Dec 2008, Volume 2 Issue 4

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  • CHEN Jia-he, YANG De-ren, QUE Duan-lin
    With the rapid development of semiconductor technology, highly integrated circuits (ICs) and future nano-scale devices require large diameter and defect-free monocrystalline silicon wafers. The ongoing innovation from silicon materials is one of the driving forces in future micro and nano-technologies. In this work, the recent developments in the controlling of large diameter silicon crystal growth processes, the improvement of material features by co-doping with the intend-introduced impurities, and the progress of defect engineered silicon wafers (epitaxial silicon wafer, strained silicon, silicon on insulator) are reviewed. It is proposed that the silicon manufacturing infrastructure could still meet the increasingly stringent requirements arising from ULSI circuits and will expand Moore’s law into a couple of decades.
  • WU Mao, HE Xin-bo, SHEN Zhuo-shen, QU Xuan-hui
    A new type of ZnO-Al2O3-B2O3-SiO2 glass-ceramics seals to Kovar in electronic packaging was developed, whose coefficient of thermal expansion (CTE) and electrical resistance were 5.2 × 10-6/°C and over 1 × 1013 ?·cm, respectively. The major crystalline phases in the glass-ceramics seals were ZnAl2O4, ZnB2O4 and NaSiAl2O4. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of the alkali metal ions into the crystal lattices. It was found that the crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner parts, which makes the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature showed great effect on the wetting angle. Strong interfacial bonding was obtained, which was mainly attributed to the interfacial reaction between SiO2 and FeO or Fe3O4.
  • SHI Yao-wu, YU Yang, XIA Zhi-dong, LEI Yong-ping, LI Xiao-yan, GUO Fu, LIU Jian-ping
    In the present work, the effect of a small amount of rare earth Er addition on the microstructure of Al-Cu-Si brazing alloy has been investigated. In the study, the Al-20Cu-7Si brazing alloys with various Er contents were prepared. 3003 aluminum alloy was chosen as a substrate. The microstructure of the brazed alloys was carefully observed. In addition, melting temperature, wettability and hardness of the brazing alloys were measured. The results indicate that the constituent of the microstructure of Al-20Cu-7Si-Er brazed alloy is similar to the Al-20Cu-7Si, which is mainly comprised of solid solutions of aluminum, silicon and the intermetallic compounds CuAl2. When the Er content increases, the size of Al phases is decreased, and the filament-like or needle-like Si phase is thickened. The Si phases dominating in the shape of a filament or needle are transformed to those in the shape of a block when Er content is increased. Moreover, adding a small amount of Er can improve the wettability and hardness of the Al-20Cu-7Si brazing alloy. However, the melting temperature of the Al-20Cu-7Si alloy is almost unchanged when a small amount of Er is added.
  • DU Cui-wei, LI Xiao-gang, WANG Wei, SONG Yi-quan
    An X70 pipeline steel and a low-carbon steel with different types of coating defects were studied using corrosion tests in Ku’erle simulated soil solution containing 0.6000 mol/L Cl-. Electrochemical characteristics of the X70 pipeline steel with planar-defect epoxy-coating in simulated solutions of Ku’erle soil were tested. The results show that in 0.6000 mol/L Cl- simulated solution, for low-carbon steel with coating defects (the area ratio is 4.91%), at free corrosion potential and with immersion time, the corrosion with disbond was more severe than that with a break or with break and disbond. In Ku’erle soil simulated solution, when the coating defect area ratio was increased gradually (0.39% → 1.57% → 6.28%), the corrosion of the X70 steel under coating with break was promoted gradually, and the influence of immersion time on the corrosion decreased. The influence of the immersion time on the corrosion was weakened when the defect area ratio increased to a certain degree.
  • QIU Bao-wen, YUAN Ze-xi, ZHOU Gui-feng
    Three-dimensional unit cell models were developed to study the damage induced by void growth in ductile materials. Special emphasis is given to the influence of the void shape and random spatial void arrangements. The periodical void arrays of body centered cubic are investigated by analyzing representative unit cells. The isotropic behavior of the matrix material is modeled using v. Mises plasticity. The cell models are analyzed by the large strain finite element method under monotonic loading while keeping the constant stress triaxiality. Results showed that when void density increased, effects of void aspects on void growth gradually diminished.
  • YU Zhi-ming, FANG Mei, XIAO Zhu
    A method of controlling the feeding concentration of methane was applied in a hot-filament chemical vapor deposition (HFCVD) in order to improve the nucleation of diamond on the beryllium oxide substrates. The nucleation density and the morphologies of diamond were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) while the thermal conductivities of substrates and the composites were detected by laser-diathermometer. The results show that the diamond thin film is in larger grain size with lower roughness when CH4 and H2 enter the chamber, respectively, rather than as a mixture, and the composites’ conductivity soared by 21%–31% compared with BeO substrates. At the conditions of separated gas entry, several projects with changes of the CH4 flux during depositing were designed to discuss the influence of CH4 concentration on diamond nucleation. The uniform and compact diamond thin films were acquired when the ratio of CH4:H2 at nucleation stage was in the range of 4%–8%.
  • ZENG Bin, FENG Zu-de, LI Si-wei, LIU Yong-sheng
    Carbon-rich amorphous boron carbide (BxC) coatings were annealed at 400°C, 700°C, 1000°C and 1200°C for 2 h in air atmosphere. The microstructure and composition of the as-deposited and annealed coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS). All of the post-anneal characterizations demonstrated the ability of carbon-rich BxC coatings to protect the graphite substrate against oxidation. Different oxidation modes of the coatings were found at low temperature (400°C), moderate temperature (700°C) and high temperature (1000°C and 1200°C). Finally, the feasibility of the application of carbon-rich BxC instead of pyrolytic carbon (PyC) as a fiber/matrix interlayer in ceramics-matrix composites (CMCs) is discussed here.
  • NI Jie, LI Zheng-cao, ZHANG Zheng-jun
    Hafnium oxide (HfO2) thin films were deposited on Si (001) substrates by electron beam evaporation at various growth temperatures. It was found that the film was amorphous when deposited at temperatures lower than 200°C. It was polycrystalline when deposited at 250°C and 300°C. At temperatures above 400°C, it was grown preferably along the Graphic
    JIANG Xiao-song, CHEN Jun-ying, HUANG Nan
    The thrombus formation ability of a biomedical microcoil for hemangioma treatment is one of the basic requirements in clinical intervention application. Surface modification of a biomedical microcoil can improve its thrombus formation ability. In this work, TiO2 films were deposited using the unbalanced magnetron sputtering method. The structures, components and micro-morphologies of the films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and scanning electron microscope (SEM). The thrombus formation ability of the films was studied by in vitro platelet adhesion test. The results indicated that a certain characteristic TiO2 film has the ability to increase thrombus formation. Furthermore, the biological behavior of cultured human umbilical vein endothelial cells (HUVECs) onto different films was investigated by an in vitro HUVECs cultured experiment. The results showed that endothelial cells on certain TiO2 film surfaces have good adherence, growth and proliferation. Additionally, the relationship between the micro-characterization and biological properties of TiO2 films is discussed.
  • WANG Jian-zhong, QU Xuan-hui, YIN Hai-qing, YI Ming-jun, YUAN Xian-jie
    Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.
  • WU Chuan-song, ZOU De-gang, GAO Jin-qiang
    It is of great significance to determine the critical transition current from globular transfer to spray transfer in gas metal arc welding (GMAW) because metal transfer modes affect the weld quality and welding productivity. In this study, a simple model is developed to calculate the critical transition current based on the analysis of various forces exerted on a pendent droplet at the electrode tip. It is found that the force exerted by the incoming molten metal from the wire on the drop, i.e., the term Graphic
    XU Wen-jing, WU Chuan-song, ZOU De-gang
    In the gas metal arc welding (GMAW) process, when the welding speed reaches a certain threshold, there will be an onset of weld bead undercut defects which limit the further increase of the welding speed. Establishing a mathematical model for high-speed GMAW to predict the tendency of bead undercuts is of great significance to prevent such defects. Under the action of various forces, the transferred metal from filler wire to the weld pool, and the geometry and dimension of the pool itself decide if the bead undercut occurs or not. The previous model simplified the pool shape too much. In this paper, based on the actual weld pool geometry and dimension calculated from a numerical model, a hydrostatic model for liquid metal surface is used to study the onset of bead undercut defects in the high-speed welding process and the effects of different welding parameters on the bead undercut tendency.
  • XIAO Jian-hua, LIU Feng, CHEN Hai-li, HU Jun, LIU Hong-lai
    Two poly(fluorine-alt-phenylenevinylene)s fluorescent conjugated polymers, poly(9,9-dioctylfluorene-alt-phenylenevinylene) (PFO/PPV1) and poly(fluorene-alt-2,5-dioctoxyphenylenevinylene) (PFO/PPV2), were obtained through a Heck polycondensation. The structures of the obtained polymers were characterized by FT-IR, 1H-NMR and GPC. The thermal stabilities of the polymers were evaluated by TGA. The photophysical properties were studied by UV and photoluminescence (PL) spectroscopy both in solution and film. Their applications in the detection of nitro compounds were researched, and the results show high fluorescence quenching sensitivity of PFO/PPV1 towards nitro compounds such as 2,4-dinitrotoluene (DNT) and 4-nitrotoluene (p-NT) in solution and thin film.
  • ZHOU Hui-yun, CHEN Xi-guang
    In this study, chitosan/cellulose acetate microspheres (CCAM) were prepared by W/O/W emulsification and solvent evaporation as a drug delivery system. The microspheres were spherical, free-flowing and non-aggregated. The CCAM had good flow and suspension ability. The loading efficiency of different model drugs increased with the increasing hydrophobicity of the drug. The loading efficiency of 6-mercaptopurine (6-MP) was more than 30% whereas that of ranitidine hydrochloride (RT) or acetaminophen (ACP) was only 10%. The pH values of solution affected the swelling ability of CCAM and the relative humidity had little effect on the characteristics of CCAM when it was not more than 75%. The CCAM system had a good effect on the controlled release of different model drugs. However, the release rate became slower with the increase of the hydrophobicity of drugs. The release rate of CCAM loaded with hydrophilic RT was almost 60% during 48 h and the release rate of CCAM loaded with hydrophobic drug of 6-MP was not more than 30%. In the meantime, the CCAM system was degradable in vitro and the degradation rate was faster in lysozyme solution than that in the medium of PBS. So the CCAM system was a degradable promising drug delivery system especially for hydrophobic drugs.
  • LIU Hui, ALKADASI Nabil A. Noman, ZHU Yan, TONG Li-fang, FANG Zheng-ping, WANG Yong-chang
    The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)2) as the filler in composites, irradiated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)2 composites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)2 in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)2 composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.
  • YANG Lin, NIE Jun, WU Wei, JIA Pei-zeng, XU Bao-hua
    Objectives: the aim of this study was to investigate the properties of UV-curable composite resin of transfer tray for indirect bonding system of the lingual brackets. Methods: the conversion of double-bond in the different concentration of UV-initiator was monitored by real time infrared (RTIR). The three-point flexure strength was measured by a universal testing machine. The storage modulus, loss modulus, and loss factor (tan delta) of the resin were measured by a Dynamic Mechanical Analyzer. The cytotoxicity of composite resin was evaluated by the agar covering test. Results: the double bond conversion exceeded 70% at [benzophenone] = 0.7 wt.%, [Ethyl 4-dimethylaminobenzoate] = 0.7 wt.% and [2-Hydroxy-2-methyl-1-phenyl propanon] = 1 wt.%. The mean value of flexural strength came to 122 MPa. The value of storage modulus was 1.04 × 109 MPa at 23°C. The glass transition temperature was 142°C. The toxicity grade was zero at 2 h and one at 24 h. Conclusions: in the preliminary evaluations, we indicated that the UV-curable composite resin of transfer tray could satisfy the clinical requirements.
  • TAKAHASHI Masashi, GOTO Shin-Ichi, MORI Kazuhisa, MATAGA Izumi
    The purpose of this study is to clarify the difference of histology and elemental composition of the cervical enamels among the human permanent teeth. The re-ground surfaces at the cervical enamels of them were observed under scanning electron microscopy (SEM). The contents of seven elements were analyzed quantitatively with electron probe microanalyzer (EPMA). The widths of the rod sections at the cervical enamels were larger than those at the cuspal enamels. The rod sections at the mesial cervical enamels in the incisors were more obscure and more decayed by acid solution than those in the premolars and molars. The calcium and phosphorus contents of the cervical enamels were significantly lower than those of the cuspal enamels. The carbon content of the cervical enamels was significantly higher than that of the cuspal enamels. The calcium and phosphorus contents of the cervical enamels were the significantly highest in the premolars. The carbon and sodium contents of the cervical enamels were significantly highest in the premolars. It is thought that the calcification level is lower, while the content of organic matter is higher at the cervical enamels than those at the cuspal enamels. It is considered that the sodium causes high calcification.