Preparation and characterization of GaN films grown on Ga-diffused Si （111） substrates

Hexagonal GaN films were prepared by nitriding Ga2O3 films with flowing ammonia. Ga2O3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. This paper have investigated the change of structural properties of GaN films nitrided in NH3 atmosphere at the temperatures of 850, 900, and 950℃ for 15 min and nitrided at the temperature of 900℃ for 10, 15, and 20 rain, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure, surface morphology and composition of synthesized samples. The results reveal that the as-grown films are polycrystalline GaN with hexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained when nitrided at 900℃ for 15 min.     

Intermetallic phase formation in directionally solidified Al−Si−Fe alloy

The present study has been undertaken to better understand the solidification behavior of Al−Si−Fe alloys containing 7wt.% Si and 0.9wt.% Fe, with particular regard to the formation of phase during controlled solidification and influence of growth rates on intermetallic phase selection. The alloys studied were Al-7Si-0.9Fe alloys, which were produced by a modified Bridgman solidification arrangement. These alloys were solidified unidirectionally with different growth rates (1–30mm/min). The solidified microstructure of these alloys consists of the growth of primary aluminum and multiple second phase reactions.     

烧结与冷镦过程中铝硅共晶合金显微结构与密度的演变

采用烧结及后续的镦粗工艺制备了铝硅共晶合金块体材料,研究了烧结温度对烧结体显微结构、抗压强度及相对密度的影响。结果表明：烧结温度显著影响烧结体的显微结构和抗压强度,以临近铝硅共晶合金液相线的温度烧结时,发生了局部熔化,产生的熔融液体破坏了颗粒表面的氧化膜,颗粒之间相互黏结,形成了烧结骨架。以优化的555℃烧结,Si颗粒呈球状,抗压强度达到最佳,但相对密度未发生变化。在后续的冷镦过程中,烧结骨架及粉末颗粒均产生变形,孔隙减小,颗粒呈扁平状,相对密度达到了98%。     

Effects of Solid-State Reaction Synthesis Processing Parameters on Thermoelectric Properties of MgaSi

The Mg2 Si-matrix thermoelectric material was stnthesized by low temperature solid-state renc-tion.This paper studies the effects of holding time and reaction temperatare on the particle size and the properties of the material, and also studies effects of doping elemental Sb, Te and their doping seqence on the properties of the materiol. The result shows that excessirely high temperature and elongated holding time of solid-state reaction are harmful, there is a range of partiele size to ensure optimum properties and the doping sequence of Sb or Te without influencing the properties.     

Annealing process of fine grained co-stabilised (Y,Mg)-PSZ/MgAl2O4 ceramics

Abstract

Co-stabilised (Y,Mg) partially stabilised zirconia (PSZ) ceramics with MgAl₂O₄ spinel additions were produced, with industrial zirconia as the main starting material. Powders were prepared using a mechanical milling–mixing process. The effect of the annealing process on the mechanical properties, phase compositions, and microstructure of fine grained PSZ ceramics was investigated.     

Quantitative measurement of oxygen content in Si targets

Enriched self-supporting targets of ^28,29,30Si are often used in the field of high resolution nuclear physics experiments. The Si targets were prepared by the thermal evaporation deposition or reduction-deposition methods. The targets, however, are always contaminated by oxygen as Si-material is easily oxidised. These contaminated targets lead to poor data with low S/N ratio. Thus it is very useful if one can estimate the amount of oxygen in the target quantitatively before experiments.In this work we have developed a method to estimate the amount of oxygen in the Si target. We used α-ray and β-ray thickness gauges, which have different sensitivity to oxygen atoms. Namely, the α-ray gauge is more sensitive to light elements such as oxygen compared to the β-ray gauge. Thus one can deduce the amount of oxygen by comparing the oxygen thickness measured by α-ray gauge with that of the β-ray gauge.Accuracy of a few percents can be obtained for the oxygen content in Si targets with a thickness of 1 mg/cm². The present method can also be applied to heavy elements such as Ta₂O₅.     

Luminescence hydrogenated nanoamorphous Si films fabricated by reactive pulsed laser ablation

Hydrogenated nanoamorphous Si (na-Si:H) films have been fabricated by reactive pulsed laser ablation technique with hydrogen as reactive gas. It is found that the hydrogen pressure has a great effect on both the structure and photoluminescence (PL) properties of the films. Increasing the hydrogen pressure leads to a structural transition of the films from amphorous Si to na-Si:H, and the PL center wavelength of the na-Si:H films is varied with the hydrogen pressure. The PL decay times of the na-Si:H films are in the nanosecond scale and are shorter on the high energy side of their PL spectrum. The results demonstrate that the na-Si:H films are promising candidates for visible, tunable and high-performance light-emitting devices.     

Effect of Film Thickness on Properties of a—Si：H Films

The a -Si:H film with different thickness smaller than 1μm were deposited by plasma enhanced chemical vapor deposition (PECVD) under the optimum deposition contitions.The effect of diferent thickness on film properties is analyzed.The results show that,with the increase of the film thickness,the dark conductivity ,photoconductivity and threshold voltage increase,the optical gap and peak ratio of TA to TO in the Raman spectra decrease, the refractive index keeps almost constant, and the optical absorption coefficient and current ration of on/off state first maximize and then reduce.