1-mm gate periphery AlGaN/AIN/GaN HEMTs on SiC with output power of 9.39 W at 8 GHz

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with high mobility GaN channel layer were grown on 50 min diameter semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition and large periphery HEMT devices were fabricated and characterized. High two-dimensional electron gas mobility of 2215 cm(2)/V s at room temperature with sheet electron concentration of 1.044 x 10(13)/cm(2) was achieved. The 50 mm diameter HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with the resistance uniformity of 2.02%. Atomic force microscopy measurements revealed a smooth AlGaN surface with a root-mean-square roughness of 0.27 nm for a scan area of 5 mu mi x 5 pm. The 1-mm gate width devices fabricated using the materials demonstrated a very high continuous wave output power of 9.39 W at 8 GHz, with a power added efficiency of 46.2% and power gain of 7.54 dB. A maximum drain current density of 1300 mA/mm, an extrinsic transconductance of 382 mS/mm, a current gain cutoff frequency of 31 GHz and a maximum frequency of oscillation 60 GHz were also achieved in the same devices. (C) 2007 Elsevier Ltd. All rights reserved.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

Hard magnetic properties of Sm3Fe26.7VxN4 and Sm3Fe26.7VxCy

Sm3Fe26.7V2.3N4 nitrides and Sm3Fe26.7V2.3Cy carbides have been synthesized by gas-solid phase reaction. Their hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm3Fe26.7V2.3N4 almost decreases linearly with increasing ball-milling time t, but that of Sm3Fe26.7V2.3Cy has no obvious change when the ball-milling time increases from t = 1 to 28 h. As a preliminary result, the maximum remanence B-r of 0.94 and 0.88 T, the coercivity mu(0i)H(C) of 0.75 and 0.25 T, and the maximum energy product (BH) of 108.5 and 39.1 kJ/m(3) for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Hydrogenation and anisotropic expansions in R3Fe29-xTx (R = Y, Ce, Nd, Sm, Gd, Tb and Dy; T = V and Cr)

A systematic study of the phase formation, structure and magnetic properties of the R3Fe29-xTx compounds (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) has been performed upon hydrogenation. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions mainly along the a- and b-axis rather than along the c-axis are observed for all of the compounds upon hydrogenation. Hydrogenation leads to an increase in the Curie temperature and a corresponding increase in the saturation magnetization at room temperature for each compound. First order magnetization processes (FOMP) occur in the external magnetic fields for Nd3Fe24.5Cr4.5H5.0, Tb3Fe27.0Cr2.0H2.8, and Gd3Fe28.0Cr1.0H4.2 compounds.

Thermomagnetic behavior and first order magnetization processes of Sm3Fe29-xTx and Sm3Fe29-xTxN4 (T = V and Cr)

A systematic investigation of structure and intrinsic magnetic properties of the compounds Sm3Fe29-xTx (T = V and Cr) and their nitrides has been performed. Nitrogenation resulted in remarkable improvements in the saturation magnetization and anisotropy fields at 4.2 K and room temperature. First order magnetization processes are observed at around 5.7 T for Sm3Fe26.7V2.3 and around 2.8 T for Sm3Fe24.0Cr5.0 and Sm3Fe24.0Cr5.0N4, respectively. The spin reorientation of the easy magnetization direction of Sm3Fe26.7V2.3 is observed at around 230 K. As a preliminary result, the maximum remanence B-r of 0.94 T, the coercivity mu(0)H(C) of 0.75 T, and the maximum energy product (BH) of 108.5 kJ/m(3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

Ni-Cr系光谱选择性吸收薄膜制备与表征

太阳能选择性吸收薄膜是中高温太阳能集热器的最关键部分，目前世界很多国家都在积极研究工艺简单、成本低廉、性能优良稳定的中高温光谱选择性吸收薄膜。本论文根据金属陶瓷型太阳能光谱选择性吸收表面和磁控溅射技术的原理，在国内外研究发展的基础上，针对目前国内平板型太阳能集热器的现有状况，结合太阳能热水器建筑一体化的发展趋势，开展了磁控溅射制备光谱选择性吸收薄膜的研究。本工作以直流反应磁控溅射方法作为制备手段，选择Ni-Cr合金作为靶材，以N2, 02两种气体为反应气体，反应溅射制备折射率变化的NiCr-NiCrO,N

Cr~(3+)对土壤脲酶活性特征的影响

采用模拟方法对Cr3+的土壤脲酶效应进行了研究,结果表明,土壤pH对Cr3+的生态毒性有重要影响;酸性土壤脲酶受到显著抑制,活性及动力学特征参数与Cr3+浓度间达显著或极显著负相关,而且模型U=β0(/β1×C+1)揭示其间机理为完全抑制,动力学则进一步细化为非竞争性抑制;获得土壤轻微和中度污染时的生态剂量ED10和ED50分别为50.59和865.7 mg.kg-1;酸性土壤中脲酶活性、Vmax、k可作为土壤Cr3+污染的监测指标之一,而碱性土壤则反应不敏感,其随铬浓度增加,脲酶活性及动力学参数呈先增加后降低的规律性变化,总体变幅较小;两类土壤的差别可能主要是由于土壤环境引起了不同价态铬转变的缘故。

Ti-V-Cr固溶体储氢合金的结构及电化学性能研究

本论文首先研究了Ni、Zr分别对Ti-V－Cr固溶体储氢合金中Cr和Ti部分取代的影响，得到了性能良好的Ti0．17Zr0．08V0．35Cr0．10Ni030基质合金。在此基础上进一步研究了入甄、B、Fe、Co、Al元素的添加或取代对基质合金的结构及电化学性能的影响。采用XRD、ICP、SEM一EDX、XPS、EIS、线性极化和阳极极化等表征手段对Ti一V－Cr固溶体储氢合金的结构及电化学性能进行分析和表征，主要结果如下：①Ti一V－Cr合金自身在碱性电解液中几乎无电化学活性。当用Ni部分取代Cr后，合金中出现具有电化学活性的第二相，其电化学性能得到有效地改善和提高。②Ti0.25-xZr_xV0.35Cr0.1Ni0.3（x＝0．05-0．15）合金主要是由bcc相和c14Laves相组成。随Zr含量从0．05增加到0．08，合金电极的放电容量和倍率放电能力增加；当x继续从0．08增加到0．15时，其变化较小。合金电极的电荷转移电阻随x增加而降低，当x在0．08到0．15之间变化时，电荷转移电阻变化也比较小。表明电荷转移电阻的大小与合金的电化学性能密切相关。③经过50次充、放电循环后，Tio．17zr"sV时scrol0Ni03。合金电极在303K和313K的放电容量能保持在90％以上；在70℃时的放电容量仍能达到275mA扮g。根据不同温度时的交换电流密度，计算了Ti。，17Zr008V时SCr川0Ni030合金电极表面电化学反应的表观活化能，其值约为50kJ／mol。④通过Nln、B、Fe、C。、AI对Tio．17zroosvo35Crol0Nio3。合金基质的添加与取代的研究，得到了具有高容量的储氢合金。其中Tio．17Zr008Vo35Cro．10Ni020Mnol。合金室温最高放电容量达到390n1A扮g；在253一343K的温度范围内，Tiol7Zr08V035Cr0JONioz5Mnoos合金具有高的放电容量，其容量在167一298mA树g之间变化，但是这些合金的稳定性有待进一步的提高。⑤合金充、放电过程中，晶格的扭曲和膨胀、Zr和V的溶解使得合金结构发生变化；合金的严重粉化及表面致密氧化膜的形成，是导致Ti一V－Cr合金电化学性能的衰减的主要原因。

全同1，2－聚丁二烯的合成及用~(13)C-NMR方法研究1，2－聚丁二烯的序列结构

采用Cr／Al催化体系，成功地合成了全同1，2－聚丁二烯（PBD），并用DSC方法、X－射线衍射、红外光谱及~(13)C－NMR的方法进行结构与物性测定，得如下结果：全同1，2－PBD的熔点为124.3℃；三角晶系中，分子链成了螺旋，晶胞参数为a＝17.3A，c＝ 6.5A；在红外光谱中，其特征谱带出现在694.4 cm~(-1)处；在~(13)C－NMR谱中仅出现四条谱峰，其化学位移分别为142.51、111.56、39.26、37.43 ppm。全同1，2－PBD的~(13)C－NMR谱提供的实验数据表明，在~(13)C－NMR谱中1，2－PBD－CH二碳十个五元组谱峰的归属是有别于Elgert、Kumar已有的归属。它属于一种新的归属，与半经验方法所推演的结果相符。它恰巧同聚丙烯侧甲基五元组谱峰的归属一致。采用半经验方法研究了1，2－PBD的~(13)C－NMR增中CH二碳五元组、CH_2－碳四元组及六元组共振谱峰，同时讨论了模型链的链长、温度以及立构序列的排列对各立构序列键概率的影响，求得了相应的r值。同时采用经验方法对1，2－PBD的~(13)C－NMR谱中CH_2=碳、CH－碳五元组及CH_2－碳四元组谱峰做了归属。两种方法对CH_2－碳谱峰的归属得到了一致的结果。