Fourier transformation study of the Franz-Keldysh Oscillation in SIN+ GaAs structures

Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectance measurements. The FT spectra of a part of the samples,including of the real part,imaginary part, and mode of the FT,are well consistent with the theoretical lineshapes. The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH), root mu(1)/root mu(h), obtained in the analysis was in the range of 0.805 to 0.816 for different samples. In addition,the built-in electric field F-1, and the modulation field delta F = F-1 - F-2 induced by photo-modulation were also obtained in the analysis. However,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape. In this case the mode of the FT spectra still can be used to obtain useful information.

Observation of "ghost" islands and surfactant effect of surface gallium atoms during GaN growth by molecular beam epitaxy

We observe "ghost" islands formed on terraces during homoepitaxial nucleation of GaN. We attribute the ghost islands to intermediate nucleation states, which can be driven into "normal" islands by scanning tunneling microscopy. The formation of ghost islands is related to excess Ga atoms on the surface. The excess Ga also affect island number density: by increasing Ga coverage, the island density first decreases, reaching a minimum at about 1 monolayer (ML) Ga and then increases rapidly for coverages above 1 ML. This nonmonotonic behavior points to a surfactant effect of the Ga atoms.

Observation of field-driven blue shift in delta-doped Si n-i-p-i multiple quantum wells

We report the observation of the field-driven blue shift at near absorption edge in the photo-current response spectra of delta-doped Si n-i-p-i multiple quantum wells due to the widening of the effective energy gap. This phenomenon differs from the observed results in GaAs/AlGaAs and GeSi/Si superlattices, because the physical mechanisms of forming energy band in these superlattice samples are different. Our experimental results are interpreted satisfactorily by the theoretical calculation. (C) 1999 Elsevier Science Ltd. All rights reserved.

The photon scanning tunneling microscope and its applications

A simple photon scanning tunneling microscope (PSTM) is described. Its lateral resolution (similar to 10nm with a maximal scanning range of 10 mu m x 10 mu m ) is much better than that of a conventional optical microscope. Its principle, the fiber optic tip fabrication and PSTM images of different samples such as mica, HDPE and LiNbO3 are presented.

A novel ultra low power temperature sensor for UHF RFID tag chip

A novel ultra low power temperature sensor for UHF RFID tag chip is presented. The sensor consists of a constant pulse generator, a temperature related oscillator, a counter and a bias. Conversion of temperature to digital output is fulfilled by counting the number of the clocks of the temperature related oscillator in a constant pulse period. The sensor uses time domain comparing, where high power consumption bandgap voltage references and traditional ADCs are not needed. The sensor is realized in a standard 0.18 mu m CMOS process, and the area is only 0.2mm(2). The accuracy of the temperature sensor is +/- 1 degrees C after calibration. The power consumption of the sensor is only 0.9 mu W.

High efficiency RFID UHF power converter

The paper proposes a high efficiency RFID UHF power converter unit to overcome the low efficiency problem. This power converter is mainly composed of an RF-DC converter and a DC-DC converter. In order to overcome the low efficiency problem in low current consuming condition, a DC-DC converter is added to conventional single RF-DC converter rectifier to increase the rectifying efficiency of the RFDC rectifier. The power converter is implemented in a 0.18 um mixed signal, 1p6m CMOS technology. Simulation shows the power converter has an average improvement of 5% and can achieve efficiency as high as 30% with 900MHz, 16uW RF input power and 1.3 V 3.6uA DC output.

Temperature and power-density-dependent inter-shell energy states in InAs/GaAs quantum dots

We have investigated the evolution of exciton state filling in InAs/GaAs quantum dot (QD) structures as a function of the excitation power density by using rnicro-photoluminescence spectroscopy at different temperatures. In addition to the emission bands of exciton recombination corresponding to the atom-like S, P and D, etc. shells of QDs, it was observed that some extra states V between the S and P shells, and D' between the P and D shells appear in the spectra with increasing number of excitons occupying the QDs at a certain temperature. The emergence of these inter-shell excitonic levels is power density and temperature dependent, which is an experimental demonstration of strong exciton-exciton exchange interaction, state hybridization, and coupling of a multi-exciton system in QDs. (c) 2006 Elsevier B.V. All rights reserved.

Low-threshold diode-pumped CW passively mode-locked Nd:YVO4 lase

A low-threshold passively continuous-wave (CW) mode-locked Nd:YVO4 solid-state laser was demonstrated by use of a semiconductor saturable absorber mirror (SESAM). The threshold for continuous-wave mode-locked is relatively low, about 2.15 W. The maximum average output power was 2.12 W and the optical to optical conversion efficiency was about 32%. The pulse width was about 15 ps with the repetition rate of 105 MHz. (C) 2008 Elsevier GmbH. All rights reserved.

用分子动力学模拟水合物储氢

用分子动力学（MD）模拟方法系统研究了结构Ⅰ型（SⅠ）和结构H型（SH）氢气水合物中氢气的占据情况并确定了氢气水合物的稳定结构：SⅠ水合物氢气分子数小胞中为2，大胞中为3；SH水合物氢气分子数小胞中为2，中胞中为2，大胞中为11．分析了稳定情况下水合物各胞腔内氢气分子之间的径向分布函数（RDF），得出了氢气分子在各胞腔内的稳定位置．由稳定位置得到了稳定结构下氢气水合物的储氢质量分数：SⅠ为5．085％，SH为6．467％．与实验对比得出结论：SH水合物稳定结构下的储氢能力最强．

Experimental investigation on TBAB clathrate hydrate slurry flows in a horizontal tube: Forced convective heat transfer behaviors

Tetra-n-butyl-ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is one kind of secondary refrigerants, which is promising to be applied into air-conditioning or latent-heat transportation systems as a thermal storage or cold carrying medium for energy saving. It is a solid-liquid two phase mixture which is easy to produce and has high latent heat and good fluidity. In this paper, the heat transfer characteristics of TBAB slurry were investigated in a horizontal stainless steel tube under different solid mass fractions and flow velocities with constant heat flux. One velocity region of weakened heat transfer was found. Moreover, TBAB CHS was treated as a kind of Bingham fluids, and the influences of the solid particles, flow velocity and types of flow on the forced convective heat transfer coefficients of TBAB CHS were investigated. At last, criterial correlations of Nusselt number for laminar and turbulent flows in the form of power function were summarized, and the error with experimental results was within 20%.

Generation of the high efficiency high peak-power femtosecond blue optical pulse

The analysis and calculation of the compensation for the phase mismatch of the frequency-doubling using the frequency space chirp introduced from prisms are made. The result shows that suitable lens can compensate the phase mismatch in a certain extent resulting from wide femtosecond spectrum when the spectrum is space chirped. By means of this method, the experiment of second harmonic generation is carried out using a home-made femtosecond KLM Ti:sapphire laser and BBO crystal. The conversion efficiency of SHG is 63 %. The average output power of blue light is 320 mW. The central wavelength is 420 nm. The spectrum bandwidth is 5.5 nm. It can sustain the pulse width of 33.6 fs. The tuning range of blue light is 404-420 nm,when the femtosecond Ti:sapphire optical pulse is tuned using the prisms in the cavity.

巯基化合物在分析化学中的应用及其机理研究

本文利用活性碳吸附蔗糖后再与巯基乙酸反应合成了一种新的分离吸附剂-巯基活性碳吸附剂，详细研究了其各种制备条件。实验表明，用这种方法合成的吸附剂是一种非常好的固体吸附剂，不仅能定量吸附各种重金属离子，而且具有很好的吸附脱附特性，其饱和吸附量是目前广泛应用的巯基绵的3～20倍。既克服了因巯基含量高对重金属离子难以洗脱的缺点，又大大提高了分离富集效率。探讨了巯基活性碳吸附剂中吸附因素对吸附能力的贡献，其中活性碳作用占17.3%，蔗糠作用占19.2%，巯基化后引入的吸附作用占63.5%。此三方面相互渗透，相互补充，相互加强，共同完成对重金属子离子的吸附作用。本文还从热力学和动力学两个方面研究了吸附剂对重金属离子的吸附机理。结果表明其吸附过程以化学吸附为主。外表面、内表面吸附率对Cu~(2+)分别为19%；81%；对Pb~(2+)分别为6%，94%，对Zn~(2+)分别为17%和83%，而吸附Cd~(2+)完全由内扩散所控制。并且发现其吸附Cu~(2+)的同时，还将其还原成Cu~o。从静态和动态两个方面探讨了溶液酸度、温度、吸附时间、Ca~(2+)、Na~+等干扰离子，以及重金属离子浓度等对新型分离吸附剂吸附能力的影响。结果表明，此吸附剂具有很高的吸附能力和很好的稳定性，可以应用于实际样品的测定。通过用表面有机合成法将巯基键合在玻碳电极的表面，得到了巯基修饰电极（MAMGCE），此种修饰电极与未加修饰的玻碳电极（GCE）相比，不仅可化学吸附重金属离子如汞离子，而且灵敏度提高了近10倍。当富集时间为3分钟时，其线性范围为1X_(10~(-8))mol/L～1X_(10~(-9))mol/L,相对标准偏差为7.7%。采用电子能谱等方法对MAMGCE电化学性质、电极反应机理进行了探讨，结果表明MAMGCE与Hg~(2+)的反应的产物在氧化及还原状态都存在弱吸附。通过将巯基乙酸作为一种支持电解质将巯基固定在导电聚吡咯薄膜电极上，制得巯基-聚吡咯薄膜修饰电极，该修饰电极保持了巯基的螯合性能，并具有良好的稳定性。此种修饰电极对水溶液中的重金属离子具有很好的吸附作用，其灵敏度与未修饰玻碳电极相比，测汞离子时电沉积提高了三倍，化学吸附时提高了近5倍。对其吸附机理进行的初步探讨证明其对汞离子的吸附为不可逆的产物弱吸附。本文研究了聚苯胺薄膜化学修饰电极对巯基化合物氧化还原的促进作用，系统地探讨了不同聚合介质、酸度等对PAn薄膜化学修饰电极对巯基乙醇促进作用的影响。采用扫描电镜、电子能谱、交流阻抗及拉曼光谱等各种检测手段对这种促进作用进行了探讨，结果表明这种促进作用是对巯基乙醇在PAn薄膜表面的氧化还原过程的一种加强，而这种加强作用是通过-SH与PAn中的N以质子形式加成的。

黑白仰鼻猴（Rhinopithecus bieti）的种群现状、云南境内生境退化和藏猕猴（Macaca thibetana）的叫声

黑白仰鼻猴仅分布于滇西北和藏东南境内，金沙江和澜沧江间的一个狭小区域内。根据以前的研究结果，将暗针叶林和针阔混交林定义为其适宜生境（SH）黑白仰鼻猴的适宜生境由于当地人砍树烧树形成夏季高山牧场逐渐被侵蚀。为了解云南省境内黑白仰鼻猴适宜生境的现状，我们比较了1997年卫星图片和1958年以航片为基础绘制的地形图上夏季牧场和适宜生境的面积，得到以下结果：1）1997年黑白仰鼻猴的适宜生境面积为4169平方公里；2）夏季牧场面积为1923平方公里；3）过去的40年中，适宜生境面积减少了31％（1887平方公里），夏季牧场面积增加了204％（1291平方公里）；4）森林斑块的平均面积从15.6平方公．里减小到5.4平方公里。另外，夏季牧场的面积和当地人口成正相关（R2=053），这意味着黑白仰鼻猴生境的减少和破碎化是当地传统生产方式和人口增长共同作用的结果。目前在云南和西藏境内分别尚存11群和2群黑白仰鼻猴。