Surface acoustic wave velocity and electromechanical coupling coefficient of GaN grown on (0001) sapphire by metal-organic vapour phase epitaxy

High-quality and high-resistivity GaN films were grown on (0001) sapphire face by metal-organic vapour phase epitaxy. To measure the surface acoustic wave properties accurately, we deposited metallized interdigital transducers on the GaN surface. The acoustic surface wave velocity and electromechanical coupling coefficient were measured, respectively, to be 5667 m/s and 1.9% by the pulse method.

Optical properties and band lineup in GaNxAs1-x/GaAs single quantum wells

The optical properties and the band lineup in GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) technique were investigated. It was found that the low-temperature PL is dominated by the intrinsic localized exciton emission. By fitting the experimental datawith a simple calculation, band offset of the GaN0.015As0.985/GaAs heterostructure was estimated. Moreover, DeltaE(c), the discontinuity of the conduction band was found to be a nonlinear function of the nitrogen composition (chi) and the average variation of DeltaE(c) is about 0. 110eV per % N, such smaller than that reported on the literature to (0.156 similar to 0.175 eV/N %). In addition, Qc has little change whtn N composition increares, with an experimential relation of QC approximate tox(0.25). The band bowing coefficient (b) was also studied in this paper. The measured band bowing coefficient shows a strong function of chi, giving an experimental support to the theoretic calculation of Wei Su-Huai and Zunger Alex (1996).

Investigation on the nonlinear optical properties of the DCNP/PEK-c guest-host polymer films

The polyetherketone (PEK-c) guest-host polymer thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. The polymer films were investigated with in situ second-harmonic generation (SHG) measurement. The corona poling temperature was optimized by the temperature dependence of the in situ SHG signal intensity under the poling electric field applying. The temporal and temperature stability of the second-order properties of the poled polymer film were measured by the in situ SHG signal intensity probing. The second-order NLO coefficient chi ((2))(33) = 32.65 pm/V at lambda = 1064 nm was determined by using the Makel fringe method after poling under the optimal poling condition. The dispersion of the NLO coefficient of the guest-host polymer system was determined by the measured value of chi ((2))(33) at 1064 nm and the two-level model.

Effect of the electrostatic interactions of chromophores on the macroscopic second-order nonlinear optical properties of the polymer films

The polyetherketone (PEK-c) guest-host system thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. Their second-order nonlinear optical (NLO) coefficients chi(33)((2)) were measured by using Maker fringe method for the polymer films doped with different weight percents of DCNP. Experimental results indicate that the second-order NLO properties of the poled polymer films could decrease with the chromophore loading increasing when the chromophore loading reaches a fairly high level. In this paper, the relationship between the macroscopic second-order NLO coefficient and the chromophore number density was modified under considering the role of the electrostatic interactions of chromophores in the polymer film. According to the modified relationship, the macroscopic second-order NLO coefficient is no longer in direct proportion with the chromophore number density in the polymer film. The effect of the electrostatic interactions of chromophores on second-order NLO properties was discussed. The attenuation of the macroscopic second-order NLO activity can be demonstrated by the role of the chromophore electrostatic interactions at high loading of chromophore in the polymer systems.

Electro-optical properties and temporal stability of the guest-host DCNP/PEK-c polymer thin film

The polyetherketone (PEK-c) guest-host system thin films in which the range of the weight percent of 3-(1,1-dicyanothenyl)-1-phenyl-4, 5- dihydro-1H-pryazole (DCNP) is from 20% to 50% were prepared. The predicted high value of electro-optical (EO) coefficient gamma(33) = 48.8 pm/V by using two-level model was obtained when the weight percent of DCNP in the polymer system is 40%, whereas EO coefficients are attenuated at higher chromophore loading then 40%. The temporal stability of the EO activity of the guest-host polymer was evaluated by probing the decay of the orientational order of the chromophores in the polymer system.

Investigation of the polyetherketone guest-host DR1/PEK-c polymer films by real-time monitoring of the second-harmonic generation

The real-time monitoring of the second-harmonic generation (SHG) was used to optimize the poling condition and to study the nonlinear optical (NLO) properties of the polyetherketone (PEK-c) guest-host polymer films. The high second-order NLO coefficient chi(33)((2)) = 11.02 pm/v measured at 1.064 mu m was achieved when the weight percent of DR1 guest in the polymer system is 20%. The NLO activity of the poled DR1/PEK-c polymer film can maintain more than 80% of its initial value when temperature is under 100 degrees C, and the normalized second-order NLO coefficient can maintain more than 85% after 2400 s at 80 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.

Growth and characterization of strained superlattices delta-GaNxAs1-x/GaAs by molecular beam epitaxy

A series of superlattices delta-GaNxAs1-x/GaAs were grown by a DC plasma-N-2-assisted molecular beam epitaxy. The evolution of the surface reconstruction during the growth has been studied with the use of in situ reflection high-energy electron diffraction. The superlattices have been characterized by high-resolution X-ray diffraction measurements. Distinct satellite peaks indicate that the superlattices are of good quality. The N compositions in strained GaNxAs1-x monolayers are obtained from the dynamical simulations of the measured X-ray diffraction patterns. The periodicity fluctuations of N composition are obtained from a kinematical method dependent on the broadening of the satellite peaks of the X-ray diffraction. (C) 2000 Elsevier Science B.V. All rights reserved.

Influence of dispersive coupling coefficient in microring channel drop filters

Wide transmission dips are observed in the through spectra in microring and racetrack channel drop filters by two-dimensional finite-difference time-domain (FDTD) simulation. The transmission spectra, which reflect the coupling efficiency, are also calculated from the FDTD output as the pulse just travels one circle inside the resonator. The results indicate that the dips are caused by the dispersion of the coupling coefficient between the input waveguide and the resonator. In addition, a near-zero channel drop on resonance and a large channel drop off resonance are observed due to the near zero coupling coefficient and a large coupling coefficient, respectively. If the width of the input waveguide is different from that of the ring resonator, the oscillation of the coupling coefficient can be greatly suppressed.

Evaluation of thermal radiation dependent performance of GaSb thermophotovoltaic cell based on an analytical absorption coefficient model

Applying the model dielectric function method, we have expressed the absorption coefficient of GaSb analytically at room temperature relating to the contribution of various critical points of its electronic band structure. The calculated absorption spectrum shows good agreement with the reported experimental data obtained by spectral ellipsometry on nominally undoped sample. Based on this analytical absorption spectrum, we have qualitatively evaluated the response of active absorbing layer structure and its photoelectric conversion properties of GaSb thermophotovoltaic device on the perturbation of external thermal radiation induced by the varying radiator temperature or emissivity. Our calculation has demonstrated that desirable thickness to achieve the maximum conversion efficiency should be decreased with the increment of radiator temperature and the performance degradation brought by any structure deviation from its optimal one would be stronger meanwhile. For the popular radiator temperature, no more than 1500 K in a real solar thermophotovoltaic system, and typical doping profile in GaSb cell, a reasonable absorbing layer structure parameter should be controlled within 100-300 nm for the emitter while 3000-5000 nm for the base.

[PMMA-b-PAN］-Fe络合物制备有机一无机杂化薄膜

本论文通过聚甲基丙烯酸甲酯-b-聚丙烯睛嵌段共聚物同铁（III）离子络合物（［PMMA-b-PAN］-Fe）制备有机一无机杂化薄膜，并利用妨M对薄膜的表面形态进行了表征。结果表明，通过控制［PMMA-b-PAN］-Fe络合物溶液热处理时间（T=120℃）及络合物溶液中精基同铁＜III）离子的摩尔比率，可以得到不同表面形态的有机一无机杂化薄膜。并借助抑S对［PMMA-b-PAN〕-Fe络合物配位作用进行了研究，发现铁（III）离子与PMMA-b-PAN嵌段共聚物中的睛基配位。此外，对掺杂有FeSO4·7H2O 的均聚甲基丙烯酸甲酷（PMMA）溶液、均聚丙烯睛(PAN)溶液和FeSO4·7H2O（溶解在DMF中）溶液经不同时间热处理（T=120℃）后的薄膜表面形态进行了研究，结果发现，掺杂有FeSO4·7H2O 的PMMA 溶液经20in热处理后，薄膜的表面形态与FeS04·7H2O。溶液经20in热处理后薄膜的表面形态基本相同，而掺杂有FesO4·7H2O的PAN溶液经不同时间热处理后，薄膜的表面形态没有明显的变化。与此同时，对匡[PMMA-b-PAN]-Fe络合物高温热解制备碳材料进行了初步的研究，研究结果表明，利用PMMA-b-PAN］-e杂化薄膜炭化制备具有纳米尺寸孔洞的碳薄膜是可能的，但控制好热解条件至关重要。

PAN－聚氨酯泡沫分离富集ICP－AES测定水及化学试剂中痕量元素的研究

高频感耦等离子体发射光谱法（ICP－AES）具有测量精度好、线性范围宽、多元素同时测定等优点。经过20年来的发展已广泛应用于环境、地质、高纯材料等样品的分析中，成为分析实验室常备的分析手段之一。尽管ICP－AES在过去的20年中有很大的发展，但是依然存在着某些不足，例如：基体元素产生光谱干扰以及某些元素的含量低于检测限，使得ICP－AES对天然水等样品的直接分析上存在着一定的困难。为此，人们往往采取化学分离和富集的手段，从而使化学分离富集ICP－AES分析技术得以不断发展。在化学分离富集方法中，离子变换和吸附分离是一种较受欢迎的方法，其中所使用过的吸附剂有阴、阳离子交换树脂、螯合树脂以及螯合剂负载型吸附剂。螯合剂负载型吸附剂是一种将螯合剂以离子交换及物理吸附的方式固定在某些载体之上而成的新型吸附剂，近年来已引起人们的关注。PAN－聚氨酯泡沫是负载型吸附剂之一，它具有原料易得、制备简单、分离速度快、操作简便等特点。虽然，已有人做过研究，然而，目前的方法只限于单一或少数几个元素的富集分离，此外，与ICP－AES相结合的工作尚无人研究。本文在系统地研究了PAN－聚氨酯泡沫性质的基础上，建立了PAN－聚氨酯泡沫分离富集ICP－AES分析方法，并用此方法测定了天然水及化学试剂中的痕量元素，获得满意结果。本文首先研究比较了PAN－硅胶、PAN－GDX－401、PAN－聚四氟乙烯、PAN－聚氨酯泡沫的吸附性能。发现PAN－聚氨酯泡沫较适合ICP－AES多元素同时测定的特点，并且，操作简单，分离迅速。因此，我们对PAN－聚氨酯泡沫体系进行了深入的考察。我们研究了pH＝2－9.5范围内PAN－聚氨酯泡沫对Cu、En、Cd等17种离子的吸附特征，确定了同时富集Cu、En、Cd、Mn、Fe、Co、Pb长种离子的pH值为7.4-8.5。在吸附离子的解脱方式上，我们研究了1－4M HCl, 1-4M HCl-丙酮混合液以及消解泡沫三种解脱方式，结果发现，采用5ml 4 M HCl 可同时解脱Cu、En、Cd、Mn、Pb五种离子。采用5ml 4 HCl－丙酮混合液可同时解脱Cu、En、Cd、Mn、Fe、Co、Pb七种离子，解脱液经消解，转入无机介质后便可进样测定。实验发现，聚氨酯泡沫较易消解，因此，消解泡沫的方法也是一种实用的解脱方式。本文研究了样品体积在250－1000ml内变化时，各金属离子的回收率变化。发现此体积变化范围内，Cu、En、Cd、Mn、Pb、Fe、Co七种离子的回收率在90％以上。我们研究了试液流速对上述离子吸附性能的影响，确立了定量富集上述元素的流速为2－10ml/min。在基体元素干扰的研究中，我们对k、Na、Ca、Mg四种基体元素分别进行了考察，结果表明，k的含量为3％时，Mn的回收率低于90％，Na为3％时，Fe、Co、En回收率低于90％，Ca为0.1％时，Co、Fe、Mn回收率低于90％，Mg为0.5%时，Co、Mn、En回收率低于90％。本文还研究了PAN在聚氨酯泡沫上的动态吸附和洗脱特征，结果表明，PAN在聚氨酯泡沫上的动态饱和吸附量为60mg/g。同时，确立了PAN的动态负载方式为，以20ml 0.5% PAN-丙酮液通过泡沫柱床，经水洗后用于富集分离。实验发现，5ml 4 M HCl通过PAN－聚氨酯泡沫柱床后，流出液中PAN浓度为200Mg/ml左右。为此，我们研究了微量PAN进样时，对ICP－AES测定的影响，结果表明，进样介质中50－400Mg/ml的PAN对仪器的测定不产生影响。在化学条件研究之后，我们对仪器的工作参数进行了选择，确定了5％HG进样的工作条件为：正向功率1.3kw，载光流量为0.8 L/min，观察高度为16.5mn。最后，我们确立了PAN－聚氨酯泡沫的最佳分离条件，建立了PAN－聚氨酯泡沫分离富集ICP－AES分析方法，并用此方法分析了长春净月潭水样及优级纯NaCl中痕量元素。变异系数和标加回收实验表明，结果令人满意。

Optical transitions in GaNAs/GaAs single quantum well

We have investigated GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL), time-resolved PL (TRPL) and photovoltaic (PV) techniques. The low temperature PL is dominated by spatially direct transitions involving electrons confined in GaNAs well and holes localized in the same GaNAs layer. This assignment was supported by PL decay time measurements and absorption line-shape analysis derived from the PV measurements. By fitting the experimental data with a simple calculation, the band offset of the GaN0.015As0.985/GaAS heterostructure was estimated, and a type II band lineup in GaN0.015As0.985/GaAs QWs was suggested. Moreover, DeltaE(C), the discontinuity of conductor band, is found to be a nonlinear function of the nitrogen (N) composition (x), and the average variation of DeltaE(C) is about 0.110eV per %N, The measured band bowing coefficient shows a strong function of x, giving an experimental support to the theoretic calculation of Wei et al [Ref.2].