Study of Si/SiO2 hybrid antireflective coatings on SLD prepared by DSEBET - art. no. 69842P

We introduce a double source electron beam evaporation (DSEBET) technique in this paper. The refractive index coatings were fabricated on K9 glass substrate by adjusting the evaporation rates of two independent sources. The coatings, which were described by atomic force microscopy (AFM), show good compactness and homogeneity. The antireflective (AR) coatings were fabricated on Superluminescent Diodes (SLD) by DSEBET. The hybrid AR coatings on the facets of SLD were prepared in evaporation rates of 0.22nm/s and 0.75nm/s for silicon and silicon dioxide, respectively. The results of AFM and spectral performance of coated SLD show that DSEBET has a promising future in preparing the coatings on optoelectronic devices.

Zinc phthalocyanine (ZnPc) incorporated into silicon matrix grown by plasma enhanced chemical vapor deposition (PECVD)

Hybrid composites composed of zinc phthalocyanine embedded in silicon matrixes have attracted attention because of the potential for solar energy conversion. We produce hybrid composites by thermal evaporation for the plithalocyanine and PECVD (Plasma Enhanced Chemical Vapor Deposition) for the silicon matrix. Deposition of ZnPc/a-Si(amorphous silicon) composites was achieved in a sequential manner. The compound films were characterized by optical transmittance spectra and photoconductivity measurement. The optical transmittance measurements were carried out in the visible region (500 - 800 nm). Compared to pure silicon film, the photosensitivity of compound functional films was enhanced by one order of magnitude. This demonstrates the Si sensitized by adding ZnPc.

Effect of channel surface wettability and temperature gradients on the boiling flow pattern in a single microchannel

The objective of this paper is to investigate the effects of channel surface wettability and temperature gradients on the boiling flow pattern in a single microchannel. The test section consists of a bottom silicon substrate bonded with a top glass cover. Three consecutive parts of an inlet fluid plenum, a central microchannel and an outlet fluid plenum were etched in the silicon substrate. The central microchannel had a width of 800 mu m and a depth of 30 mu m. Acetone liquid was used as the working fluid. High outlet vapor qualities were dealt with here. The flow pattern consists of a fluid triangle (shrinkage of the liquid films) and a connected long liquid rivulet, which is generated in the central microchannel in the timescale of milliseconds. The peculiar flow pattern is formed due to the following reasons: (1) the liquid rivulet tends to have a large contact area with the top hydrophilic channel surface of the glass cover, but a smaller contact area with the bottom silicon hydrophobic surface. (2) The temperature gradient in the chip width direction at the top channel surface of the glass cover not only causes the shrinkage of the liquid films in the central microchannel upstream, but also attracts the liquid rivulet populated near the microchannel centerline. (3) The zigzag pattern is formed due to the competition between the evaporation momentum forces at the vapor-liquid interfaces and the force due to the Marangoni effect. The former causes the rivulet to deviate from the channel centerline and the latter draws the rivulet toward the channel centerline. (4) The temperature gradient along the flow direction in the central microchannel downstream causes the breakup of the rivulet to form isolated droplets there. (5) Liquid stripes inside the upstream fluid triangle were caused by the small capillary number of the liquid film, at which the large surface tension force relative to the viscous force tends to populate the liquid film locally on the top glass cover surface.

Chaotic behavior of pulsating heat pipes

Chaotic behavior of closed loop pulsating heat pipes (PHPs) was studied. The PHPs were fabricated by capillary tubes with outer and inner diameters of 2.0 and 1.20 mm. FC-72 and deionized water were used as the working fluids. Experiments cover the following data ranges: number of turns of 4, 6, and 9, inclination angles from 5 degrees (near horizontal) to 90, (vertical), charge ratios from 50% to 80%, heating powers from 7.5 to 60.0 W. The nonlinear analysis is based on the recorded time series of temperatures on the evaporation, adiabatic, and condensation sections. The present study confirms that PHPs are deterministic chaotic systems. Autocorrelation functions (ACF) are decreased versus time, indicating prediction ability of the system is finite. Three typical attractor patterns are identified. Hurst exponents are very high, i.e., from 0.85 to 0.95, indicating very strong persistent properties of PHPs. Curves of correlation integral versus radius of hypersphere indicate two linear sections for water PHPs, corresponding to both high frequency, low amplitude, and low frequency, large amplitude oscillations. At small inclination angles near horizontal, correlation dimensions are not uniform at different turns of PHPs. The non-uniformity of correlation dimensions is significantly improved with increases in inclination angles. Effect of inclination angles on the chaotic parameters is complex for FC-72 PHPs, but it is certain that correlation dimensions and Kolmogorov entropies are increased with increases in inclination angles. The optimal charge ratios are about 60-70%, at which correlation dimensions and Kolmogorov entropies are high. The higher the heating power, the larger the correlation dimensions and Kolmogorov entropies are. For most runs, large correlation dimensions and Kolmogorov entropies correspond to small thermal resistances, i.e., better thermal performance, except for FC-72 PHPs at small inclination angles of theta < 15 degrees.

Uniform mems chip temperatures in the nucleate boiling heat transfer region by selecting suitable, medium boiling number range

The not only lower but also uniform MEMS chip temperatures can he reached by selecting suitable boiling number range that ensures the nucleate boiling heat transfer. In this article, boiling heat transfer experiments in 10 silicon triangular microchannels with the hydraulic diameter of 55.4 mu m were performed using acetone as the working fluid, having the inlet liquid temperatures of 24-40 degrees C, mass fluxes of 96-360 kg/m(2)s, heat fluxes of 140-420 kW/m(2), and exit vapor mass qualities of 0.28-0.70. The above data range correspond to the boiling number from 1.574 x 10(-3) to 3.219 x 10(-3) and ensure the perfect nucleate boiling heat transfer region, providing a very uniform chip temperature distribution in both streamline and transverse directions. The boiling heat transfer coefficients determined by the infrared radiator image system were found to he dependent on the heat Axes only, not dependent on the mass Axes and the vapor mass qualities covering the above data range. The high-speed flow visualization shows that the periodic flow patterns take place inside the microchannel in the time scale of milliseconds, consisting of liquid refilling stage, bubble nucleation, growth and coalescence stage, and transient liquid film evaporation stage in a full cycle. The paired or triplet bubble nucleation sites can occur in the microchannel corners anywhere along the flow direction, accounting for the nucleate boiling heat transfer mode. The periodic boiling process is similar to a series of bubble nucleation, growth, and departure followed by the liquid refilling in a single cavity for the pool boiling situation. The chip temperature difference across the whole two-phase area is found to he small in a couple of degrees, providing a better thermal management scheme for the high heat flux electronic components. Chen's [11 widely accepted correlation for macrochannels and Bao et al.'s [21 correlation obtained in a copper capillary tube with the inside diameter of 1.95 mm using R11 and HCFC123 as working fluids can predict the present experimental data with accepted accuracy. Other correlations fail to predict the correct heat transfer coefficient trends. New heat transfer correlations are also recommended.

PAA对不同土壤保水和蒸发性能的影响

采用土柱法研究了不同PAA施入量对3种黄土高原主要土壤类型(黄绵土、黑垆土和塿土)的持水性能、土壤饱和导水率和土壤蒸发量的影响,以进一步阐明PAA的保水和蒸发作用。结果表明,施入PAA提高了土壤的持水性能。在未加入PAA之前黑垆土的持水性能最低,塿土的最高,黄绵土的次之;加入PAA后,黑垆土的持水能力显著增加,几乎为对照的2倍,塿土和黄绵土也都比对照高。土壤的供水能力随PAA用量的增加而增强,不同土壤类型之间表现为:塿土>黑垆土>黄绵土。未加入PAA时,3种土壤饱和导水率大小为:塿土>黑垆土>黄绵土;加入PAA后,3种土壤的饱和导水率都降低,且基本随PAA用量的增加而降低。在一定水分条件下,PAA的施入提高了土壤的抗蒸发性能,随PAA用量的增加,塿土和黑垆土的土壤蒸发量增加,但都低于对照,而黄绵土的土壤蒸发量随PAA用量的增加而降低。其中施PAA54.5 mg/kg的塿土、黑垆土和施PAA225.8 mg/kg的黄绵土与对照相比,土壤蒸发量分别减少了44.0%,44.6%和30.6%。

砂石覆盖厚度和粒径对土壤蒸发的影响

在干旱半干旱地区,砂石覆盖作为一项传统的覆盖技术,可以明显减少土壤蒸发,为作物生长提供良好的水分条件。为研究不同粒径和厚度砂石覆盖对土壤蒸发的影响,进行了室内模拟试验,对3种粒径(2.5~10、10~25和25~40 mm)和2种覆盖厚度(8 cm和14 cm)以及不同粒径砂石配比条件下土壤水分蒸发进行了研究。结果表明,砂石覆盖能有效地抑制土壤蒸发,在土壤含水量较高的阶段,这种抑制作用更加明显。砂石覆盖对土壤蒸发的抑制作用与粒径和覆盖厚度密切相关,在2.5~40 mm粒径范围内,随着砂石粒径的增大,砂石覆盖对蒸发的抑制作用降低,对蒸发过程的影响减弱,覆盖厚度越大,蒸发量越小。有效的砂石配比应选择细砂石处理,不宜过粗。

无压灌溉日光温室番茄作物-皿系数研究

以-25 kPa作为土壤水势临界值,将作物—皿系数(Kcp)设为0.2,0.4,0.6,0.8,1.0,1.2六个处理,研究了不同灌溉水量时的番茄产量、品质和灌溉水利用效率。通过经济效益评价,研究了杨凌地区无压灌溉温室番茄获得最高经济效益时的作物—皿系数。通过张力计读数变化规律,研究了利用张力计测量无压灌溉湿润体内土壤水势的特点。研究结果表明,Kcp为0.2~0.8时,灌溉水量的增加对番茄产量影响不大;Kcp为1.0~1.2时,灌溉水量的增加能显著提高番茄产量和果实大小;Kcp为0.2时的灌溉水量能极显著提高番茄的灌溉水利用效率。在综合考虑了杨凌地区水价、番茄使用目的和市场价格波动规律后,Kcp取值1.2能获得最高的经济效益。作物—皿系数法计算灌溉水量时的滞后性特点和张力计埋设位置,是判断利用张力计监测土壤水势临界值方法有效性的两个重要因素。

黄土高原(土娄)覆盖层与黏化层的土壤水文效应

黄土高原(土娄)土在《中国土壤系统分类(修订方案)》中属土垫旱耕人为土类的相应亚类,其土壤水分状况是诊断表层所属人为表层类堆垫表层(覆盖层)和诊断表下层(黏化层)的重要诊断特征。以土壤持水性能、蒸发性能和水分移动性能为切入点,对(土娄)土覆盖层和黏化层的土壤水文效应进行研究论证,以期对土垫旱耕人为土类及其亚类的诊断层与诊断特征获取更深层的认识。

两种高分子保水材料对盆栽甘蓝影响研究

采用盆栽试验,研究了两种高分子化合物聚丙烯酸钠(sodium polyacrylate,SP)与聚丙烯酰胺(Polyacrylamide,PAM)对甘蓝生长的影响。结果表明:在土壤中施入2/1000的两种高分子材料均能抑制土壤蒸发,砂土、粘土蒸发强度分别较对照降低35.5%、22.8%;甘蓝叶绿素受两种材料的影响不显著,受肥料影响较大;两种高分子材料施入土壤中增加了甘蓝产量、降低了根冠比,地上、地下生物量砂土较对照分别增加了61.1%、16.1%,粘土分别增加了55.2%、28.7%,根冠比砂土较对照平均降低了26.9%,粘土降低16%;PAM与SP使砂土容重较对照降低了13.9%,而粘土仅降低了4.1%;单施高分子处理水分利用效率平均较对照增加59.1%,与肥料混合使用时增加77.1%。总体来看,PAM与SP作用效果相近。

提高人工植被培育中土壤抗旱性的综合措施

干旱条件下培育人工植被,采取适当的抗旱措施是必不可少的,其中作为植物生长发育所需水分、营养的载体,土壤是显著的可调控对象,对其合理处置与抗旱有着密切的关系。以土蓄水、抑制蒸发、改良土壤、培肥地力等有利于对有限水分的利用。提高土壤抗旱性的综合措施包括土壤耕作、土壤培肥、土壤覆盖、防止水分深层渗漏等方面。在气候暖化的背景下,为增强土壤抗旱措施的效果,提高其技术水平,分析了与蓄水、保水、集水以及用水有关的土壤抗旱方式及其特点。在综合述评的基础上,还讨论了土壤抗旱措施的技术应用问题和需要研究的主要方面。

土壤砂砾覆盖对入渗和蒸发影响研究进展

砂砾覆盖能防止土壤表面受到雨滴侵蚀,切断土壤的毛细管作用,从而对土壤入渗和蒸发规律产生影响。介绍了国内外砂砾覆盖对入渗和蒸发规律影响的研究成果,现有研究结果表明,降雨入渗与砾石覆盖度之间既有正相关关系,又有负相关关系,入渗不仅与砂砾粒径有关,还与砂砾在土壤表面所处的位置有关;砂砾覆盖能够抑制蒸发,抑制效果与砂砾粒径大小、颜色和厚度等有关。另外,一些国外学者通过定量化模型描述了砂砾覆盖条件下入渗和蒸发规律,但这些定量化模型还是最基本的简化模型,主要偏重于理论说明,直接应用于实践还存在一些问题。

STUDIES OF THE PROMISING MATERIAL COSI2 ON GAAS SUBSTRATES

The thermal stability of CoSi2 thin films on GaAs substrates has been studied using a variety of techniques. The CoSi2 thin films were formed by depositing Co(500 angstrom) and Si(1800 angstrom) layers on GaAs substrates by electron-beam evaporation followed by annealing processes, where the Si inter-layer was used as a diffusion/reaction barrier at the interface. The resistivity of CoSi2 thin films formed is about 30 muOMEGA cm. The Schottky barrier height of CoSi2/n-GaAs is 0.76 eV and the ideality factor is 1.14 after annealing at 750-degrees-C for 30 min. The CoSi2/GaAs interface is determined to be thermally stable and the thin film morphologically uniform on GaAs after 900-degrees-C/30 s anneal. The CoSi2 thin films fulfill the requirements in GaAs self-aligned gate technology.

EFFECT OF A SI LAYER ON THE SUPERCONDUCTIVE PROPERTIES OF A BIPBSRCACUO THIN-FILM

The Pb-doped BiSrCaCuO superconducting films were grown by the single source mixed evaporation technique. The microbridges of dimensions 50 mum x 40 mum were fabricated by standard photolithography technologies. Si films with a thickness of 2500 angstrom were deposited on the microbridge area surfaces of BiPbSrCaCuO superconducting films by rf-magnetron sputtering. A greatly lowered zero resistance temperature of the microbridge area of the BiPbSrCaCuO film after Si sputtering was found. A non-linear effect of the current-voltage (I-V) characteristics at 78 K was shown. The high-frequency capacitance-voltage (C-V) curve of this structure at 78 K was symmetrical with the maximum capacitance at V = 0, and the capacitance decreased with increasing applied bias voltage. Afl experimental results are discussed.

THIN-FILM BIPBSRCACUO DIRECT-CURRENT SUPERCONDUCTING QUANTUM INTERFERING DEVICES OPERATING AT 78-K

Direct current SQUIDs (superconducting quantum interference devices) have been successfully fabricated by using a Pb-doped BiSrCaCuO superconducting thin film made by mixed evaporation of a single source composed of related components with a resistance heater. The dc SQUID comprises a square washer with a small hole. These SQUIDs show perfectly periodic voltage-flux characteristics without magnetic shield, that is, typically, the flux noise and energy resolution at a frequency range from dc to 1 Hz and at 78 K being 1.7 x 10(-3) PHI-0/ square-root Hz and 3.6 x 10(-26) J/Hz, respectively. Meanwhile, we have found out that one of the SQUIDs still was able to operate on flux-locked mode without bias currents and showed voltage-flux second harmonic characteristics. This phenomenon is not well understood, but it may be related to I-V (current-voltage) characteristics of the dc SQUID.