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Sample records for single crystal molybdenum

  1. Solar thermal thruster made of single crystal molybdenum

    NASA Astrophysics Data System (ADS)

    Shimizu, Morio; Itoh, Katsuya; Sato, Hitoshi; Fujii, Tadayuki; Igarashi, Tadashi; Okamoto, Ken-ichi

    1997-07-01

    The heart element of solar thermal propulsion (STP) system is a thruster made of refractory metals such as tungsten, tantalum and molybdenum or advance high temperature ceramics because of the high operating temperature (1000-2500 K) involved. In this paper, design, fabrication and preliminary experimental results in the JSUS Research Plan are presented, using 20 mm diameter of thrusters made of single crystal molybdenum which NRIM has patented and is a perfect (non-defect) material, namely no brittleness due to recrystallization under high operating temperature conditions. The working gas temperature within the thruster chamber reached higher than 1850 K (namely, the Isp is approximately 700 s for hydrogen gas propellant) at 0.2 MPa of the plenum chamber pressure, using the small solar concentrator (1.6 m diameter of half paraboloid and 0.65 m of the focal length).

  2. Growth of phase-pure, crack-free single crystals and large-grained polycrystals of molybdenum disilicide

    NASA Technical Reports Server (NTRS)

    Rossetti, M.

    1970-01-01

    High purity molybdenum disilicide crystals are prepared by zone melting sintered compacts. This method yields single crystals or polycrystals free from macrocracks which allow better measurement and evaluation of mechanical properties.

  3. Deformation of Single Crystal Molybdenum at High Pressure

    SciTech Connect

    Bonner, B P; Aracne, C; Farber, D L; Boro, C O; Lassila, D H

    2004-02-24

    Single crystal samples of micron dimensions oriented in the [001] direction were shortened 10 to 40% in uniaxial compression with superposed hydrostatic pressure to begin investigation of how the onset of yielding evolves with pressure. A testing machine based on opposed anvil geometry with precision pneumatic control of the applied force and capability to measure sub micron displacements was developed to produce shape changing deformation at pressure. The experiments extend observations of pressure dependent deformation to {approx}5Gpa at shortening rates of {approx}2*10{sup -4}. Samples have been recovered for post run characterization and analysis to determine if deformation mechanisms are altered by pressure. Experiments under hydrostatic pressure provide insight into the nature of materials under extreme conditions, and also provide a means for altering deformation behavior in a controlled fashion. The approach has a long history demonstrating that pressure enhances ductility in general, and produces enhanced hardening relative to that expected from normal cold work in the BCC metals Mo, Ta and Nb{sup 2}. The pressure hardening is in excess of that predicted from the measured increase in shear modulus at pressure, and therefore is likely due to a dislocation mechanism, such as suppression of kink pair formation or the interaction of forest dislocation cores, and not from lattice resistance. The effect has not been observed in FCC metals, suggesting a fundamental difference between deformation mechanisms at pressure for the two classes. The purpose of this letter is to investigate the origin of pressure hardening with new experiments that extend the pressure range beyond 3 GPa, the upper limit of conventional large sample (1cm{sup 3}) testing methods. Most previous high pressure deformation studies have been on poly crystals, relying on model dependent analysis to infer the maximum deviatoric stress that a deformed sample can support. In one experiment, a

  4. Elastic-plastic deformation of molybdenum single crystals shocked along [100

    DOE PAGES

    Mandal, A.; Gupta, Y. M.

    2017-01-24

    To understand the elastic-plastic deformation response of shock-compressed molybdenum (Mo) – a body-centered cubic (BCC) metal, single crystal samples were shocked along the [100] crystallographic orientation to an elastic impact stress of 12.5 GPa. Elastic-plastic wave profiles, measured at different propagation distances ranging between ~0.23 to 2.31 mm using laser interferometry, showed a time-dependent material response. Within experimental scatter, the measured elastic wave amplitudes were nearly constant over the propagation distances examined. These data point to a large and rapid elastic wave attenuation near the impact surface, before reaching a threshold value (elastic limit) of ~3.6 GPa. Numerical simulations ofmore » the measured wave profiles, performed using a dislocation-based continuum model, suggested that {110}<111> and/or {112}<111> slip systems are operative under shock loading. In contrast to shocked metal single crystals with close-packed structures, the measured wave profiles in Mo single crystals could not be explained in terms of dislocation multiplication alone. A dislocation generation mechanism, operative for shear stresses larger than that at the elastic limit, was required to model the rapid elastic wave attenuation and to provide a good overall match to the measured wave profiles. However, the physical basis for this mechanism was not established for the high-purity single crystal samples used in this study. As a result, the numerical simulations also suggested that Mo single crystals do not work harden significantly under shock loading in contrast to the behavior observed under quasi-static loading.« less

  5. Elastic-plastic deformation of molybdenum single crystals shocked along [100

    NASA Astrophysics Data System (ADS)

    Mandal, A.; Gupta, Y. M.

    2017-01-01

    To understand the elastic-plastic deformation response of shock-compressed molybdenum (Mo) - a body-centered cubic metal, single crystal samples were shocked along the [100] crystallographic orientation to an elastic impact stress of 12.5 GPa. Elastic-plastic wave profiles, measured at different propagation distances ranging between ˜0.23 to 2.31 mm using laser interferometry, showed a time-dependent material response. Within the experimental scatter, the measured elastic wave amplitudes were nearly constant over the propagation distances examined. These data point to a large and rapid elastic wave attenuation near the impact surface, before reaching a threshold value (elastic limit) of ˜3.6 GPa. Numerical simulations of the measured wave profiles, performed using a dislocation-based continuum model, suggested that {110}⟨111⟩ and/or {112}⟨111⟩ slip systems are operative under shock loading. In contrast to shocked metal single crystals with close-packed structures, the measured wave profiles in Mo single crystals could not be explained in terms of dislocation multiplication alone. A dislocation generation mechanism, operative for shear stresses larger than that at the elastic limit, was required to model the rapid elastic wave attenuation and to provide a good overall match to the measured wave profiles. However, the physical basis for this mechanism was not established for the high-purity single crystal samples used in this study. The numerical simulations also suggested that Mo single crystals do not work harden significantly under shock loading in contrast to the behavior observed under quasi-static loading.

  6. Molybdenum Silicide Formation on Single Crystal, Polycrystalline and Amorphous Silicon: Growth, Structure and Electrical Properties

    NASA Astrophysics Data System (ADS)

    Doland, Charles Michael

    The solid state reactions that occur between a thin metal film and a silicon substrate are of scientific and technological interest. The initial interactions are poorly understood, yet the final state may critically depend on the initial interactions. In this work, the reactions of thin molybdenum films on amorphous, polycrystalline, and single crystal silicon substrates were studied, with an emphasis on the initial interdiffusion and the nucleation of the crystalline silicide phase. Our research was carried out in an ultrahigh vacuum (UHV) system in order to minimize effects of contaminants. In situ Raman scattering and Auger electron spectroscopy were used to probe the structure and composition of the films. Electron microscopy, low energy electron diffraction and Schottky barrier height measurements were used to obtain additional information. The hexagonal phase of the disilicide (h-MoSi _2) is the first phase formed. This occurs after 30 minute annealing at 400^ circC on clean samples. Impurities interfere with this reaction, but substrate crystallinity has no effect. The hexagonal phase transforms to the tetragonal phase (t-MoSi_2) after 800 ^circC annealing for all substrate types. Contamination retards this reaction, resulting in films containing both phases. For the thin films in this study, the transformation to t-MoSi_2 is accompanied by agglomeration of the films. From bulk thermodynamics, t-MoSi_2 is expected to be the first phase formed, but h -MoSi_2 is the first phase observed. This phase nucleates before t-MoSi_2, due to a lower silicide-silicon interfacial energy. Detailed knowledge of interfacial energies and effects of impurities are required to understand the initial phases of thin film solid state reactions.

  7. Comparison of silver and molybdenum microfocus X-ray sources for single-crystal structure determination

    PubMed Central

    Krause, Lennard; Herbst-Irmer, Regine; Sheldrick, George M.; Stalke, Dietmar

    2015-01-01

    The quality of diffraction data obtained using silver and molybdenum microsources has been compared for six model compounds with a wide range of absorption factors. The experiments were performed on two 30 W air-cooled Incoatec IµS microfocus sources with multilayer optics mounted on a Bruker D8 goniometer with a SMART APEX II CCD detector. All data were analysed, processed and refined using standard Bruker software. The results show that Ag Kα radiation can be beneficial when heavy elements are involved. A numerical absorption correction based on the positions and indices of the crystal faces is shown to be of limited use for the highly focused microsource beams, presumably because the assumption that the crystal is completely bathed in a (top-hat profile) beam of uniform intensity is no longer valid. Fortunately the empirical corrections implemented in SADABS, although originally intended as a correction for absorption, also correct rather well for the variations in the effective volume of the crystal irradiated. In three of the cases studied (two Ag and one Mo) the final SHELXL R1 against all data after application of empirical corrections implemented in SADABS was below 1%. Since such corrections are designed to optimize the agreement of the intensities of equivalent reflections with different paths through the crystal but the same Bragg 2θ angles, a further correction is required for the 2θ dependence of the absorption. For this, SADABS uses the transmission factor of a spherical crystal with a user-defined value of μr (where μ is the linear absorption coefficient and r is the effective radius of the crystal); the best results are obtained when r is biased towards the smallest crystal dimension. The results presented here suggest that the IUCr publication requirement that a numerical absorption correction must be applied for strongly absorbing crystals is in need of revision. PMID:26089746

  8. Comparison of silver and molybdenum microfocus X-ray sources for single-crystal structure determination.

    PubMed

    Krause, Lennard; Herbst-Irmer, Regine; Sheldrick, George M; Stalke, Dietmar

    2015-02-01

    The quality of diffraction data obtained using silver and molybdenum microsources has been compared for six model compounds with a wide range of absorption factors. The experiments were performed on two 30 W air-cooled Incoatec IµS microfocus sources with multilayer optics mounted on a Bruker D8 goniometer with a SMART APEX II CCD detector. All data were analysed, processed and refined using standard Bruker software. The results show that Ag Kα radiation can be beneficial when heavy elements are involved. A numerical absorption correction based on the positions and indices of the crystal faces is shown to be of limited use for the highly focused microsource beams, presumably because the assumption that the crystal is completely bathed in a (top-hat profile) beam of uniform intensity is no longer valid. Fortunately the empirical corrections implemented in SADABS, although originally intended as a correction for absorption, also correct rather well for the variations in the effective volume of the crystal irradiated. In three of the cases studied (two Ag and one Mo) the final SHELXL R1 against all data after application of empirical corrections implemented in SADABS was below 1%. Since such corrections are designed to optimize the agreement of the intensities of equivalent reflections with different paths through the crystal but the same Bragg 2θ angles, a further correction is required for the 2θ dependence of the absorption. For this, SADABS uses the transmission factor of a spherical crystal with a user-defined value of μr (where μ is the linear absorption coefficient and r is the effective radius of the crystal); the best results are obtained when r is biased towards the smallest crystal dimension. The results presented here suggest that the IUCr publication requirement that a numerical absorption correction must be applied for strongly absorbing crystals is in need of revision.

  9. Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

    DOE PAGES

    Fleischmann, Ernst; Miller, Michael K.; Affeldt, Ernst; ...

    2015-01-31

    Here, the solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980 °C and 30–75 MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is moremore » than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ' precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.« less

  10. Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

    SciTech Connect

    Fleischmann, Ernst; Miller, Michael K.; Affeldt, Ernst; Glatzel, Uwe

    2015-01-31

    Here, the solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980 °C and 30–75 MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is more than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ' precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.

  11. Influence of molybdenum on the creep properties of nickel-base superalloy single crystals

    NASA Technical Reports Server (NTRS)

    Mackay, R. A.; Nathal, M. V.; Pearson, D. D.

    1990-01-01

    The Mo content of an alloy series based on Ni-6 wt pct Al-6 wt pct Ta was systematically varied from 9.8 to 14.6 wt pct, in order to ascertain the influence of Mo on the creep properties of single crystals. The optimum initial gamma-gamma prime microstructure for raft development and creep strength was established in each alloy before testing. It was found that, as the Mo content increased from 9.8 to 14.0 percent, the magnitude of the lattice mismatch increased; upon reaching 14.6 percent, a degradation of mechanical properties occurred due to the precipitation of a third phase. These results suggest that small refractory metal content and initial gamma-prime variations can profoundly affect mechanical properties.

  12. Anisotropic transport in single-crystal molybdenum bronze, Li0.33MoO3

    NASA Astrophysics Data System (ADS)

    Moshfeghyeganeh, Saeed; Cohn, Joshua L.; Neumeier, John J.

    2015-03-01

    We present transport measurements (resistivity, thermopower, thermal conductivity) on single crystals of the quasi-one-dimensional semiconductor Li0.33MoO3 in the temperature range 200-500 K. First synthesized and studied long ago, the thermal and thermoelectric properties for this compound have not been previously reported. We find extreme anisotropy in the Seebeck coefficient within the a - c planes, with Sc -Sa ~= 300 μ V/K near room temperature. The thermal conductivity at room temperature in the a - c planes was ~ 1 . 5 - 2 W/mK and 7-8 times smaller along b*. We also report x-ray studies of the out-of-plane (b*) lattice constants indicating a small structural transition at T ~ 350 K that coincides with anomalies in the transport properties. This material is based upon work supported by the U.S. Department of Energy Office of Basic Energy Sciences Grant DE-FG02-12ER46888 (Univ. Miami) and the National Science Foundation under Grant DMR-0907036 (Mont. St. Univ.).

  13. The relationship between surface defects and surface reaction pathways on defective molybdenum sulfide(0001) single crystal surfaces

    NASA Astrophysics Data System (ADS)

    Wiegenstein, Christopher G.

    Hydrodesulfurization (HDS), the removal of sulfur from organic compounds, is important in the processing of crude oil. The industrial catalyst used is sulfided molybdenum promoted with Co or Ni supported on alumina. The present investigation examines MoS2 single crystals as model HDS catalysts. MoS2(0001) was chosen because it has the closest structure to the real catalyst, and still can be easily characterized with standard surface science techniques. This study is divided into two main areas of interest. The first area examined methods to create vacancies on the (0001) surface of MoS2, since the MoS2(0001) surface has been found to be relatively un-reactive for HDS. One way to create vacancies is to use hydrogen to remove sulfur from the surface. This would mimic the way defects are created in the real catalyst environment and develop a better understanding of hydrogen and hydrogen sulfide in HDS reactivity. The other method to create vacancies is to bombard the surface with argon ions to physically remove sulfur atoms from the surface, creating defect sites. Due to the limitation of the amount of hydrogen exposure needed to create sufficient vacancies to effect the surface reactivity, ion bombardment was favored to study the effects of sulfur defects on the HDS reactivity. The second part of this study is to determine the effect of site vacancies on the changes in surface reactivity using two probe molecules. Methanethiol was chosen as the first test molecule because it is the simplest organosulfur molecule and would be the easiest to determine the reaction pathways. Methanethiol HDS on both MoS2(0001) and defective MoS2(0001) surfaces show products of hydrogen, methane, ethane, ethylene and methanethiol, desorbing at 125 K and 300 K. Thiophene was chosen because it is the simplest of the aromatic organosulfur compounds. Thiophene only showed HDS reactivity on defective MoS2(0001) surfaces. Thiophene products were hydrogen, methane, ethylene, propadiene, and

  14. Anisotropic transport and structure of single-crystal molybdenum bronze, Li0.33MoO3

    NASA Astrophysics Data System (ADS)

    Moshfeghyeganeh, Saeed; Cohn, Joshua L.; Neumeier, John J.

    We present transport measurements (resistivity, thermopower, thermal conductivity) on single crystals of the quasi-one-dimensional (Q1D), small-gap semiconductora Li0.33MoO3 in the temperature range 150-500 K. The Q1D character of this material is reflected in T = 300 K resistivity ratios, ρc:ρa:ρb* ~= 1:20:180, and extreme anisotropy in the Seebeck coefficient within the a - c planes, Sc -Sa ~= 250 μ V/K. A weak structural anomaly near Ts = 355 K (0.001Å expansions along c* and b* directions, comparable contraction along a*) is identified in the temperature-dependent lattice constants from x-ray diffraction, and is coincident with changes in the transport coefficients. Analysis of the transport data at T >Ts shows that an intrinsic semiconductor model can be applied to explain transport along the most conducting c axis, but along a and b* the transport is better described by a non-adiabatic, small-polaron picture. a B.T. Collins et al., J. Sol. St. Chem. 76, 319 (1988). This material is based upon work supported by the U.S. Department of Energy Office of Basic Energy Sciences Grant DE-FG02-12ER46888 (Univ. Miami) and the National Science Foundation under Grant DMR-0907036 (Mont. St. Univ.).

  15. Single-crystal micro/nanostructures and thin films of lamellar molybdenum oxide by solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene

    NASA Astrophysics Data System (ADS)

    Díaz, Carlos; Lavayen, Vladimir; O'Dwyer, Colm

    2010-07-01

    The solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene is demonstrated to be a new, simple and versatile solid-state templating method for obtaining single-crystal micro- and nanocrystals of transition and valve metal oxides. The technique, when applied to Mo-containing organometallics N 3P 3[OC 6H 4CH 2CN·Mo(CO) 5] 6 and N 3P 3[OC 6H 4CH 2CN·Mo(CO) 4 py] 6, results in stand-alone and surface-deposited lamellar MoO 3 single crystals, as determined by electron and atomic force microscopies and X-ray diffraction. The size and morphology of the resulting crystals can be tuned by the composition of the precursor. X-ray photoelectron and infrared spectroscopies indicate that the deposition of highly lamellar MoO 3 directly on an oxidized (400 nm SiO 2) surface or (100) single-crystal silicon surfaces yields a layered uniphasic single-crystal film formed by cluster diffusion on the surface during pyrolysis of the metal-carbonyl derivatives. For MoO 3 in its layered form, this provides a new route to an important intercalation material for high energy density battery materials.

  16. Measured oscillator strengths in singly ionized molybdenum

    NASA Astrophysics Data System (ADS)

    Mayo-García, R.; Aragón, C.; Aguilera, J. A.; Ortiz, M.

    2015-11-01

    In this article, 112 oscillator strengths from Mo II have been measured, 79 of which for the first time. The radiative parameters have been obtained by laser-induced breakdown spectroscopy (LIBS). The plasma is produced from a fused glass sample prepared from molybdenum oxide with a Mo atomic concentration of 0.1%. The plasma evolved in air at atmospheric pressure, and measurements were carried out with the following plasma parameters: an electron density of (2.5+/- 0.1)\\cdot {10}17 cm-3 and an electron temperature of 14,400+/- 200 K. In these conditions, a local thermodynamic equilibrium environment and an optically thin plasma were confirmed for the measurements. The relative intensities were placed on an absolute scale by combining branching fractions with the measured lifetimes and by comparing well-known lines using the plasma temperature. Comparisons were made to previously obtained experimental and theoretical values wherever possible.

  17. Molybdenum

    Integrated Risk Information System (IRIS)

    Molybdenum ; CASRN 7439 - 98 - 7 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effec

  18. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

    SciTech Connect

    Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M.; Lou, Jun; Taylor, Antoinette J.; Prasankumar, Rohit P.

    2016-02-15

    We performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. Furthermore, the ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems.

  19. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

    PubMed Central

    Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M.; Lou, Jun; Taylor, Antoinette J.; Prasankumar, Rohit P.

    2016-01-01

    We have performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. The ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems. PMID:26876194

  20. SINGLE CRYSTAL NEUTRON DIFFRACTION.

    SciTech Connect

    KOETZLE,T.F.

    2001-03-13

    Single-crystal neutron diffraction measures the elastic Bragg reflection intensities from crystals of a material, the structure of which is the subject of investigation. A single crystal is placed in a beam of neutrons produced at a nuclear reactor or at a proton accelerator-based spallation source. Single-crystal diffraction measurements are commonly made at thermal neutron beam energies, which correspond to neutron wavelengths in the neighborhood of 1 Angstrom. For high-resolution studies requiring shorter wavelengths (ca. 0.3-0.8 Angstroms), a pulsed spallation source or a high-temperature moderator (a ''hot source'') at a reactor may be used. When complex structures with large unit-cell repeats are under investigation, as is the case in structural biology, a cryogenic-temperature moderator (a ''cold source'') may be employed to obtain longer neutron wavelengths (ca. 4-10 Angstroms). A single-crystal neutron diffraction analysis will determine the crystal structure of the material, typically including its unit cell and space group, the positions of the atomic nuclei and their mean-square displacements, and relevant site occupancies. Because the neutron possesses a magnetic moment, the magnetic structure of the material can be determined as well, from the magnetic contribution to the Bragg intensities. This latter aspect falls beyond the scope of the present unit; for information on magnetic scattering of neutrons see Unit 14.3. Instruments for single-crystal diffraction (single-crystal diffractometers or SCDs) are generally available at the major neutron scattering center facilities. Beam time on many of these instruments is available through a proposal mechanism. A listing of neutron SCD instruments and their corresponding facility contacts is included in an appendix accompanying this unit.

  1. Single crystal growth and characterization of the first reduced lanthanum molybdenum oxychloride, La20Mo12O63Cl4, with an unusual trigonal prismatic MoO6 unit

    NASA Astrophysics Data System (ADS)

    Cortese, Anthony J.; Wilkins, Branford; Smith, Mark D.; Morrison, Gregory; zur Loye, Hans-Conrad

    2015-10-01

    The use of a KCl/CsCl alkali eutectic flux under reducing conditions facilitated the crystal growth of the mixed valent Mo(V)/Mo(VI) compound La20Mo12O63Cl4. La20Mo12O63Cl4 crystallizes in the noncentrosymmetric hexagonal space group P-62m with a = 10.2241(2) Å and c = 15.0768(4) Å, which represents a new structure type exhibiting a three-dimensional crystal structure containing three different molybdenum coordination environments, MoO5 square pyramids, MoO6 trigonal prisms, and MoO5 trigonal bipyramids. The temperature dependence of the magnetic susceptibility was measured and La20Mo12O63Cl4 was found to be paramagnetic across the entire 2-300 K temperature range measured. Although noncentrosymmetric, La20Mo12O63Cl4 was not found to be second harmonic generation active. La20Mo12O63Cl4 was further characterized by UV/Vis spectroscopy.

  2. Single crystals of chitosan.

    PubMed

    Cartier, N; Domard, A; Chanzy, H

    1990-10-01

    Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology.

  3. Synthesis, growth, structure and characterization of molybdenum zinc thiourea complex crystals.

    PubMed

    Rajasekar, M; Muthu, K; Aditya Prasad, A; Agilandeshwari, R; Meenakshisundaram, S P

    2015-06-01

    Single crystals of molybdenum-incorporated tris(thiourea)zinc(II) sulfate (MoZTS) are grown by the slow evaporation solution growth technique. Crystal composition as determined by single-crystal X-ray diffraction analysis reveals that it belongs to the orthorhombic system with space group Pca21 and cell parameters a = 11.153 (2), b = 7.7691 (14), c = 15.408 (3) Å, V = 1335.14 (4) Å(3) and Z = 4. The surface morphological changes are studied by scanning electron microscopy. The vibrational patterns in FT-IR are used to identify the functional group and TGA/DTA (thermogravimetric analysis/differential thermal analysis) indicates the stability of the material. The structure and the crystallinity of the material were confirmed by powder X-ray diffraction analysis and the simulated X-ray diffraction (XRD) closely matches the experimental one with varied intensity patterns. The band gap energy is estimated using diffuse reflectance data by the application of the Kubelka-Munk algorithm. The relative second harmonic generation (SHG) efficiency measurements reveal that MoZTS has an efficiency comparable to that of tris(thiourea)zinc(II) sulfate (ZTS). Hirshfeld surfaces were derived using single-crystal X-ray diffraction data. Investigation of the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveal that the close contacts are associated with strong interactions. Intermolecular interactions as revealed by the fingerprint plot and close packing could be the possible reasons for facile charge transfer leading to SHG activity.

  4. Electrodeposition of single-crystalline molybdenum layers from tungstate-molybdate melts

    SciTech Connect

    Esina, N.O.; Tarasova, K.P.; Baraboshkin, A.N.

    1987-07-01

    The structure and growth rates of single-crystalline molybdenum layers produced by electrolysis of tungstate-molybdate melts on single-crystalline substrates with the orientations (110), (112), (100), and (111) were investigated. Growth pyramids having a symmetry coincident with that of the substrate plane were revealed as the characteristic feature of surface structure of these layers. The change from single- to polycrystalline molybdenum structure occurs via the development of twinning defects.

  5. A Method for the Calculation of Lattice Energies of Complex Crystals with Application to the Oxides of Molybdenum

    NASA Technical Reports Server (NTRS)

    Chaney, William S.

    1961-01-01

    A theoretical study has been made of molybdenum dioxide and molybdenum trioxide in order to extend the knowledge of factors Involved in the oxidation of molybdenum. New methods were developed for calculating the lattice energies based on electrostatic valence theory, and the coulombic, polarization, Van der Waals, and repulsion energie's were calculated. The crystal structure was examined and structure details were correlated with lattice energy.

  6. Processing tungsten single crystal by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xiao, Zhigang; Zee, Ralph H.; Begg, Lester L.

    2000-01-01

    A tungsten single crystal layer has been fabricated on molybdenum single crystal substrate through the hydrogen (H2) reduction of the tungsten hexafluoride (WF6) in low pressure. Substrate temperature, reaction chamber pressure, and flow rate of WF6 and H2, are critical process parameters during deposition. A comprehensive analysis for the effects of these parameters on single crystal layer growth has been processed and optimized growth conditions have been achieved. The different orientation of the substrate shows the different deposition rate for tungsten. Low index plane has higher deposition rate than high index plane. The kinetics of the deposition process has also been investigated. SEM surface analysis indicates that the single crystal layer is smooth in macro-scale and rough and step-growth format in micro-scale. .

  7. Crystallization and preliminary crystallographic analysis of molybdenum-cofactor biosynthesis protein C from Thermus thermophilus

    SciTech Connect

    Kanaujia, Shankar Prasad; Ranjani, Chellamuthu Vasuki; Jeyakanthan, Jeyaraman; Baba, Seiki; Chen, Lirong; Liu, Zhi-Jie; Wang, Bi-Cheng; Nishida, Masami; Ebihara, Akio; Shinkai, Akeo; Kuramitsu, Seiki; Shiro, Yoshitsugu; Sekar, Kanagaraj; Yokoyama, Shigeyuki

    2010-12-03

    The Gram-negative aerobic eubacterium Thermus thermophilus is an extremely important thermophilic microorganism that was originally isolated from a thermal vent environment in Japan. The molybdenum cofactor in this organism is considered to be an essential component required by enzymes that catalyze diverse key reactions in the global metabolism of carbon, nitrogen and sulfur. The molybdenum-cofactor biosynthesis protein C derived from T. thermophilus was crystallized in two different space groups. Crystals obtained using the first crystallization condition belong to the monoclinic space group P2{sub 1}, with unit-cell parameters a = 64.81, b = 109.84, c = 115.19 {angstrom}, {beta} = 104.9{sup o}; the crystal diffracted to a resolution of 1.9 {angstrom}. The other crystal form belonged to space group R32, with unit-cell parameters a = b = 106.57, c = 59.25 {angstrom}, and diffracted to 1.75 {angstrom} resolution. Preliminary calculations reveal that the asymmetric unit contains 12 monomers and one monomer for the crystals belonging to space group P2{sub 1} and R32, respectively.

  8. Creep of Oxide Single Crystals

    DTIC Science & Technology

    1990-08-01

    literature data on Gd 3Ga5O1 2 (8) indicate that garnets may be highly deformation resistant at temperatures very close to their melting points...Data for Yttrium Aluminum Garnet Single Crystals Temperature Stress Creep Rate (sec 1 ) for Given Stress Direction (0C) (MPa) [111] [110] [100] 1650...Gadolinium Gallium Garnet Single Crystals," J.Mat.Sci., 17, 878-884 (1982). 9. B.M. Wanklyn, Clarendon Laboratory, personal communicaticn. 10. S.B. Austerman

  9. Optoelectronic crystal of artificial atoms in strain-textured molybdenum disulphide

    PubMed Central

    Li, Hong; Contryman, Alex W.; Qian, Xiaofeng; Ardakani, Sina Moeini; Gong, Yongji; Wang, Xingli; Weisse, Jeffery M.; Lee, Chi Hwan; Zhao, Jiheng; Ajayan, Pulickel M.; Li, Ju; Manoharan, Hari C.; Zheng, Xiaolin

    2015-01-01

    The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping the visible light spectrum, with calculations showing the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. Here we realize and confirm this ‘artificial atom' concept via capillary-pressure-induced nanoindentation of monolayer molybdenum disulphide from a tailored nanopattern, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such two-dimensional semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics. PMID:26088550

  10. Development of single crystal membranes

    NASA Technical Reports Server (NTRS)

    Stormont, R. W.; Cocks, F. H.

    1972-01-01

    The design and construction of a high pressure crystal growth chamber was accomplished which would allow the growth of crystals under inert gas pressures of 2 MN/sq m (300 psi). A novel crystal growth technique called EFG was used to grow tubes and rods of the hollandite compounds, BaMgTi7O16, K2MgTi7O16, and tubes of sodium beta-alumina, sodium magnesium-alumina, and potassium beta-alumina. Rods and tubes grown are characterized using metallographic and X-ray diffraction techniques. The hollandite compounds are found to be two or three-phase, composed of coarse grained orientated crystallites. Single crystal c-axis tubes of sodium beta-alumina were grown from melts containing excess sodium oxide. Additional experiments demonstrated that crystals of magnesia doped beta-alumina and potassium beta-alumina also can be achieved by this EFG technique.

  11. Single Crystal Surfaces

    NASA Astrophysics Data System (ADS)

    Aguilar-Santillan, Joaquin

    2014-06-01

    The present work studies (0001) Al2O3 and (111) Al2MgO4 wetting with pure molten Al by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) under Ar at PO2 10-15 Pa. Al pure liquid wets a smooth and chemically homogeneous surface of an inert solid, the wetting driving force ( t, T) can be readily studied when surface solid roughness increases in the system. Both crystals planes (0001) Al2O3 and (111) Al2MgO4 have crystallographic surfaces with identical O-2 crystalline positions however considering Mg2+ content in Al2MgO4 structure may influence a reactive mode. Kinetic models results under similar experimental conditions show that Al wetting on (0001) Al2O3 is less reactive than (111) Al2MgO4, however at >1273 K (1000 °C) (0001) Al2O3 transformation occurs and a transition of wetting improves. The (111) Al2MgO4 and Al system promotes interface formations that slow its wetting process.

  12. Polymer-Controlled Crystallization of Molybdenum Oxides from Peroxomolybdates: Structural Diversity and Application to Catalytic Epoxidation

    SciTech Connect

    Munoz-Espf, R.; Burger, C; Krishnan, C; Chu, B

    2008-01-01

    The influence of polyoxyethylene-containing polymers on the crystal structure and habit of molybdenum-oxide-based products crystallized from peroxomolybdate solutions was investigated. Polyoxyethylene homopolymers of various molar masses were compared with a polyoxyethylene alkyl ether and a triblock copolymer of polyoxyethylene and polypropylene. Conventional hydrothermal synthesis at temperatures between 70 and 180 C was compared with an ultrasonic pathway at 70 C. The structure of the products was investigated by small- and wide-angle X-ray scattering. Different crystal phases were obtained depending on the polymer concentration and the preparation methods. At 70 C, a compound with tentative formula MoO3-x(O2)x nH2O (n ? 1), showing X-ray diffraction patterns matching those of triclinic monohydrate molybdenum trioxide, was the product found in the absence of any polymer. However, small concentrations of any polyoxyethylene-containing polymer led to a monoclinic hemihydrate phase under the same conditions and temperature. At temperatures above 90 C, the patterns of the resulting products could be indexed according to orthorhombic anhydrous MoO3, although the blue color of certain samples indicated an oxygen deficiency. At high polymer concentrations and temperatures under 90 C, the material crystallized in an unusual primitive cubic structure, independent of the exact type of polyoxyethylene polymer used, with a very large cubic lattice constant of 5 nm. However, the molar mass and the structure of the polymer do influence the lattice constants of the final crystal leading to a slight decrease with increasing molar mass. At high polymer concentrations and 180 C, the product was identified as MoO2. The polymer acts not only as a structure-directing agent but also as a mild reducing agent, as judged from the nontrivial redox behavior of the molybdenum ions when the crystallization occurs in the presence of polymer. The excellent catalytic properties of

  13. Crystal ball single event display

    SciTech Connect

    Grosnick, D.; Gibson, A.; Allgower, C.; Alyea, J. |

    1997-10-15

    The Single Event Display (SED) is a routine that is designed to provide information graphically about a triggered event within the Crystal Ball. The SED is written entirely in FORTRAN and uses the CERN-based HICZ graphing package. The primary display shows the amount of energy deposited in each of the NaI crystals on a Mercator-like projection of the crystals. Ten different shades and colors correspond to varying amounts of energy deposited within a crystal. Information about energy clusters is displayed on the crystal map by outlining in red the thirteen (or twelve) crystals contained within a cluster and assigning each cluster a number. Additional information about energy clusters is provided in a series of boxes containing useful data about the energy distribution among the crystals within the cluster. Other information shown on the event display include the event trigger type and data about {pi}{sup o}`s and {eta}`s formed from pairs of clusters as found by the analyzer. A description of the major features is given, along with some information on how to install the SED into the analyzer.

  14. Stacking fault energy in some single crystals

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2012-06-01

    The stacking fault energy of single crystals has been reported using the peak shift method. Presently studied all single crystals are grown by using a direct vapor transport (DVT) technique in the laboratory. The structural characterizations of these crystals are made by XRD. Considerable variations are shown in deformation (α) and growth (β) probabilities in single crystals due to off-stoichiometry, which possesses the stacking fault in the single crystal.

  15. Dislocation “Bubble-Like-Effect” and the Ambient Temperature Super-plastic Elongation of Body-centred Cubic Single Crystalline Molybdenum

    PubMed Central

    Lu, Yan; Xiang, Sisi; Xiao, Lirong; Wang, Lihua; Deng, Qingsong; Zhang, Ze; Han, Xiaodong

    2016-01-01

    With our recently developed deformation device, the in situ tensile tests of single crystal molybdenum nanowires with various size and aspect ratio were conducted inside a transmission electron microscope (TEM). We report an unusual ambient temperature (close to room temperature) super-plastic elongation above 127% on single crystal body-centred cubic (bcc) molybdenum nanowires with an optimized aspect ratio and size. A novel dislocation “bubble-like-effect” was uncovered for leading to the homogeneous, large and super-plastic elongation strain in the bcc Mo nanowires. The dislocation bubble-like-effect refers to the process of dislocation nucleation and annihilation, which likes the nucleation and annihilation process of the water bubbles. A significant plastic deformation dependence on the sample’s aspect ratio and size was revealed. The atomic scale TEM observations also demonstrated that a single crystal to poly-crystal transition and a bcc to face-centred cubic phase transformation took place, which assisted the plastic deformation of Mo in small scale. PMID:26956918

  16. Purification of molybdenum oxide, growth and characterization of medium size zinc molybdate crystals for the LUMINEU program

    NASA Astrophysics Data System (ADS)

    Shlegel, V. N.; Berge, L.; Boiko, R. S.; Chapellier, M.; Chernyak, D. M.; Coron, N.; Danevich, F. A.; Decourt, R.; Degoda, V. Ya.; Devoyon, L.; Drillien, A.; Dumoulin, L.; Enss, C.; Fleischmann, A.; Gastaldo, L.; Giuliani, A.; Gros, M.; Herve, S.; Ivanov, I. M.; Kobychev, V. V.; Kogut, Ya. P.; Koskas, F.; Loidl, M.; Magnier, P.; Makarov, E. P.; Mancuso, M.; de Marcillac, P.; Marnieros, S.; Marrache-Kikuchi, C.; Nasonov, S. G.; Navick, X. F.; Nones, C.; Olivieri, E.; Paul, B.; Penichot, Y.; Pessina, G.; Plantevin, O.; Poda, D. V.; Redon, T.; Rodrigues, M.; Strazzer, O.; Tenconi, M.; Torres, L.; Tretyak, V. I.; Vasiliev, Ya. V.; Velazquez, M.; Viraphong, O.; Zhdankov, V. N.

    2014-01-01

    The LUMINEU program aims at performing a pilot experiment on neutrinoless double beta decay of 100Mo using radiopure ZnMoO4 crystals operated as scintillating bolometers. Growth of high quality radiopure crystals is a complex task, since there are no commercially available molybdenum compounds with the required levels of purity and radioactive contamination. This paper discusses approaches to purify molybdenum and synthesize compound for high quality radiopure ZnMoO4 crystal growth. A combination of a double sublimation (with addition of zinc molybdate) with subsequent recrystallization in aqueous solutions (using zinc molybdate as a collector) was used. Zinc molybdate crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski technique, their optical, luminescent, diamagnetic, thermal and bolometric properties were tested.

  17. GALLIUM ARSENIDE DENDRITE SINGLE CRYSTAL PROGRAM

    DTIC Science & Technology

    ARSENIDES, *GALLIUM COMPOUNDS, *LABORATORY FURNACES, * SOLAR CELLS , CRUCIBLES, DESIGN, DIFFUSION, EXPLOSIONS, INTERMETALLIC COMPOUNDS, MATERIALS, PHOSPHORUS, SINGLE CRYSTALS, TEMPERATURE CONTROL, ZINC

  18. Superconducting molybdenum-rhenium electrodes for single-molecule transport studies

    SciTech Connect

    Gaudenzi, R.; Island, J. O.; Bruijckere, J. de; Burzurí, E.; Zant, H. S. J. van der; Klapwijk, T. M.

    2015-06-01

    We demonstrate that electronic transport through single molecules or molecular ensembles, commonly based on gold (Au) electrodes, can be extended to superconducting electrodes by combining gold with molybdenum-rhenium (MoRe). This combination induces proximity-effect superconductivity in the gold to temperatures of at least 4.6 K and magnetic fields of 6 T, improving on previously reported aluminum based superconducting nanojunctions. As a proof of concept, we show three-terminal superconductive transport measurements through an individual Fe{sub 4} single-molecule magnet.

  19. Full hyperfine structure analysis of singly ionized molybdenum

    NASA Astrophysics Data System (ADS)

    Bouazza, Safa

    2017-03-01

    For a first time a parametric study of hyperfine structure of Mo II configuration levels is presented. The newly measured A and B hyperfine structure (hfs) constants values of Mo II 4d5, 4d45s and 4d35s2 configuration levels, for both 95 and 97 isotopes, using Fast-ion-beam laser-induced fluorescence spectroscopy [1] are gathered with other few data available in literature. A fitting procedure of an isolated set of these three lowest even-parity configuration levels has been performed by taking into account second-order of perturbation theory including the effects of closed shell-open shell excitations. Moreover the same study was done for Mo II odd-parity levels; for both parities two sets of fine structure parameters as well as the leading eigenvector percentages of levels and Landé-factor gJ, relevant for this paper are given. We present also predicted singlet, triplet and quintet positions of missing experimental levels up to 85000 cm-1. The single-electron hfs parameter values were extracted in their entirety for 97Mo II and for 95Mo II: for instance for 95Mo II, a4d01 =-133.37 MHz and a5p01 =-160.25 MHz for 4d45p; a4d01 =-140.84 MHz, a5p01 =-170.18 MHz and a5s10 =-2898 MHz for 4d35s5p; a5s10 =-2529 (2) MHz and a4d01 =-135.17 (0.44) MHz for the 4d45s. These parameter values were analysed and compared with diverse ab-initio calculations. We closed this work with giving predicted values of magnetic dipole and electric quadrupole hfs constants of all known levels, whose splitting are not yet measured.

  20. Temperature-dependent mechanical properties of single-layer molybdenum disulphide: Molecular dynamics nanoindentation simulations

    NASA Astrophysics Data System (ADS)

    Zhao, Junhua; Jiang, Jin-Wu; Rabczuk, Timon

    2013-12-01

    The temperature-dependent mechanical properties of single-layer molybdenum disulphide (MoS2) are obtained using molecular dynamics (MD) nanoindentation simulations. The Young's moduli, maximum load stress, and maximum loading strain decrease with increasing temperature from 4.2 K to 500 K. The obtained Young's moduli are in good agreement with those using our MD uniaxial tension simulations and the available experimental results. The tendency of maximum loading strain with different temperature is opposite with that of metal materials due to the short range Stillinger-Weber potentials in MoS2. Furthermore, the indenter tip radius and fitting strain effect on the mechanical properties are also discussed.

  1. Additive manufacturing of micrometric crystallization vessels and single crystals

    PubMed Central

    Halevi, Oded; Jiang, Hui; Kloc, Christian; Magdassi, Shlomo

    2016-01-01

    We present an all-additive manufacturing method that is performed at mild conditions, for the formation of organic single crystals at specific locations, without any photolithography prefabrication process. The method is composed of two steps; inkjet printing of a confinement frame, composed of a water soluble electrolyte. Then, an organic semiconductor solution is printed within the confinement to form a nucleus at a specific location, followed by additional printing, which led to the growth of a single crystal. The specific geometry of the confinement enables control of the specific locations of the single crystals, while separating the nucleation and crystal growth processes. By this method, we printed single crystals of perylene, which are suitable for the formation of OFETs. Moreover, since this method is based on a simple and controllable wet deposition process, it enables formation of arrays of single crystals at specific locations, which is a prerequisite for mass production of active organic elements on flexible substrates. PMID:27830827

  2. Additive manufacturing of micrometric crystallization vessels and single crystals.

    PubMed

    Halevi, Oded; Jiang, Hui; Kloc, Christian; Magdassi, Shlomo

    2016-11-10

    We present an all-additive manufacturing method that is performed at mild conditions, for the formation of organic single crystals at specific locations, without any photolithography prefabrication process. The method is composed of two steps; inkjet printing of a confinement frame, composed of a water soluble electrolyte. Then, an organic semiconductor solution is printed within the confinement to form a nucleus at a specific location, followed by additional printing, which led to the growth of a single crystal. The specific geometry of the confinement enables control of the specific locations of the single crystals, while separating the nucleation and crystal growth processes. By this method, we printed single crystals of perylene, which are suitable for the formation of OFETs. Moreover, since this method is based on a simple and controllable wet deposition process, it enables formation of arrays of single crystals at specific locations, which is a prerequisite for mass production of active organic elements on flexible substrates.

  3. Additive manufacturing of micrometric crystallization vessels and single crystals

    NASA Astrophysics Data System (ADS)

    Halevi, Oded; Jiang, Hui; Kloc, Christian; Magdassi, Shlomo

    2016-11-01

    We present an all-additive manufacturing method that is performed at mild conditions, for the formation of organic single crystals at specific locations, without any photolithography prefabrication process. The method is composed of two steps; inkjet printing of a confinement frame, composed of a water soluble electrolyte. Then, an organic semiconductor solution is printed within the confinement to form a nucleus at a specific location, followed by additional printing, which led to the growth of a single crystal. The specific geometry of the confinement enables control of the specific locations of the single crystals, while separating the nucleation and crystal growth processes. By this method, we printed single crystals of perylene, which are suitable for the formation of OFETs. Moreover, since this method is based on a simple and controllable wet deposition process, it enables formation of arrays of single crystals at specific locations, which is a prerequisite for mass production of active organic elements on flexible substrates.

  4. van der Waals screening by single-layer graphene and molybdenum disulfide.

    PubMed

    Tsoi, Stanislav; Dev, Pratibha; Friedman, Adam L; Stine, Rory; Robinson, Jeremy T; Reinecke, Thomas L; Sheehan, Paul E

    2014-12-23

    A sharp tip of atomic force microscope is employed to probe van der Waals forces of a silicon oxide substrate with adhered graphene. Experimental results obtained in the range of distances from 3 to 20 nm indicate that single-, double-, and triple-layer graphenes screen the van der Waals forces of the substrate. Fluorination of graphene, which makes it electrically insulating, lifts the screening in the single-layer graphene. The van der Waals force from graphene determined per layer decreases with the number of layers. In addition, increased hole doping of graphene increases the force. Finally, we also demonstrate screening of the van der Waals forces of the silicon oxide substrate by single- and double-layer molybdenum disulfide.

  5. Theoretical and experimental determination of the crystal structures of cesium-molybdenum chloride

    NASA Astrophysics Data System (ADS)

    Saito, Norio; Wada, Yoshiki; Lemoine, Pierric; Cordier, Stéphane; Grasset, Fabien; Ohsawa, Takeo; Saito, Noriko; Cross, Jeffrey S.; Ohashi, Naoki

    2016-07-01

    We herein report the structure-property relationships of the octahedral molybdenum metal cluster compound, Cs2[Mo6Cl14]. Using purified samples, we attempted to determine if Cs2[Mo6Cl14] possesses crystalline polarity. Heat treatment was performed prior to characterization to remove impurities, as X-ray powder diffraction and Fourier transformation infrared spectroscopy studies suggested the unit cell of Cs2[Mo6Cl14] expanded with the insertion of water molecules and/or hydroxyl moieties. Geometry optimization and total energy calculations by density functional theory calculations were conducted to determine whether Cs2[Mo6Cl14] crystallizes in centrosymmetric (P\\bar{3}1c) or non-centrosymmetric (P31c) space groups. Furthermore, the results of the optical studies, along with the absence of a second harmonic generation, and the observation of a strong third harmonic generation, supported the hypothesis that inversion symmetry exists in the Cs2[Mo6Cl14] lattice. The space group of Cs2[Mo6Cl14] was therefore identified as P\\bar{3}1c symmetry.

  6. Large area single crystal (0001) oriented MoS2

    NASA Astrophysics Data System (ADS)

    Laskar, Masihhur R.; Ma, Lu; Kannappan, Santhakumar; Sung Park, Pil; Krishnamoorthy, Sriram; Nath, Digbijoy N.; Lu, Wu; Wu, Yiying; Rajan, Siddharth

    2013-06-01

    Layered metal dichalcogenide materials are a family of semiconductors with a wide range of energy band gaps and properties, the potential for exciting physics and technology applications. However, obtaining high crystal quality thin films over a large area remains a challenge. Here we show that chemical vapor deposition (CVD) can be used to achieve large area single crystal Molybdenum Disulfide (MoS2) thin films. Growth temperature and choice of substrate were found to critically impact the quality of film grown, and high temperature growth on (0001) oriented sapphire yielded highly oriented single crystal MoS2 films. Films grown under optimal conditions were found to be of high structural quality from high-resolution X-ray diffraction, transmission electron microscopy, and Raman measurements, approaching the quality of reference geological MoS2. Photoluminescence and electrical measurements confirmed the growth of optically active MoS2 with a low background carrier concentration, and high mobility. The CVD method reported here for the growth of high quality MoS2 thin films paves the way towards growth of a variety of layered 2D chalcogenide semiconductors and their heterostructures.

  7. Reactivity of a Carbon-Supported Single-Site Molybdenum Dioxo Catalyst for Biodiesel Synthesis

    SciTech Connect

    Mouat, Aidan R.; Lohr, Tracy L.; Wegener, Evan C.; Miller, Jeffrey T.; Delferro, Massimiliano; Stair, Peter C.; Marks, Tobin J.

    2016-08-23

    A single-site molybdenum dioxo catalyst, (Oc)2Mo(=O)2@C, was prepared via direct grafting of MoO2Cl2(dme) (dme = 1,2-dimethoxyethane) on high-surface- area activated carbon. The physicochemical and chemical properties of this catalyst were fully characterized by N2 physisorption, ICP-AES/OES, PXRD, STEM, XPS, XAS, temperature-programmed reduction with H2 (TPR-H2), and temperature-programmed NH3 desorption (TPD-NH3). The single-site nature of the Mo species is corroborated by XPS and TPR-H2 data, and it exhibits the lowest reported MoOx Tmax of reduction reported to date, suggesting a highly reactive MoVI center. (Oc)2Mo(=O)2@C catalyzes the transesterification of a variety of esters and triglycerides with ethanol, exhibiting high activity at moderate temperatures (60-90 °C) and with negligible deactivation. (Oc)2Mo(=O)2@C is resistant to water and can be recycled at least three times with no loss of activity. The transesterification reaction is determined experimentally to be first order in [ethanol] and first order in [Mo] with ΔH = 10.5(8) kcal mol-1 and ΔS = -32(2) eu. The low energy of activation is consistent with the moderate conditions needed to achieve rapid turnover. This highly active carbon-supported single-site molybdenum dioxo species is thus an efficient, robust, and lowcost catalyst with significant potential for transesterification processes.

  8. Transfer of molybdenum disulfide to various metals

    NASA Technical Reports Server (NTRS)

    Barton, G. C.; Pepper, S. V.

    1977-01-01

    Sliding friction experiments were conducted with molybdenum disulfide single crystals in contact with sputter cleaned surfaces of copper, nickel, gold, and 304 stainless steel. Transfer of the molybdenum disulfide to the metals was monitored with Auger electron spectroscopy. Results of the investigation indicate molybdenum disulfide transfers to all clean metal surfaces after a single pass over the metal surface with film thickness observed to increase with repeated passes over the same surfaces. Large particle transfer occurs when the orientation of the crystallites is other than basal. This is frequently accompanied by abrasion of the metal. Adhesion of molybdenum disulfide films occurred readily to copper and nickel, less readily to 304 stainless steel, and even less effectively to the gold, which indicates a chemical effect.

  9. Synthesis and structural characterization of a single-crystal to single-crystal transformable coordination polymer.

    PubMed

    Tian, Yuyang; Allan, Phoebe K; Renouf, Catherine L; He, Xiang; McCormick, Laura J; Morris, Russell E

    2014-01-28

    A single-crystal to single-crystal transformable coordination polymer compound was hydrothermally synthesized. The structural rearrangement is induced by selecting a ligand that contains both strong and weaker coordinating groups. Both hydrated and dehydrated structures were determined by single crystal X-ray analysis.

  10. Ames Lab 101: Single Crystal Growth

    SciTech Connect

    Schlagel, Deborah

    2013-09-27

    Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

  11. Confinement stabilises single crystal vaterite rods.

    PubMed

    Schenk, Anna S; Albarracin, Eduardo J; Kim, Yi-Yeoun; Ihli, Johannes; Meldrum, Fiona C

    2014-05-11

    Single-crystals of vaterite, the least-stable anhydrous polymorph of CaCO3, are rare in biogenic and synthetic systems. We here describe the synthesis of high aspect ratio single crystal vaterite rods under additive-free conditions by precipitating CaCO3 within the cylindrical pores of track-etch membranes.

  12. Ultratough single crystal boron-doped diamond

    DOEpatents

    Hemley, Russell J [Carnegie Inst. for Science, Washington, DC ; Mao, Ho-Kwang [Carnegie Inst. for Science, Washington, DC ; Yan, Chih-Shiue [Carnegie Inst. for Science, Washington, DC ; Liang, Qi [Carnegie Inst. for Science, Washington, DC

    2015-05-05

    The invention relates to a single crystal boron doped CVD diamond that has a toughness of at least about 22 MPa m.sup.1/2. The invention further relates to a method of manufacturing single crystal boron doped CVD diamond. The growth rate of the diamond can be from about 20-100 .mu.m/h.

  13. Ames Lab 101: Single Crystal Growth

    ScienceCinema

    Schlagel, Deborah

    2016-07-12

    Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

  14. Method of making single crystal fibers

    NASA Technical Reports Server (NTRS)

    Westfall, Leonard J. (Inventor)

    1990-01-01

    Single crystal fibers are made from miniature extruded ceramic feed rods. A decomposable binder is mixed with powders to inform a slurry which is extruded into a small rod which may be sintered, either in air or in vacuum, or it may be used in the extruded and dried condition. A pair of laser beams focuses onto the tip of the rod to melt it thereby forming a liquid portion. A single crystal seed fiber of the same material as the feed rod contacts this liquid portion to establish a zone of liquid material between the feed rod and the single crystal seed fiber. The feed rod and the single crystal feed fiber are moved at a predetermined speed to solidify the molten zone onto the seed fiber while simultaneously melting additional feed rod. In this manner a single crystal fiber is formed from the liquid portion.

  15. Single-crystal silicon optical fiber by direct laser crystallization

    SciTech Connect

    Ji, Xiaoyu; Lei, Shiming; Yu, Shih -Ying; Cheng, Hiu Yan; Liu, Wenjun; Poilvert, Nicolas; Xiong, Yihuang; Dabo, Ismaila; Mohney, Suzanne E.; Badding, John V.; Gopalan, Venkatraman

    2016-12-05

    Semiconductor core optical fibers with a silica cladding are of great interest in nonlinear photonics and optoelectronics applications. Laser crystallization has been recently demonstrated for crystallizing amorphous silicon fibers into crystalline form. Here we explore the underlying mechanism by which long single-crystal silicon fibers, which are novel platforms for silicon photonics, can be achieved by this process. Using finite element modeling, we construct a laser processing diagram that reveals a parameter space within which single crystals can be grown. Utilizing this diagram, we illustrate the creation of single-crystal silicon core fibers by laser crystallizing amorphous silicon deposited inside silica capillary fibers by high-pressure chemical vapor deposition. The single-crystal fibers, up to 5.1 mm long, have a very welldefined core/cladding interface and a chemically pure silicon core that leads to very low optical losses down to ~0.47-1dB/cm at the standard telecommunication wavelength (1550 nm). Furthermore, tt also exhibits a photosensitivity that is comparable to bulk silicon. Creating such laser processing diagrams can provide a general framework for developing single-crystal fibers in other materials of technological importance.

  16. Single-crystal silicon optical fiber by direct laser crystallization

    DOE PAGES

    Ji, Xiaoyu; Lei, Shiming; Yu, Shih -Ying; ...

    2016-12-05

    Semiconductor core optical fibers with a silica cladding are of great interest in nonlinear photonics and optoelectronics applications. Laser crystallization has been recently demonstrated for crystallizing amorphous silicon fibers into crystalline form. Here we explore the underlying mechanism by which long single-crystal silicon fibers, which are novel platforms for silicon photonics, can be achieved by this process. Using finite element modeling, we construct a laser processing diagram that reveals a parameter space within which single crystals can be grown. Utilizing this diagram, we illustrate the creation of single-crystal silicon core fibers by laser crystallizing amorphous silicon deposited inside silica capillarymore » fibers by high-pressure chemical vapor deposition. The single-crystal fibers, up to 5.1 mm long, have a very welldefined core/cladding interface and a chemically pure silicon core that leads to very low optical losses down to ~0.47-1dB/cm at the standard telecommunication wavelength (1550 nm). Furthermore, tt also exhibits a photosensitivity that is comparable to bulk silicon. Creating such laser processing diagrams can provide a general framework for developing single-crystal fibers in other materials of technological importance.« less

  17. The reactivity of lattice carbon and nitrogen species in molybdenum (oxy)carbonitrides prepared by single-source routes

    SciTech Connect

    AlShalwi, M.; Hargreaves, J.S.J.; Liggat, J.J.; Todd, D.

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Molybdenum (oxy)carbonitrides have been prepared from single source routes. Black-Right-Pointing-Pointer Nitrogen species are more reactive than carbon species within the carbonitrides. Black-Right-Pointing-Pointer The reactivity of nitrogen species is a function of carbonitride composition. -- Abstract: Molybdenum (oxy)carbonitrides of different compositions have been prepared from hexamethylenetetramine molybdate and ethylenediamine molybdate precursors and the reactivity of the lattice carbon and nitrogen species within them has been determined by temperature programmed reduction and thermal volatilisation studies. Nitrogen is found to be much more reactive than carbon and the nature of its reactivity is influenced by composition with the presence of carbon enhancing the reactivity of nitrogen. The difference in reactivity observed indicates that molybdenum carbonitrides are not suitable candidates as reagents for which the simultaneous loss of nitrogen and carbon from the lattice would be desirable.

  18. High-resolution microdiffraction study of notch-tip deformation in Mo single crystals using x-ray synchrotron radiation

    SciTech Connect

    Ice, G.; Habenschuss, A.; Bilello, J.C.; Rebonato, R.

    1989-12-31

    A new technique is presented for the determination of strain fields in single crystals, based on the simultaneous recording of the energy and position of a diffracted beam, with a resolution of 25 micrometers under current experimental conditions. The technique can be profitably used for perfect to highly deformed crystals, in materials as highly absorbing as Molybdenum, and allows a spatial resolution of one part in 10{sup 4}. Indications are given as to possible refinements and improvements of the method.

  19. High-resolution microdiffraction study of notch-tip deformation in Mo single crystals using x-ray synchrotron radiation

    SciTech Connect

    Ice, G.; Habenschuss, A. ); Bilello, J.C. ); Rebonato, R. . Physical Chemistry Lab.)

    1989-01-01

    A new technique is presented for the determination of strain fields in single crystals, based on the simultaneous recording of the energy and position of a diffracted beam, with a resolution of 25 micrometers under current experimental conditions. The technique can be profitably used for perfect to highly deformed crystals, in materials as highly absorbing as Molybdenum, and allows a spatial resolution of one part in 10{sup 4}. Indications are given as to possible refinements and improvements of the method.

  20. Crystal structures, dynamics and functional implications of molybdenum-cofactor biosynthesis protein MogA from two thermophilic organisms

    PubMed Central

    Kanaujia, Shankar Prasad; Jeyakanthan, Jeyaraman; Shinkai, Akeo; Kuramitsu, Seiki; Yokoyama, Shigeyuki; Sekar, Kanagaraj

    2011-01-01

    Molybdenum-cofactor (Moco) biosynthesis is an evolutionarily conserved pathway in almost all kingdoms of life, including humans. Two proteins, MogA and MoeA, catalyze the last step of this pathway in bacteria, whereas a single two-domain protein carries out catalysis in eukaryotes. Here, three crystal structures of the Moco-biosynthesis protein MogA from the two thermophilic organisms Thermus thermophilus (TtMogA; 1.64 Å resolution, space group P21) and Aquifex aeolicus (AaMogA; 1.70 Å resolution, space group P21 and 1.90 Å resolution, space group P1) have been determined. The functional roles and the residues involved in oligomerization of the protein molecules have been identified based on a comparative analysis of these structures with those of homologous proteins. Furthermore, functional roles have been proposed for the N- and C-terminal residues. In addition, a possible protein–protein complex of MogA and MoeA has been proposed and the residues involved in protein–protein interactions are discussed. Several invariant water molecules and those present at the subunit interfaces have been identified and their possible structural and/or functional roles are described in brief. In addition, molecular-dynamics and docking studies with several small molecules (including the substrate and the product) have been carried out in order to estimate their binding affinities towards AaMogA and TtMogA. The results obtained are further compared with those obtained for homologous eukaryotic proteins. PMID:21206014

  1. Crystal structures, dynamics and functional implications of molybdenum-cofactor biosynthesis protein MogA from two thermophilic organisms.

    PubMed

    Kanaujia, Shankar Prasad; Jeyakanthan, Jeyaraman; Shinkai, Akeo; Kuramitsu, Seiki; Yokoyama, Shigeyuki; Sekar, Kanagaraj

    2011-01-01

    Molybdenum-cofactor (Moco) biosynthesis is an evolutionarily conserved pathway in almost all kingdoms of life, including humans. Two proteins, MogA and MoeA, catalyze the last step of this pathway in bacteria, whereas a single two-domain protein carries out catalysis in eukaryotes. Here, three crystal structures of the Moco-biosynthesis protein MogA from the two thermophilic organisms Thermus thermophilus (TtMogA; 1.64 Å resolution, space group P2(1)) and Aquifex aeolicus (AaMogA; 1.70 Å resolution, space group P2(1) and 1.90 Å resolution, space group P1) have been determined. The functional roles and the residues involved in oligomerization of the protein molecules have been identified based on a comparative analysis of these structures with those of homologous proteins. Furthermore, functional roles have been proposed for the N- and C-terminal residues. In addition, a possible protein-protein complex of MogA and MoeA has been proposed and the residues involved in protein-protein interactions are discussed. Several invariant water molecules and those present at the subunit interfaces have been identified and their possible structural and/or functional roles are described in brief. In addition, molecular-dynamics and docking studies with several small molecules (including the substrate and the product) have been carried out in order to estimate their binding affinities towards AaMogA and TtMogA. The results obtained are further compared with those obtained for homologous eukaryotic proteins.

  2. Spray printing of organic semiconducting single crystals

    PubMed Central

    Rigas, Grigorios-Panagiotis; Payne, Marcia M.; Anthony, John E.; Horton, Peter N.; Castro, Fernando A.; Shkunov, Maxim

    2016-01-01

    Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics. PMID:27874001

  3. Spray printing of organic semiconducting single crystals

    NASA Astrophysics Data System (ADS)

    Rigas, Grigorios-Panagiotis; Payne, Marcia M.; Anthony, John E.; Horton, Peter N.; Castro, Fernando A.; Shkunov, Maxim

    2016-11-01

    Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.

  4. Unusual isotope effect on thermal transport of single layer molybdenum disulphide

    SciTech Connect

    Wu, Xufei; Yang, Nuo; Luo, Tengfei

    2015-11-09

    Thermal transport in single layer molybdenum disulfide (MoS{sub 2}) is critical to advancing its applications. In this paper, we use molecular dynamics simulations with first-principles force constants to study the isotope effect on the thermal transport of single layer MoS{sub 2}. Through phonon modal analysis, we found that isotopes can strongly scatter phonons with intermediate frequencies, and the scattering behavior can be radically different from that predicted by conventional scattering model based on perturbation theory, where Tamura's formula is combined with Matthiessen's rule to include isotope effects. Such a discrepancy becomes smaller for low isotope concentrations. Natural isotopes can lead to a 30% reduction in thermal conductivity for large size samples. However, for small samples where boundary scattering becomes significant, the isotope effect can be greatly suppressed. It was also found that the Mo isotopes, which contribute more to the phonon eigenvectors in the intermediate frequency range, have stronger impact on thermal conductivity than S isotopes.

  5. Molybdenum metallization, and step-induced defects in active-matrix liquid crystal displays

    NASA Astrophysics Data System (ADS)

    Quli, Farhat Abbas

    The objective of this work was to identify the causes of the step-induced preferential etching which occurs during the patterning of molybdenum (Mo) interconnects for the source/drain line metallization of the thin-film transistor array of active matrix liquid crystal displays. The morphology of Mo films deposited on steps under various conditions using sputtering and electron beam physical vapor deposition (EB-PVD) was studied to identify the causes of preferential etching, and determine processing conditions leading to defect-free interconnects. It was found that columnar growth domains grown from the steps were misaligned with the columnar growth from the substrate, causing the creation of high-angle grain boundaries where the columns impinged upon one another. This boundary region is believed to be responsible for the preferential etching in the Mo films. Columnar growth of silicon dioxide, an amorphous film, did not result in preferential etching due to the lack of grain boundaries. Neon (Ne) sputtering of Mo did not lead to amorphous films due to higher film bombardment during Ne sputtering, as reported by other researchers. Instead, the low rate of deposition during Ne sputtering was found to cause the incorporation of high amounts of impurities that lead to amorphization of the growing film. At extremely low rates and high impurity concentrations, it was found that the film grew in a fcc rather than bcc structure. Mo deposited under high levels of argon ion bombardment was found to have an isotropic rather than columnar morphology which led to interconnects that were free from preferential etching. The maximum ratio of depositing atoms to bombarding ions necessary to modify the microstructure was found to be 1.5 for Mo deposited by EB-PVD at 400°C substrate temperature and --600 volts substrate bias. The processing window for bias sputtering conditions leading to an isotropic morphology was also identified. Thermally induced grain growth in metal films was

  6. Single Crystals Grown Under Unconstrained Conditions

    NASA Astrophysics Data System (ADS)

    Sunagawa, Ichiro

    Based on detailed investigations on morphology (evolution and variation in external forms), surface microtopography of crystal faces (spirals and etch figures), internal morphology (growth sectors, growth banding and associated impurity partitioning) and perfection (dislocations and other lattice defects) in single crystals, we can deduce how and by what mechanism the crystal grew and experienced fluctuation in growth parameters through its growth and post-growth history under unconstrained condition. The information is useful not only in finding appropriate way to growing highly perfect and homogeneous single crystals, but also in deciphering letters sent from the depth of the Earth and the Space. It is also useful in discriminating synthetic from natural gemstones. In this chapter, available methods to obtain molecular information are briefly summarized, and actual examples to demonstrate the importance of this type of investigations are selected from both natural minerals (diamond, quartz, hematite, corundum, beryl, phlogopite) and synthetic crystals (SiC, diamond, corundum, beryl).

  7. Fatigue hardening in niobium single crystals.

    NASA Technical Reports Server (NTRS)

    Doner, M.; Diprimio, J. C.; Salkovitz, E. I.

    1973-01-01

    Nb single crystals of various orientations were cyclically deformed in tension-compression under strain control. At low strain amplitudes all crystals oriented for single slip and some oriented for multiple slip showed a two stage hardening. When present, the first stage was characterized with almost no cyclic work hardening. The rate of hardening in the second stage increased with strain amplitude and the amount of secondary slip. In crystals oriented for single slip kink bands developed on their side faces during rapid hardening stage which resulted in considerable amount of asterism in Laue spots. A cyclic stress-strain curve independent of prior history was found to exist which was also independent of crystal orientation. Furthermore, this curve differed only slightly from that of polycrystalline Nb obtained from data in literature.

  8. Characterization of zinc selenide single crystals

    NASA Technical Reports Server (NTRS)

    Gerhardt, Rosario A.

    1996-01-01

    ZnSe single crystals of high quality and low impurity levels are desired for use as substrates in optoelectronic devices. This is especially true when the device requires the formation of homoepitaxial layers. While ZnSe is commercially available, it is at present extremely expensive due to the difficulty of growing single crystal boules with low impurity content and the resultant low yields. Many researchers have found it necessary to heat treat the crystals in liquid Zn in order to remove the impurities, lower the resistivity and activate the photoluminescence at room temperature. The physical vapor transport method (PVT) has been successfully used at MSFC to grow many single crystals of II-VI semiconducting materials including ZnSe. The main goal at NASA has been to try to establish the effect of gravity on the growth parameters. To this effect, crystals have been grown vertically upwards or horizontally. Both (111) and (110) oriented ZnSe crystals have been obtained via unseeded PVT growth. Preliminary characterization of the horizontally grown crystals has revealed that Cu is a major impurity and that the low temperature photoluminescence spectra is dominated by the copper peak. The ratio of the copper peak to the free exciton peak is being used to determine variations in composition throughout the crystal. It was the intent of this project to map the copper composition of various crystals via photoluminescence first, then measure their electrical resistivity and capacitance as a function of frequency before proceeding with a heat treatment designed to remove the copper impurities. However, equipment difficulties with the photoluminescence set up, having to establish a procedure for measuring the electrical properties of the as-grown crystals and time limitations made us re-evaluate the project goals. Vertically grown samples designated as ZnSe-25 were chosen to be measured electrically since they were not expected to show as much variation in their

  9. Performance of Single Crystal Niobium Cavities

    SciTech Connect

    Kneisel, Peter; Ciovati, Gianluigi; Singer, Waldemar; Singer, Xenia; Reschke, Detlef; Brinkmann, A.

    2008-07-01

    We have fabricated and tested a total of six single cell niobium cavities, made from single crystal, high purity niobium. Two of the three cavities of the TESLA shape (1300 MHz) were made from Heraeus niobium by extending a smaller single crystal by rolling and annealing steps; the third cavity was made by spinning from CBMM material. The three other cavities of the scaled "Low Loss" (LL) shape (two) and "High Gradient" (HG) shape (one) resonated at 2.3 GHz and were fabricated from "as received" single crystals, both from Heraeus and CBMM niobium. After appropriate surface treatments by buffered chemical polishing and electropolishing most cavities performed quite nicely and peak surface magnetic fields of ~ 160 mT or above corresponding to accelerating gradients between 38 MV/m and 45 MV/m were reached. This paper reports about the performance of these cavities.

  10. Neutron detection with single crystal organic scintillators

    SciTech Connect

    Zaitseva, N; Newby, J; Hamel, S; Carman, L; Faust, M; Lordi, V; Cherepy, N; Stoeffl, W; Payne, S

    2009-07-15

    Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10-diphenylanthracene and diphenylacetylene.

  11. Oxygen Incorporation in Rubrene Single Crystals

    PubMed Central

    Mastrogiovanni, Daniel D. T.; Mayer, Jeff; Wan, Alan S.; Vishnyakov, Aleksey; Neimark, Alexander V.; Podzorov, Vitaly; Feldman, Leonard C.; Garfunkel, Eric

    2014-01-01

    Single crystal rubrene is a model organic electronic material showing high carrier mobility and long exciton lifetime. These properties are detrimentally affected when rubrene is exposed to intense light under ambient conditions for prolonged periods of time, possibly due to oxygen up-take. Using photoelectron, scanning probe and ion-based methods, combined with an isotopic oxygen exposure, we present direct evidence of the light-induced reaction of molecular oxygen with single crystal rubrene. Without a significant exposure to light, there is no reaction of oxygen with rubrene for periods of greater than a year; the crystal's surface (and bulk) morphology and chemical composition remain essentially oxygen-free. Grand canonical Monte Carlo computations show no sorbtion of gases into the bulk of rubrene crystal. A mechanism for photo-induced oxygen inclusion is proposed. PMID:24786311

  12. Single crystals of metal solid solutions

    NASA Technical Reports Server (NTRS)

    Miller, J. F.; Austin, A. E.; Richard, N.; Griesenauer, N. M.; Moak, D. P.; Mehrabian, M. R.; Gelles, S. H.

    1974-01-01

    The following definitions were sought in the research on single crystals of metal solid solutions: (1) the influence of convection and/or gravity present during crystallization on the substructure of a metal solid solution; (2) the influence of a magnetic field applied during crystallization on the substructure of a metal solid solution; and (3) requirements for a space flight experiment to verify the results. Growth conditions for the selected silver-zinc alloy system are described, along with pertinent technical and experimental details of the project.

  13. Bioperformance of shape memory alloy single crystals.

    PubMed

    Yahia, L'h; Manceur, A; Chaffraix, P

    2006-01-01

    Shape memory alloys (SMA) represent a large family of alloys that show unique characteristics. They have been exploited in several fields for diverse applications. For the last 20 years, these alloys and more particularly Ni-Ti alloys have revolutionized the field of metallic biomaterials. Applications in the biomedical area are multiple and these materials improve significantly the quality of the diagnostics, treatments and surgeries. To our knowledge, most devices are made of SMAs in the polycrystalline form. Nevertheless, the single crystal form shows several promising advantages especially concerning its mechanical performances. In this paper we describe the advantages, advances and limits of using different SMA single crystals for biomedical applications, including biocompatibility and corrosion resistance. We also discuss the low response time of classical thermal SMAs as well as the new advances in research on magnetic SMA single crystals.

  14. Crystal-phase control of molybdenum carbide nanobelts for dehydrogenation of benzyl alcohol.

    PubMed

    Li, Zhongcheng; Chen, Chunhui; Zhan, Ensheng; Ta, Na; Li, Yong; Shen, Wenjie

    2014-05-04

    Belt-shaped molybdenum carbides in α- and β-phases were synthesized by reducing and carburizing a nano-sized α-MoO3 precursor with hydrocarbon-hydrogen mixtures at appropriate temperatures; the β-Mo2C nanobelts with a higher fraction of coordinatively unsaturated Mo sites were more active than the α-MoC1-x nanobelts in dehydrogenation of benzyl alcohol to benzaldehyde.

  15. Magnetoelasticity of Fe-Si single crystals

    SciTech Connect

    Xing, Q; Wu, D.; Lograsso, T. A.

    2010-04-20

    The tetragonal magnetostriction constant, (3/2){lambda}{sub 100}, of Fe-Si single crystals was measured and was found to be structure dependent. Similar to that of Fe-Ge single crystals, (3/2){lambda}{sub 100} is positive in the single phase A2 regime, becomes negative in the single phase D0{sub 3} regime, and changes from positive to negative between the two regimes. Short-range order in the A2 regime decreases the magnetostriction prior to the onset of long range order. In the single phase regions of both A2 and D0{sub 3}, thermal history does not show any obvious effect on the magnetostriction, contrary to that found for Fe-Ga alloys. However, in the regions of phase mixture involving A2, B2, and D0{sub 3} phases, quenching pushes the change in magnetostriction from positive to negative to higher Si contents.

  16. Characterization of KHCO3 Single Crystals

    NASA Astrophysics Data System (ADS)

    Abouelhassan, S.; Salman, F.; Elmansy, M.; Sheha, E.

    Single crystals of KHCO3 were grown by the slow evaporation technique of an aqueous solution. Characterization of the sample was done using different techniques such as X-ray diffraction, infrared spectra (IR) and the differential scanning calorimeter (DSC) technique. The analysis of the X-ray diffraction pattern indicated that the sample was a single crystal. The results obtained by IR and DSC indicated the presence of phase transition. From the analysis of DSC, the activation energy of transition was carried out by two methods (Kissinger and Ozawa).

  17. Inkjet printing of single-crystal films

    NASA Astrophysics Data System (ADS)

    Minemawari, Hiromi; Yamada, Toshikazu; Matsui, Hiroyuki; Tsutsumi, Jun'ya; Haas, Simon; Chiba, Ryosuke; Kumai, Reiji; Hasegawa, Tatsuo

    2011-07-01

    The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. `Printed electronics' is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials. However, because of the strong self-organizing tendency of the deposited materials, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4cm2V-1s-1. This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.

  18. Comparison of the local and the average crystal structure of proton conducting lanthanum tungstate and the influence of molybdenum substitution.

    PubMed

    Magrasó, Anna; Frontera, Carlos

    2016-03-07

    We report on the comparison of the local and average structure reported recently for proton conducting lanthanum tungstate, of general formula La28-xW4+xO54+δv2-δ, and the impact of molybdenum-substitution on the crystal structure of the material. Partial replacement of W with 10 and 30 mol% Mo is investigated here, i.e. La27(W1-xMox)5O55.5 for x = 0.1 and 0.3. This study addresses the interpretation and the description of a disordered cation and anion sublattice in this material, which enables the understanding of the fundamental properties related to hydration, transport properties and degradation in lanthanum tungstate. The report shows that Mo-substituted lanthanum tungstate is a promising material as a dense oxide membrane for hydrogen separation at intermediate temperatures.

  19. Microhardness studies of sulfamic acid single crystal

    NASA Astrophysics Data System (ADS)

    Santhosh Kumar, A.; Joseph, Cyriac; Paulose, Reshmi; R, Rajesh; Joseph, Georgekutty; Louis, Godfrey

    2015-02-01

    Vicker's microhardness study of (100), (010) and (001) faces of a non-linear optical crystal sulfamic acid have been reported. Single crystals of sulfamic acid have been grown by slow evaporation method. The load dependence of the Vickers microhardness of sulfamic acid crystal were investigated and analyzed from the stand point of various theoretical models. Crystal samples in a, b and c-axes exhibit reverse indentation effect which is best described by Meyer's law, Hays-Kendall's approach and proportional specimen resistance (PSR) models. The negative values of load dependent quantities in Hays-Kendall's approach and PSR model suggest that the origin of indentation size effect is associated with the process of relaxation of indentation stresses.

  20. Growth of single-crystal gallium nitride

    NASA Technical Reports Server (NTRS)

    Clough, R.; Richman, D.; Tietjen, J.

    1970-01-01

    Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces.

  1. MAGNETORESISTANCE AND HALL EFFECT IN SINGLE CRYSTALS OF ALUMINUM

    DTIC Science & Technology

    ALUMINUM, *SINGLE CRYSTALS, CRYSTALS, HALL EFFECT , IMPURITIES, LOW PRESSURE, MAGNETIC FIELDS, MAGNETIC PROPERTIES, PARTICLE TRAJECTORIES, ELECTRICAL RESISTANCE, SOLID STATE PHYSICS, SURFACE PROPERTIES.

  2. Single crystal complex oxide on flexible substrate

    NASA Astrophysics Data System (ADS)

    Bakaul, Saidur; Serrao, Claudy; Lee, Oukjae; Salahuddin, Sayeef

    Flexible ferroelectrics are needed for various applications such as biocompatible energy harvesting and flexible memory. In this sector, most of the current research is focused on organic piezoelectric materials which have advantage of flexibility but suffers severely from poor energy conversion and generation efficiency. On the contrary, owing to very high electromechanical coupling factor (representing energy conversion efficiency) complex oxides are the best choices as energy harvesting and transduction elements, especially for transforming mechanical energies into electronic energy. Still their usage in energy harvesting is very limited mainly due to the stringent growth conditions of single crystals, high temperature needed for crystallization and lack of flexibility and stretchability. We have shown that single crystal Pb0.8Zr0.2TiO3 can be epitaxially transferred on flexible plastic substrate. The transferred PZT shows 70 uC/cm2 remnant polarization and dielectric constant over 100 even when it is bent. These results suggest the possibility of single crystal complex oxide devices on flexible platform.

  3. Preparation and characterization of single crystal samples for high-pressure experiments

    SciTech Connect

    Farber, D; Antonangeli, D; Aracne, C; Benterou, J

    2005-10-26

    To date, most research utilizing the diamond anvil cell (DAC) has been conducted with polycrystalline samples, thus the results are limited to addressing average bulk properties. However, experiments on single crystals can yield data on a range of orientation dependent properties such as thermal and electrical conductivity, magnetic susceptibility, elasticity and plasticity. Here we report new procedures to produce extremely high-quality metallic single crystal samples of size compatible with DAC experiments in the Mbar range. So far, we have produced samples of zinc, Al{sub 2}O{sub 3}, cobalt, molybdenum and cerium, and have evaluated the quality of the finished samples with white-light interferometry, synchrotron x-ray diffraction and inelastic x-ray scattering.

  4. Lightweight optical mirrors formed in single crystal substrate

    NASA Technical Reports Server (NTRS)

    Bly, Vincent T. (Inventor)

    2006-01-01

    This invention is directed to a process for manufacturing a lightweight mirror from a single crystal material, such as single crystal silicon. As a near perfect single crystal material, single crystal silicon has much lower internal stress than a conventional material. This means much less distortion of the optical surface during the light weighting process. After being ground and polished, a single crystal silicon mirror is light weighted by removing material from the back side using ultrasonic machining. After the light weighting process, the single crystal silicon mirror may be used as-is or further figured by conventional polishing or ion milling, depending on the application and the operating wavelength.

  5. Growth of Solid Solution Single Crystals

    NASA Technical Reports Server (NTRS)

    Lehoczky, Sandor L.; Szofran, Frank R.; Gillies, Donald C.; Watring, Dale A.

    1999-01-01

    The objective of the study is to establish the effects of processing semiconducting, solid solution, single crystals in a microgravity environment on the metallurgical, compositional, electrical, and optical characteristics of the crystals. The alloy system being investigated is the solid solution semiconductor Hg(1-x)Cd(x)Te, with x-values appropriate for infrared detector applications in the 8 to 14 mm wavelength region. Both melt and Te-solvent growth are being performed. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. The ground-based portion of the investigation also includes the evaluation of the relative effectiveness of stabilizing techniques, such as applied magnetic fields, for suppressing convective flow during the melt growth of the crystals.

  6. Single-crystal gallium nitride nanotubes.

    PubMed

    Goldberger, Joshua; He, Rongrui; Zhang, Yanfeng; Lee, Sangkwon; Yan, Haoquan; Choi, Heon-Jin; Yang, Peidong

    2003-04-10

    Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

  7. Macrodeformation Twins in Single-Crystal Aluminum

    NASA Astrophysics Data System (ADS)

    Zhao, F.; Wang, L.; Fan, D.; Bie, B. X.; Zhou, X. M.; Suo, T.; Li, Y. L.; Chen, M. W.; Liu, C. L.; Qi, M. L.; Zhu, M. H.; Luo, S. N.

    2016-02-01

    Deformation twinning in pure aluminum has been considered to be a unique property of nanostructured aluminum. A lingering mystery is whether deformation twinning occurs in coarse-grained or single-crystal aluminum at scales beyond nanotwins. Here, we present the first experimental demonstration of macrodeformation twins in single-crystal aluminum formed under an ultrahigh strain rate (˜106 s-1 ) and large shear strain (200%) via dynamic equal channel angular pressing. Large-scale molecular dynamics simulations suggest that the frustration of subsonic dislocation motion leads to transonic deformation twinning. Deformation twinning is rooted in the rate dependences of dislocation motion and twinning, which are coupled, complementary processes during severe plastic deformation under ultrahigh strain rates.

  8. Optimizing Scale Adhesion on Single Crystal Superalloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Pint, Bruce A.

    2000-01-01

    To improve scale adhesion, single crystal superalloys have been desulfurized to levels below 1 ppmw by hydrogen annealing. A transition to fully adherent behavior has been shown to occur at a sulfur level of about 0.2 ppmw, as demonstrated for PWA 1480, PWA 1484, and Rene N5 single crystal superalloys in 1100-1150 C cyclic oxidation tests up to 2000 h. Small additions of yttrium (15 ppmw) also have been effective in producing adhesion for sulfur contents of about 5 ppmw. Thus the critical Y/S ratio required for adhesion was on the order of 3-to-1 by weight (1-to-1 atomic), in agreement with values estimated from solubility products for yttrium sulfides. While hydrogen annealing greatly improved an undoped alloy, yielding <= 0.01 ppmw S, it also produced benefits for Y-doped alloys without measurably reducing the sulfur content.

  9. Thermal properties of UO2 single crystal

    NASA Astrophysics Data System (ADS)

    Gofryk, K.; Du, S.; Andersson, A. D.; Stanek, C. R.; Schulze, R.; Safarik, D.; Mihaila, B.; Lashley, J. C.; Smith, J. L.

    2013-03-01

    For decades UO2 has been the most widely studied actinide oxide because of its technological importance as fuel material for nuclear reactors. Therefore there is a large interest in understanding its thermal, transport and thermodynamic properties. We present recent experimental results for the thermal conductivity and thermal expansion of high quality UO2 single crystal, obtained for different crystallographic directions, and compare with results of molecular dynamics simulations. We will discuss the implications of this study.

  10. Growth of single crystals under hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Popolitov, Vladislav Ivanovich; Litvin, Boris Nikolaevich

    The book summarizes the available theoretical, methodological, and experimental data on the hydrothermal growth of inorganic compounds, such as simple and complex oxides, sulfides, silicates, germanates, phosphates, niobates, and tantalates. Attention is given to the physicochemical, hydrodynamic, and kinetic characteristics of the growth of these compounds, as well as hydrothermal growth techniques and equipment. The discussion also covers the morphogenetic characteristics of hydrothermally grown single crystals, their principal physical properties, and X-ray diffraction and structural data.

  11. A creep mechanism for metal single crystals

    SciTech Connect

    Cuitino, A.M.

    1995-12-31

    In this paper we present a mechanism of creep for metal single crystals. This creep mechanism is consistent with the hardening mechanism in metals single crystals, i.e. forest hardening. Hardening in metals is mainly due to the resistance to the dislocation motion opposed by obstacles. In single crystals, obstacles are generated by dislocation segments crossing the glide plane (forest dislocations). When a dislocation is released from an obstacle, it moves until stopped at the following obstacle inducing plastic deformation. It has been proposed as a mechanisms of creep that obstacles can be overcome by dislocation climb. However, the kind of obstacles remains in planes parallel to the gliding plane. Thus, the dislocation segment after climb is still stopped at the same obstacle and unable to glide, unless, a second jog moving in the forest dislocation meets simultaneously with the jog in the gliding segment. In this case, the gliding segment can move by the height of the forest jog. The gliding area is proportional to this height and the distance between obstacles. We call this mechanism of glide by congruent climb. Creep rate depends on the jog density and jog velocity. For a well-annealed material the number of jogs is relatively low. As plastic deformation proceeds, new jogs are formed by mainly two mechanisms: dislocation intersection and double cross slip. For a crystal undergoing single slip, the cross-slip contribution dominates jog generation, since dislocation intersections are relatively rare due to the low forest dislocation density. The situation is reversed for multiple glide as a consequence of the rapid dislocation multiplication which takes place in the active slip systems, which results in a high rate of dislocation intersection. The number of cross slip events and dislocation intersections can be readily estimated by our dislocation model of plastic deformation. Jog velocity is determined based on vacancy diffusion along the dislocation core.

  12. Ionic diffusion in single crystals of vermiculite

    SciTech Connect

    Maraqah, H.R.

    1993-01-01

    Novel guest-host compounds, based on single crystal vermiculite, were synthesized by diffusive techniques through a new hydrogen vermiculite. Single crystals were chosen because of the ease of characterization. An investigation of the ion transport properties of these single crystals was done to determine the mechanism of conductivity including the predominant charge carrier. Measurements of the ionic conductivity using impedance spectroscopy and X-ray lattice parameters of the ion-exchanged samples strongly suggest that the native cations and not protons are the major current carriers. Single crystals of hydrogen vermiculite were synthesized at room temperature by ion exchange from sodium-vermiculite using 1 molar acetic acid for a one week. Subsequent ion exchange with other cations was found to be much enhanced. Thus transition metals were exchanged in about a week in contrast to the need of several months using previous methods. The ionic conductivity of hydrogen vermiculite was measured and shown to be much lower than that of many other monovalent cations in the same host lattice. Its enthalpy of motion is also much lower. These marked differences suggest that protonic species do not play a significant role in charge transport in these layered materials. These materials were characterized by x-ray powder diffraction, thermogravimetric analysis and acid-base titration. Hydrogen-vermiculite was found to react with organic bases, like methylamine, ethylamine, n-butylamine, n-hexylamine, n-octylamine, n-decylamine, aniline, acrylamide, methacrylaminde, urea, 1,10phenanthroline, and 1,1phenanthroline ferrous sulfate complex, to undergo ion exchange with metal cations like sodium, zinc, copper(II) ions and polymerization reactions could be performed in the galleries of the structure like pyrrole and aniline. Its behavior was compared with that of powdered montmorillonite.

  13. Flexible single-crystal silicon nanomembrane photonic crystal cavity.

    PubMed

    Xu, Xiaochuan; Subbaraman, Harish; Chakravarty, Swapnajit; Hosseini, Amir; Covey, John; Yu, Yalin; Kwong, David; Zhang, Yang; Lai, Wei-Cheng; Zou, Yi; Lu, Nanshu; Chen, Ray T

    2014-12-23

    Flexible inorganic electronic devices promise numerous applications, especially in fields that could not be covered satisfactorily by conventional rigid devices. Benefits on a similar scale are also foreseeable for silicon photonic components. However, the difficulty in transferring intricate silicon photonic devices has deterred widespread development. In this paper, we demonstrate a flexible single-crystal silicon nanomembrane photonic crystal microcavity through a bonding and substrate removal approach. The transferred cavity shows a quality factor of 2.2×10(4) and could be bent to a curvature of 5 mm radius without deteriorating the performance compared to its counterparts on rigid substrates. A thorough characterization of the device reveals that the resonant wavelength is a linear function of the bending-induced strain. The device also shows a curvature-independent sensitivity to the ambient index variation.

  14. Anisotropy of sapphire single crystal sputtering

    SciTech Connect

    Minnebaev, K. F.; Tolpin, K. A.; Yurasova, V. E.

    2015-08-15

    We have studied the spatial distribution of particles sputtered from the base (0001) plane of a sapphire single crystal with trigonal crystalline lattice (α-Al{sub 2}O{sub 3}) that can be considered a superposition of two hexagonal close packed (hcp) structures–the ideal sublattice of oxygen and a somewhat deformed sublattice of aluminum. It is established that the particles sputtered from the base plane of sapphire are predominantly deposited along the sides of an irregular hexagon with spots at its vertices. The patterns of spots have been also studied for sputtering of particles from the (0001) face of a zinc single crystal with the hcp lattice. The spots of sputtered Zn atoms are arranged at the vertices of concentric equilateral hexagons. In both cases, the observed anisotropy of sputtering is related to focused collisions (direct and assisted focusing) and the channeling process. The chemical composition of spots has been determined in various regions of sputtered sapphire deposition. The results are discussed in comparison to analogous earlier data for secondary ion emission from an α-Al{sub 2}O{sub 3} single crystal.

  15. Secondary particle emission from sapphire single crystal

    NASA Astrophysics Data System (ADS)

    Minnebaev, K. F.; Khvostov, V. V.; Zykova, E. Yu.; Tolpin, K. A.; Colligon, J. S.; Yurasova, V. E.

    2015-07-01

    Secondary ion emission from sapphire single crystal has been studied experimentally and by means of computer simulation. The particular oscillations of secondary ion energy spectra and two specific maxima of O+ and Al+ ions were observed under irradiation of (0001) sapphire face by 1 and 10 keV Ar+ ions. We have explained this by the interplay of the charge exchange processes between moving particles and solids. The existence of two maxima in energy spectra of O+ and Al+ secondary ions can be also connected with special features of single-crystal sputtering: the low-energy peak can be formed by random sputtering and the high-energy peak from focusing collisions. In addition some similarity was found between the positions of low-energy maximum in energy spectra of Al+ ions emitted from sapphire and the principal maxima of Al+ ions ejected from the aluminum single crystal. This indicates a possibility to explain the presence of low-energy maximum in energy spectra of secondary ions ejecting from sapphire by emission of Al+ ions from aluminum islands appearing in a number of cases on the sapphire surface due to preferential sputtering of oxygen. These different mechanisms of creating the energy spectra of ions emitted from sapphire should be taken in account.

  16. Single crystal diamond detector for radiotherapy

    NASA Astrophysics Data System (ADS)

    Schirru, F.; Kisielewicz, K.; Nowak, T.; Marczewska, B.

    2010-07-01

    The new generation of synthetic diamonds grown as a CVD single crystal on a high pressure high temperature substrate offers a wide range of applications. In particular, because of the near tissue equivalence and its small size (good spatial resolution), CVD single crystal diamond finds applicability in radiotherapy as a dosemeter of ionizing radiation. In this paper we report the electrical and dosimetric properties of a new diamond detector which was fabricated at IFJ based on a single crystal detector-grade CVD diamond provided with a novel contact metallization. Diamond properties were assessed at IFJ using a Theratron 680E therapeutic 60Co gamma rays unit and at COOK with 6 and 18 MV x-rays Varian Clinac CL2300 C/D accelerator. The new dosemeter showed high electric and dosimetric performances: low value of dark current, high current at the level of some nanoamperes during irradiation, very fast dynamic response with a rise time amounting to parts of a second, good stability and repeatability of the current and linearity of the detector signal at different dose and dose rate levels typically applied in radiotherapy. The results confirm the potential applicability of diamond material as a dosemeter for applications in radiotherapy.

  17. Charge transport in single crystal organic semiconductors

    NASA Astrophysics Data System (ADS)

    Xie, Wei

    Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form

  18. Single Crystal Technology for Making RRR Niobium Sheet

    SciTech Connect

    Graham, Ronald A.

    2007-08-09

    This paper reviews methods used to produce metallic single crystals. Methods are assessed in terms of being able to use the technique to produce RRR niobium single crystals for RF superconducting accelerator cavities.

  19. A nanoporous two-dimensional polymer by single-crystal-to-single-crystal photopolymerization.

    PubMed

    Kissel, Patrick; Murray, Daniel J; Wulftange, William J; Catalano, Vincent J; King, Benjamin T

    2014-09-01

    In contrast to the wide number and variety of available synthetic routes to conventional linear polymers, the synthesis of two-dimensional polymers and unambiguous proof of their structure remains a challenge. Two-dimensional polymers-single-layered polymers that form a tiling network in exactly two dimensions-have potential for use in nanoporous membranes and other applications. Here, we report the preparation of a fluorinated hydrocarbon two-dimensional polymer that can be exfoliated into single sheets, and its characterization by high-resolution single-crystal X-ray diffraction analysis. The procedure involves three steps: preorganization in a lamellar crystal of a rigid monomer bearing three photoreactive arms, photopolymerization of the crystalline monomers by [4 + 4] cycloaddition, and isolation of individual two-dimensional polymer sheets. This polymer is a molecularly thin (~1 nm) material that combines precisely defined monodisperse pores of ~9 Å with a high pore density of 3.3 × 10(13) pores cm(-2). Atomic-resolution single-crystal X-ray structures of the monomer, an intermediate dimer and the final crystalline two-dimensional polymer were obtained and prove the single-crystal-to-single-crystal nature and molecular precision of the two-dimensional photopolymerization.

  20. Ho:YAG Single Crystal Fiber: Fabrication and Optical Characterization

    DTIC Science & Technology

    2014-06-16

    optical characterization 0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using Laser Heated Pedestal Growth (LHPG) method and...ABSTRACT Ho:YAG single crystal fiber: fabrication and optical characterization Report Title 0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was...0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using Laser Heated Pedestal Growth (LHPG) method and characterized for its

  1. Guest exchange through single crystal-single crystal transformations in a flexible hydrogen-bonded framework.

    PubMed

    Xiao, Wenchang; Hu, Chunhua; Ward, Michael D

    2014-10-08

    A molecular framework based on guanidinium cations and 1,2,4,5-tetra(4-sulfonatophenyl)benzene (TSPB), an aromatic tetrasulfonate with nominal 2-fold and mirror symmetry, exhibits three crystallographically unique one-dimensional channels as a consequence of molecular symmetry and complementary hydrogen bonding between the guanidinium (G) ions and the sulfonate (S) groups of TSPB. Unlike previous GS frameworks, this new topology is sufficiently flexible to permit reversible release and adsorption of guest molecules in large single crystals through a cyclic shrinkage and expansion of the channels with retention of single crystallinity, as verified by single crystal X-ray diffraction. Moreover, the G4TSPB framework permits guest exchange between various guest molecules through SCSCTs as well as exchange discrimination based on the size and character of the three different channels. The exchange of guest molecules during single crystal-single crystal transformations (SCSCT), a rare occurrence for hydrogen-bonded frameworks, is rather fast, with diffusivities of approximately 10(-6) cm(2) s(-1). Rapid diffusion in the two channels having cross sections sufficient to accommodate two guest molecules can be explained by two-way or ring diffusion, most likely vacancy assisted. Surprisingly, rapid guest exchange also is observed in a smaller channel having a cross-section that accommodates only one guest molecule, which can only be explained by guest-assisted single-file unidirectional diffusion. Several single crystals of inclusion compounds can be realized only through guest exchange in the intact framework, suggesting an approach to the synthesis of single crystalline inclusion compounds that otherwise cannot be attained through direct crystallization methods.

  2. X-ray crystal structure of arsenite-inhibited xanthine oxidase: μ-sulfido,μ-oxo double bridge between molybdenum and arsenic in the active site.

    PubMed

    Cao, Hongnan; Hall, James; Hille, Russ

    2011-08-17

    Xanthine oxidoreductase is a molybdenum-containing enzyme that catalyzes the hydroxylation reaction of sp(2)-hybridized carbon centers of a variety of substrates, including purines, aldehydes, and other heterocyclic compounds. The complex of arsenite-inhibited xanthine oxidase has been characterized previously by UV-vis, electron paramagnetic resonance, and X-ray absorption spectroscopy (XAS), and the catalytically essential sulfido ligand of the square-pyrimidal molybdenum center has been suggested to be involved in arsenite binding through either a μ-sulfido,μ-oxo double bridge or a single μ-sulfido bridge. However, this is contrary to the crystallographically observed single μ-oxo bridge between molybdenum and arsenic in the desulfo form of aldehyde oxidoreductase from Desulfovibrio gigas (an enzyme closely related to xanthine oxidase), whose molybdenum center has an oxo ligand replacing the catalytically essential sulfur, as seen in the functional form of xanthine oxidase. Here we use X-ray crystallography to characterize the molybdenum center of arsenite-inhibited xanthine oxidase and solve the structures of the oxidized and reduced inhibition complexes at 1.82 and 2.11 Å resolution, respectively. We observe μ-sulfido,μ-oxo double bridges between molybdenum and arsenic in the active sites of both complexes. Arsenic is four-coordinate with a distorted trigonal-pyramidal geometry in the oxidized complex and three-coordinate with a distorted trigonal-planar geometry in the reduced complex. The doubly bridged binding mode is in agreement with previous XAS data indicating that the catalytically essential sulfur is also essential for the high affinity of reduced xanthine oxidoreductase for arsenite.

  3. X-ray Crystal Structure of Arsenite-Inhibited Xanthine Oxidase:[mu]-Sulfido,[mu]-Oxo Double Bridge between Molybdenum and Arsenic in the Active Site

    SciTech Connect

    Cao, Hongnan; Hall, James; Hille, Russ

    2012-10-23

    Xanthine oxidoreductase is a molybdenum-containing enzyme that catalyzes the hydroxylation reaction of sp{sup 2}-hybridized carbon centers of a variety of substrates, including purines, aldehydes, and other heterocyclic compounds. The complex of arsenite-inhibited xanthine oxidase has been characterized previously by UV-vis, electron paramagnetic resonance, and X-ray absorption spectroscopy (XAS), and the catalytically essential sulfido ligand of the square-pyrimidal molybdenum center has been suggested to be involved in arsenite binding through either a {mu}-sulfido,{mu}-oxo double bridge or a single {mu}-sulfido bridge. However, this is contrary to the crystallographically observed single {mu}-oxo bridge between molybdenum and arsenic in the desulfo form of aldehyde oxidoreductase from Desulfovibrio gigas (an enzyme closely related to xanthine oxidase), whose molybdenum center has an oxo ligand replacing the catalytically essential sulfur, as seen in the functional form of xanthine oxidase. Here we use X-ray crystallography to characterize the molybdenum center of arsenite-inhibited xanthine oxidase and solve the structures of the oxidized and reduced inhibition complexes at 1.82 and 2.11 {angstrom} resolution, respectively. We observe {mu}-sulfido,{mu}-oxo double bridges between molybdenum and arsenic in the active sites of both complexes. Arsenic is four-coordinate with a distorted trigonal-pyramidal geometry in the oxidized complex and three-coordinate with a distorted trigonal-planar geometry in the reduced complex. The doubly bridged binding mode is in agreement with previous XAS data indicating that the catalytically essential sulfur is also essential for the high affinity of reduced xanthine oxidoreductase for arsenite.

  4. Single-crystal to single-crystal transformations in discrete hydrated dimeric copper complexes.

    PubMed

    Mobin, Shaikh M; Srivastava, Ashwini K; Mathur, Pradeep; Lahiri, Goutam Kumar

    2010-02-14

    The single crystals of discrete hydrated [(OAc)Cu(mu-hep)(2)Cu(OAc)].2H(2)O (.2H(2)O) and [(OAc)Cu(mu-hep)(2) Cu(O(n)Pr)].2H(2)O (.2H(2)O) (the lattice H(2)O molecules exist as a tetrameric water cluster, hep-H = 2-(2-hydroxyethyl)pyridine), OAc(-) = acetate and O(n)Pr(-) = n-propionate) undergo single-crystal to single-crystal (SCSC) transformations to the dehydrated and , respectively, under the influence of heat. The reverse SCSC processes of /-->.2H(2)O/.2H(2)O involving the regeneration of the lattice water tetramers take place on exposure of / to water vapour. However, the blue single crystal of discrete hydrated [(O(n)Pr)Cu(mu-hep)(2)Cu(O(n)Pr)].2H(2)O (.2H(2)O), incorporating the two bulkier O(n)Pr(-) terminal bidentate ligands, irreversibly converts to the green single crystal of a unique discrete tetrameric [Cu(4)(mu(3)hep)(2)(mu-hep)(2)(mu-O(n)Pr)(2)(O(n)Pr)(2)] () with double open cubane core either by heating or by a simple vapour diffusion technique via the breaking and forming of multiple covalent bonds.

  5. Gas hydrate single-crystal structure analyses.

    PubMed

    Kirchner, Michael T; Boese, Roland; Billups, W Edward; Norman, Lewis R

    2004-08-04

    The first single-crystal diffraction studies on methane, propane, methane/propane, and adamantane gas hydrates SI, SII, and SH have been performed. To circumvent the problem of very slow crystal growth, a novel technique of in situ cocrystallization of gases and liquids resulting in oligocrystalline material in a capillary has been developed. With special data treatment, termed oligo diffractometry, structural data of the gas hydrates of methane, acetylene, propane, a propane/ethanol/methane-mixture and an adamantane/methane-mixture were obtained. Cell parameters are in accord with reported values. Host network and guest are subject to extensive disorder, reducing the reliability of structural information. It was found that most cages are fully occupied by a guest molecule with the exception of the dodecahedral cage in the acetylene hydrate which is only filled to 60%. For adamantane in the icosahedral cage a disordered model is proposed.

  6. Single crystal to single crystal polymerization of a columnar assembled diacetylene macrocycle

    NASA Astrophysics Data System (ADS)

    Xu, Weiwei

    Organic tubular materials have attracted lots of attentions for their potential applications as nanoscale fluidic transport systems, specific ion sensors, molecular sieves and confined molecular reaction containers. While conjugated polymers, due to delocalized Pi electrons, exhibit interesting solar cells and sensors applications. In this thesis, we developed a conjugated polymer which combines the attributes of conjugated polymers with tubular materials, which should have great potential to work as a sensing material. We reproduced and scaled-up the synthesis of a polymerizable macrocycle 1 that contains two rigidly separated diacetylene units. We found that, through hydrogen bonding, 1 can assemble into columnar crystals and can be polymerized under a single crystal to single crystal transformation process to afford porous polydiacetylene (PDA) crystals. We studied the assembly of the macrocycles 1 under different conditions to give three different crystalline forms and micro-phase crystals, and also investigated their subsequent polymerizations. The macrocycle assembly and polymerized materials were characterized by a variety of technique. Since the gas adsorption measurement exhibited PDA crystals still retained its porosity and the polymer should have ability to uptake suitable guest molecules, therefore the absorption of iodine for PDA crystals was investigated as well.

  7. Direct shear of olivine single crystals

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob A.; Zimmerman, Mark E.; Kohlstedt, David L.

    2016-12-01

    Knowledge of the strengths of the individual dislocation slip systems in olivine is fundamental to understanding the flow behavior and the development of lattice-preferred orientation in olivine-rich rocks. The most direct measurements of the strengths of individual slip systems are from triaxial compression experiments on olivine single crystals. However, such experiments only allow for determination of flow laws for two of the four dominant slip systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip systems independently, we performed deformation experiments on single crystals of San Carlos olivine in a direct shear geometry. Experiments were carried out at temperatures of 1000 ° to 1300 °C, a confining pressure of 300 MPa, shear stresses of 60 to 334 MPa, and resultant shear strain rates of 7.4 × 10-6 to 2.1 × 10-3 s-1. At high-temperature (≥1200 °C) and low-stress (≤200 MPa) conditions, the strain rate of crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system follows a power law relationship with stress, whereas at lower temperatures and higher stresses, strain rate depends exponentially on stress. The flow laws derived from the mechanical data in this study are consistent with a transition from the operation of a climb-controlled dislocation mechanism during power-law creep to the operation of a glide-controlled dislocation mechanism during exponential creep. In the climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker than crystals orientated for shear on the (100)[001] slip system. In contrast, in the glide-controlled regime the opposite is observed. Extrapolation of flow laws determined for crystals sheared in orientations favorable for slip on these two slip systems to upper mantle conditions reveals that the (001)[100] slip system is weaker at temperatures and stresses that are typical of the asthenospheric mantle, whereas the (100

  8. Direct Shear of Olivine Single Crystals

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob; Zimmerman, Mark; Kohlstedt, David

    2016-04-01

    Knowledge of the strength of individual dislocation slip systems in olivine is fundamental to understanding the flow behavior and the development of lattice-preferred orientation in olivine-rich rocks. The most direct measurements of the strengths of individual slip systems are from triaxial compression experiments on olivine single crystals. However, such experiments only allow for determination of flow laws for two of the four dominate slip systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip systems independently, we performed deformation experiments on single crystals of San Carlos olivine in a direct shear geometry. Experiments were carried out at temperatures of 1000° to 1300°C, a confining pressure of 300 MPa, shear stresses of 60 to 334 MPa, and resultant shear strain rates of 7.4 x 10-6 to 6.7 x 10-4 s-1. At high-temperature (≥1200°C) and low-stress (≤200 MPa) conditions, the strain rate of crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system follows a power law relationship with stress, whereas at lower temperatures and higher stresses, strain rate depends exponentially on stress. The flow laws derived from the mechanical data in this study are consistent with a transition from the operation of a climb-controlled dislocation mechanism during power-law creep to the operation of a glide-controlled dislocation mechanism during exponential creep. In the climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker than crystals orientated for shear on the (100)[001] slip system. In contrast, in the glide-controlled regime the opposite is observed. Extrapolation of flow laws determined for crystals sheared in orientations favorable for slip on these two slip systems to upper mantle conditions reveals that the (001)[100] slip system is weaker at temperatures and stresses that are typical of the asthenospheric mantle, whereas the (100)[001] slip

  9. Chemical vapor deposition of graphene single crystals.

    PubMed

    Yan, Zheng; Peng, Zhiwei; Tour, James M

    2014-04-15

    As a two-dimensional (2D) sp(2)-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and low yields. Recently developed chemical vapor deposition (CVD) techniques have emerged as an important method for the scalable production of large-size and high-quality graphene for various applications. However, CVD-derived graphene is polycrystalline and demonstrates degraded properties induced by grain boundaries. Thus, the next critical step of graphene growth relies on the synthesis of large graphene single crystals. In this Account, we first discuss graphene grain boundaries and their influence on graphene's properties. Mechanical and electrical behaviors of CVD-derived polycrystalline graphene are greatly reduced when compared to that of exfoliated graphene. We then review four representative pathways of pretreating Cu substrates to make millimeter-sized monolayer graphene grains: electrochemical polishing and high-pressure annealing of Cu substrate, adding of additional Cu enclosures, melting and resolidfying Cu substrates, and oxygen-rich Cu substrates. Due to these pretreatments, the nucleation site density on Cu substrates is greatly reduced, resulting in hexagonal-shaped graphene grains that show increased grain domain size and comparable electrical properties as to exfoliated graphene. Also, the properties of graphene can be engineered by its shape, thickness and spatial structure. Thus, we further discuss recently developed methods of making graphene grains with special spatial structures, including snowflakes, six-lobed flowers, pyramids and hexagonal graphene onion rings. The fundamental growth mechanism and practical applications of these well-shaped graphene structures should be interesting topics and

  10. Optical properties of lithium niobate single crystals

    NASA Astrophysics Data System (ADS)

    Palatnikov, M. N.; Sidorov, N. V.; Biryukova, I. V.; Kalinnikov, V. T.; Bormanis, K.

    2005-01-01

    Studies of thermal and -irradiation effects on the optical properties in congruous lithium niobate single crystals containing Y, Mg, Gd, B, and Zn dopants including samples with double dopants Y, Mg and Gd, Mg are reported. Formation of defects at irradiation and thermal treatment of the samples is explored by electron absorption spectra. Considerable increase of absorption with the dose of -radiation is observed at 500 nm. The changes of absorption examined under different conditions are explained by creation and destruction of Nb4+ defects.

  11. Phase transition in sarcosine phosphite single crystals

    NASA Astrophysics Data System (ADS)

    Lemanov, V. V.; Popov, S. N.; Pankova, G. A.

    2011-06-01

    Single crystals of sarcosine phosphite (SarcH3PO3) have been grown. The amino acid sarcosine is an isomer of the protein amino acid alanine. Both amino acids are described by the same chemical formula but have different structures; or, more specifically, in contrast to the alanine molecule, the sarcosine molecule has a symmetric structure. It has been found that the sarcosine phosphite compound undergoes a structural phase transition at a temperature of approximately 200 K. This result has demonstrated that compounds of achiral amino acids are more susceptible to structural phase transitions.

  12. Conduction mechanism of single-crystal alumina

    NASA Technical Reports Server (NTRS)

    Will, Fritz G.; Delorenzi, Horst G.; Janora, Kevin H.

    1992-01-01

    The fully guarded three-terminal technique was used to perform conductivity measurements on single-crystal alumina at temperatures of 400-1300 C. The conductivity was also determined as a function of time at various temperatures and applied fields. Further, the fractions of the current carried by Al and O ions (ionic transference numbers) were determined from long-term transference experiments in the temperature range 1100-1300 C. A mathematical model of the conduction mechanism is proposed, and model predictions are compared with experimental results.

  13. Compositional Effects on Nickel-Base Superalloy Single Crystal Microstructures

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Gabb, Timothy P.; Garg,Anita; Rogers, Richard B.; Nathal, Michael V.

    2012-01-01

    Fourteen nickel-base superalloy single crystals containing 0 to 5 wt% chromium (Cr), 0 to 11 wt% cobalt (Co), 6 to 12 wt% molybdenum (Mo), 0 to 4 wt% rhenium (Re), and fixed amounts of aluminum (Al) and tantalum (Ta) were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, volume fraction of topologically close-packed (TCP) phases, phase chemistries, and gamma - gamma'. lattice mismatch. Regression models were developed to describe the influence of bulk alloy composition on the microstructural parameters and were compared to predictions by a commercially available software tool that used computational thermodynamics. Co produced the largest change in gamma' solvus over the wide compositional range used in this study, and Mo produced the largest effect on the gamma lattice parameter and the gamma - gamma' lattice mismatch over its compositional range, although Re had a very potent influence on all microstructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had a significant impact on their concentrations in the gamma matrix and, to a smaller extent, in the gamma' phase. The gamma phase chemistries exhibited strong temperature dependencies that were influenced by the gamma and gamma' volume fractions. A computational thermodynamic modeling tool significantly underpredicted gamma' solvus temperatures and grossly overpredicted the amount of TCP phase at 982 C. Furthermore, the predictions by the software tool for the gamma - gamma' lattice mismatch were typically of the wrong sign and magnitude, but predictions could be improved if TCP formation was suspended within the software program. However, the statistical regression models provided excellent estimations of the microstructural parameters based on bulk alloy composition, thereby demonstrating their usefulness.

  14. Thermodynamic forces in single crystals with dislocations

    NASA Astrophysics Data System (ADS)

    Van Goethem, Nicolas

    2014-06-01

    A simple model for the evolution of macroscopic dislocation regions in a single crystal is presented. This model relies on maximal dissipation principle within Kröner's geometric description of the dislocated crystal. Mathematical methods and tools from shape optimization theory provide equilibrium relations at the dislocation front, similarly to previous work achieved on damage modelling (J Comput Phys 33(16):5010-5044, 2011). The deformation state variable is the incompatible strain as related to the dislocation density tensor by a relation involving the Ricci curvature of the crystal underlying elastic metric. The time evolution of the model variables follows from a novel interpretation of the Einstein-Hilbert flow in terms of dislocation microstructure energy. This flow is interpreted as the dissipation of non-conservative dislocations, due to the climb mechanism, modelled by an average effect of mesoscopic dislocations moving normal to their glide planes by adding or removing points defects. The model equations are a fourth-order tensor parabolic equation involving the operator "incompatibility," here appearing as a tensorial counterpart of the scalar Laplacian. This work encompasses and generalizes results previously announced (C R Acad Sci Paris Ser I 349:923-927, 2011), with in addition a series of physical interpretations to give a meaning to the newly introduced concepts.

  15. Heterogeneous growth of single crystals on polycrystals

    NASA Astrophysics Data System (ADS)

    Wang, Zumin; Jeurgens, Lars P. H.; Gu, Lin; Mittemeijer, Eric J.

    2017-03-01

    This work discloses a surprising, previously unknown heterogeneous growth mode. Namely, large-area, thin sheets of single-crystalline Ge were observed to grow laterally on top of a polycrystalline Al substrate, covering as many as tens of differently oriented Al grains at low temperatures. The observation of the Ge crystal-growth process by in situ heating transmission electron microscopy demonstrates an intriguing type of "faceted" growth: the growth of single-crystalline Ge thin sheets proceeding Al-grain by Al-grain on top of the polycrystalline Al substrate. The crystalline Ge growth front tends to align along the lines of intersection of the Al grain boundaries with the Al surface. Such an unusual heterogeneous growth mode has been shown to be a consequence of the strong anisotropy of the energy of the crystalline/crystalline (here: c-Ge/c-Al) interfaces.

  16. Biaxial constitutive equation development for single crystals

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1984-01-01

    Current gas turbine engines utilize large single crystal superalloy components in the hot section. Structural analysis of these components requires a valid stress strain temperature constitutive equation. The goal of the program described is to create one or more models and verify these models. A constitutive equation based on an assumed slip behavior of a single slip system was formulated, programmed, and debugged. Specifically, the basic theory for a model based on aggravating slip behavior on individual slip systems was formulated and programmed and some simulations were run using assumed values of constants. In addition, a formulation allowing strain controlled simulations was completed. An approach to structural analysis of the specimen was developed. This approach uses long tube consistancy conditions and finite elements specially formulated to take advantage of the symmetry of 100 oriented specimens.

  17. Cutting fluid study for single crystal silicon

    SciTech Connect

    Chargin, D.

    1998-05-05

    An empirical study was conducted to evaluate cutting fluids for Single Point Diamond Turning (SPDT) of single crystal silicon. The pH of distilled waster was adjusted with various additives the examine the effect of pH on cutting operations. Fluids which seemed to promote ductile cutting appeared to increase tool wear as well, an undesirable tradeoff. High Ph sodium hydroxide solutions showed promise for further research, as they yielded the best combination of reduced tool wear and good surface finish in the ductile regime. Negative rake tools were verified to improve the surface finish, but the negative rake tools used in the experiments also showed much higher wear than conventional 0{degree} rake tools. Effects of crystallographic orientation on SPDT, such as star patterns of fracture damage forming near the center of the samples, were observed to decrease with lower feedrates. Silicon chips were observed and photographed, indicative of a ductile materials removal process.

  18. Structure and Electronic Properties of Single- to Few Layers Molybdenum Disulfide Films

    NASA Astrophysics Data System (ADS)

    Trainer, D.; Putilov, A.; Wolak, M.; Chandrasena, R. U.; Kronast, F.; Gray, A. X.; Xi, X. X.; Iavarone, M.

    Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS) we have investigated the electronic properties of mono- to few layers molybdenum disulfide films grown on HOPG using ambient pressure chemical vapor deposition (APCVD). Atomic force microscopy and STM show that this growth technique produces crystalline triangular and hexagonal islands with varying thicknesses in 1ML increments. The films exhibited a suppression of quasiparticle band-gap as a function of layer number as measured by local spectroscopy. Changes in the valence band edge were supported by photoemission electron microscopy (PEEM) measurements. We also report on a strain-induced contraction of the quasiparticle band-gap in proximity to grain boundaries and defects. This work was supported as part of the Center for the Computational Design of Functional Layered Materials, an Energy Frontier Research Center funded by the U.S. DOE, BES under Award DE-SC0012575.

  19. Tension-induced phase transition of single-layer molybdenum disulphide (MoS2) at low temperatures.

    PubMed

    Zhao, Junhua; Kou, Liangzhi; Jiang, Jin-Wu; Rabczuk, Timon

    2014-07-25

    We show that the hexagonal structure of single-layer molybdenum disulphide (MoS2), under uniaxial tension along a zigzag direction for large deformations, can transfer to a new quadrilateral structure by molecular dynamics (MD) simulations when the temperature is below 40 K. The new phase remains stable after unloading, even at room temperature. The Young's modulus of the new phase along the zigzag direction is about 2.5 times higher than that of normal MoS2. Checking against density functional theory calculations shows that the new phase is preserved and displays excellent electrical conductivity. Our results provide physical insights into the origins of the new phase transition of MoS2 at low temperatures.

  20. Growing single crystals in silica gel

    NASA Technical Reports Server (NTRS)

    Rubin, B.

    1970-01-01

    Two types of chemical reactions for crystal growing are discussed. The first is a metathetical reaction to produce calcium tartrate tetrahydrate crystals, the second is a decomplexation reaction to produce cuprous chloride crystals.

  1. Growth of single crystals of BaFe12O19 by solid state crystal growth

    NASA Astrophysics Data System (ADS)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-10-01

    Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

  2. Piezoelectric single crystals for ultrasonic transducers in biomedical applications.

    PubMed

    Zhou, Qifa; Lam, Kwok Ho; Zheng, Hairong; Qiu, Weibao; Shung, K Kirk

    2014-10-01

    Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state-of-art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will be addressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN-PT and PIN-PMN-PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single-element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging, and microbeam applications of the single crystal transducers will be discussed.

  3. Experimental dynamic metamorphism of mineral single crystals

    USGS Publications Warehouse

    Kirby, S.H.; Stern, L.A.

    1993-01-01

    This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a-?? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ??? clinoenstatite and w u ??rtzite ??? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO ?? nAl2O3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to

  4. Solar cell structure incorporating a novel single crystal silicon material

    DOEpatents

    Pankove, Jacques I.; Wu, Chung P.

    1983-01-01

    A novel hydrogen rich single crystal silicon material having a band gap energy greater than 1.1 eV can be fabricated by forming an amorphous region of graded crystallinity in a body of single crystalline silicon and thereafter contacting the region with atomic hydrogen followed by pulsed laser annealing at a sufficient power and for a sufficient duration to recrystallize the region into single crystal silicon without out-gassing the hydrogen. The new material can be used to fabricate semiconductor devices such as single crystal silicon solar cells with surface window regions having a greater band gap energy than that of single crystal silicon without hydrogen.

  5. Tunable color temperature solid state white light source using flux grown phosphor crystals of Eu3+, Dy3+ and Tb3+ activated calcium sodium molybdenum oxide

    NASA Astrophysics Data System (ADS)

    Khanna, A.; Dutta, P. S.

    2014-11-01

    Solid state light sources with dynamically tunable color temperature in the range of 3000-6000 K with chromaticity coordinates lying on the Planckian black body curve has been designed using mixtures of narrow emissions at 615 nm, 575 nm and 550 nm. These respective emissions lines were generated by individual phosphor crystals of trivalent rare earth (RE3+) species, europium (Eu3+), dysprosium (Dy3+) and terbium (Tb3+) activated calcium sodium molybdenum oxide (Ca1-2xNaxMoO4:RE3+x), when excited by near-ultra-violet (NUV) light emitting diode (LED) with emission wavelength of 380 nm. Highly luminescent crystals of these compounds have been grown from molten solutions (flux) of molybdenum (VI) oxide. The flux grown crystals exhibit emission intensity 2-4 times more than phosphor powders of the same compounds synthesized by traditional solid-state reactions. An optimum flux to solute ratio of 2.5 and solute dissolution temperature of 1100 °C resulted in the largest size crystals.

  6. Mechanical properties of single crystal YAg

    SciTech Connect

    Russell, A.M.; Zhang, Z.; Lograsso, T.A.; Lo, C.C.H.; Pecharsky, A.O.; Morris, J.R.; Ye, Y.; Gschneidner, K.A.; Slager, A.J

    2004-08-02

    YAg, a rare earth-precious metal 'line compound', is one member of the family of B2 rare earth intermetallic compounds that exhibit high ductilities. Tensile tests of polycrystalline YAg specimens have produced elongations as high as 27% before failure. In the present work, single crystal specimens of YAg with the B2, CsCl-type crystal structure were tensile tested at room temperature. Specimens with a tensile axis orientation of [0 1 1-bar] displayed slip lines on the specimen faces corresponding to slip on the {l_brace}1 1 0{r_brace}<0 1 0> with a critical resolved shear stress of 13 MPa. A specimen with a tensile axis orientation of [1 0 0] showed no slip lines and began to crack at a stress of 300 MPa. The test specimens also displayed some slip lines whose position corresponded to slip on the {l_brace}1 0 0{r_brace}<0 1 0>; these slip lines were found near intersections of {l_brace}1 1 0{r_brace}<0 1 0> slip lines, which suggests that the {l_brace}1 0 0{r_brace}<0 1 0> may be a secondary slip system in YAg. Transmission electron microscope (TEM) examination of the crystals was performed after tensile testing and the dislocations observed were analyzed by g {center_dot} b=0 out of contrast analysis. This TEM analysis indicated that the predominant Burgers vector for the dislocations present was <1 1 1> with some <0 1 1> dislocations also being observed. This finding is inconsistent with the <0 1 0> slip direction determined by slip line analysis, and possible explanations for this surprising finding are presented.

  7. Noncontact atomic force microscopy of perfect single crystals of pentacene prepared by crystallization from solution.

    PubMed

    Sato, Kazuya; Sawaguchi, Takahiro; Sakata, Masafumi; Itaya, Kingo

    2007-12-18

    Nearly perfect single crystals of pentacene were grown from trichlorobenzene solution. The surface structure of pentacene single crystals has been investigated by frequency modulation atomic force microscopy. Molecularly flat and extraordinarily wide terraces, extended over the width of more than a few micrometers with monomolecular steps, were consistently observed, suggesting that those pentacene crystals were nearly perfect single crystals. Molecular packing arrangements were revealed by FM-AFM for the first time.

  8. Method of Making Lightweight, Single Crystal Mirror

    NASA Technical Reports Server (NTRS)

    Bly, Vincent T. (Inventor)

    2015-01-01

    A method of making a mirror from a single crystal blank may include fine grinding top and bottom surfaces of the blank to be parallel. The blank may then be heat treated to near its melting temperature. An optical surface may be created on an optical side of the blank. A protector may be bonded to the optical surface. With the protector in place, the blank may be light weighted by grinding a non-optical surface of the blank using computer controlled grinding. The light weighting may include creating a structure having a substantially minimum mass necessary to maintain distortion of the mirror within a preset limit. A damaged layer of the non-optical surface caused by light weighting may be removed with an isotropic etch and/or repaired by heat treatment. If an oxide layer is present, the entire blank may then be etched using, for example, hydrofluoric acid. A reflecting coating may be deposited on the optical surface.

  9. Thermal debracketing of single crystal sapphire brackets.

    PubMed

    Rueggeberg, F A; Lockwood, P E

    1992-01-01

    Because of their optical clarity, single crystal sapphire brackets provide an esthetic advantage over many other types of orthodontic brackets. However, debonding of these brackets has caused iatrogenic damage to enamel. Thermal debonding has been proposed for use in removing sapphire brackets without causing damage to teeth. This study determined the temperature required at the enamel/resin interface to thermally debond sapphire brackets from etched bovine enamel using 23 different commercially available orthodontic resins and one experimental product. The results indicate a wide range of debonding temperatures for the various resins. As a group, the powder-liquid materials had a statistically lower debonding temperature than the two-paste, the no-mix products, or the light-cured materials, for which the temperatures were all similar. This paper presents relative information a clinician can use in selecting an orthodontic bonding resin to minimize thermal damage to the teeth while debonding sapphire brackets.

  10. Constitutive modeling for single crystal superalloys

    NASA Technical Reports Server (NTRS)

    Stouffer, Donald C.; Dame, L. Thomas; Jayaraman, N.

    1985-01-01

    A crystallographic approach to constitutive modeling of single crystal superalloys is discussed. The approach is based on identifying the active slip planes and slip directions. The shear stresses are computed on each of the slip planes from applied stress components. The slip rate is then computed on each slip system and the microscopic inelastic strain rates are the sum of the slip in the individual slip systems. The constitutive model was implemented in a finite element code using twenty noted isoparametric solid elements. Constants were determined for octahedral and cube slip systems. These constants were then used to predict tension-compression asymmetry and fatigue loops. Other data was used to model the tensile and creep response.

  11. Controlled Folding of Single Crystal Graphene.

    PubMed

    Wang, Bin; Huang, Ming; Kim, Na Yeon; Cunning, Benjamin V; Huang, Yuan; Qu, Deshun; Chen, Xianjue; Jin, Sunghwan; Biswal, Mandakini; Zhang, Xu; Lee, Sun Hwa; Lim, Hyunseob; Yoo, Won Jong; Lee, Zonghoon; Ruoff, Rodney S

    2017-03-08

    Folded graphene in which two layers are stacked with a twist angle between them has been predicted to exhibit unique electronic, thermal, and magnetic properties. We report the folding of a single crystal monolayer graphene film grown on a Cu(111) substrate by using a tailored substrate having a hydrophobic region and a hydrophilic region. Controlled film delamination from the hydrophilic region was used to prepare macroscopic folded graphene with good uniformity on the millimeter scale. This process was used to create many folded sheets each with a defined twist angle between the two sheets. By identifying the original lattice orientation of the monolayer graphene on Cu foil, or establishing the relation between the fold angle and twist angle, this folding technique allows for the preparation of twisted bilayer graphene films with defined stacking orientations and may also be extended to create folded structures of other two-dimensional nanomaterials.

  12. Vibration-assisted machining of single crystal

    NASA Astrophysics Data System (ADS)

    Zahedi, S. A.; Roy, A.; Silberschmidt, V. V.

    2013-07-01

    Vibration-assisted machining offers a solution to expanding needs for improved machining, especially where accuracy and precision are of importance, such as in micromachining of single crystals of metals and alloys. Crystallographic anisotropy plays a crucial role in determining on overall response to machining. In this study, we intend to address the matter of ultra-precision machining of material at the micron scale using computational modelling. A hybrid modelling approach is implemented that combines two discrete schemes: smoothed particle hydrodynamics and continuum finite elements. The model is implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine (VUMAT) and used to elucidate the effect of crystallographic anisotropy on a response of face centred cubic (f.c.c.) metals to machining.

  13. Submicron diameter single crystal sapphire optical fiber

    DOE PAGES

    Hill, Cary; Homa, Daniel; Liu, Bo; ...

    2014-10-02

    In this work, a submicron-diameter single crystal sapphire optical fiber was demonstrated via wet acid etching at elevated temperatures. Etch rates on the order 2.3 µm/hr were achievable with a 3:1 molar ratio sulfuric-phosphoric acid solution maintained at a temperature of 343°C. A sapphire fiber with an approximate diameter of 800 nm was successfully fabricated from a commercially available fiber with an original diameter of 50 µm. The simple and controllable etching technique provides a feasible approach to the fabrication of unique waveguide structures via traditional silica masking techniques. The ability to tailor the geometry of sapphire optical fibers ismore » the first step in achieving optical and sensing performance on par with its fused silica counterpart.« less

  14. Submicron diameter single crystal sapphire optical fiber

    SciTech Connect

    Hill, Cary; Homa, Daniel; Liu, Bo; Yu, Zhihao; Wang, Anbo; Pickrell, Gary

    2014-10-02

    In this work, a submicron-diameter single crystal sapphire optical fiber was demonstrated via wet acid etching at elevated temperatures. Etch rates on the order 2.3 µm/hr were achievable with a 3:1 molar ratio sulfuric-phosphoric acid solution maintained at a temperature of 343°C. A sapphire fiber with an approximate diameter of 800 nm was successfully fabricated from a commercially available fiber with an original diameter of 50 µm. The simple and controllable etching technique provides a feasible approach to the fabrication of unique waveguide structures via traditional silica masking techniques. The ability to tailor the geometry of sapphire optical fibers is the first step in achieving optical and sensing performance on par with its fused silica counterpart.

  15. CVT Growth of Single Crystal Zinc Oxide

    NASA Astrophysics Data System (ADS)

    Kjar, Michael J.; Boone, Jack L.; Cantwell, Gene; Thomas, J. E.

    1997-03-01

    The growth of single crystal ZnO by chemical vapor transport using hydrogen as the transporting agent is being investigated both theoretically and experimentally. A mathematical model has been developed for the growth process using a quasi-equilibrium approach. By calculating the equilibrium constants at both the source and growing ends of the growth ampoule, a transport equation has been developed. The transport calculations have been made under the assumption of a "leaky" ampoule in which the hydrogen , water vapor, and inert gas pressures can be controlled externally. The chemical reactions at the source and growth surfaces are being investigated to ascertain their effect on the transport and growth processes. Also, the effects of varying the "communication" between the ampoule interior and the large containment vessel on the overall growth process have been investigated. The parameters for the growth process are being refined through a correlation of the theoretical model predictions with experimental data.

  16. A simple low-cost single-crystal NMR setup.

    PubMed

    Vinding, Mads S; Kessler, Tommy O; Vosegaard, Thomas

    2016-08-01

    A low-cost single-crystal NMR kit is presented along with a web-based post-processing software. The kit consists of a piezo-crystal motor and a goniometer for the crystal, both embedded in a standard wide-bore NMR probe with a 3D printed scaffold. The NMR pulse program controls the angle setting automatically, and the post-processing software incorporates a range of orientation-angle discrepancies present in the kit and other single-crystal setups. Results with a NaNO3 single-crystal show a high degree of reproducibility and excellent agreement with previous findings for the anisotropic quadrupolar interaction.

  17. A simple low-cost single-crystal NMR setup

    NASA Astrophysics Data System (ADS)

    Vinding, Mads S.; Kessler, Tommy O.; Vosegaard, Thomas

    2016-08-01

    A low-cost single-crystal NMR kit is presented along with a web-based post-processing software. The kit consists of a piezo-crystal motor and a goniometer for the crystal, both embedded in a standard wide-bore NMR probe with a 3D printed scaffold. The NMR pulse program controls the angle setting automatically, and the post-processing software incorporates a range of orientation-angle discrepancies present in the kit and other single-crystal setups. Results with a NaNO3 single-crystal show a high degree of reproducibility and excellent agreement with previous findings for the anisotropic quadrupolar interaction.

  18. Development of novel growth methods for halide single crystals

    NASA Astrophysics Data System (ADS)

    Yokota, Yuui; Kurosawa, Shunsuke; Shoji, Yasuhiro; Ohashi, Yuji; Kamada, Kei; Yoshikawa, Akira

    2017-03-01

    We developed novel growth methods for halide scintillator single crystals with hygroscopic nature, Halide micro-pulling-down [H-μ-PD] method and Halide Vertical Bridgman [H-VB] method. The H-μ-PD method with a removable chamber system can grow a single crystal of halide scintillator material with hygroscopicity at faster growth rate than the conventional methods. On the other hand, the H-VB method can grow a large bulk single crystal of halide scintillator without a quartz ampule. CeCl3, LaBr3, Ce:LaBr3 and Eu:SrI2 fiber single crystals could be grown by the H-μ-PD method and Eu:SrI2 bulk single crystals of 1 and 1.5 inch in diameter could be grown by the H-VB method. The grown fiber and bulk single crystals showed comparable scintillation properties to the previous reports using the conventional methods.

  19. Piezoelectric single crystals for ultrasonic transducers in biomedical applications

    PubMed Central

    Zhou, Qifa; Lam, Kwok Ho; Zheng, Hairong; Qiu, Weibao; Shung, K. Kirk

    2014-01-01

    Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state–of–art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will be addressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN–PT and PIN–PMN–PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single–element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging, and microbeam applications of the single crystal transducers will be discussed. PMID:25386032

  20. Single Crystal Preparation for High-Pressure Experiments in the Diamond Anvil Cell

    SciTech Connect

    Aracne, C; Farber, D; Benterou, J; Occelli, F; Krisch, M; Antonangeli, D; Requardt, H; Fiquet, G

    2003-07-01

    Most research conducted in diamond anvil cells (DAC) is performed on polycrystalline samples. While data from polycrystalline samples are sufficient for determining the bulk properties, high-pressure experiments on single crystals allow for measurements on a range of tensor properties such as: thermal and electrical conductivity; magnetic susceptibility; elasticity; and plasticity. However, in order to achieve pressures above 1 Mbar in a DAC, single crystal samples must be <50 m in diameter and <15 m thick while maintaining a high degree of crystallinity. Thus, we have developed new procedures for producing extremely high-quality micro single crystal samples from commercially available material. Our sample preparation steps include cutting, classical metallographic polishing, and laser ablation. The key to our new process is the preservation of crystallinity during cutting and thinning. We have been successful in maintaining orientation, along with an extremely high degree of crystallinity in completed metal samples. To date, we have analyzed cobalt and molybdenum samples with both white-light interferometry and synchrotron x-ray diffraction, and are in the process of extending these methods to other metals and ceramics.

  1. Dynamic Actuation of Single-Crystal Diamond Nanobeams

    DTIC Science & Technology

    2014-08-25

    ar X iv :1 40 8. 58 22 v1 [ co nd -m at .m es -h al l] 2 5 A ug 2 01 4 Dynamic Actuation of Single-Crystal Diamond Nanobeams Young-Ik Sohn...United States E-mail: loncar@seas.harvard.edu KEYWORDS: Single-crystal diamond , nanoelectromechanical systems (NEMS), nanofabrica- tion...dielectrophoresis Abstract We show the dielectrophoretic actuation of single-crystal diamond nanomechanical devices using gradient radio-frequency electromagnetic

  2. Functionalizing single crystals: incorporation of nanoparticles inside gel-grown calcite crystals.

    PubMed

    Liu, Yujing; Yuan, Wentao; Shi, Ye; Chen, Xiaoqiang; Wang, Yong; Chen, Hongzheng; Li, Hanying

    2014-04-14

    Synthetic single crystals are usually homogeneous solids. Biogenic single crystals, however, can incorporate biomacromolecules and become inhomogeneous solids so that their properties are also extrinsically regulated by the incorporated materials. The discrepancy between the properties of synthetic and biogenic single crystals leads to the idea to modify the internal structure of synthetic crystals to achieve nonintrinsic properties by incorporation of foreign material. Intrinsically colorless and diamagnetic calcite single crystals are turned into colored and paramagnetic solids, through incorporation of Au and Fe3O4 nanoparticles without significantly disrupting the crystalline lattice of calcite. The crystals incorporate the nanoparticles and gel fibers when grown in agarose gel media containing the nanoparticles, whereas the solution-grown crystals do not. As such, our work extends the long-history gel method for crystallization into a platform to functionalize single-crystalline materials.

  3. The hierarchical characterization of deformation heterogeneities in compressed metal single crystals

    NASA Astrophysics Data System (ADS)

    Magid, Karen Ruth

    Plastic deformation is an inherently heterogeneous process whose understanding is still incomplete after more than 50 years of study. The traditional methods of analysis look at both bulk material deformation and properties and the microscale features which comprise the inherent deformation processes. A large amount of information occurring on the mesoscale, from 1 to 100 microns, has not been analyzed. Here we present the results from an x-ray diffraction technique with submicron spatial resolution used to analyze compressed metal single crystals. The mesoscopic structure of the inhomogeneous macroscopic deformation pattern was explored with selected area diffraction, using a focused synchrotron radiation polychromatic beam with a resolution of 1-3 mum. Single crystals of copper, molybdenum, and zinc were oriented for single slip tested to ˜2-14% strain in nearly uniaxial compression, using a specifically designed 6 degree of freedom compressive test device. The macroscopic strain field was monitored during the test by optical image correlation methods that mapped the strain field with a spatial resolution of about 100 mum. The copper and molybdenum crystals deformed unexpectedly, exhibiting significant amounts of secondary slip activity alongside the primary slip. Areas of interest from adjacent faces were identified from the image correlation and mapped for their orientation, excess defect density, and shear stress. The mesoscopic defect structure in the copper specimens consisted of broad, somewhat irregular primary bands that lay nominally parallel to (111), in an almost periodic distribution with a period of about 30 mum. These primary bands were dominant even in the region of conjugate strain. There were also broad conjugate defect bands, almost precisely perpendicular to the primary bands that tended to bridge primary bands and terminate at them. In addition, a tantalum bicrystal, previously compressed and characterized using electron back

  4. Ultratough CVD single crystal diamond and three dimensional growth thereof

    DOEpatents

    Hemley, Russell J.; Mao, Ho-kwang; Yan, Chih-shiue

    2009-09-29

    The invention relates to a single-crystal diamond grown by microwave plasma chemical vapor deposition that has a toughness of at least about 30 MPa m.sup.1/2. The invention also relates to a method of producing a single-crystal diamond with a toughness of at least about 30 MPa m.sup.1/2. The invention further relates to a process for producing a single crystal CVD diamond in three dimensions on a single crystal diamond substrate.

  5. Hydrothermal synthesis, crystal structure, and catalytic potential of a one-dimensional molybdenum oxide/bipyridinedicarboxylate hybrid.

    PubMed

    Amarante, Tatiana R; Neves, Patrícia; Valente, Anabela A; Paz, Filipe A Almeida; Fitch, Andrew N; Pillinger, Martyn; Gonçalves, Isabel S

    2013-04-15

    The reaction of MoO3, 2,2'-bipyridine-5,5-dicarboxylic acid (H2bpdc), water, and dimethylformamide in the mole ratio 1:1:1730:130 at 150 °C for 3 days in a rotating Teflon-lined digestion bomb leads to the isolation of the molybdenum oxide/bipyridinedicarboxylate hybrid material (DMA)[MoO3(Hbpdc)]·nH2O (1) (DMA = dimethylammonium). Compound 1 was characterized by scanning electron microscopy, FT-IR and (13)C{(1)H} CP MAS NMR spectroscopies, and elemental and thermogravimetric analyses. The solid state structure of 1 was solved and refined through Rietveld analysis of high resolution synchrotron X-ray powder diffraction data in conjunction with information derived from the above techniques. The material, crystallizing in the noncentrosymmetric monoclinic space group Pc, is composed of an anionic one-dimensional organic-inorganic hybrid polymer, ∞(1)[MoO3(Hbpdc)](-), formed by corner-sharing distorted {MoO4N2} octahedra, which cocrystallizes with charge-balancing DMA(+) cations and one water molecule per metal center. In the crystal structure of 1, the close packing of individual anionic polymers, DMA(+) cations, and water molecules is mediated by a series of supramolecular contacts, namely strong (O-H···O, N(+)-H···O(-)) and weak (C-H···O) hydrogen bonding interactions, and π-π contacts involving adjacent coordinated Hbpdc(-) ligands. The catalytic potential of 1 was investigated in the epoxidation reactions of the bioderived olefins methyl oleate (Ole) and DL-limonene (Lim) using tert-butylhydroperoxide (TBHP) as the oxygen donor and 1,2-dichloroethane (DCE) or (trifluoromethyl)benzene (BTF) as cosolvent, at 55 or 75 °C. Under these conditions, 1 acts as a source of active soluble species, leading to epoxide yields of up to 98% for methyl 9,10-epoxystearate (BTF, 75 °C, 100% conversion of Ole) and 89% for 1,2-epoxy-p-menth-8-ene (DCE, 55 °C, 95% conversion of Lim). Catalytic systems employing the ionic liquid 1-butyl-3-methylimidazolium bis

  6. Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

    DOEpatents

    Todt, Volker; Miller, Dean J.; Shi, Donglu; Sengupta, Suvankar

    1998-01-01

    A method of fabricating bulk YBa.sub.2 Cu.sub.3 O.sub.x where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa.sub.2 Cu.sub.3 O.sub.x are heated in the presence of a Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y seed crystal to a temperature sufficient to form a liquid phase in the YBa.sub.2 Cu.sub.3 O.sub.x while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa.sub.2 Cu.sub.3 O.sub.x material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material.

  7. Oxygen diffusion in single crystal barium titanate.

    PubMed

    Kessel, Markus; De Souza, Roger A; Martin, Manfred

    2015-05-21

    Oxygen diffusion in cubic, nominally undoped, (100) oriented BaTiO3 single crystals has been studied by means of (18)O2/(16)O2 isotope exchange annealing and subsequent determination of the isotope profiles in the solid by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Experiments were carried out as a function of temperature 973 < T/K < 1173, at an oxygen activity of aO2 = 0.200, and as a function of oxygen activity 0.009 < aO2 < 0.900 at T = 1073 K. The oxygen isotope profiles comprise two parts: slow diffusion through a space-charge zone at the surface depleted of oxygen vacancies followed by faster diffusion in a homogeneous bulk phase. The entire isotope profile can be described by a single solution to the diffusion equation involving only three fitting parameters: the surface exchange coefficient ks*, the space-charge potential Φ0 and the bulk diffusion coefficient D*(∞). Analysis of the temperature and oxygen activity dependencies of D*(∞) and Φ0 yields a consistent picture of both the bulk and the interfacial defect chemistry of BaTiO3. Values of the oxygen vacancy diffusion coefficient DV extracted from measured D*(∞) data are compared with literature data; consequently a global expression for the vacancy diffusivity in BaTiO3 for the temperature range 466 < T/K < 1273 is obtained, with an activation enthalpy of vacancy migration, ΔHmig,V = (0.70 ± 0.04) eV.

  8. Fabrication of polypyrrole nano-arrays in lysozyme single crystals

    NASA Astrophysics Data System (ADS)

    England, Matt W.; Lambert, Elizabeth M.; Li, Mei; Turyanska, Lyudmila; Patil, Avinash J.; Mann, Stephen

    2012-10-01

    A template-directed method for the synthesis and organization of partially oxidized polypyrrole (PPy) nanoscale arrays within the solvent channels of glutaraldehyde-cross-linked lysozyme single crystals is presented. Macroscopic single crystals of the periodically arranged protein-polymer superstructure are electrically conductive, insoluble in water and organic solvents, and display increased levels of mechanical plasticity compared with native cross-linked lysozyme crystals.A template-directed method for the synthesis and organization of partially oxidized polypyrrole (PPy) nanoscale arrays within the solvent channels of glutaraldehyde-cross-linked lysozyme single crystals is presented. Macroscopic single crystals of the periodically arranged protein-polymer superstructure are electrically conductive, insoluble in water and organic solvents, and display increased levels of mechanical plasticity compared with native cross-linked lysozyme crystals. Electronic supplementary information (ESI) available: Optical microscopy, SEM, TEM images, FTIR spectra and tables, conductivity plot. Experimental methods. See DOI: 10.1039/c2nr32413j

  9. Giant rotating magnetocaloric effect in RNi5 single crystals

    NASA Astrophysics Data System (ADS)

    de Oliveira, N. A.

    2017-04-01

    In this paper we theoretically discuss the rotating magnetocaloric effect in RNi5 (R = Nd , Tb , Dy , Er) single crystals, by using a model of interacting magnetic moments including the interaction with the crystal electric field. Our theoretical calculations show that the rotating magnetocaloric effect in RNi5 single crystals is as large as the conventional one. This fact points out that these single crystals are also good candidates to be used in magnetic refrigerators working at low temperatures and based on the rotating magnetocaloric effect.

  10. Microscale Laser Peen Forming of Single Crystal

    SciTech Connect

    Wang,Y.; Fan, Y.; Kysar, J.; Vukelic, S.; Yao, Y.

    2008-01-01

    As the result of quickly increased requirement in many industrial products resulting from microtechnology, laser thermal microforming and microsurface treatment [microscale laser shock peening (?LSP)] have been well studied. By combining the beneficial effects of these two processes with a controlled bending deformation, microscale laser peen forming (?LPF) attracts more attention recently since it not only improves the fatigue life of the material but also shapes microscale metallic parts at the same time. In the present study, ?LSP of single crystal aluminum was presented to study anisotropic material response. Local plastic deformation was characterized by lattice rotation measured through electron backscatter diffraction. Residual stress distributions of both sides of a peened sample, characterized by x-ray microdiffraction, were compared with the results obtained from finite element method simulation. ?LPF anisotropic behavior was investigated in three effective slip systems via both the anisotropic slip line theory and numerical method. Also, the work hardening effect resulted from self-hardening, and latent hardening was analyzed through comparing the results with and without considering hardening.

  11. Excitonic polaritons of zinc diarsenide single crystals

    NASA Astrophysics Data System (ADS)

    Syrbu, N. N.; Stamov, I. G.; Zalamai, V. V.; Dorogan, A.

    2017-02-01

    Excitonic polaritons of ZnAs2 single crystals had been investigated. Parameters of singlet excitons with D2bar(z) symmetry and orthoexcitons 2D1bar(y)+D2bar(x) had been determined. Spectral dependencies of ordinary and extraordinary dispersion of refractive index had been calculated using interferential reflection and transmittance spectra. It was shown, that A excitonic series were due to hole (V1) and electron (C1) bands. The values of effective masses of electrons (mc*=0.10 m0) and holes (mv1*=0.89 m0) had been estimated. It was revealed that the hole mass mv1* changes from 1.03 m0 to 0.55 m0 at temperature increasing from 10 K up to 230 K and that the electron mass mc* does not depend on temperature. The integral absorption A (eV cm-1) of the states n=1, 2 and 3 of D2bar(z) excitons depends on the An≈n-3 equality, which it is characteristic for S-type excitonic functions. Temperature dependences of the integral absorption of ground states for D2bar(z) and D2bar(D) excitons differ. The ground states of B and C excitons formed by V3 - C1 and V4 - C1 bands and its parameters had been determined.

  12. Advanced single crystal for SSME turbopumps

    NASA Technical Reports Server (NTRS)

    Fritzemeier, L. G.

    1989-01-01

    The objective of this program was to evaluate the influence of high thermal gradient casting, hot isostatic pressing (HIP) and alternate heat treatments on the microstructure and mechanical properties of a single crystal nickel base superalloy. The alloy chosen for the study was PWA 1480, a well characterized, commercial alloy which had previously been chosen as a candidate for the Space Shuttle Main Engine high pressure turbopump turbine blades. Microstructural characterization evaluated the influence of casting thermal gradient on dendrite arm spacing, casting porosity distribution and alloy homogeneity. Hot isostatic pressing was evaluated as a means of eliminating porosity as a preferred fatigue crack initiation site. The alternate heat treatment was chosen to improve hydrogen environment embrittlement resistance and for potential fatigue life improvement. Mechanical property evaluation was aimed primarily at determining improvements in low cycle and high cycle fatigue life due to the advanced processing methods. Statistically significant numbers of tests were conducted to quantitatively demonstrate life differences. High thermal gradient casting improves as-cast homogeneity, which facilitates solution heat treatment of PWA 1480 and provides a decrease in internal pore size, leading to increases in low cycle and high cycle fatigue lives.

  13. Single crystal micromechanical resonator and fabrication methods thereof

    DOEpatents

    Olsson, Roy H.; Friedmann, Thomas A.; Homeijer, Sara Jensen; Wiwi, Michael; Hattar, Khalid Mikhiel; Clark, Blythe; Bauer, Todd; Van Deusen, Stuart B.

    2016-12-20

    The present invention relates to a single crystal micromechanical resonator. In particular, the resonator includes a lithium niobate or lithium tantalate suspended plate. Also provided are improved microfabrication methods of making resonators, which does not rely on complicated wafer bonding, layer fracturing, and mechanical polishing steps. Rather, the methods allow the resonator and its components to be formed from a single crystal.

  14. A Quick Method for Determining the Density of Single Crystals.

    ERIC Educational Resources Information Center

    Roman, Pascual; Gutierrez-Zorrilla, Juan M.

    1985-01-01

    Shows how the Archimedes method is used to determine the density of a single crystal of ammonium oxalate monohydrate. Also shows how to calculate the density of other chemicals when they are available as single crystals. Experimental procedures and materials needed are included. (JN)

  15. Mercuric iodide single crystals for nuclear radiation detectors

    SciTech Connect

    Li, W.; Li, Z.; Zhu, S.; Yin, S.; Zhao, B.; Chen, G.; Yin, S.; Yuan, H.; Xu, H.

    1996-06-01

    Large size HgI{sub 2} single crystals were grown using the Modified Temperature Oscillation Method (MTOM) with low dislocation densities in a relatively stable temperature environment. Radiation detectors were fabricated from the single crystals which showed good energy resolution with small polarization. Applications have been found in geological explorations, marine mineral analysis, environment pollution monitoring, industrial material quality assurance, and space explorations.

  16. Semiconductor single crystal external ring resonator cavity laser and gyroscope

    SciTech Connect

    Spitzer, M.P.

    1993-08-31

    A ring laser is described comprising: a semiconductor single crystal external ring resonator cavity having a plurality of reflecting surfaces defined by the planes of the crystal and establishing a closed optical path; and a discrete laser medium disposed in said semiconductor single crystal external ring resonator cavity for generating coherent light in said cavity, wherein said resonator cavity is decoupled from the laser medium.

  17. Role of curvature elasticity in sectorization and ripple formation during melt crystallization of polymer single crystals.

    PubMed

    Mehta, Rujul; Keawwattana, Wirunya; Guenthner, Andrew L; Kyu, Thein

    2004-06-01

    The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation captures ripple formation running across the long lamellar growth front, which may be attributed to lamellar buckling caused by the volume shrinkage. Of particular interest is that these simulated topologies of the single crystals are in good accord with the growth character of syndiotactic polypropylene single crystals observed experimentally by us during isothermal crystallization from the melt.

  18. Study of single crystals of metal solid solutions

    NASA Technical Reports Server (NTRS)

    Doty, J. P.; Reising, J. A.

    1973-01-01

    The growth of single crystals of relatively high melting point metals such as silver, copper, gold, and their alloys was investigated. The purpose was to develop background information necessary to support a space flight experiment and to generate ground based data for comparison. The ground based data, when compared to the data from space grown crystals, are intended to identify any effects which zero-gravity might have on the basic process of single crystal growth of these metals. The ultimate purposes of the complete investigation are to: (1) determine specific metals and alloys to be investigated; (2) grow single metal crystals in a terrestrial laboratory; (3) determine crystal characteristics, properties, and growth parameters that will be effected by zero-gravity; (4) evaluate terrestrially grown crystals; (5) grow single metal crystals in a space laboratory such as Skylab; (6) evaluate the space grown crystals; (7) compare for zero-gravity effects of crystal characteristics, properties, and parameters; and (8) make a recommendation as to production of these crystals as a routine space manufacturing proceses.

  19. Segmentation Effect on Inhomogeneity of [110]-Single Crystal Deformation

    NASA Astrophysics Data System (ADS)

    Lychagin, D. V.; Nesterenko, E. A. Alfyorova V. P.

    2016-08-01

    This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations.

  20. Growth dynamics of isotactic polypropylene single crystals during isothermal crystallization from a miscible polymeric solvent.

    PubMed

    Mehta, Rujul; Keawwattana, Wirunya; Kyu, Thein

    2004-02-22

    The present article presents a spatiotemporal growth of isotactic polypropylene (iPP) single crystals, melt crystallized from a polymeric solvent, i.e., poly (ethylene octene) copolymer that is known to be miscible with iPP. Optical and atomic force microscopic investigations reveal that the melt grown single crystals of iPP develop in the form of two parallel rows of crystal lamellae, but these crystals merge at the tips. To elucidate the mechanism of these emerging parallel rows of iPP crystals, a phase field model pertaining to solidification phenomena has been employed that involves a nonconserved crystal order parameter and a chain-tilting angle. This phase field model is based on the free energy of crystallization, having an asymmetric double well, and a tensorial surface free energy of the crystal interface coupled with a curvature elastic free energy that is possessed by the solid-liquid interface. The spatiotemporal simulation of iPP single crystal growth has been carried out on a square lattice based on the finite difference method for spatial steps and an explicit method for temporal steps with a periodic boundary condition. The appearance of the seemingly twin crystal is captured in the simulation, which may be attributed to the sector demarcation that is taking place in the anisotropically growing single crystal of iPP.

  1. Growth dynamics of isotactic polypropylene single crystals during isothermal crystallization from a miscible polymeric solvent

    NASA Astrophysics Data System (ADS)

    Mehta, Rujul; Keawwattana, Wirunya; Kyu, Thein

    2004-02-01

    The present article presents a spatiotemporal growth of isotactic polypropylene (iPP) single crystals, melt crystallized from a polymeric solvent, i.e., poly (ethylene octene) copolymer that is known to be miscible with iPP. Optical and atomic force microscopic investigations reveal that the melt grown single crystals of iPP develop in the form of two parallel rows of crystal lamellae, but these crystals merge at the tips. To elucidate the mechanism of these emerging parallel rows of iPP crystals, a phase field model pertaining to solidification phenomena has been employed that involves a nonconserved crystal order parameter and a chain-tilting angle. This phase field model is based on the free energy of crystallization, having an asymmetric double well, and a tensorial surface free energy of the crystal interface coupled with a curvature elastic free energy that is possessed by the solid-liquid interface. The spatiotemporal simulation of iPP single crystal growth has been carried out on a square lattice based on the finite difference method for spatial steps and an explicit method for temporal steps with a periodic boundary condition. The appearance of the seemingly twin crystal is captured in the simulation, which may be attributed to the sector demarcation that is taking place in the anisotropically growing single crystal of iPP.

  2. Method for harvesting rare earth barium copper oxide single crystals

    DOEpatents

    Todt, Volker R.; Sengupta, Suvankar; Shi, Donglu

    1996-01-01

    A method of preparing high temperature superconductor single crystals. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals of the high temperature superconductor, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals of the high temperature superconductor on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals melted, allowing the wicking away of the peritectic liquid.

  3. Method for harvesting single crystals from a peritectic melt

    DOEpatents

    Todt, V.R.; Sengupta, S.; Shi, D.

    1996-08-27

    A method of preparing single crystals is disclosed. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals unmelted, allowing the wicking away of the peritectic liquid. 2 figs.

  4. Method for harvesting single crystals from a peritectic melt

    DOEpatents

    Todt, Volker R.; Sengupta, Suvankar; Shi, Donglu

    1996-01-01

    A method of preparing single crystals. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals unmelted, allowing the wicking away of the peritectic liquid.

  5. Stability of Detached Grown Germanium Single Crystals

    NASA Technical Reports Server (NTRS)

    Schweizer, M.; Volz, M. P.; Cobb, S. D.; Vujisic, L.; Szofran, F. R.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Detachment of the melt meniscus from the crucible during semiconductor Bridgman growth experiments has been observed in recent years, especially under microgravity experiments. Under earth conditions, the hydrostatic pressure counteracts the mechanism, whereby it is more difficult to achieve detached Bridgman growth. Attempts to get stable detached growth under terrestrial conditions have been discussed in the literature and have been the subject of recent experiments in our own group. The advantage of crystals grown without wall contact is obvious: In general, they possess a higher crystal quality than conventional Bridgman grown crystals with wall contact. However, due to the interaction of different parameters such as the wetting behavior of the melt with the crucible, and the dependence of the growth angle with the shape of the melt meniscus, the mechanism leading to detachment is very complicated and not completely understood. We have grown several doped and undoped Germanium crystals with the detached Bridgman and the normal Bridgman growth technique. Pyrolytic boron nitride containers were used for all growth experiments. In the detached grown crystals the typical gap thickness between the pBN crucible and the crystal is in the range of 10 to 100 micrometers, which was determined by performing profilometer measurements. Etch pit density measurements were also performed and a comparison between detached and attached grown crystals will be given. An interesting feature was detected on the surface of a detached grown crystal. Strong surface striations with an average axial distance of 0.5 mm were observed around the whole circumference. The maximum fluctuation of the gap thickness is in the range of 5-10 micrometers. These variations of the detached gap along the crystal axis can be explained by a kind of stiction of the melt/crucible interface and thus by a variation of the meniscus shape. This phenomenon leading to the fluctuation of the gap thickness will be

  6. Stability of Detached Grown Germanium Single Crystals

    NASA Technical Reports Server (NTRS)

    Schweizer, M.; Volz, M. P.; Cobb, S. D.; Motakef, S.; Szofran, F. R.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Detachment of the melt meniscus from the crucible during semiconductor Bridgman growth experiments has been observed in recent years especially, under microgravity experiments. Under earth conditions, the hydrostatic pressure counteracts the mechanism, whereby it is more difficult to achieve detached Bridgman growth. Attempts to get stable detached growth under terrestrial conditions have been discussed in the literature and have been the subject of recent experiments in our own group. The advantage of crystals grown without wall contact is obvious: In general, they possess a higher crystal quality than conventional Bridgman grown crystals with wall contact. However, due to the interaction of different parameters such as the wetting behavior of the melt with the crucible, and the dependence of the growth angle with the shape of the melt meniscus, the mechanism leading to detachment is very complicated and not completely understood. We have grown several doped and undoped Germanium crystals with the detached Bridgman and the normal Bridgman growth technique. Pyrolytic boron nitride containers were used for all growth experiments. In the detached grown crystals the typical gap thickness between the pBN crucible and the crystal is in the range of 10 to 100 microns, which was determined by performing profilometer measurements. Etch pit density measurements were also performed and a comparison between detached and attached grown crystals will be given. An interesting feature was detected on the surface of a detached grown crystal. Strong surface striations with an average axial distance of 0.5mm were observed around the whole circumference. The maximum fluctuation of the gap thickness is in the range of 5-10 microns. These variations of the detached gap along the crystal axis can be explained by a kind of stiction of the melt/crucible interface and thus by a variation of the meniscus shape. This phenomenon leading to the fluctuation of the gap thickness will be

  7. Basic ammonothermal GaN growth in molybdenum capsules

    NASA Astrophysics Data System (ADS)

    Pimputkar, S.; Speck, J. S.; Nakamura, S.

    2016-12-01

    Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIMS) analysis revealed transition metal free (<1×1017 cm-3) GaN crystals. Anomalously low oxygen concentrations ((2-6)×1018 cm-3) were measured in a {0001} seeded crystal boule grown using a Mo capsule, despite higher source material oxygen concentrations ((1-5)×1019 cm-3) suggesting that molybdenum (or molybdenum nitrides) may act to getter oxygen under certain conditions. Total system pressure profiles from growth runs in a Mo capsule system were comparable to those without a capsule, with pressures peaking within 2 days and slowly decaying due to hydrogen diffusional losses. Measured Mo capsule GaN growth rates were comparable to un-optimized growth rates in capsule-free systems and appreciably slower than in Ag-capsule systems. Crystal quality replicated that of the GaN seed crystals for all capsule conditions, with high quality growth occurring on the (0001) Ga-face. Optical absorption and impurity concentration characterization suggests reduced concentrations of hydrogenated gallium vacancies (VGa-Hx).

  8. The Growth of Large Single Crystals.

    ERIC Educational Resources Information Center

    Baer, Carl D.

    1990-01-01

    Presented is an experiment which demonstrates principles of experimental design, solubility, and crystal growth and structure. Materials, procedures and results are discussed. Suggestions for adapting this activity to the high school laboratory are provided. (CW)

  9. Barium iodide single-crystal scintillator detectors

    NASA Astrophysics Data System (ADS)

    Cherepy, Nerine J.; Hull, Giulia; Niedermayr, Thomas R.; Drobshoff, Alexander; Payne, Stephen A.; Roy, Utpal N.; Cui, Yunlong; Bhattacharaya, Ajanta; Harrison, Melissa; Guo, Mingsheng; Groza, Michael; Burger, Arnold

    2007-09-01

    We find that the high-Z crystal Barium Iodide is readily growable by the Bridgman growth technique and is less prone to crack compared to Lanthanum Halides. We have grown Barium Iodide crystals: undoped, doped with Ce 3+, and doped with Eu 2+. Radioluminescence spectra and time-resolved decay were measured. BaI II(Eu) exhibits luminescence from both Eu 2+ at 420 nm (~450 ns decay), and a broad band at 550 nm (~3 μs decay) that we assign to a trapped exciton. The 550 nm luminescence decreases relative to the Eu 2+ luminescence when the Barium Iodide is zone refined prior to crystal growth. We also describe the performance of BaI II(Eu) crystals in experimental scintillator detectors.

  10. A study of crystal growth by solution technique. [triglycine sulfate single crystals

    NASA Technical Reports Server (NTRS)

    Lal, R. B.

    1979-01-01

    The advantages and mechanisms of crystal growth from solution are discussed as well as the effects of impurity adsorption on the kinetics of crystal growth. Uncertainities regarding crystal growth in a low gravity environment are examined. Single crystals of triglycine sulfate were grown using a low temperature solution technique. Small components were assembled and fabricated for future space flights. A space processing experiment proposal accepted by NASA for the Spacelab-3 mission is included.

  11. Physicochemical principles of high-temperature crystallization and single crystal growth methods

    NASA Astrophysics Data System (ADS)

    Bagdasarov, Kh. S.

    The mechanisms of crystal growth are reviewed, with attention given to the physicochemical reactions taking place in the melt near the phase boundary; phenomena determining physical and chemical kinetics directly at the growth front; solid-phase processes occurring within the crystal. Methods for growing refractory single crystals are discussed with particular reference to the Verneuil method, zone melting, Czhochralskii growth, horizontal directional solidification, and the Stockbarger method. Methods for growing crystals of complex geometrical shapes are also discussed.

  12. Growing Single Crystals of Compound Semiconductors

    NASA Technical Reports Server (NTRS)

    Naumann, Robert J.; Lehoczky, Sandor L.; Frazier, Donald O.

    1987-01-01

    Defect reduced by preventing melt/furnace contact and suppressing convention. Large crystals of compound semiconductors with few defects grown by proposed new method. Such materials as gallium arsenide and cadmium telluride produced, with quality suitable for very-large-scale integrated circuits or for large focal-plane arrays of photodetectors. Method used on small scale in Earth gravity, but needs microgravity to provide crystals large enough for industrial use.

  13. Single-drop optimization of protein crystallization.

    PubMed

    Meyer, Arne; Dierks, Karsten; Hilterhaus, Dierk; Klupsch, Thomas; Mühlig, Peter; Kleesiek, Jens; Schöpflin, Robert; Einspahr, Howard; Hilgenfeld, Rolf; Betzel, Christian

    2012-08-01

    A completely new crystal-growth device has been developed that permits charting a course across the phase diagram to produce crystalline samples optimized for diffraction experiments. The utility of the device is demonstrated for the production of crystals for the traditional X-ray diffraction data-collection experiment, of microcrystals optimal for data-collection experiments at a modern microbeam insertion-device synchrotron beamline and of nanocrystals required for data collection on an X-ray laser beamline.

  14. Single-drop optimization of protein crystallization

    PubMed Central

    Meyer, Arne; Dierks, Karsten; Hilterhaus, Dierk; Klupsch, Thomas; Mühlig, Peter; Kleesiek, Jens; Schöpflin, Robert; Einspahr, Howard; Hilgenfeld, Rolf; Betzel, Christian

    2012-01-01

    A completely new crystal-growth device has been developed that permits charting a course across the phase diagram to produce crystalline samples optimized for diffraction experiments. The utility of the device is demonstrated for the production of crystals for the traditional X-ray diffraction data-collection experiment, of microcrystals optimal for data-collection experiments at a modern microbeam insertion-device synchrotron beamline and of nanocrystals required for data collection on an X-ray laser beamline. PMID:22869140

  15. A Single Crystal Niobium RF Cavity of the TESLA Shape

    SciTech Connect

    Singer, W.; Singer, X.; Kneisel, P.

    2007-08-09

    A fabrication method for single crystal niobium cavities of the TESLA shape was proposed on the basis of metallographic investigations and electron beam welding tests on niobium single crystals. These tests showed that a cavity can be produced without grain boundaries even in the welding area. An appropriate annealing allows the outgassing of hydrogen and stress relaxation of the material without destruction of the single crystal. A prototype single crystal single cell cavity was build. An accelerating gradient of 37.5 MV/m was reached after approximately 110 {mu}m of Buffered Chemical Polishing (BCP) and in situ baking at 120 deg. C for 6 hrs with a quality factor exceeding 2x1010 at 1.8 K. The developed fabrication method can be extended to fabrication of multi cell cavities.

  16. A Single Crystal Niobium RF Cavity of the TESLA Shape

    SciTech Connect

    W. Singer; X. Singer; P. Kneisel

    2007-09-01

    A fabrication method for single crystal niobium cavities of the TESLA shape was proposed on the basis of metallographic investigations and electron beam welding tests on niobium single crystals. These tests showed that a cavity can be produced without grain boundaries even in the welding area. An appropriate annealing allows the outgassing of hydrogen and stress relaxation of the material without destruction of the single crystal. A prototype single crystal single cell cavity was built. An accelerating gradient of 37.5 MV/m was reached after approximately 110 mu-m of Buffered Chanical Polishing (BCP) and in situ baking at 120°C for 6 hrs with a quality factor exceeding 2x1010 at 1.8 K. The developed fabrication method can be extended to fabrication of multi cell cavities.

  17. Growth and characterization of diammonium copper disulphate hexahydrate single crystal

    SciTech Connect

    Siva Sankari, R.; Perumal, Rajesh Narayana

    2014-03-01

    Graphical abstract: Diammonium copper disulphate hexahydrate (DACS) is one of the most promising inorganic dielectric crystals with exceptional mechanical properties. Good quality crystals of DACS were grown by using solution method in a period of 30 days. The grown crystals were subjected to single crystal X-ray diffraction analysis in order to establish their crystalline nature. Thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis were performed for the crystal. Several solid state physical parameters have been determined for the grown crystals. The dielectric constant and the dielectric loss and AC conductivity of the grown crystal were studied as a function of frequency and temperature has been calculated and plotted. - Highlights: • Diammonium copper disulphate is grown for the first time and CCDC number obtained. • Thermal analysis is done to see the stability range of the crystals. • Band gap and UV cut off wavelength of the crystal are determined to be 2.4 eV and 472.86 nm, respectively. • Dielectric constant, dielectric loss and AC conductivity are plotted as a function of applied field. - Abstract: Diammonium copper disulphate hexahydrate is one of the most promising inorganic crystals with exceptional dielectric properties. A good quality crystal was harvested in a 30-day period using solution growth method. The grown crystal was subjected to various characterization techniques like single crystal X-ray diffraction analysis, thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis. Unit cell dimensions of the grown crystal have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Thermal stability of the samples was checked by TG/DTA studies. Band gap of the crystal was calculated. The dielectric constant and dielectric loss were studied as a function of frequency of the applied field. AC conductivity was plotted as a function

  18. Single crystal Processing and magnetic properties of gadolinium nickel

    SciTech Connect

    Shreve, Andrew John

    2012-01-01

    GdNi is a rare earth intermetallic material that exhibits very interesting magnetic properties. Spontaneous magnetostriction occurs in GdNi at T{sub C}, on the order of 8000ppm strain along the c-axis and only until very recently the mechanism causing this giant magnetostriction was not understood. In order to learn more about the electronic and magnetic structure of GdNi, single crystals are required for anisotropic magnetic property measurements. Single crystal processing is quite challenging for GdNi though since the rare-earth transition-metal composition yields a very reactive intermetallic compound. Many crystal growth methods are pursued in this study including crucible free methods, precipitation growths, and specially developed Bridgman crucibles. A plasma-sprayed Gd2O3 W-backed Bridgman crucible was found to be the best means of GdNi single crystal processing. With a source of high-quality single crystals, many magnetization measurements were collected to reveal the magnetic structure of GdNi. Heat capacity and the magnetocaloric effect are also measured on a single crystal sample. The result is a thorough report on high quality single crystal processing and the magnetic properties of GdNi.

  19. Growing intermetallic single crystals using in situ decanting

    SciTech Connect

    Petrovic, Cedomir; Canfield, Paul; Mellen, Jonathan

    2012-05-16

    High temperature metallic solution growth is one of the most successful and versatile methods for single crystal growth, and is particularly suited for exploratory synthesis. The method commonly utilizes a centrifuge at room temperature and is very successful for the synthesis of single crystal phases that can be decanted from the liquid below the melting point of the silica ampoule. In this paper, we demonstrate the extension of this method that enables single crystal growth and flux decanting inside the furnace at temperatures above 1200°C. This not only extends the number of available metallic solvents that can be used in exploratory crystal growth but also can be particularly well suited for crystals that have a rather narrow exposed solidification surface in the equilibrium alloy phase diagram.

  20. Fabrication of graded index single crystal in glass

    PubMed Central

    Veenhuizen, Keith; McAnany, Sean; Nolan, Daniel; Aitken, Bruce; Dierolf, Volkmar; Jain, Himanshu

    2017-01-01

    Lithium niobate crystals were grown in 3D through localized heating by femtosecond laser irradiation deep inside 35Li2O-35Nb2O5-30SiO2 glass. Laser scanning speed and power density were systematically varied to control the crystal growth process and determine the optimal conditions for the formation of single crystal lines. EBSD measurements showed that, in principle, single crystals can be grown to unlimited lengths using optimal parameters. We successfully tuned the parameters to a growth mode where nucleation and growth occur upon heating and ahead of the scanning laser focus. This growth mode eliminates the problem reported in previous works of non-uniform polycrystallinity because of a separate growth mode where crystallization occurs during cooling behind the scanning laser focus. To our knowledge, this is the first report of such a growth mode using a fs laser. The crystal cross-sections possessed a symmetric, smooth lattice misorientation with respect to the c-axis orientation in the center of the crystal. Calculations indicate the observed misorientation leads to a decrease in the refractive index of the crystal line from the center moving outwards, opening the possibility to produce within glass a graded refractive index single crystal (GRISC) optically active waveguide. PMID:28287174

  1. Fabrication of graded index single crystal in glass

    NASA Astrophysics Data System (ADS)

    Veenhuizen, Keith; McAnany, Sean; Nolan, Daniel; Aitken, Bruce; Dierolf, Volkmar; Jain, Himanshu

    2017-03-01

    Lithium niobate crystals were grown in 3D through localized heating by femtosecond laser irradiation deep inside 35Li2O-35Nb2O5-30SiO2 glass. Laser scanning speed and power density were systematically varied to control the crystal growth process and determine the optimal conditions for the formation of single crystal lines. EBSD measurements showed that, in principle, single crystals can be grown to unlimited lengths using optimal parameters. We successfully tuned the parameters to a growth mode where nucleation and growth occur upon heating and ahead of the scanning laser focus. This growth mode eliminates the problem reported in previous works of non-uniform polycrystallinity because of a separate growth mode where crystallization occurs during cooling behind the scanning laser focus. To our knowledge, this is the first report of such a growth mode using a fs laser. The crystal cross-sections possessed a symmetric, smooth lattice misorientation with respect to the c-axis orientation in the center of the crystal. Calculations indicate the observed misorientation leads to a decrease in the refractive index of the crystal line from the center moving outwards, opening the possibility to produce within glass a graded refractive index single crystal (GRISC) optically active waveguide.

  2. Rotating lattice single crystal architecture on the surface of glass

    PubMed Central

    Savytskii, D.; Jain, H.; Tamura, N.; Dierolf, V.

    2016-01-01

    Defying the requirements of translational periodicity in 3D, rotation of the lattice orientation within an otherwise single crystal provides a new form of solid. Such rotating lattice single (RLS) crystals are found, but only as spherulitic grains too small for systematic characterization or practical application. Here we report a novel approach to fabricate RLS crystal lines and 2D layers of unlimited dimensions via a recently discovered solid-to-solid conversion process using a laser to heat a glass to its crystallization temperature but keeping it below the melting temperature. The proof-of-concept including key characteristics of RLS crystals is demonstrated using the example of Sb2S3 crystals within the Sb-S-I model glass system for which the rotation rate depends on the direction of laser scanning relative to the orientation of initially formed seed. Lattice rotation in this new mode of crystal growth occurs upon crystallization through a well-organized dislocation/disclination structure introduced at the glass/crystal interface. Implications of RLS growth on biomineralization and spherulitic crystal growth are noted. PMID:27808168

  3. Rotating lattice single crystal architecture on the surface of glass

    NASA Astrophysics Data System (ADS)

    Savytskii, D.; Jain, H.; Tamura, N.; Dierolf, V.

    2016-11-01

    Defying the requirements of translational periodicity in 3D, rotation of the lattice orientation within an otherwise single crystal provides a new form of solid. Such rotating lattice single (RLS) crystals are found, but only as spherulitic grains too small for systematic characterization or practical application. Here we report a novel approach to fabricate RLS crystal lines and 2D layers of unlimited dimensions via a recently discovered solid-to-solid conversion process using a laser to heat a glass to its crystallization temperature but keeping it below the melting temperature. The proof-of-concept including key characteristics of RLS crystals is demonstrated using the example of Sb2S3 crystals within the Sb-S-I model glass system for which the rotation rate depends on the direction of laser scanning relative to the orientation of initially formed seed. Lattice rotation in this new mode of crystal growth occurs upon crystallization through a well-organized dislocation/disclination structure introduced at the glass/crystal interface. Implications of RLS growth on biomineralization and spherulitic crystal growth are noted.

  4. Some Properties Of Synthetic Single Crystal And Thin Film Diamonds

    NASA Astrophysics Data System (ADS)

    Yazu, Shuji; Sato, Shuichi; Fujimori, Naoji

    1989-01-01

    Large synthetic diamond single crystals, in sizes up to 1.4 ct, are produced on 4 commercial basis for some industrial application fields by Sumitomo Electric. The crystals are yellow colored type Ib stones which contain lower amounts of nitrogen (up to about 100 ppm) dispersed through the crystal structure in the form of singly substituting atoms. The impurity controlled type lb crystals have the highest thermal conductivity which is equivalent to that of pure type IIa crystals. Optical and thermal properties of diamond crystals are strongly affected by dispersed impurities. We studied the kinds of dispersed impurities and amounts of those impurity atoms in our synthesized crystals by SIMS. A relation of the thermal conductivities and the nitrogen concentrations of the crystals was examined. The state of nitrogen impurity in the crystals could be transformed by electron irradiation and subsequent high temperature annealing. The reaction rates for the transformation Ib nitrogen to type IaA aggregates and differences in crystal growth sectors have been studied. Vapor phase deposited diamond films are hopeful candidates for optical application of diamond. Preliminary spectroscopic analysis has been done for the free standing polycrystalline films.

  5. Measurement of single crystal surface parameters

    NASA Technical Reports Server (NTRS)

    Swanson, L. W.; Bell, A. E.; Strayer, R. W.

    1972-01-01

    The sticking coefficient and thermal desorption spectra of Cs from the (110) plane of W was investigated. A sticking coefficient of unity for the monolayer region was measured for T 250 K. Several distinct binding states were observed in the thermal desorption spectrum. Work function and electron reflection measurements were made on the (110) and (100) crystal faces of Mo. Both LEED and Auger were used to determine the orientation and cleanliness of the crystal surfaces. The work function values obtained for the (110) and (100) planes of Mo were 4.92 and 4.18 eV respectively.

  6. Growth of single crystals by vapor transport

    NASA Technical Reports Server (NTRS)

    Wiedemeier, H.

    1978-01-01

    The primary objectives of the program were to establish basic vapor transport and crystal growth properties and to determine thermodynamic, kinetic and structural parameters relevant to chemical vapor transport systems for different classes of materials. An important aspect of these studies was the observation of the effects of gravity-caused convection on the mass transport rate and crystal morphology. These objectives were accomplished through extensive vapor transport, thermochemical and structural studies on selected Mn-chalcogenides, II-VI and IV-VI compounds.

  7. High-temperature alloys: Single-crystal performance boost

    NASA Astrophysics Data System (ADS)

    Schütze, Michael

    2016-08-01

    Titanium aluminide alloys are lightweight and have attractive properties for high-temperature applications. A new growth method that enables single-crystal production now boosts their mechanical performance.

  8. Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

    DOEpatents

    Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

    1998-07-07

    A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

  9. Crystal Structure of a Molybdopterin Synthase-Precursor Z Complex: Insight into its Sulfur Transfer Mechanism and Its Role in Molybdenum Cofactor Dificiency

    SciTech Connect

    Daniels,J.; Wuebbens, M.; Rajagopalan, K.; Schindelin, H.

    2008-01-01

    In almost all biological life forms, molybdenum and tungsten are coordinated by molybdopterin (MPT), a tricyclic pyranopterin containing a cis-dithiolene group. Together, the metal and the pterin moiety form the redox reactive molybdenum cofactor (Moco). Mutations in patients with deficiencies in Moco biosynthesis usually occur in the enzymes catalyzing the first and second steps of biosynthesis, leading to the formation of precursor Z and MPT, respectively. The second step is catalyzed by the heterotetrameric MPT synthase protein consisting of two large (MoaE) and two small (MoaD) subunits with the MoaD subunits located at opposite ends of a central MoaE dimer. Previous studies have determined that the conversion of the sulfur- and metal-free precursor Z to MPT by MPT synthase involves the transfer of sulfur atoms from a C-terminal MoaD thiocarboxylate to the C-1' and C-2' positions of precursor Z. Here, we present the crystal structures of non-thiocarboxylated MPT synthase from Staphylococcus aureus in its apo form and in complex with precursor Z. A comparison of the two structures reveals conformational changes in a loop that participates in interactions with precursor Z. In the complex, precursor Z is bound by strictly conserved residues in a pocket at the MoaE dimer interface in close proximity of the C-terminal glycine of MoaD. Biochemical evidence indicates that the first dithiolene sulfur is added at the C-2' position.

  10. Process for Forming a High Temperature Single Crystal Canted Spring

    NASA Technical Reports Server (NTRS)

    DeMange, Jeffrey J (Inventor); Ritzert, Frank J (Inventor); Nathal, Michael V (Inventor); Dunlap, Patrick H (Inventor); Steinetz, Bruce M (Inventor)

    2017-01-01

    A process for forming a high temperature single crystal canted spring is provided. In one embodiment, the process includes fabricating configurations of a rapid prototype spring to fabricate a sacrificial mold pattern to create a ceramic mold and casting a canted coiled spring to form at least one canted coil spring configuration based on the ceramic mold. The high temperature single crystal canted spring is formed from a nickel-based alloy containing rhenium using the at least one coil spring configuration.

  11. Synthesis and Single-Crystal Growth of Ca

    SciTech Connect

    Nakatsuji, Satoru; Maeno, Yoshiteru

    2001-01-01

    For the study of the quasi-two-dimensional Mott transition system Ca{sub 2-x}Sr{sub x}RuO{sub 4}, we have succeeded in synthesizing polycrystalline samples and also growing single crystals by a floating-zone method. Details of the preparations for the entire solution range are described. The structural, transport, and magnetic properties of both polycrystalline and single-crystal samples are fully in agreement.

  12. Inhomogeneities in single crystals of cuprate oxide superconductors

    NASA Technical Reports Server (NTRS)

    Moorjani, K.; Bohandy, J.; Kim, B. F.; Adrian, F. J.

    1991-01-01

    The next stage in the evolution of experimental research on the high temperature superconductors will require high quality single crystals and epitaxially grown crystalline films. However, inhomogeneities and other defects are not uncommon in single crystals of cuprate oxide superconductors, so a corollary requirement will be a reliable method for judging the quality of these materials. The application of magnetically modulated resistance methods in this task is briefly described and illustrated.

  13. Thermal and dielectric studies of nickel malonate dihydrate single crystals

    NASA Astrophysics Data System (ADS)

    Mathew, Varghese; Mathai, K. C.; Mahadeven, C. K.; Abraham, K. E.

    2011-02-01

    Single crystals of nickel malonate dihydrate were grown by the gel technique, employing the single diffusion method. Thermal dehydration of the crystal was investigated by thermogravimetric and differential thermal analyses. The title compound exhibits a steady thermal behaviour at higher temperature range of 350-800 °C. The dielectric properties of the prepared sample were analyzed as a function of frequency in the range of 1 kHz-1 MHz and at temperatures between 40 and 140 °C.

  14. Fatigue damage modeling for coated single crystal superalloys

    NASA Technical Reports Server (NTRS)

    Nissley, David M.

    1988-01-01

    A high temperature, low-cycle fatigue life prediction method for coated single crystal nickel-base superalloys is being developed. The method is being developed for use in predicting crack initiation life of coated single crystal turbine airfoils. Although the models are being developed using coated single crystal PWA 1480, they should be readily adaptable to other coated nickel-base single crystal materials. The coatings choosen for this effort were of two generic types: a low pressure plasma sprayed NiCoCrAlY overlay, designated PWA 286, and an aluminide diffusion, designated PWA 273. In order to predict the useful crack initiation life of airfoils, the constitutive and failure behavior of the coating/substrate combination must be taken into account. Coatings alter the airfoil surface microstructure and are a primary source from which cracks originate. The adopted life prediction approach addresses this complexity by separating the coating and single crystal crack initiation regimes. This provides a flexible means for using different life model formulations for the coating and single crystal materials. At the completion of this program, all constitutive and life model formulations will be available in equation form and as software. The software will use the MARC general purpose finite element code to drive the constitutive models and calculate life parameters.

  15. Blocks and residual stresses in shaped sapphire single crystals

    NASA Astrophysics Data System (ADS)

    Krymov, V. M.; Nosov, Yu. G.; Bakholdin, S. I.; Maslov, V. N.; Shul‧pina, I. L.; Nikolaev, V. I.

    2017-01-01

    The formation of blocks and residual stresses in shaped sapphire crystals grown from the melt by the Stepanov method (EFG) has been studied. The probability of block formation is higher for the growth along the c axis compared to that grown in the a-axis direction. The distribution of residual stress in sapphire crystals of tubular, rectangular and round cross section was measured by the conoscopy method. It was found that the magnitude of the residual stress increases from the center to the periphery of the crystal and reaches up to about 20 MPa. Residual stress tensor components for solid round rod and tubular single crystals were determined by numerical integration.

  16. Elastic bending modulus of single-layer molybdenum disulfide (MoS2): finite thickness effect.

    PubMed

    Jiang, Jin-Wu; Qi, Zenan; Park, Harold S; Rabczuk, Timon

    2013-11-01

    We derive, from an empirical interaction potential, an analytic formula for the elastic bending modulus of single-layer MoS2 (SLMoS2). By using this approach, we do not need to define or estimate a thickness value for SLMoS2, which is important due to the substantial controversy in defining this value for two-dimensional or ultrathin nanostructures such as graphene and nanotubes. The obtained elastic bending modulus of 9.61 eV in SLMoS2 is significantly higher than the bending modulus of 1.4 eV in graphene, and is found to be within the range of values that are obtained using thin shell theory with experimentally obtained values for the elastic constants of SLMoS2. This increase in bending modulus as compared to monolayer graphene is attributed, through our analytic expression, to the finite thickness of SLMoS2. Specifically, while each monolayer of S atoms contributes 1.75 eV to the bending modulus, which is similar to the 1.4 eV bending modulus of monolayer graphene, the additional pairwise and angular interactions between out of plane Mo and S atoms contribute 5.84 eV to the bending modulus of SLMoS2.

  17. Mapping the formation areas of giant molybdenum blue clusters: a spectroscopic study

    SciTech Connect

    Botar, Bogdan; Ellern, Arkady; Kogerler, Paul

    2012-05-18

    The self-assembly of soluble molybdenum blue species from simple molybdate solutions has primarily been associated with giant mixed-valent wheel-shaped cluster anions, derived from the {MoV/VI154/176} archetypes, and a {MoV/VI368} lemon-shaped cluster. The combined use of Raman spectroscopy and kinetic precipitation as self-assembly monitoring techniques and single-crystal X-ray diffraction is key to mapping the realm of molybdenum blue species by establishing spherical {MoV/VI102}-type Keplerates as an important giant molybdenum blue-type species. We additionally rationalize the empirical effect of reducing agent concentration on the formation of all three relevant skeletal types: wheel, lemon and spheres. Whereas both wheels and the lemon-shaped {MoV/VI368} cluster are obtained from weakly reduced molybdenum blue solutions, considerably higher reduced solutions lead to {MoV/VI102}-type Keplerates.

  18. Growth and properties of benzil doped benzimidazole (BMZ) single crystals

    SciTech Connect

    Babu, R. Ramesh; Sukumar, M.; Vasudevan, V.; Shakir, Mohd.; Ramamurthi, K.; Bhagavannarayana, G.

    2010-09-15

    In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.

  19. The optical properties of alkali nitrate single crystals

    NASA Astrophysics Data System (ADS)

    Anan'ev, Vladimir; Miklin, Mikhail

    2000-08-01

    Absorption of non-polarized light by a uniaxial crystal has been studied. The degree of absorption polarization has been calculated as a function of the ratio of optical densities in the region of low and high absorbances. This function is proposed for analysis of the qualitative and quantitative characteristics of uniaxial crystal absorption spectra. Non-polarized light spectra of alkali nitrate single crystals, both pure and doped with thallium, have been studied. It is shown that the absorption band at 300 nm is due to two transitions, whose intensities depend on temperature in various ways. There is a weak band in a short wavelength range of the absorption spectrum of potassium nitrate crystal, whose intensity increases with thallium doping. The band parameters of alkali nitrate single crystals have been calculated. Low-energy transitions in the nitrate ion have been located.

  20. Fatigue Failure Criteria for Single Crystal Nickel Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.

    1999-01-01

    High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine and rocket engine turbopump blades is a pervasive problem. Single crystal turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry and NASA because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the pan geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades is complicated to predict due to the material orthotropy and variations in crystal orientations. A fatigue failure criteria based on the maximum shear stress amplitude [delta t max] on the 30 slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criteria reduces the scatter in uniaxial LCF test data, for four different specimen orientations, for PWA 1484 at 1200 F in air, quite well. A power law curve fit of the failure parameter, delta t max, vs. cycles to failure is presented.

  1. Anisotropy of nickel-base superalloy single crystals

    NASA Technical Reports Server (NTRS)

    Mackay, R. A.; Maier, R. D.; Dreshfield, R. L.

    1980-01-01

    The effects of crystal orientation on the mechanical properties of single crystals of the nickel-based superalloy Mar-M247 are investigated. Tensile tests at temperatures from 23 to 1093 C and stress rupture tests at temperatures from 760 to 1038 C were performed for 52 single crystals at various orientations. During tensile testing between 23 and 760 C, single crystals with high Schmid factors were found to be favorably oriented for slip and to exhibit lower strength and higher ductility than those with low Schmid factors. Crystals which required large rotations to become oriented for cross slip were observed to have the shortest stress rupture lives at 760 C, while those which required little or no rotation had the longest lives. In addition, stereographic triangles obtained for Mar-M247 and Mar-M200 single crystals reveal that crystals with orientations near the -111 had the highest lives, those near the 001 had high lives, and those near the 011 had low lives.

  2. An analytical model for porous single crystals with ellipsoidal voids

    NASA Astrophysics Data System (ADS)

    Mbiakop, A.; Constantinescu, A.; Danas, K.

    2015-11-01

    A rate-(in)dependent constitutive model for porous single crystals with arbitrary crystal anisotropy (e.g., FCC, BCC, HCP, etc.) containing general ellipsoidal voids is developed. The proposed model, denoted as modified variational model (MVAR), is based on the nonlinear variational homogenization method, which makes use of a linear comparison porous material to estimate the response of the nonlinear porous single crystal. Periodic multi-void finite element simulations are used in order to validate the MVAR for a large number of parameters including cubic (FCC, BCC) and hexagonal (HCP) crystal anisotropy, various creep exponents (i.e., nonlinearity), several stress triaxiality ratios, general void shapes and orientations and various porosity levels. The MVAR model, which involves a priori no calibration parameters, is found to be in good agreement with the finite element results for all cases considered in the rate-dependent context. The model is then used in a predictive manner to investigate the complex response of porous single crystals in several cases with strong coupling between the anisotropy of the crystal and the (morphological) anisotropy induced by the shape and orientation of the voids. Finally, a simple way of calibrating the MVAR with just two adjustable parameters is depicted in the rate-independent context so that an excellent agreement with the FE simulation results is obtained. In this last case, this proposed model can be thought as a generalization of the Gurson model in the context of porous single crystals and general ellipsoidal void shapes and orientations.

  3. Cladded single crystal fibers for high power fiber lasers

    NASA Astrophysics Data System (ADS)

    Kim, W.; Shaw, B.; Bayya, S.; Askins, C.; Peele, J.; Rhonehouse, D.; Meyers, J.; Thapa, R.; Gibson, D.; Sanghera, J.

    2016-09-01

    We report on the recent progress in the development of cladded single crystal fibers for high power single frequency lasers. Various rare earth doped single crystal YAG fibers with diameters down to 17 μm with length > 1 m have been successfully drawn using a state-of-the-art Laser Heated Pedestal Growth system. Single and double cladding on rare earth doped YAG fibers have been developed using glasses where optical and physical properties were precisely matched to doped YAG core single crystal fiber. The double clad Yb:YAG fiber structures have dimensions analogous to large mode area (LMA) silica fiber. We also report successful fabrications of all crystalline core/clad fibers where thermal and optical properties are superior over glass cladded YAG fibers. Various fabrication methods, optical characterization and gain measurements on these cladded YAG fibers are reported.

  4. Shock Driven Twinning in Tantalum Single Crystals

    SciTech Connect

    McNaney, J M; HSUING, L M; Barton, N R; Kumar, M

    2009-07-20

    Recovery based observations of high pressure material behavior generated under high explosively driven flyer based loading conditions are reported. Two shock pressures, 25, and 55 GPa and four orientations {l_brace}(100), (110), (111), (123){r_brace} were considered. Recovered material was characterized using electron backscatter diffraction along with a limited amount of transmission electron microscopy to assess the occurrence of twinning under each test condition. Material recovered from 25 GPa had a very small fraction of twinning for the (100), (110), and (111) oriented crystals while a more noticeable fraction of the (123) oriented crystal was twinned. Material recovered from 55 GPa showed little twinning for (100) orientation slightly more for the (111) orientation and a large area fraction for the (123) orientation. The EBSD and TEM observations of the underlying deformation substructure are rationalized by comparing with previous static and dynamic results.

  5. Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, N. K.; Swanson, G.

    2002-01-01

    High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297

  6. Swimming photochromic azobenzene single crystals in triacrylate solution.

    PubMed

    Milam, Kenneth; O'Malley, Garrett; Kim, Namil; Golovaty, Dmitry; Kyu, Thein

    2010-06-17

    Self-motion of a growing single crystal of azobenzene chromophore in triacrylate solution (TA) is investigated in relation to the solid-liquid phase diagram bound by the solidus and liquidus lines. Upon thermal quenching from the isotropic melt to the crystal + liquid gap, various single crystals develop in a manner dependent on concentration and supercooling depth. During the crystal growth, TA solvent is rejected from the growing faceted fronts, enriching with TA in close proximity to the crystal-solution interface. The concentration gradient that formed as the result of TA expulsion induces convective flows in the solution and generates spatial variability of surface tension usually responsible for Marangoni effect. Either or both of these phenomena may have contributed to the observed self-motion including swimming, sinking, and floating of the azobenzene rhomboidal crystal in TA solution. A stationary rhomboidal crystal is also shown to swim upon irradiation with the UV light because of a mechanical torque generated by the trans-cis isomerization. Judging from the sinking or floating behavior of the azobenzene crystal, it may be inferred that the nucleation occurs at the solution-air interface.

  7. Method of making macrocrystalline or single crystal semiconductor material

    NASA Technical Reports Server (NTRS)

    Shlichta, P. J. (Inventor); Holliday, R. J. (Inventor)

    1986-01-01

    A macrocrystalline or single crystal semiconductive material is formed from a primary substrate including a single crystal or several very large crystals of a relatively low melting material. This primary substrate is deposited on a base such as steel or ceramic, and it may be formed from such metals as zinc, cadmium, germanium, aluminum, tin, lead, copper, brass, magnesium silicide, or magnesium stannide. These materials generally have a melting point below about 1000 C and form on the base crystals the size of fingernails or greater. The primary substrate has an epitaxial relationship with a subsequently applied layer of material, and because of this epitaxial relationship, the material deposited on the primary substrate will have essentially the same crystal size as the crystals in the primary substrate. If required, successive layers are formed, each of a material which has an epitaxial relationship with the previously deposited layer, until a layer is formed which has an epitaxial relationship with the semiconductive material. This layer is referred to as the epitaxial substrate, and its crystals serve as sites for the growth of large crystals of semiconductive material. The primary substrate is passivated to remove or otherwise convert it into a stable or nonreactive state prior to deposition of the seconductive material.

  8. Inspection of Single Crystal Aerospace Components with Ultrasonic Arrays

    NASA Astrophysics Data System (ADS)

    Lane, C. J. L.; Dunhill, A.; Drinkwater, B. W.; Wilcox, P. D.

    2010-02-01

    Single crystal metal alloys are used extensively in the manufacture of jet engine components for their excellent mechanical properties at elevated temperatures. The increasing use of these materials and demand for longer operational life and improved reliability motivates the requirement to have capable NDE methods available. Ultrasonic arrays are well established at detecting sub-surface defects however these methods are not currently suitable to the inspection of single crystal components due to their high elastic anisotropy causing directional variation in ultrasonic waves. In this paper a model of wave propagation in anisotropic material is used to correct an ultrasonic imaging algorithm and is applied to single crystal test specimens. The orientation of the crystal in a specimen must be known for this corrected-algorithm; therefore a crystal orientation method is also presented that utilizes surface skimming longitudinal waves under a 2D array. The work detailed in this paper allows an ultrasonic 2D array to measure the orientation of a single crystal material and then perform accurate volumetric imaging to detect and size defects.

  9. Low-cost single-crystal turbine blades, volume 2

    NASA Technical Reports Server (NTRS)

    Strangman, T. E.; Dennis, R. E.; Heath, B. R.

    1984-01-01

    The overall objectives of Project 3 were to develop the exothermic casting process to produce uncooled single-crystal (SC) HP turbine blades in MAR-M 247 and higher strength derivative alloys and to validate the materials process and components through extensive mechanical property testing, rig testing, and 200 hours of endurance engine testing. These Program objectives were achieved. The exothermic casting process was successfully developed into a low-cost nonproperietary method for producing single-crystal castings. Single-crystal MAR-M 247 and two derivatives DS alloys developed during this project, NASAIR 100 and SC Alloy 3, were fully characterized through mechanical property testing. SC MAR-M 247 shows no significant improvement in strength over directionally solidified (DS) MAR-M 247, but the derivative alloys, NASAIR 100 and Alloy 3, show significant tensile and fatigue improvements. Firtree testing, holography, and strain-gauge rig testing were used to determine the effects of the anisotropic characteristics of single-crystal materials. No undesirable characteristics were found. In general, the single-crystal material behaved similarly to DS MAR-M 247. Two complete engine sets of SC HP turbine blades were cast using the exothermic casting process and fully machined. These blades were successfully engine-tested.

  10. Enhancing the Mechanical Properties of Single-Crystal CVD Diamond

    SciTech Connect

    Liang, Q.; Yan, C; Meng, Y; Lai, J; Krasnicki, S; Mao, H; Hemley, R

    2009-01-01

    Approaches for enhancing the strength and toughness of single-crystal diamond produced by chemical vapor deposition (CVD) at high growth rates are described. CVD processes used to grow single-crystal diamond in high density plasmas were modified to incorporate boron and nitrogen. Semi-quantitative studies of mechanical properties were carried out using Vickers indentation techniques. The introduction of boron in single-crystal CVD diamond can significantly enhance the fracture toughness of this material without sacrificing its high hardness ({approx}78 GPa). Growth conditions were varied to investigate its effect on boron incorporation and optical properties by means of photoluminescence, infrared, and ultraviolet-visible absorption spectroscopy. Boron can be readily incorporated into single-crystal diamond by the methods used, but with nitrogen addition, the incorporation of boron was hindered. The spectroscopic measurements indicate that nitrogen and boron coexist in the diamond structure, which helps explain the origin of the enhanced fracture toughness of this material. Further, low pressure/high temperature annealing can enhance the intrinsic hardness of single-crystal CVD diamond by a factor of two without appreciable loss in fracture toughness. This doping and post-growth treatment of diamond may lead to new technological applications that require enhanced mechanical properties of diamond.

  11. Growth of solid solution single crystals

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the presence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized.

  12. Growth of solid solution single crystals

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the prescence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized.

  13. Method for harvesting rare earth barium copper oxide single crystals

    DOEpatents

    Todt, V.R.; Sengupta, S.; Shi, D.

    1996-04-02

    A method of preparing high temperature superconductor single crystals is disclosed. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals of the high temperature superconductor, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals of the high temperature superconductor on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals melted, allowing the wicking away of the peritectic liquid. 2 figs.

  14. Geometric constraints on phase coexistence in vanadium dioxide single crystals

    NASA Astrophysics Data System (ADS)

    McGahan, Christina; Gamage, Sampath; Liang, Jiran; Cross, Brendan; Marvel, Robert E.; Haglund, Richard F.; Abate, Yohannes

    2017-02-01

    The appearance of stripe phases is a characteristic signature of strongly correlated quantum materials, and its origin in phase-changing materials has only recently been recognized as the result of the delicate balance between atomic and mesoscopic materials properties. A vanadium dioxide (VO2) single crystal is one such strongly correlated material with stripe phases. Infrared nano-imaging on low-aspect-ratio, single-crystal VO2 microbeams decorated with resonant plasmonic nanoantennas reveals a novel herringbone pattern of coexisting metallic and insulating domains intercepted and altered by ferroelastic domains, unlike previous reports on high-aspect-ratio VO2 crystals where the coexisting metal/insulator domains appear as alternating stripe phases perpendicular to the growth axis. The metallic domains nucleate below the crystal surface and grow towards the surface with increasing temperature as suggested by the near-field plasmonic response of the gold nanorod antennas.

  15. Single-crystal structure of a covalent organic framework.

    PubMed

    Zhang, Yue-Biao; Su, Jie; Furukawa, Hiroyasu; Yun, Yifeng; Gándara, Felipe; Duong, Adam; Zou, Xiaodong; Yaghi, Omar M

    2013-11-06

    The crystal structure of a new covalent organic framework, termed COF-320, is determined by single-crystal 3D electron diffraction using the rotation electron diffraction (RED) method for data collection. The COF crystals are prepared by an imine condensation of tetra-(4-anilyl)methane and 4,4'-biphenyldialdehyde in 1,4-dioxane at 120 °C to produce a highly porous 9-fold interwoven diamond net. COF-320 exhibits permanent porosity with a Langmuir surface area of 2400 m(2)/g and a methane total uptake of 15.0 wt % (176 cm(3)/cm(3)) at 25 °C and 80 bar. The successful determination of the structure of COF-320 directly from single-crystal samples is an important advance in the development of COF chemistry.

  16. Single-Crystal Structure of a Covalent Organic Framework

    SciTech Connect

    Zhang, YB; Su, J; Furukawa, H; Yun, YF; Gandara, F; Duong, A; Zou, XD; Yaghi, OM

    2013-11-06

    The crystal structure of a new covalent organic framework, termed COF-320, is determined by single-crystal 3D electron diffraction using the rotation electron diffraction (RED) method for data collection. The COF crystals are prepared by an imine condensation of tetra-(4-anilyl)methane and 4,4'-biphenyldialdehyde in 1,4-dioxane at 120 degrees C to produce a highly porous 9-fold interwoven diamond net. COF-320 exhibits permanent porosity with a Langmuir surface area of 2400 m(2)/g and a methane total uptake of 15.0 wt % (176 cm(3)/cm(3)) at 25 degrees C and 80 bar. The successful determination of the structure of COF-320 directly from single-crystal samples is an important advance in the development of COF chemistry.

  17. Studying the magnetic properties of CoSi single crystals

    SciTech Connect

    Narozhnyi, V. N. Krasnorussky, V. N.

    2013-05-15

    The magnetic properties of CoSi single crystals have been measured in a range of temperatures T = 5.5-450 K and magnetic field strengths H {<=} 11 kOe. A comparison of the results for crystals grown in various laboratories allowed the temperature dependence of magnetic susceptibility {chi}(T) = M(T)/H to be determined for a hypothetical 'ideal' (free of magnetic impurities and defects) CoSi crystal. The susceptibility of this ideal crystal in the entire temperature range exhibits a diamagnetic character. The {chi}(T) value significantly increases in absolute value with decreasing temperature and exhibits saturation at the lowest temperatures studied. For real CoSi crystals of four types, paramagnetic contributions to the susceptibility have been evaluated and nonlinear (with respect to the field) contributions to the magnetization have been separated and taken into account in the calculations of {chi}(T).

  18. Growth and characterization of lithium yttrium borate single crystals

    SciTech Connect

    Singh, A. K.; Singh, S. G.; Tyagi, M.; Desai, D. G.; Sen, Shashwati

    2014-04-24

    Single crystals of 0.1% Ce doped Li{sub 6}Y(BO{sub 3}){sub 3} have been grown using the Czochralski technique. The photoluminescence study of these crystals shows a broad emission at ∼ 420 nm corresponding to Ce{sub 3+} emission from 5d→4f energy levels. The decay profile of this emission shows a fast response of ∼ 28 ns which is highly desirable for detector applications.

  19. Isotropic behavior of an anisotropic material: single crystal silicon

    NASA Astrophysics Data System (ADS)

    McCarter, Douglas R.; Paquin, Roger A.

    2013-09-01

    Zero defect single crystal silicon (Single-Crystal Si), with its diamond cubic crystal structure, is completely isotropic in most properties important for advanced aerospace systems. This paper will identify behavior of the three most dominant planes of the Single-Crystal Si cube (110), (100) and (111). For example, thermal and optical properties are completely isotropic for any given plane. The elastic and mechanical properties however are direction dependent. But we show through finite element analysis that in spite of this, near-isotropic behavior can be achieved with component designs that utilize the optimum elastic modulus in directions with the highest loads. Using glass frit bonding to assemble these planes is the only bonding agent that doesn't degrade the performance of Single-Crystal Si. The most significant anisotropic property of Single-Crystal Si is the Young's modulus of elasticity. Literature values vary substantially around a value of 145 GPa. The truth is that while the maximum modulus is 185 GPa, the most useful <110< crystallographic direction has a high 169 GPa, still higher than that of many materials such as aluminum and invar. And since Poisson's ratio in this direction is an extremely low 0.064, distortion in the plane normal to the load is insignificant. While the minimum modulus is 130 GPa, a calculated average value is close to the optimum at approximately 160 GPa. The minimum modulus is therefore almost irrelevant. The (111) plane, referred to as the natural cleave plane survives impact that would overload the (110) and/or (100) plane due to its superior density. While mechanical properties vary from plane to plane each plane is uniform and response is predictable. Understanding the Single-Crystal Si diamond cube provides a design and manufacture path for building lightweight Single-Crystal Si systems with near-isotropic response to loads. It is clear then that near-isotropic elastic behavior is achievable in Single-Crystal Si

  20. Skylab experiments on semiconductors and alkali halides. [single crystal growth

    NASA Technical Reports Server (NTRS)

    Lundquist, C. A.

    1974-01-01

    The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

  1. Lithium niobate single-crystal and photo-functional device

    DOEpatents

    Gopalan, Venkatraman; Mitchell, Terrence E.; Kitamura, Kenji; Furukawa, Yasunori

    2001-01-01

    Provided are lithium niobate single-crystal that requires a low voltage of not larger than 10 kV/nm for its ferroelectric polarization inversion and of which the polarization can be periodically inverted with accuracy even at such a low voltage, and a photo-functional device comprising the crystal. The crystal has a molar fraction of Li.sub.2 O/(Nb.sub.2 O.sub.5 +Li.sub.2 O) of falling between 0.49 and 0.52. The photo-functional device can convert a laser ray being incident thereon.

  2. Single Crystal Fibers of MGO:LiNbO3

    DTIC Science & Technology

    1990-08-07

    Fibers, MgO:LiNbO39 Nonlinear Optics Crystal Growth 19 ABSTRACT (Continue on reverse if necessary and identify by block number) As optical instruments...Significant success has already been achieved at Stanford University in the growth of single crystal fibers of MgO:LiNbO3 as frequency doublers. LaserGenics...preparpd frnm singlye crystal material grown y Crstal Inc We also investigated the post growth anneai to minimize loof Prtc, ;jnon ro\\en loss in the

  3. Low dimensional magnetic solids and single crystal elpasolites: Need for improved crystal growing techniques

    NASA Technical Reports Server (NTRS)

    Good, M. L.; Watkins, S.; Schwartz, R. W.

    1979-01-01

    The need for extensive crystal growing experiments to develop techniques for preparing crystals suitable for magnetic anisotropy measurements and detailed X-ray and neutron diffraction studies is rationalized on the basis of the unique magnetic properties of the materials and their hydrogen bonded structures which have many features in common with metalloenzyme and metalloprotein active sites. Single crystals of the single and mixed lanthanide species are prepared by the Bridgeman technique of gradient solidification of molten samples. The effects of crystal imperfections on the optical properties of these materials are an important part of the projected research. A series of a-amido acid complexes of first row transition metals were prepared which crystallize as infinite linear chains and exhibit low dimensional magnetic ordering (one or two) at temperature below 40 K.

  4. Fabrication and characterization of dielectric strontium titanium oxynitride single crystal

    NASA Astrophysics Data System (ADS)

    Hoshina, Takuya; Sahashi, Akira; Takeda, Hiroaki; Tsurumi, Takaaki

    2015-10-01

    In this paper, we show a fabrication method and the dielectric properties of strontium titanium oxynitride (SrTiO3:N) single crystals. Oxynitride single crystals were prepared by annealing SrTiO3 single crystals in gaseous ammonia. SrTiO3:N was assumed to have the chemical composition SrTiO3-3xN2x, which contained oxygen vacancies. To reduce the number of oxygen vacancies, SrTiO3 crystals co-doped with nitrogen and niobium (SrTiO3:N,Nb) were fabricated. The semiconducting Nb-doped SrTiO3 crystals changed to dielectric N,Nb-codoped SrTiO3 crystals with a resistivity of 6 × 1012 Ω·cm with annealing in gaseous ammonia. XPS measurement indicated that niobium doping was effective for increasing the amount of dopant nitrogen. The dielectric permittivity increased with the amount of dopant nitrogen, indicating the effectivity of nitrogen doping for increasing the dielectric permittivity of perovskite oxides.

  5. Single-Crystal Elasticity of Earth Materials: An Appraisal

    NASA Astrophysics Data System (ADS)

    Duffy, T. S.

    2015-12-01

    The elastic properties of minerals are of central importance for interpreting seismic data for the Earth's crust, mantle, and core. Mineral elasticity data also have more general applications towards understanding equations of state, phase equilibria, interatomic forces, material strength, and phase transitions. The singe-crystal elastic properties are the most generally useful as they provide complete information on the anisotropy of elastic moduli (e.g. Poisson's ratio, Young's modulus), sound velocities, and compressibility. Measurement of the full set of single-crystal elastic properties remains challenging especially for lower symmetry crystals. In this talk, I present an overview of our current understanding of single-crystal elasticity based on a newly constructed database of single-crystal elastic properties. At ambient conditions the full elastic tensor of about 150 minerals have now been measured, along with about another 60 related compounds that are not formally minerals. About two-thirds of the measured minerals are oxides or silicates. A limitation of the existing database is that only about 10% of the measurements are on crystals of monoclinic or triclinic symmetry, while these two systems account for about 40% of known minerals. Additionally, only a smaller subset of minerals have been examined at high pressure or temperature conditions. Several applications of the database will be presented emphasizing trends in elastic anisotropy. The pyroxenes will be used as an illustrative example.

  6. Growth of Solid Solution Single Crystals

    NASA Technical Reports Server (NTRS)

    Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.; Watring, D. A.

    1999-01-01

    The solidification of a solid solution semiconductor, having a wide separation between liquidus and serious has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; mercury cadmium telluride with 80.0 mole percent of HgTe and 84.8 mole percent respectively. These alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed of residual acceleration effects. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system by a previously processed sample, the sample was not received until May 1998, and the preliminary analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. Early results are indicating that the sample may not accomplish the desired objectives. As with the USMP-2 mission, the results of the ground based experiments were compared with the crystal grown in orbit under microgravity conditions. On the earth, it has been demonstrated that the

  7. Effect of Crystal Orientation on Analysis of Single-Crystal, Nickel-Based Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Swanson, G. R.; Arakere, N. K.

    2000-01-01

    High-cycle fatigue-induced failures in turbine and turbopump blades is a pervasive problem. Single-crystal nickel turbine blades are used because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant and complicating factor. A fatigue failure criterion based on the maximum shear stress amplitude on the 24 octahedral and 6 cube slip systems is presented for single-crystal nickel superalloys (FCC crystal). This criterion greatly reduces the scatter in uniaxial fatigue data for PWA 1493 at 1,200 F in air. Additionally, single-crystal turbine blades used in the Space Shuttle main engine high pressure fuel turbopump/alternate turbopump are modeled using a three-dimensional finite element (FE) model. This model accounts for material orthotrophy and crystal orientation. Fatigue life of the blade tip is computed using FE stress results and the failure criterion that was developed. Stress analysis results in the blade attachment region are also presented. Results demonstrate that control of crystallographic orientation has the potential to significantly increase a component's resistance to fatigue crack growth without adding additional weight or cost.

  8. Mechanical properties of hydroxyapatite single crystals from nanoindentation data

    PubMed Central

    Zamiri, A.; De, S.

    2011-01-01

    In this paper we compute elasto-plastic properties of hydroxyapatite single crystals from nanindentation data using a two-step algorithm. In the first step the yield stress is obtained using hardness and Young’s modulus data, followed by the computation of the flow parameters. The computational approach is first validated with data from existing literature. It is observed that hydroxyapatite single crystals exhibit anisotropic mechanical response with a lower yield stress along the [1010] crystallographic direction compared to the [0001] direction. Both work hardening rate and work hardening exponent are found to be higher for indentation along the [0001] crystallographic direction. The stress-strain curves extracted here could be used for developing constitutive models for hydroxyapatite single crystals. PMID:21262492

  9. Surface enhanced raman spectroscopy studies on triglycine sulphate single crystals

    NASA Astrophysics Data System (ADS)

    Parameswari, A.; Mohamed Asath, R.; Premkumar, R.; Milton Franklin Benial, A.

    2017-01-01

    Adsorption characteristics of triglycine sulphate (TGS) on silver (Ag) surface were investigated based on density functional theory calculations and surface enhanced Raman spectroscopy (SERS) technique. The single crystals of TGS were grown by slow evaporation method. Ag nanoparticles (Ag NPs) were prepared by solution combustion method and characterized. The calculated and observed structural parameters of TGS molecule were compared. Raman and SERS spectra for TGS single crystal were studied experimentally and validated theoretically. Frontier molecular orbitals (FMOs) analysis was carried out for TGS and TGS adsorbed on Ag surface. The second harmonic generation measurements confirm the nonlinear optical (NLO) activity of the TGS molecule. SERS spectral analysis reveals that the TGS adsorbed as tilted orientation on the silver surface. The theoretical and experimental results evidence the suitability of the grown TGS single crystal for optoelectronic applications.

  10. The Load Capability of Piezoelectric Single Crystal Actuators

    NASA Technical Reports Server (NTRS)

    Xu, Tian-Bing; Su, Ji; Jiang, Xiaoning; Rehrig, Paul W.; Hackenberger, Wesley S.

    2006-01-01

    Piezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed.

  11. The Load Capability of Piezoelectric Single Crystal Actuators

    NASA Technical Reports Server (NTRS)

    Xu, Tian-Bing; Su, Ji; Jiang, Xiaoning; Rehrig, Paul W.; Hackenberger, Wesley S.

    2007-01-01

    Piezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed.

  12. Single crystal optic elements for helium atom microscopy

    NASA Astrophysics Data System (ADS)

    MacLaren, D. A.; Allison, W.; Holst, B.

    2000-07-01

    Focusing characteristics of asymmetrically bent single crystal mirrors are discussed in the context of fabricating an optic element for an helium atom microscope. We demonstrate the principle that deforming a clamped, elliptical, single crystal under electrostatic pressure can produce submicron focusing of an helium beam. We present a systematic procedure that may be used to fabricate high precision mirrors close to the Cartesian ideal of any chosen optical configuration. In particular, imaging systems with asymmetric mirror profiles are discussed. Results are independent of crystal characteristics and can be adapted to fit a range of experimental geometries. The calculations indicate that mirror-induced aberrations can be eliminated to fourth order by use of a single actuation electrode in an ideal system.

  13. Mechanical properties of hydroxyapatite single crystals from nanoindentation data.

    PubMed

    Zamiri, A; De, S

    2011-02-01

    In this paper we compute elastoplastic properties of hydroxyapatite single crystals from nanoindentation data using a two-step algorithm. In the first step the yield stress is obtained using hardness and Young's modulus data, followed by the computation of the flow parameters. The computational approach is first validated with data from the existing literature. It is observed that hydroxyapatite single crystals exhibit anisotropic mechanical response with a lower yield stress along the [1010] crystallographic direction compared to the [0001] direction. Both work hardening rate and work hardening exponent are found to be higher for indentation along the [0001] crystallographic direction. The stress-strain curves extracted here could be used for developing constitutive models for hydroxyapatite single crystals.

  14. Single Crystal Synthesis and STM Studies of High Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Barrientos, Alfonso

    1997-01-01

    This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

  15. Heterogeneous Monolithic Integration of Single-Crystal Organic Materials.

    PubMed

    Park, Kyung Sun; Baek, Jangmi; Park, Yoonkyung; Lee, Lynn; Hyon, Jinho; Koo Lee, Yong-Eun; Shrestha, Nabeen K; Kang, Youngjong; Sung, Myung Mo

    2017-02-01

    Manufacturing high-performance organic electronic circuits requires the effective heterogeneous integration of different nanoscale organic materials with uniform morphology and high crystallinity in a desired arrangement. In particular, the development of high-performance organic electronic and optoelectronic devices relies on high-quality single crystals that show optimal intrinsic charge-transport properties and electrical performance. Moreover, the heterogeneous integration of organic materials on a single substrate in a monolithic way is highly demanded for the production of fundamental organic electronic components as well as complex integrated circuits. Many of the various methods that have been designed to pattern multiple heterogeneous organic materials on a substrate and the heterogeneous integration of organic single crystals with their crystal growth are described here. Critical issues that have been encountered in the development of high-performance organic integrated electronics are also addressed.

  16. Anisotropy of nickel-base superalloy single crystals

    NASA Technical Reports Server (NTRS)

    Mackay, R. A.; Dreshfield, R. L.; Maier, R. D.

    1980-01-01

    The influence of orientation on the tensile and stress rupture behavior of 52 Mar-M247 single crystals was studied. Tensile tests were performed at temperatures between 23 and 1093 C; stress rupture behavior was examined between 760 and 1038 C. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factor contours for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The tensile properties correlated well with the appropriate Schmid factor contours. The stress rupture lives at lower testing temperatures were greatly influenced by the lattice rotations required to produce cross slip. A unified analysis was attained for the stress rupture life data generated for the Mar-M247 single crystals at 760 and 774 C under a stress of 724 MPa and the data reported for Mar-M200 single crystals tested at 760 C under a stress of 689 MPa. Based on this analysis, the stereographic triangle was divided into several regions which were rank ordered according to stress rupture life for this temperature regime.

  17. Modeling of elastic and plastic waves for HCP single crystals in a 3D formulation based on zinc single crystal

    NASA Astrophysics Data System (ADS)

    Krivosheina, Marina; Kobenko, Sergey; Tuch, Elena; Kozlova, Maria

    2016-11-01

    This paper investigates elastic and plastic waves in HCP single crystals through the numerical simulation of strain processes in anisotropic materials based on a zinc single crystal. Velocity profiles for compression waves in the back surfaces of single-crystal zinc plates with impact loading oriented in 0001 and 10 1 ¯0 are presented in this work as a part of results obtained in numerical simulations. The mathematical model implemented in this study reflects the following characteristics of the mechanical properties inherent in anisotropic (transtropic) materials: varying degree of anisotropy of elastic and plastic properties, which includes reverse anisotropy, dependence of distribution of all types of waves on the velocity orientation, and the anisotropy of compressibility. Another feature of elastic and plastic waves in HCP single crystals is that the shock wave does not split into an elastic precursor and "plastic" compression shock wave, which is inherent in zinc single crystals with loading oriented in 0001. The study compares numerical results obtained in a three-dimensional formulation with the results of velocity profiles from the back surfaces of target plates obtained in real experiments. These results demonstrate that the mathematical model is capable of describing the properties of the above-mentioned anisotropic (transtropic) materials.

  18. Crystal growth and characterization of new semiorganic nonlinear optical single crystals

    NASA Astrophysics Data System (ADS)

    Kulshrestha, Shobha; Shrivastava, A. K.

    2016-05-01

    An organic material of a L-histidine monohydrochloride single crystal was grown in a distilled water solution using the slow evaporation method at 40-45°C. The grown crystal was transparent and colourless, with a size of about 20 × 9 × 5 mm3, obtained within a period of 21 days. The solubility of grown crystals have found out at various temperatures. The UV-visible transmittance studies show that the grown crystals have wide optical transparency in the entire visible region It is observed that the crystal has transparency window from 255nm to 700nm and its energy gap (Eg) found to be is 3.1eV. The grown crystal was subjected to powder X-ray diffraction analysis, confirming that the orthorhombic crystalline nature of the crystal. To identify the surface morphology, the as grown crystal was subjected to FE-SEM technique. The chemical composition of the grown crystal was estimated by Energy dispersive X-ray analysis. The optical behaviour of the grown crystal was analyzed by PL study.

  19. Apparatus And Method For Producing Single Crystal Metallic Objects

    DOEpatents

    Huang, Shyh-Chin; Gigliotti, Jr., Michael Francis X.; Rutkowski, Stephen Francis; Petterson, Roger John; Svec, Paul Steven

    2006-03-14

    A mold is provided for enabling casting of single crystal metallic articles including a part-defining cavity, a sorter passage positioned vertically beneath and in fluid communication with the part-defining cavity, and a seed cavity positioned vertically beneath and in fluid communication with the sorter passage. The sorter passage includes a shape suitable for encouraging a single crystal structure in solidifying molten metal. Additionally, a portion of the mold between the sorter passage and the part-defining cavity includes a notch for facilitating breakage of a cast article proximate the notch during thermal stress build-up, so as to prevent mold breakage or the inclusion of part defects.

  20. Lead pyrovanadate single crystal as a new SRS material

    SciTech Connect

    Basiev, Tasoltan T; Voronko, Yu K; Maslov, Vladislav A; Sobol, A A; Shukshin, V E

    2011-02-28

    Lead pyrovanadate Pb{sub 2}V{sub 2}O{sub 7} single crystals of optical quality suitable for laser experiments are obtained. Vibrational modes are identified based on the analysis of the polarised Raman spectra of the single crystals. The main parameters (width at half maximum, peak and integral intensities) of the spectral lines most promising for SRS conversion in this material are estimated. These parameters are compared with the corresponding parameters of the most frequently used lines of known Raman materials: yttrium and gadolinium vanadates, potassium and lead tungstates, and lead molybdate. (active media)

  1. Current Noise in Sodium Beta Alumina Ceramics and Single Crystals.

    DTIC Science & Technology

    1986-08-01

    AD-Ai7O 412 CURRENT NOISE IN SODIUM BETA ALUMINA CERAMICS AIND t/l SINGLE CRYSTALS(U) UTAH UNIV SALT LAKE CITY DEPT OF PHYSICS J J BROPHY’ 81 AUG 86...ZIP C-0- UNIVERSITY OF UTAH UNIVERSITY OF NEW MEXICO SALT LAKE CITY, UTAH 84112 Bandelier Hall West Albuquerque, NM 87131 go NAME OF FUNDING...bloeS nIumbe Conductivity fluctuations and contact noise observed in ceramic and single crystal silver 811 alumina are very pilar to those in sodium 8

  2. Growth of Solid Solution Single Crystals

    NASA Technical Reports Server (NTRS)

    Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.

    2001-01-01

    The solidification of a solid solution semiconductor, having a wide separation between liquidus and solidus has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; with 80.0 mole percent of HgTe and 84.8 mole percent of HgTe respectively, the remainder being cadmium telluride. Such alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed correlating composition variations to measured residual acceleration. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system, analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. The results indicate that the sample did accomplish the desired objectives.

  3. Insertion of Guest Molecules into a Mixed Ligand Metal-Organic Framework via Single-Crystal-to-Single Crystal Guest Exchange

    DTIC Science & Technology

    2014-07-01

    Insertion of Guest Molecules into a Mixed Ligand Metal−Organic Framework via Single-Crystal-to-Single- Crystal Guest Exchange by Lily Giri...Research Laboratory Aberdeen Proving Ground, MD 21005-5069 ARL-TR-7004 July 2014 Insertion of Guest Molecules into a Mixed Ligand Metal−Organic...Framework via Single-Crystal-to-Single- Crystal Guest Exchange Lily Giri, Rose Pesce-Rodriguez, Shashi P Karna, and Nirupam J Trivedi Weapons

  4. Deformation of ⊥m single quartz crystals

    NASA Astrophysics Data System (ADS)

    Krasner, P.; Holyoke, C. W., III; Kronenberg, A. K.

    2015-12-01

    The rheology of quartz deformed by dislocation creep is essential to understanding the strength of the mid to lower continental crust. Our current understanding of quartz rheology is derived primarily from studies of polycrystalline quartz and little is known about the temperature, strain rate, or water dependence of the individual quartz slip systems. In order to better understand the rheology of quartz slip systems, we have deformed synthetic quartz single crystals with the prism oriented at 45° to the compression direction (⊥m orientation). We converted the gel-type water found in synthetic quartz crystals to free water fluid inclusions, similar to water observed in milky quartz crystals, by annealing the crystals at 900°C/0.1 MPa for 24 hours. The single crystals were deformed at a confining pressure of 1.5 GPa with temperatures of 850 to 1000°C and strain rates of 10-6 to 10-4/s. FTIR measurements of water concentrations in the starting material, annealed synthetic crystals and deformed synthetic quartz crystals indicate that the water concentrations (125-300 H/106Si) are not affected by the annealing process or deformation. However, the spectra in the annealed and deformed samples are similar to those of natural milky quartz rather than those of synthetic quartz. Results of temperature and strain rate stepping experiments indicate that the strength of the crystals decreases with increasing temperature and/or decreasing strain rate. Undulatory extinction is the predominant microstructure observed in deformed samples, which is consistent with deformation by dislocation creep. The strength of the ⊥m oriented quartz crystals deformed in this study with free water is greater than those of the studies of synthetic quartz with gel type water (Linker and Kirby, 1981 and Muto et al., 2011).

  5. Mineral resource of the month: molybdenum

    USGS Publications Warehouse

    Magyar, Michael J.

    2004-01-01

    Molybdenum is a metallic element that is most frequently used in alloy and stainless steels, which together represent the single largest market for molybdenum. Molybdenum has also proven invaluable in carbon steel, cast iron and superalloys. Its alloying versatility is unmatched because its addition enhances material performance under high-stress conditions in expanded temperature ranges and in highly corrosive environments. The metal is also used in catalysts, other chemicals, lubricants and many other applications.

  6. Role of crystal orientation on chemical mechanical polishing of single crystal copper

    NASA Astrophysics Data System (ADS)

    Zhu, Aibin; He, Dayong; Luo, Wencheng; Liu, Yangyang

    2016-11-01

    The material removal mechanism of single crystal copper in chemical mechanical polishing (CMP) has not been intensively investigated. And the role of crystal orientation in CMP of single crystal cooper is not quite clear yet. Quasi-continuum method was adopted in this paper to simulate the process of nano-particles grinding on single crystal copper in CMP process. Three different crystal orientations, i.e. x[100]y[001], x[001]y[110] and x[-211]y[111], were chosen for analysis. The atom displacement diagrams, stress distribution diagrams and load-displacement curves were obtained. After analyzing the deformation mechanism, residual stress of the work piece material and cutting force, results showed that, the crystal orientation of work piece has great influence on the deformation characteristics and surface quality of work piece during polishing. In the A(001)[100] orientation, the residual stress distribution after polishing is deeper, and the stress is larger than that in the B(110)[001] and C(111)[-211] orientations. And the average tangential cutting force in the A(001)[100] orientation is much larger than those in the other two crystal orientation. This research is helpful to revealing the material removal mechanism of CMP process.

  7. Roflumilast - A reversible single-crystal to single-crystal phase transition at 50 °C

    NASA Astrophysics Data System (ADS)

    Viertelhaus, Martin; Holst, Hans Christof; Volz, Jürgen; Hummel, Rolf-Peter

    2013-01-01

    Roflumilast is a selective phosphodiesterase type 4 inhibitor and is marketed under the brand names Daxas®, Daliresp® and Libertec®. A phase transition of the drug substance roflumilast was observed at 50 °C. The low temperature form, the high temperature form and the phase transition were characterised by differential scanning calorimetry, variable temperature powder X-ray diffraction and single crystal X-ray diffraction, Raman spectroscopy and solid state NMR spectroscopy. The phase transition of roflumilast at 50 °C is completely reversible, the high temperature form cannot be stabilised by quench cooling and the phase transition does not influence the quality of the active pharmaceutical ingredient (API) and the drug product. It was observed to be a single crystal to single crystal phase transition.

  8. High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization

    PubMed Central

    Saidaminov, Makhsud I.; Abdelhady, Ahmed L.; Murali, Banavoth; Alarousu, Erkki; Burlakov, Victor M.; Peng, Wei; Dursun, Ibrahim; Wang, Lingfei; He, Yao; Maculan, Giacomo; Goriely, Alain; Wu, Tom; Mohammed, Omar F.; Bakr, Osman M.

    2015-01-01

    Single crystals of methylammonium lead trihalide perovskites (MAPbX3; MA=CH3NH3+, X=Br− or I−) have shown remarkably low trap density and charge transport properties; however, growth of such high-quality semiconductors is a time-consuming process. Here we present a rapid crystal growth process to obtain MAPbX3 single crystals, an order of magnitude faster than previous reports. The process is based on our observation of the substantial decrease of MAPbX3 solubility, in certain solvents, at elevated temperatures. The crystals can be both size- and shape-controlled by manipulating the different crystallization parameters. Despite the rapidity of the method, the grown crystals exhibit transport properties and trap densities comparable to the highest quality MAPbX3 reported to date. The phenomenon of inverse or retrograde solubility and its correlated inverse temperature crystallization strategy present a major step forward for advancing the field on perovskite crystallization. PMID:26145157

  9. Growth and characterization of morpholinium dihydrogenphosphate single crystal

    NASA Astrophysics Data System (ADS)

    Babu, D. Rajan; Arul, H.; Vizhi, R. Ezhil

    2016-10-01

    Morpholinium dihydrogenphosphate (MDP) single crystals were synthesized, and were subsequently grown by controlled evaporation technique at room temperature for nonlinear optical applications. The grown crystal, which belongs to the monoclinic system with the space group P21, was subjected to single crystal X-ray diffraction to confirm the structure. UV-vis-NIR spectroscopy was done on the grown crystal and it showed good optical transparency in the entire visible region with a minimum cut-off wavelength of 289 nm. The optical band gap was computed as a function of photon energy using Tauc's plot. The refractive index of the grown crystal was determined using a Metricon Prism Coupler. The thermogravimetric (TG) and differential thermal analysis (DTA) traces disclosed the thermal stability of the compound. The mechanical strength of the crystal was investigated by a Vickers microhardness tester. Dielectric constant and dielectric loss were calculated and plotted as a function of frequency at different temperatures. The second harmonic conversion efficiency was determined using the Kurtz-Perry powder technique, and the efficiency was found to be 1.2 times greater than that of standard KDP.

  10. Relaxor-PT Single crystals: Observations and Developments

    PubMed Central

    Zhang, Shujun; Shrout, Thomas R.

    2011-01-01

    Relaxor-PT based ferroelectric single crystals Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZNT) and Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) attracted lot of attentions in last decade due to their ultra high electromechanical coupling factors and piezoelectric coefficients. However, owing to a strongly curved morphotropic phase boundary (MPB), the usage temperature of these perovskite single crystals is limited by TRT - the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature TC. Furthermore, the low mechanical quality factors and coercive fields of these crystals, usually being on the order of ~70 and 2–3kV/cm, respectively, restrict their usage in high power applications. Thus, it is desirable to have high performance crystals with high temperature usage range and high power characteristics. In this survey, different binary and ternary crystal systems were explored, with respect to their temperature usage range, general trends of dielectric and piezoelectric properties of relaxor-PT crystal systems were discussed related to their TC/TRT. In addition, two approaches were proposed to improve mechanical Q values, including acceptor dopant strategy, analogous to “hard” polycrystalline ceramics, and anisotropic domain engineering configurations. PMID:20889397

  11. Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Swanson, Gregory

    2000-01-01

    Single crystal nickel base superalloy turbine blades are being utilized in rocket engine turbopumps and turbine engines because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal nickel base turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. High Cycle Fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Blade attachment regions are prone to fretting fatigue failures. Single crystal nickel base superalloy turbine blades are especially prone to fretting damage because the subsurface shear stresses induced by fretting action at the attachment regions can result in crystallographic initiation and crack growth along octahedral planes. Furthermore, crystallographic crack growth on octahedral planes under fretting induced mixed mode loading can be an order of magnitude faster than under pure mode I loading. This paper presents contact stress evaluation in the attachment region for single crystal turbine blades used in the NASA alternate Advanced High Pressure Fuel Turbo Pump (HPFTP/AT) for the Space Shuttle Main Engine (SSME). Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Blades and the attachment region are modeled using a large-scale 3D finite element (FE) model capable of accounting for contact friction, material orthotrophy, and variation in primary and secondary crystal orientation. Contact stress analysis in the blade attachment regions is presented as a function of coefficient of friction and primary and secondary crystal orientation, Stress results are used to discuss fretting fatigue failure analysis of SSME blades. Attachment stresses are seen to reach

  12. Photocatalytic and photoelectrochemical hydrogen production on strontium titanate single crystals

    SciTech Connect

    Wagner, F.T.; Somorjai, G.A.

    1980-01-01

    Sustained photogeneration of hydrogen was observed on metal-free as well as on platinized SrTiO/sub 3/ single crystals illuminated in aqueous alkaline electrolytes or in the presence of electrolyte films. Hydrogen evolution rates increased with electrolyte hydroxide concentration, most strongly at hydroxide concentrations above 5 N. Both stoichiometric and prereduced metal-free crystals were active for hydrogen photoproduction. No activity was observed from crystals in neutral or acidic solutions or in water vapor in the absence of a crust of a basic deliquescent compounds. Metal-free crystals appear to evolve hydrogen via a photocatalytic mechanism in which all chemistry occurs at the illuminated surface. The results allow direct comparison of the photocatalytic and photoelectrochemical processes and have implications for the development of heterogeneous photocatalysis at the gas-solid interface.

  13. Monte Carlo simulations of single crystals from polymer solutions

    NASA Astrophysics Data System (ADS)

    Zhang, Jianing; Muthukumar, M.

    2007-06-01

    A novel "anisotropic aggregation" model is proposed to simulate nucleation and growth of polymer single crystals as functions of temperature and polymer concentration in dilute solutions. Prefolded chains in a dilute solution are assumed to aggregate at a seed nucleus with an anisotropic interaction by a reversible adsorption/desorption mechanism, with temperature, concentration, and seed size being the control variables. The Monte Carlo results of this model resolve the long-standing dilemma regarding the kinetic and thermal roughenings, by producing a rough-flat-rough transition in the crystal morphology with increasing temperature. It is found that the crystal growth rate varies nonlinearly with temperature and concentration without any marked transitions among any regimes of polymer crystallization kinetics. The induction time increases with decreasing the seed nucleus size, increasing temperature, or decreasing concentration. The apparent critical nucleus size is found to increase exponentially with increasing temperature or decreasing concentration, leading to a critical nucleus diagram composed in the temperature-concentration plane with three regions of different nucleation barriers: no growth, nucleation and growth, and spontaneous growth. Melting temperatures as functions of the crystal size, heating rate, and concentration are also reported. The present model, falling in the same category of small molecular crystallization with anisotropic interactions, captures most of the phenomenology of polymer crystallization in dilute solutions.

  14. Single particle detection in CMOS compatible photonic crystal nanobeam cavities.

    PubMed

    Quan, Qimin; Floyd, Daniel L; Burgess, Ian B; Deotare, Parag B; Frank, Ian W; Tang, Sindy K Y; Ilic, Rob; Loncar, Marko

    2013-12-30

    We report the label-free detection of single particles using photonic crystal nanobeam cavities fabricated in silicon-on-insulator platform, and embedded inside microfluidic channels fabricated in poly-dimethylsiloxane (PDMS). Our system operates in the telecommunication wavelength band, thus leveraging the widely available, robust and tunable telecom laser sources. Using this approach, we demonstrated the detection of polystyrene nanoparticles with dimensions down to 12.5nm in radius. Furthermore, binding events of a single streptavidin molecule have been observed.

  15. Single crystal plasticity with bend-twist modes

    NASA Astrophysics Data System (ADS)

    Elkhodary, Khalil I.; Bakr, Mohamed A.

    2015-06-01

    In this work a formulation is proposed and computationally implemented for rate dependent single crystal plasticity, which incorporates plastic bend-twist modes that arise from dislocation density based poly-slip mechanisms. The formulation makes use of higher order continuum theory and may be viewed as a generalized micromechanics model. The formulation is then linked to the burgers and Nye tensors, showing how their material rates are derivable from a newly proposed third-rank tensor Λp, which incorporates a crystallographic description of bend-twist plasticity through selectable slip-system level constitutive laws. A simple three-dimensional explicit finite element implementation is outlined and employed in three simulations: (a) bi-crystal bending; (b) tension on a notched single crystal; and (c) the large compression of a microstructure to induce the plastic buckling of secondary phases. All simulation are transient, for computational expediency. The results shed light on the physics resulting from dynamic inhomogeneous plastic deformation.

  16. Growth, mechanical, thermal and dielectric properties of pure and doped KHP single crystal

    NASA Astrophysics Data System (ADS)

    M, Lakshmipriya.; Babu, D. Rajan; Vizhi, R. Ezhil

    2015-06-01

    L-Arginine doped potassium hydrogen phthalate and L-Histidine doped potassium hydrogen phthalate single crystals were grown by slow evaporation method at room temperature. The grown crystal crystallizes in orthorhombic system which is confirmed by single crystal XRD analysis. The grown crystals are subjected to thermal, mechanical and dielectric analysis.

  17. Area detectors in single-crystal neutron diffraction

    NASA Astrophysics Data System (ADS)

    McIntyre, Garry J.

    2015-12-01

    The introduction of area detectors has brought about a gentle revolution in the routine application of single-crystal neutron diffractometry. Implemented first for macromolecular crystallography, electronic detectors subsequently gradually spread to chemical and physics-oriented crystallography at steady-state sources. The volumetric surveying of reciprocal space implicit in the Laue technique has required area detectors right from the start, whether using film and more recently image plates and CCD-based detectors at reactors, or scintillation detectors at spallation sources. Wide-angle volumetric data collection has extended application of neutron single-crystal diffractometry to chemical structures, sample volumes, and physical phenomena previously deemed impossible. More than 30 of the dedicated single-crystal neutron diffractometers at steady-state reactor and neutron spallation sources worldwide and accessible via peer-review proposal mechanisms are currently equipped with area detectors. Here we review the historical development of the various types of area detectors used for single crystals, discuss experimental aspects peculiar to experiments with such detectors, highlight the scientific fields where the use of area detectors has had a special impact, and forecast future developments in hardware, implementation, and software.

  18. A Study of Single Crystal Fatigue Failure Criteria

    NASA Technical Reports Server (NTRS)

    Sayyah, Tarek; Swanson, Gregory R.; Schonberg, William P.

    2000-01-01

    This paper presents the results of a study whose objective was to study the applicability of different failure equations in modeling low cycle fatigue (LCF) test data for single crystal test specimens. A total of four failure criteria were considered in this study. One of the failure equations was developed by Pratt & Whitney and is based on normal and shear strains on the primary crystallographic slip planes of the single crystal material. Other failure equations considered are based on isotropic criteria. Because these failure equations were originally developed for isotropic materials such as structural steel, they were modified to be applicable to the single crystal slip systems of the LCF specimen material. By observing how closely the various equations were able to reduce the scatter in the LCF test data, the applicability of those equations in modeling the LCF test data was assessed. It is desired to subsequently use the failure equation with the highest correlation in the development of a new single crystal failure criterion for the Alternative Turbopump Development (ATD) for the space shuttle main engine (SSME) High Pressure Fuel Turbopump (HPFTP).

  19. Transverse Mode Multi-Resonant Single Crystal Transducer

    NASA Technical Reports Server (NTRS)

    Snook, Kevin A. (Inventor); Liang, Yu (Inventor); Luo, Jun (Inventor); Hackenberger, Wesley S. (Inventor); Sahul, Raffi (Inventor)

    2015-01-01

    A transducer is disclosed that includes a multiply resonant composite, the composite having a resonator bar of a piezoelectric single crystal configured in a d(sub 32) transverse length-extensional resonance mode having a crystallographic orientation set such that the thickness axis is in the (110) family and resonance direction is the (001) family.

  20. TOPICAL REVIEW: Organic field-effect transistors using single crystals

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tatsuo; Takeya, Jun

    2009-04-01

    Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm2 Vs-1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

  1. Organic field-effect transistors using single crystals.

    PubMed

    Hasegawa, Tatsuo; Takeya, Jun

    2009-04-01

    Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm(2) Vs(-1), achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

  2. Organic field-effect transistors using single crystals

    PubMed Central

    Hasegawa, Tatsuo; Takeya, Jun

    2009-01-01

    Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for ‘plastic electronics’. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20–40 cm2 Vs−1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps. PMID:27877287

  3. Reliability analysis of single crystal NiAl turbine blades

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan; Noebe, Ronald; Wheeler, Donald R.; Holland, Fred; Palko, Joseph; Duffy, Stephen; Wright, P. Kennard

    1995-01-01

    As part of a co-operative agreement with General Electric Aircraft Engines (GEAE), NASA LeRC is modifying and validating the Ceramic Analysis and Reliability Evaluation of Structures algorithm for use in design of components made of high strength NiAl based intermetallic materials. NiAl single crystal alloys are being actively investigated by GEAE as a replacement for Ni-based single crystal superalloys for use in high pressure turbine blades and vanes. The driving force for this research lies in the numerous property advantages offered by NiAl alloys over their superalloy counterparts. These include a reduction of density by as much as a third without significantly sacrificing strength, higher melting point, greater thermal conductivity, better oxidation resistance, and a better response to thermal barrier coatings. The current drawback to high strength NiAl single crystals is their limited ductility. Consequently, significant efforts including the work agreement with GEAE are underway to develop testing and design methodologies for these materials. The approach to validation and component analysis involves the following steps: determination of the statistical nature and source of fracture in a high strength, NiAl single crystal turbine blade material; measurement of the failure strength envelope of the material; coding of statistically based reliability models; verification of the code and model; and modeling of turbine blades and vanes for rig testing.

  4. Unified constitutive model for single crystal deformation behavior with applications

    NASA Technical Reports Server (NTRS)

    Walker, K. P.; Meyer, T. G.; Jordan, E. H.

    1988-01-01

    Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code.

  5. Dynamic actuation of single-crystal diamond nanobeams

    SciTech Connect

    Sohn, Young-Ik; Burek, Michael J.; Lončar, Marko; Kara, Vural; Kearns, Ryan

    2015-12-14

    We show the dielectrophoretic actuation of single-crystal diamond nanomechanical devices. Gradient radio-frequency electromagnetic forces are used to achieve actuation of both cantilever and doubly clamped beam structures, with operation frequencies ranging from a few MHz to ∼50 MHz. Frequency tuning and parametric actuation are also studied.

  6. Some Debye temperatures from single-crystal elastic constant data

    USGS Publications Warehouse

    Robie, R.A.; Edwards, J.L.

    1966-01-01

    The mean velocity of sound has been calculated for 14 crystalline solids by using the best recent values of their single-crystal elastic stiffness constants. These mean sound velocities have been used to obtain the elastic Debye temperatures ??De for these materials. Models of the three wave velocity surfaces for calcite are illustrated. ?? 1966 The American Institute of Physics.

  7. Single crystal ternary oxide ferroelectric integration with Silicon

    NASA Astrophysics Data System (ADS)

    Bakaul, Saidur; Serrao, Claudy; Youun, Long; Khan, Asif; Salahuddin, Sayeef

    2015-03-01

    Integrating single crystal, ternary oxide ferroelectric thin film with Silicon or other arbitrary substrates has been a holy grail for the researchers since the inception of microelectronics industry. The key motivation is that adding ferroelectric materials to existing electronic devices could bring into new functionality, physics and performance improvement such as non-volatility of information, negative capacitance effect and lowering sub-threshold swing of field effect transistor (FET) below 60 mV/decade in FET [Salahuddin, S, Datta, S. Nano Lett. 8, 405(2008)]. However, fabrication of single crystal ferroelectric thin film demands stringent conditions such as lattice matched single crystal substrate and high processing temperature which are incompatible with Silicon. Here we report on successful integration of PbZr0.2Ti0.8O3 in single crystal form with by using a layer transfer method. The lattice structure, surface morphology, piezoelectric coefficient d33, dielectric constant, ferroelectric domain switching and spontaneous and remnant polarization of the transferred PZT are as good as these characteristics of the best PZT films grown by pulsed laser deposition on lattice matched oxide substrates. We also demonstrate Si based, FE gate controlled FET devices.

  8. Low-cost single-crystal turbine blades, volume 1

    NASA Technical Reports Server (NTRS)

    Strangman, T. E.; Heath, B.; Fujii, M.

    1983-01-01

    The exothermic casting process was successfully developed into a low cost nonproprietary method for producing single crystal (SC) castings. Casting yields were lower than expected, on the order of 20 percent, but it is felt that the casting yield could be significantly improved with minor modifications to the process. Single crystal Mar-M 247 and two derivative SC alloys were developed. NASAIR 100 and SC Alloy 3 were fully characterized through mechanical property testing. SC Mar-M 247 shows no significant improvement in strength over directionally solidified (DS) Mar-M 247, but the derivative alloys, NASAIR 100 and Alloy 3, show significant tensile and fatigue improvements. The 1000 hr/238 MPa (20 ksi) stress rupture capability compared to DS Mar-M 247 was improved over 28 C. Firtree testing, holography, and strain gauge rig testing were used to evaluate the effects of the anisotropic characteristics of single crystal materials. In general, the single crystal material behaved similarly to DS Mar-M 247. Two complete engine sets of SC HP turbine blades were cast using the exothermic casting process and fully machined.

  9. Low temperature magnetic transitions of single crystal HoBi

    SciTech Connect

    Fente, A.; Suderow, H.; Vieira, S.; Nemes, N. M.; García-Hernández, M.; Bud'ko, S. L.; Canfield, P. C.

    2013-10-01

    We present resistivity, specific heat and magnetization measurements in high quality single crystals of HoBi, with a residual resistivity ratio of 126. We find, from the temperature and field dependence of the magnetization, an antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields, into a series of up to five metamagnetic phases.

  10. Electronic states of pyrene single crystal and of its single molecule inserted in a molecular vessel of cyclodextrin

    NASA Astrophysics Data System (ADS)

    Takahashi, Nobuaki; Gombojav, Bold; Yoshinari, Takehisa; Nagasaka, Shin-ichiro; Takahashi, Yoshio; Yamamoto, Aishi; Goto, Takenari; Kasuya, Atsuo

    2004-10-01

    Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The absorption spectra of the single crystal have been transformed from the reflection spectra between 2.5 and 6.5 eV at 2, 77 K and room temperature. The dry powder of β-cyclodextrin including pyrene single molecule were prepared in vacuum to investigate the electronic states of the isolated molecule. The absorption spectra of the single molecule show similar spectra to those of the single crystal. The pyrene molecule keeps its electronic character even in the single crystal.

  11. Growth and characterization of terbium fumarate heptahydrate single crystals

    NASA Astrophysics Data System (ADS)

    Want, B.; Shah, M. D.

    2014-03-01

    The growth of terbium fumarate heptahydrate single crystals was achieved by single gel diffusion technique using silica gel as a medium of growth. The effect of various growth parameters on the nucleation rate of these crystals was studied. The crystals were characterized by different physico-chemical techniques of characterization. Powder X-ray diffraction pattern showed that terbium fumarate is a crystalline compound. Fourier transform infrared spectroscopy was performed for the identification of water and other functional groups present in the compound. UV-vis and photoluminescence spectrophotometric experiments were carried out to study the optical properties of the grown crystals. Elemental analysis suggested the chemical formula of the crystals to be Tb2(C4H2O4)3·7H2O. The presence of seven molecules of water was also supported by the thermogravimetric analysis. The hydrated compound was found to be thermally stable upto a temperature of about 110 °C and its anhydrous form up to the temperature of 410 °C. The thermal decomposition of the compound in the nitrogen atmosphere leads to the formation of terbium oxide as the final product. An attempt was made to relate the experimental results with the classical nucleation theory.

  12. Understanding the Cubic Phase Stabilization and Crystallization Kinetics in Mixed Cations and Halides Perovskite Single Crystals.

    PubMed

    Xie, Li-Qiang; Chen, Liang; Nan, Zi-Ang; Lin, Hai-Xin; Wang, Tan; Zhan, Dong-Ping; Yan, Jia-Wei; Mao, Bing-Wei; Tian, Zhong-Qun

    2017-03-08

    The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI3)1-x(MAPbBr3)x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1-0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI3 single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA(+) is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation disorder. Moreover, we find that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase. These findings benefit the understanding of α-phase stabilization behavior, and have led to fabrication of perovskite solar cells with highest efficiency of 19.9% via solvent management.

  13. Microwave Induced Direct Bonding of Single Crystal Silicon Wafers

    NASA Technical Reports Server (NTRS)

    Budraa, N. K.; Jackson, H. W.; Barmatz, M.

    1999-01-01

    We have heated polished doped single-crystal silicon wafers in a single mode microwave cavity to temperatures where surface to surface bonding occurred. The absorption of microwaves and heating of the wafers is attributed to the inclusion of n-type or p-type impurities into these substrates. A cylindrical cavity TM (sub 010) standing wave mode was used to irradiate samples of various geometry's at positions of high magnetic field. This process was conducted in vacuum to exclude plasma effects. This initial study suggests that the inclusion of impurities in single crystal silicon significantly improved its microwave absorption (loss factor) to a point where heating silicon wafers directly can be accomplished in minimal time. Bonding of these substrates, however, occurs only at points of intimate surface to surface contact. The inclusion of a thin metallic layer on the surfaces enhances the bonding process.

  14. Spatially resolved micro-photoluminescence imaging of porphyrin single crystals

    NASA Astrophysics Data System (ADS)

    Marin, Dawn M.; Castaneda, Jose; Kaushal, Meesha; Kaouk, Ghallia; Jones, Daniel S.; Walter, Michael G.

    2016-08-01

    We describe the collection of both time-resolved and steady-state micro-photoluminescence data from solution-grown single crystals of 5,15-bis(4-carbomethoxyphenyl)porphyrin (BCM2PP). Linking molecular orientation and structure with excited-state dynamics is crucial for engineering efficient organic solar cells, light-emitting diodes, and related molecular electronics. Photoluminescence features of single porphyrin crystals were imaged using a laser scanning confocal microscope equipped with time-correlated single photon counting (TCSPC). We show enhanced exciton lifetimes (τs1 = 2.6 ns) and stronger steady-state emission in crystalline BCM2PP samples relative to semicrystalline thin films (τs1 = 1.8 ns).

  15. Differences between individual ZSM-5 crystals in forming hollow single crystals and mesopores during base leaching.

    PubMed

    Fodor, Daniel; Krumeich, Frank; Hauert, Roland; van Bokhoven, Jeroen A

    2015-04-13

    After base treatment of ZSM-5 crystals below 100 nm in size, TEM shows hollow single crystals with a 10 nm shell. SEM images confirm that the shell is well- preserved even after prolonged treatment. Determination of the Si/Al ratios with AAS and XPS in combination with argon sputtering reveals aluminum zoning of the parent zeolite, and the total pore volume increases in the first two hours of base treatment. In corresponding TEM images, the amount of hollow crystals are observed to increase during the first two hours of base treatment, and intact crystals are visible even after 10 h of leaching; these observations indicate different dissolution rates between individual crystals. TEM of large, commercially available ZSM-5 crystals shows inhomogeneous distribution of mesopores among different crystals, which points to the existence of structural differences between individual crystals. Only tetrahedrally coordinated aluminum is detected with (27) Al MAS NMR after the base leaching of nano-sized ZSM-5.

  16. Single crystal growth and anisotropic crystal-fluid interfacial free energy in soft colloidal systems.

    PubMed

    Nguyen, Van Duc; Hu, Zhibing; Schall, Peter

    2011-07-01

    We measure the anisotropy of the crystal-fluid interfacial free energy in soft colloidal systems. A temperature gradient is used to direct crystal nucleation and control the growth of large single crystals in order to achieve well-equilibrated crystal-fluid interfaces. Confocal microscopy is used to follow both the growth process and the equilibrium crystal-fluid interface at the particle scale: heterogeneous crystal nucleation, the advancing interface, and the stationary equilibrium interface. We use the measured growth velocity to determine the chemical potential difference between crystal and fluid phases. Well-equilibrated, large crystal-fluid interfaces are then used to determine the interfacial free energy and its anisotropy directly from thermally excited interface fluctuations. We find that while the measured average interfacial free energy is in good agreement with values found in simulations, the anisotropy is significantly larger than simulation values. Finally, we investigate the effect of impurities on the advancing interface. We determine the critical force needed to overcome impurity particles from the local interface curvature.

  17. Plastic Deformation of O+ Oriented Quartz Single Crystals

    NASA Astrophysics Data System (ADS)

    Poston, E. J.; Holyoke, C. W., III; Kronenberg, A. K.

    2015-12-01

    The strength of wet quartz deforming by dislocation creep significantly influences the strength of mid to lower crust. Dislocation creep of quartz in Earth's crust is dominated by slip on the basal slip system. However, very little is known about the temperature, strain rate, or water fugacity dependence of this slip system. In order to better understand the rheology of the basal slip system, we deformed single crystals of synthetic quartz, with the basal slip system oriented at 45° to the compression direction (O+ orientation). Each core was annealed at 900°C and 1 atm for 24 hours to convert the gel-type water defects found in synthetic quartz into fluid inclusions, like those observed in milky quartz. FTIR analysis indicate that water contents (200-450 H/106Si) were not affected by the annealing process. The annealed single crystals were then deformed in a Griggs piston-cylinder rock deformation apparatus using a solid salt assembly, at temperatures from 800 to 900°C, strain rates from 10-6 to 10-4/s, and a confining pressure of 1.5 GPa. The strength of the quartz crystals increases with faster strain rates and decreases with increasing temperature. During some of the faster strain rate steps at 800°C, the crystals did not deform plastically before the differential stress reached the confining pressure, whereas they deformed at low stresses at 800°C and 10-6/s. The microstructures visible in the deformed samples are consistent with dislocation creep. The samples exhibit undulatory extinction, and show no deformation lamellae or subgrain formation. The strength of synthetic quartz crystals with low water contents deformed in this study is greater than milky quartz single crystals with high water contents deformed at the same conditions in other studies. These results indicate that the strength of basal slip system in quartz is affected by both water content and water fugacity.

  18. Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik C.; Duke, Greg; Battista, Gilda; Swanson, Greg

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.

  19. Mechanism of the emergence of the photo-EMF upon silicon liquid crystal-single crystal contact

    NASA Astrophysics Data System (ADS)

    Budagov, K. M.; Guseinov, A. G.; Pashaev, B. G.

    2017-03-01

    The effect light has on a silicon liquid crystal-single crystal contact at different temperatures of the surface doping of silicon, and when BaTiO3 nanoparticles are added to the composition of a liquid crystal, is studied. The mechanism of the emergence of the photo-EMF in the liquid crystal-silicon structure is explained.

  20. Low Energy Sputter Yields for Diamond, Carbon-Carbon Composite, and Molybdenum Subject to Xenon Ion Nombardment

    NASA Technical Reports Server (NTRS)

    Blandino, J.; Goodwin, D.; Garner, C.

    1999-01-01

    Sputter yields have been measured for polycrystalline diamond, single crystal diamond, a carbon-carbon composite, and molybdenum subject to bombardment with xenon. The tests were performed using a 3 cm Kaufman ion source to produce incident ions with energy in the range of 150 - 750 eV and profilometry based technique to measure the amount of sputtered material.

  1. Scintillation of Un-doped ZnO Single Crystals

    SciTech Connect

    Colosimo, A. M.; Ji, Jianfeng; Stepanov, P. S.; Boatner, L. A.; Selim, F. A.

    2016-01-07

    In this paper, scintillation properties are often studied by photo-luminescence (PL) and scintillation measurements. In this work, we combine X-ray-induced luminescence (XRIL) spectroscopy [Review of Scientific Instruments 83, 103112 (2012)] with PL and standard scintillation measurements to give insight into the scintillation properties of un-doped ZnO single crystals. XRIL revealed that ZnO luminescence proportionally increases with X-ray power and exhibits excellent linearity - indicating the possibility of developing radiation detectors with good energy resolution. Finally, by coupling ZnO crystals to fast photomultiplier tubes and monitoring the anode signal, rise times as fast as 0.9 ns were measured.

  2. Antifreeze glycopeptide adsorption on single crystal ice surfaces using ellipsometry

    PubMed Central

    Wilson, P. W.; Beaglehole, D.; DeVries, A. L.

    1993-01-01

    Antarctic fishes synthesise antifreeze proteins which can effectively inhibit the growth of ice crystals. The mechanism relies on adsorption of these proteins to the ice surface. Ellipsometry has been used to quantify glycopeptide antifreeze adsorption to the basal and prism faces of single ice crystals. The rate of accumulation was determined as a function of time and at concentrations between 0.0005 and 1.2 mg/ml. Estimates of packing density at saturation coverage have been made for the basal and prism faces. PMID:19431902

  3. Dielectric Constant Measurements on Lead Azide Single Crystals

    DTIC Science & Technology

    1980-09-01

    1000 Hz. The dielectric constants of the azides of TI, Na, and K Vere also measured and compared to published values. Calculations takf’ into account ...and W. McCrone , "Lead Azide, Pb(N 3 ) 2 , Aial. Chem. 28, 1791 (1956). 9 5 i:% 8. W.L. Garrett, "The Growth of Large Lead Azide Crystals," Mat. Res...10. Handbook of Chemistry and Physics, The Chemical Rubber Publishing Co., 1963. 11. J.N. Appleton, and J. Sharma, "Growth of Single Crystals of

  4. Heavy ion passive dosimetry with silver halide single crystals

    NASA Technical Reports Server (NTRS)

    Childs, C. B.; Parnell, T. A.

    1972-01-01

    A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

  5. Melting behavior of single two-dimensional crystal

    NASA Astrophysics Data System (ADS)

    Zheng, X. H.; Grieve, R.

    2006-02-01

    In an experimental system millimeter-sized steel balls repel each other through the Coulomb force to imitate a two-dimensional (2D) atomic lattice in a vacuum both topologically and dynamically. Care has been taken to avoid the formation of grain boundaries. This 2D single crystal melts into a liquid via the hexatic state consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young scenario. Initially in the melting process defects of the 2D lattice tend to emerge from the edge of the crystal. These defects are found to be close to the liquid state according to the Lindemann and Born criteria, confirming the idea of edge melting.

  6. A novel tridentate Schiff base dioxo-molybdenum(VI) complex: synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, ¹H NMR and ¹³C NMR spectra.

    PubMed

    Saheb, Vahid; Sheikhshoaie, Iran; Stoeckli-Evans, Helen

    2012-09-01

    A new dioxo-molybdenum(VI) complex [MoO(2)(L)(H(2)O)] has been synthesized, using 5-methoxy 2-[(2-hydroxypropylimino)methyl]phenol as tridentate ONO donor Schiff base ligand (H(2)L) and MoO(2)(acac)(2). The yellow crystals of the compound are used for single-crystal X-ray analysis and measuring Fourier Transform Infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the UV-visible, FTIR, (1)H NMR and (13)C NMR spectra of the compound. Vibrational assignments and analysis of the fundamental modes of the compound are performed. Time-dependent density functional theory (TDDFT) method is used to calculate the electronic transitions of the complex. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR shielding tensors computed at the B3LYP/DGDZVP level of theory is in agreement with experimental (1)H NMR spectra. However, the (13)C NMR shielding tensors computed at the B3LYP level, employing a combined basis set of DGDZVP for Mo and 6-31+G(2df,p) for other atoms, are in better agreement with experimental (13)C NMR spectra. The electronic transitions calculated at the B3LYP/DGDZVP level by using TD-DFT method is in accordance with the observed UV-visible spectrum of the compound.

  7. Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik; Swanson, Gregory R.; Duke, Gregory; Ham-Battista, Gilda

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves

  8. A design for single-polarization single-mode photonic crystal fiber with rectangular lattice

    NASA Astrophysics Data System (ADS)

    Zhang, Wan; Li, Shu-guang; Bao, Ya-jie; Fan, Zhen-kai; An, Guo-wen

    2016-01-01

    A design for single-polarization single-mode photonic crystal fiber with rectangular lattice is proposed in this paper. The proposed fiber is studied by the full vector finite element method with perfectly matched layers. The single-polarization single-mode operation region of the fiber is achieved in a certain wavelength range with low confinement loss include the wavelength of 1.55 μm. The loss of one polarization is 0.124 dB/km at the wavelength of 1.55 μm and the confinement loss of the other one polarization is very high which can not ensure the transmission in the fiber. The single-polarization single-mode photonic crystal fiber is desirable for some polarization-sensitive applications such as high-power fiber lasers, fiber optic gyroscopes, current sensors and optical coherent communication systems.

  9. β-NMR on single-crystal surfaces: Method

    NASA Astrophysics Data System (ADS)

    Widdra, W.; Detje, M.; Ebinger, H.-D.; Jänsch, H. J.; Preyss, W.; Reich, H.; Veith, R.; Fick, D.; Röckelein, M.; Völk, H.-G.

    1995-03-01

    A new and highly sensitive β-NMR method to study adsorbates on single-crystal surfaces is presented. Contrary to conventional NMR, this method combines (via optical pumping) a high, nonthermal polarization of the adsorbed species with a particle counting method. Here, the β-active isotope 8Li is produced in the nuclear reaction D(7Li, 8Li)H using a high-pressure deuterium gas target. The fast 8Li ions are subsequently implanted into a hot graphite block where they thermally diffuse to the surface and desorb. The desorbing thermal velocity 8Li atoms are shaped into an atomic beam. Using a frequency modulated laser beam the atoms are transferred into a single hyperfine state by optical pumping. The so-achieved nuclear polarization of the atoms (before impinging on the single-crystal surface) is approximately 0.8 and can be switched in sign by an adiabatic high-frequency transition. The atoms adsorb on the single-crystal surface and their polarization—either freely decaying on the surface or driven by an external radio-frequency field—is observed via the decay asymmetry of the nuclear β-decay of the 8Li nuclei. This method realizes an effective sensitivity to the active NMR isotope of 5×103 atoms/cm2, which corresponds to a stationary coverage of 10-11 of a monolayer. The typical electron count rate is 400 Hz during β-NMR experiments.

  10. Semiconducting polymer single crystals and devices (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Dong, Huanli

    2016-11-01

    Highly ordered organic semiconductors in solid state with optimal molecular packing are critical to their electrical performance. Single crystals with long-range molecular orders and nearly perfect molecular packing are the best candidates, which already have been verified to exhibit the highest performance whether based on inorganic or small organic materials. However, in comparison, preparing high quality polymer crystals remains a big challenge in polymer science because of the easy entanglements of the long and flexible polymer chains during self-assembly process, which also significantly limits the development of their crystalline polymeric electronic devices. Here we have carried out systematical investigations to prepare high quality semiconducting polymers and high performance semiconducting polymer crystal optoelectronic devices have been successfully fabricated. The semiconducting polymeric devices demonstrate significantly enhanced charge carreir transport compared to their thin films, and the highest carreir mobiltiy could be approcahing 30 cm2 V-1s-1, one of the highest mobiltiy values for polymer semiconductors.

  11. Crystallization of inorganic nonlinear optical zinc di-magnesium chloro sulphate (ZDMCS) single crystal

    NASA Astrophysics Data System (ADS)

    Arivuselvi, R.; Ruban Kumar, A.

    2017-02-01

    The growth of inorganic zinc di-magnesium chloro sulphate (ZDMCS) nonlinear optical material from low temperature evaporation technique at ambient temperature has been reported. The dimension of harvested crystal is 28×10×2 mm3 and is possess rectangular shape morphology. The single crystal X-ray diffraction studies confirmed that the grown crystal belongs to the system of trigonal. The S-Cl stretching vibrations and Mg2+ ions present in the sample were observed by FTIR spectrometer. The cut-off wavelength of the grown crystal is about 203 nm is found by UV-visible absorption spectrum. The nonlinear optical efficiency was determined by powder Kurtz Perry technique. EDAX spectrum confirms the presence of elements within the material. Dielectric nature of the sample was analyzed for the frequency range 50 Hz to 5 MHz at different temperatures. The mechanical behaviour of the title compound was investigated using Vicker's microhardness tester.

  12. Molybdenum, molybdenum oxides, and their electrochemistry.

    PubMed

    Saji, Viswanathan S; Lee, Chi-Woo

    2012-07-01

    The electrochemical behaviors of molybdenum and its oxides, both in bulk and thin film dimensions, are critical because of their widespread applications in steels, electrocatalysts, electrochromic materials, batteries, sensors, and solar cells. An important area of current interest is electrodeposited CIGS-based solar cells where a molybdenum/glass electrode forms the back contact. Surprisingly, the basic electrochemistry of molybdenum and its oxides has not been reviewed with due attention. In this Review, we assess the scattered information. The potential and pH dependent active, passive, and transpassive behaviors of molybdenum in aqueous media are explained. The major surface oxide species observed, reversible redox transitions of the surface oxides, pseudocapacitance and catalytic reduction are discussed along with carefully conducted experimental results on a typical molybdenum glass back contact employed in CIGS-based solar cells. The applications of molybdenum oxides and the electrodeposition of molybdenum are briefly reviewed.

  13. Flux free growth of superconducting FeSe single crystals

    NASA Astrophysics Data System (ADS)

    Maheshwari, P. K.; Joshi, L. M.; Gahtori, Bhasker; Srivastava, A. K.; Gupta, Anurag; Patnaik, S. P.; Awana, V. P. S.

    2016-07-01

    We report flux free growth of superconducting FeSe single crystals by an easy and versatile high temperature melt and slow cooling method for first time. The room temperature x-ray diffraction (XRD) on the surface of the piece of such obtained crystals showed single [101] plane of β-FeSe tetragonal phase. The bulk powder XRD, being obtained by crushing the part of crystal chunk showed majority (˜87%) β-FeSe tetragonal (space group P4/nmm) and minority (˜13%) δ-FeSe hexagonal (space group P63/mmc) crystalline phases. Detailed high resolution transmission electron microscope images along with selected area electron diffraction showed the abundance of both majority β-FeSe and minority δ-FeSe phases. Both transport (ρ-T) and magnetization exhibited superconductivity at below around 10 K. Interestingly, the magnetization signal of these crystals is dominated by the magnetism of minority δ-FeSe magnetic phase, and hence the isothermal magnetization at 4 K was seen to be ferromagnetic like. Transport (ρ-T) measurements under magnetic field showed superconductivity onset at below 12 K, and ρ = 0 (T c) at 9 K. Superconducting transition temperature (T c) decreases with applied field to around 6 K at 7 T, with dT c/dH of ˜0.4 K T-1, giving rise to an H c2(0) value of around 50 , 30 and 20 T for normal resistivity ρ n = 90%, 50% and 10% respectively, which are calculated from conventional one band Werthamer-Helfand-Hohenberg equation. FeSe single crystal activation energy is calculated from thermally activated flux flow model which is found to decreases with field from 12.1 meV for 0.2 T to 3.77 meV for 7 T.

  14. Synthesis of mesoporous zeolite single crystals with cheap porogens

    SciTech Connect

    Tao Haixiang; Li Changlin; Ren Jiawen; Wang Yanqin; Lu Guanzhong

    2011-07-15

    Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, {sup 27}Al magic angle spinning nuclear magnetic resonance ({sup 27}Al MAS NMR), temperature-programmed desorption of ammonia (NH{sub 3}-TPD) and ultraviolet-visible spectroscopy (UV-vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. {sup 27}Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV-vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites. - Graphical abstract: Mesoporous zeolite single crystals were synthesized by using cheap porogens as template. Highlights: > Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals were synthesized. > Soluble starch or sodium carboxymethyl cellulose (CMC) was used as porogens. > The mesoporous zeolites had connected mesopores although closed pores existed. > Higher catalytic activities were obtained.

  15. Single crystal growth, crystal structure characterization and magnetic properties of UCo0.5Sb2

    SciTech Connect

    Bukowski, Z. . E-mail: bukowski@int.pan.wroc.pl; Tran, V.H.; Stepien-Damm, J.; Troc, R.

    2004-11-01

    Single crystals of uranium intermetallic compound UCo0.5Sb2 were grown by means of the antimony-flux technique. The characterization of the samples has been carried out utilizing single crystal X-ray diffraction and magnetization measurements. UCo0.5Sb2 is found to crystallize in the tetragonal HfCuSi2-type structure, space group P4/nmm with Z=2 formula units per cell, and the lattice parameters a=0.4300(1) and c=0.8958(2)nm. The refinement of the occupancy parameters and the energy dispersive X-ray analysis have indicated a distinct deficiency on the cobalt sites. The results of magnetization measurements showed that UCo0.5Sb2 orders ferromagnetically below 65K with a huge magnetocrystalline anisotropy with the c direction being the easy magnetization axis.

  16. A new material for single crystal modulators: BBO

    NASA Astrophysics Data System (ADS)

    Bammer, F.; Schumi, T.; Petkovsek, R.

    2011-06-01

    Single crystal photo-elastic modulators (SCPEM) are based on a single piezo-electric crystal which is electrically excited on a resonance frequency such that the resulting resonant oscillation causes a modulated artificial birefringence due to the photo-elastic effect. Polarized light experience in such a crystal a strong modulation of polarization, which, in connection with a polarizer, can be used for Q-switching of lasers with pulse repetition frequencies in the range of 100- 1000 kHz. A particularly advantageous configuration is possible with crystals from the symmetry class 3m. Besides LiTaO3 and LiNbO3, both already well explored as SCPEM-materials, we introduce now BBO, which offers a very low absorption in the near infrared region and is therefore particularly suited for Q-switching of solid state lasers. We demonstrate first results of such a BBO-modulator with the dimensions 8.6 x 4.05 x 4.5mm in x-, y-, z- direction, which offers a useful resonance and polarization modulation at 131.9 kHz. Since the piezo-electric effect is small, the voltage amplitude for achieving Q-switching for an Nd:YAG-laser is expected to be in the range of 100V. Nevertheless it is a simple and robust device to achieve Q-switching with a high fixed repetition rate for high power solid state lasers.

  17. Plastic strain arrangement in copper single crystals in sliding

    SciTech Connect

    Chumaevskii, Andrey V. Lychagin, Dmitry V.; Tarasov, Sergei Yu.

    2014-11-14

    Deformation of tribologically loaded contact zone is one of the wear mechanisms in spite of the fact that no mass loss may occur during this process. Generation of optimal crystallographic orientations of the grains in a polycrystalline materials (texturing) may cause hardening and reducing the deformation wear. To reveal the orientation dependence of an individual gain and simplify the task we use copper single crystals with the orientations of the compression axis along [111] and [110]. The plastic deformation was investigated by means of optical, scanning electron microscopy and EBSD techniques. It was established that at least four different zones were generated in the course of sliding test, such as non-deformed base metal, plastic deformation layer sliding, crystalline lattice reorientation layer and subsurface grain structure layer. The maximum plastic strain penetration depth was observed on [110]-single crystals. The minimum stability of [111]-crystals with respect to rotation deformation mode as well as activation of shear in the sliding contact plane provide for rotation deformation localization below the worn surface. The high-rate accumulation of misorientations and less strain penetration depth was observed on [111]-crystals as compared to those of [110]-oriented ones.

  18. Mutiple Czochralski growth of silicon crystals from a single crucible

    NASA Technical Reports Server (NTRS)

    Lane, R. L.; Kachare, A. H.

    1980-01-01

    An apparatus for the Czochralski growth of silicon crystals is presented which is capable of producing multiple ingots from a single crucible. The growth chamber features a refillable crucible with a water-cooled, vacuum-tight isolation valve located between the pull chamber and the growth furnace tank which allows the melt crucible to always be at vacuum or low argon pressure when retrieving crystal or introducing recharge polysilicon feed stock. The grower can thus be recharged to obtain 100 kg of silicon crystal ingots from one crucible, and may accommodate crucibles up to 35 cm in diameter. Evaluation of the impurity contents and I-V characteristics of solar cells fabricated from seven ingots grown from two crucibles reveals a small but consistent decrease in cell efficiency from 10.4% to 9.6% from the first to the fourth ingot made in a single run, which is explained by impurity build-up in the residual melt. The crystal grower thus may offer economic benefits through the extension of crucible lifetime and the reduction of furnace downtime.

  19. Properties of salt-grown uranium single crystals.

    SciTech Connect

    Cooley, J. C.; Hanrahan, R. J.; Hults, W. L.; Lashley, J. C.; Manley, M. E.; Mielke, C. H.; Smith, J. L.; Thoma, D. J.; Clark, R. G.; Hamilton, A. R.; O'Brien, J. L.; Gay, E. C.; Lumpkin, N. E.; McPheeters, C. C.; Willit, J.; Schmiedeshoff, G. M.; Touton, S.; Woodfield, B. F.; Lang, B. E.; Boerio-Goates, Juliana

    2001-01-01

    Recently single crystals of {alpha}-uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than those in past work. The resistive signatures of the CDW transitions at 43, 37 and 22 K are obvious to the naked eye. The transition at 22 K exhibits temperature hysteresis that increases with magnetic field. In addition the superconducting transition temperature from resistivity is 820 mK and the critical field is 80 mT. Contrary to earlier work where the Debye temperature ranged from 186 to 218 K, the Debye temperature extracted from the heat capacity is 254 K in good agreement with the predicted value of 250 K. Magnetoresistance, Hall effect and magnetic susceptibility measurements are underway. In time, measurements made on these crystals may help us to understand the origin of superconductivity and its relation to the CDW transitions in pure uranium.

  20. Growth of EuO single crystals at reduced temperatures

    NASA Astrophysics Data System (ADS)

    Ramirez, Daniel C.; Besara, Tiglet; Whalen, Jeffrey B.; Siegrist, Theo

    2017-01-01

    Single crystals of (E u1 -xB ax)O have been grown in a molten barium-magnesium metal flux at temperatures up to 1000 °C, producing single crystals of (E u1 -xB ax)O with barium doping levels ranging from x =0.03 to x =0.25 . Magnetic measurements show that the ferromagnetic Curie temperature TC correlates with the Ba doping levels, and a modified Heisenberg model was used to describe the stoichiometry dependence of TC. Extrapolation of the results indicates that a sample with Ba concentration of x =0.72 should have a TC of 0 K, potentially producing a quantum phase transition in this material.

  1. A piezoelectric single-crystal ultrasonic microactuator for driving optics.

    PubMed

    Guo, Mingsen; Dong, Shuxiang; Ren, Bo; Luo, Haosu

    2011-12-01

    At the millimeter scale, the motions or force out puts generated by conventional piezoelectric, magnetostrictive, photostrictive, or electromagnetic actuators are very limited. Here, we report a piezoelectric ultrasonic microactuator (size: 1.5 × 1.5 × 5 mm, weight: 0.1 g) made of PIN-PMN-PT single crystal. The actuator converts its high-frequency microscopic displacements (nanometer to micrometer scale) into a macro scopic, centimeter-scale linear movement of a slider via frictional force, resulting in a speed up to 50 mm/s and a very high unit volume direct driving force of 26 mN/mm(3) (which is ~100 times higher than a voice coil motor and ~4 times higher than a piezoceramic ultrasonic motor). This work shows the feasibility of using piezoelectric single-crystal-based ultrasonic microactuator for miniature drive of optics in next-generation mobiles and cameras.

  2. Single crystals fiber technology design. Where we are today?

    NASA Astrophysics Data System (ADS)

    Lebbou, K.

    2017-01-01

    Because of its performed mechanical, physical and optical properties, today single crystal fiber shape (SCFS) can be used for a large wide of application. As a function of the needed, it can be used as active or passive element in the component. The potential of single crystal fiber is extremely high. Intensive research has been devoted to design and optimize the technology process, but the increased technological requirements require continuous improvements at all stages of the fiber design: Fiber processing (growth fiber machine), starting raw materials, crucibles, growth direction, thermal gradient, gas atmosphere, fibers polishing, dopants segregation, packaging … This is demonstrated by the successful fiber pulling from the melt of more than 1 m length of sapphire, YAG and LuAG with performed properties.

  3. Flextensional Single Crystal Piezoelectric Actuators for Membrane Deformable Mirrors

    NASA Technical Reports Server (NTRS)

    Jiang, Xiaoning; Sahul, Raffi; Hackenberger, Wesley S.

    2006-01-01

    Large aperture and light weight space telescopes requires adaptive optics with deformable mirrors capable of large amplitude aberration corrections at a broad temperature range for space applications including NASA missions such as SAFIR, TPF, Con-X, etc. The single crystal piezoelectric actuators produced at TRS offer large stroke, low hysteresis, and an excellent cryogenic strain response. Specifically, the recently developed low profile, low voltage flextensional single crystal piezoelectric actuators with dimensions of 18 x 5 x 1 mm showed stroke larger than 95 microns under 300 V. Furthermore, flextensional actuator retained approx. 40-50% of its room temperature strain at liquid Nitrogen environment. In this paper, ATILA FEM design of flextensional actuators, actuator fabrication, and characterization results will be presented for the future work on membrane deformable mirror.

  4. Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Johnson, R D; Young, A P; Schwope, A D

    1956-01-01

    This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

  5. Formation of auxetic surfaces in rhombic syngony single crystals

    NASA Astrophysics Data System (ADS)

    Raransky, Mykola D.; Balazyuk, Vitaliy N.; Gunko, Mikhailo M.; Gevik, Vasyl B.; Struk, Andriy Y.

    2015-11-01

    By using elasticity Cijkl and compliance moduli Sijkl for rhombic syngony single crystals the necessary and sufficient conditions for axial and non-axial auxetic properties occurrence were defined. Indicative surfaces for single crystals Ga, I2, SnSe, Hg2Cl2, CaCO3, AgN3, BaMnF4, C6H6, LiGaO2, Cd(COOH)2, (C6H5)2CO, C6H10(CH2)2, Ca(COOH)2, Na2CoGeO4, NH4B5O8.4H2O auxetic properties were built for the first time. The basic mechanisms and regularities of auxetic surfaces formation were stated. The auxetic oscillation effect in C6H6 was found.

  6. Constitutive modeling of superalloy single crystals with verification testing

    NASA Technical Reports Server (NTRS)

    Jordan, Eric; Walker, Kevin P.

    1985-01-01

    The goal is the development of constitutive equations to describe the elevated temperature stress-strain behavior of single crystal turbine blade alloys. The program includes both the development of a suitable model and verification of the model through elevated temperature-torsion testing. A constitutive model is derived from postulated constitutive behavior on individual crystallographic slip systems. The behavior of the entire single crystal is then arrived at by summing up the slip on all the operative crystallographic slip systems. This type of formulation has a number of important advantages, including the prediction orientation dependence and the ability to directly represent the constitutive behavior in terms which metallurgists use in describing the micromechanisms. Here, the model is briefly described, followed by the experimental set-up and some experimental findings to date.

  7. Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Swanson, Gregory R.

    2000-01-01

    High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

  8. Life Prediction of Turbine Blade Nickel Base Superalloy Single Crystals.

    DTIC Science & Technology

    1986-08-01

    different types of coatings . They are the conventional aluminide coating and the overlay coating with improved temperature capability.5 These coatings ...0.6% with a 2 min. hold in compression. Transverse cracks behaved differently in the aluminide (Codep) coated Ren6 N4+, and an example is given in...PREDICTION OF TURBINE BLADE NICKEL BASE SUPERALLOY SINGLE CRYSTALS N Dr. V. Srinivasan 0 Universal Energy Systems, Inc. 4401 Dayton-Xenia Road Dayton, Ohio

  9. Creep, Plasticity, and Fatigue of Single Crystal Superalloy. (Preprint)

    DTIC Science & Technology

    2011-07-01

    control mode ( 1R ) using servo- hydraulic machines. The test specimen was heated using a low frequency (10 kHz) induction generator. Tests were...1989), Thermomechanical Fatigue , Oxidation, and Creep. Part II. Life Prediction, Metallurgical Transactions A: Physical Metallurgy and Materials...AFRL-RX-WP-TP-2011-4223 CREEP, PLASTICITY, AND FATIGUE OF SINGLE CRYSTAL SUPERALLOY Alexander Staroselsky United Technologies

  10. Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal

    SciTech Connect

    Sankari, R. Siva; Perumal, Rajesh Narayana

    2014-04-24

    Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.

  11. ATMOSPHERIC EFFECTS ON THE PERFORMANCE OF CDZNTE SINGLE CRYSTAL DETECTORS

    SciTech Connect

    Washington, A.; Duff, M.; Teague, L.

    2010-05-12

    The production of high-quality ternary single-crystal materials for radiation detectors has progressed over the past 15 years. One of the more common materials being studied is CdZnTe (CZT), which can be grown using several methods to produce detector-grade materials. The work presented herein examines the effects of environmental conditions including temperature and humidity on detector performance [full-width at half-maximum (FWHM)] using the single pixel with guard detector configuration. The effects of electrical probe placement, reproducibility, and aging are also presented.

  12. Method for thermal processing alumina-enriched spinel single crystals

    DOEpatents

    Jantzen, Carol M.

    1995-01-01

    A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly.

  13. Method for thermal processing alumina-enriched spinel single crystals

    DOEpatents

    Jantzen, C.M.

    1995-05-09

    A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly. 12 figs.

  14. Diamond turning of Si and Ge single crystals

    SciTech Connect

    Blake, P.; Scattergood, R.O.

    1988-12-01

    Single-point diamond turning studies have been completed on Si and Ge crystals. A new process model was developed for diamond turning which is based on a critical depth of cut for plastic flow-to-brittle fracture transitions. This concept, when combined with the actual machining geometry for single-point turning, predicts that {open_quotes}ductile{close_quotes} machining is a combined action of plasticity and fracture. Interrupted cutting experiments also provide a meant to directly measure the critical depth parameter for given machining conditions.

  15. Chiral multichromic single crystals for optical devices (LDRD 99406).

    SciTech Connect

    Kemp, Richard Alan; Felix, Ana M. (University of New Mexico, Albuquerque, NM)

    2006-12-01

    This report summarizes our findings during the study of a novel system that yields multi-colored materials as products. This system is quite unusual as it leads to multi-chromic behavior in single crystals, where one would expect that only a single color would exist. We have speculated that these novel solids might play a role in materials applications such as non-linear optics, liquid crystal displays, piezoelectric devices, and other similar applications. The system examined consisted of a main-group alkyl compound (a p block element such as gallium or aluminum) complexed with various organic di-imines. The di-imines had substituents of two types--either alkyl or aromatic groups attached to the nitrogen atoms. We observed that single crystals, characterized by X-ray crystallography, were obtained in most cases. Our research during January-July, 2006, was geared towards understanding the factors leading to the multi-chromic nature of the complexes. The main possibilities put forth initially considered (a) the chiral nature of the main group metal, (b) possible reduction of the metal to a lower-valent, radical state, (c) the nature of the ligand(s) attached to the main group metal, and (d) possible degradation products of the ligand leading to highly-colored products. The work carried out indicates that the most likely explanation considered involves degradation of the aromatic ligands (a combination of (c) and (d)), as the experiments performed can clearly rule out (a) and (b).

  16. Interfacial dislocation motion and interactions in single-crystal superalloys

    SciTech Connect

    Liu, B.; Raabe, D.; Roters, F.; Arsenlis, A.

    2014-10-01

    The early stage of high-temperature low-stress creep in single-crystal superalloys is characterized by the rapid development of interfacial dislocation networks. Although interfacial motion and dynamic recovery of these dislocation networks have long been expected to control the subsequent creep behavior, direct observation and hence in-depth understanding of such processes has not been achieved. Incorporating recent developments of discrete dislocation dynamics models, we simulate interfacial dislocation motion in the channel structures of single-crystal superalloys, and investigate how interfacial dislocation motion and dynamic recovery are affected by interfacial dislocation interactions and lattice misfit. Different types of dislocation interactions are considered: self, collinear, coplanar, Lomer junction, glissile junction, and Hirth junction. The simulation results show that strong dynamic recovery occurs due to the short-range reactions of collinear annihilation and Lomer junction formation. The misfit stress is found to induce and accelerate dynamic recovery of interfacial dislocation networks involving self-interaction and Hirth junction formation, but slow down the steady interfacial motion of coplanar and glissile junction forming dislocation networks. The insights gained from these simulations on high-temperature low-stress creep of single-crystal superalloys are also discussed.

  17. Spin reorientation transition in dysprosium-samarium orthoferrite single crystals

    NASA Astrophysics Data System (ADS)

    Zhao, Weiyao; Cao, Shixun; Huang, Ruoxiang; Cao, Yiming; Xu, Kai; Kang, Baojuan; Zhang, Jincang; Ren, Wei

    2015-03-01

    We report the control of spin reorientation (SR) transition in perovskite D y1 -xS mxFe O3 , a whole family of single crystals grown by an optical floating zone method from x =0 to 1 with an interval of 0.1. Powder x-ray diffractions and Rietveld refinements indicate that lattice parameters a and c increase linearly with Sm doping concentration, whereas b keeps a constant. Temperature dependence of the magnetizations under zero-field-cooling (ZFC) and field-cooling (FC) processes are studied in detail. We have found a remarkable linear change of SR transition temperature in Sm-rich samples for x >0.2 , which covers an extremely wide temperature range including room temperature. The a -axis magnetization curves under the FC during cooling (FCC) process bifurcate from and then jump back to that of the ZFC and FC warming process in single crystals when x =0.5 -0.9 , suggesting complicated 4 f -3 d electron interactions among D y3 + -S m3 +,D y3 + -F e3 + , and S m3 + -F e3 + sublattices of diverse magnetic configurations. The magnetic properties from the doping effect on SR transition temperature in these single crystals might be useful in the material physics and device design applications.

  18. Single crystal plasticity by modeling dislocation density rate behavior

    SciTech Connect

    Hansen, Benjamin L; Bronkhorst, Curt; Beyerlein, Irene; Cerreta, E. K.; Dennis-Koller, Darcie

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  19. Large-lattice-parameter perovskite single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Uecker, Reinhard; Bertram, Rainer; Brützam, Mario; Galazka, Zbigniew; Gesing, Thorsten M.; Guguschev, Christo; Klimm, Detlef; Klupsch, Michael; Kwasniewski, Albert; Schlom, Darrell G.

    2017-01-01

    The pseudobinary system LaLuO3-LaScO3 was explored in hopes of discovering new perovskite-type substrates with pseudocubic lattice parameters above 4 Å. A complete solid solution of the type (LaLuO3)1-x(LaScO3)x forms between the end members LaLuO3 and LaScO3, enabling large single crystals of (LaLuO3)1-x(LaScO3)x to be grown from the melt. A single crystal with x≈0.34 was demonstrated. Considering the maximum thermal load of the iridium crucibles appropriate for Czochralski growth of this solid solution, the theoretically maximum achievable x-value is 0.67. Based on the phase diagram determined, it is anticipated that single crystals with pseudocubic lattice constants between 4.09 and 4.18 Å can be grown in this system by the Czochralski method.

  20. Physical properties of CuAlO 2 single crystal

    NASA Astrophysics Data System (ADS)

    Brahimi, R.; Bellal, B.; Bessekhouad, Y.; Bouguelia, A.; Trari, M.

    2008-09-01

    CuAlO 2 single crystal elaborated by the flux method is a narrow band gap semiconductor crystallizing in the delafossite structure (SG R3¯m). Oxygen insertion in the layered lattice generates p-type conductivity where most holes are trapped in surface-polaron states. The detailed photoelectrochemical characterization and electrochemical impedance spectroscopy (EIS) have been reported for the first time on the single crystal. The study is confined in the basal plan and reversible oxygen insertion is evidenced from the intensity potential characteristics. The oxide is characterized by an excellent chemical stability; the semi-logarithmic plot gave a corrosion potential of-0.82 V SCE and an exchange current density of 0.022 μA cm -2 in KCl (0.5 M) electrolyte. The capacitance measurement ( C-2- V) shows a linear behavior from which a flat band potential of +0.42 V SCE and a doping density NA of 10 16 cm -3 have been determined. The valence band, located at 5.24 eV (0.51 V SCE) below vacuum, is made up of Cu-3d orbital. The Nyquist plot exhibits a pseudo-semicircle whose center is localized below the real axis with an angle of 20°. This can be attributed to a single relaxation time of the electrical equivalent circuit and a constant phase element (CPE). The absence of straight line indicates that the process is under kinetic control.

  1. Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.

    2003-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.

  2. Single crystalline hollow metal-organic frameworks: a metal-organic polyhedron single crystal as a sacrificial template.

    PubMed

    Kim, Hyehyun; Oh, Minhak; Kim, Dongwook; Park, Jeongin; Seong, Junmo; Kwak, Sang Kyu; Lah, Myoung Soo

    2015-02-28

    Single crystalline hollow metal-organic frameworks (MOFs) with cavity dimensions on the order of several micrometers and hundreds of micrometers were prepared using a metal-organic polyhedron single crystal as a sacrificial hard template. The hollow nature of the MOF crystal was confirmed by scanning electron microscopy of the crystal sliced using a focused ion beam.

  3. Acquisition of Single Crystal Growth and Characterization Equipment

    SciTech Connect

    Maple, M. Brian; Zocco, Diego A.

    2008-12-09

    Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As a result, many user facilities are not being used optimally. The number of proficient crystal growers is too small. In addition, insufficient attention is being paid to the enterprise of finding new and interesting materials, which is the driving force behind much of condensed matter research and, ultimately, technology. While a detailed assessment of this situation is clearly needed, enough evidence of a problem already exists to compel a general consensus that the situation must be addressed promptly. This final report describes the work carried out during the last four years in our group, in which a state-of-the-art single crystal growth and characterization facility was established for the study of novel oxides and intermetallic compounds of rare earth, actinide and transition metal elements. Research emphasis is on the physics of superconducting (SC), magnetic, heavy fermion (HF), non-Fermi liquid (NFL) and other types of strongly correlated electron phenomena in bulk single crystals. Properties of these materials are being studied as a function of concentration of chemical constituents, temperature, pressure, and magnetic field, which provide information about the electronic, lattice, and magnetic excitations at the root of various strongly correlated electron phenomena. Most importantly, the facility makes possible the investigation of material properties that can only be achieved in high quality bulk single crystals, including magnetic and transport phenomena, studies of the effects of disorder, properties in the clean limit, and spectroscopic and scattering

  4. Influence of solvents on the habit modification of alpha lactose monohydrate single crystals

    NASA Astrophysics Data System (ADS)

    Parimaladevi, P.; Srinivasan, K.

    2013-02-01

    Restricted evaporation of solvent method was adopted for the growth of alpha lactose monohydrate single crystals from different solvents. The crystal habits of grown crystals were analysed. The form of crystallization was confirmed by powder x-ray diffraction analysis. Thermal behaviour of the grown crystals was studied by using differential scanning calorimetry.

  5. Advanced piezoelectric single crystal based transducers for naval sonar applications

    NASA Astrophysics Data System (ADS)

    Snook, Kevin A.; Rehrig, Paul W.; Hackenberger, Wesley S.; Jiang, Xiaoning; Meyer, Richard J., Jr.; Markley, Douglas

    2006-03-01

    Transducers incorporating single crystal piezoelectric Pb(Mg 1/3Nb 2/3) x-1Ti xO 3 (PMN-PT) exhibit significant advantages over ceramic piezoelectrics such as PZT, including both high electromechanical coupling (k 33 > 90%) and piezoelectric coefficients (d 33 > 2000 pC/N). Conventional <001> orientation gives inherently larger bandwidth and output power than PZT ceramics, however, the anisotropy of the crystal also allows for tailoring of the performance by orienting the crystal along different crystallographic axes. This attribute combined with composition refinements can be used to improve thermal or mechanical stability, which is important in high power, high duty cycle sonar applications. By utilizing the "31" resonance mode, the high power performance of PMN-PT can be improved over traditional "33" mode single crystal transducers, due to an improved aspect ratio. Utilizing novel geometries, effective piezoelectric constants of -600 pC/N to -1200 pC/N have been measured. The phase transition point induced by temperature, pre-stress or field is close to that in the "33" mode, and since the prestress is applied perpendicular to the poling direction in "31" mode elements, they exhibit lower loss and can therefore be driven harder. The high power characteristics of tonpilz transducers can also be affected by the composition of the PMN-PT crystal. TRS modified the composition of PMN-PT to improve the thermal stability of the material, while keeping the loss as low as possible. Three dimensional modeling shows that the useable bandwidth of these novel compositions nearly equals that of conventional PMN-PT. A decrease in the source level of up to 6 dB was calculated, which can be compensated for by the higher drive voltages possible.

  6. Laser generation in opal-like single-crystal and heterostructure photonic crystals

    NASA Astrophysics Data System (ADS)

    Kuchyanov, A. S.; Plekhanov, A. I.

    2016-11-01

    This study describes the laser generation of a 6Zh rhodamine in artificial opals representing single-crystal and heterostructure films. The spectral and angular properties of emission and the threshold characteristics of generation are investigated. In the case where the 6Zh rhodamine was in a bulk opal, the so-called random laser generation was observed. In contrast to this, the laser generation caused by a distributed feedback inside the structure of the photonic bandgap was observed in photonic-crystal opal films.

  7. Standard Reference Material (SRM 1990) For Single Crystal Diffractometer Alignment

    PubMed Central

    Wong-Ng, W.; Siegrist, T.; DeTitta, G. T.; Finger, L. W.; Evans, H. T.; Gabe, E. J.; Enright, G. D.; Armstrong, J. T.; Levenson, M.; Cook, L. P.; Hubbard, C. R.

    2001-01-01

    An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material® for single crystal diffractometer alignment. This SRM is a set of ≈3500 units of Cr-doped Al2O3, or ruby spheres [(0.420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals: the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 ű0.0062 Å, and c=12.9979 ű0.020 Å (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Hägg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies– are rhombohedral, with space group R3¯c. The certified mean unit cell parameters are a=4.76080±0.00029 Å, and c=12.99568 ű0.00087 Å (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Hägg transmission measurements on five samples of powdered rubies (a=4.7610 ű0.0013 Å, and c = 12

  8. Standard Reference Material (SRM 1990) For Single Crystal Diffractometer Alignment.

    PubMed

    Wong-Ng, W; Siegrist, T; DeTitta, G T; Finger, L W; Evans, H T; Gabe, E J; Enright, G D; Armstrong, J T; Levenson, M; Cook, L P; Hubbard, C R

    2001-01-01

    An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material(®) for single crystal diffractometer alignment. This SRM is a set of ≈3500 units of Cr-doped Al2O3, or ruby spheres [(0.420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals: the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 ű0.0062 Å, and c=12.9979 ű0.020 Å (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Hägg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies- are rhombohedral, with space group [Formula: see text]. The certified mean unit cell parameters are a=4.76080±0.00029 Å, and c=12.99568 ű0.00087 Å (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Hägg transmission measurements on five samples of powdered rubies (a=4.7610 ű0.0013

  9. Standard Reference Material (SRM 1990) for Single Crystal Diffractometer Alignment

    USGS Publications Warehouse

    Wong-Ng, W.; Siegrist, T.; DeTitta, G.T.; Finger, L.W.; Evans, H.T.; Gabe, E.J.; Enright, G.D.; Armstrong, J.T.; Levenson, M.; Cook, L.P.; Hubbard, C.R.

    2001-01-01

    An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material?? for single crystal diffractometer alignment. This SRM is a set of ???3500 units of Cr-doped Al2O3, or ruby spheres [(0 420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals' the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 A?? ?? 0.0062 A??, and c=12.9979 A?? ?? 0.020 A?? (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Ha??gg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies_ are rhombohedral, with space group R3c. The certified mean unit cell parameters are a=4.76080 ?? 0.00029 A??, and c=12 99568 A?? ?? 0.00087 A?? (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Ha??gg transmission measurements on five samples of powdered rubies (a=4.7610 A?? ?? 0

  10. Spectroscopic characterization of YAG and Nd:YAG single crystals

    NASA Astrophysics Data System (ADS)

    Kostić, S.; Lazarević, Z.; Romčević, M.; Radojević, V.; Milutinović, A.; Stanišić, G.; Gilić, M.

    2014-09-01

    In this paper, we used the Czochralski method to obtain good quality yttrium aluminium garnet (YAG, Y3Al5O12) and yttrium aluminium garnet doped with neodymium (Nd:YAG) crystals. The investigations were based on the growth mechanisms and the shape of the liquid/solid interface crystallization front on the crystal properties and incorporation of Nd3+ ions. The obtained single YAG and Nd:YAG crystals were studied by use of x-ray diffraction, Raman and IR spectroscopy. There are strong metal oxygen vibrations in the region of 650-800 cm-1 which are characteristics of Al-O bond: peaks at 784/854, 719/763 and 691/707 cm-1 correspond to asymmetric stretching vibrations in tetrahedral arrangement. Peaks at 566/582, 510/547 and 477/505 cm-1 are asymmetric stretching vibrations and 453/483 cm-1 is the symmetric vibration of the Al-O bond in octahedral arrangements of the garnet structure. Lower energy peaks correspond to translation and vibration of cations in different coordinations—tetrahedral, octahedral and dodecahedral in the case of the lowest modes.

  11. Employing a cylindrical single crystal in gas-surface dynamics.

    PubMed

    Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W; Juurlink, Ludo B F

    2012-03-21

    We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.

  12. Large pyramid shaped single crystals of BiFeO{sub 3} by solvothermal synthesis method

    SciTech Connect

    Sornadurai, D.; Ravindran, T. R.; Paul, V. Thomas; Sastry, V. Sankara

    2012-06-05

    Synthesis parameters are optimized in order to grow single crystals of multiferroic BiFeO{sub 3}. 2 to 3 mm size pyramid (tetrahedron) shaped single crystals were successfully obtained by solvothermal method. Scanning electron microscopy with EDAX confirmed the phase formation. Raman scattering spectra of bulk BiFeO3 single crystals have been measured which match well with reported spectra.

  13. Large pyramid shaped single crystals of BiFeO3 by solvothermal synthesis method

    NASA Astrophysics Data System (ADS)

    Sornadurai, D.; Ravindran, T. R.; Paul, V. Thomas; Sastry, V. Sankara

    2012-06-01

    Synthesis parameters are optimized in order to grow single crystals of multiferroic BiFeO3. 2 to 3 mm size pyramid (tetrahedron) shaped single crystals were successfully obtained by solvothermal method. Scanning electron microscopy with EDAX confirmed the phase formation. Raman scattering spectra of bulk BiFeO3 single crystals have been measured which match well with reported spectra.

  14. Room-Temperature Tensile Behavior of Oriented Tungsten Single Crystals with Rhenium in Dilute Solid Solution

    DTIC Science & Technology

    1966-01-01

    SINGLE CRYSTALS WITH RHENIUM IN DILUTE SOLID SOLUTION Sby M. Garfinkle Lewis Research Center Cleveland, Ohio 20060516196 NATIONAL AERONAUTICS AND...WITH RHENIUM IN DILUTE SOLID SOLUTION By M. Garfinkle Lewis Research Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by...ORIENTED TUNGSTEN SINGLE CRYSTALS WITH RHENIUM IN DILUTE SOLID SOLUTION * by M. Garfinkle Lewis Research Center SUMMARY Tungsten single crystals

  15. Magnesium single crystals for biomedical applications grown in vertical Bridgman apparatus

    NASA Astrophysics Data System (ADS)

    Salunke, Pravahan; Joshi, Madhura; Chaswal, Vibhor; Zhang, Guangqi; Rosenbaum, Leonard A.; Dowling, Kevin; Decker, Paul; Shanov, Vesselin

    2016-10-01

    This paper describes successful efforts to design, build, test, and utilize a single crystal apparatus using the Bridgman approach for directional solidification. The created instrument has been successfully tested to grow magnesium single crystals from melt. Preliminary mechanical tests carried out on these single crystals indicate unique and promising properties, which can be harnessed for biomedical applications.

  16. Growth of high quality bulk size single crystals of inverted solubility lithium sulphate monohydrate

    SciTech Connect

    Silambarasan, A.; Rajesh, P. Ramasamy, P.

    2015-06-24

    The paper summarizes the processes of growing large lithium sulfate monohydrate (LSMH) single crystals. We have established a procedure to grow high quality bulk size single crystals of inverted solubility LSMH by a newly developed unidirectional crystallization technique called the Sankeranarayenan - Ramasamy (SR) method. The convective flow of crystal growth processes from solution and the conditions of growing crystals of various aspects were discussed. Good quality LSMH single crystal is grown of the size 20 mmX80 mm without cracks, localized-defects and inclusions. The as-grown crystals are suitable for piezoelectric and nonlinear optical applications.

  17. ESR Study on Irradiated Ascorbic Acid Single Crystal

    NASA Astrophysics Data System (ADS)

    Tuner, H.; Korkmaz, M.

    2007-04-01

    Food irradiation is a ``cold'' process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. The small temperature increase, absence of residue and effectiveness of treatment of pre-packed food are the main advantages. In food industry, ascorbic acid and its derivatives are frequently used as antioxidant agents. However, irradiation is expected to produces changes in the molecules of food components and of course in the molecules of the agents added as preservation agents such as ascorbic acid. These changes in the molecular structures could cause decreases in the antioxidant actions of these agents. Therefore, the radiation resistance of these agents must be known to determine the amount of radiation dose to be delivered. Electron spin resonance (ESR) is one of the leading methods for identification of intermediates produced after irradiation. ESR spectrum of irradiated solid powder of ascorbic acid is fairly complex and determinations of involved radical species are difficult. In the present work, single crystals of ascorbic acid irradiated by gamma radiation are used to determine molecular structures of radiation induced radicalic species and four radicalic species related in pair with P21 crystal symmetry are found to be responsible from experimental ESR spectrum of gamma irradiated single crystal of ascorbic acid.

  18. Strength anomaly in B2 FeAl single crystals

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H.; Matsumoto, N.

    1994-12-31

    Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). The orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.

  19. ESR Study on Irradiated Ascorbic Acid Single Crystal

    SciTech Connect

    Tuner, H.; Korkmaz, M.

    2007-04-23

    Food irradiation is a 'cold' process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. The small temperature increase, absence of residue and effectiveness of treatment of pre-packed food are the main advantages. In food industry, ascorbic acid and its derivatives are frequently used as antioxidant agents. However, irradiation is expected to produces changes in the molecules of food components and of course in the molecules of the agents added as preservation agents such as ascorbic acid. These changes in the molecular structures could cause decreases in the antioxidant actions of these agents. Therefore, the radiation resistance of these agents must be known to determine the amount of radiation dose to be delivered. Electron spin resonance (ESR) is one of the leading methods for identification of intermediates produced after irradiation. ESR spectrum of irradiated solid powder of ascorbic acid is fairly complex and determinations of involved radical species are difficult. In the present work, single crystals of ascorbic acid irradiated by gamma radiation are used to determine molecular structures of radiation induced radicalic species and four radicalic species related in pair with P21 crystal symmetry are found to be responsible from experimental ESR spectrum of gamma irradiated single crystal of ascorbic acid.

  20. Structural peculiarities of single crystal diamond needles of nanometer thickness

    NASA Astrophysics Data System (ADS)

    Orekhov, Andrey S.; Tuyakova, Feruza T.; Obraztsova, Ekaterina A.; Loginov, Artem B.; Chuvilin, Andrey L.; Obraztsov, Alexander N.

    2016-11-01

    Diamond is attractive for various applications due to its unique mechanical and optical properties. In particular, single crystal diamond needles with high aspect ratios and sharp apexes of nanometer size are demanded for different types of optical sensors including optically sensing tip probes for scanning microscopy. This paper reports on electron microscopy and Raman spectroscopy characterization of the diamond needles having geometrically perfect pyramidal shapes with rectangular atomically flat bases with (001) crystallography orientation, 2-200 nm sharp apexes, and with lengths from about 10-160 μm. The needles were produced by selective oxidation of (001) textured polycrystalline diamond films grown by chemical vapor deposition. Here we study the types and distribution of defects inside and on the surface of the single crystal diamond needles. We show that sp3 type point defects are incorporated into the volume of the diamond crystal during growth, while the surface of the lateral facets is enriched by multiple extended defects. Nitrogen addition to the reaction mixture results in increase of the growth rate on {001} facets correlated with the rise in the concentration of sp3 type defects.

  1. Phase transitions in potassium ammonium dihydrogen phosphate single crystals

    NASA Astrophysics Data System (ADS)

    Bromberek, Marek

    An apparatus for growing single crystals from aqueous solution by the slow evaporation method was constructed. Mixed crystals of K1-x(NH 4)xH2PO4 (KADP) with (NH4)H 2PO4 (ADP) fractions of 0.021 and 0.12 were successfully grown. Their composition was determined by means of the x-ray powder diffraction method. This analysis also suggests that those crystals are a mixture of two phases even at room temperature. The details of the structure of the additional phase could not be determined. The dielectric constant epsilon of the mixed crystals as well as pure KH2PO4 (KDP) was measured along the polar axis in the temperature range from 20 K to 300 K. The frequency range of the applied electric field was from 100 Hz to 10 MHz. The data were analyzed by means of the standard Landau theory of phase transitions with coupling terms reflecting the interaction between the electric and elastic degrees of freedom. The temperature dependence of epsilon follows a typical Curie-Weiss behavior in the range of approximately 30 K aboveTc for all crystals studied. The value of the critical temperature decreases with increasing ammonium ion content in agreement with previously published results. The analysis of the frequency dependence of the dielectric susceptibility clearly indicates the existence of two dispersion processes: resonant and relaxational. The former is attributed to the piezoelectric activity of all the crystals studied. The latter is the result of the response of the permanent dipole moments present in ferroelectric crystals to the applied electric field. In the case of mixed crystals the relaxational dispersion is characterized by a distribution of relaxation times. Its mean relaxation time as well as its width increases with decreasing T. This is a typical behavior for mixed crystals for which the two end members of the solid solution in their pure form undergo ferroelectric and antiferroelectric phase transitions, respectively. This behavior is a result of competing

  2. Physical properties of stoichiometric GdN single crystals

    NASA Astrophysics Data System (ADS)

    Wachter, P.

    2012-01-01

    The preparation and definition of stoichiometric large (3-5 mm edge length) single crystals of GdN are described. The Hall effect and the electrical conductivity were found to be metallic. The optical reflectivity between 30 meV and 13 eV has been measured and the dielectric functions have been obtained. A plasma edge in the infrared region confirmed the metallic character. A shift of this plasma edge with temperature through the magnetic ordering temperature has been observed as a new effect. The band structure is discussed. A high sensitive SQUID confirmed that the crystals are antiferromagnets in low magnetic fields, but turn ferromagnetic in larger fields. The theoretical exchange interaction is derived.

  3. Drift mobility of holes in phenanthrene single crystals

    NASA Technical Reports Server (NTRS)

    Sonnonstine, T. J.; Hermann, A. M.

    1974-01-01

    The temperature dependence of drift mobilities of holes in single crystals of phenanthrene was measured in the range from 203 to 353 K in three crystallographic directions. Below the anomaly temperature of 72 C, the mobility temperature dependences are consistent with the Munn and Siebrand slow-phonon hopping process in the b direction and the Munn and Siebrand slow-phonon coherent mode in the a and c prime directions. The drift mobility temperature dependences in crystals that have been cooled through the anomaly temperature in the presence of illumination and an electric field are consistent with the model of Spielberg et al. (1971), in which the hindered vibration of the 4,5 hydrogens introduces a new degree of freedom above 72 C.

  4. Crystal oscillators using negative voltage gain, single pole response amplifiers

    NASA Technical Reports Server (NTRS)

    Kleinberg, Leonard L. (Inventor)

    1989-01-01

    A simple and inexpensive crystal oscillator is provided which employs negative voltage gain, single pole response amplifiers. The amplifiers may include such configurations as gate inverters, operational amplifiers and conventional bipolar transistor amplifiers, all of which operate at a frequency which is on the roll-off portion of their gain versus frequency curve. Several amplifier feedback circuit variations are employed to set desired bias levels and to allow the oscillator to operate at the crystal's fundamental frequency or at an overtone of the fundamental frequency. The oscillator is made less expensive than comparable oscillators by employing relatively low frequency amplifiers and operating them at roll-off, at frequencies beyond which they are customarily used. Simplicity is provided because operation at roll-off eliminates components ordinarily required in similar circuits to provide sufficient phase-shift in the feedback circuitry for oscillation to occur.

  5. Rolling-contact deformation of MgO single crystals

    NASA Technical Reports Server (NTRS)

    Dufrane, K. F.; Glaeser, W. A.

    1976-01-01

    Magnesium oxide single crystals were used as a model bearing material and deformed by rolling contact with a steel ball 0.64 cm in diameter. A dependence of depth of slip on rolling velocity which persisted with increasing numbers of rolling-contact cycles was discovered. The track width, track hardness and dislocation interactions as observed by transmission electron microscopy all increased in a consistent manner with increasing cycles. The rolling-contact state of stress produces a high density of dislocations in a localized zone. Dislocation interaction in this zone produces cleavage-type cracks after a large number of rolling-contact cycles. The orientation of the crystal influences the character of dislocation accumulation.

  6. Substrate Orientation and Catalysis at the Molybdenum Site in Xanthine Oxidase CRYSTAL STRUCTURES IN COMPLEX WITH XANTHINE AND LUMAZINE

    SciTech Connect

    Pauff, James M.; Cao, Hongnan; Hille, Russ

    2010-01-12

    Xanthine oxidoreductase is a ubiquitous cytoplasmic protein that catalyzes the final two steps in purine catabolism. We have previously investigated the catalytic mechanism of the enzyme by rapid reaction kinetics and x-ray crystallography using the poor substrate 2-hydroxy-6-methylpurine, focusing our attention on the orientation of substrate in the active site and the role of Arg-880 in catalysis. Here we report additional crystal structures of as-isolated, functional xanthine oxidase in the course of reaction with the pterin substrate lumazine at 2.2 {angstrom} resolution and of the nonfunctional desulfo form of the enzyme in complex with xanthine at 2.6 {angstrom} resolution. In both cases the orientation of substrate is such that the pyrimidine subnucleus is oriented opposite to that seen with the slow substrate 2-hydroxy-6-methylpurine. The mechanistic implications as to how the ensemble of active site functional groups in the active site work to accelerate reaction rate are discussed.

  7. Crystal growth and anisotropy of high temperature thermoelectric properties of yttrium borosilicide single crystals

    SciTech Connect

    Hossain, M. Anwar; Tanaka, Isao; Tanaka, Takaho; Khan, A. Ullah; Mori, Takao

    2016-01-15

    We studied thermoelectric properties of YB{sub 41}Si{sub 1.3} single crystals grown by the floating zone method. The composition of the grown crystal was confirmed by electron probe micro-analysis. We have determined the growth direction for the first time for these borosilicides, and discovered relatively large anisotropy in electrical properties. We measured the electrical resistivity and Seebeck coefficient along [510] (the growth direction) and [052] directions and we found that this crystal exhibits strong electrical anisotropy with a maximum of more than 8 times. An interesting layered structural feature is revealed along [510] with dense boron cluster layers and yttrium layers, with conductivity enhanced along this direction. We obtained 3.6 times higher power factor along [510] compared to that along [052]. Although the ZT of the present system is low, anisotropy in the thermoelectric properties of a boride was reported for the first time, and can be a clue in developing other boride systems also. - Graphical abstract: The growth direction ([510]) was determined for the first time in YB{sub 41}Si{sub 1.3} single crystals and revealed an interesting layered feature of boron clusters and metal atoms, along which the electrical conductivity and thermoelectric power factor was strongly enhanced. - Highlights: • We have grown YB{sub 41}Si{sub 1.3} single crystals by the floating zone method. • Growth direction of [510] determined for first time in REB{sub 41}Si{sub 1.2}. • Electrical resistivity was strongly anisotropic with possible enhancement along metal layers. • The obtained power factor along [510] is 3.6 times higher than that along [052].

  8. Display projector technology by way of single crystal faceplate technology

    NASA Astrophysics Data System (ADS)

    Tucker, A.; Kindl, H. J.

    1993-09-01

    Three single crystal faceplates were to be integrated into Cathode Ray Tube (CRT) envelopes with the intent of evaluating the light output from Ce:YAG (Green), modified Ce:GD, YAG (Orange), and CE:BEL (Blue). These CRT's were to be mounted in the projection test bed developed under Contract N61339-90-C-0047 and furnished G.F.P. to Trident International, Inc. for use and delivery during this contract. Three 3 inch diameter Ce:YAG faceplates were supplied as G.F.P. from the previous contract N61339-90-C-0047. One of these three was to be used for construction of a CRT, the remaining two were to be used for the coating test. During the processing of the CRT's, one of the crystals was destroyed. The other two single crystal faceplates were incorporated in test CRT's. An additional Ce:Gd, YAG (Red shifted green) faceplate of 1.5 inches diameter and two Ce:BEL (Blue) crystals of 0.75 inch diameter were obtained from Allied Signal, Inc, by Trident. Investigations were made to provide optimum optical coupling of the CRT light output into a projection lens. Index matching heat dissipation fluids were used. A wide angle lens was selected and supplied by the contractor. Filtering of the light output of the Ce:YAG, Ce:Gd, YAG and Ce:BEL faceplates was investigated for use in producing green, red, and blue light outputs suitable for a full color video projector.

  9. Single Crystal Structure Determination of Alumina to 1 Mbar

    NASA Astrophysics Data System (ADS)

    Dong, H.; Zhang, L.; Prakapenka, V.; Mao, H.

    2014-12-01

    Aluminum oxide (Al2O3) is an important ceramic material and a major oxide in the earth. Additionally, alumina is a widely used pressure standard in static high-pressure experiments (Cr3+-bearing corundum, ruby). The changes of its crystal structure with pressure (P) and temperature (T) are important for its applications and understanding its physical properties in the deep Earth. There have been numerous reports on the high P-T polymorphs of alumina. Previous theoretical calculations and experiments suggest that the crystal structure of Al2O3 evolves greatly at high P-T. In this study, we used the newly developed multigrain crystallography method combined with single-crystal x-ray diffraction analysis technique for the structure determination of alumina at high P-T to provide single-crystal structure refinement for high-pressure phases of Al2O3. Alumina powder was mixed with ~10% Pt and Ne was used as both pressure transmitting media and thermal insulating layers during laser-heating. Coarse-grained aggregates of Al2O3 were synthesized in a laser-heated diamond anvil cell. The structure change of Al2O3 was monitored by in situ x-ray diffraction at ~1 Mbar and 2700 K. The results allow us to distinguish the structural differences between the Rh2O3 (II) structure (space group Pbcn) and perovskite structure (space group Pbnm) for the first high-pressure phase of Al2O3. More detailed results will be discussed in the later work.

  10. Modeling the anisotropic shock response of single-crystal RDX

    NASA Astrophysics Data System (ADS)

    Luscher, Darby

    Explosives initiate under impacts whose energy, if distributed homogeneously throughout the material, translates to temperature increases that are insufficient to drive the rapid chemistry observed. Heterogeneous thermomechanical interactions at the meso-scale (i.e. between single-crystal and macroscale) leads to the formation of localized hot spots. Direct numerical simulations of mesoscale response can contribute to our understanding of hot spots if they include the relevant deformation mechanisms that are essential to the nonlinear thermomechanical response of explosive molecular crystals. We have developed a single-crystal model for the finite deformation thermomechanical response of cyclotrimethylene trinitramine (RDX). Because of the low symmetry of RDX, a complete description of nonlinear thermoelasticity requires a careful decomposition of free energy into components that represent the pressure-volume-temperature (PVT) response and the coupling between isochoric deformation and both deviatoric and hydrostatic stresses. An equation-of-state (EOS) based on Debye theory that defines the PVT response was constructed using experimental data and density functional theory calculations. This EOS replicates the equilibrium states of phase transformation from alpha to gamma polymorphs observed in static high-pressure experiments. Lattice thermoelastic parameters defining the coupled isochoric free energy were obtained from molecular dynamics calculations and previous experimental data. Anisotropic crystal plasticity is modeled using Orowan's expression relating slip rate to dislocation density and velocity. Details of the theory will be presented followed by discussion of simulations of flyer plate impact experiments, including recent experiments diagnosed with in situ X-ray diffraction at the Advanced Photon Source. Impact conditions explored within the experimental effort have spanned shock pressures ranging from 1-10 GPa for several crystallographic orientations

  11. Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

    SciTech Connect

    Prokhorov, I. A.; Ralchenko, V. G.; Bolshakov, A. P.; Polskiy, A. V.; Vlasov, A. V.; Subbotin, I. A.; Podurets, K. M.; Pashaev, E. M.; Sozontov, E. A.

    2013-12-15

    Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.

  12. Thermal neutron dosimeter by synthetic single crystal diamond devices.

    PubMed

    Almaviva, S; Marinelli, Marco; Milani, E; Prestopino, G; Tucciarone, A; Verona, C; Verona-Rinati, G; Angelone, M; Pillon, M

    2009-07-01

    We report on a new solid state dosimeter based on chemical vapor deposition (CVD) single crystal diamond fabricated at Roma "Tor Vergata" University laboratories. The dosimeter has been specifically designed for direct neutron dose measurements in boron neutron capture therapy (BNCT). The response to thermal neutrons of the proposed diamond dosimeter is directly due to (10)B and, therefore, the dosimeter response is directly proportional to the boron absorbed doses in BNCT. Two single crystal diamond detectors are fabricated in a p-type/intrinsic/metal configuration and are sandwiched together with a boron containing layer in between the metallic contacts (see Fig.1). Neutron irradiations were performed at the Frascati Neutron Generator (FNG) using the 2.5 MeV neutrons produced through the D(d,n)(3)He fusion reaction. Thermal neutrons were then produced by slowing down the 2.5 MeV neutrons using a cylindrical polymethylmethacrylate (PMMA) moderator. The diamond dosimeter was placed in the center of the moderator. The products of (10)B(n,alpha)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed.

  13. Isomeric ionic lithium isonicotinate three-dimensional networks and single-crystal-to-single-crystal rearrangements generating microporous materials.

    PubMed

    Abrahams, Brendan F; Dharma, A David; Grannas, Martin J; Hudson, Timothy A; Maynard-Casely, Helen E; Oliver, Graham R; Robson, Richard; White, Keith F

    2014-05-19

    Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, viz., Li(+)inic(-)·S (where S = 0.5 morpholine, 0.5 dioxane, 0.25 n-hexanol, 0.5 N-methylpyrrolidinone, 0.5 N,N-dimethylformamide, 0.5 n-propanol, 0.5 cyclohexanol, 0.5 pyridine, 0.5 t-butanol, 0.5 ethanol, and 0.5 methanol). Three-dimensional Li(+)inic(-) frameworks containing solvent-filled channels are present in all of these except for the MeOH and EtOH solvates. The nondirectional character of the electrostatic interactions between the Li(+) and inic(-) ions bestows an element of "plasticity" upon the framework, manifested in the observation of no less than five different framework structures within the family. Unusual single-crystal-to-single-crystal transformations accompany desolvation of Li(+)inic(-)·S in which the Li(+)inic(-) framework undergoes a major rearrangement (from a structure containing "8484 chains" to one with "6666 chains"). The "before and after" structures are strongly suggestive of the mechanism and the driving force for these solid state framework rearrangements: processes which further demonstrate the "plasticity" of the ionic Li(inic) framework. A solid-state mechanism for these desolvation processes that accounts very satisfactorily for the formation of the channels and for the diverse geometrical/topological aspects of the transformation is proposed. The reverse process allows the regeneration of the solvated 8484 form. When the 6666 Li(+)inic(-) form is immersed in carbon disulfide, a single-crystal-to-single-crystal transformation occurs to generate Li(+)inic(-)·0.25CS2. The hydrate, Li(+)inic(-)·2H2O which consists of discrete Li(inic)·H2O chains obtained by recrystallizing the salt from water, can also be obtained by hydration of the 6666 form. A dense 3D network with the formula, Li(inic) can be obtained in a reversible process by the removal of the

  14. Large-mode-area single-polarization single-mode photonic crystal fiber: design and analysis.

    PubMed

    Kumar, Ajeet; Saini, Than Singh; Naik, Kishor Dinkar; Sinha, Ravindra Kumar

    2016-07-01

    A rectangular core photonic crystal fiber structure has been presented and analyzed for single-polarization single-mode operation. Single-polarization is obtained with asymmetric design and by introducing different loss for x-polarization and y-polarization of fundamental modes. Single-polarization single-mode operation of the proposed photonic crystal fiber is investigated in detail by using a full vector finite element method with an anisotropic perfectly matched layer. The variations of the confinement loss and effective mode area of x-polarization and y-polarization of fundamental modes have been simulated by varying the structural parameters of the proposed photonic crystal fiber. At the optimized parameters, confinement loss and effective mode area is obtained as 0.94 dB/m and 60.67  μm2 for y-polarization as well as 26.67 dB/m and 67.23  μm2 for x-polarization of fundamental modes, respectively, at 1.55 μm. Therefore simulation results confirmed that, 0.75 m length of fiber will be sufficient to get a y-polarized fundamental mode with an effective mode area as large as 60.67  μm2.

  15. Pressure-induced superconductivity in Bi single crystals

    NASA Astrophysics Data System (ADS)

    Li, Yufeng; Wang, Enyu; Zhu, Xiyu; Wen, Hai-Hu

    2017-01-01

    Measurements on resistivity and magnetic susceptibility have been carried out for Bi single crystals under pressures up to 10.5 GPa. The temperature dependent resistivity shows a semimetallic behavior at ambient and low pressures (below about 1.6 GPa). This is followed by an upturn of resistivity in the low temperature region when the pressure is increased, which is explained as a semiconductor behavior. This feature gradually gets enhanced up to a pressure of about 2.52 GPa. Then a nonmonotonic temperature dependent resistivity appears upon further increasing pressure, which is accompanied by a strong suppression to the low temperature resistivity upturn. Simultaneously, a superconducting transition occurs at about 3.92 K under a pressure of about 2.63 GPa. With further increasing pressure, a second superconducting transition emerges at about 7 K under about 2.8 GPa. For these two superconducting states, the superconductivity induced magnetic screening volumes are quite large. As the pressure further increases to 8.1 GPa, we observe the third superconducting transition at about 8.2 K. The resistivity measurements under magnetic field allow us to determine the upper critical fields μ0Hc 2 of the superconducting phases. The upper critical field for the phase with Tc=3.92 K is extremely low. Based on the Werthamer-Helfand-Hohenberg (WHH) theory, the estimated value of μ0Hc 2 for this phase is about 0.103 T, while the upper critical field for the phase with Tc=7 K is very high with a value of about 4.56 T. Finally, we present a pressure dependent phase diagram of Bi single crystals. Our results reveal the interesting and rich physics in bismuth single crystals under high pressure.

  16. High Pressure Single Crystal Diffraction at PX^2

    PubMed Central

    Zhang, Dongzhou; Dera, Przemyslaw K.; Eng, Peter J.; Stubbs, Joanne E.; Zhang, Jin S.; Prakapenka, Vitali B.; Rivers, Mark L.

    2017-01-01

    In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the GSECARS 13-BM-C beamline at the Advanced Photon Source. The DAC program at 13-BM-C is part of the Partnership for Extreme Xtallography (PX^2) project. BX-90 type DACs with conical-type diamond anvils and backing plates are recommended for these experiments. The sample chamber should be loaded with noble gas to maintain a hydrostatic pressure environment. The sample is aligned to the rotation center of the diffraction goniometer. The MARCCD area detector is calibrated with a powder diffraction pattern from LaB6. The sample diffraction peaks are analyzed with the ATREX software program, and are then indexed with the RSV software program. RSV is used to refine the UB matrix of the single crystal, and with this information and the peak prediction function, more diffraction peaks can be located. Representative single crystal diffraction data from an omphacite (Ca0.51Na0.48)(Mg0.44Al0.44Fe2+0.14Fe3+0.02)Si2O6 sample were collected. Analysis of the data gave a monoclinic lattice with P2/n space group at 0.35 GPa, and the lattice parameters were found to be: a = 9.496 ±0.006 Å, b = 8.761 ±0.004 Å, c = 5.248 ±0.001 Å, β = 105.06 ±0.03º, α = γ = 90º. PMID:28117811

  17. High Pressure Single Crystal Diffraction at PX^2.

    PubMed

    Zhang, Dongzhou; Dera, Przemyslaw K; Eng, Peter J; Stubbs, Joanne E; Zhang, Jin S; Prakapenka, Vitali B; Rivers, Mark L

    2017-01-16

    In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the GSECARS 13-BM-C beamline at the Advanced Photon Source. The DAC program at 13-BM-C is part of the Partnership for Extreme Xtallography (PX^2) project. BX-90 type DACs with conical-type diamond anvils and backing plates are recommended for these experiments. The sample chamber should be loaded with noble gas to maintain a hydrostatic pressure environment. The sample is aligned to the rotation center of the diffraction goniometer. The MARCCD area detector is calibrated with a powder diffraction pattern from LaB6. The sample diffraction peaks are analyzed with the ATREX software program, and are then indexed with the RSV software program. RSV is used to refine the UB matrix of the single crystal, and with this information and the peak prediction function, more diffraction peaks can be located. Representative single crystal diffraction data from an omphacite (Ca0.51Na0.48)(Mg0.44Al0.44Fe(2+)0.14Fe(3+)0.02)Si2O6 sample were collected. Analysis of the data gave a monoclinic lattice with P2/n space group at 0.35 GPa, and the lattice parameters were found to be: a = 9.496 ±0.006 Å, b = 8.761 ±0.004 Å, c = 5.248 ±0.001 Å, β = 105.06 ±0.03º, α = γ = 90º.

  18. Advanced piezoelectric single crystal based transducers for naval sonar applications

    NASA Astrophysics Data System (ADS)

    Snook, Kevin A.; Rehrig, Paul W.; Hackenberger, Wesley S.; Jiang, Xiaoning; Meyer, Richard J., Jr.; Markley, Douglas

    2005-05-01

    TRS is developing new transducers based on single crystal piezoelectric materials such as Pb(Mg1/3Nb2/3)x-1TixO3 (PMN-PT). Single crystal piezoelectrics such as PMN-PT exhibit very high piezoelectric coefficients (d33 ~ 1800 to >2000 pC/N) and electromechanical coupling factors (k33 > 0.9), respectively, which may be exploited for improving the performance of broad bandwidth and high frequency sonar. Apart from basic performance, much research has been done on reducing the size and increasing the output power of tonpilz transducers for sonar applications. Results are presented from two different studies. "33" mode single crystal tonpilz transducers have reduced stack lengths due to their low elastic stiffness relative to PZTs, however, this produces non-ideal aspect ratios due to large lateral dimensions. Alternative "31" resonance mode tonpilz elements are proposed to improve performance over these "33" designs. d32 values as high as 1600 pC/N have been observed, and since prestress is applied perpendicular to the poling direction, "31" mode Tonpilz elements exhibit lower loss and higher reliability than "33" mode designs. Planar high power tonpilz arrays are the optimum way to obtain the required acoustic pressure and bandwidth for small footprint, high power sensors. An important issue for these sensors is temperature and prestress stability, since fluctuations in tonpilz properties affects power delivery and sensing electronic design. TRS used the approach of modifying the composition of PMN-PT to improve the temperature dependence of properties of the material. Results show up to a 50% decrease in temperature change while losing minimal source level.

  19. Single crystal silicon capacitors with low microwave loss in the single photon regime

    NASA Astrophysics Data System (ADS)

    Weber, S. J.; Murch, K. W.; Slichter, D. H.; Vijay, R.; Siddiqi, I.

    2011-04-01

    We have fabricated superconducting microwave resonators in a lumped element geometry using single crystal silicon dielectric parallel plate capacitors with C >2 pF. Aluminum devices with resonant frequencies between 4.0 and 6.5 GHz exhibited an average internal quality factor Qi of 2×105 in the single photon excitation regime at T =20 mK. Attributing the observed loss solely to the capacitive element, our measurements place an upper bound on the loss tangent of the silicon dielectric layer of tan δi=5×10-6. This level of loss is an order of magnitude lower than is currently observed in structures incorporating amorphous dielectric materials, thus making single crystal silicon capacitors an attractive, robust route for realizing long-lived quantum circuits.

  20. Annealing of deformed olivine single-crystals under 'dry' conditions

    NASA Astrophysics Data System (ADS)

    Blaha, Stephan; Katsura, Tomoo

    2013-04-01

    Knowledge of rheological properties of Earth's materials is essential to understand geological processes. Open questions are the water content and crystallographic orientation dependences of dislocation creep rate, because the dominant slip system changes with increasing water content, which suggest different dislocations have different water content dependence. This project focuses on olivine, which is the most abundant mineral of the upper mantle. It is also considered to be the weakest phase and hence should control the rheology of the upper mantle. Several slip systems were reported for olivine, which are [100](010), [001](010), [001](100) and [100](001), each of which appear under different water content and stress conditions [1]. For this purpose we started to obtain data for 'dry' conditions, providing basic knowledge to understand the effect of water. Variation in dislocation creep rate according to change in physical conditions can be estimated by dislocation recovery experiments [2]. In this technique, deformed crystals are annealed, in which the dislocation density is expected to decrease due to coalescence of two dislocations. Dislocation densities are measured before and after the annealing. Dislocation mobility, which should be directly proportional to the dislocation creep rate, is estimated based on the change in dislocation density and duration of annealing. This technique has significant advantages partly because informations of strain rate and deviatoric stress, which are difficult to measure, are unnecessary, and partly because dislocation annealing is conducted under quasi-hydrostatic conditions, which allows wide ranges of P and T conditions. The first step of the experiments is to deform a single crystal of olivine. For this purpose, we developed an assembly, which deforms a single crystal in simple-shear geometry and prevent breakage, sub-grain formation and recrystallization of the crystal. Olivine single-crystals were placed in the high

  1. Physical properties of stoichiometric CeN single crystals

    NASA Astrophysics Data System (ADS)

    Wachter, P.; Zhigadlo, N. D.

    The preparation and definition of stoichiometric large (3-5 mm edge length) single crystals of CeN are described. The band structure is discussed and compared with X-ray-photoemission-spectra (XPS), Bremsstrahlen-isochromat-spectroscopy (BIS) and optical reflectivity. CeN is intermediate valent with partially occupied and empty 4f states near EF. The specific heat is measured until 0.3 K and the γ term exhibits a sharp upturn toward the lowest temperatures. The Debye temperature is evaluated. The magnetic susceptibility is a large Pauli term pointing to a high density of states at EF as expected for a fractionally filled 4f1 state.

  2. Self-diffusion of oxygen in single crystal alumina

    NASA Astrophysics Data System (ADS)

    Oishi, Y.; Ando, Ken; Kubota, Y.

    1980-08-01

    The self-diffusion coefficient of oxygen in (polished slices of a Verneuil) single-crystal alumina was determined in the temperature range 1500-1770 °C by means of the gas-solid isotope exchange technique. The results were represented by D=1.12×103 exp (-155×103/RT) cm2/s. The activation energy was interpreted to be for intrinsic diffusion. By comparison of the results with the oxygen self-diffusion coefficients previously reported for crushed particles of a Verneuil alumina and a vapor-grown alumina, the extrinsic diffusion exhibited by the crushed particles was confirmed to be due to a dislocation enhancement process.

  3. A macroscopic model for magnetic shape-memory single crystals

    NASA Astrophysics Data System (ADS)

    Bessoud, Anne-Laure; Kružík, Martin; Stefanelli, Ulisse

    2013-04-01

    A rate-independent model for the quasi-static magneto-elastic evolution of a magnetic shape-memory single crystal is presented. In particular, the purely mechanical Souza-Auricchio model for shape-memory alloys is here combined with classical micro-magnetism by suitably associating magnetization and inelastic strain. By balancing the effect of conservative and dissipative actions, a nonlinear evolution PDE system of rate-independent type is obtained. We prove the existence of so-called energetic solutions to this system. Moreover, we discuss several limits for the model corresponding to parameter asymptotics by means of a rigorous Γ-convergence argument.

  4. Raman Investigations of Rare Earth Arsenate Single Crystals

    SciTech Connect

    Barros, G; Santos, C. C.; Ayala, A. P.; Guedes, I.; Boatner, Lynn A; Loong, C. K.

    2010-01-01

    Polarized Raman Spectroscopy was used to investigate the room-temperature phonon characteristics of a series of rare-earth arsenate (REAsO4, RE = Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) single crystals. The Raman data were interpreted in a systematic manner based on the known tetragonal zircon structure of these compounds, and assignments and correlations were made for the observed bands. We found that the wavenumber of the internal modes of the AsO4 tetrahedron increased with increasing atomic number, and for three out of four lattice wavenumbers observed, this tendency was not nearly so marked as in the case of the internal mode wavenumber.

  5. Carrier doping and interlayer coupling in HTSC single crystals

    SciTech Connect

    Kishio, K.; Shimoyama, J.; Kimura, T.; Kotaka, Y.; Kitazawa, K.; Yamafuji, K.; Li, Q.; Suenaga, M.

    1994-09-01

    Experimental results of the effect of carrier doping on the irreversibility lines in (La,Sr){sub 2}CuO{sub 4{minus}{delta}} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8 + {delta}} single crystals are summarized. As a function of Sr or oxygen contents, systematic and dramatic widening of the irreversible regions in the B {minus} T phase diagram was observed in both systems. The present study suggests the critical importance of carrier concentration which directly affects the interlayer coupling strength and dimensionality of the flux line lattice in all the layered HTSC compounds as a universal feature.

  6. Silica based polishing of {100} and {111} single crystal diamond

    PubMed Central

    Thomas, Evan L H; Mandal, Soumen; Brousseau, Emmanuel B; Williams, Oliver A

    2014-01-01

    Diamond is one of the hardest and most difficult to polish materials. In this paper, the polishing of {111} and {100} single crystal diamond surfaces by standard chemical mechanical polishing, as used in the silicon industry, is demonstrated. A Logitech Tribo Chemical Mechanical Polishing system with Logitech SF1 Syton and a polyurethane/polyester polishing pad was used. A reduction in roughness from 0.92 to 0.23 nm root mean square and 0.31 to 0.09 nm rms for {100} and {111} samples respectively was observed. PMID:27877689

  7. Nonlinear microwave switching response of BSCCO single crystals

    SciTech Connect

    Jacobs, T.; Sridhar, S.; Willemsen, B.A. |; Li, Qiang; Gu, G.D.; Koshizuka, N.

    1996-06-01

    Measurements of the surface impedance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal with microwave currents flowing along the {cflx c} axis show clear evidence of a step-like nonlinearity. The surface resistance switches between apparently quantized levels for microwave field strength changes < 1 mG. This nonlinear response can arise from the presence of intrinsic Josephson junctions along the {cflx c} axis of these samples driven by the microwave current.

  8. Optical properties of Eu2+ doped antipervoskite fluoride single crystals

    NASA Astrophysics Data System (ADS)

    Daniel, D. Joseph; Nithya, R.; Ramasamy, P.; Madhusoodanan, U.

    2013-02-01

    Single crystals of pure and Eu2+ doped LiBaF3 have been grown from melt by using a vertical Bridgman-Stockbarger method. Absorption and luminescence spectra for pure and rare-earth-doped LiBaF3 were studied. At ambient conditions the photoluminescence spectra consisted of sharp lines peaked at ˜359 nm attributed to the 6P7/2→8S7/2 transitions in the 4f7 electronic configuration of Eu2+ and a broad band extending between 370 and 450 nm attributed to Eu2+ trapped exciton recombination. The effect of 60Co gamma irradiation has also been investigated.

  9. Quantification of the Void Volume in Single-Crystal Silicon.

    PubMed

    D'Agostino, Giancarlo; Di Luzio, Marco; Mana, Giovanni; Martino, Luca; Oddone, Massimo; Sasso, Carlo Paolo

    2016-12-06

    This paper investigates the use of a method based on Cu decoration and neutron activation to determine the total volume of voids in a silicon single crystal. A measurement protocol was developed and tested in an experiment carried out with a 5 cm(3) volume and 10 g mass high-purity natural silicon sample. The few percent uncertainty reached in the determination of the Cu concentration, at a 10(14) cm(-3) level, makes this method a candidate to set an upper limit to the concentration of the vacancies contributing to the void volume in the enriched silicon material used to determine the Avogadro constant.

  10. Single Molecule Studies on Dynamics in Liquid Crystals

    PubMed Central

    Täuber, Daniela; von Borczyskowski, Christian

    2013-01-01

    Single molecule (SM) methods are able to resolve structure related dynamics of guest molecules in liquid crystals (LC). Highly diluted small dye molecules on the one hand explore structure formation and LC dynamics, on the other hand they report about a distortion caused by the guest molecules. The anisotropic structure of LC materials is used to retrieve specific conformation related properties of larger guest molecules like conjugated polymers. This in particular sheds light on organization mechanisms within biological cells, where large molecules are found in nematic LC surroundings. This review gives a short overview related to the application of highly sensitive SM detection schemes in LC. PMID:24077123

  11. Experiment MA-028 crystal growth. [low gravity manufacturing of single crystals from Apollo/Soyuz Test Project

    NASA Technical Reports Server (NTRS)

    Lind, D. M.

    1976-01-01

    A crystal growth experiment is reported on orbital space flights. The experiment was performed during the Apollo-Soyuz Test Project. The Crystal Growth Experiment assessed a novel process for growing single crystals of insoluble substances by allowing two or more reactant solutions to diffuse toward each other through a region of pure solvent in zero gravity. The experiment was entirely successful and yielded crystals of about the expected size, quality, and number.

  12. Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.

    PubMed

    Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

    2011-12-23

    Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.

  13. Synthesis of mesoporous zeolite single crystals with cheap porogens

    NASA Astrophysics Data System (ADS)

    Tao, Haixiang; Li, Changlin; Ren, Jiawen; Wang, Yanqin; Lu, Guanzhong

    2011-07-01

    Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, 27Al magic angle spinning nuclear magnetic resonance ( 27Al MAS NMR), temperature-programmed desorption of ammonia (NH 3-TPD) and ultraviolet-visible spectroscopy (UV-vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. 27Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV-vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites.

  14. Single nanoparticle detection using photonic crystal enhanced microscopy.

    PubMed

    Zhuo, Yue; Hu, Huan; Chen, Weili; Lu, Meng; Tian, Limei; Yu, Hojeong; Long, Kenneth D; Chow, Edmond; King, William P; Singamaneni, Srikanth; Cunningham, Brian T

    2014-03-07

    We demonstrate a label-free biosensor imaging approach that utilizes a photonic crystal (PC) surface to detect surface attachment of individual dielectric and metal nanoparticles through measurement of localized shifts in the resonant wavelength and resonant reflection magnitude from the PC. Using a microscopy-based approach to scan the PC resonant reflection properties with 0.6 μm spatial resolution, we show that metal nanoparticles attached to the biosensor surface with strong absorption at the resonant wavelength induce a highly localized reduction in reflection efficiency and are able to be detected by modulation of the resonant wavelength. Experimental demonstrations of single-nanoparticle imaging are supported by finite-difference time-domain computer simulations. The ability to image surface-adsorption of individual nanoparticles offers a route to single molecule biosensing, in which the particles can be functionalized with specific recognition molecules and utilized as tags.

  15. Note: Fabrication and characterization of molybdenum tips for scanning tunneling microscopy and spectroscopy

    SciTech Connect

    Carrozzo, P.; Tumino, F.; Facibeni, A.; Passoni, M.; Casari, C. S.; Li Bassi, A.

    2015-01-15

    We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt.

  16. Single-crystal structure of vanadium-doped La{sub 2}Mo{sub 2}O{sub 9}

    SciTech Connect

    Alekseeva, O. A. Antipin, A. M.; Gagor, A.; Pietraszko, A.; Novikova, N. E.; Sorokina, N. I.; Kharitonova, E. P.; Voronkova, V. I.

    2013-11-15

    A high-precision X-ray diffraction study of single crystals of two compositions-La{sub 2}Mo{sub 1.78}V{sub 0.22}O{sub 8.89} and La{sub 2}Mo{sub 1.64}V{sub 0.36}O{sub 8.82}-was performed. In the vanadium-doped compounds, as in the structure of the metastable {beta}{sub ms} phase of pure La{sub 2}Mo{sub 2}O{sub 9}, the La and Mo atoms and one of the three oxygen atoms are displaced from the threefold axis, on which they are located in the high-temperature {beta} phase. The structure contains two partially occupied oxygen sites. It was shown that molybdenum atoms are partially replaced by vanadium atoms, which are not involved in the disordering, are located on the threefold axis, and are shifted toward one of the oxygen atoms. This is consistent with the temperature-induced changes in the structure of La{sub 2}Mo{sub 2}O{sub 9} and the changes in the properties of these crystals caused by the introduction of vanadium atoms into the structure.

  17. Q-switching with single crystal photo-elastic modulators

    NASA Astrophysics Data System (ADS)

    Bammer, F.; Petkovsek, R.

    2010-09-01

    An overview is given about experiments with a new method for Q-switching lasers at a constant pulse repetition frequency. It uses inside the laser resonator a Single Crystal Photo-Elastic Modulator (SCPEM). This consists of one piezo-electric crystal electrically excited on a mechanical resonance frequency. In resonance mechanical stresses are induced that lead via the photo-elastic effect to a strongly modulated birefringence. Polarized light going through such an oscillating crystal will experience a significant modulation of its polarization and of transmission through a polarizer. Suitable materials should not be optically active, as it is for example the case for SiO2, and should allow the excitation of a longitudinal oscillation with an electric field perpendicular to the travelling direction of the light. Crystals of the group 3m, like LiTaO3 and LiNbO3, proved to be ideally suited for SCPEMS for the NIR- and VIS-region. For the infrared GaAs can be used. We demonstrated SCPEM-Q-switching for a Nd:YAG-fiber, a Nd:YVO4-slab- and a Nd:YAG-rod-laser with typical pulse repetition rates of 100-200kHz, pulse enhancement factors of ~100 and pulse durations ~1/100 of the period time. Typically the average power during pulsed operation is nearly the same as the cw-power, when the modulator is switched off. The most stable results were achieved up to now with the Nd:YVO4-slab-laser at 10W average power, 1.1 kW peak power, 127 kHz pulse repetition rate, and 70ns pulse durations.

  18. Q-switching with single crystal photo-elastic modulators

    NASA Astrophysics Data System (ADS)

    Bammer, F.; Petkovsek, R.

    2011-02-01

    An overview is given about experiments with a new method for Q-switching lasers at a constant pulse repetition frequency. It uses inside the laser resonator a Single Crystal Photo-Elastic Modulator (SCPEM). This consists of one piezo-electric crystal electrically excited on a mechanical resonance frequency. In resonance mechanical stresses are induced that lead via the photo-elastic effect to a strongly modulated birefringence. Polarized light going through such an oscillating crystal will experience a significant modulation of its polarization and of transmission through a polarizer. Suitable materials should not be optically active, as it is for example the case for SiO2, and should allow the excitation of a longitudinal oscillation with an electric field perpendicular to the travelling direction of the light. Crystals of the group 3m, like LiTaO3 and LiNbO3, proved to be ideally suited for SCPEMS for the NIR- and VIS-region. For the infrared GaAs can be used. We demonstrated SCPEM-Q-switching for a Nd:YAG-fiber, a Nd:YVO4-slab- and a Nd:YAG-rod-laser with typical pulse repetition rates of 100-200kHz, pulse enhancement factors of 100 and pulse durations {1/100 of the period time. Typically the average power during pulsed operation is nearly the same as the cw-power, when the modulator is switched off. The most stable results were achieved up to now with the Nd:YVO4-slab-laser at 10W average power, 1.1 kW peak power, 127 kHz pulse repetition rate, and 70ns pulse durations.

  19. Growth and properties of Lithium Salicylate single crystals

    SciTech Connect

    Zaitseva, N; Newby, J; Hull, G; Saw, C; Carman, L; Cherepy, N; Payne, S

    2009-02-13

    An attractive feature of {sup 6}Li containing fluorescence materials that determines their potential application in radiation detection is the capture reaction with slow ({approx}< 100 keV) neutrons: {sup 6}Li + n = {sup 4}He + {sup 3}H + 4.8MeV. The use of {sup 6}Li-salicylate (LiSal, LiC{sub 6}H{sub 5}O{sub 3}) for thermal neutron detection was previously studied in liquid and polycrystalline scintillators. The studies showed that both liquid and polycrystalline LiSal scintillators could be utilized in pulse shape discrimination (PSD) techniques that enable separation of neutrons from the background gamma radiation. However, it was found that the efficiency of neutron detection using LiSal in liquid solutions was severely limited by its low solubility in commonly used organic solvents like, for example, toluene or xylene. Better results were obtained with neutron detectors containing the compound in its crystalline form, such as pressed pellets, or microscopic-scale (7-14 micron) crystals dispersed in various media. The expectation drown from these studies was that further improvement of pulse height, PSD, and efficiency characteristics could be reached with larger and more transparent LiSal crystals, growth of which has not been reported so far. In this paper, we present the first results on growth and characterization of relatively large, a cm-scale size, single crystals of LiSal with good optical quality. The crystals were grown both from aqueous and anhydrous (methanol) media, mainly for neutron detection studies. However, the results on growth and structural characterization may be interesting for other fields where LiSal, together with other alkali metal salicylates, is used for biological, medical, and chemical (as catalyst) applications.

  20. Process for Making Single-Domain Magnetite Crystals

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

    2004-01-01

    A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with

  1. Bithermal fatigue of a nickel-base superalloy single crystal

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.

    1988-01-01

    The thermomechanical fatigue behavior of a nickel-base superalloy single crystal was investigated using a bithermal test technique. The bithermal fatigue test was used as a simple alternative to the more complex thermomechanical fatigue test. Both in-phase and out-of-phase bithermal tests were performed on (100)-oriented coated and bare Rene N4 single crystals. In out-of-plane bithermal tests, the tensile and compressive halves of the cycle were applied isothermally at 760 and 982 C, respectively, while for the in-phase bithermal tests the temperature-loading sequence was reversed. The bithermal fatigue lives of bare specimens were shorter than the isothermal fatigue lives at either temperature extreme when compared on an inelastic strain basis. Both in-phase and out-of-phase bithermal fatigue life curves converged in the large strain regime and diverged in the small strain regime, out-of-phase resulting in the shortest lives. The coating had no effect on life for specimens cycled in-phase; however, the coating was detrimental for isothermal fatigue at 760 C and for out-of-phase fatigue under large strains.

  2. Ultrafast dynamic response of single crystal β-HMX

    NASA Astrophysics Data System (ADS)

    Zaug, Joseph M.; Armstrong, Michael R.; Crowhurst, Jonathan C.; Radousky, Harry B.; Ferranti, Louis; Swan, Raymond; Gross, Rick; Teslich, Nick E.; Wall, Mark A.; Austin, Ryan A.; Fried, Laurence E.

    2017-01-01

    We report results from ultrafast compression experiments conducted on β-HMX single crystals. Results consist of nominally 12 picosecond time-resolved wave profile data, (ultrafast time domain interferometry -TDI measurements), that were analyzed to determine high-velocity wave speeds as a function of piston velocity. TDI results are used to validate calculations of anisotropic stress-strain behavior of shocked loaded energetic materials. Our previous results derived using a 350 ps duration compression drive revealed anisotropic elastic wave response in single crystal β-HMX from (110) and (010) impact planes. Here we present results using a 1.05 ns duration compression drive with a 950 ps interferometry window to extend knowledge of the anisotropic dynamic response of β-HMX within eight microns of the initial impact plane. We observe two distinct wave profiles from (010) and three wave profiles from (010) impact planes. The (110) impact plane wave speeds typically exceed (010) impact plane wave speeds at the same piston velocities. The development of multiple hydrodynamic wave profiles begins at 20 GPa for the (110) impact plane and 28 GPa for the (10) impact plane. We compare our ultrafast TDI results with previous gun and plate impact results on β-HMX and PBX9501.

  3. Photonic crystals possessing single and double Weyl points (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Chan, Che Ting

    2016-09-01

    The concepts of topological states have captured much attention in condensed-matter physics and the importance of these systems is subsequently realized in other subfields, such as cold atom and classical waves. In the past few years, the attention was focused on "topological insulators" while very recently, the attention is shifting to "Weyl semi-metals" which have gapless bulk band structures with pairs of topological points (called Weyl points) and topologically-protected surface states. In this work, we designed, fabricated and experimentally characterized a Weyl photonic crystal with both single and double Weyl points. We used tight-binding Hamiltonian as a starting point to guide us to the structures that have the correct symmetry to support topological features including synthetic gauge flux and associated Weyl points. We fabricated for the first time a system that exhibits Weyl points of topological charge higher than 1. In our photonic crystal, the existence of the double Weyl point is made possible by the degeneracy between the two single Weyl points which is protected by C3 symmetry and time reversal. Once the C3 symmetry is broken, two Weyl points with charge of ±1 will separate and each forms a linear dispersion in all three directions. Nontrivial 2D bulk band gaps for fixed kz and Weyl points were confirmed by angle-resolved transmission spectra. The robustness of the associated surface states against kz-preserved scattering was experimentally observed.

  4. Synthesis of millimeter-scale transition metal dichalcogenides single crystals

    DOE PAGES

    Gong, Yongji; Ye, Gonglan; Lei, Sidong; ...

    2016-02-10

    The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe2 layers is reported, in which the nucleation density can be reduced from 105 to 25 nuclei cm-2, leading to millimeter-scale MoSe2 single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe2 films with well-defined stacking orientation can also bemore » controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm2 V-1 s-1, for back-gated MoSe2 transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter-scale WSe2 single crystals.« less

  5. Synthesis of millimeter-scale transition metal dichalcogenides single crystals

    SciTech Connect

    Gong, Yongji; Ye, Gonglan; Lei, Sidong; Shi, Gang; Vajtai, Robert; Pantelides, Sokrates T.; Zhou, Wu; Li, Bo; Ajayan, Pullikel M.

    2016-02-10

    The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe2 layers is reported, in which the nucleation density can be reduced from 105 to 25 nuclei cm-2, leading to millimeter-scale MoSe2 single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe2 films with well-defined stacking orientation can also be controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm2 V-1 s-1, for back-gated MoSe2 transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter-scale WSe2 single crystals.

  6. A crystallographic model for nickel base single crystal alloys

    NASA Technical Reports Server (NTRS)

    Dame, L. T.; Stouffer, D. C.

    1988-01-01

    The purpose of this research is to develop a tool for the mechanical analysis of nickel-base single-crystal superalloys, specifically Rene N4, used in gas turbine engine components. This objective is achieved by developing a rate-dependent anisotropic constitutive model and implementing it in a nonlinear three-dimensional finite-element code. The constitutive model is developed from metallurgical concepts utilizing a crystallographic approach. An extension of Schmid's law is combined with the Bodner-Partom equations to model the inelastic tension/compression asymmetry and orientation-dependence in octahedral slip. Schmid's law is used to approximate the inelastic response of the material in cube slip. The constitutive equations model the tensile behavior, creep response and strain-rate sensitivity of the single-crystal superalloys. Methods for deriving the material constants from standard tests are also discussed. The model is implemented in a finite-element code, and the computed and experimental results are compared for several orientations and loading conditions.

  7. Self-assembled single-crystal silicon circuits on plastic.

    PubMed

    Stauth, Sean A; Parviz, Babak A

    2006-09-19

    We demonstrate the use of self-assembly for the integration of freestanding micrometer-scale components, including single-crystal, silicon field-effect transistors (FETs) and diffusion resistors, onto flexible plastic substrates. Preferential self-assembly of multiple microcomponent types onto a common platform is achieved through complementary shape recognition and aided by capillary, fluidic, and gravitational forces. We outline a microfabrication process that yields single-crystal, silicon FETs in a freestanding, powder-like collection for use with self-assembly. Demonstrations of self-assembled FETs on plastic include logic inverters and measured electron mobility of 592 cm2/V-s. Finally, we extend the self-assembly process to substrates each containing 10,000 binding sites and realize 97% self-assembly yield within 25 min for 100-microm-sized elements. High-yield self-assembly of micrometer-scale functional devices as outlined here provides a powerful approach for production of macroelectronic systems.

  8. Joint Development of a Fourth Generation Single Crystal Superalloy

    NASA Technical Reports Server (NTRS)

    Walston, S.; Cetel, A.; MacKay, R.; OHara, K.; Duhl, D.; Dreshfield, R.

    2004-01-01

    A new, fourth generation, single crystal superalloy has been jointly developed by GE Aircraft Engines, Pratt & Whitney, and NASA. The focus of the effort was to develop a turbine airfoil alloy with long-term durability for use in the High Speed Civil Transport. In order to achieve adequate long-time strength improvements at moderate temperatures and retain good microstructural stability, it was necessary to make significant composition changes from 2nd and 3rd generation single crystal superalloys. These included lower chromium levels, higher cobalt and rhenium levels and the inclusion of a new alloying element, ruthenium. It was found that higher Co levels were beneficial to reducing both TCP precipitation and SRZ formation. Ruthenium caused the refractory elements to partition more strongly to the ' phase, which resulted in better overall alloy stability. The final alloy, EPM 102, had significant creep rupture and fatigue improvements over the baseline production alloys and had acceptable microstructural stability. The alloy is currently being engine tested and evaluated for advanced engine applications.

  9. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  10. Modal reduction in single crystal sapphire optical fiber

    SciTech Connect

    Cheng, Yujie; Hill, Cary; Liu, Bo; Yu, Zhihao; Xuan, Haifeng; Homa, Daniel; Wang, Anbo; Pickrell, Gary

    2015-10-12

    A new type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high and low index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying the effective core diameter and the dimensions of the “windmill” shaped cladding. The simulation results showed that the number of guided modes were significantly reduced in the “windmill” fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the “windmill” SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.

  11. A study of latent hardening behavior in aluminum single crystals

    SciTech Connect

    Wang Mingzhang; Lin Shi; Li Chenghua; Xiao Jimei; Wang Zhongguang

    1996-11-15

    In order to obtain a better understanding or a complete description of plastic properties of polycrystals, especially in polycrystal modelling viewpoint, investigations on latent hardening behavior of single crystals have been performed in a great number. Recently, however, Wu et al. have pointed out that the definition of the yield stress of latent system using the conventional back extrapolation is ambiguous in terms of determining the latent hardening moduli because the initial rapid work-hardening of the transient zone is neglected. They proposed a more precise measure of the yield stress of latent system based on the decrease of the tangent modulus from the linear elastic modulus, and showed that the latent hardening, which would not plus the initial work-hardening of the transient zone, is actually lower than that obtained from the backward extrapolation. Thus, in their opinion, it is considered that the hardening behavior of latent system (such as the directionality, the effects of relative orientation and prestrain) need be newly or further studied in detail. Single crystals of aluminum have been grown with high purity to investigate this behavior.

  12. Single Crystal Diamond Needle as Point Electron Source

    PubMed Central

    Kleshch, Victor I.; Purcell, Stephen T.; Obraztsov, Alexander N.

    2016-01-01

    Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2–0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics. PMID:27731379

  13. OSL studies of alkali fluoroperovskite single crystals for radiation dosimetry

    NASA Astrophysics Data System (ADS)

    Daniel, D. Joseph; Raja, A.; Madhusoodanan, U.; Annalakshmi, O.; Ramasamy, P.

    2016-08-01

    This paper presents a preliminary investigation of the optically stimulated luminescence (OSL) of alkali fluoroperovskite single crystals for radiation dosimetry. The perovskite-like KMgF3, NaMgF3 and LiBaF3 polycrystalline compounds doped with rare earths (Eu2+ and Ce3+) were synthesized by standard solid state reaction technique. Phase purity of the synthesized compounds was analyzed by powder X-ray diffraction technique. Single crystals of these compounds have been grown from melt by using vertical Bridgman-Stockbarger method. The Linearly Modulated OSL and Continuous Wave OSL measurements were performed in these alkali fluorides using blue light stimulation. Thermal bleaching experiments have shown that OSL signals originate from traps which are unstable near 200 °C, thus proving the suitability of the signals for dosimetric purposes. Optical bleaching measurements were also performed for these fluoride samples. OSL dose response was studied as a function of dose which was found to increase with beta dose.

  14. Single Crystal Diamond Needle as Point Electron Source

    NASA Astrophysics Data System (ADS)

    Kleshch, Victor I.; Purcell, Stephen T.; Obraztsov, Alexander N.

    2016-10-01

    Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2–0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics.

  15. Modal reduction in single crystal sapphire optical fiber

    DOE PAGES

    Cheng, Yujie; Hill, Cary; Liu, Bo; ...

    2015-10-12

    A new type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high and low index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying themore » effective core diameter and the dimensions of the “windmill” shaped cladding. The simulation results showed that the number of guided modes were significantly reduced in the “windmill” fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the “windmill” SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.« less

  16. Microwave absorption in single crystals of lanthanum aluminate

    NASA Astrophysics Data System (ADS)

    Zuccaro, Claudio; Winter, Michael; Klein, Norbert; Urban, Knut

    1997-12-01

    A very sensitive dielectric resonator technique is employed to measure loss tangent tan δ and relative permittivity ɛr of lanthanum aluminate (LaAlO3) single crystals at 4-300 K and 4-12 GHz. A variety of single crystals grown by different techniques and purchased from different suppliers are considered. For T>150 K the loss tangent tan δ is almost sample independent with linear frequency dependence and monotonous temperature variation from 8×10-6 at 300 K to 2.5×10-6 at 150 K and 4.1 GHz. In this temperature range the experimental data are explained by a model based on lifetime broadened two-phonon difference processes. The loss tangent below 150 K is characterized by a peak in tan δ(T) at about 70 K. The height of this peak is frequency and strongly sample dependent. This leads to a variation of the loss tangent from 10-6 to 1.5×10-5 at 77 K and 8.6 GHz, the lowest values are generally achieved with Verneuil grown crystals and approach the intrinsic lower limit predicted by the phonon model. The peak is explained by defect dipole relaxation (local motions of ions). The activation energy of the relaxation process is determined from the measured data to be 31 meV. This low value indicates that the defect dipoles are associated with interstitials, possibly impurities in interstitial positions. Considering absorption due to phonons and due to defect dipole relaxation the loss tangent is calculated for a wide frequency range.

  17. Deformation of olivine single crystals under lithospheric conditions

    NASA Astrophysics Data System (ADS)

    Demouchy, S.; Tommasi, A.; Cordier, P.

    2012-12-01

    The rheology of mantle rocks at lithospheric temperatures (<1000°C) remains poorly constrained, in contrast to the extensive experimental data on creep of olivine single crystals and polycrystalline aggregates at high temperature (T > 1200°C). Consequently, we have performed tri-axial compression experiments on oriented single crystals and polycrystalline aggregates of San Carlos olivine at temperatures ranging from 800° to 1090°C. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at constant strain rates ranging from 7 × 10-6 s-1 to 1 × 10-4 s-1 . Compression was applied along three different crystallographic directions: [101]c, [110]c and [011]c, to activate the several slip systems. Yield differential stresses range from 88 to 1076 MPa. To constrain hardening, stick-and-slip, or strain localization behaviors, all samples were deformed at constant displacement rate for finite strains between 4 to 23 %. Hardening was observed in all experiments and the maximum differential stress often overcame the confining pressure. EBSD mapping highlights macroscale bending of the crystalline network in three crystals. TEM observations on several samples show dislocations with [100] and [001] Burgers vectors in all samples, but dislocation arrangements vary. The results from the present study permit to refining the power-law expressing the strain rate dependence on stress and temperature for olivine, allowing its application to the lithospheric mantle. Our experiments confirm that previous published high-temperature power flow laws overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at higher temperatures than it has previously been established.

  18. Growth of bulk single crystals of organic materials for nonlinear optical devices - An overview

    NASA Technical Reports Server (NTRS)

    Penn, Benjamin G.; Cardelino, Beatriz H.; Moore, Craig E.; Shields, Angela W.; Frazier, D. O.

    1991-01-01

    Highly perfect single crystals of nonlinear optical organic materials are required for use in optical devices. An overview of the bulk crystal growth of these materials by melt, vapor, and solution processes is presented. Additionally, methods that may be used to purify starting materials, detect impurities at low levels, screen materials for crystal growth, and process grown crystals are discussed.

  19. Crystal growth and electrical properties of CuFeO 2 single crystals

    NASA Astrophysics Data System (ADS)

    Dordor, P.; Chaminade, J. P.; Wichainchai, A.; Marquestaut, E.; Doumerc, J. P.; Pouchard, M.; Hagenmuller, P.; Ammar, A.

    1988-07-01

    Delafossite-type CuFeO 2 single crystals have been prepared by a flux method: crystals obtained in a Cu crucible with LiBO 2 as flux are n-type whereas those prepared in a Pt crucible with a Cu 2O flux are p-type. Electrical measurements have revealed that n-type crystals exhibit weak anisotropic conductivities with large activation energies and small mobilities (r.t. values perpendicular and parallel to the c-axis: μ⊥ = 5 × 10 -5 and μ‖ = 10 -7 cm -2 V -1 sec -1). p-type crystals, less anisotropic, are characterized by low activation energies and higher mobilities ( μ⊥ = 34 and μ‖ = 8.9 cm 2 V -1 sec -1). A two -conduction-band model is proposed to account for the difference observed between the energy gap value deduced from photoelectrochemical measurements and the activation energy of the electrical conductivity in the intrinsic domain.

  20. Magnetic measurements on single crystals of dysprosium trifluoromethanesulfonate nonahydrate; effects of crystal field perturbed energy levels

    NASA Astrophysics Data System (ADS)

    Neogy, D.; Paul, P.; Chattopadhyay, K. N.; Bisui, D.

    2002-07-01

    Magnetic susceptibility measurements on single crystals of dysprosium trifluoromethanesulfonate (DyTFMS) have been carried out from 300 K down to 13 K. The hexagonal crystal structure of DyTFMS renders the crystal uniaxial with the Kramers ion Dy 3+ occupying a site of C 3h symmetry. The principal magnetic susceptibilities, observed by us and the Friedberg group, over the wide range 300 to ˜1.0 K find an excellent theoretical simulation by the crystal field perturbed J-mixed eigenvectors with due consideration of the intermediate coupling effects. No ordering effects were noticed down to ˜13 K indicating the interionic interaction to be predominantly of the dipolar type which is consistent with the discovery of a ferromagnetic transition at T˜0.111 K by the Friedberg group. The g-values derived from other sources are reasonably accounted for. The thermal behavior of quadrupole splitting and that of electronic and nuclear heat capacities is also worked out.

  1. CH3NH3PbCl3 Single Crystals: Inverse Temperature Crystallization and Visible-Blind UV-Photodetector.

    PubMed

    Maculan, Giacomo; Sheikh, Arif D; Abdelhady, Ahmed L; Saidaminov, Makhsud I; Haque, Md Azimul; Murali, Banavoth; Alarousu, Erkki; Mohammed, Omar F; Wu, Tom; Bakr, Osman M

    2015-10-01

    Single crystals of hybrid perovskites have shown remarkably improved physical properties compared to their polycrystalline film counterparts, underscoring their importance in the further development of advanced semiconductor devices. Here we present a new method of growing sizable CH3NH3PbCl3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCl3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectronic applications.

  2. Pre-treatment for molybdenum or molybdenum-rich alloy articles to be plated

    DOEpatents

    Wright, Ralph R.

    1980-01-01

    This invention is a method for etching a molybdenum or molybdenum-rich alloy surface to promote the formation of an adherent bond with a subsequently deposited metallic plating. In a typical application, the method is used as a pre-treatment for surfaces to be electrolessly plated with nickel. The pre-treatment comprises exposing the crystal boundaries of the surface by (a) anodizing the surface in acidic solution to form a continuous film of gray molybdenum oxide thereon and (b) removing the film.

  3. The molybdenum cofactor.

    PubMed

    Mendel, Ralf R

    2013-05-10

    The transition element molybdenum needs to be complexed by a special cofactor to gain catalytic activity. Molybdenum is bound to a unique pterin, thus forming the molybdenum cofactor (Moco), which, in different variants, is the active compound at the catalytic site of all molybdenum-containing enzymes in nature, except bacterial molybdenum nitrogenase. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also require iron, ATP, and copper. After its synthesis, Moco is distributed, involving Moco-binding proteins. A deficiency in the biosynthesis of Moco has lethal consequences for the respective organisms.

  4. HYDROGEN CHEMISORPTION ON Pt SINGLE CRYSTAL SURFACES IN ACIDIC SOLUTIONS

    SciTech Connect

    Ross, Jr., Philip N.

    1980-04-01

    Hydrogen chemisorption from dilute acidic solution onto Pt single crystal surfaces was examined using an electrochemical cell directly coupled to LEED/Auger analytical system. No pre-anodization was used prior to observing hydrogen adsorption by cyclic voltammetry so that clean surfaces having the ordered structures indicated by LEED were studied. The problem of contributions from non-ordered parts of the electrode like support wires and edges was solved by using a gold evaporation masking technique. The specific contribution of atomic imperfections to the voltammetry curve was deduced from the ordered and countable imperfections occurring on high Miller index single crystal surfaces that have a stepped structure. The H-Pt bond energy Has found to be structure sensitive, and sensitive both to local site geometry and long range order in the surface. The bond strength was found to vary systematically: n(111)x(100) > (100) > n(111)x(111) > (110) > (111). Distinct states for hydrogen at steps versus hydrogen on terraces could be distinguished. The (110) surface is shown to be a (111) vicinal, probably the [3(111) x 2(111)] microfacetted surface. The zero coverage heat of adsorption on the well-ordered (111) surface (48 kJ/mol) in solutions is the same as the value reported by Ertl and co-workers for adsorption on a (111) surface in vacuum. Adsorption Isotherms for hydrogen on the (111) and (100) surfaces is adequately fit by the classical model for immobile adsorption at single sites with nearest neighbor repulsive interaction.

  5. DISLOCATIONS AND PLASTIC BEHAVIOR OF IRON SINGLE CRYSTALS

    DTIC Science & Technology

    IRON , CRYSTAL STRUCTURE , CRYSTALLIZATION, DEFORMATION, ELASTIC PROPERTIES, GRAIN STRUCTURES(METALLURGY), GROWTH(PHYSIOLOGY), HEAT TREATMENT, METALLURGY, MICROSTRUCTURE, PLASTIC PROPERTIES, SPECTROGRAPHY.

  6. Postsynthetic Improvement of the Physical Properties in a Metal-Organic Framework through a Single Crystal to Single Crystal Transmetallation.

    PubMed

    Grancha, Thais; Ferrando-Soria, Jesús; Zhou, Hong-Cai; Gascon, Jorge; Seoane, Beatriz; Pasán, Jorge; Fabelo, Oscar; Julve, Miguel; Pardo, Emilio

    2015-05-26

    A single crystal to single crystal transmetallation process takes place in the three-dimensional (3D) metal-organic framework (MOF) of formula Mg(II) 2 {Mg(II) 4 [Cu(II) 2 (Me3 mpba)2 ]3 }⋅45 H2 O (1; Me3 mpba(4-) =N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)). After complete replacement of the Mg(II) ions within the coordination network and those hosted in the channels by either Co(II) or Ni(II) ions, 1 is transmetallated to yield two novel MOFs of formulae Co2 (II) {Co(II) 4 [Cu(II) 2 (Me3 mpba)2 ]3 }⋅56 H2 O (2) and Ni2 (II) {Ni(II) 4 [Cu(II) 2 (Me3 mpba)2 ]3 }⋅ 54 H2 O (3). This unique postsynthetic metal substitution affords materials with higher structural stability leading to enhanced gas sorption and magnetic properties.

  7. Crystal growth and optical properties of indium doped LiCaAlF6 scintillator single crystals

    NASA Astrophysics Data System (ADS)

    Tanaka, Chieko; Yokota, Yuui; Kurosawa, Shunsuke; Yamaji, Akihiro; Jary, Vitezslav; Babin, Vladimir; Pejchal, Jan; Ohashi, Yuji; Kamada, Kei; Nikl, Martin; Yoshikawa, Akira

    2017-03-01

    The In-doped LiCaAlF6 [In:LiCAF] single crystals were grown by the micro-pulling-down (μ-PD) method, and the phases, chemical compositions, transmittance and radioluminescence spectra were investigated. All the grown crystals showed high transparency and single phase of LiCAF without visible cracks and inclusions except for the end part of In2%:LiCAF crystal which included the impurity phase. In the radioluminescence spectra of the In:LiCAF crystals under X-ray irradiation, the emission peak around 750 nm was revealed.

  8. Design and analysis of large-core single-mode windmill single crystal sapphire optical fiber

    SciTech Connect

    Cheng, Yujie; Hill, Cary; Liu, Bo; Yu, Zhihao; Xuan, Haifeng; Homa, Daniel; Wang, Anbo; Pickrell, Gary

    2016-06-01

    We present a large-core single-mode “windmill” single crystal sapphire optical fiber (SCSF) design, which exhibits single-mode operation by stripping off the higher-order modes (HOMs) while maintaining the fundamental mode. The “windmill” SCSF design was analyzed using the finite element analysis method, in which all the HOMs are leaky. The numerical simulation results show single-mode operation in the spectral range from 0.4 to 2 μm in the windmill SCSF, with an effective core diameter as large as 14 μm. Such fiber is expected to improve the performance of many of the current sapphire fiber optic sensor structures.

  9. A preliminary review of organic materials single crystal growth by the Czochralski technique

    NASA Technical Reports Server (NTRS)

    Penn, B. G.; Shields, A. W.; Frazier, D. O.

    1988-01-01

    The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed.

  10. Single Crystal DMs for Space-Based Observatories

    NASA Astrophysics Data System (ADS)

    Bierden, Paul

    We propose to demonstrate the feasibility of a new manufacturing process for large aperture, high-actuator count microelectromechanical deformable mirrors (MEMS-DMs). These DMs are designed to fill a critical technology gap in NASA s plan for high- contrast space-based exoplanet observatories. We will manufacture a prototype DM with a continuous mirror facesheet, having an active aperture of 50mm diameter, supported by 2040 electrostatic actuators (50 across the diameter of the active aperture), spaced at a pitch of 1mm. The DM will be manufactured using silicon microfabrication tools. The strategic motivation for the proposed project is to advance MEMS DMs as an enabling technology in NASA s rapidly emerging program for extrasolar planet exploration. That goal is supported by an Astro2010 white paper on Technologies for Direct Optical Imaging of Exoplanets, which concluded that DMs are a critical component for all proposed internal coronagraph instrument concepts. That white paper pointed to great strides made by DM developers in the past decade, and acknowledged the components made by Boston Micromachines Corporation to be the most notable MEMS-based technology option. The principal manufacturing innovation in this project will be assembly of the DM through fusion bonding of three separate single crystal silicon wafers comprising the device s substrate, actuator array, and facesheet. The most significant challenge of this project will be to develop processes that allow reliable fusion bonds between multiple compliant silicon layers while yielding an optically flat surface and a robust electromechanical system. The compliance of the DM, which is required for its electromechanical function, will make it challenging to achieve the intimate, planar contact that is generally needed for success in fusion bonding. The manufacturing approach will use photolithography and reactive ion etching to pattern structural layers. Three wafer-scale devices will be patterned and

  11. Ignition and growth modeling of detonation reaction zone experiments on single crystals of PETN and HMX

    NASA Astrophysics Data System (ADS)

    White, Bradley W.; Tarver, Craig M.

    2017-01-01

    It has long been known that detonating single crystals of solid explosives have much larger failure diameters than those of heterogeneous charges of the same explosive pressed or cast to 98 - 99% theoretical maximum density (TMD). In 1957, Holland et al. demonstrated that PETN single crystals have failure diameters of about 8 mm, whereas heterogeneous PETN charges have failure diameters of less than 0.5 mm. Recently, Fedorov et al. quantitatively determined nanosecond time resolved detonation reaction zone profiles of single crystals of PETN and HMX by measuring the interface particle velocity histories of the detonating crystals and LiF windows using a PDV system. The measured reaction zone time durations for PETN and HMX single crystal detonations were approximately 100 and 260 nanoseconds, respectively. These experiments provided the necessary data to develop Ignition and Growth (I&G) reactive flow model parameters for the single crystal detonation reaction zones. Using these parameters, the calculated unconfined failure diameter of a PETN single crystal was 7.5 +/- 0.5 mm, close to the 8 mm experimental value. The calculated failure diameter of an unconfined HMX single crystal was 15 +/- 1 mm. The unconfined failure diameter of an HMX single crystal has not yet been determined precisely, but Fedorov et al. detonated 14 mm diameter crystals confined by detonating a HMX-based plastic bonded explosive (PBX) without initially overdriving the HMX crystals.

  12. Twin nucleation and migration in FeCr single crystals

    SciTech Connect

    Patriarca, L.; Abuzaid, Wael; Sehitoglu, Huseyin; Maier, Hans J.; Chumlyakov, Y.

    2013-01-15

    Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88 MPa, while twinning nucleates at a CRSS of about 191 MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress ( Almost-Equal-To 114-153 MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. - Highlights: Black-Right-Pointing-Pointer Digital image correlation allows to capture slip/twin initiation for bcc FeCr. Black-Right-Pointing-Pointer Crystal orientations from EBSD allow slip/twin system indexing. Black-Right-Pointing-Pointer Nucleation of slip always precedes twinning. Black-Right-Pointing-Pointer Twin growth is sustained with a lower stress than required for nucleation. Black-Right-Pointing-Pointer Twin-slip interactions provide high hardening at the onset of plasticity.

  13. Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals

    NASA Astrophysics Data System (ADS)

    Mahadevan, M.; Ramachandran, K.; Anandan, P.; Arivanandhan, M.; Bhagavannarayana, G.; Hayakawa, Y.

    2014-12-01

    Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method.

  14. Effect of the modulating of organic content on optical properties of single-crystal perovskite

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Yan, Jun; Wang, Ji; Chen, Yunlin

    2016-12-01

    Most of the systematic studies on affecting photoluminescence (PL) properties in single-crystal perovskite (MAPbX3: MA = CH3NH3, X = Br, I) have focused on changing the compositions of inorganic content. Here, a serious of MAPbX3 perovskite single crystals with different molar ratio of organic to inorganic were successfully prepared by inverse temperature crystallization (ITC) method. The morphology and the PL properties of the single crystals with different ratios of organic to inorganic content were investigated. We demonstrated that the PL intensity of MAPbX3 was increased with increasing the organic content of the perovskite single crystals. It was found that morphology and lattice constants of the perovskite crystals were varied with changing of the organic content. The mechanism of the effect of organic content on optical properties of single-crystal perovskite was discussed.

  15. Crystal growth and spectroscopic properties of Er3+ ions doped CdF2 single crystals

    NASA Astrophysics Data System (ADS)

    Djellab, S.; Diaf, M.; Labbaci, K.; Guerbous, L.

    2014-04-01

    Single crystals of Er3+:CdF2 with good optical quality were grown by a Bridgman technique after purification of the starting materials. Absorption and emission spectra are recorded at room temperature. The Judd-Ofelt (JO) analysis was applied to obtain the three phenomenological intensity parameters and the transition strengths. These JO parameters are used to calculate the radiative transition probabilities, the radiation lifetimes and the branching ratios. The results obtained are in good agreement with those of other fluoride laser materials. We also carried out luminescence measurements for red and green emission. The studied host may offer infrared and visible laser emissions.

  16. Compensation mechanism of bromine dopants in cadmium telluride single crystals

    DOE PAGES

    Bolotnikov, A. E.; Fochuk, P. M.; Verzhak, Ye. V.; ...

    2015-01-02

    We grew single crystals of cadmium telluride, doped with bromine by the Bridgman method, annealed them under a cadmium overpressure (PCd = 10² - 10⁵ Pa) at 800-1100 K, and investigated their electrical properties at high- and low-temperature. The influence of impurities on the crystals' electrical properties were analyzed using the defect subsystem model; the model includes the possibility of the formation of point intrinsic defects (V²⁻Cd, Cd²⁺i, V²⁺Te, Te²⁻i), and substitutional ones (Br⁰Te, Br⁺Te), as well as complexes of point defects, i.e., (Br⁺Te V²⁻Cd)⁻ and (2Br⁺Te V²⁻Cd)⁰. We established the concentration dependence between free charge carriers and themore » parameters of the annealing process. Here, n(T) and n(PCd) are determined by two dominant defects – Br⁺Te and (2Br⁺Te V²⁻Cd)⁰. Their content varies with the annealing temperature and the vapor pressure of the component; the concentration of other defects is much smaller and almost does not affect the electron density.« less

  17. Channels of oxygen diffusion in single crystal rubrene revealed.

    PubMed

    Thompson, Robert J; Bennett, Thomas; Fearn, Sarah; Kamaludin, Muhammad; Kloc, Christian; McPhail, David S; Mitrofanov, Oleg; Curson, Neil J

    2016-11-30

    Electronic devices made from organic materials have the potential to support a more ecologically friendly and affordable future. However, the ability to fabricate devices with well-defined and reproducible electrical and optical properties is hindered by the sensitivity to the presence of chemical impurities. Oxygen in particular is an impurity that can trap electrons and modify conductive properties of some organic materials. Until now the 3-dimensional profiling of oxygen species in organic semiconductors has been elusive and the effect of oxygen remains disputed. In this study we map out high-spatial resolution 3-dimensional distributions of oxygen inclusions near the surface of single crystal rubrene, using Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). Channels of diffused oxygen are found extending from uniform oxygen inclusion layers at the surface. These channels extend to depths in excess of 1.8 μm and act as an entry point for oxygen to diffuse along the ab-plane of the crystal with at least some of the diffused oxygen molecularly binding to rubrene. Our investigation of surfaces at different stages of evolution reveals the extent of oxygen inclusion, which affects rubrene's optical and transport properties, and is consequently of importance for the reliability and longevity of devices.

  18. From protein structure to function via single crystal optical spectroscopy

    PubMed Central

    Ronda, Luca; Bruno, Stefano; Bettati, Stefano; Storici, Paola; Mozzarelli, Andrea

    2015-01-01

    The more than 100,000 protein structures determined by X-ray crystallography provide a wealth of information for the characterization of biological processes at the molecular level. However, several crystallographic “artifacts,” including conformational selection, crystallization conditions and radiation damages, may affect the quality and the interpretation of the electron density maps, thus limiting the relevance of structure determinations. Moreover, for most of these structures, no functional data have been obtained in the crystalline state, thus posing serious questions on their validity in infereing protein mechanisms. In order to solve these issues, spectroscopic methods have been applied for the determination of equilibrium and kinetic properties of proteins in the crystalline state. These methods are UV-vis spectrophotometry, spectrofluorimetry, IR, EPR, Raman, and resonance Raman spectroscopy. Some of these approaches have been implemented with on-line instruments at X-ray synchrotron beamlines. Here, we provide an overview of investigations predominantly carried out in our laboratory by single crystal polarized absorption UV-vis microspectrophotometry, the most applied technique for the functional characterization of proteins in the crystalline state. Studies on hemoglobins, pyridoxal 5′-phosphate dependent enzymes and green fluorescent protein in the crystalline state have addressed key biological issues, leading to either straightforward structure-function correlations or limitations to structure-based mechanisms. PMID:25988179

  19. Solidification microstructures in single-crystal stainless steel melt pools

    SciTech Connect

    Sipf, J.B.; Boatner, L.A.; David, S.A.

    1994-03-01

    Development of microstructure of stationary melt pools of oriented stainless steel single crystals (70%Fe-15%Ni-15%Cr was analyzed. Stationary melt pools were formed by electron-beam and gas-tungsten-arc heating on (001), (011), and (111) oriented planes of the austenitic, fcc-alloy crystals. Characterization and analysis of resulting microstructure was carried out for each crystallographic plane and welding method. Results showed that crystallography which favors ``easy growth`` along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. These results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.

  20. Compensation mechanism of bromine dopants in cadmium telluride single crystals

    SciTech Connect

    Bolotnikov, A. E.; Fochuk, P. M.; Verzhak, Ye. V.; Parashchuk, T. O.; Freik, D. M.; Panchuk, O. E.; James, R. B.; Gorichok, I. V.

    2015-01-02

    We grew single crystals of cadmium telluride, doped with bromine by the Bridgman method, annealed them under a cadmium overpressure (PCd = 10² - 10⁵ Pa) at 800-1100 K, and investigated their electrical properties at high- and low-temperature. The influence of impurities on the crystals' electrical properties were analyzed using the defect subsystem model; the model includes the possibility of the formation of point intrinsic defects (V²⁻Cd, Cd²⁺i, V²⁺Te, Te²⁻i), and substitutional ones (Br⁰Te, Br⁺Te), as well as complexes of point defects, i.e., (Br⁺Te V²⁻Cd)⁻ and (2Br⁺Te V²⁻Cd)⁰. We established the concentration dependence between free charge carriers and the parameters of the annealing process. Here, n(T) and n(PCd) are determined by two dominant defects – Br⁺Te and (2Br⁺Te V²⁻Cd)⁰. Their content varies with the annealing temperature and the vapor pressure of the component; the concentration of other defects is much smaller and almost does not affect the electron density.

  1. Liquid crystal deposition on poled, single crystalline lithium niobate

    NASA Astrophysics Data System (ADS)

    Bharath, S. C.; Pimputkar, K. R.; Pronschinske, A. M.; Pearl, T. P.

    2008-01-01

    For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), 'Z-cut' along the (0 0 0 1) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4- n-octyl-4'-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur.

  2. Ion implantation of CdTe single crystals

    NASA Astrophysics Data System (ADS)

    Wiecek, Tomasz; Popovich, Volodymir; Bester, Mariusz; Kuzma, Marian

    2016-12-01

    Ion implantation is a technique which is widely used in industry for unique modification of metal surface for medical applications. In semiconductor silicon technology ion implantation is also widely used for thin layer electronic or optoelectronic devices production. For other semiconductor materials this technique is still at an early stage. In this paper based on literature data we present the main features of the implantation of CdTe single crystals as well as some of the major problems which are likely to occur when dealing with them. The most unexpected feature is the high resistance of these crystals against the amorphization caused by ion implantation even at high doses (1017 1/cm2). The second property is the disposal of defects much deeper in the sample then it follows from the modeling calculations. The outline of principles of the ion implantation is included in the paper. The data based on RBS measurements and modeling results obtained by using SRIM software were taken into account.

  3. Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite

    NASA Technical Reports Server (NTRS)

    Wilkins, R.; Powell, Kirk St. A.; Loregnard, Kieron R.; Lin, Sy-Chyi; Muthusami, Jayakumar; Zhou, Feng; Pandey, R. K.; Brown, Geoff; Hawley, M. E.

    1998-01-01

    Ilmenite (FeTiOs) is a wide bandgap semiconductor with an energy gap of 2.58 eV. Ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Single crystal ilmenite has been grown from the melt using the Czochralski method. Growth conditions have a profound effect on the microstructure of the samples. Here we present data from a variety of analytical techniques which indicate that some grown crystals exhibit distinct phase separation during growth. This phase separation is apparent for both post-growth annealed and unannealed samples. Under optical microscopy, there appear two distinct areas forming a matrix with an array of dots on order of 5 pm diameter. While appearing bright in the optical micrograph, atomic force microscope (AFM) shows the dots to be shallow pits on the surface. Magnetic force microscope (MFM) shows the dots to be magnetic. Phase identification via electron microprobe analysis (EMPA) indicates two major phases in the unannealed samples and four in the annealed samples, where the dots appear to be almost pure iron. This is consistent with micrographs taken with a scanning probe microscope used in the magnetic force mode. Samples that do not exhibit the phase separation have little or no discernible magnetic structure detectable by the MFM.

  4. Growth and characterization of nonlinear optical single crystal: Nicotinic L-tartaric

    SciTech Connect

    Sheelarani, V.; Shanthi, J.

    2015-06-24

    Nonlinear optical single crystals were grown from Nicotinic and L-Tartaric acid by slow evaporation technique at room temperature. Structure of the grown crystal was confirmed by single crystal X-ray diffraction studies, The crystallinity of the Nicotinic L-Tartaric (NLT) crystals was confirmed from the powder XRD pattern. The transparent range and cut off wavelength of the grown crystal was studied by the UV–Vis spectroscopic analysis.The thermal stability of the crystal was studied by TG-DTA. The second harmonic generation (SHG) efficiency of NLT was confirmed by Kurtz Perry technique.

  5. Growth and characterization of nonlinear optical single crystal: Nicotinic L-tartaric

    NASA Astrophysics Data System (ADS)

    Sheelarani, V.; Shanthi, J.

    2015-06-01

    Nonlinear optical single crystals were grown from Nicotinic and L-Tartaric acid by slow evaporation technique at room temperature. Structure of the grown crystal was confirmed by single crystal X-ray diffraction studies, The crystallinity of the Nicotinic L-Tartaric (NLT) crystals was confirmed from the powder XRD pattern. The transparent range and cut off wavelength of the grown crystal was studied by the UV-Vis spectroscopic analysis.The thermal stability of the crystal was studied by TG-DTA. The second harmonic generation (SHG) efficiency of NLT was confirmed by Kurtz Perry technique.

  6. Single crystal metal wedges for surface acoustic wave propagation

    DOEpatents

    Fisher, E.S.

    1980-05-09

    An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

  7. Shock compression experiments on Lithium Deuteride single crystals.

    SciTech Connect

    Knudson, Marcus D.; Desjarlais, Michael Paul; Lemke, Raymond W.

    2014-10-01

    S hock compression exper iments in the few hundred GPa (multi - Mabr) regime were performed on Lithium Deuteride (LiD) single crystals . This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17 - 32 km/s. Measurements included pressure, density, and temperature between %7E200 - 600 GPa along the Principal Hugoniot - the locus of end states achievable through compression by large amplitude shock waves - as well as pressure and density of re - shock states up to %7E900 GPa . The experimental measurements are compared with recent density functional theory calculations as well as a new tabular equation of state developed at Los Alamos National Labs.

  8. Shock Hugoniot behavior of single crystal titanium using atomistic simulations

    NASA Astrophysics Data System (ADS)

    Mackenchery, Karoon; Dongare, Avinash

    2017-01-01

    Atomistic shock simulations are performed for single crystal titanium using four different interatomic potentials at impact velocities ranging from 0.5 km/s to 2.0 km/s. These potentials comprise of three parameterizations in the formulation of the embedded atom method and one formulation of the modified embedded atom method. The capability of the potentials to model the shock deformation and failure behavior is investigated by computing the shock hugoniot response of titanium and comparing to existing experimental data. In addition, the capability to reproduce the shock induced alpha (α) to omega (ω) phase transformation seen in Ti is investigated. The shock wave structure is discussed and the velocities for the elastic, plastic and the α-ω phase transformation waves are calculated for all the interatomic potentials considered.

  9. Oxidation resistance and critical sulfur content of single crystal superalloys

    SciTech Connect

    Smialek, J.L.

    1998-04-01

    Single crystal superalloys had greatly improved cyclic oxidation resistance when their sulfur content was reduced from impurity levels, typically 5--10 ppmw in past years, down to 1 ppmw or below currently. Excellent alumina scale adhesion has been documented for PWA 1480, PWA 1484, Rene`N5, Rene`N6, and CMSX 4, all without reactive element (Y) additions. Hydrogen annealing was used for effective desulfurization to below 0.1 ppmw, as well as for achieving controlled intermediate levels. This paper summarizes the direct relationship between cyclic oxidation behavior and sulfur content. An adhesion criterion has been proposed based on the concentration of sulfur needed to initiate spallation due to a monolayer of interfacial segregation. This suggests that a level down to {approximately}0.2 ppmw would be needed to maximize adhesion for a 1 mm thick sample. It is in reasonable agreement with the experimental results.

  10. Fishtail effect in twinned and detwinned YBCO single crystals

    NASA Astrophysics Data System (ADS)

    Boudissa, M.; Halimi, R.; Frikach, K.; Senoussi, S.

    2006-09-01

    We have studied the magnetization hysteresis loops of a twinned and detwinned single crystals in a temperature range between 4.2 and 100 K and a magnetic field (H) range between 0 and 6 T. We carried out relaxation measurements on the samples at different temperatures and magnetic fields. We investigated the twin pinning as a function of temperature (T) and the fishtail anomaly in the critical current density of the two samples. We tried in this study to confirm or infirm the different models which explain the fishtail effect by confronting them to our experimental results We found that the collective creep theory is consistent with the results of our experiment in the field region where the magnetization is at its minimum. This field marks a crossover between the small and large bundle pinning regimes.

  11. Light-induced ESR centres in single crystal rutile

    NASA Astrophysics Data System (ADS)

    Hodgskiss, S. W.; Thorp, J. S.

    1983-04-01

    Electron spin resonance studies have been made on Verneuil-grown rutile single crystals, which were doped with a variety of transition gorup ions. Measurements were made at 9 GHz, both before and after UV irradiation, at temperatures in the range from 4.2 to 300 K. UV irradiation had two effects: (a) to affect the relative intensities of esr lines due to species already present, (b) to generate new esr spectra. Both effects are interpreted as representing a redistribution of charge amongst trapping centres. Seven UV generated centres have been identified and characterised in terms of their spin Hamiltonian parameters. Isochronal annealing techniques have been used to determine the ionisation temperatures of the traps. Observation of interactions and charge transfers between centres during isochronal annealing was used to determine the polarity and type of each centre.

  12. InPBi single crystals grown by molecular beam epitaxy.

    PubMed

    Wang, K; Gu, Y; Zhou, H F; Zhang, L Y; Kang, C Z; Wu, M J; Pan, W W; Lu, P F; Gong, Q; Wang, S M

    2014-06-26

    InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III-V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4-2.7 μm which can't be explained by the existing theory.

  13. A neutron sensor based on synthetic single crystal diamond

    SciTech Connect

    Schmid, G J; Koch, J A; Lerche, R A; Moran, M J

    2003-10-17

    We report the first neutron data for a single crystal Chemical Vapor Deposition (CVD) diamond sensor. Results are presented for 2.5, 14.1, and 14.9 MeV incident neutrons. We show that the energy resolution for 14.1 MeV neutrons is at least 2.9% (as limited by the energy spread of the incident neutrons), and perhaps as good as 0.4% (as extrapolated from high resolution {alpha} particle data). This result could be relevant to fusion neutron spectroscopy at machines like the International Thermonuclear Experimental Reactor (ITER). We also show that our sensor has a high neutron linear attenuation coefficient, due to the high atomic density of diamond, and this could lead to applications in fission neutron detection.

  14. Photoinduced surface voltage mapping study for large perovskite single crystals

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojing; Liu, Yucheng; Gao, Fei; Yang, Zhou; Liu, Shengzhong Frank

    2016-05-01

    Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH3NH3PbX3 (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

  15. Progress in organic molecular single crystal FET electronics

    NASA Astrophysics Data System (ADS)

    Butko, Vladimir; Chi, Xiaoliu; Ramirez, Arthur

    2004-03-01

    Semiconducting organic materials have received increased attention because they promise bulk processing of flexible, large-area electronic devices. Field Effect Transistors (FETs) provide a powerful method of investigating two-dimensional properties of these materials. We report on fabrication and characterization of FETs on organic molecular single-crystals of pentacene and tetracene [1,2]. The FETs exhibit hole conductivity with room temperature record effective mobility, up to 2 -3 cm^2/Vs and on/off ratios up to 2*10^7. We were able to suppress an activation energy of pentacene down to ˜ 30 mK by applying gate voltage of 45 V. 1. V.Y. Butko, X. Chi, D. V. Lang and A. P. Ramirez, Applied Physics Letters, v.83, #23, pp. 4773-4775, December 8, 2003 2. V.Y. Butko, X. Chi, A. P. Ramirez , Solid State Communications, v. 128/11, pp. 431, 2003

  16. The lattice stiffening transition in UO2 single crystals

    NASA Astrophysics Data System (ADS)

    Young, Christopher; Petrosky, James; Mann, J. Matthew; Hunt, Eric M.; Turner, David; Dowben, Peter A.

    2017-01-01

    The effective Debye temperatures ({{\\Theta}\\text{DE}} ) of the surface region of UO2 single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K-623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500  ±  59 K below 475 K and 165  ±  21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO2 Debye temperature, with the changes in the lattice expansion coefficient for UO2, support strong lattice-phonon interaction arising from the Jahn-Teller distortion.

  17. Single crystal metal wedges for surface acoustic wave propagation

    DOEpatents

    Fisher, Edward S.

    1982-01-01

    An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

  18. Synthetic single crystal diamond diodes for radiotherapy dosimetry

    NASA Astrophysics Data System (ADS)

    Almaviva, S.; Marinelli, Marco; Milani, E.; Tucciarone, A.; Verona-Rinati, G.; Consorti, R.; Petrucci, A.; De Notaristefani, F.; Ciancaglioni, I.

    2008-09-01

    Synthetic single crystal diamonds in a p-type/intrinsic/metal structure were tested as dosimeters for radiotherapy. The devices have been analyzed by using 6 and 10 MV Bremsstrahlung X-ray beams and electron beams from 6 MeV up to 18 MeV from a CLINAC DHX Varian accelerator. All measurements have been performed in a water phantom and ionization chambers were used for calibration and comparison. The dosimeters were operated in photovoltaic regime with no external bias voltage applied. A few Gy pre-irradiation was performed in order to stabilize the device output, resulting in fluctuations sensitivity below ±0.5%. No dose rate dependence of the detector response was observed. Very good reproducibility and linearity were obtained as well.

  19. Large electrocaloric effects in single-crystal ammonium sulfate.

    PubMed

    Crossley, S; Li, W; Moya, X; Mathur, N D

    2016-08-13

    Electrocaloric (EC) effects are typically studied near phase transitions in ceramic and polymer materials. Here, we investigate EC effects in an inorganic salt, namely ammonium sulfate (NH4)2SO4, with an order-disorder transition whose onset occurs at 223 K on cooling. For a single crystal thinned to 50 μm, we use a Maxwell relation to find a large isothermal entropy change of 30 J K(-1) kg(-1) in response to a field change of 400 kV cm(-1) The Clausius-Clapeyron equation implies a corresponding adiabatic temperature change of 4.5 K.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  20. Surface recrystallization of a single crystal nickel-base superalloy

    NASA Astrophysics Data System (ADS)

    Meng, Jie; Jin, Tao; Sun, Xiao-Feng; Hu, Zhuang-Qi

    2011-04-01

    The recrystallization behavior of a single crystal nickel-base superalloy was investigated by shot peening and subsequent annealing. Two kinds of recrystallization microstructures, which are intensively dependent on the annealing temperature, are shown in the nickel-base superalloy after shot peening and subsequent annealing. Surface recrystallized grains are obtained when the superalloy is annealed at solution treatment temperature. The nucleation of recrystallization originates from the dendritic core, where rapid dissolution of γ' particles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the moving boundary and more γ' particles dissolution led by residual stress are developed from the surface region. Recrystallized kinetics of the shot-peened alloy annealed at 1050°C accords with the Johnson-Mehl-Avrami-Kolmogorov equation. The low Avrami exponent is caused by the inhomogeneous distribution of stored energy, the decreasing of stored energy during recovery, and the strong resistance of boundary migration by γ' particles.

  1. Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1998-01-01

    Single crystal superalloys exhibit excellent cyclic oxidation resistance if their sulfur content is reduced from typical impurity levels of approximately 5 ppmw to below 0.5 ppmw. Excellent alumina scale adhesion was documented for PWA 1480 and PWA 1484 without yttrium additions. Hydrogen annealing produced effective desulfurization of PWA 1480 to less than 0.2 ppmw and was also used to achieve controlled intermediate levels. The direct relationship between cyclic oxidation behavior and sulfur content was shown. An adhesion criterion was proposed based on the total amount of sulfur available for interfacial segregation, e.g., less than or equal to 0.2 ppmw S will maximize adhesion for a 1 mm thick sample. PWA 1484, melt desulfurized to 0.3 ppmw S, also exhibited excellent cyclic oxidation resistance and encouraging TBC lives (10 mils of 8YSZ, plasma sprayed without a bond coat) in 1100 C cyclic oxidation tests.

  2. Friction and deformation behavior of single-crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.

  3. Growth of single-crystal YAG fiber optics.

    PubMed

    Nie, Craig D; Bera, Subhabrata; Harrington, James A

    2016-07-11

    Single-crystal YAG (Y3Al5O12) fibers have been grown by the laser heated pedestal growth technique with losses as low as 0.3 dB/m at 1.06 μm. These YAG fibers are as long as about 60 cm with diameters around 330 μm. The early fibers were grown from unoriented YAG seed fibers and these fibers exhibited facet steps or ridges on the surface of the fiber. However, recently we have grown fibers using an oriented seed to grow step-free fibers. Scattering losses made on the fibers indicate that the scattering losses are equal to about 30% of the total loss.

  4. Analysis of ripple formation in single crystal spot welds

    NASA Technical Reports Server (NTRS)

    Rappaz, M.; Corrigan, D.; Boatner, L. A.

    1997-01-01

    Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

  5. Electrical conduction in nanodomains in congruent lithium tantalate single crystal

    SciTech Connect

    Cho, Yasuo

    2014-01-27

    The electrical current flow behavior was investigated for nanodomains formed in a thin congruent lithium tantalate (LiTaO{sub 3}) single-crystal plate. When the nanodomains were relatively large, with diameters of about 100 nm, current flow was detected along the domain wall. However, when they were about 40 nm or smaller, the current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. Unlike the case of LiNbO{sub 3}, optical illumination was not required for current conduction in LiTaO{sub 3}. A clear temperature dependence of the current was found indicating that the conduction mechanism for nanodomains in LiTaO{sub 3} may involve thermally activated carrier hopping.

  6. Paleomagnetism and paleointensity recorded by single silicate crystals

    NASA Astrophysics Data System (ADS)

    Tarduno, J. A.

    2008-12-01

    Silicate minerals can contain minute magnetic inclusions that are well suited as recorders of the ancient magnetic field. In a magnetic hysteresis survey of natural minerals in 1997-1998, workers in the University of Rochester lab found that natural olivine and pyroxene separated from mafic lavas tended to contain multi- domain magnetic inclusions, whereas plagioclase feldspars hosted smaller single domain particles. These findings led to Thellier analyses of plagioclase crystals to define field strength for reversing and non- reversing (i.e. Superchron) time intervals; data available to date support an inverse relationship between field strength and reversal rate suggested by Cox (1968) and seen in some numerical simulations of the geodynamo that call upon mantle forcing. A key part of these studies are comparisons of single crystals and whole rock results; these show that bulk lava samples are often biased by alteration on geologic and laboratory time scales, and by the presence of non-ideal carriers. I will review the status of our efforts to further constrain field strength versus reversal rate, and the special challenges posed in the investigation of the earliest magnetic field. The latter work has motivated the development of new heating techniques and a further exploration of silicate carriers of magnetization. Although technically challenging, these studies have yielded the oldest field strength record based on a TRM (i.e. the field was within 50% of the modern value 3.2 billion-years-ago). Efforts to test for the presence of an even older dynamo will be discussed.

  7. Process development for single-crystal silicon solar cells

    NASA Astrophysics Data System (ADS)

    Bohra, Mihir H.

    Solar energy is a viable, rapidly growing and an important renewable alternative to other sources of energy generation because of its abundant supply and low manufacturing cost. Silicon still remains the major contributor for manufacturing solar cells accounting for 80% of the market share. Of this, single-crystal solar cells account for half of the share. Laboratory cells have demonstrated 25% efficiency; however, commercial cells have efficiencies of 16% - 20% resulting from a focus on implementation processes geared to rapid throughput and low cost, thereby reducing the energy pay-back time. An example would be the use of metal pastes which dissolve the dielectric during the firing process as opposed to lithographically defined contacts. With current trends of single-crystal silicon photovoltaic (PV) module prices down to 0.60/W, almost all other PV technologies are challenged to remain cost competitive. This presents a unique opportunity in revisiting the PV cell fabrication process and incorporating moderately more expensive IC process practices into PV manufacturing. While they may drive the cost toward a 1/W benchmark, there is substantial room to "experiment", leading to higher efficiencies which will help maintain the overall system cost. This work entails a turn-key process designed to provide a platform for rapid evaluation of novel materials and processes. A two-step lithographic process yielding a baseline 11% - 13% efficient cell is described. Results of three studies have shown improvements in solar cell output parameters due to the inclusion of a back-surface field implant, a higher emitter doping and also an additional RCA Clean.

  8. Growth and microtopographic study of CuInSe2 single crystals

    NASA Astrophysics Data System (ADS)

    Chauhan, Sanjaysinh M.; Chaki, Sunil; Tailor, J. P.; Deshpande, M. P.

    2016-05-01

    The CuInSe2 single crystals were grown by chemical vapour transport (CVT) technique using iodine as transporting agent. The elemental composition of the as-grown CuInSe2 single crystals was determined by energy dispersive analysis of X-ray (EDAX). The unit cell crystal structure and lattice parameters were determined by X-ray diffraction (XRD) technique. The surface microtopographic study of the as-grown CuInSe2 single crystals surfaces were done to study the defects, growth mechanism, etc. of the CVT grown crystals.

  9. Single crystal growth and X-ray structure analysis of non-peripheral octahexyl phthalocyanine

    NASA Astrophysics Data System (ADS)

    Ohmori, Masashi; Nakano, Chika; Higashi, Takuya; Miyano, Tetsuya; Tohnai, Norimitsu; Fujii, Akihiko; Ozaki, Masanori

    2016-07-01

    The single-crystal structure of metal-free non-peripheral octahexyl-substituted phthalocyanine (C6PcH2) has been investigated by single-crystal X-ray structure analysis. Two types of C6PcH2 single crystal, bulk and needle crystals, were separately grown by controlling the recrystallization conditions. The structures of the two types of crystal were determined, and were found to be completely different, that is, C6PcH2 exhibits structural polymorphism. It has been clarified that the C6PcH2 microcrystals in thin films used in previously reported electronic devices have the needle structure.

  10. Method for the preparation of inorganic single crystal and polycrystalline electronic materials

    NASA Technical Reports Server (NTRS)

    Groves, W. O. (Inventor)

    1969-01-01

    Large area, semiconductor crystals selected from group 3-5 compounds and alloys are provided for semiconductor device fabrication by the use of a selective etching operation which completely removes the substrate on which the desired crystal was deposited. The substrate, selected from the same group as the single crystal, has a higher solution rate than the epitaxial single crystal which is essentially unaffected by the etching solution. The preparation of gallium phosphide single crystals using a gallium arsenide substrate and a concentrated nitric acid etching solution is described.

  11. Comparative study of intrinsic luminescence in undoped transparent ceramic and single crystal garnet scintillators

    NASA Astrophysics Data System (ADS)

    Fujimoto, Yutaka; Yanagida, Takayuki; Yagi, Hideki; Yanagidani, Takagimi; Chani, Valery

    2014-10-01

    Scintillation properties associated with intrinsic lattice defects of undoped Y3A5O12 (YAG) and Lu3A5O12 (LuAG) transparent ceramics and single crystals are compared. The ceramics excited with X-ray demonstrated relatively low emission intensity when compared with that of the single crystals. Decay times of the ceramics and the single crystals were similar. These parameters were approximately 430 ns (YAG ceramic), 460 ns (YAG single crystal), 30 ns and 1090 ns (LuAG ceramic), and 25 ns and 970 ns (LuAG single crystal). According to the pulse height spectra recorded under 137Cs gamma-ray irradiation, the scintillation light yield of the both ceramics were about 2950 ± 290 ph/MeV. However, the single crystals had greater kight yield of about about 14,300 ± 1430 ph/MeV for YAG and 8350 ± 830 ph/MeV for LuAG.

  12. Growth and characterization of WSe2 single crystals using TeCl4 as transport agent

    NASA Astrophysics Data System (ADS)

    Bougouma, Moussa; Nisol, Bernard; Doneux, Thomas; Guel, Boubié; Segato, Tiriana; Reniers, François; Delplancke-Ogletree, Marie-Paule; Legma, Jean B.; Buess-Herman, Claudine

    2016-11-01

    The growth of WSe2 single crystals, using TeCl4 as transport agent was performed successfully from slowly cooled polycrystalline powders as precursors. The resulting single crystals were characterized by X-ray diffraction (XRD) and their surfaces examined by scanning electron microscopy (SEM) presented fewer defects than single crystals prepared from air-quenched polycrystalline powders. Energy Dispersive X-ray microanalysis (EDX), inductively coupled plasma (ICP) spectroscopy and X-ray photoelectron spectroscopy (XPS) revealed that the single crystals are homogeneous and stoichiometric. Electrical conductivity and photocurrent measurements have confirmed the semiconducting character of the single crystals and a photocurrent of 75 mA cm-2 has been reached. In addition, single crystals with areas in the 25-100 mm2 range can be obtained under the reported growth conditions.

  13. Water weakening in experimentally deformed milky quartz single crystals

    NASA Astrophysics Data System (ADS)

    Stunitz, H.; Thust, A.; Kilian, R.; Heilbronner, R.; Behrens, H.; Tarantola, A.; Fitz Gerald, J. D.

    2015-12-01

    Natural single crystals of quartz have been experimentally deformed in two orientations: (1) normal to one prism-plane, (2) In O+ orientation at temperatures of 900 and 1000°C, pressures of 1.0 and 1.5 GPa, and strain rates of ~1 x 10-6s-1. The starting material is milky quartz, consisting of dry quartz (H2O contents of <150 H/106Si) with fluid inclusions (FI). During pressurization many FI´s decrepitate. Cracks heal and small neonate FI´s form, increasing the number of FI´s drastically. During subsequent deformation, the size of FI´s is further reduced (down to ~10 nm). Sample deformation occurs by dominant dislocation glide on selected slip systems, accompanied by some dynamic recovery. Strongly deformed regions show FTIR spectra with a pointed broad absorption band in the ~3400 cm-1 region as a superposition of molecular H2O bands and three discrete absorption bands (at 3367, 3400, and 3434 cm-1). In addition, there is a discrete absorption band at 3585 cm-1, which only occurs in deformed regions. The 3585 cm-1 band is reduced or even disappears after annealing. This band is polarized and represents structurally bound H, its H-content is estimated to be 1-3% of the total H2O-content and appears to be associated with dislocations. The H2O weakening effect in our FI-bearing natural quartz crystals is assigned to the processes of dislocation generation and multiplication at small FI´s. The deformation processes in these crystals represent a recycling of H2O between FI´s, dislocation generation at very small fluid inclusions, incorporation of structurally bound H into dislocation cores, and release of H2O from dislocations back into FI´s during recovery. Cracking and crack healing play an important role in the recycling process and imply a close interrelationship between brittle and crystal plastic deformation. The H2O weakening by this process is of a disequilibrium nature and thus depends on the amount of H2O available.

  14. Hexaazide octahedral molybdenum cluster complexes: Synthesis, properties and the evidence of hydrolysis

    NASA Astrophysics Data System (ADS)

    Vorotnikov, Yuri A.; Efremova, Olga A.; Novozhilov, Igor N.; Yanshole, Vadim V.; Kuratieva, Natalia V.; Brylev, Konstantin A.; Kitamura, Noboru; Mironov, Yuri V.; Shestopalov, Michael A.

    2017-04-01

    This article reports the synthesis, crystal structure of new molybdenum hexaazide cluster complex (nBu4N)2[{Mo6I8}(N3)6] (3) and comparison of its photophysical and electrochemical properties to those of earlier reported analogues (nBu4N)2[{Mo6X8}(N3)6] (X = Cl, Br). Additionally, the dimerisation of 3 as a result of hydrolysis was revealed by mass spectrometry and single crystal X-Ray diffraction. Indeed, the structurally characterised compound (nBu4N)4[({Mo6I8}(N3)5)2O] represents the first example of oxo-bridged dimer of octahedral molybdenum clusters complexes.

  15. Controlled Synthesis of Polymer Brushes via Polymer Single Crystal Templates

    NASA Astrophysics Data System (ADS)

    Zhou, Tian

    A novel synthetic method of polymer brushes using polymer single crystals (PSCs) as solid-state templates is introduced in this study. PSC has a quasi-2D lamellae structure with polymer chains fold back-and-forth perpendicular to the lamellae surfaces. During crystallization, the chain ends are excluded from the unit cell onto the lamellae surfaces, which makes the material extremely versatile in its functionality. Such structure holds the unique capability to harvest nanoparticles, or being immobilized onto macroscopic flat surfaces. After dissolving PSCs in good solvent, polymer brushes are chemically tethered on either nanoparticles or flat macroscopic surfaces. Because the chain-folding structure can be conveniently tailored by changing the molecular weight of polymer and the crystallization temperature, the thickness, grafting density and morphology of resulted polymer brushes can be precisely controlled. As a model system, poly(?-caprolactone) with thiol or alkoxysilane terminal groups was used, and polymer brushes were successfully prepared on both nanoparticles and glass/Au flat surfaces. The structure-property relationships of the as-prepared polymer brushes were studied in detail using multiple characterization techniques. First of all, when functionalizing nanoparticles, by engineering the chain-folding structure of the PSCs, interesting complex nanostructures can be formed by nanoparticles including Janus nanoparticles and nanoparticle dimers. These unique structures render hybrid nanoparticles very interesting responsive behavior which have been studied in detail in this dissertation. When grafted onto a flat surface on the other hand, not only the molecular weight and grafting density can be precisely controlled, the tethering points of a single polymer chain can also be conveniently tailored, resulting polymer brushes with either tail or loop structures. Such difference in brush structure can significantly alter the properties of functional surface

  16. Structure of cleaved (001) USb2 single crystal

    SciTech Connect

    Chen, Shao-ping; Hawley, Marilyn; Bauer, Eric D; Stockum, Phil B; Manoharan, Hari C

    2009-01-01

    We have achieved what we believe to be the first atomic resolution STM images for a uranium compound taken at room temperature. The a, b, and c lattice parameters in the images confirm that the USb{sub 2} crystals cleave on the (001) basal plane as expected. The a and b dimensions were equal, with the atoms arranged in a cubic pattern. Our calculations indicate a symmetric cut between Sb planes to be the most favorable cleavage plane and U atoms to be responsible for most of the DOS measured by STM. Some strange features observed in the STM will be discussed in conjunction with ab initio calculations. The purpose of this work is to demonstrate the power of scanning tunneling microscopy (STM) techniques combined with a theoretical underpinning to determine the surface atomic structure and properties of actinide materials, such as the quasi 2-dimensional uranium dipnictide USb{sub 2} single crystal, thereby contributing to the understanding of their surface structural and electronic properties. The members of this interesting UX{sub 2} (X=P, As, Sb, Bi) series of compounds display dual localized and itinerant 5f electron behavior within the same compound due to the hybridization of the 5f orbitals with the conduction band. With the exception of UO{sub 2}, which has to be studied at elevated temperature to generate enough carriers for STM imaging, STM techniques have not been applied successfully to the characterization of the surface atomic structure of any other single crystal actinide compound, to the best of our knowledge. However, STM has been used to a limited extent for the study of some cerium compounds. STM probes electronic properties at the atomic level and can directly provide information about the local density of filled and empty states (LDOS) states simultaneously. A STM topograph provides the local atomic arrangement and spacing of the atoms on the surface, local defect structures (e.g. steps, vacancies, and kink sites) and the presence of contaminants

  17. The Strength of PIN-PMN-PT Single Crystals under Bending with a Longitudinal Electric Field

    DTIC Science & Technology

    2011-04-06

    The strength of PIN– PMN – PT single crystals under bending with a longitudinal electric field This article has been downloaded from IOPscience. Please...COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE The Strength Of PIN- PMN - PT Single Crystals Under Bending With A Longitudinal Electric Field... PMN ? PT ) single crystals was measured using a four point bending apparatus with a longitudinal electric field applied to the bar during bending. The

  18. Superlubricity of molybdenum disulphide

    NASA Astrophysics Data System (ADS)

    Martin, J. M.; Donnet, C.; Le Mogne, Th.; Epicier, Th.

    1993-10-01

    We have studied the atomistic origins of the ultralow friction coefficient of a molybdenum disulphide (MoS2) coating in ultrahigh vacuum conditions. A friction coefficient in the 10-3 range is associated with friction-induced orientation of ``easy shear'' basal planes of the MoS2 crystal structure parallel to the sliding direction. In addition to this basal plane orientation, an orientation disorder around the c axis is observed, indicating that frictional anisotropy during intercrystallite slip could be at the origin of the vanishing of the friction force. Experimental HRTEM lattice fringe imaging of MoS2 wear particles clearly show the existence of characteristic Moiré patterns. We have simulated TEM lattice fringe images of a [0001] MoS2 crystal and produced rotational Moiré patterns by superimposing two such images. A qualitative agreement between experimental and simulated Moiré patterns is demonstrated, which gives credence that ultralow friction of MoS2 in high vacuum can be attributed to a superlubric situation, by frictional anisotropy of sulphur-rich basal planes during intercrystallite slip.

  19. Unusual formation of single-crystal manganese sulfide microboxes co-mediated by the cubic crystal structure and shape.

    PubMed

    Zhang, Lei; Zhou, Liang; Wu, Hao Bin; Xu, Rong; Lou, Xiong Wen David

    2012-07-16

    Kept cubic: MnS microboxes, which act as an anode material for lithium ion batteries, are synthesized by a simple H(2)S gas sulfidation approach (TEM images show porous and hollow microcubes and a microbox). The formation of the single crystals is aided by the intrinsic cubic crystal structure and the nearly cubic shape of the MnCO(3) precursor.

  20. Structural and optical properties of Cd2+ ion on the growth of sulphamic acid single crystals

    NASA Astrophysics Data System (ADS)

    Rajyalakshmi, S.; Rao, Valluru Srinivasa; Reddy, P. V. S. S. S. N.; Krishna, V. Y. Rama; Samatha, K.; Rao, K. Ramachandra

    2016-05-01

    Transparent single crystals of Cadmium doped Sulphamic acid (SA) was grown by Conventional slow evaporation solution technique (SEST) which had the size of 13 × 8 × 7 mm3. The grown single crystals have been characterized using single crystal X-ray diffraction UV-visible Spectral studies and Second harmonic generation (SHG) efficiency and the results were discussed. The lattice parameters of the grown Cd2+ ion doped SA crystal are confirmed by single crystal X-ray diffraction and belong to orthorhombic system. Optical transmittance of the crystal was recorded using UV-vis NIR spectrophotometer with its lower cut off wavelength around 259nm. SHG measurements indicate that the SHG efficiency of the grown Cd2+ ion doped SA crystal at a fundamental wavelength of 1064 nm is approximately equal to KDP.

  1. A COMPARISON OF FAR INFRARED AND RAMAN SPECTRA OF SOME RARE EARTH GARNET SINGLE CRYSTALS,

    DTIC Science & Technology

    RARE EARTH COMPOUNDS, *INFRARED SPECTRA), (*GARNET, RARE EARTH COMPOUNDS), (* RAMAN SPECTROSCOPY, RARE EARTH COMPOUNDS), SINGLE CRYSTALS, ALUMINATES...PHONONS, YTTRIUM COMPOUNDS, YTTERBIUM COMPOUNDS, TERBIUM COMPOUNDS, DYSPROSIUM COMPOUNDS, CANADA

  2. Synthesis, Crystal Growth and Characterization of bis Dl-Valine Picrate Single Crystal for Second-Order Nonlinear Optical Applications

    NASA Astrophysics Data System (ADS)

    Silambarasan, A.; Krishna Kumar, M.; Sudhahar, S.; Thirunavukkarasu, A.; Mohan Kumar, R.; Umarani, P. R.

    2013-08-01

    An organic compound Bis DL-Valine picrate (BDLVP) was synthesized successfully and single crystal was grown by slow evaporation solution growth method. The presence of functional groups in the compound was identified by FTIR spectral analysis. Single crystal X-ray diffraction study revealed that the grown crystal belongs to P21/n space group of monoclinic crystal system. Powder X-ray diffraction pattern was recorded to know the crystalline perfection of the grown crystal. The reaction mechanism, thermal decomposition stages and thermal stability of the grown crystal were studied by using TG/DTA analysis. From the UV-visible spectral study, the electronic band gap energy (Eg) of the grown crystal was found to be 2.43 eV. The second harmonic generation (SHG) efficiency of grown crystal was found to be 1.3 times higher than KDP crystal by using Kurtz powder SHG technique. The microhardness property of the grown crystal was examined by Vicker's microhardness test.

  3. Single crystal growth and enhancing effect of glycine on characteristic properties of bis-thiourea zinc acetate crystal

    NASA Astrophysics Data System (ADS)

    Anis, Mohd; Muley, G. G.

    2016-08-01

    A single crystal of glycine-doped bis-thiourea zinc acetate (G-BTZA) with a dimension of 15 × 6 × 4 mm3 has been grown using the slow solution evaporation technique. The structural parameters of the crystals were determined using the single crystal XRD technique. The increase in optical transparency of the doped BTZA crystal was ascertained in the range of 200 to 900 nm using UV-visible spectral analysis. The improved optical band gap of the G-BTZA crystal is found to be 4.19 eV, and vital optical constants have been calculated using the transmittance data. The influence of glycine on the mechanical parameters of the BTZA crystal has been investigated via microhardness studies. The thermal stability of pure and doped BTZA crystals has been determined by employing the thermogravimetric and differential thermal analysis technique. The improvement in the dielectric properties of the BTZA crystal after the addition of glycine has been evaluated in a temperature range of 30 to 120 °C at a frequency of 100 KHz. The SHG efficiency of the glycine-doped BTZA crystal is found to be much higher than KDP and BTZA crystal material in a Kurtz-Perry powder analysis.

  4. Single crystal nuclear magnetic resonance in spinning powders.

    PubMed

    Pell, Andrew J; Pintacuda, Guido; Emsley, Lyndon

    2011-10-14

    We present a method for selectively exciting nuclear magnetic resonances (NMRs) from well-defined subsets of crystallites from a powdered sample under magic angle spinning. Magic angle spinning induces a time dependence in the anisotropic interactions, which results in a time variation of the resonance frequencies which is different for different crystallite orientations. The proposed method exploits this by applying selective pulses, which we refer to as XS (for crystallite-selective) pulses, that follow the resonance frequencies of nuclear species within particular crystallites, resulting in the induced flip angle being orientation dependent. By selecting the radiofrequency field to deliver a 180° pulse for the target orientation and employing a train of such pulses combined with cogwheel phase cycling, we obtain a high degree of orientational selectivity with the resulting spectrum containing only contributions from orientations close to the target. Typically, this leads to the selection of between 0.1% and 10% of the crystallites, and in extreme cases to the excitation of a single orientation resulting in single crystal spectra of spinning powders. Two formulations of this method are described and demonstrated with experimental examples on [1-(13)C]-alanine and the paramagnetic compound Sm(2)Sn(2)O(7).

  5. Single crystal nuclear magnetic resonance in spinning powders

    NASA Astrophysics Data System (ADS)

    Pell, Andrew J.; Pintacuda, Guido; Emsley, Lyndon

    2011-10-01

    We present a method for selectively exciting nuclear magnetic resonances (NMRs) from well-defined subsets of crystallites from a powdered sample under magic angle spinning. Magic angle spinning induces a time dependence in the anisotropic interactions, which results in a time variation of the resonance frequencies which is different for different crystallite orientations. The proposed method exploits this by applying selective pulses, which we refer to as XS (for crystallite-selective) pulses, that follow the resonance frequencies of nuclear species within particular crystallites, resulting in the induced flip angle being orientation dependent. By selecting the radiofrequency field to deliver a 180 ○ pulse for the target orientation and employing a train of such pulses combined with cogwheel phase cycling, we obtain a high degree of orientational selectivity with the resulting spectrum containing only contributions from orientations close to the target. Typically, this leads to the selection of between 0.1% and 10% of the crystallites, and in extreme cases to the excitation of a single orientation resulting in single crystal spectra of spinning powders. Two formulations of this method are described and demonstrated with experimental examples on [1 - 13C]-alanine and the paramagnetic compound Sm2Sn2O7.

  6. Anisotropic Second Harmonic Generation at Single Crystal Metal Surfaces.

    NASA Astrophysics Data System (ADS)

    Kexiang, He.

    The work in this thesis comprises a set of experiments designed to study the anisotropic spatial dependence of second harmonic generation (SHG) from the surface of single crystal metals. The anisotropic dependence of reflected SHG from Al_2O_3 Al(111) interface was studied. The isotropic dependence of the SHG signal is used to probe the structural symmetry of the Al_2O_3Al(111) interface. For P- and S-polarized laser light incident at a fixed angle of 45^circ, the intensities of S- and P-polarized components of SHG signal were measured as a function of rotation angle during rotation of the surface about its normal. Anisotropic SHG studies were also performed on high Miller index surface of Al(331) and on a Al surface cut at 22.5^ circ with respect to the Al(111) surface. For the Al(331) surface, the anisotropic dependence of the SHG signal was measured for both the S- and P-polarized signals under both S- and P-polarized laser excitation. The anisotropy of the SHG from Al(331) were fit with theory using the assumption that symmetry is retained for this surface at the metal oxide-metal interface. Existing theory is used to derive the theoretical expressions predicting the anisotropic dependence of SHG from Al(331). The SHG probe was also used to follow pulsed laser annealing (PLA) of the Al_2O_3/Al(111) interface from on a chemically polished Al(111) surface. Using P-polarized pump laser light, the P-polarized SHG signal exhibits three equally spaced, equal intensity maxima during a single complete rotation of Al_2O _3/Al(111) interface about the interface normal. Annealing of the interface is found to occur when the P-polarized 1064nm pump laser light has an incident peak power of 11 times 10 ^6W/cm^2 per pulse. The intensity of the P-polarized 532nm SHG signal generated in reflection from this annealed interface exhibits a reduced anisotropic component in the SHG signal. Measurements of the anisotropic SHG signal from ionized beam deposited Al thin-films on Si(111

  7. A 3D hybrid praseodymium-antimony-oxochloride compound: single-crystal-to-single-crystal transformation and photocatalytic properties.

    PubMed

    Zou, Guo-Dong; Zhang, Gui-Gang; Hu, Bing; Li, Jian-Rong; Feng, Mei-Ling; Wang, Xin-Chen; Huang, Xiao-Ying

    2013-11-04

    A 3D organic-inorganic hybrid compound, (2-MepyH)3[{Fe(1,10-phen)3}3][{Pr4Sb12O18(OH)Cl(11.5)}(TDC)(4.5)({Pr4Sb12O18(OH)Cl(9.5)} Cl)]·3(2-Mepy)·28H2O (1; 2-Mepy=2-methylpyridine, 1,10-phen=1,10-phenanthroline, H2TDC=thiophene-2,5-dicarboxylic acid), was hydrothermally synthesized and structurally characterized. Unusually, two kinds of high-nuclearity clusters, namely [(Pr4Sb12O18(OH)Cl11)(COO)5](5-) and [(Pr4Sb12O18(OH)Cl9)Cl(COO)5](4-), coexist in the structure of compound 1; two of the latter clusters are doubly bridged by two μ2-Cl(-) moieties to form a new centrosymmetric dimeric cluster. An unprecedented spontaneous and reversible single-crystal-to-single-crystal transformation was observed, which simultaneously involved a notable organic-ligand movement between the metal ions and an alteration of the bridging ion in the dimeric cluster, induced by guest-release/re-adsorption, thereby giving rise to the interconversion between compound 1 and the compound (2-MepyH)3[{Fe(1,10-phen)3}3][{Pr4Sb12O18(OH)Cl(11.5)}(TDC)4({Pr4Sb12O18Cl(10.5)(TDC)(0.5)(H2O)(1.5)}O(0.5))]·25H2O (1'). The mechanism of this transformation has also been discussed in great detail. Photocatalytic H2-evolution activity was observed for compound 1' under UV light with Pt as a co-catalyst and MeOH as a sacrificial electron donor.

  8. Enhanced Catalysis Activity in a Coordinatively Unsaturated Cobalt-MOF Generated via Single-Crystal-to-Single-Crystal Dehydration.

    PubMed

    Ren, Hai-Yun; Yao, Ru-Xin; Zhang, Xian-Ming

    2015-07-06

    Hydrothermal reaction of Co(NO3)2 and terphenyl-3,2",5",3'-tetracarboxyate (H4tpta) generated Co3(OH)2 chains based 3D coordination framework Co3(OH)2(tpta)(H2O)4 (1) that suffered from single-crystal-to-single-crystal dehydration by heating at 160 °C and was transformed into dehydrated Co3(OH)2(tpta) (1a). During the dehydration course, the local coordination environment of part of the Co atoms was transformed from saturated octahedron to coordinatively unsaturated tetrahedron. Heterogenous catalytic experiments on allylic oxidation of cyclohexene show that dehydrated 1a has 6 times enhanced catalytic activity than as-synthesized 1 by using tert-butyl hydroperoxide (t-BuOOH) as oxidant. The activation energy for the oxidation of cylcohexene with 1a catalyst was 67.3 kJ/mol, far below the value with 1 catalysts, which clearly suggested that coordinatively unsaturated Co(II) sites in 1a have played a significant role in decreasing the activation energy. It is interestingly found that heterogeneous catalytic oxidation of cyclohexene in 1a not only gives the higher conversion of 73.6% but also shows very high selectivity toward 2-cyclohexene-1-one (ca. 64.9%), as evidenced in high turnover numbers (ca. 161) based on the open Co(II) sites of 1a catalyst. Further experiments with a radical trap indicate a radical chain mechanism. This work demonstrates that creativity of coordinatively unsaturated metal sites in MOFs could significantly enhance heterogeneous catalytic activity and selectivity.

  9. Mechanical properties of tricalcium phosphate single crystals grown by molten salt synthesis.

    PubMed

    Viswanath, B; Raghavan, R; Gurao, N P; Ramamurty, U; Ravishankar, N

    2008-09-01

    Mechanical properties of flux-grown tricalcium phosphate (TCP) single crystals ranging in size from 50 to 75microm have been characterized by performing micro- and nanoindentation on their facets. Notwithstanding the inherent brittleness and anisotropy, these single crystals exhibit nanoscale plasticity in the form of pile-up around the edges of indents. A similar plastic response was observed in hydroxyapatite (HA) single crystals during nanoindentation in an earlier study. The hardness and elastic modulus obtained during nanoindentation are discussed in comparison with the polycrystalline forms of both TCP and HA found in the literature. The indentation fracture toughness values of TCP single crystals were found to be higher than those of HA single crystals. The higher values are attributed not only to the difference in crystal structure and corresponding differences in surface energy, but also to extensive crack bridging by ligament formation across crack faces during crack propagation.

  10. Fabrication of Single Crystal MgO Capsules

    NASA Technical Reports Server (NTRS)

    Danielson, Lisa

    2012-01-01

    A method has been developed for machining MgO crystal blocks into forms for containing metallic and silicate liquids at temperatures up to 2,400 C, and pressures up to at least 320 kilobars. Possible custom shapes include tubes, rods, insulators, capsules, and guides. Key differences in this innovative method include drilling along the crystallographic zone axes, use of a vibration minimizing material to secure the workpiece, and constant flushing of material swarf with a cooling medium/lubricant (water). A single crystal MgO block is cut into a section .5 mm thick, 1 cm on a side, using a low-speed saw with a 0.004 blade. The cut is made parallel to the direction of cleavage. The block may be cut to any thickness to achieve the desired length of the piece. To minimize drilling vibrations, the MgO block is mounted on a piece of adhesive putty in a vise. The putty wad cradles the bottom half of the entire block. Diamond coring tools are used to drill the MgO to the desired custom shape, with water used to wet and wash the surface of swarf. Compressed air may also be used to remove swarf during breaks in drilling. The MgO workpiece must be kept cool at all times with water. After all the swarf is rinsed off, the piece is left to dry overnight. If the workpiece is still attached to the base of the MgO block after drilling, it may be cut off by using a diamond cutoff wheel on a rotary hand tool or by using a low-speed saw.

  11. Elasticity of Single-Crystal Quartz to 10 GPa

    NASA Astrophysics Data System (ADS)

    Wang, J.; Mao, Z.; Jiang, F.; Duffy, T. S.

    2010-12-01

    Quartz is a geologically abundant and technically important mineral. Upon static compression at 300 K, alpha-quartz is found to undergo pressure-driven amorphization and related phase transition, which provide insights into the metastable behavior of materials as a function of pressure [Hemley et al.1988, Haines et al. 2001]. This metastable behavior may be related to the elastic instabilities of quartz. The elasticity of alpha-quartz is also fundamental to a range of solid-state phenomena including elastic wave propagation and the equation of state. Despite this, the single-crystal elastic constants of quartz at high pressures are poorly constrained. Previous studies of quartz elasticity at high pressures by Brillouin scattering, ultrasonic interferometry and density functional theory (DFT) exhibit discrepancies that are unresolved [Gregoryanz et al. 2000, Calderon et al. 2007, Kimizuka et al. 2007]. Here, we report new high-quality Brillouin scattering data using two different orientations of carefully characterized, untwined crystals of pure alpha-quartz compressed in hydrostatic pressure media. Our results provide new insights into the evolution of the mechanical behavior of SiO2 with compression up to 10.2 GPa. Using our measured elastic constants, we directly compared our individual Cijs with previous studies within this pressure range. Our data are more consistent with DFT calculations. Extrapolation of ultrasonic data measured below 1 GPa to high pressure yields poor agreement with our data. Equation of state data obtained from this study match previous synchrotron X-ray studies [Angel et al. 1997, Levien et al. 1980, Hazen et al. 1989] with uncertainties. Calculation of linear compressibility shows that quartz remains strongly anisotropic with compression.

  12. Single-crystal elasticity of hydrous wadsleyite by Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Mao, Z.; Jiang, F.; Jacobsen, S. D.; Smyth, J. R.; Holl, C.; Duffy, T. S.; Frost, D. J.

    2006-12-01

    Wadsleyite (β-Mg2SiO4) is the high-pressure polymorph of olivine that is expected to be a dominant mineral in the transition zone from 410 km to 520 km depth in the mantle. The elasticity of wadsleyite is crucial to constrain the mineralogy of the transition zone. Previous studies show wadsleyite can incorporate variable amounts of water up to 3.3 wt% of water (Kohlstedt et al. 1996; Inoue et al. 1995; Smyth et al. 1987, 1994). The effect of water on the bulk modulus of wadsleyite was studied by x-ray diffraction (Yusa and Inoue, 1997; Smyth et al. 2005) but no constraints on the shear modulus exist. We have measured the single-crystal elastic constants of hydrous wadsleyite with varying water content using Brillouin spectroscopy at ambient conditions. We carried out measurements for samples containing 0.3 wt%, 0.6 wt% and 1.6 wt% water using at least 2 crystal planes for each sample. By computing the aggregate elastic properties, we find that the bulk (K0S) and shear modulus (G0) of hydrous wadsleyite decrease linearly with water content according to the following relations: K0S=169.0-11.8X_W; G0=115.1-12.5X_W; where X_W is the water H2O weight percent. Compared with anhydrous wadsleyite, 1 wt% of water will lead to 7.0% decrease in bulk modulus, 10.9% decrease in shear modulus. Water has a greater effect on the elastic moduli of wadsleyite than that of olivine or ringwoodite. The olivine to wadsleyite phase transition is believed to be the origin of the seismic discontinuity near 410 km. Using these new results, the possible effect of water content on the velocity contrast across the 410-km discontinuity will be examined.

  13. Single Crystal Substrates for Surface Acoustic Wave Devices.

    DTIC Science & Technology

    1981-01-01

    APPROVED: aJ. 2 .C. PAUL H. CARR Project Engineer APPROVED: PHILIPP BLACKSMITH , Acting Chief Electromagnetic Sciences Division FOR THE COMMANDER: /?p...relations between properties, composition and crystal structure . (ii) Both exploratory and systematic crystal arowth studies on a variety of materials...the piezoelectric constants for a qiven crystal structure . In conjunction with earlier criteria for identifyina temperature compensated materials

  14. Molybdenum disilicide composites

    DOEpatents

    Rodriguez, Robert P.; Petrovic, John J.

    2001-01-01

    Molybdenum disilicide/.beta.'-Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z, wherein z=a number from greater than 0 to about 5, composites are made by use of in situ reactions among .alpha.-silicon nitride, molybdenum disilicide, and aluminum. Molybdenum disilicide within a molybdenum disilicide/.beta.'-Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z eutectoid matrix is the resulting microstructure when the invention method is employed.

  15. Calcium self-diffusion in natural diopside single crystals

    NASA Astrophysics Data System (ADS)

    Dimanov, Alexandre; Jaoul, Olivier; Sautter, Violaine

    1996-11-01

    We have measured the diffusion coefficient of 44Ca along and perpendicular to c direction in natural Fe-bearing (˜2 at.%) diopside single crystals. Specimens were annealed at temperatures ranging from 1000 to 1250°C, with controlled oxygen fugacity. Diffusion profiles were analysed by Rutherford Back-Scattering Spectrometry (RBS) of α-particles. The diffusion of Ca is isotropic along c and b directions. In addition, the results clearly show two distinct diffusional regimes for the natural diopside, revealed by silica precipitates occurrence in the diopside matrix when T ≥ 1150°C. In this case the oxygen partial pressure pO 2 does not influence the self-diffusion coefficient which is characterized by the activation energy E = 396 ± 38 kJ/mol. For T ≤ 1100°C the diffusional process has a lower activation energy ( E = 264 ± 33 kJ/mol) and varies as ( pO 2) -0.14±0.01 in the investigated range (from 10 -16 atm to 10 -6 atm). These results are consistent with previously reported results on electrical conductivity (Huebner and Voigt, 1988) and high temperature plastic deformation of natural diopside single crystals (Jaoul and Raterron, 1994). According to the point defects model, elaborated by Jaoul and Raterron (1994), the diffusional mechanism of Ca should be essentially interstitial. Furthermore, this mechanism should be the same for different diopside samples with iron content ranging from 0.4 to 2.42 at.%. Indeed, for Ca diffusion in synthetic diopside (0.4 at.% Fe) the activation enthalpy is very similar (281 ± 26 kJ/mol, Dimanov and Ingrin, 1995). On the other hand, the Fe content indoubtly influences the preexponential factor. The present paper reports Ca self-diffusion in diopside as a function of T, pO 2 crystallographic orientation, and Fe content. In fact, among all diffusion coefficients previously reported in diopside, but Si, DCa is the lowest. Thereby, Ca should be a kinetically limiting species for diffusion-controlled processes such as

  16. Investigation of Advanced Processed Single-Crystal Turbine Blade Alloys

    NASA Technical Reports Server (NTRS)

    Peters, B. J.; Biondo, C. M.; DeLuca, D. P.

    1995-01-01

    This investigation studied the influence of thermal processing and microstructure on the mechanical properties of the single-crystal, nickel-based superalloys PWA 1482 and PWA 1484. The objective of the program was to develop an improved single-crystal turbine blade alloy that is specifically tailored for use in hydrogen fueled rocket engine turbopumps. High-gradient casting, hot isostatic pressing (HIP), and alternate heat treatment (HT) processing parameters were developed to produce pore-free, eutectic-free microstructures with different (gamma)' precipitate morphologies. Test materials were cast in high thermal gradient solidification (greater than 30 C/cm (137 F/in.)) casting furnaces for reduced dendrite arm spacing, improved chemical homogeneity, and reduced interdendritic pore size. The HIP processing was conducted in 40 cm (15.7 in.) diameter production furnaces using a set of parameters selected from a trial matrix study. Metallography was conducted on test samples taken from each respective trial run to characterize the as-HIP microstructure. Post-HIP alternate HT processes were developed for each of the two alloys. The goal of the alternate HT processing was to fully solution the eutectic gamma/(gamma)' phase islands and to develop a series of modified (gamma)' morphologies for subsequent characterization testing. This was accomplished by slow cooling through the (gamma)' solvus at controlled rates to precipitate volume fractions of large (gamma)'. Post-solution alternate HT parameters were established for each alloy providing additional volume fractions of finer precipitates. Screening tests included tensile, high-cycle fatigue (HCF), smooth and notched low-cycle fatigue (LCF), creep, and fatigue crack growth evaluations performed in air and high pressure (34.5 MPa (5 ksi)) hydrogen at room and elevated temperature. Under the most severe embrittling conditions (HCF and smooth and notched LCF in 34.5 MPa (5 ksi) hydrogen at 20 C (68 F), screening test

  17. SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION

    SciTech Connect

    A. Wang; G. Pickrell; R. May

    2002-09-10

    Accurate measurement of temperature is essential for the safe and efficient operation and control of a wide range of industrial processes. Appropriate techniques and instrumentation are needed depending on the temperature measurement requirements in different industrial processes and working environments. Harsh environments are common in many industrial applications. These harsh environments may involve extreme physical conditions, such as high-temperature, high-pressure, corrosive agents, toxicity, strong electromagnetic interference, and high-energy radiation exposure. Due to these severe environmental conditions, conventional temperature sensors are often difficult to apply. This situation has opened a new but challenging opportunity for the sensor society to provide robust, high-performance, and cost-effective temperature sensors capable of operating in those harsh environments. The focus of this research program has been to develop a temperature measurement system for temperature measurements in the primary and secondary stages of slagging gasifiers. For this application the temperature measurement system must be able to withstand the extremely harsh environment posed by the high temperatures and corrosive agents present in these systems. Real-time, accurate and reliable monitoring of temperature for the coal gasification process is important to realize the full economic potential of these gasification systems. Long life and stability of operation in the high temperature environment is essential for the temperature measurement system to ensure the continuous running of the coal gasification system over the long term. In this high temperature and chemically corrosive environment, rather limited high temperature measurement techniques such as high temperature thermocouples and optical/acoustic pyrometers are available, each with their own limitations. In this research program, five different temperature sensing schemes based on the single crystal sapphire

  18. Synthesis, crystal growth, solubility, structural, optical, dielectric and microhardness studies of Benzotriazole-4-hydroxybenzoic acid single crystals

    NASA Astrophysics Data System (ADS)

    Silambarasan, A.; Krishna Kumar, M.; Thirunavukkarasu, A.; Mohan Kumar, R.; Umarani, P. R.

    2015-06-01

    Organic Benzotriazole-4-hydroxybenzoic acid (BHBA), a novel second-order nonlinear optical single crystal was grown by solution growth method. The solubility and nucleation studies were performed for BHBA crystal at different temperatures 30, 35, 40 45 and 50 °C. Single crystal X-ray diffraction study reveals that the BHBA belongs to Pna21 space group of orthorhombic crystal system. The crystal perfection of BHBA was examined from powder and high resolution X-ray diffraction analysis. UV-visible and photoluminescence spectra were recorded to study its transmittance and excitation, emission behaviors respectively. Kurtz powder second harmonic generation test reveals that, the frequency conversion efficiency of BHBA is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal. The dielectric constant and dielectric loss values were estimated for BHBA crystal at various temperatures and frequencies. The mechanical property of BHBA crystal was studied on (110), (010) and (012) planes by using Vicker's microhardness test. The chemical etching study was performed on (012) facet of BHBA crystal to analyze its growth feature.

  19. Synthesis, growth, structural, thermal and optical studies of pyrrolidinium-2-carboxylate-4-nitrophenol single crystals

    NASA Astrophysics Data System (ADS)

    Swarna Sowmya, N.; Sampathkrishnan, S.; Vidyalakshmi, Y.; Sudhahar, S.; Mohan Kumar, R.

    2015-06-01

    Organic nonlinear optical material, pyrrolidinium-2-carboxylate-4-nitrophenol (PCN) was synthesized and single crystals were grown by slow evaporation solution growth method. Single crystal X-ray diffraction analysis confirmed the structure and lattice parameters of PCN crystals. Infrared, Raman and NMR spectral analyses were used to elucidate the functional groups present in the compound. The thermal behavior of synthesized compound was studied by thermogravimetric and differential scanning calorimetry (TG-DSC) analyses. The photoluminescence property was studied by exciting the crystal at 360 nm. The relative second harmonic generation (SHG) efficiency of grown crystal was estimated by using Nd:YAG laser with fundamental wavelength of 1064 nm.

  20. Deterministically Polarized Fluorescence from Single Dye Molecules Aligned in Liquid Crystal Host

    SciTech Connect

    Lukishova, S.G.; Schmid, A.W.; Knox, R.; Freivald, P.; Boyd, R. W.; Stroud, Jr., C. R.; Marshall, K.L.

    2005-09-30

    We demonstrated for the first time to our konwledge deterministically polarized fluorescence from single dye molecules. Planar aligned nematic liquid crystal hosts provide deterministic alignment of single dye molecules in a preferred direction.

  1. Growth, Structural And Optical Studies On Bis L-alanine Lithium Chloride (BLALC) Single Crystal

    NASA Astrophysics Data System (ADS)

    Rose, A. S. J. Lucia; Selvarajan, P.; Perumal, S.

    2011-10-01

    Bis L-alanine Lithium Chloride (BLALC) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 15 x 9 x 4 mm3 have been obtained in 28 days. The grown crystals were colourless and transparent. Single crystal X-ray diffraction (XRD) study showed that BLALC belongs to orthorhombic system with a non-centro-symmetric space group P212121. The crystallinity of BLALC crystal was confirmed by the powder X-ray diffraction study and diffraction peaks were indexed. The functional groups of the grown crystals have been identified by FTIR studies. UV-visible transmittance spectrum was recorded to study the optical transparency of BLALC crystal. The nonlinear optical (NLO) property of the grown crystal was confirmed by Kurtz-Perry powder technique.

  2. Crystal growth, characterization, and testing of Cd0.9Zn0.1Te single crystals for radiation detectors

    NASA Astrophysics Data System (ADS)

    Mandal, Krishna C.; Noblitt, Caleb; Choi, Michael; Rauh, R. D.; Roy, Utpal N.; Groza, Michael; Burger, Arnold; Holcomb, David E.; Jellison, Gerald E., Jr.

    2004-10-01

    This paper describes our recent research in growing large single crystals of Cd0.9Zn0.1Te (CZT) by the vertical Bridgman technique using in-house processed zone refined precursor materials (Cd, Zn, and Te). The grown semi-insulating CZT crystals have shown high promise for high-resolution room-temperature radiation detectors due to their high dark resistivity (~1010 Ωcm), reasonably good charge transport properties [(μτ)e = (2-5) x 10-3 cm2/V] and low cost. The grown CZT single crystals (~2.5 cm diameter and up to 10 cm long) have demonstrated a very low radial Zn concentration deviation, low dislocation densities and Te precipitate/inclusions, and high infrared transmission. Details of the CZT single crystal growth, their physical and chemical analysis, surface processing, nuclear radiation detector fabrication, and testing of these devices are also presented.

  3. The kinetics of hydrogen diffusion in single crystal orthopyroxene

    NASA Astrophysics Data System (ADS)

    Carpenter, Susan Jean

    The kinetics of hydrogen diffusion in single crystals of orthopyroxene were investigated parallel to the [100], [010] and [001] crystallographic directions during dehydration and hydrogenation. The two groups of samples investigated spanned a range of metal composition, most notably iron, 4.5--8.5 wt % FeO, and aluminum, 2.1--3.5 wt % Al2O3; the aluminum was bound in both regular metal sites (AlVI) and in tetrahedral sites (AlIV). Xenolithic crystals from the San Carlos, Arizona, region contain on average, about 5.3 wt % FeO and 2.4 wt % Al2O3, and the gem-quality crystals from Sri Lanka contain between 4.5 and 8.5 wt % FeO, and between 2.1 and 3.6 wt % Al 2O3. Dehydration was performed in a 1 atm gas-mixing furnace at temperatures between 800 and 1100°C, using mixtures of CO and CO 2 to maintain the oxygen fugacity at 10-14 atm, close to the nickel/nickel oxide (NNO) solid buffer. Hydrogenation was performed in a piston-cylinder apparatus at 1 GPa within the same range of temperatures, using welded platinum capsules to contain the samples, water and NNO solid buffer. After a heating event, samples were polished so that the central region of the crystal could be analyzed. Changes in hydrogen concentration as a function of heating time were plotted as hydroxyl concentration profiles across the central sections of the samples, obtained by using polarized FTIR spectroscopy with the electric vector E, oriented parallel to the c crystallographic direction, the direction in which hydroxyl dipoles in clinopyroxene are primarily oriented. Hydrogen diffusivities were obtained by fitting the hydroxyl concentration profiles to theoretical profiles generated by finite solution numerical modeling for diffusion within a finite slab to/from an infinite source. During dehydration, hydrogen diffusion was found to be anisotropic in San Carlos enstatite and isotropic in the Sri Lankan samples, with more rapid hydrogen diffusion occurring in the Sri Lankan samples that contain

  4. Single shot ultrafast dynamic ellipsometry of laser-driven shocks in single crystal explosives and thin films of metals

    NASA Astrophysics Data System (ADS)

    Whitley, Von; McGrane, Shawn; Moore, David; Eakins, Dan; Bolme, Cynthia

    2009-06-01

    Ultrafast dynamic ellipsometry (UDE) was used to measure the shock conditions of single-crystal energetic materials and metal thin films. Explosive crystals are coated with aluminum, which through frustrated laser ablation acts as a shock drive layer. UDE data on shocked explosives and different potential metal drive layers will be reported and experimental considerations will be discussed.

  5. Electric-field-assisted position and orientation control of organic single crystals.

    PubMed

    Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro

    2014-12-02

    We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2. The pentacene crystal with a large aspect ratio tended to direct the [1̅10] orientation parallel to the conduction direction, which will be suitable from a viewpoint of anisotropy in mobility. The present result shows a possibility of controlling the position and orientation of organic single crystals by the use of an electric field, which leads to high throughput and low cost industrial manufacturing of the single crystal array from solution.

  6. Structural, spectral, optical and dielectric properties of copper and glycine doped LAHCl single crystals.

    PubMed

    Sangeetha, K; Babu, R Ramesh; Bhagavannarayana, G; Ramamurthi, K

    2011-09-01

    Cu2+ and glycine doped L-arginine monohydrochloride monohydrate (LAHCl) single crystals were grown by slow solvent evaporation technique. The grown single crystals were confirmed by X-ray diffraction study and the interaction of dopants with LAHCl molecule was identified in Fourier transform infrared spectra. The crystalline perfection of pure and doped crystals was analyzed by high resolution X-ray diffraction studies. Vickers microhardness and UV-visible spectroscopy were carried out respectively to study the mechanical stability and optical transmittance of pure and doped LAHCl single crystals. He-Ne laser of wavelength 632.8 nm was used to measure refractive index and birefringence of grown crystals. The second harmonic generation efficiency was also measured for pure and doped LAHCl single crystals using Nd:YAG laser.

  7. Design and fabrication of PIN-PMN-PT single-crystal high-frequency ultrasound transducers.

    PubMed

    Sun, Ping; Zhou, Qifa; Zhu, Benpeng; Wu, Dawei; Hu, Changhong; Cannata, Jonathan M; Tian, Jin; Han, Pengdi; Wang, Gaofeng; Shung, K Kirk

    2009-12-01

    High-frequency PIN-PMN-PT single crystal ultrasound transducers at center frequencies of 35 MHz and 60 MHz were successfully fabricated using lead indium niobate-lead magnesium niobate-lead titanate (0.23PIN- 0.5PMN-0.27PT) single crystal. The new PIN-PMN-PT single crystal has higher coercivity (6.0 kV/cm) and higher Curie temperature (160 degrees C) than PMN-PT crystal. Experimental results showed that the PIN-PMN-PT transducers have similar performance but better thermal stability compared with the PMN-PT transducers.

  8. ESTIMATING THE STRENGTH OF SINGLE-ENDED DISLOCATION SOURCES IN MICROMETER-SIZED SINGLE CRYSTALS

    SciTech Connect

    Rao, S I; Dimiduk, D M; Tang, M; Parthasarathy, T A; Uchic, M D; Woodward, C

    2007-05-03

    A recent study indicated that the behavior of single-ended dislocation sources contributes to the flow strength of micrometer-scale crystals. In this study 3D discrete dislocation dynamics simulations of micrometer-sized volumes are used to calculate the effects of anisotropy of dislocation line tension (increasing Poisson's ratio, {nu}) on the strength of single-ended dislocation sources and, to compare them with the strength of double-ended sources of equal length. This is done by directly modeling their plastic response within a 1 micron cubed FCC Ni single crystal using DDS. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with Poisson ratio ({nu}), exhibiting an increase of about 50% at u = 0.38 (value for Ni) as compared to the value at {nu} = 0. Independent of dislocation line direction, for {nu} greater than 0.20, the strengths of single-ended sources depend upon the sense of the stress applied. The value for {alpha}, in the expression for strength, {tau} = {alpha}(L){micro}b/L is shown to vary from 0.4 to 0.84 depending upon the character of the dislocation and the direction of operation of the source at {nu} corresponding to that of Ni, 0.38 and a length of 933b. By varying the lengths of the sources from 933b to 233b, it was shown that the scaling of the strength of single-ended and double-ended sources with their length both follow a ln(L/b)/(L/b) dependence. Surface image stresses are shown to have little effect on the critical stress of single-ended sources at a length of {approx}250b or greater. The relationship between these findings and a recent statistical model for the hardening of small volumes is also discussed.

  9. On plastic flow in notched hexagonal close packed single crystals

    NASA Astrophysics Data System (ADS)

    Selvarajou, Balaji; Kondori, Babak; Benzerga, A. Amine; Joshi, Shailendra P.

    2016-09-01

    The micromechanics of anisotropic plastic flow by combined slip and twinning is investigated computationally in single crystal notched specimens. Constitutive relations for hexagonal close packed materials are used which take into account elastic anisotropy, thirty potential deformation systems, various hardening mechanisms and rate-sensitivity. The specimens are loaded perpendicular to the c-axis but the presence of a notch generates three-dimensional triaxial stress states. The study is motivated by recent experiments on a polycrystalline magnesium alloy. To enable comparisons with these where appropriate, three sets of activation thresholds for the various deformation systems are used. For the conditions that most closely mimic the alloy material, attention is focused on the relative roles of pyramidal < c + a > and prismatic < a > slip, as well as on the emergence of {1012bar}[101bar1] extension twinning at sufficiently high triaxiality. In all cases, the spatial variations of stress triaxiality and plastic strain, inclusive of various system activities, are quantified along with their evolution upon straining. The implications of these findings in fundamental understanding of ductile failure of HCP alloys in general and Mg alloys in particular are discussed.

  10. Ultraviolet Laser-induced ignition of RDX single crystal

    PubMed Central

    Yan, Zhonghua; Zhang, Chuanchao; Liu, Wei; Li, Jinshan; Huang, Ming; Wang, Xuming; Zhou, Guorui; Tan, Bisheng; Yang, Zongwei; Li, Zhijie; Li, Li; Yan, Hongwei; Yuan, Xiaodong; Zu, Xiaotao

    2016-01-01

    The RDX single crystals are ignited by ultraviolet laser (355 nm, 6.4 ns) pulses. The laser-induced damage morphology consisted of two distinct regions: a core region of layered fracture and a peripheral region of stripped material surrounding the core. As laser fluence increases, the area of the whole crack region increases all the way, while both the area and depth of the core region increase firstly, and then stay stable over the laser fluence of 12 J/cm2. The experimental details indicate the dynamics during laser ignition process. Plasma fireball of high temperature and pressure occurs firstly, followed by the micro-explosions on the (210) surface, and finally shock waves propagate through the materials to further strip materials outside and yield in-depth cracks in larger surrounding region. The plasma fireball evolves from isotropic to anisotropic under higher laser fluence resulting in the damage expansion only in lateral direction while maintaining the fixed depth. The primary insights into the interaction dynamics between laser and energetic materials can help developing the superior laser ignition technique. PMID:26847854

  11. Understanding surface structure and chemistry of single crystal lanthanum aluminate

    NASA Astrophysics Data System (ADS)

    Pramana, Stevin S.; Cavallaro, Andrea; Qi, Jiahui; Nicklin, Chris L.; Ryan, Mary P.; Skinner, Stephen J.

    2017-03-01

    The surface crystallography and chemistry of a LaAlO3 single crystal, a material mainly used as a substrate to deposit technologically important thin films (e.g. for superconducting and magnetic devices), was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy. The surface was determined to be terminated by Al-O species, and was significantly different from the idealised bulk structure. Termination reversal was not observed at higher temperature (600 °C) and chamber pressure of 10‑10 Torr, but rather an increased Al-O occupancy occurred, which was accompanied by a larger outwards relaxation of Al from the bulk positions. Changing the oxygen pressure to 10‑6 Torr enriched the Al site occupancy fraction at the outermost surface from 0.245(10) to 0.325(9). In contrast the LaO, which is located at the next sub-surface atomic layer, showed no chemical enrichment and the structural relaxation was lower than for the top AlO2 layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3 is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.

  12. Conductivity of boules of single crystal sodium beta-alumina

    NASA Technical Reports Server (NTRS)

    Fielder, W. L.; Kautz, H. E.; Fordyce, J. S.; Singer, J.

    1974-01-01

    The ionic and electrochemical polarization characteristics of two boules of single crystal sodium beta-alumina (Na2O.8Al2O3), 2 cm in diameter, were investigated over the range of 25 to 300 C using 2- and 4-probe ac and dc techniques with reversible and ion-blocking electrodes. Textural (or internal) polarization at 27 C was present only in boule 1 which cleaved easily. Interfacial polarization, using solid sodium electrodes, was present at 27 C in the 2-probe conductivities for both boules. Cleaning with liquid sodium at 300 C reduced its magnitude, but some interfacial polarization was still present in the 2-probe conductivities for boule 2 below about 140 C. Above 140 C, with liquid sodium electrodes, the 2-probe conductivities, essentially polarization-free, were given by KT = 3300 exp(-3650/RT). The conductivity of boule 2 at 180 C remained essentially constant with increasing current density up to about 140 milliamps per square centimeter.

  13. DEVELOPMENT OF PROTECTIVE COATINGS FOR SINGLE CRYSTAL TURBINE BLADES

    SciTech Connect

    Amarendra K. Rai

    2006-12-04

    Turbine blades in coal derived syngas systems are subject to oxidation and corrosion due to high steam temperature and pressure. Thermal barrier coatings (TBCs) are developed to address these problems. The emphasis is on prime-reliant design and a better coating architecture, having high temperature and corrosion resistance properties for turbine blades. In Phase I, UES Inc. proposed to develop, characterize and optimize a prime reliant TBC system, having smooth and defect-free NiCoCrAlY bond layer and a defect free oxide sublayer, using a filtered arc technology. Phase I work demonstrated the deposition of highly dense, smooth and defect free NiCoCrAlY bond coat on a single crystal CMSX-4 substrate and the deposition of alpha-alumina and yttrium aluminum garnet (YAG) sublayer on top of the bond coat. Isothermal and cyclic oxidation test and pre- and post-characterization of these layers, in Phase I work, (with and without top TBC layer of commercial EB PVD YSZ) revealed significant performance enhancement.

  14. Understanding surface structure and chemistry of single crystal lanthanum aluminate.

    PubMed

    Pramana, Stevin S; Cavallaro, Andrea; Qi, Jiahui; Nicklin, Chris L; Ryan, Mary P; Skinner, Stephen J

    2017-03-02

    The surface crystallography and chemistry of a LaAlO3 single crystal, a material mainly used as a substrate to deposit technologically important thin films (e.g. for superconducting and magnetic devices), was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy. The surface was determined to be terminated by Al-O species, and was significantly different from the idealised bulk structure. Termination reversal was not observed at higher temperature (600 °C) and chamber pressure of 10(-10) Torr, but rather an increased Al-O occupancy occurred, which was accompanied by a larger outwards relaxation of Al from the bulk positions. Changing the oxygen pressure to 10(-6) Torr enriched the Al site occupancy fraction at the outermost surface from 0.245(10) to 0.325(9). In contrast the LaO, which is located at the next sub-surface atomic layer, showed no chemical enrichment and the structural relaxation was lower than for the top AlO2 layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3 is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.

  15. A face-shear mode single crystal ultrasonic motor

    NASA Astrophysics Data System (ADS)

    Li, Shiyang; Jiang, Wenhua; Zheng, Limei; Cao, Wenwu

    2013-05-01

    We report a face-shear mode ultrasonic motor (USM) made of [011]c poled Zt ± 45° cut 0.24Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal, which takes advantage of the extremely large d36 = 2368 pC/N. This motor has a maximum no-load linear velocity of 182.5 mm/s and a maximum output force of 1.03 N under the drive of Vp = 50 V, f = 72 kHz. Compared with the k31 mode USM made of Pb(Zr,Ti)O3 (PZT), our USM has simpler structure, lower driving frequency, much higher electromechanical coupling factor, and twice power density. This USM can be used for low frequency operation as well as cryogenic actuation with a large torque.

  16. Single crystal Mo solar thermal thruster for microsatellites

    NASA Astrophysics Data System (ADS)

    Shimizu, Mono; Itoh, Katsuya; Sato, Hitoshi; Fujii, Tadayuki; Okamoto, Ken-ichi; Takaoka, Shigehiko; Shiina, Kotaro; Nakamura, Yoshihiro

    1999-09-01

    One potentially attractive propulsion concept offering significant payload gains for orbit transfer from LEO to higher orbits, station keeping and attitude control of spacecraft is thermal propulsion using light gas (typically hydrogen) as propellant and various kinds of heat energy. Solar Thermal Propulsion (STP) is a typical thermal propulsion with high Isp (500 - 1,000 s) in an appropriate thrust magnitude range and provides possibly much less space pollution than conventional chemical propulsion. This paper presents the test results of a 30 mm dia. (medium-sized) windowless type of single crystal Mo thruster for orbit transfer of 50 kg class microsatellites. The cavity dia. is 20 mm, double the size of the previous model, and can apply to a primary solar reflector of up to 3.5 m dia., which is the maximum size containable in the H-II rocket fairing without segmentation. The performed mission analyses indicate that this size of STP is suitable to orbit transfer of 50 kg class microsatellites, such as LEO to GEO, or only multiple apogee kicks from GTO to GEO or deep space missions.

  17. Reduction of precursor decay anomaly in single crystal lithium fluoride

    NASA Astrophysics Data System (ADS)

    Sano, Yukio

    2000-08-01

    The purpose of this study is to reveal that the precursor decay anomaly in single crystal lithium fluoride is reduced by Sano's decay curve [Y. Sano, J. Appl. Phys. 85, 7616 (1999)], which is much smaller in slope than Asay's decay curve [J. R. Asay, G. R. Fowles, G. E. Duvall, M. H. Miles, and R. F. Tinder, J. Appl. Phys. 43, 2132 (1972)]. To this end, strain, particle, velocity, and stress in a precursor and near the leading edge of the follower changing with time along Sano's decay curve are first analyzed quantitatively. The analysis verified the existence of degenerate contraction waves I and II and a subrarefaction wave R', and the decay process [Y. Sano, J. Appl. Phys. 77, 3746 (1995)] caused in sequence by evolving followers C, I, II, R', Rb. Next, inequalities relating decay rates qualitatively to plastic strain rates at the leading edge of the follower, which are derived using the properties of the followers, are incorporated into the analysis. Calculation results showed that the plastic strain rates were reduced by low decay rates. This indicates that the precursor decay anomaly might be greatly reduced by Sano's decay curve.

  18. Thermal diffusion boron doping of single-crystal natural diamond

    NASA Astrophysics Data System (ADS)

    Seo, Jung-Hun; Wu, Henry; Mikael, Solomon; Mi, Hongyi; Blanchard, James P.; Venkataramanan, Giri; Zhou, Weidong; Gong, Shaoqin; Morgan, Dane; Ma, Zhenqiang

    2016-05-01

    With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occurs at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.

  19. Study of growth of single crystal ribbon in space

    NASA Technical Reports Server (NTRS)

    Wood, V. E.; Markworth, A. J.

    1975-01-01

    The technical feasibility is studied of growing single-crystal silicon ribbon in the space environment. Procedures are described for calculating the electromagnetic fields produced in a silicon ribbon by an rf shaping coil. The forces on the ribbon and the degree of shaping to be expected are determined. The expected steady-state temperature distribution in the ribbon is calculated in the one-dimensional approximation. Calculations on simplified models indicate, that lack of flatness of the shaped ribbon and excessive heating of the melt by the eddy currents induced by the shaping fields may pose problems. An analysis of the relative effects of various kinds of forces other than electromagnetic showed that in the space environment capillarity forces would dominate, and that the shape of the melt is thus principally determined by the shape of any solids with which it comes in contact. This suggests that ribbon may be produced simply by drawing between parallel wires. A concept is developed for a process of off-angle growth, in which the ribbon is pulled at an angle to the solidification front. Such a process promises to offer increased growth rate, better homogeneity, and thinner ribbon.

  20. Single Crystal Diamond Beam Position Monitors with Radiofrequency Electronic Readout

    SciTech Connect

    Solar, B.; Graafsma, H.; Potdevin, G.; Trunk, U.; Morse, J.; Salome, M.

    2010-06-23

    Over the energy range 5{approx}30 keV a suitably contacted, thin ({approx}100 {mu}m) diamond plate can be operated in situ as a continuous monitor of X-ray beam intensity and position as the diamond absorbs only a small percentage of the incident beam. Single crystal diamond is a completely homogeneous material showing fast (ns), spatially uniform signal response and negligible (