Structural characteristic of cubic GaN nucleation layers on GaAs(001) substrates by MOCVD

The structural characteristic of cubic GaN (C-GaN) nucleation layers on GaAs(0 0 1) substrates by metalorganic chemical vapor deposition was in detail investigated first by X-ray diffraction (XRD) measurements, using a Huber five-circle diffractometer and an intense synchrotron X-ray source. The XRD results indicate that the C-GaN nucleation layers are highly crystallized. Phi scans and pole figures of the (1 1 1) reflections give a convincing proof that the GaN nucleation layers show exactly cubic symmetrical structure. The GaN(1 1 1) reflections at 54.74degrees in chi are a measurable component, however (002) components parallel to the substrate surface are not detected. Possible explanations are suggested. The pole figures of {1 0 (1) over bar 0} reflections from H-GaN inclusions show that the parasitic H-GaN originates from the C-GaN nucleation layers. The coherence lengths along the close-packed [1 1 1] directions estimated from the (1 1 1) peaks are nanometer order of magnitude. (C) 2002 Elsevier Science B.V. All rights reserved.

X-Ray diffraction determination of the fractions of hexagonal and twinned phases in cubic GaN layers grown on (001)GaAs substrate

Being an established qualitative method for investigating presence of additional phases in single crystal materials, X-ray diffraction has been used widely to characterize their structural qualities and to improve the preparation techniques. Here quantitative X-ray diffraction analysis is described which takes into account diffraction geometry and multiplicity factors. Using double-crystal X-ray four-circle diffractometer, pole figures of cubic (002), {111} and hexagonal {10 (1) over bar0} and reciprocal space mapping were measured to investigate the structural characters of mixed phases and to obtain their diffraction geometry and multiplicity factors. The fractions of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {10 (1) over bar0} and hexagonal {10 (1) over bar1}. Without multiplicity factors, the calculated results are portions of mixed phases in only one {111} plane of cubic GaN. Diffraction geometry factor can eliminate the effects of omega and X angles on the irradiated surface areas for different scattered planes. (C) 2001 Elsevier Science B.V. All rights reserved.

Microtwins and twin inclusions in the 3C-SiC epilayers grown on Si(001) by APCVD

Microtwins in the 3C-SiC films grown on Si(001) by APCVD were analyzed in detail using an X-ray four-circle diffractometer. The empty set scan shows that 3C-SiC films can grow on Si substrates epitaxially and the epitaxial relationship is revealed as (001)(3C-SiC)//(001)(Si), [111](3C-SiC)//[111](Si). Other diffractions emerged in the pole figures of the (111) 3C-SiC. We performed the (10 (1) over bar0) h-SiC and the reciprocal space mapping of the (002) plane of twins for the first time, finding that the diffractions at chi = 15.8 degrees result from not hexagonal SiC but microtwins of 3C-SiC, and twin inclusions are estimated to be 1%.

Multiplicity factor and diffraction geometry factor for single crystal X-ray diffraction analysis and measurement of phase content in cubic GaN/GaAs(001) epilayers

On the basis of integrated intensity of rocking curves, the multiplicity factor and the diffraction geometry factor for single crystal X-ray diffraction (XRD) analysis were proposed and a general formula for calculating the content of mixed phases was obtained. With a multifunction four-circle X-ray double-crystal diffractometer, pole figures of cubic (002), {111} and hexagonal {1010} and reciprocal space mapping were measured to investigate the distributive character of mixed phases and to obtain their multiplicity factors and diffraction geometry factors. The contents of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {1010} and {1011}.

Structural characterization of cubic GaN grown on GaAs(001) substrates

Structural characteristics of cubic GaN epilayers grown on GaAs(001) were studied using X-ray double-crystal diffraction technique. The structure factors of cubic GaN(002) and (004) components are approximately identical. However, the integrated intensities of the rocking curve for cubic (002) components are over five times as those of (004) components. The discrepancy has been interpreted in detail considering other factors. In the conventional double crystal rocking curve, the peak broadening includes such information caused by the orientation distribution (mosaicity) and the distribution of lattice spacing. These two kinds of distributions can be distinguished by the triple-axis diffraction in which an analyser crystal is placed in front of the detector. Moreover, the peak broadening was analysed by reciprocal lattice construction and Eward sphere. By using triple-axis diffraction of cubic (002) and (113) components, domain size and dislocation density were estimated. The fully relaxed lattice parameter of cubic GaN was determined to be about 0.451 +/- 0.001nm.

The content calculation of hexagonal phase inclusions in cubic GaN films on GaAs(001) substrates grown by metalorganic chemical vapor deposition

Cubic GaN(c-GaN) films are grown on GaAs(001) substrates by metalorganic chemical vapor deposition (MOCVD). Two GaN samples were grown with different buffer layer, the deposition time of each was 1 and 3 min, respectively. 4-circle X-ray double crystal diffraction (XRDCD) was used to study the secondary crystallographic phases presented in the c-GaN films. The phase composition of the epilayers was determined by X-ray reciprocal space mapping. The intensities of the c-GaN(002) and h-GaN(10 (1) over bar 1) planes detected in the mapping were investigated by omega scans. The content of the hexagonal phase inclusions in the c-GaN films was calculated to about 1.6 and 7.9%, respectively. The thicker buffer layer is not preferable for growing high quality pure c-GaN films. (C) 2000 Elsevier Science S.A. All rights reserved.

Sputtering of ZnO buffer layer on Si for GaN blue light emitting materials

The preparation of high quality ZnO/Si substrates for the growth of GaN blue light emitting materials is considered. ZnO thin films have been deposited on Si(100) and Si(lll) substrates by conventional magnetron sputtering. Morphology, crystallinity and c-axis preferred orientation of ZnO thin films have been investigated by transmitting electron microscopy (TEM), X-ray diffraction (XRD) and X-ray rocking curve (XRC). It is proved that the ZnO thin films have perfect structure. The full-width-at-half-maximum (FWHM) of the ZnO(002) XRC of these films is about 1 degrees, while the minimum is 0.353 degrees. This result is better than the minimum FWHM (about 2 degrees) reported by other research groups. Moreover, comparison and discussion are given on film structure of ZnO/Si(100) and ZnO/Si(lll).

Triclinic deformation and anisotropic strain relaxation of an InAs film on a GaAs(001) substrate measured by a series of symmetric double crystal X-ray diffraction

We presented a series of symmetric double crystal X-ray diffraction (DCXD) measurements, (0 0 4), (2 2 0) and (2 - 2 0) diffraction, to investigate the strain relaxation in an InAs film grown on a GaAs(0 0 1) substrate. The strain tensor and rotation tensor were calculated according to the DCXD results. It is found that the misfit strain is relaxed nearly completely and the strain relaxation caused a triclinic deformation in the epilayer. The lattice parameter along the [1 1 0] direction is a little longer than that along the [1 - 1 0] direction. Furthermore, a significant tilt, 0.2 degrees, towards the [1 1 0] direction while a very slight one: 0.002 degrees, towards [1 - 1 0] direction were discussed. This anisotropic strain relaxation is attributed to the asymmetric distribution of misfit dislocations, which is also indicated by the variation of the full-width at half-maximum (FWHM) of (0 0 4) diffraction along four azimuth angles. (C) 1998 Elsevier Science B.V. All rights reserved.

The influence of substrate nucleation on HVPE-grown GaN thick films - art. no. 684105

Thick GaN films were grown on sapphire in a home-made vertical HVPE reactor. Effect of nucleation treatments on the properties of GaN films was investigated, including the nitridation of sapphire, low temperature GaN buffer and MOCVD-template. Various material characterization techniques, including AFM, SEM, XRD, CL and PL have been used to assess these GaN epitaxial films. It was found that the surface of sapphire after high temperature nitridation was flat and showed high density nucleation centers. In addition, smooth Ga-polarity surface of epitaxial layer can be obtained on the nitridation sapphire placed in air for several days due to polarity inversion. This may be caused by the atoms re-arrangement because of oxidation. The roughness of N-polarity film was caused by the huge inverted taper domains, which can penetrate up to the surface. The low temperature GaN buffer gown at 650 degrees C is favorable for subsequent epitaxial film, which had narrow FWHM of 307 arcsec. The epitaxial growth on MOCVD-template directly came into quasi-2D growth mode due to enough nucleation centers, and high quality GaN films were acquired with the values of the FWHM of 141 arcsec for (002) reflections. After etching in boiled KOH, that the total etch-pit density was only 5 x 106 cm(-2) illustrated high quality of the thick film on template. The photoluminescence spectrum of GaN film on the MOCVD-template showed the narrowest line-width of the band edge emission in comparison with other two growth modes.

Heteroepitaxial Growth of 3C-SiC on Si (111) Substrate using AlN as a Buffer Layer

Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100 degrees was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300 degrees C indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.

黄土高原坡地密植枣园土壤质地与肥力状况分析

采用田间取样与实验室分析相结合的方法,研究了黄土高原坡地密植枣园土壤质地与肥力状况。结果表明,坡地枣园土壤肥力低,氮、磷严重缺乏,钾相对丰富,土壤属于砂壤土,通气性强,保肥、保水性差。0~60 cm土壤有机质含量为1.687~5.002 mg/kg;全氮为0.072~0.316 g/kg;硝酸盐为2.325~16.846 g/kg;铵态氮为1.187~2.146 g/kg,速效磷为0.270~2.480 mg/kg,速效钾为51.9~169.1 mg/kg,并且含量均随剖面向下减少。颗粒组成大部分为粉砂粒,含量一般在65.75%~68.98%;随有机质含量升高,0.25~0.05 mm微团聚体数量呈上升趋势,二者为正相关;<0.05 mm微团聚体含量则逐渐下降,二者呈负相关。黄土高原坡地密植枣园土壤肥力总体水平很低。除了速效钾为中等级外,有机质、全氮、碱解氮、速效磷均为很低等级。

黄土丘陵区两种典型灌木群落坡面侵蚀泥沙颗粒组成及养分流失的比较

在野外模拟降雨条件下,比较研究了黄土丘陵区柠条(Caragana korshinkii)和狼牙刺(Sophora viciifolia)径流小区产流产沙、侵蚀泥沙颗粒组成、比表面积(SSA)及养分流失特征。结果表明,两种灌木群落均能显著减小坡面径流泥沙的流失。产流后流失泥沙黏粒、SSA与养分含量随降雨时间总体呈现降低趋势,其中有机质变化显著,全磷变化不显著。受植被盖度影响,泥沙中黏粒与养分含量均表现为柠条群落>狼牙刺群落>对照裸地。侵蚀泥沙具有富集黏粒和富集养分的特征,富集率随群落盖度增大而增大(柠条>狼牙刺>裸地)。不同形态养分富集率不同,其中有机质均在2.5以上,全氮平均富集率为2.13,全磷为1.23。富集率随产流时间呈线性递减。流失泥沙养分含量与黏粒(粒径<0.002 mm)含量及SSA达到极显著的正相关。坡面土壤养分主要以黏粒为载体流失。SSA的变化不仅能体现土壤颗粒组成的变化,而且能够反映土壤养分的变化。

毛细管电泳电化学发光的研究

毛细管电泳以其强大的分离能力日益受到重视，特别是成功完成人类基因组计划的测定工作，随着微全分析系统的深入研究，毛细管电泳的理论和技术在各方面都需要突破，其中毛细管电泳检测器是制约发展毛细管电泳更广泛地用于实际工作的因素之一。本论文以发展新型的毛细管电泳电化学发光检测技术为出发点，在以下几个方面作了研究。1．三联吡啶钌在玻碳电极上的阴极电化学发光我们首次发现了一种新型的基于溶液中氧的还原引发的三联毗淀钉（TBR）阴极电化学发光，结果表明，这种阴极电化学发光的发光电位仅为-0.4V，从而大大地降低了电化学发光的激发电位。所有能够增强阳极电化学发光的物质如三丙胺（TPA）都能够增强阴极电化学发光。阴极电化学发光光谱证实，阴极发光是激发态的TBR跃迁回到基态所产生的发光行为，我们认为在电极上氧还原所产生的活性氧氧化了TBR分子和发光增强剂从而导致了阴极发光。一些不能够增强阳极电化学发光的物质如柠檬酸，也能够增强阴极电化学发光，从而扩展了电化学发光的检测范围。采用阴极电化学方法对TPA和柠檬酸根的检测结果表明，对TPA在1*10~（-7）-1*10~（-5）M之间的检测呈较好线性相关性，相关系数为0.9994，最低检测限（S/N＝3）为7.5*10-8M，对柠檬酸根在1*10~（-5）-1*10~（-4）M之间呈较好的线性关系，相关系数为0.999，最低检测限（S/N＝3）为1.2*10~（-6）M。2．毛细管电泳直接电化学发光离柱检测技术的研究研究在没有场分离器的情况下高压电场对电化学发光检测器的影响。基于此目的我们采用75件m内径的毛细管为分离柱，300μm直径的铂丝为工作电极，以不同电导率的溶液作为电泳流动相。在高压电场的影响下，动态循环伏安和与此相对应的电化学发光表明电泳电流并不会引起电化学发光信号的淬灭，高压电场只会导致电化学发光激发电位向更正方向的偏移。进一步的研究表明，毛细管与工作电极之间的间距是影响电化学发光信号和理论塔板数的重要因素。基于以上的认识，我们发展了无需电场分离器的毛细管电泳一电化学发光检测系统，从而大大地简便了毛细管电泳一电化学发光检测系统。以三丙胺（TPA）作为分析对象，对该系统进行了表征，该系统对TPA的检测在1*10~（-10）-1*10~（-5）mol/L之间的线性相关系数为0.998，峰高的相对标准偏差为5．6％，检测限（S加＝3）达到5.0*10~(-11)mol/L。采用这一方法对尿样中的利多卡因进行了分析，在5.0*10~(-8)-1.0*10~(-5) mo/L之间的相关系数为：0.998，最低检测限（S/N＝3）为2.0*10-8mo／L。3．毛细管电泳一固态电化学发光检测器检测的研究我们首次报道将TBR固定在聚苯乙烯磺酸-溶胶-凝胶-接枝共聚物构成的膜中，采用旋涂的方法涂敷在铂电极的表面，制备用于毛细管电泳的固态电化学发光检测器，以TPA和脯氨酸作为研究对象表征了毛细管电泳-固态电化学发光检测系统的特征，该系统可以稳定工作24小时，完全可以满足实际应用的需要。采用该系统实现了对TPA和脯氨酸的同时检测，对TPA和脯氨酸检测的相对标准偏差分别为8.7％和7.5％，分离的理论塔板数分别为70000和16000，对TPA和脯氨酸的测定的最低检测限分别为0.002μM和2μM。4．离散小波分析去除毛细管电泳电化学发光检测信号的噪音毛细管电泳电化学发光检测信号因为TBR与溶液中的氢氧根的化学发光反应使得信号的噪音变得很大，从而影响了峰的定量，降低了检测灵敏度。这里我们采用离散小波'分析技术去除电泳中的噪音。对一些典型的小波基如HaaroDaublets，Coiflets和Symmlets去除噪音的效果作了比较。各种不同的计算阀值的方法和确定阀值的技术导致的去噪结果的差异作了比较。结果表明，采用Symmlet 4小波基和启发式无偏向风险估算法-软阀门确定阀值是最优的去噪方案，采用这一策略对毛细管电泳电化学发光电泳信号的去噪结果表明，噪音成功地得到了去除，同时电泳的峰型和轮廓得到了保留，该去噪技术明显地优于通常的SG和FT去噪技术。5．毛细管电泳柱端电化学发光同时检测尿样中的曲马多和利多卡因曲马多和利多卡因是手术中常用的镇静剂和麻醉剂，部分药物以原形从肾脏排除，我们研究了简单、快速的采用毛细管电泳柱端电化学发光同时检测曲马多和利多卡因的方法。我们使用25μm内径的毛细管作为分离柱，由于使用的毛细管内径很小，从而大大地降低了分离电压对检测器的影响，因此毛细管与电化学发光检侧器直接连接而无需电场分离器。使用300μm直径的铂盘电极作为工作电极，使得在毛细管的出口有足够的氧化态的TBR存在。为消除尿样中的离子强度对分析造成的影响，样品在分析前经萃取分离，以TPA为内标，采用两步萃取寻去对尿中的曲马多和利多卡因的测定回收率分别为94-96％和93-97％。在1.0*10-7to 1.0*10-4的浓度范围内曲马多和利多卡因的检测的线性相关系数为0.998，检测的相对标准偏差分别为2.9％和2.7％，对尿中曲马多和利多卡因测定的最低检测限（S/N=3）分别为6.0*10~(-8)mol/L和4.5*10~(-8)mol/L。应用该方法对临床两例术后病人尿样中的曲马多和利多卡因的代谢进行了测定。6．毛细管电泳电化学发光检测尿样中的利血平提出了一种快速、简便的毛细管电泳电化学发光法测定尿样中的利血平的方法。我们以25拼m内径的毛细管为分离柱，不用场分离器直接与300μm直径的铂二〔作电极连接，为提高检测的灵敏度和克服尿样中的离子强度对检测的影响，我于门采用场放大电动进样的技术用于毛细管电泳的直接进样和分离，样品不经任何预处理。由于利血平是中性分子，采用毛细管区带电泳不能将利血平与中性的干扰物分离出，因此我们在电泳流动相中加入十二烷基磺酸钠（SDS），成功地将利血平与中性干扰物质分离开。该方法对尿样中的利血平检测范围在l*10~(-6)~(-1)*10~(-4)mol/L 比的线性相关系数为0.996，相对标准偏差为4.3％，最低检测限为7.0*10~(-8)mol/L。

直接型生物燃料电池酶催化剂的研究

生物燃料电池作为一种真正意义上的理想绿色环保电源，由于可作为小功率长寿命的体内植入电源，已成为人们研究的热点课题之一。目前对生物燃料电池的研究主要集中在间接型生物燃料电池，已取得一定进展。但是间接型生物燃料电池具有电子传递链长、效率低等弱点，而直接型生物燃料电池有望克服以上缺点，成为更具研究潜力的新一代生物燃料电池。本文从探索简单、有效的酶固定方法入手，制备炭载辣根过氧化物酶（HRP）、漆酶（Lac）、酪氨酸酶（Tyr）作直接型生物燃料电池的阴极催化剂和炭载葡萄糖氧化酶（GoD）作阳极催化剂。用多种谱学方法表征了炭载酶催化剂的结构特征和用电化学方法研究了炭载酶的直接电化学及电催化性能。得到的主要结果和结论如下：1．以比活性高、稳定、结构清楚、有纯的商品化试剂且价廉的HRP为模型分子来探索用平衡吸附法将HRP固定到活性炭表面，用Nofion膜加固并修饰到玻碳（GC）电极上，以期制备得到炭载HRP修饰的Gc电极（HRP-C／GC）。实验结果表明，炭载HRP能进行准可逆的直接电化学反应，式电位（0）在50-700mv／s的范围内几乎不随扫速变化，平均值为C0．362±0．001）v，表观速率常数（ks）为（3．4±0．69）s-1HRP-C/GC电极对HZoZ还原有很好和稳定的电催化活性，表明固定在活性炭上的HRP能保持其生物活性，而且能稳定数月时间。因此，固定在活性炭上的HRP有可能用作直接型生物燃料电池的阴极催化剂。由上述结果可见，用平衡吸附法把HRP固载到活性炭上，并用Nofion膜加固的酶电极的制备方法具有简单且有效的特点，有可能作为直接型生物燃料电池酶催化剂的制备方法。2．用平衡吸附法将Lac和Tyr分别固定到活性炭上，发现炭载Lac和Tyr都能进行准可逆的直接电化学反应，其0，在10-150mv／s的范围内几乎不随扫速而变化，分别为-0．166和-0．139v。另外，还发现炭载Lac和Tyr对02的还原有明显的电催化作用，表明炭载Lac和Tyr仍能保持它们的生物活性，因而能作直接型生物燃料电池的阴极催化剂。3．用平衡吸附法将葡萄糖氧化酶（GOD）固定到活性炭表面，发现炭载GOD能进行准可逆的直接电化学反应，其0，在10-200mv／s的范围内几乎不随扫速而变化，平均值为C0．467±0．002）v；ks值为（1．18±0．59）5-1；且其直接电化学反应是2e＋ZH＋的过程。另外，还发现炭载GOD对p-D（＋）葡萄糖的氧化有明显的电催化作用，表明炭载GOD没有发生变性，仍保持其生物活性，所以能用作直接型生物燃料电池的阳极催化剂。

一种新型的用于ICP－AES的氢化物元素和非氢化物元素同时分析的氢化物发生雾化装置的研究

氢化物发生－高频感耦等离子体原子发射光谱分析（HY－ICP－AES），由于它的灵敏度高和多元素同时分析等特点，近年来受到越来越多的科学工作者的重视。本文对HY－ICP－AES的原理、发展及应用作了比较详细的综述，并根据氢化物元素和非氢化物元素同时测定的实际要求，提出了一种新型的氢化物发生－雾化系统。文献上已报导了两种氢化物元素和非氢化物元素同时测定的方案，并取得了令人满意的结果。但在这些方案中，存在一些问题需要解决，而且装置比较复杂，操作也比较麻烦。在我们的氢化物发生－雾化系统中，用一个同心玻璃雾化器将待测的样品溶液雾化，细雾滴形成气溶胶，较大液滴被收集在一个玻璃槽中，硼氢化钾溶液用蠕动泵从玻璃槽底部送入，与收集的样品溶液混合并发生化学反应，产生挥发性的共价氢化物。生成的气态氢化物和样品气溶胶以及载气一起进入等离子体，因而可以进行氢化元素和非氢化物元素的同时测定。砷、锑、硒和碲的检出限分别为0.0075，0.0006，0.008，0.003，0.002 μg/ml，比传统的气动雾化方法得到的检出限好20－30倍。而对非氢化物元素，检出限可与双简雾室雾化相当。本系统进样量小（约2 ml)，且样品的利用率大为提高，有利于小量样品的分析。但由于进样量较小，限制了灵敏度的进一步提高。本系统的另一个特点是不仅可以用于氢化物元素和非氢化物元素的同时测定，而且在需要的情况下，不需拆换雾化装置，不需灭火，即可在1－2分钟内转变成为普通的测定非氢化物元素的雾化系统。只要将蒸馏水取代硼氢化钾溶液把收集样品溶液的玻璃槽冲洗干净，即可作为普通的雾化系统之用。我们用这种氢化物发生－雾化系统研究了等离子体功率、载气流量、观测高度、样品介质酸度、硼氢化钾溶液和流量对待测元素信号强度、信－背比和检出限的影响以及硼氢化钾溶液的稳定性和硼氢化钾的引入量对等离子体稳定性的影响等。我们还研究了几种共存干扰元素对氢化物形成的干扰情况。为了消除或减小共存元素对氢化物生成过程的干扰，我们试验了EDTA，8－羟基喹啉，氨三乙酸，硫脲等对干扰元素的掩蔽作用，最后选EDTA作为掩蔽剂，对消除或减小共存元素的干扰起了明显的作用。我们用本雾化系统分析了一种甜菜颗粒粕样品和桃叶82301标准参考物质。分析结果与其它方法或标准值比较吻合。在甜菜颗粒粕样品的分析中，我们发现基体中大量镁、钙对砷等低含量元素的光谱干扰比较严重，利用元素间干扰比不能予以准确扣除。我们用标准和样品的基体相匹配的方法解决了镁、钙的光谱干扰问题。