Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility transistors （mHEMTs） grown on GaAs substrate by metal organic chemical vapour deposition （MOCVD） are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance Rc was as low as 0.02 Ω- ram. The unity current gain cut-off frequency （fT） and the maximum oscillation frequency （fmax） were 146 GHz and 189 GHz, respectively. This device has the highest fT yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6, Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.

Influence of double AlN buffer layers on the qualities of GaN films prepared by metal-organic chemical vapour deposition

In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire （0001） substrate with double A1N buffer layers. The buffer layer consists of a low-temperature （LT） A1N layer and a high-temperature （HT） A1N layer that are grown at 600 ℃ and 1000 ℃, respectively. It is observed that the thickness of the LT-A1N layer drastically influences the quality of GaN thin film, and that the optimized 4.25-min-LT-A1N layer minimizes the dislocation density of GaN thin film. The reason for the improved properties is discussed in this paper.

Metal Organic Chemical Vapour Deposited Thin Films of Cobalt Oxide Prepared via Cobalt Acetylacetonate

The single solid source precursor, cobalt （Ⅱ） acetylacetonate was prepared and characterized by infrared spectroscopy. Thin films of cobalt oxide were deposited on soda lime glass substrates through the pyrolysis （metal organic chemical vapour deposition （MOCVD）） of single solid source precursor, cobalt acetylacetonate, Co[C5H7O2]2 at a temperature of 420℃. The compositional characterization carried out by rutherford backscattering spectroscopy and X-ray diffraction （XRD）, showed that the films have a stoichiometry of Co2O3 and an average thickness of 227±0.2 nm. A direct energy gap of 2,15±0.01 eV was calculated by the data obtained by optical absorption spectroscopy. The morphology of the films obtained by scanning electron microscopy, showed that the grains were continuous and uniformly distributed at various magnifications, while the average grain size was less than i micron for the deposited thin films of cobalt oxide.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence （PL） and lasing properties of InAs/GaAs quantum dots （QDs） with different growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the low growth rate sample shows a greater blueshift of PL peak wavelength. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blueshift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

Synthesis and Characterization of Metal Organic Chemical Vapour Deposited Chromium Doped Zinc Oxide Thin Film for Gas Sensing Applications

Chromium (Cr) doped Zinc oxide ZnO thin films were deposited onto glass substrates by Metal Organic Chemical Vapour Deposition (MOCVD) technique with varying dopant concentration at a temperature of 420°C. The effect of the chromium concentration on morphological, structural, optical, electrical and gas sensing properties of the films were investigated. The scanning electron microscopy results revealed that the Cr concentration has great influence on the crystallinity, surface smoothness and grain size. X-ray diffraction (XRD) studies shows that films were polycrystalline in nature and grown as a hexagonal wurtzite structure. A direct optical band energy gap of 3.32 to 3.10 eV was obtained from the optical measurements. The transmission was found to decrease with increasing Cr doping concentration. Rutherford Backscattering Spectroscopy (RBS) analysis also demonstrates that Cr ions are substitutionally incorporated into ZnO. I-V characteristic of the film shows a resistivity ranges from 1.134 × 10-2 · cm to 1.24 × 10-2 · cm at room temperature. The gas sensing response of the films were enhanced with incorporation of Cr as a dopant with optimum operating temperature around 200°C.

Metal vapor behavior in double electrodes TIG welding

In present paper, the metal vapour behavior in double electrodes TIG welding was investigated by a numerical model, including the arc plasma and weld pool. The thermodynamic parameters and transport coefficients of the arc plasma were dependent on both the local temperature and the mass ratio of the metal vapour. A second viscosity approximation was used to formulate the diffusion coefficient of the metal vapour in the arc plasma. The temperature and flow fields together with the metal vapour concentration were simulated, and the influences of metal vapour on the arc plasma and the weld pool were analyzed. It was found that the metal vapour transport in the arc plasma was significantly influenced by the flow of the arc plasma, and the distribution of the metal vapour was more extended in the direction perpendicular to the line through the double electrodes tips. Both the arc plasma and the heat flux at the weld pool were constricted by the presence of the metal vapour, while the metal vapour had a minor effect on the total heat input to the work piece and the weld pool profile as a whole.

Influence of Silver Vapours on the Transport of Nitrogen Plasma Properties

Theoretical investigation of nitrogen-silver arc transport properties and an arc plasma model in stationary state have studied at low temperature i.e. between 3500 K and 13,000 K at atmospheric pressure. Results showed that the presence of small amounts of metal vapours, which have low ionization potential such as silver, modify the plasma characteristics. The solution of Elenbaas-Heller gives us some information about the effect of metal vapours emitted from electrode on the characteristics of the arc column. We concluded that a small fraction of metal vapours in the arc column modify the electric field, current and the axial temperature.

核聚变用CLF-1钢真空激光焊接

针对核聚变用CLF-1钢的焊接问题,采用真空激光焊(VLW)技术研究了VLW焊接特性、焊缝的显微组织和力学性能.结果表明:随着真空度的降低,金属蒸气羽烟得到了良好抑制,焊缝金属氧化程度降低;相比常压激光焊接(ALW),热输入约降低了20%,VLW焊缝晶粒尺寸明显减小,富Cr、Fe、W和C的椭圆状碳化物(M_(23)C_(6))及富Ta或V的高密度球状碳化物(MX)尺寸有所减小,起到了良好的弥散强化效果,且焊缝组织中无残余铁素体(δ-Fe)存在;VLW焊缝经高温回火(PWHT)后的冲击韧性为280 J,高出母材43 J,约为ALW焊缝冲击韧性的2.4倍,冲击试样断口为韧性断裂.

溶剂化金属原子浸渍法制备高分散负载型催化剂——Ⅱ,Fe,Co,Ni催化剂的分散度和催化性能研究

本文利用一种新的方法-溶剂化金属原子浸渍法制备了Fe/γ-Al_2O_3,Fe/SiO_2,Co/γ-Al_2O_3,Co/SiO_2,Ni/γ-Al_2O_3和Ni/SiO_2六种催化剂。H_2化学吸附,TEM和XRD测定结果表明这些催化剂中Fe,Co,Ni金属颗粒平均直径都小于30A,金属分散度均大于50%。作者研究了Fe/γ-Al_2O_3,Co/γ-Al_2O_3和Ni/γ-Al_2O_3三种催化剂在CO+H_2反应中的催化行为,测定了碳氢产物分布和比催化活性,表明随着H_2/CO比增大和反应温度升高。较高分子量物种产量减少,有利于生成甲烷。催化剂的活性大小次序为Fe>Ni>Co。

煤基热气体净化技术的新进展——多功能高温气体净化剂的开发

介绍了热气体高温净化的新进展。热气体中的污染物，除了尘粒和无机硫化合物之外，还有有机硫、碱金属蒸汽、氯化物、重质烃类及氨等，它们的危害性也很大，必须设法除去。

紫外铜离子激光器的理论研究

系统研究了连续工作的紫外铜离子激光器理论，即空心阴极放电的阴极位降理论，阴极溅射，放电等离子体中粒子的扩散和粒子数密度的速率方程。计算结果由实验得到验证。

用MOCVD法制备TiO_2/Fe_2O_3双包覆层珠光颜料

研究了在常压喷动流化反应器中 ,以金属有机化学气相沉积 (MOCVD)法制备双包覆层珠光颜料的工艺 .实验结果表明 :以Ti(OC2 H5) 4 为物源 ,在有氧情况下用高纯氮气作为载气 ,沉积温度为 30 0℃时 ,沉积的TiO2 膜晶形为锐钛型 ,温度升高至 5 0 0℃时 ,TiO2 膜晶形为金红石型 ,且包覆致密 .在此基础上控制不同的包覆时间 ,再包覆以Fe2 O3 为主的铁氧化物 ,可获得橘红。

MOCVD法制备金属陶瓷功能梯度材料的研究

利用金属有机化学气相沉积(MOCVD)方法,以Mo(CO)6,Si(OC2H5)4为物源,在Al2O3陶瓷基片上制备了金属陶瓷功能梯度材料,并用XPS,XRD,SEM等技术对其成分分布,物相组成和表面形貌进行测试和表征.结果表明:材料的组成沿厚度方向呈连续梯度变化,符合功能梯度材料的变化规律.

MOCVD法制备Fe/Mo功能梯度材料

利用金属有机化学气相沉积(MOCVD)方法,以Mo(CO)6,Fe(CO)5为物源,在Al2O3陶瓷基片上制备了 Fe/Mo功能梯度材料,并用XPS,XRD,SEM和台阶仪等技术对其成分分布、物相组成、表面形貌和厚度进行测试 和表征.结果表明:材料的组成沿厚度方向呈连续梯度变化,符合功能梯度材料的变化规律.

羰基金属复合材料的研究与应用

本文对羰基金属复合材料的制备方法、研究现状及进展、以及羰基金属复合材料的应用前景进行了综述。

MOCVD法制备云母珠光颜料光学性能及微结构研究

在流化床反应器中以羰基铁为物源,用金属有机化学气相沉积(MOCVD)法制备了云母珠光颜料.由颜料的SEM和EPMA图分析表明:云母微粒为片状结构,平均粒径为50μm;沉积在云母表面上的是均匀分布的30～150nm的透明氧化铁微粒,这种结构对光能产生多重散射、折射、反射,从而呈现出绚丽的珠光光泽.

三维开孔Ni-Cr-Fe合金泡沫的准静态压缩性能和能量吸收特性(英文)

采用固体粉末法在1050°C下对三维网状开孔泡沫Ni表面进行CrFe共沉积,然后经过1200°C高温固相扩散处理对开孔泡沫NiCrFe进行表面合金化。研究不同保温条件下Cr、Fe含量对NiCrFe合金泡沫的准静态压缩性能和能量吸收性能。同时,将开孔NiCrFe合金泡沫的真实力学性能与纯泡沫Ni和假设的NiCrFe合金泡沫模型进行比较。结果表明:不同Cr、Fe含量的开孔NiCrFe合金泡沫骨架显示出相似的硬度,整体上开孔NiCrFe合金泡沫的压缩强度和能量吸收性能随着合金泡沫中Cr、Fe含量的增加而明显增大。开孔NiCrFe合金泡沫的应力—应变行为与纯泡沫Ni相似,表明NiCrFe合金泡沫具有典型韧性金属泡沫的变形特性。同时,单位体积开孔NiCrFe合金泡沫的能量吸收最大值与泡沫Ni相比增加了22倍。经计算得出的NiFeCr合金泡沫的理论屈服强度与实际屈服强度大体一致。

GaN基发光材料

本文概述了GaN基发光材料的基本特性和GaN基器件的应用领域及未来的发展前景。简述了GaN基材料的生长技术 。

GMAW电弧等离子体平衡成分计算及其在光谱学中的应用

计算了常压下3 000~25 000K范围内熔化极气体保护焊(GMAW)保护气体Ar,CO_2,82%Ar-18%CO_2及其与Fe蒸汽的混合物的平衡成分。上述气体被看作一种Ar-CO_2-Fe等离子体,等离子体中的39种粒子被分为5种主元粒子和34种非主元粒子。根据化学方程,非主元粒子由主元粒子表示以减少未知数的个数和求解量,再利用牛顿迭代法对平衡方程进行求解,最终实现了成分求解。计算结果表明,Ar气随着温度升高依次发生一次电离和二次电离,CO_2气体除了在高温时发生原子电离外,在低温时(T<8 000K)还存在CO_2,O_2,CO等分子的解离,82%Ar-18%CO_2混合气则既有解离又有电离。Fe的加入会增加等离子体的电子密度,特别是在15 000K以下。等离子体成分的确定为GMAW电弧等离子体辐射属性计算以及电弧中Fe蒸汽浓度的光谱测定奠定了基础。