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Sample records for 1x mango 1x

  1. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus.

    PubMed

    Cardoso, Adauto Lima; Pieczarka, Julio Cesar; Nagamachi, Cleusa Yoshiko

    2015-05-01

    Several types of sex chromosome systems have been recorded among Gymnotiformes, including male and female heterogamety, simple and multiple sex chromosomes, and different mechanisms of origin and evolution. The X1X1X2X2/X1X2Y systems identified in three species of this order are considered homoplasic for the group. In the genus Brachyhypopomus, only B. gauderio presented this type of system. Herein we describe the karyotypes of Brachyhypopomus pinnicaudatus and B. n. sp. FLAV, which have an X1X1X2X2/X1X2Y sex chromosome system that evolved via fusion between an autosome and the Y chromosome. The morphology of the chromosomes and the meiotic pairing suggest that the sex chromosomes of B. gauderio and B. pinnicaudatus have a common origin, whereas in B . n. sp. FLAV the sex chromosome system evolved independently. However, we cannot discard the possibility of common origin followed by distinct processes of differentiation. The identification of two new karyotypes with an X1X1X2X2/X1X2Y sex chromosome system in Gymnotiformes makes it the most common among the karyotyped species of the group. Comparisons of these karyotypes and the evolutionary history of the taxa indicate independent origins for their sex chromosomes systems. The recurrent emergence of the X1X1X2X2/X1X2Y system may represent sex chromosomes turnover events in Gymnotiformes. PMID:26273225

  2. Anomalous Flavor U(1)_X for Everything

    SciTech Connect

    Dreiner, Herbi K.; Murayama, Hitoshi; Thormeier, Marc

    2003-12-01

    We present an ambitious model of flavor, based on an anomalous U(1)_X gauge symmetry with one flavon, only two right-handed neutrinos and only two mass scales: M_{grav} and m_{3/2}. In particular, there are no new scales introduced for right-handed neutrino masses. The X-charges of the matter fields are such that R-parity is conserved exactly, higher-dimensional operators are sufficiently suppressed to guarantee a proton lifetime in agreement with experiment, and the phenomenology is viable for quarks, charged leptons, as well as neutrinos. In our model one of the three light neutrinos automatically is massless. The price we have to pay for this very successful model are highly fractional X-charges which can likely be improved with less restrictive phenomenological ansatze for mass matrices.

  3. Ares 1X Hybrid Modeling with Comparisons to Flight Data

    NASA Technical Reports Server (NTRS)

    Niedermaier, Dan; Kaouk, Mo

    2010-01-01

    This slide presentation reviews the Ares 1X test flight and compares the resultant flight data with the results of modeled data from siumulations of the flight. It includes: (1) Ares 1X Flight Summary, (2) Ares 1X Data Summary (3) Model Descriptions (4) Model Comparisons to Flight Data in three areas: (a) Liftoff, (b) Transonic and (c) Roll Control Firings (RCS) Firings.

  4. Driving force for martensitic transformation in Ni2Mn1 +xSn1 -x

    NASA Astrophysics Data System (ADS)

    Pal, Soumyadipta; Sarkar, Sagar; Pandey, S. K.; Maji, Chhayabrita; Mahadevan, Priya

    2016-09-01

    The martensitic transformation in Ni2Mn1 +xSn1 -x alloys has been investigated within ab initio density functional theory. The experimental trend of a martensitic transition happening beyond x =0.36 is captured within these calculations. The microscopic considerations leading to this are traced to increased Ni-Mn hybridization which results from the Ni atom experiencing a resultant force along a lattice vector and moving towards the Mn atoms above a critical concentration. The presence of the lone pair electrons on Sn forces the movement of Ni atoms away from Sn. While band Jahn Teller effects have been associated with this transition, we show quantitatively that at least in this class of compounds they have a minor role.

  5. Negative luminescence from In1 - xAlxSb and Cdx Hg1 - x Te diodes

    NASA Astrophysics Data System (ADS)

    Ashley, T.; Elliott, C. T.; Gordon, N. T.; Hall, R. S.; Johnson, A. D.; Pryce, G. J.

    1995-12-01

    Indium aluminium antimonide (In 1- xAl xSb) and cadmium mercury telluride (Cd xHg 1- xTe) heterostructure diodes, which comprise a near intrinsic active region bounded by more highly doped contact regions, exhibit positive or negative luminescence at medium to long infrared wavelengths when forward or reverse biased respectively at room temperature. In reverse bias, the carrier densities in the near intrinsic region are reduced below their equilibrium values by the effects of exclusion and extraction. In consequence, the radiative recombination is reduced and the devices emit less infrared radiation than the thermal equilibrium value. The observed intensity of the negative luminescence is in general agreement with expected values.

  6. Phase transformations in multiferroics Bi1- x Ca x Fe1- x Mn x O3

    NASA Astrophysics Data System (ADS)

    Troyanchuk, I. O.; Bushinsky, M. V.; Karpinsky, D. V.; Chobot, A. N.; Tereshko, N. V.; Franz, A.

    2016-09-01

    The crystal structure and the magnetic properties of multiferroics Bi1- x Ca x Fe1- x Mn x O3 ( x ≤ 0.22) have been studied. It has been found that the stoichiometric compositions undergo a crystal-structure transformation from the rhombohedral (space group R3 c) polar phase ( x ≤ 0.18) to the orthorhombic (space group Pnma) nonpolar phase ( x ≥ 0.20) via a two-phase structural state. The polar phase is antiferromagnetic at x < 0.10 and exhibits a metamagnetic behavior. The polar ( x ≥ 0.10) and nonpolar phases are weak ferromagnets at room temperature with a spontaneous magnetization close to 0.07 emu/g ( x = 0.18 and 0.22). A decrease in temperature leads to the transition to a state close to an antiferromagnetic one.

  7. KSC Engineering Academy (KEA): Ares 1-X Overview

    NASA Technical Reports Server (NTRS)

    Ess, Bob

    2007-01-01

    The presentation provides an overview of the ARES 1-X program. Videos include avionics ATVC actuator testing, GS damper retractor, GS vortex shedding, RoCS hot fire at WSTF, RoCS Peacekeeper tests, RoCS installation, thrust OSC, amd Ares 1-X fly through.

  8. Structural and optical features of novel Tl1-xIn1-xGexSe2 chalcogenide crystals

    NASA Astrophysics Data System (ADS)

    Zamurueva, O. V.; Myronchuk, G. L.; Lakshminarayana, G.; Parasyuk, O. V.; Piskach, L. V.; Fedorchuk, A. O.; AlZayed, N. S.; El-Naggar, A. M.; Kityk, I. V.

    2014-11-01

    The novel infrared Tl1-xIn1-xGexSe2 single crystals were synthesized by the modified Bridgman-Stockbarger method. The parameters of their energy band structure were determined. The temperature changes of the infrared parameters were studied and the phonon subsystem were evaluated. Analysis of the data is performed following the model of intrinsic defect states. The band structure calculation have established a principal role of the phonon subsystem for the observed effects.

  9. Hand weakness in Charcot-Marie-Tooth disease 1X.

    PubMed

    Arthur-Farraj, P J; Murphy, S M; Laura, M; Lunn, M P; Manji, H; Blake, J; Ramdharry, G; Fox, Z; Reilly, M M

    2012-07-01

    There have been suggestions from previous studies that patients with Charcot-Marie-Tooth disease (CMT) have weaker dominant hand muscles. Since all studies to date have included a heterogeneous group of CMT patients we decided to analyse hand strength in 43 patients with CMT1X. We recorded handedness and the MRC scores for the first dorsal interosseous and abductor pollicis brevis muscles, median and ulnar nerve compound motor action potentials and conduction velocities in dominant and non-dominant hands. Twenty-two CMT1X patients (51%) had a weaker dominant hand; none had a stronger dominant hand. Mean MRC scores were significantly higher for first dorsal interosseous and abductor pollicis brevis in non-dominant hands compared to dominant hands. Median nerve compound motor action potentials were significantly reduced in dominant compared to non-dominant hands. We conclude that the dominant hand is weaker than the non-dominant hand in patients with CMT1X.

  10. Hand weakness in Charcot-Marie-Tooth disease 1X

    PubMed Central

    Arthur-Farraj, P.J.; Murphy, S.M.; Laura, M.; Lunn, M.P.; Manji, H.; Blake, J.; Ramdharry, G.; Fox, Z.; Reilly, M.M.

    2012-01-01

    There have been suggestions from previous studies that patients with Charcot–Marie–Tooth disease (CMT) have weaker dominant hand muscles. Since all studies to date have included a heterogeneous group of CMT patients we decided to analyse hand strength in 43 patients with CMT1X. We recorded handedness and the MRC scores for the first dorsal interosseous and abductor pollicis brevis muscles, median and ulnar nerve compound motor action potentials and conduction velocities in dominant and non-dominant hands. Twenty-two CMT1X patients (51%) had a weaker dominant hand; none had a stronger dominant hand. Mean MRC scores were significantly higher for first dorsal interosseous and abductor pollicis brevis in non-dominant hands compared to dominant hands. Median nerve compound motor action potentials were significantly reduced in dominant compared to non-dominant hands. We conclude that the dominant hand is weaker than the non-dominant hand in patients with CMT1X. PMID:22464564

  11. Linear optical response of Si1-xGex compounds

    NASA Astrophysics Data System (ADS)

    Ferriera da Silva, A.; Souza Dantas, N.; Ahuja, R.; Pepe, I.; da Silva, Eronides F., Jr.; Nur, O.; Willander, M.; Persson, C.

    2005-03-01

    Si1-xGex is a good candidate as a substitute material for Si in a low-power and high-speed semiconductor device technologies. Optical devices, such as heterojunction bipolar transistors, are already in industrial production. The samples are grown on Si(001) with both n- and p-type impurities and with different Ge concentrations. The linear optical response of Si1-xGex is investigated theoretically using a full-potential linearized augmented plane wave method with respect to composition x. The calculated real and imaginary parts of the dielectric function ɛ(ω) = ɛ1(ω) + iɛ2(ω) were found to be in good agreement with recent spectroscopic ellipsometry measurements performed by Bahng et al., J. Phys.: Condens. Matter 13, 777 (2001). We also perform absorption measurements for different type of samples showing the variation of energy gaps as a function of Ge concentrations.

  12. Si(1-x)Ge(x)/Si Infrared Photodiodes

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon

    1991-01-01

    Cutoff wavelengths depend on x and also adjusted somewhat via reverse bias. Si1-xGex photodiodes with cutoff wavelengths in and beyond practically important range of 8 to 12 micrometers made by molecular-beam epitaxy. Compatible (in terms of fabrication processes) with silicon readout circuitry, exhibit long-term stability, manufactured with sufficient uniformity for use in focal-plane arrays; and operate at temperatures approximately greater than 65 K, for which temperatures small, portable refrigerators available.

  13. Illuminating the 1/x Moment of Parton Distribution Functions

    SciTech Connect

    Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; Szczepaniak, Adam P.; /Indiana U.

    2007-10-15

    The Weisberger relation, an exact statement of the parton model, elegantly relates a high-energy physics observable, the 1/x moment of parton distribution functions, to a nonperturbative low-energy observable: the dependence of the nucleon mass on the value of the quark mass or its corresponding quark condensate. We show that contemporary fits to nucleon structure functions fail to determine this 1/x moment; however, deeply virtual Compton scattering can be described in terms of a novel F1/x(t) form factor which illuminates this physics. An analysis of exclusive photon-induced processes in terms of the parton-nucleon scattering amplitude with Regge behavior reveals a failure of the high Q2 factorization of exclusive processes at low t in terms of the Generalized Parton-Distribution Functions which has been widely believed to hold in the past. We emphasize the need for more data for the DVCS process at large t in future or upgraded facilities.

  14. Electronic and optical properties of TaO{sub 1-x}N{sub 1+x}-based alloys

    SciTech Connect

    Al-Aqtash, Nabil; Apostol, Florin; Mei, Wai-Ning; Sabirianov, Renat F.

    2013-02-15

    TaON is considered as a potential candidate as a visible-light responsive photocatalyst. We report the results of ab initio studies of electronic structure of TaON-based alloys. Specifically, we show that the position of conduction and valence band can be modified by varying the oxygen and nitrogen concentrations in TaO{sub 1-x}N{sub 1+x}. We find that the band gap decreases monotonically with the increase of N/O ratio. The band gap energy is decreased in monoclinic TaON from near 2.3 eV to just over 1.7 eV (i.e., by 35%) when N/O ratio is increased from 3/5 to 5/3. Our calculations show that the band gap reduces in a series of experimentally fabricated alloys ZrTa{sub 3}O{sub 5}N{sub 3}{yields}TaON{yields}YTa{sub 7}O{sub 7}N{sub 8}. The band gap reduction is mostly associated with the change in the position of the valence band due to the hybridization of N 2p states, while the conduction band consisting mostly of Ta 5d-states is not sensitive to N content. The calculated optical absorption spectra show reduction in the optical band gap with increasing N/O ratio. - Graphical abstract: Band gap energy of TaO{sub 1-x}N{sub 1+x} as a function of N/O ratio. Highlights: Black-Right-Pointing-Pointer The electronic and optical properties of TaON-based alloys are studied using DFT. Black-Right-Pointing-Pointer The position of conduction and valence bands can be modified by varying N/O ratio. Black-Right-Pointing-Pointer The band gap decreases monotonically with the increase of N/O ratio in TaO{sub 1-x}N{sub 1+x}. Black-Right-Pointing-Pointer The band gap reduces in a series of fabricated alloys ZrTa{sub 3}O{sub 5}N{sub 3}{yields}TaON{yields}YTa{sub 7}O{sub 7}N{sub 8}. Black-Right-Pointing-Pointer The optical band gap decreases with the increase of N/O ratio.

  15. Infrared optical conductivity for Ni1-xPtx alloys and Ni1-xPtxSi monosilicides

    NASA Astrophysics Data System (ADS)

    Abdallah, Lina; Zollner, S.; Lavoie, C.; Ozcan, A.; Raymond, M.

    2014-03-01

    We used infrared spectroscopic ellipsometry to measure the optical constants of Ni1-xPtx alloys and Ni1-xPtxSi monosilicides in the infrared region (200-6000 wave numbers). Nickel platinum alloys (up to 30% Pt) were deposited on top of a thick layer of thermal oxide. Similar alloys were deposited on top of silicon and were annealed at 500 ° for 30 seconds to create monosilicides. The Pt composition dependence of the optical conductivity of the unreacted metal and monosilicide was investigated. We also studied the thickness dependence of Ni1-xPtx alloys. Four different fitting techniques were applied to our data using a point-by-point fit as well as an oscillator fit where we found a two carrier effect in the dielectric function of the unreacted metal. The data obtained from the IR region was combined with previous data in the visible spectrum to get more comprehensive optical constants for both unreacted metal and reacted silicide. Results indicate that optical conductivity is higher for thicker samples. Furthermore SiO2 has a strong absorption peak at 1040 wave numbers caused by bond stretching vibration. This absorption peak appears in the ellipsometric data of the thinner films and is absent in thicker ones. Supported by NSF (DMR-1104934).

  16. Biased deposition of nanocrystalline Be1-x Cux coatings

    SciTech Connect

    Jankowski, A

    2000-11-03

    Coatings of Be{sub 1-x}Cu{sub x} are prepared by magnetron sputter deposition onto spherical polymer mandrels. The application of an applied bias during deposition refines the columnar morphology of the coating and surface finish to the nanoscale. A mechanical testing technique is developed to load the thin-walled spherical capsules under uniaxial tension at constant strain to fracture. The bias-deposited material exhibits an increase in strength by a factor of three or more following a Hall-Petch type relationship with surface roughness.

  17. Planar Vacancies in Sn1-xBixTe Nanoribbons.

    PubMed

    Zou, Yi-Chao; Chen, Zhi-Gang; Kong, Fantai; Lin, Jing; Drennan, John; Cho, Kyeongjae; Wang, Zhongchang; Zou, Jin

    2016-05-24

    Vacancy engineering is a crucial approach to manipulate physical properties of semiconductors. Here, we demonstrate that planar vacancies are formed in Sn1-xBixTe nanoribbons by using Bi dopants via a facile chemical vapor deposition. Through combination of sub-angstrom-resolution imaging and density functional theory calculations, these planar vacancies are found to be associated with Bi segregations, which significantly lower their formation energies. The planar vacancies exhibit polymorphic structures with local variations in the lattice relaxation level, determined by their proximity to the nanoribbon surface. Such polymorphic planar vacancies, in conjunction with Bi dopants, trigger distinct localized electronic states, offering platforms for device applications of ternary chalcogenide materials. PMID:27116636

  18. Study of x CNFO + (1-x) PLZT magnetoelectric composites

    NASA Astrophysics Data System (ADS)

    Dipti, Singh, Sangeeta; Juneja, J. K.; Pant, R. P.; Raina, K. K.; Prakash, Chandra

    2014-04-01

    In the present paper, we are reporting the studies on structural, dielectric, ferroelectric and magnetic properties of Lanthanum (La) substituted Lead Zirconate Titanate (PZT) and Cobalt Nickel ferrite (CNFO) composites with compositional formula x(Co0.80Ni0.20Fe2O4)+(1-x)(Pb1.01625La0.0025Zr0.55Ti0.45O3) (x = 0.00,0.10). The materials were synthesized by solid state reaction route. XRD analysis confirms the presence of both ferrite and ferroelectric phases. Dielectric properties were studied as a function of frequency and temperature. Ferroelectric P-E and Magnetic M-H hysteresis loops were measured at room temperature.

  19. Magnetostructural phase transformations in Tb 1-x Mn 2

    DOE PAGES

    Zou, Junding; Paudyal, Durga; Liu, Jing; Mudryk, Yaroslav; Pecharsky, Vitalij K.; Gschneidner, Karl A.

    2015-01-16

    Magnetism and phase transformations in non-stoichiometric Tb1-xMn2 (x = 0.056, 0.039) have been studied as functions of temperature and magnetic field using magnetization, heat capacity, and X-ray powder diffraction measurements. Lowering the temperature, the compounds sequentially order ferrimagnetically and antiferromagnetically, and finally, exhibit spin reorientation transitions. Moreover, these structural distortions from room temperature cubic to low temperature rhombohedral structures occur at TN, and are accompanied by large volume changes reaching ~-1.27% and -1.42%, respectively. First principles electronic structure calculations confirm the phase transformation from the ferrimagnetic cubic structure to the antiferromagnetic rhombohedral structure in TbMn2.

  20. Magnetocapacitance effect in Gd x Mn1- x S

    NASA Astrophysics Data System (ADS)

    Aplesnin, S. S.; Sitnikov, M. N.

    2016-06-01

    The capacitance and dielectric loss tangent of Gd x Mn1- x S ( x ≤ 0.2) solid solutions have been measured at a frequency of 10 kHz without magnetic field and in a magnetic field of 8 kOe in the temperature range of 90-450 K. An increase in the permittivity and a dielectric loss maximum have been detected in the low-temperature region. It has been found that the temperature of the maximum of the imaginary part of the permittivity shifts to higher temperatures with increasing concentration. The magnetocapacitance effect has been revealed for two compositions. The dielectric loss has been described in the Debye model with "freezing" dipole moments and in the orbital-charge ordering model.

  1. Compositional Modulation in InxGa1-xN

    SciTech Connect

    Liliental-Weber, Z.; Zakharov, D.N.; Yu, K.M.; Ager III, J.W.; Walukiewicz, W.; Haller, E.E.; Lu, H.; Schaff, W.J.

    2005-07-20

    Transmission Electron Microscopy and x-ray diffraction were used to study compositional modulation in In{sub x}Ga{sub 1-x} N layers grown with compositions close to the miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200-nm-thick AlN or GaN buffer layer grown on a sapphire substrate. In the TEM imaging mode this modulation is seen as black/white fringes which can be considered as self-assembled thin quantum wells. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in x-ray diffraction in the {theta}-2{theta} coupled geometry. The modulation period was determined using both methods. Larger modulation periods were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. Compositional modulation was not observed for a sample with x = 0.34 grown on a GaN buffer layer. Modulated films tend to have large 'Stokes shifts' between their absorption edge and photoluminescence peak.

  2. Carrier diffusion in Cd1-xMnxTe

    NASA Astrophysics Data System (ADS)

    Moussu, C.; Zaquine, I.; Maruani, A.; Frey, R.

    1998-09-01

    Carrier diffusion and electron-hole recombination are shown to be considerably slowed down in Cd1-xMnxTe semimagnetic semiconductors due to the efficient trapping of electrons on manganese sites. The theoretical interpretation is based on population dynamics, charge continuity equations, and Poisson's law. A simple analytical solution of this complicated system of equations is in very good agreement with the numerical one for a large range of durations of the write pulses (from 100 ps to 1 μs). Both calculations predict a reduction of electron mobility by a factor of 6000. These theoretical predictions are confirmed by the results of an experimental study performed by using the simple grating technique: We observe the temporal evolution of the diffracted signal when a continuous read beam is used to read gratings of different wavelengths encoded in the material by interfering write laser pulses. An effective ambipolar mobility of 0.54 cm2/V s is measured, which provides a value of 3400 cm2/V s for the intrinsic mobility in Cd0.7Mn0.3Te. This low ambipolar mobility could make this efficient material potentially interesting for parallel optical processing in the microsecond range.

  3. Prospects of nanostructures Bi1-xSbx for thermoelectricity

    NASA Astrophysics Data System (ADS)

    Nikolaeva, Albina A.; Konopko, Leonid A.; Huber, Tito E.; Bodiul, Pavel P.; Popov, Ivan A.

    2012-09-01

    It has been predicted that surface states of topological insulators have large a thermopower and also ultrahigh mobilities. The authors report results of a magneto-thermoelectric investigation of single crystal Bi1-xSbx nanowires in a glass cover with diameters ranging from 90 nm to 5 μm. The wide-ranging antimony concentration enabled us to study the effect of nanowire dimensionality in the semimetal, semi-conductor and gapless regimes. Quantum size effects in Bi-2 at%Sb nanowires, which are shown in temperature dependences of resistance R(T) and thermopower α(T) for the diameters significantly higher than the critical diameter for pure Bi-wires, are observed. The thermopower in weak magnetic fields, reaches values +400 μV/K at Т=20-40 K. Power factor α2σ depending on diameter of wires, structure, temperature and magnetic field is calculated. In connection with topological insulators, we will discuss the surface effect in the thermoelectric properties that we observe.

  4. Hybrid metrology solution for 1X node technology

    NASA Astrophysics Data System (ADS)

    Vaid, Alok; Elia, Alexander; Kelling, Mark; Allgair, John; Hartig, Carsten; Ebersbach, Peter; McLellan, Erin; Sendelbach, Matthew; Saleh, Nedal; Rana, Narender; Kawada, Hiroki; Ikegami, Toru; Ikeno, Masahiko; Kawasaki, Takahiro; Bozdog, Cornel; Kim, Helen; Arnon, Elad; Koret, Roy; Turovets, Igor

    2012-03-01

    The accelerated pace of the semiconductor industry in recent years is putting a strain on existing dimensional metrology equipments (such as CDSEM, AFM, Scatterometry) to keep up with ever-increasing metrology challenges. However, a revolution appears to be forming with the recent advent of Hybrid Metrology (HM) - a practice of combining measurements from multiple equipment types in order to enable or improve measurement performance. In this paper we extend our previous work on HM to measure advanced 1X node layers - EUV and Negative Tone Develop (NTD) resist as well as 3D etch structures such as FinFETs. We study the issue of data quality and matching between toolsets involved in hybridization, and propose a unique optimization methodology to overcome these effects. We demonstrate measurement improvement for these advanced structures using HM by verifying the data with reference tools (AFM, XSEM, TEM). We also study enhanced OCD models for litho structures by modeling Line-edge roughness (LER) and validate its impact on profile accuracy. Finally, we investigate hybrid calibration of CDSEM to measure in-die resist line height by Pattern Top Roughness (PTR) methodology.

  5. Dirac-fermionic dark matter in U(1)X models

    NASA Astrophysics Data System (ADS)

    Alves, Alexandre; Berlin, Asher; Profumo, Stefano; Queiroz, Farinaldo S.

    2015-10-01

    We study a number of U(1)X models featuring a Dirac fermion dark matter particle. We perform a comprehensive analysis which includes the study of corrections to the muon magnetic moment, dilepton searches with LHC data, as well as direct and indirect dark matter detection constraints. We consider four different coupling structures, namely U(1) B-L , U(1) d-u , U(1)universal, and U{(1)}_{10+overline{5}} , all motivated by compelling extensions to the standard model. We outline the viable and excluded regions of parameter space using a large set of probes. Our key findings are that (i) the combination of direct detection and collider constraints rule out dark matter particle masses lighter than ˜ 1 TeV, unless rather suppressed Z '-fermion couplings exist, and that (ii) for several of the models under consideration, collider constraints rule out Z ' masses up to ˜ 3 TeV. Lastly, we show that we can accommodate the recent Diboson excess reported by ATLAS collaboration within the U(1) d- u model.

  6. Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni{sub 1-x}Mn{sub 1+x}Sb

    SciTech Connect

    Ekholm, M.; Larsson, P.; Alling, B.; Helmersson, U.; Abrikosov, I. A.

    2010-11-15

    We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric Ni{sub 1-x}Mn{sub 1+x}Sb in the half-Heusler crystal phase. Our work is motivated by the need for strategies to engineer the magnetism of potentially half-metallic materials, such as NiMnSb, for improved performance at elevated temperatures. By means of ab initio calculations we investigate Ni{sub 1-x}Mn{sub 1+x}Sb over the whole composition range 0{<=}x{<=}1 of Ni replacing Mn and show that at relevant temperatures, the half-Heusler phase should be thermodynamically stable up to at least x=0.20 with respect to the competing C38 structure of Mn{sub 2}Sb. Furthermore we find that half-Heusler Ni{sub 1-x}Mn{sub 1+x}Sb retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional Mn{sub Ni} atoms display magnetic exchange interactions an order of magnitude larger than the Ni-Mn interaction in NiMnSb. We also demonstrate experimentally that the alloys indeed can be created by synthesizing off-stoichiometric Ni{sub 1-x}Mn{sub 1+x}Sb films on MgO substrates by means of magnetron sputtering.

  7. BRIEF COMMUNICATIONS: Single crystals of ZnSe1-xTex, Zn1-xCdxSe, and ZnxCd1-xS solid solutions for electron-beam-pumped lasers

    NASA Astrophysics Data System (ADS)

    Akhekyan, A. M.; Kozlovskiĭ, V. I.; Korostelin, Yurii V.; Nasibov, A. S.; Popov, Yurii M.; Shapkin, P. V.

    1985-05-01

    Single-crystal ingots of ZnSe1-xTex, (0 <= x <= 0.03), Zn1-xCdxSe (0 <= x <= 0.15), and ZnxCd1-xS (0 <= x <= 0.35) with diameters up to 50 mm and height up to 20 mm were prepared from the vapor phase. Investigations were made of the cathodoluminescence emitted by these crystals and of the characteristics of the lasers made from them and subjected to longitudinal pumping with an electron beam. In contrast to the two other systems, single crystals of ZnSe1-xTex were unsuitable for semiconductor lasers emitting in the dark blue range because deep levels appeared in the band gap at low Te concentrations.

  8. Evolution of Structure and Photoluminescence by Cation Cosubstitution in Eu(2+)-Doped (Ca(1-x)Li(x))(Al(1-x)Si(1+x))N3 Solid Solutions.

    PubMed

    Wang, Ting; Xiang, Qianchuan; Xia, Zhiguo; Chen, Jun; Liu, Quanlin

    2016-03-21

    Red-emitting nitride phosphors excited with blue light have great potential for the fabrication of warm white light-emitting diodes (WLEDs). Chemical composition and structural modification are generally adopted to optimize the photoluminescence behaviors of the targeted phosphors. Herein, on the basis of the famous CaAlSiN3 phosphors, Eu(2+)-doped (Ca(1-x)Li(x))(Al(1-x)Si(1+x))N3 solid solutions via the cations' cosubstitution of (CaAl)(5+) pair by (LiSi)(5+) pair are successfully synthesized by a solid state reaction, and the lattice parameters show a linear decrease with chemical compositions suggesting the formation of the isostructural phase relationship. Four types of coordinated structure models, corresponding to different coordination environments of Eu(2+), are proposed over the course of structural evolution, which induces different structural rigidity and stability, and then they are responsible for three-stage changes of emission spectra of Eu(2+) in (Ca(1-x)Li(x))(Al(1-x)Si(1+x))N3 solid solution. PMID:26930108

  9. Non-magnetic compensation in ferromagnetic Ga1-xMnxAs and Ga1-xMnxP synthesized by ion implantation and pulsed-laser melting

    SciTech Connect

    Scarpulla, M.A.; Stone, P.R.; Sharp, I.D.; Haller, E.E.; Dubon, O.D.; Beeman, J.W.; Yu, K.M.

    2008-02-05

    The electronic and magnetic effects of intentional compensation with non-magnetic donors are investigated in the ferromagnetic semiconductors Ga1-xMnxAs and Ga1-xMnxP synthesized using ion implantation and pulsed-laser melting (II-PLM). It is demonstrated that compensation with non-magnetic donors and MnI have similarqualitative effects on materials properties. With compensation TC decreases, resistivity increases, and stronger magnetoresistance and anomalous Hall effect attributed to skew scattering are observed. Ga1-xMnxAs can be controllably compensated with Te through a metal-insulator transition through which the magnetic and electrical properties vary continuously. The resistivity of insulating Ga1-xMnxAs:Te can be described by thermal activation to the mobility edge and simply-activated hopping transport. Ga1-xMnxP doped with S is insulating at all compositions but shows decreasing TC with compensation. The existence of a ferromagnetic insulating state in Ga1-xMnxAs:Te and Ga1-xMnxP:S having TCs of the same order as the uncompensated materials demonstrates that localized holes are effective at mediating ferromagnetism in ferromagnetic semiconductors through the percolation of ferromagnetic 'puddles' which at low temperatures.

  10. Comparison of thermodynamic properties of cubic Cr1-xAlxN and Ti1-xAlxN from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Alling, B.; Marten, T.; Abrikosov, I. A.; Karimi, A.

    2007-08-01

    In order to investigate the stability of the cubic phase of Cr1-xAlxN at high AlN content, first principles calculations of magnetic properties, lattice parameters, electronic structure, and mixing enthalpies of the system were performed. The mixing enthalpy was calculated on a fine concentration mesh to make possible the accurate determination of its second concentration derivative. The results are compared to calculations performed for the related compound Ti1-xAlxN and with experiments. The mixing enthalpy is discussed in the context of isostructural spinodal decomposition. It is shown that the magnetism is the key to understand the difference between the Cr- and Ti-containing systems. Cr1-xAlxN turns out to be more stable against spinodal decomposition than Ti1-xAlxN, especially for AlN-rich samples which are of interest in cutting tools applications.

  11. Preparation, characterization and performance of Ti1-xAlxN/Ag/Ti1-xAlxN low-emissivity films

    NASA Astrophysics Data System (ADS)

    Huang, Jiamu; Xiang, Chengjie; Li, Shaohui; Zhao, Xiaoli; He, Guoqing

    2014-02-01

    In this paper, Ti1-xAlxN/Ag/Ti1-xAlxN sandwich structure low-emissivity (Low-E) films were prepared by radio frequency reactive magnetron sputtering (RF-MS) on glass substrates. The morphology, chemical state and performance of the film system were characterized by FIB-SEM, XPS, FT-IR, UV-vis spectrophotometer and electrochemical workstation. The results showed that the multilayer films exhibit an excellent visible light transmittance (T% > 85% at λ = 550 nm) and remarkable high infrared reflectivity (R% > 96% in the 2.5 ˜ 25 μm range). The Ti1-xAlxN dielectric-layer could not only increase transmittance in the visible light range of Ag film based on an anti-reflection effect, but also modify the intrinsic color of Ag film from sapphire to total color neutrality. In addition, Ti1-xAlxN layer could enhance the chemical stability of the Ag film. In principle, the approach to obtain Ti1-xAlxN/Ag/Ti1-xAlxN sandwich structure in our work could provide an alternative way to fabricate outstanding Low-E films.

  12. Modelling the thermal conductivity of (UxTh1-x)O2 and (UxPu1-x)O2

    DOE PAGES

    Cooper, M. W. D.; Middleburgh, S. C.; Grimes, R. W.

    2015-07-15

    The degradation of thermal conductivity due to the non-uniform cation lattice of (UxTh1-x)O2 and (UxPu1-x)O2 solid solutions has been investigated by molecular dynamics, using the non-equilibrium method, from 300 to 2000 K. Degradation of thermal conductivity is predicted in (UxTh1-x)O2 and (UxPu1-x)O2 as compositions deviate from the pure end members: UO2, PuO2 and ThO2. The reduction in thermal conductivity is most apparent at low temperatures where phonon-defect scattering dominates over phonon-phonon interactions. The effect is greater for (UxTh1-x)O2 than UxPu1-x)O2 due to the greater mismatch in cation size. Parameters for an analytical expressions have been developed that describe the predictedmore » thermal conductivities over the full temperature and compositional ranges. Finally, these expressions may be used in higher level fuel performance codes.« less

  13. Infrared Detectors Containing Stacked Si(1-x)Ge(x)/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, Jin S.; Lin, True-Lon; Jones, Eric; Del Castillo, Hector; Gunapala, Sarath

    1996-01-01

    Long-wavelength-infrared detectors containing multiple layers of high-quality crystalline p(+) Si(1-x)Ge(x) alternating with layers of Si undergoing development. Each detector comprises stack of Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) photodetectors. In comparison with older HIP detectors containing single Si(1-x)Ge(x)/Si heterojunctions, developmental detectors feature greater quantum efficiencies and stronger photoresponses.

  14. Photoluminescence properties of MgxZn1-xSe single crystals

    NASA Astrophysics Data System (ADS)

    Park, Sang-An; Song, Ho-Jun; Kim, Wha-Tek; Kim, Hyung-Gon; Jin, Moon-Seog; Kim, Chang-Dae; Yoon, Chang-Sun

    1998-03-01

    MgxZn1-xSe single crystals were grown by the closed tube sublimation method. The MgxZn1-xSe single crystals crystallized into zincblende and wurtzite structures in the composition ranges of x=0.0-0.1 and x=0.2-0.6, respectively. Blue and violet emissions with LO phonon replica and self-activated emissions in the MgxZn1-xSe single crystals were observed at 10 K.

  15. FP-LAPW investigations of SrS1-xSex, SrS1-xTex and SrSe1-xTex ternary alloys

    NASA Astrophysics Data System (ADS)

    Labidi, S.; Meradji, H.; Ghemid, S.; Labidi, M.; El Haj Hassan, F.

    2008-11-01

    The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT) was applied to study the effect of composition on the structural, electronic, optical and thermodynamic properties of SrS1-xSex, SrS1-xTex and SrSe1-xTex ternary alloys. For exchange-correlation energy and corresponding potential, the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE) and Engel-Vosko (EVGGA) have been used. Deviation of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the three alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The refractive index and optical dielectric constant for the alloys of interest are calculated by using different models. In addition the thermodynamic stability of the alloys was investigated by calculating the critical temperatures of alloys.

  16. [Preparation of MgxZn1-xO/Au/MgxZn1-xO multilayer transparent conductive film and studies of its photoelectric properties].

    PubMed

    Lü, Shan-Shan; Fang, Xuan; Wang, Jia-Qi; Fang, Fang; Zhao, Hai-Feng; Chu, Xue-Ying; Li, Jin-Hua; Fang, Dan; Tang, Ji-Long; Wei, Zhi-Peng; Ma, Xiao-hui; Wang, Xiao-Hua; Pu, Shuang-Shuang; Xu, Li

    2014-09-01

    In the present paper, MgxZn1-xO and MgxZn1-xO/Au/MgxZn1-xO multilayer structures of transparent conductive film were prepared by the simple operation of sol-gel and RF magnetron sputtering method on quartz substrate respectively and then they were annealed. The surface, electrical, crystal and optical properties of the films at different annealing temperature were determined by UV-Vis spectrophotometer, X-ray diffraction, photoluminescence and Hall effect, respectively. The influence of annealing temperature on the films was also investigated. The testing results indicated that the films with good c-axis orientation presented hexagonal wurtzite structure. With increasing Mg components, the optical band gap of ZnO thin film increased gradually. There was an obvious blue shift phenomenon in PL spectrum and absorption spectrum line. But the electrical properties of the films declined. In MgxZn1-xO/Au/MgxZn1-xO multilayer structure of thin film samples, the existence of Au interlining led to the poor optical properties of thin film, and the light transmittance in the ultraviolet region was 60%. Compared with MgxZn1-xO film, the electrical properties of MgxZn1-xO/Au/MgxZn1-xO multilayer structure of transparent conductive film were improved, the resistivity and migration rate were significantly increased. In addition, high temperature annealing treatment could effectively improve the crystal quality of thin film and further improve the electrical characteristics of the samples. After the annealing treatment at 500 °C, migration rate of the film reached to 40.9 cm2 · 1 Vs(-1) while the resistivity was 0.0057 Ω · cm. Due to the rising of temperature, the crystal size increased from 25.1 to 32.4 nm to reduce the mobility of the film. Therefore, MgxZn1-xO/Au/MgxZn1-xO multilayer structure of transparent conductive film played an important role in promoting the ZnO transparent conductive film application in deep ultraviolet devices.

  17. [Preparation of MgxZn1-xO/Au/MgxZn1-xO multilayer transparent conductive film and studies of its photoelectric properties].

    PubMed

    Lü, Shan-Shan; Fang, Xuan; Wang, Jia-Qi; Fang, Fang; Zhao, Hai-Feng; Chu, Xue-Ying; Li, Jin-Hua; Fang, Dan; Tang, Ji-Long; Wei, Zhi-Peng; Ma, Xiao-hui; Wang, Xiao-Hua; Pu, Shuang-Shuang; Xu, Li

    2014-09-01

    In the present paper, MgxZn1-xO and MgxZn1-xO/Au/MgxZn1-xO multilayer structures of transparent conductive film were prepared by the simple operation of sol-gel and RF magnetron sputtering method on quartz substrate respectively and then they were annealed. The surface, electrical, crystal and optical properties of the films at different annealing temperature were determined by UV-Vis spectrophotometer, X-ray diffraction, photoluminescence and Hall effect, respectively. The influence of annealing temperature on the films was also investigated. The testing results indicated that the films with good c-axis orientation presented hexagonal wurtzite structure. With increasing Mg components, the optical band gap of ZnO thin film increased gradually. There was an obvious blue shift phenomenon in PL spectrum and absorption spectrum line. But the electrical properties of the films declined. In MgxZn1-xO/Au/MgxZn1-xO multilayer structure of thin film samples, the existence of Au interlining led to the poor optical properties of thin film, and the light transmittance in the ultraviolet region was 60%. Compared with MgxZn1-xO film, the electrical properties of MgxZn1-xO/Au/MgxZn1-xO multilayer structure of transparent conductive film were improved, the resistivity and migration rate were significantly increased. In addition, high temperature annealing treatment could effectively improve the crystal quality of thin film and further improve the electrical characteristics of the samples. After the annealing treatment at 500 °C, migration rate of the film reached to 40.9 cm2 · 1 Vs(-1) while the resistivity was 0.0057 Ω · cm. Due to the rising of temperature, the crystal size increased from 25.1 to 32.4 nm to reduce the mobility of the film. Therefore, MgxZn1-xO/Au/MgxZn1-xO multilayer structure of transparent conductive film played an important role in promoting the ZnO transparent conductive film application in deep ultraviolet devices. PMID:25532325

  18. Measurements of Local Strain Variation in Si(1-x)Ge(x)/Si Heterostructures

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.; Manion, S. J.; Milliken, S. J.; Pike, W. T.; Fathauer, R. W.

    1995-01-01

    The energy splitting of the conduction-band minimum of Si(1-x), Ge(x), due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si(1-x), Ge(x) structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si(1-x), Ge(x), however, heterogeneity in the strain of the Si(1-x), Ge(x) layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si(1-x)Ge(x) surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.

  19. Event-specific qualitative and quantitative PCR detection methods for transgenic rapeseed hybrids MS1xRF1 and MS1xRF2.

    PubMed

    Wu, Yuhua; Wu, Gang; Xiao, Ling; Lu, Changming

    2007-10-17

    Except for the events RT73, MS8, RF3, and T45, event-specific detection methods for most commercialized genetically modified (GM) rapeseed varieties have not been established, and as a result, the enforcement of genetically modified organism labeling policies has been hindered. The genetically modified rapeseeds, MS1xRF1 and MS1xRF2, are 2 of 11 approved GM-rapeseed varieties for commercialization. In this study, the right border junction fragments between the gene construct and the rapeseed genome of events RF1, RF2, and MS1 were isolated using the commercially available GenomeWalker technology. Homology analysis indicated that the gene construct of RF1 integrated upstream of the nuclease gene, and that of the RF2 and MS1 inserted into the exon region of a gene encoding for an unknown protein. The event-specific primer pairs and corresponding probes were designed on the basis of the revealed right border junction fragments. Then, we successfully developed the identification and quantification methods for the gene-stacked hybrids MS1xRF1 and MS1xRF2 using those primers and probes. The relative limit of detection in the qualitative polymerase chain reaction (PCR) was 0.013% for the RF2 and MS1 assays using 100 ng of rapeseed DNA per reaction and 0.13% for the RF1 assay. The absolute limit of detection in the quantitative PCR was approximately one to two initial copies for each of the three event-specific assays. The evaluation of the real-time PCR assays revealed that the qualitative and quantitative methods developed by focusing on the gene-stacked hybrids MS1xRF1 and MS1xRF2 were highly specific, sensitive, and suitable for samples with a low quantity of DNA.

  20. GaSe1-xSx and GaSe1-xTex thick crystals for broadband terahertz pulses generation

    NASA Astrophysics Data System (ADS)

    Nazarov, M. M.; Yu. Sarkisov, S.; Shkurinov, A. P.; Tolbanov, O. P.

    2011-08-01

    We demonstrate the possibility of broadband THz pulse generation in mixed GaSe1-xSx and GaSe1-xTex crystals. The ordinary and extraordinary refractive indices of the crystals have been measured by the terahertz time-domain spectroscopy method, those values strongly influence the efficiency of THz generation process. The high birefringence and transparency of pure GaSe and mixed crystals allow optical rectification of femtosecond laser pulses in the several millimeters thick crystal using the еее interaction process (with two pumping waves and generated THz wave all having extraordinary polarization in the crystal).

  1. Competing magnetic ground states in the A -site layer-ordered manganite La1-xBa1+xMn2O6

    NASA Astrophysics Data System (ADS)

    Chmaissem, O.; Brown, D. E.; Ren, Y.; Kolesnik, S.; Mais, J.; Dabrowski, B.

    2010-01-01

    Using neutron and x-ray diffraction, we report the discovery of competing ground states near a multicritical point in A -site layer-ordered La1-xBa1+xMn2O6 materials. We demonstrate the dual effects of deliberate disorder on the system’s stability, the freezing of the competing states, and the drastic reduction in magnetic fields required for the suppression of charge- and orbital-ordered phases. Our work suggests that quenched disorder is not the primary reason for phase separation and magnetoresistance and that increased doping leads to electronic phase separation.

  2. Hydrogen-Substituted Superconductors SmFeAsO(1-x)Hx Misidentified As Oxygen-Deficient SmFeAsO(1-x).

    PubMed

    Muraba, Yoshinori; Iimura, Soshi; Matsuishi, Satoru; Hosono, Hideo

    2015-12-01

    We investigated the preferred electron dopants at the oxygen sites of 1111-type SmFeAsO by changing the atmospheres around the precursor with the composition of Sm:Fe:As:O = 1:1:1:1 - x in high-pressure synthesis. Under H2O and H2 atmospheres, hydrogens derived from H2O or H2 molecules were introduced into the oxygen sites as a hydride ion, and SmFeAsO(1-x)Hx was obtained. However, when the H2O and H2 sources were removed from the synthetic process, nearly stoichiometric SmFeAsO was obtained and the maximum amount of oxygen vacancies introduced remained x = 0.05(4). Density functional theory calculations indicated that substitution of hydrogen in the form of H(-) is more stable than the formation of an oxygen vacancy at the oxygen site of SmFeAsO. These results strongly imply that oxygen-deficient SmFeAsO(1-x) reported previously is SmFeAsO(1-x)Hx with hydride ion incorporated unintentionally during high-pressure synthesis. PMID:26587763

  3. Optical properties of amorphous Ge1- x Se x and Ge1- x- y Se x As y thin films — optical gap bowing and phonon modes

    NASA Astrophysics Data System (ADS)

    Lee, Hosuk; So, Hyeon Seob; Lee, Hosun; Shin, Hae-Young; Yoon, Seokhyun; Ahn, Hyung-Woo; Kim, Su-Dong; Lee, Suyoun; Jeong, Doo-Seok; Cheong, Byung-ki

    2014-06-01

    We investigated the optical properties of Ge1- x Se x and Ge1- x- y Se x As y amorphous films by using spectroscopic ellipsometry and Raman spectroscopy. The dielectric functions and absorption coefficients ( α) of the amorphous films were determined from the measured ellipsometric angles (Ψ,Δ). We obtained the optical gap energies and the Urbach energies from the absorption coefficients and found a strong bowing effect in the optical gap energy of Ge1- x- y Se x As y , where the endpoint binaries were Ge0.50Se0.50 and Ge0.31As0.69. Based on the correlation between the optical gap energies and the Urbach energies, we attributed the large bowing parameter to electronic disorder. Using Raman spectroscopy, we measured the phonon modes and discussed the composition dependence of the phonon peak frequencies and lineshapes in terms of structural units. Based on the composition dependence of the phonons in Ge1- x- y Se x As y , we identified the phonon modes of Ge0.31As0.69. A resonant Raman phenomenon was observed in Ge0.40Se0.60 at a laser excitation of 514 nm (2.41 eV). We verified that this laser energy corresponded to the transition energy of Ge0.40Se0.60 by using the second derivative of the dielectric function of Ge0.40Se0.60.

  4. Preparation and transport properties of single-phase TlBa1+xLa1-xCuO5 (0<=x<=0.5)

    NASA Astrophysics Data System (ADS)

    Manako, Takashi; Kubo, Yoshimi

    1994-09-01

    The preparation of polycrystalline TlBa1+xLa1-xCuO5 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) is investigated using Tl-free precursors. Single-phase samples are obtained except for x=0.5, in which a small amount of impurity phase is detected. Compositional and structural analyses confirm good homogeneity of the Ba and La distribution in each sample. In this system, hole-carrier doping increases with increasing x. The sample with x=0, TlBaLaCuO5, shows semiconductive resistivity (ρ) and a T-independent Hall coefficient (RH), indicating two-dimensional (2D) variable range hopping. As x increases, the resistivity becomes metallic and superconductivity is observed for 0.1<=x<=0.4, with a maximum Tc value of 45 K at x=0.2. For x=0.5, the sample is metallic but not superconducting. In all metallic samples (0.1<=x<=0.5), RH has a broad maximum at about 100 K, as seen in most high-Tc cuprates. The inverse Hall mobility, μ-1H≡ρ/RH, roughly obeys a T2 dependence regardless of the Tc value, which is widely observed in other oxide superconductors.

  5. Superconducting behaviors in (Y1 - xLax)Ba2Cu3Oy (0 <= x <= 1)

    NASA Astrophysics Data System (ADS)

    Okada, M.; Matsuoka, D.; Zou, H.; Homma, M.

    1988-11-01

    The superconducting behavior of (Y1-xLax)Ba2Cu3Oy compounds for 0≤x≤1 was studied. It was found that Tc decreased with increasing La content. (Y1-xLax)Ba2Cu3Oy for 0≤x≤0.4, fired at 1050 °C in air, shows onset temperatures above 90 K. Annealing (Y1-xLax)Ba2Cu3Oy at 300 °C in O2 enhanced the onset temperature above 70 K for all studied compositions (x=0-1), and altered the crystal structure from tetragonal to orthorhombic.

  6. a Study of Photoconductivity of Neutron Doped Si1-xGex-ALLOYS

    NASA Astrophysics Data System (ADS)

    Yevseyev, V.; Chekanov, V.

    The research results of photoelectric, optical and recombination properties of neutron transmutation doped (NTD) semiconductor solid alloys Si1-xGex (x = 0.008-0.112) are presented in spectral range 0.8-10.6 μm. It is shown that these properties of NTD Si1-xGex are determined by creation of transmutation impurities of Se and Ga as well as by variation of Ge content and compensation. The theoretical and applied aspects of the NTD Si1-xGex have been also considered.

  7. Origin of the X1X1X2X2/X1X2Y sex chromosome system of Harttia punctata (Siluriformes, Loricariidae) inferred from chromosome painting and FISH with ribosomal DNA markers.

    PubMed

    Blanco, Daniel Rodrigues; Vicari, Marcelo Ricardo; Lui, Roberto Laridondo; Artoni, Roberto Ferreira; de Almeida, Mara Cristina; Traldi, Josiane Baccarin; Margarido, Vladimir Pavan; Moreira-Filho, Orlando

    2014-04-01

    Harttia is a genus in the subfamily Loricariinae that accommodates fishes popularly known as armored catfishes. They show extensive karyotypic diversity regarding interspecific numerical/structural variation of the karyotypes, with the presence of the XX/XY1Y2 multiple sex chromosome system, as found in H. carvalhoi. In this context, this study aimed to characterize Harttia punctata chromosomally, for the first time, and to infer the rearrangements that originated the X1X1X2X2/X1X2Y multiple sex chromosome system present in this species. The data obtained in this study, with classical (Giemsa, C-banding and AgNORs) and molecular methodologies (fluorescence in situ hybridization) and chromosome microdissection, indicated that a translocation between distinct acrocentric chromosomes bearing rRNA genes, accompanied by deletions in both chromosomes, might have originated the neo-Y chromosome in this species. The data also suggest that the multiple sex chromosome systems present in H. carvalhoi and H. punctata had an independent origin, evidencing the recurrence of chromosome alterations in species from this genus.

  8. Chromosomal distribution of two multigene families and the unusual occurrence of an X1X1X2X2/X1X2Y sex chromosome system in the dolphinfish (Coryphaenidae): an evolutionary perspective.

    PubMed

    Soares, R X; Bertollo, L A C; Cioffi, M B; Costa, G W W F; F Molina, W

    2014-01-01

    Dolphinfishes (Coryphaenidae) are pelagic predators distributed throughout all tropical and subtropical oceans and are very important for commercial, traditional, and sport fishing. This small family contains the Coryphaena hippurus and Coryphaena equiselis species whose chromosomal aspects remain unknown, despite recent advances in cytogenetic data assimilation for Perciformes. In this study, both species were cytogenetically analyzed using different staining techniques (C-, Ag-, and CMA3 banding) and fluorescence in situ hybridization, to detect 18S rDNA and 5S rDNA. C. hippurus females exhibit 2n = 48 chromosomes, with 2m+4sm+42a (NF = 54). In C. equiselis, where both sexes could be analyzed, females displayed 2n = 48 chromosomes (2m+6sm+40a) and males exhibited 2n = 47 chromosomes (3m+6sm+38a) (NF = 56), indicating the presence of X1X1X2X2/X1X2Y multiple sex chromosomes. Sex-chromosome systems are rare in Perciformes, with this study demonstrating the first occurrence in a marine pelagic species. It remains unknown as to whether this system extends to other populations; however, these data are important with respect to evolutionary, phylogenetic, and speciation issues, as well as for elucidating the genesis of this unique sex system. PMID:24782001

  9. Noise Characteristcs of Cd1-xZnxS Films Deposited From Solution

    NASA Astrophysics Data System (ADS)

    Guseinov, Emil; Jafarov, Maarif; Nasibov, Ilgar

    1997-12-01

    The study of Cd1-xZnxS (0≤ x ≤ 0.6) films obtained by method of chemical deposition from aqueous solution on glass ceramic substrates via interaction of thiourea with cadmium and zinc salts. In Cd1-xZnxS films just subsequent to their deposition 1/f-type noise is clearly revealed and is attributed to collective barries. In the frequency range above a few kilohertz the generation-recombination noises predominate In Cd1-xZnxS films after heat treatment in air at 500°C, generation-recombination noise dominates at relative frequencies. The noise level of Cd1-xZnxS films (0≤ x≤ 0,2) after heat treatment shows that they are useful as threshold radiation detectors (Pthr=10-12W).

  10. Numerical simulation of impact ionization in Ge/AlxGa1-xAs avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Chia, C. K.

    2010-08-01

    Impact ionization in Ge/AlxGa1-xAs p-i-n heterostructures has been studied using the Monte Carlo technique. The thin (<300 nm) Ge/AlxGa1-xAs single heterojunction structure was found to exhibit large hole (β) to electron (α) ionization coefficient ratio, owing to a higher β in the Ge layer and a lower α in the AlxGa1-xAs layer, together with the dead space effects. The Ge/AlxGa1-xAs avalanche photodiodes are attractive for applications where a wide wavelength detection range is required for compatibility with multiple sources such as in the emerging active optical cable and optical interconnect applications, as well as in the established optical fiber telecommunication systems.

  11. Nanocrystal growth of single-phase Si1-xGex alloys

    NASA Astrophysics Data System (ADS)

    Giang, Nguyen Truong; Cong, Le Thanh; Dung, Nguyen Duc; Quang, Tran Van; Ha, Ngo Ngoc

    2016-06-01

    We present the formation of single-phase Si1-xGex (x=0.2, 0.4, 0.6, and 0.8) alloy nanocrystals dispersed in a SiO2 matrix. The studied samples were prepared by co-sputtering with excess Si1-xGex in SiO2 of approximately 33 at%. Upon heat treatment, crystallization of Si1-xGex alloys was examined by using X-ray diffraction and high-resolution transmission electron microscopy measurements. Single structure of face-centered cubic nanocrystals in a space group Fd-3m was concluded. The average nanocrystal size (from 2 nm to 10 nm) and the lattice constant a of the single-phase Si1-xGex nanocrystals were found to increase with the Ge composition parameter x. Density functional theory-generalized gradient approximation calculation showed the replacement of Ge into the Si sites and vice versa.

  12. Window type: 2x3 fixed multipaned steel window flanked by 1x3 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Window type: 2x3 fixed multipaned steel window flanked by 1x3 multipaned steel casements. Concrete sill and spandrel also illustrated. Building 43, facing east - Harbor Hills Housing Project, 26607 Western Avenue, Lomita, Los Angeles County, CA

  13. Diode p-i-n-STRUCTURES Based on Neutron Doped Si1-xGex-ALLOYS

    NASA Astrophysics Data System (ADS)

    Chekanov, V.; Yevseyev, V.; Kuryatkov, V.; Prokofyeva, T.

    Photoelectric properties of neutron transmutation doped (NTD) Si1-xGex solid solutions (alloy) with variable composition are presented. It is shown that the application of NTD method to Si1-xGex solid solutions with gradient composition (x = 0-2 at.%) along an ingot allows to receive p-i-n-structures with typical diode characteristics. We studied electrical and photoelectrical properties of that structure. Deep level transient spectroscopy of p-i-n diode has revealed the energy levels in the forbidden zone of Si1-xGex, connected with transmutation Se impurity. It is established that p-i-n-structures possess high spectral sensitivity with a maximum at hν = 1.2-1.5 eV (300 K). Possible application of Si1-xGex-alloys in development of uncooled photodiodes with large effective area was considered.

  14. Engineering Zn1-xCdxS/CdS Heterostructures with Enhanced Photocatalytic Activity.

    PubMed

    Li, Kui; Chen, Rong; Li, Shun-Li; Xie, Shuai-Lei; Dong, Long-Zhang; Kang, Zhen-Hui; Bao, Jian-Chun; Lan, Ya-Qian

    2016-06-15

    Various porous Zn1-xCdxS/CdS heteorostructures were achieved via in situ synthesis method with organic amines as the templates. Because of the larger radius of Cd(2+) than that of Zn(2+), CdS quantum dots are formed and distributed uniformly in the network of Zn1-xCdxS. The Zn1-xCdxS/CdS heterostructure with small Cd content (10 at%) derived from ethylenediamine shows very high H2-evolution rate of 667.5 μmol/h per 5 mg photocatalyst under visible light (λ ≥ 420 nm) with an apparent quantum efficiency of 50.1% per 5 mg at 420 nm. Moreover, this Zn1-xCdxS/CdS heterostructure photocatalyst also shows an excellent photocatalytic stability over 100 h. PMID:27172231

  15. MOVPE of Al xGa 1- xAs alloys above 850° C

    NASA Astrophysics Data System (ADS)

    Basmaji, P.; Leycuras, A.; Leymarie, J.; Gibart, P.; Gauthier, D.; Portal, J. C.; Gil, B.

    1988-12-01

    Undoped and Sn-doped Al xGa 1- xAs epitaxial layers were grown at high temperatures (850-950° C) by MOVPE. Undoped samples reveal better quality optical properties than alloys grown at the usual temperatures. This is shown by low temperature photoluminescence and reflectivity measurements. Highly doped Sn-Al xGa 1- xAs samples do not show typical features related to DX centers.

  16. Euler-type transformations for the generalized hypergeometric function r+2 F r+1( x)

    NASA Astrophysics Data System (ADS)

    Miller, A. R.; Paris, R. B.

    2011-02-01

    We provide generalizations of two of Euler's classical transformation formulas for the Gauss hypergeometric function extended to the case of the generalized hypergeometric function r+2 F r+1( x) when there are additional numeratorial and denominatorial parameters differing by unity. The method employed to deduce the latter is also implemented to obtain a Kummer-type transformation formula for r+1 F r+1 ( x) that was recently derived in a different way.

  17. Superlattice of Fe(x)Ge(1-x) nanodots and nanolayers for spintronics application.

    PubMed

    Nie, Tianxiao; Kou, Xufeng; Tang, Jianshi; Fan, Yabin; Lang, Murong; Chang, Li-Te; Chu, Chia-Pu; He, Liang; Lee, Sheng-Wei; Xiu, Faxian; Zou, Jin; Wang, Kang L

    2014-12-19

    Fe(x)Ge(1-x) superlattices with two types of nanostructures, i.e. nanodots and nanolayers, were successfully fabricated using low-temperature molecular beam epitaxy. Transmission electron microscopy (TEM) characterization clearly shows that both the Fe(x)Ge(1-x) nanodots and nanolayers exhibit a lattice-coherent structure with the surrounding Ge matrix without any metallic precipitations or secondary phases. The magnetic measurement reveals the nature of superparamagnetism in Fe(x)Ge(1-x) nanodots, while showing the absence of superparamagnetism in Fe(x)Ge(1-x) nanolayers. Magnetotransport measurements show distinct magnetoresistance (MR) behavior, i.e. a negative to positive MR transition in Fe(x)Ge(1-x) nanodots and only positive MR in nanolayers, which could be due to a competition between the orbital MR and spin-dependent scatterings. Our results open a new growth strategy for engineering Fe(x)Ge(1-x) nanostructures to facilitate the development of Ge-based spintronics and magnetoelectronics devices.

  18. The structure and band gap design of high Si doping level Ag1-xGa1-xSixSe2 (x=1/2)

    NASA Astrophysics Data System (ADS)

    Zhang, Shiyan; Mei, Dajiang; Du, Xin; Lin, Zheshuai; Zhong, Junbo; Wu, Yuandong; Xu, Jingli

    2016-06-01

    Ag1-xGa1-xSixSe2 solutions with high Si doping level (x=1/2) are considered and new compound AgGaSiSe4 has been synthesized. It crystallizes in space group Aea2 and possesses very long axis of a=63.06(1)Å. The three-dimensional framework in AgGaSiSe4 is composed of AgSe3 trigonal planar units, AgSe4 tetrahedra and MSe4(M=Si, Ga) tetrahedra. AgGaSiSe4 is a congruently melting compound with the melt temperature of 759 °C. The diffuse reflectance measurements reveal the band gap of 2.63 eV in AgGaSiSe4 and the value is 0.33 eV larger than that of Ag3Ga3SiSe8 (2.30 eV).

  19. Drastic change in density of states upon martensitic phase transition for metamagnetic shape memory alloy Ni2Mn1+xIn1-x

    NASA Astrophysics Data System (ADS)

    Zhu, Siyuan; Ye, Mao; Shirai, Kaito; Taniguchi, Masaki; Ueda, Shigenori; Miura, Yoshio; Shirai, Masafumi; Yamauchi Umetsu, Rie; Kainuma, Ryosuke; Kanomata, Takeshi; Kimura, Akio

    2015-09-01

    We have unravelled the electronic structure of a class of metamagnetic shape memory alloy Ni2Mn1+xIn1-x by combining bulk-sensitive hard x-ray photoelectron spectroscopy and first-principles density-functional calculations. A sharp drop in the Ni 3d {{e}\\text{g}} density of states forming a pseudogap in the martensitic phase transition (MPT) for x   =   0.36 has been observed near the Fermi level. As a feature of MPT, hysteretic behaviour of this drop has been confirmed in both cooling and warming. This pseudogap is responsible for the giant negative magnetoresistance. The experimental result is well reproduced by the first principle calculation. We have also clarified theoretically that the MPT is linked to a competition of ferromagnetic and anti-ferromagnetic coupling between ordinary and anti-site Mn atoms.

  20. Crystal structure study of dielectric oxynitride perovskites La1-xSrxTiO2+xN1-x (x=0, 0.2)

    NASA Astrophysics Data System (ADS)

    Habu, Daiki; Masubuchi, Yuji; Torii, Shuki; Kamiyama, Takashi; Kikkawa, Shinichi

    2016-05-01

    As is the case with SrTaO2N, both cis-ordering of nitride anions and octahedral titling are also preferable in La1-xSrxTiO2+xN1-x (x=0, 0.2) oxynitride perovskites. A larger dielectric constant of εr≈5.0×103 was estimated for the pure oxynitride with x=0.2, compared with εr≈750 for the product with x=0, by extrapolating the εr values obtained from powders mixed with paraffin at various mixing ratios. The crystal structure of x=0.2 with larger tolerance factor than x=0 increased the octahedral tilting, which contributes to the increased dielectric constant. The increased dielectric constant supports the exchange mechanism for the dielectric property between two kinds of -Ti-N- helical coils (clockwise and anticlockwise) derived from the above cis-ordering of nitride anions.

  1. (La1-xBax)(Zn1-xMnx)AsO: A two-dimensional 1111-type diluted magnetic semiconductor in bulk form

    NASA Astrophysics Data System (ADS)

    Ding, Cui; Man, Huiyuan; Qin, Chuan; Lu, Jicai; Sun, Yunlei; Wang, Quan; Yu, Biqiong; Feng, Chunmu; Goko, T.; Arguello, C. J.; Liu, L.; Frandsen, B. A.; Uemura, Y. J.; Wang, Hangdong; Luetkens, H.; Morenzoni, E.; Han, W.; Jin, C. Q.; Munsie, T.; Williams, T. J.; D'Ortenzio, R. M.; Medina, T.; Luke, G. M.; Imai, T.; Ning, F. L.

    2013-07-01

    We report the synthesis and characterization of a bulk diluted magnetic semiconductor (La1-xBax)(Zn1-xMnx)AsO (0 ⩽ x ⩽ 0.2) with a layered crystal structure identical to that of the 1111-type FeAs superconductors. No ferromagnetic order occurs with (Zn,Mn) substitution in the parent compound LaZnAsO without charge doping. Together with carrier doping via (La,Ba) substitution, a small amount of Mn substituting for Zn results in ferromagnetic order with TC up to ˜40 K, although the system remains semiconducting. Muon spin relaxation measurements confirm the development of ferromagnetic order in the entire volume, with the relationship between the internal field and TC consistent with the trend found in (Ga,Mn)As and the 111-type Li(Zn,Mn)As and the 122-type (Ba,K)(Zn,Mn)2As2 systems.

  2. Synthesis of the off-stoichiometric oxide system Sr2Fe1+xMo1-xO6 with -1≤x≤0.25

    NASA Astrophysics Data System (ADS)

    Soto, T. E.; Valenzuela, J. L.; Mondragón, R.; Morales, R.; Lemus-Ruíz, J.; Navarro, O.

    2014-12-01

    The half-metallic ferromagnetic oxide compounds are extensively studied in view of their spintronic applications. In this work, we have synthesized and characterized the off-stoichiometric double perovskite Sr2Fe1+xMo1-xO6 with x being in the range -1≤x≤0.25, the composition x=0 corresponding to the well-known ferromagnetic system Sr2FeMoO6. The double perovskite has been prepared in a polycrystalline form by the solid-state reaction method and ball milling, calcination in air and reduction in a mixture of He and H2 atmosphere in a thermogravimetric analyzer. Characterization has been done by X-ray diffraction and scanning electron microscopy techniques. Our results show that mechanochemical activation prior to the reaction synthesis helps to reduce the synthesis temperature and avoid the sublimation of MoO3 at high temperatures. The Curie temperature has also been obtained.

  3. Tunable spin current due to bulk insulating property in the topological insulator Tl1 -xBi1 +xSe2 -δ

    NASA Astrophysics Data System (ADS)

    Kuroda, Kenta; Eguchi, Gaku; Shirai, Kaito; Shiraishi, Masashi; Ye, Mao; Miyamoto, Koji; Okuda, Taichi; Ueda, Shigenori; Arita, Masashi; Namatame, Hirofumi; Taniguchi, Masaki; Ueda, Yoshifumi; Kimura, Akio

    2015-05-01

    The surfaces of three-dimensional topological insulators characterized by spin-helical Dirac fermions provide a fertile ground for realizing exotic phenomena, and they have the potential for wide-ranging applications. To realize most of their special properties, the Dirac point must be located near the Fermi energy with a bulk insulating property. However, this is barely achieved in most of the discovered topological insulators. It was found recently that TlBiSe2 features an in-gap Dirac point, where the upper and lower parts of the Dirac-cone surface state are both utilized. Nevertheless, investigations of the surface transport properties of this material are limited due to the lack of bulk insulating characteristics. Here, we present a realization of the bulk insulating property by tuning the composition of Tl1 -xBi1 +xSe2 -δ without introducing guest atoms. This result promises to shed light on exotic topological phenomena on the surface.

  4. Components-dependent optical nonlinearity in a series of CdSexS1-x and CdSexS1-x/ZnS QDs

    NASA Astrophysics Data System (ADS)

    Zhao, Shunlong; Wu, Feng; Zhang, Siwen; Wang, Qian; Li, Songtao; Cheng, Xiaoman

    2016-08-01

    The different compositions of the ternary alloyed CdSexS1-x and CdSexS1-x/ZnS core/shell quantum dots(CSQDs) have been synthesized by the chemical routes. The nonlinear optical properties of these QDs were investigated using Z-scan technique under the excitation of the 1064 nm picosecond laser pulse. The Z-scan results reveal that the nonlinear refractive indices of these QDs can be tuned by changing the ratio of Se and S components. Nonlinear optical (NLO) properties have been shown to be enhanced in CSQDs as compared to their core semiconductor counterparts. These QDs exhibit the components-tuned nonlinear refraction indices, which lead to a wide application in the photonic field.

  5. Electronic self-organization in the single-layer manganite $\\rm Pr_{1-x}Ca_{1+x}MnO4$

    SciTech Connect

    Ye, Feng; Chi, Songxue; Fernandez-Baca, Jaime A; Moreo, Adriana; Dagotto, Elbio R; Lynn, J. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.; Dai, Pengcheng

    2009-01-01

    We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite $\\rm Pr_{\\it 1-x}Ca_{\\it 1+x}MnO_4$, away from the $x=0.5$ composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped ($x<0.5$), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with $x=0.5$ are separated by electron-rich domain walls with short range magnetic correlations. This behavior is strikingly different than for the three-dimensional $\\rm Pr_{\\it 1-x}Ca_{\\it x}MnO_3$, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around $x=0.5$.

  6. Evidence for room temperature ferromagnetism in CuxZn1-xO from magnetic studies in CuxZn1-xO/CuO composite

    NASA Astrophysics Data System (ADS)

    Seehra, M. S.; Dutta, P.; Singh, V.; Zhang, Y.; Wender, I.

    2007-05-01

    Magnetic studies in bulk 57% CuxZn1-xO/43% CuO composite prepared chemically with x =0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Néel temperature TN≃230K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc≃50Oe at 300K with strong temperature dependence for T <300K. A negative exchange bias He at 5K is observed when the sample is cooled from RT in H =20kOe, and its temperature dependence yields He→0 at TN=230K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the CuxZn1-xO phase with x ≃0.10 is a ferromagnet with Tc≃400K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in CuxZn1-xO is also observed.

  7. Spectral characteristics of different structural modifications of Lu1 - x Eu x BO3

    NASA Astrophysics Data System (ADS)

    Shmurak, S. Z.; Kedrov, V. V.; Kiselev, A. P.; Smyt'ko, I. M.

    2015-01-01

    The spectral and structural characteristics of polycrystals of Eu3+-doped lutetium borates Lu1 - x Eu x BO3) annealed at different temperatures have been investigated over a wide range of europium concentrations. The conditions for the preparation of Lu1 - x Eu x BO3 in the calcite and vaterite phases have been determined. It has been found that there is a radical difference between the excitation spectra of the main emission bands of the calcite and vaterite phases of the Lu1 - x Eu x BO3 borates. The influence of the europium concentration on the structure of Lu1 - x Eu x BO3 has been analyzed. It has been established that, at europium concentrations of higher than 15 at %, only the vaterite structure is formed independently of the annealing temperature. Thus, by varying the Eu3+ concentration and the annealing temperature of Lu1 - x Eu x BO3, it is possible to directionally synthesize a specific structural modification and, consequently, to control the spectral characteristics of this compound.

  8. The BiCu1-xOS oxysulfide: Copper deficiency and electronic properties

    NASA Astrophysics Data System (ADS)

    Berthebaud, D.; Guilmeau, E.; Lebedev, O. I.; Maignan, A.; Gamon, J.; Barboux, P.

    2016-05-01

    An oxysulfide series of nominal compositions BiCu1-xOS with x<0.20 has been prepared and its structural properties characterized by combining powder X-ray diffraction and transmission electron microscopy techniques. It is found that this oxysulfide, crystallizing in the P4/nmm space group, tends to adopt a constant amount of copper vacancy corresponding to x=0.05 in the BiCu1-xOS formula. The presence of Cu vacancies is confirmed by HAADF-STEM analysis showing, in the Cu atomic columns, alternating peaks of different intensities in some very localized regions. For larger Cu deficiencies (x>0.05 in the nominal composition), other types of structural nanodefects are evidenced such as bismuth oxysulfides of the "BiOS" ternary system which might explain the report of superconductivity for the BiCu1-xOS oxysulfide. Local epitaxial growth of the BiCuOS oxysulfide on top of CuO is also observed. In marked contrast to the BiCu1-xOSe oxyselenide, these results give an explanation to the limited impact of Cu deficiency on the Seebeck coefficient in BiCu1-xOS compounds.

  9. Compositional tuning of ferromagnetism in Ga1-xMnxP

    SciTech Connect

    Farshchi, R.; Scarpulla, M.A.; Stone, P.R.; Yu, K.M.; Sharp,I.D.; Beeman, J.W.; Silvestri, H.H.; Reichertz, L.A.; Haller E.E.; Dubon,O.D.

    2006-05-23

    We report the magnetic and transport properties of Ga{sub 1-x}Mn{sub x}P synthesized via ion implantation followed by pulsed laser melting over a range of x, namely 0.018 to 0.042. Like Ga{sub 1-x}Mn{sub x}As, Ga{sub 1-x}Mn{sub x}P displays a monotonic increase of the ferromagnetic Curie temperature with x associated with the hole-mediated ferromagnetic phase while thermal annealing above 300 C leads to a quenching of ferromagnetism that is accompanied by a reduction of the substitutional fraction of Mn. However, contrary to observations in Ga{sub 1-x}Mn{sub x}As, Ga{sub 1-x}Mn{sub x}P is non-metallic over the entire composition range. At the lower temperatures over which the films are ferromagnetic, hole transport occurs via hopping conduction in a Mn-derived band; at higher temperatures it arises from holes in the valence band which are thermally excited across an energy gap that shrinks with x.

  10. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stern, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire single-photon detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize Nb(x)Ti(1-x)N in the high-superconducting-transition temperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  11. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stem, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire singlephoton detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize NbxTi1 xN in the high-superconducting-transitiontemperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  12. Structural and Optical Properties of SnxGe1-x thin films and Quantum Dots

    NASA Astrophysics Data System (ADS)

    Blacksberg, Jordana

    2005-03-01

    SnxGe1-x layers and quantum dots (QDs) are of great interest as materials that could provide tunable direct band gaps, allowing completely group IV-based optoelectronic devices. These materials could be used in a wide range of applications such as emitters, infrared detectors, and thermophotovoltaics. However, substantial challenges remain in the growth and processing of these materials. We have grown SnxGe1-x films by Molecular Beam Epitaxy (MBE), using low growth temperatures (<200^oC) in order to grow fully strained layers. X-ray diffraction, transmission electron microscopy, and Rutherford backscattering spectroscopy data indicate high-quality epitaxial films. Post-growth annealing was used to form QDs. Either QDs or quantum wires may be formed depending on annealing parameters. The effects of varying substrate temperature between 400C (wires) and 750C (QDs) on size and distribution of quantum structures were explored and will be discussed. Sn concentration (0-10%) and film thickness (40nm - 200nm) were also varied. Optical properties probed by Fourier transform infrared spectroscopy (FTIR) will be presented. FTIR spectra clearly show the decrease in band gap of SnxGe1-x layers with increasing Sn fraction up to 10%. Photomodulated reflectance (PR) is another sensitive method for probing critical points in SnxGe1-x band structure, and can detect both direct and indirect transitions. PR results for SnxGe1-x layers will also be discussed.

  13. Coherently Strained Si-SixGe1-x Core-Shell Nanowire Heterostructures.

    PubMed

    Dillen, David C; Wen, Feng; Kim, Kyounghwan; Tutuc, Emanuel

    2016-01-13

    Coherently strained Si-SixGe1-x core-shell nanowire heterostructures are expected to possess a positive shell-to-core conduction band offset, allowing for quantum confinement of electrons in the Si core. We report the growth of epitaxial, coherently strained Si-SixGe1-x core-shell heterostructures through the vapor-liquid-solid mechanism for the Si core, followed in situ by the epitaxial SixGe1-x shell growth using ultrahigh vacuum chemical vapor deposition. The Raman spectra of individual nanowires reveal peaks associated with the Si-Si optical phonon mode in the Si core and the Si-Si, Si-Ge, and Ge-Ge vibrational modes of the SixGe1-x shell. The core Si-Si mode displays a clear red-shift compared to unstrained, bare Si nanowires thanks to the lattice mismatch-induced tensile strain, in agreement with calculated values using a finite-element continuum elasticity model combined with lattice dynamic theory. N-type field-effect transistors using Si-SixGe1-x core-shell nanowires as channel are demonstrated.

  14. Mid-Gap Electronic States in Zn1 xMnxO

    SciTech Connect

    Johnson, Claire A.; Kittilstved, Kevin R.; Kaspar, Tiffany C.; Droubay, Timothy C.; Chambers, Scott A.; Salley, G. Mackay; Gamelin, Daniel R.

    2010-09-02

    Electronic absorption, magnetic circular dichroism, photoconductivity, and valence-band X-ray photoelectron (XPS) spectroscopic measurements were performed on epitaxial Zn1 xMnxO films to investigate the origin of the new mid-gap band that appears upon introduction of Mn2+ into the ZnO lattice. Absorption and MCD spectroscopies reveal Mn2+-related intensity at energies below the first excitonic transition of ZnO, tailing well into the visible energy region, with an onset at ~2.2 eV. Photoconductivity measurements show that excitation into this visible band generates mobile charge carriers, consistent with assignment as a Mn2+/3+ photoionization transition. XPS measurements reveal the presence of occupied Mn2+ levels just above the valence-band edge, supporting this assignment. Magnetic circular dichroism measurements additionally show a change in sign and large increase in magnitude of the excitonic Zeeman splitting in Zn1 xMnxO relative to ZnO, suggesting that sp-d exchange in Zn1 xMnxO is not as qualitatively different from those in other II-VI diluted magnetic semiconductors as has been suggested. The singular electronic structure feature of Zn1 xMnxO is its Mn2+/3+ ionization level within the gap, and the influence of this level on other physical properties of Zn1 xMnxO is discussed.

  15. Topological characters in Fe (Te1 -xSex ) thin films

    NASA Astrophysics Data System (ADS)

    Wu, Xianxin; Qin, Shengshan; Liang, Yi; Fan, Heng; Hu, Jiangping

    2016-03-01

    We investigate topological properties in the Fe(Te,Se) thin films. We find that the single layer FeTe1 -xSex has nontrivial Z2 topological invariance which originates from the parity exchange at the Γ point of the Brillouin zone. The nontrivial topology is mainly controlled by the Te(Se) height. Adjusting the anion height, which can be realized as the function of lattice constants and x in FeTe1 -xSex , can drive a topological phase transition. In a bulk material, the two-dimensional Z2 topology invariance is extended to a strong three-dimensional one. In a thin film, we predict that the topological invariance oscillates with the number of layers. The results can also be applied to iron pnictides. Our research establishes FeTe1 -xSex as a unique system to integrate high-Tc superconductivity and topological properties in a single electronic structure.

  16. Growth and structure of Cd1-xDyxTe crystals

    NASA Astrophysics Data System (ADS)

    Sochinskii, Nikolai V.; Rubio, Sandra; Plaza, José Luis; Diéguez, Ernesto

    2016-09-01

    CdTe crystals doped with dysprosium were grown by the vertical Bridgman method to explore the possibility of obtaining Cd1-xDyxTe ternary compound. The growth was carried out from the Cd1-xDyxTe pre-synthesized feeds with the charge composition in the range of x=0.001-0.05. The as-grown crystals were studied by scanning electron microscopy, X-ray diffraction and optical spectroscopy. Experimental findings testify that the Cd1-xDyxTe crystals have the homogeneous cubic structure similar to CdTe in the narrow composition range of x≈0-0.01. At higher compositions x≥0.01, the crystals become a mixture of several phases such as CdTe host, Dy2Te3 textures and DyTe-rich inclusions.

  17. Luminescence properties of MgxZn1-xSe prepared by Mg diffusion

    NASA Astrophysics Data System (ADS)

    Łożykowski, H. J.; Holtz, P. O.; Monemar, B.

    1983-07-01

    The photoluminescence of ZnSe doped with the isoelectronic substituent Mg with a simple diffusion procedure has been studied. It was found that Mg easily enters substitutionally on Zn-site to form MgxZn1-xSe. The diffused samples therefore show a graded bandgap due to a composition gradient in the surface region. In contrast to ZnSe the photoluminescence spectrum of MgxZn1-xSe is dominated by a near bandgap emission at all temperatures between 1.5 and 300 K. The bandgap shift compared with “pure” ZnSe is estimated from photoluminescence excitation spectra. The luminous efficiency of MgxZn1-xSe makes the material promising for future applications as light emitting diodes with a well defined narrow emission band at a wavelength determined by the Mg content x.

  18. Kondo lattice mixed valence behavior in the Ce(SnxPb1 - x)3 system

    NASA Astrophysics Data System (ADS)

    Teter, J.; Freitag, R.; Maury*, A.; Crow, J. E.; Mihalisin, T.

    1982-11-01

    Measurements of the electrical resistivity versus x and temperature T, for 1.5≤T≤300 K for the fcc system Ce(SnxPb1-x)3 are reported. CeSn3 has been shown to be a strongly mixed valent system with an average occupation number of the Ce 4f level nf of ˜0.4 at low temperatures. The electrical resistivity for Ce(SnxPb1-x)3 is compared to that obtained for other Ce based mixed valent-trivalent systems and to the predictions of the Newns and Hewson theory. These comparisons suggest that Ce(SnxPb1-x)3 is mixed valent for x≳0.5 and the scaling of the resistivity supports the previous result that CeSn3 is strong mixed valent with nf≂0.4.

  19. Thermal stability of amorphous GaN{sub 1-x}As{sub x} alloys

    SciTech Connect

    Levander, A. X.; Broesler, R.; Dubon, O. D.; Wu, J.; Liliental-Weber, Z.; Hawkridge, M. E.; Walukiewicz, W.; Yu, K. M.; Novikov, S. V.; Foxon, C. T.

    2011-04-18

    GaN{sub 1-x}As{sub x} alloys grown across the composition range by low temperature molecular beam epitaxy have great technological potential for photovoltaic applications owing to their strong absorption coefficient and wide tunability of band gap and band edges. We found that amorphous GaN{sub 1-x}As{sub x} alloys that are formed for the compositions x, in the range of x{approx}0.3-0.7 are stable up to 700 deg. C. This is surprising since growth of GaN{sub 1-x}As{sub x} above 400 deg. C results in phase segregation. At annealing temperatures higher than 700 deg. C the alloy phase segregates into GaAs:N and GaN:As. The relative size of the nanocrystals depends on the initial film composition and annealing conditions.

  20. Structural characterisation of energetically deposited Zn1-xMgxO films

    NASA Astrophysics Data System (ADS)

    Mayes, E. L. H.; McCulloch, D. G.; Partridge, J. G.

    2015-02-01

    Zn1-xMgxO thin films have been energetically deposited from a filtered catholic vacuum arc at moderate temperatures and microstructurally characterised. Partial oxidation ('poisoning') of the Zn0.8Mg0.2 cathode caused layering and phase separation in the films. However, periods of non-reactive ablation steps incorporated into the deposition process minimised the effects of cathode poisoning and enabled dense, phase-pure, wurtzite Zn1-xMgxO to be grown at room temperature and 200 °C. Elevated substrate temperature resulted in enlarged grains and increased surface roughness. Increased substrate bias caused reduced crystalline order. X-ray absorption spectra from the homogeneous Zn1-xMgxO films, revealing local atomic bonding, were similar to spectra from single crystal ZnO but with features indicative of defects related to oxygen deficiency.

  1. Oxygen deficient ZnO1-x nanosheets with high visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Guo, Hong-Li; Zhu, Qing; Wu, Xi-Lin; Jiang, Yi-Fan; Xie, Xiao; Xu, An-Wu

    2015-04-01

    Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light absorption of ZnO1-x into the visible-light region due to the fact that the energy of the localized state is located in the forbidden gap. Thus, our obtained ZnO1-x shows a higher photodegradation of methyl orange (MO) compared to defect-free ZnO under visible light illumination. Additionally, the high content of &z.rad;OH radicals with a strong photo-oxidation capability over the ZnO1-x nanosheets significantly contributes to the improvement in the photocatalytic performance. Our oxygen deficient ZnO1-x sample shows a very high photocatalytic activity for the degradation of MO even after 5 cycles without any obvious decline. The results demonstrate that defect engineering is a powerful tool to enhance the optoelectronic and photocatalytic performances of nanomaterials.Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light

  2. Doping of GaN{sub 1-x}As{sub x} with high As content

    SciTech Connect

    Levander, A.X.; Novikov, S.V.; Liliental-Weber, Z.; dos Reis, R.; Dubon, O.D.; Wu, J.; Foxon, C.T.; Yu, K.M.; Walukiewicz, W.

    2011-09-22

    Recent work has shown that GaN{sub 1-x}As{sub x} can be grown across the entire composition range by low temperature molecular beam epitaxy with intermediate compositions being amorphous, but control of the electrical properties through doping is critical for functionalizing this material. Here we report the bipolar doping of GaN{sub 1-x}As{sub x} with high As content to conductivities above 4 S/cm at room temperature using Mg or Te. The carrier type was confirmed by thermopower measurements. Doping requires an increase in Ga flux during growth resulting in a mixed phase material of polycrystalline GaAs:N embedded in amorphous GaN{sub 1-x}As{sub x}.

  3. Thermoelectric properties of Zintl compound Ca1-xNaxMg2Bi1.98

    NASA Astrophysics Data System (ADS)

    Shuai, Jing; Kim, Hee Seok; Liu, Zihang; He, Ran; Sui, Jiehe; Ren, Zhifeng

    2016-05-01

    Motivated by good thermoelectric performance of Bi-based Zintl compounds Ca1-xYbxMg2Biy, we further studied the thermoelectric properties of Zintl compound CaMg2Bi1.98 by doping Na into Ca as Ca1-xNaxMg2Bi1.98 via mechanical alloying and hot pressing. We found that the electrical conductivity, Seebeck coefficient, power factor, and carrier concentration can be effectively adjusted by tuning the Na concentration. Transport measurement and calculations revealed that an optimal doping of 0.5 at. % Na achieved better average ZT and efficiency. The enhancement in thermoelectric performance is attributed to the increased carrier concentration and power factor. The low cost and nontoxicity of Ca1-xNaxMg2Bi1.98 makes it a potentially promising thermoelectric material for power generation in the mid-temperature range.

  4. Diamagnetic vortex barrier stripes in underdoped BaFe2(As1-xPx) 2

    NASA Astrophysics Data System (ADS)

    Yagil, A.; Lamhot, Y.; Almoalem, A.; Kasahara, S.; Watashige, T.; Shibauchi, T.; Matsuda, Y.; Auslaender, O. M.

    2016-08-01

    We report magnetic force microscopy (MFM) measurements on underdoped BaFe2(As1 -xPx)2 (x =0.26 ) that show enhanced superconductivity along stripes parallel to twin boundaries. These stripes of enhanced diamagnetic response repel superconducting vortices and act as barriers for them to cross. The width of the stripes is hundreds of nanometers, on the scale of the penetration depth, well within the inherent spatial resolution of MFM and implying that the width is set by the interaction of the superconductor with the MFM's magnetic tip. Unlike similar stripes observed previously by scanning SQUID in the electron doped Ba (Fe1 -xCox)2As2 , the stripes in the isovalently doped BaFe2(As1 -xPx)2 disappear gradually when we warm the sample towards the superconducting transition temperature. Moreover, we find that the stripes move well below the reported structural transition temperature in BaFe2(As1 -xPx)2 and that they can be much denser than in the Ba (Fe1 -xCox)2As2 study. When we cool in finite magnetic field we find that some vortices appear in the middle of stripes, suggesting that the stripes may have an inner structure, which we cannot resolve. Finally, we use both vortex decoration at higher magnetic field and deliberate vortex dragging by the MFM magnetic tip to obtain bounds on the strength of the interaction between the stripes and vortices. We find that this interaction is strong enough to play a significant role in determining the critical current in underdoped BaFe2(As1 -xPx)2 .

  5. CdSxTe1-x Alloying in CdS/CdTe Solar Cells

    SciTech Connect

    Duenow, J. N.; Dhere, R. G.; Moutinho, H. R.; To, B.; Pankow, J. W.; Kuciauskas, D.; Gessert, T. A.

    2011-05-01

    A CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thin-film CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by RF magnetron sputtering and co-evaporation from CdTe and CdS sources. Both radio-frequency-magnetron-sputtered and co-evaporated CdSxTe1-x films of lower S content (x<0.3) have a cubic zincblende (ZB) structure akin to CdTe, while those of higher S content have a hexagonal wurtzite (WZ) structure like that of CdS. Films become less preferentially oriented as a result of a CdCl2 heat treatment at ~400 degrees C for 5 min. Films sputtered in a 1% O2/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl2 heat treatment (HT). Films sputtered in O2 partial pressure have a much wider bandgap (BG) than expected. This may be explained by nanocrystalline size effects seen previously [2] for sputtered oxygenated CdS (CdS:O) films.

  6. Dilatometric study of U1-xAmxO2±δ and U1-xCexO2±δ reactive sintering

    NASA Astrophysics Data System (ADS)

    Horlait, Denis; Feledziak, Alex; Lebreton, Florent; Clavier, Nicolas; Prieur, Damien; Dacheux, Nicolas; Delahaye, Thibaud

    2013-10-01

    In order to reduce the radiotoxicity of nuclear fuel waste, the transmutation of americium in U1-xAmxO2±δ dedicated fuels is considered. A convenient route to produce such fuels is reactive sintering from a UO2+δ/AmO2-δ green pellet, i.e., a single heat treatment during which both the densification and the formation of the U1-xAmxO2±δ solid solution occur. The mechanisms of such sintering are however barely known and require experimental data. In this aim, the densification through reactive sintering of a UO2+δ/AmO2-δ sample was monitored by dilatometry. The obtained results were compared to those reported for the formation of the U1-xAmxO2±δ solid solution monitored by in situ high-temperature X-ray diffraction. To assess the use of Ce as a substitute of Am, similar dilatometric studies were also carried out on UO2+δ/CeO2 pellets. Obtained results show that the use of a reactive sintering causes a delay in the densification process associated to the competition between solid solution formation and densification, which yields limitations in pellet final densities. The importance of redox behavior of Am (or Ce) on the achievement of solid solution formation and densification are also discussed, especially based on discrepancies in densification behavior between UO2+δ/AmO2-δ and UO2+δ/CeO2.

  7. Strain-induced island scaling during Si1-xGex heteroepitaxy

    NASA Astrophysics Data System (ADS)

    Dorsch, W.; Strunk, H. P.; Wawra, H.; Wagner, G.; Groenen, J.; Carles, R.

    1998-01-01

    We investigated the composition-dependent size of pseudomorphic Si1-xGex islands on Si(001). Si1-xGex layers with 0.05⩽x⩽0.54 were deposited from metallic solution. The island growth occurs near thermodynamic equilibrium and facilitates a comparison of the results with predictions based on energetics. We find pseudomorphic islands with base widths ranging from several μm to a few nm. We show that it is possible to adjust the island size by simply choosing the appropriate layer composition. Varying deposition temperatures and growth velocities do not affect the scaling behavior.

  8. In(x)Ga(1-x)As/GaAs Quantum-Well Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D.; Park, Jin S.; Lin, True-Lon; Liu, John K.

    1995-01-01

    Choice of materials for present quantum-well infrared photodetectors (QWIPs) affected principally by two considerations. One was that in comparison with GaAs, In(x)Ga(1-x)As is potentially superior quantum-well material because of its stronger absorption of infrared radiation. Other consideration was that in comparison with Al(x)Ga(1-x)As, which is usual barrier material in older devices, GaAs potentially superior barrier material because it exhibits superior transport properties (lower scattering and higher mobility of charge carriers). GaAs is well material in older devices and barrier material in present devices.

  9. Structural and optical properties of Sn1-xMnxO2 thin films

    NASA Astrophysics Data System (ADS)

    Tripathi, Akhilesh; Mishra, Sheo K.; Shukla, R. K.

    2015-06-01

    Sn1-xMnxO2 thin films are deposited by spray pyrolysis method. XRD of all the thin films show the amorphous nature. Synthesis of SnO2 is also confirmed by FTIR spectroscopy. Undoped SnO2 thin film is 60-70 % transparent in visible and near IR region and it increases up to 80-90% for 20 at. % Mn doped SnO2 thin film. The optical band gap is tunable linearly between 3.34 to 3.96 eV for 0≤x≤0.20 for Sn1-xMnxO2 amorphous thin films.

  10. Epitaxial alloys of AlxGa1-xAs:Mg with different types of conductivity

    NASA Astrophysics Data System (ADS)

    Seredin, P. V.; Lenshin, A. S.; Arsentyev, I. N.; Tarasov, I. S.; Prutskij, Tatiana; Leiste, Harald; Rinke, Monika

    2016-10-01

    This project employed high-resolution X-ray diffraction, Raman spectroscopy and photoluminescence spectroscopy to investigate the structural, optical and band energy properties of the MOCVD epitaxial heterostructures, AlxGa1-xAs:Mg/GaAs(100), with different levels of magnesium doping. It was shown that the choice of technological conditions used in the preparation of the AlxGa1-xAs:Mg alloy allowed different types of conductivity and it was also possible to achieve significantly different concentrations of the charge carriers in the epitaxial film.

  11. Band structure engineering of ZnO1-xSex alloys

    NASA Astrophysics Data System (ADS)

    Mayer, Marie A.; Speaks, Derrick T.; Yu, Kin Man; Mao, Samuel S.; Haller, Eugene E.; Walukiewicz, Wladek

    2010-08-01

    ZnO1-xSex films have been prepared through pulsed laser deposition as a step toward stable films with a band gap appropriate for water splitting. The films show a clear red shift in absorption with increasing Se content and a shift in the flat band voltage toward spontaneity. Due to the films' electron affinities, there exists a natural tunnel junction between these n- ZnO1-xSex films when grown on the p-side of a Si diode. The overall performance, emphasized by flat band potential measurements, can be improved by growing films on Si p-n diodes.

  12. Negative infrared photoconductivity in CdS1-xSex films

    NASA Astrophysics Data System (ADS)

    Abdinov, A. S.; Jafarov, M. A.; Mamedov, H. M.; Nasirov, E. F.

    2003-09-01

    The negative infrared photoconductivity (NPH) has been observed for the first time in CdS1-xSex films, in the wavelength region of 0.700 - 1.23 μm. at values of stimulating light intensity Φ = 100 - 400 Lk. electrical field E = 0.5 - 130 V/cm and temperature T = 265 - 310 Κ. It is established, that basic laws of NPH explains on the basis of two-barrier model and in the considered conditions a charge carriers, overcome a barrier by tunneling. A films of CdS1-xSex can be used in IR engineering and negatronics.

  13. AlxGa1-xAs Single-Quantum-Well Surface-Emitting Lasers

    NASA Technical Reports Server (NTRS)

    Kim, Jae H.

    1992-01-01

    Surface-emitting solid-state laser contains edge-emitting Al0.08Ga0.92As single-quantum-well (SQW) active layer sandwiched between graded-index-of-refraction separate-confinement-heterostructure (GRINSCH) layers of AlxGa1-xAs, includes etched 90 degree mirrors and 45 degree facets to direct edge-emitted beam perpendicular to top surface. Laser resembles those described in "Pseudomorphic-InxGa1-xAs Surface-Emitting Lasers" (NPO-18243). Suitable for incorporation into optoelectronic integrated circuits for photonic computing; e.g., optoelectronic neural networks.

  14. Ga/1-x/Al/x/As LED structures grown on GaP substrates.

    NASA Technical Reports Server (NTRS)

    Woodall, J. M.; Potemski, R. M.; Blum, S. E.; Lynch, R.

    1972-01-01

    Ga(1-x)Al(x)As light-emitting diode structures have been grown on GaP substrates by the liquid-phase-epitaxial method. In spite of the large differences in lattice constants and thermal-expansion coefficients, room-temperature efficiencies up to 5.5% in air have been observed for a peak emission of 8500 A. Using undoped GaP substrates, which are transparent to the infrared and red portions of the spectrum, thin structures of Ga(1-x)Al(x)As with large external efficiencies can now be made.

  15. Zone centre mode behavior of ternary mixed nitrides InxGa1-xN

    NASA Astrophysics Data System (ADS)

    Singh, Daljit; Sinha, M. M.

    2015-08-01

    We have studied the transverse optical phonon mode behavior of the ternary mixed InxGa1-xN at zone centre using de Launey Angular force constant model. The phonon frequency at zone centre has been calculated for InxGa1-xN for all composition. The present calculation predicts one mode behavior in this ternary mixed compound. The zone center phonons frequency varies linearly from one end member to other. The calculated results are in good agreement with the existing experimental and theoretical results.

  16. High-temperature heat capacity of orthovanadates Ce1- x Bi x VO4

    NASA Astrophysics Data System (ADS)

    Denisova, L. T.; Chumilina, L. G.; Belousova, N. V.; Denisov, V. M.

    2016-09-01

    Orthovanadates Ce1- x Bi x VO4 (1 ≥ x ≥ 0) have been produced by solid-phase synthesis from initial oxides CeO2, Bi2O3, and V2O5 upon step-by-step burning. The high-temperature heat capacity of Ce1- x Bi x VO4 has been measured by differential scanning calorimetry. The experimental data on C p = f(T) were used to calculate the thermodynamic properties (the enthalpy changes, the entropy changes, and the Gibbs energy).

  17. Infrared probe of the insulator-to-metal transition in Ga1-xMnxAs and Ga1-xBexAs

    NASA Astrophysics Data System (ADS)

    Chapler, B. C.; Myers, R. C.; Mack, S.; Frenzel, A.; Pursley, B. C.; Burch, K. S.; Singley, E. J.; Dattelbaum, A. M.; Samarth, N.; Awschalom, D. D.; Basov, D. N.

    2011-08-01

    We report infrared studies of the insulator-to-metal transition (IMT) in GaAs doped with either magnetic (Mn) or nonmagnetic acceptors (Be). We observe a resonance with a natural assignment to impurity states in the insulating regime of Ga1-xMnxAs, which persists across the IMT to the highest doping (16%). Beyond the IMT boundary, behavior combining insulating and metallic trends also persists to the highest Mn doping. Be-doped samples, however, display conventional metallicity just above the critical IMT concentration, with features indicative of transport within the host valence band.

  18. Distribution of cations in wurtzitic InxGa1-xN and InxAl1-xN alloys: Consequences for energetics and quasiparticle electronic structures

    DOE PAGES

    de Carvalho, Luiz Cláudio; Schleife, André; Furthmüller, Jürgen; Bechstedt, Friedhelm

    2012-03-27

    The ternary, isostructural, wurtzite-derived group-III mononitride alloys InxGa1-xN andInxAl1-xN are reexamined within a cluster expansion approach. Using density functional theory together with the AM05 exchange-correlation functional, the total energies and the optimized atomic geometries of all 22 clusters classes of the cluster expansion for each material system are calculated. The computationally demanding calculation of the corresponding quasiparticle electronic structures is achieved for all cluster classes by means of a recently developed scheme to approximately solve the quasiparticle equation based on the HSE06 hybrid functional and the G₀W₀ approach. Using two different alloy statistics, the configurational averages for the lattice parameters,more » the mixing enthalpies, and the bulk moduli are calculated. The composition-dependent electronic structures of the alloys are discussed based on configurationally averaged electronic states, band gaps, and densities of states. Ordered cluster arrangements are found to be energetically rather unfavorable, however, they possess the smallest energy gaps and, hence, contribute to light emission. The influence of the alloy statistics on the composition dependencies and the corresponding bowing parameters of the band gaps is found to be significant and should, hence, lead to different signatures in the optical-absorption or -emission spectra.« less

  19. The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La(1-x)Ca(x))(Zn(1-x) Mn(x))AsO.

    PubMed

    Ding, Cui; Guo, Shengli; Zhao, Yao; Man, Huiyuan; Fu, Licheng; Gu, Yilun; Wang, Zhouyang; Liu, L; Frandsen, B A; Cheung, S; Uemura, Y J; Goko, T; Luetkens, H; Morenzoni, E; Zhao, Yang; Ning, F L

    2016-01-20

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature T(c) ∼30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, T(c) increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La(0.90)Ca(0.10))(Zn(0.90)Mn(0.10)) AsO below 300 K. PMID:26679223

  20. Influence of Ni/Mo ratio on structural and electrical properties of double perovskite system Sr2Ni1+ x Mo1- x O6- δ

    NASA Astrophysics Data System (ADS)

    Kumar, Pravin; Singh, Nitish Kumar; Singh, Rajesh Kumar; Singh, Prabhakar

    2015-11-01

    Technologically important double perovskite system Sr2Ni1+ x Mo1- x O6- δ with x = 0.00, 0.05, 0.10, and 0.15 was prepared by solution combustion method. The structural and the Rietveld analysis of compositions revealed the formation of double perovskite tetragonal phase Sr2NiMoO6 with space group I4/m as a major phase. SrMoO4 and NiO were also observed as minor phases. Microstructural studies depicted the formation of uniform grains for all the samples. The average grain size was found to lie between the ranges of 1-4 μm. XPS analysis of the synthesized compositions showed the decreasing ratio of Mo5+ to Mo6+ ions in the system with increasing Ni content, which played an important role in the conduction mechanism. The thermal expansion coefficient (TEC) of all compositions indicated that it is more compatible to the TEC of standard electrolytes. The electrical conductivity for all the compositions was studied using impedance spectroscopy in the temperature range 200-600 °C. Composition with x = 0.05 showed better electrical conductivity with good catalytic activity.

  1. Preparation and physical properties of the solid solutions Cu{sub 1+x}Mn{sub 1-x}O{sub 2} (0=

    SciTech Connect

    Trari, M.; Toepfer, J.; Dordor, P.; Grenier, J.C.; Pouchard, M.; Doumerc, J.P. . E-mail: doumerc@icmcb-bordeaux.cnrs.fr

    2005-09-15

    Solid solutions of formula Cu{sub 1+x}Mn{sub 1-x}O{sub 2} (0= 0.05. The crednerite solid solutions are p-type semiconductors. Modeling the thermoelectric power behavior suggests that charge carriers are Cu{sup 2+} holes diffusing in Cu layers for small x values and Mn{sup 4+} holes diffusing in Mn layers for x>0.05. For larger x values a saturation effect limits the charge carrier concentration.

  2. Structural transformation of Bi1-x/3V1-xMoxO4 solid solutions for light-driven water oxidation.

    PubMed

    Terebilenko, Kateryna V; Bychkov, Konstantin L; Baumer, Vyacheslav N; Slobodyanik, Nikolay S; Pavliuk, Mariia V; Thapper, Anders; Tokmenko, Inna I; Nasieka, Iurii M; Strelchuk, Viktor V

    2016-03-01

    The influence of molybdenum content in the solid solutions of Bi1-x/3V1-xMoxO4 (x = 0.05-0.20) on the morphology, band gap, structure and light-driven water oxidation properties has been studied by scanning electron microscopy, X-ray powder diffraction and vibrational spectroscopy (Raman and infrared). To find out the peculiarities of structural changes for bismuth scheelite-related oxides containing both vanadium and molybdenum crystals of Bi0.98V0.93Mo0.07O4 have been grown from a K-Bi-V-Mo-O high-temperature melt and characterized by single crystal X-ray diffraction. For the scheelite-related framework both V and Mo were found to occupy the same positions lowering the point group symmetry of tetrahedra from 4/m to 2/m giving monoclinic distortion for solid solutions with x = 0.05-0.10. The most promising photocatalytic performance was obtained for Bi0.96Mo0.10V0.90O4, in which the oxygen evolution could reach 21 μM in 50 s under visible light of LEDs, λ = 470 ± 10 nm, and 820 μE cm(-2) s(-1). The changes in catalytic properties are shown to be governed by a crystal structure strain with a maximum obtained for the boundary sample between the monoclinic and tetragonal phase.

  3. Structural, Dielectric, and Electrical Properties of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3

    NASA Astrophysics Data System (ADS)

    Panda, Niranjan; Pattanayak, Samita; Choudhary, R. N. P.

    2015-12-01

    Polycrystalline samples of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3 (BPFZTO) with x = 0.0, 0.2, 0.3, and 0.4 were prepared by high-temperature solid-state reaction. Preliminary structural analysis of calcined powders of the materials by use of x-ray powder diffraction confirmed formation of single-phase systems with the tetragonal structure. Room-temperature scanning electron micrographs of the samples revealed uniform distribution of grains of low porosity and different dimensions on the surface of the samples. The frequency-temperature dependence of dielectric and electric properties was studied by use of dielectric and complex impedance spectroscopy over a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25-500°C). The dielectric constant of BiFeO3 (BFO) was enhanced by substitution with Pb(Zr0.5Ti0.5)O3 (PZT) whereas the dielectric loss of the BPFZTO compounds decreased with increasing PZT content. A significant contribution of both grains and grain boundaries to the electrical response of the materials was observed. The frequency-dependence of the ac conductivity of BPFZTO followed Jonscher's power law. Negative temperature coefficient of resistance behavior was observed for all the BPFZTO samples. Conductivity by thermally excited charge carriers and oxygen vacancies in the materials was believed to be of the Arrhenius-type.

  4. 1. "X15 RUN UP AREA 230." A somewhat blurred, very ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. "X-15 RUN UP AREA 230." A somewhat blurred, very low altitude low oblique view to the northwest. This view predates construction of observation bunkers. Photo no. "14,696 58 A-AFFTC 17 NOV 58." - Edwards Air Force Base, X-15 Engine Test Complex, Rogers Dry Lake, east of runway between North Base & South Base, Boron, Kern County, CA

  5. Comments on a peak of AlxGa1-xN observed by infrared reflectance

    NASA Astrophysics Data System (ADS)

    Marx, G.; Engelbrecht, J. A. A.; Lee, M. E.; Wagener, M. C.; Henry, A.

    2016-05-01

    AlxGa1-xN epilayers, grown on c-plane oriented sapphire substrates by metal organic chemical vapour deposition (MOCVD), were evaluated using FTIR infrared reflectance spectroscopy. A peak at ∼850 cm-1 in the reflectance spectra, not reported before, was observed. Possible origins for this peak are considered and discussed.

  6. Al 2p core exciton in AlxGa1-xAs

    NASA Astrophysics Data System (ADS)

    Nithianandam, Jeyasingh; Schnatterly, Stephen E.

    1990-08-01

    Al L2,3 x-ray emission spectra from AlxGa1-xAs of varying aluminum concentration are presented. The nature of the Al 2p core exciton observed in these spectra is discussed. Some comments are also made on the effects of anion disorder in these alloys.

  7. Thermophysical properties and oxygen transport in the (Ux,Pu1-x)O2 lattice

    NASA Astrophysics Data System (ADS)

    Cooper, M. W. D.; Murphy, S. T.; Rushton, M. J. D.; Grimes, R. W.

    2015-06-01

    Using molecular dynamics, the thermophysical properties of the (Ux,Pu1-x)O2 system have been investigated between 300 and 3200 K. The variation with temperature of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure, are explained in terms of defect formation and diffusivity on the oxygen sublattice. Vegard's Law is approximately observed for the thermal expansion of the solid solutions below 2000 K. Deviation from Vegard's Law above this temperature occurs due to the different superionic transition temperatures of the solid solutions (2200-2900 K). Similarly, a spike in the specific heat, associated with the superionic transition, occurs at lower temperatures in solid solutions that have a high Pu content. While oxygen diffusivity is higher in pure PuO2 than in pure UO2, lower oxygen defect enthalpies in (Ux,Pu1-x)O2 solid solutions cause higher oxygen mobility than would be expected by interpolation between the diffusivities of the end members. In comparison to UO2 and PuO2 there is considerable variety of oxygen vacancy and oxygen interstitial sites in solid solutions generating a wide range of property values. Trends in the defect enthalpies are discussed in terms of composition and the lattice parameter of (Ux,Pu1-x)O2. Comparison is made with previous work on (Ux,Th1-x)O2.

  8. Synthesis of magnetic multicomponent nanoparticles CuxNi1-xFe2O4

    NASA Astrophysics Data System (ADS)

    Bingölbali, A.; Doğan, N.; Yeşil, Z.; Asiltürk, M.

    2015-01-01

    Magnetic nanoparticles (MNPs) are of great importance in many biomedical applications, such as drug delivery, hyperthermia, and magnetic resonance imaging (MRI) contrast enhancement. To build the most effective magnetic nanoparticle systems for various biomedical applications, characteristics of particle, including size, surface chemistry, magnetic properties, and toxicity have to be fully investigated. In this work, the effects of some production methods of the magnetic nanoparticles for the bio-medical applications are discussed. In this study, multicomponents of CuxNi1-xFe2O4 nanoparticles (where x=0, 0.6, and 1) were prepared by the hydrothermal synthesis method. In addition, X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), and a vibrating scanning magnetometer (VSM) were used to characterize the structural, morphological and magnetic properties of the nanoparticles. The particle sizes of the samples were measured by Malvern Instruments Zeta Sizer Nano-ZS instrument. The data were recorded under magnetic fields for different ratios of CuxNi1-xFe2O4 nanoparticles. The temperature dependence of field cooled (FC) magnetization of the CuxNi1-xFe2O4 samples has been shown in this work. Magnetizations change with decreasing the dopant value of Cu. The magnetic phase transition was observed for CuxNi1-xFe2O4 nanoparticles.

  9. Signature of Griffith phase in (Tb1-xCex)MnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Abhishek; Dwivedi, G. D.; Singh, A.; Singh, R.; Shukla, K. K.; Yang, H. D.; Ghosh, A. K.; Chatterjee, Sandip

    2016-05-01

    Griffith phase phenomena is attributed to existence of FM (ferromagnetic) cluster in AFM (antiferromagnetic) ordering which usually occurs in ferromagnetic and antiferromagnetic bilayers or multilayers. In (Tb1-xCex)MnO3 evolution of Griffith phase have been observed. The observed Griffith phase might be due to the exchange interaction between Mn3+/Mn2+ states.

  10. Mutual Passivation in Dilulte GaNxAs1-x Alloys

    SciTech Connect

    Yu, K.M.; Walukiewicz, W.; Wu, J.; Mars, D.E.; Scarpulla, M.A.; Dubon, O.D.; Ridgway, M.C.; Geisz, J.F.

    2005-03-21

    The dilute GaN{sub x}As{sub 1-x} alloys (with x up to 0.05) have exhibited many unusual properties as compared to the conventional binary and ternary semiconductor alloys. We report on a new effect in the GaN{sub x}As{sub 1-x} alloy system in which electrically active substitutional group IV donors and isoelectronic N atoms passivate each other's activity. This mutual passivation occurs in dilute GaN{sub x}As{sub 1-x} doped with group IV donors through the formation of nearest neighbor IV{sub Ga-}N{sub As} pairs when the samples are annealed under conditions such that the diffusion length of the donors is greater than or equal to the average distance between donor and N atoms. The passivation of the shallow donors and the N{sub As} atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental band gap. This mutual passivation effect is demonstrated in both Si and Ge doped GaN{sub x}As{sub 1-x} alloys. Analytical calculations of the passivation process based on Ga vacancies mediated diffusion show good agreement with the experimental results.

  11. Elasticity of the Sm1-xYxS alloy Based on Ultrasonic Measurements

    NASA Astrophysics Data System (ADS)

    Soboleva, EG; Igisheva, AL; Wojciechowski, KW

    2016-08-01

    The elastic moduli, sound velocities, Gruneisen parameter, Poisson's ratios and brittleness-plasticity criterion ratios are studied for the Sm1-xYxS alloys. Their dependence on the concentration of alloy components including a valence transition from semiconductors into the metal phase is presented. Auxeticity (negative Poisson's ratio) is found for some concentrations.

  12. New monocrystalline Si{sub 1-x}Ge{sub x} solar cells

    SciTech Connect

    Losada, B.R.; Moehlecke, A.; Ruiz, J.M.; Luque, A.

    1995-08-01

    The development of solar cells on Si{sub 1-x}Ge{sub x} might be interesting because they might present more current photo-response than the silicon cells, based on the lower bandgap of the alloyed crystal. In particular the use of Si{sub 1-x}Ge{sub x} solar cells in dual bandgap concentration structures as GaAs/Si{sub 1-x}Ge{sub x} can lead to total efficiency increase of about 1% as compared to the GaAs/Si structure, according to our calculations. Our effort is devoted to solar cells with low content of Ge, lower than 20% at. This choice is based on two previous hypothesis (1) A low content of Ge suggests that the well known silicon cell process, slightly modified, can be applied to the Si{sub 1-x}Ge{sub x} cells. (2) Calculations suggest that for utilisation in tandem with GaAs cells, the gain of efficiency is low above 20at % Ge.

  13. Window type: 4x4 multipaned steel window flanked by 1x4 multipaned ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Window type: 4x4 multipaned steel window flanked by 1x4 multipaned steel, casements. Concrete stoop, entry overhang and pipe rail detail also illustrated. Building 36, facing northwest - Harbor Hills Housing Project, 26607 Western Avenue, Lomita, Los Angeles County, CA

  14. Window type: paired 2x4 multipaned steel windows flanked by 1x4 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Window type: paired 2x4 multipaned steel windows flanked by 1x4 multipaned steel casements, breaking building corner. Raised panel door front entry also illustrated. Ground floor detail Building 19, facing north - Harbor Hills Housing Project, 26607 Western Avenue, Lomita, Los Angeles County, CA

  15. Window type: paired 3x2 multipaned steel window flanked by 1x3 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Window type: paired 3x2 multipaned steel window flanked by 1x3 multipaned steel casements, breaking building corner. Broad overhanging eave also illustrated. Second story detail. Building 13, facing east - Harbor Hills Housing Project, 26607 Western Avenue, Lomita, Los Angeles County, CA

  16. Magnetic phase diagram in CePd 1- xAg x

    NASA Astrophysics Data System (ADS)

    Besnus, M. J.; Godart, C.; Kappler, J. P.; Sereni, J.

    1994-04-01

    Magnetic susceptibility, high field magnetization and specific heat measurements are presented on CePd 1- xAg x for 0 ≤ x ≤ 0.175. The strong effect of Pd substitution by Ag stresses the instability of the compound towards noble metals solutes or electron-like impurities.

  17. Theoretical investigation of elastic and phononic properties of Zn1-xBexO alloys

    NASA Astrophysics Data System (ADS)

    Elhamra, F.; Lakel, S.; Ibrir, M.; Almi, K.; Meradji, H.

    2015-08-01

    Our calculations were conducted within density functional theory (DFT) and density functional perturbation theory (DFPT) using norm-conserving pseudo-potential and the local density approximation. The elastic constants of Zn1-xBexO were calculated, C11, C33 and C44 increase with the increase of Be content, whereas the C12 shows a non-monotonic variation and C13 decreases when Be concentration increases. The values of bulk modulus B, Young’s modulus E and shear modulus G increase with the increase of Be content. Poisson’s ratio σ decreases with increased Be concentration. The ductility decreases with increasing Be concentration and the compressibility for Zn1-xBexO along c-axis is smaller than along a-axis. Phonon dispersion curves show that Zn1-xBexO is dynamically stable (no soft modes). Quantities such as refractive index, Born effective charge, dielectric constants and optical phonon frequencies were calculated as a function of the Be molar fraction x. The agreement between the present results and the known data that are available only for ZnO and BeO is generally satisfactory. Our results for Zn1-xBexO (0 < x < 1) are predictions.

  18. Band gap bowing in NixMg1-xO.

    PubMed

    Niedermeier, Christian A; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A

    2016-01-01

    Epitaxial transparent oxide NixMg1-xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1-xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1-xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1-xO solid solution system. PMID:27503808

  19. Spectroscopic ellipsometry for characterization of InAs/Ga1-xInxSb superlattices

    NASA Astrophysics Data System (ADS)

    Wagner, J.; Schmitz, J.; Herres, N.; Fuchs, F.; Walther, M.

    1998-05-01

    The pseudodielectric function of InAs/Ga1-xInxSb superlattices (SLs) grown by solid-source molecular-beam epitaxy, was measured by spectroscopic ellipsometry (SE) for photon energies ranging from 1.2 to 5 eV. The width of the extrema in the SL pseudodielectric function derived from the E1 and E1+Δ1 interband transitions of the SL constituents InAs and Ga1-xInxSb, was found to depend on the structural quality of the SL. Differences in the SL quality caused by different sequences of InSb- like and GaAs-like interfaces, were easily detected by SE. The formation of the intended interface alternations was verified by Raman spectroscopy. The extrema in the SL pseudodielectric function originating from the E1 and E1+Δ1 interband transitions of Ga1-xInxSb were found to shift to lower energies with increasing In content x. Finally SE has been applied to the analysis of a complete InAs/Ga1-xInxSb SL detector structure.

  20. Magnetostrictive and piezomagnetic properties of Tb1-xDyxZn at low temperatures

    NASA Astrophysics Data System (ADS)

    Wun-Fogle, Marilyn; Restorff, James B.; Clark, Arthur E.; Cullen, James B.; Lograsso, Thomas A.

    2001-07-01

    Tb1-xDyxZn(01-xDyx alloys exist in the hexagonal phase, with the c-axis extremely hard, whereas for Tb1-xDyxFe2, a cubic Laves phase alloy, very hard <111> axes can be changed to very hard <100> axes by increasing x from 0 to 1. (In fact, the existence of a near zero magnetic anisotropy by the proper choice of x is the origin of the well-known Terfenol-D alloys, Tb1-xDyxFe2). The Tb$1-x)DyxZn system discussed here is particularly attractive because of the simplicity of its crystal structure (CsCl), its relatively high Curie temperatures (for rare earth alloys), and the existence of a large (uv0) phase for T < 50K. A summary of some of the important properties of these three alloy systems is given in Table I. In all these systems, at least one of the magnetostriction constraints is very large.

  1. Deep-level-driven anomalous temperature dependence of lattice constants and energy gaps in MgxZn1-xSe and MgxZn1-xSe:Co2+ single crystals

    NASA Astrophysics Data System (ADS)

    Kim, Wha-Tek

    1999-02-01

    Pure MgxZn1-xSe (type C) single crystals were grown by the closed-tube sublimation method. MgxZn1-xSe (type D) and MgxZn1-xSe:Co2+ single crystals in which deep levels exist were grown by the chemical transport reaction method. The temperature dependence of the optical energy gaps of the MgxZn1-xSe (type C) single crystals fitted well with the Manoogian-Leclerc equation. However, the temperature dependence of the optical energy gaps of the MgxZn1-xSe (type D) and MgxZn1-xSe:Co2+ single crystals was anomalous in the temperature range of 10-70 K. This anomalous temperature dependence was analyzed as originating from a volume dilation effect due to deep-level defects.

  2. Study of electric properties of amorphous AgGe1+xAs1-xS3 with content of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Melnikova, Nina; Kurochka, Kirill; Volkova, Yana

    2013-06-01

    Multicomponent copper and silver chalcogenides have been known as promising materials for scientific and applied purposes. These materials are also under intense investigation for application in a phase-change random access memory. In order to obtain materials with a high ionic conductivity component, glassy silver chalcogenides AgGe1+xAs1-xS3 with the addition of nanotubes were synthesized. In this work the study of electrical properties of the amorphous chalcogenide AgGe1.4As0.6S3 (x = 0.4) with carbon nanotube content at a frequency of the alternating-current electric field varying from 1 Hz to 5 MHz and on direct current at ambient pressure and at pressure up to 30 GPa are presented. The ion transport was confirmed by means DC measurements in cells with blocking ion component of conductivity electrodes. An evaluation of the proportion of ionic conductivity can make a preliminary conclusion that the ionic component of the conductivity of at least 98%. Analyze of the baric dependences of AC properties have shown that the dielectric loss tangent and the real part of an admittance of the AgGe1.4As0.6S3 with carbon nanotube content compound exponentially increase with a pressure increase from 1 up to 30 GPa. The study was supported in part by the Ural Federal University development program with the financial support of young scientists; and by the Russian Foundation for Basic Research, project No. 12-02-31607.

  3. Gettering effects in Si{sub x}Ge{sub 1-x} single crystalline wafers

    SciTech Connect

    Wollweber, J.; Schulz, D.; Schroeder, W.

    1995-08-01

    The new interest in single crystal growth of SiGe solid solutions is caused by the development of advanced electronics. The SiGe alloys are mostly used in the form of Si/Si{sub x}Ge{sub 1-x} epitaxial layers in heterostructures, the perfect bulk crystals are required to study fundamental properties. Furthermore, Si{sub x}Ge{sub 1-x} crystals can be used as a substrate material instead of Silicon in order to avoid the buffer layers between the Silicon substrate and strained Si{sub x}Ge{sub 1-x}. Monocrystalline SiGe alloys may be a potential candidate as a base material for infrared solar cells too because of an enhanced IR-sensitivity. In this paper we report a new approach to the growth of Si{sub x}Ge{sub 1-x} single crystals (up to 2{double_prime} in diameter) using the crucible free rf-heated float zone technique as well as the Czochralski-technique for solar cells. The goal is to produce solar cells with an increased photo current in comparison to Silicon cells. based on the lower bandgap of the alloyed crystal. In order to be able to use the Si cells technology (a matter still pending to be proven), low contents of Ge are intended, desirably in the range of about x=0.2. It is worth to mention, that in the conventional Silicon cell processes which give efficiencies up to 18-19%, this efficiency is not limited by the bulk base recombination in the lifetime is above 200 {mu}s there. We can conclude, that there is no basic limitation did prevents Si{sub x}Ge{sub 1-x} wafers to present high lifetimes, above 200{mu}s, at least if the Ge content is below 5%. We can also conclude that the phosphorous gettering from a POCl{sub 3} source, used in silicon, can be successfully used to enhance lifetimes in Si{sub x}Ge{sub 1-x}, at least for the Ge concentration used here.

  4. General properties of CePd1-xRhx at quantum critical point

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Popov, K. G.

    2009-10-01

    The heavy-fermion metal CePd1-xRhx evolves from ferromagnetism at x=0 to a non-magnetic state at some critical concentration xc. Utilizing the quasiparticle picture and the concept of fermion condensation quantum phase transition (FCQPT), we address the non-Fermi liquid (NFL) behavior of ferromagnet CePd1-xRhx and show that it coincides with that of antiferromagnets YbRh2(Si0.95Ge0.05)2 and CeCoIn 5, paramagnets CeRu 2Si 2 and CeNi 2Ge 2 and 2D 3He. We show that the NFL behavior is independent of the peculiarities of specific alloy and universal. Our study of the NFL behavior allows us to calculate the magnetoresistance of CeCoIn 5. Obtained results are in good agreement with facts and reveal a new scaling behavior of magnetoresistance.

  5. Band gap bowing and electron localization of (GaxIn1-x)N

    SciTech Connect

    Lee, Byounghak; Wang, Lin-Wang

    2006-05-09

    The band gap bowing and the electron localization ofGaxIn1-xN are calculated using both the local density approximation (LDA)and screened-exchange local density functional (sX-LDA) methods. Thecalculated sX-LDA band gaps are in good agreement with the experimentallyobserved values, with errors of -0.26 and 0.09 eV for bulk GaN and InN,respectively. The LDA band gap errors are 1.33 and 0.81 eV for GaN andInN, in order. In contrast to the gap itself, the band gap bowingparameter is found to be very similar in sX-LDA and LDA. We identify thelocalization of hole states in GaxIn1-xN alloys along In-N-In chains. Thepredicted localizationis stronger in sX-LDA.

  6. Composition measurement of epitaxial Sc x Ga1-x N films

    NASA Astrophysics Data System (ADS)

    Tsui, H. C. L.; Goff, L. E.; Barradas, N. P.; Alves, E.; Pereira, S.; Palgrave, R. G.; Davies, R. J.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.

    2016-06-01

    Four different methods for measuring the compositions of epitaxial Sc x Ga1-x N films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial Sc x Ga1-x N films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indirectly using c lattice parameter measurements from x-ray diffraction and c/a ratio measurements from electron diffraction patterns. RBS measurements were taken as a standard reference. XPS was found to underestimate the Sc content, whereas c lattice parameter and c/a ratio were not reliable for composition determination due to the unknown degree of strain relaxation in the film. However, the Sc flux used during growth was found to relate linearly with x and could be used to estimate the Sc content.

  7. Compositional dependence of the band-gap of Ge1-x-ySixSny alloys

    NASA Astrophysics Data System (ADS)

    Wendav, Torsten; Fischer, Inga A.; Montanari, Michele; Zoellner, Marvin Hartwig; Klesse, Wolfgang; Capellini, Giovanni; von den Driesch, Nils; Oehme, Michael; Buca, Dan; Busch, Kurt; Schulze, Jörg

    2016-06-01

    The group-IV semiconductor alloy Ge1-x-ySixSny has recently attracted great interest due to its prospective potential for use in optoelectronics, electronics, and photovoltaics. Here, we investigate molecular beam epitaxy grown Ge1-x-ySixSny alloys lattice-matched to Ge with large Si and Sn concentrations of up to 42% and 10%, respectively. The samples were characterized in detail by Rutherford backscattering/channeling spectroscopy for composition and crystal quality, x-ray diffraction for strain determination, and photoluminescence spectroscopy for the assessment of band-gap energies. Moreover, the experimentally extracted material parameters were used to determine the SiSn bowing and to make predictions about the optical transition energy.

  8. Influence of Bi-related impurity states on the bandgap and spin-orbit splitting energy of dilute III-V-Bi alloys: InP1-xBix, InAs1-xBix, InSb1-xBix and GaSb1-xBix

    NASA Astrophysics Data System (ADS)

    Samajdar, D. P.; Dhar, S.

    2016-01-01

    Valence Band Anticrossing (VBAC) Model is used to calculate the changes in band structure of Bi containing alloys such as InP1-xBix, InAs1-xBix, InSb1-xBix and GaSb1-xBix due to the incorporation of dilute concentrations of bismuth. The coupling parameter CBi which gives the magnitude of interaction of Bi impurity states with the LH, HH and SO sub bands in VBAC depends on the increase in the HH/LH related energy level EHH/LH+, location of the Bi related impurity level EBi and valence band offset ΔEVBM between the endpoint compounds in the corresponding III-V-Bi. The reduction in band gap as well as the enhancement of the spin-orbit splitting energy is well explained using this model and the calculated results are compared with the results of Virtual Crystal Approximation (VCA) and Density Functional Theory (DFT) calculations, as well as with the available experimental data and are found to have good agreement. The incorporation of Bi mainly perturbs the valence band due to the interaction of the Bi impurity states with the HH, LH and SO bands. The lowering of the conduction band minimum (CBM) due to VCA is added with the upward movement of the HH/LH bands to get the total reduction in band gap for the bismides. The valence band shifts of 31.9, 32.5, 20.8 and 12.4 meV/at%Bi for InP1-xBix, InAs1-xBix, InSb1-xBix and GaSb1-xBix respectively constitute 65, 76, 59 and 31% of the total band gap reduction and the rest is the contribution of the conduction band shift. The spin-orbit splitting energy also shows significant increase with the maximum change in InPBi and the minimum in InSbBi. The same is true for Ga containing bismides if we make a comparison with the available values for GaAsBi and GaPBi with that of GaSbBi. It has also been observed that the increase in splitting energy is greater in case of the bismides such as InAsBi, InPBi and GaAsBi than the bismides such as InSbBi and GaSbBi with the parent substrates having higher values of splitting energy. This may

  9. Optical properties of ZnxMg1-xSe/GaAs heterojunctions grown by MBE

    NASA Astrophysics Data System (ADS)

    Bala, Waclaw; Glowacki, Grzegorz; Gapinski, Adam

    1997-06-01

    This works focuses on the study of optical properties of ZnxMg1-xSe epilayers grown by molecular beam epitaxy on n-type (001) GaAs substrates. Luminescence, reflectivity and Raman spectroscopy are studied. Photoluminescence spectra of the samples are dominated by blue emission bands, which can be associated with radiative recombination of free excitons. The reflectivity spectra were used to investigate the refractive index value and the thickness of the layers. Moreover the temperature dependence of the band-gap energy of ZnxMg1-xSe epilayers was determined. Using Raman spectroscopy we can obtain information about two kinds of longitudinal optical phonon modes observed at room temperature, whose frequencies and intensities depend characteristically on Mg content.

  10. Microscopic dynamics of an amorphous C60 x /C70(1 - x) fullerene mixture

    NASA Astrophysics Data System (ADS)

    Khusnutdinoff, R. M.; Mokshin, A. V.; Takhaviev, I. D.

    2015-02-01

    This paper presents the results of investigation of the propagation mechanism of collective excitations in amorphous C60 x /C70(1 - x) fullerene mixtures (with equimolar concentration x = 0.50), which were obtained using molecular dynamics simulation. The critical glass-transition temperature of the system T c = 1548 K was determined from the change in the behavior of the Wendt-Abraham parameter. Spectral densities of the time correlation functions of the longitudinal and transverse currents for a wide region of wave numbers at temperatures below the glass-transition temperature were calculated. It was found that the dynamics of density fluctuations in amorphous C60 x /C70(1 - x) fullerene mixtures is characterized by two dispersion acoustic-like branches of the longitudinal and transverse polarizations. The influence of poly-dispersity and form factor of the molecule of the mixture component on the microscopic dynamics of the density fluctuation in multicomponent systems was established.

  11. Antiferromagnetic spin excitations in single crystals of nonsuperconducting Li$_{1-x}$FeAs

    SciTech Connect

    Wang, Meng; Wang, X.C.; Harriger, Leland W; Luo, H.Q.; Zhao, Yang; Lynn, J. W.; Liu, Q.Q.; Jin, C.Q.; Fang, Chen; Hu, Jiangping; Dai, Pengcheng

    2011-01-01

    We use neutron scattering to determine spin excitations in single crystals of nonsuperconducting Li1 xFeAs throughout the Brillouin zone. Although angle resolved photoemission experiments and local density approximation calculations suggest poor Fermi surface nesting conditions for antiferromagnetic (AF) order, spin excitations in Li1 xFeAs occur at the AF wave vectors Q = (1,0) at low energies, but move to wave vectors Q = ( 0.5, 0.5) near the zone boundary with a total magnetic bandwidth comparable to that of BaFe2As2. These results reveal that AF spin excitations still dominate the low-energy physics of these materials and suggest both itinerancy and strong electron-electron correlations are essential to understand the measured magnetic excitations.

  12. Thermal properties of Er:LuxGd1-xVO4 crystals

    NASA Astrophysics Data System (ADS)

    Yan, Zhenghuo; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Ma, Changqin; Wang, Jiyang

    2014-06-01

    A new series Er:LuxGd1-xVO4 (x=0.1,0.24,0.48,0.57,0.79 and 0.9)mixed laser crystals have been successfully grown by the Czochralski method with 1% Er3+ concentration.The thermal properties of Er:LuxGd1-xVO4crystals series crystals were investigated systematically, including the thermal expansion, specific heat, thermal diffusion coefficients, and thermal conductivities. The anisotropy and variation of the thermal properties with the component x were also achieved and discussed based on their structure. All the results showed that this mixed crystals should have promising applications in the moderate-power lasers.

  13. Direct Observation of the E_ Resonant State in GaAs1-xBix

    SciTech Connect

    Alberi, Kirstin; Beaton, Daniel A.; Mascarenhas, Angelo

    2015-12-15

    Bismuth-derived resonant states with T2 symmetry are detected in the valence band of GaAs1-xBix using electromodulated reflectance. A doublet is located 42 meV below the valence band edge of GaAs that is split by local strain around isolated Bi impurity atoms. A transition associated with a singlet is also observed just above the GaAs spin orbit split-off band. These states move deeper into the valence band with increasing Bi concentration but at a much slower rate than the well-known giant upward movement of the valence band edge in GaAs1-xBix. Our results provide key new insights for clarifying the mechanisms by which isovalent impurities alter the bandstructure of the host semiconductor.

  14. Study of electrical and thermoelecrical properties of sulfides Tm x Mn1- x S

    NASA Astrophysics Data System (ADS)

    Aplesnin, S. S.; Romanova, O. B.; Galyas, A. I.; Sokolov, V. V.

    2016-01-01

    Variable-valence Tm x Mn1- x S (0 ⩽ x ⩽ 0.15) compounds have been synthesized and their structural, electrical, and thermoelectrical properties have been studied in the temperature range of 80-1100 K. The regions of existence of solid solutions of sulfides Tm x Mn1- x S with the NaCl-type fcc lattice have been determined. It has been found that, as thulium ions are substituted for manganese cations, the electrical resistivity increases, and the lattice parameter increases more sharply than that corresponding to the Vegard's law. The study of the temperature dependences of the thermopower coefficient has revealed that the current carrier sign is retained to 500 K for all the substitution concentrations, and the charge carrier type changes from the hole type to the electron type with variations in the temperature. The experimental data have been explained in terms of the exciton model.

  15. Dry-wet digital etching of Ge1-xSnx

    NASA Astrophysics Data System (ADS)

    Shang, Colleen K.; Wang, Vivian; Chen, Robert; Gupta, Suyog; Huang, Yi-Chiau; Pao, James J.; Huo, Yijie; Sanchez, Errol; Kim, Yihwan; Kamins, Theodore I.; Harris, James S.

    2016-02-01

    The development of a precise micromachining process for Ge1-xSnx has the potential to enable both the fabrication and optimization of Ge1-xSnx-based devices in photonics and microelectromechanical systems. We demonstrate a digital etching scheme for Ge0.922Sn0.078 based on a two-stage, highly selective CF4 plasma dry etch and HCl wet etch. Using X-Ray Reflectivity, we show consistent etch control as low as 1.5 nm per cycle, which is defined as one dry etch step followed by one wet etch step. The etch rate increases to 3.2 nm per cycle for a longer dry etch time due to physical sputtering contributions, accompanied by an increase in RMS surface roughness. By operating within a regime with minimal sputtering, we demonstrate that good digital etch depth control and surface quality can be achieved using this technique.

  16. Robust superconductivity and transport properties in (Li1- x Fe x )OHFeSe single crystals

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Xing, Jie; Zhu, XiYu; Yang, Huan; Wen, Hai-Hu

    2016-05-01

    The recently discovered (Li1- x Fe x )OHFeSe superconductor with T c about 40 K provides a good platform for investigating the magnetization and electrical transport properties of FeSe-based superconductors. By using a hydrothermal ion-exchange method, we have successfully grown crystals of (Li1- x Fe x )OHFeSe. X-ray diffraction on the sample shows the single crystalline PbO-type structure with the c-axis preferential orientation. Magnetic susceptibility and resistive measurements show an onset superconducting transition at around T c =38.3 K. Using the magnetization hysteresis loops and Bean critical state model, a large critical current J s is observed in low temperature region. The critical current density is suppressed exponentially with increasing magnetic field. Temperature dependencies of resistivity under various currents and fields are measured, revealing a robust superconducting current density and bulk superconductivity.

  17. Quantum criticality in CePt1-xNixSi2

    NASA Astrophysics Data System (ADS)

    Baumbach, R. E.; Lu, X.; Ronning, F.; Thompson, J. D.; Bauer, E. D.

    2012-12-01

    We report measurements of the specific heat, electrical resistivity, and magnetic susceptibility for CePt1-xNixSi2 from which we develop a T - x phase diagram that includes a quantum critical point near xcr ≈ 0.125 and accompanying non-Fermi-liquid behavior in a "v"-shaped region. This phase diagram is strikingly similar to that of CePtSi2 under applied pressure P, suggesting that CePt1-xNixSi2 provides a model system in which a T - P - x phase diagram can be smoothly generated, thereby allowing a systematic study of the influence of disorder on quantum criticality.

  18. Pressure-induced structural transition of CdxZn1-xO alloys

    NASA Astrophysics Data System (ADS)

    Chen, Yabin; Zhang, Shuai; Gao, Weiwei; Ke, Feng; Yan, Jinyuan; Saha, Bivas; Ko, Changhyun; Suh, Joonki; Chen, Bin; Ager, Joel W.; Walukiewicz, Wladek; Jeanloz, Raymond; Wu, Junqiao

    2016-04-01

    CdxZn1-xO alloys, as a transparent conducting oxide, have recently attracted much attention for potential optoelectronic applications. In this letter, we report a hydrostatic pressure-induced phase transition of CdxZn1-xO alloys from the wurtzite to the rocksalt structure and its phase diagram probed using a diamond anvil cell. It is found that the transition pressure, determined by changes in optical and structural properties, depends sensitively on the composition. As the Cd content increases, the critical pressure decreases, until at x = 0.67 where the alloy is intrinsically stable in the rocksalt phase even at ambient pressure. The wurtzite phase is light emitting with a direct bandgap that slightly widens with increasing pressure, while the rocksalt phase has a much wider bandgap that is indirect. The pressure-sensitive light emission and phase transition may find potential applications in fields such as stress sensing and energy storage.

  19. ARPES Study on the Strongly Correlated Iron Chalcogenides Fe1+ySexTe1-x

    NASA Astrophysics Data System (ADS)

    Liu, Zhongkai

    2014-03-01

    The level of electronic correlation has been one of the key questions in understanding the nature of iron-based superconductivity. Using Angle Resolved Photoemission Spectroscopy (ARPES), we systematically investigated the correlation level in the iron chalcogenide family Fe1+ySexTe1-x. For the parent compound Fe1.02Te, we discovered ``peak-dip-hump'' spectra with heavily renormalized quasiparticles in the low temperature antiferromagnetic (AFM) state, characteristic of coherent polarons seen in other correlated materials with complex electronic and lattice interactions. As the temperature (or Se ratio x) increases and Fe1.02SexTe1-x is in the paramagnetic (PM) phase, we observed dissociation behavior of polarons, suggestive of connection between the weakening electron-phonon coupling and AFM. Further increase of x leads to an incoherent to coherent crossover in the electronic structure, indicating a reduction in the electronic correlation as the superconductivity emerges. Furthermore, the reduction of the electronic correlation in Fe1+ySexTe1-x evolves in an orbital-dependent way, where the dxy orbital is influenced most significantly. At the other end of the phase diagram (FeSe) where the single crystal is not stable, we have studied the MBE-grown thin film which also reveals orbital-dependent strong correlation in the electronic structure. Our findings provide a quantitative comprehension on the correlation level and its evolution on the phase diagram of Fe1+ySexTe1-x. We discuss the physical scenarios leading to strong correlations and its connection to superconductivity.

  20. Investigation of thermoelectromotive force in Al(x)In(1-x)Sb solid solultions

    NASA Astrophysics Data System (ADS)

    Agaev, Ia.; Mikhailov, A. P.; Sadykov, K. B.; Ismailov, O.; Toilyev, A.

    The compensation method was used to determine the differential thermoelectromotive force of Al(x)In(1-x)Sb (x = 0.05, 0.1, 0.2) solid solutions in the 100-300 K temperature range. The behavior of the thermoemf in this low-temperature range was found to be anomalous, a fact that is explained by the phonon entrainment of holes.

  1. Thermographic analyses of the growth of Cd1-xZnxTe single crystals

    SciTech Connect

    Kopach, O.V.; Bolotnikov, A.; Shcherbak, Larysa P.; Fochuk, Petro M.; and James, Ralph B.

    2010-08-01

    Bulk Cd1-xZnxTe (0

  2. Multi-point quasi-rational approximants for the modified Bessel function I1(x)

    NASA Astrophysics Data System (ADS)

    Martin, P.; Olivares, J.; Cortés-Vega, L.; Sotomayor, A.

    2016-08-01

    Approximants for the modified Bessel function I1(x) has been found using the multi-point quasi-rational technique. The approximations here determined has good accuracy for any positive value of the variable, and it seems to be adequate for most of the works where this function are used. Furthermore, the approximants are simple to calculate numerically in a direct way or using any usual MAPLE or MATLAB software.

  3. Capacitance properties in n-type AlxGa1 - xAs

    NASA Astrophysics Data System (ADS)

    Izpura, I.; Muñoz, E.; Hill, G.; Roberts, J.; Pate, M. A.; Mistry, P.; Hall, N. Y.

    1989-12-01

    The electrical properties of n-type AlxGa1-x As, for x>0.2, are governed by deep donor states (formerly called DX centers) created by the isolated donor atoms. We have studied the capacitance properties of such layers for Si and Sn dopants. The meanings of the capacitance-voltage carrier profiling and of the capacitance dependence with temperature have been considered. The deep donor energy position with respect to the Γ minimum has been determined.

  4. Arsenic-terminated Ge(111): An ideal 1 x 1 surface

    SciTech Connect

    Bringans, R.D.; Uhrberg, R.I.G.; Bachrach, R.Z.; Northrup, J.E.

    1985-07-29

    Arsenic interaction with the Ge(111) surface results in the replacement of the outer Ge layer with an As layer. This system has a 1 x 1 symmetry and the calculated positions of the As atoms are very close to the positions expected from bulk bond lengths. Ge(111):As is thus a model ideal surface and a comparison is made of an experimental and a theoretical determination of its fully occupied surface band.

  5. Investigation of Properties of As x Se1- x Thin Films for Direct Conversion

    NASA Astrophysics Data System (ADS)

    Bharathan, P.

    2015-08-01

    The electrical characteristics of metal/As x Se1- x /metal structures for potential use in direct-conversion x-ray detectors and imaging applications are reported. The structures exhibit current rectification in both solid (amorphous, crystalline) and liquid As x Se1- x phases. Capacitance-voltage measurements of the device in the amorphous phase find that the capacitance is essentially independent of bias. Transport phenomenon in the amorphous phase of the film was found to be influenced by trapping and the space-charge effect. In the liquid and crystalline phases, transport in the devices was characteristic of thermionic emission. The indium tin oxide (ITO)/a-As0.01Se0.99/Au 2.85- μm-thick device gave a short-circuit current ( I sc) of 0.16 μA, an open-circuit voltage ( V oc) of 0.1 V, and a fill factor of 0.29 at 384 K under irradiation from visible light. An interpretation of the current-voltage characteristics in the amorphous phase has been made using the self-consistent drift-diffusion model of transport, and material parameters of a-As x Se1- x films have been extracted by fitting the experimentally measured I- V data. The model indicated that transport in the ITO/a-As0.01Se0.99/Au film was dominated by shallow-level traps with density of 5 × 1015 cm-3 at depth of 0.3 eV from the band edge. The photoconversion efficiency was found to be limited by low photogeneration efficiency, high amount of recombination losses, and the level of charge injection in the a-As x Se1- x films.

  6. Nanocrystalline Ce1- x La x O2- δ Solid Solutions Synthesized by Hydrolyzing and Oxidizing

    NASA Astrophysics Data System (ADS)

    Hou, Xueling; Xue, Yun; Han, Ning; Lu, Qianqian; Wang, Xiaochen; Phan, Manh-Huong; Zhong, Yunbo

    2016-05-01

    We undertook a novel batch production approach for the synthesis of CeO2 nanopowders doped with rare earth elements. Solid solution nanopowders of Ce1- x La x O2- δ ( x = 0.15) were successfully synthesized in a large-scale and low-cost production by hydrolyzing and oxidizing Ce-La-C alloys at room temperature and subsequent calcining of their powders at different temperatures (873-1073 K) for 1 h. The Ce-La-C alloys were prepared in a vacuum induction melting furnace. The final products were characterized by x-ray diffraction, transmission electron microscopy, Brunner-Emmet-Teller (BET) surface area analyzer, and Raman spectroscopy. The calculated lattice parameters of the cubic fluorite-type phase of CeO2 tended to increase when La3+ was incorporated into CeO2. The F 2g band shift and the absence of a peak corresponding to La2O3 in the Raman spectra consistently confirmed the incorporation of the La3+ ion into CeO2, and the formation of Ce1- x La x O2- δ solid solutions as manifested by increased oxygen vacancy defects. High-quality Ce1- x La x O2- δ nanopowders of ~10-15 nm diameter with a high BET surface area of ~77 m2 g-1 were obtained. The average crystallite size of Ce1- x La x O2- δ was found to be smaller than that of CeO2 for the same calcination temperature of 1073 K, demonstrating that the introduction of La3+ into CeO2 can stabilize the host lattice and refine the grain size at high temperatures.

  7. Photovoltaic Devices Employing Ternary PbSxSe1-x Nanocrystals

    SciTech Connect

    Ma, Wanli; Luther, Joseph; Zheng, Haimei; Wu, Yue; Alivisatos, A. Paul

    2009-02-05

    We report solar cells based on highly confined nanocrystals of the ternary compound PbSxSe1-x. Crystalline, monodisperse alloyed nanocrystals are obtained using a one-pot, hot injection reaction. Rutherford back scattering and energy filtered transmission electron microscopy suggest that the S and Se anions are uniformly distributed in the alloy nanoparticles. Photovoltaic devices made using ternary nanoparticles are more efficient than either pure PbS or pure PbSe based nanocrystal devices.

  8. Development of (MnO)1-x(ZnO)x Alloys for Water Splitting Applications

    NASA Astrophysics Data System (ADS)

    Ndione, Paul; Warren, Emily; Peng, Haowei; Lany, Stephan; Ginley, David; Zakutayev, Andriy

    2014-03-01

    Using high throughput combinatorial synthesis, measurement and analysis methodologies, we rapidly investigate the composition related structural, optical, and electrical properties of (MnO)1-x(ZnO)x alloys and identify candidates materials for a more detailed study in PEC applications. The (MnO)1-x(ZnO)x thin films are synthesized using combinatorial pulsed laser deposition with continuous orthogonal gradients in both chemical composition and substrate temperature. The solubility limit of ZnO into MnO is determined using the disappearing phase method and found to decrease with increasing temperature. For example, (MnO)1-x(ZnO)x deposited at 300 C exhibit only the tetrahedral wurzite (WZ) structure instead of the rocksalt (RS) one at x>0.4. Optical measurements indicate the strong reduction of the optical band gap associated with the RS to WZ transition, and are consistent with the first-principles theory prediction of Egap = 2.1 eV at a x =0.5 alloy composition. The values of the electrical conductivity for the Ga-doped (MnO)1-x(ZnO)x samples deposited at 300 C from a 4% Ga-doped ZnO target are determined to be <2 S/cm and 100 S/cm for the RS and WZ structure respectively per atom of Ga. These results suggest that Ga-doped MnO-ZnO alloys present a promising materials system for water oxidation in a PEC cell. This work was supported through the Center for Inverse Design, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  9. Highly mismatched GaN1-x Sb x alloys: synthesis, structure and electronic properties

    NASA Astrophysics Data System (ADS)

    Yu, K. M.; Sarney, W. L.; Novikov, S. V.; Segercrantz, N.; Ting, M.; Shaw, M.; Svensson, S. P.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

    2016-08-01

    Highly mismatched alloys (HMAs) is a class of semiconductor alloys whose constituents are distinctly different in terms of size, ionicity and/or electronegativity. Electronic properties of the alloys deviate significantly from an interpolation scheme based on small deviations from the virtual crystal approximation. Most of the HMAs were only studied in a dilute composition limit. Recent advances in understanding of the semiconductor synthesis processes allowed growth of thin films of HMAs under non-equilibrium conditions. Thus reducing the growth temperature allowed synthesis of group III-N-V HMAs over almost the entire composition range. This paper focuses on the GaN x Sb1-x HMA which has been suggested as a potential material for solar water dissociation devices. Here we review our recent work on the synthesis, structural and optical characterization of GaN1-x Sb x HMA. Theoretical modeling studies on its electronic structure based on the band anticrossing (BAC) model are also reviewed. In particular we discuss the effects of growth temperature, Ga flux and Sb flux on the incorporation of Sb, film microstructure and optical properties of the alloys. Results obtained from two separate MBE growths are directly compared. Our work demonstrates that a large range of direct bandgap energies from 3.4 eV to below 1.0 eV can be achieved for this alloy grown at low temperature. We show that the electronic band structure of GaN1-x Sb x HMA over the entire composition range is well described by a modified BAC model which includes the dependence of the host matrix band edges as well as the BAC model coupling parameters on composition. We emphasize that the modified BAC model of the electronic band structure developed for the full composition of GaN x Sb1-x is general and is applicable to any HMA.

  10. Infrared waveguiding in Si 1-x- y Ge x C y upon silicon

    NASA Astrophysics Data System (ADS)

    Soref, Richard A.; Atzman, Ziv; Shaapur, Farhad; Robinson, Mcdonald; Westhoff, Richard

    1996-03-01

    Polarization-independent waveguiding at 1.32 and 1.54 mu m was observed in single-crystal S1-x-y GexC y grown nearly lattice matched upon Si(100) by chemical vapor deposition. Losses were <5 dB / cm at 1.54 mu m . Experiments indicate that the band gap of three SiGeC alloy waveguides was in the 0.93-0.99-eV range, in agreement with theory.

  11. Purification, growth, and characterization of Zn(x)Cd(1-x)Se crystals

    NASA Technical Reports Server (NTRS)

    Silberman, E.; Burger, A.; Chen, W.; Henderson, D. O.; Morgan, S. H.; Springer, John M.; Yao, Y.

    1989-01-01

    The purification of starting materials which were used in the growth of Zn(x)Cd(1-x)Se (x = 0.2) single crystals using the traveling solution method (TSM) is reported. Up to 13 cm long single crystals and as grown resistivities of 6 x 10(exp 12) ohm/cm could be achieved. Infrared and Raman spectra of Zn(0.2)Cd(0.8)Se are also presented and discussed.

  12. OPTICAL PROPERTIES OF THE CUBIC AlxGa1-xN ALLOY

    NASA Astrophysics Data System (ADS)

    Hadji, S.; Berrah, S.; Abid, H.

    2013-07-01

    In this paper, we present numerical calculations based on the full potential augmented plane wave (FP-LAPW) method within the local density approximation (LDA) to study the optical properties of the ternary alloy AlxGa1-xN. The shape of the dielectric function, the refractive index, and the absorption coefficient versus photon energy were presented. From the results, we deduce the possibility of this alloy to be used in the optoelectronic and photovololtaic area.

  13. High-Gain AlxGa1-xAs/GaAs Transistors For Neural Networks

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Hoon; Lin, Steven H.

    1991-01-01

    High-gain AlxGa1-xAs/GaAs npn double heterojunction bipolar transistors developed for use as phototransistors in optoelectronic integrated circuits, especially in artificial neural networks. Transistors perform both photodetection and saturating-amplification functions of neurons. Good candidates for such application because structurally compatible with laser diodes and light-emitting diodes, detect light, and provide high current gain needed to compensate for losses in holographic optical elements.

  14. Metal free growth and characterization of InAs1-xPx nanowires

    SciTech Connect

    Mandl, Bernhard; Stangl, Julian; Brehm, Moritz; Fromherz, Thomas; Bauer, Guenther; Maartensson, Thomas; Samuelson, Lars; Seifert, Werner

    2007-04-10

    InAs nanowires have been grown without the use of Au or other metal particles as catalyst by metal-organic vapor phase epitaxy. The nanowires growth is initiated by a thin layer of SiOx. The wires exhibit a non-tapered shape with a hexagonal cross section. In addition to InAs also InAs1-xPx wires are grown and the incorporation of P is studied by photoluminescence.

  15. Ni ohmic contacts to n-type Ge1-x-ySixSny using phosphorous implant and segregation

    NASA Astrophysics Data System (ADS)

    Wang, Suyuan; Zheng, Jun; Xue, Chunlai; Li, Chuanbo; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2015-12-01

    N-type Ge1-x-ySixSny ternary alloy was successfully grown by the Sb in situ doping technique through sputter epitaxy method. A study comparing the electrical contact characteristic of n- Ge1-x-ySixSny with and without phosphorous implantation was performed. Ohmic contacts to n-type Ge1-x-ySixSny are realized by shallow P implant and Ni(Ge1-x-ySixSny) formation after rapid thermal annealing at 400 °C. It is proposed that the ohmic behavior is mainly attributed to the phosphorous segregation effect confirmed by secondary ion mass spectroscopy.

  16. Thermophysical and anion diffusion properties of (U x ,Th1-x )O2.

    PubMed

    Cooper, Michael W D; Murphy, Samuel T; Fossati, Paul C M; Rushton, Michael J D; Grimes, Robin W

    2014-11-01

    Using molecular dynamics, the thermophysical properties of the (U x ,Th1-x )O2 system have been investigated between 300 and 3600 K. The thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure is explained in terms of defect formation and diffusivity on the oxygen sublattice. Vegard's law is approximately observed for solid solution thermal expansion below 2000 K. Different deviations from Vegard's law above this temperature occur owing to the different temperatures at which the solid solutions undergo the superionic transition (2500-3300 K). Similarly, a spike in the specific heat, associated with the superionic transition, occurs at lower temperatures in solid solutions that have a high U content. Correspondingly, oxygen diffusivity is higher in pure UO2 than in pure ThO2. Furthermore, at temperatures below the superionic transition, oxygen mobility is notably higher in solid solutions than in the end members. Enhanced diffusivity is promoted by lower oxygen-defect enthalpies in (U x ,Th1-x )O2 solid solutions. Unlike in UO2 and ThO2, there is considerable variety of oxygen vacancy and oxygen interstitial sites in solid solutions generating a wide range of property values. Trends in the defect enthalpies are discussed in terms of composition and the lattice parameter of (U x ,Th1-x )O2.

  17. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  18. Required composition uniformity of Hg1-xCdxTe substrate for focal plane arrays

    NASA Astrophysics Data System (ADS)

    Gopal, Vishnu

    1996-10-01

    This paper presents a comparison of theoretically predicted spatial NETD and mean temporal NETD as a function of the composition uniformity of Hg(subscript 1-x)Cd(subscript x)Te substrate used in the fabrication of IR detector arrays. The prediction of the spatial NETD is based on the residual spatial noise left behind in the FPA after implementing a linear two point nonuniformity compensation algorithm. The effect of using an optical filter on the spatial NETD is also included to show that the specifications on the composition uniformity of the Hg(subscript 1-x)Cd(subscript x)Te substrate can be partially relaxed by using an optical filter whose cut-off wavelength is less than the cutoff wavelength of the photodiodes of mean response. The composition uniformity leading to temporal noise rather than the spatial noise limited performances are suggested to be indicating the required composition uniformity of Hg(subscript 1-x)Cd(subscript x)Te substrate for focal plane arrays (FPA). The results are presented for both MWIR and LWIR HgCdTe hybrid FPAs.

  19. Spectral and structural features of Lu1 - x RE x BO3 compounds

    NASA Astrophysics Data System (ADS)

    Shmurak, S. Z.; Kedrov, V. V.; Kiselev, A. P.; Fursova, T. N.; Shmyt'ko, I. M.

    2015-08-01

    The luminescence spectra, luminescence excitation spectra, IR absorption spectra, and crystal structure of orthoborates Lu1 - x RE x BO3 ( RE = Eu, Gd, Tb, Y, Dy) have been investigated. It has been found that the solid solution consisting of a LuBO3 orthoborate, which has two stable structural modifications (calcite and vaterite), and an REBO3 orthoborate, which has one structural modification (vaterite), crystallizes only in the vaterite structure when the concentration of a rare-earth ion substituting for lutetium exceeds 15-20 at %. The investigation of the photoluminescence spectra has demonstrated that, for rare-earth ions Lu3+, Eu3+, Y3+, and Gd3+ in the vaterite modification of Lu1 - x RE x BO3 orthoborates, there are at least two positions that are not equivalent in the symmetry of the local environment. It has been established that the maximum intensity of the luminescence of the vaterite modification of Lu1 - x Tb x BO3 compounds synthesized at 970°C, which is observed at a terbium concentration of 15 at %, is several times higher than the maximum intensity of the luminescence of the calcite modification.

  20. Nanoscopy of Phase Separation in InxGa1-xN Alloys.

    PubMed

    Abate, Yohannes; Seidlitz, Daniel; Fali, Alireza; Gamage, Sampath; Babicheva, Viktoriia; Yakovlev, Vladislav S; Stockman, Mark I; Collazo, Ramon; Alden, Dorian; Dietz, Nikolaus

    2016-09-01

    Phase separations in ternary/multinary semiconductor alloys is a major challenge that limits optical and electronic internal device efficiency. We have found ubiquitous local phase separation in In1-xGaxN alloys that persists to nanoscale spatial extent by employing high-resolution nanoimaging technique. We lithographically patterned InN/sapphire substrates with nanolayers of In1-xGaxN down to few atomic layers thick that enabled us to calibrate the near-field infrared response of the semiconductor nanolayers as a function of composition and thickness. We also developed an advanced theoretical approach that considers the full geometry of the probe tip and all the sample and substrate layers. Combining experiment and theory, we identified and quantified phase separation in epitaxially grown individual nanoalloys. We found that the scale of the phase separation varies widely from particle to particle ranging from all Ga- to all In-rich regions and covering everything in between. We have found that between 20 and 25% of particles show some level of Ga-rich phase separation over the entire sample region, which is in qualitative agreement with the known phase diagram of In1-xGaxN system. PMID:27533107

  1. Optical absorption spectra of substitutional Co2+ ions in Mgx Cd1-x Se alloys

    NASA Astrophysics Data System (ADS)

    Jin, Moon-Seog; Kim, Chang-Dae; Jang, Kiwan; Park, Sang-An; Kim, Duck-Tae; Kim, Hyung-Gon; Kim, Wha-Tek

    2006-09-01

    Optical absorption spectra of substitutional Co2+ ions in Mgx Cd1-x Se alloys were investigated in the composition region of 0.0 x 0.4 and in the wavelength region of 300 to 2500 nm at 4.8 K and 290 K. We observed several absorption bands in the wavelength regions corresponding to the 4A2(4F) 4T1(4P) transition and the 4A2(4F) 4T1(4F) transition of Co2+ at a tetrahedral Td point symmetry point in the host crystals, as well as unknown absorption bands. The several absorption bands were analyzed in the framework of the crystal-field theory along with the second-order spin-orbit coupling. The unknown absorption bands were assigned as due to phonon-assisted absorption bands. We also investigated the variations of the crystal-field parameter Dq and the Racah parameter B with composition x in the Mgx Cd1-x Se system. The results showed that the crystal-field parameter (Dq ) increases, on the other hand, the Racah parameter (B ) decreases with increasing composition x, which may be connected with an increase in the covalency of the metal-ligand bond with increasing composition x in the Mgx Cd1-x Se system.

  2. Transport properties of Y1-xNdxCo2 compounds

    NASA Astrophysics Data System (ADS)

    Uchima, K.; Takeda, M.; Zukeran, C.; Nakamura, A.; Arakaki, N.; Komesu, S.; Takaesu, Y.; Hedo, M.; Nakama, T.; Yagasaki, K.; Uwatoko, Y.; Burkov, A. T.

    2012-12-01

    Electrical resistivity ρ and thermopower S of light rare earth-based pseudo-binary Y1-xNdxCo2 alloys have been measured at temperatures from 2 K to 300 K and under pressures up to 3.5 GPa. The Curie temperature of the alloys, TC, determined from characteristic features in the temperature dependences of the transport properties, decreases with decreasing Nd concentration x and vanishes around xc = 0.3. The residual resistivity has a pronounced maximum at x = xc. The temperature coefficient of thermopower dS/dT at low temperature limit shows a complex dependence on alloy composition: it changes its sign from negative to positive at x ≍ 0.2, having a maximum at x = xc, and is nearly composition independent at x > 0.5. The pressure dependences of TC and ρ0 of Yo.6Ndo.4Co2 reveal the behavior similar to that observed in the Y1-xRxHCo2 (RH = heavy rare earth) alloy systems, which implies that the magnetic state of the Co-3d electron subsystem is responsible for the transport properties in the Y1-xNdxCo2 alloys.

  3. Imaginary part of the optical conductivity of Ba1-xKxBiO3

    NASA Astrophysics Data System (ADS)

    Marsiglio, F.; Carbotte, J. P.; Puchkov, A.; Timusk, T.

    1996-04-01

    The frequency dependence of the imaginary part of the infrared conductivity is calculated for a superconductor. Sharp structure, characteristic of superconductivity with an order parameter with s-wave symmetry, appears in the BCS limit as a minimum at a frequency equal to twice the gap value. This structure scales with temperature but gets progressively smeared and shifted as impurity scattering is increased. The relationship between low-frequency results and the zero-frequency limit is investigated. Experimental results on Ba1-xKxBiO3 are also presented. The low-frequency imaginary part of the conductivity displays a minimum at 2Δ~=12 meV, and provides unequivocal evidence of an s-wave superconducting order parameter. Strong-coupling (Eliashberg) results show similar trends. Using this formulation we find that the electron-phonon coupling in Ba1-xKxBiO3 must necessarily be small, with coupling constant λ~=0.2, in agreement with conclusions drawn from measurements of the real part of the conductivity. Thus Ba1-xKxBiO3 is an s-wave superconductor that is not driven by the conventional electron-phonon interaction.

  4. Phase diagram for Bi1-xCaxMnO3 (x < 0.5)

    NASA Astrophysics Data System (ADS)

    Qin, Yuhai; Tyson, Trevor; Cheong, Sang-Wook; Xu, Xiaonong

    2007-03-01

    The multiferroic BiMnO3 system, in which ferroelectronic and ferromagnetic orders can coexist, has attracted much research work in the past years for its potential technological applications. For the more general system Bi1-xCaxMnO3, the phase diagram for the Ca rich region (x > 0.4) has been established [1]. In order to understand the multiferroic behavior near the x=0 system, the hole-doped region (01-xCaxMnO3, by performing detailed structural (XRD and XAFS), magnetization (ZFC/FC) and electrical measurements on Bi1-xCaxMnO3 (0

  5. Structural and luminescent properties of KY(1-x)DyxBO3 phosphors.

    PubMed

    G, Sowjanya; L, Rama Moorthy; Ch, Basavapoornima; C K, Jayasankar

    2017-01-01

    Yttrium borate phosphors (KY(1-x)DyxBO3) doped with Dy(3+) ions were synthesized by the solid-state reaction method. The structural and morphological characteristics were studied by XRD, FTIR and SEM measurements. Luminescent properties of different concentrations of KY(1-x)DyxBO3 phosphors were investigated from the excitation, emission and decay analyses. The emission spectra exhibited characteristic blue (460-500nm) and yellow (555-610nm) bands of Dy(3+) ions which combines to give white light. The evaluated color co-ordinates (x, y) were found to lie within the white light region of CIE chromaticity diagram. All the decay curves of Dy(3+) ions exhibited non-exponential nature and the experimental lifetimes for the (4)F9/2 excited level were found to decrease from 0.87, 0.47, 0.35, 0.26 and 0.13ms with the increase of Dy(3+) ion concentrations from 0.05, 0.1, 0.15, 0.2 and 0.3mol%, respectively. In order to understand the energy transfer mechanism, the decay curves were fitted to Inokutti-Hirayama model and found that the energy transfer is of dipole-dipole type. From the results of these investigations, it is concluded that the KY(1-x)DyxBO3 phosphors are more useful for white light emitting diodes. PMID:27442292

  6. Direct Band Gap Gallium Antimony Phosphide (GaSbxP1-x) Alloys

    NASA Astrophysics Data System (ADS)

    Russell, H. B.; Andriotis, A. N.; Menon, M.; Jasinski, J. B.; Martinez-Garcia, A.; Sunkara, M. K.

    2016-02-01

    Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1-2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1-x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x = 0.0092 or higher Sb incorporation into GaSbxP1-x. Furthermore, these calculations indicate band edge straddling of the hydrogen evolution and oxygen evolution reactions for compositions ranging from x = 0.0092 Sb up to at least x = 0.065 Sb making it a candidate for use in a Schottky type photoelectrochemical water splitting device. GaSbxP1-x nanowires were synthesized by reactive transport utilizing a microwave plasma discharge with average compositions ranging from x = 0.06 to x = 0.12 Sb and direct band gaps between 2.21 eV and 1.33 eV. Photoelectrochemical experiments show that the material is photoactive with p-type conductivity. This study brings attention to a relatively uninvestigated, tunable band gap semiconductor system with tremendous potential in many fields.

  7. Valence band hybridization in N-rich GaN1-xAsx alloys

    SciTech Connect

    Wu, J.; Walukiewicz, W.; Yu, K.M.; Denlinger, J.D.; Shan, W.; Ager III, J.W.; Kimura, A.; Tang, H.F.; Kuech, T.F.

    2004-05-04

    We have used photo-modulated transmission and optical absorption spectroscopies to measure the composition dependence of interband optical transitions in N-rich GaN{sub 1-x}As{sub x} alloys with x up to 0.06. The direct bandgap gradually decreases as x increases. In the dilute x limit, the observed band gap approaches 2.8 eV; this limiting value is attributed to a transition between the As localized level, which has been previously observed in As-doped GaN at 0.6 eV above the valence band maximum in As-doped GaN, and the conduction band minimum. The structure of the valence band of GaN{sub 1-x}As{sub x} is explained by the hybridization of the localized As states with the extended valence band states of GaN matrix. The hybridization is directly confirmed by soft x-ray emission experiments. To describe the electronic structure of the GaN{sub 1-x}As{sub x} alloys in the entire composition range a linear interpolation is used to combine the effects of valence band hybridization in N-rich alloys with conduction band anticrossing in As-rich alloys.

  8. Magnetic properties of Cd(1 - x)Mn(x)Te/C nanocrystals.

    PubMed

    Bhattacharyya, Sayan; Zitoun, D; Gedanken, A

    2011-02-18

    Mn doped CdTe nanocrystals coated by carbon (Cd(1 - x)Mn(x)Te/C) were synthesized by a one-step, kinetically controlled solid state reaction under autogenic pressure at elevated temperatures. Electron microscopic analysis confirmed that the 40-52 nm Cd(1 - x)Mn(x)Te core was encapsulated by a 6-9 nm carbon shell. The efficient doping by Mn(2+) in the zinc blende Cd(1 - x)Mn(x)Te lattice, up to an atomic ratio of Mn/Cd of 0.031, was confirmed from electron paramagnetic resonance (EPR) experiments. In the case of higher doping, it is likely that manganese is partially expelled to the nanocrystal surface. All the doped samples exhibit ferromagnetism at room temperature. The lowest doped sample has the highest magnetic moment (1.91 ± 0.02 µ(B)/Mn). The more concentrated samples exhibit weaker ferromagnetic interactions, probably due to an incomplete coupling between carriers in the host CdTe semiconductor and dopant spins.

  9. Identification of topological surface states in (Bi1 - xSbx)2Te3 alloy films

    NASA Astrophysics Data System (ADS)

    Walrath, J. C.; Stoica, V. A.; Chang, A. S.; Lin, Yen-Hsiang; Liu, Wei; Endicott, L.; Clarke, R.; Uher, C.; Goldman, R. S.

    Topological insulators (TIs) have emerged as an exciting class of quantum materials, with an insulating bulk and spin-momentum-locked topologically-protected surface states, making them desirable for spintronics and other applications. Recently, tunable surface to bulk conduction has been demonstrated in ternary TI alloys (Bi1-xSbx)2 Te3, providing an ideal candidate for TI spintronic devices. Although room-temperature topological surface transport is desirable for device applications, direct detection topological surface states at room temperature has yet to be demonstrated in (Bi1-xSbx)2 Te3 systems. Here, we use scanning tunneling microscopy and spectroscopy (STM/STS) to characterize the band structure of (Bi1-xSbx)2 Te3 alloy films and directly detect the presence of topological surface states at room temperature. We will discuss the thickness and composition dependence of the band structure, including the Fermi level energy, Dirac point, and carrier type, comparing STM/STS and macroscopic transport data.

  10. Growth and characterization of Fe1-xGax thin films from citrate-based electrolytes

    NASA Astrophysics Data System (ADS)

    Ranchal, R.; Maestre, D.

    2014-09-01

    In this work we report on the growth of Fe1-xGax films by means of the electrodeposition technique in baths containing sodium citrate as an antioxidant agent. We have investigated the effect of the electrolyte composition in terms of its Ga content on the structural and magnetic properties. Our experimental results indicate that for the optimized bath composition, O-free Fe1-xGax alloys can be achieved for a potential of E = -1.4 V and magnetic stirring at 500 rpm. Both the composition and the coercivity of the samples deposited from this electrolyte can be tuned by means of the duration of the rest pulse at E = -1.12 V. However, when the composition of the bath is not optimized the films exhibit a large amount of O that cannot be dissolved during the rest pulse. Our experimental results show that O-free Fe1-xGax alloys with a Ga content of around 19 at% and optimum magnetic properties can be deposited on Au substrates when using an optimized electrolyte and long rest pulses.

  11. Ferromagnetism and infrared electrodynamics of Ga1-xMnxAs

    NASA Astrophysics Data System (ADS)

    Chapler, B. C.; Mack, S.; Myers, R. C.; Frenzel, A.; Pursley, B. C.; Burch, K. S.; Dattelbaum, A. M.; Samarth, N.; Awschalom, D. D.; Basov, D. N.

    2013-05-01

    We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga1-xMnxAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature TC with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find nonmonotonic behavior of trends in TC with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found only to be consistent with a Mn-induced IB scenario. Furthermore, our detailed exploration of these spectral features demonstrates that seemingly conflicting trends reported in the literature regarding a broad mid-IR resonance with respect to carrier density in Ga1-xMnxAs are in fact not contradictory. Our study thus provides a consistent experimental picture of the magnetic and electronic properties of Ga1-xMnxAs.

  12. Tuning structural, electrical, and optical properties of oxide alloys: ZnO1-xSex

    NASA Astrophysics Data System (ADS)

    Mayer, Marie A.; Yu, Kin Man; Haller, Eugene E.; Walukiewicz, Wladek

    2012-06-01

    Previously we showed that it is possible to narrow the band gap of zinc oxide from 3.3 to ˜2 eV through the addition of Se. Here, we use thin film samples of ZnO1-xSex grown by pulsed laser deposition to describe in detail the effect of growth parameters (temperature, pressure, and fluence) on the chemistry, structure, and optoelectronic properties of oxide alloys. We analyze the influences of temperature, laser fluence, and pressure during growth on the structure and composition of the films and define the parameter space in which homogeneous ZnO1-xSex alloy films can in fact be synthesized. Electronic transport in films grown under different conditions was characterized by resistivity, thermopower, and Hall effect measurements. We discuss how the electron affinity and native defects in polycrystalline oxide alloys enable reasonable mobilities (˜15 cm2/Vs) relative to their single crystalline counterparts. Finally, we elaborate on the model of optical structure in ZnO1-xSex and discuss the dependence of optical properties on growth temperature and fluence.

  13. Effect of Pressure on Some Optical Properties of GaxIn1-xP Semiconductors

    NASA Astrophysics Data System (ADS)

    Vyas, P.; Gajjar, P.; Jani, A.

    2013-06-01

    A theoretical procedure is presented for the study of optical properties of ternary alloy GaxIn1-xP. The calculations are based on the pseudopotential formalism in which local potential coupled with the virtual crystal approximation (VCA) is applied to evaluate the effect of pressure on the optical properties like refractive index, electronic polarizability, plasmon energy, dielectric constant and equation of state for gallium concentration x = 0, 0.25, 0.50, 0.75 and 1 of the ternary alloy GaxIn1-xP. To incorporate the screening effect, local field correction functions due to Hartree, Taylor, Ichimaru et al. and Nagy are employed. The refractive index, electronic polarizability and dielectric constant computed for the parent binary compounds GaP and InP are found to be satisfactorily agreeing with the experimental report. It is seen that the refractive index of GaxIn1-xP decreases nonlinearly with the increase in pressure. The results obtained using Hartree's screening functions are not very close to the experimental data as it does not include any exchange and correlation effects. Overall good agreement with the experimental and other theoretical findings confirms the application. The author P. S. Vyas is thankful to UGC, New Delhi, India for providing financial support under minor research project No. F.: 47-651/08(WRO).

  14. Hollow ZnxCd1-xS nanospheres with enhanced photocatalytic activity under visible light.

    PubMed

    Jin, Ying; Zhang, Haoyun; Song, Chuang; Wang, Lanfang; Lu, Qingyi; Gao, Feng

    2016-07-22

    Formation of solid solutions is a good strategy to acquire materials with special properties and bring forth new type of applications or enhance the performance of currently existing devices. In this study, hollow ZnxCd1-xS nanospheres with different molar ratios were synthesized via a facile hydrothermal process. The products were fully characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis absorption spectroscopy. It was found that the photocatalysis performance of the as-prepared samples could be enhanced by formation of ZnxCd1-xS solid solutions. In addition, their photocatalytic activities are dependent on the Zn/Cd molar ratios and nanostructures of ZnxCd1-xS solid solutions. Hollow Zn0.2Cd0.8S spheres exhibit extremely high photocatalytic activity and good re-usability, and the photocatalytic conversion of RhB reaches as high as 96% after 50 min of irradiation.

  15. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

    PubMed Central

    Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  16. Piezoelectricity in K1-xNaxNbO3: First-principles calculation

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Rui, Zhang; Lv, Tian-Quan; Zheng, Li-Mei

    2015-05-01

    The piezoelectric properties of K1-xNaxNbO3 are studied by using first-principles calculations within virtual crystal approximation. To understand the critical factors for the high piezoelectric response in K1-xNaxNbO3, the total energy, piezoelectric coefficient, elastic property, density of state, Born effective charge, and energy barrier on polarization rotation paths are systematically investigated. The morphotropic phase boundary in K1-xNaxNbO3 is predicted to occur at x = 0.521, which is in good agreement with the available experimental data. At the morphotropic phase boundary, the longitudinal piezoelectric coefficient d33 of orthorhombic K0.5Na0.5NbO3 reaches a maximum value. The rotated maximum of is found to be along the 50° direction away from the spontaneous polarization (close to the [001] direction). The moderate bulk and shear modulus are conducive to improving the piezoelectric response. By analyzing the energy barrier on polarization rotation paths, it is found that the polarization rotation of orthorhombic K0.5Na0.5NbO3 becomes easier compared with orthorhombic KNbO3, which proves that the high piezoelectric response is attributed to the flattening of the free energy at compositions close to the morphotropic phase boundary. Project supported by the National Basic Research Program of China (Grant No. 2013CB632900).

  17. THE STRUCTURAL AND ELECTRONIC PROPERTIES OF BNxAs1-x ALLOYS

    NASA Astrophysics Data System (ADS)

    Mohammad, Rezek; Katircioğlu, Şenay

    2012-10-01

    The structural and electronic properties of BNxAs1-x alloys have been investigated in the total range of nitrogen by the FP-LAPW method based on DFT within the EV-PW-GGA scheme. The equilibrium lattice constants, bulk moduli, first-order pressure derivatives of the bulk moduli, and cohesive energies have been obtained by total energy calculations of the alloys after both volume and geometry optimizations. The large bowing parameters found for the lattice constants and bulk moduli have demonstrated that the validity of Vegard's linear rule in the definitions of these structural features of the BNxAs1-x alloys is broken. The energy bands and the effective masses of the alloys have been calculated as a function of nitrogen concentration. The large bowing displayed by the variation of the energy gaps has indicated the band gap engineering capacity of the BNxAs1-x alloys and again in deviations from Vegard's linear rule. The effective electron masses calculated either at the edges of the conduction bands or along the directions approaching the edges of the conduction bands are all found to be small with respect to the effective electron masses in the BAs and BN compounds calculated at the Δmin and X points, respectively.

  18. Low Temperature Properties and Quantum Criticality of CrAs1-x Px single crystal

    NASA Astrophysics Data System (ADS)

    Luo, Jianlin; Institute of Physics, Chinese Academy of Sciences Team

    We report a systematically study of resistivity and specific heat on phosphorus doped CrAs1-xPx single crystals with x =0 to 0.2. With the increasing of phosphorus doping concentration x, the magnetic and structural transition temperature TN is suppressed. Non-fermi liquid behavior and quantum criticality phenomenon are observed from low temperature resistivity around critical doping with xc ~0.05 where the long-range antiferromagnetic ordering is completely suppressed. The low temperature specific heat of CrAs1-xPx is contributed by the thermal excitation of phonons and electrons. The electronic specific heat coefficient γ, which reflects the effective mass of quasi-particles, shows maximum around xc ~0.05, also indicating the existence of quantum critical phenomenon around the critical doping. The value of Kadowaki-Woods ratio of CrAs1-xPx shows no significant different from that of CrAs. Work is done in collaboration with Fukun Lin, Wei Wu, Ping Zheng, Guozhi Fan, Jinguang Cheng.

  19. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-05-29

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals.

  20. Optoelectrical and magnetic characteristics of Mn doped Zn1-xSnxO nanorods

    NASA Astrophysics Data System (ADS)

    Hsu, Tsung-Yin; Lai, Shang-Hung; Hsieh, Hui-Huang; Lan, Ming-Der; Su, Chih-Chuan; Ho, Mon-Shu

    2013-01-01

    This paper describes a new method of fabricating Mn doped Zn1-xSnxO nanorod arrays on a silicon (111) substrate. The proposed method is a gold catalytic vapor-liquid-solid mechanism in a multi-layer deposition process using nanosphere lithographic patterning. Each step of the growth process was monitored using atomic force microscopy to ensure uniformity in the patterns and nanorods. The crystal structure and characteristics of the Mn doped Zn1-xSnxO nanaorods were determined using the X-ray diffraction analysis, scanning electron microscopy, high resolution transmission electron microscopy, and electron diffraction patterns corresponding to the selected area. The lattice constant along the Z-axis was calculated from the indexed pattern, as approximately 5.1 Å. This differs slightly from what was expected for undoped ZnO nanorods. Energy dispersive X-ray spectrometry provided information related to the chemistry of the ZnO nanorods and electro-optical properties at 363 nm were determined from photoluminescence emissions. Using conductive AFM, the band gap for single doped-ZnO nanorods was determined to be 3-3.45 eV. The magnetic properties were characterized by the measurement of a hysteresis loop. This investigation demonstrates the outstanding potential of patterned Mn doped Zn1-xSnxO nanorods for applications requiring dilute magnetic semiconductors in the future.

  1. Thermoluminescence studies of bismuth doped Ba xCa 1- xS nanostructures

    NASA Astrophysics Data System (ADS)

    Singh, Surender; Lochab, S. P.; Kumar, Ravi; Singh, Nafa

    2011-01-01

    Bismuth doped Ba 1- xCa xS:Bi ( x=0-1) nanocrystallities have been prepared by the solid state reaction method and characterized by XRD and TEM. X-ray diffraction analysis shows the formation of the compounds in cubic structure at room temperature. Only partial replacement of Ba is possible and we found that Ba 0.5Ca 0.5S:Bi could not be prepared due to the difference between ionic radii of barium and calcium. Thermoluminescence studies of these samples after exposure to UV radiation have been carried out. The TL glow curve of Ba xCa 1 -xS:Bi has been found to be a simple structure with a single peak at 405, 428 and 503 K for x=1, 0.8 and 0, respectively. The kinetic parameters at various heating rates namely activation energy ( E), order of kinetics ( b) and frequency factor ( s) of the Ba 1- xCa xS:Bi ( x=0.2) (0.4 mol%) sample have been determined using Chen’s method. The deconvolution of curve was done using the GCD function suggested by Kitis. The effect of different heating rates and different amount of dose has also been discussed.

  2. Radiation Effects in ALUMINUM(X)GALLIUM(1-X)ARSENIDE and Indium-Phosphorus

    NASA Astrophysics Data System (ADS)

    Cross, T. A.

    Available from UMI in association with The British Library. Radiation effects in Al_{ rm x}Ga_{rm 1-x}As and InP produced by hydrogen ion bombardment have been studied using mainly electrical resistivity measurements and thermal annealing techniques. Multiple energy ion bombardments at 400 keV to 100 keV were used in most experiments at beam power densities of below 100 mW cm^{-2}. Two terminal, through layer, resistivity measurements were made on Al_{rm x}Ga _{rm 1-x}As:Se with Al mole fraction, x, from 0 (GaAs) to 0.82. In all cases, a maximum resistivity of 1E8 to 1E10 ohm cm was achieved with proton or deuteron bombardment. As x is increased from 0 the resistivity maximum rises gradually from 1E8 to 1E10 ohm cm at x = 0.45 and then gently falls. This behaviour has been explained by considering a single deep level with an activation energy which varies with x in a similar manner to that of the shallow donor levels in Al_{rm x}Ga _{rm 1-x}As. Using an interdigital contact geometry, the first in-situ measurements of the change in Al_ {rm x}Ga_{rm 1-x}As resistivity with ion dose have been made. This has enabled repeated irradiation-measurement cycles, resulting in a rapid determination of the resistivity behaviour and a more accurate measurement of the optimum ion dose for maximum resistivity. The observed anomalously efficient carrier removal of deuterons in GaAs:Si has not been observed in any GaAs:Se or Al_{rm x}Ga _{rm 1-x}As:Se. Proton bombardment is less efficient in GaAs:Si than in GaAs:Se, perhaps due to a parasitic interaction of the protons with the silicon donor species. The thermal stability of the isolation in Al _{rm x}Ga_ {rm 1-x}As:Se, over the whole composition range, appears to be suitable for device applications if post-implant process steps are kept below 400^ circC. Whilst the isolation in InP was observed to be stable to up to 300^circC, some indications of room temperature annealing were noted. The electrical properties of proton and

  3. High-pressure synthesis and structural, physical properties of CaIr1-xPtxO3 and CaIr1-xRhxO3

    NASA Astrophysics Data System (ADS)

    Hirai, S.; Bromiley, G. D.; Klemme, S.; Irifune, T.; Ohfuji, H.; Attfield, P.; Nishiyama, N.

    2010-12-01

    in terms of materials science applications. To our knowledge, this will be the first report on structural, magnetic and charge-transport properties of B-site substituted solid solutions of post-perovskite oxides with 4d/5d transition metals. High-quality polycrystalline samples of CaIr1-xPtxO3 and CaIr1-xRhxO3 have been obtained at high pressures, and structural, magnetic and charge-transport properties of the compounds will be reported. ODF analysis reveals that solutions of CaIrO3, CaPtO3 and CaRhO3 exhibit similar grain growth features to the mother compound, although growth in [0 1 0] plays a more dominant role than the growth in [0 0 1] for the solid solutions. CaIrO3 is a characteristic hard magnet suitable for applications such as magnetic recording, with TN = 108K. A new phase of CaIr1-xPtxO3 synthesized at a high P/T condition has Raman modes which resemble those of CaIrO3 perovskite, suggesting this phase has a perovskite structure.The instability of the perovskite phase of CaIr1-xPtxO3 reveals why the post-perovskite to peovskite phase transition has not been observed for CaPtO3 unlike the case for CaIrO3, CaRhO3 and CaRuO3.

  4. Thermal Property of DyxEr1-xAl2 and Gd5(SixGe1-x)4 for Hydrogen Magnetic Refrigeration

    NASA Astrophysics Data System (ADS)

    Kamiya, K.; Numazawa, T.; Koen, T.; Okano, T.; Matsumoto, K.

    2004-06-01

    The New Energy and Industrial Technology Development Organization (NEDO) in Japan has built a project called World Energy Network (WE-NET). The aim of WE-NET is development of a new infrastructure of hydrogen technology for the upcoming hydrogen energy society. Among several element technologies to be achieved, high efficient liquefaction and storage of hydrogen have been identified as key technologies. Active Magnetic Regenerative Refrigeration (AMRR) is thought to have the best performance in cooling efficiency for hydrogen liquefaction. AMRR makes use of magnetic materials so that a magnetic field can create the cooling power. Therefore, magnetic and thermal properties of the materials are of crucial importance to the design and development of the AMRR system. In this paper, we focused specially on thermal expansion among the thermal properties of magnetic materials for AMRR to provide a fundamental database for the design of the AMRR. Correlation between magnetic property and thermal expansion of the Gd5(SixGe1-x)4 system is also examined.

  5. 1 x N star coupler as a distributed fiber-optic strain sensor in a white-light interferometer.

    PubMed

    Yuan, L; Zhou, L

    1998-07-01

    A novel technique of using a 1 x N star fiber optic coupler as a distributed strain sensor in a white-light interferometer to measure the distribution of strain is presented. The measuring principle and 1 x 4 star coupler with four fiber optic strain sensors are demonstrated. The experiment is performed with four sensors attached to a combination plastic specimen.

  6. Direct imaging of InSb (110)-(1x1) surface grown by molecular beam epitaxy

    SciTech Connect

    Mishima, T. D.

    2011-10-01

    High-resolution transmission electron microscopy under a profile imaging condition (HR-profile TEM) was employed to determine the structural model for the InSb(110)-(1x1) relaxation surface grown by molecular beam epitaxy (MBE). HR-profile TEM analyses indicate that the chevron model, which is widely accepted for zinc-blende-type III-V(110)-(1x1) surfaces prepared by cleavage, is also applicable to the InSb(110)-(1x1) surface prepared under an Sb-rich MBE condition. The assignment of atomic species (In or Sb) of InSb(110)-(1x1) surfaces was confirmed based on a HR-profile TEM image that captures the connected facets of InSb(110)-(1x1) and InSb(111)B-(2x2). On the basis of the well-known atomic species of InSb(111)B-(2x2), the atomic species of the InSb(110)-(1x1) surface were deduced straightforwardly: the atoms shifted upward and downward at the topmost layer of the InSb(110)-(1x1) surface are Sb and In, respectively. The atomic arrangements of the InSb(110)-(1x1)-InSb(111)B-(2x2) facet determined by HR-profile TEM may represent the atomic arrangements of zinc-blende-type III-V(331)B surfaces.

  7. Language Learning Actions in Two 1x1 Secondary Schools in Catalonia: The Case of Online Language Resources

    ERIC Educational Resources Information Center

    Calvo, Boris Vázquez; Cassany, Daniel

    2016-01-01

    This paper identifies and describes current attitudes towards classroom digitization and digital language learning practices under the umbrella of EduCAT 1x1, the One-Laptop-Per-Child (OLPC or 1x1) initiative in place in Catalonia. We thoroughly analyze practices worked out by six language teachers and twelve Compulsory Secondary Education (CSE)…

  8. Influence of Surface Mobility of Charge Carriers on Cdx Hg1-x Te (x=0,2-0,3) Photoconductivity

    NASA Astrophysics Data System (ADS)

    Salaev, Eldar; Guseýnov, Emil; Ýsmaýlov, Namýk; Tezer, Ateþ

    1997-10-01

    Experimental data on the photoconductivity of CdxHg1-xTe with different surface states are presented. The results are interpreted by he influence of surface mobility of charge carriers on photoeffect phenomena and the value of surface mobility for chemically treated, for polished surface and for aluminium covered surfaces of CdxHg1-xTe crystals are given.

  9. Enhancement of the magnetic properties in (Ga1-xMnx)N thin films due to Mn-delta doping

    NASA Astrophysics Data System (ADS)

    Jeon, H. C.; Kang, T. W.; Kim, T. W.; Kang, Joongoo; Chang, K. J.

    2005-08-01

    The effects of Mn delta-doping on the magnetic properties of (Ga1-xMnx)N thin films grown on GaN buffer layers by molecular-beam epitaxy were studied. The magnetization curve as a function of the magnetic field as 5K indicated that ferromagnetisms existed in the Mn delta-doped (Ga1-xMnx)N and (Ga1-xMnx)N thin films and that the magnetization in the Mn delta-doped (Ga1-xMnx)N thin film was significantly enhanced. The magnetization curve as a function of the temperature showed that the Curie temperature of the Mn delta-doped (Ga1-xMnx)N thin film was estimated to be above room temperature. The increase of the magnetization in the Mn delta-doped (Ga1-xMnx)N thin film in comparison with that in the (Ga1-xMnx)N thin film was attributed to the enhancement of the carrier-mediated ferromagnetism due to increased hole concentrations. The theoretical results showed that Ga vacancies near the Mn delta-doping layer were likely to cause p-type conductance, indicating that the enhancement of the magnetic properties in (Ga1-xMnx)N thin films originated from Mn delta doping.

  10. FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR-BLODGETT TECHNOLOGY

    NASA Astrophysics Data System (ADS)

    Tang, Dongyan; Feng, Qian; Jiang, Enying; He, Baozhu

    2012-08-01

    By transferring MgxZn1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir-Blodgett (LB) multilayers of MgxZn1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, MgxZn1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with MgxZn1-xO sols under Π-A isotherms inferred the interaction of stearic acid with MgxZn1-xO sols during the formation of monolayer at air-water interface. X-ray diffraction (XRD) was used to determine the crystal structures of MgxZn1-xO nanoparticles and ultrathin films. The surface morphologies of MgxZn1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of MgxZn1-xO were detected and discussed based on photoluminescence (PL) spectra.

  11. Magnetic, Caloric and Crystallographic Properties of Dy5(SixGe1-x)4 Alloys

    SciTech Connect

    Vitaliy Vladislavovich Ivchenko

    2002-07-19

    Polycrystals of the intermetallic compound of the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system, where x = 0, 0.25, 0.5, 0.625, 0.675, 0.725, 0.75, 0.775, 0.825, 0.875, and 1, have been prepared by electric-arc-melting on water-cooled copper hearth in an argon atmosphere. A study of phase relationships and crystallography in the pseudobinary system Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} using X-ray powder diffraction data and optical metallography was completed. It revealed that silicides in the composition range from 0.825 to 1 crystallize in the Gd{sub 5}Si{sub 4}-type crystal structure: germanides in the composition range from 0 to 0.625 crystallize in the Sm{sub 5}Ge{sub 4}-type structure, and alloys with intermediate composition range from 0.675 to 0.775 crystallize in the monoclinic Gd{sub 5}Si{sub 2}Ge{sub 2}-type structure. The -{Delta}S{sub m} values were determined from magnetization measurements for 7 alloys. The alloys with a monoclinic crystal structure which belong to an intermediate phase region have large MCE value, which exceeds those observed in the other two phase regions by 300 to 500%. The nature of the observed magnetic and structural transformations in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system seems to be similar with those reported for the Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system. However, the interval and concentration range of three different phase regions in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system are different from that observed in Gd-based alloys. A non-collinear ordering of magnetic moments at low temperature was observed for the alloys with monoclinic crystal structure. The Dy{sub 5}Si{sub 3}Ge alloy exhibited FM phase transition below Curie temperature. A series of magnetic transitions were observed at low temperature in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} alloys. The number of transitions increased and the magnetization decreased with increasing germanium content in the alloys. The -{Delta}S{sub m} and

  12. The dielectric behavior of Zn1-xNixO/NiO two-phase composites

    NASA Astrophysics Data System (ADS)

    Joshi, D. C.; Thota, S.; Nayak, S.; Harish, D. D.; Mahesh, P.; Kumar, A.; Pamu, D.; Qureshi, Md

    2014-10-01

    The effect of nickel content on the dielectric permittivity ‘ɛr’ and the ac-electrical conductivity of Zn1-xNixO/NiO (0 ≤ x ≤ 0.55) two-phase composites were investigated. The antiferro to the paramagnetic Néel temperature TN (~ 523 K) of the NiO associated with the structural phase transition from the rhombohedral to the cubic phase has been exploited to realize a dielectric anomaly across 523-541 K in the Zn1-xNixO/NiO composite system. Also, a giant dielectric peak across 410 °C in pure NiO was observed together with an anomaly across TN. The formation of tiny polar clusters due to the compositional heterogeneity for the samples with x ≥ 0.16 drove the system to exhibit a weakly coupled relaxor-like behavior with a locally varying maximum temperature of T* (~ 530 K at 106 Hz), obeying the Vogel-Fulcher law and the Uchino-Nomura criteria. The values of the diffuseness-exponent ‘γ’ (1.91) and the shape-parameter ‘δ’ (88 °C) were determined by using the empirical scaling relation (ɛA/ɛr = 1 + 0.5 (T - TA)2/ δ2), which is often used to describe relaxor-like behavior. Our results provide strong evidence for the variable-range-hopping of charge carriers between the localized states. The effects of non-ohmic sample-electrode contact impedance and negative-capacitance on the global dielectric behavior of a Zn1-xNixO/NiO composite system are discussed.

  13. Evolution of magnetic properties in the solid solution UCo1-xPdx Ge

    NASA Astrophysics Data System (ADS)

    Gralak, D.; Zaleski, A. J.; Tran, V. H.

    2016-10-01

    We have investigated the evolution of magnetic properties in pseudo-ternary UCo1-xPdxGe (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) intermetallics by measurements of ac-magnetic susceptibility and dc-magnetization. The measured samples have been prepared by arc-melting and characterized by powder X-ray diffraction and X-ray energy-dispersive electron spectroscopy technique. Rietveld refinements of the X-ray patterns indicate that the pseudo-ternaries crystallize in the orthorhombic TiNiSi-type structure with Pnma space group as the parent UCoGe and UPdGe compounds do. The magnetic measurements reveal that in addition to an increase in 5f-electron localization degree with increasing Pd concentration, an interesting magnetic phase diagram, which is more complex than that expected from the gradual change in magnetic ground state due to the substitution. Three compositional ranges with different magnetic properties have been established; the coexistence of spin-glass and itinerant-electron ferromagnetic orderings for x ≤ 0.3 , antiferromagnetic order occurs in the range 0.4 ≤ x ≤ 0.7 , and a complex ferromagnetic structure of more localized 5f moments takes place in x ≥ 0.8 . The evolution of magnetic ground states in UCo1-xPdxGe is discussed in terms of interplay between cooperative magnetic interactions. We consider also implications of increasing conduction electrons upon the Pd substitution in Ruderman-Kittel-Kasuya-Yosida interactions, which would give rise to the evolution of magnetic properties in UCo1-xPdxGe pseudo-ternaries.

  14. Three Dirac points on the (110) surface of the topological insulator Bi1-xSbx

    NASA Astrophysics Data System (ADS)

    Zhu, Xie-Gang; Stensgaard, Malthe; Barreto, Lucas; Silva, Wendell Simoes e.; Ulstrup, Søren; Michiardi, Matteo; Bianchi, Marco; Dendzik, Maciej; Hofmann, Philip

    2013-10-01

    Topological insulator surfaces support metallic surface states with closed Fermi contours, encircling an odd number of Dirac points. Experimental studies have so far concentrated on surfaces with only one Dirac point, but three Dirac points can be expected for certain surface orientations of several topological insulator materials. Here we experimentally realize the Bi1-xSbx(110) surface for which an electronic structure with three Dirac points has been predicted (Teo et al 2008 Phys. Rev. B 78 045426), in contrast to the closed-packed (111) surface of the same material that supports only one Dirac point. We study the electronic structure of Bi1-xSbx(110) with angle-resolved photoemission and tight-binding calculations. We observe several metallic surface states, confirming not only the expectation that a topological insulator should be enclosed by metallic surfaces on all faces, but also the prediction of the surface state topology. Tight-binding calculations of the electronic structure are found to reproduce the expected topology of the surface states but they show one Dirac point that is not observed in the experiment, in the mirror line of the surface Brillouin zone. As in the case of Bi1-xSbx(111), this can be ascribed to an incorrect value of the mirror Chern number in the tight-binding parameters employed for the calculation. The quantitative agreement of the tight-binding calculation and the experiment is poorer than in the case of the (111) surface, something that is ascribed to the existence of dangling bonds on the (110) surface.

  15. The optical spectrum of ternary alloy BBi1-xAsx

    NASA Astrophysics Data System (ADS)

    Yalcin, Battal G.; Aslan, M.; Ozcan, M. H.; Rahnamaye Aliabad, H. A.

    2016-06-01

    Among the III-V semiconductors, boron BBi and BAs as well as their alloys have attracted both scientific and technological interest in recent years. We present a calculation of the structural, electronic and optical properties of ternary alloy BBi1-xAsx by means of the WIEN2k software package. The exchange-correlation potential is treated by the generalized gradient approximation (GGA) within the schema of Wu and Cohen. Also, we have used the modified Becke-Johnson (mBJ) formalism to improve the band gap results. All the calculations have been performed after geometry optimization. In this study, we have investigated structural properties such as the lattice constant (a0), bulk modulus (B0) and its pressure derivative (B‧), and calculated the electronic band structures of the studied materials. Accurate calculation of linear optical properties, such as real (ɛ 1) and imaginary (ɛ 2) dielectric functions, reflectivity (R), electron energy loss spectrum, absorption coefficient (α), refractive index (n) and sum rule (Neff) are investigated. Our obtained results for studied binary compounds, BBi and BAs, fairly coincide with other theoretical calculations and experimental measurements. According to the best of our knowledge, no experimental or theoretical data are presently available for the studied ternary alloy BBi1-xAsx (0 < x < 1). The role of electronic band structure calculation with regards to the linear optical properties of BBi1-xAsx is discussed. The effect of the spin-orbit interaction (SOI) is also investigated and found to be quite small.

  16. Growth of La1-xSrxFeO3 thin films by atomic layer deposition.

    PubMed

    Lie, Martin; Nilsen, Ola; Fjellvåg, Helmer; Kjekshus, Arne

    2009-01-21

    Thin films of La1-xSrxFeO3 have been prepared by the ALD (atomic layer deposition) technique using La(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Sr(thd)2, Fe(thd)3, and ozone as precursors. A so-called ALD window is found in the temperature range 200 to 360 degrees C for LaFeO3. The effect of the pulsing procedure for the precursors on the composition of the films is examined. The results are discussed in relation to a model which ascribes differences between pulsed and obtained stoichiometries to individually different surface-area demands of the precursors. The La1-xSrxFeO3 films turned out to contain only small amounts of carbonate impurities despite the fact that films prepared from Sr(thd)2 and ozone under the same conditions contains virtually pure SrCO3. Films of La1-xSrxFeO3 have been deposited on substrates of (amorphous) soda-lime glass and single crystals of Si(100), SrTiO3(100), and LaAlO3(012). Annealed films on soda-lime glass and Si(100) substrates turned out to be polycrystalline with virtually random orientation of the crystallites. Those on MgO(100) and SrTiO3(100) substrates showed some degree of crystal orientation, whereas the annealed films on LaAlO3(012) proved to contain distinctly oriented crystallites with mosaic features.

  17. Evolution of superconductivity and magnetism in La1-xYbxRu2P2

    NASA Astrophysics Data System (ADS)

    Roncaioli, Connor; Hodovanets, Halyna; Saha, Shanta; Paglione, Johnpierre

    LaRu2P2, with a 4.1 K transition, is the first known pnictide-based superconductor. Sharing structural and electronic elements similar to those of the unconventional Fe-pnictide superconductors, it is of interest to investigate the parameter space in which a superconducting ground state survives. We present preliminary indications of more interesting magnetic behavior and structural tuning behavior when paramagnetic Yb is substituted for La in La1-xYbxRu2P2, and investigate potential heavy fermion behavior in the Yb end-member of this series.

  18. Ultra fast pulse-plating of NixCu1-x alloy nanowires

    NASA Astrophysics Data System (ADS)

    Kazeminezhad, I.; Schwarzacher, W.

    2006-02-01

    Since nanotechnology is one of the interesting new topics for scientists, fabrication of nanomaterials may be extremely important. This article shows that electrodeposition is one of the best techniques to fabricate metallic nanomaterials. Here we show that a NixCu1-x alloy nanowire of arbitrary composition may be grown within a nuclear track-etched polycarbonate membrane by electrodepositing well-defined submonolayer quantities of Ni and Cu in alternation. The microstructure of the alloy wires was investigated using TEM in both imaging and diffraction modes. Magnetic measurements were carried out at 5 K and 300 K using a SQUID magnetometer to characterize the compositional homogeneity of the electrodeposited nanowires.

  19. Evidence of spin glass dynamics in dilute LiHoxY1-xF4.

    PubMed

    Quilliam, J A; Meng, S; Mugford, C G A; Kycia, J B

    2008-10-31

    ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet LiHoxY1-xF4 for a concentration x=0.045. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of 43+/-2 mK with an exponent znu=7.8+/-0.2.

  20. Exciton mobility edge in CdS 1-xSe x solid solutions

    NASA Astrophysics Data System (ADS)

    Permogorov, S.; Reznitsky, A.; Verbin, S.; Lysenko, V.

    1983-07-01

    Low temperature emission spectra of localized excitons in CdS 1-xSe x solid solutions under the monochromatic excitation with tunable laser have been studied. It has been found that the luminescence of localized excitons has a high degree of linear polarization with respect to the polarization direction of exciting light. This polarization reflects the "hidden" anisotropy of macroscopically isotropic localized exciton system and strongly depends on the frequency of exciting light. Study of this dependence has permitted for the first time a determination of position of the "mobility edge" for exciton migration in disordered semiconductor solid solution.

  1. Mott Physics in lightly doped (Sr1-xLax)3Ir2O7

    NASA Astrophysics Data System (ADS)

    Affeldt, Gregory; Hogan, Tom; Smallwood, Christopher; Das, Tanmoy; Denlinger, Jonathan; Mo, Sung-Kwan; Wilson, Stephen; Lanzara, Alessandra

    The layered perovskite iridates Sr2IrO4 and Sr3Ir2O7 exhibit a spin-orbit Mott insulating state that becomes metallic upon sufficient carrier doping. While Sr2IrO4 presents striking similarities to cuprates upon electron doping, Sr3Ir2O7 appears to be a correlated metal. We show a detailed doping and temperature-dependent ARPES study which reveals important similarities between (Sr1-xLax)3Ir2O7 and doped Sr2IrO4, as well as other doped Mott insulators.

  2. Ferroelectric phase transitions in multiferroic Ge1 -xMnxTe driven by local lattice distortions

    NASA Astrophysics Data System (ADS)

    Kriegner, Dominik; Furthmüller, Jürgen; Kirchschlager, Raimund; Endres, Jan; Horak, Lukas; Cejpek, Petr; Reichlova, Helena; Marti, Xavier; Primetzhofer, Daniel; Ney, Andreas; Bauer, Günther; Bechstedt, Friedhelm; Holy, Vaclav; Springholz, Gunther

    2016-08-01

    The evolution of local ferroelectric lattice distortions in multiferroic Ge1 -xMnxTe is studied by x-ray diffraction, x-ray absorption spectroscopy, and density functional theory. We show that the anion/cation displacements smoothly decrease with increasing Mn content, thereby reducing the ferroelectric transition from 700 to 100 K at x =0.5 , where the ferromagnetic Curie temperature reaches its maximum. First principles calculations explain this quenching by different local bond contributions of the Mn 3 d shell compared to the Ge 4 s shell in excellent quantitative agreement with the experiments.

  3. The magneto-structural transition in Mn1-x Fe x CoGe

    NASA Astrophysics Data System (ADS)

    Ren, Q. Y.; Hutchison, W. D.; Wang, J. L.; Studer, A. J.; Din, M. F. Md; Muñoz Pérez, S.; Cadogan, J. M.; Campbell, S. J.

    2016-05-01

    Large refrigeration capacities, between 212(30) J kg-1 and 261(40) J kg-1 for a magnetic field change from 0 T to 5 T, were obtained in Mn1-x Fe x CoGe (x  =  0.01, 0.02, 0.03 and 0.04) compounds. A partial magnetic phase diagram has been derived on the basis of magnetic transition and martensitic transformation temperatures determined from differential scanning calorimetry (200 K to 450 K), variable temperature x-ray diffraction (20 K to 310 K) and magnetisation measurements (5 K to 340 K 0.01 T). Mn1-x Fe x CoGe compounds with compositions in the range x  =  0.01 to 0.03 exhibit magneto-structural transitions. Neutron diffraction experiments were carried out on the Mn0.98Fe0.02CoGe sample over the temperature range of 5 K to 450 K. The diffraction patterns were analysed based on irreducible representation theory which confirms a ferromagnetic structure in the sample with an atomic magnetic moment of 3.7(1)μ B at 5 K on the Mn sublattice, oriented along the orthorhombic c axis. More significantly, a magneto-structural transition around T M ~ 297(1) K with a full width at half maximum of 29 K is demonstrated directly via neutron diffraction. Larger magnetic entropy changes are obtained for the Mn1-x Fe x CoGe (x  =  0.01, 0.02 and 0.03) samples than for Mn0.96Fe0.04CoGe which has separate structural and magnetic transitions. In addition, it is noted that standard Arrott plots do not provide unambiguous insight to the nature of the magneto-structural transition in the Mn1-x Fe x CoGe compounds.

  4. Infrared reflection and Raman scattering on Ba 1-xRb xBiO 3

    NASA Astrophysics Data System (ADS)

    Inoue, A.; Iyo, A.; Oiji, Y.; Tanaka, Y.; Tokumoto, M.; Uwe, H.; Sakudo, T.

    1991-12-01

    Measurements of infrared (IR) reflectivity and Raman scattering have been performed on Ba 1-xRb xBiO 3. The oscillator strength of the Bi-Bi stretching mode decreases with increasing Rb concentration, while the frequency change is small. The phonons detected by the Raman scattering experiment have the same frequencies as the LO phonons, although the system has the center of symmetry in the average structure. It is suggested that the coherence length of the charge density wave shorter than the incident laser wavelength 5145Å gets shorter with increasing the Rb concentration.

  5. Bismuth-induced Raman modes in GaP1- x Bi x

    NASA Astrophysics Data System (ADS)

    Christian, Theresa M.; Fluegel, Brian; Beaton, Daniel A.; Alberi, Kirstin; Mascarenhas, Angelo

    2016-10-01

    Dilute bismide semiconductor alloys are a promising material platform for optoelectronic devices due to drastic impacts of bismuth on the electronic structure of the alloy. At the same time, the details of bismuth incorporation in the lattice are not fully understood. In this work, we conduct Raman scattering spectroscopy on GaP1- x Bi x epilayers grown by molecular beam epitaxy (MBE) and identify several bismuth-related Raman features including gap vibration modes at 296, 303, and 314 cm-1. This study paves the way for more detailed analysis of the local symmetry at bismuth incorporation sites in the dilute bismide alloy regime.

  6. Conduction electron spin resonance in Mg 1 - x Al x B2

    NASA Astrophysics Data System (ADS)

    Likodimos, V.; Koutandos, S.; Pissas, M.; Papavassiliou, G.; Prassides, K.

    2003-01-01

    Conduction electron spin resonance is employed to study the interplay of the electronic and structural properties in the normal state of Mg 1 - x Al x B2 alloys as a function of Al-doping for 0 <= x <= 1. The x-dependence of the spin susceptibility reveals considerable reduction of the total density of states N(EF) with increasing Al concentration, complying with theoretical predictions for a predominant filling effect of the hole σ bands by electron doping. The CESR linewidth exhibits significant broadening, especially prominent in the high-Al-content region, indicative of the presence of enhanced structural disorder, consistent with the presence of compositional fluctuations.

  7. Thermoelectric power of Ce(In 1- xSn x) 3

    NASA Astrophysics Data System (ADS)

    Sakurai, J.; Murata, K.; Komura, Y.

    1984-01-01

    Thermoelectric power, S, of a pseudo-binary system Ce(In 1- xSn x) 3 was measured in the temperature range from 4.2 to 300 K. S as a function of temperature, T, has common features for all our samples; at low temperature, S is nearly proportional to T, it attains to a large maximum value and then it decreases as further increase of T. These features of S are shown to be understandable on the basis of the model on the intermediate valence state of 4 f-electron of Ce proposed by Newns and Hewson.

  8. Consequences of Broken Translational Symmetry in FeSexTe1-x

    NASA Astrophysics Data System (ADS)

    Moreschini, L.; Lin, P.-H.; Lin, C.-H.; Ku, W.; Innocenti, D.; Chang, Y. J.; Walter, A. L.; Kim, K. S.; Brouet, V.; Yeh, K.-W.; Wu, M.-K.; Rotenberg, E.; Bostwick, A.; Grioni, M.

    2014-02-01

    We investigate the consequences of broken translational symmetry in the superconductor FeSexTe1-x using angle-resolved photoemission spectroscopy. We find that the intensity does not follow the periodicity dictated by the crystal structure, owing to the form of the perturbing potential and the symmetries of the Fe d orbitals. Their interplay leads to substantial differences in the orbital character and spectral features observed at nominally equivalent locations in the reciprocal space. Such differences cannot be accounted for by the usual dipole matrix element effects and are due instead to the structure factor, which must be explicitly considered whenever more than one atom is present in the unit cell.

  9. ARPES studies on FeTe1-x Se x iron chalcogenides epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Innocenti, Davide; Moreschini, Luca; Chang, Young Jun; Walter, Andrew; Bostwick, Aaron; di Castro, Daniele; Tebano, Antonello; Medaglia, Pier Gianni; Bellingeri, Emilio; Pallecchi, Ilaria; Ferdeghini, Carlo; Balestrino, Giuseppe; Rotenberg, Eli

    2011-03-01

    The physics of iron-based chalcogenides raises fundamental questions on the interplay of magnetic order and electron pairing at the origin of the superconducting state. We have performed angle-resolved photemission spectroscopy (ARPES) studies on high-quality epitaxial thin films of FeTe 1-x Se x , grown by in situ pulsed laser deposition (PLD) on beamline 7.0.1 at the ALS. Specifically, we are able to show the evolution of the band structure as a function of x. We discuss our experimental results in comparison to the available theoretical band calculations.

  10. Scanning tunneling spectroscopy on SrFe2(As1 -xPx )2

    NASA Astrophysics Data System (ADS)

    Jandke, Jasmin; Wild, Petra; Schackert, Michael; Suga, Shigemasa; Kobayashi, Tatsuya; Miyasaka, Shigeki; Tajima, Setsuko; Wulfhekel, Wulf

    2016-03-01

    We investigated SrFe 2 (As 1 -xPx )2 single crystals with four different phosphorus concentrations x in the superconducting phase (x =0.35 ,0.46 ) and in the magnetic phase (x =0 ,0.2 ). The superconducting samples display a V-shaped superconducting gap, which suggests nodal superconductivity. Furthermore, we determined the superconducting coherence length by measuring the spatially resolved superconducting density of states. Using inelastic tunneling spectroscopy, we investigated excitations in the samples with four different phosphorus concentrations. Inelastic peaks are related to bosonic modes. The phonon and nonphonon mechanisms for the origin of these peaks are discussed.

  11. Specific heat of new perovskite-type cobaltates Pr1-xNdxCoO3

    NASA Astrophysics Data System (ADS)

    Thakur, Rasna; Srivastava, Archana; Thakur, Rajesh K.; Gaur, N. K.

    2016-05-01

    Specific heat and Bulk modulus (B) of new perovskite-type cobaltates Pr1-xNdxCoO3 has been studied by means of a Modified Rigid Ion Model (MRIM) and Atoms in Molecules (AIM) theory in a wide temperature range (1K ≤ T ≤1000K). The effect of Nd doping on the elastic, cohesive and thermal properties of PrCoO3 have been studied probably for the first time by an atomistic approach. The computed results are in good agreement with the available experimental data.

  12. Superconductivity and magnetism in intermetallic Bi3Ni1-xFex superconductor

    NASA Astrophysics Data System (ADS)

    Gonsalves, Silvio Henrique; Opata, Yuri Aparecido; Pinheiro, Lincoln Brum Leite Gusmão; Da Silva Leal, Adriane Consuelo; Monteiro, João Frederico Haas Leandro; Siqueira, Ezequiel Costa; de Andrade, André Vitor Chaves; Jurelo, Alcione Roberto

    2016-09-01

    In this work, we investigated the apparent coexistence of superconductivity and magnetism in polycrystalline Bi3Ni1-xFex samples for low concentrations of iron (0 ≤ x ≤ 0.10). The compound was synthesized by the solid-state reaction method and characterized by X-ray diffraction and magnetic measurements. From X-ray, it was observed that the main phase corresponds to an orthorhombic structure with space group Pnma and shows no dependence on the Fe concentration. From magnetic measurements, it was observed that the critical temperature was not affected by iron doping and that ferromagnetism and superconductivity coexist apparently in an interesting interplay.

  13. Thin films of FexNi1-x electroplated on silicon (100)

    NASA Astrophysics Data System (ADS)

    Spada, E. R.; de Oliveira, L. S.; da Rocha, A. S.; Pasa, A. A.; Zangari, G.; Sartorelli, M. L.

    2004-05-01

    FexNi1-x thin films were electroplated in the constant current mode directly onto n-type Si (100) using saccharin as a leveller agent. Fe content varied between 7 and 20at%. Current efficiency increased with current density and also with film thickness, ranging from 35% to 76%. Films with a nominal thickness of 2800nm showed a magnetoresistance of 3.6% and a coercive field of 3.5Oe for deposits grown at 12.6mA/cm2. For x<20, magnetization curves displayed a skewed shape, characteristic of a stripe domain configuration perpendicular to the plane of the film.

  14. Anisotropic Ti x Sn1- x O2 nanostructures prepared by magnetron sputter deposition

    NASA Astrophysics Data System (ADS)

    Chen, Shutian; Li, Zhengcao; Zhang, Zhengjun

    2011-12-01

    Regular arrays of Ti x Sn1- x O2 nanoflakes were fabricated through glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter polystyrene spheres. The morphology of nanostructures could be controlled by simply adjusting the sputtering power of the Ti target. The reflectance measurements showed that the melon seed-shaped nanoflakes exhibited optimal properties of antireflection in the entire visible and ultraviolet region. In addition, we determined their anisotropic reflectance in the direction parallel to the surface of nanoflakes and perpendicular to it, arising from the anisotropic morphology.

  15. Photocatalysis on (CdS) x (ZnTe)1 - x solid solutions

    NASA Astrophysics Data System (ADS)

    Karpova, E. O.; Nagibina, I. Yu.; Makarova, A. S.

    2015-01-01

    Photocatalytic properties of the surface of binary compounds (CdS, ZnTe) and solid solutions (CdS) x (ZnTe)1 - x formed on their basis are studied by means of potentiometry and chromatography. The values of forbidden gap Δ E are calculated from the resulting UV spectra, according to which the components of the CdS-ZnTe system can display photocatalytic activity in the wavelength range of 364 to 670 nm. A scheme of a model setup for producing hydrogen from water is proposed using the authors' method.

  16. SPIN-FRUSTRATED EFFECT AND THE MAGNETIC PROPERTIES IN YMn1-xAlxO3

    NASA Astrophysics Data System (ADS)

    Zhang, A. M.; Zhu, W. H.; Wu, X. S.; Bian, Q.

    2013-08-01

    Polycrystalline samples YMn1-xAlxO3 with different Al doping concentration were synthesized by standard solid-state reaction. Effect of Al doping on the magnetic properties was studied. Magnetization measurements show that the magnetization increases, while the calculated frustration factor decreases with the doping content of Al3+ ion increasing. And the spin-glass behavior becomes more and more obvious with increasing the Al doping content. These results were ascribed to the broken exchange path between Mn ions by Al doping.

  17. Scaling theory of magnetoresistance and carrier localization in Ga1-xMnxAs.

    PubMed

    Moca, C P; Sheu, B L; Samarth, N; Schiffer, P; Janko, B; Zarand, G

    2009-04-01

    We compare experimental resistivity data on Ga1-xMnxAs films with theoretical calculations using a scaling theory for strongly disordered ferromagnets. The characteristic features of the temperature dependent resistivity can be quantitatively understood through this approach as originating from the close vicinity of the metal-insulator transition. However, accounting for thermal fluctuations is crucial for a quantitative description of the magnetic field induced changes in resistance. While the noninteracting scaling theory is in reasonable agreement with the data, we find clear evidence for interaction effects at low temperatures. PMID:19392399

  18. Morphotropic Phase Boundaries in Ferromagnets: Tb1 xDyxFe2 Alloys

    SciTech Connect

    Bergstrom, Richard; Wuttig, Manfred; Cullen, James; Zavalij, Peter; Dennis, Cindi; Garlea, Vasile O; Laver, Mark

    2013-01-01

    The structure and properties of the ferromagnet Tb1 xDyxFe2 are explored through the morphotropic phase boundary (MPB) separating ferroic phases of differing symmetry. Our synchrotron data support a first order structural transition, with a broadening MPB width at higher temperatures. The optimal point for magnetomechanical applications is not centered on the MPB but lies on the rhombohedral side, where the high striction of the rhombohedral majority phase combines with the softened anisotropy of the MPB. We compare our findings with single ion crystal field theory and with ferroelectric MPBs.

  19. Preparation and optical properties of GA(x)IN(1-x)P alloys

    NASA Technical Reports Server (NTRS)

    Rodot, H.; Horak, J.; Rouy, G.; Bourneix, J.

    1986-01-01

    The solution crystallization method was used to obtain Ga(z)In(1-x)P alloys for all values of x desired between zero and 1. The method of preparation makes it possible to crystallize the solid at a constant temperature. The points obtained by cathodoluminescence are nearly in straight lines. The optical absorption thresholds are confirmed in the results and make it possible to define the nature of the transitions except when x is in the neighborhood of 0.65. These determinations agree with those of Hilsum and Porteus (1968), but are not in agreement with those obtained by Lorenz et al, (1968).

  20. Cation non-stoichiometry in pulsed laser deposited Sr{sub 2+y}Fe{sub 1+x}Mo{sub 1-x}O₆ epitaxial films

    SciTech Connect

    Meyer, T. L.; Woodward, P. M.; Dixit, M.; Williams, R. E. A.; Susner, M. A.; Fraser, H. L.; McComb, D. W.; Sumption, M. D.; Lemberger, T. R.

    2014-07-07

    Sr₂FeMoO₆ (SFMO) films were grown on SrTiO₃ (100)- and (111)-oriented substrates via pulsed laser deposition (PLD). In order to study the fundamental characteristics of deposition, films were grown in two different PLD chambers. In chamber I, the best films were grown with a relatively long substrate-to-target distance (89 mm), high substrate temperature (850 °C), and low pressure (50 mTorr) in a 95% Ar/5% H₂ atmosphere. Although X-ray diffraction (XRD) measurements indicate these films are single phase, Rutherford Backscattering (RBS) measurements reveal considerable non-stoichiometry, corresponding to a Sr₂Fe{sub 1–x}Mo{sub 1+x}O₆ composition with x≅0.2–0.3. This level of non-stoichiometry results in inferior magnetic properties. In chamber II, the best films were grown with a much shorter substrate-to-target distance (38 mm), lower temperature (680 °C), and higher pressure (225 mTorr). XRD measurements show that the films are single phase, and RBS measurements indicate that they are nearly stoichiometric. The degree of ordering between Fe and Mo was dependent on both the temperature and pressure used during deposition, reaching a maximum order parameter of 85%. The saturation magnetization increases as the Fe/Mo ordering increases, reaching a maximum of 2.4 μB/f.u. Based on prior studies of bulk samples, one would expect a higher saturation magnetization for this degree of Fe/Mo order. The presence of extra strontium oxide layers in the form of Ruddlesden-Popper intergrowths appears to be responsible for the lower than expected saturation magnetization of these films.

  1. XPS and electroluminescence studies on SrS 1- xSe x and ZnS 1- xSe x thin films deposited by atomic layer deposition technique

    NASA Astrophysics Data System (ADS)

    Ihanus, Jarkko; Lambers, Eric; Holloway, Paul H.; Ritala, Mikko; Leskelä, Markku

    2004-01-01

    SrS 1- xSe x and ZnS 1- xSe x thin films were deposited by the atomic layer deposition (ALD) technique using elemental selenium as the Se source, thus avoiding use of H 2Se or organometallic selenium compounds. X-ray diffraction (XRD) analysis showed that the films were solid solutions and X-ray photoelectron spectroscopy (XPS) data showed that the surface of both ZnS 1- xSe x and SrS 1- xSe x were covered with an oxide and carbon-containing contaminants from exposure to air. The oxidation of SrS 1- xSe x extended into the film and peak shifts from sulfate were found on the surface. Luminance measurements showed that emission intensity of the ZnS 1- xSe x:Mn alternating current thin film electroluminescent (ACTFEL) devices at fixed voltage was almost the same as that of the ZnS:Mn device, while emission intensity of the SrS 1- xSe x:Ce devices decreased markedly as compared to the SrS:Ce device. Emission colors of the devices were altered only slightly due to selenium addition.

  2. Thermodynamical and electronic properties of Bx Al1-x N alloys: A first principle study

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Joshi, Suman; Joshi, B.; Auluck, S.

    2015-11-01

    A series of first principle calculations were carried out to investigate thermodynamical, electronic and optical properties of cubic Bx Al1-x N ordered alloys using supercell approach within density functional theory (DFT). Here we calculate the lattice constants using van der Waals density functional (vdW-DF) at several concentrations (x) of boron. We find that the vdW-DF prediction shows slightly better agreement with experiment in contrast to local density approximation (LDA)/generalized gradient approximation (GGA). The results show that the direct energy band gap (Γv-Γc) has strong nonlinear dependence on the concentration (x). At x=0.04 and 0.84, Bx Al1-x N has a phase transition from direct to an indirect band gap semiconductor. To describe the alloys' solubility, formation enthalpy were calculated and fitted to quadratic function to obtain interaction parameter. The calculated T-x phase diagram shows a broad miscibility gap with a high critical temperature equal to 3063 K. The calculated dielectric function is explained in terms of band structure and density of states and compared with the available experimental data, showing good agreement.

  3. Interplay between superconductivity and magnetism in Fe(1-x)Pd(x)Te.

    PubMed

    Karki, Amar B; Garlea, V Ovidiu; Custelcean, Radu; Stadler, Shane; Plummer, E W; Jin, Rongying

    2013-06-01

    The attractive/repulsive relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions, and Fe pnictides, showed superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds [RRh4B4 (R = Nd, Sm, Tm, Er), R'Mo6X8 (R' = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As(1-x)P(x))2, etc.], providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe(1-x)Pd(x)Te. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature T(N/S), and turns into short-range AFM correlation with a characteristic peak in magnetic susceptibility at T'(N). Superconductivity sets in when T'(N) reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (short-range) cross-over regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic (FM and AFM) interactions.

  4. Nanoscale Inhomogeneous Superconductivity in Fe(Te1-xSex) Probed by Nanostructure Transport.

    PubMed

    Yue, Chunlei; Hu, Jin; Liu, Xue; Sanchez, Ana M; Mao, Zhiqiang; Wei, Jiang

    2016-01-26

    Among iron-based superconductors, the layered iron chalcogenide Fe(Te1-xSex) is structurally the simplest and has attracted considerable attention. It has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. In this work, through simple micromechanical exfoliation and high-precision low-energy ion milling thinning, we prepared Fe(Te0.5Se0.5) nanoflakes with various thicknesses and systematically studied the correlation between the thickness and superconducting phase transition. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te0.5Se0.5) flake is reduced to less than the characteristic inhomogeneity length (around 12 nm), both the superconducting current path and the metallicity of the normal state in Fe(Te0.5Se0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneous nature of superconductivity in Fe(Te1-xSex).

  5. Element Specific Spin and Orbital Moments in Fe1-x Vx Alloys

    SciTech Connect

    Guan, Y.; Scheck, C; Bailey, W

    2009-01-01

    We present transmission-mode X-ray magnetic circular dichroism (XMCD) measurements of element-specific magnetic moments for Fe and V at the L2,3 edges in polycrystalline Fe1-xVx ultrathin films. We find that the orbital-to-spin moment ratio of Fe does not change within experimental error. The V XMCD is not very informative, and a nearly pure-spin type V impurity moment ({approx}1.0 {mu}{sub B}/atom, antiparallel to the Fe host moment) is assumed to match known magnetization data. Data are further reduced to a two-sublattice model and found to be compatible with known spectroscopic splitting g-factor data in the alloy. The results confirm that the very low Gilbert damping, attained through the introduction of V into epitaxial Fe1-xVx films and found by ferromagnetic resonance (FMR), does not result from the reduction of orbital moment content in the alloy.

  6. Twinning in vapour-grown, large volume Cd1-xZnxTe crystals

    NASA Astrophysics Data System (ADS)

    Tanner, B. K.; Mullins, J. T.; Pym, A. T. G.; Maneuski, D.

    2016-08-01

    The onset of twinning from (2 bar 1 bar 1 bar) to (1 bar 3 bar 3 bar) in large volume Cd1-xZnxTe crystals, grown by vapour transport on (2 bar 1 bar 1 bar) , often referred to as (211)B, oriented GaAs seeds, has been investigated using X-ray diffraction imaging (X-ray topography). Twinning is not associated with strains at the GaAs/CdTe interface as the initial growth was always in (2 bar 1 bar 1 bar) orientation. Nor is twinning related to lattice strains associated with injection of Zn subsequent to initial nucleation and growth of pure CdTe as in both cases twinning occurred after growth of several mm length of Cd1-xZnxTe. While in both cases examined, there was a region of disturbed growth prior to the twinning transition, in neither crystal does this strain appear to have nucleated the twinning process. In both cases, un-twinned material remained after twinning was observed, the scale of the resulting twin boundaries being sub-micron. Simultaneous twinning across the whole sample surface was observed in one sample, whereas in the other, twinning was nucleated at different points and times in the growth.

  7. Magneto-optical study of uranium additions to amorphous TbxFe1 - x

    NASA Astrophysics Data System (ADS)

    Dillon, J. F., Jr.; van Dover, R. B.; Hong, M.; Gyorgy, E. M.; Albiston, S. D.

    1987-02-01

    Recent reports of huge magneto-optical Kerr rotations in certain crystalline metallic uranium compounds prompted a study of the magnetic and magneto-optical effects of uranium additions to a rare-earth transition metal amorphous alloy. Using variable composition samples, the polar Kerr effect at a small spot (e.g., 0.5 mm diam) was measured as field, temperature, and composition were varied. Points on the Curie line and the edges of the compensation region were determined from these observations. The compositions studied included (TbxFe1-x)1-yUy with 0.125≤x≤0.550 and y=0.0, 0.04, 0.07, 0.16. The addition of uranium to TbxFe1-x depresses the TC of Tb-rich material much more strongly than that of Tb-poor material. The compensation region does not shift at all with increasing y. It appears that uranium does not contribute to the magnetization of these amorphous alloys, nor does it significantly affect the magneto-optical effects.

  8. Quantum phase transition and Fermi liquid behavior in Pd1 -xNix nanoalloys

    NASA Astrophysics Data System (ADS)

    Swain, P.; Srivastava, Suneel K.; Srivastava, Sanjeev K.

    2015-01-01

    The Pd1 -xNix alloy system is an established ideal transition-metal system possessing a composition-induced paramagnetic-to-ferromagnetic quantum phase transition (QPT) at the critical concentration xc˜0.026 in bulk. A low-temperature non-Fermi liquid (NFL) behavior around xc usually indicates the presence of quantum criticality (QC) in this system. In this work, we explore the existence of such a QPT in nanoparticles of this alloy system. We synthesized single-phase, polydispersed and 40-50 nm mean diameter crystalline nanoparticles of Pd1 -xNix alloys, with x near xc and beyond, by a chemical reflux method. In addition to the determination of the size, composition, phase, and crystallinity of the alloys by microscopic and spectroscopic techniques, the existence of a possible QPT was explored by resistivity and dc magnetization measurements. A dip in the value of the exponent n near xc, and a concomitant peak in the constant A of the A Tn dependence of the low-temperature (T ) resistivity indicate the presence of a quantum-like phase transition in the system. The minimum value of n , however, remains within the Fermi liquid regime (n >2 ). The dc magnetization results suggest an anticipatory presence of a superparamagnetic-to-ferromagnetic QPT in the mean-sized nanoparticles. The observation of a possible quantum critical NFL behavior (n <2 ) through resistivity is argued to be inhibited by the electron-magnon scatterings present in the smaller nanoparticles.

  9. Emergence of half-metallic ferromagnetism in Ga1- x Cr x As

    NASA Astrophysics Data System (ADS)

    Rani, Anita; Kumar, Ranjan

    2016-08-01

    We have studied the structural, electronic and half-metallic ferromagnetic properties of Ga1- x Cr x As compounds at dopant concentrations x = 0.25, 0.125 and 0.0625. First principle calculations based on density functional theories as implemented in SIESTA code using LDA + U (local density approximation + U) as exchange correlation potential have been used to study the properties of these compounds. Here, U is the Hubbard's parameter. The calculated results predict that Cr-doped GaAs diluted magnetic semiconductors exhibit half-metallic properties at different concentrations, in which Cr atoms form deep levels in forbidden energy gap. The results also predict that with increase of fraction of Cr atoms, half-metallic energy band gap of Ga1- x Cr x As decreases. Total magnetic moment of these compounds is due to Cr states, and also p-d hybridization between Ga-p and Cr-d induces small magnetic moment on nonmagnetic atoms (Ga and As) for all concentrations.

  10. History dependence of the magnetic properties of single-crystal Fe1 -xCoxSi

    NASA Astrophysics Data System (ADS)

    Bauer, A.; Garst, M.; Pfleiderer, C.

    2016-06-01

    We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of Fe1 -xCoxSi , 0.20 ≤x ≤0.50 . We determine the magnetic phase diagrams for all major crystallographic directions and cooling histories. After zero-field cooling, the phase diagrams resemble that of the archetypal stoichiometric cubic chiral magnet MnSi. Besides the helical and conical state, we observe a pocket of skyrmion lattice phase just below the helimagnetic ordering temperature. At the phase boundaries between these states evidence for slow dynamics is observed. When the sample is cooled in small magnetic fields, the phase pocket of skyrmion lattice may persist metastably down to the lowest temperatures. Taken together with the large variation in the transition temperatures, transition fields, and helix wavelength as a function of the composition, this hysteresis identifies Fe1 -xCoxSi as an ideal material for future experiments exploring, for instance, the topological unwinding of the skyrmion lattice.

  11. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    PubMed

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity. PMID:27382157

  12. Studies on vacuum evaporated PbS 1- xSe x thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Majeed Khan, M. A.; Khan, Shamshad A.; Husain, M.

    2004-02-01

    The narrow gap IV-VI semiconductors have been the subject of extensive research owing to their technological importance. The fabrication of devices with alloys of these compounds with detecting and lasing capabilities has been an important recent technological development. The high quality polycrystalline thin films of PbS 1- xSe x with variable composition (0⩽ x⩽1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. Asdeposited films were annealed in vacuum at 350 K. Structural, electrical and optical properties of PbS 1- xSe x thin films have been examined. The X-ray diffraction patterns were used to determine the sample quality, crystal structure and lattice parameter of the films. The dc conductivity and activation energy of the films were measured in the temperature range 300-380 K. The absorption coefficient and band gap of the films were determined by absorbance measurements in wavelength range 2500-5000 nm using FTIR spectrophotometer.

  13. Structural, electrical and optical properties of Cdx Zn1-xSe thin films

    NASA Astrophysics Data System (ADS)

    Soliman, H. S.; Ali, N. A.; El-Shazly, A. A.

    1995-07-01

    X-ray diffraction and electron diffraction techniques indicate that Cdx Zn1-xSe thin films on glass substrates have a polycrystalline nature, with sphalerite structure for x≤0.5 and wurtzite structure for x≥0.6. The crystalline size in each composition increases with increasing the film thickness. The room temperature dark resistivity π varies from one composition to another showing a transition at x=0.55 The temperature dependence of π of the deposited films revealed two conduction mechanisms, one below 352 K due to shallow levels, surface states, and defects introduced during the film growth, and over 352 K due to deep-level ionization following the ordinary semiconducting behaviour. The thermal activation energy of the free charge carriers decreases linearly with increasing the molar fraction x of the CdSe content up to x=0.55, above which it increases with increasing x. The optical constants of Cdx Zn1-xSe thin films of different compositions were determined in the spectral range 400 2000 nm. The analysis of the absorption coefticient at and near the absorption edge indicates the existence of allowed direct transition energy gaps decreasing with increasing x.

  14. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    PubMed

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  15. Half-metallicity in Heusler-type Fe2Cr1-x Co x Si alloys

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Inamdar, Swaleha; Arout Chelvane, J.; Manivel Raja, M.; Kamat, S. V.

    2016-02-01

    The effects of the substitution of Cr with Co on microstructure, phase composition, structure, magnetic, and electrical properties in \\text{F}{{\\text{e}}2}\\text{C}{{\\text{r}}1-x}\\text{C}{{\\text{o}}x}\\text{Si} (0  ⩽  x  ⩽  1) alloys was investigated to identify the compositions with the potential to exhibit half-metallicity. The microstructural and structural studies revealed that only \\text{F}{{\\text{e}}2}\\text{C}{{\\text{r}}1-x}\\text{C}{{\\text{o}}x}\\text{Si} alloys with x  ⩾  0.5 exhibited the desired single phase L21 full Heusler alloy structure. Both the saturation magnetization (M s) and Curie temperature (T C) were found to increase with the increase in Co concentration. The experimentally measured M s values are in good agreement with the Slater-Pauling rule. The electrical resistivity measurements in the temperature range 10-300 K gives indirect evidence of half-metallic behaviour in these alloys at low temperatures. The temperature range in which the half-metallic behaviour was observed also increased with an increase in Co concentration.

  16. Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

    1993-01-01

    Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

  17. Wet thermal oxidation of Al(x)Ga(1-x)As compounds

    NASA Astrophysics Data System (ADS)

    Burton, R. S.; Schlesinger, T. E.

    1994-11-01

    Results are presented on the wet thermal oxidation of Al(x)Ga(1-x)As. The growth of wet thermal oxides of Al(x)Ga(1-x)As is shown to be linear with time. An O2 carrier gas was found to form a self-terminating oxide for compositions investigated (x greater than 0.4), but required elevated temperature for substantial growth. The use of a medium oxygen concentration (about 20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al(0.6)Ga(0.4)As from 1.9 to 1.0 eV while increasing the activation energy of Al(0.8)Ga(0.2)As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.

  18. CoxFe1-x oxide coatings on metallic interconnects for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Shen, Fengyu; Lu, Kathy

    2016-10-01

    In order to improve the performance of Cr-containing steel as an interconnect material for solid oxide fuel cells, CoFe alloy coatings with Co:Fe ratios of 9:1, 8:2, 7:3, 6:4, and 5:5 are deposited by electrodeposition and then oxidized to CoxFe1-x oxide coatings with a thickness of ∼6 μm as protective layers on the interconnect. The area specific resistance of the coated interconnect increases with the Fe content. Higher Co content oxide coatings are more effective in limiting the growth of the chromia scale while all coatings are effective in inhibiting Cr diffusion and evaporation. With the Co0.8Fe0.2 oxide coated interconnect, the electrochemical performance of the Sm0.5Sr0.5Co0.2Fe0.8O3 cathode is improved. Only 1.54 atomic percentage of Cr is detected on the surface of the Sm0.5Sr0.5Co0.2Fe0.8O3 cathode while no Cr is detected 0.66 μm or more into the cathode. CoxFe1-x oxide coatings are promising candidates for solid oxide fuel cell interconnects with the advantage of using existing cathode species for compatibility and performance enhancement.

  19. Electronic and optical properties of mixed perovskites CsSnxPb(1-x)I3

    NASA Astrophysics Data System (ADS)

    Wang, Guang-Tao; Wei, Jun-Hong; Peng, Yu-Feng

    2016-06-01

    The electronic structure and optical properties of the new solar cells absorber material: mixed perovskites CsSnxPb(1-x)I3 are studied by the first-principle calculations with mBJ + SOC (modified Beak Johnson approximation plus spin-orbit coupling) method. The band gap of the serial of compounds almost quasi-linearly reduces with increasing Sn content from 0.96 eV (x = 0) to 0.16 eV (x = 1). Optical absorption coefficient revealed a progressive red shift with the increment of the Sn content, accompanying with the absorption edge broadening. The absorption coefficient and Ideal Power Absorption Coefficient (IPAC) increase greatly with the Pb atoms being partially substituted by Sn atoms. The pure CsSnI3 has the highest IPAC, but it is unstable in the air because the Sn2+ will be oxidized to Sn4+. So our results indicate that partially substituted CsSnxPb(1-x)I3 might be the good solar cell absorption material.

  20. Moment enhancement in dilute magnetic semiconductors: MnxSi1-x with x = 0.1%

    SciTech Connect

    Shaughnessy, M; Fong, C Y; Snow, R; Liu, K; Pask, J E; Yang, L H

    2009-03-12

    The experimentally determined magnetic moments/Mn, M, in Mn{sub x}Si{sub 1-x} are considered, with particular attention to the case with 5.0 {micro}{sub B}/Mn, obtained for x = 0.1%. The existing theoretical M values for neutral Mn range from 2.83 to 3.78 {micro}B/Mn. To understand the observed M = 5.0 {micro}{sub B}/Mn, we investigated Mn{sub x}Si{sub 1-x} for a series of Mn concentrations and defect configurations using a first-principles density functional method. We find a structure in which the moment is enhanced. It has 5.0 {micro}B/Mn, the Mn at a substitutional site, and a Si at a second-neighbor interstitial site in a large unit cell. Subsequent analysis shows that the observed large moment can be understood as a consequence of the weakened d-p hybridization resulting from the introduction of the second-neighbor interstitial Si and substantial isolation of the Mn-second-neighbor Si complex at such concentrations.

  1. Charge density wave in layered La1 -xCexSb2

    NASA Astrophysics Data System (ADS)

    Luccas, R. F.; Fente, A.; Hanko, J.; Correa-Orellana, A.; Herrera, E.; Climent-Pascual, E.; Azpeitia, J.; Pérez-Castañeda, T.; Osorio, M. R.; Salas-Colera, E.; Nemes, N. M.; Mompean, F. J.; García-Hernández, M.; Rodrigo, J. G.; Ramos, M. A.; Guillamón, I.; Vieira, S.; Suderow, H.

    2015-12-01

    The layered rare-earth diantimonides R Sb2 are anisotropic metals with generally low electronic densities whose properties can be modified by substituting the rare earth. LaSb2 is a nonmagnetic metal with a low residual resistivity presenting a low-temperature magnetoresistance that does not saturate with the magnetic field. It has been proposed that the latter can be associated to a charge density wave (CDW), but no CDW has yet been found. Here we find a kink in the resistivity above room temperature in LaSb2 (at 355 K) and show that the kink becomes much more pronounced with substitution of La by Ce along the La1 -xCexSb2 series. We find signatures of a CDW in x-ray scattering, specific heat, and scanning tunneling microscopy (STM) experiments in particular for x ≈0.5 . We observe a distortion of rare-earth-Sb bonds lying in-plane of the tetragonal crystal using x-ray scattering, an anomaly in the specific heat at the same temperature as the kink in resistivity and charge modulations in STM. We conclude that LaSb2 has a CDW which is stabilized in the La1 -xCexSb2 series due to substitutional disorder.

  2. Catalytic combustion of methane on La1-xCexFeO3 oxides

    NASA Astrophysics Data System (ADS)

    Xiang, Xian-Ping; Zhao, Lei-Hong; Teng, Bo-Tao; Lang, Jia-Jian; Hu, Xin; Li, Tie; Fang, Yi-An; Luo, Meng-Fei; Lin, Jian-Jun

    2013-07-01

    A series of La1-xCexFeO3 (x = 0-0.5) perovskite oxides were prepared by a sol-gel method. X-ray diffraction spectrometer (XRD), BET surface area measurements, scanning electron microscopy (SEM) images, and temperature-programmed reduction (TPR) were used to characterize their physical structures and redox properties. Catalytic methane combustion tests for La1-xCexFeO3 (x = 0-0.5) perovskite oxides show that the activity of LaFeO3 was highly improved due to the introduction of Ce in the A-site of the perovskite catalysts. Among all the catalysts, La0.7Ce0.3FeO3 has the maximum oxidative performance with the corresponding T90 as low as 510 °C. Combining with density functional theory calculation, it was suggested that the electrons of Fe ions increase in La0.875Ce0.125FeO3 due to the introduction of Ce4+ ion, which leads to stronger interactions with adsorbed O2. Correspondingly, the adsorption energy of O2 on La0.875Ce0.125FeO3 increases and the Osbnd O bond is activated. Thus, the Ce doped perovskite has higher oxidative activity than pure LaFeO3.

  3. Effect of cross-sectional geometry on thermal conductivity of Si1-xGex nanowires

    NASA Astrophysics Data System (ADS)

    Qu, Peixin

    2016-06-01

    By incorporating the direction-dependent phonon-boundary scattering from the surface of the nanowires with different cross-sectional shapes into the linearized phonon Boltzmann transport equation, we theoretically investigate the effect of cross-sectional geometry on the thermal conductivity of Si1-xGex nanowires. It is demonstrated that the surface-to-volume ratio (SVR) is a universal gauge for both pure silicon nanowires (SiNWs) and silicon-germanium nanowires (SiGe NWs), and the thermal conductivity of nanowires decreases monotonically with the increase of SVR. We also find that the thermal conductivity of high-frequency phonons in nanowires is more strongly SVR dependent than that of low-frequency phonons, and the thermal conductivity of high-frequency phonons is severely suppressed by alloy scattering, therefore the SVR dependence on thermal conductivity of Si1-xGex NWs decreases with the increase of Ge atom concentration x (x < 0.5). These findings are useful for understanding and tuning the thermal conductivity of nanowires by geometry.

  4. High Compositional Homogeneity of CdTexSe1-x Crystals Grown by the Bridgman Method

    DOE PAGES

    Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Lee, K.; Lee, W.; Tappero, R.; Yang, G.; Gul, R.; et al

    2015-02-03

    We obtained high-quality CdTexSe1-x (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL’s National Synchrotron Light Source X27A beam line. The resulting compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ~1.0. This uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-raymore » detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional CdxZn1-xTe (CdZnTe or CZT).« less

  5. Structural and magnetic properties of MnCo1-xFexSi alloys

    NASA Astrophysics Data System (ADS)

    Chen, J. H.; Wei, Z. Y.; Liu, E. K.; Qi, X.; Wang, W. H.; Wu, G. H.

    2015-08-01

    The crystal structures, martensitic structural transitions and magnetic properties of MnCo1-xFexSi (0≤x≤0.50) alloys were studied by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and magnetic measurements. In high-temperature paramagnetic state, the alloys undergo a martensitic structural transitions from the Ni2In-type hexagonal parent phase to the TiNiSi-type orthorhombic martensite. Both the martensitic transition temperature (TM) and Curie temperatures of martensite (TCM) decrease with increasing Fe content. The introduced Fe atoms establish ferromagnetic (FM) coupling within Fe-6Mn atom configurations and destroy the double spiral antiferromagnetic (AFM) coupling in MnCoSi compound, resulting in a magnetic change in the martensite phase from a spiral AFM state to an FM state. For the alloys with x=0.10, 0.15 and 0.20, a metamagnetic transition was observed in between the two magnetic states. A magnetostructural phase diagram of MnCo1-xFexSi (0≤x≤0.50) alloys was proposed.

  6. Temperature dependence of Raman scattering in amorphous films of In 1- xSe x alloys

    NASA Astrophysics Data System (ADS)

    Weszka, J.; Daniel, Ph.; Burian, A. M.; Burian, A.; Żelechower, M.

    2001-08-01

    Raman scattering (RS) in amorphous films of In 1- xSe x with 0.70≥ x≥0.38 has been studied in backscattering geometry with the use of a single channel Raman spectrometer at room and 10 K temperatures. The recorded RS spectra reveal dominant vibrational density-of-states character. They exhibit a continuum, spanning the Rayleigh line up to a shoulder at about 250 cm -1, that moves towards lower frequencies as x decreases from 0.70 to 0.38. The bands at about 104, 125 and at 143 and 237 cm -1 are attributed to In-In, Se 8 ring molecules and Se-chain oscillations, respectively. The structure of In 1- xSe x alloys is deduced to be a continuous random network based on InSe 4/2 tetrahedral clusters interconnected by Se atoms at the shared corners or local Se-chain fragments or Se 8 rings. With growing In content, some Se atoms in such clusters are replaced by In atoms to an extent dependent on In content. The disappearance of the 143 and 237 cm -1 bands in the low temperature spectra taken on the In 0.30Se 0.70 film is attributed to the contraction of interatomic bonds, making conditions favorable for breaking Se polymer chains and Se 8 ring molecule formation.

  7. Phase separation in the iron chalcogenide superconductor Fe1+yTexSe1-x

    NASA Astrophysics Data System (ADS)

    Hu, Hefei; Zuo, Jian-Min; Wen, Jinsheng; Xu, Zhijun; Lin, Zhiwei; Li, Qiang; Gu, Genda; Park, Wan Kyu; Greene, Laura H.

    2011-05-01

    We present direct evidence for phase separation and chemical inhomogeneity in Fe1+yTexSe1-x single crystals from scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) data. In STEM, images recorded using a high-angle annular dark field (HAADF) detector show characteristic nanometer-scale patterns of phase separation from the Z-dependent image contrast. The separation was observed both in non-superconducting samples with excess iron and in superconducting samples. Using EELS, we determined ~20% (or lower) fluctuation in Te concentration from the average local compositions by integrating the intensity of the Te-M4,5 edge. The energy-loss near-edge structure (ELNES) of the Fe-L2,3 edge changes with varying composition, especially the L3/L2 white-line intensity ratio, which is sensitive to the d-state occupancy of the Fe. The results suggest a miscibility gap in the Fe1+yTexSe1-x system and changes in the d-electron states at the nanometer scale from the separated phases.

  8. Nanoscale Inhomogeneous Superconductivity in Fe(Te1-xSex) Probed by Nanostructure Transport.

    PubMed

    Yue, Chunlei; Hu, Jin; Liu, Xue; Sanchez, Ana M; Mao, Zhiqiang; Wei, Jiang

    2016-01-26

    Among iron-based superconductors, the layered iron chalcogenide Fe(Te1-xSex) is structurally the simplest and has attracted considerable attention. It has been speculated from bulk studies that nanoscale inhomogeneous superconductivity may inherently exist in this system. However, this has not been directly observed from nanoscale transport measurements. In this work, through simple micromechanical exfoliation and high-precision low-energy ion milling thinning, we prepared Fe(Te0.5Se0.5) nanoflakes with various thicknesses and systematically studied the correlation between the thickness and superconducting phase transition. Our result revealed a systematic thickness-dependent evolution of superconducting transition. When the thickness of the Fe(Te0.5Se0.5) flake is reduced to less than the characteristic inhomogeneity length (around 12 nm), both the superconducting current path and the metallicity of the normal state in Fe(Te0.5Se0.5) atomic sheets are suppressed. This observation provides the first transport evidence for the nanoscale inhomogeneous nature of superconductivity in Fe(Te1-xSex). PMID:26691639

  9. Novel synthesis and photocatalytic performance of Ce1 - xZrxO2/silica fiber

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Chen, Pengfei; Gu, Guoqiang; Wu, Qiang; Yao, Weifeng

    2016-09-01

    A series of Ce1 - xZrxO2/silica fiber composites were successfully synthesized via a carbon nanofiber (CNF) template-assisted alcohol-thermal procedure. The resulting samples were characterized by X-Ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, Brunauer-Emmett-Teller (BET) apparatus, and Raman spectroscopy. Furthermore, their photocatalytic activities were evaluated by UV-light photocatalytic degradation of methylene blue (MB) solution. The results show that the photocatalytic degradation of MB was fairly effective for the as-prepared Ce1 - xZrxO2/silica fiber samples. Particularly, with zirconium (Zr) doping, Ce0.75Zr0.25O2/silica fiber composites clearly exhibit enhanced photocatalytic efficiencies, compared with CeO2/silica fiber samples. The incorporation of Zr into the CeO2 lattice not only causes a decrease in particle size but also brings about an increase in BET specific area and UV absorption ability, which should be responsible for the enhanced photocatalytic performance.

  10. Transport properties and anisotropy of superconducting (Li1-x Fe x )OHFeSe single crystals

    NASA Astrophysics Data System (ADS)

    Wang, Chunlei; Yi, Xiaolei; Qiu, Yang; Tang, Qingbin; Zhang, Xinwei; Luo, Yongsong; Yu, Benhai

    2016-05-01

    Large size single crystals of (Li1-x Fe x )OHFeSe have been synthesized via a hydrothermal ion-exchange technique using K0.8Fe2Se2 single crystals as the main raw material. The onset superconducting transition temperature is up to 40.3 K. The critical current density is as large as 1.9 × 105 A cm-2 at 5 K and self field. The upper critical fields have been determined by analyzing the relationship between resistivity and temperature under different applied fields along c-axis and ab-plane, respectively. An anisotropic factor about 11 is obtained, which is further confirmed by fitting the data obtained from the angle-dependent resistivity according to the anisotropic Ginzburg-Landau theory. The flux pinning potential (U 0/k B) is as large as 6429 and 3115 K at 0.1 T in H//ab and H//c orientation, respectively. However, the flux pinning potentials are very sensitive to the applied magnetic field and will fast decrease with increase of the magnetic field in both directions, which are obviously different from the Ba1-x K x Fe2As2 superconductor indicating a different flux pinning mechanism in the two kinds of superconductors.

  11. Interplay between Superconductivity and Magnetism in Fe1-xPdxTe

    SciTech Connect

    Karki, A B; Garlea, Vasile O; Custelcean, Radu; Stadler, S.; Plummer, E. W.; Jin, Rongying

    2013-01-01

    The love/hate relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions and Fe pnictides, show superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. On the other hand, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds (RRh4B4 (R = Nd, Sm, Tm, Er), R'Mo6X8 (R' = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn5, EuFe2(As1-xPx)2 etc.), providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe1-xPdxTe. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature TN/S, and turns into short-range (SR) AFM correlation with a characteristic peak in magnetic susceptibility at T'N. Superconductivity sets in when T'N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (SR) crossover regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic interactions (FM and AFM).

  12. Observations of flow in Inx Ga1-xAs multilayers

    NASA Astrophysics Data System (ADS)

    Korte, S.; McLaughlin, K. K.; Farrer, I.; Clegg, W. J.

    2008-08-01

    Work elsewhere has shown that the hardnesses of coherent InxGa1-xAs multilayer structures in which the misfit stresses are controlled by varying the indium content in each layer are influenced by the thicknesses and the coherency strains in the layers. These results have been interpreted in terms of the length-scale for flow being greater than the layer thickness and associated with deformation size effects. However, nanoindentation of InxGa1-x As suggests an influence of the flow stress of the individual layers on the overall multilayer flow stress. Consequently, initiation of flow in the weaker layer is expected. A deformed multilayer has been characterized by measurement of the lattice rotations measured from energy-filtered convergent beam electron diffraction (CBED) patterns recorded in scanning transmission electron microscopy (STEM) mode. Based on the movement of Kikuchi lines as a result of rotations of the lattice the local orientation of the crystal can be extracted, allowing the local orientations to be estimated. The small probe-size in CBED of ~1 nm used here ensures the region sampled is smaller than the thickness of the individual layers. These measurements have been used to construct a map of the axes of rotation in the lattice which demonstrates the ability to distinguish the individual layers.

  13. Growth and characterization of Hg(1-x)Zn(x)Se

    NASA Technical Reports Server (NTRS)

    Andrews, R. N.

    1986-01-01

    Hg sub 1-xZn sub xSe alloys of composition x=0.10 were grown in a Bridgman-Stockbarger growth furnace at translation rates of 0.3 and 0.1 micron sec. The axial and radial composition profiles were determined using precision density measurements and IR transmission-edge-mapping, respectively. A more radially homogeneous alloy was produced at the slower growth rate, while the faster growth rate produced more axially homogeneous alloys. A determination of the electrical properties of the Hg sub 1-xZn sub xSe samples in the temperature range 300K-20K was also made. Typical carrier concentrations were on the order of magnitude of 10 to the 18th power cu/cm, and remained fairly constant as a function of temperature. A study was also made of the temperature dependence of the resistivity and Hall mobility. The effect of annealing in a selenium vapor on both the IR transmission and the electrical properties was determined. Annealing was effective in reducing the number of native donor defects and at the resulting lower carrier concentrations, charge carrier concentration was shown to be a function of temperature. Annealing caused the mobility to increase, primarily at the lower temperature, and the room temperature resistivity to increase. Annealing was also observed to greatly enhance the % IR transmittance of the samples. This was due primarily to the effect of annealing on decreasing the charge carrier concentration.

  14. Surface state conductivity in epitaxially grown Bi1-x Sb x (111) films

    NASA Astrophysics Data System (ADS)

    Koch, Julian; Kröger, Philipp; Pfnür, Herbert; Tegenkamp, Christoph

    2016-09-01

    Topologically non-trivial surface states were reported first on {{Bi}}1-xSb x bulk crystals. In this study we present transport measurements performed on thin {{Bi}}1-xSb x -films (up to 24 nm thickness) grown epitaxially on Si(111) with various Sb-concentrations (up to x = 0.22). The analysis of the temperature dependency allowed us to distinguish between different transport channels originating from surface and bulk bands as well as impurity states. At temperatures below 30 K the transport is mediated by surface states while at higher temperatures activated transport via bulk channels sets in. The surface state conductivity and bulk band gaps can be tuned by the Sb-concentration and film thickness, respectively. For films as thin as 4 nm the surface state transport is strongly suppressed in contrast to Bi(111) films grown under identical conditions. The impurity channel is of intrinsic origin due to the growth and alloy formation process and turns out to be located at the buried interface.

  15. Lattice dynamics of II-VI mixed semiconductor ZnS 1- xSe x

    NASA Astrophysics Data System (ADS)

    Kushwaha, A. K.

    2008-09-01

    Lattice dynamical properties of II-VI compounds having zinc-blende structure have been calculated by three-body shell model. This model incorporates the effect of the short-range repulsive interactions up to and including the second nearest neighbours, in addition to the long-range Coulombic interactions in the frame work of the rigid-shell model with both the ions are polarizable. The model involves in total eleven disposable parameters. Using the above proposed model the phonon dispersion relations for mixed II-VI semiconductor ZnS 1- xSe x are plotted. We find an overall good agreement with the experimental results. The application of the present model has been made to calculate the phonon dispersion relations of ZnS, ZnSe and mixed semiconductor ZnS 1- xSe x. The comparison of the theoretical results with the available experimental has been made along high symmetry directions. A reasonably good agreement is observed between theory and experiments.

  16. Electron doping evolution of the magnetic excitations in NaFe1 xCoxAs

    DOE PAGES

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Perring, T. G.; Dai, Pengcheng

    2016-06-13

    We use time-of-flight (TOF) inelastic neutron scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1-xCoxAs with x = 0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron-doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden and suppress low energy (E 80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high energy (E > 80 meV) spin excitations are weakly Co-doping dependent. Integration of the local spin dynamic susceptibility "(!) of NaFe1-xCoxAs reveals a total fluctuating moment of 3.6 μ2 B/Fe andmore » a small but systematic reduction with electron doping. The presence of a large spin gap in the Cooverdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel Ni-doping evolution of spin excitations in BaFe2-xNixAs2, confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping dependent high-energy spin excitations result from localized moments.« less

  17. Giant thermal vibrations in the framework compounds Ba1 -xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishii, Y.; Tanaka, E.; Tsukasaki, H.; Kubota, Y.; Mori, S.

    2016-08-01

    Synchrotron x-ray diffraction experiments were performed on the network compounds Ba1 -xSrxAl2O4 at temperatures between 15 and 800 K. The ferroelectric phase of the parent BaAl2O4 is largely suppressed by substituting a small amount of Sr for Ba and disappears for x ≥0.1 . Structural refinements reveal that the isotropic atomic displacement parameter Biso in the bridging oxygen atom is largely independent of temperature and retains an anomalously large value in the adjacent paraelectric phase even at the lowest temperature. The Biso systematically increases as x increases, exhibiting an especially large value for x =0.5 . According to previous electron diffraction experiments for Ba1 -xSrxAl2O4 with x ≥0.1 , strong thermal diffuse scattering occurs at two reciprocal points relating to two distinct soft modes at the M and K points over a wide range of temperatures below 800 K [Y. Ishii et al., Sci. Rep. 6, 19154 (2016), 10.1038/srep19154]. Although the latter mode disappears at approximately 200 K, the former does not condense, at least down to 100 K. The anomalously large Biso observed in this study is ascribed to these soft modes existing in a wide temperature range.

  18. Local Structure of the Te/Si(001)-(1x1) Surface.

    NASA Astrophysics Data System (ADS)

    Bedzyk, M. J.; Lyman, P. F.; Montano, P. A.

    1996-03-01

    Adsorption of Te on Si is the critical first step in CdTe/Si growth. Apart from this potential commercial importance, adsorption of a group VI element (Te) on the (001) face of a group IV semiconductor (Si) might result in near-perfect passivation of the Si surface; the Si dangling bonds could be satisfied by a (1x1) arrangement of hexavalent Te. A recent LEED and STM study of the Te/Si(001) surface(S.A. Yoshikawa et al., Surf. Sci. 321, L183 (1994)) revealed that although the local arrangement of Te atoms does appear to be (1x1), the larger size of the strongly adsorbed Te atoms results in occasional missing rows of Te; these relieve strain by allowing lateral expansion of the Te layer. We undertook an x-ray standing wave study to quantify the adsorption site, spatial distribution, and structural perfection of the Te layer. Although good agreement with the STM was found for the lateral expansion of Te, a surprisingly large spatial distribution was found in the surface-normal direction, not evident in the STM work.

  19. P-type electronic and thermal transport properties of Mg2Sn1-xSix

    NASA Astrophysics Data System (ADS)

    Kim, Sunphil; Wiendlocha, Bartlomiej; Heremans, Joseph P.

    2013-03-01

    P-type Mg2Sn doped with various acceptors(1)(2) has been studied as a potential thermoelectric material. Because of its narrow band gap and high lattice thermal conductivity, the zT values of the binary compound are limited: zTmax reported is 0.3(3). In this work, we synthesize and characterize p-type-doped Mg2Sn1-xSix with various acceptors. Silicon is added in order to widen the band gap and scatter the phonons. The conduction band degeneracy that yields excellent zT in n-type material in the Mg2Sn1-xSix alloy system unfortunately does not apply to p-type material. Thermomagnetic and galvanomagnetic properties (electrical resistivity, Seebeck, Hall, and Nernst coefficients) are measured, along with thermal conductivity and band gap measurements. Finally, zT values are reported. (1) H. Y. Chen et al. Journal of Electronic Materials, Vol. 38, No. 7, 2009 (2) S. Choi et al. Journal of Electronic Materials, Vol. 41, No. 6, 2012 (3) H. Y. Chen et al. Phys. Status Solidi A 207, No. 11, 2523-2531 (2010) The work is supported by the joint NSF/DOE program on thermoelectrics, NSF-CBET-1048622

  20. Interplane resistivity of isovalent doped BaFe2(As1-xPx)2

    SciTech Connect

    Tanatar, Michael A.; Hashimoto, K.; Kasahara, S.; Shibauchi, T.; Matsuda, Y.; Prozorov, Ruslan

    2013-03-07

    Temperature-dependent interplane resistivity ρc(T) was measured for the iron-based superconductor BaFe2(As1-xPx)2 over a broad isoelectron phosphorus substitution range from x=0 to x=0.60, from nonsuperconducting parent compound to heavily overdoped superconducting composition with Tc≈10K. The features due to structural and magnetic transitions are clearly resolved in ρc(T) of the underdoped crystals. A characteristic maximum in ρc(T), found in the parent BaFe2As2 at around 200 K, moves rapidly with phosphorus substitution to high temperatures. At the optimal doping, the interplane resistivity shows T-linear temperature dependence without any crossover anomalies, similar to the previously reported in-plane resistivity. This observation is in stark contrast with dissimilar temperature dependencies found at optimal doping in electron-doped Ba(Fe1-xCox)2As2. Our finding suggests that despite similar values of the resistivity and its anisotropy, the temperature-dependent transport in the normal state is very different in electron and isoelectron-doped compounds. Similar temperature dependence of both in-plane and interplane resistivities, in which the dominant contributions are coming from different parts of the Fermi surface, suggests that scattering is the same on the whole Fermi surface. Since magnetic fluctuations are expected to be much stronger on the quasinested sheets, this observation may point to the importance of the interorbital scattering between different sheets.

  1. Water electrolysis on La1-xSrxCoO3-δ perovskite electrocatalysts

    NASA Astrophysics Data System (ADS)

    Mefford, J. Tyler; Rong, Xi; Abakumov, Artem M.; Hardin, William G.; Dai, Sheng; Kolpak, Alexie M.; Johnston, Keith P.; Stevenson, Keith J.

    2016-03-01

    Perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B-O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co-O bond and the concentration of oxygen vacancies are controlled through Sr2+ substitution into La1-xSrxCoO3-δ. We attempt to rationalize the high activities of La1-xSrxCoO3-δ through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through ab initio modelling. Using this approach, we report a material, SrCoO2.7, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.

  2. Water electrolysis on La(1-x)Sr(x)CoO(3-δ) perovskite electrocatalysts.

    PubMed

    Mefford, J Tyler; Rong, Xi; Abakumov, Artem M; Hardin, William G; Dai, Sheng; Kolpak, Alexie M; Johnston, Keith P; Stevenson, Keith J

    2016-01-01

    Perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B-O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co-O bond and the concentration of oxygen vacancies are controlled through Sr(2+) substitution into La(1-x)Sr(x)CoO(3-δ) . We attempt to rationalize the high activities of La(1-x)Sr(x)CoO(3-δ) through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through ab initio modelling. Using this approach, we report a material, SrCoO2.7, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.

  3. Self-catalysed InAs{sub 1-x}Sb{sub x} nanowires grown directly on bare Si substrates

    SciTech Connect

    Anyebe, E.A. Zhuang, Q.

    2014-12-15

    Highlights: • Self-catalysed InAs{sub 1-x}Sb{sub x} nanowires grown directly on bare Si substrates. • InAs{sub 1-x}Sb{sub x} nanowires directly grown on bare Si substrates without employing the commonly used nucleation nanowire stems which could be problematic in device applications. • Pre-deposited Indium droplets were employed to facilitate InAs{sub 1-x}Sb{sub x} nanowire nucleation and growth. • Unravels a promising route for the direct integration of InAs{sub 1-x}Sb{sub x} nanowires with the well-established Silicon platform. - Abstract: We report the self-catalysed growth of InAs{sub 1-x}Sb{sub x} nanowires directly on bare Si substrates. Vertically aligned and non-tapered InAs{sub 1-x}Sb{sub x} nanowires were realized via indium-assisted nucleation without using nanowire stems. The compositions of the InAs{sub 1-x}Sb{sub x} nanowires were determined by high resolution X-ray diffraction (HRXRD). It is observed that the geometry of the nanowires is modified by the Sb flux resulting in an almost doubling of the lateral dimension and a corresponding suppression in the axial growth of the InAs{sub 1-x}Sb{sub x} nanowires. This observation unravels a method to modify the geometry of InAs nanowire and open up a promising route for the direct integration of InAs{sub 1-x}Sb{sub x} nanowires with the well-established Si platform.

  4. Segregation at the surfaces of CuxPd1 - x alloys in the presence of adsorbed S

    NASA Astrophysics Data System (ADS)

    Miller, James B.; Priyadarshini, Deepika; Gellman, Andrew J.

    2012-10-01

    The influence of adsorbed S on surface segregation in CuxPd1 - x alloys (S/CuxPd1 - x) was characterized over a wide range of bulk alloy compositions (x = 0.05 to 0.95) using high-throughput Composition Spread Alloy Film (CSAF) sample libraries. Top-surface and near-surface compositions of the CSAFs were measured as functions of bulk Cu composition, x, and temperature using spatially resolved low energy ion scattering spectroscopy (LEISS) and X-ray photoemission spectroscopy (XPS). Preferential segregation of Cu to the top-surface of the S/CuxPd1 - x CSAF was observed at all bulk compositions, x, but the extent of Cu segregation to the S/CuxPd1 - x surface was lower than the Cu segregation to the surface of a clean CuxPd1 - x CSAF, clear evidence of an S-induced "segregation reversal." The Langmuir-McLean formulation of the Gibbs isotherm was used to estimate the enthalpy and entropy of Cu segregation to the top-surface, ΔHseg(x) and ΔSseg(x), at saturation sulfur coverages. While Cu segregation to the top-surface of the clean CuxPd1 - x is exothermic (ΔHseg < 0) for all bulk Cu compositions, it is endothermic (ΔHseg > 0) for S/CuxPd1 - x. Segregation to the S/CuxPd1 - x surface is driven by entropy. Changes in segregation patterns that occur upon adsorption of S onto CuxPd1 - x appear to be related to formation of energetically favored Pdsbnd S bonds at the surface, which counterbalance the enthalpic driving forces for Cu segregation to the clean surface.

  5. Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys

    NASA Astrophysics Data System (ADS)

    Baldissera, Gustavo; Persson, Clas

    2016-01-01

    ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy Eg(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O,Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O,S) is more stable as alloy than Zn(O,Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, ΔEg(0.50) = Eg(ZnO) - Eg(x = 0.50) ≈ 2.2 eV) compared with that of the S-based alloy (ΔEg(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function ɛ(ω) = ɛ1(ω) + iɛ2(ω) and the absorption coefficient α(ω). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant ɛ∞ is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

  6. Scrutinizing Hall Effect in Mn1 -xFex Si : Fermi Surface Evolution and Hidden Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Glushkov, V. V.; Lobanova, I. I.; Ivanov, V. Yu.; Voronov, V. V.; Dyadkin, V. A.; Chubova, N. M.; Grigoriev, S. V.; Demishev, S. V.

    2015-12-01

    Separating between the ordinary Hall effect and anomalous Hall effect in the paramagnetic phase of Mn1 -xFex Si reveals an ordinary Hall effect sign inversion associated with the hidden quantum critical (QC) point x*˜0.11 . The effective hole doping at intermediate Fe content leads to verifiable predictions in the field of fermiology, magnetic interactions, and QC phenomena in Mn1 -xFex Si . The change of electron and hole concentrations is considered as a "driving force" for tuning the QC regime in Mn1 -xFex Si via modifying the Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism.

  7. Magnetic phase transitions in Pr(1-x)Lu(x)Mn(2)Ge(2) compounds.

    PubMed

    Wang, J L; Campbell, S J; Studer, A J; Avdeev, M; Zeng, R; Dou, S X

    2009-03-25

    The effects of replacing Pr by Lu on the magnetic behaviour and structures of Pr(1-x)Lu(x)Mn(2)Ge(2) (x = 0.2,x = 0.4) have been investigated using x-ray diffraction, Mössbauer spectroscopy, magnetization and neutron diffraction measurements. The substitution of Lu for Pr leads to a decrease in the lattice constants a, c and the unit cell volume V at room temperature with this contraction of the unit cell resulting in modifications of the Pr(1-x)Lu(x)Mn(2)Ge(2) magnetic structures. Four and five magnetic phase transitions-linked primarily with temperature driven changes in the intralayer Mn-Mn separation distances-have been detected within the temperature range 4.5-550 K for Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2), respectively, with re-entrant ferromagnetism being detected around T(C)(Pr)∼31 K for Pr(0.6)Lu(0.4)Mn(2)Ge(2). It was found that T(C)(inter) and T(C)(Pr) increase with increasing applied field while T(N)(inter) decreases for Pr(0.6)Lu(0.4)Mn(2)Ge(2), indicating that the canted antiferromagnetic AFmc region contracts with increasing field. The Debye temperatures for Pr(1-x)Lu(x)Mn(2)Ge(2) with x = 0.2 and 0.4 were evaluated as θ(D) = 320 ± 40 K and θ(D) = 400 ± 20 K respectively from the temperature dependence of the average isomer shift. The magnetic structures of both compounds have been determined by means of neutron diffraction measurements over the temperature range 3-300 K with formation of the Fmi magnetic state below T(c/c) = 192 K for Pr(0.8)Lu(0.2)Mn(2)Ge(2) and the occurrence of re-entrant ferromagnetism below T(C)(Pr) = 31 K for Pr(0.6)Lu(0.4)Mn(2)Ge(2) being confirmed. PMID:21817459

  8. Modelling the thermal conductivity of (UxTh1-x)O2 and (UxPu1-x)O2

    SciTech Connect

    Cooper, M. W. D.; Middleburgh, S. C.; Grimes, R. W.

    2015-07-15

    The degradation of thermal conductivity due to the non-uniform cation lattice of (UxTh1-x)O2 and (UxPu1-x)O2 solid solutions has been investigated by molecular dynamics, using the non-equilibrium method, from 300 to 2000 K. Degradation of thermal conductivity is predicted in (UxTh1-x)O2 and (UxPu1-x)O2 as compositions deviate from the pure end members: UO2, PuO2 and ThO2. The reduction in thermal conductivity is most apparent at low temperatures where phonon-defect scattering dominates over phonon-phonon interactions. The effect is greater for (UxTh1-x)O2 than UxPu1-x)O2 due to the greater mismatch in cation size. Parameters for an analytical expressions have been developed that describe the predicted thermal conductivities over the full temperature and compositional ranges. Finally, these expressions may be used in higher level fuel performance codes.

  9. Far-infrared spectroscopy of CdTe1-xSex(In): Phonon properties

    NASA Astrophysics Data System (ADS)

    Petrović, M.; Romčević, N.; Trajić, J.; Dobrowolski, W. D.; Romčević, M.; Hadžić, B.; Gilić, M.; Mycielski, A.

    2014-11-01

    The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spatial distribution of free carriers as well as their influence on the plasmon-phonon interaction. We found that the long wavelength optical phonon modes of CdTe1-xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm-1 is observed. In both sample, a surface layer with a low concentration of free carriers (depleted region) are formed.

  10. Bandgap in Al{sub 1-x}Sc{sub x}N

    SciTech Connect

    Deng, Ruopeng; Evans, Sarah R.; Gall, Daniel

    2013-03-18

    Aluminum scandium nitride (Al{sub 1-x}Sc{sub x}N) layers deposited by reactive magnetron co-sputtering on sapphire 0001 substrates at 850 Degree-Sign C are epitaxial single-crystals for x {<=} 0.20. Their in-plane lattice constant increases linearly (3.111 + 0.744x A) while the out-of-plane constant remains at 4.989 {+-} 0.005 A. Optical absorption indicates a band gap of 6.15-9.32x eV and a linearly increasing density of defect states within the gap. The average bond angle decreases linearly with x, suggesting a trend towards the metastable hexagonal-ScN structure. However, an anomalous decrease at x = 0.20 indicates a structural instability which ultimately leads to phase separated rock-salt ScN grains for x > 0.4.

  11. Investigation of Cd1-xMgxTe Alloys for Tandem Solar Cell Applications (Poster)

    SciTech Connect

    Dhere, R.; Ramanathan, K.; Scharf, J.; Moutinho, H.; To, B.; Duda, A.; Noufi, R.

    2006-05-01

    Fabrication and characterization of Cd{sub 1-x}Mg{sub x}Te(CMT) alloys and to determine their potential for device applications. Main emphasis is on the development of the devices in 1.5 to 1.8 eV range for the top cell of two-junction tandem solar cells. The conclusions are: (1) CMT alloy films with a wide composition range were fabricated; (2) the optical band gap shows a systematic variation with composition and CMT alloy films withstood the commonly used device processing steps for CdTe; and (3) they have fabricated cells with 5% efficiency in the energy gap range of 1.5 to 1.7 eV and established the viability of CMT for device applications.

  12. Ensemble Monte Carlo characterization of graded Al(x)Ga(1-x)As heterojunction barriers

    NASA Technical Reports Server (NTRS)

    Kamoua, R.; East, J. R.; Haddad, G. I.

    1990-01-01

    The current-voltage characteristics of graded Al(x)Ga(1-x)As heterojunction barriers were investigated using a self-consistent ensemble Monte Carlo method. Results are presented for barriers with two doping levels (10 to the 15th/cu cm and 10 to the 17th/cu cm) and two barrier heights (100 and 265 meV). It was found that the lower barrier structure exhibited little rectification at room temperature at both doping levels, while the higher barrier exhibited considerable rectification. The structures with the lower doping value exhibited a smaller current in both forward and reverse regions, due to space-charge effect. The results of studies of the energy and momentum distribution functions along the barrier indicate that the assumption of drifted Maxwellian distribution used in energy-momentum models is not justified for Gamma valley electrons.

  13. La 1-x Ca x MnO 3 semiconducting nanostructures: morphology and thermoelectric properties.

    PubMed

    Culebras, Mario; Torán, Raquel; Gómez, Clara M; Cantarero, Andrés

    2014-01-01

    Semiconducting metallic oxides, especially perosvkite materials, are great candidates for thermoelectric applications due to several advantages over traditionally metallic alloys such as low production costs and high chemical stability at high temperatures. Nanostructuration can be the key to develop highly efficient thermoelectric materials. In this work, La 1-x Ca x MnO 3 perosvkite nanostructures with Ca as a dopant have been synthesized by the hydrothermal method to be used in thermoelectric applications at room temperature. Several heat treatments have been made in all samples, leading to a change in their morphology and thermoelectric properties. The best thermoelectric efficiency has been obtained for a Ca content of x=0.5. The electrical conductivity and Seebeck coefficient are strongly related to the calcium content. PMID:25206315

  14. Development of Si(1-x)Ge(x) technology for microwave sensing applications

    NASA Technical Reports Server (NTRS)

    Mena, Rafael A.; Taub, Susan R.; Alterovitz, Samuel A.; Young, Paul E.; Simons, Rainee N.; Rosenfeld, David

    1993-01-01

    The progress for the first year of the work done under the Director's Discretionary Fund (DDF) research project entitled, 'Development of Si(1-x)Ge(x) Technology for Microwave Sensing Applications.' This project includes basic material characterization studies of silicon-germanium (SiGe), device processing on both silicon (Si) and SiGe substrates, and microwave characterization of transmission lines on silicon substrates. The material characterization studies consisted of ellipsometric and magneto-transport measurements and theoretical calculations of the SiGe band-structure. The device fabrication efforts consisted of establishing SiGe device processing capabilities in the Lewis cleanroom. The characterization of microwave transmission lines included studying the losses of various coplanar transmission lines and the development of transitions on silicon. Each part of the project is discussed individually and the findings for each part are presented. Future directions are also discussed.

  15. Laser power dependence of the band edge of CdSxSe1-x quantum dots

    NASA Astrophysics Data System (ADS)

    Verma, Prabhat; Irmer, Gert; Yamada, Masayoshi

    2000-04-01

    We present a systematic study of the influence of probing laser power-density on the band-edge of CdSxSe1-x nanoparticles embedded in a glass matrix. Both the position and the strength of the band-edge luminescence are found to be very sensitive to the laser power. It is observed that the band-edge luminescence shifts initially towards low energy and then towards high energy with increasing laser power. The result are analyzed in terms of laser induced local heating and band-filling mechanism, both of which are found to be very effective processes for nanoparticle systems. Laser induced local heating of the nanoparticles are determined by analyzing temperature- dependent Raman spectra from the sample.

  16. Origin of background electron concentration in InxGa1-xN alloys

    DOE PAGES

    Pantha, B. N.; Wang, H.; Khan, N.; Lin, J. Y.; Jiang, H. X.

    2011-08-15

    The origin of high background electron concentration (n) in InxGa1-xN alloys has been investigated. A shallow donor was identified as having an energy level (ED1) that decreases with x (ED1 = 16 meV at x = 0 and ED1 = 0 eV at x ~ 0.5) and that crossover the conduction band at x ~ 0.5. This shallow donor is believed to be the most probable cause of high n in InGaN. This understanding is consistent with the fact that n increases sharply with an increase in x and becomes constant for x > 0.5. A continuous reduction in nmore » was obtained by increasing the V/III ratio during the epilayer growth, suggesting that nitrogen vacancy-related impurities are a potential cause of the shallow donors and high background electron concentration in InGaN« less

  17. Optical Properties of Hg1- x- y Cd x Dy y Se Crystals

    NASA Astrophysics Data System (ADS)

    Kovalyuk, T. T.; Maryanchuk, P. D.; Maistruk, É. V.; Koziarskyi, D. P.

    2013-12-01

    Results of investigations of the optical properties of Hg1- x- y Cd x Dy y Se crystals by the Bridgeman method are presented. Based on independent measurements of the reflection and transmission coefficients with a Nicolet 6700 spectrometer at Т = 300 K for wavelengths 0.9 ≤ λ ≤ 26.6 μm, values of the refractive and absorption indices and of the absorption coefficient are determined for the examined crystals. From the dependences α = f(hν) it is established that direct interband optical transitions are allowed in the crystals, and values of the gap width are determined. The effects of the temperature on the transmission coefficient and on the gap width at Т = 118-297 K are investigated.

  18. Monopolar photoelectromagnetic effect in Pb1-xSnxTe(In) under terahertz laser radiation

    NASA Astrophysics Data System (ADS)

    Chernichkin, V. I.; Ryabova, L. I.; Nicorici, A. V.; Khokhlov, D. R.

    2012-03-01

    We report on the observation of a new effect—the appearance of a galvanic signal in the narrow-gap semiconductor Pb1-xSnxTe(In) in the magnetic field under the action of strong 100 ns-long terahertz laser pulses. The signal changes its sign and kinetics as the temperature increases from 4.2 K to 25 K. This semiconductor possesses inversion symmetry of the crystalline lattice making impossible the observation of the magnetophotogalvanic effect which looks similar in its experimental manifestation. On the other hand, the laser quantum energy is much less than the bandgap of the semiconductor making the effect considerably different from the conventional Kikoin-Noskov photoelectromagnetic effect. Possible mechanisms responsible for the appearance of the effect are discussed.

  19. First-principles study on the formation energies of Ga1_xCrxAs

    NASA Astrophysics Data System (ADS)

    Martínez, N.; Rodríguez Martínez, J. A.

    2016-08-01

    The electronic structure and formation energy of the Ga1-xCrxAs compound has been studied by principles of methods based on the Density Functional Theory. The formation energy of the compound is calculated, as well as the vacancies and substitutions. The equations of Kohn-Sham are solved employing the plane wave method and the ultra-soft atomic pseudopotentials approximation. The generalized gradient approximation was employed for the exchange and correlation energy in the Perdew-Burke-Ernzerhof (PBE) parametrization as it is implemented in the computational code Quantum Espresso. It was found that the most favourable configuration is the GaAs lattice by doing the substitution of one Ga atom by one Cr in the analyzed lattices.

  20. Photoluminescence in modulation-doped GaAs/Ga1-xAlxAs heterojunctions

    NASA Astrophysics Data System (ADS)

    Shen, J. X.; Oka, Y.; Hu, C. Y.; Ossau, W.; Landwehr, G.; Friedland, K.-J.; Hey, R.; Ploog, K.; Weimann, G.

    1999-03-01

    We investigated the physical properties of modulation-doped GaAs/Ga1-xAlxAs heterojunctions by photoluminescence. We found two types of transitions and attributed them to the space direct excitons in the GaAs flat band region and the space indirect excitons near the heterojunction notch. We propose the vertical transport of photoexcited carriers prior to the actual exciton formation under the influence of the two-dimensional carrier gas. Therefore, the photoluminescence intensities of the two types of excitons are correlated. The vertical transport model explains successfully the experimental results of the optically detected cyclotron resonance, the photoluminescence intensity oscillation with magnetic field and the long rise time of the photoluminescence intensity for the excitonic transitions.

  1. Superconductivity and magnetic ordering in YBa2(Cu1- x Fe x )3O7

    NASA Astrophysics Data System (ADS)

    Kossler, W. J.; Yu, X. H.; Greer, A.; Schone, H. E.; Stronach, C. E.; Davis, M.; Cary, R. S.; Lankford, W. F.; Moodenbaugh, A.; Oostens, J.

    1991-02-01

    Transverse-and zero-field μSR measurements have been made for YBa2(Cu1- x Fe x )3O7 with x=0.04, 0.08 and 0.12. The temperature range studied was from approximately 7.5 K to 100 K. The onset of magnetic ordering commences at about 7.5 K for x=0.04, 10 K for x=0.08 and 20 K for x=0.12. The Gaussian depolarization parameter, σ of G x ( t) = exp(-σ2 t 2/2), is depressed by a factor of about 0.6 for x=0.04, but for the x=0.08 sample σ is depressed by a factor of 10 and increasing suppression is seen as the temperature is lowered below 45 K. This decrease in σ is interpreted in terms of decreasing electronic mean free paths.

  2. Structure and magnetism of quasicrystalline and crystalline Al1-xMnx alloys

    NASA Astrophysics Data System (ADS)

    Youngquist, S. E.; Miceli, P. F.; Wiesler, D. G.; Zabel, H.; Fraser, H. L.

    1986-08-01

    We have performed x-ray structural studies of quenched and annealed Al1-xMnx alloys in the range of 0.14<=x<=0.20. The quenched samples exhibit a coexistence of Al with an icosahedral phase, the latter having a maximum volume fraction at x=0.20. Magnetic susceptibility measurements for x=0.14 and 0.20 show a dramatically enhanced magnetic moment in the icosahedral phase (p=0.747 and 1.27, respectively) as compared to the annealed samples (p=0 and 0.617, respectively). The increase of magnetic moment per Mn ion with increasing Mn concentration indicates a range of stoichiometries and microstructures over which the icosahedral phase can exist.

  3. LiHoxY1 - xF4 in the highly-diluted limit

    NASA Astrophysics Data System (ADS)

    Andresen, Juan Carlos; Schechter, Moshe; Oganesyan, Vadim; Katzgraber, Helmut G.

    2014-03-01

    The rare-earth material LiHoxY1 - xF4 has attracted much attention recently, not only because it is well described by a long-range dipolar Ising model, but also because it has a rich phase diagram in the temperature-concentration plane that makes it especially interesting to explore exotic magnetic phenomena. The existence of a spin-glass phase in this material has been a long-standing controversy. In particular, it is unclear if the spin-glass phase extends to the low-concentration limit, or if an exotic anti-glass state emerges. Using large-scale Monte Carlo simulations we probe this difficult regime of the phase diagram.

  4. Concentration dependence of magnetic moment in Ce1-xFexO2

    NASA Astrophysics Data System (ADS)

    Beausoleil, Geoffrey L.; Thurber, Aaron; Rao, S. S.; Alanko, Gordon; Hanna, C. B.; Punnoose, Alex

    2012-04-01

    In this study, we examined the impact of iron doping on the structural, chemical, and magnetic properties of ceria (Ce1-xFexO2). Samples were produced in triplicate through a coprecipitation approach in a forced hydrolysis synthesis that yielded consistently sized nanocrystals using three different cerium precursors: cerium chloride, cerium ammonium nitrate, and cerium nitrate. Particles were characterized by x ray diffraction (XRD), x ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, and vibrating sample magnetometry (VSM). XPS and EPR data shows iron to be in the Fe3+ state and confirms the nominal dopant concentration. The moment per Fe ion found was largest at the lowest dopant concentrations, and quickly decreased as the concentration was increased. We used XPS to estimate the Ce3+/Ce4+ ratio and observed a linear relation between the saturation magnetization and the Ce3+/Ce4+ ratio.

  5. Zn1-xCoxO nanoparticles: Synthesis and study of enhanced optical and structural properties

    NASA Astrophysics Data System (ADS)

    Ahad, Abdul; Majid, Suhail; Rahman, F.

    2016-05-01

    We have synthesized the Zn1-xCoxO (x= 0, 0.01, 0.03 and 0.05) using Sol-gel method. The structural properties were characterized using X-ray diffraction. Optical properties were characterized using UV-VIS and FT-IR spectroscopy. The lattice parameters were refined using Reitveld refinement which also reveals that all the peaks in XRD patterns were indexed in the wurtzite type hexagonal structure with space group P 63 mc. The FT-IR spectra confirmed the presence of functional groups and chemical bonding. The band gap of each sample was calculated by adopting Kubelka-Munk transformed reflectance spectra and effect of doping on band gap is also studied.

  6. Doping-enhanced antiferromagnetism in Ca1 -xLaxFeAs2

    NASA Astrophysics Data System (ADS)

    Kawasaki, Shinji; Mabuchi, Tomosuke; Maeda, Satoki; Adachi, Tomoki; Mizukami, Tasuku; Kudo, Kazutaka; Nohara, Minoru; Zheng, Guo-qing

    2015-11-01

    In iron pnictides, high temperature superconductivity emerges after suppressing antiferromagnetism by doping. Here, we show that antiferromagnetism in Ca1 -xLaxFeAs2 is robust against and even enhanced by doping. Using 75As-nuclear magnetic resonance and nuclear quadrupole resonance techniques, we find that an antiferromagnetic order occurs below the Néel temperature TN=62 K at a high doping concentration (x =0.15 ) where superconductivity sets in at the transition temperature Tc=35 K. In the superconducting state coexisting with antiferromagnetism, the nuclear-spin-lattice relaxation rate 1 /T1 becomes proportional to T , indicating gapless excitations. Unexpectedly, TN is enhanced with increasing doping, rising up to TN=70 K at x =0.24 . The obtained phase diagram of this system enriches the physics of iron-based high-Tc superconductors.

  7. Evolution of the superconducting properties in FeSe1 -xSx

    NASA Astrophysics Data System (ADS)

    Moore, S. A.; Curtis, J. L.; Di Giorgio, C.; Lechner, E.; Abdel-Hafiez, M.; Volkova, O. S.; Vasiliev, A. N.; Chareev, D. A.; Karapetrov, G.; Iavarone, M.

    2015-12-01

    We present scanning tunneling microscopy and spectroscopy measurements on FeSe1 -xSx single crystals with x =0 , 0.04 , and 0.09 . The S substitution into the Se site is equivalent to a positive chemical pressure, since S and Se have the same valence and S has a smaller ionic radius than Se. The subsequent changes in the electronic structure of FeSe induce a decrease of the structural transition temperature and a small increase in the superconducting critical temperature. The evolution of the gaps with increasing S concentration suggests an increase of the hole Fermi surface. Moreover, the vortex core anisotropy, that likely reflects the Fermi surface anisotropy, is strongly suppressed by the S substitution.

  8. Charge transfer effects on the chemical reactivity of PdxCu1-x nanoalloys

    NASA Astrophysics Data System (ADS)

    Castegnaro, M. V.; Gorgeski, A.; Balke, B.; Alves, M. C. M.; Morais, J.

    2015-12-01

    This work reports on the synthesis and characterization of PdxCu1-x (x = 0.7, 0.5 and 0.3) nanoalloys obtained via an eco-friendly chemical reduction method based on ascorbic acid and trisodium citrate. The average size of the quasi-spherical nanoparticles (NPs) obtained by this method was about 4 nm, as observed by TEM. The colloids containing different NPs were then supported on carbon in order to produce powder samples (PdxCu1-x/C) whose electronic and structural properties were probed by different techniques. XRD analysis indicated the formation of crystalline PdCu alloys with a nanoscaled crystallite size. Core-level XPS results provided a fingerprint of a charge transfer process between Pd and Cu and its dependency on the nanoalloy composition. Additionally, it was verified that alloying was able to change the NP's reactivity towards oxidation and reduction. Indeed, the higher the amount of Pd in the nanoalloy, less oxidized are both the Pd and the Cu atoms in the as-prepared samples. Also, in situ XANES experiments during thermal treatment under a reducing atmosphere showed that the temperature required for a complete reduction of the nanoalloys depends on their composition. These results envisage the control at the atomic level of novel catalytic properties of such nanoalloys.This work reports on the synthesis and characterization of PdxCu1-x (x = 0.7, 0.5 and 0.3) nanoalloys obtained via an eco-friendly chemical reduction method based on ascorbic acid and trisodium citrate. The average size of the quasi-spherical nanoparticles (NPs) obtained by this method was about 4 nm, as observed by TEM. The colloids containing different NPs were then supported on carbon in order to produce powder samples (PdxCu1-x/C) whose electronic and structural properties were probed by different techniques. XRD analysis indicated the formation of crystalline PdCu alloys with a nanoscaled crystallite size. Core-level XPS results provided a fingerprint of a charge transfer process

  9. Valley splitting of Si/Si1-xGex heterostructures in tilted magnetic fields.

    SciTech Connect

    Pan, Wei; Schaffler, F.; Muhlberger, M.; Lyon, S.; Xie, Ya-Hong; Lai, K. W.; Tsuri, D.; Liu, J.; Lu, T.M.

    2006-01-01

    We have investigated the valley splitting of two-dimensional electrons in high-quality Si/Si{sub 1-x}Ge{sub x} heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor {nu} = 3 ({Delta}{sub 3}) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear dependence of {Delta}{sub 3} on the electron density was observed, while the slope of these two configurations differs by more than a factor of 2. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of {Delta}{sub 3} before and after the coincidence.

  10. Fe x Ga1- x BO3 single crystals: synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Yagupov, S.; Strugatsky, M.; Seleznyova, K.; Maksimova, E.; Nauhatsky, I.; Yagupov, V.; Milyukova, E.; Kliava, J.

    2015-10-01

    A series of Fe x Ga1- x BO3 single crystals in the concentration range 0 ≤ x ≤ 1 has been synthesized by solution in the melt method. In order to determine optimal crystallization regimes, two settings have been worked out and applied in the present study: the first one, for precise differential thermal analysis and the second one, for the probe method. X-ray fluorescence and X-ray diffraction analysis have allowed accurate determination of iron contents and lattice parameters for synthesized crystals with different x. Computer-assisted EPR studies of Fe3+ have revealed a high perfection of the crystals: low degree of disorder and the absence of twinning.

  11. Topological transition in Bi1-xSbx studied as a function of Sb doping

    NASA Astrophysics Data System (ADS)

    Nakamura, Fumitaka; Kousa, Yuka; Taskin, Alexey A.; Takeichi, Yasuo; Nishide, Akinori; Kakizaki, Akito; D'Angelo, Marie; Lefevre, Patrick; Bertran, Francois; Taleb-Ibrahimi, Amina; Komori, Fumio; Kimura, Shin-Ichi; Kondo, Hiroshi; Ando, Yoichi; Matsuda, Iwao

    2011-12-01

    Spin- and angle-resolved photoemission spectroscopy measurements were performed on Bi1-xSbx samples at x=0.04, 0.07, and 0.21 to study the change of the surface band structure from nontopological to topological. Energy shift of the T and Ls bulk bands with Sb concentration is quantitatively evaluated. An edge state becomes topologically nontrivial at x=0.04. An additional trivial edge state appears at the L band gap that forms at x>0.04 and apparently hybridize with the nontrivial edge state. A scenario for the topological transition mechanism is presented. Related issues of self-energy and temperature dependence of the surface state are also considered.

  12. Temperature-induced phase transformation of Fe1-xNix alloys: molecular-dynamics approach

    NASA Astrophysics Data System (ADS)

    Sak-Saracino, Emilia; Urbassek, Herbert M.

    2015-07-01

    Using molecular-dynamics simulation, we study the temperature induced bcc/fcc phase transformation of random Fe1-xNix alloys in the concentration range of x ≤ 40 at%. The Meyer-Entel potential describes faithfully the decrease of the transition temperature with increasing Ni concentration. The austenite transformation proceeds by homogeneous nucleation and results in a fine-grained poly-crystalline structure. The transformation follows the Nishiyama-Wassermann orientation relationship. The martensite phase nucleates at the grain boundaries (heterogeneous nucleation). Even for the largest crystallite studied (2.75 × 105 atoms) the back-transformation results in a single-crystalline grain containing only a small amount of defects. The morphological changes in the transformed material show no significant dependence on Ni content.

  13. What is the valence of Mn in Ga1-xMnxN?

    DOE PAGES

    Berlijn, Tom; Jarrell, Mark; Nelson, Ryky; Ku, Wei; Moreno, Juana

    2015-11-04

    Motivated by the potential high Curie temperature of Ga1-xMnxN, we investigate the controversial Mn valence in this diluted magnetic semiconductor. From a first-principles Wannier-function analysis of the high energy Hilbert space, we find unambiguously the Mn valence to be close to 2+(d5), but in a mixed spin configuration with average magnetic moments of 4µB. By integrating out high-energy degrees of freedom differently, we further demonstrate the feasibility of both effective d4 and d5 descriptions. These two descriptions offer simple pictures for local and extended properties of the system, and highlight the dual nature of its doped hole. Specifically, in themore » effective d5 description, we demonstrate novel physical effects absent in previous studies. Thus, our derivation highlights the richness of low-energy sectors in interacting many-body systems and the generic need for multiple effective descriptions.« less

  14. Bi1-xSbx(110): A non-closed packed surface of a topological insulator

    NASA Astrophysics Data System (ADS)

    Barreto, Lucas; Silva, Wendell Simoes E.; Stensgaard, Malthe; Ulstrup, Søren; Bianchi, Marco; Zhu, Xie-Gang; Michiardi, Matteo; Dendzik, Maciej; Hofmann, Philip

    2013-03-01

    Topological insulators are characterised by an insulating bulk band structure, but topological considerations require their surfaces to support gap-less, metallic states. Meanwhile, many examples of such materials have been predicted and found experimentally, but experimental effort has concentrated on the closed-packed (111) surface of these materials. Thus, the theoretical picture of an insulating bulk embedded in a metallic surface from all sides of a crystal still needs to be confirmed. Here we present angle-resolved photoemission spectroscopy results from the (110) surface of the topological insulator Bi1-xSbx (x ~ 0 . 15). The observed band structure and Fermi contour are in excellent agreement with theoretical predictions and slightly different from the electronic structure of the parent surface Bi(110), in particular around the X1 time-reversal invariant momentum. We argue that the preparation of surfaces different from (111) opens the possibility to tailor the detailed electronic structure and properties of the topological surface states.

  15. Electronic and magnetic properties of Nd1 -xSrxMnAsO oxyarsenides

    NASA Astrophysics Data System (ADS)

    Wildman, E. J.; Emery, N.; Mclaughlin, A. C.

    2014-12-01

    The oxypnictides Nd1 -xSrxMnAsO have been successfully synthesized with x up to 0.1. A synchrotron x-ray diffraction study demonstrates that there is no change in crystal symmetry upon doping with Sr. An expansion of the interlayer distance between Nd-O-Nd and As-Mn-As blocks is observed with increasing x . Results from variable temperature neutron diffraction and resistivity measurements show that the local moment antiferromagnetic order of the Mn spins is preserved as the [MnAs] - layers are hole doped and the materials are driven metallic for x ≥ 0.05. A sizable positive magnetoresistance is observed at low temperature which demonstrates that multiple MR mechanisms are possible in LnMnAsO oxypnictides.

  16. Fine structure of DX(Sn) centers in AlxGa1-xAs

    NASA Astrophysics Data System (ADS)

    Zhan, H. H.; Kang, J. Y.; Wu, Z. Y.; Huang, Q. S.

    1998-09-01

    High resolution Laplace defect spectroscopy was used to study the fine structure of the electron emission process of DX(Sn) centers in AlxGa1-xAs (x=0.26,0.53). Two groups of peaks in the spectra of electron emission rates were found to correspond to two DX-like centers observed by deep level transient spectroscopy. The line splitting in both groups derives from the alloy disorder effect attributed to the different local configurations of Al and Ga atoms around two DX-like centers. Experimental evidence for the microscopic nature of two DX-like centers in Sn-doped AlGaAs is provided.

  17. Photoluminescence Properties of Sn-Related Donor State in AlxGa1-xAs

    NASA Astrophysics Data System (ADS)

    Kang, Junyong; Iida, Seishi; Huang, Qisheng; Fukuda, Tsuguo

    1993-08-01

    We have investigated the near-gap recombinations in Sn-doped AlxGa1-xAs by photoluminescence. By analyzing the variations of spectral lineshapes under various excitation intensities, only one type of recombination was assigned to associate with the Sn-related donor state, which was different from the hydrogenlike shallow donor states and the DX centers. Phonon replicas were observed to accompany the recombination in the samples with high AlAs mole fractions of direct gaps, as well as in those of indirect gaps. The Franck-Condon shift and the phonon energy of the recombination were found to increase with increasing AlAs mole fraction. This behavior was explained in terms of a variation of local lattice distortion around an ionized Sn-related donor and a weighted average of two local vibrational mode frequencies of the Sn-related donor.

  18. Field dependent magnetic anisotropy of Fe1-xZnx thin films

    NASA Astrophysics Data System (ADS)

    Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

    2013-05-01

    Using longitudinal magneto-optical Kerr effect in combination with a variable strength rotating magnetic field, called the Rotational Magneto-Optic Kerr Effect (ROTMOKE) method, we show that the magnetic anisotropy for thin Fe82Zn18 single crystal films, grown on MgO(001) substrates, depends linearly on the strength of the applied magnetic field at low fields but is constant (saturates) at fields greater than 350 Oe. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial and cubic anisotropy with the addition of a cubic anisotropy that depends linearly on the applied magnetic field. The field dependent term is evidence of a large effect on the effective magnetic anisotropy in Fe1-xZnx thin films by the magnetostriction.

  19. Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

    NASA Technical Reports Server (NTRS)

    Samanta, K.; Bhattacharya, P.; Katiyar, R. S.; Iwamoto, W.; Pagiluso, P. G.; Rettori, C.

    2006-01-01

    Raman spectra of ZnO and Co substituted Zn1-xCoxO (ZCO) were carried out using the Raman microprobe system with an p.,+ ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E210w mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization (1.2micron Beta/ErCo) for 10% Co substitution, which decreased wi th at further increase in Co concentrations. The intensities of E1(LO) at 584 cm-1 and multiphonon modes at 540 cm-1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution (x=15%-20%) were identified to be due to the spinel ZnCo2O4 secondary phase.

  20. Synthesis and Characterization of Compositionally Graded Si1-xGex Layers on Si substrate

    SciTech Connect

    Yu, Zhongqing; Zhang, Yanwen; Wang, Chong M.; Shutthanandan, V.; Lyubinetsky, Igor; Engelhard, Mark H.; Saraf, Laxmikant V.; Mccready, David E.; Henager, Charles H.; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai

    2007-08-01

    Thin film of silicon germanium (Si1-xGex) with tailored composition was grown on Si (100) substrate at 650oC in an ultrahigh vacuum molecular beam epitaxy system. The nominal x-value is ranged from 0 to 0.14. The quality of the film was investigated by Rutherford backscattering spectrometry (RBS) in random and channeling geometries, glancing angle x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy (EDX), and atomic force microscopy (AFM). RBS/Channeling measurements indicate that the strain associated with lattice mismatch is compressive in the film. Both RBS and EDX analyses indicate the compositional graded incorporation of Ge in the film with x ranging from 0 to 0.14. The film shows island growth with each island centering around an interface dislocation.

  1. Doping induced modification in polyhedral tilt in hexagonal Ho1-xYxMnO3

    NASA Astrophysics Data System (ADS)

    Kaushik, S. D.; Rayaprol, S.

    2012-06-01

    We have studied the effect of systematic doping of Y at Ho site on the crystal structure of hexagonal HoMnO3 We have carried out room temperature neutron diffraction (ND) study on Ho1-xYxMnO3 (x = 0, 0.25, 0.50, 0.75), and by analyzing this ND data we have determined the cell parameters, Mn-O bond length, O-Mn-O bond angle. The variation in certain M-O bond length and O-Mn-O bond angles has been understood in terms of modifications in tilt of the MnO5 polyhedra due to Ho site Y doping in hexagonal HoMnO3.

  2. The structure and optical properties of Sr1-xCaxMoO3

    NASA Astrophysics Data System (ADS)

    Hopper, H. A.; Macphee, D. E.; Mclaughlin, A. C.

    2016-10-01

    The solid solution Sr1-xCaxMoO3 (x=0.00, 0.05, 0.10, 0.13, 0.15 and 0.17) has successfully been synthesised and X-ray Powder diffraction has revealed the occurrence of structural phase transitions, from cubic Pm-3m to tetragonal I4/mcm, and then to orthorhombic Imma as the value of x increased. Discontinuities were observed in the cell parameters and bond lengths and angles at the transition from tetragonal to orthorhombic symmetry as a result of the switching of the octahedral rotation axis at the tetragonal to orthorhombic transition. The increased octahedral tilting could also be linked to the decrease in the band gap from 2.20 eV to 2.10 eV as x increased from 0 to 0.17.

  3. Lattice anharmonicity and thermal properties of strongly correlated Fe1- x Co x Si alloys

    NASA Astrophysics Data System (ADS)

    Povzner, A. A.; Nogovitsyna, T. A.; Filanovich, A. N.

    2015-10-01

    The temperature dependences of the thermal and elastic properties of strongly correlated metal alloys Fe1- x Co x Si ( x = 0.1, 0.3, 0.5) with different atomic chiralities have been calculated in the framework of the self-consistent thermodynamic model taking into account the influence of lattice anharmonicity. The lattice contributions to the heat capacity and thermal expansion coefficient of the alloys have been determined using the experimental data. It has been demonstrated that the invar effect in the thermal expansion of the lattice observed in the magnetically ordered region of Fe0.7Co0.3Si and Fe0.5Co0.5Si is not related to the lattice anharmonicity, even though its appearance correlates with variations in the atomic chirality.

  4. Spectroscopic study of mixed oxide SAT 1- x:LA x perovskite crystals

    NASA Astrophysics Data System (ADS)

    Runka, T.; Łapsa, K.; Łapiński, A.; Aleksiyko, R.; Berkowski, M.; Drozdowski, M.

    2004-10-01

    Mixed perovskite crystals have been grown from multicomponent melts using the Czochralski method. The Raman, FT-IR and Brillouin investigations of perovskite (1- x)Sr(Al 0.5Ta 0.5)O 3: xLaAlO 3 crystals are reported. The measurements have been performed for several LA concentrations in the range 0.22≤ x≤0.36 at room temperature. The assignment of vibrational modes of IR and Raman spectra was proposed. The experimental results were correlated with structural data, obtained from X-ray diffraction study. The dependence of hypersonic velocity of transverse and longitudinal modes as a function of LA content was also determined. Spectroscopic investigations confirmed the disordered Al/Ta distribution, which increases with the increase of LA content.

  5. Magnetic properties of delafossite oxide: CuCr1-xTixO2

    NASA Astrophysics Data System (ADS)

    Majee, M. K.; Bhobe, P. A.; Nigam, A. K.

    2016-05-01

    In order to increase the possibility for technological applications of CuCrO2, there have been attempts to introduce ferromagnetic (FM) order by doping at B-site. With this aim, we present here study of polycrystalline CuCr1-xTixO2 with x=0.0, 0.05, 0.1. The samples have been prepared using solid state synthesis method and characterized for its crystal structure and magnetic properties. All the samples crystallize in the 2H delafossite structure with R-3m space group. Ti substitution causes the expansion of unit cell with increase in both the lattice constants. Antiferromagnetic ordering temperature is seen to decrease with increasing Ti. Ferromagnetic-like signature is obtained in one of the compositions at low applied magnetic field of 100 Oe.

  6. Bond length variation in Ga1-xInxAs crystals from the Tersoff potential

    NASA Astrophysics Data System (ADS)

    Titantah, J. T.; Lamoen, D.; Schowalter, M.; Rosenauer, A.

    2007-06-01

    In this work we show that a reparametrized Tersoff potential accurately reproduces the bond length variations observed in ternary Ga1-xInxAs mixed crystals. The reparametrization is based on accurate first-principles electronic structure calculations. Previous parametrizations of the Tersoff potential for GaAs and InAs structures, although they accurately reproduce the properties of the zinc-blende GaAs and InAs crystals, are shown to be unable to reproduce the bond length variations in these mixed crystals. In addition to correcting the bond length inconsistencies, the new set of parameters is also shown to yield the elastic constants of GaAs and InAs that agree fairly well with measurements and to reproduce accurately their respective melting temperature.

  7. Optical studies of SnTe xSe 1-x sintered films

    NASA Astrophysics Data System (ADS)

    Saini, R. K.; Kumar, R.; Jain, Garima

    2009-12-01

    Large scale applications are based on the economical polycrystalline material prepared by convenient, reproducible and commercially viable methods. Polycrystalline sintered films of SnTe xSe 1-x were deposited on glass substrate by screen printing technique. The optical and structural studies of the films were carried out by UV-Vis-NIR spectrophotometer and X-ray diffraction, respectively. The films were polycrystalline in nature with the average grain size 27.77 nm. The solid solution shows a change from orthorhombic to cubic in structure. The energy band gap of the films was determined using absorption spectra. It was found to vary with composition from 1.02 to 0.35 eV.

  8. Characterization of (As.Te)1-xSex thin films

    NASA Astrophysics Data System (ADS)

    Hafiz, M. M.; Moharram, A. H.; Abu-Sehly, A. A.

    Optical absorption at room temperature and electrical resistivity at temperatures between 200 and 320 K for (As.Te)1-xSex thin films (where x=0.20, 0.23, 0.27, 0.32 and 0.44) have been studied. Increasing the Se content was found to increase the optical energy gap and the activation energy for conduction of the investigated films. The optical energy gap of the As0.40Te0.40Se0.20 films was increased up to 1.21 eV by increasing the film thickness to 120 nm, while thermal annealing at 480 K reduced it down to 0.83 eV. The decrease of the optical gap is discussed on the basis of amorphous-crystalline transformations.

  9. Electrical and optical stimulation of luminescence in Ca 1-xCd xS

    NASA Astrophysics Data System (ADS)

    Viney, I. V. F.; Arterton, B. W.; Ray, B.; Brightwell, J. W.

    1994-04-01

    Mixtures of CaS and CdS treated at 1020°C for 2 h in a nitrogen atmosphere with an excess sulphur pressure have resulted in solid solutions, Ca 1- xCd xS up to x=0.41. Fluorescence emission studies have indicated massively enhanced broad band emission spectra for x between 0.01 and 0.10 at both 77 and 300 K. Electroluminescence studies of copper-coated powder-based samples under AC excitation conditions at x=0.05 have indicated significant emission intensities broadly aligned spectrally with those from photo-stimulation at the same composition. Further investigations are being directed at optimization of composition, particle size, layer thickness and excitation conditions for enhanced electroluminescence emission intensities.

  10. A magnetic glassy phase in Fe(1+y)Se(x)Te(1-x) single crystals.

    PubMed

    Lamura, G; Shiroka, T; Bonfà, P; Sanna, S; Bernardini, F; De Renzi, R; Viennois, R; Giannini, E; Piriou, A; Emery, N; Cimberle, M R; Putti, M

    2013-04-17

    The evolution of magnetic order in Fe1+ySexTe1-x crystals as a function of Se content was investigated by means of ac/dc magnetometry and muon-spin spectroscopy. Experimental results and self-consistent density functional theory calculations both indicate that muons are implanted in vacant iron-excess sites, where they probe a local field mainly of dipolar origin, resulting from an antiferromagnetic (AFM) bicollinear arrangement of iron spins. This long-range AFM phase becomes progressively disordered with increasing Se content. At the same time all the tested samples manifest a marked glassy character that vanishes for high Se contents. The presence of local electronic/compositional inhomogeneities most likely favours the growth of clusters whose magnetic moment 'freezes' at low temperature. This glassy magnetic phase justifies both the coherent muon precession seen at short times in the asymmetry data, as well as the glassy behaviour evidenced by both dc and ac magnetometry.

  11. Zeeman splitting and spin-orbit interaction in Hg1-xCdxTe inversion layers

    NASA Astrophysics Data System (ADS)

    Sun, Lei; Lv, Meng; Liu, Xinzhi; Xu, Yonggang; Wang, Reng; Lin, Tie; Yu, Guolin; Dai, Ning; Chu, Junhao

    2016-07-01

    We studied the suppression of the weak antilocalization (WAL) effect and the dependence of spin dynamics for a two-dimensional electron gas in the inversion layers of two different Hg1-x Cd x Te samples in the presence of in-plane magnetic field (B//) . The WAL magnetoconductance is fitted by the Golub model to acquire the variations of phase coherence time with increasing B// . The effective g-factors in the form of \\vert mr\\ast g\\ast\\vert (mr\\ast is the relative effective mass) at zero magnetic field and high magnetic field are obtained by investigating the electron dephasing with varying B// and measuring the spin splitting of the Shubnikov-de Hass oscillations, respectively. As the obtained g-factors are in accordance with the reported results, the suppression of the WAL effect can be attributed to the competition between Zeeman splitting and spin-orbit interaction rather than to the microroughness scattering.

  12. Octahedral tilt transitions in relaxed epitaxial Pb(Zr1-xTix)O3 films

    NASA Astrophysics Data System (ADS)

    Tinberg, Daniel S.; Johnson-Wilke, Raegan L.; Fong, Dillon D.; Fister, Timothy T.; Streiffer, Stephen K.; Han, Yisong; Reaney, Ian M.; Trolier-McKinstry, Susan

    2011-05-01

    Relaxed epitaxial {100}pc and {111}pc oriented films (350 nm) of Pb(Zr1-xTix)O3 (0.2 ≤ x ≤ 0.4) on SrRuO3/SrTiO3 substrates were grown by pulsed laser deposition and studied using high resolution synchrotron X-ray diffraction and transmission electron microscopy. The dielectric behavior and ferroelectric phase transition temperatures of the films were consistent with bulk PZT. However, weak 1/2{311}pc reflections in x-ray diffraction profiles were recorded above bulk TTilt (as indicated in the Jaffe, Cooke, and Jaffe phase diagram, where pc denotes pseudocubic indices). Moreover, anomalies in the dielectric and ferroelectric response were detected above TTilt which are explained by coupling of short coherence or weakly tilted regions to the ferroelectric polarization.

  13. Challenges for 1x-nm device fabrication using EUVL: scanner and mask

    NASA Astrophysics Data System (ADS)

    Arnold, William H.

    2011-11-01

    EUVL lithography using high resolution step and scan systems operating at 13.5nm is being inserted in leading edge production lines for memory and logic devices. These tools use mirror optics and either laser produced plasma (LPP) or discharge produced plasma (DPP) sources along with reflective reduction masks to image circuit features. These tools show their capability to meet the challenging device requirements for imaging and overlay. Next generation scanners with resolution and overlay capability to produce 1X nm (10 nm class) memory and logic devices are in preparation. Challenges remain for EUVL, the principal of which are increasing source power enabling high productivity, building a volume mask business encouraging rapid learning cycles, and improving resist performance so it is capable of sub 20nm resolution.

  14. Hidden Magnetic Configuration in Epitaxial La1-x SrxMnO3 Films

    SciTech Connect

    Lee, J.S.; Arena, D.A.; Yu, P.; Nelson, C.S.; Fan, R.; Kinane, C.J.; Langridge, S.; Rossell, M.D.; Ramesh, R.; Kao, C.C.

    2010-12-17

    We present an unreported magnetic configuration in epitaxial La{sub 1-x}Sr{sub x}MnO{sub 3} (x {approx} 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn{sup 3+}/Mn{sup 4+} to an enriched Mn{sup 3+} region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e{sub g} orbital (d{sub 3z{sup 2}-r{sup 2}}). This reconstruction may provide a mechanism for coupling the Mn{sup 3+} moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

  15. Properties of (Ga1-x In x )2O3 over the whole x range

    NASA Astrophysics Data System (ADS)

    Maccioni, M. B.; Ricci, F.; Fiorentini, V.

    2016-06-01

    Using density-functional ab initio theoretical techniques, we study (Ga1-x In x )2O3 in both its equilibrium structures (monoclinic β and bixbyite) and over the whole range of composition. We establish that the alloy exhibits a large and temperature-independent miscibility gap. On the low-x side, the favored phase is isostructural with β -Ga2O3; on the high-x side, it is isostructural with bixbyite In2O3. The miscibility gap opens between approximately 15% and 55% In content for the bixbyite alloy grown epitaxially on In2O3, and 15% and 85% In content for the free-standing bixbyite alloy. The gap, volume and band offsets to the parent compound also exhibit anomalies as function of x. Specifically, the offsets in epitaxial conditions are predominantly type-B staggered, but have opposite signs in the two end-of-range phases.

  16. Magnetostructural phase transformations in Tb 1-x Mn 2

    SciTech Connect

    Zou, Junding; Paudyal, Durga; Liu, Jing; Mudryk, Yaroslav; Pecharsky, Vitalij K.; Gschneidner, Karl A.

    2015-01-16

    Magnetism and phase transformations in non-stoichiometric Tb1-xMn2 (x = 0.056, 0.039) have been studied as functions of temperature and magnetic field using magnetization, heat capacity, and X-ray powder diffraction measurements. Lowering the temperature, the compounds sequentially order ferrimagnetically and antiferromagnetically, and finally, exhibit spin reorientation transitions. Moreover, these structural distortions from room temperature cubic to low temperature rhombohedral structures occur at TN, and are accompanied by large volume changes reaching ~-1.27% and -1.42%, respectively. First principles electronic structure calculations confirm the phase transformation from the ferrimagnetic cubic structure to the antiferromagnetic rhombohedral structure in TbMn2.

  17. Characterization of directionally solidified Hg(1-x)Zn(x)Se semiconducting alloys

    NASA Technical Reports Server (NTRS)

    Cobb, S. D.; Szofran, F. R.; Lehoczky, S. L.; Andrews, R. N.

    1991-01-01

    Hg(1-x)Zn(x)Se alloys with composition between x = 0.08 and 0.115 were synthesized from elemental constituents and were resolidified using a Bridgman-Stockbarger growth technique. By performing precision mass-density measurements on selected wafers cut perpendicular to the growth axis, it was shown that the axial compositional profiles fit a numerical solution to the 1D diffusion equation which takes into account the variation of interface velocity with time. Infrared transmission-edge measurements performed on selected transverse slices from each ingot showed that the relative radial variations in composition decreased with decreasing growth rate. Van der Pauw measurements on selected wafers showed that the 10 exp 18/cu cm electron concentration, typical of as-grown crystals, could be reduced by approximately an order of magnitude by annealing in Se vapor.

  18. Optical and Phonon Characterization of Ternary CdSe x S1- x Alloy Quantum Dots

    NASA Astrophysics Data System (ADS)

    Thi, L. A.; Cong, N. D.; Dang, N. T.; Nghia, N. X.; Quang, V. X.

    2016-05-01

    Ternary CdSe x S1- x alloy quantum dots (QDs) were synthesized using a wet chemical method. Their morphology, particle size, structural, optical, and vibrational properties were investigated using transmission electron microscopy, x-ray diffraction, UV-Vis, fluorescence and Raman spectroscopy, respectively. The optical and vibrational properties of the QDs can be controlled by adjusting the Se/S molar ratio. The absorption and emission peaks shift to a longer wavelength range when increasing the Se content. The presence of two CdSe-like and CdS-like longitudinal optical phonon modes was observed. The dependencies of the optical and phonon modes on the Se content are discussed in detail.

  19. Ga{sub 1-x}Mn{sub x}N epitaxial films with high magnetization

    SciTech Connect

    Kunert, G.; Kruse, C.; Figge, S.; Hommel, D.; Dobkowska, S.; Jakiela, R.; Stefanowicz, W.; Sawicki, M.; Li, Tian; Bonanni, A.; Reuther, H.; Grenzer, J.; Borany, J. von; Dietl, T.

    2012-07-09

    We report on the fabrication of pseudomorphic wurtzite Ga{sub 1-x}Mn{sub x}N grown on GaN with Mn concentrations up to 10% using molecular beam epitaxy. According to Rutherford backscattering, the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, and no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm{sup 3}.

  20. Ab initio studies of Co2FeAl1-xSix Heusler alloys

    NASA Astrophysics Data System (ADS)

    Szwacki, N. Gonzalez; Majewski, Jacek A.

    2016-07-01

    We present results of extensive theoretical studies of Co2FeAl1-xSix Heusler alloys, which have been performed in the framework of density functional theory employing the all-electron full-potential linearized augmented plane-wave scheme. It is shown that the Si-rich alloys are more resistive to structural disorder and as a consequence Si stabilizes the L21 structure. Si alloying changes position of the Fermi level, pushing it into the gap of the minority spin-band. It is also shown that the hyperfine field on Co nuclei increases with the Si concentration, and this increase originates mostly from the changes in the electronic density of the valence electrons.

  1. Magnetic Properties of the Dy1-xUxCo3 System

    NASA Astrophysics Data System (ADS)

    Lupşa, Ileana; Petrişor, T.; Balasz-Mureşan, I.

    The magnetic properties of Dy1-xUxCo3 system were investigated in the 4.3-1150 K temperature range and magnetic field up to 120 kOe. The crystalline structure is rhombohedral of PuNi3 type. For x≤0.8, the samples exhibit a ferrimagnetic behavior. The uranium substitution for dysprosium leads to the decreasing of the exchange field and the reducing of the magnetization and the transition temperatures. The Co mean moments (1.9μB/Co for x=0) opposite to the dysprosium ones and the mean effective Co moments (3.75μB/Co for x=0) are gradually decreasing as Dy is replaced by uranium.

  2. Nonuniform paramagnetic state in nonstoichiometric lanthanum manganites La1- x Mn1- y O3

    NASA Astrophysics Data System (ADS)

    Arbuzova, T. I.; Naumov, S. V.

    2016-06-01

    The magnetic properties of nonstoichiometric lanthanum manganites La1- x Mn1- y O3 have been studied in the temperature range 80 K < T < 650 K. The Curie temperature T C changes nonmonotonically as the number of Mn4+ ions increases. In the paramagnetic region, there exist isolated Mn ions and magnetic polarons which can be conserved to T ⩽ 4 T C, independent of the lattice symmetry. In the T C < T < T pol region, the temperature dependences of the magnetic susceptibility are nonlinear and can be described by the Curie law with a temperature-dependent Curie constant C. The sample has been prepared having a composition near the O' → O structural transition; the spontaneous magnetization of the sample at T ⩽ 1.6 T C is associated to correlated polarons forming due to the double exchange in chains of the E-type antiferromagnetic phase.

  3. Magnetic transitions in the perovskites Pr1-xSrxCoO3

    NASA Astrophysics Data System (ADS)

    Deac, Iosif G.; Tetean, Romulus; Balasz, Istvan; Andreica, Daniel; Vladescu, Adrian; Dudric, Roxana; Tunyagi, Arthur R.; Burzo, Emil

    2010-01-01

    The magnetic and electrical properties of Pr1-xSrxCoO3 cobaltites with 0.3 <= x <= 0.5 were studied in the temperature range 5 K <= T <= 1000 K and field, up to 7 T. These cobaltites exhibit two phase transitions: a paramagnetic-ferromagnetic phase transition below about 240 K and a second one below 110 K. The temperature dependences of the magnetizations of Sr doped samples show differences in the FC and ZFC data. The samples were also investigated by μSR experiments in zero field (ZF) and weak transverse field (wTF). The μSR data clearly indicate the existence of the two transitions. The samples show small negative magnetoresistances that are controlled by grain-boundary effects. The results suggest a change in the nature of magnetic coupling between Co ions at low temperature magnetic transition.

  4. μSR study on CuCr1-xMgxO2

    NASA Astrophysics Data System (ADS)

    Ikedo, Yutaka; Sugiyama, Jun; Nozaki, Hiroshi; Mukai, Kazuhiko; Russo, Peter L.; Andreica, Daniel; Amato, Alex; Ono, Yasuhiro; Kajitani, Tsuyoshi

    2009-04-01

    In order to clarify the magnetic nature of a delafossite-type oxide, CuCr1-xMgxO2 ( x=0 and 0.03), we have performed zero field (ZF-) and weak transversal field (wTF-) μ+SR measurements in the temperature range between 1.8 and 50 K using polycrystalline samples. The wTF- μ+SR measurements suggested that both samples undergo a magnetic transition at Tm=26 K, clarifying that Tm is not altered by the Cr substitution with Mg. The ZF- μ+SR measurements indicated the existence of a clear muon-spin precession ( ∼50 MHz at T→0 K) signal for the x=0 sample below Tm, indicating a long-range antiferromagnetic order state, whereas the absence of long-range order for the x=0.03 sample even at 1.8 K.

  5. MnxGa1-x nanodots with high coercivity and perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Karel, J.; Casoli, F.; Lupo, P.; Celegato, F.; Sahoo, R.; Ernst, B.; Tiberto, P.; Albertini, F.; Felser, C.

    2016-11-01

    A MnxGa1-x (x = 0.70) epitaxial thin film with perpendicular magnetic anisotropy and a large coercivity (μ0Hc = 1 T) was patterned into nanodots using a combined self-assembly nanolithography and plasma etching procedure. Nanostructuring is achieved by self-assembly of polystyrene nanospheres acting as a mask on the magnetic film. This procedure allows easy patterning of a large area although introduced some chemical disorder, which resulted in a soft magnetic component in the magnetic hysteresis loops. However, chemical order was recovered after vacuum annealing at low temperature. The resulting nanodots retain the properties of the original film, i.e. magnetization oriented perpendicular to the particle and large coercivity. Our results suggest this lithography procedure could be a promising direction for nanostructuring tetragonal Heusler alloys.

  6. Sputtering and native oxide formation on (110) surfaces of Cd(1-x)Mn(x)Te

    NASA Technical Reports Server (NTRS)

    Neff, H.; Lay, K. Y.; Abid, B.; Lange, P.; Lucovsky, G.

    1986-01-01

    Native oxides on the surface of Cd(1-x)Mn(x)Te (X between 0 and 0.7) have been analyzed on the basis of X-ray photoemission spectroscopy measurements. Depth profile analysis revealed a significant increase in the thickness at higher Mn concentrations and a strong Mn segregation to the surface, respectively. Sputter-induced damage on cleaved (110)-oriented surfaces was analyzed by photoreflectance and photoluminescence measurements. The damage was found to be larger on CdTe than on the alloy. Thermal annealing showed nearly complete restoration for the surface of the alloy, while CdTe revealed irreversible modifications in the near-surface regime upon sputtering and post annealing.

  7. Electronic properties of unstrained unrelaxed narrow gap InAs x Sb1-x alloys

    NASA Astrophysics Data System (ADS)

    Suchalkin, S.; Ludwig, J.; Belenky, G.; Laikhtman, B.; Kipshidze, G.; Lin, Y.; Shterengas, L.; Smirnov, D.; Luryi, S.; Sarney, W. L.; Svensson, S. P.

    2016-03-01

    The electronic properties of unstrained unrelaxed InAs x Sb1-x alloys have been determined in a wide range of alloy compositions using IR magnetospectroscopy, magnetotransport and IR photoluminescence. All studied alloys have n-type background doping with electron concentration decreasing with the Sb content. The composition dependence of the background doping concentration follows an empirical exponential law in a wide range of compositions. Both bandgap and electron effective mass dependence on alloy composition exhibit negative bowing reaching lowest values at x  =  0.63: E g  =  0.10 eV, m*  =  0.0082 m 0 at 4.2 K. The bowing coefficient of 0.038 m 0 obtained for the electron effective mass is in good agreement with that obtained from the Kane model.

  8. InAs/Ga1-xInxSb infrared superlattice photodiodes for infrared detection

    NASA Astrophysics Data System (ADS)

    Fuchs, Frank; Weimar, U.; Ahlswede, E.; Pletschen, Wilfried; Schmitz, J.; Walther, Martin

    1998-04-01

    Electric and optical properties of IR photodiodes based on InAs/(GaIn)Sb superlattices were investigations. Mesa diodes were fabricated with cut-off wavelengths ranging from 7.5 to 12 micrometers , showing 77 K detectivities between 1 X 1012 cmHz0.5/W and 5 X 1010 cmHz0.5/W, respectively. At least two leakage current mechanisms are observed in the reverse bias branch of the current-voltage characteristics. At high reverse bias band-to-band tunneling currents dominate. Close to zero voltage surface leakage currents become important. The leakage currents are studied with gate controlled mesa diodes, allowing depletion or inversion of the mesa side walls. In addition, the band-to- band tunneling currents are investigated by applying magnetic fields oriented parallel and perpendicular to the electric field across the p-n junction of the diode.

  9. Density functional theory calculations of magnetocrystalline anisotropy energies for (Fe1-xCox)2B

    DOE PAGES

    Daene, Markus; Kim, Soo Kyung; Surh, Michael P.; Aberg, Daniel; Benedict, Lorin X.

    2015-06-15

    We present and discuss density functional theory calculations of magnetic properties of the family of ferromagnetic compounds, (Fe1-xCox)2B, focusing specifically on the magnetocrystalline anisotropy energy (MAE). Using periodic supercells of various sizes (up to 96 atoms), it is shown that the general qualitative features of the composition dependence of the MAE is in agreement with experimental findings, while our predicted magnitudes are larger than those of experiment. We find that the use of small supercells (6 and 12-atom) favors larger MAE values relative to a statistical sample of configurations constructed with 96-atom supercells. As a result, the effect of latticemore » relaxations is shown to be small. Calculations of the Curie temperature for this alloy are also presented.« less

  10. Thin single-crystalline Bi2(Te1-xSex)3 ternary nanosheets synthesized by a solvothermal technique

    NASA Astrophysics Data System (ADS)

    Guo, Jing; Jian, Jikang; Zhang, Zhihua; Wu, Rong; Li, Jin; Sun, Yanfei

    2016-01-01

    Bi2(Te1-xSex)3 ternary nanosheets have been successfully synthesized through a facile solvothermal technique using diethylenetriamine as solvent, where x can vary from 0 to 1. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) indicate that the as-synthesized Bi2(Te1-xSex)3 samples are nanosheets with rhombohedral structure, and the thickness of the nanosheets can be as thin as several nanometers. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) reveal that the nanosheets are single crystalline with a rhombohedral structure. Energy disperse spectroscopy (EDS) and XRD analysis by Vegard's law confirm that the ternary Bi2(Te1-xSex)3 nanosheets have been obtained here. The growth of the nanosheets is discussed based on an amine-based molecular template mechanism that has been employed to synthesize some other metal chalcogenides.

  11. Research Update: Magnetic phase diagram of EuTi1-xBxO3 (B = Zr, Nb)

    DOE PAGES

    Li, Ling; Zhou, Haidong; Yan, Jiaqiang; Mandrus, David; Keppens, Veerle

    2014-11-21

    Herein, we report the magnetic phase diagram of EuTi1-xBxO3 (B = Zr, Nb), determined from magnetization and heat capacity measurements. Upon Zr-doping, the antiferromagnetic ordering temperature TN of EuTi1-xZrxO3 gradually decreases from 5.6 K (x = 0) to 4.1 K (x = 1). Whereas a similar decrease in TN is observed for small amounts of Nb doping (x ≤ 0.05), ferromagnetism is induced in EuTi1-xNbxO3 with x > 0.05. Lastly, the ferromagnetic interaction between localized Eu 4f spins mediated by itinerant electrons introduced by Nb doping results in the ferromagnetism in EuTi1-xNbxO3.

  12. Thermodynamic properties of CexTh1-xO2 solid solution from first-principles calculations

    SciTech Connect

    Xiao, Haiyan Y.; Zhang, Yanwen; Weber, William J.

    2012-11-02

    A systematic study based on first-principles calculations along with a quasi-harmonic approximation has been conducted to calculate the thermodynamic properties of the CexTh1xO2 solid solution. The predicted density, thermal expansion coefficients, heat capacity and thermal conductivity for the CexTh1xO2 solid solution all agree well with the available experimental data. The thermal expansion coefficient for ThO2 increases with CeO2 substitution, and complete substitution shows the highest expansion coefficient. On the other hand, the mixed CexTh1xO2 (0 < x < 1) solid solution generally exhibits lower heat capacity and thermal conductivity than the ThO2 and CeO2 end members. Our calculations indicate a strong effect of Ce concentration on the thermodynamic properties of the CexTh1xO2 solid solution.

  13. Thermodynamic properties of CexTh1-xO2 solid solution from first-principles calculations

    SciTech Connect

    Xiao, Haiyan; Zhang, Yanwen; Weber, William J

    2013-01-01

    A systematic study based on first-principles calculations along with the quasi-harmonic approximation has been conducted to calculate the thermodynamic properties of the CexTh1-xO2 solid solution. The predicted density, thermal expansion coefficients, heat capacity and thermal conductivity for the CexTh1-xO2 solid solution all agree well with available experimental data. The thermal expansion coefficient for ThO2 increases with CeO2 substitution, and complete substitution shows the highest expansion coefficient. On the other hand, the mixed CexTh1-xO2 (01-xO2 solid solution.

  14. ULTRAFAST ELECTRON SPIN DYNAMICS OF AS-GROWN Ga1-xMnxAs WITH APPROPRIATE Mn DOPING

    NASA Astrophysics Data System (ADS)

    Yue, Han

    2013-06-01

    The electron spin dynamics in the as-grown Ga1-xMnxAs films with appropriate Mn doping of x 2-5% is studied using time-resolved magneto-optical Kerr effect measurements. Due to the existence of Mn interstitials, the s-d exchange scattering is found to play an important role for the as-grown Ga1-xMnxAs, and compete with p-d exchange coupling to dominate the electron spin relaxation process. The contribution of electron-electron Coulomb scattering to the electron spin dynamics for the as-grown Ga1-x MnxAs appears to be as important as that of the annealed ones. Our findings are fundamentally important for better understanding the electron spin dynamics in Ga1-xMnxAs for its future spintronic applications.

  15. Mechanisms for p -type behavior of ZnO, Zn1 -xMgxO , and related oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Urban, Daniel F.; Körner, Wolfgang; Elsässer, Christian

    2016-08-01

    The possibilities of turning intrinsically n -type oxide semiconductors like ZnO and Zn1 -xMgxO into p -type materials are investigated. Motivated by recent experiments on Zn1 -xMgxO doped with nitrogen, we analyze the electronic defect levels of point defects NO,vZn, and NO-vZn pairs in ZnO and Zn1 -xMgxO by means of self-interaction-corrected density functional theory calculations. We show how the interplay of defects can lead to shallow acceptor defect levels, although the levels of individual point defects NO are too deep in the band gap to be responsible for p -type conduction. We relate our results to p -type conduction paths at grain boundaries seen in polycrystalline ZnO and develop an understanding of a p -type mechanism which is common to ZnO, Zn1 -xMgxO , and related materials.

  16. Preparation, Characterization and Photocatalytic Properties of CdS and Cd1-xZnxS nanostructures

    NASA Astrophysics Data System (ADS)

    Nirmal, R. Marx; Paulraj, P.; Pandian, K.; Sivakumar, K.

    2011-10-01

    Synthesis and photocatalytic properties of CdS and CdxZn1-xS nanoparticles from thermal decomposition of metal complexes in presence of long chain amines are presented. Thermal decomposition can be achieved by conventional heating process. The prepared samples were characterized by powder x-ray diffraction and UV-Visible spectroscopy. The absorption response in the UV region has been applied for the photocatalytic degradation of Rhodamine-B dye. The photocatalytic degradation reactions were performed on CdS and CdxZn1-xS nanoparticles under UV light irradiation. CdxZn1-xS nanoparticles show better photocatalytic degradation activity compared to CdS nanoparticles. Our studies prove that with the appropriate particle size, CdxZn1-xS can efficiently decompose organic dyes under UV light irradiation with 415 nm.

  17. CBD-Cd1-xZnxS thin films and their application in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Zhou, J.; Wu, X.; Teeter, G.; To, B.; Yan, Y.; Dhere, R. G.; Gessert, T. A.

    2004-02-01

    Composition, optical properties, structure properties, and surface morphology of thin films of Cd1-xZnxS (x 10%) prepared by chemical bath deposition (CBD) are reported. The best cell efficiency was 15.7%. It used a Cd1-xZnxS window layer, was confirmed by NREL (Voc = 840.1 mV, Jsc = 24.81 mA/cm2, and FF = 75.55%), and had a CTO/ZTO/Cd0.92Zn0.08S/CdTe cell structure. The use of low zinc concentration in the Cd1-xZnxS layer and interdiffusion between Cd1-xZnxS and CdTe layers were assumed to be the reasons for maintaining high Voc and FF.

  18. Evolution of the magnetic field-temperature phase diagram in UAs1-xSex

    NASA Astrophysics Data System (ADS)

    Plackowski, Tomasz; Matusiak, Marcin; Sznajd, Jozef

    2010-09-01

    The evolution of the magnetic field-temperature phase diagram of UAs1-xSex with x in the range of 0-0.1 is studied by means of magnetocaloric and specific-heat measurements. Our interest is focused on the high-temperature phase transitions and especially on the point, where the paramagnetic (P) and two ordered phases meet. For undoped UAs these two ordered states are the ferrimagnetic (Fi) and the type-I antiferromagnetic phases. According to Sinha [Phys. Rev. Lett. 45, 1028 (1980)]10.1103/PhysRevLett.45.1028 the antiferromagnetic phase transition is in the vicinity of a Lifshitz point. Furthermore, Kuznietz [J. Magn. Magn. Mater. 61, 246 (1986)]10.1016/0304-8853(86)90033-8 showed that an incommensurate phase (IC) emerges between the type-I (or type-IA) antiferromagnetic and paramagnetic phases in the case of UAs1-xSex with 0

  19. Efficient CO2 frequency doubling with Hg1-xCdxGa2S4

    NASA Astrophysics Data System (ADS)

    Ren, Deming; Huang, Jinzhe; Hu, Xiaoyong; Qu, Yanchen; Andreev, Yuri M.; Geiko, Pavel P.; Badikov, Valerii V.

    2004-02-01

    As it is known well, using of frequency doubling in differential absorption CO2 laser lidars increases the number of atmospheric gases under the control. Additional improvement in potential and gas analyses accuracy, technical and exploitation parameters has to be waited for with design of frequency doublers with more efficient nonlinear crystals. In this work for the first time detailed investigation results are represented on physial properties of new mixed nonlinear crystals grown in accordance with diagram HgGa2S4:CdGa2S4-->Hg1-xCdxGa2S4, phase-matching and potential efficiencies of second harmonic generation, so as on results of experimental investigation of TEA and mini TEA CO2 laser frequency doubling with it use. In spite of two time lower nonlinear susceptibility coefficients of both parent crystals in comparison with most efficient middle IR crystals high efficiency of frequency doubling is fixed in mixed crystals at room temperature. It is tree time in comparison with frequency doubling with, for example, popular ZnGeP2 and 5.5 time with AgGaSe2. These advantages are reached because realization of optimal non-critical phase-matching by choose of mixing ratio x=0.5, so as 2.3 time higher damage threshold, lower phonon absorption at CO2 laser wavelengths and lower meanings of refractive indexes at fundamental and second harmonic wavelengths. Exploitation parameters of mixed Hg1-xCdxGa2S4 crystal doublers are not worse than parameters of doublers with well-known crystals.

  20. Properties of the deep donor states of AlxGa1 - xAs:Se

    NASA Astrophysics Data System (ADS)

    Oh, E. G.; Hanna, M. C.; Lu, Z. H.; Szmyd, D. M.; Majerfeld, A.

    1993-07-01

    A study of the electrical and optical properties of the Se deep donor states in AlxGa1-xAs:Se grown by metalorganic vapor phase epitaxy (MOVPE) process is reported. A novel experimental technique is presented to determine the absolute energy and the true density of the deep donor. The characteristics of the Se deep donor states are obtained from deep level transient spectroscopy, photoluminescence, photocapacitance, Hall effect measurements, isothermal capacitance transient measurements, and a quasistatic capacitance voltage technique. It is found that the Se dopant gives rise to at least two energy levels in the band gap. One is the generally observed deep donor level, commonly called the DX level and the other is a new shallower donor state which also exhibits DX-like properties. The concentration of the shallower state is less than 5% of the deep donor density. The densities of both donors increase with the mole fraction of H2Se used during MOVPE growth. Thermal emission activation energies of 0.29±0.01 and 0.24±0.01 eV were found for the deep and shallower donor states, respectively, for 0.23≤x≤0.41. The Se donor ionization energies relative to the Γ minimum are determined for samples with different AlAs mole fractions, and also, the true densities of Se donors are obtained. We propose a macroscopic model for the emission and capture mechanisms of Se donors in AlxGa1-xAs, which allows a consistent interpretation of the results obtained by different measurement techniques and provides a natural explanation for the low temperature Hall density saturation phenomenon and the persistent photoconductivity effect.

  1. Structural Metastability and Quantum Confinement in Zn1-xCoxO Nanoparticles.

    PubMed

    Almonacid, G; Martín-Rodríguez, R; Renero-Lecuna, C; Pellicer-Porres, J; Agouram, S; Valiente, R; González, J; Rodríguez, F; Nataf, L; Gamelin, D R; Segura, A

    2016-08-10

    This paper investigates the electronic structure of wurtzite (W) and rock-salt (RS) Zn1-xCoxO nanoparticles (NPs) by means of optical measurements under pressure (up to 25 GPa), X-ray absorption, and transmission electron microscopy. W-NPs were chemically synthesized at ambient conditions and RS-NPs were obtained by pressure-induced transformation of W-NPs. In contrast to the abrupt phase transition in W-Zn1-xCoxO as thin film or single crystal, occurring sharply at about 9 GPa, spectroscopic signatures of tetrahedral Co(2+) are observed in NPs from ambient pressure to about 17 GPa. Above this pressure, several changes in the absorption spectrum reveal a gradual and irreversible W-to-RS phase transition: (i) the fundamental band-to-band edge shifts to higher photon energies; (ii) the charge-transfer absorption band virtually disappears (or overlaps the fundamental edge); and (iii) the intensity of the crystal-field absorption peaks of Co(2+) around 2 eV decreases by an order of magnitude and shifts to 2.5 eV. After incomplete phase transition pressure cycles, the absorption edge of nontransformed W-NPs at ambient pressure exhibits a blue shift of 0.22 eV. This extra shift is interpreted in terms of quantum confinement effects. The observed gradual phase transition and metastability are related to the NP size distribution: the larger the NP, the lower the W-to-RS transition pressure.

  2. Helical antiferromagnetic ordering in Lu1-xScxMnSi

    SciTech Connect

    Goetsch, Ryan J; Anand, V K; Johnston, David C

    2014-08-01

    Polycrystalline samples of Lu1-xScxMnSi (x=0, 0.25, 0.5) are studied using powder x-ray diffraction, heat capacity Cp, magnetization, magnetic susceptibility χ, and electrical resistivity ρ measurements versus temperature T and magnetic field H. This system crystallizes in the primitive orthorhombic TiNiSi-type structure (space group Pnma) as previously reported. The ρ(T) data indicate metallic behavior. The Cp(T), χ(T), and ρ(T) measurements consistently indicate long-range antiferromagnetic (AF) transitions with AF ordering temperatures TN=246, 215, and 188 K for x=0, 0.25, and 0.5, respectively. A second transition is observed at somewhat lower T for each sample from the χ(T) and ρ(T) measurements, which we speculate are due to spin reorientation transitions; these second transitions are completely suppressed in H=5.5 T. The Cp data below 10 K for each composition indicate an enhanced Sommerfeld electronic heat capacity coefficient for the series in the range γ=24–29 mJ/mol K2. The χ(T) measurements up to 1000 K were fitted by local-moment Curie-Weiss behaviors which indicate a low Mn spin S~1. The χ data below TN are analyzed using the Weiss molecular field theory for a planar noncollinear cycloidal AF structure with a composition-dependent pitch, following the previous neutron diffraction work of Venturini et al. [J. Alloys Compd. 256, 65 (1997)]. Within this model, the fits indicate a turn angle between Mn ordered moments along the cycloid axis of ~100° or ~145°, either of which indicate dominant AF interactions between the Mn spins in the Lu1-xScxMnSi series of compounds.

  3. Electron doping evolution of the magnetic excitations in NaFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Perring, T. G.; Dai, Pengcheng

    2016-06-01

    We use time-of-flight (TOF) inelastic-neutron-scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1 -xCoxAs with x =0 , 0.0175, 0.0215, 0.05, and 0.11 . The effect of electron doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden, and suppress low-energy (E ≤80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high-energy (E >80 meV) spin excitations are weakly Co-doping-dependent. Integration of the local spin dynamic susceptibility χ''(ω ) of NaFe1 -xCoxAs reveals a total fluctuating moment of 3.6 μB2/Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in Co-overdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel the Ni-doping evolution of spin excitations in BaFe2 -xNixAs2 in spite of the differences in crystal structures and Fermi surface evolution in these two families of iron pnictides, thus confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping-dependent high-energy spin excitations result from localized moments.

  4. Structural Metastability and Quantum Confinement in Zn1-xCoxO Nanoparticles.

    PubMed

    Almonacid, G; Martín-Rodríguez, R; Renero-Lecuna, C; Pellicer-Porres, J; Agouram, S; Valiente, R; González, J; Rodríguez, F; Nataf, L; Gamelin, D R; Segura, A

    2016-08-10

    This paper investigates the electronic structure of wurtzite (W) and rock-salt (RS) Zn1-xCoxO nanoparticles (NPs) by means of optical measurements under pressure (up to 25 GPa), X-ray absorption, and transmission electron microscopy. W-NPs were chemically synthesized at ambient conditions and RS-NPs were obtained by pressure-induced transformation of W-NPs. In contrast to the abrupt phase transition in W-Zn1-xCoxO as thin film or single crystal, occurring sharply at about 9 GPa, spectroscopic signatures of tetrahedral Co(2+) are observed in NPs from ambient pressure to about 17 GPa. Above this pressure, several changes in the absorption spectrum reveal a gradual and irreversible W-to-RS phase transition: (i) the fundamental band-to-band edge shifts to higher photon energies; (ii) the charge-transfer absorption band virtually disappears (or overlaps the fundamental edge); and (iii) the intensity of the crystal-field absorption peaks of Co(2+) around 2 eV decreases by an order of magnitude and shifts to 2.5 eV. After incomplete phase transition pressure cycles, the absorption edge of nontransformed W-NPs at ambient pressure exhibits a blue shift of 0.22 eV. This extra shift is interpreted in terms of quantum confinement effects. The observed gradual phase transition and metastability are related to the NP size distribution: the larger the NP, the lower the W-to-RS transition pressure. PMID:27390839

  5. Structural phase transitions in Ti-doped Bi1-xNdxFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Kalantari, Kambiz; Sterianou, Iasmi; Sinclair, Derek C.; Bingham, Paul A.; Pokorný, Jan; Reaney, Ian M.

    2012-03-01

    Recently, it was demonstrated that donor doping with Ti on the B-site significantly reduces the conductivity in Bi0.85Nd0.15FeO3 ceramics [Kalantari et al., Adv. Funct. Mater. 21, 3737 (2011)]. In this contribution, the phase transitions as a function of Nd concentration are investigated in 3% Ti doped Bi1-xNdxFeO3 ceramics. Paraelectric (PE) to ferroelectric (FE) transitions were observed for compositions with x ≤ 0.125 which manifested themselves as peaks in permittivity. In contrast, PE to antiferroelectric (AFE) transitions for 0.15 ≤ x ≤ 0.20 gave rise to a step-like change in the permittivity with x = 0.25 exhibiting no sharp anomalies and remaining PE until room temperature. The large volume change at the PE to FE/AFE transitions, reported by Levin and co-workers [Phys. Rev. B 81, 020103 (2011)] and observed here by dilatometry, coupled with their first-order character constrain the transitions to occur uniformly throughout the material in an avalanche-like manner. Hence, the anomalies in DSC, permittivity and thermal expansion occur over a commensurately narrow temperature interval. However, despite the large volume change and eye-catching anomalies in DSC, the latent heats for the transitions in Ti-doped Bi1-xNdxFeO3 are similar to Pb(Zr,Ti)O3 (1-3 kJ/mol) with each an order of magnitude greater than BaTiO3 (˜0.2 kJ/mol). A broad frequency dependent dielectric anomaly of unknown origin in the temperature range 250-450 °C was also observed in all samples.

  6. Weak antilocalization in Bi2(Se(x)Te(1-x))3 nanoribbons and nanoplates.

    PubMed

    Cha, Judy J; Kong, Desheng; Hong, Seung-Sae; Analytis, James G; Lai, Keji; Cui, Yi

    2012-02-01

    Studying the surface states of Bi(2)Se(3) and Bi(2)Te(3) topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi(2)(Se(x)Te(1-x))(3) may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi(2)(Se(x)Te(1-x))(3) nanoribbons and nanoplates via vapor-liquid-solid and vapor-solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi(2)Se(3) to Bi(2)Te(3) in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (~10(19) cm(-3)) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives α of -0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is ~T(-0.49) within the appropriate field range (~0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other.

  7. Higgs phenomenology in the minimal S U (3 )L×U (1 )X model

    NASA Astrophysics Data System (ADS)

    Okada, Hiroshi; Okada, Nobuchika; Orikasa, Yuta; Yagyu, Kei

    2016-07-01

    We investigate the phenomenology of a model based on the S U (3 )c×S U (3 )L×U (1 )X gauge theory, the so-called 331 model. In particular, we focus on the Higgs sector of the model which is composed of three S U (3 )L triplet Higgs fields and is the minimal form for realizing a phenomenologically acceptable scenario. After the spontaneous symmetry breaking S U (3 )L×U (1 )X→S U (2 )L×U (1 )Y , our Higgs sector effectively becomes that with two S U (2 )L doublet scalar fields, in which the first- and the second-generation quarks couple to a different Higgs doublet from that which couples to the third-generation quarks. This structure causes the flavor-changing neutral current mediated by Higgs bosons at the tree level. By taking an alignment limit of the mass matrix for the C P -even Higgs bosons, which is naturally realized in the case with the breaking scale of S U (3 )L×U (1 )X much larger than that of S U (2 )L×U (1 )Y, we can avoid current constraints from flavor experiments such as the B0-B¯ 0 mixing even for the Higgs bosons masses that are O (100 ) GeV . In this allowed parameter space, we clarify that a characteristic deviation in quark Yukawa couplings of the Standard Model-like Higgs boson is predicted, which has a different pattern from that seen in two Higgs doublet models with a softly broken Z2 symmetry. We also find that the flavor-violating decay modes of the extra Higgs boson, e.g., H /A →t c and H±→t s , can be dominant, and they yield the important signature to distinguish our model from the two Higgs doublet models.

  8. Defect structure of epitaxial CrxV1-x thin films on MgO(001)

    SciTech Connect

    Kaspar, Tiffany C.; Bowden, Mark E.; Wang, Chongmin; Shutthanandan, V.; Manandhar, Sandeep; van Ginhoven, Renee M.; Wirth, Brian D.; Kurtz, Richard J.

    2014-01-01

    Epitaxial thin films of CrxV1-x over the entire composition range were deposited on MgO(001) by molecular beam epitaxy. The films exhibited the expected 45° in-plane rotation with no evidence of phase segregation or spinodal decomposition. Pure Cr, with the largest lattice mismatch to MgO, exhibited full relaxation and cubic lattice parameters. As the lattice mismatch decreased with alloy composition, residual epitaxial strain was observed. For 0.2 ≤ x ≤ 0.4 the films were coherently strained to the substrate with associated tetragonal distortion; near the lattice-matched composition of x = 0.33, the films exhibited strain-free pseudomorphic matching to MgO. Unusually, films on the Cr-rich side of the lattice-matched composition exhibited more in-plane compression than expected from the bulk lattice parameters; this result was confirmed with both x-ray diffraction and Rutherford backscattering spectrometry channeling measurements. Although thermal expansion mismatch in the heterostructure may play a role, the dominant mechanism for this phenomenon is still unknown. High resolution transmission electron microscopy was utilized to characterize the misfit dislocation network present at the film/MgO interface. Dislocations were found to be present with a non-uniform distribution, which is attributed to the Volmer-Weber growth mode of the films. The CrxV1-x / MgO(001) system can serve as a model system to study both the fundamentals of defect formation in bcc films and the interplay between nanoscale defects such as dislocations and radiation damage.

  9. Formation of highly luminescent Zn1-xCdxSe nanocrystals using CdSe and ZnSe seeds

    NASA Astrophysics Data System (ADS)

    Zhang, Ruili; Yang, Ping

    2013-05-01

    High-quality colloidal Zn1-xCdxSe nanocrystals (NCs) with tunable photoluminescence (PL) from blue to orange were synthesized using oleic acid as a capping agent. The Zn1-xCdxSe NCs were prepared through two approaches: using CdSe or ZnSe seeds. In the case of CdSe NCs as seeds, Zn1-xCdxSe NCs were fabricated by the reaction of Zn, Cd, and Se precursors in the coordinating solvent system at high temperature. The Zn1-xCdxSe NCs revealed orange emitting. A significant blue-shift of absorption and PL spectra were observed with time, indicating the formation of ternary NCs. In contrast, Zn1-xCdxSe NCs revealed blue to green PL for ZnSe NCs as seeds. This is ascribed to an embryonic nuclei-induced alloying process. With increasing time, the Zn1-xCdxSe NCs exhibited a red-shift both in their absorption and PL spectra. This is attributed to the engineering in band gap energy via the control of NC composition. The PL properties of as-prepared alloyed NCs are comparable or even better than those for the parent binary systems. The PL peak wavelength of the Zn1-xCdxSe NCs depended strongly on reaction time and the molar ratio of Cd/Zn. The Zn1-xCdxSe NCs revealed a spherical morphology and exhibited a wurtzite structure according to transmission electron microscopy observation and an X-ray diffraction analysis.

  10. Magnetic properties of the layered III-VI diluted magnetic semiconductor Ga1-xFexTe

    NASA Astrophysics Data System (ADS)

    Pekarek, T. M.; Edwards, P. S.; Olejniczak, T. L.; Lampropoulos, C.; Miotkowski, I.; Ramdas, A. K.

    2016-05-01

    Magnetic properties of single crystalline Ga1-xFexTe (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 Ga1-xMnxSe and Ga1-xMnxS and reaches a maximum of 0.68 emu/g at 2 K in 7 T. The magnetization of Ga1-xFexTe 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 at 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 Ga1-xFexSe. Neither the broad thermal hysteresis observed from 100-300 K in In1-xMnxSe nor the spin-glass behavior observed around 10.9 K in Ga1-xMnxS are observed in Ga1-xFexTe. 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 Å3.

  11. Low-temperature growth of InxGa1-xN films by radio-frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, J.; Shi, X. J.; Zhu, J.

    2013-01-01

    The low-temperature growth of InxGa1-xN films on quartz glass substrates utilizing radio-frequency magnetron sputtering is investigated. In the InxGa1-xN films prepared using an In-Ga alloy target, grazing incidence X-ray diffraction (GIXRD) peaks corresponding to wurtzite structure were observed. X-ray photoelectron spectroscopy (XPS) was applied to study the extent of oxygen contamination and chemical states, and secondary ion mass spectrometry (SIMS) was used to evaluate the distribution profiles of oxygen impurity in the as-grown InxGa1-xN thin films. XPS and SIMS analysis indicate that the entire thin films have oxide phases. However, no evidence of In2O3, Ga2O3, or indium oxynitride phases was shown in XRD studies. It may be predicted that the oxygen impurities formed amorphous oxide phases embedded in InxGa1-xN matrix. According to our findings, indium is a major phase in the InxGa1-xN thin films which suggests that a significant amount of indium remains un-reacted with N2. The optical transmittance spectra of the as-grown films show interference fringe patterns. The indium fraction x of the as-deposited InxGa1-xN thin films can be calculated out by the transmittance data.

  12. Compositionally-tuned epitaxial cubic MgxZn1-xO on Si(100) for deep ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Yang, W.; Hullavarad, S. S.; Nagaraj, B.; Takeuchi, I.; Sharma, R. P.; Venkatesan, T.; Vispute, R. D.; Shen, H.

    2003-05-01

    We report on the epitaxial growth of wide-band-gap cubic-phase MgxZn1-xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and MgxZn1-xO have been overcome by using a thin SrTiO3 buffer layer. The heteroepitaxy of cubic-phase MgxZn1-xO on Si was established with epitaxial relationship of MgxZn1-xO(100)//SrTiO3(100)//Si(100) and MgxZn1-xO[100]//SrTiO3[100]//Si[110]. The minimum yield of the Rutherford backscattering ion channeling in MgxZn1-xO layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg0.68Zn0.32O/SrTiO3/Si show peak photoresponse at 225 nm, which is in the deep UV region.

  13. Al Incorporation at All Growth Stages of Al x Ga1- x N Epilayers Using SiN Treatment

    NASA Astrophysics Data System (ADS)

    Benzarti, Z.; Halidou, I.; Touré, A.; El Jani, B.

    2016-02-01

    Al compositional distribution of Al x Ga1- x N epilayers grown on SiN-treated sapphire substrate by atmospheric pressure metalorganic vapor phase epitaxy is investigated. The growth process was interrupted at various stages allowing a systematic study of Al x Ga1- x N epilayers during the smoothing process. A transition from three-dimensional (3D) to two-dimensional (2D) growth mode is revealed by in situ laser reflectometry (λ = 632.8 nm) as well as by atomic force microscopic images. Then, ion mass spectrometry analysis was performed to obtain the solid Al composition ( x) profile as well as by photoluminescence measurements. Moreover, the in situ reflectivity signal is simulated; thereby Al x Ga1- x N growth rate is derived and compared with that of GaN layer in order to study the effect of the aluminum incorporation on the growth mechanism. It is worth emphasising that the growth mode of Al x Ga1- x N layers is dictated by SiN treatment, which influences the Al compositional distribution. Electron mobility and refractive index against the thickness of Al x Ga1- x N layers have similar trends, which confirm a competitive mechanism between growth mode and Al incorporation. Therefore, the correlation between the Al composition and morphological, optical, and electrical properties of Al x Ga1- x N layers is established.

  14. Growth and Properties of MERCURY(1-X) Cadmium (x) Tellurium Alloys and Quantum Well Structures

    NASA Astrophysics Data System (ADS)

    Han, Jeong-Whan

    1990-01-01

    Photoassisted molecular beam epitaxy was employed to grow Hg-based films, which include Hg_{1-x}Cd_{x}Te alloys, modulation-doped HgCdTe, modulation-doped HgCdTe quantum well structures and HgCdTe heterostructures. The structural, electrical and optical properties of these films were studied. A series of Hg_{1 -x}Cd_{x}Te films were deposited on lattice-matched (111)B CdZnTe substrates. The rm Hg_{1-x}Cd_{x}Te films grown under the optimum growth conditions exhibited both high structural perfections and outstanding electrical properties, which can be attributed to the role played by the photons in the growth process. For the first time, conducting p-type and n-type modulation-doped HgCdTe were successfully prepared using arsenic and indium as the p-type and n-type dopants, respectively. Most of them exhibited both excellent structural qualities and very sharp interfaces. The hole concentrations of p-type samples showed no evidence of carrier freeze-out at low temperatures. The electron concentrations of n-type samples also exhibited temperature independence up to 300K. PL measurements exhibited two peaks due to the subband transitions. Many of the modulation-doped HgCdTe superlattices samples exhibited very bright and narrow PL peaks at 4.2K. Both electron and hole mobilities of modulation-doped HgCdTe superlattices increase monotonically with decreasing temperature. The electrical properties of n-type modulation-doped HgCdTe heterostructures having spacer layers were also studied. A series of p-type HgTe-Hg_ {0.15}Cd_{0.85}Te superlattices were grown on (100) CdTe substrates by MBE for an extensive study of the optical and electrical properties of such structures. The absorption coefficient versus photon energy spectra show consecutive rises and plateaus characteristic of two-dimensional quantum structures. Temperature-dependent free carrier mobilities and densities were obtained from a mixed-conduction analysis of the Hall and resistivity data as a function of

  15. Prospects of nanostructures Bi{sub 1-x}Sb{sub x} for thermoelectricity

    SciTech Connect

    Nikolaeva, Albina A.; Konopko, Leonid A.; Huber, Tito E.; Bodiul, Pavel P.; Popov, Ivan A.

    2012-09-15

    It has been predicted that surface states of topological insulators have large a thermopower and also ultrahigh mobilities. The authors report results of a magneto-thermoelectric investigation of single crystal Bi{sub 1-x}Sb{sub x} nanowires in a glass cover with diameters ranging from 90 nm to 5 {mu}m. The wide-ranging antimony concentration enabled us to study the effect of nanowire dimensionality in the semimetal, semi-conductor and gapless regimes. Quantum size effects in Bi-2 at%Sb nanowires, which are shown in temperature dependences of resistance R(T) and thermopower {alpha}(T) for the diameters significantly higher than the critical diameter for pure Bi-wires, are observed. The thermopower in weak magnetic fields, reaches values +400 {mu}V/K at T=20-40 K. Power factor {alpha}{sup 2}{sigma} depending on diameter of wires, structure, temperature and magnetic field is calculated. In connection with topological insulators, we will discuss the surface effect in the thermoelectric properties that we observe. - Graphical abstract: Temperature dependences of resistance R{sub T}/R{sub 300}(T) (a) for Bi-2 at%Sb wires various diameters d: 1-d=300 nm, 2-d=400 nm, 3-d=600 nm, 4-d=1600 nm. Inset (a) SEM cross sectional image of the 650 nm Bi-2 at%Sb wire (clear) in glass envelope (gray). The magnetic field dependences thermopower (H Double-Vertical-Line {Delta}T) (b) Bi-2 at%Sb wires, with different diameters: (1). d=300 nm, (2). d=400 nm, (3). d=600 nm, T=26 K. Highlights: Black-Right-Pointing-Pointer SMSC transition in semimetal Bi-Sb wires due to the quantum size effect is observed. Black-Right-Pointing-Pointer In Bi-6 at%Sb wires alloys has been realized the gapless (GL) state. Black-Right-Pointing-Pointer In the area GS state abnormal growth thermopower in magnetic fields is found out. Black-Right-Pointing-Pointer Semiconductor Bi{sub 1-x} Sb{sub x} nanowires manifest properties of the topological insulators.

  16. Degradation of antibiotic amoxicillin using 1 x 1 molecular sieve-structured manganese oxide.

    PubMed

    Kuan, Wen-Hui; Hu, Ching-Yao; Liu, Bin-Sheng; Tzou, Yu-Min

    2013-01-01

    The kinetics and mechanism ofamoxicillin (AMO) degradation using a 1 x 1 molecular sieve-structured manganese oxide (MnO2) was studied. The presence of the buffer solution (i.e., NaHCO3, NaH2PO4 and KH2PO4) diminished AMO binding to MnO2, thus reducing AMO degradation in the pretest; therefore, all other experiments in this study were conducted without the addition of a buffer. Third-order rate constants, second-order on AMO and first-order on MnO2 increased with elevating pH level (2.81-7.23) from 0.54 to 9.17 M(-2) s(-1), and it decreased to 4.27 M(-2) s(-1) at pH 8.53 beyond the pk(a2) of AMO (7.3). The dissolution of the MnO2 suspension with and without AMO exhibited a similar trend; that is, Mn2+ concentration increased with decreasing pH. However, the dissolution of MnO2 with AMO was greater than that without AMO, except for the reaction occurring at pH 8.53, partially indicating that MnO2 acts as an oxidant in AMO degradation. The preliminary chromatogram data display different products with varying pH reaction s, implying that AMO elimination using this 1 x 1 molecular sieve-structured MnO2 is by adsorption as well as oxidative degradation. A complementary experiment indicates that the amount of oxidatively degraded AMO increases substantially from 65.5% at 4 h to 95% at 48 h, whereas the AMO adsorbed onto MnO2 decreases slightly from 4.5% at4 h to 2.4% at 48 h. The oxidative degradation accounted for more AMO removal than adsorption over the whole reaction course, indicating that the oxidative reaction of AMO on MnO2 dominated the AMO removal. PMID:24350501

  17. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy.

    PubMed

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L S; Chattopadhyay, M K; Ganguli, Tapas; Lodha, G S; Pandey, Sudhir K; Phase, D M; Roy, S B

    2016-08-10

    We studied the electronic structure of Mo-rich Mo1-x Re x alloys ([Formula: see text]) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x. PMID:27301550

  18. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Ganguli, Tapas; Lodha, G. S.; Pandey, Sudhir K.; Phase, D. M.; Roy, S. B.

    2016-08-01

    We studied the electronic structure of Mo-rich Mo1-x Re x alloys (0≤slant x≤slant 0.4 ) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

  19. Magnetic phase diagram of pseudo-ternary solid solution URu1-xPdx Ge

    NASA Astrophysics Data System (ADS)

    Gralak, D.; Tran, V. H.

    2015-03-01

    A systematic study of the solid solution URu1-xPdx Ge by means of X-ray diffraction, dc-magnetization, specific heat and electrical resistivity measurements is presented. The investigated alloys (0.0 ≤ x ≤ 0.9) crystallize in the orthorhombic TiNiSi-type structure with space group Pnma. The variation of the unit cell volume with Pd content x follows approximately Vegard's law, through the lattice parameters a, b and c exhibit a little anomaly around x=0.35, 0.7 and 0.8, respectively. It is found that the magnetic ground state of URu1-xPdx Ge strongly depends on Pd content. The compositions with x ≤ 0.32 are nonmagnetic down to 0.4 K, while these in the concentration range 0.35 ≤ x ≤ 0.8 order antiferromagnetically. The Néel temperature TN is found to follow a relation TN ∝(x - 0.32) 2 / 3 for the alloys x < 0.45 and to attain a maximum value of 32 K at x=0.8. The composition x=0.9 alike UPdGe manifests a complex magnetic order, probably undergoes two successive magnetic phase transitions: ferromagnetic-like at TC=33 K and unknown ground state characterized by an irreversible magnetization below TIR. The observed development of magnetism has been discussed in terms of changes in the degree of 5f electron localization as well as due to the competition between the Kondo and Ruderman-Kittel-Kausuya-Yosida interactions. Remarkably, in the compound x=0.32 located at the nonmagnetic-magnetic border, we found a non-Fermi liquid behaviour reflected by the power-law temperature dependencies of magnetic susceptibility χ(T) ∝T-0.48, specific heat Cp(T) ∝ -√{ T } and electrical resistivity ρ(T) ∝T 3 / 2. We compared the results with theoretical predictions for systems with spin fluctuations nearby antiferromagnetic quantum critical point.

  20. NMR study of spin fluctuations and superconductivity in LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Yoichi; Kontani, Hiroshi

    2013-03-01

    We have performed NMR measurements in LaFeAsO1-xHx, an isomorphic compound of LaFeAsO1-xFx. LaFeAsO1-xHx is most recently known for having double superconducting (SC) domes on H doping. LaFeAsO1-xHx is an electron- doped system, and protons act as H-1 as well as F-1. The first SC dome is very similar between F and H doping, suggesting that H doping supplies the same amount of electrons as F doping. Interestingly, an excess amount of H up to x=0.5 can be replaced with O2-. In the H-overdoped regime (x > 0 . 2), LaFeAsO1-xHx undergoes the second superconducting state. We measured the relaxation rate of LaFeAsO1-xHx for x=0.2 and 0.4, and fond an anomalous electronic state; spin fluctuations measured from 1 /T1 T is enhanced with increasing the doping level from x = 0 . 2 to 0.4. The enhancement of spin fluctuations with increasing carrier doping is a new phenomenon that has not observed in LaFeAsO1-xFx in which the upper limit of the doping level is at most x = 0 . 2 . We will discuss the phenomenon in relation to superconductivity. Grant (KAKENHI 23340101) from the Ministry of Education, Sports and Science, Japan

  1. Magnetic properties of Co2Fe(Ga1-xSix) alloys

    NASA Astrophysics Data System (ADS)

    Deka, Bhargab; Chakraborty, Dibyashree; Srinivasan, Ananthakrishnan

    2014-09-01

    Magnetic and crystallographic properties of bulk Co2Fe(Ga1-xSix) alloys with 0≤x≤1 are reported in this work. The alloys with x=0.75 and 1.00 exhibit L21 structure whereas the alloys with x=0, 0.25 and 0.50 crystallized in the disordered A2 phase. Unit cell volume of this series of alloys decreased from 189.1 to 178.5 Å3 as x was increased from 0 to 1.00. All alloy compositions exhibit ferromagnetic behavior with a high Curie temperature (TC) which showed a systematic variation with x (1089 K, 1075 K, 1059 K, 1019 K and 1015 K for x=0, 0.25, 0.5, 0.75 and 1.00, respectively). The saturation magnetization moment Ms for the alloys with x=0, 0.25 and 0.50 are 5.05μB, 5.23μB, 5.49μB, respectively, in accordance with the Slater-Pauling rule, but alloys with x=0.75 and 1.00 deviated from this rule. The effective moment per magnetic atom (pc) of the alloys was estimated from the inverse DC magnetic susceptibility data above TC. A comparison of Ms with pc reveals the half-metallic character of the alloys.

  2. Spin and orbital ordering in Y1-xLaxVO₃

    DOE PAGES

    Yan, J.-Q.; Zhou, J.-S.; Cheng, J. G.; Goodenough, J. B.; Ren, Y.; Llobet, A.; McQueeney, R. J.

    2011-12-02

    The spin and orbital ordering in Y1-xLaxVO₃ (0.30 ≤ x ≤ 1.0) has been studied to map out the phase diagram over the whole doping range 0 ≤ x ≤ 1. The phase diagram is compared with that for RVO₃ (R = rare earth or Y) perovskites without A-site variance. For x > 0.20, no long-range orbital ordering was observed above the magnetic ordering temperature TN; the magnetic order is accompanied by a lattice anomaly at a Tt ≤ TN as in LaVO₃. The magnetic ordering below Tt ≤ TN is G type in the compositional range 0.20 ≤ xmore » ≤ 0.40 and C type in the range 0.738 ≤ x ≤ 1.0. Magnetization and neutron powder diffraction measurements point to the coexistence below TN of the two magnetic phases in the compositional range 0.4 < x < 0.738. Samples in the compositional range 0.20 < x ≤ 1.0 are characterized by an additional suppression of a glasslike thermal conductivity in the temperature interval TN < T < T* and a change in the slope of 1/χ(T). We argue that T* represents a temperature below which spin and orbital fluctuations couple together via λL∙S.« less

  3. Superconductivity and non-Fermi-liquid behavior in Ce1-xYbxCoIn5

    NASA Astrophysics Data System (ADS)

    Shu, L.; Gonzales, E.; Huang, K.; Sayles, T. A.; Baumbach, R. E.; Hamlin, J. J.; Zocco, D. A.; McElroy, C. A.; Maple, M. B.; Paglione, J.; O'Brien, J.; Ho, P.-C.

    2010-03-01

    Single-crystals of Ce1-xYbxCoIn5 were investigated by specific heat CP(T), electrical resistivity ρ(T), and magnetic susceptibility χ(T) measurements as a function of x. As Yb is substituted for Ce, Tc(x) is gradually suppressed to 0.9 K at x=0.8. In the low Yb concentration region near x = 0.1, there is a feature in the lattice constants and residual resistivity, a crossover in the anisotropy of χ(T), the development of NFL T-dependences of χ(T) and CP(T) in the normal state,indicating the existence of a quantum critical point, and a plateau in Tc(x). In the high Yb concentration region near x=0.8, there is an abrupt drop in the lattice parameters that is accompanied by a precipitous drop in Tc(x). The features in the physical properties at x=0.1 and 0.8 indicate the occurrence of some incipient electronic phase transitions, possibly involving the Ce and Yb valences at these compositions.

  4. First-principles study of electronic properties of FeSe1-xSx alloys

    NASA Astrophysics Data System (ADS)

    Kumar, Sandeep; Singh, Prabhakar P.

    2016-05-01

    We have studied the electronic and superconducting properties of FeSe1-xSx (x = 0.0, 0.04) alloys by first-principles calculations using the Korringa-Kohn-Rostoker Atomic Sphere Approximation within the coherent potential approximation (KKR-ASA-CPA). The electronic structure calculations show the ground states of S-doped FeSe to be nonmagnetic. We present the results of our unpolarized calculations for these alloys in terms of density of states (DOS), band structures, Fermi surfaces and the superconducting transition temperature of FeSe and FeSe0.96S0.04 alloys. We find that the substitution of S at Se site into FeSe exhibit the subtle changes in the electronic structure with respect to the parent FeSe. We have also estimated bare Sommerfeld constant (γb), electron-phonon coupling constant (λ) and the superconducting transition temperature (Tc) for these alloys, which were found to be in good agreement with experiments.

  5. Nematic quantum criticality in FeSe1-x Sx revealed by elastoresistance measurements

    NASA Astrophysics Data System (ADS)

    Hosoi, Suguru; Matsuura, Kohei; Wang, Hao; Ishida, Kousuke; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    Electronic nematicity and its connection to the high-temperature superconductivity is one of the central issues in iron-based superconductors. Among them, FeSe is unique in that it exhibits a tetragonal-to-orthorhombic structural transition but no antiferromagnetic order, which enables us to study the nematicity without the effect of magnetism. Here we report on elastoresistance measurements in FeSe1- x Sx evidencing a nonmagnetic nematic quantum critical point near x ~ 0.2. When the Se site is substituted by the isovalent S, the structural transition temperature is reduced gradually and it vanishes above x ~ 0.2. From the changes in in-plane resistivity induced by anisotropic strain, we evaluate the nematic susceptibility which shows Curie-Weiss-like temperature dependence. We find that with increasing x the Weiss temperature changes its sign indicating a quantum critical point, while there is no sign of antiferromagnetism for all samples. The superconducting transition temperature does not show a significant change with S concentration, suggesting that the nonmagnetic nematic quantum criticality does not help to enhance superconductivity in this system.

  6. Exchange Bias Effect in La1-xAgxMnO3 Nanopowders

    NASA Astrophysics Data System (ADS)

    Mihalik, M.; Antoňák, M.; Csach, K.; Fitta, M.; Mihalik, M.; Vavra, M.; Zentková, M.

    2013-01-01

    Exchange bias (EB) phenomena were first observed in the La1-xAgxMnO3 as prepared and heat treated (300 °C/2 hours) nanopowders (x = 0.10, 0.15 and 0.20) which were synthetized by self-combustion glycine-nitrate method. These nanoparticles have an average size of about 25 nm and adopt orthorhombic Pnma crystal structure. Cooling in magnetic field Hcf ≠ 0 through the Curie temperature TC shifts hysteresis loop in horizontal and vertical direction. The values of exchange bias field HE, coercive field Hc, remnant asymmetry μE and coercive magnetization μc increase with increasing value of cooling field Hcf. In addition the training effect was observed. Basic magnetic properties like the Curie temperature TC and the saturated magnetization µs increase and HE or µE decrease with heat treatment. Heat treatment at 600 °C/2 hours increases the average size of nanoparticles to about 55 nm, crystal structure changes to rhombohedral structure (space group R3c) and EB effect vanishes.

  7. Solid solubility, phase transitions, thermal expansion, and compressibility in Sc1-xAlxF3

    NASA Astrophysics Data System (ADS)

    Morelock, Cody R.; Gallington, Leighanne C.; Wilkinson, Angus P.

    2015-02-01

    With the goal of thermal expansion control, the synthesis and properties of Sc1-xAlxF3 were investigated. The solubility limit of AlF3 in ScF3 at ~1340 K is ~50%. Solid solutions (x≤0.50) were characterized by synchrotron powder diffraction at ambient pressure between 100 and 900 K and at pressures <0.414 GPa while heating from 298 to 523 K. A phase transition from cubic to rhombohedral is observed. The transition temperature increases smoothly with Al3+ content, approaching 500 K at the solid solubility limit, and also upon compression at fixed Al3+ content. The slope of the pressure-temperature phase boundary is ~0.5 K MPa-1, which is steep relative to that for most symmetry-lowering phase transitions in perovskites. The volume coefficient of thermal expansion (CTE) for the rhombohedral phase is strongly positive, but the cubic-phase CTE varies from negative (x<0.15) to near-zero (x=0.15) to positive (x>0.20) between ~600 and 800 K. The cubic solid solutions elastically stiffen on heating, while Al3+ substitution causes softening at a given temperature.

  8. InxAl1-xN chiral nanorods mimicking the polarization features of scarab beetles

    NASA Astrophysics Data System (ADS)

    Magnusson, R.; Birch, J.; Hsiao, C.-L.; Sandström, P.; Arwin, H.; Järrendahl, K.

    2015-03-01

    The scarab beetle Cetonia aurata is known to reflect light with brilliant colors and a high degree of circular polarization. Both color and polarization effects originate from the beetles exoskeleton and have been attributed to a Bragg reflection of the incident light due to a twisted laminar structure. Our strategy for mimicking the optical properties of the Cetonia aurata was therefore to design and fabricate transparent, chiral films. A series of films with tailored transparent structures of helicoidal InxAl1-xN nanorods were grown on sapphire substrates using UHV magnetron sputtering. The value of x is tailored to gradually decrease from one side to the other in each nanorod normal to its growth direction. This introduces an in-plane anisotropy with different refractive indices in the direction of the gradient and perpendicular to it. By rotating the sample during film growth the in-plane optical axis will be rotated from bottom to top and thereby creating a chiral film. Based on Muellermatrix ellipsometry, optical modeling has been done suggesting that both the exoskeleton of Cetonia aurata and our artificial material can be modeled by an anisotropic film made up of a stack of thin layers, each one with its in-plane optical axis slightly rotated with respect to the previous layer. Simulations based on the optical modeling were used to investigate how pitch and thickness of the film together with the optical properties of the constitutive materials affects the width and spectral position of the Bragg reflection band.

  9. Photoluminescence and contactless electroreflectance characterization of BexCd1-xSe alloys

    NASA Astrophysics Data System (ADS)

    Huang, P. J.; Huang, Y. S.; Firszt, F.; Meczynska, H.; Maksimov, O.; Tamargo, M. C.; Tiong, K. K.

    2007-01-01

    A detailed optical characterization of a Bridgman-grown wurtzite- (WZ-) type Be0.075Cd0.925Se mixed crystal and three zinc-blende (ZB) BexCd1-xSe epilayers grown by MBE on InP substrates has been carried out via photoluminescence (PL) and contactless electroreflectance (CER) in the temperature range of 15-400 K. The PL spectrum of the WZ-BeCdSe at low temperature consists of an exciton line, an edge emission feature due to recombination of donor-acceptor pairs, and a broad band related to recombination through deep-level defects, while the PL emission peaks of the ZB-BeCdSe epilayers show an asymmetric shape with a tail on the low-energy side. Various interband transitions, originating from the band edge and spin-orbit splitting critical points, of the samples have been observed in the CER spectra. The peak positions of the exciton emission lines in the PL spectra correspond quite well to the energies of the fundamental transitions determined from electromodulation data. The parameters that describe the temperature dependence of the fundamental and spin split-off bandgaps and the broadening function of the band-edge exciton are evaluated and discussed.

  10. High thermoelectric potential of n-type Pb1-xTixTe alloys

    NASA Astrophysics Data System (ADS)

    Komisarchik, Genady; Fuks, David; Gelbstein, Yaniv

    2016-08-01

    In an attempt to reduce the reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of n-type Pb1-xTixTe alloys, with x values of up to 3%. A solubility limit of 0.5 at. % Ti in PbTe was identified, while beyond this composition, a precipitation of a TiTe2 phase was occurred. An impressive maximal dimensionless thermoelectric figure of merit ZT of ˜1.2 was obtained upon 0.1% Ti doping at 500 °C, indicating a ˜9% efficiency enhancement compared to an undoped PbTe. It is shown that generating a functionally graded material based on undoped PbTe as a low temperature segment and a 0.1% Ti doped PbTe as a high temperature segment has a potential to enhance the efficiency by ˜14% compared to the undoped sample.

  11. Anisotropic flux pinning energy in FeSexTe1-x single crystals

    NASA Astrophysics Data System (ADS)

    Wu, Zhaofeng; Tao, Jian; Xu, Xibin; Qiu, Li; Yang, Shaoguang; Wang, Zhihe

    2016-09-01

    FeSexTe1 - x (x = 0.3, 0.4, 0.5, 0.6, 0.7) single crystals have been prepared by the chemical reaction of the elements. The field dependence of flux pinning energy shows a power law behavior, U∝H-α, where α displays a crossover at H ∼ 2 T from small value at low field to large value at high field for both magnetic fields perpendicular and parallel to c-axis. At same field, the flux pinning energy for H//ab-plane is higher than that for H//c-axis, showing an anisotropic behavior. The crossover maybe correspond to the flux pinning from single vortex pinning to collective pinning with magnetic field increasing. Based on the anisotropic G-L theory, the angular dependence of in-plane resistivity ρ in different magnetic fields at fixed temperature can be scaled by the equation, Hc2 GL (θ) =Hc2c /√{(cos2(θ) +γ-2sin2(θ)) } . The weak temperature dependence of anisotropic parameter γ near Tc was given for FeSe0.5Te0.5 and FeSe0.4Te0.6 crystals, respectively.

  12. Morphotropic phase boundary and magnetoelastic behaviour in ferromagnetic Tb1-xGdxFe2 system

    SciTech Connect

    Adil, Murtaza; Yang, Sen; Mi, Meng; Zhou, Chao; Wang, Jieqiong; Zhang, Rui; Liao, Xiaoqi; Wang, Yu; Ren, Xiaobing; Song, Xiaoping; Ren, Yang

    2015-03-30

    Morphotropic phase boundary (MPB), separating two ferroic phases of different crystal symmetries, has been studied extensively for its extraordinary enhancement of piezoelectricity in ferroelectrics. Based on the same mechanism, we have designed a magnetic MPB in the pseudobinary ferromagnetic system of Tb1-xGdxFe2 and the corresponding crystal structure, magnetic properties, and magnetostriction are explored. With the synchrotron x-ray diffractometry, the structure symmetry of TbFe2-rich compositions is detected to be rhombohedral (R) and that of GdFe2-rich compositions is tetragonal (T) below T-c. With the change of concentration, the value of magnetostriction of the samples changes monotonously, while the MPB composition Tb0.1Gd0.9Fe2, which corresponds to the coexistence of R and T phases, exhibits the maximum magnetization among all available compositions and superposition of magnetostriction behaviour of R and T phases. Our result of MPB phenomena in ferromagnets may provide an effective route to design functional magnetic materials with exotic properties. (C) 2015 AIP Publishing LLC.

  13. Doping effects of Sb in FeTe1-xSbx single crystals

    NASA Astrophysics Data System (ADS)

    Wang, X. F.; Zhang, Z. T.; Chen, X. L.; Kan, X. C.; Li, L.; Sun, Y. P.; Zhang, L.; Xi, C. Y.; Pi, L.; Yang, Z. R.; Zhang, Y. H.

    2015-06-01

    We investigated the doping effects of Sb on the magnetic, transport and structural properties in FeTe1-xSbx single crystals. Resistivity, magnetic susceptibility and heat capacity experiments consistently reveal that the magnetic/structural transition temperature TN ∼ 70K in undoped Fe1.05Te is gradually suppressed by Sb doping, but no superconductivity is observed for x up to 10%. It is found that the electronic heat capacity coefficient γ increases with Sb content, implying the increase of the density of states at Fermi level. Referring to previous calculation reports, this means that the Sb substituent plays a role of hole carrier doping, which is consistent with our measurements on Hall coefficient. Structural analysis shows that Sb doping induces an expansion of the lattice along the a axis and a shrinkage along the c axis. Our work suggests that the antiferromagnetism in Fe1+yTe may be different in nature with other parent compounds of FeAs-based systems.

  14. Bandlike electrical transport in P r1 -xC axMn O3 manganites

    NASA Astrophysics Data System (ADS)

    Kadyrov, L. S.; Zhang, T.; Zhukova, E. S.; Anzin, V. B.; Trotsenko, V. G.; Torgashev, V. I.; Dressel, M.; Gorshunov, B. P.

    2016-05-01

    The conductivity and dielectric permittivity spectra of polycrystalline manganites P r1 -xC axMn O3 with x =0.3 , 0.4, and 0.5 have been measured in a broad frequency range (5 -3000 c m-1 ) down to low temperatures. From the dispersion analysis the existence of a Drude component can be established that is associated with small polarons coherently moving within a band several meV wide. The temperature-dependent conductivity shows an activated behavior with an activation energy of approximately 165 meV above 170 K and 4.8 meV below 120 K. The change in the activation energy is assigned to the onset of magnetic order at 120 K. In all three samples an absorption band is discovered at 40 -60 c m-1 that is associated with the transition between Stark-split P r3 + electron states which gain optical activity due to coupling to acoustical phonons.

  15. Superconductivity in LaFe1-xCoxAsO

    SciTech Connect

    Safa-Sefat, Athena; Huq, Ashfia; McGuire, Michael A; Jin, Rongying; Sales, Brian C; Mandrus, David; Cranswick, Lachlan M.D.; Stephens, Peter W; Stone, Kevin H.

    2008-01-01

    Here we report the synthesis and basic characterization of LaFe{sub 1?x}Co{sub x}AsO for several values of x. The parent phase LaFeAsO orders antiferromagnetically (T{sub N} {approx} 145 K). Replacing Fe with Co is expected both to electron dope and introduce disorder in the FeAs layer. For x=0.05 antiferromagnetic order is destroyed and superconductivity is observed at T{sub c}{sup onset} = 11.2 K. For x = 0.11 superconductivity is observed at T{sub c}{sup onset} = 14.3 K and for x = 0.15 it is observed at T{sub c}{sup onset} = 6.0 K. For x = 1, and the material appears to be ferromagnetic as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.

  16. Quantum Griffiths phase in the weak itinerant ferromagnetic alloy Ni(1-x)V(x).

    PubMed

    Ubaid-Kassis, Sara; Vojta, Thomas; Schroeder, Almut

    2010-02-12

    We present magnetization (M) data of the d-metal alloy Ni(1-x)V(x) at vanadium concentrations close to x(c) approximately = 11.4% where the onset of long-range ferromagnetic (FM) order is suppressed to zero temperature. Above x(c), the temperature (T) and magnetic field (H) dependencies of the magnetization are best described by simple nonuniversal power laws. The exponents of M/H approximately T(-gamma) and M approximately H(alpha) are related by 1-gamma = alpha for wide temperature (10 < T < or = 300 K) and field (H < or = 5 T) ranges. gamma is strongly x dependent, decreasing from 1 at x approximately = x(c) to gamma < 0.1 for x = 15%. This behavior is not compatible with either classical or quantum critical behavior in a clean 3D FM. Instead it closely follows the predictions for a quantum Griffiths phase associated with a quantum phase transition in a disordered metal. Deviations at the lowest temperatures hint at a freezing of large clusters and the onset of a cluster glass phase. PMID:20366837

  17. Unusual magnetic properties of (Er1-xGdx)5Si4 compounds

    SciTech Connect

    Singh, N.; Pecharsky, V.; Gschneidner, K.

    2008-02-13

    Magnetic and magnetocaloric properties of polycrystalline (Er{sub 1?x}Gd{sub x}){sub 5}Si{sub 4} with x = 0.1 and 0.25 have been studied. The temperature dependencies of the dc magnetization and ac susceptibility indicate two magnetic transitions: the high temperature transitions are antiferromagnetic in character, whereas the low temperature ones are of ferromagnetic nature. The isothermal magnetization of these compounds shows metamagnetic like transitions at 5 K and no saturation in fields up to 70 kOe. Time dependencies of the magnetization data below the Neel temperature exhibit unusually strong relaxation effects with logarithmic time dependence. The ac susceptibility data reveal that magnetic state of these compounds is distinctly different from spin glasses and the relaxation behavior seen in the magnetization data is a consequence of complex magnetic interactions. The existence of complex magnetic interactions leads to an easy formation of field induced short range ferromagnetic correlations in the paramagnetic state and greatly affects both the magnetic and magnetocaloric properties of these compounds.

  18. Structural and magnetic properties CuAl1-xCrxS2 alloys

    NASA Astrophysics Data System (ADS)

    Ortega López, C.; Casiano Jiménez, G.; Espitia, M. J.

    2016-02-01

    In this paper computational calculations were performed based on the density functional theory DFT, to investigate the structural, electronic and magnetic properties of CuAl1-xCrxS2 (x=0.0, 0.50 and 1.00) alloys. Pseudopotential method was used, as is implemented in the Quantum-Espresso code. We found that the alloys crystallize in a tetragonal structure belonging to space group 122 (I-42d) with lattice constants a=5.290Å, c=10.378Å for x=0.5 and a=5.283Å, c=10.366Å for x=1.00. These values are in good agreement with experimental results. Additionally, we found that the alloys possess an antiferromagnetic behaviour with magnetic moments 4,20μβ/cell and 4,05μβ/cell, respectively. From the analysis of the density of states, it is clear that the alloys have a half-metallic behaviour due to the Cr-d and Cu-d states crossing the Fermi level. This compounds can be used in spintronic.

  19. Orbital Moment Determination in (MnxFe1-x)3O4 Nanoparticles

    SciTech Connect

    Pool, V. L.; Jolley, C.; Douglas, T.; Arenholz, E.; Idzerda, Y. U.

    2010-10-22

    Nanoparticles of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} with a concentration ranging from x = 0 to 1 and a crystallite size of 14-15 nm were measured using X-ray absorption spectroscopy and X-ray magnetic circular dichroism to determine the ratio of the orbital moment to the spin moment for Mn and Fe. At low Mn concentrations, the Mn substitutes into the host Fe{sub 3}O{sub 4} spinel structure as Mn{sup 2+} in the tetrahedral A-site. The net Fe moment, as identified by the X-ray dichroism intensity, is found to increase at the lowest Mn concentrations then rapidly decrease until no dichroism is observed at 20% Mn. The average Fe orbit/spin moment ratio is determined to initially be negative and small for pure Fe{sub 3}O{sub 4} nanoparticles and quickly go to 0 by 5%-10% Mn addition. The average Mn moment is anti-aligned to the Fe moment with an orbit/spin moment ratio of 0.12 which gradually decreases with Mn concentration.

  20. Raman investigation of optical phonons in the ion implanted Hg1-xCdxTe

    NASA Astrophysics Data System (ADS)

    Singh, Anand; Shukla, A. K.; Pal, R.

    2016-07-01

    Raman scattering is studied here for Hg1-xCdxTe (x = 0.3) samples implanted with 180-keV of B11 ions with various doses up to 1 × 1015 cm-2. Considering disorder in the implanted HgCdTe material, the correlation length of Raman active optical phonons is determined as a short range order in the nanocrystals. Phonon softening and asymmetric broadening are investigated for HgTe like LO and TO phonon modes in the Raman spectrum while CdTe like modes almost disappeared for the dose greater than 5 × 1013 cm-2. Disorder is measured quantitatively for wide ranges of doses on the basis of phonon confinement model. Nanostructures of the near-surface implantation-induced damage layer are known to consist of a mixture of amorphous HgCdTe and its nanocrystals. A significant reduction of the nanocrystallites size is reported here with increasing dose i.e. L = 34-46 A0 at dose of 1 × 1015 cm-2.

  1. Dark current in GaAs/AlxGa1-xAs quantum well infrared detectors

    NASA Astrophysics Data System (ADS)

    Nathan, Vaidya

    2013-01-01

    It is not clear whether the tunneling current in QWIPs depends just on the energy corresponding to motion perpendicular to the plane of the quantum well or on the total energy. In order to get a quantitative assessment of the contribution of energy corresponding to motion in the plane of the quantum well to the dark current we use the following approach. We calculate the dark current in GaAs/AlxGa1-x s quantum well infrared detectors for both tunneling dependent only on Ez, and tunneling dependent on the total energy, and compare the results to experimental data. Comparison of theoretical results with experimental data at 40K shows that motion in the plane of the quantum well plays a significant role in determining the tunneling dark current. Corrections are made to Levine's original formula. Variation of the dark current with barrier width and doping density is systematically studied. It is shown that increasing the barrier width and/or decreasing the doping density in the well do not always reduce the dark current.

  2. Low-cost Ce1-xSmx(Fe, Co, Ti)12 alloys for permanent magnets

    NASA Astrophysics Data System (ADS)

    Gabay, A. M.; Martín-Cid, A.; Barandiaran, J. M.; Salazar, D.; Hadjipanayis, G. C.

    2016-05-01

    Ce1-xSmxFe9Co2Ti alloys based on the ThMn12-type crystal structure have been synthesized via melt-spinning of prefabricated alloys and via mechanochemical processing of CeO2- Sm2O3- Fe2O3-TiO2- Co - Ca - CaO powder mixtures. Coercive fields up to 0.8 kOe and 2.1 kOe were obtained in annealed melt-spun alloys with x = 0 and x = 0.5, respectively. Submicron, partially anisotropic particles collected after the mechanochemical synthesis for x = 0.5 and x = 1 exhibited coercivity (energy product) of 1.8 kOe (5.4 MGOe) and 5.8 kOe (9.9 MGOe), respectively. The low magnetic anisotropy field of CeFe9Co2Ti alloy requires at least a partial Sm-substitution for Ce in order to develop a reasonably high coercivity.

  3. Alloy enhanced anisotropy in the thermal conductivity of SixGe1-x nanowires

    NASA Astrophysics Data System (ADS)

    Li, Wu; Mingo, Natalio

    2013-08-01

    A strong dependence on crystalline orientation with a most conductive ⟨001⟩ growth direction is theoretically predicted for the thermal conductivity (κ) of SixGe1-x nanowires, even above room temperature and above 1 μm thickness. For instance, the room temperature κ of a 100 nm thick Si0.6Ge0.4 nanowire in the ⟨001⟩ direction is 16% higher than in the ⟨111⟩ direction. In contrast, the dependence for Si or Ge nanowires of the same diameter is much weaker at the same temperature, and ⟨111⟩ direction can be the most conductive one at relatively thin nanowires. In the low temperature limit, the anisotropy of κ can reach 87% at any alloy concentration. The anisotropy arises from the phonon focusing effect on the long mean free path phonons. The low frequency phonons focus in the ⟨001⟩ direction, while the intermediate frequency phonons focus in the ⟨111⟩ direction. The relative contribution to κ from the low frequency phonons is largely enhanced by alloying. Moreover, alloying eliminates the anisotropy caused by the intermediate frequency phonons. Our results imply that orientation has to be taken into account when engineering alloyed nanowire devices, such as thermoelectric modules, even if the corresponding bulk material is completely isotropic.

  4. Phonon density of states in nanocrystalline Si1-xGex explored by inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Wilson, Stephen; Dhital, Chetan; Ren, Zhifeng; Abernathy, Doug

    2012-02-01

    Recently there have been significant advances in the efficiencies of traditional thermoelectric compounds gained via the creation of thermoelectric nanocomposites possessing substantially reduced thermal conductivity relative to their bulk counterparts [1,2]. The dramatic reduction in the heat transport of these nanocomposites is often attributed to the increased interface scattering of phonons or induced surface/boundary modes; however notably little work has been put worth into exploring the detailed changes in the phonon density of states in many of these functional nanocomposite samples. Here we present inelastic neutron scattering measurements exploring the phonon density of states in a series of Si1-xGex thermoelectric nanocomposites. The evolution of the phonon spectral weight distribution and linewidths as a function of Ge-doping will be discussed and compared to the known bulk phonon density of states in this system. [4pt] [1] Giri Joshi et al., Nano Letters 8, 4670 (2008). [0pt] [2] X. Wang et al., App. Phys. Lett. 93, 193121 (2008).

  5. Magnetic Interactions in the Diluted Magnetic Semiconductor Mn_xGe_1-x

    NASA Astrophysics Data System (ADS)

    Erwin, Steven C.; Hellberg, C. Stephen

    2001-03-01

    Much current debate has focused on the origins of ferromagnetism in III-V magnetic semiconductors. Less attention has been paid to magnetically doped Group-IV semiconductors, although they have been predicted to have Curie temperatures of the same order [1]. We use density-functional theoretical (DFT) methods to study the electronic structure and magnetic interactions in Mn_xGe_1-x, the first such elemental magnetic semiconductor to be realized experimentally [2]. We use ordered supercells to simulate 6% Mn concentration, and calculate total energies within DFT for a variety of positional and magnetic arrangements of Mn at fixed concentration. We then fit these energies to a Heisenberg model to extract the spin coupling constants. The result is a strong but very short-ranged antiferromagnetic interaction between Mn atoms, and a weaker but longer-ranged ferromagnetic interaction. The ferromagnetic interaction dominates at all Mn-Mn distances beyond nearest neighbor. [1] T. Dietl et al., Science 287, 1019 (2000). [2] Y.D. Park, J. Mattson, A. Hanbicki, and B. Jonker (unpublished).

  6. Controlled p-type Sb doping in LPE-grown Hg1-x Cdx Te epilayers

    NASA Astrophysics Data System (ADS)

    Harman, Theodore C.

    1993-09-01

    A Te-rich liquid-phase-epitaxial growth process is reported whereby reproducible Sb-doped layers are prepared with hole concentrations and hole mobilities ranging from 1.8×1016 to 1.3×1019 cm-3 and 280 to 29 cm2/V s, respectively, at 77K for x-values ranging from 0.23 to 0.29. An effective electronic distribution coefficient for Sb of 0.01 is calculated from the hole concentration at 77K and the concentration of Sb in the growth solution. The process for group Va doping of low-x Hg1-x Cdx Te from Te-rich solutions and the procedure for the growth of a CdZnTe buffer layer on a CdTeSe substrate are described. For Te-rich Cd-Zn-Te growth solutions the distribution coefficient of Zn was found to be 18. The growth of a structure consisting of an Sb-doped HgCdTe epilayer on a CdZnTe buffer layer lattice matched (Δa/a<10-4) to a CdSeTe substrate has been demonstrated.

  7. Thermal, magnetic and electrical properties of Tb1-xDyxMnO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Pavan Kumar, N.; Jitender, Thakur; Laxmi, Vijaya; Venugopal Reddy, P.

    2016-03-01

    A series of multiferroic materials with the compositional formula, Tb1-xDyxMnO3 (where x=0, 0.1, 0.2, 0.3 and 0.4) were prepared by the sol gel method. After characterizing the samples structurally, a systematic investigation of specific heat, magnetization and dielectric properties over the temperature range, 4-300 K, was undertaken. Based on these studies, it was found that all the samples exhibit a transition at 40 K and the observed behavior may be attributed to the ordering of Mn3+ ions. Further, all the five samples are found to exhibit a ferroelectric transition in the temperature range 20-24 K. Finally, yet another transition was also exhibited by all the samples at temperatures below 10 K and is attributed to the antiferromagnetic (AF) ordering of rare-earth ionic moments. The magnetic entropy of all the samples was also computed with the help of their heat capacity data.

  8. Phase transitions and relaxation dynamics in (NH 4I) x(KI) 1- x mixed crystals

    NASA Astrophysics Data System (ADS)

    Güthoff, F.; Ohl, M.; Reehuis, M.; Loidl, A.

    1999-06-01

    Dielectric studies, as well as elastic and quasielastic neutron scattering experiments were performed on the mixed molecular system (NH 4I) x(KI) 1- x for ammonium concentrations 0.55⩽ x⩽0.8. Based on these experiments we present a detailed and improved phase diagram, which reveals a variety of different structural phases with different degrees of orientational order, as well as different glass states with frozen-in orientational disorder. Special attention has been devoted to the recently discovered ε-phase which is characterized by the appearance of a superstructure reflection at the (3 0 0) reciprocal lattice point. In constant- Q scans at zero energy transfer we followed the temperature dependencies of these superstructure reflections and determined correlation lengths for all concentrations investigated. We found short-range order of the ε-type structure for x=0.55, while long-range order has been observed for all other concentrations. In addition, we performed constant- Q scans at the (3 0 0) reciprocal lattice point for several temperatures. From a purely phenomenological analysis, two time scales were observed which we attributed (i) to structural relaxations at the phase transition from the cubic high-temperature to the trigonal low-temperature ε-phase and (ii) to orientational relaxations of the NH 4+-tetrahedra in a slightly distorted environment. This interpretation is in accordance with the dielectric results which also provide experimental evidence for the appearance of two time scales.

  9. Femtosecond laser ablation of CuxZr1-x bulk metallic glasses: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Marinier, Sébastien; Lewis, Laurent J.

    2015-11-01

    Molecular-dynamics simulations combined with a two-temperature model are used to study laser ablation in CuxZr1-x (x =0.33 ,0.50 ,0.67 ) metallic glasses as well as crystalline CuZr2 in the C11b (MoSi2) structure. Ablation thresholds are found to be 430 ±10 ,450 ±10 ,510 ±10 , and 470 ±10 J/m 2 for a-Cu2Zr , a-CuZr, a-CuZr2, and c-CuZr2, respectively. The larger threshold in amorphous CuZr2 results from a weaker electron-phonon coupling and thus longer electron-ion equilibration time. We observe that the velocity of the pressure waves in the amorphous samples is not affected by the fluence, in contrast to the crystal; this is due to differences in the behavior of the shear modulus with increasing pressure. The heat-affected zone in the different systems is characterized in terms of the melting depth as well as inelastic deformations. The melting depth is found to be smaller in the crystal than in the amorphous targets because of its higher melting temperature. The inelastic deformations are investigated in terms of the von Mises shear strain invariant ηMises; the homogeneous nucleation of shear transformation zones is observed in the glass as reported in previous theoretical and experimental studies. The coalescence of the shear transformation zones is also found at higher fluence.

  10. Channelling study of La1-xSrxCoO3 films on different substrates

    NASA Astrophysics Data System (ADS)

    Szilágyi, E.; Kótai, E.; Rata, D.; Németh, Z.; Vankó, G.

    2014-08-01

    The cobalt oxide system LaCoO3 and its Sr-doped child compounds have been intensively studied for decades due to their intriguing magnetic and electronic properties. Preparing thin La1-xSrxCoO3 (LSCO) films on different substrates allows for studies with a new type of perturbation, as the films are subject to substrate-dependent epitaxial strain. By choosing a proper substrate for a thin film grow, not only compressing but also tensile strain can be applied. The consequences for the fundamental physical properties are dramatic: while compressed films are metallic, as the bulk material, films under tensile strain become insulating. The goal of this work is to determine the strain tensor in LSCO films prepared on LaAlO3 and SrTiO3 substrates by pulsed laser deposition using RBS/channelling methods. Apart from the composition and defect structure of the samples, the depth dependence of the strain tensor, the cell parameters, and the volume of the unit cell are also determined. Asymmetric behaviour of the strained cell parameters is found on both substrates. This asymmetry is rather weak in the case of LSCO film grown on LaAlO3, while stronger on SrTiO3 substrate. The strain is more effective at the interface, some relaxation can be observed near to the surface.

  11. Phonon-drag magnetothermopower oscillations in GaAs/AsxGa1-xAs heterojunctions

    NASA Astrophysics Data System (ADS)

    Fromhold, T. M.; Butcher, P. N.; Qin, G.; Mulimani, B. G.; Oxley, J. P.; Gallagher, B. L.

    1993-08-01

    The tensor M--> which determines the heat flux U=M-->E in a weak electric field E is calculated for a two-dimensional electron gas in a perpendicular magnetic field B. The dominant phonon-drag contribution is calculated using Boltzmann transport, allowing for the two-dimensional (2D) character of the electron gas. The Landau levels are taken to have Gaussian line shapes with the rms level width γ=CB1/2 where C is the only adjustable parameter. Setting C=0.5 meV T-1/2 gives good agreement with new experimental values of Myx obtained for GaAs/AlxGa1-xAs heterojunctions when B varies between 2 and 10 T and the temperature varies between 1 and 5 K. Myx is negative and contains strong magneto-oscillations in phase with the density of states at the Fermi level. The model also predicts Mxx=0, whereas experiment gives peak values of ||Mxx|| up to 60% of those of ||Myx||. We demonstrate that setting Mxx=0 in the calculation has little effect on the predicted thermopower component Sxx but yields poor approximations to the experimental values of Syx.

  12. A magnetic glassy phase in Fe1+ySexTe1-x single crystals

    NASA Astrophysics Data System (ADS)

    Lamura, G.; Shiroka, T.; Bonfà, P.; Sanna, S.; Bernardini, F.; De Renzi, R.; Viennois, R.; Giannini, E.; Piriou, A.; Emery, N.; Cimberle, M. R.; Putti, M.

    2013-04-01

    The evolution of magnetic order in Fe1+ySexTe1-x crystals as a function of Se content was investigated by means of ac/dc magnetometry and muon-spin spectroscopy. Experimental results and self-consistent density functional theory calculations both indicate that muons are implanted in vacant iron-excess sites, where they probe a local field mainly of dipolar origin, resulting from an antiferromagnetic (AFM) bicollinear arrangement of iron spins. This long-range AFM phase becomes progressively disordered with increasing Se content. At the same time all the tested samples manifest a marked glassy character that vanishes for high Se contents. The presence of local electronic/compositional inhomogeneities most likely favours the growth of clusters whose magnetic moment ‘freezes’ at low temperature. This glassy magnetic phase justifies both the coherent muon precession seen at short times in the asymmetry data, as well as the glassy behaviour evidenced by both dc and ac magnetometry.

  13. Preparation and Thermoelectric Properties of Pb1-x Fe x Te Alloys Doped with Iodine

    NASA Astrophysics Data System (ADS)

    Cao, X. L.; Cai, W.; Deng, H. D.; Gao, R. L.; Fu, C. L.; Pan, F. S.

    2016-09-01

    This is the first systematic report on the preparation and thermoelectric properties of n-type Pb1-x Fe x Te alloys. Iodine-doped n-type Pb0.85Fe0.15Te polycrystalline was prepared by melting and hot-pressing techniques. The morphology and phase structure of the prepared materials were analyzed by scanning electron microscopy and x-ray diffraction, which indicated that the samples possessed a rock-salt crystal structure and showed a biphase structure. The major phase was the polycrystalline PbTe compound and the second phase was the FeTe compound. The FeTe nano-/micro-precipitates were homogeneously distributed in the PbTe matrix, which is beneficial for the reduction of the lattice thermal conductivity. The effects of the iodine content on the thermoelectric properties of I-doped Pb0.85Fe0.15Te have been investigated. The measurement results of electrical resistivity, carrier concentration, Seebeck coefficient, and thermal conductivity in the temperature range of 300-850 K indicate that the thermoelectric transport properties of the obtained samples are sensitive to the iodine content. When the concentration of iodine is about 0.6 at.%, the maximum dimensionless figure-of-merit value of ˜0.65 at 800 K was obtained.

  14. Infrared longitudinal and Hall conductivities in Ga1-xMnxAs films

    NASA Astrophysics Data System (ADS)

    Acbas, Gheorghe; Kim, M.-H.; Cerne, J.; Cukr, M.; Novak, V.; Jungwirth, T.; Sinova, J.

    2008-03-01

    We determine the complete infrared (0.1-1.2 eV) magneto-conductivity tensor of a series of Ga1-xMnxAs films from the complex Faraday and Kerr angles as outlined in M.-H. Kim, et al., Phys. Rev. B 75, 214416 (2007). A systematic series of samples with varying Mn and hole concentrations is studied. The samples range from insulating to metallic. The frequency dependence of the real part of the longitudinal conductivity σxx is consistent with the values determined from transmission and reflection measurements. The complex transverse (Hall) conductivity σxy shows resonances associated with the inter-valence band transitions. As the Mn concentration decreases these transitions become broadened due to increased disorder. The temperature dependence shows non-monotonic behavior with sign changes at certain wavelengths. The data is compared with predictions from a disordered valence band model (T. Jungwirth, et al., Phys. Rev. B 76, 125206 (2007)). This work is supported by the Research Corporation Cottrell Scholar Award (Buffalo and Texas A&M), NSF-CAREER-DMR0449899 (Buffalo), an instrumentation award from the CAS, Univ. at Buffalo, ERAS-CT-2003-980409 (Prague)and NSF-CAREER-DMR-0547875 (Texas A&M).

  15. Composition dependent ultraviolet photoresponse in MgxZn1-xO thin films

    NASA Astrophysics Data System (ADS)

    Ghosh, R.; Basak, D.

    2007-06-01

    MgxZn1-xO (0.0⩽x⩽0.12) thin films have been deposited on glass substrates by sol-gel process. The hexagonal wurtzite structure of ZnO is retained in the Mg-substituted films. From the photoresponse measurements, it is observed that both ZnO and substituted films are UV sensitive and with increasing Mg content, the sensitivity shifts toward the shorter wavelength side with a gradual decrease in magnitude. The UV-to-visible current ratio remains almost constant up to x =0.08 and thereafter decreases. The decay time for 90% photocurrent gradually decreases to less than 4s for x =0.05 followed by an increase for higher values of x. The decay time is faster than the growth time for all the substituted films. The change in the photoconductivity with Mg content (x) is correlated to the microstructural change. A trap level, found to be involved in the photoconductivity, is located at ˜0.8eV below the conduction band. The photo-to-dark current ratio (Iph/Id) gradually decreases from three orders of magnitude to one order with the increase in the Mg content.

  16. Crystalline spin-orbit interaction and the Zeeman splitting in Pb1-x Sn x Te

    NASA Astrophysics Data System (ADS)

    Hayasaka, Hiroshi; Fuseya, Yuki

    2016-08-01

    The ratio of the Zeeman splitting to the cyclotron energy (M=Δ {{E}Z}/\\hslash {ωc} ), which characterizes the relative strength of the spin-orbit interaction in crystals, is examined for the narrow gap IV-VI semiconductors PbTe, SnTe, and their alloy Pb1-x Sn x Te on the basis of the multiband \\boldsymbol{k}\\centerdot \\boldsymbol{p} theory. The inverse mass α, the g-factor g, and M are calculated numerically by employing the relativistic empirical tight-binding band calculation. On the other hand, a simple but exact formula of M is obtained for the six-band model based on the group theoretical analysis. It is shown that M  <  1 for PbTe and M  >  1 for SnTe, which are interpreted in terms of the relevance of the interband couplings due to the crystalline spin-orbit interaction. It is clarified both analytically and numerically that M is not a quantized value but a continuous one, and M  =  1 is obtained just at the band inversion point, where the transition from trivial to nontrivial topological crystalline insulator occurs. By using this property, one can detect the transition point only with the bulk measurements. It is also proposed that M is useful to evaluate quantitatively a degree of the Dirac electrons in solids.

  17. Electron-phonon induced complex quasiparticles in the 1x1 H/W(110) surface.

    NASA Astrophysics Data System (ADS)

    Eiguren, Asier; Ambrosch-Draxl, Claudia

    2008-03-01

    We show that the solution of the complex Dyson equation for the electron-phonon problem induces several quasiparticle states for a given wave vector. The Dyson equation is considered in the full complex plane and it is solved without considering the imaginary part of the self-energy as an small parameter. By a first principle application of the formalism to the 1x1 H covered W(110) surface, we show that some aspects of the surface band splitting [Rotenberg et. al., Phys. Rev. Lett. 84, 2925 (2000)] can be traced back to electron-phonon coupling, where we present the energy and lifetimes of each quasiparticle. Despite this breakdown of the single quasi-particle picture, it is remarkable that the spectral functions are very well Represented by the predicted multiple quasi-particles. From these results, we can deduce that some of the features that previously where prescribed in ARPES spectra as incoherent structure could eventually be re-interpreted as contributions from additional quasi-particle states. Our method could also help to understand similar phenomena observed in high Tc cuprates and various other surfaces.

  18. Structural aspects of the. alpha. transition in off-stoichiometric Fe sub 1-x crystals

    SciTech Connect

    Keller-Besrest, F.; Collin, G. )

    1990-02-01

    Study of the {alpha} transition in the Fe {sub 1-x}S system (NiAs-type solid solution) is completed by structural analysis versus temperature of the cation-deficient crystals Fe{sub 0.985}S and Fe{sub 0.975}S. The influence of x and T on the disorder phenomena and on the gradual change of the cationic lattice is analyzed in the LT hexagonal {radical}3a,2c phase (a and c are NiAs-type substructure lattice constants). The hypothesis of the existence of an S{sup {minus}1} impurity level in the band gap of FeS, originating from the formation of covalent pairs (S-S){sup 2{minus}} around each vacancy, leads to a model of conductivity by polarons. This accounts for the decrease with x in the transition energy. The transition is suppressed for x = 0.05, which corresponds to the critical polaron concentration beyond which the polaron gas becomes degenerate.

  19. Thermal and transport properties of U2Pt x Ir1-x C2

    NASA Astrophysics Data System (ADS)

    Kang, Mingu; Wakeham, N.; Ni, Ni; Bauer, E. D.; Kim, Jeehoon; Ronning, F.

    2015-09-01

    We report thermal and transport properties of U2Pt x Ir1-x C2 from which a magnetic phase diagram is obtained. Pure U2IrC2 is an antiferromagnet at 6.5 K, whose Néel temperature initially rises to 13.2 K at x = 0.2 and subsequently is suppressed to zero temperature with increasing Pt content near x = 0.6. Heat capacity divided by temperature at x = 0.6 shows an upturn at low temperature, consistent with the expectations of enhanced quantum fluctuations in the presence of an underlying quantum critical point. The entropy after the phonon contribution has been subtracted has a value of 0.24 Rln2 at the Néel temperature of U2IrC2, revealing an itinerant nature of the 5 f electrons in this compound. On the Pt rich side of the phase diagram, superconductivity is suppressed by x = 0.85. The residual resistivity increases by a factor of 10 from pure Pt (x = 1) to x = 0.85 where superconductivity is suppressed to zero. By comparing the phase diagram of Ir doped U2PtC2 with the phase diagram of pressure tuned and Rh doped U2PtC2 we demonstrate the role of electronic tuning in this system.

  20. Thermodynamic modelling of miscibility in (InAs) x (GaAs)1-x solid solutions

    NASA Astrophysics Data System (ADS)

    Adhikari, Jhumpa

    2013-05-01

    Current methods used to model the solution thermodynamics of III-V compound semiconductors involve the use of the valence force field as the molecular model and the regular solution model (with the temperature independent interaction parameter and underlying assumption of random mixing) as the engineering model. In this study, excess free energy models (with three or less adjustable parameters) are investigated to predict the solid-solid miscibility of (InAs) x (GaAs)1- x . The models investigated include the Porter/one-constant Margules (OCM) model, the two-constant Margules (TCM) model and the non-random two liquid (NRTL) model. These models are fit to excess free energy values derived from free energy change of mixing (variation with composition) data available from molecular simulations at different temperatures. The parameters in all the models have been found to be temperature dependent. The coexistence compositions are best predicted by the NRTL model, indicating the need to consider non-random mixing effects present in these solid solutions. The TCM model predicts better equilibrium composition data as compared to the OCM model.

  1. Structural and magnetic phase transitions inEuTi1-xNbxO3

    DOE PAGES

    Li, Ling; Morris, James R.; Koehler, Michael R.; Dun, Zhiling; Zhou, Haidong; Yan, Jiaqiang; Mandrus, David; Keppens, Veerle

    2015-07-30

    We have investigated the structural and magnetic phase transitions in EuTi1-xNbxO3 (0 ≤ x ≤ 0.3) with synchrotron powder x-ray diffraction, resonant ultrasound spectroscopy, and magnetization measurements. Upon Nb doping, the Pm3¯m ↔ I4/mcm structural transition shifts to higher temperatures and the room temperature lattice parameter increases while the magnitude of the octahedral tilting decreases. In addition, Nb substitution for Ti destabilizes the antiferromagnetic ground state of the parent compound and long-range ferromagnetic order is observed in the samples with x ≥ 0.1. The structural transition in pure and doped compounds is marked by a dramatic steplike softening of themore » elastic moduli near TS , which resembles that of SrTiO3 and can be adequately modeled using the Landau free energy model employing the same coupling between strain and octahedral tilting order parameter as previously used to model SrTiO3.« less

  2. Magnetic properties and magnetic phase diagram of frustrated Co1 - xFexPt3 compounds

    NASA Astrophysics Data System (ADS)

    Kim, T. H.; Cadeville, M. C.; Dinia, A.; Rakoto, H.

    1997-04-01

    The investigation of the magnetic properties of the pseudobinary Co1-xFexPt3 L12 ordered compounds resulting from alloying ferromagnet CoPt3 and frustrated antiferromagnet FePt3 is reported. The magnetic phase diagram of this system shows the presence of a pure spin glass phase that separates the ferromagnetic region from the antiferromagnetic one. On the Co-rich side (x<0.6), two re-entrant spin glass phases are found to emerge at low temperature in the ferromagnetic region. On the iron-rich side, an antiferromagnetic region with two antiferromagnetic [1/2 1/20] and [1/200] structures is observed for 1⩾x⩾0.8. This magnetic phase diagram is discussed comparatively with the previously determined (Fe-Mn)Pt3 and (Co-Mn)Pt3 phase diagrams. The randomness of the average exchange interaction is suggested to arise from a competition between the three dominant magnetic interactions JCoCo, JFeFe, and JCoFe of 3d atoms in sites of second nearest neighbors in the L12 structure.

  3. Nano Mg(1-x)Ni(x)Al₂O₄ spinel pigments for advanced applications.

    PubMed

    Sadek, H E H; Khattab, R M; Gaber, A A; Zawrah, M F

    2014-05-01

    Nano Mg(1-x)Ni(x)Al2O4 spinel pigments were synthesized via polymeric combustion technique upon heat treatment at 210 °C. Citric acid in the presence of ethylene glycol polymer, with mass ratio of 60:40, was successfully used as a host network for the synthesis process. The obtained spinel was calcined at different temperatures; 300-1200°C and investigated by thermal analysis (TG-DTG/DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). UV-Vis and diffuse reflectance spectroscopy (DRS) using CIE-Lab/parameters methods have been used for color measurements. The addition of colored pigment on different types of glazes was studied. The results revealed that NiMgAl2O4 spinel beside MgNiO phases were crystallized with particle sizes of 9-21 nm at 600 °C and 52-180 nm at 1200 °C. All prepared samples exhibited green to pale green colors due to the inclusion of Ni(2+) inside the spinel structure. The pale green color intensity increased with increasing calcination temperature. The prepared pigment was suitable to convert commercial and opaque glazes to color product to be used in different applications.

  4. Dynamical X-ray Diffraction from In x Ga1- x As Heterostructures with Dislocations

    NASA Astrophysics Data System (ADS)

    Rago, P. B.; Ayers, J. E.

    2013-08-01

    High-resolution x-ray diffraction is an important nondestructive tool for structural characterization of semiconductor heterostructures, and the diffraction intensity profiles contain information on the depth profiles of strain, composition, and defect densities in device heterostructures. Much of this information remains inaccessible because the lack of phase information prevents direct inversion of the rocking curves. The current practice is to use dynamical simulations in conjunction with a curve-fitting procedure to indirectly extract the profiles of strain and composition, but such dynamical simulations have been based on perfect, dislocation-free laminar crystals, which renders the analysis inapplicable to highly mismatched structures containing dislocation densities greater than about 106 cm-2. In this work we present a dynamical model for Bragg x-ray diffraction in semiconductor device structures with nonuniform composition, strain, and dislocation density, which is based on the Takagi-Taupin equation for distorted crystals and accounts for the diffuse scattering arising from the strain mosaicity and angular mosaicity associated with dislocations. We show theoretically that the x-ray diffraction profiles from In x Ga1- x As/GaAs (001) heterostructures are strongly affected by the depth distribution of the dislocation density as well as the composition and strain, so that in principle all three distributions may be obtained by the analysis of the measured diffraction profiles.

  5. Ti1-xAgx electrodes deposited on polymer based sensors

    NASA Astrophysics Data System (ADS)

    Marques, S. M.; Manninen, N. K.; Ferdov, Stanislav; Lanceros-Mendez, S.; Carvalho, S.

    2014-10-01

    Piezoelectric materials are interesting for the development of sensors and actuators for biomedical applications in areas such as smart prosthesis, implantable biosensors and biomechanical signal monitoring, among others. For acquiring or applying the electrical signal from/to the piezoelectric material, suitable electrodes can be produced from Ti based coatings with tailored multifunctional properties: conductivity and antibacterial characteristics through Ag inclusions. This work reports on Ti1-xAgx electrodes with different Ag/Ti atomic ratios deposited by dc and pulsed magnetron sputtering at room temperature on poly(vinylidene fluoride), PVDF. The X-ray diffraction (XRD) results revealed that the deposition conditions preserve the polymer structure and suggested the presence of crystalline Tiβ phase in pure titanium coating and fcc-Ag phase in pure silver coating. According to the results obtained from scanning electron microscopy (SEM) analysis, the coatings are homogeneous and no clusters were found; since β-PVDF is anisotropic, the deposited coatings replicate the underlying substrate surface. Sheet resistivity values show a typical behavior of a binary alloy system, with low resistivity values for coatings of zone 1 (Ti rich) and zone 3 (Ag rich) and a slightly higher resistivity values in zone 2. The piezoelectricity of the different samples show similar values.

  6. Inorganic selenium speciation in groundwaters by solid phase extraction on Dowex 1X2.

    PubMed

    Lin, Tser-Sheng

    2007-10-01

    A Dowex 1X2 resin separation technique followed by analysis with atomic absorption spectroscopy was evaluated for the study of inorganic selenium speciation in groundwaters. After Se(IV) and Se(VI) were retained on the resin column, Se(IV) and Se(VI) were eluted out by 0.1 and 1M nitric acid solutions. The method detection limit was 5.6 ng/L for both Se(IV) and Se(VI). Analysis of synthetic solutions consistently yielded more than 90% recovery of these two selenium forms with negligible cross-contamination. The results of spiked well waters show that this method can be applied at ultra-trace level of Se in groundwater and the interference of chloride ion can be neglected. Water samples collected from the monitoring wells in the Science-based Industrial Park, Hsin-Chu, Taiwan, were analyzed. Average dissolved selenium concentrations were 32.1+/-17.6 ng/L. The proportion of Se(VI) to the total dissolved selenium ranged from 47.6 to 61.2% and an average of 53.8% in water samples analyzed.

  7. Thermal and transport properties of U2Pt(x)Ir(1-x)C2.

    PubMed

    Kang, Mingu; Wakeham, N; Ni, Ni; Bauer, E D; Kim, Jeehoon; Ronning, F

    2015-09-16

    We report thermal and transport properties of U2Pt x Ir1-x C2 from which a magnetic phase diagram is obtained. Pure U2IrC2 is an antiferromagnet at 6.5 K, whose Néel temperature initially rises to 13.2 K at x = 0.2 and subsequently is suppressed to zero temperature with increasing Pt content near x = 0.6. Heat capacity divided by temperature at x = 0.6 shows an upturn at low temperature, consistent with the expectations of enhanced quantum fluctuations in the presence of an underlying quantum critical point. The entropy after the phonon contribution has been subtracted has a value of 0.24 Rln2 at the Néel temperature of U2IrC2, revealing an itinerant nature of the 5 f electrons in this compound. On the Pt rich side of the phase diagram, superconductivity is suppressed by x = 0.85. The residual resistivity increases by a factor of 10 from pure Pt (x = 1) to x = 0.85 where superconductivity is suppressed to zero. By comparing the phase diagram of Ir doped U2PtC2 with the phase diagram of pressure tuned and Rh doped U2PtC2 we demonstrate the role of electronic tuning in this system. PMID:26302330

  8. Effect of microstructure on the thermoelectric performance of La1-xSrxCoO3

    NASA Astrophysics Data System (ADS)

    Viskadourakis, Z.; Athanasopoulos, G. I.; Kasotakis, E.; Giapintzakis, J.

    2016-11-01

    We present a case where the microstructure has a profound effect on the thermoelectric properties of oxide compounds. Specifically, we have investigated the effect of different sintering treatments on La1-xSrxCoO3 samples synthesized using the Pechini method. We found that the samples, which are dense and consist of inhomogeneously-mixed grains of different size, exhibit both higher Seebeck coefficient and thermoelectric figure of merit than the samples, which are porous and consist of grains with almost identical size. The enhancement of Seebeck coefficient in the dense samples is attributed to the so-called "energy-filtering" mechanism that is related to the energy barrier of the grain boundary. On the other hand, the thermal conductivity for the porous compounds is significantly reduced in comparison to the dense compounds. It is suggested that a fine-manipulation of grain size ratio combined with a fine-tuning of porosity could considerably enhance the thermoelectric performance of oxides.

  9. Magnetism of Rapidly Quenched Sm1-xZrxCo5 Nanocrystalline Materials

    SciTech Connect

    Zhang, WY; Valloppilly, S; Li, XZ; Liu, Y; Michalski, S; George, TA; Skomski, R; Shield, JE; Sellmyer, DJ

    2013-07-01

    The effect of Zr addition on nanostructure and magnetic properties in nanocrystalline Sm1-xZrxCo5 (x = 0 - 0.6) has been investigated. (Sm, Zr)Co-5 with the CaCu5 structure was synthesized by melt spinning. The lattice parameters a and b decrease with x, whereas c increases. Thus, the unit cell volume of (Sm, Zr)Co-5 shrinks because the smaller Zr atoms occupy the sites of the larger Sm atoms. Zr addition decreases the grain size and induces the formation of planar defects. The coercivity decreases with x, due to weakening of magnetocrystalline anisotropy energy and effective intergrain exchange coupling. A very high coercivity of 39 kOe and energy product of 13.9 MGOe are obtained for x = 0. The remanence of (Sm, Zr)Co-5 increases with x. For x <= 0.4, the energy product slightly decreases with x. The results show that 40% of the Sm can be replaced by the less expensive Zr, with an energy-product reduction of only 10%. In addition, the planar defects are responsible for the change of coercivity mechanism from the nucleation-type of reverse domain for the x = 0 to the pinning-type of domain wall for the x = 0.4.

  10. Charge ordering and magnetoresistance of Ca1-xCexMnO3

    NASA Astrophysics Data System (ADS)

    Zeng, Z.; Greenblatt, M.; Croft, M.

    2001-06-01

    The two-electron (2e) doped Ca1-xCexMnO3 (0<=x<=0.2) system was prepared by sol-gel method and investigated by x-ray absorption spectroscopy (XAS), X-ray diffraction, and temperature and field dependent magnetic and transport measurements. The results are compared in detail to the one-electron (1e)-doped La1-yCayMnO3 system, facilitated by the analogous y=1-2x parametrization as Ca(1+y)/2Ce(1-y)/2MnO3 (0.6<=y<=1.0). The XAS results indicate: that the formal valence of cerium is Ce4+, thereby validating the charge transfer of 2e per doped Ce to Mn. The XAS also shows separate Mn3+ and Mn4+ spectral components, in dramatic contrast to results on 1e-doped systems. Low Ce doping (x=0.025 and 0.05) rapidly stabilizes a robust ferromagnetic component in addition to a persistent antiferromagnetic component in the ordered state. Higher Ce doping (0.075<=x<=0.20) induces a charge/orbital ordering transition that increases with composition to near 255 K. In different composition ranges the magnetoresistance manifests inter-grain-tunneling and a field coupling of the local charge/orbital order parameter mechanisms. The latter mechanism appears to induce a large magnetoresistance, as high as -72%, in Ca0.925Ce0.075MnO3.

  11. Structural, electrical, and magnetic properties of BaCo1-xCuxS2

    NASA Astrophysics Data System (ADS)

    Schweitzer, J. W.

    2006-03-01

    Compounds of the layered transition-metal-sulfide series BaCo1-xCuxS2 (0⩽x⩽0.5) were prepared, and structural, electrical, and magnetic properties were investigated. The semiconductor BaCoS2 is antiferromagnetically ordered below 310K . With increasing Cu content x the structure becomes more anisotropic as the lattice parameter perpendicular to the layers elongates while the parallel parameter contracts. The resistivity is nonmetallic for all the compounds in this series. The Néel temperature TN decreases with x , reaching TN≈0 by x≈0.2 . The susceptibility in the high-temperature paramagnetic phase, which for BaCoS2 is consistent with Co2+ ions in the low-spin S=1/2 state, shows a Curie constant that is very much smaller than expected for Cu1+ and a mixture of Co2+ and Co3+ in the ratio of 1-2x to x . At sufficiently low temperatures there is a spin-glass phase for all x>0 . The magnetic phase diagram obtained is remarkably similar to that of normal state La2-xSrxCuO4 (x⩽0.06) .

  12. Quantum Phase Transitions and Multicriticality in Ta(Fe1-xVx)2

    NASA Astrophysics Data System (ADS)

    Brando, Manuel; Kerkau, Alexander; Todorova, Adriana; Yamada, Yoshihiro; Khuntia, Panchanan; Förster, Tobias; Burkhard, Ulrich; Baenitz, Michael; Kreiner, Guido

    2016-08-01

    We present a comprehensive study of synthesis, structure analysis, transport and thermodynamic properties of the C14 Laves phase Ta(Fe1-xVx)2. Our measurements confirm the appearance of spin-density wave (SDW) order within a dome-like region of the x-T phase diagram with vanadium content 0.02 < x < 0.3. Our results indicate that on approaching TaFe2 from the vanadium-rich side, ferromagnetic (FM) correlations increase faster than the antiferromagnetic (AFM) ones. This results in an exchange-enhanced susceptibility and in the suppression of the SDW transition temperature for x < 0.13 forming the dome-like shape of the phase diagram. This effect is strictly related to a significant lattice distortion of the crystal structure manifested in the c/a ratio. At x = 0.02 both FM and AFM energy scales have similar strength and the system remains paramagnetic down to 2 K with an extremely large Stoner enhancement factor of about 400. Here, spin fluctuations dominate the temperature dependence of the resistivity ρ ∝ T3/2 and of the specific heat C/T ∝ -log(T) which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point of dual nature.

  13. MnxGe1-x dilute magnetic semiconductor studied by XAFS

    NASA Astrophysics Data System (ADS)

    Ye, Jian; Jiang, Yong; Liu, Qinghua; Sun, Yu; Pan, Zhiyun; Wei, Shiqiang

    2009-11-01

    Fluorescence X-ray absorption fine structure (XAFS) technique was used to investigate the local structures of the doped Mn in the MnxGe1-x dilute magnetic semiconductors (DMSs) with different Mn content (x=0.07, 0.25, 0.36) prepared by magnetron cosputtering method. The results indicate that for the sample with low Mn content (x=0.07), the Mn atoms are mainly incorporated into the lattice of Ge, and locate at the substitutional sites of Ge atoms with the ratio of 75%. With the Mn content increasing to 0.25 or higher, only part of Mn atoms enter the lattice of Ge and the others exist in the form of the Mn5Ge3 phase whose content increases with the doped Mn concentration. It is found that, in the Mn0.07Ge0.93 the bond length of the first (Mn-Ge) shell is RMn-Ge = 2.50 Å, which is bigger than the first (Ge-Ge) shell distance in Ge by about 0.05 Å. These results imply that local structure expansion is induced by dilute Mn substituting into Ge sites.

  14. Magnetic phase diagram of Ce(Mn1-xCux)2Si2

    NASA Astrophysics Data System (ADS)

    Liang, G.; Yen, F.

    2008-04-01

    The magnetic structure of mixed valence-Kondo-heavy fermion series Ce(Mn1-xCux)2Si2 (0⩽x ⩽1) is reported. The magnetic susceptibility results indicate that for 0⩽x⩽0.3, Mn moments are antiferromagnetically (AFM) ordered and the Neel temperature TN decreases rapidly with decreasing x. For 0.4⩽x⩽0.7, ferromagnetic (FM) phase is observed below 140K and both the ordering temperature Tc and Curie-Weiss temperature θp decrease with increasing x, showing the weakening of in-plane FM magnetic coupling between Mn moments due to the substitution of Mn by nonmagnetic Cu. For 0.8⩽x⩽1, samples exhibit only paramagnetic behavior. The types of magnetic order in this series are basically consistent with the criterion that FM (AFM) phase is favored when intralayer Mn-Mn spacing RMn-Mna is greater (smaller) than a critical value of 2.865Å. A magnetic phase diagram is constructed for this compound series.

  15. Magnetotransport in (Ce1-xNdx)Cu6 Kondo alloys

    NASA Astrophysics Data System (ADS)

    Strydom, André M.; du Plessis, Paul de V.

    1999-03-01

    The results of electrical resistivity ρ(T) and magnetoresistivity MR(T, B) for $1.5 \\le T \\le 580$1-xNdx)Cu6 alloy system. For small Nd substitutions in the heavy-fermion CeCu6 parent compound, the Kondo lattice is characterized through coherence effects in ρ(T) at low temperatures. The ρ(T) data above room temperature are used to resolve the electron-phonon scattering, and it is indicated that the single-ion Kondo interaction dominates both ρ(T) and MR(B) for a wide range of intermediate Ce concentrations. Based on this, the MR(B) data for different isotherms and alloy compositions are analysed according to the Bethe- ansatz description. We also discuss the observed deviations of our data from the preceding theoretical description due to the onset of magnetic order in alloys with high Nd content, and to phase coherence at low temperatures.

  16. Gd5(SixGe1-x)4 system - updated phase diagram

    NASA Astrophysics Data System (ADS)

    Melikhov, Yevgen; Hadimani, R. L.; Raghunathan, Arun

    2015-12-01

    Gd5(SixGe1-x)4 for 0.41

  17. Energy Gap Tuning and Carrier Dynamics in Colloidal Ge1-xSnx Quantum Dots.

    PubMed

    Hafiz, Shopan A; Esteves, Richard J Alan; Demchenko, Denis O; Arachchige, Indika U; Özgür, Ümit

    2016-09-01

    Optical transition energies and carrier dynamics in colloidally synthesized 2.0 ± 0.8 nm Ge1-xSnx quantum dots (x = 0.055-0.236) having visible luminescence were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopy supported by first-principles calculations. By changing Sn content from x = 0.055 to 0.236, experimentally determined HOMO-LUMO gap at 15 K was tuned from 1.88 to 1.61 eV. Considering the size and compositional variations, these values were consistent with theoretically calculated ones. At 15 K, time-resolved PL revealed slow decay of luminescence (3-27 μs), likely due to the recombination of spin-forbidden dark excitons and recombination of carriers trapped at surface states. Increasing Sn concentration to 23.6% led to 1 order of magnitude faster recombination. At 295 K, PL decays were 3 orders of magnitude faster (9-28 ns) owing to the thermal activation of bright excitons and carrier detrapping from surface states. PMID:27513723

  18. Defect chemistry and characterization of Hg sub 1x Cd sub x Te

    NASA Technical Reports Server (NTRS)

    Vydyanath, H. R.

    1982-01-01

    Single crystal samples of undoped and doped Hg sub 1-x Cd sub x Te were annealed at varying temperatures and partial pressures of Hg. Hall effect and mobility measurements were carried out on these samples after quenching to room temperature. Based on the variation of the carrier concentration and the carrier mobility as a function of the partial pressure of Hg temperature, and dopant concentration, defect models were established for the doped and the undoped crystals. These models indicate that the native acceptor defects in both Hg0.8Cd0.2Te and Hg0.6Cd0.4Te doubly ionized and the native donor defects are negligible in concentration, implying that p to n conversion in these alloys occurs due only to residual donors. Incorporation mechanism of copper, indium, iodine, and phosphorus were investigated. A large concentration of indium is found to be paired with the native acceptor defects. Results on crystals doped with phosphorus indicate that phosphorus behaves amphoterically, acting as a donor on Hg lattice sites and as an acceptor intersitially on Te lattice sites. A majority of the phosphorus is found to be present as neutral species formed from the pairing reaction between phosphorus on Hg lattice sites and phosphorus in interstitial sites. Equilibrium constants for the intrinsic excitation reaction, as well as for the incorporation of the different dopants and the native acceptor defects were established.

  19. A carbon based spintronic material Fe(x)-C(1-x)/Si structure.

    PubMed

    Zhang, Xiaozhong; Wu, Lihua; Wan, Caihua; Zhang, Xin; Gao, Xili; Tan, Xinyu

    2011-03-01

    The decay of spin polarization poses serious problems for spintronic devices. It will be greatly helped by the availability of spintronic materials with a long spin diffusion length. Carbon has small spin-orbital interaction and longer coherent length. This makes carbon suitable material for exploitation in the spintronic materials and devices. A great deal of magnetoresistance (MR) research has been carried out in carbon nanotubes, grapheme and small carbon molecules. However, the MRs of these materials are normally observed at low temperature, making these carbon materials difficult used in information industry. In this paper, we introduce a novel class of carbon based hybrid materials Fe(x)-C(1-x)/Si structure which show larger MR at room temperature. These materials have also some other novel physical properties, such as electromagnetoresistance, switch effect, pressure sensitivity, gas sensitivity and photoconductivity. This kind of carbon based materials has shown early sign of being excellent candidates for spintronic materials operating at room temperature. PMID:21449431

  20. Cooperative nucleation modes in polycrystalline CoxPd1-x nanowires

    NASA Astrophysics Data System (ADS)

    Viqueira, M. S.; Pozo-López, G.; Urreta, S. E.; Condó, A. M.; Cornejo, D. R.; Fabietti, L. M.

    2015-05-01

    Polycrystalline CoxPd1-x (x = 1, 0.60, 0.45, 0.23, and 0.11) cylindrical nanowires (ø = 18-35 nm, about 1 μm length) are produced by AC electrodeposition into hexagonally ordered alumina pores. Single-phase nanowires of an fcc Co-Pd solid solution, with randomly oriented equiaxed grains (7-12 nm) are obtained; in all the cases, the grain size is smaller than the wire diameter. The coercive field and the reduced remanence of Co-rich nanowire arrays are hardly sensitive to temperature within the range varying from 4 K to 300 K. On the other hand, in Pd-rich nanowires both magnitudes are smaller and they largely increase when cooling below 100 K. This behavior also depends on the mean grain size. These facts are systematized considering two main aspects: the non-trivial temperature and composition dependence of the crystalline anisotropy and the saturation magnetostriction in Co-Pd alloys; and a random anisotropy effect, which defines a nucleation localization length that may involve more than a single grain, and thus promotes more cooperative nucleation modes.

  1. Perpendicular magnetic anisotropy in Fe2Cr1 - xCoxSi Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Qiu, Jin-Jun; Lu, Hui; Ji, Rong; Han, Gu-Chang; Teo, Kie-Leong

    2014-12-01

    Perpendicular magnetic anisotropy (PMA) was achieved in annealed Fe2Cr1 - xCoxSi (FCCS) Heusler alloys with different Co compositions x. The Co composition is varied to tune the Fermi level in order to achieve both higher spin polarization and better thermal stability. The PMA is thermally stable up to 400 oC for FCCS with x = 0, 0.3, 0.5 and 350 oC for FCCS with x = 0.7, 0.9, 1. The thickness of FCCS films with PMA ranges from 0.6 to 1.2 nm. The annealing temperature and FCCS thickness are found to greatly affect the PMA. The magnetic anisotropy energy density KU is 2.8  ×  106 erg cm-3 for 0.8 nm Fe2CrSi, and decreases as the Co composition x increases, suggesting that the PMA induced at the FCCS/MgO interface is dominated by the contribution of Fe atoms. There is a trade-off between high spin polarization and strong PMA by adjusting the Co composition.

  2. Synthesis and characterization of nanocrystalline Ti(1-x)Al(x)N by reactive magnetron sputtering.

    PubMed

    Jose, Feby; Ramaseshan, R; Dash, S; Dasgupta, Arup; Saroja, S; Tyagi, A K

    2009-09-01

    Ti(1-x)Al(x)N metastable films were synthesized by reactive magnetron co-sputtering with different Ti to Al ratios. XRD studies showed that as-deposited films were crystalline for concentrations of Al (35, 40, 55 and 64%) and become amorphous at 81% Al. These films were annealed at 1073 K to study the phase separation. Films up to 55% Al did not show any phase separation after annealing. But films with 64% Al splits into c-TiAIN and c-AIN, whereas films with 81% Al split into cubic-TiN and hex-AIN. Distribution of crystallites and their size were analyzed by TEM. High density of crystallites with dimensions between 3-11 nm was dispersed in amorphous matrix for 64% Al films. Nanoindentation technique was used to determine the mechanical properties of these films without substrate effect. Maximum hardness obtained for as deposited and annealed films (64% Al) were 35 GPa and 38 GPa, respectively.

  3. Coherently strained epitaxial Pb(Zr1-xTix)O3 thin films

    NASA Astrophysics Data System (ADS)

    Johnson-Wilke, Raegan L.; Tinberg, Daniel S.; Yeager, C.; Qu, Weiguo; Fong, Dillon D.; Fister, Timothy T.; Streiffer, Stephen K.; Han, Yisong; Reaney, Ian M.; Trolier-McKinstry, Susan

    2013-10-01

    Coherently strained Pb(Zr1-xTix)O3, 0.2 ≤ x ≤ 0.35, thin films were grown by pulsed laser deposition on (001) and (111) oriented SrTiO3 substrates. A buffer layer of Pb(Zr0.6Ti0.4)O3 was used to improve the lattice matching and induce compressive strain in Zr-rich compositions. The (001)pc (pc = pseudocubic) films showed an increased ferroelectric transition temperature, TC, compared to bulk ceramics, but the transition from an untilted to a tilted ferroelectric (TTilt) exhibited only a modest increase in temperature. This suggests that it may be possible to enlarge the untilted ferroelectric phase field by compressive strain. Consistent with previous work on relaxed PZT films, coherently strained PZT films do not exhibit an abrupt transition from an untilted to a tilted state; rather, a region of non-zero tilt exists above TTilt. (111)pc films also showed an increased ferroelectric transition temperature with a weak strain dependence on TTilt. The compressive strain in (111)pc films induced a preferred domain structure with only 180° domain walls, in contrast to bulk materials and relaxed films which are polydomain.

  4. Magnetic properties of the FeAl1 - xCux system

    NASA Astrophysics Data System (ADS)

    Saleh, A. S.; Mankikar, R. M.; Yoon, S.; Okpalugo, D. E.; Booth, J. G.

    1985-04-01

    The substitution of a 3d transition metal (T) for Al in the equiatomic intermetallic compound FeAl results in the onset of ferromagnetism beyond a certain critical concentration of (T). The system appears magnetically and structurally similar to the equivalent Co(GaT) alloys for which the critical concentration appeared to be related to an average electron concentration parameter. The present paper discusses Cu substitution in FeAl, i.e., the series FeAl1-xCux. It was found using x-ray and neutron diffraction techniques that the alloys remain single phase up to x=0.35 and that the crystallographic order remains B2 throughout. The site occupancy has also been determined and compared with the predictions of theoretical models. Ferromagnetism is observed to occur in the alloys with x>0.2. For these ferromagnetic alloys the inverse susceptibility against temperature curves (for T>TC) all have the same slope independent of composition suggesting an interpretation in terms of an itinerant model. This interpretation is also supported by a Rhodes-Wohlfarth plot. A region of superparamagnetism presages the onset of ferromagnetism and from this the size of the magnetic clusters is estimated to be 20-25 Å in radius.

  5. Thermal Conductivity and Electrical Resistivity of FeTe1-xSx Sintered Samples

    NASA Astrophysics Data System (ADS)

    Kikegawa, Takako; Sato, Kazuki; Ishikawa, Keisuke

    The temperature dependence of thermal conductivity and the temperature and magnetic field dependence of electrical resistivity have been measured for FeTe1-xSx polycrystalline samples. The samples were prepared by solid state reaction with a three-step procedure. For FeTe0.8S0.2 and FeTe0.7S0.3, zero resistivity due to the superconducting transition was observed not only in oxygen post-annealed samples but also in as-grown ones. These samples include the certain amount of impurities FeTe2 and Fe3O4. The formation of these ion compounds reduces the excess Fe atoms leading to the appearance of the zero resistivity in as-grown samples. Positive magnetoresistivity and/or negative magnetoresistivity, which were extremely small, were observed for FeTe and S-doped samples. The magnetoresistivity curves show B2 dependence. It was observed that the thermal conductivity κ of FeTe exhibits a hump structure below 72 K which corresponds to the crystal structural and magnetic transitions. The enhancement of κ due to the superconducting transition could not be detected for as-grown FeTe0.8S0.2 and FeTe0.7S0.3 because of the absence of the bulk superconductivity in the as-grown samples and the extremely small ratio of the electronic contribution to κ.

  6. Magnetoelectric coupling tuned by competing anisotropies in Mn1-xNixTiO3

    DOE PAGES

    Chi, Songxue; Ye, Feng; Zhou, H. D.; Choi, E. S.; Hwang, J.; Cao, Huibo; Fernandez-Baca, Jaime A.

    2014-10-24

    A flop of electric polarization from Pmore » $$\\|$$c (Pc) to P$$\\|$$ a (Pa) is observed in MnTiO3 as a spin flop transtion is triggered by a c-axis magnetic field, H$$\\|$$c=7 T. The critical magnetic field for Pa is significantly reduced in Mn1-xNixTiO3 (x=0.33). Neutron diffraction measurements revealed similar magnetic arrangements for the two compositions where the ordered spins couple antiferromagnetically with their nearest intra- and inter-planar neighbors. In the x=0.33 system, the single ion anisotropies of Mn2+ and Ni2+ compete and give rise to an additional spin reorientation transition at TR. A magnetic field, Hc, aligns the spins along c for TRN. The rotation of the collinear spins away from the c-axis for TR alters the magnetic point symmetry and gives rise to new ME susceptibility tensor form. Such linear ME response provides satisfactory explanation for behavior of field-induced electric polarization in both compositions. As the Ni content increases to x=0.5 and 0.68, the ME effect disappears as a new magnetic phase emerges.« less

  7. Spatial atmospheric atomic layer deposition of Al(x)Zn(1-x)O.

    PubMed

    Illiberi, A; Scherpenborg, R; Wu, Y; Roozeboom, F; Poodt, P

    2013-12-26

    The possibility of growing multicomponent oxides by spatial atmospheric atomic layer deposition has been investigated. To this end, Al(x)Zn(1-x)O films have been deposited using diethyl zinc (DEZ), trimethyl aluminum (TMA), and water as Zn, Al, and O precursors, respectively. When the metal precursors (i.e., TMA and DEZ) are coinjected in the deposition region, the Al/(Al + Zn) ratio can be accurately controlled by either varying the TMA flow to the reactor or the exposure time of the substrate to the precursors. A high doping efficiency level (up to 70%) is achieved in Al-doped ZnO, resulting in films with a high carrier density (5 × 10(20) cm(-3)), low resistivity (2 × 10(-3) Ω cm), and good optical transparency (>85%) in the visible range. The morphology of the films changes from polycrystalline, in conductive i-ZnO and Al-doped ZnO, to amorphous, in highly resistive Al-rich films. The unique combination of the fine tuning of the composition, morphology, and electrical properties of the films with high deposition rates (>0.2 nm/s) paves the way for spatial ALD as an emerging disruptive technique for the growth of multicomponent oxides over large areas.

  8. Anomalous dielectric nonlinearity and dielectric relaxation in xBST-(1- x) (LMT-LNT) ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Cheng; Liu, Peng

    2011-11-01

    xwt%Ba0.6Sr0.4TiO3-(1- x)wt%[0.4La (Mg0.5Ti0.5)O3-0.6(La0.5Na0.5)TiO3] ( x=0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 0.95) ceramics were prepared via a traditional solid-state reaction route. Interesting anomalous dielectric nonlinearity (ADN)—permittivity increased with dc bias electric field ( E-field), and low-temperature dielectric relaxation (LTDR) behaviors—were observed within a x range of 0.30˜0.70 for the first time. Based on our experimental facts, it was suggested that the LTDR was originated from a charge-associated process between electron-oxygen vacancy pairs during a thermal stimulation, while the ADN was related with a metastable state of polarized nano-regions (PNRs).

  9. High-efficiency (6+1)x1 combiner for high power fiber lasers and amplifiers

    NASA Astrophysics Data System (ADS)

    Neugroschl, Dan; Park, Jongchul; Wlodawski, Mitchell; Singer, Jonathan; Kopp, Victor I.

    2013-02-01

    We have developed a (6+1)x1 combiner for fiber lasers and amplifiers based on a glass fusion technology. We have combined a conventional fiber fusion technology for pump channels with a new design for a single mode signal channel, which utilizes a vanishing core technology. The approach has been developed for single channel spot size converters and pitch reducing optical fiber arrays (PROFAs). Flexibility of this technology allows a custom design to match both a single or large mode area fiber at the input and a required active fiber at the output. The technology allows two parameters, mode field diameter (MFD) and taper diameter or channel spacing to be adjusted independently resulting in low loss coupling for signal channel at input and output. Utilizing this approach we have obtained better than 0.3 dB coupling for a signal channel at 1550 nm with a standard SMF28 fiber at the input and an active fiber at the output, while using six conventional 105/125 micron fibers as pump channels operating at 974 nm efficiently coupled to a double-clad fiber. Low signal loss results in high efficiency lasing or amplification suitable for high power applications. This unique technology allows excellent coupling for the signal channel as well as for the pump channels and is amenable to even more pump channels if desired.

  10. Crystalline spin-orbit interaction and the Zeeman splitting in Pb1-x Sn x Te.

    PubMed

    Hayasaka, Hiroshi; Fuseya, Yuki

    2016-08-10

    The ratio of the Zeeman splitting to the cyclotron energy ([Formula: see text]), which characterizes the relative strength of the spin-orbit interaction in crystals, is examined for the narrow gap IV-VI semiconductors PbTe, SnTe, and their alloy Pb1-x Sn x Te on the basis of the multiband [Formula: see text] theory. The inverse mass α, the g-factor g, and M are calculated numerically by employing the relativistic empirical tight-binding band calculation. On the other hand, a simple but exact formula of M is obtained for the six-band model based on the group theoretical analysis. It is shown that M  <  1 for PbTe and M  >  1 for SnTe, which are interpreted in terms of the relevance of the interband couplings due to the crystalline spin-orbit interaction. It is clarified both analytically and numerically that M is not a quantized value but a continuous one, and M  =  1 is obtained just at the band inversion point, where the transition from trivial to nontrivial topological crystalline insulator occurs. By using this property, one can detect the transition point only with the bulk measurements. It is also proposed that M is useful to evaluate quantitatively a degree of the Dirac electrons in solids. PMID:27301789

  11. Lifshitz transition and chemical instabilities in Ba1-xKxFe2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Khan, Suffian; Johnson, Duane

    2014-03-01

    For solid-solution Ba1-xKxFe2As2, the Fermi surface (spectral function) evolution due to chemical disorder from x = 0.6-1.0 is mapped using density functional theory. Dissolution of electron cylinders occurs near x=0.9 with a non-uniform topological (Lifshitz) transitions, which influence s+/- superconductivity to the presence of line nodes in disordered samples and suggest the origin for the deviation from BNC scaling (i.e., specific heat jump ΔcS ~ Tc3).The formation energies indicate alloying at x=0.35, as observed, and a tendency for segregation on the K-rich side, with chemical instabilities for x > 0.6, explaining the difficulty of controlling sample quality and the conflicting results between characterized electronic structures. Supported by the U.S. DOE, Office of BES, Division of Materials Science and Engineering, and by the Center for Defect Physics, an EFRC at ORNL. The Ames Lab is operated by the DOE by Iowa State University under contract DE-AC02-07CH11358.

  12. Semiconductor ultraviolet photodetectors based on ZnO and MgxZn1-xO

    NASA Astrophysics Data System (ADS)

    Hou, Yaonan; Mei, Zengxia; Du, Xiaolong

    2014-07-01

    It is indispensable to develop wide-band-gap based ultraviolet (UV) photodetectors (PDs), which are one of the basic building blocks of solid state UV optoelectronic devices. In the last two decades, we have witnessed the renaissance of ZnO as a wide-band-gap semiconductor and an enormous development of ZnO-based UV PDs as a result of its superb optical and electronic properties. Since the first demonstration, a great variety of UV PDs based on ZnO and its related materials have been proposed and demonstrated. These PDs, with diverse device geometries, exhibit either high performance or multiple functions, reflecting a state-of-the-art technology of UV optoelectronics. In this review, we study the latest progress of UV PDs made on ZnO and MgxZn1-xO, which is a representative alloy of ZnO for band-gap engineering techniques. The discussion focuses on the device performance and the behind device physics according to the architecture of UV PDs.

  13. Vertical spin Hall magnetoresistance in T a1 -xP tx/YIG bilayers

    NASA Astrophysics Data System (ADS)

    Han, J. H.; Shi, G. Y.; Zhou, X. J.; Yang, Q. H.; Rao, Y. H.; Li, G.; Zhang, H. W.; Pan, F.; Song, C.

    2016-10-01

    The spin Hall effect and the magnetic proximity effect are two main sources of the magnetoresistance (MR) effects in heavy metal/ferromagnet bilayers, where they play isolated roles but are usually contaminated by each other. In T a1-xP tx/YIG (=Y3F e5O12) bilayers consisting of Ta and Pt nanograins, these effects are intrinsically coupled to generate new MR with 360° direction sensitivity to the magnetic field and proportionality to the out-of-plane magnetization of YIG. Due to the opposite spin Hall angle of Ta and Pt, vertical spin accumulation is generated via the spin Hall effect at the transverse boundaries between Ta and Pt grains. The spin-dependent scattering by the proximity-induced Pt magnetization finally leads to the MR, which is named as vertical spin Hall MR taking the role of spin Hall angle into account. Besides fundamental insight to spin transport physics, our work provides an approach to detecting perpendicular magnetization in a variety of magnets.

  14. Visible photoluminescence of porous Si(1-x)Ge(x) obtained by stain etching

    NASA Technical Reports Server (NTRS)

    Ksendzov, A.; Fathauer, R. W.; George, T.; Pike, W. T.; Vasquez, R. P.; Taylor, A. P.

    1993-01-01

    We have investigated visible photoluminescence (PL) from thin porous Si(1-x)Ge(x) alloy layers prepared by stain etching of molecular-beam-epitaxy-grown material. Seven samples with nominal Ge fraction x varying from 0.04 to 0.41 were studied at room temperature and 80 K. Samples of bulk stain etched Si and Ge were also investigated. The composition of the porous material was determined using X-ray photoemission spectroscopy and Rutherford backscattering techniques to be considerably more Ge-rich than the starting epitaxial layers. While the luminescence intensity drops significantly with the increasing Ge fraction, we observe no significant variation in the PL wavelength at room temperature. This is clearly in contradiction to the popular model based on quantum confinement in crystalline silicon which predicts that the PL energy should follow the bandgap variation of the starting material. However, our data are consistent with small active units containing only a few Si atoms that are responsible for the light emission. Such units are present in many compounds proposed in the literature as the cause of the visible PL in porous Si.

  15. Crystallographic and Mössbauer investigations on Np1- xPuxB2

    NASA Astrophysics Data System (ADS)

    Chipaux, R.; Bonnisseau, D.; Bogé, M.; Larroque, J.

    1988-08-01

    The diborides of neptunium and plutonium and their solid solutions Np 1- xPu xB 2 have been synthesized by direct reaction with a good purity. The lattice parameters follow Vegard's law. The magnetic properties of the samples containing neptunium have been investigated by Mössbauer spectrometry. The isomer shift is almost constant in all compounds (-14.5 (0.2) mm/s resp. to NpAl 2), suggesting tetravalent Np ions. At high temperatures, a large quadrupolar interaction, clearly connected to the crystal structure, is observed in all compounds, decreasing slowly with the neptunium concentration. At low temperature, magnetic patterns appear for x ⩽ 0.5. The magnetic moments are ordered perpendicular to the c-axis and equal to 0.57μ B for x = 0. In Np 0.5Pu 0.5B 2 and, in less degree in Np 0.7Pu 0.3B 2 and Np 0.33Pu 0.67B 2, magnetic fluctuations are detec ted.

  16. Magnetic phase diagram of Sr1-xCaxCo2P2

    NASA Astrophysics Data System (ADS)

    Sugiyama, J.; Nozaki, H.; Umegaki, I.; Harada, M.; Higuchi, Y.; Ansaldo, E. J.; Brewer, J. H.; Imai, M.; Michioka, C.; Yoshimura, K.; Månsson, M.

    2014-12-01

    In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-μ+SR spectra for the Sr1-xCaxCo2P2 powder samples with x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of μ+SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as x increases from 0, a Pauli-paramagnetic phase is observed even at the lowest T measured (1.8 K) until x = 0.4, then, a spin-glass like phase appears at 0.5 <= x <= 0.6, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for x = 0.8, and finally, a commensurate A-type AF ordered phase (for x = 1) is stabilized below TN ~ 80 K. Such change is most likely reasonable and connected to the shrink of the c-axis length with x, which naturally enhances the magnetic interaction between the two adjacent Co planes.

  17. Photoelectrochemical properties of CdS{sub x}Se{sub 1-x} films

    SciTech Connect

    Murali, K.R.; Thilagavathy, K.; Vasantha, S.; Gopalakrishnan, P.; Rachel Oommen, P.

    2010-04-15

    CdS{sub x}Se{sub 1-x} films of different composition (0 < x < 1) were deposited by pulse plating technique at different duty cycles in the range of 10-50%. The films were polycrystalline and exhibited hexagonal structure. The band gap of the films varies from 1.68 to 2.39 eV as the concentration of CdS increases. Energy Dispersive analysis of X-rays (EDAX) measurements indicate that the composition of the films are nearly the same as that of the precursors considered for the deposition. Atomic force microscopy studies indicated that the grain size increased from 20 to 200 nm as the concentration of CdSe increased. Photoelectrochemical (PEC) cell studies indicated that the films of composition CdS{sub 0.9}Se{sub 0.1} exhibited maximum photoactivity. Mott-Schottky studies indicated that the films exhibit n-type behaviour. Spectral response measurements indicated that the photocurrent maxima occurred at the wavelength value corresponding to the band gap of the films. (author)

  18. Morphotropic phase boundary and magnetoelastic behaviour in ferromagnetic Tb1-xGdxFe2 system

    NASA Astrophysics Data System (ADS)

    Adil, Murtaza; Yang, Sen; Mi, Meng; Zhou, Chao; Wang, Jieqiong; Zhang, Rui; Liao, Xiaoqi; Wang, Yu; Ren, Xiaobing; Song, Xiaoping; Ren, Yang

    2015-03-01

    Morphotropic phase boundary (MPB), separating two ferroic phases of different crystal symmetries, has been studied extensively for its extraordinary enhancement of piezoelectricity in ferroelectrics. Based on the same mechanism, we have designed a magnetic MPB in the pseudobinary ferromagnetic system of Tb1-xGdxFe2 and the corresponding crystal structure, magnetic properties, and magnetostriction are explored. With the synchrotron x-ray diffractometry, the structure symmetry of TbFe2-rich compositions is detected to be rhombohedral (R) and that of GdFe2-rich compositions is tetragonal (T) below Tc. With the change of concentration, the value of magnetostriction of the samples changes monotonously, while the MPB composition Tb0.1Gd0.9Fe2, which corresponds to the coexistence of R and T phases, exhibits the maximum magnetization among all available compositions and superposition of magnetostriction behaviour of R and T phases. Our result of MPB phenomena in ferromagnets may provide an effective route to design functional magnetic materials with exotic properties.

  19. Inkjet Printed Metallizations for Cu(In1-xGax)Se2 Photovoltaic Cells

    SciTech Connect

    Hersh, P. A.; Curtis, C. J.; van Hest, M. F. A. M.; Kreuder, J. J.; Pasquarelli, R.; Miednaer, A.; Ginley, D. S.

    2011-12-01

    This study reports the inkjet printing of Ag front contacts on Aluminum doped Zinc Oxide (AZO)/intrinsic Zinc Oxide (i-ZnO)/CdS/Cu(In{sub 1-x}Ga{sub x})Se{sub 2} (CIGS)/Mo thin film photovoltaic cells. The printed Ag contacts are being developed to replace the currently employed evaporated Ni/Al bi-layer contacts. Inkjet deposition conditions were optimized to reduce line resistivity and reduce contact resistance to the Al:ZnO layer. Ag lines printed at a substrate temperature of 200 C showed a line resistivity of 2.06 {mu}{Omega} {center_dot} cm and a contact resistance to Al:ZnO of 8.2 {+-} 0.2 m{Omega} {center_dot} cm{sup 2} compared to 6.93 {+-} 0.3 m{Omega} {center_dot} cm{sup 2} for thermally evaporated contacts. These deposition conditions were used to deposit front contacts onto high quality CIGS thin film photovoltaic cells. The heating required to print the Ag contacts caused the performance to degrade compared to similar devices with evaporated Ni/Al contacts that were not heated. Devices with inkjet printed contacts showed 11.4% conversion efficiency compared to 14.8% with evaporated contacts. Strategies to minimize heating, which is detrimental for efficiency, during inkjet printing are proposed.

  20. The missing boundary in the phase diagram of PbZr(1-x)TixO₃.

    PubMed

    Zhang, N; Yokota, H; Glazer, A M; Ren, Z; Keen, D A; Keeble, D S; Thomas, P A; Ye, Z-G

    2014-01-01

    PbZr(1-x)Ti(x)O3 (PZT) is one of the most important and widely used piezoelectric materials. The study of its local and average structures is of fundamental importance in understanding the origin of its high-performance piezoelectricity. Pair distribution function analysis and Rietveld refinement have been carried out to study both the short- and long-range order in the Zr-rich rhombohedral region of the PZT phase diagram. The nature of the monoclinic phase across the Zr-rich and morphotropic phase boundary area of PZT is clarified. Evidence is found that long-range average rhombohedral and both long- and short-range monoclinic regions coexist at all compositions. In addition, a boundary between a monoclinic (M(A)) structure and another monoclinic (M(B)) structure has been found. The general advantage of a particular monoclinic distortion (M(A)) for high piezoactivity is discussed from a spatial structural model of susceptibility to stress and electric field, which is applicable across the wide field of perovskite materials science. PMID:25342592

  1. Composition spread studies of Nd1-xLaxNiO3 combinatorial thin films

    NASA Astrophysics Data System (ADS)

    Suchoski, Richard; Jin, Kui; Yasui, Shintaro; Greene, Richard; Takeuchi, Ichiro

    2013-03-01

    Rare earth nickelates have attracted a great deal of attention in recent years due to a host of interesting features, one being a transition from paramagnetic metal to antiferromagnetic insulator through distortions from the ideal perovskite unit cell. This metal-to-insulator transition (MIT) can be manipulated by modifying variables such as temperature, rare earth ion size, oxygen content, or stress from lattice-mismatched epitaxial thin film growth. Research on this family has been extensive, though there still exists an absence of thin film studies focusing on intermediate compositions. We have fabricated epitaxial thin film composition spreads of Nd1-xLaxNiO3 grown via combinatorial PLD to investigate these transitional compositions. While our films exhibit a smooth composition progression, we observe a composition threshold where orthorhombic NdNiO3 transforms to rhombohedral LaNiO3, correlating with disappearance of the MIT, and displays a non-Vegard evolution of the film's in-plane lattice constant in HRXRD and Raman scattering data of the A1g rotational mode. This work was performed at the Center for Nanophysics and Advanced Materials (CNAM) at UMD, and supported by AFO SR MURI Grant #FA95500910603.

  2. Segregation at the surfaces of CuxPd1-x alloys in the presence of adsorbed S

    SciTech Connect

    Miller, James B.; Priyadarshini, Deepika; Gellman, Andrew J.

    2012-10-01

    The influence of adsorbed S on surface segregation in Cu{sub x}Pd{sub 1 - x} alloys (S/Cu{sub x}Pd{sub 1 - x)} was characterized over a wide range of bulk alloy compositions (x = 0.05 to 0.95) using high-throughput Composition Spread Alloy Film (CSAF) sample libraries. Top-surface and near-surface compositions of the CSAFs were measured as functions of bulk Cu composition, x, and temperature using spatially resolved low energy ion scattering spectroscopy (LEISS) and X-ray photoemission spectroscopy (XPS). Preferential segregation of Cu to the top-surface of the S/Cu{sub x}Pd{sub 1 - x} CSAF was observed at all bulk compositions, x, but the extent of Cu segregation to the S/Cu{sub x}Pd{sub 1 - x} surface was lower than the Cu segregation to the surface of a clean Cu{sub x}Pd{sub 1 - x} CSAF, clear evidence of an S-induced “segregation reversal.” The Langmuir–McLean formulation of the Gibbs isotherm was used to estimate the enthalpy and entropy of Cu segregation to the top-surface, ΔH{sub seg}(x) and ΔS{sub seg}(x), at saturation sulfur coverages. While Cu segregation to the top-surface of the clean Cu{sub x}Pd{sub 1 - x} is exothermic (ΔH{sub seg} < 0) for all bulk Cu compositions, it is endothermic (ΔH{sub seg} > 0) for S/Cu{sub x}Pd{sub 1 - x}. Segregation to the S/Cu{sub x}Pd{sub 1 - x} surface is driven by entropy. Changes in segregation patterns that occur upon adsorption of S onto Cu{sub x}Pd{sub 1 - x} appear to be related to formation of energetically favored Pd{single bond}S bonds at the surface, which counterbalance the enthalpic driving forces for Cu segregation to the clean surface.

  3. Interfacial solid-state reaction at thermally oxidized In1 - xGaxAsyP1 - y alloys

    NASA Astrophysics Data System (ADS)

    Kubo, Minoru; Sasai, Yoichi; Ogura, Mototsugu; Kohiki, Shigemi

    1988-07-01

    The interfacial reaction between thermally oxidized In1-xGaxAsyP1-y and an In1-xGaxAsyP1-y epilayer was studied using Raman and x-ray photoelectron spectroscopy (XPS) analyses. In Raman spectra, it was found that the appearance of the phonon modes, i.e., the first-order longitudinal (LO) and transverse-optical (TO) modes for crystalline arsenic, was due to the In1-xGaxAsyP1-y -oxide interfacial reaction. The XPS analyses showed that this reaction corresponded to the GaAs-oxide interfacial reaction, i.e., As2O3+2GaAs→Ga2O3+4As. Furthermore, the reaction depends on the composition y of In1-xGaxAsyP1-y, which may be due to the enhancement in the initial transient reaction by thermal damage of In1-xGaxAsyP1-y occurring at the interface.

  4. Structural and Thermal Diffusivity Studies of Polycrystalline (CuSe)1-xSex Metal Chalcogenide Compound

    NASA Astrophysics Data System (ADS)

    Josephine, L. Y. C.; Talib, Z. A.; Yunus, W. M. M.; Zainal, Z.; Moksin, M. M.; Lim, K. P.; Yusoff, W. D. W.

    2007-05-01

    This paper reports the preparation and the characterization of the (CuSe)1-xSex metal chalcogenide semiconductor compounds with different stoichiometric compositions of Se (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) in bulk form. The (CuSe)1-xSex compounds were prepared using the solid state reaction by varying the ratio of CuSe:Se in the reaction mixture. X-ray powder diffraction analysis is used to identify and measure the mass absorption coefficient of the (CuSe)1-xSex compounds to support the thermal diffusivity behaviour. The thermal diffusivity of the polycrystalline (CuSe)1-xSex compounds were measured and analyzed for the first time, using the photoflash technique. The thermal diffusivity values were determined to be in the range of 2.524 × 10-3 cm 2 /s to 1.125 × 10-2 cm 2 /s. It was found that the thermal diffusivity value tends to decrease as the parameter x increases. The relationship between the thermal diffusivity, mass absorption coefficient and density of the (CuSe)1-xSex are discussed in detail.

  5. Density functional study for crystalline structures and electronic properties of Si1- x Sn x binary alloys

    NASA Astrophysics Data System (ADS)

    Nagae, Yuki; Kurosawa, Masashi; Shibayama, Shigehisa; Araidai, Masaaki; Sakashita, Mitsuo; Nakatsuka, Osamu; Shiraishi, Kenji; Zaima, Shigeaki

    2016-08-01

    We have carried out density functional theory (DFT) calculation for Si1- x Sn x alloy and investigated the effect of the displacement of Si and Sn atoms with strain relaxation on the lattice constant and E- k dispersion. We calculated the formation probabilities for all atomic configurations of Si1- x Sn x according to the Boltzmann distribution. The average lattice constant and E- k dispersion were weighted by the formation probability of each configuration of Si1- x Sn x . We estimated the displacement of Si and Sn atoms from the initial tetrahedral site in the Si1- x Sn x unit cell considering structural relaxation under hydrostatic pressure, and we found that the breaking of the degenerated electronic levels of the valence band edge could be caused by the breaking of the tetrahedral symmetry. We also calculated the E- k dispersion of the Si1- x Sn x alloy by the DFT+U method and found that a Sn content above 50% would be required for the indirect-direct transition.

  6. Mid-IR band gap engineering of CdxPb1-xS nanocrystals by mechanochemical reaction

    NASA Astrophysics Data System (ADS)

    Tan, Guo-Long; Liu, Limin; Wu, Weibing

    2014-06-01

    Composition-tunable ternary CdxPb1-xS nanocrystals (NCs) are very important materials for remote sensing and detecting in the infrared (IR) wavelength region. They are, however, almost exclusively prepared by wet chemical routes which lead to surface-capped nanoparticles. The surface capping molecules could move their absorption peaks from mid-IR to near IR wavelength region. However, surface clean CdxPb1-xS nanocrystals (NCs) would demonstrate intrinsic optical spectrum in the mid-IR region. Herein, we present a physical mechanical alloying (MA) process being applied to prepare tens of grams of surface clean CdxPb1-xS nanocrystals within the composition range of x = 0.0 to 0.4. The average particle size is smaller than 9 nm. The as-milled nanocrystals are chemically homogenous. The CdxPb1-xS nanocrystals show a continuous lattice contraction with Cd content. There is an exponential indirect band gap-composition relationship. This MA method shows the ability to continuously and precisely tune the band gap energies of ternary CdxPb1-xS semiconductor nanocrystals from mid-IR region (2638 nm) to NIR wavelength region (1240 nm) through chemical composition.

  7. Luminescent Characteristics of Ba(1--x)Al2Si2O8:xTb3+ Green Phosphors.

    PubMed

    Hakeem, D A; Kim, Y; Park, K

    2016-02-01

    Ba(1--x)Al2Si2O8:xTb3+ (0.03 < or = x < or = 0.12) green phosphors are prepared by solution combustion method. The photoluminescence properties of the Ba(1--x)Al2Si2O8:xTb3+ phosphors are studied as a function of Tb3+ concentration. The Ba(1--x)Al2Si2O8:xTb3+ phosphors crystallize in a hexagonal crystal structure. The excitation spectra consist of two broad bands with maxima at 238 nm and 265 nm and several weak peaks in the range of 310-500 nm. Strong emission peaks are observed at 484, 540, 589, and 612 nm due to the (5)D4 --> (7)F6, (5)D4 --> (7)F5, (5)D4 --> (7)F4, and (5)D4 --> (7)F3 tran- sitions of the Tb3+, respectively. The emission peak (540 nm) from the (5)D4 --> (7)F3 transition is dominant, indicating green light emission. Ba(1--x)Al2Si2O8:xTb3+ phosphor shows the strongest green emission intensity. The Ba(1--x)Al2Si2O8:xTb3+ can be considered a promising green phosphor for white LEDs applications. PMID:27433666

  8. Temperature and frequency dependence on electrical properties of polyaniline/Ni(1-x)CoxFe2O4 nanocomposites

    NASA Astrophysics Data System (ADS)

    Chitra, Palanisamy; Muthusamy, Athianna; Dineshkumar, Sengottuvelu; Jayaprakash, Rajan; Chandrasekar, J.

    2015-06-01

    Two nanocomposites of polyaniline (PANI) varying in their percentage composition of Ni(1-x)CoxFe2O4 nanoparticle (20%, 10% w/w of fine powders) were prepared by in-situ chemical oxidative polymerization method with and without ultrasonic treatment. The spinel ferrite nanoparticles of chemical composition Ni(1-x)CoxFe2O4 were prepared by auto combustion method. The structure and morphology of PANI and nanocomposites were characterized by X-ray diffraction (XRD) and High resolution transmission electron microscopy (HRTEM). The chemical structure of Ni(1-x)CoxFe2O4 nanoparticles and its composites were characterized by using Fourier transform infrared (FTIR), UV-visible absorption spectrometer and XRD techniques. Dielectric properties of nanocomposites at different temperature have been performed in the frequency range of 50 Hz to 5 MHz. Dielectric constant, dielectric loss and AC conductivity of PANI/Ni(1-x)CoxFe2O4 nanocomposites are significantly increasing with increase in ferrite content due to the polaron/bipolaron formation. The optical absorption experiments of PANI/Ni(1-x)CoxFe2O4 nanocomposite illustrate a direct transition with an energy band gap of Eg around 1.7.

  9. Competing magnetic ground states in the A-site layer-ordered manganite La{sub 1-x}Ba{sub 1+x}Mn{sub 2}O{sub 6}.

    SciTech Connect

    Chmaissem, O.; Brown, D. E.; Ren, Y.; Kolesnik, S.; Mais, J.; Dabrowski, B.

    2010-01-01

    Using neutron and x-ray diffraction, we report the discovery of competing ground states near a multicritical point in A-site layer-ordered La{sub 1-x}Ba{sub 1+x}Mn{sub 2}O{sub 6} materials. We demonstrate the dual effects of deliberate disorder on the system's stability, the freezing of the competing states, and the drastic reduction in magnetic fields required for the suppression of charge- and orbital-ordered phases. Our work suggests that quenched disorder is not the primary reason for phase separation and magnetoresistance and that increased doping leads to electronic phase separation.

  10. Smectic C liquid crystal growth through surface orientation by ZnxCd1-xSe thin films

    NASA Astrophysics Data System (ADS)

    Katranchev, B.; Petrov, M.; Bineva, I.; Levi, Z.; Mineva, M.

    2012-12-01

    A smectic C liquid crystal (LC) texture, consisting of distinct local single crystals (DLSCs) was grown using predefined orientation of ternary nanocrystalline thin films of ZnxCd1-xSe. The surface morphology and orientation features of the ZnxCd1-xSe films were investigated by AFM measurements and micro-texture polarization analysis. The ZnxCd1-xSe surface causes a substantial enlargement of the smectic C DLSCs and induction of a surface bistable state. The specific character of the morphology of this coating leads to the decrease of the corresponding anchoring energy. Two new chiral states, not typical for this LC were indicated. The physical mechanism providing these new effects is presented.

  11. The U-shaped Fe (1-x)S micro-slots: growth, characterization, and magnetic property

    NASA Astrophysics Data System (ADS)

    Ma, Xuchu; Xu, Fen; Wang, Xiong; Du, Yi; Chen, Liyong; Zhang, Zude

    2005-04-01

    The micro-meter-sized Fe (1-x)S U-shaped slots can be successfully synthesized on a large scale from a β-cyclodextrin (CD)-assisted intercalation-induced growth process at 230 °C for 48 h, which uses the reaction of ferrocene, S and β-CD in ethylenediamine solvent. The structure, the morphology and the property of the products are derived from X-ray power diffraction (XRD) pattern, X-ray photoelectron spectra (XPS), scanning electronic microscope (SEM), transmission electronic microscope (TEM), thermal gravimetric (TG) analysis and magnetization measurement. The as-prepared magnetic Fe (1-x)S U-shaped slots are ferromagnetic and their magnetization at room temperature is ˜15 emu g -1. The possible growth mechanism for the micro-sized Fe (1-x)S U-shaped slots is discussed.

  12. Evolution of the magnetic and structural properties of Fe1 -xCoxV2O4

    NASA Astrophysics Data System (ADS)

    Sinclair, R.; Ma, J.; Cao, H. B.; Hong, T.; Matsuda, M.; Dun, Z. L.; Zhou, H. D.

    2015-10-01

    The magnetic and structural properties of single-crystal Fe1 -xCoxV2O4 samples have been investigated by performing specific heat, susceptibility, neutron diffraction, and x-ray diffraction measurements. As the orbital-active Fe2 + ions with larger ionic size are gradually substituted by the orbital-inactive Co2 + ions with smaller ionic size, the system approaches the itinerant electron limit with decreasing V-V distance. Then, various factors such as the Jahn-Teller distortion and the spin-orbital coupling of the Fe2 + ions on the A sites and the orbital ordering and electronic itinerancy of the V3 + ions on the B sites compete with each other to produce a complex magnetic and structural phase diagram. This phase diagram is compared to those of Fe1 -xMnxV2O4 and Mn1 -xCoxV2O4 to emphasize several distinct features.

  13. Superconducting Properties of FeSe_{1-x} Sx Crystals for x up to 0.19

    NASA Astrophysics Data System (ADS)

    Ovchenkov, Y. A.; Chareev, D. A.; Presnov, D. E.; Volkova, O. S.; Vasiliev, A. N.

    2016-03-01

    We report on the transport properties of FeSe_{1-x} Sx single crystals for x = 0.04, 0.09, and 0.19. These compounds show a consequent increase in the superconducting transition temperature to about 10.5 K for x = 0.04 and 0.09 followed by a decrease to 8.5 K for x = 0.19, completing the superconducting dome of the FeSe_{1-x} Sx series phase diagram. The sample with the highest substitution level x = 0.19 shows no transition to an orthorhombic phase at low temperatures. Therefore, the suppression of the low temperature structural transition in FeSe_{1-x} Sx coincides with the start of the steep decrease in the superconducting transition temperature.

  14. High Coke-Resistance Pt/Mg1-xNixO Catalyst for Dry Reforming of Methane

    PubMed Central

    Al-Doghachi, Faris A. J.; Islam, Aminul; Zainal, Zulkarnain; Saiman, Mohd Izham; Embong, Zaidi; Taufiq-Yap, Yun Hin

    2016-01-01

    A highly active and stable nano structured Pt/Mg1-xNixO catalysts was developed by a simple co-precipitation method. The obtained Pt/Mg1-xNixO catalyst exhibited cubic structure nanocatalyst with a size of 50–80 nm and realized CH4 and CO2 conversions as high as 98% at 900°C with excellent stability in the dry reforming of methane. The characterization of catalyst was performed using various kinds of analytical techniques including XRD, BET, XRF, TPR-H2, TGA, TEM, FESEM, FT-IR, and XPS analyses. Characterization of spent catalyst further confirms that Pt/Mg1-xNixO catalyst has high coke-resistance for dry reforming. Thus, the catalyst demonstrated in this study, offers a promising catalyst for resolving the dilemma between dispersion and reducibility of supported metal, as well as activity and stability during high temperature reactions. PMID:26745623

  15. Magnetic properties of Ho{sub 1-x}Er{sub x}Al{sub 2} alloys

    SciTech Connect

    Khan, Mahmud; Paudyal, D.; Gschneidner, K. A. Jr.; Pecharsky, V. K.

    2013-05-07

    HoAl{sub 2} exhibits a first order spin reorientation transition at 20 K. Heat capacity measurements showed that when Ho is partially replaced by Er in Ho{sub 1-x}Er{sub x}Al{sub 2}, the spin reorientation transition is gradually suppressed, while slowly shifting to higher temperatures with increasing Er concentration. In this paper, we investigate the magnetic properties of pseudo binary Ho{sub 1-x}Er{sub x}Al{sub 2} alloys by ac and dc magnetization measurements. The magnetization data show that the magnetic interactions below T{sub C} are dramatically modified when Er is added in Ho{sub 1-x}Er{sub x}Al{sub 2}. For a better explanation of the experimental data, results of first principles calculations have been presented as well.

  16. Strong enhancement of piezoelectric constants in ScxAl1-xN: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Momida, Hiroyoshi; Teshigahara, Akihiko; Oguchi, Tamio

    2016-06-01

    We theoretically investigate the piezoelectricity of ScxAl1-xN in the entire range of x by first-principles calculations. We find that the piezoelectric constants of wurtzite-type ScxAl1-xN significantly enhance as x increases from 0 to 0.75. However, the energy stability analyses between structure phases show that the cubic-type phases become more stable than the wurtzite-type phases at x of approximately 0.5 and higher, interfering with the ability of wurtzite-type ScxAl1-xN to realize the maximum piezoelectricity. Moreover, our study on element combination dependences on piezoelectricity in A0.5B0.5N (A = Sc, Y, La and B = Al, Ga, In) indicates that Sc, Y, and La have the strongest effect on the enhancement of piezoelectric constants in AlN, GaN, and InN, respectively.

  17. Study of gamma-ray detector performance of Cd1-xZnxTe crystal treated by different etchants

    NASA Astrophysics Data System (ADS)

    Chen, Henry; Egarievwe, Stephen U.; Hu, Z.; Tong, J.; Shi, Detang T.; Wu, G. H.; Chen, Kuo-Tong; George, M. A.; Collins, W. E.; Burger, Arnold; James, Ralph B.; Stahle, Carl M.; Bartlett, Lyle M.

    1996-07-01

    Radiation detectors have been fabricated from Cd1-xZnxTe crystals and their performance has been studied with respect their Cd1-xZnxTe surface preparation. Energy resolution, leakage current, resistivity, ohmicity as well as surface roughness of the detectors were measured and compared for various chemical treatments. Etching in lactic acid has been found to lead to better ohmic contract, a rougher surface and higher leakage current. Bromine is effective in removing the damaged layer and when added to 20 percent lactic acid in ethylene glycol leads to a lower leakage current and consequently a better energy resolution. The best detector performance was obtained with a two step treatment consisting of a standard etchant (5 percent Br in methanol) followed by 2 percent Br in'20 percent lactic acid in ethylene glycol'. The results clearly demonstrate the important of surface chemical treatments in the fabrication of Cd1-xZnxTe radiation detectors.

  18. High Coke-Resistance Pt/Mg1-xNixO Catalyst for Dry Reforming of Methane.

    PubMed

    Al-Doghachi, Faris A J; Islam, Aminul; Zainal, Zulkarnain; Saiman, Mohd Izham; Embong, Zaidi; Taufiq-Yap, Yun Hin

    2016-01-01

    A highly active and stable nano structured Pt/Mg1-xNixO catalysts was developed by a simple co-precipitation method. The obtained Pt/Mg1-xNixO catalyst exhibited cubic structure nanocatalyst with a size of 50-80 nm and realized CH4 and CO2 conversions as high as 98% at 900°C with excellent stability in the dry reforming of methane. The characterization of catalyst was performed using various kinds of analytical techniques including XRD, BET, XRF, TPR-H2, TGA, TEM, FESEM, FT-IR, and XPS analyses. Characterization of spent catalyst further confirms that Pt/Mg1-xNixO catalyst has high coke-resistance for dry reforming. Thus, the catalyst demonstrated in this study, offers a promising catalyst for resolving the dilemma between dispersion and reducibility of supported metal, as well as activity and stability during high temperature reactions. PMID:26745623

  19. Energy levels of GaAs/AlxGa1-xAs/AlAs spherical quantum dot with an impurity

    NASA Astrophysics Data System (ADS)

    Boz, Figen Karaca; Nisanci, Beyza; Aktas, Saban; Okan, S. Erol

    2016-11-01

    We have calculated the energy levels and the radial probability distributions of an electron with an impurity in a spherical quantum dot which is layered as GaAs/AlxGa1-xAs/AlAs. The numerical method used is the fourth-order Runge-Kutta method in the framework of the effective mass approximation. The variation of the energy levels have been calculated as functions of the radius of the GaAs sphere and the thickness of AlxGa1-xAs spherical layer considering effective mass and dielectric constant mismatches. The results have presented the importance of the geometry on the electronic properties of the spherical GaAs/AlxGa1-xAs/AlAs quantum dot.

  20. Tailoring Mg(x)Mn(1-x)Fe(2)O(4) superparamagnetic nanoferrites for magnetic fluid hyperthermia applications.

    PubMed

    Jeun, Minhong; Park, Sungwook; Jang, Gun Hyuk; Lee, Kwan Hyi

    2014-10-01

    A superparamagnetic nanoferrite (SPNF) with high magnetic moment, AC magnetically induced heating (AC-heating) capacity, and good biocompatibility is the most vital part of magnetic fluid hyperthermia for utilizing it in the clinics. Herein, we precisely tune magnetic properties and AC-heating characteristics of MgxMn1-xFe2O4 SPNF via chemically controlling the cations' concentration and distribution to develop a tailored MgxMn1-xFe2O4 SPNF as a potential magnetic fluid hyperthermia agent. The magnetic and AC-heating characteristics of the tailored MgxMn1-xFe2O4 SPNF are strongly dependent on the Mg/Mn cations' concentration and distribution, and Mg0.285Mn0.715Fe2O4 SPNF exhibits the highest saturation magnetization and AC-heating capacity as well as high biocompatibility.

  1. Universal heat conduction in Ce1 -xYbxCoIn5 : Evidence for robust nodal d -wave superconducting gap

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Dong, J. K.; Lum, I. K.; Zhang, J.; Hong, X. C.; He, L. P.; Wang, K. F.; Ma, Y. C.; Petrovic, C.; Maple, M. B.; Shu, L.; Li, S. Y.

    2016-02-01

    In the heavy-fermion superconductor Ce1 -xYbxCoIn5 , Yb doping was reported to cause a possible change from nodal d -wave superconductivity to a fully gapped d -wave molecular superfluid of composite pairs near x ≈0.07 (nominal value xnom=0.2 ). Here we present systematic thermal conductivity measurements on Ce1 -xYbxCoIn5 (x =0.013 , 0.084, and 0.163) single crystals. The observed finite residual linear term κ0/T is insensitive to Yb doping, verifying the universal heat conduction of the nodal d -wave superconducting gap in Ce1 -xYbxCoIn5 . Similar universal heat conduction is also observed in the CeCo (In1 -yCdy )5 system. These results reveal a robust nodal d -wave gap in CeCoIn5 upon Yb or Cd doping.

  2. X-ray photoelectron spectroscopy study of disordering in Gd2(Ti1-xZrx)2O7 pyrochlores.

    PubMed

    Chen, J; Lian, J; Wang, L M; Ewing, R C; Wang, R G; Pan, W

    2002-03-11

    The dramatic increases in ionic conductivity in Gd2(Ti1-xZrx)2O7 solid solution are related to disordering on the cation and anion lattices. Disordering in Gd2(Ti1-xZrx)2O7 was characterized using x-ray photoelectron spectroscopy (XPS). As Zr substitutes for Ti in Gd2Ti2O7 to form Gd2(Ti1-xZrx)2O7 (0.25 < x < or =0.75), the corresponding O 1s XPS spectrum merges into a single symmetric peak. This confirms that the cation antisite disorder occurs simultaneously with anion disorder. Furthermore, the O 1s XPS spectrum of Gd2Zr2O7 experimentally suggests the formation of a split vacancy.

  3. X-ray Photoelectron Spectroscopy Study of Disordering in Gd2(Ti1-xZrx)2O7 Pyrochlores

    NASA Astrophysics Data System (ADS)

    Chen, J.; Lian, J.; Wang, L. M.; Ewing, R. C.; Wang, R. G.; Pan, W.

    2002-03-01

    The dramatic increases in ionic conductivity in Gd2(Ti1-xZrx)2O7 solid solution are related to disordering on the cation and anion lattices. Disordering in Gd2(Ti1-xZrx)2O7 was characterized using x-ray photoelectron spectroscopy (XPS). As Zr substitutes for Ti in Gd2Ti2O7 to form Gd2(Ti1-xZrx)2O7 (0.25

  4. Magnetic and structural properties of MnCo1-xFexGe (0 ≤ x ≤ 0.12)

    NASA Astrophysics Data System (ADS)

    Ozono, Kosuke; Mitsui, Yoshifuru; Umetsu, Rie. Y.; Hiroi, Masahiko; Takahashi, Kohki; Koyama, Keiichi

    2016-08-01

    Structural, magnetic and thermal properties of ferromagnetic MnCo1-xFexGe (0 ≤ x ≤ 0.12) compounds were investigated. The Curie temperature TC and the martensitic transformation temperature TM of MnCoGe (x = 0) were determined to be 340 K and 510 K, respectively. With increasing x from 0 to 0.08, TM decreased and reached room temperature (290 K) for x ˜ 0.08. For x > 0.09, MnCo1-x Fex Ge did not exhibit the martensitic transformation. The compound for x ˜ 0.08 showed a first-order magnetic transition with a thermal hysteresis of 20 K and was accompanied by the martensitic transformation in the vicinity of room temperature. The phase diagram of MnCo1-x Fex Ge (0 ≤ x ≤ 0.12) is presented.

  5. Controllable synthesis of ZnxCd1-xS@ZnO core-shell nanorods with enhanced photocatalytic activity.

    PubMed

    Xie, Shilei; Lu, Xihong; Zhai, Teng; Gan, Jiayong; Li, Wei; Xu, Ming; Yu, Minghao; Zhang, Yuan-Ming; Tong, Yexiang

    2012-07-17

    We report the synthesis of Zn(x)Cd(1-x)S@ZnO nanorod arrays via a facile two-step process and the implementation of these core-shell nanorods as an environmental friendly and recyclable photocatalyst for methyl orange degradation. The band gap of Zn(x)Cd(1-x)S@ZnO core-shell nanorods can be readily tunable by adjusting the ratio of Zn/Cd during the synthesis. These Zn(x)Cd(1-x)S@ZnO core-shell nanorods exhibit a high photocatalytic activity and good stability in the degradation of the methyl orange. Moreover, these films grown on FTO substrates make the collection and recycle of the photocatalyst easier. These findings may open new opportunities for the design of effective, stable, and easy-recyclable photocatalytic materials.

  6. The characteristics of MBE-grown InxAl1-xN/GaN surface states

    NASA Astrophysics Data System (ADS)

    Jiao, Wenyuan; Kong, Wei; Li, Jincheng; Collar, Kristen; Kim, Tong-Ho; Losurdo, Maria; Brown, April S.

    2016-08-01

    The density and energy distribution of InxAl1-xN/GaN surface donor states are studied for InxAl1-xN structures with varying indium compositions. The results support a surface states model with a constant energy distribution of 2.17-2.63 eV below the conduction band minimum and a concentration of 4.64-8.27 × 1013 cm-2 eV-1. It is shown that the properties of the surface states are affected by the surface indium composition xs, as opposed to the bulk composition, xb (InxAl1-xN). Higher surface indium composition xs increases the density of surface states and narrows their energy distribution.

  7. Tailoring Mg(x)Mn(1-x)Fe(2)O(4) superparamagnetic nanoferrites for magnetic fluid hyperthermia applications.

    PubMed

    Jeun, Minhong; Park, Sungwook; Jang, Gun Hyuk; Lee, Kwan Hyi

    2014-10-01

    A superparamagnetic nanoferrite (SPNF) with high magnetic moment, AC magnetically induced heating (AC-heating) capacity, and good biocompatibility is the most vital part of magnetic fluid hyperthermia for utilizing it in the clinics. Herein, we precisely tune magnetic properties and AC-heating characteristics of MgxMn1-xFe2O4 SPNF via chemically controlling the cations' concentration and distribution to develop a tailored MgxMn1-xFe2O4 SPNF as a potential magnetic fluid hyperthermia agent. The magnetic and AC-heating characteristics of the tailored MgxMn1-xFe2O4 SPNF are strongly dependent on the Mg/Mn cations' concentration and distribution, and Mg0.285Mn0.715Fe2O4 SPNF exhibits the highest saturation magnetization and AC-heating capacity as well as high biocompatibility. PMID:25238143

  8. Spin-wave resonance in Ge{sub 1-x}Mn{sub x} films exhibiting percolation ferromagnetism

    SciTech Connect

    Dmitriev, A. I.; Morgunov, R. B. Kazakova, O. L.; Tanimoto, Y.

    2009-06-15

    Magnetic properties of Ge{sub 1-x}Mn{sub x} (x = 0.02, 0.04, 0.08) thin films obtained by ion-implanting Mn{sup +} ions into single-crystal Ge plates are investigated. The contributions of the subsystem of dispersed Mn{sup 2+} ions, Ge{sup 3}Mn{sup 5} ferromagnetic clusters, and Mn-enriched ferromagnetic domains of Ge to the magnetic moment of Ge{sub 1-x}Mn{sub x} films are distinguished. In the subsystem of dispersed Mn{sup 2+} ions in Ge{sub 1-x}Mn{sub x} films at temperatures below 10 K, a spin-wave resonance is observed in the magnetically ordered state due to percolation ferromagnetism. It is established that, in the films with percolation ferromagnetism, the exchange integrals determined from static measurements correspond to those determined by dynamic measurements.

  9. Inelastic x-ray scattering measurements of phonon dispersion and lifetimes in PbTe1-x Se x alloys.

    PubMed

    Tian, Zhiting; Li, Mingda; Ren, Zhensong; Ma, Hao; Alatas, Ahmet; Wilson, Stephen D; Li, Ju

    2015-09-23

    PbTe1-x Se x alloys are of special interest to thermoelectric applications. Inelastic x-ray scattering determination of phonon dispersion and lifetimes along the high symmetry directions for PbTe1-x Se x alloys are presented. By comparing with calculated results based on the virtual crystal model calculations combined with ab initio density functional theory, the validity of virtual crystal model is evaluated. The results indicate that the virtual crystal model is overall a good assumption for phonon frequencies and group velocities despite the softening of transverse acoustic phonon modes along [1 1 1] direction, while the treatment of lifetimes warrants caution. In addition, phonons remain a good description of vibrational modes in PbTe1-x Se x alloys.

  10. High Coke-Resistance Pt/Mg1-xNixO Catalyst for Dry Reforming of Methane.

    PubMed

    Al-Doghachi, Faris A J; Islam, Aminul; Zainal, Zulkarnain; Saiman, Mohd Izham; Embong, Zaidi; Taufiq-Yap, Yun Hin

    2016-01-01

    A highly active and stable nano structured Pt/Mg1-xNixO catalysts was developed by a simple co-precipitation method. The obtained Pt/Mg1-xNixO catalyst exhibited cubic structure nanocatalyst with a size of 50-80 nm and realized CH4 and CO2 conversions as high as 98% at 900°C with excellent stability in the dry reforming of methane. The characterization of catalyst was performed using various kinds of analytical techniques including XRD, BET, XRF, TPR-H2, TGA, TEM, FESEM, FT-IR, and XPS analyses. Characterization of spent catalyst further confirms that Pt/Mg1-xNixO catalyst has high coke-resistance for dry reforming. Thus, the catalyst demonstrated in this study, offers a promising catalyst for resolving the dilemma between dispersion and reducibility of supported metal, as well as activity and stability during high temperature reactions.

  11. X-ray absorption investigation of the valence state and electronic structure of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} in comparison with La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}

    SciTech Connect

    Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R.N.; Braun, A.; Graule, T.

    2011-12-15

    3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t{sub 2g}{sup Low-Asterisk} and a decrease in e{sub g}{sup Low-Asterisk} orbital occupancy, which is most accentuated in the LaCoO{sub 3} sample. Virtually no Co K-edge shift was observed for the La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially substituted by Ca{sup 2+} or Sr{sup 2+}. From the pre-edge features of these perovskites we are tended to conclude that the t{sub 2g}{sup Low-Asterisk} orbitals are less, and the e{sub g}{sup Low-Asterisk} orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3{sup +} in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites in fact increase as much as x increases. - Graphical abstract: Co K and Fe K pre-edge of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites one of the

  12. Facile growth and composition-dependent photocatalytic activity of flowerlike BiOCl1-xBrx hierarchical microspheres

    NASA Astrophysics Data System (ADS)

    Qin, Qin; Guo, Yingna; Zhou, Dandan; Yang, Yuxin; Guo, Yihang

    2016-12-01

    A group of nanosheet-assembled three-dimensional BiOCl1-xBrx hierarchical microspheres (x = 0, 0.3, 0.4, 0.5, 0.7, 0.8 and 1.0) with layered tetragonal crystal phase were prepared by 2-methoxyethanol-assisted solvothermal route and using ionic liquids as both halogen sources and structure-directing agent. By the combination of the results including XRD, XPS and UV-vis/DR spectra, lattice substitution of halogen atoms each other and then formation of BiOCl1-xBrx solid solution was evidenced. Additionally, the BiOCl1-xBrx microspheres exhibited interesting composition-dependent band gaps. The simulated sunlight and visible-light photocatalytic properties including degradation, mineralization and reusability of the BiOCl1-xBrx microspheres were evaluated by selecting p-nitrophenol (PNP) and tetrabromobisphenol-A (TBBPA) as the target pollutant compounds, finding that the balance between the suitable band gap and adequate potential of the valence band in BiOCl1-xBrx crystals dominated their photocatalytic activity. Additionally, the BiOCl1-xBrx microspheres with advantages such as enhanced photon utilization efficiency, larger BET surface area and favorable (110) exposed reactive surface gave the positive influence on their photocatalytic activity. Based on the results of photoelectrochemistry experiment and indirect chemical probe testing, direct •O2- and hVB+ photooxidation for the decomposition of PNP or TBBPA was revealed.

  13. Transmission Electron Microscopy (TEM) Sample Preparation of Si(1-x)Gex in c-Plane Sapphire Substrate

    NASA Technical Reports Server (NTRS)

    Kim, Hyun Jung; Choi, Sang H.; Bae, Hyung-Bin; Lee, Tae Woo

    2012-01-01

    The National Aeronautics and Space Administration-invented X-ray diffraction (XRD) methods, including the total defect density measurement method and the spatial wafer mapping method, have confirmed super hetero epitaxy growth for rhombohedral single crystalline silicon germanium (Si1-xGex) on a c-plane sapphire substrate. However, the XRD method cannot observe the surface morphology or roughness because of the method s limited resolution. Therefore the authors used transmission electron microscopy (TEM) with samples prepared in two ways, the focused ion beam (FIB) method and the tripod method to study the structure between Si1-xGex and sapphire substrate and Si1?xGex itself. The sample preparation for TEM should be as fast as possible so that the sample should contain few or no artifacts induced by the preparation. The standard sample preparation method of mechanical polishing often requires a relatively long ion milling time (several hours), which increases the probability of inducing defects into the sample. The TEM sampling of the Si1-xGex on sapphire is also difficult because of the sapphire s high hardness and mechanical instability. The FIB method and the tripod method eliminate both problems when performing a cross-section TEM sampling of Si1-xGex on c-plane sapphire, which shows the surface morphology, the interface between film and substrate, and the crystal structure of the film. This paper explains the FIB sampling method and the tripod sampling method, and why sampling Si1-xGex, on a sapphire substrate with TEM, is necessary.

  14. Crystal structure and Raman scattering characterization of Cu2Fe1-xCoxSnS4 chalcogenide compounds

    NASA Astrophysics Data System (ADS)

    López-Vergara, F.; Galdámez, A.; Manríquez, V.; González, Guillermo

    2015-11-01

    This work reports the synthesis by solid-state reaction of Cu2Fe1-xCoxSnS4 solid solutions. Crystal structures of Cu2Fe0.8Co0.2SnS4 and Cu2Fe0.6Co0.4SnS4 were investigated by single crystal X-ray diffraction. Both phases crystallize in the tetragonal stannite-type structure. The volume of the tetrahedral [MS4] (M = Fe, Co) presented the highest distortion, with Edge-Length Distortion (ELD) indices ˜2% from the ideal tetrahedron. The powder X-ray diffraction (XRD) patterns of Cu2Fe1-xCoxSnS4 (x = 0.2, 0.4, 0.6 and 0.8) has been refined by Rietveld method. No secondary phases were detected in XRD patterns. An analysis of the vibrational properties of Cu2Fe1-xCoxSnS4 was performed using Raman scattering measurements. The Raman peaks were analyzed by fitting of the spectra and subsequently identifying the vibrational modes by comparison with experimental and theoretical data from Cu2FeSnS4 (CFTS) and Cu2CoSnS4 (CCTS) end-members. The spectra from Cu2Fe1-xCoxSnS4 show that there is a variation in the frequency of the main A1 peak at ˜320 cm-1 together with a decrease in the secondary mode intensity at ˜285 cm-1. Full Width at Half Maximum (FWHM) and the intensity of the Raman peaks reflect the high crystallinity of Cu2Fe1-xCoxSnS4 solid solutions. The oxidation states of the metals were confirmed by temperature-dependent magnetization measurements performed in the antiferromagnetic Cu2Fe1-xCoxSnS4 solid solutions.

  15. Effects of varying indium composition on the thermoelectric properties of In x Ga1- x Sb ternary alloys

    NASA Astrophysics Data System (ADS)

    Nirmal Kumar, V.; Arivanandan, M.; Koyoma, T.; Udono, H.; Inatomi, Y.; Hayakawa, Y.

    2016-10-01

    In x Ga1- x Sb ( x = 0-1), a III-V ternary alloy, was grown by melt solidification process. The effects of varying indium composition on the thermoelectric properties of In x Ga1- x Sb polycrystals were studied for the first time. The segregations of indium and gallium elements were observed in the grown crystals, and the defects present in crystals were revealed by etching process. Room-temperature Raman measurement revealed that the dominant optical modes of phonon vibrations in InSb and GaSb binaries were suppressed in In x Ga1- x Sb ternaries. The in-phase vibrations of acoustic mode phonons were scattered more effectively in In x Ga1- x Sb by the present defects, and the relative value of lattice thermal conductivity was reduced. Thus, the thermal conductivity of InSb and GaSb binaries was drastically reduced in In x Ga1- x Sb by alloy scattering. InSb indicated the highest ZT 0.51 because of its higher power factor 70 µW/cmK2. Next to InSb, In0.8Ga0.2Sb had higher ZT value of 0.29 at 600 K among the In x Ga1- x Sb ternaries. The ZT of In0.8Ga0.2Sb was increased about 30 times than that of GaSb by the increase of power factor as well as the decrease of thermal conductivity.

  16. Glassy ferromagnetism and magnetic phase separation in La1-xSrxCoO3

    NASA Astrophysics Data System (ADS)

    Wu, J.; Leighton, C.

    2003-05-01

    We present the results of a comprehensive investigation of the dc magnetization, ac susceptibility, and magnetotransport properties of the glassy ferromagnet La1-xSrxCoO3. The compositions studied span the range from the end-member LaCoO3 (x=0.0) through to x=0.7. These materials have attracted attention recently, primarily due to the spin-state transition phenomena in LaCoO3 and the unusual nature of the magnetic ground state for finite x. In this paper we present a consistent picture of the magnetic behavior of La1-xSrxCoO3 in terms of short-range ferromagnetic ordering and intrinsic phase separation. At high Sr doping (x>0.2) the system exhibits unconventional ferromagnetism (with a Curie temperature up to 250 K), which is interpreted in terms of the coalescence of short-range-ordered ferromagnetic clusters. Brillouin function fits to the temperature dependence of the magnetization as well as high-temperature Curie-Weiss behavior suggest that the Co3+ and Co4+ ions are both in the intermediate spin state. At lower Sr doping (x<0.18) the system enters a mixed phase that displays the characteristics of both a spin glass and a ferromagnet. A cusp in the zero-field-cooled dc magnetization, a frequency-dependent peak in the ac susceptibility and time-dependent effects in both dc and ac magnetic properties all point towards glassy behavior. On the other hand, field cooling results in a relatively large ferromagneticlike moment, with zero-field-cooled and field-cooled magnetizations bifurcating at an irreversibility point. Even in the region above x=0.2 the out-of-phase component of the ac susceptibility shows frequency-dependent peaks below the Curie temperature (indicative of glassy behavior) which have previously been interpreted in terms of the freezing of clusters. All of the results are consistent with the existence of a strong tendency towards magnetic phase separation in this material, a conclusion which is further reinforced by consideration of the electronic

  17. Effects of Structure on Magnetic Properties in La1-xSrxMnO3

    NASA Astrophysics Data System (ADS)

    Louca, Despo; Egami, Takeshi

    1996-03-01

    Pair Distribution Function (PDF) analysis was carried out on pulsed neutron powder diffaction data of x=0 and x=0.15 Sr-doped La1-xSrxMnO3 to study the local structure as a function of temperature. In the undoped case, strong Jahn-Teller (JT) distortions are observed with an elongation of x or y-axes. This has been established crystallographically and confirmed by PDF. A split in the PDF peak of the nearest neighbor Mn-O pairs is observed at 2.0 and 2.2 A with the ratio of 2:1. In the doped case, x=0.15, two levels of JT distor- tions are observed. At low temperatures, JT distortions are reduced by do- ping in the crystallographic picture, but PDF shows that some sites are dis- torted and some are not. As a result, the 2.0 A peak remains but the 2.2 A peak gets weaker. Ar room temperature, another secondary JT effect is obser- ved. This is seen by the breaking of symmetry between two undistorted dire- ctions. Real space refinement suggested the displacement of the B cation, Mn. At this temperature, in addition to the low T effects, splitting of the 2.0 A peak is observed to 1.89 A and 2.06 A. This is the first observance of such a structural change. This structural change should have huge effects on the change of resistivity at the Curie temperature. Physical implications will be discussed. This work was supported by NSF DMR93-00728.

  18. Evolution of magnetic structures in NpAs1-xSex solid solutions

    NASA Astrophysics Data System (ADS)

    Bombardi, A.; Bourdarot, F.; Burlet, P.; Sanchez, J. P.; Vulliet, P.; Colineau, E.; Rebizant, J.; Wastin, F.; Lander, G. H.; Vogt, O.; Mattenberger, K.

    2000-12-01

    We report Mössbauer spectroscopy, magnetization, and neutron-diffraction measurements on four samples (x=0.05, 0.10, 0.15, and 0.20) in the mixed system NpAs1-xSex. The evolution of magnetic phase diagram vs the temperature T and the Se concentration x has been determined. Up to x=0.15, three distinct phase transitions are present. The first antiferromagnetic (AF) at TN(x) is from paramagnetism to an incommensurate phase, the second, at TC(x), is to a ferromagnetic (FM) phase, the third at Tm(x) is from pure FM to a mixed phase where AF and FM ordering coexist along perpendicular directions. The temperatures of the transitions are functions of Se concentration x. The incommensurate structure is described by a longitudinal amplitude modulated sinusoidal wave with a wave vector k--> in the range (0 0 0.14-0.24) that is shifted toward the center of the Brillouin zone with increasing x. A squaring up of this wave, if present, is too small to be detected. At TC(x) all Np sites become equivalent and the moment directions become <1 1 1>. Surprisingly, at Tm(x) AF interactions again become important and cause the moments to rotate and to align along <221> directions. Measurements in an external magnetic field up to 4.8 T have allowed us to determine the 1k--> nature of the AF component for T

  19. Electroweak theory based on S U (4 )L⊗U (1 )X gauge group

    NASA Astrophysics Data System (ADS)

    Long, H. N.; Hue, L. T.; Loi, D. V.

    2016-07-01

    This paper includes two main parts. In the first part, we present generalized gauge models based on the S U (3 )C⊗S U (4 )L⊗U (1 )X (3-4-1) gauge group with arbitrary electric charges of exotic leptons. The mixing matrix of neutral gauge bosons is analyzed, and the eigenmasses and eigenstates are obtained. The anomaly-free as well as matching conditions are discussed precisely. In the second part, we present a new development of the original 3-4-1 model [R. Foot, H. N. Long, and T. A. Tran, Phys. Rev. D 50, R34 (1994), F. Pisano and V. Pleitez, Phys. Rev. D 51, 3865 (1995).]. Different from previous works, in this paper the neutrinos, with the help of the scalar decuplet H , get the Dirac masses at the tree level. The vacuum expectation value (VEV) of the Higgs boson field in the decuplet H acquiring the VEV responsible for neutrino Dirac mass leads to mixing in separated pairs of singly charged gauge bosons, namely the Standard Model (SM) W boson and K , the new gauge boson acting in the right-handed lepton sector, as well as the singly charged bileptons X and Y . Due to the mixing, there occurs a right-handed current carried by the W boson. From the expression of the electromagnetic coupling constant, ones get the limit of the sine-squared of the Weinberg angle, sin2θW<0.25 , and a constraint on electric charges of extra leptons. In the limit of lepton number conservation, the Higgs sector contains all massless Goldstone bosons for massive gauge bosons and the SM-like Higgs boson. Some phenomenology is discussed.

  20. Characterization of La1-xSrxMnO3 perovskite catalysts for hydrogen peroxide reduction.

    PubMed

    Yunphuttha, C; Porntheeraphat, S; Wongchaisuwat, A; Tangbunsuk, S; Marr, D W M; Viravathana, P

    2016-06-22

    We investigated the crystalline phase and electronic structure of perovskite-type La1-xSrxMnO3 (0.0 ≤ x ≤ 1.0) (LSMx) catalysts synthesized via the citric sol-gel route, for H2O2 reduction. The resulting materials were characterized by XRD, XANES, TR-XANES, and TPO and, after calcination, consisted of cubic perovskite for 0.0 ≤ x ≤ 0.8 and hexagonal perovskite for x = 1.0. Mn species in the precalcined catalysts were oxidized to Mn(3+) for x = 0.0 to 0.6 and to Mn(2+) for x = 0.8 and 1.0. After calcination, Mn species were present in a mixed oxidation state of Mn(3+)/Mn(4+), while Sr(2+) and La(3+) were not altered. TR-XANES and TPO showed that Mn species were oxidized at 210-220 °C and formed active perovskites LSM0.4 and LSM0.0 at 580 °C and 640 °C. This shows that Sr doping can reduce the oxidation temperature of LSMx with 0.2 ≤ x ≤ 0.4. However, the concentration of Mn(4+) in LSMx is increased which is useful for enhancing their catalytic activity and stability. When tested in an alkaline electrolyte, LSM0.6 containing the optimum Mn(4+)/Mn(3+) ratio promoted the formation of hydroxyl via the oxygen intercalation reaction and exhibited low polarization resistance and the highest catalytic activity for H2O2 reduction. PMID:27271119

  1. High temperature operation In1-xAlxSb infrared focal plane

    NASA Astrophysics Data System (ADS)

    Lyu, Yanqiu; Si, Junjie; Cao, Xiancun; Zhang, Liang; Peng, Zhenyu; Ding, Jiaxin; Yao, Guansheng; Zhang, Xiaolei; Reobrazhenskiy, Valeriy

    2016-05-01

    A high temperature operation mid-wavelength 128×128 infrared focal plane arrays (FPA) based on low Al component In1-xAlxSb was presented in this work. InAlSb materials were grown on InSb (100) substrates using MBE technology, which was confirmed by XRD and AFM analyses. We have designed and grown two structures with and without barrier. The pixel of the detector had a conventional PIN structure with a size of 50μmx50μm. The device fabrication process consisted of mesa etching, passivation, metallization and flip-chip hybridization with readout integrated circuit (ROIC), epoxy backfill, lap and polish. Diode resistance, imaging, NETD and operability results are presented for a progression of structures that reduce the diode leakage current as the temperature is raised above 80K. These include addition of a thin region of InAlSb to reduce p-contact leakage current, and construction of the whole device from InAlSb to reduce thermal generation in the active region of the detector. An increase in temperature to 110K, whilst maintaining full 80K performance, is achieved. The I-V curves were measured at different temperature. Quantum efficiency, pixel operability, non-uniformity, and the mean NETD values of the FPAs were measured at 110K. This gives the prospect of significant benefits for the cooling systems, including, for example, use of argon in Joule-Thomson coolers or an increase in the life and/or decrease in the cost, power consumption and cool-down time of Stirling engines by several tens of percent.

  2. Characterization of La1-xSrxMnO3 perovskite catalysts for hydrogen peroxide reduction.

    PubMed

    Yunphuttha, C; Porntheeraphat, S; Wongchaisuwat, A; Tangbunsuk, S; Marr, D W M; Viravathana, P

    2016-06-22

    We investigated the crystalline phase and electronic structure of perovskite-type La1-xSrxMnO3 (0.0 ≤ x ≤ 1.0) (LSMx) catalysts synthesized via the citric sol-gel route, for H2O2 reduction. The resulting materials were characterized by XRD, XANES, TR-XANES, and TPO and, after calcination, consisted of cubic perovskite for 0.0 ≤ x ≤ 0.8 and hexagonal perovskite for x = 1.0. Mn species in the precalcined catalysts were oxidized to Mn(3+) for x = 0.0 to 0.6 and to Mn(2+) for x = 0.8 and 1.0. After calcination, Mn species were present in a mixed oxidation state of Mn(3+)/Mn(4+), while Sr(2+) and La(3+) were not altered. TR-XANES and TPO showed that Mn species were oxidized at 210-220 °C and formed active perovskites LSM0.4 and LSM0.0 at 580 °C and 640 °C. This shows that Sr doping can reduce the oxidation temperature of LSMx with 0.2 ≤ x ≤ 0.4. However, the concentration of Mn(4+) in LSMx is increased which is useful for enhancing their catalytic activity and stability. When tested in an alkaline electrolyte, LSM0.6 containing the optimum Mn(4+)/Mn(3+) ratio promoted the formation of hydroxyl via the oxygen intercalation reaction and exhibited low polarization resistance and the highest catalytic activity for H2O2 reduction.

  3. Anisotropic perpendicular axis magnetostriction in twinned TbxDy1 - xFe1.95

    NASA Astrophysics Data System (ADS)

    Teter, J. P.; Wun-Fogle, M.; Clark, A. E.; Mahoney, K.

    1990-05-01

    The longitudinal magnetostriction (Δl/l) for twinned TbxDy1-xFe1.95 material, prepared by the free-standing float-zone method, has been previously measured and found to be very large (2000×10-6) at room temperature. The magnetostrictions for the [111] and [11¯0] crystallographic axes perpendicular to the applied stress and magnetic-field [112¯] direction are presented as functions of temperature, applied stress, and applied magnetic field. The temperature range is ±60 °C centered about the anisotropy compensation temperature of Terfenol-D (+10 °C). The stress ranges from 2 to 32 MPa and the magnetic field to ±2000 Oe. The temperature dependence of the perpendicular axes magnetostriction is similar to that of the conventional magnetostriction measured parallel to the [112¯] growth axis. Relative values for the saturation magnetostriction exhibit a large anisotropy in the perpendicular direction, ranging from -117% for the [111] to +19% for the [11¯0] direction. This ratio stays constant as a function of temperature above the compensation temperature for a given prestress above 8 MPa. The largest absolute value of magnetostriction (2260×10-6) occurs in the [111] direction at 10 °C at a prestress pressure of 12 MPa. Above this temperature the magnetostriction falls at a rate of -8.5×10-6/°C. The volume magnetostriction is shown to be small and highly sample dependent. All data is consistent with the parent-twin magnetization model and also the magnetostriction values along nonprincipal axes.

  4. Magnetoelastic properties of substituted Er1-xGdxMn6Sn6 intermetallic system

    NASA Astrophysics Data System (ADS)

    Tabatabai Yazdi, Sh.; Tajabor, N.; Roknabadi, M. Rezaee; Behdani, M.; Pourarian, F.

    2014-06-01

    The forced magnetostriction of polycrystalline samples of Er1-xGdxMn6Sn6 (0≤x≤1) intermetallics with hexagonal HfFe6Ge6-type structure is investigated in the temperature range of 77-480 K. Gd substitution has a significant effect on interatomic distances and especially on inter-sublattice R-Mn couplings. The replacement of Er by Gd results in increasing the ordering temperature followed by reinforcement of the R-Mn coupling, as well as decreasing the magnetostriction values owing to the S-state character of Gd3+ ions. The results show that the contribution of Er sublattice to anisotropic magnetoelastic effects is positive, while that of Gd and Mn is negative. All the examined samples exhibit considerable magnetovolume anomalies at the ordering temperature (TC=338, 381, 412 and 434 K for the samples with x=0, 0.2, 0.6 and 1.0, respectively). While the unsubstituted sample exhibits metamagnetic transitions, Gd-contained compounds do not show this behavior, owing to the strong Gd-Mn coupling. The experimental results obtained are discussed in the framework of the two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in these layered compounds. From the temperature dependence of magnetostriction values and considering the magnetostriction equation for a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for these compounds and the influence of Gd substitution on them.

  5. Magnetism of the solid solution GdGa1 - xGex (abstract)

    NASA Astrophysics Data System (ADS)

    Leithe-Jasper, A.; Hiebl, K.

    1996-04-01

    Ternary metal excess rare-earth gallides and germanides have been extensively investigated concerning their interesting physical properties with respect to magnetic and electronic correlations, such as magnetic ordering, intermediate valency, Kondo or heavy fermion behavior. A solid solution of the binary phases GdGa and GdGe was found investigating the phase equilibria in the pseudobinary system Gd-Ga-Ge at T=800 °C. Samples with the composition GdGa1-xGex (x=0, 0.1, 0.15, 0.25, 0.5) were prepared by arc melting the elements under inert atmosphere and subsequent annealing (350 h) in evacuated silica capsules. The crystal structure and unit-cell dimensions were determined by x-ray powder analyses (Guinier technique, Cu Kα1 radiation). Powder patterns were indexed on the basis of a C-centered orthorhombic unit cell. No deviations of the structure type α-ITI (CrB) have been encountered. A monotonic decrease of the unit-cell volume versus Ge concentration is observed. However, a significant decrease of the b and c parameters is thereby compensated by an increase of the a parameter. Magnetic measurements were performed by SQUID and ac techniques over a temperature range T=5-300 K and in external fields up to 6 T. All samples exhibit ferromagnetic order with slightly decreasing Tc as well as values of magnetization (at T=5 K and H=0.1 T) with increasing concentration x. However, metamagnetic transitions are revealed for all samples with x≳0. The results are discussed within the concept of indirect exchange interaction (RKKY-type interaction).

  6. Massive free-space optical 1xN fiber switch using an adaptive membrane mirror

    NASA Astrophysics Data System (ADS)

    Gonte, Frederic; Peter, Yves-Alain; Herzig, Hans Peter; Daendliker, Rene

    2002-02-01

    We present a 1xN switch for single mode fiber optical communication systems, which is composed of an array of fibers, an achromatic lens, and an adaptive membrane mirror. The working principle of the optical switch is as follows: the center fiber of the array delivers the input signal, this signal is collimated by the lens, back reflected on the membrane mirror and refocused by the lens to an other fiber. The addressing of the receiving fiber is made by lateral displacement of the lens. However, using the achromatic lens under off-axis conditions introduces aberrations, which cause coupling losses to the receiving single-mode fibers. The deformable membrane mirror is used to adaptively correct these aberrations. The optimization of the coupling efficiency is made with the help of a genetic algorithm. For each position of the lens, the optimized voltages on the electrodes of the membrane mirror can be stored during the calibration procedure and afterwards recalled during operation of the switch. A demonstrator has been set up with a commercially available linear array of 32 single-mode fibers disposed in V-grooves, an achromatic lens mounted on a two-dimensional translation stage, and a membrane mirror made of silicon nitride coated with aluminum and electro-statically activated by thirty-seven electrodes. To demonstrate the capabilities of the aberration correction we used the first fiber in the array as input fiber and optimized the coupling efficiency to all the other fibers in the array. We obtained insertion losses of less than 3 dB and a cross talk below 30 dB. These results prove the feasibility to build a switch with a two-dimensional array of more than 1000 addressable fibers.

  7. Growth Mechanism and Some Properties of Cd1-xMnx Se Semimagnetic Semiconductor Thin Films

    NASA Astrophysics Data System (ADS)

    Karande, V. S.; Mane, S. H.; Pujari, V. B.; Deshmukh, Lalasaheb P.

    2003-11-01

    (Cd, Mn) Se dilute semiconductor or semimagnetic semiconductors have recently became the focus of intense research due to their interesting combination of magnetic and semiconducting properties, and are employed in a variety of devices including solar cells, gas sensors etc. A series of thin films of this material, Cd1 - xMnxSe (0 ≤ x ≤ 0.5), were therefore synthesized onto precleaned amorphous glass substrates using a solution growth technique. The sources of cadmium (Cd2+) and manganese (Mn2+) were aqueous solutions of cadmium sulphate and manganese sulphate, and selenium (Se2-) was extracted from a reflux of sodium selenosulphite. The different deposition parameters such as temperature, time of deposition, speed of mechanical churning, pH of the reaction mixture etc were optimized to yield good quality deposits. The as-grown samples were thin, relatively uniform, smooth and tightly adherent to the substrate support. The colour of the deposits changed from deep red-orange to yellowish-orange as the composition parameter, x, was varied from 0 to 0.5. The terminal layer thickness decreased with increasing value of, x. The optical energy gap decreased from 1.84 eV to 1.34 eV for the chang e of x from 0 to 0.5. The coefficient of optical absorption a is of the order of 104 - 105 cm-1 and the type of transition (m \\cong 0.5) is of the band-to-band direct type. The dc electrical conductivities were measured at room temperature and in the temperature range 300 K - 500 K. It was observed that the room temperature electrical conductivity increased with the composition parameter x up to 0.1, gradually decreasing thereafter. The thermo power measurements showed n-type conduction in these films.

  8. Importance of uniaxial compression for the appearance of superconductivity in NdO1-xFxBiS2

    NASA Astrophysics Data System (ADS)

    A, Omachi; T, Hiroi; J, Kajitani; O, Miura; Y, Mizuguchi

    2014-05-01

    We have investigated the crystal structure and superconducting properties of the new layered superconductor NdO1-xFxBiS2. Bulk superconductivity with a Tc above 4.5 K was observed. It was found that the Tc depended on both F concentration and crystal structure. Uniaxial compression along the c axis upon F substitution seemed to be linked with the appearance of bulk superconductivity. Furthermore, we considered that a higher Tc can be achieved when the c/a parameter was optimized in the NdO1-xFxBiS2 system.

  9. Double-Peak Emission Rate Spectrum of DX-Centers in AlxGa1-xAs

    NASA Astrophysics Data System (ADS)

    Fudamoto, Michihiro; Tahira, Kenichiro; Tashiro, Syuuji; Morimoto, Jun; Miyakawa, Toru

    1989-10-01

    Emission rate spectra S(λ) of the DX-centers in AlxGa1-xAs were studied for dopants, such as Te, Sn, Si and Se, using the SADLTS (spectral analysis of deep level transient spectroscopy) method. The double peak emission rate spectra were observed for these DX-centers in AlxGa1-xAs at around x{=}0.5 of Al mole fraction. The band effect (crossover of L-band and \\varGamma-band) is the dominant contribution to the rather broadened spectra of DX-centers appearing in the conventional DLTS.

  10. DX Deep Centers in AlxGa1-xAs Grown by Liquid-Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Tachikawa, Masami; Mizuta, Masashi; Kukimoto, Hiroshi

    1984-12-01

    Deep levels, the so-called DX centers, in the AlxGa1-xAs alloy system grown by liquid-phase epitaxy (LPE) were investigated by junction-capacitance spectroscopy. The dependence of the activation energy of the DX center in Sn-doped AlxGa1-xAs on the alloy composition was determined by DLTS. This dependence seems to reflect the change in the nature of the conduction bands in this alloy system. The other donor species studied: Si, Te and Se, were also found to form DX centers. An anomalously high concentration of DX centers was determined using low-temperature C-V techniques.

  11. Direct imaging of doped fluorine in LaFeAsO1-xFx superconductor by atomic scale spectroscopy

    NASA Astrophysics Data System (ADS)

    Tohei, Tetsuya; Mizoguchi, Teruyasu; Hiramatsu, Hidenori; Kamihara, Yoichi; Hosono, Hideo; Ikuhara, Yuichi

    2009-11-01

    We report direct observation of fluorine ion dopants in the recently discovered LaFeAsO1-xFx superconductor, where the doping is critical for the superconductivity. Employing spectroscopic imaging based on scanning transmission electron microscopy, the spatial distribution of the doped fluorine ions, which are invisible in Z-contrast imaging, is clearly visualized with atomic-scale resolution. The observation directly proves that fluorine substitutes into the oxygen site in the superconducting LaFeAsO1-xFx compound. Our results demonstrate the potential of the present method for revealing dopants undetectable by conventional microscopy imaging.

  12. The Influence of Sublimated Aluminium Films on the Properties of Real Cdx Hg1-xTe Surface

    NASA Astrophysics Data System (ADS)

    Guseinov, Emil; Ismailov, Namýk; Tezer, Ateþ

    1996-05-01

    The electron properties of the Al-Cdx Hg1-x Te interface have been studied using conventional C-V, I-V measurements, spectral dependece of the photoconductivity, capacitor photolocomitive force and the photoelectromagnetic effect. A significant change of the spectral dependence of photoconductivity and the surface lifetime of charge carriers in Cdx Hg1-xTe samples covered by aluminium films has been revealed. The results obtained were interpreted by the influence of space charge region (SCR) on the photoconductivity.

  13. Variation of refractive index in strained In(x)Ga(1-x)As-GaAs heterostructures

    NASA Technical Reports Server (NTRS)

    Das, U.; Bhattacharya, P. K.

    1986-01-01

    In(x)Ga(1-x)As-GaAs heterostructures and strained-layer superlattices can be used as optical waveguides. For such applications it is important to know explicitly the refractive index variation with mismatch strain and with alloying in the ternary layer. Starting from the Kramers-Kronig integral dispersion relations, a model has been developed from which the refractive index change in the ternary layer of In(x)Ga(1-x)As-GaAs heterojunctions can be calculated. The results are presented and discussed. The expected changes in a superlattice have been qualitatively predicted.

  14. Evidence of Inhomogeneous Superconductivity in FeTe1-xSex by Scotch-Tape Method

    NASA Astrophysics Data System (ADS)

    Okazaki, Hiroyuki; Watanabe, Tohru; Yamaguchi, Takahide; Kawasaki, Yasuna; Deguchi, Keita; Demura, Satoshi; Ozaki, Toshinori; Denholme, Saleem. J.; Mizuguchi, Yoshikazu; Takeya, Hiroyuki; Takano, Yoshihiko

    2012-11-01

    We have fabricated thin films of FeTe1-xSex using a scotch-tape method. The superconductivities of the thin films are different from each other although these films were fabricated from the same bulk sample. The result clearly presents the inhomogeneous superconductivity in FeTe1-xSex. The difference might arise from inhomogeneity due to the excess Fe concentration. The resistivity of a thin film with low excess Fe shows good superconductivity with the sharp superconducting-transition width and more isotropic superconductivity.

  15. Preparation and physical properties of (M1-xYbx) Fe2As2 (M = Ca, Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Chen, S. C.; Syu, K. J.; Lee, W. H.; Chen, Y. Y.

    2014-03-01

    As judged by x-ray diffraction data, single crystals in the series (M1-xYbx) Fe2As2 (M = Ca, Ba) with 0 < x <0.22 have been made by flux method. Magnetic and electrical properties as well as the specific heat data in the systems (M1-xYbx) Fe2As2 (M = Ca, Ba) investigated will be discussed. Supported by the National Science Council of Republic of China under Contract Number NSC-102-2112-M-194-005-MY3.

  16. Ultrasensitive Thin-Film-Based Alx Ga1-x N Piezotronic Strain Sensors via Alloying-Enhanced Piezoelectric Potential.

    PubMed

    Wang, Chao-Hung; Lai, Kun-Yu; Li, Yi-Chang; Chen, Yen-Chih; Liu, Chuan-Pu

    2015-10-28

    Alx Ga1-x N thin-film-based piezotronic strain sensors with ultrahigh strain sensitivity are fabricated through alloying of AlN with GaN. The strain sensitivity of the ternary compound Alx Ga1-x N is higher than those of the individual binary compounds GaN and AlN. Such a high performance can be attributed to the piezoelectric constant enhancement via intercalation of Al atoms into the GaN matrix, the effect of residual strain, and a suppressed screening effect.

  17. Resonant tunneling in the ZnO/Zn1-xCdxO/ZnO double barrier structures: Theoretical study

    NASA Astrophysics Data System (ADS)

    Shtepliuk, I. I.

    2014-07-01

    Numerical simulations of Zn1-xCdxO/ZnO-based resonant tunneling diode structures are presented, employing the transfer matrix formalism and the Tsu-Esaki model. The factors influencing on the effective electron mass of the two-dimensional electron gas in the Zn1-xCdxO/ZnO heterointerface - a conduction band nonparabolicity, a quantum confinement and a polaron effect - were analyzed and evaluated. The simulated current-voltage characteristics show a strong dependence on a well width, a barrier thickness and an internal electric field induced by a spontaneous and a piezoelectric polarization.

  18. Voltage-Controlled Emission Wavelength Switching in a Pseudomorphic Si1-xGex/Si Double Quantum Well

    NASA Astrophysics Data System (ADS)

    Yasuhara, Nozomu; Fukatsu, S.

    2004-04-01

    Voltage-controlled emission wavelength switching (VCEWS) is demonstrated in a pseudomorphic Si1-xGex/Si double quantum well (DQW). Under cw excitation, photoluminescence (PL) of the DQW was found to exhibit a clear switchover of emission wavelengths under longitudinal electric field, where an extinction ratio of more than 100 was obtained. In the time domain, antiphase oscillations of PL decays synchronized with the polarity switch of driving voltages were observed. The unique band line-up of pseudomorphic Si1-xGex/Si QWs which makes loosely bound electrons susceptible to longitudinal electric fields underlies the operation of VCEWS.

  19. Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds

    NASA Astrophysics Data System (ADS)

    Berenov, A.; Le Goupil, F.; Alford, N.

    2016-06-01

    A series of Ba1-x-ySrxCayTiO3 compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, TC, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO6 octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of TC. The effects of A-site ionic radii on the temperatures of phase transitions in Ba1-x-ySrxCayTiO3 were discussed.

  20. Spin glass instead of superconductivity in Ba(Fe1-xCrx/2Nix/2)2As2

    NASA Astrophysics Data System (ADS)

    Xu, Sheng-Gao; Sun, Yun-Lei; Jiang, Shuai; Xing, Hui; Jiao, Lin; Yuan, Hui-Qiu; Feng, Chun-Mu; Xu, Zhu-An; Cao, Guang-Han

    2012-12-01

    We have studied an “isoelectronic” Fe-site doping with Cr and Ni in Ba(Fe1-xCrx/2Nix/2)2As2 system. With increasing x, the antiferromagnetic SDW in the parent compound is suppressed quickly. Spin glass state emerges in the range of 0.1 <= x < 0.2. The spin glass state evolves into cluster glass with further doping, and finally becomes ferromagnetism at x = 1.0. No superconductivity was observed down to 0.5 K. The electronic phase diagram is established, and the underlying physics is discussed.