Analysis of the characteristics of a two-fiber sensor for monitorship of a turbid medium

Summary Certain characteristics of a two-fiber sensor device, of the type proposed by Papaet al. for sea water turbidity monitorship, are examined. The extension of medium from which most of the received backscattered power originates is investigated, together with possible effects of multiple scattering on the received power. Laboratory measurements testing the results of the analysis are reported.

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Riassunto Sono esaminate alcune caratteristiche di un sensore a due fibre, del tipo di quello proposto da Papaet al. per il monitoraggio della torbidità dell'acqua di mare. è stata studiata l'estensione della zona del mezzo da cui proviene la maggior parte della radiazione retrodiffusa ricevuta. Sono stati considerati effetti di diffusione multipla. I risultati dell'analisi sono stati controllati con misure in laboratorio.

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Резюме Исследуются некоторые характеристики дву-qh-нитевого датчика, предложенного Папа и др. для мониторирования мутности морской воды. Исследуется расширение зоны в среде, из которой формируется основная часть рассеянного назад излучения. Также рассматриваются эффекты многократного рассеяния. На основе лабораторных измерений проводится проверка результатов анализа.

     

Kinetic studies of antimony and selenium atomization processes including a chemical modifier during their determination by electrothermal atomic absorption spectrometry

We have studied antimony and selenium atomization processes including a chemical matrix modifier (palladium-containing activated carbon) during their determination by electrothermal atomic absorption spectrometry. We have developed and fine-tuned an experimental setup for determining the kinetic characteristics (activation energy and frequency factor) for element atomization processes from measurements in the initial section of the analytical signal. We provide a rationale for the most likely mechanism for the interactions that occur. The results of the kinetic studies of the atomization processes showed that the modifier we developed was highly effective, as a result of formation of a thermally stable condensed system C-Pd-A (where A is the analyte). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 530–534, July–August, 2006.     

基于原位等离子体氮化及低压化学气相沉积-Si_3N_4栅介质的高性能AlGaN/GaN MIS-HEMTs器件的研究

通过对低压化学气相沉积(LPCVD)系统进行改造,实现在沉积Si_3N_4薄膜前的原位等离子体氮化处理,氮等离子体可以有效地降低器件界面处的氧含量和悬挂键,从而获得了较低的LPCVD-Si_3N_4/GaN界面态,通过这种技术制作的MIS-HEMTs器件,在扫描栅压范围V_(G-sweep)=(-30 V,+24 V)时,阈值回滞为186 mV,据我们所知为目前高扫描栅压V_(G+)(20 V)下的最好结果.动态测试表明,在400 V关态应力下,器件的导通电阻仅仅上升1.36倍(关态到开态的时间间隔为100μs).     

An easy way to controllably synthesize one-dimensional Sm B_6 topological insulator nanostructures and exploration of their field emission applications

A convenient fabrication technique for samarium hexaboride(SmB_6) nanostructures(nanowires and nanopencils) is developed, combining magnetron-sputtering and chemical vapor deposition. Both nanostructures are proven to be single crystals with cubic structure, and they both grow along the [001] direction. Formation of both nanostructures is attributed to the vapor-liquid-solid(VLS) mechanism, and the content of boron vapor is proposed to be the reason for their different morphologies at various evaporation distances. Field emission(FE) measurements show that the maximum current density of both the as-grown nanowires and nanopencils can be several hundred μA/cm~2, and their FN plots deviate only slightly from a straight line. Moreover, we prefer the generalized Schottky-Nordheim(SN) model to comprehend the difference in FE properties between the nanowires and nanopencils. The results reveal that the nonlinearity of FN plots is attributable to the effect of image potential on the FE process, which is almost independent of the morphology of the nanostructures.All the research results suggest that the SmB_6 nanostructures would have a more promising future in the FE area if their surface oxide layer was eliminated in advance.     

超长定向含铁多壁碳纳米管阵列的制备

采用无模板化学气相沉积法,以二茂铁为催化剂,二甲苯为碳源,利用单温炉加热装置制备了定向碳纳米管阵列。运用扫描电子显微镜、透射电子显微镜、拉曼光谱和X射线衍射仪等对定向碳纳米管阵列的形貌、成分和物相进行细致的分析和表征。结果表明:制得的碳纳米管阵列具有良好的定向性和多壁管状结构,并且石墨化程度高;碳纳米管中除碳元素外,管中包含有少量以纳米颗粒和纳米线形式存在的铁及其化合物,主要成分是铁和碳化铁。结合碳纳米管的制备和透射电子显微镜分析表征结果,认为超长碳纳米管阵列的生长模式为底部生长方式,即经历催化剂分解、催化、成核、长大、中毒、凝聚成粒和连接成线的循环过程,正是由于碳源和催化剂的连续供应促成了碳纳米管阵列的快速定向生长。     

射频功率对类金刚石薄膜性能的影响

在不同射频功率条件下,实验研究了射频等离子体化学气相沉积类金刚石薄膜的金刚石相分数、光学常数和硬度。利用Raman光谱仪、椭圆偏振仪、数字式显微硬度计分别测试了不同条件下单层类金刚石薄膜的金刚石相分数、光学常数和硬度。实验表明,随着功率的增加,金刚石相的相对分数减少,薄膜的折射率先减小再增加然后减小,射频功率大于910 W时,沉积速率急剧增大。而薄膜的硬度先增加后减小,在射频功率为860 W处获得最大值。     

3种黄酮醇类化合物核磁共振碳谱的理论研究

在B3LYP/6-31G水平下优化了3种黄酮醇类（山奈酚,槲皮素,杨梅素）化合物的几何构型. 在振动分析中,均未出现虚频率. 在B3LYP/6-31G的水平下计算了该类化合物的核磁共振碳谱. 研究结果表明：3种分子均有分子内氢键形成,且分子内氢键的键长为0.17~0.18 nm左右 . 本文讨论了羟基引入之后对邻近C的化学位移的影响. 从取代基对NMR的影响来看,随着取代基对苯环的供电子能力的加强,取代基邻近的一些C的化学位移有所改变.      

Effect of emitter layer doping concentration on the performance of silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15 nm)/a-Si:H(10 nm)/ epitaxial c-Si(47 μm)/epitaxial c-Si(3 μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot-wire chemical vapour deposition. The effect of the doping concentration of emitter layer S_d (S_d=PH₃/(PH₃+SiH₄+H₂)) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S_d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S_d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm², a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

6H-SiC衬底上AlGaN基垂直结构紫外LED的制备

利用金属有机物化学气相沉积方法,在n型6H-SiC衬底上制备了15对Si掺杂Al_(0.19)Ga_(0.81)N/Al_(0.37)Ga_(0.63)N DBR,并采用低温AlN缓冲层有效抑制了DBR结构中裂纹的产生,得到了表面均方根粗糙度仅为0.4 nm且导电性能良好的n型DBR,其在369 nm处峰值反射率为68%,阻带宽度为10 nm。在获得导电DBR的基础上,进一步在n型6H-SiC衬底上构建了有、无DBR的垂直结构紫外LED。对比两者电致发光光谱,发现DBR结构的引入有效增强了LED紫外发光强度。     

非故意掺杂GaN层厚度对蓝光LED波长均匀性的影响

通过调整非故意掺杂氮化镓层的厚度,分析氮化镓基LED外延生长过程中应力的演变行为,以控制外延片表面的翘曲程度,从而获得高均匀性与一致性的外延片。由于衬底与外延层之间的热膨胀系数差别较大,在生长温度不断变化的过程中,外延片的翘曲状态也随之改变。在n型氮化镓生长结束时,外延片处于凹面变形状态。在随后的过程中,外延薄膜"凹面"变形程度不断减小,甚至转变为"凸面"变形,所以n型氮化镓生长结束时外延片的变形程度会直接影响多量子阱沉积时外延片的翘曲状态。当非掺杂氮化镓沉积厚度为3.63μm时,外延片在n型氮化镓层生长结束时变形程度最大,在沉积多量子阱时表面最为平整,这与PLmapping测试所得波长分布以及标准差值最小相一致。通过合理控制非故意掺杂氮化镓层的厚度以调节外延层中的应力状态,可获得均匀性与一致性良好的LED外延片。