铁钝化多孔硅的制备及光致发光机理研究

采用水热腐蚀法在相同环境下制备了不同晶型的铁钝化多孔硅样品。同一样品表面具有相似的孔隙结构,不同样品形貌存在差异。在300 nm光激发下,样品发光峰位于618 nm附近,半高宽约为132 nm。傅立叶红外变换光谱显示样品中有强的Si-Si、Si-O-Si、O_<em>y-Si-H_x化学键振动吸收。结果表明,水热腐蚀法制备的铁钝化多孔硅表面形貌与腐蚀过程的局域电极分布关系密切。样品的光致发光行为可归因于量子限制-发光中心作用,并受非桥氧空穴发光中心数量影响。     

水热腐蚀时间对铁钝化多孔硅表面形貌和光致发光的影响

采用水热腐蚀法制备了4个腐蚀时间不同的铁钝化多孔硅样品,铁钝化多孔硅样品表面呈海绵结构,随着腐蚀时间增加,样品表面的平整度下降,腐蚀孔尺寸差别有增大的趋势。在250nm光激发下,样品发光峰位于620nm附近,半峰全宽约130nm。腐蚀时间从10min增加到40min,4个样品的发光峰并未出现定向的红移或蓝移。结合样品傅里叶变换红外吸收光谱的结果,铁钝化多孔硅的光致发光行为可归因于量子限制-发光中心作用,相应的辐射复合发光中心为非桥氧空穴。     

非桥氧空穴发光中心对铁钝化多孔硅光致发光的影响

采用水热腐蚀法制备了铁钝化多孔硅样品,样品光致发光谱的荧光峰位于2.0eV附近,半峰宽约为0.40eV。激发波长从240nm增大到440nm的过程中,荧光峰先红移再蓝移,最后基本稳定,变化曲线呈勺型。通过分析15片发光多孔硅样品的统计结果,发现荧光峰逆转所对应的激发波长位于330nm附近,相应的激发光子能量约为3.8eV。样品光致发光谱随激发波长的勺型变化过程与≡Si—O↑和≡Si—O↑…H—O—Si≡两类非桥氧空穴发光中心共同作用时的发光行为一致。     

多孔硅量子点中的电子局域态

经过激光辐照和高温退火加工能够生成多孔硅样品,在650—780 nm处检测到很强的光致荧光（PL）峰,并且有明显的钉扎和增强效应.实验表明,这种PL发光的强度与样品受辐照和退火的时间短密切相关.通过第一性原理模拟计算发现,样品表面用SiO 双键和Si—O—Si桥键钝化,能隙中会出现电子局域态.激光辐照和高温退火的时间长短决定了样品表面SiO双键和Si—O—Si桥键的密度,而该密度正是影响多孔硅量子点中电子局域态生成的关键. 关键词： 多孔硅量子点 硅氧钝化键 电子局域态     

少子寿命和表面形貌与多孔硅发光性能的关系

研究了不同时间腐蚀的多孔硅的光致发光性能与多孔硅的表面形貌和少子寿命之间的关系。结果表明,多孔硅的发光来自与氧空位有关的缺陷,而多孔硅表面的氢原子能够钝化多孔硅表面的非辐射中心从而提高多孔硅的发光效率。多孔硅的空隙度随腐蚀时间的延长而增大,这也导致了多孔硅的少子寿命的降低,从而造成多孔硅的光致发光效率随多孔硅空隙度的增大以及少子寿命的降低而提高。另外,原子力显微照片表明长时间的腐蚀使多孔硅表面层被化学腐蚀,从而降低了多孔硅表面的粗糙度。     

氢等离子体气氛中退火多孔硅的表面和光荧光特性

用电化学腐蚀法制备了多孔硅(PS),在氢等离子体气氛中不同温度下对多孔硅样品进行了退火处理,并进行了光致发光(PL)谱和原子力显微镜(AFM)表面形貌的测量。不同退火温度给PS表面形态带来较大变化,也影响了其PL谱特性。在退火的样品中观察到的PL谱高效蓝光和紫光谱带,我们认为主要源于量子限制发光峰和非平衡载流子被带隙中浅杂质能级所俘获而引起的辐射复合所产生的。在420—450℃退火处理的多孔硅的PL谱上观察到了一个未见诸于报道的紫光新谱带(3．24eV,382nm),其发光机理有待于进一步研究。     

n型多孔硅光致发光研究

对在无光照条件下,电化学阳极腐蚀方法制备的n型多孔硅进行了光致发光性能研究.在325nm的激发光照射下,多孔硅样品的发光峰在620nm处,其橙红色的发光肉眼可见,并随阳极电流密度与腐蚀时间乘积的增加.先增强,后减弱.其发光峰位置与量子限制效应、表面态及缺陷态有关,发光强度与样品表面深度较浅孔洞所占的面积比成正比.     

多孔硅的光致发光和红外吸收光谱研究

用电化学腐蚀法制备出多孔硅系列样品.室温下具有明亮可见的光致发光.增大电解电流或延长腐蚀时间,发光光谱明显地“蓝移”;提高样品测量温度,发光光谱也明显地“蓝移”。红外吸收光谱表明多孔硅中除了硅丝骨架以外,还含有H、F及O等元素,随着腐蚀时间的增加,F和O原子的相对含量增加.实验结果表明,多孔硅在可见光区的发光现象是一种量子尺寸效应.     

多孔硅光致发光峰半峰全宽的压缩

硅发光对于在单一硅片上实现光电集成是至关重要的.目前已有的使硅产生发光的方法有:掺杂深能级杂质、掺稀土离子、多孔硅、纳米硅以及Si/SiO₂超晶格.声空化所引发的特殊的物理、化学环境为制备光致发光多孔硅薄膜提供了一条重要的途径.实验表明,声化学处理对于改善多孔硅的微结构,提高发光效率和发光稳定性都是一项非常有效的技术.超声波加强阳极电化学腐蚀制备发光多孔硅薄膜,比目前通用的常规方法制备的样品显示出更优良的性质.这种超声波的化学效应源于声空化,即腐蚀液中气泡的形成、生长和急剧崩溃.在多孔硅的腐蚀过程中,由于超声波的作用增加了孔中氢气泡的逸出比率和塌缩,有利于孔沿垂直方向的腐蚀,使多孔硅光致发光峰的半峰全宽压缩到了3.8nm.     

多孔硅紫外发光性质的研究

采用水热刻蚀技术制备多孔硅粉末。紫外激光244 nm激发时,多孔硅呈现出310 nm的强紫外发光。随着研磨时间的延长,多孔硅结构消失,紫外发光带也随之消失。氧气热处理后,多孔硅表面被氧化生成氧化硅薄层,同样造成紫外发光带的消失。我们认为310 nm紫外发光来源于硅纳米结构中电子和空穴的直接禁带结构辐射复合。     

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.