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Sample records for 119m te atoms

  1. Interactions of Pb and Te atoms with graphene.

    PubMed

    Gong, Chuncheng; Robertson, Alex W; He, Kuang; Ford, Camden; Watt, Andrew A R; Warner, Jamie H

    2014-05-28

    PbTe nanocrystals were deposited onto the surface of graphene and used as a reservoir of Pb and Te atoms. Electron beam irradiation at 80 kV caused Pb and Te atoms to mobilize and disperse across the surface of graphene. We studied the dynamics of these atoms in real time using aberration-corrected transmission electron microscopy. The Pb and Te atoms were found to attach to the surface layer of amorphous carbon that resides upon the graphene, as well as its edge. Pb and Te atoms were not found residing on pristine graphene, but were found to bond to the free edge states along graphene hole edges. Small PbTe nanoclusters tended to only form on the surface of the amorphous carbon regions and not on pristine graphene.

  2. Atomic Structure of Twin Boundaries in CdTe

    SciTech Connect

    Yan, Y.; Jones, K. M.; Al-Jassim, M. M.

    2003-05-01

    Using the combination of high-resolution transmission electron microscopy, first-principles density-functional total energy calculations, and image simulations, we determined the atomic structure of lamellar twin and double-positioning twin boundaries in CdTe. We find that the structure of lamellar twin boundaries has no dangling bonds or wrong bonds; thus, it results in negligible effects on the electronic properties. The structure of double-positioning twin boundaries, however, contain both Cd and Te dangling bonds, and therefore produce energy states in the bandgap that are detrimental to the electronic properties of CdTe.

  3. Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

    SciTech Connect

    Li, C. W.; Ma, J.; Cao, H. B.; May, A. F.; Abernathy, D. L.; Ehlers, G.; Hoffmann, C.; Wang, X.; Hong, T.; Huq, A.; Gourdon, O.; Delaire, O.

    2014-12-29

    The structure and lattice dynamics of rock-salt thermoelectric materials SnTe and PbTe are investigated with single crystal and powder neutron diffraction, inelastic neutron scattering (INS), and first-principles simulations. Our first-principles calculations of the radial distribution function (RDF) in both SnTe and PbTe show a clear asymmetry in the first nearest-neighbor (1NN) peak, which increases with temperature, in agreement with experimental reports (Ref. 1,2). We show that this peak asymmetry for the 1NN Sn–Te or Pb–Te bond results from large-amplitude anharmonic vibrations (phonons). No atomic off-centering is found in our simulations. In addition, the atomic mean square displacements derived from our diffraction data reveal stiffer bonding at the anion site, in good agreement with the partial phonon densities of states from INS, and first-principles calculations. In conclusion, these results provide clear evidence for large-amplitude anharmonic phonons associated with the resonant bonding leading to the ferroelectric instability.

  4. Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

    DOE PAGESBeta

    Li, C. W.; Ma, J.; Cao, H. B.; May, A. F.; Abernathy, D. L.; Ehlers, G.; Hoffmann, C.; Wang, X.; Hong, T.; Huq, A.; et al

    2014-12-29

    The structure and lattice dynamics of rock-salt thermoelectric materials SnTe and PbTe are investigated with single crystal and powder neutron diffraction, inelastic neutron scattering (INS), and first-principles simulations. Our first-principles calculations of the radial distribution function (RDF) in both SnTe and PbTe show a clear asymmetry in the first nearest-neighbor (1NN) peak, which increases with temperature, in agreement with experimental reports (Ref. 1,2). We show that this peak asymmetry for the 1NN Sn–Te or Pb–Te bond results from large-amplitude anharmonic vibrations (phonons). No atomic off-centering is found in our simulations. In addition, the atomic mean square displacements derived from ourmore » diffraction data reveal stiffer bonding at the anion site, in good agreement with the partial phonon densities of states from INS, and first-principles calculations. In conclusion, these results provide clear evidence for large-amplitude anharmonic phonons associated with the resonant bonding leading to the ferroelectric instability.« less

  5. Adsorption process, atomic geometry, electronic structure and stability of Si(001)/Te surface

    NASA Astrophysics Data System (ADS)

    Miwa, R. H.; Ferraz, A. C.

    2000-03-01

    The adsorption process, atomic geometry, electronic structure and energetics of a Si(001) surface covered by Te atoms have been studied using first-principles total-energy calculations. Our findings indicate that the Te atoms adsorb in the 'bridge' site on the surface Si dimer bond, in agreement with recent experimental results. We have also verified that the Si dimers (underneath adsorbed Te atoms) do not dissociate. The subsequent atomic exchange between the adsorbed Te atom and the surface Si atom, giving rise to an interdiffusion process of Te atoms towards Si substrate, is not an exothermic process. We have considered a number of possible coverages of Te atoms on Si(001) surface and our results indicate that for a coverage of one monolayer (1 ML), the Si(001)/Te-(1×1) surface represents the energetically more stable configuration. For a coverage of 2/3 ML, we have verified the formation of TeSiTe mixed trimers, in a (3×1) reconstructed surface. At 1/3 ML coverage, we have obtained the formation of Si dimers with a single Te atom at the surface, in a (3×1) reconstruction. Finally, for a coverage of 1/2 ML, we have obtained the formation of SiTe mixed dimers, in a (2×1) reconstructed surface, but the calculated formation energy indicates that this atomic configuration is not energetically favourable.

  6. Atomic collisions with 33-TeV lead ions

    SciTech Connect

    Vane, C.R.; Datz, S.; Krause, H.F.

    1996-10-01

    Recent availability of relativistic and ultrarelativistic beams of heavy ions has permitted the first controlled studies of atomic collisions at energies sufficient to measure effects of several new basic phenomena. These include measurements substantiating recently predicted finite nuclear size effects resulting in a reduction in the total electronic energy loss of heavy ions in matter, and measurements of Coulomb collisions in which electrons are excited from the Dirac negative energy continuum. Measurements of total energy loss, free electron-positron pair production, and electron capture from pair production have been recently performed using 33-TeV Pb{sup 82+} ions from the CERN SPS accelerator in Geneva. Results of these studies are presented, along with comparisons with relevant theory.

  7. Ab initio study of molecular and atomic oxygen on GeTe(111) surfaces

    SciTech Connect

    Deringer, Volker L.; Dronskowski, Richard

    2014-11-07

    Oxidation of the phase-change material germanium telluride (GeTe) is an atomic-scale process of fundamental importance, as it is detrimental to the stability of GeTe-based data-storage devices. Here, we present comprehensive density-functional theory simulations of molecular and atomic oxygen in contact with GeTe(111) surfaces. Molecular O{sub 2} is predicted to readily adsorb on the Ge-terminated (111) surface; the pristine Te-terminated counterpart, by contrast, appears quite inert. The coverage-dependent adsorption of O atoms is then investigated, and based on these data, a surface phase diagram for GeTe(111)/O is constructed. These results afford a detailed, atom-resolved picture of the initial surface oxidation of GeTe, and they harmonize well with a previous X-ray photoelectron spectroscopy study on this very topic.

  8. Impurity lattice sites after implantation of Te and Sb in GaAs: Search for the DX centre

    NASA Astrophysics Data System (ADS)

    Zhang, G. L.; Mo, D.; Liang, Z. N.; Niesen, L.

    1990-07-01

    119Sn Mössbauer Spectroscopy has been applied to study the nearest environment of radioactive119mTe and119Sb atoms implanted into GaAs. After a low-dose implantation and annealing above 300°C the impurity atoms are found at As sites. High-dose implantation and annealing above 600°C results in the population of at least two additional sites; these are clearly different for Te and Sb. No evidence is found for the population of DX-centres. A likely possibility is the formation of coherent Ga2Te3 precipitates.

  9. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    NASA Astrophysics Data System (ADS)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  10. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    PubMed Central

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-01-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature. PMID:27220411

  11. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures.

    PubMed

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-25

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  12. The adsorption of atomic hydrogen on tellurium and formation of H 2Te

    NASA Astrophysics Data System (ADS)

    Outka, Duane A.

    1990-09-01

    The adsorption of hydrogen on a polycrystalline tellurium surface has been studied with temperature programmed desorption. Atomic hydrogen adsorbs on a tellurium surface and reacts to form H 2Te. Molecular hydrogen, in contrast, does not adsorb or react with tellurium at temperatures down to 80 K. When a tellurium surface which has been exposed to atomic hydrogen is heated, two desorption products are observed, H 2 and H 2Te. The H 2Te desorbs in three peaks at 130, 150, and 270 K. The H 2 desorbs in two peaks at 150 and 270 K. The desorption peaks at 270 K for both H 2 and H 2Te are unusually broad with a half-width of 80 K, and standard kinetic analysis of these peaks yields unusual desorption parameters. Overall, the adsorption of hydrogen on tellurium is similar to hydrogen adsorption on other covalent solids and differs in several respects from hydrogen adsorbed on metal surfaces.

  13. Performance of CdZnTe detectors passivated with energetic oxygen atoms

    SciTech Connect

    Prettyman, T.H.; Hoffbauer, M.A.; Rennie, J.

    1998-12-01

    Noise caused by surface-leakage current can degrade the performance of CdZnTe spectrometers, particularly devices with closely spaced contacts such as coplanar grid detectors. In order to reduce surface leakage, the authors are treating CdZnTe detector surfaces with energetic, neutral oxygen atoms. Energetic oxygen atoms react with the surface to form a resistive oxide layer. Because the reaction is effective at room temperature, deleterious heating of the substrate is avoided. In most cases, leakage current and noise are shown to decrease significantly after treatment. The effect of the treatment on the performance of coplanar grid detectors is presented.

  14. The role of atomic vacancies on phonon confinement in α-GeTe

    SciTech Connect

    Kalra, Geetanjali; Murugavel, Sevi

    2015-04-15

    Atomic defects and their dynamics play a vital role in controlling the behavior of non-volatile phase change memory materials used in advanced optical storage devices. Synthesis and structural analysis by XRD and Raman spectroscopy on α-GeTe single crystal with different sizes are reported. The spectroscopic measurements on micron and nano sized α-GeTe single crystal reveal the evolution of phonon confinement with crystal sizes of few hundred nanometers. The characteristic vibrational modes of bulk α-GeTe structure are found to downshift and asymmetrically broaden to lower frequency with decreasing the single crystal size. We attribute the observed downshift of Raman lines in α-GeTe is largely due to the presence of high concentration of atomic vacancies. The crystal size and temperature dependent Raman spectra provide explicitly the dynamics of vacancies on optical phonon confinement in α-GeTe structure. Thus, the observed large concentration of vacancies and their size dependency might influence the phase change phenomenon in GeTe based alloys.

  15. Atomic-force microscopy and photoluminescence of nanostructured CdTe

    SciTech Connect

    Babentsov, V.; Sizov, F.; Franc, J.; Luchenko, A.; Svezhentsova, E. Tsybrii, Z.

    2013-09-15

    Low-dimensional CdTe nanorods with a diameter of 10-30 nm and a high aspect ratio that reaches 100 are studied. The nanorods are grown by the physical vapor transport method with the use of Bi precipitates on the substrates. In addition, thin films of closely packed CdTe nanorods with the transverse dimensions {approx}(100-200) nm are grown. Atomic-force microscopy shows that the cross sections of all of the nanorods were hexagonally shaped. By photoluminescence measurements, the inference about the wurtzite structure of CdTe is supported, and the structural quality, electron-phonon coupling, and defects are analyzed. On the basis of recent ab initio calculations, the nature of defects responsible for the formation of deep levels in the CdTe layers and bulk crystals are analyzed.

  16. Electrical characterization of HgTe nanowires using conductive atomic force microscopy

    SciTech Connect

    Gundersen, P.; Kongshaug, K. O.; Selvig, E.; Haakenaasen, R.

    2010-12-01

    Self-organized HgTe nanowires grown by molecular beam epitaxy (MBE) have been characterized using conductive atomic force microscopy. As HgTe will degrade or evaporate at normal baking temperatures for electron beam lithography (EBL) resists, an alternative method was developed. Using low temperature optical lithography processes, large Au contacts were deposited on a sample covered with randomly oriented, lateral HgTe nanowires. Nanowires partly covered by the large electrodes were identified with a scanning electron microscope and then localized in the atomic force microscope (AFM). The conductive tip of the AFM was then used as a movable electrode to measure current-voltage curves at several locations on HgTe nanowires. The measurements revealed that polycrystalline nanowires had diffusive electron transport, with resistivities two orders of magnitude larger than that of an MBE-grown HgTe film. The difference can be explained by scattering at the rough surface walls and at the grain boundaries in the wires. The method can be a solution when EBL is not available or requires too high temperature, or when measurements at several positions along a wire are required.

  17. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements.

    PubMed

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei Ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R J Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-Ya; Nakamura, Kazutaka G

    2016-07-14

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

  18. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements.

    PubMed

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei Ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R J Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-Ya; Nakamura, Kazutaka G

    2016-07-14

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results. PMID:27421417

  19. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements

    NASA Astrophysics Data System (ADS)

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei'ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R. J. Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-ya; Nakamura, Kazutaka G.

    2016-07-01

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

  20. Static atomic displacements in a CdTe epitaxial layer on a GaAs substrate

    NASA Astrophysics Data System (ADS)

    Horning, R. D.; Staudenmann, J.-L.

    1987-05-01

    A (001)CdTe epitaxial layer on a (001)GaAs substrate was studied by x-ray diffraction between 10 and 360 K. The CdTe growth took place at 380 °C in a vertical gas flow metalorganic chemical vapor deposition reactor. Lattice parameters and integrated intensities of both the substrate and the epitaxial layer using the (00l) and (hhh) Bragg reflections reveal three important features. Firstly, the GaAs substrate does not exhibit severe strain after deposition and it is as perfect as a bulk GaAs. Secondly, the CdTe unit cell distorts tetragonally with a⊥>a∥ below 300 K. The decay of the (00l) reflection intensities as a function of the temperature yields a Debye temperature of 142 K, the same value as for bulk CdTe. Thirdly, a temperature-dependent isotropic static displacement of the Cd and the Te atoms is introduced to account for the anomalous behavior of the (hhh) intensities.

  1. States of antimony and tin atoms in lead chalcogenides

    SciTech Connect

    Bordovsky, G. A.; Nemov, S. A.; Marchenko, A. V.; Zaiceva, A. V.; Kozhokar, M. Yu.; Seregin, P. P.

    2011-04-15

    It is shown by Moessbauer spectroscopy of the {sup 119}Sb({sup 119m}Sn) isotope that impurity antimony atoms in PbS, PbSe, and PbTe lattices are distributed between cation and anion sublattices. In n-type samples, the greatest part of antimony is located in the anion sublattice; in hole ones, in the cation sublattice. The tin atoms formed as a result of radioactive decay of {sup 119}Sb (antisite state) are electrically inactive in the anion sub-lattice of PbS and PbSe, while, in the cation sublattice, they form donor U{sup -} centers. Electron exchange between the neutral and doubly ionized tin U{sup -} centers via the allowed band states is observed. The tin atoms formed after radioactive decay of {sup 119}Sb are electrically inactive in the anion and cation sublattices of PbTe.

  2. Electronics and atomic scale properties of defects and dopants in 2H-MoTe2

    NASA Astrophysics Data System (ADS)

    Longobardi, Maria; Ubaldini, Alberto; Giannini, Enrico; Bowler, David R.; Renner, Christoph

    2015-03-01

    We present a detailed STM/STS investigation and corresponding DFT modeling of native dopants and atomic scale defects and their influence on the local electron density of states of 2H-MoTe2. Semiconducting transition metal dichalcogenides (TMDs) are attracting increasing interest in the field of electronics and optoelectronics owing to their layered structure and the indirect-to-direct band gap transition when approaching the single-layer limit. 2H-MoTe2 is a semiconducting TMD with a bulk band gap of around 1.0 eV. This compound shows very high mobility at room temperature and strong absorption throughout the solar spectrum. Previous studies demonstrated the possibility to achieve gate-induced ambipolar transport at the surface. 2H-MoTe2 is thus an attractive candidate for novel optoelectronic devices such as light-emitting diodes, photo detectors and solar cell technology. Controlling the atomic nature and density of defects and dopants is crucial for the development of the aforementioned applications and devices.

  3. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

    NASA Astrophysics Data System (ADS)

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

    2016-06-01

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.

  4. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface.

    PubMed

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K Y; Klie, Robert F; Kim, Moon J

    2016-06-03

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1-10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.

  5. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

    PubMed Central

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

    2016-01-01

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis. PMID:27255415

  6. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

    DOE PAGESBeta

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

    2016-06-03

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/ (110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocationmore » cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. In conclusion, this report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.« less

  7. Accuracy of existing atomic potentials for the CdTe semiconductor compound.

    PubMed

    Ward, D K; Zhou, X W; Wong, B M; Doty, F P; Zimmerman, J A

    2011-06-28

    CdTe and CdTe-based Cd(1-x)Zn(x)Te (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided.

  8. Accuracy of existing atomic potentials for the CdTe semiconductor compound

    NASA Astrophysics Data System (ADS)

    Ward, D. K.; Zhou, X. W.; Wong, B. M.; Doty, F. P.; Zimmerman, J. A.

    2011-06-01

    CdTe and CdTe-based Cd1-xZnxTe (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided.

  9. Atomic-scale quantification of interdiffusion and dopant localization in GeSbTe-based memory devices

    NASA Astrophysics Data System (ADS)

    Chae, B.-G.; Seol, J.-B.; Song, J.-H.; Jung, W.-Y.; Hwang, H.; Park, C.-G.

    2016-09-01

    Fabrication of phase-change memory devices at modest or ambient temperatures leads to nanoscale compositional variations in phase-transition layers, where amorphous-polycrystalline phase change takes place via electrical switching, and can alter the device's performances. Here, by transmission electron microscopy and atom probe tomography, we address that thermal annealing at 400 °C for 20 min induces an elemental interdiffusion in the devices consisting of TiN (top electrode), carbon-doped GeSbTe (phase-transition layer), and TiSiN (bottom heater). With respect to the employed annealing process, the Ge atoms of GeSbTe layer have diffused into TiSiN layer at a given sample volume, while the Ti atoms of TiSiN layer into GeSbTe layer. Furthermore, non-random nature of dopant distribution in the GeSbTe materials leads to a Ti-localization including dopants at the GeSbTe/TiSiN interfaces. Our findings have two important implications: First, the annealing-driven interdiffusion of Ge and Ti is a predominant mechanism responsible for nanoscale compositional variations in GeSbTe layer; second, such an interdiffusion and the resultant dopant localization play a crucial role on the driving force for amorphous-polycrystalline transition of GeSbTe-based memory devices.

  10. Atomic arrangement at ZnTe/CdSe interfaces determined by high resolution scanning transmission electron microscopy and atom probe tomography

    SciTech Connect

    Bonef, Bastien; Rouvière, Jean-Luc; Jouneau, Pierre-Henri; Bellet-Amalric, Edith; Gérard, Lionel; Mariette, Henri; André, Régis; Bougerol, Catherine; Grenier, Adeline

    2015-02-02

    High resolution scanning transmission electron microscopy and atom probe tomography experiments reveal the presence of an intermediate layer at the interface between two binary compounds with no common atom, namely, ZnTe and CdSe for samples grown by Molecular Beam Epitaxy under standard conditions. This thin transition layer, of the order of 1 to 3 atomic planes, contains typically one monolayer of ZnSe. Even if it occurs at each interface, the direct interface, i.e., ZnTe on CdSe, is sharper than the reverse one, where the ZnSe layer is likely surrounded by alloyed layers. On the other hand, a CdTe-like interface was never observed. This interface knowledge is crucial to properly design superlattices for optoelectronic applications and to master band-gap engineering.

  11. Raman scattering and anomalous Stokes–anti-Stokes ratio in MoTe2 atomic layers

    NASA Astrophysics Data System (ADS)

    Goldstein, Thomas; Chen, Shao-Yu; Tong, Jiayue; Xiao, Di; Ramasubramaniam, Ashwin; Yan, Jun

    2016-06-01

    Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, and find the effect to be tunable by excitation frequency and number of atomic layers. These observations are interpreted as a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center in the photon-electron-phonon interaction process.

  12. Raman scattering and anomalous Stokes-anti-Stokes ratio in MoTe2 atomic layers.

    PubMed

    Goldstein, Thomas; Chen, Shao-Yu; Tong, Jiayue; Xiao, Di; Ramasubramaniam, Ashwin; Yan, Jun

    2016-01-01

    Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, and find the effect to be tunable by excitation frequency and number of atomic layers. These observations are interpreted as a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center in the photon-electron-phonon interaction process. PMID:27324297

  13. Raman scattering and anomalous Stokes–anti-Stokes ratio in MoTe2 atomic layers

    PubMed Central

    Goldstein, Thomas; Chen, Shao-Yu; Tong, Jiayue; Xiao, Di; Ramasubramaniam, Ashwin; Yan, Jun

    2016-01-01

    Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, and find the effect to be tunable by excitation frequency and number of atomic layers. These observations are interpreted as a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center in the photon-electron-phonon interaction process. PMID:27324297

  14. Observation of anomalous Stokes versus anti-Stokes ratio in MoTe2 atomic layers

    NASA Astrophysics Data System (ADS)

    Goldstein, Thomas; Chen, Shao-Yu; Xiao, Di; Ramasubramaniam, Ashwin; Yan, Jun

    We grow hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor, with chemical vapor transport methods and investigate its atomic layers with Stokes and anti-Stokes Raman scattering. We report observation of all six types of zone center optical phonons. Quite remarkably, the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, creating an illusion of 'negative temperature'. This effect is tunable, and can be switched from anti-Stokes enhancement to suppression by varying the excitation wavelength. We interpret this observation to be a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center, which are robust even for multiple layers of MoTe2. The intense anti-Stokes Raman scattering provides a cooling channel for the crystal and opens up opportunities for laser cooling of atomically thin TMDC semiconductor devices. Supported by the University of Massachusetts Amherst, the National Science Foundation Center for Hierarchical Manufacturing (CMMI-1025020) and Office of Emerging Frontiers in Research and Innovation (EFRI-1433496).

  15. Preliminary studies in the electrodeposition of PbSe/PbTe superlattice thin films via electrochemical atomic layer deposition (ALD).

    PubMed

    Vaidyanathan, Raman; Cox, Steven M; Happek, Uwe; Banga, Dhego; Mathe, Mkhulu K; Stickney, John L

    2006-12-01

    This paper concerns the electrochemical growth of compound semiconductor thin film superlattice structures using electrochemical atomic layer deposition (ALD). Electrochemical ALD is the electrochemical analogue of atomic layer epitaxy (ALE) and ALD, methods based on nanofilm formation an atomic layer at a time, using surface-limited reactions. Underpotential deposition (UPD) is a type of electrochemical surfaced-limited reaction used in the present studies for the formation of PbSe/PbTe superlattices via electrochemical ALD. PbSe/PbTe thin-film superlattices with modulation wavelengths (periods) of 4.2 and 7.0 nm are reported here. These films were characterized using electron probe microanalysis, X- ray diffraction, atomic force microscopy (AFM), and infrared reflection absorption measurements. The 4.2 nm period superlattice was grown after deposition of 10 PbSe cycles, as a prelayer, resulting in an overall composition of PbSe0.52Te0.48. The 7.0 nm period superlattice was grown after deposition of 100 PbTe cycle prelayer, resulting for an overall composition of PbSe0.44Te0.56. The primary Bragg diffraction peak position, 2theta, for the 4.2 superlattice was consistent with the average (111) angles for PbSe and PbTe. First-order satellite peaks, as well as a second, were observed, indicating a high-quality superlattice film. For the 7.0 nm superlattice, Bragg peaks for both the (200) and (111) planes of the PbSe/PbTe superlattice were observed, with satellite peaks shifted 1 degrees closer to the (111), consistent with the larger period of the superlattice. AFM suggested conformal superlattice growth on the Au on glass substrate. Band gaps for the 4.2 and 7.0 nm period superlattices were measured as 0.48 and 0.38 eV, respectively.

  16. Reduction of surface leakage current by surface passivation of CdZn Te and other materials using hyperthermal oxygen atoms

    DOEpatents

    Hoffbauer, Mark A.; Prettyman, Thomas H.

    2001-01-01

    Reduction of surface leakage current by surface passivation of Cd.sub.1-x Zn.sub.x Te and other materials using hyperthermal oxygen atoms. Surface effects are important in the performance of CdZnTe room-temperature radiation detectors used as spectrometers since the dark current is often dominated by surface leakage. A process using high-kinetic-energy, neutral oxygen atoms (.about.3 eV) to treat the surface of CdZnTe detectors at or near ambient temperatures is described. Improvements in detector performance include significantly reduced leakage current which results in lower detector noise and greater energy resolution for radiation measurements of gamma- and X-rays, thereby increasing the accuracy and sensitivity of measurements of radionuclides having complex gamma-ray spectra, including special nuclear materials.

  17. Atomic scale insight into the amorphous structure of Cu doped GeTe phase-change material

    SciTech Connect

    Zhang, Linchuan; Sa, Baisheng; Zhou, Jian; Sun, Zhimei; Song, Zhitang

    2014-10-21

    GeTe shows promising application as a recording material for phase-change nonvolatile memory due to its fast crystallization speed and extraordinary amorphous stability. To further improve the performance of GeTe, various transition metals, such as copper, have been doped in GeTe in recent works. However, the effect of the doped transition metals on the stability of amorphous GeTe is not known. Here, we shed light on this problem for the system of Cu doped GeTe by means of ab initio molecular dynamics calculations. Our results show that the doped Cu atoms tend to agglomerate in amorphous GeTe. Further, base on analyzing the pair correlation functions, coordination numbers and bond angle distributions, remarkable changes in the local structure of amorphous GeTe induced by Cu are obviously seen. The present work may provide some clues for understanding the effect of early transition metals on the local structure of amorphous phase-change compounds, and hence should be helpful for optimizing the structure and performance of phase-change materials by doping transition metals.

  18. Mechanical and Electrical Properties of CdTe Tetrapods Studied byAtomic Force Microscopy

    SciTech Connect

    Fang, Liang; Park, Jeong Young; Cui, Yi; Alivisatos, Paul; Shcrier, Joshua; Lee, Byounghak; Wang, Lin-Wang; Salmeron, Miquel

    2007-08-30

    The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with the ends of three arms. The length of these arms was found to be 130 {+-} 10 nm. A large fraction of the tetrapods had a shortened vertical arm as a result of fracture during sample preparation. Fracture also occurs when the applied load is a few nanonewtons. Compression experiments with the AFM tip indicate that tetrapods with the shortened vertical arm deform elastically when the applied force was less than 50 nN. Above 90 nN additional fracture events occurred that further shorted the vertical arm. Loads above 130 nN produced irreversible damage to the other arms as well. Current-voltage characteristics of tetrapods deposited on gold indicated semiconducting behavior with a current gap of {approx}2 eV at low loads (<50 nN) and a narrowing to about 1 eV at loads between 60 and 110 nN. Atomic calculation of the deformation suggests that the ends of the tetrapod arms are stuck during compression so that the deformations are due to bending modes. The reduction of the current gap is due to electrostatic effects, rather than strain deformation effects inside the tetrapod.

  19. Atomic force microscopy study of laser induced phase transitions in Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Weidenhof, V.; Friedrich, I.; Ziegler, S.; Wuttig, M.

    1999-11-01

    Micron- and submicron-size changes induced by local laser heating in thin films of Ge2Sb2Te5 are studied by atomic force microscopy (AFM). This material is presently used for rewritable data storage that employs phase change recording. Reversible switching between the amorphous and crystalline states, which is accompanied by a considerable change in optical properties and film density, is exploited to store bits of information. The density change can be detected by AFM, which we use here to study the amorphization (writing) and recrystallization (erasure) of single bits. Both processes have been measured as a function of modification pulse power and duration. Morphology changes can be detected even if the phase change film is covered by a thin protective layer. AFM allows a precise determination of the bit size and bit depth, which characterizes the progress of the phase change in the direction of the surface normal. The present setup allows the correlation of the change in optical reflectance ΔR caused by a specific laser pulse to the bit topography. This enables a detailed study of the mechanisms of bit writing and erasure.

  20. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    DOE PAGESBeta

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; Guo, Wei; Yan, Yanfa; Pennycook, Stephen J.

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative ofmore » a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.« less

  1. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    SciTech Connect

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; Guo, Wei; Yan, Yanfa; Pennycook, Stephen J.

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative of a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.

  2. Thermoelectric transport and Hall measurements of low defect Sb2Te3 thin films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zastrow, S.; Gooth, J.; Boehnert, T.; Heiderich, S.; Toellner, W.; Heimann, S.; Schulz, S.; Nielsch, K.

    2013-03-01

    Sb2Te3 has recently been an object of intensive research since its promising applicability in thermoelectric, in phase-change memory devices and as a topological insulator. In this work, we report highly textured Sb2Te3 thin films, grown by atomic layer deposition on Si/SiO2 wafers based on the reaction of SbCl3 and (Et3Si)2Te. The low deposition temperature at 80 °C allows the pre-patterning of the Sb2Te3 by standard lithography processes. A platform to characterize the Seebeck coefficient S, the electrical conductivity σ as well as the Hall coefficient RH on the same film has been developed. Comparing all temperature-dependent transport properties, three different conductive regions in the temperature range of 50-400 K are found. Room temperature values of S = 146 × 10-6 VK-1, σ = 104 Sm-1 and mobility µ = 270.5 × 10-4 m2 V-1 s-1 are determined. The low carrier concentration in the range of n = 2.4 × 1018 cm-3 at 300 K quantifies the low defect content of the Sb2Te3 thin films.

  3. Passivation Effect of Atomic Layer Deposition of Al2O3 Film on HgCdTe Infrared Detectors

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Ye, Zhen-Hua; Sun, Chang-Hong; Chen, Yi-Yu; Zhang, Tian-Ning; Chen, Xin; Lin, Chun; Ding, Ring-Jun; He, Li

    2016-09-01

    The passivation effect of atomic layer deposition of (ALD) Al2O3 film on a HgCdTe infrared detector was investigated in this work. The passivation effect of Al2O3 film was evaluated by measuring the minority carrier lifetime, capacitance versus voltage ( C- V) characteristics of metal-insulator-semiconductor devices, and resistance versus voltage ( R- V) characteristics of variable-area photodiodes. The minority carrier lifetime, C- V characteristics, and R- V characteristics of HgCdTe devices passivated by ALD Al2O3 film was comparable to those of HgCdTe devices passivated by e-beam evaporation of ZnS/CdTe film. However, the baking stability of devices passivated by Al2O3 film is inferior to that of devices passivated by ZnS/CdTe film. In future work, by optimizing the ALD Al2O3 film growing process and annealing conditions, it may be feasible to achieve both excellent electrical properties and good baking stability.

  4. Element-resolved atomic structure imaging of rocksalt Ge2Sb2Te5 phase-change material

    NASA Astrophysics Data System (ADS)

    Zhang, Bin; Zhang, Wei; Shen, Zhenju; Chen, Yongjin; Li, Jixue; Zhang, Shengbai; Zhang, Ze; Wuttig, Matthias; Mazzarello, Riccardo; Ma, Evan; Han, Xiaodong

    2016-05-01

    Disorder-induced electron localization and metal-insulator transitions (MITs) have been a very active research field starting from the seminal paper by Anderson half a century ago. However, pure Anderson insulators are very difficult to identify due to ubiquitous electron-correlation effects. Recently, an MIT has been observed in electrical transport measurements on the crystalline state of phase-change GeSbTe compounds, which appears to be exclusively disorder driven. Subsequent density functional theory simulations have identified vacancy disorder to localize electrons at the Fermi level. Here, we report a direct atomic scale chemical identification experiment on the rocksalt structure obtained upon crystallization of amorphous Ge2Sb2Te5. Our results confirm the two-sublattice structure resolving the distribution of chemical species and demonstrate the existence of atomic disorder on the Ge/Sb/vacancy sublattice. Moreover, we identify a gradual vacancy ordering process upon further annealing. These findings not only provide a structural underpinning of the observed Anderson localization but also have implications for the development of novel multi-level data storage within the crystalline phases.

  5. Cross-Sectional Conductive Atomic Force Microscopy of CdTe/CdS Solar Cells: Effects of Etching and Back-Contact Processes; Preprint

    SciTech Connect

    Moutinho, H. R.; Dhere, R. G.; Jiang, C.-S.; Gessert, T. A.; Duda, A. M.; Young, M.; Metzger, W. K.; Li, X.; Al-Jassim, M. M.

    2006-05-01

    We investigated the effects of the etching processes using bromine and nitric-phosphoric acid solutions, as well as of Cu, in the bulk electrical conductivity of CdTe/CdS solar cells using conductive atomic force microscopy (C-AFM). Although the etching process can create a conductive layer on the surface of the CdTe, the layer is very shallow. In contrast, the addition of a thin layer of Cu to the surface creates a conductive layer inside the CdTe that is not uniform in depth, is concentrated at grains boundaries, and may short circuit the device if the CdTe is too thin. The etching process facilitates the Cu diffusion and results in thicker conductive layers. The existence of this inhomogeneous conductive layer directly affects the current transport and is probably the reason for needing thick CdTe in these devices.

  6. Synthesis of ZnTe dendrites on multi-walled carbon nanotubes/polyimide nanocomposite membrane by electrochemical atomic layer deposition and photoelectrical property research

    SciTech Connect

    Jiang, Yimin; Kou, Huanhuan; Li, Jiajia; Yu, Shengjiao; Du, Yongling; Ye, Weichun; Wang, Chunming

    2012-10-15

    We report on the electrochemical atomic layer deposition (EC-ALD) of ZnTe dendrites on the carboxyl-functionalized multi-walled carbon nanotubes/polyimide (COOH-MWCNTs/PI) membrane. Electrochemical characteristics were studied by cyclic voltammetry (CV) and the deposition of ZnTe dendrites was completed using amperometric method (I-t). The prepared ZnTe dendrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The growth mechanism of ZnTe dendrites was elucidated to give a deep understanding of crystal growth. The concentration of reagents and deposition cycle had a significant effect on the morphology and structure of deposits. UV-vis transmission study indicated a direct band gap of 2.26 eV. Photoelectrical measurement confirmed the p-type conductivity of ZnTe dendrites, which indicated that the dendritic ZnTe crystals may have potential practical application in optoelectronic devices. - Graphical abstract: Representative SEM images of ZnTe dendrites. (a) Panorama of ZnTe dendrites; (b) a single dendrite. The regular branches appeared like leaves and showed a parallel arrangement layer upon layer between each other. Highlights: Black-Right-Pointing-Pointer ZnTe dendrites were successfully synthesized on CNTs/PI membrane by electrodeposition. Black-Right-Pointing-Pointer The growth mechanism of ZnTe dendritic structures was investigated in detail. Black-Right-Pointing-Pointer The concentration and deposition cycle greatly affected the morphology of ZnTe. Black-Right-Pointing-Pointer OCP and I-t studies showed that ZnTe can be beneficial to photoelectric applications.

  7. Existence of tetrahedral site symmetry about Ge atoms in a single-crystal film of Ge2Sb2Te5 found by x-ray fluorescence holography

    NASA Astrophysics Data System (ADS)

    Hosokawa, S.; Ozaki, T.; Hayashi, K.; Happo, N.; Fujiwara, M.; Horii, K.; Fons, P.; Kolobov, A. V.; Tominaga, J.

    2007-03-01

    The authors discuss x-ray fluorescence holography (XFH) measurements taken from an epitaxial layer of the digital versatile disk random access memory (DVD-RAM) material Ge2Sb2Te5 grown on a single-crystal GaSb(100) substrate. By using fluorescent photons from the Ge atoms in the matrix, a three-dimensional atomic image was obtained around the Ge atoms in a Ge2Sb2Te5 film; details of the three-dimensional atomic arrangement will aim at clarification of the high-speed writing and erasing mechanism of the laser-induced crystal-amorphous phase transition in this DVD-RAM material. Analysis of the XFH images revealed that the epitaxial layer did not possess a hexagonal structure as in the equilibrium phase of Ge2Sb2Te5, but a cubic structure with tetrahedral site symmetry about Ge atoms, different from the previous powder diffraction result. The present structure may support the umbrella-flip model of the Ge atoms between the octahedral site in the distorted rocksalt crystal and the tetrahedral site in the amorphous phase on the laser-induced phase transition.

  8. Specific features of the electronic, spin, and atomic structures of a topological insulator Bi2Te2.4Se0.6

    NASA Astrophysics Data System (ADS)

    Filyanina, M. V.; Klimovskikh, I. I.; Eremeev, S. V.; Rybkina, A. A.; Rybkin, A. G.; Zhizhin, E. V.; Petukhov, A. E.; Rusinov, I. P.; Kokh, K. A.; Chulkov, E. V.; Tereshchenko, O. E.; Shikin, A. M.

    2016-04-01

    The specific features of the electronic and spin structures of a triple topological insulator Bi2Te2.4Se0.6, which is characterized by high-efficiency thermoelectric properties, have been studied with the use of angular- and spin-resolved photoelectron spectroscopy and compared with theoretical calculations in the framework of the density functional theory. It has been shown that the Fermi level for Bi2Te2.4Se0.6 falls outside the band gap and traverses the topological surface state (the Dirac cone). Theoretical calculations of the electronic structure of the surface have demonstrated that the character of distribution of Se atoms on the Te-Se sublattice practically does not influence the dispersion of the surface topological electronic state. The spin structure of this state is characterized by helical spin polarization. Analysis of the Bi2Te2.4Se0.6 surface by scanning tunnel microscopy has revealed atomic smoothness of the surface of a sample cleaved in an ultrahigh vacuum, with a lattice constant of ~4.23 Å. Stability of the Dirac cone of the Bi2Te2.4Se0.6 compound to deposition of a Pt monolayer on the surface is shown.

  9. Atomic-resolution study of dislocation structures and interfaces in poly-crystalline thin film CdTe using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Paulauskas, Tadas; Colegrove, Eric; Buurma, Chris; Kim, Moon; Klie, Robert

    2014-03-01

    Commercial success of CdTe-based thin film photovoltaic devices stems from its nearly ideal direct band gap which very effectively couples to Sun's light spectrum as well as ease of manufacturing and low cost of these modules. However, to further improve the conversion efficiency beyond 20 percent, it is important to minimize the harmful effects of grain boundaries and lattice defects in CdTe. Direct atomic-scale characterization is needed in order identify the carrier recombination centers. Likewise, it is necessary to confirm that passivants in CdTe, such as Cl, are able to diffuse and bind to the target defects. In this study, we characterize dislocation structures and grain boundaries in poly-crystalline CdTe using aberration-corrected cold-field emission scanning transmission electron microscopy (STEM). The chemical composition of Shockley partial, Frank and Lomer-Cottrell dislocations is examined via atomic column-resolved X-ray energy dispersive (XEDS) and electron energy-loss spectroscopies (EELS). Segregation of Cl towards dislocation cores and grain boundaries is shown in CdCl2 treated samples. We also investigate interfaces in ultra-high-vacuum bonded CdTe bi-crystals with pre-defined misorientation angles which are intended to mimic grain boundaries. Funded by: DOE EERE Sunshot Award EE0005956.

  10. Nanoscale multilevel switching in Ge2Sb2Te5 thin film with conductive atomic force microscopy.

    PubMed

    Yang, Fei; Xu, Ling; Chen, Jing; Xu, Jun; Yu, Yao; Ma, Zhongyuan; Chen, Kunji

    2016-01-22

    We demonstrate three-level data storage in amorphous Ge2Sb2Te5 (GST) thin film by conductive atomic force microscopy (C-AFM). Due to the high resolution and current sensitivity of AFM, the electrical properties of GST are investigated in the nanoscale. By applying an electric field between an AFM probe tip and the GST surface, well-resolved threshold switching and memory switching are obtained successively in a current-voltage sweeping. Correspondingly, three states with high, intermediate and low resistances, which are assigned data values '0', '1' and '2' respectively, are observed in an IV-spectrum. The electrical resistance of GST thin film decreases by over two orders of magnitude in both switching processes, which provides a clear contrast to distinguish the three logical states. We also discuss the threshold electrical field of threshold switching in the amorphous GST thin film. Nanoscale conductive marks in the amorphous ON state and crystalline state are successfully fabricated by applying IV-spectra with different voltage ranges on the GST thin films.

  11. Atomic-resolution characterization of the effects of CdCl{sub 2} treatment on poly-crystalline CdTe thin films

    SciTech Connect

    Paulauskas, T. Buurma, C.; Colegrove, E.; Guo, Z.; Sivananthan, S.; Klie, R. F.

    2014-08-18

    Poly-crystalline CdTe thin films on glass are used in commercial solar-cell superstrate devices. It is well known that post-deposition annealing of the CdTe thin films in a CdCl{sub 2} environment significantly increases the device performance, but a fundamental understanding of the effects of such annealing has not been achieved. In this Letter, we report a change in the stoichiometry across twin boundaries in CdTe and propose that native point defects alone cannot account for this variation. Upon annealing in CdCl{sub 2}, we find that the stoichiometry is restored. Our experimental measurements using atomic-resolution high-angle annular dark field imaging, electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope are supported by first-principles density functional theory calculations.

  12. First-principles study of atomic and electronic structures of 60° perfect and 30°/90° partial glide dislocations in CdTe

    DOE PAGESBeta

    Kweon, Kyoung E.; Aberg, Daniel; Lordi, Vincenzo

    2016-05-16

    The atomic and electronic structures of 60° glide perfect and 30°/90° glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dislocation lines from the singly-periodic (SP) structures, yielding either doubly-periodic (DP) ordering by forming a dimer or quadruply-periodic (QP) ordering by alternating a dimer and a missing dimer. Charge modulation along the dislocation line, accompanied by the QP reconstruction for the Cd-/Te-core 60° perfect and 30° partials or the DP reconstruction for the Cd-core 90° partial, results in semiconducting character,more » as opposed to the metallic character of the SP dislocation cores. Dislocation-induced defect states for the 60° Cd-/Te-core are located relatively close to the band edges, whereas the defect states lie in the middle of the band gap for the 30° Cd-/Te-core partial dislocations. In addition to the intracore charge modulation within each QP core, the possibility of intercore charge transfer between two different dislocation cores when they are paired together in the same system is discussed. As a result, the analysis of the electronic structures reveals the potential role of the dislocations on charge transport in CdTe, particularly in terms of charge trapping and recombination.« less

  13. First-principles study of atomic and electronic structures of 60∘ perfect and 30∘/90∘ partial glide dislocations in CdTe

    NASA Astrophysics Data System (ADS)

    Kweon, Kyoung E.; Åberg, Daniel; Lordi, Vincenzo

    2016-05-01

    The atomic and electronic structures of 60∘ glide perfect and 30∘/90∘ glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dislocation lines from the singly-periodic (SP) structures, yielding either doubly-periodic (DP) ordering by forming a dimer or quadruply-periodic (QP) ordering by alternating a dimer and a missing dimer. Charge modulation along the dislocation line, accompanied by the QP reconstruction for the Cd-/Te-core 60∘ perfect and 30∘ partials or the DP reconstruction for the Cd-core 90∘ partial, results in semiconducting character, as opposed to the metallic character of the SP dislocation cores. Dislocation-induced defect states for the 60∘ Cd-/Te-core are located relatively close to the band edges, whereas the defect states lie in the middle of the band gap for the 30∘ Cd-/Te-core partial dislocations. In addition to the intracore charge modulation within each QP core, the possibility of intercore charge transfer between two different dislocation cores when they are paired together in the same system is discussed. The analysis of the electronic structures reveals the potential role of the dislocations on charge transport in CdTe, particularly in terms of charge trapping and recombination.

  14. Unusually Slow Electron Cooling to Charge-Transfer State in Gradient CdTeSe Alloy Nanocrystals Mediated through Mn Atom.

    PubMed

    Debnath, Tushar; Maiti, Sourav; Ghosh, Hirendra N

    2016-04-01

    We have synthesized Mn-doped CdTeSe gradient alloy nanocrystals (NCs) by a colloidal synthetic method, and charge carrier dynamics have been revealed through ultrafast transient absorption (TA) spectroscopy. Due to the reactivity difference between Te and Se, a CdTe-rich core and CdSe-rich shell have been formed in the CdTeSe alloy with the formation of a gradient type II core-shell structure. Electron paramagnetic resonance studies suggest Mn atoms are located in the surface of the alloy NCs. Steady-state optical absorption and emission studies suggest formation of a charge-transfer (CT) state in which electrons are localized in a CdSe-rich shell and holes are localized in a CdTe-rich core which appears in the red region of the spectra. Electron transfer in the CT state is found to take place in the Marcus inverted region. To understand charge-transfer dynamics in the CdTeSe alloy NCs and to determine the effect of Mn doping on the alloy, ultrafast transient absorption studies have been carried out. In the case of the undoped alloy, formation of the CT state is found to take place through electron relaxation to the conduction band of the CT state with a time of 600 fs and through hole relaxation (from the CdSe-rich state to the CdTe-rich state) to the valence band of the CT state with a time scale of 1 ps. However, electron relaxation in the presence of Mn dopants takes place initially via an electron transfer to the Mn 3d state (d(5)) followed by transfer from the Mn 3d state (d(6)) to the CT state, which has been found to take place with a >700 ps time scale in addition to the hole relaxation time of 2 ps. Charge recombination time of the CT state is found to be extremely slow in the Mn-doped CdTeSe alloy NCs as compared to the undoped one, where the Mn atom acts as an electron storage center.

  15. Phase separation and nanostructuring in the thermoelectric material PbTe[subscript 1−x]S[subscript x] studied using the atomic pair distribution function technique

    SciTech Connect

    Lin, He; Božin, E.S.; Billinge, S.J.L.; Androulakis, J.; Malliakas, C.D.; Lin, C.H.; Kanatzidis, M.G.

    2009-08-13

    The average and local structures of the (PbTe){sub 1-x}(PbS){sub x} system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function methods. Samples with 0.25 {le} x are macroscopically phase separated. Phase separation was suppressed in a quenched x=0.5 sample which, nonetheless, exhibited a partial spinodal decomposition. The promising thermoelectric material with x=0.16 showed intermediate behavior. Combining TEM and bulk scattering data suggests that the sample is a mixture of PbTe-rich material and a partially spinodally decomposed phase similar to the quenched 50% sample. This confirms that, in the bulk, this sample is inhomogeneous on a nanometer length scale, which may account for its enhanced thermoelectric figure of merit.

  16. Direct versus indirect band gap emission and exciton-exciton annihilation in atomically thin molybdenum ditelluride (MoTe2)

    NASA Astrophysics Data System (ADS)

    Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

    2016-08-01

    We probe the room temperature photoluminescence of N -layer molybdenum ditelluride (MoTe2) in the continuous wave (cw) regime. The photoluminescence quantum yield of monolayer MoTe2 is three times larger than in bilayer MoTe2 and 40 times greater than in the bulk limit. Mono- and bilayer MoTe2 display almost symmetric emission lines at 1.10 and 1.07 eV, respectively, which predominantly arise from direct radiative recombination of the A exciton. In contrast, N ≥3 -layer MoTe2 exhibits a much reduced photoluminescence quantum yield and a broader, redshifted, and seemingly bimodal photoluminescence spectrum. The low- and high-energy contributions are attributed to emission from the indirect and direct optical band gaps, respectively. Bulk MoTe2 displays a broad emission line with a dominant contribution at 0.94 eV that is assigned to emission from the indirect optical band gap. As compared to related systems (such as MoS2,MoSe2,WS2, and WSe2), the smaller energy difference between the monolayer direct optical band gap and the bulk indirect optical band gap leads to a smoother increase of the photoluminescence quantum yield as N decreases. In addition, we study the evolution of the photoluminescence intensity in monolayer MoTe2 as a function of the exciton formation rate Wabs up to 3.6 ×1022cm-2s-1 . The line shape of the photoluminescence spectrum remains largely independent of Wabs, whereas the photoluminescence intensity grows sublinearly above Wabs˜1021cm-2s-1 . This behavior is assigned to exciton-exciton annihilation and is well captured by an elementary rate equation model.

  17. Self-Driven Photodetector and Ambipolar Transistor in Atomically Thin GaTe-MoS2 p-n vdW Heterostructure.

    PubMed

    Yang, Shengxue; Wang, Cong; Ataca, Can; Li, Yan; Chen, Hui; Cai, Hui; Suslu, Aslihan; Grossman, Jeffrey C; Jiang, Chengbao; Liu, Qian; Tongay, Sefaattin

    2016-02-01

    Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS2 p-n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron-hole pairs are readily separated by large built-in potential formed at the GaTe-MoS2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface. PMID:26796869

  18. Self-Driven Photodetector and Ambipolar Transistor in Atomically Thin GaTe-MoS2 p-n vdW Heterostructure.

    PubMed

    Yang, Shengxue; Wang, Cong; Ataca, Can; Li, Yan; Chen, Hui; Cai, Hui; Suslu, Aslihan; Grossman, Jeffrey C; Jiang, Chengbao; Liu, Qian; Tongay, Sefaattin

    2016-02-01

    Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS2 p-n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron-hole pairs are readily separated by large built-in potential formed at the GaTe-MoS2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface.

  19. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

    PubMed

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J C Séamus; Ghigo, Gianluca; Gu, Genda D; Kwok, Wai-Kwong

    2015-05-01

    Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

  20. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

    PubMed

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J C Séamus; Ghigo, Gianluca; Gu, Genda D; Kwok, Wai-Kwong

    2015-05-01

    Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

  1. Rectification and tunneling effects enabled by Al2O3 atomic layer deposited on back contact of CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Liang, Jun; Lin, Qinxian; Li, Hao; Su, Yantao; Yang, Xiaoyang; Wu, Zhongzhen; Zheng, Jiaxin; Wang, Xinwei; Lin, Yuan; Pan, Feng

    2015-07-01

    Atomic layer deposition (ALD) of Aluminum oxide (Al2O3) is employed to optimize the back contact of thin film CdTe solar cells. Al2O3 layers with a thickness of 0.5 nm to 5 nm are tested, and an improved efficiency, up to 12.1%, is found with the 1 nm Al2O3 deposition, compared with the efficiency of 10.7% without Al2O3 modification. The performance improvement stems from the surface modification that optimizes the rectification and tunneling of back contact. The current-voltage analysis indicates that the back contact with 1 nm Al2O3 maintains large tunneling leakage current and improves the filled factor of CdTe cells through the rectification effect. XPS and capacitance-voltage electrical measurement analysis show that the ALD-Al2O3 modification layer features a desired low-density of interface state of 8 × 1010 cm-2 by estimation.

  2. Ultrasound-assisted emulsification solidified floating organic drops microextraction of ultra trace amount of Te (IV) prior to graphite furnace atomic absorption spectrometry determination.

    PubMed

    Fathirad, Fariba; Afzali, Daryoush; Mostafavi, Ali; Ghanbarian, Maryam

    2012-01-15

    In the present study, a new, simple and efficient method for the preconcentration of ultra trace amounts of Te (IV) is developed using ultrasound-assisted emulsification solidified floating organic drops microextraction (USAE-SFODME) before graphite furnace atomic absorption spectrometry determination. In this method, tellurium is extracted into the fine droplets of 1-undecanol after chelate formation with the water soluble ligand, ammonium pyrrolidinedithiocarbamate (APDC). Several factors such as pH, chelating agent amount, type and volume of the extracting solvent, sonication and centrifuging time that influence the extraction and complex formation are optimized. Under the optimum conditions, the calibration graph is linear in the range of 0.01-0.24ngmL(-1) of tellurium in the original solution, with limit of detection of 0.003ngmL(-1). The relative standard deviation (RSD) for seven replicated determinations of tellurium ion at 0.08ngmL(-1) concentration level is calculated as 3.4%. The proposed method was successfully applied to the determination of Te (IV) in a standard soil and several water samples. PMID:22265571

  3. Rectification and tunneling effects enabled by Al{sub 2}O{sub 3} atomic layer deposited on back contact of CdTe solar cells

    SciTech Connect

    Liang, Jun; Lin, Qinxian; Li, Hao; Su, Yantao; Yang, Xiaoyang; Wu, Zhongzhen; Zheng, Jiaxin; Wang, Xinwei; Lin, Yuan; Pan, Feng

    2015-07-06

    Atomic layer deposition (ALD) of Aluminum oxide (Al{sub 2}O{sub 3}) is employed to optimize the back contact of thin film CdTe solar cells. Al{sub 2}O{sub 3} layers with a thickness of 0.5 nm to 5 nm are tested, and an improved efficiency, up to 12.1%, is found with the 1 nm Al{sub 2}O{sub 3} deposition, compared with the efficiency of 10.7% without Al{sub 2}O{sub 3} modification. The performance improvement stems from the surface modification that optimizes the rectification and tunneling of back contact. The current-voltage analysis indicates that the back contact with 1 nm Al{sub 2}O{sub 3} maintains large tunneling leakage current and improves the filled factor of CdTe cells through the rectification effect. XPS and capacitance-voltage electrical measurement analysis show that the ALD-Al{sub 2}O{sub 3} modification layer features a desired low-density of interface state of 8 × 10{sup 10 }cm{sup −2} by estimation.

  4. Ultrasound-assisted emulsification solidified floating organic drops microextraction of ultra trace amount of Te (IV) prior to graphite furnace atomic absorption spectrometry determination.

    PubMed

    Fathirad, Fariba; Afzali, Daryoush; Mostafavi, Ali; Ghanbarian, Maryam

    2012-01-15

    In the present study, a new, simple and efficient method for the preconcentration of ultra trace amounts of Te (IV) is developed using ultrasound-assisted emulsification solidified floating organic drops microextraction (USAE-SFODME) before graphite furnace atomic absorption spectrometry determination. In this method, tellurium is extracted into the fine droplets of 1-undecanol after chelate formation with the water soluble ligand, ammonium pyrrolidinedithiocarbamate (APDC). Several factors such as pH, chelating agent amount, type and volume of the extracting solvent, sonication and centrifuging time that influence the extraction and complex formation are optimized. Under the optimum conditions, the calibration graph is linear in the range of 0.01-0.24ngmL(-1) of tellurium in the original solution, with limit of detection of 0.003ngmL(-1). The relative standard deviation (RSD) for seven replicated determinations of tellurium ion at 0.08ngmL(-1) concentration level is calculated as 3.4%. The proposed method was successfully applied to the determination of Te (IV) in a standard soil and several water samples.

  5. Low power ovonic threshold switching characteristics of thin GeTe6 films using conductive atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Manivannan, Anbarasu; Myana, Santosh Kumar; Miriyala, Kumaraswamy; Sahu, Smriti; Ramadurai, Ranjith

    2014-12-01

    Minimizing the dimensions of the electrode could directly impact the energy-efficient threshold switching and programming characteristics of phase change memory devices. A ˜12-15 nm AFM probe-tip was employed as one of the electrodes for a systematic study of threshold switching of as-deposited amorphous GeTe6 thin films. This configuration enables low power threshold switching with an extremely low steady state current in the on state of 6-8 nA. Analysis of over 48 different probe locations on the sample reveals a stable Ovonic threshold switching behavior at threshold voltage, VTH of 2.4 ± 0.5 V and the off state was retained below a holding voltage, VH of 0.6 ± 0.1 V. All these probe locations exhibit repeatable on-off transitions for more than 175 pulses at each location. Furthermore, by utilizing longer biasing voltages while scanning, a plausible nano-scale control over the phase change behavior from as-deposited amorphous to crystalline phase was studied.

  6. Low power ovonic threshold switching characteristics of thin GeTe{sub 6} films using conductive atomic force microscopy

    SciTech Connect

    Manivannan, Anbarasu E-mail: ranjith@iith.ac.in; Sahu, Smriti; Myana, Santosh Kumar; Miriyala, Kumaraswamy; Ramadurai, Ranjith E-mail: ranjith@iith.ac.in

    2014-12-15

    Minimizing the dimensions of the electrode could directly impact the energy-efficient threshold switching and programming characteristics of phase change memory devices. A ∼12–15 nm AFM probe-tip was employed as one of the electrodes for a systematic study of threshold switching of as-deposited amorphous GeTe{sub 6} thin films. This configuration enables low power threshold switching with an extremely low steady state current in the on state of 6–8 nA. Analysis of over 48 different probe locations on the sample reveals a stable Ovonic threshold switching behavior at threshold voltage, V{sub TH} of 2.4 ± 0.5 V and the off state was retained below a holding voltage, V{sub H} of 0.6 ± 0.1 V. All these probe locations exhibit repeatable on-off transitions for more than 175 pulses at each location. Furthermore, by utilizing longer biasing voltages while scanning, a plausible nano-scale control over the phase change behavior from as-deposited amorphous to crystalline phase was studied.

  7. Influence of copper to indium atomic ratio on the properties of Cu-In-Te based thin-film solar cells prepared by low-temperature co-evaporation

    SciTech Connect

    Mise, Takahiro; Nakada, Tokio

    2012-09-15

    The influence of copper to indium atomic ratio (Cu/In) on the properties of Cu-In-Te based thin films and solar cells was investigated. The films (Cu/In = 0.38-1.17) were grown on both bare and Mo-coated soda-lime glass substrates at 250 Degree-Sign C by single-step co-evaporation using a molecular beam epitaxy system. Highly (112)-oriented CuInTe{sub 2} films were obtained at Cu/In ratios of 0.84-0.99. However, stoichiometric and Cu-rich films showed a poor film structure with high surface roughness. The films consist of polyhedron-shaped grains, which are related to the coexistence of a Cu{sub 2-x}Te phase, and significant evidence for the coexistence of the Cu{sub 2-x}Te phase in the stoichiometric and Cu-rich films is presented. KCN treatment was performed for the films in order to remove the Cu{sub 2-x}Te phase. The stoichiometric CuInTe{sub 2} thin films exhibited a high mobility above 50 cm{sup 2}/V s at room temperature after the KCN treatment. A preliminary solar cell fabricated using a 1.4-{mu}m-thick Cu-poor CuInTe{sub 2} thin film (Cu/In = 0.84, E{sub g} = 0.988 eV) yielded a total-area efficiency of 2.10%. The photovoltaic performance of the cell was improved after long-term ambient aging in dark conditions.

  8. First-principles investigations of the atomic, electronic, and thermoelectric properties of equilibrium and strained Bi2Se3 and Bi2Te3 including van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Luo, Xin; Sullivan, Michael B.; Quek, Su Ying

    2012-11-01

    Bi2Se3 and Bi2Te3 are layered compounds of technological importance, being excellent thermoelectric materials as well as topological insulators. We report density functional theory calculations of the atomic, electronic, and thermoelectric properties of strained bulk and thin-film Bi2Se3 and Bi2Te3, focusing on an appropriate description of van der Waals (vdW) interactions. The calculations show that the van der Waals density functional (vdW-DF) with Cooper's exchange (vdW-DFC09x) can reproduce closely the experimental interlayer distances in unstrained Bi2Se3 and Bi2Te3. Interestingly, we predict atomic structures that are in much better agreement with the experimentally determined structure from Nakajima than that obtained from Wyckoff, especially for Bi2Se3, where the difference in atomic structures qualitatively changes the electronic band structure. The band structure obtained using the Nakajima structure and the vdW-DFC09x optimized structure are in much better agreement with previous reports of photoemission measurements, than that obtained using the Wyckoff structure. Using vdW-DFC09x to fully optimize atomic structures of bulk and thin-film Bi2Se3 and Bi2Te3 under different in-plane and uniaxial strains, we predict that the electronic bandgap of both the bulk materials and thin films decreases with tensile in-plane strain and increases with compressive in-plane strain. We also predict, using the semiclassical Boltzmann approach, that the magnitude of the n-type Seebeck coefficient of Bi2Te3 can be increased by the compressive in-plane strain while that of Bi2Se3 can be increased with tensile in-plane strain. Further, the in-plane power factor of n-doped Bi2Se3 can be increased with compressive uniaxial strain while that of n-doped Bi2Te3 can be increased by compressive in-plane strain. Strain engineering thus provides a direct method to control the electronic and thermoelectric properties in these thermoelectric topological insulator materials.

  9. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3.

    PubMed

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J L; Zhong, Ruidan; Schneeloch, John A; Liu, Tiansheng; Valla, Tonica; Tranquada, John M; Gu, Genda; Davis, J C Séamus

    2015-02-01

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a "Dirac-mass gap" in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship [Formula: see text] is confirmed throughout and exhibits an electron-dopant interaction energy J* = 145 meV·nm(2). These observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  10. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    PubMed Central

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  11. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-05-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers.

  12. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films.

    PubMed

    Bouška, M; Pechev, S; Simon, Q; Boidin, R; Nazabal, V; Gutwirth, J; Baudet, E; Němec, P

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  13. Quantum phase transition in Fe1 +x(Te,Se) induced by Single-atomic Impurities studied by STM/S

    NASA Astrophysics Data System (ADS)

    Yin, J. X.; Wu, Zheng; Huang, Xiong; Ye, Z. Y.; Wu, Rui; Liang, X. J.; Mao, H. Q.; Li, Jian; Ting, C.-S.; Hu, J. P.; Wang, Z. Q.; Hor, P.-H.; Ding, Hong; Pan, S. H.

    Previously we discovered a robust zero-energy bound state at an interstitial Fe impurity (IFIs) in Fe1 +x(Te,Se), which resembles the Majorana mode (Nature Physics 11, 543, (2015)). Here we report our comprehensive study, using scanning tunneling microscopy/spectroscopy technique, of the global effect of IFIs on the ground state of Fe1 +x(Te,Se) over a wide range of IFI concentration x. Our high resolution tunneling spectroscopy and quasi-particle interference data at very low temperature demonstrate that IFIs do not affect the electron pairing strength, while they cause significant dephasing effect, which eventually drives the ground state of the system from strong-coupling-superconductivity to diffusive-Bose-metal.

  14. ATOMIC AND MOLECULAR PHYSICS: Synthesizing Metastable Rocksalt-Type MgTe Based on High-Pressure Solid-State Phase Transition: A First-Principles Study

    NASA Astrophysics Data System (ADS)

    Cai, Ying-Xiang; Xu, Rui

    2009-11-01

    The controllability of pressure-induced structural transformation in the hexagonal wurtzite-type MgTe is studied by a first-principles pseudopotential method within the generalized gradient approximation (GGA). Based on the transitional mechanisms of the wurtzite→—NiAs and the wurtzite→—rocksalt, a special method of loading biaxial pressure on the (010) and (001) planes of an orthorhombic cell is designed. At equal biaxial pressure of 2.75 GPa, an abrupt volume collapse is found and the WZ phase transforms into an orthorhombic phase with a tiny distortion. While the pressure decreases to zero, three lattice parameters a, b and c become equal and a metastable rocksalt-type MgTe is obtained.

  15. Determination of the surface atomic geometry of PbTe(100) by dynamical low-energy electron-diffraction intensity analysis

    NASA Astrophysics Data System (ADS)

    Lazarides, A. A.; Duke, C. B.; Paton, A.; Kahn, A.

    1995-11-01

    Contrary to expectations based on results for other cubic binary semiconductors, an analysis of surface Pb core-level shifts from rocksalt structure PbS(100) suggests large top-layer contractions for group-IV A element chalcogenides. To examine this possibility, we performed a surface-structure analysis for PbTe(100) using eight beams of low-energy electrons diffracted from PbTe(100) at 50 K. A dynamical analysis of the intensities of these beams, based on relativistic potentials shown to be accurate for fifth-row elements, leads to the conclusion that the Pb sublattice in the outer layer is relaxed into the bulk by 0.22 Å (7%) relative to the outer-layer Te sublattice. The average spacing between the first and second layers is 4% smaller than the bulk interlayer spacing, while the average second-to-third-layer spacing is expanded 2% relative to the bulk spacing. Our results are analogous to those found for the (100) surfaces of other cubic materials. A covariance analysis of parameter estimation error indicates that the relaxation detected by the normal-incidence low-energy electron-diffraction experiment is statistically significant, i.e., the deviations of the three surface-structure parameters from the corresponding bulk-structure values are many times larger than the parameter estimation error levels associated with errors in the measured intensities. Moreover, deviations from the bulk structure of the top two layers alone suffice to describe the measurements. Surface-structure optimization that allowed two additional structural parameters (second-layer rumple and third-to-fourth interlayer spacing) to vary yielded a structure insignificantly different from that produced by the three-variable-parameter optimization.

  16. Local Distortions in PbTe:Tl

    NASA Astrophysics Data System (ADS)

    Keiber, Trevor; Bridges, Frank; Sales, Brian

    2013-03-01

    Lead Telluride (PbTe) is a well characterized thermoelectric material. Tl doping increases the figure of merit with a maximum at 2% Tl. Recent X-ray diffraction and total neutron scattering experiments suggest Pb moves off-center along the 100 axis as T increases. To investigate the local structure we present an Extended X-ray Absorption Fine Structure (EXAFS) analysis for 0-3% Tl concentrations at the Tl and Pb L3 edges and at the Te K edge. At 10K the local structure about Pb is well ordered, the Pb-Te (Te-Pb) pair distribution function (PDF) broadens rapidly with T. Attempts to model the increase in σ2(T) for the Pb-Te pair (σ is the width of the PDF) with a 100 Pb off-center displacement, were not successful. However σ2(T) for the Pb-Te pair is well described by a correlated Debye model with a low correlated Debye temperature. The Te edge shows increased disorder for the the Te-Te pair and later peaks which may be caused by a structural change around the Te atom. For Tl, the environment is distorted even at 10K within the host material. This indicates a large variation of the Tl-Te bond lengths, presumably as a result of the presence of Tl(+1). We discuss possible models for the disorder about Tl, Pb, and Te in PbTe:Tl. Support: NSF DMR 1005568

  17. Evidences of the existence of SiTe2 crystalline phase and a proposed new Si-Te phase diagram

    NASA Astrophysics Data System (ADS)

    Mishra, R.; Mishra, P. K.; Phapale, S.; Babu, P. D.; Sastry, P. U.; Ravikumar, G.; Yadav, A. K.

    2016-05-01

    The existence of two distinct crystalline phases viz., Si2Te3 and SiTe2, in the Si-Te system is established from differential thermal analysis (DTA) studies. Thermo-gravimetric (TG) data on SiTe2 indicate that the compound decomposes to Si in multiple steps via intermediate Si2Te3 phase. X-ray diffraction (XRD) reveals that SiTe2 crystallizes in P 3 ̅m1 space group with CdI2 trigonal structure, whereas Si2Te3 crystallizes in trigonal structure with space group P 3 ̅1c with varying occupation of octahedral voids. Single Si atoms fill only 1/2 of the octahedral voids in SiTe2 structure whereas in Si2Te3, Si atoms are arranged in pairs occupying 2/3 of the octahedral voids in alternating planes along c-axis. Further, X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) confirm the distinctness of the chemical environment in the two crystalline structures confirming the uniqueness of both the phases. DTA results on the two compounds indicate the presence of one crystallographic phase-transition in each of the compound with transition temperatures at 441 °C for Si2Te3 and 392 °C for SiTe2. At the same time both Si2Te3 and SiTe2 undergo peritectic decomposition at 683 °C and 432 °C forming [Si(s)+Te(liq)] and [α-Si2Te3(s)+Te(liq)], respectively. The system revealed eutectic reaction between β-SiTe2 and Te at 398 °C [L=Te+SiTe2]. Consequently, the phase diagram in the Si-Te system has been delineated.

  18. Effective atomic number, energy loss and radiation damage studies in some materials commonly used in nuclear applications for heavy charged particles such as H, C, Mg, Fe, Te, Pb and U

    NASA Astrophysics Data System (ADS)

    Kurudirek, Murat

    2016-05-01

    Commonly used nuclear physics materials such as water, concrete, Pb-glass, paraffin, freon and P 10 gases, some alloys such as brass, bronze, stainless-steel and some scintillators such as anthracene, stilbene and toluene have been investigated with respect to the heavy charged particle interaction as means of projected range and effective atomic number (Zeff) in the energy region 10 keV to 10 MeV. Calculations were performed for heavy ions such as H, C, Mg, Fe, Te, Pb and U. Also, the energy loss and radiation damage were studied using SRIM Monte Carlo code for anthracene for different heavy ions of 100 keV kinetic energy. It has been observed that the variation in Zeff becomes less when the atomic number of the ions increase. Glass-Pb, bronze, brass, stainless-steel and Freon gas were found to vary less than 10% in the energy region 10 keV to 10 MeV. For total proton interaction, discrepancies up to 10% and 18% between two databases namely PSTAR and SRIM were noted in mass stopping power and Zeff of water, respectively. The range calculations resulted with a conclusion that the metal alloys and glass-Pb have lowest values of ranges confirming best shielding against energetic heavy ions whereas freon and P 10 gases have the highest values of ranges in the entire energy region. The simulation results showed that the energy loss (%) to target electrons decreases as the Z of the incident ion increases. Also, it was observed that the radiation damage first increases with Z of the ion and then keeps almost constant for ions with Z≥52.

  19. Molecular beam epitaxial re-growth of CdTe, CdTe/CdMgTe and CdTe/CdZnTe double heterostructures on CdTe/InSb(1 0 0) substrates with As cap

    NASA Astrophysics Data System (ADS)

    Seyedmohammadi, Shahram; DiNezza, Michael J.; Liu, Shi; King, Paul; LeBlanc, Elizabeth G.; Zhao, Xin-Hao; Campbell, Calli; Myers, Thomas H.; Zhang, Yong-Hong; Malik, Roger J.

    2015-09-01

    Molecular beam epitaxial growth on CdTe substrates is challenging since the CdTe film crystalline and optical quality is limited by residual defects including threading dislocations and stacking faults. This remains an obstacle in spite of exhausting variables including pre-growth substrate preparation as well as epitaxial growth conditions including thermal oxide desorption, growth temperature, and II/VI flux ratios. We propose a new technique to re-grow structures with low defect densities and high optical and structural quality on InSb substrates. The "CdTe virtual wafer" is made by growing a thin CdTe film on an InSb(1 0 0) substrate which is then covered with a thin As cap layer to prevent oxidation of the CdTe surface. The As cap can be removed by thermal desorption at about 300 C leaving a clean CdTe surface for subsequent epitaxial growth. This method eliminates the need for chemical etching of CdTe substrates which has been found to lead to an atomically rough surface with residual Carbon and Oxygen contamination. XRD and SEM characterization show a smooth transition from the buffer CdTe to re-grown CdTe layer with identical crystalline quality as for virtual wafer. Steady-state PL and time-resolved PL from CdTe/CdMgTe double heterostructures show substantial improvement in luminescence intensity and carrier lifetime comparable to values for identical samples grown without exposure to atmosphere. We will also report on CdTe/CdZnTe double heterostructures grown on virtual wafers compared to identical structures on conventional CdTe(2 1 1)B substrates.

  20. Pb(3)Te(2)O(6)Br(2).

    PubMed

    Weil, Matthias; Stöger, Berthold

    2010-01-16

    Single crystals of the title compound, trilead(II) bis-[tellurate(IV)] dibromide, have been grown under hydro-thermal conditions. The structure is isotypic with that of the chloride analogue, Pb(3)Te(2)O(6)Cl(2), and consists of three Pb, two Te, two Br and four O atoms in the asymmetric unit. Except for two of the O atoms, all atoms are located on mirror planes. The Pb(3)Te(2)O(6)Br(2) structure can be described as being built up from (∞) (2)[Pb(3)Te(2)O(6)](2+) layers extending parallel to (20) and Br(-) anions between the layers. Cohesion of the structure is accomplished through Pb-Br contacts of two of the three lead atoms, leading to highly asymmetric coordination polyhedra. The lone-pair electrons of both Te(IV) and Pb(II) atoms are stereochemically active and point towards the anionic halide layers.

  1. Revised values of the bond-valence parameters for Te(IV)-O, Te(VI)-O and Te(IV)-Cl.

    PubMed

    Mills, Stuart J; Christy, Andrew G

    2013-04-01

    Bond-valence parameters r0 and b have been re-determined for Te(IV)-O: r0 = 1.9605 Å, b = 0.41; Te(VI)-O: r0 = 1.921 Å, b = 0.56; and Te(IV)-Cl: r0 = 2.3115 Å, b = 0.555. Bond distance data from 208 independent Te(IV)-O polyhedra, 118 Te(VI)-O polyhedra and 26 Te(IV)-Cl polyhedra were used, and all neighbours out to 3.5 Å were included. Root-mean square deviations of bond-valence sums on Te from ideal values were 0.1934, 0.1939 and 0.0865 v.u. The good fit for Te(IV)-O over a range of Te coordination numbers from 3 to 12 demonstrates that there is no essential difference in character between short `primary' Te-O bonds, oriented away from the Te lone pair, and longer `secondary' Te-O bonds on the same side of the Te atom as the lone pair. Comparison of bond-valence sums for Te-O polyhedra obtained using the new parameters with those calculated using earlier literature values shows that the new parameters give a narrower spread of calculated bond-valence sums, which means much closer to the formal valence for both oxidation states of tellurium.

  2. Thermoelectric properties of p-type PbTe/Ag{sub 2}Te bulk composites by extrinsic phase mixing

    SciTech Connect

    Lee, Min Ho; Rhyee, Jong-Soo

    2015-12-15

    We investigated the thermoelectric properties of PbTe/Ag{sub 2}Te bulk composites, synthesized by hand milling, mixing, and hot press sintering. From x-ray diffraction and energy dispersive x-ray spectroscopy measurements, we observed Ag{sub 2}Te phase separation in the PbTe matrix without Ag atom diffusion. In comparison with previously reported pseudo-binary (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} composites, synthesized by high temperature phase separation, the PbTe/Ag{sub 2}Te bulk composites fabricated with a low temperature phase mixing process give rise to p-type conduction of carriers with significantly decreased electrical conductivity. This indicates that Ag atom diffusion in the PbTe matrix changes the sign of the Seebeck coefficient to n-type and also increases the carrier concentration. Effective p-type doping with low temperature phase separation by mixing and hot press sintering can enhance the thermoelectric performance of PbTe/Ag{sub 2}Te bulk composites, which can be used as a p-type counterpart of n-type (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} bulk composites.

  3. Analysis of Etched CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Arias, J. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Jones, K.; Johnson, S. M.; Lofgreen, D. D.

    2016-09-01

    State-of-the-art as-received (112)B CdZnTe substrates have been examined for surface impurity contamination and polishing residue. Two 4 cm × 4 cm and one 6 cm × 6 cm (112)B state-of-the-art as-received CdZnTe wafers were analyzed. A maximum surface impurity concentration of Al = 1.7 × 1015 atoms cm-2, Si = 3.7 × 1013 atoms cm-2, Cl = 3.12 × 1015 atoms cm-2, S = 1.7 × 1014 atoms cm-2, P = 1.1 × 1014 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 1.2 × 1014 atoms cm-2, and Cu = 4 × 1012 atoms cm-2 was observed on the as-received CdZnTe wafers. CdZnTe particulates and residual SiO2 polishing grit were observed on the surface of the as-received (112)B CdZnTe substrates. The polishing grit/CdZnTe particulate density on CdZnTe wafers was observed to vary across a 6 cm × 6 cm wafer from ˜4 × 107 cm-2 to 2.5 × 108 cm-2. The surface impurity and damage layer of the (112)B CdZnTe wafers dictate that a molecular beam epitaxy (MBE) preparation etch is required. The contamination for one 4 cm × 4 cm and one 6 cm × 6 cm CdZnTe wafer after a standard MBE Br:methanol preparation etch procedure was also analyzed. A maximum surface impurity concentration of Al = 2.4 × 1015 atoms cm-2, Si = 4.0 × 1013 atoms cm-2, Cl = 7.5 × 1013 atoms cm-2, S = 4.4 × 1013 atoms cm-2, P = 9.8 × 1013 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 2.9 × 1014 atoms cm-2, and Cu = 5.2 × 1012 atoms cm-2 was observed on the MBE preparation-etched CdZnTe wafers. The MBE preparation-etched surface contamination consists of Cd(Zn)Te particles/flakes. No residual SiO2 polishing grit was observed on the (112)B surface.

  4. The phase evolution mechanism in Fe(Se, Te) system

    NASA Astrophysics Data System (ADS)

    Liu, Jixing; Li, Chengshan; Zhang, Shengnan; Feng, Jianqing; Zhang, Pingxiang; Zhou, Lian

    2016-08-01

    The phase evolution mechanism in Fe(Se, Te) system during sintering was investigated with step-by-step heat treatment process. It was noticed that the diffusion processes between Fe and Se (Te) as well as that between Se and Te were both very important to the formation of superconducting Fe(Se, Te) phase with very uniform chemical composition. During heat treatment, solid solutions of (Se, Te)ss with different chemical composition were formed with the diffusion of Se atoms into Te solids and Te atoms into Se melts, simultaneously. Then with the increasing temperature, Fe atoms diffused into (Se, Te)ss, Fe(Se, Te)2 and Fe(Se, Te) phases were formed in sequence with the increasing Fe content. The chemical composition in melts became more and more uniform with the further increasing of sintering temperature and dwell time. Therefore, it was suggested that in order to achieve Fe(Se, Te) phase with high superconducting properties, it was necessary to enhance the diffusion process during sintering. The critical temperature of the sample, which was sintered at 700 °C for 12 h with slow cooling process and an O2-annealing process for 24 h, was above 14.0 K. This Tc value proved that a good superconducting β phase could be obtained under this sintering condition.

  5. Novel Surface Structure of Te/Ge(001)

    NASA Astrophysics Data System (ADS)

    Sakata, O.; Walko, D. A.; Tinkham, B. P.; Bedzyk, M. J.

    2000-03-01

    Structures formed by the adsorption of Te on Ge(001) have been studied by the complementary techniques of surface x-ray diffraction (SXRD), x-ray standing waves (XSW), LEED, and AES. Two structures with qualititatively different LEED patterns, corresponding to high- and low-coverage states, are found by annealing to different temperatures. While Te atoms in the high-coverage (1×1) phase adsorb at the expected bridge sites, the low-coverage c(2×2) phase, with 0.5 ML Te, is marked by Te-Ge heterodimers. Previous XSW analysis the (004) and (022) reflections precisely located the well-ordered Te atoms, with a significant height difference of 0.07 Å between the two structures [P.F. Lyman et al., Phys. Rev. B 60, 8704 (1999)]. SXRD was used to characterize the geometry of the heterodimer and investigate the strain-induced multilayer relaxations of the subsurface Ge atoms.

  6. {CdTe(111) B}/{Si(100) } structure grown by metalorganic vapor phase epitaxy with Te adsorption and annealing

    NASA Astrophysics Data System (ADS)

    Nishino, Hironori; Nishijima, Yoshito

    1996-10-01

    We studied the crystal structure of CdTe(111)B layers directly grown on Si(100) by MOVPE using a new pre-growth process, which includes a metalorganic Te adsorption and an annealing process. In this paper, we discussed the CdTe structure from the three aspects of antiphase, twinning and tilt. We investigated the dependence of the antiphase content in CdTe(111)B on the anneal temperature and the Si misorientation angle. From the results, we assume that the origin of the antiphase formation is the difference in the arrangement of adsorbed Te atoms. Te arrangement leading to antiphase formation occurs on Si terraces away from steps at relatively low temperatures. We reduced most of the twinning in epilayers by optimizing the {VI}/{II} ratio. We think the remaining twinning was confined to near the interface and it nucleated from the Te arrangement on terraces. We found that the Si(100)-CdTe(111) tilt was much smaller than that expected from the well-known Nagai model. We propose that a negative tilt is induced to reduce the lateral mismatch. To adjust the lateral distance of unit cells, 30 CdTe lattices match to 31 Si lattices. CdTe(111)B planes are inclined to reduce the remaining mismatch between two lattices. This initial tilt also causes wider CdTe terraces. We modified Nagai's tilting model for this reconstructed CdTe surface. The total tilt angle is defined by these two tilting mechanisms.

  7. Real space probe of short-range interaction between Cr in a ferromagnetic semiconductor ZnCrTe.

    PubMed

    Kanazawa, Ken; Nishimura, Taku; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

    2014-12-21

    The short-range interaction between Cr atoms was directly examined by scanning tunneling microscopy measurements on a Zn(0.95)Cr(0.05)Te film. Our measurements revealed that a Cr atom formed a localized state within the bandgap of ZnTe and this state was broadened for a pair of Cr atoms within a distance of ∼ 1 nm.

  8. Finite temperature studies of Te adsorption on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Sen, Prasenjit; Ciraci, S.; Batra, Inder P.; Grein, C. H.; Sivananthan, S.

    2002-11-01

    We perform first principles density functional calculations to investigate the adsorption of Te on the Si(0 0 1) surface from low coverage up to a monolayer coverage. At low coverage, a Te atom is adsorbed on top of the Si surface dimer bond. At higher coverages, Te atoms adsorption causes the Si-Si dimer bond to break, lifting the (2×1) reconstruction. We find no evidence of the Te-Te dimer bond formation as a possible source of the (2×1) reconstruction at a monolayer coverage. Finite temperature ab initio molecular dynamics calculations show that Te covered Si(0 0 1) surfaces do not have any definitive reconstruction. Vibrations of the bridged Te atoms in the strongly anharmonic potentials prevent the reconstruction structure from attaining any permanent, two-dimensional periodic geometry. This explains why experiments attempting to find a definite model for the reconstruction reached conflicting conclusions.

  9. Ferroelectric switching in epitaxial GeTe films

    SciTech Connect

    Kolobov, A. V. Fons, P.; Tominaga, J.; Kim, D. J.; Gruverman, A.; Giussani, A.; Calarco, R.

    2014-06-01

    In this paper, using a resonance-enhanced piezoresponse force microscopy approach supported by density functional theory computer simulations, we have demonstrated the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with thickness on the order of several nanometers reversible reorientation of polarization occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the material. It is also hinted that for ultra thin films consisting of just several atomic layers weakly bonded to the substrate, ferroelectric switching may proceed through exchange of Ge and Te planes within individual GeTe layers.

  10. Substitutionality of Te- and Sn-related DX centers in AlxGa1-xAs

    NASA Astrophysics Data System (ADS)

    Yu, Kin Man; Khachaturyan, Ken; Weber, Eicke R.; Lee, Henry P.; Kolas, Etienne G.

    1991-01-01

    The lattice locations of Te and Sn atoms forming DX centers in AlxGa1-xAs were determined by particle-induced x-ray emission and ion-beam-channeling methods. The Te atoms were found to be in the As substitutional sites while the Sn atoms were in the Ga(Al) sites. No off-center displacement of Te and Sn larger than 0.14 Å from the substitutional sites was observed in either system.

  11. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3

    DOE PAGESBeta

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J. L.; Zhong, Ruidan D.; Schneeloch, John A.; Liu, Tiansheng S.; Valla, Tonica; Tranquada, John M.; Gu, Genda D.; et al

    2015-01-20

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a “Dirac-mass gap” in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in themore » ferromagnetic TI Cr₀.₀₈(Bi₀.₁Sb₀.₉)₁.₉₂Te₃. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm². In addition, these observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.« less

  12. Study of the initial stages of growth of CdTe on (001)GaAs

    NASA Astrophysics Data System (ADS)

    Mar, H. A.; Salansky, N.; Chee, K. T.

    1984-05-01

    The initial stages of growth of CdTe on (001) GaAs have been studied using Auger electron spectroscopy and reflection high-energy electron techniques. At the growth temperature of 225 °C tellurium atoms are observed to be adsorbed to a thickness of one to two monolayers on a thermally cleaned GaAs substrate. However, cadmium atoms are adsorbed only when tellurium atoms are present. An analysis of the Auger electron spectra and the reflection high-energy electron diffraction patterns taken at intervals during the initial growth of CdTe films from a CdTe compound source indicates that growth takes place first by the deposition of one to two monolayers of tellurium. This is followed by the nucleation and growth of CdTe crystallites which increase in size and coalesce to form a single crystal of CdTe with a (111) CdTe ∥ (001) GaAs orientation.

  13. Role of missing rows in the adsorption of Te on Si(001)

    NASA Astrophysics Data System (ADS)

    Takeuchi, Noboru

    1999-08-01

    We have studied the atomic structure of up to one monolayer of Te on Si(001) using first-principles total-energy calculations. A low amount of Te atoms deposited on Si(001) is adsorbed on top of symmetric Si dimers. This configuration is preferred to adsorption on cave sites between Si dimers. For the one-monolayer coverage the most favorable structure corresponds to adsorption of Te atoms on near bridge sites. The (1×1) symmetry is broken by a small shift of Te atoms from perfect bridge positions, giving rise to a slightly disordered surface. This is a way to relieve the strain due to the size difference between Te and Si atoms. Missing Te rows is another way, and it is the one observed experimentally. We have calculated the atomic structure of the surface when one out of every five Te rows is missing. Two possibilities were examined. The most favorable corresponds to missing Te rows orthogonal to original Si rows. In all cases, our results are in good agreement with experimental data.

  14. Reverse Monte Carlo simulation of Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} glasses

    SciTech Connect

    Abdel-Baset, A. M.; Rashad, M.; Moharram, A. H.

    2013-12-16

    Two-dimensional Monte Carlo of the total pair distribution functions g(r) is determined for Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} alloys, and then it used to assemble the three-dimensional atomic configurations using the reverse Monte Carlo simulation. The partial pair distribution functions g{sub ij}(r) indicate that the basic structure unit in the Se{sub 80}Te{sub 15}Sb{sub 5} glass is di-antimony tri-selenide units connected together through Se-Se and Se-Te chain. The structure of Se{sub 80}Te{sub 20} alloys is a chain of Se-Te and Se-Se in addition to some rings of Se atoms.

  15. Theoretical study of intrinsic defects in CdTe

    NASA Astrophysics Data System (ADS)

    Menéndez-Proupin, E.; Orellana, W.

    2016-05-01

    The quantum states and thermodynamical properties of the Cd and Te vacancies in CdTe are studied by first principles calculations. It is shown that the band structure of a cubic 64-atoms supercell with a Te vacancy is dramatically different from the band structure of the perfect crystal, suggesting that it cannot be used as model to calculate isolated defects. This flaw is solved modeling the Te vacancy within a cubic 216-atoms supercell. However, even with this large supercell, the 2— charge state relaxes to an incorrect distorted structure. This distortion is driven by partial filling of the conduction band induced by the k-point sampling. The correct structures and formation energies are obtained by relaxation with restriction of system symmetry, followed by band-filling correction to the energy, or by using a larger supercell that allows sampling the Brillouin zone with a single k-point.

  16. Microstructural Investigation of SexTe100-x Thin Films Deposited on Si(100) Substrates by X-ray Diffractometer and Transmission Electron Microscopy Analysis

    NASA Astrophysics Data System (ADS)

    Kim, Eun Tae; Lee, Jeong Yong; Kim, Yong Tae

    2007-11-01

    The microstructural properties of SexTe100-x (x=16,29,38) thin films are investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. SexTe100-x thin films have a Te hexagonal structure and Te{011} interplanar spacing decreases because some Se atoms occupy Te atomic sites, forming Se helical chains within the Te helical chains. By increasing the Se contents from 16 to 29 at. %, Se5.95Te1.05 monoclinic and Se hexagonal structures coexist in a grain and at 38 at. %, a Se hexagonal structure is observed within the Te hexagonal grain. This means that SexTe100-x thin films maintain the Te hexagonal structure and that phase separation does not occur owing to the short diffusion time.

  17. APT mass spectrometry and SEM data for CdTe solar cells

    DOE PAGESBeta

    Li, Chen; Paudel, Naba R.; Yan, Yanfa; Pennycook, Stephen J.; Poplawsky, Jonathan D.; Guo, Wei

    2016-03-16

    Atom probe tomography (APT) data acquired from a CAMECA LEAP 4000 XHR for the CdS/CdTe interface for a non-CdCl2 treated CdTe solar cell as well as the mass spectrum of an APT data set including a GB in a CdCl2-treated CdTe solar cell are presented. Scanning electron microscopy (SEM) data showing the evolution of sample preparation for APT and scanning transmission electron microscopy (STEM) electron beam induced current (EBIC) are also presented. As a result, these data show mass spectrometry peak decomposition of Cu and Te within an APT dataset, the CdS/CdTe interface of an untreated CdTe solar cell, preparationmore » of APT needles from the CdS/CdTe interface in superstrate grown CdTe solar cells, and the preparation of a cross-sectional STEM EBIC sample.« less

  18. Atomic Disorder in Tetrahedrite

    NASA Astrophysics Data System (ADS)

    Salasin, John Robert; Chakoumakos, Bryan; Rawn, Claudia; May, Andrew; Lara-Curzio, Edgar; McGuire, Michael; Cao, Huibo

    2015-03-01

    Thermoelectrics (TE) are materials which turn heat energy into electrical energy with applications spanning multiple disciplines including space exploration, Peltier cooling, and engine efficiency. Tetrahedrite is a copper sulfosalt with the general formula Cu12-xMx(Sb,As)4S13. Where M denotes a Cu2+ site frequently replaced in natural tetrahedrite with Zn, Fe, Hg, or Mn. It has a cubic structure with an I-43m symmetry, a = 10.4 Å, and only a handful of adjustable parameters. This structural study corroborates theoretical calculations on atomic disorder. Positional disorder of the trigonally coordinated Cu(2) site is suggested from the temperature dependence of the atomic displacement parameters determine from single-crystal x-ray and neutron diffraction. The displacements are extremely anisotropic for Cu(2) with a maximum rms static displacement of ~ 0.25 Å.

  19. Exploration of GaTe for Gamma Detectors

    SciTech Connect

    Conway, A M; Reinhardt, C E; Nikolic, R J; Nelson, A J; Wang, T F; Wu, K J; Payne, S A; Mertiri, A; Pabst, G; Roy, R; Mandal, K C; Bhattacharya, P; Cui, Y; Groza, M; Burger, A

    2007-11-16

    The layered III-VI semiconductor Gallium Telluride has potential for room temperature gamma ray spectroscopy applications due to its band gap of 1.67 eV, and average atomic number of 45:31 (Ga) and 52 (Te). The physical properties of GaTe are highly anisotropic due to covalent bonding within the layer and van der Waals bonding between layers. This work reports the results of surface and bulk processing, surface characterization, and electrical characterization of diodes formed on both the laminar and non-laminar GaTe surfaces. Alpha detection measurements were also performed.

  20. Coexistence of optically active radial and axial CdTe insertions in single ZnTe nanowire.

    PubMed

    Wojnar, P; Płachta, J; Zaleszczyk, W; Kret, S; Sanchez, Ana M; Rudniewski, R; Raczkowska, K; Szymura, M; Karczewski, G; Baczewski, L T; Pietruczik, A; Wojtowicz, T; Kossut, J

    2016-03-14

    We report on the growth, cathodoluminescence and micro-photoluminescence of individual radial and axial CdTe insertions in ZnTe nanowires. In particular, the cathodoluminescence technique is used to determine the position of each emitting object inside the nanowire. It is demonstrated that depending on the CdTe deposition temperature, one can obtain an emission either from axial CdTe insertions only, or from both, radial and axial heterostructures, simultaneously. At 350 °C CdTe grows only axially, whereas at 310 °C and 290 °C, there is also significant deposition on the nanowire sidewalls resulting in radial core/shell heterostructures. The presence of Cd atoms on the sidewalls is confirmed by energy dispersive X-ray spectroscopy. Micro-photoluminescence study reveals a strong linear polarization of the emission from both types of heterostructures in the direction along the nanowire axis.

  1. Thermoelectric properties of Tl-doped PbTeSe crystals grown by directional solidification

    NASA Astrophysics Data System (ADS)

    Su, Ching-Hua

    2016-04-01

    Three Tl-doped PbTe and two Tl-doped PbTeSe crystals were grown by vertical un-seeded directional solidification method. Among them, two Tl-doped PbTe ingots, with starting composition of (Pb0.99Tl0.01)Te, were grown under Pb or Te pressure over the melt provided by a Pb or Te reservoir, respectively, whereas another ingot, with starting composition of (Pb0.98Tl0.02)Te, was grown under Te overpressure. Two Tl-doped PbTeSe crystals, with starting composition of (Pb0.98Tl0.02)(Te0.85Se0.15) and (Pb0.96Tl0.04)(Te0.85Se0.15), were grown without any over-pressure. Disk-shaped samples were sliced at different locations along the growth axis and their thermal conductivities were determined from thermal diffusivity, density, and heat capacity measurements. The electrical conductivity and Seebeck coefficient were simultaneously measured as a function of temperature for each disk sample. The Figure of Merit for the thermoelectric application, zT, was calculated from these properties from room temperature to about 640 °C. The Tl-doped PbTeSe samples have the highest zT value of 1.63 at temperature range of 425 to 475 °C, comparing to 1.13 at 410 °C for the Tl-doped PbTe samples. By substituting 15% of the Te atoms in the Tl-doped PbTe by Se atoms, the Figure of Merit of PbTeSe was enhanced by reducing the thermal conductivity about 26% and, at the same time, increasing the electrical conductivity by 43%.

  2. Chemical-state-resolved x-ray standing-wave analysis of Te-adsorbed GaAs(001)-(2×1) surface

    NASA Astrophysics Data System (ADS)

    Sugiyama, Munehiro; Maeyama, Satoshi

    1998-03-01

    A Te-adsorbed GaAs(001)-(2×1) surface is studied by back-reflection x-ray standing-wave analysis, and average position of adsorbed Te atoms on GaAs(001) is found to be close to the As atomic site and bond with Ga atoms. Chemical-state-resolved x-ray standing-wave analysis using chemical shift in Te 3d5/2 core-level photoelectron spectra suggest that Te atoms in two different chemical states correspond to two different distributions. Te atoms in a lower binding-energy chemical state are found to be in higher atomic positions and to be less ordered, whereas those in a higher binding-energy chemical state are found to be in lower atomic position and are highly ordered.

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

    NASA Astrophysics Data System (ADS)

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

    1996-03-01

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

  4. Atomic polarizabilities

    SciTech Connect

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  5. Dynamic and static behaviors of N-Z-N σ(3c-4e) (Z = S, Se, and Te) interactions: atoms-in-molecules dual functional analysis with high-resolution X-ray diffraction determination of electron densities for 2-(2-pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine.

    PubMed

    Nakanishi, Waro; Hayashi, Satoko; Pitak, Mateusz B; Hursthouse, Michael B; Coles, Simon J

    2011-10-27

    The structure of 2-(2-pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine (NSN) indicates that the molecule has a planar geometry with a linear N···S···N linkage, creating a tetracyclic structure of the formal C(2v) symmetry. To clarify the nature of the NSN σ(3c-4e) bonding, together with the related NSeN and NTeN, the dynamic and static behaviors are investigated by applying atoms-in-molecules (AIM) dual functional analysis to both the fully optimized and perturbed structures. The structures were optimized computationally, retaining C(2v) symmetry. All bond critical points are detected as expected and exhibited on both sides of the N···Z···N moiety which supports the formation of NZN σ(3c-4e). It is confirmed that N···S···N is of the covalent nature close to Me(2)S(+)-∗-Cl or Me(2)Se(+)-∗-Br, whereas N···Se···N and N···Te···N have the (regular) CS nature close to the CT adducts of Me(2)S(-∗-Cl)(2) (TBP) and Me(2)Se-∗-Br(2) (MC), respectively. An experimental high-resolution charge density determination has been performed on NSN, which thoroughly supports the theoretical results. Very similar results are obtained in the analogous pyrimidyl derivatives for N···S···N, N···Se···N, and N···Te···N. AIM dual functional analysis, as validated by experimental high-resolution charge densities, is thus confirmed to be an excellent method to elucidate the nature of these interactions.

  6. Strain-engineered diffusive atomic switching in two-dimensional crystals

    NASA Astrophysics Data System (ADS)

    Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

    2016-06-01

    Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3-GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3-GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways.

  7. Thermoelectric properties of Nb3SbxTe7-x compounds

    NASA Technical Reports Server (NTRS)

    Snyder, J.; Wang, S.; Caillat, T.

    2002-01-01

    Niobium antimony telluride, Nb3Sbx,Te7-x, was synthesized and tested for thermoelectric properties in the Thermoelectrics group at the Jet Propulsion Laboratory. The forty atoms per unit cell of Nb3Sb2Te5 and its varied mixture of atoms yield acomplicated structure, suggesting that Nb3Sb2Te5 and related compounds may exhibit low thermal conductivity and hence a higher ZT value. Nb3SbxTe7-x, compounds were synthesized and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate that Nb3Sb2Te5 is a heavily doped semiconductor whose thermoelectric properties are compromised by compensating n-type and p-type carriers. Attempts to dope in favor of either carrier by varying the Sb:Te ratio yielded samples containing secondary metallic phases that dominated the transport properties of the resulting compounds.

  8. Te-defect interaction in GaSb: donor-vacancy pair or DX-center?

    NASA Astrophysics Data System (ADS)

    Wende, L.; Sielemann, R.; Weyer, G.

    1999-09-01

    We have studied 119Te donor atoms in GaSb incorporated by a recoil implantation technique by applying emission Mössbauer spectroscopy on 119Sn. Since 119Te decays via the intermediate 119Sb the thermal stability of the microscopic environment of the implanted Te atoms can be probed either in the Te state or, after transmutation, in the Sb state. It is found that part of the probes is situated in a strongly distorted configuration which cannot be annealed as long as the probes are Te. After transmutation to Sb the distorted state anneals at 405 K. From these results we conclude that the distorted configuration is implantation induced (very likely a probe-vacancy association) stabilized by the Te chemistry and not a DX center which should anneal with a much lower barrier.

  9. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor

    PubMed Central

    He, M. Q.; Shen, J. Y.; Petrović, A. P.; He, Q. L.; Liu, H. C.; Zheng, Y.; Wong, C. H.; Chen, Q. H.; Wang, J. N.; Law, K. T.; Sou, I. K.; Lortz, R.

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

  10. Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

    SciTech Connect

    Zielony, E.; Placzek-Popko, E.; Henrykowski, A.; Gumienny, Z.; Kamyczek, P.; Jacak, J.; Nowakowski, P.; Karczewski, G.

    2012-09-15

    Micro-Raman spectroscopy has been applied to investigate the impact of laser irradiation on semiconducting CdTe/ZnTe quantum dots (QDs) structures. A reference sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the p-type GaAs substrate. The Raman spectra have been recorded for different time of a laser exposure and for various laser powers. The spectra for both samples exhibit peak related to the localized longitudinal (LO) ZnTe phonon of a wavenumber equal to 210 cm{sup -1}. For the QD sample, a broad band corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm{sup -1}. With increasing time of a laser beam exposure and laser power, the spectra get dominated by tellurium-related peaks appearing at wavenumbers around 120 cm{sup -1} and 140 cm{sup -1}. Simultaneously, the ZnTe surface undergoes rising damage, with the formation of Te aggregates at the pinhole edge as reveal atomic force microscopy observations. Local temperature of irradiated region has been estimated from the anti-Stokes/Stokes ratio of the Te modes intensity and it was found to be close or exceeding ZnTe melting point. Thus, the laser damage can be explained by the ablation process.

  11. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

    PubMed

    He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

  12. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

    PubMed

    He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.

  13. Effects of Surface Composition on CdTe/CdS Device Performance

    SciTech Connect

    Levi, D.; Albin, D.; King, D.

    2000-01-01

    The atomic composition of the back surface of the CdTe layer in a CdTe/CdS photovoltiac (PV) device has a significant influence on the quality of the electrical contact to this layer. This paper reports the results of a systematic study that correlates the composition of the back surface with pre-contact processing and device performance.

  14. Adsorption of Te on Ge(001): Nearly Perfect Dereconstruction and Structural Phase Transition

    NASA Astrophysics Data System (ADS)

    Lyman, P. F.; Marasco, D. L.; Bedzyk, M. J.

    1998-03-01

    The (001) face of a diamond-structure semiconductor has two dangling bonds per surface atom. Therefore, the adsorption of 1 ML of a hexavalent group VI element could saturate all available surface bonds, resulting in a perfect (1×1) termination. This adsorbate-induced dereconstruction has previously been demonstrated for S/Ge(001) and, somewhat imperfectly, for Te/Si(001). Here we describe a study of the local structure and long-range order of Te/Ge(001) using x-ray standing waves (XSW) and LEED for annealing temperatures of 540 K and 670 K. At 540 K, Te exclusively occupied the expected bridge sites, forming a (1×1) local structure. Thus, the Te atoms caused a nearly perfect dereconstruction of the Ge(001) dimerized clean surface. The streaky (2×1) LEED pattern betrayed a small remaining pairing tendency. Upon annealing to 670 K, the Te exhibited a new and surprising behavior. A clear phase transition occurred, indicated both by a dramatic change in the LEED pattern to a streaky c(2×2), and decrease of the Te adsorption height by 0.07 ÅWe hypothesize that approximately half of the Te desorbed, and some of the Ge surface atoms redimerized; the remaining Te atoms occupy "cave" (or long bridge) sites, between two Ge dimers.

  15. AsTeRICS.

    PubMed

    Drajsajtl, Tomáš; Struk, Petr; Bednárová, Alice

    2013-01-01

    AsTeRICS - "The Assistive Technology Rapid Integration & Construction Set" is a construction set for assistive technologies which can be adapted to the motor abilities of end-users. AsTeRICS allows access to different devices such as PCs, cell phones and smart home devices, with all of them integrated in a platform adapted as much as possible to each user. People with motor disabilities in the upper limbs, with no cognitive impairment, no perceptual limitations (neither visual nor auditory) and with basic skills in using technologies such as PCs, cell phones, electronic agendas, etc. have available a flexible and adaptable technology which enables them to access the Human-Machine-Interfaces (HMI) on the standard desktop and beyond. AsTeRICS provides graphical model design tools, a middleware and hardware support for the creation of tailored AT-solutions involving bioelectric signal acquisition, Brain-/Neural Computer Interfaces, Computer-Vision techniques and standardized actuator and device controls and allows combining several off-the-shelf AT-devices in every desired combination. Novel, end-user ready solutions can be created and adapted via a graphical editor without additional programming efforts. The AsTeRICS open-source framework provides resources for utilization and extension of the system to developers and researches. AsTeRICS was developed by the AsTeRICS project and was partially funded by EC.

  16. AsTeRICS.

    PubMed

    Drajsajtl, Tomáš; Struk, Petr; Bednárová, Alice

    2013-01-01

    AsTeRICS - "The Assistive Technology Rapid Integration & Construction Set" is a construction set for assistive technologies which can be adapted to the motor abilities of end-users. AsTeRICS allows access to different devices such as PCs, cell phones and smart home devices, with all of them integrated in a platform adapted as much as possible to each user. People with motor disabilities in the upper limbs, with no cognitive impairment, no perceptual limitations (neither visual nor auditory) and with basic skills in using technologies such as PCs, cell phones, electronic agendas, etc. have available a flexible and adaptable technology which enables them to access the Human-Machine-Interfaces (HMI) on the standard desktop and beyond. AsTeRICS provides graphical model design tools, a middleware and hardware support for the creation of tailored AT-solutions involving bioelectric signal acquisition, Brain-/Neural Computer Interfaces, Computer-Vision techniques and standardized actuator and device controls and allows combining several off-the-shelf AT-devices in every desired combination. Novel, end-user ready solutions can be created and adapted via a graphical editor without additional programming efforts. The AsTeRICS open-source framework provides resources for utilization and extension of the system to developers and researches. AsTeRICS was developed by the AsTeRICS project and was partially funded by EC. PMID:23739379

  17. The deviation from a stoichiometry and the amphoteric behaviour of Ga in PbTe/Si films

    NASA Astrophysics Data System (ADS)

    Samoylov, A. M.; Belenko, S. V.; Sharov, M. K.; Dolgopolova, E. A.; Zlomanov, V. P.

    2012-07-01

    The experimental results, which have been received during the examination of the crystal structure and electronic properties of PbTe/Si heterostructures doped with Ga by means of two different techniques, are systematised in this study. The first doping procedure is based on the two-zone annealing of previously formed by modified HWE technique PbTe/Si heterostructures in the saturated vapour which corresponds to the three-phase equilibrium L1-GaTe(S)-V in Ga-Te binary system. The second method of preparation of PbTe/Si heterostructures offers the direct one stage synthesis, in which the doping and the layer condensation processes proceed simultaneously. The experimental results clearly demonstrate the different character in the charge carrier densities evolutions with the Ga impurity concentration for PbTe/Si films prepared by these techniques. The measurements of conductivity and Hall coefficient have shown that Ga atoms behave as the donor impurities only in PbTe/Si films with little excess of Te, which were fabricated by vapour phase doping. On the contrary, in PbTe films prepared by a direct one-stage synthesis the character of electrical activity of Ga impurities depends upon both the concentration and the deviation from stoichiometry. It has been found that the Pb1-yGayTe1+δ films with yGa>0.015, which are heterogeneous and consist of two (PbTe+GaTe) or three phases (PbTe+GaTe+Ga2Te3) have the best sensitivity to IR radiation. In the scope of quasi chemical approach it is possible to explain the complicated amphoteric behaviour of Ga atoms by different mechanisms of substitution (GaPb×, GaPb1- and GaPb1+) or implantation (Gai3+) of impurity atoms in the PbTe crystal structure.

  18. Atomic supersymmetry

    NASA Technical Reports Server (NTRS)

    Kostelecky, V. Alan

    1993-01-01

    Atomic supersymmetry is a quantum-mechanical supersymmetry connecting the properties of different atoms and ions. A short description of some established results in the subject are provided and a few recent developments are discussed including the extension to parabolic coordinates and the calculation of Stark maps using supersymmetry-based models.

  19. Atomic Calligraphy

    NASA Astrophysics Data System (ADS)

    Imboden, Matthias; Pardo, Flavio; Bolle, Cristian; Han, Han; Tareen, Ammar; Chang, Jackson; Christopher, Jason; Corman, Benjamin; Bishop, David

    2013-03-01

    Here we present a MEMS based method to fabricate devices with a small number of atoms. In standard semiconductor fabrication, a large amount of material is deposited, after which etching removes what is not wanted. This technique breaks down for structures that approach the single atom limit, as it is inconceivable to etch away all but one atom. What is needed is a bottom up method with single or near single atom precision. We demonstrate a MEMS device that enables nanometer position controlled deposition of gold atoms. A digitally driven plate is swept as a flux of gold atoms passes through an aperture. Appling voltages on four comb capacitors connected to the central plate by tethers enable nanometer lateral precision in the xy plane over 15x15 sq. microns. Typical MEMS structures have manufacturing resolutions on the order of a micron. Using a FIB it is possible to mill apertures as small as 10 nm in diameter. Assuming a low incident atomic flux, as well as an integrated MEMS based shutter with microsecond response time, it becomes possible to deposit single atoms. Due to their small size and low power consumption, such nano-printers can be mounted directly in a cryogenic system at ultrahigh vacuum to deposit clean quench condensed metallic structures.

  20. Study of the Topological Crystalline Insulator, SnTe and Sn-In-Te systems in the form of nanomaterials

    NASA Astrophysics Data System (ADS)

    Saghir, M.; Lees, M. R.; York, S. J.; Balakrishnan, G.

    2014-03-01

    We have studied the Topological Crystalline Insulator SnTe and the superconducting variant which arises due to the partial substitution of Sn atoms with indium, Sn1-xInxTe, in this rock salt structure. The observable topological features are thought to be enhanced by increasing the surface area to volume ratio of the materials and therefore suppressing contributions from the bulk. We report the first evidence for the growth of SnTe and SnInTe nanowires starting from bulk crystals. The nanowires produced are typically 20 μm in length and 20 nm wide. The stoichiometries of these structures have been determined to compare with that of the source material. Various morphologies of nanomaterials are observed and the optimal conditions and processes involved to obtain these are discussed.

  1. Masses of Te130 and Xe130 and Double-β-Decay Q Value of Te130

    NASA Astrophysics Data System (ADS)

    Redshaw, Matthew; Mount, Brianna J.; Myers, Edmund G.; Avignone, Frank T., III

    2009-05-01

    The atomic masses of Te130 and Xe130 have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M(Te130)=129.906222744(16)u and M(Xe130)=129.903509351(15)u. From the mass difference the double-β-decay Q value of Te130 is determined to be Qββ(Te130)=2527.518(13)keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi , Nucl. Phys. A729, 337 (2003)NUPABL0375-947410.1016/j.nuclphysa.2003.11.003].

  2. Masses of {sup 130}Te and {sup 130}Xe and Double-{beta}-Decay Q Value of {sup 130}Te

    SciTech Connect

    Redshaw, Matthew; Mount, Brianna J.; Myers, Edmund G.; Avignone, Frank T. III

    2009-05-29

    The atomic masses of {sup 130}Te and {sup 130}Xe have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M({sup 130}Te)=129.906 222 744(16) u and M({sup 130}Xe)=129.903 509 351(15) u. From the mass difference the double-{beta}-decay Q value of {sup 130}Te is determined to be Q{sub {beta}}{sub {beta}}({sup 130}Te)=2527.518(13) keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi et al., Nucl. Phys. A729, 337 (2003)].

  3. Bonding analysis of telluroketones H₂A = Te (A = C, Si, Ge).

    PubMed

    Jaufeerally, Naziah B; Ramasami, Ponnadurai; Jerabek, Paul; Frenking, Gernot

    2014-10-01

    Quantum chemical calculations using density functional theory BP86/def2-TZVPP and ab initio methods at CCSD(T)/def2-TZVPP have been carried for the telluroketones H2A=Te (A = C, Si, Ge). DFT calculations have also been carried out for the ketones H2C=E (E = O, S, Se, Te) and for the complexes NHC → [H2A=Te] → B(C6F5)3. The nature of the bonding has been investigated with charge- and energy decomposition analyses. The calculated bond dissociation energies for the double bonds of the H2C = E and H2A = Te molecules show the expected trends O > S > Se > Te for atom E and C > Si > Ge for atom A. Complexation of the telluroketones in NHC → [H2A = Te] → B(C6F5)3 leads to longer and weaker A-Te bonds which exhibit the surprising trend for the bond dissociation energy Si > Ge > C. The contribution of the π bonding in H2A = Te increases for the heavier atoms with the sequence C < Si < Ge. PMID:25241160

  4. The low-symmetry lanthanum(III) oxotellurate(IV), La10Te12O39

    PubMed Central

    Wang, Peng Li; Mozharivskyj, Yurij

    2013-01-01

    Single crystals of deca­lanthanum(III) dodeca­oxotellurate(IV), La10Te12O39, were obtained by reacting La2O3 and TeO2 in a CsCl flux. Its crystal structure can be viewed as a three-dimensional network of corner- and edge-sharing LaO8 polyhedra with TeIV atoms filling the inter­stitial sites. The TeIV atoms with their 5s 2 electron lone pairs distort the LaO8 polyhedra through variable Te—O bonds. Among the six unique Te sites, four of them define empty channels extending parallel to the a axis. The formation of these channels is a result of the stereochemically active electron lone pairs on the TeIV atoms. The atomic arrangement of the Te—O units can be understood on the basis of the valence shell electron pair repulsion (VSEPR) model. A certain degree of disorder is observed in the crystal structure. As a result, one of the five different La sites is split into two positions with an occupancy ratio of 0.875 (2):0.125 (2). Also, one of the oxygen sites is split into two positions in a 0.559 (13):0.441 (13) ratio, and one O site is half-occupied. Such disorder was observed in all measured La10Te12O39 crystals. PMID:23794967

  5. Substitutionality of Te- and Sn-related DX centers in Al sub x Ga sub 1 minus x As

    SciTech Connect

    Yu, K.M. ); Khachaturyan, K.; Weber, E.R. Department of Materials Science and Mineral Engineering, University of California, Berkeley, California ); Lee, H.P. ); Kolas, E.G. )

    1991-01-15

    The lattice locations of Te and Sn atoms forming {ital DX} centers in Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As were determined by particle-induced x-ray emission and ion-beam-channeling methods. The Te atoms were found to be in the As substitutional sites while the Sn atoms were in the Ga(Al) sites. No off-center displacement of Te and Sn larger than 0.14 A from the substitutional sites was observed in either system.

  6. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  7. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  8. Local order origin of thermal stability enhancement in amorphous Ag doping GeTe

    NASA Astrophysics Data System (ADS)

    Xu, L.; Li, Y.; Yu, N. N.; Zhong, Y. P.; Miao, X. S.

    2015-01-01

    We demonstrate the impacts of Ag doping on the local atomic structure of amorphous GeTe phase-change material. The variations of phonon vibrational modes, boding nature, and atomic structure are shown by Raman, X-ray photoelectron spectroscopy, and ab initio calculation. Combining the experiments and simulations, we observe that the number of Ge atoms in octahedral site decreases and that in tetrahedral site increases. This modification in local order of GeTe originating from the low valence element will affect the crystallization behavior of amorphous GeTe, which is verified by differential scanning calorimetry and transmission electron microscope results. This work not only gives the analysis on the structural change of GeTe with Ag dopants but also provides a method to enhance the thermal stability of amorphous phase-change materials for memory and brain-inspired computing applications.

  9. Local order origin of thermal stability enhancement in amorphous Ag doping GeTe

    SciTech Connect

    Xu, L.; Li, Y.; Yu, N. N.; Zhong, Y. P.; Miao, X. S.

    2015-01-19

    We demonstrate the impacts of Ag doping on the local atomic structure of amorphous GeTe phase-change material. The variations of phonon vibrational modes, boding nature, and atomic structure are shown by Raman, X-ray photoelectron spectroscopy, and ab initio calculation. Combining the experiments and simulations, we observe that the number of Ge atoms in octahedral site decreases and that in tetrahedral site increases. This modification in local order of GeTe originating from the low valence element will affect the crystallization behavior of amorphous GeTe, which is verified by differential scanning calorimetry and transmission electron microscope results. This work not only gives the analysis on the structural change of GeTe with Ag dopants but also provides a method to enhance the thermal stability of amorphous phase-change materials for memory and brain-inspired computing applications.

  10. Effect of intermixing at CdS/CdTe interface on defect properties

    NASA Astrophysics Data System (ADS)

    Park, Ji-Sang; Yang, Ji-Hui; Barnes, Teresa; Wei, Su-Huai

    2016-07-01

    We investigated the stability and electronic properties of defects in CdTe1-xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe1-xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

  11. Large-Area Synthesis of High-Quality Uniform Few-Layer MoTe2.

    PubMed

    Zhou, Lin; Xu, Kai; Zubair, Ahmad; Liao, Albert D; Fang, Wenjing; Ouyang, Fangping; Lee, Yi-Hsien; Ueno, Keiji; Saito, Riichiro; Palacios, Tomás; Kong, Jing; Dresselhaus, Mildred S

    2015-09-23

    The controlled synthesis of large-area, atomically thin molybdenum ditelluride (MoTe2) crystals is crucial for its various applications based on the attractive properties of this emerging material. In this work, we developed a chemical vapor deposition synthesis to produce large-area, uniform, and highly crystalline few-layer 2H and 1T' MoTe2 films. It was found that these two different phases of MoTe2 can be grown depending on the choice of Mo precursor. Because of the highly crystalline structure, the as-grown few-layer 2H MoTe2 films display electronic properties that are comparable to those of mechanically exfoliated MoTe2 flakes. Our growth method paves the way for the large-scale application of MoTe2 in high-performance nanoelectronics and optoelectronics. PMID:26305492

  12. Characterization of CdTe Films Deposited at Various Bath Temperatures and Concentrations Using Electrophoretic Deposition

    PubMed Central

    Daud, Mohd Norizam Md; Zakaria, Azmi; Jafari, Atefeh; Ghazali, Mohd Sabri Mohd; Abdullah, Wan Rafizah Wan; Zainal, Zulkarnain

    2012-01-01

    CdTe film was deposited using the electrophoretic deposition technique onto an ITO glass at various bath temperatures. Four batch film compositions were used by mixing 1 to 4 wt% concentration of CdTe powder with 10 mL of a solution of methanol and toluene. X-ray Diffraction analysis showed that the films exhibited polycrystalline nature of zinc-blende structure with the (111) orientation as the most prominent peak. From the Atomic Force Microscopy, the thickness and surface roughness of the CdTe film increased with the increase of CdTe concentration. The optical energy band gap of film decreased with the increase of CdTe concentration, and with the increase of isothermal bath temperature. The film thickness increased with respect to the increase of CdTe concentration and bath temperature, and following, the numerical expression for the film thickness with respect to these two variables has been established. PMID:22754325

  13. Atomic research

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Connatser, Robert; Cothren, Bobby; Johnson, R. B.

    1993-01-01

    Work performed by the University of Alabama in Huntsville's (UAH) Center for Applied Optics (CAO) entitled Atomic Research is documented. Atomic oxygen (AO) effects on materials have long been a critical concern in designing spacecraft to withstand exposure to the Low Earth Orbit (LEO) environment. The objective of this research effort was to provide technical expertise in the design of instrumentation and experimental techniques for analyzing materials exposed to atomic oxygen in accelerated testing at NASA/MSFC. Such testing was required to answer fundamental questions concerning Space Station Freedom (SSF) candidate materials and materials exposed to atomic oxygen aboard the Long-Duration Exposure Facility (LDEF). The primary UAH task was to provide technical design, review, and analysis to MSFC in the development of a state-of-the-art 5eV atomic oxygen beam facility required to simulate the RAM-induced low earth orbit (LEO) AO environment. This development was to be accomplished primarily at NASA/MSFC. In support of this task, contamination effects and ultraviolet (UV) simulation testing was also to be carried out using NASA/MSFC facilities. Any materials analysis of LDEF samples was to be accomplished at UAH.

  14. Actuated atomizer

    NASA Technical Reports Server (NTRS)

    Tilton, Charles (Inventor); Weiler, Jeff (Inventor); Palmer, Randall (Inventor); Appel, Philip (Inventor)

    2008-01-01

    An actuated atomizer is adapted for spray cooling or other applications wherein a well-developed, homogeneous and generally conical spray mist is required. The actuated atomizer includes an outer shell formed by an inner ring; an outer ring; an actuator insert and a cap. A nozzle framework is positioned within the actuator insert. A base of the nozzle framework defines swirl inlets, a swirl chamber and a swirl chamber. A nozzle insert defines a center inlet and feed ports. A spool is positioned within the coil housing, and carries the coil windings having a number of turns calculated to result in a magnetic field of sufficient strength to overcome the bias of the spring. A plunger moves in response to the magnetic field of the windings. A stop prevents the pintle from being withdrawn excessively. A pintle, positioned by the plunger, moves between first and second positions. In the first position, the head of the pintle blocks the discharge passage of the nozzle framework, thereby preventing the atomizer from discharging fluid. In the second position, the pintle is withdrawn from the swirl chamber, allowing the atomizer to release atomized fluid. A spring biases the pintle to block the discharge passage. The strength of the spring is overcome, however, by the magnetic field created by the windings positioned on the spool, which withdraws the plunger into the spool and further compresses the spring.

  15. Effects of CdTe growth conditions and techniques on the efficiency limiting defects and mechanisms in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Rohatgi, A.; Chou, H. C.; Jokerst, N. M.; Thomas, E. W.; Ferekides, C.; Kamra, S.; Feng, Z. C.; Dugan, K. M.

    1996-01-01

    CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO2/glass substrates using close-spaced sublimation (CSS) and metalorganic chemical vapor deposition (MOCVD). Te/Cd mole ratio was varied in the range of 0.02 to 6 in the MOCVD growth ambient in an attempt to vary the native defect concentration. Polycrystalline CdTe layers grown by MOCVD and CSS both showed average grain size of about 2 μm. However, the CdTe films grown by CSS were found to be less faceted and more dense compared to the CdTe grown by MOCVD. CdTe growth techniques and conditions had a significant impact on the electrical characteristics of the cells. The CdTe solar cells grown by MOCVD in the Te-rich growth condition and by the CSS technique gave high cell efficiencies of 11.5% and 12.4%, respectively, compared to 6.6% efficient MOCVD cells grown in Cd-rich conditions. This large difference in efficiency is explained on the basis of (a) XRD measurements which showed a higher degree of atomic interdiffusion at the CdS/CdTe interface in high performance devices, (b) Raman measurements which endorsed more uniform and preferred grain orientation by revealing a sharp CdTe TO mode in the high efficiency cells, and (c) carrier transport mechanism which switched from tunneling/interface recombination to depletion region recombination in the high efficiency cells. In this study, Cu/Au layers were evaporated on CdTe for the back contact. Lower efficiency of the Te-rich MOCVD cells, compared to the CSS cells, was attributed to contact related additional loss mechanisms, such as Cd pile-up near Cu/CdTe interface which can give rise to Cd-vacancy defects in the bulk, and higher Cu concentration in the CdTe layer which can cause shunts in the device. Finally, SIMS measurements on the CdTe films of different crystallinity and grain size confirmed that grain boundaries are the main conduits for Cu migration into the CdTe film. Thus larger CdTe grain size or lower grain boundary area per unit volume

  16. Atom Interferometry

    SciTech Connect

    Kasevich, Mark

    2008-05-08

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton's constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gyroscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be used to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  17. Atom Interferometry

    SciTech Connect

    Mark Kasevich

    2008-05-07

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  18. Atom Interferometry

    ScienceCinema

    Mark Kasevich

    2016-07-12

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  19. High-quality CdTe films from nanoparticle precursors

    SciTech Connect

    Schulz, D.L.; Pehnt, M.; Urgiles, E.

    1996-05-01

    In this paper the authors demonstrate that nanoparticulate precursors coupled with spray deposition offers an attractive route into electronic materials with improved smoothness, density, and lower processing temperatures. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent, resulting in the formation of soluble NaI and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25-75 {Angstrom} diameter) onto substrates at elevated temperatures (T = 280-440{degrees}C) with no further thermal treatment. These films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD, with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C and substantial O. AFM gave CdTe grain sizes of {approx}0.1-0.3 {mu}m for film sprayed at 400{degrees}C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.

  20. Exfoliation and characterization of bismuth telluride atomic quintuples and quasi-two-dimensional crystals.

    PubMed

    Teweldebrhan, Desalegne; Goyal, Vivek; Balandin, Alexander A

    2010-04-14

    Bismuth telluride (Bi(2)Te(3)) and its alloys are the best bulk thermoelectric materials known today. In addition, stacked quasi-two-dimensional (2D) layers of Bi(2)Te(3) were recently identified as promising topological insulators. In this Letter we describe a method for "graphene-inspired" exfoliation of crystalline bismuth telluride films with a thickness of a few atoms. The atomically thin films were suspended across trenches in Si/SiO(2) substrates, and subjected to detail material characterization, which included atomic force microscopy and micro-Raman spectroscopy. The presence of the van der Waals gaps allowed us to disassemble Bi(2)Te(3) crystal into its quintuple building blocks-five monatomic sheets-consisting of Te((1))-Bi-Te((2))-Bi-Te((1)). By altering the thickness and sequence of atomic planes, we were able to create "designer" nonstoichiometric quasi-2D crystalline films, change their composition and doping, the type of charge carriers as well as other properties. The exfoliated quintuples and ultrathin films have low thermal conductivity, high electrical conductivity, and enhanced thermoelectric properties. The obtained results pave the way for producing stacks of crystalline bismuth telluride quantum wells with the strong spatial confinement of charge carriers and acoustic phonons, beneficial for thermoelectric devices. The developed technology for producing free-standing quasi-2D layers of Te((1))-Bi-Te((2))-Bi-Te((1)) creates an impetus for investigation of the topological insulators and their possible practical applications.

  1. Influence of Se Substitution in GeTe on Phase and Thermoelectric Properties

    NASA Astrophysics Data System (ADS)

    Yang, L.; Li, J. Q.; Chen, R.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2016-11-01

    Lead-free GeTe compound shows good electrical properties but also high thermal conductivity. GeTe1- x Se x alloys with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by conventional melting, quenching, and spark plasma sintering (SPS) techniques to study their phases and thermoelectric properties. Se was chosen as dopant element in GeTe to reduce the thermal conductivity. Experimental results showed that all alloys formed rhombohedral GeTe-based solid solution and minor cubic Ge phase without any phase arising from Se. The alloys retained the p-type conduction of GeTe. Substitution of Se for Te in GeTe increased its electrical resistivity, but increased its Seebeck coefficient and reduced its thermal conductivity significantly. Reduction of the carrier mobility was responsible for the increase of the electrical resistivity and Seebeck coefficient. Enhancement of the phonon scattering on Se solute atoms and minor phase Ge was responsible for the reduction of the thermal conductivity. As a result, the figure of merit ZT of GeTe1- x Se x alloys can be enhanced with proper Se substitution. A maximum ZT value of 1.17 at 773 K was eventually achieved in the GeTe0.7Se0.3 sample, being 26% higher than that of pure GeTe.

  2. HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization

    NASA Astrophysics Data System (ADS)

    Haakenaasen, R.; Selvig, E.; Tonheim, C. R.; Kongshaug, K. O.; Lorentzen, T.; Trosdahl-Iversen, L.; Andersen, J. B.; Gundersen, P.

    2010-07-01

    This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg1- x Cd x Te have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg1- x Cd x Te with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by ˜30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.

  3. Influence of Se Substitution in GeTe on Phase and Thermoelectric Properties

    NASA Astrophysics Data System (ADS)

    Yang, L.; Li, J. Q.; Chen, R.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2016-07-01

    Lead-free GeTe compound shows good electrical properties but also high thermal conductivity. GeTe1-x Se x alloys with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by conventional melting, quenching, and spark plasma sintering (SPS) techniques to study their phases and thermoelectric properties. Se was chosen as dopant element in GeTe to reduce the thermal conductivity. Experimental results showed that all alloys formed rhombohedral GeTe-based solid solution and minor cubic Ge phase without any phase arising from Se. The alloys retained the p-type conduction of GeTe. Substitution of Se for Te in GeTe increased its electrical resistivity, but increased its Seebeck coefficient and reduced its thermal conductivity significantly. Reduction of the carrier mobility was responsible for the increase of the electrical resistivity and Seebeck coefficient. Enhancement of the phonon scattering on Se solute atoms and minor phase Ge was responsible for the reduction of the thermal conductivity. As a result, the figure of merit ZT of GeTe1-x Se x alloys can be enhanced with proper Se substitution. A maximum ZT value of 1.17 at 773 K was eventually achieved in the GeTe0.7Se0.3 sample, being 26% higher than that of pure GeTe.

  4. Phase stability and lattice thermal conductivity reduction in CoSb3 skutterudites, doped with chalcogen atoms

    NASA Astrophysics Data System (ADS)

    Battabyal, M.; Priyadarshini, B.; Pradipkanti, L.; Satapathy, Dillip K.; Gopalan, R.

    2016-07-01

    We report a significant reduction in the lattice thermal conductivity of the CoSb3 skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb3 skutterudite samples (Te0.1Co4Sb12, Se0.1Co4Sb12, Te0.05Se0.05Co4Sb12) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb3 skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773 K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb3 skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb3 skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb3 skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ˜ 0.9 W/mK at 773 K is achieved in Te0.1Co4Sb12 skutterudites, which is the lowest value reported so far in CoSb3 skutterudites, doped with single Te chalcogen atom.

  5. As-Received CdZnTe Substrate Contamination

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Arias, J. M.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Vilela, M. F.; Johnson, S. M.; Lofgreen, D. D.; Yulius, A.; Carmody, M.; Hirsch, R.; Fiala, J.; Motakef, S.

    2015-09-01

    State-of-the-art as-received (112)B CdZnTe substrates were examined for surface impurity contamination, polishing damage, and tellurium precipitates/inclusions. A maximum surface impurity concentration of Al = 7.5 × 1014, Si = 3.7 × 1013, Cl = 3.12 × 1015, S = 1.7 × 1014, P = 7.1 × 1013, Fe = 1.0 × 1013, Br = 1.9 × 1012, and Cu = 4 × 1012 atoms cm-2 was observed on an as-received 6 × 6 cm wafer. As-received CdZnTe substrates have scratches and residual polishing grit on the (112)B surface. Polishing scratches are 0.3 nm in depth and 0.1 μm wide. The polishing grit density was observed to vary from wafer-to-wafer from ˜5 × 106 to 2 × 108 cm-2. Te precipitate/inclusion size and density was determined by near-infrared automated microscopy. A Te precipitate/inclusion diameter histogram was obtained for the near-surface (top ~140 μm) of a 6 × 6 cm substrate. The average areal Te precipitate/inclusion density was observed to be fairly uniform. However, there was a large density of Te precipitates/inclusions with a diameter significantly greater than the mean. Te precipitate/inclusion density >10 μm diameter = 2.8 × 103 cm-3. The large Te precipitates/inclusions are laterally non-uniformly distributed across the wafer.

  6. High performance as-grown and annealed high band gap tunnel junctions: Te behavior at the interface

    NASA Astrophysics Data System (ADS)

    Bedair, S. M.; Harmon, Jeffrey L.; Carlin, C. Zachary; Hashem Sayed, Islam E.; Colter, P. C.

    2016-05-01

    The performance of n+-InGaP(Te)/p+-AlGaAs(C) high band gap tunnel junctions (TJ) is critical for achieving high efficiency in multijunction photovoltaics. Several limitations for as grown and annealed TJ can be attributed to the Te doping of InGaP and its behavior at the junction interface. Te atoms in InGaP tend to get attached at step edges, resulting in a Te memory effect. In this work, we use the peak tunneling current (Jpk) in this TJ as a diagnostic tool to study the behavior of the Te dopant at the TJ interface. Additionally, we used our understanding of Te behavior at the interface, guided by device modeling, to modify the Te source shut-off procedure and the growth rate. These modifications lead to a record performance for both the as-grown (2000 A/cm2) and annealed (1000 A/cm2) high band gap tunnel junction.

  7. Atomic ordering in cubic bismuth telluride alloy phases at high pressure

    NASA Astrophysics Data System (ADS)

    Loa, I.; Bos, J.-W. G.; Downie, R. A.; Syassen, K.

    2016-06-01

    Pressure-induced transitions from ordered intermetallic phases to substitutional alloys to semi-ordered phases were studied in a series of bismuth tellurides. By using angle-dispersive x-ray diffraction, the compounds Bi4Te5 , BiTe, and Bi2Te were observed to form alloys with the disordered body-centered cubic (bcc) crystal structure upon compression to above 14-19 GPa at room temperature. The BiTe and Bi2Te alloys and the previously discovered high-pressure alloys of Bi2Te3 and Bi4Te3 were all found to show atomic ordering after gentle annealing at very moderate temperatures of ˜100 ∘C . Upon annealing, BiTe transforms from bcc to the B2 (CsCl) crystal-structure type, and the other phases adopt semi-disordered variants thereof, featuring substitutional disorder on one of the two crystallographic sites. The transition pressures and atomic volumes of the alloy phases show systematic variations across the BimTen series including the end members Bi and Te. First-principles calculations were performed to characterize the electronic structure and chemical bonding properties of B2-type BiTe and to identify the driving forces of the ordering transition. The calculated Fermi surface of B2-type BiTe has an intricate structure and is predicted to undergo three topological changes between 20 and 60 GPa.

  8. Atomic rivals

    SciTech Connect

    Goldschmidt, B.

    1990-01-01

    This book is a memoir of rivalries among the Allies over the bomb, by a participant and observer. Nuclear proliferation began in the uneasy wartime collaboration of the United States, England, Canada, and Free France to produce the atom bomb. Through the changes of history, a young French chemist had a role in almost every act of this international drama. This memoir is based on Goldschmidt's own recollections, interviews with other leading figures, and 3,000 pages of newly declassified documents in Allied archives. From his own start as Marie Curie's lab assistant, Goldschmidt's career was closely intertwined with Frances complicated rise to membership in the nuclear club. As a refugee from the Nazis, he became part of the wartime nuclear energy project in Canada and found himself the only French scientist to work (although briefly) on the American atom bomb project.

  9. Atomic arias

    NASA Astrophysics Data System (ADS)

    Crease, Robert P.

    2009-01-01

    The American composer John Adams uses opera to dramatize controversial current events. His 1987 work Nixon in China was about the landmark meeting in 1972 between US President Richard Nixon and Chairman Mao Zedong of China; The Death of Klinghoffer (1991) was a musical re-enactment of an incident in 1985 when Palestinian terrorists kidnapped and murdered a wheelchair-bound Jewish tourist on a cruise ship. Adams's latest opera, Doctor Atomic, is also tied to a controversial event: the first atomic-bomb test in Alamogordo, New Mexico, on 16 June 1945. The opera premièred in San Francisco in 2005, had a highly publicized debut at the Metropolitan Opera in New York in 2008, and will have another debut on 25 February - with essentially the same cast - at the English National Opera in London.

  10. Atomic physics

    SciTech Connect

    Livingston, A.E.; Kukla, K.; Cheng, S.

    1995-08-01

    In a collaboration with the Atomic Physics group at Argonne and the University of Toledo, the Atomic Physics group at the University of Notre Dame is measuring the fine structure transition energies in highly-charged lithium-like and helium-like ions using beam-foil spectroscopy. Precise measurements of 2s-2p transition energies in simple (few-electron) atomic systems provide stringent tests of several classes of current atomic- structure calculations. Analyses of measurements in helium-like Ar{sup 16+} have been completed, and the results submitted for publication. A current goal is to measure the 1s2s{sup 3}S{sub 1} - 1s2p{sup 3}P{sub 0} transition wavelength in helium-like Ni{sup 26+}. Measurements of the 1s2s{sup 2}S{sub 1/2} - 1s2p{sup 2}P{sub 1/2,3/2} transition wavelengths in lithium-like Kr{sup 33+} is planned. Wavelength and lifetime measurements in copper-like U{sup 63+} are also expected to be initiated. The group is also participating in measurements of forbidden transitions in helium-like ions. A measurement of the lifetime of the 1s2s{sup 3}S{sub 1} state in Kr{sup 34+} was published recently. In a collaboration including P. Mokler of GSI, Darmstadt, measurements have been made of the spectral distribution of the 2E1 decay continuum in helium-like Kr{sup 34+}. Initial results have been reported and further measurements are planned.

  11. Heterojunction double dumb-bell Ag2Te-Te-Ag2Te nanowires

    NASA Astrophysics Data System (ADS)

    Som, Anirban; Pradeep, T.

    2012-07-01

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag2Te-Te-Ag2Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic

  12. Synthesis and Characterization of a Series of Quaternary Chalcogenides Ba LnMQ3 ( Ln=Rare Earth, M=Coinage Metal, Q=Se or Te)

    NASA Astrophysics Data System (ADS)

    Yang, Yuting; Ibers, James A.

    1999-10-01

    The compounds BaGdAuSe3, BaLaCuTe3, BaYCuTe3, BaYAgTe3, BaLaAgTe3, BaYbCuTe3, BaGdAgTe3, BaNdCuTe3, and BaPrCuTe3 were prepared by the reaction in a BaBr2/KBr flux at 850°C of a rare earth, a coinage-group metal, a chalcogen, and BaSe or BaTe. The unit cells of all of the compounds and the crystal structures of the first four compounds were determined by single-crystal X-ray diffraction methods. With the exception of BaLaCuTe3, which crystallizes with four formula units in the orthorhombic space group Pnma, all of these compounds crystallize with four formula units in the orthorhombic space group Cmcm. BaLaCuTe3, isostructural with β-BaLaCuSe3 and Eu2CuS3 (i.e., Eu2+Eu3+Cu+(S2-)3), and BaGdAuSe3, BaYCuTe3, and BaYAgTe3, isostructural with KZrCuS3, crystallize in a layered structure in which there are 2∞[LnMQ2-3] layers separated by Ba2+ ions. Ln atoms are coordinated by six Q atoms at the corners of a distorted octahedron, and M atoms are coordinated by four Q atoms at the corners of a tetrahedron. The layers are formed by the connection of edge-sharing octahedral chains and corner-sharing tetrahedral chains. Ba atoms are coordinated by seven Q atoms in BaLaCuTe3 and by eight Q atoms in BaGdAuSe3, BaYCuTe3, and BaYAgTe3. BaNdAgTe3 shows temperature-dependent paramagnetism. Its magnetic susceptibility follows the Curie-Weiss law. The effective magnetic moment of 3.4(3) μB is in agreement with the theoretical value of 3.6 μB for Nd3+.

  13. Redetermination of Ba(2)CdTe(3) from single-crystal X-ray data.

    PubMed

    Yang, Min; Xia, Sheng-Qing; Tao, Xu-Tang

    2012-10-01

    The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999 ▶). J. Solid State Chem.148, 464-467]. In the current redetermination from single-crystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba(2)CdTe(3) is isotypic with Ba(2)MX(3) (M = Mn, Cd; X = S, Se) and features (1) (∞)[CdTe(2/2)Te(2/1)](4-) chains of corner-sharing CdTe(4) tetra-hedra running parallel [010]. The two Ba(2+) cations are located between the chains, both within distorted monocapped trigonal-prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.

  14. Preparation and structure of BiCrTeO{sub 6}: A new compound in Bi–Cr–Te–O system. Thermal expansion studies of Cr{sub 2}TeO{sub 6}, Bi{sub 2}TeO{sub 6} and BiCrTeO{sub 6}

    SciTech Connect

    Vats, Bal Govind; Phatak, Rohan; Krishnan, K.; Kannan, S.

    2013-09-01

    Graphical abstract: A new compound BiCrTeO{sub 6} in the Bi–Cr–Te–O system was prepared by solid state route and characterized by X-ray diffraction method. The crystal structure of BiCrTeO{sub 6} shows that there is one distinct site for bismuth (Bi) atom (pink color), one chromium rich (Cr/Te = 68/32) (blue/green color), one tellurium rich (Te/Cr = 68/32) sites (green/blue color), and one distinct site for oxygen (O) atom (red color) in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogram (TG) of the compound in air shows that it is stable up to 1103 K and decomposes thereafter. The thermal expansion behaviour of BiCrTeO{sub 6} was studied using high temperature X-ray diffraction method from room temperature to 923 K under vacuum of 10{sup −8} atmosphere and showed positive thermal expansion with the average volume thermal expansion coefficients of 16.0 × 10{sup −6}/K. - Highlights: • A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared and characterized. • The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method. • The structure of BiCrTeO{sub 6} shows an octahedral coordination for all the metal ions. • The thermal expansion behavior of BiCrTeO{sub 6} from room temperature to 923 K showed a positive thermal expansion. • The average volume thermal expansion coefficient for BiCrTeO{sub 6} is 16.0 × 10{sup −6}/K. - Abstract: A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared by solid state reaction of Bi{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} and H{sub 6}TeO{sub 6} in oxygen and characterized by X-ray diffraction (XRD) method. It could be indexed on a trigonal lattice, with the space group P-31c, unit cell parameters a = 5.16268(7) Å and c = 9.91861(17) Å. The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method using the powder XRD data. Structure shows that there is one distinct

  15. Resonant Levels, Vacancies, and Doping in Bi2Te3, Bi2Te2Se, and Bi2Se3 Tetradymites

    NASA Astrophysics Data System (ADS)

    Wiendlocha, Bartlomiej

    2016-07-01

    The electronic structure of the tetradymites, Bi_2Te_3, Bi_2Te_2Se, and Bi_2Se_3, containing various dopants and vacancies, has been studied using first-principles calculations. We focus on the possibility of formation of resonant levels (RL), confirming the formation of RL by Sn in Bi_2Te_3 and predicting similar behavior of Sn in Bi_2Te_2Se and Bi_2Se_3. Vacancies, which are likely present on chalcogen atom sites in real samples of Bi_2Te_2Se and Bi_2Se_3, are also studied and their charged donor and resonant behavior discussed. Doping of vacancy-containing materials with regular acceptors, such as Ca or Mg, is shown to compensate the donor effect of vacancies, and n-p crossover, while increasing the dopant concentration, is observed. We verify that the RL on Sn is not disturbed by chalcogen vacancies in Bi_2Te_2Se or Bi_2Se_3, and for the Sn-doped materials with Se or Te vacancies, double doping, instead of heavy doping with Sn, is suggested as an effective way of obtaining the resonant level. This should help to avoid smearing of the RL, a possible reason for earlier unsuccessful experimental observation of the influence of the RL on the thermoelectric properties of Sn-doped Bi_2Te_2Se. Finally, we show that Al and Ga are possible new resonant impurities in tetradymites, hoping that this will stimulate further experimental studies.

  16. Neutron capture of /sup 122/Te, /sup 123/Te, /sup 124/Te, /sup 125/Te, and /sup 126/Te

    SciTech Connect

    Macklin, R.L.; Winters, R.R.

    1989-07-01

    Isotopically enriched samples of the tellurium isotopes from mass 122 to mass 126 were used to measure neutron capture in the energy range 2.6 keV to 600 keV at the Oak Ridge Electron Linear Accelerator pulsed neutron source. Starting at 2.6 keV, over 200 Breit-Wigner resonances for each isotope were used to describe the capture data. Least-squares adjustment gave parameters and their uncertainties for a total of 1659 resonances. Capture cross sections averaged over Maxwellian neutron distributions with temperatures ranging from kT = 5 keV to kT = 100 keV were derived for comparison with stellar nucleosynthesis calculations. For the three isotopes shielded from the astrophysical r-process, /sup 122/Te, /sup 123/Te and /sup 124/Te at kT = 30 keV the respective values were (280 /plus minus/ 10) mb, (819 /plus minus/ 30) mb and (154 /plus minus/ 6) mb. The corresponding products of cross section and solar system abundance are nearly equal in close agreement with s-process nucleosynthesis calculations. 26 refs., 8 figs., 10 tabs.

  17. First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Miao, Masoehng; Kioussis, Nicholas; Aqariden, Fikri; Chang, Y.; Grein, Christoph

    CdZnTe and CdTe based semiconductor X-Ray and Gamma-Ray detectors have been intensively studied recently due to their promising potentials for achieving high-resolution, high signal-to-noise ratios and low leakage current, all are desirable features in applications ranging from medical diagnostics to homeland security. Using density functional calculations, we systematically studied the stability, the atomic and electronic structures of the interfaces between CdTe (111) surfaces (Cd- and Te-terminated) and the selected metals (Cu, Al Ni, Pd and Pt). We also calculated the Schottky barrier height (SBH) by aligning the electrostatic potentials in semiconductor and metal regions. Our calculations revealed significant differences between the Cd- and Te- terminated interfaces. While metals tend to deposit directly on reconstructed Te-terminated surfaces, they form a Te-metal alloy layer at the Cd-Terminated metal/CdTe interface. For both Te- and Cd- terminated interfaces, the Schottky barrier heights do not depend much on the choice of metals despite the large variation of the work functions. On the other hand, the interface structure is found to have large effect on the SBH, which is attributed to the metal induced states in the gap.

  18. Te/C nanocomposites for Li-Te Secondary Batteries

    PubMed Central

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm−3), excellent cyclability (ca. 705 mA h cm−3 over 100 cycles), and fast rate capability (ca. 550 mA h cm−3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems. PMID:25609035

  19. Te/C nanocomposites for Li-Te Secondary Batteries.

    PubMed

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li(+)/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm(-3)), excellent cyclability (ca. 705 mA h cm(-3) over 100 cycles), and fast rate capability (ca. 550 mA h cm(-3) at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  20. Te/C nanocomposites for Li-Te Secondary Batteries

    NASA Astrophysics Data System (ADS)

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm-3), excellent cyclability (ca. 705 mA h cm-3 over 100 cycles), and fast rate capability (ca. 550 mA h cm-3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  1. CdZnTe background measurements at balloon altitudes

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Barthelmy, Scott D.; Bartlett, Lyle M.; Birsa, F. B.; Gehrels, Neil A.; Naya, Juan E.; Odom, James L.; Singh, S.; Stahle, Carl M.; Tueller, Jack; Teegarden, Bonnard J.

    1996-10-01

    Because of its high atomic number and convenient room temperature operation, CdZnTe has great potential for use in both balloon and space borne hard x-ray (5 - 200 keV) astrophysics experiments. Here we present preliminary results from the first CdZnTe background measurements made by a balloon instrument. Measurements of the CdZnTe internal background are essential to determine which physical processes make the most important background contributions and are critical in the design of future scientific instruments. The PoRTIA CdZnTe balloon instrument was flown three times in three different shielding configurations. PoRTIA was passively shielded during its first flight from Palestine, Texas and actively shielded as a piggyback instrument on the GRIS balloon experiment during flights 2 and 3 from Alice Springs, Australia. PoRTIA flew twice during the Fall 1995 Alice Springs, Australia campaign using the thick GRIS NaI anticoincidence shield. A significant CdZnTe background reduction was achieved during the third flight with PoRTIA placed completely inside the GRIS shield and blocking crystal, and thus completely surrounded by 15 cm of NaI. These background results are presented and contributions from different background processes are discussed.

  2. Optical modeling of graphene contacted CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Aldosari, Marouf; Sohrabpoor, Hamed; Gorji, Nima E.

    2016-04-01

    For the first time, an optical model is applied on CdS/CdTe thin film solar cells with graphene front or back contact. Graphene is highly conductive and is as thin as a single atom which reduces the light reflection and absorption, and thus enhances the light transmission to CdTe layer for a wide range of wavelengths including IR. Graphene as front electrode of CdTe devices led to loss in short circuit current density of 10% ΔJsc ≤ 15% compared to the conventional electrodes of TCO and ITO at CdS thickness of dCdS = 100 nm. In addition, all the multilayer graphene electrodes with 2, 4, and 7 graphene layers led to Jsc ≤ 20 mA/cm2. Therefore, we conclude that a single monolayer graphene with hexagonal carbon network reduces optical losses and enhances the carrier collection measured as Jsc. In another structure design, we applied the optical model to graphene back contacted CdS/CdTe device. This scheme allows double side irradiation of the cell which is expected to enhance the Jsc. We obtained 1 ∼ 6 , 23, and 38 mA/cm2 for back, front and bifacial illumination of graphene contacted CdTe cell with CdS = 100 nm. The bifacial irradiated cell, to be efficient, requires an ultrathin CdTe film with dCdTe ≤ 1 μm. In this case, the junction electric field extends to the back region and collects out the generated carriers efficiently. This was modelled by absorptivity rather than transmission rate and optical losses. Since the literature suggest that ZnO can increase the graphene conductivity and enhance the Jsc, we performed our simulations for a graphene/ZnO electrode (ZnO = 100 nm) instead of a single graphene layer.

  3. Rotation sensing with a circular atomic waveguide

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-jie; Yan, Xiao-jun; Zhang, Guo-wan; Zhang, An-ning

    2016-01-01

    The hollow metallic optical fibers not only retain the advantage of flexibility but possess a greater intensity gradient for atomic waveguide. Therefore, based on the vector model of Maxwell's equations, we exactly calculated the intensity distribution of the TE01 mode in a typical metallic fiber, and analyzed the optical potential for 85Rb atom. Most of all, based on a circular atomic waveguide, we creatively proposed a novel measurement scheme for rotation sensing, explained the specific measurement principle, and built a mathematical model for this novel scheme. By measuring the number of atoms in the final states, we could get the rotation rate for this typical rotation system. This novel rotation sensor not only possessed a higher measurement precision, but realized the continuity measurement. It will be widely used in navigation, geophysics and general relativity.

  4. Structural evolution of Ga-Ge-Te glasses by combined EXAFS and XPS analysis

    SciTech Connect

    Golovchak, R.; Calvez, L.; Bureau, B.; Jain, H.

    2013-08-07

    The structural evolution of Ga{sub x}Ge{sub y}Te{sub 100−x−y} glasses in the vicinity of GeTe{sub 4}-GaTe{sub 3} pseudo-binary tie-line is determined with high-resolution X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The analysis of XPS data is complicated by similar electronegativity values for the constituent chemical elements, but then the interpretation is facilitated by information from complementary EXAFS analysis of the structure around each element independently. The results show 4/4/2 coordination for Ga/Ge/Te atoms and absence of Ga(Ge)-Ge(Ga) bonds or extended Te clusters in significant concentrations within the whole range of studied composition. The observed structural features correlate well with the measured basic physical properties of Ga-containing germanium telluride glasses.

  5. Synthesis, phase and reaction mechanism of nonlinear optical material MnTeMoO6

    NASA Astrophysics Data System (ADS)

    Jin, Chengguo; Shao, Juxiang; Luo, Huafeng; Huang, Xingyong; Yang, Junsheng; Wan, Mingjie; Wang, Fanhou

    2016-09-01

    Pure polycrystalline MnTeMoO6 is highly desirable to crystal growth. Polycrystalline MnTeMoO6 has been synthesized by solid-state reaction techniques. The optimized preparation process, phase purity and reaction mechanism of polycrystalline MnTeMoO6 were investigated. The reaction will be paused if the atoms cannot pass through the grain boundary and restarted after ground intimately. A new method combined with X-ray diffraction and microscopic observation is employed to determine the phase purity of polycrystalline MnTeMoO6. Pure polycrystalline MnTeMoO6 with gray color and single crystalline phase can be obtained after the reactant was calcined at 500 °C for 20 h three times and can be used to crystal growth. This method for determining the phase purity of powder sample can be used in the synthesis of other polycrystalline powders.

  6. Ab initio investigation of the structural and electronic properties of amorphous HgTe.

    PubMed

    Zhao, Huxian; Chen, Xiaoshuang; Lu, Jianping; Shu, Haibo; Lu, Wei

    2014-01-29

    We present the structure and electronic properties of amorphous mercury telluride obtained from first-principle calculations. The initial configuration of amorphous mercury telluride is created by computation alchemy. According to different exchange–correlation functions in our calculations, we establish two 256-atom models. The topology of both models is analyzed in terms of radial and bond angle distributions. It is found that both the Te and the Hg atoms tend to be fourfold, but with a wrong bond rate of about 10%. The fraction of threefold and fivefold atoms also shows that there are a significant number of dangling and floating bonds in our models. The electronic properties are also obtained. It is indicated that there is a bandgap in amorphous HgTe, in contrast to the zero bandgap for crystalline HgTe. The structures of the band tail and defect states are also discussed. PMID:24592480

  7. Collisional-radiative nonequilibrium in partially ionized atomic nitrogen

    NASA Technical Reports Server (NTRS)

    Kunc, J. A.; Soon, W. H.

    1989-01-01

    A nonlinear collisional-radiative model for determination of nonequilibrium production of electrons, excited atoms, and bound-bound, dielectronic and continuum line intensities in stationary partially ionized atomic nitrogen is presented. Populations of 14 atomic levels and line intensities are calculated in plasma with T(e) = 8000-15,000 K and N(t) = 10 to the 12th - 10 to the 18th/cu cm. Transport of radiation is included by coupling the rate equations of production of the electrons and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions.

  8. Ion-beam treatment to prepare surfaces of p-CdTe films

    DOEpatents

    Gessert, Timothy A.

    2001-01-01

    A method of making a low-resistance electrical contact between a p-CdTe layer and outer contact layers by ion beam processing comprising: a) placing a CdS/CdTe device into a chamber and evacuating the chamber; b) orienting the p-CdTe side of the CdS/CdTe layer so that it faces apparatus capable of generating Ar atoms and ions of preferred energy and directionality; c) introducing Ar and igniting the area of apparatus capable of generating Ar atoms and ions of preferred energy and directionality in a manner so that during ion exposure, the source-to-substrate distance is maintained such that it is less than the mean-free path or diffusion length of the Ar atoms and ions at the vacuum pressure; d) allowing exposure of the p-CdTe side of the device to said ion beam for a period less than about 5 minutes; and e) imparting movement to the substrate to control the real uniformity of the ion-beam exposure on the p-CdTe side of the device.

  9. Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems

    NASA Astrophysics Data System (ADS)

    Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin

    2015-08-01

    The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.

  10. Crystal orientation mechanism of ZnTe epilayers formed on different orientations of sapphire substrates by molecular beam epitaxy

    SciTech Connect

    Nakasu, T. Yamashita, S.; Aiba, T.; Hattori, S.; Sun, W.; Taguri, K.; Kazami, F.; Kobayashi, M.

    2014-10-28

    The electrooptic effect in ZnTe has recently attracted research attention, and various device structures using ZnTe have been explored. For application to practical terahertz wave detector devices based on ZnTe thin films, sapphire substrates are preferred because they enable the optical path alignment to be simplified. ZnTe/sapphire heterostructures were focused upon, and ZnTe epilayers were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. Epitaxial relationships between the ZnTe thin films and the sapphire substrates with their various orientations were investigated using an X-ray diffraction pole figure method. (0001) c-plane, (1-102) r-plane, (1-100) m-plane, and (11-20) a-plane oriented sapphire substrates were used in this study. The epitaxial relationship between ZnTe and c-plane sapphire was found to be (111) ZnTe//(0001) sapphire with an in-plane orientation relationship of [−211] ZnTe//[1-100] sapphire. It was found that the (211)-plane ZnTe layer was grown on the m-plane of the sapphire substrates, and the (100)-plane ZnTe layer was grown on the r-plane sapphire. When the sapphire substrates were inclined from the c-plane towards the m-axis direction, the orientation of the ZnTe thin films was then tilted from the (111)-plane to the (211)-plane. The c-plane of the sapphire substrates governs the formation of the (111) ZnTe domain and the ZnTe epilayer orientation. These crystallographic features were also related to the atom arrangements of ZnTe and sapphire.

  11. Optical properties and band gap of single- and few-layer MoTe2 crystals.

    PubMed

    Ruppert, Claudia; Aslan, Ozgur Burak; Heinz, Tony F

    2014-11-12

    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared.

  12. Optical properties and band gap of single- and few-layer MoTe2 crystals.

    PubMed

    Ruppert, Claudia; Aslan, Ozgur Burak; Heinz, Tony F

    2014-11-12

    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared. PMID:25302768

  13. Radioisotope Thermoelectric Generators Based on Segmented BiTe/PbTe-BiTe/TAGS/PbSnTe

    NASA Astrophysics Data System (ADS)

    McAlonan, Malachy; Patel, Kalpesh; Cummer, Keith

    2006-01-01

    This paper reports on Phase 1 of a multifaceted effort to develop a more efficient radioisotope thermoelectric generator (RTG) for future NASA missions. The conversion efficiency goal is 10% or higher at a power level of 20 watt or higher. The thermoelectric (T/E) efficiency achievable with present T/E materials is about 8% for favorable temperatures. Thermoelectric converter designs, T/E material properties, and T/E couple thermal and electrical performance were investigated in Phase 1 of this program to find paths to improve conversion efficiency. T/E properties can be improved by optimizing the composition of the materials and by improving the micro structural characteristics such as homogeneity, grain size, and phases present. T/E couple performance can be improved by reducing the electrical and thermal contact resistances of the couple and within the segmented T/E elements. Performance and reliability improvements can be achieved by reducing the thermo-mechanical stresses, improving the quality of the bonds and interfaces, minimizing the number of required bonds, and reducing the degradation rates of both the T/E materials and the bonds. This paper focuses on one portion of the activity, i.e., the design of a small converter. In the converter design effort, a prototypic 20-watt device, suitable for use with a single general-purpose heat source (GPHS), was built using an optimized converter design of segmented thermoelectric elements of heritage composition. The 20-watt prototype achieved the power predicted for the test conditions. The chosen couple design used segmented BiTe/PbTe for the n-type element and BiTe/TAGS/PbSnTe, for the p-type T/E element. Use of the BiTe segment exploits the opportunity of the small RTG to operate at lower heat rejection temperatures and results in much higher conversion efficiency, the main objective of the NASA program. Long term data on similarly segmented couples at Teledyne together with the 20-watt module test results

  14. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    SciTech Connect

    Naderi, Ebadollah; Nanavati, Sachin; Majumder, Chiranjib; Ghaisas, S. V.

    2015-01-15

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as A{sub a} site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from A{sub a} (occupied) to A{sub a} (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  15. Atom Skimmers and Atom Lasers Utilizing Them

    NASA Technical Reports Server (NTRS)

    Hulet, Randall; Tollett, Jeff; Franke, Kurt; Moss, Steve; Sackett, Charles; Gerton, Jordan; Ghaffari, Bita; McAlexander, W.; Strecker, K.; Homan, D.

    2005-01-01

    Atom skimmers are devices that act as low-pass velocity filters for atoms in thermal atomic beams. An atom skimmer operating in conjunction with a suitable thermal atomic-beam source (e.g., an oven in which cesium is heated) can serve as a source of slow atoms for a magneto-optical trap or other apparatus in an atomic-physics experiment. Phenomena that are studied in such apparatuses include Bose-Einstein condensation of atomic gases, spectra of trapped atoms, and collisions of slowly moving atoms. An atom skimmer includes a curved, low-thermal-conduction tube that leads from the outlet of a thermal atomic-beam source to the inlet of a magneto-optical trap or other device in which the selected low-velocity atoms are to be used. Permanent rare-earth magnets are placed around the tube in a yoke of high-magnetic-permeability material to establish a quadrupole or octupole magnetic field leading from the source to the trap. The atoms are attracted to the locus of minimum magnetic-field intensity in the middle of the tube, and the gradient of the magnetic field provides centripetal force that guides the atoms around the curve along the axis of the tube. The threshold velocity for guiding is dictated by the gradient of the magnetic field and the radius of curvature of the tube. Atoms moving at lesser velocities are successfully guided; faster atoms strike the tube wall and are lost from the beam.

  16. First-principles study of amorphous Ga4Sb6Te3 phase-change alloys

    NASA Astrophysics Data System (ADS)

    Bouzid, Assil; Gabardi, Silvia; Massobrio, Carlo; Boero, Mauro; Bernasconi, Marco

    2015-05-01

    First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the Ga4Sb6Te3 phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition Ga4Sb6Te3 lies on the pseudobinary Ga Sb -Sb2Te3 tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.

  17. Adsorbate induced mesoscopic surface reconstruction of the system Te/Pd(1 0 2)

    NASA Astrophysics Data System (ADS)

    Godzik, G.; Pfnür, H.

    2001-08-01

    Low energy electron diffraction (LEED) measurements have been carried out on the clean and Te covered Pd(1 0 2) surface. This is the surface into which the Pd(1 0 0) surface is reconstructed by a concentration of more than 0.5 ML of Te. The Pd(1 0 2) surface was produced with a terrace width of more than 1000 Å. Up to 0.5 ML the adsorption of Te takes place on the flat (1 0 2) surface, on which islands with (2×1) structure are formed coupled with a reduction of the terrace widths to about half the initial value. Above 0.5 ML, and up to 1 ML, the adsorbed Te atoms produce a structural change of the surface, i.e. a terrace structure is formed with a clear average terrace length that depends on Te concentration and with step edges in [ 2¯ 0 1] direction. As concluded from the characteristic splitting of LEED spots as a function of energy, these terraces occupy only two height levels in an alternating sequence and are separated by steps of single atomic height. The terrace width of the alternating terraces increases with increasing Te-concentration. Again a flat surface is formed at 1 ML of Te. A geometrical model is established and discussed.

  18. Instability of nitrogen doped Sb{sub 2}Te{sub 3} for phase change memory application

    SciTech Connect

    Li Xuelai; Zhu Min; Rao Feng; Song Zhitang; Liu Weili; Sun Zhimei

    2011-11-01

    By means of experimental methods and ab initio total energy calculations, we have studied the stability and properties of nitrogen doped Sb{sub 2}Te{sub 3} (NST). The NST film displayed a higher crystallization temperature and sheet resistance than undoped Sb{sub 2}Te{sub 3} (ST) film. Nevertheless, the sheet resistance of the crystalline NST film unexpectedly increased as the temperature increased when the temperature was above 260 deg. C. The X-ray photoelectron spectroscopy (XPS) showed that the nitrogen concentration and the Sb-N bonds were decreasing as the annealing temperature increased, and no nitrogen existed in the NST when annealed at 300 deg. C for 5 min. Our theoretical calculations showed that the incorporation of nitrogen into crystalline Sb{sub 2}Te{sub 3} was not energetically favorable, and the nitrogen atoms preferred forming chemical bonds with Sb atoms to Te atoms.

  19. Viewing minerals, atom by atom

    NASA Astrophysics Data System (ADS)

    Maggs, William Ward

    With state-of-the-art technology supported by scissors and bungy cords, Earth scientists are beginning to look at mineral surfaces and mineral-fluid interactions on an atomic scale.The instrument that can provide such a detailed view is the scanning tunneling microscope (STM), which made a great theoretical and practical splash when it was introduced in 1981 by Gerd Binnig and Heinrich Rohrer, physicists at IBM's laboratory in Zurich. They won a Nobel Prize in Physics for their work 5 years later.

  20. Heterojunction double dumb-bell Ag₂Te-Te-Ag₂Te nanowires.

    PubMed

    Som, Anirban; Pradeep, T

    2012-08-01

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag(2)Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag(2)Te-Te-Ag(2)Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.

  1. Atomic magnetometer

    DOEpatents

    Schwindt, Peter; Johnson, Cort N.

    2012-07-03

    An atomic magnetometer is disclosed which uses a pump light beam at a D1 or D2 transition of an alkali metal vapor to magnetically polarize the vapor in a heated cell, and a probe light beam at a different D2 or D1 transition to sense the magnetic field via a polarization rotation of the probe light beam. The pump and probe light beams are both directed along substantially the same optical path through an optical waveplate and through the heated cell to an optical filter which blocks the pump light beam while transmitting the probe light beam to one or more photodetectors which generate electrical signals to sense the magnetic field. The optical waveplate functions as a quarter waveplate to circularly polarize the pump light beam, and as a half waveplate to maintain the probe light beam linearly polarized.

  2. Effects of Composition and Compositional Distribution on the Electronic Structure of ZnSe(1-x)Te(x) Ternary Quantum Dots

    SciTech Connect

    Pandey, Sumeet C.; Maroudas, Dimitrios

    2011-01-01

    We report results of first-principles density functional theory(DFT) calculations for the electronic structure of ZnSe1- x Te x ternary quantum dots (TQDs) and the effects of composition and compositional distribution on the electron density distribution, electronic density of states, and band gap. We analyze the electronic structure of five types of nanocrystal configurations, namely, pristine ZnSe and ZnTe quantum dots, as well as ZnSe/ZnTe core/shell, ZnTe/ZnSe reverse core/shell, and randomly alloyed ZnSe1- x Te x TQDs. We find that the band gaps for ZnSe/ZnTe core/shell TQDs are nonlinearly dependent on the number of Te atoms in the shell, whereas presence of Te in the core of alloyed ZnSe1- x Te x TQDs modifies the electronic energy levels abruptly and significantly in the limits of x → 0 and x → 1. Our results imply that distribution of Te atoms in the TQD in the form of a ZnSe/ZnTe core/shell configuration allows for optimum tunability of the band gap and wave function confinement in TQDs.

  3. Viscosity Relaxation in Molten HgZnTe

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Lehoczky, S. L.; Kim, Yeong Woo; Baird, James K.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Rotating cup measurements of the viscosity of the pseudo-binary melt, HgZnTe have shown that the isothermal liquid with zinc mole fraction 0.16 requires tens of hours of equilibration time before a steady viscous state can be achieved. Over this relaxation period, the viscosity at 790 C increases by a factor of two, while the viscosity at 810 C increases by 40%. Noting that the Group VI elements tend to polymerize when molten, we suggest that the viscosity of the melt is enhanced by the slow formation of Te atom chains. To explain the build-up of linear Te n-mers, we propose a scheme, which contains formation reactions with second order kinetics that increase the molecular weight, and decomposition reactions with first order kinetics that inactivate the chains. The resulting rate equations can be solved for the time dependence of each molecular weight fraction. Using these molecular weight fractions, we calculate the time dependence of the average molecular weight. Using the standard semi-empirical relation between polymer average molecular weight and viscosity, we then calculate the viscosity relaxation curve. By curve fitting, we find that the data imply that the rate constant for n-mer formation is much smaller than the rate constant for n-mer deactivation, suggesting that Te atoms only weakly polymerize in molten HgZnTe. The steady state toward which the melt relaxes occurs as the rate of formation of an n-mer becomes exactly balanced by the sum of the rate for its deactivation and the rate for its polymerization to form an (n+1)-mer.

  4. Exploring nanoscale fluctuations and ferroelectric phase stabilization in S doped PbTe thermoelectrics

    NASA Astrophysics Data System (ADS)

    Knox, Kevin; Bozin, Emil; Malliakas, Christos; Kanatzidis, Mercouri; Billinge, Simon

    2013-03-01

    PbTe is one of the most important commercial thermoelectric materials for applications above room temperature. A paraelectric phase of fluctuating ferroelectric-like Pb structural dipoles emerges in PbTe at elevated temperatures, although it adopts an average rock-salt structure at all temperatures. These intrinsic nanoscale fluctuations are believed to improve the thermoelectric properties of PbTe by limiting the lattice thermal conductivity. Additionally, alloying and chemical substitution in PbTe appreciably improve the thermoelectric figure of merit, as is the case in PbTe1-xSx. However, the exact mechanism for this enhancement is not well understood. It has been shown that PbTe1-xSx exhibits a peak in resistivity at a doping dependent temperature. By analogy with Ge doped PbTe, this anomalous resistivity may be the signature of a ferroelectric phase stabilization. In this talk, we explore this possibility by characterizing the average and the local structure of PbTe1-xSx as a function of temperature and doping using a neutron based atomic pair distribution function (PDF) approach.

  5. Characterization of Highly Efficient CdTe Thin Film Solar Cells by Low-Temperature Photoluminescence

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Matsuzaki, Yuichi; Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    1998-07-01

    Highly efficient CdTe thin film solar cells prepared by close-spaced sublimation (CSS) method with a glass/ITO/CdS/CdTe/Cu-doped carbon/Ag structure were characterized by low-temperature photoluminescence (PL) measurement. A broad 1.42 eV band probably due to VCd Cl defect complexes appeared as a result of CdCl2 treatment. CdS/CdTe junction PL revealed that a CdSxTe1-x mixed crystal layer was formed at the CdS/CdTe interface region during the deposition of CdTe by CSS and that CdCl2 treatment promoted the formation of the mixed crystal layer. Furthermore, in the PL spectra of the heat-treated CdTe after screen printing of the Cu-doped carbon electrode, a neutral-acceptor bound exciton (ACu0, X) line at 1.590 eV was observed, suggesting that Cu atoms were incorporated into CdTe as effective acceptors after the heat treatment.

  6. Thermal Conductivity and Electrical Resistivity of FeTe1-xSx Sintered Samples

    NASA Astrophysics Data System (ADS)

    Kikegawa, Takako; Sato, Kazuki; Ishikawa, Keisuke

    The temperature dependence of thermal conductivity and the temperature and magnetic field dependence of electrical resistivity have been measured for FeTe1-xSx polycrystalline samples. The samples were prepared by solid state reaction with a three-step procedure. For FeTe0.8S0.2 and FeTe0.7S0.3, zero resistivity due to the superconducting transition was observed not only in oxygen post-annealed samples but also in as-grown ones. These samples include the certain amount of impurities FeTe2 and Fe3O4. The formation of these ion compounds reduces the excess Fe atoms leading to the appearance of the zero resistivity in as-grown samples. Positive magnetoresistivity and/or negative magnetoresistivity, which were extremely small, were observed for FeTe and S-doped samples. The magnetoresistivity curves show B2 dependence. It was observed that the thermal conductivity κ of FeTe exhibits a hump structure below 72 K which corresponds to the crystal structural and magnetic transitions. The enhancement of κ due to the superconducting transition could not be detected for as-grown FeTe0.8S0.2 and FeTe0.7S0.3 because of the absence of the bulk superconductivity in the as-grown samples and the extremely small ratio of the electronic contribution to κ.

  7. Three-Dimensional Atom-Probe Tomographic Analyses of Lead-Telluride Based Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Kim, Yoon-Jun; Blum, Ivan D.; He, Jiaqing; Kanatzidis, Mercouri G.; Dravid, Vinayak P.; Seidman, David N.

    2014-11-01

    Precipitates in bulk p-type thermoelectric materials, PbTe-SrTe and PbTe-PbS, are studied using three-dimensional (3-D) atom-probe tomography (APT). APT is capable of characterizing chemically materials in 3-D with subnano-scale spatial resolution on an atom-by-atom basis, which enables us to characterize secondary phases in the PbTe matrix as well as the dopant distributions at different imperfections. We demonstrate that APT provides accurate information about the compositions and morphologies of nanoprecipitates. In the PbTe-SrTe system, different morphology of precipitates is observed and the SrTe composition is confirmed. Also, segregation of Na dopants at mesoscale imperfections, dislocations and grain boundaries, and at matrix/precipitate interfaces is observed. In the PbTe-PbS system, PbS precipitates are observed. The PbS precipitates exhibit faceting, and have a morphology that depends on the bulk Na concentration. A predominance of {100} faceted precipitates is observed for 2 mol.% Na. Using 3-D APT, we demonstrate that Na segregation at matrix/precipitate interfaces is most likely responsible for the change in their morphologies, which occurs by reducing the interfacial free energy of {100} facets.

  8. Three-Dimensional Atom-Probe Tomographic Analyses of Lead-Telluride Based Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Kim, Yoon-Jun; Blum, Ivan D.; He, Jiaqing; Kanatzidis, Mercouri G.; Dravid, Vinayak P.; Seidman, David N.

    2014-09-01

    Precipitates in bulk p-type thermoelectric materials, PbTe-SrTe and PbTe-PbS, are studied using three-dimensional (3-D) atom-probe tomography (APT). APT is capable of characterizing chemically materials in 3-D with subnano-scale spatial resolution on an atom-by-atom basis, which enables us to characterize secondary phases in the PbTe matrix as well as the dopant distributions at different imperfections. We demonstrate that APT provides accurate information about the compositions and morphologies of nanoprecipitates. In the PbTe-SrTe system, different morphology of precipitates is observed and the SrTe composition is confirmed. Also, segregation of Na dopants at mesoscale imperfections, dislocations and grain boundaries, and at matrix/precipitate interfaces is observed. In the PbTe-PbS system, PbS precipitates are observed. The PbS precipitates exhibit faceting, and have a morphology that depends on the bulk Na concentration. A predominance of {100} faceted precipitates is observed for 2 mol.% Na. Using 3-D APT, we demonstrate that Na segregation at matrix/precipitate interfaces is most likely responsible for the change in their morphologies, which occurs by reducing the interfacial free energy of {100} facets.

  9. Near-infrared emission spectra of TeS, TeSe and Te2

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.

    2014-10-01

    Emission spectra of the radicals TeS, TeSe and Te2 in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The molecules were generated in a fast-flow system by reacting microwave-discharged mixtures of Tex, Sx, and/or Sex vapour and Ar carrier gas and excited by energy transfer and energy pooling processes in collisions with metastable oxygen O2(a1Δg). The b1Σ+(b0+) → X3Σ-(X10+,X21) electric dipole transitions of TeS and TeSe and the b1Σ+g(b0+g) → X3Σ-g(X21g) magnetic dipole transition of Te2 were measured at medium and high spectral resolution. A very weak emission at 3356 cm-1 observed in the spectrum of TeSe was identified to be the 0-0 band of the hitherto unknown a1Δ(a2) → X3Σ-(X21) transition of the molecule. Analyses of the spectra have yielded a number of new or improved spectroscopic parameters of the molecules.

  10. Chemical thermodynamics of Cs and Te fission product interactions in irradiated LMFBR mixed-oxide fuel pins

    NASA Astrophysics Data System (ADS)

    Adamson, M. G.; Aitken, E. A.; Lindemer, T. B.

    1985-02-01

    A combination of fuel chemistry modelling and equilibrium thermodynamic calculations has been used to predict the atom ratios of Cs and Te fission products (Cs:Te) that find their way into the fuel-cladding interface region of irradiated stainless steel-clad mixed-oxide fast breeder reactor fuel pins. It has been concluded that the ratio of condensed, chemically-associated Cs and Te in the interface region,Čs:Te, which in turn determines the Te activity, is controlled by an equilibrium reaction between Cs 2Te and the oxide fuel, and that the value of Čs:Te is, depending on fuel 0:M, either equal to or slightly less than 2:1. Since Cs and Te fission products are both implicated as causative agents in FCCI (fission product-assisted inner surface attack of stainless steel cladding) and in FPLME (fission product-assisted liquid metal embrittlement of AISI-Type 316), the observed out-of-pile Cs:Te thresholds for FCCI (4˜:1) and FPLME (2˜:1) have been rationalized in terms of Cs:Te thermochemistry and phase equilibria. Also described in the paper is an updated chemical evolution model for reactive/volatile fission product behavior in irradiated oxide pins.

  11. Synthesis, crystal and electronic structure, and physical properties of the new lanthanum copper telluride La{sub 3}Cu{sub 5}Te{sub 7}

    SciTech Connect

    Zelinska, Mariya; Assoud, Abdeljalil; Kleinke, Holger

    2011-03-15

    The new lanthanum copper telluride La{sub 3}Cu{sub 5-x}Te{sub 7} has been obtained by annealing the elements at 1073 K. Single-crystal X-ray diffraction studies revealed that the title compound crystallizes in a new structure type, space group Pnma (no. 62) with lattice dimensions of a=8.2326(3) A, b=25.9466(9) A, c=7.3402(3) A, V=1567.9(1) A{sup 3}, Z=4 for La{sub 3}Cu{sub 4.86(4)}Te{sub 7}. The structure of La{sub 3}Cu{sub 5-x}Te{sub 7} is remarkably complex. The Cu and Te atoms build up a three-dimensional covalent network. The coordination polyhedra include trigonal LaTe{sub 6} prisms, capped trigonal LaTe{sub 7} prisms, CuTe{sub 4} tetrahedra, and CuTe{sub 3} pyramids. All Cu sites exhibit deficiencies of various extents. Electrical property measurements on a sintered pellet of La{sub 3}Cu{sub 4.86}Te{sub 7} indicate that it is a p-type semiconductor in accordance with the electronic structure calculations. -- Graphical abstract: Oligomeric unit comprising interconnected CuTe{sub 3} pyramids and CuTe{sub 4} tetrahedra. Display Omitted Research highlights: {yields} La{sub 3}Cu{sub 5-x}Te{sub 7} adopts a new structure type. {yields} All Cu sites exhibit deficiencies of various extents. {yields} The coordination polyhedra include trigonal LaTe{sub 6} prisms, capped trigonal LaTe{sub 7} prisms, CuTe{sub 4} tetrahedra and CuTe{sub 3} pyramids. {yields} La{sub 3}Cu{sub 5-x}Te{sub 7} is a p-type semiconductor.

  12. Viscosity Relaxation in Molten HgZnTe

    NASA Technical Reports Server (NTRS)

    Baird, James K.

    2002-01-01

    Because of its narrow electronic band-gap, HgZnTe solid solutions have been proposed as effective detectors for infrared radiation. To produce the best single crystals of these materials for this application, knowledge of the phase diagram that governs the freezing of the liquid is essential. Besides the phase diagram, however, some information concerning the thermophysical properties of the melt, such as viscosity, density, specific heat, and enthalpy of mixing, can also be useful. Of these thermophysical properties, the viscosity is perhaps of the most interest scientifically. Measurements using the oscillating cup method have shown that the isothermal melt requires tens of hours of equilibration time before a steady value of the viscosity can be achieved. Over this equilibration time, which depends upon temperature, the viscosity can increase by as much as a factor of two before reaching a steady state. We suggest that this relaxation phenomenon may be due to a slight polymerization of Te atoms in the melt. To account for the time dependence of the viscosity in the HgZnTe melt, we propose that the liquid acts as a solvent that favors the formation of Te atom chains. We suggest that as the melt is cooled from a high temperature to the temperature for measurement of the viscosity, a free radical polymerization of Te atoms begins. To estimate this average molecular weight, we use a simple free radical polymerization mechanism, including a depolymerization step, to calculate the time dependence to the concentration of each Te polymer molecular weight fraction. From these molecular weight fractions, we compute the weight average molecular weight of the distribution. Using the semi-empirical relation between average molecular weight and viscosity, we obtain a formula for the time dependence of the viscosity of the melt. Upon examining this formula, we find that the viscosity achieves a steady value when a balance is achieved between the rate of formation of the chains

  13. A computational ab initio study of surface diffusion of sulfur on the CdTe (111) surface

    NASA Astrophysics Data System (ADS)

    Naderi, Ebadollah; Ghaisas, S. V.

    2016-08-01

    In order to discern the formation of epitaxial growth of CdS shell over CdTe nanocrystals, kinetics related to the initial stages of the growth of CdS on CdTe is investigated using ab-initio methods. We report diffusion of sulfur adatom on the CdTe (111) A-type (Cd-terminated) and B-type (Te-terminated) surfaces within the density functional theory (DFT). The barriers are computed by applying the climbing Nudge Elastic Band (c-NEB) method. From the results surface hopping emerges as the major mode of diffusion. In addition, there is a distinct contribution from kick-out type diffusion in which a CdTe surface atom is kicked out from its position and is replaced by the diffusing sulfur atom. Also, surface vacancy substitution contributes to the concomitant dynamics. There are sites on the B- type surface that are competitively close in terms of the binding energy to the lowest energy site of epitaxy on the surface. The kick-out process is more likely for B-type surface where a Te atom of the surface is displaced by a sulfur adatom. Further, on the B-type surface, subsurface migration of sulfur is indicated. Furthermore, the binding energies of S on CdTe reveal that on the A-type surface, epitaxial sites provide relatively higher binding energies and barriers than on B-type.

  14. Heavy hydrides: H{sub 2}Te ultraviolet photochemistry

    SciTech Connect

    Underwood, J.; Chastaing, D.; Lee, S.; Wittig, C.

    2005-08-22

    The room-temperature ultraviolet absorption spectrum of H{sub 2}Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH({sup 2}{pi}{sub 1/2}) selectively relative to the TeH({sup 2}{pi}{sub 3/2}) ground state. This is attributed to the role of the 3A{sup '} state, which has a shallow well at large R{sub H-TeH} and correlates to H+TeH({sup 2}{pi}{sub 1/2}). Note that the {sup 2}{pi}{sub 1/2} state is analogous to the {sup 2}P{sub 1/2} spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A{sup '} state is crossed at large R only by 2A{sup ''}, with which it does not interact. The character of 3A{sup '} at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, {sup 2}{pi}{sub 1/2} has a higher degree of spherical symmetry than does {sup 2}{pi}{sub 3/2} (recall that I({sup 2}P{sub 1/2}) is spherically symmetric), and consequently {sup 2}{pi}{sub 1/2} is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A{sup '}<-X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3A{sup '}. The main absorption feature that is peaked at {approx}240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A{sup ''} surface. The 4A{sup ''}<-X transition

  15. The atomic orbitals of the topological atom.

    PubMed

    Ramos-Cordoba, Eloy; Salvador, Pedro; Mayer, István

    2013-06-01

    The effective atomic orbitals have been realized in the framework of Bader's atoms in molecules theory for a general wavefunction. This formalism can be used to retrieve from any type of calculation a proper set of orthonormalized numerical atomic orbitals, with occupation numbers that sum up to the respective Quantum Theory of Atoms in Molecules (QTAIM) atomic populations. Experience shows that only a limited number of effective atomic orbitals exhibit significant occupation numbers. These correspond to atomic hybrids that closely resemble the core and valence shells of the atom. The occupation numbers of the remaining effective orbitals are almost negligible, except for atoms with hypervalent character. In addition, the molecular orbitals of a calculation can be exactly expressed as a linear combination of this orthonormalized set of numerical atomic orbitals, and the Mulliken population analysis carried out on this basis set exactly reproduces the original QTAIM atomic populations of the atoms. Approximate expansion of the molecular orbitals over a much reduced set of orthogonal atomic basis functions can also be accomplished to a very good accuracy with a singular value decomposition procedure.

  16. "Bohr's Atomic Model."

    ERIC Educational Resources Information Center

    Willden, Jeff

    2001-01-01

    "Bohr's Atomic Model" is a small interactive multimedia program that introduces the viewer to a simplified model of the atom. This interactive simulation lets students build an atom using an atomic construction set. The underlying design methodology for "Bohr's Atomic Model" is model-centered instruction, which means the central model of the…

  17. Topography and structure of ultrathin topological insulator Sb2Te3 films on Si(111) grown by means of molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lanius, M.; Kampmeier, J.; Kölling, S.; Mussler, G.; Koenraad, P. M.; Grützmacher, D.

    2016-11-01

    We have studied the growth process of the topological insulator (TI) Sb2 Te3 on Si(111) by scanning tunneling microscopy. High quality thin films from more than 22 nm down to 1 nm in thickness have been deposited by molecular beam epitaxy. To determine the thickness and domain formation of the films, x-ray reflectivity and x-ray diffraction were utilized. In comparison to previous studies of the TI Bi2 Te3 , the growth mechanism of Sb2 Te3 shows a similar transition from nucleation and growth in Sb-Te and Te-Te bilayers, respectively, to mound formation for thicker films. Atom probe tomography measurements reveal a intermixed interface between Sb2 Te3 and Si(111) substrate. These findings can explain the high density of defects and domains.

  18. Peculiarities of vaporization of vitreous alloys of the As-Te system. Heat of formation of gaseous arsenic tellurides

    SciTech Connect

    Alikhanyan, A.S.; Steblevskii, A.V.; Gorgoraki, V.I.; Pashinkin, A.S.; Malyusov, V.A.

    1986-11-01

    Interpretation of the mass spectrum of the gas phase above vitreous alloys of the system As-Te showed virtual absence of AsTe molecules in the saturated vapor; to be precise, the content of these molecules does not exceed 5 x 10/sup -5/ Pa at 550 K. Taking this value as the upper limit of the partial pressure of AsTe, they determined, on the basis of the third law of thermodynamics, the limiting values of the enthalpy of formation and the energy of atomization of AsTe. The requisite values of the entropy of gaseous AsTe and the enthalpy of formation of As/sub (g)/ and Te/sub (g)/ were taken. The calculated results referred to 298.15 K are given. The energy of atomization of the AsTe molecule estimated thus agrees well with the value D/sub 298//sup 0/ (AsTe) = 307.2 kJ/mole calculated by the Pauling's equation with allowance for the electronegativities of arsenic and tellurium.

  19. Raman scattering of few-layers MoTe2

    NASA Astrophysics Data System (ADS)

    Grzeszczyk, M.; Gołasa, K.; Zinkiewicz, M.; Nogajewski, K.; Molas, M. R.; Potemski, M.; Wysmołek, A.; Babiński, A.

    2016-06-01

    We report on room-temperature Raman scattering measurements in few-layer crystals of exfoliated molybdenum ditelluride (MoTe2) performed with the use of 632.8 nm (1.96 eV) laser light excitation. In agreement with a recent study reported by Froehlicher et al (2015 Nano Lett. 15 6481) we observe a complex structure of the out-of-plane vibrational modes ({{{A}}}1{{g}}{/{{A}}}1\\prime ), which can be explained in terms of interlayer interactions between single atomic planes of MoTe2. In the case of low-energy shear and breathing modes of rigid interlayer vibrations, it is shown that their energy evolution with the number of layers can be well reproduced within a linear chain model with only the nearest neighbor interaction taken into account. Based on this model the corresponding in-plane and out-of-plane force constants are determined. We also show that the Raman scattering in MoTe2 measured using 514.5 nm (2.41 eV) laser light excitation results in much simpler spectra. We argue that the rich structure of the out-of-plane vibrational modes observed in Raman scattering spectra excited with the use of 632.8 nm laser light results from its resonance with the electronic transition at the M point of the MoTe2 first Brillouin zone.

  20. Enhanced thermoelectric performance in Cd doped CuInTe{sub 2} compounds

    SciTech Connect

    Cheng, N.; Liu, R.; Bai, S.; Shi, X. Chen, L.

    2014-04-28

    CuIn{sub 1−x}Cd{sub x}Te{sub 2} materials (x = 0, 0.02, 0.05, and 0.1) are prepared using melting-annealing method and the highly densified bulk samples are obtained through Spark Plasma Sintering. The X-ray diffraction data confirm that nearly pure chalcopyrite structures are obtained in all the samples. Due to the substitution of Cd at In sites, the carrier concentration is greatly increased, leading to much enhanced electrical conductivity and power factor. The single parabolic band model is used to describe the electrical transport properties of CuInTe{sub 2} and the low temperature Hall mobility is also modeled. By combing theoretical model and experiment data, the optimum carrier concentration in CuInTe{sub 2} is proposed to explain the greatly enhanced power factors in the Cd doped CuInTe{sub 2}. In addition, the thermal conductivity is reduced by extra phonon scattering due to the atomic mass and radius fluctuations between Cd and In atoms. The maximum zTs are observed in CuIn{sub 0.98}Cd{sub 0.02}Te{sub 2} and CuIn{sub 0.9}Cd{sub 0.1}Te{sub 2} samples, which are improved by over 100% at room temperature and around 20% at 600 K.

  1. Aluminum-centered tetrahedron-octahedron transition in advancing Al-Sb-Te phase change properties.

    PubMed

    Xia, Mengjiao; Ding, Keyuan; Rao, Feng; Li, Xianbin; Wu, Liangcai; Song, Zhitang

    2015-02-24

    Group IIIA elements, Al, Ga, or In, etc., doped Sb-Te materials have proven good phase change properties, especially the superior data retention ability over popular Ge2Sb2Te5, while their phase transition mechanisms are rarely investigated. In this paper, aiming at the phase transition of Al-Sb-Te materials, we reveal a dominant rule of local structure changes around the Al atoms based on ab initio simulations and nuclear magnetic resonance evidences. By comparing the local chemical environments around Al atoms in respective amorphous and crystalline Al-Sb-Te phases, we believe that Al-centered motifs undergo reversible tetrahedron-octahedron reconfigurations in phase transition process. Such Al-centered local structure rearrangements significantly enhance thermal stability of amorphous phase compared to that of undoped Sb-Te materials, and facilitate a low-energy amorphization due to the weak links among Al-centered and Sb-centered octahedrons. Our studies may provide a useful reference to further understand the underlying physics and optimize performances of all IIIA metal doped Sb-Te phase change materials, prompting the development of NOR/NAND Flash-like phase change memory technology.

  2. Aluminum-Centered Tetrahedron-Octahedron Transition in Advancing Al-Sb-Te Phase Change Properties

    PubMed Central

    Xia, Mengjiao; Ding, Keyuan; Rao, Feng; Li, Xianbin; Wu, Liangcai; Song, Zhitang

    2015-01-01

    Group IIIA elements, Al, Ga, or In, etc., doped Sb-Te materials have proven good phase change properties, especially the superior data retention ability over popular Ge2Sb2Te5, while their phase transition mechanisms are rarely investigated. In this paper, aiming at the phase transition of Al-Sb-Te materials, we reveal a dominant rule of local structure changes around the Al atoms based on ab initio simulations and nuclear magnetic resonance evidences. By comparing the local chemical environments around Al atoms in respective amorphous and crystalline Al-Sb-Te phases, we believe that Al-centered motifs undergo reversible tetrahedron-octahedron reconfigurations in phase transition process. Such Al-centered local structure rearrangements significantly enhance thermal stability of amorphous phase compared to that of undoped Sb-Te materials, and facilitate a low-energy amorphization due to the weak links among Al-centered and Sb-centered octahedrons. Our studies may provide a useful reference to further understand the underlying physics and optimize performances of all IIIA metal doped Sb-Te phase change materials, prompting the development of NOR/NAND Flash-like phase change memory technology. PMID:25709082

  3. Sb-Te alloy nanostructures produced on a graphite surface by a simple annealing process

    NASA Astrophysics Data System (ADS)

    Kuwahara, Masashi; Uratsuji, Hideaki; Abe, Maho; Sone, Hayato; Hosaka, Sumio; Sakai, Joe; Uehara, Yoichi; Endo, Rie; Tsuruoka, Tohru

    2015-08-01

    We have produced Sb-Te alloy nanostructures from a thin Sb2Te3 layer deposited on a highly oriented pyrolytic graphite substrate using a simple rf-magnetron sputtering and annealing technique. The size, shape, and chemical composition of the structures were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectrometry (EDX), respectively. The shape of the nanostructures was found to depend on the annealing temperature; nanoparticles appear on the substrate by annealing at 200 °C, while nanoneedles are formed at higher temperatures. Chemical composition analysis has revealed that all the structures were in the composition of Sb:Te = 1:3, Te rich compared to the target composition Sb2Te3, probably due to the higher movability of Te atoms on the substrate compared with Sb. We also tried to observe the production process of nanostructures in situ using SEM. Unfortunately, this was not possible because of evaporation in vacuum, suggesting that the formation of nanostructures is highly sensitive to the ambient pressure.

  4. Exposure of LDEF materials to atomic oxygen: Results of EOIM 3

    NASA Technical Reports Server (NTRS)

    Jaggers, C. H.; Meshishnek, M. J.

    1995-01-01

    The third Effects of Oxygen Atom Interaction with Materials (EOIM 3) experiment flew on STS-46 from July 31 to August 8, 1992. The EOIM-3 sample tray was exposed to the low-earth orbit space environment for 58.55 hours at an altitude of 124 nautical miles resulting in a calculated total atomic oxygen (AO) fluence of 1.99 x 10(exp 20) atoms/sq cm. Five samples previously flown on the Long Duration Exposure Facility (LDEF) Experiment M0003 were included on the Aerospace EOIM 3 experimental tray: (1) Chemglaze A276 white thermal control paint from the LDEF trailing edge (TE); (2) S13GLO white thermal control paint from the LDEF TE; (3) S13GLO from the LDEF leading edge (LE) with a visible contamination layer from the LDEF mission; (4) Z306 black thermal control paint from the LDEF TE with a contamination layer from the LDEF mission; and (5) anodized aluminum from the LDEF TE with a contamination layer from the LDEF mission. The purpose of this experiment was twofold: (l) investigate the response of trailing edge LDEF materials to atomic oxygen exposure, thereby simulating LDEF leading edge phenomena; (2) investigate the response of contaminated LDEF samples to atomic oxygen in attempts to understand LDEF contamination-atomic oxygen interactions. This paper describes the response of these materials to atomic oxygen exposure, and compares the results of the EOIM 3 experiment to the LDEF mission and to ground-based atomic oxygen exposure studies.

  5. Theoretical and experimental investigations of the properties of Ge2Sb2Te5 and indium-doped Ge2Sb2Te5 phase change material

    NASA Astrophysics Data System (ADS)

    Singh, Gurinder; Kaura, Aman; Mukul, Monika; Singh, Janpreet; Tripathi, S. K.

    2014-06-01

    We have carried out comprehensive computational and experimental study on the face-centered cubic Ge2Sb2Te5 (GST) and indium (In)-doped GST phase change materials. Structural calculations, total density of states and crystal orbital Hamilton population have been calculated using first-principle calculation. 5 at.% doping of In weakens the Ge-Te, Sb-Te and Te-Te bond lengths. In element substitutes Sb to form In-Te-like structure in the GST system. In-Te has a weaker bond strength compared with the Sb-Te bond. However, both GST and doped alloy remain in rock salt structure. It is more favorable to replace Sb with In than with any other atomic position. X-ray diffraction (XRD) analysis has been carried out on thin film of In-doped GST phase change materials. XRD graph reveals that In-doped phase change materials have rock salt structure with the formation of In2Te3 crystallites in the material. Temperature dependence of impedance spectra has been calculated for thin films of GST and doped material. Thickness of the as-deposited films is calculated from Swanepoel method. Absorption coefficient (α) has been calculated for amorphous and crystalline thin films of the alloys. The optical gap (indirect band gap) energy of the amorphous and crystalline thin films has also been calculated by the equation α hν = β (hν - E_{{g }} )2 . Optical contrast (C) of pure and doped phase change materials have also been calculated. Sufficient optical contrast has been found for pure and doped phase change materials.

  6. Photoluminescence characteristics of ZnTe bulk crystal and ZnTe epilayer grown on GaAs substrate by MOVPE

    NASA Astrophysics Data System (ADS)

    Lü, Hai-Yan; Mu, Qi; Zhang, Lei; Lü, Yuan-Jie; Ji, Zi-Wu; Feng, Zhi-Hong; Xu, Xian-Gang; Guo, Qi-Xin

    2015-12-01

    Excitation power and temperature-dependent photoluminescence (PL) spectra of the ZnTe epilayer grown on (100) GaAs substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the GaAs substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor-acceptor pair (DAP) nor conduction band-acceptor (e-A) emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal. Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120131110006), the Key Science and Technology Program of Shandong Province, China (Grant No. 2013GGX10221), the Key Laboratory of Functional Crystal Materials and Device (Shandong University, Ministry of Education), China (Grant No. JG1401), the National Natural Science Foundation of China (Grant No. 61306113), the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91433112), and the Partnership Project for Fundamental Technology Researches of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

  7. Glass frit nebulizer for atomic spectrometry

    USGS Publications Warehouse

    Layman, L.R.

    1982-01-01

    The nebuilizatlon of sample solutions Is a critical step In most flame or plasma atomic spectrometrlc methods. A novel nebulzatlon technique, based on a porous glass frit, has been Investigated. Basic operating parameters and characteristics have been studied to determine how thte new nebulizer may be applied to atomic spectrometrlc methods. The results of preliminary comparisons with pneumatic nebulizers Indicate several notable differences. The frit nebulizer produces a smaller droplet size distribution and has a higher sample transport efficiency. The mean droplet size te approximately 0.1 ??m, and up to 94% of the sample te converted to usable aerosol. The most significant limitations In the performance of the frit nebulizer are the stow sample equMbratton time and the requirement for wash cycles between samples. Loss of solute by surface adsorption and contamination of samples by leaching from the glass were both found to be limitations only In unusual cases. This nebulizer shows great promise where sample volume te limited or where measurements require long nebullzatlon times.

  8. Atomic Energy Basics, Understanding the Atom Series.

    ERIC Educational Resources Information Center

    Atomic Energy Commission, Oak Ridge, TN. Div. of Technical Information.

    This booklet is part of the "Understanding the Atom Series," though it is a later edition and not included in the original set of 51 booklets. A basic survey of the principles of nuclear energy and most important applications are provided. These major topics are examined: matter has molecules and atoms, the atom has electrons, the nucleus,…

  9. Optical phonons in PbTe/CdTe multilayer heterostructures

    SciTech Connect

    Novikova, N. N.; Yakovlev, V. A.; Kucherenko, I. V.; Karczewski, G.; Aleshchenko, Yu. A.; Muratov, A. V.; Zavaritskaya, T. N.; Melnik, N. N.

    2015-05-15

    The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

  10. Coherent phonon study of (GeTe){sub l}(Sb{sub 2}Te{sub 3}){sub m} interfacial phase change memory materials

    SciTech Connect

    Makino, Kotaro Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2014-10-13

    The time-resolved reflectivity measurements were carried out on the interfacial phase change memory (iPCM) materials ([(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 4}]{sub 8} and [(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 1}]{sub 20}) as well as conventional Ge{sub 2}Sb{sub 2}Te{sub 5} alloy at room temperature and above the RESET-SET phase transition temperature. In the high-temperature phase, coherent phonons were clearly observed in the iPCM samples while drastic attenuation of coherent phonons was induced in the alloy. This difference strongly suggests the atomic rearrangement during the phase transition in iPCMs is much smaller than that in the alloy. These results are consistent with the unique phase transition model in which a quasi-one-dimensional displacement of Ge atoms occurs for iPCMs and a conventional amorphous-crystalline phase transition takes place for the alloy.

  11. Nondestructive Characterization of Residual Threading Dislocation Density in HgCdTe Layers Grown on CdZnTe by Liquid-Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Fourreau, Y.; Pantzas, K.; Patriarche, G.; Destefanis, V.

    2016-09-01

    The performance of mercury cadmium telluride (MCT)-based infrared (IR) focal-plane arrays is closely related to the crystalline perfection of the HgCdTe thin film. In this work, Te-rich, (111)B-oriented HgCdTe epilayers grown by liquid-phase epitaxy on CdZnTe substrates have been studied. Surface atomic steps are shown on as-grown MCT materials using atomic force microscopy (AFM) and white-light interferometry (WLI), suggesting step-flow growth. Locally, quasiperfect surface spirals are also evidenced. A demonstration is given that these spirals are related to the emergence of almost pure screw threading dislocations. A nondestructive and quantitative technique to measure the threading dislocation density is proposed. The technique consists of counting the surface spirals on the as-grown MCT surface from images obtained by either AFM or WLI measurements. The benefits and drawbacks of both destructive—chemical etching of HgCdTe dislocations—and nondestructive surface imaging techniques are compared. The nature of defects is also discussed. Finally, state-of-the-art threading dislocation densities in the low 104 cm-2 range are evidenced by both etch pit density (EPD) and surface imaging measurements.

  12. Ba{sub 2}TeO: A new layered oxytelluride

    SciTech Connect

    Besara, T.; Ramirez, D.; Sun, J.; Whalen, J.B.; Tokumoto, T.D.; McGill, S.A.; Singh, D.J.; Siegrist, T.

    2015-02-15

    Single crystals of the new semiconducting oxytelluride phase, Ba{sub 2}TeO, were synthesized from barium oxide powder and elemental tellurium in a molten barium metal flux. Ba{sub 2}TeO crystallizes in tetragonal symmetry with space group P4/nmm (#129), a=5.0337(1) Å, c=9.9437(4) Å, Z=2. The crystals were characterized by single crystal x-ray diffraction, heat capacity and optical measurements. The optical measurements along with electronic band structure calculations indicate semiconductor behavior with a band gap of 2.93 eV. Resistivity measurements show that Ba{sub 2}TeO is highly insulating. - Graphical abstract: Starting from a simple stacking of rocksalt layers, the final structure of Ba{sub 2}TeO can be obtained by accommodation of structural strain via atom displacements. Density of states calculations and optical absorbance measurements show that Ba{sub 2}TeO has a band gap of 2.93 eV, indicative of semiconductor behavior. - Highlights: • Single crystal synthesis of a new layered oxytelluride, Ba{sub 2}TeO. • The structure features inverse PbO-type BaO layers and NaCl-type BaTe layers. • Optical absorbance show Ba{sub 2}TeO to be a semiconductor with a 2.93 eV gap. • Density of states indicate a small hybridization between Te 5p and Ba 5d states. • The BaTe (BaO) layers dominate the heat capacity at low (high) temperatures.

  13. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    DOE PAGESBeta

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Wang, Jun; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show thatmore » the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.« less

  14. Determination of iridium in mafic rocks by atomic absorption

    USGS Publications Warehouse

    Grimaldi, F.S.; Schnepfe, M.M.

    1970-01-01

    Iridium is determined in mineralized mafic rocks by atomic absorption after fire-assay concentration into a gold bead. Interelement interferences in the atomic-absorption determination are removed and Ir sensitivity is increased by buffering the solutions with a mixture of copper and sodium sulphates. Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated in the atomic-absorption determination. The sensitivity and detection limits are 3.2 and 0.25 ppm of Ir, respectively. ?? 1970.

  15. Nanoscale Superconducting Honeycomb Charge Order in IrTe2

    NASA Astrophysics Data System (ADS)

    Kim, Hyo Sung; Kim, Sooran; Kim, Kyoo; Min, Byung Il; Cho, Yong-Heum; Wang, Lihai; Cheong, Sang-Wook; Yeom, Han Woong

    2016-07-01

    Entanglement of charge orderings and other electronic orders such as superconductivity is in the core of challenging physics issues of complex materials including high temperature superconductivity. Here, we report on the observation of a unique nanometer scale honeycomb charge ordering of the cleaved IrTe2 surface, which hosts a superconducting state. IrTe2 was recently established to exhibit an intriguing cascade of stripe charge orders. The stripe phases coexist with a hexagonal phase, which is formed locally and falls into a superconducting state below 3 K. The atomic and electronic structures of the honeycomb and hexagon pattern of this phase are consistent with the charge order nature but the superconductivity does not survive on neighboring stripe charge order domains. The present work provides an intriguing physics issue and a new direction of functionalization for two dimensional materials.

  16. DX centers in CdTe: a density functional study

    SciTech Connect

    Du, Mao-Hua

    2008-01-01

    DX centers induced by both group-III and group-VII donors in CdTe are studied using density functional calculations. The results show that, for group-VII donors, the DX centers with a cation-cation bond ({alpha}- and {beta}-CCB-DX centers) are more stable than the previously proposed broken-bond DX (BB-DX) center and the {beta}-CCB-DX center is the most stable. The stability trend found for the CCB-DX centers for different donors in CdTe is consistent with that for GaAs and GaSb, which suggests a general rule that the CCB-DX centers are favored for small donor atoms on anion site especially for semiconductors with large anion size.

  17. Nanoscale Superconducting Honeycomb Charge Order in IrTe2.

    PubMed

    Kim, Hyo Sung; Kim, Sooran; Kim, Kyoo; Min, Byung Il; Cho, Yong-Heum; Wang, Lihai; Cheong, Sang-Wook; Yeom, Han Woong

    2016-07-13

    Entanglement of charge orderings and other electronic orders such as superconductivity is in the core of challenging physics issues of complex materials including high temperature superconductivity. Here, we report on the observation of a unique nanometer scale honeycomb charge ordering of the cleaved IrTe2 surface, which hosts a superconducting state. IrTe2 was recently established to exhibit an intriguing cascade of stripe charge orders. The stripe phases coexist with a hexagonal phase, which is formed locally and falls into a superconducting state below 3 K. The atomic and electronic structures of the honeycomb and hexagon pattern of this phase are consistent with the charge order nature, but the superconductivity does not survive on neighboring stripe charge order domains. The present work provides an intriguing physics issue and a new direction of functionalization for two-dimensional materials. PMID:27221583

  18. Phase patterning for ohmic homojunction contact in MoTe2

    NASA Astrophysics Data System (ADS)

    Cho, Suyeon; Kim, Sera; Kim, Jung Ho; Zhao, Jiong; Seok, Jinbong; Keum, Dong Hoon; Baik, Jaeyoon; Choe, Duk-Hyun; Chang, K. J.; Suenaga, Kazu; Kim, Sung Wng; Lee, Young Hee; Yang, Heejun

    2015-08-01

    Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T’) molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 106. In situ scanning transmission electron microscopy results combined with theoretical calculations reveal that the Te vacancy triggers the local phase transition in MoTe2, achieving a true 2D device with an ohmic contact.

  19. Elastic properties of sulphur and selenium doped ternary PbTe alloys by first principles

    SciTech Connect

    Bali, Ashoka Chetty, Raju Mallik, Ramesh Chandra

    2014-04-24

    Lead telluride (PbTe) is an established thermoelectric material which can be alloyed with sulphur and selenium to further enhance the thermoelectric properties. Here, a first principles study of ternary alloys PbS{sub x}Te{sub (1−x)} and PbSe{sub x}Te{sub (1−x)} (0≤x≤1) based on the Virtual Crystal Approximation (VCA) is presented for different ratios of the isoelectronic atoms in each series. Equilibrium lattice parameters and elastic constants have been calculated and compared with the reported data. Anisotropy parameter calculated from the stiffness constants showed a slight improvement in anisotropy of elastic properties of the alloys over undoped PbTe. Furthermore, the alloys satisfied the predicted stability criteria from the elastic constants, showing stable structures, which agreed with the previously reported experimental results.

  20. Photoluminescence of Cu-related states in CdTe and CdS

    NASA Astrophysics Data System (ADS)

    Price, K. J.

    2000-10-01

    We present results of Cu-related photoluminescence (PL) in CdTe and CdS single crystals, and CdS/CdTe polycrystalline devices, doped by diffusion of thermally evaporated Cu. In crystalline CdTe:Cu our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming pairs involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-related states in CdTe:Cu samples exhibit a reversible "aging" behavior. In crystalline CdS:Cu, the main effect of Cu diffusion is a quenching of the PL intensity. We also show evidence of an exciton bound to a Cu-related site that is stable under short-term light illumination. In addition, a donor-acceptor pair transition may be observed in CdS:Cu using excitation energies below the transition emission energy. We find that PL from polycrystalline CdS/CdTe solar cells with Cu back contacts is qualitatively similar to that in crystalline CdTe:Cu and CdS:Cu. We relate the results to stability behavior of CdS/CdTe solar cells with Cu contacts. This work is supported by NREL.

  1. Electronic properties of mixed molybdenum dichalcogenide MoTeSe: LCAO calculations and Compton spectroscopy

    NASA Astrophysics Data System (ADS)

    Ahuja, Ushma; Kumar, Kishor; Joshi, Ritu; Bhavsar, D. N.; Heda, N. L.

    2016-07-01

    We have employed linear combination of atomic orbitals (LCAO) method to compute the Mulliken's population (MP), energy bands, density of states (DOS) and Compton profiles for hexagonal MoTeSe. The density functional theory (DFT) and hybridization of Hartree-Fock with DFT (B3LYP) have been used within the LCAO approximation. Performance of theoretical models has been tested by comparing the theoretical momentum densities with the experimental Compton profile of MoTeSe measured using 137Cs Compton spectrometer. It is seen that the B3LYP prescription gives a better agreement with the experimental data than other DFT based approximations. The energy bands and DOS depict an indirect band gap character in MoTeSe. In addition, a relative nature of bonding in MoTeSe and its isovalent MoTe2 is discussed in terms of equal-valence-electron-density (EVED) profiles. On the basis of EVED profiles it is seen that MoTeSe is more covalent than MoTe2.

  2. Metalorganic vapor phase epitaxy growth of ternary tetradymite Bi2Te3-xSex compounds

    NASA Astrophysics Data System (ADS)

    Kuznetsov, P. I.; Yakushcheva, G. G.; Luzanov, V. A.; Temiryazev, A. G.; Shchamkhalova, B. S.; Jitov, V. A.; Sizov, V. E.

    2015-01-01

    We report on a metal organic vapor epitaxy (MOVPE) of Bi2Te3-xSex films over the entire range of compositions (0 ≤ x ≤ 3) for the first time. The films were grown on Al2O3(0001) substrates at 465 °C using trimethylbismuth (Bi2Me3), diethyltellurium (Et2Te) and diisopropylselenium (iPro2Se) as metalorganic sources. To realize the 2D growth mode and to grow films with flat surfaces and high crystalline quality, a thin ZnTe buffer layer was used. As-grown films were studied using optical and AFM microscopy techniques and X-ray diffraction. It was found that under steady growth conditions the composition of Bi2Te3-xSex films strongly depends on the film thickness. But a high rate of interdiffusion of chalcogens at the growth temperature rapidly leads to a homogeneous composition of the film in the growth direction. Dependence of the intensity of X-ray reflection (0012) on the composition of Bi2Te3-xSex films x has extremes near x=1 (Bi2Te2 Se) and x=2 (Bi2Se2 Te). The AFM micrographs and profiles show large (above 2 μm) triangle-shaped atomically flat terraces with step height of a quintuple layer (0.90 nm) of the tetradymite-type compounds. The electronic properties of the grown films have been characterized via four probe magnetotransport measurements.

  3. Mesityltellurenyl cations stabilized by triphenylpnictogens [MesTe(EPh(3))](+) (E = P, As, Sb).

    PubMed

    Beckmann, Jens; Bolsinger, Jens; Duthie, Andrew; Finke, Pamela; Lork, Enno; Lüdtke, Carsten; Mallow, Ole; Mebs, Stefan

    2012-11-19

    The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes2)]O3SCF3 (1) featuring the cation [MesTe(TeMes2)](+) (1a) was obtained by the reaction of Mes2Te with HO3SCF3. The reaction of 1 with Ph3E (E = P, As, Sb, Bi) proceeded with substitution of Mes2Te and provided the heteroleptic 1:1 LP complexes [MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) and [MesTe(SbPh3)][Ph2Sb(O3SCF3)2] (4) featuring the cations [MesTe(EPh3)](+) (2a, E = P; 3a, E = As; 4a, E = Sb) and the anion [Ph2Sb(O3SCF3)2](-) (4b). In the reaction with Ph3Bi, the crude product contained the cation [MesTe(BiPh3)](+) (5a) and the anion [Ph2Bi(O3SCF3)2](-) (5b); however, the heteroleptic 1:1 LP complex [MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5) could not be isolated because of its limited stability. Instead, fractional crystallization furnished a large amount of Ph2BiO3SCF3 (6), which was also obtained by the reaction of Ph3Bi with HO3SCF3. The formation of the anions 4b and 5b involves a phenyl group migration from Ph3E (E = Sb, Bi) to the MesTe(+) cation and afforded MesTePh as the byproduct, which was identified in the mother liquor. The heteroleptic 1:1 LP complexes 2-4 were also obtained by the one-pot reaction of Mes2Te, Ph3E (E = P, As, Sb) and HO3SCF3. Compounds 1-4 and 6 were investigated by single-crystal X-ray diffraction. The molecular structures of 1a-4a were used for density functional theory calculations at the B3PW91/TZ level of theory and studied using natural bond order (NBO) analyses as well as real-space bonding descriptors derived from an atoms-in-molecules (AIM) analysis of the theoretically obtained electron density. Additionally, the electron localizability indicator (ELI-D) and the delocalization index are derived from the corresponding pair density. PMID:23134409

  4. Mesityltellurenyl cations stabilized by triphenylpnictogens [MesTe(EPh(3))](+) (E = P, As, Sb).

    PubMed

    Beckmann, Jens; Bolsinger, Jens; Duthie, Andrew; Finke, Pamela; Lork, Enno; Lüdtke, Carsten; Mallow, Ole; Mebs, Stefan

    2012-11-19

    The homoleptic 1:1 Lewis pair (LP) complex [MesTe(TeMes2)]O3SCF3 (1) featuring the cation [MesTe(TeMes2)](+) (1a) was obtained by the reaction of Mes2Te with HO3SCF3. The reaction of 1 with Ph3E (E = P, As, Sb, Bi) proceeded with substitution of Mes2Te and provided the heteroleptic 1:1 LP complexes [MesTe(EPh3)]O3SCF3 (2, E = P; 3, E = As) and [MesTe(SbPh3)][Ph2Sb(O3SCF3)2] (4) featuring the cations [MesTe(EPh3)](+) (2a, E = P; 3a, E = As; 4a, E = Sb) and the anion [Ph2Sb(O3SCF3)2](-) (4b). In the reaction with Ph3Bi, the crude product contained the cation [MesTe(BiPh3)](+) (5a) and the anion [Ph2Bi(O3SCF3)2](-) (5b); however, the heteroleptic 1:1 LP complex [MesTe(BiPh3)][Ph2Bi(O3SCF3)2] (5) could not be isolated because of its limited stability. Instead, fractional crystallization furnished a large amount of Ph2BiO3SCF3 (6), which was also obtained by the reaction of Ph3Bi with HO3SCF3. The formation of the anions 4b and 5b involves a phenyl group migration from Ph3E (E = Sb, Bi) to the MesTe(+) cation and afforded MesTePh as the byproduct, which was identified in the mother liquor. The heteroleptic 1:1 LP complexes 2-4 were also obtained by the one-pot reaction of Mes2Te, Ph3E (E = P, As, Sb) and HO3SCF3. Compounds 1-4 and 6 were investigated by single-crystal X-ray diffraction. The molecular structures of 1a-4a were used for density functional theory calculations at the B3PW91/TZ level of theory and studied using natural bond order (NBO) analyses as well as real-space bonding descriptors derived from an atoms-in-molecules (AIM) analysis of the theoretically obtained electron density. Additionally, the electron localizability indicator (ELI-D) and the delocalization index are derived from the corresponding pair density.

  5. Structural insights into the thermal decomposition sequence of barium tetrahydrogenorthotellurate(VI), Ba[H4TeO6

    NASA Astrophysics Data System (ADS)

    Weil, Matthias; Stöger, Berthold; Gierl-Mayer, Christian; Libowitzky, Eugen

    2016-09-01

    The compounds Ba[H4TeO6] (I), Ba[H2TeO5] (II), Ba[Te2O6(OH)2] (III) and Ba[TeO4] (IV) were prepared by application of a diffusion method (I), under hydrothermal conditions (II and III) and from solid state reactions (IV), respectively. Structure analysis on the basis of single crystal X-ray diffraction data revealed novel structure types for (I), (II) and (III) and isotypism of (IV) with PrSbO4 and LaSbO4. Common feature of the four oxotellurate(VI) structures are [TeO6] octahedra. Whereas in the crystal structure of (I) the octahedral units are isolated, they are condensed into chains via corner-sharing in (II) and via edge-sharing in (III) and (IV). The coordination numbers of the barium cations in the four structures range from seven to ten. Although hydrogen atom positions could not be located for the structures of (I) and (II), short interpolyhedral O···O contacts are evident for strong hydrogen bonding. The temperature behaviour of (I), (II) and (IV) was monitored by simultaneous thermal analysis (STA) measurements and in situ powder X-ray diffraction, revealing the decomposition sequence Ba[H4TeO6] → Ba[H2TeO5] → Ba[TeO4]→ Ba[TeO3] upon heating to temperatures up to 900 °C.

  6. Strain-engineered diffusive atomic switching in two-dimensional crystals

    PubMed Central

    Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

    2016-01-01

    Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563

  7. BOREAS TE-7 Dendrology Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Varem-Sanders, T. M. L.; Campbell, I. D.

    2000-01-01

    The BOREAS TE-7 team collected data sets in support of its efforts to characterize and interpret information on the sapflow and dendrology of boreal vegetation. This data set contains dendrology measurements, consisting of tree ring width and density taken at several points within each ring,.Measurements were taken near the TE towers at the OJP and OBS sites in NSA. In the SSA, measurements were taken near the TE towers at the MIX, OBS, and OJP sites; at the AIM- 1 3 and BMH-9 sites; and near the TF-YJP site. All data were collected during the summer of 1994. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  8. Ultracold-Atom Accelerometers

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1995-01-01

    Proposed class of accelerometers and related motion sensors based on use of ultracold atoms as inertial components of motion transducers. Ultracold atoms supplant spring-and-mass components of older accelerometers. As used here, "ultracold atoms" means atoms with kinetic energies equivalent to temperatures equal to or less than 20 mK. Acclerometers essentially frictionless. Primary advantage high sensitivity.

  9. M@TE - Monitoring at TeV Energies

    NASA Astrophysics Data System (ADS)

    Tovmassian, Gagik; Dorner, Daniela; Bretz, Thomas; González, Magdalena; Alfaro, Ruben

    2016-06-01

    A dedicated long-term monitoring programm at TeV energies has been started by the FACT project about four years ago. Being limited to one site, gaps due to the rotation of the Earth remain in the measured light curves. This makes it difficult to study typical variability time scales of few hours to one day. To allow for systematic studies of continuous observations over up to 12 hours, a second telescope is being installed at a site in about six hours distance in longitude. For the M@TE (Monitoring at TeV energies) telescope, a mount from a previous experiment is being refurbished and will be equipped with a new camera. Using silicon based photo sensors like in FACT, an excellent and stable performance will be achieved. M@TE is a joint project of German and Mexican universities which aims at extending the blazar monitoring to so far unexplored time ranges. In the presentation, the status of this emerging project will be reported.

  10. Structure and energetics of As dimers on GaAs:(chalcogen) (001) surfaces and GaAs/Te/InAs interface

    NASA Astrophysics Data System (ADS)

    Miwa, R. H.; Ferraz, A. C.

    1998-01-01

    We have performed first principles calculations for the adsorption of As2 molecules over GaAs:Te, GaAs:Se and GaAs:S(001) surfaces. We investigate the dimer exchange process between the adsorbed As2 dimer and the sublayer chalcogen atoms. The adsorption on Te terminated surface and the subsequent exchange process, confirm the surfactant action of Te atoms. For Se and S covered surfaces, the adsorption of As2 molecule is an exothermic process, but the subsequent Se(S) ↔ As exchange process is not energetically favourable. The GaAs/Te/InAs interface with half a monolayer of Te is also considered. For the interface we find a valence-band offset of 0.18 eV.

  11. A monotopic aluminum telluride with an Al=Te double bond stabilized by N-heterocyclic carbenes

    PubMed Central

    Franz, Daniel; Szilvási, Tibor; Irran, Elisabeth; Inoue, Shigeyoshi

    2015-01-01

    Aluminum chalcogenides are mostly encountered in the form of bulk aluminum oxides that are structurally diverse but typically consist of networks with high lattice energy in which the chalcogen atoms bridge the metal centres. This makes their molecular congeners difficult to synthesize because of a pronounced tendency for oligomerization. Here we describe the isolation of the monotopic aluminum chalcogenide (LDipN)AlTe(LEt)2 (LDip=1,3-(2,6-diisopropylphenyl)-imidazolin-2-imine, LEt=1,3-diethyl-4,5-dimethyl-imidazolin-2-ylidene). Unique features of (LDipN)AlTe(LEt)2 are the terminal position of the tellurium atom, the shortest aluminum–tellurium distance hitherto reported for a molecular complex and the highest bond order reported for an interaction between these elements, to the best of our knowledge. At elevated temperature (LDipN)AlTe(LEt)2 equilibrates with dimeric {(LDipN)AlTe(LEt)}2 in which the chalcogen atoms assume their common role as bridges between the metal centres. These findings demonstrate that (LDipN)AlTe(LEt)2 comprises the elusive Al=Te double bond in the form of an N-heterocyclic carbene-stabilized species. PMID:26612781

  12. Synthesis of alpha-MoTe2 nanorods via annealing Te-seeded amorphous MoTe2 particles.

    PubMed

    Qiu, Longhui; Wei, Yun; Pol, Vilas G; Gedanken, Aharon

    2004-09-20

    Semiconductor alpha-MoTe2 nanorods have been synthesized by annealing Te-seeded particles of an amorphous MoTe2 intermediate. This intermediate is prepared by a solution reaction between Mo(CO)6 and elemental Te in diphenylmethane. The as-synthesized products were characterized by structural, compositional, and morphological techniques of X-ray diffraction, selected area electron diffraction, selected area energy dispersive spectroscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The results of the annealing process are MoTe2 nanorods with diameters of 50-200 nm and lengths ranging from 0.1 to 3.0 microm. Here, the rodlike structure of MoTe2 is reported for the first time, and added to the list as one kind of new morphology of MoTe2 nanomaterials. A mechanism for the formation of the nanorods is proposed. The sandwich-layered structure of Te-Mo-Te and the similarity in the structure between hexagonal alpha-MoTe2 and hexagonal Te are responsible for the formation of nanorods of MoTe2. PMID:15360257

  13. Neutral atom traps.

    SciTech Connect

    Pack, Michael Vern

    2008-12-01

    This report describes progress in designing a neutral atom trap capable of trapping sub millikelvin atom in a magnetic trap and shuttling the atoms across the atom chip from a collection area to an optical cavity. The numerical simulation and atom chip design are discussed. Also, discussed are preliminary calculations of quantum noise sources in Kerr nonlinear optics measurements based on electromagnetically induced transparency. These types of measurements may be important for quantum nondemolition measurements at the few photon limit.

  14. Study on the nitrogen-doped W-Sb-Te material for phase change memory application

    SciTech Connect

    Ren, Kun; Xia, Mengjiao; Ding, Keyuan; Ji, Xinglong; Rao, Feng Song, Zhitang; Wu, Liangcai; Liu, Bo; Feng, Songlin

    2014-04-28

    N doping is proposed to enlarge sensing margin of W{sub 0.08}(Sb{sub 2}Te){sub 0.92} based high-temperature phase-change memories (PCMs). The sensing margin is increased from 30 to 5 × 10{sup 3}, with an increase from 145 °C to 158 °C in data retention. The grain size is reduced to 10 nm. The PCM based on N-W{sub 0.08}(Sb{sub 2}Te){sub 0.92} shows the fast operation speed of 30 ns and good cycling ability of >10{sup 3}. By X-ray photoelectron spectroscopy and ab initio calculation, the W atoms are suggested to locate in the Sb positions and interstices of the lattice. The W atoms in interstice will bond to N atoms during N doping.

  15. Single-crystal structure study of iron chalcogenides Fe{sub 1+δ}Te{sub 1−x}S{sub x}

    SciTech Connect

    Shchichko, I. O.; Makarova, I. P.; Presnyakov, M. Yu.; Kazakov, S. M.; Antipov, E. V.; Chareev, D. A.; Mitrofanova, E. S.; Mikhutkin, A. A.; Vasil’ev, A. L.

    2015-03-15

    Single crystals of iron chalcogenides Fe{sub 1+δ}Te{sub 1−x}S{sub x} (x = 0, 0.09, and 0.1) were studied by scanning, transmission, and scanning transmission electron microscopy. In addition, a sample with x = 0 was studied by X-ray diffraction. The Te-site disorder observed in Fe{sub 1+δ} samples is, apparently, assigned to the incorporation of superstoichiometric iron Fe2 into the structure. The Fe1 atoms were found to be displaced from their ideal positions, which can only partially be attributed to electro-optical effects. The replacement of Te atoms by S in Fe{sub 1+δ}Te{sub 1−x}S{sub x} crystals gives rise to domains with ordered S atoms in some regions of the single crystal, resulting in the formation of a 2 × 1 or 2 × 2 superstructure.

  16. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3

    SciTech Connect

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J. L.; Zhong, Ruidan D.; Schneeloch, John A.; Liu, Tiansheng S.; Valla, Tonica; Tranquada, John M.; Gu, Genda D.; Davis, J. C. Séamus

    2015-01-20

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a “Dirac-mass gap” in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr₀.₀₈(Bi₀.₁Sb₀.₉)₁.₉₂Te₃. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm². In addition, these observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  17. Photoemission determination of the band diagram of the Te/CdTe interface

    NASA Astrophysics Data System (ADS)

    Niles, David W.; Li, Xiaonan; Sheldon, Peter

    1995-05-01

    A band diagram of the Te/CdTe interface was believed to be a prerequisite in understanding how the Te layer on the CdTe surface lowered the resistance of contacts to CdTe solar cell devices. A two-stage experiment was therefore designed. First, the application of x-ray photoelectron and Auger electron spectroscopies was discussed to comprehend the etching process. Second, the valence-band offset by vacuum deposition of Te on a sputtered CdTe surface was measured employing ultraviolet photoemission spectroscopy.

  18. Studies of low temperature photoluminescence spectra and excitonic valley polarization in monolayer MoTe2

    NASA Astrophysics Data System (ADS)

    Koirala, Sandhaya; Mouri, Shinichiro; Miyauchi, Yuhei; Matsuda, Kazunari; Kyoto University Team

    Recently, atomically thin layered transition-metal dichalcogenide (TMDs) in the form MX2 (M = Mo, W, X = S, Se, Te) have attracted much interest from the viewpoints of their fundamental physics and potential applications. The characteristic optical features of semiconducting TMDs arise from excitons confined in their atomically thin layers. Molybdenum ditelluride MoTe2 has attracted emerging research interest because of optical gap energy (lowest exciton transition) of 1.09 eV, and large spin-orbit coupling of 250 meV. Temperature-dependent photoluminescence (PL) and polarization-resolved PL measurement were performed for mechanically exfoliated monolayer MoTe2 from 4.4 to 300 K. At a low temperature, the PL spectra from MoTe2 show two sharp peaks for excitons and charged excitons (trions). The systematic temperature-dependent PL measurements revel that the homogeneous linewidth of the exciton peak broadens linearly as the temperature increased due to exciton-acoustic-phonon interactions. From polarization-resolved PL measurements, the valley polarization of above 40 % in the exciton state has been observed at low temperatures. In this meeting, we will discuss about exciton dephasing and valley polarization in monolayer MoTe2.

  19. Atomic Particle Detection, Understanding the Atom Series.

    ERIC Educational Resources Information Center

    Hellman, Hal

    This booklet is one of the booklets in the "Understanding the Atom Series" published by the U. S. Atomic Energy Commission for high school science teachers and their students. The instruments used to detect both particles and electromagnetic radiation that emerge from the nucleus are described. The counters reviewed include ionization chambers,…

  20. Atomic Fuel, Understanding the Atom Series. Revised.

    ERIC Educational Resources Information Center

    Hogerton, John F.

    This publication is part of the "Understanding the Atom" series. Complete sets of the series are available free to teachers, schools, and public librarians who can make them available for reference or use by groups. Among the topics discussed are: What Atomic Fuel Is; The Odyssey of Uranium; Production of Uranium; Fabrication of Reactor Fuel…

  1. In-situ crystallization of GeTe\\GaSb phase change memory stacked films

    SciTech Connect

    Velea, A.; Borca, C. N.; Grolimund, D.; Socol, G.; Galca, A. C.; Popescu, M.; Bokhoven, J. A. van

    2014-12-21

    Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.

  2. Study of adhesion of vertically aligned carbon nanotubes to a substrate by atomic-force microscopy

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Blinov, Yu. F.; Il'ina, M. V.; Il'in, O. I.; Smirnov, V. A.; Tsukanova, O. G.

    2016-02-01

    The adhesion to a substrate of vertically aligned carbon nanotubes (VA CNT) produced by plasmaenhanced chemical vapor deposition has been experimentally studied by atomic-force microscopy in the current spectroscopy mode. The longitudinal deformation of VA CNT by applying an external electric field has been simulated. Based on the results, a technique of determining VA CNT adhesion to a substrate has been developed that is used to measure the adhesion strength of connecting VA CNT to a substrate. The adhesion to a substrate of VA CNT 70-120 nm in diameter varies from 0.55 to 1.19 mJ/m2, and the adhesion force from 92.5 to 226.1 nN. When applying a mechanical load, the adhesion strength of the connecting VA CNT to a substrate is 714.1 ± 138.4 MPa, and the corresponding detachment force increases from 1.93 to 10.33 μN with an increase in the VA CNT diameter. As an external electric field is applied, the adhesion strength is almost doubled and is 1.43 ± 0.29 GPa, and the corresponding detachment force is changed from 3.83 to 20.02 μN. The results can be used in the design of technological processes of formation of emission structures, VA CNT-based elements for vacuum microelectronics and micro- and nanosystem engineering, and also the methods of probe nanodiagnostics of VA CNT.

  3. PHYSICS: Toward Atom Chips.

    PubMed

    Fortágh, József; Zimmermann, Claus

    2005-02-11

    As a novel approach for turning the peculiar features of quantum mechanics into practical devices, researchers are investigating the use of ultracold atomic clouds above microchips. Such "atom chips" may find use as sensitive probes for gravity, acceleration, rotation, and tiny magnetic forces. In their Perspective, Fortagh and Zimmermann discuss recent advances toward creating atom chips, in which current-carrying conductors in the chips create magnetic microtraps that confine the atomic clouds. Despite some intrinsic limits to the performance of atom chips, existing technologies are capable of producing atom chips, and many possibilities for their construction remain to be explored.

  4. Atom probe tomography

    SciTech Connect

    Miller, M.K.; Forbes, R.G.

    2009-06-15

    This introductory tutorial describes the technique of atom probe tomography for materials characterization at the atomic level. The evolution of the technique from the initial atom probe field ion microscope to today's state-of-the-art three dimensional atom probe is outlined. An introduction is presented on the basic physics behind the technique, the operation of the instrument, and the reconstruction of the three-dimensional data. The common methods for analyzing the three-dimensional atom probe data, including atom maps, isoconcentration surfaces, proximity histograms, maximum separation methods, and concentration frequency distributions, are described.

  5. Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

  6. New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current.

    PubMed

    Park, Yong-Jin; Cho, Ju-Young; Jeong, Min-Woo; Na, Sekwon; Joo, Young-Chang

    2016-02-23

    The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm(2)), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current.

  7. New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current

    PubMed Central

    Park, Yong-Jin; Cho, Ju-Young; Jeong, Min-Woo; Na, Sekwon; Joo, Young-Chang

    2016-01-01

    The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm2), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current. PMID:26902593

  8. New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current.

    PubMed

    Park, Yong-Jin; Cho, Ju-Young; Jeong, Min-Woo; Na, Sekwon; Joo, Young-Chang

    2016-01-01

    The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm(2)), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current. PMID:26902593

  9. RHEED study of the (1 1 0) cleavage surface of CdTe:Cr single crystals

    NASA Astrophysics Data System (ADS)

    Sagan, P.; Kuzma, M.

    2007-03-01

    The structure of (1 1 0) plane of Cr-doped CdTe single crystals has been studied by reflection high energy electron diffraction and scanning electron microscopy. Diffraction patterns consist of diffraction spots and Kikuchi lines. However, for very small incident angle, the Debye rings are observed. The constant lattice attributed to these rings is 0.8% less then for pure CdTe. These anomalous properties of the near surface layer are likely to occur due to the concentration of Cr atoms creating compressive surface strains or the effect of crystal cleavage.

  10. Structural Study of Liquid Se-Te Alloys by Neutron Diffraction

    NASA Astrophysics Data System (ADS)

    Takeda, Shin'ichi; Tamaki, Shigeru; Waseda, Yoshio

    1986-12-01

    The neutron diffraction study of liquid Se-Te system has been carried out to reveal the origin of characteristic temperature dependence of various properties related to the structural order in atomic scale. The temperature dependence of measured structural functions of liquid SexTe1-x system could be explained by a gradual transition from two-fold coordinated component (non-metallic) to the three-fold coordinated one (metallic). The partial structure factors of these two-fold and three-fold coordinations are separated with the help of the thermodynamic data. A configurational model satisfying these situations is also presented.

  11. Graphene/CdTe heterostructure solar cell and its enhancement with photo-induced doping

    SciTech Connect

    Lin, Shisheng Chen, Hongsheng; Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian

    2015-11-09

    We report a type of solar cell based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.10%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by field effect transport, Raman, photoluminescence, and quantum efficiency measurements. This work demonstrates a feasible way of improving the performance of graphene/semiconductor heterostructure solar cells by combining one dimensional with two dimensional materials.

  12. Learning To Use TeX

    NASA Astrophysics Data System (ADS)

    Hammons, Derek; Close, Hunter

    2012-03-01

    TeX is a useful tool for any scientific professional, but it can also be used by undergraduates to create high quality documents for courses. My presentation will focus on why TeX is a useful program for undergraduates to learn. It can create higher quality lab reports and other documents for courses than other commonly used word processors such as Microsoft Word. TeX can be utilized by anyone through use of a TeX document preparation system such as LaTeX and only a few simple commands. Perhaps best of all, TeX is free to download and use! By taking the time to understand how to use TeX, students will learn a valuable skill that will be continue to be useful throughout their academic and professional careers.

  13. BSA activated CdTe quantum dot nanosensor for antimony ion detection.

    PubMed

    Ge, Shenguang; Zhang, Congcong; Zhu, Yuanna; Yu, Jinghua; Zhang, Shuangshuang

    2010-01-01

    A novel fluorescent nanosensor for Sb(3+) determination was reported based on thioglycolic acid (TGA)-capped CdTe quantum dot (QD) nanoparticles. It was the first antimony ion sensor using QD nanoparticles in a receptor-fluorophore system. The water-soluable TGA-capped CdTe QDs were prepared through a hydrothermal route, NaHTe was used as the Te precursor for CdTe QDs synthesis. Bovine serum albumin (BSA) conjugated to TGA-capped CdTe via an amide link interacting with carboxyl of the TGA-capped CdTe. When antimony ion enters the BSA, the lone pair electrons of the nitrogen and oxygen atom become involved in the coordination, switching off the QD emission and a dramatic quenching of the fluorescence intensity results, allowing the detection of low concentrations of antimony ions. Using the operating principle, the antimony ion sensor based on QD nanoparticles showed a very good linearity in the range 0.10-22.0 microg L(-1), with the detection limit lower than 2.94 x 10(-8) g L(-1) and the relative standard deviation (RSD) 2.54% (n = 6). In a study of interferences, the antimony-sensitive TGA-QD-BSA sensor showed good selectivity. Therefore, a simple, fast, sensitive, and highly selective assay for antimony has been built. The presented method has been applied successfully to the determination of antimony in real water samples (n = 6) with satisfactory results.

  14. Thickness identification of epitaxial Bi2Te3 via optical contrast

    NASA Astrophysics Data System (ADS)

    Vajner, Cooper; Yan, Haoming; Guo, Lingling; Mathews, Melissa; Kuhlman, Michael; Benefield, Shellby; Ulrich, Steven; Zolghadr, Ehsan; Kung, Patrick; Li, Lin; Araujo, Paulo T.; Wang, Hung-Ta

    2016-06-01

    Two-dimensional (2D) nanosheet thickness identification is effective for rapidly determining thickness-dependent properties of 2D materials. Bismuth telluride (Bi2Te3) is a 2D material known for its promising thermoelectric properties and potential dissipationless charge transport in the topological surface states. To date, thickness measurements of Bi2Te3 2D nanosheets are mainly carried out via atomic force microscope or Raman spectroscopy. Here, we investigate a practical, rapid, inexpensive, and non-invasive thickness measurement technique that utilizes the optical contrast of Bi2Te3 2D nanosheets on a mica substrate (i.e., as-grown) and a SiO2/Si substrate (i.e., transferred). The reflected optical intensity and the corresponding contrast are studied as a function of Bi2Te3 thickness, illumination wavelength, and substrate thickness. Disagreement between experimental and calculated optical contrast values is observed, which is ascribed to the thickness-dependent refractive indices of Bi2Te3, mica thickness error, and the deviation from normal light incidence. Despite thin film interference in mica, the monotonic relationship between nanosheet’s contrast and thickness makes mica a better substrate for identifying Bi2Te3 thickness. In addition, a brief recipe is provided for such a thickness identification method to be generally applied in any laboratory.

  15. Pulsars at TeV

    NASA Astrophysics Data System (ADS)

    Edwards, P.

    1994-04-01

    The atmospheric Cerenkov technique is used to search for emission at energies above several hundred GeV from a variety of objects, including pulsars (see, e.g., reviews by Weekes, 1988, Phys. Rep., 160, 1; Weekes, 1992, Sp. Sci. Rev., 59, 315). Claims for TeV emission (from any source) should be of high significance, show gamma-ray-like properties, and be independently confirmed. By these criteria the Crab nebula is currently the only established pulsar-driven system to be observed at TeV energies (Weekes et al., 1989, Astrophys. J., 342, 379; Vacanti et al., 1991, Astrophys. J., 377, 467; Goret et al., 1993, Astron. Astrophys., 270, 401). The gamma-ray signal is not pulsed at TeV energies, leading to models of synchrotron self-Compton emission from the Crab nebula (e.g., De Jager and Harding, 1992, Astrophys. J., 396, 161), although other models have also been proposed (Kwok et al., 1991, Astrophys. J., 379, 653). While claims exist for TeV emission from, amongst others, the Vela pulsar (e.g., Bhat et al., 1987, Astron. Astrophys., 178, 242, Geminga (Vishwanath et al., 1993, Astron. Astrophys., 267, L5; Bowden et al., 1993, J. Phys. G: Nucl. Part. Phys., 19, L29), and PSR 1509-58 (Nel et al., 1992, Astrophys. TeV sources. *The detection of TeV gamma-rays from millisecond pulsars has been considered recently by Smith (1993, Astrophys. -J., 408, 468).

  16. Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

    SciTech Connect

    Belianinov, Alex; Panchapakesan, G.; Lin, Wenzhi; Sales, Brian C.; Sefat, Athena Safa; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.

    2014-12-02

    Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1 x Sex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

  17. Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

    NASA Astrophysics Data System (ADS)

    Belianinov, Alex; Ganesh, Panchapakesan; Lin, Wenzhi; Sales, Brian C.; Sefat, Athena S.; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.

    2014-12-01

    Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1-xSex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

  18. Determination of tellurium by hydride generation with in situ trapping flame atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Matusiewicz, Henryk; Krawczyk, Magdalena

    2007-03-01

    The analytical performance of coupled hydride generation — integrated atom trap (HG-IAT) atomizer flame atomic absorption spectrometry (FAAS) system was evaluated for determination of Te in reference material (GBW 07302 Stream Sediment), coal fly ash and garlic. Tellurium, using formation of H 2Te vapors, is atomized in air-acetylene flame-heated IAT. A new design HG-IAT-FAAS hyphenated technique that would exceed the operational capabilities of existing arrangements (a water-cooled single silica tube, double-slotted quartz tube or an "integrated trap") was investigated. An improvement in detection limit was achieved compared with using either of the above atom trapping techniques separately. The concentration detection limit, defined as 3 times the blank standard deviation (3 σ), was 0.9 ng mL - 1 for Te. For a 2 min in situ pre-concentration time (sample volume of 2 mL), sensitivity enhancement compared to flame AAS, was 222 fold, using the hydride generation — atom trapping technique. The sensitivity can be further improved by increasing the collection time. The precision, expressed as RSD, was 7.0% ( n = 6) for Te. The designs studied include slotted tube, single silica tube and integrated atom trap-cooled atom traps. The accuracy of the method was verified using a certified reference material (GBW 07302 Stream Sediment) by aqueous standard calibration curves. The measured Te contents of the reference material was in agreement with the information value. The method was successfully applied to the determination of tellurium in coal fly ash and garlic.

  19. Presenting the Bohr Atom.

    ERIC Educational Resources Information Center

    Haendler, Blanca L.

    1982-01-01

    Discusses the importance of teaching the Bohr atom at both freshman and advanced levels. Focuses on the development of Bohr's ideas, derivation of the energies of the stationary states, and the Bohr atom in the chemistry curriculum. (SK)

  20. n-(CdMgTe/CdTe)/(p-(CdTe/ZnCdTe/ZnTe)/p-GaAs heterostructure diode for photosensor applications

    NASA Astrophysics Data System (ADS)

    Yahia, I. S.; AlFaify, S.; Abutalib, M. M.; Chusnutdinow, S.; Wojtowicz, T.; Karczewski, G.; Yakuphanoglu, F.; Al-Bassam, A.; El-Naggar, A. M.; El-Bashir, S. M.

    2016-05-01

    High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole-Cole plots. The radius of the Cole-Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.

  1. Aqueous synthesis of ZnTe/dendrimer nanocomposites and their antimicrobial activity: implications in therapeutics

    NASA Astrophysics Data System (ADS)

    Ghosh, S.; Ghosh, D.; Bag, P. K.; Bhattacharya, S. C.; Saha, A.

    2011-03-01

    have a good degree of crystallinity with a hexagonal crystal phase. The antibacterial activities of the ZnTe/dendrimer nanocomposites (ZnTe DNCs) as well other semiconductor nanocomposites were evaluated against enteropathogenic bacteria including multi-drug resistant Vibrio cholerae serogroup O1 and enterotoxigenic Escherichia coli (ETEC). ZnTe DNCs had significant antibacterial activity against strains of V. cholerae and ETEC with minimum inhibitory concentrations ranging from 64 to 512 μg ml-1 and minimum bactericidal concentrations ranging from 128 to 1000 μg ml-1. Thus, the observed results suggest that these water-soluble active nanocomposites have potential for the treatment of enteric diseases like diarrhoea and cholera. Electronic supplementary information (ESI) available: Dynamic light scattering, atomic force microscopy and hemolytic activity of the nanocomposites. See DOI: 10.1039/c0nr00610f

  2. Atomizing nozzle and process

    DOEpatents

    Anderson, Iver E.; Figliola, Richard S.; Molnar, Holly M.

    1992-06-30

    High pressure atomizing nozzle includes a high pressure gas manifold having a divergent expansion chamber between a gas inlet and arcuate manifold segment to minimize standing shock wave patterns in the manifold and thereby improve filling of the manifold with high pressure gas for improved melt atomization. The atomizing nozzle is especially useful in atomizing rare earth-transition metal alloys to form fine powder particles wherein a majority of the powder particles exhibit particle sizes having near-optimum magnetic properties.

  3. Atoms in Action

    SciTech Connect

    2009-01-01

    This movie produced with Berkeley Lab's TEAM 0.5 microscope shows the growth of a hole and the atomic edge reconstruction in a graphene sheet. An electron beam focused to a spot on the sheet blows out the exposed carbon atoms to make the hole. The carbon atoms then reposition themselves to find a stable configuration. http://newscenter.lbl.gov/press-releases/2009/03/26/atoms-in-action/

  4. Atomizing nozzle and process

    DOEpatents

    Anderson, I.E.; Figliola, R.S.; Molnar, H.M.

    1993-07-20

    High pressure atomizing nozzle includes a high pressure gas manifold having a divergent expansion chamber between a gas inlet and arcuate manifold segment to minimize standing shock wave patterns in the manifold and thereby improve filling of the manifold with high pressure gas for improved melt atomization. The atomizing nozzle is especially useful in atomizing rare earth-transition metal alloys to form fine powder particles wherein a majority of the powder particles exhibit particle sizes having near-optimum magnetic properties.

  5. Adaptive atom-optics in atom interferometry

    NASA Astrophysics Data System (ADS)

    Marable, M. L.; Savard, T. A.; Thomas, J. E.

    1997-02-01

    We suggest a general technique for creating virtual atom-optical elements which are adaptive. The shape and position of these elements is determined by the frequency distribution for optical fields which induce transitions in a high gradient potential. This adaptive method is demonstrated in an all-optical atom interferometer, by creating either a variable optical slit or a variable optical grating which is scanned across the atomic spatial patterns to measure the fringes. This method renders mechanical motion of the interferometer elements unnecessary.

  6. Atomic Spectra Database (ASD)

    National Institute of Standards and Technology Data Gateway

    SRD 78 NIST Atomic Spectra Database (ASD) (Web, free access)   This database provides access and search capability for NIST critically evaluated data on atomic energy levels, wavelengths, and transition probabilities that are reasonably up-to-date. The NIST Atomic Spectroscopy Data Center has carried out these critical compilations.

  7. The Nature of Atoms.

    ERIC Educational Resources Information Center

    Holden, Alan

    This monograph was written for the purpose of presenting physics to college students who are not preparing for careers in physics. It deals with the nature of atoms, and treats the following topics: (1) the atomic hypothesis, (2) the chemical elements, (3) models of an atom, (4) a particle in a one-dimensional well, (5) a particle in a central…

  8. Images of Atoms.

    ERIC Educational Resources Information Center

    Wright, Tony

    2003-01-01

    Recommends using a simple image, such as the fuzzy atom ball to help students develop a useful understanding of the molecular world. Explains that the image helps students easily grasp ideas about atoms and molecules and leads naturally to more advanced ideas of atomic structure, chemical bonding, and quantum physics. (Author/NB)

  9. Effect of Na Incorporation on the Growth and Properties of CdTe/CdS Devices OF CdTe/CdS DEVICES

    SciTech Connect

    Dhere, R.; Ramanathan, K.; Keane, J.; Zhou, J.; Moutinho, H.; Asher, S.; Noufi, R.

    2005-02-01

    Sodium is known to enhance p-type doping in copper indium diselenide (CIS)-based devices fabricated on soda-lime glass substrates, and similar amounts of Na are present in commercial cadmium telluride (CdTe) devices. We present the results on the effects of Na incorporation on the properties of CdTe/CdS solar cells prepared on borosilicate glass substrates. A NaF layer 10 to 30 nm thick was incorporated at either the CdS/CdTe interface or on the CdTe surface, as a source of Na. CdTe layers were deposited by close-spaced sublimation at substrate temperatures from 425 C (LT) to 620 C (HT), followed by heat-treatment in the presence of CdCl2 vapor. Atomic force microscopy analysis showed that the samples with NaF at the CdS/CdTe interface deposited in He ambient have larger grains with a sub-grain structure that disappears after CdCl2 heat treatment accompanied by an increase in grain size. Samples deposited in O2 ambient have smaller grains without a sub-grain structure. For samples with NaF deposited on the CdTe surface, LT samples with CdCl2 heat treatment showed a morphology similar to samples without NaF layers; but samples heat-treated in He ambient at 500 C prior to CdCl2 treatment showed a different microstructure with platelets on the surface.

  10. HgTe-CdTe-InSb heterostructures by molecular beam epitaxy

    SciTech Connect

    Ballingall, J.M.; Leopold, D.J.; Peterman, D.J.

    1985-08-01

    HgTe-CdTe heterostructures have been grown by molecular beam epitaxy on (100) InSb substrates. Separate elemental Hg and Te beams were used for the HgTe growth at a substrate temperature of 160 C. X-ray diffraction measurements indicate that thin epitaxial layers are of high crystalline quality. Secondary-ion mass spectroscopy measurements show substantial In and Sb diffusion into the epitaxial layers with a concentration enhancement at the HgTe-CdTe interface. 9 references.

  11. Development of electrodeposited ZnTe layers as window materials in ZnTe/CdTe/CdHgTe multi-layer solar cells

    SciTech Connect

    Islam, A.B.M.O. Chaure, N.B.; Wellings, J.; Tolan, G.; Dharmadasa, I.M.

    2009-02-15

    Zinc telluride (ZnTe) thin films have been deposited on glass/conducting glass substrates using a low-cost electrodeposition method. The resulting films have been characterized using various techniques in order to optimize growth parameters. X-ray diffraction (XRD) has been used to identify the phases present in the films. Photoelectrochemical (PEC) cell and optical absorption measurements have been performed to determine the electrical conductivity type, and the bandgap of the layers, respectively. It has been confirmed by XRD measurement that the deposited layers mainly consist of ZnTe phases. The PEC measurements indicate that the ZnTe layers are p-type in electrical conduction and optical absorption measurements show that their bandgap is in the range 2.10-2.20 eV. p-Type ZnTe window materials have been used in CdTe based solar cell structures, following new designs of graded bandgap multi-layer solar cells. The structures of FTO/ZnTe/CdTe/metal and FTO/ZnTe/CdTe/CdHgTe/metal have been investigated. The results are presented in this paper using observed experimental data.

  12. Single atom electrochemical and atomic analytics

    NASA Astrophysics Data System (ADS)

    Vasudevan, Rama

    In the past decade, advances in electron and scanning-probe based microscopies have led to a wealth of imaging and spectroscopic data with atomic resolution, yielding substantial insight into local physics and chemistry in a diverse range of systems such as oxide catalysts, multiferroics, manganites, and 2D materials. However, typical analysis of atomically resolved images is limited, despite the fact that image intensities and distortions of the atoms from their idealized positions contain unique information on the physical and chemical properties inherent to the system. Here, we present approaches to data mine atomically resolved images in oxides, specifically in the hole-doped manganite La5/8Ca3/8MnO3, on epitaxial films studied by in-situ scanning tunnelling microscopy (STM). Through application of bias to the STM tip, atomic-scale electrochemistry is demonstrated on the manganite surface. STM images are then further analyzed through a suite of algorithms including 2D autocorrelations, sliding window Fourier transforms, and others, and can be combined with basic thermodynamic modelling to reveal relevant physical and chemical descriptors including segregation energies, existence and strength of atomic-scale diffusion barriers, surface energies and sub-surface chemical species identification. These approaches promise to provide tremendous insights from atomically resolved functional imaging, can provide relevant thermodynamic parameters, and auger well for use with first-principles calculations to yield quantitative atomic-level chemical identification and structure-property relations. This research was sponsored by the Division of Materials Sciences and Engineering, BES, DOE. Research was conducted at the Center for Nanophase Materials Sciences, which also provided support and is a DOE Office of Science User Facility.

  13. PbTe and SnTe quantum dot precipitates in a CdTe matrix fabricated by ion implantation

    SciTech Connect

    Kaufmann, E.; Schwarzl, T.; Groiss, H.; Hesser, G.; Schaeffler, F.; Palmetshofer, L.; Springholz, G.; Heiss, W.

    2009-08-15

    We present rock-salt IV-VI semiconductor quantum dots fabricated by implantation of Pb{sup +}, Te{sup +}, or Sn{sup +} ions into epitaxial zinc-blende CdTe layers. PbTe and SnTe nanoprecipitates of high structural quality are formed after implantation by thermal annealing due to the immiscibility of dot and matrix materials. For samples implanted only with Pb{sup +}, intense continuous-wave photoluminescence peaked at 1.6 mum at 300 K is found. In contrast, for PbTe quantum dots fabricated by coimplantation of Pb{sup +} and Te{sup +}, the 300 K emission peak is observed at 2.9 mum, indicating luminescence from much larger dots.

  14. Multilevel Atomic Coherent States and Atomic Holomorphic Representation

    NASA Technical Reports Server (NTRS)

    Cao, Chang-Qi; Haake, Fritz

    1996-01-01

    The notion of atomic coherent states is extended to the case of multilevel atom collective. Based on atomic coherent states, a holomorphic representation for atom collective states and operators is defined. An example is given to illustrate its application.

  15. Determination of palladium and platinum by atomic absorption

    USGS Publications Warehouse

    Schnepfe, M.M.; Grimaldi, F.S.

    1969-01-01

    Palladium and platinum are determined by atomic absorption after fire-assay concentration into a gold bead. The limit of determination is ~0??06 ppm in a 20-g sample. Serious depressive interelement interferences are removed by buffering the solutions with a mixture of cadmium and copper sulphates with cadmium and copper concentrations each at 0??5%. Substantial amounts of Ag, Al, Au, Bi, Ca, Co, Cr, Fe, Hg, K, La, Mg, Mn, Mo, Na, Ni, Pb, Te, Ti, V, Y, Zn, and the platinum metals do not interfere in the atomic-absorption determination. ?? 1969.

  16. Atomic-absorption determination of rhodium in chromite concentrates

    USGS Publications Warehouse

    Schnepfe, M.M.; Grimaldi, F.S.

    1969-01-01

    Rhodium is determined in chromite concentrates by atomic absorption after concentration either by co-precipitation with tellurium formed by the reduction of tellurite with tin(II) chloride or by fire assay into a gold bead. Interelement interferences in the atomic-absorption determination are removed by buffering the solutions with lanthanum sulphate (lanthanum concentration 1%). Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Na, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated. A lower limit of approximately 0.07 ppm Rh can be determined in a 3-g sample. ?? 1969.

  17. Variability of structural and electronic properties of bulk and monolayer Si2Te3

    NASA Astrophysics Data System (ADS)

    Shen, X.; Puzyrev, Y. S.; Combs, C.; Pantelides, S. T.

    2016-09-01

    Silicon telluride has diverse properties for potential applications in Si-based devices ranging from fully integrated thermoelectrics to optoelectronics to chemical sensors. This material has a unique layered structure: it has a hexagonal closed-packed Te sublattice, with Si dimers occupying octahedral intercalation sites. Here, we report a theoretical study of this material in both bulk and monolayer form, unveiling an array of diverse properties arising from reorientations of the silicon dimers between planes of Te atoms. The band gap varies up to 30% depending on dimer orientations. The variation of dimer orientations gives rise to thermal contraction, arising from more dimers aligning out of the plane as the material is heated. Strain also affects the dimer orientations and provides a degree of control of the materials properties, making Si2Te3 a promising candidate for nanoscale mechanical, optical, and memristive devices.

  18. Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals

    NASA Astrophysics Data System (ADS)

    Aslan, Ozgur Burak; Ruppert, Claudia; Heinz, Tony

    2015-03-01

    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared. Supported by the NSF through Grant DMR-1124894 for sample preparation and characterization by the O?ce of Naval Research for analysis. C.R. acknowledges support from the Alexander von Humboldt Foundation.

  19. Response of CdZnTe Detectors on the Swift Burst Alert Telescope

    NASA Astrophysics Data System (ADS)

    Suzuki, M.; Tashiro, M.

    Swift (Gehrels, 2000) is the Gamma Ray Bursts (GRBs) explorer, that is scheduled for launch in 2004. The Swift's major instrument Burst Alert Telescope (BAT) detector array sits Cadmium Zinc Telluride (CdZnTe, CZT) semiconductor devices under a coded mask. The array has 32,768 individual Cd0.9Zn0.1Te1.0 detectors (4 × 4 mm^2 large, 2mm thick) that have a total detector area of 5240 cm^2. CdZnTe materials are able to operate at room temperature for its large band gap, and also have a high average atomic number which makes them sensitive to hard X-rays (15 ˜ 150 keV). We investigate energy response of the BAT detector for which to dedicate spectroscopy and imaging in observations of GRBs.

  20. Bonding nature of local structural motifs in amorphous GeTe.

    PubMed

    Deringer, Volker L; Zhang, Wei; Lumeij, Marck; Maintz, Stefan; Wuttig, Matthias; Mazzarello, Riccardo; Dronskowski, Richard

    2014-09-26

    Despite its simple chemical constitution and unparalleled technological importance, the phase-change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond-analysis tools. Herein, we introduce a bonding indicator for amorphous structures, dubbed "bond-weighted distribution function" (BWDF), and we apply this method to amorphous GeTe. The results underline a peculiar role of homopolar Ge-Ge bonds, which locally stabilize tetrahedral fragments but not the global network. This atom-resolved (i.e., chemical) perspective has implications for the stability of amorphous "zero bits" and thus for the technologically relevant resistance-drift phenomenon.

  1. Solutal diffusion coefficient for liquid PbTe-SnTe

    NASA Technical Reports Server (NTRS)

    Clark, I. O.; Fripp, A. L.; Debnam, W. J., Jr.; Crouch, R. K.; Brewer, W. D.

    1983-01-01

    The solutal diffusion coefficient has been determined for liquid lead telluride-tin telluride using a modified shear cell technique. Postdiffusion concentration profiles are presented for several diffusion couples. The best analytical curve fit to the data gives a composition-dependent diffusion coefficient of (/3/7/ to the C power) x 0.00014 sq cm/sec, where C is the PbTe concentration. In addition, data are presented to show the importance of solutal convection in the lead-tin-telluride system.

  2. Glass-forming ability of TeO2 and temperature induced changes on the structure of the glassy, supercooled, and molten states

    NASA Astrophysics Data System (ADS)

    Kalampounias, A. G.; Tsilomelekis, G.; Boghosian, S.

    2015-04-01

    Polarized (VV) and depolarized (VH) Raman spectra are obtained for glassy, supercooled, and molten TeO2 at temperatures up to 1000 K in order to elucidate the temperature evolution of the pertinent structural and vibrational properties. The intrinsic tendency of the system for crystallization is avoided by means of a newly applied protocol, thereby enabling the recording of Raman spectra of pure TeO2 on going from the molten to the supercooled liquid and to the room temperature glass states. Following an appropriate fitting procedure, the revealed bands are assigned to specific modes of structural polymorphs. A weak polarised band at ˜880 cm-1 is assigned to Te=O terminal stretching in agreement with the literature ab initio molecular orbital calculations. Subtle changes to the relative band intensities within the 550-900 cm-1 stretching region are caused by temperature increase. The network-like structure of the glass/melt is composed by TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. With increasing temperature, TeO4 units convert to TeO3 units with a concurrent increase in the number of Te=O sites resulting from cleavages within the network structure. The fraction of such terminal oxygen atoms has been directly estimated from the spectroscopic data. The relative populations of the basic building blocks and the average number of O atoms around Te have been estimated for a wide temperature range directly from the Raman spectra, implying a gradual transformation of TeO4/2 to TeO2/2(= O) trigonal pyramid units. The results are discussed in the context of the current phenomenological and theoretical status of the field.

  3. Glass-forming ability of TeO{sub 2} and temperature induced changes on the structure of the glassy, supercooled, and molten states

    SciTech Connect

    Kalampounias, A. G.; Tsilomelekis, G.; Boghosian, S.

    2015-04-21

    Polarized (VV) and depolarized (VH) Raman spectra are obtained for glassy, supercooled, and molten TeO{sub 2} at temperatures up to 1000 K in order to elucidate the temperature evolution of the pertinent structural and vibrational properties. The intrinsic tendency of the system for crystallization is avoided by means of a newly applied protocol, thereby enabling the recording of Raman spectra of pure TeO{sub 2} on going from the molten to the supercooled liquid and to the room temperature glass states. Following an appropriate fitting procedure, the revealed bands are assigned to specific modes of structural polymorphs. A weak polarised band at ∼880 cm{sup −1} is assigned to Te=O terminal stretching in agreement with the literature ab initio molecular orbital calculations. Subtle changes to the relative band intensities within the 550-900 cm{sup −1} stretching region are caused by temperature increase. The network-like structure of the glass/melt is composed by TeO{sub 4} trigonal bipyramid and TeO{sub 3} trigonal pyramid units. With increasing temperature, TeO{sub 4} units convert to TeO{sub 3} units with a concurrent increase in the number of Te=O sites resulting from cleavages within the network structure. The fraction of such terminal oxygen atoms has been directly estimated from the spectroscopic data. The relative populations of the basic building blocks and the average number of O atoms around Te have been estimated for a wide temperature range directly from the Raman spectra, implying a gradual transformation of TeO{sub 4/2} to TeO{sub 2/2}(= O) trigonal pyramid units. The results are discussed in the context of the current phenomenological and theoretical status of the field.

  4. Reaction Mechanism Underlying Atomic Layer Deposition of Antimony Telluride Thin Films.

    PubMed

    Han, Byeol; Kim, Yu-Jin; Park, Jae-Min; Yusup, Luchana L; Ishii, Hana; Lansalot-Matras, Clement; Lee, Won-Jun

    2016-05-01

    The mechanism underlying the deposition of SbTe films by alternating exposures to Sb(NMe2)3 and Te(GeMe3)2 was investigated. Sb(NMe2)3 and Te(GeMe3)2 were selected because they have very high vapor pressure and are free of Si, Cl, and O atoms in the molecules. The mechanism of deposition was proposed by density functional theory (DFT) calculation and was verified by in-situ quartz crystal microbalance (QCM) analysis. DFT calculation expected the ligand-exchange reactions between the Sb and Te precursors to form Me2NGeMe3 as the byproduct. QCM analysis indicated that a single -NMe2 group in Sb(NMe2)3 reacts with -TeGeMe3 on the surface to form an Sb2Te3 film, and that a small fraction of Sb is incorporated into the film by the thermal decomposition of Sb(NMe2)3. The Te(GeMe3)2 molecules were thermally stable up to 120 degrees C, while the Sb(NMe2)3 molecules decomposed at temperatures of 60 degrees C and higher. Sb-rich SbTe films with different Sb contents were prepared by controlling the partial decomposition of Sb(NMe2)3 molecules, which was enhanced by increasing the pulse time of the precursor. PMID:27483847

  5. Advanced Superlattice BiTe-PbTe/TAGS Milliwatt Radioisotope Power System

    NASA Astrophysics Data System (ADS)

    Drinker, Richard W.; Reddy, Anil; Heshmatpour, Ben; Snyder, G. Jeffrey; Tuttle, Karen L.

    2005-02-01

    The objective of this effort, under NASA's Project Prometheus, the Nuclear Systems Program, is to develop a high efficiency thermoelectric (T/E) energy conversion device to power milliwatt radioisotope power systems (mWRPS) for future NASA space science applications. The conversion efficiency goal is 8% at a power output level of 50 to several hundred mW. A two stage cascaded T/E module design is being used to achieve these program objectives. This concept incorporates the advanced superlattice BiTe thermoelectric device technology, which is under development by Research Triangle institute (RTI), with Teledyne's segmented T/E couple technology. The hot stage device in the cascade is comprised of Teledyne's PbTe/TAGS/PbSnTe segmented T/E couple which is glass bonded into a monolithic multicouple configuration. The cold stage device is an RTI developed thin film superlattice BiTe based multicouple device.

  6. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-01-01

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate and electrolyzing the leachate to separate Cd from Te, wherein the Te is deposits onto a cathode while the Cd remains in solution.

  7. Hydrothermal synthesis and characterization of two new layered vanadium tellurites Cu(TATP)V{sub 2}TeO{sub 8} and Cu(DPPZ)V{sub 2}Te{sub 2}O{sub 10}

    SciTech Connect

    Han Guangxi; Song Yongjuan; Han Zhengbo

    2009-08-15

    Two new vanadium tellurites, Cu(TATP)V{sub 2}TeO{sub 8}(1) and Cu(DPPZ)V{sub 2}Te{sub 2}O{sub 10}(2), (TATP=1,4,8,9-tetranitrogen-trisphene, DPPZ=dipyridophenazine) have been synthesized under hydrothermal conditions and structurally characterized by elemental analyses, IR, and single-crystal X-ray diffraction. Compound 1 features an interesting two-dimensional layer structure constructed by [V{sub 2}TeO{sub 8}]{sub n} double-chain-like ribbons linked by [Cu(TATP)]{sup 2+} bridges. Compound 2 consists of two types of chiral layers: one left-handed and the other right-handed, which lead to racemic solid-state compound. In each layer, there exist two types of inorganic helical chains (V{sub 4}Te{sub 4}O{sub 8}){sub n} and (Te{sub 2}O{sub 2}){sub n}, with same handedness. Two types of helical chains are linked by mu{sub 3}(O6) atoms to generate a V/Te/O inorganic anionic layer. The [Cu(DPPZ)]{sup 2+} cationic complex fragments are covalently bonded to the layer, projecting below and above the vanadium tellurites layer. - Graphical abstract: The changes of the size of the rigid aromatic chelate ligands may influence the structures of the V-Te-O framework.

  8. Time-resolved photoluminescence of type-II quantum dots and isoelectronic centers in Zn-Se-Te superlattice structures

    NASA Astrophysics Data System (ADS)

    Cheung, M. C.-K.; Cartwright, A. N.; Sellers, I. R.; McCombe, B. D.; Kuskovsky, I. L.

    2008-01-01

    Spectrally and time-resolved photoluminescence of a ZnTe /ZnSe superlattice reveals a smooth transition of the photoluminescence (PL) lifetime from ˜100ns at 2.35eV to less than a few nanoseconds at 2.8eV. The significant increase of the lifetime in the low energy region is strong evidence to support the formation of type-II quantum dots (QDs), since in these nanostructures the spatial separation of carriers is increased. The shorter lived emission above 2.5eV is attributed to excitons bound to Te isoelectronic centers in the ZnSe matrix. The smooth transition of the PL lifetime confirms that clusters of these Te atoms evolve into type-II ZnTe /ZnSe QDs.

  9. Weak Topological Insulators in PbTe/SnTe superlattice

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Liu, Junwei; Fu, Liang; Duan, Wenhui; Liu, Chaoxing

    2014-03-01

    It is desirable to realize topological phases in artificial structures by engineering electronic band structures. In this paper, we investigate (PbTe)m(SnTe)2n-m superlattices along the [001] direction and find a robust weak topological insulator phase for a large variety of layer numbers m and 2 n - m . We confirm this topologically non-trivial phase by calculating Z2 topological invariants and topological surface states based on the first-principles calculations. We show that the folding of Brillouin zone due to the superlattice structure plays an essential role in inducing topologically non-trivial phases in this system. This mechanism can be generalized to other systems in which band inversion occurs at multiple momenta, and gives us a brand-new way to engineer topological materials in artificial structures. We acknowledge support from the Ministry of Science and Technology of China and the National Natural Science Foundation of China. LF is supported by the DOE Office of Basic Energy Sciences.

  10. Effects of postdeposition treatments on surfaces of CdTe/CdS solar cells

    NASA Astrophysics Data System (ADS)

    Pookpanratana, S.; Liu, X.; Paudel, N. R.; Weinhardt, L.; Bär, M.; Zhang, Y.; Ranasinghe, A.; Khan, F.; Blum, M.; Yang, W.; Compaan, A. D.; Heske, C.

    2010-10-01

    Soft x-ray spectroscopy has been used to follow the effects of postdeposition steps (CdCl2 activation and back contact treatment) on surfaces and interfaces in CdTe-based superstrate solar cells. We find that the CdCl2 activation drives sulfur atoms from the CdS layer toward the back contact but not to its surface. Using atomic force microscopy, we find that both treatments strongly influence the morphology of the Au/Cu back contact. The spectroscopic results, in contrast, suggest that CdCl2 activation exhibits a larger impact on the surface composition and chemical structure of the interfaces involved in CdTe solar cells.

  11. The structural and electronic properties of amorphous HgCdTe from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Zhao, Huxian; Chen, Xiaoshuang; Lu, Jianping; Shu, Haibo; Lu, Wei

    2014-01-01

    Amorphous mercury cadmium telluride (a-MCT) model structures, with x being 0.125 and 0.25, are obtained from first-principles calculations. We generate initial structures by computation alchemy method. It is found that most atoms in the network of amorphous structures tend to be fourfold and form tetrahedral structures, implying that the chemical ordered continuous random network with some coordination defects is the ideal structure for a-MCT. The electronic structure is also concerned. The gap is found to be 0.30 and 0.26 eV for a-Hg0.875Cd0.125Te and a-Hg0.75Cd0.25Te model structures, independent of the composition. By comparing with the properties of crystalline MCT with the same composition, we observe a blue-shift of energy band gap. The localization of tail states and its atomic origin are also discussed.

  12. MBE-Grown CdTe Layers on GaAs with In-assisted Thermal Deoxidation

    NASA Astrophysics Data System (ADS)

    Arı, Ozan; Bilgilisoy, Elif; Ozceri, Elif; Selamet, Yusuf

    2016-10-01

    Molecular beam epitaxy (MBE) growth of thin (˜2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm-2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.

  13. Optical and electrical characterizations of highly efficient CdTe thin film solar cells prepared by close-spaced sublimation

    NASA Astrophysics Data System (ADS)

    Okamoto, T.; Yamada, A.; Konagai, M.

    2000-06-01

    The effects of the Cu diffusion on the optical and electrical properties of CdTe thin film solar cells prepared by close-spaced sublimation (CSS) were investigated by capacitance-voltage ( C- V) measurement and low-temperature photoluminescence (PL) measurement. C- V measurement revealed that the net acceptor concentration in the CdTe layer was independent of the heat treatment after screen printing of the Cu-doped graphite electrode for Cu diffusion into the CdTe layer, although it greatly affected the solar cell performance. Furthermore, the depth profile of PL spectrum of CdTe layer implies that the heat treatment for Cu diffusion facilitates the formation of low-resistance contact to CdTe through the formation of a heavily doped (p +) region in the CdTe adjacent to the back electrode, but Cu atoms do not act as effective acceptors in the CdTe layer except the region near the back electrode.

  14. The Origin of Ultralow Thermal Conductivity in InTe: Lone-Pair-Induced Anharmonic Rattling.

    PubMed

    Jana, Manoj K; Pal, Koushik; Waghmare, Umesh V; Biswas, Kanishka

    2016-06-27

    Understanding the origin of intrinsically low thermal conductivity is fundamentally important to the development of high-performance thermoelectric materials, which can convert waste-heat into electricity. Herein, we report an ultralow lattice thermal conductivity (ca. 0.4 W m(-1)  K(-1) ) in mixed valent InTe (that is, In(+) In(3+) Te2 ), which exhibits an intrinsic bonding asymmetry with coexistent covalent and ionic substructures. The phonon dispersion of InTe exhibits, along with low-energy flat branches, weak instabilities associated with the rattling vibrations of In(+) atoms along the columnar ionic substructure. These weakly unstable phonons originate from the 5s(2) lone pair of the In(+) atom and are strongly anharmonic, which scatter the heat-carrying acoustic phonons through strong anharmonic phonon-phonon interactions, as evident in anomalously high mode Grüneisen parameters. A maximum thermoelectric figure of merit (z T) of about 0.9 is achieved at 600 K for the 0.3 mol % In-deficient sample, making InTe a promising material for mid-temperature thermoelectric applications.

  15. First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces

    NASA Astrophysics Data System (ADS)

    Dorj, Odkhuu; Miao, M. S.; Kioussis, N.; Tari, S.; Aqariden, F.; Chang, Y.; Grein, C.

    2015-03-01

    CdZnTe and CdTe based semiconductor X-Ray and Gamma-Ray detectors have been intensively studied recently due to their promising potentials for achieving high-resolution, high signal-to-noise ratios and low leakage current, all are desirable features in applications ranging from medical diagnostics to homeland security. Understanding the atomic and electronic structures of the metal/semiconductor interfaces is essential for the further improvements of performance. Using density functional calculations, we systematically studied the stability, the atomic and electronic structures of the interfaces between Cd-terminated CdTe (111) surface and the selected metals. We also calculated the Schottky barrier height (SBH) by aligning the electrostatic potentials in semiconductor and metal regions. Our calculations revealed the importance of intermixing between semiconductor and metal layers and the formation of Te-metal alloys at the interface. The obtained SBH does not depend much on the choice of metals despite the large variation of the work functions. On the other hand, the interface structure is found to have large effect to the SBH, which is attributed to the metal induced states in the gap. The position of such states is insensitive to the metal work functions, as revealed by the analysis of the electronic structures.

  16. The Origin of Ultralow Thermal Conductivity in InTe: Lone-Pair-Induced Anharmonic Rattling.

    PubMed

    Jana, Manoj K; Pal, Koushik; Waghmare, Umesh V; Biswas, Kanishka

    2016-06-27

    Understanding the origin of intrinsically low thermal conductivity is fundamentally important to the development of high-performance thermoelectric materials, which can convert waste-heat into electricity. Herein, we report an ultralow lattice thermal conductivity (ca. 0.4 W m(-1)  K(-1) ) in mixed valent InTe (that is, In(+) In(3+) Te2 ), which exhibits an intrinsic bonding asymmetry with coexistent covalent and ionic substructures. The phonon dispersion of InTe exhibits, along with low-energy flat branches, weak instabilities associated with the rattling vibrations of In(+) atoms along the columnar ionic substructure. These weakly unstable phonons originate from the 5s(2) lone pair of the In(+) atom and are strongly anharmonic, which scatter the heat-carrying acoustic phonons through strong anharmonic phonon-phonon interactions, as evident in anomalously high mode Grüneisen parameters. A maximum thermoelectric figure of merit (z T) of about 0.9 is achieved at 600 K for the 0.3 mol % In-deficient sample, making InTe a promising material for mid-temperature thermoelectric applications. PMID:26918541

  17. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.

  18. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity. PMID:23146658

  19. Copper-incorporated mono- and di-TeRu5 metal carbonyl complexes: syntheses, structures, and an unusual skeletal arrangement.

    PubMed

    Shieh, Minghuey; Miu, Chia-Yeh; Hsing, Kai-Jieah; Jang, Li-Fing; Lin, Chien-Nan

    2015-04-14

    Two sandwich-type Cu3Cl- or Cu2{Te2Ru4(CO)10}-bridging di-TeRu5 clusters, [{TeRu5(CO)14}2Cu3Cl](2-) () and [{TeRu5(CO)14}2Cu2{Te2Ru4(CO)10}](4-) (), were obtained from the reaction of [TeRu5(CO)14](2-) with 1 equiv. of [Cu(MeCN)4][BF4] in CH2Cl2 or THF at 0 °C, respectively, depending on the solvents. The chloride-abstracted was structurally characterized to have two TeRu5 cores that were linked by a Cu3Cl moiety with two Cu-Cu bonds. If the reaction was carried out in a molar ratio of 1 : 2 at 0 or 30 °C in CH2Cl2, the structural isomers [TeRu5(μ-CO)2(CO)12(CuMeCN)2] () and [TeRu5(μ-CO)3(CO)11Cu2(MeCN)2] () were produced, respectively, as the major product. Cluster displayed a TeRu5 core with two adjacent Ru3 triangles each capped by a μ3-Cu(MeCN) fragment, while contained a TeRu5 core with one triangle Ru3 plane capped by a Cu2(MeCN)2 fragment with two Cu atoms covalently bonded. Upon heating, the isomerization of into proceeded to undergo an unusual skeletal arrangement of Cu(MeCN) and migration of CO, with the TeRu5 core remaining intact. An electrochemical study revealed that and each exhibited only one oxidation while cluster had two consecutive oxidations, suggesting significant electronic communication between the two TeRu5 metal cores in via the Cu3 moiety. This work describes the facile synthesis of a series of semiconducting Cux-bridging Te-Ru carbonyl clusters, in which the incorporation of the Cux fragments has significantly influenced their resulting structures, rearrangements, and electronic properties, which was further elucidated by DFT calculations. PMID:25757103

  20. Enhanced Thermoelectric Properties of Sn0.8Pb0.2Te Alloy by Mn Substitution

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Lu, Z. W.; Wang, C. Y.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2016-06-01

    A series of (Sn0.8Pb0.2)1- x Mn x Te alloys with x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15 were prepared by melting, quenching and spark plasma sintering (SPS) techniques to investigate their phases and thermoelectric properties. Mn was used as doped element in Sn0.8Pb0.2Te solid solution to reduce the carrier concentration, enhance the Seebeck coefficient and reduce the thermal conductivity of the material. Experimental results show that the SnTe-based solid solution single phase was formed in the alloys with x = 0 and 0.03. The minor irregular-shaped MnTe2 phase presents in the alloys with x ≥ 0.06, while the minor needle-like MnTe phase appears in the alloys with x ≥ 0.12, together with the SnTe-based solid solution matrix. The lattice parameter a of SnTe-based solid solution decreases nearly linearly as Mn content x increases up to 0.12, but keeps constant as x further increases. All the samples show p-type conduction. Mn doping in Sn0.8Pb0.2Te decreases its carrier concentration and thus increases its Seebeck coefficient. The solute Mn and Pb atoms in the SnTe-based solid solution, and the minor phases MnTe2 and MnTe, enhance the phonon scattering and thus reduce the thermal conductivity. As a result, the figure-of-merit ZT of the (Sn0.8Pb0.2)1- x Mn x Te composites can be enhanced with proper Mn substitution. The maximum ZT of 0.65 was obtained in the sample (Sn0.8Pb0.2)0.88Mn0.12Te at 723 K, which is higher than the 0.29 of its parent alloy Sn0.8Pb0.2Te.

  1. Atomic homodyne detection of weak atomic transitions.

    PubMed

    Gunawardena, Mevan; Elliott, D S

    2007-01-26

    We have developed a two-color, two-pathway coherent control technique to detect and measure weak optical transitions in atoms by coherently beating the transition amplitude for the weak transition with that of a much stronger transition. We demonstrate the technique in atomic cesium, exciting the 6s(2)S(1/2) --> 8s(2)S(1/2) transition via a strong two-photon transition and a weak controllable Stark-induced transition. We discuss the enhancement in the signal-to-noise ratio for this measurement technique over that of direct detection of the weak transition rate, and project future refinements that may further improve its sensitivity and application to the measurement of other weak atomic interactions.

  2. Atomic Oxygen Effects

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K. R.

    2014-01-01

    Atomic oxygen, which is the most predominant species in low Earth orbit, is highly reactive and can break chemical bonds on the surface of a wide variety of materials leading to volatilization or surface oxidation which can result in failure of spacecraft materials and components. This presentation will give an overview of how atomic oxygen reacts with spacecraft materials, results of space exposure testing of a variety of materials, and examples of failures caused by atomic oxygen.

  3. Metal atom oxidation laser

    DOEpatents

    Jensen, R.J.; Rice, W.W.; Beattie, W.H.

    1975-10-28

    A chemical laser which operates by formation of metal or carbon atoms and reaction of such atoms with a gaseous oxidizer in an optical resonant cavity is described. The lasing species are diatomic or polyatomic in nature and are readily produced by exchange or other abstraction reactions between the metal or carbon atoms and the oxidizer. The lasing molecules may be metal or carbon monohalides or monoxides. (auth)

  4. Metal atom oxidation laser

    DOEpatents

    Jensen, R.J.; Rice, W.W.; Beattie, W.H.

    1975-10-28

    A chemical laser which operates by formation of metal or carbon atoms and reaction of such atoms with a gaseous oxidizer in an optical resonant cavity is described. The lasing species are diatomic or polyatomic in nature and are readily produced by exchange or other abstraction reactions between the metal or carbon atoms and the oxidizer. The lasing molecules may be metal or carbon monohalides or monoxides.

  5. Advances in atomic physics

    PubMed Central

    El-Sherbini, Tharwat M.

    2013-01-01

    In this review article, important developments in the field of atomic physics are highlighted and linked to research works the author was involved in himself as a leader of the Cairo University – Atomic Physics Group. Starting from the late 1960s – when the author first engaged in research – an overview is provided of the milestones in the fascinating landscape of atomic physics. PMID:26425356

  6. Element substitution from substrates in Bi2Se3, Bi2Te3 and Sb2Te3 overlayers deposited by hot wall epitaxy

    NASA Astrophysics Data System (ADS)

    Takagaki, Y.; Jahn, U.; Jenichen, B.; Berlin, K.; Kong, X.; Biermann, K.

    2014-09-01

    In depositing Bi2Se3, Bi2Te3 or Sb2Te3 layers on certain substrates by hot wall epitaxy, the Bi and Sb atoms in the layers are replaced by the atoms supplied from the substrates. We extend our exploration on this substitution phenomenon for a number of combinations of the layer and the substrate to infer the factors that determine the occurrence of the substitution. Using a series of Ga- and In-based III-V substrates, it is evidenced that the group III atoms substitute the group V overlayer atoms when the bonds in the substrates are weak. We demonstrate that Ag triggers the substitution more effectively than Cu as a catalyst. The competition between the catalyst-induced substitutions on ternary alloy substrates shows that the dependence on the bond strength is not as strong as to be exclusive. Additionally, defectiveness around the interface between a semicoherently grown α-In2Se3 layer produced by the substitution and the InAs substrate is demonstrated. The cathodeluminescence properties are also provided focusing on the dependence on the phase of In2Se3.

  7. Visualization of atom's orbits.

    PubMed

    Kim, Byungwhan

    2014-02-01

    High-resolution imaging techniques have been used to obtain views of internal shapes of single atoms or columns of atoms. This review article focuses on the visualization of internal atomic structures such as the configurations of electron orbits confined to atoms. This is accomplished by applying visualization techniques to the reported images of atoms or molecules as well as static and dynamic ions in a plasma. It was found that the photon and electron energies provide macroscopic and microscopic views of the orbit structures of atoms, respectively. The laser-imaged atoms showed a rugged orbit structure, containing alternating dark and bright orbits believed to be the pathways for an externally supplied laser energy and internally excited electron energy, respectively. By contrast, the atoms taken by the electron microscopy provided a structure of fine electron orbits, systematically formed in increasing order of grayscale representing the energy state of an orbit. This structure was identical to those of the plasma ions. The visualized electronic structures played a critical role in clarifying vague postulates made in the Bohr model. Main features proposed in the atomic model are the dynamic orbits absorbing an externally supplied electromagnetic energy, electron emission from them while accompanying light radiation, and frequency of electron waves not light. The light-accompanying electrons and ionic speckles induced by laser light signify that light is composed of electrons and ions.

  8. High pressure atomization

    NASA Astrophysics Data System (ADS)

    Bracco, F. V.

    1982-03-01

    The main objective of these grants has been to study the fundamental processes which lead to the atomization of high pressure jets injected into compressed gases through single hole nozzles. Specific topics include: Dependence of Spray Angle and Other Spray Parameters on Nozzle Design and Operating Conditions; Ultra High Speed Filming of Atomizing Jets; Mechanism of Breakup of Highly Super Heated Liquid Jets; Measurements of the Spray Angle of Atomizing Jets; Mechanism of Atomization of a Liquid Jet; Scaling of Transient Laminar, Turbulent, and Spray Jets; Computations of Drop Sizes in Pulsating Sprays and of Liquid Core Length in Vaporizing Sprays; and Scaling of Impulsively Started Sprays.

  9. Improved graphite furnace atomizer

    DOEpatents

    Siemer, D.D.

    1983-05-18

    A graphite furnace atomizer for use in graphite furnace atomic absorption spectroscopy is described wherein the heating elements are affixed near the optical path and away from the point of sample deposition, so that when the sample is volatilized the spectroscopic temperature at the optical path is at least that of the volatilization temperature, whereby analyteconcomitant complex formation is advantageously reduced. The atomizer may be elongated along its axis to increase the distance between the optical path and the sample deposition point. Also, the atomizer may be elongated along the axis of the optical path, whereby its analytical sensitivity is greatly increased.

  10. Quantum Anomalous Hall Effect in Hg_1-yMn_yTe Quantum Wells

    SciTech Connect

    Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    The quantum Hall effect is usually observed when the two-dimensional electron gas is subjected to an external magnetic field, so that their quantum states form Landau levels. In this work we predict that a new phenomenon, the quantum anomalous Hall effect, can be realized in Hg{sub 1-y}Mn{sub y}Te quantum wells, without the external magnetic field and the associated Landau levels. This effect arises purely from the spin polarization of the Mn atoms, and the quantized Hall conductance is predicted for a range of quantum well thickness and the concentration of the Mn atoms. This effect enables dissipationless charge current in spintronics devices.

  11. Response of Cds/CdTe Devices to Te Exposure of Back Contact: Preprint

    SciTech Connect

    Gessert, T. A.; Burst, J. M.; Ma, J.; Wei, S. H.; Kuciauskas, D.; Barnes, T. M.; Duenow, J. N.; Young, M. R.; Rance, W. L.; Li, J. V.; Dippo, P.

    2012-06-01

    Theoretical predictions of thin-film CdS/CdTe photovoltaic (PV) devices have suggested performance may be improved by reducing recombination due to Te-vacancy (VTe) or Te-interstitial (Tei) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it also may be coupled to formation of beneficial cadmium vacancy (VCd) defects. If this is true, reducing potential effects of VTe or Tei may be difficult without also reducing the density of VCd. In contrast, post-deposition processes can sometimes afford a greater degree of defect control. Here we explore a post-deposition process that appears to influence the Te-related defects in polycrystalline CdTe. Specifically, we have exposed the CdTe surface to Te prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing VTe but without significantly reducing VCd. Initial results show that when this modified contact is used on a CdCl2-treated CdS/CdTe device, significantly poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or CuTe or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of VTe (e.g., oxygen and chlorine additions to the CdTe), adding even a small amount of Te may produce detrimental defects.

  12. Dislocation reduction in HgCdTe grown on CdTe/Si

    NASA Astrophysics Data System (ADS)

    Wijewarnasuriya, Priyalal S.

    2016-05-01

    Bulk-grown CdZnTe (Zn = 3%) substrates are the natural choice for HgCdTe epitaxy since it is lattice matched to long wave LW-HgCdTe alloy. However, lack of large area CdZnTe substrates, high production costs, and more importantly, the difference in thermal expansion coefficients between CdZnTe and silicon Read out Integrated Circuits (ROIC) are some of the inherent drawbacks of CdZnTe substrates. Consequently, Hg1-xCdxTe detectors fabricated on silicon substrates are an attractive alternative. Recent developments in the molecular beam epitaxy (MBE) buffer layer growth technology on Si substrates has revolutionized the HgCdTe research and offered a new dimension to HgCdTe-based IR technology. Si substrates provide advantages in terms of relatively large area (3 to 6-inch diameter is easily obtained) compared to CZT substrate materials, durability during processing, and reliability to thermal cycling. Innovations in Si-based composite substrates made it possible to fabricate very large-format IR arrays that offer higher resolution, low-cost arrays and more dies per wafer. Between Si substrates and HgCdTe has large lattice mismatch of 19%. This leads to dislocation densities of low-107 cm-2 for optimal growth of HgCdTe on silicon-based substrates as compared to the mid-104 cm-2 dislocation density of HgCdTe grown on CdZnTe. This paper present dislocation reduction by two orders of magnitude using thermal cycle anneal under Hg environment on HgCdTe grown on Si substrates and as well as defect reduction in Cd(Se)Te buffer layers grown on Si Substrates.

  13. 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).

  14. Strain relaxation of CdTe on Ge studied by medium energy ion scattering

    NASA Astrophysics Data System (ADS)

    Pillet, J. C.; Pierre, F.; Jalabert, D.

    2016-10-01

    We have used the medium energy ion scattering (MEIS) technique to assess the strain relaxation in molecular-beam epitaxial (MBE) grown CdTe (2 1 1)/Ge (2 1 1) system. A previous X-ray diffraction study, on 10 samples of the same heterostructure having thicknesses ranging from 25 nm to 10 μm has allowed the measurement of the strain relaxation on a large scale. However, the X-ray diffraction measurements cannot achieve a stress measurement in close proximity to the CdTe/Ge interface at the nanometer scale. Due to the huge lattice misfit between the CdTe and Ge, a high degree of disorder is expected at the interface. The MEIS in channeling mode is a good alternative in order to profile defects with a high depth resolution. For a 21 nm thick CdTe layer, we observed, at the interface, a high density of Cd and/or Te atoms moved from their expected crystallographic positions followed by a rapid recombination of defects. Strain relaxation mechanisms in the vicinity of the interface are discussed

  15. DX centers and persistent photoconductivity in CdTe In films

    NASA Astrophysics Data System (ADS)

    Rivera-Alvarez, Z.; Hernández, L.; Becerril, M.; Picos-Vega, A.; Zelaya-Angel, O.; Ramírez-Bon, R.; Vargas-García, J. R.

    2000-02-01

    In this work, we study the nature and behavior of the persistent photoconductivity (PPC) in CdTe-In films grown by co-sputtering of CdTe-In-Cd targets. It was found that only when In atoms are substantially incorporated into CdTe films, the persistent photoconductivity is observed with a quenching temperature of about 270 K. We have also investigated the trapping centers in the CdTe films by using the thermally stimulated conductivity technique. Two localized deep levels were determined. One of them, with an activation energy of 0.42 eV, has been ascribed as a direct evidence of DX centers that are formed by Cd vacancies and In donors complexes. By formulating the PPC build-up and decay kinetics, we have associated the PPC effect in our films to the photoionization of this deep level (DX like centers). Up to date, the existence of DX centers in CdTe-In polycrystalline films have not been previously reported.

  16. Synthesis and characterization of nanocrystalline MoBi2Te5 thin films for photoelectrode applications

    NASA Astrophysics Data System (ADS)

    Salunkhe, M. M.; Kharade, R. R.; Mane, R. M.; Bhosale, P. N.

    2012-10-01

    Molybdenum bismuth telluride thin films have been prepared on clean glass substrate using arrested precipitation technique which is based on self-organized growth process. As deposited MoBi2Te5 thin films were dried in constant temperature oven at 110°C and further characterized for their optical, structural, morphological, compositional, and electrical analysis. Optical absorption spectra recorded in the wavelength range 300-800 nm showed band gap (E g) 1.44 eV. X-ray diffraction pattern and scanning electron microscopic images showed that MoBi2Te5 thin films are granular, nanocrystalline having rhombohedral structure. The compositional analysis showed close agreements in theoretical and experimental atomic percentages of Mo4+, Bi3+, and Te2- suggest that chemical formula MoBi2Te5 assigned to as deposited molybdenum bismuth telluride new material is confirmed. The electrical conductivity and thermoelectric power measurement showed that the films are semiconducting with n-type conduction. The fill factor and conversion efficiency was characterized by photoelectrochemical (PEC) technique. In this article, we report the optostructural, morphological, compositional, and electrical characteristics of nanocrystalline MoBi2Te5 thin films to check its suitability as photoelectrode in PEC cell.

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

    PubMed

    Bhattacharyya, Sayan; Zitoun, D; Gedanken, A

    2011-02-18

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

  18. 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

  19. Tellurium precipitates in (Cd,Mn)Te:V crystals: Effects of annealing

    SciTech Connect

    Kochanowska,D.; Mycielski, A.; Witkowska-Baran, M.; Szadkowski, A.; Witkowska, B.; Kaliszek, W.; Cui, Y.; James, R. B.

    2008-10-19

    We suggest that (Cd,Mn)Te is a suitable material for fabricating gamma- and X-ray detectors. Our investigations, reported here, are focused on producing high-quality (Cd,Mn)Te crystals with high resistivity (10{sup 9} {Omega}-cm) by the Bridgman method. As-grown, undoped (Cd,Mn)Te crystals are typically p-type, signifying that they contain excess Cd vacancies (acting as acceptors), accumulated during growth. Doping with vanadium atoms, which function as compensating centers, results in a semi-insulating material (Cd,Mn)Te:V. Properly annealing the platelets in cadmium vapors at uniform temperature reduces the number of cadmium vacancies, and lowers the level of the vanadium doping required for compensation. We found that annealing in cadmium vapors not only decreases the concentration of the native cadmium vacancies but also improves the crystal's quality. Infrared observations of the interior of the samples show that annealing in a temperature gradient perpendicular to the platelet has an additional effect, viz., the tellurium precipitates migrate towards the side where the temperature is higher. We demonstrate, with IR pictures of monocrystalline (Cd,Mn)Te:V platelets cut parallel to the (111) crystal planes, the influence on tellurium inclusions and precipitates of various conditions of annealing in cadmium vapors.

  20. Spectroscopic, topological, and electronic characterization of ultrathin a-CdTe:O tunnel barriers

    NASA Astrophysics Data System (ADS)

    Dolog, Ivan; Mallik, Robert R.; Malz, Dan; Mozynski, Anthony

    2004-03-01

    Ultrathin oxygenated amorphous CdTe (a-CdTe:O) films are prepared by rf sputtering of CdTe in a background of argon or argon/nitrogen/oxygen mixtures. Atomic force microscopy (AFM) is used to characterize the films and shows that they have an island structure typical of most sputtered thin films. However, when sufficiently low powers and deposition rates are employed during sputtering, the resulting films are remarkably smooth and sufficiently thin for use as barrier layers in inelastic electron tunneling (IET) junctions. Four terminal current-voltage data are recorded for Al/a-CdTe:O/Pb tunnel junctions and conductance-voltage curves are derived numerically. WKB fits to the conductance-voltage curves are obtained using a two-component trapezoidal plus square (TRAPSQR) model barrier potential to determine values for the tunnel barrier parameters (height, shape, and width); these parameters are consistent with AFM topological measurements and values from similar devices reported in the literature. IET spectra are presented which confirm that electrons tunnel through ultrathin regions of the a-CdTe:O films, which contain aluminum oxide subregions in a manner consistent with the TRAPSQR barrier model. Because tunneling occurs predominantly through these ultrathin regions, IET spectroscopic data obtained are representative of states at, or within a few tenths of nanometers from, the surface and confirm that the a-CdTe:O surface stoichiometry is very sensitive to changes in the argon/oxygen/nitrogen concentration ratios during film growth. Full IET spectra, current-voltage, and conductance-voltage data are presented together with tunnel barrier parameters derived from (WKB) fits to the data. The results presented here indicate that inelastic electron tunneling spectroscopy is a useful tool for characterizing the surface states of a-CdTe:O and possibly other photovoltaic materials.

  1. Effect of annealing temperature on structure and electrical properties of topological insulator Bi2Te3

    NASA Astrophysics Data System (ADS)

    Urkude, R. R.; Palikundwar, U. A.

    2016-05-01

    Bi2Te3 samples were prepared by precipitation method. The samples were annealed in evacuated quartz tubes and were treated at different temperature for different duration of time. Effects of annealing temperature and time on the structure of Bi2Te3 were studied in detail. The Bi2Te3 samples annealed at temperature 300°C and 450°C for 48Hrs, 72Hrs and 96Hrs were selected for the present study. The structure of Bi2Te3 and related phases were investigated by the X-ray powder diffraction technique. Morphology and chemical compositions of the samples were investigated by scanning electron microscope and energy dispersive X-ray spectroscopy respectively. All the samples were indexed in rhombohedral crystal structure, with a space group R-3m. The structure consists of repeated quintuple layers of atoms, Te2-Bi-Te1-Bi-Te2 stacking along the z-axis of the unit cell. Electrical properties of the sample annealed at 300°C for 96Hrs was evaluated by measurements of the electrical resistivity and magnetoresistance. The magnetoresistance data at low temperature (1.5 to 50 K) were analyzed to investigate weak antilocalization (WAL) effect. MR data followed the Hikami-Larkin-Nagaoka (HLN) equation with a fit parameter α close to -1 as expected for topological surface states at 1.5 K, but for other temperatures the small oscillations were observed which may be due to the phenomena like Shubnikov-de Hass effect.

  2. Ferromagnetism and topological surface states of manganese doped Bi{sub 2}Te{sub 3}: Insights from density-functional calculations

    SciTech Connect

    Li, Yuanchang; Zou, Xiaolong; Li, Jia; Zhou, Gang

    2014-03-28

    Based on first-principles calculations, the electronic, magnetic, and topological characters of manganese (Mn) doped topological insulator Bi{sub 2}Te{sub 3} were investigated. The Mn substitutionally doped Bi{sub 2}Te{sub 3}, where Mn atoms tend to be uniformly distributed, was shown to be p-type ferromagnetic, arising from hole-mediated Ruderman-Kittel-Kasuya-Yosida interaction. Mn doping leads to an intrinsic band splitting at Γ point, which is substantially different from that of nonmagnetic dopant. The topological surface state of Bi{sub 2}Te{sub 3} is indeed gapped by Mn doping; however, the bulk conductance limits the appearance of an insulating state. Moreover, the n-type doping behavior of Bi{sub 2}Te{sub 3} is derived from Mn entering into the van der Waals gap of Bi{sub 2}Te{sub 3}.

  3. Evanescent Wave Atomic Mirror

    NASA Astrophysics Data System (ADS)

    Ghezali, S.; Taleb, A.

    2008-09-01

    A research project at the "Laboratoire d'électronique quantique" consists in a theoretical study of the reflection and diffraction phenomena via an atomic mirror. This poster presents the principle of an atomic mirror. Many groups in the world have constructed this type of atom optics experiments such as in Paris-Orsay-Villetaneuse (France), Stanford-Gaithersburg (USA), Munich-Heidelberg (Germany), etc. A laser beam goes into a prism with an incidence bigger than the critical incidence. It undergoes a total reflection on the plane face of the prism and then exits. The transmitted resulting wave out of the prism is evanescent and repulsive as the frequency detuning of the laser beam compared to the atomic transition δ = ωL-ω0 is positive. The cold atomic sample interacts with this evanescent wave and undergoes one or more elastic bounces by passing into backward points in its trajectory because the atoms' kinetic energy (of the order of the μeV) is less than the maximum of the dipolar potential barrier ℏΩ2/Δ where Ω is the Rabi frequency [1]. In fact, the atoms are cooled and captured in a magneto-optical trap placed at a distance of the order of the cm above the prism surface. The dipolar potential with which interact the slow atoms is obtained for a two level atom in a case of a dipolar electric transition (D2 Rubidium transition at a wavelength of 780nm delivered by a Titane-Saphir laser between a fundamental state Jf = l/2 and an excited state Je = 3/2). This potential is corrected by an attractive Van der Waals term which varies as 1/z3 in the Lennard-Jones approximation (typical atomic distance of the order of λ0/2π where λ0 is the laser wavelength) and in 1/z4 if the distance between the atom and its image in the dielectric is big in front of λ0/2π. This last case is obtained in a quantum electrodynamic calculation by taking into account an orthornormal base [2]. We'll examine the role of spontaneous emission for which the rate is inversely

  4. Atomic Oxygen Fluence Monitor

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.

    2011-01-01

    This innovation enables a means for actively measuring atomic oxygen fluence (accumulated atoms of atomic oxygen per area) that has impinged upon spacecraft surfaces. Telemetered data from the device provides spacecraft designers, researchers, and mission managers with real-time measurement of atomic oxygen fluence, which is useful for prediction of the durability of spacecraft materials and components. The innovation is a compact fluence measuring device that allows in-space measurement and transmittance of measured atomic oxygen fluence as a function of time based on atomic oxygen erosion yields (the erosion yield of a material is the volume of material that is oxidized per incident oxygen atom) of materials that have been measured in low Earth orbit. It has a linear electrical response to atomic oxygen fluence, and is capable of measuring high atomic oxygen fluences (up to >10(exp 22) atoms/sq cm), which are representative of multi-year low-Earth orbital missions (such as the International Space Station). The durability or remaining structural lifetime of solar arrays that consist of polymer blankets on which the solar cells are attached can be predicted if one knows the atomic oxygen fluence that the solar array blanket has been exposed to. In addition, numerous organizations that launch space experiments into low-Earth orbit want to know the accumulated atomic oxygen fluence that their materials or components have been exposed to. The device is based on the erosion yield of pyrolytic graphite. It uses two 12deg inclined wedges of graphite that are over a grit-blasted fused silica window covering a photodiode. As the wedges erode, a greater area of solar illumination reaches the photodiode. A reference photodiode is also used that receives unobstructed solar illumination and is oriented in the same direction as the pyrolytic graphite covered photodiode. The short-circuit current from the photodiodes is measured and either sent to an onboard data logger, or

  5. Cyclotron resonance in HgTe/CdTe-based heterostructures in high magnetic fields

    PubMed Central

    2012-01-01

    Cyclotron resonance study of HgTe/CdTe-based quantum wells with both inverted and normal band structures in quantizing magnetic fields was performed. In semimetallic HgTe quantum wells with inverted band structure, a hole cyclotron resonance line was observed for the first time. In the samples with normal band structure, interband transitions were observed with wide line width due to quantum well width fluctuations. In all samples, impurity-related magnetoabsorption lines were revealed. The obtained results were interpreted within the Kane 8·8 model, the valence band offset of CdTe and HgTe, and the Kane parameter EP being adjusted. PMID:23013642

  6. Atomic layer-by-layer thermoelectric conversion in topological insulator bismuth/antimony tellurides.

    PubMed

    Sung, Ji Ho; Heo, Hoseok; Hwang, Inchan; Lim, Myungsoo; Lee, Donghun; Kang, Kibum; Choi, Hee Cheul; Park, Jae-Hoon; Jhi, Seung-Hoon; Jo, Moon-Ho

    2014-07-01

    Material design for direct heat-to-electricity conversion with substantial efficiency essentially requires cooperative control of electrical and thermal transport. Bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3), displaying the highest thermoelectric power at room temperature, are also known as topological insulators (TIs) whose electronic structures are modified by electronic confinements and strong spin-orbit interaction in a-few-monolayers thickness regime, thus possibly providing another degree of freedom for electron and phonon transport at surfaces. Here, we explore novel thermoelectric conversion in the atomic monolayer steps of a-few-layer topological insulating Bi2Te3 (n-type) and Sb2Te3 (p-type). Specifically, by scanning photoinduced thermoelectric current imaging at the monolayer steps, we show that efficient thermoelectric conversion is accomplished by optothermal motion of hot electrons (Bi2Te3) and holes (Sb2Te3) through 2D subbands and topologically protected surface states in a geometrically deterministic manner. Our discovery suggests that the thermoelectric conversion can be interiorly achieved at the atomic steps of a homogeneous medium by direct exploiting of quantum nature of TIs, thus providing a new design rule for the compact thermoelectric circuitry at the ultimate size limit. PMID:24937706

  7. Atomic layer-by-layer thermoelectric conversion in topological insulator bismuth/antimony tellurides.

    PubMed

    Sung, Ji Ho; Heo, Hoseok; Hwang, Inchan; Lim, Myungsoo; Lee, Donghun; Kang, Kibum; Choi, Hee Cheul; Park, Jae-Hoon; Jhi, Seung-Hoon; Jo, Moon-Ho

    2014-07-01

    Material design for direct heat-to-electricity conversion with substantial efficiency essentially requires cooperative control of electrical and thermal transport. Bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3), displaying the highest thermoelectric power at room temperature, are also known as topological insulators (TIs) whose electronic structures are modified by electronic confinements and strong spin-orbit interaction in a-few-monolayers thickness regime, thus possibly providing another degree of freedom for electron and phonon transport at surfaces. Here, we explore novel thermoelectric conversion in the atomic monolayer steps of a-few-layer topological insulating Bi2Te3 (n-type) and Sb2Te3 (p-type). Specifically, by scanning photoinduced thermoelectric current imaging at the monolayer steps, we show that efficient thermoelectric conversion is accomplished by optothermal motion of hot electrons (Bi2Te3) and holes (Sb2Te3) through 2D subbands and topologically protected surface states in a geometrically deterministic manner. Our discovery suggests that the thermoelectric conversion can be interiorly achieved at the atomic steps of a homogeneous medium by direct exploiting of quantum nature of TIs, thus providing a new design rule for the compact thermoelectric circuitry at the ultimate size limit.

  8. Modification of band gap in surface layer in Cd 1-xZn xTe by YAG:Nd +3 laser radiation

    NASA Astrophysics Data System (ADS)

    Medvid, Artur; Fedorenko, Leonid L.; Korbutjak, Dmytro V.; Kryluk, Sergiy G.; Yusupov, Mikola M.; Mychko, Aleksandr

    2007-02-01

    A mechanism of formation of graded band-gap based on Thermogradient Effect (TGE) is proposed in Cd 1-xZn xTe at irradiation by second harmonic of a Q-switched YAG:Nd laser. According to the effect, the interstitial atoms of Cd (Cd i) in Cd 1-xZn xTe move along the temperature gradient while the Cd vacancies (V Cd) and Zn atoms - in the opposite direction, into the bulk of the semiconductor where temperature is lower. Photoluminescence (PL) spectra studied at 5 K show that concentration of Zn atoms increases due to aggregation of VCd with Zn after laser irradiation. Formation of a graded band-gap in Cd 1-xZn xTe crystal at irradiation by second harmonica of YAG:Nd laser by is shown to be possible.

  9. Identification of ^109Xe and ^105Te

    NASA Astrophysics Data System (ADS)

    Liddick, S.; Batchelder, J. C.; Grzywacz, R.; Mazzocchi, C.; Bingham, C. R.; Drafta, G.; Korgul, A.; Tantawy, M. N.; Page, R. D.; Darby, I. G.; Joss, D. T.; Thomson, J.; Rykaczewski, K. P.; Gross, C.; Goodin, C.; Hamilton, J. H.; Hwang, J. K.; Li, K.; Ilyushkin, S.; Winger, J. A.; Lagergren, K.; Krolas, W.; Hecht, A. A.

    2006-10-01

    The existence of a region of alpha emitting nuclei above ^100Sn is due to the presence of the Z=50 shell closures. The region is a fertile area to investigate possible enhanced correlations between neutrons and protons filling the same single-particle orbits and could lead to the observation of superallowed alpha decay as an approach is made towards ^100Sn. The new isotope ^109Xe was produced at the HRIBF at Oak Ridge National Laboratory. The lightest mass α-radioactivity identified to date, ^105Te, was detected through the ^109Xe->^105Te ->^101Sn alpha decay chain. This marks the closest approach to the N = Z line above ^100Sn. The half-life and Qα value for ^105Te were used to determine the reduced α-decay width, 2̂. The ratio 2̂^105Te/2̂^213Po of 2.7 indicates a superallowed character of the α-emission from ^105Te. Fine structure in the millisecond alpha decay of ^109Xe to ^105Te was identified and the energy difference between the νd5/2 ground state and the νg7/2 first excited state was determined to be around 150 keV in ^105Te. Prospects for reaching the superallowed alpha decay chain ^108Xe->^104Te ->^100Sn will also be discussed.

  10. The NuTeV anomaly: solved?

    SciTech Connect

    Londergan, J. T.

    2010-07-27

    The NuTeV extraction of the Weinberg angle is reported to differ by 3{sigma} from measurements at the Z pole. We review various effects within the Standard Model, and conclude that corrections from these effects bring the NuTeV measurement within 1{sigma} of the expected result.

  11. CdTe devices and method of manufacturing same

    SciTech Connect

    Gessert, Timothy A.; Noufi, Rommel; Dhere, Ramesh G.; Albin, David S.; Barnes, Teresa; Burst, James; Duenow, Joel N.; Reese, Matthew

    2015-09-29

    A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.

  12. Device Fabrication using Crystalline CdTe and CdTe Ternary Alloys Grown by MBE

    SciTech Connect

    Zaunbrecher, Katherine; Burst, James; Seyedmohammadi, Shahram; Malik, Roger; Li, Jian V.; Gessert, Timothy A.; Barnes, Teresa

    2015-06-14

    We fabricated epitaxial CdTe:In/CdTe:As homojunction and CdZnTe/CdTe and CdMgTe/CdTe heterojunction devices grown on bulk CdTe substrates in order to study the fundamental device physics of CdTe solar cells. Selection of emitter-layer alloys was based on passivation studies using double heterostructures as well as band alignment. Initial results show significant device integration challenges, including low dopant activation, high resistivity substrates and the development of low-resistance contacts. To date, the highest open-circuit voltage is 715 mV in a CdZnTe/CdTe heterojunction following anneal, while the highest fill factor of 52% was attained in an annealed CdTe homojunction. In general, all currentvoltage measurements show high series resistance, capacitancevoltages measurements show variable doping, and quantum efficiency measurements show low collection. Ongoing work includes overcoming the high resistance in these devices and addressing other possible device limitations such as non-optimum junction depth, interface recombination, and reduced bulk lifetime due to structural defects.

  13. Rational design and controlled synthesis of Te/Bi2Te3 heterostructure nanostring composites

    NASA Astrophysics Data System (ADS)

    Zhang, Yuzhuo; Chen, Hong; Li, Zhiliang; Huang, Ting; Zheng, Shuqi

    2015-07-01

    Te/Bi2Te3 heterostructure nanostring composites composed of several Bi2Te3 nanoplates, which were perpendicularly strung together by Te nanorod, were rationally designed and synthesized via a facile solvothermal method on a large scale. The X-ray diffraction (XRD) characterization demonstrated that the Bi2Te3 nanoplates were rhombohedral phase and the Te nanorods were trigonal phase. The uniform nanostring morphologies were well characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Detailed heterostructures were proved via energy dispersive spectrometer (EDS) and high-resolution transmission electron microscope (HRTEM). The morphology transformation from Bi2Te3 nanoplates to Te/Bi2Te3 heterostructure nanostrings could be controlled by adjusting the ratio of bismuth oxide to tellurium oxide. NaOH, serving as catalytic reduction agent and morphology controlling agent, played an important role in the synthesis of Te/Bi2Te3 heterostructure nanostrings. The reaction mechanism was also proposed to explain the formation process of the composites and the specific function of reagents in this reaction system.

  14. Modified Embedded Atom Method

    2012-08-01

    Interatomic force and energy calculation subroutine to be used with the molecular dynamics simulation code LAMMPS (Ref a.). The code evaluated the total energy and atomic forces (energy gradient) according to a cubic spline-based variant (Ref b.) of the Modified Embedded Atom Method (MEAM) with a additional Stillinger-Weber (SW) contribution.

  15. Atomic and Molecular Physics

    NASA Technical Reports Server (NTRS)

    Bhatia, Anand K.

    2005-01-01

    A symposium on atomic and molecular physics was held on November 18, 2005 at Goddard Space Flight Center. There were a number of talks through the day on various topics such as threshold law of ionization, scattering of electrons from atoms and molecules, muonic physics, positron physics, Rydberg states etc. The conference was attended by a number of physicists from all over the world.

  16. Greek Atomic Theory.

    ERIC Educational Resources Information Center

    Roller, Duane H. D.

    1981-01-01

    Focusing on history of physics, which began about 600 B.C. with the Ionian Greeks and reaching full development within three centuries, suggests that the creation of the concept of the atom is understandable within the context of Greek physical theory; so is the rejection of the atomic theory by the Greek physicists. (Author/SK)

  17. Atomic Power Safety.

    ERIC Educational Resources Information Center

    Hogerton, John F.

    This publication is one of a series of information booklets for the general public published by The United States Atomic Energy Commission. Among the topics discussed are: What is Atomic Power?; What Does Safety Depend On?; Control of Radioactive Material During Operation; Accident Prevention; Containment in the Event of an Accident; Licensing and…

  18. When Atoms Want

    ERIC Educational Resources Information Center

    Talanquer, Vicente

    2013-01-01

    Chemistry students and teachers often explain the chemical reactivity of atoms, molecules, and chemical substances in terms of purposes or needs (e.g., atoms want or need to gain, lose, or share electrons in order to become more stable). These teleological explanations seem to have pedagogical value as they help students understand and use…

  19. Atomic Scale Plasmonic Switch.

    PubMed

    Emboras, Alexandros; Niegemann, Jens; Ma, Ping; Haffner, Christian; Pedersen, Andreas; Luisier, Mathieu; Hafner, Christian; Schimmel, Thomas; Leuthold, Juerg

    2016-01-13

    The atom sets an ultimate scaling limit to Moore's law in the electronics industry. While electronics research already explores atomic scales devices, photonics research still deals with devices at the micrometer scale. Here we demonstrate that photonic scaling, similar to electronics, is only limited by the atom. More precisely, we introduce an electrically controlled plasmonic switch operating at the atomic scale. The switch allows for fast and reproducible switching by means of the relocation of an individual or, at most, a few atoms in a plasmonic cavity. Depending on the location of the atom either of two distinct plasmonic cavity resonance states are supported. Experimental results show reversible digital optical switching with an extinction ratio of 9.2 dB and operation at room temperature up to MHz with femtojoule (fJ) power consumption for a single switch operation. This demonstration of an integrated quantum device allowing to control photons at the atomic level opens intriguing perspectives for a fully integrated and highly scalable chip platform, a platform where optics, electronics, and memory may be controlled at the single-atom level.

  20. The dehydration of SrTeO3(H2O)--a topotactic reaction for preparation of the new metastable strontium oxotellurate(IV) phase ε-SrTeO3.

    PubMed

    Stöger, Berthold; Weil, Matthias; Baran, Enrique J; González-Baró, Ana C; Malo, Sylvie; Rueff, Jean Michel; Petit, Sebastien; Lepetit, Marie Bernadette; Raveau, Bernard; Barrier, Nicolas

    2011-05-28

    Microcrystalline single-phase strontium oxotellurate(IV) monohydrate, SrTeO(3)(H(2)O), was obtained by microwave-assisted hydrothermal synthesis under alkaline conditions at 180 °C for 30 min. A temperature of 220 °C and longer reaction times led to single crystal growth of this material. The crystal structure of SrTeO(3)(H(2)O) was determined from single crystal X-ray diffraction data: P2(1)/c, Z = 4, a = 7.7669(5), b = 7.1739(4), c = 8.3311(5) Å, β = 107.210(1)°, V = 443.42(5) Å(3), 1403 structure factors, 63 parameters, R[F(2)>2σ(F(2))] = 0.0208, wR(F(2) all) = 0.0516, S = 1.031. SrTeO(3)(H(2)O) is isotypic with the homologous BaTeO(3)(H(2)O) and is characterised by a layered assembly parallel to (100) of edge-sharing [SrO(6)(H(2)O)] polyhedra capped on each side of the layer by trigonal-prismatic [TeO(3)] units. The cohesion of the structure is accomplished by moderate O-H···O hydrogen bonding interactions between donor water molecules and acceptor O atoms of adjacent layers. In a topochemical reaction, SrTeO(3)(H(2)O) condensates above 150 °C to the metastable phase ε-SrTeO(3) and transforms upon further heating to δ-SrTeO(3). The crystal structure of ε-SrTeO(3), the fifth known polymorph of this composition, was determined from combined electron microscopy and laboratory X-ray powder diffraction studies: P2(1)/c, Z = 4, a = 6.7759(1), b = 7.2188(1), c = 8.6773(2) Å, β = 126.4980(7)°, V = 341.20(18) Å(3), R(Fobs) = 0.0166, R(Bobs) = 0.0318, Rwp = 0.0733, Goof = 1.38. The structure of ε-SrTeO(3) shows the same basic set-up as SrTeO(3)(H(2)O), but the layered arrangement of the hydrous phase transforms into a framework structure after elimination of water. The structural studies of SrTeO(3)(H(2)O) and ε-SrTeO(3) are complemented by thermal analysis and vibrational spectroscopic measurements.

  1. Moving Single Atoms

    NASA Astrophysics Data System (ADS)

    Stuart, Dustin

    2016-05-01

    Single neutral atoms are promising candidates for qubits, the fundamental unit of quantum information. We have built a set of optical tweezers for trapping and moving single Rubidium atoms. The tweezers are based on a far off-resonant dipole trapping laser focussed to a 1 μm spot with a single aspheric lens. We use a digital micromirror device (DMD) to generate dynamic holograms of the desired arrangement of traps. The DMD has a frame rate of 20 kHz which, when combined with fast algorithms, allows for rapid reconfiguration of the traps. We demonstrate trapping of up to 20 atoms in arbitrary arrangements, and the transport of a single-atom over a distance of 14 μm with continuous laser cooling, and 5 μm without. In the meantime, we are developing high-finesse fibre-tip cavities, which we plan to use to couple pairs of single atoms to form a quantum network.

  2. Atomic Oxygen Textured Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Hunt, Jason D.; Drobotij, Erin; Cales, Michael R.; Cantrell, Gidget

    1995-01-01

    Atomic oxygen can be used to microscopically alter the surface morphology of polymeric materials in space or in ground laboratory facilities. For polymeric materials whose sole oxidation products are volatile species, directed atomic oxygen reactions produce surfaces of microscopic cones. However, isotropic atomic oxygen exposure results in polymer surfaces covered with lower aspect ratio sharp-edged craters. Isotropic atomic oxygen plasma exposure of polymers typically causes a significant decrease in water contact angle as well as altered coefficient of static friction. Such surface alterations may be of benefit for industrial and biomedical applications. The results of atomic oxygen plasma exposure of thirty-three (33) different polymers are presented, including typical morphology changes, effects on water contact angle, and coefficient of static friction.

  3. Coaxial airblast atomizers

    NASA Technical Reports Server (NTRS)

    Hardalupas, Y.; Whitelaw, J. H.

    1993-01-01

    An experimental investigation was performed to quantify the characteristics of the sprays of coaxial injectors with particular emphasis on those aspects relevant to the performance of rocket engines. Measurements for coaxial air blast atomizers were obtained using air to represent the gaseous stream and water to represent the liquid stream. A wide range of flow conditions were examined for sprays with and without swirl for gaseous streams. The parameters varied include Weber number, gas flow rate, liquid flow rate, swirl, and nozzle geometry. Measurements were made with a phase Doppler velocimeter. Major conclusions of the study focused upon droplet size as a function of Weber number, effect of gas flow rate on atomization and spray spread, effect of nozzle geometry on atomization and spread, effect of swirl on atomization, spread, jet recirculation and breakup, and secondary atomization.

  4. 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.

  5. Comparison between TeV and non-TeV BL Lac Objects

    NASA Astrophysics Data System (ADS)

    Lin, Chao; Fan, Jun-Hui

    2016-07-01

    BL Lacertae objects (BL Lacs) are the dominant population of TeV emitting blazars. In this work, we investigate whether there are any special observational properties associated with TeV sources. To do so, we will compare the observational properties of TeV detected BL Lacs (TeV BLs) with non-TeV detected BL Lac objects (non-TeV BLs). From the 3rd Fermi/LAT source catalog (3FGL), we can obtain 662 BL Lacs, out of which 47 are TeV BLs and 615 are non-TeV BLs. Their multi-wavelength flux densities (F R, F O, F X and F γ), photon spectral indexes (αX ph and αph γ), and effective spectral indexes (αRO and αOX) are compiled from the available literature. Then the luminosities (log vL R, log vL O, log vL X, log vL γ) are calculated. From comparisons, we find that TeV BLs are different from low synchrotron peaked BLs and intermediate synchrotron peaked BLs, but TeV BLs show similar properties to high synchrotron peaked (HSP) BLs. Therefore, we concentrated on a comparison between TeV HSP BLs and non-TeV HSP BLs. Analysis results suggest that TeV HSP BLs and non-TeV HSP BLs exhibit some differences in their αRO and αγ ph, but their other properties are quite similar.

  6. GW quasiparticle energy study of ternary tetradymite Bi{sub 2}Te{sub 2}Se and Bi{sub 2}Te{sub 2}S thin films

    SciTech Connect

    Shuaibu, Alhassan; Rahman, Md. Mahmudur; Zainuddin, Hishamuddin; Talib, Zainal Abidin; Muhida, Rifki

    2015-04-24

    In this work, we have evaluated the quasiparticle energies of ternary tetradymite Bi{sub 2}Te{sub 2}Se and Bi{sub 2}Te{sub 2}S using first-principles calculation within the G{sub 0}W{sub 0} methods. We have also performed a broad convergence tests in order to investigate the quasiparticle corrections to the structural parameters and to the semi core d electrons in both of the compounds. For each case, we have calculated the many-body corrections within a one-shot GW method of the compounds. Our results have shown that for Bi{sub 2}Te{sub 2}Se the GW corrections increase the band gap to almost 10%, and for specific atomic positions, the band structure shows a close value to the experimental one. For Bi{sub 2}Te{sub 2}S, despite increase in the band gap due to the GW corrections, possibility of bulk resistivity that can be significant for photovoltaic applications was observed.

  7. Formation of tellurium nanocrystals during anaerobic growth of bacteria that use Te oxyanions as respiratory electron acceptors

    USGS Publications Warehouse

    Baesman, S.M.; Bullen, T.D.; Dewald, J.; Zhang, Dongxiao; Curran, S.; Islam, F.S.; Beveridge, T.J.; Oremland, R.S.

    2007-01-01

    Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here, we demonstrate that two anaerobes previously shown to be capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable stable-Te-isotopic fractionation (isotopic enrichment factor [??] = -0.4 to -1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods (???10-nm diameter by 200-nm length), which cluster together, forming larger (???1,000-nm) rosettes composed of numerous individual shards (???100-nm width by 1,000-nm length). In contrast, Sulfurospirillium barnesii forms extremely small, irregularly shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy-dispersive X-ray spectroscopy and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The use of microorganisms to generate Te nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods. Copyright ?? 2007, American Society for Microbiology. All Rights Reserved.

  8. Formation of Tellurium Nanocrystals during Anaerobic Growth of Bacteria That Use Te Oxyanions as Respiratory Electron Acceptors▿

    PubMed Central

    Baesman, Shaun M.; Bullen, Thomas D.; Dewald, James; Zhang, Donghui; Curran, Seamus; Islam, Farhana S.; Beveridge, Terry J.; Oremland, Ronald S.

    2007-01-01

    Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here, we demonstrate that two anaerobes previously shown to be capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable stable-Te-isotopic fractionation (isotopic enrichment factor [ɛ] = −0.4 to −1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods (∼10-nm diameter by 200-nm length), which cluster together, forming larger (∼1,000-nm) rosettes composed of numerous individual shards (∼100-nm width by 1,000-nm length). In contrast, Sulfurospirillum barnesii forms extremely small, irregularly shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy-dispersive X-ray spectroscopy and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The use of microorganisms to generate Te nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods. PMID:17277198

  9. Impact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface

    SciTech Connect

    Horsley, K. Hanks, D. A.; Weir, M. G.; Beal, R. J.; Wilks, R. G.; Blum, M.; Häming, M.; Hofmann, T.; Weinhardt, L.; and others

    2014-07-14

    To enable an understanding and optimization of the optoelectronic behavior of CdTe-ZnO nanocomposites, the morphological and chemical properties of annealed CdTe/ZnO interface structures were studied. For that purpose, CdTe layers of varying thickness (4–24 nm) were sputter-deposited on 100 nm-thick ZnO films on surface-oxidized Si(100) substrates. The morphological and chemical effects of annealing at 525 °C were investigated using X-ray Photoelectron Spectroscopy (XPS), X-ray-excited Auger electron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. We find a decrease of the Cd and Te surface concentration after annealing, parallel to an increase in Zn and O signals. While the as-deposited film surfaces show small grains (100 nm diameter) of CdTe on the ZnO surface, annealing induces a significant growth of these grains and separation into islands (with diameters as large as 1 μm). The compositional change at the surface is more pronounced for Cd than for Te, as evidenced using component peak fitting of the Cd and Te 3d XPS peaks. The modified Auger parameters of Cd and Te are also calculated to further elucidate the local chemical environment before and after annealing. Together, these results suggest the formation of tellurium and cadmium oxide species at the CdTe/ZnO interface upon annealing, which can create a barrier for charge carrier transport, and might allow for a deliberate modification of interface properties with suitably chosen thermal treatment parameters.

  10. High thermoelectric performance of p-type SnTe via a synergistic band engineering and nanostructuring approach.

    PubMed

    Tan, Gangjian; Zhao, Li-Dong; Shi, Fengyuan; Doak, Jeff W; Lo, Shih-Han; Sun, Hui; Wolverton, Chris; Dravid, Vinayak P; Uher, Ctirad; Kanatzidis, Mercouri G

    2014-05-14

    SnTe is a potentially attractive thermoelectric because it is the lead-free rock-salt analogue of PbTe. However, SnTe is a poor thermoelectric material because of its high hole concentration arising from inherent Sn vacancies in the lattice and its very high electrical and thermal conductivity. In this study, we demonstrate that SnTe-based materials can be controlled to become excellent thermoelectrics for power generation via the successful application of several key concepts that obviate the well-known disadvantages of SnTe. First, we show that Sn self-compensation can effectively reduce the Sn vacancies and decrease the hole carrier density. For example, a 3 mol % self-compensation of Sn results in a 50% improvement in the figure of merit ZT. In addition, we reveal that Cd, nominally isoelectronic with Sn, favorably impacts the electronic band structure by (a) diminishing the energy separation between the light-hole and heavy-hole valence bands in the material, leading to an enhanced Seebeck coefficient, and (b) enlarging the energy band gap. Thus, alloying with Cd atoms enables a form of valence band engineering that improves the high-temperature thermoelectric performance, where p-type samples of SnCd(0.03)Te exhibit ZT values of ~0.96 at 823 K, a 60% improvement over the Cd-free sample. Finally, we introduce endotaxial CdS or ZnS nanoscale precipitates that reduce the lattice thermal conductivity of SnCd(0.03)Te with no effect on the power factor. We report that SnCd(0.03)Te that are endotaxially nanostructured with CdS and ZnS have a maximum ZTs of ~1.3 and ~1.1 at 873 K, respectively. Therefore, SnTe-based materials could be ideal alternatives for p-type lead chalcogenides for high temperature thermoelectric power generation.

  11. High thermoelectric performance of p-type SnTe via a synergistic band engineering and nanostructuring approach.

    PubMed

    Tan, Gangjian; Zhao, Li-Dong; Shi, Fengyuan; Doak, Jeff W; Lo, Shih-Han; Sun, Hui; Wolverton, Chris; Dravid, Vinayak P; Uher, Ctirad; Kanatzidis, Mercouri G

    2014-05-14

    SnTe is a potentially attractive thermoelectric because it is the lead-free rock-salt analogue of PbTe. However, SnTe is a poor thermoelectric material because of its high hole concentration arising from inherent Sn vacancies in the lattice and its very high electrical and thermal conductivity. In this study, we demonstrate that SnTe-based materials can be controlled to become excellent thermoelectrics for power generation via the successful application of several key concepts that obviate the well-known disadvantages of SnTe. First, we show that Sn self-compensation can effectively reduce the Sn vacancies and decrease the hole carrier density. For example, a 3 mol % self-compensation of Sn results in a 50% improvement in the figure of merit ZT. In addition, we reveal that Cd, nominally isoelectronic with Sn, favorably impacts the electronic band structure by (a) diminishing the energy separation between the light-hole and heavy-hole valence bands in the material, leading to an enhanced Seebeck coefficient, and (b) enlarging the energy band gap. Thus, alloying with Cd atoms enables a form of valence band engineering that improves the high-temperature thermoelectric performance, where p-type samples of SnCd(0.03)Te exhibit ZT values of ~0.96 at 823 K, a 60% improvement over the Cd-free sample. Finally, we introduce endotaxial CdS or ZnS nanoscale precipitates that reduce the lattice thermal conductivity of SnCd(0.03)Te with no effect on the power factor. We report that SnCd(0.03)Te that are endotaxially nanostructured with CdS and ZnS have a maximum ZTs of ~1.3 and ~1.1 at 873 K, respectively. Therefore, SnTe-based materials could be ideal alternatives for p-type lead chalcogenides for high temperature thermoelectric power generation. PMID:24785377

  12. Impact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface

    NASA Astrophysics Data System (ADS)

    Horsley, K.; Beal, R. J.; Wilks, R. G.; Blum, M.; Häming, M.; Hanks, D. A.; Weir, M. G.; Hofmann, T.; Weinhardt, L.; Bär, M.; Potter, B. G.; Heske, C.

    2014-07-01

    To enable an understanding and optimization of the optoelectronic behavior of CdTe-ZnO nanocomposites, the morphological and chemical properties of annealed CdTe/ZnO interface structures were studied. For that purpose, CdTe layers of varying thickness (4-24 nm) were sputter-deposited on 100 nm-thick ZnO films on surface-oxidized Si(100) substrates. The morphological and chemical effects of annealing at 525 °C were investigated using X-ray Photoelectron Spectroscopy (XPS), X-ray-excited Auger electron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. We find a decrease of the Cd and Te surface concentration after annealing, parallel to an increase in Zn and O signals. While the as-deposited film surfaces show small grains (100 nm diameter) of CdTe on the ZnO surface, annealing induces a significant growth of these grains and separation into islands (with diameters as large as 1 μm). The compositional change at the surface is more pronounced for Cd than for Te, as evidenced using component peak fitting of the Cd and Te 3d XPS peaks. The modified Auger parameters of Cd and Te are also calculated to further elucidate the local chemical environment before and after annealing. Together, these results suggest the formation of tellurium and cadmium oxide species at the CdTe/ZnO interface upon annealing, which can create a barrier for charge carrier transport, and might allow for a deliberate modification of interface properties with suitably chosen thermal treatment parameters.

  13. BOREAS TE-6 Allometry Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Gower, Stith T.; Vogel, Jason G.

    2000-01-01

    The BOREAS TE-6 team collected several data sets in support of its efforts to characterize and interpret information on the plant biomass, allometry, biometry, sapwood, leaf area index, net primary production, soil temperature, leaf water potential, soil CO2 flux, and multivegetation imagery of boreal vegetation. This data set includes tree measurements conducted on the above-ground biomass of trees in the BOREAS NSA and SSA during the growing seasons of 1994 and 1995 and the derived allometric relationships/equations. The data are stored in ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distrobuted Activity Archive Center (DAAC).

  14. Producing and Detecting Correlated Atoms

    SciTech Connect

    Westbrook, C. I.; Schellekens, M.; Perrin, A.; Krachmalnicoff, V.; Viana Gomes, J.; Trebbia, J.-B.; Esteve, J.; Chang, H.; Bouchoule, I.; Boiron, D.; Aspect, A.; Jeltes, T.; McNamara, J.; Hogervorst, W.; Vassen, W.

    2006-11-07

    We discuss experiments to produce and detect atom correlations in a degenerate or nearly degenerate gas of neutral atoms. First we treat the atomic analog of the celebrated Hanbury Brown Twiss experiment, in which atom correlations result simply from interference effects without any atom interactions. We have performed this experiment for both bosons and fermions. Next we show how atom interactions produce correlated atoms using the atomic analog of spontaneous four-wave mixing. Finally, we briefly mention experiments on a one dimensional gas on an atom chip in which correlation effects due to both interference and interactions have been observed.

  15. Energy loss rate of a charged particle in HgTe/(HgTe, CdTe) quantum wells

    SciTech Connect

    Chen, Qinjun; Sin Ang, Yee; Wang, Xiaolin; Lewis, R. A.; Zhang, Chao

    2013-11-04

    The energy loss rate (ELR) of a charged particle in a HgTe/(HgTe, CdTe) quantum well is investigated. We consider scattering of a charged particle by the bulk insulating states in this type of topological insulator. It is found that the ELR characteristics due to the intraband excitation have a linear energy dependence while those due to interband excitation depend on the energy exponentially. An interesting quantitative result is that for a large range of the incident energy, the mean inelastic scattering rate is around a few terahertz.

  16. Synthesis of new Ga{sub 7}Ge{sub 3}Te{sub 11}—One-dimensional phase in Ga–Ge–Te ternary system: Crystal structure and physical properties

    SciTech Connect

    Drasar, Cestmir; Cisarova, Ivana; Kucek, Vladimir; Benes, Ludvik; Prokleska, Jan; Kratochvilova, Marie

    2015-02-15

    Ga{sub 7}Ge{sub 3}Te{sub 11} single crystals were grown using transport in a temperature gradient. The prepared single crystals have a needle-like appearance, 1 to 40 μm in diameter and 2 to 20 mm in length. The Ga{sub 7}Ge{sub 3}Te{sub 11} single crystals were characterized by both single crystalline and powder X-ray diffraction. The structure consists of one-dimensional molecular strings bonded together through tellurium atoms by a weak bond of the van der Waals type. A large unit cell volume indicates the complexity of the structure. The room temperature theoretical density is 5.73 g cm{sup −3}. The compound shows semiconducting properties and possesses peculiar magnetic properties. - Graphical abstract: 1D Ga{sub 7}Ge{sub 3}Te{sub 11} - cross-view of the molecular string. - Highlights: • We prepared and characterized novel compound Ga{sub 7}Ge{sub 3}Te{sub 11}in single crystalline form. • Ga{sub 7}Ge{sub 3}Te{sub 11} is one-dimensional structure; orthorhombic lattice; space group Pnma. • Ga{sub 7}Ge{sub 3}Te{sub 11} is an intrinsic semiconductor; E{sub g}≅0.7 eV. • Ga{sub 7}Ge{sub 3}Te{sub 11} is paramagnetic with an effective magnetic moment of p{sub eff}=0.06 μ{sub B} per atom. • Crossover from para – to diamagnetism is observed in field dependence of susceptibility.

  17. Low temperature magnetothermoelectric effect and magnetoresistance in Te vapor annealed Bi2Te3.

    PubMed

    Hor, Y S; Qu, D; Ong, N P; Cava, R J

    2010-09-22

    The electrical properties of single crystals of p-type Bi(2)Te(3) are shown to be tuned by annealing as-grown crystals in elemental Te vapor at temperatures in the range of 400-420 °C. While as-grown nominally stoichiometric Bi(2)Te(3) has p-type conductivity below room temperature, Te vapor annealed Bi(2)Te(3) shows a cross over from p- to n-type behavior. The temperature dependent resistivity of the Te annealed crystals shows a characteristic broad peak near 100 K. Applied magnetic fields give rise to a large low temperature magnetothermoelectric effect in the Te annealed samples and enhance the low temperature peak in the resistivity. Further, Te annealed Bi(2)Te(3) shows a large positive magnetoresistance, ∼ 200% at 2 K, and ∼ 15% at room temperature. The annealing procedure described can be employed to optimize the properties of Bi(2)Te(3) for study as a topological insulator.

  18. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    NASA Astrophysics Data System (ADS)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-06-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {{Te}}_{{Cd}}^{2 + } - {{V}}_{{Cd}}^{2 - } (D complex), {{In}}_{{Cd}}^{ + } - {{V}}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {{V}}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  19. Raman characterization of a new Te-rich binary compound: CdTe2.

    PubMed

    Rousset, Jean; Rzepka, Edouard; Lincot, Daniel

    2009-04-01

    Structural characterization by Raman spectroscopy of CdTe thin films electrodeposited in acidic conditions is considered in this work. This study focuses on the evolution of material properties as a function of the applied potential and the film thickness, demonstrating the possibility to obtain a new Te-rich compound with a II/VI ratio of 1/2 under specific bath conditions. Raman measurements carried out on etched samples first allow the elimination of the assumption of a mixture of phases CdTe + Te and tend to confirm the formation of the CdTe(2) binary compound. The signature of this phase on the Raman spectrum is the increase of the LO band intensity compared to that obtained for the CdTe. The influence of the laser power is also considered. While no effect is observed on CdTe films, the increase of the incident irradiation power leads to the decomposition of the CdTe(2) compound into two more stable phases namely CdTe and Te.

  20. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    NASA Astrophysics Data System (ADS)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-10-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {Te}_{{Cd}}^{2 + } - {V}_{{Cd}}^{2 - } (D complex), {In}_{{Cd}}^{ + } - {V}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {V}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  1. A facile method for gold decoration of Te@CdTe nanorods in aqueous solution.

    PubMed

    Shao, Haibao; Wang, Chunlei; Wang, Zhuyuan; Li, Rongqing; Xu, Qinying; Xu, Shuhong; Jiang, Yuan; Sun, Qingfeng; Bo, Fan; Cui, Yiping

    2012-10-01

    Colloidal synthesis of metal-semiconductor hybrid nanostructures is mainly achieved in organic solution. In some applications of hybrid nanoparticles relevant in aqueous media, phase transfer of hydrophobic metal-semiconductor hybrid nanostructures is essential. In this work, we present a simple method for direct synthesis of water-soluble gold (Au) decorated Te@CdTe hybrid nanorods (NRs) at room temperature by using aqueous Te@CdTe NRs as templates, which were preformed by using CdTe nanocrystals (NCs) as precursor in the presence of hydrazine hydrate (N(2)H(4)). Our results showed that NRs were decorated with Au islands both on tips and along the surface of the NRs. The size and density of Au islands can be controlled by varying the amount of Au precursor (mixture of HAuCl(4) and thioglycolic acid (TGA)) and TGA/HAuCl(4) ratio. A possible growth mechanism for the Au decoration of Te@CdTe NRs is concluded as three steps: (1) the formation of AuTe(1.7) via the substitution reaction of Cd(2+) by Au(3+), (2) adsorption of Au-TGA complex onto the preformed AuTe(1.7) anchors and following reduction by CdTe and N(2)H(4), leading to the formation of small Au NCs, (3) Au NCs grow to bigger ones, followed by reduction of more Au precursor by N(2)H(4). PMID:22795043

  2. Precisely detecting atomic position of atomic intensity images.

    PubMed

    Wang, Zhijun; Guo, Yaolin; Tang, Sai; Li, Junjie; Wang, Jincheng; Zhou, Yaohe

    2015-03-01

    We proposed a quantitative method to detect atomic position in atomic intensity images from experiments such as high-resolution transmission electron microscopy, atomic force microscopy, and simulation such as phase field crystal modeling. The evaluation of detection accuracy proves the excellent performance of the method. This method provides a chance to precisely determine atomic interactions based on the detected atomic positions from the atomic intensity image, and hence to investigate the related physical, chemical and electrical properties.

  3. Atomic mass evaluation

    SciTech Connect

    Wang, M.; Audi, G.; Kondev, F. G.; Xu, X.; Pfeiffer, B.

    2012-11-12

    The atomic masses are important input parameters for nuclear astrophysics calculations. The Atomic Mass Evaluation (AME) is the most reliable source for comprehensive information related to atomic masses. The latest AME was published in 2003. A new version, which will include the impact of a wealth of new, high-precision experimental data, will be published in December 2012. In this paper we will give the current status of AME2012. The mass surface has been changed significantly compared to AME2003, and the impact on astrophysics calculations is discussed.

  4. Atomic and molecular supernovae

    NASA Technical Reports Server (NTRS)

    Liu, Weihong

    1997-01-01

    Atomic and molecular physics of supernovae is discussed with an emphasis on the importance of detailed treatments of the critical atomic and molecular processes with the best available atomic and molecular data. The observations of molecules in SN 1987A are interpreted through a combination of spectral and chemical modelings, leading to strong constraints on the mixing and nucleosynthesis of the supernova. The non-equilibrium chemistry is used to argue that carbon dust can form in the oxygen-rich clumps where the efficient molecular cooling makes the nucleation of dust grains possible. For Type Ia supernovae, the analyses of their nebular spectra lead to strong constraints on the supernova explosion models.

  5. Atom trap trace analysis

    SciTech Connect

    Lu, Z.-T.; Bailey, K.; Chen, C.-Y.; Du, X.; Li, Y.-M.; O'Connor, T. P.; Young, L.

    2000-05-25

    A new method of ultrasensitive trace-isotope analysis has been developed based upon the technique of laser manipulation of neutral atoms. It has been used to count individual {sup 85}Kr and {sup 81}Kr atoms present in a natural krypton sample with isotopic abundances in the range of 10{sup {minus}11} and 10{sup {minus}13}, respectively. The atom counts are free of contamination from other isotopes, elements,or molecules. The method is applicable to other trace-isotopes that can be efficiently captured with a magneto-optical trap, and has a broad range of potential applications.

  6. Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals.

    PubMed

    Jang, Youngjin; Yanover, Diana; Čapek, Richard Karel; Shapiro, Arthur; Grumbach, Nathan; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2016-07-01

    Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs. PMID:27331900

  7. Magnetic Field-Dependent Magneto-Optical Kerr Effect in [(GeTe)2(Sb2Te3)1]8 Topological Superlattice

    NASA Astrophysics Data System (ADS)

    Bang, Do; Awano, Hiroyuki; Saito, Yuta; Tominaga, Junji

    2016-05-01

    We studied the magnetic field dependence of magneto-optical Kerr rotation of the [(GeTe)2/(Sb2Te3)1]8 topological superlattice at different temperatures (from 300 K to 440 K). At low temperatures (less than 360 K), the Kerr signal was within noise level. However, large Kerr rotation peaks with a mirror symmetric loop were at high temperatures (higher than 360 K). The temperature dependence of the observed Kerr signal can be attributed to the breaking of spatial inversion symmetry, which induces a narrow gap in surface state bands due to the Ge atomic layer movement-induced phase transition in the superlattice. We found that the resonant field of each Kerr peak gradually decreases with increasing temperature. On the other hand, the phase transition from a high temperature phase to a low temperature one could be controlled by external magnetic fields.

  8. Morphology and Electric Conductance Change Induced by Voltage Pulse Excitation in (GeTe)2/Sb2Te3 Superlattices

    PubMed Central

    Bolotov, Leonid; Saito, Yuta; Tada, Tetsuya; Tominaga, Junji

    2016-01-01

    Chalcogenide superlattice (SL) phase-change memory materials are leading candidates for non-volatile, energy-efficient electric memory where the electric conductance switching is caused by the atom repositioning in the constituent layers. Here, we study the time evolution of the electric conductance in [(GeTe)2/(Sb2Te3)1]4 SLs upon the application of an external pulsed electric field by analysing the structural and electrical responses of the SL films with scanning probe microscopy (SPM) and scanning probe lithography (SPL). At a low pulse voltage (1.6–2.3 V), a conductance switching delay of a few seconds was observed in some SL areas, where the switch to the high conductance state (HCS) is accompanied with an SL expansion under the strong electric field of the SPM probe. At a high pulse voltage (2.5–3.0 V), the HCS current was unstable and decayed in a few seconds; this is ascribed to the degradation of the HCS crystal phase under excessive heating. The reversible conductance change under a pulse voltage of opposite polarity emphasised the role of the electric field in the phase-transition mechanism. PMID:27618797

  9. Morphology and Electric Conductance Change Induced by Voltage Pulse Excitation in (GeTe)2/Sb2Te3 Superlattices.

    PubMed

    Bolotov, Leonid; Saito, Yuta; Tada, Tetsuya; Tominaga, Junji

    2016-01-01

    Chalcogenide superlattice (SL) phase-change memory materials are leading candidates for non-volatile, energy-efficient electric memory where the electric conductance switching is caused by the atom repositioning in the constituent layers. Here, we study the time evolution of the electric conductance in [(GeTe)2/(Sb2Te3)1]4 SLs upon the application of an external pulsed electric field by analysing the structural and electrical responses of the SL films with scanning probe microscopy (SPM) and scanning probe lithography (SPL). At a low pulse voltage (1.6-2.3 V), a conductance switching delay of a few seconds was observed in some SL areas, where the switch to the high conductance state (HCS) is accompanied with an SL expansion under the strong electric field of the SPM probe. At a high pulse voltage (2.5-3.0 V), the HCS current was unstable and decayed in a few seconds; this is ascribed to the degradation of the HCS crystal phase under excessive heating. The reversible conductance change under a pulse voltage of opposite polarity emphasised the role of the electric field in the phase-transition mechanism. PMID:27618797

  10. Morphology and Electric Conductance Change Induced by Voltage Pulse Excitation in (GeTe)2/Sb2Te3 Superlattices

    NASA Astrophysics Data System (ADS)

    Bolotov, Leonid; Saito, Yuta; Tada, Tetsuya; Tominaga, Junji

    2016-09-01

    Chalcogenide superlattice (SL) phase-change memory materials are leading candidates for non-volatile, energy-efficient electric memory where the electric conductance switching is caused by the atom repositioning in the constituent layers. Here, we study the time evolution of the electric conductance in [(GeTe)2/(Sb2Te3)1]4 SLs upon the application of an external pulsed electric field by analysing the structural and electrical responses of the SL films with scanning probe microscopy (SPM) and scanning probe lithography (SPL). At a low pulse voltage (1.6–2.3 V), a conductance switching delay of a few seconds was observed in some SL areas, where the switch to the high conductance state (HCS) is accompanied with an SL expansion under the strong electric field of the SPM probe. At a high pulse voltage (2.5–3.0 V), the HCS current was unstable and decayed in a few seconds; this is ascribed to the degradation of the HCS crystal phase under excessive heating. The reversible conductance change under a pulse voltage of opposite polarity emphasised the role of the electric field in the phase-transition mechanism.

  11. Hydrothermal synthesis and characterization of two new layered vanadium tellurites Cu(TATP)V 2TeO 8 and Cu(DPPZ)V 2Te 2O 10

    NASA Astrophysics Data System (ADS)

    Han, Guang-Xi; Song, Yong-Juan; Han, Zheng-Bo

    2009-08-01

    Two new vanadium tellurites, Cu(TATP)V 2TeO 8(1) and Cu(DPPZ)V 2Te 2O 10(2), (TATP=1,4,8,9-tetranitrogen-trisphene, DPPZ=dipyridophenazine) have been synthesized under hydrothermal conditions and structurally characterized by elemental analyses, IR, and single-crystal X-ray diffraction. Compound 1 features an interesting two-dimensional layer structure constructed by [V 2TeO 8] n double-chain-like ribbons linked by [Cu(TATP)] 2+ bridges. Compound 2 consists of two types of chiral layers: one left-handed and the other right-handed, which lead to racemic solid-state compound. In each layer, there exist two types of inorganic helical chains (V 4Te 4O 8) n and (Te 2O 2) n, with same handedness. Two types of helical chains are linked by μ3(O6) atoms to generate a V/Te/O inorganic anionic layer. The [Cu(DPPZ)] 2+ cationic complex fragments are covalently bonded to the layer, projecting below and above the vanadium tellurites layer.

  12. Low-dimensional Te-based nanostructures.

    PubMed

    Wang, Qisheng; Safdar, Muhammad; Wang, Zhenxing; He, Jun

    2013-07-26

    Low-dimensional Te-based nanomaterials have attracted intense attention in recent years due to their novel physical properties including surface-state effects, photoelectricity, phase changes, and thermoelectricity. The recent development of synthesis methods of low-dimensional Te-based nanostructures is reviewed, such as van der Waals expitaxial growth and template-assisted solution-phase deposition. In addition, the unique properties of these materials, such as tunable surface states, high photoresponsivity, fast phase change, and high thermoelectricity figure of merit, are reviewed. The potential applications of low-dimensional Te-based nanostructures are broad but particularly promising for nanoscale electronic and photoelectronic devices. PMID:24048978

  13. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, R.E.; Long, M.O.; Drinkard, W.F. Jr.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base. 3 figs.

  14. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base.

  15. The CHIANTI atomic database

    NASA Astrophysics Data System (ADS)

    Young, P. R.; Dere, K. P.; Landi, E.; Del Zanna, G.; Mason, H. E.

    2016-04-01

    The freely available CHIANTI atomic database was first released in 1996 and has had a huge impact on the analysis and modeling of emissions from astrophysical plasmas. It contains data and software for modeling optically thin atom and positive ion emission from low density (≲1013 cm-3) plasmas from x-ray to infrared wavelengths. A key feature is that the data are assessed and regularly updated, with version 8 released in 2015. Atomic data for modeling the emissivities of 246 ions and neutrals are contained in CHIANTI, together with data for deriving the ionization fractions of all elements up to zinc. The different types of atomic data are summarized here and their formats discussed. Statistics on the impact of CHIANTI to the astrophysical community are given and examples of the diverse range of applications are presented.

  16. Atomic bomb health benefits.

    PubMed

    Luckey, T D

    2008-01-01

    Media reports of deaths and devastation produced by atomic bombs convinced people around the world that all ionizing radiation is harmful. This concentrated attention on fear of miniscule doses of radiation. Soon the linear no threshold (LNT) paradigm was converted into laws. Scientifically valid information about the health benefits from low dose irradiation was ignored. Here are studies which show increased health in Japanese survivors of atomic bombs. Parameters include decreased mutation, leukemia and solid tissue cancer mortality rates, and increased average lifespan. Each study exhibits a threshold that repudiates the LNT dogma. The average threshold for acute exposures to atomic bombs is about 100 cSv. Conclusions from these studies of atomic bomb survivors are: One burst of low dose irradiation elicits a lifetime of improved health.Improved health from low dose irradiation negates the LNT paradigm.Effective triage should include radiation hormesis for survivor treatment.

  17. The Atomic Dating Game.

    ERIC Educational Resources Information Center

    Cummo, Evelyn; Matthews, Catherine E.

    2002-01-01

    Presents an activity designed to provide students with opportunities to practice drawing atomic models and discover the logical pairings of whole families on the periodic table. Follows the format of a television game show. (DDR)

  18. Atomic hydrogen rocket engine

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Flurchick, K.

    1981-01-01

    A rocket using atomic hydrogen propellant is discussed. An essential feature of the proposed engine is that the atomic hydrogen fuel is used as it is produced, thus eliminating the necessity of storage. The atomic hydrogen flows into a combustion chamber and recombines, producing high velocity molecular hydrogen which flows out an exhaust port. Standard thermodynamics, kinetic theory and wall recombination cross-sections are used to predict a thrust of approximately 1.4 N for a RF hydrogen flow rate of 4 x 10 to the 22nd/sec. Specific impulses are nominally from 1000 to 2000 sec. It is predicted that thrusts on the order of one Newton and specific impulses of up to 2200 sec are attainable with nominal RF discharge fluxes on the order of 10 to the 22nd atoms/sec; further refinements will probably not alter these predictions by more than a factor of two.

  19. Atomic branching in molecules

    NASA Astrophysics Data System (ADS)

    Estrada, Ernesto; Rodríguez-Velázquez, Juan A.; Randić, Milan

    A graph theoretic measure of extended atomic branching is defined that accounts for the effects of all atoms in the molecule, giving higher weight to the nearest neighbors. It is based on the counting of all substructures in which an atom takes part in a molecule. We prove a theorem that permits the exact calculation of this measure based on the eigenvalues and eigenvectors of the adjacency matrix of the graph representing a molecule. The definition of this measure within the context of the Hückel molecular orbital (HMO) and its calculation for benzenoid hydrocarbons are also studied. We show that the extended atomic branching can be defined using any real symmetric matrix, as well as any Hermitian (self-adjoint) matrix, which permits its calculation in topological, geometrical, and quantum chemical contexts.

  20. Atom chip gravimeter

    NASA Astrophysics Data System (ADS)

    Schubert, Christian; Abend, Sven; Gebbe, Martina; Gersemann, Matthias; Ahlers, Holger; Müntinga, Hauke; Matthias, Jonas; Sahelgozin, Maral; Herr, Waldemar; Lämmerzahl, Claus; Ertmer, Wolfgang; Rasel, Ernst

    2016-04-01

    Atom interferometry has developed into a tool for measuring rotations [1], accelerations [2], and testing fundamental physics [3]. Gravimeters based on laser cooled atoms demonstrated residual uncertainties of few microgal [2,4] and were simplified for field applications [5]. Atomic gravimeters rely on the interference of matter waves which are coherently manipulated by laser light fields. The latter can be interpreted as rulers to which the position of the atoms is compared. At three points in time separated by a free evolution, the light fields are pulsed onto the atoms. First, a coherent superposition of two momentum states is produced, then the momentum is inverted, and finally the two trajectories are recombined. Depending on the acceleration the atoms experienced, the number of atoms detected in the output ports will change. Consequently, the acceleration can be determined from the output signal. The laser cooled atoms with microkelvin temperatures used in state-of-the-art gravimeters impose limits on the accuracy [4]. Therefore, ultra-cold atoms generated by Bose-Einstein condensation and delta-kick collimation [6,7] are expected to be the key for further improvements. These sources suffered from a low flux implying an incompatible noise floor, but a competitive performance was demonstrated recently with atom chips [8]. In the compact and robust setup constructed for operation in the drop tower [6] we demonstrated all steps necessary for an atom chip gravimeter with Bose-Einstein condensates in a ground based operation. We will discuss the principle of operation, the current performance, and the perspectives to supersede the state of the art. The authors thank the QUANTUS cooperation for contributions to the drop tower project in the earlier stages. This work is supported by the German Space Agency (DLR) with funds provided by the Federal Ministry for Economic Affairs and Energy (BMWi) due to an enactment of the German Bundestag under grant numbers DLR 50WM

  1. Improved Atomizer Resists Clogging

    NASA Technical Reports Server (NTRS)

    Dea, J. Y.

    1983-01-01

    Improved constant-output atomizer has conical orifice that permits air to sweep out all liquid thoroughly and prevent any buildup of liquid or dissolved solids. Capillary groove guides liquid to gas jet. Simple new design eliminates clogging.

  2. Atomic Chain Electronics

    NASA Technical Reports Server (NTRS)

    Yamada, Toshishige; Saini, Subhash (Technical Monitor)

    1998-01-01

    Adatom chains, precise structures artificially created on an atomically regulated surface, are the smallest possible candidates for future nanoelectronics. Since all the devices are created by combining adatom chains precisely prepared with atomic precision, device characteristics are predictable, and free from deviations due to accidental structural defects. In this atomic dimension, however, an analogy to the current semiconductor devices may not work. For example, Si structures are not always semiconducting. Adatom states do not always localize at the substrate surface when adatoms form chemical bonds to the substrate atoms. Transport properties are often determined for the entire system of the chain and electrodes, and not for chains only. These fundamental issues are discussed, which will be useful for future device considerations.

  3. Preparation of Copper Telluride Films by Co-Reduction of Cu(I) and Te(IV) Ions in Choline Chloride: Ethylene Glycol Ionic Liquid

    NASA Astrophysics Data System (ADS)

    Golgovici, Florentina; Catrangiu, Adriana-Simona; Stoian, Andrei Bogdan; Anicai, Liana; Visan, Teodor

    2016-07-01

    Cathodic processes of direct co-reduction of Cu+ and Te4+ ions on Pt electrode at 60°C were investigated using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The ionic liquid as background electrolyte consisted of a mixture of choline chloride and ethylene glycol (ChCl-EG 1:2 mol ratio) in which 5-20 mM CuCl and 8 mM TeO2 were dissolved. The voltammograms exhibited the following successive cathodic processes: Cu2+/Cu+ reduction, Te underpotential deposition, simultaneous deposition of Cu metal and CuTe compound, and deposition of Te-rich CuTe compound at the most negative potentials (from -0.5 V to -0.8 V). Corresponding dissolution or oxidation peaks were recorded on the anodic branch. The voltammetric results were confirmed by electrochemical impedance spectra. Copper telluride films have been synthesized on platinum substrate via potentiostatic electrodeposition at 60°C. It was found from atomic force microscopy that CuTe film samples prepared from ChCl-EG + 5 mM CuCl + 8 mM TeO2 ionic liquid have high growth rates. The x-ray diffraction patterns of the deposited films from ChCl-EG + 10 mM CuCl + 8 mM TeO2 ionic liquid indicated the presence of a Cu2Te phase for film deposited at -0.7 V and a Cu0.656Te0.344 phase for film deposited at -0.6 V.

  4. Defect energetics and magnetic properties of 3 d-transition-metal-doped topological crystalline insulator SnTe

    NASA Astrophysics Data System (ADS)

    Wang, Na; Wang, JianFeng; Si, Chen; Gu, Bing-Lin; Duan, WenHui

    2016-08-01

    The introduction of magnetism in SnTe-class topological crystalline insulators is a challenging subject with great importance in the quantum device applications. Based on the first-principles calculations, we have studied the defect energetics and magnetic properties of 3 d transition-metal (TM)-doped SnTe. We find that the doped TM atoms prefer to stay in the neutral states and have comparatively high formation energies, suggesting that the uniform TMdoping in SnTe with a higher concentration will be difficult unless clustering. In the dilute doping regime, all the magnetic TMatoms are in the high-spin states, indicating that the spin splitting energy of 3 d TM is stronger than the crystal splitting energy of the SnTe ligand. Importantly, Mn-doped SnTe has relatively low defect formation energy, largest local magnetic moment, and no defect levels in the bulk gap, suggesting that Mn is a promising magnetic dopant to realize the magnetic order for the theoretically-proposed large-Chern-number quantum anomalous Hall effect (QAHE) in SnTe.

  5. Effects of various deposition times and RF powers on CdTe thin film growth using magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ghorannevis, Z.; Akbarnejad, E.; Ghoranneviss, M.

    2016-09-01

    Cadmium telluride (CdTe) is a p-type II-VI compound semiconductor, which is an active component for producing photovoltaic solar cells in the form of thin films, due to its desirable physical properties. In this study, CdTe film was deposited using the radio frequency (RF) magnetron sputtering system onto a glass substrate. To improve the properties of the CdTe film, effects of two experimental parameters of deposition time and RF power were investigated on the physical properties of the CdTe films. X-ray Diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer were used to study the structural, morphological and optical properties of the CdTe samples grown at different experimental conditions, respectively. Our results suggest that film properties strongly depend on the experimental parameters and by optimizing these parameters, it is possible to tune the desired structural, morphological and optical properties. From XRD data, it is found that increasing the deposition time and RF power leads to increasing the crystallinity as well as the crystal sizes of the grown film, and all the films represent zinc blende cubic structure. Roughness values given from AFM images suggest increasing the roughness of the CdTe films by increasing the RF power and deposition times. Finally, optical investigations reveal increasing the film band gaps by increasing the RF power and the deposition time.

  6. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    DOE PAGESBeta

    Cingarapu, Sreeram; Yang, Zhiqiang; Sorensen, Christopher M.; Klabunde, Kenneth J.

    2012-01-01

    We report synthesis of CdSe and CdTe quantum dots (QDs) from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD) technique and refined digestive ripening. The outcomes of this new process are (1) the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO) and oleylamine (OA)) as capping agent as well as digestive ripening solvent, (2) ability to tune the photoluminescence (PL) from 410 nm to 670 nm, (3) demonstrate the ability of SMAD synthesis technique for other semiconductors (CdTe), (4) direct comparison of CdSe QDs growth with CdTe QDs growth based on digestivemore » ripening times, and (5) enhanced PL quantum yield (QY) of CdSe QDs and CdTe QDs upon covering with a ZnS shell. Further, the merit of this synthesis is the use of bulk CdSe and CdTe as the starting materials, which avoids usage of toxic organometallic compounds, eliminates the hot injection procedure, and size selective precipitation processes. It also allows the possibility of scale up. These QDs were characterized by UV-vis, photoluminescence (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and powder XRD.« less

  7. X-ray absorption fine structure study of aging behavior of oxidized copper in CdTe films

    SciTech Connect

    Liu, Xiangxin; Compaan, A.D.; Terry, J.

    2005-10-19

    We have used the MR-CAT beamline of the Advanced Photon Source at Argonne National Laboratory to study the fine structure in the Cu K-edge X-ray absorption in 2 {micro}m thick polycrystalline films of CdTe on fused silica. 4 nm of evaporated Cu is diffused either with or without prior vapor CdCl{sub 2} treatments in dry air. The phase-uncorrected radial distribution function inferred from the absorption fine structure indicates predominantly Cu{sub 2}Te when Cu is diffused into the as-deposited CdTe film but indicates a Cu{sub 2}O environment when Cu is diffused after the vapor CdCl{sub 2} treatment. We believe most of the diffused Cu decorates grain boundaries as oxides, consistent with the low doping densities typically observed in CdTe solar cells. This Cu{sub 2}O likely plays a role in grain-boundary passivation. We also found that the chemical environment around Cu atoms in both CdTe and real cells can change with light soaking. This instability of Cu{sub 2}O in sputtered CdTe could contribute to cell degradation.

  8. Effect of vacancies on the structure and properties of Ga2(Se0.33Te0.67)3

    NASA Astrophysics Data System (ADS)

    Abdul-Jabbar, N. M.; Forrest, T. R.; Gronsky, R.; Bourret-Courchesne, E. D.; Wirth, B. D.

    2015-08-01

    Ga2(Se0.33Te0.67)3 belongs to a family of materials with large intrinsic vacancy concentrations that are being actively studied due to their potential for diverse applications that include thermoelectrics and phase-change memory. In this article, the Ga2(Se0.33Te0.67)3 structure is investigated via synchrotron x-ray diffraction, electron microscopy, and x-ray absorption experiments. Diffraction and microscopy measurements showed that the extent of vacancy ordering in Ga2(Se0.33Te0.67)3 is highly dependent on thermal annealing. It is posited that stoichiometric vacancies play a role in local atomic distortions in Ga2(Se0.33Te0.67)3 (based on the fine structure signals in the collected x-ray absorption spectra). The effect of vacancy ordering on Ga2(Se0.33Te0.67)3 material properties is also examined through band gap and Hall effect measurements, which reveal that the Ga2(Se0.33Te0.67)3 band gap redshifts by ≈0.05 eV as the vacancies order and accompanied by gains in charge carrier mobility. The results serve as an encouraging example of altering material properties via intrinsic structural rearrangement as opposed to extrinsic means, such as doping.

  9. Strong anisotropy and magnetostriction in the two-dimensional Stoner ferromagnet Fe3GeTe2

    DOE PAGESBeta

    Zhuang, Houlong L.; Kent, P. R. C.; Hennig, Richard G.

    2016-04-06

    Comore » mputationally characterizing magnetic properies of novel two-dimensional (2D) materials serves as an important first step of exploring possible applications. Using density-functional theory, we show that single-layer Fe3GeTe2 is a potential 2D material with sufficiently low formation energy to be synthesized by mechanical exfoliation from the bulk phase with a van der Waals layered structure. In addition, we calculated the phonon dispersion demonstrating that single-layer Fe3GeTe2is dynamically stable. Furthermore, we find that similar to the bulk phase, 2D Fe3GeTe2 exhibits amagnetic moment that originates from a Stoner instability. In contrast to other 2D materials, we find that single-layer Fe3GeTe2 exhibits a significant uniaxial magnetocrystalline anisotropy energy of 920μ eV per Fe atom originating from spin-orbit coupling. In conclusion, we show that applying biaxial tensile strains enhances the anisotropy energy, which reveals strong magnetostriction in single-layer Fe3GeTe2 with a sizable magneostrictive coefficient. Our results indicate that single-layer Fe3GeTe2 is potentially useful for magnetic storage applications.« less

  10. Growth and analysis of micro and nano CdTe arrays for solar cell applications

    NASA Astrophysics Data System (ADS)

    Aguirre, Brandon Adrian

    CdTe is an excellent material for infrared detectors and photovoltaic applications. The efficiency of CdTe/CdS solar cells has increased very rapidly in the last 3 years to ˜20% but is still below the maximum theoretical value of 30%. Although the short-circuit current density is close to its maximum of 30 mA/cm2, the open circuit voltage has potential to be increased further to over 1 Volt. The main limitation that prevents further increase in the open-circuit voltage and therefore efficiency is the high defect density in the CdTe absorber layer. Reducing the defect density will increase the open-circuit voltage above 1 V through an increase in the carrier lifetime and concentration to tau >10 ns and p > 10 16 cm-3, respectively. However, the large lattice mismatch (10%) between CdTe and CdS and the polycrystalline nature of the CdTe film are the fundamental reasons for the high defect density and pose a difficult challenge to solve. In this work, a method to physically and electrically isolate the different kinds of defects at the nanoscale and understand their effect on the electrical performance of CdTe is presented. A SiO2 template with arrays of window openings was deposited between the CdTe and CdS to achieve selective-area growth of the CdTe via close-space sublimation. The diameter of the window openings was varied from the micro to the nanoscale to study the effect of size on nucleation, grain growth, and defect density. The resulting structures enabled the possibility to electrically isolate and individually probe micrometer and nanoscale sized CdTe/CdS cells. Electron back-scattered diffraction was used to observe grain orientation and defects in the miniature cells. Scanning and transmission electron microscopy was used to study the morphology, grain boundaries, grain orientation, defect structure, and strain in the layers. Finally, conducting atomic force microscopy was used to study the current-voltage characteristics of the solar cells. An

  11. Sharing the atom bomb

    SciTech Connect

    Chace, J.

    1996-01-01

    Shaken by the devastation of Hiroshima and Nagasaki and fearful that the American atomic monopoly would spark an arms race, Dean Acheson led a push in 1946 to place the bomb-indeed, all atomic energy-under international control. But as the memories of wartime collaboration faded, relations between the superpowers grew increasingly tense, and the confrontational atmosphere undid his proposal. Had Acheson succeeded, the Cold War might not have been. 2 figs.

  12. Atomizing nozzle and method

    DOEpatents

    Ting, Jason; Anderson, Iver E.; Terpstra, Robert L.

    2000-03-16

    A high pressure close-coupled gas atomizing nozzle includes multiple discrete gas jet discharge orifices having aerodynamically designed convergent-divergent geometry with an first converging section communicated to a gas supply manifold and to a diverging section by a constricted throat section to increase atomizing gas velocity. The gas jet orifices are oriented at gas jet apex angle selected relative to the melt supply tip apex angle to establish a melt aspiration condition at the melt supply tip.

  13. Metal atomization spray nozzle

    DOEpatents

    Huxford, T.J.

    1993-11-16

    A spray nozzle for a magnetohydrodynamic atomization apparatus has a feed passage for molten metal and a pair of spray electrodes mounted in the feed passage. The electrodes, diverging surfaces which define a nozzle throat and diverge at an acute angle from the throat. Current passes through molten metal when fed through the throat which creates the Lorentz force necessary to provide atomization of the molten metal. 6 figures.

  14. Metal atomization spray nozzle

    DOEpatents

    Huxford, Theodore J.

    1993-01-01

    A spray nozzle for a magnetohydrodynamic atomization apparatus has a feed passage for molten metal and a pair of spray electrodes mounted in the feed passage. The electrodes, diverging surfaces which define a nozzle throat and diverge at an acute angle from the throat. Current passes through molten metal when fed through the throat which creates the Lorentz force necessary to provide atomization of the molten metal.

  15. Optical atomic magnetometer

    SciTech Connect

    Budker, Dmitry; Higbie, James; Corsini, Eric P.

    2013-11-19

    An optical atomic magnetometers is provided operating on the principles of nonlinear magneto-optical rotation. An atomic vapor is optically pumped using linearly polarized modulated light. The vapor is then probed using a non-modulated linearly polarized light beam. The resulting modulation in polarization angle of the probe light is detected and used in a feedback loop to induce self-oscillation at the resonant frequency.

  16. Correctly Expressing Atomic Weights

    NASA Astrophysics Data System (ADS)

    Paolini, Moreno; Cercignani, Giovanni; Bauer, Carlo

    2000-11-01

    Very often, atomic or molecular weights are expressed as dimensionless quantities, but although the historical importance of their definition as "pure numbers" is acknowledged, it is inconsistent with experimental formulas and with the theory of measure in general. Here, we propose on the basis of clear-cut formulas that, contrary to customary statements, atomic and molecular weights should be expressed as dimensional quantities (masses) in which the Dalton (= 1.663 x 10-24 g) is taken as the unit.

  17. Hirshfeld atom refinement.

    PubMed

    Capelli, Silvia C; Bürgi, Hans-Beat; Dittrich, Birger; Grabowsky, Simon; Jayatilaka, Dylan

    2014-09-01

    Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-made ab initio quantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustrated via the example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly-l-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree-Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints - even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu's), all other structural parameters agree within less than 2 csu's. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å(2) as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements - an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å.

  18. On Atomization in Carburetors

    NASA Technical Reports Server (NTRS)

    Scheubel, F N

    1931-01-01

    The outstanding quantity of the whole atomization problem is the characteristic K, and therefore the ratio of the static pressure of the air stream with respect to the liquid to the surface tension of the liquid. The higher its value, the better the atomization. The shape of the Venturi tube plays a secondary role. The increase of section beyond the throat had best not be too abrupt.

  19. High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies

    NASA Astrophysics Data System (ADS)

    Lindström, A.; Mirbt, S.; Sanyal, B.; Klintenberg, M.

    2016-01-01

    In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers.

  20. Nonlinear terahertz response of HgTe/CdTe quantum wells

    SciTech Connect

    Chen, Qinjun; Sanderson, Matthew; Zhang, Chao

    2015-08-24

    Without breaking the topological order, HgTe/CdTe quantum wells can have two types of bulk band structure: direct gap type (type I) and indirect gap type (type II). We report that the strong nonlinear optical responses exist in both types of bulk states under a moderate electric field in the terahertz regime. Interestingly, for the type II band structure, the third order conductivity changes sign when chemical potentials lies below 10 meV due to the significant response of the hole excitation close to the bottom of conduction band. Negative nonlinear conductivities suggest that HgTe/CdTe quantum wells can find application in the gain medium of a laser for terahertz radiation. The thermal influences on nonlinear optical responses of HgTe/CdTe quantum wells are also studied.

  1. Growth and optical properties of CdTe quantum dots in ZnTe nanowires

    SciTech Connect

    Wojnar, Piotr; Janik, Elzbieta; Baczewski, Lech T.; Kret, Slawomir; Karczewski, G.; Wojtowicz, Tomasz

    2011-09-12

    We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV-2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.

  2. NONLINEAR ATOM OPTICS

    SciTech Connect

    T. MILONNI; G. CSANAK; ET AL

    1999-07-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The project objectives were to explore theoretically various aspects of nonlinear atom optics effects in cold-atom waves and traps. During the project a major development occurred the observation, by as many as a dozen experimental groups, of Bose-Einstein condensation (BEC) in cold-atom traps. This stimulated us to focus our attention on those aspects of nonlinear atom optics relating to BEC, in addition to continuing our work on a nonequilibrium formalism for dealing with the interaction of an electromagnetic field with multi-level atomic systems, allowing for macroscopic coherence effects such as BEC. Studies of several problems in BEC physics have been completed or are near completion, including the suggested use of external electric fields to modify the nature of the interatomic interaction in cold-atom traps; properties of two-phase condensates; and molecular loss processes associated with BEC experiments involving a so-called Feshbach resonance.

  3. Atomic mass compilation 2012

    SciTech Connect

    Pfeiffer, B.; Venkataramaniah, K.; Czok, U.; Scheidenberger, C.

    2014-03-15

    Atomic mass reflects the total binding energy of all nucleons in an atomic nucleus. Compilations and evaluations of atomic masses and derived quantities, such as neutron or proton separation energies, are indispensable tools for research and applications. In the last decade, the field has evolved rapidly after the advent of new production and measuring techniques for stable and unstable nuclei resulting in substantial ameliorations concerning the body of data and their precision. Here, we present a compilation of atomic masses comprising the data from the evaluation of 2003 as well as the results of new measurements performed. The relevant literature in refereed journals and reports as far as available, was scanned for the period beginning 2003 up to and including April 2012. Overall, 5750 new data points have been collected. Recommended values for the relative atomic masses have been derived and a comparison with the 2003 Atomic Mass Evaluation has been performed. This work has been carried out in collaboration with and as a contribution to the European Nuclear Structure and Decay Data Network of Evaluations.

  4. Growth and characterization of nonlinear optical telluromolybdate CoTeMoO{sub 6} single crystals

    SciTech Connect

    Mączka, Mirosław; Hermanowicz, Krzysztof; Majchrowski, Andrzej; Kroenke, Łukasz; Pietraszko, Adam; Ptak, Maciej

    2014-12-15

    Nonlinear optical (NLO) crystals CoTeMoO{sub 6} have been grown from high temperature solution by means of spontaneous crystallization. These crystals have been characterized by temperature-dependent X-ray diffraction, infrared and electron absorption methods. Moreover, polarized Raman spectra have been measured at room temperature. These studies showed that the Mo{sup 6+} and Te{sup 4+} ions are in asymmetric coordination environment, and CoTeMoO{sub 6} has the largest flexibility index among MTeMoO{sub 6} family of telluro-molybdates (M=Zn, Mg, Cd, Mn, Co), making this compound attractive NLO material. Raman and IR studies allowed assigning the observed modes to respective motions of atoms in the unit cell. They have also showed evidence for spin–phonon coupling at low temperatures and suggested that CoTeMoO{sub 6} is prospective material for solid-state Raman laser-frequency converters. Analysis of electron absorption data has shown that Co{sup 2+} ions are located in sites of weak crystal field with the crystal field parameters Dq and B equal to 548 cm{sup −1} and 882 cm{sup −1}, respectively. - Graphical abstract: View of CoTeMoO{sub 6} crystal structure along the b-axis. - Highlights: • Single crystals of nonlinear optical telluromolybdate CoTeMoO{sub 6} were grown. • Crystal structure was solved by means of single crystal X-ray diffraction. • Raman and IR spectra were measured and analyzed. • Crystal field strength acting on Co{sup 2+} ions was established from analysis of electron absorption spectra.

  5. Perspective on TeV-scale physics

    SciTech Connect

    Chanowitz, M.S.

    1989-02-01

    These lectures review theoretical motivations and experimental prospects for the study of TeV-scale physics. Three clues to the importance of TeV physics are discussed: implications of quantum corrections for the masses of a fourth generation quark-lepton family, the gauge hierarchy problem and known solutions, and implications of symmetry and unitarity for the symmetry-breaking sector of the electroweak gauge theory. The experimental prospects are reviewed with emphasis on the multi-TeV pp colliders that may be built in the 1990's. The topics include new phenomena that might occur - e.g., a fourth generation, heavy gauge bosons, composite structure, and supersymmetry - as well as the signals of the unknown SU(2)/sub L/ /times/ U(1)/sub Y/ breaking mechanism that must occur within the TeV domain. 96 refs., 21 figs.

  6. RF magnetron sputtering deposition of CdTe passivation on HgCdTe

    NASA Astrophysics Data System (ADS)

    Rutkowski, Jaroslaw; Adamiec, Krzysztof; Rogalski, Antoni

    1998-04-01

    In this study, we report the RF magnetron sputtering growth and characterization of CdTe passivant on bulk n-type HgCdTe. Our investigations include the HgCdTe surface preparation and in-situ pretreatment, deposition-induced surface damage, interface charge, CdTe film stoichiometry, and thermal stability. The metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage characteristics. The heterostructures are also characterized by reflectance measurement. In order to investigate the passivation properties of CdTe/HgCdTe heterostructures, we have modeled the band diagram of abrupt CdTe/HgCdTe heterojunction. The effect of sputtering growth condition parameters is also reported. The sputtering CdTe layers, exhibit excellent dielectric, insulating and mechano- chemical properties, as well as interface properties. The interfaces are characterized by slight accumulation and a small hysteresis. A carefully controlled growth process and surface pretreatment tailored to the specific material are required in order to obtain near flat band conditions on n- type materials. Additional informations on surface limitations are obtained from analyzing the I-V characteristics of photodiodes with metal gates covering the p-n junction surface location.

  7. Thermodynamic and Transport Properties of YTe3, LaTe3 and CeTe3

    SciTech Connect

    Ru, N.

    2011-08-19

    Measurements of heat capacity, susceptibility, and electrical resistivity are presented for single crystals of the charge density wave compounds YTe{sub 3}, LaTe{sub 3}, and CeTe{sub 3}. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe{sub 3} is found to be a weak Kondo lattice, with an antiferromagnetic ground state and T{sub N} = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

  8. Atom-atom inelastic collisions and three-body atomic recombination in weakly ionized argon plasmas

    NASA Technical Reports Server (NTRS)

    Braun, C. G.; Kunc, J. A.

    1989-01-01

    A stationary collisional-radiative model including both inelastic electron-atom and atom-atom collisions is used to examine nonequilibrium weakly ionized argon plasmas with atomic densities 10 to the 16th to 10 to the 20th/cu cm, temperatures below 6000 K, and with different degrees of radiation trapping. It is shown that three-body atomic recombination becomes important at high particle densities. Comparison is made between the present approach and Thomson's theory for atomic recombination.

  9. GaTe semiconductor for radiation detection

    DOEpatents

    Payne, Stephen A.; Burger, Arnold; Mandal, Krishna C.

    2009-06-23

    GaTe semiconductor is used as a room-temperature radiation detector. GaTe has useful properties for radiation detectors: ideal bandgap, favorable mobilities, low melting point (no evaporation), non-hygroscopic nature, and availability of high-purity starting materials. The detector can be used, e.g., for detection of illicit nuclear weapons and radiological dispersed devices at ports of entry, in cities, and off shore and for determination of medical isotopes present in a patient.

  10. Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

    SciTech Connect

    Kim, Jeongwoo; Jhi, Seung-Hoon

    2015-05-21

    The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge{sub 2}Sb{sub 2}Te{sub 5} and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

  11. Impact of Pb content on the physical parameters of Se-Te-Pb system

    SciTech Connect

    Anjali,; Sharma, Raman; Thakur, Nagesh; Patial, Balbir Singh; Tripathi, S. K.

    2015-05-15

    In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and mean bond energy are found to decrease with Pb atomic percentage.

  12. The helical surface states of the S-covered topological insulator Sb2Te3(0001).

    PubMed

    Zhao, Xu; Dai, Xian-Qi; Zhao, Bao; Wang, Ning; Ji, Yuan-Yuan

    2013-07-01

    The effects of S atom surface adsorption and substitution on the helical surface states of Sb2Te3 are studied by the density-functional theory with spin-orbit coupling being taken into account self-consistently. It is found that S atoms play the role of surface passivation when adsorbed on both surfaces of a 6QL Sb2Te3 film in symmetrical configuration. For symmetrical surfaces with both the top and bottom surfaces of a thin film with adsorbed S atoms, the linear dispersion of the surface states is found to be preserved and the topological surface states survive. The spatial distribution of charge density of the surface state at the Γ[overline] point is also symmetric. For a film with asymmetric S atom adsorption, i.e., only one of the surfaces has adsorbed S atoms, the surface band structure is found to be very different. The degeneracy of the surface states from the two sides of a film is broken. The gap opens slightly at Γ[overline] and the spatial distribution of charge density of the surface state at the Γ[overline] point is also modified greatly. The Fermi level is robust against S impurity adsorption on the surface of Sb2Te3. Compared with S substitution, the effect of single surface S adsorption on electron structures is more prominent. This supports the idea that the topological insulator surface electronic states are dominated by its structural symmetry and the effect of the asymmetric environment of topological insulator Sb2Te3 films should thus be considered.

  13. Near-infrared emitting AgInTe2 and Zn-Ag-In-Te colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Langevin, Marc-Antoine; Pons, Thomas; Ritcey, Anna M.; Nì. Allen, Claudine

    2015-06-01

    The synthesis of AgInTe2 nanocrystals emitting between 1095 nm and 1160 nm is presented. Evolution of the Ag:In:Te ratio shows progressive incorporation of In3+ in Ag2Te, leading to the formation of orthorhombic AgInTe2. When zinc is added to the synthesis, the photoluminescence quantum yield reaches 3.4 %.

  14. Incommensurate phase of Te adsorbed on (001) GaAs

    NASA Astrophysics Data System (ADS)

    Cibert, J.; Saminadayar, K.; Tatarenko, S.; Gobil, Y.

    1989-06-01

    Occurrence of commensurate and incommensurate phases is reported for adsorption of Te on Ga-rich (001) GaAs surfaces. The Te coverage is measured directly through x-ray photoelectron spectroscopy, and the incommensurate phase is studied in detail as a function of Te coverage; two regimes are demonstrated, one at low coverage where Te is mainly bound to Ga, and another one at high coverage where Te mainly bound to As is also present.

  15. Structural origin of resistance drift in amorphous GeTe

    NASA Astrophysics Data System (ADS)

    Zipoli, Federico; Krebs, Daniel; Curioni, Alessandro

    2016-03-01

    We used atomistic simulations to study the origin of the change of resistance over time in the amorphous phase of GeTe, a prototypical phase-change material (PCM). Understanding the cause of resistance drift is one of the biggest challenges to improve multilevel storage technology. For this purpose, we generated amorphous structures via classical molecular-dynamics simulations under conditions as close as possible to the experimental operating ones of such memory devices. Moreover, we used the replica-exchange technique to generate structures comparable with those obtained in the experiment after long annealing that show an increase of resistance. This framework allowed us to overcome the main limitation of previous simulations, based on density-functional theory, that suffered from being computationally too expensive therefore limited to the nanosecond time scale. We found that resistance drift is caused by consumption of Ge atom clusters in which the coordination of at least one Ge atom differs from that of the crystalline phase and by removal of stretched bonds in the amorphous network, leading to a shift of the Fermi level towards the middle of the band gap. These results show that one route to design better memory devices based on current chalcogenide alloys is to reduce the resistance drift by increasing the rigidity of the amorphous network.

  16. A Model for Predicting Thermoelectric Properties of Bi2Te3

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon; VonAllmen, Paul

    2009-01-01

    A parameterized orthogonal tight-binding mathematical model of the quantum electronic structure of the bismuth telluride molecule has been devised for use in conjunction with a semiclassical transport model in predicting the thermoelectric properties of doped bismuth telluride. This model is expected to be useful in designing and analyzing Bi2Te3 thermoelectric devices, including ones that contain such nano - structures as quantum wells and wires. In addition, the understanding gained in the use of this model can be expected to lead to the development of better models that could be useful for developing other thermoelectric materials and devices having enhanced thermoelectric properties. Bi2Te3 is one of the best bulk thermoelectric materials and is widely used in commercial thermoelectric devices. Most prior theoretical studies of the thermoelectric properties of Bi2Te3 have involved either continuum models or ab-initio models. Continuum models are computationally very efficient, but do not account for atomic-level effects. Ab-initio models are atomistic by definition, but do not scale well in that computation times increase excessively with increasing numbers of atoms. The present tight-binding model bridges the gap between the well-scalable but non-atomistic continuum models and the atomistic but poorly scalable ab-initio models: The present tight-binding model is atomistic, yet also computationally efficient because of the reduced (relative to an ab-initio model) number of basis orbitals and flexible parameterization of the Hamiltonian.

  17. Manipulation of the presence of helical surface states of topological insulators using Sb2Te3-GeTe superlattices

    NASA Astrophysics Data System (ADS)

    Takagaki, Y.; Saito, Yuta; Tominaga, Junji

    2016-03-01

    Ab initio calculations have predicted a transition between topological insulators and band insulators in superlattices consisting of Sb2Te3 and GeTe, when the periodicity is varied. We examine the amplitude of the weak antilocalization effect to confirm the transition. In agreement with the predictions, robust surface states are present for (Sb2Te3)1(GeTe)2 but absent when the content of the well-known topological insulator Sb2Te3 is increased as (Sb2Te3)4(GeTe)2, manifesting that the electronic coupling in the superlattices affects the emergence of the helical surface states nontrivially.

  18. Atomic resolution holography.

    PubMed

    Hayashi, Kouichi

    2014-11-01

    Atomic resolution holography, such as X-ray fluorescence holography (XFH)[1] and photoelectron holography (PH), has the attention of researcher as an informative local structure analysis, because it provides three dimensional atomic images around specific elements within a range of a few nanometers. It can determine atomic arrangements around a specific element without any prior knowledge of structures. It is considered that the atomic resolution holographic is a third method of structural analysis at the atomic level after X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). As known by many researchers, XRD and XAFS are established methods that are widespread use in various fields. XRD and XAFS provide information on long-range translational periodicities and very local environments, respectively, whereas the atomic resolution holography gives 3D information on the local order and can visualize surrounding atoms with a large range of coordination shells. We call this feature "3D medium-range local structure observation".In addition to this feature, the atomic resolution holography is very sensitive to the displacement of atoms from their ideal positions, and one can obtain quantitative information about local lattice distortions by analyzing reconstructed atomic images[2] When dopants with different atomic radii from the matrix elements are present, the lattices around the dopants are distorted. However, using the conventional methods of structural analysis, one cannot determine the extent to which the local lattice distortions are preserved from the dopants. XFH is a good tool for solving this problem.Figure 1 shows a recent achievement on a relaxor ferroelectric of Pb(Mg1/3Nb2/3)O3 (PMN) using XFH. The structural studies of relaxor ferroelectrics have been carried out by X-ray or neutron diffractions, which suggested rhombohedral distortions of their lattices. However, their true pictures have not been obtained, yet. The Nb Kα holograms showed

  19. Effect of ZnTe and CdZnTe Alloys at the Back Contact of 1-μm-Thick CdTe Thin Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    2002-05-01

    N2-doped ZnTe was introduced onto 1-μm-thick CdTe absorbers in order to reduce the carrier recombination at the back contact of CdS/CdTe/C/Ag configuration solar cells. ZnTe films were grown by molecular beam epitaxy (MBE) on GaAs and Corning glass substrates to investigate the characteristics of the films. Epitaxial growth of ZnTe was realized on GaAs substrates and a hole concentration of 8 × 1018 cm-3 with a resistivity of 0.045 Ω \\cdotcm was achieved as a result of nitrogen doping. In contrast, polycrystalline ZnTe films were grown on Corning glass and CdTe thin films. Dark and photoconductivity of ZnTe films increased to 1.43 × 10-5 S/cm and 1.41 × 10-4 S/cm, respectively, while the Zn to Te ratio was decreased to 0.25 during MBE growth. These ZnTe films with different thicknesses were inserted into close-spaced sublimation (CSS)-grown 1-μm-thick CdTe solar cells. A conversion efficiency of 8.31% (Voc: 0.74 V, Jsc: 22.98 mA/cm2, FF: 0.49, area: 0.5 cm2) was achieved for a 0.2-μm-thick ZnTe layer with a cell configuration of CdS/CdTe/ZnTe/Cu-doped-C/Ag. Furthermore, to overcome the problem of possible recombination loss in the interface layer of CdTe and ZnTe, the intermediate ternary CdZnTe is investigated. The compositional factor in Cd1-xZnxTe:N alloy is varied and the dependence of the conductivity is evaluated. For instance, Cd0.5Zn0.5Te:N, with dark and photoconductivity of 2.13 × 10-6 and 2.9 × 10-5 S/cm, respectively, is inserted at the back contact of a 1-μm-thick CdTe solar cell. A conversion efficiency of 7.46% (Voc: 0.68 V, Jsc: 22.60 mA/cm2, FF: 0.49, area: 0.086 cm2) was achieved as the primary result for a 0.2-μm-thick Cd0.5Zn0.5Te:N layer with the cell configuration of CdS/CdTe/Cd0.5Zn0.5Te:N/Au.

  20. High thermoelectric performance by resonant dopant indium in nanostructured SnTe

    PubMed Central

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-01-01

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K. PMID:23901106

  1. High thermoelectric performance by resonant dopant indium in nanostructured SnTe.

    PubMed

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-08-13

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

  2. Nanostructure investigation of the layered ternary compound Ni3-x Sn1-y Te2

    NASA Astrophysics Data System (ADS)

    Dankwort, T.; Duppel, V.; Deiseroth, H.-J.; Reiner, C.; Schlosser, M.; Kienle, L.

    2016-09-01

    The structure of Ni3-x Sn1-y Te2 is characterized by layered structural motifs related to an average NiAs/Ni2In-type. Order/disorder phenomena were analyzed via a detailed nanostructure investigation including electron diffraction and high resolution transmission electron microscopy (HRTEM) in conjunction with image simulation. Dependent on the stoichiometry, commensurate and incommensurate satellite reflections with respect to the parent NiAs structure were observed in Fourier transform and electron diffraction pattern as a result of occupational modulation of Te and Sn atoms. For the commensurate case a triplication of the c-lattice parameter is evident as a result of Sn-Te-Te stacking. Further, HRTEM micrographs indicate additional ordering phenomena along the c* direction depending on Ni/vacancy ordering which was rationalized by an alternating filling of van der Waals gaps with Ni. Also morphological defects in bright field images were observed. HRTEM investigations prove that these morphological defects are of structural nature, i.e. they are based on domains shifted relative to each other (antiphase boundaries).

  3. Resonance photoelectron spectroscopy of TiX{sub 2} (X = S, Se, Te) titanium dichalcogenides

    SciTech Connect

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Yablonskikh, M. V.; Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N.

    2012-11-15

    The photoelectron valence band spectra of TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS{sub 2} and TiTe{sub 2}. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS{sub 2} is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe{sub 2} is caused by occupation of the 3d band in Ti.

  4. Pb2MnTeO6 Double Perovskite: An Antipolar Anti-ferromagnet.

    PubMed

    Retuerto, Maria; Skiadopoulou, Stella; Li, Man-Rong; Abakumov, Artem M; Croft, Mark; Ignatov, Alexander; Sarkar, Tapati; Abbett, Brian M; Pokorný, Jan; Savinov, Maxim; Nuzhnyy, Dmitry; Prokleška, Jan; Abeykoon, Milinda; Stephens, Peter W; Hodges, Jason P; Vaněk, Přemysl; Fennie, Craig J; Rabe, Karin M; Kamba, Stanislav; Greenblatt, Martha

    2016-05-01

    Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s(2) lone-pair electrons, together with a surprising off-centering of Mn(2+) (d(5)) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6. PMID:27058393

  5. Computational discovery of ferromagnetic semiconducting single-layer CrSnTe3

    DOE PAGESBeta

    Zhuang, Houlong L.; Xie, Yu; Kent, P. R. C.; Ganesh, P.

    2015-07-06

    Despite many single-layer materials being reported in the past decade, few of them exhibit magnetism. Here we perform first-principles calculations using accurate hybrid density functional methods (HSE06) to predict that single-layer CrSnTe3 (CST) is a ferromagnetic semiconductor, with band gaps of 0.9 and 1.2 eV for the majority and minority spin channels, respectively. We determine the Curie temperature as 170 K, significantly higher than that of single-layer CrSiTe3 (90K) and CrGeTe3 (130 K). This is due to the enhanced ionicity of the Sn-Te bond, which in turn increases the superexchange coupling between the magnetic Cr atoms. We further explore themore » mechanical and dynamical stability and strain response of this single-layer material for possible epitaxial growth. Lastly, our study provides an intuitive approach to understand and design novel single-layer magnetic semiconductors for a wide range of spintronics and energy applications.« less

  6. Nanoscale Imaging of Band Gap and Defects in Polycrystalline CdTe Photovoltaic Devices

    NASA Astrophysics Data System (ADS)

    Zhitenev, Nikolai; Yoon, Yohan; Chae, Jungseok; Katzenmeyer, Aaron; Yoon, Heayoung; An, Sangmin; Shumacher, Joshua; Centrone, Andrea

    To further increase the power efficiency of polycrystalline thin film photovoltaic (PV) technology, a detailed understanding of microstructural properties of the devices is required. In this work, we investigate the microstructure of CdTe PV devices using two optical spectroscopies. Sub-micron thickness lamella samples were cut out from a PV device, either in cross-section or in-plane, by focused ion beam. The first technique is the photothermal induced resonance (PTIR) used to obtain absorption spectra over a broad range of wavelengths. In PTIR, a wavelength tunable pulsed laser is combined with an atomic force microscope to detect the local thermal expansion of lamella CdTe sample induced by light absorption. The second technique based on a near-field scanning optical microscope maps the local absorption at fixed near-IR wavelengths with energies at or below CdTe band-gap energy. The variation of the band gap throughout the CdTe absorber determined from PTIR spectra is ~ 20 meV. Both techniques detect strong spatial variation of shallow defects over different grains. The spatial distribution of mid-gap defects appears to be more uniform. The resolution, the sensitivity and the applicability of these two approaches are compared.

  7. Lateral Diffusion Length Changes in HgCdTe Detectors in a Proton Environment

    NASA Technical Reports Server (NTRS)

    Hubbs, John E.; Marshall, Paul W.; Marshall, Cheryl J.; Gramer, Mark E.; Maestas, Diana; Garcia, John P.; Dole, Gary A.; Anderson, Amber A.

    2007-01-01

    This paper presents a study of the performance degradation in a proton environment of very long wavelength infrared (VLWIR) HgCdTe detectors. The energy dependence of the Non-Ionizing Energy Loss (NIEL) in HgCdTe provides a framework for estimating the responsivity degradation in VLWIR HgCdTe due to on orbit exposure from protons. Banded detector arrays that have different detector designs were irradiated at proton energies of 7, 12, and 63 MeV. These banded detector arrays allovedin sight into how the fundamental detector parameters degraded in a proton environment at the three different proton energies. Measured data demonstrated that the detector responsivity degradation at 7 MeV is 5 times larger than the degradation at 63 MeV. The comparison of the responsivity degradation at the different proton energies suggests that the atomic Columbic interaction of the protons with the HgCdTe detector is likely the primary mechanism responsible for the degradation in responsivity at proton energies below 30 MeV.

  8. Growth and fabrication method of CdTe and its performance as a radiation detector

    NASA Astrophysics Data System (ADS)

    Choi, Hyojeong; Jeong, Manhee; Kim, Han Soo; Kim, Young Soo; Ha, Jang Ho; Chai, Jong-Seo

    2015-01-01

    A CdTe crystal ingot doped with 2000 ppm of Cl was grown by using the low-pressure Bridgman (LPB) method at the Korea Atomic Energy Research Institute (KAERI). A Semiconductor detector as a radiation detection sensor with a size of 7 (W) × 6.5 (D) × 2 (H) mm3 was fabricated from the CdTe ingot. In addition, the properties of the CdTe sample were observed through four kinds of experiments to analyze its performance. The resistivity was obtained as 1.41 × 1010 Ωcm by using a Keithley 6517A high-precision electrometer. The mobility-lifetime products for electrons and holes were 3.137 × 10-4 cm2/V and 4.868 × 10-5 cm2/V, respectively. Finally, we achieved a 16.8% energy resolution at 59.5 keV for the 241Am gamma-ray source. The CdTe semiconductor detector grown at KAERI has a performance good enough to detect low-energy gamma-rays.

  9. Atomic oxygen stimulated outgassing

    NASA Technical Reports Server (NTRS)

    Linton, Roger C.; Reynolds, John M.

    1991-01-01

    The passive Long Duration Exposure Facility (LDEF) Experiment A0034, Atomic Oxygen Simulated Outgassing, consisted of two identical one-sixth tray modules, exposing selected thermal control coatings to atomic oxygen and the combined space environment on the leading edge and, for reference, to the relative wake environment on the trailing edge. Optical mirrors were included adjacent to the thermal coatings for deposition of outgassing products. Ultraviolet grade windows and metal covers were provided for additional assessment of the effects of the various environmental factors. Preliminary results indicate that orbital atomic oxygen is both a degrading and a optically restorative factor in the thermo-optical properties of selected thermal coatings. There is evidence of more severe optical degradation on collector mirrors adjacent to coatings that were exposed to the RAM-impinging atomic oxygen. This evidence of atomic oxygen stimulated outgassing is discussed in relation to alternative factors that could affect degradation. The general effects of the space environment on the experiment hardware as well as the specimens are discussed.

  10. High thermoelectric potential of Bi2Te3 alloyed GeTe-rich phases

    NASA Astrophysics Data System (ADS)

    Madar, Naor; Givon, Tom; Mogilyansky, Dmitry; Gelbstein, Yaniv

    2016-07-01

    In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)1-x(Bi2Te3)x alloys, with x values of up to 20%. Higher solubility limit of Bi2Te3 in GeTe, than previously reported, was identified around ˜9%, extending the doping potential of GeTe by the Bi2Te3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ˜1.55 at ˜410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%-17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge8Bi2Te11 and Ge4Bi2Te7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi2Te3), was suggested for further electronic optimization of the thermoelectric properties.

  11. Effects of Sb Content (x) on (Bi(1-x)Sb(x))2Te3 Thermoelectric Thin Film Deposited by Effusion Cell Evaporator.

    PubMed

    Yong, Ho; Na, Sekwon; Gang, Jun-Gu; Jeon, Seong-Jae; Hyun, Seungmin; Lee, Hoo-Jeong

    2015-10-01

    This paper investigates the effects of the Sb content (x) on (Bi(1-x)Sb(x))2Te3 thermoelectric films with x changing widely from 0 (Sb2Te3) to 1 (Bi2Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45~0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 μW/K(2) whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 μW/K(2)cm.

  12. Effects of Sb Content (x) on (Bi(1-x)Sb(x))2Te3 Thermoelectric Thin Film Deposited by Effusion Cell Evaporator.

    PubMed

    Yong, Ho; Na, Sekwon; Gang, Jun-Gu; Jeon, Seong-Jae; Hyun, Seungmin; Lee, Hoo-Jeong

    2015-10-01

    This paper investigates the effects of the Sb content (x) on (Bi(1-x)Sb(x))2Te3 thermoelectric films with x changing widely from 0 (Sb2Te3) to 1 (Bi2Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45~0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 μW/K(2) whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 μW/K(2)cm. PMID:26726497

  13. Study of Pb-doped Ge{sub 2}Sb{sub 2}Te{sub 5} in crystalline phase using first principle calculations

    SciTech Connect

    Singh, Janpreet; Tripathi, S. K. E-mail: surya-tr@yahoo.com; Singh, Gurinder; Kaura, Aman

    2015-08-28

    To improve the phase change characteristics of Ge{sub 2}Sb{sub 2}Te{sub 5} (GST), doping is used as one of the effective methods. 4.4 atomic % of Pb doped GST has been studied using first principle calculations. No effect of doping on Te-Ge and Te-Sb bond length has been observed, but the Te-Te bond gets shrink with Pb doping. Due to which the Sb{sub 2}Te{sub 3} segregates as a second phase, with increased doping concentration of Pb in GST alloy. Using such type of calculation, we can calculate the desirable concentration of dopant atoms to prepare the desired material. We can control any segregation in required material with pre-theoretical calculations. The metallic nature of Pd doped GST has been discussed with band structure plots. The metallic character of alloys calculated as in this paper will be helpful to understand the tuning of conductivity of phase change materials, which helps to enhance the phase change properties.

  14. Nitric-phosphoric acid etching effects on the surface chemical composition of CdTe thin film.

    NASA Astrophysics Data System (ADS)

    Irfan, Irfan; Ding, Huanjun; Xia, Wei; Lin, Hao; Tang, Ching W.; Gao, Yongli

    2009-03-01

    Nitric-phosphoric (NP) acid etching has been regarded as one of the most successful methods for the formation of low resistance back contact with the metal electrode in CdTe based solar cells. We report back surface chemical composition for eight different durations of NP etching of CdTe polycrystalline thin film. We studied the surfaces with x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IEPS) and atomic force microscopy (AFM). Etching dependence on the back surface composition and electronic structure was observed. Valence and conduction band shifts relative to the Fermi level of the system with different etching duration were analyzed. The sample was left in open ambient condition for three weeks and XPS data were obtained again in order to study the difference in surface chemical composition with the pristine CdTe film. Unetched and highly etched part of the sample were sputtered and the depth profile analyzed.

  15. Computer Modeling Of Atomization

    NASA Technical Reports Server (NTRS)

    Giridharan, M.; Ibrahim, E.; Przekwas, A.; Cheuch, S.; Krishnan, A.; Yang, H.; Lee, J.

    1994-01-01

    Improved mathematical models based on fundamental principles of conservation of mass, energy, and momentum developed for use in computer simulation of atomization of jets of liquid fuel in rocket engines. Models also used to study atomization in terrestrial applications; prove especially useful in designing improved industrial sprays - humidifier water sprays, chemical process sprays, and sprays of molten metal. Because present improved mathematical models based on first principles, they are minimally dependent on empirical correlations and better able to represent hot-flow conditions that prevail in rocket engines and are too severe to be accessible for detailed experimentation.

  16. Atomic Force Microscope

    SciTech Connect

    Day, R.D.; Russell, P.E.

    1988-12-01

    The Atomic Force Microscope (AFM) is a recently developed instrument that has achieved atomic resolution imaging of both conducting and non- conducting surfaces. Because the AFM is in the early stages of development, and because of the difficulty of building the instrument, it is currently in use in fewer than ten laboratories worldwide. It promises to be a valuable tool for obtaining information about engineering surfaces and aiding the .study of precision fabrication processes. This paper gives an overview of AFM technology and presents plans to build an instrument designed to look at engineering surfaces.

  17. Hirshfeld atom refinement

    PubMed Central

    Capelli, Silvia C.; Bürgi, Hans-Beat; Dittrich, Birger; Grabowsky, Simon; Jayatilaka, Dylan

    2014-01-01

    Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-made ab initio quantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustrated via the example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly–l-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree–Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints – even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu’s), all other structural parameters agree within less than 2 csu’s. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å2 as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements – an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å. PMID:25295177

  18. Iowa Powder Atomization Technologies

    ScienceCinema

    None

    2016-07-12

    The same atomization effect seen in a fuel injector is being applied to titanium metal resulting in fine titanium powders that are less than half the width of a human hair. Titanium melts above 3,000°F and is highly corrosive therefore requiring specialized containers. The liquid titanium is poured through an Ames Laboratory - USDOE patented tube which is intended to increase the energy efficiency of the atomization process, which has the ability to dramatically decrease the cost of fine titanium powders. This novel process could open markets for green manufacturing of titanium components from jet engines to biomedical implants.

  19. Iowa Powder Atomization Technologies

    SciTech Connect

    2012-01-01

    The same atomization effect seen in a fuel injector is being applied to titanium metal resulting in fine titanium powders that are less than half the width of a human hair. Titanium melts above 3,000°F and is highly corrosive therefore requiring specialized containers. The liquid titanium is poured through an Ames Laboratory - USDOE patented tube which is intended to increase the energy efficiency of the atomization process, which has the ability to dramatically decrease the cost of fine titanium powders. This novel process could open markets for green manufacturing of titanium components from jet engines to biomedical implants.

  20. Atom Tunneling in Chemistry.

    PubMed

    Meisner, Jan; Kästner, Johannes

    2016-04-25

    Quantum mechanical tunneling of atoms is increasingly found to play an important role in many chemical transformations. Experimentally, atom tunneling can be indirectly detected by temperature-independent rate constants at low temperature or by enhanced kinetic isotope effects. In contrast, the influence of tunneling on the reaction rates can be monitored directly through computational investigations. The tunnel effect, for example, changes reaction paths and branching ratios, enables chemical reactions in an astrochemical environment that would be impossible by thermal transition, and influences biochemical processes. PMID:26990917

  1. Atomization and Mixing Study

    NASA Technical Reports Server (NTRS)

    Ferrenberg, A.; Hunt, K.; Duesberg, J.

    1985-01-01

    The primary objective was the obtainment of atomization and mixing performance data for a variety of typical liquid oxygen/hydrocarbon injector element designs. Such data are required to establish injector design criteria and to provide critical inputs to liquid rocket engine combustor performance and stability analysis, and computational codes and methods. Deficiencies and problems with the atomization test equipment were identified, and action initiated to resolve them. Test results of the gas/liquid mixing tests indicated that an assessment of test methods was required. A series of 71 liquid/liquid tests were performed.

  2. Korean atomic bomb victims.

    PubMed

    Sasamoto, Yukuo

    2009-01-01

    After colonizing Korea, Japan invaded China, and subsequently initiated the Pacific War against the United States, Britain, and their allies. Towards the end of the war, U.S. warplanes dropped atomic bombs on Hiroshima and Nagasaki, which resulted in a large number of Koreans who lived in Hiroshima and Nagasaki suffering from the effects of the bombs. The objective of this paper is to examine the history of Korea atomic bomb victims who were caught in between the U.S., Japan, the Republic of Korea (South Korea) and the Democratic People's Republic of Korea (North Korea).

  3. Korean atomic bomb victims.

    PubMed

    Sasamoto, Yukuo

    2009-01-01

    After colonizing Korea, Japan invaded China, and subsequently initiated the Pacific War against the United States, Britain, and their allies. Towards the end of the war, U.S. warplanes dropped atomic bombs on Hiroshima and Nagasaki, which resulted in a large number of Koreans who lived in Hiroshima and Nagasaki suffering from the effects of the bombs. The objective of this paper is to examine the history of Korea atomic bomb victims who were caught in between the U.S., Japan, the Republic of Korea (South Korea) and the Democratic People's Republic of Korea (North Korea). PMID:20521424

  4. Topological states and phase transitions in Sb2Te3-GeTe multilayers.

    PubMed

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-01-01

    Topological insulators (TIs) are bulk insulators with exotic 'topologically protected' surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases. PMID:27291288

  5. S–Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells

    SciTech Connect

    Li, C.; Poplawsky, J.; Paudel, N.; Pennycook, T. J.; Haigh, S. J.; Al-Jassim, M. M.; Yan, Y.; Pennycook, S. J.

    2014-09-19

    At the CdTe/CdS interface, a significant Te-S interdiffusion has been found a few nanometers into the grain interiors with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). S substitution at Te sites has been directly resolved in CdTe with STEM Z-contrast images. Moreover, when enough S substitutes for Te, a structural transformation from zinc-blende to wurtzite has been observed. Cl segregation has also been found at the interface. STEM electron-beam-induced current (EBIC) shows that the p-n junction occurs a few nm into the CdTe grains, which is consistent with the S diffusion range we observe. The shift of the p-n junction suggests a buried homo-junction which would help reduce non-radiative recombination at the junction. Meanwhile, long-range S diffusion in CdTe grain boundaries (GBs) has been detected, as well as Te and Cl diffusion in CdS GBs.

  6. S–Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells

    DOE PAGESBeta

    Li, C.; Poplawsky, J.; Paudel, N.; Pennycook, T. J.; Haigh, S. J.; Al-Jassim, M. M.; Yan, Y.; Pennycook, S. J.

    2014-09-19

    At the CdTe/CdS interface, a significant Te-S interdiffusion has been found a few nanometers into the grain interiors with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). S substitution at Te sites has been directly resolved in CdTe with STEM Z-contrast images. Moreover, when enough S substitutes for Te, a structural transformation from zinc-blende to wurtzite has been observed. Cl segregation has also been found at the interface. STEM electron-beam-induced current (EBIC) shows that the p-n junction occurs a few nm into the CdTe grains, which is consistent with the S diffusion range we observe. The shiftmore » of the p-n junction suggests a buried homo-junction which would help reduce non-radiative recombination at the junction. Meanwhile, long-range S diffusion in CdTe grain boundaries (GBs) has been detected, as well as Te and Cl diffusion in CdS GBs.« less

  7. Propagation loss reduction of ZnMgTe/ZnTe waveguide devices

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Che; Kazami, Fukino; Wang, Jing; Nakasu, Taizo; Hattori, Shota; Kizu, Takeru; Hashimoto, Yuki; Kobayashi, Masakazu; Asahi, Toshiaki

    2016-08-01

    A ZnMgTe/ZnTe electro-optic (EO) waveguide has great potential to be utilized for practical applications. A low-dislocation ZnMgTe/ZnTe waveguide can be fabricated when the cladding layer thickness is below 20-fold the calculated critical layer thickness (CCLT × 20). To improve optical confinement, a waveguide with a thicker cladding layer or a higher Mg% should be considered. However, the device performance might be affected because of crystal quality deterioration since the lattice mismatch between MgTe and ZnTe was around 4.1%. In this study, optical confinement and propagation loss were examined by changing the dimensions of the ZnMgTe/ZnTe waveguide structure. The propagation loss, EO characteristics, and crystal quality of the fabricated waveguides were mainly studied. A waveguide with a cladding layer thickness of around 1.5-fold the 1/e penetration depth of the evanescent wave (d p 1/e × 1.5, corresponding to CCLT × 100) showed better optical properties than other waveguides, although its interface defect density was reasonably high.

  8. Weak Te,Te interactions through the looking glass of NMR spin-spin coupling.

    PubMed

    Bühl, Michael; Knight, Fergus R; Křístková, Anezka; Malkin Ondík, Irina; Malkina, Olga L; Randall, Rebecca A M; Slawin, Alexandra M Z; Woollins, J Derek

    2013-02-25

    Across the bay: J((125)Te, (125)Te) spin-spin coupling is a highly sensitive probe into the electronic and geometric structure of 1,8-peri-substituted naphthalene tellurium derivatives. The coupling is related to the onset of multicenter bonding in these systems.

  9. Topological states and phase transitions in Sb2Te3-GeTe multilayers

    NASA Astrophysics Data System (ADS)

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A.; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-06-01

    Topological insulators (TIs) are bulk insulators with exotic ‘topologically protected’ surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases.

  10. Topological states and phase transitions in Sb2Te3-GeTe multilayers

    PubMed Central

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A.; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-01-01

    Topological insulators (TIs) are bulk insulators with exotic ‘topologically protected’ surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases. PMID:27291288

  11. First-principles study of the structures and electronic band properties of Bi 2 Te 3 { 0 1 1 ¯ 5 } nanoribbons

    NASA Astrophysics Data System (ADS)

    Ma, Jing; Zhou, Jian-Ping; Yang, Jia; Zhao, Hong-Sheng; Chen, Xiao-Ming; Deng, Chao-Yong

    2015-06-01

    Bi2Te3 is known to be an excellent thermoelectric material as well as a topological insulator. We prepare Bi 2 Te 3 { 0 1 1 ¯ 5 } nanosheets with a hydrothermal method and find that the interplanar spacings have a little difference though they belong to a same family of crystal planes. Then, we investigate the structural and electronic properties of Bi 2 Te 3 { 0 1 1 ¯ 5 } nanoribbons with one to six atomic layers by density-functional theory. The results indicate that the nanoribbons exhibit insulator with a band gap except the three-atomic-layer ribbon, which unexpectedly shows a metallic behavior with a gapless band structure.

  12. Spatially resolved photoionization of ultracold atoms on an atom chip

    SciTech Connect

    Kraft, S.; Guenther, A.; Fortagh, J.; Zimmermann, C.

    2007-06-15

    We report on photoionization of ultracold magnetically trapped Rb atoms on an atom chip. The atoms are trapped at 5 {mu}K in a strongly anisotropic trap. Through a hole in the chip with a diameter of 150 {mu}m, two laser beams are focused onto a fraction of the atomic cloud. A first laser beam with a wavelength of 778 nm excites the atoms via a two-photon transition to the 5D level. With a fiber laser at 1080 nm the excited atoms are photoionized. Ionization leads to depletion of the atomic density distribution observed by absorption imaging. The resonant ionization spectrum is reported. The setup used in this experiment is suitable not only to investigate mixtures of Bose-Einstein condensates and ions but also for single-atom detection on an atom chip.

  13. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications

    PubMed Central

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-01-01

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future. PMID:26861380

  14. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications.

    PubMed

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-02-06

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future.

  15. Structural ordering in liquid K-Te alloys

    SciTech Connect

    Fortner, J.; Saboungi, M.L.; Enderby, J.E.

    1994-03-01

    Neutron diffraction from molten K{sub x}Te{sub 1{minus}x} is reported for x = 0.12 and x = 0.50 semiconducting alloys. The measured radial distribution functions (rdf) demonstrate the persistence of covalently bonded tellurium in the liquid. The rdf of the liquid K{sub 0.12}Te{sub 0.88}, which is dominated by the Te-Te contribution, is remarkably similar to that of pure liquid tellurium, the notable exception being that the nearest neighbor peak is largely resolved and found to have a coordination number slightly less than 2. The K{sub 0.50}Te{sub 0.50} rdf clearly indicates Te-Te pairing in the melt, and unexpected departure from the presumed similar Cu{sub 0.50}Te{sub 0.50}. These paired tellurium are most likely of the form (Te{sub 2}){sup 2{minus}} Zintl ions.

  16. Glass-forming ability and rigidity percolation in SeTePb lone-pair semiconductors

    NASA Astrophysics Data System (ADS)

    Sharma, Pankaj

    2016-04-01

    Correlating the various physical parameters of known semiconductors and pointing the properties of new ones, a number of parameters have been employed recently with different levels of success. Taking this into account an attempt has been made to correlate the physical properties of Pb-doped Se-Te lone-pair semiconductors. The small band gap and large Bohr radius of lead (Pb) containing lone-pair semiconductors assist them with specific optical, electrical and thermal properties. The various physical parameters like number of constraints, lone pair of electron, heat of atomization, density, compactness, free volume percentage have been analyzed in terms of mean coordination number for (Se90Te10)100- x Pb x (x = 0, 4, 8, 12, 16, 20, 24). The band gap for the compositions has been determined theoretically, and the obtained results are very well explained in terms of cohesive energy, electronegativity and average single bond energy.

  17. Moiré superlattices at the topological insulator Bi2Te3

    PubMed Central

    Schouteden, Koen; Li, Zhe; Chen, Taishi; Song, Fengqi; Partoens, Bart; Van Haesendonck, Chris; Park, Kyungwha

    2016-01-01

    We report on the observation of complex superlattices at the surface of the topological insulator Bi2Te3. Scanning tunneling microscopy reveals the existence of two different periodic structures in addition to the Bi2Te3 atomic lattice, which is found to strongly affect the local electronic structure. These three different periodicities are interpreted to result from a single small in-plane rotation of the topmost quintuple layer only. Density functional theory calculations support the observed increase in the DOS near the Fermi level, and exclude the possibility that strain is at the origin of the observed Moiré pattern. Exploration of Moiré superlattices formed by the quintuple layers of topological insulators holds great potential for further tuning of the properties of topological insulators. PMID:26854069

  18. CdTe surface roughness by Raman spectroscopy using the 830 nm wavelength.

    PubMed

    Frausto-Reyes, C; Molina-Contreras, J Rafael; Medina-Gutiérrez, C; Calixto, Sergio

    2006-09-01

    A Raman spectroscopic study was performed to detect the surface roughness of a cadmium telluride (CdTe) wafer sample, using the 514.5, 632.8 and 830.0 nm excitations wavelengths. To verify the relation between the roughness and the structure of Raman spectra, in certain zones of the sample, we measured their roughness with an atomic force microscopy. It was found that, using the 830 nm wavelength there is a direct correspondence between the spectrum structure and the surface roughness. For the others wavelengths it was found, however, that there is not a clearly correspondence between them. Our results suggest that, using the excitation wavelength of 830 nm the Raman spectroscopy can be used as an on-line roughness monitor on the CdTe growth.

  19. Identification of critical stacking faults in thin-film CdTe solar cells

    SciTech Connect

    Yoo, Su-Hyun; Walsh, Aron; Butler, Keith T.; Soon, Aloysius; Abbas, Ali; Walls, John M.

    2014-08-11

    Cadmium telluride (CdTe) is a p-type semiconductor used in thin-film solar cells. To achieve high light-to-electricity conversion, annealing in the presence of CdCl{sub 2} is essential, but the underlying mechanism is still under debate. Recent evidence suggests that a reduction in the high density of stacking faults in the CdTe grains is a key process that occurs during the chemical treatment. A range of stacking faults, including intrinsic, extrinsic, and twin boundary, are computationally investigated to identify the extended defects that limit performance. The low-energy faults are found to be electrically benign, while a number of higher energy faults, consistent with atomic-resolution micrographs, are predicted to be hole traps with fluctuations in the local electrostatic potential. It is expected that stacking faults will also be important for other thin-film photovoltaic technologies.

  20. Cr impurity-induced electronic states in ZnTe(110) surface

    NASA Astrophysics Data System (ADS)

    Kanazawa, Ken; Nishimura, Taku; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

    2015-08-01

    The impurity states of Cr atoms, which substituted Zn sites in the topmost layer of a p-type ZnTe(110) surface, were investigated by scanning tunneling microscopy/spectroscopy (STM/STS) and we firstly observed Cr-induced impurity states in the energy gap region of the host ZnTe including the unoccupied states by STS. Furthermore, we compared the observed energy levels and spatial distributions of the local density of states with those in the previous theoretical study [Katayama-Yoshida et al., Phys. Status Solidi A 204, 15 (2007)] and successfully identified the impurity states as the respective spin-polarized impurity states predicted by the theoretical study.

  1. Thermoelectric Enhancement in PbTe with K or Na codoping from tuning the interaction of the light- and heavy-hole valence bands

    SciTech Connect

    Androulakis, John; Todorov, Iliya; Chung, Duck Young; Ballikaya, Sedat; Wang, Guoyu Y; Uher, Ctirad; Kanatzidis, Mercouri G.

    2010-09-16

    The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p -type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1–15x1019 cm-3 .

  2. Thermoelectric enhancement in PbTe with K or Na codoping from tuning the interaction of the light- and heavy-hole valence bands.

    SciTech Connect

    Androulakis, J.; Todorov, I.; Chung, D.-Y.; Ballikaya, S.; Wang, G.; Uher, C.; Kanatzidis, M.; Materials Science Division; Northwestern Univ.; Univ. of Michigan at Ann Arbor; Univ. of Istanbul

    2010-09-15

    The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1-15 x 10{sup 19} cm{sup -3}.

  3. Direct observations of Ge{sub 2}Sb{sub 2}Te{sub 5} recording marks in the phase-change disk

    SciTech Connect

    Naito, Muneyuki; Ishimaru, Manabu; Hirotsu, Yoshihiko; Kojima, Rie; Yamada, Noboru

    2010-05-15

    Atomistic structures of the Ge{sub 2}Sb{sub 2}Te{sub 5} thin film in the real phase-change disk have been investigated using transmission electron microscopy (TEM). As-deposited amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} films were laser-irradiated for initialization (crystallization) and recording. Cross-sectional TEM observations revealed that the recording mark was fully amorphized by laser irradiation. A slight difference between the as-deposited and the laser irradiation-induced amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} was observed in the intensity profile of nanobeam electron diffraction patterns and atomic pair distribution functions. This difference was attributed to structural relaxation of amorphous Ge{sub 2}Sb{sub 2}Te{sub 5}, which gives rise to the alteration of chemical order.

  4. Atomic Oxygen Task

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.

    1997-01-01

    This report details work performed by the Center for Applied Optics (CAO) at the University of Alabama in Huntsville (UAH) on the contract entitled 'Atomic Oxygen Task' for NASA's Marshall Space Flight Center (contract NAS8-38609, Delivery Order 109, modification number 1). Atomic oxygen effects on exposed materials remain a critical concern in designing spacecraft to withstand exposure in the Low Earth Orbit (LEO) environment. The basic objective of atomic oxygen research in NASA's Materials & Processes (M&P) Laboratory is to provide the solutions to material problems facing present and future space missions. The objective of this work was to provide the necessary research for the design of specialized experimental test configurations and development of techniques for evaluating in-situ space environmental effects, including the effects of atomic oxygen and electromagnetic radiation on candidate materials. Specific tasks were performed to address materials issues concerning accelerated environmental testing as well as specifically addressing materials issues of particular concern for LDEF analysis and Space Station materials selection.

  5. INL Laboratory Scale Atomizer

    SciTech Connect

    C.R. Clark; G.C. Knighton; R.S. Fielding; N.P. Hallinan

    2010-01-01

    A laboratory scale atomizer has been built at the Idaho National Laboratory. This has proven useful for laboratory scale tests and has been used to fabricate fuel used in the RERTR miniplate experiments. This instrument evolved over time with various improvements being made ‘on the fly’ in a trial and error process.

  6. Chiral atomically thin films

    NASA Astrophysics Data System (ADS)

    Kim, Cheol-Joo; Sánchez-Castillo, A.; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm–1) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

  7. Bonds Between Atoms.

    ERIC Educational Resources Information Center

    Holden, Alan

    The field of inquiry into how atoms are bonded together to form molecules and solids crosses the borderlines between physics and chemistry encompassing methods characteristic of both sciences. At one extreme, the inquiry is pursued with care and rigor into the simplest cases; at the other extreme, suggestions derived from the more careful inquiry…

  8. Light antiprotonic atoms

    SciTech Connect

    Gotta, Detlev

    2005-10-19

    The present knowledge on strong-interaction effects in light antiprotonic atoms is reviewed. Data were obtained during the LEAR era, where the high flux made possible the use of high-resolution devices like semiconductor detectors and a crystal spectrometer. Open questions and possible extensions at the future antiproton facilities are discussed.

  9. Energy from the Atom.

    ERIC Educational Resources Information Center

    Smith, Patricia L.

    This curriculum guide was written to supplement fifth and sixth grade science units on matter and energy. It was designed to provide more in-depth material on the atom. The first part, "Teacher Guide," contains background information, biographical sketches of persons in the history of nuclear energy, vocabulary, answer sheets, management sheets…

  10. Rutherford-Bohr atom

    NASA Astrophysics Data System (ADS)

    Heilbron, J. L.

    1981-03-01

    Bohr used to introduce his attempts to explain clearly the principles of the quantum theory of the atom with an historical sketch, beginning invariably with the nuclear model proposed by Rutherford. That was sound pedagogy but bad history. The Rutherford-Bohr atom stands in the middle of a line of work initiated by J.J. Thomson and concluded by the invention of quantum mechanics. Thompson's program derived its inspiration from the peculiar emphasis on models characteristic of British physics of the 19th century. Rutherford's atom was a late product of the goals and conceptions of Victorian science. Bohr's modifications, although ultimately fatal to Thomson's program, initially gave further impetus to it. In the early 1920s the most promising approach to an adequate theory of the atom appeared to be the literal and detailed elaboration of the classical mechanics of multiply periodic orbits. The approach succeeded, demonstrating in an unexpected way the force of an argument often advanced by Thomson: because a mechanical model is richer in implications than the considerations for which it was advanced, it can suggest new directions of research that may lead to important discoveries.

  11. Atoms in Astronomy.

    ERIC Educational Resources Information Center

    Blanchard, Paul A.

    This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. A Basic Topics section discusses atomic structure, emphasizing states of matter at high temperature and spectroscopic analysis of light from the stars. A section…

  12. Atomism, Pragmatism, Holism.

    ERIC Educational Resources Information Center

    Miller, John P.

    1986-01-01

    Examines three world views influencing curriculum development--atomism (underpinning competency-based education), pragmatism (promoting inquiry-based approaches), amd holism (associated with confluent or Waldorf education). Holism embodies the perennial philosophy and attempts to integrate cognitive, affective, and transpersonal dimensions,…

  13. Chiral atomically thin films

    NASA Astrophysics Data System (ADS)

    Kim, Cheol-Joo; Sánchez-Castillo, A.; Ziegler, Zack; Ogawa, Yui; Noguez, Cecilia; Park, Jiwoong

    2016-06-01

    Chiral materials possess left- and right-handed counterparts linked by mirror symmetry. These materials are useful for advanced applications in polarization optics, stereochemistry and spintronics. In particular, the realization of spatially uniform chiral films with atomic-scale control of their handedness could provide a powerful means for developing nanodevices with novel chiral properties. However, previous approaches based on natural or grown films, or arrays of fabricated building blocks, could not offer a direct means to program intrinsic chiral properties of the film on the atomic scale. Here, we report a chiral stacking approach, where two-dimensional materials are positioned layer-by-layer with precise control of the interlayer rotation (θ) and polarity, resulting in tunable chiral properties of the final stack. Using this method, we produce left- and right-handed bilayer graphene, that is, a two-atom-thick chiral film. The film displays one of the highest intrinsic ellipticity values (6.5 deg μm-1) ever reported, and a remarkably strong circular dichroism (CD) with the peak energy and sign tuned by θ and polarity. We show that these chiral properties originate from the large in-plane magnetic moment associated with the interlayer optical transition. Furthermore, we show that we can program the chiral properties of atomically thin films layer-by-layer by producing three-layer graphene films with structurally controlled CD spectra.

  14. Conformal atoms in Supergravity

    NASA Astrophysics Data System (ADS)

    Jankowski, Jakub

    2016-01-01

    In this note, we summarize recent attempts to construct holographic models of atoms and lattices in the context of applications to solid state physics. The simplest setup turned out to impose strong constraints on the choice of matter interactions of dual gravitational theory.

  15. Atomic collisions, inelastic indeed

    NASA Astrophysics Data System (ADS)

    Bercegol, Herve; Ferrando, Gwenael; Lehoucq, Roland

    At the turn of the twentieth century, a hot controversy raged about the ability of Boltzmann's framework to take care of irreversibility. The so-called Loschmidt's paradox progressively faded with time during the last hundred years, due to the predictive efficiency of statistical mechanics. However, one detail at the origin of the controversy - the elasticity of atomic collisions - was not completely challenged. A semi-classical treatment of two atoms interacting with the vacuum zero-point field permits to predict a friction force acting against the rotation of the pair of atoms. By its form and its level, the calculated torque is a candidate as a physical cause for diffusion of energy and angular momentum, and consequently for entropy growth. It opens the way to a revision of the standard vision of irreversibility. This presentation will focus on two points. First we will discuss the recent result in a broader context of electromagnetic interactions during microscopic collisions. The predicted friction phenomenon can be compared to and distinguished from Collision-Induced Emission and other types of inelastic collisions. Second we will investigate the consequences of the friction torque on calculated trajectories of colliding atoms, quantifying the generation of dimers linked by dispersion forces.

  16. Global anisotropies in TeV cosmic rays related to the Sun's local galactic environment from IBEX.

    PubMed

    Schwadron, N A; Adams, F C; Christian, E R; Desiati, P; Frisch, P; Funsten, H O; Jokipii, J R; McComas, D J; Moebius, E; Zank, G P

    2014-02-28

    Observations with the Interstellar Boundary Explorer (IBEX) have shown enhanced energetic neutral atom (ENA) emission from a narrow, circular ribbon likely centered on the direction of the local interstellar medium (LISM) magnetic field. Here, we show that recent determinations of the local interstellar velocity, based on interstellar atom measurements with IBEX, are consistent with the interstellar modulation of high-energy (tera-electron volts, TeV) cosmic rays and diffusive propagation from supernova sources revealed in global anisotropy maps of ground-based high-energy cosmic-ray observatories (Milagro, Asγ, and IceCube). Establishing a consistent local interstellar magnetic field direction using IBEX ENAs at hundreds to thousands of eV and galactic cosmic rays at tens of TeV has wide-ranging implications for the structure of our heliosphere and its interactions with the LISM, which is particularly important at the time when the Voyager spacecraft are leaving our heliosphere.

  17. Global Anisotropies in TeV Cosmic Rays Related to the Sun's Local Galactic Environment from IBEX

    NASA Technical Reports Server (NTRS)

    Schwadron, N. A.; Adams, F. C.; Christian, E. R.; Desiati, P.; Frisch, P.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G. P.

    2014-01-01

    Observations with the Interstellar Boundary Explorer (IBEX) have shown enhanced energetic neutral atom (ENA) emission from a narrow, circular ribbon likely centered on the direction of the local interstellar medium (LISM) magnetic field. Here, we show that recent determinations of the local interstellar velocity, based on interstellar atom measurements with IBEX, are consistent with the interstellar modulation of high-energy (tera-electron volts, TeV) cosmic rays and diffusive propagation from supernova sources revealed in global anisotropy maps of ground-based high-energy cosmic-ray observatories (Milagro, Asg, and IceCube). Establishing a consistent local interstellar magnetic field direction using IBEX ENAs at hundreds to thousands of eV and galactic cosmic rays at tens of TeV has wide-ranging implications for the structure of our heliosphere and its interactions with the LISM, which is particularly important at the time when the Voyager spacecraft are leaving our heliosphere.

  18. HgCdTe barrier infrared detectors

    NASA Astrophysics Data System (ADS)

    Kopytko, M.; Rogalski, A.

    2016-05-01

    In the last decade, new strategies to achieve high-operating temperature (HOT) detectors have been proposed, including barrier structures such as nBn devices, unipolar barrier photodiodes, and multistage (cascade) infrared detectors. The ability to tune the positions of the conduction and valence band edges independently in a broken-gap type-II superlattices is especially helpful in the design of unipolar barriers. This idea has been also implemented in HgCdTe ternary material system. However, the implementation of this detector structure in HgCdTe material system is not straightforward due to the existence of a valence band discontinuity (barrier) at the absorber-barrier interface. In this paper we present status of HgCdTe barrier detectors with emphasis on technological progress in fabrication of MOCVD-grown HgCdTe barrier detectors achieved recently at the Institute of Applied Physics, Military University of Technology. Their performance is comparable with state-of-the-art of HgCdTe photodiodes. From the perspective of device fabrication their important technological advantage results from less stringent surface passivation requirements and tolerance to threading dislocations.

  19. MBE HgCdTe heterostructure detectors

    NASA Technical Reports Server (NTRS)

    Schulman, Joel N.; Wu, Owen K.

    1990-01-01

    HgCdTe has been the mainstay for medium (3 to 5 micron) and long (10 to 14 micron) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using molecular beam epitaxy (MBE) provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition, and thus band gap, at will. The heterostructure junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/liquid phase epitaxy (LPE)/bulk structures are given. Quantum structures include the HgTe-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

  20. Ba2Cu2Te2P2O13: A new telluro-phosphate with S=1/2 Heisenberg chain

    NASA Astrophysics Data System (ADS)

    Xia, Mingjun; Shen, Shipeng; Lu, Jun; Sun, Young; Li, R. K.

    2015-10-01

    A new telluro-phosphate compound Ba2Cu2Te2P2O13 with S=1/2 Heisenberg chain has been successfully synthesized by solid state reaction and grown by flux method. Single crystal X-ray diffraction reveals that Ba2Cu2Te2P2O13 crystallizes into a monoclinic space group C2/c and cell parameters of a=17.647(3) Å, b=7.255(2) Å, c=9.191(2) Å and β=100.16 (3)°. In the structure of Ba2Cu2Te2P2O13, one dimensional [CuTePO7]3- chains are formed by tetrahedral PO4 and trigonal bi-pyramidal TeO4 joining square planar CuO4 groups. Those [CuTePO7]3- chains are inter-connected by sharing one oxygen atom from the TeO4 group to form two dimensional layers. Magnetic susceptibility and specific heat measurements confirm that the title compound is a model one dimensional Heisenberg antiferromagnetic chain system.

  1. Differential Thermal Analysis of Hg(1-x)Mn(x)Te Alloys in the X=0 to 0.3 Range

    NASA Technical Reports Server (NTRS)

    Price, M. W.; Scripa, R. N.; Szofran, F. R.; Lehoczky, S. L.; Su, C-H

    1998-01-01

    Understanding the experimental conditions necessary for the development of radial and axial compositional homogeneity in directionally solidified Hg(0.89)Mn(0.11)Te(MMT) crystals has been difficult due to the lack of segregation coefficient data on the Hg(1-x)Mn(x)Te alloy system in the X = 0 to 0.3 composition range. Determining segregation coefficient data from the available Hg(1-x)Mn(x)Te alloy phase equilibria data is not practical due to discrepancies in the shape of the reported solidus and liquidus curves in the X = 0 to 0.3 range. To resolve these discrepancies and to obtain segregation coefficient data which can be used to understand homogeneity in directionally solidified MMT crystals, the solidus and liquidus temperatures of seven Hg(1-x)Mn(x)Te alloys in the X = 0 to 0.3 range were determined using differential thermal analysis (DTA). The Hg(1-x)Mn(x)Te phase diagram constructed for the X = 0 to 0.3 range of this alloy system from the DTA measurements clarifies the shape of the solidus and liquidus curves in this range. The segregation coefficient for the Hg(1-x)Mn(x)Te system was found to vary from 5 to 4.4 as the solidus composition increased from 0-30 atomic percent MnTe. This information will be useful in the analysis of axial and radial homogeneity of directionally solidified MMT crystals.

  2. Correlation between the electronic structures and diffusion paths of interstitial defects in semiconductors: The case in CdTe

    SciTech Connect

    Ma, Jie; Yang, Jihui; Da Silva, J. L.F.; Wei, Su-Huai

    2014-10-30

    Using first-principles calculations, we study the diffusions of interstitial defects Cd, Cu, Te, and Cl in CdTe. We find that the diffusion behavior is strongly correlated with the electronic structure of the interstitial diffuser. For Cd and Cu, because the defect state is the non-degenerated slike state under Td symmetry, the diffusions are almost along the [111] directions between the tetrahedral sites, although the diffusion of Cu shows some deviation due to the s - d coupling. The diffusions of the neutral and charged Cd and Cu follow similar paths. However, for Te and Cl atoms, because the defect state is the degenerated p-like state under Td symmetry, large distortions occur. Therefore, the diffusion paths are very different from those of Cd and Cu interstitials, and depend strongly on the charge states of the interstitial atoms. For Te, we find that the distortion is mostly stabilized by the crystal-field splitting, but for Cl, the exchange splitting plays a more important role.

  3. Electronic and transport properties of the Mn-doped topological insulator Bi2Te3 : A first-principles study

    NASA Astrophysics Data System (ADS)

    Carva, K.; Kudrnovský, J.; Máca, F.; Drchal, V.; Turek, I.; Baláž, P.; Tkáč, V.; Holý, V.; Sechovský, V.; Honolka, J.

    2016-06-01

    We present a first-principles study of the electronic, magnetic, and transport properties of the topological insulator Bi2Te3 doped with Mn atoms in substitutional (MnBi) and interstitial van der Waals gap positions (Mni), which act as acceptors and donors, respectively. The effect of native BiTe- and TeBi-antisite defects and their influence on calculated electronic transport properties is also investigated. We have studied four models representing typical cases, namely, (i) Bi2Te3 with and without native defects, (ii) MnBi defects with and without native defects, (iii) the same, but for Mni defects, and (iv) the combined presence of MnBi and Mni. It has been found that lattice relaxations around MnBi defects play an important role for both magnetic and transport properties. The resistivity is strongly influenced by the amount of carriers, their type, and by the relative positions of the Mn-impurity energy levels and the Fermi energy. Our results suggest strategies to tune bulk resistivities and also clarify the location of Mn atoms in samples. Calculations indicate that at least two of the considered defects have to be present simultaneously in order to explain the experimental observations, and the role of interstitials may be more important than expected.

  4. Correlation between the electronic structures and diffusion paths of interstitial defects in semiconductors: The case in CdTe

    DOE PAGESBeta

    Ma, Jie; Yang, Jihui; Da Silva, J. L.F.; Wei, Su-Huai

    2014-10-30

    Using first-principles calculations, we study the diffusions of interstitial defects Cd, Cu, Te, and Cl in CdTe. We find that the diffusion behavior is strongly correlated with the electronic structure of the interstitial diffuser. For Cd and Cu, because the defect state is the non-degenerated slike state under Td symmetry, the diffusions are almost along the [111] directions between the tetrahedral sites, although the diffusion of Cu shows some deviation due to the s - d coupling. The diffusions of the neutral and charged Cd and Cu follow similar paths. However, for Te and Cl atoms, because the defect statemore » is the degenerated p-like state under Td symmetry, large distortions occur. Therefore, the diffusion paths are very different from those of Cd and Cu interstitials, and depend strongly on the charge states of the interstitial atoms. For Te, we find that the distortion is mostly stabilized by the crystal-field splitting, but for Cl, the exchange splitting plays a more important role.« less

  5. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    SciTech Connect

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-28

    Amorphous Ge{sub x}Si{sub x}Te{sub 1−2x} glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions x{sub c1}=7.5% and atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from  {sup 119}Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge{sub 20}Te{sub 80}, Si{sub 20}Te{sub 80}, and Ge{sub 10}Si{sub 10}Te{sub 80}). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp{sup 3} geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  6. Impurity Gettering Effect of Te Inclusions in Cdznte Single Crystals

    SciTech Connect

    Yang, G.; Bolotnikov, A; Cui, Y; Camarda, G; Hossain, A; James, R

    2009-01-01

    The local impurity distribution in Te inclusions of CdZnTe (CZT) crystal was investigated by the time-of-flight secondary ion mass spectrometry (Tof-SIMS) technique. Direct evidence of impurity gettering in Te inclusions has been observed for the first time. The impurity gettering in Te inclusions originated from the diffusion mechanism during crystal growth and segregation mechanism during crystal cooling. This phenomenon is meaningful, because it reveals how Te inclusions affect CZT properties and provides a possible approach to reduce the impurities in CZT by the way of removing Te inclusions.

  7. Adsorption of Te on Ge(001): Density-functional calculations

    NASA Astrophysics Data System (ADS)

    Çakmak, M.; Srivastava, G. P.; Ellialtıoğlu, Ş.

    2003-05-01

    We present ab initio density-functional calculations for the adsorption of Te on the Ge(001) surface. Various possible adsorption geometries for the 0.5-, 0.8-, 1-, and 2-ML (monolayer) coverages of Te have been investigated. Our results for sub-monolayer coverages confirm earlier results as well as provide some new insight into the adsorption of Te. Furthermore, our results for the 2-ML coverage of Te suggest that the bonding between the overlayer and the substrate has changed significantly. This may provide useful information on possible desorption of Te in the form of strongly bonded Te2 units.

  8. HPAM: Hirshfeld Partitioned Atomic Multipoles.

    PubMed

    Elking, Dennis M; Perera, Lalith; Pedersen, Lee G

    2012-02-01

    An implementation of the Hirshfeld (HD) and Hirshfeld-Iterated (HD-I) atomic charge density partitioning schemes is described. Atomic charges and atomic multipoles are calculated from the HD and HD-I atomic charge densities for arbitrary atomic multipole rank l(max) on molecules of arbitrary shape and size. The HD and HD-I atomic charges/multipoles are tested by comparing molecular multipole moments and the electrostatic potential (ESP) surrounding a molecule with their reference ab initio values. In general, the HD-I atomic charges/multipoles are found to better reproduce ab initio electrostatic properties over HD atomic charges/multipoles. A systematic increase in precision for reproducing ab initio electrostatic properties is demonstrated by increasing the atomic multipole rank from l(max) = 0 (atomic charges) to l(max) = 4 (atomic hexadecapoles). Both HD and HD-I atomic multipoles up to rank l(max) are shown to exactly reproduce ab initio molecular multipole moments of rank L for L ≤ l(max). In addition, molecular dipole moments calculated by HD, HD-I, and ChelpG atomic charges only (l(max) = 0) are compared with reference ab initio values. Significant errors in reproducing ab initio molecular dipole moments are found if only HD or HD-I atomic charges used.

  9. Band structure and Optical properties CdTe and CdSn3Te4 thin films

    NASA Astrophysics Data System (ADS)

    Venkatachalam, T.; Velumani, S.; Ganesan, S.; Sakthivel, K.

    2008-04-01

    CdTe and CdSn3Te4 compounds were prepared by direct reaction of their high purity elemental constituents using rotating furnace. Optimal deposition conditions for the deposition of CdTe and CdSn3Te4 thin films in hot wall evaporation setup were simulated using Monte Carlo technique. Thin films of CdTe and CdSn3Te4 were deposited on glass substrates by hot wall evaporation method. From the XRD measurements it was found that the films of CdTe and CdSn3Te4 were of cubic zinc-blende and rock salt structures respectively. The lattice parameters were determined as a = 6.476 Å (CdTe) and a = 6.238 Å (CdSn3Te4) from the XRD data. The UV-Vis-NIR optical transmittance spectra of thin films of different films were obtained and it was found that the direct optical band gaps were 1.4 eV (CdTe) and 0.8 eV (CdSn3Te4). Electronic structure, band parameters and optical spectra of CdTe and CdSn3Te4 were calculated from ab initio studies within the GGA approximation. The experimental results were in good agreement with the theoretical values.

  10. Comparison of crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te nanocrystalline thin films: Effects of homogeneous irradiation with an electron beam

    SciTech Connect

    Takashiri, Masayuki Imai, Kazuo; Uyama, Masato; Nishi, Yoshitake; Hagino, Harutoshi; Miyazaki, Koji; Tanaka, Saburo

    2014-06-07

    The effects of homogenous electron beam (EB) irradiation on the crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te thin films were investigated. Both types of thin films were prepared by flash evaporation, after which homogeneous EB irradiation was performed at an acceleration voltage of 0.17 MeV. For the n-type thin films, nanodots with a diameter of less than 10 nm were observed on the surface of rice-like nanostructures, and crystallization and crystal orientation were improved by EB irradiation. The resulting enhancement of mobility led to increased electrical conductivity and thermoelectric power factor for the n-type thin films. In contrast, the crystallization and crystal orientation of the p-type thin films were not influenced by EB irradiation. The carrier concentration increased and mobility decreased with increased EB irradiation dose, possibly because of the generation of defects. As a result, the thermoelectric power factor of p-type thin films was not improved by EB irradiation. The different crystallization behavior of the n-type and p-type thin films is attributed to atomic rearrangement during EB irradiation. Selenium in the n-type thin films is more likely to undergo atomic rearrangement than the other atoms present, so only the crystallinity of the n-type Bi-Se-Te thin films was enhanced.

  11. Morphology control of nanostructures: Na-doped PbTe-PbS system.

    PubMed

    He, Jiaqing; Blum, I D; Wang, Hui-Qiong; Girard, S N; Doak, J; Zhao, Li-Dong; Zheng, Jin-Cheng; Casillas, G; Wolverton, C; Jose-Yacaman, M; Seidman, D N; Kanatzidis, M G; Dravid, V P

    2012-11-14

    The morphology of crystalline precipitates in a solid-state matrix is governed by complex but tractable energetic considerations driven largely by volume strain energy minimization and anisotropy of interfacial energies. Spherical precipitate morphologies are favored by isotropic systems, while anisotropic interfacial energies give energetic preference to certain crystallographically oriented interfaces, resulting in a faceted precipitate morphology. In conventional solid-solution precipitation, a precipitate's morphological evolution is mediated by surface anchoring of capping molecules, which dramatically alter the surface energy in an anisotropic manner, thereby providing exquisite morphology control during crystal growth. Herein, we present experimental evidence and theoretical validation for the role of a ternary element (Na) in controlling the morphology of nanoscale PbS crystals nucleating in a PbTe matrix, an important bulk thermoelectric system. The PbS nanostructures formed by phase separation from a PbI(2)-doped or undoped PbTe matrix have irregular morphologies. However, replacing the iodine dopant with Na (1-2 mol %) alters dramatically the morphology of the PbS precipitates. Segregation of Na at PbTe/PbS interfaces result in cuboidal and truncated cuboidal morphologies for PbS. Using analytical scanning/transmission electron microscopy and atom-probe tomography, we demonstrate unambiguously that Na partitions to the precipitates and segregates at the matrix/precipitate interfaces, inducing morphological anisotropy of PbS precipitates. First-principles and semiclassical calculations reveal that Na as a solute in PbTe has a higher energy than in PbS and that Na segregation at a (100) PbTe/PbS interface decreases the total energy of matrix/precipitate system, resulting in faceting of PbS precipitates. These results provide an impetus for a new strategy for controlling morphological evolution in matrix/precipitate systems, mediated by solute partitioning

  12. Anisotropies in TeV Cosmic Rays Related to the IBEX Ribbon

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Adams, F. C.; Christian, E.; Desiati, P.; Frisch, P.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G.

    2014-08-01

    The Interstellar Boundary Explorer (IBEX) observes enhanced Energetic Neutral Atoms (ENAs) emission in the keV energy range from a narrow (~20° wide) "ribbon" in the sky that appears to be centered on the direction of the local interstellar (LIS) magnetic field. The Milagro collaboration, the Asγ collaboration and the IceCube observatory have recently made global maps of cosmic ray fluxes in the TeV energy range, revealing anisotropic structures ordered in part by the local interstellar magnetic field and the interstellar flow. This paper following from a recent publication in Science makes the link between these disparate observations by developing a simple model of the magnetic structure surrounding the heliosphere in the Local Interstellar Medium (LISM) that is consistent with both IBEX ENA fluxes and TeV cosmic ray anisotropies. The model also employs the revised velocity direction of the LIC derived from neutral He observations by IBEX. By modeling the propagation of cosmic rays through this magnetic field structure, we specifically show that (1) the large-scale TeV anisotropy provides a roughly consistent orientation for the local interstellar magnetic field at the center of the IBEX Ribbon and corroborates the ~ 3 μG magnitude of the local interstellar magnetic field derived from IBEX observations of the global heliosphere; (2) and small-scale structures in cosmic rays (over < 30° angular scales) are influenced by the interstellar field interaction with the heliosphere at energies < 10 TeV. Thus, we provide a link between IBEX ENA observations, IBEX neutral observations of interstellar He, and TeV cosmic ray anisotropies, which are strongly influenced by the interactions between the local interstellar magnetic field, the flow of the local interstellar plasma, and the global heliosphere.

  13. Atom inlays performed at room temperature using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sugimoto, Yoshiaki; Abe, Masayuki; Hirayama, Shinji; Oyabu, Noriaki; Custance, Óscar; Morita, Seizo

    2005-02-01

    The ability to manipulate single atoms and molecules laterally for creating artificial structures on surfaces is driving us closer to the ultimate limit of two-dimensional nanoengineering. However, experiments involving this level of manipulation have been performed only at cryogenic temperatures. Scanning tunnelling microscopy has proved, so far, to be a unique tool with all the necessary capabilities for laterally pushing, pulling or sliding single atoms and molecules, and arranging them on a surface at will. Here we demonstrate, for the first time, that it is possible to perform well-controlled lateral manipulations of single atoms using near-contact atomic force microscopy even at room temperature. We report the creation of 'atom inlays', that is, artificial atomic patterns formed from a few embedded atoms in the plane of a surface. At room temperature, such atomic structures remain stable on the surface for relatively long periods of time.

  14. Biosynthetic incorporation of telluromethionine into dihydrofolate reductase and crystallographic analysis of the distribution of tellurium atoms in the protein molecule

    SciTech Connect

    Kunkle, M.G.; Lewinski, K.; Boles, J.O.; Dunlap, R.B.; Odom, J.D.; Lebioda, L.

    1994-12-01

    Recent successes in crystallographic studies of proteins with methionine (Met) residues replaced with SeMet, pioneered by Hendrickson and coworkers, inspired us to replace Met with TeMet in Escherichia coli dihydrofolate reductase (DHFR). E. coli DHFR, which catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate, consists of 159 residues, 5 of which are Met. TeMet was incorporated into DHFR using the Met auxotroph, E. coli DL41, carrying the expression vector pWT8 with an IPTG inducible promoter and ampicillin resistance gene. The enzyme was purified by successive chromatography on Q-Sepharose and PHenyl Sepharose resins, yielding milligram quantities of homogeneous enzyme with a specific activity of 40 units/mg. TeMet DHFR exhibits kinetic properties similar to those of wt DHFR. Amino acid analysis indicated 3 authentic Met residues in TeMet DHFR, whereas atomic absorption spectroscopy detected 2 Te per protein molecule. Amino acid sequence analysis results suggested that only authentic Met was present in the first three Met positions (1,16,and 20). Crystals of Te-DHFR were grown in the presence of methotrexate from PEG 4000 and were isomorphous with wt-DHFR crystals grown from ethanol. Difference Fourier maps and restrained least-squares refinement show very little, if any, Te in the first three Met positions: Met{sup 1}, Met{sup 16}, and Met{sup 20}, whereas the occupancy of Te in positions 42 and 92 is 0.64. Apparently, the process of folding, subsequent purification, and crystallization select DHFR molecules with Te in Met{sup 42} and Met{sup 92}. Replacing Met with TeMet provides an internal probe that should facilitate structural and mechanistic studies of proteins.

  15. Enhanced electrical properties at boundaries including twin boundaries of polycrystalline CdTe thin-film solar cells.

    PubMed

    Li, H; Liu, X X; Lin, Y S; Yang, B; Du, Z M

    2015-05-01

    The effect of grain boundaries (GBs), in particular twin boundaries (TBs), on CdTe polycrystalline thin films is studied by conductive atomic force microscopy (C-AFM), electron-beam-induced current (EBIC), scanning Kelvin probe microscopy (SKPM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). Four types of CdTe grains with various densities of {111} Σ3 twin boundaries (TBs) are found in Cl-treated CdTe polycrystalline thin films: (1) grains having multiple {111} Σ3 TBs with a low angle to the film surface; (2) grains having multiple {111} Σ3 TBs parallel to the film surfaces; (3) small grains on a scale of not more than 500 nm, composed of Cd, Cl, Te, and O; and (4) CdTe grains with not more than two {111} Σ3 TBs. Grain boundaries (including TBs) exhibit enhanced current transport phenomena. However, the {111} Σ3 TB is much more beneficial to micro-current transport. The enhanced current transport can be explained by the lower electron potential at GBs (including TBs) than the grain interiors (GIs). Our results open new opportunities for enhancing solar cell performances by controlling the grain boundaries, and in particular TBs.

  16. Hydrogen effect on electronic and magnetic properties of Cd1-xMnxTe: Ab initio study

    NASA Astrophysics Data System (ADS)

    Larabi, A.; Merad, G.; Abdelaoui, I.; Sari, A.

    2016-07-01

    Hydrogen effect on electronic and magnetic properties of diluted magnetic semiconductor (DMS) Cd1-xMnxTe for x composition of 0.125 has been investigated using the projected augmented wave (PAW) based on density functional theory (DFT) formalism within the generalized gradient approximation (GGA). The results show that the Mn dopant is spin-polarized with magnetic moment of 4.189 μB per Mn atom at x≈0.125. The calculated formation energies indicate that the hydrogen is not stable in CdTe and the lowest energy position for H is at the Cd-Mn bond center in Cd0.875Mn0.125Te. We find also that the existence of interstitial hydrogen decreases the magnetic moment of Cd0.875Mn0.125Te diluted magnetic semiconductor. From the calculated density of state, we observed that the presence of hydrogen does not cause a change in electronic properties of Cd0.875Mn0.125Te.

  17. High thermal stability Sb{sub 3}Te-TiN{sub 2} material for phase change memory application

    SciTech Connect

    Ji, Xinglong; Zhou, Wangyang; Wu, Liangcai Zhu, Min; Rao, Feng; Song, Zhitang; Cao, Liangliang; Feng, Songlin

    2015-01-12

    For phase change memory (PCM) applications, it has been widely accepted that δ phase Sb-Te has fast operation speed and good phase stability. However, the fast growth crystallization mechanism will cause poor amorphous phase stability and overlarge grain size. We introduce TiN{sub 2} into δ phase Sb-Te (Sb{sub 3}Te) to enhance the amorphous thermal stability and refine the grain size. With TiN{sub 2} incorporating, the temperature for 10-year data retention increases from 79 °C to 124 °C. And the grain size decreases to dozens of nanometers scale. Based on X-ray photoelectron spectroscopy and transmission electron microscopy results, we knew that nitrogen atoms bond with titanium, forming disorder region at the grain boundary of Sb{sub 3}Te-TiN{sub 2} (STTN). Thus, STTN has a quite different crystallization mechanism from Sb{sub 3}Te. Furthermore, PCM device based on STTN can realize reversible phase change under 20 ns electrical pulse.

  18. Cu-doped CdS and its application in CdTe thin film solar cell

    NASA Astrophysics Data System (ADS)

    Deng, Yi; Yang, Jun; Yang, Ruilong; Shen, Kai; Wang, Dezhao; Wang, Deliang

    2016-01-01

    Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the VCd- and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl2 annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.

  19. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    SciTech Connect

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show that the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.

  20. PythonTeX: reproducible documents with LaTeX, Python, and more

    NASA Astrophysics Data System (ADS)

    Poore, Geoffrey M.

    2015-01-01

    PythonTeX is a LaTeX package that allows Python code in LaTeX documents to be executed and provides access to the output. This makes possible reproducible documents that combine results with the code required to generate them. Calculations and figures may be next to the code that created them. Since code is adjacent to its output in the document, editing may be more efficient. Since code output may be accessed programmatically in the document, copy-and-paste errors are avoided and output is always guaranteed to be in sync with the code that generated it. This paper provides an introduction to PythonTeX and an overview of major features, including performance optimizations, debugging tools, and dependency tracking. Several complete examples are presented. Finally, advanced features are summarized. Though PythonTeX was designed for Python, it may be extended to support additional languages; support for the Ruby and Julia languages is already included. PythonTeX contains a utility for converting documents into plain LaTeX, suitable for format conversion, sharing, and journal submission.