Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.     

Effects of Y2O3 and ZrO2 on the Densification of Si3N4-Zr(Y)O2 Composites

The effects of ZrO₂ and Y₂O₃ on the densification of hotpressed Si₃N₄-Zr(Y)O₂ composites have been studied. High density could not be obtained by the addition of pure or 3-mol%-Y₂O₃-doped ZrO₂ in this composite; however, nearly full density (>97%) could be obtained in Si₃N₄ using 6- and 8-mol%-Y₂O₃-doped ZrO₂. It is concluded that Y₂O₃ diffusing out from the added Zr(Y)O₂ promoted the densification and that ZrO₂ also had some role in the formation of an oxynitride glass.     

Nitridation of the Sol–Gel-Derived Titanium Oxide Films by Heating in Ammonia Gas

Dip-coated sol–gel-derived TiO₂ films on an alumina substrate were converted to nonstoichiometric titanium nitride (TiN _x ( x ≦ 1)) films by heating at approxmately 1000°C in NH₃ gas. TiO₂ films made from TiO₂ sols prepared from Ti(O– i -C₃H₇)₄ and stabilized by diethanolamine were more easily nitrided than those from sols containing HCl as a deflocculant reagent. This appears to be a result of the more porous structure of the former films.     

Thermodynamic Analysis of Chemical Vapor Deposition of BN + AIN Composite Coatings

Thermodynamic calculations were performed using a modified solgasmix-pv computer program in order to study the feasibility of codepositing boron nitride (BN) plus aluminum nitride (AIN) by chemical vapor deposition. Reactants considered were AICl₃, BCl₃ or B₂H₆, NH₃, and H₂. Deposition diagrams were generated for the BCl₃-AICl₃-NH₃ system over a range of processing conditions such as temperature, total system pressure, and reagent concentrations. Codeposition of BN + AIN was predicted by the calculations for temperatures in the range of 900 to 1700 K and pressures of 10.13 to 101.3 kPa. The predicted deposition efficiency at equilibrium was much higher for BN than for AlN at most reagent compositions. The AlN deposition efficiency increased with decreasing temperature and decreasing BCl₃ content, with increasing NH₃ content, or with the addition of H₂. Aluminum chlorides were found to be the dominant gaseous species.     

超薄氮氧叠层栅介质的金属栅pMOS电容的电学特性

研究了高质量超薄氮化硅/氮氧化硅(N/O)叠层栅介质的金属栅pMOS电容的电学特性,制备了栅介质等效厚度小于2nm的N/O复合叠层栅介质,该栅介质具有很强的抗硼穿通能力和低的漏电流.实验表明这种N/O复合栅介质与优化溅射W/TiN金属栅相结合的技术具有良好的发展前景.     

Large-area,high-quality self-assembly electron transport layer for organic optoelectronic devices

We propose a self-assembly method for forming large-area high-quality solution-processed titanium oxide (TiO₂) films as efficient electron transport layer for organic solar cells. The self-assembled solution-processed TiO₂ layers are highly ordered and significantly improved in surface morphology over commonly-used spin-coating process resulting in better charge collection and significant material saving. When incorporated into polymer solar cells, the TiO₂ device shows enhanced performance. Furthermore, we demonstrate the TiO₂ can form large-area films, and achieve very uniform and improved device performances. Consequently, the self-assembled TiO₂ films can be efficient and low-cost electron transport layer potentially for large-area organic optoelectronics.     

Lightweight,Superelastic Boron Nitride/Polydimethylsiloxane Foam as Air Dielectric Substitute for Multifunctional Capacitive Sensor Applications

Porous polymeric foams as dielectric layer for highly sensitive capacitive based pressure sensors have been extensively explored owing to their excellent flexibility and elasticity. Despite intensive efforts, most of previously reported porous polymer foams still suffer from difficulty in further lowering the attainable density limit of ≈0.1 g cm^?3 while retaining high sensitivity and compressibility due to the limitations on existing fabrication techniques and materials. Herein, utilizing 3D interconnected networks of few‐layer hexagonal boron nitride foams (h‐BNFs) as supporting frameworks, lightweight and highly porous BN/polydimethylsiloxane composite foams (BNF@PDMS) with densities reaching as low as 15 mg cm^?3 and permittivity close to that of air are fabricated. This is the lightest PDMS‐based foam reported to date. Owing to the synergistic effects between BN and PDMS, these lightweight composite foams possess excellent mechanical resilience, extremely high compressibility (up to 95% strain), good cyclic performance, and superelasticity. Being electrically nonconductive, the potential application of BNF@PDMS as a dielectric layer for capacitive sensors is further demonstrated. Remarkably, the as‐fabricated device can perform multiple sensing functions such as noncontact touch sensor, environmental monitoring sensor, and high sensitivity pressure sensor that can detect extremely low pressures of below 1 Pa.     

TC4钛合金引信天线零件精密加工研究

TC4钛合金引信天线上零件有腰型槽尺寸小、精度高、机械加工性能差等特点。通过多因素正交实验方法和多元线性逐步回归分析建立0.4mm超小刀具TC4钛合金切削力数学模型,分析了各切削参数对切削力的影响程度。通过该数学模型和实际生产经验优化了切削参数。通过MasterCAM软件对刀路轨迹进行优化、模拟和仿真。     

Controlled Nucleation of GaN Nanowires Grown with Molecular Beam Epitaxy

The location of GaN nanowires is controlled with essentially perfect selectivity using patterned SiN_x prior to molecular beam epitaxy growth. Nanowire growth is uniform within mask openings and absent on the mask surface for over 95% of the usable area of a 76 mm diameter substrate. The diameters of the resulting nanowires are controlled by the size of the mask openings. Openings of approximately 500 nm or less produce single nanowires with symmetrically faceted tips.     

Optimization of Al_2O_3/SiN_x stacked antireflection structures for N-type surface-passivated crystalline silicon solar cells

In the case of N-type solar cells,the anti-reflection property,as one of the important factors to further improve the energy-conversion efficiency,has been optimized using a stacked Al₂O₃/SiN_x layer.The effect of SiN_x layer thickness on the surface reflection property was systematically studied in terms of both experimental and theoretical measurement.In the stacked Al₂O₃/SiN_x layers,results demonstrated that the surface reflection property can be effectively optimized by adding a SiN_x layer,leading to the improvement in the final photovoltaic characteristic of the N-type solar cells.