3,677 research outputs found
Selective-Area MOCVD Growth and Carrier-Transport-Type Control of InAs(Sb)/GaSb Core-Shell Nanowires
No full textWe
report the first selective-area growth of high quality InAs(Sb)/GaSb
core–shell nanowires on Si substrates using metal–organic
chemical vapor deposition (MOCVD) without foreign catalysts. Transmission
electron microscopy (TEM) analysis reveals that the overgrowth of
the GaSb shell is highly uniform and coherent with the InAs(Sb) core
without any misfit dislocations. To control the structural properties
and reduce the planar defect density in the self-catalyzed InAs core
nanowires, a trace amount of Sb was introduced during their growth.
As the Sb content increases from 0 to 9.4%, the crystal structure
of the nanowires changes from a mixed wurtzite (WZ)/zinc-blende (ZB)
structure to a perfect ZB phase. Electrical measurements reveal that
both the n-type InAsSb core and p-type GaSb shell can work as active
carrier transport channels, and the transport type of core–shell
nanowires can be tuned by the GaSb shell thickness and back-gate voltage.
This study furthers our understanding of the Sb-induced crystal-phase
control of nanowires. Furthermore, the high quality InAs(Sb)/GaSb
core–shell nanowire arrays obtained here pave the foundation
for the fabrication of the vertical nanowire-based devices on a large
scale and for the study of fundamental quantum physics
Origin of the low thermal conductivity of the thermoelectric material beta-Zn(4)Sb(3): An ab initio theoretical study
No full textBy modeling beta-Zn(4)Sb(3) material as a Zn(36)Sb(30) crystal with defects, the crystal structure and thermal properties of beta-Zn(4)Sb(3) are studied by ab initio method to explain its extremely low thermal conductivity at moderate temperature. The formation and migration energies of defects are calculated and used to explain the partial occupation of Zn at the lattice sites, the disordered local structures and the origin of the low thermal conductivity of beta-Zn(4)Sb(3). Our study also unravels the puzzling dependence of thermal conductivity on doping in beta-Zn(4)Sb(3). A doping strategy is proposed to improve the thermoelectric performance of beta-Zn(4)Sb(3). (C) 2011 American Institute of Physics. [doi:10.1063/1.3599483
Stability of Sb-Te layered structures: First-principles study
Full text linkUsing an effective one-dimensional cluster expansion in combination with first-principles electronic structure calculations we have studied the energetics and electronic properties of Sb-Te layered systems. For a Te concentration between 0 and 60 at. % an almost continuous series of metastable structures is obtained consisting of consecutive Sb bilayers next to consecutive Sb2Te3 units, with the general formula (Sb2)n(Sb2Te3)m (n,m=1,2,...). Between 60 and 100 at. % no stable structures are found. We account explicitly for the weak van der Waals bonding between Sb bilayers and Sb2Te3 units by using a recently developed functional, which strongly improves the interlayer bonding distances. At T=0 K, no evidence is found for the existence of two separate single-phase regions ? and ? and a two-phase region ?+?. Metastable compounds with a Te concentration between 0 and 40 at. % are semimetallic, whereas compounds with a Te concentration between 50 and 60 at. % are semiconducting. Compounds with an odd number of Sb layers are metallic and have a much higher formation energy than those with an even number of consecutive Sb layers, thereby favoring the formation of Sb bilayers.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
Legal and Financial Problems of International Joint Custody of Children
Full text linkThe aim of this article is to analyze very interesting and currently up-to-date area of children living in international joint custody from the legal and financial point of view. This covers the situation when custody of a child is awarded to both parents living in different states of the European Union (or also other states). The number of marriages contracted between Czech nationals and foreign nationals and also between nationals from two different states (not necessarily inside European Union) increases every year while free movement of people is a real practice today. Because these international marriages are becoming more common they bring new problems that must be solved by contemporary law. This regulation needs to result from the knowledge of the children psychology that is affecting family law the most but also has its practical aspects in the area of taxation and payment issues that will be analyzed deeply as well.juridical problems, financial problems, international joint custody, family.
Nonlinear influence of excess Mn on the magnetoelastic transition in (Mn,Cr)<sub>2</sub>Sb
No full textThe influence of excess Mn on the magnetoelastic ferromagnetic-to-antiferromagnetic transition Tt in the magnetocaloric compound (Mn,Cr)2Sb has been studied. With increasing excess Mn the magnetoelastic transition temperature for (Mn,Cr)2Sb initially increases and then decreases. This trend is accompanied by a strong reduction of the (Mn,Cr)Sb secondary phase. With increasing excess Mn a higher Cr content was found in the (Mn,Cr)Sb secondary phase in comparison to the matrix phase. This competition for Cr leads to a nonlinear dependence of Tt with increasing excess Mn at a fixed nominal Cr content. However, we observed that Tt depends linear on the c/a ratio for a wide range of temperatures from 170 to 350 K. A compositional diagram of the c/a ratio was constructed to assist the selection of (Mn,Cr)2Sb alloys with a desired transition temperature.RST/Fundamental Aspects of Materials and Energ
Fabrication and properties of Sb-doped ZnO thin films grown by radio frequency (RF) magnetron sputtering
No full textSb-doped and undoped ZnO thin films were deposited on Si (100) substrates by radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that all the films had polycrystalline wurtzite structure and c-axis preferred orientation. Room temperature Hall measurements showed that the as-grown films were n-type and conducting (rho similar to 1-10 Omega cm). Annealing in a nitrogen ambient at 400 degrees C for 1 h made both samples highly resistive (rho > 10(3) Omega cm). Increasing the annealing temperature up to 800 C, the resistivity of the ttndoped ZnO film decreased gradually, but it increased for the Sb-doped ZnO film. In the end, the Sb-doped ZnO film annealed at 800 C became semi-insulating with a resistivity of 10(4)Omega cm. In addition, the effects of annealing treatment and Sb-doping on the structural and electrical properties are discussed. (c) 2006 Elsevier B.V. All rights reserved
Homologous series of layered structures in binary and ternary Bi-Sb-Te-Se systems: Ab initio study
No full textIn order to account explicitly for the existence of long-periodic layered structures and the strong structural relaxations in the most common binary and ternary alloys of the Bi-Sb-Te-Se system, we have developed a one-dimensional cluster expansion (CE) based on first-principles electronic structure calculations, which accounts for the Bi and Sb bilayer formation. Excellent interlayer distances are obtained with a van der Waals density functional. It is shown that a CE solely based on pair interactions is sufficient to provide an accurate description of the ground-state energies of Bi-Sb-Te-Se binary and ternary systems without making the data set of ab initio calculated structures unreasonably large. For the binary alloys A1?xQx (A=Sb, Bi; Q=Te, Se), a ternary CE yields an almost continuous series of (meta)stable structures consisting of consecutive A bilayers next to consecutive A2Q3 for 00.6, the binary alloy segregates into pure Q and A2Q3. The Bi-Sb system is described by a quaternary CE and is found to be an ideal solid solution stabilized by entropic effects at T?0 K but with an ordered structure of alternating Bi and Sb layers for x=0.5 at T=0 K. A quintuple CE is used for the ternary Bi-Sb-Te system, where stable ternary layered compounds with an arbitrary stacking of Sb2Te3, Bi2Te3, and Te-Bi-Te-Sb-Te quintuple units are found, optionally separated by mixed Bi/Sb bilayers. Electronic properties of the stable compounds were studied taking spin-orbit coupling into account.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
p-type Zn1-xMgxO Films with Sb Doping by Radio-Frequency Magnetron Sputtering
No full textSb-doped Zn1-xMgxO films were grown on c-plane sapphire ubstrates by radio-frequency magnetron sputtering. The p-type conduction of the films (0.05 <= x <= 0.13) was confirmed by Hall measurements, revealing a hole concentration of 10(15)-10(16) cm(-3) and a mobility of 0.6-4.5 cm(2)/V s. A p-n homojunction comprising an undoped ZnO layer and an Sb-doped Zn0.95Mg0.05O layer shows a typical rectifying characteristic. Sb-doped p-type Zn1-xMgxO films also exhibit a changeable wider band gap as a function of x, implying that they can probably be used for fabrication of ZnO-based quantum wells and ultraviolet optoelectronic devices. (c) 2006 American Institute of Physics
The effects of gamma irradiation on electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure
No full textIn this research, we have investigated the electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure before and after Co-60 gamma (gamma)-ray source irradiation with the total dose range of 0-500 kGy at room temperature. Electrical measurements of this structure have been performed using current-voltage (I-V) and capacitance-voltage (C-V) techniques. Experimental results show that the values of the ideality factor obtained from I-V measurements increased and the values of the barrier height obtained from reverse-bias C-V measurements decreased after gamma-irradiation. The results show that the main effect of the radiation is the generation of laterally inhomogeneous defects near the semiconductor surface
Antimony isotopes as indicators of redox reactions in aqueous systems: fractionation during Sb(V) reduction by sulfide and isotope exchange kinetics between dissolved Sb(III) and Sb(V)
Full text linkAntimony (Sb) has a history of being overlooked as an aqueous contaminant. The widespread commercial use of Sb has caused scientists to realize the importance of studying the fate and transport of Sb. For other contaminant elements, stable isotopic ratio measurements have been useful for source tracing and detection of environmentally critical chemical reactions (e.g., Wiederhold 2015). We seek to develop Sb isotopic ratios as tools for detecting and quantifying Sb in the environment. Currently, processes that generate shifts in 123Sb/121Sb are not well studied, though they can be inferred from theory and the isotopic systematics of other elements. To provide a more precise understanding of the drivers of Sb isotope variation, the magnitude of isotopic fractionation for individual reactions must be determined. In this study, we determine the magnitude of isotopic fractionation in environmentally relevant reactions. We use anion exchange resin and hydride generation MC-ICP-MS methods to obtain precise measurements of 123Sb/121Sb. The anion exchange method is also effective for separating Sb(III) from Sb(V).
First, we find that isotopic exchange between aqueous Sb(V) and Sb(III) at higher than natural concentrations (3 mM Sb) is negligible over a timescale of 6 weeks. At the lower concentrations of natural systems, exchange is likely to be much slower. Accordingly, we conclude that kinetic isotope effects that occur during Sb redox reactions are not overprinted by isotopic exchange, which would drive coexisting Sb(III) and Sb(V) toward isotopic equilibrium. Second, we quantified isotopic fractionation during reduction of 8.2 μM aqueous Sb(V) by sulfide to form amorphous Sb2S3. The data mostly conform to a Rayleigh distillation model, with 5 out of 11 data points deviating from the model slightly more than the measurement uncertainty. During experimentation it was found that the dissolved portion contained about 75% Sb(V) and 25% Sb(III). The best-fit model corresponds to an isotopic fractionation factor of 0.9986; Sb2S3 product was lower in 123Sb/121Sb, relative to the dissolved portion. This is a larger magnitude of 123Sb/121Sb shift during Sb(V) reduction than observed by Rouxel et. al. (2003).Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2018-05-01The student, Joel MacKinney, accepted the attached license on 2016-04-22 at 12:55.The student, Joel MacKinney, submitted this Thesis for approval on 2016-04-22 at 13:08.This Thesis was approved for publication on 2016-04-22 at 14:25.DSpace SAF Submission Ingestion Package generated from Vireo submission #9439 on 2016-07-07 at 14:17:55Made available in DSpace on 2016-07-07T21:18:00Z (GMT). No. of bitstreams: 2
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