Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

NASA Astrophysics Data System (ADS)

Kang, Joongoo; Park, Ji-Sang; Stradins, Pauls; Wei, Su-Huai

2017-07-01

Nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent S i2AlP (or S i2ZnS ) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, S i2AlP (or S i2ZnS ) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronic and optical properties of the nonisovalent alloys.

Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

DOE PAGES

Kang, Joongoo; Park, Ji -Sang; Stradins, Pauls; ...

2017-07-13

In this paper, nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent Si 2AlP (or Si 2ZnS) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, Si2AlP (or Si2ZnS) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronicmore » and optical properties of the nonisovalent alloys.« less

Bulk Growth of Wide Band Gap II-VI Compound Semiconductors by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua

1997-01-01

The mechanism of physical vapor transport of II-VI semiconducting compounds was studied both theoretically, using a one-dimensional diffusion model, as well as experimentally. It was found that the vapor phase stoichiometry is critical in determining the vapor transport rate. The experimental heat treatment methods to control the vapor composition over the starting materials were investigated and the effectiveness of the heat treatments was confirmed by partial pressure measurements using an optical absorption technique. The effect of residual (foreign) gas on the transport rate was also studies theoretically by the diffusion model and confirmed experimentally by the measurements of total pressure and compositions of the residual gas. An in-situ dynamic technique for the transport rate measurements and a further extension of the technique that simultaneously measured the partial pressures and transport rates were performed and, for the first time, the experimentally determined mass fluxes were compared with those calculated, without any adjustable parameters, from the diffusion model. Using the information obtained from the experimental transport rate measurements as guideline high quality bulk crystal of wide band gap II-VI semiconductor were grown from the source materials which undergone the same heat treatment methods. The grown crystals were then extensively characterized with emphasis on the analysis of the crystalline structural defects.

Spectroscopic characterization of iron-doped II-VI compounds for laser applications

NASA Astrophysics Data System (ADS)

Martinez, Alan

The middle Infrared (mid-IR) region of the electromagnetic spectrum between 2 and 15 ?m has many features which are of interest to a variety of fields such as molecular spectroscopy, biomedical applications, industrial process control, oil prospecting, free-space communication and defense-related applications. Because of this, there is a demand for broadly tunable, laser sources operating over this spectral region which can be easily and inexpensively produced. II-VI semiconductor materials doped with transition metals (TM) such as Co 2+, Cr2+, or Fe2+ exhibit highly favorable spectroscopic characteristics for mid-IR laser applications. Among these TM dopants, Fe2+ has absorption and emission which extend the farthest into the longer wavelength portion of the mid-IR. Fe2+:II-VI crystals have been utilized as gain elements in laser systems broadly tunable over the 3-5.5 microm range [1] and as saturable absorbers to Q -switch [2] and mode-lock [3] laser cavities operating over the 2.7-3 microm. TM:II-VI laser gain elements can be fabricated inexpensively by means of post-growth thermal diffusion with large homogeneous dopant concentration and good optical quality[4,5]. The work outlined in this dissertation will focus on the spectroscopic characterization of TM-doped II-VI semiconductors. This work can be categorized into three major thrusts: 1) the development of novel laser materials, 2) improving and extending applications of TM:II-VI crystals as saturable absorbers, and 3) fabrication of laser active bulk crystals. Because current laser sources based on TM:II-VI materials do not cover the entire mid-IR spectral region, it is necessary to explore novel laser sources to extend available emissions toward longer wavelengths. The first objective of this dissertation is the spectroscopic characterization of novel ternary host crystals doped with Fe2+ ions. Using crystal field engineering, laser materials can be prepared with emissions placed in spectral regions not

Structural and optical properties of II-VI and III-V compound semiconductors

NASA Astrophysics Data System (ADS)

Huang, Jingyi

This dissertation is on the study of structural and optical properties of some III-V and II-VI compound semiconductors. The first part of this dissertation is a study of the deformation mechanisms associated with nanoindentation and nanoscratching of InP, GaN, and ZnO crystals. The second part is an investigation of some fundamental issues regarding compositional fluctuations and microstructure in GaInNAs and InAlN alloys. In the first part, the microstructure of (001) InP scratched in an atomic force microscope with a small diamond tip has been studied as a function of applied normal force and crystalline direction in order to understand at the nanometer scale the deformation mechanisms in the zinc-blende structure. TEM images show deeper dislocation propagation for scratches along <110> compared to <100>. High strain fields were observed in <100> scratches, indicating hardening due to locking of dislocations gliding on different slip planes. Reverse plastic flow have been observed in <110> scratches in the form of pop-up events that result from recovery of stored elastic strain. In a separate study, nanoindentation-induced plastic deformation has been studied in c-, a-, and m-plane ZnO single crystals and c-plane GaN respectively, to study the deformation mechanism in wurtzite hexagonal structures. TEM results reveal that the prime deformation mechanism is slip on basal planes and in some cases, on pyramidal planes, and strain built up along particular directions. No evidence of phase transformation or cracking was observed in both materials. CL imaging reveals quenching of near band-edge emission by dislocations. In the second part, compositional inhomogeneity in quaternary GaInNAs and ternary InAlN alloys has been studied using TEM. It is shown that exposure to antimony during growth of GaInNAs results in uniform chemical composition in the epilayer, as antimony suppresses the surface mobility of adatoms that otherwise leads to two-dimensional growth and

Interacting quasi-band model for electronic states in compound semiconductor alloys: Zincblende structure

NASA Astrophysics Data System (ADS)

Shinozuka, Yuzo; Oda, Masato

2015-09-01

The interacting quasi-band model proposed for electronic states in simple alloys is extended for compound semiconductor alloys with general lattice structures containing several atoms per unit cell. Using a tight-binding model, a variational electronic wave function for quasi-Bloch states yields a non-Hermitian Hamiltonian matrix characterized by matrix elements of constituent crystals and concentration of constituents. Solving secular equations for each k-state yields the alloy’s energy spectrum for any type of randomness and arbitrary concentration. The theory is used to address III-V (II-VI) alloys with a zincblende lattice with crystal band structures well represented by the sp3s* model. Using the resulting 15 × 15 matrix, the concentration dependence of valence and conduction bands is calculated in a unified scheme for typical alloys: Al1-xGaxAs, GaAs1-xPx, and GaSb1-xPx. Results agree well with experiments and are discussed with respect to the concentration dependence, direct-indirect gap transition, and band-gap-bowing origin.

The New Class of Layered Iii-Vi Diluted Magnetic Semiconductors and Their Magnetic MEASUREMENTS*

NASA Astrophysics Data System (ADS)

Pekarek, T. M.; Maymi, C.; Watson, E.; Fuller, C. L.; Garner, J. L.; Crooker, B. C.; Miotkowski, I.; Ramdas, A. K.

2002-03-01

A new class of diluted magnetic semiconductors (DMS) based on III-VI semiconductor hosts has been studied. To date three III-VI DMS systems have been investigated (Ga1-xMnxS, Ga1-xMnxSe, and Ga1-xFexSe). Magnetization measurements on all three systems will be presented. Recent theoretical calculations (based on a Hamiltonian including crystal-field, spin-orbit, spin-spin, and Zeeman terms) have been made for Ga1-xMnxS showing excellent agreement with the experimental data. This establishes Ga1-xMnxS as the first III-VI DMS to be understood both experimentally and theoretically. This new class of III-VI DMS complements the more extensive work on II-VI DMS and III-V DMS. *Support: Research Corporation Cottrell College Science Awards CC4719, CC4845, and CC4668, FL Space Grant Consortium, NHMFL, Purdue Academic Reimbursement Grant, and NSF No. DMR-99-72196, DMR-99-75887, DMR-01-02699, and ECS-01-29853.

Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

NASA Astrophysics Data System (ADS)

Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

2016-05-01

This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III-V and II-VI wurtzite alloys: cation-substituted Al1- x Ga x N and Ga1- x In x N and anion-substituted CdS1- x Se x and ZnO1- x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

Group I-III-VI.sub.2 semiconductor films for solar cell application

DOEpatents

Basol, Bulent M.; Kapur, Vijay K.

1991-01-01

This invention relates to an improved thin film solar cell with excellent electrical and mechanical integrity. The device comprises a substrate, a Group I-III-VI.sub.2 semiconductor absorber layer and a transparent window layer. The mechanical bond between the substrate and the Group I-III-VI.sub.2 semiconductor layer is enhanced by an intermediate layer between the substrate and the Group I-III-VI.sub.2 semiconductor film being grown. The intermediate layer contains tellurium or substitutes therefor, such as Se, Sn, or Pb. The intermediate layer improves the morphology and electrical characteristics of the Group I-III-VI.sub.2 semiconductor layer.

Chemical trend of exchange coupling in diluted magnetic II-VI semiconductors: Ab initio calculations

NASA Astrophysics Data System (ADS)

Chanier, T.; Virot, F.; Hayn, R.

2009-05-01

We have calculated the chemical trend of magnetic exchange parameters ( Jdd , Nα , and Nβ ) of Zn-based II-VI semiconductors ZnA ( A=O , S, Se, and Te) doped with Co or Mn. We show that a proper treatment of electron correlations by the local spin-density approximation (LSDA)+U method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling Jdd between localized 3d spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band Nα are in good agreement with experiment as well. But the values for Nβ (coupling to doped holes in the valence band) indicate a crossover from weak coupling (for A=Te and Se) to strong coupling (for A=O ) and a localized hole state in ZnO:Mn. This hole localization explains the apparent discrepancy between photoemission and magneto-optical data for ZnO:Mn.

Bioengineered II-VI semiconductor quantum dot-carboxymethylcellulose nanoconjugates as multifunctional fluorescent nanoprobes for bioimaging live cells

NASA Astrophysics Data System (ADS)

Mansur, Alexandra A. P.; Mansur, Herman S.; Mansur, Rafael L.; de Carvalho, Fernanda G.; Carvalho, Sandhra M.

2018-01-01

Colloidal semiconductor quantum dots (QDs) are light-emitting ultra-small nanoparticles, which have emerged as a new class of nanoprobes with unique optical properties for bioimaging and biomedical diagnostic. However, to be used for most biomedical applications the biocompatibility and water-solubility are mandatory that can achieved through surface modification forming QD-nanoconjugates. In this study, semiconductor II-VI quantum dots of type MX (M = Cd, Pb, Zn, X = S) were directly synthesized in aqueous media and at room temperature using carboxymethylcellulose sodium salt (CMC) behaving simultaneously as stabilizing and surface biofunctional ligand. These nanoconjugates were extensively characterized using UV-visible spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, dynamic light scattering and zeta potential. The results demonstrated that the biopolymer was effective on nucleating and stabilizing the colloidal nanocrystals of CdS, ZnS, and PbS with the average diameter ranging from 2.0 to 5.0 nm depending on the composition of the semiconductor core, which showed quantum-size confinement effect. These QD/polysaccharide conjugates showed luminescent activity from UV-visible to near-infrared range of the spectra under violet laser excitation. Moreover, the bioassays performed proved that these novel nanoconjugates were biocompatible and behaved as composition-dependent fluorescent nanoprobes for in vitro live cell bioimaging with very promising perspectives to be used in numerous biomedical applications and nanomedicine.

Optical properties of II-VI structures for solar energy utilization

NASA Astrophysics Data System (ADS)

Schrier, Joshua; Demchenko, Denis; Wang, Lin-Wang

2007-03-01

Although II-VI semiconductor materials are abundant, stable, and have direct band gaps, the band gaps are too large for optimal photovoltaic efficiency. However, staggered band alignments of pairs of these materials, and also the formation of intermediate impurity levels in the band gap (which has been demonstrated to increase the efficiency as compared to both single-junction devices), could be utilized to improve the suitability of these materials for solar energy utilization. Previous theoretical studies of these materials are limited, due to the well-known band gap underestimation by density-functional theory. To calculate the absorption spectra, we utilize a band-corrected planewave pseudopotential approach, which gives agreements of within 0.1 eV of the bulk optical gaps values. In this talk, I will present our work on predicting the optical properties of ZnO/ZnS and ZnO/ZnTe heterostructures, nanostructures, and alloys. This work was supported by U.S. Department of Energy under Contract No.DE-AC02-05CH11231 and used the resources of the National Energy Research Scientific Computing Center.

Semiconductor Alloy Theory.

DTIC Science & Technology

1985-09-27

REPORT & PERIOD COVERED -v Semiconductor Alloy Theory Annual 0) 84-9-1 to 85-8-31 M’) 6. PERFORMING O𔃾G. REPORT NUMBER 7. AUTHOR(@) 8. CONTRACT OR...GRANT NUMBER(s) An-Ban Chen AFOSR-84-0282 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK AREA & W R UNT NUMBERS Auburn...and the effective mass. We generalized the formula for indirect-gap alloys with multiple bands and applied it to SiGe alloy. Our results, correlated

Method of passivating semiconductor surfaces

DOEpatents

Wanlass, Mark W.

1990-01-01

A method of passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.

Recent Progress in Photocatalysis Mediated by Colloidal II-VI Nanocrystals

PubMed Central

Wilker, Molly B; Schnitzenbaumer, Kyle J; Dukovic, Gordana

2012-01-01

The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This review focuses on recent research efforts to understand and control the photocatalytic processes mediated by colloidal II-VI nanocrystalline materials, such as cadmium and zinc chalcogenides. First, we highlight how nanocrystal properties govern the rates and efficiencies of charge-transfer processes relevant to photocatalysis. We then describe the use of nanocrystal catalyst heterostructures for fuel-forming reactions, most commonly H2 generation. Finally, we review the use of nanocrystal photocatalysis as a synthetic tool for metal–semiconductor nano-heterostructures. PMID:24115781

Method of passivating semiconductor surfaces

DOEpatents

Wanlass, M.W.

1990-06-19

A method is described for passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.

Structural and elastic properties of AIBIIIC 2 VI semiconductors

NASA Astrophysics Data System (ADS)

Kumar, V.; Singh, Bhanu P.

2018-01-01

The plane wave pseudo-potential method within density functional theory has been used to calculate the structural and elastic properties of AIBIIIC 2 VI semiconductors. The electronic band structure, density of states, lattice constants (a and c), internal parameter (u), tetragonal distortion (η), energy gap (Eg), and bond lengths of the A-C (dAC) and B-C (dBC) bonds in AIBIIIC 2 VI semiconductors have been calculated. The values of elastic constants (Cij), bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson's ratio (υ), Zener anisotropy factor (A), Debye temperature (ϴD) and G/B ratio have also been calculated. The values of all 15 parameters of CuTlS2 and CuTlSe2 compounds, and 8 parameters of 20 compounds of AIBIIIC 2 VI family, except AgInS2 and AgInSe2, have been calculated for the first time. Reasonably good agreement has been obtained between the calculated, reported and available experimental values.

Surface Charge Transfer Doping via Transition Metal Oxides for Efficient p-Type Doping of II-VI Nanostructures.

PubMed

Xia, Feifei; Shao, Zhibin; He, Yuanyuan; Wang, Rongbin; Wu, Xiaofeng; Jiang, Tianhao; Duhm, Steffen; Zhao, Jianwei; Lee, Shuit-Tong; Jie, Jiansheng

2016-11-22

Wide band gap II-VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices. However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p-n homojunctions and complementary circuits, which are the fundamental components for high-performance devices. Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO 3 , WO 3 , CrO 3 , and V 2 O 5 as dopants. Our calculations revealed that these oxides were capable of drawing electrons from II-VI nanostructures, leading to accumulation of positive charges (holes injection) in the II-VI nanostructures. As a result, Fermi levels of the II-VI nanostructures were shifted toward the valence band regions after surface modifications, along with the large enhancement of work functions. In situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations verified the significant interfacial charge transfer between II-VI nanostructures and surface dopants. Both theoretical calculations and electrical transfer measurements on the II-VI nanostructure-based field-effect transistors clearly showed the p-type conductivity of the nanostructures after surface modifications. Strikingly, II-VI nanowires could undergo semiconductor-to-metal transition by further increasing the SCTD level. SCTD offers the possibility to create a variety of electronic and optoelectronic devices from the II-VI nanostructures via realization of complementary doping.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A Paul [Oakland, CA; Scher, Erik C [San Francisco, CA; Manna, Liberato [Palo Del Collie, IT

2009-05-19

Disclosed herein is a graded core/shell semiconductor nanorod having at least a first segment of a core of a Group II-VI, Group III-V or a Group IV semiconductor, a graded shell overlying the core, wherein the graded shell comprises at least two monolayers, wherein the at least two monolayers each independently comprise a Group II-VI, Group III-V or a Group IV semiconductor.

Study of surface and bulk electronic structure of II-VI semiconductor nanocrystals using Cu as a nanosensor.

PubMed

Grandhi, G Krishnamurthy; Tomar, Renu; Viswanatha, Ranjani

2012-11-27

Efficiency of the quantum dots based solar cells relies on charge transfer at the interface and hence on the relative alignment of the energy levels between materials. Despite a high demand to obtain size specific band offsets, very few studies exist where meticulous methods like photoelectron spectroscopy are used. However, semiconductor charging during measurements could result in indirect and possibly inaccurate measurements due to shift in valence and conduction band position. Here, in this report, we devise a novel method to study the band offsets by associating an atomic like state with the conduction band and hence obtaining an internal standard. This is achieved by doping copper in semiconductor nanocrystals, leading to the development of a characteristic intragap Cu-related emission feature assigned to the transition from the conduction band to the atomic-like Cu d state. Using this transition we determine the relative band alignment of II-VI semiconductor nanocrystals as a function of size in the below 10 nm size regime. The results are in excellent agreement with the available photoelectron spectroscopy data as well as the theoretical data. We further use this technique to study the excitonic band edge variation as a function of temperature in CdSe nanocrystals. Additionally, surface electronic structure of CdSe nanocrystals have been studied using quantitative measurements of absolute quantum yield and PL decay studies of the Cu related emission and the excitonic emission. The role of TOP and oleic acid as surface passivating ligand molecules has been studied for the first time.

Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, Shen; Li, Chao; Scripa, R.; Lehoczky, Sandra L.; Kim, Y. W.; Baird, J. K.; Lin, B.; Ban, Heng; Benmore, Chris

2003-01-01

The objectives of the project are to conduct ground-based experimental and theoretical research on the structural fluctuations and thermophysical properties of molten II-VI compounds to enhance the basic understanding of the existing flight experiments in microgravity materials science programs as well as to study the fundamental heterophase fluctuation phenomena in these melts by: 1) conducting neutron scattering analysis and measuring quantitatively the relevant thermophysical properties of the II-VI melts (such as viscosity, electrical conductivity, thermal diffusivity and density) as well as the relaxation characteristics of these properties to advance the understanding of the structural properties and the relaxation phenomena in these melts and 2) performing theoretical analyses on the melt systems to interpret the experimental results. All the facilities required for the experimental measurements have been procured, installed and tested. It has long been recognized that liquid Te presents a unique case having properties between those of metals and semiconductors. The electrical conductivity for Te melt increases rapidly at melting point, indicating a semiconductor-metal transition. Te melts comprise two features, which are usually considered to be incompatible with each other: covalently bound atoms and metallic-like behavior. Why do Te liquids show metallic behavior? is one of the long-standing issues in liquid metal physics. Since thermophysical properties are very sensitive to the structural variations of a melt, we have conducted extensive thermophysical measurements on Te melt.

Tuning and synthesis of semiconductor nanostructures by mechanical compression

DOEpatents

Fan, Hongyou; Li, Binsong

2015-11-17

A mechanical compression method can be used to tune semiconductor nanoparticle lattice structure and synthesize new semiconductor nanostructures including nanorods, nanowires, nanosheets, and other three-dimensional interconnected structures. II-VI or IV-VI compound semiconductor nanoparticle assemblies can be used as starting materials, including CdSe, CdTe, ZnSe, ZnS, PbSe, and PbS.

Photophysical Properties of II-VI Semiconductor Nanocrystals

NASA Astrophysics Data System (ADS)

Gong, Ke

As it is well known, semiconductor nanocrystals (also called quantum dots, QDs) are being actively pursued for use in many different types of luminescent optical materials. These materials include the active media for luminescence downconversion in artificial lighting, lasers, luminescent solar concentrators and many other applications. Chapter 1 gives general introduction of QDs, which describe the basic physical properties and optical properties. Based on the experimental spectroscopic study, a semiquantitative method-effective mass model is employed to give theoretical prediction and guide. The following chapters will talks about several topics respectively. A predictive understanding of the radiative lifetimes is therefore a starting point for the understanding of the use of QDs for these applications. Absorption intensities and radiative lifetimes are fundamental properties of any luminescent material. Meantime, achievement of high efficiency with high working temperature and heterostructure fabrication with manipulation of lattice strain are not easy and need systematic investigation. To make accurate connections between extinction coefficients and radiative recombination rates, chapter 2 will consider three closely related aspects of the size dependent spectroscopy of II-VI QDs. First, it will consider the existing literature on cadmium selenide (CdSe) QD absorption spectra and extinction coefficients. From these results and fine structure considerations Boltzmann weighted radiative lifetimes are calculated. These lifetimes are compared to values measured on very high quality CdSe and CdSe coated with zinc selenide (ZnSe) shells. Second, analogous literature data are analyzed for cadmium telluride (CdTe) nanocrystals and compared to lifetimes measured for very high quality QDs. Furthermore, studies of the absorption and excitation spectra and measured radiative lifetimes for CdTe/CdSe Type-II core/shell QDs are reported. These results are also analyzed in

Single-particle spectroscopy of I-III-VI semiconductor nanocrystals: spectral diffusion and suppression of blinking by two-color excitation.

PubMed

Sharma, Dharmendar Kumar; Hirata, Shuzo; Bujak, Lukasz; Biju, Vasudevanpillai; Kameyama, Tatsuya; Kishi, Marino; Torimoto, Tsukasa; Vacha, Martin

2016-07-14

Ternary I-III-VI semiconductor nanocrystals have been explored as non-toxic alternatives to II-VI semiconductors for optoelectronic and sensing applications, but large photoluminescence spectral width and moderate brightness restrict their practical use. Here, using single-particle photoluminescence spectroscopy on nanocrystals of (AgIn)xZn2(1-x)S2 we show that the photoluminescence band is inhomogeneously broadened and that size distribution is the dominant factor in the broadening. The residual homogeneous linewidth of individual nanocrystals reaches up to 75% of the ensemble spectral width. Single nanocrystals undergo spectral diffusion which also contributes to the inhomogeneous band. Excitation with two lasers with energies above and below the bandgap reveals coexistence of two emitting donor states within one particle. Spectral diffusion in such particles is due to temporal activation and deactivation of one such state. Filling of a trap state with a lower-energy laser enables optical modulation of photoluminescence intermittency (blinking) and leads to an almost two-fold increase in brightness.

Trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant photovoltaics.

PubMed

Hong, Feng; Lin, Wenjun; Meng, Weiwei; Yan, Yanfa

2016-02-14

We propose trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant solar cell applications. Through density functional theory calculations, we show that these compounds exhibit similar electronic and optical properties to kesterite Cu2ZnSnS4 (CZTS): high optical absorption with band gaps suitable for efficient single-junction solar cell applications. However, the trigonal Cu2-II-Sn-VI4 compounds exhibit defect properties more suitable for photovoltaic applications than those of CZTS. In CZTS, the dominant defects are the deep acceptors, Cu substitutions on Zn sites, which cause non-radiative recombination and limit the open-circuit voltages of CZTS solar cells. On the contrary, the dominant defects in trigonal Cu2-II-Sn-VI4 are the shallow acceptors, Cu vacancies, similar to those in CuInSe2. Our results suggest that the trigonal Cu2-II-Sn-VI4 quaternary compounds could be promising candidates for efficient earth-abundant thin-film solar cell and photoeletrochemical water-splitting applications.

TOPICAL REVIEW: The shallow-to-deep instability of hydrogen and muonium in II VI and III V semiconductors

NASA Astrophysics Data System (ADS)

Cox, S. F. J.

2003-11-01

The structure and electrical activity of monatomic hydrogen defect centres are inferred from the spectroscopy and charge-state transitions of muonium, the light pseudo-isotope of hydrogen. Introductions are given to all these topics. Special attention is paid to the shallow-donor behaviour recently established in a number of II VI compounds and one III nitride. This contrasts with trapped-atom states suggestive of an acceptor function in other members of the II VI family as well as with the deep-level amphoteric behaviour which has long been known in the elemental group-IV semiconductors and certain III V compounds. The systematics of this remarkable shallow-to-deep instability are examined in terms of simple chemical considerations, as well as current theoretical and computational models. The muonium data appear to confirm predictions that the switch from shallow to deep behaviour is governed primarily by the depth of the conduction-band minimum below the vacuum continuum. The threshold electron affinity is around 3.5 eV, which compares favourably with computational estimates of a so-called pinning level for hydrogen (+/-) charge-state transitions of between -3 and -4.5 eV. A purely ionic model gives some intuitive understanding of this behaviour as well as the invariance of the threshold. Another current description applies equally to covalent materials and relates the threshold to the origin of the electrochemical scale. At the present level of approximation, zero-point energy corrections to the transition levels are small, so that muonium data should provide a reliable guide to the behaviour of hydrogen. Muonium spectroscopy proves to be more sensitive to the (0/+) donor level than to the (+/-) pinning level but, as a tool which does not rely on favourable hydrogen solubility, it looks set to test further predictions of these models in a large number of other materials, notably oxides. Certain candidate thin-film insulators and high-permittivity gate

Hybrid bandgap engineering for super-hetero-epitaxial semiconductor materials, and products thereof

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

"Super-hetero-epitaxial" combinations comprise epitaxial growth of one material on a different material with different crystal structure. Compatible crystal structures may be identified using a "Tri-Unity" system. New bandgap engineering diagrams are provided for each class of combination, based on determination of hybrid lattice constants for the constituent materials in accordance with lattice-matching equations. Using known bandgap figures for previously tested materials, new materials with lattice constants that match desired substrates and have the desired bandgap properties may be formulated by reference to the diagrams and lattice matching equations. In one embodiment, this analysis makes it possible to formulate new super-hetero-epitaxial semiconductor systems, such as systems based on group IV alloys on c-plane LaF.sub.3; group IV alloys on c-plane langasite; Group III-V alloys on c-plane langasite; and group II-VI alloys on c-plane sapphire.

Zinc Alloys for the Fabrication of Semiconductor Devices

NASA Technical Reports Server (NTRS)

Ryu, Yungryel; Lee, Tae S.

2009-01-01

ZnBeO and ZnCdSeO alloys have been disclosed as materials for the improvement in performance, function, and capability of semiconductor devices. The alloys can be used alone or in combination to form active photonic layers that can emit over a range of wavelength values. Materials with both larger and smaller band gaps would allow for the fabrication of semiconductor heterostructures that have increased function in the ultraviolet (UV) region of the spectrum. ZnO is a wide band-gap material possessing good radiation-resistance properties. It is desirable to modify the energy band gap of ZnO to smaller values than that for ZnO and to larger values than that for ZnO for use in semiconductor devices. A material with band gap energy larger than that of ZnO would allow for the emission at shorter wavelengths for LED (light emitting diode) and LD (laser diode) devices, while a material with band gap energy smaller than that of ZnO would allow for emission at longer wavelengths for LED and LD devices. The amount of Be in the ZnBeO alloy system can be varied to increase the energy bandgap of ZnO to values larger than that of ZnO. The amount of Cd and Se in the ZnCdSeO alloy system can be varied to decrease the energy band gap of ZnO to values smaller than that of ZnO. Each alloy formed can be undoped or can be p-type doped using selected dopant elements, or can be n-type doped using selected dopant elements. The layers and structures formed with both the ZnBeO and ZnCdSeO semiconductor alloys - including undoped, p-type-doped, and n-type-doped types - can be used for fabricating photonic and electronic semiconductor devices for use in photonic and electronic applications. These devices can be used in LEDs, LDs, FETs (field effect transistors), PN junctions, PIN junctions, Schottky barrier diodes, UV detectors and transmitters, and transistors and transparent transistors. They also can be used in applications for lightemitting display, backlighting for displays, UV and

E-beam-pumped semiconductor lasers

NASA Astrophysics Data System (ADS)

Rice, Robert R.; Shanley, James F.; Ruggieri, Neil F.

1995-04-01

The collapse of the Soviet Union opened many areas of laser technology to the West. E-beam- pumped semiconductor lasers (EBSL) were pursued for 25 years in several Soviet Institutes. Thin single crystal screens of II-VI alloys (ZnxCd1-xSe, CdSxSe1-x) were incorporated in laser CRTs to produce scanned visible laser beams at average powers greater than 10 W. Resolutions of 2500 lines were demonstrated. MDA-W is conducting a program for ARPA/ESTO to assess EBSL technology for high brightness, high resolution RGB laser projection application. Transfer of II-VI crystal growth and screen processing technology is underway, and initial results will be reported. Various techniques (cathodoluminescence, one- and two-photon laser pumping, etc.) have been used to assess material quality and screen processing damage. High voltage (75 kV) video electronics were procured in the U.S. to operate test EBSL tubes. Laser performance was documented as a function of screen temperature, beam voltage and current. The beam divergence, spectrum, efficiency and other characteristics of the laser output are being measured. An evaluation of the effect of laser operating conditions upon the degradation rate is being carried out by a design-of-experiments method. An initial assessment of the projected image quality will be performed.

Bond-strength inversion in (In,Ga)As semiconductor alloys

NASA Astrophysics Data System (ADS)

Eckner, Stefanie; Ritter, Konrad; Schöppe, Philipp; Haubold, Erik; Eckner, Erich; Rensberg, Jura; Röder, Robert; Ridgway, Mark C.; Schnohr, Claudia S.

2018-05-01

The atomic-scale structure and vibrational properties of semiconductor alloys are determined by the energy required for stretching and bending the individual bonds. Using temperature-dependent extended x-ray absorption fine-structure spectroscopy, we have determined the element-specific In-As and Ga-As effective bond-stretching force constants in (In,Ga)As as a function of the alloy composition. The results reveal a striking inversion of the bond strength where the originally stiffer bond in the parent materials becomes the softer bond in the alloy and vice versa. Our findings clearly demonstrate that changes of both the individual bond length and the surrounding matrix affect the bond-stretching force constants. We thus show that the previously used common assumptions about the element-specific force constants in semiconductor alloys do not reproduce the composition dependence determined experimentally for (In,Ga)As.

Surface stability and the selection rules of substrate orientation for optimal growth of epitaxial II-VI semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Wan-Jian; Department of Physics & Astronomy, and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, Ohio 43606; Yang, Ji-Hui

2015-10-05

The surface structures of ionic zinc-blende CdTe (001), (110), (111), and (211) surfaces are systematically studied by first-principles density functional calculations. Based on the surface structures and surface energies, we identify the detrimental twinning appearing in molecular beam epitaxy (MBE) growth of II-VI compounds as the (111) lamellar twin boundaries. To avoid the appearance of twinning in MBE growth, we propose the following selection rules for choosing optimal substrate orientations: (1) the surface should be nonpolar so that there is no large surface reconstructions that could act as a nucleation center and promote the formation of twins; (2) the surfacemore » structure should have low symmetry so that there are no multiple equivalent directions for growth. These straightforward rules, in consistent with experimental observations, provide guidelines for selecting proper substrates for high-quality MBE growth of II-VI compounds.« less

Chemical bath deposition of II-VI compound thin films

NASA Astrophysics Data System (ADS)

Oladeji, Isaiah Olatunde

II-VI compounds are direct bandgap semiconductors with great potentials in optoelectronic applications. Solar cells, where these materials are in greater demand, require a low cost production technology that will make the final product more affordable. Chemical bath deposition (CBD) a low cost growth technique capable of producing good quality thin film semiconductors over large area and at low temperature then becomes a suitable technology of choice. Heterogeneous reaction in a basic aqueous solution that is responsible for the II-VI compound film growth in CBD requires a metal complex. We have identified the stability constant (k) of the metal complex compatible with CBD growth mechanism to be about 106.9. This value is low enough to ensure that the substrate adsorbed complex relax for subsequent reaction with the chalcogen precursor to take place. It is also high enough to minimize the metal ion concentration in the bath participating in the precipitation of the bulk compounds. Homogeneous reaction that leads to precipitation in the reaction bath takes place because the solubility products of bulk II-VI compounds are very low. This reaction quickly depletes the bath of reactants, limit the film thickness, and degrade the film quality. While ZnS thin films are still hard to grow by CBD because of lack of suitable complexing agent, the homogeneous reaction still limits quality and thickness of both US and ZnS thin films. In this study, the zinc tetraammine complex ([Zn(NH3) 4]2+) with k = 108.9 has been forced to acquire its unsaturated form [Zn(NH3)3]2+ with a moderate k = 106.6 using hydrazine and nitrilotriacetate ion as complementary complexing agents and we have successfully grown ZnS thin films. We have also, minimized or eliminated the homogeneous reaction by using ammonium salt as a buffer and chemical bath with low reactant concentrations. These have allowed us to increase the saturation thickness of ZnS thin film by about 400% and raise that of US film

Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Maksimov, A. A.; Yakovlev, D. R.; Debus, J.; Tartakovskii, I. I.; Waag, A.; Karczewski, G.; Wojtowicz, T.; Kossut, J.; Bayer, M.

2010-07-01

The magnetization dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te were studied optically and simulated numerically. In samples with inhomogeneous magnetic ion distribution, these dynamics are contributed by spin-lattice relaxation and spin diffusion in the Mn spin system. A spin-diffusion coefficient of 7×10-8cm2/s was evaluated for Zn0.99Mn0.01Se from comparison of experiment and theory. Calculations of the exciton giant Zeeman splitting and the magnetization dynamics in ordered alloys and digitally grown parabolic quantum wells show perfect agreement with the experimental data. In both structure types, spin diffusion contributes essentially to the magnetization dynamics.

Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures

NASA Technical Reports Server (NTRS)

Ban, H.; Li, C.; Lin, B.; Emoto, K.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The change of the thermal properties of semiconductor melts reflects the structural changes inside the melts, and a fundamental understanding of this structural transformation is essential for high quality semiconductor crystal growth process. This paper focused on the technical development and the measurement of thermal properties of III-VI semiconductor melts at high temperatures. Our previous work has improved the laser flash method for the specialized quartz sample cell. In this paper, we reported the results of our recent progress in further improvements of the measurement system by minimizing the free convection of the melt, adding a front IR detector, and placing the sample cell in a vacuum environment. The results for tellurium and selenium based compounds, some of which have never been reported in the literature, were obtained at different temperatures as a function of time. The data were compared with other measured thermophysical properties to shed light on the structural transformations of the melt.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A. Paul; Scher, Erik C.; Manna, Liberato

2010-12-14

Graded core/shell semiconductor nanorods and shaped nanorods are disclosed comprising Group II-VI, Group III-V and Group IV semiconductors and methods of making the same. Also disclosed are nanorod barcodes using core/shell nanorods where the core is a semiconductor or metal material, and with or without a shell. Methods of labeling analytes using the nanorod barcodes are also disclosed.

Graded core/shell semiconductor nanorods and nanorod barcodes

DOEpatents

Alivisatos, A. Paul; Scher, Erik C.; Manna, Liberato

2013-03-26

Graded core/shell semiconductor nanorods and shapped nanorods are disclosed comprising Group II-VI, Group III-V and Group IV semiconductors and methods of making the same. Also disclosed are nanorod barcodes using core/shell nanorods where the core is a semiconductor or metal material, and with or without a shell. Methods of labeling analytes using the nanorod barcodes are also disclosed.

Multi-crystalline II-VI based multijunction solar cells and modules

DOEpatents

Hardin, Brian E.; Connor, Stephen T.; Groves, James R.; Peters, Craig H.

2015-06-30

Multi-crystalline group II-VI solar cells and methods for fabrication of same are disclosed herein. A multi-crystalline group II-VI solar cell includes a first photovoltaic sub-cell comprising silicon, a tunnel junction, and a multi-crystalline second photovoltaic sub-cell. A plurality of the multi-crystalline group II-VI solar cells can be interconnected to form low cost, high throughput flat panel, low light concentration, and/or medium light concentration photovoltaic modules or devices.

Electronic structure and chemical bonding of the electron-poor II-V semiconductors ZnSb and ZnAs

NASA Astrophysics Data System (ADS)

Benson, Daryn; Sankey, Otto F.; Häussermann, Ulrich

2011-09-01

The binary compounds ZnSb and ZnAs with the CdSb structure are semiconductors (II-V), although the average electron concentration (3.5 per atom) is lower than that of the tetrahedrally bonded III-V and II-VI archetype systems (four per atom). We report a detailed electronic structure and chemical bonding analysis for ZnSb and ZnAs based on first-principles calculations. ZnSb and ZnAs are compared to the zinc blende-type semiconductors GaSb, ZnTe, GaAs, and ZnSe, as well as the more ionic, hypothetical, II-V systems MgSb and MgAs. We establish a clearly covalent bonding scenario for ZnSb and ZnAs where multicenter bonded structural entities (rhomboid rings Zn2Sb2 and Zn2As2) are connected to each other by classical two-center, two-electron bonds. This bonding scenario is only compatible with a weak ionicity in II-V semiconductor systems, and weak ionicity appears as a necessary condition for the stability of the CdSb structure type. It is argued that a chemical bonding scenario with mixed multicenter and two-center bonding resembles that of boron and boron-rich compounds and is typical of electron-poor sp-bonded semiconductors with average valence electron concentrations below four per atom.

Anion Exchange in II-VI Semiconducting Nanostructures via Atomic Templating.

PubMed

Agarwal, Rahul; Krook, Nadia M; Ren, Ming-Liang; Tan, Liang Z; Liu, Wenjing; Rappe, Andrew M; Agarwal, Ritesh

2018-03-14

Controlled chemical transformation of nanostructures is a promising technique to obtain precisely designed novel materials, which are difficult to synthesize otherwise. We report high-temperature vapor-phase anion-exchange reactions to chemically transform II-VI semiconductor nanostructures (100-300 nm length scale) while retaining the single crystallinity, crystal structure, morphology, and even defect distribution of the parent material via atomic templating. The concept of atomic templating is employed to obtain kinetically controlled, thermodynamically metastable structural phases such as zincblende CdSe and CdS from zincblende CdTe upon complete chemical replacement of Te with Se or S. The underlying transformation mechanisms are explained through first-principles density functional theory calculations. Atomic templating is a unique path to independently tune materials' phase and composition at the nanoscale, allowing the synthesis of novel materials.

Macroporous Semiconductors

PubMed Central

Föll, Helmut; Leisner, Malte; Cojocaru, Ala; Carstensen, Jürgen

2010-01-01

Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds of pores obtained in semiconductors like Ge, Si, III-V, and II-VI compound semiconductors are systematically reviewed, emphasizing macropores. Essentials of pore formation mechanisms will be discussed, focusing on differences and some open questions but in particular on common properties. Possible applications of porous semiconductors, including for example high explosives, high efficiency electrodes for Li ion batteries, drug delivery systems, solar cells, thermoelectric elements and many novel electronic, optical or sensor devices, will be introduced and discussed.

Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II-VI Semiconductor Epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Yijun; Rowland, Clare E; Schaller, Richard D

2014-08-26

Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II–VI, III–V and IV–VI semiconductor quantum dots. Here, we use relatively unexplored IV/II–VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch comparedmore » with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II–VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II–VI nanocrystals are reproducibly 1–3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II–VI nanocrystals. We expect this synthetic IV/II–VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.« less

Epitaxial Growth of Cubic Crystalline Semiconductor Alloys on Basal Plane of Trigonal or Hexagonal Crystal

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor)

2011-01-01

Hetero-epitaxial semiconductor materials comprising cubic crystalline semiconductor alloys grown on the basal plane of trigonal and hexagonal substrates, in which misfit dislocations are reduced by approximate lattice matching of the cubic crystal structure to underlying trigonal or hexagonal substrate structure, enabling the development of alloyed semiconductor layers of greater thickness, resulting in a new class of semiconductor materials and corresponding devices, including improved hetero-bipolar and high-electron mobility transistors, and high-mobility thermoelectric devices.

Chemical trends of the luminescence in wide band gap II 1-xMn xVI semimagnetic semiconductors

NASA Astrophysics Data System (ADS)

Benecke, C.; Busse, W.; Gumlich, H.-E.

1990-04-01

Time resolved emission and excitation spectroscopy is used to investigate the Mn correlated luminescence in wide band gap II-VI compounds, i.e. Zn 1-xMn xS, Cd 1-xMn xSe, Zn 1-xMn xTe and Cd 1-xMn xTe. Additional Information has been obtained with CdxZnyMnzTe( x+ y+ z=1) in checking the luminescence by variation of the ratio of the cations Cd and Zn. Generally speaking, at least two distinct emissions bands can be observed for each II 1- xMn xVI compound. One emissions band is attributed to the internal transition 4T 1(G)→ 6A 1(S) of the 3d 5 electron of the Mn 2+ on regular metal sites with energies of about ≈2 eV. The other emission band is found to occur in the near infrared range of about ≈1.3 eV. This emission band is tentatively interpreted as a transition of Mn 2+ ions on interstitial sites or in small Mn chalcogenide clusters, both interpretations assuming cubic symmetry. This model is supported by the existence of low energy excitation bands and by the great similarity of the shape of the two emission bands which lead to comparable Huang-Rhys factors and effective phonon energies. Also the established trend in the experimental data of the II-VI compounds under consideration confirm this interpretation. For both the IR and the yellow Mn 2+ center, the Racah parameters B and C and the crystal field parameter Dq are determined on the basis of experimental data. As a result, the energy of both the emission and the excitation bands is predominantly determined by the sorrounding anions. These bands shift to higher energies when the anions are changed in the fixed order: Te→Se→S. Regularly, there is also a spectral shift when Zn is replaced by Cd, which is smaller than the shift due to the variation of onions.

Integrated Multi-Color Light Emitting Device Made with Hybrid Crystal Structure

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor)

2017-01-01

An integrated hybrid crystal Light Emitting Diode ("LED") display device that may emit red, green, and blue colors on a single wafer. The various embodiments may provide double-sided hetero crystal growth with hexagonal wurtzite III-Nitride compound semiconductor on one side of (0001) c-plane sapphire media and cubic zinc-blended III-V or II-VI compound semiconductor on the opposite side of c-plane sapphire media. The c-plane sapphire media may be a bulk single crystalline c-plane sapphire wafer, a thin free standing c-plane sapphire layer, or crack-and-bonded c-plane sapphire layer on any substrate. The bandgap energies and lattice constants of the compound semiconductor alloys may be changed by mixing different amounts of ingredients of the same group into the compound semiconductor. The bandgap energy and lattice constant may be engineered by changing the alloy composition within the cubic group IV, group III-V, and group II-VI semiconductors and within the hexagonal III-Nitrides.

Integrated Multi-Color Light Emitting Device Made with Hybrid Crystal Structure

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor)

2016-01-01

An integrated hybrid crystal Light Emitting Diode ("LED") display device that may emit red, green, and blue colors on a single wafer. The various embodiments may provide double-sided hetero crystal growth with hexagonal wurtzite III-Nitride compound semiconductor on one side of (0001) c-plane sapphire media and cubic zinc-blended III-V or II-VI compound semiconductor on the opposite side of c-plane sapphire media. The c-plane sapphire media may be a bulk single crystalline c-plane sapphire wafer, a thin free standing c-plane sapphire layer, or crack-and-bonded c-plane sapphire layer on any substrate. The bandgap energies and lattice constants of the compound semiconductor alloys may be changed by mixing different amounts of ingredients of the same group into the compound semiconductor. The bandgap energy and lattice constant may be engineered by changing the alloy composition within the cubic group IV, group III-V, and group II-VI semiconductors and within the hexagonal III-Nitrides.

Modeling of mechanical properties of II-VI materials

NASA Technical Reports Server (NTRS)

Sher, A.; Berding, M. A.; Van Schilfgaarde, M.; Chen, A.-B.; Patrick, R.

1988-01-01

This paper reviews some new developments in the theory of alloy correlations, order-disorder transitions, and solidus phase-transition curves. It is argued that semiconductor alloys are never truly random, and the various phenomena that drive deviations from random arrangements are introduced. Likely consequences of correlations on the ability to fine-tune the lattice match of epitaxial layers to substrates, on vacancy formation, on diffusion, and on vapor-phase crystal growth are discussed. Examples are chosen for the alloys Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, Cd(1-y)Zn(y)Te, and CdSe(1-y)Te(y).

Surface catalysis of uranium(VI) reduction by iron(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liger, E.; Charlet, L.; Van Cappellen, P.

1999-10-01

Colloidal hematite ({alpha}-Fe{sub 2}O{sub 3}) is used as model solid to investigate the kinetic effect of specific adsorption interactions on the chemical reduction of uranyl (U{sup VI}O{sub 2}{sup 2+}) by ferrous iron. Acid-base titrations and Fe(II) and uranyl adsorption experiments are performed on hematite suspensions, under O{sub 2}- and CO{sub 2}-free conditions. The results are explained in terms of a constant capacitance surface complexation model of the hematite-aqueous solution interface. Two distinct Fe(II) surface complexes are required to reproduce the data: ({equivalent{underscore}to}Fe{sup III}OFe{sup II}){sup +} (or {equivalent{underscore}to}Fe{sup III}OFe{sup II}(OH{sub 2}){sub n}{sup +}) and {equivalent{underscore}to}Fe{sup III}OFe{sup II}OH{sup 0} (or {equivalent{underscore}to}Fe{sup III}OFe{supmore » II}(OH{sub 2}){sub n{minus}1}OH{sup 0}). The latter complex represents a significant fraction of total adsorbed Fe(II) at pH {gt} 6.5. Uranyl binding to the hematite particles is characterized by a sharp adsorption edge between pH 4 and pH 5.5. Because of the absence of competing aqueous carbonate complexes, uranyl remains completely adsorbed at pH {gt} 7. A single mononuclear surface complex accounts for the adsorption of uranyl over the entire range of experimental conditions. Although thermodynamically feasible, no reaction between uranyl and Fe(II) is observed in homogeneous solution at pH 7.5, for periods of up to three days. In hematite suspensions, however, surface-bound uranyl reacts on a time scale of hours. Based on Fourier Transformed Infrared spectra, chemical reduction of U(VI) is inferred to be the mechanism responsible for the disappearance of uranyl. The kinetics of uranyl reduction are quantified by measuring the decrease with time of the concentration of U(VI) extractable from the hematite particles by NaHCO{sub 3}. In the presence of excess Fe(II), the initial rate of U(VI) reduction exhibits a first-order dependence on the

Semiconductor structures having electrically insulating and conducting portions formed from an AlSb-alloy layer

DOEpatents

Spahn, Olga B.; Lear, Kevin L.

1998-01-01

A semiconductor structure. The semiconductor structure comprises a plurality of semiconductor layers formed on a substrate including at least one layer of a III-V compound semiconductor alloy comprising aluminum (Al) and antimony (Sb), with at least a part of the AlSb-alloy layer being chemically converted by an oxidation process to form superposed electrically insulating and electrically conducting portions. The electrically insulating portion formed from the AlSb-alloy layer comprises an oxide of aluminum (e.g. Al.sub.2 O.sub.3), while the electrically conducting portion comprises Sb. A lateral oxidation process allows formation of the superposed insulating and conducting portions below monocrystalline semiconductor layers for forming many different types of semiconductor structures having particular utility for optoelectronic devices such as light-emitting diodes, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodetectors and optical modulators (waveguide and surface normal), and for electronic devices such as heterojunction bipolar transistors, field-effect transistors and quantum-effect devices. The invention is expected to be particularly useful for forming light-emitting devices for use in the 1.3-1.6 .mu.m wavelength range, with the AlSb-alloy layer acting to define an active region of the device and to effectively channel an electrical current therein for efficient light generation.

Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

DOEpatents

Mascarenhas, Angelo

2015-07-07

Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mascarenhas, Angelo

Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

Metal-doped semiconductor nanoparticles and methods of synthesis thereof

NASA Technical Reports Server (NTRS)

Ren, Zhifeng (Inventor); Wang, Wenzhong (Inventor); Chen, Gang (Inventor); Dresselhaus, Mildred (Inventor); Poudel, Bed (Inventor); Kumar, Shankar (Inventor)

2009-01-01

The present invention generally relates to binary or higher order semiconductor nanoparticles doped with a metallic element, and thermoelectric compositions incorporating such nanoparticles. In one aspect, the present invention provides a thermoelectric composition comprising a plurality of nanoparticles each of which includes an alloy matrix formed of a Group IV element and Group VI element and a metallic dopant distributed within the matrix.

Metal-doped semiconductor nanoparticles and methods of synthesis thereof

DOEpatents

Ren, Zhifeng [Newton, MA; Chen, Gang [Carlisle, MA; Poudel, Bed [West Newton, MA; Kumar, Shankar [Newton, MA; Wang, Wenzhong [Beijing, CN; Dresselhaus, Mildred [Arlington, MA

2009-09-08

The present invention generally relates to binary or higher order semiconductor nanoparticles doped with a metallic element, and thermoelectric compositions incorporating such nanoparticles. In one aspect, the present invention provides a thermoelectric composition comprising a plurality of nanoparticles each of which includes an alloy matrix formed of a Group IV element and Group VI element and a metallic dopant distributed within the matrix.

P and n-type microcrystalline semiconductor alloy material including band gap widening elements, devices utilizing same

DOEpatents

Guha, Subhendu; Ovshinsky, Stanford R.

1988-10-04

An n-type microcrystalline semiconductor alloy material including a band gap widening element; a method of fabricating p-type microcrystalline semiconductor alloy material including a band gap widening element; and electronic and photovoltaic devices incorporating said n-type and p-type materials.

Chemical routes to nanocrystalline and thin-film III-VI and I-III-VI semiconductors

NASA Astrophysics Data System (ADS)

Hollingsworth, Jennifer Ann

1999-11-01

The work encompasses: (1) catalyzed low-temperature, solution-based routes to nano- and microcrystalline III-VI semiconductor powders and (2) spray chemical vapor deposition (spray CVD) of I-III-VI semiconductor thin films. Prior to this work, few, if any, examples existed of chemical catalysis applied to the synthesis of nonmolecular, covalent solids. New crystallization strategies employing catalysts were developed for the regioselective syntheses of orthorhombic InS (beta-InS), the thermodynamic phase, and rhombohedral InS (R-InS), a new, metastable structural isomer. Growth of beta-InS was facilitated by a solvent-suspended, molten-metal flux in a process similar to the SolutionLiquid-Solid (SLS) growth of InP and GaAs fibers and single-crystal whiskers. In contrast, metastable R-InS, having a pseudo-graphitic layered structure, was prepared selectively when the molecular catalyst, benzenethiol, was present in solution and the inorganic "catalyst" (metal flux) was not present. In the absence of any crystal-growth facilitator, metal flux or benzenethiol, amorphous product was obtained under the mild reaction conditions employed (T ≤ 203°C). The inorganic and organic catalysts permitted the regio-selective syntheses of InS and were also successfully applied to the growth of network and layered InxSey compounds, respectively, as well as nanocrystalline In2S3. Extensive microstructural characterization demonstrated that the layered compounds grew as fullerene-like nanostructures and large, colloidal single crystals. Films of the I-III-VI compounds, CuInS2, CuGaS2, and Cu(In,Ga)S 2, were deposited by spray CVD using the known single-source metalorganic precursor, (Ph3P)2CuIn(SEt)4, a new precursor, (Ph3P)2CuGa(SEt)3, and a mixture of the two precursors, respectively. The CulnS2 films exhibited a variety of microstructures from dense and faceted or platelet-like to porous and dendritic. Crystallographic orientations ranged from strongly [112] to strongly [220

Semiconductor structures having electrically insulating and conducting portions formed from an AlSb-alloy layer

DOEpatents

Spahn, O.B.; Lear, K.L.

1998-03-10

The semiconductor structure comprises a plurality of semiconductor layers formed on a substrate including at least one layer of a III-V compound semiconductor alloy comprising aluminum (Al) and antimony (Sb), with at least a part of the AlSb-alloy layer being chemically converted by an oxidation process to form superposed electrically insulating and electrically conducting portions. The electrically insulating portion formed from the AlSb-alloy layer comprises an oxide of aluminum (e.g., Al{sub 2}O{sub 3}), while the electrically conducting portion comprises Sb. A lateral oxidation process allows formation of the superposed insulating and conducting portions below monocrystalline semiconductor layers for forming many different types of semiconductor structures having particular utility for optoelectronic devices such as light-emitting diodes, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodetectors and optical modulators (waveguide and surface normal), and for electronic devices such as heterojunction bipolar transistors, field-effect transistors and quantum-effect devices. The invention is expected to be particularly useful for forming light-emitting devices for use in the 1.3--1.6 {mu}m wavelength range, with the AlSb-alloy layer acting to define an active region of the device and to effectively channel an electrical current therein for efficient light generation. 10 figs.

Suitability of II-VI semiconductors for photonic applications: common-anion versus common-cation superlattices

NASA Astrophysics Data System (ADS)

Tit, Nacir

2003-12-01

Based on the sp3s tight-binding method, the electronic band strcutures of both common-anion and common-cation II-VI superlattices (SLs) are investigated. As models, we took for the former the case of CdTe/ZnTe(001) SLs where the common anion is confirmed to yield a vanishing or a small valence-band offset (VBO) and the biaxial strain, of course, contributes in the valence-band splittings and yield type-I SLs in most of the studied cases. Whereas, we tok as a second model two different SLs: the ZnS/ZnSe(001) and ZnSe/ZnTe(001) SLs. We have confirmed that the common-cation SLs cannot have a vanishing conduction-band offsets (CBO), as speculated, but rather the CBO could be as large as the VBO. The biaxial strain, again, can participate here in the formation of the band offsets and yield either type-I SLs, as in the case of the ZnS/ZnSe, or type-II SLs, as in the case of ZnSe/ZnTe. Moreover, the reason why some type-II SLs, such as ZnSe/ZnTe(001), could be useful as photonic devices is explained by the tendency of the carriers to confine near the interface as a result of a strong photoluminenscence data and conclusions have been drawn about the strain morpholgy and the structural and optical qualities of the experimental samples.

40 CFR 144.19 - Transitioning from Class II to Class VI.

Code of Federal Regulations, 2011 CFR

2011-07-01

... primary purpose of long-term storage into an oil and gas reservoir must apply for and obtain a Class VI geologic sequestration permit when there is an increased risk to USDWs compared to Class II operations. In... Class II operations and a Class VI permit is required. In order to make this determination the Director...

Semiconductor radiation detector

DOEpatents

Bell, Zane W.; Burger, Arnold

2010-03-30

A semiconductor detector for ionizing electromagnetic radiation, neutrons, and energetic charged particles. The detecting element is comprised of a compound having the composition I-III-VI.sub.2 or II-IV-V.sub.2 where the "I" component is from column 1A or 1B of the periodic table, the "II" component is from column 2B, the "III" component is from column 3A, the "IV" component is from column 4A, the "V" component is from column 5A, and the "VI" component is from column 6A. The detecting element detects ionizing radiation by generating a signal proportional to the energy deposited in the element, and detects neutrons by virtue of the ionizing radiation emitted by one or more of the constituent materials subsequent to capture. The detector may contain more than one neutron-sensitive component.

Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals.

PubMed

Joe-Wong, Claresta; Brown, Gordon E; Maher, Kate

2017-09-05

Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments.

Vapour phase growth and characterization of II-VI mixed crystals

NASA Astrophysics Data System (ADS)

Reddy, D. R.; Reddy, B. K.

1992-02-01

All II-VI semiconductors with melting temperatures well above 1000 degree(s)C and with appreciable congruent vaporization well below their melting temperatures leave little scope for any growth technique except for the slow but efficient vaporphase growth method. Theoretical flaw in diffusion models of vapor phase growth was corrected by Factor and Garrett by incorporating the flow velocity term which otherwise would lead to segregation of constituents. An additional degree of freedom arising from the presence of two components was well utilized to finely control the stoichiometry in binaries. In mixed II-VI systems the components are either three or four, depending on whether the system is a ternary or a quaternary. The added degrees of freedom make it very difficult to control stoichiometry. However, Igaki et al. demonstrated the feasibility of control of stoichiometry in CdSxSe1-x. In this paper, a self-sealing vaporphase growth technique used for both ternary and quaternary system is described. The systems studied are CdSxSe1-x, (ZnSe)x(CdTe)1-x and (ZnTe)x(CdSe)1-x. Results on growth mechanism, miscibility, structure, band gap variation, conductivity type variation with 'x' and transport properties are presented in a comparative way and discussed. CdSxSe1-x system in the entire 'X' has the same crystal structure and type of conductivity. The second system has the same zincblend structure but the type of conductivity is very sensitive to thermal treatment. In the last system both structure and types of conductivity are different. The discontinuities in properties associated with this divergent end compound are presented and discussed. Among the physical properties/parameters studied crystal structure, bandgap and nature of conductivity are tailorable, and magnitudes of conductivity and dielectric properties are very difficult to control in the crystals grown by this vapor phase method.

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Burger, Arnold; Dudley, Michael; Matyi, Richard J.; Ramachandran, Narayanan; Sha, Yi-Gao; Volz, Martin; Shih, Hung-Dah

1998-01-01

Interest in optical devices which can operate in the visible spectrum has motivated research interest in the II-VI wide band gap semiconductor materials. The recent challenge for semiconductor opto-electronics is the development of a laser which can operate at short visible wavelengths, In the past several years, major advances in thin film technology such as molecular beam epitaxy and metal organic chemical vapor deposition have demonstrated the applicability of II-VI materials to important devices such as light-emitting diodes, lasers, and ultraviolet detectors.The demonstration of its optical bistable properties in bulk and thin film forms also make ZnSe a possible candidate material for the building blocks of a digital optical computer. Despite this, developments in the crystal growth of bulk II-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology. The electrical and optical properties of semiconductor materials depend on the native point defects, (the deviation from stoichiometry), and the impurity or dopant distribution. To date, the bulk growth of ZnSe substrates has been plagued with problems related to defects such as non-uniform distributions of native defects, impurities and dopants, lattice strain, dislocations, grain boundaries, and second phase inclusions which greatly effect the device performance. In the bulk crystal growth of some technologically important semiconductors, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials.

β-FeSi II as a Kankyo (environmentally friendly) semiconductor for solar cells in the space application

NASA Astrophysics Data System (ADS)

Makita, Yunosuke; Ootsuka, Teruhisa; Fukuzawa, Yasuhiro; Otogawa, Naotaka; Abe, Hironori; Liu, Zhengxin; Nakayama, Yasuhiko

2006-04-01

β-FeSi II defined as a Kankyo (Environmentally Friendly) semiconductor is regarded as one of the 3-rd generation semiconductors after Si and GaAs. Versatile features about β-FeSi II are, i) high optical absorption coefficient (>10 5cm -1), ii) chemical stability at temperatures as high as 937°C, iii) high thermoelectric power (Seebeck coefficient of k ~ 10 -4/K), iv) a direct energy band-gap of 0.85 eV, corresponding to 1.5μm of quartz optical fiber communication, v) lattice constant nearly well-matched to Si substrate, vi) high resistance against the humidity, chemical attacks and oxidization. Using β-FeSi II films, one can fabricate various devices such as Si photosensors, solar cells and thermoelectric generators that can be integrated basically on Si-LSI circuits. β-FeSi II has high resistance against the exposition of cosmic rays and radioactive rays owing to the large electron-empty space existing in the electron cloud pertinent to β-FeSi II. Further, the specific gravity of β-FeSi II (4.93) is placed between Si (2.33) and GaAs ((5.33). These features together with the aforementioned high optical absorption coefficient are ideal for the fabrication of solar cells to be used in the space. To demonstrate fascinating capabilities of β-FeSi II, one has to prepare high quality β-FeSi II films. We in this report summarize the current status of β-FeSi II film preparation technologies. Modified MBE and facing-target sputtering (FTS) methods are principally discussed. High quality β-FeSi II films have been formed on Si substrates by these methods. Preliminary structures of n-β-FeSi II /p-Si and p-β-FeSi II /n-Si solar cells indicated an energy conversion efficiency of 3.7%, implying that β-FeSi II is practically a promising semiconductor for a photovoltaic device.

Overcoming Limitations in Semiconductor Alloy Design

NASA Astrophysics Data System (ADS)

Christian, Theresa Marie

Inorganic semiconductors provide an astonishingly versatile, robust, and efficient platform for optoelectronic energy conversion devices. However, conventional alloys and growth regimes face materials challenges that restrict the full potential of these devices. Novel alloy designs based on isoelectronic co-doping, metamorphic growth and controllable atomic ordering offer new pathways to practical and ultra-high-efficiency optoelectronic devices including solar cells and light-emitting diodes. Abnormal isoelectronic alloys of GaP1-xBix, GaP 1-x-yBixNy, and GaAs1-xBix with unprecedented bismuth incorporation fractions and crystalline quality are explored in this thesis research. Comparative studies of several GaP1-xBix and GaP1-x-yBixNy alloys demonstrate that the site-specific incorporation of bismuth during epitaxial growth is sensitive to growth temperature and has dramatic effects on carrier transfer processes in these alloys. Additionally, distinctive bismuth-related localized states are spectrally identified for the first time in samples of GaAs1-xBix grown by laser-assisted epitaxial growth. These results address fundamental questions about the nature of bismuth-bismuth inter-impurity interactions. Finally, a metamorphic growth strategy for a novel light-emitting diode (LED) design is also discussed. This work utilized direct-bandgap AlxIn1-xP active layers with atomic ordering-based electron confinement to improve emission in the yellow and green spectral regions, where incumbent technologies are least effective, and demonstrated the feasibility of non-lattice-matched LED active materials for visible light emission.

Differential distribution of annexins-I, -II, -IV, and -VI in synovium.

PubMed Central

Goulding, N J; Dixey, J; Morand, E F; Dodds, R A; Wilkinson, L S; Pitsillides, A A; Edwards, J C

1995-01-01

OBJECTIVES--To examine the distribution of four annexins in non-inflamed rheumatoid arthritic and osteoarthritic synovial tissue. METHODS--Frozen sections were stained with monoclonal antibodies (MAb) specific for annexins-I, -II, -IV, and -VI, and for cell lineage related markers including CD68 and CD14 (macrophages), prolyl hydroxylase (fibroblasts), and CD3 (T cells). RESULTS--Each of the annexins was present in synovial tissues in significant amounts in the three groups studied. Annexin-I was predominantly found within the synovial lining layer and double labelling showed it to be present predominantly in cells of the macrophage lineage. In rheumatoid specimens there was increased staining within the lining layer, perivascularly and on macrophages within the tissue stroma. Annexin-II was present in a distribution similar to that of annexin-I, but with more prominent perivascular staining. Annexins-IV and -VI were seen chiefly in association with areas of lymphocyte infiltration in rheumatoid tissue, whereas annexins-I and -II were absent from these areas. Endothelial cells stained weakly positive for annexins-I and -II, and more strongly for -IV and -VI. CONCLUSIONS--This study demonstrates that annexins (particularly annexin-I, a putative mediator of the anti-inflammatory activities of glucocorticoids) are abundant in rheumatoid and non-rheumatoid synovial tissue, annexins-IV and -VI having a distribution distinct from that of -I and -II. Images PMID:7492225

Transforming common III-V/II-VI insulating building blocks into topological heterostructure via the intrinsic electric polarization

NASA Astrophysics Data System (ADS)

Zunger, Alex; Zhang, Xiuwen; Abdalla, Leonardo; Liu, Qihang

Currently known topological insulators (TIs) are limited to narrow gap compounds incorporating heavy elements, thus severely limiting the material pool available for such applications. We show how a heterovalent superlattice made of common semiconductor building blocks can transform its non-TI components into a topological heterostructure. The heterovalent nature of such interfaces sets up, in the absence of interfacial atomic exchange, a natural internal electric field that along with the quantum confinement leads to band inversion, transforming these semiconductors into a topological phase while also forming a giant Rashba spin splitting. We demonstrate this paradigm of designing TIs from ordinary semiconductors via first-principle calculations on III-V/II-VI superlattice InSb/CdTe. We illustrate the relationship between the interfacial stability and the topological transition, finding a ``window of opportunity'' where both conditions can be optimized. This work illustrates the general principles of co-evaluation of TI functionality with thermodynamic stability as a route of identifying realistic combination of common insulators that could produce topological heterostructures. This work was supported by Basic Energy Science, MSE division (Grant DE-FG02-13ER46959).

ECG-ViEW II, a freely accessible electrocardiogram database

PubMed Central

Park, Man Young; Lee, Sukhoon; Jeon, Min Seok; Yoon, Dukyong; Park, Rae Woong

2017-01-01

The Electrocardiogram Vigilance with Electronic data Warehouse II (ECG-ViEW II) is a large, single-center database comprising numeric parameter data of the surface electrocardiograms of all patients who underwent testing from 1 June 1994 to 31 July 2013. The electrocardiographic data include the test date, clinical department, RR interval, PR interval, QRS duration, QT interval, QTc interval, P axis, QRS axis, and T axis. These data are connected with patient age, sex, ethnicity, comorbidities, age-adjusted Charlson comorbidity index, prescribed drugs, and electrolyte levels. This longitudinal observational database contains 979,273 electrocardiograms from 461,178 patients over a 19-year study period. This database can provide an opportunity to study electrocardiographic changes caused by medications, disease, or other demographic variables. ECG-ViEW II is freely available at http://www.ecgview.org. PMID:28437484

Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

NASA Technical Reports Server (NTRS)

Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Ramdas, A.; Su, Ching-Hua; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(x)V(1-x), alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(x),V(1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(x)Te(l-x) and ZnSe(Y)Te(1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(y)Te(1-y) alloys in the entire composition range, 0 less than or equal to y less than or equal to 1. The samples used in this study are bulk ZnSe(y)Te(1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between

Control of GaAs Microwave Schottky Diode Electrical Characteristics by Contact Geometry: The Gap Diode.

DTIC Science & Technology

1982-05-01

semiconductor Schottky-barrier contacts are used in many semiconductor devices, including switches, rectifiers, varactors , IMPATTs, mixer and detector...ionic materials such as most of the II-VI compound semiconductors (e.g. ZnS and ZnO) and the transition-metal oxides , the barrier height is strongly...the alloying process described above is nonuniformity, due to the incomplete removal of residual surface oxides prior to the evaporation of the metal

Continuous flow operation with appropriately adjusting composites in influent for recovery of Cr(VI), Cu(II) and Cd(II) in self-driven MFC-MEC system.

PubMed

Li, Ming; Pan, Yuzhen; Huang, Liping; Zhang, Yong; Yang, Jinhui

2017-03-01

A self-driven microbial fuel cell (MFC) - microbial electrolysis cell (MEC) system, where electricity generated from MFCs is in situ utilized for powering MECs, has been previously reported for recovering Cr(VI), Cu(II) and Cd(II) with individual metals fed in different units of the system in batch operation. Here it was advanced with treating synthetic mixed metals' solution at appropriately adjusting composites in fed-batch and continuous flow operations for complete separation of Cr(VI), Cu(II) and Cd(II) from each other. Under an optimal condition of hydraulic residence time of 4 h, matching of two serially connected MFCs with one MEC, and fed with a composite of either 5 mg L -1 Cr(VI), 1 mg L -1 Cu(II) and 5 mg L -1 Cd(II), or 1 mg L -1 Cr(VI), 5 mg L -1 Cu(II) and 5 mg L -1 Cd(II), the self-driven MFC-MEC system can completely and sequentially recover Cu(II), Cr(VI) and Cd(II) from mixed metals. This study provides a true sustainable and zero-energy-consumed approach of using bioelectrochemical systems for completely recovering and separating Cr(VI), Cu(II) and Cd(II) from each other or from wastes or contaminated sites.

Radiative d–d transitions at tungsten centers in II–VI semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ushakov, V. V., E-mail: ushakov@lebedev.ru; Krivobok, V. S.; Pruchkina, A. A.

2017-03-15

The luminescence spectra of W impurity centers in II–VI semiconductors, specifically, ZnSe, CdS, and CdSe, are studied. It is found that, if the electron system of 5d (W) centers is considered instead of the electron system of 3d (Cr) centers, the spectral characteristics of the impurity radiation are substantially changed. The electron transitions are identified in accordance with Tanabe–Sugano diagrams of crystal field theory. With consideration for the specific features of the spectra, it is established that, in the crystals under study, radiative transitions at 5d W centers occur between levels with different spins in the region of a weakmore » crystal field.« less

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Brebrick, Robert F.; Burger, Arnold; Dudley, Michael; Matyi, Richard J.; Ramachandran, Narayanan; Sha, Yi-Gao; Volz, Martin; Shih, Hung-Dah

2000-01-01

Interest in optical devices which can operate in the visible spectrum has motivated research interest in the II-VI wide band gap semiconductor materials. The recent challenge for semiconductor opto-electronics is the development of a laser which can operate at short visible wavelengths. In the past several years, major advances in thin film technology such as molecular beam epitaxy and metal organic chemical vapor deposition have demonstrated the applicability of II-VI materials to important devices such as light-emitting diodes, lasers, and ultraviolet detectors. With an energy gap of 2.7 eV at room temperature, and an efficient band- to-band transition, ZnSe has been studied extensively as the primary candidate for a blue light emitting diode for optical displays, high density recording, and military communications. By employing a ternary or quaternary system, the energy band gap of II-VI materials can be tuned to a specific range. While issues related to the compositional inhomogeneity and defect incorporation are still to be fully resolved, ZnSe bulk crystals and ZnSe-based heterostructures such as ZnSe/ZnSeS, ZnSe/ZnCdSe and ZnCdSe/ZnSeS have showed photopumped lasing capability in the blue-green region at a low threshold power and high temperatures. The demonstration of its optical bistable properties in bulk and thin film forms also make ZnSe a possible candidate material for the building blocks of a digital optical computer. Despite this, developments in the crystal growth of bulk H-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology.

Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

NASA Technical Reports Server (NTRS)

Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

2001-01-01

Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the

30 CFR 57.22232 - Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines). 57.22232 Section 57.22232 Mineral Resources MINE SAFETY AND HEALTH....22232 Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines). If methane reaches 0.5...

IV-VI semiconductor lasers for gas phase biomarker detection

NASA Astrophysics Data System (ADS)

McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

2007-09-01

A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

In vitro evaluation of bioremediation capacity of a commercial probiotic, Bacillus coagulans, for chromium (VI) and lead (II) toxicity.

PubMed

Belapurkar, Pranoti; Goyal, Pragya; Kar, Anand

2016-01-01

The bioaccumulation of heavy metals including chromium (VI) (Cr (VI)) and lead (II) (Pb (II)) causes fatal toxicity in humans. Some naturally occurring bacterial genera such as Bacillus and Pseudomonas help in bioremediation of these heavy metals and some of the species of Bacillus are proven probiotics. However, no study has been conducted on Bacillus coagulans , which is a proven probiotic species of genus Bacillus . The primary objective of the present study was to assess the potential of a proven probiotic, B. coagulans , marketed as "Sporlac-DS," to survive in the presence of Cr (VI) and Pb (II) and its ability to reduce its concentration in vitro . The Minimum inhibitory concentration (MIC) of the organism for Cr (VI) and Pb (II) was determined followed by its biochemical and morphological characterization. Its antibiotic sensitivity and probiotic efficacy were assessed. Further, its bioremediation capacity was observed in vitro by determining the residual Cr (VI) and Pb (II) concentration after 72 h. B. coagulans could tolerate up to 512 ppm concentration of Cr (VI) and had an MIC of 128 ppm for Pb (II). After 72 h, the organism reduced 32 ppm Cr (VI) and 64 ppm Pb (II) by 93% and 89%, respectively. When B. coagulans was studied before and after growing on Cr (VI) and Pb (II) for 24 h, an increase was seen in sensitivity toward the tested antibiotics whereas no change was observed in morphological and biochemical characters. It also showed no change in their bile and acid tolerance, indicating that it retains its probiotic efficacy. The tested probiotic B. coagulans may have a potential role in bioremediation of Cr (VI) and Pb (II), in vivo .

Electrochemical photovoltaic cell having ternary alloy film

DOEpatents

Russak, Michael A.

1984-01-01

A thin film compound semiconductor electrode comprising CdSe.sub.1-x Te.sub.x (0.ltoreq.x.ltoreq.1) is deposited on a transparent conductive substrate. An electrolyte contacts the film to form a photoactive site. The semiconductor material has a narrow energy bandgap permitting high efficiency for light conversion. The film may be fabricated by: (1) co-evaporation of two II-VI group compounds with a common cation, or (2) evaporation of three elements, concurrenty.

In vitro evaluation of bioremediation capacity of a commercial probiotic, Bacillus coagulans, for chromium (VI) and lead (II) toxicity

PubMed Central

Belapurkar, Pranoti; Goyal, Pragya; Kar, Anand

2016-01-01

Introduction: The bioaccumulation of heavy metals including chromium (VI) (Cr (VI)) and lead (II) (Pb (II)) causes fatal toxicity in humans. Some naturally occurring bacterial genera such as Bacillus and Pseudomonas help in bioremediation of these heavy metals and some of the species of Bacillus are proven probiotics. However, no study has been conducted on Bacillus coagulans, which is a proven probiotic species of genus Bacillus. Objectives: The primary objective of the present study was to assess the potential of a proven probiotic, B. coagulans, marketed as “Sporlac-DS,” to survive in the presence of Cr (VI) and Pb (II) and its ability to reduce its concentration in vitro. Materials and Methods: The Minimum inhibitory concentration (MIC) of the organism for Cr (VI) and Pb (II) was determined followed by its biochemical and morphological characterization. Its antibiotic sensitivity and probiotic efficacy were assessed. Further, its bioremediation capacity was observed in vitro by determining the residual Cr (VI) and Pb (II) concentration after 72 h. Results: B. coagulans could tolerate up to 512 ppm concentration of Cr (VI) and had an MIC of 128 ppm for Pb (II). After 72 h, the organism reduced 32 ppm Cr (VI) and 64 ppm Pb (II) by 93% and 89%, respectively. When B. coagulans was studied before and after growing on Cr (VI) and Pb (II) for 24 h, an increase was seen in sensitivity toward the tested antibiotics whereas no change was observed in morphological and biochemical characters. It also showed no change in their bile and acid tolerance, indicating that it retains its probiotic efficacy. Conclusion: The tested probiotic B. coagulans may have a potential role in bioremediation of Cr (VI) and Pb (II), in vivo. PMID:28216949

Polyethylene imine modified hydrochar adsorption for chromium (VI) and nickel (II) removal from aqueous solution.

PubMed

Shi, Yuanji; Zhang, Tao; Ren, Hongqiang; Kruse, Andrea; Cui, Ruofan

2018-01-01

An adsorbent hydrochar was synthesized from corn cobs and modified with polyethylene imine (PEI). The hydrochars before and after modification were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis. FTIR and XPS revealed that the PEI was grafted onto the hydrochar via ether and imine bonds formed with glutaraldehyde. The maximum adsorption capacities for Cr(VI) (33.663mg/g) and Ni(II) (29.059mg/g) on the modified hydrochars were 365% and 43.7% higher, respectively, than those on the unmodified hydrochar. A pseudo-second-order model described the adsorption of Ni(II) and Cr(VI) on all the adsorbents. The adsorption of Cr(VI) was endothermic, spontaneous, increased disorder, and obeyed the Langmuir model. By contrast, the adsorption of Ni(II) was exothermic, spontaneous, decreased disorder, and obeyed the Freundlich model. XPS confirmed that the adsorption sites and mechanisms for Ni(II) and Cr(VI) on the modified hydrochars were different. Copyright © 2017 Elsevier Ltd. All rights reserved.

Phonon structures of GaN-based random semiconductor alloys

NASA Astrophysics Data System (ADS)

Zhou, Mei; Chen, Xiaobin; Li, Gang; Zheng, Fawei; Zhang, Ping

2017-12-01

Accurate modeling of thermal properties is strikingly important for developing next-generation electronics with high performance. Many thermal properties are closely related to phonon dispersions, such as sound velocity. However, random substituted semiconductor alloys AxB1-x usually lack translational symmetry, and simulation with periodic boundary conditions often requires large supercells, which makes phonon dispersion highly folded and hardly comparable with experimental results. Here, we adopt a large supercell with randomly distributed A and B atoms to investigate substitution effect on the phonon dispersions of semiconductor alloys systematically by using phonon unfolding method [F. Zheng, P. Zhang, Comput. Mater. Sci. 125, 218 (2016)]. The results reveal the extent to which phonon band characteristics in (In,Ga)N and Ga(N,P) are preserved or lost at different compositions and q points. Generally, most characteristics of phonon dispersions can be preserved with indium substitution of gallium in GaN, while substitution of nitrogen with phosphorus strongly perturbs the phonon dispersion of GaN, showing a rapid disintegration of the Bloch characteristics of optical modes and introducing localized impurity modes. In addition, the sound velocities of both (In,Ga)N and Ga(N,P) display a nearly linear behavior as a function of substitution compositions. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-80481-0.

A first principles investigation of electron transfer between Fe(II) and U(VI) on insulating Al- vs. semiconducting Fe-oxide surfaces via the proximity effect

NASA Astrophysics Data System (ADS)

Taylor, S. D.; Marcano, M. C.; Becker, U.

2017-01-01

This study investigates how the intrinsic chemical and electronic properties of mineral surfaces and their associated electron transfer (ET) pathways influence the reduction of U(VI) by surface-associated Fe(II). Density functional theory (DFT), including the Hubbard U correction to the exchange-correlation functional, was used to investigate sorption/redox reactions and ET mechanisms between Fe(II) and U(VI) coadsorbed on isostructural, periodic (0 0 1) surfaces of the insulator corundum (α-Al2O3) vs. the semiconductor hematite (α-Fe2O3). Furthermore, the coadsorbed Fe(II) and U(VI) ions are spatially separated from one another on the surfaces (⩾5.9 Å) to observe whether electronic-coupling through the semiconducting hematite surface facilitates ET between the adsorbates, a phenomenon known as the proximity effect. The calculations show that the different chemical and electronic properties between the isostructural corundum and hematite (0 0 1) surfaces lead to considerably different ET mechanisms between Fe(II) and U(VI). ET on the insulating corundum (0 0 1) surface is limited by the adsorbates' structural configuration. When Fe(II) and U(VI) are spatially separated and do not directly interact with one another (e.g. via an inner-sphere complex), U(VI) reduction by Fe(II) cannot occur as there is no physical pathway enabling ET between the adsorbates. In contrast to the insulating corundum (0 0 1) surface, the hematite (0 0 1) surface can potentially participate in ET reactions due to the high number of electron acceptor sites from the Fe d-states near the Fermi level at the hematite surface. The adsorption of Fe(II) also introduces d-states near the Fermi level as well as shifts unoccupied d-states of the Fe cations at the hematite surface to lower energies, making the surface more conductive. In turn, electronic coupling through the surface can link the spatially separated adsorbates to one another and provide distinct ET pathways for an electron from Fe(II

Single-layer group IV-V and group V-IV-III-VI semiconductors: Structural stability, electronic structures, optical properties, and photocatalysis

NASA Astrophysics Data System (ADS)

Lin, Jia-He; Zhang, Hong; Cheng, Xin-Lu; Miyamoto, Yoshiyuki

2017-07-01

Recently, single-layer group III monochalcogenides have attracted both theoretical and experimental interest at their potential applications in photonic devices, electronic devices, and solar energy conversion. Excited by this, we theoretically design two kinds of highly stable single-layer group IV-V (IV =Si ,Ge , and Sn; V =N and P) and group V-IV-III-VI (IV =Si ,Ge , and Sn; V =N and P; III =Al ,Ga , and In; VI =O and S) compounds with the same structures with single-layer group III monochalcogenides via first-principles simulations. By using accurate hybrid functional and quasiparticle methods, we show the single-layer group IV-V and group V-IV-III-VI are indirect bandgap semiconductors with their bandgaps and band edge positions conforming to the criteria of photocatalysts for water splitting. By applying a biaxial strain on single-layer group IV-V, single-layer group IV nitrides show a potential on mechanical sensors due to their bandgaps showing an almost linear response for strain. Furthermore, our calculations show that both single-layer group IV-V and group V-IV-III-VI have absorption from the visible light region to far-ultraviolet region, especially for single-layer SiN-AlO and SnN-InO, which have strong absorption in the visible light region, resulting in excellent potential for solar energy conversion and visible light photocatalytic water splitting. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting.

Simultaneous removal of Cu(II) and Cr(VI) by Mg-Al-Cl layered double hydroxide and mechanism insight.

PubMed

Yue, Xianyang; Liu, Weizhen; Chen, Zuliang; Lin, Zhang

2017-03-01

Mg-Al-Cl layered double hydroxide (Cl-LDH) was prepared to simultaneously remove Cu(II) and Cr(VI) from aqueous solution. The coexisting Cu(II) (20mg/L) and Cr(VI) (40mg/L) were completely removed within 30min by Cl-LDH in a dosage of 2.0g/L; the removal rate of Cu(II) was accelerated in the presence of Cr(VI). Moreover, compared with the adsorption of single Cu(II) or Cr(VI), the adsorption capacities of Cl-LDH for Cu(II) and Cr(VI) can be improved by 81.05% and 49.56%, respectively, in the case of coexisting Cu(II) (200mg/L) and Cr(VI) (400mg/L). The affecting factors (such as solution initial pH, adsorbent dosage, and contact time) have been systematically investigated. Besides, the changes of pH values and the concentrations of Mg 2+ and Al 3+ in relevant solutions were monitored. To get the underlying mechanism, the Cl-LDH samples before and after adsorption were thoroughly characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. On the basis of these analyses, a possible mechanism was proposed. The coadsorption process involves anion exchange of Cr(VI) with Cl - in Cl-LDH interlayer, isomorphic substitution of Mg 2+ with Cu 2+ , formation of Cu 2 Cl(OH) 3 precipitation, and the adsorption of Cr(VI) by Cu 2 Cl(OH) 3 . This work provides a new insight into simultaneous removal of heavy metal cations and anions from wastewater by Cl-LDH. Copyright © 2016. Published by Elsevier B.V.

Sorption of Cr(VI), Cu(II) and Pb(II) by growing and non-growing cells of a bacterial consortium.

PubMed

Sannasi, P; Kader, J; Ismail, B S; Salmijah, S

2006-03-01

This paper reports the sorption of three metallic ions, namely Cr(VI), Cu(II) and Pb(II) in aqueous solution by a consortium culture (CC) comprising an acclimatised mixed bacterial culture collected from point and non-point sources. Metal sorption capability of growing and non-growing cells at initial pH of between 3 and 8 in the 1-100mg/L concentration range were studied based on Q(max) and K(f) values of the Langmuir and linearised Freundlich isotherm models, respectively. Maximal metal loading was generally observed to be dependent on the initial pH. Growing cells displayed significant maximal loading (Q(max)) for Pb(II) (238.09 mg/g) and Cu(II) (178.87 mg/g) at pH 6 and at pH 7 for Cr(VI) (90.91 mg/g) compared to non-growing cells (p < 0.05). At the pH range of 6-8, growing cells showed higher loading capacity compared to non-growing cells i.e. 38-52% for Cr, 17-28% for Cu and 3-17% for Pb. At lower metal concentrations and at more acidic pH (3-4) however, non-growing cells had higher metal loading capacity than growing cells. The metal sorption capacity for both populations were as follows: Pb(II) > Cu(II) > Cr(VI).

The stochastic model for ternary and quaternary alloys: Application of the Bernoulli relation to the phonon spectra of mixed crystals

NASA Astrophysics Data System (ADS)

Marchewka, M.; Woźny, M.; Polit, J.; Kisiel, A.; Robouch, B. V.; Marcelli, A.; Sheregii, E. M.

2014-03-01

To understand and interpret the experimental data on the phonon spectra of the solid solutions, it is necessary to describe mathematically the non-regular distribution of atoms in their lattices. It appears that such description is possible in case of the strongly stochastically homogenous distribution which requires a great number of atoms and very carefully mixed alloys. These conditions are generally fulfilled in case of high quality homogenous semiconductor solid solutions of the III-V and II-VI semiconductor compounds. In this case, we can use the Bernoulli relation describing probability of the occurrence of one n equivalent event which can be applied, to the probability of finding one from n configurations in the solid solution lattice. The results described in this paper for ternary HgCdTe and GaAsP as well as quaternary ZnCdHgTe can provide an affirmative answer to the question: whether stochastic geometry, e.g., the Bernoulli relation, is enough to describe the observed phonon spectra.

Localization-delocalization transition of electrons at the percolation threshold of semiconductor GaAs1-xNx alloys: The appearance of a mobility edge

NASA Astrophysics Data System (ADS)

Alberi, K.; Fluegel, B.; Beaton, D. A.; Ptak, A. J.; Mascarenhas, A.

2012-07-01

Electrons in semiconductor alloys have generally been described in terms of Bloch states that evolve from constructive interference of electron waves scattering from perfectly periodic potentials, despite the loss of structural periodicity that occurs on alloying. Using the semiconductor alloy GaAs1-xNx as a prototype, we demonstrate a localized to delocalized transition of the electronic states at a percolation threshold, the emergence of a mobility edge, and the onset of an abrupt perturbation to the host GaAs electronic structure, shedding light on the evolution of electronic structure in these abnormal alloys.

Traditional Semiconductors in the Two-Dimensional Limit.

PubMed

Lucking, Michael C; Xie, Weiyu; Choe, Duk-Hyun; West, Damien; Lu, Toh-Ming; Zhang, S B

2018-02-23

Interest in two-dimensional materials has exploded in recent years. Not only are they studied due to their novel electronic properties, such as the emergent Dirac fermion in graphene, but also as a new paradigm in which stacking layers of distinct two-dimensional materials may enable different functionality or devices. Here, through first-principles theory, we reveal a large new class of two-dimensional materials which are derived from traditional III-V, II-VI, and I-VII semiconductors. It is found that in the ultrathin limit the great majority of traditional binary semiconductors studied (a series of 28 semiconductors) are not only kinetically stable in a two-dimensional double layer honeycomb structure, but more energetically stable than the truncated wurtzite or zinc-blende structures associated with three dimensional bulk. These findings both greatly increase the landscape of two-dimensional materials and also demonstrate that in the double layer honeycomb form, even ordinary semiconductors, such as GaAs, can exhibit exotic topological properties.

Theoretical Study of Defect Signatures in III-V and II-VI Semiconductors

DTIC Science & Technology

2006-03-01

collaboration with experimentalists at Linköpin University (Sweden), we identified the recently observed EPR signals in diluted GaPN to be Gallium ...the results from USPP calculations to all electron calculations. o Study NO-Zni complexes and other point defects in ZnO using USPP calculations...parameters for point defects in semiconductors. o Results on stability of NO-Zni complexes in ZnO and preliminary results on their electronic

Lattice thermal expansion for normal tetrahedral compound semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omar, M.S.

2007-02-15

The cubic root of the deviation of the lattice thermal expansion from that of the expected value of diamond for group IV semiconductors, binary compounds of III-V and II-VI, as well as several ternary compounds from groups I-III-VI{sub 2}, II-IV-V{sub 2} and I-IV{sub 2}V{sub 3} semiconductors versus their bonding length are given straight lines. Their slopes were found to be 0.0256, 0.0210, 0.0170, 0.0259, 0.0196, and 0.02840 for the groups above, respectively. Depending on the valence electrons of the elements forming these groups, a formula was found to correlate all the values of the slopes mentioned above to that ofmore » group IV. This new formula which depends on the melting point and the bonding length as well as the number of valence electrons for the elements forming the compounds, will gives best calculated values for lattice thermal expansion for all compounds forming the groups mentioned above. An empirical relation is also found between the mean ionicity of the compounds forming the groups and their slopes mentioned above and that gave the mean ionicity for the compound CuGe{sub 2}P{sub 3} in the range of 0.442.« less

Isoelectronic co-doping

DOEpatents

Mascarenhas, Angelo

2004-11-09

Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

The reduction of chromium (VI) by iron (II) in aqueous solutions

NASA Astrophysics Data System (ADS)

Pettine, Maurizio; D'Ottone, Luca; Campanella, Luigi; Millero, Frank J.; Passino, Roberto

1998-05-01

The rates of the reduction of Cr(VI) with Fe(II) were measured in NaCl, NaClO 4, and natural seawater as a function of pH (1.5-8.7), temperature (5-40°C) and ionic strength (I = 0.01-2 M). The pseudo first-order rate constant (log k 1) showed a parabolic dependence on pH decreasing from 1.5 to 4.5 and increasing from 5.5 to 8.7. The kinetics of the reaction in these two regions of pH also showed different influences of temperature, ionic strength, and reductant concentration. The rate of Cr(VI) reduction is described by the general expression -d[Cr(VI)]/dt = k [Cr(VI)] [Fe(II)] where k (M -1 min -1) can be determined from the log k=6.74-1.01 pH-188.5/T for the pH range 1.5-4.5 (σ = 0.2) and log k=11.93+0.95 pH-4260.1/T-1.06 I 0.5 for the pH range 5-8.7 (σ = 0.2) from 5 to 40°C and 0.01 to 2 M ionic strength. The effect of pH, temperature, and ionic strength on the reaction indicates that the reactions at low pH are due to H2CrO4+ Fe2+limit→k H2 A-Feproducts While the reactions at high pH are due to HCrO4-+ FeOH+limit→k HA-FeOHproductsHCrO4-+ Fe(OH)2limit→k HA-Fe(OH)2 products The overall rate expression over the entire pH range can be determined from (H 2A = H 2CrO 4) k=k H2 A-Feα( H2A)α( Fe2+)+k HA-FeOHα( HA-)α( FeOH+)+k HA-Fe(OH)2 α( HA-)α( Fe(OH)2) where k H2A-Fe = 5 x 10 6, k HA-FeOH = 1 x 10 6, k HA-Fe (OH)2= 5 x 10 11. In oxic aqueous systems Cr(VI) competes with O 2 in the oxidation of Fe(II) and an extension of the rate law for Cr(VI) reduction with Fe(II) in oxygenated solutions is proposed. The application of this extended rate law to environmental conditions suggests that this reaction influences the distribution of oxidized and reduced species of chromium in oxic and anoxic waters.

Calculation of the electron structure of vacancies and their compensated states in III-VI semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehrabova, M. A., E-mail: Mehrabova@mail.ru; Madatov, R. S.

2011-08-15

The Green's functions theory and the bond-orbital model are used as a basis for calculations of the electron structure of local defects-specifically, vacancies and their compensated states in III-VI semiconductors. The energy levels in the band gap are established, and the changes induced in the electron densities in the GaS, GaSe, and InSe semiconductors by anion and cation vacancies and their compensated states are calculated. It is established that, if a vacancy is compensated by an atom of an element from the same subgroup with the same tetrahedral coordination and if the ionic radius of the compensating atom is smallermore » than that of the substituted atom, the local levels formed by the vacancy completely disappear. It is shown that this mechanism of compensation of vacancies provides a means not only for recovering the parameters of the crystal, but for improving the characteristics of the crystal as well.« less

Lattice matched semiconductor growth on crystalline metallic substrates

DOEpatents

Norman, Andrew G; Ptak, Aaron J; McMahon, William E

2013-11-05

Methods of fabricating a semiconductor layer or device and said devices are disclosed. The methods include but are not limited to providing a metal or metal alloy substrate having a crystalline surface with a known lattice parameter (a). The methods further include growing a crystalline semiconductor alloy layer on the crystalline substrate surface by coincident site lattice matched epitaxy. The semiconductor layer may be grown without any buffer layer between the alloy and the crystalline surface of the substrate. The semiconductor alloy may be prepared to have a lattice parameter (a') that is related to the lattice parameter (a). The semiconductor alloy may further be prepared to have a selected band gap.

Compact Models for Defect Diffusivity in Semiconductor Alloys.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, Alan F.; Modine, Normand A.; Lee, Stephen R.

Predicting transient effects caused by short - pulse neutron irradiation of electronic devices is an important part of Sandia's mission. For example , predicting the diffusion of radiation - induced point defects is needed with in Sandia's Qualification Alternative to the Sandia Pulsed Reactor (QASPR) pro gram since defect diffusion mediates transient gain recovery in QASPR electronic devices. Recently, the semiconductors used to fabricate radiation - hard electronic devices have begun to shift from silicon to III - V compounds such as GaAs, InAs , GaP and InP . An advantage of this shift is that it allows engineers tomore » optimize the radiation hardness of electronic devices by using alloy s such as InGaAs and InGaP . However, the computer codes currently being used to simulate transient radiation effects in QASP R devices will need to be modified since they presume that defect properties (charge states, energy levels, and diffusivities) in these alloys do not change with time. This is not realistic since the energy and properties of a defect depend on the types of atoms near it and , therefore, on its location in the alloy. In particular, radiation - induced defects are created at nearly random locations in an alloy and the distribution of their local environments - and thus their energies and properties - evolves with time as the defects diffuse through the alloy . To incorporate these consequential effects into computer codes used to simulate transient radiation effects, we have developed procedures to accurately compute the time dependence of defect energies and properties and then formulate them within compact models that can be employed in these computer codes. In this document, we demonstrate these procedures for the case of the highly mobile P interstitial (I P ) in an InGaP alloy. Further dissemination only as authorized to U.S. Government agencies and their contractors; other requests shall be approved by the originating facility or higher DOE

Catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid under an irradiation of simulated solar light.

PubMed

Li, Ying; Chen, Cheng; Zhang, Jing; Lan, Yeqing

2015-05-01

The catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid with simulated solar light was investigated. The results demonstrated that Cu(II) could significantly accelerate Cr(VI) reduction and the reaction obeyed to pseudo zero-order kinetics with respect to Cr(VI). The removal of Cr(VI) was related to the initial concentrations of Cu(II), citric acid, and the types of organic acids. The optimal removal of Cr(VI) was achieved at pH 4, and the rates of Cu(II) photocatalytic reduction of Cr(VI) by organic acids were in the order: tartaric acid (two α-OH groups, two -COOH groups)>citric acid (one α-OH group, three -COOH groups)>malic acid (one α-OH group, two -COOH groups)>lactic acid (one α-OH group, one -COOH group)≫succinic acid (two -COOH groups), suggesting that the number of α-OH was the key factor for the reaction, followed by the number of -COOH. The formation of Cu(II)-citric acid complex could generate Cu(I) and radicals through a pathway of metal-ligand-electron transfer, promoting the reduction of Cr(VI). This study is helpful to fully understanding the conversion of Cr(VI) in the existence of both organic acids and Cu(II) with solar light in aquatic environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Sandwich-like nano-system for simultaneous removal of Cr(VI) and Cd(II) from water and soil.

PubMed

Wang, Dongfang; Zhang, Guilong; Dai, Zhangyu; Zhou, Linglin; Bian, Po; Zheng, Kang; Wu, Zhengyan; Cai, Dongqing

2018-05-07

In this work, a novel nano-system with sandwich-like structure was synthesized via face-to-face combination of two pieces of waste cotton fabrics (CFs) carrying ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide (CFFM) respectively, and the obtained nano system was named as FeS/CFFM/CF. Therein, FeS has high reduction and adsorption capabilities for hexavalent chromium (Cr(VI)), CFFM possesses a high adsorption ability on cadmium ion (Cd(II)) through electrostatics attraction and chelation, and CF displays high immobilization ability for FeS and CFFM and adsorption performance on Cd(II). FeS/CFFM/CF could simultaneously remove Cr(VI) and Cd(II) from water, inhibit the uptake of Cr and Cd by fish and water spinach, ensuring the food safety. Besides, this technology could efficiently control migration of Cr(VI) and Cd(II) in sand-soil mixture, which was favorable to prevent their wide diffusion. Importantly, FeS/CFFM/CF possessed a high flexibility and could be conveniently produced with needed scale and shape, and easily separated from water and soil, displaying a promising approach to remediate Cr(VI)/Cd(II)-contaminated water and soil and a huge application potential.

Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: the role of Fe(II) and Fe(III).

PubMed

Yan, Sen; Chen, Yongheng; Xiang, Wu; Bao, Zhengyu; Liu, Chongxuan; Deng, Baolin

2014-12-01

The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.

Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: The role of Fe(II) and Fe(III)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Sen; Chen, Yongheng; Xiang, Wu

2014-12-01

The role of Fe(II) and Fe(III) on U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.92 to 9.03. For instance, at pH 6.92 the observed U(VI) reduction rates decreased by 80.7% and 82.3% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can bemore » enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) probably acted as an electron shuttle to mediate the transfer of electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 can facilitate the U(VI) reductive immobilization in the contaminated groundwater.« less

A study of the kinetics and isotherms for Cr(VI) adsorption in a binary mixture of Cr(VI)-Ni(II) using hierarchical porous carbon obtained from pig bone.

PubMed

Li, Chengxian; Huang, Zhe; Huang, Bicheng; Liu, Changfeng; Li, Chengming; Huang, Yaqin

2014-01-01

Cr(VI) adsorption in a binary mixture Cr(VI)-Ni(II) using the hierarchical porous carbon prepared from pig bone (HPC) was investigated. The various factors affecting adsorption of Cr(VI) ions from aqueous solutions such as initial concentration, pH, temperature and contact time were analyzed. The results showed excellent efficiency of Cr(VI) adsorption by HPC. The kinetics and isotherms for Cr(VI) adsorption from a binary mixture Cr(VI)-Ni(II) by HPC were studied. The adsorption equilibrium described by the Langmuir isotherm model is better than that described by the Freundlich isotherm model for the binary mixture in this study. The maximum adsorption capacity was reliably found to be as high as 192.68 mg/g in the binary mixture at pH 2. On fitting the experimental data to both pseudo-first- and second-order equations, the regression analysis of the second-order equation gave a better R² value.

Narrow band gap amorphous silicon semiconductors

DOEpatents

Madan, A.; Mahan, A.H.

1985-01-10

Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

van der Waals epitaxial two-dimensional CdSxSe(1-x) semiconductor alloys with tunable-composition and application to flexible optoelectronics.

PubMed

Xia, Jing; Zhao, Yun-Xuan; Wang, Lei; Li, Xuan-Ze; Gu, Yi-Yi; Cheng, Hua-Qiu; Meng, Xiang-Min

2017-09-21

Despite the substantial progress in the development of two-dimensional (2D) materials from conventional layered crystals, it still remains particularly challenging to produce high-quality 2D non-layered semiconductor alloys which may bring in some unique properties and new functions. In this work, the synthesis of well-oriented 2D non-layered CdS x Se (1-x) semiconductor alloy flakes with tunable compositions and optical properties is established. Structural analysis reveals that the 2D non-layered alloys follow an incommensurate van der Waals epitaxial growth pattern. Photoluminescence measurements show that the 2D alloys have composition-dependent direct bandgaps with the emission peak varying from 1.8 eV to 2.3 eV, coinciding well with the density functional theory calculations. Furthermore, photodetectors based on the CdS x Se (1-x) flakes exhibit a high photoresponsivity of 703 A W -1 with an external quantum efficiency of 1.94 × 10 3 and a response time of 39 ms. Flexible devices fabricated on a thin mica substrate display good mechanical stability upon repeated bending. This work suggests a facile and general method to produce high-quality 2D non-layered semiconductor alloys for next-generation optoelectronic devices.

UV-luminescent MgZnO semiconductor alloys: nanostructure and optical properties

DOE PAGES

Thapa, Dinesh; Huso, Jesse; Miklos, Kevin; ...

2016-10-24

MgZnO is emerging as a vital semiconductor-alloy system with desirable optical properties that can span a large range of the UV spectrum. Due to its benign chemical character, MgZnO is considered to be an environmentally friendly material. This paper presents studies on annealing as a useful and straightforward approach for the enhancement of the optical and crystal quality of Mg 0.17Zn 0.83O nanocrystalline films grown via DC sputtering. The alloys were studied via several imaging and optical techniques. It was found that high-temperature annealing, ~900 °C, in Argon atmosphere, significantly improves the solubility of the alloy. This temperature range ismore » consistent with the thermal diffusion temperature of Mg needed for the creation of a soluble alloy. Moreover, the annealing process was found to minimize the undesirable visible luminescence, attributed to Mg and Zn interstitials, while significantly enhancing the bandgap sharpness and the efficiency of the UV-luminescence at ~3.5 eV. The analysis indicated that these optical attributes were achieved due to the combined effects of good solubility, an improved morphology, and a reduction of native defects. The annealing was also proven to be beneficial for the reduction of the compressive stress in the alloy: a relaxation ~1.8 GPa was calculated via Raman scattering. The inherent stress was inferred to originate mainly from the granular morphology of the alloys.« less

Emergent properties resulting from type-II band alignment in semiconductor nanoheterostructures.

PubMed

Lo, Shun S; Mirkovic, Tihana; Chuang, Chi-Hung; Burda, Clemens; Scholes, Gregory D

2011-01-11

The development of elegant synthetic methodologies for the preparation of monocomponent nanocrystalline particles has opened many possibilities for the preparation of heterostructured semiconductor nanostructures. Each of the integrated nanodomains is characterized by its individual physical properties, surface chemistry, and morphology, yet, these multicomponent hybrid particles present ideal systems for the investigation of the synergetic properties that arise from the material combination in a non-additive fashion. Of particular interest are type-II heterostructures, where the relative band alignment of their constituent semiconductor materials promotes a spatial separation of the electron and hole following photoexcitation, a highly desirable property for photovoltaic applications. This article highlights recent progress in both synthetic strategies, which allow for material and architectural modulation of novel nanoheterostructures, as well as the experimental work that provides insight into the photophysical properties of type-II heterostructures. The effects of external factors, such as electric fields, temperature, and solvent are explored in conjunction with exciton and multiexciton dynamics and charge transfer processes typical for type-II semiconductor heterostructures.

Controlled metal-semiconductor sintering/alloying by one-directional reverse illumination

DOEpatents

Sopori, Bhushan L.

1993-01-01

Metal strips deposited on a top surface of a semiconductor substrate are sintered at one temperature simultaneously with alloying a metal layer on the bottom surface at a second, higher temperature. This simultaneous sintering of metal strips and alloying a metal layer on opposite surfaces of the substrate at different temperatures is accomplished by directing infrared radiation through the top surface to the interface of the bottom surface with the metal layer where the radiation is absorbed to create a primary hot zone with a temperature high enough to melt and alloy the metal layer with the bottom surface of the substrate. Secondary heat effects, including heat conducted through the substrate from the primary hot zone and heat created by infrared radiation reflected from the metal layer to the metal strips, as well as heat created from some primary absorption by the metal strips, combine to create secondary hot zones at the interfaces of the metal strips with the top surface of the substrate. These secondary hot zones are not as hot as the primary hot zone, but they are hot enough to sinter the metal strips to the substrate.

II-VI Semiconductor Superlattices

DTIC Science & Technology

1992-12-01

N. Otsuka, H. icon, J. Ding, and A.V. Nurmikko, " Blue /Green Injection Lasers and Light Emitting Diodes" J. Vac. Sci. Technology B, 10(2) March/April...34Indium tin oxide as transparent electrode material for ZnSe-based blue quantum well light emitters" AppI. Phys. Lett. 60(23) 8 June 1992, p. 2825...characteristics of this contact scheme have been demon- strated tI)gether with their use Jn both blue ,/groen light lip emitting diodes and diode laser:- The

Localization-delocalization transition of electrons at the percolation threshold of semiconductor GaAs 1–xN x alloys: The appearance of a mobility edge

DOE PAGES

Alberi, K.; Fluegel, B.; Beaton, D. A.; ...

2012-07-09

Electrons in semiconductor alloys have generally been described in terms of Bloch states that evolve from constructive interference of electron waves scattering from perfectly periodic potentials, despite the loss of structural periodicity that occurs on alloying. Using the semiconductor alloy GaAs₁₋ xN x as a prototype, we demonstrate a localized to delocalized transition of the electronic states at a percolation threshold, the emergence of a mobility edge, and the onset of an abrupt perturbation to the host GaAs electronic structure, shedding light on the evolution of electronic structure in these abnormal alloys.

Accurate critical pressures for structural phase transitions of group IV, III-V, and II-VI compounds from the SCAN density functional

NASA Astrophysics Data System (ADS)

Shahi, Chandra; Sun, Jianwei; Perdew, John P.

2018-03-01

Most of the group IV, III-V, and II-VI compounds crystallize in semiconductor structures under ambient conditions. Upon application of pressure, they undergo structural phase transitions to more closely packed structures, sometimes metallic phases. We have performed density functional calculations using projector augmented wave (PAW) pseudopotentials to determine the transition pressures for these transitions within the local density approximation (LDA), the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and the strongly constrained and appropriately normed (SCAN) meta-GGA. LDA underestimates the transition pressure for most of the studied materials. PBE under- or overestimates in many cases. SCAN typically corrects the errors of LDA and PBE for the transition pressure. The accuracy of SCAN is comparable to that of computationally expensive methods like the hybrid functional HSE06, the random phase approximation (RPA), and quantum Monte Carlo (QMC), in cases where calculations with these methods have been reported, but at a more modest computational cost. The improvement from LDA to PBE to SCAN is especially clearcut and dramatic for covalent semiconductor-metal transitions, as for Si and Ge, where it reflects the increasing relative stabilization of the covalent semiconducting phases under increasing functional sophistication.

Design and exploration of semiconductors from first principles: A review of recent advances

NASA Astrophysics Data System (ADS)

Oba, Fumiyasu; Kumagai, Yu

2018-06-01

Recent first-principles approaches to semiconductors are reviewed, with an emphasis on theoretical insight into emerging materials and in silico exploration of as-yet-unreported materials. As relevant theory and methodologies have developed, along with computer performance, it is now feasible to predict a variety of material properties ab initio at the practical level of accuracy required for detailed understanding and elaborate design of semiconductors; these material properties include (i) fundamental bulk properties such as band gaps, effective masses, dielectric constants, and optical absorption coefficients; (ii) the properties of point defects, including native defects, residual impurities, and dopants, such as donor, acceptor, and deep-trap levels, and formation energies, which determine the carrier type and density; and (iii) absolute and relative band positions, including ionization potentials and electron affinities at semiconductor surfaces, band offsets at heterointerfaces between dissimilar semiconductors, and Schottky barrier heights at metal–semiconductor interfaces, which are often discussed systematically using band alignment or lineup diagrams. These predictions from first principles have made it possible to elucidate the characteristics of semiconductors used in industry, including group III–V compounds such as GaN, GaP, and GaAs and their alloys with related Al and In compounds; amorphous oxides, represented by In–Ga–Zn–O transparent conductive oxides (TCOs), represented by In2O3, SnO2, and ZnO; and photovoltaic absorber and buffer layer materials such as CdTe and CdS among group II–VI compounds and chalcopyrite CuInSe2, CuGaSe2, and CuIn1‑ x Ga x Se2 (CIGS) alloys, in addition to the prototypical elemental semiconductors Si and Ge. Semiconductors attracting renewed or emerging interest have also been investigated, for instance, divalent tin compounds, including SnO and SnS; wurtzite-derived ternary compounds such as ZnSnN2 and Cu

The removal of chromium (VI) and lead (II) from groundwater using sepiolite-supported nanoscale zero-valent iron (S-NZVI).

PubMed

Fu, Rongbing; Yang, Yingpin; Xu, Zhen; Zhang, Xian; Guo, Xiaopin; Bi, Dongsu

2015-11-01

In this study, the synthesis and characterization of sepiolite-supported nanoscale zero-valent iron particles (S-NZVI) was investigated for the adsorption/reduction of Cr(VI) and Pb(II) ions. Nanoscale zero-valent iron (NZVI) supported on sepiolite was successfully used to remove Cr(VI) and Pb(II) from groundwater with high efficiency. The removal mechanism was proposed as a two-step interaction including both the physical adsorption of Cr(VI) and Pb(II) on the surface or inner layers of the sepiolite-supported NZVI particles and the subsequent reduction of Cr(VI) to Cr(III) and Pb(II) to Pb(0) by NZVI. The immobilization of the NZVI particles on the surface of sepiolite could help to overcome the disadvantage of NZVI particles, which have strong tendency to agglomerate into larger particles, resulting in an adverse effect on both the effective surface area and reaction performance. The techniques of XRD, XPS, BET, Zeta potential, and TEM were used to characterize the S-NZVI and interaction between S-NZVI and heavy metals. The appropriate S-NZVI dosage was 1.6 g L(-1). The removal efficiency of Cr(VI) and Pb(II) by S-NZVI was not affected to any considerable extent by the presence of co-existing ions, such as H2PO4(-), SiO3(2-), Ca(2+) and HCO3(-). The Cr(VI) and Pb(II) removal kinetics followed a pseudo-first-order rate expression, and both Langmuir isotherm model and Freundlich isotherm model were proposed. The results suggested that supporting NZVI on sepiolite had the potential to become a promising technique for in situ heavy metal-contaminated groundwater remediation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Biosorption of Cr (VI), Cr (III), Pb (II) and Cd (II) from aqueous solutions by Sargassum wightii and Caulerpa racemosa algal biomass

NASA Astrophysics Data System (ADS)

Tamilselvan, Narayanaswamy; Saurav, Kumar; Kannabiran, Krishnan

2012-03-01

Heavy metal pollution is one of the most important environmental problems today. Biosorption is an innovative technology that employs biological materials to accumulate heavy metals from waste water through metabolic process or physicochemical pathways of uptake. Even though several physical and chemical methods are available for removal of heavy metals, currently many biological materials such as bacteria, algae, yeasts and fungi have been widely used due to their good performance, low cost and large quantity of availability. The aim of the present study is to explore the biosorption of toxic heavy metals, Cr(VI), Cr(III), Pb(II) and Cd(II) by algal biomass obtained from algae Sargassum wightii (brown) and Caulerpa racemosa (green). Biosorption of algal biomass was found to be biomass concentration- and pH-dependent, while the maximal biosorption was found at pH 5.0 and with the metal concentration of 100 mg L-1. S. wightii showed the maximal metal biosorption at the biomass concentration of 25 g L-1, followed by C. racemosa with the maximal biosorption at 30 g L-1. S. wightii showed 78% biosorption of Cr(VI), Cr(III), Pb(II) and Cd(II) ions. C. racemosa exhibited 85% biosorption of Cd(II) and Cr(VI), and 50% biosorption of Cr(III) and Pb(II). The results of our study suggest that seaweed biomass can be used efficiently for biosorption of heavy metals.

Nonvolatile Memories Using Quantum Dot (QD) Floating Gates Assembled on II-VI Tunnel Insulators

NASA Astrophysics Data System (ADS)

Suarez, E.; Gogna, M.; Al-Amoody, F.; Karmakar, S.; Ayers, J.; Heller, E.; Jain, F.

2010-07-01

This paper presents preliminary data on quantum dot gate nonvolatile memories using nearly lattice-matched ZnS/Zn0.95Mg0.05S/ZnS tunnel insulators. The GeO x -cladded Ge and SiO x -cladded Si quantum dots (QDs) are self-assembled site-specifically on the II-VI insulator grown epitaxially over the Si channel (formed between the source and drain region). The pseudomorphic II-VI stack serves both as a tunnel insulator and a high- κ dielectric. The effect of Mg incorporation in ZnMgS is also investigated. For the control gate insulator, we have used Si3N4 and SiO2 layers grown by plasma- enhanced chemical vapor deposition.

Structural transformations of sVI tert-butylamine hydrates to sII binary hydrates with methane.

PubMed

Prasad, Pinnelli S R; Sugahara, Takeshi; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

2009-10-22

Binary clathrate hydrates with methane (CH(4), 4.36 A) and tert-butylamine (t-BuNH(2), 6.72 A) as guest molecules were synthesized at different molar concentrations of t-BuNH(2) (1.00-9.31 mol %) with methane at 7.0 MPa and 250 K, and were characterized by powder X-ray diffraction (PXRD) and Raman microscopy. A structural transformation from sVI to sII of t-BuNH(2) hydrate was clearly observed on pressurizing with methane. The PXRD showed sII signatures and the remnant sVI signatures were insignificant, implying the metastable nature of sVI binary hydrates. Raman spectroscopic data on these binary hydrates suggest that the methane molecules occupy the small cages and vacant large cages. The methane storage capacity in this system was nearly doubled to approximately 6.86 wt % for 5.56 mol % > t-BuNH(2) > 1.0 mol %.

III-V semiconductor solid solution single crystal growth

NASA Technical Reports Server (NTRS)

Gertner, E. R.

1982-01-01

The feasibility and desirability of space growth of bulk IR semiconductor crystals for use as substrates for epitaxial IR detector material were researched. A III-V ternary compound (GaInSb) and a II-VI binary compound were considered. Vapor epitaxy and quaternary epitaxy techniques were found to be sufficient to permit the use of ground based binary III-V crystals for all major device applications. Float zoning of CdTe was found to be a potentially successful approach to obtaining high quality substrate material, but further experiments were required.

Interfacial charge separation and recombination in InP and quasi-type II InP/CdS core/shell quantum dot-molecular acceptor complexes.

PubMed

Wu, Kaifeng; Song, Nianhui; Liu, Zheng; Zhu, Haiming; Rodríguez-Córdoba, William; Lian, Tianquan

2013-08-15

Recent studies of group II-VI colloidal semiconductor heterostuctures, such as CdSe/CdS core/shell quantum dots (QDs) or dot-in-rod nanorods, show that type II and quasi-type II band alignment can facilitate electron transfer and slow down charge recombination in QD-molecular electron acceptor complexes. To explore the general applicability of this wave function engineering approach for controlling charge transfer properties, we investigate exciton relaxation and dissociation dynamics in InP (a group III-V semiconductor) and InP/CdS core/shell (a heterostructure beween group III-V and II-VI semiconductors) QDs by transient absorption spectroscopy. We show that InP/CdS QDs exhibit a quasi-type II band alignment with the 1S electron delocalized throughout the core and shell and the 1S hole confined in the InP core. In InP-methylviologen (MV(2+)) complexes, excitons in the QD can be dissociated by ultrafast electron transfer to MV(2+) from the 1S electron level (with an average time constant of 11.4 ps) as well as 1P and higher electron levels (with a time constant of 0.39 ps), which is followed by charge recombination to regenerate the complex in its ground state (with an average time constant of 47.1 ns). In comparison, InP/CdS-MV(2+) complexes show similar ultrafast charge separation and 5-fold slower charge recombination rates, consistent with the quasi-type II band alignment in these heterostructures. This result demonstrates that wave function engineering in nanoheterostructures of group III-V and II-VI semiconductors provides a promising approach for optimizing their light harvesting and charge separation for solar energy conversion applications.

Orbital frustration induced unusual ordering in semiconductor alloys

NASA Astrophysics Data System (ADS)

Liu, Kai; Yin, Wanjian; Chen, Shiyou; Gong, Xingao; Wei, Suhuai; Xiang, Hongjun

It is well known that ternary zinc-blende semiconductors are always more stable in the chalcopyrite (CH) structure than the Cu-Au (CA) structure because CH structure has large Coulomb interaction and reduced strain energy. Surprisingly, an experimental study showed that ZnFeSe2 alloy takes the CA order as the ground state structure, which is consistent with our density function theory (DFT) calculations showing that the CA order has lower energy than the CH order for ZnFeSe2. We reveal that the orbital degree of freedom of high-spin Fe2+ ion (d6) in the tetrahedral crystal field plays a key role in stabilizing the CA order. First, the spin-minority d electron of the Fe2+ ion tends to occupy the dx2-y 2 -like orbital instead of the d3z2 -r2 -like orbital because of its large negative Coulomb energy. Second, for a nearest-neighboring Fe2+ pair, two spin-minority d electrons with occupied dx2-y 2 -like orbitals in the plane containing the Fe-Fe bond has lower electronic kinetic energy. Both conditions can be satisfied in the CA ordered ZnFeSe2 alloy, while there is an orbital frustration in the CH structure. Our results suggest that orbital degree of freedom provides a new way to manipulate the structure and properties of alloys. Work at Fudan was supported by NSFC (11374056), the Special Funds for Major State Basic Research (2012CB921400, 2015CB921700), Program for Professor of Special Appointment (Eastern Scholar), and Fok Ying Tung Education Foundation.

Statistical Analysis of Main and Interaction Effects on Cu(II) and Cr(VI) Decontamination by Nitrogen-Doped Magnetic Graphene Oxide

NASA Astrophysics Data System (ADS)

Hu, Xinjiang; Wang, Hui; Liu, Yunguo

2016-10-01

A nitrogen-doped magnetic graphene oxide (NMGO) was synthesized and applied as an adsorbent to remove Cu(II) and Cr(VI) ions from aqueous solutions. The individual and combined effects of various factors (A: pH, B: temperature, C: initial concentration of metal ions, D: CaCl2, and E: humic acid [HA]) on the adsorption were analyzed by a 25-1 fractional factorial design (FFD). The results from this study indicated that the NMGO had higher adsorption capacities for Cu(II) ions than for Cr(VI) ions under most conditions, and the five selected variables affected the two adsorption processes to different extents. A, AC, and C were the very important factors and interactions for Cu(II) adsorption. For Cr(VI) adsorption, A, B, C, AB, and BC were found to be very important influencing variables. The solution pH (A) was the most important influencing factor for removal of both the ions. The main effects of A-E on the removal of Cu(II) were positive. For Cr(VI) adsorption, the main effects of A and D were negative, while B, C, and E were observed to have positive effects. The maximum adsorption capacities for Cu(II) and Cr(VI) ions over NMGO were 146.365 and 72.978 mg/g, respectively, under optimal process conditions.

High- and Reproducible-Performance Graphene/II-VI Semiconductor Film Hybrid Photodetectors

PubMed Central

Huang, Fan; Jia, Feixiang; Cai, Caoyuan; Xu, Zhihao; Wu, Congjun; Ma, Yang; Fei, Guangtao; Wang, Min

2016-01-01

High- and reproducible-performance photodetectors are critical to the development of many technologies, which mainly include one-dimensional (1D) nanostructure based and film based photodetectors. The former suffer from a huge performance variation because the performance is quite sensitive to the synthesis microenvironment of 1D nanostructure. Herein, we show that the graphene/semiconductor film hybrid photodetectors not only possess a high performance but also have a reproducible performance. As a demo, the as-produced graphene/ZnS film hybrid photodetector shows a high responsivity of 1.7 × 107 A/W and a fast response speed of 50 ms, and shows a highly reproducible performance, in terms of narrow distribution of photocurrent (38–65 μA) and response speed (40–60 ms) for 20 devices. Graphene/ZnSe film and graphene/CdSe film hybrid photodetectors fabricated by this method also show a high and reproducible performance. The general method is compatible with the conventional planar process, and would be easily standardized and thus pay a way for the photodetector applications. PMID:27349692

30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION... Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 2.0 percent in the mine...

30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). 57.22231 Section 57.22231 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION... Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 0.25 percent in the...

CATALYTIC PROPERTIES OF SEMICONDUCTORS.

DTIC Science & Technology

SEMICONDUCTORS, CATALYSTS), (*CATALYSIS, REACTION KINETICS), (* SODIUM COMPOUNDS, TUNGSTATES), (*GALLIUM ALLOYS, ARSENIC ALLOYS), (*YTTERBIUM...COMPOUNDS, SILICIDES ), (*GERMANIUM, CATALYSIS), INTERNAL CONVERSION, EXCHANGE REACTIONS, HEAT OF ACTIVATION, THERMODYNAMICS, DEUTERIUM, POWDERS, SURFACES, HYDROGEN

Phase diagram of nanoscale alloy particles used for vapor-liquid-solid growth of semiconductor nanowires.

PubMed

Sutter, Eli; Sutter, Peter

2008-02-01

We use transmission electron microscopy observations to establish the parts of the phase diagram of nanometer sized Au-Ge alloy drops at the tips of Ge nanowires (NWs) that determine their temperature-dependent equilibrium composition and, hence, their exchange of semiconductor material with the NWs. We find that the phase diagram of the nanoscale drop deviates significantly from that of the bulk alloy, which explains discrepancies between actual growth results and predictions on the basis of the bulk-phase equilibria. Our findings provide the basis for tailoring vapor-liquid-solid growth to achieve complex one-dimensional materials geometries.

Effect of pH and Fe/U ratio on the U(VI) removal rate by the synergistic effect of Fe(II) and O2

NASA Astrophysics Data System (ADS)

Fu, Yukui; Luo, Yingfeng; Fang, Qi; Xie, Yanpei; Wang, Zhihong; Zhu, Xiangyu

2018-02-01

As for the decommissioned uranium deposits of acid in-situ leaching, both of the concentrations of U(VI) and Fe(II) are relatively high in groundwater. In the presence of O2, the oxidation of Fe(II) into Fe(III) that forms Fe-hydroxides could effectively remove U(VI) in the forms of sorption or co-precipitation. In this process, pH condition and Fe content will have a significant effect on the U(VI) removal rate by the synergistic effect of Fe(II) and O2. In the present work, a series of batch experiments were carried out to investigate the effect of pH values and Fe/U mass ratio on the U(VI) removal rate by the synergistic effect of Fe(II) and O2. Experiment results show that the removal rate of U(VI) is mainly controlled by pH and secondly by Fe/U mass ratio. In the neutral conditions with pH at 7 and 8, the removal rate of U(VI) reaches up to 90% for all solutions with different initial Fe(II) concentrations. The optimal pH for the removal rate of U(VI) is above 7. In the acidic conditions with pH below 6, the effect of Fe/U mass ratio on the removal rate of U(VI) becomes more obvious and the optimal Fe/U mass ratio for U(VI) removal is 1:2.

30 CFR 57.22232 - Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 0.5 percent methane (I-B, II-A, II-B...-UNDERGROUND METAL AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22232 Actions at 0.5 percent methane (I-B, II-A, II-B, IV, V-B, and VI mines). If methane reaches 0.5...

Controlled growth of semiconductor crystals

DOEpatents

Bourret-Courchesne, Edith D.

1992-01-01

A method for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B.sub.x O.sub.y are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T.sub.m1 of the oxide of boron (T.sub.m1 =723.degree. K. for boron oxide B.sub.2 O.sub.3), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T.sub.m2 of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm.sup.2. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 .mu.m.

Methods for forming thin-film heterojunction solar cells from I-III-VI{sub 2}

DOEpatents

Mickelsen, R.A.; Chen, W.S.

1985-08-13

An improved thin-film, large area solar cell, and methods for forming the same are disclosed, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n type heterojunction formed of: (i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI{sub 2} chalcopyrite ternary materials which is vacuum deposited in a thin ``composition-graded`` layer ranging from on the order of about 2.5 microns to about 5.0 microns ({approx_equal}2.5 {mu}m to {approx_equal}5.0 {mu}m) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (ii) a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion occurs (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer. 16 figs.

Ferrate(VI) oxidation of zinc-cyanide complex.

PubMed

Yngard, Ria; Damrongsiri, Seelawut; Osathaphan, Khemarath; Sharma, Virender K

2007-10-01

Zinc-cyanide complexes are found in gold mining effluents and in metal finishing rinse water. The effect of Zn(II) on the oxidation of cyanide by ferrate(VI) (Fe(VI)O(4)(2-), Fe(VI)) was thus investigated by studying the kinetics of the reaction of Fe(VI) with cyanide present in a potassium salt of a zinc cyanide complex (K(2)Zn(CN)(4)) and in a mixture of Zn(II) and cyanide solutions as a function of pH (9.0-11.0). The rate-law for the oxidation of Zn(CN)(4)(2-) by Fe(VI) was found to be -d[Fe(VI)]/dt=k[Fe(VI)][Zn(CN)(4)(2-)](0.5). The rate constant, k, decreased with an increase in pH. The effect of temperature (15-45 degrees C) on the oxidation was studied at pH 9.0, which gave an activation energy of 45.7+/-1.5kJmol(-1). The cyanide oxidation rate decreased in the presence of the Zn(II) ions. However, Zn(II) ions had no effect on the cyanide removal efficiency by Fe(VI) and the stoichiometry of Fe(VI) to cyanide was approximately 1:1; similar to the stoichiometry in absence of Zn(II) ions. The destruction of cyanide by Fe(VI) resulted in cyanate. The experiments on removal of cyanide from rinse water using Fe(VI) demonstrated complete conversion of cyanide to cyanate.

Defect-Rich Dopant-Free ZrO2 Nanostructures with Superior Dilute Ferromagnetic Semiconductor Properties.

PubMed

Rahman, Md Anisur; Rout, S; Thomas, Joseph P; McGillivray, Donald; Leung, Kam Tong

2016-09-14

Control of the spin degree of freedom of an electron has brought about a new era in spin-based applications, particularly spin-based electronics, with the potential to outperform the traditional charge-based semiconductor technology for data storage and information processing. However, the realization of functional spin-based devices for information processing remains elusive due to several fundamental challenges such as the low Curie temperature of group III-V and II-VI semiconductors (<200 K), and the low spin-injection efficiencies of existing III-V, II-VI, and transparent conductive oxide semiconductors in a multilayer device structure, which are caused by precipitation and migration of dopants from the host layer to the adjacent layers. Here, we use catalyst-assisted pulsed laser deposition to grow, for the first time, oxygen vacancy defect-rich, dopant-free ZrO2 nanostructures with high TC (700 K) and high magnetization (5.9 emu/g). The observed magnetization is significantly greater than both doped and defect-rich transparent conductive oxide nanomaterials reported to date. We also provide the first experimental evidence that it is the amounts and types of oxygen vacancy defects in, and not the phase of ZrO2 that control the ferromagnetic order in undoped ZrO2 nanostructures. To explain the origin of ferromagnetism in these ZrO2 nanostructures, we hypothesize a new defect-induced bound polaron model, which is generally applicable to other defect-rich, dopant-free transparent conductive oxide nanostructures. These results provide new insights into magnetic ordering in undoped dilute ferromagnetic semiconductor oxides and contribute to the design of exotic magnetic and novel multifunctional materials.

Synthesis and electronic properties of nanophase semiconductor materials

NASA Astrophysics Data System (ADS)

Sailor, Michael J.

1993-05-01

The objective of the research effort is to understand and learn to control the morphologic and electronic properties of electrodeposited nanophase semiconductors. The initial work has focused on electrodeposition of nanophase CdSe, using a sequential monolayer deposition technique that we are developing. We are currently extending the synthesis phase of this project into silicon, silicon carbide, and phosphor materials. This work also encompasses studying semiconductor electrodeposition into materials with restricted dimensions, such as microporous alumina and porous silicon membranes. By growing films with very small grain sizes, we hope to produce and study materials that display unusual electronic or luminescent effects. We are primarily interested in the electronic properties of the II-VI and group IV materials, for potential applications in nanoscale electronics and optical detector technologies. The phosphors are being studied for their potential as efficient high-resolution display materials.

Functionalization of semiconductors for biosensing applications

NASA Astrophysics Data System (ADS)

Estephan, E.; Larroque, C.; Martineau, P.; Cloitre, T.; Gergely, Cs.

2007-05-01

Functionalization of semiconductors (SC) has been widely used for various electronic, photonic and biomedical applications. In this paper, we report on selective functionalization achieved by peptides that reveal specific recognition of the SC surfaces. A M13 bacteriophage library was used to screen 10 10 different 12-mer peptide on various SC substrates to successfully isolate after 3 cycles one specific peptide for the majority of semiconductors. Our results conclude that GaAs(100) and GaN(0001) retain the same sequence of 12-mer peptide, suggesting that the specificity does not depend on the crystallographic structure but it depends on the chemical composition and the electronegativity of the surface, thus on the orientation of the material. We also note the presence of at least one proline (Pro) amino acid in each peptide, and the presence of the histidine (His) in the specific peptides for the II-VI class SC. Pro imprints a constraint to the peptide to facilitate adhesion to the surface, whereas the basic side chain His is known for its affinity towards some of the elements of class II SC. Finally, fluorescence microscopy has been employed to demonstrate the preferential attachment of the peptide to their specific SC surface in close proximity to a surface of different chemical and structural composition. The use of selected peptides expressed by phage display can be extended to encompass a variety of nanostructured semiconductor based devices.

Structural Fluctuation and Thermophysical Properties of Molten II-VI Compounds

NASA Technical Reports Server (NTRS)

2003-01-01

The objectives of the project is to conduct ground-based experimental and theoretical research on the structural fluctuations and thermophysical properties of molten II-VI compounds to enhance the basic understanding of the existing flight experiments in microgravity materials science programs and to study the fundamental heterophase fluctuations phenomena in these melts by: 1) Conducting neutron scattering analysis and measuring quantitatively the relevant thermophysical properties of the II-VI melts such as viscosity, electrical conductivity, thermal diffusivity and density as well as the relaxation characteristics of these properties to advance the understanding of the structural properties and the relaxation phenomena in these melts and 2) Performing theoretical analyses on the melt systems to interpret the experimental results. All the facilities required for the experimental measurements have been procured, installed and tested. A relaxation phenomenon, which shows a slow drift of the measured thermal conductivity toward the equilibrium value after cooling of the sample, was observed for the first time. An apparatus based on the transient torque induced by a rotating magnetic field has been developed to determine the viscosity and electrical conductivity of semiconducting liquids. Viscosity measurements on molten tellurium showed similar relaxation behavior as the measured diffusivity. Neutron scattering experiments were performed on the HgTe and HgZnTe melts and the results on pair distribution showed better resolution than previous reported.

Controlled growth of semiconductor crystals

DOEpatents

Bourret-Courchesne, E.D.

1992-07-21

A method is disclosed for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B[sub x]O[sub y] are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T[sub m1] of the oxide of boron (T[sub m1]=723 K for boron oxide B[sub 2]O[sub 3]), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T[sub m2] of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm[sup 2]. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 [mu]m. 7 figs.

Zn(1-x)MnxTe diluted magnetic semiconductor nanowires grown by molecular beam epitaxy.

PubMed

Zaleszczyk, Wojciech; Janik, Elzbieta; Presz, Adam; Dłuzewski, Piotr; Kret, Sławomir; Szuszkiewicz, Wojciech; Morhange, Jean-François; Dynowska, Elzbieta; Kirmse, Holm; Neumann, Wolfgang; Petroutchik, Aleksy; Baczewski, Lech T; Karczewski, Grzegorz; Wojtowicz, Tomasz

2008-11-01

It is shown that the growth of II-VI diluted magnetic semiconductor nanowires is possible by the catalytically enhanced molecular beam epitaxy (MBE). Zn(1-x)MnxTe NWs with manganese content up to x=0.60 were produced by this method. X-ray diffraction, Raman spectroscopy, and temperature dependent photoluminescence measurements confirm the incorporation of Mn(2+) ions in the cation substitutional sites of the ZnTe matrix of the NWs.

Optical phonon modes of III-V nanoparticles and indium phosphide/II-VI core-shell nanoparticles: A Raman and infrared study

NASA Astrophysics Data System (ADS)

Manciu, Felicia Speranta

The prospects for realizing efficient nanoparticle light emitters in the visible/near IR for communications and bio-medical applications have benefited from progress in chemical fabrication of nanoparticles. III-V semiconductor nanopaticles such as GaP and InP are promising materials for the development of "blue" and "green" emitters, respectively, due to their large effective bandgaps. Enhanced emission efficiency has been achieved for core-shell nanoparticles, since inorganic shell materials increase electronic tunability and may decrease surface defects that often occur for nanoparticles capped with organic molecules. Also, the emission wavelength of InP nanoparticle cores can be tuned from green to red by changing the shell material in InP/II-VI core-shell nanoparticles. Investigations of phonon modes in nanocrystals are of both fundamental and applied interest. In the former case the optical phonon modes, such as surface/interface modes, are dependent on the nanoparticle dimensions, and also can provide information about dynamical properties of the nanoparticles and test the validity of various theoretical approaches. In the latter case the vibronic properties of nanoparticle emitters are controlled by confined phonons and modifications of the electron-phonon interaction by the confinement. Thus, the objective of the present thesis is the detailed study of the phonon modes of III-V nanoparticles (GaP and InP) and InP/II-VI core-shell nanoparticles by IR absorption and Raman scattering spectroscopies, and an elucidation of their complex vibrational properties. With the exception of three samples (two GaP and one InP), all samples were synthesized by a novel colloidal chemistry method, which does not requires added surfactant, but rather treatment of the corresponding precursors in octadecene noncoordinative solvent. Sample quality was characterized by ED, TEM and X-ray diffraction. Based on a comparison with a dielectric continuum model, the observed features

InAs/GaSb type-II superlattices versus HgCdTe ternary alloys: future prospect

NASA Astrophysics Data System (ADS)

Rogalski, A.

2017-10-01

InAs/GaSb T2SL photodetectors offer similar performance to HgCdTe at an equivalent cutoff wavelength, but with a sizeable penalty in operating temperature, due to the inherent difference in Shockley-Read lifetimes. It is predicted that since the future IR systems will be based on the room temperature operation of depletion-current limited arrays with pixel densities that are fully consistent with background- and diffraction-limited performance due to the system optics, the material system with long Shockley-Read lifetime will be required. Since T2SLs are much resisted in attempts to improve its SR lifetime, currently the only material that meets this requirement is HgCdTe. Due to less ionic chemical bonding, III-V semiconductors are more robust than their II-VI counterparts. As a result, III-V-based FPAs excel in operability, spatial uniformity, temporal stability, scalability, producibility, and affordability - the so-called "ibility" advantages.

Enhancement strategies for Cu(II), Cr(III) and Cr(VI) remediation by a variety of seaweed species.

PubMed

Murphy, V; Hughes, H; McLoughlin, P

2009-07-15

Various chemical treatments have been applied to six brown, red and green seaweed species with a view to enhancing their metal removal for Cu(II), Cr(III) and Cr(VI). Treatment with acetone resulted in the greatest enhancement for both cationic and anionic species with relatively low mass losses (15-35%), indicating its low risk to biomass operational stability. Cation binding was increased by 69%, while the total Cr removal was augmented by 15%. Cr(VI) binding was shown to be an adsorption-coupled reduction, whereby Cr(VI) was bound to the biomass surface at pH 2 and subsequently reduced to Cr(III). Acetone treatment also resulted in biomasses that were capable of converting up to 83% of Cr(VI) in solution to Cr(III). Blocking of carboxyl and amino functionalities had significant negative effects both on total Cr removal as well as percentage conversion of Cr(VI) to Cr(III). Results therefore indicated the significant role played by these moieties in metal binding to these seaweeds. Potentiometric titrations displayed agreement between the degree of esterification and the decrease in Cu(II) removal for Ulva spp. and Polysiphonia lanosa. FTIR analysis identified changes in biomass functionality and availability after chemical modification, the results of which were in agreement with metal removal studies. In conclusion, these biosorbents represent suitable candidates to replace conventional removal technologies for metal bearing wastewaters, in particular for the detoxification of hazardous Cr(VI) waste streams.

Methods for forming thin-film heterojunction solar cells from I-III-VI.sub. 2

DOEpatents

Mickelsen, Reid A [Bellevue, WA; Chen, Wen S [Seattle, WA

1985-08-13

An improved thin-film, large area solar cell, and methods for forming the same, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n type heterojunction formed of: (i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI.sub.2 chalcopyrite ternary materials which is vacuum deposited in a thin "composition-graded" layer ranging from on the order ot about 2.5 microns to about 5.0 microns (.congruent.2.5 .mu.m to .congruent.5.0 .mu.m) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (ii), a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, causes the The Government has rights in this invention pursuant to Contract No. EG-77-C-01-4042, Subcontract No. XJ-9-8021-1 awarded by the U.S. Department of Energy.

Electron Transfer Pathways Facilitating U(VI) Reduction by Fe(II) on Al- vs Fe-Oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, S. D.; Becker, U.; Rosso, K. M.

This study continues mechanistic development of heterogeneous electron transfer (ET) pathways at mineral surfaces in aquatic environments that enable the reduction U(VI) by surface-associated Fe(II). Using computational molecular simulation within the framework of Marcus Theory, our findings highlight the importance of the configurations and interaction of the electron donor and acceptor species with the substrate, with respect to influencing its electronic structure and thereby the ability of semiconducting minerals to facilitate ET. U(VI) reduction by surface-associated Fe(II) (adsorbed or structurally incorporated into the lattice) on an insulating, corundum (001) surface (α-Al2O3) occurs when proximal inner-sphere (IS) surface complexes are formed,more » such that ET occurs through a combination of direct exchange (i.e., Fe d- and U f-orbitals overlap through space) and superexchange via intervening surface oxygen atoms. U(VI) reduction by coadsorbed Fe(II) on the isostructural semiconducting hematite (α-Fe2O3) basal surface requires either their direct electronic interaction (e.g., IS complexation) or mediation of this interaction indirectly through the surface via an intrasurface pathway. Conceptually possible longer-range ET by charge-hopping through surface Fe atoms was investigated to determine whether this indirect pathway is competitive with direct ET. The calculations show that energy barriers are large for this conduction-based pathway; interfacial ET into the hematite surface is endothermic (+80.1 kJ/mol) and comprises the rate-limiting step (10–6 s–1). The presence of the IS adsorbates appears to weaken the electronic coupling between underlying Fe ions within the surface, resulting in slower intra-surface ET (10–5 s–1) than expected in the bulk basal plane. Our findings lay out first insights into donor-acceptor communication via a charge-hopping pathway through the surface for heterogeneous reduction of U(VI) by Fe(II) and help provide

Method of fabricating n-type and p-type microcrystalline semiconductor alloy material including band gap widening elements

DOEpatents

Guha, Subhendu; Ovshinsky, Stanford R.

1990-02-02

A method of fabricating doped microcrystalline semiconductor alloy material which includes a band gap widening element through a glow discharge deposition process by subjecting a precursor mixture which includes a diluent gas to an a.c. glow discharge in the absence of a magnetic field of sufficient strength to induce electron cyclotron resonance.

Rhombohedral cubic semiconductor materials on trigonal substrate with single crystal properties and devices based on such materials

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

Growth conditions are developed, based on a temperature-dependent alignment model, to enable formation of cubic group IV, group II-V and group II-VI crystals in the [111] orientation on the basal (0001) plane of trigonal crystal substrates, controlled such that the volume percentage of primary twin crystal is reduced from about 40% to about 0.3%, compared to the majority single crystal. The control of stacking faults in this and other embodiments can yield single crystalline semiconductors based on these materials that are substantially without defects, or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. These methods can selectively yield a cubic-on-trigonal epitaxial semiconductor material in which the cubic layer is substantially either directly aligned, or 60 degrees-rotated from, the underlying trigonal material.

Green synthesis of water soluble semiconductor nanocrystals and their applications

NASA Astrophysics Data System (ADS)

Wang, Ying

II-VI semiconductor nanomaterials, e.g. CdSe and CdTe, have attracted great attention over the past decades due to their fascinating optical and electrical properties. The research presented here focuses on aqueous semiconductor nanomaterials. The work can be generally divided into three parts: synthesis, property study and application. The synthetic work is devoted to develop new methods to prepare shape- and structure-controlled II-VI semiconductor nanocrystals including nanoparticles and nanowires. CdSe and CdSe CdS semiconductor nanocrystals have been synthesized using sodium citrate as a stabilizer. Upon prolonged illumination with visible light, photoluminescence quantum yield of those quantum dots can be enhanced up to 5000%. The primary reason for luminescence enhancement is considered to be the removing of specific surface states (photocorrosion) and the smoothing of the CdSe core surface (photoannealing). CdTe nanowires are prepared through self-organization of stabilizer-depleted CdTe nanoparticles. The dipolar-dipolar attraction is believed to be the driving force of nanowire formation. The rich surface chemistry of CdTe nanowire is reflected by the formation of silica shell with different morphologies when nanowires with different capping ligands are used. Te and Se nanowires are prepared by chemical decomposition of CdTe and CdSe nanoparticles in presence of an external chemical stimulus, EDTA. These results not only provide a new example of NP→NW transformation, but also lead to a better understanding of the molecular process occurring in the stabilizer-depleted nanoparticles. The applications of those semiconductor materials are primarily based on the construction of nano-structured ultrathin films with desirable functions by using layer-by-layer technique (LBL). We demonstrate that light-induced micro-scale multicolor luminescent patterns can be obtained on photoactivable CdSe/CdS nanoparticles thin films by combining the advantages of LBL as

Severity of Chagasic Cardiomyopathy Is Associated With Response To A Novel Rapid Diagnostic Test For Trypanosoma cruzi TcII/V/VI.

PubMed

Bhattacharyya, Tapan; Messenger, Louisa A; Bern, Caryn; Mertens, Pascal; Gilleman, Quentin; Zeippen, Nicolas; Bremer Hinckel, Bruno C; Murphy, Niamh; Gilman, Robert H; Miles, Michael A

2018-02-09

Trypanosoma cruzi causes Chagas disease in the Americas. Outcome of infection ranges from lifelong asymptomatic status to severe disease. Understanding how history of T. cruzi lineage (TcI-TcVI) infection relates to clinical prognosis is challenging. We previously described peptide-based lineage-specific ELISA with Trypomastigote Small Surface Antigen (TSSA). A novel rapid diagnostic test (Chagas Sero K-SeT) incorporating a peptide corresponding to the TSSA-II/V/VI common epitope was developed, and validated by comparison with ELISA. Patients from Bolivia and Peru were then tested by Chagas Sero K-SeT, including individuals with varying cardiac pathology, and matched mothers and neonates. Chagas Sero K-SeT and ELISAs, with a Bolivian subset of cardiac patients, mothers and neonates, were in accord. In adult chronic infections (n = 121), comparison of severity class A (no evidence of Chagas cardiomyopathy) against classes B (ECG suggestive of Chagas cardiomyopathy) and C/D (moderate/severe Chagas cardiomyopathy) revealed statistically significant increase in Chagas Sero K-SeT reactivity with increasing severity (Chi Square for trend 7.39; p = 0.007). In Peru, where TcII/V/VI lineages are rarely reported, Chagas Sero K SeT detected sporadic infections. We develop a novel, low-cost, point-of-care, rapid test and demonstrate that it can replace ELISA for identification of lineage-specific TSSA II/V/VI IgG. Most importantly, we show that response to the TSSA II/V/VI epitope in this RDT is associated with severity of Chagas cardiomyopathy, and thus may have prognostic value. Repeated challenge with T. cruzi infection may both exacerbate disease progression and boost the immune response to the TSSApep-II/V/VI epitope. © The Author(s) 2018. Published by Oxford University Press for the Infectious Diseases Society of America.

Production of High-Purity Anhydrous Nickel(II) Perrhenate for Tungsten-Based Sintered Heavy Alloys

PubMed Central

Leszczyńska-Sejda, Katarzyna; Benke, Grzegorz; Kopyto, Dorota; Majewski, Tomasz; Drzazga, Michał

2017-01-01

This paper presents a method for the production of high-purity anhydrous nickel(II) perrhenate. The method comprises sorption of nickel(II) ions from aqueous nickel(II) nitrate solutions, using strongly acidic C160 cation exchange resin, and subsequent elution of sorbed nickel(II) ions using concentrated perrhenic acid solutions. After the neutralization of the resulting rhenium-nickel solutions, hydrated nickel(II) perrhenate is then separated and then dried at 160 °C to obtain the anhydrous form. The resulting compound is reduced in an atmosphere of dissociated ammonia in order to produce a Re-Ni alloy powder. This study provides information on the selected properties of the resulting Re-Ni powder. This powder was used as a starting material for the production of 77W-20Re-3Ni heavy alloys. Microstructure examination results and selected properties of the produced sintered heavy alloys were compared to sintered alloys produced using elemental W, Re, and Ni powders. This study showed that the application of anhydrous nickel(II) perrhenate in the production of 77W-20Re-3Ni results in better properties of the sintered alloys compared to those made from elemental powders. PMID:28772808

Special quasiordered structures: Role of short-range order in the semiconductor alloy (GaN) 1 -x(ZnO) x

NASA Astrophysics Data System (ADS)

Liu, Jian; Fernández-Serra, Maria V.; Allen, Philip B.

2016-02-01

This paper studies short-range order (SRO) in the semiconductor alloy (GaN) 1 -x(ZnO) x. Monte Carlo simulations performed on a density functional theory (DFT)-based cluster expansion model show that the heterovalent alloys exhibit strong SRO because of the energetic preference for the valence-matched nearest-neighbor Ga-N and Zn-O pairs. To represent the SRO-related structural correlations, we introduce the concept of special quasiordered structure (SQoS). Subsequent DFT calculations reveal the dramatic influence of SRO on the atomic, electronic, and vibrational properties of the (GaN) 1 -x(ZnO) x alloy. Due to the enhanced statistical presence of the energetically unfavored Zn-N bonds with the strong Zn 3 d -N 2 p repulsion, the disordered alloys exhibit much larger lattice bowing and band-gap reduction than those of the short-range ordered alloys. Lattice vibrational entropy tilts the alloy toward less SRO.

Microsensors based on GaN semiconductors covalently functionalized with luminescent Ru(II) complexes.

PubMed

López-Gejo, Juan; Arranz, Antonio; Navarro, Alvaro; Palacio, Carlos; Muñoz, Elías; Orellana, Guillermo

2010-02-17

Covalent tethering of a Ru(II) dye to gallium nitride surfaces has been accomplished as a key step in the development of innovative sensing devices in which the indicator support (semiconductor) plays the role of both support and excitation source. Luminescence emission decays and time-resolved emission spectra confirm the presence of the dye on the semiconductor surfaces, while X-ray photoelectron spectroscopy proves its covalent bonding. The O(2) sensitivity of the new device is comparable to those of other ruthenium-based sensor systems. This achievement paves the way to a new generation of integrable ultracompact microsensors that combine semiconductor emitter-probe assemblies.

First principles study of thermoelectric properties of IV-VI semiconductor superlattices

NASA Astrophysics Data System (ADS)

Borges, P. D.; Petersen, J. E.; Scolfaro, L.; Leite Alves, H. W.; Myers, T. H.

2015-03-01

Thermoelectric materials (TE) have attracted great attention due to their ability to convert heat directly into electricity. However, to be commercially competitive with existing technology, TE devices must have a higher value of figure of merit ZT. It has been proposed to improve ZT by using multilayered systems or superlattices (SLs) resulting in 1D or 2D carrier confinement, reduction of the phonon thermal conductivity, and introduction of anisotropy effects. Here we study the TE properties of IV-VI derived semiconductor SLs. By using the Boltzmann transport theory, within the constant scattering time approximation, in conjunction with first principles calculations, we study the Seebeck coefficient (S) and ZT of PbTe/SnTe SLs. The calculated S shows good agreement with recent experimental data. An anisotropic behavior is observed for low carrier concentrations less than 10⌃18cm⌃-3. For T = 900 K, a large value of ZTparallel to the SL axis equal to 2.6 is predicted for n =1.2x10⌃18cm⌃-3, whereas ZT perpendicular to the SL axis peaks at the value 1.4 for n =5.5x10⌃17 cm⌃-3. Both electrical conductivity enhancement and reduction of thermal conductivity are analyzed, and a comparison with other multilayered systems such as planar-doped PbTe is done. Support from CNPq and Texas State University.

The Reaction between Iron(II) Iodide and Potassium Dichromate(VI) in Acidified Aqueous Solution

ERIC Educational Resources Information Center

Talbot, Christopher

2013-01-01

This "Science note" teaching lesson explores the possible reaction between the ions in a reaction mixture consisting of iron(II) iodide and potassium dichromate(VI) in acidified aqueous solution. The electrode potentials will be used to deduce any spontaneous reactions under standard thermodynamic conditions (298 K, 1 bar (approximately…

Mn-based ferromagnetic semiconductors

NASA Astrophysics Data System (ADS)

Dietl, Tomasz; Sawicki, Maciej

2003-07-01

The present status of research and prospects for device applications of ferromagnetic (diluted magnetic) semiconductors (DMS) is presented. We review the nature of the electronic states and the mechanisms of the carrier-mediated exchange interactions (mean-field Zener model) in p-type Mn-based III-V and II-VI compounds, highlighting a good correspondence of experimental findings and theoretical predictions. An account of the latest progress on the road of increasing the Currie point to above the room temperature is given for both families of compounds. We comment on a possibility of obtaining ferromagnetism in n-type materials, taking (Zn,Mn)O:Al as the example. Concerning technologically important issue of easy axis and domain engineering, we present theoretical predictions and experimental results on the temperature and carrier concentration driven change of magnetic anisotropy in (Ga,Mn)As.

Adsorption of Fe(II) and U(VI) to carboxyl-functionalized microspheres: The influence of speciation on uranyl reduction studied by titration and XAFS

NASA Astrophysics Data System (ADS)

Boyanov, Maxim I.; O'Loughlin, Edward J.; Roden, Eric E.; Fein, Jeremy B.; Kemner, Kenneth M.

2007-04-01

The chemical reduction of U(VI) by Fe(II) is a potentially important pathway for immobilization of uranium in subsurface environments. Although the presence of surfaces has been shown to catalyze the reaction between Fe(II) and U(VI) aqueous species, the mechanism(s) responsible for the enhanced reactivity remain ambiguous. To gain further insight into the U-Fe redox process at a complexing, non-conducting surface that is relevant to common organic phases in the environment, we studied suspensions containing combinations of 0.1 mM U(VI), 1.0 mM Fe(II), and 4.2 g/L carboxyl-functionalized polystyrene microspheres. Acid-base titrations were used to monitor protolytic reactions, and Fe K-edge and U L-edge X-ray absorption fine structure spectroscopy was used to determine the valence and atomic environment of the adsorbed Fe and U species. In the Fe + surface carboxyl system, a transition from monomeric to oligomeric Fe(II) surface species was observed between pH 7.5 and pH 8.4. In the U + surface carboxyl system, the U(VI) cation was adsorbed as a mononuclear uranyl-carboxyl complex at both pH 7.5 and 8.4. In the ternary U + Fe + surface carboxyl system, U(VI) was not reduced by the solvated or adsorbed Fe(II) at pH 7.5 over a 4-month period, whereas complete and rapid reduction to U(IV) nanoparticles occurred at pH 8.4. The U(IV) product reoxidized rapidly upon exposure to air, but it was stable over a 4-month period under anoxic conditions. Fe atoms were found in the local environment of the reduced U(IV) atoms at a distance of 3.56 Å. The U(IV)-Fe coordination is consistent with an inner-sphere electron transfer mechanism between the redox centers and involvement of Fe(II) atoms in both steps of the reduction from U(VI) to U(IV). The inability of Fe(II) to reduce U(VI) in solution and at pH 7.5 in the U + Fe + carboxyl system is explained by the formation of a transient, "dead-end" U(V)-Fe(III) complex that blocks the U(V) disproportionation pathway after the

Performance of TcI/TcVI/TcII Chagas-Flow ATE-IgG2a for universal and genotype-specific serodiagnosis of Trypanosoma cruzi infection

PubMed Central

Alessio, Glaucia Diniz; de Araújo, Fernanda Fortes; Côrtes, Denise Fonseca; Sales Júnior, Policarpo Ademar; Lima, Daniela Cristina; Gomes, Matheus de Souza; do Amaral, Laurence Rodrigues; Xavier, Marcelo Antônio Pascoal; Teixeira-Carvalho, Andréa; Martins-Filho, Olindo Assis; de Lana, Marta

2017-01-01

Distinct Trypanosoma cruzi genotypes have been considered relevant for patient management and therapeutic response of Chagas disease. However, typing strategies for genotype-specific serodiagnosis of Chagas disease are still unavailable and requires standardization for practical application. In this study, an innovative TcI/TcVI/TcII Chagas Flow ATE-IgG2a technique was developed with applicability for universal and genotype-specific diagnosis of T. cruzi infection. For this purpose, the reactivity of serum samples (percentage of positive fluorescent parasites-PPFP) obtained from mice chronically infected with TcI/Colombiana, TcVI/CL or TcII/Y strain as well as non-infected controls were determined using amastigote-AMA, trypomastigote-TRYPO and epimastigote-EPI in parallel batches of TcI, TcVI and TcII target antigens. Data demonstrated that “α-TcII-TRYPO/1:500, cut-off/PPFP = 20%” presented an excellent performance for universal diagnosis of T. cruzi infection (AUC = 1.0, Se and Sp = 100%). The combined set of attributes “α-TcI-TRYPO/1:4,000, cut-off/PPFP = 50%”, “α-TcII-AMA/1:1,000, cut-off/PPFP = 40%” and “α-TcVI-EPI/1:1,000, cut-off/PPFP = 45%” showed good performance to segregate infections with TcI/Colombiana, TcVI/CL or TcII/Y strain. Overall, hosts infected with TcI/Colombiana and TcII/Y strains displayed opposite patterns of reactivity with “α-TcI TRYPO” and “α-TcII AMA”. Hosts infected with TcVI/CL strain showed a typical interweaved distribution pattern. The method presented a good performance for genotype-specific diagnosis, with global accuracy of 69% when the population/prototype scenario include TcI, TcVI and TcII infections and 94% when comprise only TcI and TcII infections. This study also proposes a receiver operating reactivity panel, providing a feasible tool to classify serum samples from hosts infected with distinct T. cruzi genotypes, supporting the potential of this method for universal and genotype

Packed-bed column biosorption of chromium(VI) and nickel(II) onto Fenton modified Hydrilla verticillata dried biomass.

PubMed

Mishra, Ashutosh; Tripathi, Brahma Dutt; Rai, Ashwani Kumar

2016-10-01

The present study represents the first attempt to investigate the biosorption potential of Fenton modified Hydrilla verticillata dried biomass (FMB) in removing chromium(VI) and nickel(II) ions from wastewater using up-flow packed-bed column reactor. Effects of different packed-bed column parameters such as bed height, flow rate, influent metal ion concentration and particle size were examined. The outcome of the column experiments illustrated that highest bed height (25cm); lowest flow rate (10mLmin(-1)), lowest influent metal concentration (5mgL(-1)) and smallest particle size range (0.25-0.50mm) are favourable for biosorption. The maximum biosorption capacity of FMB for chromium(VI) and nickel(II) removal were estimated to be 89.32 and 87.18mgg(-1) respectively. The breakthrough curves were analyzed using Bed Depth Service Time (BDST) and Thomas models. The experimental results obtained agree to both the models. Column regeneration experiments were also carried out using 0.1M HNO3. Results revealed good reusability of FMB during ten cycles of sorption and desorption. Performance of FMB-packed column in treating secondary effluent was also tested under identical experimental conditions. Results demonstrated significant reduction in chromium(VI) and nickel(II) ions concentration after the biosorption process. Copyright © 2016 Elsevier Inc. All rights reserved.

Methods for forming thin-film heterojunction solar cells from I-III-VI.sub. 2

DOEpatents

Mickelsen, Reid A.; Chen, Wen S.

1982-01-01

An improved thin-film, large area solar cell, and methods for forming the same, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n type heterojunction formed of: (i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI.sub.2 chalcopyrite ternary materials which is vacuum deposited in a thin "composition-graded" layer ranging from on the order of about 2.5 microns to about 5.0 microns (.congruent.2.5.mu.m to .congruent.5.0.mu.m) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (ii), a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, causes the transient n-type material in The Government has rights in this invention pursuant to Contract No. EG-77-C-01-4042, Subcontract No. XJ-9-8021-1 awarded by the U.S. Department of Energy.

Interpretation of ESR results for some semimagnetic semiconductor alloys

NASA Astrophysics Data System (ADS)

Woolley, J. C.; Chehab, S. F.; Donofrio, T.; Manhas, S.; Manoogian, A.; Lamarche, G.

1987-03-01

Previously reported values of the ESR linewidth variation with temperature for the alloys (i) Cd xZn yMn zSe (ii) Cd xZn yMn zTe and (iii) Cd 1- zMn zTe 1- ySe y have been analyzed in terms of the relation, δ H = Γ exp (- T/ T0) + B{1 - exp(- T/ T0)}(1-θ/ T), where the first term is attributed to spatial inhomogeneity effects and the second to paramagnetic behaviour. Values of the parameters, Γ, T0 and B have been determined as a function of composition in each alloy system. The parameter T0, which measures the potential barrier separating two neighbouring ground states of the disordered spin system, is found to satisfy the relation T0 = (α + β f) z, where f = y/( x + y) for (i) and (ii) and f = y for (iii). β is positive for (i) and (ii) and negative for (iii), consistent with previous suggestions of Kremer and Furdyna, and may be correlated with the exchange constants Jsp-d discussed by Hass et al. The parameter Γ, which measures the width of the distribution of the local field seen by manganese ions in the lattice, is found to satisfy the relation Γ = Dz2(1 - z), where D appears to be characteristic of the crystal structure. The parameter B which measures the linewidth δ H at high temperatures due to paramagnetic effects is found to vary as B = B0 + γ z and the values of the coefficient γ appear to be related to the exchange parameters of the materials.

Dynamics of Chromium(VI) Removal from Drinking Water by Iron Electrocoagulation.

PubMed

Pan, Chao; Troyer, Lyndsay D; Catalano, Jeffrey G; Giammar, Daniel E

2016-12-20

The potential for new U.S. regulations for Cr(VI) in drinking water have spurred strong interests in improving technologies for Cr(VI) removal. This study examined iron electrocoagulation for Cr(VI) removal at conditions directly relevant to drinking water treatment. Cr(VI) is chemically reduced to less soluble Cr(III) species by the Fe(II) produced from an iron anode, and XANES spectra indicate that the Cr is entirely Cr(III) in solid-phases produced in electrocoagulation. The dynamics of Cr(VI) removal in electrocoagulation at pH 6 and pH 8 at both oxic and anoxic conditions can be described by a new model that incorporates Fe(II) release from the anode and heterogeneous and homogeneous reduction of Cr(VI) by Fe(II). Heterogeneous Cr(VI) reduction by adsorbed Fe(II) was critical to interpreting Cr(VI) removal at pH 6, and the Fe- and Cr-containing EC product was found to catalyze the redox reaction. Dissolved oxygen (DO) did not observably inhibit Cr(VI) removal because Fe(II) reacts with DO more slowly than it does with Cr(VI), and Cr(VI) removal was faster at higher pH. Even in the presence of common groundwater solutes, iron electrocoagulation lowered Cr(VI) concentrations to levels well below California's 10 μg/L.

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys and superlattices

NASA Technical Reports Server (NTRS)

Lambrecht, Walter R. L.

1992-01-01

This proposal was mainly concerned with the theoretical study of semiconductor compounds, alloys, and superlattices of interest for photovoltaic applications. In the last year (1991) a study was devoted to metal/graphite bonding in relation to use of graphite fiber reinforcement of Cu for high thermal conductivity applications. The main research topics addressed during the full period of the grant are briefly described: studies of the In-Ga-As ternary system; band-offsets at common anion and InAs/GaSb/AlSb heterojunctions; alloy theory (cluster variation method); and Cu/graphite bonding. Most of the work was described more extensively in previous yearly reports and renewal applications and in publications. The last topic is described more fully in a separate report attached. A list of publications resulting directly from this grant or from other grants but related to this work and of conference presentations is given at the end.

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys and superlattices

NASA Astrophysics Data System (ADS)

Lambrecht, Walter R. L.

1992-08-01

This proposal was mainly concerned with the theoretical study of semiconductor compounds, alloys, and superlattices of interest for photovoltaic applications. In the last year (1991) a study was devoted to metal/graphite bonding in relation to use of graphite fiber reinforcement of Cu for high thermal conductivity applications. The main research topics addressed during the full period of the grant are briefly described: studies of the In-Ga-As ternary system; band-offsets at common anion and InAs/GaSb/AlSb heterojunctions; alloy theory (cluster variation method); and Cu/graphite bonding. Most of the work was described more extensively in previous yearly reports and renewal applications and in publications. The last topic is described more fully in a separate report attached. A list of publications resulting directly from this grant or from other grants but related to this work and of conference presentations is given at the end.

Unification of the phonon mode behavior in semiconductor alloys: Theory and ab initio calculations

NASA Astrophysics Data System (ADS)

Pagès, O.; Postnikov, A. V.; Kassem, M.; Chafi, A.; Nassour, A.; Doyen, S.

2008-03-01

We demonstrate how to overcome serious problems in understanding and classification of vibration spectra in semiconductor alloys, following from traditional use of the virtual crystal approximation (VCA). We show that such different systems as InGaAs (1- bond→1 -mode behavior), InGaP (modified 2-mode), and ZnTeSe (2- bond→1 -mode) obey, in fact, the same phonon mode behavior—hence probably a universal one—of a percolation type (1- bond→2 -mode). The change of paradigm from the “VCA insight” (an averaged microscopic one) to the “percolation insight” (a mesoscopic one) offers a promising link toward the understanding of alloy disorder. The discussion is supported by ab initio simulation of the phonon density of states at the zone center of representative supercells at intermediary composition (ZnTeSe) and at the impurity-dilute limits (all systems). In particular, we propose a simple ab initio “protocol” to estimate the basic input parameters of our semiempirical “percolation” model for the calculation of the 1- bond→2 -mode vibration spectra of zinc blende alloys. With this, the model turns self-sufficient.

Precipitation of anion inclusions and plasticity under hydrostatic pressure in II-VI crystals

NASA Astrophysics Data System (ADS)

Lindberg, G. P.; Weinstein, B. A.

2016-10-01

Precipitation of anion nanocrystals (NCs) in initially stoichiometric II-VI crystals under hydrostatic pressure and light exposure is explored by Raman spectroscopy, and the mechanism for this effect is analyzed by model calculations. ZnSe, ZnTe, and CdSe crystals are studied in bulk and/or epitaxial-film forms. Se and Te NCs in the trigonal (t) phase precipitate in ZnSe and ZnTe, but the effect is absent or minimal in CdSe. The precipitation is induced by pressure and assisted by sub-band-gap light. In ZnSe, t-Se NCs appear for pressure exceeding 4.8 GPa and light flux above 50 -70 W /m m2 . In ZnTe, the precipitation of t-Te NCs requires less pressure to initiate, and there is a clear upper-pressure limit for t-Te nuclei to form. We find also that ZnTe samples with cleavage damage or elevated zinc-vacancy content are more prone to form t-Te NCs at lower pressures (even 1 atm in some cases) and lower flux. The precipitation seen in ZnSe and ZnTe occurs at pressures far below their phase transitions, and cannot be due to those transitions. Rather, we propose that the NCs nucleate on dislocations that arise from hydrostatic-pressure induced plastic flow triggered by noncubic defect sites. Calculations of the kinetic barrier for growth of an optimally shaped nucleus are performed, including hydrostatic pressure in the energy minimization scheme. Using sensible values for the model parameters related to the cohesive energies of Se and Te, the calculations account for our main observations, including the existence of an upper pressure limit for precipitation, and the absence of precipitation in CdSe. We consider the effects of pressure-induced precipitate formation on the I-II phase transitions in a variety of binary semiconductors and make predictions of when this effect should be important.

New Insights into Intrinsic Point Defects in V2VI3 Thermoelectric Materials.

PubMed

Zhu, Tiejun; Hu, Lipeng; Zhao, Xinbing; He, Jian

2016-07-01

Defects and defect engineering are at the core of many regimes of material research, including the field of thermoelectric study. The 60-year history of V 2 VI 3 thermoelectric materials is a prime example of how a class of semiconductor material, considered mature several times, can be rejuvenated by better understanding and manipulation of defects. This review aims to provide a systematic account of the underexplored intrinsic point defects in V 2 VI 3 compounds, with regard to (i) their formation and control, and (ii) their interplay with other types of defects towards higher thermoelectric performance. We herein present a convincing case that intrinsic point defects can be actively controlled by extrinsic doping and also via compositional, mechanical, and thermal control at various stages of material synthesis. An up-to-date understanding of intrinsic point defects in V 2 VI 3 compounds is summarized in a (χ, r)-model and applied to elucidating the donor-like effect. These new insights not only enable more innovative defect engineering in other thermoelectric materials but also, in a broad context, contribute to rational defect design in advanced functional materials at large.

Characterizing Semiconductor Alloys for Infrared Sensors

NASA Technical Reports Server (NTRS)

Lehoczky, B. S. L.; Szofran, F. R.; Martin, B. G.

1986-01-01

Report presents results of continuing program aimed at characterizing mercury/cadmium/tellurium alloys and eventually developing improved methods of preparing alloys for use as infrared sensors. Work covered by report includes series of differential thermal analysis (DTA) measurements of alloy compositions with x varied from 9 to 1 in 0.1 increments.

Cobalt (II) oxide and nickel (II) oxide alloys as potential intermediate-band semiconductors: A theoretical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alidoust, Nima; Lessio, Martina; Carter, Emily A., E-mail: eac@princeton.edu

2016-01-14

Solar cells based on single pn junctions, employing single-gap semiconductors can ideally achieve efficiencies as high as 34%. Developing solar cells based on intermediate-band semiconductors (IBSCs), which can absorb light across multiple band gaps, is a possible way to defy this theoretical limit and achieve efficiencies as high as 60%. Here, we use first principles quantum mechanics methods and introduce CoO and Co{sub 0.25}Ni{sub 0.75}O as possible IBSCs. We show that the conduction band in both of these materials is divided into two distinct bands separated by a band gap. We further show that the lower conduction band (i.e., themore » intermediate band) is wider in Co{sub 0.25}Ni{sub 0.75}O compared with CoO. This should enhance light absorption from the valence band edge to the intermediate band, making Co{sub 0.25}Ni{sub 0.75}O more appropriate for use as an IBSC. Our findings provide the basis for future attempts to partially populate the intermediate band and to reduce the lower band gap in Co{sub 0.25}Ni{sub 0.75}O in order to enhance the potential of this material for use in IBSC solar cell technologies. Furthermore, with proper identification of heterojunctions and dopants, CoO and Co{sub 0.25}Ni{sub 0.75}O could be used in multi-color light emitting diode and laser technologies.« less

Two Photon Absorption in II-VI Semiconductors: The Influence of Dimensionality and Size.

PubMed

Scott, Riccardo; Achtstein, Alexander W; Prudnikau, Anatol; Antanovich, Artsiom; Christodoulou, Sotirios; Moreels, Iwan; Artemyev, Mikhail; Woggon, Ulrike

2015-08-12

We report a comprehensive study on the two-photon absorption cross sections of colloidal CdSe nanoplatelets, -rods, and -dots of different sizes by the means of z-scan and two-photon excitation spectroscopy. Platelets combine large particle volumes with ultra strong confinement. In contrast to weakly confined nanocrystals, the TPA cross sections of CdSe nanoplatelets scale superlinearly with volume (V(∼2)) and show ten times more efficient two-photon absorption than nanorods or dots. This unexpectedly strong shape dependence goes well beyond the effect of local fields. The larger the particles' aspect ratio, the greater is the confinement related electronic contribution to the increased two-photon absorption. Both electronic confinement and local field effects favor the platelets and make them unique two-photon absorbers with outstanding cross sections of up to 10(7) GM, the largest ever reported for (colloidal) semiconductor nanocrystals and ideally suited for two-photon imaging and nonlinear optoelectronics. The obtained results are confirmed by two independent techniques as well as a new self-referencing method.

Optimization of the photorefractivity in II-IV semiconductors. Final report, March 1996--March 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jagannathan, G.V.; Trivedi, S.B.; Kutcher, S.W.

1998-11-01

This work was aimed at optimization of the photorefractivity in the II-VI semiconductors CdTe, ZnTe and Cd{sub x{minus}1}Zn{sub (x)}Te for real-time optical signal processing applications at near infrared wavelengths. During this work, several crystals of ZnTe, CdTe and Cd{sub x{minus}1}Zn{sub (x)}Te were grown. Crystal growth of ZnTe and CdTe was carried out using low supersaturation nucleation and `contactless` growth by Vertical Physical Vapor Transport (PVT) in closed ampoules and the CdTe and Cd{sub x{minus}1}Zn{sub (x)}Te crystals were grown using the vertical Bridgman technique. The quality of the crystals grown during this work was evaluated based on optical, electrical and structuralmore » characterization. Infrared microscopy was used to examine the internal crystalline structure of the samples. Most of the crystals grown during this work exhibited photorefractivity and photoconductivity. The resistivity of the vanadium doped crystals under dark conditions was found to be between 10 {sup 8} to 10 {sup 10} ohms cm. The resistivity decreased significantly in the presence of illumination indicating that the crystals were highly photoconductive. The photorefractive properties of the crystals grown during this project were characterized by two beam coupling. All of the measurements revealed a strong photorefractive nonlinear effect.« less

Single, simultaneous and consecutive biosorption of Cr(VI) and Orange II onto chemically modified masau stones.

PubMed

Albadarin, Ahmad B; Solomon, Samuel; Kurniawan, Tonni Agustiono; Mangwandi, Chirangano; Walker, Gavin

2017-12-15

Novel and low cost chemically modified masau stone (CMMS) was investigated for its biosorption of an anionic azo dye, Orange II (OII), and toxic hexavalent chromium (Cr(VI)) from aqueous systems: individually, simultaneously and consecutively. XPS and FTIR analyses indicated the introduction of quaternary-Nitrogen to the CMMS surface after activation with epichlorohydrin (etherifying agent) and diethylenetriamine (crosslinking agent). The effects of pH, contact time and initial concentration (C o ), and loading order on mechanisms of biosorption/reduction of OII and Cr(VI) onto CMMS were examined in detail. Several analytical techniques were employed to characterise the physio-chemical properties of the CMMS and determine the biosorption mechanisms. The pseudo second order and redox models were able to adequately predict the kinetics of biosorption. The Langmuir maximum OII biosorption capacity (q max ) was calculated as 136.8 mg/g for the dye onto the Cr(VI)-loaded CMMS consecutive system at C o  = 100 mg/dm 3 . The q max for the Cr(VI) system was found to be 87.32 mg/g at the same C o max. This reveals that the biosorption of OII and Cr(VI) mainly takes place via two different mechanisms i.e. hydrogen bonding and electrostatic attraction for the dye, and biosorption-coupled reduction for Cr(VI). Copyright © 2017 Elsevier Ltd. All rights reserved.

Ultratrace Determination of Cr(VI) and Pb(II) by Microsample Injection System Flame Atomic Spectroscopy in Drinking Water and Treated and Untreated Industrial Effluents

PubMed Central

Baig, Jameel Ahmed; Kazi, Tasneem Gul; Elci, Latif; Afridi, Hassan Imran; Khan, Muhammad Irfan; Naseer, Hafiz Muhammad

2013-01-01

Simple and robust analytical procedures were developed for hexavalent chromium (Cr(VI)) and lead (Pb(II)) by dispersive liquid-liquid microextraction (DLLME) using microsample injection system coupled with flame atomic absorption spectrophotometry (MIS-FAAS). For the current study, ammonium pyrrolidine dithiocarbamate (APDC), carbon tetrachloride, and ethanol were used as chelating agent, extraction solvent, and disperser solvent, respectively. The effective variables of developed method have been optimized and studied in detail. The limit of detection of Cr(VI) and Pb(II) were 0.037 and 0.054 µg/L, respectively. The enrichment factors in both cases were 400 with 40 mL of initial volumes. The relative standard deviations (RSDs, n = 6) were <4%. The applicability and the accuracy of DLLME were estimated by the analysis of Cr(VI) and Pb(II) in industrial effluent wastewater by standard addition method (recoveries >96%). The proposed method was successfully applied to the determination of Cr(VI) and Pb(II) at ultratrace levels in natural drinking water and industrial effluents wastewater of Denizli. Moreover, the proposed method was compared with the literature reported method. PMID:24163779

X-ray absorption fine structure and X-ray excited optical luminescence studies of II-VI semiconducting nanostructures

NASA Astrophysics Data System (ADS)

Murphy, Michael Wayne

2010-06-01

of 0, 1,3, and 10% and annealed at 400, 600 and 800°C in air. XAFS spectra show that low dopant concentrations and low processing temperatures limit the amount of secondary phase formation. The nanopowders did not show roomtemperature ferromagnetism and increased secondary phase formation increases the paramagnetic character of the hysteresis curves at 5°K. Keywords: X-ray absorption fine structures (XAFS), X-ray absorption near-edge structures (XANES), extended X-ray absorption fine structure (EXAFS), X-ray absorption spectroscopy(XAS), X-ray excited optical luminescence (XEOL), time-resolved, II-VI semiconductors, nanostructure, nanomaterial, nanoribbon, nanowire, nanopartic1e, heterostructure, ZnO, ZnS, ZnO-ZnS, CdS, CdSe, CdSSe, ZnO:Mn, ZnO:Co, ZnS:Mn, dilute magnetic semiconductor (DMS), dilute magnetic oxide (DMO), spintronics, magnetism, paramagnetism, ferromagnetism.

Light-matter Interactions in Semiconductors and Metals: From Nitride Optoelectronics to Quantum Plasmonics

NASA Astrophysics Data System (ADS)

Narang, Prineha

This thesis puts forth a theory-directed approach coupled with spectroscopy aimed at the discovery and understanding of light-matter interactions in semiconductors and metals. The first part of the thesis presents the discovery and development of Zn-IV nitride materials. The commercial prominence in the optoelectronics industry of tunable semiconductor alloy materials based on nitride semiconductor devices, specifically InGaN, motivates the search for earth-abundant alternatives for use in efficient, high-quality optoelectronic devices. II-IV-N2 compounds, which are closely related to the wurtzite-structured III-N semiconductors, have similar electronic and optical properties to InGaN namely direct band gaps, high quantum efficiencies and large optical absorption coefficients. The choice of different group II and group IV elements provides chemical diversity that can be exploited to tune the structural and electronic properties through the series of alloys. The first theoretical and experimental investigation of the ZnSnxGe1--xN2 series as a replacement for III-nitrides is discussed here. The second half of the thesis shows ab-initio calculations for surface plasmons and plasmonic hot carrier dynamics. Surface plasmons, electromagnetic modes confined to the surface of a conductor-dielectric interface, have sparked renewed interest because of their quantum nature and their broad range of applications. The decay of surface plasmons is usually a detriment in the field of plasmonics, but the possibility to capture the energy normally lost to heat would open new opportunities in photon sensors, energy conversion devices and switching. A theoretical understanding of plasmon-driven hot carrier generation and relaxation dynamics in the ultrafast regime is presented here. Additionally calculations for plasmon-mediated upconversion as well as an energy-dependent transport model for these non-equilibrium carriers are shown. Finally, this thesis gives an outlook on the

EPR and Ferromagnetism in Diluted Magnetic Semiconductor Quantum Wells

NASA Astrophysics Data System (ADS)

König, Jürgen; MacDonald, Allan H.

2003-08-01

Motivated by recent measurements of electron paramagnetic resonance spectra in modulation-doped CdMnTe quantum wells [

Process for preparing group Ib-IIIa-VIa semiconducting films

DOEpatents

Birkmire, R.W.; Schultz, J.M.; Marudachalam, M.; Hichri, H.

1997-10-07

Methods are provided for the production of supported monophasic group I-III-VI semiconductor films. In the subject methods, a substrate is coated with group I and III elements and then contacted with a reactive group VI element containing atmosphere under conditions sufficient to produce a substrate coated with a composite of at least two different group I-III-IV alloys. The resultant composite coated substrate is then annealed in an inert atmosphere under conditions sufficient to convert the composite coating to a monophasic group I-III-VI semiconductor film. The resultant supported semiconductor films find use in photovoltaic applications, particularly as absorber layers in solar cells. 4 figs.

Process for preparing group Ib-IIIa-VIa semiconducting films

DOEpatents

Birkmire, Robert W.; Schultz, Jerold M.; Marudachalam, Matheswaran; Hichri, Habib

1997-01-01

Methods are provided for the production of supported monophasic group I-III-VI semiconductor films. In the subject methods, a substrate is coated with group I and III elements and then contacted with a reactive group VI element containing atmosphere under conditions sufficient to produce a substrate coated with a composite of at least two different group I-III-IV alloys. The resultant composite coated substrate is then annealed in an inert atmosphere under conditions sufficient to convert the composite coating to a monophasic group I-III-VI semiconductor film. The resultant supported semiconductor films find use in photovoltaic applications, particularly as absorber layers in solar cells.

Growth of In x Ga1-x Sb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments.

PubMed

Inatomi, Y; Sakata, K; Arivanandhan, M; Rajesh, G; Nirmal Kumar, V; Koyama, T; Momose, Y; Ozawa, T; Okano, Y; Hayakawa, Y

2015-01-01

In x Ga 1- x Sb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed. To investigate the dissolution and growth process of In x Ga 1- x Sb alloy semiconductors via a sandwiched structure of GaSb(seed)/InSb/GaSb(feed) under normal and μG conditions. In x Ga 1- x Sb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated. The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG. Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the In x Ga 1- x Sb alloy semiconductor.

Characterization of Amoeba proteus myosin VI immunoanalog.

PubMed

Dominik, Magdalena; Kłopocka, Wanda; Pomorski, Paweł; Kocik, Elzbieta; Redowicz, Maria Jolanta

2005-07-01

Amoeba proteus, the highly motile free-living unicellular organism, has been widely used as a model to study cell motility. However, molecular mechanisms underlying its unique locomotion and intracellular actin-based-only trafficking remain poorly understood. A search for myosin motors responsible for vesicular transport in these giant cells resulted in detection of 130-kDa protein interacting with several polyclonal antibodies against different tail regions of human and chicken myosin VI. This protein was binding to actin in the ATP-dependent manner, and immunoprecipitated with anti-myosin VI antibodies. In order to characterize its possible functions in vivo, its cellular distribution and colocalization with actin filaments and dynamin II during migration and pinocytosis were examined. In migrating amoebae, myosin VI immunoanalog localized to vesicular structures, particularly within the perinuclear and sub-plasma membrane areas, and colocalized with dynamin II immunoanalog and actin filaments. The colocalization was even more evident in pinocytotic cells as proteins concentrated within pinocytotic pseudopodia. Moreover, dynamin II and myosin VI immunoanalogs cosedimented with actin filaments, and were found on the same isolated vesicles. Blocking endogenous myosin VI immunoanalog with anti-myosin VI antibodies inhibited the rate of pseudopodia protrusion (about 19% decrease) and uroidal retraction (about 28% decrease) but did not affect cell morphology and the manner of cell migration. Treatment with anti-human dynamin II antibodies led to changes in directionality of amebae migration and affected the rate of only uroidal translocation (about 30% inhibition). These results indicate that myosin VI immunoanalog is expressed in protist Amoeba proteus and may be involved in vesicle translocation and cell locomotion.

The reactivity of Fe(II) associated with goethite formed during short redox cycles toward Cr(VI) reduction under oxic conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomaszewski, Elizabeth J.; Lee, Seungyeol; Rudolph, Jared

Chromium (Cr) is a toxic metal that causes a myriad of health problems and enters the environment as a result of anthropogenic activities and/or natural processes. The toxicity and solubility of chromium is linked to its oxidation state; Cr(III) is poorly soluble and relatively nontoxic, while Cr(VI) is soluble and a known carcinogen. Solid Fe(II) in iron-bearing minerals, such as pyrite, magnetite, and green rusts, reduce the oxidation state of chromium, reducing its toxicity and mobility. However, these minerals are not the only potential sources of solid-associated Fe(II) available for Cr(VI) reduction. For example, ferric (Fe(III)) (hydr)oxides, such as goethitemore » or hematite, can have Fe(II) in the solid without phase transformation; however, the reactivity of Fe(II) within Fe(III) (hydr)oxides with contaminants, has not been previously investigated. Here, we cyclically react goethite with dissolved Fe(II) followed by dissolved O2, leading to the formation of reactive Fe(II) associated with goethite. In separate reactors, the reactivity of this Fe(II) is probed under oxic conditions, by exposure to chromate (CrO42 -) after either one, two, three or four redox cycles. Cr is not present during redox cycling; rather, it is introduced to a subset of the solid after each oxidation half-cycle. Analysis of X-ray absorption near edge structure (XANES) spectra reveals that the extent of Cr(VI) reduction to Cr(III) depends not only on solid Fe(II) content but also surface area and mean size of ordered crystalline domains, determined by BET surface area analysis and X-ray diffraction (XRD), respectively. Shell-by-shell fitting of the extended X-ray absorption fine structure (EXAFS) spectra demonstrates chromium forms both single and double corner sharing complexes on the surface of goethite, in addition to sorbed Cr(III) species. Finally, transmission electron microscope (TEM) imaging and X-ray energy-dispersive spectroscopy (EDS) illustrate that Cr preferentially

Syntheses and applications of manganese-doped II-VI semiconductor nanocrystals

NASA Astrophysics Data System (ADS)

Yang, Heesun

Syntheses, characterizations, and applications of two different Mn-doped semiconductor nanocrystals, ZnS:Mn and CdS:Mn/ZnS core/shell, were investigated. ZnS:Mn nanocrystals with sizes between 3 and 4 nm were synthesized via a competitive reaction chemistry. A direct current (dc) electroluminescent (EL) device having a hybrid organic/inorganic multilayer structure of an indium tin oxide (ITO) transparent conducting electrode, a (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS) and a poly(N-vinylcarbazole) (PVK) bilayer hole transport film, a ZnS:Mn nanocrystal layer, and Al dot contacts was demonstrated to emit blue (˜445 and ˜495 nm) from PVK and yellow (˜600 nm) light from Mn activator in ZnS. The EL emission spectrum was dependent upon both the voltage and Mn concentration, showing a decreasing nanocrystal to PVK emission ratio from 10 at 20 V to 4 at 28 V, and an increasing ratio from 1.3 at 0.40 mol % to 4.3 at 2.14 mol %. Mn-doped CdS core nanocrystals were produced ranging from 1.5 to 2.3 nm in diameter with a ZnS shell via a reverse micelle process. In contrast to CdS:Mn nanocrystals passivated by n-dodecanethiol, ZnS-passivated CdS:Mn (CdS:Mn/ZnS core/shell) nanocrystals were efficient and photostable. CdS:Mn/ZnS core/shell nanocrystals exhibited a quantum yield of ˜18%, and the photoluminescence (PL) intensity increased by 40% after 400 nm UV irradiation in air. X-ray photoelectron spectroscopy (XPS) data showed that UV irradiation of CdS:Mn/ZnS nanocrystals induces the photooxidation of the ZnS shell surface to ZnSO4. This photooxidation product is presumably responsible for the increased PL emission by serving as a passivating surface layer. Luminescent lifetime data from the core/shell nanocrystals could be fit with two exponential functions, with a time constant of ˜170 nsec for the defect-related centers and of ˜1 msec for the Mn centers. The CdS:Mn/ZnS nanocrystals with a core crystal diameter of 2.3 nm and a 0.4 nm thick Zn

Statistical correction of atom probe tomography data of semiconductor alloys combined with optical spectroscopy: The case of Al{sub 0.25}Ga{sub 0.75}N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rigutti, L., E-mail: lorenzo.rigutti@univ-rouen.fr; Mancini, L.; Hernández-Maldonado, D.

2016-03-14

The ternary semiconductor alloy Al{sub 0.25}Ga{sub 0.75}N has been analyzed by means of correlated photoluminescence spectroscopy and atom probe tomography (APT). We find that the composition measured by APT is strongly dependent on the surface electric field, leading to erroneous measurements of the alloy composition at high field, due to the different evaporation behaviors of Al and Ga atoms. After showing how a biased measurement of the alloy content leads to inaccurate predictions on the optical properties of the material, we develop a correction procedure which yields consistent transition and localization energies for the alloy photoluminescence.

Visible-light-enhanced Cr(VI) reduction at Pd-decorated silicon nanowire photocathode in photoelectrocatalytic microbial fuel cell.

PubMed

Han, He-Xing; Shi, Chen; Zhang, Nan; Yuan, Li; Sheng, Guo-Ping

2018-10-15

Hexavalent chromium (Cr(VI)) is a prominent toxic metal with significant adverse human health effects. Photocatalytic reduction of Cr(VI) to less-toxic trivalent chromium (Cr(III)) is a promising method for removing Cr(VI) from aquatic environments. However, this technique often suffers from electron-hole recombination of semiconductors and poor reduction efficiency. The photoelectrocatalytic microbial fuel cell (Photo-MFC), which can use wastewater and light to recover electricity, has recently been proven to improve the separation of photocarriers of semiconductors and enhance cathodic reduction of pollutants. Here, the reduction of Cr(VI) was investigated in a Photo-MFC with a Pd-decorated p-type silicon nanowire (Pd/SiNW) photocathode and a bioanode under visible light. The Cr(VI) reduction efficiency reached 98.7% in 8 h under visible light, which was much higher than that under dark condition (56.2%) and open-circuit condition (19.4%). The enhanced Cr(VI) removal was mainly attributed to the synergistic effect of Pd/SiNW photocathode and bioanode. Cr(VI) reduction in the Photo-MFC fitted well with pseudo-first-order kinetics. The kinetics constants and reduction efficiencies of Cr(VI) decreased with the increase of pH, initial Cr(VI) concentration and external resistance. This work provides a promising alternative to mitigate Cr(VI) pollution in aquatic environments. Copyright © 2018 Elsevier B.V. All rights reserved.

High-resistant castable corrosion-resistant nickel alloy for monocrystalline casting by the directional crystallization method

NASA Astrophysics Data System (ADS)

Belikov, S. B.; Andrienko, A. G.; Gaiduk, S. V.; Kononov, V. V.; Zamkovoi, V. E.

2008-01-01

A high-resistant corrosion-resistant nickel-based alloy has been developed for monocrystalline casting using the directional crystallization method. Its mechanical properties are close to those of aircraft alloys ZhS6K-VI and ZhS6U-VI with an equiaxial structure and ZhS26-VI with an oriented structure. The technology of producing blades for turboprop engines from the new alloy has been developed and tested.

Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I-type-II transition of natural band offsets in nonpolar zinc-blende AlxGa1 -xN /AlyGa1 -yN composites

NASA Astrophysics Data System (ADS)

Landmann, M.; Rauls, E.; Schmidt, W. G.

2017-04-01

The composition dependence of the natural band alignment at nonpolar AlxGa1 -xN /AlyGa1 -yN heterojunctions is investigated via hybrid functional based density functional theory. Accurate band-gap data are provided using Heyd-Scuseria-Ernzerhof (HSE) type hybrid functionals with a composition dependent exact-exchange contribution. The unstrained band alignment between zincblende (zb) AlxGa1 -xN semiconductor alloys is studied within the entire ternary composition range utilizing the Branch-point technique to align the energy levels related to the bulklike direct Γv→Γc and indirect, pseudodirect, respectively, Γv→Xc type transitions in zb-AlxGa1 -xN . While the zb-GaN/AlxGa1 -xN band edges consistently show a type-I alignment, the relative position of fundamental band edges changes to a type-II alignment in the Al-rich composition ranges of zb-AlxGa1 -xN /AlN and zb-AlxGa1 -xN /AlyGa1 -yN systems. The presence of a direct-indirect band-gap transition at xc=0.63 in zb-AlxGa1 -xN semiconductor alloys gives rise to a notably different composition dependence of band discontinuities in the direct and indirect energy-gap ranges. Below the critical direct-indirect Al/Ga-crossover concentration, the band offsets show a close to linear dependence on the alloy composition. In contrast, notable bowing characteristics of all band discontinuities are observed above the critical crossover composition.

Fabrication of optically reflecting ohmic contacts for semiconductor devices

DOEpatents

Sopori, B.L.

1995-07-04

A method is provided to produce a low-resistivity ohmic contact having high optical reflectivity on one side of a semiconductor device. The contact is formed by coating the semiconductor substrate with a thin metal film on the back reflecting side and then optically processing the wafer by illuminating it with electromagnetic radiation of a predetermined wavelength and energy level through the front side of the wafer for a predetermined period of time. This method produces a thin epitaxial alloy layer between the semiconductor substrate and the metal layer when a crystalline substrate is used. The alloy layer provides both a low-resistivity ohmic contact and high optical reflectance. 5 figs.

Fabrication of optically reflecting ohmic contacts for semiconductor devices

DOEpatents

Sopori, Bhushan L.

1995-01-01

A method is provided to produce a low-resistivity ohmic contact having high optical reflectivity on one side of a semiconductor device. The contact is formed by coating the semiconductor substrate with a thin metal film on the back reflecting side and then optically processing the wafer by illuminating it with electromagnetic radiation of a predetermined wavelength and energy level through the front side of the wafer for a predetermined period of time. This method produces a thin epitaxial alloy layer between the semiconductor substrate and the metal layer when a crystalline substrate is used. The alloy layer provides both a low-resistivity ohmic contact and high optical reflectance.

Synthesis of Zn-In-S Quantum Dots with Tunable Composition and Optical Properties.

PubMed

Wang, Xianliang; Damasco, Jossana; Shao, Wei; Ke, Yujie; Swihart, Mark T

2016-03-03

II-III-VI semiconductors are of interest due to their chemical stability and composition-tunable optical properties. Here, we report a methodology for the synthesis of monodisperse zinc-indium-sulfide (ZIS) alloy quantum dots (QDs, mean diameter from ∼2 to 3.5 nm) with an In content substantially below that of the stoichiometric ZnIn2 S4 compound. The effects of indium incorporation on the size, lattice constant, and optical properties of ZIS QDs are elucidated. In contrast to previous reports, we employ sulfur dissolved in oleic acid as the sulfur donor rather than thioacetamide (TAA). The size of the ZIS QDs and their crystal lattice constant increased with increasing In incorporation, but they maintained the cubic sphalerite phase of ZnS, rather than the hexagonal phase typical of ZnIn2 S4 . The QDs' absorbance onset at UV wavelengths red-shifts with increasing In content and the accompanying increase in NC size. The ZIS NCs and related materials, whose synthesis is enabled by the approach presented here, provide new opportunities to apply II-III-VI semiconductors in solution-processed UV optoelectronics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lattice matched crystalline substrates for cubic nitride semiconductor growth

DOEpatents

Norman, Andrew G; Ptak, Aaron J; McMahon, William E

2015-02-24

Disclosed embodiments include methods of fabricating a semiconductor layer or device and devices fabricated thereby. The methods include, but are not limited to, providing a substrate having a cubic crystalline surface with a known lattice parameter and growing a cubic crystalline group III-nitride alloy layer on the cubic crystalline substrate by coincident site lattice matched epitaxy. The cubic crystalline group III-nitride alloy may be prepared to have a lattice parameter (a') that is related to the lattice parameter of the substrate (a). The group III-nitride alloy may be a cubic crystalline In.sub.xGa.sub.yAl.sub.1-x-yN alloy. The lattice parameter of the In.sub.xGa.sub.yAl.sub.1-x-yN or other group III-nitride alloy may be related to the substrate lattice parameter by (a')= 2(a) or (a')=(a)/ 2. The semiconductor alloy may be prepared to have a selected band gap.

Reactively-sputtered zinc semiconductor films of high conductivity for heterojunction devices

NASA Technical Reports Server (NTRS)

Stirn, Richard J. (Inventor)

1986-01-01

A high conductivity, n-doped semiconductor film is produced from zinc, or Zn and Cd, and group VI elements selected from Se, S and Te in a reactive magnetron sputtering system having a chamber with one or two targets, a substrate holder, means for heating the substrate holder, and an electric field for ionizing gases in the chamber. Zinc or a compound of Zn and Cd is placed in the position of one of the two targets and doping material in the position of the other of the two targets. Zn and Cd may be placed in separate targets while a dopant is placed in the third target. Another possibility is to place an alloy of Zn and dopant, or Zn, Cd and dopant in one target, thus using only one target. A flow of the inert gas is ionized and directed toward said targets, while a flow of a reactant gas consisting of hydrides of the group VI elements is directed toward a substrate on the holder. The targets are biased to attract negatively ionized inert gas. The desired stochiometry for high conductivity is achieved by controlling the temperature of the substrate, and partial pressures of the gases, and the target power and total pressure of the gases in the chamber.

Growth of InxGa1−xSb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments

PubMed Central

Inatomi, Y; Sakata, K; Arivanandhan, M; Rajesh, G; Nirmal Kumar, V; Koyama, T; Momose, Y; Ozawa, T; Okano, Y; Hayakawa, Y

2015-01-01

Background: InxGa1−xSb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed. Aims: To investigate the dissolution and growth process of InxGa1−xSb alloy semiconductors via a sandwiched structure of GaSb(seed)/InSb/GaSb(feed) under normal and μG conditions. Methods: InxGa1−xSb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated. Results: The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG. Conclusions: Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the InxGa1−xSb alloy semiconductor. PMID:28725715

Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions

NASA Astrophysics Data System (ADS)

Rubel, O.; Bokhanchuk, A.; Ahmed, S. J.; Assmann, E.

2014-09-01

Supercells are often used in ab initio calculations to model compound alloys, surfaces, and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include formation of donorlike states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.

Metal-chelate dye-controlled organization of Cd32S14(SPh)40(4-) nanoclusters into three-dimensional molecular and covalent open architecture.

PubMed

Zheng, Nanfeng; Lu, Haiwei; Bu, Xianhui; Feng, Pingyun

2006-04-12

Chalcogenide II-VI nanoclusters are usually prepared as isolated clusters and have defied numerous efforts to join them into covalent open-framework architecture with conventional templating methods such as protonated amines or inorganic cations commonly used to direct the formation of porous frameworks. Herein, we report the first templated synthesis of II-VI covalent superlattices from large II-VI tetrahedral clusters (i.e., [Cd32S14(SPh)38]2-). Our method takes advantage of low charge density of metal-chelate dyes that is a unique match with three-dimensional II-VI semiconductor frameworks in charge density, surface hydrophilicity-hydrophobicity, and spatial organization. In addition, metal-chelate dyes also serve to tune the optical properties of resulting dye semiconductor composite materials.

30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B... AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22238 Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 2.0 percent in the mine...

30 CFR 57.22231 - Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 0.25 percent methane (I-B, II-B, V-B... AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22231 Actions at 0.25 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 0.25 percent in the...

Electronic properties of electron and hole in type-II semiconductor nano-heterostructures

NASA Astrophysics Data System (ADS)

Rahul, K. Suseel; Souparnika, C.; Salini, K.; Mathew, Vincent

2016-05-01

In this project, we record the orbitals of electron and hole in type-II (CdTe/CdSe/CdTe/CdSe) semiconductor nanocrystal using effective mass approximation. In type-II the band edges of both valance and conduction band are higher than that of shell. So the electron and hole get confined in different layers of the hetero-structure. The energy eigen values and eigen functions are calculated by solving Schrodinger equation using finite difference matrix method. Based on this we investigate the effect of shell thickness and well width on energy and probability distribution of ground state (1s) and few excited states (1p,1d,etc). Our results predict that, type-II quantum dots have significant importance in photovoltaic applications.

Bis(tetra­methyl­ammonium) tetra­chlorido­zincate(II), phase VI

PubMed Central

Curtiss, Ashley B. S.; Musie, Ghezai T.; Powell, Douglas R.

2008-01-01

Phase VI of bis­(tetra­methyl­ammonium) tetra­chloro­zincate(II), (C4H12N)2[ZnCl4], contains three formula units per asymmetric unit. Several short C—H⋯Cl contacts [2.70 (3) and 2.72 (4) Å] are observed, but they are believed to participate only in van der Waals inter­actions. The crystal studied exhibited inversion twinning. PMID:21200531

Room-temperature ductile inorganic semiconductor.

PubMed

Shi, Xun; Chen, Hongyi; Hao, Feng; Liu, Ruiheng; Wang, Tuo; Qiu, Pengfei; Burkhardt, Ulrich; Grin, Yuri; Chen, Lidong

2018-05-01

Ductility is common in metals and metal-based alloys, but is rarely observed in inorganic semiconductors and ceramic insulators. In particular, room-temperature ductile inorganic semiconductors were not known until now. Here, we report an inorganic α-Ag 2 S semiconductor that exhibits extraordinary metal-like ductility with high plastic deformation strains at room temperature. Analysis of the chemical bonding reveals systems of planes with relatively weak atomic interactions in the crystal structure. In combination with irregularly distributed silver-silver and sulfur-silver bonds due to the silver diffusion, they suppress the cleavage of the material, and thus result in unprecedented ductility. This work opens up the possibility of searching for ductile inorganic semiconductors/ceramics for flexible electronic devices.

Room-temperature ductile inorganic semiconductor

NASA Astrophysics Data System (ADS)

Shi, Xun; Chen, Hongyi; Hao, Feng; Liu, Ruiheng; Wang, Tuo; Qiu, Pengfei; Burkhardt, Ulrich; Grin, Yuri; Chen, Lidong

2018-05-01

Ductility is common in metals and metal-based alloys, but is rarely observed in inorganic semiconductors and ceramic insulators. In particular, room-temperature ductile inorganic semiconductors were not known until now. Here, we report an inorganic α-Ag2S semiconductor that exhibits extraordinary metal-like ductility with high plastic deformation strains at room temperature. Analysis of the chemical bonding reveals systems of planes with relatively weak atomic interactions in the crystal structure. In combination with irregularly distributed silver-silver and sulfur-silver bonds due to the silver diffusion, they suppress the cleavage of the material, and thus result in unprecedented ductility. This work opens up the possibility of searching for ductile inorganic semiconductors/ceramics for flexible electronic devices.

Semiconductor Alloy Theory.

DTIC Science & Technology

1986-01-14

0.15 0.352 GaPAs) 3.5 191 0.10 0.11 0.307 In(As,SbJ 6.8 635 0.52 0.79 0.840 Ga(As,Sb) 7.6 924 0.53 0.94 0.844 AI(As,Sb) 8.1 1030 0.56 0.78 0.810 - ln(PSb...to prov ide good estimiates, of the mixing enthalpies *T, /T 2 is plotted against bi8 ) alone, the FPT points are fl of pseudobinaryN alloys. The

Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, S.; Li, C.; Scripa, R.; Lehoczky, S. L.; Kim, Y. M.; Baird, J. K.; Lin, B.; Ban, H.; Benmore, Chris;

Characterization of β-FeSi II films as a novel solar cell semiconductor

NASA Astrophysics Data System (ADS)

Fukuzawa, Yasuhiro; Ootsuka, Teruhisa; Otogawa, Naotaka; Abe, Hironori; Nakayama, Yasuhiko; Makita, Yunosuke

2006-04-01

β-FeSi II is an attractive semiconductor owing to its extremely high optical absorption coefficient (α>10 5 cm -1), and is expected to be an ideal semiconductor as a thin film solar cell. For solar cell use, to prepare high quality β-FeSi II films holding a desired Fe/Si ratio, we chose two methods; one is a molecular beam epitaxy (MBE) method in which Fe and Si were evaporated by using normal Knudsen cells, and occasionally by e-gun for Si. Another one is the facing-target sputtering (FTS) method in which deposition of β-FeSi II films is made on Si substrate that is placed out of gas plasma cloud. In both methods to obtain β-FeSi II films with a tuned Fe/Si ratio, Fe/Si super lattice was fabricated by varying Fe and Si deposition thickness. Results showed significant in- and out-diffusion of host Fe and Si atoms at the interface of Si substrates into β-FeSi II layers. It was experimentally demonstrated that this diffusion can be suppressed by the formation of template layer between the epitaxial β-FeSi II layer and the substrate. The template layer was prepared by reactive deposition epitaxy (RDE) method. By fixing the Fe/Si ratio as precisely as possible at 1/2, systematic doping experiments of acceptor (Ga and B) and donor (As) impurities into β-FeSi II were carried out. Systematical changes of electron and hole carrier concentration in these samples along variation of incorporated impurities were observed through Hall effect measurements. Residual carrier concentrations can be ascribed to not only the remaining undesired impurities contained in source materials but also to a variety of point defects mainly produced by the uncontrolled stoichiometry. A preliminary structure of n-β-FeSi II/p-Si used as a solar cell indicated a conversion efficiency of 3.7%.

Defect engineering of complex semiconductor alloys: Cu2-2xMxO1-yXy

NASA Astrophysics Data System (ADS)

Lany, Stephan; Stevanovic, Vladan

2013-03-01

The electrical properties of semiconductors are generally controlled via doping, i.e., the incorporation of dilute concentrations of aliovalent impurity atoms, whereas the band structure properties (gap, effective masses, optical properties) are manipulated by alloying, i.e., the incorporation of much larger amounts of isovalent elements. Theoretical approaches usually address either doping or alloying, but rarely both problems at the same time. By combining defect supercell calculations, GW quasi-particle energy calculation, and thermodynamic modeling, we study the range of electrical and band structure properties accessible by alloying aliovalent cations (M = Mg, Zn, Cd) and isovalent anions (X = S, Se) in Cu2O. In order to extend dilute defect models to higher concentrations, we take into account the association/dissociation of defect pairs and complexes, as well as the composition dependence of the band gap and the band edge energies. Considering a composition window for the Cu2-2xMxO1-yXy alloys of 0 <= (x,y) <= 0.2, we predict a wide range of possible band gaps from 1.7 to 2.6 eV, and net doping concentrations between p = 1019 cm-3 and n = 1017cm-3, notably achieving type conversion from p- to n-type at Zn or Cd compositions around x = 0.1. This work is supported as part of the SunShot initiative by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy under Contract No. DE-AC36-08GO28308 to NREL.

Self-organized MBE growth of II VI epilayers on patterned GaSb substrates

NASA Astrophysics Data System (ADS)

Wissmann, H.; Tran Anh, T.; Rogaschewski, S.; von Ortenberg, M.

1999-05-01

We report on the self-organized MBE growth of II-VI epilayers on patterned and unpatterned GaSb substrates resulting in quantum wires and quantum wells, respectively. The HgSe : Fe quantum wires were grown on (0 0 1)GaSb substrates with a buffer of lattice-matched ZnTe 1- xSe x. Due to the anisotropic growth of HgSe on the A-oriented stripes roof-like overgrowth with a definite ridge was obtained. Additional Fe doping in the direct vicinity of the ridge results in a highly conductive quantum wire.

Digital Alloy Absorber for Photodetectors

NASA Technical Reports Server (NTRS)

Hill, Cory J. (Inventor); Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor)

2016-01-01

In order to increase the spectral response range and improve the mobility of the photo-generated carriers (e.g. in an nBn photodetector), a digital alloy absorber may be employed by embedding one (or fraction thereof) to several monolayers of a semiconductor material (insert layers) periodically into a different host semiconductor material of the absorber layer. The semiconductor material of the insert layer and the host semiconductor materials may have lattice constants that are substantially mismatched. For example, this may performed by periodically embedding monolayers of InSb into an InAsSb host as the absorption region to extend the cutoff wavelength of InAsSb photodetectors, such as InAsSb based nBn devices. The described technique allows for simultaneous control of alloy composition and net strain, which are both key parameters for the photodetector operation.

PREFACE: Theory, Modelling and Computational methods for Semiconductors

NASA Astrophysics Data System (ADS)

Migliorato, Max; Probert, Matt

2010-04-01

These conference proceedings contain the written papers of the contributions presented at the 2nd International Conference on: Theory, Modelling and Computational methods for Semiconductors. The conference was held at the St Williams College, York, UK on 13th-15th Jan 2010. The previous conference in this series took place in 2008 at the University of Manchester, UK. The scope of this conference embraces modelling, theory and the use of sophisticated computational tools in Semiconductor science and technology, where there is a substantial potential for time saving in R&D. The development of high speed computer architectures is finally allowing the routine use of accurate methods for calculating the structural, thermodynamic, vibrational and electronic properties of semiconductors and their heterostructures. This workshop ran for three days, with the objective of bringing together UK and international leading experts in the field of theory of group IV, III-V and II-VI semiconductors together with postdocs and students in the early stages of their careers. The first day focused on providing an introduction and overview of this vast field, aimed particularly at students at this influential point in their careers. We would like to thank all participants for their contribution to the conference programme and these proceedings. We would also like to acknowledge the financial support from the Institute of Physics (Computational Physics group and Semiconductor Physics group), the UK Car-Parrinello Consortium, Accelrys (distributors of Materials Studio) and Quantumwise (distributors of Atomistix). The Editors Acknowledgements Conference Organising Committee: Dr Matt Probert (University of York) and Dr Max Migliorato (University of Manchester) Programme Committee: Dr Marco Califano (University of Leeds), Dr Jacob Gavartin (Accelrys Ltd, Cambridge), Dr Stanko Tomic (STFC Daresbury Laboratory), Dr Gabi Slavcheva (Imperial College London) Proceedings edited and compiled by Dr

Pb(II), Cr(VI) and atrazine sorption behavior on sludge-derived biochar: role of humic acids.

PubMed

Zhou, Fengsa; Wang, Hong; Fang, Sheng'en; Zhang, Weihua; Qiu, Rongliang

2015-10-01

Pyrolyzing municipal wastewater treatment sludge into biochar can be a promising sludge disposal approach, especially as the produced sludge-derived biochar (SDBC) is found to be an excellent sorbent for heavy metals and atrazine. The aim of this study was to investigate how and why the coexisting humic acids influence the sorption capacity, kinetic, and binding of these contaminants on SDBC surface. Results showed humic acids enhanced Pb(II)/Cr(VI) sorption binding, and increased the corresponding Pb(II) Langmuir sorption capacity at pH 5.0 from 197 to 233 μmol g(-1), and from 688 to 738 μmol g(-1) for Cr(VI) at pH 2.0. It can be mainly attributed to the sorbed humic acids, whose active functional groups can offer the additional sites to form stronger inner-sphere complexes with Pb(2+), and supply more reducing agent to facilitate the transformation of Cr(VI) to Cr(III). However, humic acids reduced the atrazine adsorption Freundlich constant from 1.085 to 0.616 μmol g(-1). The pore blockage, confirmed by the decreased BET-specific surface area, as well as the more hydrophilic surface with more sorbed water molecules may be the main reasons for that suppression. Therefore, the coexisting humic acids may affect heavy metal stabilization or pesticide immobilization during SDBC application to contaminated water or soils, and its role thus should be considered especially when organic residues are also added significantly to increase the humic acid content there.

Apparatus for forming thin-film heterojunction solar cells employing materials selected from the class of I-III-VI.sub.2 chalcopyrite compounds

DOEpatents

Mickelsen, Reid A.; Chen, Wen S.

1983-01-01

Apparatus for forming thin-film, large area solar cells having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n-type heterojunction formed of: (i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI.sub.2 chalcopyrite ternary materials which is vacuum deposited in a thin "composition-graded" layer ranging from on the order of about 2.5 microns to about 5.0 microns (.congruent.2.5 .mu.m to .congruent.5.0 .mu.m) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (ii), a second semiconductor layer comprising a low resistivity n-type semiconductor material wherein interdiffusion (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, causes the transient n-type material in the first semiconductor layer to evolve into p-type material, thereby defining a thin layer heterojunction device characterized by the absence of voids, vacancies and nodules which tend to reduce the energy conversion efficiency of the system.

Neutron imaging systems utilizing lithium-containing semiconductor crystals

DOEpatents

Stowe, Ashley C.; Burger, Arnold

2017-04-25

A neutron imaging system, including: a plurality of Li-III-VI.sub.2 semiconductor crystals arranged in an array, wherein III represents a Group III element and VI represents a Group VI element; and electronics operable for detecting and a charge in each of the plurality of crystals in the presence of neutrons and for imaging the neutrons. Each of the crystals is formed by: melting the Group III element; adding the Li to the melted Group III element at a rate that allows the Li and Group III element to react, thereby providing a single phase Li-III compound; and adding the Group VI element to the single phase Li-III compound and heating. Optionally, each of the crystals is also formed by doping with a Group IV element activator.

ZIRCONIUM-TITANIUM-BERYLLIUM BRAZING ALLOY

DOEpatents

Gilliland, R.G.; Patriarca, P.; Slaughter, G.M.; Williams, L.C.

1962-06-12

A new and improved ternary alloy is described which is of particular utility in braze-bonding parts made of a refractory metal selected from Group IV, V, and VI of the periodic table and alloys containing said metal as a predominating alloying ingredient. The brazing alloy contains, by weight, 40 to 50 per cent zirconium, 40 to 50 per cent titanium, and the balance beryllium in amounts ranging from 1 to 20 per cent, said alloy having a melting point in the range 950 to 1400 deg C. (AEC)

Lattice thermal transport in group II-alloyed PbTe

NASA Astrophysics Data System (ADS)

Xia, Yi; Hodges, James M.; Kanatzidis, Mercouri G.; Chan, Maria K. Y.

2018-04-01

PbTe, one of the most promising thermoelectric materials, has recently demonstrated a thermoelectric figure of merit (ZT) of above 2.0 when alloyed with group II elements. The improvements are due mainly to significant reduction of lattice thermal conductivity (κl), which was in turn attributed to nanoparticle precipitates. However, a fundamental understanding of various phonon scattering mechanisms within the bulk alloy is still lacking. In this work, we apply the newly-developed density-functional-theory-based compressive sensing lattice dynamics approach to model lattice heat transport in PbTe, MTe, and Pb0.94M0.06Te (M = Mg, Ca, Sr, and Ba) and compare our results with experimental measurements, with focus on the strain effect and mass disorder scattering. We find that (1) CaTe, SrTe, and BaTe in the rock-salt structure exhibit much higher κl than PbTe, while MgTe in the same structure shows anomalously low κl; (2) lattice heat transport of PbTe is extremely sensitive to static strain induced by alloying atoms in solid solution form; (3) mass disorder scattering plays a major role in reducing κl for Mg/Ca/Sr-alloyed PbTe through strongly suppressing the lifetimes of intermediate- and high-frequency phonons, while for Ba-alloyed PbTe, precipitated nanoparticles are also important.

Hydrocarbon oxidation by beta-halogenated dioxoruthenium(VI) porphyrin complexes: effect of reduction potential (RuVI/V) and C-H bond-dissociation energy on rate constants.

PubMed

Che, Chi-Ming; Zhang, Jun-Long; Zhang, Rui; Huang, Jie-Sheng; Lai, Tat-Shing; Tsui, Wai-Man; Zhou, Xiang-Ge; Zhou, Zhong-Yuan; Zhu, Nianyong; Chang, Chi Kwong

2005-11-18

beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and

The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdul-Jabbar, N. M.; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Kalkan, B.

2014-08-04

We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10–11 GPa in contrast to those with aperiodic structures, which amorphize around 7–8 GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga{sub 2}SeTe{sub 2} provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This ismore » corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.« less

Growth of Bulk Wide Bandgap Semiconductor Crystals and Their Potential Applications

NASA Technical Reports Server (NTRS)

Chen, Kuo-Tong; Shi, Detang; Morgan, S. H.; Collins, W. Eugene; Burger, Arnold

1997-01-01

Developments in bulk crystal growth research for electro-optical devices in the Center for Photonic Materials and Devices since its establishment have been reviewed. Purification processes and single crystal growth systems employing physical vapor transport and Bridgman methods were assembled and used to produce high purity and superior quality wide bandgap materials such as heavy metal halides and II-VI compound semiconductors. Comprehensive material characterization techniques have been employed to reveal the optical, electrical and thermodynamic properties of crystals, and the results were used to establish improved material processing procedures. Postgrowth treatments such as passivation, oxidation, chemical etching and metal contacting during the X-ray and gamma-ray device fabrication process have also been investigated and low noise threshold with improved energy resolution has been achieved.

Use of separate ZnTe interface layers to form ohmic contacts to p-CdTe films

DOEpatents

Gessert, T.A.

1999-06-01

A method of is disclosed improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurium-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact. 11 figs.

Use of separate ZnTe interface layers to form OHMIC contacts to p-CdTe films

DOEpatents

Gessert, Timothy A.

1999-01-01

A method of improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurim-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact.

Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

DOEpatents

Ren, Zhifeng [Newton, MA; Chen, Gang [Carlisle, MA; Poudel, Bed [Watertown, MA; Kumar, Shankar [Watertown, MA; Wang, Wenzhong [Newton, MA; Dresselhaus, Mildred [Arlington, MA

2007-08-14

The present invention provides methods for synthesis of IV VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20.degree. C. to about 360.degree. C., for a duration sufficient for generating nanoparticles as binary alloys of the IV VI elements.

Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

NASA Technical Reports Server (NTRS)

Chen, Gang (Inventor); Poudel, Bed (Inventor); Kumar, Shankar (Inventor); Dresselhaus, Mildred (Inventor); Ren, Zhifeng (Inventor); Wang, Wenzhong (Inventor)

2007-01-01

The present invention provides methods for synthesis of IV VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20.degree. C. to about 360.degree. C., for a duration sufficient for generating nanoparticles as binary alloys of the IV VI elements.

Collective thermal transport in pure and alloy semiconductors.

PubMed

Torres, Pol; Mohammed, Amr; Torelló, Àlvar; Bafaluy, Javier; Camacho, Juan; Cartoixà, Xavier; Shakouri, Ali; Alvarez, F Xavier

2018-03-07

Conventional models for predicting thermal conductivity of alloys usually assume a pure kinetic regime as alloy scattering dominates normal processes. However, some discrepancies between these models and experiments at very small alloy concentrations have been reported. In this work, we use the full first principles kinetic collective model (KCM) to calculate the thermal conductivity of Si 1-x Ge x and In x Ga 1-x As alloys. The calculated thermal conductivities match well with the experimental data for all alloy concentrations. The model shows that the collective contribution must be taken into account at very low impurity concentrations. For higher concentrations, the collective contribution is suppressed, but normal collisions have the effect of significantly reducing the kinetic contribution. The study thus shows the importance of the proper inclusion of normal processes even for alloys for accurate modeling of thermal transport. Furthermore, the phonon spectral distribution of the thermal conductivity is studied in the framework of KCM, providing insights to interpret the superdiffusive regime introduced in the truncated Lévy flight framework.

Reversible interconversion between a nitrido complex of Os(VI) and an ammino complex of osmium(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pipes, D.W.; Bakir, M.; Vitols, S.E.

1990-07-04

The reaction between (N(n-Bu){sub 4})(Os(N)(X){sub 4}) (X = Cl, Br) and 2,2{prime}:6{prime},2{double prime}-terpyridine (tpy) in acetone under reflux gave the salts (Os(N)(typ)(X){sub 2})X. The X-ray crystal structure of (Os(N)(tpy)(Cl){sub 2})Cl showed that the chloride ligands occupy mutually trans axial positions relative to the nitrido ligand. Reduction potentials were measured or estimated at pH = 3 for the intermediate Os(VI/V), Os(V/IV), Os(IV/III), and Os(III/II) couples. From those measurements, it was shown that the Os(V) intermediate, (Os{sup V}(N)(tpy)(Cl){sub 2}), is both a powerful oxidant and a strong reductant, highly unstable with respect to disproportionation into Os(VI) and Os(IV).

Improved Reagents for Newborn Screening of Mucopolysaccharidosis Types I, II, and VI by Tandem Mass Spectrometry

PubMed Central

2015-01-01

Tandem mass spectrometry for the multiplex and quantitative analysis of enzyme activities in dried blood spots on newborn screening cards has emerged as a powerful technique for early assessment of lysosomal storage diseases. Here we report the design and process-scale synthesis of substrates for the enzymes α-l-iduronidase, iduronate-2-sulfatase, and N-acetylgalactosamine-4-sulfatase that are used for newborn screening of mucopolysaccharidosis types I, II, and VI. The products contain a bisamide unit that is hypothesized to readily protonate in the gas phase, which improves detection sensitivity by tandem mass spectrometry. The products contain a benzoyl group, which provides a useful site for inexpensive deuteration, thus facilitating the preparation of internal standards for the accurate quantification of enzymatic products. Finally, the reagents are designed with ease of synthesis in mind, thus permitting scale-up preparation to support worldwide newborn screening of lysosomal storage diseases. The new reagents provide the most sensitive assay for the three lysosomal enzymes reported to date as shown by their performance in reactions using dried blood spots as the enzyme source. Also, the ratio of assay signal to that measured in the absence of blood (background) is superior to all previously reported mucopolysaccharidosis types I, II, and VI assays. PMID:24694010

Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

NASA Technical Reports Server (NTRS)

Li, Jian-Zhong; Kolokolov, Kanstantin I.; Ning, Cun-Zheng

2003-01-01

Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

Structural distortions in monolayers of binary semiconductors

NASA Astrophysics Data System (ADS)

Kumari, Poonam; Debnath, Saikat; Mahadevan, Priya

2018-01-01

We examine the structural properties of free-standing II-VI and III-V semiconductors at the monolayer limit within first principle density functional theory calculations. A nonpolar buckled structure was found to be favored over a polar buckled structure. While an obvious reason for this may be traced to the contribution from dipole-dipole interactions present in the polar structure which would destabilize it with respect to the nonpolar structure, Coulomb interactions between electrons on the cations and anions are found to be the reason for the nonpolar structure to be favoured. A route to tune the Coulomb interaction between the electrons on the cations and anions is through biaxial tensile strain. This allows for a planar graphitic phase in CdS to be stabilized at just 2% tensile strain. Strain also shifts the valence band maximum from the Γ point to the K point, opening up opportunities for exploring spin-valley physics in these materials.

Alloy design for intrinsically ductile refractory high-entropy alloys

NASA Astrophysics Data System (ADS)

Sheikh, Saad; Shafeie, Samrand; Hu, Qiang; Ahlström, Johan; Persson, Christer; Veselý, Jaroslav; Zýka, Jiří; Klement, Uta; Guo, Sheng

2016-10-01

Refractory high-entropy alloys (RHEAs), comprising group IV (Ti, Zr, Hf), V (V, Nb, Ta), and VI (Cr, Mo, W) refractory elements, can be potentially new generation high-temperature materials. However, most existing RHEAs lack room-temperature ductility, similar to conventional refractory metals and alloys. Here, we propose an alloy design strategy to intrinsically ductilize RHEAs based on the electron theory and more specifically to decrease the number of valence electrons through controlled alloying. A new ductile RHEA, Hf0.5Nb0.5Ta0.5Ti1.5Zr, was developed as a proof of concept, with a fracture stress of close to 1 GPa and an elongation of near 20%. The findings here will shed light on the development of ductile RHEAs for ultrahigh-temperature applications in aerospace and power-generation industries.

Ferrate(VI)-Prompted Removal of Metals in Aqueous Media: Mechanistic Delineation of Enhanced Efficiency via Metal Entrenchment in Magnetic Oxides

EPA Science Inventory

The removal efficiency of heavy metal ions (cadmium(II) – Cd(II), cobalt(II) – Co(II), nickel(II) – Ni(II), and copper(II) – Cu(II)) by potassium ferrate(VI) (K2FeO4, Fe(VI)), was studied as a function of added amount of Fe(VI) (or Fe) and varying pH. At pH = 6.6, the effective r...

The O VI Mystery: Mismatch between X-Ray and UV Column Densities

NASA Astrophysics Data System (ADS)

Mathur, S.; Nicastro, F.; Gupta, A.; Krongold, Y.; McLaughlin, B. M.; Brickhouse, N.; Pradhan, A.

2017-12-01

The UV spectra of Galactic and extragalactic sightlines often show O VI absorption lines at a range of redshifts, and from a variety of sources from the Galactic circumgalactic medium to active galactic nuclei (AGN) outflows. Inner shell O VI absorption is also observed in X-ray spectra (at λ =22.03 Å), but the column density inferred from the X-ray line was consistently larger than that from the UV line. Here we present a solution to this discrepancy for the z = 0 systems. The O II Kβ line {}4{S}0\\to {(}3D)3{p}4P at 562.40 eV (≡22.04 Å) is blended with the O VI Kα line in X-ray spectra. We estimate the strength of this O II line in two different ways, and show that in most cases the O II line accounts for the entire blended line. The small amount of O VI equivalent width present in some cases has column density entirely consistent with the UV value. This solution to the O VI discrepancy, however, does not apply to high column-density systems like AGN outflows. We discuss other possible causes to explain their UV/X-ray mismatch. The O VI and O II lines will be resolved by gratings on board the proposed mission Arcus and the concept mission Lynx, and would allow the detection of weak O VI lines not just at z = 0, but also at higher redshift.

Fate of Adsorbed U(VI) during Sulfidization of Lepidocrocite and Hematite

PubMed Central

2017-01-01

The impact on U(VI) adsorbed to lepidocrocite (γ-FeOOH) and hematite (α-Fe2O3) was assessed when exposed to aqueous sulfide (S(-II)aq) at pH 8.0. With both minerals, competition between S(-II) and U(VI) for surface sites caused instantaneous release of adsorbed U(VI). Compared to lepidocrocite, consumption of S(-II)aq proceeded slower with hematite, but yielded maximum dissolved U concentrations that were more than 10 times higher, representing about one-third of the initially adsorbed U. Prolonged presence of S(-II)aq in experiments with hematite in combination with a larger release of adsorbed U(VI), enhanced the reduction of U(VI): after 24 h of reaction about 60–70% of U was in the form of U(IV), much higher than the 25% detected in the lepidocrocite suspensions. X-ray absorption spectra indicated that U(IV) in both hematite and lepidocrocite suspensions was not in the form of uraninite (UO2). Upon exposure to oxygen only part of U(IV) reoxidized, suggesting that monomeric U(IV) might have become incorporated in newly formed iron precipitates. Hence, sulfidization of Fe oxides can have diverse consequences for U mobility: in short-term, desorption of U(VI) increases U mobility, while reduction to U(IV) and its possible incorporation in Fe transformation products may lead to long-term U immobilization. PMID:28121137

Thermal conductivity of ternary III-V semiconductor alloys: The role of mass difference and long-range order

NASA Astrophysics Data System (ADS)

Mei, S.; Knezevic, I.

2018-03-01

Thermal transport in bulk ternary III-V arsenide (III-As) semiconductor alloys was investigated using equilibrium molecular dynamics with optimized Albe-Tersoff empirical interatomic potentials. Existing potentials for binary AlAs, GaAs, and InAs were optimized to match experimentally obtained acoustic-phonon dispersions and temperature-dependent thermal conductivity. Calculations of thermal transport in ternary III-Vs commonly employ the virtual-crystal approximation (VCA), where the structure is assumed to be a random alloy and all group-III atoms (cations) are treated as if they have an effective weighted-average mass. Here, we showed that it is critical to treat atomic masses explicitly and that the thermal conductivity obtained with explicit atomic masses differs considerably from the value obtained with the average VCA cation mass. The larger the difference between the cation masses, the poorer the VCA prediction for thermal conductivity. The random-alloy assumption in the VCA is also challenged because X-ray diffraction and transmission electron microscopy show order in InGaAs, InAlAs, and GaAlAs epilayers. We calculated thermal conductivity for three common types of order (CuPt-B, CuAu-I, and triple-period-A) and showed that the experimental results for In0.53Ga0.47As and In0.52Al0.48As, which are lattice matched to the InP substrate, can be reproduced in molecular dynamics simulation with 2% and 8% of random disorder, respectively. Based on our results, thermal transport in ternary III-As alloys appears to be governed by the competition between mass-difference scattering, which is much more pronounced than the VCA suggests, and the long-range order that these alloys support.

Antimicrobial, spectral, magnetic and thermal studies of Cu(II), Ni(II), Co(II), UO(2)(VI) and Fe(III) complexes of the Schiff base derived from oxalylhydrazide.

PubMed

Melha, Khlood Abou

2008-04-01

The Schiff base ligand, oxalyl [( 2 - hydroxybenzylidene) hydrazone] [corrected].H(2)L, and its Cu(II), Ni(II), Co(II), UO(2)(VI) and Fe(III) complexes were prepared and tested as antibacterial agents. The Schiff base acts as a dibasic tetra- or hexadentate ligand with metal cations in molar ratio 1:1 or 2:1 (M:L) to yield either mono- or binuclear complexes, respectively. The ligand and its metal complexes were characterized by elemental analyses, IR, (1)H NMR, Mass, and UV-Visible spectra and the magnetic moments and electrical conductance of the complexes were also determined. For binuclear complexes, the magnetic moments are quite low compared to the calculated value for two metal ions complexes and this shows antiferromagnetic interactions between the two adjacent metal ions. The ligand and its metal complexes were tested against a Gram + ve bacteria (Staphylococcus aureus), a Gram -ve bacteria (Escherichia coli), and a fungi (Candida albicans). The tested compounds exhibited high antibacterial activities.

Creating ligand-free silicon germanium alloy nanocrystal inks.

PubMed

Erogbogbo, Folarin; Liu, Tianhang; Ramadurai, Nithin; Tuccarione, Phillip; Lai, Larry; Swihart, Mark T; Prasad, Paras N

2011-10-25

Particle size is widely used to tune the electronic, optical, and catalytic properties of semiconductor nanocrystals. This contrasts with bulk semiconductors, where properties are tuned based on composition, either through doping or through band gap engineering of alloys. Ideally, one would like to control both size and composition of semiconductor nanocrystals. Here, we demonstrate production of silicon-germanium alloy nanoparticles by laser pyrolysis of silane and germane. We have used FTIR, TEM, XRD, EDX, SEM, and TOF-SIMS to conclusively determine their structure and composition. Moreover, we show that upon extended sonication in selected solvents, these bare nanocrystals can be stably dispersed without ligands, thereby providing the possibility of using them as an ink to make patterned films, free of organic surfactants, for device fabrication. The engineering of these SiGe alloy inks is an important step toward the low-cost fabrication of group IV nanocrystal optoelectronic, thermoelectric, and photovoltaic devices.

Investigation of simultaneous biosorption of copper(II) and chromium(VI) on dried Chlorella vulgaris from binary metal mixtures: Application of multicomponent adsorption isotherms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aksu, Z.; Acikel, U.; Kutsal, T.

1999-02-01

Although the biosorption of single metal ions to various kinds of microorganisms has been extensively studied and the adsorption isotherms have been developed for only the single metal ion situation, very little attention has been given to the bioremoval and expression of adsorption isotherms of multimetal ions systems. In this study the simultaneous biosorption of copper(II) and chromium(VI) to Chlorella vulgaris from a binary metal mixture was studied and compared with the single metal ion situation in a batch stirred system. The effects of pH and single- and dual-metal ion concentrations on the equilibrium uptakes were investigated. In previous studiesmore » the optimum biosorption pH had been determined as 4.0 for copper(II) and as 2.0 for chromium(VI). Multimetal ion biosorption studies were performed at these two pH values. It was observed that the equilibrium uptakes of copper(II) or chromium(VI) ions were changed due to the biosorption pH and the presence of other metal ions. Adsorption isotherms were developed for both single- and dual-metal ions systems at these two pH values, and expressed by the mono- and multicomponent Langmuir and Freundlich adsorption models. Model parameters were estimated by nonlinear regression. It was seen that the adsorption equilibrium data fitted very well to the competitive Freundlich model in the concentration ranges studied.« less

Non-enzymatic U(VI) interactions with biogenic mackinawite

NASA Astrophysics Data System (ADS)

Veeramani, H.; Qafoku, N. P.; Kukkadapu, R. K.; Murayama, M.; Hochella, M. F.

2011-12-01

Reductive immobilization of hexavalent uranium [U(VI)] by stimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB or DSRB) has been extensively researched as a remediation strategy for subsurface U(VI) contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors, often utilizing organic substrates as electron donors. Thus, when evaluating the potential for in-situ uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Iron, an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the formation of dissolved Fe(II) or to reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) minerals could be a potentially important process for uranium immobilization. In our study, the DMRB Shewanella putrefaciens CN32 was used to synthesize a biogenic Fe(II)-bearing sulfide mineral: mackinawite, that has been characterized by XRD, SEM, HRTEM and Mössbauer spectroscopy. Batch experiments involving treated biogenic mackinawite and uranium (50:1 molar ratio) were carried out at room temperature under strict anoxic conditions. Following complete removal of uranium from solution, the biogenic mackinawite was analyzed by a suite of analytical techniques including XAS, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and investigate concomitant Fe(II)-phase transformation. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates non-enzymatic/abiotic molecular scale redox interactions between biogenic mackinawite and uranium.

Semiconductor cooling by thin-film thermocouples

NASA Technical Reports Server (NTRS)

Tick, P. A.; Vilcans, J.

1970-01-01

Thin-film, metal alloy thermocouple junctions do not rectify, change circuit impedance only slightly, and require very little increase in space. Although they are less efficient cooling devices than semiconductor junctions, they may be applied to assist conventional cooling techniques for electronic devices.

Electron beam pumped semiconductor laser

NASA Technical Reports Server (NTRS)

Hug, William F. (Inventor); Reid, Ray D. (Inventor)

2009-01-01

Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.

Bond Strength of Gold Alloys Laser Welded to Cobalt-Chromium Alloy

PubMed Central

Watanabe, Ikuya; Wallace, Cameron

2008-01-01

The objective of this study was to investigate the joint properties between cast gold alloys and Co-Cr alloy laser-welded by Nd:YAG laser. Cast plates were fabricated from three types of gold alloys (Type IV, Type II and low-gold) and a Co-Cr alloy. Each gold alloy was laser-welded to Co-Cr using a dental laser-welding machine. Homogeneously-welded and non-welded control specimens were also prepared. Tensile testing was conducted and data were statistically analyzed using ANOVA. The homogeneously-welded groups showed inferior fracture load compared to corresponding control groups, except for Co-Cr. In the specimens welded heterogeneously to Co-Cr, Type IV was the greatest, followed by low-gold and Type II. There was no statistical difference (P<0.05) in fracture load between Type II control and that welded to Co-Cr. Higher elongations were obtained for Type II in all conditions, whereas the lowest elongation occurred for low-gold welded to Co-Cr. This study indicated that, of the three gold alloys tested, the Type IV gold alloy was the most suitable alloy for laser-welding to Co-Cr. PMID:19088892

Simultaneous biosorption of chromium(VI) and copper(II) on Rhizopus arrhizus in packed column reactor: Application of the competitive Freundlich model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sag, Y.; Atacoglu, I.; Kutsal, T.

1999-12-01

The simultaneous biosorption of Cr(VI) and Cu(II) on free Rhizopus arrhizus in a packed column operated in the continuous mode was investigated and compared to the single metal ion situation. The breakthrough curves were measured as a function of feed flow rate, feed pH, and different combinations of metal ion concentrations in the feed solutions. Column competitive biosorption data were evaluated in terms of the maximum (equilibrium) capacity in the column, the amount of metal loading on the R. arrhizus surface, the adsorption yield, and the total adsorption yield. In the single-ion situation the adsorption isotherms were developed for optimummore » conditions, and it was seen that the adsorption equilibrium data fit the noncompetitive Freundlich model. For the multicomponent adsorption equilibrium the competitive adsorption isotherms were also developed. The competitive Freundlich model for binary metal mixtures represented most the column adsorption equilibrium data of Cr(VI) and Cu(II) on R. arrhizus satisfactorily.« less

Characterization of PVT Grown ZnSe by Low Temperature Photoluminescence

NASA Technical Reports Server (NTRS)

Wang, Ling Jun

1998-01-01

ZnSe, a II-VI semiconductor with a large direct band gap of 2.7 eV at room temperature and 2.82 eV at 10 K, is considered a promising material for optoelectric applications in the blue-green region of the spectrum. Photoemitting devices and diode laser action has been demonstrated as a result of decades of research. A key issue in the development of II-VI semiconductors is the control of the concentration of the various impurities. The II-VI semiconductors seem to defy the effort of high level doping due to the well known self compensation of the donors and the acceptors. A good understanding of roles of the impurities and the behavior of the various intrinsic defects such as vacancies, interstitials and their complexes with impurities is necessary in the development and application of these materials. Persistent impurities such as Li and Cu have long played a central role in the photoelectronic properties of many II-VI compounds, particularly ZnSe. The shallow centers which may promote useful electrical conductivity are of particular interest. They contribute the richly structured near gap edge luminescence, containing weak to moderate phonon coupling and therefore very accessible information about the energy states of the different centers. Significance of those residual impurities which may contribute such centers in II-VI semiconductors must be fully appreciated before improved control of their electrical properties may be possible. Low temperature photoluminescence spectroscopy is an important source of information and a useful tool of characterization of II-VI semiconductors such as ZnSe. The low temperature photoluminescence spectrum of a ZnSe single crystal typically consists of a broad band emission peaking at 2.34 eV, known as the Cu-green band, and some very sharp lines near the band gap. These bands and lines are used to identify the impurity ingredients and the defects. The assessment of the quality of the crystal based on the photoluminescence

Dry etching method for compound semiconductors

DOEpatents

Shul, Randy J.; Constantine, Christopher

1997-01-01

A dry etching method. According to the present invention, a gaseous plasma comprising, at least in part, boron trichloride, methane, and hydrogen may be used for dry etching of a compound semiconductor material containing layers including aluminum, or indium, or both. Material layers of a compound semiconductor alloy such as AlGaInP or the like may be anisotropically etched for forming electronic devices including field-effect transistors and heterojunction bipolar transistors and for forming photonic devices including vertical-cavity surface-emitting lasers, edge-emitting lasers, and reflectance modulators.

Dry etching method for compound semiconductors

DOEpatents

Shul, R.J.; Constantine, C.

1997-04-29

A dry etching method is disclosed. According to the present invention, a gaseous plasma comprising, at least in part, boron trichloride, methane, and hydrogen may be used for dry etching of a compound semiconductor material containing layers including aluminum, or indium, or both. Material layers of a compound semiconductor alloy such as AlGaInP or the like may be anisotropically etched for forming electronic devices including field-effect transistors and heterojunction bipolar transistors and for forming photonic devices including vertical-cavity surface-emitting lasers, edge-emitting lasers, and reflectance modulators. 1 fig.

Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles

PubMed Central

2017-01-01

The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of particular importance for semiconductor/PNPs composites, because by changing the alloy composition their absorption spectra can be tuned to accurately extend the light absorption of the semiconductor. This work experimentally compares the HEI efficiency from Ag, Au, and Ag/Au alloy nanoparticles to TiO2 photoanodes for the photoproduction of hydrogen. Alloy PNPs not only exhibit tunable absorption but can also improve the stability and electronic and catalytic properties of the pure metal PNPs. In this work, we find that the Ag/Au alloy PNPs extend the stability of Ag in water to larger applied potentials while, at the same time, increasing the interband threshold energy of Au. This increasing of the interband energy of Au suppresses the visible-light-induced interband excitations, favoring intraband excitations that result in higher hot electron energies and HEI efficiencies. PMID:29354665

Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

1990-01-01

A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, wherein a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd.sub.1-x Mn.sub.x Te, wherein 0.ltoreq..times..ltoreq.0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) maganese (TCPMn) is employed. To prevent TCPMn condensation during the introduction thereof int the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, wherein the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

Proteomic Discovery and Development of a Multiplexed Targeted MRM-LC-MS/MS Assay for Urine Biomarkers of Extracellular Matrix Disruption in Mucopolysaccharidoses I, II, and VI.

PubMed

Heywood, Wendy E; Camuzeaux, Stephane; Doykov, Ivan; Patel, Nina; Preece, Rhian-Lauren; Footitt, Emma; Cleary, Maureen; Clayton, Peter; Grunewald, Stephanie; Abulhoul, Lara; Chakrapani, Anupam; Sebire, Neil J; Hindmarsh, Peter; de Koning, Tom J; Heales, Simon; Burke, Derek; Gissen, Paul; Mills, Kevin

2015-12-15

The mucopolysaccharidoses (MPS) are lysosomal storage disorders that result from defects in the catabolism of glycosaminoglycans. Impaired muscle, bone, and connective tissue are typical clinical features of MPS due to disruption of the extracellular matrix. Markers of MPS disease pathology are needed to determine disease severity and monitor effects of existing and emerging new treatments on disease mechanisms. Urine samples from a small cohort of MPS-I, -II, and -VI patients (n = 12) were analyzed using label-free quantative proteomics. Fifty-three proteins including many associated with extracellular matrix organization were differently expressed. A targeted multiplexed peptide MRM LC-MS/MS assay was used on a larger validation cohort of patient samples (MPS-I n = 18, MPS-II n = 12, MPS-VI n = 6, control n = 20). MPS-I and -II groups were further subdivided according to disease severity. None of the markers assessed were altered significantly in the mild disease groups compared to controls. β-galactosidase, a lysosomal protein, was elevated 3.6-5.7-fold significantly (p < 0.05) in all disease groups apart from mild MPS-I and -II. Collagen type Iα, fatty-acid-binding-protein 5, nidogen-1, cartilage oligomeric matrix protein, and insulin-like growth factor binding protein 7 concentrations were elevated in severe MPS I and II groups. Cartilage oligomeric matrix protein, insulin-like growth factor binding protein 7, and β-galactosidase were able to distinguish the severe neurological form of MPS-II from the milder non-neurological form. Protein Heg1 was significantly raised only in MPS-VI. This work describes the discovery of new biomarkers of MPS that represent disease pathology and allows the stratification of MPS-II patients according to disease severity.

A modified model for calculating lattice thermal expansion of I{sub 2}-IV-VI{sub 3} and I{sub 3}-V-VI{sub 4} tetrahedral compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omar, M.S.

2007-05-03

A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I{sub 2}-IV-VI{sub 3} and I{sub 3}-V-VI{sub 4}. The difference in the valence electrons for cations and anions in the compound was used to correlate the deviations caused by the compound ionicity. The ionicity effects, which are due to their different numbers for their types, were also added to the correlation equation. In general, the lattice thermal expansionmore » for a compound semiconductor can be calculated from a relation containing melting point, mean atomic distance and number of valence electrons for the atoms forming the compound. The mean ionicity for the group compounds forming I{sub 2}-IV-VI{sub 3} was found to be 0.323 and 0.785 for the ternary group compounds of I{sub 3}-V-VI{sub 4}.« less

Solid-state semiconductor optical cryocooler based on CdS nanobelts.

PubMed

Li, Dehui; Zhang, Jun; Wang, Xinjiang; Huang, Baoling; Xiong, Qihua

2014-08-13

We demonstrate the laser cooling of silicon-on-insulator (SOI) substrate using CdS nanobelts. The local temperature change of the SOI substrate exactly beneath the CdS nanobelts is deduced from the ratio of the Stokes and anti-Stokes Raman intensities from the Si layer on the top of the SOI substrate. We have achieved a 30 and 20 K net cooling starting from 290 K under a 3.8 mW 514 nm and a 4.4 mW 532 nm pumping, respectively. In contrast, a laser heating effect has been observed pumped by 502 and 488 nm lasers. Theoretical analysis based on the general static heat conduction module in the Ansys program package is conducted, which agrees well with the experimental results. Our investigations demonstrate the laser cooling capability of an external thermal load, suggesting the applications of II-VI semiconductors in all-solid-state optical cryocoolers.

Metal-Semiconductor Nanocomposites for High Efficiency Thermoelectric Power Generation

DTIC Science & Technology

2013-12-07

standard III–V compound semiconductor processing techniques with terbium- doped InGaAs of high terbium concentration, Journal of Vacuum Science...even lower the required temperature for strong covalent bonding. We performed the oxide bonding for this substrate transfer task (see Figure 16 for...appropriate controls for assessing ErSb:InGaSb and other nanocomposites of p-type III-V compound semiconductors and their alloys. UCSC group calculated

Alloy and heterostructure architectures as promising tools for controlling electronic properties of semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Vaxenburg, Roman; Lifshitz, Efrat

2012-02-01

Tunability of energy levels and wavefunctions of carriers in colloidal quantum dots (CQDs) has a marked effect on numerous physical aspects, such as Coulomb interactions and charge separation, which in turn has a direct impact on the functioning of CQD-based opto-electronic devices. The electronic properties of CQDs are conventionally controlled by variation of their size. Here we demonstrate a theoretical approach to engineer the electronic properties of IV-VI CQDs by introducing an alloy composition in core and core/shell heterostructures, having the general chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), while maintaining a constant size. The theoretical model considered an effective mass anisotropy and smooth potential step at the core/shell interface. The model revealed the influence induced by variation of chemical composition and core-to-shell division on the band-gap energy, remote states’ density, internal charge separation, electron-hole Coulomb interaction, and optical transition oscillator strength.

Variation of crystal structure and optical properties of wurtzite-type oxide semiconductor alloys of β-Cu(Ga,Al)O2

NASA Astrophysics Data System (ADS)

Nagatani, Hiraku; Mizuno, Yuki; Suzuki, Issei; Kita, Masao; Ohashi, Naoki; Omata, Takahisa

2017-06-01

Band-gap engineering of β-CuGaO2 was demonstrated by the alloying of gallium with aluminum, that is, Cu(Ga1-xAlx)O2. The ternary wurtzite β-NaFeO2-type alloys were obtained in the range 0 ≤ x ≤ 0.7, and γ-LiAlO2-type phase appeared in the range 0.7 ≤ x ≤ 1. The energy band gap of wurtzite β-CuGaO2 was controlled in the range between 1.47 and 2.09 eV. A direct band gap for x < 0.6 and indirect band gap for x ≥ 0.6 were proposed based on the structural distortion in the β-NaFeO2-type phase and density functional theory (DFT) calculation of β-CuAlO2. The DFT calculation also indicated that the γ-LiAlO2-type phases appeared in 0.7 ≤ x ≤ 1 are also indirect-gap semiconductors.

Ab initio study of II-(VI)2 dichalcogenides.

PubMed

Olsson, P; Vidal, J; Lincot, D

2011-10-12

The structural stabilities of the (Zn,Cd)(S,Se,Te)(2) dichalcogenides have been determined ab initio. These compounds are shown to be stable in the pyrite phase, in agreement with available experiments. Structural parameters for the ZnTe(2) pyrite semiconductor compound proposed here are presented. The opto-electronic properties of these dichalcogenide compounds have been calculated using quasiparticle GW theory. Bandgaps, band structures and effective masses are proposed as well as absorption coefficients and refraction indices. The compounds are all indirect semiconductors with very flat conduction band dispersion and high absorption coefficients. The work functions and surface properties are predicted. The Te and Se based compounds could be of interest as absorber materials in photovoltaic applications.

Design of Metastable Tin Titanium Nitride Semiconductor Alloys

DOE PAGES

Bikowski, Andre; Siol, Sebastian; Gu, Jing; ...

2017-07-07

Here, we report on design of optoelectronic properties in previously unreported metastable tin titanium nitride alloys with spinel crystal structure. Theoretical calculations predict that Ti alloying in metastable Sn 3N 4 compound should improve hole effective mass by up to 1 order of magnitude, while other optical bandgaps remains in the 1–2 eV range up to x ~ 0.35 Ti composition. Experimental synthesis of these metastable alloys is predicted to be challenging due to high required nitrogen chemical potential (Δμ N ≥ +1.0 eV) but proven to be possible using combinatorial cosputtering from metal targets in the presence of nitrogenmore » plasma. Characterization experiments confirm that thin films of such (Sn 1–xTi x) 3N 4 alloys can be synthesized up to x = 0.45 composition, with suitable optical band gaps (1.5–2.0 eV), moderate electron densities (10 17 to 10 18 cm –3), and improved photogenerated hole transport (by 5×). Overall, this study shows that it is possible to design the metastable nitride materials with properties suitable for potential use in solar energy conversion applications.« less

Nanoscale semiconductor Pb1-xSnxSe (x = 0.2) thin films synthesized by electrochemical atomic layer deposition

NASA Astrophysics Data System (ADS)

Lin, Shaoxiong; Zhang, Xin; Shi, Xuezhao; Wei, Jinping; Lu, Daban; Zhang, Yuzhen; Kou, Huanhuan; Wang, Chunming

2011-04-01

In this paper the fabrication and characterization of IV-VI semiconductor Pb1-xSnxSe (x = 0.2) thin films on gold substrate by electrochemical atomic layer deposition (EC-ALD) method at room temperature are reported. Cyclic voltammetry (CV) is used to determine approximate deposition potentials for each element. The amperometric I-t technique is used to fabricate the semiconductor alloy. The elements are deposited in the following sequence: (Se/Pb/Se/Pb/Se/Pb/Se/Pb/Se/Sn …), each period is formed using four ALD cycles of PbSe followed by one cycle of SnSe. Then the deposition manner above is cyclic repeated till a satisfactory film with expected thickness of Pb1-xSnxSe is obtained. The morphology of the deposit is observed by field emission scanning electron microscopy (FE-SEM). X-ray diffraction (XRD) pattern is used to study its crystalline structure; X-ray photoelectron spectroscopy (XPS) of the deposit indicates an approximate ratio 1.0:0.8:0.2 of Se, Pb and Sn, as the expected stoichiometry for the deposit. Open-circuit potential (OCP) studies indicate a good p-type property, and the good optical activity makes it suitable for fabricating a photoelectric switch.

Application of the bond valence method in the non-isovalent semiconductor alloy (GaN) 1–x (ZnO) x

DOE PAGES

Liu, Jian

2016-09-29

This paper studies the bond valence method (BVM) and its application in the non-isovalent semiconductor alloy (GaN) 1-x(ZnO) x. Particular attention is paid to the role of short-range order (SRO). A physical interpretation based on atomic orbital interaction is proposed and examined by density-functional theory (DFT) calculations. Combining BVM with Monte-Carlo simulations and a DFT-based cluster expansion model, bond-length distributions and bond-angle variations are predicted. The correlation between bond valence and bond stiffness is also revealed. Lastly the concept of bond valence is extended into the modelling of an atomistic potential.

Mixed ternary heterojunction solar cell

DOEpatents

Chen, Wen S.; Stewart, John M.

1992-08-25

A thin film heterojunction solar cell and a method of making it has a p-type layer of mixed ternary I-III-VI.sub.2 semiconductor material in contact with an n-type layer of mixed binary II-VI semiconductor material. The p-type semiconductor material includes a low resistivity copper-rich region adjacent the back metal contact of the cell and a composition gradient providing a minority carrier mirror that improves the photovoltaic performance of the cell. The p-type semiconductor material preferably is CuInGaSe.sub.2 or CuIn(SSe).sub.2.

The stochastic model for ternary and quaternary alloys: Application of the Bernoulli relation to the phonon spectra of mixed crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchewka, M., E-mail: marmi@ur.edu.pl; Woźny, M.; Polit, J.

2014-03-21

To understand and interpret the experimental data on the phonon spectra of the solid solutions, it is necessary to describe mathematically the non-regular distribution of atoms in their lattices. It appears that such description is possible in case of the strongly stochastically homogenous distribution which requires a great number of atoms and very carefully mixed alloys. These conditions are generally fulfilled in case of high quality homogenous semiconductor solid solutions of the III–V and II–VI semiconductor compounds. In this case, we can use the Bernoulli relation describing probability of the occurrence of one n equivalent event which can be applied,more » to the probability of finding one from n configurations in the solid solution lattice. The results described in this paper for ternary HgCdTe and GaAsP as well as quaternary ZnCdHgTe can provide an affirmative answer to the question: whether stochastic geometry, e.g., the Bernoulli relation, is enough to describe the observed phonon spectra.« less

Band structure engineering of semiconductors for enhanced photoelectrochemical water splitting: The case of TiO2

NASA Astrophysics Data System (ADS)

Yin, Wan-Jian; Tang, Houwen; Wei, Su-Huai; Al-Jassim, Mowafak M.; Turner, John; Yan, Yanfa

2010-07-01

Here, we propose general strategies for the rational design of semiconductors to simultaneously meet all of the requirements for a high-efficiency, solar-driven photoelectrochemical (PEC) water-splitting device. As a case study, we apply our strategies for engineering the popular semiconductor, anatase TiO2 . Previous attempts to modify known semiconductors such as TiO2 have often focused on a particular individual criterion such as band gap, neglecting the possible detrimental consequence to other important criteria. Density-functional theory calculations reveal that with appropriate donor-acceptor coincorporation alloys with anatase TiO2 hold great potential to satisfy all of the criteria for a viable PEC device. We predict that (Mo, 2N) and (W, 2N) are the best donor-acceptor combinations in the low-alloy concentration regime whereas (Nb, N) and (Ta, N) are the best choice of donor-acceptor pairs in the high-alloy concentration regime.

Adsorption of Cr(VI) on cerium immobilized cross-linked chitosan composite in single system and coexisted with Orange II in binary system.

PubMed

Zhu, Tianyi; Huang, Wei; Zhang, Lingfan; Gao, Jie; Zhang, Wenqing

2017-10-01

In this work, cerium immobilized cross-linked chitosan (CTS-Ce) composite, employed as an efficient adsorbent for Cr(VI) in single system and coexisted with Orange II (OII) in binary system, was prepared by co-precipitation method. The as-obtained adsorbent was characterized by FTIR, SEM, EDS and XPS before and after adsorption. The adsorption behaviors of Cr(VI) in single and binary system were systematically studied. The maximum adsorption capacity of Cr(VI) on CTS-Ce (202.8mg/g) was calculated by Langmuir equation in single metal system, but it decreased to 112.9mg/g with initial concentration of 100mg/L OII in binary system at pH 2 and 293K. The adsorption data for Cr(VI) followed the Langmuir model in single system, while fitted Temkin model well in binary system. In both single and binary system, the kinetics of adsorption exhibited pseudo-second order behavior and adsorption capacity increased with increasing temperature. Moreover, the data of thermodynamic parameters (ΔG°<0, ΔH°>0) indicated that the adsorption was a spontaneous and endothermic process. Besides, |ΔG Cr |>|ΔG Cr-OII | at the same temperature further suggested that Cr(VI) was adsorbed on the CTS-Ce composite faster in binary system than in single system. Copyright © 2017 Elsevier B.V. All rights reserved.

Systematic approach for simultaneously correcting the band-gap and p - d separation errors of common cation III-V or II-VI binaries in density functional theory calculations within a local density approximation

DOE PAGES

Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang

2015-07-31

We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X = N,P,As,Sb, and II-VI compounds, (Zn or Cd)X, with X = O,S,Se,Te. By correcting (1) the binary band gaps at high-symmetry points , L, X, (2) the separation of p-and d-orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles methodmore » can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.« less

Systematic approach for simultaneously correcting the band-gap and p -d separation errors of common cation III-V or II-VI binaries in density functional theory calculations within a local density approximation

NASA Astrophysics Data System (ADS)

Wang, Jianwei; Zhang, Yong; Wang, Lin-Wang

2015-07-01

We propose a systematic approach that can empirically correct three major errors typically found in a density functional theory (DFT) calculation within the local density approximation (LDA) simultaneously for a set of common cation binary semiconductors, such as III-V compounds, (Ga or In)X with X =N ,P ,As ,Sb , and II-VI compounds, (Zn or Cd)X , with X =O ,S ,Se ,Te . By correcting (1) the binary band gaps at high-symmetry points Γ , L , X , (2) the separation of p -and d -orbital-derived valence bands, and (3) conduction band effective masses to experimental values and doing so simultaneously for common cation binaries, the resulting DFT-LDA-based quasi-first-principles method can be used to predict the electronic structure of complex materials involving multiple binaries with comparable accuracy but much less computational cost than a GW level theory. This approach provides an efficient way to evaluate the electronic structures and other material properties of complex systems, much needed for material discovery and design.

II-I2-IV-VI4 (II = Sr,Ba; I = Cu,Ag; IV = Ge,Sn; VI = S,Se): Earth-Abundant Chalcogenides for Thin Film Photovoltaics

NASA Astrophysics Data System (ADS)

Zhu, Tong; Huhn, William P.; Shin, Donghyeop; Mitzi, David B.; Blum, Volker; Saparov, Bayrammurad

Chalcogenides such as CdTe, CIGSSe, and CZTSSe are successful for thin film photovoltaics (PV) but contain elements that are rare, toxic, or prone to the formation of detrimental antisite disorder. Recently, the BaCu2SnS4-xSex system has been shown to offer a prospective path to circumvent these problems. While early prototypes show efficiencies of a few percent, many avenues remain to optimize the materials, including the underlying chemical composition. In this work, we explore 16 compounds II-I2-IV-VI4 to help identify new candidate materials for PV, with predictions based on both known experimental and computationally derived structures that belong to five different space groups. We employ hybrid density functional theory (HSE06) to explore the band gap tunability by substituting different elements, and other characteristics such as the effective mass and the absorption coefficient. Compounds containing Cu (rather than Ag) are found to have direct or nearly direct band gaps. Depending on the compound, replacing S with Se leads to a decrease of the predicted band gaps by 0.2-0.8 eV and to somewhat decreasing hole effective masses.

Electromagnetic pulse-driven spin-dependent currents in semiconductor quantum rings.

PubMed

Zhu, Zhen-Gang; Berakdar, Jamal

2009-04-08

We investigate the non-equilibrium charge and spin-dependent currents in a quantum ring with a Rashba spin-orbit interaction (SOI) driven by two asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge and persistent spin-dependent currents are investigated as well. It is shown that the dynamical charge and the dynamical spin-dependent currents vary smoothly with a static external magnetic flux and the SOI provides a SU(2) effective flux that changes the phases of the dynamic charge and the dynamic spin-dependent currents. The period of the oscillation of the total charge current with the delay time between the pulses is larger in a quantum ring with a larger radius. The parameters of the pulse fields control to a certain extent the total charge and the total spin-dependent currents. The calculations are applicable to nanometre rings fabricated in heterojunctions of III-V and II-VI semiconductors containing several hundreds of electrons.

Optical determination of crystal phase in semiconductor nanocrystals

PubMed Central

Lim, Sung Jun; Schleife, André; Smith, Andrew M.

2017-01-01

Optical, electronic and structural properties of nanocrystals fundamentally derive from crystal phase. This is especially important for polymorphic II–VI, III–V and I-III-VI2 semiconductor materials such as cadmium selenide, which exist as two stable phases, cubic and hexagonal, each with distinct properties. However, standard crystallographic characterization through diffraction yields ambiguous phase signatures when nanocrystals are small or polytypic. Moreover, diffraction methods are low-throughput, incompatible with solution samples and require large sample quantities. Here we report the identification of unambiguous optical signatures of cubic and hexagonal phases in II–VI nanocrystals using absorption spectroscopy and first-principles electronic-structure theory. High-energy spectral features allow rapid identification of phase, even in small nanocrystals (∼2 nm), and may help predict polytypic nanocrystals from differential phase contributions. These theoretical and experimental insights provide simple and accurate optical crystallographic analysis for liquid-dispersed nanomaterials, to improve the precision of nanocrystal engineering and improve our understanding of nanocrystal reactions. PMID:28513577

Preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films.

PubMed

Chen, Zhiwen; Jiao, Zheng; Wu, Minghong; Shek, Chan-Hung; Wu, C M Lawrence; Lai, Joseph K L

2012-01-01

Metal/semiconductor thin films are a class of unique materials that are widespread technological applications, particularly in the field of microelectronic devices. Assessment strategies of fractal and tures are of fundamental importance in the development of nano/microdevices. This review presents the preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films including Au/Ge bilayer films and Pd-Ge alloy thin films, which show in the form of fractals and nanocrystals. Firstly, the extended version of Au/Ge thin films for the fractal crystallization of amorphous Ge and the formation of nanocrystals developed with improved micro- and nanostructured features are described in Section 2. Secondly, the nano/microstructural characteristics of Pd/Ge alloy thin films during annealing have been investigated in detail and described in Section 3. Finally, we will draw the conclusions from the present work as shown in Section 4. It is expected that the preparation methodologies developed and the knowledge of nano/microstructural evolution gained in metal/semiconductor thin films, including Au/Ge bilayer films and Pd-Ge alloy thin films, will provide an important fundamental basis underpinning further interdisciplinary research in these fields such as physics, chemistry, materials science, and nanoscience and nanotechnology, leading to promising exciting opportunities for future technological applications involving these thin films.

Demonstration of Ultra High-Strength Nanocrystalline Copper Alloys for Military Applications

DTIC Science & Technology

2012-01-22

Powder Processing vi Acknowledgements The development of these Cu -Ta alloys was accomplished with assistance from the following...nanostructured Cu -Ta based alloy powders with a unique ability to retain their ultrahigh strength properties to temperatures nearing the melting point of the Cu ...nanostructured Cu -Ta based alloy powders with the unique ability to retain their ultrahigh strength properties to temperatures

Technique of investigations of thermomagnetic Nernst-Ettingshausen and Maggi-Righi-Leduc effects in micro-samples at ultrahigh pressure

NASA Astrophysics Data System (ADS)

Ovsyannikov, Sergey; Shchennikov, Vladimir

2004-03-01

In the present work the novel technique of investigation of thermomagnetic effects (longitudinal and transverse Nernst-Ettingshausen effects, Maggi-Righi-Leduc effects) on semiconductor micro-samples at high pressure up to 30 GPa has been developed. The technique has been applied for characterisation of semiconductor micro-samples and minerals of VI, IV-VI, and II-VI Groups. Advantages of thermomagnetic effects over the traditional galvanomagnetic ones have been demonstrated. It has been shown that technique of thermomagnetic measurements at high pressure is a powerful tool in studying of parameters of electron structure of semiconductors and being the perspective one for any technological applications. The work was supported by the Russian Foundation for Basic Research, Gr. No. 01-02-17203.

Methods for forming thin-film heterojunction solar cells from I-III-VI[sub 2

DOEpatents

Mickelsen, R.A.; Chen, W.S.

1982-06-15

An improved thin-film, large area solar cell, and methods for forming the same are disclosed, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n type heterojunction formed of: (1) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI[sub 2] chalcopyrite ternary materials which is vacuum deposited in a thin composition-graded'' layer ranging from on the order of about 2.5 microns to about 5.0 microns ([approx equal]2.5[mu]m to [approx equal]5.0[mu]m) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (2), a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, is allowed.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

NASA Astrophysics Data System (ADS)

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-12-01

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V-1 s-1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass.

PubMed

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-12-08

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co 28.6 Fe 12.4 Ta 4.3 B 8.7 O 46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm 2  V -1  s -1 . Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

PubMed Central

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-an; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-01-01

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III–V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p–n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V−1 s−1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities. PMID:27929059

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

PubMed Central

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; Peng, Haowei; Deml, Ann M.; Matthews, Bethany E.; Schelhas, Laura T.; Toney, Michael F.; Gordon, Roy G.; Tumas, William; Perkins, John D.; Ginley, David S.; Gorman, Brian P.; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-01-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region. PMID:28630928

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

PubMed

Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-06-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

1988-01-01

A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, in which a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd(sub 1-x)Mn(sub x)Te, in which 0 is less than or equal to x less than or equal to 0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) is employed. To prevent TCPMn condensation during its introduction into the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, in which the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

Equivalent crystal theory of alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Ferrante, John

1991-01-01

Equivalent Crystal Theory (ECT) is a new, semi-empirical approach to calculating the energetics of a solid with defects. The theory has successfully reproduced surface energies in metals and semiconductors. The theory of binary alloys to date, both with first-principles and semi-empirical models, has not been very successful in predicting the energetics of alloys. This procedure is used to predict the heats of formation, cohesive energy, and lattice parameter of binary alloys of Cu, Ni, Al, Ag, Au, Pd, and Pt as functions of composition. The procedure accurately reproduces the heats of formation versus composition curves for a variety of binary alloys. The results are then compared with other approaches such as the embedded atom and lattice parameters of alloys from pure metal properties more accurately than Vegard's law is presented.

Fundamental Investigation of Fatigue Crack Growth Retardation in Aluminum Alloys

DTIC Science & Technology

1976-09-01

Fatigue Crack Propagation in 2024 -T3 Aluminum Alloy , " ASTM STP 536, p. 115, 1973. 9. J. Schijve, " Effect of Load Sequences...Hertzberg, " Effect of Multiple Over- loads on Fatigue Crack Propagation in 2024 -T3 Aluminum Alloy , " ASTM STP-536, p. 115, 1973. 9. J. Schijve... Effect of Thickness on Retardation Behavior of 7075 and 2024 Aluminum Alloys .......... 185 vi LIST OF ILLUSTRATIONS FIGURE PAGE 1 SEN

Structural phase transition, electronic structure and optical properties of half Heusler alloys LiBeZ (Z = As, Sb)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amudhavalli, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com

2016-05-23

Ab initio calculations are performed to investigate the structural stability, electronic structure, mechanical properties and optical properties of half Heusler alloys (LiBeAs and LiBeSb) for three different phases of zinc blende crystal structure. Among the considered phases, α- phase is found to be the most stable phase for these alloys at normal pressure. A pressure induced structural phase transition from α-phase to β- phase is observed for LiBeAs. The electronic structure reveals that these alloys are semiconductors. The optical properties confirm that these alloys are semiconductor in nature.

Nanocrystal structures

DOEpatents

Eisler, Hans J [Stoneham, MA; Sundar, Vikram C [Stoneham, MA; Walsh, Michael E [Everett, MA; Klimov, Victor I [Los Alamos, NM; Bawendi, Moungi G [Cambridge, MA; Smith, Henry I [Sudbury, MA

2008-12-30

A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II-VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

Nanophase diagram of binary eutectic Au-Ge nanoalloys for vapor-liquid-solid semiconductor nanowires growth

NASA Astrophysics Data System (ADS)

Lu, Haiming; Meng, Xiangkang

2015-06-01

Although the vapor-liquid-solid growth of semiconductor nanowire is a non-equilibrium process, the equilibrium phase diagram of binary alloy provides important guidance on the growth conditions, such as the temperature and the equilibrium composition of the alloy. Given the small dimensions of the alloy seeds and the nanowires, the known phase diagram of bulk binary alloy cannot be expected to accurately predict the behavior of the nanowire growth. Here, we developed a unified model to describe the size- and dimensionality-dependent equilibrium phase diagram of Au-Ge binary eutectic nanoalloys based on the size-dependent cohesive energy model. It is found that the liquidus curves reduce and shift leftward with decreasing size and dimensionality. Moreover, the effects of size and dimensionality on the eutectic composition are small and negligible when both components in binary eutectic alloys have the same dimensionality. However, when two components have different dimensionality (e.g. Au nanoparticle-Ge nanowire usually used in the semiconductor nanowires growth), the eutectic composition reduces with decreasing size.

First-Principles Calculations of Structural, Electronic and Optical Properties of Ternary Semiconductor Alloys ZAs x Sb1- x ( Z = B, Al, Ga, In)

NASA Astrophysics Data System (ADS)

Bounab, S.; Bentabet, A.; Bouhadda, Y.; Belgoumri, Gh.; Fenineche, N.

2017-08-01

We have investigated the structural and electronic properties of the BAs x Sb 1- x , AlAs x Sb 1- x , GaAs x Sb 1- x and InAs x Sb 1- x semiconductor alloys using first-principles calculations under the virtual crystal approximation within both the density functional perturbation theory and the pseudopotential approach. In addition the optical properties have been calculated by using empirical methods. The ground state properties such as lattice constants, both bulk modulus and derivative of bulk modulus, energy gap, refractive index and optical dielectric constant have been calculated and discussed. The obtained results are in reasonable agreement with numerous experimental and theoretical data. The compositional dependence of the lattice constant, bulk modulus, energy gap and effective mass of electrons for ternary alloys show deviations from Vegard's law where our results are in agreement with the available data in the literature.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

DOE PAGES

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; ...

2017-06-07

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

Group III nitride semiconductors for short wavelength light-emitting devices

NASA Astrophysics Data System (ADS)

Orton, J. W.; Foxon, C. T.

1998-01-01

The group III nitrides (AlN, GaN and InN) represent an important trio of semiconductors because of their direct band gaps which span the range 1.95-6.2 eV, including the whole of the visible region and extending well out into the ultraviolet (UV) range. They form a complete series of ternary alloys which, in principle, makes available any band gap within this range and the fact that they also generate efficient luminescence has been the main driving force for their recent technological development. High brightness visible light-emitting diodes (LEDs) are now commercially available, a development which has transformed the market for LED-based full colour displays and which has opened the way to many other applications, such as in traffic lights and efficient low voltage, flat panel white light sources. Continuously operating UV laser diodes have also been demonstrated in the laboratory, exciting tremendous interest for high-density optical storage systems, UV lithography and projection displays. In a remarkably short space of time, the nitrides have therefore caught up with and, in some ways, surpassed the wide band gap II-VI compounds (ZnCdSSe) as materials for short wavelength optoelectronic devices. The purpose of this paper is to review these developments and to provide essential background material in the form of the structural, electronic and optical properties of the nitrides, relevant to these applications. We have been guided by the fact that the devices so far available are based on the binary compound GaN (which is relatively well developed at the present time), together with the ternary alloys AlGaN and InGaN, containing modest amounts of Al or In. We therefore concentrate, to a considerable extent, on the properties of GaN, then introduce those of the alloys as appropriate, emphasizing their use in the formation of the heterostructures employed in devices. The nitrides crystallize preferentially in the hexagonal wurtzite structure and devices have so

Composition dependent band offsets of ZnO and its ternary alloys

NASA Astrophysics Data System (ADS)

Yin, Haitao; Chen, Junli; Wang, Yin; Wang, Jian; Guo, Hong

2017-01-01

We report the calculated fundamental band gaps of wurtzite ternary alloys Zn1-xMxO (M = Mg, Cd) and the band offsets of the ZnO/Zn1-xMxO heterojunctions, these II-VI materials are important for electronics and optoelectronics. Our calculation is based on density functional theory within the linear muffin-tin orbital (LMTO) approach where the modified Becke-Johnson (MBJ) semi-local exchange is used to accurately produce the band gaps, and the coherent potential approximation (CPA) is applied to deal with configurational average for the ternary alloys. The combined LMTO-MBJ-CPA approach allows one to simultaneously determine both the conduction band and valence band offsets of the heterojunctions. The calculated band gap data of the ZnO alloys scale as Eg = 3.35 + 2.33x and Eg = 3.36 - 2.33x + 1.77x2 for Zn1-xMgxO and Zn1-xCdxO, respectively, where x being the impurity concentration. These scaling as well as the composition dependent band offsets are quantitatively compared to the available experimental data. The capability of predicting the band parameters and band alignments of ZnO and its ternary alloys with the LMTO-CPA-MBJ approach indicate the promising application of this method in the design of emerging electronics and optoelectronics.

Low Temperature Photoluminescence Characterization of Orbitally Grown CdZnTe

NASA Technical Reports Server (NTRS)

Ritter, Timothy M.; Larson, D. J.

1998-01-01

The II-VI ternary alloy CdZnTe is a technologically important material because of its use as a lattice matched substrate for HgCdTe based devices. The increasingly stringent requirements on performance that must be met by such large area infrared detectors also necessitates a higher quality substrate. Such substrate material is typically grown using the Bridgman technique. Due to the nature of bulk semiconductor growth, gravitationally dependent phenomena can adversely affect crystalline quality. The most direct way to alleviate this problem is by crystal growth in a reduced gravity environment. Since it requires hours, even days, to grow a high quality crystal, an orbiting space shuttle or space station provides a superb platform on which to conduct such research. For well over ten years NASA has been studying the effects of microgravity semiconductor crystal growth. This paper reports the results of photoluminescence characterization performed on an arbitrary grown CdZnTe bulk crystal.

Coronal gas in the galaxy. II. A statistical analysis of O VI absorptions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jenkins, E.B.

Results from the survey of interstellar O VI by Jenkins and by Jenkins and Meloy are analyzed to synthesize a global description of the properties of the coronal gas. Tests for correlations of column densities or velocities with properties of the target stars showed no evidence for a circumstellar origin for the absorption lines. An overall average density n (O VI) =2.8 x 10/sup -8/ cm/sup -3/ was found in the galactic plane, with a decrease which approximately follows exp (-z/300 pc) away from the plane.Fluctuations in column densities over various lines of sight suggest that existence of six hotmore » gas regions kpc/sup -/1, randomly distributed in space, each with an O VI column density of about 10/sup 13/ cm/sup -2/. These regions account for an average density n (O VI) =2.1 x 10/sup -8/ cm/sup -3/; the remaining 7 x 10/sup -9/ cm/sup -3/ is produced by more sparsely distributed but thicker parcels of hot gas which are seen toward 10% of the stars. The statistics of radial velocity centroids and widths support the interpretation of distinct domains; each region has an internal velocity dispersion consistent with a Doppler broadening of a plasma at T> or approx. =2 x 10/sup 5/ K (near the characteristic temperature for a maximum concentration of O VI in collisional equilibrium), while the regions themselves move about with a dispersion of radial velocities equal to 26 km s/sup -1/. Systematic motions of gas away from the galactic plane could not be seen, however.Excursions from the normal O VI per unit distance have no perceptible anicorrelation with deviations in reddening by cool interstellar coulds: a fact which suggests that the average filling factor of O VI gas is less than 20% if coronal gas really displaces the cooler material and does not have large variations in density and temperature.« less

Visible-wavelength semiconductor lasers and arrays

DOEpatents

Schneider, Jr., Richard P.; Crawford, Mary H.

1996-01-01

A visible semiconductor laser. The visible semiconductor laser includes an InAlGaP active region surrounded by one or more AlGaAs layers on each side, with carbon as the sole p-type dopant. Embodiments of the invention are provided as vertical-cavity surface-emitting lasers (VCSELs) and as edge-emitting lasers (EELs). One or more transition layers comprised of a substantially indium-free semiconductor alloy such as AlAsP, AlGaAsP, or the like may be provided between the InAlGaP active region and the AlGaAS DBR mirrors or confinement layers to improve carrier injection and device efficiency by reducing any band offsets. Visible VCSEL devices fabricated according to the invention with a one-wavelength-thick (1.lambda.) optical cavity operate continuous-wave (cw) with lasing output powers up to 8 mW, and a peak power conversion efficiency of up to 11%.

Tuning the Luminescence Properties of Colloidal I-III-VI Semiconductor Nanocrystals for Optoelectronics and Biotechnology Applications.

PubMed

Zhong, Haizheng; Bai, Zelong; Zou, Bingsuo

2012-11-01

In the past 5 years, colloidal I-III-VI nanocrystals such as CuInS2, CuInSe2, and AgInS2 have been intensively investigated for the potential to replace commonly available colloidal nanocrystals containing toxic elements in light-emitting and solar-harvesting applications. Many researchers from different disciplines are working on developing new synthetic protocols, performing spectroscopic studies to understand the luminescence mechanisms, and exploring various applications. To achieve enhanced performance, it is very desirable to obtain high-quality materials with tunable luminescence properties. In this Perspective, we highlight the current progress on tuning the luminescence properties of I-III-VI nanocrystals, especially focusing on the advances in the synthesis, spectroscopic properties, as well as the primary applications in light-emitting devices and bioimaging techniques. Finally, we outline the challenges concerning luminescent I-III-VI NCs and list a few important research tasks in this field.

Interfaces of electrical contacts in organic semiconductor devices

NASA Astrophysics Data System (ADS)

Demirkan, Korhan

Progress in organic semiconductor devices relies on better understanding of interfaces as well as material development. The engineering of interfaces that exhibit low resistance, low operating voltage and long-term stability to minimize device degradation is one of the crucial requirements. Photoelectron spectroscopy is a powerful technique to study the metal-semiconductor interfaces, allowing: (i) elucidation of the energy levels of the semiconductor and the contacts that determine Schottky barrier height, (ii) inspection of electrical interactions (such as charge transfer, dipole formation, formation of induced density of states or formation of polaron/bi-polaron states) that effect the energy level alignment, (iii) determination of interfacial chemistry, and (iv) estimation of interface morphology. In this thesis, we have used photoelectron spectroscopy extensively for detailed analysis of the metal organic semiconductor interfaces. In this study, we demonstrate the use of photoelectron spectroscopy for construction of energy level diagrams and display some results related to chemical tailoring of materials for engineering interfaces with lowered Schottky barriers. Following our work on the energy level alignment of poly(p-phenyene vinylene) based organic semiconductors on various substrates [Au, indium tin oxide, Si (with native oxide) and Al (with native oxide)], we tested controlling the energy level alignment by using polar self assembled molecules (SAMs). Photoelectron spectroscopy showed that, by introducing SAMs on the Au surface, we successfully changed the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. To investigate the chemical interactions at the metal/organic interface, we studied the metallization of poly(2-methoxy-5

Systematic study of the spin stiffness dependence on phosphorus alloying in the ferromagnetic semiconductor (Ga,Mn)As

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shihab, S.; Thevenard, L.; Bardeleben, H. J. von

2015-04-06

We study the dependence of the spin stiffness constant on the phosphorus concentration in the ferromagnetic semiconductor (Ga,Mn)(As,P) with the aim of determining whether alloying with phosphorus is detrimental, neutral, or advantageous to the spin stiffness. Time-resolved magneto-optical experiments are carried out in thin epilayers. Laser pulses excite two perpendicular standing spin wave modes, which are exchange related. We show that the first mode is spatially uniform across the layer corresponding to a k≈0 wavevector. From the two frequencies and k-vector spacings we obtain the spin stiffness constant for different phosphorus concentrations using weak surface pinning conditions. The mode assessmentmore » is checked by comparison to the spin stiffness obtained from domain pattern analysis for samples with out-of-plane magnetization. The spin stiffness is found to exhibit little variation with phosphorus concentration in contradiction with ab-initio predictions.« less

Magnetic Damping of Solid Solution Semiconductor Alloys

NASA Technical Reports Server (NTRS)

Szofran, Frank R.; Benz, K. W.; Croell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar

1999-01-01

The objective of this study is to: (1) experimentally test the validity of the modeling predictions applicable to the magnetic damping of convective flows in electrically conductive melts as this applies to the bulk growth of solid solution semiconducting materials; and (2) assess the effectiveness of steady magnetic fields in reducing the fluid flows occurring in these materials during processing. To achieve the objectives of this investigation, we are carrying out a comprehensive program in the Bridgman and floating-zone configurations using the solid solution alloy system Ge-Si. This alloy system has been studied extensively in environments that have not simultaneously included both low gravity and an applied magnetic field. Also, all compositions have a high electrical conductivity, and the materials parameters permit reasonable growth rates. An important supporting investigation is determining the role, if any, that thermoelectromagnetic convection (TEMC) plays during growth of these materials in a magnetic field. TEMC has significant implications for the deployment of a Magnetic Damping Furnace in space. This effect will be especially important in solid solutions where the growth interface is, in general, neither isothermal nor isoconcentrational. It could be important in single melting point materials, also, if faceting takes place producing a non-isothermal interface. In conclusion, magnetic fields up to 5 Tesla are sufficient to eliminate time-dependent convection in silicon floating zones and possibly Bridgman growth of Ge-Si alloys. In both cases, steady convection appears to be more significant for mass transport than diffusion, even at 5 Tesla in the geometries used here. These results are corroborated in both growth configurations by calculations.

Electrical and Optical Tunability in All-Inorganic Halide Perovskite Alloy Nanowires.

PubMed

Lei, Teng; Lai, Minliang; Kong, Qiao; Lu, Dylan; Lee, Woochul; Dou, Letian; Wu, Vincent; Yu, Yi; Yang, Peidong

2018-06-13

Alloying different semiconductors is a powerful approach to tuning the optical and electronic properties of semiconductor materials. In halide perovskites (ABX 3 ), alloys with different anions have been widely studied, and great band gap tunability in the visible range has been achieved. However, perovskite alloys with different cations at the "B" site are less understood due to the synthetic challenges. Herein, we first have developed the synthesis of single-crystalline CsPb x Sn 1- x I 3 nanowires (NWs). The electronic band gaps of CsPb x Sn 1- x I 3 NWs can be tuned from 1.3 to 1.78 eV by varying the Pb/Sn ratio, which leads to the tunable photoluminescence (PL) in the near-infrared range. More importantly, we found that the electrical conductivity increases as more Sn 2+ is alloyed with Pb 2+ , possibly due to the increase of charge carrier concentration when more Sn 2+ is introduced. The wide tunability of the optical and electronic properties makes CsPb x Sn 1- x I 3 alloy NWs promising candidates for future optoelectronic device applications.

Fabrication of Si-As-Te ternary amorphous semiconductor in the microgravity environment (M-13)

NASA Technical Reports Server (NTRS)

Hamakawa, Yoshihiro

1993-01-01

Ternary chalcogenide Si-As-Te system is an interesting semiconductor from the aspect of both basic physics and technological applications. Since a Si-As-Te system consists of a IV-III-II hedral bonding network, it has a very large glass forming region with a wide physical constant controllability. For example, its energy gap can be controlled in a range from 0.6 eV to 2.5 eV, which corresponds to the classical semiconductor Ge (0.66 eV), Si (1.10 eV), GaAs (1.43 eV), and GaP (2.25 eV). This fact indicates that it would be a suitable system to investigate the compositional dependence of the atomic and electronic properties in the random network of solids. In spite of these significant advantages in the Si-As-Te amorphous system, a big barrier impending the wide utilization of this material is the huge difficulty encountered in the material preparation which results from large differences in the weight density, melting point, and vapor pressure of individual elements used for the alloying composition. The objective of the FMPT/M13 experiment is to fabricate homogeneous multi-component amorphous semiconductors in the microgravity environment of space, and to make a series of comparative characterizations of the amorphous structures and their basic physical constants on the materials prepared both in space and in normal terrestrial gravity.

Thermal expansion and microstructural analysis of experimental metal-ceramic titanium alloys.

PubMed

Zinelis, Spiros; Tsetsekou, Athena; Papadopoulos, Triantafillos

2003-10-01

Statement of problem Low-fusing porcelains for titanium veneering have demonstrated inferior color stability and metal-ceramic longevity compared to conventional porcelains. This study evaluated the microstructure and thermal expansion coefficients of some experimental titanium alloys as alternative metallic substrates for low-fusing conventional porcelain. Commercially pure titanium (CP Ti) and various metallic elements (Al, Co, Sn, Ga, In, Mn) were used to prepare 8 titanium alloys using a commercial 2-chamber electric-arc vacuum/inert gas dental casting machine (Cyclarc). The nominal compositions of these alloys were the following (wt%): I: 80Ti-18Sn-1.5In-0.5Mn; II: 76Ti-12Ga-7Sn-4Al-1Co; III: 87Ti-13Ga; IV: 79Ti-13Ga-7Al-1Co; V: 82Ti-18In; VI: 75.5Ti-18In-5Al-1Co-0.5Mn; VII: 85Ti-10Sn-5Al; VIII: 78Ti-12Co-7Ga-3Sn. Six rectangular wax patterns for each test material (l = 25 mm, w = 3 mm, h = 1 mm) were invested with magnesia-based material and cast with grade II CP Ti (control) and the 8 experimental alloys. The porosity of each casting was evaluated radiographically, and defective specimens were discarded. Two cast specimens from CP Ti and alloys I-VIII were embedded in epoxy resin and, after metallographic grinding and polishing, were studied by means of scanning electron microscopy and wavelength dispersive electron probe microanalysis. One specimen of each material was utilized for the determination of coefficient of thermal expansion (CTE) with a dilatometer operating from room temperature up to 650 degrees C at a heating rate of 5 degrees C/minute. Secondary electron images (SEI) and compositional backscattered electron images (BEI-COMPO) revealed that all cast specimens consisted of a homogeneous matrix except Alloy VIII, which contained a second phase (possibly Ti(2)Co) along with the titanium matrix. The results showed that the coefficient of thermal expansion (CTE) varied from 10.1 to 13.1 x 10(-6)/ degrees C (25 degrees -500 degrees C), depending on

25th anniversary article: semiconductor nanowires--synthesis, characterization, and applications.

PubMed

Dasgupta, Neil P; Sun, Jianwei; Liu, Chong; Brittman, Sarah; Andrews, Sean C; Lim, Jongwoo; Gao, Hanwei; Yan, Ruoxue; Yang, Peidong

2014-04-09

Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Size, surface, and compositional tuning of the electronic and photocatalytic properties of II-VI quantum-size semiconductor nanocrystals

NASA Astrophysics Data System (ADS)

Korgel, Brian Allan

1997-11-01

Phosphatidylcholine vesicles provide reaction compartments for synthesis of size-quantized CdS nanocrystals of dimension predicted to within ±2 A based on initial encapsulated CdClsb2 concentration and vesicle diameter. Vesicle formation by detergent dialysis of phosphatidylcholine/hexylglucoside mixed micelles yields highly monodisperse lipid capsules within which monodisperse CdS nanoparticles are precipitated with sulfide. Size-quantized CdS nanocrystals, with diameters ranging from 20 to 60 A, have been produced with typical standard deviations about the mean diameter of ±8% as measured by transmission electron microscopy. By including ZnClsb2 or HgClsb2 in the dialyzate prior to vesicle formation, quantum-sized Znsb{y}Cdsb{1-y}S or Hgsb{y}Cdsb{1-y}S nanocrystal alloys with controlled stoichiometry are generated. Spectrophotometric and spectrofluorimetric measurements are consistent with highly crystalline, monodisperse particles with few core or surface defects. The alloyed nanocrystal spectra shift consistently with composition indicating a high degree of compositional control. Measured exciton energies for CdS show excellent agreement with data in the literature. The empirical pseudopotential model presented by Ramakrishna and Friesner for a cubic CdS lattice, correcting for experimentally measured lattice contractions, best fits the data. Size-quantized CdS nanocrystals serve as photocatalysts for nitrate reduction at neutral pH under conditions that mimic illumination by sunlight with overall product quantum yields of up to 4% for {˜}20 A, amine-terminated particles. Due to the effects of quantum confinement on electron and hole redox potentials, photocatalyzed nitrate reduction rates depend strongly on the particle size, and the fastest reduction rates are observed with the smallest nanocrystals. Using a Tafel plot and the empirical pseudopotential model to estimate electron redox potentials, the apparent electron transfer coefficient and the apparent

VizieR Online Data Catalog: OGLE II. VI photometry of Galactic Bulge (Udalski+, 2002)

NASA Astrophysics Data System (ADS)

Udalski, A.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Wozniak, P.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

2003-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive (2 data files).

Internal gettering by metal alloy clusters

DOEpatents

Buonassisi, Anthony; Heuer, Matthias; Istratov, Andrei A.; Pickett, Matthew D.; Marcus, Mathew A.; Weber, Eicke R.

2010-07-27

The present invention relates to the internal gettering of impurities in semiconductors by metal alloy clusters. In particular, intermetallic clusters are formed within silicon, such clusters containing two or more transition metal species. Such clusters have melting temperatures below that of the host material and are shown to be particularly effective in gettering impurities within the silicon and collecting them into isolated, less harmful locations. Novel compositions for some of the metal alloy clusters are also described.

Incompatibility and preferred morphology in the self-accommodation microstructure of β-titanium shape memory alloy

NASA Astrophysics Data System (ADS)

Inamura, T.; Hosoda, H.; Miyazaki, S.

2013-02-01

The frequency distribution of habit plane variant (HPV) clusters and the deviation from twin orientation relationships (ORs) at the junction plane (JP) are investigated by transmission electron microscopy together with theoretical evaluation of the kinematic compatibility (KC) at the JP in a β-titanium shape memory alloy. Even though there are more than 10 types of possible HPV clusters, only three types are formed. V-shaped couplings of HPVs by {111} type I twins (VI: 49%) and by ⟨211⟩ type II twins (VII: 42%) are the predominant types. A triangular morphology due to coupling of {111} type I twins is observed with a frequency of only 9%. These preferred morphologies are well explained by the degree of incompatibility (the rotation necessary for compatible connection of HPVs). The exact twin OR and KC are maintained at the JP in a VI cluster instead of KC at the habit plane (HP), whereas the JP in a VII cluster is incompatible and the ⟨211⟩ type II twin OR shows slight deviation at the JP by about 0.4°. The competition between KC at the JP and KC at the HP (invariant plane) is responsible for the frequency distribution of HPV clusters and the character of the interfaces in the self-accommodation microstructure.

Surface Conduction in III-V Semiconductor Infrared Detector Materials

NASA Astrophysics Data System (ADS)

Sidor, Daniel Evan

III-V semiconductors are increasingly used to produce high performance infrared photodetectors; however a significant challenge inherent to working with these materials is presented by unintended electrical conduction pathways that form along their surfaces. Resulting leakage currents contribute to system noise and are ineffectively mitigated by device cooling, and therefore limit ultimate performance. When the mechanism of surface conduction is understood, the unipolar barrier device architecture offers a potential solution. III-V bulk unipolar barrier detectors that effectively suppress surface leakage have approached the performance of the best II-VI pn-based structures. This thesis begins with a review of empirically determined Schottky barrier heights and uses this information to present a simple model of semiconductor surface conductivity. The model is validated through measurements of degenerate n-type surface conductivity on InAs pn junctions, and non-degenerate surface conductivity on GaSb pn junctions. It is then extended, along with design principles inspired by the InAs-based nBn detector, to create a flat-band pn-based unipolar barrier detector possessing a conductive surface but free of detrimental surface leakage current. Consideration is then given to the relative success of these and related bulk detectors in suppressing surface leakage when compared to analogous superlattice-based designs, and general limitations of unipolar barriers in suppressing surface leakage are proposed. Finally, refinements to the molecular beam epitaxy crystal growth techniques used to produce InAs-based unipolar barrier heterostructure devices are discussed. Improvements leading to III-V device performance well within an order of magnitude of the state-of-the-art are demonstrated.

Development of epitaxial Al xSc 1-xN for artificially structured metal/semiconductor superlattice metamaterials

DOE PAGES

Sands, Timothy D.; Stach, Eric A.; Saha, Bivas; ...

2015-02-01

Epitaxial nitride rocksalt metal/semiconductor superlattices are emerging as a novel class of artificially structured materials that have generated significant interest in recent years for their potential application in plasmonic and thermoelectric devices. Though most nitride metals are rocksalt, nitride semiconductors in general have hexagonal crystal structure. We report rocksalt aluminum scandium nitride (Al,Sc)N alloys as the semiconducting component in epitaxial rocksalt metal/semiconductor superlattices. The Al xSc 1-xN alloys when deposited directly on MgO substrates are stabilized in a homogeneous rocksalt (single) phase when x < 0.51. Employing 20 nm TiN as a seed layer on MgO substrates, the homogeneity rangemore » for stabilizing the rocksalt phase has been extended to x < 0.82 for a 120 nm film. The rocksalt Al xSc 1-xN alloys show moderate direct bandgap bowing with a bowing parameter, B = 1.41 ± 0.19 eV. The direct bandgap of metastable rocksalt AlN is extrapolated to be 4.70 ± 0.20 eV. The tunable lattice parameter, bandgap, dielectric permittivity, and electronic properties of rocksalt Al xSc 1-xN alloys enable high quality epitaxial rocksalt metal/Al xSc 1-xN superlattices with a wide range of accessible metamaterials properties.« less

Ligational behaviour of lomefloxacin drug towards Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Th(IV) and UO(2)(VI) ions: synthesis, structural characterization and biological activity studies.

PubMed

Abd el-Halim, Hanan F; Mohamed, Gehad G; el-Dessouky, Maher M I; Mahmoud, Walaa H

2011-11-01

Nine new mononuclear Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Th(IV) and UO(2)(VI) complexes of lomefloxacin drug were synthesized. The structures of these complexes were elucidated by elemental analyses, IR, XRD, UV-vis, (1)H NMR as well as conductivity and magnetic susceptibility measurements and thermal analyses. The dissociation constants of lomefloxacin and stability constants of its binary complexes have been determined spectrophotometrically in aqueous solution at 25±1°C and at 0.1 M KNO(3) ionic strength. The discussion of the outcome data of the prepared complexes indicate that the lomefloxacin ligand behaves as a neutral bidentate ligand through OO coordination sites and coordinated to the metal ions via the carbonyl oxygen and protonated carboxylic oxygen with 1:1 (metal:ligand) stoichiometry for all complexes. The molar conductance measurements proved that the complexes are electrolytes. The powder XRD study reflects the crystalline nature for the investigated ligand and its complexes except Mn(II), Zn(II) and UO(2)(II). The geometrical structures of these complexes are found to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose water molecules of hydration in the first steps followed by decomposition of the anions, coordinated water and ligand molecules in the subsequent steps. The activation thermodynamic parameters are calculated using Coats-Redfern and Horowitz-Metzger methods. A comparative study of the inhibition zones of the ligand and its metal complexes indicates that metal complexes exhibit higher antibacterial effect against one or more bacterial species than the free LFX ligand. The antifungal and anticancer activities were also tested. The antifungal effect of almost metal complexes is higher than the free ligand. LFX, [Co(LFX)(H(2)O)(4)]·Cl(2) and [Zn(LFX)(H(2)O)(4)]·Cl(2) were found to be very active with IC50 values 14, 11.2 and 43.1, respectively. While, other

Materials Science and Device Physics of 2-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Fang, Hui

Materials and device innovations are the keys to future technology revolution. For MOSFET scaling in particular, semiconductors with ultra-thin thickness on insulator platform is currently of great interest, due to the potential of integrating excellent channel materials with the industrially mature Si processing. Meanwhile, ultra-thin thickness also induces strong quantum confinement which in turn affect most of the material properties of these 2-dimensional (2-D) semiconductors, providing unprecedented opportunities for emerging technologies. In this thesis, multiple novel 2-D material systems are explored. Chapter one introduces the present challenges faced by MOSFET scaling. Chapter two covers the integration of ultrathin III V membranes with Si. Free standing ultrathin III-V is studied to enable high performance III-V on Si MOSFETs with strain engineering and alloying. Chapter three studies the light absorption in 2-D membranes. Experimental results and theoretical analysis reveal that light absorption in the 2-D quantum membranes is quantized into a fundamental physical constant, where we call it the quantum unit of light absorption, irrelevant of most of the material dependent parameters. Chapter four starts to focus on another 2-D system, atomic thin layered chalcogenides. Single and few layered chalcogenides are first explored as channel materials, with focuses in engineering the contacts for high performance MOSFETs. Contact treatment by molecular doping methods reveals that many layered chalcogenides other than MoS2 exhibit good transport properties at single layer limit. Finally, Chapter five investigated 2-D van der Waals heterostructures built from different single layer chalcogenides. The investigation in a WSe2/MoS2 hetero-bilayer shows a large Stokes like shift between photoluminescence peak and lowest absorption peak, as well as strong photoluminescence intensity, consistent with spatially indirect transition in a type II band alignment in this

Mechanical Properties of Semiconductors and Their Alloys

DTIC Science & Technology

1992-02-01

Sher, Associate Director M.A. Berding, Research Physicist A.T. Paxton, International Fellow S. Krishnamurthy, Research Physicist Physical Electronics...Laboratory A.-B. Chen Auburn University Auburn, Alabama SRI Project 6682 Prepared for: . - Office of Scientific Research United States Air Force...THEIR ALLOYS A. Sher, Associate Director M.A. Berding, Research Physicist A.T. Paxton, International Fellow S. Knshnamurthy, Research Physicist Physical

Efficient color-tunable multiexcitonic dual wavelength emission from Type II semiconductor tetrapods.

PubMed

Wu, Wen-Ya; Li, Mingjie; Lian, Jie; Wu, Xiangyang; Yeow, Edwin K L; Jhon, Mark H; Chan, Yinthai

2014-09-23

We synthesized colloidal InP/ZnS seeded CdS tetrapods by harnessing the structural stability of the InP/ZnS seed nanocrystals at the high reaction temperatures needed to grow the CdS arms. Because of an unexpected Type II band alignment at the interface of the InP/ZnS core and CdS arms that enhanced the occurrence of radiative excitonic recombination in CdS, these tetrapods were found to be capable of exhibiting highly efficient multiexcitonic dual wavelength emission of equal intensity at spectrally distinct wavelengths of ∼485 and ∼675 nm. Additionally, the Type II InP/ZnS seeded CdS tetrapods displayed a wider range of pump-dependent emission color-tunability (from red to white to blue) within the context of a CIE 1931 chromaticity diagram and possessed higher photostability due to suppressed multiexcitonic Auger recombination when compared to conventional Type I CdSe seeded CdS tetrapods. By employing time-resolved spectroscopy measurements, we were able to attribute the wide emission color-tunability to the large valence band offset between InP and CdS. This work highlights the importance of band alignment in the synthetic design of semiconductor nanoheterostructures, which can exhibit color-tunable multiwavelength emission with high efficiency and photostability.

Reactive codoping of GaAlInP compound semiconductors

DOEpatents

Hanna, Mark Cooper [Boulder, CO; Reedy, Robert [Golden, CO

2008-02-12

A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

Flow-through Column Experiments and Modeling of Microbially Mediated Cr(VI) Reduction at Hanford 100H

NASA Astrophysics Data System (ADS)

Yang, L.; Molins, S.; Beller, H. R.; Brodie, E. L.; Steefel, C.; Nico, P. S.; Han, R.

2010-12-01

under sulfate-reducing/fermentative conditions exhibited the greatest Cr(VI) reduction capacity. Two sulfate columns evolved to complete lactate fermentation with acetate and propionate produced in the column effluent after 40 days of experiments. These fermenting columns showed a complete removal of injected Cr(VI), visible precipitation of sulfide minerals, and a significant increase in effluent Fe and Mn concentrations. Reactive transport simulations suggested that direct reduction of Cr(VI) by Fe(II) and Mn(II) released from the sediment could account for the observed Cr(VI) removal. The biogeochemical modeling was employed to test two hypotheses that could explain the release of Fe(II) and Mn(II) from the column sediments: 1) acetate produced by lactate fermentation provided the substrate for the growth of iron(III) and manganese(IV) oxide reducers, and 2) direct reduction of iron(III) and manganese(IV) oxides by hydrogen sulfide generated during sulfate reduction. Overall, experimental and modeling results suggested that Cr(VI) reduction in the sulfate-reducing columns occurred through a complex network of microbial reactions that included fermentation, sulfate reduction, and possibly the stimulated iron-reducing communities.

Sulphur alters chromium (VI) toxicity in Solanum melongena seedlings: Role of sulphur assimilation and sulphur-containing antioxidants.

PubMed

Singh, Madhulika; Kushwaha, Bishwajit Kumar; Singh, Samiksha; Kumar, Vipin; Singh, Vijay Pratap; Prasad, Sheo Mohan

2017-03-01

The present study investigates modulation in hexavalent chromium [Cr(VI) 25 μM] toxicity by sulphur (S; 0.5, 1.0 and 1.5 mM S as low (LS), medium (MS) and high sulphur (HS), respectively) in Solanum melongena (eggplant) seedlings. Biomass accumulation (fresh and dry weights), photosynthetic pigments, photosynthetic oxygen evolution and S content were declined by Cr(VI) toxicity. Furthermore, fluorescence characteristics (JIP-test) were also affected by Cr(VI), but Cr(VI) toxicity on photosystem II photochemistry was ameliorated by HS treatment via reducing damaging effect on PS II reaction centre and its reduction side. Enhanced respiration, Cr content and oxidative biomarkers: superoxide radical, hydrogen peroxide, lipid peroxidation and membrane damage were observed under Cr(VI) stress. Though Cr(VI) enhanced adenosine triphasphate sulfurylase (ATPS) and o-acetylserine(thiol)lyase (OASTL), glutathione-S-transferase (GST), glutathione reductase (GR) and ascorbate peroxidase (APX) activity, and content of total glutathione, cysteine and NP-SH, however, their levels/activity were further enhanced by S being maximum with HS treatment. The results show that Cr(VI) toxicity does increase under LS treatment while HS protected Cr(VI)-induced damaging effects in brinjal seedlings. Under HS treatment, in mitigating Cr(VI) toxicity, S assimilation and its associated metabolites such as cysteine, glutathione and NP-SH play crucial role. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

High-temperature ferromagnetism in new n-type Fe-doped ferromagnetic semiconductor (In,Fe)Sb

NASA Astrophysics Data System (ADS)

Thanh Tu, Nguyen; Hai, Pham Nam; Anh, Le Duc; Tanaka, Masaaki

2018-06-01

Over the past two decades, intensive studies on various ferromagnetic semiconductor (FMS) materials have failed to realize reliable FMSs that have a high Curie temperature (T C > 300 K), good compatibility with semiconductor electronics, and characteristics superior to those of their nonmagnetic host semiconductors. Here, we demonstrate a new n-type Fe-doped narrow-gap III–V FMS, (In1‑ x ,Fe x )Sb. Its T C is unexpectedly high, reaching ∼335 K at a modest Fe concentration (x) of 16%. The anomalous Hall effect and magnetic circular dichroism (MCD) spectroscopy indicate that the high-temperature ferromagnetism in (In,Fe)Sb thin films is intrinsic and originates from the zinc-blende (In,Fe)Sb alloy semiconductor.

Graded Index Silicon Geranium on Lattice Matched Silicon Geranium Semiconductor Alloy

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R., Jr. (Inventor); Stoakley, Diane M. (Inventor)

2009-01-01

A lattice matched silicon germanium (SiGe) semiconductive alloy is formed when a {111} crystal plane of a cubic diamond structure SiGe is grown on the {0001} C-plane of a single crystalline Al2O3 substrate such that a <110> orientation of the cubic diamond structure SiGe is aligned with a <1,0,-1,0> orientation of the {0001} C-plane. A lattice match between the substrate and the SiGe is achieved by using a SiGe composition that is 0.7223 atomic percent silicon and 0.2777 atomic percent germanium. A layer of Si(1-x), ,Ge(x) is formed on the cubic diamond structure SiGe. The value of X (i) defines an atomic percent of germanium satisfying 0.2277ii) is approximately 0.2777 where the layer of Si(1-x)Ge(x)interfaces with the cubic diamond structure SiGe, and (iii) increases linearly with the thickness of the layer of Si(1-x)Ge(x).

Reduction of Cr(VI) to Cr(III) by green rust - sulphate

NASA Astrophysics Data System (ADS)

Skovbjerg, L.; Stipp, S.

2003-04-01

Chromium is widely used in industrial processes such as leather tanning, electro-plating and as colour pigments. Unfortunately, hexavalent chromium is both toxic and very soluble so it can be a problem for groundwater resources. Given the right redox conditions, however, Cr(VI) can be reduced to trivalent chromium, which is much less soluble and is an essential trace nutrient. Fe(II), an element common in soil and sediments under anaerobic conditions, can serve as a reducing agent for Cr(VI). Green Rust (GR) is a layered Fe(II),Fe(III)-hydroxide with various anions compensating charge in the interlayers. It is very effective in reducing Cr(VI) to Cr(III). GR exists in nature and is thought to be precursor for the formation of Fe(III)-oxides and oxyhydroxides at the redox boundary. It may be that the formation of GR is a key process in the effectiveness of reactive barriers for groundwater remediation that are based on Fe(0). The purpose of this work is to investigate the mechanisms controlling Cr(VI) reduction by Green Rust, to examine the effect of Cr adsorption and incorporation on GR morphology and composition, and to define the role of parameters such as interlayer anion, initial Cr(VI) concentration and time. We are using freshly synthesised material that has not been dried to avoid structural changes that may accompany dehydration and rehydration. X-Ray Diffraction (XRD) is used to characterise mineral structural changes and Atomic Force Microscopy (AFM), to examine changes in morphology as reactions take place. By adjusting the concentration of Cr(VI), we can control the rate of surface change and we can observe the nanoscale particles directly.

PREFACE: Semiconductor Nanostructures towards Electronic and Optoelectronic Device Applications II (Symposium K, E-MRS 2009 Spring Meeting)

NASA Astrophysics Data System (ADS)

Nötzel, Richard

2009-07-01

This volume of IOP Conference Series: Materials Science and Engineering contains papers that were presented at the special symposium K at the EMRS 2009 Spring Meeting held 8-12 June in Strasbourg, France, which was entitled 'Semiconductor Nanostructures towards Electronic and Optoelectronic Device Applications II'. Thanks to the broad interest a large variety of quantum dots and quantum wires and related nanostructures and their application in devices could be covered. There was significant progress in the epitaxial growth of semiconductor quantum dots seen in the operation of high-power, as well as mode locked laser diodes and the lateral positioning of quantum dots on patterned substrates or by selective area growth for future single quantum dot based optoelectronic and electronic devices. In the field of semiconductor nanowires high quality, almost twin free structures are now available together with a new degree of freedom for band structure engineering based on alternation of the crystal structure. In the search for Si based light emitting structures, nanocrystals and miniband-related near infrared luminescence of Si/Ge quantum dot superlattices with high quantum efficiency were reported. These highlights, among others, and the engaged discussions of the scientists, engineers and students brought together at the symposium emphasize how active the field of semiconductor nanostructures and their applications in devices is, so that we can look forward to the progress to come. Guest Editor Richard Nötzel COBRA Research Institute Department of Applied Physics Eindhoven University of Technology 5600 MB Eindhoven The Netherlands Tel.: +31 40 247 2047; fax: +31 40 246 1339 E-mail address: r.noetzel@tue.nl

Electronic modification of Cu-based chalcopyrite semiconductors induced by lattice deformation and composition alchemy

NASA Astrophysics Data System (ADS)

Jiang, F. D.; Feng, J. Y.

2008-02-01

Using first principles calculation, we systematically investigate the electronic modification of Cu-based chalcopyrite semiconductors induced by lattice deformation and composition alchemy. It is shown that the optical band gap Eg is remarkably sensitive to the anion displacement μ, resulting from the opposite shifts of conduction band minimum and valence band maximum. Meanwhile, the dependence of structural parameters of alloyed compounds on alloy composition x is demonstrated for both cation and anion alloying. The d orbitals of group-III cations are found to be of great importance in the calculation. Abnormal changes in the optical band gap Eg induced by anion alloying are addressed.

Ferrate(VI)-prompted removal of metals in aqueous media: mechanistic delineation of enhanced efficiency via metal entrenchment in magnetic oxides.

PubMed

Prucek, Robert; Tuček, Jiří; Kolařík, Jan; Hušková, Ivana; Filip, Jan; Varma, Rajender S; Sharma, Virender K; Zbořil, Radek

2015-02-17

The removal efficiency of heavy metal ions (cadmium(II), Cd(II); cobalt(II), Co(II); nickel(II), Ni(II); copper(II), Cu(II)) by potassium ferrate(VI) (K2FeO4, Fe(VI)) was studied as a function of added amount of Fe(VI) (or Fe) and varying pH. At pH = 6.6, the effective removal of Co(II), Ni(II), and Cu(II) from water was observed at a low Fe-to-heavy metal ion ratio (Fe/M(II) = 2:1) while a removal efficiency of 70% was seen for Cd(II) ions at a high Fe/Cd(II) weight ratio of 15:1. The role of ionic radius and metal valence state was explored by conducting similar removal experiments using Al(III) ions. The unique combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in-field Mössbauer spectroscopy, and magnetization measurements enabled the delineation of several distinct mechanisms for the Fe(VI)-prompted removal of metal ions. Under a Fe/M weight ratio of 5:1, Co(II), Ni(II), and Cu(II) were removed by the formation of MFe2O4 spinel phase and partially through their structural incorporation into octahedral positions of γ-Fe2O3 (maghemite) nanoparticles. In comparison, smaller sized Al(III) ions got incorporated easily into the tetrahedral positions of γ-Fe2O3 nanoparticles. In contrast, Cd(II) ions either did not form the spinel ferrite structure or were not incorporated into the lattic of iron(III) oxide phase due to the distinct electronic structure and ionic radius. Environmentally friendly removal of heavy metal ions at a much smaller dosage of Fe than those of commonly applied iron-containing coagulants and the formation of ferrimagnetic species preventing metal ions leaching back into the environment and allowing their magnetic separation are highlighted.

Raman-scattered O VI λ1032 and He II λ1025 and Bipolar Outflow in the Symbiotic Star V455 Sco

NASA Astrophysics Data System (ADS)

Heo, Jeong-Eun; Angeloni, Rodolfo; Di Mille, Francesco; Palma, Tali; Chang, Seok-Jun; Hong, Chae-Lin; Lee, Hee-Won

2016-07-01

Raman-scattering by atomic hydrogen is a unique spectroscopic process that may probe the mass transfer and mass loss phenomena in symbiotic stars(SSs). In the optical high- resolution spectra of the S-type SS V455 Sco, we note the presence of two Raman-scattered features, one at around 6825 Å with a triple-peak profile formed from Raman-scattering of O VI λ1032 and the other Raman-scattered He II λ1025 at around 6545 Å. Adopting an accretion flow model with additional contribution from a collimated bipolar outflow, we propose that the blue and central peaks are contributed from the accretion flow and the bipolar flow is responsible for the remaining red peak. With the absence of [N II] λ6548, the Raman-scattered He II λ1025 at around 6545 Å is immersed in the broad Ha wings that appear to be formed by Raman-scattering of far-UV continuum near Lyman series.

Home treatment with Elaprase and Naglazyme is safe in patients with mucopolysaccharidoses types II and VI, respectively.

PubMed

Bagewadi, S; Roberts, J; Mercer, J; Jones, S; Stephenson, J; Wraith, J E

2008-12-01

Enzyme replacement therapy for lysosomal storage disorders has made an important contribution to improving the quality of life of affected patients. The treatment, however, is invasive and onerous, involving weekly or biweekly intravenous infusions of product over a 3-4 h period. Such therapy can be extremely disruptive of normal family life and the provision of a safe, home treatment regimen is greatly appreciated by affected families. In this report we demonstrate the safety of home treatment with Elaprase for mucopolysaccharidosis type II (17 patients) and Naglazyme for mucopolysaccharidosis type VI (6 patients). Careful patient selection, an experienced home care company and a detailed management plan for potential anaphylaxis and infusion-associated reactions are important components in a successful home treatment programme.

Asymmetric severe skeletal Class II division 1 patient with temporomandibular joint disorder treated with zygomatic anchorage devices and Ni-Ti alloy wires.

PubMed

Ishida, Takayoshi; Ono, Takashi

2014-09-01

To describe the orthodontic treatment of a nongrowing 30-year-old woman with asymmetric severe skeletal Class II malocclusions (asymmetric Angle Class II), large overjet (16 mm), large overbite (8 mm), two congenitally missing mandibular incisors (presenting a deciduous anterior tooth), and signs and symptoms of temporomandibular joint disorder (TMD). We used novel improved super-elastic Ni-Ti alloy wires (ISWs) combined with Ni-Ti alloy coil springs, power hooks, and a zygomatic implant as reinforced anchorage to provide a constant and continuous mild force to the dentition. We successfully distalized maxillary molars, premolars, and retracted anterior teeth and corrected the asymmetric Angle Class II molar relationship using this system of zygomatic anchorage in conjunction with ISWs, Ni-Ti alloy open-coil springs, and crimpable power hook. The maxillary molars were distalized, and postero-occlusal relationships were improved to achieve Class I canine and molar relationships on both sides. Intrusion of the upper molars made the mandibular plane close. Ideal overbite and overjet relationships were established. Facial esthetics were improved with decreased upper and lower lip protrusion, and no symptoms of TMD were observed after treatment. The orthodontic treatment described here is a promising anchorage technique alternative to traditional techniques to improve severe skeletal Class II with TMD.

Imaging the motion of electrons across semiconductor heterojunctions.

PubMed

Man, Michael K L; Margiolakis, Athanasios; Deckoff-Jones, Skylar; Harada, Takaaki; Wong, E Laine; Krishna, M Bala Murali; Madéo, Julien; Winchester, Andrew; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M; Dani, Keshav M

2017-01-01

Technological progress since the late twentieth century has centred on semiconductor devices, such as transistors, diodes and solar cells. At the heart of these devices is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. Here, by combining femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy, we imaged the motion of photoexcited electrons from high-energy to low-energy states in a type-II 2D InSe/GaAs heterostructure. At the instant of photoexcitation, energy-resolved photoelectron images revealed a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observed the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we produced a movie lasting a few trillionths of a second of the electron-transfer process in the photoexcited type-II heterostructure-a fundamental phenomenon in semiconductor devices such as solar cells. Quantitative analysis and theoretical modelling of spatial variations in the movie provide insight into future solar cells, 2D materials and other semiconductor devices.

Imaging the motion of electrons across semiconductor heterojunctions

NASA Astrophysics Data System (ADS)

Man, Michael K. L.; Margiolakis, Athanasios; Deckoff-Jones, Skylar; Harada, Takaaki; Wong, E. Laine; Krishna, M. Bala Murali; Madéo, Julien; Winchester, Andrew; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M.; Dani, Keshav M.

2017-01-01

Technological progress since the late twentieth century has centred on semiconductor devices, such as transistors, diodes and solar cells. At the heart of these devices is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. Here, by combining femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy, we imaged the motion of photoexcited electrons from high-energy to low-energy states in a type-II 2D InSe/GaAs heterostructure. At the instant of photoexcitation, energy-resolved photoelectron images revealed a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observed the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we produced a movie lasting a few trillionths of a second of the electron-transfer process in the photoexcited type-II heterostructure—a fundamental phenomenon in semiconductor devices such as solar cells. Quantitative analysis and theoretical modelling of spatial variations in the movie provide insight into future solar cells, 2D materials and other semiconductor devices.

40 CFR 144.19 - Transitioning from Class II to Class VI.

Code of Federal Regulations, 2014 CFR

2014-07-01

... primary purpose of long-term storage into an oil and gas reservoir must apply for and obtain a Class VI...) Quality of abandoned well plugs within the area of review; (7) The owner's or operator's plan for recovery...

40 CFR 144.19 - Transitioning from Class II to Class VI.

Code of Federal Regulations, 2013 CFR

2013-07-01

... primary purpose of long-term storage into an oil and gas reservoir must apply for and obtain a Class VI...) Quality of abandoned well plugs within the area of review; (7) The owner's or operator's plan for recovery...

40 CFR 144.19 - Transitioning from Class II to Class VI.

Code of Federal Regulations, 2012 CFR

2012-07-01

... primary purpose of long-term storage into an oil and gas reservoir must apply for and obtain a Class VI...) Quality of abandoned well plugs within the area of review; (7) The owner's or operator's plan for recovery...

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors.

PubMed

Fluegel, Brian; Mialitsin, Aleksej V; Beaton, Daniel A; Reno, John L; Mascarenhas, Angelo

2015-05-28

Semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10(-4). Comparing our strain sensitivity and signal strength in Al(x)Ga(1-x)As with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 10(3), thus obviating key constraints in semiconductor strain metrology.

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors

PubMed Central

Fluegel, Brian; Mialitsin, Aleksej V.; Beaton, Daniel A.; Reno, John L.; Mascarenhas, Angelo

2015-01-01

Semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10−4. Comparing our strain sensitivity and signal strength in AlxGa1−xAs with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 103, thus obviating key constraints in semiconductor strain metrology. PMID:26017853

Ultraviolet observations of cool stars. VI - L alpha and Mg II emission line profiles /and a search for flux variability/ in Arcturus

NASA Technical Reports Server (NTRS)

Mcclintock, W.; Moos, H. W.; Henry, R. C.; Linsky, J. L.; Barker, E. S.

1978-01-01

High-precision, high-resolution profiles of the L alpha and Mg II k chromospheric emission lines from Arcturus (alpha Boo) obtained with the Princeton Experimental Package aboard the Copernicus satellite are presented. Asymmetries seen in the profiles of these lines are probably intrinsic to the star, rather than the result of interstellar absorption. In contrast to previous observations of the Ca II K emission line, no evidence is found during a three-year period for variability in the profiles or in the total fluxes from these lines on time scales ranging from hours to months. Also presented is a flux profile of the O I 1302 line and flux upper limits for L beta, O VI 1032, Si III 1206, and O V 1218.

Quantifying Cr(VI) Production and Export from Serpentine Soil of the California Coast Range.

PubMed

McClain, Cynthia N; Fendorf, Scott; Webb, Samuel M; Maher, Kate

2017-01-03

Hexavalent chromium (Cr(VI)) is generated in serpentine soils and exported to surface and groundwaters at levels above health-based drinking water standards. Although Cr(VI) concentrations are elevated in serpentine soil pore water, few studies have reported field evidence documenting Cr(VI) production rates and fluxes that govern Cr(VI) transport from soil to water sources. We report Cr speciation (i) in four serpentine soil depth profiles derived from the California Coast Range serpentinite belt and (ii) in local surface waters. Within soils, we detected Cr(VI) in the same horizons where Cr(III)-minerals are colocated with biogenic Mn(III/IV)-oxides, suggesting Cr(VI) generation through oxidation by Mn-oxides. Water-extractable Cr(VI) concentrations increase with depth constituting a 7.8 to 12 kg/km 2 reservoir of Cr(VI) in soil. Here, Cr(VI) is produced at a rate of 0.3 to 4.8 kg Cr(VI)/km 2 /yr and subsequently flushed from soil during water infiltration, exporting 0.01 to 3.9 kg Cr(VI)/km 2 /yr at concentrations ranging from 25 to 172 μg/L. Although soil-derived Cr(VI) is leached from soil at concentrations exceeding 10 μg/L, due to reduction and dilution during transport to streams, Cr(VI) levels measured in local surface waters largely remain below California's drinking water limit.

Effect of Humic Acid on the Removal of Chromium(VI) and the Production of Solids in Iron Electrocoagulation.

PubMed

Pan, Chao; Troyer, Lyndsay D; Liao, Peng; Catalano, Jeffrey G; Li, Wenlu; Giammar, Daniel E

2017-06-06

Iron-based electrocoagulation can be highly effective for Cr(VI) removal from water supplies. However, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with the greatest decreases in Cr(VI) removal rate at higher pH. This inhibition was probably due to the formation of Fe(II) complexes with HA that are more rapidly oxidized than uncomplexed Fe(II) by dissolved oxygen, making less Fe(II) available for reduction of Cr(VI). Close association of Fe(III), Cr(III), and HA in the solid products formed during electrocoagulation influenced the fate of both Cr(III) and HA. At pH 8, the solid products were colloids (1-200 nm) with Cr(III) and HA concentrations in the filtered fraction being quite high, while at pH 6 these concentrations were low due to aggregation of small particles. X-ray diffraction and X-ray absorption fine structure spectroscopy indicated that the iron oxides produced were a mixture of lepidocrocite and ferrihydrite, with the proportion of ferrihydrite increasing in the presence of HA. Cr(VI) was completely reduced to Cr(III) in electrocoagulation, and the coordination environment of the Cr(III) in the solids was similar regardless of the humic acid loading, pH, and dissolved oxygen level.

Inorganic Chemistry Solutions to Semiconductor Nanocrystal Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

2014-03-15

The optoelectronic and chemical properties of semiconductor nanocrystals heavily depend on their composition, size, shape and internal structure, surface functionality, etc. Available strategies to alter these properties through traditional colloidal syntheses and ligand exchange methods place a premium on specific reaction conditions and surfactant combinations. In this invited review, we apply a molecular-level understanding of chemical precursor reactivity to reliably control the morphology, composition and intimate architecture (core/shell vs. alloyed) of semiconductor nanocrystals. We also describe our work aimed at achieving highly selective, low-temperature photochemical methods for the synthesis of semiconductor–metal and semiconductor–metal oxide photocatalytic nanocomposites. In addition, we describemore » our work on surface modification of semiconductor nanocrystal quantum dots using new approaches and methods that bypass ligand exchange, retaining the nanocrystal's native ligands and original optical properties, as well as on spectroscopic methods of characterization useful in determining surface ligand organization and chemistry. Using recent examples from our group and collaborators, we demonstrate how these efforts have lead to faster, wider and more systematic application of semiconductor nanocrystal-based materials to biological imaging and tracking, and to photocatalysis of unconventional substrates. We believe techniques and methods borrowed from inorganic chemistry (including coordination, organometallic and solid state chemistry) have much to offer in reaching a better understanding of the synthesis, functionalization and real-life application of such exciting materials as semiconductor nanocrystals (quantum dots, rods, tetrapods, etc.).« less

Novel Quantum Dot Gate FETs and Nonvolatile Memories Using Lattice-Matched II-VI Gate Insulators

NASA Astrophysics Data System (ADS)

Jain, F. C.; Suarez, E.; Gogna, M.; Alamoody, F.; Butkiewicus, D.; Hohner, R.; Liaskas, T.; Karmakar, S.; Chan, P.-Y.; Miller, B.; Chandy, J.; Heller, E.

2009-08-01

This paper presents the successful use of ZnS/ZnMgS and other II-VI layers (lattice-matched or pseudomorphic) as high- k gate dielectrics in the fabrication of quantum dot (QD) gate Si field-effect transistors (FETs) and nonvolatile memory structures. Quantum dot gate FETs and nonvolatile memories have been fabricated in two basic configurations: (1) monodispersed cladded Ge nanocrystals (e.g., GeO x -cladded-Ge quantum dots) site-specifically self-assembled over the lattice-matched ZnMgS gate insulator in the channel region, and (2) ZnTe-ZnMgTe quantum dots formed by self-organization, using metalorganic chemical vapor-phase deposition (MOCVD), on ZnS-ZnMgS gate insulator layers grown epitaxially on Si substrates. Self-assembled GeO x -cladded Ge QD gate FETs, exhibiting three-state behavior, are also described. Preliminary results on InGaAs-on-InP FETs, using ZnMgSeTe/ZnSe gate insulator layers, are presented.

Measurement of Typhi Vi antibodies can be used to assess adaptive immunity in patients with immunodeficiency.

PubMed

Evans, C; Bateman, E; Steven, R; Ponsford, M; Cullinane, A; Shenton, C; Duthie, G; Conlon, C; Jolles, S; Huissoon, A P; Longhurst, H J; Rahman, T; Scott, C; Wallis, G; Harding, S; Parker, A R; Ferry, B L

2018-01-29

Vaccine-specific antibody responses are essential in the diagnosis of antibody deficiencies. Responses to Pneumovax II are used to assess the response to polysaccharide antigens, but interpretation may be complicated. Typhim Vi ® , a polysaccharide vaccine for Salmonella typhoid fever, may be an additional option for assessing humoral responses in patients suspected of having an immunodeficiency. Here we report a UK multi-centre study describing the analytical and clinical performance of a Typhi Vi immunoglobulin (Ig)G enzyme-linked immunosorbent assay (ELISA) calibrated to an affinity-purified Typhi Vi IgG preparation. Intra- and interassay imprecision was low and the assay was linear, between 7·4 and 574 U/ml (slope = 0·99-1·00; R 2  > 0·99); 71% of blood donors had undetectable Typhi Vi IgG antibody concentrations. Of those with antibody concentrations  > 7·4 U/ml, the concentration range was 7·7-167 U/ml. In antibody-deficient patients receiving antibody replacement therapy the median Typhi Vi IgG antibody concentrations were  < 25 U/ml. In vaccinated normal healthy volunteers, the median concentration post-vaccination was 107 U/ml (range 31-542 U/ml). Eight of eight patients (100%) had post-vaccination concentration increases of at least threefold and six of eight (75%) of at least 10-fold. In an antibody-deficient population (n = 23), only 30% had post-vaccination concentration increases of at least threefold and 10% of at least 10-fold. The antibody responses to Pneumovax II and Typhim Vi ® correlated. We conclude that IgG responses to Typhim Vi ® vaccination can be measured using the VaccZyme Salmonella typhi Vi IgG ELISA, and that measurement of these antibodies maybe a useful additional test to accompany Pneumovax II responses for the assessment of antibody deficiencies. © 2018 The Authors. Clinical & Experimental Immunology published by John Wiley & Sons Ltd on behalf of British Society for Immunology.

Search for effective spin injection heterostructures based on half-metal Heusler alloys/gallium arsenide semiconductors: A theoretical investigation

NASA Astrophysics Data System (ADS)

Sivakumar, Chockalingam

Efficient electrical spin injection from half-metal (HM) electrodes into semiconducting (SC) channel material is a desirable aspect in spintronics, but a challenging one. Half-metals based on the Heusler alloy family are promising candidates as spin sources due to their compatibility with compound SCs, and very high Curie temperatures. Numerous efforts were made in the past two decades to grow atomically abrupt interfaces between HM_Heusler and SC heterostructures. However, diffusion of magnetic impurities into the semiconductor, defects and disorder near the interface, and formation of reacted phases were great challenges. A number of theoretical efforts were undertaken to understand the role of such material defects in destroying the half-metallicity and also to propose promising half-metal/SC heterostructures based on first principles. This dissertation summarizes the investigations undertaken to decode the complexity of, and to understand the various physical properties of, a number of real-world Heusler/SC heterostructure samples, based on the ab initio density functional theory (DFT) approach. In addition, it summarizes various results from the first principles-based search for promising half-metal/SC heterostructures. First, I present results from DFT-based predictive models of actual Co 2MnSi (CMS)/GaAs heterostructures grown in (001) texture. I investigate the physical, chemical, electronic, and magnetic properties to understand the complexity of these structures and to pinpoint the origin of interfacial effects, when present. Based on the investigations of such models, I discuss the utility of those actual samples in spintronic applications. Next, I summarise the results from an ab initio DFT-based survey of 6 half-Heusler half-metal/GaAs heterostructure models in (110) texture, since compound semiconductors such as GaAs have very long spin lifetime in (110) layering. I show 3 half-Heusler alloys (CoVAs, NiMnAs, and RhFeGe), that when interfaced with Ga

Temperature dependence Infrared and Raman studies of III-V/II-VI core-shell nanostructures

NASA Astrophysics Data System (ADS)

Manciu, Felicia S.; McCombe, Bruce D.; Lucey, Derrick

2005-03-01

The temperature dependence (8 K < T < 300 K) of optical phonon modes confined in InP/II-VI core-shell nanostructures have been investigated by far-infrared (FIR) and Raman scattering spectroscopies. The core-shell nanostructures were fabricated by colloidal chemistry and characterized by transmission electron microscopy and X-ray diffraction prior to being embedded in a polycrystalline CsI matrix for the present studies. The FIR measurements of InP/ZnSe sample exhibits three absorption features, one clearly due to the Froelich mode of the InP cores, and the others related to modes associated with the shell layer and its coupling to the matrix. Strong mixing of the characteristic vibrations of each constituent material was observed for InP/ZnS sample. Raman scattering (457.9 nm excitation) features were determined without polarization selection in the backscattering geometry. Interesting T-dependent resonant Raman effect of the surface optical phonon modes has been discovered in InP/ZnSe sample. Reasonable agreement is obtained between the Raman and FIR results, as well as with theoretical calculations.

Chromium(VI) release from leather and metals can be detected with a diphenylcarbazide spot test.

PubMed

Bregnbak, David; Johansen, Jeanne D; Jellesen, Morten S; Zachariae, Claus; Thyssen, Jacob P

2015-11-01

Along with chromium, nickel and cobalt are the clinically most important metal allergens. However, unlike for nickel and cobalt, there is no validated colorimetric spot test that detects chromium. Such a test could help both clinicians and their patients with chromium dermatitis to identify culprit exposures. To evaluate the use of diphenylcarbazide (DPC) as a spot test reagent for the identification of chromium(VI) release. A colorimetric chromium(VI) spot test based on DPC was prepared and used on different items from small market surveys. The DPC spot test was able to identify chromium(VI) release at 0.5 ppm without interference from other pure metals, alloys, or leather. A market survey using the test showed no chromium(VI) release from work tools (0/100). However, chromium(VI) release from metal screws (7/60), one earring (1/50), leather shoes (4/100) and leather gloves (6/11) was observed. We found no false-positive test reactions. Confirmatory testing was performed with X-ray fluorescence (XRF) and spectrophotometrically on extraction fluids. The use of DPC as a colorimetric spot test reagent appears to be a good and valid test method for detecting the release of chromium(VI) ions from leather and metal articles. The spot test has the potential to become a valuable screening tool. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors

DOE PAGES

Fluegel., Brian; Mialitsin, Aleksej V.; Beaton, Daniel A.; ...

2015-05-28

In this study, the semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10 –4. Comparing our strain sensitivity andmore » signal strength in Al xGa 1–xAs with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 10 3, thus obviating key constraints in semiconductor strain metrology.« less

Visible-wavelength semiconductor lasers and arrays

DOEpatents

Schneider, R.P. Jr.; Crawford, M.H.

1996-09-17

The visible semiconductor laser includes an InAlGaP active region surrounded by one or more AlGaAs layers on each side, with carbon as the sole p-type dopant. Embodiments of the invention are provided as vertical-cavity surface-emitting lasers (VCSELs) and as edge-emitting lasers (EELs). One or more transition layers comprised of a substantially indium-free semiconductor alloy such as AlAsP, AlGaAsP, or the like may be provided between the InAlGaP active region and the AlGaAS DBR mirrors or confinement layers to improve carrier injection and device efficiency by reducing any band offsets. Visible VCSEL devices fabricated according to the invention with a one-wavelength-thick (1{lambda}) optical cavity operate continuous-wave (cw) with lasing output powers up to 8 mW, and a peak power conversion efficiency of up to 11%. 5 figs.

Asymptotic Analysis of Melt Growth for Antimonide-Based Compound Semiconductor Crystals in Magnetic and Electric Fields

DTIC Science & Technology

2006-10-01

F. Bliss, Gerald W. Iseler and Piotr Becla, "Combining static and rotating magnetic fields during modified vertical Bridgman crystal growth ," AIAA...Wang and Nancy Ma, "Semiconductor crystal growth by the vertical Bridgman process with rotating magnetic fields," ASME Journal of Heat Transfer...2005. 15. Stephen J. LaPointe, Nancy Ma and Donald W. Mueller, Jr., " Growth of binary alloyed semiconductor crystals by the vertical Bridgman

Formation and function of chromate conversion coating on aircraft aluminum alloy probed by vibrational spectroscopy

NASA Astrophysics Data System (ADS)

Xia, Lin

2000-10-01

A Chromate Conversion Coating (CCC) is currently one of the most effective methods for protecting aluminum alloys from corrosion. Its unique "self-healing" property has been proved to be critical in corrosion prevention. During the formation process, CrVI, is "stored" in the CCC films. Under in-field conditions, most of the CrVI can leach out and diffuse to local defects, and stop corrosion. However, the involvement of highly toxic CrVI makes CCC system environmentally hazardous. In order to find less-toxic alternatives, the formation and protection mechanisms of CCC must be understood. Formation and function of CCC film are the focus of this study, and vibrational spectroscopy was chosen due to its superior structural sensitivity. First, the structure of CCC film was characterized. The structural similarity between CCC film and a synthetic Cr-mixed-oxide was found, and certain tests were conducted on the bulk synthetic powder which were not feasible on the thin film. All of the structural studies indicated that CCC film is mainly a CrIII-hydroxide gel layer, which adsorbs CrVI-oxy species through CrIII-O-Cr VI chemical bonds. Further analysis revealed the reversible Cr III-CrVI adsorption-desorption equilibrium, and a mathematical model ("Langmuir" model) was established to explain the Cr VI storage-release mechanism quantitatively. In addition, the function of Fe(CN)63-, an additive in the coating solution, was studied. The results indicate that Fe(CN)63- mediates the slow reaction between Al and CrVI, and the mediation mechanism can be illustrated as below: FeCN 3- 6+Al=FeCN 4-6+Al3+ ↑ FeCN 4- 6+CrVI=FeCN 3-6+CrIII In general, the formation of CCC is mediated by Fe(CN)63-, thus Al reduces CrVI quickly and generates CrIII-hydroxide on the alloy surface. The nascent CrIII-hydroxide is chemically active enough to form chemical bonds with CrVI from the solution, through Cr III-O-CrVI bonding. Such CrIII-O-Cr VI structure can form and break up reversibly according

Comparative assessment of marginal accuracy of grade II titanium and Ni–Cr alloy before and after ceramic firing: An in vitro study

PubMed Central

Patil, Abhijit; Singh, Kishan; Sahoo, Sukant; Suvarna, Suraj; Kumar, Prince; Singh, Anupam

2013-01-01

Objective: The aims of the study are to assess the marginal accuracy of base metal and titanium alloy casting and to evaluate the effect of repeated ceramic firing on the marginal accuracy of base metal and titanium alloy castings. Materials and Methods: Twenty metal copings were fabricated with each casting material. Specimens were divided into 4 groups of 10 each representing base metal alloys castings without (Group A) and with metal shoulder margin (Group B), titanium castings without (Group C) and with metal shoulder margin (Group D). The measurement of fit of the metal copings was carried out before the ceramic firing at four different points and the same was followed after porcelain build-up. Results: Significant difference was found when Ni–Cr alloy samples were compared with Grade II titanium samples both before and after ceramic firings. The titanium castings with metal shoulder margin showed highest microgap among all the materials tested. Conclusions: Based on the results that were found and within the limitations of the study design, it can be concluded that there is marginal discrepancy in the copings made from Ni–Cr and Grade II titanium. This marginal discrepancy increased after ceramic firing cycles for both Ni–Cr and Grade II titanium. The comparative statistical analysis for copings with metal-collar showed maximum discrepancy for Group D. The comparative statistical analysis for copings without metal-collar showed maximum discrepancy for Group C. PMID:24926205

Heavy Metal Resistances and Chromium Removal of a Novel Cr(VI)-Reducing Pseudomonad Strain Isolated from Circulating Cooling Water of Iron and Steel Plant.

PubMed

Zhang, Jian-Kun; Wang, Zhen-Hua; Ye, Yun

2016-12-01

Three bacterial isolates, GT2, GT3, and GT7, were isolated from the sludge and water of a circulating cooling system of iron and steel plant by screening on Cr(VI)-containing plates. Three isolates were characterized as the members of the genus Pseudomonas on the basis of phenotypic characteristics and 16S rRNA sequence analysis. All isolates were capable of resisting multiple antibiotics and heavy metals. GT7 was most resistant to Cr(VI), with a minimum inhibitory concentration (MIC) of 6.5 mmol L -1 . GT7 displayed varied rates of Cr(VI) reduction in M2 broth, which was dependent on pH, initial Cr(VI) concentration, and inoculating dose. Total chromium analysis revealed that GT7 could remove a part of chromium from the media, and the maximum rate of chromium removal was up to 40.8 %. The Cr(VI) reductase activity of GT7 was mainly associated with the soluble fraction of cell-free extracts and reached optimum at pH 6.0∼8.0. The reductase activity was apparently enhanced by external electron donors and Cu(II), whereas it was seriously inhibited by Hg(II), Cd(II), and Zn(II). The reductase showed a K m of 74 μmol L -1 of Cr(VI) and a V max of 0.86 μmol of Cr(VI) min -1  mg -1 of protein. The results suggested that GT7 could be a promising candidate for in situ bioremediation of Cr(VI).

Quantifying Cr(VI) Production and Export from Serpentine Soil of the California Coast Range

DOE PAGES

McClain, Cynthia N.; Fendorf, Scott; Webb, Samuel M.; ...

2016-11-22

Here, hexavalent chromium (Cr(VI)) is generated in serpentine soils and exported to surface and groundwaters at levels above health-based drinking water standards. Although Cr(VI) concentrations are elevated in serpentine soil pore water, few studies have reported field evidence documenting Cr(VI) production rates and fluxes that govern Cr(VI) transport from soil to water sources. We report Cr speciation (i) in four serpentine soil depth profiles derived from the California Coast Range serpentinite belt and (ii) in local surface waters. Within soils, we detected Cr(VI) in the same horizons where Cr(III)-minerals are colocated with biogenic Mn(III/IV)-oxides, suggesting Cr(VI) generation through oxidation bymore » Mn-oxides. Water-extractable Cr(VI) concentrations increase with depth constituting a 7.8 to 12 kg/km 2 reservoir of Cr(VI) in soil. Here, Cr(VI) is produced at a rate of 0.3 to 4.8 kg Cr(VI)/km 2/yr and subsequently flushed from soil during water infiltration, exporting 0.01 to 3.9 kg Cr(VI)/km 2/yr at concentrations ranging from 25 to 172 μg/L. Although soil-derived Cr(VI) is leached from soil at concentrations exceeding 10 μg/L, due to reduction and dilution during transport to streams, Cr(VI) levels measured in local surface waters largely remain below California’s drinking water limit.« less

Ferrate(VI) oxidation of polychlorinated diphenyl sulfides: Kinetics, degradation, and oxidized products.

PubMed

Chen, Jing; Xu, Xinxin; Zeng, Xiaolan; Feng, Mingbao; Qu, Ruijuan; Wang, Zunyao; Nesnas, Nasri; Sharma, Virender K

2018-06-13

This paper presents oxidation of polychlorinated diphenyl sulfides (PCDPSs), dioxin-like compounds, by ferrate(VI) (Fe VI O 4 2- , Fe(VI)). Kinetics of the reactions of Fe(VI) with seventeen PCDPSs, differ in number and positions of chlorine atoms (from 2 to 7), were investigated at pH 8.0. The second-order rate constants (k, M -1 s -1 ) of the reactions varied with the numbers and positions of chlorine atoms and appeared to be related with standard Gibbs free energy of formation (Δ f G 0 ) of PCDPSs. Degradation experiments in the presence of ions and humic acid demonstrated complete removal of PeCDPS by Fe(VI) in minutes. Pathways of the reaction were investigated by identifying oxidized products (OPs) of the reaction between Fe(VI) and 2,2',3',4,5-pentachlorodiphenyl sulfide (PeCDPS) at pH 8.0. Pathways of oxidation involved major pathway of attack on sulfur(II) by Fe(VI) in steps to yield sulfoxide type products, and subsequent breakage of C-S bond with the formation of sulfonic acid-containing trichloro compound. Minor pathways were hydroxylation of benzene ring and substitution of chlorine atom with hydroxyl group. Estimation of toxicity of OPs of the oxidation of PeCDPS by Fe(VI) suggested the decreased toxicity from the parent contaminant. Copyright © 2018. Published by Elsevier Ltd.

Contribution of extracellular polymeric substances from Shewanella sp. HRCR-1 biofilms to U(VI) immobilization.

PubMed

Cao, Bin; Ahmed, Bulbul; Kennedy, David W; Wang, Zheming; Shi, Liang; Marshall, Matthew J; Fredrickson, Jim K; Isern, Nancy G; Majors, Paul D; Beyenal, Haluk

2011-07-01

The goal of this study was to quantify the contribution of extracellular polymeric substances (EPS) to U(VI) immobilization by Shewanella sp. HRCR-1. Through comparison of U(VI) immobilization using cells with bound EPS (bEPS) and cells with minimal EPS, we show that (i) bEPS from Shewanella sp. HRCR-1 biofilms contribute significantly to U(VI) immobilization, especially at low initial U(VI) concentrations, through both sorption and reduction; (ii) bEPS can be considered a functional extension of the cells for U(VI) immobilization and they likely play more important roles at lower initial U(VI) concentrations; and (iii) the U(VI) reduction efficiency is dependent upon the initial U(VI) concentration and decreases at lower concentrations. To quantify the relative contributions of sorption and reduction to U(VI) immobilization by EPS fractions, we isolated loosely associated EPS (laEPS) and bEPS from Shewanella sp. HRCR-1 biofilms grown in a hollow fiber membrane biofilm reactor and tested their reactivity with U(VI). We found that, when reduced, the isolated cell-free EPS fractions could reduce U(VI). Polysaccharides in the EPS likely contributed to U(VI) sorption and dominated the reactivity of laEPS, while redox active components (e.g., outer membrane c-type cytochromes), especially in bEPS, possibly facilitated U(VI) reduction.

Imaging Atomic-Scale Clustering in III–V Semiconductor Alloys

DOE PAGES

Hirst, Louise C.; Kotulak, Nicole A.; Tomasulo, Stephanie; ...

2017-03-13

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III–V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this paper, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Finally, image quantification of atomicmore » column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.« less

The semiconductor waveguide facet reflectivity problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herzinger, C.M.; Lu, C.C.; DeTemple, T.A.

1993-08-01

The problem of the facet reflectivity of a semiconductor slab waveguide is reexamined as an extension of Ikegami's original approach but which includes radiation-like modes. The latter are included, using a guide-within-a-guide geometry, as modes bound to a thick air-cladding guide which contains the core profile of interest. In this model with a relatively simple analysis, the coupling from the fundamental mode to radiation modes can be analyzed. The cross-coupling to the radiation modes is considered in detail for the simple double heterostructure waveguide and is shown to be important only for large core-cladding index differences and for strong modalmore » confinement wherein it results in a true facet loss. The conditions for this are the same as for low threshold lasers so that the loss sets a maximum limit on the equivalent internal quantum efficiency. A separate one-dimensional finite element, numerical mode matching program, which treats evanescent and propagating radiation modes, is used as a comparison. The two methods of accounting for radiation modes are shown to be in good agreement: both predict reduced extremes in reflectivity when compared with the original Ikegami model. Modern graded core cases are treated as general examples along with the specific quantum well laser structures taken from the literature. These include II-VI and III-V structures spanning wavelengths from 0.5 [mu]m to 10.0 [mu]m.« less

EDITORIAL The 23rd Nordic Semiconductor Meeting The 23rd Nordic Semiconductor Meeting

NASA Astrophysics Data System (ADS)

Ólafsson, Sveinn; Sveinbjörnsson, Einar

2010-12-01

A Nordic Semiconductor Meeting is held every other year with the venue rotating amongst the Nordic countries of Denmark, Finland, Iceland, Norway and Sweden. The focus of these meetings remains 'original research and science being carried out on semiconductor materials, devices and systems'. Reports on industrial activity have usually featured. The topics have ranged from fundamental research on point defects in a semiconductor to system architecture of semiconductor electronic devices. Proceedings from these events are regularly published as a topical issue of Physica Scripta. All of the papers in this topical issue have undergone critical peer review and we wish to thank the reviewers and the authors for their cooperation, which has been instrumental in meeting the high scientific standards and quality of the series. This meeting of the 23rd Nordic Semiconductor community, NSM 2009, was held at Háskólatorg at the campus of the University of Iceland, Reykjavik, Iceland, 14-17 June 2009. Support was provided by the University of Iceland. Almost 50 participants presented a broad range of topics covering semiconductor materials and devices as well as related material science interests. The conference provided a forum for Nordic and international scientists to present and discuss new results and ideas concerning the fundamentals and applications of semiconductor materials. The meeting aim was to advance the progress of Nordic science and thus aid in future worldwide technological advances concerning technology, education, energy and the environment. Topics Theory and fundamental physics of semiconductors Emerging semiconductor technologies (for example III-V integration on Si, novel Si devices, graphene) Energy and semiconductors Optical phenomena and optical devices MEMS and sensors Program 14 June Registration 13:00-17:00 15 June Meeting program 09:30-17:00 and Poster Session I 16 June Meeting program 09:30-17:00 and Poster Session II 17 June Excursion and dinner

Contribution of Extracellular Polymeric Substances from Shewanella sp. HRCR-1 Biofilms to U(VI) Immobilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Bin; Ahmed, B.; Kennedy, David W.

2011-06-05

The goal of this study was to quantify the contribution of extracellular polymeric substances (EPS) in U(VI) immobilization by Shewanella sp. HRCR-1. Through comparison of U(VI) immobilization using cells with bound EPS (bEPS) and cells without EPS, we showed that i) bEPS from Shewanella sp. HRCR-1 biofilms contributed significantly to U(VI) immobilization, especially at low initial U(VI) concentrations, through both sorption and reduction; ii) bEPS could be considered as a functional extension of the cells for U(VI) immobilization and they likely play more important roles at initial U(VI) concentrations; and iii) U(VI) reduction efficiency was found to be dependent uponmore » initial U(VI) concentration and the efficiency decreased at lower concentrations. To quantify relative contribution of sorption and reduction in U(VI) immobilization by EPS fractions, we isolated loosely associated EPS (laEPS) and bEPS from Shewanella sp. HRCR-1 biofilms grown in a hollow fiber membrane biofilm reactor and tested their reactivity with U(V). We found that, when in reduced form, the isolated cell-free EPS fractions could reduce U(VI). Polysaccharides in the EPS likely contributed to U(VI) sorption and dominated reactivity of laEPS while redox active components (e.g., outer membrane c-type cytochromes), especially in bEPS, might facilitate U(VI) reduction.« less

Structural and phase transformation of A{sup III}B{sup V}(100) semiconductor surface in interaction with selenium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bezryadin, N. N.; Kotov, G. I., E-mail: giktv@mail.ru; Kuzubov, S. V., E-mail: kuzub@land.ru

2015-03-15

Surfaces of GaAs(100), InAs(100), and GaP(100) substrates thermally treated in selenium vapor have been investigated by transmission electron microscopy and electron probe X-ray microanalysis. Some specific features and regularities of the formation of A{sub 3}{sup III}B{sub 4}{sup VI} (100)c(2 × 2) surface phases and thin layers of gallium or indium selenides A{sub 2}{sup III}B{sub 3}{sup VI} (100) on surfaces of different A{sup III}B{sup V}(100) semiconductors are discussed within the vacancy model of surface atomic structure.

Involvement of myosin VI immunoanalog in pinocytosis and phagocytosis in Amoeba proteus.

PubMed

Sobczak, Magdalena; Wasik, Anna; Kłopocka, Wanda; Redowicz, Maria Jolanta

2008-12-01

Recently, we found a 130-kDa myosin VI immunoanalog in amoeba, which bound to actin in an ATP-sensitive manner and in migrating amoebae colocalized to filamentous actin and dynamin II-containing vesicular structures. To further characterize this protein, we assessed its involvement in amoeba pinocytosis and phagocytosis. Confocal immunofluorescence microscopy and electron microscopy of immunogold-stained cells revealed that, in pinocytotic and phagocytotic amoebae, the myosin VI immunoanalog was visible throughout the cells, including pinocytotic channels and pinocytotic vesicles as well as phagosomes and emerging phagocytic cups. Blocking endogenous protein with anti-porcine myosin VI antibody (introduced into cells by means of microinjection) caused severe defects in pinocytosis and phagocytosis. In comparison with control cells, the treated amoebae formed ~75% less pinocytotic channels and phagocytosed ~65% less Tetrahymena cells. These data indicate that the myosin VI immunoanalog has an important role in pinocytosis and phagocytosis in Amoeba proteus (Pal.).

The Reduction of Cr(VI) to Cr(III) by Natural Fe-Bearing Minerals: A Synchrotron XAS Study

NASA Astrophysics Data System (ADS)

Xu, H.; Guo, X.; Ding, M.; Migdissov, A. A.; Boukhalfa, H.; Sun, C.; Roback, R. C.; Reimus, P. W.; Katzman, D.

2017-12-01

Cr(VI) in the form of CrO42- is a pollutant species in groundwater and soils that can pose health and environmental problems. Cr(VI) associated with use as a corrosion inhibitor at a power plant from 1956-1972 is present in a deep groundwater aquifer at Los Alamos National Laboratory. A potential remediation strategy for the Cr contamination is reduction of Cr(VI) to Cr(III) via the acceptance of electrons from naturally occurring or induced Fe(II) occurring in Fe-bearing minerals. In this work, using synchrotron-based X-ray techniques, we investigated the Cr reduction behavior by Fe-bearing minerals from outcrop and core samples representative of the contaminated portion of the aquifer. Samples were exposed to solutions with a range of known Cr (VI) concentrations. XANES and EXAFS spectra showed that all the Cr(VI) had been reduced to Cr(III), and micro XRF mapping revealed close correlation of Cr and Fe distribution, implying that Fe(II) in minerals reduced Cr(VI) in the solution. Similar behavior was observed from in-situ XANES measurements on Cr reduction and adsorption by mineral separates from the rock samples in Cr(VI)-bearing solutions. In addition, to obtain reference parameters for interpreting the data of natural samples, we collected Cr and Fe EXAFS spectra of Cr(III)-Fe(III) hydroxide solid solutions, which show progressive changes in the local structure around Cr and Fe over the whole series.

Ta-Pt Alloys as Gate Materials for Metal-Oxide-Semiconductor Field Effect Transistor Application

NASA Astrophysics Data System (ADS)

Huang, Chih-Feng; Tsui, Bing-Yue

2009-03-01

In this work we explore the thermal stability of sputter-deposited Ta-rich Ta-Pt alloys. The effects of group III and V impurities on their work function are also investigated. The Ta content ranges from 65 to 82 at. %. The main phase is σ Ta-Pt. The binding energies of core-level electrons of Ta and Pt are changed due to the intermixing of Ta and Pt, which is evidence that the work function of alloys is changed in metallic alloy systems. Binding energies are thermally stable up to 800 °C. Moreover, the incorporation of Pt in Ta film induces poor crystallization and a compound phase of Ta-Pt alloys. Transmission electron microscopy analysis confirmed the absence of a clear grain boundary in Ta-Pt alloys. The Ta and Pt depth profile shows uniformity in depth after 800 °C annealing for 30 min. The diffusion and distribution of impurities in the alloys were studied by secondary ion mass spectroscopy. Arsenic cannot diffuse in the alloys following annealing at 800 °C for 30 s. In contrast, boron can easily diffuse at 800 °C. The incorporation of impurities with a dosage of 5 ×1015 cm-2 in 60 nm Ta-Pt alloy by implantation did not significantly change the flat-band voltage following annealing at 800 °C.

Inhalation Toxicology. VI. Evaluation of the Relative Toxicity of Thermal Decomposition Products from Nine Aircraft Panel Materials.

DTIC Science & Technology

1986-02-01

AD-R168 250 INHALATION TOXICOLOGY VI EVALUATION OF THE RELATIVE i/I TOXICITY OF THERMAL D. (U) FEDERAL AVIATION ADMINISTRATION WASHINGTON DC OFFICE...FAA/AM-8613 INHALATION TOXICOLOGY : (0 Office of Aviation Medicine Vi. Evaluation of the Relative Washington, D.C. 20591 Toxicity of Thermal...Government Accession No. 3. Recipient’s Catalog No. /XO/FAA/AM-86/3 /1j, 14 4F d Y_0 4. Title and Subtitle 5. Report Date INHALATION TOXICOLOGY : VI

Bridgman growth of semiconductors

NASA Technical Reports Server (NTRS)

Carlson, F. M.

1985-01-01

The purpose of this study was to improve the understanding of the transport phenomena which occurs in the directional solidification of alloy semiconductors. In particular, emphasis was placed on the strong role of convection in the melt. Analytical solutions were not deemed possible for such an involved problem. Accordingly, a numerical model of the process was developed which simulated the transport. This translates into solving the partial differential equations of energy, mass, species, and momentum transfer subject to various boundary and initial conditions. A finite element method with simple elements was initially chosen. This simulation tool will enable the crystal grower to systematically identify and modify the important design factors within her control to produce better crystals.

Growth of II-VI Solid Solutions in the Presence of a Rotating Magnetic Field

NASA Technical Reports Server (NTRS)

Gillies, D. C; Motakef, S.; Dudley, M.; Matyi, R.; Volz, H.

1999-01-01

The application of a rotating magnetic field (RMF)in the frequency range 60-400 Hz and field strength of the order of 2-8 mT to crystal growth has received increasing attention in recent years. To take full advantage of the control of fluid flow by the forces applied by the field, the liquid column must be electrically conducting. Also, the application of RMF to the directional solidification of a column of liquid can result in complete mixing in the resultant solid. Thus, the technique of RMF is suited to solvent zones and float zones where the composition of the liquid is more readily controlled. In the work we report on, numerical modeling has been applied to II-VI systems, particularly tellurium based traveling heater techniques (THM). Results for a spectrum of field strengths and acceleration levels will be presented. These show clearly the effects of competing buoyancy forces and electromagnetic stirring. Crystals of cadmium zinc telluride and mercury cadmium telluride have been grown terrestrially from a tellurium solvent zone. The effects of the RMF during these experiments will be demonstrated with micrographs showing etch pits, white beam x-ray synchrotron topographs and triple axis x-ray diffraction.

Amorphous metallizations for high-temperature semiconductor device applications

NASA Technical Reports Server (NTRS)

Wiley, J. D.; Perepezko, J. H.; Nordman, J. E.; Kang-Jin, G.

1981-01-01

The initial results of work on a class of semiconductor metallizations which appear to hold promise as primary metallizations and diffusion barriers for high temperature device applications are presented. These metallizations consist of sputter-deposited films of high T sub g amorphous-metal alloys which (primarily because of the absence of grain boundaries) exhibit exceptionally good corrosion-resistance and low diffusion coefficients. Amorphous films of the alloys Ni-Nb, Ni-Mo, W-Si, and Mo-Si were deposited on Si, GaAs, GaP, and various insulating substrates. The films adhere extremely well to the substrates and remain amorphous during thermal cycling to at least 500 C. Rutherford backscattering and Auger electron spectroscopy measurements indicate atomic diffussivities in the 10 to the -19th power sq cm/S range at 450 C.

Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

NASA Astrophysics Data System (ADS)

Sheibani, Hamdi

2002-01-01

Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate

NASA Technical Reports Server (NTRS)

Choi, Sang; King, Glen; Park, Yeonjoon

2009-01-01

SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than

Two-dimensional wide-band-gap II-V semiconductors with a dilated graphene-like structure

NASA Astrophysics Data System (ADS)

Zhang, Xue-Jing; Liu, Bang-Gui

2016-12-01

Since the advent of graphene, two-dimensional (2D) materials have become very attractive and there is growing interest in exploring new 2D materials beyond graphene. Here, through density-functional theory (DFT) calculations, we predict 2D wide-band-gap II-V semiconductor materials of M3X2 (M = Zn, Cd and X = N, P, As) with a dilated graphene-like honeycomb structure. In this structure the group-V X atoms form two X-atomic planes symmetrically astride the centering group-IIB M atomic plane. Our DFT calculation shows that 2D Zn3N2, Zn3P2 and Zn3As2 have direct band gaps of 2.87, 3.81 and 3.55 eV, respectively, and 2D Cd3N2, Cd3P2 and Cd3As2 exhibit indirect band gaps of 2.74, 3.51 and 3.29 eV, respectively. Each of the six 2D materials is shown to have effective carrier (either hole or electron) masses down to 0.03m 0-0.05m 0. The structural stability and feasibility of experimental realization of these 2D materials has been shown in terms of DFT phonon spectra and total energy comparison with related existing bulk materials. On the experimental side, there already are many similar two-coordinate structures of Zn and other transition metals in various organic materials. Therefore, these 2D semiconductors can enrich the family of 2D electronic materials and may have promising potential for achieving novel transistors and optoelectronic devices.

Chemical composition of matrix-embedded ternary II-VI nanocrystals derived from first- and second-order Raman spectra

NASA Astrophysics Data System (ADS)

Azhniuk, Yu. M.; Hutych, Yu. I.; Lopushansky, V. V.; Prymak, M. V.; Gomonnai, A. V.; Zahn, D. R. T.

2016-12-01

A one- and multiphonon Raman scattering study is performed for an extensive set of CdS1-xSex, Cd1-yZnyS, Cd1-yZnySe, and CdSe1-xTex nanocrystals to investigate the applicability of first- and second-order Raman spectra for the determination of the matrix-embedded ternary nanocrystal composition. For one-mode ternary systems both the LO and 2LO phonon frequencies in the Raman spectra are shown to be a good measure of the nanocrystal composition. For two-mode systems, the approaches based on the difference of the LO phonon frequencies (first-order Raman spectra) or double LO overtone and combination tone frequencies (second-order Raman spectra) as well as on the LO phonon band intensity ratios are analysed. The weak electron-phonon coupling in the II-VI nanocrystals and the polaron constant values for the nanocrystal sublattices are discussed.

The effect of anticoagulants on the distribution of chromium VI in blood fractions.

PubMed

Afolaranmi, Grace A; Tettey, Justice N A; Murray, Helen M; Meek, R M Dominic; Grant, M Helen

2010-01-01

Metal-on-metal resurfacing arthroplasty is associated with elevated circulating levels of cobalt and chromium ions. To establish the long-term safety of metal-on-metal resurfacing arthroplasty, it has been recommended that during clinical follow-up of these patients, the levels of these metal ions in blood be monitored. In this article, we provide information on the distribution of chromium VI ions (the predominant form of chromium released by cobalt-chrome alloys in vivo and in vitro) in blood fractions. Chromium VI is predominantly partitioned into red blood cells compared with plasma (analysis of variance, P < .05). The extent of accumulation in red blood cells is influenced by the anticoagulant used to collect the blood, with EDTA giving a lower partitioning into red cells compared with sodium citrate and sodium heparin. 2010 Elsevier Inc. All rights reserved.

Impurity gettering in semiconductors

DOEpatents

Sopori, B.L.

1995-06-20

A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.

Impurity gettering in semiconductors

DOEpatents

Sopori, Bhushan L.

1995-01-01

A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.

TEM in situ cube-corner indentation analysis using ViBe motion detection algorithm

NASA Astrophysics Data System (ADS)

Yano, K. H.; Thomas, S.; Swenson, M. J.; Lu, Y.; Wharry, J. P.

2018-04-01

Transmission electron microscopic (TEM) in situ mechanical testing is a promising method for understanding plasticity in shallow ion irradiated layers and other volume-limited materials. One of the simplest TEM in situ experiments is cube-corner indentation of a lamella, but the subsequent analysis and interpretation of the experiment is challenging, especially in engineering materials with complex microstructures. In this work, we: (a) develop MicroViBE, a motion detection and background subtraction-based post-processing approach, and (b) demonstrate the ability of MicroViBe, in combination with post-mortem TEM imaging, to carry out an unbiased qualitative interpretation of TEM indentation videos. We focus this work around a Fe-9%Cr oxide dispersion strengthened (ODS) alloy, irradiated with Fe2+ ions to 3 dpa at 500 °C. MicroViBe identifies changes in Laue contrast that are induced by the indentation; these changes accumulate throughout the mechanical loading to generate a "heatmap" of features in the original TEM video that change the most during the loading. Dislocation loops with b = ½ <111> identified by post-mortem scanning TEM (STEM) imaging correspond to hotspots on the heatmap, whereas positions of dislocation loops with b = <100> do not correspond to hotspots. Further, MicroViBe enables consistent, objective quantitative approximation of the b = ½ <111> dislocation loop number density.

Heterojunctions of model CdTe/CdSe mixtures

DOE PAGES

van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; ...

2015-03-18

We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization tomore » find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.« less

Photoconductivity response time in amorphous semiconductors

NASA Astrophysics Data System (ADS)

Adriaenssens, G. J.; Baranovskii, S. D.; Fuhs, W.; Jansen, J.; Öktü, Ö.

1995-04-01

The photoconductivity response time of amorphous semiconductors is examined theoretically on the basis of standard definitions for free- and trapped-carrier lifetimes, and experimentally for a series of a-Si1-xCx:H alloys with x<0.1. Particular attention is paid to its dependence on carrier generation rate and temperature. As no satisfactory agreement between models and experiments emerges, a simple theory is developed that can account for the experimental observations on the basis of the usual multiple-trappping ideas, provided a small probability of direct free-carrier recombination is included. The theory leads to a stretched-exponential photocurrent decay.

Synthesis of Germanium-Tin Alloys by Ion Implantation and Pulsed Laser Melting: Towards a Group IV Direct Band Gap Semiconductor

NASA Astrophysics Data System (ADS)

Tran, Tuan Thien

The germanium-tin (Ge1-xSnx) material system is expected to be a direct bandgap group IV semiconductor at a Sn content of 6.5-11 at.%. Hence there has been much interest in preparing such alloys since they are compatible with silicon and they raise the possibility of integrating photonics functionality into silicon circuitry. However, the maximum solid solubility of Sn in Ge is around 0.5 at.% and non-equilibrium deposition techniques such as molecular beam epitaxy or chemical vapour deposition have been used to achieve the desired high Sn concentrations. In this PhD work, the combination of ion implantation and pulsed laser melting (PLM) is demonstrated to be an alternative promising method to produce a highly Sn concentrated alloy with good crystal quality. In initial studies, it was shown that 100 keV Sn implants followed by PLM produced high quality alloys with up to 6.2 at.%Sn but above these Sn concentrations the crystal quality was poor. The structural properties of the ≤6.2 at.% alloys such as soluble Sn concentration, strain distribution and crystal quality have been characterised by Rutherford backscattering spectrometry (RBS), Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties and electronic band structure have been studied by spectroscopic ellipsometry. The introduction of substitutional Sn into Ge is shown to either induce a splitting between light and heavy hole subbands or lower the conduction band at the Gamma valley. However, at higher implant doses needed to achieve >6.2 at.% Sn, ion-beam-induced porosity in Ge starts to occur, which drastically reduces the retained amount of the implanted Sn and such microstructure also hinders good crystallisation of the material during PLM. To solve this problem, it was shown that a nanometer thick SiO2 layer deposited on the Ge substrate prior to the implantation can largely eliminate the formation of porosity. This capping SiO2 layer also helps to

EDITORIAL: Focus on Dilute Magnetic Semiconductors FOCUS ON DILUTE MAGNETIC SEMICONDUCTORS

NASA Astrophysics Data System (ADS)

Chambers, Scott A.; Gallagher, Bryan

2008-05-01

Chisholm, J D Budai and D P Norton Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2 T Fukumura, H Toyosaki, K Ueno, M Nakano and M Kawasaki Ab-initio study of exchange constants and electronic structure in diluted magnetic group-IV semiconductors Silvia Picozzi and Marjana Ležaić Phase coherent transport in (Ga,Mn)As D Neumaier, K Wagner, U Wurstbauer, M Reinwald, W Wegscheider and D Weiss Hydrogen interstitials-mediated ferromagnetism in MnxGe1-x magnetic semiconductors Xin-Xin Yao, Shi-Shen Yan, Shu-Jun Hu, Xue-Ling Lin, Chong Han, Yan-Xue Chen, Guo-Lei Liu and Liang-Mo Mei Electronic structures of magnetic semiconductors FeCr2Se4 and Fe0.5Cu0.5Cr2Se4 B I Min, Seung Su Baik, H C Choi, S K Kwon and J-S Kang Investigation of pure and Co2+-doped ZnO quantum dot electronic structures using the density functional theory: choosing the right functional Ekaterina Badaeva, Yong Feng, Daniel R Gamelin and Xiaosong Li Magnetic properties of sol-gel-derived doped ZnO as a potential ferromagnetic semiconductor: a synchrotron-based study N R S Farley, K W Edmonds, A A Freeman, G van der Laan, C R Staddon, D H Gregory and B L Gallagher Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor Zn1-xCrxTe M Kobayashi, Y Ishida, J I Hwang, G S Song, A Fujimori, C S Yang, L Lee, H-J Lin, D J Huang, C T Chen, Y Takeda, K Terai, S-I Fujimori, T Okane, Y Saitoh, H Yamagami, K Kobayashi, A Tanaka, H Saito and K Ando Lack of ferromagnetism in n-type cobalt-doped ZnO epitaxial thin films T C Kaspar, T Droubay, S M Heald, P Nachimuthu, C M Wang, V Shutthanandan, C A Johnson, D R Gamelin and S A Chambers XMCD studies on Co and Li doped ZnO magnetic semiconductors Thomas Tietze, Milan Gacic, Gisela Schütz, Gerhard Jakob, Sebastian Brück and Eberhard Goering Ferromagnetic semiconductors and the role of disorder B W Wessels An extensive comparison of anisotropies in MBE grown (Ga,Mn)As material C Gould, S Mark, K Pappert, R G Dengel, J Wenisch, R P

Uranium Reduction by Fe(II) in the Presence of Montmorillonite and Nontronite.

PubMed

Tsarev, Sergey; Waite, T David; Collins, Richard N

2016-08-02

Uranium(VI) interactions with three smectites (one montmorillonite and two nontronites - NAu1 and NAu2) were examined with 0, 1, and 2 mM aqueous concentrations of Fe(II) over the pH range of 3-9.5 in a background electrolyte of 100 mM NaCl and 1 mM CaCl2 in equilibration with 400 ppmv CO2(g) ([U(VI)] = 4 μM and 0.5 g smectite/L). In the absence of Fe(II), no differences were observed in the U(VI) sorption curves for the three clay minerals. In the presence of 1 or 2 mM Fe(II), under anoxic conditions, U(VI) uptake by the smectites changed slightly between ∼pH 3 and 6; however, uranium uptake increased significantly above ∼pH 6 and was proportional to the concentration of Fe(II) added to the system, particularly at pH values >8. The uptake of Fe(II) showed a sharp edge starting from ∼pH 6.5 with 95%-100% uptake occurring at pH values >7.5, with no difference observed between the iron-rich nontronites and montmorillonite. After 3 days of reaction at pH 7.6 (i.e., above the Fe(II) "sorption" edge), U(VI) was transformed to a mixture of U(IV) and U(VI) sorption complexes, and after 14 days of reaction, 100% of the U was found to be reduced to U(IV) in the form of nanocrystalline uraninite. In contrast, U remained as sorbed species until 14 days of reaction at pH 6.5. Ferrihydrite (NAu1), lepidocrocite, and magnetite (NAu2) were detected as secondary mineralization products upon reaction of the nontronites with Fe(II) but appeared to have no effect on the partitioning or speciation of uranium.

III-V/II-VI Hybrid Quantum Well Mid-Infrared Lasers

DTIC Science & Technology

2005-01-25

semiconductor lasers are of great importance for many applications such as laser diode spectroscopy , pollution monitoring, low-loss optical communication...great importance for many applications such as laser diode spectroscopy, pollutant monitoring, low-losses longwavelength optical communication...InAsSb/CdMgSe laser structure 1.2. Characterization of the laser structures and interface quality (STM, EPFM etc) 1.3. Study of spontaneous and

First-principles study of alloying effects on fluorine incorporation in Al x Ga1-x N alloys

NASA Astrophysics Data System (ADS)

Wang, Rong; Tan, Wei; Zhang, Jian; Chen, Feng-Xiang; Wei, Su-Huai

2018-02-01

Incorporation of fluorine (F) into the AlGaN layer is crucial to the fabrication of enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs). However, the understanding of properties of F doping in AlGaN alloys is rather limited. Using first-principles calculations and the special quasirandom structure (SQS) approach, we investigate the alloying effects on the doping properties of F-incorporated Al x Ga1-x N alloys. We find that substitutional F on N sites (FN) and interstitial F (Fi) are dominant defects for F in Al x Ga1-x N alloys. For these two types of defects, both the global composition x and the local motif surrounding the dopant play important roles. On contrary, the incorporation of substitutional F on Ga sites (FGa) or Al sites (FAl) are affected only by the composition x. We also find that there exists a large asymmetric bowing for the effective formation energies of FN and Fi. These results are explained in terms of local structural distortion and electronic effects. The mechanism discussed in this paper can also be used in understanding doping in other semiconductor alloys.

Catalytic determination of molybdenum(VI) by means of an iodide ion-selective electrode and a landolt-type hydrogen peroxide-iodide reaction.

PubMed

Kataoka, M; Nishimura, K; Kambara, T

1983-12-01

A trace amount of molybdenum(VI) can be determined by using its catalytic effect on the oxidation of iodide to iodine by hydrogen peroxide in acidic medium. Addition of ascorbic acid added to the reaction mixture produces the Landolt effect, i.e., the iodine produced by the indicator reaction is reduced immediately by the ascorbic add. Hence the concentration of iodide begins to decrease once all the ascorbic acid has been consumed. The induction period is measured by monitoring the concentration of iodide ion with an iodide ion-selective electrode. The reciprocal of the induction period varies linearly with the concentration of molybdenum(VI). The most suitable pH and concentrations of hydrogen peroxide and potassium iodide are found to be 1.5, 5 and 10mM, respectively. An appropriate amount of ascorbic acid is added to the reaction mixture according to the concentration of molybdenum(VI) in the sample solution. A calibration graph with good proportionality is obtained for the molybdenum(VI) concentration range from 0.1 to 160 muM. Iron(III), vanadium(IV), zirconium(IV), tungsten(VI), copper(II) and chromium(VI) interfere, but iron(III) and copper(II) can be masked with EDTA.

First principles examination of electronic structure and optical features of 4H-GaN1-xPx polytype alloys

NASA Astrophysics Data System (ADS)

Laref, A.; Hussain, Z.; Laref, S.; Yang, J. T.; Xiong, Y. C.; Luo, S. J.

2018-04-01

By using first-principles calculations, we compute the electronic band structures and typical aspects of the optical spectra of hexagonally structured GaN1-xPx alloys. Although a type III-V semiconductor, GaP commonly possesses a zinc-blende structure with an indirect band gap; as such, it may additionally form hexagonal polytypes under specific growth conditions. The electronic structures and optical properties are calculated by combining a non-nitride III-V semiconductor and a nitride III-V semiconductor, as GaP and GaN crystallizing in a 4H polytype, with the N composition ranging between x = 0-1. For all studied materials, the energy gap is found to be direct. The optical properties of the hexagonal materials may illustrate the strong polarization dependence owing to the crystalline anisotropy. This investigation for GaN1-xPx alloys is anticipated to supply paramount information for applications in the visible/ultraviolet spectral regions. At a specific concentration, x, these alloys would be exclusively appealing candidates for solar-cell applications.

Imaging the motion of electrons in 2D semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Dani, Keshav

Technological progress since the late 20th century has centered on semiconductor devices, such as transistors, diodes, and solar cells. At the heart of these devices, is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. In this talk, we combine femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy to image the motion of photoexcited electrons from high-energy to low-energy states in a 2D InSe/GaAs heterostructure exhibiting a type-II band alignment. At the instant of photoexcitation, energy-resolved photoelectron images reveal a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observe the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we make a movie lasting a few tens of picoseconds of the electron transfer process in the photoexcited type-II heterostructure - a fundamental phenomenon in semiconductor devices like solar cells. Quantitative analysis and theoretical modeling of spatial variations in the video provide insight into future solar cells, electron dynamics in 2D materials, and other semiconductor devices.

Study of Cr(VI) adsorption onto magnetite nanoparticles using synchrotron-based X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Yen-Hua; Liu, Dian-Yu; Lee, Jyh-Fu

2018-04-01

In this study, the efficiency of Cr(VI) adsorption onto nano-magnetite was examined by batch experiments, and the Cr(VI) adsorption mechanism was investigated using synchrotron-based X-ray absorption spectroscopy. Magnetite nanoparticles with a mean diameter of 10 nm were synthesized using an inexpensive and simple co-precipitation method. It shows a saturation magnetization of 54.3 emu/g, which can be recovered with an external magnetic field. The adsorption data fitted the Langmuir adsorption isotherm well, implying a monolayer adsorption behavior of Cr(VI) onto nano-magnetite. X-ray absorption spectroscopy results indicate that the adsorption mechanism involves electron transfer between Fe(II) in nano-magnetite (Fe2+OFe3+ 2O3) and Cr(VI) to transform into Cr(III), which may exist as an Fe(III)-Cr(III) mixed solid phase. Moreover, the Cr(III)/Cr(VI) ratio in the final products can be determined by the characteristic pre-edge peak area of Cr(VI) in the Cr K-edge spectrum. These findings suggest that nano-magnetite is effective for Cr(VI) removal from wastewater because it can transform highly poisonous Cr(VI) species into nontoxic Cr(III) compounds, which are highly insoluble and immobile under environmental conditions.

Functionalization of Magnetic Chitosan Particles for the Sorption of U(VI), Cu(II) and Zn(II)—Hydrazide Derivative of Glycine-Grafted Chitosan

PubMed Central

Hamza, Mohammed F.; Aly, Mohsen M.; Abdel-Rahman, Adel A.-H.; Ramadan, Samar; Raslan, Heba; Wang, Shengye; Vincent, Thierry; Guibal, Eric

2017-01-01

A new magnetic functionalized derivative of chitosan is synthesized and characterized for the sorption of metal ions (environmental applications and metal valorization). The chemical modification of the glycine derivative of chitosan consists of: activation of the magnetic support with epichlorohydrin, followed by reaction with either glycine to produce the reference material (i.e., Gly sorbent) or glycine ester hydrochloride, followed by hydrazinolysis to synthesize the hydrazide functionalized sorbent (i.e., HGly sorbent). The materials are characterized by titration, elemental analysis, FTIR analysis (Fourrier-transform infrared spectrometry), TGA analysis (thermogravimetric analysis) and with SEM-EDX (scanning electron microscopy coupled to energy dispersive X-ray analysis). The sorption performances for U(VI), Cu(II), and Zn(II) are tested in batch systems. The sorption performances are compared for Gly and HGly taking into account the effect of pH, the uptake kinetics (fitted by the pseudo-second order rate equation), and the sorption isotherms (described by the Langmuir and the Sips equations). The sorption capacities of the modified sorbent reach up to 1.14 mmol U g−1, 1.69 mmol Cu g−1, and 0.85 mmol Zn g−1. In multi-metal solutions of equimolar concentration, the chemical modification changes the preferences for given metal ions. Metal ions are desorbed using 0.2 M HCl solutions and the sorbents are re-used for five cycles of sorption/desorption without significant loss in performances. PMID:28772896

Magnetic properties of the layered III-VI diluted magnetic semiconductor Ga{sub 1−x}Fe{sub x}Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pekarek, T. M.; Edwards, P. S.; Olejniczak, T. L.

2016-05-15

Magnetic properties of single crystalline Ga{sub 1−x}Fe{sub x}Te (x = 0.05) have been measured. GaTe and related layered III-VI semiconductors exhibit a rich collection of important properties for THz generation and detection. The magnetization versus field for an x = 0.05 sample deviates from the linear response seen previously in Ga{sub 1−x}Mn{sub x}Se and Ga{sub 1−x}Mn{sub x}S and reaches a maximum of 0.68 emu/g at 2 K in 7 T. The magnetization of Ga{sub 1−x}Fe{sub x}Te saturates rapidly even at room temperature where the magnetization reaches 50% of saturation in a field of only 0.2 T. In 0.1 T atmore » temperatures between 50 and 400 K, the magnetization drops to a roughly constant 0.22 emu/g. In 0 T, the magnetization drops to zero with no hysteresis present. The data is consistent with Van-Vleck paramagnetism combined with a pronounced crystalline anisotropy, which is similar to that observed for Ga{sub 1−x}Fe{sub x}Se. Neither the broad thermal hysteresis observed from 100-300 K in In{sub 1−x}Mn{sub x}Se nor the spin-glass behavior observed around 10.9 K in Ga{sub 1−x}Mn{sub x}S are observed in Ga{sub 1−x}Fe{sub x}Te. Single crystal x-ray diffraction data yield a rhombohedral space group bearing hexagonal axes, namely R3c. The unit cell dimensions were a = 5.01 Å, b = 5.01 Å, and c = 17.02 Å, with α = 90°, β = 90°, and γ = 120° giving a unit cell volume of 369 Å{sup 3}.« less

Viscosity of Industrially Important Zn-Al Alloys Part II: Alloys with Higher Contents of Al and Si

NASA Astrophysics Data System (ADS)

Nunes, V. M. B.; Queirós, C. S. G. P.; Lourenço, M. J. V.; Santos, F. J. V.; Nieto de Castro, C. A.

2018-05-01

The viscosity of Zn-Al alloys melts, with industrial interest, was measured for temperatures between 693 K and 915 K, with an oscillating cup viscometer, and estimated expanded uncertainties between 3 and 5 %, depending on the alloy. The influence of minor components, such as Si, Mg and Ce + La, on the viscosity of the alloys is discussed. An increase in the amount of Mg triggers complex melt/solidification processes while the addition of Ce and La renders alloys viscosity almost temperature independent. Furthermore, increases in Al and Si contents decrease melts viscosity and lead to an Arrhenius type behavior. This paper complements a previous study describing the viscosity of Zn-Al alloys with quasi-eutectic compositions.

WOCSDICE󈧇 The 27th Workshop on Compound Semiconductor Devices and Integrated Circuits Held in Europe May 26 - 28, 2003 Forigen, Switzerland

DTIC Science & Technology

2003-05-28

Rodrigues-Girones, M. Saglam, A. Megej, H.L. Hartnagel vi Recent Advances, Remaining Challenges in Wide Bandgap Semiconductors Colin ...R. H. Friend, and H. Sirringhaus, Science, 299, pp. 1881-1884, 2003. 19. C. J. Drury , C. M. J. Mutsaers, C. M. Hart, M. Matters, and D. M. de Leeuw

Electronic Raman Scattering as an Ultra-Sensitive Probe of Strain Effects in Semiconductors

NASA Astrophysics Data System (ADS)

Mascarenhas, Angelo; Fluegel, Brian; Beaton, Dan

Semiconductor strain engineering has become a critical feature of high-performance electronics due to the significant device performance enhancements it enables. These improvements that emerge from strain induced modifications to the electronic band structure necessitate new ultra-sensitive tools for probing strain in semiconductors. Using electronic Raman scattering, we recently showed that it is possible to measure minute amounts of strain in thin semiconductor epilayers. We applied this strain measurement technique to two different semiconductor alloy systems, using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10-4. Comparing our strain sensitivity and signal strength in AlxGa1-xAs with those obtained using the industry-standard technique of phonon Raman scattering we found a sensitivity improvement of ×200, and a signal enhancement of 4 ×103 thus obviating key constraints in semiconductor strain metrology. The sensitivity of this approach rivals that of contemporary techniques and opens up a new realm for optically probing strain effects on electronic band structure. We acknowledge the financial support of the DOE Office of Science, BES under DE-AC36-80GO28308.

Observations of O VI Emission from the Diffuse Interstellar Medium

NASA Technical Reports Server (NTRS)

Shelton, R. L.; Kruk, J. W.; Murphy, E. M.; Andersson, B. G.; Blair, W. P.; Dixon, W. V.; Edelstein, J.; Fullerton, A. W.; Gry, C.; Howk, J. C.;

Carrier dynamics and recombination mechanisms in staggered-alignment heterostructures

NASA Astrophysics Data System (ADS)

Wilson, Barbara A.

1988-08-01

The experimental and theoretical work on carrier dynamics and recombination mechanisms in semiconductor heterostructures with staggered type II alignments is reviewed. Examples from the literature are discussed for each of the III-V, II-VI, and IV-VI systems, as well as cross-column examples, with a focus on AlGaAs structures. The key optical properties which have benn identified as signatures of staggered-alignment behavior are summarized. A discussion of other epitaxial systems likely to exhibit staggered lineups is presented, and additional experimental and theoretical work is suggested, which could increase understanding of staggered-system behavior.

Seeded Nanowire and Microwire Growth from Lithium Alloys.

PubMed

Han, Sang Yun; Boebinger, Matthew G; Kondekar, Neha P; Worthy, Trevor J; McDowell, Matthew T

2018-06-06

Although vapor-liquid-solid (VLS) growth of nanowires from alloy seed particles is common in various semiconductor systems, related wire growth in all-metal systems is rare. Here, we report the spontaneous growth of nano- and microwires from metal seed particles during the cooling of Li-rich bulk alloys containing Au, Ag, or In. The as-grown wires feature Au-, Ag-, or In-rich metal tips and LiOH shafts; the results indicate that the wires grow as Li metal and are converted to polycrystalline LiOH during and/or after growth due to exposure to H 2 O and O 2 . This new process is a simple way to create nanostructures, and the findings suggest that metal nanowire growth from alloy seeds is possible in a variety of systems.

Model-based Analysis of Mixed Uranium(VI) Reduction by Biotic and Abiotic Pathways During in Situ Bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jiao; Scheibe, Timothy D.; Mahadevan, Radhakrishnan

2013-10-24

Uranium bioremediation has emerged as a potential strategy of cleanup of radionuclear contamination worldwide. An integrated geochemical & microbial community model is a promising approach to predict and provide insights into the bioremediation of a complicated natural subsurface. In this study, an integrated column-scale model of uranium bioremediation was developed, taking into account long-term interactions between biotic and abiotic processes. It is also combined with a comprehensive thermodynamic analysis to track the fate and cycling of biogenic species. As compared with other bioremediation models, the model increases the resolution of the connection of microbial community to geochemistry and establishes directmore » quantitative correlation between overall community evolution and geochemical variation, thereby accurately predicting the community dynamics under different sedimentary conditions. The thermodynamic analysis examined a recently identified homogeneous reduction of U(VI) by Fe(II) under dynamic sedimentary conditions across time and space. It shows that the biogenic Fe(II) from Geobacter metabolism can be removed rapidly by the biogenic sulphide from sulfate reducer metabolism, hence constituting one of the reasons that make the abiotic U(VI) reduction thermodynamically infeasible in the subsurface. Further analysis indicates that much higher influent concentrations of both Fe(II) and U(VI) than normal are required to for abiotic U(VI) reduction to be thermodynamically feasible, suggesting that the abiotic reduction cannot be an alternative to the biotic reduction in the remediation of uranium contaminated groundwater.« less

21 CFR 872.3060 - Noble metal alloy.

Code of Federal Regulations, 2014 CFR

2014-04-01

... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3060 Noble metal alloy. (a) Identification. A noble metal... “Class II Special Controls Guidance Document: Dental Noble Metal Alloys.” The devices are exempt from the...

Technology of welding aluminum alloys-II

NASA Technical Reports Server (NTRS)

1978-01-01

Step-by-step procedures were developed for high integrity manual and machine welding of aluminum alloys. Detailed instructions are given for each step with tables and graphs to specify materials and dimensions. Throughout work sequence, processing procedure designates manufacturing verification points and inspection points.

Position-dependent effective masses in semiconductor theory. II

NASA Technical Reports Server (NTRS)

Von Roos, O.; Mavromatis, H.

1985-01-01

A compound semiconductor possessing a slowly varying position-dependent chemical composition is considered. An effective-mass equation governing the dynamics of electron (or hole) motion using the Kohn-Luttinger representation and canonical transformations is derived. It is shown that, as long as the variation in chemical composition may be treated as a perturbation, the effective masses become constant, position-independent quantities. The effective-mass equation derived here is identical to the effective-mass equation derived previously by von Roos (1983), using a Wannier representation.

Half-metallicity in new Heusler alloys NaTO2 (T=Sc, Ti, V, Cr, and Mn): A first-principles study

NASA Astrophysics Data System (ADS)

Rajabi, Kh; Ahmadian, F.

2018-03-01

On the basis of the full-potential linearized augmented plane wave (FPLAPW) method within density functional theory (DFT), electronic structure and magnetic properties of Heusler alloys NaTO2 (T = Sc, Ti, V, Cr, and Mn) were investigated. The negative values of formation energy showed that these compounds can be experimentally synthesized. Results showed that in all compounds, AlCu2Mn-type structure was the most favorable one. The NaTO2 (T = Sc, Ti, V, Cr, and Mn) alloys were HM ferromagnets except NaScO2 (in both structures which were nonmagnetic semiconductors) and NaVO2 (in AlCu2Mn-type structure which was a magnetic semiconductor). The origin of half-metallicity was also verified in HM alloys. NaCrO2 and NaVO2 alloys had higher half-metallic band gaps in comparison with Heusler alloys including and excluding transition metals. The total magnetic moments of HM NaTO2 (T = Ti, V, Cr, and Mn) alloys obeyed Slater-Pauling rule (Mtot = Ztot-12). Among NaTO2 (T = Sc, Ti, V, Cr, and Mn) alloys, NaCrO2 had the highest robustness of half-metallicity with variation of lattice constant in both structures.

Occurrence of Cr(VI) in drinking water of Greece and relation to the geological background.

PubMed

Kaprara, E; Kazakis, N; Simeonidis, K; Coles, S; Zouboulis, A I; Samaras, P; Mitrakas, M

2015-01-08

This study provides a survey on potential Cr(VI) exposure attributed to drinking water in Greece. For this reason, a wide sampling and chemical analysis of tap waters from around 600 sites, supplied by groundwater resources, was conducted focusing on areas in which the geological substrate is predominated by ultramafic minerals. Results indicate that although violations of the current chromium regulation limit in tap water are very rare, 25% of cases showed Cr(VI) concentrations above 10 μg/L, whereas Cr(VI) was detectable in 70% of the samples (>2 μg/L). Mineralogy and conditions of groundwater reservoirs were correlated to suggest a possible Cr(VI) leaching mechanism. Higher Cr(VI) values are observed in aquifers in alluvial and neogene sediments of serpentine and amphibolite, originating from the erosion of ophiolithic and metamorphic rocks. In contrast, Cr(VI) concentration in samples from ophiolithic and metamorphic rocks was always below 10 μg/L due to both low contact time and surface area, as verified by low conductivity and salt concentration values. These findings indicate that under specific conditions, pollution of water by Cr(VI) is favorable by a slow MnO2-catalyzed oxidation of soluble Cr(III) to Cr(VI) in which manganese products [Mn(III)/Mn(II)] are probably re-oxidized by oxygen. Copyright © 2014 Elsevier B.V. All rights reserved.

All-aluminum-alloy UHV chamber for molecular beam epitaxy, 1

NASA Astrophysics Data System (ADS)

Suemitsu, M.; Miyamoto, N.

1984-03-01

The first all aluminum alloy (ex. JIS.6263-t6,2219-t87 etc) MBE chamber is constructed and described. After exposure to atmosphere, the chamber is drown to 10(-9) torr in 24 hours, and reaches an ultrahigh vacuum of 1.6x10(-10) torr by a 115 C, 24 bakeout process. The light weight and low cost as well as the short pump-down time and the law outgassing rate of the all aluminum alloy vacuum system seems to have a considerable applicative potentiality for equipment used in semiconductor ultrahigh vacuum processes.

Determination of chromium (VI) in primary and secondary fertilizer and their respective precursors.

PubMed

Krüger, Oliver; Fiedler, Francesca; Adam, Christian; Vogel, Christian; Senz, Rainer

2017-09-01

Hexavalent chromium species (Cr(VI)) are often carcinogenic, of high acute toxicity, highly mobile, and thus pose a severe risk to health and environment. Fertilizers usually contain significant amounts of chromium. Therefore, a reliable analysis of chromium and the fraction of Cr(VI) are crucial for safe use of fertilizers. This problem is expected to increase in the future, since more and more recycled fertilizers emerge due to increasing fertilizer demand and respective supply risks. However, existing analytical methods have been developed for conventional fertilizers and have to be tested whether they are suitable for the new materials. Thus, we performed a wet-chemical extraction for Cr(VI) on several matrices as well as respective quality control experiments including spiking with Cr(III) and Cr(VI) compounds. We found the Cr(VI) amounts to be below 2 mg/kg except for a thermally post-treated sewage sludge ash (SSA) that showed 12.3 mg/kg. The presence of organic matter e.g. in sludge or precipitated struvite caused a reduction of spiked Cr(VI) and thus no satisfying recovery for quality control. Cr(VI) reduction was also observed for SSA, presumably due to the presence of Fe(II) compounds. Even though the tested procedure can be hampered in some recycled fertilizer matrices, it might be adapted to be applicable also for these complex samples. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ünlü, Hilmi, E-mail: hunlu@itu.edu.tr

We propose a non-orthogonal sp{sup 3} hybrid bond orbital model to determine the electronic properties of semiconductor heterostructures. The model considers the non-orthogonality of sp{sup 3} hybrid states of nearest neighboring adjacent atoms using the intra-atomic Coulomb interactions corrected Hartree-Fock atomic energies and metallic contribution to calculate the valence band width energies of group IV elemental and group III-V and II-VI compound semiconductors without any adjustable parameter.

Reduction of Cr (VI) into Cr (III) by organelles of Chlorella vulgaris in aqueous solution: An organelle-level attempt.

PubMed

Chen, Zunwei; Song, Shufang; Wen, Yuezhong

2016-12-01

The priority pollutant chromium (Cr) was ubiquitous and great efforts have been made to reduce Cr (VI) into less-toxic Cr (III) by alga for the convenient availability and low expense. However, the functional role of organelle inside the algal cell in Cr (VI) reduction was poorly understood. In this study, organelles in green algae Chlorella vulgaris were extracted and further decorated for Cr (VI) reduction tests. Results showed that the chloroplast exhibited not only adsorption ability of total Cr (21.18% comparing to control) but also reduction potential of Cr (VI) (almost 70% comparing to control), whose most suitable working concentration was at 17μg/mL. Furtherly, the isolated thylakoid membrane (ITM) showed better Cr (VI) reduction potential with the presence of sodium alginate (SA), even though the Hill reaction activity (HRA) was inhibited. As for photosystem II (PSII), the addition of mesoporous silica SBA-15 enhanced the reduction ability through improving the light-harvesting complex (LHC) II efficiency and electron transport rate. On the whole, the reduction ability order of the three kinds of materials based on chloroplast in C. vulgaris was PSII@SBA-15>Chloroplast>ITM@SA. The attempt made in this study to reduce the Cr (VI) with C. vulgaris organelles might not only offer basement to detect the potential action mechanism of Cr (VI) reduction by C. vulgaris but also provide a new sight for the scavenge of heavy metal with biological materials. Copyright © 2016 Elsevier B.V. All rights reserved.

Band crossing in isovalent semiconductor alloys with large size mismatch

NASA Astrophysics Data System (ADS)

Deng, Hui-Xiong; Wei, Su-Huai

2012-02-01

Mixing isovalent compounds AC with BC to form alloys A1-xBxC has been an effective way in band structure engineering to enhance the availability of material properties. In most cases, the mixed isovalent atoms A and B, such as Al and Ga in Al1-xGaxAs or As and Sb in GaAs1-xSbx are similar in their atomic sizes and chemical potentials; therefore, the physical properties of A1-xBxC change smoothly from AC to BC. However, in some cases when the chemical and size differences between the isovalent atoms A and B are large, adding a small amount of B to AC or vice versa can lead to a discontinuous change in the electronic band structure. These large size- and chemicalmismatched (LSCM) systems often show unusual and abrupt changes in the alloys' material properties, which provide great potential in material design for novel device applications. In this report, based on first-principles band-structure calculations we show that for LSCM GaAs1-xNx and GaAs1-xBix alloys at the impurity limit the N (Bi)-induced impurity level is above (below) the conduction-(valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

Conduction band position tuning and Ga-doping in (Cd,Zn)S alloy thin films

DOE PAGES

Baranowski, Lauryn L.; Christensen, Steven; Welch, Adam W.; ...

2017-02-13

In recent years, the number of novel photovoltaic absorber materials under exploration has rapidly increased. However, to reap the most benefit from these new absorbers, alternative device structures and components must also be considered. In particular, the choice of a heterojunction partner, or contact layer, is critical to device optimization. In this work, we explore alternative n-type contact layer candidates that could be widely applicable to a variety of new absorbers. We use theory to calculate the band edge tuning provided by a variety of II-VI alloy systems, and select the (Cd,Zn)S system as one that affords a wide rangemore » of conduction band tuning. The synthesis of (Cd,Zn)S alloys is explored using atomic layer deposition, which afforded precise compositional control and produced crystalline thin films. The predicted tuning of the band gap and conduction band minimum is confirmed through X-ray photoelectron spectroscopy and optical absorption measurements. In addition, we investigated Ga-doping in Cd 0.6Zn 0.4S films to decrease their series resistance when used as contact layers in photovoltaic devices. In conclusion, this study provides a framework for exploring and optimizing alternative contact layer materials, which will prove critical to the success of new PV absorbers.« less

PREFACE: 3rd Workshop on Theory, Modelling and Computational Methods for Semiconductors (TMCSIII)

NASA Astrophysics Data System (ADS)

Califano, Marco; Migliorato, Max; Probert, Matt

2012-05-01

These conference proceedings contain the written papers of the contributions presented at the 3rd International Conference on Theory, Modelling and Computational Methods for Semiconductor materials and nanostructures. The conference was held at the School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK on 18-20 January 2012. The previous conferences in this series took place in 2010 at St William's College, York and in 2008 at the University of Manchester, UK. The development of high-speed computer architectures is finally allowing the routine use of accurate methods for calculating the structural, thermodynamic, vibrational, optical and electronic properties of semiconductors and their hetero- and nano-structures. The scope of this conference embraces modelling, theory and the use of sophisticated computational tools in semiconductor science and technology, where there is substantial potential for time-saving in R&D. Theoretical approaches represented in this meeting included: Density Functional Theory, Tight Binding, Semiempirical Pseudopotential Methods, Effective Mass Models, Empirical Potential Methods and Multiscale Approaches. Topics included, but were not limited to: Optical and Transport Properties of Quantum Nanostructures including Colloids and Nanotubes, Plasmonics, Magnetic Semiconductors, Graphene, Lasers, Photonic Structures, Photovoltaic and Electronic Devices. This workshop ran for three days, with the objective of bringing together UK and international leading experts in the theoretical modelling of Group IV, III-V and II-VI semiconductors, as well as students, postdocs and early-career researchers. The first day focused on providing an introduction and overview of this vast field, aimed particularly at students, with several lectures given by recognised experts in various theoretical approaches. The following two days showcased some of the best theoretical research carried out in the UK in this field, with several

Time-resolved optical studies of wide-gap II-VI semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Wang, Hong

ZnSe and ZnSe-based quantum well and superlattice structures are potential candidates for light emitting devices and other optical devices such as switches and modulators working in the blue-green wavelength range. Carrier dynamics studies of these structures are important in evaluating device performance as well as understanding the underlying physical processes. In this thesis, a carrier dynamics investigation is conducted for temperature from 77K to 295K on CdZnSSe/ZnSSe single quantum well structure (SQW) and ZnSe/ZnSTe superlattice fabricated by molecular beam epitaxy (MBE). Two experimental techniques with femtosecond time resolution are used in this work: up-conversion technique for time- resolved photoluminescence (PL) and pump-probe technique for time-resolved differential absorption studies. For both heterostructures, the radiative recombination is dominated by exciton transition due to the large exciton binding energy as a result of quantum confinement effect. The measured decay time of free exciton PL in CdZnSSe/ZnSSe SQW increases linearly with increasing temperature which agrees with the theoretical prediction by considering the conservation of momentum requirement for radiative recombination. However, the recombination of free carriers is also observed in CdZnSSe/ZnSSe SQW for the whole temperature range studied. On the other hand, in ZnSe/ZnSTe superlattice structures, the non- radiative recombination processes are non-negligible even at 77K and become more important in higher temperature range. The relaxation processes such as spectral hole burning, carrier thermalization and hot-carrier cooling are observed in ZnSe/ZnSTe superlattices at room temperature (295K) by the femtosecond pump-probe measurements. A rapid cooling of the thermalized hot- carrier from 763K to 450K within 4ps is deduced. A large optical nonlinearity (i.e., the induced absorption change) around the heavy-hole exciton energy is also obtained.

Synthesis of colloidal Zn(Te,Se) alloy quantum dots

NASA Astrophysics Data System (ADS)

Asano, H.; Arai, K.; Kita, M.; Omata, T.

2017-10-01

Colloidal Zn(Te1-x Se x ) quantum dots (QDs), which are highly mismatched semiconductor alloys, were synthesized by the hot injection of an organometallic solution, and the composition and size dependence of their optical gap were studied together with the theoretical calculation using the finite-depth-well effective mass approximation. The optical gaps exhibited considerable negative deviation from the mole fraction weighted mean optical gaps of ZnTe and ZnSe, i.e. a large optical gap bowing was observed, similar to the bulk and thin-film alloys. The composition and size dependence of optical gaps agreed well with theoretically calculated ones employing a bowing parameter similar to that of the bulk alloys; therefore, the extent of the optical gap bowing in these alloy QDs is concluded to be the same as that in bulk and thin-film alloys. The optical gaps of Zn(Te1-x Se x ) QDs with diameters of 3.5-5 nm, where x ~ 0.35, were close to the energy corresponding to green light, indicating that those QDs are very promising as green QD-phosphors.

Role of an organic carbon-rich soil and Fe(III) reduction in reducing the toxicity and environmental mobility of chromium(VI) at a COPR disposal site.

PubMed

Ding, Weixuan; Stewart, Douglas I; Humphreys, Paul N; Rout, Simon P; Burke, Ian T

2016-01-15

Cr(VI) is an important contaminant found at sites where chromium ore processing residue (COPR) is deposited. No low cost treatment exists for Cr(VI) leaching from such sites. This study investigated the mechanism of interaction of alkaline Cr(VI)-containing leachate with an Fe(II)-containing organic matter rich soil beneath the waste. The soil currently contains 0.8% Cr, shown to be present as Cr(III)(OH)3 in EXAFS analysis. Lab tests confirmed that the reaction of Cr(VI) in site leachate with Fe(II) present in the soil was stoichiometrically correct for a reductive mechanism of Cr accumulation. However, the amount of Fe(II) present in the soil was insufficient to maintain long term Cr(VI) reduction at historic infiltration rates. The soil contains a population of bacteria dominated by a Mangroviflexus-like species, that is closely related to known fermentative bacteria, and a community capable of sustaining Fe(III) reduction in alkaline culture. It is therefore likely that in situ fermentative metabolism supported by organic matter in the soil produces more labile organic substrates (lactate was detected) that support microbial Fe(III) reduction. It is therefore suggested that addition of solid phase organic matter to soils adjacent to COPR may reduce the long term spread of Cr(VI) in the environment. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

A first-principles study of group IV and VI atoms doped blue phosphorene

NASA Astrophysics Data System (ADS)

Bai, Ruimin; Chen, Zheng; Gou, Manman; Zhang, Yixin

2018-02-01

Using first-principles calculations, we have systematically investigated the structural, electronic and magnetic properties of blue phosphorene doped by group IV and VI atoms, including C, Si, Ge, Sn, O, S, Se and Te. All the doped systems are energetically stable. Only C, Si, Ge and O-substituted systems show the characteristics of spin polarization and the magnetic moments are all 1.0 μB. Moreover, we found that C, Si, Ge and O doped systems are indirect bandgap semiconductors, while Sn, S, Se and Te doped systems present metallic property. These results show that blue phosphorene can be used prospectively in optoelectronic and spintronic devices.

Thermophysical property of undercooled liquid binary alloy composed of metallic and semiconductor elements

NASA Astrophysics Data System (ADS)

Wang, H. P.; Wei, B.

2009-02-01

The thermophysical properties of the liquid Ni-Si binary alloy system were investigated by the molecular dynamics method. The properties investigated include density, excessive volume, enthalpy, mixing enthalpy and specific heat at both superheated and undercooled states. It is found that the density decreases with an increase in the Si content, and so do the temperature coefficients. If the Si content is smaller than 30%, the density changes linearly with the temperature. If it is larger than 30%, the density is a quadratic function of the temperature. The simulated enthalpies of different composition alloys increase linearly with a rise in temperature. This indicates that the specific heats of Ni-Si alloys change little with temperature. The specific heat versus composition first decreases to a minimum value at 50% Si, then experiences a rise to a maximum value at 90% Si and finally falls again. According to the excessive volume and mixing enthalpy, it can be deduced that the Ni-Si alloy system seriously deviates from the ideal solution. Moreover, a comparison was also performed between the present results and the approximated values by the Neumann-Kopp rule. It reveals that this work provides reasonable data in a broad temperature range, especially for the metastable undercooled liquid state.

Selective adsorption and separation of chromium (VI) on the magnetic iron-nickel oxide from waste nickel liquid.

PubMed

Wei, Linsen; Yang, Gang; Wang, Ren; Ma, Wei

2009-05-30

The selective adsorption of Cr (VI) from the wastewater of Cr (VI)-Ni (II) by magnetically iron-nickel oxide was investigated in this study. Synthetic iron-nickel oxide magnetic particles in the co-sedimentation method were used as adsorbent to remove hexavalent chromium ions. The characteristic of adsorption was evaluated by Langmuir, Freundlich isotherm and Dubinin-Kaganer-Radushkevich (DKR) equations in the simulation wastewater of Cr (VI)-Ni (II) bi-system. The energy spectra and FT-IR analysis were used to test adsorbent before and after adsorption. The obtained results suggest that the uptake of chromium (VI) effect is obvious from phosphate anions and that from others is unobvious. The maximum adsorption capacity of hexavalent chromium is about 30 mg/g at pH 5.00+/-0.02, and it was reduced by increasing the total dissolved substance (TDS) of system. Adsorption energies E are about 10.310-21.321 kJ/mol which were obtained from DKR equation in difference TDS conditions. The regeneration shows that the iron-nickel oxide has good reuse performance and the hexavalent chromium was recycled. The major adsorption mechanism proposed was the ions exchange; however the surface coordination was a main role in the condition of TDS less than 200mg/L.

Cr(VI) and Cr(III) removal from aqueous solution by raw and modified lignocellulosic materials: a review.

PubMed

Miretzky, P; Cirelli, A Fernandez

2010-08-15

In aqueous systems, chromium usually exists in both trivalent and hexavalent oxidation states, being Cr(VI) of particular importance and concern due to its great toxicity. Industrial sources of Cr(VI) are leather tanning, mining of chrome ore, production of steel and alloys, etc. The most common conventional method for Cr(VI) removal is reduction to Cr(III) at pH 2.0 and precipitation of Cr (OH)(3) with lime at pH 9-10. The disadvantage of precipitation is the disposal of the solid waste. Adsorption of Cr by different low cost materials seems to be a suitable choice for wastewater treatment. Many by-products of agriculture have proved to be suitable low cost adsorbents for Cr(VI) and Cr(III) removal from water. Lignocellulosic residues, which include both wood residues and agricultural residues, have adsorption capacity comparable to other natural sorbents, but they have the advantage of very low or no cost, great availability and simple operational process. This study is a review of the recent literature on the use of natural and modified lignocellulosic residues for Cr adsorption. The Cr maximum adsorption capacity and the adsorption mechanism under different experimental conditions are reported when possibly. Copyright 2010 Elsevier B.V. All rights reserved.

Enhanced Materials Based on Submonolayer Type-II Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamargo, Maria C; Kuskovsky, Igor L.; Meriles, Carlos

2017-04-15

We have investigated a nanostructured material known as sub-monolayer type-II QDs, made from wide bandgap II-VI semiconductors. Our goal is to understand and exploit their tunable optical and electrical properties by taking advantage of the type-II band alignment and quantum confinement effects. Type-II ZnTe quantum dots (QDs) in a ZnSe host are particularly interesting because of their relatively large valence band and conduction band offsets. In the current award we have developed new materials based on sub-monolayer type-II QDs that may be advantageous for photovoltaic and spintronics applications. We have also expanded the structural characterization of these materials by refiningmore » the X-ray diffraction methodologies needed to investigate them. In particular, we have 1) demonstrated ZnCdTe/ZnCdSe type-II QDs materials that have ideal properties for the development of novel high efficiency “intermediate band solar cells”, 2) we developed a comprehensive approach to describe and model the growth of these ultra-small type-II QDs, 3) analysis of the evolution of the photoluminescence (PL) emission, combined with other characterization probes allowed us to predict the size and density of the QDs as a function of the growth conditions, 4) we developed and implemented novel sophisticated X-ray diffraction techniques from which accurate size and shape of the buried type-II QDs could be extracted, 5) a correlation of the shape anisotropy with polarization dependent PL was observed, confirming the QDs detailed shape and providing insight about the effects of this shape anisotropy on the physical properties of the type-II QD systems, and 6) a detailed “time-resolved Kerr rotation” investigation has led to the demonstration of enhanced electron spin lifetimes for the samples with large densities of type-II QDs and an understanding of the interplay between the QDs and Te-isoelectroic centers, a defect that forms in the spacer layers that separate the QDs.« less

Spin-Polarization Control in a Two-Dimensional Semiconductor

NASA Astrophysics Data System (ADS)

Appelbaum, Ian; Li, Pengke

2016-05-01

Long carrier spin lifetimes are a double-edged sword for the prospect of constructing "spintronic" logic devices: Preservation of the logic variable within the transport channel or interconnect is essential to successful completion of the logic operation, but any spins remaining past this event will pollute the environment for subsequent clock cycles. Electric fields can be used to manipulate these spins on a fast time scale by careful interplay of spin-orbit effects, but efficient controlled depolarization can only be completely achieved with amenable materials properties. Taking III-VI monochalcogenide monolayers as an example 2D semiconductor, we use symmetry analysis, perturbation theory, and ensemble calculation to show how this longstanding problem can be solved by suitable manipulation of conduction electrons.

KENO-VI Primer: A Primer for Criticality Calculations with SCALE/KENO-VI Using GeeWiz

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowman, Stephen M

2008-09-01

The SCALE (Standardized Computer Analyses for Licensing Evaluation) computer software system developed at Oak Ridge National Laboratory is widely used and accepted around the world for criticality safety analyses. The well-known KENO-VI three-dimensional Monte Carlo criticality computer code is one of the primary criticality safety analysis tools in SCALE. The KENO-VI primer is designed to help a new user understand and use the SCALE/KENO-VI Monte Carlo code for nuclear criticality safety analyses. It assumes that the user has a college education in a technical field. There is no assumption of familiarity with Monte Carlo codes in general or with SCALE/KENO-VImore » in particular. The primer is designed to teach by example, with each example illustrating two or three features of SCALE/KENO-VI that are useful in criticality analyses. The primer is based on SCALE 6, which includes the Graphically Enhanced Editing Wizard (GeeWiz) Windows user interface. Each example uses GeeWiz to provide the framework for preparing input data and viewing output results. Starting with a Quickstart section, the primer gives an overview of the basic requirements for SCALE/KENO-VI input and allows the user to quickly run a simple criticality problem with SCALE/KENO-VI. The sections that follow Quickstart include a list of basic objectives at the beginning that identifies the goal of the section and the individual SCALE/KENO-VI features that are covered in detail in the sample problems in that section. Upon completion of the primer, a new user should be comfortable using GeeWiz to set up criticality problems in SCALE/KENO-VI. The primer provides a starting point for the criticality safety analyst who uses SCALE/KENO-VI. Complete descriptions are provided in the SCALE/KENO-VI manual. Although the primer is self-contained, it is intended as a companion volume to the SCALE/KENO-VI documentation. (The SCALE manual is provided on the SCALE installation DVD.) The primer provides specific

A two-dimensional organic–inorganic hybrid compound, poly[(ethylenediamine)tri-μ-oxido-oxidocopper(II)molybdenum(VI)

PubMed Central

Gun, Ozgul; VanDerveer, Don; Emirdag-Eanes, Mehtap

2008-01-01

A new organic–inorganic two-dimensional hybrid compound, [CuMoO4(C2H8N2)], has been hydro­thermally synthesized at 443 K. The unit cell contains layers composed of CuN2O4 octa­hedra and MoO4 tetra­hedra. Corner-sharing MoO4 and CuN2O4 polyhedra form CuMoO4 bimetallic sites that are joined together through O atoms, forming an edge-sharing Cu2Mo2O4 chain along the c axis. The one-dimensional chains are further linked through bridging O atoms that join the Cu and Mo atoms into respective chains along the b axis, thus establishing layers in the bc plane. The ethyl­enediamine ligand is coordinated to the Cu atom through its two N atoms and is oriented perpendicularly to the two-dimensional –Cu—O—Mo– layers. The average distance between adjacent layers, as calculated by consideration of the closest and furthest distances between two layers, is 8.7 Å. The oxidation states of the Mo and Cu atoms of VI and II, respectively, were confirmed by bond-valence sum calculations. PMID:21200997

Computational modeling and simulation study of electronic and thermal properties in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Paul, Abhijeet

2011-07-01

The technological progress in dimensional scaling has not only kept Silicon CMOS industry on Moore's law for the past five decades but has also benefited many other areas such as thermoelectricity, photo-voltaics, and energy storage. Extending CMOS beyond Si (More Moore, MM) and adding functional diversity to CMOS (More Than Moore, MTM) requires a thorough understanding of the basic electron and heat flow in semiconductors. Along with experiments computer modeling and simulation are playing an increasingly vital role in exploring the numerous possibilities in materials, devices and systems. With these aspects in mind the present work applies computational physics modeling and simulations to explore the, (i) electronic, (ii) thermal, and (iii) thermoelectric properties in nano-scale semiconductors. The electronic structure of zinc-blende and lead-chalcogenide nano-materials is calculated using an atomistic Tight-Binding model. The phonon dispersion in zinc-blende materials is obtained using the Modified Valence Force Field model. Electronic and thermal transport at the nano-scale is explored using Green's function method and Landauer's method. Thermoelectric properties of semiconductor nanostructures are calculated using Landauer's method. Using computer modeling and simulations the variation of the three physical properties (i-iii) are explored with varying size, transport orientation, shape, porosity, strain and alloying of nanostructures. The key findings are, (a) III-Vs and Ge with optimized strain and orientation can improve transistors' and thermoelectric performance, (b) porous Si nanowires provide a lucrative idea for enhancing the thermoelectric efficiency at room temperature, and (c) Si/Ge superlattice nanowires can be used for nano-scale tuning of lattice thermal conductivity by period control. The present work led to the development of two new interface trap density extraction methods in ultra-scaled FinFETs and correlation of the phonon shifts in Si

Hematite enhances the removal of Cr(VI) by Bacillus subtilis BSn5 from aquatic environment.

PubMed

Ma, Shuai; Song, Chang-Shun; Chen, Yuefang; Wang, Fei; Chen, Hui-Lun

2018-06-05

In the present study, we investigated the removal of Cr(VI) and the associated bacterial activity in the systems containing Bacillus subtilis BSn5 (B. subtilis BSn5) and hematite. The microcalorimetry was used to study the effect of hematite on the normal physiological functions of B. subtilis BSn5 towards the removal of Cr(VI) for the first time. The results of the heat flux and the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that hematite does not affect the normal physiological functions of B. subtilis BSn5, and can help the strains maintain their activity in the presence of Cr(VI). More importantly, the relative capacity and intensity of Cr(VI) and total Cr removal by B. subtilis BSn5 in the presence of hematite were higher than that in the absence of hematite. The enhancement effect could be associated with their mineral adsorption, biosorption, Fe(II) reduction, bioreduction and immobilization functions. This study demonstrates the possibility of reducing the toxicity of Cr(VI) and enhancing the Cr(VI) removal efficiency in contaminated environments using a combination of hematite and B. subtilis BSn5. Copyright © 2018 Elsevier Ltd. All rights reserved.

Chromium (VI)-induced oxidative stress, apoptotic cell death and modulation of p53 tumor suppressor gene.

PubMed

Bagchi, D; Bagchi, M; Stohs, S J

2001-06-01

Chromium (VI) is a widely used industrial chemical, extensively used in paints, metal finishes, steel including stainless steel manufacturing, alloy cast irons, chrome, and wood treatment. On the contrary, chromium (III) salts such as chromium polynicotinate, chromium chloride and chromium picolinate, are used as micronutrients and nutritional supplements, and have been demonstrated to exhibit a significant number of health benefits in rodents and humans. However, the cause for the hexavalent chromium to induce cytotoxicity is not entirely understood. A series of in vitro and in vivo studies have demonstrated that chromium (VI) induces an oxidative stress through enhanced production of reactive oxygen species (ROS) leading to genomic DNA damage and oxidative deterioration of lipids and proteins. A cascade of cellular events occur following chromium (VI)-induced oxidative stress including enhanced production of superoxide anion and hydroxyl radicals, increased lipid peroxidation and genomic DNA fragmentation, modulation of intracellular oxidized states, activation of protein kinase C, apoptotic cell death and altered gene expression. In this paper, we have demonstrated concentration- and time-dependent effects of sodium dichromate (chromium (VI) or Cr (VI)) on enhanced production of superoxide anion and hydroxyl radicals, changes in intracellular oxidized states as determined by laser scanning confocal microscopy, DNA fragmentation and apoptotic cell death (by flow cytometry) in human peripheral blood mononuclear cells. These results were compared with the concentration-dependent effects of chromium (VI) on chronic myelogenous leukemic K562 cells and J774A.1 murine macrophage cells. Chromium (VI)-induced enhanced production of ROS, as well as oxidative tissue and DNA damage were observed in these cells. More pronounced effect was observed on chronic myelogenous leukemic K562 cells and J774A.1 murine macrophage cells. Furthermore, we have assessed the effect of a

Can high pressure I-II transitions in semiconductors be affected by plastic flow and nanocrystal precipitation in phase I?

NASA Astrophysics Data System (ADS)

Weinstein, B. A.; Lindberg, G. P.

Pressure-Raman spectroscopy in ZnSe and ZnTe single crystals reveals that Se and Te nano-crystals (NCs) precipitate in these II-VI hosts for pressures far below their I-II phase transitions. The inclusions are evident from the appearance and negative pressure-shift of the A1 Raman peaks of Se and Te (trigonal phase). The Se and Te NCs nucleate at dislocations and grain boundaries that arise from pressure-induced plastic flow. This produces chemical and structural inhomogeneities in the zincblende phase of the host. At substantially higher pressures, the I-II transition proceeds in the presence of these inhomogenities. This can affect the transition's onset pressure Pt and width ΔPt, and the occurrence of metastable phases along the transition path. Precipitation models in metals show that nucleation of inclusions depends on the Peierls stress τp and a parameter α related to the net free energy gained on nucleation. For favorable values of τp and α, NC precipitation at pressures below the I-II transition could occur in other compounds. We propose criteria to judge whether this is likely based on the observed ranges of τp in the hosts, and estimates of α derived from the cohesive energy densities of the NC materials. One finds trends that can serve as a useful guide, both to test the proposed criteria, and to decide when closer scrutiny of phase transition experiments is warranted, e.g., in powders where high dislocation densities are initially created

Evidence of Type-II Band Alignment in III-nitride Semiconductors: Experimental and theoretical investigation for In0.17Al0.83N/GaN heterostructures

PubMed Central

Wang, Jiaming; Xu, Fujun; Zhang, Xia; An, Wei; Li, Xin-Zheng; Song, Jie; Ge, Weikun; Tian, Guangshan; Lu, Jing; Wang, Xinqiang; Tang, Ning; Yang, Zhijian; Li, Wei; Wang, Weiying; Jin, Peng; Chen, Yonghai; Shen, Bo

2014-01-01

Type-II band alignment structure is coveted in the design of photovoltaic devices and detectors, since it is beneficial for the transport of photogenerated carriers. Regrettably, for group-III-nitride wide bandgap semiconductors, all existing devices are limited to type-I heterostructures, owing to the unavailable of type-II ones. This seriously restricts the designing flexibility for optoelectronic devices and consequently the relevant performance of this material system. Here we show a brandnew type-II band alignment of the lattice-matched In0.17Al0.83N/GaN heterostructure from the perspective of both experimental observations and first-principle theoretical calculations. The band discontinuity is dominated by the conduction band offset ΔEC, with a small contribution from the valence band offset ΔEV which equals 0.1 eV (with being above). Our work may open up new prospects to realize high-performance III-Nitrides optoelectronic devices based on type-II energy band engineering. PMID:25283334

Evidence of type-II band alignment in III-nitride semiconductors: experimental and theoretical investigation for In 0.17 Al 0.83 N/GaN heterostructures.

PubMed

Wang, Jiaming; Xu, Fujun; Zhang, Xia; An, Wei; Li, Xin-Zheng; Song, Jie; Ge, Weikun; Tian, Guangshan; Lu, Jing; Wang, Xinqiang; Tang, Ning; Yang, Zhijian; Li, Wei; Wang, Weiying; Jin, Peng; Chen, Yonghai; Shen, Bo

2014-10-06

Type-II band alignment structure is coveted in the design of photovoltaic devices and detectors, since it is beneficial for the transport of photogenerated carriers. Regrettably, for group-III-nitride wide bandgap semiconductors, all existing devices are limited to type-I heterostructures, owing to the unavailable of type-II ones. This seriously restricts the designing flexibility for optoelectronic devices and consequently the relevant performance of this material system. Here we show a brandnew type-II band alignment of the lattice-matched In 0.17 Al 0.83 N/GaN heterostructure from the perspective of both experimental observations and first-principle theoretical calculations. The band discontinuity is dominated by the conduction band offset ΔEC, with a small contribution from the valence band offset ΔEV which equals 0.1 eV (with E(AlInN(VBM) being above E(GaN)(VBM)). Our work may open up new prospects to realize high-performance III-Nitrides optoelectronic devices based on type-II energy band engineering.

Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor (B a1 -xKx ) (Zn1-yM ny ) 2A s2

NASA Astrophysics Data System (ADS)

Sun, F.; Zhao, G. Q.; Escanhoela, C. A.; Chen, B. J.; Kou, R. H.; Wang, Y. G.; Xiao, Y. M.; Chow, P.; Mao, H. K.; Haskel, D.; Yang, W. G.; Jin, C. Q.

2017-03-01

We investigate doping- and pressure-induced changes in the electronic state of Mn 3 d and As 4 p orbitals in II-II-V-based diluted magnetic semiconductor (B a1 -xKx ) (Zn1-yM ny ) 2A s2 to shed light into the mechanism of indirect exchange interactions leading to high ferromagnetic ordering temperature (T c =230 K in optimally doped samples). A suite of x-ray spectroscopy experiments (emission, absorption, and dichroism) show that the emergence and further enhancement of ferromagnetic interactions with increased hole doping into the As 4 p band is accompanied by a decrease in local 3 d spin density at Mn sites. This is a result of increasing Mn 3 d -As 4 p hybridization with hole doping, which enhances indirect exchange interactions between Mn dopants and gives rise to induced magnetic polarization in As 4 p states. On the contrary, application of pressure suppresses exchange interactions. While Mn K β emission spectra show a weak response of 3 d states to pressure, clear As 4 p band broadening (hole delocalization) is observed under pressure, ultimately leading to loss of ferromagnetism concomitant with a semiconductor to metal transition. The pressure response of As 4 p and Mn 3 d states is intimately connected with the evolution of the As-As interlayer distance and the geometry of the MnA s4 tetrahedral units, which we probed with x-ray diffraction. Our results indicate that hole doping increases the degree of covalency between the anion (As) p states and cation (Mn) d states in the MnA s4 tetrahedron, a crucial ingredient to promote indirect exchange interactions between Mn dopants and high T c ferromagnetism. The instability of ferromagnetism and semiconducting states against pressure is mainly dictated by delocalization of anion p states.

Microgravity sciences application visiting scientist program

NASA Technical Reports Server (NTRS)

1994-01-01

Contract NAS8-38785, Microgravity Experimental and Theoretical Research, is a project involving a large number of individual research programs related to: determination of the structure of human serum albumin and other biomedically important proteins; analysis of thermodynamic properties of various proteins and models of protein nucleation; development of experimental techniques for the growth of protein crystals in space; study of the physics of electrical double layers in the mechanics of liquid interfaces; computational analysis of vapor crystal growth processes in microgravity; analysis of the influence of magnetic fields in damping residual flows in directional solidification processes; crystal growth and characterization of II-VI semiconductor alloys; and production of thin films for nonlinear optics. It is not intended that the programs will be necessarily limited to this set at any one time. The visiting scientists accomplishing these programs shall serve on-site at MSFC to take advantage of existing laboratory facilities and the daily opportunities for technical communications with various senior scientists.

Electron spin resonance study of CuGa1-xMnxSe2 magnetic semiconducting compounds

NASA Astrophysics Data System (ADS)

Fermin, José R.; Nava, Alexander; Durante-Rincón, C. A.; Castro, Jaime; Silva, Pedro J.

2013-02-01

We report on the magnetic properties of the diluted magnetic semiconductor CuGa1-xMnxSe2. For this, Electron spin resonance (ESR) experiments in the temperature range 70 KII-Mn-VI alloys, and can be described by the modified Huber equation.

Complexation of Eu(III), Pb(II), and U(VI) with a Paramecium glycoprotein: Microbial transformation of heavy elements in the aquatic environment.

PubMed

Kozai, Naofumi; Sakamoto, Fuminori; Tanaka, Kazuya; Ohnuki, Toshihiko; Satoh, Takahiro; Kamiya, Tomihiro; Grambow, Bernd

2018-04-01

This study investigated the interaction of inorganic aqueous Eu(III), Pb(II), and U(VI) with Paramecium sp., a representative single-celled protozoan that lives in freshwater. Living and prekilled Paramecium cells were tested. The prekilled cells were killed with a fixative. After 24 h exposure of the cells to inorganic aqueous solutions containing Eu(III) or U(VI), analyses by microparticle-induced X-ray emission with a focused beam (<1 μm) did not detect Eu and U in the living cells, whereas Eu and U were detected in the prekilled cells. Size exclusion chromatography coupled with on-line ultraviolet-visible detection and elemental detection by inductively coupled plasma mass spectrometry of the aqueous phases collected after the living cell experiments revealed that a fraction of the Eu, Pb, and U in the aqueous phase bound to a large (ca. 250 kDa) Paramecium biomolecule and formed a metal-organic complex. The characteristics of the biomolecule were consistent with those of the soluble glycoproteins covering the surfaces of Paramecium cells. These results show that Paramecium cells transform inorganic aqueous Eu, Pb, and U to organic complexes. This paper discusses the relation between this novel complexation and the sorption of these heavy elements on Paramecium cells. Copyright © 2017 Elsevier Ltd. All rights reserved.

Micromechanical Structures Fabrication

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajic, S

2001-05-08

Work in materials other than silicon for MEMS applications has typically been restricted to metals and metal oxides instead of more ''exotic'' semiconductors. However, group III-V and II-VI semiconductors form a very important and versatile collection of material and electronic parameters available to the MEMS and MOEMS designer. With these materials, not only are the traditional mechanical material variables (thermal conductivity, thermal expansion, Young's modulus, etc.) available, but also chemical constituents can be varied in ternary and quaternary materials. This flexibility can be extremely important for both friction and chemical compatibility issues for MEMS. In addition, the ability to continuallymore » vary the bandgap energy can be particularly useful for many electronics and infrared detection applications. However, there are two major obstacles associated with alternate semiconductor material MEMS. The first issue is the actual fabrication of non-silicon micro-devices and the second impediment is communicating with these novel devices. We have implemented an essentially material independent fabrication method that is amenable to most group III-V and II-VI semiconductors. This technique uses a combination of non-traditional direct write precision fabrication processes such as diamond turning, ion milling, laser ablation, etc. This type of deterministic fabrication approach lends itself to an almost trivial assembly process. We also implemented a mechanical, electrical, and optical self-aligning hybridization technique for these alternate-material MEMS substrates.« less

Activity of pyramidal I and II < c + a > slip in Mg alloys as revealed by texture development

NASA Astrophysics Data System (ADS)

Zecevic, Miroslav; Beyerlein, Irene J.; Knezevic, Marko

2018-02-01

Due to the geometry of the hexagonal close-packed (HCP) lattice, there are two types of pyramidal slip modes: { 10 1 bar 1 } 〈 11 2 bar 3 bar 〉 or type I and { 1 bar 1 bar 22 } 〈 11 2 bar 3 〉 or type II in HCP crystalline materials. Here we use crystal plasticity to examine the importance of crystallographic slip by pyramidal type I and type II on texture evolution. The study is applied to an Mg-4%Li alloy. An elastic-plastic polycrystal model is employed to elucidate the reorientation tendencies of these two slip modes in rolling of a textured polycrystal. Comparisons with experimental texture measurements indicate that both pyramidal I and II type slip were active during rolling deformation, with pyramidal I being the dominant mode. A single-slip-mode analysis is used to identify the orientations that prefer pyramidal I vs. II type slip when acting alone in a crystal. The analysis applies not only to Mg-4%Li, but identifies the key texture components in HCP crystals that would help distinguish the activity of pyramidal I from pyramidal II slip in rolling deformation.

4-d magnetism: Electronic structure and magnetism of some Mo-based alloys

NASA Astrophysics Data System (ADS)

Liu, Yong; Bose, S. K.; Kudrnovský, J.

2017-02-01

We report results of a first-principles density-functional study of alloys of the 4 d -element Mo with group IV elements Si, Ge and Sn in zinc blende (ZB) and rock salt (RS) structures. The study was motivated by a similar study of ours based on the 4 d -element Tc, which showed the presence of half-metallic states with integer magnetic moment (1μB) per formula unit in TcX (X=C, Si, Ge) alloys. The calculated Curie temperatures for the ferromagnetic (FM) phases were low, around or less than 300 K. Searching for the possibility of 4 d -based alloys with higher Curie temperatures we have carried out the study involving the elements Mo, Ru and Rh. Among these the most promising case appears to be that involving the element Mo. Among the MoX (X=Si, Ge, Sn) alloys in ZB and RS structures, both MoGe and MoSn in ZB structures are found to possess an integer magnetic moment of 2μB per formula unit. ZB MoSn can be classified as a marginal/weak half-metal or a spin gapless semiconductor, while ZB MoGe would be best described as a gapless magnetic semiconductor. The calculated Curie temperatures are in the range 300-700 K. Considering the theoretical uncertainty in the band gaps due not only to the treatment of exchange and correlation effects, but density functional theory itself, these classifications may change somewhat, but both merit investigation from the viewpoint of potential spintronic application. Based on their higher Curie temperatures, Mo-based alloys would serve such purpose better than the previously reported Tc-based ones.

Reduction of Cr(VI) under acidic conditions by the facultative Fe(III)-reducing bacterium Acidiphilium cryptum

DOE Office of Scientific and Technical Information (OSTI.GOV)

David E. Cummings; Scott Fendorf; Rajesh K. Sani

2007-01-01

The potential for biological reduction of Cr(VI) under acidic conditions was evaluated with the acidophilic, facultatively metal-reducing bacterium Acidiphilium cryptum strain JF-5 to explore the role of acidophilic microorganisms in the Cr cycle in low-pH environments. An anaerobic suspension of washed A. cryptum cells rapidly reduced 50 M Cr(VI) at pH 3.2; biological reduction was detected from pH 1.7-4.7. The reduction product, confirmed by XANES analysis, was entirely Cr(III) that was associated predominantly with the cell biomass (70-80%) with the residual residing in the aqueous phase. Reduction of Cr(VI) showed a pH optimum similar to that for growth and wasmore » inhibited by 5 mM HgCl2, suggesting that the reaction was enzyme-mediated. Introduction of O2 into the reaction medium slowed the reduction rate only slightly, whereas soluble Fe(III) (as ferric sulfate) increased the rate dramatically, presumably by the shuttling of electrons from bioreduced Fe(II) to Cr(VI) in a coupled biotic-abiotic cycle. Starved cells could not reduce Cr(VI) when provided as sole electron acceptor, indicating that Cr(VI) reduction is not an energy-conserving process in A. cryptum. We speculate, rather, that Cr(VI) reduction is used here as a detoxification mechanism.« less

Oxidation of manganese(II) with ferrate: Stoichiometry, kinetics, products and impact of organic carbon.

PubMed

Goodwill, Joseph E; Mai, Xuyen; Jiang, Yanjun; Reckhow, David A; Tobiason, John E

2016-09-01

Manganese is a contaminant of concern for many drinking water utilities, and future regulation may be pending. An analysis of soluble manganese (Mn(II)) oxidation by ferrate (Fe(VI)) was executed at the bench-scale, in a laboratory matrix, both with and without the presence of natural organic matter (NOM) and at two different pH values, 6.2 and 7.5. In the matrix without NOM, the oxidation of Mn(II) by Fe(VI) followed a stoichiometry of 2 mol Fe(VI) to 3 mol Mn(II). The presence of NOM did not significantly affect the stoichiometry of the oxidation reaction, indicating relative selectivity of Fe(VI) for Mn(II). The size distribution of resulting particles included significant amounts of nanoparticles. Resulting manganese oxide particles were confirmed to be MnO2 via X-ray photoelectron spectroscopy. The rate of the Mn(II) oxidation reaction was fast relative to typical time scales in drinking water treatment, with an estimated second order rate constant of approximately 1 × 10(4) M(-1) s(-1) at pH 9.2 and > 9 × 10(4) M(-1) s(-1) at pH 6.2. In general, ferrate is a potential option for Mn(II) oxidation in water treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Criteria for extending the operation periods of thermoelectric converters based on IV-VI compounds

NASA Astrophysics Data System (ADS)

Sadia, Yatir; Ohaion-Raz, Tsion; Ben-Yehuda, Ohad; Korngold, Meidad; Gelbstein, Yaniv

2016-09-01

The recent energy demands affected by the dilution of conventional energy resources and the growing awareness of environmental considerations, had positioned the research of renewable energy conversion methods in general and of thermoelectric direct conversion of thermal into electrical energies in particular, in the forefront of the currently active applicative sciences. IV-VI thermoelectric compounds (e.g. GeTe, PbTe and SnTe) and their alloys comprise some of the most efficient thermoelectric compositions ever reported. Yet a proper utilization of such materials in practical thermoelectric devices, still requires an overcoming the so-called technological "valley of death", including among others, transport properties' degradation, due to sublimation of volatile Te rich species, while being subjected to elevated temperatures for long periods of time. In an attempt to establish practical operation criteria for extending the operation periods of such thermoelectric converters, it is currently shown based on thermal gravimetric and metallurgical considerations that such harmful sublimation can be practically bridged over by limiting the maximal operating temperatures to the 410-430 °C range for GeTe rich alloys and to 510-530 °C for PbTe and SnTe rich alloys, depending of the thermoelectric leg's diameter.

Microbially-mediated method for synthesis of non-oxide semiconductor nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phelps, Tommy J.; Lauf, Robert J.; Moon, Ji-Won

The invention is directed to a method for producing non-oxide semiconductor nanoparticles, the method comprising: (a) subjecting a combination of reaction components to conditions conducive to microbially-mediated formation of non-oxide semiconductor nanoparticles, wherein said combination of reaction components comprises i) anaerobic microbes, ii) a culture medium suitable for sustaining said anaerobic microbes, iii) a metal component comprising at least one type of metal ion, iv) a non-metal component comprising at least one non-metal selected from the group consisting of S, Se, Te, and As, and v) one or more electron donors that provide donatable electrons to said anaerobic microbes duringmore » consumption of the electron donor by said anaerobic microbes; and (b) isolating said non-oxide semiconductor nanoparticles, which contain at least one of said metal ions and at least one of said non-metals. The invention is also directed to non-oxide semiconductor nanoparticle compositions produced as above and having distinctive properties.« less

Microbially-mediated method for synthesis of non-oxide semiconductor nanoparticles

DOEpatents

Phelps, Tommy J.; Lauf, Robert J.; Moon, Ji Won; Rondinone, Adam J.; Love, Lonnie J.; Duty, Chad Edward; Madden, Andrew Stephen; Li, Yiliang; Ivanov, Ilia N.; Rawn, Claudia Jeanette

2014-06-24

The invention is directed to a method for producing non-oxide semiconductor nanoparticles, the method comprising: (a) subjecting a combination of reaction components to conditions conducive to microbially-mediated formation of non-oxide semiconductor nanoparticles, wherein said combination of reaction components comprises i) anaerobic microbes, ii) a culture medium suitable for sustaining said anaerobic microbes, iii) a metal component comprising at least one type of metal ion, iv) a non-metal component containing at least one non-metal selected from the group consisting of S, Se, Te, and As, and v) one or more electron donors that provide donatable electrons to said anaerobic microbes during consumption of the electron donor by said anaerobic microbes; and (b) isolating said non-oxide semiconductor nanoparticles, which contain at least one of said metal ions and at least one of said non-metals. The invention is also directed to non-oxide semiconductor nanoparticle compositions produced as above and having distinctive properties.

Metal release and speciation of released chromium from a biomedical CoCrMo alloy into simulated physiologically relevant solutions.

PubMed

Hedberg, Yolanda; Odnevall Wallinder, Inger

2014-05-01

The objective of this study was to investigate the extent of released Co, Cr(III), Cr(VI), and Mo from a biomedical high-carbon CoCrMo alloy exposed in phosphate-buffered saline (PBS), without and with the addition of 10 µM H2 O2 (PBS + H2 O2 ), and 10 g L(-1) bovine serum albumin (PBS + BSA) for time periods up to 28 days. Comparative studies were made on AISI 316L for the longest time period. No Cr(VI) release was observed for any of the alloys in either PBS or PBS + H2 O2 at open-circuit potential (no applied potential). However, at applied potentials (0.7 V vs. Ag/AgCl), Cr was primarily released as Cr(VI). Co was preferentially released from the CoCrMo alloy at no applied potential. As a consequence, Cr was enriched in the utmost surface oxide reducing the extent of metal release over time. This passivation effect was accelerated in PBS + H2 O2 . As previously reported for 316L, BSA may also enhance metal release from CoCrMo. However, this was not possible to verify due to the precipitation of metal-protein complexes with reduced metal concentrations in solution as a consequence. This was particularly important for Co-BSA complexes after sufficient time and resulted in an underestimation of metals in solution. Copyright © 2013 Wiley Periodicals, Inc.

TCNQ molecular semiconductor of the Cu(II)TAAB macrocycle: Optical and electrical properties.

PubMed

Sánchez Vergara, M E; Salcedo, R; Molina, Bertha; Carrera-Téllez, R; Álvarez-Bada, J R; Hernández-García, A; Gómez-Vidales, V

2018-07-05

The present study reports the doping of a semiconducting molecular material through the formation of hydrogen bonds between the macrocycle Cu(II)(TAAB) and the electronic acceptor TCNQ. According to density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis, the doped compound has the shape of a distorted square pyramid, with four nitrogen atoms in the equatorial position and the apical oxygen atom from the water ligands. These water molecules can generate strong hydrogen bonds with TCNQ and the TAAB metallic complex. Thin films of copper molecular material were obtained through high vacuum evaporation and were structurally characterized by IR spectroscopy, EPR and scanning electron microscopy (SEM). Additionally, the absorption coefficient (α) and photon energy (hν) were calculated from UV-vis spectroscopy and used to determine the optical activation energy in each film, from which its semiconducting behavior was established. An important aspect to consider is that the presence of hydrogen bonds is essential to establish the semiconducting nature of these species; this chemical behavior, as well as the resulting electronic mobility, have been studied by DFT theoretical calculations, which reinforce the experimental conclusion of a relationship between Cu(II)TAAB and TCNQ moieties generated by a weak bond. Finally, I-V characteristics have been obtained from a glass/ITO/doped molecular semiconductor/Ag device using Ag and ITO electrodes. Results for the copper-based device show that, at low voltages, the conduction process is of an ohmic nature while, at higher voltages, space-charge-limited current (SCLC) is found. It is highly probable that the doping effect in TCNQ favors electronic transport due to the formation of conduction channels caused by dopant-favored anisotropy. Copyright © 2018 Elsevier B.V. All rights reserved.

29 CFR 1926.1126 - Chromium (VI).

Code of Federal Regulations, 2014 CFR

2014-07-01

... activity involving chromium cannot release dusts, fumes, or mists of chromium (VI) in concentrations at or... 29 Labor 8 2014-07-01 2014-07-01 false Chromium (VI). 1926.1126 Section 1926.1126 Labor... Chromium (VI). (a) Scope. (1) This standard applies to occupational exposures to chromium (VI) in all forms...

29 CFR 1926.1126 - Chromium (VI).

Code of Federal Regulations, 2012 CFR

2012-07-01

... activity involving chromium cannot release dusts, fumes, or mists of chromium (VI) in concentrations at or... 29 Labor 8 2012-07-01 2012-07-01 false Chromium (VI). 1926.1126 Section 1926.1126 Labor... Chromium (VI). (a) Scope. (1) This standard applies to occupational exposures to chromium (VI) in all forms...

29 CFR 1926.1126 - Chromium (VI).

Code of Federal Regulations, 2011 CFR

2011-07-01

... activity involving chromium cannot release dusts, fumes, or mists of chromium (VI) in concentrations at or... 29 Labor 8 2011-07-01 2011-07-01 false Chromium (VI). 1926.1126 Section 1926.1126 Labor... Chromium (VI). (a) Scope. (1) This standard applies to occupational exposures to chromium (VI) in all forms...

29 CFR 1926.1126 - Chromium (VI).

Code of Federal Regulations, 2013 CFR

2013-07-01

... activity involving chromium cannot release dusts, fumes, or mists of chromium (VI) in concentrations at or... 29 Labor 8 2013-07-01 2013-07-01 false Chromium (VI). 1926.1126 Section 1926.1126 Labor... Chromium (VI). (a) Scope. (1) This standard applies to occupational exposures to chromium (VI) in all forms...

Production of FR Tubing from Advanced ODS Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maloy, Stuart Andrew; Lavender, Curt; Omberg, Ron

2016-10-25

Significant research is underway to develop LWR nuclear fuels with improved accident tolerance. One of the leading candidate materials for cladding are the FeCrAl alloys. New alloys produced at ORNL called Gen I and Gen II FeCrAl alloys possess excellent oxidation resistance in steam up to 1400°C and in parallel methods are being developed to produce tubing from these alloys. Century tubing continues to produce excellent tubing from FeCrAl alloys. This memo reports receipt of ~21 feet of Gen I FeCrAl alloy tubing. This tubing will be used for future tests including burst testing, mechanical testing and irradiation testing.

Improvement of chemical composition, structure and mechanical properties of heat-resistant chromium-nickel alloy

NASA Astrophysics Data System (ADS)

Varlamova, S.; Trushnikova, A.; Rumyantsev, B.; Butrim, V.; Simonov, V.

2018-04-01

A thermodynamic analysis of a multicomponent system of the Cr-Ni alloy (Cr-32Ni-1,5W-0,25V-0,5Ti) with small additions of refractory metals was carried out. The microstructure and phase composition of the base alloy (I) and alloy with additional alloying (II) were studied. The effect of additives on the mechanical properties of the Cr-Ni alloy at 20, 900 and 1080 °C was shown. The microstructure of alloys I and II was studied in the fracture zone of samples after tensile tests at different temperatures. We studied the effect of small additives on the microstructure of alloys and changes in the morphology of the structural components (phases) as a function of temperature and degree of deformation.

On VI /lambda equals 1032 A/ profiles in and above an active region prominence, compared to quiet sun center and limb profiles

NASA Astrophysics Data System (ADS)

Vial, J. C.; Lemaire, P.; Artzner, G.; Gouttebroze, P.

1980-11-01

O VI (λ = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H I, Mg II, Ca II resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb. Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3"); at the top of the prominence (15" above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s-1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s-1) is lower than in Ca II lines. The O VI profile recorded 30" above the limb outside the filament is wider (FWHM 0.33 Å). It can be interpreted as a coronal emission of 0 VI ions with a temperature of about 106 K, and a non-thermal velocity (NTV) of 49 km s-1. This NTV is twice the NTV of quiet Sun center O VI profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of EUV lines.

Redox transformation and reductive immobilization of Cr(VI) in the Columbia River hyporheic zone sediments

NASA Astrophysics Data System (ADS)

Xu, Fen; Liu, Yuanyuan; Zachara, John; Bowden, Mark; Kennedy, David; Plymale, Andrew E.; Liu, Chongxuan

2017-12-01

An experimental and modeling study was conducted to investigate the redox transformation and reductive immobilization of groundwater contaminant Cr in hyporheic zone (HZ) sediments from U.S. DOE's Hanford Site, where groundwater Cr(VI) is migrating and discharging to the nearby Columbia River. Experimental results revealed that Cr(VI) can be reduced and immobilized by the HZ sediments in the presence/absence of O2. Anaerobic pre-incubation of the sediments increased the effective rate of Cr reduction that was correlated with the increase in HCl-extractable Fe(II) content in the sediments. The reduced Cr was stable when exposed to O2 under field-relevant pH (7.5) with and without dissolved Mn(II), which might be oxidized to form Mn(III/IV) oxides that may oxidize reduced Cr. The Cr(VI) reduction rate showed a multi-rate behavior, apparently reflecting the presence of reductants with different reactivity in the sediments. The results from this study indicated that the HZ sediments can reductively immobilize Cr and the sediment redox capacity can be recharged through microbial activities. The results implied that HZ can play a role as a natural permeable redox barrier for removing groundwater Cr before it discharges into a river system.

Launcher Roadmap for the CrVI Substitution of Surface Treatments. Screening of Trivalent-Chromium Conversion Solutions and First Promising Results for Repair Applications on Aluminium Alloys

NASA Astrophysics Data System (ADS)

Debout, Vincent; Pettier, Sophie

2014-06-01

Airbus Defence and Space, Space System is involved in a global roadmap for launchers in order to substitute hexavalent chromium (CrVI) and Cadmium in the current surface treatments on metallic structures.Within this framework, a screening of trivalent chromium (CrIII) conversion solutions for touch-up applications has been carried out since this step is crucial to perform local application or to repair minor damages on launcher structures but it leads to higher risks of exposure for the workers.Three commercial CrIII conversion solutions have been evaluated on high performance aluminum alloys such as AA2024 T3 and AA7175 T7351 that are often used as structural materials.This preliminary investigation highlights the effect of surface preparation, rinsing and conversion process on the final corrosion performance of conversion coatings (CCs). The results are also discussed in terms of visual aspect and adhesion with new Cr-free primers.Two operating sets of parameters are identified with promising results that represent the first steps towards the development of a new Cr-free touch-up process.