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排序方式: 共有441条查询结果,搜索用时 228 毫秒
91.
碳化硅(SiC)是制作高温、高频、大功率电子器件的理想电子材料,近20年来随着外延设备和工艺技术水平不断提升,外延膜生长速率和品质逐步提高,碳化硅在新能源汽车、光伏产业、高压输配线和智能电站等领域的应用需求越来越大。与硅半导体产业不同,碳化硅器件必须在外延膜上进行加工,因此碳化硅外延设备在整个产业链中占据承上启下的重要位置,而且也是整个产业链中最复杂、最难开发的设备。本文从碳化硅外延生长机理出发,结合反应室设计和材料科学的发展,介绍了化学气相沉积(CVD)法碳化硅外延设备反应室、加热系统和旋转系统等的技术进展,最后分析了CVD法碳化硅外延设备未来的研究重点和发展方向。 相似文献
92.
Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS), ICP sector field mass spectrometry (ICP-SFMS) and ICP atomic emission spectrometry (ICP-AES) were compared with regard to the direct determination of rare earth elements (REEs) in geological samples. In order to reduce the polyatomic interferences occurring in ICP-QMS, the use of a cooled spray chamber was optimized, obtaining a significant decrease of the oxide ions formation (about 50%) and a consequent mitigation of the interfering effects. Precision and accuracy of the method were demonstrated by the analyses of sediment and soil certified reference materials. ICP-SFMS working in high-resolution mode also provided accurate results, with similar precision to ICP-QMS (RSD%: 3-8%) and comparable or better limits of detection. Quantification limits of the procedures were 18-52 ng g−1 and 10-780 ng g−1 for sector field- and quadrupole-ICP-MS, respectively. Accurate and precise determination of most REEs was also achieved by ICP-AES using both pneumatic and ultrasonic nebulization, after a careful selection of the emission lines and compensation for non-spectral interferences by internal standardization. The three techniques were finally applied to glaciomarine sediment samples collected in Antarctica, providing comparable analytical data on REE abundance and depth pattern. 相似文献
93.
B. Ravel C. Scorzato D. P. Siddons S. D. Kelly S. R. Bare 《Journal of synchrotron radiation》2010,17(3):380-385
A four‐channel ionization chamber has been designed, constructed and tested. This ionization chamber allows X‐ray absorption spectra to be collected in transmission from up to four samples simultaneously. This results in spectra that are free of systematic uncertainty in relative energy alignment introduced by scan‐to‐scan stability of the monochromator or of numerical uncertainty associated with a post‐processing alignment algorithm, allowing, in a single shot, an absolute measure of edge shift between four samples of different valence. As four samples can be measured in parallel, the time expended over the course of an experiment to cycle the measurement environment between its rest state and the measurement condition is substantially reduced. The ionization chamber is simple in design and could be implemented at virtually any XAFS beamline with a horizontal fan of radiation such as that provided by a bend magnet or wiggler. 相似文献
94.
Warunya Boonjob María Rosende Manuel Miró Víctor Cerdà 《Analytical and bioanalytical chemistry》2009,394(1):337-349
Two novel dynamic extraction approaches, the so-called sequential injection microcolumn extraction and sequential injection
stirred-flow chamber extraction, based on the implementation of a sample-containing container as an external extraction reactor
in a sequential injection network, are for the first time, optimized and critically appraised for fractionation assays. The
three steps of the original Community Bureau of Reference (BCR) sequential extraction scheme have been performed in both automated
dynamic fractionation systems to evaluate the extractability of Cr, Cu, Ni, Pb, and Zn in a standard reference material of
coal fly ash (NIST 1633b). In order to find the experimental conditions with the greatest influence on metal leachability
in dynamic BCR fractionation, a full-factorial design was applied, in which the solid sample weight (100–500 mg) and the extraction
flow rate (3.0–6.0 mL min−1) were selected as experimental factors. Identical cumulative extractabilities were found in both sequential injection (SI)-based
methods for most of assayed trace elements regardless of the extraction conditions selected, revealing that both dynamic fractionation
systems, as opposed to conventional steady-state BCR extraction, are not operationally defined within the selected range of
experimental conditions. Besides, the proposed automated SI assemblies offer a significant saving of operational time with
respect to classical BCR test, that is, 3.3 h versus 48 h, for complete fractionation with minimum analyst involvement.
Schematic illustration of automatic flow-based setups for dynamic fractionation of trace metals in fly ash
相似文献
Manuel MiróEmail: |
95.
Shear-flow induced detachment of Saccharomyces cerevisiae from stainless steel: influence of yeast and solid surface properties 总被引:5,自引:0,他引:5
Guillemot G Vaca-Medina G Martin-Yken H Vernhet A Schmitz P Mercier-Bonin M 《Colloids and surfaces. B, Biointerfaces》2006,49(2):126-135
The present study focused on the shear-induced detachment of Saccharomyces cerevisiae in adhesive contact with a 316L stainless steel surface using a shear stress flow chamber, with a view to determining the respective influence of the yeast surface properties and the support characteristics. The effect of cultivation of S. cerevisiae yeast cells on their subsequent detachment from the solid surface was particularly investigated. In order to elucidate the role of stainless steel, non-metallic supports were used as control, covering a broad range of surface properties such as surface free energy and roughness: polypropylene (hydrophobic), polystyrene (mildly hydrophobic, similar to stainless steel) and glass (hydrophilic). All materials were very smooth with respect to the size of yeast. First, experiments were carried out on two types of yeast cells, just rehydrated in saline solution, a biological model widely used in the literature. The influence of the ionic strength (1.5 and 150 mM NaCl) on glass and stainless steel was evaluated. Unlike on glass, no clear evidence was found for electrostatic repulsion with stainless steel since high adhesion was observed whatever the ionic strength. A lack of correlation in adhesion results was also obtained when considering the surface physico-chemical characteristics of type I (hydrophilic) and type II (hydrophobic) rehydrated cells and those of both polymers. It was postulated that unavoidable “sticky” compounds were present on the cell wall, which could not be completely removed during the successive washings of the rehydrated cell suspension before use. This could dramatically alter the yeast surface properties and modify the adhesion strength, thus clearly demonstrating the necessity to work with yeast coming from fresh cultures. Biologically active yeast cells were then used. Once cultured, type I- and type II-yeast cells were shown to exhibit the same hydrophilic properties. Regardless of the material used, for the same ionic strength (150 mM NaCl), yeast adhesion was drastically reduced compared to rehydrated yeast cells. Among all the materials tested, the specificity of 316L stainless steel was clearly established. Indeed, for glass and polymers, cell adhesion was substratum-dependent and driven by the balance between the Lifshitz-van der Waals and Lewis acid/base interactions. Despite nearly identical surface free energies for polystyrene and stainless steel, the metallic surface promoted a totally distinct behaviour which was characterized by a strong – although highly variable – yeast adhesion. 相似文献
96.
Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry 总被引:2,自引:0,他引:2
Akihiro Matsumoto Shusuke Osaki Bunji Hashimoto Taketoshi Nakahara 《Microchemical Journal》2010,95(1):85-3730
An improved double chamber electrothermal vaporization (ETV) system was designed. A new inner chamber and its bottom plate made of quartz glass were attached with carrier support gas inlet port for the determination of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The use of the inner chamber in combination with the plate played important roles to transport the metal vapor efficiently into argon ICP. Ten-μl sample aliquots were dried at 100 °C and subsequently heated at 1000 °C on the tungsten boat furnace. The evolved vapor was swept into the ICP source through PTFE tubing and the inner chamber by a 0.8 l/min H2 (7%)-Ar carrier gas. The performance parameters of ETV-ICP-AES such as temperature program and gas flow rate were evaluated using cadmium standard solution. Under the optimized experimental conditions, the best attainable detection limit at Cd II 214.438 nm line was 0.2 ng/ml with linear dynamic ranges of 50 to 10,000 ng/ml for cadmium. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 10,000 ng/ml for cadmium by ETV-ICP-AES was 0.85%. The present method has been successfully applied to the determination of cadmium in zinc-base materials. 相似文献
97.
98.
由于Nb2O5与Ta2O5物理、化学性质相似,主体Nb2O5对Ta分析线强度干扰很大。因此,Nb2O5中光谱测定Ta2O5的灵敏度很差,为了提高Ta分析线强度,通常的光谱条件选择是无效的。实验表明在旋流气室中,采用高含量Ar的(Ar、O2)控制气氛电弧激发,提高了Nb2O5中Ta2O5的光谱分析灵敏度。然而,由于Nb2O5在高温下易于被碳还原,虽然用Stallwood喷咀可以改善蒸发,减慢样品还原 相似文献
99.
Y. Masada K. Hashimoto T. Inoue Y. Sumida T. Kishi Y. Suwa 《Journal of separation science》1979,2(7):400-404
A novel method is described for the preparation of stable glass capillary columns (glass open tubular columns), including the etching and formation of a polymer film on the inner glass capillary surfaces. The approach used here is based on low-temperature plasma etching and polymerization. Under the influence of a field of radio frequency discharge, low pressure gases of fluoric compounds, introduced into the glass capillary tube, generate excited fluorine radicals which etch the inner surface. The plasma of organosilicone monomer in the glass capillary yields a uniform polymerized film on the inner surface. The resultant material functions as a good stationary phase for glass capillary gas chromatography (GC2). The inner surfaces treated with such a plasma, can be studied by means of a scanning electron microscope (SEM). The flexibility of this method permits the use of various stationary phases and surface modification. 相似文献
100.
A. D. Alexadrov 《Colloid and polymer science》1994,272(2):181-183
The dependence of the critical supersaturation on the degree of the initial undersaturation has been analyzed in detail.This dependence is explained by means of the Richarch-Powell equation, taking into account the dependence of the -ratio upon the partial pressures of the inert gas and the liquid under investigation. 相似文献