Advanced Materials Research Vols. 194-196

Abstract: Porous reaction-bonded silicon nitride ceramics with different values of α/β ratio were obtained by setting the nitriding temperature and time. The influence of α/β phase transformation on the dielectric properties of porous silicon nitride ceramics has been investigated. The results show that the α/β transformation occurs when the nitriding temperature is higher than 1400°C . The values of α/β ratio decrease with increase of nitriding temperature and time. The dielectric constant ε′ and the dielectric loss tan δ of the samples increase because of the α/β transformation, and the change of the dielectric loss is more obvious. The increase of concentrations of point defects due to the α/β transformation leads to the significant increase of the dielectric loss.

Abstract: The effect of loss of transmission line on the transmission signal can’t be ignored in microwave circuits. Based on the theory of loss and microwave network principle, the effect of the width, parallel length and space of transmission lines on the scattering parameters’ insertion loss is analyzed in perspective of scattering parameters of the odd mode and even mode. The simulation results show that: when the other parameters are fixed, both the characteristic impedance and the conductor loss decrease non-linearly with the line width broadening; due to the coupling effect between micro-strip lines, the first trough frequency of the scattering parameter S21 curved line, that is the point the signal energy attenuate most seriously, decreases linearly with line width broadening and increases non- linearly with line spaces broadening.

Abstract: ZnO-based ceramic targets with 50mm in diameter and 3mm in depth were prepared by the traditional solid-state sintering process. ZnO-based ceramic films were deposited on Au/Si substrates by R.F. magnetron sputtering using ZnO-based ceramic target. The films have been characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy. The ZnO-based ceramic films, with thickness close to 1 μm, show a good c-axis orientation, corresponding to vertical growth with respect to the substrate. The surface of the films looks very smooth and dense, and the films are the same composition as the ZnO ceramic target composed of Zn, Bi, Sb, Co, Cr and Mn. The ZnO-based ceramic films with nonlinear coefficient of 6.4, nonlinear voltage of 1.6V and the leakage current density 0.3μA/mm² could be achieved.

Abstract: A novel preparation of aluminum diethylphosphinate (AlPi) as a novel class of phosphorous based flame retardants was carried out with gas-liquid free-radical addition reaction under atmospheric pressure. The ethylene was bubbled into the reaction mixture with the addition of the initiator. With this novel method the gas-liquid contact surface and the initiator concentration in the gas-liquid interface were increased largely, and the yield of the final product was improved to at least 80%. The molecular structure of the samples was confirmed by FTIR, ¹H NMR and ³¹P NMR spectroscopic analysis. Thermal stability of the final products was investigated in detail by TG-DTA.

Abstract: The InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) were grown by metalorganic chemical vapor deposition (MOCVD) on silicon and sapphire substrates, respectively. The Optical and crystal properties of InGaN/GaN MQWs LEDs were investigated by room temperature photoluminescence (PL), temperature dependent PL measurements, Raman spectra and high-resolution double crystal X-ray diffraction(DCXRD). These results indicate that the crystal quality of InGaN/GaN MQWs growth on sapphire substrate are more preferable than that of InGaN/GaN MQWs growth on silicon substrate, and the interface of MQWs growth on substrate or silicon substrate is level. The peak positions of InGaN/GaN MQWs are 2.78 eV (446nm) and 2.64 eV (468.8nm) growth on sapphire substrate and silicon substrate, respectively.

Abstract: Basing on a L-S phase inversion method, cellulose hollow fiber membranes were spinned using room temperature ionic liquid 1-allyl-3-methylimidazolium chloride ([Amim]Cl) as solvent. The concentration of cellulose/[Amim]Cl solutions (dope) was varied from 6 to 9wt% by an increment of 1wt%. Effects of the dope concentration on the hollow fiber membranes structure and properties were investigated. Inner- and outer- surfaces morphology of the prepared membranes were observed using field emission scanning electron microscope (FESEM). Besides, various properties of the membranes, including apparent viscosity, pure water flux (PWF), retention rate (Rt), equilibrium water content (EWC), ultimate tensile strength (UTS) and elongation at break (Eb) were also tested. The results induced that, with the increase of dope concentration, the both surfaces showed more regular. Pure water flux and equilibrium water content of the membranes decreased with a increasing dope concentration, properties of retention rate, ultimate tensile strength and elongation at break showed a increased tendency oppositely.

Abstract: Electrical properties and microstructures of Mg(Zr_0.05Ti_0.95)O₃ thin films prepared by sol-gel method on n-type Si(100) substrates at different annealing temperatures have been investigated. The diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited Mg(Zr_0.05Ti_0.95)O₃ peaks orientation perpendicular to the substrate surface and the grain size with the increase in the annealing temperature. A low leakage current density of 1.1×10^-4 A/cm², a dielectric constant of 9.4 and an optical bandgap of 3.6 were obtained for the prepared films. It may find application in dynamic random access memories and wireless communication devices.

Abstract: Effect of thermal treatments on the structural and electrical properties of the chemical bath deposition derived Ti-doped ZnO thin films are studied. XRD results show that the annealed Ti-doped ZnO films with wurtzite structure are randomly oriented. Crystallite structure, carrier concentration, resistivity and mobility are found to be dependent on the treatment temperature. At a treatment temperature of 100°C, the Ti-doped ZnO film possesses a carrier concentration of 2.5×10²⁰ cm^-3, a resistivity of 2.8×10^-3 Ω-cm, and a mobility of 12 cm²/Vs.

Abstract: Nanocrystalline ZnS thin films are prepared on glass substrates under various deposition conditions (radio frequency power, and sputtering pressure) using radio frequency magnetron sputtering at room temperature. Through optimization of deposition process, very thin and uniform ZnS layer was deposited to minimize the light blocking effect in short wavelength region. This paper investigates the influence of ZnS buffer layer by magnetron sputtering,and analyses structure,surface topography,and optical properties of ZnS films by using X-ray diffraction (XRD), UV-spectroscopy measurements and scanning electronic microscope (SEM) analysis techniques. Findings show that the high-quality ZnS thin films with a good crystallinity and optical properties, which is zinc blende cubic structure with a preferred orientation, can be grown by sputtering at 300W and 0.6Pa. The films exhibit the optical transparency as high as 80% in the visible region, and the resultant ZnS thin films have a high crystallinity, low defect concentration and good optical properties with the band gap of 3.50eV.

Abstract: The compound fibers were melt-spun by co-extrusion of polypropylene and polypropylene/ fillers master-batches. The melt-spun fibers were characterized by DSC, SEM and MSERA. Crystallinity of compound fibers with carbon black (CB) was more than that of PP alone. SEM results showed that inorganic particles in fibers had relatively good dispersibility. The electrical resistance of fibers containing CB particles reached minimum at the 10 Wt% CB content. Fibers with CB showed the good radar absorption effects and the absorption property was improved with the increase in CB content.