GaInP/GaAs HBT高频噪声特性分析

通过器件Z参数分析噪声等效电路及计算最小噪声系数，利用HP ADS软件仿真了等效电路元件对最小噪声系数的影响，从而得出了根据器件几何、物理参数来改进器件高频噪声性能的有效途径。     

GSMBE InGaP/GaAs材料大面积均匀性研究

报道了气态源分子束外延 (GSMBE)技术生长的Φ5 0mm ,Φ75mmInGaP/GaAs材料的晶体完整性 ,组分均匀性和表面缺陷密度。用PhilipsX Pert′s四晶衍射仪沿Φ5 0mm ,Φ75mmInGaP/GaAs样品的x轴和y轴以 5mm间隔测量ω/2θ双晶摇摆曲线 ,获得沿x轴和y轴方向的晶格失配度分布和组分涨落分布。结果表明 ,用GSMBE生长的Φ5 0mm和Φ75mmIn0 .4 9Ga0 .51 P与GaAs衬底的失配度分别为 1× 10 - 4和 1× 10 - 5,组分波动Φ5 0mm沿x轴和y轴分别为± 0 .1%和± 0 .2 % ,Φ75mm <± 1%。表面缺陷密度在 1× 10～ 1× 10 2 cm- 2 。     

气态源分子束外延生长GexSi1-x/Si异质结合金

采用气态源分子束外延法成功地生长了ＧｅｘＳｉ１－ｘ／Ｓｉ异质结合金材料，所使用的气体分别是乙硅烷和锗烷。高能电子衍射被用于原位监控生长层的表面重构状态。在一定的生长温度下，ＧｅｘＳｉ１－ｘ合金组分ｘ取决于锗烷和乙硅烷的流量比。外延层的表面形貌与锗组分的大小、生长层的厚度及生长温度有关。结果表明，较大的锗组分和较高的生长温度利于由二维模式向三维模式转变的外延生长。     

垂直堆垛InAs量子点材料的分子束外延生长

用MBF设备以Stranski-Krastanov生长方式外延生长了5个周期垂直堆垛的InAs量子点，在生长过程中使用对形状尺寸控制法来提高垂直堆垛InAs量子点质量和均匀性。样品外延的主要结构是500nm的GaAs外延层，15nm的Al0．5Ga0．5As势垒外延层，5个周期堆跺的InAs量子点，50nm的Al0．5Ga0．5Asnm势垒外延层等。在生长过程中用反射式高能电子衍射仪(RHEED)实时监控。生长后用原子力显微镜(AFM)进行表面形貌的表征，再利用光制发光(PL)对InAs量子点进行观测。     

四阱耦合InGaAs/InAlAs/InP量子级联激光器材料的结构特性研究

报道了用气态源分子束外延 (GSMBE)技术生长的InAlAs/InGaAs四阱耦合量子级联激光器 (QCL)材料的结构特性。X射线双晶回摆曲线谱测量结果表明所生长的QCL有源区的界面 (含 770层外延层 )、厚度达到单厚子层控制 ,组份波动≤ 1% ,晶格失配≤ 1× 10 - 3。采用特殊的优化工艺 ,Φ5 0mm外延片的表面缺路陷密度降至 1× 10cm- 2 ,达到了器件质量的要求。     

分子束外延InAs量子点材料的透射电子显微镜研究

报道了利用分子束外延技术在(001)GaAs衬底上生长的单层及多层InAs量子点材料的透射电子显微镜(TEM)研究结果,并对量子点的结构特性进行了讨论.结果表明:多层量子点呈现明显的垂直成串排列趋势;随着InAs量子点层数的增加,量子点的密度下降,其尺寸随层数的增加趋向均匀.在试验条件下,5层量子点材料的InAs量子点厚度和GaAs隔离层的厚度的选择都比较合理,其生长过程中的应变场更有利于自组织量子的形成.     

Ag2C2O4/TiO2异质结的制备及其光催化性能研究

采用溶胶-凝胶法制备了锐钛矿型TiO₂,通过沉淀法成功将Ag₂C₂O₄沉积于TiO₂表面制备了Ag₂C₂O₄/TiO₂异质结。采用孔隙比表面分析仪(BET)、X-射线衍射仪(XRD)等对Ag₂C₂O₄/TiO₂异质结结构和光响应能力进行了表征;运用表面光电压仪(SPS)等对光催化剂的光生电荷分离特性进行了研究;考察了异质结光催化剂对模拟污染物罗丹明B的催化降解性能。结果表明：当Ag₂C₂O₄/TiO₂摩尔比为7.0%时,异质结光催化剂的光生电子-空穴分离速率最高,该光催化剂对罗丹明B的光催化降解性能最好。     

CuS-Ag/g-C3N4三相复合材料的合成及其光催化性能研究

二维(2D)石墨相氮化碳(g-C₃N₄)作为一种n型半导体,因其无金属、成本低、易于热制备、无毒和高光稳定性等特点而受到广泛研究,但单一相的g-C₃N₄材料仍存在诸如光生载流子易复合、可见光利用率较低、量子效率偏低等缺陷。以硫脲为前驱体,经二次煅烧得到g-C₃N₄,利用光沉积法引入Ag,最后将通过溶剂热法制备的Cu S通过超声混合和蒸发溶剂的方法引入,成功制备了三相复合材料Cu S-Ag/g-C₃N₄。结果表明,Cu S-Ag/g-C₃N₄复合材料仍然保持片层状结构,材料的比表面积增加且材料的禁带宽度减小,大幅提高了其对可见光的吸收范围,从而提高了材料的光催化降解罗丹明B的性能。当Cu S含量为10%时Cu S-Ag/CN复合材料的光催化降解速率是g-C₃N₄的4.3倍。     

双Z型异质结BiOI/MoO3/g-C3N4的构建及其光催化性能研究

通过简单的溶剂热法将半导体MoO₃、BiOI与g-C₃N₄复合,构建双Z型异质结BiOI(x)/MoO₃/g-C₃N₄(x=6.25%、12.50%、18.75%、25.00%,x为BiOI的质量分数)三元复合材料,从HRTEM结果可知样品出现了2种间距分别为0.28 nm和0.33 nm的晶格条纹,结合XRD表征结果可知分别属于BiOI(110)和MoO₃(021)晶面,且g-C₃N₄是非晶态物质,由此表明BiOI/MoO₃/g-C₃N₄复合材料成功复合。UV-Vis DRS分析表明复合样品的带隙变窄,光学响应范围增强,PL和光电化学测试表征说明异质结的存在有效延缓了电子和空穴的复合,在模拟太阳光条件下对染料甲基橙(MO)进行降解并研究其光催化活性,BiOI(18.75)/MoO₃/g-C_3<...     

Performance of Bridge Materials by Structural Deficiency Analysis

The diagnostic concept of the structural deficiency of bridges is an essential engineering and management consideration with implications of performance. The structural deficiency analysis reflects the constructed system performance at the serviceability limit states. This paper analyzes trends in the structural deficiency of bridge inventory on the basis of material kind. A multiple-criteria diagnostic approach defines measures for condition, durability, and longevity performances and determines the overall equivalent performance. Thus, the structural performance levels reflect the structural reliability and vulnerability indices for bridge serviceability. The application of the approach analyzes the raw database of the entire bridge inventory in the United States. This comprehensive operational experience provides a national network-level comparative basis. The comparison suggests a relative need for improvements in one or more areas, such as design details or maintenance level, to increase the desirability of bridge construction materials. The results support more objective bridge management and decision making on distribution of funds, updating of policies, perfection of practices, and trade-off analyses for design, construction, maintenance, and replacement.     

Growth of High Quality Semi-Insulating InP Single Crystal by Suppression of Compensation Defects

Deep level defects in as-grown and annealed SI-InP samples were investigated by thermally stimulated current spectroscopy. Correlations between electrical property, compensation ratio, thermal stability and deep defect concentration in SI-InP were revealed. An optimized crystal growth condition for high quality SI-InP was demonstrated based on the experimental results.     

Growth and Characterization of Semi-Insulating GaN Films Grown by MOCVD

High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arcmin, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 ℃ was measured to be approximate 109 and 106 Ω·cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.     

Effects of Processing Residual Stresses on Fatigue Crack Growth Behavior of Structural Materials: Experimental Approaches and Microstructural Mechanisms

Fatigue crack growth mechanisms of long cracks through fields with low and high residual stresses were investigated for a common structural aluminum alloy, 6061-T61. Bulk processing residual stresses were introduced in the material by quenching during heat treatment. Compact tension (CT) specimens were fatigue crack growth (FCG) tested at varying stress ratios to capture the closure and K _max effects. The changes in fatigue crack growth mechanisms at the microstructural scale are correlated to closure, stress ratio, and plasticity, which are all dependent on residual stress. A dual-parameter ΔK–K _max approach, which includes corrections for crack closure and residual stresses, is used uniquely to connect fatigue crack growth mechanisms at the microstructural scale with changes in crack growth rates at various stress ratios for low- and high-residual-stress conditions. The methods and tools proposed in this study can be used to optimize existing materials and processes as well as to develop new materials and processes for FCG limited structural applications.     

Characterization of Steel Thixoforming Tool Materials by High Temperature Compression Tests

The experimental set‐up and the results of high temperature compression tests for the characterization of tool materials for steel thixoforming are presented. The scope of this test is to reproduce the load profile of steel thixoforming processes consisting of mechanical, thermal, tribological, and chemical components on the forming mould. Tool materials were chosen following a concept within the Collaborative Research Center ‐ SFB 289 ‐ “Forming of metals in the semi‐solid state and their properties”. Three materials groups are distinguished: thin film deposited by physical vapor deposition (PVD) and plasma assisted chemical vapour deposition (PACVD), thick coatings (thermal spraying), and bulk ceramic materials. Samples were characterized using scanning electron microscopy (SEM), electron‐dispersive spectroscopy (EDS) and X‐Ray diffraction analysis (XRD). The results show varying resistance of the tool materials concerning the load profile. In order to provide an appropriate tool solution for the thixoforming of steels, different load profiles within the forming moulds are identified and the corresponding tool part is made from that material with the best performance.     

碳酸盐燃料电池用材料的腐蚀研究与展望

介绍了熔融碳酸盐燃料电池用材抗腐蚀研究的进展,通过对熔融碳酸盐腐蚀机理和Ｎｉ、Ｎｉ－Ｆｅ合金、Ｃｒ以及Ｎｉ－Ａｌ系金属间化合物在熔碳酸盐中的腐蚀行为的分析,认为Ｎｉ－Ａｌ系金属间化合物作为熔融碳酸盐燃料电池的结构材料具有广阔的应用前景。     

Synthesis and Characterization of Mesoporous Materials MCM-41 Incorporated by Yttrium, Neodymium and Samarium

Synthesis and Characterization of Mesoporous Materials MCM-41 Incorporated by Yttrium, Neodymium and Samarium     

Synthesis and Characterization of Mesoporous Materials MCM-41 Incorporated by Yttrium, Neodymium and Samarium

Zeolitemolecularsieves,withtheuniformchan nelstructureandshapeselectiveproperty,arewidely usedascatalystsinindustriesofoil refining,petro chemicals,fine chemicalsandsoon.However,the poresizesofzeolitemolecularsievesusuallyaresmall erthan2nm,itgreatlypreve…     

锂离子电池中高容量Si-Cu/C复合负极材料的制备与性能研究

采用高能球磨方法制备了用作锂离子电池负极材料的Si—Cu／C复合材料。X射线衍射和扫描电子显微镜结果表明，复合材料中Si和Cu5Si是共存的，活性硅颗粒均匀地分散在石墨和惰性的铜硅合金基体中。电化学测试在电流密度0．2mA·cm^-2，电压范围0—1．4V条件下进行，其结果表明高分散Si—Cu／C复合材料首次可逆容量为524mAh·g^-1，远高于目前普遍使用的中间相碳微球；循环寿命也远优于同粒度的硅单体，经过30次循环后容量仍保持531mAh·g^-1。其高比容量和良好的循环性能表明：高分散Si—Cu／C复合材料有望替代碳成为锂离子电池负极材料。