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.     

Structural, electronic and magnetic properties of the 3d transition metal-doped GaN nanotubes

We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets.     

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。     

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.     

ICP-AES法测定铅精矿中的杂质元素

用HNO3-KClO3-H2SO4溶样,采用ICP-AES测定铅精矿中的杂质元素。并试验了酸度、共存元素对测定的影响,方法的精密度、检出限及回收率均能满足要求。     

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.     

Effects of dimethylhydrazine on Zn, C, and H doping of GaP

Surfactants are beginning to be used during vapor-phase growth to provide control of the materials characteristics of epitaxial layers. This paper reports the effects of utilizing N, from pyrolysis of dimethylhydrazine (DMHy), as a surfactant during the organometallic vapor-phase epitaxial growth of GaP. Nitrogen is isoelectronic with the group V host element; thus, it generates no free carriers. Additionally, due to its small size, N is strongly rejected from the solid, so little incorporation is expected. This is confirmed by the determination of the very low N distribution coefficient (3.2×10⁻⁵). Using secondary ion mass spectroscopy analysis, we observe an increase in the distribution coefficient of the acceptor Zn when DMHy is added during growth, resulting in an increase in the doping efficiency by nearly an order of magnitude. Furthermore, the Zn doping efficiency increases linearly with the amount of DMHy added during growth over the range of partial pressures from 2.83×10⁻⁴ to 2.20×10⁻³ atm. The increase of doping for Zn is believed to be mainly a N surfactant effect. The addition of DMHy also leads to increases in both H and C incorporation. The concentrations of both are linear functions of DMHy concentration. Both H and C incorporation most likely arise mainly from pyrolysis of the DMHy. We propose a simple mechanism for the surfactant effect due to an increase in the Zn incorporation coefficients at the step edge induced by the presence of N (and probably H) on the surface.