Oxidation behavior of silicide coating on Ti3SiC2-based ceramic

A silicide coating was prepared on Ti₃SiC₂-based ceramic by pack cementation to improve the oxidation resistance of Ti₃SiC₂, which is a technologically important material for high temperature applications. The microstructure, phase composition and oxidation resistance of the coated sample were investigated. The results demonstrated that the silicide coating was mainly composed of TiSi₂ and SiC. A single layer of a mixture of SiO₂ and TiO₂ was formed on the surface of the coated sample during isothermal oxidation at 1100 °C and 1200 °C for 20h. Compared to Ti₃SiC₂, the parabolic rate constant of silicide coated Ti₃SiC₂ decreased by 2~3 orders of magnitude. Furthermore, the coated sample showed much better cyclic oxidation resistance than Ti₃SiC₂ during the cyclic oxidation at 1100 °C for 400 times. However, during the preparation of the coating, a number of fine cracks formed in the outer layer of the coating. When these cracks penetrated the whole coating during the cyclic oxidation, the oxidation rate was accelerated, which degraded the oxidation resistance. Electronic Publication     

Origin of visible photoluminescence from porous silicon as studied by Raman spectroscopy

In this paper we discuss the different models proposed to explain the visible luminescence in porous silicon (PS). We review our recent photoluminescence and Raman studies on PS as a function of different preparation conditions and isochronal thermal annealing. Our results can be explained by a hybrid model which incorporates both nanostructures for quantum confinement and silicon complexes (such as SiH _x and siloxene) and defects at Si/SiO₂ interfaces as luminescent centres.     

氢化非晶硅磷掺杂工艺条件的研究

本文对氧化非晶硅磷掺杂的工艺条件进行了研究，得出掺磷氢化非晶硅的电导率随衬底温度、气体流量、气体压力、射频功率、淀积时间的变化关系，为非晶硅的有效掺杂和器件研究提供了依据。     

Microstructure-related fracture toughness and fatigue crack growth behaviour in toughened, anhydride-cured epoxy resins

Fracture toughness and fatigue crack propagation (FCP) of plain and modified anhydride-cured epoxy resin (EP) were studied at ambient temperature. Liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon (SI) rubber dispersions were used as tougheners for the EP. The morphology of the modified EP was characterized by dynamic mechanical analysis (DMA) and by scanning electron microscopy (SEM). The fracture toughness, K_c, of the compositions decreased with increasing deformation rate. K_c of the EP was slightly improved by CTBN addition and practically unaffected by incorporation of the SI dispersion when tests were performed at low cross-head speed, v. Both modifiers improved K_c at high v, and also the resistance to FCP, by shifting the curves to higher stress intensity factor ranges, ΔK, by comparison with the plain EP. It was established that both fracture and fatigue performance rely on the compliance, J_R, at the rubbery plateau, and thus on the apparent molecular mass between crosslinks, M_c. The failure mechanisms were less dependent upon the loading mode (fracture, fatigue), but differed basically for the various modifiers. Rubber-induced cavitation and shear yielding of the EP were dominant for CTBN, whereas crack bifurcation and branching controlled the cracking in SI-modified EP. The simultaneous use of both modifiers resulted in a synergistic effect for both the fracture toughness at high deformation rate and the FCP behavior.     

Oxidation of Silicon Carbide in Environments Containing Potassium Salt Vapor

At high temperatures in clean oxidizing environments, SiC forms a very protective SiO₂ film, but, in environments containing low levels of gaseous alkali salt contaminants or where condensed salts may deposit on the surface, the resistance of the film is significantly reduced. Oxidation kinetics of SiC were measured by continuous thermogravimetric analysis in a controlled environment containing CO₂, H₂O, and O₂ plus low levels of potassium-containing salts. Potassium was found to be incorporated into the SiO₂ scale and to significantly change its transport properties and its morphology. The rate of scale formation was found to increase directly in proportion to K in the scale. A change in mechanism was observed when water vapor was added to the reacting gas stream.     

Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

Influence of deposition parameters on hole mobility in polymorphous silicon

Time-of-flight transient photoconductivity measurements reveal a monotonic increase with the deposition pressure in the hole mobility in polymorphous silicon for samples deposited under hydrogen dilution. With helium dilution, a maximum mobility that matches the highest value from H-dilution samples is measured at the intermediate pressure of 1.4 Torr. The deposition rate of those samples is twice the rate for the H-dilution ones. For the samples with the best hole mobilities, the valence-band tail is comparable to the one of standard hydrogenated amorphous silicon.     

Synthesis of silicon oxynitride by infiltration-mediated combustion

Silicon oxynitride Si₂N₂ O was synthesized from a mixture of Si, SiO₂, and Si₃N₄ by infiltrationmediated combustion in nitrogen gas. The chemical/phase composition of product and process parameters (temperature and burning velocity) were studied upon variation in charge composition and initial pressure of gas reagent. Parameters of the reaction yielding single-phase Si₂N₂O have been optimized.      

Estimating thermal stress in BIPV modules

The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd.     

TFT有源矩阵α－Si∶H薄膜PECVD淀积工艺研究

分析了α－Ｓｉ∶Ｈ薄膜的质量和厚度对α－Ｓｉ∶ＨＴＦＴ关键性指标的影响，深入、详细地讨论了其ＰＥＣＶＤ淀积工艺，并在实验的基础上确定了最佳淀积工艺参数，从而获得了高性能的７５ｍｍ３７２×２７６像素α－Ｓｉ∶ＨＴＦＴ有源矩阵