长为632.8nm的氦氖激光照射ZnO薄膜的表面,产生了明显的光伏效应。     

ZnO薄膜的反射、透射光谱及能带结构测量

采用正入射的方法研究了生长在硅基片上的氧化锌薄膜的反射光谱，测量出氧化锌薄膜的光学吸收边在370nm，所对应的能量值为3.35eV，测量生长在石英玻璃基片上的氧化锌薄膜的透射光谱，得到相同的吸收边，表明ZnO薄膜的光学禁带宽度与体材料的禁带宽度一致，反射谱中，在550－600nm之间观察到一个吸收峰，吸收峰的位置以及吸收边的陡峭程度都薄膜的结晶状况的不同而有所不同。     

薄膜厚度对射频磁控溅射β-Ga2O3薄膜光电性能的影响

本文在室温下利用射频磁控溅射技术在(001)蓝宝石衬底上制备了不同厚度的β-Ga₂O₃薄膜,随后将其置于氩气气氛中800℃退火1 h.利用XRD,SEM,UV-Vis分光光度计、PL光致发光光谱仪和Keithley 4200-SCS半导体表征系统等考察薄膜厚度对所得氧化镓薄膜相组成、表面形貌、光学性能以及光电探测性能的影响.结果表明,随着薄膜厚度的增加,薄膜结晶质量提高,840 nm薄膜最佳,1050 nm薄膜结晶质量略有降低.不同厚度β-Ga₂O₃薄膜在波长200—300 nm日盲区域内均具有明显的紫外光吸收,禁带宽度随着薄膜厚度的增加而增加.PL谱中各发光峰峰强随着薄膜厚度的增加而减小,表明氧空位及其相关缺陷受到抑制.在β-Ga₂O₃薄膜基础上制备出日盲紫外光电探测器的探测性能(光暗电流比,响应度,探测率,外量子效率)也随薄膜厚度的增加呈先增后减的趋势.厚度约为840 nm的β-Ga₂O₃紫外光电探测器,在5...     

钛酸锶钡薄膜的室温光学性能研究

采用溶胶-凝胶法制备了(Ba0.75Sr0.25)TiO3薄膜,研究了不同退火温度下样品的物相结构、薄膜的光致发光性能和光学透过率。结果表明:室温下非晶钛酸锶钡薄膜在蓝光激发下具有明显的发光现象,发光波长范围是500～650 nm,峰值在525 nm附近。延长非晶态薄膜的退火时间能够显著提高样品的发光强度,且发光强度随薄膜厚度增加而增大。晶态薄膜有微弱的发光现象。透射谱测试结果表明,钛酸锶钡薄膜在可见光范围内具有良好的光学透过率。     

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.