Kinetics of residual doping in 4H-SiC epitaxial layers grown in vacuum

Investigation on residual Al, B, and N co-doping of 4H-SiC epitaxial layers is reported. The layers were produced by sublimation epitaxy in Ta growth cell environment at different growth temperatures and characterized by secondary ion mass spectrometry. The vapor interaction with Ta was considered through calculations of cohesive energies of several Si-, Al-, B-, and N-containing vapor molecules and also of diatomic Ta–X molecules. An analysis of kinetic mechanisms responsible for impurity incorporation is performed. Among residuals, B exhibits a stronger incorporation dependence on temperature and growth at lower temperatures can favor B decrease in the layers. Under the growth conditions in this study (Ta environment and presence of attendant Al and N), B incorporation is assisted by Si₂C vapor molecule. Boron tends to occupy carbon sites at higher temperatures, i.e. higher growth rates.     

Direct Spectrographic Determination of In,La, Nb and Sr in Thorium Oxide

Abstract

A d.c. are emission spectrographic method is described for the determination of ppm levels of In, La, Nb and Sr in thorium oxide. The method permits determination of the above low and high volatile impurity elements in thoria using AgCl as carrier in an atmosphere of oxygen. The carrier-distillation technique reported makes possible the following range of estimations: In : 1–50 ppm; La, Nb : 10–500 ppm and Sr: 2–100 ppm. The method is simple and rapid and its precision ranges from 14% for In to 18% for Nb. Observations made on the choice of carrier and internal standard are presented.     

Entanglement in S states of two-electron quantum dots with Coulomb impurities at the center

We study a system of two Coulombically interacting electrons in an external harmonic potential in the presence of an on-centre Coulomb impurity. Detailed results for the dependencies of the reduced von Neumann entropy on the control parameters of the system are provided for both the ground state and the triplet S states with the lowest energy. Among other features, it is found that in the weak confinement regime the entanglement is strongly affected by the presence of an acceptor impurity.     

串联毛细管柱对甲基叔丁基醚产品及其杂质的色谱分析

采用非极性的OV-1柱及极性的FFAP柱串联而成的毛细管柱分析甲基叔丁基醚(MTBE)产品的全组成,该法能完全分离MTBE及其杂质组分,相对标准偏差小于3．5％。具有分离效果好、结果准确、操作简单等优点。     

ICP-AES 分析超导粉中杂质元素的干扰系数矩阵校正法

利用ICP-AES法测定了铋系超导前驱粉（BSCCO）中Fe,Cr,Ni,Si,Al和Ba等微量杂质元素,优化了仪器测定参数并研究了酸的种类及浓度对测定结果的影响。系统研究了BSCCO基体元素Bi,Sr,Pb,Ca和Cu对微量杂质元素测定的干扰,分别测定了每个基体元素对测定元素的校正系数并组成交互干扰校正矩阵,采用全选主元高斯消去法计算出基体元素产生的背景等效浓度,再计算出样品的真实浓度。用此方法对合成标样中的上述微量杂质元素进行了测定,分析结果的回收率99.5％～100.5％,测定了实际样品中的杂质元素,并与ICP-MS法进行了对比,二者结果一致。     

Standards and GC-MS analysis: An answer to the requirement of compound confirmation

Summary The attribution of an unknown GC-MS chromatographic peak to a specific substance should be confirmed whenever possible by comparison with a standard compound analysed under the same experimental conditions. The range of chemicals supplied by various companies is very wide but can never be completely comprehensive. This paper proposes two simple ways by which a reference compound may be obtained. Firstly, it may occur as an impurity in a commercial sample as a synthesis by-product. Alternatively, the compound may be synthesized by a simple procedure, preferably a single step one, by putting small amounts of reagents in a sealed glass vial placed in a programmable oven. Examples of these two approaches are described.     

电感耦合等离子体质谱法测定高纯氧化铈中11个稀土杂质的研究

报道了用电感耦合等离子体质谱法（ＩＣＰ－ＭＳ）测定高纯氧化铈１１个痕量稀土杂质的方法。分析讨论了氧化铈对测定元素所产生的谱干扰和基体效应，考察了Ｔｌ，Ｇａ，Ｃｓ，Ｉｎ等内标补偿基本抑制效应的作用，用此方法测定１１个稀土杂质的检出限为０．０１７－０．４０ｎｇ／ｍＬ，精密度（ＲＳＤ）为２．６％－８．２％，加标回收率为９６．７％－１０７．９％，分析时，不需要预分离和富集，酸溶后可以直接测定。     

Development of an impurity test for 3-tropanyl-3,5-dichlorobenzoate using capillary gas chromatography

Summary A simple, accurate and sensitive capillary gas chromatographic test procedure was developed for the detection and quantification of impurities in bulk 3-tropanyl-3,5-dichlorobenzoate, a drug which is a neural serotonin 5HT₃ receptor antagonist. The drug substance was dissolved in acetonitrile and chromatographed on a 30 m×0.32 mm 0.25 μm film DB-5 column operated with a temperature program of 80 to 230°C. A flame ionization detector was used, and the impurities detected in the drug were estimated from peak areas on a percent basis compared to the parent peak. Validation of this procedure included a recovery study of spiked impurities from 0.1 to 1.2% (w/w) and a repeatability study using two different synthesized batch lots of the drug.     

Structural and electronic properties of Fe 3+ -O 2− Pairs in KMF 3 lattices (M=Mg,Zn): Is the superposition model valid?

The geometrical and electronic properties of the tetragonal FeF 5 O 4 m complex which is likely formed in KMgF 3 and KZnF 3 fluoroperovskites have been investigated by means of Density Functional calculations. The properties of this centre are dependent on the Fe-O distance ( R ox ) and also on the distances R eq and R ax between Fe 3+ and the four equatorial F m ions and the apical F m ion respectively. The calculated equilibrium distance for the isolated Fe 3+ -O 2 m pair is equal to R ox =1.63 v + while when it is introduced in KMF 3 lattices ( M =Mg, Zn) R ox ～1.82 v + . Compared to FeF 6 3 m in KMgF 3 ( R eq = R ax =1.94 v + ) the obtained equilibrium distances R ax =2.05 v + and R eq =2.02 v + mean an outwards relaxation of 6% and 4% respectively induced by the F m M O 2 m substitution. The ratio of the associated superhyperfine ( shf ) constants of equatorial ( A eq ) and axial ( A ax ) F m ligands is A eq / A ax , 2 and thus account for an experimental fingerprint of this centre. The huge difference between A s (eq) and A s (ax) cannot be explained assuming that the law relating A s to the metal-ligand distance, R , for the octahedral FeF 6 3 m unit can be transferred to the present case involving a lower symmetry . The present analysis casts doubts on the conclusions previously reached using the empirical superposition model.