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Sample records for 119m te atoms

  1. Isomeric Yields Ratios in 120Te(γ,n)119m,gTe Reaction in the E1-GIANT Resonance Region

    NASA Astrophysics Data System (ADS)

    Mazur, V. M.; Symochko, D. M.; Bigan, Z. M.; Poltorzhytska, T. V.

    Isomeric state excitation in the 120Te(γ,n)119m,gTe reaction within the 10-20 MeV energy range has been studied with bremsstrahlung beams. Energy dependences of experimental isomeric yields ratios and reaction cross-sections have been obtained. Experimental results are compared with TALYS-1.2 calculations.

  2. 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.

  3. Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

    DOE PAGES

    Li, C. W.; Ma, J.; Cao, H. B.; ...

    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

  4. 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.

  5. 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.

  6. 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.

  7. Growth and atomic structure of tellurium thin films grown on Bi2Te3

    NASA Astrophysics Data System (ADS)

    Okuyama, Yuma; Sugiyama, Yuya; Ideta, Shin-ichiro; Tanaka, Kiyohisa; Hirahara, Toru

    2017-03-01

    We have grown tellurium (Te) thin films on Bi2Te3 and investigated the atomic structure. From low-energy electron diffraction (LEED) measurements, we found that the Te films are [10 1 bar0]-oriented with six domains. A detailed analysis of the reflection high-energy electron diffraction (RHEED) pattern revealed that the films are strained with the in-plane lattice constant compressed by ∼1.5% compared to the bulk value due to the epitaxy between Te and Bi2Te3. These films will be interesting systems to investigate the predicted topological phases that occur in strained Te.

  8. Avalanche atomic switching in strain engineered Sb2Te3–GeTe interfacial phase-change memory cells

    NASA Astrophysics Data System (ADS)

    Zhou, Xilin; Behera, Jitendra K.; Lv, Shilong; Wu, Liangcai; Song, Zhitang; Simpson, Robert E.

    2017-09-01

    By confining phase transitions to the nanoscale interface between two different crystals, interfacial phase change memory heterostructures represent the state of the art for energy efficient data storage. We present the effect of strain engineering on the electrical switching performance of the {{Sb}}2{{Te}}3–GeTe superlattice van der Waals devices. Multiple Ge atoms switching through a two-dimensional Te layer reduces the activation barrier for further atoms to switch; an effect that can be enhanced by biaxial strain. The out-of-plane phonon mode of the GeTe crystal remains active in the superlattice heterostructures. The large in-plane biaxial strain imposed by the {{Sb}}2{{Te}}3 layers on the GeTe layers substantially improves the switching speed, reset energy, and cyclability of the superlattice memory devices. Moreover, carefully controlling residual stress in the layers of {{Sb}}2{{Te}}3–GeTe interfacial phase change memories provides a new degree of freedom to design the properties of functional superlattice structures for memory and photonics applications.

  9. Fluorescence XAFS Study on Local Structure around Cr Atoms Doped in ZnTe

    SciTech Connect

    Ofuchi, Hironori; Ozaki, Nobuhiko; Kinjyo, Hidekazu; Kuroda, Shinji; Takita, Koki; Nishizawa, Nozomi

    2007-02-02

    The geometric structures for ferromagnetic Zn1-xCrxTe films grown by molecular beam epitaxy were investigated by fluorescence XAFS measurements in order to elucidate the relationship between the geometric structure and the magnetic properties. XAFS analysis suggested that the majority of Cr atoms doped in CrTe substituted the Zn-site in the ZnTe lattice below the Cr content x = 0.048, and formed Cr-Te compounds such as Cr2Te3 and CrTe above x = 0.090. It is suggested that ferromagnetism of the Zn1-xCrxTe films above x = 0.090 is due to the formation of Cr-Te compounds.

  10. Pair potential modeling of atomic rearrangement in GeTe-Sb2Te3 superlattice via first-principles calculations

    NASA Astrophysics Data System (ADS)

    Song, Young-Sun; Kim, Jeongwoo; Jhi, Seung-Hoon

    2017-03-01

    We study the nature of atomic rearrangement during the phase-change processes in the superlattice of GeTe and Sb2Te3 by developing a new approach combining the first-principles calculations and a pair-potential model. We investigate the phase-change process in terms of energy changes from individual pairs or atoms by applying the pair (atom)-projection analysis to the intermediate structures between the initial and final states obtained from the climbing-image nudged elastic band method. Among the prototypical steps that can lead to the atomic layer rearrangement, we find that the required energy for the phase change is dominated by specific atoms responsible for the intrinsic energy barrier and the response to external pressure. Our approach of combining the first-principles methods and pair potential model with the projecting analysis can be a very efficient method in revealing the detailed atomic motions and the mechanism of fast atomic transition of the phase-change materials.

  11. Formation of the bismuth-bilayer film at BiTeCl surface by atomic hydrogen deposition

    NASA Astrophysics Data System (ADS)

    Shvets, I. A.; Eremeev, S. V.; Chulkov, E. V.

    2017-07-01

    On the base of density functional theory calculations we investigate the atomic hydrogen adsorption on Cl- and Te-terminations of giant Rashba-split semiconductor BiTeCl and show that it leads to removal of the halogen and chalcogen top layer atoms by means of desorption of HCl and H2Te molecules. This mechanism accompanied by swapping of next Bi and deeper Te(Cl) layers with subsequent hydrogen-induced removal of Te(Cl) layer results in formation of Bi2 layer covering BiTeCl. The electronic structure of the formed Bi2@BiTeCl[Cl-term] and Bi2@BiTeCl[Te-term] interfaces shows a strong hybridization between Bi2-derived spin-split bands and BiTeCl interface states.

  12. 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.

  13. 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

  14. Determination of Te in soldering tin using continuous flowing electrochemical hydride generation atomic fluorescence spectrometry

    NASA Astrophysics Data System (ADS)

    Jiang, Xianjuan; Gan, Wuer; Han, Suping; He, Youzhao

    2008-06-01

    An electrochemical hydride generation system was developed for the detection of Te by coupling an electrochemical hydride generator with atomic fluorescence spectrometry. Since TeH 2 is unstable and easily decomposes in solution, a reticular W filament cathode was used in the present system. The TeH 2 generated on the cathode surface was effectively driven out by sweeping gas from the cathode chamber. In addition, a low temperature electrochemical cell (10 °C) was applied to reduce the decomposition of TeH 2 in solution. The limit of detection (LOD) was 2.2 ng ml - 1 and the relative standard deviation (RSD) was 3.9% for nine consecutive measurements of standard solution. This method was successfully employed for determination of Te in soldering tin material.

  15. Effects of heat treatment on diffusion of Cu atoms into CdTe single crystals

    SciTech Connect

    Soo, Y. L.; Huang, S.; Kim, S.; Kioseoglou, G.; Kao, Y. H.; Compaan, A. D.; Grecu, D.; Albin, D.

    2000-06-19

    Angular dependence of x-ray fluorescence and x-ray absorption fine structure techniques have been used to study the diffusion of Cu atoms into the photovoltaic material CdTe. Depth profile, effective valency, and local structure of Cu atoms in a Cu-doped single crystal of CdTe were investigated before and after a second heat treatment. Enhanced Cu diffusion into the CdTe single crystal was observed as a result of heating at a moderate temperature around 200 degree sign C, resulting in a redistribution of the Cu impurities through a broader depth profile. Some of the Cu atoms are believed either to form small complexes with Te or occupy interstitial sites in the host but accompanied by a large local lattice distortion while others substitute for Cd on the cation sites. The results thus demonstrate that these nondestructive x-ray characterization methods are useful for probing microstructural changes in CdTe photovoltaic materials/devices in which some Cu-containing compounds are used as back contacts. (c) 2000 American Institute of Physics.

  16. 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.

  17. 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.

  18. Aggregation of BiTe monolayer on Bi2Te3 (111) induced by diffusion of intercalated atoms in the van der Waals gap

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Wen; Huang, Wen-Kai; Zhang, Kai-Wen; Shu, Da-Jun; Wang, Mu; Li, Shao-Chun

    2017-03-01

    We report a postgrowth aging mechanism of Bi2Te3 (111) films with scanning tunneling microscopy in combination with density functional theory calculation. It is found that a monolayered structure with a squared lattice symmetry gradually aggregates from the surface steps. Theoretical calculations indicate that the van der Waals (vdW) gap not only acts as a natural reservoir for self-intercalated Bi and Te atoms, but also provides them easy diffusion pathways. Once hopping out of the gap, these defective atoms prefer to develop into a two-dimensional BiTe superstructure on the Bi2Te3 (111) surface driven by positive energy gain. Considering the common nature of weak bonding between vdW layers, we expect such unusual diffusion and aggregation of the intercalated atoms may be of general importance for most kinds of vdW layered materials.

  19. 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.

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

    SciTech Connect

    Horning, R.D.; Staudenmann, J.

    1987-05-25

    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 /sup 0/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/sub perpendicular/>a/sub parallel/ 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.

  2. Clustering of zirconium atoms in Zr5Te6: a novel NiAs-type-related telluride with ordered vacancies.

    PubMed

    Orlygsson, G; Harbrecht, B

    2000-11-17

    Zr5Te6 has been synthesized and its structure determined by means of single crystal X-ray diffraction to be trigonal, P3m1, Z=3, Pearson symbol hP33, a = 1172.8(2) pm, c = 707.0(1) pm. Zr5Te6 adopts a metal-deficient, vacancy-ordered 3a x 3a x 1c superstructure of the NiAs type structure. In the Zr atom layers, alternately one and two out of nine Zr atoms are missing. The less densely populated layers (7/9) consist of star-shaped Zr7 clusters with intracluster contacts of 351.1 pm; the shortest Zr-Zr intercluster distance is 470.5 pm. In the more densely populated Zr atom layers (8/9), three quarters of the Zr atoms are arranged to pairs (326.4 pm). The distinctive distribution of the vacancies affords a topologically uniform fivefold Zr coordination (283.5 - 302.6 pm) for all three crystallographically inequivalent Te atoms. They are shifted towards the vacancies in the Zr atom layers. The associated corrugation of the Te atom layers is characterized by an amplitude of 28 pm. The Te-Te contacts are > or =368.1 pm. According to extended Hückel calculations, the defects in the Zr atom layers lead to a reduction in overall Zr-Te bonding interactions relative to ZrTe (NiAs). However, through the clustering the total attractive intralayer Zr-Zr interactions increase considerably, thus providing decisive stabilization of the structure. As revealed by thermal analyses, Zr5Te6 undergoes a reversible phase transition at 1,513 +/- 5 K. On the Zr-rich side, Zr5Te6 coexists with ZrTe (WC), and, above 1,438 +/- 5 K with the hitherto unknown ZrTe (MnP). Zr5Te6 exhibits temperature independent paramagnetic properties (chimol = 0.7 x 10(-3) cm3 mol(-1)) that are typical for a metallic conductor. An abrupt increase in the magnitude of the diamagnetic susceptibility below 2.2 K in a weak magnetic field indicates a superconducting transition.

  3. Thin films of topological crystalline insulator SnTe in contact with heterogeneous atomic layers

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Hsuan; Yang, Chih-Kai

    2016-12-01

    Tin telluride is a topological crystalline insulator that has gapless surface states protected by mirror symmetry. The symmetry remains intact when the insulator is reduced in thickness and becomes a thin film, according to ab initio calculations based on density functional theory. Furthermore, a SnTe thin film in contact with a heterogeneous atomic layer is capable of closing energy gap caused by quantum tunneling between the two thin film surfaces and therefore distinguishes two conducting channels through surface and interface states respectively. Our calculations of SnTe films deposited with a lead telluride layer have two Dirac cones separated in energy, while the same film in contact with strontium telluride have the cones separated in momentum. The composite with a magnetic manganese telluride layer, however, loses both the mirror and time-reversal symmetry.

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

    SciTech Connect

    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. 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.

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

    DOE PAGES

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; ...

    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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  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. Topological phase transition induced by atomic displacements in PbS and PbTe

    NASA Astrophysics Data System (ADS)

    Kim, Jinwoong; Jhi, Seung-Hoon

    2013-03-01

    Discovery of 3D topological insulator initiates exploration of finding new materials having topological insulating phase or mechanisms for topological phase transitions. Introducing interactions or strains into non-interacting electron systems, for example, can produce non-trivial topological phases in them otherwise having trivial band insulating phase at equilibrium conditions. Using first-principles methods, we study emerging topological phases in band insulating PbS and PbTe, which are induced by selective atomic displacements. Phonon modes corresponding to the displacements are identified and conditions of inducing the topological phase transition are suggested. We show that surface states develop flickering Dirac cones at band-inversion k-points upon dynamic atomic displacements with sufficient amplitude. Our results demonstrate that elementary excitation modes like phonon can induce topological phases in trivial band insulators.

  12. 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.

  13. Phase change properties of Ti-Sb-Te thin films deposited by thermal atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Song, Sannian; Shen, Lanlan; Song, Zhitang; Yao, Dongning; Guo, Tianqi; Li, Le; Liu, Bo; Wu, Liangcai; Cheng, Yan; Ding, Yuqiang; Feng, Songlin

    2016-10-01

    Phase change random access memory (PCM) appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density PCM depends heavily on the thin film growth technique for the phase changing chalcogenide material. In this study, TiSb2Te4 (TST) thin films were deposited by thermal atomic layer deposition (ALD) method using TiCl4, SbCl3, (Et3Si)2Te as precursors. The threshold voltage for the cell based on thermal ALD-deposited TST is about 2.0 V, which is much lower than that (3.5 V) of the device based on PVD-deposited Ge2Sb2Te5 (GST) with the identical cell architecture. Tests of TST-based PCM cells have demonstrated a fast switching rate of 100 ns. Furthermore, because of the lower melting point and thermal conductivities of TST materials, TST-based PCM cells exhibit 19% reduction of pulse voltages for Reset operation compared with GST-based PCM cells. These results show that thermal ALD is an attractive method for the preparation of phase change materials.

  14. 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.

  15. 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).

  16. Interface morphology studies of liquid phase epitaxy grown HgCdTe films by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-04-01

    In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. The precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.

  17. 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

    2006-12-05

    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.

  18. 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.

  19. Conductive Atomic Free Microscopy of CdTe/CdS Solar Cells

    SciTech Connect

    Moutinho, H. R.; Dhere, R. G.; Jiang, C. S.; Al-Jassim, M. M.; Kazmerski, L. L.

    2005-01-01

    Conductive atomic force microscopy (C-AFM) is a recently developed technique that applies an electric voltage between a very sharp tip and the sample, permitting the study of the electrical properties of the sample with very high spatial resolution. It also provides current-voltage measurements at well-defined spots. C-AFM is applied simultaneously with atomic force microscopy, providing topographic and current images of the same region. In this work, we analyze CdTe/CdS samples, before and after CdCl2 treatment, and after bromine/methanol and nitric/phosphoric etches. The as-deposited samples show grains with different contrasts, indicating that the material is not electrically uniform. The CdCl2 treatment resulted in less conductive grain boundaries, suggesting a relative decrease in the conductivity at these locations. After the bromine/methanol etch, the conductivity at grains boundaries was higher than inside the grains, whereas for the nitric/phosphoric etch the conductivity increased over the entire surface.

  20. 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.

  1. Modifications of the electronic structure of GaSb surface by chalcogen atoms: S, Se, and Te

    NASA Astrophysics Data System (ADS)

    Liu, Z. Y.; Gokhale, A. A.; Mavrikakis, M.; Saulys, D. A.; Kuech, T. F.

    2004-10-01

    Modifications to the electronic properties and chemical structures of the GaSb surface using the chalcogen atoms S, Se, and Te were investigated theoretically and experimentally. A self-consistent density-functional theory study indicates that an adsorption of a full monolayer coverage of chalcogen atoms on a Ga-terminated surface reduces the density of gap region states significantly. A greater photoluminescence enhancement was observed from GaSb samples treated by chalcogenide (Na2S, Na2Se, or Na2Te) in a nonaqueous than in an aqueous passivation medium. X-ray photoelectron spectroscopy reveals a Ga-rich surface after a nonaqueous passivation, with sulfidization providing a higher concentration of Ga(Sb)-chalcogen bonds than does a passivation with Na2Se or Na2Te. The uptake of chalcogen during the passivation is accompanied by the loss of surface antimony. The formation of Sb-X(X =S, Se, or Te) bonds competes with X displacing surface Sb, which dominates Se or Te incorporation in the GaSb surface lattice. The passivation kinetics was analyzed on basis of a single precursor-mediated coverage-dependent chemisorption proces.

  2. Atomic and electronic structure of CdTe/metal (Cu, Al, Pt) interfaces and their influence to the Schottky barrier

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj; Miao, Mao-sheng; Aqariden, F.; Grein, Christoph; Kioussis, Nicholas

    2016-11-01

    Schottky barrier heights (SBHs) and other features of the interfaces are determining factors for the performance of the CdTe based high-energy photon detectors. Although known for long time that SBH is sensitive to surface treatment and metal contact growth method, there is a lack of understanding of the effect of the atomic and electronic structures of CdTe/metal interface on the SBH. Employing first-principles electronic structure calculations, we have systematically studied the structural stability and electronic properties of a number of representing structures of Cd Terminated CdTe/metal (Cu, Pt, and Al) interfaces. Comparison of the total energies of the various optimized structural configurations allows to identify the existence of Te-metal alloy formation at the interface. The SBHs of Cu, Pt, and Al metal contacts with a number of stable interface structures are determined by aligning the band edges of bulk CdTe with the Fermi level of the metal/CdTe system. We find that the metal-induced states in the gap play an essential role in determining the SBH.

  3. Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Luria, Justin; Kutes, Yasemin; Moore, Andrew; Zhang, Lihua; Stach, Eric A.; Huey, Bryan D.

    2016-11-01

    The influence of microstructural defects on the device properties in CdTe remains largely unknown. This is partly because characterization techniques have been unable to image electrical pathways throughout three-dimensional grains and grain boundaries with nanoscale resolution. Here, we employ a conductive and tomographic variation of atomic force microscopy to study charge transport at the nanoscale in a functioning thin-film solar cell with 12.3% efficiency. Images of electric current collected through the device thickness reveal spatially dependent short-circuit and open-circuit performance, and confirm that grain boundaries are preferential pathways for electron transport. Results on samples with and without cadmium chloride treatment reveal little difference in grain structure at the microscale, with samples without treatment showing almost no photocurrent either at planar defects or at grain boundaries. Our results supports an energetically orthogonal transport system of grain boundaries and interconnected planar defects as contributing to optimal solar cell performance, contrary to the conventional wisdom of the deleterious role of planar defects on polycrystalline thin-film solar cells.

  4. Tip-force induced surface deformation in the layered commensurate tellurides NbA xTe 2 (A = Si, Ge) during atomic force microscopy measurements

    NASA Astrophysics Data System (ADS)

    Bengel, H.; Cantow, H.-J.; Magonov, S. N.; Monconduit, L.; Evain, M.; Whangbo, M.-H.

    1994-12-01

    The Te-atom surfaces of commensurate layered tellurides NbA xTe 2 ( A = Si, x = {1}/{2}; A = Ge, x = {1}/{3}, {2}/{5}, {3}/{7}) were examined by atomic force microscopy (AFM) at different applied forces. Although the bulk crystal structures show a negligible height corrugation in the surface Te-atom sheets, the AFM images exhibit dark linear patterns that become strongly pronounced at high applied forces (several hundreds nN). This feature comes about because the tip-sample force interactions induce a surface corrugation according to the local hardness variation of the surface.

  5. Phase-change properties of GeSbTe thin films deposited by plasma-enchanced atomic layer depositon.

    PubMed

    Song, Sannian; Yao, Dongning; Song, Zhitang; Gao, Lina; Zhang, Zhonghua; Li, Le; Shen, Lanlan; Wu, Liangcai; Liu, Bo; Cheng, Yan; Feng, Songlin

    2015-01-01

    Phase-change access memory (PCM) appears to be the strongest candidate for next-generation high-density nonvolatile memory. The fabrication of ultrahigh-density PCM depends heavily on the thin-film growth technique for the phase-changing chalcogenide material. In this study, Ge2Sb2Te5 (GST) and GeSb8Te thin films were deposited by plasma-enhanced atomic layer deposition (ALD) method using Ge [(CH3)2 N]4, Sb [(CH3)2 N]3, Te(C4H9)2 as precursors and plasma-activated H2 gas as reducing agent of the metallorganic precursors. Compared with GST-based device, GeSb8Te-based device exhibits a faster switching speed and reduced reset voltage, which is attributed to the growth-dominated crystallization mechanism of the Sb-rich GeSb8Te films. These results show that ALD is an attractive method for preparation of phase-change materials.

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

    DOE PAGES

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; ...

    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

  7. 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.

  8. 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.

  9. 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.

  10. Variable-Temperature Tin-119m Moessbauer Study of the Chlorodimethyltin (IV) Derivatives of L-Cysteine and DL-Penicillamine.

    DTIC Science & Technology

    1981-06-15

    TECHNICAL REPORT No. 31 ("!. Variable-Temperature Tin-119m M0ssbauer Study of the Chlorodimethyltin(IV) Derivatives of L-Cysteine and DL- Penicillamine K...and DL- Penicillamine -6. PERFORMING ORG. REPO’T NUMBER 7. AUTHOR(,) ... /- . CONTRACT OR GRANT NU AUER(,) K olloy an4_J.J./Zuckerman I N,,0 / .4-77-C...Cysteine, Penicillamine , M?5ssbauer spectroscopy, Hydrogen bonding, Variable-Temperature Mbssbauer, Tin 20. ABSTRACT (Continue an reverse side If neceeesty

  11. Electron-phonon coupling and surface Debye temperature of Bi2Te3 (111) from helium atom scattering

    NASA Astrophysics Data System (ADS)

    Tamtögl, Anton; Kraus, Patrick; Avidor, Nadav; Bremholm, Martin; Hedegaard, Ellen M. J.; Iversen, Bo B.; Bianchi, Marco; Hofmann, Philip; Ellis, John; Allison, William; Benedek, Giorgio; Ernst, Wolfgang E.

    2017-05-01

    We have studied the topological insulator Bi2Te3 (111) by means of helium atom scattering. The average electron-phonon coupling λ of Bi2Te3 (111) is determined by adapting a recently developed quantum-theoretical derivation of the helium scattering probabilities to the case of degenerate semiconductors. Based on the Debye-Waller attenuation of the elastic diffraction peaks of Bi2Te3 (111), measured at surface temperatures between 110 and 355 K , we find λ to be in the range of 0.04 -0.11 . This method allows us to extract a correctly averaged λ and to address the discrepancy between previous studies. The relatively modest value of λ is not surprising even though some individual phonons may provide a larger electron-phonon interaction. Furthermore, the surface Debye temperature of Bi2Te3 (111) is determined as ΘD=(81 ±6 ) K . The electronic surface corrugation was analyzed based on close-coupling calculations. By using a corrugated Morse potential a peak-to-peak corrugation of 9% of the lattice constant is obtained.

  12. Atomic Layering, Intermixing and Switching Mechanism in Ge-Sb-Te based Chalcogenide Superlattices

    NASA Astrophysics Data System (ADS)

    Yu, Xiaoming; Robertson, John

    2016-11-01

    GeSbTe-based chalcogenide superlattice (CSLs) phase-change memories consist of GeSbTe layer blocks separated by van der Waals bonding gaps. Recent high resolution electron microscopy found two types of disorder in CSLs, a chemical disorder within individual layers, and SbTe bilayer stacking faults connecting one block to an adjacent block which allows individual block heights to vary. The disorder requires a generalization of the previous switching models developed for CSL systems. Density functional calculations are used to describe the stability of various types of intra-layer disorder, how the block heights can vary by means of SbTe-based stacking faults and using a vacancy-mediated kink motion, and also to understand the nature of the switching process in more chemically disordered CSLs.

  13. Atomic Layering, Intermixing and Switching Mechanism in Ge-Sb-Te based Chalcogenide Superlattices

    PubMed Central

    Yu, Xiaoming; Robertson, John

    2016-01-01

    GeSbTe-based chalcogenide superlattice (CSLs) phase-change memories consist of GeSbTe layer blocks separated by van der Waals bonding gaps. Recent high resolution electron microscopy found two types of disorder in CSLs, a chemical disorder within individual layers, and SbTe bilayer stacking faults connecting one block to an adjacent block which allows individual block heights to vary. The disorder requires a generalization of the previous switching models developed for CSL systems. Density functional calculations are used to describe the stability of various types of intra-layer disorder, how the block heights can vary by means of SbTe-based stacking faults and using a vacancy-mediated kink motion, and also to understand the nature of the switching process in more chemically disordered CSLs. PMID:27853289

  14. Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Houston Dycus, J.; White, Ryan M.; Pierce, Jonathan M.; Venkatasubramanian, Rama; LeBeau, James M.

    2013-02-01

    Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga-Te that terminates GaAs dangling bonds.

  15. An observation of nanotwin lamellae in Cd 0.6Mn 0.4Te crystal by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Collins, W. E.; Burger, A.; Silberman, E.

    1993-05-01

    Atomic force microscopy (AFM) is used to examine the structure of freshly cleaved Cd 0.6Mn 0.4Te surfaces. The present report complements previous results obtained with X-ray diffraction and optical microscopy which showed the existence of microtwins. The AFM analysis was performed under ambient conditions and yielded nanometer scale resolution images of single twin lamellae that ranged between 20 and 100 nm in width. This is a first observation using AFM of such a substructure, which we interpret as evidence for the presence of nonotwins.

  16. Topological transport and atomic tunnelling-clustering dynamics for aged Cu-doped Bi2Te3 crystals

    NASA Astrophysics Data System (ADS)

    Chen, Taishi; Chen, Qian; Schouteden, Koen; Huang, Wenkai; Wang, Xuefeng; Li, Zhe; Miao, Feng; Wang, Xinran; Li, Zhaoguo; Zhao, Bo; Li, Shaochun; Song, Fengqi; Wang, Jinlan; Wang, Baigeng; Van Haesendonck, Chris; Wang, Guanghou

    2014-09-01

    Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.1Bi0.9)2Te3.06 crystals. Here we report the suppression of the bulk conductance of the material by four orders of magnitude by intense ageing. The weak antilocalization analysis, Shubnikov-de Haas oscillations and scanning tunnelling spectroscopy corroborate the transport of the topological surface states. Scanning tunnelling microscopy reveals that Cu atoms are initially inside the quintuple layers and migrate to the layer gaps to form Cu clusters during the ageing. In combination with first-principles calculations, an atomic tunnelling-clustering picture across a diffusion barrier of 0.57 eV is proposed.

  17. Topological transport and atomic tunnelling–clustering dynamics for aged Cu-doped Bi2Te3 crystals

    PubMed Central

    Chen, Taishi; Chen, Qian; Schouteden, Koen; Huang, Wenkai; Wang, Xuefeng; Li, Zhe; Miao, Feng; Wang, Xinran; Li, Zhaoguo; Zhao, Bo; Li, Shaochun; Song, Fengqi; Wang, Jinlan; Wang, Baigeng; Van Haesendonck, Chris; Wang, Guanghou

    2014-01-01

    Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.1Bi0.9)2Te3.06 crystals. Here we report the suppression of the bulk conductance of the material by four orders of magnitude by intense ageing. The weak antilocalization analysis, Shubnikov–de Haas oscillations and scanning tunnelling spectroscopy corroborate the transport of the topological surface states. Scanning tunnelling microscopy reveals that Cu atoms are initially inside the quintuple layers and migrate to the layer gaps to form Cu clusters during the ageing. In combination with first-principles calculations, an atomic tunnelling–clustering picture across a diffusion barrier of 0.57 eV is proposed. PMID:25247692

  18. Local atomic and electronic structures in ferromagnetic topological insulator Cr-doped (BixSb1-x) 2Te3 studied by XAFS and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Wei, Xinyuan; Wang, Jiajia; Pan, Hong; Ji, Fuhao; Ye, Mao; Yang, Zhongqin; Qiao, Shan

    2015-09-01

    The local atomic and electronic structures around the dopants in Cr-doped (BixSb1 -x )2Te3 are studied by x-ray absorption fine structure (XAFS) measurements and first-principles calculations. Both Cr and Bi are confirmed substituting Sb sites (CrSb and BiSb). The six nearest Te atoms around Cr move towards Cr and shorten the Cr-Te bond lengths to 2.76 Å and 2.77 Å for x =0.1 and x =0.2 , respectively. Importantly, we reveal the hybridization between the Sb/Te p states and Cr d states by the presence of a pre-edge peak at Cr K -absorption edge, which is also supported by our ab initio calculations. These findings provide important clues to understand the mechanism of ferromagnetic order in this system with quantum anomalous Hall effect.

  19. Thin Layer Electrochemical Studies of ZnS, ZnSe, and ZnTe Formation by Electrochemical Atomic Layer Epitaxy (ECALE)

    DTIC Science & Technology

    1997-10-16

    Thin-layer electrochemical studies of the underpotential deposition (UPD) of Zn, Te, Se, and S on polycrystalline Au substrates have been performed...was scanned. Sulfur atomic layers were spontaneously deposited below -0.6 V from a sulfide solution. Thermodynamic effects are clearly evident during...the first monolayer of deposition . Zinc deposition onto Te, Se, and S coated electrodes occurs at progressively more positive potentials as the

  20. 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.

  1. Post-patterning of an electronic homojunction in atomically thin monoclinic MoTe2

    NASA Astrophysics Data System (ADS)

    Kim, Sera; Kim, Jung Ho; Kim, Dohyun; Hwang, Geunwoo; Baik, Jaeyoon; Yang, Heejun; Cho, Suyeon

    2017-06-01

    Monoclinic group 6 transition metal dichalcogenides (TMDs) have been extensively studied for their intriguing 2D physics (e.g. spin Hall insulator) as well as for ohmic homojunction contacts in 2D device applications. A critical prerequisite for those applications is thickness control of the monoclinic 2D materials, which allows subtle engineering of the topological states or electronic bandgaps. Local thickness control enables the realization of clean homojunctions between different electronic states, and novel device operation in a single material. However, conventional fabrication processes, including chemical methods, typically produce non-homogeneous and relatively thick monoclinic TMDs, due to their distorted octahedral structures. Here, we report on a post-patterning technique using laser-irradiation to fabricate homojunctions between two different thickness areas in monoclinic MoTe2. A thickness-dependent electronic change from a metallic to semiconducting state, resulting in an electronic homojunction, was realized by the optical patterning of pristine MoTe2 flakes, and a pre-patterned device channel of monoclinic MoTe2 with a thickness-resolution of 5 nm. Our work provides insight on an optical post-process method for controlling thickness, as a promising approach for fabricating impurity-free 2D TMDs homojunction devices.

  2. Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

    DOE PAGES

    Luria, Justin; Kutes, Yasemin; Moore, Andrew; ...

    2016-09-26

    Polycrystalline photovoltaics comprising cadmium telluride (CdTe) represent a growing portion of the solar cell market, yet the physical picture of charge transport through the meso-scale grain morphology remains a topic of debate. It is unknown how thin film morphology affects the transport of electron-hole pairs. Accordingly this study is the first to generate three dimensional images of photocurrent throughout a thin-film solar cell, revealing the profound influence of grain boundaries and stacking faults on device efficiency.

  3. Single-Atom Scale Structural Selectivity in Te Nanowires Encapsulated Inside Ultranarrow, Single-Walled Carbon Nanotubes.

    PubMed

    Medeiros, Paulo V C; Marks, Samuel; Wynn, Jamie M; Vasylenko, Andrij; Ramasse, Quentin M; Quigley, David; Sloan, Jeremy; Morris, Andrew J

    2017-06-27

    Extreme nanowires (ENs) represent the ultimate class of crystals: They are the smallest possible periodic materials. With atom-wide motifs repeated in one dimension (1D), they offer a privileged perspective into the physics and chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs) provide ideal environments for the creation of such materials. Here we present a comprehensive study of Te ENs encapsulated inside ultranarrow SWCNTs with diameters between 0.7 nm and 1.1 nm. We combine state-of-the-art imaging techniques and 1D-adapted ab initio structure prediction to treat both confinement and periodicity effects. The studied Te ENs adopt a variety of structures, exhibiting a true 1D realization of a Peierls structural distortion and transition from metallic to insulating behavior as a function of encapsulating diameter. We analyze the mechanical stability of the encapsulated ENs and show that nanoconfinement is not only a useful means to produce ENs but also may actually be necessary, in some cases, to prevent them from disintegrating. The ability to control functional properties of these ENs with confinement has numerous applications in future device technologies, and we anticipate that our study will set the basic paradigm to be adopted in the characterization and understanding of such systems.

  4. Gene therapy approach to FAP: in vivo influence of T119M in TTR deposition in a transgenic V30M mouse model.

    PubMed

    Batista, A R; Gianni, D; Ventosa, M; Coelho, A V; Almeida, M R; Sena-Esteves, M; Saraiva, M J

    2014-12-01

    Familial amyloidotic polyneuropathy (FAP) is a neurodegenerative disorder characterized by extracellular deposition of amyloid fibrils composed by mutated transthyretin (TTR) mainly in the peripheral nervous system. At present, liver transplantation is still the standard treatment to halt the progression of clinical symptoms in FAP, but new therapeutic strategies are emerging, including the use of TTR stabilizers. Here we propose to establish a new gene therapy approach using adeno-associated virus (AAV) vectors to deliver the trans-suppressor TTR T119M variant to the liver of transgenic TTR V30M mice at different ages. This TTR variant is known for its ability to stabilize the tetrameric protein. Analysis of the gastrointestinal tract of AAV-treated animals revealed a significant reduction in deposition of TTR non-fibrillar aggregates in as much as 34% in stomach and 30% in colon, as well as decreased levels of biomarkers associated with TTR deposition, namely the endoplasmic reticulum stress marker BiP and the extracellular matrix protein MMP-9. Moreover, we showed with different studies that our approach leads to an increase in tetrameric and more stable forms of TTR, in favor of destabilized monomers. Altogether our data suggest the possibility to use this gene therapy approach in a prophylactic manner to prevent FAP pathology.

  5. 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.

  6. X-ray photoelectron spectroscopy and atomic force microscopy characterization of the effects of etching Zn xCd 1- xTe surfaces

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Burger, A.; Collins, W. E.; Silberman, E.

    1993-10-01

    X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was used for the first time to characterize the chemical composition of modified surfaces of Zn xCd 1- xTe single crystals. These surface treatments were selected for their relevance to device preparation procedures. The XPS peaks indicated an increase of the tellurium and a depletion of the cadmium concentrations upon etching in bromine methanol solution. AFM revealed the formation of pronounced Te inclusions. Higher x values correlated with a decrease in residual bromine left on the surface, while cut and polished samples had higher oxide concentrations and increased bromination of the surface than cleaved samples.

  7. Large-scale production of (GeTe)x (AgSbTe2)100$-$x (x=75, 80, 85, 90) with enhanced thermoelectric properties via gas-atomization and spark plasma sintering

    DOE PAGES

    Kim, Hyo-Seob; Ames Lab., Ames, IA; Dharmaiah, Peyala; ...

    2017-01-30

    (GeTe)x(AgSbTe2)100$-$x: TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. Here in the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe)x(AgSbTe2)100$-$x where x = 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. The nanoscale twins and antiphase boundaries servemore » as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was ~94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (KIC) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary.« less

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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.

  9. 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.

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

    SciTech Connect

    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, 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.

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

    SciTech Connect

    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, 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.

  12. 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.

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

    DOE PAGES

    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

  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

    2016-04-07

    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. Structural phase transitions of (Bi1$-$xSbx )2(Te1$-$y Se y)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

    DOE PAGES

    Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; ...

    2016-12-14

    Recently, A2B3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi2Te2Se, BiSbTeSe2, and Sb2Te2Se tetradymites under high pressure. Bi2Te2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi2Te3. Thus, the compression behavior of Bi2Te2Se is the same as that of Bi2Se3,more » which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe2 and Sb2Te2Se undergo similar structural phase transitions to Bi2Te2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A2B3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.« less

  16. Structural phase transitions of (Bi1−xSbx )2(Te1−y Se y)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

    DOE PAGES

    Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; ...

    2016-12-14

    Recently, A2B3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi2Te2Se, BiSbTeSe2, and Sb2Te2Se tetradymites under high pressure. Bi2Te2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi2Te3. Thus, the compression behavior of Bi2Te2Se is the same as that of Bi2Se3,more » which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe2 and Sb2Te2Se undergo similar structural phase transitions to Bi2Te2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A2B3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.« less

  17. Structural phase transitions of (Bi1-xSbx)2(Te1-ySey)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites.

    PubMed

    Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; Wang, Yong; Schneeloch, John; Li, Chunyu; Zhong, Ruidan; Wang, Yi; Liu, Zhiguo; Gu, Genda

    2017-01-18

    Recently, A2B3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi2Te2Se, BiSbTeSe2, and Sb2Te2Se tetradymites under high pressure. Bi2Te2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi2Te3. Thus, the compression behavior of Bi2Te2Se is the same as that of Bi2Se3, which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe2 and Sb2Te2Se undergo similar structural phase transitions to Bi2Te2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A2B3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. The influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.

  18. New barium copper chalcogenides synthesized using two different chalcogen atoms: Ba2Cu(6-x)STe4 and Ba2Cu(6-x)Se(y)Te(5-y).

    PubMed

    Mayasree, Oottil; Sankar, Cheriyedath Raj; Assoud, Abdeljalil; Kleinke, Holger

    2011-05-16

    Ba(2)Cu(6-x)STe(4) and Ba(2)Cu(6-x)Se(y)Te(5-y) were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) Å, b = 14.0533(9) Å, c = 4.3524(3) Å, and V = 590.61(7) Å(3) in the case of Ba(2)Cu(5.53(3))STe(4). A significant phase width was observed in the case of Ba(2)Cu(6-x)Se(y)Te(5-y) with at least 0.17(3) ≤ x ≤ 0.57(4) and 0.48(1) ≤ y ≤ 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba(2)Cu(6-x)STe(4), Cu-Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba(2)Cu(6-x)Se(y)Te(5-y), the bridging atom is either a Se atom or a Se/Te mixture when y ≤ 1, and the Te atoms of the Cu-Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba(2+), Cu(+), S(2-), Se(2-), and Te(2-). Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples.

  19. Two-dimensional Mineral [Pb2BiS3 ][AuTe2 ]: High mobility Charge Carriers in Single-atom-thick Layers

    NASA Astrophysics Data System (ADS)

    Fang, Lei; Im, J.; Stoumpos, C.; Shi, F.; Dravid, V.; Leroux, M.; Freeman, A.; Kwok, W.-K.,; Chung, D.-Y.; Kanatzidis, M.

    2015-03-01

    We report that [Pb2BiS3][AuTe2], known as a naturally occurring mineral buckhornite, hosts 2D carriers in single-atom-thick layers. The structure is composed of stacking layers of weakly coupled [Pb2BiS3] and [AuTe2] sheets. The insulating [Pb2BiS3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe2] layer. Magneto-transport measurements and theoretical calculations show a property of multiband semimetal with compensated density of electrons and holes, which exhibit high hole carrier mobility of 1360 cm2/Vs. This material possesses an extremely large anisotropy 104, comparable to benchmark materials graphite. The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 106 m/s which are virtually identical to that of graphene. The weak interlayer coupling gives rise to the highly cleavable property of single crystal specimens, indicating a prospect for monolayer system. This research was supported by the DoE, BES, under Contract No. DE-AC02-06CH11357, and NUANCE Center at the Northwestern Univeristy.

  20. Two-dimensional mineral [Pb2BiS3][AuTe2]: high-mobility charge carriers in single-atom-thick layers.

    PubMed

    Fang, Lei; Im, Jino; Stoumpos, Constantinos C; Shi, Fengyuan; Dravid, Vinayak; Leroux, Maxime; Freeman, Arthur J; Kwok, Wai-Kwong; Chung, Duck Young; Kanatzidis, Mercouri

    2015-02-18

    Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb2BiS3][AuTe2], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atom-thick layers. The structure is composed of stacking layers of weakly coupled [Pb2BiS3] and [AuTe2] sheets. The insulating [Pb2BiS3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe2] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb2BiS3][AuTe2] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of ∼1360 cm(2)/(V s). This material possesses an extremely large anisotropy, Γ = ρ(c)/ρ(ab) ≈ 10(4), comparable to those of the benchmark 2D materials graphite and Bi2Sr2CaCu2O(6+δ). The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 10(6) m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties.

  1. How grain boundaries affect the efficiency of poly-CdTe solar-cells: A fundamental atomic-scale study of grain boundary dislocation cores using CdTe bi-crystal thin films.

    SciTech Connect

    Klie, Robert

    2016-10-25

    It is now widely accepted that grain boundaries in poly-crystalline CdTe thin film devices have a detrimental effect on the minority carrier lifetimes, the open circuit voltage and therefore the overall solar-cell performance. The goal of this project was to develop a fundamental understanding of the role of grain boundaries in CdTe on the carrier life-time, open-circuit voltage, Voc, and the diffusion of impurities. To achieve this goal, i) CdTe bi-crystals were fabricated with various misorientation angels, ii) the atomic- and electronic structures of the grain boundaries were characterized using scanning transmission electron microscopy (STEM), and iii) first-principles density functional theory modeling was performed on the structures determined by STEM to predict the grain boundary potential. The transport properties and minority carrier lifetimes of the bi-crystal grain boundaries were measured using a variety of approaches, including TRPL, and provided feedback to the characterization and modeling effort about the effectiveness of the proposed models.

  2. Atomic Migration Induced Crystal Structure Transformation and Core-Centered Phase Transition in Single Crystal Ge2Sb2Te5 Nanowires.

    PubMed

    Lee, Jun-Young; Kim, Jeong-Hyeon; Jeon, Deok-Jin; Han, Jaehyun; Yeo, Jong-Souk

    2016-10-12

    A phase change nanowire holds a promise for nonvolatile memory applications, but its transition mechanism has remained unclear due to the analytical difficulties at atomic resolution. Here we obtain a deeper understanding on the phase transition of a single crystalline Ge2Sb2Te5 nanowire (GST NW) using atomic scale imaging, diffraction, and chemical analysis. Our cross-sectional analysis has shown that the as-grown hexagonal close-packed structure of the single crystal GST NW transforms to a metastable face-centered cubic structure due to the atomic migration to the pre-existing vacancy layers in the hcp structure going through iterative electrical switching. We call this crystal structure transformation "metastabilization", which is also confirmed by the increase of set-resistance during the switching operation. For the set to reset transition between crystalline and amorphous phases, high-resolution imaging indicates that the longitudinal center of the nanowire mainly undergoes phase transition. According to the atomic scale analysis of the GST NW after repeated electrical switching, partial crystallites are distributed around the core-centered amorphous region of the nanowire where atomic migration is mainly induced, thus potentially leading to low power electrical switching. These results provide a novel understanding of phase change nanowires, and can be applied to enhance the design of nanowire phase change memory devices for improved electrical performance.

  3. ZnS thin films grown by atomic layer deposition on GaAs and HgCdTe substrates at very low temperature

    NASA Astrophysics Data System (ADS)

    Sun, C. H.; Zhang, P.; Zhang, T. N.; Chen, X.; Chen, Y. Y.; Ye, Z. H.

    2017-09-01

    ZnS films grown on GaAs and HgCdTe substrates by atomic layer deposition (ALD) under very low temperature were investigated in this work. ZnS films were grown under several temperatures lower than 140 °C. The properties of the films were investigated with high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed the ZnS films were polycrystalline. The growth rate monotonically decreased with temperature, as well as the root mean square (r.m.s) roughness measured by AFM. XPS measurement revealed the films were stoichiometric in Zn and S.

  4. Understanding individual defects in CdTe thin-film solar cells via STEM: From atomic structure to electrical activity

    DOE PAGES

    Li, Chen; Poplawsky, Jonathan; Yan, Yanfa; ...

    2017-07-01

    Here in this paper we review a systematic study of the structure-property correlations of a series of defects in CdTe solar cells. A variety of experimental methods, including aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy, and electron-beam-induced current have been combined with density-functional theory. The research traces the connections between the structures and electrical activities of individual defects including intra-grain partial dislocations, grain boundaries and the CdTe/CdS interface. The interpretations of the physical origin underlying the structure-property correlation provide insights that should further the development of future CdTe solar cells.

  5. 125Te NMR chemical-shift trends in PbTe-GeTe and PbTe-SnTe alloys.

    PubMed

    Njegic, B; Levin, E M; Schmidt-Rohr, K

    2013-01-01

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in (125)Te NMR chemical shift due to bonding to dopant or "solute" atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the (125)Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS (125)Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the (125)Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  6. Use of Atomic Hydrogen to Prepare GaSb Substrates for Subsequent ZnTe Growth by MBE

    DTIC Science & Technology

    2014-03-11

    electron microscopy as well as x-ray photoelectron spectroscopy , x-ray diffraction, atomic force 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE...cross-section transmission electron microscopy as well as x-ray photoelectron spectroscopy , x-ray diffraction, atomic force microscopy and imaging...electron microscopy as well as x- ray photoelectron spectroscopy , x-ray diffraction, atomic force microscopy and imaging photoluminescence measurements

  7. Creation and Analysis of Atomic Structures for CdTe Bi-crystal Interfaces by the Grain Boundary Genie

    SciTech Connect

    Buurma, Christopher; Sen, Fatih G.; Paulauskas, Tadas; Sun, Ce; Kim, Moon; Sivananthan, Sivalingam; Klie, Robert F; Chan, Maria K. Y.

    2015-01-01

    Grain boundaries (GB) in poly-CdTe solar cells play an important role in species diffusion, segregation, defect formation, and carrier recombination. While the creation of specific high-symmetry interfaces can be straight forward, the creation of general GB structures in many material systems is difficult if periodic boundary conditions are to be enforced. Here we describe a novel algorithm and implementation to generate initial general GB structures for CdTe in an automated way, and we investigate some of these structures using density functional theory (DFT). Example structures include those with bi-crystals already fabricated for comparison, and those planning to be investigated in the future.

  8. Element-resolved atomic structure imaging of rocksalt Ge{sub 2}Sb{sub 2}Te{sub 5} phase-change material

    SciTech Connect

    Zhang, Bin; Chen, Yongjin; Han, Xiaodong E-mail: ema@jhu.edu; Zhang, Wei E-mail: ema@jhu.edu; Shen, Zhenju; Li, Jixue; Zhang, Shengbai; Zhang, Ze; Wuttig, Matthias; Mazzarello, Riccardo; and others

    2016-05-09

    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 Ge{sub 2}Sb{sub 2}Te{sub 5}. 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.

  9. Studies on Microstructure and Thermoelectric Properties of p-Type Bi-Sb-Te Based Alloys by Gas Atomization and Hot Extrusion Processes

    NASA Astrophysics Data System (ADS)

    Park, Ki-Chan; Madavali, Babu; Kim, Eun-Bin; Koo, Kyung-Wan; Hong, Soon-Jik

    2016-10-01

    p-Type Bi2Te3 + 75% Sb2Te3 based thermoelectric materials were fabricated via gas atomization and the hot extrusion process. The gas atomized powder showed a clean surface with a spherical shape, and expanded in a wide particle size distribution (average particle size 50 μm). The phase of the fabricated extruded and R-extruded bars was identified using x-ray diffraction. The relative densities of both the extruded and R-extruded samples were measured by Archimedes principle with ˜98% relative density. The R-extruded bar exhibited finer grain microstructure than that of single extrusion process, which was attributed to a recrystallization mechanism during the fabrication. The R-extruded sample showed improved Vickers hardness compared to the extruded sample due to its fine grain microstructure. The electrical conductivity improved for the extruded sample whereas the Seebeck coefficient decreases due to its high carrier concentration. The peak power factor, ˜4.26 × 10-3 w/mK2 was obtained for the single extrusion sample, which is higher than the R-extrusion sample owing to its high electrical properties.

  10. Studies on Microstructure and Thermoelectric Properties of p-Type Bi-Sb-Te Based Alloys by Gas Atomization and Hot Extrusion Processes

    NASA Astrophysics Data System (ADS)

    Park, Ki-Chan; Madavali, Babu; Kim, Eun-Bin; Koo, Kyung-Wan; Hong, Soon-Jik

    2017-05-01

    p-Type Bi2Te3 + 75% Sb2Te3 based thermoelectric materials were fabricated via gas atomization and the hot extrusion process. The gas atomized powder showed a clean surface with a spherical shape, and expanded in a wide particle size distribution (average particle size 50 μm). The phase of the fabricated extruded and R-extruded bars was identified using x-ray diffraction. The relative densities of both the extruded and R-extruded samples were measured by Archimedes principle with ˜98% relative density. The R-extruded bar exhibited finer grain microstructure than that of single extrusion process, which was attributed to a recrystallization mechanism during the fabrication. The R-extruded sample showed improved Vickers hardness compared to the extruded sample due to its fine grain microstructure. The electrical conductivity improved for the extruded sample whereas the Seebeck coefficient decreases due to its high carrier concentration. The peak power factor, ˜4.26 × 10-3 w/mK2 was obtained for the single extrusion sample, which is higher than the R-extrusion sample owing to its high electrical properties.

  11. 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.

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

    SciTech Connect

    Massee, F.; Sprau, P. O.; Wang, Y. -L.; Davis, J. C. S.; Ghigo, G.; Gu, G. D.; Kwok, W. -K.

    2015-05-01

    Maximizing the sustainable supercurrent density, JC, is crucial to high-current applications of superconductivity, and to achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with highenergy 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 JC 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 FeSexTe1$-$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 but suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how amixed pinning landscape is created, with the strongest pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

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

    PubMed Central

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

    2015-01-01

    Maximizing the sustainable supercurrent density, JC, 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 JC 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 FeSexTe1−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

  14. On the role of Pb0 atoms on the nucleation and growth of PbSe and PbTe nanoparticles

    NASA Astrophysics Data System (ADS)

    Garcia-Gutierrez, Domingo I.; De Leon-Covian, Lina M.; Garcia-Gutierrez, Diana F.; Treviño-Gonzalez, M.; Garza-Navarro, M. A.; Sepulveda-Guzman, S.

    2013-05-01

    In this contribution, a nucleation and growth mechanism of PbSe and PbTe nanoparticles are proposed. The formation and growth of PbSe and PbTe nanoparticles during their reaction synthesis were studied and followed using transmission electron microscopy, and their related techniques. In the synthesis method, trioctylphosphine-selenide and telluride were used as the chalcogen precursors, while lead oleate was employed as the lead precursor. Different synthesis conditions were tested to assess the effect of varying the reaction time, lead to chalcogen ratio, reaction temperature, and lead oleate concentration. The synthesized nanoparticles were characterized by means of electron diffraction, energy dispersive X-ray spectroscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy, to obtain information related to their morphology, crystal structure, and composition. The experimental results suggest that the growth of the lead chalcogenide nanoparticles greatly relies on the reduction of Pb2+ ions to Pb0 atoms at early reaction times; this reduction of the lead precursor is evidenced by the formation of Pb nanoparticles with sizes between 1 and 3 nm under certain synthesis conditions. These Pb nanoparticles gradually disappear as the reaction progresses, suggesting that the reduced Pb0 atoms are able to contribute to the growth of the PbSe and PbTe nanoparticles, reaching sizes between 8 and 18 nm. The current results contribute to a better understanding of the nucleation and growth mechanisms of lead chalcogenide nanoparticles, which will enable the definition of more efficient synthesis routes of these types of nanostructures.

  15. 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.

  16. Role of thermal history in atomic dynamics of chalcogenide glass: A case study on Ge20Te80 glass

    NASA Astrophysics Data System (ADS)

    Sharma, Yashika; Kalra, Geetanjali; Murugavel, Sevi

    2016-05-01

    The non-existence of thermodynamic equilibrium in glasses, their thermal history plays a very crucial role in explaining the relaxation behavior in various time scales and its configurational states. More importantly, the associated relaxation behavior is related mainly to the structural phenomenon of the glasses. Here, we report the dependence of quenching rate on the variation of structural units. The local structures of these glasses are monitored by recording the Raman spectroscopy and related to the different configurational states. The observed variations in structural differences are reflected in the measured density of the corresponding glasses. The quenching rate dependent of the relative fractions of edge-shared and corner-shared GeTe4 tetrahedral units are shown to be consistent with the corresponding variations in the measured density values.

  17. Observation of acoustic-phonon-like mode driven by magnetic imbalance between neighboring Fe atoms in Fe1+yTe (y < 0 . 12)

    NASA Astrophysics Data System (ADS)

    Fobes, David; Zaliznyak, Igor; Xu, Zhijun; Gu, Genda; Tranquada, John M.; He, Xu-Gang; Ku, Wei; Garlea, Ovidiu

    2014-03-01

    We have studied the evolution with temperature of the low-energy inelastic spectra of Fe1+yTe (y < 0 . 12), a parent compound of the iron-chalcogenide superconductor family, revealing an acoustic mode at an unexpected position. Recently, we found evidence for the formation of a bond-order wave leading to ferro-orbital order in the monoclinic phase, in part due to the observation of an elastic structural peak at (100) in the low-temperature monoclinic phase [D. Fobes, et al., arXiv:1307.7162]. In the inelastic spectra we observe a sharp acoustic-phonon-like mode dispersing out of the (100) position in the monoclinic phase. Surprisingly, the mode survives in the tetragonal phase, despite the absence of a Bragg peak at (100); such a peak is forbidden by symmetry. LDA calculations suggest this mode could involve significant magnetic scattering. By assuming in-phase virtual displacement of the Fe atoms from their equilibrium position in a frozen phonon calculation, we have found a small but significant imbalance in the magnetic moments between the two Fe atoms within the unit cell, suggesting magnetic contribution to the mode. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886. Research conducted at ORNL Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE.

  18. Structural Channels and Atomic-Cluster Insertion in CsxBi4Te6 (1 ≤ x ≤ 1.25) As Observed by Aberration-Corrected Scanning Transmission Electron Microscopy.

    PubMed

    Zhang, Ruixin; Yang, Huaixin; Guo, Cong; Tian, Huanfang; Shi, Honglong; Chen, Genfu; Li, Jianqi

    2016-12-19

    Microstructural analyses based on aberration-corrected scanning transmission electron microscopy (STEM) observations demonstrate that low-dimensional CsxBi4Te6 materials, known to be a novel thermoelectric and superconducting system, contain notable structural channels that go directly along the b axis, which can be partially filled by atom clusters depending on the thermal treatment process. We successfully prepared two series of CsxBi4Te6 single-crystalline samples using two different sintering processes. The CsxBi4Te6 samples prepared using an air-quenching method show superconductivity at approximately 4 K, while the CsxBi4Te6 with the same nominal compositions prepared by slowly cooling are nonsuperconductors. Moreover, atomic structural investigations of typical samples reveal that the structural channels are often empty in superconducting materials; thus, we can represent the superconducting phase as Cs1-yBi4Te6 with considering the point defects in the Cs layers. In addition, the channels in the nonsuperconducting crystals are commonly partially occupied by triplet Bi clusters. Moreover, the average structures for these two phases are also different in their monoclinic angles (β), which are estimated to be 102.3° for superconductors and 100.5° for nonsuperconductors.

  19. 125Te NMR and Seebeck Effect in Bi2Te3 Synthesized from Stoichiometric and Te-Rich Melts

    DOE PAGES

    Levin, E. M.; Iowa State Univ., Ames, IA; Riedemann, T. M.; ...

    2016-10-14

    Bi2Te3 is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi2Te3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125Te nuclear magnetic resonance (NMR). Here we report on 125Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric compositionmore » by Bridgman technique and (#2) grown out of Te-rich, high temperature flux. The Seebeck coefficients of these samples show p- and n-type conductivity, respectively, arising from different atomic defects. 125Te NMR spectra and spin–lattice relaxation measurements demonstrate that both Bi2Te3 samples are electronically inhomogeneous at the atomic scale, which can be attributed to a different Te environment due to spatial variation of the Bi/Te ratio and formation of atomic defects. In conclusion, correlations between 125Te NMR spectra, spin–lattice relaxation times, the Seebeck coefficients, carrier concentrations, and atomic defects are discussed. Our data demonstrate that 125Te NMR is an effective probe to study antisite defects in Bi2Te3.« less

  20. 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.

  1. Te homogeneous precipitation in Ge dislocation loop vicinity

    SciTech Connect

    Perrin Toinin, J.; Portavoce, A. Texier, M.; Bertoglio, M.; Hoummada, K.

    2016-06-06

    High resolution microscopies were used to study the interactions of Te atoms with Ge dislocation loops, after a standard n-type doping process in Ge. Te atoms neither segregate nor precipitate on dislocation loops, but form Te-Ge clusters at the same depth as dislocation loops, in contradiction with usual dopant behavior and thermodynamic expectations. Atomistic kinetic Monte Carlo simulations show that Te atoms are repulsed from dislocation loops due to elastic interactions, promoting homogeneous Te-Ge nucleation between dislocation loops. This phenomenon is enhanced by coulombic interactions between activated Te{sup 2+} or Te{sup 1+} ions.

  2. Effect of Doping with Substituent Bi Atoms on the Electrical Transport Properties of a Bi0.4Sb1.6Te3 Film Fabricated by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Zhichong; Zhang, Xiangpeng; Wu, Yigui; Hu, Zhiyu

    2015-10-01

    A highly crystalline Bi0.4Sb1.6Te3 film was fabricated on a Si substrate by molecular beam epitaxy (MBE) at a substrate temperature of 280°C. On the basis of study of x-ray diffraction patterns and high-resolution transmission electron microscopy lattice fringes it was inferred that Bi atoms were successfully incorporated into Sb lattice sites, forming substituent Bi impurities. Reduction of the carrier concentration was ascribed to the increased resistance to formation of antisite defects when Sb was substituted by Bi. The reduced mobility was a result of enhanced grain boundary scattering and attraction by substituent Bi atoms. Analysis of temperature-dependent electrical transport properties revealed that introduction of Bi atoms resulted in deeper energy level impurities in the Bi0.4Sb1.6Te3 film and higher activation energy (43.2 meV) than the normal value at room temperature, leading to semiconductor characteristics of the film in the temperature range -50°C to 150°C.

  3. Two-Dimensional Mineral [Pb 2 BiS 3 ][AuTe 2 ]: High-Mobility Charge Carriers in Single-Atom-Thick Layers

    SciTech Connect

    Fang, Lei; Im, Jino; Stoumpos, Constantinos C.; Shi, Fengyuan; Dravid, Vinayak; Leroux, Maxime; Freeman, Arthur J.; Kwok, Wai-Kwong; Chung, Duck Young; Kanatzidis, Mercouri

    2015-02-18

    Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb2BiS3][AuTe2], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atom-thick layers. The structure is composed of stacking layers of weakly coupled [Pb2BiS3] and [AuTe2] sheets. The insulating [Pb2BiS3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe2] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb2BiS3][AuTe2] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of similar to 1360 cm(2)/(V s). This material possesses an extremely large anisotropy, G = rho(c)/rho(ab) approximate to 10(4), comparable to those of the benchmark 2D materials graphite and Bi2Sr2CaCu2O6+delta. The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 10(6) m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties.

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

    PubMed Central

    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

    2015-01-01

    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 Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm2. 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. PMID:25605947

  5. 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

    2015-02-03

    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.

  6. Structure of Te-rich Te-Ge-X (X = I, Se, Ga) glasses.

    PubMed

    Jóvári, Pál; Kaban, Ivan; Bureau, Bruno; Wilhelm, Allison; Lucas, Pierre; Beuneu, Brigitte; Zajac, Dariusz A

    2010-10-13

    The structure of glassy Te(78)Ge(11)Ga(11), Te(79)Ge(16)Ga(5), Te(70)Ge(20)Se(10) and Te(73)Ge(20)I(7)--promising materials for far infrared applications--was investigated by means of x-ray and neutron diffraction as well as extended x-ray absorption fine structure measurements at various edges. Experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation technique. Short range order in Te(85)Ge(15) was reinvestigated by fitting a new x-ray diffraction measurement together with available neutron diffraction and extended x-ray absorption fine structure data. It was found that Te(85)Ge(15) consists mostly of GeTe(4) structural units linked together directly or via bridging Te atoms. Te is predominantly twofold coordinated in Te(85)Ge(15), Te(70)Ge(20)Se(10) and Te(73)Ge(20)I(7) while in Te(78)Ge(11)Ga(11) and Te(79)Ge(16)Ga(5) the Te coordination number is significantly higher than 2. The Te-Te bond length is 2.80 ± 0.02 Å in Te(78)Ge(11)Ga(11) while it is as short as 2.70 ± 0.02 Å and 2.73 ± 0.02 Å in Te(73)Ge(20)I(7) and Te(70)Ge(20)Se(10), respectively. Our results show that the strengths of GeTe(4) (GeTe(3)I, GeTe(3)Se) 'units' are very similar in all glasses investigated but the connection between these units depends on the third component. Differences in the Te coordination number suggest that unlike Se or I, Ga does not build into the Ge-Te covalent network. Instead, it forms a covalent bond with the non-bonding p electrons of Te, which results in an increase in the average Te coordination number.

  7. Theory versus experiment for a family of single-layer compounds with a similar atomic arrangement: (Tl,X )/Si(111 )√{3 }×√{3 }(X =Pb,Sn,Bi,Sb,Te,Se)

    NASA Astrophysics Data System (ADS)

    Matetskiy, A. V.; Kibirev, I. A.; Mihalyuk, A. N.; Eremeev, S. V.; Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Zotov, A. V.; Saranin, A. A.

    2017-08-01

    Two-dimensional compounds made of one monolayer of Tl and one-third monolayer of Pb, Bi, Te, or Se (but not of Sn or Sb) on Si(111) have been found to have a similar atomic arrangement which can be visualized as a √{3 }×√{3 } -periodic honeycomb network of chained Tl trimers with atoms of the second adsorbate occupying the centers of the honeycomb units. Structural and electronic properties of the compounds have been examined in detail theoretically using density functional theory (DFT) calculations and experimentally using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) observations. It has been found that though structural parameters of the compounds are very similar for all species, the only common feature of their band structure is a considerable spin-splitting of the surface-state bands, while other basic electronic properties vary greatly with a change of species. The Tl-Pb compound is strongly metallic with two metallic surface-state bands; the Tl-Bi compound is also metallic but with a single metallic band; the Tl-Te and Tl-Se compounds appear to be insulators.

  8. Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Crx(Bi0.1Sb0.9)2-x Te3 - Part I

    NASA Astrophysics Data System (ADS)

    Kim, Chung Koo; Lee, Inhee; Lee, Jinho; Billinge, Simon; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Tranquada, John; Gu, Genda; Davis, J. C. Seamus

    2015-03-01

    Topological insulators (TI) have a gapless surface state of Dirac fermions protected by the time reversal symmetry (TRS). However, TRS can be broken in the ferromagnetic state induced by magnetic doping. This leads to the opening of ``mass gap'' at the Dirac point. Such a gap is predicted to involve many exotic phenomena for which understanding the microscopic role of magnetic dopants is critical. But it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92 Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate directly is related to fluctuations in n(r), the areal Cr atom density at the surface. The relationship of the surface-state Fermi wavevectors to both the correlation length and anisotropic structure of Δ(r) are found consistent with predictions for ferromagnetism mediated by the surface states.

  9. 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.

  10. 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

    2016-05-20

    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.

  11. 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

  12. Nuclear Magnetic Resonance Studies of Tellurium and Antimony Bonding in Crystal Sb2Te3, GeTe, and Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Bobela, David C.; Taylor, P. Craig

    2008-10-01

    As a starting point in understanding the magnetic resonance data for amorphous Ge2Sb2Te5, the prototypical phase change material, we have used 121Sb and 125Te nuclear magnetic resonance (NMR) to study crystalline Sb2Te3, GeTe, and Ge2Sb2Te5. The frequency space data are affected by a quadrupole (121Sb only) and chemical shift (121Sb and 125Te) interaction, which reflect the bonding asymmetries occurring around each nuclei. The 125Te data indicate there are two distinct Te sites in Sb2Te3 and one Te site in the GeTe, in agreement with the known crystal structures. The Ge2Sb2Te5125Te data are less well-resolved, which is probably a consequence of the random arrangement of Sb/Ge atoms around the Te sites. Despite the lack of resolution, these data do correspond to the spectral positions and breadths observed in Sb2Te3 and GeTe, which suggests that Ge2Sb2Te5 contains similar Te bonding structures. The 121Sb data in Sb2Te3 show that the Sb sites have an approximately axially symmetric bonding environment. The Sb data in Ge2Sb2Te5 reveal that the average bonding structure of Sb is very different from the Sb sites occurring in Sb2Te3.

  13. Structural phase transitions of (Bi1$-$xSbx )2(Te1$-$y Se y)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

    SciTech Connect

    Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; Wang, Yong; Schneeloch, John; Li, Chunyu; Zhong, Ruidan; Wang, Yi; Liu, Zhiguo; Gu, Genda

    2016-12-14

    Recently, A2B3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi2Te2Se, BiSbTeSe2, and Sb2Te2Se tetradymites under high pressure. Bi2Te2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi2Te3. Thus, the compression behavior of Bi2Te2Se is the same as that of Bi2Se3, which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe2 and Sb2Te2Se undergo similar structural phase transitions to Bi2Te2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A2B3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.

  14. Structural phase transitions of (Bi1$-$xSbx )2(Te1$-$y Se y)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

    SciTech Connect

    Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; Wang, Yong; Schneeloch, John; Li, Chunyu; Zhong, Ruidan; Wang, Yi; Liu, Zhiguo; Gu, Genda

    2016-12-14

    Recently, A2B3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi2Te2Se, BiSbTeSe2, and Sb2Te2Se tetradymites under high pressure. Bi2Te2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi2Te3. Thus, the compression behavior of Bi2Te2Se is the same as that of Bi2Se3, which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe2 and Sb2Te2Se undergo similar structural phase transitions to Bi2Te2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A2B3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.

  15. Exceptional suppression of flux-flow resistivity in FeSe0.4Te0.6 by back-flow from excess Fe atoms and Se /Te substitutions

    NASA Astrophysics Data System (ADS)

    Okada, Tatsunori; Nabeshima, Fuyuki; Takahashi, Hideyuki; Imai, Yoshinori; Maeda, Atsutaka

    2015-02-01

    We measured the microwave surface impedance of FeSe0.4Te0.6 single crystals with and without external magnetic fields. The superfluid density exhibited a quadratic temperature dependence, indicating a strong pair-breaking effect. The flux-flow resistivity behaved as ρf(B ≪Bc 2) /ρn=α B /Bc 2 . The observed α value of ≈0.66 was considerably smaller than that of other Fe-based materials (α ≥1 ) and was attributed to a back-flow of superfluids remarkable in disordered superconductors. This is an observation of the back-flow phenomenon caused by an origin other than the vortex pinning in multiple-band systems.

  16. Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Crx(Bi0.1Sb0.9)2-xTe3 - Part II

    NASA Astrophysics Data System (ADS)

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Tranquada, John; Gu, Genda; Davis, J. C.

    2015-03-01

    We present Part II of the spectroscopic imaging - scanning tunneling microscopy (SI-STM) study of ferromagnetic Crx(Bi0.1Sb0.9)2-xTe3 single crystals measured at 4.5 K. As Part II we show how both spectroscopic analysis in real and momentum space demonstrate the coincident Dirac mass gap identified. Distribution of gap width, gap center, and gap anisotropy will be discussed. The anticipated relationship Δ (r) ~ n (r) is confirmed throughout, and exhibits an electron-dopant interaction energy J* = 145 meV .nm2. These observations reveal how magnetic dopant atoms actually generate the TI mass gap 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. Adsorption of Te atoms on Au(1 1 1) and the emergence of an adatom-induced bound state

    NASA Astrophysics Data System (ADS)

    Schouteden, Koen; Debehets, Jolien; Muzychenko, Dmitry; Li, Zhe; Seo, Jin Won; Van Haesendonck, Chris

    2017-03-01

    We report on the adsorption of Te adatoms on Au(1 1 1), which are identified and investigated relying on scanning tunnelling microscopy, Auger electron spectroscopy, and density functional theory. The Te adatoms lift the 23  ×  √3 surface reconstruction of the Au(1 1 1) support and their organization is similar to that of previously reported chalcogen adatoms on Au(1 1 1), which are also known to lift the herringbone reconstruction and can adopt a (√3  ×  √3)R30° structure. The adatoms show strong interaction with the Au(1 1 1) surface, resulting in scattering and confinement of the Au surface state (SS) electrons near the Fermi level. More remarkably, scanning tunnelling spectroscopy reveals the existence of an electronic resonance at high voltages well above the Fermi level. This resonance can be interpreted as a bound state that is split off from the bottom of the Au(1 1 1) bulk conduction band. A similar split-off state may exist for other types of adatoms on metallic surfaces that exhibit a surface band gap.

  18. Microstructure and a Nucleation Mechanism for Nanoprecipitates In PbTe-AgSbTe2

    SciTech Connect

    Ke, X.; Chen, C.; Yang, J.; Wu, L.; Zhou, J.; Li, Q.; Zhu, Y.; Kent, P.R.C.

    2009-10-02

    Many recent advances in thermoelectric (TE) materials are attributed to their nanoscale constituents. Determination of the nanocomposite structures has represented a major experimental and computational challenge and eluded previous attempts. Here we present the first atomically resolved structures of high performance TE material PbTe-AgSbTe{sub 2} by transmission electron microscopy imaging and density functional theory calculations. The results establish an accurate structural characterization for PbTe-AgSbTe{sub 2} and identify the interplay of electric dipolar interactions and strain fields as the driving mechanism for nanoprecipitate nucleation and aggregation.

  19. Superstrengthening Bi2Te3 through Nanotwinning

    NASA Astrophysics Data System (ADS)

    Li, Guodong; Aydemir, Umut; Morozov, Sergey I.; Wood, Max; An, Qi; Zhai, Pengcheng; Zhang, Qingjie; Goddard, William A.; Snyder, G. Jeffrey

    2017-08-01

    Bismuth telluride (Bi2Te3 ) based thermoelectric (TE) materials have been commercialized successfully as solid-state power generators, but their low mechanical strength suggests that these materials may not be reliable for long-term use in TE devices. Here we use density functional theory to show that the ideal shear strength of Bi2Te3 can be significantly enhanced up to 215% by imposing nanoscale twins. We reveal that the origin of the low strength in single crystalline Bi2Te3 is the weak van der Waals interaction between the Te1 coupling two Te 1 - Bi - Te 2 - Bi - Te 1 five-layer quint substructures. However, we demonstrate here a surprising result that forming twin boundaries between the Te1 atoms of adjacent quints greatly strengthens the interaction between them, leading to a tripling of the ideal shear strength in nanotwinned Bi2Te3 (0.6 GPa) compared to that in the single crystalline material (0.19 GPa). This grain boundary engineering strategy opens a new pathway for designing robust Bi2Te3 TE semiconductors for high-performance TE devices.

  20. Role of thermal history in atomic dynamics of chalcogenide glass: A case study on Ge{sub 20}Te{sub 80} glass

    SciTech Connect

    Sharma, Yashika; Kalra, Geetanjali; Murugavel, Sevi

    2016-05-23

    The non-existence of thermodynamic equilibrium in glasses, their thermal history plays a very crucial role in explaining the relaxation behavior in various time scales and its configurational states. More importantly, the associated relaxation behavior is related mainly to the structural phenomenon of the glasses. Here, we report the dependence of quenching rate on the variation of structural units. The local structures of these glasses are monitored by recording the Raman spectroscopy and related to the different configurational states. The observed variations in structural differences are reflected in the measured density of the corresponding glasses. The quenching rate dependent of the relative fractions of edge-shared and corner-shared GeTe{sub 4} tetrahedral units are shown to be consistent with the corresponding variations in the measured density values.

  1. 125Te NMR and Seebeck Effect in Bi2Te3 Synthesized from Stoichiometric and Te-Rich Melts

    SciTech Connect

    Levin, E. M.; Riedemann, T. M.; Howard, A.; Jo, N. H.; Bud’ko, S. L.; Canfield, P. C.; Lograsso, T. A.

    2016-10-14

    Bi2Te3 is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi2Te3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125Te nuclear magnetic resonance (NMR). Here we report on 125Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric composition by Bridgman technique and (#2) grown out of Te-rich, high temperature flux. The Seebeck coefficients of these samples show p- and n-type conductivity, respectively, arising from different atomic defects. 125Te NMR spectra and spin–lattice relaxation measurements demonstrate that both Bi2Te3 samples are electronically inhomogeneous at the atomic scale, which can be attributed to a different Te environment due to spatial variation of the Bi/Te ratio and formation of atomic defects. In conclusion, correlations between 125Te NMR spectra, spin–lattice relaxation times, the Seebeck coefficients, carrier concentrations, and atomic defects are discussed. Our data demonstrate that 125Te NMR is an effective probe to study antisite defects in Bi2Te3.

  2. 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.

  3. Toward Single Atom Chains with Exfoliated Tellurium.

    PubMed

    Churchill, Hugh O H; Salamo, Gregory J; Yu, Shui-Qing; Hironaka, Takayuki; Hu, Xian; Stacy, Jeb; Shih, Ishiang

    2017-08-10

    We demonstrate that the atom chain structure of Te allows it to be exfoliated as ultra-thin flakes and nanowires. Atomic force microscopy of exfoliated Te shows that thicknesses of 1-2 nm and widths below 100 nm can be exfoliated with this method. The Raman modes of exfoliated Te match those of bulk Te, with a slight shift (4 cm(-1)) due to a hardening of the A1 and E modes. Polarized Raman spectroscopy is used to determine the crystal orientation of exfoliated Te flakes. These experiments establish exfoliation as a route to achieve nanoscale trigonal Te while also demonstrating the potential for fabrication of single atom chains of Te.

  4. Vacancy-associated Te sites in GaAs

    NASA Astrophysics Data System (ADS)

    Wuyts, K.; Langouche, G.; van Rossum, M.; Silverans, R. E.

    1992-03-01

    Defect structures, observed by 129I Mössbauer spectroscopy in high-dose Te-doped GaAs, are identified by a reference study of the semiconducting compound Ga2Te3. The formation of TeAs-VGa complexes (tellurium atoms quasisubstitutional on an As site with a gallium vacancy in the first-neighbor shell) is proposed, in agreement with theoretical predictions. The relevance of this assignment in relation to the earlier proposed Te DX configuration is also discussed.

  5. 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.

  6. First-principle studies on the Li-Te system

    NASA Astrophysics Data System (ADS)

    Wang, Youchun; Tian, Fubo; Li, Da; Duan, Defang; Liu, Yunxian; Liu, Bingbing; Zhou, Qiang; Cui, Tian

    2017-01-01

    First-principle evolutionary calculation was performed to search for all probable stable lithium tellurium compounds. In addition to the well-known structures of Fm-3m Li2Te and Pnma Li2Te, several novel structures, including those of P4/nmm Li2Te, Imma Li8Te2, and C2/m Li9Te2, were determined under high pressure. The transformation sequence of Li2Te induced by pressure was presented as follows. The phase transition occurred at 7.5 GPa while transforming from Fm-3m phase to Pnma structure, then transformed to P4/nmm phase at 14 GPa. P4/nmm Li2Te can remain stable at least up to 140 GPa. Li8Te2 and Li9Te2 were stable at 8-120 GPa and 80-120 GPa, respectively. Interestingly, Li8Te2 and Li9Te2 were predicted to be metallic under high pressure, Li2Te would metalize on compression. P4/nmm Li2Te is likely a super ionic conductor due to the special characteristic. Metallic P4/nmm Li2Te may be a candidate mixed conductor material under extreme pressure. Charge transfer was studied using Bader charge analysis. Charge transferred from Li to Te, and the relative debilitated ionicity between Li and Te atoms existed at high pressure.

  7. 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.

  8. 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.

  9. 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.

  10. Electrochemical Atomic Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Gregory, Brian Wayne

    1992-01-01

    Presented here are initial investigations into an electrochemical method whereby thin films of compound semiconductors are produced by epitaxial growth of the constituent elements. This method is the electrochemical analogue of atomic layer epitaxy (ALE) (a vacuum-based technique which relies on sequential formation of atomic layers of the constituent elements) and has been termed "Electrochemical atomic layer epitaxy" (ECALE). These preliminary studies are centered on the formation of CdTe, though in principle they could be extended to a number of other compound semiconductors. A background introduction on topics relevant to epitaxial growth in electrochemical systems will be presented. Predictions of underpotential behavior in the CdTe system will be made using potential -pH (Pourbaix) diagrams. Development of the method will proceed from our initial studies of Cd and Te underpotential deposition (UPD) on a number of metallic substrates, followed by results demonstrating the ECALE formation of two monolayers of CdTe on polycrystalline and single crystal gold substrates. The final chapter will present current attempts to design and construct an automated, computer-controlled thin-layer electrochemical flow cell, which is to be used for the deposition of thicker layers (up to 1 mu m) of compound semiconductors.

  11. Local Structure Around Te in Heavily Doped GaAs:Te using X-Ray Absorption Fine Structure

    SciTech Connect

    Pietnoczka, A.; Bacewicz, R.; Slupinski, T.; Antonowicz, J.; Wei, Su-Huai

    2012-04-01

    The annealing of heavily doped GaAs:Te can significantly change the free electron concentration in a reversible manner. These changes of electrical properties are accompanied by the structural changes of GaAs:Te solid solution. We used X-ray Absorption Fine Structure at K-edge of tellurium to determine local changes around Te atoms for different states of the GaAs:Te crystals caused by the annealing corresponding to different electron concentrations. The best EXAFS fit for the samples with high electron concentration was obtained for the substitutional Te{sub As} model with elongated Te-Ga bonds (as compared to the As-Ga distance). For the samples in the low concentration state the best fit was for the pairs of Te atoms forming a rhombohedral symmetry double-DX centre, with the proportional admixture of the substitutional tellurium.

  12. Determining and Controlling the Magnesium Composition in CdTe/CdMgTe Heterostructures

    NASA Astrophysics Data System (ADS)

    LeBlanc, E. G.; Edirisooriya, M.; Ogedengbe, O. S.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Rab, S.; Swartz, C. H.; Diercks, D. R.; Burton, G. L.; Gorman, B. P.; Wang, A.; Barnes, T. M.; Myers, T. H.

    2017-09-01

    The relationships between Mg composition, band gap, and lattice characteristics are investigated for Cd1- x Mg x Te barrier layers using a combination of cathodoluminescence, energy dispersive x-ray spectroscopy, variable angle spectral ellipsometry, and atom probe tomography. The use of a simplified, yet accurate, variable angle spectral ellipsometry analysis is shown to be appropriate for fast determination of composition in thin Cd1- x Mg x Te layers. The validity of using high-resolution x-ray diffraction for CdTe/Cd1- x Mg x Te double heterostructures is discussed. The stability of CdTe/Cd1- x Mg x Te heterostructures are investigated with respect to thermal processing.

  13. Determining and Controlling the Magnesium Composition in CdTe/CdMgTe Heterostructures

    DOE PAGES

    LeBlanc, E. G.; Edirisooriya, M.; Ogedengbe, O. S.; ...

    2017-06-05

    The relationships between Mg composition, band gap, and lattice characteristics are investigated for Cd1-xMgxTe barrier layers using a combination of cathodoluminescence, energy dispersive x-ray spectroscopy, variable angle spectral ellipsometry, and atom probe tomography. The use of a simplified, yet accurate, variable angle spectral ellipsometry analysis is shown to be appropriate for fast determination of composition in thin Cd1-xMgxTe layers. The validity of using high-resolution x-ray diffraction for CdTe/Cd1-xMgxTe double heterostructures is discussed. Furthermore, the stability of CdTe/Cd1-xMgxTe heterostructures are investigated with respect to thermal processing.

  14. Insights into the Structure of the Stable and Metastable (GeTe)m(Sb2Te3)n Compounds

    SciTech Connect

    Da Silva, J. L. F.; Walsh, A.; Lee, H.

    2008-01-01

    Using first-principles calculations, we identify the mechanisms that lead to the lowest energy structures for the stable and metastable (GeTe){sub m}(Sb{sub 2}Te{sub 3}){sub n} (GST) compounds, namely, strain energy release by the formation of superlattice structures along of the hexagonal [0001] direction and by maximizing the number of Te atoms surrounded by three Ge and three Sb atoms (3Ge-Te-3Sb rule) and Peierls-type bond dimerization. The intrinsic vacancies form ordered planes perpendicular to the stacking direction in both phases, which separate the GST building blocks. The 3Ge-Te-3Sb rule leads to the intermixing of Ge and Sb atoms in the (0001) planes for Ge{sub 3}Sb{sub 2}Te{sub 6} and Ge{sub 2}Sb{sub 2}Te{sub 5}, while only single atomic species in the (0001) planes satisfy this rule for the GeSb{sub 2}Te{sub 4} and GeSb{sub 4}Te{sub 7} compositions. Furthermore, we explain the volume expansion of the metastable phase with respect to the stable phase as a consequence of the different stacking sequence of the Te atoms in the stable and metastable phases, which leads to a smaller Coulomb repulsion in the stable phase. The calculated equilibrium lattice parameters are in excellent agreement with experimental results and differ by less than 1% from the lattice parameters derived from a combination of the GeTe and Sb{sub 2}Te{sub 3} parent compounds.

  15. Manufacturing Te/PEDOT Films for Thermoelectric Applications.

    PubMed

    Culebras, Mario; Igual-Muñoz, Ana María; Rodríguez-Fernández, Carlos; Gómez-Gómez, María Isabel; Gómez, Clara; Cantarero, Andrés

    2017-06-21

    In this work, flexible Te films have been synthesized by electrochemical deposition using PEDOT [poly(3,4-ethylenedioxythiophene)] nanofilms as working electrodes. The Te electrodeposition time was varied to find the best thermoelectric properties of the Te/PEDOT double layers. To show the high quality of the Te films grown on PEDOT, the samples were analyzed by Raman spectroscopy, showing the three Raman active modes of Te: E1, A1, and E2. The X-ray diffraction spectra also confirmed the presence of crystalline Te on top of the PEDOT films. The morphology of the Te/PEDOT films was studied using scanning electron microscopy, showing a homogeneous distribution of Te along the film. Also an atomic force microscope was used to analyze the quality of the Te surface. Finally, the electrical conductivity and the Seebeck coefficient of the Te/PEDOT films were measured as a function of the Te deposition time. The films showed an excellent thermoelectric behavior, giving a maximum power factor of about 320 ± 16 μW m(-1) K(-2) after 2.5 h of Te electrochemical deposition, a value larger than that reported for thin films of Te. Qualitative arguments to explain this behavior are given in the discussion.

  16. Te-centric view of the phase change mechanism in Ge-Sb-Te alloys.

    PubMed

    Sen, S; Edwards, T G; Cho, J-Y; Joo, Y-C

    2012-05-11

    The short-range structure of amorphous and fcc Ge1Sb2Te4 and Ge2Sb2Te5 phase-change alloys is investigated using 125Te NMR spectroscopy. Both amorphous and fcc structures consist solely of heteropolar Ge/Sb-Te bonds that may enable rapid displacive phase transformation without the need for extensive atomic rearrangement. The vacancy distribution is random in microcrystalline fcc phases while significant clustering is observed in their nanocrystalline counterparts that may result in the formation of tetrahedrally coordinated Ge atoms in the latter. This structural commonality may further facilitate the kinetics of transformation between amorphous and nanocrystalline fcc phases, a situation relevant for high-density memory storage.

  17. Gold derivatives of eight rare-earth-metal-rich tellurides: monoclinic R7Au2Te2 and orthorhombic R6AuTe2 types.

    PubMed

    Chai, Ping; Corbett, John D

    2012-03-19

    Two series of rare-earth-metal (R) compounds, R(7)Au(2)Te(2) (R = Tb, Dy, Ho) and R(6)AuTe(2) (R = Sc, Y, Dy, Ho, Lu), have been synthesized by high-temperature techniques and characterized by X-ray diffraction analyses as monoclinic Er(7)Au(2)Te(2)-type and orthorhombic Sc(6)PdTe(2)-type structures, respectively. Single-crystal diffraction results are reported for Ho(7)Au(2)Te(2), Lu(6)AuTe(2), Sc(6)Au(0.856(2))Te(2), and Sc(6)Au(0.892(3))Te(2). The structure of Ho(7)Au(2)Te(2) consists of columns of Au-centered tricapped trigonal prisms (TCTPs) of Ho condensed into 2D zigzag sheets that are interbridged by Te and additional Ho to form the 3D network. The structure of Lu(6)AuTe(2) is built of pairs of Au-centered Lu TCTP chains condensed with double Lu octahedra in chains into 2D zigzag sheets that are separated by Te atoms. Tight binding-linear muffin-tin orbital-atomic sphere approximation electronic structure calculations on Lu(6)AuTe(2) indicate a metallic property. The principal polar Lu-Au and Lu-Te interactions constitute 75% of the total Hamilton populations, in contrast to the small values for Lu-Lu bonding even though these comprise the majority of the atoms. A comparison of the theoretical results for Lu(6)AuTe(2) with those for isotypic Lu(6)AgTe(2) and Lu(6)CuTe(2) provides clear evidence of the greater relativistic effects in the bonding of Au. The parallels and noteworthy contrasts between Ho(7)Au(2)Te(2) (35 valence electrons) and the isotypic but much electron-richer Nb(7)P(4) (55 valence electrons) are analyzed and discussed. © 2012 American Chemical Society

  18. 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.

  19. 125Te and 51V static NMR study of V2O5-TeO2 glasses

    NASA Astrophysics Data System (ADS)

    Sakida, Shinichi; Hayakawa, Satoshi; Yoko, Toshinobu

    2000-03-01

    The structures of V2 O5 -TeO2 glasses are investigated by means of 125 Te and 51 V static NMR spectroscopies and the local structures around the Te and V atoms are discussed in detail from the respective NMR spectra. The fraction of TeO3 trigonal pyramids increases and that of TeO4 trigonal bipyramids decreases with increasing V2 O5 content. The structures of V2 O5 -TeO2 glasses are quite different from those of tellurite glasses containing network-modifying oxides. The fraction of VO4 tetrahedra increases and that of VO5 trigonal bipyramids decreases with increasing V2 O5 content. Both chains consisting of tellurite structural units and those consisting of vanadate structural units contribute to the formation of the glass network in V2 O5 -TeO2 glasses.

  20. Tellurium speciation, connectivity, and chemical order in As(x)Te(100-x) glasses: results from two-dimensional 125Te NMR spectroscopy.

    PubMed

    Kaseman, Derrick C; Hung, Ivan; Lee, Kathleen; Kovnir, Kirill; Gan, Zhehong; Aitken, Bruce; Sen, Sabyasachi

    2015-02-05

    The short-range structure, connectivity, and chemical order in As(x)Te(100-x) (25 ≤ x ≤ 65) glasses are studied using high-resolution two-dimensional projection magic-angle-turning (pjMAT) (125)Te nuclear magnetic resonance (NMR) spectroscopy. The (125)Te pjMAT NMR results indicate that the coordination of Te atoms obeys the 8-N coordination rule over the entire composition range. However, in strong contrast with the analogous glass-forming As-S and As-Se chalcogenides, significant violation of chemical order is observed in As-Te glasses over the entire composition range in the form of homopolar As-As (Te-Te) bonds, even in severely As (Te)-deficient glasses. The speciation of the Te coordination environments can be explained with the dissociation reaction model As2Te3 → 2As + 3Te(II), characterized by a dissociation constant that is independent of glass composition. These structural characteristics can be attributed to the high metallicity of Te and the strong energetic similarity between the Te-Te, Te-As, and As-As bonds, and they are consistent with the monotonic and often nearly linear variation of physical properties observed in telluride glasses as a function of the Te content.

  1. {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.

  2. Structure of molten Ga-Te eutectic

    SciTech Connect

    Dutchak, Ya.I.; Mudryi, S.I.; Kozyrenko, V.N.

    1988-02-01

    We have made an x-ray study of the Ga-Te eutectic liquid. The phase diagram shows a series of compounds as well as immiscibility regions for two liquid phases and the eutectic. The compounds GaTe and Ga/sub 2/Te/sub 3/ melt congruently. The phase diagram is complicated, and the phase state varies substantially with the component ratio. The liquid eutectic (87 at. % Te) was examined with a high-temperature diffractometer intended particularly for liquids; Cu K..cap alpha.. radiation was used, which was monochromatized with LiF. An integral Fourier transformation was used to calculate the radial distributions for the atoms and the density; the first were used to derive the most likely shortest interatomic distances, while the second gave the mean coordination numbers.

  3. Selenium-tellurium sequences in binary glasses as depicted by 77Se and 125Te NMR.

    PubMed

    Bureau, Bruno; Boussard-Plédel, Catherine; LeFloch, Marie; Troles, Johann; Smektala, Frédéric; Lucas, Jacques

    2005-04-07

    Some resolved solid state (77)Se NMR spectra are presented in the Te(x)Se(1-x) vitreous system at ambient temperature. They exhibit three different kinds of Se lines assigned to the following Se atom neighborhoods: Se-Se-Se, Se-Se-Te, and Te-Se-Te. Different models were considered to describe the way the Se and Te atoms are linked into the chains: clustering process, homogeneous distribution, random distribution. Finally, thanks to the measurements of the relative intensities of the lines, it appears that Se and Te atoms are mainly randomly distributed with a small preference for heteropolar bonds. The (125)Te spectra are also shown but their resolution is too weak to be informative concerning the vitreous network.

  4. Electrical properties of PbTe single crystals with excess tellurium

    SciTech Connect

    Bagiyeva, G. Z. Mustafayev, N. B.; Abdinova, G. Dj.; Abdinov, D. Sh.

    2011-11-15

    The effects of excess (up to 0.1 at %) Te atoms and heat treatment at 473 and 573 K for 120 h on the conductivity {sigma}, thermopower {alpha}, and Hall coefficient R of PbTe single crystals are studied. It is shown that excess Te atoms and annealing strongly affect the values and character of the temperature dependences of these parameters and the signs of {alpha} and R at low temperatures, which is caused by the acceptor effect of these atoms and the formation of antisite defects due to localization of Te in vacancies of the lead sublattice upon annealing.

  5. 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.

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

    DOE PAGES

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; ...

    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

  7. New Mo6 Te6 Sub-Nanometer-Diameter Nanowire Phase from 2H-MoTe2.

    PubMed

    Zhu, Hui; Wang, Qingxiao; Zhang, Chenxi; Addou, Rafik; Cho, Kyeongjae; Wallace, Robert M; Kim, Moon J

    2017-03-10

    A novel phase transition, from multilayered 2H-MoTe2 to a parallel bundle of sub-nanometer-diameter metallic Mo6 Te6 nanowires (NWs) driven by catalyzer-free thermal-activation (400-500 °C) under vacuum, is demonstrated. The NWs form along the 〈11-20〉 2H-MoTe2 crystallographic directions with lengths in the micrometer range. The metallic NWs can act as an efficient hole injection layer on top of 2H-MoTe2 due to favorable band-alignment. In particular, an atomically sharp MoTe2 /Mo6 Te6 interface and van der Waals gap with the 2H layers are preserved. The work highlights an alternative pathway for forming a new transition metal dichalcogenide phase and will enable future exploration of its intrinsic transportation properties.

  8. High-Resolution ^125Te NMR of Novel Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Schmidt-Rohr, K.; Cook, B. A.; Han, Mi-Kyung; Kanatzidis, M. G.

    2008-03-01

    Several novel Te-based thermoelectric materials with extraordinary figure of merit ZT >=1.4 have been studied by high-resolution 25 kHz magic angle spinning ^125Te nuclear magnetic resonance (NMR) in order to investigate variations in composition on the nano-scale. A 20-fold wider ^125Te NMR signal of both AgSbGe4Te6 and AgSbGe5.67Te7.67 (˜90 kHz) compared to that of PbTe (4.5 kHz) indicates a variation of shifts due to local composition fluctuations. The similar total shift of the main peak in Ag0.53Pb18Sb1.2Te20 (-1790 ppm) and PbTe (-1750 ppm) and similarly long T2 relaxation time show that the majority of Te atoms in both materials has a similar environment. A second peak in Ag0.53Pb18Sb1.2Te20 at -1600 ppm shows the presence of a second type of Te site, accounting for ˜1/3 of all Te. These are apparently located in Ag,Sb-rich inclusions, as indicated by a much shorter T2, which can be due to the effect of quadrupolar relaxation of ^121Sb or ^123Sb (spin 5/2 or 7/2, respectively) on ^125Te. Our data confirm suggestions made by Hsu et al., Science (2004) and by Chen et al., Appl. Phys. Lett. (2005) about the presence of nano-scale inclusions in Ag0.53Pb18Sb1.2Te20, which result in low lattice thermal conductivity and high ZT.

  9. Reassessment of the carrier concentration in GeTe-based thermoelectric materials by ^125Te NMR

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Acton, J. D.; Schmidt-Rohr, K.

    2012-02-01

    Ge1-xAgx/2Sbx/2Te p-type thermoelectric materials (``TAGS-n'') were studied extensively in the 1970s and then again recently. They exhibit an unusual combination of large thermopower, S, and high hole concentration, p, reported based on the Hall effect data, which has not been explained. To solve this puzzle, we have synthesized GeTe, GeTe:Bi, and TAGS-n with n = 97, 94, 90, and 85 and studied XRD, thermopower, electrical resistivity, thermal conductivity, and ^125Te NMR. Most importantly, we have determined the carrier concentrations using ^125Te NMR spin-lattice relaxation and Knight shift. In GeTe and GeTe:Bi, we found that carrier concentrations generally agree with the values reported from Hall effect. In TAGS-n, they are much lower but agree better with the values expected from S vs. p for GeTe-based materials, solving the puzzle partially. The NMR vs. Hall effect discrepancy in TAGS-n can be due to the presence not only of holes but also electrons generated by Sb atoms, which results in artificially high hole concentration from Hall effect. Even though the true hole concentration is lower than reported, the thermopower of TAGS-n is still significantly larger than that of GeTe and GeTe:Bi at similar carrier concentration. This can be explained by energy filtering enhanced by potential barriers formed due to Ag-Sb pairs in the TAGS-n lattice.

  10. Polymorphism in Thermoelectric As2Te3.

    PubMed

    Morin, Cedric; Corallini, Serena; Carreaud, Julie; Vaney, Jean-Baptiste; Delaizir, Gaelle; Crivello, Jean-Claude; Lopes, Elsa Branco; Piarristeguy, Andrea; Monnier, Judith; Candolfi, Christophe; Nassif, Vivian; Cuello, Gabriel Julio; Pradel, Annie; Goncalves, Antonio Pereira; Lenoir, Bertrand; Alleno, Eric

    2015-10-19

    Metastable β-As2Te3 (R3̅m, a = 4.047 Å and c = 29.492 Å at 300 K) is isostructural to layered Bi2Te3 and is known for similarly displaying good thermoelectric properties around 400 K. Crystallizing glassy-As2Te3 leads to multiphase samples, while β-As2Te3 could indeed be synthesized with good phase purity (97%) by melt quenching. As expected, β-As2Te3 reconstructively transforms into stable α-As2Te3 (C2/m, a = 14.337 Å, b = 4.015 Å, c = 9.887 Å, and β = 95.06°) at 480 K. This β → α transformation can be seen as the displacement of part of the As atoms from their As2Te3 layers into the van der Waals bonding interspace. Upon cooling, β-As2Te3 displacively transforms in two steps below T(S1) = 205-210 K and T(S2) = 193-197 K into a new β'-As2Te3 allotrope. These reversible and first-order phase transitions give rise to anomalies in the resistance and in the calorimetry measurements. The new monoclinic β'-As2Te3 crystal structure (P2(1)/m, a = 6.982 Å, b = 16.187 Å, c = 10.232 Å, β = 103.46° at 20 K) was solved from Rietveld refinements of X-ray and neutron powder patterns collected at low temperatures. These analyses showed that the distortion undergone by β-As2Te3 is accompanied by a 4-fold modulation along its b axis. In agreement with our experimental results, electronic structure calculations indicate that all three structures are semiconducting with the α-phase being the most stable one and the β'-phase being more stable than the β-phase. These calculations also confirm the occurrence of a van der Waals interspace between covalently bonded As2Te3 layers in all three structures.

  11. Study of the structure and chemical bonding of crystalline Ge{sub 4}Sb{sub 2}Te{sub 7} using first principle calculations

    SciTech Connect

    Singh, Janpreet; Singh, Satvinder; Tripathi, S. K. E-mail: surya-tr@yahoo.com; Singh, Gurinder; Kaura, Aman

    2016-05-06

    The atomic arrangements and chemical bonding of stable Ge{sub 4}Sb{sub 2}Te{sub 7} (GeTe rich), a phase-change material, have been investigated by means of ab initio total energy calculations. To study the atomic arrangement, GeTe block is considered into -TeSbTeSbTe- block and -Te-Te- layer in the stacking I and II respectively. The stacking I is energetically more stable than the stacking II. The reason for more stability of the stacking I has been explained. The chemical bonding has been studied with the electronic charge density distribution around the atomic bonds. The quantity of electronic charge loosed or gained by atoms has been calculated using the Bader charge analysis. The metallic character has been studied using band structures calculations. The band gap for the stacking I and II is 0.463 and 0.219 eV respectively.

  12. Ferrimagnetic Co1+δ Te nanostructures

    NASA Astrophysics Data System (ADS)

    Dahal, Bishnu R.; Dulal, Rajendra P.; Pegg, Ian L.; Philip, John

    2016-11-01

    Transition metal telluride, Co1+δ Te nanostructures are synthesized using the hydrothermal method. These nanostructures exhibit filled NiAs-type hexagonal crystal structure also known as Ni2In structure with the space group p63/mmc. The Co1+ δ Te nanostructures exhibit hard ferrimagnetic behavior below 40 K. The coercivity increases with the decrease in temperature, which is around 4.90 kOe at 3 K. The saturation magnetization is 0.6 μ B/Co atom. Electrical transport measurements show that the Co1+ δ Te nanostructures are nonmetallic in nature with the resistance increases with the decrease in temperature. It does not follow the thermal excitation law for semiconductors, but can be explained by the Motts three-dimensional variable range hopping model.

  13. Microstructural characterization of sulfur-doped Bi{sub 2}Te{sub 3} crystals

    SciTech Connect

    Liang, Chaolun; Liu, Lin; Li, Hui; Qian, Dong; Liu, Canhua; Jia, Jinfeng; Chen, Jian

    2016-04-15

    In this study, the detailed microstructure of sulfur-doped Bi{sub 2}Te{sub 3} and the distribution of sulfur dopants were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD result indicates that the interplanar distances of Bi{sub 2}Te{sub 3} are shortened after introducing sulfur dopants. HRTEM reveals that the unit cell lengths along [001, 100] are decreased as a result of the substitution of Te by smaller S atoms on the anion lattice. XRD and HRTEM analysis suggest that the distortion of the crystal lattice in Bi{sub 2}Te{sub 3} is induced by doping sulfur. High annular angler dark field scanning electron microscopy (HAADF-STEM) image shows obvious contrast variations in the Te atomic columns, indicating that Te sites were unevenly substituted by S dopants. Te columns with least contrast intensity correspond to the preferential occupation sites of S atoms. The replacement of Te atoms by S can be attributed to the evaporated sulfur powder in the gas reaction procedure. The present work is not only contributed to obtain a better understanding of the distribution of sulfur dopants introduced by gas reaction, but also can help explore the structural-property relationship of sulfur-doped Bi{sub 2}Te{sub 3}. - Highlights: • Sulfur-doped Bi{sub 2}Te{sub 3} was synthesized through modified Bridgeman method. • The introduction of S dopants results in shortening the lattice spacing of Bi{sub 2}Te{sub 3}. • HRTEM analysis indicates that S was doped through substituting Te atoms instead of incorporating interstitially. • HAADF-STEM analysis shows that Te columns with least intensity correspond to the preferential occupation sites of S.

  14. Remarkable metal-rich ternary chalcogenides Sc14M3Te8 (M = Ru, Os).

    PubMed

    Chen, Ling; Corbett, John D

    2003-02-05

    In this novel motif, scandium atoms define infinite parallel chains of alternate trans-face-sharing cubes and pairs of square antiprisms in which each polyhedron is also centered by an M atom (M = Ru, Os). These chains are further linked into a three-dimensional structure by Sc(Te2Te4/2) octahedra. Physical property measurements show Sc14Ru3Te8 to be metallic and Pauli-paramagnetic, consistent with the results of extended Hückel band structure calculations. Matrix effects are evident in the dimensions within the chains. The major interactions are Sc-M and Sc-Te.

  15. 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.

  16. 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.

  17. Te-Te and Te-C bond cleavage reactions using a monovalent gallanediyl.

    PubMed

    Ganesamoorthy, Chelladurai; Bendt, Georg; Bläser, Dieter; Wölper, Christoph; Schulz, Stephan

    2015-03-21

    LGa (L = [(2,6-i-Pr2-C6H3)NC(Me)]2CH) reacts with elemental tellurium with formation of the Te-bridged compound [LGa-μ-Te]2 1, whereas the reactions with Ph2Te2 and i-Pr2Te occurred with cleavage of the Te-Te and Te-C bond, respectively, and subsequent formation of LGa(TePh)2 2 and LGa(i-Pr)Tei-Pr 3. 1-3 were characterized by heteronuclear NMR ((1)H, (13)C, (125)Te) and IR spectroscopy and their solid state structures were determined by single crystal X-ray analyses.

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

    DOE PAGES

    Li, Chen; Paudel, Naba R.; Yan, Yanfa; ...

    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

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

    PubMed

    Wang, Peng Li; Mozharivskyj, Yurij

    2013-06-01

    Single crystals of deca-lanthanum(III) dodeca-oxotellurate(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 Te(IV) atoms filling the inter-stitial sites. The Te(IV) 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 Te(IV) 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.

  20. New μ-SnTe4 and μ-Sn2Te6 ligands to transition metal: Solvothermal syntheses and characterizations of zinc tellurostannates containing polyamine ligands

    NASA Astrophysics Data System (ADS)

    Lu, Jialin; Wang, Fang; Shen, Yali; Tang, Chunying; Zhang, Yong; Jia, Dingxian

    2014-08-01

    Zinc tellurostannates [{Zn(teta)}2(μ-1κ:2κ-SnTe4)] (1), [{Zn(teta)}3(μ3-1κ:2κ:3κ-SnTe4)]I2 (2), [{Zn(tren)}2(μ-1κ:2κ-Sn2Te6)] (3), and [Zn(dien)2]4(Sn2Te6)1.75(Sn2Te8)0.25·dien (4) were prepared by the reactions of Zn, Sn, and Te with iodine ion assistant in teta and dien. The tetrahedral [SnTe4]4- anion coordinates to two [Zn(teta)]2+ units as a bidentate μ-1κ:2κ-SnTe4 ligand to form the neutral complex 1. It coordinates to three [Zn(teta)]2+ units with a tridentate μ3-1κ:2κ:3κ coordination modes, generating a complex cation [{Zn(teta)}3(μ3-1κ:2κ:3κ- SnTe4)]2+ in 2. In 3, the [Sn2Te6]4- anion joins two [Zn(tren)]2+cations with the trans terminal Te atoms, forming neutral complex 3. The μ-1κ:2κ-SnTe4, μ3-1κ:2κ:3κ-SnTe4, and μ-1κ:2κ-Sn2Te6 ligands to TM centers in 1-3 have not been observed before. Compound 4 contains a normal [Sn2Te6]4- and an abnormal [(Sn2Te6)0.75(Sn2Te8)0.25]4- anions. Compounds 1-4 exhibit narrow band gaps in the range of 1.47-1.98 eV, and a distinct red-shift of the band gaps is observed from 4 to 1-3.

  1. Knowledge Extraction from Atomically Resolved Images.

    PubMed

    Vlcek, Lukas; Maksov, Artem; Pan, Minghu; Vasudevan, Rama K; Kalinin, Sergei V

    2017-10-03

    Tremendous strides in experimental capabilities of scanning transmission electron microscopy and scanning tunneling microscopy (STM) over the past 30 years made atomically resolved imaging routine. However, consistent integration and use of atomically resolved data with generative models is unavailable, so information on local thermodynamics and other microscopic driving forces encoded in the observed atomic configurations remains hidden. Here, we present a framework based on statistical distance minimization to consistently utilize the information available from atomic configurations obtained from an atomically resolved image and extract meaningful physical interaction parameters. We illustrate the applicability of the framework on an STM image of a FeSexTe1-x superconductor, with the segregation of the chalcogen atoms investigated using a nonideal interacting solid solution model. This universal method makes full use of the microscopic degrees of freedom sampled in an atomically resolved image and can be extended via Bayesian inference toward unbiased model selection with uncertainty quantification.

  2. 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.

  3. Sur le ternaire Tl sbnd Ge sbnd Te: Etude structurale de la phase Tl 2GeTe 5

    NASA Astrophysics Data System (ADS)

    Toure, Abdoulaye Abba; Kra, Gabrielle; Eholie, Rose; Olivier-Fourcade, Josette; Jumas, Jean-Claude; Maurin, Maurice

    1990-02-01

    Tl 2GeTe 5 is orthorhombic, space group Cmmm, with cell dimensions a = 11.657 (5), b = 11.657 (5), c = 14.917 (5), AandZ = 8. The crystal structure was determined by means of direct methods based on three-dimensional X-ray data. Atomic parameters were refined by a least-squares method to a final R value of 0.077 (507 observed reflexions). The structure can be described in terms of layers parallel to the [001] plane and characterized by (Ge 2Te 6) 4- anions and Te 4 clusters.

  4. Photoluminescence of ZnS 1-xSex:Te Prepared by Solution Growth Using Sb-Chalcogenides as Solvent

    NASA Astrophysics Data System (ADS)

    Araki, Hiroyuki; Kanie, Hisashi; Sano, Masatoshi

    1995-06-01

    Photoluminescences due to Te isoelectronic traps were investigated for Te-doped ZnS1-xSex crystals (0 ≤x ≤1) grown from Sb-chalcogenide solutions. The optical depths of the isolated Te atom center and the nearest-neighbor Te Te pair center were determined from the emission spectra and the excitation spectra at 77 K. These depths decreased monotonically with increasing Se composition x. The theoretical relation between the optical depth and the composition x on the basis of the Koster-Slater one-band one-site approximation was best fitted to the experimental data by assuming the values of the matrix element of the impurity potential J ZnS:Te = 2.41 eV, J ZnSe:Te = 1.27 eV, and the effective width of the valence band T ZnS = 6.02 eV, T ZnSe = 6.21 eV. According to the criteria in the theory, excitons bound to the isolated Te atoms exist in ZnS1-xSex:Te for 0 ≤x < 0.85 and excitons bound to the Te Te pairs exist throughout the entire composition range. The emission band observed at 2.61 eV in ZnSe:Te was shown to be due to the excitons bound to the Te Te pairs.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  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. 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

    2016-09-02

    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.

  11. 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.

  12. Structure of Se-Te glasses studied using neutron, X-ray diffraction and reverse Monte Carlo modelling

    NASA Astrophysics Data System (ADS)

    Itoh, Keiji

    2017-02-01

    Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on Se100-xTex bulk glasses with x=10, 20, 30 and 40. The coordination numbers obtained from the diffraction results demonstrate that Se and Te atoms are twofold coordinated and the glass structure is formed by the chain network. The three-dimensional structure model for Se60Te40 glass obtained by using reverse Monte Carlo modelling shows that the alternating arrangements of Se and Te atoms compose the major part of the chain clusters but several other fragments such as Sen chains and Te-Te dimers are also present in large numbers. The chain clusters have geometrically disordered forms and the interchain atomic order is different from those in the crystal structures of trigonal Se and trigonal Te.

  13. 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.

  14. Electrical and Optical Properties of ZnS:Sb, Te Grown from Sb0.4Te0.6 Solution

    NASA Astrophysics Data System (ADS)

    Nagano, Masahiro; Kanie, Hisashi; Yoshida, Iwao; Sano, Masatoshi; Aoki, Masaharu

    1992-04-01

    ZnS crystals doped with Sb and Te were grown from an Sb0.4Te0.6 solution by means of a temperature-difference method. The grown crystals were transparent and platelike with a cubic structure. The Te concentration in the grown crystals varied from 0.10 atom% to 0.20 atom% as the growth temperature rose from 700°C to 1000°C, whereas the Sb concentration was 0.01 atom% in the entire range of growth temperature. All the crystals showed n-type conduction. The resistivity of the crystals grown at 700°C was 104 Ω\\cdotcm. They showed blue luminescence at room temperature. The emission intensity was higher than that of ZnS:Te.

  15. 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)

  16. 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)

  17. 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)

  18. 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)

  19. Dirac's HdCdTe semimetals grown by MBE technology

    NASA Astrophysics Data System (ADS)

    Grendysa, Jakub; Becker, Charles R.; Trzyna, Malgorzata; Wojnarowska-Nowak, Renata; Bobko, Ewa; Sheregii, Eugen M.

    2016-12-01

    Peculiarities of the MBE growth technology for the Dirac's semimetal based on the Hg1-xCdxTe alloys have been presented. Composition of layers was controlled by ToF-SIMS, FTIR measurements, and by the E1+Δ1 maximum position of optical reflectivity in visible reason. The surface morphology has by determined via atomic force and electron microscopy.

  20. Why pressure induces an abrupt structural rearrangement in PdTe{sub 2} but not in PtTe{sub 2}

    SciTech Connect

    Soulard, C.; Petit, P.E.; Deniard, P.; Evain, M.; Jobic, S. . E-mail: stephane.jobic@cnrs-imn.fr; Whangbo, M.-H.; Dhaussy, A.-C.

    2005-06-15

    High-pressure X-ray diffraction measurements were carried out for polymeric CdI{sub 2}-type compounds MTe{sub 2} (M=Pt, Pd) to investigate if they undergo a structural phase transition under pressure as does IrTe{sub 2}. Up to 27GPa at room temperature PtTe{sub 2} does not undergo any structural phase transition. In contrast, however, an abrupt change in the inter-atomic distances occurs in PdTe{sub 2} above 15.7GPa at room temperature, and above 5GPa at 300 deg. C, but the volume vs. pressure curve exhibits no discontinuity. To account for the differences between the isostructural compounds PtTe{sub 2}, PdTe{sub 2} and IrTe{sub 2}, their electronic structures and bonding were analyzed on the basis of first principles electronic band structure calculations.

  1. Local Bonding Arrangements in Amorphous Ge2Sb2Te5: The Importance of GE and TE Bonding

    DTIC Science & Technology

    2006-12-01

    total constraints around the Sb atoms to be 4.5. Table 1 indicates overcoordination of Te, which is supported by the following bond-counting exercise ...Sayers, F.W. Lytle, and E.A. Stern, Phys. Rev. B., 11, 4836 (1975). 4. A.V. Kolobov, P. Fons, A.I. Frenkel , A.L. Ankudinov, J. Tominaga, T. Uruga

  2. 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.

  3. 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)].

  4. 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].

  5. Surface Texture and Crystallinity Variation of ZnTe Epilayers Grown on the Step-Terrace Structure of the Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Nakasu, Taizo; Kizu, Takeru; Yamashita, Sotaro; Aiba, Takayuki; Hattori, Shota; Sun, Wei-Che; Taguri, Kosuke; Kazami, Fukino; Hashimoto, Yuki; Ozaki, Shun; Kobayashi, Masakazu; Asahi, Toshiaki

    2016-04-01

    ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. A sapphire substrate possessing an atomically-smooth step-terrace structure was used to improve the crystallinity and morphology of the produced ZnTe film. The growth mode of the ZnTe thin film on a sapphire substrate with an atomically-smooth step-terrace structure was found to shift to a two-dimensional growth mode, and a ZnTe thin film possessing a flat surface was obtained. The crystallographic properties of the ZnTe film suggested that the resulting layer consisted of a single (111)-oriented domain. The photoluminescence property was also improved, and the interface lattice alignment between the ZnTe and sapphire was also affected by the atomically-smooth step-terrace structure.

  6. 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?

  7. 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?

  8. 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?

  9. 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

  10. 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.

  11. 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.

  12. Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy.

    PubMed

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

    2015-02-01

    The reconstructed surface structure of the II-VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III-V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn-Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

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

    SciTech Connect

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

    2016-07-25

    We investigated the stability and electronic properties of defects in CdTe 1- 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 CdTe 1- xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

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

    SciTech Connect

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

    2016-07-25

    We investigated the stability and electronic properties of defects in CdTe{sub 1−x}S{sub x} 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, V{sub Cd}, and Te on Cd antisite, Te{sub Cd}, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of V{sub Cd} and Te{sub Cd} 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 CdTe{sub 1−x}S{sub x} increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

  15. [Transluminal esophagoplasty (TE)].

    PubMed

    Simonetti, G; Meloni, G B; Urigo, F; Canalis, G C; Tomiselli, A; Trignano, M; Bresadola, F

    1985-10-01

    The authors analyze their experience on 9 cases of esophageal stenosis dilated by "Grüntzig" type balloon catheter under fluoroscopic examination (transluminal esophagus plastica: TE). This procedure also allows dilatation of severe narrowing, offering distinct advantages represented by: low risk, easy performance, good tolerance, reduction or disappearance of disphagia. Esophageal perforation is possible, though it never appeared in author's experience.

  16. High-frequency electromechanical resonators based on thin GaTe

    NASA Astrophysics Data System (ADS)

    Chitara, Basant; Ya’akobovitz, Assaf

    2017-10-01

    Gallium telluride (GaTe) is a layered material, which exhibits a direct bandgap (∼1.65 eV) regardless of its thickness and therefore holds great potential for integration as a core element in stretchable optomechanical and optoelectronic devices. Here, we characterize and demonstrate the elastic properties and electromechanical resonators of suspended thin GaTe nanodrums. We used atomic force microscopy to extract the Young’s modulus of GaTe (average value ∼39 GPa) and to predict the resonance frequencies of suspended GaTe nanodrums of various geometries. Electromechanical resonators fabricated from suspended GaTe revealed fundamental resonance frequencies in the range of 10–25 MHz, which closely match predicted values. Therefore, this study paves the way for creating a new generation of GaTe based nanoelectromechanical devices with a direct bandgap vibrating element, which can serve as optomechanical sensors and actuators.

  17. Characterization of CdTe films deposited at various bath temperatures and concentrations using electrophoretic deposition.

    PubMed

    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.

  18. 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

  19. High-frequency electromechanical resonators based on thin GaTe.

    PubMed

    Chitara, Basant; Ya'akobovitz, Assaf

    2017-10-20

    Gallium telluride (GaTe) is a layered material, which exhibits a direct bandgap (∼1.65 eV) regardless of its thickness and therefore holds great potential for integration as a core element in stretchable optomechanical and optoelectronic devices. Here, we characterize and demonstrate the elastic properties and electromechanical resonators of suspended thin GaTe nanodrums. We used atomic force microscopy to extract the Young's modulus of GaTe (average value ∼39 GPa) and to predict the resonance frequencies of suspended GaTe nanodrums of various geometries. Electromechanical resonators fabricated from suspended GaTe revealed fundamental resonance frequencies in the range of 10-25 MHz, which closely match predicted values. Therefore, this study paves the way for creating a new generation of GaTe based nanoelectromechanical devices with a direct bandgap vibrating element, which can serve as optomechanical sensors and actuators.

  20. Fabrication of CdTe quantum dots-apoferritin arrays for detection of dopamine

    NASA Astrophysics Data System (ADS)

    Le, Thi Hoa; Kim, Ji Hyeon; Park, Sang Joon

    2017-06-01

    A method was proposed for detecting dopamine using a two-dimensional CdTe quantum dots (QDs)-apoferritin array fabricated on a modified silicon (Si) surface. First, CdTe QDs were synthesized in the cavity of horse spleen apoferritin (HsAFr). Then, the characterization of CdTe QDs in apoferritin was performed using photoluminescence (PL) spectroscopy. Transmission electron microscopy was used to analyze the size and structure of CdTe QDs. An atomic force microscopy image was obtained to evaluate the topography of the Si surface. In addition, the PL change resulting from the conjugation reaction of the CdTe QDs-apoferritin array with dopamine was investigated. When the array was linked to dopamine, a significant quenching of fluorescence was observed. Accordingly, the CdTe QDs-apoferritin arrays could be employed as useful sensing media for dopamine detection.

  1. Pressure-induced disordered substitution alloy in Sb2Te3.

    PubMed

    Zhao, Jinggeng; Liu, Haozhe; Ehm, Lars; Chen, Zhiqiang; Sinogeikin, Stanislav; Zhao, Yusheng; Gu, Genda

    2011-11-21

    A new type of disordered substitution alloy of Sb and Te at above 15.1 GPa was discovered by performing in situ high-pressure angle-dispersive X-ray diffraction experiments on antimony telluride (Sb(2)Te(3)), a topological insulator and thermoelectric material, at room temperature. In this disordered substitution alloy, Sb(2)Te(3) crystallizes into a monoclinic structure with the space group C2/m, which is different from the corresponding high-pressure phase of the similar isostructural compound Bi(2)Te(3). Above 19.8 GPa, Sb(2)Te(3) adopts a body-centered-cubic structure with the disordered atomic array in the crystal lattice. The in situ high-pressure experiments down to about 13 K show that Sb(2)Te(3) undergoes the same phase-transition sequence with increasing pressure at low temperature, with almost the same phase-transition pressures.

  2. 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.

  3. Phase stability and lattice thermal conductivity reduction in CoSb{sub 3} skutterudites, doped with chalcogen atoms

    SciTech Connect

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

    2016-07-15

    We report a significant reduction in the lattice thermal conductivity of the CoSb{sub 3} skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb{sub 3} skutterudite samples (Te{sub 0.1}Co{sub 4}Sb{sub 12}, Se{sub 0.1}Co{sub 4}Sb{sub 12}, Te{sub 0.05}Se{sub 0.05}Co{sub 4}Sb{sub 12}) 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 CoSb{sub 3} 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 CoSb{sub 3} 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 CoSb{sub 3} 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 CoSb{sub 3} skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ∼ 0.9 W/mK at 773 K is achieved in Te{sub 0.1}Co{sub 4}Sb{sub 12} skutterudites, which is the lowest value reported so far in CoSb{sub 3} skutterudites, doped with single Te chalcogen atom.

  4. 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.

  5. 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.

  6. Bis(μ-phenyl­tellurido-κ2 Te:Te)bis­[tetra­carbonyl­rhenium(I)

    PubMed Central

    Muthukumaran, J.; Kannan, M.; Vanitha, A.; Manimaran, Bala; Krishna, R.

    2010-01-01

    The title compound, [Re2(C6H5Te)2(CO)8], crystallizes with two mol­ecules in the asymmetric unit, in which two Re atoms are coordinated in a slightly distorted octa­hedral environment and are bridged by two Te atoms, which show a distorted trigonal-pyramidal geometry. The torsion angles for the Te—Re—Te—Re sequence of atoms are 19.29 (18) and 16.54 (16)° in the two mol­ecules. Thus, the Re—Te four-membered rings in the two mol­ecules deviate significantly from planarity. Two intra­molecular C—H⋯O inter­actions occur in one of the mol­ecules. Te—Te [4.0551 (10) Å] inter­actions between the two mol­ecules and weak inter­molecular C—H⋯O inter­actions stabilize the crystal packing. PMID:21579041

  7. Superconductivitiy in CuxNbTe4

    NASA Astrophysics Data System (ADS)

    de Lima, Bruno; Dos Santos, Carlos; Machado, Antonio Jefferson

    2014-03-01

    Layered transition metal dichalcogenides normally named TMDC's of the type MX2 (M is transition metal, X = S, Se, Te) have been extensively studied for their rich electronic properties due to low dimensionality. In these MX2 materials each layer correspond to the transition metal intercalated by two similar chalcogen sheets and the interaction between MX2 layers is weak as van der Walls bonding between chalcogen element (X). In general charge density wave (CDW) and superconductivity coexist in these kinds of materials. Indeed, various compounds of this material class exhibits this coexistence such as 2H-TaS2 2H-NbS2, 2H-NbSe2 etc. Within this scenario, NbTe4 is well known as a layered compound which also display CDW instability at room temperature. In this work we show a systematic study of copper intercalation between van der Walls gap of the Te atoms. Our results show unambiguously that the copper intercalation is able to induce superconductivity with superconducting critical temperature close to 8.0 K. This work was financed by the Brazilian agencies CNPq (grant no. 142016/2013-6) and FAPESP (grant no. 2010/11770-3).

  8. 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.

  9. Ultracold plasmas and guiding center drift atoms

    NASA Astrophysics Data System (ADS)

    Kuzmin, Stanislav Gennadyevich

    This thesis discusses theory questions suggested by recent experiments with ultracold plasmas. In one class of experiments, ultracold plasmas are produced by abruptly photoionizing small clouds of laser cooled atoms, adjusting the photon energy to barely exceed the ionization energy of the cooled atoms. The thesis presents molecular dynamics simulation for the early time evolution of such plasmas. Contrary to earlier speculation, no evidence of strong electron-electron correlations is observed in the simulations even if the initial value of the coupling parameter (Gammae = e2/akTe) is much larger than unity. As electron-electron correlations begin to develop, the correlation energy is released to heat the electrons, raising the electron temperature to the point where Gammae ˜ 1 and limiting further development of correlation. Further heating of the electrons occurs as a by-product of three-body recombination. When a model of laser cooling is added to the simulation, the formation of strong ion-ion correlation is observed. Contrary to earlier suggestion, the rate of three-body recombination is observed to be in reasonable agreement with the traditional formula, R = 3.9 x 10-9 sec-1[ n (cm-3)]2 [Te(° K)]-9/2, but care must be taken to use the correct temporally evolving temperature, Te. Also, the thesis describes the novel dynamics of "guiding center drift atoms". The weakly bound and strongly magnetized antihydrogen atoms recently produced in ultracold plasmas at CERN are examples of such atoms. The atoms are quasi-classical, and the dynamics of the positron is well described by guiding center drift theory. Because of a frequency ordering, the dynamics is integrable, and the thesis characterizes the possible motions of the weakly bound positron-antiproton pair as a function of constants of the motion. Quantum numbers are assigned using the Bohr-Sommerfeld prescription. The thesis also discusses the center of mass motion of the atoms in an electric and magnetic

  10. Atomic Databases

    NASA Astrophysics Data System (ADS)

    Mendoza, Claudio

    2000-10-01

    Atomic and molecular data are required in a variety of fields ranging from the traditional astronomy, atmospherics and fusion research to fast growing technologies such as lasers, lighting, low-temperature plasmas, plasma assisted etching and radiotherapy. In this context, there are some research groups, both theoretical and experimental, scattered round the world that attend to most of this data demand, but the implementation of atomic databases has grown independently out of sheer necessity. In some cases the latter has been associated with the data production process or with data centers involved in data collection and evaluation; but sometimes it has been the result of individual initiatives that have been quite successful. In any case, the development and maintenance of atomic databases call for a number of skills and an entrepreneurial spirit that are not usually associated with most physics researchers. In the present report we present some of the highlights in this area in the past five years and discuss what we think are some of the main issues that have to be addressed.

  11. Crystal chemistry peculiarities of Cs{sub 2}Te{sub 4}O{sub 12}

    SciTech Connect

    Hamani, David; Mirgorodsky, Andrei; Masson, Olivier; Merle-Mejean, Therese; Colas, Maggy; Smirnov, Mikhael; Thomas, Philippe

    2011-03-15

    The Raman and IR-absorption spectra of the Cs{sub 2}Te{sub 4}O{sub 12} lattice are first recorded and interpreted. Extraordinary features observed in the structure and Raman spectra of Cs{sub 2}Te{sub 4}O{sub 12} are analyzed by using ab initio and lattice-dynamical model calculations. This compound is specified as a caesium-tellurium tellurate Cs{sub 2}Te{sup IV}(Te{sup VI}O{sub 4}){sub 3} in which Te{sup IV} atoms transfer their 5p electrons to [Te{sup VI}O{sub 4}]{sub 3}{sup 6-} tellurate anions, thus fulfilling (jointly with Cs atoms) the role of cations. The Te{sup VI}-O-Te{sup VI} bridge vibration Raman intensity is found abnormally weak, which is reproduced by model treatment including the Cs{sup +} ion polarizability properties in consideration. -- Graphical abstract: Two versions of the BPM estimations of the Raman intensity for the Cs{sub 2}Te{sub 4}O{sub 12} lattice vibrations: (a) without including effects of the Cs-O bonds and (b) including the above mentioned effects. Experimentally observed peaks are characterized by their frequency positions. Display Omitted Research highlights: > Extraordinary features observed in the structure and Raman spectra of Cs{sub 2}Te{sub 4}O{sub 12}. > Ab initio and lattice-dynamical model calculations. > Abnormally weak Raman intensities of the symmetric Te{sup VI}-O-Te{sup VI} bridge. > The monovalent Cs{sup +} cations profoundly influence the polarizability properties.

  12. 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.

  13. Ion implantation and SIMS profiling of impurities in II-VI materials (HgCdTe and CdTe)

    NASA Astrophysics Data System (ADS)

    Wilson, R. G.

    1990-01-01

    Ions from throughout the periodic table have been implanted into HgCdTe and CdTe under a variety of conditions, and the resulting atom depth distributions measured using oxygen and cesium secondary-ion mass spectrometry (SIMS). Many of these ions were implanted in the <110> crystal direction as well as in a random orientation close to <111>. Most of the HgCdTe material implanted was solid-state-recrystallized bulk Hg 1- xCd xTe ( x = 0.19 to 0.35) thermally processed at 350°C for 3 or 4 weeks (device-quality material) and etched prior to implantation. Ions from H to Ta were implanted at energies from 100 to 700 keV and fluences from 10 13 to 3x10 15 cm -2. Both oxygen and cesium SIMS techniques were studied and developed. Many of the implanted elements were profiled using both oxygen and cesium SIMS. Implant profiles and determinations of range and range straggle versus atomic number ( Z1) of the elements implanted in a random (111) orientation and in some cases, profile moments determined from a Pearson IV computer-fitting routine are illustrated. Profiles for <110> channeled implantations and the deeper channeled ranges and impurity densities achievable in the deep <110> channeled regions are shown. Determinations of the electronic stopping Se and its Z1-dependent nature (oscillations) are described in the channeling range as a function of Z1. The SIMS technology developed for this work is discussed. SIMS sensitivity factors for HgCdTe and CdTe are shown to be the same within experimental accuracy (relative to Te).

  14. 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

  15. 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.

  16. Impact of ⁷⁷Te on the structure and Se NMR spectra of Se-rich Ge-Te-Se glasses: a combined experimental and computational investigation.

    PubMed

    Bouëssel du Bourg, Lila; Roiland, Claire; le Pollès, Laurent; Deschamps, Michaël; Boussard-Plédel, Catherine; Bureau, Bruno; Pickard, Chris J; Furet, Eric

    2015-11-21

    Selenium-rich Ge-Te-Se glasses have been synthesized along the GeSe4-GeTe4 pseudo-composition line and acquired by (77)Se Hahn echo magic-angle spinning NMR. The comparison with the GeSe4 spectrum shows a drastic modification of the typical double-resonance lineshape even at low Te concentrations (<10%). In order to rationalize this feature and to understand the effect of Te on the structure of our glasses, first-principles molecular dynamics simulations and gauge including projector augmented wave NMR parameter calculations have been performed. The distribution of the tellurium atoms in the selenium phase was shown to be mainly responsible for the (77)Se lineshape changes. Another possible factor related to the perturbation of the δiso value due to Te proximity appears to be much more limited in the bulk, while the results obtained using molecular models suggest shifts of several hundreds of ppm.

  17. EDITORIAL: Atomic layer deposition Atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Godlewski, Marek

    2012-07-01

    The growth method of atomic layer deposition (ALD) was introduced in Finland by Suntola under the name of atomic layer epitaxy (ALE). The method was originally used for deposition of thin films of sulphides (ZnS, CaS, SrS) activated with manganese or rare-earth ions. Such films were grown for applications in thin-film electroluminescence (TFEL) displays. The ALE mode of growth was also tested in the case of molecular beam epitaxy. Films grown by ALD are commonly polycrystalline or even amorphous. Thus, the name ALE has been replaced by ALD. In the 80s ALD was developed mostly in Finland and neighboring Baltic countries. Deposition of a range of different materials was demonstrated at that time, including II-VI semiconductors (e.g. CdTe, CdS) and III-V (e.g. GaAs, GaN), with possible applications in e.g. photovoltaics. The number of publications on ALD was slowly increasing, approaching about 100 each year. A real boom in interest came with the development of deposition methods of thin films of high-k dielectrics. This research was motivated by a high leakage current in field-effect transistors with SiO2-based gate dielectrics. In 2007 Intel introduced a new generation of integrated circuits (ICs) with thin films of HfO2 used as gate isolating layers. In these and subsequent ICs, films of HfO2 are deposited by the ALD method. This is due to their unique properties. The introduction of ALD to the electronics industry led to a booming interest in the ALD growth method, with the number of publications increasing rapidly to well above 1000 each year. A number of new applications were proposed, as reflected in this special issue of Semiconductor Science and Technology. The included articles cover a wide range of possible applications—in microelectronics, transparent electronics, optoelectronics, photovoltaics and spintronics. Research papers and reviews on the basics of ALD growth are also included, reflecting a growing interest in precursor chemistry and growth

  18. 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.

  19. First-principles calculation of lattice thermal conductivity in crystalline phase change materials: GeTe, Sb2Te3 , and Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Campi, Davide; Paulatto, Lorenzo; Fugallo, Giorgia; Mauri, Francesco; Bernasconi, Marco

    2017-01-01

    Thermal transport is a key feature for the operation of phase change memory devices which rest on a fast and reversible transformation between the crystalline and amorphous phases of chalcogenide alloys upon Joule heating. In this paper we report on the ab initio calculations of bulk thermal conductivity of the prototypical phase change compounds Ge2Sb2Te5 and GeTe in their crystalline form. The related Sb2Te3 compound is also investigated for the sake of comparison. Thermal conductivity is obtained from the solution of the Boltzmann transport equation with phonon scattering rates computed within density functional perturbation theory. The calculations show that the large spread in the experimental data on the lattice thermal conductivity of GeTe is due to a variable content of Ge vacancies which at concentrations realized experimentally can halve the bulk thermal conductivity with respect to the ideal crystal. We show that the very low thermal conductivity of hexagonal Ge2Sb2Te5 of about 0.45 Wm -1K-1 measured experimentally is also resulting from disorder in the form of a random distribution of Ge/Sb atoms in one sublattice.

  20. Exploring Resonance Levels and Nanostructuring in the PbTe-CdTe System and Enhancement of the Thermoelectric Figure of Merit

    SciTech Connect

    Ahn, Kyunghan; Han, Mi-Kyung; He, Jiaqing; Androulakis, John; Ballikaya, Sedat; Uher, Ctirad; Dravid, Vinayak; Kanatzidis, Mercouri G.

    2010-04-14

    We explored the effect of Cd substitution on the thermoelectric properties of PbTe in an effort to test a theoretical hypothesis that Cd atoms on Pb sites of the rock salt lattice can increase the Seebeck coefficient via the formation of a resonance level in the density of states near the Fermi energy. We find that the solubility of Cd is less than previously reported, and CdTe precipitation occurs to create nanostructuring, which strongly suppresses the lattice thermal conductivity. We present detailed characterization including structural and spectroscopic data, transmission electron microscopy, and thermoelectric transport properties of samples of PbTe-x% CdTe-0.055% PbI2 (x = 1, 3, 5, 7, 10), PbTe-1% CdTe-y% PbI2 (y = 0.03, 0.045, 0.055, 0.08, 0.1, 0.2), PbTe-5% CdTe-y% PbI2 (y = 0.01, 0.03, 0.055, 0.08), and PbTe-1% CdTe-z% Sb (z = 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6). All samples follow the Pisarenko relationship, and no enhancement of the Seebeck coefficient was observed that could be attributed to a resonance level or a distortion in the density of states. A maximum ZT of 1.2 at 720 K was achieved for the PbTe-1% CdTe-0.055% PbI2 sample arising from a high power factor of 17 μW/(cm K2) and a very low lattice thermal conductivity of 0.5 W/(m K) at 720 K.

  1. Revisiting the Si-Te System: SiTe2 Finally Found by Means of Experimental and Quantum-Chemical Techniques.

    PubMed

    Göbgen, Kai C; Steinberg, Simon; Dronskowski, Richard

    2017-08-28

    Through explorations of the silicon-tellurium system we identified the extremely air-sensitive, red Si1.67(4)Te3≡Si1.11(3)Te2 that is a silicon-deficient relative of the previously reported Si2Te3. The crystal structure features hexagonal closest packed layers of tellurium atoms with disordered [Si2] dumbbells residing in about 50% of the octahedra of every second layer enclosed by the tellurium atoms. In addition to the determination of the crystal structure for this silicon telluride, we probed the opportunity of the existence of a SiTe2 adopting the Si2Te3-structure by means of quantum chemical techniques. The investigations of the electronic structures and a subsequent chemical bonding analysis based on the projected Crystal Orbital Hamilton Population (pCOHP) technique for two "SiTe2" models revealed a tendency to align the [Si2] dumbbells parallel to the c axis to maximize Si-Te bonding. However, the disorder of the [Si2] dumbbells appears to be a consequence of non-equilibrium condensation into the solid state.

  2. 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.

  3. Internal conversion to bound final states in 125Te

    NASA Astrophysics Data System (ADS)

    Harston, M. R.; Carreyre, T.; Chemin, J. F.; Karpeshin, F.; Trzhaskovskaya, M. B.

    2000-08-01

    Theoretical results are presented for rate of decay of the 3/2+ isomeric nuclear state of 125Te by excitation of atomic electrons to bound states in the ions Te 45+ and Te 46+. In these ions the nuclear transition energy lies just below the threshold for emission of a K-shell electron to the continuum with the result that normal K-shell internal conversion is energetically forbidden. However recent experimental results indicate that excitation of K-shell electrons is still significant in these ions. The theoretical results presented here for internal conversion to bound final states are in quantitative agreement with experiment and thereby confirm the contribution of near-resonant electron-nucleus transitions involving a bound final state.

  4. Crystal structure and physical properties of the new chalcogenides Ba3Cu(17-x)(S,Te)11 and Ba3Cu(17-x)(S,Te)11.5 with two different Cu clusters.

    PubMed

    Kuropatwa, Bryan A; Assoud, Abdeljalil; Kleinke, Holger

    2011-08-15

    The sulfide-tellurides Ba(3)Cu(17-x)(S,Te)(11) and Ba(3)Cu(17-x)(S,Te)(11.5) were synthesized from the elements in stoichiometric ratios heated to 1073 K, followed by slow cooling to 873 K over 100 h. Ba(3)Cu(17-x)(S,Te)(11) is isostructural to Ba(3)Cu(17-x)(Se,Te)(11) when [S] > [Te], space group R ̅3m, with lattice dimensions of a = 12.009(1) Å, c = 27.764(2) Å, V = 3467.6(5) Å(3), for Ba(3)Cu(15.7(4))S(7.051(5))Te(3.949) (Z = 6). The structure is composed of Cu atoms forming paired hexagonal antiprisms, capped on the two outer hexagonal faces, where each Cu atom is tetrahedrally coordinated by four Q (= S, Te) atoms. The new variant is formed when [Te] > [S]; then Ba(3)Cu(17-x)(S,Te)(11.5) adopts space group Fm3̅m with a = 17.2095(8) Å, V = 5096.9(4) Å(3), for Ba(3)Cu(15.6(2))S(5.33(4))Te(6.17) (Z = 8). This structure consists of eight Te-centered Cu(16) icosioctahedra per cell interconnected by cubic Cu(8) units centered by Q atoms. Electronic structure calculations and property measurements illustrate that these compounds behave as extrinsic p-type semiconductors-toward metallic behavior for the latter compound. With standard oxidation states Ba(2+), Cu(+), and Q(2-), the electron precise formulas are Ba(3)Cu(16)Q(11) and Ba(3)Cu(17)Q(11.5).

  5. Atomic memory

    NASA Astrophysics Data System (ADS)

    Brewer, R. G.; Hahn, E. L.

    1984-12-01

    The fundamental principles of atomic-memory effects related to the Loschmidt paradox in the second law of thermodynamics are introduced and illustrated with simple analogies, photographs, and diagrams; and the results of RF and laser experiments are summarized. Nuclear-spin echoes in response to RF pulses and the NMR free-induction decay phenomenon are described, and the extension of these concepts to the visible spectrum in laser-frequency-switching and multipulsed-laser experiments is examined with an emphasis on studies of free-induction decay in LaF3 crystals containing Pr impurities (DeVoe and Brewster). The laser-induced phenomena can be applied to studies of intramolecular and intermolecular interactions, and an improved understanding of the RF effects is needed to enhance the performance of medical NMR imaging systems.

  6. Atomic magnetometer

    DOEpatents

    Schwindt, Peter [Albuquerque, NM; Johnson, Cort N [Albuquerque, NM

    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.

  7. 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

  8. Phase transition in IrTe2 induced by spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Koley, S.

    2016-12-01

    IrTe2 has been renewed as an interesting system showing competing phenomenon between a questionable density-wave transition near 270 K followed by superconductivity with doping of high atomic number materials. Higher atomic numbers of Te and Ir supports strong spin-orbital coupling in this system. Using dynamical mean field theory with LDA band structure I have introduced Rashba spin orbit coupling in this system to get the interpretation for anomalous resistivity and related transition in this system. While no considerable changes are observed in DMFT results of Ir-5d band other than orbital selective pseudogap 'pinned' to Fermi level, Te-p band shows a van Hove singularity at the Fermi level except low temperature. Finally I discuss the implications of these results in theoretical understanding of ordering in IrTe2.

  9. Properties of Defects in Hg1-xCdxTe.

    DTIC Science & Technology

    1984-11-01

    Warsaw (Poland), 1977 (unpublished). ’C. C. Wang, M. Chu, S. H. Shin. W. E. Tennant, J. T. Cheung, M. Lanir. "J. Blakemore , Semiconductor Statistics ...of this important - "" alloy semiconductor system. One of the most important needs in the fundamental study of HgCdTe is the understanding of the...replaced by a Cd atom. Second, it has been observed that in 11-IV semiconductors which exhibit anion precipitation phenomena, high temperature post-anneals

  10. 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

  11. 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.

  12. 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.

  13. Crystal symmetry breaking in few quintuple Bi2Te3 nanosheets: applications in nanometrology of topological insulators and low-temperature thermoelectrics.

    PubMed

    Srivastava, Punita; Kumar, Pushpendra; Singh, Kedar

    2014-08-01

    Bismuth telluride (Bi2Te3) and its associated compounds are the best bulk thermoelectric (TE) materials known in present day. In addition, stacked two-dimensional (2D) layers of Bi2Te3 have attracted brawny interest due to topologically protected surface state property. The authors herein report results of micro-Raman spectroscopy study of the "graphene-like" crystalline Bi2Te3 nanosheets with a thickness of a few atoms (few-quintuples) synthesized by convenient solvothermal route which is chiefly attractive from physics point of view. It is investigated that the optical phonon mode A1u, which is not-Raman active in bulk Bi2Te3 crystals, appears in atomically-thin nanosheets due to crystal-symmetry breaking in few quintuples layers (FQLs) and can be used in nanometrology of topological insulators (TIs). It is also suggested that sheets thinning to FQLs and tuning of Fermi level can help in achieving TI surface transport regime with enhance thermoelectric power. From seebeck measurements, Bi2Te3 sample exhibit p-type conduction having higher TE power at low temperature (40 K). Thus, Bi2Te3 nanosheets with strong spatial confinement of charge carriers are beneficial for TE devices. The developed technology for producing 2D layers of -Te(1)-Bi-Te(2)-Bi-Te(1)- creates an thrust for exploration of TIs and their possibility in practical applications.

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

    PubMed

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

    2015-01-22

    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.

  15. 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.

  16. 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.

  17. Novel two-dimensional ferroelectric PbTe under tension: A first-principles prediction

    NASA Astrophysics Data System (ADS)

    Zhang, Xilin; Yang, Zongxian; Chen, Yue

    2017-08-01

    Enhanced ferroelectricity in two-dimensional (2D) SnTe exhibiting a higher transition temperature (Tc) than its bulk counterpart was recently discovered [Chang et al., Science 353(6296), 274-278 (2016)]. Herein, we report that nonferroelectric PbTe can be transformed into a ferroelectric phase by downsizing to two dimensions with suitable equi-biaxial tension. The crystal structure of the ferroelectric phase of 2D PbTe was determined using evolutionary algorithms and density functional theory. The dynamic stabilities of the predicted new phases were investigated using phonon calculations. To validate our results obtained using PbTe, we have also studied the ferroelectricity in GeTe and SnTe at the 2D level and compared them with the literature. The unequal lattice constants and the relative atomic displacements are found to be responsible for ferroelectricity in 2D GeTe, SnTe, and strained PbTe. This study facilitates the development of new 2D ferroelectrics via strain engineering and promotes the integration of ferroelectric devices.

  18. 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.

  19. Photoluminescence of vapor and solution grown ZnTe single crystals

    NASA Astrophysics Data System (ADS)

    Biao, Y.; Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.; Su, C.-H.; Volz, M. E.; Szofran, F. R.; Gillies, D. C.

    1994-04-01

    ZnTe single crystals grown by horizontal physical vapor transport (PVT) and by vertical traveling heater method (THM) from a Te solution were characterized by photoluminescence (PL) at 10.6 K and by atomic force microscopy (AFM). Copper was identified by PL as a major impurity existing in both crystals, forming a substitutional acceptor, Cu Zn. The THM ZnTe crystals were found to contain more Cu impurity than the PVT ZnTe crystals. The formation of Cu Zn-V Te complexes and the effects of annealing, oxygen contamination and intentional Cu doping were also studied. Finally, the surface morphology analyzed by AFM was correlated to the PL results.

  20. Mechanisms and Kinetics of Tellurium Precipitation in CdTe-based Materials

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo

    2012-02-01

    CdTe and related alloys are important materials for solar photovoltaic application as well as for high-resolution room-temperature gamma radiation detectors. However, the performance of devices, particularly in high-energy applications, is limited by various material defects. Among the most important defects are Te precipitates of various sizes caused by non-stoichiometric growth conditions. In this work, we study the kinetics of Te aggregation and precipitation at the atomic scale. Density functional theory is used to compute the energetics, migration rates, and binding energies of point defects involved in Te aggregation, which include various interstitials, vacancies, and anti-site defects. Kinetic Monte Carlo is then used to simulate the aggregation process leading to precipitation nuclei. The mechanisms and kinetics of formation of these Te-rich regions are analyzed for various conditions. Prepared by LLNL under Contract DE-AC52-07NA27344.

  1. 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.

  2. [Te8][NbOCl4]2 containing an infinite chain-like {[Te-Te-Te-(Te5)]2+}n polycation.

    PubMed

    Feldmann, Claus; Freudenmann, Dominic

    2012-10-01

    The title compound, [Te(8)][NbOCl(4)](2), was obtained as translucent black crystals by reaction of elemental tellurium, niobium(V) chloride and niobium(V) oxychloride in the ionic liquid BMImCl (BMImCl is 1-butyl-3-methylimidazolium chloride). The synthesis was performed in argon-filled glass ampoules. According to X-ray structure analysis based on single crystals, the title compound crystallizes with triclinic lattice symmetry and consists of infinite {[Te(8)](2+)}(n) cations associated with pyramidal [NbOCl(4)](-) anions. The novel catena-octatellurium(2+) cation is composed of Te(5) rings that are linked via Te(3) units [Te-Te = 2.6455 (18)-2.8164 (19) Å]. The composition and purity of [Te(8)][NbOCl(4)](2) were further confirmed by energy-dispersive X-ray diffraction (EDX) analysis.

  3. 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.

  4. Intrinsic pinning by naturally occurring correlated defects in FeSe1-x Te x superconductors

    NASA Astrophysics Data System (ADS)

    Amigó, M. L.; Ale Crivillero, M. V.; Franco, D. G.; Badía–Majós, A.; Guimpel, J.; Campo, J.; Damay, F.; Porcher, F.; Condó, A. M.; Nieva, G.

    2017-08-01

    We study the angular dependence of dissipation in the superconducting state of FeSe and Fe(Se1-x Te x ) through electrical transport measurements, using crystalline intergrown materials. We reveal the key role of the inclusions of the non superconducting magnetic phase Fe1-y (Se1-x Te x ), growing into the Fe(Se1-x Te x ) pure β-phase, in the development of a correlated defect structure. The matching of both atomic structures defines the growth habit of the crystalline material as well as the correlated planar defects orientation.

  5. New high-pressure phases of MoSe2 and MoTe2

    NASA Astrophysics Data System (ADS)

    Kohulák, Oto; MartoÅák, Roman

    2017-02-01

    Three Mo-based transition-metal dichalcogenides MoS2,MoSe2, and MoTe2 share at ambient conditions the same structure 2 Hc , consisting of layers where Mo atoms are surrounded by six chalcogen atoms in trigonal prism coordination. The knowledge of their high-pressure behavior is, however, limited, particularly in case of MoSe2 and MoTe2. The latter materials do not undergo a layer-sliding transition 2 Hc→ 2 Ha known in MoS2 and currently no other stable phase aside from 2 Hc is known in these systems at room temperature. Employing evolutionary crystal structure prediction in combination with ab initio calculations, we study the zero-temperature phase diagram of both materials up to Mbar pressures. We find a tetragonal phase with space group P4/mmm, previously predicted in MoS2, to become stable in MoSe2 at 118 GPa. In MoTe2, we predict at 50 GPa a transition to a new layered tetragonal structure with space group I4/mmm, similar to CaC2, where Mo atoms are surrounded by eight Te atoms. The phase is metallic already at the transition pressure and becomes a good metal beyond 1 Mbar. We discuss chemical trends in the family of Mo-based transition-metal dichalcogenides and suggest that MoTe2 likely offers the easiest route towards the post-2 H phases.

  6. Effects of Various RF Powers on CdTe Thin Film Growth Using RF Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Alibakhshi, Mohammad; Ghorannevis, Zohreh

    2016-09-01

    Cadmium telluride (CdTe) film was deposited using the magnetron sputtering system onto a glass substrate at various deposition times and radio frequency (RF) powers. Ar gas was used to generate plasma to sputter the CdTe atoms from CdTe target. 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) analysis showed that the films exhibited polycrystalline nature of CdTe structure with the (111) orientation as the most prominent peak. Optimum condition to grow the CdTe film was obtained and it was found that increasing the deposition time and RF power increases the crystallinity of the films. From the profilometer and XRD data's, the thicknesses and crystal sizes of the CdTe films increased at the higher RF power and the longer deposition time, which results in affecting the band gap as well. From atomic force microscopy (AFM) analysis we found that roughnesses of the films depend on the deposition time and is independent of the RF power.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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 Aa 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 Aa (occupied) to Aa (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.

  8. 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.

  9. 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.

  10. "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…

  11. "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…

  12. The atomic orbitals of the topological atom.

    PubMed

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

    2013-06-07

    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.

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

    PubMed

    Som, Anirban; Pradeep, T

    2012-08-07

    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.

  14. Substrate preparation effects on defect density in molecular beam epitaxial growth of CdTe on CdTe (100) and (211)B

    DOE PAGES

    Perkins, Craig; Barnes, Teresa M; Burton, George L.; ...

    2017-07-01

    Recent studies have demonstrated that growth of CdTe on CdTe (100) and (211)B substrates via molecular beam epitaxy (MBE) results in planar defect densities 2 and 3 orders of magnitude higher than growth on InSb (100) substrates, respectively. To understand this shortcoming, MBE growth on CdTe substrates with a variety of substrate preparation methods is studied by scanning electron microscopy, secondary ion mass spectrometry, x-ray photoelectron spectroscopy, cross sectional transmission electron microscopy, and atom probe tomography (APT). Prior to growth, carbon is shown to remain on substrate surfaces even after atomic hydrogen cleaning. APT revealed that following the growth ofmore » films, trace amounts of carbon remained at the substrate/film interface. This residual carbon may lead to structural degradation, which was determined as the main cause of higher defect density.« less

  15. Stripe structure CdTe-CdZnTe-CdTe in a bulk single crystal

    NASA Astrophysics Data System (ADS)

    Azoulay, M.; Sinvani, M.; Mizrachi, M.; Feldstein, H.

    1994-03-01

    In this paper we present a study that was aimed at performing a selective diffusion of Zn into CdTe. A single crystal CdTe wafer fabricated into a "tooth-like" structure which was further subjected to high temperature annealing in the presence of Zn vapour. The sample was then cut parallel to the diffusion direction and a Zn concentration analysis, using an electron microprobe, was performed. As expected, the stripe structure CdTe-CdZnTe-CdTe has been confirmed. The Zn decay profiles were fitted to a modified diffusion model, suggesting a bulk diffusion mechanism coupled with a surface reaction. Practical implementation of this stripe structure for an infrared light waveguide is being evaluated.

  16. Heptacarbonyl-1κ3 C,2κ4 C-(4-phenyl­pyridine-1κN)di-μ-phenyltellurido-1:2κ4 Te:Te-dirhenium(I)

    PubMed Central

    Vanitha, A.; Muthukumaran, J.; Krishna, R.; Manimaran, Bala

    2010-01-01

    In the title complex, [Re2(C6H5Te)2(C11H9N)(CO)7], two Re atoms are coordinated in slightly distorted octa­hedral coordination environments and are bridged by two Te atoms, which are coordinated in trigonal-pyramidal environments. The torsion angle for the Te—Re—Te—Re sequence of atoms is 17.06 (3)°. The crystal structure is stabilized by weak C—H⋯O and C—H⋯π inter­actions. In addition, there are Te⋯Te distances [4.0392 (12) Å] and O⋯O distances [2.902 (19) Å] which are shorter than the sum of the van der Waals radii for these atoms. A short inter­molecular lone pair⋯π distance [C O⋯Cg = 3.31 (2) Å] is also observed. PMID:21579015

  17. 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,…

  18. 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.

  19. 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.

  20. Nanoscale chemical phase separation in FeTe0.55Se0.45 as seen via scanning tunneling spectroscopy

    SciTech Connect

    He, Xiaobo; Li, Guorong; Zhang, Jiandi; Karki, A B; Jin, Rongying; Sales, Brian C; Safa-Sefat, Athena; McGuire, Michael A; Mandrus, David; Plummer, E. W.

    2011-01-01

    Atomically resolved structural and electronic properties of FeTe{sub 1-x}Se{sub x} (x = 0 and 0.45) have been studied with scanning tunneling microscopy/spectroscopy (STM/STS). In contrast to the extreme flatness of the Te-terminated FeTe surface, nanoscale chemical phase separation between Te and Se atoms is unambiguously revealed on the surface of FeTe{sub 0.55}Se{sub 0.45}. A statistical counting of the two kinds of atoms has the same ratio as that in the bulk. Remarkably, there is no electronic phase separation seen in the tunneling spectroscopy. This indicates that the optimally doped superconductor is chemically inhomogeneous but electronically homogeneous, in contrast to many correlated electron materials.

  1. Syntheses, structure, some band gaps, and electronic structures of CsLnZnTe3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y).

    PubMed

    Yao, Jiyong; Deng, Bin; Sherry, Leif J; McFarland, Adam D; Ellis, Donald E; Van Duyne, Richard P; Ibers, James A

    2004-11-29

    Eleven new quaternary rare-earth tellurides, CsLnZnTe3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Y), were prepared from solid-state reactions at 1123 K. These isostructural materials crystallize in the layered KZrCuS3 structure type in the orthorhombic space group Cmcm. The structure is composed of LnTe6 octahedra and ZnTe4 tetrahedra that share edges to form [LnZnTe3] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing CsTe8 bicapped trigonal prisms. There are no Te-Te bonds in the structure of these CsLnZnTe3 compounds so the formal oxidation states of Cs/Ln/Zn/Te are 1+/3+/2+/2-. Optical band gaps of 2.13 eV for CsGdZnTe3 and 2.12 eV for CsTbZnTe3 were deduced from single-crystal optical absorption measurements. A first-principles calculation of the density of states and the frequency-dependent optical properties was performed on CsGdZnTe3. The calculated band gap of 2.1 eV is in good agreement with the experimental value. A quadratic fit for the lanthanide contraction of the Ln-Te distance is superior to a linear one if the closed-shell atom is included.

  2. Recent Results on Growth of (211)B CdTe on (211)Si with Intermediate Ge and ZnTe Buffer Layers by Metalorganic Vapor-Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Shintri, Shashidhar; Rao, Sunil; Wijewarnasuriya, Priyalal; Trivedi, Sudhir; Bhat, Ishwara

    2012-10-01

    We report on the investigation of epitaxial cadmium telluride grown by metalorganic vapor-phase epitaxy (MOVPE) on (211)Si, with particular emphasis on studying the effect of changing the reactor parameters and thermal annealing conditions on the epilayer quality. The CdTe films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The best CdTe films were observed when the Te/Cd precursor partial pressure ratio was close to 3.1. It was also observed that, though annealing improved the crystal quality, a slight increase in surface roughness was observed. Similar attempts were made to improve the growth conditions of ZnTe intermediate buffer layer, which showed similar trends with changes in precursor flows.

  3. Fractal features of CdTe thin films grown by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Hosseinpanahi, Fayegh; Raoufi, Davood; Ranjbarghanei, Khadijeh; Karimi, Bayan; Babaei, Reza; Hasani, Ebrahim

    2015-12-01

    Cadmium telluride (CdTe) thin films were prepared by RF magnetron sputtering on glass substrates at room temperature (RT). The film deposition was performed for 5, 10, and 15 min at power of 30 W with a frequency of 13.56 MHz. The crystal structure of the prepared CdTe thin films was studied by X-ray diffraction (XRD) technique. XRD analyses indicate that the CdTe films are polycrystalline, having zinc blende structure of CdTe irrespective of their deposition time. All CdTe films showed a preferred orientation along (1 1 1) crystalline plane. The surface morphology characterization of the films was studied using atomic force microscopy (AFM). The quantitative AFM characterization shows that the RMS surface roughness of the prepared CdTe thin films increases with increasing the deposition time. The detrended fluctuation analysis (DFA) and also multifractal detrended fluctuation analysis (MFDFA) methods showed that prepared CdTe thin films have multifractal nature. The complexity, roughness of the CdTe thin films and strength of the multifractality increase as deposition time increases.

  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. 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.

  6. Enhancement of Thermoelectric Properties in SnTe with (Ag, In) Co-Doping

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Yang, N.; Li, S. M.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2017-09-01

    A lead-free SnTe compound shows good electrical property but high thermal conductivity, resulting in a low figure-of-merit ZT. We present a significant enhancement of the thermoelectric properties of p-type SnTe with (Ag, In) co-doping. The Ag and In co-doped Sn1-2x Ag x In x Te (x = 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) are prepared by melting, quenching and spark plasma sintering. A homogeneous NaCl-type SnTe-based solid solution forms in the alloys at low Ag and In content (x ≤ 0.02), while a AgInTe2 minor secondary phase precipitates for higher x. Similar to In doping, the introduction of Ag and In at Sn sites in SnTe considerably increases the Seebeck coefficient and power factor by creating resonant levels near the Fermi energy. In addition, the Ag and In solute atoms in the SnTe-based solid solution and the minor secondary phase AgInTe2 enhance phonon scattering and thus significantly reduce the carrier and lattice thermal conductivity. Ag and In co-doping shows a collective advantage on the overall thermoelectric performance of SnTe or In-doped SnTe. A maximum ZT of 1.23 at 873 K and average ZT of 0.58 can be obtained in the alloy Sn1-2x Ag x In x Te with x = 0.03.

  7. Barrier formation at graded HgTe/CdTe heterojunctions

    NASA Astrophysics Data System (ADS)

    Goren, D.; Asa, G.; Nemirovsky, Y.

    1996-11-01

    Numerical calculations of graded HgTe/CdTe heterojunction (HJ) band diagrams at equilibrium are presented and discussed. The calculations are performed in the entire compositional range (0Te contacts to extrinsic CdTe are possible, provided that the graded region is wider than one micron, and that it has the same doping type as the doping of the substrate with equal or higher absolute value. Further numerical calculations take into consideration the possible existence of distributed interface charges in the graded region of the HJ. It is shown that by assuming a classical transport over the potential barrier, the effective graded interface charge can be determined from the zero bias differential resistance of the HJ. Experimental transport measurements of metalorganic chemical vapor deposition (MOCVD) grown HgTe/p-CdTe graded HJs show a varying degree of rectification, indicating variations in the graded interface charge distributions which result from different MOCVD growth conditions.

  8. 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.

  9. 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

  10. Reconfigurable Antenna Aperture with Optically Controlled GeTe-Based RF Switches

    DTIC Science & Technology

    2015-03-31

    electrical resistivity and OFF state capacitance of GeTe- Based RF Switches under direct optical laser excitation. Our tightly-coupled dipole array...relative to their neighbors. Rapid quench cooling (~100ns) then freezes these atoms into an amorphous solid, locking in a high electrical resistance ...temperature. If the pulse is of appropriately long duration, the structure experiences atomic bond rearrangement and leads to the low resistance phase

  11. 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.

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

    SciTech Connect

    Naderi, Ebadollah; Ghaisas, S. V.

    2016-08-15

    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.

  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. Crystal structure of Sr5Te4O12(OH)2, the first basic strontium oxotellurate(IV)

    PubMed Central

    Weil, Matthias; Shirkhanlou, Mahdi

    2016-01-01

    The asymmetric unit of the title basic strontium oxotellurate(IV), Sr5Te4O12(OH)2 {systematic name penta­strontium tetra­kis­[oxotellurate(IV)] di­hydroxide}, comprises three SrII cations (one with site symmetry 2) and two TeIV atoms, as well as seven O atoms. The coordination numbers of the alkaline earth cations to nearby O atoms range from seven (2 ×) to eight, and the TeIV atoms are surrounded by three oxygen partners in the form of trigonal pyramids. The SrOx polyhedra share corners and edges to build up a three-dimensional framework structure encapsulating channels propagating along [010]. The TeIV atoms flank the framework O atoms and are situated at the outer array of the channels with the 5s 2 lone electron pairs protruding into the empty space of the channels (diameter ≃ 4 Å). Although the H atom of the OH group could not be located, bond-valence-sum calculations and typical O⋯O distances (range 2.81–3.06 Å) clearly indicate hydrogen bonding of medium to weak strengths. PMID:27840701

  15. 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.

  16. Local structure of amorphous Ag5In5Sb60Te30 and In3SbTe2 phase change materials revealed by X-ray photoelectron and Raman spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Sahu, Smriti; Manivannan, Anbarasu; Shaik, Habibuddin; Mohan Rao, G.

    2017-07-01

    Reversible switching between highly resistive (binary "0") amorphous phase and low resistive (binary "1") crystalline phase of chalcogenide-based Phase Change Materials is accredited for the development of next generation high-speed, non-volatile, data storage applications. The doped Sb-Te based materials have shown enhanced electrical/optical properties, compared to Ge-Sb-Te family for high-speed memory devices. We report here the local atomic structure of as-deposited amorphous Ag5In5Sb60Te30 (AIST) and In3SbTe2 (IST) phase change materials using X-ray photoelectron and Raman spectroscopic studies. Although AIST and IST materials show identical crystallization behavior, they differ distinctly in their crystallization temperatures. Our experimental results demonstrate that the local environment of In remains identical in the amorphous phase of both AIST and IST material, irrespective of its atomic fraction. In bonds with Sb (˜44%) and Te (˜56%), thereby forming the primary matrix in IST with a very few Sb-Te bonds. Sb2Te constructs the base matrix for AIST (˜63%) along with few Sb-Sb bonds. Furthermore, an interesting assimilation of the role of small-scale dopants such as Ag and In in AIST, reveals rare bonds between themselves, while showing selective substitution in the vicinity of Sb and Te. This results in increased electronegativity difference, and consequently, the bond strength is recognized as the factor rendering stability in amorphous AIST.

  17. 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.

  18. Epitaxial formation of core-shell heterostructured Bi2Te3@Sb2Te3 hexagonal nanoplates

    NASA Astrophysics Data System (ADS)

    Liang, Li-Xing; Deng, Yuan; Wang, Yao; Gao, Hong-Li

    2014-01-01

    The core-shell heterostructured Bi2Te3@Sb2Te3 hexagonal nanoplates with a thickness range of 22-26 nm were fabricated by a ligand auxiliary solution process. After complete ligand removal by a facile NH3-based procedure, the platelets are spark plasma-sintered to a good p-type nanostructured bulk material with crystal grain sizes preserved. Resultant crystal structures and microstructures were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, energy dispersed X-ray spectroscopy, selected area electron diffraction, and atomic force microscopy measurements. The influences of solvent ratios of H2O/ethylene glycol, molar concentration of source materials, and PVP on the formation of the core-shell structures were studied in detail. Based on the time-dependent experiment, a possible formation mechanism related to epitaxial attachment was presented for the growth of the core-shell heterostructured Bi2Te3@Sb2Te3 nanoplates. The thermoelectric Seebeck coefficient, S, is in the range of 133-171 μV K-1 and the electric conductivity for the Bi2Te3@Sb2Te3 is in the range of 48,400-79,200 S m-1. The final power factor is in the range of 0.97-2.04 mW m-1 K-2, which is close to those of physical method synthesized bulk pellets. Furthermore, this result is about several to tens of times higher than those of the recent reported works on chemically synthesized nanocrystalline pnictogen chalcogenide materials. These unique features of our core-shell nanoplates make them attractive for the manufacture of high-performance 3D-embedded matrixthermoelectric materials.

  19. Structural variability and electronic properties of bulk and monolayer Si2 Te3

    NASA Astrophysics Data System (ADS)

    Combs, Corey; Shen, Xiao; Puzyrev, Yevgeniy; Pan, Lida; Pantelides, Sokrates

    Silicon telluride, a layered material recently experimentally made to a few atomic layer-thick (1) has intriguing variations of optical and electronic properties, associated with the flexibility of its structure. In Si2Te3, the Te atoms form a hexagonal close packed structure, while Si atoms form Si-Si dimers and fill 2/3 of the allowed sites. There are 4 possible orientations of the Si-Si dimers, 3 in-plane directions 60 degrees to each other and one out-of-plane direction perpendicular to 2D plane. X-ray and electron diffraction data on bulk Si2Te3 suggested that 1/4 of the dimers are vertical while the other 3/4 of the dimers are randomly oriented horizontally. We performed density functional calculations to show that both bulk and monolayer Si2Te3 exhibit large variations in properties, resulting from reorientation of silicon dimers. These variations are up to 5 percent in lattice constant and up to 40 percent in electron band gap. Transition of Si2Te3 from bulk to monolayer configuration also shows an increase in the band gap and lattice constant. We show that these properties are, in principle, controllable by temperature and strain, making Si2T3 a promising candidate as optomechanical and optoelectronic material. (1) Keuleyan, S. et al. Nano Lett. 2015, 15 (4), 2285-2290. Research funded by NSF Grant: NSF EPS-1004083.

  20. Exotic Atoms and Muonium

    NASA Astrophysics Data System (ADS)

    Horváth, D.

    In exotic atoms, one of the atomic electrons is replaced by a negatively charged particle, whereas muonium consists of a positive muon and an electron. After a general review of the theoretical and experimental aspects, the present knowledge of this field is summarized. These include muonium and the application of the muon spin resonance method in solid-state physics and chemistry, muonic hydrogen atoms, muonic molecules and muon-catalyzed fusion, pionic hydrogen atoms and their use in chemistry, testing quantum electrodynamics on heavy muonic atoms, measuring particle and nuclear properties using hadronic atoms, and testing basic symmetry principles with antiprotonic helium atoms and antihydrogen.

  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. 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.

  3. 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.

  4. Inelastic neutron scattering of the itinerant magnets Cr2Te3 and tr-Cr5Te8

    NASA Astrophysics Data System (ADS)

    Aczel, Adam; Granroth, Garrett; Ghimire, Nirmal; McGuire, Michael; Mandrus, David; Nagler, Steve

    2012-02-01

    Itinerant magnets based on transition metal chalcogenide compounds are of current interest, in part due to their relationship to the parent compounds of Fe-based superconductors. Two particularly interesting systems in this family are the chromium tellurides Cr2Te3 and trigonal (tr) Cr5Te8. These materials crystallize in layered structures with alternating partially and fully-occupied planes of Cr atoms stacked along the c-axis. Magnetization measurements along different crystallographic directions show a net ferromagnetic response and large magnetic anisotropy. In addition, the saturation moments are smaller than predicted by an ionic model; consistent with itinerant behavior. Previous neutron diffraction results for Cr2Te3 revealed an ordered moment of < 0.2 μB in the partially-occupied planes. We examined the magnetic excitations in these materials by powder neutron spectroscopy measurements using the SEQUOIA instrument at the SNS. We find similar moment sizes for the magnetic Cr atoms of both systems. However, despite their similar crystal structures, ordered moment sizes, and chemical compositions, their magnetic excitation spectra are strikingly different. We compare our data to the predictions of various models in an effort to determine the relevant exchange parameters, put constraints on their magnitudes, and understand the differences between the inelastic magnetic spectra. We find that exchange along the c-direction is critical to explain our data.

  5. 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.

  6. High Atom Number in Microsized Atom Traps

    DTIC Science & Technology

    2015-12-14

    2012 conference of the Division of Atomic , Molecular, and Optical Physics (DAMOP) of the American Physical Society (APS). We have reconfigured the...Final Performance Report on ONR Grant N00014-12-1-0608 High atom number in microsized atom traps for the period 15 May 2012 through 14 September...2015 J. M. Grossman Department of Physics St. Mary’s College of Maryland 18952 E. Fisher Road St. Mary’s City, MD 20686 jmgrossman @smcm. edu

  7. 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.

  8. 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.

  9. 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.

  10. First principles study of crystal Si-doped Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Yan, Beibei; Yang, Fei; Chen, Tian; Wang, Minglei; Chang, Hong; Ke, Daoming; Dai, Yuehua

    2017-02-01

    Ge2Sb2Te5 (GST) and Si-doped GST with hexagonal structure were investigated by means of First-principles calcucations. We performed many kinds of doping types and studied the electronic properties of Si-doped GST with various Si concentrations. The theoretical calculations show that the lowest formation energy appeared when Si atoms substitute the Sb atoms (SiSb). With the increasing of Si concentrations from 10% to 30%, the impurity states arise around the Fermi level and the band gap of the SiSb structure broadens. Meanwhile, the doping supercell has the most favorable structure when the doping concentration keeps in 20%. The Si-doped GST exhibits p-type metallic characteristics more distinctly owing to the Fermi level moves toward the valence band. The Te p, d-orbitals electrons have greater impact on electronic properties than that of Te s-orbitals.

  11. EXAFS Studies of Ga Doped Pb1-xMnxTe

    SciTech Connect

    Radisavljevic, I.; Ivanovic, N.; Novakovic, N.; Romcevic, N.; Mahnke, H.-E.

    2007-04-23

    We have employed the X-Rays Absorption Fine Structure (EXAFS) technique to resolve the local structure of Pb1-xMnxTe (Ga) in order to provide answers on questions concerning the exact positions and charge states of constitutive and impurity atoms, possibilities and features of their ordering and (or) clustering, as well as configurational and thermal disorder in the system.

  12. 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.

  13. Phase-field Simulations of Te-Precipitate Morphology and Evolution Kinetics in Te-Rich CdTe Crystals

    SciTech Connect

    Hu, Shenyang Y.; Henager, Charles H.

    2009-05-15

    Te precipitates are one of main defects that form during the cooling process of as–grown CdTe crystals. Many factors such as the kinetic properties of intrinsic point defects (vacancy, interstitial, and antisites), internal stresses around the precipitates associated with the lattice mismatch between the precipitate and matrix, thermal stresses due to temperature gradients, extended defects (dislocations, twin and grain boundaries), non-stoichiometric composition, and the thermal treatment processing might all affect the formation and growth/dissolution of Te precipitates. A good understanding of these effects on Te precipitate evolution kinetics is technically important in order to optimize the material process and obtain high quality crystals. This work aims to develop a phase-field model for investigating the evolution of a Te-precipitate in a Te-rich CdTe crystal under cooling. Cd vacancies and Te interstitials are assumed to be the diffusion species in the system. We also assume that the system is in two phase equilibrium (matrix CdTe and liquid Cd-Te droplet) at high temperatures and three phase equilibrium (matrix CdTe, Te-precipitate, and void) at low temperatures. With the thermodynamic and kinetic properties from experimental phase diagrams and thermodynamic calculations, the effect of Te and vacancy mobility, cooling rates and internal stresses on Te-precipitate and void evolution kinetics are investigated.

  14. 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 PAGES

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; ...

    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

  15. 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

  16. Ion velocity dependence of mixing in Bi/Te bilayer

    NASA Astrophysics Data System (ADS)

    Diana, T.; Agarwal, D. C.; Kulriya, P. K.; Tripathi, S. K.; Sarma, H. N. K.

    2014-11-01

    This paper reports an unusual extent of mixing in Bi/Te thin bilayer system using 90 MeV Au and 95 MeV Ag ions of energies having same electronic energy loss ( S e ) value. The analysis is made using Rutherford backscattering spectroscopy and atomic force microscopy. The mixing variance as observed from the depth profiles extracted from RBS data using Rutherford universal manipulation program is found to be higher for Au irradiated samples. Similarly higher sputtering yield is observed for Au ions than Ag ions. These have been accounted to ion velocity effect of Bi/Te with Au ions having velocity 1.3 times slower to Ag ions.

  17. 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.

  18. Low-Roughness Plasma Etching of HgCdTe Masked with Patterned Silicon Dioxide

    NASA Astrophysics Data System (ADS)

    Ye, Z. H.; Hu, W. D.; Yin, W. T.; Huang, J.; Lin, C.; Hu, X. N.; Ding, R. J.; Chen, X. S.; Lu, W.; He, L.

    2011-08-01

    A novel mask technique utilizing patterned silicon dioxide films has been exploited to perform mesa etching for device delineation and electrical isolation of HgCdTe third-generation infrared focal-plane arrays (IRFPAs). High-density silicon dioxide films were deposited at temperature of 80°C, and a procedure for patterning and etching of HgCdTe was developed by standard photolithography and wet chemical etching. Scanning electron microscopy (SEM) showed that the surfaces of inductively coupled plasma (ICP) etched samples were quite clean and smooth. Root-mean-square (RMS) roughness characterized by atomic force microscopy (AFM) was less than 1.5 nm. The etching selectivity between a silicon dioxide film and HgCdTe in the samples masked with patterned silicon dioxide films was greater than 30:1. These results show that the new masking technique is readily available and promising for HgCdTe mesa etching.

  19. Large scale ZnTe nanostructures on polymer micro patterns via capillary force photolithography

    SciTech Connect

    Florence, S. Sasi Can, N.; Adam, H.; Sachan, P.; Gupta, R. K.; Arockiasamy, L.; Umadevi, M.

    2016-06-10

    A novel approach to prepare micro patterns ZnTe nanostructures on Si (100) substrate using thermal evaporation is proposed by capillary Force Lithography (CFL) technique on a self-assembled sacrificial Polystyrene mask. Polystyrene thin films on Si substrates are used to fabricate surface micro-relief patterns. ZnTe nanoparticles have been deposited by thermal evaporation method. The deposited ZnTe nanoparticles properties were assessed by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM). SEM studies indicated that the particles are uniform in size and shape, well dispersed and spherical in shape. This study reports the micro-arrays of ZnTe nanoparticles on a self-assembled sacrificial PS mask using a capillary flow photolithography process which showed excellent, morphological properties which can be used in photovoltaic devices for anti-reflection applications.

  20. 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.

  1. Tellurium(0) as a ligand: synthesis and characterization of 2-pyridyltellurolates of platinum(II) and structures of [Pt{2-Te-3-(R)C5H3N}2Te(PR'3)] (R = H or Me).

    PubMed

    Chauhan, Rohit Singh; Kedarnath, G; Wadawale, Amey; Muñoz-Castro, Alvaro; Arratia-Perez, Ramiro; Jain, Vimal K; Kaim, Wolfgang

    2010-05-03

    Treatment of toluene solutions of the ditellurides [Te(2){C(5)H(3)N(R)-3}(2)] (R = H or Me) with [Pt(PPh(3))(4)] yielded two types of complexes, [Pt{2-Te-3-(R)C(5)H(3)N}(2)(PPh(3))(2)] (1a-d) as the major products and [Pt{2-Te-3-(R)C(5)H(3)N}(2)Te(PPh(3))] (2a-d) as minor products. The above complexes can also be obtained by the reaction of [PtCl(2)(PR'(3))(2)] (PR'(3) = PPh(3) or PPh(2)(2-C(5)H(4)N)) with 2 equiv of Na(2-Te-C(5)H(3)R). The complexes were characterized by elemental analyses and UV-vis, NMR ((1)H and (31)P), and (in part) XPS spectroscopy. The molecular structures of [Pt(2-Te-C(5)H(4)N)(2)Te(PPh(3))] (2a) and [Pt{2-Te-C(5)H(3)(Me)N}(2)Te(PPh(3))] (2b) were established by single crystal X-ray diffraction. Both complexes exhibit a distorted square-planar configuration at the platinum(II) centers. The two mutually trans positioned 2-pyridinetellurolate ligands [2-Te-C(5)H(3)(R)N] coordinate to the central platinum atom in a monodentate fashion through the tellurium atoms. The tellurium(0) atom adopts a "bent T" configuration as it is bridging the 2-Te- C(5)H(3)(R)N molecules via N-Te-N bonds (166 degrees angle) and coordinates to Pt(II) in the trans position to PPh(3). The novel bis(pyridine)tellurium(0) arrangement resembles the bis(pyridine)iodonium structure. The calculated NICS indices and ELF functions clearly show that the compounds 2a and 2b are aromatic in the region defined by the Te-C-N-Te-Pt five-membered rings.

  2. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1 +yTe1 -xSex

    NASA Astrophysics Data System (ADS)

    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 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.

  3. Giant multiferroic effects in topological GeTe-Sb2Te3 superlattices

    PubMed Central

    Tominaga, Junji; Kolobov, Alexander V; Fons, Paul J; Wang, Xiaomin; Saito, Yuta; Nakano, Takashi; Hase, Muneaki; Murakami, Shuichi; Herfort, Jens; Takagaki, Yukihiko

    2015-01-01

    Multiferroics, materials in which both magnetic and electric fields can induce each other, resulting in a magnetoelectric response, have been attracting increasing attention, although the induced magnetic susceptibility and dielectric constant are usually small and have typically been reported for low temperatures. The magnetoelectric response usually depends on d-electrons of transition metals. Here we report that in [(GeTe)2(Sb2Te3)l]m superlattice films (where l and m are integers) with topological phase transition, strong magnetoelectric response may be induced at temperatures above room temperature when the external fields are applied normal to the film surface. By ab initio computer simulations, it is revealed that the multiferroic properties are induced due to the breaking of spatial inversion symmetry when the p-electrons of Ge atoms change their bonding geometry from octahedral to tetrahedral. Finally, we demonstrate the existence in such structures of spin memory, which paves the way for a future hybrid device combining nonvolatile phase-change memory and magnetic spin memory. PMID:27877740

  4. 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…

  5. 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,…

  6. Theoretical investigation of phase separation in thermoelectric AgSbTe2

    NASA Astrophysics Data System (ADS)

    Shinya, Hikari; Masago, Akira; Fukushima, Tetsuya; Katayama-Yoshida, Hiroshi

    2017-08-01

    The pseudo-binary alloy (GeTe) x (AgSbTe2)1- x , which is one of the highly efficient thermoelectric materials, shows the anomalous lattice thermal conductivity and figure of merit ZT, when the GeTe concentration (x) is around 0.8. These singularities are considered to be due to the inherent instability of AgSbTe2, derived from the antibonding contributions at the valence band maximum. Here, we investigate the defect physics in AgSbTe2 by first-principles electronic structure calculations. It is found, from our calculations, that one must carefully control the atomic chemical potentials of Ag and Sb to grow AgSbTe2 in thermal equilibrium, and that a defect complex 2VAg+SbAg, which has a low formation energy, is easily generated under the Ag-poor crystal growth condition. Additionally, we propose spinodal nanodecomposition between AgSbTe2 and ordered defect compounds using 2VAg+SbAg, which is a crucial rule for the experimentally observed unusual thermoelectric properties.

  7. 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.

  8. 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.

  9. Applications of the Infrared Measurement Analyzer: Hydrogenated LWIR HgCdTe Detectors

    NASA Astrophysics Data System (ADS)

    Buurma, Christopher; Boieriu, Paul; Bommena, Ramana; Sivananthan, Sivalingam

    2013-11-01

    Low-cost silicon-based alternative substrates are an attractive choice for next-generation large-area high-resolution multicolor infrared (IR) detector arrays. However, the high density of dislocations formed during molecular-beam epitaxy growth of HgCdTe/CdTe/Si limits the performance of IR arrays, especially in the long-wavelength infrared (LWIR) region. Atomic hydrogen introduced by inductively coupled plasma (ICP) into HgCdTe is expected to passivate dislocations, bulk and surface defects, removing their contributions to dark current. Passivation using ICP hydrogenation can have different effects on HgCdTe photodiode performance, depending on which class of defects is being passivated. The infrared measurement analyzer (IRMA) was used to deconvolute the effects of hydrogenation on LWIR HgCdTe photodiodes through a reverse-modeling fit of the current-voltage ( I- V) characteristic. This approach results in a fit with fewer false minima, low parameter error and bias, and high confidence in extracted device parameters. A description of this tool and its application to hydrogenated HgCdTe LWIR detectors is presented. Lower dark currents have been observed after hydrogenation of fully fabricated devices. Model-fits performed on a wide variety of LWIR HgCdTe photodiodes suggest that hydrogenation provides both surface and bulk quality improvements. These benefits of ICP hydrogenation have been retained over several months.

  10. 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.

  11. 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.

  12. Self-Assembled Formation of Well-Aligned Cu-Te Nano-Rods on Heavily Cu-Doped ZnTe Thin Films

    NASA Astrophysics Data System (ADS)

    Liang, Jing; Cheng, Man Kit; Lai, Ying Hoi; Wei, Guanglu; Yang, Sean Derman; Wang, Gan; Ho, Sut Kam; Tam, Kam Weng; Sou, Iam Keong

    2016-11-01

    Cu doping of ZnTe, which is an important semiconductor for various optoelectronic applications, has been successfully achieved previously by several techniques. However, besides its electrical transport characteristics, other physical and chemical properties of heavily Cu-doped ZnTe have not been reported. We found an interesting self-assembled formation of crystalline well-aligned Cu-Te nano-rods near the surface of heavily Cu-doped ZnTe thin films grown via the molecular beam epitaxy technique. A phenomenological growth model is presented based on the observed crystallographic morphology and measured chemical composition of the nano-rods using various imaging and chemical analysis techniques. When substitutional doping reaches its limit, the extra Cu atoms favor an up-migration toward the surface, leading to a one-dimensional surface modulation and formation of Cu-Te nano-rods, which explain unusual observations on the reflection high energy electron diffraction patterns and apparent resistivity of these thin films. This study provides an insight into some unexpected chemical reactions involved in the heavily Cu-doped ZnTe thin films, which may be applied to other material systems that contain a dopant having strong reactivity with the host matrix.

  13. 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.

  14. 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).

  15. The surprising metastability of TeH2+.

    PubMed

    de Oliveira-Filho, Antonio G S; Ornellas, Fernando R

    2013-06-14

    A high-level ab initio investigation of a manifold of electronic states of the diatomic dication TeH(2+) is presented. Potential energy curves for both Λ + S and relativistic (Ω) states are constructed not only making evident the metastability of this system, but also the large energy splitting due to spin-orbit interactions. This effect is also very significant in the region close to the crossing of the (2)Π and (4)Σ(-) states, where avoided crossings between the Ω states have a relatively large impact on the height of the energy barriers. In contrast to TeH, with only two bound states (X1 (2)Π3∕2 and X2 (2)Π1∕2) below about 25,000 cm(-1), in the case of TeH(2+) a much richer energy profile is obtained indicating various possibilities of electronic transitions. Guided by the results of this study, the experimental characterization of these states is now a challenge to spectroscopists. Since close to the equilibrium region the double positive charge is centered on the tellurium atom, the binding in this system can be rationalized as a simple covalent bond between the pz and s orbitals of Te(2+) and H, respectively. As the internuclear distance increases, the electron affinity of Te(2+) overcomes that of H(+) and the system dissociates into two singly charged fragments. A simulation of the double ionization spectra complements the characterization of the electronic states, and results of a mass spectrometric investigation corroborates the predicted transient existence of this metastable species.

  16. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    PubMed Central

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1−xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

  17. TeV-Scale Strings

    NASA Astrophysics Data System (ADS)

    Berenstein, David

    2014-10-01

    This review discusses the status of string physics where the string tension is around the TeV scale. It covers model-building basics for perturbative strings, based on D-brane configurations. The effective low-energy physics description of such string constructions is analyzed: how anomaly cancellation is implemented, how fast proton decay is avoided, and how D-brane models lead to additional Z' particles. This review also discusses direct search bounds for strings at the TeV scale, as well as theoretical issues with model building related to flavor physics and axions.

  18. 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)

  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. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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/

  5. HYDROGEN ATOM THERMAL PARAMETERS.

    PubMed

    JENSEN, L H; SUNDARALINGAM, M

    1964-09-11

    Isotropic hydrogen atom thermal parameters for N,N'- hexamethylenebispropionamide have been determined. They show a definite trend and vary from approximately the same as the mean thermal parameters for atoms other than hydrogen near the center of the molecule to appreciably greater for atoms near the end. The indicated trend for this compound, along with other results, provides the basis for a possible explanation of the anomolous values that have been obtained for hydrogen atom thermal parameters.

  6. Atomizing nozzle and process

    DOEpatents

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

  7. 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.

  8. 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.

  9. High Thermoelectric Performance SnTe–In 2 Te 3 Solid Solutions Enabled by Resonant Levels and Strong Vacancy Phonon Scattering

    SciTech Connect

    Tan, Gangjian; Zeier, Wolfgang G.; Shi, Fengyuan; Wang, Pengli; Snyder, G. Jeffery; Dravid, Vinayak P.; Kanatzidis, Mercouri G.

    2015-11-06

    Herein, we report a significantly improved thermoelectric figure of merit ZT of ~1.1 at ~923 K in p-type SnTe through In2Te3 alloying and iodine doping. We propose that the introduction of indium at Sn sites in SnTe creates resonant levels inside the valence bands, thereby considerably increasing the Seebeck coefficients and power factors in the low-to-middle temperature range. Unlike SnTe–InTe, the SnTe–In2Te3 system displays much lower lattice thermal conductivity. Utilizing a model for point defect scattering, we analyze the origin of the low thermal conductivity in SnTe–In2Te3 and attribute it mainly to the strong vacancy originated phonon scattering between Sn atoms and the vacancies introduced by In2Te3 alloying and partly to the interfacial scattering by In-rich nanoprecipitates present in SnTe matrix. By alloying only In2Te3 with SnTe, a ZT value of ~0.9 at 923 K was achieved. ZT can be further increased to ~1.1 at 923 K through adjusting the charge carriers by iodine doping at Te sites.

  10. Structural characterization of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature using neutron powder diffraction and extended X-ray absorption fine structure techniques

    SciTech Connect

    Mansour, A. N.; Wong-Ng, W.; Huang, Q.; Tang, W.; Thompson, A.; Sharp, J.

    2014-08-28

    The structure of Bi{sub 2}Te{sub 3} (Seebeck coefficient Standard Reference Material (SRM™ 3451)) and the related phase Sb{sub 2}Te{sub 3} have been characterized as a function of temperature using the neutron powder diffraction (NPD) and the extended X-ray absorption fine structure (EXAFS) techniques. The neutron structural studies were carried out from 20 K to 300 K for Bi{sub 2}Te{sub 3} and from 10 K to 298 K for Sb{sub 2}Te{sub 3}. The EXAFS technique for studying the local structure of the two compounds was conducted from 19 K to 298 K. Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} are isostructural, with a space group of R3{sup ¯}m. The structure consists of repeated quintuple layers of atoms, Te2-M-Te1-M-Te2 (where M = Bi or Sb) stacking along the c-axis of the unit cell. EXAFS was used to examine the bond distances and static and thermal disorders for the first three shells of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature. The temperature dependencies of thermal disorders were analyzed using the Debye and Einstein models for lattice vibrations. The Debye and Einstein temperatures for the first two shells of Bi{sub 2}Te{sub 3} are similar to those of Sb{sub 2}Te{sub 3} within the uncertainty in the data. However, the Debye and Einstein temperatures for the third shell of Bi-Bi are significantly lower than those of the third shell of Sb-Sb. The Einstein temperature for the third shell is consistent with a soft phonon mode in both Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3}. The lower Einstein temperature of Bi-Bi relative to Sb-Sb is consistent with the lower value of thermal conductivity of Bi{sub 2}Te{sub 3} relative to Sb{sub 2}Te{sub 3}.

  11. 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.

  12. 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)

  13. Materials at Atomic Pressure

    SciTech Connect

    Hicks, Damien

    2010-06-10

    Atomic units give the scale at which quantum processes operate. As combinations of fundamental constants they concisely encapsulate qualities of the atom, e.g. atomic length and energy scales are given by the Bohr radius and the Hartree (or Rydberg) respectively. Although many of these quantities were probed in the early part of the 20th Century the atomic unit of time, at tens of attoseconds, was first probed in 2001. Today, the only atomic unit that remains to be studied experimentally is the atomic unit of pressure, at 294 Mbar (or 147 Mbar in Rydberg atomic units). This is nature’s definition of the ‘high’ in high-pressure science, and it sets the scale for new physics and chemistry. Among experimental facilities, only the NIF can attain and accurately probe atomic pressures. We propose to directly study material properties at these conditions by examining the short-range ordering of atoms using x-ray absorption fine structure spectroscopy (XAFS) of layers in spherical, ignition-type imploding shells. What happens at atomic pressures? The atomic unit of pressure represents the quantum mechanical pressure exerted by an orbiting electron to prevent collapse into the nucleus. Applying external pressure of this magnitude seriously disrupts orbitals and alters the character of the atom itself. Core electron orbitals overlap and chemical bonds are no longer constrained to occur between valence electron orbitals alone. The most direct probe of bonding requires a short-range order diagnostic such as XAFS.

  14. 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…

  15. 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)

  16. Theory of Atomic Games

    NASA Astrophysics Data System (ADS)

    Zhang, Yikun

    2003-04-01

    A new atomic theory is proposed based on radiation mechanics. Atoms cannot be regarded as unrelated individuals, but in a game of claiming to emit photons. Every atom aims to minimize its expected energy by using mixed strategy in the game. Equilibrium points exist as the non-cooperative solution of an atomic game. In a gas composed of same atoms, every equilibrium point determines an optimum probability distribution of energy of each atom as well as of all atoms. The individual optimum is equivalent to the over-all optimum. In an ideal gas of identical atoms, the spin angular momentum of an electron in each atom can only take a series of discrete numerical values between the ground and excited states. There are two fundamental kinds of phase transitions, accomplished respectively by aggregation of atoms to form larger coalitions or by transformation of preexisting coalitions into new configurations. For the first kind, atomic games in both phases have the unique solution. The expected energies of two phases are equal at the critical point. For the second kind, atomic games have multiple solutions. There is often a fall of the expected energies between two phases at the critical point.

  17. Replacement of Ge in GeTe by [Ag +Sb] and rare earths: effect on thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Hanson, M.; Hanus, R.; Schmidt-Rohr, K.

    2013-03-01

    High-efficiency p-type Te-Sb-Ge-Ag (TAGS) thermoelectric materials are based on the GeTe narrow-band self-dopant semiconductor where Ge can be replaced by up to 16 at.% [Ag +Sb]. To understand the effect of Ge replacement by 4 at.% [Ag +Sb] as well as rare earths atoms, we have synthesized and studied XRD, thermopower, electrical resistivity, thermal conductivity, and 125Te NMR of GeTe and Ag2Sb2Ge46-xRxTe50 with R =Gd, Dy and x = 1, 2. At 700 K, GeTe exhibits a thermopower of +146 μVK-1 and a large power factor, 42 μWcm-1K-2. Replacement of Ge by [Ag +Sb] and rare earths enhances the thermopower, but slightly reduces the power factor due to an increase in electrical resistivity. The thermal conductivity at 300 K of all alloys studied is reduced by a factor of two compared to GeTe. 125Te NMR spin-lattice relaxation time and resonance frequency reflect changes in carrier concentration. However, decrease of thermal conductivity due to carriers and increase of electrical resistivity are mostly due to a reduction of carrier mobility and indicate strong scattering produced by [Ag +Sb] and rare earth atoms. At 700 K, the thermoelectric figure of merit of GeTe is 0.8, whereas that in Ag2Sb2Ge45Dy1Te50 is much larger, 1.2, due to a reduction in thermal conductivity. Enhancement of thermopower is discussed within a model of energy filtering.

  18. Growth, properties and applications of HgCdTe

    NASA Astrophysics Data System (ADS)

    Schmit, J. L.

    1983-12-01

    This paper provides primarily a review of the methods used to grow HgCdTe with a summary of some of its basic properties and applications. Methods of crystal growth fall generally into three classes: growth from the melt, from solution and from the vapor phase. All three methods have been and are being used to grow HgCdTe. The high vapor pressure of HgCdTe at the melting point, combined with a large segregation coefficient, have effectively limited the use of Czochralski or zone melting techniques, but two melt growth techniques have survived: (1) a variation of Bridgman growth called quench-anneal wherein a dendritic crystal is formed by quenching the melt and is homogenized by solid state recrystallization below the melting point, (2) a variation of freezing from a large volume called slush-growth wherein a melt is held in a temperature gradient for several weeks while a crystal grows. Growth from solution has taken the form of liquid phase epitaxy (LPE) on CdTe with the LPE systems including growth from Hg-rich, HgTe-rich and Te-rich solutions and using tipping, vertical dipping, vertical sliding and horizontal sliding. Vapor phase growth is very promising but is not yet in production. Techniques include growth by isothermal close spaced epitaxy in which HgTe is transported isothermally by chemical potential onto CdTe, molecular beam epitaxy (MBE) in which elements are evaporated in a high vacuum, and metal organic chemical vapor deposition (MOCVD) in which some of the metal atoms are carried to the substrate bound to organic radicals before being freed by pyrolysis. In all these methods, control of Hg pressure is a major concern. The fundamental properties discussed briefly are those of prime interest to detector manufacturers: energy gap ( Eg), intrinsic carrier concentration ( ni), and electrical activity of dopants. A reasonable fit to the Eg data from ˜ 20 papers is given by Eg = -0.302+1.93x+5.35×10 -4T(1-2x)-0.810x 2+0.832x 3. This gap, combined with k

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Structure of AsxTe100-x (20<=x<=60) glasses investigated with x-ray absorption fine structure, x-ray and neutron diffraction, and reverse Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Jóvári, P.; Yannopoulos, S. N.; Kaban, I.; Kalampounias, A.; Lishchynskyy, I.; Beuneu, B.; Kostadinova, O.; Welter, E.; Schöps, A.

    2008-12-01

    A systematic and detailed investigation of the structure of AsxTe100-x glasses (20⩽x⩽60) has been undertaken using a combination of structure-probing techniques including high energy x-ray diffraction, neutron diffraction, and x-ray absorption fine structure measurements at the As and TeK edges. The experimental datasets were modeled simultaneously with the reverse Monte Carlo simulation technique. The results revealed that homonuclear bonding for both As and Te atoms is important over the whole glass concentration region studied. At the stoichiometric composition (As40Te60) the average As-As and Te-Te coordination numbers are as high as 1.7±0.2 and 1.3±0.1, respectively. The number of As-As and Te-Te bonds, as well as the average number of bonds/atom, evolves monotonically with composition. Arsenic atoms are threefold coordinated for all compositions investigated. It has also been shown that, in contrast to the results of previous studies, Te is predominantly twofold coordinated for x ⩽50. Our results suggest that (i) chemical ordering does not play a decisive role in the formation of short-range order and (ii) similar to some other amorphous tellurides (e.g., Ge2Sb2Te5, GeSb2Te4, and As25Si40Te35) binary AsxTe100-x (x ⩽50) alloys obey the "8-N" rule. A detailed comparison has been advanced between the structural details obtained from the present study and several physicochemical properties of As-Te. The comparison revealed striking similarities between the concentration dependence of structural and physicochemical properties.

  5. Effects of Mass Fluctuation on Thermal Transport Properties in Bulk Bi2Te3

    NASA Astrophysics Data System (ADS)

    Huang, Ben; Zhai, Pengcheng; Yang, Xuqiu; Li, Guodong

    2016-10-01

    In this paper, we applied large-scale molecular dynamics and lattice dynamics to study the influence of mass fluctuation on thermal transport properties in bulk Bi2Te3, namely thermal conductivity (K), phonon density of state (PDOS), group velocity (v g), and mean free path (l). The results show that total atomic mass change can affect the relevant vibrational frequency on the micro level and heat transfer rate in the macro statistic, hence leading to the strength variation of the anharmonic phonon processes (Umklapp scattering) in the defect-free Bi2Te3 bulk. Moreover, it is interesting to find that the anharmonicity of Bi2Te3 can be also influenced by atomic differences of the structure such as the mass distribution in the primitive cell. Considering the asymmetry of the crystal structure and interatomic forces, it can be concluded by phonon frequency, lifetime, and velocity calculation that acoustic-optical phonon scattering shows the structure-sensitivity to the mass distribution and complicates the heat transfer mechanism, hence resulting in the low lattice thermal conductivity of Bi2Te3. This study is helpful for designing the material with tailored thermal conductivity via atomic substitution.

  6. 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.

  7. CdTe-HgTe core-shell nanowire growth controlled by RHEED

    NASA Astrophysics Data System (ADS)

    Kessel, M.; Hajer, J.; Karczewski, G.; Schumacher, C.; Brüne, C.; Buhmann, H.; Molenkamp, L. W.

    2017-07-01

    We present results on the growth of CdTe-HgTe core-shell nanowires, a realization of a quasi-one-dimensional heterostructure of the topological insulator HgTe. The growth is a two step process consisting of the growth of single crystalline zinc blende CdTe nanowires with the vapor-liquid-solid method and the overgrowth of these wires with HgTe such that a closed shell is formed around the CdTe core structure. The CdTe wire growth is monitored by RHEED allowing us to infer information on the crystal properties from the electron diffraction pattern. This information is used to find and control the optimal growth temperature. High quality single crystal CdTe nanowires grow with a preferred orientation. For the growth of the conductive HgTe shell structure we find that the supplied Hg:Te ratio is the crucial parameter to facilitate growth on all surface facets.

  8. Fletching-shaped Bi4Te3-ZnTe heterostructure nanowires

    NASA Astrophysics Data System (ADS)

    Song, Man Suk; Kim, Yong

    2014-12-01

    We investigated Bi4Te3-ZnTe axial heterostructure nanowires grown by physical vapor transport at the substrate temperature of 450 °C, utilizing ZnTe as the source and Bi2Te3 as the catalyst. The temperatures of the source and catalyst materials were individually controlled by separating the source and catalyst boats. The axial heterostructure nanowires consisted of ZnTe and Bi4Te3 segments. The Bi4Te3 segment had an interesting fletching shape with three wings surrounded by a ZnO shell. A systematic redshift in the nanowire’s photoluminescence was observed as the excitation laser spot was moved from the heterojunction toward the root of the ZnTe segment, attributed to the formation of deep defect states under the Te-rich environment that resulted from using Bi2Te3 as the catalyst instead of Bi.

  9. Phase-shifting electron holography for atomic image reconstruction.

    PubMed

    Yamamoto, Kazuo; Sugawara, Yoshihiro; McCartney, Martha R; Smith, David J

    2010-08-01

    Phase-shifting electron holography was used to reconstruct the object-wave function of high-spatial-frequency specimens of HgCdTe, and the requirements for precise measurements were investigated. Fresnel fringes due to the electrostatic biprism caused serious calculation errors during the phase-shifting reconstruction. Uniform interference fringes, obtained by adjusting the biprism voltage to cancel out the Fresnel fringes, were needed to minimize these errors. High-resolution holograms of a HgCdTe single crystal were recorded with coarse interference fringes and a high visibility of 65% and then used to reconstruct the atomic-scale object wave. Although the spatial resolution (0.25 nm) of the transmission electron microscope was worse than the separation (0.16 nm) between Hg (or Cd) and Te columns, the crystal polarity was determined from the aberration-corrected object wave.

  10. Sulfide bonded atomic radii

    NASA Astrophysics Data System (ADS)

    Gibbs, G. V.; Ross, N. L.; Cox, D. F.

    2017-03-01

    The bonded radius, r b(S), of the S atom, calculated for first- and second-row non-transition metal sulfide crystals and third-row transition metal sulfide molecules and crystals indicates that the radius of the sulfur atom is not fixed as traditionally assumed, but that it decreases systematically along the bond paths of the bonded atoms with decreasing bond length as observed in an earlier study of the bonded radius of the oxygen atom. When bonded to non-transition metal atoms, r b(S) decreases systematically with decreasing bond length from 1.68 Å when the S atom is bonded to the electropositive VINa atom to 1.25 Å when bonded to the more electronegative IVP atom. In the case of transition metal atoms, rb(S) likewise decreases with decreasing bond length from 1.82 Å when bonded to Cu and to 1.12 Å when bonded to Fe. As r b(S) is not fixed at a given value but varies substantially depending on the bond length and the field strength of the bonded atoms, it is apparent that sets of crystal and atomic sulfide atomic radii based on an assumed fixed radius for the sulfur atom are satisfactory in that they reproduce bond lengths, on the one hand, whereas on the other, they are unsatisfactory in that they fail to define the actual sizes of the bonded atoms determined in terms of the minima in the electron density between the atoms. As such, we urge that the crystal chemistry and the properties of sulfides be studied in terms of the bond lengths determined by adding the radii of either the atomic and crystal radii of the atoms but not in terms of existing sets of crystal and atomic radii. After all, the bond lengths were used to determine the radii that were experimentally determined, whereas the individual radii were determined on the basis of an assumed radius for the sulfur atom.

  11. Sulfide bonded atomic radii

    NASA Astrophysics Data System (ADS)

    Gibbs, G. V.; Ross, N. L.; Cox, D. F.

    2017-09-01

    The bonded radius, r b(S), of the S atom, calculated for first- and second-row non-transition metal sulfide crystals and third-row transition metal sulfide molecules and crystals indicates that the radius of the sulfur atom is not fixed as traditionally assumed, but that it decreases systematically along the bond paths of the bonded atoms with decreasing bond length as observed in an earlier study of the bonded radius of the oxygen atom. When bonded to non-transition metal atoms, r b(S) decreases systematically with decreasing bond length from 1.68 Å when the S atom is bonded to the electropositive VINa atom to 1.25 Å when bonded to the more electronegative IVP atom. In the case of transition metal atoms, rb(S) likewise decreases with decreasing bond length from 1.82 Å when bonded to Cu and to 1.12 Å when bonded to Fe. As r b(S) is not fixed at a given value but varies substantially depending on the bond length and the field strength of the bonded atoms, it is apparent that sets of crystal and atomic sulfide atomic radii based on an assumed fixed radius for the sulfur atom are satisfactory in that they reproduce bond lengths, on the one hand, whereas on the other, they are unsatisfactory in that they fail to define the actual sizes of the bonded atoms determined in terms of the minima in the electron density between the atoms. As such, we urge that the crystal chemistry and the properties of sulfides be studied in terms of the bond lengths determined by adding the radii of either the atomic and crystal radii of the atoms but not in terms of existing sets of crystal and atomic radii. After all, the bond lengths were used to determine the radii that were experimentally determined, whereas the individual radii were determined on the basis of an assumed radius for the sulfur atom.

  12. Fast Neutron Detection using Pixelated CdZnTe Spectrometers

    DOE PAGES

    Streicher, Michael; Goodman, David; Zhu, Yuefeng; ...

    2017-05-29

    One important important signature of special nuclear materials (SNM) are fast neutrons. Fast neutrons have a low natural background rate and readily penetrate high atomic number materials which easily shield gamma-ray signatures. Thus, fast neutrons provide a complementary signal to gamma rays for detecting shielded SNM. Scattering kinematics dictate that a large nucleus (such as Cd or Te) will recoil with small kinetic energy after an elastic collision with a fast neutron. Charge carrier recombination and quenching further reduce the recorded energy deposited. Thus, the energy threshold of CdZnTe detectors must be very low in order to sense the smallmore » signals from these recoils. Here, the threshold was reduced to less than 5 keVee to demonstrate that the 5.9 keV x-ray line from 55Fe could be separated from electronic noise. Elastic scattering neutron interactions were observed as small energy depositions (less than 20 keVee) using digitally-sampled pulse waveforms from pixelated CdZnTe detectors. Characteristic gamma-ray lines from inelastic neutron scattering were also observed.« less

  13. Properties of Ag layered in Te/Cd stack prepared by stacked elemental layer method

    NASA Astrophysics Data System (ADS)

    Subramani, Shanmugan; Devarajan, Mutharasu; Ibrahim, Kamarulazizi

    2012-06-01

    Ag layered Te/Cd stack thin films (<1 µm thick) were prepared by the Stacked Elemental Layer (SEL) method. The XRD results revealed that the synthesized films had a polycrystalline nature. The synthesized films were preferentially oriented with (111) directions with a cubic phase. Structural studies were evidenced the formation of Ag related alloys at high annealing temperatures as a result of thermal diffusion in elemental stack. Optical and photo-resistivity studies revealed the influence of Ag on the CdTe lattice at high annealing temperatures. Surface morphology and the influence of Ag atoms on surface roughness are also presented.

  14. Phonons in Bi2Te3 and Bi2Se3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Fen; Cheng, Wei

    2010-03-01

    Bi2Te3 and Bi2Se3 are topological insulators with interesting surface properties that have attracted great research attention in recent years. In this research, phonon dispersion curves and phonon density of states of Bi2Te3 and Bi2Se3 thin films with five atomic-layers are calculated by Medea-VASP program, and thermal dynamic functions are also analyzed. Phonon results of these two thin films are compared with each other and are also compared with available bulk measurements. Symmetry broken is found in the Brillouin zone center phonon modes.

  15. Grain boundary enhanced carrier collection in CdTe solar cells

    SciTech Connect

    Li, Chen; Wu, Yelong; Poplawsky, Jonathan D; Paudel, Naba; Yin, Wanjian; Pennycook, Timothy; Haigh, Sarah; Oxley, Mark P; Lupini, Andrew R; Al-jassim, Mowafak; Pennycook, Stephen J; Yan, Yanfa

    2014-01-01

    The atomic structure and composition of grain boundaries in CdCl2 treated CdTe solar cells have been determined with aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy. A high fraction of Te in the grain boundary regions has been substituted by Cl. Density functional calculations reveal the origin of such segregation levels, and further indicate the GBs are likely inverted to n-type, establishing local P-N junctions, which help to separate electron-hole carriers. The results are in good agreement with electron beam induced current observations of high collection efficiency at grain boundaries.

  16. 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.

  17. Basis set effects on the Hartree-Fock description of confined many-electron atoms

    NASA Astrophysics Data System (ADS)

    Garza, Jorge; Hernández-Pérez, Julio M.; Ramírez, José-Zeferino; Vargas, Rubicelia

    2012-01-01

    In this work, the basis sets designed by Clementi, Bunge and Thakkar, for atomic systems, have been used to obtain the electronic structure of confined many-electron atoms by using Roothaan's approach in the Hartree-Fock context with a new code written in C, which uses the message-passing interface library. The confinement was imposed as Ludeña suggested to simulate walls with infinity potential. For closed-shell atoms, the Thakkar basis set functions give the best total energies (TE) as a function of the confinement radius, obtaining the following ordering: TE(Thakkar) < TE(Bunge) < TE(Clementi). However, for few open-shell atoms this ordering is not preserved and a trend, for the basis sets, is not observed. Although there are differences between the TE predicted by these basis set functions, the corresponding pressures are similar to each other; it means that changes in the total energy are described almost in the same way by using any of these basis sets. By analysing the total energy as a function of the inverse of the volume we propose an equation of state; for regions of small volumes, this equation predicts that the pressure is inversely proportional to the square of the volume.

  18. 125Te NMR study of IrTe 2

    NASA Astrophysics Data System (ADS)

    Mizuno, Kiyoshi; Magishi, Ko-ichi; Shinonome, Yasuaki; Saito, Takahito; Koyama, Kuniyuki; Matsumoto, Nobuhiro; Nagata, Shoichi

    2002-03-01

    We have measured 125Te NMR of IrTe2 in order to elucidate the origin of the anomalous behaviors in electrical and magnetic properties around 270 K. In high-temperature region, the NMR spectrum exhibits a sharp line. On the other hand, in low-temperature region, the spectrum shifts to higher magnetic field and splits into three lines. Also, the nuclear spin-lattice relaxation rate, 1/T1, is proportional to the temperature in both temperature sides; Korringa-like behavior which is characteristic of a metallic state. From the T dependences of the spectrum and 1/T1 around 270 K, it is suggested that these anomalous behaviors may not be due to the charge density wave formation but be caused by a kind of lattice distortion at low temperature.

  19. Lattice dynamics in Bi2Te3 and Sb2Te3: Te and Sb density of phonon states

    NASA Astrophysics Data System (ADS)

    Bessas, D.; Sergueev, I.; Wille, H.-C.; Perßon, J.; Ebling, D.; Hermann, R. P.

    2012-12-01

    The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using 121Sb and 125Te nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements. In combination with earlier inelastic neutron scattering data, the element-specific density of phonon states was obtained for both compounds and phonon polarization analysis was carried out for Bi2Te3. A prominent peak in the Te specific density of phonon states at 13meV, that involves mainly in-plane vibrations, is mostly unaffected upon substitution of Sb with Bi revealing vibrations with essentially Te character. A significant softening is observed for the density of vibrational states of Bi with respect to Sb, consistently with the mass homology relation in the long-wavelength limit. In order to explain the energy mismatch in the optical phonon region, a ˜20% force constant softening of the Sb-Te bond with respect to the Bi-Te bond is required. The reduced average speed of sound at 20K in Bi2Te3, 1.75(1)km/s, compared to Sb2Te3, 1.85(4)km/s, is not only related to the larger mass density but also to a larger Debye level. The observed low lattice thermal conductivity at 295K, 2.4Wm-1K-1 for Sb2Te3 and 1.6Wm-1K-1 for Bi2Te3, cannot be explained by anharmonicity alone given the rather modest Grüneisen parameters, 1.7(1) for Sb2Te3 and 1.5(1) for Bi2Te3, without accounting for the reduced speed of sound and more importantly the low acoustic cutoff energy.

  20. 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.

  1. Crystal growth of Bi{sub 2}Te{sub 3} and noble cleaved (0001) surface properties

    SciTech Connect

    Atuchin, V.V.; Golyashov, V.A.; Kokh, K.A.; Korolkov, I.V.; Kozhukhov, A.S.; Kruchinin, V.N.; Loshkarev, I.D.; Pokrovsky, L.D.; Prosvirin, I.P.; and others

    2016-04-15

    A high quality Bi{sub 2}Te{sub 3} crystal has been grown by Bridgman method with the use of rotating heat field. The phase purity and bulk structural quality of the crystal have been verified by XRD analysis and rocking curve observation. The atomically smooth Bi{sub 2}Te{sub 3}(0001) surface with an excellent crystallographic quality is formed by cleavage in the air. The chemical and microstructural properties of the surface have been evaluated with RHEED, AFM, STM, SE and XPS. The Bi{sub 2}Te{sub 3}(0001) cleaved surface is formed by atomically smooth terraces with the height of the elemental step of ~1.04±0.1 nm, as estimated by AFM. There is no surface oxidation process detected over a month keeping in the air at normal conditions, as shown by comparative core level photoelectron spectroscopy. - Graphical abstract: A high quality Bi{sub 2}Te{sub 3} crystal has been grown by Bridgman method with the use of rotating heat field and the Bi{sub 2}Te{sub 3}(0001) cleaved surface has been evaluated with RHEED, AFM, STM, SE and XPS. - Highlights: • High-quality Bi{sub 2}Te{sub 3} crystal of 10 mm in diameter and 50 mm long have been grown. • The high-purity cleaved Bi{sub 2}Te{sub 3}(0001) surface has been evaluated by RHEED, AFM, STM and XPS methods. • The Bi{sub 2}Te{sub 3} surface covered by atomically smooth (0001) terraces is chemically stable for a long time.

  2. Manipulation of type-I and type-II Dirac points in PdTe2 superconductor by external pressure

    NASA Astrophysics Data System (ADS)

    Xiao, R. C.; Gong, P. L.; Wu, Q. S.; Lu, W. J.; Wei, M. J.; Li, J. Y.; Lv, H. Y.; Luo, X.; Tong, P.; Zhu, X. B.; Sun, Y. P.

    2017-08-01

    A pair of type-II Dirac cones in PdTe2 was recently predicted by theories and confirmed in experiments, making PdTe2 the first material that processes both superconductivity and type-II Dirac fermions. In this paper, we study the evolution of Dirac cones in PdTe2 under hydrostatic pressure by first-principles calculations. Our results show that the pair of type-II Dirac points disappears at 6.1 GPa. Interestingly, a new pair of type-I Dirac points from the same two bands emerges at 4.7 GPa. Due to the distinctive band structures compared with those of PtSe2 and PtTe2, the two types of Dirac points can coexist in PdTe2 under proper pressure (4.7-6.1 GPa). The emergence of type-I Dirac cones and the disappearance of type-II Dirac ones are attributed to an increase/decrease of the energy of the states at the Γ and A points, which have antibonding/bonding characters of the interlayer Te-Te atoms. On the other hand, we find that the superconductivity of PdTe2 slightly decreases with pressure. The pressure-induced types of Dirac cones combined with superconductivity may open a promising way to investigate the complex interactions between Dirac fermions and superconducting quasiparticles.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. Indium donor complexes with cation vacancies in CdTe and ZnSe

    SciTech Connect

    Griffith, J.W.; Lundquist, R.; Platzer, R.; Gardner, J.A.; Karczewski, G.; Furdyna, J.K.

    1993-11-01

    Very dilute (10{sub 12} cm{sup {minus}3}) indium donors in CdTe and ZnSe powders and in CdTe single crystals were investigated using {sup 111}In Perturbed angular correlation spectroscopy. Most indium atoms are in uncomplexed sites but can form weakly-bound complexes with native defects in very defective material. The only complex observed in CdTe is an indium-Cd vacancy pair. The CdTe in which these pairs occur is apparently n-type, most Cd vacancies are free and doubly-charged, and the binding energy with indium is 0.15 eV. In ZnSe, indium can pair with a Zn vacancy or with some other presently unidentified defect. These complexes form in ZnSe containing large concentrations of both free Zn vacancies and complexes of Zn vacancies with other defects. In CdTe, the pair formation equilibration time constant is two days at 15C,an implication that Cd vacancies are mobile at room temperature. Lattice relaxation around a Cd vacancy in CdTe was probed by single crystal PAC experiments.

  8. Thermochemical properties of silver tellurides including empressite (AgTe) and phase diagrams for Ag-Te and Ag-Te-O

    NASA Astrophysics Data System (ADS)

    Voronin, Mikhail V.; Osadchii, Evgeniy G.; Brichkina, Ekaterina A.

    2017-04-01

    This study compiles original experimental and literature data on the thermodynamic properties (ΔfG°, S°, ΔfH°) of silver tellurides (α-Ag2Te, β-Ag2Te, Ag1.9Te, Ag5Te3, AgTe) obtained by the method of solid-state galvanic cell with the RbAg4I5 and AgI solid electrolytes. The thermodynamic data for empressite (AgTe, pure fraction from Empress Josephine Mine, Colorado USA) have been obtained for the first time by the electrochemical experiment with the virtual reaction Ag + Te = AgTe. The Ag-Te phase diagrams in the T - x and logfTe2 (gas) - 1/T coordinates have been refined, and the ternary Ag-Te-O diagrams with Ag-Te-TeO2 (paratellurite) composition range have been calculated.

  9. M@TE - Monitoring at TeV energies

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    Blazars are extremely variable objects emitting radiation across the electromagnetic spectrum and showing variability on time scales from minutes to years. For the understanding of the emission mechanisms, simultaneous multi-wavelength observations are crucial. Various models for flares predict simultaneous flux increases in the X-ray and in the gamma-ray band or more complex variability patterns, depending on the dominant process responsible for the gamma-ray emission. Monitoring at TeV energies is providing important information to distinguish between different emission mechanisms. To study the duty cycle and the variability time scales of the object, an unbiased data sample is essential, and a good sensitivity and continuous monitoring are needed to resolve variability on smaller time scales. A dedicated long-term monitoring program at TeV energies has been started by the FACT project more than four years ago. The success of the project clearly illustrated that the usage of silicon based photo sensors (SIPMs) is ideally suited for long-term monitoring. They provide not only an excellent and stable detector performance, but also allow for observations during bright ambient light like full moon minimizing observational gaps and increasing the duty cycle of the instrument. The observation time in a single longitude is limited to six hours. To study typical variability time scales of few hours to one day, the ultimate goal is 24/7 monitoring with a network of small telescopes around the globe (DWARF project). The installation of an Imaging Air Cherenkov Telescope is planned at the site in San Pedro Martir in Mexico. For the M@TE (Monitoring at TeV energies) telescope, a mount from a previous experiment is being refurbished and will be equipped with a camera using the new generation of SiPMs. In the presentation, the status of the M@TE project will be reported and the scientific potential, including the possibility to extend monitoring campaigns to 12 hours by

  10. 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

  11. Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

    NASA Astrophysics Data System (ADS)

    Yu, Chia-Chi; Wu, Hsin-Jay; Deng, Ping-Yuan; Agne, Matthias T.; Snyder, G. Jeffrey; Chu, Jinn P.

    2017-03-01

    The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8-360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10-20-10-23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10-14-10-17(m2/s)] and Cu [10-8-10-11(m2/s)] in Bi2Te3, respectively.

  12. Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

    PubMed Central

    Yu, Chia-Chi; Wu, Hsin-jay; Deng, Ping-Yuan; Agne, Matthias T.; Snyder, G. Jeffrey; Chu, Jinn P.

    2017-01-01

    The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10−20–10−23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10−14–10−17(m2/s)] and Cu [10−8–10−11(m2/s)] in Bi2Te3, respectively. PMID:28327655

  13. Global Anisotropies in TeV Cosmic Rays Related to the Sun's Local Galactic Environment from IBEX (Invited)

    NASA Astrophysics Data System (ADS)

    Schwadron, N.; Adams, F.; Christian, E. R.; Desiati, P.; Frisch, P. C.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G. P.

    2013-12-01

    The Interstellar Boundary Explorer (IBEX) observes enhanced Energetic Neutral Atoms (ENAs) emission from a narrow 'ribbon' likely centered on the local interstellar (LIS) magnetic field direction. Further, IBEX has revised the local interstellar velocity based on interstellar atom measurements. These new determinations are shown to be consistent with the interstellar modulation of TeV cosmic rays revealed in global anisotropy maps of Milagro, Asγ and IceCube.

  14. Donor-deactivating defects above the equilibrium doping limit in GaAs:Te,Ge and GaAs:Te studied by annealing and Hall effect under pressure

    NASA Astrophysics Data System (ADS)

    Slupinski, T.; Wasik, D.; Przybytek, J.

    2017-06-01

    High temperature annealing experiments of n-type double-doped (co-doped) GaAs:Te,Ge single crystal samples close to or above the equilibrium doping limit are presented and compared to annealing results of very highly doped GaAs:Te known for a long time, but still not clarified satisfactorily. An addition of Ge impurity to GaAs:Te shifted the equilibrium doping limit to a lower free electron concentration - a result which is difficult to describe within models of doping limit assuming an electrical compensation mainly by native acceptors. Hall effect under hydrostatic pressure up to 1.5 GPa allowed to directly measure the change of concentration of GeGa donors caused by annealing, in addition to free electron concentration changes in GaAs:Te,Ge. GeGa donors were detected by the capture of free electrons by Ge DX states at high pressure, following the method described by Baj et al. [Phys. Rev. Lett.71, 3529 (1993)]. In highly doped GaAs:Te,Ge, the measured ratio of changes of free electrons and GeGa donors concentrations caused by high temperature annealing at 1100 °C, Δn / Δ [ GeGa ] =4.2+/- 0.6, supports the model of chemically bonded impurity-impurity molecules, probably of type Ge-Tem (where m =3÷4 atoms), which may be consistent with recently proposed models of paired impurities: DDX or double-DX centers.

  15. Role of the nano amorphous interface in the crystallization of Sb2Te3 towards non-volatile phase change memory: insights from first principles.

    PubMed

    Wang, Xue-Peng; Chen, Nian-Ke; Li, Xian-Bin; Cheng, Yan; Liu, X Q; Xia, Meng-Jiao; Song, Z T; Han, X D; Zhang, S B; Sun, Hong-Bo

    2014-06-14

    The nano amorphous interface is important as it controls the phase transition for data storage. Yet, atomic scale insights into such kinds of systems are still rare. By first-principles calculations, we obtain the atomic interface between amorphous Si and amorphous Sb2Te3, which prevails in the series of Si-Sb-Te phase change materials. This interface model reproduces the experiment-consistent phenomena, i.e. the amorphous stability of Sb2Te3, which defines the data retention in phase change memory, and is greatly enhanced by the nano interface. More importantly, this method offers a direct platform to explore the intrinsic mechanism to understand the material function: (1) by steric effects through the atomic "channel" of the amorphous interface, the arrangement of the Te network is significantly distorted and is separated from the p-orbital bond angle in the conventional phase-change material; and (2) through the electronic "channel" of the amorphous interface, high localized electrons in the form of a lone pair are "projected" to Sb2Te3 from amorphous Si by a proximity effect. These factors set an effective barrier for crystallization and improve the amorphous stability, and thus data retention. The present research and scheme sheds new light on the engineering and manipulation of other key amorphous interfaces, such as Si3N4/Ge2Sb2Te5 and C/Sb2Te3, through first-principles calculations towards non-volatile phase change memory.

  16. Solar Spectroscopy: Atomic Processes

    NASA Astrophysics Data System (ADS)

    Mason, H.; Murdin, P.

    2000-11-01

    A Greek philosopher called DEMOCRITUS (c. 460-370 BC) first introduced the concept of atoms (which means indivisible). His atoms do not precisely correspond to our atoms of today, which are not indivisible, but made up of a nucleus (protons with positive charge and neutrons which have no charge) and orbiting electrons (with negative charge). Indeed, in the solar atmosphere, the temperature is suc...

  17. Optical atomic clocks

    NASA Astrophysics Data System (ADS)

    Ludlow, Andrew D.; Boyd, Martin M.; Ye, Jun; Peik, E.; Schmidt, P. O.

    2015-04-01

    Optical atomic clocks represent the state of the art in the frontier of modern measurement science. In this article a detailed review on the development of optical atomic clocks that are based on trapped single ions and many neutral atoms is provided. Important technical ingredients for optical clocks are discussed and measurement precision and systematic uncertainty associated with some of the best clocks to date are presented. An outlook on the exciting prospect for clock applications is given in conclusion.

  18. Atomicity in Electronic Commerce,

    DTIC Science & Technology

    1996-01-01

    tremendous demand for the ability to electronically buy and sell goods over networks. Electronic commerce has inspired a large variety of work... commerce . It then briefly surveys some major types of electronic commerce pointing out flaws in atomicity. We pay special attention to the atomicity...problems of proposals for digital cash. The paper presents two examples of highly atomic electronic commerce systems: NetBill and Cryptographic Postage Indicia.

  19. Electrochemical Atomic Layer Processing

    DTIC Science & Technology

    1994-06-25

    where an atomic layer of an element is deposited , or removed, in a surface limited reaction. The potentials used are referred to as underpotentials in...the electrochemical literature. The atomic layer deposition process is referred to as underpotential deposition (UPD). 14. SUBJECT TERMS 15, NUMBER OF...reaction. The potentials used are referred to as underpotentials in the electrochemical literature. The atomic layer deposition process is referred to as

  20. 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)

  1. 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.

  2. The Software Atom

    NASA Astrophysics Data System (ADS)

    Javanainen, Juha

    2017-03-01

    By putting together an abstract view on quantum mechanics and a quantum-optics picture of the interactions of an atom with light, we develop a corresponding set of C++ classes that set up the numerical analysis of an atom with an arbitrary set of angular-momentum degenerate energy levels, arbitrary light fields, and an applied magnetic field. As an example, we develop and implement perturbation theory to compute the polarizability of an atom in an experimentally relevant situation.

  3. 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

  4. 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.

  5. Graphite filter atomizer in atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Katskov, Dmitri A.

    2007-09-01

    Graphite filter atomizers (GFA) for electrothermal atomic absorption spectrometry (ETAAS) show substantial advantages over commonly employed electrothermal vaporizers and atomizers, tube and platform furnaces, for direct determination of high and medium volatility elements in matrices associated with strong spectral and chemical interferences. Two factors provide lower limits of detection and shorter determination cycles with the GFA: the vaporization area in the GFA is separated from the absorption volume by a porous graphite partition; the sample is distributed over a large surface of a collector in the vaporization area. These factors convert the GFA into an efficient chemical reactor. The research concerning the GFA concept, technique and analytical methodology, carried out mainly in the author's laboratory in Russia and South Africa, is reviewed. Examples of analytical applications of the GFA in AAS for analysis of organic liquids and slurries, bio-samples and food products are given. Future prospects for the GFA are discussed in connection with analyses by fast multi-element AAS.

  6. Epitaxy: Programmable Atom Equivalents versus Atoms

    SciTech Connect

    Wang, Mary X.; Seo, Soyoung E.; Gabrys, Paul A.; Fleischman, Dagny; Lee, Byeongdu; Kim, Youngeun; Atwater, Harry A.; MacFarlane, Robert J.; Mirkin, Chad A.

    2017-01-01

    The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of nanoparticle thin films. Under optimized equilibrium conditions, single crystal, multilayer thin films can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in thin film atomic deposition, allowing for these processes to be understood in the context of well-studied atomic epitaxy, and potentially enabling a nanoscale model to study fundamental crystallization processes.

  7. 125Te and 139La NMR Studies of Single Crystal LaTe3

    NASA Astrophysics Data System (ADS)

    Chudo, Hiroyuki; Michioka, Chishiro; Itoh, Yutaka; Yoshimura, Kazuyoshi

    2007-12-01

    We report 125Te and 139La NMR studies for single crystals of LaTe3 between 10 and 160 K under an applied field of H = 7.4841 T. We observed the broad 125Te(1) NMR signals of metallic Te(1) sheets with a superlattice modulation and the sharp 125Te(2) and 139La NMR signals of LaTe(2) bi-layers. Temperature dependence of 125Te(1) nuclear spin-lattice relaxation times of the modulated Te(1) sheets obeys a modified Korringa relation. The results indicate that the electronic state on the Te(1) sheets is a Landau-Fermi liquid on a misfit superlattice or a Tomonaga-Luttinger liquid in a two-dimensional charge-density wave ordering state.

  8. 125Te NMR in the single crystal of CeTe3: Spin polarized CDW

    NASA Astrophysics Data System (ADS)

    Chudo, H.; Michioka, C.; Itoh, Y.; Yoshimura, K.

    2007-03-01

    We report 125Te NMR studies for single crystals of CeTe3 between 22 and 307 K, under an applied field of H=7.4847 T along a- or b-axis. The 125Te NMR spectrum consists of superposition of broad and sharp peaks, which are assigned to the signals of 125Te(1) in Te(1) sheets and 125Te(2) in CeTe(2) bi-layers, respectively. The broad 125Te(1) NMR spectrum consists of three distinguishable lines, regarded as an evidence for the presence of the incommensurate charge-density wave (ICDW) modulation. The Knight shifts of 125Te(1) widely distribute from -0.16% to +0.58% at 110 K and the temperature dependence of each Knight shift is proportional to the bulk susceptibility, indicating that the conduction electron spin density is polarized by the Ce local moments in the CDW state.

  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. A square-planar tellurium(II) complex with Te,Te'-chelating ligands.

    PubMed

    Chivers, Tristram; Ritch, Jamie S

    2015-05-01

    While exploring the chemistry of tellurium-containing dichalcogenidoimidodiphosphinate ligands, the first all-tellurium member of a series of related square-planar E(II)(E')4 complexes (E and E' are group 16 elements), namely bis(P,P,P',P'-tetraphenylditelluridoimidodiphosphinato-κ(2)Te,Te')tellurium(II) (systematic name: 2,2,4,4,8,8,10,10-octaphenyl-1λ(3),5,6λ(4),7λ(3),11-pentatellura-3,9-diaza-2λ(5),4λ(5),8λ(5),10λ(5)-tetraphosphaspiro[5.5]undeca-1,3,7,9-tetraene), C48H40N2P4Te5, was obtained unexpectedly. The formally Te(II) centre is situated on a crystallographic inversion centre and is Te,Te'-chelated to two anionic [(TePPh2)2N](-) ligands in an anti conformation. The central Te(II)(Te)4 unit is approximately square planar [Te-Te-Te = 93.51 (3) and 86.49 (3)°], with Te-Te bond lengths of 2.9806 (6) and 2.9978 (9) Å.

  11. Pressure dependence of the band-gap energy in BiTeI

    NASA Astrophysics Data System (ADS)

    Güler-Kılıç, Sümeyra; Kılıç, ćetin

    2016-10-01

    The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.

  12. Photo-thermal deflection and electrical switching studies on Ge Te I chalcohalide glasses

    NASA Astrophysics Data System (ADS)

    Pattanayak, Pulok; Manikandan, N.; Paulraj, M.; Asokan, S.

    2007-01-01

    Measurements on thermal diffusivity (α) and electrical switching studies have been undertaken on bulk, melt-quenched Ge22Te78-xIx (3<=x<=10) chalcohalide glasses. The thermal diffusivity values of Ge22Te78-xIx glasses lie in the range 0.09-0.02 cm2 s-1, and are found to decrease with increase in iodine content. The variation of α with composition has been understood on the basis of fragmentation of the Ge-Te network with the addition of iodine. The composition x = 5 (\\overline {r_{\\mathrm {c}} }=2.39 ), at which a cusp is seen in the composition dependence of thermal diffusivity, has been identified to be the inverse rigidity percolation threshold of the Ge22Te78-xIx system at which the network connectivity is completely lost. Further, Ge22Te78-xIx glasses are found to exhibit memory-type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content, in comparison with the switching voltage of the Ge22Te78 base glass. The observed initial decrease in the switching voltages with the addition of iodine is due to the decrease in network connectivity. An increase is seen in switching voltages of Ge22Te78-xIx glasses at higher iodine contents, which suggests the domination of the metallicity factor of the additive atoms on the switching voltages at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the Ge22Te78-xIx system.

  13. New μ-SnTe{sub 4} and μ-Sn{sub 2}Te{sub 6} ligands to transition metal: Solvothermal syntheses and characterizations of zinc tellurostannates containing polyamine ligands

    SciTech Connect

    Lu, Jialin; Wang, Fang; Shen, Yali; Tang, Chunying; Zhang, Yong; Jia, Dingxian

    2014-08-15

    Zinc tellurostannates [(Zn(teta)){sub 2}(μ-1κ:2κ-SnTe{sub 4})] (1), [(Zn(teta)){sub 3}(μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4})]I{sub 2} (2), [(Zn(tren)){sub 2}(μ-1κ:2κ-Sn{sub 2}Te{sub 6})] (3), and [Zn(dien){sub 2}]{sub 4}(Sn{sub 2}Te{sub 6}){sub 1.75}(Sn{sub 2}Te{sub 8}){sub 0.25}·dien (4) were prepared by the reactions of Zn, Sn, and Te with iodine ion assistant in teta and dien. The tetrahedral [SnTe{sub 4}]{sup 4−} anion coordinates to two [Zn(teta)]{sup 2+} units as a bidentate μ-1κ:2κ-SnTe{sub 4} ligand to form the neutral complex 1. It coordinates to three [Zn(teta)]{sup 2+} units with a tridentate μ{sub 3}-1κ:2κ:3κ coordination modes, generating a complex cation [(Zn(teta)){sub 3}(μ{sub 3}-1κ:2κ:3κ- SnTe{sub 4})]{sup 2+} in 2. In 3, the [Sn{sub 2}Te{sub 6}]{sup 4−} anion joins two [Zn(tren)]{sup 2+}cations with the trans terminal Te atoms, forming neutral complex 3. The μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands to TM centers in 1–3 have not been observed before. Compound 4 contains a normal [Sn{sub 2}Te{sub 6}]{sup 4−} and an abnormal [(Sn{sub 2}Te{sub 6}){sub 0.75}(Sn{sub 2}Te{sub 8}){sub 0.25}]{sup 4−} anions. Compounds 1–4 exhibit narrow band gaps in the range of 1.47–1.98 eV, and a distinct red-shift of the band gaps is observed from 4 to 1−3. - Graphical abstract: Zinc tellurostannates were prepared with iodine ion assistant in polyamines, and first μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands TM centers were obtained. - Highlights: • Zinc-tellurostannates were first prepared with iodine ion assistant. • Novel μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands were obtained. • The Zinc tellurostannates exhibit optical bandgaps between 1.47 and 1.98 eV.

  14. 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.

  15. Positron Annihilation Study of Ternary Sb2Te3- x Se x for Its Tuning Electrical and Thermal Properties

    NASA Astrophysics Data System (ADS)

    Zheng, Wenwen; Yang, Dongwang; Bi, Peng; He, Chunqing; Liu, Fengming; Shi, Jing; Ding, Yi; Wang, Ziyu; Xiong, Rui

    2017-05-01

    Atomic scale point defects play important roles in tuning the carrier concentration and ultimately influencing electrical and thermal properties. Herein, we fabricated the ternary Sb2Te3- x Se x alloys to study the intimate relationship of internal point defects and thermoelectric performance. The Se substitution of Te atoms in the Sb2Te3 lattice decreased the electrical conductivity from 2.2 × 105 S/m to 6.4 × 104 S/m owing to the reduced holes concentration. The declined point defects, including antisite defects and vacancies in materials, gave rise to the decrease in carrier concentration. The Seebeck coefficient of the ternary Sb2Te3- x Se x exhibited an increase with doping of Se atoms. Simultaneously, the thermal conductivity behaved a fallihg trend as well as increasing Se content. As a result, the ZT value reached the maximum from the corresponding Sb2Te2.9Se0.1 pellet. Positron annihilation measurement revealed that the average positron lifetime showed a monotonic decrease with Se addition, demonstrating the reduced point defects, which was in agreement with the thermoelectric performance.

  16. Positron Annihilation Study of Ternary Sb2Te3-x Se x for Its Tuning Electrical and Thermal Properties

    NASA Astrophysics Data System (ADS)

    Zheng, Wenwen; Yang, Dongwang; Bi, Peng; He, Chunqing; Liu, Fengming; Shi, Jing; Ding, Yi; Wang, Ziyu; Xiong, Rui

    2016-10-01

    Atomic scale point defects play important roles in tuning the carrier concentration and ultimately influencing electrical and thermal properties. Herein, we fabricated the ternary Sb2Te3-x Se x alloys to study the intimate relationship of internal point defects and thermoelectric performance. The Se substitution of Te atoms in the Sb2Te3 lattice decreased the electrical conductivity from 2.2 × 105 S/m to 6.4 × 104 S/m owing to the reduced holes concentration. The declined point defects, including antisite defects and vacancies in materials, gave rise to the decrease in carrier concentration. The Seebeck coefficient of the ternary Sb2Te3-x Se x exhibited an increase with doping of Se atoms. Simultaneously, the thermal conductivity behaved a fallihg trend as well as increasing Se content. As a result, the ZT value reached the maximum from the corresponding Sb2Te2.9Se0.1 pellet. Positron annihilation measurement revealed that the average positron lifetime showed a monotonic decrease with Se addition, demonstrating the reduced point defects, which was in agreement with the thermoelectric performance.

  17. 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

  18. 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

  19. Electron - Atom Bremsstrahlung

    NASA Astrophysics Data System (ADS)

    Kim, Longhuan

    In this work we study the features of bremsstrahlung radiation from neutral atoms and atoms in hot dense plasmas. Predictions for the distributions of electron-atom bremsstrahlung radiation for both the point Coulomb potential and screened potentials are obtained using a classical numerical method. The results agree with exact quantum mechanical partial wave results for low incident electron energies in both the point Coulomb and screened potentials. In the screened potential the asymmetry parameter of a spectrum is reduced from the Coulomb values. The difference increases with decreasing energy and begins to oscillate at very low energies. We also studied the scaling properties of bremsstrahlung spectra and energy losses. It is found that the ratio of the radiative energy loss for positrons to that for electrons obeys a simple scaling law, being expressible fairly accurately as a function only of the quantity T(,1)/Z('2). This scaling is exact in the case of the point Coulomb potential, both for classical bremsstrahlung and for the nonrelativistic dipole Sommerfeld formula. We also studied bremsstrahlung from atoms in hot dense plasmas, describing the atomic potentials by the temperature-and-density dependent Thomas - Fermi model. Gaunt factors are obtained with the relativistic partial wave method for atoms in plasmas of various densities and temperatures. Features of the bremsstrahlung from atoms in such environments are discussed. The dependence of predicted bremsstrahlung spectra on the choice of potential from various average atom potential models for strongly coupled plasmas are also studied. For the energy range and plasma densities were considered, the choice of potential model among the elaborate atomic potentials is less important than the choice of the method of calculation. The use of a detailed configuration accounting method for bremsstrahlung processes in dense plasmas is less important than for some other atomic processes. We justify the usefulness

  20. 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.

  1. Reduction in coherent phonon lifetime in Bi2Te3/Sb2Te3 superlattices

    NASA Astrophysics Data System (ADS)

    Wang, Yaguo; Xu, Xianfan; Venkatasubramanian, Rama

    2008-09-01

    Femtosecond pulses are used to excite A1g optical phonons in Bi2Te3, Sb2Te3, and Bi2Te3/Sb2Te3 superlattice. Time-resolved reflectivity measurements show both the low-frequency and high-frequency components of A1g phonon modes. By comparing the phonon lifetime, it is found that the scattering rate (inverse of lifetime) in superlattice is significantly higher than those in Bi2Te3 and Sb2Te3. This represents the direct measurement of coherent phonon lifetime reduction in superlattice structures, consistent with the observed reduction in thermal conductivity in superlattices.

  2. Impurity gettering effect of Te inclusions in CdZnTe single crystals

    NASA Astrophysics Data System (ADS)

    Yang, G.; Bolotnikov, A. E.; Cui, Y.; Camarda, G. S.; Hossain, A.; James, R. B.

    2008-12-01

    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.

  3. 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.

  4. 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)

  5. 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.

  6. 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)

  7. 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…

  8. Neutrino-atom collisions

    NASA Astrophysics Data System (ADS)

    Kouzakov, Konstantin A.; Studenikin, Alexander I.

    2016-05-01

    Neutrino-atom scattering provides a sensitive tool for probing nonstandard interactions of massive neutrinos in laboratory measurements. The ionization channel of this collision process plays an important role in experiments searching for neutrino magnetic moments. We discuss some theoretical aspects of atomic ionization by massive neutrinos. We also outline possible manifestations of neutrino electromagnetic properties in coherent elastic neutrino-nucleus scattering.

  9. 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.

  10. 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…

  11. 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…

  12. Modified Embedded Atom Method

    SciTech Connect

    Rudd, R. E.

    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.

  13. Atomic Ferris wheel beams

    NASA Astrophysics Data System (ADS)

    Lembessis, Vasileios E.

    2017-07-01

    We study the generation of atom vortex beams in the case where a Bose-Einstein condensate, released from a trap and moving in free space, is diffracted from a properly tailored light mask with a spiral transverse profile. We show how such a diffraction scheme could lead to the production of an atomic Ferris wheel beam.

  14. 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.

  15. PAL spectroscopy of rare-earth doped Ga-Ge-Te/Se glasses

    NASA Astrophysics Data System (ADS)

    Shpotyuk, Ya.; Ingram, A.; Shpotyuk, O.

    2016-04-01

    Positron annihilation lifetime (PAL) spectroscopy was applied for the first time to study free-volume void evolution in chalcogenide glasses of Ga-Ge-Te/Se cut-section exemplified by glassy Ga10Ge15Te75 and Ga10Ge15Te72Se3 doped with 500 ppm of Tb3+ or Pr3+. The collected PAL spectra reconstructed within two-state trapping model reveal decaying tendency in positron trapping efficiency in these glasses under rare-earth doping. This effect results in unchanged or slightly increased defect-related lifetimes τ2 at the cost of more strong decrease in I2 intensities, as well as reduced positron trapping rate in defects and fraction of trapped positrons. Observed changes are ascribed to rare-earth activated elimination of intrinsic free volumes associated mainly with negatively-charged states of chalcogen atoms especially those neighboring with Ga-based polyhedrons.

  16. 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.

  17. Recent Progress in Nanoelectrical Characterizations of CdTe and Cu(In,Ga)Se2

    SciTech Connect

    Jiang, Chun-Sheng; To, Bobby; Glynn, Stephen; Mahabaduge, Hasitha; Barnes, Teresa; Al-Jassim, Mowafak M.

    2016-11-21

    We report two recent nanoelectrical characterizations of CdTe and Cu(In, Ga)Se2 (CIGS) thin-film solar cells by developing atomic force microscopy-based nanoelectrical probes. Charges trapped at defects at the CdS/CdTe interface were probed by Kelvin probe force microscopy (KPFM) potential mapping and by ion-milling the CdTe superstrate device in a bevel glancing angle of ~0.5 degrees. The results show randomly distributed donor-like defects at the interface. The effect of K post-deposition treatment on the near-surface region of the CIGS film was studied by KPFM potential and scanning spreading resistance microscopy (SSRM) resistivity mapping, which shows passivation of grain-boundary potential and improvement of resistivity uniformity by the K treatment.

  18. Optical properties and electronic structure of BiTeCl and BiTeBr compounds

    NASA Astrophysics Data System (ADS)

    Makhnev, A. A.; Nomerovannaya, L. V.; Kuznetsova, T. V.; Tereshchenko, O. E.; Kokh, K. A.

    2016-09-01

    Optical properties of BiTeCl and BiTeBr compounds with a strong Rashba spin-orbit coupling are studied in the 0.08-5.0 eV range using the optical ellipsometry method. Fundamental characteristics of the electronic structure are obtained. Similarly to BiTeI, spectra of the imaginary part of dielectric permittivity constant ɛ2( E) in the energy interval between the plasma edge and the threshold of an intense interband absorption (0.7 eV in BiTeCl and 0.6 eV in BiTeBr) display a fine structure of electronic transitions at 0.25 and 0.55 eV in BiTeCl and 0.20 and 0.50 eV in BiTeBr. These features are assigned to electronic transitions between the bulk conduction zones split by the Rashba spin-orbit interaction. The parameters of the electronic structure of BiTeCl and BiTeBr are compared with the BiTeI compound that was studied earlier. In the BiTeCl-BiTeBr-BiTeI row, the absorption edge and main features of the fundamental absorption exhibit a shift to low energies.

  19. Long-range Antiferromagnetic Order in [MnTe/ZnTe] Superlattices

    NASA Astrophysics Data System (ADS)

    Rhyne, J.; Lin, J.; Furdyna, J.; Giebultowicz, T.

    1997-03-01

    Long range antiferromagnetic order has been found in epitaxially-grown superlattices of [(MnTe)_x/(ZnTe)_y] with thin ZnTe interlayers (e.g, y=3D4-6 monolayers) and MnTe layer thicknesses x =3D 10 and 20. Previous studies(T.M. Giebultowicz, P. Klosowski, N. Samarth, H. Luo, J. K. Furdyna, and J.J. Rhyne, Phys. Rev. B 48), 12817 (1993). of [MnTe/ZnTe] superlattices with thicker ZnTe interlayers (e.g., y=3D18) revealed antiferromagnetic order confined to single MnTe layers consistent with strong nearest-neighbor (NN) exchange and relatively weak higher-neighbor exchange. The thin ZnTe layer superlattices show an inphase antiferromagnetic interlayer coupling coherent across several bilayers with spin directions on adjacent MnTe layers determined by assuming "phantom" spins on the ZnTe layers with the same AFM order as the MnTe layers. As the temperature is raised, this ordering slowly transforms into an antiphase coupling with spin directions in alternate MnTe layers reversed from their low temperature structure. The magnetic scattered intensity from both co-existing phases vanishes at a common Neel temperature near 75 K.

  20. Segregation formation, thermal and electronic properties of ternary cubic CdZnTe clusters: MD simulations and DFT calculations

    NASA Astrophysics Data System (ADS)

    Kurban, Mustafa; Erkoç, Şakir

    2017-04-01

    Surface and core formation, thermal and electronic properties of ternary cubic CdZnTe clusters are investigated by using classical molecular dynamics (MD) simulations and density functional theory (DFT) calculations. In this work, MD simulations of the CdZnTe clusters are performed by means of LAMMPS by using bond order potential (BOP). MD simulations are carried out at different temperatures to study the segregation phenomena of Cd, Zn and Te atoms, and deviation of clusters and heat capacity. After that, using optimized geometries obtained, excess charge on atoms, dipole moments, highest occupied molecular orbitals, lowest unoccupied molecular orbitals, HOMO-LUMO gaps (Eg) , total energies, spin density and the density of states (DOS) have been calculated with DFT. Simulation results such as heat capacity and segregation formation are compared with experimental bulk and theoretical results.

  1. 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.

  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. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Surface passivation for CdTe devices

    DOEpatents

    Reese, Matthew O.; Perkins, Craig L.; Burst, James M.; Gessert, Timothy A.; Barnes, Teresa M.; Metzger, Wyatt K.

    2017-08-01

    In one embodiment, a method for surface passivation for CdTe devices is provided. The method includes adjusting a stoichiometry of a surface of a CdTe material layer such that the surface becomes at least one of stoichiometric or Cd-rich; and reconstructing a crystalline lattice at the surface of the CdTe material layer by annealing the adjusted surface.

  9. Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Gebauer, J.; Weber, E. R.; Jäger, N. D.; Urban, K.; Ebert, Ph.

    2003-03-01

    We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (TeAs), Ga vacancies (VGa), and Ga vacancy-donor complexes (VGa-TeAs). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy-donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a -3e charge state of VGa in bulk GaAs.

  10. Ca2CuTe4O10Cl2, a new synthetic tellurium(IV) oxochloride.

    PubMed

    Takagi, Rie; Johnsson, Mats

    2005-10-01

    Single crystals of dicalcium copper tetratellurium decaoxide dichloride, Ca2CuTe4O10Cl2, were synthesized via a transport reaction in sealed evacuated quartz glass tubes. The building units of the structure are irregular CaO7 polyhedra, centrosymmetric CuO4Cl2 octahedra and two crystallographically distinct TeO4E distorted bipyramids (E being the 5s2 lone pair of TeIV). The TeO4E and CuO4Cl2 polyhedra together form planes that are connected by the Ca atoms. The CuO4Cl2 octahedra are isolated from each other by the other building units.

  11. N-doped GeTe phase change material for high-temperature data retention and low-power consumption

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhao; Hu, Yifeng; Zhu, Xiaoqin; Zou, Hua; Yuan, Li; Xue, Jianzhong; Sui, Yongxing; Wu, Weihua; Song, Sannian; Song, Zhitang

    2016-10-01

    The amorphous-to-crystalline transitions of N-doped GeTe films are investigated by in situ film resistance measurements. Both the crystallization temperature and resistance of the N-doped films increase. The analysis of X-ray diffraction (XRD) measurement indicates that the grain size of the films with more nitrogen content can be refined, leading to the improvement in the resistance and thermal stability of the phase change films. The N-doped GeTe films have higher activation energy for crystallization. The 10-year lifetime is raised from 90°C of undoped GeTe film to 138°C of the N-doped GeTe film. The better surface roughness is confirmed by atomic force microscopy. The phase change speed is evaluated by the picosecond laser pump-probe technology.

  12. 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.

  13. 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.

  14. Ab Initio Investigation of the Structural and Electronic Properties of HgTe/CdTe Superlattices

    NASA Astrophysics Data System (ADS)

    Laref, A.; Alsagri, M.; Laref, S.; Luo, S. J.

    2017-08-01

    We carried out first-principle calculations to examine the impact of layer periodicity and strain on the structural and electronic features of HgTe/CdTe superlattices (SLs). The full-potential linearized augmented plane wave methodology is used to determine the electronic characteristics of these CdTe-HgTe heterojunctions. The CdTe and HgTe layers have a strong effect on the emerged fundamental energy gap of the SLs owing to the peculiar quantum confinement effect. The impact of layer thickness changes and strain are indispensable for engineering the energy band gap of HgTe/CdTe SLs. This could lead to an enormous development in the optoelectronic characteristics of these SLs, which may result in their broad applications in electronic devices.

  15. 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.

  16. MOVPE deposition of Sb2Te3 and other phases of Sb-Te system on sapphire substrate

    NASA Astrophysics Data System (ADS)

    Kuznetsov, P. I.; Shchamkhalova, B. S.; Yapaskurt, V. O.; Shcherbakov, V. D.; Luzanov, V. A.; Yakushcheva, G. G.; Jitov, V. A.; Sizov, V. E.

    2017-08-01

    The films of Sb-Te system have been deposited by MOVPE on (0 0 0 1) Al2O3 substrates with thin ZnTe buffer layers at different temperatures and Te/Sb ratios in the vapor phase. X-ray diffractometry, SEM microscopy, Raman and EDX spectroscopy were used to study as-grown films. The surface morphology and stoichiometry of Sb-Te films strongly depend on Te/Sb ratio in vapor phase. We have deposited the phases of homologous series nSb2·mSb2Te3 with following stoichiometries: Sb2Te3, Sb4Te5, Sb8Te9, Sb10Te9, Sb4Te3, Sb2Te, Sb8Te3, Sb10Te3, Sb16Te3, Sb18Te3 and Sb. Transport properties of Sb2Te3, Sb4Te5, Sb8Te9, Sb4Te3, Sb2Te were evaluated using Van der Pauw technique at 300 K.

  17. 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.

  18. Microstructure evolution of the phase change material TiSbTe

    NASA Astrophysics Data System (ADS)

    Chen, Yongjin; Zhang, Bin; Ding, Qingqing; Deng, Qingsong; Cheng, Yan; Song, Zhitang; Li, Jixue; Zhang, Ze; Han, Xiaodong

    2016-10-01

    The crystallization process and crystal structure of the phase change material TiSbTe alloy have been successfully established, which is essential for applying this alloy in phase change memory. Specifically, transmission electron microscopy (TEM) analyses of the film annealed in situ were used in combination with selected-area electron diffraction (SAED) and radial distribution function (RDF) analyses to investigate the structural evolution from the amorphous phase to the polycrystalline phase. Moreover, the presence of structures with medium-range order in amorphous TST, which is beneficial to high-speed crystallization, was indicated by the structure factors S(Q)s. The crystallization temperature was determined to be approximately 170°C, and the grain size varied from several to dozens of nanometers. As the temperature increased, particularly above 200°C, the first single peak of the rG(r) curves transformed into double shoulder peaks due to the increasing impact of the Ti-Te bonds. In general, the majority of Ti atoms enter the SbTe lattice, whereas the remainder of the Ti atoms aggregate, leading to the appearance of TiTe2 phase separation, as confirmed by the SAED patterns, high-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) images and the corresponding energy-dispersive X-ray (EDX) mappings.

  19. Tunability of giant Rashba spin splitting in BiTeI

    NASA Astrophysics Data System (ADS)

    Fu, Huaxiang

    2013-02-01

    Giant Rashba spin splitting was recently discovered in bismuth tellurohalide (BiTeI) [K. Ishizaka , Nat. Mater.1476-112210.1038/nmat3051 10, 521 (2011)]. In this work, biaxial strain is used to modify the interatomic interaction in BiTeI, and the strain dependence of spin splitting is determined theoretically by first-principles density functional calculations. Large tunability is found for the Rashba energy ER, momentum offset kR, and coupling constant αR, showing that the spin splitting in BiTeI can be significantly modified by atom-atom interaction in a solid. The maximum values of ER and αR occur at strain η=-1.5%. Furthermore, tensile strain is shown to favor the increase of kR, and compressive strain favors the increase of ER. Moreover, contrast of the spin splittings between the electron at CBM and the hole at VBM reveals that ERe of the electron and ERh of the hole display drastically different behaviors under tensile strains. However, under compressive strains, the strain dependencies of ERe and ERh are interestingly similar (so are the strain dependencies of kRe and kRh). By examining microscopic electron states, the anomalous Bi-I interaction is found to be important for the spin splitting in BiTeI, and qualitative explanation for the strain dependence of the spin splitting is provided.

  20. Enhanced thermoelectric performance of a quintuple layer of Bi{sub 2}Te{sub 3}

    SciTech Connect

    Zhang, J.; Liu, H. J. Cheng, L.; Wei, J.; Shi, J.; Tang, X. F.; Uher, C.

    2014-07-14

    The electronic structure of a quintuple layer (QL) of Bi{sub 2}Te{sub 3} is calculated using the first-principles pseudopotential method. It is found that the band gap of an isolated QL is considerably larger than that of bulk Bi{sub 2}Te{sub 3}. The electronic transport of the QL is, then, evaluated using the semiclassical Boltzmann theory within the relaxation time approximation. By fitting the energy surface from first-principles calculations, a suitable Morse potential is constructed and used to predicate the lattice thermal conductivity via equilibrium molecular dynamics simulations. By optimizing the carrier concentration of the system, the ZT of Bi{sub 2}Te{sub 3} QL can be enhanced to a relatively high value. Moreover, the ZT value exhibits strong temperature dependence and can reach as high as 2.0 at 800 K. This value can be further increased to 2.2 by the substitution of Bi atoms with Sb atoms, giving nominal formula of (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3}. The significantly enhanced ZT value makes QL a very appealing candidate for thermoelectric applications.

  1. Advanced Microstructural Characterization for Development of Improved HgCdTe Detectors and Devices

    DTIC Science & Technology

    2014-09-21

    J. Smith. Atomic-Scale Characterization of II–VI Compound Semiconductors, Journal of Electronic Materials, (08 2013): 0. doi: 10.1007/s11664-013...Grown ZnTe/Si: A New Low-Cost Composite Substrate for 6.1A? III-V and II-VI Compound Semiconductors", by Y.Chen, G. Brill, P. Wijewarnasuriya, N. Dhar, X...Seattle, Nov. 27-29, 2012. 7) (invited paper) "Atomic-Scale characterization of II-VI compound semiconductors", by D.J. Smith, J.J. Kim, M.R

  2. 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.

  3. Improvements in Materials and Processes for Segmented BiTe/PbTe-BiTe/TAGS/PbSnTe based Thermoelectric Generators

    NASA Astrophysics Data System (ADS)

    Flanders, Laffite A.; Drinker, Richard W.; Heshmatpour, Ben; Moul, David S.; Fleurial, Jean-Pierre; 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 radioisotope power systems (RPS) for future NASA space science applications. The conversion efficiency goal is 10% or higher at a power output level of 20 W or higher. The T/E efficiency achievable with the present T/E materials is about 8.5%. To increase the conversion efficiency, the T/E material properties as well as the T/E couple thermal and electrical performance need to be improved. By altering and optimizing the compositional make up, homogeneity and the microstructural characteristics such as the grain size and the phases present the T/E material properties can be improved. The T/E couple performance can be improved by reducing the electrical and thermal contact resistances as well as the physical integrity of the segmented T/E elements. The latter characteristics are improved by reducing the thermo-mechanical stresses, improving the quality of the bonds and interfaces, minimizing the number of required bonds, and reducing the degradation rate of the T/E materials and the bonds.

  4. Contact Formation (Hg, CD)Te

    DTIC Science & Technology

    1989-12-01

    AD-A21 7 088 0 a CONTACT FORMATION ON (HG, CD )TE FINAL REPORT W.A. BECK AND G.D. DAVIS V C ELECTE , I DECEMBER 1989 JAN22 1990 U.S. ARMY RESEARCH...27709-2211 I N I 11. TITLE (Include Security Clasification) Contact Formation on (Hg, CD )Te (u) 12. PERSONAL AUTHOR(S) W.A. Beck and G.D. Davis 13a...whereas the 1/f noise of the Au contacts originated at th i/" Cd )Te interface or in the underlying (Hg, Cd )Te, the 1/f noise of the Al contacts orig.L

  5. Electronic structure of the CdTe(111) A-(2 × 2) surface

    NASA Astrophysics Data System (ADS)

    Bekenev, V. L.; Zubkova, S. M.

    2015-09-01

    Based on data of scanning tunneling microscopy, ab initio calculations of the electronic structure were performed for the first time for four variants of Cd-terminated polar CdTe(111) A-(2 × 2) surfaces, namely, ideal, relaxed, reconstructed with a Cd vacancy, and reconstructed with the subsequent relaxation. In the approximation of a layered superlattice, the surfaces were simulated by a film with a thickness of 12 atomic layers and a vacuum gap of ˜16 Å. Dangling bonds of Te atoms were closed by adding, on the opposite side of the film, four fictive hydrogen atoms, each having a charge of 0.5 electrons. Ab initio calculations were performed with the QUANTUM ESPRESSO program based on the density functional theory. In each of the variants, the equilibrium coordinates of 16 (15) atoms of cadmium and tellurium of the upper four freestanding layers were determined. It was shown that the relaxation leads to a splitting of layers of both the unreconstructed and reconstructed surfaces. For four variants of the surfaces, the band structures were calculated and analyzed, as well as the total densities of states of the surfaces and densities of states of individual layers. After the relaxation of the reconstructed surface, the upper two atomic layers 11 and 12 changed their places, which can be responsible for the specific features of the surface structure of these layers.

  6. 78 FR 58571 - Maine Yankee Atomic Power Company, Connecticut Yankee Atomic Power Company, and The Yankee Atomic...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-24

    ... Atomic Power Company, Connecticut Yankee Atomic Power Company, and The Yankee Atomic Electric Company... Power Company (Maine Yankee), Connecticut Yankee Atomic Power Company (Connecticut Yankee), and the Yankee Atomic Electric Company (Yankee Atomic) (together, ``licensees'' or ``the Yankee Companies'')...

  7. Molecular Dynamics Study of Poly And Monocrystalline CdS/CdTe Junctions and Cu Doped Znte Back Contacts for Solar Cell Applications

    NASA Astrophysics Data System (ADS)

    Aguirre, Rodolfo, II

    Cadmium telluride (CdTe) is a material used to make solar cells because it absorbs the sunlight very efficiently and converts it into electricity. However, CdTe modules suffer from degradation of 1% over a period of 1 year. Improvements on the efficiency and stability can be achieved by designing better materials at the atomic scale. Experimental techniques to study materials at the atomic scale, such as Atomic Probe Tomography (APT) and Transmission Electron Microscope (TEM) are expensive and time consuming. On the other hand, Molecular Dynamics (MD) offers an inexpensive and fast computer simulation technique to study the growth evolution of materials with atomic scale resolution. In combination with advance characterization software, MD simulations provide atomistic visualization, defect analysis, structure maps, 3-D atomistic view, and composition profiles. MD simulations help to design better quality materials by predicting material behavior at the atomic scale. In this work, a new MD method to study several phenomena such as polycrystalline growth of CdTe-based materials, interdiffusion of atoms at interfaces, and deposition of a copper doped ZnTe back contact is established. Results are compared with experimental data found in the literature and experiments performed and shown to be in remarkably good agreement.

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

    SciTech Connect

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

    2016-05-16

    The performance of n{sup +}-InGaP(Te)/p{sup +}-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 (J{sub pk}) 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/cm{sup 2}) and annealed (1000 A/cm{sup 2}) high band gap tunnel junction.

  9. Influence of substrate materials on the properties of CdTe thin films grown by hot-wall epitaxy

    NASA Astrophysics Data System (ADS)

    Bilevych, Ye.; Soshnikov, A.; Darchuk, L.; Apatskaya, M.; Tsybrii, Z.; Vuychik, M.; Boka, A.; Sizov, F.; Boelling, O.; Sulkio-Cleff, B.

    2005-02-01

    Growth of high-quality CdTe thin films by hot-wall epitaxy (HWE) under different temperature conditions and the control of their physical, electrical and structural properties have been examined by various ways. CdTe (1 1 0), Zn 0.04Cd 0.96Te (1 1 1), Hg 0.2Cd 0.8Te (1 1 1), Si (1 1 1) and BaF 2 (1 1 1) were used as substrates. The obtained films have the cut-off wavelength at 0.84-0.85 μm and the transmission of about 55-60% out of the fundamental absorption domain. The current-voltage investigations have shown that the contact properties strongly depend on the contact material and contact fabrication method and less depend on substrate materials. The film-specific resistances (4-7)×10 4 Ω cm were determined. The CdTe deposition (layer thickness about 1000 Å) on Cd xHg 1-xTe resulted in significant increase in photodiodes electrical parameters. All samples showed the crystalline structure according to the XRD data with strong influence on lattice mismatch between CdTe and substrate materials. Atomic force microscope (AFM) investigations have shown a smooth and defect-free surface with a roughness range of 15-100 nm for 50 μm of basic length.

  10. ZnTe Alloying Effect on Enhanced Thermoelectric Properties of p-Type PbTe.

    PubMed

    Ahn, Kyunghan; Shin, Hocheol; Im, Jino; Park, Sang Hyun; Chung, In

    2017-02-01

    We investigate the effect of ZnTe incorporation on PbTe to enhance thermoelectric performance. We report structural, microscopic, and spectroscopic characterizations, ab initio theoretical calculations, and thermoelectric transport properties of Pb0.985Na0.015Te-x% ZnTe (x = 0, 1, 2, 4). We find that the solid solubility limit of ZnTe in PbTe is less than 1 mol %. The introduction of 2% ZnTe in p-type Pb0.985Na0.015Te reduces the lattice thermal conductivity through the ZnTe precipitates at the microscale. Consequently, a maximum thermoelectric figure of merit (ZT) of 1.73 at 700 K is achieved for the spark plasma-sintered Pb0.985Na0.015Te-2% ZnTe, which arises from a decreased lattice thermal conductivity of ∼0.69 W m(-1) K(-1) at ∼700 K in comparison with Pb0.985Na0.015Te.

  11. 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.

  12. 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.

  13. CW Atom Laser

    DTIC Science & Technology

    2006-08-04

    propagation and energy filtering of a cold atomic beam in a long high-gradient magnetic atom guide,” Spencer E. Olson, Rahul R. Mhaskar , and Georg...Open-channel fluorescence imaging of atoms in high-gradient magnetic fields,” Rahul R. Mhaskar , Spencer E. Olson and Georg Raithel (2006). 7 FIG. 6...graduate student, graduated in May 2006. He currently is employed as a NRC post-doc at the NRL in Washington, DC. R. Mhaskar , graduate student. R. van de

  14. 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.

  15. Epitaxy: Programmable Atom Equivalents Versus Atoms.

    PubMed

    Wang, Mary X; Seo, Soyoung E; Gabrys, Paul A; Fleischman, Dagny; Lee, Byeongdu; Kim, Youngeun; Atwater, Harry A; Macfarlane, Robert J; Mirkin, Chad A

    2017-01-24

    The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm(2) areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size.

  16. 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.

  17. 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.

  18. Te inclusion-induced electrical field perturbation in CdZnTe single crystals revealed by Kelvin probe force microscopy.

    PubMed

    Gu, Yaxu; Jie, Wanqi; Li, Linglong; Xu, Yadong; Yang, Yaodong; Ren, Jie; Zha, Gangqiang; Wang, Tao; Xu, Lingyan; He, Yihui; Xi, Shouzhi

    2016-09-01

    To understand the effects of tellurium (Te) inclusions on the device performance of CdZnTe radiation detectors, the perturbation of the electrical field in and around Te inclusions was studied in CdZnTe single crystals via Kelvin probe force microscopy (KPFM). Te inclusions were proved to act as lower potential centers with respect to surrounding CdZnTe matrix. Based on the KPFM results, the energy band diagram at the Te/CdZnTe interface was established, and the bias-dependent effects of Te inclusion on carrier transportation is discussed.

  19. 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.

  20. Determination of tellurium in geochemical materials by flameless atomic-absorption spectroscopy.

    PubMed

    Sighinolfi, G P; Santos, A M; Martinelli, G

    1979-02-01

    A method is described for the determination of tellurium at nanogram levels in rocks and in other complex materials by the use of flameless atomic-absorption spectroscopy. A very selective organic extraction procedure is applied to avoid matrix interference effects during extraction of Te and the atomization stage in the graphite furnace. Prior separation of iron and other interfering elements is achieved by a combined cupferron-ethyl acetate extraction. Tellerium is extracted from 6M hydrochloric acid with MIBK and stripped into aqueous medium. Pipetting of the aqueous extract into the graphite furnace gives fairly good instrumental reproducibility (2-3% error). Detection limits of about 10 ppM Te for a 0.5-g sample have been achieved with the medium-performance apparatus used. Results for Te in some geochemical reference materials are reported. Indications are given for the determination of Sb and Mo in the same solutions.

  1. Magnetic properties of Cd1 - xMnxTe/C nanocrystals

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Sayan; Zitoun, D.; Gedanken, A.

    2011-02-01

    Mn doped CdTe nanocrystals coated by carbon (Cd1 - xMnxTe/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 Cd1 - xMnxTe core was encapsulated by a 6-9 nm carbon shell. The efficient doping by Mn2 + in the zinc blende Cd1 - xMnxTe 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 µB/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.

  2. Growth and Crystal Orientation of ZnTe on m-Plane Sapphire with Nanofaceted Structure

    NASA Astrophysics Data System (ADS)

    Nakasu, Taizo; Sun, Wei-Che; Kobayashi, Masakazu; Asahi, Toshiaki

    2017-04-01

    ZnTe thin films on sapphire substrate with nanofaceted structure have been studied. The nanofaceted structure of the m-plane (10-10) sapphire was obtained by heating the substrate at above 1100°C in air, and the r-plane (10-12) and S-plane (1-101) were confirmed. ZnTe layers were prepared on the nanofaceted m-plane sapphire substrates by molecular beam epitaxy (MBE). The effect of the nanofaceted structure on the orientation of the thin films was examined based on x-ray diffraction (XRD) pole figures. Transmission electron microscopy (TEM) was also employed to characterize the interface structures. The ZnTe layer on the nanofaceted m-plane sapphire substrate exhibited (331)-plane orientation, compared with (211)-plane without the nanofaceted structure. After thermal treatment, the m-plane surface vanished and (211) layer could not be formed because of the lack of surface lattice matching. On the other hand, (331)-plane thin film was formed on the nanofaceted m-plane sapphire substrate, since the (111) ZnTe domains were oriented on the S-facet. The orientation of the ZnTe epilayer depended on the atomic ordering on the surface and the influence of the S-plane.

  3. 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

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

    PubMed

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

    2016-01-26

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

  5. 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.

  6. Spin Texture on the Fermi Surface of Strained HgTe

    NASA Astrophysics Data System (ADS)

    Zaheer, Saad; Young, Steve; Cellucci, Daniel; Teo, Jeffrey; Kane, Charles; Mele, Eugene; Rappe, Andrew

    2012-02-01

    We present ab initio and k.p calculations of the Fermi surface of strained HgTe obtained by stretching the Zinc-Blende lattice along the (111) axis. Near the Fermi level, strained HgTe exhibits point-like accidental degeneracies between a two-fold degenerate and two non-degenerate bands along the (111) axis. The three bands disperse linearly in all directions about the degenerate points and their low energy physics is described by an effective four band k.p Hamiltonian. The Fermi surface consists of two ellipsoids which contact only at the point where the Fermi level crosses the two-fold degenerate band along the (111) axis. The spin expectation value on both ellipsoids is constrained to vanish along the (111) axis due to mirror symmetry about a plane that contains that axis. Furthermore the winding number of spins around the two ellipsoids changes from one end to the other indicating the existence of singular points in the spin texture. Indeed, the ab initio and k.p calculations confirm the existence of such spin singularities on the Fermi ellipsoids. We show that doping HgTe with Zinc atoms chemically strains the HgTe Zinc-Blende lattice and present ab initio calculations on HgZnTe that confirm the above results.

  7. 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.

  8. The Casimir atomic pendulum

    NASA Astrophysics Data System (ADS)

    Razmi, H.; Abdollahi, M.

    2008-11-01

    We want to introduce an atomic pendulum whose driving force (torque) is due to the quantum vacuum fluctuations. Applying the well-known Casimir-Polder effect to a special configuration (a combined structure of an atomic nanostring and a conducting plate), an atomic pendulum (Casimir atomic pendulum) is designed. Using practically acceptable data corresponding to the already known world of nanotechnology and based on reasonable/reliable numerical estimates, the period of oscillation for the pendulum is computed. This pendulum can be considered as both a new micro(nano)-electromechanical system and a new simple vacuum machine. Its design may be considered as a first step towards realizing the visualized vacuum (Casimir) clock!

  9. 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.

  10. 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.

  11. Atomic Bomb Health Benefits

    PubMed Central

    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. PMID:19088902

  12. 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.

  13. 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)

  14. Atomic & Molecular Interactions

    SciTech Connect

    2002-07-12

    The Gordon Research Conference (GRC) on Atomic & Molecular Interactions was held at Roger Williams University, Bristol, RI. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  15. 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)

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Atom Interferometer Modeling Tool

    DTIC Science & Technology

    2011-08-08

    definition is to import conductor geometry from an outside CAD tool such as AutoCAD . This allows users to specify the more complex layouts using a...fully-featured tool of their choice, while significantly reducing the complexity of LiveAtom. Furthermore, most groups have already been using a 2D ...specifying conductor geometry LiveAtom offers the user a 3D visualization of their experiment. Once the experiment is fully specified, computing the

  2. Anonymous Atomic Transactions,

    DTIC Science & Technology

    1996-07-01

    We show here an example of a protocol that satisfies anonymity properties while providing strong ACID (atomic, consistent, isolated, durable...transactional properties, resolving an open question. Blinded signatures are used to certify an anonymous asymmetric key which authorizes the use of a...key is spent. We show here an example of a protocol that satisfies anonymity properties while providing strong ACID (atomic, consistent, isolated

  3. 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.

  4. 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.

  5. Optical atomic magnetometer

    DOEpatents

    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.

  6. Fundamental Mechanism of Atomization

    DTIC Science & Technology

    1989-07-01

    2Sk, The relation between the spatial amplification rate and (21) the wavelength is shown in Fig. 2 for the case of A 2 = 100 where Tin ...hand without the interference from the pressure fluctuation. Finally, in order to induce the shear waves to assist the atomization, we require ’c - a and...condition is satisfied. This example demonstrates how hard it is to induce the shear wave to assist in the onset of atomization. It should be

  7. 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.

  8. 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.

  9. 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.

  10. Assembling hierarchical cluster solids with atomic precision.

    PubMed

    Turkiewicz, Ari; Paley, Daniel W; Besara, Tiglet; Elbaz, Giselle; Pinkard, Andrew; Siegrist, Theo; Roy, Xavier

    2014-11-12

    Hierarchical solids created from the binary assembly of cobalt chalcogenide and iron oxide molecular clusters are reported. Six different molecular clusters based on the octahedral Co6E8 (E = Se or Te) and the expanded cubane Fe8O4 units are used as superatomic building blocks to construct these crystals. The formation of the solid is driven by the transfer of charge between complementary electron-donating and electron-accepting clusters in solution that crystallize as binary ionic compounds. The hierarchical structures are investigated by single-crystal X-ray diffraction, providing atomic and superatomic resolution. We report two different superstructures: a superatomic relative of the CsCl lattice type and an unusual packing arrangement based on the double-hexagonal close-packed lattice. Within these superstructures, we demonstrate various compositions and orientations of the clusters.

  11. Particulate contacts to Si and CdTe: Al, Ag, Hg-Cu-Te, and Sb-Te

    NASA Astrophysics Data System (ADS)

    Schulz, Douglas L.; Ribelin, Rosine; Curtis, Calvin J.; Ginley, David S.

    1999-03-01

    Our team has been investigating the use of particle-based contacts in both Si and CdTe solar cell technologies. First, in the area of contacts to Si, powders of Al and Ag prepared by an electroexplosion process have been characterized by transmission electron microscopy (TEM), TEM elemental determination X-ray spectroscopy (TEM-EDS), and TEM electron diffraction (TEM-ED). These Al and Ag particles were slurried and tested as contacts to p- and n-type silicon wafers, respectively. Linear current-voltage (I-V) was observed for Ag on n-type Si, indicative of an ohmic contact, whereas the Al on p-type Si sample was non-ideal. A wet-chemical surface treatment was performed on one Al sample and TEM-EDS indicated a substantial decrease in the O contaminant level. The treated Al on p-type Si films exhibited linear I-V after annealing. Second, in the area of contacts to CdTe, particles of Hg-Cu-Te and Sb-Te have been applied as contacts to CdTe/CdS/SnO2 heterostructures prepared by the standard NREL protocol. First, Hg-Cu-Te and Sb-Te were prepared by a metathesis reaction. After CdCl2 treatment and NP etch of the CdTe layer, particle contacts were applied. The Hg-Cu-Te contacted cells exhibited good electrical characteristics, with Voc>810 mV and efficiencies > 11.5% for most cells. Although Voc>800 mV were observed for the Sb-Te contacted cells, efficiencies in these devices were limited to 9.1% presumably by a large series resistance (>20 Ω) observed in all samples.

  12. A study of Sn addition on bonding arrangement of Se-Te alloys using far infrared transmission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kumar, Rajneesh; Sharma, Parikshit; Katyal, S. C.; Sharma, Pankaj; Rangra, V. S.

    2011-07-01

    Far infrared transmission spectra of Se92Te8-xSnx (x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained in the spectral range 50-600 cm-1 at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way so as to preserve fourfold and twofold coordination for Sn and chalcogen atoms (Se,Te), respectively. With the addition of Sn, Far-IR spectra shift toward high frequency side and some new bands start appearing. Sn atoms appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Theoretical calculations of bond energy, relative probability of bond formation, force constant, and wave number were also made to justify the result.

  13. Etude structurale des sulfotellurures de terres rares ( LS) 2Te 1 + x ( L = Tb, Dy, Ho, Er, Tm et Y). II. Surstructure des phases ordonnées. Macles d'ordre

    NASA Astrophysics Data System (ADS)

    Ghémard, Geneviève; Etienne, Jean; Schiffmacher, Gérard; Flahaut, Jean

    1982-11-01

    The ( LS) 2Te 1 + x compounds have an orthorhombic subcell, with a layered structure and vacant Te sites, and a monoclinic superstructure ( a = b = 6.658, c = 13.657 Å, γ = 102°43' for (HoS) 2Te 1.34). The order-disorder transition occurs at about 450°C. In the superstructure Te planes between ( L4S) tetrahedra layers are ordered with {B2}/{m} symmetry; however, some sites remain partially vacant. The S atoms conserve mmm symmetry, but the metallic atoms are slightly displaced from their substructure position ( R = 0.037). Ordering occurs so that each Te plane can be oriented in two different ways. Therefore, there are two kinds of domains, with respect to a twinning rule. These domains are observed by direct-imaging high-resolution electronic microscopy and are about 100 Å wide.

  14. The role of atomic and molecular physics for dissipative divertor operation in helium and deuterium plasmas

    NASA Astrophysics Data System (ADS)

    Canik, J. M.

    2016-10-01

    Recent experiments in DIII-D helium plasmas are examined to resolve the role of atomic and molecular physics in major discrepancies between experiment and modeling of dissipative divertor operation. Helium operation removes the complicated molecular processes of deuterium plasmas that are a prime candidate for the inability of standard fluid models (SOLPS, UEDGE) to reproduce dissipative divertor operation, primarily the consistent under-prediction of radiated power. With helium fueling, a high-recycling divertor was established with divertor densities increasing to ne,div >= 3 ×1020m-3 and temperatures decreasing to Te,div <= 2 eV as measured by divertor Thomson scattering (DTS). The electron pressure, pe , div decreased gradually with increasing density to less than 30% of the low density value. However, the ion flux to the divertor target did not decrease until the highest densities and lowest temperatures, Te,div <= 2 eV. In contrast, with deuterium operation, increasing density leads to a rapid transition from Te,div >= 10 eV to Te,div <= 3 eV, though both pe , div and ion flux do not decrease until Te,div <= 2 eV. These differences indicate an important role for molecular and atomic physics in the dynamics of divertor dissipation. Initial SOLPS modeling has reproduced ne and Te profiles at the midplane and divertor target, as well as the spatial structure of radiation patterns measured in moderate density helium plasmas. However, the modeled divertor radiation is less than measured, similar to deuterium simulations, suggesting processes more universal than species-specific atomic or molecular physics may be the source of radiation deficit. Detailed assessments of ne, Te profiles in the divertor volume, uniquely determined at DIII-D using DTS, are made along with analysis of measured and modeled line radiation to shed more light on these intriguing findings. Supported by the US DOE under DE-AC05-00OR22725.

  15. Atoms talking to SQUIDs

    NASA Astrophysics Data System (ADS)

    Hoffman, J. E.; Grover, J. A.; Ravets, S.; Voigt, K. D.; Lee, J.; Kim, Z.; Wood, A. K.; Schoch, I.; Anderson, J. R.; Dragt, A. J.; Hafezi, M.; Lobb, C. J.; Orozco, L. A.; Rolston, S. L.; Taylor, J. M.; Wellstood, F. C.

    2012-02-01

    We present our advances towards a hybrid quantum system of ^87Rb atoms coupled to a superconducting flux qubit through the magnetic dipole transition. We plan to trap atoms in the evanescent field outside a 500 nm nanofiber. This will allow us to bring the atoms less than 5 μm above the surface of the superconductor without producing excessive heating or changing magnetic fields. As an intermediate step, we plan on coupling the atoms to a superconducting LC resonator. Current progress includes production of nanofibers with >98% transmission, and a tunable high-Q superconducting resonator. Additionally, we show how to use our system as a unified interface for microwave and optical photons, in which the atoms act both as a quantum memory and transduce excitations between the two frequency domains. Using coherent control techniques, we examine conversion and storage of quantum information between microwave photons in superconducting resonators, ensembles of ultracold atoms, and optical photons as well as a method for transferring information between two resonators.

  16. 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.

  17. 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.

  18. Chemical synthesis and characterization of PdTe-Ag{sub 2}Te nanowires heterostructure

    SciTech Connect

    Bhatt, Ranu Bhattacharya, Shovit; Bohra, Anil; Basu, Ranita; Singh, Ajay; Aswal, D. K.; Gupta, S. K.; Krishnan, Gopika; Bhatt, Pramod

    2016-05-23

    Ag{sub 2}Te and Pd doped Ag{sub 2}Te nanowires are synthesized using chemical route. Field Emission Scanning Electron Microscopy (FESEM) shows the presence of nanowires of nearly few micron length and ~ 200 nm diameter. The composition analysis performed using Electron Dispersive Spectroscopy (EDS) shows the presence of almost 1.98 at% palladium. Reitveld refinement of X-ray diffraction (XRD) shows the presence of 0.3 % of PdTe phase in addition to Ag{sub 2}Te in Pd doped Ag{sub 2}Te sample.

  19. Inhibition of Te surfactant effect on surface morphology of heavily Te-doped GaAs

    NASA Astrophysics Data System (ADS)

    Paquette, Bernard; Ilahi, Bouraoui; Aimez, Vincent; Arès, Richard

    2013-11-01

    The surface morphology and incorporation behavior of heavily Te-doped GaAs were studied for various growth parameters by chemical beam epitaxy (CBE). The Te precursor, DIPTe (diisopropyl telluride), acts as a volatile dopant in the growth temperature range of 475-595 °C. Electrical activation of Te is increased for lower growth temperatures. The Te surfactant effect was shown to lead to three-dimensional growth, which greatly affected the resulting surface morphology. We have shown that growth parameters can be tuned to reduce the Te surfactant effect through kinetic limitation, thus obtaining improved surface morphologies.

  20. A DFT study of structural and electronic properties of Zn1-xSbxTe with x = (0.25,0.50,0.75)

    NASA Astrophysics Data System (ADS)

    Diwaker; Kumar, Ashwani

    2017-01-01

    In the present work, we report the structural and the electronic properties of the alloy Zn1-xSbxTe with x = (0.25%, 0.50% and 0.75%). Ab initio calculations are based upon the density functional theory with generalized gradient approximation and Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. In our calculations, we found that antimony (Sb) doping in zinc telluride (ZnTe) system introduces some bands which mainly originate from s- and p-states of Te and Sb atom and are primarily responsible for n-type and p-type conductivity.