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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. Amorphization of Ti1- x Mn x

    NASA Astrophysics Data System (ADS)

    Chu, B.-L.; Chen, C.-C.; Perng, T.-P.

    1992-08-01

    Three amorphous Ti1- x Mn x alloy powders, with x = 0.4, 0.5, and 0.6, were prepared by mechanical alloying (MA) of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by X-ray diffraction (XRD) and high-resolution transmission elec- tron microscopy (HRTEM). The crystallization temperatures for these alloys detected by dif- ferential scanning calorimetry (DSC) varied from 769 to 830 K. The calculated enthalpies of mixing in these amorphous phases are relatively small compared with those for other Ti-base binary alloys. The criteria for solid-state amorphization reaction are examined. It is suggested that the kinetics of nucleation and growth favors the formation of the amorphous phases and the supply of atoms for nucleation and growth is predominantly through the defective regions induced by MA.

  4. 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.

  5. 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.

  6. A case of pregnancy complicated with dilated cardiomyopathy 1X

    PubMed Central

    Oki, Shinya; Nagamatsu, Takeshi; Iriyama, Takayuki; Komatsu, Atsushi; Osuga, Yutaka; Fujii, Tomoyuki

    2015-01-01

    Dilated cardiomyopathy 1X (CMD1X) is characterized by dilated cardiomyopathy (DCM) with mildest limb-girdle muscle symptoms and normal intelligence. Compound heterozygous mutation in fukutin gene is known as its genetic cause. Here, we report a pregnancy case complicated with CMD1X. A 25-year-old primiparous woman, who had been diagnosed as CMD1X at the age of 19, was referred to our hospital at 6 weeks of gestation. In early pregnancy, the evaluation of her cardiac function showed ejection fraction 47% and NYHA class II. Worsening of cardiac function was observed from 30 weeks, manifesting reduced cardiac load with left ventricular dilatation and in-hospital bed rest was necessary. Elective cesarean section was performed at 35 weeks to prevent deterioration of cardiac function. The parameters of her cardiac function returned to the pre-pregnancy status in a month after delivery, whereas she realized persistent worsening of muscular weakness at postpartum. PMID:26566449

  7. Thermal conductivity of K1-xLixTaO3 and KTa1-xNbxO3

    NASA Astrophysics Data System (ADS)

    Tachibana, Makoto

    2015-11-01

    Thermal conductivity data between 1.8 and 300 K are reported for K1-xLixTaO3 (0≤x≤0.03) and KTa1-xNbxO3 (0≤x≤0.16) single crystals. Whereas lightly Li- and Nb-doped crystals exhibit relaxor-like behavior in dielectric susceptibility, they do not show the glasslike thermal transport found in conventional relaxors such as PbMg1/3Nb2/3O3 and Na1/2Bi1/2TiO3. The lack of glasslike behavior in K1-xLixTaO3 and KTa1-xNbxO3 is confirmed by the absence of temperature-linear contribution in heat capacity.

  8. Average and Local Crystal Structures of (Ga(1-x)Znx)(N(1-x)Ox) Solid Solution Nanoparticles.

    PubMed

    Feygenson, Mikhail; Neuefeind, Joerg C; Tyson, Trevor A; Schieber, Natalie; Han, Wei-Qiang

    2015-12-01

    We report a comprehensive study of the crystal structure of (Ga(1-x)Znx)(N(1-x)Ox) solid solution nanoparticles by means of neutron and synchrotron X-ray scattering. In our study, we used four different types of (Ga(1-x)Znx)(N(1-x)Ox) nanoparticles, with diameters of 10-27 nm and x = 0.075-0.51, which show energy band gaps from 2.21 to 2.61 eV. Rietveld analysis of the neutron diffraction data revealed that the average crystal structure is hexagonal wurtzite (space group P63mc) for the larger nanoparticles, while the crystal structure of smaller nanoparticles is disordered hexagonal. Pair-distribution-function analysis found that the intermediate crystal structure retains a "motif" of the average one; however, the local structure is more disordered. The implications of disorder on the reduced energy band gap are discussed. PMID:26544911

  9. Raman probe of new laser materials GaAs1-xBixand InAs1-xBix

    NASA Astrophysics Data System (ADS)

    Verma, Prabhat; Herms, Martin; Irmer, Gert; Yamada, Masayoshi; Okamoto, Hiroshi; Oe, Kunishige

    2000-03-01

    Inclusion of a small amount of Bi in InAs and GaAs changes the temperature dependent behavior of the band gap. Both InAs1- xBix and GaAs1-xBix tend to have temperature insensitive band gap with increasing Bi content. Raman scattering has been performed on the epilayers of InAs1- xBix and GaAs1-xBix compounds grown by MOVPE technique for varying Bi content. Good single crystalline growth with spatial homogeneity was confirmed using micro- Raman technique. Vibrational modes of InBi and GaBi were observed in the two materials, respectively. In addition, vibrational modes corresponding to Bi and phonon-plasmon coupled modes were also observed. Experimental results indicate that Bi atoms homogeneously replace some of the As atoms in both InAs as well as in GaAs to provide good crystalline structures of InAs1-xBix and GaAs1- xBix compounds, respectively.

  10. Memristive Switching in Bi(1-x)Sb(x) Nanowires.

    PubMed

    Han, Nalae; Park, Myung Uk; Yoo, Kyung-Hwa

    2016-04-13

    We investigated the memristive switching behavior in bismuth-antimony alloy (Bi(1-x)Sb(x)) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi(1-x)Sb(x) single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10(4) and narrow variations in switching parameters. Moreover, the resistance values in the low-resistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi(1-x)Sb(x) single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross sections of the Bi(1-x)Sb(x) single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plasticity and long-term potentiation, could be implemented in Bi(1-x)Sb(x) nanowires by applying a sequence of voltage pulses with different repetition intervals. PMID:27042861

  11. Density of liquid Hg(1-x)Cd(x)Te

    NASA Technical Reports Server (NTRS)

    Chandra, D.; Holland, L. R.

    1983-01-01

    Negative thermal expansion has been established in liquid Hg(1-x)Cd(x)Te for x less than 0.2 employing a pycnometric method. Pure HgTe increases in density from its melting point at 670 C to a maximum value at 750 C, where normal thermal expansion progressively resumes. The dependence of density on temperature for liquid Hg(1-x)Cd(x)Te arises almost exclusively from the HgTe portion of the melt, while CdTe acts as a diluent. The temperature corresponding to the maximum density changes slightly with composition, increasing by about 5 C for x = 0.1.

  12. Dielectric and ferroelectric properties of (BixBa1-x)(Znx/2Ti1-x/2)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoli; Yang, Aihong

    2009-04-01

    (BixBa1-x)(Znx/2Ti1-x/2)O3 [xBi(Zn1/2Ti1/2)O3-(1 - x)BaTiO3, x <= 0.30] solid solution ceramics with a pure perovskite structure were synthesized by a conventional solid-state reaction method. A change in symmetry from tetragonal to cubic was observed as the mole fraction of Bi(Zn1/2Ti1/2)O3 increased. All compositions show a dielectric anomaly over the temperature range 30-120 °C. In the tetragonal phase region, the temperature Tm of the maximum dielectric constant decreases with increasing Bi(Zn1/2Ti1/2)O3 content. In the cubic phase area, the compositions show general dielectric relaxation of linear dielectrics, and Tm increases with increasing Bi(Zn1/2Ti1/2)O3 content. The phase transition, dielectric and ferroelectric properties of (BixBa1-x)(Znx/2Ti1-x/2)O3 ceramics are sensitive to nano-regional chemistries.

  13. Large magnetocaloric effect in Pr1-xPbxMnO3 (0.1<=x<=0.5) perovskites

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Tho, Nguyen Duc; Hanh, Duong Thi; Chau, Nguyen

    2006-04-01

    This research reports the findings of large low-field magnetocaloric effect in polycrystalline Pr1-xPbxMnO3 (0.1<=x<=0.5) perovskites. It is found that, upon an applied field of 13.5 kOe, the magnetic entropy change (ΔSM) reached values of 3.91, 3.68, and 3.34 J/kg K for x=0.1, 0.4, and 0.5 compositions, respectively. These values are larger than that of Gd (3.32 J/kg K) and were attained by a low applied magnetic field that can be generated by permanent magnets. These superior magnetocaloric features together with a relatively low material cost make the Pr1-xPbxMnO3 perovskites attractive candidate materials for magnetic refrigerators in a temperature range of 150-270 K.

  14. Selective vignetting of Type 1 X-ray telescopes

    NASA Technical Reports Server (NTRS)

    Mangus, J.

    1969-01-01

    Selective vignetting technique optimizes the performance of a Type 1 X-ray telescope. The image quality of the telescope system is improved by matching the detector to the optimum focal surface and by vignetting rays which formerly contributed to the flare in comatic images.

  15. Exciton absorption in CdS1- xSex and ZnSe1- xTex solid solutions

    NASA Astrophysics Data System (ADS)

    Naumov, A.; Permogorov, S.; Reznitsky, A.; Verbin, S.; Klochikhin, A.

    1990-04-01

    Absorption spectra of CdS1- xSex and ZnSe1- xTex semiconductor solid solutions have been studied at T = 2 K in the region of fundamental absorption edge for composition range (0.02 < x < 0.6). It is shown that potential fluctuations due to compositional disorder of the alloy have a strong effect on both the exciton state broadening and the band gap shift. A model for description of the exciton absorption spectra is developed. The contribution of the fluctuations to the part of the band gap shift which is nonlinear in concentration is separated from the other mechanisms.

  16. Nanomaterials of the topological crystalline insulators, Pb1-xSnxTe and Pb1-xSnxSe

    NASA Astrophysics Data System (ADS)

    Saghir, Mohammed; Sanchez, Anna; Hindmarsh, Steve; York, Steve; Balakrishnan, Geetha

    The study of topological insulators and their derivatives, in both 1D and 2D forms, has been the subject of great interest which has grown vastly in recent years. Topological insulators (TIs) and Topological Crystalline insulators (TCIs) exhibit exotic surface properties which are thought to be difficult to detect due to the surface signal being overwhelmed by that arising from the bulk of the material. As a result, by increasing the surface area to volume ratio, the signal from the surface states could be easier to investigate. We present results of the growth and characterisation of nanomaterials for the TCIs, Pb1-xSnxTe and Pb1-xSnxSe. Bulk crystals were used as starting materials for the growth, from which various morphologies of these TCIs were obtained. Nanowires of Pb1-xSnxTe have been produced with a Sn composition of ~ x = 0 . 25 , at which a transition from trivial to non-trivial insulator has been reported for bulk materials. The results obtained on the growth of nanomaterials of Pb1-xSnxSe are also described, all of which were characterised using various x-ray diffraction and electron microscopy techniques.

  17. On threshold resummation beyond leading 1 - x order

    NASA Astrophysics Data System (ADS)

    Grunberg, G.; Ravindran, V.

    2009-10-01

    We check against exact finite order three-loop results for the non-singlet F2 and F3 structure functions the validity of a class of momentum space ansaetze for threshold resummation at the next-to-leading order in 1 - x, which generalize results previously obtained in the large-β0 limit. We find that the ansaetze do not work exactly, pointing towards an obstruction to threshold resummation at this order, but still yield correct results at the leading logarithmic level for each color structures, as well as at the next-to-next-to-leading logarithmic level for the specific CF3 color factor. A universality of the leading logarithm contributions to the physical evolution kernels of F2 and F3 at the next-to-leading order in 1 - x is observed.

  18. Structural transitions in liquid Te1-xSex alloys

    NASA Astrophysics Data System (ADS)

    Magaña, J. R.; Lannin, J. S.

    1984-05-01

    Polarized and depolarized Raman scattering measurements are reported in liquid Te1-xSex alloys near the melting point. The results provide the first direct evidence for a structural transition within the range x=0.2-0.3 from a twofold, chainlike bonding to a threefold, pyramidal As-like bonding. Higher-temperature polarized Raman measurements at x=0.3 do not indicate a twofold to threefold transition, as has been suggested, but rather indicate increased intrachain disorder.

  19. Optical properties of Hg(1-x)Cd(x)Te

    NASA Astrophysics Data System (ADS)

    Tong, Fei-Ming; Ravindra, N. M.

    1993-04-01

    Optical properties of Hg(1-x)Cd(x)Te are summarized. Based on Penn-type (1962) models, the Moss (1950) relation, and the Wemple and DiDomenico (1971) approach, calculations of energy gap, plasmon energy, Fermi energy, oscillator strength and electronic polarizability have been made. Comparisons are made with the data available in the literature. Details of the dependency of the properties on composition are presented.

  20. 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.

  1. 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.; Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588

    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.

  2. Raman studies on GaAs1-xBix and InAs1-xBix

    NASA Astrophysics Data System (ADS)

    Verma, Prabhat; Oe, K.; Yamada, M.; Harima, H.; Herms, M.; Irmer, G.

    2001-02-01

    The lattice vibrational properties of new semiconductor alloys, GaAs1-xBix and InAs1-xBix, are reported. These alloys, which were grown by metalorganic vapor phase epitaxy technique, contain a small amount (1.2%-3.8%) of Bi. A detail Raman scattering study of these new alloys, which exhibit weak temperature dependence of the band gap with increasing amount of Bi, is reported here. Good crystalline quality and spatial homogeneity was confirmed using micro-Raman technique. The alloys show ternary compound behavior, confirming substitutional incorporation of Bi into the lattice site. New vibrational modes observed were assigned to GaBi-like and InBi-like modes. In addition, phonon-plasmon coupled modes and vibrational modes corresponding to Bi and As materials were also observed. Results are discussed to characterize these new alloys in detail.

  3. Neutron diffraction studies of RSn{sub 1+x}Ge{sub 1-x} (R=Tb-Er) compounds

    SciTech Connect

    Gil, A.; Hoser, A.; Szytula, A.

    2011-07-15

    The magnetic structures of RSn{sub 1+x}Ge{sub 1-x} (R=Tb, Dy, Ho and Er, x{approx}0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn{sub 1.12}Ge{sub 0.88} is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) {mu}{sub B} at 1.62 K. It lies in the b-c plane and form an angle {theta}=17.4(2) deg. with the c-axis. This structure is stable up to the Neel temperature equal to 31 K. The magnetic structures of RSn{sub 1+x}Ge{sub 1-x}, where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2, 0) with the sequence (++-+) of magnetic moments in the crystal unit cell. In DySn{sub 1.09}Ge{sub 0.91} and HoSn{sub 1.1}Ge{sub 0.9} magnetic moments equal 7.25(15) and 8.60(6) {mu}{sub B} at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T{sub N}=10.7 K. For ErSn{sub 1.08}Ge{sub 0.92}, the Er magnetic moment equals 7.76(7) {mu}{sub B} at T=1.5 K and it is parallel to the b-axis. At T{sub t}=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k{sub x} component and a quick decrease of k{sub y} component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3) deg. with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Neel temperature is observed. - Graphical abstract: The magnetic structures of RSn{sub 1+x}Ge{sub 1-x} (R=Tb, Dy, Ho and Er, x{approx}0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The magnetic ordering in Tb

  4. Optical phase conjugation in Hg1 - xCdxTe.

    PubMed

    Khan, M A; Kruse, P W; Ready, J F

    1980-06-01

    We have observed phase-conjugate signals at 12, 77, and 295 K in n-type Hg1 - xCdxTe (x = 0.216-0.232) using degenerate four-wave mixing at 10.6 microm. The external power-reflection coefficient increases with the product of pump-power densities and saturates at 9%. The values of the third-order nonlinear susceptibility X(3) derived from these measurements agree with the theory of Wolff and Pearson [Phys. Rev. Lett. 17, 1015 (1966)] for X(3) that is due to conduction-band nonparabolicity. PMID:19693194

  5. Valence band anticrossing in GaBixAs1-x

    SciTech Connect

    Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K.; Krotkus, A.

    2007-07-11

    The optical properties of GaBixAs1-x (0.04< x< 0.08) grown by molecular beam epitaxy have been studied by photomodulated reflectance spectroscopy. The alloys exhibit a strong reduction in the bandgap as well as an increase in the spin-orbit splitting energy with increasing Bi concentration. These observations are explained by a valence band anticrossing model, which shows that a restructuring of the valence band occurs as the result of an anticrossing interaction between the extended states of the GaAs valence band and the resonant T2 states of the Bi atoms.

  6. 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.

  7. Valence band anticrossing in GaBixAs1-x

    NASA Astrophysics Data System (ADS)

    Alberi, K.; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K.; Krotkus, A.

    2007-07-01

    The optical properties of GaBixAs1-x(0.04

  8. Electron paramagnetic resonance in Zn1-xCoxO

    NASA Astrophysics Data System (ADS)

    Acosta-Humánez, F.; Cogollo Pitalúa, R.; Almanza, O.

    2013-03-01

    In this paper is reported the Electron Paramagnetic Resonance (EPR) studies in Zn1-xCoxO powder, with 0.01≤x≤0.05, at many temperatures (105-250 K). These samples were synthesized by the sol-gel method (citrate route). Results suggest that the ferromagnetism behavior of the materials is governed by ferromagnetic coupling among cobalt ions. For cobalt concentration higher than 3% were obtained mean size particle higher than 25 nm, measured by X-ray diffraction, and for this were also observed shallow free radical.

  9. Dielectric investigations on co-substituted bismuth ferrite (Bi1-xLaxFe1-xMnxO3)

    NASA Astrophysics Data System (ADS)

    Kumar, Sunil; Supriya, Sweety; Kumar, Pawan; Kar, Manoranjan

    2016-05-01

    Bi1-xLaxFe1-xMnxO3 ceramics with x=0.00, 0.05, 0.10 and 0.20 were synthesized by the tartaric acid modified sol-gel technique with required optimization. The co-substitution suppresses the impurities phases in bismuth ferrite which is usually observed. It was observed that the composition-driven structural transition from rhombohedral (R3c space group) to orthorhombic symmetry (Pbnm space group) plays an important role in modifying the dielectric properties of bismuth ferrite. The dielectric constant was found to be increased in La and Mn co-substituted BiFeO3 due to significant large off-center movement of Fe3+ ions in the oxygen octahedra. The dispersion of dielectric constant in the frequency range of 100 Hz to 1 MHz has been analyzed by employing the modified Debye's function which suggests the contribution of multiple charge carriers in the dielectric relaxation.

  10. Molecular structure of Si_xS_(1-x) glasses

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Boolchand, P.

    2000-03-01

    Bulk Si_xS_1-x glasses in the 0.15

  11. Thermoelectric properties of Cr1-xMoxSi2

    NASA Astrophysics Data System (ADS)

    Ohishi, Yuji; Mohamad, Afiqa; Miyazaki, Yoshinobu; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke

    2015-12-01

    The thermoelectric properties of Mo-substituted CrSi2 were studied. Dense polycrystalline samples of Mo-substituted hexagonal C40 phase Cr1-xMoxSi2 (x=0-0.30) were fabricated by arc melting followed by spark plasma sintering. Mo substitution substantially increases the carrier concentration. The lattice thermal conductivity of CrSi2 at room temperature was reduced from 9.0 to 4.5 W m-1 K-1 by Mo substitution due to enhanced phonon-impurity scattering. The thermoelectric figure of merit, ZT, increases with increasing Mo content because of the reduced lattice thermal conductivity. The maximum ZT value obtained in the present study was 0.23 at 800 K, which was observed for the sample with x=0.30. This value is significantly greater than that of undoped CrSi2 (ZT=0.13).

  12. Raman study of strained Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Chen, Robert; Huo, Yijie; Kamins, Theodore I.; Harris, James S.

    2011-06-01

    The Ge-Ge longitudinal optical Raman peak has been measured in strained Ge1-xSnx alloy layers grown on top of relaxed InyGa1-yAs buffer layers on GaAs substrates by molecular beam epitaxy. The experimental result shows that the peak frequency shift increases linearly from the value for bulk Ge with the Sn fraction x and the strain ɛ, Δω = ω - ωGe = ax + bɛ. In these experiments alloy and strain contributions are decoupled and measured separately, and a and b are determined to be a = - 82 ± 4 cm-1 and b = - 563 ± 34 cm-1, over the entire composition and strain range investigated.

  13. 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

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

    DOE PAGESBeta

    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.

  15. Anomalous photoluminescence in InP1-xBix.

    PubMed

    Wu, Xiaoyan; Chen, Xiren; Pan, Wenwu; Wang, Peng; Zhang, Liyao; Li, Yaoyao; Wang, Hailong; Wang, Kai; Shao, Jun; Wang, Shumin

    2016-01-01

    Low temperature photoluminescence (PL) from InP1-xBix thin films with Bi concentrations in the 0-2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 μm in optical coherent tomography (OCT). PMID:27291823

  16. 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.

  17. MgxZn1-xO/Ag/MgxZn1-xO Multilayers As High-Performance Transparent Conductive Electrodes.

    PubMed

    Lee, Hyo-Ju; Kang, Jang-Won; Hong, Sang-Hyun; Song, Sun-Hye; Park, Seong-Ju

    2016-01-27

    We report on the optical and electrical properties of MgxZn1-xO/Ag/MgxZn1-xO transparent conductive electrodes. The transmittance and sheet resistance of MgxZn1-xO/Ag/MgxZn1-xO multilayers deposited at room temperature were strongly dependent on the thickness and surface morphology of Ag layer. The optical absorption edge of MgxZn1-xO/Ag/MgxZn1-xO showed a blue shift with increasing Mg composition due to the increased band gap of MgxZn1-xO. The Haack figure of merit value of Mg0.28Zn0.72O/Ag/Mg0.28Zn0.72O with a 14 nm-thick Ag layer, which has a sheet resistance of 6.36 Ω/sq and an average transmittance of 89.2% at wavelengths in the range from 350 to 780 nm, was 69% higher than that of a ZnO/Ag/ZnO multilayer electrode. These results indicate that MgxZn1-xO/Ag/MgxZn1-xO multilayers, which also show low surface roughness, can be used as highly conductive transparent electrodes in various optoelectronic devices operating over a wide wavelength region. PMID:26752616

  18. 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.

  19. Valence Band Anticrossing in GaBixAs1-x

    NASA Astrophysics Data System (ADS)

    Alberi, Kirstin; Dubon, O. D.; Walukiewicz, W.; Yu, K. M.; Bertulis, K.; Krotkus, A.

    2007-03-01

    Recently, significant attention has been devoted to exploring the large bandgap bowing and spin-orbit splitting in GaBixAs1-x. alloys. We attribute the origins of these effects to a restructuring of the alloy valence band induced by an anticrossing interaction between the delocalized GaAs p-like states and the resonant localized Bi p-like states. Hybridization of like-symmetry states leads to the splitting of the heavy hole, light hole and spin-orbit split-off bands into sets of E+ and E- subbands. The splitting is confirmed experimentally by photomodulated reflectance spectroscopy in alloys with Bi concentrations up to x = 0.084. The bandgap bowing is a direct consequence of the strong upward shift of the uppermost heavy and light hole E+ bands with increasing Bi concentration, while the much slower ascent of the spin-orbit split-off E+ band produces the large rise in the spin-orbit splitting energy.

  20. 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.

  1. 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.

  2. Reflective masks for 1X deep ultraviolet lithography

    NASA Astrophysics Data System (ADS)

    Hsieh, Robert L.; Lee, Julienne Y.; Maluf, Nadim I.; Browning, Raymond; Jerabek, Paul; Pease, R. Fabian W.; Owen, Geraint

    1992-01-01

    Recent work has demonstrated the high resolution optical performance possible with simple 1X mostly-reflective optics: using 248 nm light from a mercury arc lamp, 0.25 micrometers features were delineated across a 2 mm radius semicircular field, and much large fields are possible with a scaled up version. The mask required for this system consists of a quartz substrate, a patterned thin film reflector, and a nonreflective backing which also serves to protect the reflector film. The mask is reflective at the quartz/reflector interface so the substrate is part of the projection optical path and so acts as the pellicle. We have investigated chromium, silicon, and aluminum for the reflector material; their reflection coefficients at 248 nm at the quartz-reflector interface are 30, 55, and 90 percent, respectively. Silicon has been chosen because it has a practical combination of reflectivity and ease of deposition and etching. Moreover films as thin as 30 nm provide the full (bulk-value) reflection and so precise etching is further facilitated. Among possible absorber materials, novolak photoresist is a practical choice having a quartz/film reflectivity of 1%. Features down to 0.25 micrometers are regularly patterned for these masks with a MEBES I using Shipley SAL-601 or PMMA electron beam resist.

  3. Analytical representation of the thermal conductivity and electrical resistivity of UC/sub 1 +- x/, PuC/sub 1-x/, and (U/sub y/Pu/sub 1-y/)C/sub 1 +- x/

    SciTech Connect

    Storms, E.K.

    1982-12-01

    This report uses selected measurements from the literature to construct analytical expressions that describe the electrical and thermal conductivity of pure, high-density UC/sub 1 +- x/, PuC/sub 1-x/, and (U/sub y/Pu/sub 1-y/C/sub 1 +- x/ as a function of x,y, and temperature. The approach shows that many of the differences between the reported measurements can be resolved if the carbon cntent of the single-phase material is taken into account. Analytical expressions are also given that describe the temperature variation of the phase boundaries for these phases. 16 figures.

  4. 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.

  5. Alloying of GaNxAs1-x with InNxAs1-x: A simple formula for the band gap parametrization of Ga1-yInyNxAs1-x alloys

    NASA Astrophysics Data System (ADS)

    Kudrawiec, R.

    2007-01-01

    It has been shown that the band gap energy of dilute nitride ternary alloys (Ga1-yInyNxAs1-x in this case) can be predicted by knowing the band gap energy for dilute nitride binary alloys (GaNxAs1-x and InNxAs1-x alloys in this case) and a bowing parameter. The band gap energy for GaNxAs1-x and InNxAs1-x can be calculated after the band anticrossing (BAC) model [W. Shan et al., Phys. Rev. Lett. 82, 1221 (1999)] or other formula, whereas the bowing parameter can be assumed to be the same as for the GaInAs alloy. This approach does not require the BAC parameters related to Ga1-yInyNxAs1-x and can be applied for other dilute nitride ternary alloys. The obtained band gap predictions are in good agreement with available experimental data for as-grown GaInNAs materials. It means that the proposed energy gap parametrization corresponds to the random environment of N atoms by Ga and In atoms since alloying of GaNxAs1-x with InNxAs1-x also corresponds to alloying of Ga-rich environment of N atoms (which is expected for the as-grown GaInNAs material with low indium content) with In-rich environment of N atoms (which is expected for the as-grown GaInNAs material with high indium content).

  6. Robustness of Sn precipitation during thermal oxidation of Ge1-xSnx on Ge(001)

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Asano, Takanori; Taoka, Noriyuki; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-08-01

    The thermal robustness of Sn segregation and precipitation in epitaxial Ge1-xSnx layers on Ge(001) substrates with a Sn content greater than the equilibrium solubility limit has been investigated for applications of Ge1-xSnx in high-performance metal-oxide-semiconductor field-effect transistors (MOSFETs). Sn segregation and precipitation occur on the Ge1-xSnx surface after epitaxial growth of the Ge1-xSnx layer at 150 °C. After the thermal oxidation of the Ge1-xSnx layer below 500 °C, there are no significant decreases in the average Sn content in the Ge1-xSnx layer and no additional Sn segregation on the Ge1-xSnx surface. However, Sn precipitation occurs at the Ge1-xSnx surface during the thermal oxidation of the Ge1-xSnx layer with an average Sn content as high as 8.7% at 600 °C, causing a decrease in the Sn content in the Ge1-xSnx layer. The Sn content in the Ge1-xSnx oxide is 1.5 times greater than that observed near the Ge1-xSnx surface for the sample with a Sn content of 8.7% after the thermal oxidation at 400 to 500 °C. The capacitance-voltage characteristics of the Al/Al2O3/Ge1-xSnx/Ge MOS capacitors treated with thermal oxidation at 400 °C indicate that the slow state density increases with the Sn content. Meanwhile, the small interface state density could be achieved via thermal oxidation of the Ge1-xSnx layer, even with a high Sn content.

  7. Growth of BxGa1-xAs, BxAl1-xAs and BxGa1-x-yInyAs epilayers on (001)GaAs by LP-MOCVD

    NASA Astrophysics Data System (ADS)

    Wang, Qi; Ren, Xiaomin; Huang, Yongqing; Huang, Hui; Cai, Shiwei; Zhang, Xia

    2008-11-01

    High quality zinc-blende BxGa1-xAs, BxAl1-xAs, BxGa1-x-yInyAs epilayers and relevant MQW structures containing 10- period BGaAs(10nm)/GaAs(50nm) and BGaInAs(10nm)/GaAs(50nm) have been successfully grown on exactly-oriented (001)GaAs substrates by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). Triethylboron, trimethylgallium, trimethylaluminium, trimethylindium and arsine were used as the precursors. Boron incorporation behaviors have been studied as a function of growth temperature and gas-phase triethylboron mole fraction. In this study, the maximum boron composition x of 5.8% and 1.3% was achieved at the same growth temperature of 580°C for bulk BxGa1-xAs and BxAl1-xAs, respectively. 11K photoluminescence (PL) peak wavelength of lattice-matched BxGa1-x-yInyAs epilayer with boron composition of about 4% reached 1.24μm.

  8. 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.

  9. Impact of hydrogen surfactant on crystallinity of Ge1-xSnx epitaxial layers

    NASA Astrophysics Data System (ADS)

    Asano, Takanori; Taoka, Noriyuki; Hozaki, Koya; Takeuchi, Wakana; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2015-04-01

    The effect of a hydrogen surfactant on the crystallinity of a Ge1-xSnx epitaxial layer was investigated. The improvement of crystallinity on the in-plane uniformity of Ge1-xSnx epitaxial layer was observed by X-ray diffuse scattering and transmission electron microscopy. We also observed the decrease in the surface roughness of the Ge1-xSnx epitaxial layer. This indicates the suppression of the three-dimensional growth mode of Ge1-xSnx epitaxial layer due to a compressive strain. In addition, we observed the reduction in acceptor-like defect density in an undoped-Ge1-xSnx epitaxial layer from the capacitance-voltage characteristics of a metal-oxide-semiconductor capacitor. Consequently, introducing hydrogen during the growth leads to the improvement of the crystalline quality of the Ge1-xSnx epitaxial layer.

  10. Study on the Ge1-xSnx/HfO2 interface and its impacts on Ge1-xSnx tunneling transistor

    NASA Astrophysics Data System (ADS)

    Qiu, Yingxin; Wang, Runsheng; Huang, Qianqian; Huang, Ru

    2014-06-01

    In this paper, we employ first-principle calculation to investigate the Ge1-xSnx/HfO2 interface, and then evaluate its impacts on Ge1-xSnx tunneling field-effect transistor (TFET). First-principle calculations of Ge1-xSnx/HfO2 interfaces in the oxygen-rich process atmosphere indicate that the interface states originate from the Ge and Sn dangling bond, rather than Hf-bond. The total density of state shows that there are more interface states in the semiconductor bandgap with increasing Sn fraction. By further incorporating the material and interface parameters from density functional theory calculation into advanced device simulation, the electrical characteristics of Ge1-xSnx TFET are investigated. Removing the Sn atom from the first atom layer of Ge1-xSnx in device processes is found to be beneficial to reduce the degradations. For the degradation mechanisms, the trap-assisted-tunneling is the dominant mechanism at the low Sn fraction, and enhanced Shockley-Read-Hall recombination induced by traps becomes the dominant mechanism with increasing Sn fraction. The results are helpful for the interface optimization of Ge1-xSnx TFET.

  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 PAGESBeta

    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. Compositional Dependence of Critical Point Transitions in Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Cook, Candi S.; D'Costa, Vijay; Kouvetakis, John; Zollner, Stefan; Menéndez, José

    2005-06-01

    The compositional dependence of the E1, E1+Δ1, E0', and E2 optical transition energies in Ge1-xSnx alloys has been measured in the 0 < x < 0.18 range. Deviations from linearity are clearly observed and characterized by a bowing parameter b. The value of this parameter is much larger in Ge1-xSnx alloys than in the isoelectronic Si1-xGex system.

  14. 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.

  15. Chemical Unit Cosubstitution and Tuning of Photoluminescence in the Ca2(Al(1-x)Mg(x))(Al(1-x)Si(1+x))O7:Eu(2+) Phosphor.

    PubMed

    Xia, Zhiguo; Ma, Chonggeng; Molokeev, Maxim S; Liu, Quanlin; Rickert, Karl; Poeppelmeier, Kenneth R

    2015-10-01

    The union of structural and spectroscopic modeling can accelerate the discovery and improvement of phosphor materials if guided by an appropriate principle. Herein, we describe the concept of "chemical unit cosubstitution" as one such potential design scheme. We corroborate this strategy experimentally and computationally by applying it to the Ca2(Al(1-x)Mg(x))(Al(1-x)Si(1+x))O7:Eu(2+) solid solution phosphor. The cosubstitution is shown to be restricted to tetrahedral sites, which enables the tuning of luminescent properties. The emission peaks shift from 513 to 538 nm with a decreasing Stokes shift, which has been simulated by a crystal-field model. The correlation between the 5d crystal-field splitting of Eu(2+) ions and the local geometry structure of the substituted sites is also revealed. Moreover, an energy decrease of the electron-phonon coupling effect is explained on the basis of the configurational coordinate model. PMID:26389578

  16. 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.

  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. Growth and Photoluminescence of Crystalline SILICON(1-X) Germanium(x)/silicon and SILICON(1-X-Y) Germanium(x) Carbon(y)/silicon

    NASA Astrophysics Data System (ADS)

    St. Amour, Anthony Andeol

    We have measured and modeled, both analytically and numerically, the temperature dependence of the luminescence intensity in strained Si_{1-x} Ge_{x}/Si (001) heterostructures. The high-temperature (T>150 K) Si_{1-x}Ge _{x} photoluminescence (PL) intensity in high-quality material is limited by recombination at the top Si surface, and this intensity can be dramatically increased by passivating the top surface with oxide. Also, due to Auger recombination suppressing the low temperature PL, we achieved essentially constant PL intensity from 77 to 250 K at high pump power density (30 W/cm ^2). We have identified two causes for the observed difference in the temperature dependence of photo - and electroluminescence. By Rapid Thermal Chemical Vapor Deposition, we have formed device quality pseudomorphic Si_ {1-x-y}Ge_{x} C_{y} thin films on Si (001), containing up to 1.2% substitutional carbon. The band gap of these strained films, as measured by PL, increased +21 meV/%C, and we predict that the band gap of relaxed Si_{1-x-y}Ge_ {x}C_{y} decreases -20 meV/%C. Also, we have demonstrated that, for a given band gap, Si_{1-x -y}Ge_{x}C _{y} has less strain and a greater critical thickness than does Si_ {1-x}Ge_{x}. We have fabricated Si_{1-x -y}Ge_{x}C _{y} p-i-n diodes, which, for (C) < 1.0%, showed no degradation in reverse-bias leakage compared to C-free devices. The infrared absorption spectra of these diodes showed increased sub -band gap absorption as the carbon content was increased.

  19. Comparative analysis of high-performance infrared avalanche InxGa1-xAsyP1-y and Hg1-xCdxTe heterophotodiodes

    NASA Astrophysics Data System (ADS)

    Kholodnov, Viacheslav; Drugova, Albina; Nikitin, Mikhail; Chekanova, Galina

    2012-10-01

    Technology of infrared (IR) avalanche photodiodes (APDs) gradually moves from simple single element APD to 2D focal plane arrays (FPA). Spectral covering of APDs is expanded continuously from classic 1.3 μm to longer wavelengths due to using of narrow-gap semiconductor materials like Hg1-xCdxTe. APDs are of great interest to developers and manufacturers of different optical communication, measuring and 3D reconstruction thermal imaging systems. Major IR detector materials for manufacturing of high-performance APDs became heteroepitaxial structures InxGa1-xAsyP1-y and Hg1-xCdxTe. Progress in IR APD technology was achieved through serious improvement in material growing techniques enabling forming of multilayer heterostuctures with separate absorption and multiplication regions (SAM). Today SAM-APD design can be implemented both on InxGa1-xAsyP1-y and Hg1-xCdxTe multilayer heteroepitaxial structures. To create the best performance optimal design avalanche heterophotodiode (AHPD) it is necessary to carry out a detailed theoretical analysis of basic features of generation, avalanche breakdown and multiplication of charge carriers in proper heterostructure. Optimization of AHPD properties requires comprehensive estimation of AHPD's pixel performance depending on pixel's multi-layer structure design, layers doping, distribution of electric field in the structure and operating temperature. Objective of the present article is to compare some features of 1.55 μm SAM-AHPDs based on InxGa1-xAsyP1-y and Hg1-xCdxTe.

  20. Jurassic-Cretaceous palynomorphs, palynofacies, and petroleum potential of the Sharib-1X and Ghoroud-1X wells, north Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Zobaa, Mohamed K.; El Beialy, Salah Y.; El-Sheikh, Hassan A.; El Beshtawy, Mohamed K.

    2013-02-01

    Palynomorph and palynofacies analyses have been performed on 93 cutting samples from the Jurassic Masajid Formation and Cretaceous Alam El Bueib, Alamein, Dahab, Kharita, and Bahariya formations in the Sharib-1X and Ghoroud-1X wells, north Western Desert, Egypt. Two palynological biozones are proposed for the studied interval of the Sharib-1X well: the Systematophora penicillata-Escharisphaeridia pocockii Assemblage Zone (Middle to Late Jurassic) and the Cretacaeiporites densimurus-Elateroplicites africaensis-Reyrea polymorpha Assemblage Zone (mid-Cretaceous: late Albian to early Cenomanian). Spore coloration and visual kerogen analysis are used to assess the thermal maturation and source rock potential. Mature oil prone to overmature gas prone source rocks occur in the studied interval of the Sharib-1X well, whereas highly mature to overmature gas prone source rocks occur in the studied interval of the Ghoroud-1X well. Palynofacies and palynomorph assemblages in both wells reflect shallow marine conditions throughout the Jurassic and the late Albian and early Cenomanian. During these times, warm and dry climatic conditions prevailed. The Cretaceous palynomorph assemblages of the Sharib-IX well correlate with the Albian-Cenomanian Elaterates Province of Herngreen et al. (1996).

  1. Ge1-xSnx alloys synthesized by ion implantation and pulsed laser melting

    NASA Astrophysics Data System (ADS)

    Gao, Kun; Prucnal, S.; Huebner, R.; Baehtz, C.; Skorupa, I.; Wang, Yutian; Skorupa, W.; Helm, M.; Zhou, Shengqiang

    2014-07-01

    The tunable bandgap and the high carrier mobility of Ge1-xSnx alloys stimulate a large effort for bandgap and strain engineering for Ge based materials using silicon compatible technology. In this Letter, we present the fabrication of highly mismatched Ge1-xSnx alloys by ion implantation and pulsed laser melting with Sn concentration ranging from 0.5 at. % up to 1.5 at. %. According to the structural investigations, the formed Ge1-xSnx alloys are monocrystalline with high Sn-incorporation rate. The shrinkage of the bandgap of Ge1-xSnx alloys with increasing Sn content is proven by the red-shift of the E1 and E1 + Δ1 critical points in spectroscopic ellipsometry. Our investigation provides a chip technology compatible route to prepare high quality monocrystalline Ge1-xSnx alloys.

  2. 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.

  3. Lattice dynamics of Ga1-xMnxN and Ga1-xMnxAs by first-principle calculations.

    PubMed

    Leite Alves, Horacio W; Scolfaro, Luísa Mr; da Silva, Eronides F

    2012-01-01

    In this work, we present theoretical results, using first-principle methods associated to the virtual crystal approximation model, for the vibrational mode frequencies of both the Ga1-xMnxN (in both cubic and hexagonal structures) and the Ga1-xMnxAs alloys, with the Mn contents in the range of 0% to 20%. The dependence of the calculated phonon frequencies with the Mn content was analyzed, and the results indicate that the phonon frequencies decrease with the increasing of Mn composition, leading to the false impression that they obey the Vegard rule in some cases. Moreover, the hexagonal Ga1-xMnxN alloys are elastically unstable for Mn concentrations at the order of 20%, which explains in part the experimentally observed deterioration of these alloys. These findings can be used in future technologies as a guide for the synthesis of spintronic nanostructured devices, such as nanowires, based on these materials. PMID:23075051

  4. Multifunctional Ultrathin PdxCu(1-x) and Pt∼PdxCu(1-x) One-Dimensional Nanowire Motifs for Various Small Molecule Oxidation Reactions.

    PubMed

    Liu, Haiqing; Adzic, Radoslav R; Wong, Stanislaus S

    2015-12-01

    Developing novel electrocatalysts for small molecule oxidation processes, including formic acid oxidation (FAOR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR), denoting the key anodic reactions for their respective fuel cell configurations, is a significant and relevant theme of recent efforts in the field. Herein, in this report, we demonstrated a concerted effort to couple and combine the benefits of small size, anisotropic morphology, and tunable chemical composition in order to devise a novel "family" of functional architectures. In particular, we have fabricated not only ultrathin 1-D Pd(1-x)Cu(x) alloys but also Pt-coated Pd(1-x)Cu(x) (i.e., Pt∼Pd(1-x)Cu(x); herein the ∼ indicates an intimate association, but not necessarily actual bond formation, between the inner bimetallic core and the Pt outer shell) core-shell hierarchical nanostructures with readily tunable chemical compositions by utilizing a facile, surfactant-based, wet chemical synthesis coupled with a Cu underpotential deposition technique. Our main finding is that our series of as-prepared nanowires are functionally flexible. More precisely, we demonstrate that various examples within this "family" of structural motifs can be tailored for exceptional activity with all 3 of these important electrocatalytic reactions. In particular, we note that our series of Pd(1-x)Cu(x) nanowires all exhibit enhanced FAOR activities as compared with not only analogous Pd ultrathin nanowires but also commercial Pt and Pd standards, with Pd9Cu representing the "optimal" composition. Moreover, our group of Pt∼Pd(1-x)Cu(x) nanowires consistently outperformed not only commercial Pt NPs but also ultrathin Pt nanowires by several fold orders of magnitude for both the MOR and EOR reactions in alkaline media. The variation of the MOR and EOR performance with the chemical composition of our ultrathin Pt∼Pd(1-x)Cu(x) nanowires was also discussed. PMID:26580482

  5. Surface Shubnikov-de Haas oscillations and nonzero Berry phases of the topological hole conduction in Tl1 -xBi1 +xSe2

    NASA Astrophysics Data System (ADS)

    Eguchi, G.; Kuroda, K.; Shirai, K.; Kimura, A.; Shiraishi, M.

    2014-11-01

    We report the observation of two-dimensional Shubnikov-de Haas (SdH) oscillations in the topological insulator Tl1 -xBi1 +xSe2 . Hall effect measurements exhibited electron-hole inversion in samples with bulk insulating properties. The SdH oscillations accompanying the hole conduction yielded a large surface carrier density of ns=5.1 ×1012 cm -2, with the Landau-level fan diagram exhibiting the π Berry phase. These results showed the electron-hole reversibility around the in-gap Dirac point and the hole conduction on the surface Dirac cone without involving the bulk metallic conduction.

  6. 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).

  7. Application of the Inhomogeneous Sample Model in Piezoelectric Photothermal Spectroscopy of Zn1-x BexTe and Cd1-xMnxTe Mixed Crystals

    NASA Astrophysics Data System (ADS)

    Malinski, M.; Zakrzewski, J.

    2005-01-01

    This paper presents the basic details of the inhomogeneous sample model. This is one of the models that can be used for describing piezoelectric photothermal (PPT) spectra observed for mixed crystals. The experimental PPT spectra of Zn1-x Be xTe and Cd 1-x MnxTe mixed crystals presented in this paper exhibited the character of the crystal structure that was interpreted with the model of the inhomogeneous sample. The analysis of the spectra, performed with this model, enabled determination of both the basic optical parameters of the two crystal regions observed in the investigated samples and the composition of the crystals.

  8. Thermophysical properties of Ba1-xSrxMoO3(s)

    NASA Astrophysics Data System (ADS)

    Sahu, Manjulata; Krishnan, K.; Saxena, M. K.; Dash, Smruti

    2015-02-01

    Ba1-xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid-solutions were synthesized by reduction of corresponding Ba1-xSrxMoO4(s) and were characterized using X-ray diffraction (XRD). Thermal expansion behavior of Ba1-xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) were investigated in the temperature range 298-873 K by high temperature X-ray diffraction (HTXRD). The average volume thermal expansion coefficient of Ba1-xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) was found to be 2.83 × 10-5, 2.20 × 10-5, 2.02 × 10-5 and 2.27 × 10-5 K-1, respectively. Heat capacity of Ba1-xSrxMoO3(s) (x = 0, 0.4, 0.8, 1) was measured with a heat flux-type differential scanning calorimeter (DSC) in the temperature range 290-870 K. The specific heat of Ba1-xSrxMoO3(s) was found to increase with increase in concentration of strontium. The thermodynamic functions such as enthalpy increment, entropy and Gibbs energy functions of Ba1-xSrxMoO3(s) were also calculated.

  9. Antiferromagnetic Kondo lattice in the layered compound CePd1 -xBi2 and comparison to the superconductor LaPd1 -xBi2

    NASA Astrophysics Data System (ADS)

    Han, Fei; Wan, Xiangang; Phelan, Daniel; Stoumpos, Constantinos C.; Sturza, Mihai; Malliakas, Christos D.; Li, Qing'an; Han, Tian-Heng; Zhao, Qingbiao; Chung, Duck Young; Kanatzidis, Mercouri G.

    2015-07-01

    The layered compound CePd1 -xBi2 with the tetragonal ZrCuSi2-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd1 -xBi2 show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the a b plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of 0.191 J mol Ce -1 K -2 obtained from specific-heat measurement suggests a moderate Kondo effect in CePd1 -xBi2. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulderlike behavior around 75 K which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd1 -xBi2 around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures.

  10. Morphine-induced MOR-1X and ASF/SF2 Expressions Are Independent of Transcriptional Regulation: Implications for MOR-1X Signaling.

    PubMed

    Regan, Patrick M; Sariyer, Ilker K; Langford, T Dianne; Datta, Prasun K; Khalili, Kamel

    2016-07-01

    Recently, multiple μ-opioid receptor (MOR) isoforms have been identified that originate from a single gene, OPRM1; however, both their regulation and their functional significance are poorly characterized. The objectives of this study were to decipher, first, the regulation of alternatively spliced μ-opioid receptor isoforms and the spliceosome components that determine splicing specificity and, second, the signaling pathways utilized by particular isoforms both constitutively and following agonist binding. Our studies demonstrated that the expression of a particular splice variant, MOR-1X, was up-regulated by morphine, and this coincided with an increase in the essential splicing factor ASF/SF2. Structural comparison of this isoform to the prototypical variant MOR-1 revealed that the unique distal portion of the C-terminal domain contains additional phosphorylation sites, whereas functional comparison found distinct signaling differences, particularly in the ERK and p90 RSK pathways. Additionally, MOR-1X expression significantly reduced Bax expression and mitochondrial dehydrogenase activity, suggesting a unique functional consequence for MOR-1X specific signaling. Collectively, these findings suggest that alternative splicing of the MOR is altered by exogenous opioids, such as morphine, and that individual isoforms, such as MOR-1X, mediate unique signal transduction with distinct functional consequence. Furthermore, we have identified for the first time a potential mechanism that involves the essential splicing factor ASF/SF2 through which morphine regulates splicing specificity of the MOR encoding gene, OPRM1. PMID:26553431

  11. 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.

  12. 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.

  13. 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).

  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. 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

  16. Anharmonicity in light scattering by optical phonons in GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Joshya, R. S.; Rajaji, V.; Narayana, Chandrabhas; Mascarenhas, A.; Kini, R. N.

    2016-05-01

    We present a Raman spectroscopic study of GaAs1-xBix epilayers grown by molecular beam epitaxy. We have investigated the anharmonic effect on the GaAs-like longitudinal optical phonon mode ( LOGaAs' ) of GaAs1-xBix for different Bi concentrations at various temperatures. The results are analyzed in terms of the anharmonic damping effect induced by thermal and compositional disorder. We have observed that the anharmonicity increases with Bi concentration in GaAs1-xBix as evident from the increase in the anharmonicity constants. In addition, the anharmonic lifetime of the optical phonon decreases with increasing Bi concentration in GaAs1-xBix.

  17. Ge1-xSnx alloys pseudomorphically grown on Ge(001)

    NASA Astrophysics Data System (ADS)

    Ladrón de Guevara, H. Pérez; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2003-12-01

    Ge1-xSnx alloys were grown on Ge(001) substrates in a conventional rf sputtering system. We determined the in-plane and in-growth lattice parameters, as well as the alloy bulk lattice parameter of the alloys for different Sn concentrations by high resolution x-ray diffraction. The Sn concentration was determined assuming Vegard's law for the alloy lattice parameter. At low concentrations, we observed that Ge1-xSnx layers have pseudomorphic characteristics for layer thickness from 320 to 680 nm. These characteristics of Ge1-xSnx layers agree with the People and Bean critical thickness model. This structural study opens the possibility of growing dislocation-free Ge1-xSnx alloys below the critical thickness.

  18. Achieving enhanced hole transport capability of Ge1-xSnx alloys through uniaxial compressive strain

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Liang, Renrong; Wang, Jing; Xu, Jun

    2015-11-01

    The hole transport capability of Ge1-xSnx alloys under the uniaxial compressive strain is comprehensively investigated by calculations using the nonlocal empirical pseudopotential method. The results indicate that the [110] uniaxial compressive strain is favorable for the hole transport of Ge1-xSnx alloys. For the [110] uniaxial compression, the strain-parallel hole effective mass of the top most valance band is the smallest, and the corresponding valance band splitting energy is the largest compared with the [100] uniaxial and the (001) biaxial compressive strain. In addition, the large uniaxial compressive strain and the high Sn composition are both beneficial for boosting the hole mobility of strained Ge1-xSnx alloys. The enhanced hole transport capability can be achieved through the [110] uniaxial compressive strain for high-performance Ge1-xSnx pMOSFETs applications.

  19. 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.

  20. Phase diagram of BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Hu, Ding; Li, Shiliang; Luo, Huiqian; Dai, Pengcheng

    2015-03-01

    As a unique system of high temperature Iron-based superconductors, recent experimental results indicate that there is a quantum critical point (QCP) around the optimal level in BaFe2(As1-xPx)2 . We use neutron diffraction, high resolution X-ray scattering and NMR techniques to map out the detailed phase diagram. It is found that the long-range antiferromagnetic (AF) order survives up to the optimal doping level within the instrument resolution. Our results suggest that the evolution of the AF order upon doping in BaFe2(As1-xPx)2 is different from that in the electron-doped Ba(Fe1-xCox)2 As2 or Ba(Fe1-xNix)2 As2.

  1. Ge 1- xC x double-layer antireflection and protection coatings

    NASA Astrophysics Data System (ADS)

    Hu, C. Q.; Zheng, W. T.; Li, J. J.; Jiang, Q.; Tian, H. W.; Lu, X. Y.; Liu, J. W.; Xu, L.; Wang, J. B.

    2006-09-01

    The antireflection Germanium carbide (Ge 1- xC x) coating, deposited using RF reactive sputtering, on both sides of ZnS substrate wafer has been developed. The infrared (IR) transmittance spectra show that the IR transmittance in the wavelength region between 8 and 12 μm for the designed system Ge 1- xC x/ZnS/Ge 1- xC x is greatly enhanced compared to that for ZnS substrate. In addition, the double-layer coated ZnS substrate is approximately four times as hard as uncoated ZnS substrate. This investigation indicates that a double-layer Ge 1- xC x coating can be used as an effective antireflection and protection coating on ZnS infrared window.

  2. Phonon mean free path spectrum and thermal conductivity for Si1-xGex nanowires

    NASA Astrophysics Data System (ADS)

    Xie, Guofeng; Guo, Yuan; Wei, Xiaolin; Zhang, Kaiwang; Sun, Lizhong; Zhong, Jianxin; Zhang, Gang; Zhang, Yong-Wei

    2014-06-01

    We reformulate the linearized phonon Boltzmann transport equation by incorporating the direction-dependent phonon-boundary scattering, and based on this equation, we study the thermal conductivity of Si1-xGex nanowires and derive their phonon mean free path spectrum. Due to the severe suppression of high-frequency phonons by alloy scattering, the low frequency phonons in Si1-xGex nanowires have a much higher contribution to the thermal conductivity than pure silicon nanowires. We also find that Si1-xGex nanowires possess a stronger length-dependent, weaker diameter-dependent, and weaker surface roughness-dependent thermal conductivity than silicon nanowires. These findings are potentially useful for engineering Si1-xGex nanowires for thermoelectric applications.

  3. 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.

  4. Photoacoustic investigation of Cd1-xMnxTe mixed crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Firszt, F.; ŁÈ©gowski, S.; MÈ©czyńska, H.; Marasek, A.; Pawlak, M.

    2003-01-01

    Ternary diluted magnetic semiconductors Cd1-xMnxTe obtained by Bridgman method in the range of composition 0⩽x⩽0.7 were investigated. The photoacoustic spectroscopy with a piezoelectric transducer was employed to evaluate the energy gaps of Cd1-xMnxTe bulk mixed crystals at room temperature. A linear increase of energy gap with increasing x value has been observed. Photoacoustic data were correlated with ellipsometric measurements.

  5. Photoacoustic study of Cd{1-x-y}BexMnyTe mixed crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Firszt, F.; Legowski, S.; Męczyńska, H.; Marasek, A.; Pawlak, M.

    2003-06-01

    Quaternary diluted niagnetic semiconductors Cd{1-x-y}BexMnyTe obtained by Bridgman method for x=0.01 and 0leq yleq 0.15 were investigated. The photoacoustic spectroscopy with a piezoelectric transducer was employed to evaluate the energy gaps of Cd{1-x-y}BexMnyTe bulk mixed crystals at room temperature. The increase of the energy gap with increasing x value has been observed. Characteristic features of amplitude and phase photoacoustic spectra were discussed.

  6. 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.

  7. The magnetic entropy changes in Gd 1- xB x alloys

    NASA Astrophysics Data System (ADS)

    Dunhui, Wang; Songling, Huang; Zhida, Han; Zhenghua, Su; Yi, Wang; Youwei, Du

    2004-07-01

    A series of Gd (1- x) B x alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd (1- x) B x alloys may be utilized as refrigerant in household magnetic refrigeration.

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

    PubMed

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

    2015-04-28

    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 ZnO 1-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 ZnO 1-x. The incorporation of oxygen defects could effectively extend the light absorption of ZnO 1-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 ZnO 1-x shows a higher photodegradation of methyl orange (MO) compared to defect-free ZnO under visible light illumination. Additionally, the high content of ˙OH radicals with a strong photo-oxidation capability over the ZnO 1-x nanosheets significantly contributes to the improvement in the photocatalytic performance. Our oxygen deficient ZnO 1-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. PMID:25812132

  9. 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.

  10. Drastic change in density of states upon martensitic phase transition for metamagnetic shape memory alloy Ni2Mn(1+x)In(1-x).

    PubMed

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

    2015-09-16

    We have unravelled the electronic structure of a class of metamagnetic shape memory alloy Ni2Mn1+x In1-x by combining bulk-sensitive hard x-ray photoelectron spectroscopy and first-principles density-functional calculations. A sharp drop in the Ni 3d e(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. PMID:26289060

  11. Synthesis of fatty acid methyl ester from used vegetable cooking oil by solid reusable Mg 1-x Zn 1+x O2 catalyst.

    PubMed

    Olutoye, M A; Hameed, B H

    2011-02-01

    Fatty acid methyl ester was produced from used vegetable cooking oil using Mg(1-)(x) Zn(1+)(x)O(2) solid catalyst and the performance monitored in terms of ester content obtained. Used vegetable cooking oil was employed to reduce operation cost of biodiesel. The significant operating parameters which affect the overall yield of the process were studied. The highest ester content, 80%, was achieved with the catalyst during 4h 15 min reaction at 188°C with methanol to oil ratio of 9:1 and catalyst loading of 2.55 wt% oil. Also, transesterification of virgin oil gave higher yield with the heterogeneous catalyst and showed high selectivity towards ester production. The used vegetable cooking oil did not require any rigorous pretreatment. Catalyst stability was examined and there was no leaching of the active components, and its performance was as good at the fourth as at the first cycle. PMID:21183335

  12. (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.

  13. Statistical model structure of A1-xZxB2 Laves phase C15 system—the superconducting alloy Ce1-xLaxRu2

    NASA Astrophysics Data System (ADS)

    Robouch, B. V.; Marcelli, A.; Saini, N. L.; Kisiel, A.

    2009-01-01

    The local structure of the Ce1-xLaxRu2 system measured by EXAFS is re-examined and correlated to the statistical ad hoc model recently applied to the sphalerite, wurtzite, and other intermetallic ternary alloys. Deconvolution of the EXAFS data shows that the Ce1-xLaxRu2 ternary system is essentially a mixture of CeRu2 and LaRu2 binary alloys with a small proportion of the Ce0.5La0.5Ru2 ternary configuration, which is maximum for the intermediate concentration. Moreover, the analysis reveals that while the LaRu2 configuration exhibits a Bernoulli random distribution, the presence of a Ce atom affects both the CeRu2 and Ce0.5La0.5Ru2 distributions, strongly favoring the configuration with the CeCe pair, while keeping rare that with a single Ce ion.

  14. 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.

  15. 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).

  16. 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 $x=0.5$.

  17. Molecular beam epitaxy of free-standing wurtzite AlxGa1-xN layers

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Staddon, C. R.; Martin, R. W.; Kent, A. J.; Foxon, C. T.

    2015-09-01

    Recent developments with group III nitrides present AlxGa1-xN based LEDs as realistic devices for new alternative deep ultra-violet light sources. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite AlxGa1-xN films were grown by PA-MBE on 2-in. GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. X-ray microanalysis measurements confirm that the AlN fraction is uniform across the wafer and mass spectroscopy measurements show that the composition is also uniform in depth. We have demonstrated that free-standing wurtzite AlxGa1-xN wafers can be achieved by PA-MBE for a wide range of AlN fractions. In order to develop a commercially viable process for the growth of wurtzite AlxGa1-xN substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8 μm/h on 2-in. diameter GaAs and sapphire wafers.

  18. 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.

  19. Electronic band structure and effective mass parameters of Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Lu Low, Kain; Yang, Yue; Han, Genquan; Fan, Weijun; Yeo, Yee-Chia

    2012-11-01

    This work investigates the electronic band structures of bulk Ge1-xSnx alloys using the empirical pseudopotential method (EPM) for Sn composition x varying from 0 to 0.2. The adjustable form factors of EPM were tuned in order to reproduce the band features that agree well with the reported experimental data. Based on the adjusted pseudopotential form factors, the band structures of Ge1-xSnx alloys were calculated along high symmetry lines in the Brillouin zone. The effective masses at the band edges were extracted by using a parabolic line fit. The bowing parameters of hole and electron effective masses were then derived by fitting the effective mass at different Sn compositions by a quadratic polynomial. The hole and electron effective mass were examined for bulk Ge1-xSnx alloys along specific directions or orientations on various crystal planes. In addition, employing the effective-mass Hamiltonian for diamond semiconductor, band edge dispersion at the Γ-point calculated by 8-band k.p. method was fitted to that obtained from EPM approach. The Luttinger-like parameters were also derived for Ge1-xSnx alloys. They were obtained by adjusting the effective-mass parameters of k.p method to fit the k.p band structure to that of the EPM. These effective masses and derived Luttinger parameters are useful for the design of optical and electronic devices based on Ge1-xSnx alloys.

  20. Mobility Behavior of Ge1-xSnx Layers Grown on Silicon-on-Insulator Substrates

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Tsutsui, Norimasa; Shimura, Yosuke; Takeuchi, Shotaro; Sakai, Akira; Zaima, Shigeaki

    2010-04-01

    We have investigated the behaviors of the carrier mobility and concentration of the undoped Ge1-xSnx layers epitaxially grown on silicon-on-insulator (SOI) substrates. Hall measurement revealed the conduction of holes excited from acceptor levels related to vacancy defects whose concentration was as high as 1018 cm-3 in Ge1-xSnx layers. The temperature dependences of the carrier mobility and concentration in the valence band was estimated by reducing the parallel conduction component in the impurity band. The incorporation of Sn at a content lower than 4.0% hardly degraded the hole mobility of heteroepitaxial Ge1-xSnx layers. In contrast, the mobility of the Ge1-xSnx layers was improved by reducing the carrier concentration of the Ge1-xSnx layers by Sn incorporation compared with that of the Ge layer formed under the same growth and annealing conditions. This result suggests that the incorporation of Sn into Ge leads to reducing the hole concentration of the electrically active vacancy defects due to the formation of Sn-vacancy pairs.

  1. 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.

  2. Synthesis of Ni1-xZnxO hollow structures by a facile method

    NASA Astrophysics Data System (ADS)

    Li, H.; Song, B.; Cai, G. M.

    2015-02-01

    By a sol-gel method, we obtained Ni1-xZnxO polycrystalline powders. The obtained Ni1-xZnxO was characterized by scanning electron microscope and transmission electron microscope techniques. The characterized results showed that the obtained Ni1-xZnxO showed hollow structure. The grain sizes of the obtained hollow Ni1-xZnxO were quite uniform, typically in the range of 400-500 nm. This method is a simple and effective method for large-scale synthesis of hollow Ni1-xZnxO quasi-spheres. The present method is very promising for large-scale production because the method is only involves commercial Zn(AC)2·2H2O and NiCl2·6H2O powders and the reaction is achieved in an open system free of autoclave and organic chemical reagents. This template-free method is facile but effective and therefore it is very promising for large-scale industrial production.

  3. 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.

  4. 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.

  5. 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.

  6. Origin of the black-golden transition in Sm1-xYxS

    NASA Astrophysics Data System (ADS)

    Imura, Keiichiro; Saito, Mai; Kaneko, Masaki; Ito, Takahiro; Hajiri, Tetsuya; Matsunami, Masaharu; Kimura, Shin-ichi; Deguchi, Kazuhiko; Suzuki, Hiroyuki S.; Sato, Noriaki K.

    2015-03-01

    We report angle-resolved photoemission spectroscopy, electrical resistivity and Hall effect measurements on Sm1-xYxS. At the smallest doping concentration x = 0.03, the system changes from a semiconducting to metallic conductivity, whereas it is at a critical concentration xc ≊ 0.19 that there occurs the volume collapse accompanied by a color change from black to golden. It appears that the band gap between 4f and 5d bands vanishes at xc. From these results, we suggest that the black-to-golden transition of Sm1-xYxS has the same mechanism as the pressure-induced valence transition of SmS, but the semiconductor-to-metal transition has a different origin for Sm1-xYxS and SmS.

  7. Sn diffusion during Ni germanide growth on Ge1-xSnx

    NASA Astrophysics Data System (ADS)

    Demeulemeester, J.; Schrauwen, A.; Nakatsuka, O.; Zaima, S.; Adachi, M.; Shimura, Y.; Comrie, C. M.; Fleischmann, C.; Detavernier, C.; Temst, K.; Vantomme, A.

    2011-11-01

    We report on the redistribution of Sn during Ni germanide formation on Ge1-xSnx/ and its influence on the thin film growth and properties. These results show that the reaction involves the formation of Ni5Ge3 and NiGe. Sn redistributes homogenously in both phases, in which the Sn/Ge ratio retains the ratio of the as-deposited Ge1-xSnx film. Sn continues to diffuse after full NiGe formation and segregates in two regions: (1) at the interface between the germanide and Ge1-xSnx and (2) at the surface, which has major implications for the thin film and contact properties.

  8. 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.

  9. 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.

  10. The growth and characterization of Al(x)Ga(1-x)As/Ge heterostructures

    NASA Technical Reports Server (NTRS)

    Choi, S. W.; Bachmann, K. J.; Timmons, M. L.; Colpitts, T. S.; Posthill, J. B.

    1992-01-01

    The effects of the growth temperature and the Al(x)Ga(1-x)As layer thickness on the structural, optical, and electrical properties of Al(x)Ga(1-x)As/Ge heterostructures grown for photovoltaic applications were investigated using different-thickness (between 1 micron and 5 microns) Al(x)Ga(1-x)As layers grown by MOCVD in the temperature range between 660 and 780 C. Results obtained from double-crystal X-ray rocking curve measurements, electron beam induced current, cross-sectional TEM, Raman spectroscopy, SIMS, and steady-state and time-resolved photoluminescence measurements are presented. It was found that the highest minority carrier lifetime, 2.41 ns, was obtained for T(G) = 780 C, but the lowest interfacial recombination velocity, 1.6 x 10 exp 4, was obtained at 660 C.

  11. 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.

  12. Ti1-xAux Alloys: Hard Biocompatible Metals and Their Possible Applications

    NASA Astrophysics Data System (ADS)

    Svanidze, Eteri; Besara, Tiglet; Ozaydin, M. Fevzi; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Morosan, Emilia

    2015-03-01

    The search for new hard materials is often challenging from both theoretical and experimental points of view. Furthermore, using materials for biomedical applications calls for alloys with high biocompatibility which are even more sparse. The Ti1-xAux (0 . 22 <= x <= 0 . 8) exhibit extreme hardness and strength values, elevated melting temperatures (compared to those of constituent elements), reduced density compared to Au, high malleability, bulk metallicity, high biocompatibility, low wear, reduced friction, potentially high radio opacity, as well as osseointegration. All these properties render the Ti1-xAux alloys particularly useful for orthopedic, dental, and prosthetic applications, where they could be used as both permanent and temporary components. Additionally, the ability of Ti1-xAux alloys to adhere to ceramic parts could reduce the weight and cost of these components. The work at Rice was supported by NSF DMR 0847681 (E.M. and E.S.).

  13. 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}.

  14. 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.

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

    SciTech Connect

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

    2011-11-01

    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}.

  16. Precise AuxPt1-x Alloy Nanoparticle Array of Tunable Composition for Catalytic Applications

    NASA Astrophysics Data System (ADS)

    Jahn, Sarah; Lechner, Sebastian J.; Freichels, Helene; Möller, Martin; Spatz, Joachim P.

    2016-02-01

    A 3-dimensional Block Copolymer Micellar nanoLithography (BCML) process was used to prepare AuxPt1-x alloy nanoparticles (NPs) monodisperse in size and composition, strongly anchored onto SiO2-particles (0.2 wt.% AuxPt1-x/SiO2). The particles possess a face-centered cubic (fcc) crystal structure and their size could be varied from 3-12 nm. We demonstrate the uniformity of the Au/Pt composition by analyzing individual NPs by energy-dispersive X-ray spectroscopy. The strongly bound AuxPt1-x NPs catalyzed the oxidation of CO with high activity. Thermal ageing experiments in pure CO2 as well as in ambient atmosphere demonstrated stability of the size distribution for times as long as 22 h.

  17. Polycrystalline ZnS(x)Se(1 - x) thin films deposited on ITO glass by MBE.

    PubMed

    Shen, Da-Ke; Sou, I K; Han, Gao-Rong; Du, Pi-Yi; Que, Duan-Lin

    2003-01-01

    MBE growth of ZnS(x)Se(1 - x) thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270 degrees C to 330 degrees C . The XRD theta/2theta spectra resulted from these films indicated that the as-grown polycrystalline ZnS(x)Se(1 - x) thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 degrees C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnS(x)Se(1 - x) thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure. PMID:12659224

  18. Study of Nb/NbxSi1-x/Nb Josephson junction arrays

    NASA Astrophysics Data System (ADS)

    Cao, Wen-Hui; Li, Jin-Jin; Zhong, Yuan; He, Qing

    2015-12-01

    Owing to the adjustable characteristics and superior etching properties of co-sputtered NbxSi1 - x film, we are trying to fabricate Nb/NbxSi1 - x/Nb Josephson junction arrays for voltage standard. It is important to find the suitable NbxSi1 - x barrier for the junctions. Josephson junctions with different barrier content are fabricated. Current-voltage characteristics are measured and analyzed. It is demonstrated in this paper that critical current can be adjusted by using different barrier content and thickness. Shapiro steps of five hundred junctions in series are observed. Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2011BAK15B00), the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61401418), and the Basic Research Foundation of National Institute of Metrology of China (Grant No. 20-AKY1415).

  19. 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.

  20. Epitaxial semimetallic HfxZr1-xB2 templates for optoelectronic integration on silicon

    NASA Astrophysics Data System (ADS)

    Roucka, Radek; An, YuJin; Chizmeshya, Andrew V. G.; Tolle, John; Kouvetakis, John; D'Costa, Vijay R.; Menéndez, José; Crozier, Peter

    2006-12-01

    High quality heteroepitaxial HfxZr1-xB2 (x=0-1) buffers were grown directly on Si(111). The compositional dependence of the film structure and ab initio elastic constants were used to show that hexagonal HfxZr1-xB2 possess tensile in-plane strain (0.5%) as grown. High quality HfB2 films were also grown on strain compensating ZrB2-buffered Si(111). Initial reflectivity measurements of thick ZrB2 films agree with first principles calculations which predict that the reflectivity of HfB2 increases by 20% relative to ZrB2 in the 2-8eV range. These tunable structural, thermoelastic, and optical properties suggest that HfxZr1-xB2 templates should be suitable for broad integration of III nitrides with Si.

  1. Microstructural properties of {InAs}/{InAsxSb1 - x} superlattices and InAs xSb 1 - x ordered alloys grown by modulated molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Y.-H.; Lew, A.; Yu, E.; Chen, Y.

    1997-05-01

    Modulated molecular beam epitaxy (MMBE) has been demonstrated to be useful in controlling group-V alloys such as InAs xSb 1 - x and AlAs xSb 1 - x. Further studies of the MMBE grown InAs xSb 1 - x ordered alloys and {InAs}/{InAsxSb1 - x} superlattices by using cross-sectional scanning tunneling microscopy show well defined interfaces between InAs xSb 1 - x ordered alloys and InAs. Clear composition modulation is observed in the InAs xSb 1 - x ordered alloy layers. Transmission electron diffraction and microscopy, X-ray diffraction, and low temperature photoluminescence experiments show no obvious sign of CuPt orderings. These results suggest that MMBE provides a possible means to bypass the ordering problem of InAs xSb 1 - x random alloys.

  2. 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.

    2011-01-01

    A CdS{sub x}Te{sub 1-x} layer forms by interdiffusion of CdS and CdTe during the fabrication of thin film CdTe photovoltaic (PV) devices. The CdS{sub x}Te{sub 1-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 has indicated that the electrical junction is located in this interdiffused CdS{sub x}Te{sub 1-x} region. Further understanding, however, is essential to predict the role of this CdS{sub x}Te{sub 1-x} layer in the operation of CdS/CdTe devices. In this study, CdS{sub x}Te{sub 1-x} alloy films were deposited by radio-frequency magnetron sputtering and coevaporation from CdTe and CdS sources. Both radio-frequency-magnetron-sputtered and coevaporated CdS{sub x}Te{sub 1-x} films of lower S content (x < 0.3) have a cubic zincblende (ZB) structure akin to CdTe, whereas 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 CdCl{sub 2} heat treatment at {approx}400 C for 5 min. Films sputtered in a 1% O{sub 2}/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl{sub 2} heat treatment. Films sputtered in O{sub 2} partial pressure have a much wider bandgap than expected. This may be explained by nanocrystalline size effects seen previously for sputtered oxygenated CdS (CdS:O) films.

  3. Validation of interstitial iron and consequences of nonstoichiometry in mackinawite (Fe(1+x)S).

    PubMed

    Brgoch, Jakoah; Miller, Gordon J

    2012-03-01

    A theoretical investigation of the relationship between chemical composition and electronic structure was performed on the nonstoichiometric iron sulfide, mackinawite (Fe(1+x)S), which is isostructural and isoelectronic with the superconducting Fe(1+x)Se and Fe(1+x)(Te(1-y)Se(y)) phases. Even though Fe(1+x)S has not been measured for superconductivity, the effects of stoichiometry on transport properties and electronic structure in all of these iron-excess chalcogenide compounds has been largely overlooked. In mackinawite, the amount of Fe that has been reported ranges from a large excess, Fe(1.15)S, to nearly stoichiometric, Fe(1.00(7))S. Here, we analyze, for the first time, the electronic structure of Fe(1+x)S to justify these nonstoichiometric phases. First principles electronic structure calculations using supercells of Fe(1+x)S yield a wide range of energetically favorable compositions (0 < x < 0.30). The incorporation of interstitial Fe atoms originates from a delicate balance between the Madelung energy and the occupation of Fe-S and Fe-Fe antibonding orbitals. A theoretical assessment of various magnetic structures for "FeS" and Fe(1.06)S indicate that striped magnetic ordering along [110] is the lowest energy structure and the interstitial Fe affects the values of moments in the square planes as a function of distance. Moreover, the formation of the magnetic moment is dependent on the unit cell volume, thus relating it to composition. Finally, changes in the composition cause a modification of the Fermi surface and ultimately the loss of a nested vector. PMID:22260375

  4. Molecular-beam epitaxy and characteristics of GaNyAs1-x-yBix

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Oe, Kunishige; Feng, Gan; Yoshimoto, Masahiro

    2005-09-01

    GaNyAs1-x-yBix alloys were grown by molecular-beam epitaxy using solid Ga, Bi, and As sources and nitrogen radicals generated from nitrogen gas in rf plasma. Changing the growth temperature is found to be a convenient method for controlling the GaBi molar fraction in the alloy reproducibly. The photoluminescence (PL) spectra show that the PL peak energy of GaNyAs1-x-yBix alloy decreased with increasing GaBi and GaN molar fractions. The redshift coefficients of ~62 meV/%Bi and ~130 meV/%N at the PL peak energy of GaNyAs1-x-yBix were observed at room temperature. The temperature dependence of the PL peak energy in the temperature range of 150-300 K is much smaller than the temperature dependence of the band gap of InGaAsP. The temperature coefficients of GaAs1-xBix and GaNyAs1-x-yBix band gaps are governed by the GaBi molar fraction and they decrease with increasing GaBi molar fraction. GaNyAs1-x-yBix alloys with different PL peak energies and lattice matched to GaAs substrates were obtained. The photoluminescence peak energy was located at a predicted wavelength for the sample lattice matched to GaAs which was found to have the structure of Ga(N0.33Bi0.67)zAs1-z.

  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. 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 .

  7. Thermodynamic properties of Ba1-xLaxCoO3

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    We have predicted the thermodynamic behavior of Ba1-xLaxCoO3 family at temperature 1K≤T≤300K using the Modified Rigid Ion Model (MRIM). The specific heat of BaCoO3 with La doping in the perovskite structure at A-site has been reported. Also, the cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD), specific heat (C) and Gruneisen parameter (γ) of Ba1-xLaxCoO3 compounds are discussed.

  8. Simultaneous electronic and magnetic transitions in La1 - xKxMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Che; de Lozanne, Alex

    1997-09-01

    We have fabricated perovskite La1-xKxMnO3 (x=0.14 and 0.2) thin films on SrTiO3 (100) by e-beam/thermal coevaporation. From the electrical and magnetic studies, we found a simultaneous occurrence of the paramagnetic to ferromagnetic state and insulating to metallic state, as predicted by the double exchange theory. The magnetoresistance is relatively small compared to that of the divalent cation doped La1-xAxMnO3 in fields up to 5 T.

  9. Fermi level tuning of topological insulator Bi2(SexTe1-x)3 nanoplates

    NASA Astrophysics Data System (ADS)

    Hao, Guolin; Qi, Xiang; Xue, Lin; Cai, Canying; Li, Jun; Wei, Xiaolin; Zhong, Jianxin

    2013-01-01

    The crystal structures and morphologies of ternary Bi2(SexTe1-x)3 nanoplates have been systematically characterized by employing atomic force microscopy, scanning electron microscopy, high-resolution transmission electron microscopy equipped with the energy dispersive X-ray spectrometer, and the X-ray diffraction. We find that the Bi2(SexTe1-x)3 nanoplates exhibit uniform charge and surface potential distributions. And their Fermi levels can be effectively tuned up to 0.23 eV by varying the selenium/tellurium composition ratios.

  10. 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.

  11. Investigations in MnAs1-xSbx: Experimental validation of a new magnetocaloric composite

    NASA Astrophysics Data System (ADS)

    de Campos, A.; da Luz, M. S.; de Campos, Adriana; Coelho, A. A.; Cardoso, L. P.; dos Santos, A. O.; Gama, S.

    2015-01-01

    An overview of the magnetocaloric properties of the MnAs1-xSbx is presented. The temperature dependence of the isothermal magnetic entropy, ΔSmag, and the refrigerant capacity, RC, have been investigated theoretically and experimentally in a composite based on second order MnAs1-xSbx phases. This work demonstrates the outstanding agreement between the experimental results and the continuous curves predicted by numerical calculations, indicating that this approach can be used to design magnetic refrigerant materials with enhanced magnetocaloric response in magnetic refrigerator performing an Ericsson cycle near room temperature.

  12. 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.

  13. 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.

  14. Chemical-Vapor Deposition Of Cd1-xMnxTe

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar; Stirn, Richard J.

    1989-01-01

    Experimental process makes films with interesting magnetic and magneto-optical properties. Films of dilute magnetic semiconductor alloy Cd1-xMnxTe deposited on glass and GaAs substrates by metalorganic chemical-vapor deposition (MOCVD). Devices made with Cd1-xMnxTe films known to exhibit strong photoluminescence, stimulated emission, and magnetically-tunable lasing action. In addition, energy-band gaps of such material tailored by altering its composition - property giving flexibility in development of high-efficiency cascade solar photovoltaic cells. Performs at atmospheric pressure, resulting in more-uniform films, covering larger area, and enabling higher production rate.

  15. 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.

  16. Impurity-Band Model for GaP1-xNx

    SciTech Connect

    Fluegel, B.; Zhang, Y.; Geisz, J. F.; Mascarenhas, A.

    2005-11-01

    Low-temperature absorption studies on free-standing GaP1-xNx films provide direct experimental evidence that the host conduction-band minimum (CBM) near X1C does not plunge downward with increased nitrogen doping, contrary to what has been suggested recently; rather, it remains stationary for x up to 0.1%. This fact, combined with the results of earlier studies of the CBM at ..GAMMA.. and conduction-band edge near L, confirms that the giant bandgap lowering observed in GaP1-xNx results from a CBM that evolves purely from nitrogen impurity bands.

  17. 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.

  18. Huge operation by energy gap of novel narrow band gap Tl1-x In1-x B x Se2 (B = Si, Ge): DFT, x-ray emission and photoconductivity studies

    NASA Astrophysics Data System (ADS)

    Piasecki, M.; Myronchuk, G. L.; Zamurueva, O. V.; Khyzhun, O. Y.; Parasyuk, O. V.; Fedorchuk, A. O.; Albassam, A.; El-Naggar, A. M.; Kityk, I. V.

    2016-02-01

    It is shown that narrow band gap semiconductors Tl1-x In1-x GexSe2 are able effectively to vary the values of the energy gap. DFT simulations of the principal bands during the cationic substitutions is done. Changes of carrier transport features is explored. Relation with the changes of the near the surface states is explored . Comparison on a common energy scale of the x-ray emission Se Kβ 2 bands, representing energy distribution of the Se 4p states, indicates that these states contribute preliminary to the top of the valence band. The temperature dependence of electrical conductivity and spectral dependence photoconductivity for the Tl1-x In1-x Ge x Se2 and Tl1-x In1-x Si x Se2 single crystals were explored and compared with previously reported Tl1-x In1-x Sn x Se2. Based on our investigations, a model of centre re-charging is proposed. Contrary to other investigated crystals in Tl1-x In1-x Ge x Se2 single crystals for x = 0.1 we observe extraordinarily enormous photoresponse, which exceed more than nine times the dark current. X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of Tl1-x In1-x GexSe2 (x = 0.1 and 0.2) single crystals have been studied. These results indicate that the relatively low hygroscopicity of the studied single crystals is typical for the Tl1-x In1-x Ge x Se2 crystals, a property that is very important for handling these quaternary selenides as infrared materials operating at ambient conditions.

  19. Pb/sub 1-x/Bi/sub x//Bi/Pb/sub 1-x/Bi/sub x/ Josephson junction

    SciTech Connect

    Sekine, M.; Kubota, T.; Musha, T.

    1988-12-01

    A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb/sub 1-x/Bi/sub x/ (0 less than or equal to x less than or equal to 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses theta in /angstroms/ and bismuth weight ratios x. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratios x at the temperature of 4.2 K.

  20. 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

  1. The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La1-x Ca x )(Zn1-x Mn x )AsO

    NASA Astrophysics Data System (ADS)

    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.

    2016-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La1-x Ca x )(Zn1-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}\\text{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}\\text{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 (La1-x Ca x )(Zn1-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 (La0.90Ca0.10)(Zn0.90Mn0.10)AsO below 300 K.

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

    DOE PAGESBeta

    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

  3. 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.

  4. The synthesis and characterization of 1111-type diluted magnetic semiconductors (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co)

    NASA Astrophysics Data System (ADS)

    Lu, Jicai; Man, Huiyuan; Ding, Cui; Wang, Quan; Yu, Biqiong; Guo, Shengli; Wang, Hangdong; Chen, Bin; Han, Wei; Jin, Changqing; Uemura, Yasutomo J.; Ning, Fanlong

    2013-09-01

    The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap semiconductor LaZnAsO has been investigated. Our results indicate that the single phase ZrCuSiAs-type tetragonal crystal structure is preserved in (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co) with the doping level up to x = 0.1 . While the system remains semiconducting, doping with Sr and Mn results in ferromagnetic order with T_C\\sim30\\ \\text{K} , and doping with Sr and Fe results in a spin-glass-like state below {\\sim}6\\ \\text{K} with a saturation moment of ˜0.02 μB/Fe, an order of magnitude smaller than the ˜0.4 μB/Mn of Sr- and Mn-doped samples. The same type of magnetic state is observed neither for (Zn,Fe) substitution without carrier doping, nor for Sr- and Co-doped specimens.

  5. 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.

  6. Synthesis of (Ga1-xZnx)(N1-xOx) with Enhanced Visible-Light Absorption and Reduced Defects by Suppressing Zn Volatilization.

    PubMed

    Chen, Dennis P; Skrabalak, Sara E

    2016-04-18

    (Ga1-xZnx)(N1-xOx) (GZNO) particles with enhanced optical absorption were synthesized by topotactic transformation of Zn(2+)/Ga(3+) layered double hydroxides. This outcome was achieved by suppressing Zn volatilization during nitridation by maintaining a low partial pressure of O2 (pO2). Zn-rich (x > (1)/3) variants of GZNO were achieved and compared to those prepared by conventional ammonoylsis conditions. The optical absorption and structural properties of these samples were compared to those prepared in the absence of O2 by diffuse-reflectance spectroscopy and powder X-ray diffraction methods. Notably, suppression of Zn volatilization leads to smaller-band-gap materials (2.30 eV for x = 0.42 versus 2.71 eV for x = 0.21) and reduced structural defects. This synthetic route and set of characterizations provide useful structure-property studies of GZNO and potentially other oxynitrides of interest as photocatalysts. PMID:26840948

  7. Exchange interaction between magnetic impurities on surfaces of Cu(x)Pd(1-x) and Cu(x)Au(1-x) random substitutional alloys.

    PubMed

    Ujfalussy, B; Simon, E

    2014-07-01

    We present fully relativistic first principles calculations of the exchange interactions between magnetic impurities deposited on the (1 1 1) surfaces of CuxPd1-x and CuxAu1-x random substitutional alloys, described using the coherent potential approximation. We show that as with pure surfaces of Cu and Au, where Shockley-type surface states mediate an RKKY-type interaction, a surface state and its dispersion can be obtained from studying the Bloch spectral function. In the second part of the paper we show how the details of the interaction are determined by the properties and dispersion of the surface states of the host material. We find an extra exponential decay in the range of the interactions compared to the 1/R(2) decay on surfaces of pure metals. The similar topology of the Fermi surface of Cu and Au allows us to scale the spin-orbit coupling and to study the Bychkov-Rashba splitting. Alternatively, the entirely different topology of the Cu and Pd Fermi surfaces allows us to study changes in the surface-state dispersion of the RKKY interaction between surface impurities. PMID:24934437

  8. 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.

  9. Superconductor-Metal-Insulator Transitions in two dimensional amorphous NbxSi1-x

    NASA Astrophysics Data System (ADS)

    Humbert, Vincent; Couëdo, François; Crauste, Olivier; Bergé, Laurent; Drillien, Anne-Aelle; Akiko Marrache-Kikuchi, Claire; Dumoulin, Louis

    2014-12-01

    We report on the study of the two-dimensional Disorder-induced Superconductor- Insulator Transition (D-SIT) in NbxSi1-x thin films. In this proceeding, we present new results on the emergence of an insulating state from a 2d metallic state.

  10. Fe-vacancy order and superconductivity in tetragonal β-Fe1-xSe

    PubMed Central

    Chen, Ta-Kun; Chang, Chung-Chieh; Chang, Hsian-Hong; Fang, Ai-Hua; Wang, Chih-Han; Chao, Wei-Hsiang; Tseng, Chuan-Ming; Lee, Yung-Chi; Wu, Yu-Ruei; Wen, Min-Hsueh; Tang, Hsin-Yu; Chen, Fu-Rong; Wang, Ming-Jye; Wu, Maw-Kuen; Van Dyck, Dirk

    2014-01-01

    Several superconducting transition temperatures in the range of 30–46 K were reported in the recently discovered intercalated FeSe system (A1-xFe2-ySe2, A = K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively decided, more than one magnetic phase with particular orders of iron vacancy and/or potassium vacancy were identified, and some were argued to be the parent phase. Here we show the discovery of the presence and ordering of iron vacancy in nonintercalated FeSe (PbO-type tetragonal β-Fe1-xSe). Three types of iron-vacancy order were found through analytical electron microscopy, and one was identified to be nonsuperconducting and magnetic at low temperature. This discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive in Fe-Se and related superconductors. In addition, the magnetic β-Fe1-xSe phases with particular iron-vacancy orders are more likely to be the parent phase of the FeSe superconducting system instead of the previously assigned β-Fe1+δTe. PMID:24351933

  11. 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

  12. 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

  13. 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

  14. Analysis and modeling of AlxGa1-xN-based Schottky barrier photodiodes

    NASA Astrophysics Data System (ADS)

    Monroy, E.; Calle, F.; Pau, J. L.; Sánchez, F. J.; Muñoz, E.; Omnès, F.; Beaumont, B.; Gibart, P.

    2000-08-01

    Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1-xN(0⩽x⩽0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1-xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (<0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1-xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1-xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to improve bandwidth and responsivity, and to achieve good ohmic contacts, a moderate n-type doping level (˜1018cm-3) is recommended.

  15. Further comments on segregation during Bridgman growth of Cd(x)Hg(1-x)Te

    NASA Technical Reports Server (NTRS)

    Lehoczky, S. L.; Szofran, F. R.

    1984-01-01

    The authors comment on recent papers published by Capper et al. (1983) and Jones et al. (1983) which report and discuss the variation of composition with axial position in Bridgman-grown Cd(x)Hg(1-x)Te alloys. The validity of a diffusion-controlled model for non-mixing growth conditions is particularly noted.

  16. Study of the Vibrational Spectra of the Mixed Crystal ZnS1-xSex

    NASA Astrophysics Data System (ADS)

    Basak, Tista; Rao, Mala N.; Chaplot, S. L.

    2011-07-01

    A simple transferable potential model has been employed to study the vibrational mode behavior of the mixed system ZnS1-xSex as a function of concentration and pressure. Further, the existence of a localized resonance mode has also been confirmed, in agreement with experimental data from Raman scattering.

  17. Synthesis Of Ir(1-x-y)Rh(x)Co(y)Sb(3) Semiconductors

    NASA Technical Reports Server (NTRS)

    Caillat, Thierry; Borshchevsky, Alexander; Fleurial, Jean-Pierre

    1994-01-01

    Ir(1-x-y)Rh(x)Co(y)Sb(3) semiconductors synthesized by gradient-freeze and sintering techniques. Sintering techniques used for variety of compositions; gradient-freeze technique used for RhSb(3) and CoSb(3).

  18. 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.

  19. Piezoelectric and pyroelectric study of Zn1-x-yBexMnySe mixed crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Firszt, F.; Legowski, S.; Meczynska, H.; Pawlak, M.; Marasek, A.

    2003-01-01

    This paper deals with investigations of thermal properties of Zn1-x-yBexMnySe bulk crystals by the photoacoustic (PA) method. Piezoelectric and pyroelectric transducers were used for investigation of continuous wave photoacoustic spectra. The values of thermal diffusivity were estimated using the dependence of amplitude and phase of the PA signal on the light modulation frequency.

  20. Neutron diffraction study of 154SmFeAsO1-xDx

    NASA Astrophysics Data System (ADS)

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Ikeda, Kazutaka; Hansen, Thomas; Otomo, Toshiya; Hosono, Hideo

    Hot issue in unconventional superconductors (SC) is why the 2nd highest-Tc of 56 K after cuprates is accomplished in the 1111-type iron-oxyarsenides LnFeAsO1-xFx (Ln = lanthanide). Recently, utilizing a hydride-substitution-method (O2- = H- + e-) in the LnFeAsO1 -xHx, we found a second SC phase in 0.18 <= x <= 0.45 at Ln = La in addition to the first one adjacent to the antiferromagnetic (AFM) order, and another AFM order accompanying a unique structural transition in over-doped region x >0.4. However, since the Tc of La-system is lower than the other systems, i.e., Ln = Ce, Sm and so on, it is still unclear whether the second AFM phase is essential for their high-Tc or not. Thus, we synthesized the isotope-substituted 154SmFeAsO1-xDx and performed neutron powder diffraction (NPD) to examine the structural and magnetic properties of the high-Tc 1111 system. In this talk, we show the results of NPD data and discuss the relation between the superconducting, magnetic, and structural properties of the 154SmFeAsO1-xDx and electron-doping-effect on it.

  1. Controllable Synthesis of Bandgap-Tunable CuSx Se(1-x) Nanoplate Alloys.

    PubMed

    Xu, Jun; Yang, Xia; Yang, Qing-Dan; Huang, Xing; Tang, Yongbing; Zhang, Wenjun; Lee, Chun-Sing

    2015-07-01

    Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS(x)Se(1-x) nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu(2+) cations with polysulfide/-selenide ((S(n)Se(m))(2-)) anions rather than independent S(n)(2-) and Se(m)(2-) anions is responsible for the low-temperature and rapid synthesis of CuS(x)Se(1-x) alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se-Se and the S-S bonds. The lattice parameters 'a' and 'c' of the hexagonal CuS(x)Se(1-x) alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S-Se stretching mode are observed, thus further confirming formation of the alloyed CuS(x)Se(1-x) phase. PMID:25864726

  2. Surface photovoltage spectroscopy analyses of Cd{sub 1-x}Zn{sub x}Te

    SciTech Connect

    Cavalcoli, D.; Fraboni, B.; Cavallini, A.

    2008-02-15

    Cd{sub 1-x}Zn{sub x}Te alloys have been studied by surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS). The analyses of surface photovoltage spectra have been perfomed at near and above band gap energies. Surface recombination effects on the surface photovoltage have been investigated. SPS analyses of Cd{sub 1-x}Zn{sub x}Te alloys with different surface conditions have shown that the surface recombination velocity significantly affects the SPS determination of the material band gap. Accounting for this and preparing the surfaces accordingly, SPS spectra of Cd{sub 1-x}Zn{sub x}Te samples have allowed an accurate determination of the optical band gap as a function of the Zn concentration, determined via EDS analyses. The local increases in the density of states associated with band structure features in Cd{sub 1-x}Zn{sub x}Te alloys have been investigated by SPS spectra in the above band gap energy range.

  3. 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

  4. Structural and optical properties of sol-gel synthesised Zn1-xMgxO nanocrystals

    NASA Astrophysics Data System (ADS)

    Chandrasekaran, P.; Anandan, P.; Srinivasan, N.

    2013-12-01

    Zn1-xMgxO nanocrystals with various compositions (x = 0-0.1) were synthesised by sol-gel process using tri ethanol amine (TEA) as a capping agent. The structural properties of the prepared materials were studied by X-ray diffraction analysis. Un-agglomerated nanocrystals with spherical morphology were observed by scanning electron microscope (SEM). The presence of Mg in the Zn1-xMgxO was confirmed by X-ray photoelectron spectroscopy (XPS). Moreover, the Mg composition relatively increases in the synthesised nanocrystals as it increases in the precursor solution. The optical absorption studies of the Zn1-xMgxO samples show the blue shift from the pure ZnO due to the incorporation of Mg in ZnO lattice. The photoluminescence studies demonstrated that the intensity of defect related deep level emission increases drastically with increasing the x value from 0.02 to 0.08 and decreases sharply on further increase of Mg from 0.08 to 0.1. The mechanism for the enhanced green emission was explained based on the structural properties of the Zn1-xMgxO samples.

  5. S{sup 1}xS{sup 2} Gowdy supersymmetric constraint

    SciTech Connect

    Maceda, Marco; Macias, Alfredo

    2011-02-15

    We obtain the supersymmetric constraint for S{sup 1}xS{sup 2} Gowdy spacetime in the N=1 supergravity formalism of quantum cosmology in four dimensions. The physical states of the model for both polarized and unpolarized cases are presented.

  6. Intercallation of Li1-xFexO2 in the superconducting FeSe

    NASA Astrophysics Data System (ADS)

    Louca, Despina; Yang, Junjie

    The intercallation of LiFeO2 in the tetragonal lattice of the 8 K superconductor Fe1-ySe leads to a great enhancement of the superconducting transition temperature, TC ~ 43 K, and to an antiferromagnetic transition at 8.5 K. While the LiFeO2 layer acts as a charge reservoir, its Fe3+ ion (3d5) is magnetic creating a magnetic buffer layer. Most recently, we developed a new synthesis method to control the Fe concentration in the intercallating layer as well as the filling ratio of the Li1-xFexO2 : FeSe layers. Neutron scattering measurements were carried out on powder samples of (Li1-xFexO2)yFeSe. With the intercallation, no crystal structural transition from the P4/nmm symmetry occurs but the c-axis lattice constant expands substantially, evidence of the intercallation. At the same time, the tetrahedral FeSe layers remain intact with no compression or expansion and free of vacancies. Moreover, the intercallation along the c-axis although not uniform leads to a reduction in TC when the ratio of Li1 - x FexO2 : FeSe layers is about 1 to 3. Our results also indicate that the amount of Fe in the Li1 - x FexO2 layer has a direct correlation to the transition temperature as well.

  7. 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.

  8. 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.

  9. 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.

  10. P-type Semiconducting Behavior of BaSn1-xRuxO3 system

    NASA Astrophysics Data System (ADS)

    Kwon, Hyukwoo; Shin, Juyeon; Char, Kookrin

    2015-03-01

    BaSnO3 is a promising transparent perovskite oxide semiconductor due to its high mobility and chemical stability. Exploiting such properties, we have applied BaSnO3 to the field effect, the 2-dimensional electron gas, and the pn-junction devices. In spite of the success of the K-doped BaSnO3 as a p-type doped, its carrier density at room temperature is rather small due to its high activation energy of about 0.5 eV. In continuation of our previous study on SrSn1-xRuxO3 system, we studied the p-type semiconducting behavior of BaSn1-xRuxO3 system. We have epitaxially grown the BaSn1-xRuxO3 (0 <=x <=0.12) thin films by pulsed laser deposition. X-ray diffraction measurements show that the films maintain a single phase over the entire doping range and the lattice constants of the system decrease monotonously as the doping increases. Transport measurements show that the films are semiconducting and their resistivities dramatically decrease as the Ru doping increases. Hall measurement data show that the charge carriers are p-type and its corresponding mobility values vary from 0.3 ~ 0.04 cm2/V .s, depending on the doping rate. The hole carrier densities, measured to be 1017 ~ 1019 /cm3, are larger than those of K-doped BaSnO3. Using BaSn1-xRuxO3 and Ba1-xLaxSnO3 as p-type and n-type semiconductors, we will fabricate pn-junctions and report its performance.

  11. Tunnel optical radiation in InxGa1-xN

    NASA Astrophysics Data System (ADS)

    Alexandrov, Dimiter; Skerget, Shawn

    2014-02-01

    An investigation of tunnel optical radiation in epitaxial layers of n-type InxGa1-xN grown on p-type GaN by novel plasma based migration enhanced epitaxy is presented. Experimental results of electro-luminescence spectra for InxGa1-xN/p-GaN hetero-junctions were obtained and they show two well expressed optical bands - one in range 500-540 nm and other in range 550-610 nm. An interesting detail is that each band begins and ends by sharp drops of the radiation, which nearly approach zero. A theoretical investigation of the unusual behavior of these spectra was done using LCAO electron band structure calculations. The optical ranges of these bands show that the radiation occurs in the InxGa1-xN region. In fact, substitutions of In atoms in Ga sites creates defects in the structure of InxGa1-xN and the corresponding LCAO matrix elements are found on this basis. The LCAO electron band structures are calculated considering the interactions between nearest-neighbor orbitals. Electron energy pockets are found in both the conduction and the valence bands at the Γ point of the electron band structures. Also it is found that these pockets are separated by distances, for which there is overlapping between the electron wave functions describing localized states belonging to the pockets, and as a result tunnel optical radiation can take place. This type of electron transition - between such a pocket in the conduction band and a pocket in the valence band - occurs in InxGa1-xN, causing the above described optical bands. This conclusion concurs with the fact that the shapes of these bands change with change of the applied voltage.

  12. Electronic structures and the estimated Curie temperatures of (Ga1-yIny)1-xMnxAs

    NASA Astrophysics Data System (ADS)

    Miura, K.; Iwasawa, M.; Imanaga, S.; Ami, T.

    2003-12-01

    The electronic structures of (Ga1-yIny)1-xMnxAs have been investigated using the Korringa, Kohn and Rostoker (KKR) method with the coherent potential approximation (CPA). The estimated Curie temperature (TC) of Ga1-xMnxAs is higher than that of (Ga0.5In0.5)1-xMnxAs and In1-xMnxAs when x≲0.10. On the other hand, the estimated TC of Ga1-xMnxAs saturates with an increase of x when x≳0.05, but that of (Ga0.5In0.5)1-xMnxAs and In1-xMnxAs does not saturate even when x>0.10. These results are in good agreement with the previous experimental results. Our calculated results predict that the TC of (Ga0.5In0.5)1-xMnxAs and In1-xMnxAs will be higher than that of Ga1-xMnxAs when x≳0.10.

  13. 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.

  14. 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.

  15. Synthesis and charge-discharge properties of Li 1+ xNi 1- x- yCo yO 2- zF z

    NASA Astrophysics Data System (ADS)

    Kubo, K.; Arai, S.; Yamada, S.; Kanda, M.

    LiNiO 2 is one of the best cathode active materials for applying to lithium rechargeable batteries because of large capacity. However, its unsatisfactory cycling properties and difficulties in handling are not yet to be improved. It was found by some groups [M.G.S.R. Thomas, W.I.F. David, J.B. Goodenough, P. Groves, Mater. Res. Bull. 20 (1985) 1137; J.R. Dahn, U. von Sacken, C.A. Michal, Solid State Ionics 44 (1990) 87] that cation substitution reduces the lattice deformation during charging or discharging and improves the cycling properties. On the other hand, we reported [T. Ohzuku, A. Ueda, M. Kouguchi, J. Electrochem. Soc. 12 (1995) 4033] that addition of LiF to the starting materials, causing fluorine substitution for the anion, is also effective to obtain a better cycling life for LiNiO 2, though the problem of the lattice deformation is not alleviated. Thus, it was expected that simultaneous substitution of cation- and anion sites might be useful. We synthesized Li 1+ xNi 1- x- yCo yO 2- zF z by an ordinary solid state reaction and evaluated the charge-discharge properties of this series of samples. The initial discharge capacity of Li 1.075Ni 0.755Co 0.17O 1.9F 0.1 was 182 mAh/g.The capacity decrease rate was only 2.8% in the first 100 cycles, and became even smaller as the cycle number increased. The result suggests that each of the Co- and F substitution independently contributes to the improvement of cycling properties of LiNiO 2.

  16. 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.

  17. Cu-doped Cd1- x Zn x S alloy: synthesis and structural investigations

    NASA Astrophysics Data System (ADS)

    Yadav, Indu; Ahlawat, Dharamvir Singh; Ahlawat, Rachna

    2016-03-01

    Copper doped Cd1- x Zn x S ( x ≤ 1) quantum dots have been synthesized using chemical co-precipitation method. Structural investigation of the synthesized nanomaterials has been carried out by powder XRD method. The XRD results have confirmed that as-prepared Cu-doped Cd1- x Zn x S quantum dots have hexagonal structure. The average nanocrystallite size was estimated in the range 2-12 nm using Debye-Scherrer formula. The lattice constants, lattice plane, d-spacing, unit cell volume, Lorentz factor and dislocation density were also calculated from XRD data. The change in particle size was observed with the change in Zn concentration. Furthermore, FTIR spectra of the prepared samples were observed for identification of COO- and O-H functional groups. The TEM study has also reported the same size range of nanoparticles. The increase in agglomeration has been observed with the increase in Zn concentration in the prepared samples.

  18. Thermal Diffusivity and Conductivity of Hg(1-x)Zn(x)Te Solids and Melts

    NASA Technical Reports Server (NTRS)

    Sha, Yi-Gao; Su, Ching-Hua; Mazuruk, K.; Lehoczky, S. L.

    1996-01-01

    The thermal diffusivity of pseudobinary Hg(1-x)Zn(x)Te solids and melts was measured by the laser flash method. The measured diffusivities for the solids of 0.10 less than or equal to x less than or equal to 0.30 are about 60% of that of the HgTe solid. Those for the melts rise rapidly with temperature but less so with increasing x. For x = 0.30, the diffusivity of the melt is about one third of that of the HgTe melt. Using the calculated beat capacity data from the associated solution model and measured density values, the thermal conductivity for the pseudobinary Hg(1-x)Zn(x)Te solids of 0.10 less than or equal to x less than or equal to 0.30 and for the melts of x = O.10, 0.16, and 0.30 was determined.

  19. Competition of optical transitions between direct and indirect bandgaps in Ge1-xSnx

    NASA Astrophysics Data System (ADS)

    Du, Wei; Ghetmiri, Seyed A.; Conley, Benjamin R.; Mosleh, Aboozar; Nazzal, Amjad; Soref, Richard A.; Sun, Greg; Tolle, John; Margetis, Joe; Naseem, Hameed A.; Yu, Shui-Qing

    2014-08-01

    Temperature-dependent photoluminescence (PL) study has been conducted in Ge1-xSnx films with Sn compositions of 0.9%, 3.2%, and 6.0% grown on Si. The competing between the direct and indirect bandgap transitions was clearly observed. The relative peak intensity of direct transition with respect to the indirect transition increases with an increase in temperature, indicating the direct transition dominates the PL at high temperature. Furthermore, as Sn composition increases, a progressive enhancement of direct transition was observed due to the reduction of direct-indirect valley separation, which experimentally confirms that the Ge1-xSnx could become the group IV-based direct bandgap material grown on Si by increasing the Sn content.

  20. Nonlinear behavior of the energy gap in Ge1-xSnx alloys at 4 K

    NASA Astrophysics Data System (ADS)

    Pérez Ladrón de Guevara, H.; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2007-10-01

    The optical energy gap of Ge1-xSnx alloys (x⩽0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1-xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT=2.30±0.10eV and b04K=2.84±0.15eV, at room temperature and 4K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Magnetocrystalline anisotropy of Er2(Fe1 - x V x )17 compounds

    NASA Astrophysics Data System (ADS)

    Terentev, P. B.; Mushnikov, N. V.; Gerasimov, E. G.; Gaviko, V. S.; Stashkova, L. A.

    2015-08-01

    The magnetic properties and magnetic anisotropy of the Er2(Fe1- x V x )17 compounds (with x = 0-0.05) have been studied. The Curie temperature ( T C) of the compounds has been found to increase as the vanadium concentration increases. It has been shown that the Er2(Fe1 - x V x )17 compounds have the easy-plane anisotropy in the temperature range from, 77 K to T C. Magnetization curves have been measured and the temperature dependences of the K 1 and K 2 anisotropy constants have been calculated. Contributions from the Er and Fe magnetic sublattices to the magnetic anisotropy constants were distinguished. An analysis of the obtained data allowed us to conclude that the cause for the existence of first-order magnetization processes in Er2Fe17 at low temperatures is a positive contribution from the Er sublattice to K 1 and a negative contribution from it to K 2.

  9. 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.

  10. Electronic structure of the unoccupied electron energy states in FeSe1-xTex

    NASA Astrophysics Data System (ADS)

    Mishra, Pramita; Lohani, Himanshu; Maniraj, M.; Nayak, Jayita; Zargar, R. A.; Awana, V. P. S.; Barman, Sudipta Roy; Sekhar, Biju Raja

    2015-10-01

    Inverse photoemission spectroscopic (IPES) measurements along with LDA based band structure calculations have been used to investigate the unoccupied electronic structure of FeSe1-xTex system. The observed doping and temperature dependent pseudogap in this system is found to be linked to the change in the chalcogen height in their geometric structure. The depletion in spectral weight from the near EF states at low temperature in IPES has been correlated with the enhancement of the 3z2-r2 orbitals in the photoemission spectroscopy (PES). The Coulomb correlation energy U, estimated from the combined PES and IPES spectra, signifies the enhancement in electron correlations in FeSe1-xTex, with doping. The formation of pseudogap in PES and IPES confirms the importance of correlations in the 11 family of Fe superconductors.

  11. 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.

  12. 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.

  13. 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

  14. Effect of Native Defects on Optical Properties of InxGa1-xNAlloys

    SciTech Connect

    Li, S.X.; Haller, E.E.; Yu, K.M.; Walukiewicz, W.; Ager III,J.W.; Wu, J.; Shan, W.; Lu, Hai; Schaff, William J.

    2005-05-09

    The energy position of the optical absorption edge and the free carrier populations in In{sub x}Ga{sub 1-x}N ternary alloys can be controlled using high energy {sup 4}He{sup +} irradiation. The blue shift of the absorption edge after irradiation in In-rich material (x > 0.34) is attributed to the band-filling effect (Burstein-Moss shift) due to the native donors introduced by the irradiation. In Ga-rich material, optical absorption measurements show that the irradiation-introduced native defects are inside the bandgap, where they are incorporated as acceptors. The observed irradiation-produced changes in the optical absorption edge and the carrier populations in In{sub x}Ga{sub 1-x}N are in excellent agreement with the predictions of the amphoteric defect model.

  15. 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.

  16. Lifshitz Transition and Chemical Instabilities in Ba1 xKxFe2As2 Superconductors

    SciTech Connect

    Khan, Suffian N.; Johnson, Duane D.

    2014-01-01

    Forsolid-solutionBa1 xKxFe2As2FermisurfaceevolutionismappedviaBlochspectralfunctionscalculatedusingdensityfunctionaltheoryimplementedinKorringa-Kohn-Rostokermultiplescatteringtheorywiththecoherent-potentialapproximation.Spectralfunctionsrevealelectronicdispersion,topology,orbitalcharacter,andbroadening(electron-lifetimeeffects)duetochemicaldisorder.Dissolutionofelectroncylindersoccursnearx 0.9withanonuniform,topological(Lifshitz)transition,reducingtheinterbandinteractions;yetthedispersionmaintainsitsdxzordyzcharacter.Formationenergiesindicatealloyingatx 0.35,asobserved,andatendencyforsegregationontheK-rich(x>0.6)side,explainingthedifficultyofcontrollingsamplequalityandtheconflictingresultsbetweencharacterizedelectronicstructures.OurresultsrevealFermisurfacetransitionsinalloyedsamplesthatinfluencestonodalsuperconductivityandsuggesttheoriginfordeviationsofcommontrendsinFe-basedsuperconductors,suchasBud ko-Ni-Canfieldscaling.

  17. 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.

  18. Carrier dynamics in ZnxCd1-xO films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cheng, F. J.; Lee, Y. C.; Hu, S. Y.; Lin, Y. C.; Tiong, K. K.; Chou, W. C.

    2016-05-01

    In this work, the carrier dynamics in Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system have been investigated using photoluminescence and time-resolved photoluminescence measurements. The carrier lifetime can be estimated from the PL decay curve fitted by triple exponential function. The emission energy dependence and temperature dependence of the PL decay time indicate that carrier localization dominate the luminescence mechanism of the ZnCdO alloy semiconductor.

  19. Oriented Growth of Pb1- x Snx Te Nanowire Arrays for Integration of Flexible Infrared Detectors.

    PubMed

    Wang, Qisheng; Li, Jie; Lei, Yin; Wen, Yao; Wang, Zhenxing; Zhan, Xueying; Wang, Feng; Wang, Fengmei; Huang, Yun; Xu, Kai; He, Jun

    2016-05-01

    Assembling nanowires into highly ordered arrays is crucial for developing integration circuits. Oriented growth of mid-infrared Pb1- x Snx Te nanowire arrays on bendable mica, extending the function of existing nanowire arrays, is reported. The flexible photodetectors of these nanowire arrays show a high photoresponsivity of 276 A W(-1) (at 800 nm), which is higher than many previously reported infrared nanosensors. PMID:26990637

  20. Composition variation of In1-xGaxAs epitaxially grown in narrow trenches on Si

    NASA Astrophysics Data System (ADS)

    Favia, P.; Richard, O.; Geypen, J.; Waldron, N.; Merckling, C.; Guo, W.; Caymax, M.; Bender, H.

    2013-11-01

    In this work we investigate the indium content in In1-xGaxAs narrow trenches on Si by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and nano beam diffraction (NBD). We find a higher indium content in wider trenches and by scanning a trench from bottom to top we observe an increase of indium up to a maximum value close to the level of the surface of the shallow trench isolation oxide.

  1. 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.

  2. 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

  3. Infrared reflectivity spectra of GaS 1-xSe x mixed crystals

    NASA Astrophysics Data System (ADS)

    Riede, V.; Neumann, H.; Sobotta, H.; Lévy, F.

    1980-04-01

    Infrared reflectivity spectra of GaS 1- xSe x mixed crystals are measured for E ‖ c in the wavenumber range from 180 to 4000 cm -1. Two-mode behaviour is found for the infrared active optical modes. The composition dependence of the mode frequencies can be described by the MREI model if a nonlinear change of the force constants with composition is assumed.

  4. First-principles prediction of superconductivity in LiBSi1-xAlx

    NASA Astrophysics Data System (ADS)

    Miao, Rende; Yang, Jun; Bai, Zhong; Can, Dan; Zhang, Xi; Jiang, Min; Liu, Cuicui; Wu, Fangping; Ma, Shuyun

    2015-02-01

    Electronic structure, lattice dynamics and superconducting properties for theoretically devised superconductor LiBSi1-x Alx are obtained by first-principles calculations. We assume that Lithium Boron Silicon (LiBSi) has the same crystal structure as that of Lithium borocarbide (LiBC). The pristine LiBSi is predicted to be a zero-gap semiconductor. Hole doping of LiBSi through partial substitution of Si by SiAl atoms can produce a semiconductor-metal transition and develop superconductivity. To assess the thermodynamic stability of LiBSi1-xAlx, the formation energies are calculated using the supercell method. For LiBSi0.75 Al0.25 and LiBSi0.875Al0.125, the obtained formation energies are -5.9 and -6.1 eV, respectively, indicating that LiBSi1-xAlx is energetically favorable at least in the range of 0 ≤ x ≤ 0.25. Phonon spectra and superconducting properties are obtained within the virtual-crystal approximation (VCA) treatment. The results show that LiBSi1-xAlx is dynamically stable approximately in the range of 0 ≤ x ≤ 0.35. For LiBSi0.8Al0.2, the obtained electron-phonon coupling constant λ is 0.86 and superconducting transition temperature TC is predicted to be in the range of 11-13 K (0.14 ≥ μ* ≥ 0.1).

  5. Coulomb interaction of acceptors in Cd1-xMnxTe/CdTe quantum dot

    NASA Astrophysics Data System (ADS)

    Kalpana, P.; Reuben, A. Merwyn Jasper D.; Nithiananthi, P.; Jayakumar, K.

    2014-04-01

    The investigation on the effect of confining potential like isotropic harmonic oscillator type potential on the binding and the Coulomb interaction energy of the double acceptors in the presence of magnetic field in a Cd1-xMnxTe/CdTe Spherical Quantum Dot has been made for the Mn ion composition x=0.3 and compared with the results obtained from the square well type potential using variational procedure in the effective mass approximation.

  6. Photoacoustic study of Zn1-xBexSe mixed crystals

    NASA Astrophysics Data System (ADS)

    Firszt, F.; Legowski, S.; Meczynska, H.; Szatkowski, J.; Zakrzewski, J.

    1999-03-01

    The photoacoustic spectroscopy (PAS) with piezoelectric transducer was employed to evaluate band gap energies in Zn1-xBexSe mixed crystals of different composition. The spectra were measured at 300 K and 90 K using continuos wave excitation. The Jackson-Amer model of photoacoustic effect was applied. The increase of the band-gap energy with increasing Be content is observed. The photoacoustic results are compared with those from photoluminescence spectra.

  7. Piezoelectric photothermal study of Cd{1-x-y}BexZnySe crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Firszt, F.; Łęgowski, S.; Męczyńska, H.; Marasek, A.; Pawlak, M.; Strzałkowski, K.; Maliński, M.; Bychto, L.

    2005-06-01

    The piezoelectric photothermal results obtained for a series of CdSe and Cd{1-x-y}BexZnySe mixed crystals are presented and discussed. The experimental results comprise the piezoelectric amplitude and phase spectra of these crystals. The thermal diffusivities were determined from the experimental piezoelectric phase spectra. The optical absorption spectra of the crystals were determined by the fitting of the piezoelectric amplitude spectra.

  8. 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.

  9. 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.

  10. Growth of InAs/Ga 1-xIn xSb infrared superlattices

    NASA Astrophysics Data System (ADS)

    Chow, D. H.; Miles, R. H.; Nieh, C. W.; McGill, T. C.

    1991-05-01

    A set of InAs/Ga 1-xIn xSb superlattices has been grown by molecular beam epitaxy. The superlattices are deposited on thick, stress-relaxed buffer layers of GaSb on (100)-oriented GaAs substrates. A short-period, heavily strained superlattice has been inserted at the GaAs/GaSb interface. Transmission electron microscope (TEM) images reveal that a dense network of dislocations forms at this interface, with the vast majority of threading dislocations propagating no further than the first 1000 Å of the GaSb buffer layer. Planar superlattice layers are observed, with ni evidence of stress relaxation between the layers or between the InAs/Ga 1- x In xSb superlattice and GaSb buffer. Analysis of X-ray diffraction satellites reveals that cross-incorporation of As in GaSb and Ga 1-xIn xSb layers is virtually eliminated at low growth temperatures. Photoconductivity spectra from the superlattices display sharp photocurrent threshold energies, in agreement with previously published energy gaps derived from calculations and photoluminescence data. Thresholds in the 8-14 μm range are obtained from superlattices with very thin layers ( ≈ 40 Å), which are necessary for strong optical absorption in a type II superlattice. Finally, an absorption coefficient of ≈ 2000 cm -1 is measured at 10 μm from a superlattice with an energy gap of 11.4 μm. This value is comparable to that of bulk Hg 1-xCd xTe, the current industry standard for infrared detectors in the 8-14 μm range.

  11. Image analysis of the AXAF VETA-1 X-ray mirror

    NASA Technical Reports Server (NTRS)

    Freeman, M.; Hughes, J.; Van Speybroeck, L.; Bilbro, J.; Weisskopf, M.

    1993-01-01

    Initial core scan data of the VETA-1 X-ray mirror proved disappointing, showing considerable unpredicted image structure and poor measured FWHM. 2-D core scans were performed, providing important insight into the nature of the distortion. Image deconvolutions using a raytraced model PSF was performed successfully to reinforce our conclusion regarding the origin of the astigmatism. A mechanical correction was made to the optical structure, and the minor was tested successfully (FWHM 0.22 arcsec) as a result.

  12. 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.

  13. Structure and electronic properties of conducting, ternary TixTa1-xN films

    NASA Astrophysics Data System (ADS)

    Matenoglou, G. M.; Lekka, Ch. E.; Koutsokeras, L. E.; Karras, G.; Kosmidis, C.; Evangelakis, G. A.; Patsalas, P.

    2009-05-01

    We report on the electronic structure and optical properties of conducting ternary transition metal nitrides consisting of metals of different groups of the periodic table of elements. For the study of the bonding, electronic structure, and optical properties of conducting TixTa1-xN film growth, optical spectroscopy and ab initio calculations were used. Despite the different valence electron configuration of the constituent elements, Ta(d3s2) and Ti(d2s2), we show that TiN and TaN are completely soluble due to the hybridization of the d and sp electrons of the metals and N, respectively, that stabilizes the ternary TixTa1-xN systems to the rocksalt structure. The optical properties of TixTa1-xN have been studied using spectroscopic methods and detailed electronic structure calculations, revealing that the plasma energy of the fully dense TixTa1-xN is varying between 7.8 and 9.45 eV. Additional optical absorption bands are manifested due to the N p →Ti/Ta d interband transition the t2g→eg transition due to splitting of the metals' d band, with the major exception of the Ti0.50Ta0.50N, where the eg unoccupied states are not manifested due to the local structure of the ternary system; this finding is observed for the first time and proves previous assignments of optical transitions in TaN.

  14. Superconducting properties of K1-xNaxFe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Grinenko, V.; Schottenhamel, W.; Wolter, A. U. B.; Efremov, D. V.; Drechsler, S.-L.; Aswartham, S.; Kumar, M.; Wurmehl, S.; Roslova, M.; Morozov, I. V.; Holzapfel, B.; Büchner, B.; Ahrens, E.; Troyanov, S. I.; Köhler, S.; Gati, E.; Knöner, S.; Hoang, N. H.; Lang, M.; Ricci, F.; Profeta, G.

    2014-09-01

    The effects of hydrostatic pressure and partial Na substitution on the normal-state properties and the superconducting transition temperature (Tc) of K1-xNaxFe2As2 single crystals were investigated. It was found that a partial Na substitution leads to a deviation from the standard T2 Fermi-liquid behavior in the temperature dependence of the normal-state resistivity. It was demonstrated that non-Fermi-liquid like behavior of the resistivity for K1-xNaxFe2As2 and some KFe2As2 samples can be explained by a disorder effect in the multiband system with rather different quasiparticle effective masses. Concerning the superconducting state our data support the presence of a shallow minimum around 2 GPa in the pressure dependence of Tc for stoichiometric KFe2As2. The analysis of Tc in K1-xNaxFe2As2 at pressures below 1.5 GPa showed that the reduction of Tc with Na substitution follows the Abrikosov-Gor'kov law with the critical temperature Tc0 of the clean system (without pair breaking), which linearly depends on the pressure. Our observations also suggest that Tc of K1-xNaxFe2As2 is nearly independent of the lattice compression produced by the Na substitution. Further, we theoretically analyzed the behavior of the band structure under pressure within the generalized gradient approximation (GGA). A qualitative agreement between the calculated and the recently measured—in de Haas-van Alphen experiments [T. Terashima et al., Phys. Rev. B 89, 134520 (2014), 10.1103/PhysRevB.89.134520]—pressure dependencies of the Fermi-surface cross sections has been found. These calculations also indicate that the observed minimum around 2 GPa in the pressure dependence of Tc may occur without a change of the pairing symmetry.

  15. Long-wavelength infrared photoconductor technology based on epitaxially grown Hg1-xCdxTe

    NASA Astrophysics Data System (ADS)

    Siliquini, John F.; Fynn, Kevin A.; Musca, Charles A.; Nener, Brett D.; Dell, John M.; Faraone, Lorenzo

    1995-09-01

    The performance of Hg1-xCdxTe long wavelength infrared (LWIR) photoconductors is strongly dependent on the semiconductor surface conditions and contact characteristics. In this paper we review these effects in relation to obtaining an optimum device technology suitable for use in two-dimensional infrared focal plane arrays (IRFPAs) based on the fabrication of high performance LWIR photoconductors on epitaxially grown Hg1-xCdxTe. Although the proposed design can be applied to a variety of epitaxially grown Hg1-xCdxTe material, for optimum performance the starting Hg1-xCdxTe semiconductor consists of epitaxially grown heterostructure layers in which a two-dimensional mosaic of lateral design photoconductors are fabricated. The heterostructure layer provides high performance devices at greatly reduced power dissipation levels, while the unique design allows for the high density integration of photoconductors in a two-dimensional array geometry with high fill factor. The proposed photoconductor array with n+ blocking contacts has been experimentally verified in a 3 X 3 array format with all elements in the array exhibiting background limited infrared photodetector (BLIP) performance at 80 K. Performance issues such as response uniformity, pixel yield, fill factor, crosstalk, power dissipation, detector impedance, array architecture, and maximum array size are discussed in relation to the suitability of the proposed photoconductor structure for use in IRFPA modules. It is found that in many cases the proposed photoconductor technology has the potential to deliver significant advantages, such as higher yield, higher fill factor, better uniformity, less crosstalk, and larger potential array size, in comparison to an IRFPA design based on photovoltaic technology.

  16. 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.

  17. Magnetic properties of Sm1-xYxSe solid solutions

    NASA Astrophysics Data System (ADS)

    Beeken, R. B.; Bissell, P. R.

    1991-05-01

    Sm1-xYxSe solid solutions prepared as sintered pellets exhibit a miscibility gap in the composition range from x = 0.50 to x = 0.80. Lattice parameter and magnetic susceptibility determinations on alloys within the remaining composition regions indicate that the samarium cations remain essentially divalent throughout this series of solid solutions. An enhancement of the SmSe Van Vleck paramagnetism with increasing yttrium substitution is attributed to the conduction electrons introduced by chemical alloying.

  18. 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.

  19. Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Maserjian, Joseph; Ksendzov, A.; Huberman, Mark L.; Terhune, R.; Krabach, T. N.

    1990-01-01

    There is a major need for long-wavelength-infrared (LWIR) detector arrays in the range of 8 to 16 microns which operate with close-cycle cryocoolers above 65 K. In addition, it would be very attractive to have Si-based infrared (IR) detectors that can be easily integrated with Si readout circuitry and have good pixel-to-pixel uniformity, which is critical for focal plane array (FPA) applications. Here, researchers report a novel Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) detector approach with a tailorable long wavelength infrared cutoff wavelength, based on internal photoemission over the Si(1-x)Ge(x)/Si heterojunction. The HIP detectors were grown by molecular beam epitaxy (MBE), which allows one to optimize the device structure with precise control of doping profiles, layer thickness and composition. The feasibility of a novel Si(1-x)Ge(x)/Si HIP detector has been demonstrated with tailorable cutoff wavelength in the LWIR region. Photoresponse at wavelengths 2 to 10 microns are obtained with quantum efficiency (QE) above approx. 1 percent in these non-optimized device structures. It should be possible to significantly improve the QE of the HIP detectors by optimizing the thickness, composition, and doping concentration of the Si(1-x)Ge(x) layers and by configuring the detector for maximum absorption such as the use of a cavity structure. With optimization of the QE and by matching the barrier energy to the desired wavelength cutoff to minimize the thermionic current, researchers predict near background limited performance in the LWIR region with operating temperatures above 65K. Finally, with mature Si processing, the relatively simple device structure offers potential for low-cost producible arrays with excellent uniformity.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Does Bi form clusters in GaAs1 - xBi x alloys?

    NASA Astrophysics Data System (ADS)

    Punkkinen, M. P. J.; Laukkanen, P.; Kuzmin, M.; Levämäki, H.; Lång, J.; Tuominen, M.; Yasir, M.; Dahl, J.; Lu, S.; Delczeg-Czirjak, E. K.; Vitos, L.; Kokko, K.

    2014-11-01

    GaAs1 - xBi x alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 - xBi x with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 - xBi x film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.

  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. Transport properties of Ho1- x Lu x B12 solid solutions

    NASA Astrophysics Data System (ADS)

    Gabáni, S.; Bat'ko, I.; Bat'ková, M.; Flachbart, K.; Gaz̆o, E.; Pristás̆, G.; Takác̆ová, I.; Bogach, A. V.; Sluchanko, N. E.; Shitsevalova, N. Yu.

    2013-05-01

    Our studies of Ho1- x Lu x B12 solid solutions have shown that the temperature of antiferromagnetic (AF) order in geometrically frustrated system of HoB12 ( T N = 7.4 K) is linearly suppressed to zero temperature, i.e. T N → 0, as lutetium concentration increases to x→ x c ≈ 0.9. In this contribution, we present original results of electrical resistivity measurements on Ho1- x Lu x B12 single crystalline samples with x = 0, 0.2, 0.5, 0.7, 0.9, 1 in the temperature range 0.06-300 K and in magnetic fields ( B) up to 8 T. Complex B vs T N phase diagrams were received from precise temperature ρ( T) and field ρ( B) dependences of resistivity with several AF phases for x ≤ 0.5 pointing to a possibility of quantum critical point at x c ≈ 0.9. The scattering of conduction electrons in the AF phase and in the paramagnetic phase as well as Hall effect results are analyzed and discussed for various concentrations x, when magnetic dilution increases with the increasing content of nonmagnetic Lu ions in the Ho1- x Lu x B12 system.

  7. AP-MOVPE of thin GaAs 1-xBi x alloys

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Moussa, I.; Rebey, A.; Fouzri, A.; El Jani, B.

    2006-10-01

    GaAs 1-xBi x alloy was grown by atmospheric-pressure metalorganic vapour-phase epitaxy using a horizontal reactor. GaAs 1-xBi x epilayers were elaborated on exactly (1 0 0)-oriented p-GaAs substrates. Trimethyl-gallium, trimethyl bismuth (TMBi), and arsine were used as precursor sources at a growth temperature of 420 °C within a very narrow range of V/III ratios and molar flow rates of TMBi. The lattice mismatch between the layer and the substrate was examined by using high-resolution X-ray diffraction technique. The measurements were performed on (0 0 4) and (1 1 5) planes. The solid composition of GaBi content in the GaAs 1-xBi x alloy reaches a maximum value of about 3.7%. In analyzing the surface morphology, scanning electron microscopy (SEM) and SEM-energy dispersive X-ray spectrometer were used to qualify films properties.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. Microscopic basis for the band engineering of Mo1-xWxS2-based heterojunction

    NASA Astrophysics Data System (ADS)

    Yoshida, Shoji; Kobayashi, Yu; Sakurada, Ryuji; Mori, Shohei; Miyata, Yasumitsu; Mogi, Hiroyuki; Koyama, Tomoki; Takeuchi, Osamu; Shigekawa, Hidemi

    2015-10-01

    Transition-metal dichalcogenide layered materials, consisting of a transition-metal atomic layer sandwiched by two chalcogen atomic layers, have been attracting considerable attention because of their desirable physical properties for semiconductor devices, and a wide variety of pn junctions, which are essential building blocks for electronic and optoelectronic devices, have been realized using these atomically thin structures. Engineering the electronic/optical properties of semiconductors by using such heterojunctions has been a central concept in semiconductor science and technology. Here, we report the first scanning tunneling microscopy/spectroscopy (STM/STS) study on the electronic structures of a monolayer WS2/Mo1-xWxS2 heterojunction that provides a tunable band alignment. The atomically modulated spatial variation in such electronic structures, i.e., a microscopic basis for the band structure of a WS2/Mo1-xWxS2 heterojunction, was directly observed. The macroscopic band structure of Mo1-xWxS2 alloy was well reproduced by the STS spectra averaged over the surface. An electric field of as high as 80 × 106 Vm-1 was observed at the interface for the alloy with x = 0.3, verifying the efficient separation of photoexcited carriers at the interface.

  13. 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. PMID:25383028

  14. 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.

  15. High temperature magnetic behavior of multiferroics Bi1-xCaxFeO3

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Su, J.; Liu, Z. Y.; Fu, Z. M.; Wang, X. W.; Song, G. L.; Chang, F. G.

    2014-04-01

    We investigate the room temperature microstructure and high temperature magnetic properties of Ca2+-substituted Bi1-xCaxFeO3 (0 ≤ x ≤ 0.2) ceramics. The Bi1-xCaxFeO3 compound transforms from rhombohedral into tetragonal structure with the phase boundary lying around x = 0.1. Based on this, the magnetic modulation becomes significant and the strongest remnant magnetization Mr is obtained at x = 0.1 compound. An important observation is the ferromagnetic-like phase transition revealed at TFM = 878 K in pure BiFeO3. The TFM of Bi1-xCaxFeO3 varies with Ca concentration and is close to the TAFM when x = 0.1. The convergence between TFM and TAFM implies the severe competition between Fe3+-O2--Fe3+ and unbalanced Fe3+-O2--Fe2+ antiferromagnetic exchange interactions, which leads to the dramatic change around TAFM in the M-T curve of x = 0.1 compound. The structure-related modulation of magnetic structure and complex interaction between Fe3+ and Fe2+ may be the driving force for the excellent magnetic properties of x = 0.1 sample.

  16. Raman scattering of the Li 1+xTi 2-xO 4 superconducting system

    NASA Astrophysics Data System (ADS)

    Liu, D. Z.; Hayes, W.; Kurmoo, M.; Dalton, M.; Chen, C.

    1994-12-01

    We have measured Raman spectra of polycrystalline samples of the Li 1+xTi 2-xO 4 superconducting system ( 0⩽x⩽ {1}/{3}) at room temperature. For LiTi 2O 4 (x=0), which is a superconductor (Tc=13K), the frequencies of the detected phonon modes are 200, 339, 429, 494 and 628 cm -1, corresponding to the expected five zone-centre Raman active modes for the spinel-type structure. For Li[Li {1}/{3}Ti {5}/{3}]O 4( x= {1}/{3}), which is an insulator, we observe five phonon peaks centred on 239, 274, 367, 427 and 675 cm -1. However for intermediate values of x, the scattering peaks broaden; in the range of 0.1 < x < 0.2, the Raman spectra can barely be resolved, consistent with chemical inhomogeneity of Li 1+xTi 2-xO 4 due to a spinodal decomposition.

  17. Effect of pressure on some optical properties of GaxIn1-xP semiconductors

    NASA Astrophysics Data System (ADS)

    Vyas, P. S.; Gajjar, P. N.; Jani, A. R.

    2014-05-01

    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 in satisfactory agreement 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.

  18. Effects of Si-doping on magnetic properties of Ga1-xCrxN

    NASA Astrophysics Data System (ADS)

    Zhou, Zhongpo; Yang, Zongxian; Liu, Chang

    2015-01-01

    Ga1-xCrxN thin films with and without the Si doping have been prepared by molecular beam epitaxy. The samples have been investigated by X-ray diffraction, X-ray photoemission spectroscopy, photoluminescence, optical absorption spectra and magnetic measurements. It has been confirmed that for the undoped samples Cr in GaN is predominantly trivalent when substituting for Ga and that the Cr 3d state appears within the band gap of GaN. In Si doped specimens the upward shifts of the chemical potential are observed, and the electrons supplied by the Si doping are trapped at Cr sites forming Cr2+. As a result, the Si doping effects show an increase of the Curie temperature, and a reduction of the saturation magnetization in the Ga1-xCrxN:Si samples. The significant effect on the ferromagnetism with Si doping in Ga1-xCrxN is explained by the percolation theory of bound magnetic polarons.

  19. Synthesis of ZnxCd1-xS Solid Solution by Stratified Method

    SciTech Connect

    Arai, Takeo; Nakazato, Makoto; Shinoda, Kozo; Jeyadevan, Balachandran; Tohji, Kazuyuki

    2006-05-15

    In this study, we focused our attention on photocatalytic decomposition of hydrogen sulfide as the resource of hydrogen using solar energy and prepared ZnxCd1-xS solid solution as photocatalyst. Samples were prepared by 'stratified' method using Zn and Cd hydroxides as precursors and 'coprecipitation' method under various Zn/ Cd ratios to study the influence of Cd concentration on the properties such as crystal structure, light absorption and reactivity. The continuous change in the crystal lattice constant and UV-VIS reflection spectra from ZnS to CdS was observed in the ZnxCd1-xS samples prepared by both 'coprecipitation' and 'stratified' methods with increasing concentration of Cd. In the case of coprecipitation method, the reactivity was improved with the increase of Cd. But, in the case of stratified method, the particles prepared at Zn:Cd=2:1 showed higher reactivity than the samples prepared at higher ratios of Cd and the samples prepared by coprecipitation method with similar Zn/Cd ratios. The samples prepared by stratified method at higher ratio of Zn/Cd turned black from yellow in color when exposed to light irradiation. This was believed due to the metal deposited by photocatalytic reduction of precursors. This metal deposition influences the photoreactivity of ZnxCd1-xS particles and is optimum for Zn0.67Cd0.33S.

  20. Magnetic diffusion anomaly at the Néel temperature of pyrrhotite, Fe(1-x)S.

    PubMed

    William Herbert, F; Krishnamoorthy, Aravind; Rands, Lucy; Van Vliet, Krystyn J; Yildiz, Bilge

    2015-04-28

    Cation diffusion is an important rate-limiting process in the growth of pyrrhotite (Fe1-xS) in passivating films on steels exposed to sulfidic environments, and for proposed synthetic applications of Fe1-xS, for example single-phase magnetic switching devices. Above the Néel temperature TN of 315 °C, where Fe1-xS is paramagnetic and structurally disordered, iron self-diffusivity *DFe predictably follows a standard, established Arrhenius law with temperature. However, we report (57)Fe tracer diffusion measurements below TN, obtained using secondary ion mass spectrometry (SIMS), that demonstrate a 100-fold reduction in diffusion coefficient as compared to the extrapolated, paramagnetic Arrhenius trend at 150 °C. The results can be described by a magnetic diffusion anomaly, where the vacancy migration energy for the spontaneously-magnetized cation sublattice is increased by approximately 40% over the paramagnetic state. These constitute the first set of consistent diffusivity data obtained in magnetic pyrrhotite, allowing more accurate prediction of pyrrhotite growth rates and determination of magnetic properties for synthetic devices. PMID:25823983

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

    PubMed

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

    2016-01-01

    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. PMID:27444737

  2. 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.

  3. MWIR InAs1-xSbx nCBn detectors data and analysis

    NASA Astrophysics Data System (ADS)

    D'Souza, A. I.; Robinson, E.; Ionescu, A. C.; Okerlund, D.; de Lyon, T. J.; Rajavel, R. D.; Sharifi, H.; Yap, D.; Dhar, N.; Wijewarnasuriya, P. S.; Grein, C.

    2012-06-01

    In InAs1-xSbx material alloy composition was adjusted to achieve 200K cutoff wavelengths in the 5 μm range. Reflectance was minimized and absorption in the InAs1-xSbx material maximized by the use of pyramid shaped structures fabricated in the InAs1-xSbx material which function as an AR coating. Compound-barrier (CB) detectors were fabricated and tested for optical response and dark current density versus bias measurements were acquired as a function of temperature. For 5 μm cutoff detectors, QE is high, ~ 75 % between 4.0 μm and 4.6 μm and > 80 % between 2.0 μand 4.0 μm, demonstrating the efficacy of the pyramids as photon trap structures and as a replacement for multi-layer AR-coatings. Jdark in the low 10-3 A/cm2 range at 200 K and low 10-5 A/cm2 range at 150 K was measured at the bias at which the QE peaked.

  4. 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.

  5. Spectroscopic and crystallographic anomalies of (Co1-xZnx)Al2O4 spinel oxide.

    PubMed

    Nakane, Takayuki; Naka, Takashi; Sato, Koichi; Taguchi, Minori; Nakayama, Minako; Mitsui, Tadashi; Matsushita, Akiyuki; Chikyow, Toyohiro

    2015-01-21

    This work investigates the spectroscopic properties of (Co1-xZnx)Al2O4 with a range of x of 0 ≤ x ≤ 1. Spectroscopic and crystallographic evaluations using XRD, Raman, FT-IR and UV-Vis spectroscopy reveal that Zn(2+) substitution systematically changes the lattice constant, which mainly depends on the Co-O bonds, and the related optical characteristics of this material. The x dependence of these properties shows two trends, and the mutation point seems to be at x ≈ 0.5. This implies that the electronic structure of (Co1-xZnx)Al2O4 is not changed monotonically by Zn(2+) substitution. Interestingly, some of the optical phenomena observed in this study become prominent for samples with x ≥ 0.5. That is, we observed sideband peaks near the main peaks in the Raman spectra, and their relative intensities systematically and significantly increased with increasing Zn(2+) substitution. The rates of increase are not constant, and are fast for samples with x ≥ 0.5. The sideband peaks are considered to reflect the unique changes in the local electronic structure of (Co1-xZnx)Al2O4, and they are useful for evaluating the substitution level without the influence of the site change phenomenon. Thus, clarifying them is expected to be important for understanding and controlling the electronic structure of the spinel oxide. On the other hand, investigation of the visible light absorption due to the d-d transition of Co(2+) reveals that the efficiency is also high for samples with high Zn(2+) substitution (x ≥ 0.5). This is also considered to be valuable information for investigation of the optical properties and/or the catalytic function of the spinel oxide. Moreover, the fluorescence of the (Co1-xZnx)Al2O4 samples is also identified as a novel functional property of this material. The intensity of the fluorescence peak also dramatically increases for samples with x ≥ 0.7. The effect of Zn(2+) substitution on the local electronic structure of (Co1-xZnx)Al2O4 has not

  6. Photoelectrical properties and the electronic structure of Tl(1-x)In(1-x)Sn(x)Se2 (x = 0, 0.1, 0.2, 0.25) single crystalline alloys.

    PubMed

    Davydyuk, G E; Khyzhun, O Y; Reshak, A H; Kamarudin, H; Myronchuk, G L; Danylchuk, S P; Fedorchuk, A O; Piskach, L V; Mozolyuk, M Yu; Parasyuk, O V

    2013-05-14

    Photoelectrical properties of Tl1-xIn1-xSnxSe2 single crystalline alloys (x = 0, 0.1, 0.2, 0.25) grown using the Bridgman-Stockbarger method were studied. The temperature dependence of electrical and photoconductivity for the Tl1-xIn1-xSnxSe2 single crystals was explored. It has been established that photosensitivity of the Tl1-xIn1-xSnxSe2 single crystals increases with x. The spectral distribution of photocurrent in the wavelength spectral range 400-1000 nm has been investigated at various temperatures. Photoconductivity increases in all the studied crystals with temperature. Therefore, thermal activation of photoconductivity is caused by re-charging of the photoactive centers as the samples are heated. Based on our investigations, a model of center re-charging is proposed that explains the observed phenomena. X-ray photoelectron valence-band spectra for pristine and Ar(+)-ion irradiated surfaces of the Tl1-xIn1-xSnxSe2 single crystals have been measured. These results reveal that the Tl1-xIn1-xSnxSe2 single-crystal surface is sensitive to the Ar(+) ion irradiation that induced structural modification in the top surface layers. Comparison on a common energy scale of the X-ray emission Se Kβ2 bands representing energy distribution of the Se 4p-like states and the X-ray photoelectron valence-band spectra was done. PMID:23552559

  7. 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.

  8. 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)…

  9. FAST TRACK COMMUNICATION: Variation of equation of state parameters in the Mg2(Si1 - xSnx) alloys

    NASA Astrophysics Data System (ADS)

    Pulikkotil, J. J.; Alshareef, H. N.; Schwingenschlögl, U.

    2010-09-01

    Thermoelectric performance peaks up for intermediate Mg2(Si1 - xSnx) alloys, but not for isomorphic and isoelectronic Mg2(Si1 - xGex) alloys. A comparative study of the equation of state parameters is performed using density functional theory, Green's function technique, and the coherent potential approximation. Anomalous variation of the bulk modulus is found in Mg2(Si1 - xSnx) but not in the Mg2(Si1 - xGex) analogs. Assuming a Debye model, linear variations of the unit cell volume and pressure derivative of the bulk modulus suggest that lattice effects are important for the thermoelectric response. From the electronic structure perspective, Mg2(Si1 - xSnx) is distinguished by a strong renormalization of the anion-anion hybridization.

  10. Development of epitaxial growth technology for Ge1-xSnx alloy and study of its properties for Ge nanoelectronics

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Shimura, Yosuke; Takeuchi, Wakana; Taoka, Noriyuki; Zaima, Shigeaki

    2013-05-01

    We have recently developed an epitaxial growth technique for Ge1-xSnx layers with an especially high Sn content, and we investigated the crystalline properties of the Ge1-xSnx epitaxial layers. In this report, we describe our recent achievements for improving the crystalline quality of the epitaxial growth of Ge1-xSnx layers on various substrates. We also demonstrate the impacts of Sn incorporation on the defect and dopant behaviors and electrical properties of Ge1-xSnx epitaxial layers. Sn incorporation improves on the issue of unintentional hole generation due to vacancy defects and enhances the dopant activation of Ga atoms in the Ge matrix. In addition, we introduce a recent study of the optical properties of Ge1-xSnx epitaxial layers with very high Sn contents.

  11. Variation of equation of state parameters in the Mg2(Si(1-x)Sn(x)) alloys.

    PubMed

    Pulikkotil, J J; Alshareef, H N; Schwingenschlögl, U

    2010-09-01

    Thermoelectric performance peaks up for intermediate Mg(2)(Si(1-x)Sn(x)) alloys, but not for isomorphic and isoelectronic Mg(2)(Si(1-x)Ge(x)) alloys. A comparative study of the equation of state parameters is performed using density functional theory, Green's function technique, and the coherent potential approximation. Anomalous variation of the bulk modulus is found in Mg(2)(Si(1-x)Sn(x)) but not in the Mg(2)(Si(1-x)Ge(x)) analogs. Assuming a Debye model, linear variations of the unit cell volume and pressure derivative of the bulk modulus suggest that lattice effects are important for the thermoelectric response. From the electronic structure perspective, Mg(2)(Si(1-x)Sn(x)) is distinguished by a strong renormalization of the anion-anion hybridization. PMID:21403277

  12. 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

  13. Homogeneous and Heterogeneous (Fex, Cr1-x)(OH)3 Precipitation: Implications for Cr Sequestration.

    PubMed

    Dai, Chong; Zuo, Xiaobing; Cao, Bo; Hu, Yandi

    2016-02-16

    The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small-angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0-0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1-x)(OH)3 precipitates, solutions' supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, the aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1-x)(OH)3 through different mechanisms. The sequestration mechanisms of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solutions. From solutions with 0-0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1-x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments. PMID:26765070

  14. Normal state electronic properties of LaO1-x Fx BiS2 superconductors

    NASA Astrophysics Data System (ADS)

    Querales-Flores, J. D.; Ventura, C. I.; Citro, R.; Rodríguez-Núñez, J. J.

    2016-05-01

    A good description of the electronic structure of BiS2-based superconductors is essential to understand their phase diagram, normal state and superconducting properties. To describe the first reports of normal state electronic structure features from angle resolved photoemission spectroscopy (ARPES) in LaO1-x Fx BiS2, we used a minimal microscopic model to study their low energy properties. It includes the two effective tight-binding bands proposed by Usui et al., Phys. Rev. B, 86, 2012, 220501(R), and we added moderate intra- and inter-orbital electron correlations related to Bi-(pY, pX) and S-(pY, pX) orbitals. We calculated the electron Green's functions using their equations of motion, which we decoupled in second-order of perturbations on the correlations. We determined the normal state spectral density function and total density of states for LaO1-x Fx BiS2, focusing on the description of the k-dependence, effect of doping, and the prediction of the temperature dependence of spectral properties. Including moderate electron correlations, improves the description of the few experimental ARPES and soft X-ray photoemission data available for LaO1-x Fx BiS2. Our analytical approximation enabled us to calculate the spectral density around the conduction band minimum at k→0 =(0.45 π , 0.45 π), and to predict the temperature dependence of the spectral properties at different BZ points, which might be verified by temperature-dependent ARPES.

  15. Light stops in a minimal U (1 )x extension of the MSSM

    NASA Astrophysics Data System (ADS)

    Capdevilla, R. M.; Delgado, A.; Martin, A.

    2015-12-01

    In order to reproduce the measured mass of the Higgs boson mh=125 GeV in the minimal supersymmetric standard model, one usually has to rely on heavy stops. By introducing a new gauge sector, the Higgs mass gets a tree-level contribution via a nondecoupling D -term, and mh=125 GeV can be obtained with lighter stops. In this paper, we study the values of the stops masses needed to achieve the correct Higgs mass in a setup where the gauge group is extended by a single U (1 )x interaction. We derive the experimental limits on the mass of the Z' gauge boson in this setup, then discuss how the stops masses vary as a function of the free parameters introduced by the new sector. We find that the correct Higgs mass can be reproduced with stops in a region between 700-800 GeV and a Z' resonance close to the 2.5 TeV bound from the run I of the LHC, or in a higher region 800-900 GeV if the Z' resonance is heavier (3.1 TeV). This region of parameter space will be quickly accessible at run II of the LHC, and we discuss the impact of the projected run-II bounds on the U (1 )x parameter space. We also discuss the phenomenology of the Higgs-like particles introduced to break U (1 )x and conclude their effects are too small to be detected at current colliders.

  16. Moment Mapping of bcc Fe1-xMnx Alloy Films on MgO(001)

    NASA Astrophysics Data System (ADS)

    Idzerda, Yves; Bhatkar, Harsh; Arenholz, Elke

    2015-03-01

    The magnetic moments of ~ 20 nm single crystal films of compositionally graded Fe1-xMnx films (0.1 <= x <= 0.2) grown on MgO(001) are determined by spatially resolved moment mapping using X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD). RHEED measurements confirmed that the growth of Fe1-xMnx films remained epitaxial and in the bcc phase up to x =0.35 but, like Fe growth, is rotated 45 degree with respect to the MgO(001) surface net. This is beyond the bulk bcc stability limit of x =0.12. Both magnetometry and XMCD measurements show that the net magnetic moment of these alloy films behave similarly to the bulk behavior, with a gradual moment reduction at low Mn concentrations followed by an abrupt departure from the Slater-Pauling curve and disappearance of the moment at x =0.15. By generating a compositional variation around this critical concentration and subsequently using spatially resolved mapping of the X-ray absorption at the Fe and Mn L3-edge using linear and circular polarized soft X-rays, the local composition and elemental moments can be simultaneously mapped across the surface of the sample. The Fe moment is found to gradually reduce with increasing Mn content with a very abrupt decline at x =0.15. Surprisingly, the Mn moment shows a very small net moment (<0.1 muB) at all compositions, suggesting a complicated Mn spin structure.

  17. Correlation Between Surface Chemistry and Electrocatalytic Properties of Monodisperse Pt(x)Ni(1-x) Nanoparticles

    SciTech Connect

    Wang, Chao; Chi, Miaofang; Wang, Guofeng; Van der Vliet, Dennis; Li, Dongguo; More, Karren Leslie; Wang, Hsien-Hua; Schlueter, John; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Monodisperse and homogeneous Pt{sub x}Ni{sub 1-x} alloy nanoparticles of various compositions are synthesized via an organic solution approach in order to reveal the correlation between surface chemistry and their electrocatalytic properties. Atomic-level microscopic analysis of the compositional profile and modeling of nanoparticle structure are combined to follow the dependence of Ni dissolution on the initial alloy composition and formation of the Pt-skeleton nanostructures. The developed approach and acquired knowledge about surface structure-property correlation can be further generalized and applied towards the design of advanced functional nanomaterials.

  18. Anisotropic TixSn1-xO2 nanostructures prepared by magnetron sputter deposition.

    PubMed

    Chen, Shutian; Li, Zhengcao; Zhang, Zhengjun

    2011-01-01

    Regular arrays of TixSn1-xO2 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. PMID:21711849

  19. Feasibility of KTa(1-x)Nb(x)O3 as a dielectric or pyroelectric microcalorimeter

    NASA Technical Reports Server (NTRS)

    Pfafman, T. E.; Silver, E.; Labov, S.; Beeman, J.; Goulding, F.; Landis, D.; Madden, N.

    1992-01-01

    We are developing a dielectric microcalorimeter for X-ray spectroscopy. We will present the results of our measurement of the dielectric permittivity, the spontaneous polarization, and the pyroelectric coefficient of the mixed-crystal quantum ferroelectric KTa(1-x)Nb(x)O3 with a doping of x = 0.012, as a function of temperature and bias voltage across the device. The effects of surface layers on the permittivity and the pyroelectric coefficient are discussed. We also show the signal results from infrared LED and alpha-particle radiation.

  20. 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. PMID:18999860

  1. Evidence of Spin Glass Dynamics in Dilute LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

    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±2mK with an exponent zν=7.8±0.2.

  2. 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.

  3. Concentration Dependent Physical Properties of Ge1-xSnx Solid Solution

    NASA Astrophysics Data System (ADS)

    Jivani, A. R.; Jani, A. R.

    2011-12-01

    Our own proposed potential is used to investigate few physical properties like total energy, bulk modulus, pressure derivative of bulk modulus, elastic constants, pressure derivative of elastic constants, Poisson's ratio and Young's modulus of Ge1-xSnx solid solution with x is atomic concentration of α-Sn. The potential combines linear plus quadratic types of electron-ion interaction. First time screening function proposed by Sarkar et al is used to investigate the properties of the Ge-Sn solid solution system.

  4. 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.

  5. 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.

  6. Experimental and theoretical investigation of the conduction band edge of GaNxP1-x

    NASA Astrophysics Data System (ADS)

    Güngerich, M.; Klar, P. J.; Heimbrodt, W.; Weiser, G.; Geisz, J. F.; Harris, C.; Lindsay, A.; O'Reilly, E. P.

    2006-12-01

    We show that a two-level band-anticrossing (BAC) model fails to describe the evolution of N-related states in GaNxP1-x . Band structure calculations prove that a two-level model describes these states in ordered GaNP supercells. Photocurrent measurements support a BAC-related blueshift of the GaP-like direct band gap in disordered GaNP, but calculations and electromodulated absorption and pressure studies show that the wide energy distribution of the lower-lying N-related states leads to the anticrossing interaction involving many N levels in disordered GaNP.

  7. Aging in K1-xLixTaO3: A Domain Growth Interpretation

    NASA Astrophysics Data System (ADS)

    Alberici-Kious, F.; Bouchaud, J. P.; Cugliandolo, L. F.; Doussineau, P.; Levelut, A.

    1998-11-01

    The aging behavior of the ac susceptibility of randomly substituted K1-xLixTaO3 crystals reveals marked differences with spin glasses in that cooling rate effects are very important. The response to temperature steps (including temperature cycles) was carefully studied. A model based on thermally activated domain growth accounts for all the experimental results, provided one allows for a large distribution of pinning energies, in such a way that ``slow'' and ``fast'' domains coexist. Interesting similarities with deeply supercooled liquids are underlined.

  8. Photocurrents in the polar phase of K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Camagni, P.; Galinetto, P.; Giulotto, E.; Samoggia, G.; Sangalli, P.

    Experiments on photoconductivity and thermally stimulated currents were performed on Li-doped KTaO3 single crystals. The large enhancement of conductivity, caused by UV excitation at low temperature was found to correlate with a subsequent release of trapped charge between 30 and 40 K. No corresponding release was shown by pure KTaO3, consistently with a very low yield of photoconduction. It is concluded that the presence of hole traps, with the consequent quenching of electron-hole recombination, is at the origin of the photoconductive response of K1-xLixTaO3.

  9. High performance photovoltaic infrared devices in Hg(1-x)Cd(x)Te on sapphire

    NASA Astrophysics Data System (ADS)

    Reidel, R. A.; Gertner, E. R.; Edwall, D. D.; Tennant, W. E.

    1985-01-01

    A combination of organometallic vapor phase epitaxy and liquid phase epitaxy (LPE) has been used to grow CdTe on sapphire. The resultant heterostructure has been used as a substrate for LPE growth of Hg(0.7)Cd(0.3)Te. Photodiodes in the HgCdTe show excellent properties. Typical R(0)A products are higher than a million ohms at 77 K for Hg(1-x)Cd(x)Te layers with cutoff wavelengths of 4.8-5.2 microns at 77 K. The backside-illuminated spectral response was broadband with quantum efficients typically over 80 percent (without antireflection coatings).

  10. 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.

  11. Dislocation scatterings in p-type Si(1-x)Ge(x) under weak electric field.

    PubMed

    Hur, Ji-Hyun; Jeon, Sanghun

    2015-12-11

    We present a theoretical model which describes hole mobility degradation by charged dislocations in p-type Si(1-x)Ge(x). The complete analytical expression of the dislocation mobility is calculated from the momentum relaxation time of hole carriers under weak electric field. The obtained dislocation mobility shows a T(3/2)/λ relation and is proportional to the germanium density x. We also suggest a criterion for negating scatterings by dislocations in terms of the controllable parameters such as acceptor dopant density, dislocation density, temperature, and Ge density x, etc. PMID:26567870

  12. Photoacoustic spectra of Zn1-xBexTe near the energy gap

    NASA Astrophysics Data System (ADS)

    Todorović, D. M.; Zakrzewski, J.; Maliński, M.; Grozdić, T.; Firszt, F.

    2008-01-01

    The results of experimental studies of optical and structural properties in bulk crystals of Zn1-xBe_xTe (x = 0.02, 0.06 and 0.12) were presented. The amplitude and phase photoacoustic (PA) spectra were measured and analyzed in dependence on the wavelength of the excitation optical beam, at different frequencies of modulation, using the PA microphone (PAmic) and PA piezoelectric (PApze) spectroscopy methods. The differences in PA spectra of as grown and annealed in zinc vapor samples were observed.

  13. Study of Zn1-x-yBexMnySe mixed crystals by photothermal method

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Maliński, M.; Strzalkowski, K.; Firszt, F.; Łegowski, S.; Męczyńska, H.; Marasek, A.

    2008-01-01

    In this paper a series of experimental piezoelectric spectra of Zn1-x-yBe_xMn_ySe (y = 0.05, x = 0.05, 0.10, 0.15) crystals are presented and discussed. Three groups of samples exhibiting different composition with different surface treatment: grinded, polished and etched were prepared. The influence of a different surface treatment on piezoelectric amplitude spectra are discussed with in model taking into account the presence of defects located on the surfaces of the samples.

  14. Piezoelectric spectroscopic studies of Zn1-x-yBexMnymixed crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Malinski, M.; Strzałkowski, K.; Firszt, F.; Legowski, S.; Meczynska, H.

    2008-02-01

    This paper presents results of experimental and theoretical piezoelectric studies of a group of mixed crystals of the type Zn1 - x - yBexMnySe. The fittings of theoretical to experimental amplitude and phase piezoelectric spectra were performed in a modified Jackson and Amer model. The influence of the surface treatment such as grinding, polishing and etching on the PZE spectra is analysed in the model of surface defects applied for the interpretation of the spectra for energies of photons below the energy gap of the crystal.

  15. Low temperature specific heat of Pr1-xLaxVO3(0<=x<=1)

    NASA Astrophysics Data System (ADS)

    Gaur, N. K.; Parveen, Atahar; Nigam, Arun K.

    2013-06-01

    We present the low temperature specific heat of the rare earth orthovanadate Pr1-xLaxVO3 computed by the means of a Modified Rigid Ion Model (MRIM) in a wide doping range (0 ≤ x ≤ 1). Also, the effect of La doping and the impact of lattice distortions on the elastic, cohesive and thermal properties of PrVO3 have been studied by an atomistic approach. The computed results are in good agreement with the available experimental data. The results can further be improved by incorporating the spin and orbital ordering contributions to the specific heat.

  16. Fundamentals of elasticity of (Mg1-x, Fex)2SiO4 olivine

    NASA Astrophysics Data System (ADS)

    Núñez-Valdez, M.; Umemoto, K.; Wentzcovitch, R. M.

    2010-07-01

    We study the influence of iron on the elasticity of (Mg1-x, Fex)2SiO4 olivine (0 ≤ x ≤ 0.125), a major constituent of the Earth's upper mantle. We calculate static elastic properties by first principles for this solid solution and investigate the effect of atomic arrangement, an artifact of supercell calculations, on all single crystal and poly-crystalline elastic moduli. From calculated wave propagation velocities we find the heterogeneity ratios of shear to compressional wave velocity, and bulk sound to shear wave velocity. Their values are, though limited to composition considerations, marginally consistent with seismic tomography.

  17. 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.

  18. 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

  19. Carrier recombination in tailored multilayer Si/Si1-xGex nanostructures

    NASA Astrophysics Data System (ADS)

    Mala, S. A.; Tsybeskov, L.; Lockwood, D. J.; Wu, X.; Baribeau, J.-M.

    2014-11-01

    Photoluminescence (PL) measurements were performed in Si/Si1-xGex nanostructures with a single Si0.92Ge0.08 nanometer-thick layer incorporated into Si/Si0.6Ge0.4 cluster multilayers. Under pulsed laser excitation, the PL decay associated with the Si0.92Ge0.08 nano-layer is found to be nearly a 1000 times faster compared to that in Si/Si0.6Ge0.4 cluster multilayers. A model considering Si/SiGe hetero-interface composition and explaining the fast and slow time-dependent recombination rates is proposed.

  20. Electrical and Optical Properties of the CuGa(S1-xSex)2 System

    NASA Astrophysics Data System (ADS)

    Matsushita, Hiroaki; Endo, Saburo; Nakanishi, Hisayuki; Nomura, Shigetaka; Irie, Taizo

    1990-03-01

    The mixed crystal system CuGa(S1-xSex)2 was prepared by the normal freezing method. The compositional dependence of the lattice constants and the optical band gap obeyed Vergard’s law. The phase diagram of this system was studied by DTA measurement. An orange photoluminescence was observed for x{≤q}0.5 after annealing in vacuum. It was confirmed that the emission was due to D-A pair recombinations, and an increase of S-vacancy caused an increase of photoluminescence intensity. The electrical resistivity was also affected by S-vacancy.

  1. 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.

  2. 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).

  3. Local Atomic Structure and Magnetism in Amorphous FexSi1-x Thin Films

    NASA Astrophysics Data System (ADS)

    Hellman, Frances; Zhang, Yanning; Bordel, Catherine; Stone, Kevin; Jenkins, Catherine; Smith, David; Hu, J.; Wu, Ruqian; Heald, Steve; Kortright, Jeff; Karel, Julie

    2014-03-01

    Amorphous FexSi1-x thin films exhibit a large enhancement in M compared to crystalline films with the same composition (0.45< x<0.75). XMCD shows enhancement in both spin and orbital moments. Density functional theory (DFT) calculations reproduce this enhanced magnetization. DFT and EXAFS show the amorphous materials have decreased number of nearest neighbors and reduced number density relative to crystalline samples of same x, which leads to the enhanced moment. Thanks to DOE BES LBNL magnetism program for support.

  4. Electronic and magnetic structure of GaxFe1-x thin films

    SciTech Connect

    Arenholz, E.; van der Laan, G.; McClure, A.; Idzerda, Y.

    2010-09-08

    The electronic as well as magnetic properties of Ga{sub x}Fe{sub 1-x} films were studied by soft x-ray measurements. Using x-ray magnetic circular dichroism the Fe majority-spin band was found to be completely filled for x {approx} 0.3. With further enhanced Ga content, the Fe moment as well as the angular dependence of the x-ray magnetic linear dichroism decrease strongly, which we attribute to the formation of D0{sub 3} precipitates. Moreover, the magnetocrystalline anisotropy drops significantly.

  5. Surface investigation of Ca1-xPrxFe2As2 by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Huang, Dennis; Zeljkovic, Ilija; Song, Can-Li; Lv, Bing; Chu, Ching-Wu; Hoffman, Jennifer E.

    2013-03-01

    Rare-earth-doped CaFe2As2 exhibits small volume-fraction superconductivity up to 49 K of unknown origin. We use scanning tunneling microscopy to locally probe possible sources of this phase in Ca1-xPrxFe2As2. We encounter three kinds of surface morphologies and infer their chemical identities with local work function measurements. We also image Pr3+ dopants as positive-energy resonances in tunneling conductance and examine their relationship with an observed inhomogeneous spectral gap.

  6. Intrinsic Carrier Concentration and Electron Effective Mass in Hg(1-x) Zn(x) Te

    NASA Technical Reports Server (NTRS)

    Sha, Yi-Gao; Su, Ching-Hua; Lehoczky, S. L.

    1997-01-01

    In this work, the intrinsic carrier concentration and electron effective mass in Hg(l-x)Zn(x)Te were numerically calculated. We adopt the procedures similar to those used by Su et. al. for calculating intrinsic carrier concentrations in Hg(1-x)Cd(x)Te which solve the exact dispersion relation in Kane model for the calculation of the conduction band electron concentrations and the corresponding electron effective masses. No approximation beyond those inherent in the k centered dot p model was used here.

  7. Theoretical investigations on giant magnetocaloric effect in MnAs 1- xSb x

    NASA Astrophysics Data System (ADS)

    von Ranke, P. J.; de Oliveira, N. A.; Gama, S.

    2004-01-01

    In this work we apply a model to describe the magnetocaloric effect for the MnAs 1- xSb x series of compounds, 0⩽ x⩽0.4. The behavior of the material under first order phase transitions is well described, and we are able to obtain the magnetocaloric potential for the series of compounds presenting first order magnetic phase transitions. Based on these results we predict the performance of a composite comprising a combination of compositions of this compound to work as active element in a magnetic refrigerator using an Erickson cycle spanning a great temperature range down from room temperature.

  8. 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.

  9. 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.

  10. Preparation of Single-Layer MoS2 x Se2(1- x ) and Mox W1- x S2 Nanosheets with High-Concentration Metallic 1T Phase.

    PubMed

    Tan, Chaoliang; Zhao, Wei; Chaturvedi, Apoorva; Fei, Zhen; Zeng, Zhiyuan; Chen, Junze; Huang, Ying; Ercius, Peter; Luo, Zhimin; Qi, Xiaoying; Chen, Bo; Lai, Zhuangchai; Li, Bing; Zhang, Xiao; Yang, Jian; Zong, Yun; Jin, Chuanhong; Zheng, Haimei; Kloc, Christian; Zhang, Hua

    2016-04-01

    The high-yield and scalable production of single-layer ternary transition metal dichalcogenide nanosheets with ≈66% of metallic 1T phase, including MoS2x Se2(1-x) and Mox W1-x S2 is achieved via electrochemical Li-intercalation and the exfoliation method. Thin film MoS2 x Se2(1- x ) nanosheets drop-cast on a fluorine-doped tin oxide substrate are used as an efficient electrocatalyst on the counter electrode for the tri-iodide reduction in a dye-sensitized solar cell. PMID:26915628

  11. 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. PMID:23690601

  12. 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

  13. 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.

  14. Magnetic and Transport properties of single crystalline FeSi1-xGex

    NASA Astrophysics Data System (ADS)

    Yeo, Sunmog; Nakatsuji, Satoru; Bianchi, Andrea; Drymiotis, Fivos; Fisk, Zachary

    2002-03-01

    Title : Magnetic and Transport properties of single crystalline FeSi1-xGex Author : S. Yeo, S. Nakatsuji, A. D. Bianchi*, F. R. Drymiotis, Z. Fisk National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32306 The isomorphic iron intermetallic compounds FeSi and FeGe have significantly distinct ground states: Kondo insulator and ferromagnetic metal, respectively. We have recently succeeded in growing single crystals of the whole range of the solution system FeSi1-xGex and performed the susceptibility, resistivity and specific heat measurements throughout the composition range. In the Kondo insulating phase near FeSi, we find that the temperature dependence of the susceptibility is well described by a thermally activated Curie law. Starting from 622 K in the case of FeSi, the activation gap systematically decreases below 190 K for Ge concentration near xc ? 0.25. Above xc, we find the sudden appearance of a ferromagnetic phase with Curie temperature of 125 K, comparable to the gap of the neighboring Kondo insulating phase. Both resistivity and specific measurements suggest that the insulator to metal transition occurs around xc. We will show the phase diagram constructed on the basis of these results, and discuss the origin of the interesting evolution of the ground state. This works were supported by NSF-DMR-9971348 * Present address : Los Alamos National Laboratory, Los Alamos, New Mexico 87545

  15. 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.

  16. 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.

  17. Superconductivity in 3R-Ta1-xMxSe2 (M = W, Mo)

    NASA Astrophysics Data System (ADS)

    Luo, Huixia; Xie, Weiwei; Seibel, Elizabeth M.; Cava, R. J.

    2015-09-01

    The 3-layer rhombohedral (3R) polytype of TaSe2-xTex is known to display a superconducting transition temperature that is between 6 and 17 times higher than that of the two-layer hexagonal (2H) polytype. The remarkable difference in Tc, although clearly associated with a difference in polytype, could have been due to an electronic effect specific to the Te-Se substitution. Here we report that small amounts of Mo or W doping lead to a 2H to 3R polytype transition in Ta1-xMoxSe2 and Ta1-xWxSe2. The 3R polytype materials are again found to have substantially higher Tc (~2 K for Ta0.9W0.1Se2 and Ta0.9Mo0.1Se2) than the 2H material (0.15 K), eliminating the possibility that any special characteristics of the Te/Se substitution are responsible for the dramatic difference in Tc. We infer that a three-layer stacking sequence is strongly preferred for superconductivity over a two-layer stacking sequence in the TaSe2 system.

  18. Valence states and possible charge ordering in LaCo(1-x)Rh(x)O₃.

    PubMed

    Streltsov, Sergey V; Gapontsev, Vladimir V; Khomskii, Daniel I

    2016-03-01

    An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co(3+) in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh(3+) led, surprisingly, to a rapid appearance of magnetism in LaCo(1-x)Rh(x)O3, even for small amounts of doping. Different explanations for this effect were proposed in the literature. To clarify the situation we carried out unbiased ab initio calculations of this system. We concluded that, in agreement with the original assumption of Li et al, but in contrast with later statements (Knizek et al 2012 Phys. Rev. B 85 134401), this effect is caused by the valence change ('redox reaction') Co(3+) +  Rh(3+) → Co(2+) +  Rh(4+), which creates magnetic Co(2+) and Rh(4+) ions. For the half-filled case LaCo1/2Rh1/2O3 we obtained the state with charge ordering of Co(2+) and Rh(4+) ions, which according to our calculations are antiferromagnetically coupled. The obtained results reasonably explain the observed behavior of the magnetic susceptibility of LaCo(1-x)Rh(x)O3, and the novel state predicted at half-doping could be verified experimentally by detailed structural and magnetic studies and by x-ray absorption spectroscopy. PMID:26852883

  19. Temperature Modulated DSC and Stiffness Threshold in Ge_xSe_1-x Glasses

    NASA Astrophysics Data System (ADS)

    Bresser, W. J.; Feng, Xingwei; Boolchand, P.; Schilthuis, J.

    1997-03-01

    We have examined binary Ge_xSe_1-x glasses over a wide composition range 0 < x <0.34, using a TA Instruments Model 2920 MDSC. The glass transitions deduced from the heat flow increase monotonically with x or = 2(1+x), the average coordination number. The heat flow near Tg shows a rather striking threshold behavior (minimum) near x = 0.23, corresponding to the composition at which the glass network begins to abruptly stiffen as noted by an upshift in Raman mode frequencies(Xingwei Feng, et al., to be published.). The present observations suggest that the minimum in Cp change at Tg near the stiffness threshold, deduced from ordinary DSC(M. Tatsumisago, B.L. Halfpap, J.L. Green, S.M. Lindsay, and C.A. Angell, Phys. Rev. Lett. 64, 1549 (1990).), i.e., total heat flow, largely derives from the non-reversing component (relaxation related) heat flow near T_g.

  20. Optical properties of lead barium niobate (Pb1 - xBaxNb2O6) crystals

    NASA Astrophysics Data System (ADS)

    Lee, Myeongkyu; Lee, Howard; Route, Roger K.; Feigelson, Robert S.

    1997-01-01

    PBN (Pb1-xBaxNb2O6) polycrystals have been grown by the vertical Bridgman method. Transparent, stoichiometric, striation-free single-crystal specimens of millimeter size were obtained. The ordinary and extraordinary refractive indices, no and ne, of crystals with compositions Pb0.50Ba0.50Nb2O6 and Pb0.57Ba0.43Nb2O6 were measured by the minimum deviation method using optically polished prisms. Neither no nor ne was found to be strongly dependent on crystal composition, in contrast to the case of SBN (Sr1-xBaxNb2O6), in which ne is strongly dependent on composition. Optical transmission spectra showed PBN to be transparent in the range from 0.4 to 5 μm except for the OH- absorption bands around 2.87 μm. The dependence of the integrated OH- absorption intensity on polarization showed that all of the O-H bonds lie either in the a-b plane or along the c axis, with a greater density of O-H bonds in the a-b plane than along the c axis.

  1. 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

  2. Ab Initio simulations of nonstoichiometric CdxTe1-x liquids

    NASA Astrophysics Data System (ADS)

    Ko, Eunjung; Alemany, M. M. G.; Derby, Jeffrey J.; Chelikowsky, James R.

    2005-08-01

    We present ab initio molecular-dynamics simulations for CdxTe1-x liquids where the composition is nonstoichiometric. The simulations are performed following Born-Oppenheimer molecular dynamics. The required forces are obtained from a solution of the Kohn-Sham equation using ab initio pseudopotentials. We consider stoichiometries of the form: CdxTe1-x, where x =0.2, 0.4, 0.6, and 0.8. For each composition of the melt, we consider a range of temperatures near the experimentally determined liquid temperatures. We examine the microstructural properties of the melt, the viscosity, and self-diffusion properties of the liquid as a function of the stoichiometry and temperature. We also perform an analysis of the distribution of the electronic density of states in these liquids. We find that structural changes in the local order, experimentally predicted to occur when the concentration of Cd is increased, are closely related to changes in the electronic properties of the melt.

  3. 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.

  4. Magnetotransport Properties of URANIUM(1-X)THORIUM(X)BERRYLLIUM(13) in the Normal State

    NASA Astrophysics Data System (ADS)

    Schaefer, Beth Ann

    UBe_{13} is a metal which belongs to the class of materials called heavy -fermion systems (HFS). At high temperatures UBe _{13} can be described as a system of localized magnetic moments (U^{3+ } ions) which weakly interact with the conduction electrons. At low temperatures, however, the interaction causes the conduction electrons to develop an exceptionally large effective mass (m^* > 100m _{e}), along with anomalous behavior in the transport and thermodynamic properties. Among the factors contributing to this low temperature behavior are the Kondo effect, itinerant spin fluctuations, coherence effects (due to the periodic arrangement of the magnetic scatterers), crystal electric fields, and RKKY interactions. In order to understand better the low temperature properties of UBe_{13}, I have studied the effects of substituting small amounts of non-magnetic Th for U (U_{1-x}Th_ {x}Be_{13}) on the resistivity, magnetoresistance, and Hall effect. These properties have been studied for 6 samples with x = 0, 0.0062, 0.0066, 0.013, 0.015, and 0.033 at temperatures from 1 K to 13 K, and for magnetic fields up to 9 Tesla. It has been found that even these small amounts of Th drastically alter the properties. Previous studies on U _{1-x}Th_{x}Be_ {13} have been interpreted through a model which uses a low temperature coherent state of UBe _{13} that is destroyed by the addition of Th. My results indicate that itinerant spin fluctuations dominate the low temperature behavior.

  5. 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).

  6. A computational study on magnetic effects of Zn1-x Crx O type diluted magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Duru, İzzet Paruğ; Değer, Caner; Kalaycı, Taner; Arucu, Muhammet

    2015-12-01

    Diluted magnetic semiconductors (DMS) have been intensely investigated both experimentally and theoretically in recent years. In spite of large body of studies to have a better understanding on working principles of devices based on DMS materials and taking a detailed control during fabrication process, nature of the system remains largely unknown. It is proposed that dominant contribution to DMS Hamiltonian is originated from ferromagnetic interaction between antiferromagnetic Cr+3 and its nearest neighbors rather than long-range interactions which commonly reported. In the light of experimental data obtained from literature, we simulated Zn1-x Crx O wurtzite thin film based on Metropolis algorithm and Markov Chain Monte Carlo (MC-MC) method as realistic as possible. We found that the soft ferromagnetic behaviour of Zn1-x Crx O thin film emerges by increasing doping ratios up to 15% (x=0.15), then it gradually vanishes above 15% (x=0.15) at room temperature. Results obtained here was found to be highly consistent with experimental studies.

  7. 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.

  8. Shallow levels and photoconductivity in K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Galinetto, P.; Giulotto, E.; Sangalli, P.; Camagni, P.; Samoggia, G.

    1999-11-01

    We present the results of experiments performed on K1-xLixTaO3 as well as on Nb-doped and nominally pure KTaO3 single crystals, in which we compared observations of thermally stimulated currents and photoconductivity. In the Li-doped compounds, the large enhancement of conductivity caused by ultraviolet excitation at low temperature was found to correlate with the filling of shallow trapping centres, giving intense charge release below 30-40 K. No sign of a corresponding release was shown by pure or Nb-doped KTaO3, consistently with a very low yield of photocurrent which one observes in these cases. The depth of the trapping levels in K1-xLixTaO3 crystals was found to be between 50 and 70 meV. On the basis of past models and recent calculations, these levels can be identified with hole traps, originating from the perturbation of O2- states at the top of the valence band. They are a plausible source of enhanced photoconductivity, via the quenching of electron-hole recombination.

  9. Dielectric relaxation and resonance in relaxor ferroelectric K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Pattnaik, R. K.; Toulouse, J.

    1999-09-01

    Polar regions are shown to mediate a strong coupling between polarization and strain in the paraelectric phase of the mixed ferroelectric K1-xLixTaO3 (KLT) and KTa1-xNbxO3 resulting in a field-induced piezoelectric response. The coupling is shown to result in a resonance in the dielectric spectrum of the crystals. In KLT, polar nanoregions can reorient via 180° (π relaxation) or 90° (π/2 relaxation) rotations. While the π relaxation is of no consequence, the π/2 relaxation has a strong influence on the overall character of the resonance. In addition to providing a mechanism for loss and degradation of the quality factor, this relaxation alters the character of the resonance as the two cross. Experimental results from dielectric spectroscopy above and below this crossover are presented and discussed. A simple theoretical Debye model involving the electrostrictive polarization-strain coupling is presented and the calculated spectrum is shown to reproduce the experimental spectrum. The parameters derived from the model are discussed. Most significantly, the electrostrictive coefficient of KLT is found to be 100 times larger than that of BaTiO3, and is due to the presence of polar nanoregions.

  10. Photoluminescence of Energetic Particle-Irradiated InxGa1-xNAlloys

    SciTech Connect

    Li, S.X.; Jones, R.E.; Haller, E.E.; Yu, K.M.; Walukiewicz, W.; Ager III, J.W.; Liliental-Weber, Z.; Lu, Hai; Schaff, William J.

    2005-12-14

    A study of the photoluminescence (PL) characteristics of In{sub x}Ga{sub 1-x}N alloys in which the Fermi level is controlled by energetic particle irradiation is reported. In In-rich In{sub x}Ga{sub 1-x}N the intensity of the PL emission initially increases with irradiation dose before falling rapidly at high doses. This unusual trend is attributed to the location of the average energy of the dangling-bond type native defects (the Fermi level stabilization energy, or E{sub FS}), which lies about 0.9 eV above the conduction band edge of InN. As a result of this atypically high position of E{sub FS}, irradiation-induced defects formed at low doses are donors, and do not act as efficient recombination centers. Thus, low dose irradiation increases the electron concentration and leads to an increase of the photoluminescence intensity. However, at higher irradiation doses, the Fermi level approaches E{sub FS}, and the defects formed become increasingly effective as a non-radiative recombination centers and the PL quenches quickly. Our calculations of the PL intensity based on the effect of the electron concentration and the minority carrier lifetime, show good agreement with the experimental data. Finally, the blue shift of PL signal with increasing electron concentration is explained by the breakdown of momentum conservation due to the irradiation damage.

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

    DOE PAGESBeta

    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

  12. Water electrolysis on La1-xSrxCoO3-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 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. PMID:27006166

  13. Charge transfer effects on the chemical reactivity of Pd(x)Cu(1-x) nanoalloys.

    PubMed

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

    2016-01-01

    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. PMID:26647173

  14. 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.

  15. 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.

  16. Hyperfine interactions in Ho(Fe1-xCox)2 compounds at 77 K

    NASA Astrophysics Data System (ADS)

    Bednarski, M.; Stoch, P.; Zachariasz, P.; Pszczoła, J.; Bodnar, W.; Suwalski, J.

    2011-01-01

    Synthesized, x-ray studied Ho(Fe1-xCox)2 compounds (x= 0-1) have a pure cubic Fd3m, C15, MgCu2-type crystal phase. The unit cell parameter decreases nonlinearly with the composition parameter x. Mössbauer effect spectra collected at 77 K for the Ho(Fe1-xCox)2 series were composed of a number of locally originated subspectra due to random Fe/Co nearest neighbourhoods. Hyperfine interaction parameters, i.e. the isomer shift, the magnetic hyperfine field and the quadrupole interaction parameter, were determined from the fitting procedure of the spectra for the individual nearest neighbourhoods and also as average values for the sample as bulk. As a result of Fe/Co substitution, Slater-Pauling-type dependences for magnetic hyperfine fields corresponding to both the local area and the sample as bulk were observed. A correlation between the local magnetic hyperfine fields and the average magnetic hyperfine fields was noticed, and this was related to weak and strong ferromagnetism of the transition metal sublattice. The obtained magnetic hyperfine fields were compared to analogous data known for compounds with other rare earths. A numerical formula for describing the magnetic hyperfine field as a function of the composition parameter x and rare earth spin S was proposed.

  17. 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.

  18. 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.

  19. 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.

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

    DOE PAGESBeta

    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

  1. 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.

  2. Valence states and possible charge ordering in LaCo1-x Rh x O3

    NASA Astrophysics Data System (ADS)

    Streltsov, Sergey V.; Gapontsev, Vladimir V.; Khomskii, Daniel I.

    2016-03-01

    An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co3+ in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh3+ led, surprisingly, to a rapid appearance of magnetism in LaCo1-x Rh x O3, even for small amounts of doping. Different explanations for this effect were proposed in the literature. To clarify the situation we carried out unbiased ab initio calculations of this system. We concluded that, in agreement with the original assumption of Li et al, but in contrast with later statements (Knizek et al 2012 Phys. Rev. B 85 134401), this effect is caused by the valence change (’redox reaction’) Co3+   +  Rh3+ \\to Co2+   +  Rh4+ , which creates magnetic Co2+ and Rh4+ ions. For the half-filled case LaCo1/2Rh1/2O3 we obtained the state with charge ordering of Co2+ and Rh4+ ions, which according to our calculations are antiferromagnetically coupled. The obtained results reasonably explain the observed behavior of the magnetic susceptibility of LaCo1-x Rh x O3, and the novel state predicted at half-doping could be verified experimentally by detailed structural and magnetic studies and by x-ray absorption spectroscopy.

  3. 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.

  4. 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.

  5. Properties of perovskites La 1-xCd xMnO 3

    NASA Astrophysics Data System (ADS)

    Luong, N. H.; Hanh, D. T.; Chau, N.; Tho, N. D.; Hiep, T. D.

    2005-04-01

    The La1-xCdxMnO3 (x = 0.1 , 0.2, 0.3) perovskites have been prepared by solid reaction technology with sintering temperature of 1050 °C. The samples are of single phase with rhombohedral structure of R-3c symmetry. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field indicate the spin glass-like state (or cluster glass) at low temperatures and a sharp change of magnetization around the phase-transition point of composition La0.7Cd0.3MnO3. This sample exhibits large value for maximum magnetic-entropy change |ΔSm|max of 2.88 J/kg K in the field of 13.5 kOe and reveals giant magnetocaloric effect. This value for |ΔSm|max is larger than that of La0.7Sr0.3MnO3 and La0.7Pb0.3MnO3 perovskites. The resistance measurements show that the conductivity of La1-xCdxMnO3 perovskites is metallic at low temperatures and semiconducting at high temperatures but the metal-semiconductor transition temperatures are not coinciding with paramagnetic-ferromagnetic transition ones. The results can not be explained by using double-exchange (DE) model only. In addition to the DE Jahn-Teller lattice distortion plays an important role.

  6. 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.

  7. Development of a new 1x4 micro-optical switch

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Shan, Xue C.; Wang, Z. P.; Lim, Siak-Piang; Lee, K. H.; Noell, Wilfried; de Rooij, Nico F.

    2002-04-01

    In this paper, we report the development of a new 1X4 micro optical switching device which utilizes electrostatic actuation and vertical silicon mirrors. This device is fabricated using a bulk micromachining process, which allows the fabrication of vertical mirrors and U-grooves through deep reactive ion etching (DRIE) of silicon. A limited number of process steps are required in the fabrication. Moreover, the device is patterned in a single lithographic step. A relatively high yield (up to 70%) is achieved during the microfabrication due to this compact process flow. More importantly, a small footprint (<13mm2 in die size) is realized. A single mode fiber with a tapered end is placed into a U-groove and positioned passively by a fiber stopper, prior to adhesive bonding with a silicon substrate and a glass cover. Preliminary characterization on the mechanical and optical performance of this device has been carried out, which reveals the promising characteristics of this 1X4 optical switch for use in optical networks.

  8. 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.

  9. Effect of composition and annealing on electrodeposited CoxPt1-X nanowires

    NASA Astrophysics Data System (ADS)

    Khatri, Manvendra Singh; Agarwal, Shivani; Hsu, Jen-Hwa; Chien, Chia-Hua; Chen, Cheng-Lung; Chen, Yang-Yuan

    2016-05-01

    Highly ordered CoxPt1-x (x ≤ 0.82) magnetic nanowire arrays of 60 nm diameter have been fabricated successfully by electrodeposition process into the pores of anodic aluminum oxide (AAO) templates. Electrodeposition process has been used as it is one of the simplest and most inexpensive, easily controlled method for the synthesis of nanowires.It was found that deposition potential is a key factor to control the composition and thus the magnetic properties of the nanowires. The as-deposited CoxPt1-x nanowires were characterized by XRD to have fcc structure with preferred orientation of (111) or (001) along the nanowire. Co-rich nanowires exhibit ferromagnetic behavior in contrast to near superparamagnetic response of the Pt-rich nanowires. Upon annealing the effects of crystallization cause the decrease of anisotropy along the wire axis for Co82Pt18 nanowires due to the increase of magnetocrystalline anisotropy perpendicular to the wire axis. In the next phase of our work segmented CoPtP/Pt multilayers nanowires will be deposited within the AAO template. Such multilayers nanowires are expected to have the high anisotropy due to the formation of ordered Co-Pt alloy phase at the interface.

  10. 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.

  11. Microstructural Development of Directionally Solidified Hg(1-x)Zn(x)Se Alloys

    NASA Technical Reports Server (NTRS)

    Cobb, S. D.; Szofran, F. F.; Jones, K. S.; Lehoczky, S. L.

    1999-01-01

    Hg(1-x)Zn(x)Se alloys have been studied as an alternative to Hg(1-x)Cd(x)Te for the detection of electromagnetic radiation, because the shorter ZnSe and HgSe bonds have been predicted to improve lattice stability. Several ingots with x = 0.1 were directionally solidified using a modified Bridgman-Stockbarger method; one was grown in an applied magnetic field, which greatly reduced radial compositional variations. A method was developed to reduce wetting. This, combined with the convex liquid-solid interface shape, produced boules that were single crystalline after growing about 3.5 cm. Observed surface features indicated ampoule wetting was eliminated using a graphite getter. Microstructural characteristics were greatly improved over HgCdTe alloys. In six boules, a total of only one twin was observed. A method for polishing and producing dislocation etch pits was developed for these alloys, revealing dislocation etch pit densities one to two orders of magnitude less than HgTe-based alloys. A kink in the thermal profile during processing of one boule generated more dislocations than did lattice mismatch due to compositional variations. This alloy has improved microstructural properties and resistance to dislocation formation compared with similar II-VI alloys.

  12. 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.

  13. Magnetic instabilities in fcc FexNi1-x thin films

    NASA Astrophysics Data System (ADS)

    Foy, E.; Andrieu, S.; Finazzi, M.; Poinsot, R.; Teodorescu, C. M.; Chevrier, F.; Krill, G.

    2003-09-01

    We present the results obtained on FexNi1-x alloy films epitaxially grown on Cu(100). They are characterized by a fcc structure pseudomorphic to the substrate over a wide range of concentration and thickness. In particular, the martensitic transition which in bulk alloys occurs around the “Invar” concentration (x≈0.65) is suppressed. We report the concentration dependence at low temperature of the total magnetic moment and of its Fe-3d and Ni-3d projected components in such thin fcc FexNi1-x alloy films. Magnetic instabilities that might be associated with noncollinear spin alignments of Fe atoms are clearly observed for x>0.73, where the magnetic moment decreases with increasing Fe concentration. In this Fe-rich concentration range the layers are still ferromagnetic and a magnetic moment is still observed, even on Ni atoms and at room temperature, up to x=0.86. We also show how the variation of the magnetization in this region is correlated with a very small variation of the atomic volume (˜1%).

  14. Structural and antiferromagnetic properties of Ba(Fe1-x-y Cox Rhy)2 As2 compounds

    NASA Astrophysics Data System (ADS)

    Kim, Min Gyu; Heitmann, T. W.; Mulcahy, S. R.; Bourret-Courchesne, E. D.; Birgeneau, R. J.

    We present a systematic investigation of the electrical, structural, and antiferromagnetic properties for the series of Ba(Fe1-x-y CoxRhy)2 As2 compounds with fixed x = 0.027 and 0 < y <0.035. We compare our results for the Co-Rh doped Ba(Fe1-x-y CoxRhy)2 As2 compounds with Ba(Fe 1-xCox)2 As2 compounds. We demonstrate that the electrical, structural, antiferromagnetic, and superconducting properties of the Co-Rh doped compounds are similar to the properties of the Co doped compounds. We find that the overall behaviors of Ba(Fe1-x-y CoxRhy)2 As2 and Ba(Fe1-x Cox)2 As2 compounds are very similar when the total number of the extra electrons per Fe/TM (TM = transition metal) site is considered, which is consistent with the rigid band model. Despite the similarity, we find that the details of the transitions are different in between Ba(Fe1-x-y CoxRhy)2 As2 and Ba(Fe1-x Cox)2 As2 compounds. The work at the Lawrence Berkeley National Laboratory was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231.

  15. Structural and antiferromagnetic properties of Ba(Fe1 -x -yCoxRhy )2As2 compounds

    NASA Astrophysics Data System (ADS)

    Kim, M. G.; Heitmann, T. W.; Mulcahy, S. R.; Bourret-Courchesne, E. D.; Birgeneau, R. J.

    2016-03-01

    We present a systematic investigation of the electrical, structural, and antiferromagnetic properties for the series of Ba (Fe1-x-yCoxRhy) 2As2 compounds with fixed x ≈0.027 and 0 ≤y ≤0.035 . We compare our results for the Co-Rh doped Ba (Fe1-x-yCoxRhy) 2As2 compounds with the Co doped Ba (Fe1-xCox) 2As2 compounds. We demonstrate that the electrical, structural, antiferromagnetic, and superconducting properties of the Co-Rh doped compounds are similar to the properties of the Co doped compounds. We find that the overall behaviors of Ba (Fe1-x-yCoxRhy) 2As2 and Ba (Fe1-xCox) 2As2 compounds are very similar when the total number of extra electrons per Fe/TM (TM=transition metal) site is considered, which is consistent with the rigid band model. Despite the similarity, we find that the details of the transitions, for example, the temperature difference between the structural and antiferromagnetic transition temperatures and the incommensurability of the antiferromangetic peaks, are different between Ba (Fe1-x-yCoxRhy) 2As2 and Ba (Fe1-xCox) 2As2 compounds.

  16. Effect of oxidizable electrode material on resistive switching characteristics of ZnO(x)S(1-x) films.

    PubMed

    Cho, Kyoungah; Park, Sukhyung; Chung, Isaac; Kim, Sangsig

    2014-11-01

    We investigate the memory characteristics of ZnO(x(S(1-x) based resistive switching random access memory (ReRAM) devices with Al and Pt bottom electrodes (BEs). Both the ReRAM devices with Al and Pt BEs exhibit unipolar resistive switching behaviors, regardless of the materials of the BEs. The ratios of the high resistance state (HRS) to the low resistance state (LRS) of the Au/annealed ZnO(x)S(1-x)/Al and the Au/annealed ZnO(x)S(1-x)/Pt devices are more than 10(6) and 10(4), respectively. The HRS depends more significantly on the material of the BE than the LRS. The resistance in the HRS of the device with the Al BE is more stable in the endurance characteristics and higher in magnitude than that of the device with the Pt BE. For an anealed ZnO(x)S(1-x)/Al film, the oxygen signal in the auger depth profile shows the formation of an AIO(x) layer at the interface between the annealed ZnO(x)S(1-x) layer and the Al BE. The difference between the memory characteristics of the annealed ZnO(x)S(1-x) devices with the Al and Pt BEs is explained with the presence or absence of the oxidized layers formed in the interfaces between the annealed ZnO(x)S(1-x) films and the BEs. PMID:25958497

  17. 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.

  18. 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.

  19. 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.

  20. Mixing thermodynamics of TM1-xGdxN (TM=Ti,Zr,Hf) from first principles

    NASA Astrophysics Data System (ADS)

    Alling, B.; Höglund, C.; Hall-Wilton, R.; Hultman, L.

    2011-06-01

    The mixing thermodynamics of GdN with TiN, ZrN, and HfN is studied using first-principles methods. We find that while Ti1-xGdxN has a strong preference for phase separation due to the large lattice mismatch, Zr1-xGdxN and Hf1-xGdxN readily mix, possibly in the form of ordered compounds. In particular, ZrGdN2 is predicted to order in a rocksalt counterpart to the L11 structure at temperatures below 1020 K. These mixed nitrides are promising candidates as neutron absorbing, thermally and chemically stable, thin film materials.

  1. Charge transfer transitions in the photoluminescence spectra of Zn1-xMexO (Me = Mn, Ni, Co) oxide compounds

    NASA Astrophysics Data System (ADS)

    Sokolov, V. I.; Gruzdev, N. B.; Pustovarov, V. A.; Churmanov, V. N.

    2013-01-01

    Crystals of Zn1-xCoxO and Zn1-xNixO are studied by photoluminescence at temperatures of 8 and 90 K. By resolving the spectra into sums of gaussian distributions and using the known positions of donor and acceptor levels of 3d-impurities relative to the edges of the allowed bands, the observed peaks in the photoluminescence spectra are interpreted in terms of radiative recombination through donor and acceptor levels of nickel and cobalt ions. These results are compared with previously observed features of the photoluminescence spectra of Zn1-xMnxO crystals.

  2. 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.

  3. The atomic structure of ternary amorphous TixSi1-xO2 hybrid oxides.

    PubMed

    Landmann, M; Köhler, T; Rauls, E; Frauenheim, T; Schmidt, W G

    2014-06-25

    Atomic length-scale order characteristics of binary and ternary amorphous oxides are presented within the framework of ab initio theory. A combined numerically efficient density functional based tight-binding molecular dynamics and density functional theory approach is applied to model the amorphous (a) phases of SiO2 and TiO2 as well as the amorphous phase of atomically mixed TixSi1-xO2 hybrid-oxide alloys over the entire composition range. Short and mid-range order in the disordered material phases are characterized by bond length and bond-angle statistics, pair distribution function analysis, coordination number and coordination polyhedra statistics, as well as ring statistics. The present study provides fundamental insights into the order characteristics of the amorphous hybrid-oxide frameworks formed by versatile types of TiOn and SiOm coordination polyhedra. In a-SiO2 the fourfold crystal coordination of Si ions is almost completely preserved and the atomic structure is widely dominated by ring-like mid-range order characteristics. In contrast, the structural disorder of a-TiO2 arises from short-range disorder in the local coordination environment of the Ti ion. The coordination number analysis indicates a large amount of over and under-coordinated Ti ions (coordination defects) in a-TiO2. Aside from the ubiquitous distortions of the crystal-like coordinated polyhedra, even the basic coordination-polyhedra geometry type changes for a significant fraction of TiO6 units (geometry defects). The combined effects of topological and chemical disorder in a-TixSi1-xO2 alloys lead to a continuos increase in both the Si as well as the Ti coordination number with the chemical composition x. The important roles of intermediate fivefold coordination states of Ti and Si cations are highlighted for ternary a-TixSi1-xO2 as well as for binary a-TiO2. The continuous decrease in ring size with increasing Ti content reflects the progressive loss of mid-range order structure

  4. 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

  5. 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.

  6. The effects of starting materials in the synthesis of (Ga(1-x)Znx)(N(1-x)O(x)) solid solution on its photocatalytic activity for overall water splitting under visible light.

    PubMed

    Hisatomi, Takashi; Maeda, Kazuhiko; Lu, Daling; Domen, Kazunari

    2009-01-01

    The influence of starting materials on the physicochemical and photocatalytic properties of (Ga(1-x)Zn(x))(N(1-x)O(x)) were investigated in an attempt to optimize the preparation conditions. The catalyst was successfully prepared by nitriding a starting mixture of ZnO and Ga2O3. A mixture of metallic zinc and GaN, however, did not afford the desired compound. The crystallinity, surface area, composition, and absorption characteristics of the resultant (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution are found to be dependent on the morphology of ZnO but largely insensitive to the choice of Ga2O3 polymorph. The use of coarser-grained ZnO results in a coarser-grained catalyst with elevated zinc and oxygen content and reduced uniformity in composition and crystallinity. The results demonstrate the importance of selecting appropriate ZnO and Ga2O3 starting materials for maximizing the photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) for overall water splitting under visible light. PMID:19107886

  7. Research Update: Magnetic phase diagram of EuTi1-xBxO3 (B = Zr, Nb)

    DOE PAGESBeta

    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.

  8. Investigation of the direct band gaps in Ge1-xSnx alloys with strain control by photoreflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Chen, Robert; Lu, Weisheng; Huo, Yijie; Kamins, Theodore I.; Harris, James S.

    2012-03-01

    Unstrained and compressive-strained Ge1-xSnx alloys were grown on InGaAs buffer layers by molecular beam epitaxy. Photoreflectance at room temperature determines the direct bandgap energies of Ge1-xSnx alloys from the maxima of the light- and heavy-hole bands to the bottom of Γ valley. The lowest transition energies from photoreflectance are consistent with the energies derived from photoluminescence. The calculated bowing parameter is 2.42 ± 0.04 eV for the direct band gap of Ge1-xSnx alloys. The dilational and shear deformation potentials of the direct band gap are -11.04 ± 1.41 eV and -4.07 ± 0.91 eV, respectively. These basic material parameters are important in designing optoelectronic devices based on Ge1-xSnx alloys.

  9. Amber-green light-emitting diodes using order-disorder AlxIn1-xP heterostructures

    NASA Astrophysics Data System (ADS)

    Christian, Theresa M.; Beaton, Daniel A.; Mukherjee, Kunal; Alberi, Kirstin; Fitzgerald, Eugene A.; Mascarenhas, Angelo

    2013-08-01

    We demonstrate amber-green emission from AlxIn1-xP light-emitting diodes (LEDs) with luminescence peaked at 566 nm and 600 nm. The LEDs are metamorphically grown on GaAs substrates via a graded InyGa1-yAs buffer layer and feature electron confinement based on the control of AlxIn1-xP CuPt atomic ordering. A control sample fabricated without order-disorder carrier confinement is used to illustrate device improvement up to a factor of 3 in light output due to confinement at drive currents of 40 A/cm2. The light output at room temperature from our AlxIn1-xP LED structure emitting at 600 nm is 39% as bright as a GaxIn1-xP LED emitting at 650 nm.

  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. 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.

  12. Coherency effects on the mixing thermodynamics of cubic Ti1 -xAlxN /TiN (001) multilayers

    NASA Astrophysics Data System (ADS)

    Wang, Fei; Abrikosov, Igor A.; Simak, Sergei I.; Odén, Magnus; Mücklich, Frank; Tasnádi, Ferenc

    2016-05-01

    In this work, we discuss the mixing thermodynamics of cubic (B1) Ti1 -xAlxN /TiN (001 ) multilayers. We show that interfacial effects suppress the mixing enthalpy compared to bulk Ti1 -xAlxN . The strongest stabilization occurs for compositions in which the mixing enthalpy of bulk Ti1 -xAlxN has its maximum. The effect is split into a strain and an interfacial (or chemical) contribution, and we show that both contributions are significant. An analysis of the local atomic structure reveals that the Ti atoms located in the interfacial layers relax significantly different from those in the other atomic layers of the multilayer. Considering the electronic structure of the studied system, we demonstrate that the lower Ti-site projected density of states at ɛF in the Ti1 -xAlxN /TiN multilayers compared to the corresponding monolithic bulk explains a decreased tendency toward decomposition.

  13. Effect of annealing on the superconducting properties of a-NbxSi1-x thin films

    NASA Astrophysics Data System (ADS)

    Crauste, O.; Gentils, A.; Couëdo, F.; Dolgorouky, Y.; Bergé, L.; Collin, S.; Marrache-Kikuchi, C. A.; Dumoulin, L.

    2013-04-01

    a-NbxSi1-x thin films with thicknesses down to 25 Å have been structurally characterized by transmission electron microscopy measurements. As-deposited or annealed films are shown to be continuous and homogeneous in composition and thickness, up to an annealing temperature of 500 ∘C. We have carried out low-temperature transport measurements on these films close to the superconductor-to-insulator transition (SIT) and shown a qualitative difference between the effect of annealing or composition and a reduction of the film thickness on the superconducting properties of a-NbSi. These results question the pertinence of the sheet resistance R□ as the relevant parameter to describe the SIT.

  14. Noise in large-area CrlS Hg1-xCdxTe photovoltaic detectors

    NASA Astrophysics Data System (ADS)

    D'Souza, Arvind I.; Stapelbroek, Maryn G.; Masterjohn, Stacy A.; Wijewarnasuriya, Priyalal S.; DeWames, Roger E.; Smith, David S.; Ehlert, John C.

    2003-01-01

    The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometric sensor that measures earth radiances at high spectral resolution. Algorithms use the data to provide pressure, temperature, and moisture profiles of the atmosphere. The CrIS instrument contains photovoltaic detectors with spectral cut-offs denoted by SWIR, MWIR and LWIR. The CrIS instrument requires large-area, photovoltaic detectors with state-of-art detector performance at temperatures attainable with passive cooling. For example, detectors as large as 1 mm in diameter are required. To address these needs, Molecular Beam Epitaxy (MBE) is used to grow the appropriate bandgap n-type Hg1-xCdxTe on lattice matched CdZnTe. The p-side is obtained via arsenic implantation followed by appropriate annealing steps.

  15. 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.

  16. 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.

  17. Phase diagram and polarization of stable phases of (Ga1- x In x )2O3

    NASA Astrophysics Data System (ADS)

    Maccioni, Maria Barbara; Fiorentini, Vincenzo

    2016-04-01

    The full phase diagram of (Ga1- x In x )2O3 is obtained theoretically. The phases competing for the ground state are monoclinic β (low x), hexagonal (x ˜ 0.5), and bixbyite (large x). Three disconnected mixing regions interlace with two distinct phase-separation regions, and at x ˜ 0.5, the coexistence of hexagonal and β alloys with phase-separated binary components is expected. We also explore the permanent polarization of the phases, but none of them are polar. On the other hand, we find that ɛ-Ga2O3, which was stabilized in recent experiments, is pyroelectric with a large polarization and piezoelectric coupling, and could be used to produce high-density electron gases at interfaces.

  18. Ferrimagnetic ordering of single crystal Fe1-xGax thin films

    SciTech Connect

    McClure, A.; Arenholz, E.; Idzerda, Y. U.

    2009-10-19

    Molecular beam epitaxy was used to deposit body centered cubic single crystal Fe{sub 1-x}Ga{sub x} thin films on MgO(001) and ZnSe/GaAs(001) substrates well beyond the bulk stability concentration of about 28%. The crystal quality of the substrate surface and each deposited layer was monitored in situ by reflection high energy electron diffraction. The magnetization of the samples as a function of Ga is found to decrease more rapidly than a simple dilution effect, and element-specific x-ray magnetic circular dichroism ascribes this trend to a decrease in the Fe moment and an induced moment in the Ga that is antialigned to the Fe moment.

  19. Study of Structural Phase Transitions in Na1-xSrx/2NbO3

    NASA Astrophysics Data System (ADS)

    Bahuguna, Rajni; Wankhede, M. G.; Mishra, S. K.; Shinde, A. B.; Krishna, P. S. R.

    2015-02-01

    The solid solution Na1-xSrx/2NbO3 is prepared by solid state reaction method. Detailed analyses of powder x-ray diffraction data clearly suggest a change of structure from ABO3 perovskite (NaNbO3 like) to complicated Tungsten Bronze SrNb2O6 like. The presence of additional reflections clearly suggests that cell multiplicity for x>=0.20 is different to that of pure NaNbO3. For composition x>=0.20, the lattice parameters are related with pseudocubic perovskite cell parameters as follows: Ao= 4ap, Bo= 3bp Co= 5cp. The lattice parameters and volume increases monotonically with increasing concentration of Sr2+ in NaNbO3 matrix.

  20. Electronic structure and thermoelectric properties of CuRh1-xMgxO2

    NASA Astrophysics Data System (ADS)

    Maignan, Antoine; Eyert, Volker; Martin, Christine; Kremer, Stefan; Frésard, Raymond; Pelloquin, Denis

    2009-09-01

    Electronic structure calculations using the augmented spherical wave method have been performed for CuRhO2 . For this semiconductor crystallizing in the delafossite structure, it is found that the valence-band maximum is mainly due to the 4d t2g orbitals of Rh3+ . The structural characterizations of CuRh1-xMgxO2 show a broad range of Mg2+ substitution for Rh3+ in this series, up to about 12%. Measurements of the resistivity and thermopower of the doped systems show a Fermi-liquidlike behavior for temperatures up to about 1000 K, resulting in a large weakly temperature-dependent power factor. The thermopower is discussed both within the Boltzmann equation approach as based on the electronic structure calculations and the temperature-independent correlation functions ratio approximation as based on the Kubo formalism.

  1. Microstructure of In x Ga1-x N nanorods grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Soundararajah, Q. Y.; Griffiths, I. J.; Cherns, D.; Novikov, S. V.; Foxon, C. T.

    2015-11-01

    Transmission electron microscopy is used to examine the structure and composition of In x Ga1-x N nanorods grown by plasma-assisted molecular beam epitaxy. The results confirm a core-shell structure with an In-rich core and In-poor shell resulting from axial and lateral growth sectors respectively. Atomic resolution mapping by energy-dispersive x-ray microanalysis and high angle annular dark field imaging show that both the core and the shell are decomposed into Ga-rich and In-rich platelets parallel to their respective growth surfaces. It is argued that platelet formation occurs at the surfaces, through the lateral expansion of surface steps. Studies of nanorods with graded composition show that decomposition ceases for x ≥ 0.8 and the ratio of growth rates, shell:core, decreases with increasing In concentration.

  2. Measured thermal diffusivity of Hg(1-x)Cd(x)Te solids and melts

    NASA Technical Reports Server (NTRS)

    Holland, L. R.; Taylor, R. E.

    1983-01-01

    The thermal diffusivity of Hg(1-x)Cd(x)Te melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x = 0 in both the solid and the liquid, with the values observed at x = 0.3 being about 40 percent of those for x = 0. The solid diffusivity for x = 0 is 1.7 sq mm/s at 150 C, decreasing to 0.7 sq mm/s at the melting point. The x = 0 liquid diffusivity increases from 0.7 sq mm/s at the melting point to 3.5 sq mm/s at 900 C.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

    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 n 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.

  4. Electrical conduction in low-resistivity (quasiamorphous) Ag1-xCux alloys

    NASA Astrophysics Data System (ADS)

    Vancea, J.; Pukowietz, S.; Reiss, G.; Hoffmann, H.

    1987-06-01

    UHV-evaporated Ag1-xCux alloy films show a strong dependence of the crystallite sizes on the composition: In the middle of the concentration range, the mean grain size is smaller than 2 nm. The resistivity, however, is much lower than expected for such extremely-fine-grained materials (ρ<9 μΩ cm). The electrical transport parameters for these films were obtained from the thickness dependence of the conductivity without any a priori assumptions. It will be shown that the electrical transport in these alloys can be well understood as a limit of the reflection model for the electrical conductivity in polycrystalline metals [G. Reiss, J. Vancea, and H. Hoffmann, Phys. Rev. Lett. 56, 2100 (1986)].

  5. 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.

  6. Engineering of magnetostriction in Fe3Pt1-xIrx by controlling the Ir concentration

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj; Yun, Won Seok; Rhim, S. H.; Hong, Soon Cheol

    2011-04-01

    A tremendous change in both the sign and magnitude of magnetostriction (λ001) in Fe3Pt1-xIrx (x=0-1.0) was discovered through a first-principles study using the highly precise full-potential linearized augmented plane wave method. The obtained λ001 values span a wide range from -1050 (x=0) to +2670 ppm (x=0.25), a significantly large enhancement over the λ001 values attained for Galfenol, a widely investigated material. Further analysis confirmed that this large effect originates mainly from the nonmagnetic Ir and Pt with induced moments, of which the 5d orbital has larger spin-orbit coupling than the 3d orbital of Fe.

  7. 55Mn NMR study in Mn1-xTixAs

    NASA Astrophysics Data System (ADS)

    Amako, Yasushi; Nagai, Hiroyuki; Ido, Hideaki

    2004-05-01

    The nuclear magnetic resonance of 55Mn nuclei in Mn1-xTixAs has been measured at 4K. 55Mn resonance frequency in zero external field is 237MHz for MnAs of which the spontaneous magnetization at 4.2K is 3.4μB/f.u. Zero field 55Mn NMR spectra shift at the high-frequency side and they split in three signals by substituting Mn for Ti though the magnetic moment per Mn atom is constant for x less than 0.55. The transferred hyperfine field due to the nearest neighbor Mn moment is estimated to be +21kOe.

  8. 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.

  9. Specific Heat of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, J. A.; Mugford, C. G. A.; Gomez, A.; Kycia, S. W.; Kycia, J. B.

    2007-01-01

    We present specific heat data on three samples of the dilute Ising magnet LiHoxY1-xF4 with x=0.018, 0.045, and 0.080. Previous measurements of the ac susceptibility of an x=0.045 sample showed the Ho3+ moments to remain dynamic down to very low temperatures, and the specific heat was found to have unusually sharp features. In contrast, our measurements do not exhibit these sharp features in the specific heat and instead show a broad feature, for all three samples studied, which is qualitatively consistent with a spin glass state. Integrating C/T, however, reveals an increase in residual entropy with lower Ho concentration, consistent with recent Monte Carlo simulations showing a lack of spin glass transition for low x.

  10. A surface micromachined amorphous GexSi1-xOy bolometer for thermal imaging applications

    NASA Astrophysics Data System (ADS)

    Ahmed, A. H. Z.; Tait, R. N.; Oogarah, Tania B.; Liu, H. C.; Denhoff, Mike W.; Sproule, G. I.; Graham, M. J.

    2004-10-01

    We present characterization of a surface micro-machined microbolometer featuring a number of unique features. The active resistor layer is amorphous GexSi1-xOy grown by reactively co-sputtering Ge and Si in an oxygen background. Complete control over Ge, Si, and O content using this technique allows control of both temperature coefficient of resistance and resistivity of the material, enabling optimization of material characteristics for bolometer applications. The resistor layer is combined with top and bottom NiCr metalization to form a tuned absorber for 10 μm radiation, eliminating requirements for additional absorber layers or for carefully controlled air gap thickness. Characterization of device noise and performance is presented.

  11. Temperature evolution of the local order parameter in relaxor ferroelectrics (1 - x)PMN-xPZT

    NASA Astrophysics Data System (ADS)

    Gridnev, S. A.; Glazunov, A. A.; Tsotsorin, A. N.

    2005-09-01

    The temperature dependence of the local order parameter and relaxation time distribution function have been determined in (1 - x)PMN-xPZT ceramic samples via dielectric permittivity. Above the Burns temperature, the permittivity was found to follow the Currie-Weiss law, and with temperature decreasing the deviation was observed to increase. A local order parameter was calculated from the dielectric data using a modified Landau-Devonshire approach. These results are compared to the distribution function of relaxation times. It was found that a glasslike freezing of reorientable polar clusters occurs in the temperature range of diffuse relaxor transition. The evolution of the studied system to more ordered state arises from the increased PZT content.

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

    DOE PAGESBeta

    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

  13. Structural Changes of Amorphous Ge1-xSnx Alloy Films by Annealing

    NASA Astrophysics Data System (ADS)

    Fukumoto, Hirofumi; Myoren, Hiroaki; Nakashita, Toshio; Imura, Takeshi; Osaka, Yukio

    1986-09-01

    Microcrystalline (μc-) grains of Ge1-ySny (0.1≲ y≲ 0.4) were precipitated by thermal treatments of amorphous films of a Ge1-xSnx(x≲ 0.4) alloy deposited by co-sputtering. At higher temperatures grains of β-Sn came out, co-existing with those of μc-Ge1-ySny. Mössbauer spectroscopy was used to characterize states of Sn in a Ge-Sn alloy film. Optical properties, such as the real part \\varepsilon1 of the complex dielectric constant for Ge0.65Sn0.35, also changed as the structure change, especially at a photon energy of 1.6˜ 1.8 eV, where \\varepsilon1 took a maximum. It was suggested that an amorphous Ge-Sn alloy might be a good material for archival-type optical storage.

  14. Diffused phase transition of Ba1- x Eu x TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Jun, Byeong-Eog; Choi, Byung Chun; Jeong, Jung Hyun; Moon, Byung Kee

    2016-06-01

    By applying the sol-gel method, we fabricated Ba1- x Eu x TiO3 (BET) ceramics as a single peroveskite phase in the composition range of x = 0 ~ 0.20. The BET ceramics displayed a ferroelectric phase transition temperature that changed from 120 °C to 80 °C, and exhibited the coexistance of the tetragonal, and cubic structures as the Eu composition was increased. They also displayed anomalous dielectric behaviors related to structural relaxation in the temperature range from 200 °C to 600 °C. We considered the Arrhenius temperature dependence of the dielectric relaxation time by using the electric modulus formalism. The characteristic activation energy was thought to be related with the substitution of Eu (Eu2+, Eu3+) ions for Ba2+ or Ti4+ ions in the perovskite structure.

  15. 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}.

  16. Origin of the spin reorientation transitions in (Fe1-xCox)2B alloys

    NASA Astrophysics Data System (ADS)

    Belashchenko, Kirill D.; Ke, Liqin; Däne, Markus; Benedict, Lorin X.; Lamichhane, Tej Nath; Taufour, Valentin; Jesche, Anton; Bud'ko, Sergey L.; Canfield, Paul C.; Antropov, Vladimir P.

    2015-02-01

    Low-temperature measurements of the magnetocrystalline anisotropy energy K in (Fe1-xCox)2B alloys are reported, and the origin of this anisotropy is elucidated using a first-principles electronic structure analysis. The calculated concentration dependence K(x) with a maximum near x = 0.3 and a minimum near x = 0.8 is in excellent agreement with experiment. This dependence is traced down to spin-orbital selection rules and the filling of electronic bands with increasing electronic concentration. At the optimal Co concentration, K depends strongly on the tetragonality and doubles under a modest 3% increase of the c/a ratio, suggesting that the magnetocrystalline anisotropy can be further enhanced using epitaxial or chemical strain.

  17. Unabridged phase diagram for single-phased FeSe(x)Te(1-x) thin films.

    PubMed

    Zhuang, Jincheng; Yeoh, Wai Kong; Cui, Xiangyuan; Xu, Xun; Du, Yi; Shi, Zhixiang; Ringer, Simon P; Wang, Xiaolin; Dou, Shi Xue

    2014-01-01

    A complete phase diagram and its corresponding physical properties are essential prerequisites to understand the underlying mechanism of iron-based superconductivity. For the structurally simplest 11 (FeSeTe) system, earlier attempts using bulk samples have not been able to do so due to the fabrication difficulties. Here, thin FeSe(x)Te(1-x) films with the Se content covering the full range (0 ≤ x ≤ 1) were fabricated by using pulsed laser deposition method. Crystal structure analysis shows that all films retain the tetragonal structure in room temperature. Significantly, the highest superconducting transition temperature (T(C) = 20 K) occurs in the newly discovered domain, i.e., 0.6 ≤ x ≤ 0.8. The single-phased superconducting dome for the full Se doping range is the first of its kind in iron chalcogenide superconductors. Our results present a new avenue to explore novel physics as well as to optimize superconductors. PMID:25449669

  18. Unabridged phase diagram for single-phased FeSexTe1-x thin films

    PubMed Central

    Zhuang, Jincheng; Yeoh, Wai Kong; Cui, Xiangyuan; Xu, Xun; Du, Yi; Shi, Zhixiang; Ringer, Simon P.; Wang, Xiaolin; Dou, Shi Xue

    2014-01-01

    A complete phase diagram and its corresponding physical properties are essential prerequisites to understand the underlying mechanism of iron-based superconductivity. For the structurally simplest 11 (FeSeTe) system, earlier attempts using bulk samples have not been able to do so due to the fabrication difficulties. Here, thin FeSexTe1-x films with the Se content covering the full range (0 ≤ x ≤ 1) were fabricated by using pulsed laser deposition method. Crystal structure analysis shows that all films retain the tetragonal structure in room temperature. Significantly, the highest superconducting transition temperature (TC = 20 K) occurs in the newly discovered domain, i.e., 0.6 ≤ x ≤ 0.8. The single-phased superconducting dome for the full Se doping range is the first of its kind in iron chalcogenide superconductors. Our results present a new avenue to explore novel physics as well as to optimize superconductors. PMID:25449669

  19. Quantum size effects on CdTexS1 - x semiconductor-doped glass

    NASA Astrophysics Data System (ADS)

    Medeiros Neto, J. A.; Barbosa, L. C.; Cesar, C. L.; Alves, O. L.; Galembeck, F.

    1991-11-01

    We present experimental evidences of quantum confinement in borosilicate glasses with a new microcrystallite CdTexS1-x semiconductor. The microcrystallite sizes are controlled by the heat-treatment time and temperature. Transmission electron microscopy measurements show the microcrystallites average diameters near 55 Å for the sample treated for the longest time. We observe a red shift from 570 to 640 nm in the absorption and photoluminescence spectra as the size increases. These shifts agree with the expected quantum-confined energies, varying from 0.80 to 0.60 eV. The absorption spectra also show a second feature which can be assigned to the second quantum-confined transition.

  20. Electrical conductivity of SrTi1-xRuxO3

    NASA Astrophysics Data System (ADS)

    Bianchi, R. F.; Carrió, J. A. G.; Cuffini, S. L.; Mascarenhas, Y. P.; Faria, R. M.

    2000-10-01

    SrTi(1-x)RuxO3 perovskite oxide compound exhibits different physical properties depending on the x value and the temperature range. High electrical conductivity, ferromagnetism phenomena, piezoelectricity, and superconductivity are currently properties found in this perovskite family. In this paper we present a study of electronic conduction of this mixed perovskite in function of x and temperature by alternating conductivity technique. Pure SrTiO3 is an insulating material that progresses to a conductive one as x increases. The model used to explain this conductivity evolution is the random free energy barrier model developed to explain transport phenomena in disordered materials. Disorder in this perovskite is supported by diffraction studies that evidenced slight delocalizations of oxygen atoms in the lattice, added due to random substitutions of Ti4+ by Ru4+.

  1. 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

  2. Superconductivity and ferromagnetism in EuFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Cao, Guanghan; Xu, Shenggao; Ren, Zhi; Jiang, Shuai; Feng, Chunmu; Xu, Zhu'an

    2011-11-01

    Superconductivity and ferromagnetism are two antagonistic cooperative phenomena, which makes it difficult for them to coexist. Here we demonstrate experimentally that they do coexist in EuFe2(As1-xPx)2 with 0.2 ≤ x ≤ 0.4, in which superconductivity is associated with Fe 3d electrons and ferromagnetism comes from the long-range ordering of Eu 4f moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence features large saturated ferromagnetic moments, high and comparable superconducting and magnetic transition temperatures, and broad coexistence ranges in temperature and field. We ascribe this unusual phenomenon to the robustness of superconductivity as well as the multi-orbital character of iron pnictides. The main result of this paper was presented at the 12th National Conference on Low Temperature Physics, held in July 2009, and the Hangzhou Workshop on Quantum Matter, held in October 2009.

  3. Superconductivity and ferromagnetism in EuFe₂(As(1-x)P(x))₂.

    PubMed

    Cao, Guanghan; Xu, Shenggao; Ren, Zhi; Jiang, Shuai; Feng, Chunmu; Xu, Zhu'an

    2011-11-23

    Superconductivity and ferromagnetism are two antagonistic cooperative phenomena, which makes it difficult for them to coexist. Here we demonstrate experimentally that they do coexist in EuFe₂(As(1-x)P(x))₂ with 0.2 ≤ x ≤ 0.4, in which superconductivity is associated with Fe 3d electrons and ferromagnetism comes from the long-range ordering of Eu 4f moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence features large saturated ferromagnetic moments, high and comparable superconducting and magnetic transition temperatures, and broad coexistence ranges in temperature and field. We ascribe this unusual phenomenon to the robustness of superconductivity as well as the multi-orbital character of iron pnictides. PMID:22052828

  4. Pressure-dependent Raman scattering and photoluminescence of Zn1-xCdxSe epilayers

    NASA Astrophysics Data System (ADS)

    Lin, Y. C.; Chiu, C. H.; Fan, W. C.; Yang, S. L.; Chuu, D. S.; Chou, W. C.

    2007-04-01

    Raman and photoluminescence spectra of cubic Zn1-xCdxSe (0≦x≦0.32) epilayers were obtained at high pressure. The impurity mode I observed in the phonon Raman spectra at low temperature confirms the intermediate phonon mode behavior. A split transverse optical phonon mode was found in the down-stroke high-pressure Raman scattering. Additionally, the pressure-dependent longitudinal optical (LO) phonon frequencies and the Grüneisen parameter (γLO) were obtained by quadratic polynomial fitting. Pressure-driven resonant Raman scattering effect was observed in samples with a high Cd concentration (x≧0.18). The critical pressure of semiconductor-to-metal phase transition (Pt) decreases as the Cd content increases. As the Cd concentration increases from 0 to 0.32, Pt falls from 13.6to9.4GPa, according to Pt (GPa)=13.6-6.8x-20.3x2.

  5. Photoluminescence processes in k-1xLixTaO3

    NASA Astrophysics Data System (ADS)

    Camagni, P.; Galinetto, P.; Giulotto, E.; Samoggia, G.; Sangalli, P.

    A study of blue-green photoluminescence of K1-xLixTaO3 single crystals, under UV irradiation, was performed in the range 15-20 K. It was shown that the emission is strongly enhanced and thermally more stable with respect to pure KTaO3, up to ˜40 K. Above this point the yield of emission decreases abruptly with an Arrhenius-like behaviour controlled by an activation energy of 70-100 meV. After low temperature excitation, a thermoluminescence spectrally very similar to PL and giving rise to a glow peak around 30K is also observed. Correlations with recent results on photoconductivity and thermally stimulated currents are illustrated. An argument in favour of close-pair recombinations between Ta4+ and O- centers is proposed.

  6. 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.

  7. Thermal annealing effect on photoexcited carrier dynamics in GaBixAs1-x

    NASA Astrophysics Data System (ADS)

    Čechavičius, B.; Adomavičius, R.; Koroliov, A.; Krotkus, A.

    2011-08-01

    Carrier dynamics in MBE-grown GaBixAs1-x layers was investigated by the optical pump--THz probe technique. Rapid thermal annealing at temperatures up to 700 °C has a dual effect on the electron decay characteristics. For the GaBi0.04As0.96 layer it led only to a small change of the decay time, whereas for the layer with x = 0.06 this parameter decreased by two orders of magnitude and became shorter than 1 ps. It can be assumed that the recombination centers in GaBiAs are more likely to occur in the layers with a larger Bi composition, a bigger lattice mismatch with the substrate.

  8. Molecular beam epitaxy growth of GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Tixier, S.; Adamcyk, M.; Tiedje, T.; Francoeur, S.; Mascarenhas, A.; Wei, Peng; Schiettekatte, F.

    2003-04-01

    GaAs1-xBix epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 Å. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ˜84 meV per percent Bi is observed.

  9. 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.

  10. 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.

  11. 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.

  12. Magnetic properties of Ho1- x Lu x B12 solid solutions

    NASA Astrophysics Data System (ADS)

    Gabáni, S.; Gaz̆o, E.; Pristás̆, G.; Takác̆ová, I.; Flachbart, K.; Shitsevalova, N.; Siemensmeyer, K.; Sluchanko, N.

    2013-05-01

    Magnetic properties of the geometrically frustrated antiferromagnet HoB12 (with T N = 7.4 K) modified by substitution of magnetic Ho atoms through non-magnetic Lu ones are presented and discussed. In this case, in Ho1- x Lu x B12 solid solutions, both chemical pressure resulting from different Lu3+ and Ho3+ radii and magnetic dilution take place with increasing Lu content ( x) that change properties of the system. The received results show strong indication for the existence of a quantum critical point near x = 0.9, which separates the region of magnetic order (starting with HoB12 for x = 0) and the nonmagnetic region (ending with superconducting LuB12 for x = 1).

  13. Photoresponse Model for Si_(1-x)Ge_x/Si Heterojunction Internal Photoemission Infrared Detector

    NASA Technical Reports Server (NTRS)

    Lin, T.; Park, J. S.; Gunapala, S. D.; Jones, E. W.; Castillo, H. M. Del

    1993-01-01

    A photoresponse model has been developed for the Si_(1-x)Ge_x/Si heterojunction internalphotoemission (HIP) infrared detector at wavelengths corresponding to photon energies less than theFermi energy. A Si_(0.7)Ge_(0.3)/Si HIP detector with a cutoff wavelength of 23 micrometers andan emission coefficient of 0.4 eV^(-1) has been demonstrated. The model agrees with the measureddetector response at lambda greater than 8 micrometers. The potential barrier determined by themodel is in close agreement (difference similar to 4 meV) with the potential barrier determined by theRichardson plot, compared to the discrepancies of 20-50 meV usually observed for PtSi Schottkydetectors.

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

    DOE PAGESBeta

    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

  15. 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.

  16. 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.

  17. Ellipsometric study of optical properties of GaSxSe1-x layered mixed crystals

    NASA Astrophysics Data System (ADS)

    Isik, Mehmet; Gasanly, Nizami

    2016-04-01

    Spectroscopic ellipsometry measurements were performed on GaSxSe1-x mixed crystals (0 ⩽ x ⩽ 1) in the 1.2-6.2 eV range. Spectral dependence of optical parameters; real and imaginary components of pseudodielectric function, pseudorefractive index and pseudoextinction coefficient were reported in the present work. Critical point (CP) analyses on second-energy derivative spectra of the pseudodielectric function were accomplished to find the interband transition energies. The revealed energy values were associated with each other taking into account the fact that band gap energy of mixed crystals rises with increase in sulfur content. The variation of CP energies with composition (x) was also plotted. Peaks in the spectra of studied optical parameters and CP energy values were observed to be shifted to higher energy values as sulfur concentration is increased in the mixed crystals.

  18. 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.

  19. Paramagnetism of the Co sublattice in ferromagnetic Zn1-xCoxO films

    NASA Astrophysics Data System (ADS)

    Barla, A.; Schmerber, G.; Beaurepaire, E.; Dinia, A.; Bieber, H.; Colis, S.; Scheurer, F.; Kappler, J.-P.; Imperia, P.; Nolting, F.; Wilhelm, F.; Rogalev, A.; Müller, D.; Grob, J. J.

    2007-09-01

    Using the spectroscopies based on x-ray absorption, we have studied the structural and magnetic properties of Zn1-xCoxO films ( x=0.1 and 0.25) produced by reactive magnetron sputtering. These films show ferromagnetism with a Curie temperature TC above room temperature in bulk magnetization measurements. Our results show that the Co atoms are in a divalent state and in tetrahedral coordination, thus substituting Zn in the wurtzite-type structure of ZnO. However, x-ray magnetic circular dichroism at the CoL2,3 edges reveals that the Co3d sublattice is paramagnetic at all temperatures down to 2K , both at the surface and in the bulk of the films. The Co3d magnetic moment at room temperature is considerably smaller than that inferred from bulk magnetization measurements, suggesting that the Co3d electrons are not directly at the origin of the observed ferromagnetism.

  20. Mechanical Deformation of KD2xH2(1-x)PO4

    SciTech Connect

    Kucheyev, S; Siekhaus, W; Land, T; Demos, S

    2003-11-10

    The deformation behavior of rapidly-grown tetragonal KD{sub 2x} H{sub 1(1-x)} PO{sub 4} (KDP and DKDP) single crystals, with a deuteration degree x of 0.0, 0.3, and 0.6, is studied by nanoindentation with a 1 {micro}m radius spherical indenter. Within experimental error, the deformation behavior is found to be independent of deuterium content and different for (001) and (100) surfaces. Multiple discontinuities (so called ''pop-in'' events) in force-displacement curves are observed during indentation loading, but not during unloading. Slip is identified as the major mode of plastic deformation in DKDP, and pop-in events are attributed to the initiation of slip.

  1. Density functional theory calculations of magnetocrystalline anisotropy energies for (Fe1-xCox)2B

    DOE PAGESBeta

    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

  2. Optical fiber temperature sensor utilizing alloyed Zn(x)Cd(1-x)S quantum dots.

    PubMed

    Zhao, Fei; Kim, Jongsung

    2014-08-01

    In this paper, optical fiber temperature sensors have been prepared by using alloyed Zn(x)Cd(1-x)S quantum dots as sensing media. The surface of the optical fiber was silanized to enhance covalent bond between quantum dots and optical fiber. The quantum dots were bonded to the surface of optical fiber and further encapsulated via sol-gel coating using 3-glycidoxypropyl trimethoxysilane (GPTMS) and 3-aminopropyl trimethoxysilane (APTMS) in ethyl alcohol in acidic condition. Quantum dots with green, yellow, and red fluorescence were used. The dependence of photoluminescence (PL) intensity from quantum dots on ambient temperature has been studied. Linear relation between the fluorescent intensity and temperature was obtained from alloyed quantum dots immobilized on the surface of optical fiber. The PL intensity, sensitivity, and thermal stability were increased by the silica encapsulation. PMID:25936046

  3. 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.

  4. Magnetic entropy change of itinerant electron metamagnetic system Co(S1-xSex)2

    NASA Astrophysics Data System (ADS)

    Wada, H.; Mitsuda, A.; Tanaka, K.

    2006-12-01

    The magnetic entropy change, ΔSM , of Co(S1-xSex)2 has been studied for 0≤x≤0.11 . Compounds with 0.03≤x≤0.11 undergo a first-order magnetic transition and exhibit itinerant electron metamagnetism (IEM) just above the Curie temperature. We observed that the peak value of ΔSM shows a maximum at around x=0.07 . The results are compared with the theoretically calculated results based on the spin fluctuation theory of IEM reported by Yamada and Goto. It is found that the experimental results are well described by the theoretical calculations. The origin of the peak of ΔSM is discussed from the thermodynamical point of view.

  5. Local structure and superconductivity of the Ce1-xLaxRu2 Laves phase system

    NASA Astrophysics Data System (ADS)

    Saini, N. L.; Agrestini, S.; Amato, E.; Filippi, M.; di Castro, D.; Bianconi, A.; Manfrinetti, P.; Palenzona, A.; Marcelli, A.

    2004-09-01

    We have studied local structure of the Laves phase Ce1-xLaxRu2 superconductor by Ru K-edge extended x-ray absorption fine-structure measurements focusing on the small La concentration regime where the transition temperature Tc passes through a local maximum. We find that correlated Debye-Waller factor of the Ru-Ru bonds follows Tc with the varying La concentration in the system. Although, this remarkable Tc correlation on the local atomic structure suggests important role of the electron-lattice interactions, the band-structure effects seem more likely the reason to drive the anomalous superconducting behavior and the Tc maximum in this 4f system.

  6. Proximity to a Ferroelectric Instability in Ba1-xCaxZrO3

    SciTech Connect

    Kim, Hyun-Sik; Christen, Hans M; Biegalski, Michael D; Singh, David J

    2010-01-01

    The Ba1-xCaxZrO3 solid solution was investigated by structural and dielectric measurements on pulsed laser deposition grown films and by first principles calculations. Samples were synthesized on SrRuO3 coated SrTiO3 substrates for x between 0 and 0.44. The samples were found to be under mild compressive strain at least for low x. Dielectric measurements showed no evidence for ferroelectricity. First principles supercell calculations were performed as a function of lattice parameter. These calculations show ferroelectricity at expanded volume and a rapid suppression depending on cation ordering as the volume is reduced. Prospects for realizing ferroelectricity in BaZrO3 based perovskites are discussed in light of these results.

  7. Dielectric properties and specific heat of Bi1- x Sm x FeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Kallaev, S. N.; Sadykov, S. A.; Omarov, Z. M.; Kurbaitaev, A. Ya.; Reznichenko, L. A.; Khasbulatov, S. V.

    2016-04-01

    The specific heat and dielectric permittivity of Bi1- x Sm x FeO3 ( x = 0-0.30) multiferroics have been studied in the temperature range of 300-800 K. A slight substitution of bismuth with samarium is established to cause a considerable shift in the antiferromagnetic phase transition temperature and to an increase in the specific heat over a wide temperature range. Other anomalies typical of phase transitions have been found in the temperature dependences of the specific heat and dielectric permittivity for the compounds with x = 0.10 and 0.15 at T ≈ 735 and 495 K, respectively. The results of the studies of the specific heat have been discussed together with the data of the structural investigations.

  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. Electron-interface-phonon scattering in graded quantum wells of Ga1-xAlxAs

    NASA Astrophysics Data System (ADS)

    Duan, Wenhui; Zhu, Jia-Lin; Gu, Bing-Lin

    1994-05-01

    Using the method of series expansion, interface-phonon vibrational modes are calculated in the dielectric continuum model for the graded quantum well of Ga1-xAlxAs with a Ga0.6Al0.4As barrier. The intrasubband and intersubband scattering rates are obtained as functions of quantum-well width. The results reveal that the behavior of interface phonon modes is very different from that in a square quantum-well structure. It is found that the electron-interface-phonon scattering rates can be changed remarkably in a graded quantum-well structure compared with those in a square quantum-well structure, which is useful for some device applications.

  10. Low-field magnetocaloric effect in antiperovskite Mn3Ga1-xGexC compounds

    NASA Astrophysics Data System (ADS)

    Shao, Qiang; Lv, Qun; Yang, Xiaozhi; Han, Zhida; Dong, Shiyuan; Qian, Bin; Zhang, Lei; Zhang, Changliang; Fang, Yong; Jiang, Xuefan

    2015-12-01

    A series of Mn3Ga1-xGexC (x=0, 0.1, 0.2) compounds were prepared by solid state reaction, and their magnetic properties, phase transitions, and magnetocaloric effect were investigated. All samples, after becoming ferromagnetic below Curie temperature Tc, undergo a first-order ferromagnetic-antiferromagnetic transition at Tt at low temperature, giving rise to conventional and inverse magnetocaloric effect. Tt increases while Tc shows a decrease with the increase of Ge content. Isothermal magnetization curves around Tt are strongly history-dependent, which may result in spurious peak in the magnetic field induced entropy change (ΔSM). The magnetothermal properties near Tt, compared with those near Tc, are of larger ΔSM, but have larger magnetic hysteresis and smaller refrigerant capacity.

  11. 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.

  12. Analysis of local structure of Ru1-xNixO2 electrocatalytic materials

    NASA Astrophysics Data System (ADS)

    Petrykin, V.; Macounova, K.; Okube, M.; Franc, J.; Krtil, P.

    2009-11-01

    Nanocrystalline Ru1-xNixO2 materials were synthesized by a solution method. Local structure around doped Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS) functions obtained from X-ray absorption spectra acquired at Ni-K edge (8333eV). It was found that Ni ions are confined to the Ru site in the RuO2 rutile-type crystal structure, and Ni atoms tend to group by entering neighbouring sites along the body diagonal of rutile lattice. Such a neighbourhood of two Ni atoms may act as an active site for oxygen evolution by promoting simultaneous two electron transfer from the absorbed molecule of water. The refined Ni-O bond distances suggest that oxidation state of Ni ions is between +2 and +3.

  13. 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.

  14. 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.

  15. Transport properties of Nd1-xFexOF polycrystalline films

    NASA Astrophysics Data System (ADS)

    Corrales-Mendoza, I.; Rangel-Kuoppa, Victor-Tapio; Conde-Gallardo, A.

    2013-12-01

    The transport properties of Nd1-xFexOF films with 0.2

  16. 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

  17. Effect of Crystal Fields in Ho1 - xDyxNi2B2 C

    NASA Astrophysics Data System (ADS)

    Lee, W. C.

    2013-03-01

    From the anisotropy and the temperature dependence of magnetic susceptibilities of Ho1 - x Dyx Ni2B2 C system with magnetic field H perpendicular or parallel to c-axis, the crystalline electric field (CEF) effect has been studied and the magnetic exchange interaction constant Jex of rare-earth ions perpendicular to the c-axis estimated for 0 <=x <=1. The crystalline electric field parameter, B02, the first Steven parameter and the most dominant term in this system, are determined from the high-temperature-limit anisotropic Weiss temperatures of the magnetic susceptibilities and there is a broad minimum around x ~ 0.3, where superconducting transition temperature, TC, and Néel temperature, TN, are almost same.

  18. Phonon spectra of Pd(x)Fe(1-x) alloys with transferable force constants.

    PubMed

    Dutta, Biswanath; Ghosh, Subhradip

    2009-09-30

    The transferable force constant model of van de Walle et al (2002 Rev. Mod. Phys. 74 11) has been combined with the itinerant coherent potential approximation to calculate the complete phonon spectra and elastic constants in the magnetic type-II alloy Pd(x)Fe(1-x) across the concentration range. The calculated dispersion curves and elastic constants agree very well with the experiments. We discuss the results in the light of the behavior of inter-atomic force constants between various pairs of chemical species. The results demonstrate that the combination of the transferable force constant model and the ICPA method for configuration averaging serve as an efficient and reliable first-principles-based tool to compute the phonon spectra for disordered alloys at any arbitrary concentration. PMID:21832388

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Structural transformation and magnetoelectric behaviour in Bi1-xGdxFeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Lazenka, V. V.; Zhang, G.; Vanacken, J.; Makoed, I. I.; Ravinski, A. F.; Moshchalkov, V. V.

    2012-03-01

    The crystal structure, dielectric, magnetic and magnetoelectric (ME) properties of Bi1-xGdxFeO3 (BGFO, x = 0, 0.05, 0.1, 0.15, 0.2) multiferroic ceramics have been studied. The substitution of bismuth by gadolinium induces a R3c\\to {Pnma} phase structural transition at x > 0.1, which leads to the suppression of the spiral modulated spin structure and develops weak ferromagnetic properties in the BiFeO3-based materials. Through studying the temperature/magnetic field dependence of the ME coefficient, we have revealed the effect of the substitution of Gd3+ ions on the ME properties, and have demonstrated the possibility of manipulating the electric state in BGFO multiferroics by applying magnetic field at room temperature.

  5. Ultrafast Exciton Dynamics in CdxHg(1-x)Te alloy Quantum Dots

    NASA Astrophysics Data System (ADS)

    Leontiadou, Marina A.; Al-Otaify, Ali; Kershaw, Stephen V.; Zhovtiuk, Olga; Kalytchuk, Sergii; Mott, Derrick; Maenosono, Shinya; Rogach, Andrey L.; Binks, David J.

    2016-05-01

    Ultrafast transient absorption spectroscopy is used to investigate sub-nanosecond exciton dynamics in CdxHg(1-x)Te alloy colloidal quantum dots. A bleach was observed at the band gap due to state-filling, the mono-exponential decay of which had a characteristic lifetime of 91 ± 1 ps and was attributed to biexciton recombination; no evidence of surface-related trapping was observed. The rise time of the bleach, which is determined by the rate at which hot electrons cool to the band-edge, ranged between 1 and 5 ps depending on the pump photon energy. Measuring the magnitude of the bleach decay for different pump fluences and wavelengths allowed the quantum yield of multiple exciton generation to be determined, and was 115 ± 1% for pump photons with energy equivalent to 2.6 times the band gap.

  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. Thermoelectric properties of InxGa1-xN alloys

    NASA Astrophysics Data System (ADS)

    Pantha, B. N.; Dahal, R.; Li, J.; Lin, J. Y.; Jiang, H. X.; Pomrenke, G.

    2008-01-01

    Thermoelectric (TE) properties of InxGa1-xN alloys grown by metal organic chemical vapor deposition have been investigated. It was found that as indium concentration increases, the thermal conductivity decreases and power factor increases, which leads to an increase in the TE figure of merit (ZT). The value of ZT was found to be 0.08 at 300K and reached 0.23 at 450K for In0.36Ga0.64N alloy, which is comparable to those of SiGe based alloys. The results indicate that InGaN alloys could be potentially important TE materials for many applications, especially for prolonged TE device operation at high temperatures, such as for recovery of waste heat from automobile, aircrafts, and power plants due to their superior physical properties, including the ability of operating at high temperature/high power conditions, high mechanical strength and stability, and radiation hardness.

  8. Metal-insulator transition in SrTi1-xVxO3 thin films

    NASA Astrophysics Data System (ADS)

    Gu, Man; Wolf, Stuart A.; Lu, Jiwei

    2013-11-01

    Epitaxial SrTi1-xVxO3 (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization.

  9. 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.

  10. Properties of (Ga1-x In x )2O3 over the whole x range.

    PubMed

    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 [Formula: see text] 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 [Formula: see text]-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. PMID:26952634

  11. 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.

  12. Study of the magnetic behavior of Mn1-xZnx Ferrite nanoparticles at low temperature

    NASA Astrophysics Data System (ADS)

    Marin, O.; Reyes, D.; Almanza, O.; Prieto, P.; Mendoza, A.

    2008-03-01

    We report on magnetic spin resonance and magnetization hysteresis loops of Mn1-xZnx Ferrite nanoparticles with sizes ranging from 20nm to 50nm obtained via microemulsions. The samples were evaluated by VSM technique ranging from 10K<300K at ZFC and FC. EPR measurements at T=180K were carried out in the 0 <= x <= 0.75 range. Experimental results for the peak-to-peak linewidth, δHpp, have been discussed by the existence of monodomain ferrimagnetic particles. The results indicate an increase of δHpp by increasing the Zn concentration. The EPR signal shows a second EPR pick for x>0.5 at g=4.10 associated at local magnetic fields produced for Mn chains. The anisotropy constant was calculated by means of a genetic algorithm for parameter optimization of the Jiles-Atherton model.

  13. Crossover to striped magnetic domains in Fe1-xGax magnetostrictive thin films

    NASA Astrophysics Data System (ADS)

    Barturen, M.; Rache Salles, B.; Schio, P.; Milano, J.; Butera, A.; Bustingorry, S.; Ramos, C.; de Oliveira, A. J. A.; Eddrief, M.; Lacaze, E.; Gendron, F.; Etgens, V. H.; Marangolo, M.

    2012-08-01

    We have studied the magnetic properties at room temperature of Fe1-xGax (FeGa) epitaxial thin films grown on ZnSe/GaAs(100) for 0.14≤x≤0.29 range concentration, and film thicknesses, d = 36 and 72 nm. The study was performed by means of magnetometric measurements and magnetic force microscopy scans. Increasing x promotes the loss of the four-fold magnetic-crystalline anisotropy associated to an Fe-like behavior, which is lost completely above x = 0.20. Stripe domains with rotatable anisotropy are observed even in samples in which the theoretical conditions for stripe appearance are not completely fulfilled. An unexpected "saw-tooth" stripe structure has been found under certain conditions.

  14. 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.

  15. Directional solidification and characterization of Hg(1-x)Cd(x)Te alloys

    NASA Technical Reports Server (NTRS)

    Lehoczky, S. L.; Szofran, F. R.

    1982-01-01

    A series of Hg(1-x)Cd(x)Te alloy crystals was grown by high temperature gradient directional solidification at furnace translation rates ranging from 0.068 to 1.12 microns/s. For several ingots, the measured longitudinal compositional profiles were fitted to theoretical profiles to estimate the magnitude of D, the liquid HgTe-CdTe interdiffusion coefficient. The best-fit value of D was about 550,000 sq cm/s. The majority of the ingots showed significant radial compositional variations along the growth axis. These variations are attributed, at least in part, to fluid flows ahead of the growth interface. The results are discussed in terms of the heat transfer characteristics of the alloy/ampule/furnace system, and on the effects of these characteristics on the shape and stability of the growth interface in a 1-g environment.

  16. Superconductivity and magnetism in (Ho xY 1- x)Ni 2B 2C

    NASA Astrophysics Data System (ADS)

    Eversmann, K.; Handstein, A.; Fuchs, G.; Cao, L.; Müller, K.-H.

    1996-02-01

    Superconducting and magnetic properties of polycrystalline samples of the pseudoquarternary system (Ho xY 1- x)Ni 2B 2C have been investigated by resistance and susceptibility measurements. A linear depression of the superconducting transition temperature with increasing magnetic ordering temperatures was found by variation of the Ho content providing evidence for magnetic pair breaking. This behaviour is analogous to the known scaling with the de Gennes factor of the rare earth elements in the family of quaternary RNi 2B 2C compounds. Both cases are described by a common scaling behaviour including the superconducting and magnetic transition temperatures. A reetrrant behaviour observed for Ho contents x>0.5 results in maximum in the temperature dependence of the upper critical field Hc2( T). These results are compared with Hc2( T) data of the RNi 2B 2C family ( R=Tm,Er).

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. Synthesis, structure, and phase diagram of (Sr1-xNax)Fe2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Shinohara, N.; Tokiwa, K.; Fujihisa, H.; Gotoh, Y.; Ishida, S.; Kihou, K.; Lee, C. H.; Eisaki, H.; Yoshida, Y.; Iyo, A.

    2015-06-01

    (Sr1-xNax)Fe2As2 is a family of the so-called ‘122 system’ of Fe-based superconductors. So far, samples with a limited composition range, i.e. polycrystalline samples for 0 ≤ x ≤ 0.42 with a maximum transition temperature (Tc) of 26 K and a single crystal with x = 0.5 and Tc = 35 K, have been synthesized. Here, we report the synthesis of single-phase polycrystalline samples of (Sr1-xNax)Fe2As2 for a wide range of x from 0 to 0.70 using a stainless-steel pipe-and-cap method. The susceptibilities in the normal and superconducting states were measured as a function of x, and an overall superconducting phase diagram was obtained. As x increased, the structural and anti-ferromagnetic phase transition temperature decreased, and superconductivity began to emerge around x = 0.35. Tc exhibited a dome-like composition dependence with a maximum onset Tc of 36.5 K for x = 0.55. The Rietveld refinement of the powder x-ray diffraction pattern at room temperature for x = 0.55 revealed structural parameters such as the lattice parameters a = 3.857(1) Å and c = 12.564(1) Å, an Fe-As bond length lFe-As = 2.394(1) Å, an As-Fe-As bond angle αAs-Fe-As = 107.3(1)°, and an As height from the Fe layer hAs = 1.419(1) Å.

  3. Magnetic phase transitions and magnetocaloric effect of MnCoGe1-xSix

    NASA Astrophysics Data System (ADS)

    Lai, J. W.; Zheng, Z. G.; Montemayor, R.; Zhong, X. C.; Liu, Z. W.; Zeng, D. C.

    2014-12-01

    Here a cheaper alternative magnetic refrigeration material using MnCoGe1-xSix (x=0, 0.1, 0.3, and 0.5) alloys were investigated. The polycrystalline MnCoGe1-xSix alloys were prepared by arc-melting followed by annealing at 1123 K for 72 h. At a 0.5 at% Si substitution, the Curie temperatures increased by 10% to 374 K, the magnetic entropy change (|ΔSM|) values decreased by 32% to 2.1 J kg-1 K-1 in an applied field from 0 to 2 T and by 24% to 4.4 J kg-1 K-1 in an applied field from 0 to 5 T. However, the refrigeration capacity (RCFWHM) of this MnCoGe0.5Si0.5 alloy improved by 27% to 282 J kg-1 and the operation temperature range (δTFWHM) improved by 92% to 96 K in an applied field at 5 T. The MnCoGe0.5Si0.5 alloy can compete with some of the MCE properties of the MnCo0.95Ni0.05Ge, LaFe11Al2C0.5, (Fe85Co5Cr10)91Zr7B2, and even the Gd5Si2Ge2 alloys. The broad operation temperature range (96 K) at a higher Curie temperature (374 K) suggests that the MnCoGe0.5Si0.5 alloy can become a cheaper alternative MCE material (costing 70% less than a MnCoGe alloy).

  4. Dynamical and thermodynamical instabilities in the disordered RexW1-x system

    NASA Astrophysics Data System (ADS)

    Persson, Kristin; Ekman, Mathias; Grimvall, Göran

    1999-10-01

    The dynamical and thermodynamical stability of the bcc and fcc disordered RexW1-x system is studied within the density-functional theory. The configurational part of the free energy is obtained from ab initio electron structure calculations together with the cluster expansion and the cluster variation formalism. Electronic excitations are accounted for through the temperature-dependent Fermi-Dirac distribution. The lattice dynamics of Re and W is studied using the density-functional linear-response theory. The calculated dispersion curves show that fcc Re is dynamically stable while bcc Re exhibits phonon instabilities in large parts of the Brillouin zone, similar to previous results for fcc W. Interestingly, the phonon dispersion curves for fcc Re show pronounced phonon anomalies characteristic of superconductors such as TaC and NbC. Due to the instabilities in bcc Re and fcc W the vibrational entropy, and therefore the free energy, is undefined. In order to predict the regions where the disordered RexW1-x alloy is unstable we calculate the phonon dispersion curves in the virtual crystal approximation. Then we apply a concentration-dependent nonlinear interpolation to the force constants, which are calculated through a Born-von Kármán fit to the ab initio obtained dynamical matrices. The vibrational free energy is calculated in the stable regions for the phases as a function of concentration. The complete analysis gives a region where the bcc phase would become thermodynamically unstable towards a phase decomposition into disordered bcc and fcc phases.

  5. 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

  6. Investigation of Anderson lattice behavior in Yb1-xLuxAl3

    SciTech Connect

    Bauer, E.D.; Booth, C.H.; Lawrence, J.M.; Hundley, M.F.; Sarrao, J.L.; Thompson, J.D.; Riseborough, P.S.; Ebihara, T.

    2003-10-06

    Measurements of magnetic susceptibility {chi}(T), specific heat C(T), Hall coefficient R{sub H}(T), and Yb valence {nu} = 2 + n{sub f} [f-occupation number n{sub f} (T) determined from Yb L{sub 3} x-ray absorption measurements] were carried out on single crystals of Yb{sub 1-x}Lu{sub x}Al{sub 3}. The low temperature anomalies observed in {chi}(T) and C(T) corresponding to an energy scale T{sub coh} {approx} 40 K in the intermediate valence, Kondo lattice compound YbAl{sub 3} are suppressed by Lu concentrations as small as 5% suggesting these low-T anomalies are extremely sensitive to disorder and, therefore, are a true coherence effect. By comparing the temperature dependence of various physical quantities to the predictions of the Anderson Impurity Model, the slow crossover behavior observed in YbAl{sub 3}, in which the data evolve from a low-temperature coherent, Fermi-liquid regime to a high temperature local moment regime more gradually than predicted by the Anderson Impurity Model, appears to evolve to fast crossover behavior at x {approx} 0.7 where the evolution is more rapid than predicted. These two phenomena found in Yb{sub 1-x}Lu{sub x}Al{sub 3}, i.e., the low-T anomalies and the slow/fast crossover behavior are discussed in relation to recent theories of the Anderson lattice.

  7. Ferromagnetism in ion implanted amorphous and nanocrystalline MnxGe1-x

    NASA Astrophysics Data System (ADS)

    Verna, A.; Ottaviano, L.; Passacantando, M.; Santucci, S.; Picozzi, P.; D'Orazio, F.; Lucari, F.; de Biase, M.; Gunnella, R.; Berti, M.; Gasparotto, A.; Impellizzeri, G.; Priolo, F.

    2006-08-01

    The structural, electronic, and magnetic properties of a MnxGe1-x alloy prepared through room-temperature ion implantation ( 100keV , 2×1016ions/cm2 ) and subsequent 400°C annealing have been investigated with several experimental techniques. The as-implanted sample shows a quasi-Gaussian Mn concentration depth profile with a projected range (peak Mn concentration x≃12at./% ) at 55nm and end of range at 140nm . The structural investigation shows that the overall implanted Ge layer is amorphous. In particular, up to a depth of 60nm , the implanted layer is also porous and oxidized, whereas the deepest implanted region (60-140nm) is purely composed of amorphous Ge with Mn atoms diluted in it. This sample manifests magnetic hysteresis up to 20K and a strong nonlinear S-shaped magnetic response up to 150K . Upon annealing at 400°C , the top porous layer remains essentially amorphous, whereas partial reconstruction into Ge nanocrystals ( ˜10nm in diameter) occurs in the 60-140-nm -deep implanted region. Part of the Mn atoms, mainly belonging to the top porous layer, further diffuses toward the surface and forms chemical bonds with O contaminants, becoming magnetically inactive. The other Mn atoms, mainly in the region between 60 and 140nm from the surface, remain trapped in the residual amorphous matrix or in the Ge nanocrystals, whereas formation of Mn-Ge extrinsic phases (like Mn11Ge8 and Mn5Ge3 ) is excluded. The magnetic response of the annealed sample originates from the existence of a soft and a harder magnetic component, assigned to the dilution of Mn atoms in residual amorphous Ge and Ge nanocrystals, respectively. The hard component, attributable to a MnxGe1-x diluted magnetic semiconductor in nanocrystalline form, manifests magnetic hysteresis up to above 250K .

  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. 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.

  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. Coprecipitation of nickel zinc malonate: A facile and reproducible synthesis route for Ni1-xZnxO nanoparticles and Ni1-xZnxO/ZnO nanocomposites via pyrolysis

    NASA Astrophysics Data System (ADS)

    Lontio Fomekong, Roussin; Kenfack Tsobnang, Patrice; Magnin, Delphine; Hermans, Sophie; Delcorte, Arnaud; Lambi Ngolui, John

    2015-10-01

    Nanoparticles of Ni1-xZnxO and Ni1-xZnxO/ZnO, which can be good candidates for selective gas sensors, were successfully obtained via a two-step synthetic route, in which the nickel zinc malonate precursor was first synthesized by co-precipitation from an aqueous solution, followed by pyrolysis in air at a relatively low temperature (~500 °C). The precursor was characterized by ICP-AES, FTIR and TG and the results indicate the molecular structure of the precursor to be compatible with Ni1-xZnx(OOCCH2COO)·2H2O. The decomposition product, characterized using various techniques (FTIR, XRD, ToF-SIMS, SEM, TEM and XPS), was established to be a doped nickel oxide (Ni1-xZnxO for 0.01≤x≤0.1) and a composite material (Ni1-xZnxO/ZnO for 0.2≤x≤0.5). To elucidate the form in which the Zn is present in the NiO structure, three analytical techniques were employed: ToF-SIMS, XRD and XPS. While ToF SIMS provided a direct evidence of the presence of Zn in the NiO crystal structure, XRD showed that Zn actually substitutes Ni in the structure and XPS is a bit more specific by indicating that the Zn is present in the form of Zn2+ ions.

  14. Facile synthesis and photoluminescence of near-infrared-emitting CdTe(x)Se(1-x) and CdTe(x)Se(1-x)/Cd(y)Zn(-1-y)S quantum dots.

    PubMed

    Zhang, Ruili; Wang, Jianrong; Yang, Ping

    2014-03-01

    High-quality colloidal photoluminescent (PL) CdTe(x)Se(1-x) quantum dots (QDs) with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized via a facile organic method using stearic acid as a capping agent. The transmission electron microscopy observation and X-ray diffraction analysis indicated that the CdTe(x)Se(1-x) QDs revealed a "dot" shaped morphology and exhibited a zinc-blende structure which located between those of bulk CdTe and CdSe (with the lattice parameters between those of bulk CdTe and CdSe). The ternary CdTe(x)Se(1-x) QDs were emitting in the red to near-infrared (NIR) range. In order to enhance the PL properties and reduce the sensitivity to oxidation of CdTe-based QDs, the CdTe(x)Se(1-x) QDs were coated with Cd(y)Zn(1-y)S multishells by using different growth kinetics of CdS and ZnS. The coated QDs exhibited a controlled red shift of PL compared with the initial CdTe(x)Se(1-x) cores and revealed much improved PL intensity. Because of thier tunable emission from red to NIR, these composite QDs open new possibilities in band gap engineering and in developing NIR fluorescent probes for biological imaging and detection. PMID:24745260

  15. 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

  16. 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

  17. 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

  18. 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.

  19. Elastic strain reduction of finite germanium(x) silicon(1-x)/silicon structures

    NASA Astrophysics Data System (ADS)

    U'Ren, Gregory David

    The focus of this dissertation is a rigorous examination the elastic, intrinsic behavior of stress/strain for epitaxial Si1-xGe x/Si (100) structures having finite dimensions. Existing models predict that the behavior is governed primarily by geometry, which can have a profound effect should the ratio of half-width to height (l/h) be less than 50. Two main aspects of existing theories were pressed: first, the role of geometry for a fixed Si1-xGex composition and therefore strain (epsilon = 0.42%) and second, the role of misfit stress for a fixed l/b ratio of 0.5. Strict control of the fabrication process necessitated selective epitaxial growth via gas-source molecular beam epitaxy. Though experimental combinations of various thickness (50, 100, 140, and 200 nm) and variable pitch (0.09-25 mum) a wide range of l/b values was obtained (0.5-500). As the selectively grown structures are arranged into a periodic array, where the period is repeated over a large distance (mm), in addition to dynamical diffraction, Fraunhoffer diffraction was also observed. These two complementary mechanisms of diffraction were used to determine the stress distribution within these structures. Ensemble with transmission electron microscopy, a qualitative assessment of elastic strain reduction mechanisms--local curvature effects and tangential forces--was possible. The main conclusions of this dissertation are as follows: (A) An analytical reciprocal space construction was developed to facilitate the interpretation of experimental x-ray diffraction data. (B) As a corollary, arbitrary positioning and movement in reciprocal space are described, which in practice is applied to capturing scattered intensity parallel to the surface. (C) Facet growth in SiGe selective epitaxy was investigated. One key result is the persistence of a {113} facet with increasing thickness, as the {111} facet is anticipated. (D) In examining the role of geometry, elastic lattice distortions were only observed for l

  20. 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.

  1. Investigation of spin ordering in antiferromagnetic Fe1-xMnxPO4 with Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Jun Kwon, Woo; Wha Lee, Bo; Sung Kim, Chul

    2013-05-01

    We have investigated the spin ordering in Fe1-xMnxPO4, which is a possible cathode material for rechargeable lithium ion battery, with antiferromagnetic structure below Néel temperature (TN). The prepared Fe1-xMnxPO4 (x = 0.0, 0.1, and 0.3) samples have orthorhombic structures with space group of Pnma. These samples show the magnetic phase transition, caused by the strong crystalline field at the MO6 octahedral sites. According to the temperature dependence of magnetic susceptibility of Fe1-xMnxPO4, all samples show antiferromagnetic behaviors. The Néel temperature (TN) decreases from 114 K at x = 0.0 to 97 K at x = 0.3 with Mn concentrations. The magnetization of Fe1-xMnxPO4 decreases until the temperature reaches the spin-reorientation (TS) temperature, and then starts increasing as the temperature increases up to TN. The TS of the Fe1-xMnxPO4 were found to be 30, 27, and 24 K for x = 0.0, 0.1, and 0.3. In order to investigate the hyperfine interaction of Fe3+ ions in FeO6 octahedral sites, Mössbauer spectra of Fe1-xMnxPO4 have been taken at various temperatures from 4.2 to 295 K. The isomer shift (δ) values of the Fe1-xMnxPO4 were between 0.31 and 0.43 mm/s, indicating the high spin state of Fe3+ at all temperatures. The magnetic hyperfine field (Hhf) and electric quadrupole splitting (ΔEQ) values of Fe0.9Mn0.1PO4 at 4.2 K were determined to be Hhf = 498 kOe and ΔEQ = 2.1 mm/s. We have also observed the abrupt changes in Hhf and ΔEQ at 27 K for Fe0.9Mn0.1PO4, and decrease the value of TS of Fe1-xMnxPO4 with Mn concentrations. Our study suggests that these changes in Fe1-xMnxPO4 are originated from the strong electric crystalline field and spin-orbit coupling of FeO6 octahedral site.

  2. Magnetization studies and spin Hamiltonian modelling of Li2 (Li1 - xFex) N

    NASA Astrophysics Data System (ADS)

    Atkinson, James H.; Jesche, Anton; Del Barco, Enrique; Canfield, Paul C.

    2015-03-01

    The study of ferromagnetic materials has yielded many examples of compounds which exhibit large energy barriers to a reversal of magnetization and correspondingly wide magnetization versus field hysteresis loops. Some materials, such as members of the class called ``single-molecule magnets'' (SMMs), even display vivid signatures of quantum tunneling effects, manifested as step-like features in hysteresis loop measurements of crystalline ensembles. The compound Li2(Li1-xFex)N has been previously shown to display an extremely high blocking temperature (~ 20 K) and large coercive fields (>11 T), as well as step-like features like those seen in SMMs. Here we report the results of low-temperature Hall sensor magnetization studies on a crystalline sample of Li2(Li1-0.006Fe0.006)N in which we detail evidence of a preferential orientation for the observed features, as well as their dependence upon transverse component fields in their magnitude, behavior which we attempt to model with a giant spin Hamiltonian. This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

  3. Electromagnons, magnons, and phonons in E u1 -xH oxMn O3

    NASA Astrophysics Data System (ADS)

    Chen, Zhenyu; Schmidt, M.; Wang, Zhe; Mayr, F.; Deisenhofer, J.; Mukhin, A. A.; Balbashov, A. M.; Loidl, A.

    2016-04-01

    Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system E u1 -xH oxMn O3 for holmium concentrations x =0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A -type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P ∥a to P ∥c . Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40 c m-1 . A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P ∥c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P ∥a additional spectral weight must be transferred from higher frequencies.

  4. Structural and magnetic phase transitions inEuTi1-xNbxO3

    DOE PAGESBeta

    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

  5. 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.

  6. 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.

  7. Magnetism in the YxGd1-xFe3 system

    NASA Astrophysics Data System (ADS)

    Bajorek, Anna; Chrobak, Artur; Chełkowska, Grażyna; Ociepka, Krzysztof

    2015-12-01

    The series of polycrystalline YxGd1-xFe3 compounds with a PuNi3-type of crystal structure have been obtained. Based on wide-ranging SQUID magnetometer series of different magnetic measurements have been carried out. Moreover, the magnetic properties in the paramagnetic range has been studied by means of Faraday type magnetic balance. The partial replacement of Gd by Y atoms is reflected in the increase within the total saturation magnetic moment MS from 1.61 μB/f.u (x=0.0) to 5.32 μB/f.u (x=1.0) and the decrease of the Curie temperature TC from 721 K (x=0.0) to 533 K (x=1.0). Exchange coupling parameters of R-R (ARR), T-T (ATT) and R-T (ART) have been evaluated from M(T) magnetization curves based on the mean field theory (MFT) calculation. The valence band spectra as well as the core level lines obtained by the use of X-ray photoemission spectroscopy (XPS) at room temperature have been analyzed as the influence of Gd/Y substitution on the electronic structure. The valence bands near the Fermi level are dominated by Fe3d states. A quite good agreement between the values of the iron magnetic moment estimated from M(H) curves, from MFT calculations as well as from fitting of Fe3s core level lines has been obtained.

  8. 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.

  9. 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

  10. Specific Heat of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, Jeffrey; Mugford, Chas; Lettress, Lauren; Kycia, Jan

    2007-03-01

    We will present specific heat results on the dilute dipolar-coupled Ising magnet LiHoxY1-xF4. This material was previously observed to change from a spin glass to an unusual ``anti-glass'' state at a Ho concentration of x˜0.045. This state showed dynamics that are very different from those of a spin glass and also exhibited sharp features in its specific heat at around 100 and 300 mK. In contrast, our measurements of the heat capacity do not reproduce these sharp features and instead find broad curves for three concentrations (1.8%, 4.5% and 8.0%). Integrating C/T reveals a residual entropy S0 which is 0 for 8.0% Ho but increases with lower concentration (to 0.31R at 1.8% Ho). This provides some evidence for a change to a different magnetic ground state below 8.0% Ho and is qualitatively consistent with Monte Carlo simulations. AC susceptibility measurements probing the dynamics of this system are currently being performed and results will be presented. S. Ghosh et al., Science 296, 2195 (2002) S. Ghosh et al., Nature 425, 48 (2003). J. Snider and C. C. Yu, Phys. Rev. B 72, 214203 (2005).

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Impact ionization in AlxGa1-xAsySb1-y avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-01

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in AlxGa1-xAsySb1-y lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  17. Photoinduced spectra for magneto electric (1-x)BiFeO₃-xCuFe₂O₄ nanocomposites.

    PubMed

    Kityk, I V; Alzayed, N; Lakshminarayana, G; Wojciechowski, A; Plucinski, K J

    2012-11-01

    In this work, we demonstrate possibility to use spectra of the parametrically tuned laser beam for operation by magnetoelectric properties of the (1-x)BiFeO(3-)(x)CuFe(2)O(4) (BFCI). The role of the photoexcited wavelength is crucial due to photoexcited phonons. It may indicate on a spectral sensitivity of the studied nanocomposites. We have studied spectral dependences of magneto-electric constant versus the magnetic field frequency for different sizes of the nanoparticles with and without the nanosecond laser pulses illumination and we have shown an occurrence of principal spectral shifts in the corresponding magneto-electric maxima. Additionally we have explored relative changes of dielectric permittivity and coercivity versus different photoinducing wavelengths. The performed experiments unambiguously show that the external laser treatment will lead to substantial shift of corresponding dielectric and magnetic parameters in the studied nanocomposites. It is principally the finding of clear spectral dependences for the mentioned dielectric and magnetic parameters. One can see their sensitivity to the photoinduced wavelength which reflects the photoexcitations of different part of wavelengths. One can see the spectral shift up to 100 nm for the two principal spectral maxima with respect to the dielectric and magnetic changes which may indicate on the two principally different contributions to the effects observed. PMID:22885117

  18. Strained and strain-relaxed epitaxial Ge1-xSnx alloys on Si(100) substrates

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Su, Shao-Jian; Zheng, Jun; Zhang, Guang-Ze; Zuo, Yu-Hua; Cheng, Bu-Wen; Wang, Qi-Ming

    2011-06-01

    Epitaxial Ge1-xSnx alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100) substrate, a high crystalline quality strained Ge0.97Sn0.03 alloy is grown, with a χmin value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100) substrate, strain-relaxed Ge0.97Sn0.03 alloys are epitaxially grown at 150 °C-300 °C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and device performance.

  19. Statistical model for the formation of the Ge1-xSnx alloy

    NASA Astrophysics Data System (ADS)

    Ventura, C. I.; Fuhr, J. D.; Barrio, R. A.

    2009-10-01

    The electronic structures of most semiconductor alloys are smooth functions of their composition. Binary alloys of group IV semiconductors are usually easy to prepare at any concentration, but this is not the case for the Ge1-xSnx alloy. Homogeneous alloys as required for nano- and optoelectronics device applications have proved difficult to form for x above a temperature-dependent critical concentration, above which Sn exhibits the tendency to segregate in the metallic cubic β phase, spoiling the semiconducting properties. The underlying mechanism for this segregation and critical concentration was not known. Through previous accurate ab initio local defect calculations we estimated the scale of energies involved in the immediate environment around a large number of Sn defects in Ge, the relaxed configurations of the defects, and the pressure directly related to the elastic field caused by the defects. This detailed information allowed us to build a simple statistical model including the defects most relevant at low x, namely substitutional α-Sn and non-substitutional β-Sn (in which a single atom occupies the centre of a Ge divacancy). Our model enables us to determine at which concentration β defects, which exhibit a tendency to segregate, can be formed in thermal equilibrium. These results coincide remarkably well with experimental findings, concerning the critical concentration above which the homogeneous alloys cannot be formed at room temperature. Our model also predicts the observed fact that at lower temperature the critical concentration increases.

  20. Nonsubstitutional single-atom defects in the Ge1-xSnx alloy

    NASA Astrophysics Data System (ADS)

    Ventura, C. I.; Fuhr, J. D.; Barrio, R. A.

    2009-04-01

    Ge1-xSnx alloys have proved difficult to form at large x , contrary to what happens with other group IV semiconductor combinations. However, at low x they are typical examples of well-behaved substitutional compounds, which is desirable for harnessing the electronic properties of narrow-band semiconductors. In this paper, we propose the appearance of another kind of single-site defect (β-Sn) , consisting of a single Sn atom in the center of a Ge divacancy, that may account for these facts. Accordingly, we examine the electronic and structural properties of these alloys by performing extensive numerical ab initio calculations around local defects. The results show that the environment of the β defect relaxes toward a cubic octahedral configuration, facilitating the nucleation of metallic white tin and its segregation, as found in amorphous samples. Using the information stemming from these local defect calculations, we built a simple statistical model to investigate at which concentration these β defects can be formed in thermal equilibrium. These results agree remarkably well with experimental findings, concerning the critical concentration above which the homogeneous alloys cannot be formed at room temperature. Our model also predicts the observed fact that at lower temperature the critical concentration increases. We also performed single-site effective-field calculations of the electronic structure.

  1. Formation of non-substitutional β-Sn defects in Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Fuhr, J. D.; Ventura, C. I.; Barrio, R. A.

    2013-11-01

    Although group IV semiconductor alloys are expected to form substitutionally, in Ge1-xSnx this is true only for low concentrations (x < 0.13). The use of these alloys as a narrow gap semiconductor depends on the ability to produce samples with the high quality required for optoelectronic device applications. In a previous paper, we proposed the existence of a non-substitutional complex defect (β-Sn), consisting of a single Sn atom in the center of a Ge divacancy, which may account for the segregation of Sn at large x. Afterwards, the existence of this defect was confirmed experimentally. In this paper we study the local environment and the interactions of the substitutional defect (α-Sn), the vacancy in Ge, and the β-Sn defect by performing extensive numerical ab initio calculations. Our results confirm that a β-Sn defect can be formed by natural diffusion of a vacancy around the substitutional α-Sn defect, since the energy barrier for the process is very small.

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. Temperature-dependent band structure of Hg1-xZnxTe-CdTe superlattices

    NASA Astrophysics Data System (ADS)

    Manassès, J.; Guldner, Y.; Vieren, J. P.; Voos, M.; Faurie, J. P.

    1991-12-01

    We present transport and far-infrared magneto-optical measurements in narrow-band-gap n-type Hg1-xZnxTe-CdTe superlattices. Hall and conductivity data obtained over a broad temperature range (1.5-300 K) show that these superlattices are semimetallic at low temperature and are degenerate intrinsic semiconductors for T>100 K, which constitutes an interesting situation in semiconductor-superlattice physics. The analysis of the data gives the Fermi energy as well as the temperature-dependent band gap, in good agreement with the calculated band structure, which predicts a semimetal-semiconductor transition induced by temperature in these heterostructures. We have measured the electron cyclotron resonances as a function of temperature with the magnetic field B applied parallel and perpendicular to the growth axis. The observed magneto-optical intraband transitions are in very satisfactory agreement with the calculated Landau levels and the Fermi energy. We show that the semimetal-semiconductor transition is characterized by an important reduction of the cyclotron mass measured with B perpendicular to the superlattice growth axis. The large variation of the conduction-band anisotropy calculated near the transition accounts for this effect.

  8. 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.

  9. What is the Valence of Mn in Ga1 -xMnxN ?

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We investigate the current debate on the Mn valence in Ga1 -xMnxN , a diluted magnetic semiconductor (DMS) with a potentially high Curie temperature. From a first-principles Wannier-function analysis, we unambiguously find the Mn valence to be close to 2 + (d5), but in a mixed spin configuration with average magnetic moments of 4 μB . By integrating out high-energy degrees of freedom differently, we further derive for the first time from first-principles two low-energy pictures that reflect the intrinsic dual nature of the doped holes in the DMS: (1) an effective d4 picture ideal for local physics, and (2) an effective d5 picture suitable for extended properties. In the latter, our results further reveal a few novel physical effects, and pave the way for future realistic studies of magnetism. Our study not only resolves one of the outstanding key controversies of the field, but also exemplifies the general need for multiple effective descriptions to account for the rich low-energy physics in many-body systems in general.

  10. Structural and Magnetic Properties of Transition-Metal-Doped Zn 1- x Fe x O

    NASA Astrophysics Data System (ADS)

    Abdel-Baset, T. A.; Fang, Yue-Wen; Anis, B.; Duan, Chun-Gang; Abdel-Hafiez, Mahmoud

    2016-02-01

    The ability to produce high-quality single-phase diluted magnetic semiconductors (DMS) is the driving factor to study DMS for spintronics applications. Fe-doped ZnO was synthesized by using a low-temperature co-precipitation technique producing Zn 1- x Fe x O nanoparticles ( x= 0, 0.02, 0.04, 0.06, 0.08, and 0.1). Structural, Raman, density functional calculations, and magnetic studies have been carried out in studying the electronic structure and magnetic properties of Fe-doped ZnO. The results show that Fe atoms are substituted by Zn ions successfully. Due to the small ionic radius of Fe ions compared to that of a Zn ions, the crystal size decreases with an increasing dopant concentration. First-principle calculations indicate that the charge state of iron is Fe 2+ and Fe 3+ with a zinc vacancy or an interstitial oxygen anion, respectively. The calculations predict that the exchange interaction between transition metal ions can switch from the antiferromagnetic coupling into its quasi-degenerate ferromagnetic coupling by external perturbations. This is further supported and explains the observed ferromagnetic bahaviour at magnetic measurements. Magnetic measurements reveal that decreasing particle size increases the ferromagnetism volume fraction. Furthermore, introducing Fe into ZnO induces a strong magnetic moment without any distortion in the geometrical symmetry; it also reveals the ferromagnetic coupling.

  11. 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.

  12. Polar clusters in impurity-doped quantum paraelectric K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Geneste, Grégory; Kiat, Jean-Michel; Yokota, Hiroko; Uesu, Yoshiaki; Porcher, Florence

    2010-04-01

    From density-functional calculations, we show that large off-center motions (≈1.0Å) of Li impurities in the KTaO3 matrix (studied at 3.7% concentration) create very anisotropic polar clusters oriented along the Li off-center dipole. The polarization induced by Li in the matrix decreases very sharply in the lateral directions so that polar clusters are only ≈ two lattice constants thick (one-dimensional or needlelike clusters). The polarization in such polar regions is mainly constituted by the displacements in the (highly polarizable) matrix rather than by the impurity itself. These results suggest that Li-doped potassium tantalate (3.7% concentration) is not ferroelectric at low temperature and rather behaves as a relaxor. These small polar zones around Li correlate at TB to form larger polar nanoregions, in which the matrix remains however nonpolar. This is confirmed by a low temperature neutron-diffraction analysis showing that the KTaO3 matrix remains paraelectric. Li-doped KTaO3 is an order-disorder system with a very deep local potential felt by the Li impurities (≈-200meV) . The energy barrier for Li hopping is estimated at 80-90 meV. An analytic expression for this local potential is provided, as well as a simple model describing the energetics of K1-xLixTaO3 .

  13. 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).

  14. 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.

  15. Microemulsion mediated synthesis of nanocrystalline (K x,Na 1-x)NbO 3 powders

    NASA Astrophysics Data System (ADS)

    Pithan, Christian; Shiratori, Yosuke; Dornseiffer, Jürgen; Haegel, Franz-Hubert; Magrez, Arnaud; Waser, Rainer

    2005-06-01

    The present study reports on the synthesis of nanocrystalline (K x,Na 1-x)NbO 3 powders prepared via microemulsion mediated hydrolytic decomposition of mixed alkoxide solutions. Compositions with different K/Na ratios ranging between the two end members KNbO 3 and NaNbO 3 have been synthesized and characterized with respect to stoichiometry, purity, crystalline structure, particle size and powder morphology using X-ray diffraction, Raman spectroscopy and inductively coupled plasma with optical emission spectroscopy. Both raw as well as calcined powders were investigated. For the technically relevant and piezoelectric most active composition (K 0.50,Na 0.50)NbO 3 the results are presented and discussed in comparison to micron-sized and submicron-sized powders, that have been prepared by solid state reaction for reference. The study of the crystallographic structure of these reference powders by XRD and Raman spectroscopy confirms the size induced phase transition between the thermodynamically stable monoclinic modification for large particles towards a new triclinic polymorph, which has been reported for nano-powders of this composition by us previously. As possible origin for this phenomenon, internal OH - groups, variations in K-/Na-site occupancy and mechanical stresses arising from the large surface curvature of the nanocrystalline powders are addressed.

  16. Photochromism and polaronic photocharge localization in diluted KTa1-xNbxO3

    NASA Astrophysics Data System (ADS)

    Gubaev, A. I.; Kapphan, S. E.; Jastrabik, L.; Trepakov, V. A.; Syrnikov, P. P.

    2006-07-01

    Ultraviolet (UV)-light-induced optical absorption in the near infrared (NIR) region was observed in diluted KTa1-xNbxO3 single crystals (x =0,0.004,0.007,0.012,0.07) at low temperatures. Illumination by wideband light (3.10-4.13eV, 300-400nm) is accompanied by the appearance of a broad NIR absorption band with the position of the maxima varying in the 0.69-0.8eV (1.54-1.79μ, T =1.3K) region for different Nb concentrations. This UV-light-induced absorption is absent in nominally pure KTaO3, as well as in all Nb diluted specimens at elevated temperatures. The centers responsible for the photochromic NIR absorption bands are tied to interband optical transitions of pair Nb4+ electronic polarons. The photochromic experimental data, supplemented by luminescence studies in the visible range, evidence the strong localization of the photocharge carriers by pair Nb4+ polarons at low temperatures. It is suggested that namely the strong localization of the photocarriers plays a crucial role in photoinduced gigantic dielectric effects and possible phase transitions, which have been recognized recently in incipient ferroelectrics at low temperatures.

  17. Magnetoelectric coupling tuned by competing anisotropies in Mn1-xNixTiO3

    DOE PAGESBeta

    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

  18. 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.

  19. Graphene-like conjugated π bond system in Pb1-xSnxSe

    NASA Astrophysics Data System (ADS)

    Shu, G. J.; Liou, S. C.; Karna, S.; Sankar, R.; Hayashi, M.; Chu, M.-W.; Chou, F. C.

    2015-03-01

    Following the identification of the π bond in graphene, in this work, a π bond constructed through side-to-side overlap of half-filled 6pz orbitals was observed in a non-carbon crystal of Pb1-xSnxSe (x ˜ 0.34) (PSS), a prototype topological crystalline insulator and thermoelectric material with a high figure-of-merit. PSS compounds with a rock-salt type cubic crystal structure were found to consist of σ bond connected covalent chains of Pb(Sn)-Se with an additional π bond that is shared as a conjugated system among the four nearest neighbor Pb pairs in square symmetry within all {001} monoatomic layers per cubic unit cell. The π bond formed with half-filled 6pz orbitals between Pb atoms is consistent with the calculated results from quantum chemistry. The presence of π bonds was identified and verified with electron energy-loss spectroscopy through plasmonic excitations and electron density mapping via an inverse Fourier transform of X-ray diffraction.

  20. Structural properties of the quaternary Heusler alloy Co2Cr1-xFexAl

    NASA Astrophysics Data System (ADS)

    Wurmehl, Sabine; Martins Alves, Maria C.; Morais, Jonder; Ksenofontov, Vadim; Teixeira, Sergio R.; Machado, Giovanna; Fecher, Gerhard H.; Felser, Claudia

    2007-03-01

    The quarternary substitutional series Co2Cr1-xFexAl was investigated by means of surface and bulk sensitive techniques in order to exploit its structural and compositional properties. Both bulk and powder samples of the alloy series were investigated to obtain specific information about this material. The long range order was determined by means of x-ray diffraction and neutron diffraction, while the site specific (short range) order was proved by extended x-ray absorption fine structure spectroscopy. The magnetic structure was investigated by Mössbauer spectroscopy in transmission and scattering modes in order to compare and separate powder and bulk properties. The chemical composition was analysed by means of x-ray photo emission spectroscopy combined with Auger electron spectroscopy depth profiling. The results from these methods are compared to get an insight into the differences between surface and bulk properties and the appearance of disorder in such alloys. The material shows an extremely high sensitivity to oxygen. In particular, powder materials show a high amount of oxygen contamination. Therefore, an additional oxide-mediated tunnel magneto-resistance may always contribute to measurements of magneto-resistive effects because the oxide layers will provide natural tunnelling barriers. In addition, the results suggest that thin films have to be produced under ultra-high vacuum conditions.