Nafion/Silicon Oxide Composite Membrane for High Temperature Proton Exchange Membrane Fuel Cell

Nafion/Silicon oxide composite membranes were produced via in situ sol-gel reaction of tetraethylorthosilicate （TEOS） in Nafion membranes. The physicochemical properties of the membranes were studied by FT-IR,TG-DSC and tensile strength. The results show that the silicon oxide is compatible with the Nation membrane and the thermo stability of Nation/Silicon oxide composite membrane is higher than that of Nation membrane. Furthermore, the tensile strength of Nation/Silicon oxide composite membrane is similar to that of the Nation membrane. The proton conductivity of Nation/Silicon oxide composite membrane is higher than that of Nation membrane. When the Nation/Silicon oxide composite membrane was employed as an electrolyte in H2/O2 PEMFC, a higher current density value （1 000 mA/cm^2 at 0.38 V） than that of the Nafion1135 membrane （100 mA/cm^2 at 0.04 V） was obtained at 110 ℃.

Optical and Electrical Properties of Hydrogenated Silicon Oxide Thin Films Deposited by PECVD

In this work, n-type amorphous silicon oxide thin films were deposited by RF-PECVD method using a gas mixture of SiH4, CO2, H2, and PHy The deposition rate, refractive index, band gap, crystalline volume fraction, and conductivity of the silicon oxide thin films were determined and analyzed. The film with refractive index of 1.99, band gap of 2.6eV and conductivity of 10-7 S/cm was obtained, which was suitable for the intermediate reflector layer.

Gallium-Catalyzed Silicon Oxide Nanowire Growth

Silicon oxide nanowires tend to assemble into various complex morphologies through a metalcatalyzed vapor-liquid-solid （VLS） growth process. This article summarizes our recent efforts in the controlled growth of silicon oxide nanowire assemblies by using molten gallium as the catalyst and silicon wafer, SiO powder, or silane （Sill4） as the silicon sources. Silicon oxide nanowire assemblies with morphologies of carrotlike, cometlike, gourdlike, spindlelike, badmintonlike, sandwichlike, etc. were obtained. Although the morphologies of the nanowire assemblies are temperatureand silicon source-dependent, they share similar structural and compositional features： all the assemblies contain a microscale spherical liquid Ga ball and a highly aligned, closely packed amorphous silicon oxide nanowire bunch. The Ga-catalyzed silicon oxide nanowire growth reveals several interesting new nanowire growth phenomena that expand our knowledge of the conventional VLS nanowire growth mechanism.

The Role of Silion Oxide Layers in Luminescence of Ensembles of Silicon Quantum Dots

Based on the quantum confinement-luminescence center model, to ensembles of spherical silicon nanocrystals (nc-Si) containing two kinds of luminescence centers (LCs) in the layers surrounding the nc-Si, the relationship between the photoluminescence (PL) and the thickness of the layer is studied with the excitation energy flux density as a parameter. When there is no layer surrounding the nc-Si, the electron-heavy hole pair can only recombine inside the nc-Si, then the PL blueshift with reducing particle sizes roughly accords with the rule predicted by the quantum confinement model of Canham. When there presences a layer, some of the carriers may tunnel into it and recombine outside the nc-Si at the LCs to emit visible light. The thicker the layer is, the higher the radiative recombination rate occurred outside the nc-Si will be. When the central scale of the nc-Si is much smaller than the critical scale, the radiative recombination rate outside the nc-Si dominates, and visible PL will be possible for some nc-Si samples with big average radius, greater than 4 nm, for example. When there is only one kind of LC in the layer, the PL peak position does not shift with reducing particle sizes. All these conclusions are in accord with the experimental results. When there are two or more kinds of LCs in the layer, the PL peak position energy and intensity swing with reducing particle sizes.

Photoluminescence and Electroluminescence Studies on Tb-Doped Silicon Rich Oxide Materials and Devices

Photoluminescence （PL） characteristics of Tb-doped silicon rich oxide （SRO） films prepared by DC-sputtering and post-annealing processes were studied. The silicon richness of the SRO film could be controlled by varying the sputtering power and oxygen concentration in the sputtering chamber. PL emission from the as-deposited sample was found to be composed of Th^3 ＋ intra 4f transition-related emission and the silicon nano particle-related broad bandwidth emission. Thermal annealing could significantly improve the material properties as well as the PL signals. PL properties depended strongly upon the annealing scheme and silicon richness. Annealing at high temperatures （900- 1050℃） enhanced Tbrelated emission and suppressed the silicon nano particle-related emission. For samples with different silicon richness, annealing at 950 ℃ was found to produce higher PL signals than at other temperatures. It was attributed more to lifetime quenching than to concentration quenching. Electroluminescent （EL） devices with a capacitor structure were fabricated, the optimized process condition for the EL device was found to be different from that of PL emission. Among the annealing schemes that were used, wet oxidation was found to improve device performance the most, whereas, dry oxidation was found to improve material property the most. Wet oxidation allowed the breakdown electrical field to increase significantly and to reach above 10 mV·cm^-1. The EL spectra showed a typical Th^3＋ emission, agreeing well with the PL spectra. The I-V measurements indicated that for 100 nm thick film, the Fowler-Nordheim tunneling started at an electrical field of around 6 mV·cm^-1 and the light emission became detectable at a current density of around 10-4 A·cm^-2 and higher. Strong electroluminescence light emission was detected when the electrical field was close to 10 mV·cm^-1.

Optimization of heat shield for single silicon crystal growth by using numerical simulation

In integrated circuit-grade single silicon Czochralski growth, the position and material of heat shield are main parameters affecting the heat exchange and crystal growth condition. By optimizing the above parameters, we attempted to increase the growth rate and crystal quality. Numerical simulation proved to verify the results before and after optimization. Through analyses of the temperature and microdefect distribution, it is found that the optimized heat shield can further increase the pulling rate and decrease the melt/crystal interface deflection, increase the average velocity of argon flow from ~2 to ~5 m&middots-1, which is in favor of the transportation of SiO, and obtain the low defects concentration crystal and that the average temperature along the melt-free surface is 8 °C higher than before avoiding supercooled melt effectively. © The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2012.

Fabrication of Silicon Condenser Microphone Using Oxidized Porous Silicon as Sacrificial Layer

A new technique to fabricate silicon condenser microphone is presented.The technique is based on the use of oxidized porous silicon as sacrificial layer for the air gap and the heavy p+-doping silicon of approximately 15μm thickness for the stiff backplate.The measured sensitivity of the microphone fabricated with this technique is in the range from -45dB(5.6mV/Pa) to -55dB(1.78mV/Pa) under the frequency from 500Hz to 10kHz,and shows a gradual increase at higher frequency.The cut-off frequency is above 20kHz.

Ultra-thin Oxide Films on SiO_2: An STM Study of Their Thermal Stability in the Presence of Au Deposit

The annealing of Au particles deposited onto the ultrathin layers of SiO 2 on Si(111) has been studied in real time with a high temperature scanning tunnelling microscopy. Annealing did not create significant changes to the morphology of the surface until the surface was heated up to more than 920 K when the gold particles started to display a preference for the step edge. Further heating caused the decomposition of the oxide layer with the formation of voids on the surface in the surface step edge area. Comparison between the gold assisted oxide decomposition and pure oxide decomposition indicates that the two decomposition routes proceed with different mechanisms.

PREPARATION OF POLYSULFONAMIDE AND MODIFIED TITANIUM OXIDE NANOCOMPOSITES BY IN-SITU POLYMERIZATION

A kind of new nano composite with ultraviolet （UV） ray resistance and high temperature stability was prepared by in-situ polymerization in low temperature. Polysulfonamide （PSA） was synthesized with 4, 4＇-diaminodiphenyl sulfone （DDS） and terephthaloyl chloride （TPC） in the common solvent N, N-Dimethyl- -acetamide （DMAc）. Nano filler is a certain nano titanium oxide modified by silicon oxide （TMS）, which plays the role of UV resistance additives. Properties of the novel composite materials were characterized by Atomic Force microscopy （AFM）, thermal gravimetric Analysis （TGA） and Ultraviolet Spectroscopy. AFM had showed the sizes and distributions of TMS particles in the nanocomposite. Ultraviolet Spectroscopy for the nanocomposites showed a large absorption in UV band. TGA showed the decomposition temperature was increased over ten degrees with 0.5% wt TMS for this nanocomposite compared with pure PSA.

New insights into the effects of silicon content on the oxidation process in silicon-containing steels

Simultaneous thermal analysis（STA） was used to investigate the effects of silicon content on the oxidation kinetics of silicon-containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe2SiO4, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe2SiO4. Moreover, the silicon distributed in two forms： as Fe2SiO4 at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.

Laser-Induced Single Event Transients in Local Oxidation of Silicon and Deep Trench Isolation Silicon-Germanium Heterojunction Bipolar Transistors

We present a study on the single event transient （SET） induced by a pulsed laser in different silicon-germanium （SiGe） heterojunction bipolar transistors （HBTs） with the structure of local oxidation of silicon （LOCOS） and deep trench isolation （DTI）. The experimental results are discussed in detail and it is demonstrated that a SiGe HBT with the structure of LOCOS is more sensitive than the DTI SiGe HBT in the SET. Because of the limitation of the DTI structure, the charge collection of diffusion in the DTI SiGe HBT is less than that of the LOCOS SiGe HBT. The SET sensitive area of the LOCOS SiGe HBT is located in the eollector-substrate （C/S） junction, while the sensitive area of the DTI SiGe HBT is located near to the collector electrodes.

Oxidation of silicon surface with atomic oxygen radical anions

The surface oxidation of silicon （Si） wafers by atomic oxygen radical anions （O- anions） and the preparation of metal-oxide-semiconductor （MOS） capacitors on the O-oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al2sO64]^4＋·4O^- （Cl2A7-O^- for short）. After it has been irradiated by an O- anion bean： （0.5 μA/cm^2） at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy （XPS） results reveal that the oxide layer is of a mixture of SiO2, Si2 O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of 〈Al electrode/SiOx/Si〉 are investigated by measuring capacitance-voltage （C - V） and current-voltage （I - V） curves. The oxide charge density is about 6.0 × 10^1 cm^-2 derived from the （C - V curves. The leakage current density is in the order of 10^-6 A/cm^2 below 4 MV/cm, obtained from the I - V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.

NOVEL OXIDATION RESISTANT CARBON SILICON ALLOY FIBRES

Anovel silicon containing carbon precursor was synthesised by reacting a petroleum pitchfraction and polydimethylsilane. The precursor containing about 26wt% Si was meltspunintofibresand then oxidativelystabilised in airto renderthefibresinfusiblebefore pyrolysisat1200℃underinertatmospheretoproduceC Sialloy( CSA) fibres. Theextentofstabili sation wasfoundto becriticalto the development of mechanicalstrength of thefibres which varied with heattreatmenttemperature, showing a maximum at 1200 ℃when thestrength was 1 4 1 6 GPa. Thesestrengthsareremarkably goodconsideringthelow modulus whichis duetothe quite high failurestrains. Thefibrescanshow excellentresistanceto oxidation if given an initialshortexposureto oxygen athigh temperature duetotheformation of an im perceptiblelayer of silica. CSAfibreshavethe advantagesof both carbon fibresand SiCfi bres,thusextended application areascan beenvisaged .

Investigation of HNO_3 Chemincally Oxidized Porous Silicon

The stability of the photoluminescence (PS) has evidently improvedby HNO3 chemical oxidation The PL intensity and peak wavelength of PS were changed with theHNO3 of HNO3 concentration and oxidation time. Being different from other oxidation time. Being different from other oxidized ways, the PSoxidized by HNO3 remains remains sensitive to adsorbates. FTTR spectroscopic data suggest that these phenomena are attributed to the presence of HSi(SiaO30a)(a≤3)layer on PS surface.

Layer stacked SiO_(x) microparticle with disconnected interstices enables stable interphase and particle integrity for lithium-ion batteries

Severe mechanical fractu re and unstable interphase,associated with the large volumetric expansion/contraction,significantly hinder the application of high-capacity SiO_(x)materials in lithium-ion batteries.Herein,we report the design and facile synthesis of a layer stacked SiO_(x)microparticle(LS-SiO_(x))material,which presents a stacking structure of SiO_(x)layers with abundant disconnected interstices.This LS-SiO_(x)microparticle can effectively accommodate the volume expansion,while ensuring negligible particle expansion.More importantly,the interstices within SiO_(x)microparticle are disconnected from each other,which efficiently prevent the electrolyte from infiltration into the interior,achieving stable electrode/-electrolyte interface.Accordingly,the LS-SiO_(x)material without any coating delivers ultrahigh average Coulombic efficiency,outstanding cycling stability,and full-cell applicability.Only 6 cycles can attain>99.92%Coulombic efficiency and the capacity retention at 0.05 A g^(-1)for 100 cycles exceeds99%.After 800 cycles at 1 A g^(-1),the thickness swelling of LS-SiO_(x)electrode is as low as 0.87%.Moreover,the full cell with pure LS-SiO_(x)anode exhibits capacity retention of 91.2%after 300 cycles at 0.2 C.This work provides a novel concept and effective approach to rationally design silicon-based and other electrode materials with huge volume variation for electrochemical energy storage applications.

Experiment and simulation on degradation and burnout mechanisms of SiC MOSFET under heavy ion irradiation

Experiments and simulation studies on 283 MeV I ion induced single event effects of silicon carbide(SiC) metal–oxide–semiconductor field-effect transistors(MOSFETs) were carried out. When the cumulative irradiation fluence of the SiC MOSFET reached 5×10^(6)ion·cm^(-2), the drain–gate channel current increased under 200 V drain voltage, the drain–gate channel current and the drain–source channel current increased under 350 V drain voltage. The device occurred single event burnout under 800 V drain voltage, resulting in a complete loss of breakdown voltage. Combined with emission microscope, scanning electron microscope and focused ion beam analysis, the device with increased drain–gate channel current and drain–source channel current was found to have drain–gate channel current leakage point and local source metal melt, and the device with single event burnout was found to have local melting of its gate, source, epitaxial layer and substrate. Combining with Monte Carlo simulation and TCAD electrothermal simulation, it was found that the initial area of single event burnout might occur at the source–gate corner or the substrate–epitaxial interface, electric field and current density both affected the lattice temperature peak. The excessive lattice temperature during the irradiation process appeared at the local source contact, which led to the drain–source channel damage. And the excessive electric field appeared in the gate oxide layer, resulting in drain–gate channel damage.

Proton induced radiation effect of SiC MOSFET under different bias

Radiation effects of silicon carbide metal–oxide–semiconductor field-effect transistors(SiC MOSFETs)induced by 20 MeV proton under drain bias(V_(D)=800 V,V_(G)=0 V),gate bias(V_(D)=0 V,V_(G)=10 V),turn-on bias(V_(D)=0.5 V,V_(G)=4 V)and static bias(V_(D)=0 V,V_(G)=0 V)are investigated.The drain current of SiC MOSFET under turn-on bias increases linearly with the increase of proton fluence during the proton irradiation.When the cumulative proton fluence reaches 2×10^(11)p·cm^(-2),the threshold voltage of SiC MOSFETs with four bias conditions shifts to the left,and the degradation of electrical characteristics of SiC MOSFETs with gate bias is the most serious.In the deep level transient spectrum test,it is found that the defect energy level of SiC MOSFET is mainly the ON2(E_(c)-1.1 eV)defect center,and the defect concentration and defect capture cross section of SiC MOSFET with proton radiation under gate bias increase most.By comparing the degradation of SiC MOSFET under proton cumulative irradiation,equivalent 1 MeV neutron irradiation and gamma irradiation,and combining with the defect change of SiC MOSFET under gamma irradiation and the non-ionizing energy loss induced by equivalent 1 MeV neutron in SiC MOSFET,the degradation of SiC MOSFET induced by proton is mainly caused by ionizing radiation damage.The results of TCAD analysis show that the ionizing radiation damage of SiC MOSFET is affected by the intensity and direction of the electric field in the oxide layer and epitaxial layer.

Effect of SiO_2/Na_2O mole ratio on the properties of foam geopolymers fabricated from circulating fluidized bed fly ash

Geopolymers are three-dimensional aluminosilicates formed in a short time at low temperature by geopolymerization. In this pa-per, alkali-activated foam geopolymers were fabricated from circulating fluidized bed fly ash （CFA）, and the effect of SiO2/Na2O mole ratio （0.91-1.68） on their properties was studied. Geopolymerization products were characterized by mechanical testing, scanning electron mi-croscopy （SEM）, energy-dispersive X-ray spectroscopy （EDX）, and X-ray diffraction （XRD）. The results show that SiO2/Na2O mole ratio plays an important role in the mechanical and morphological characteristics of geopolymers. Foam samples prepared in 28 d with a SiO2/Na2O mole ratio of 1.42 exhibit the greatest compressive strength of 2.52 MPa. Morphological analysis reveals that these foam geo-polymers appear the relatively optimized pore structure and distribution, which are beneficial to the structure stability. Moreover, a combina-tion of the Si/Al atomic ratio ranging between 1.47 and 1.94 with the Na/Al atomic ratio of about 1 produces the samples with high strength.

Evolution of stress in evaporated silicon dioxide thin films

The evolution of stress in evaporated SiO2, used as optical coatings, is investigated experimentally through in situ stress measurement. A typical evolution pattern consisting of five subprocedures （thin film deposition, stopping deposition, cooling, venting the vacuum chamber, and exposing coated optics to the atmosphere） is put forward. Further investigations into the subprocedures reveal their features. During the deposition stage, the stresses are usually compressive and reach a stable state when the deposited film is thicker than 100 nm. An increment of compressive stress value is observed with the decrease of residual gas pressure or deposition rate. A very low stress of-20 MPa is formed in SiO2 films deposited at 3×10^-2 Pa. After deposition, the stress increases slightly in the compressive direction and is subject to the stabilization in subsequent tens of minutes. In the process of venting and exposure, the compressive component increases rapidly with the admission of room air and then reaches saturation, followed by a logarithmic decrement of the compressive state in the succeeding hours. An initial discussion of these behaviors is given.

Investigation of Microwave Surface-Wave Plasma Deposited SiO_x Coatings on Polymeric Substrates

In this paper, we reported nano-scale SiOx coatings deposited on polyethylene terephthalate （PET） webs by microwave surface-wave assisted plasma enhanced chemical vapor deposition for the purpose of improving their barrier properties. Oxygen （O2） and hexamethyl- disiloxane （HMDSO） were employed as oxidant gas and Si monomer during SiOx deposition, re- spectively. Analysis by Fourier transform infrared spectroscope （FTIR） for chemical structure and observation by atomic force microscopy （AFM） for surface morphology of SiO~ coatings demon- strated that both chemical compounds and surface feature of coatings have a remarkable influence on the coating barrier properties. It is noted that the processing parameters play a critical role in the barrier properties of coatings. After optimization of the SiOx coatings deposition conditions, i.e. the discharge power of 1500 W, 2 ： 1 of O2 ： HMDSO ratio and working pressure of 20 Pa, a better barrier property was achieved in this work.