Sample records for caf2 single crystals

  1. Evaluation of high-quality CaF2 single crystals for ultraviolet laser applications

    Microsoft Academic Search

    Shiro Sakuragi; Yutaka Taguchi; Hiroyuki Sato; Akinari Kasai; Hirokuni Nanba; Taketoshi Kawai; Satoshi Hashimoto

    2005-01-01

    High quality window\\/plate shaped CaF2 single crystals have developed by vertical Bridgman method of with diameters of 50, 100, and 200 mm and 210 mm width, 200mm length. The CaF2 windows of 30mm diameter obtained from big crystals have evaluated the transmission spectra from 120 nm to 220nm by single beam VUV spectrometer. We could obtain bulk transmission spectra by

  2. Dosimetry properties of Tm-doped single CaF 2 crystals

    Microsoft Academic Search

    B Marczewska; P Bilski; M Budzanowski; P Olko; V Chernov

    2001-01-01

    The dosimetry properties of thermoluminescence CaF2:Tm detectors with thulium concentrations of 0.1%, 0.3%, 0.5%, 0.6% and 0.7%, developed from single crystals grown by the Stockbarger method at the Institute of Geochemistry, Irkutsk, Russia, were investigated. The relative TL efficiency, ?, after 5.3MeV Am-241 ?-particle irradiation and the Cs-137 ?-ray dose response after doses up to 10Gy, of interest for radiation

  3. Comparative spectroscopic and laser properties of Yb 3+ -doped CaF 2 , SrF 2 and BaF 2 single crystals

    Microsoft Academic Search

    P. Camy; J. L. Doualan; A. Benayad; M. von Edlinger; V. Ménard; R. Moncorgé

    2007-01-01

    We present the spectroscopic properties and room-temperature cw tunable laser operation of Yb3+-doped CaF2, SrF2 and BaF2 single crystals grown and studied in the same conditions. Emission cross sections, lifetimes, laser thresholds, laser slope\\u000a efficiencies and laser wavelength tuning ranges are compared. It appears that Yb3+-doped BaF2 might be more promising for diode-pumped high power laser operation.

  4. Single-point diamond turning of CaF 2 for nanometric surface

    Microsoft Academic Search

    Jiwang Yan; Jun’ichi Tamaki; Katsuo Syoji; Tsunemoto Kuriyagawa

    2004-01-01

    Single-crystal CaF 2 is an important optical material. In this work, single-point diamond turning experiments were performed to investigate the nanometric machining characteristics of CaF 2. The effects of tool feed, tool rake angle, workpiece crystal orientation and cutting fluid were examined. It was found that two major types of microfracturing differing in mechanism limited the possibility of ductile regime

  5. Etch pit shapes on {110} surfaces of CaF 2 crystals

    Microsoft Academic Search

    G C Jain; L C Jain; T S Murty

    1981-01-01

    {110} surfaces of CaF2 crystals are etched with different concentrations of HCl. It is found that concentrated HCl produces characteristic rectangular\\u000a pyramidal etch pits and 2 volume percent HCl produces boat shaped etch pits. Such variations in the etch pit shapes on {110}\\u000a surfaces of CaF2 crystals with different concentrations of HCl have been explained. Concentrated H2SO4 is found to

  6. Photothermal transformation of color centers in CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Aksenova, K. A.; Gainutdinov, R. V.; Ryskin, A. I.

    2015-04-01

    Photothermal transformations of color centers in additively colored calcium fluoride crystals and in a colored crystal with a recorded hologram have been investigated. It is shown that the absorption spectrum of a colored crystal can be reconstructed within the entire transparency range of the matrix crystal by varying both factors affecting the sample—actinic radiation wavelength and temperature—as well as the duration of their effect. This possibility is important for the application of additively colored CaF2 crystals as a holographic medium.

  7. Effective segregation coefficient of Er3+ ions in ErF3-doped CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Munteanu, M.; Stef, M.; Bunoiu, O.; Nicoara, I.

    2010-03-01

    ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the characteristic peaks of the Er3+ ions. The dopant distribution along two crystals has been investigated using the optical absorption method. The effective segregation coefficient of the Er3+ ions has been calculated using the classical Scheil relationship between the impurity concentration and the crystal growth conditions. The effective segregation coefficient of the Er3+ions in the CaF2 host depends slightly on the doping concentration, and varies between 0.99 and 1.03, for 0.8 mol % ErF3 and 2 mol % ErF3-doped CaF2 crystals, respectively.

  8. Influence of the Er3+ Ions Concentration on the Structural Deformation in Doped CaF2 Crystals

    NASA Astrophysics Data System (ADS)

    Nicoara, I.; Munteanu, M.; Stef, M.; Preda, E.; Buse, G.

    2010-08-01

    Calcium fluoride crystals doped with ErF3 were grown using the Bridgman technique. The dissolved Er ions in CaF2 are trivalent and this leads to the formation of charge-compensating defects. The local compensation, by an interstitial or substitutional F- ion, creates the isolated centers, with various crystal field symmetries of the trivalent erbium ions in the CaF2 host. To study the charge-compensating defects in these crystals we used two methods: the optical absorption spectra and the dielectric spectra.

  9. Crystallization kinetics and spectroscopic investigations on Tb3+ and Yb3+ codoped glass ceramics containing CaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Huang, Lihui; Qin, Guanshi; Arai, Yusuke; Jose, Rajan; Suzuki, Takenobu; Ohishi, Yasutake; Yamashita, Tatsuya; Akimoto, Yusuke

    2007-11-01

    Transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramics containing CaF2 nanocrystals were prepared by melt quenching and subsequent heat treatment. Crystallization kinetics of CaF2 nanocrystals was investigated by differential scanning calorimetric method. The average apparent activation energy Ea of the crystallization was ˜498kJ /mol. Moreover, the value of the Avrami exponent n was 1.01. These results suggest that the crystallization mechanism of CaF2 is a diffusion controlled growth process of needles and plates of finite long dimensions. X-ray diffraction patterns and transmission electron microscopy image confirmed the CaF2 nanocrystals in the glass ceramic. Ultraviolet (UV) and visible emission spectra of the as-made glass and the glass ceramic with an excitation of a 974nm laser diode were recorded at room temperature. An intense UV emission at 381nm was observed in the glass ceramic. The origin of the enhancement of the emission at 381nm was investigated using spectroscopic technique and Judd-Ofelt analysis. The enhancement of the emission at 381nm could be attributed to the change of the ligand field of Tb3+ ions due to the incorporation of some Tb3+ and Yb3+ ions into CaF2 nanocrystals in the glass ceramic.

  10. Convertible holograms in CaF2 crystals with color centers

    NASA Astrophysics Data System (ADS)

    Angervaks, Alexandr E.; Shcheulin, Aleksandr S.; Ryskin, Aleksandr I.

    2013-05-01

    When recording hologram in ionic CaF2 crystal with color centers, the center conversion is accompanied with their spatial redistribution. The peculiar diffusion-drift mechanism of the recording is responsible for the extremely high hologram stability to both heating and illumination of the sample with a hologram by non-coherent radiation. However such photo-thermal treatment of the sample results in partial or total transformation of the center type and modification in their space distribution. Thus, keeping the hologram, such treatment influences its character of diffraction response, diffraction efficiency and profile. This work describes the mechanism and the character of these changes. It is shown that photo-thermal treatment can be used for fabrication of thick (up to 10 mm thickness) high stable holograms when reading out both in visible and infrared ranges of the spectrum.

  11. Kinetics of Isothermal Melt Crystallization in CaO-SiO2-CaF2-Based Mold Fluxes

    NASA Astrophysics Data System (ADS)

    Seo, Myung-Duk; Shi, Cheng-Bin; Baek, Ji-Yeon; Cho, Jung-Wook; Kim, Seon-Hyo

    2015-04-01

    A kinetic study for isothermal melt crystallization of CaO-SiO2-CaF2-based mold fluxes with different basicity of 0.94 and 1.34 has been carried out systematically by DSC measurements. The kinetic parameters were determined by Johnson-Mehl-Avrami equation. The average Avrami exponent of cuspidine (3CaO·2SiO2·CaF2) crystallization for mold flux of lower basicity (0.94) is calculated to be 3.1, implying that the crystallization mode is instantaneous nucleation followed by 3-dimensional growth. For the mold flux of higher basicity (1.34), the average Avrami exponent of cuspidine equals to 3.4, strongly suggesting that the growth is still 3 dimensional but the nucleation should be continuous. It was found that the effective crystallization rate constant for both mold fluxes increases as the crystallization temperature decreases, showing that the crystallization rate could be governed by nucleation rate. The negative effective activation energy indicates an anti-Arrhenius behavior for crystallization of the mold fluxes studied. Therefore, it is concluded that the melt crystallization for the commercial mold fluxes will be determined by thermodynamics of nucleation which is relevant to degree of undercooling. The morphology of cuspidine crystals observed by SEM agreeds well with the isothermal crystallization kinetics results.

  12. Radiation characteristics of epitaxial CaF2 on silicon

    Microsoft Academic Search

    Yasushiro Nishioka; Chih-Chen Cho; Scott R. Summerfelt; Bruce E. Gnade; George A. Brown

    1991-01-01

    The radiation characteristics of a Al\\/CaF2\\/Si capacitor have been investigated. The single-crystal CaF2 film has been grown on Si(111) at a temperature as low as 300°C by molecular beam epitaxy (MBE). Previous studies showed that CaF2 films grown on Si(111) above 500°C exhibited flat C-V curves, suggesting a pinned CaF2\\/Si(111) interface. However, the authors have been able to obtain unpinned

  13. Spatially selected synthesis of LaF 3 and Er 3+-doped CaF 2 crystals in oxyfluoride glasses by laser-induced crystallization

    NASA Astrophysics Data System (ADS)

    Kusatsugu, M.; Kanno, M.; Honma, T.; Komatsu, T.

    2008-05-01

    Oxyfluoride glasses with a small amount of NiO are prepared using a conventional melt quenching technique, and the spatially selected crystallization of LaF 3 and CaF 2 crystals is induced on the glass surface by irradiations of continuous wave lasers with a wavelength of ?=1064 or 1080 nm. Dots and lines including LaF 3 crystals are patterned by heat-assisted (300 °C) laser irradiations ( ?=1064 nm) with a power of P=1 W and an irradiation time of 10 s for dots and a scanning speed of S=5 ?m/s for lines. Lines consisting of CaF 2 crystals are also patterned in an ErF 3-doped oxyfluoride glass by laser irradiations ( ?=1080 nm) with a power of P=1.7 W and a scanning speed of S=2 ?m/s, and the incorporation of Er 3+ ions into CaF 2 crystals is confirmed from micro-photoluminescence spectrum measurements. It is proposed that the lines patterned by laser irradiations in this study are consisted of the composite of LaF 3 or CaF 2 nanocrystals and SiO 2-based oxide glassy phase. It is demonstrated that a combination of Ni 2+-dopings and laser irradiations is effective in spatially selected local crystallizations of fluorides in oxyfluoride glasses.

  14. Concentration dependence of the Judd-Ofelt parameters of Er3 + ions in CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Preda, E.; Stef, M.; Buse, G.; Pruna, A.; Nicoara, I.

    2009-03-01

    In the present study, various concentrations of ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The Judd-Ofelt intensity parameters ? t (t= 2, 4, 6) for f-f transitions of Er3 + ions were determined from optical absorption spectra. The concentration dependence of the intensity parameters radiative transition probability, oscillator strength, branching ratio and radiative lifetime was also investigated. The predicted radiative lifetimes were compared with those of the Er3 + transitions reported in various hosts. Apart from the green and red emissions, reported by other researchers, a UV (314 nm) emission band was observed, not reported previously.

  15. Cobalt epitaxial nanoparticles on CaF2/Si(111): Growth process, morphology, crystal structure, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Sokolov, N. S.; Suturin, S. M.; Krichevtsov, B. B.; Dubrovskii, V. G.; Gastev, S. V.; Sibirev, N. V.; Baranov, D. A.; Fedorov, V. V.; Sitnikova, A. A.; Nashchekin, A. V.; Sakharov, V. I.; Serenkov, I. T.; Shimada, T.; Yanase, T.; Tabuchi, M.

    2013-03-01

    We study molecular beam epitaxy growth, morphology, crystal structure, and magnetic properties of Co nanoislands on CaF2/Si(111) surface. In order to have a full appreciation of complex growth kinetics at different stages, a comprehensive study of Co growth on CaF2 is carried out by atomic force, scanning electron, and transmission electron microscopies in the direct space, as well as by x-ray and electron diffraction in the reciprocal space. These experimental data are complemented by theoretical modeling. Magnetic properties are characterized by magneto-optical Kerr effect and superconducting quantum interference device magnetometries. Key effects influencing the Co growth on fluorite are addressed, including the sticking probability, the preferential nucleation sites, the size and shape time evolution, the dependence of Co morphology on temperature and Co exposure, and the coalescence mechanism. The two-stage deposition technique is developed, whereby the low-temperature seeding stage is used to facilitate Co nucleation, and the follow-up high-temperature deposition yields Co particles with high crystalline quality. Our results enable precise control over the resulting morphology, spatial ordering, and crystal structure affecting the magnetic properties. In particular, it is demonstrated that the transformation from dense to isolated Co nanoparticles leads to the change of the in-plane and out-of-plane magnetic anisotropy and also the sign of polar and longitudinal magneto-optical Kerr effects.

  16. Biaxially textured Al film growth on CaF2 nanostructures toward a method of preparing single-crystalline Si film on glass substrates.

    PubMed

    Li, Huafang; Snow, Patrick; He, Ming; Wang, Pei-I; Wang, Gwo-Ching; Lu, Toh-Ming

    2010-10-26

    We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices. PMID:20839785

  17. Up-conversion luminescence properties and energy transfer of Er3+/Yb3+ co-doped oxyfluoride glass ceramic containing CaF2 nano-crystals

    NASA Astrophysics Data System (ADS)

    Ma, Chen-Shuo; Jiao, Qing; Li, Long-Ji; Zhou, Da-Cheng; Yang, Zheng-Wen; Song, Zhi-Guo; Qiu, Jian-Bei

    2014-05-01

    The Er3+/Yb3+ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy (TEM) images showed that CaF2 nano-crystals of 20-30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+ at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+ and Yb3+ was convinced and the possible mechanism of Er3+ up-conversion was discussed.

  18. Erase-mode recording characteristics of photochromic CaF2, SrTiO3, and CaTiO3 crystals.

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

    Erase-mode optical recording characteristics of photochromic crystal wafers of CaF2:La,Na; CaF2:Ce,Na; SrTiO3:Ni,Mo,Al; and CaTiO3:Ni,Mo have been measured. An argon laser operating at 5145 A was used for both optical recording and optical readout. Sensitometric curves of optical-density change versus logarithm of exposure are shown for a number of erase-beam intensities between 0.2 mW/sq cm and 2 W/sq cm. In this range, time-intensity reciprocity holds for the CaF2 materials but fails for the titanates, particularly at low intensities. The dependences of sensitivity, gamma, and maximum transmission contrast ratio on wafer thickness and material are discussed. Wafers of SrTiO3, CaTiO3, and CaF2 exhibiting approximately equal maximum contrast ratios have relative sensitivities approximately in the ratio 5:2:1, respectively, at an erase intensity of 1 W/sq cm.

  19. Direct Search for Spin-Dependent WIMPS with CaF2 Detector

    NASA Astrophysics Data System (ADS)

    Hazama, R.; Ogawa, I.; Mukaida, K.; Ajimura, S.; Hirano, Y.; Ichihara, K.; Ishikawa, Y.; Itamura, M.; Katsuki, A.; Kishimoto, K.; Matsuoka, K.; Miyawaki, H.; Nitta, T.; Sakai, H.; Shiomi, S.; Suzuki, N.; Tanaka, Y.; Tatewaki, Y.; Tomii, S.; Umehara, S.; Yokoyama, D.; Yoshida, S.; Kishimoto, T.

    2008-04-01

    A CaF2 scintillator complex system (ELEGANT VI) is developed to search for the axial-vector coupled dark matter (WIMPs) and study the neutrino-less double beta decay of 48Ca. Active light guides of pure CaF2 crystals which are on both sides of the central CaF2(Eu) crystal act as a 4? active shield, combined with surrounding CsI(Tl) scintillators. The whole system is in operation at the underground laboratory (Oto Cosmo Observatory) located in Nara. In this article recent several improvements and our current status of the investigation are described, especially putting emphasis on the radioactive impurities of CaF2 crystal and development of flash scaler/trigger system with FPGA (Field Programmable Gate Array) to do a single photon counting and a noise-cut via photon time distribution.

  20. Some dielectric and optical properties of ErF 3-doped CaF 2 crystals

    NASA Astrophysics Data System (ADS)

    Nicoara, Irina; Munteanu, Mihai; Preda, Eleonora; Stef, Marius

    2008-04-01

    Calcium fluoride crystals doped with ErF 3 and PbF 2 have been grown using the vertical Bridgman method. Temperature and frequency dependence of the complex dielectric constant have been measured at seven audio frequencies (1-100 kHz) over the temperature range of 150-300 K. The activation energy for dipole reorientation and the relaxation time constant, ?0, has been determined from the observed relaxation processes. The effect of Er 3+, Pb 2+ ions and the X-ray irradiation on the optical and dielectric spectra was studied. A comparison of our results with those obtained by other authors is also given.

  1. Small angle grain boundary Ge films on biaxial CaF 2/glass substrate

    NASA Astrophysics Data System (ADS)

    Gaire, C.; Clemmer, P. C.; Li, H.-F.; Parker, T. C.; Snow, P.; Bhat, I.; Lee, S.; Wang, G.-C.; Lu, T.-M.

    2010-02-01

    We demonstrated that it is possible to grow single crystal-like Ge films on a glass substrate using a biaxially textured CaF 2 buffer layer at a low temperature of ˜400 °C. The CaF 2 buffer layer with the (1 1 1)<1 2 1> biaxial orientation was grown by the oblique angle deposition technique and characterized by X-ray pole figure analysis. Transmission electron microscopy revealed that the Ge(1 1 1) heteroepitaxial films possess a single crystal-like structure with small angle grain boundaries of ?2° misorientation.

  2. Dark matter search with CaF2 scintillator at Osaka

    NASA Astrophysics Data System (ADS)

    Ogawa, I.; Hazama, R.; Mukaida, K.; Kishimoto, K.; Sakai, H.; Katsuki, A.; Itamura, T.; Umehara, S.; Yoshida, S.; Kishimoto, T.

    2008-07-01

    A CaF2 scintillator complex system (ELEGANT VI) is developed to search for the axial-vector coupled dark matter (WIMPs) and study the neutrino-less double beta decay of 48 Ca. Active light guides of pure CaF2 crystals which are on both sides of the central CaF2(Eu) crystal act as a 4? active shield, combined with surrounding CsI(T1) scintillators. The whole system is at the underground laboratory (Oto Cosmo Observatory) located in Nara. In this article our current status of the investigation are described, especially putting emphasis on the development of flash scaler to do a single photon counting.

  3. Hardness of CaF2 and BaF2 solid lubricants at 25 to 670 deg C

    NASA Technical Reports Server (NTRS)

    Deadmore, Daniel L.; Sliney, Harold E.

    1987-01-01

    Plastic deformation is a prominent factor in determining the lubricating value of solid lubricants. Little information is available and its direct measurement is difficult so hardness, which is an indirect measure of this property was determined for fluoride solid lubricant compositions. The Vickers hardness of BaF2 and CaF2 single crystals was measured up to 670 C in a vacuum. The orientation of the BaF2 was near the (013) plane and the CaF2 was about 16 degrees from the degrees from the (1'11) plane. The BaF2 has a hardness of 83 kg/sq mm at the 25 C and 9 at the 600 C. The CaF2 is 170 at 25 C and 13 at 670 C. The decrease in hardness in the temperature range of 25 to 100 C is very rapid and amounts to 40% for both materials. Melts of BaF2 and CaF2 were made in a platinum crucible in ambient air with compositions of 50 to 100 wt% BaF2. The Vickers hardness of these polycrystalline binary compositions at 25 C increased with increasing CaF2 reaching a maximum of 150 kn/sq mm near the eutectic. The polycrystalline CaF2 was 14% softer than that of the single crystal surface and BsF2 was 30% harder than the single crystal surface. It is estimated that the brittle to ductile transition temperature for CaF2 and BaF2 is less than 100 C for the conditions present in the hardness tester.

  4. December 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2767 High-power diode-pumped Yb3+:CaF2 femtosecond laser

    E-print Network

    Boyer, Edmond

    December 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2767 High-power diode-pumped Yb3+:CaF2 is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb31:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at

  5. Dependence of the profile of a hologram recorded on color centers in a CaF2 crystal on the type of hologram-forming centers

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Veniaminov, A. V.; Zakharov, V. V.; Ryskin, A. I.

    2012-12-01

    A hologram recorded in a CaF2 crystal by modulating the concentration of simple centers ( F, M, R, and N) and highly aggregated (mainly colloidal) color centers has been exposed to incoherent 365-nm light to a dose of about 4000 J/cm2 at a temperature of 80°C. As a result of this exposure, the color centers were almost completely transformed into quasi-colloidal centers. The hologram was retained, and its diffraction efficiency increased; the intensity and number of observed diffraction orders increased as well. Analysis of the angular dependences of the diffraction response made it possible to construct a spatial profile of the hologram, which turned out to be much narrower in comparison with the initial-hologram profile; both profiles differ from a sinusoidal one. The hologram's stability to such a large exposure to incoherent light at an elevated temperature is related to the peculiar diffusion-drift mechanism of hologram recording on color centers in ionic crystals.

  6. Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n

    E-print Network

    Wang, Gwo-Ching

    Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n , P.C. Clemmer demonstrated that it is possible to grow single crystal-like Ge films on a glass substrate using a biaxially such as glass results in either polycrystalline or fiber textured film, biaxially textured films of insulating

  7. Laser interactions with embedded Ca metal nanoparticles in single crystal CaF2

    E-print Network

    Dickinson, J. Thomas

    the wavelength dependence of the bleaching process to the wavelength dependence associated with Mie absorption- tals produced by rapid growth for the National Ignition Facility.3,4 When damage is caused called colloids, are readily produced by relatively low energy electrons 2 keV at modest doses 5 mC/cm2

  8. Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

    NASA Astrophysics Data System (ADS)

    Cardellach, M.; Verdaguer, A.; Fraxedas, J.

    2011-12-01

    The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

  9. Pressure dependence of the emission in CaF2?:?Yb(2.).

    PubMed

    Mahlik, S; Lazarowska, A; Grinberg, M; Wells, J-P R; Reid, M F

    2015-08-01

    We present a detailed spectroscopic investigation of CaF2 doped with Yb(2+) performed at high hydrostatic pressure which is applied in a diamond anvil cell. At ambient pressure and at temperatures lower than 175?K, the luminescence consists of a single broad band peaked at 18?500?cm(-1), attributed to the recombination of impurity-trapped excitons. Increasing pressure causes the luminescence to be observable at higher temperature. At a pressure of 72?kbar luminescence can be observed up to 275?K. The emission lineshape does not strongly depend on pressure below 85?kbar. However, at 85?kbar it is blue shifted to 21?630?cm(-1). This is attributed to the known phase transition of the CaF2 crystal from cubic to the orthorhombic phase. The absolute energy of the ground and 4f(13)5d states of Yb(2+) as well as the energy of the impurity-trapped exciton with respect to valence and conduction bands have been estimated. The results, are discussed in comparison with the pressure dependences observed for the luminescence of BaF2?:?Eu(2+) and CaF2?:?Eu(2+). The difference between the spectral properties of Eu(2+) and Yb(2+) is attributable to the fact that the ground and 4f(6)5d states of Eu(2+) are placed deeper in the CaF2 bandgap than the ground and excited 4f(13)5d states of Yb(2+), whereas the energies of the impurity-trapped exciton states for Yb(2+) and Eu(2+) with respect to the conduction band are approximately the same. PMID:26171576

  10. Effect of ZrO(2) additions on the crystallization, mechanical and biological properties of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) bioactive glass-ceramics.

    PubMed

    Li, H C; Wang, D G; Meng, X G; Chen, C Z

    2014-06-01

    A series of ZrO(2) doped MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) bioactive glass-ceramics were obtained by sintering method. The crystallization behavior, phase composition, morphology and structure of glass-ceramics were characterized. The bending strength, elastic modulus, fracture toughness, micro-hardness and thermal expansion coefficient (TEC) of glass-ceramics were investigated. The in vitro bioactivity and cytotoxicity tests were used to evaluate the bioactivity and biocompatibility of glass-ceramics. The sedimentation mechanism and growth process of apatites on sample surface were discussed. The results showed that the mainly crystalline phases of glass-ceramics were Ca(5)(PO4)3F (fluorapatite) and ?-CaSiO(3). (?-wollastonite). m-ZrO(2) (monoclinic zirconia) declined the crystallization temperatures of glasses. t-ZrO(2) (tetragonal zirconia) increased the crystallization temperature of Ca(5)(PO4)(3)F and declined the crystallization temperature of ?-CaSiO(3). t-ZrO(2) greatly increased the fracture toughness, bending strength and micro-hardness of glass-ceramics. The nanometer apatites were induced on the surface of glass-ceramic after soaking 28 days in SBF (simulated body fluid), indicating the glass-ceramic has good bioactivity. The in vitro cytotoxicity test demonstrated the glass-ceramic has no toxicity to cell. PMID:24780435

  11. Capillary and van der Waals interactions on CaF2 crystals from amplitude modulation AFM force reconstruction profiles under ambient conditions

    PubMed Central

    Calò, Annalisa; Robles, Oriol Vidal; Santos, Sergio

    2015-01-01

    Summary There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5–1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3–4 nm above the surface when the formation of a capillary neck dominates the tip–sample interaction. PMID:25977852

  12. Capillary and van der Waals interactions on CaF2 crystals from amplitude modulation AFM force reconstruction profiles under ambient conditions.

    PubMed

    Calò, Annalisa; Robles, Oriol Vidal; Santos, Sergio; Verdaguer, Albert

    2015-01-01

    There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5-1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3-4 nm above the surface when the formation of a capillary neck dominates the tip-sample interaction. PMID:25977852

  13. Lanthanide doped upconverting colloidal CaF2 nanoparticles prepared by a single-step hydrothermal method: toward efficient materials with near infrared-to-near infrared upconversion emission.

    PubMed

    Pedroni, Marco; Piccinelli, Fabio; Passuello, Tiziana; Giarola, Marco; Mariotto, Gino; Polizzi, Stefano; Bettinelli, Marco; Speghini, Adolfo

    2011-04-01

    Colloidal Er(3+)/Yb(3+), Tm(3+)/Yb(3+) and Ho(3+)/Yb(3+) doped CaF(2) nanoparticles have been prepared by a one-pot hydrothermal procedure and their upconversion properties have been investigated. PMID:21336370

  14. Solubility of niobium in the system CaCO3 CaF2 NaNbO3 at 0.1 GPa pressure: implications for the crystallization of pyrochlore from carbonatite magma

    Microsoft Academic Search

    Roger H. Mitchell; Bruce A. Kjarsgaard

    2004-01-01

    Experimental data are presented for the solubility of NaNbO3 in the ternary system CaCO3 CaF2 NaNbO3 (or calcite fluorite lueshite) over the temperature range 500 1,000°C at 0.1 GPa pressure. Liquidus to solidus phase relationships are given for the pseudo-binary join ([CaCO3]60[CaF2]40)100-x (NaNbO3)x (0

  15. Solubility of niobium in the system CaCO 3 –CaF 2 –NaNbO 3 at 0.1 GPa pressure: implications for the crystallization of pyrochlore from carbonatite magma

    Microsoft Academic Search

    Roger H. Mitchell; Bruce A. Kjarsgaard

    2004-01-01

    Experimental data are presented for the solubility of NaNbO 3 in the ternary system CaCO 3–CaF 2–NaNbO 3 (or calcite–fluorite–lueshite) over the temperature range 500–1,000°C at 0.1 GPa pressure. Liquidus to solidus phase relationships are given for the pseudo-binary join ([CaCO 3] 60[CaF 2] 40) 100- x–(NaNbO 3) x (0x3 in these liquids is about 17 wt% (or 13.8 wt% Nb 2O 5)

  16. Improvement in the quality of LiCaAlF 6 single crystal as window material

    NASA Astrophysics Data System (ADS)

    Sato, H.; Bensalah, A.; Yoshikawa, A.; Nikl, M.; Machida, H.; Fukuda, T.

    2003-10-01

    Three-in. size LiCaAlF 6 (LiCAF) single crystals were successfully grown by the Czochralski method. Both measurements of the transmission spectra in the VUV regions and the X-ray rocking curve analysis showed that the crystallinity of LiCAF single crystal was improved by the annealing. Optical absorption measurements in the UV/VIS spectral regions following X-ray irradiation were performed in order to compare the radiation damage with a lithography-grade CaF 2 crystal.

  17. Influence of CaF2 on the Viscosity and Structure of Manganese Ferroalloys Smelting Slags

    NASA Astrophysics Data System (ADS)

    Park, Joo Hyun; Ko, Kyu Yeol; Kim, Tae Sung

    2015-04-01

    Addition of CaF2 to the CaO-SiO2-MnO (CaO/SiO2 = 0.5) system, which corresponds qualitatively to a silicomanganese ferroalloy smelting slag, affected not only the critical (crystallization) temperature ( T CR) but also the viscosity at high temperatures, and its influence on slag properties was strongly dependent on the content of MnO in the slag. The viscosity of CaF2-free 10 mass pct MnO slag was relatively high, i.e., about 10 dPa s at 1773 K (1500 °C), but decreased continuously upon addition of CaF2 to the system. In contrast, the viscosity of the 40 pct MnO system was very low, i.e., 1 dPa s at 1773 K (1500 °C), and CaF2 did not have a large effect. This indicates that Mn2+ is a strong network modifier in manganese ferroalloy smelting slags. Nevertheless, CaF2 addition was very effective at decreasing the viscosity of low MnO slags at low temperatures. The activation energy for the viscous flow of silicate melts decreased linearly in response to CaF2 addition, but this tendency was less pronounced in the more basic composition of the slag. The effect of CaF2 on the viscosity and activation energy for viscous flow of melts was analyzed quantitatively using micro-Raman spectra of quenched glass samples and the silicate polymerization index, i.e., Q3/Q2 ratio. The polymerization index decreased continuously with increasing CaF2 content in less basic (10 pct MnO or C/S = 0.5) slags, whereas it was not affected by CaF2 content in highly basic (40 pct MnO and C/S = 1.0) slags. Bulk thermophysical properties of the CaO-SiO2-MnO-CaF2 slags were quantitatively correlated with the structural information of the slags.

  18. Note: Characterization of CaF2/acetone bandpass photon detector with Kr filter gas

    NASA Astrophysics Data System (ADS)

    Maniraj, M.; Sekhar, B. N. Raja; Barman, S. R.

    2012-04-01

    A modified design of a CaF2/acetone bandpass photon detector that uses Kr as a filter gas to tune the energy resolution is presented. Our design combines two standard single window detector tubes to build the Kr filter gas chamber. Synchrotron radiation has been used to determine the energy resolution of the detector, as a function of Kr pressure. The improvement in the detector energy resolution by 250 meV compared to the CaF2/acetone detector is better than that reported earlier. Substantial variation in the shape of the CaF2/acetone detector response functions is observed for different acetone pressure (?3 mbar), and anode voltage (?800 V). Our analysis reveals that the changes in the shape of the detector response function are associated to different regions of the detector operation.

  19. Initial stage of laser ablation of LiCaAlF6 single crystal under F2 laser irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Y.; Narazaki, A.; Sato, T.; Kurosaki, R.; Niino, H.; Sato, H.; Fukuda, T.

    Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 Jcm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed.

  20. Diode-pumped femtosecond mode-locked Nd, Y-codoped CaF2 laser

    NASA Astrophysics Data System (ADS)

    Zhu, Jiangfeng; Zhang, Lijuan; Gao, Ziye; Wang, Junli; Wang, Zhaohua; Su, Liangbi; Zheng, Lihe; Wang, Jingya; Xu, Jun; Wei, Zhiyi

    2015-03-01

    A passively mode-locked femtosecond laser based on an Nd, Y-codoped CaF2 disordered crystal was demonstrated. The Y3+-codoping in Nd?:?CaF2 markedly suppressed the quenching effect and improved the fluorescence quantum efficiency and emission spectra. With a fiber-coupled laser diode as the pump source, the continuous wave tuning range covering from 1042 to 1076?nm was realized, while the mode-locked operation generated 264?fs pulses with an average output power of 180?mW at a repetition rate of 85?MHz. The experimental results show that the Nd, Y-codoped CaF2 disordered crystal has potential in a new generation diode-pumped high repetition rate chirped pulse amplifier.

  1. 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.

  2. Arnold Schwarzenegger SINGLE CRYSTAL SILICON

    E-print Network

    Arnold Schwarzenegger Governor SINGLE CRYSTAL SILICON SHEET GROWTH Prepared For: California Energy CRYSTAL SILICON SHEET GROWTH EISG AWARDEE ENERGY MATERIALS RESEARCH 132 Chalmers Drive Rochester Hills, MI

  3. A solvent extraction route for CaF2 hollow spheres.

    PubMed

    Guo, Fuqiang; Zhang, Zhifeng; Li, Hongfei; Meng, Shulan; Li, Deqian

    2010-11-21

    A solvent extraction route is proposed to synthesize CaF(2) hollow spheres, which are formed by reversed micelles in a solvent extraction system templating the self-assembly of CaF(2) nanoparticles. PMID:20877846

  4. Study on TL and OSL characteristics of indigenously developed CaF 2:Mn phosphor

    NASA Astrophysics Data System (ADS)

    Bakshi, A. K.; Dhabekar, Bhushan; Rawat, N. S.; Singh, S. G.; Joshi, V. J.; Kumar, Vijay

    2009-02-01

    CaF 2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF 2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO 3, HF acid and MnCl 2 as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO 4:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn 2+ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.

  5. Resistance of LiCaAlF6 Single Crystals against F2 Laser Irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Yoshizo; Narazaki, Aiko; Niino, Hiroyuki; Sato, Hiroki; Fukuda, Tsuguo; Shimamura, Kiyoshi

    2003-08-01

    The resistance of LiCaAlF6 single crystals against F2 laser irradiation was studied to examine the possible use of LiCaAlF6 as optical components for F2 laser lithography. After the initial increase by F2 laser cleaning, transmittance of LiCaAlF6 at 157 nm remains relatively unchanged even after irradiation with an F2 laser beam up to 105 pulses at a fluence of approximately 160 mJ\\cdotcm-2\\cdotpulse-1, indicating good tolerance against the cumulative irradiation. We also discuss the mechanism of the initial increase in transmittance with the results of X-ray photoelectron spectroscopy (XPS). The threshold fluence for the onset of optical damage of LiCaAlF6 is approximately 2 J\\cdotcm-2\\cdotpulse-1, similar to that of vacuum ultraviolet (VUV) grade CaF2.

  6. CaF2(Eu): an ``old'' scintillator revisited

    NASA Astrophysics Data System (ADS)

    Plettner, C.; Pausch, G.; Scherwinski, F.; Herbach, C. M.; Lentering, R.; Kong, Y.; Römer, K.; Grodzicka, M.; Szcze?niak, T.; Iwanowska, J.; Moszy?ski, M.

    2013-06-01

    Homeland security applications demand performant two-plane Compton-camera systems, with high detector efficiency, good nuclide identification and able to perform in-field conditions. A low-Z scintillator has been proposed and studied as a promising candidate for use in the scattering plane of a scintillator-based Compton camera: CaF2(Eu) [1]. All the relevant properties for the application of this scintillator in a mobile Compton camera system, have been addressed: the energy resolution and the non-proportionality at room temperature and in the temperature range of -20°C to +55°C, the photoelectron yield and the relative light yield in the relevant temperature range. A new method of inferring the relative light output of scintillators has been proposed.

  7. Spectroscopic investigation of 2.02 ?m emission in Ho3+/Tm3+ codoped transparent glass ceramic containing CaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Chen, Q. J.; Zhang, W. J.; Qian, Q.; Yang, Z. M.; Zhang, Q. Y.

    2010-05-01

    Tm3+ and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd-Ofelt parameters were calculated based on the absorption spectra, the smaller ?2 and larger ?6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 ?m emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 ?m in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:H34+Tm3+:H36?2Tm3+:H34, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

  8. Ab initio multiconfiguration self-consistent-field calculations of the excited states of a Mn impurity in CaF2

    NASA Astrophysics Data System (ADS)

    Lewandowski, A. C.; Wilson, T. M.

    1994-08-01

    We analyze Mn absorption in CaF2:Mn by the employment of ab inito quantum-mechanical cluster calculations and ligand-field methods. The [MnF8]6- Oh cluster is chosen to represent the isolated Mn2+ substitutional impurity in an otherwise perfect crystal. The methods of unrestricted open-shell Hartree-Fock self-consistent field (SCF), Mo/ller-Plesset perturbation theory to second- and fourth-order, and singles and doubles configuration interaction are used to calculate the spin sextet and quartet ground states. With the active space consisting of the Mn 3d molecular orbitals, the spin quartet excited states are calculated by the method of multiconfiguration SCF. It was found that the presence of an external field designed to reproduce the Madelung potential difference within the cluster did not significantly affect the Mn d-to-d transitions. The crystal-field term splitting diagrams for the eight-coordinated Mn2+ impurity in Oh symmetry are calculated. The results showed a narrowing of the multiplet terms in energy with respect to the six-coordinated Oh result. This increases the crystal-field parameter Dq from the previously published value of 420-570 cm-1.

  9. Preparation of CaF 2 based phosphors by solid state metathesis

    NASA Astrophysics Data System (ADS)

    Ugemuge, N. S.; Tajne, D. S.; Dhopte, S. M.; Muthal, P. L.; Moharil, S. V.

    2011-01-01

    Synthesis of CaF 2:Eu and CaF 2:Ce phosphors by solid state metathesis is reported for the first time. CaF 2 could be prepared in few minutes using domestic microwave oven. Though CaF 2 is formed by metathesis, luminescence centres were not formed in one step; as-prepared samples did not show any luminescence. Samples reduced at 1000 °C for 1 h exhibited very intense, characteristic emission. Activator concentration, and in turn, the intensity of luminescence depends on the partition coefficient of the activator in the host and the washable reaction products (KCl in the present case). In case of Europium, most of the activator is retained by CaF 2 while for Cerium a significant fraction of the added activator is washed away with KCl.

  10. 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.

  11. Study on TL and OSL characteristics of indigenously developed CaF 2:Mn phosphor

    Microsoft Academic Search

    A. K. Bakshi; Bhushan Dhabekar; N. S. Rawat; S. G. Singh; V. J. Joshi; Vijay Kumar

    2009-01-01

    CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

  12. Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor

    Microsoft Academic Search

    A. K. Bakshi; Bhushan Dhabekar; N. S. Rawat; S. G. Singh; V. J. Joshi; Vijay Kumar

    2009-01-01

    CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

  13. X-ray scattering from surfaces and interfaces and its application to the characterization of {CaF2}/{Si(111) } interfaces

    NASA Astrophysics Data System (ADS)

    Harada, J.; Takahashi, I.; Itoh, Y.; Sokolov, N. S.; Yakovlev, N. L.; Shusterman, Y.; Alvarez, J. C.

    1996-05-01

    A survey of X-ray scattering techniques developed so far is presented keeping in mind that the appearance of the next generation of synchrotron radiation sources makes such techniques one of the promising probes for ex situ and in situ characterization of the surface and the interface of an epitaxially grown crystal. On the basis of the intensity formula given by one of the present authors [J. Harada, Ultramicroscopy 52 (1993) 233], it is shown that diffuse scattering associated with the crystal truncation rod is closely related to the local atomic arrangement on a surface. Our current X-ray scattering studies on {CaF2}/{Si(111) } films grown by the MBE method are presented and the growth condition of the four types of interface structure found in {CaF2}/{Si(111) } is discussed. A hydrogen-terminated Si(111) surface was found to be a promising substrate for the low-temperature growth of CaF 2 films.

  14. Single Crystals of Single-Walled Carbon Nanotubes Formed by

    E-print Network

    Gimzewski, James

    -assembly of single crystals of single-walled carbon nano- tubes (SWCNTs) using thermolysis of nano of carbon nanotube fabrication is to form large uniform and ordered nano- and microstructuresSingle Crystals of Single-Walled Carbon Nanotubes Formed by Self-Assembly R. R. Schlittler,1 J. W

  15. Comment on "Single Crystals of Single-Walled Carbon Nanotubes

    E-print Network

    Kono, Junichiro

    et al. (1) reported the production of single crystals of single-walled carbon nano- tubes (SWCNTsComment on "Single Crystals of Single-Walled Carbon Nanotubes Formed by Self-Assembly" Schlittler) by the thermolysis of nano- patterned structures of alternating layers of C60 and nickel. Electron diffraction, high

  16. High strength single crystal superalloys

    SciTech Connect

    Chin, S.; Duhl, D.N.

    1990-03-13

    This patent describes an alloy composition suitable for casting into a single crystal nickel base superalloy article. It comprises, on a weight percent basis, 4-5.5 Cr, 7.5-12 Co, 1.5-2.5 Mo, 1-6 W, 2-4 Re, 4.5-5.5 Al, 0.5-1.5 Ti, 8-12 Ta, 0-1 V, 0-0.5 Hf, 0.0-0.01 B, 0.0-0.2 Cb, 0.0-0.05 C, 0.0-0.01 Zr, with the balance nickel.

  17. Growth of CdTe Films on Amorphous Substrates Using CaF2 Nanorods as a Buffer Layer

    E-print Network

    Wang, Gwo-Ching

    Growth of CdTe Films on Amorphous Substrates Using CaF2 Nanorods as a Buffer Layer NICHOLAS LICAUSI biaxially textured CdTe films were grown on biaxial CaF2 buffer layers. The CaF2 nanorods were grown by oblique angle vapor deposition and possessed a {111}h121i biaxial texture. The CdTe film was deposited

  18. Altered photoemission satellites at CaF2-and SrF2-on-Si,,111... interfaces Eli Rotenberg*

    E-print Network

    Olmstead, Marjorie

    Altered photoemission satellites at CaF2- and SrF2-on-Si,,111... interfaces Eli Rotenberg diffraction, are compared for thick, thin, and monolayer films of CaF2 and SrF2 on Si 111 . Intrinsic. The most likely explanation for the new cation satellites at the CaF2/Si 111 SrF2/Si 111 interface

  19. Microstructure and IR transmittance of spark plasma sintering translucent AlN ceramics with CaF 2 additive

    Microsoft Academic Search

    Y. Xiong; Z. Y. Fu; H. Wang; Y. C. Wang; Q. J. Zhang

    2005-01-01

    Translucent AlN ceramics were fabricated by spark plasma sintering (SPS) with and without CaF2 as sintering additive. An increase in the amount of CaF2 up to 3% in mass did not further increase the density, however improved the IR transmittance. The sample doped with 3% in mass CaF2 yielded the maximum transmittance of 54.7% in medium IR region. The microstructures

  20. The Exicor DUV birefringence measurement system and its application to measuring lithography-grade CaF2 lens blanks

    NASA Astrophysics Data System (ADS)

    Wang, Baoliang; Griffiths, C. O.; Rockwell, Rick R.; List, Jennifer; Mark, Doug

    2003-11-01

    Optical lithography continues its transition to shorter wavelengths to support the semiconductor industry"s production of faster microchips to meet evolving market demands. The next step for optical lithography is likely to use the F2 excimer laser at 157.63 nm (157 nm,according to the industry" s naming convention).At 157 nm, among the limited number of fluoride crystals with acceptable optical properties calcium fluoride is the only practical lens material for step and scan systems due to its readiness for mass production. Since the discovery of intrinsic birefringence in CaF2 at deep ultraviolet (DUV)wavelengths,the optical lithography industry has developed a critical interest in measuring birefringence at 157 nm. In response to this need, we have developed a DUV birefringence measurement system. In this article,we describe the working principle, system construction, technical performance and selected applications for measuring lithography grade calcium fluoride lens blanks at DUV wavelengths.

  1. Growth and optical properties of partially transparent Eu doped CaF2 ceramic

    NASA Astrophysics Data System (ADS)

    Ghosh, Manoranjan; Sen, Shashwati; Pitale, S. S.; Goutam, U. K.; Shinde, Seema; Patra, G. D.; Gadkari, S. C.

    2014-04-01

    Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size˜12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

  2. The Analysis of Main Dosimetric Glow Peaks in CaF2:Tm (TLD-300)

    NASA Astrophysics Data System (ADS)

    Vural, E. Kafadar; Metin, Bedir; A. Necmeddin, Yaz?c?; Tülin, Günal

    2013-05-01

    The thermoluminescence properties of CaF2:Tm (TLD-300) are examined in detail after ?-irradiation at room temperature. The glow curve of the sample shows two main dosimetric glow peaks: P3 (at ~150°C) and P5 (at ~250°C). The additive dose, variable heating rate, computer glow curve deconvolution, peak shape and three points methods are used to evaluate the trapping parameters, namely the order of kinetics (b), activation energy (E) and frequency factor (s) associated with the dosimetric thermoluminescent glow peaks (P3 and P5) of CaF2:Tm (TLD-300) after different dose levels with ?-irradiation.

  3. Growth of single crystal diamond

    NASA Astrophysics Data System (ADS)

    Regmi, Murari

    The subject of the research presented in this dissertation is the growth of single crystal diamond by microwave plasma chemical vapor deposition (CVD). Both heteroepitaxial and homoepitaxial growth methods have been examined, with emphasis on producing large diamond crystals of high structural and chemical perfection. By heteroepitaxy, epitaxial growth on a foreign substrate, diamond was grown on (001) Ir thin-film epitaxial buffer layers deposited on (001) strontium titanate (SrTiO3) by DC magnetron sputtering. To nucleate diamond on Ir, the Ir surface was bombarded with low energy ions extracted from the hydrocarbon plasma, a process known as DC biasing or bias-enhanced nucleation. Since this critical process is poorly understood, attention was paid to the spatial and temporal evolution of the Ir surface during the bias treatment. It was discovered that the biased Ir surface is etched on a surprisingly short time scale during which highly correlated nanopillars, 3-4 nm in height with mean separation 15 nm, emerge. The etching process is spatially non-uniform, propagating from substrate center to substrate edge in minutes. Diamond grew on Ir without an intervening phase. Lattice images revealed that interfacial strain from the 7% Ir-diamond lattice mismatch is largely relieved by misfit dislocations within 1 nm of the interface. It is suggested that the high nucleation density obtained with specific bias conditions is associated with the roughened Ir surface. To grow heteroepitaxial diamond as thick films, a two-step growth method was explored. This process involved the transfer of a thin heteroepitaxial diamond film, still attached to a substrate, to a second reactor where high growth rate conditions were possible. Characterization of films grown by this approach showed that the resulting diamond had much lower levels of internal strain, suggesting that the process could be used to grow diamond crystals of structural quality similar to natural diamond. In homoepitaxy, epitaxial growth on a substrate of the same material, diamond was deposited by CVD directly onto high-pressure, high-temperature Type Ib diamond substrates. Methods for removing substrate surface damage, as well as other imperfections, were devised by use of plasma etching. The characteristics and statistics of pits formed during etching were studied. Diamond growth methods were developed with the aim of minimizing the formation of various structural and chemical defects. To accomplish this, several growth parameters were varied, including substrate temperature, feed gas concentration, growth rate, substrate surface, microwave power, and reactor geometry. Regions of parameter space were found in which the diamond (001) surface remained smooth during growth, and complete suppression of instabilities that create hillocks or non-epitaxial crystallites was demonstrated. A great deal of information was obtained by interrupting growth, removing the crystal from the reactor for optical inspection, and then resuming the process with no apparent negative effects. Diamond crystals were grown on 3 x 3 mm2 substrates with thicknesses greater than 0.5 mm. The chemical purity of the crystals was such that it was impossible to observe signatures of substitutional nitrogen at the ppm level.

  4. Electronic conduction through single crystals of polyethylene 

    E-print Network

    Samson, Gerald Maurice

    1966-01-01

    la-slier growths by crystallizing the polymer from dilute solutions in benzene and xylene. Since that tine, solut'on-grown lamellar single crystals have been identified for a rumber of other polymers. 5 All solution-grown polymer single crystals... lower . e""perctures thc a?-'or contribu ion . o che current is probably "eld omission (tunneling). Solution-grown single crystals we c deposi lcd upon s. microscope slide coated w' th a thin layer of otal, which served as o. . c electrode. he counter...

  5. Dark Matter Search with CaF2 Scintillators in Osaka

    NASA Astrophysics Data System (ADS)

    Ogawa, I.; Kishimoto, T.; Hazama, R.; Ajimura, S.; Matsuoka, K.; Suzuki, N.; Nitta, T.; Miyawaki, H.; Shiomi, S.; Tanaka, Y.; Ejiri, H.; Kudomi, N.; Kume, K.; Ohsumi, H.; Fushimi, K.

    2000-01-01

    A detector system which consists of CaF2 scintillators surrounded by active and passive shields, is developed to search for spin coupled dark matter. The whole system is in operation at the underground laboratory located in Nara (Oto Cosmo Observatory) which has effectively 1.2 km water equivalent shield. In this article our current status of the investigation is described.

  6. Growth of Sillenite-Structure Single Crystals

    Microsoft Academic Search

    V. M. Skorikov; Yu. F. Kargin; A. V. Egorysheva; V. V. Volkov; M. Gospodinov

    2005-01-01

    The main processes for preparing bulk single crystals and films of photorefractive and piezoelectric Bi12MxO20±? (M = Group II–VIII elements) sillenite compounds are considered. Experimental data are summarized on the crystal growth of\\u000a Bi12MxO20±? from the melt and under hydrothermal conditions, and the key morphological features of sillenites are analyzed. Various types\\u000a of macroscopic growth defects in sillenite-type crystals are

  7. The Remanent Magnetization of Haematite Single Crystals

    Microsoft Academic Search

    T. E. Gallon

    1968-01-01

    The variation of the remanent magnetization with temperature of several synthetic and natural single crystals of haematite has been measured in the temperature range 60 to -90 ^circC. Particular attention was given to the measurement of the remanence at temperatures close to the transition temperature. The remanent magnetization of the synthetic crystals showed a sharp reduction over a narrow temperature

  8. Ferromagnetic Resonance Absorption in Magnetite Single Crystals

    Microsoft Academic Search

    L. R. Bickford

    1950-01-01

    The microwave resonance absorption technique, at both 1.25 and 3.3 cm wave-lengths, was used to study the ferromagnetic crystalline anisotropy characteristics and g-factor of magnetite Fe3O4. The experiments were performed on single crystals, both synthetic and natural, from room temperature to -195°C. Depending upon the temperature, magnetite single crystals were found to have magnetic anisotropy characteristics similar to those of

  9. Nonradiative relaxation rates in CaF 2:Sm 2+ measured by photoionization spectral holeburning

    NASA Astrophysics Data System (ADS)

    Macfarlane, R. M.; Brocklesby, W. S.; Bloch, P. D.; Harley, R. T.

    1986-05-01

    The temperature dependence of the width of spectral holes burned in the 4f 6A 1g?4f 55d A 1u absorption line (6958 Å) of CaF 2:Sm 2+ has been measured and used to determine the phonon coupling which controls nonradiative relaxation between the A 1u and E u levels. We confirm an assertion made by Akimov and Kaplyanskii that the phonon coupling among the lowest three 4f 55d levels of CaF 2:Sm 2+ exhibits strong selection rules. In particular, the "deformational" E g phonons are two orders of magnitude more effective than "rotational" T 1g phonons in inducing nonradiative relaxation.

  10. The measured electron response nonproportionalities of CaF2 , BGO, and LSO

    Microsoft Academic Search

    T. D. Taulbee; B. D. Rooney; W. Mengesha; J. D. Valentine

    1997-01-01

    To study the light yield nonproportionality and intrinsic energy resolution of inorganic scintillators, a Compton coincidence technique was previously designed, implemented and benchmarked. This technique provides the ability to accurately measure the electron response of scintillation materials and thus provides an accurate means of studying these characteristics. In this study, the electron responses of two “classic” scintillators (CaF2(Eu) and Bi4

  11. Electronic structure of metal CoSi2\\/insulator CaF2 superlattice

    Microsoft Academic Search

    Koji Akai; Mitsuru Matsuura

    1999-01-01

    Electronic structure of metal CoSi2\\/insulator CaF2 superlattice is studied by the full-potential linearized augmented plane-wave method, based on the density-functional theory. From the comparison of calculated total energies for some atomic configurations in the superlattice interface, it is concluded that the Si layer is in contact with a F layer at the interface. Using this atomic configuration, the band structure

  12. Zeeman effect in CaF,,2 R. V. Krems,a)

    E-print Network

    Krems, Roman

    Zeeman effect in CaF,,2 3Õ2... R. V. Krems,a) D. Egorov, J. S. Helton, K. Maussang, S. V. Nguyen August 2004; accepted 16 September 2004 The Zeeman effect in the excited A 2 3/2 state of CaF is measured to interactions with an external mag- netic field can be controlled; measurements of the Zeeman effect may reveal

  13. Structural transitions and relaxation processes during the epitaxial growth of ultrathin CaF2 films on Si(111)

    E-print Network

    Deiter, Carsten

    The structure and morphology of ultrathin lattice matched CaF2 films of very few monolayers thickness, which were deposited on Si(111) substrates by molecular-beam epitaxy, have been studied in situ by synchrotron based ...

  14. Cutting fluid study for single crystal silicon

    Microsoft Academic Search

    Chargin

    1998-01-01

    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

  15. 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 composition through their cross-section as the horizontally grown samples.

  16. 2.7 ?m emission in Er3+:CaF2 nanocrystals embedded oxyfluoride glass ceramics.

    PubMed

    Wu, Guobo; Fan, Shaohua; Zhang, Yuanhao; Chai, Guanqi; Ma, Zhijun; Peng, Mingying; Qiu, Jianrong; Dong, Guoping

    2013-08-15

    Using conventional melt-quenching and subsequent thermal treatment, Er(3+) doped CaF(2) transparent glass ceramic (GC) was prepared. X-ray diffraction and high-resolution transmission electron microscopy confirmed the formation and microstructure of CaF(2) nanocrystals in glass. An energy-dispersive spectrometer was used to investigate the distribution of Er(3+) ions and CaF(2) nanocrystals in glass. It was found that Er(3+) ions prefer to concentrate in the CaF(2) nanocrystals rather than in a glass matrix, and the amount of Er(3+) ions plays a key role in the formation of CaF(2) nanocrystals in a glass matrix with the Er(3+) ions as nucleating agent. An intense 2.7 ?m emission due to Er(3+): I(11/2)4 ? I(13/2)4 was achieved upon excitation at 980 nm with a laser diode, while the 2.7 ?m emission can be neglected in the as-prepared glass counterpart, which confirmed the incorporation of Er(3+) ions into CaF(2) nanocrystals. An obvious enhancement of 2.7 ?m emerged in the GC doped with 3% Er(3+) and heat-treated at 620 °C. PMID:24104651

  17. Ferromagnetic Resonance in Manganese Ferrite Single Crystals

    Microsoft Academic Search

    P. E. Tannenwald

    1955-01-01

    The microwave properties of two types of manganese ferrite single crystals have been investigated by means of the ferromagnetic resonance phenomenon from 300°K to 4.2°K and at 24 000, 9100, 5600, and 2800 Mc\\/sec. The low resistivity of one of the crystals, believed to be related to the presence of divalent iron, led to significantly different microwave behavior. Resonance lines

  18. 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.

  19. Self-diffusion in ?-Zr single crystals

    NASA Astrophysics Data System (ADS)

    Lubbehusen, M.; Vieregge, K.; Hood, G. M.; Mehrer, H.; Herzig, Chr.

    1991-06-01

    Self-diffusion in ?-Zr single crystals has been measured in the temperature interval 871-1074 K. The results, extrapolated, are consistent with single crystal self-diffusion data from an early study in which measurements were reported for one temperature, 1124 K. The composite data, within the scatter of the measurements, display non-linear Arrhenius behaviour, with the effective activation enthalpy increasing with decreasing temperature. This behaviour parallels that found in a recent investigation of self-diffusion in ?-Zr single crystals: except at the low temperature limit, the present diffusion coefficients are systematically higher than those of the previous work. The last aspect, in combination with the higher Fe content of the Zr used here, supports a current view that the unusual Arrhenius behaviour reflects an extrinsic diffusion process dominated by the presence (as an impurity) of Fe.

  20. Energy deposition by heavy ions: additivity of kinetic and potential energy contributions in hillock formation on CaF2.

    PubMed

    Wang, Y Y; Grygiel, C; Dufour, C; Sun, J R; Wang, Z G; Zhao, Y T; Xiao, G Q; Cheng, R; Zhou, X M; Ren, J R; Liu, S D; Lei, Y; Sun, Y B; Ritter, R; Gruber, E; Cassimi, A; Monnet, I; Bouffard, S; Aumayr, F; Toulemonde, M

    2014-01-01

    Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe(22+) to Xe(30+)) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. PMID:25034006

  1. Graphene single crystals: size and morphology engineering.

    PubMed

    Geng, Dechao; Wang, Huaping; Yu, Gui

    2015-05-13

    Recently developed chemical vapor deposition (CVD) is considered as an effective way to large-area and high-quality graphene preparation due to its ultra-low cost, high controllability, and high scalability. However, CVD-grown graphene film is polycrystalline, and composed of numerous grains separated by grain boundaries, which are detrimental to graphene-based electronics. Intensive investigations have been inspired on the controlled growth of graphene single crystals with the absence of intrinsic defects. As the two most concerned parameters, the size and morphology serve critical roles in affecting properties and understanding the growth mechanism of graphene crystals. Therefore, a precise tuning of the size and morphology will be of great significance in scale-up graphene production and wide applications. Here, recent advances in the synthesis of graphene single crystals on both metals and dielectric substrates by the CVD method are discussed. The review mainly covers the size and morphology engineering of graphene single crystals. Furthermore, recent progress in the growth mechanism and device applications of graphene single crystals are presented. Finally, the opportunities and challenges are discussed. PMID:25809643

  2. Endlessly single-mode photonic crystal fiber.

    PubMed

    Birks, T A; Knight, J C; Russell, P S

    1997-07-01

    We made an all-silica optical fiber by embedding a central core in a two-dimensional photonic crystal with a micrometer-spaced hexagonal array of air holes. An effective-index model confirms that such a fiber can be single mode for any wavelength. Its useful single-mode range within the transparency window of silica, although wide, is ultimately bounded by a bend-loss edge at short wavelengths as well as at long wavelengths. PMID:18185719

  3. 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.

  4. Fracture in single crystal NiTi

    Microsoft Academic Search

    A. Creuziger; L. J. Bartol; K. Gall; W. C. Crone

    2008-01-01

    This paper presents an investigation of the pseudoelastic transformation of two crystallographic orientations of a single crystal NiTi shape memory alloy (SMA). Both uniaxial tension and notched tension samples are considered with the tensile axes along the [100] and [111] directions. The phase transformation is observed using optical techniques in situ. For the uniaxial tension samples, martensite plates and Lüders-band

  5. MAGNETIC PROPERTIES OF DYSPROSIUM SINGLE CRYSTALS

    Microsoft Academic Search

    D. R. Behrendt; S. Legvold; F. H. Speddin

    1958-01-01

    Single crystals of metallic dysprosium have been grown by the Bridgman ; method and their magnetic properties have been determined in different ; crystallographic directions of the hexagonal close-packed structure. Below the ; Neel point of 178.5 deg K the individual magnetic moments are aligned ; perpendicular to the c\\/sub o\\/ axis. The moments are aligned in an ; antiferromagnetic

  6. Single-polarization single-mode photonic crystal fibers

    Microsoft Academic Search

    Kunimasa Saitoh; Masanori Koshiba

    2003-01-01

    A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 ?m, where only the slow-axis mode exists and the confinement loss

  7. 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.

  8. Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2

    E-print Network

    Paris-Sud XI, Université de

    2105 Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2 B. Moine, B les propriétés de fluorescence et de photoconductivité de Yb2+ dans CaF2, SrF2 et BaF2. On présente In this paper, we analyze the fluorescence and the photoconductivity properties of Yb2+ in CaF2, SrF2 and BaF2

  9. Neutron Scattering Study of Single Crystal PZT

    NASA Astrophysics Data System (ADS)

    Phelan, Daniel; Gehring, Peter; Ye, Zuo-Guang; Long, Xifa

    2010-03-01

    Single crystal specimens of the technologically important ferroelectric material Pb(Zr1-xTix)O3, or PZT, have only recently been grown for the first time at Simon Fraser University. We have characterized the transition temperatures, thermal expansion, and crystal structure of a PZT single crystal between 10 K and 670 K using neutron scattering methods. This crystal, which has a composition (x˜0.46) that lies close to the morphotropic phase boundary (MPB), exhibits a surprisingly large thermal expansion (˜ 10-3 1/K) that changes sign near 545 K, and a rhombohedral crystal structure at 30 K. In addition we observe an enormous relief of extinction beginning around 650 K, which was observed through the temperature dependence of the (200) Bragg peak. Neutron inelastic measurements are planned as are measurements under an applied electric field. This work was supported by the U. S. Office of Naval Research (Grant No. N00014-1-06-0166). All neutron measurements were performed at the NIST Center for Neutron Research.

  10. Morphologic defects in Cr3+:LiCaAlF6 crystals grown by the Czochralski method

    NASA Astrophysics Data System (ADS)

    Klimm, D.; Seiranian, K.; Reiche, Peter; Polity, A.; Krause-Rehberg, R.

    1997-07-01

    The paper reports on the growth of Cr3+:LiCaAlF6 single crystals by the Czochralski method from a stoichiometric melt of LiF, CaF2, and AlF3. (Cr3+ doping was obtained by the replacement of about 3 Mol-% AlF3 by the corresponding quantity CrF3.) Only the peripheric region and the neck of the crystals have high optical quality, whereas scattering 'needles' of typically 5 multiplied by 5 multiplied by 35 micrometers cubed can be observed in the top region and very small particles very much less than 1 micrometer ('dust') can be observed in the bottom part of the crystals. By EDX element analysis performed after ion beam thinning of the samples the needles were determined to have an excess Ca content in comparison to the LiCaAlF6 matrix. The binary compound LiAlF4 has the highest vapor pressure in the ternary system LiF - CaF2 - AlF3. It can be concluded, that LiAlF4 evaporates continuously during crystal growth, leaving in the melt CaF2 in excess. The incongruently melting compound Ca2AlF7 is considered to be the most probable candidate for the observed scattering centers.

  11. Optical studies of anthracene single crystals

    NASA Astrophysics Data System (ADS)

    Jiang, Yuhong; Delong, Matthew; Vardeny, Z. Valy

    2001-03-01

    Recently the polyacene crystals such as pentacene, tetracene and anthracene have attracted great interest both in research and applications. These ultra-pure molecular crystals are very promising materials for FETs, organic photovoltaic diodes, LEDs and lasing. High purity anthracene crystal have been grown by physical vapor transport. High photo luminecense (PL) quantum efficiency(over 20%) was observed in these pure anthracene single crystals. The PL excitation spectrum closely follows the absorption spectrum consistent with Kasha¡¦s rule. Photo induced absorption (PA) spectroscopy showed a very small signal for the pure anthracene single crystals, indicating high purity and very few defects. By intentionally introducing defects, the PA increased substantially. Two PA bands at around 1.1eV & 1.5eV and a strong photo bleaching(PB) band due to defects were observed. Also I2 doped crystal was achieved by entraining I2 vapor in the Ar transport gas. Where doping induced IRAV absorption bands appeared in the infrared range. Compared with the difficulty of doping pure anthracene in either iodine vapor or iodine hexanes solution, doping the crystals during the growth process is an efficient way of obtaining charge carriers in the crystals.A series of substituted poly(p-phenylene-ethynylene) [PPEs] were synthesized where the substituents dibutyl(a), dioctyl(b), ditetradecyl(c), di-2-ethylhexyl(d), and di-2-cyclohexylethyl(e) were placed on the 2,5 positions of the phenyl rings. Side groups (a), (b), and (c) are linear chains with increasing length, whereas (d) is branched side chain and (e) is a bulky side chain. The photoinduced absorption (PA) spectroscopy has been applied to investigate the properties of the photoexcitations in these polymer films. The PA spectra of PPE(a) and PPE(b) show a low energy band at ca 850cm-1 and 1000cm-1, respectively. We assigned this PA as due to delocalized polaron excitations, indicating that these PPE polymers self-assembled into two-dimensional lamellae structure, similar to those that have been observed in thin films of regio-regular poly-3-hexythiophene.The low energy PA bands of PPE(c),PPE(d) and PPE(e) are at higher energies, suggesting a decrease in the polaron delocalization as the size of the side group increases. In the visible spectral range the PA spectra of PPE(a) and PPE(b) are also quite similar, showing bands at ca 2.0eV and 2.5eV, respectively.Optical studies of anthracene single crystals

  12. SSME single-crystal turbine blade dynamics

    NASA Technical Reports Server (NTRS)

    Moss, Larry A.

    1988-01-01

    A study was performrd to determine the dynamic characteristics of the Space Shuttle Main Engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified base. Crystal axis orientation optimization indicated that the third mode interference will exist in any SC orientation.

  13. The Creep of Single Crystals of Aluminum

    NASA Technical Reports Server (NTRS)

    Johnson, R D; Shober, F R; Schwope, A D

    1953-01-01

    The creep of single crystals of high-purity aluminum was investigated in the range of temperatures from room temperature to 400 F and at resolved-shear-stress levels of 200, 300, and 400 psi. The tests were designed in an attempt to produce data regarding the relation between the rate of strain and the mechanism of deformation. The creep data are analyzed in terms of shear strain rate and the results are discussed with regard to existing creep theories. Stress-strain curves were determined for the crystals in tinsel and constant-load-rate tests in the same temperature range to supplement the study of plastic deformation by creep with information regarding the part played by crystal orientation, differences in strain markings, and other variables in plastic deformation.

  14. Investigation of ion induced damage in KBr, YAG:Ce, CaF2:Eu and CsI:Tl irradiated by various-energy protons

    NASA Astrophysics Data System (ADS)

    Lin, L. Y.; Leitner, D.; Benatti, C.; Perdikakis, G.; Krause, S. W.; Rencsok, R.; Nash, S.; Wittmer, W.

    2015-03-01

    New experimental results on the scintillation processes for KBr, YAG:Ce, CaF2:Eu and CsI:Tl crystals under H2+ irradiation for the energy range of 600-2150 keV/u are systematically reported. The scintillation light yield was measured as a function of accumulated particle fluence at the rare isotope ReAccelerator (ReA) facility of the National Superconducting Cyclotron Laboratory (NSCL). The data indicates that YAG:Ce and CsI:Tl can maintain stable luminescence under continuous ion bombardment for at least a total fluence of 1.8×1012 ions/mm2 in the energy range used for this experiment. On the other hand, the luminescence of CaF2:Eu shows a rapid initial decay but then maintains a nearly constant luminescence yield. The extraordinary scintillation response of KBr is initially enhanced under ion bombardment, approaches a maximum, and then eventually decays. The scintillation efficiency of the CsI:Tl scintillator is superior to the other materials. The stability of the measured beam profile width deducted from the different scintillator materials in static beam conditions was also investigated as a function of irradiation time. We observed that the low-energy H2+ bombardment (25 keV/u) on the YAG:Ce scintillator can lead to the significant degradation of the scintillation yields. Different scintillation degradation responses for the low- and high-energy bombardments can be attributed to the transmission loss of the emitted light inside the crystal caused by displacement damages.

  15. X-ray excited optical luminescence of CaF2: A candidate for UV water treatment

    NASA Astrophysics Data System (ADS)

    Chen, W.; Ma, L.; Schaeffer, R.; Hoffmeyer, R.; Sham, T.; Belev, G.; Kasap, S.; Sammynaiken, R.

    2015-06-01

    Secondary optical processes are becoming more and more important in health and environmental applications. Ultraviolet produced from secondary emission or scintillation can damage DNA by direct photoexcitation or by the creation of reactive oxygen species. X-ray Excited Optical Luminescence (XEOL) and Time Resolved XEOL (TRXEOL) results for the fast emitter, CaF2:ZnO, that have been treated by heating in air and in vacuum, show that the scintillation from the Self Trapped Exciton (STE) emission of CaF2 at 282 nm is dominated by a slow process (>100 ns). A faster but weaker 10 ns component is also present. The ZnO and CaF2 show independent emission. The ZnO bandgap emission at 390 nm has dominant lifetimes of less than 1 ns.

  16. Accelerated Fabrication and Upconversion Luminescence of Yb3+/Er3+-Codoped CaF2 Nanocrystal by Microwave Heating

    NASA Astrophysics Data System (ADS)

    Li, Yuanyao; Liu, Tiegen; Du, Yang

    2012-08-01

    Because of the drastic reduction in processing time and energy cost, the microwave radiation applied as an alternative method to synthesize solids has been recently investigated. Yb3+/Er3+-codoped CaF2 (CaF2:Yb3+/Er3+) nanocrystals are fabricated using this approach, and the phenomenon of microwave-enhanced mass transport is observed in this process. The upconversion mechanisms and properties of such nanocrystal have also been studied. Charge compensation and microwave ponderomotive effect are considered as the cause of the specific up-conversion spectrum. This synthesis method and the as-prepared CaF2:Yb3+/Er3+ nanocrystal may be potentially useful for advanced phosphor, imaging, anti-counterfeiting labeling, etc.

  17. Q-1 of forsterite single crystals

    Microsoft Academic Search

    Y. Gueguen; M. Darot; P. Mazot; J. Woirgard

    1989-01-01

    Internal friction (Q-1) experiments have been performed on synthetic forsterite single crystals in order to investigate the role of temperature, frequency and dislocation density on the Q-1 factor. Data have been obtained for both deformed and undeformed specimens over a frequency range from 10 to 10-4 Hz at 15, 1000, 1200 and 1400°C. Measurements were done using a torsional pendulum

  18. Dependences of the density of M 1- x R x F2 + x and R 1- y M y F3- y single crystals ( M = Ca, Sr, Ba, Cd, Pb; R means rare earth elements) on composition

    NASA Astrophysics Data System (ADS)

    Sorokin, N. I.; Krivandina, E. A.; Zhmurova, Z. I.

    2013-11-01

    The density of single crystals of nonstoichiometric phases Ba1 - x La x F2 + x (0 ? x ? 0.5) and Sr0.8La0.2 - x Lu x F2.2 (0 ? x ? 0.2) with the fluorite (CaF2) structure type and R 1 - y Sr y F3 - y ( R = Pr, Nd; 0 ? y ? 0.15) with the tysonite (LaF3) structure type has been measured. Single crystals were grown from a melt by the Bridgman method. The measured concentration dependences of single crystal density are linear. The interstitial and vacancy models of defect formation in the fluorite and tysonite phases, respectively, are confirmed. To implement the composition control of single crystals of superionic conductors M 1 - x R x F2 + x and R 1 - y M y F3 - y in practice, calibration graphs of X-ray density in the MF2- RF3 systems ( M = Ca, Sr, Ba, Cd, Pb; R = La-Lu, Y) are plotted.

  19. Single crystal formation in micro/nano-confined domains by melt-mediated crystallization without seeds

    NASA Astrophysics Data System (ADS)

    Pan, Heng; Shou, Wan

    2015-06-01

    Using molecular dynamics (MD) simulation, we study the characteristics of unseeded crystallization within nano/microscale confining domains. It is demonstrated that unseeded crystallization can yield single crystal domains facilitated by the confinement effects. The stochastic nature of this process and the mechanisms leading to single crystal formation are revealed. A phenomenological model has been developed and tailored by MD simulations, which was applied to quantitatively evaluate the effects of domain size and processing laser pulse width on single crystal formation.

  20. Fabrication, properties and thermo-luminescent dosimetric application of CaF2:Mn transparent ceramic

    NASA Astrophysics Data System (ADS)

    Singh, S. G.; Sen, Shashwati; Patra, G. D.; Bhattacharya, S.; Singh, A. K.; Shinde, Seema; Gadkari, S. C.

    2012-09-01

    An optically transparent ceramic of CaF2:Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn2+, respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.

  1. 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.

  2. Inelastic deformation in shocked sapphire single crystals

    NASA Astrophysics Data System (ADS)

    Fuller, H. D.; Winey, J. M.; Gupta, Y. M.

    2013-06-01

    To gain insight into orientation-dependent inelastic deformation of shocked sapphire (?-Al2O3) single crystals, resolved shear stresses, applicable for various dislocation slip and twinning systems, were determined for shock compression along different crystal orientations. Results from our anisotropic wave propagation analysis provide an explanation for why the measured elastic limit of shocked r-cut sapphire is lower, compared to c-cut and a-cut sapphire: Shock wave compression of r-cut sapphire favors activation of basal slip and basal twinning. In contrast, shock wave compression of c-cut and a-cut sapphire favors rhombohedral twinning and prismatic slip, respectively. Also, basal slip and/or basal twinning may be important for understanding why r-cut sapphire shocked beyond the elastic limit loses optical transparency gradually, when compared to c-cut and a-cut sapphire.

  3. Morphology and texture evolution of nanostructured CaF2 films on amorphous substrates under oblique incidence flux.

    PubMed

    Gaire, C; Snow, P; Chan, T-L; Yuan, W; Riley, M; Liu, Y; Zhang, S B; Wang, G-C; Lu, T-M

    2010-11-01

    The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200?°C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100?°C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100?°C to [111] at 400?°C. In films deposited with an oblique vapour incidence at 100?°C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet. PMID:20921590

  4. Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n

    E-print Network

    Wang, Gwo-Ching

    Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n , P.C. Clemmer of semiconductor on an amorphous substrate such as glass results in either polycrystalline or fiber textured film report a heteroepitaxial growth of biaxially textured Ge film on glass substrate with biaxially textured

  5. FACTORS AFFECTING THE USE OF CAF2:MN THERMOLUMINESCENT DOSIMETERS FOR LOW-LEVEL ENVIRONMENTAL RADIATION MONITORING

    EPA Science Inventory

    An investigation was made of factors affecting the use of commercially-produced CaF2:Mn thermoluminescent dosimeters for low level environmental radiation monitoring. Calibration factors and self-dosing rates were quantified for 150 thermoluminescent dosimeters. Laboratory studie...

  6. 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.

  7. Triplet exciton dynamics in rubrene single crystals

    NASA Astrophysics Data System (ADS)

    Ryasnyanskiy, Aleksandr; Biaggio, Ivan

    2011-11-01

    The decay of the photoluminescence excited in rubrene single crystals by picosecond pulses is measured over 7 orders of magnitude and more than 4 time decades. We identify the typical decay dynamics due to triplet-triplet interaction. We show that singlet exciton fission and triplet fusion quantum yields in rubrene are both very large, and we directly determine a triplet exciton lifetime of 100±20 ?s, which explains the delayed buildup of a large photocurrent that has been reported earlier for low excitation densities.

  8. 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.

  9. 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.

  10. Single crystal diamond nanobeam waveguide optomechanics

    E-print Network

    Behzad Khanaliloo; Harishankar Jayakumar; Aaron C. Hryciw; David P. Lake; Hamidreza Kaviani; Paul E. Barclay

    2015-04-28

    Optomechanical devices sensitively transduce and actuate motion of nanomechanical structures using light. Single--crystal diamond promises to improve the performance of optomechanical devices, while also providing opportunities to interface nanomechanics with diamond color center spins and related quantum technologies. Here we demonstrate dissipative waveguide--optomechanical coupling exceeding 35 GHz/nm to diamond nanobeams supporting both optical waveguide modes and mechanical resonances, and use this optomechanical coupling to measure nanobeam displacement with a sensitivity of $9.5$ fm/$\\sqrt{\\text{Hz}}$ and optical bandwidth $>150$nm. The nanobeams are fabricated from bulk optical grade single--crystal diamond using a scalable undercut etching process, and support mechanical resonances with quality factor $2.5 \\times 10^5$ at room temperature, and $7.2 \\times 10^5$ in cryogenic conditions (5K). Mechanical self--oscillations, resulting from interplay between photothermal and optomechanical effects, are observed with amplitude exceeding 200 nm for sub-$\\mu$W absorbed optical power, demonstrating the potential for optomechanical excitation and manipulation of diamond nanomechanical structures.

  11. Growth and properties of PMN-PT single crystals

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Tang, F.; Wang, J. T.; Chen, T.-P.

    2001-11-01

    Piezoelectric single crystals of Pb(Mg 1/3Nb 2/3)O 3-PbTiO 3 (PMN-PT) show superior properties to piezoelectric ceramics and piezoelectric films in device applications. However, the applications of PMN-PT single crystals are limited by the lack of a simple and reproducible fabrication technique. By studying the effect of fabrication condition on the growth of PMN-PT single crystals in the flux method, we successfully obtained PMN-PT single crystals. The size of the obtained crystals varied from 1 to 4 mm, mostly showing regular cubic shape. X-ray diffraction technique identified the crystal phase was PMN-PT. Electron diffraction spectroscope analysis indicated that the composition of the single crystals was closed to the designed solid solution. The (0 0 1) single crystals showed a dielectric constant peak of 15,200 at 42°C. The crystals had a remnant polarization 16 ?c/cm 2, a spontaneous polarization 22.1 ?c/cm 2, and a coercive field 2.55 kV/cm. Our measurement indicated the temperature dependence and frequency dependence of the dielectric constant and dielectric loss of PMN-PT single crystals. The results will be a great help for the applications of PMN-PT single crystals.

  12. 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.

  13. 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 field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates. ?? 1993.

  14. Unidirectional crystallization of large diameter benzophenone single crystal from solution at ambient temperature

    Microsoft Academic Search

    K. Sankaranarayanan; P. Ramasamy

    2006-01-01

    Oriented organic crystals along prerequisite direction are very important in terms of reducing loss of material and cost during nonlinear optical device fabrication. In this paper, “uniaxially solution-crystallization method” [K. Sankaranarayanan, J. Crystal Growth 284 (2005) 203] was elaborated and usefulness of this method has been demonstrated by growing ?110? oriented, 60mm diameter, benzophenone single crystal ingot out of xylene

  15. Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang,

    E-print Network

    Kim, Bongsoo

    Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang, Wonjun Choi, Ilsun Yoon rainbow antenna radiation in the Fresnel region. Detailed antenna radiation properties, such as radiating

  16. Single crystal fiber for laser sources

    NASA Astrophysics Data System (ADS)

    Délen, Xavier; Aubourg, Adrien; Deyra, Loïc.; Lesparre, Fabien; Martial, Igor; Didierjean, Julien; Balembois, François; Georges, Patrick

    2015-02-01

    Single crystal fiber (SCF) is a hybrid laser architecture between conventional bulk laser crystals and active optical fibers allowing higher average powers than with conventional crystals and higher energy than with fibers in pulsed regime. The pump beam delivered by a fiber-coupled laser diode is confined by the guiding capacity of the SCF whereas the signal beam is in free propagation. In this paper, we study the pump guiding in the SCF and give an overview of the results obtained using SCF gain modules in laser oscillators and amplifiers. We report about up to 500 ?J nanosecond pulses at the output of a passively Q-switched Er:YAG SCF oscillator at 1617 nm. High power experiments with Yb:YAG allowed to demonstrate up to 250 W out of a multimode oscillator. High power 946 nm Nd:YAG SCF Q-switched oscillators followed by second and fourth harmonic generation in the blue and the UV is also presented with an average power up to 3.4 W at 473 nm and 600 mW at 236.5 nm. At 1064 nm, we obtain up to 3 mJ with a nearly fundamental mode beam in sub-nanosecond regime with a micro-chip laser amplified in a Nd:YAG SCF. Yb:YAG SCF amplifiers are used to amplify fiber based sources limited by non-linearities such as Stimulated Brillouin Scattering with a narrow linewidth laser and Self Phase Modulation with a femtosecond source. Using chirped pulse amplification, 380 fs pulses are obtained with an energy of 1 mJ and an excellent beam quality (M2<1.1).

  17. Hydroxyl concentration in orthoclase single crystals

    NASA Astrophysics Data System (ADS)

    Wang, Z.-C.; Dresen, G.; Andrut, M.

    Hydroxyl concentrations in natural orthoclase single crystals have been studied by combining high pressure and high temperature annealing experiments with Fourier Transform Infrared Spectroscopy (FTIR). Crystals (rectangular wafers) with large (100), (010) and (001) faces were hydrothemally annealed at T=800°-1200 °C, P=50-300MPa and constant oxygen fugacities set by Cu/CuO, Ni/NiO and Fe/FeO buffers for t=1-168 hours in either a cold-seal hydrothermal apparatus or a gas-medium high-temperature and high-pressure apparatus. A broad absorbance band centered near 3450 cm-1 and sharp peaks at 3431 cm-1, 3500-3550 cm-1 and 3650 cm-1 were observed. Hydroxyl concentrations from 50-70 H/106 Si (T=800 °C and P=50MPa) to 1500 H/106 Si (T=1200 °C and P=300MPa) were obtained by integrating the absorption bands in the range from 3700 cm-1 to 3000 cm-1. The FTIR-spectra suggest the presence of molecular water combined with different types of hydrogen-associated point defects.

  18. Fracture in single crystal NiTi

    NASA Astrophysics Data System (ADS)

    Creuziger, A.; Bartol, L. J.; Gall, K.; Crone, W. C.

    This paper presents an investigation of the pseudoelastic transformation of two crystallographic orientations of a single crystal NiTi shape memory alloy (SMA). Both uniaxial tension and notched tension samples are considered with the tensile axes along the [1 0 0] and [1 1 1] directions. The phase transformation is observed using optical techniques in situ. For the uniaxial tension samples, martensite plates and Lüders-band structures are observed. For the notched samples, transformation structures in the [1 0 0] sample appeared predominantly on the sides of the notch and crack tip with stable crack propagation. In the [1 1 1] notched samples transformation occurs directly ahead of the notch and unstable crack propagation is observed. An available work criterion is used to predict the location of the transformation, with good agreement to the experimental observations. The different fracture behavior of the two notched sample orientations is explained utilizing the available work calculations.

  19. Hydrogen Annealing Of Single-Crystal Superalloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Schaeffer, John C.; Murphy, Wendy

    1995-01-01

    Annealing at temperature equal to or greater than 2,200 degrees F in atmosphere of hydrogen found to increase ability of single-crystal superalloys to resist oxidation when subsequently exposed to oxidizing atmospheres at temperatures almost as high. Supperalloys in question are principal constituents of hot-stage airfoils (blades) in aircraft and ground-based turbine engines; also used in other high-temperature applications like chemical-processing plants, coal-gasification plants, petrochemical refineries, and boilers. Hydrogen anneal provides resistance to oxidation without decreasing fatigue strength and without need for coating or reactive sulfur-gettering constituents. In comparison with coating, hydrogen annealing costs less. Benefits extend to stainless steels, nickel/chromium, and nickel-base alloys, subject to same scale-adhesion and oxidation-resistance considerations, except that scale is chromia instead of alumina.

  20. 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.

  1. 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.

  2. Diffusion of Ti in ?-Zr single crystals

    NASA Astrophysics Data System (ADS)

    Hood, G. M.; Zou, H.; Schultz, R. J.; Bromley, E. H.; Jackman, J. A.

    1994-12-01

    Ti diffusion coefficients ( D) have been measured in nominally pure ?-Zr single crystals (773-1124 K) in directions both parallel ( Dpa) and perpendicular ( Dpe, few data) to the c-axis: tracer techniques and secondary ion mass spectrometry were used to determine the diffusion profiles. The results show a temperature dependence which may be interpreted in terms of two regions of diffusion behaviour. Above 1035 K, region I, diffusion conforms to the expectations of intrinsic behaviour with normal Arrhenius law constants: Dpa = 1.7 × 10 -3exp(-2.93 ± 0.08 eV/kT) m 2/s. Below 1035 K, region II, D' s appear to be enhanced with respect to an extrapolation of region I behaviour.

  3. White light generation in Dy(3+)-doped oxyfluoride glass and transparent glass-ceramics containing CaF2 nanocrystals.

    PubMed

    Babu, P; Jang, Kyoung Hyuk; Rao, Ch Srinivasa; Shi, Liang; Jayasankar, C K; Lavín, Víctor; Seo, Hyo Jin

    2011-01-31

    The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram. PMID:21368998

  4. Structural plasticity of calmodulin on the surface of CaF2 nanoparticles preserves its biological function

    NASA Astrophysics Data System (ADS)

    Astegno, Alessandra; Maresi, Elena; Marino, Valerio; Dominici, Paola; Pedroni, Marco; Piccinelli, Fabio; Dell'Orco, Daniele

    2014-11-01

    Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca2+-binding ability in the C-terminal lobe suggest that the EF-hand Ca2+-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface.Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca2+-binding ability in the C-terminal lobe suggest that the EF-hand Ca2+-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface. Electronic supplementary information (ESI) available: Supplementary methods and figures. See DOI: 10.1039/c4nr04368e

  5. Comprehensive structural and optical characterization of MBE grown MoSe2 on graphite, CaF2 and graphene

    NASA Astrophysics Data System (ADS)

    Vishwanath, Suresh; Liu, Xinyu; Rouvimov, Sergei; Mende, Patrick C.; Azcatl, Angelica; McDonnell, Stephen; Wallace, Robert M.; Feenstra, Randall M.; Furdyna, Jacek K.; Jena, Debdeep; Xing, Huili Grace

    2015-06-01

    We report the structural and optical properties of a molecular beam epitaxy (MBE) grown 2-dimensional (2D) material molybdenum diselenide (MoSe2) on graphite, CaF2 and epitaxial graphene. Extensive characterizations reveal that 2H–MoSe2 grows by van-der-Waals epitaxy on all three substrates with a preferred crystallographic orientation and a Mo:Se ratio of 1:2. Photoluminescence at room temperature (?1.56 eV) is observed in monolayer MoSe2 on both CaF2 and epitaxial graphene. The band edge absorption is very sharp, <60 meV over three decades. Overcoming the observed small grains by promoting mobility of Mo adatoms would make MBE a powerful technique to achieve high quality 2D materials and heterostructures.

  6. Monte Carlo simulation of gamma-ray response of BaF2 and CaF2

    NASA Astrophysics Data System (ADS)

    Gao, F.; Xie, Y. L.; Wang, Z. G.; Kerisit, S.; Wu, D. X.; Campbell, L. W.; Van Ginhoven, R. M.; Prange, M.

    2013-11-01

    We have employed a Monte Carlo (MC) method to study intrinsic properties of two alkaline-earth halides, namely, BaF2 and CaF2, relevant to their use as radiation detector materials. The MC method follows the fate of individual electron-hole (e-h) pairs and thus allows for a detailed description of the microscopic structure of ionization tracks created by incident ?-ray radiation. The properties of interest include the mean energy required to create an e-h pair, W, Fano factor, F, the maximum theoretical light yield, and the spatial distribution of e-h pairs resulting from ?-ray excitation. Although W and F vary with incident photon energy at low energies, they tend to constant values at energies higher than 1 keV. W is determined to be 18.9 and 19.8 eV for BaF2 and CaF2, respectively, in agreement with published data. The e-h pair spatial distributions exhibit a linear distribution along the fast electron tracks with high e-h pair densities at the end of the tracks. Most e-h pairs are created by interband transition and plasmon excitation in both scintillators, but the e-h pairs along fast electron tracks in BaF2 are slightly clustered, forming nanoscale domains and resulting in the higher e-h pair densities than in CaF2. Combining the maximum theoretical light yields calculated for BaF2 and CaF2 with those obtained for CsI and NaI shows that the theoretical light yield decreases linearly with increasing band gap energy.

  7. Monte Carlo Simulation of Gamma-Ray Response of BaF2 and CaF2

    SciTech Connect

    Gao, Fei; Xie, YuLong; Wang, Zhiguo; Kerisit, Sebastien N.; Wu, Dangxin; Campbell, Luke W.; Van Ginhoven, Renee M.; Prange, Micah P.

    2013-12-01

    We have employed a Monte Carlo (MC) method to study intrinsic properties of two alkaline-earth halides, namely BaF2 and CaF2, relevant to their use as radiation detector materials. The MC method follows the fate of individual electron-hole (e-h) pairs and thus allows for a detailed description of the microscopic structure of ionization tracks created by incident ?-ray radiation. The properties of interest include the mean energy required to create an e-h pair, W, Fano factor, F, the maximum theoretical light yield, and the spatial distribution of e-h pairs resulting from ?-ray excitation. Although W and F vary with incident photon energy at low energies, they tend to constant values at energies higher than 1 keV. W is determined to be 18.9 and 19.8 eV for BaF2 and CaF2, respectively, in agreement with published data. The e-h pair spatial distributions exhibit a linear distribution along the fast electron tracks with high e-h pair densities at the end of the tracks. Most e-h pairs are created by interband transition and plasmon excitation in both scintillators, but the e-h pairs along fast electron tracks in BaF2 are slightly clustered, forming nanoscale domains and resulting in the higher e-h pair densities than in CaF2. Combining the maximum theoretical light yields calculated for BaF2 and CaF2 with those obtained for CsI and NaI shows that the theoretical light yield decreases linearly with increasing band gap energy.

  8. Polymer single crystal membranes from curved liquid/liquid interface

    NASA Astrophysics Data System (ADS)

    Wang, Wenda; Li, Christopher; Soft Matter Research Group Team

    2014-03-01

    The weak mechanical properties of the current available vesicles such as liposomes, polymersomes, colloidosomes limit their applications for targeting delivery of drugs/genes. Recently, we developed an emulsion-crystallization method to grow polymer curved single crystals. Using polyethylene and poly(l-lactic acid)as the model systems, enclosed or partially open polymer single crystals have been obtained. Electron diffraction and XRD results confirmed their crystalline structure. The single crystal hollow sphere is structurally close to polymersomes, but with thinner wall and higher modulus.

  9. Materials for high-energy laser windows: oxyfluoride glass vs. fusion-cast CaF2

    NASA Astrophysics Data System (ADS)

    Klein, Claude A.

    2005-05-01

    The process of selecting suitable materials for high-energy laser windows involves considerations realting to (a) the flexural strength, (b) the thermal stresses, and (c) the optical distortion. Optical distortion ocnsiderations strongly favor low-absorbtion materials ythat exhibit a negitive thermo-optic coefficient (dn/dT) in conjunction with minimal stress-birefringence (qd\\overline -q? ~=0). For this reason, calcium floride has been the primary candidate for many years, but the efforts to strengthen this material have not been successful. Recently, a new glass compostion-oxyfloride glass (OFG)-has been promoted as an ideal solution in the sense that it will allow fabricating large "athermal" windows for operation at the chemical oxygen-iodine laser wavelength. It is, therefore, of interest to properly assess the merits of OFG in comparison to CaF2, which we do here on the basis of available (Dec '04) property data for fusion-cast CaF2 and OFG. Oxyfloride glass was found to be deficient in regard to thermal diffusivity, which may lead to excessive coating-induced compressive stresses, and stress- birefringence, which rules out creating a distortion-free window. It is suggested that future efforts should be directed at strengthening CaF2 in view of this material's exceptionally low absorbtion and almost no stress-birefringence

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

    DOEpatents

    Todt, Volker (Lemont, IL); Miller, Dean J. (Darien, IL); Shi, Donglu (Oak Park, OH); Sengupta, Suvankar (Columbus, OH)

    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.

  11. Deformation Induced Microtwins and Stacking Faults in Aluminum Single Crystal

    Microsoft Academic Search

    W. Z. Han; G. M. Cheng; S. D. Wu; Z. F. Zhang

    2008-01-01

    Microtwins and stacking faults in plastically deformed aluminum single crystal were successfully observed by high-resolution transmission electron microscope. The occurrence of these microtwins and stacking faults is directly related to the specially designed crystallographic orientation, because they were not observed in pure aluminum single crystal or polycrystal before. Based on the new finding above, we propose a universal dislocation-based model

  12. Mercuric iodide single crystals for nuclear radiation detectors

    Microsoft Academic Search

    Weitang Li; Zhenghui Li; Shifu Zhu; Shujun Yin; Beijun Zhao; Guanxiong Chen; Shi Yin; Hong Yuan; Huapeng Xu

    1996-01-01

    Large size HgI2 single crystals were grown using the modified temperature oscillation method 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

  13. Mercuric iodide single crystal for nuclear radiation detectors

    Microsoft Academic Search

    Weitang Li; Zhenghui Li; Shifu Zhu; Shujun Yin; Beijun Zhao; Guanxiong Chen; Shi Yin; Hong Yuan; Huapeng Xu

    1995-01-01

    Large size HgI2 single crystals are grown using the modified temperature oscillation method with low dislocation densities in a relatively stable temperature environment. Radiation detectors are fabricated from the single crystals which show good energy resolution with small polarization

  14. Crack tip deformation fields in ductile single crystals

    Microsoft Academic Search

    Jeffrey W. Kysar; Clyde L. Briant

    2002-01-01

    Crack tip deformation fields in ductile single crystal media are studied experimentally. The crack, located between two single crystals of aluminum joined by a thin ductile interlayer of tin, is introduced via selective chemical etching and can be considered “sharp”; the material surrounding the tip is fully annealed. After a Mode I loading is applied, the specimen is sectioned and

  15. Mercuric iodide single crystals for nuclear radiation detectors

    SciTech Connect

    Li, W.; Li, Z.; Zhu, S.; Yin, S.; Zhao, B.; Chen, G. [Sichuan Univ., Chengdu (China). Material Science Dept.; Yin, S. [Univ. of Southern California, Los Angeles, CA (United States). Physics Dept.; Yuan, H.; Xu, H. [Deyang Mercuric Iodide Single Crystal Plant, Sichuan (China)

    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. August 15, 2004 / Vol. 29, No. 16 / OPTICS LETTERS 1879 High-power tunable diode-pumped Yb3+:CaF2 laser

    E-print Network

    Paris-Sud XI, Université de

    will permit exploitation of these favorable characteristics, hosts with high thermal conductivities structure that leads to broad absorption and emission bands, comparable to those of glasses,5 which CaF2 potentially suitable as a ceramic l

  18. Soft X-ray emission spectroscopy study of CaF 2(film)/Si(111): non-destructive buried interface analysis

    NASA Astrophysics Data System (ADS)

    Iwami, M.; Kusaka, M.; Hirai, M.; Tagami, R.; Nakamura, H.; Watabe, H.

    1997-06-01

    A soft X-ray emission spectroscopy (SXES) study under an energetic electron irradiation is first applied to a non-destructive buried interface analysis of a CaF 2(film ˜ 40 nm)/Si(111) contact system, where the energy of primary electrons, Ep, is ? 5 keV. The present work has explored the usefulness of the application of the SXES method to the interface study to give rise to the following findings: the CaF 2/Si(111) interface shows rather sharp transition from the top CaF 2 to the substrate Si, there certainly is a Ca-silicide layer at the CaF 2/Si(111) interface, the thickness of the silicide layer is estimated to be less than several nm, and the e-beam excited SXES non-destructive study is very powerful to analyze a specimen with rather thick top film (> 40 nm) and thin interface layer (< several nm).

  19. Fatigue behavior of a single crystal nickel-base superalloy

    SciTech Connect

    Zhang, J.H.; Xu, Y.B.; Wang, Z.G.; Hu, Z.Q. [Academy of Sciences, Shenyang (China). State Key Lab. for Fatigue and Fracture of Materials] [Academy of Sciences, Shenyang (China). State Key Lab. for Fatigue and Fracture of Materials

    1995-06-15

    Many investigations indicate that high cycle fatigue cracks, in general, initiate at pores, inclusions, and grain boundaries in materials. The fatigue strength limit of a single crystal superalloy increases markedly compared to that of a conventional cast alloy, because the number of pores and inclusions in a single crystal superalloy are less than those of both conventionally cast and directionally solidified superalloys. Also, grain boundaries are eliminated in the single crystal superalloy. The fatigue fracture of a single crystal superalloy usually appears to be brittle. Therefore, it is necessary to study the micro-fracture mechanism. This paper presents an investigation of the fracture characteristics and micro-mechanism of fracture in a single crystal superalloy during high cycle fatigue.

  20. Crystal structure refinement from electron diffraction data

    NASA Astrophysics Data System (ADS)

    Dudka, A. P.; Avilov, A. S.; Lepeshov, G. G.

    2008-05-01

    A procedure of crystal structure refinement from electron diffraction data is described. The electron diffraction data on polycrystalline films are processed taking into account possible overlap of reflections and two-beam interaction. The diffraction from individual single crystals in an electron microscope equipped with a precession attachment is described using the Bloch-wave method, which takes into account multibeam scattering, and a special approach taking into consideration the specific features of the diffraction geometry in the precession technique. Investigations were performed on LiF, NaF, CaF2, and Si crystals. A method for reducing experimental data, which allows joint electron and X-ray diffraction study, is proposed.

  1. Characterization of thin epitaxial CaF2 layers on Si(111) using impurity luminescent probes, X-ray standing waves and X-ray diffractometry

    Microsoft Academic Search

    J. C. Alvarez; K. Hirano; A. Yu Kazimirov; M. V. Kovalchuk; A. Ya Kreines; N. S. Sokolov; N. L. Yakovlev

    1992-01-01

    The structure crystalline quality and elastic strain of CaF2 epitaxial layers on Si(111) substrates have been studied using an impurity photoluminescent probe, X-ray standing waves and X-ray rocking curves. Molecular beam epitaxy was used to grow 10 nm thick films. The CaF2\\/Si(111) interface was formed at 770 degrees C and the films were grown at temperatures of 100, 550, 660

  2. Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa

    Microsoft Academic Search

    S. M. Dorfman; F. Jiang; Z. Mao; A. Kubo; V. Prakapenka; T. S. Duffy

    2007-01-01

    AX2 compounds include a wide range of oxides and salts of broad interest in geoscience, materials science and chemistry, such as SiO2 and CaF2, and have in common a sequence of phase transitions dependent on ionic size ratio and electronic properties (Leger and Haines, 1997). Shock compression studies have shown that CaF2 transforms to a highly incompressible phase above 1

  3. Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar pressures

    E-print Network

    Duffy, Thomas S.

    Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar received 28 April 2010; published 27 May 2010 Phase transitions and equations of state of the alkaline at ambient conditions for the alkaline earth fluorides CaF2, SrF2, and BaF2. Fluorides are widely used

  4. Studies of the Mechanism of a Single-Crystal-to-Single-Crystal Reversible Dehydration of a Copper Carboxylate Framework

    E-print Network

    . Single crystals kept under vacuum at different temperatures (room temperature, 65 °C, and 105 °C) remain are reversible evidenced by the structural studies of the dehydrated single crystals after exposure to humid air. Magnetic measurements showed antiferromagnetic coupling between the Cu2+ ions. Homometallic ferrimagnetism

  5. 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.

  6. Generation of ultrashort 25-?J pulses at 200 nm by dual broadband frequency doubling with a thin KBe2BO3F2 crystal.

    PubMed

    Zhou, Chun; Kanai, Teruto; Wang, Xiaoyang; Zhu, Yong; Chen, Chuangtian; Watanabe, Shuntaro

    2012-06-18

    Ultrashort pulses with a 25-?J output energy were generated at 200 nm by dual broadband frequency doubling with a thin KBe(2)BO(3)F(2) (KBBF) crystal at 1 kHz as the fourth harmonic of a high power Ti:sapphire laser. The spectrum was broadened to a spectral width of 2.25 nm. The pulse duration of 56 fs was measured by single-shot autocorrelation with two-photon fluorescence from self-trapped excitons in a CaF(2) crystal. PMID:22714434

  7. Prospects for the synthesis of large single-crystal diamonds

    NASA Astrophysics Data System (ADS)

    Khmelnitskiy, R. A.

    2015-02-01

    The unique properties of diamond have stimulated the study of and search for its applications in many fields, including optics, optoelectronics, electronics, biology, and electrochemistry. Whereas chemical vapor deposition allows the growth of polycrystalline diamond plates more than 200 mm in diameter, most current diamond application technologies require large-size (25 mm and more) single-crystal diamond substrates or films suitable for the photolithography process. This is quite a challenge, because the largest diamond crystals currently available are 10 mm or less in size. This review examines three promising approaches to fabricating large-size diamond single crystals: growing large-size single crystals, the deposition of heteroepitaxial diamond films on single-crystal substrates, and the preparation of composite diamond substrates.

  8. 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.

  9. 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.

  10. Crystallization phase diagram, the growth of large single crystals of bovine ?-Lactoglobulin A

    NASA Astrophysics Data System (ADS)

    Yagi, D.; Ohnishi, Y.; Tanaka, I.; Niimura, N.

    2010-11-01

    A crystallization phase diagram defining the meta-stable region of bovine ?-lactoglobulin A (?-Lg) was firstly determined by a dialysis method. We have succeeded in growing a large single crystal of ?-Lg by selecting a crystal grown in this "meta-stable region" method described in the present paper. The quality of protein crystals was characterized quantitatively via rapid X-ray data collections, followed by the use of Wilson plots to analyze their resulting average B-factors.

  11. Last advances in Yb3+ doped CaF2 ceramics synthesis

    NASA Astrophysics Data System (ADS)

    Mortier, Michel; Lyberis, Andréas; Saganuma, Akiko; Stevenson, Adam; Vivien, Daniel; Gredin, Patrick; Patriarche, Gilles

    2011-02-01

    One at% Yb:CaF2 transparent ceramics for high power lasers are obtained by vacuum sintering and hot pressing nanoparticles synthesized through a soft chemistry route. The residual optical losses of these ceramics are as low as 0.09 cm-1 (corresponding to an in-line transmittance of 96.7%) at 1200 nm. Densification during sintering is limited by large voids, but pressure assisted densification after sintering results in high optical quality transparent ceramics. Absorption spectra are similar to Yb:CaF2 single crystal, and the fluorescence lifetime was measured to be 2 ms in the wavelength 1010 to 1050 nm range. The 1 at% Yb:CaF2 transparent ceramics successfully produced laser oscillation at 1031 nm when placed in an Omega-type laser cavity under 970 nm diode laser pumping.

  12. Single crystal Processing and magnetic properties of gadolinium nickel

    SciTech Connect

    Shreve, Andrew John [Ames Laboratory

    2012-11-02

    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 Gd{sub 2}O{sub 3} 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.

  13. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2.

    PubMed

    Tarantini, C; Kametani, F; Lee, S; Jiang, J; Weiss, J D; Jaroszynski, J; Hellstrom, E E; Eom, C B; Larbalestier, D C

    2014-01-01

    Ba(Fe(1-x)Co(x))(2)As(2) is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, J(c). Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, T(c), of the material. In this paper we demonstrate that strain induced by the substrate can further improve J(c) of both single and multilayer films by more than that expected simply due to the increase in T(c). The multilayer deposition of Ba(Fe(1-x)Co(x))(2)As(2) on CaF2 increases the pinning force density (F(p) = J(c) × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m(3) at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase. PMID:25467177

  14. Growth and characterization of organic material 4-dimethylaminobenzaldehyde single crystal.

    PubMed

    Jebin, R P; Suthan, T; Rajesh, N P; Vinitha, G; Madhusoodhanan, U

    2015-01-25

    The organic material 4-dimethylaminobenzaldehyde single crystals were grown by slow evaporation technique. The grown crystal was confirmed by the single crystal and powder X-ray diffraction analyses. The functional groups of the crystal have been identified from the Fourier Transform Infrared (FTIR) and FT-Raman studies. The optical property of the grown crystal was analyzed by UV-Vis-NIR and photoluminescence (PL) spectral measurements. The thermal behavior of the grown crystal was analyzed by thermogravimetric (TG) and differential thermal analyses (DTA). Dielectric measurements were carried out with different frequencies by using parallel plate capacitor method. The third order nonlinear optical properties of 4-dimethylaminobenzaldehyde was measured by the Z-scan technique using 532 nm diode pumped continuous wave (CW) Nd:YAG laser. PMID:25168233

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

    SciTech Connect

    Siva Sankari, R. [Department of Physics, Agni College of Technology, Thalambur, Chennai 603103 (India); Perumal, Rajesh Narayana, E-mail: r.shankarisai@gmail.com [Department of Physics, SSN College of Engineering, Kalavakkam, Chennai 603110 (India)

    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 of temperature.

  16. 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.

  17. 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 discussed in detail.

  18. 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 discussed in detail.

  19. Growth of large single crystals of the orthorhombic paracetamol

    NASA Astrophysics Data System (ADS)

    Mikhailenko, M. A.

    2004-05-01

    A new procedure for the growth of large (cm-range) single crystals of the metastable orthorhombic (s.g. Pcab) polymorph of paracetamol is described. The crystals were grown by very slow cooling of hot water solutions under the conditions, when the multiple nucleation was prevented. The samples were characterized by DSC and X-ray diffraction.

  20. The Bauschinger effect in cyclically deformed niobium single crystals

    Microsoft Academic Search

    M. Anglada; F. Guiu

    1988-01-01

    The Bauschinger effect has been studied in niobium single crystals cyclically deformed to saturation at small strain amplitudes and at different temperatures. The parameters used to characterize the Bauschinger effect have been measured from the saturation hysteresis loops. The fatigued work-hardened crystals have been modelled as a composite consisting of a hard deformable phase (the regions of high dislocation density)

  1. Synthesis and characterization of single-crystal indium nitride nanowires

    E-print Network

    Zhou, Chongwu

    Synthesis and characterization of single-crystal indium nitride nanowires Tao Tang, Song Han, Wu semiconducting III-V nitrides have long been viewed as promising materials for electronic and optoelectronic

  2. Deformation mechanisms in tungsten single crystals in ballistic impact experiments

    NASA Astrophysics Data System (ADS)

    Bruchey, W. J., Jr.; Herring, R. N.; Kingman, P. W.; Horwath, E. J.

    1993-05-01

    The performance of tungsten single crystals in ballistic impact varies strongly as a function of crystallographic orientation. The deformation structure of recovered single crystal rods fired in ballistic environments has been characterized by optical microscopy, SEM and TEM, and x-ray diffraction. The observed microstructures are varied and provide substantial insights into the factors governing the penetration and flow behavior under ballistic conditions. Crystallographic orientation influences the potential for developing shear which enhances material flow, and this enhancement ultimately maximizes the energy available for target penetration. Microstructural analysis elucidates the various mechanisms occuring during the flow process for single crystals of high-symmetry orientations, and suggests possible analogies between the penetration behavior of the tungsten single crystals and other materials.

  3. Constitutive modeling of creep of single crystal superalloys

    E-print Network

    Prasad, Sharat Chand

    2006-10-30

    In this work, a constitutive theory is developed, within the context of continuum mechanics, to describe the creep deformation of single crystal superalloys. The con- stitutive model that is developed here is based on the fact that as bodies deform...

  4. 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)

  5. NUCLEAR PHYSICS: Phonon Dispersion and Thermodynamics Properties of CaF2 via Shell Model Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Hu, Cui-E; Zeng, Zhao-Yi; Gong, Min; Gou, Qing-Quan

    2009-05-01

    The phonon and thermodynamics properties of face-centered cubic CaF2 at high pressure and high temperature are investigated by using the shell model interatomic pair potential within General Utility Lattice Program (GULP). The phonon dispersion curves and the corresponding density of state (PDOS) in this work are consistent with the experimental data and other theoretical results. The transverse optical (TO) and longitudinal optical (LO) mode splitting as well as heat capacity at constant volume CV and entropy S versus pressure and temperature are also obtained.

  6. Electrical conductivity of NaF-AlF3-CaF2-Al2O3 melts

    NASA Astrophysics Data System (ADS)

    Bakin, K. B.; Simakova, O. N.; Polyakov, P. V.; Mikhalev, Yu. G.; Simakov, D. A.; Gusev, A. O.

    2010-08-01

    The electrical conductivity of NaF-AlF3-Al2O3 melts with a CaF2 concentration of 5 wt % is measured at a continuously varying cell constant when the molar cryolitic ratio CR = [NaF]/[AlF3] changes from 1.2 to 2.0 [1, 2]. The experimental data are used to obtain a regression equation to describe the dependence of the electrical conductivity of the melts under study on CR, the alumina content, and temperature { ?] = f(CR, [Al2O3], T)}.

  7. Microwave absorption in single crystals of lanthanum aluminate

    Microsoft Academic Search

    Claudio Zuccaro; Michael Winter; Norbert Klein; Knut Urban

    1997-01-01

    A very sensitive dielectric resonator technique is employed to measure loss tangent tan ? and relative permittivity &egr;r 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 ? is almost sample independent with linear

  8. Microwave dielectric properties of lanthanum aluminate ceramics and single crystal

    Microsoft Academic Search

    T. Shimada; Ken-ich Kakimoto; Hitoshi Ohsato

    2005-01-01

    Single crystal and ceramics of LaAlO3 were prepared by a Czochralski method and conventional solid phase reaction, respectively, using high purity reagents. Far infrared reflectivity spectra for single crystals and ceramics of LaAlO3 were measured and eigenfrequencies and damping constants of transverse and longitudinal optical modes were evaluated in order to discuss variations in the dielectric properties. The observed reflectivity

  9. Aspects of single crystal and thin film high field electroluminescence

    Microsoft Academic Search

    Michael Joseph Robert Swift

    1989-01-01

    Electro-optical investigations of unimplanted and ion implanted ZnS and ZnSe direct current electroluminescent (DCEL) devices under reverse bias have enabled advances to be made in understanding some of the physical processes which govern the behavior of such devices. The three types of devices studied were ZnS thin films, ZnS single crystal diodes and ZnSe single crystal diodes. For reasons discussed

  10. 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.

  11. Dislocation structures in single-crystal tungsten and tungsten alloys

    Microsoft Academic Search

    Joseph R. Stephens

    1970-01-01

    Deformation of tungsten single crystals as a function of strain, temperature, and alloying was studied by transmission electron\\u000a microscopy. Single crystals oriented for (?101)[lll] slip were grown by electron beam zone refining. Compression specimens\\u000a of tungsten, W-l and 3 pct Re and W-l and 3 pct Ta were deformed to 2 pct strain at 150°, 300°, and 590°K (0.04, 0.08,

  12. Dislocation structures in single-crystal tungsten and tungsten alloys

    Microsoft Academic Search

    Joseph R. Stephens

    1970-01-01

    Deformation of tungsten single crystals as a function of strain, temperature, and alloying was studied by transmission electron microscopy. Single crystals oriented for (-101)[lll] slip were grown by electron beam zone refining. Compression specimens of tungsten, W-l and 3 pct Re and W-l and 3 pct Ta were deformed to 2 pct strain at 150°, 300°, and 590°K (0.04, 0.08,

  13. Effect of crystal and crucible rotations on the interface shape of Czochralski grown silicon single crystals

    NASA Astrophysics Data System (ADS)

    Asadi Noghabi, Omidreza; M'Hamdi, Mohammed; Jomâa, Moez

    2011-03-01

    A set of global heat transfer simulations in Czochralski (Cz) furnace for producing silicon single crystals have been performed to investigate the effect of crystal and crucible rotations on melt convection and crystal/melt interface shape. The 2D axisymmetric simulations are carried out taking into account radiative and conductive heat transfers between furnace components, melt convection including thermocapillary forces (Marangoni) and gas flow. Melt flow pattern and temperature distribution have been studied for several combinations of crystal and crucible rotations and for different crystal heights. The result shows that crystal/melt interface shape and melt flow regime are strongly sensitive to the rate of rotations of both crystal and crucible. Interfaces with low deflection can be achieved for certain combinations of crystal and crucible rotation rates.

  14. 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.

  15. Vapor crystal growth studies of single crystals of mercuric iodide (3-IML-1)

    NASA Technical Reports Server (NTRS)

    Vandenberg, Lodewijk

    1992-01-01

    A single crystal of mercuric iodide (HgI2) will be grown during the International Microgravity Lab. (IML-1) mission. The crystal growth process takes place by sublimation of HgI2 from an aggregate of purified material, transport of the molecules in the vapor from the source to the crystal, and condensation on the crystal surface. The objectives of the experiment are as follow: to grow a high quality crystal of HgI2 of sufficient size so that its properties can be extensively analyzed; and to study the vapor transport process, specifically the rate of diffusion transport at greatly reduced gravity where convection is minimized.

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

    SciTech Connect

    Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Sukumar, M. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Vasudevan, V. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India) [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Shakir, Mohd. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Ramamurthi, K. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Bhagavannarayana, G. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)

    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.

  17. Growth and characterization of biadmixtured TGS single crystals

    NASA Astrophysics Data System (ADS)

    Bharthasarathi, T.; Siva Shankar, V.; Jayavel, R.; Murugakoothan, P.

    2009-02-01

    Single crystals of triglycine sulfate (TGS) with L-glutamine and L-methionine were grown in aqueous solutions by a slow cooling method. The grown crystals were subjected to single crystal and powder X-ray diffraction studies to identify the morphology and the structure. FTIR and UV-visible spectra reveal the functional group identification and optical property of the grown crystals. The dielectric studies were carried out to identify the phase transition temperature and to find the dielectric constant. Microhardness studies have been carried out to assess the mechanical property. P- E hysteresis studies were carried out to find the values of spontaneous polarization and coercive field for doped TGS crystals.

  18. 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.

  19. 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.

  20. Modification of mechanical properties of e-gun evaporated MgF2 and CaF2 thin films under ion beam bombardment

    NASA Astrophysics Data System (ADS)

    Scaglione, S.; Flori, D.; Emiliani, G.

    1989-12-01

    The effect of ion beam assistance on mechanical properties (hardness and adhesion) of MgF2 and CaF2 thin films has been investigated. These films have been deposited by e-gun evaporation and bombarded during growth with an ion beam produced by a Kaufman source. The Knoop hardness has been calculated after having performed on the samples some indentation by an ultra-microindenter and measured the impression size by an eyepiece mounted on an optical microscope. The film adhesion has been measured by the scratch test technique. To investigate the influence of the ion source parameters on the mechanical properties, different ion beam energies (200-800 eV) have been used. Bombarded samples are harder (610 and 750 kg/mm2 for CaF2 and MgF2 samples, respectively) than unbombarded samples (380 and 300 kg/mm2 for CaF2 and MgF2, respectively). Critical loads (load where the delamination of the coating begins) of 12 and 3 N for bombarded MgF2 and CaF2 respectively and 4 and 1 N for unbombarded MgF2 and CaF2 samples have been found.

  1. Effects of CaF2 Coating on the Microstructures and Mechanical Properties of Tungsten Inert Gas Welded AZ31 Magnesium Alloy Joints

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Wang, Linzhi; Peng, Dong; Wang, Dan

    2012-11-01

    The effects of CaF2 coating on the macromorphologies of the welded seams were studied by morphological analysis. Microstructures and mechanical properties of butt joints welded with different amounts of CaF2 coatings were investigated using optical microscopy and tensile tests. The welding defects formed in the welded seams and the fracture surfaces were analyzed by scanning electron microscopy. An increase in the amount of CaF2 coating deteriorated the appearances of the welded seams but it improved the weld penetration depth and the depth/width ( D/ W) ratio of the tungsten inert gas (TIG) welded joints. The ?-Mg grains and Mg17(Al,Zn)12 intermetallic compound (IMC) were coarser in the case of a higher amount of CaF2 coating. The increase in the amount of CaF2 coating reduced the porosities and total length of solidification cracks in the fusion zone (FZ). The ultimate tensile strength (UTS) value and elongation increased at first and then decreased sharply.

  2. 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.

  3. Growth and characterization of ? and ?-glycine single crystals

    NASA Astrophysics Data System (ADS)

    Srinivasan, T. P.; Indirajith, R.; Gopalakrishnan, R.

    2011-03-01

    Single crystals of ?- and ?-glycine were grown by the slow evaporation solution growth method using deionised water as solvent. The ?-glycine was transformed to ?-glycine by addition of KNO3 as additive and both the forms of glycine single crystals were grown and the characteristic properties were studied and compared. From the single crystal XRD analysis the grown ?- and ?-glycine crystals are confirmed. The presence of the functional groups of ?- and ?-glycine was analyzed from the recorded FT-IR spectrum. The optical transmission was ascertained from UV-vis-NIR spectrum. The lower cut-off wavelengths of ?- and ?-glycine are 292 and 272 nm, respectively. The second harmonic generation relative efficiency was measured by the Kurtz and Perry powder technique. Group theoretical analysis predicts 120 vibrational optical modes in ?-glycine and 90 vibrational optical modes in ?-glycine. The TGA, DTA and dielectric studies were carried out to explore information about thermal and dielectric behavior, respectively, for ?- and ?-glycine.

  4. VGF growth of germanium single crystals without crucible contact

    NASA Astrophysics Data System (ADS)

    Langheinrich, D.; Pätzold, O.; Raabe, L.; Stelter, M.

    2010-08-01

    Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

  5. Preparation of bead metal single crystals by electron beam heating

    NASA Astrophysics Data System (ADS)

    Voigtländer, Bert; Linke, Udo; Stollwerk, H.; Brona, J.

    2005-11-01

    For the fabrication of small metal bead crystals a gas flame is used to melt a wire forming a liquid droplet which solidifies upon cooling into a single crystal metal bead. Due to oxidation under ambient conditions bead crystals can be formed only from noble metals using this method. Here we describe a method how to fabricate bead crystals from a wide variety of metals and metal alloys (Cu, Mo, Ru, Rh, Pd, Ag, Ta, W, Re, Ir, Pt, Au, PtPd, Pd80Pt20, PtRh, AuAg, and PtIr) by electron beam heating under vacuum conditions. Narrow x-ray diffraction peaks confirm a high crystal quality of the bead crystals.

  6. Crystal growth of lanthanum calcium borate (LCB) single crystals from melt and its characterization

    NASA Astrophysics Data System (ADS)

    Senthi lkumar, M.; Kalidasan, M.; Sugan; Dhanasekaran, R.

    2013-01-01

    Non-linear optical lanthanum calcium borate (LCB) single crystals were grown by the melt growth method using the Czohralski technique. The polycrystalline LCB compound is synthesized using the solid state reaction method. The grown crystals were characterized by XRD, EDAX, DTA, HRXRD, specific heat, dielectric and NLO studies. The powder XRD pattern revealed the formation of LCB compound and the lattice parameters of the grown crystals were identified through single crystal XRD studies. The melting point of the LCB compound is analyzed by the DTA measurements. Good crystalline nature of the grown crystal is observed from HRXRD analysis. Specific heat measurements in the temperature range 50-550 °C are carried out for the as grown crystal samples. The results obtained by the dielectric and NLO studies are also presented.

  7. 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 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767

  8. Crystal Growth, Dielectric and Polarization Reversal Properties of Bi4Ti3O12 Single Crystal

    Microsoft Academic Search

    Yoichiro Masuda; Hiroshi Masumoto; Akira Baba; Takashi Goto; Toshio Hirai

    1992-01-01

    A Bi2O3-TiO2 phase diagram was determined using differential thermal analysis (DTA) apparatus. Bi4Ti3O12 (BIT) micalike single crystals grown by a flux method were clear and slightly grayish in color. Ferroelectric and dielectric properties of BIT crystals were observed from measurements of electric displacement vs electric field hysteresis loops and the dielectric constant. Also, the polarization switching characteristics of BIT crystals

  9. Experiences in Large Grain-Single Crystal Cavity Fabrication

    Microsoft Academic Search

    Michael Pekeler; Johannes Schwellenbach; Marco Tradt

    2007-01-01

    At ACCEL instruments several single cell and 9-cell cavities have been produced out of large grain niobium sheets from different suppliers. The fabrication experience and difference to the production out of fine grain niobium sheets will be described. In addition two cavities were produced using single crystal niobium sheets. The final cavities showed no grain boundaries at all in the

  10. Electrochemical Growth of Single-Crystal Metal Nanowires via a

    E-print Network

    physical properties and potential applications as interconnects in future generations of nanometer the electro- chemical growth of copper single-crystal wires in polycar- bonate and anodic alumina membranes. The diameters of these wires range from micrometers down to nanometers (70 nm). Similarly, Pb, Bi, and Ag single

  11. Characterisation of slab waveguides, fabricated in CaF2 and Er-doped tungsten-tellurite glass by MeV energy N+ ion implantation, using spectroscopic ellipsometry and m-line spectroscopy

    NASA Astrophysics Data System (ADS)

    Bányász, I.; Berneschi, S.; Lohner, T.; Fried, M.; Petrik, P.; Khanh, N. Q.; Zolnai, Z.; Watterich, A.; Bettinelli, M.; Brenci, M.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.; Speghini, A.

    2010-05-01

    Slab waveguides were fabricated in Er-doped tungsten-tellurite glass and CaF2 crystal samples via ion implantation. Waveguides were fabricated by implantation of MeV energy N+ ions at the Van de Graaff accelerator of the Research Institute for Particle and Nuclear Physics, Budapest, Hungary. Part of the samples was annealed. Implantations were carried out at energies of 1.5 MeV (tungsten-tellurite glass) and 3.5 MeV (CaF2). The implanted doses were between 5 x 1012 and 8 x 1016 ions/cm2. Refractive index profile of the waveguides was measured using SOPRA ES4G and Woollam M-2000DI spectroscopic ellipsometers at the Research Institute for Technical Physics and Materials Science, Budapest. Functionality of the waveguides was tested using a home-made instrument (COMPASSO), based on m-line spectroscopy and prism coupling technique, which was developed at the Materials and Photonics Devices Laboratory (MDF Lab.) of the Institute of Applied Physics in Sesto Fiorentino, Italy. Results of both types of measurements were compared to depth distributions of nuclear damage in the samples, calculated by SRIM 2007 code. Thicknesses of the guiding layer and of the implanted barrier obtained by spectroscopic ellipsometry correspond well to SRIM simulations. Irradiationinduced refractive index modulation saturated around a dose of 8 x 1016 ions/cm2 in tungsten-tellurite glass. Annealing of the implanted waveguides resulted in a reduction of the propagation loss, but also reduced the number of supported guiding modes at the lower doses. We report on the first working waveguides fabricated in an alkali earth halide crystal implanted by MeV energy medium-mass ions.

  12. Exploring the retention properties of CaF2 nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid

    PubMed Central

    Köser, Joachim; Hess, Sylvia; Gnecco, Enrico; Meyer, Ernst

    2014-01-01

    Summary Amplitude-modulation atomic force microscopy (AM-AFM) is used to determine the retention properties of CaF2 nanoparticles adsorbed on mica and on tooth enamel in liquid. From the phase-lag of the forced cantilever oscillation the local energy dissipation at the detachment point of the nanoparticle was determined. This enabled us to compare different as-synthesized CaF2 nanoparticles that vary in shape, size and surface structure. CaF2 nanoparticles are candidates for additives in dental care products as they could serve as fluorine-releasing containers preventing caries during a cariogenic acid attack on the teeth. We show that the adherence of the nanoparticles is increased on the enamel substrate compared to mica, independently of the substrate roughness, morphology and size of the particles. PMID:24455460

  13. 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.

  14. ''6-Degrees of Freedom'' Single Crystal Plasticity Experiments

    SciTech Connect

    Lassila, D H; Florando, J N; LeBlanc, M M; Arsenlis, T; Rhee, M

    2003-05-21

    A deformation experiment has been developed specifically for the purpose of validation of dislocation dynamics simulations of plastic flow up to strains on the order of 1% [1]. The experiment has been designed so that a compressive uniaxial stress field is essentially super imposed on the test sample, and the crystal is free to deform with 3 orthogonal translation directions, and 3 rotation/tilt axes of freedom and has been given the name ''6-degrees of freedom'' (6DOF) experiment. The rotation, tilt and translation of the crystal are monitored by 5 laser displacement gages and 3 extensometers. Experiments are being performed on high purity Mo single crystals orientated for ''single slip''. All of the experiments are performed in pairs, with one test sample having highly polished surfaces for optical light and AFM slip-trace analyses, and the other having 4 strain gage rosettes mounted on the sides for measurement of the bi-axial surface strains during testing. All of the experimental data is used together to determine the slip activity of the orientated single crystal during deformation. Experimental results on high-purity Mo single crystals are presented. The results of these experiments show that slip behavior is in substantial deviation from the expected ''Schmid'' behavior. These experimental results bring into question some of the fundamental assumptions used in both the construction of crystal plasticity constitutive relationships and rules for dislocation mobility use in 3-D dislocation dynamics simulations.

  15. Raman spectra of deuteriated taurine single crystals

    NASA Astrophysics Data System (ADS)

    Souza, J. M. de; Lima, R. J. C.; Freire, P. T. C.; Sasaki, J. M.; Melo, F. E. A.; Filho, J. Mendes; Jones, Derry W.

    2005-05-01

    The polarized Raman spectra of partially deuteriated taurine [(ND 3+) 0.65(NH 3+) 0.35(CH 2) 2SO 3-] crystals from x( zz) x and x( zy) x scattering geometries of the A g and B g irreducible representations of the factor group C 2h are reported. The temperature-dependent Raman spectra of partially deuteriated taurine do not reveal any evidence of the structural phase transition undergone by normal taurine at about 250 K, but an anomaly observed in the 180 cm -1 band at ˜120 K implies a different dynamic for this band (which is involved in a pressure-induced phase transition) in the deuteriated crystal.

  16. 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.

  17. Crystal growth, magnetism, transport and superconductivity of two dimensional sodium cobalt oxide single crystals

    Microsoft Academic Search

    Dapeng Chen

    2008-01-01

    The objective of this work was to study the single crystal growth of NaxCoO2 by the optical floating zone technique and the intrinsic properties of the high quality single crystal samples thus produced. The properties of the superconductors derived from it will also be reported. This thesis, after a literature review on the NaxCoO2 family and the superconductors derived from

  18. 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.

  19. Modelling of Heat Transfer in Single Crystal Growth

    E-print Network

    Zhmakin, Alexander I

    2014-01-01

    An attempt is made to review the heat transfer and the related problems encountered in the simulation of single crystal growth. The peculiarities of conductive, convective and radiative heat transfer in the different melt, solution, and vapour growth methods are discussed. The importance of the adequate description of the optical crystal properties (semitransparency, specular reflecting surfaces) and their effect on the heat transfer is stresses. Treatment of the unknown phase boundary fluid/crystal as well as problems related to the assessment of the quality of the grown crystals (composition, thermal stresses, point defects, disclocations etc.) and their coupling to the heat transfer/fluid flow problems is considered. Differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated. The problems of the code verification and validation are discussed; a brief review of the experimental techniques for the study of heat transfer and flow structu...

  20. Q-switching with single crystal photo-elastic modulators

    Microsoft Academic Search

    F. Bammer; R. Petkovsek

    2010-01-01

    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

  1. Orientation effects in nanoindentation of single crystal copper

    Microsoft Academic Search

    Y. Liu; S. Varghese; J. Ma; M. Yoshino; H. Lu; R. Komanduri

    2008-01-01

    Numerical simulations and experimental results of nanoindentation on single crystal copper in three crystallographic orientations [(100), (011) and (111)] using a spherical indenter (3.4?m radius) were reported. The simulations were conducted using a commercial finite element code (ABAQUS) with a user-defined subroutine (VUMAT) that incorporates large deformation crystal plasticity constitutive model. This model can take full account of the crystallographic

  2. Sound velocity and dynamic elastic constants of lysozyme single crystals

    Microsoft Academic Search

    M. Tachibana; K. Kojima; R. Ikuyama; Y. Kobayashi; M. Ataka

    2000-01-01

    We have succeeded in the first measurement of the sound velocity of lysozyme single crystals using an ultrasonic pulse-echo method. The sound velocity along the [110] crystallographic direction in the tetragonal crystals is obtained to be 1817 m\\/s in the solution with pH 4.3 at 20°C. The corresponding elastic constant C11+C66 is evaluated to be approximately 3.99 GPa. Assuming the

  3. 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.

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

    DOEpatents

    Gopalan, Venkatraman (State College, PA); Mitchell, Terrence E. (Los Alamos, NM); Kitamura, Kenji (Tsukuba, JP); Furukawa, Yasunori (Tsukuba, JP)

    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.

  5. Plane wave simulation of elastic-viscoplastic single crystals

    NASA Astrophysics Data System (ADS)

    Lloyd, J. T.; Clayton, J. D.; Austin, R. A.; McDowell, D. L.

    2014-09-01

    Despite the large amount of research that has been performed to quantify the high strain rate response of Aluminum, few studies have addressed effects of crystal orientation and subsequent crystal-level microstructure evolution on its high strain rate response. To study orientation effects in single crystal Al, both a constitutive model and novel numerical method have been developed. A plane wave formulation is developed so that materials undergoing anisotropic viscoplastic deformation can be modeled in a thermodynamically consistent framework. Then, a recently developed high strain rate viscoplastic model is extended to include single crystal effects by incorporating higher order crystal-based thermoelasticity, anisotropic plasticity kinetics, and distinguishing influences of forest and parallel dislocation densities. Steady propagating shock waves are simulated for [100], [110], and [111] oriented single crystals and compared to existing experimental wave profile and strength measurements. Finally, influences of initial orientation and peak pressure ranging from 0 to 30 GPa are quantified. Results indicate that orientation plays a significant role in dictating the high rate response of both the wave profile and the resultant microstructure evolution of Al. The plane wave formulation can be used to evaluate microstructure-sensitive constitutive relations in a computationally efficient framework.

  6. Growth and characterization of 4-methyl benzene sulfonamide single crystals

    NASA Astrophysics Data System (ADS)

    Thirumalaiselvam, B.; Kanagadurai, R.; Jayaraman, D.; Natarajan, V.

    2014-11-01

    Single crystals of 4-methyl benzene sulfonamide (4MBS) were successfully grown from aqueous solution by low temperature solution growth technique. The grown crystal was characterized by single crystal XRD and powder XRD methods to obtain the lattice parameters and the diffraction planes of the crystal. UV-vis-NIR absorption spectrum was used to measure the range of optical transmittance and optical band gap energy. The optical transmission range was measured as 250-1200 nm. FTIR spectral studies were carried out to identify the presence of functional groups in the grown crystal. The thermal behavior of the crystal was investigated from thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) study. The absence of SHG was noticed by Kurtz and Perry powder technique. The third order NLO behavior of the material was confirmed by measuring the nonlinear optical properties using Z-scan technique and it was found that the crystal is capable of exhibiting saturation absorption and self-defocusing performance.

  7. 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.

  8. 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.

  9. Ballistic penetration phenomenology of high symmetry single crystals

    NASA Astrophysics Data System (ADS)

    Kingman, Pat W.; Herring, Rodney A.

    1995-02-01

    The ballistic performance of tungsten single crystal penetrators is known to be a function of crystallographic symmetry. The macroscopic deformation geometry of both single crystal and polycrystal tungsten penetrators is a continuous eversion of the rod into a hollow tube. The differences in energy partitioning leading to these variations in ballistic performance must therefore be accounted for by detailed material deformation processes governed by crystallographic orientation. Inferences about these processes have been drawn from microstructural characterization of recovered penetrators. Residual penetrators of both 011 and 111 orientations were found to have repeatedly deformed and recrystalized, but the actual operative processes led to quite different macrostructures, microstructures, and penetration depths. The 001 orientation deformed by a unique process which allowed very efficient deformation, resulting in maximum penetration depth. These single crystal experiments demonstrate the critical role of detailed deformation processes in determining the final penetration depths even when similar macroscopic material flow geometry occurs.

  10. 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.

  11. 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.

  12. 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 [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    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)

  13. Apparatus And Method For Producing Single Crystal Metallic Objects

    DOEpatents

    Huang, Shyh-Chin (Latham, NY); Gigliotti, Jr., Michael Francis X. (Scotia, NY); Rutkowski, Stephen Francis (Duanesburg, NY); Petterson, Roger John (Fultonville, NY); Svec, Paul Steven (Scotia, NY)

    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.

  14. Shock wave compression of single-crystal forsterite

    Microsoft Academic Search

    Ian Jackson; Thomas J. Ahrens

    1979-01-01

    Hugoniot equation of state measurements have been performed on pure synthetic single-crystal forsterite (Mg2SiO4) in the pressure range 70-160 GPa (0.7-1.6 Mbar). These and earlier data for polycrystalline forsterite are compared with theoretical Hugoniots for the assemblages 2MgO (rocksalt) +SiO2 (stishovite) and MgO (rocksalt) +MgSiO3 (perovskite). The densities attained by single-crystal forsterite at pressures in excess of 120 GPa are

  15. Two-photon-induced singlet fission in rubrene single crystal.

    PubMed

    Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E; Gurzadyan, Gagik G

    2013-05-14

    The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm?GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data. PMID:23676057

  16. Two-photon-induced singlet fission in rubrene single crystal

    NASA Astrophysics Data System (ADS)

    Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E.; Gurzadyan, Gagik G.

    2013-05-01

    The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm/GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data.

  17. Regularities of recrystallization in rolled Zr single crystals

    NASA Astrophysics Data System (ADS)

    Isaenkova, M.; Perlovich, Yu; Fesenko, V.; Krymskaya, O.; Krapivka, N.; Thu, S. S.

    2015-04-01

    Experiments by rolled single crystals give a more visible conception of the operating mechanisms of plastic deformation and the following recrystallization, than experiments by polycrystals. Studies by usage of X-ray diffraction methods were conducted by Zr single crystals. It was revealed, that regions of the ?-Zr matrix, deformed mainly by twinning, are characterized with decreased tendency to recrystallization. Orientations of recrystallized ?-Zr grains correspond to “slopes” of maxima in the rolling texture, where the level of crystalline lattice distortion is maximal and the number of recrystallization nuclei is most of all.

  18. 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.

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

    PubMed

    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

  20. Melting of Dust Crystals by Single Particles

    SciTech Connect

    Ivanov, Yuriy; Melzer, Andre [Institut fuer Physik, Ernst-Moritz-Arndt-Universitaet Greifswald, 17489 Greifswald (Germany)

    2005-10-31

    The melting transition of 2D finite dust clusters has been investigated. Therefore, a single dust particle was placed in a plane below the actual cluster plane. With reducing the gas pressure and with increase of the plasma power an instability due to the non-reciprocal attraction of the lower dust particle was excited that heats the cluster layer. The novel method of singular value decomposition (SVD) has been applied for the analysis of the cluster dynamics during melting.

  1. Exploiting polymer single crystals to assemble and functionalize nanomaterials

    NASA Astrophysics Data System (ADS)

    Li, Bing

    Nanomaterials are fundamental building blocks for nanoscience and nanotechnology. They can generally be categorized into three classes: zero-dimensional (0D) (e.g. nanoparticles), one-dimensional (1D) (e.g. carbon nanotubes) and two-dimensional (2D) (e.g. thin films) nanomaterials. Assembly of nanomaterials is the key step to transfer their fascinating mechanical, electronic and optical properties from nano- to micro- or macro-scale. Among all types of assemblies, assembling across different nanomaterial classes is of particular interest. For example, assembling 0D nanoparticles with 1D nanotubes or 2D thin films. These assembled structures have the advantage of possessing properties from both classes of nanomaterials. Functionalization of nanomaterials is important from both scientific and technological points of view. A newly developed field of functionalization is called "patchy particles". Multiple types of functional molecules form different domains on particle surface. Each domain contains only one type of functional molecules. These domains are called patches. These patchy particles are advanced building blocks, which may assemble into useful complex structures. In this thesis, polymer single crystals are exploited to assemble and functionalize nanomaterials. Polymer single crystals have a lamellar structure. Since the thickness of these lamellae is ˜10 nm, polymer single crystals are introduced as a new type of 2D nanomaterials. Different from the traditional 2D nanomaterials such as Langmuir-Blodgett films, self-assembled monolayers and thin films made by Layer-by-Layer technique, these polymer single crystals are free-standing, which means no substrate is needed. Furthermore, the surface of these polymer single crystals can be readily functionalized by crystallizing end-functionalized polymers. Based on the studied polymers, this thesis is divided into two parts. The first part is focused on single crystals of poly(ethylene oxide) (PEO). Thiol-terminated PEO is used to make functional lamellar single crystals. Assembling 0D nanoparticles with these 2D lamellae leads to nanoparticles sheets with three different structures: monolayer, bilayer and sandwich. Furthermore, by assembling nanoparticles during crystallization of PEO, nanoparticle sheets with frame-like patterns are obtained. The morphology of these frames can be readily controlled by tuning experimental parameters. Finally, as nanoparticles sheets form, patchy nanoparticles are produced as well. Structures like "bilines" and nanowires are formed by self-assembly of these patchy nanoparticles. The second part deals with single crystals of polyethylene-block -poly(ethylene oxide) (PE-b-PEO). Single crystals of PE-b-PEO are used to functionalize carbon nanotubes and assemble nanoparticles with these nanotubes. Alternating patterns are formed on carbon nanotube surface by thin film crystallization of PE-b-PEO. As a result, the surface of a carbon nanotube is uniformly divided into many sub-10 nm pieces along the tube axis. This functionalization opens the door to periodical functionalization of carbon nanotubes at nanoscale. By employing thiol-terminated PE-b-PEO, thiol groups are introduced to the alternating patterns. These periodically functionalized 1D carbon nanotubes are used to assemble 0D nanoparticles into periodical parallel nanoparticle chains.

  2. Experiences in Large Grain-Single Crystal Cavity Fabrication

    SciTech Connect

    Pekeler, Michael; Schwellenbach, Johannes; Tradt, Marco [ACCEL Instruments GmbH, Friedrich-Ebert-Str. 1, D-51429 Bergisch Gladbach (Germany)

    2007-08-09

    At ACCEL instruments several single cell and 9-cell cavities have been produced out of large grain niobium sheets from different suppliers. The fabrication experience and difference to the production out of fine grain niobium sheets will be described. In addition two cavities were produced using single crystal niobium sheets. The final cavities showed no grain boundaries at all in the cavity cell, even not in the electron beam welding seam.

  3. 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 peak values at locations where fretting cracks have been observed. Fretting stresses at the attachment region are seen to vary significantly as a function of crystal orientation. Attempts to adapt techniques used for estimating fatigue life in the airfoil region, for life calculations in the attachment region, are presented. An effective model for predicting crystallographic crack initiation under mixed mode loading is required for life prediction under fretting action.

  4. PHYSICAL REVIEW B 88, 024304 (2013) Accurate calculations of phonon dispersion in CaF2 and CeO2

    E-print Network

    Chen, Long-Qing

    2013-01-01

    In particular, CaF2 (Refs. 2,3) is a typical superionic conductor.1 CeO2 has been used in catalytic converters,16 Computationally, the advantage of the linear response method is that it directly evaluates the dynamical matrix- teractions. According to the reduced dynamical matrix from Wallace,22 the reduced dynamical matrix

  5. Polymer single crystal membrane from liquid/liquid interface

    NASA Astrophysics Data System (ADS)

    Wang, Wenda; Li, Christopher; Soft Matter Research Group-Drexel University Team

    2013-03-01

    Vesicles, mimicking the structure of cell membrane at the molecular scale, are small membrane-enclosed sacks that can store or transport substances. The weak mechanical properties and the nature of environment-sensitivity of the current available vesicles: liposomes, polymersomes, colloidsomes limit their applications as an excellent candidate for targeting delivery of drugs/genes in biomedical engineering and treatment. Recently, we developed an emulsion-based method to grow curved polymer single crystals. Varying the polymer concentration and/or the emulsification conditions (such as surfactant concentration, water-oil volume ratio), curved crystals with different sizes and different openness could be obtained. This growing process was attributed to polymer crystal growth along the liquid/liquid interface. In addition, the liquid/liquid interfacial crystal growth is promising for synthesis of enclosed hollow sphere.

  6. Microhardness studies of vapour grown tin (II) sulfide single crystals

    NASA Astrophysics Data System (ADS)

    Hegde, S. S.; Kunjomana, A. G.; Ramesh, K.

    2015-06-01

    Earth abundant tin sulfide (SnS) has attracted considerable attention as a possible absorber material for low-cost solar cells due to its favourable optoelectronic properties. Single crystals of SnS were grown by physical vapour deposition (PVD) technique. Microindentation studies were carried out on the cleaved surfaces of the crystals to understand their mechanical behaviour. Microhardness increased initially with the load, giving sharp maximum at 15 g. Quenching effect has increased the microhardness, while annealing reduced the microhardness of grown crystals. The hardness values of as-grown, annealed and quenched samples at 15 g load are computed to be 99.69, 44.52 and 106.29 kg/mm2 respectively. The microhardness of PVD grown crystals are high compared to CdTe, a leading low-cost PV material. The as-grown faces are found to be fracture resistant.

  7. Macroscale Janus polymer single crystal film and its wettability analysis

    NASA Astrophysics Data System (ADS)

    Qi, Hao; Wang, Wenda; Zhou, Tian; Li, Christopher

    2014-03-01

    Liquid-liquid interface between two immiscible solvents is crucial to studying amphiphile and colloidal self-assembly. It can also guide chain folding during the crystallization process. In this presentation, we show that crystallization of dicarboxy end functionalized poly(?-caprolactone) at water/pentyl acetate interface result in millimeter scale, uniform polymer single crystal (PSC) film. Due to the asymmetric nature at the liquid-liquid interface, the PSC film exhibit Janus property - a hydrophobic side and a hydrophilic side, which is confirmed by in-situ nano-condensation experiment using an environmental scanning electron microscope. The thickness of the PSC film changes with different polymer solution concentration, revealing a surface tension dominated crystallization process.

  8. Magnetothermal properties of single crystal dysprosium

    NASA Astrophysics Data System (ADS)

    Chernyshov, A. S.; Tishin, A. M.; Gschneidner, K. A.; Pecharsky, A. O.; Pecharsky, V. K.; Lograsso, T. A.

    2002-05-01

    The magnetocaloric properties (the adiabatic temperature change) of the high purity single crystalline dysprosium have been measured directly over the temperature range from 78 to 220 K in magnetic fields from 0 to 14 kOe applied along the easy magnetization direction (a-axis). These results are in good to excellent agreement, except for two regions (105 to 127 K, and 179 to 182 K), with the previous magnetocaloric effect data reported on lower purity dysprosium samples. The magnetic phase diagram of Dy has been refined based on the results of these measurements and two new high magnetic field phases have been identified.

  9. Electronic conduction through single crystals of polyethylene

    E-print Network

    Samson, Gerald Maurice

    1966-01-01

    ELECTRORIC CO:iC' CTIOE?TEROUCH Sl". , GLE C OISTf~S OF POL" IZLELE A Thesis Gerald Mauri co Samson Submitted to the Graduate College of' the Texas AcM University in partial Wlfillment of' the requirements f' or the degree of' MASTER OF SCIENCE... talc o Polyot! ylone . -y, i'oo Gerald !':cur"' co Samson Directed by: Zr. Joe S. The predominant conduction mechani m through single cryo' mls op polyethylene is shown to be Schott!cy ( hernal) oui "sion . or tompora- o tu. es - bove 0 C. . "or...

  10. 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.

  11. Monte Carlo simulations of single crystals from polymer solutions.

    PubMed

    Zhang, Jianing; Muthukumar, M

    2007-06-21

    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. PMID:17600443

  12. Pulsed electron beam irradiation of vanadium single crystals

    Microsoft Academic Search

    J. M. Lombaard; O. Meyer

    1983-01-01

    The damage produced by pulsed electron beam irradiation of vanadium single crystals has been studied by the channeling technique and by thin film X-ray analysis. A surface disorder peak and a small dechanneling component was produced by applying electron energy densities below the melting threshold. The structure of the surface disorder was microcrystalline or amorphous and the dechanneling component could

  13. 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.

  14. Oriented Co Nanoparticles in a Single-Crystal Alumina Matrix

    Microsoft Academic Search

    L. A. Boatner; C. W. White; T. E. Haynes; J. R. Thompson; K. D. Sorge; J. D. Budai; A. Meldrum

    2003-01-01

    Crystallographically oriented nanoparticles of Co can be formed in a single-crystal alumina host by employing ion implantation combined with thermal processing. Depending on the Co implantation and thermal processing conditions, Co particles can be created that are either almost pure hexagonal or pure cubic phase precipitates. The hexagonal Co particles are oriented with their six-fold axis parallel to the alumina

  15. Halide adsorption on single-crystal silver substrates: dynamic

    E-print Network

    Rikvold, Per Arne

    · Investigated validity of lattice-gas approach * Justified for well-localized adsorption sites · Tested MarkovHalide adsorption on single-crystal silver substrates: dynamic simulations and ab initio density State University Supported by US NSF #12;How good is lattice-gas approximation? Using 2D corrugation

  16. 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.

  17. 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.

  18. Creep, plasticity, and fatigue of single crystal superalloy

    Microsoft Academic Search

    Alexander Staroselsky; Brice N. Cassenti

    2011-01-01

    Single crystal components in gas turbine engines are subject to such extreme temperatures and stresses that life prediction becomes highly inaccurate resulting in components that can only be shown to meet their requirements through experience. Reliable life prediction methodologies are required both for design and life management. In order to address this issue we have developed a thermo-viscoplastic constitutive model

  19. Ultrabroadband single crystal composite transducers for underwater ultrasound

    Microsoft Academic Search

    S. Cochran; M. Parker; P. Marin-Franch

    2005-01-01

    Through the use of complex piezoelectric structures, it is possible to obtain resonant harmonics not observed in the usual odd- harmonic response of a conventional structure. When combined with inherently broadband components, such as composites made with PMN- PT single crystal material, this permits the realisation of ultrabroadband devices. In the work reported here, results from modelling indicate that a

  20. Direct Bonding of LiTaO3 Single Crystals

    Microsoft Academic Search

    Yoshihiro Tomita; Masato Sugimoto; Kazuo Eda; Tetsuyuki Okano

    1994-01-01

    A new fabrication method for combining lithium tantalate single crystals by direct bonding without using bonding agents has been developed. The bonded interface was found to be very uniform, and bonding on an atomic scale was achieved in spite of a relatively low heat-treatment temperature of 350°C. This method is very promising for realizing new stacked structures and new fabrication

  1. Quantum Nernst effect in a bismuth single crystal

    Microsoft Academic Search

    Mari Matsuo; Akira Endo; Naomichi Hatano; Hiroaki Nakamura; Ryoen Shirasaki; K. Sugihara

    2009-01-01

    We calculate the phonon-drag contribution to the transverse (Nernst) thermoelectric power Syx in a bismuth single crystal subjected to a quantizing magnetic field. The calculated heights of the Nernst peaks originating from the hole Landau levels and their temperature dependence reproduce the right order of magnitude for those of the pronounced magneto-oscillations recently reported by Behnia [Phys. Rev. Lett. 98,

  2. The Reactive Activity and Selectivity of Platinum Single Crystal Surfaces

    Microsoft Academic Search

    Jianhua Wang

    1994-01-01

    Alcohol, methylamine, acetylene, and ethyl iodide decomposition on platinum single crystal surfaces have been investigated in this thesis work. The objective of this research is to examine factors affecting surface reaction pathways and the rate of the reaction. Alcohol conversion on transition metals has been studied for many years. The importance of this research is to find new ways to

  3. Amplified Ferrimagnetic Echoes in Single Crystal-Polycrystal YIG Composites

    Microsoft Academic Search

    D. E. Kaplan; W. I. Dobrov; G. F. Herrmann

    1972-01-01

    To clarify the conditions for generation of amplified Hahn-type echoes in ferrimagnets, experiments were conducted with composite samples formed by imbedding single crystal YIG wafers at various positions at and near the end of a poly crystalline YIG bar of similar cross section and 4?M value. The poly crystalline component provided the internal field and field gradient needed for echo

  4. Growth of large single crystals of MgO

    SciTech Connect

    Boatner, L.A. [Oak Ridge National Lab., TN (United States); Urbanik, M. [Commercial Crystal Laboratories, Inc., Naples, FL (United States)

    1997-06-12

    The progressive identification of new high-technology applications and requirements for MgO single crystals in the commercial realm, as well as in DOE and other government-agency project areas, has resulted in an increased demand and international market for this material. Specifically, the demand for MgO crystals in large sizes and quantities is presently increasing due to existing and developing applications that include: (a) MgO substrates for the formation of electro-optic thin films and devices, (b) epitaxial substrates for high-temperature thin-film superconducting devices MgO optical components - including high-temperature windows, lenses, and prisms, and (d) specialty MgO crucibles and evaporation sources for thin-film production. In the course of CRADA ORNL92-0091, carried out with Commercial Crystal Laboratories of Naples, Florida as the commercial participant, we have made major progress in increasing the size of single crystals of MgO produced by means of the submerged-arc-fusion technique-thereby increasing the commercial utility of this material. Prior to the accomplishments realized in the course of this CRADA, the only commercially available single crystals of MgO were produced in Japan, Israel, and Russia. The results achieved in the course of CRADA ORNL92-0091 have now led to the establishment of a domestic commercial source of MgO single-crystal substrates and components, and the U.S. is no longer totally dependent on foreign sources of this increasingly important material.

  5. Single crystal growth, crystal structure and characterization of a novel crystal: L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP)

    NASA Astrophysics Data System (ADS)

    Wang, L. N.; Wang, X. Q.; Zhang, G. H.; Liu, X. T.; Sun, Z. H.; Sun, G. H.; Wang, L.; Yu, W. T.; Xu, D.

    2011-07-01

    A novel organic crystal, L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP), synthesized and grown from aqueous solution, is presented. X-ray single diffraction shows that LAPP belongs to the monoclinic crystallographic system with space group P2 1. FT-IR and UV/vis/NIR transmission spectra have been employed to characterize the crystal. The computational calculation based on the density functional theory at the B3LYP/6-31G (d, p) level has been used to compute the first-order hyperpolarizability of LAPP relating to different molecular models. The morphology, nonlinear characteristic and thermal stability of the crystal have also been investigated.

  6. 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.

  7. Transport and magnetic properties of Fe2VAl single crystal

    NASA Astrophysics Data System (ADS)

    Ishikawa, F.; Fukuda, K.; Kawase, N.; Mochigi, M.; Yamada, Yuh; Matsushita, A.

    We prepared single crystals of Fe1.95V1.05Al, Fe1.98V1.02Al, Fe2VAl, Fe2.02V0.98Al and Fe2.05V0.95Al by the conventional Czochralski pulling method in a tetra-arc furnace. The magnetization along the [1 0 0] direction was measured using a SQUID magnetometer. The Fe2VAl sample showed the smallest value of magnetization among the samples. The magnetization of the single crystalline sample was smaller than that of the polycrystalline sample with the same composition. These results for the single crystal suggest that the Fe2VAl has the lower concentration of magnetic antisite defects. The Seebeck coefficients were measured in the temperature range from 10 to 300 K. Fe2VAl showed the largest absolute value of the Seebeck coefficient S among the present samples, about |S|=180 ?V/K.

  8. Optical properties of anhydrous copper(II) formate single crystal

    NASA Astrophysics Data System (ADS)

    Narsimlu, N.; Sivarama Sastry, G.

    1996-12-01

    Infrared (IR) (450-4500 cm -1) spectroscopy, electron paramagnetic resonance (EPR) and optical absorption (52 631-3225 cm -1) studies of anhydrous copper(II) formate single crystal have been carried out at 300 K. The IR spectrum of Cu(COOH) 2 single crystal shows four strong absorption bands at 3199, 1569, 1363 and 833 cm -1 which are attributed to the stretching and bending vibrations between the formate ion atoms. Analysis of EPR spectra using crystal field theory reveals that the Jahn-Teller active copper(II) ion is present in a tetragonally elongated square pyramidal site. The optical absorption in the UV and visible region is characterized by a charge transfer band, and a cubic field splitting of 3 d energy level of Cu 2+ ion. In addition, in the near infrared region eight absorption peaks are recorded. These transitions in the near infrared are assigned variously to the d- d transitions of copper(II) ion between the admixtured quantized energy levels of copper and oxygen orbitals, to the transitions arising out of the Hubbard energy gap of the crystal, and to the Fermi energy gap of the crystal, respectively. Finally the weak absorptions that are recorded are attributed to the linear combinations of the IR bands.

  9. Structure and mechanical properties of biogenic single calcite crystals

    NASA Astrophysics Data System (ADS)

    Aizenberg, Joanna; Weiner, Steve; Addadi, Lia

    2000-03-01

    Composite materials, in which the organic host is stiffened by guest crystalline particles, are widely used in nature (bones, teeth, mollusk shells) and are produced synthetically by man (fiber-reinforced composites). Organisms also produce a different type of composite in which the host is a single crystal and the guests are macromolecules occluded in an orderly fashion within the crystal. The best-studied examples, to date, are skeletal elements composed of a single calcite crystal. These skeletons have unique mechanical properties, and fracture with a glassy conchoidal surface, which is quite different from the smooth planar cleavage of pure calcite. The specific positions of macromolecules in calcite crystals were identified by in vitro crystallization experiments and synchrotron X-ray studies. We show that the occluded macromolecules introduced specifically along crystallographic planes that are oblique to the cleavage planes of calcite strengthen the material against failure by both absorbing and deviating the advancing cracks. These novel, "reverse" fiber-reinforced, composites may be just one example of strategies used in nature for producing materials with improved properties.

  10. Single crystal to single crystal transition in (10, 3)-d framework with pyrazine-2-carboxylate ligand: Synthesis, structures and magnetism

    SciTech Connect

    Yang, Qian [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China) [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Department of Chemistry, Tianjin Key Lab on Metal and Molecule-based Material Chemistry, Nankai University, Tianjin 300071 (China); Zhao, Jiong-Peng, E-mail: horryzhao@yahoo.com [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China)] [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Liu, Zhong-Yi [College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387 (China)] [College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387 (China)

    2012-12-15

    Assembling of pyrazine-2-carboxylate (Pzc) acid with nickel chlorine under solvothermal condition with MeOH as solvent gave a porous complex 1 {l_brace}[Ni(Pzc)ClH{sub 2}O]{center_dot}MeOH{r_brace}{sub n} with 1D channels. In 1 the ligands and metal ions are connected by three of each other and a rare (10,3)-d topology net is gained. The MeOH molecules filled in the 1D channels as guests. It is interesting that 1 undergoes a single-crystal-to-single-crystal transformation to another complex 2 when the guest MeOH molecules in the channels are exchanged by water molecules. Magnetic study indicates anti-ferromagnetic couplings exist in the two complexes and the guest exchange in the complex has little influence on the magnetism. - Graphical abstract: A porous complex 1 with rare (10,3)-d net was gained, and 1 underwent a single-crystal-to-single-crystal transformation to another phase 2. Highlights: Black-Right-Pointing-Pointer New (10,3)-d net was obtained with pyrazine-2-carboxylate ligands as a triangular node. Black-Right-Pointing-Pointer The complex 1 has a 1D channel filled with methanol molecules as guests. Black-Right-Pointing-Pointer 1 could undergo SCSC structural transition to 2 after guests exchanged. Black-Right-Pointing-Pointer Antiferromagnetic interactions were found in 1 and 2.

  11. 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.

  12. 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 considerable post-processing work. For these reasons it is very advantageous to develop analytical solution schemes for subsurface stresses, whenever possible.

  13. Journal of Crystal Growth 304 (2007) 114117 Single crystal growth of YbRh2Si2 using Zn flux

    E-print Network

    Broholm, Collin Leslie

    2007-01-01

    Journal of Crystal Growth 304 (2007) 114­117 Single crystal growth of YbRh2Si2 using Zn flux-temperature solution technique, using Zn flux and followed by a decanting process. As opposed from the crystals growth: A1. Growth from high-temperature solutions; A1. Single crystal; B2. YbRh2Si2 1. Introduction YbRh2Si

  14. Photoluminescence of Neutron-Irradiated LiF Single Crystals

    NASA Astrophysics Data System (ADS)

    Jonane, I.; Podins, A.; Ivanova, A.

    2010-01-01

    In 1980, a single LiF crystal was irradiated by thermal neutrons up to the exposition dose 1019 n/cm2 at the Salaspils nuclear reactor. The crystal has been kept at room temperature for 29 years. Samples in size of 5×4×1 mm3 were cut from the crystal and some of them annealed at 920 K for 30 min. To study photoluminescence, measurements with a confocal laser scanning microscope Leica TCS SP5 were performed, during which 3D-defects of size of ~1?m3 were revealed. Photoluminescence was observed in the red spectral region with the peak of ~ 655 nm when excited with an argon laser (? = 458 nm).

  15. Synthesis, crystal structure and EPR spectra of tetraaquabis(methylisonicotinate) copper(II) disaccharinate single crystal

    NASA Astrophysics Data System (ADS)

    Çelik, Yunus; Bozkurt, Esat; Uçar, ?brahim; Karabulut, Bünyamin

    2011-10-01

    The crystal structure of the [Cu(mein)2(H2O)4]·(sac)2 complex (mein: methylisonicotinate, sac: saccharine) was investigated by single crystal X-ray diffraction technique. The vibrational spectrum was also discussed in relation with the other compounds containing methylisonicotinate and saccharinate complexes. The EPR spectra of [Cu(mein)2(H2O)4]·(sac)2 single crystal have been studied in the temperature range between 113 and 300 K in three mutually perpendicular planes and exhibit two sets of four hyperfine lines of Cu2+ ion. The ground state wave function of the Cu2+ ion is an admixture of dx2-y2 and dz2 states.

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

    SciTech Connect

    Bukowski, Z. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw (Poland)]. E-mail: bukowski@int.pan.wroc.pl; Tran, V.H. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw (Poland); Stepien-Damm, J. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw (Poland); Troc, R. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw (Poland)

    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.

  17. Crystal growth and characterization of CuI single crystals by solvent evaporation technique

    SciTech Connect

    Gu, Mu, E-mail: mgu@tongji.edu.cn [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Department of Physics, Tongji University, No. 1239 Siping Road, Yangpu District, Shanghai 200092 (China)] [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Department of Physics, Tongji University, No. 1239 Siping Road, Yangpu District, Shanghai 200092 (China); Gao, Pan; Liu, Xiao-Lin; Huang, Shi-Ming; Liu, Bo; Ni, Chen [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Department of Physics, Tongji University, No. 1239 Siping Road, Yangpu District, Shanghai 200092 (China)] [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Department of Physics, Tongji University, No. 1239 Siping Road, Yangpu District, Shanghai 200092 (China); Xu, Rong-Kun; Ning, Jia-min [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China)] [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China)

    2010-05-15

    Cuprous iodide (CuI) crystals are grown by slow evaporation technique in three different solvents. Large CuI single crystals with dimensions of 7.5 mm x 5 mm x 3 mm are obtained in pure acetonitrile solvent at 40 {sup o}C. The as-grown crystals are analyzed by X-ray diffraction, energy-dispersive X-ray analysis, differential scanning calorimetry, current-voltage characteristic and photoluminescence spectrum. The results show that the CuI crystal has the zinc-blende structure with no secondary phase. The elemental Cu/I ratio is 1.09:1. The melting point of the crystal is 875 K and two phase transitions occur from room temperature to its melting point. The electrical conductivity of CuI platelet crystal is in the range of 1.11-2.38 {Omega}{sup -1} cm{sup -1}. Under ultraviolet excitation, the CuI crystals exhibit three emission bands with peak positions at 426, 529 and 671 nm. The nature of the luminescence is discussed.

  18. 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.

  19. Electron paramagnetic resonance characterization of gamma irradiation damage centers in S-butyrylthiocholine iodide single crystal

    Microsoft Academic Search

    Betül Çali?kan; Mehmet Çivi; Mehmet Birey

    2007-01-01

    Radiation-induced S-butyrylthiocholine Iodide (SBTCI) (C9H20INOS) single crystals have been ana-lysed as results from the use of electron paramagnetic resonance (EPR) spectroscopy. SBTCI single crystals were irradiated with Co–? rays at 296 K and their EPR spectrum was studied as a function of temperature. The single crystals have been investigated between 120 and 445 K. The single crystal spectra were taken at 5°

  20. Laser radiation frequency doubling in a single-crystal fibre based on a stoichiometric LiNbO3 crystal

    NASA Astrophysics Data System (ADS)

    Kashin, V. V.; Nikolaev, D. A.; Rusanov, S. Ya; Tsvetkov, V. B.

    2015-01-01

    We demonstrate the employment of single-crystal optical fibres based on lithium niobate for doubling the laser radiation frequency. The measured characteristics of the fibre confirm its high quality and spatial homogeneity. Parameters of the frequency doublers for neodymium laser radiation (? = 1 mm) based on fibre and bulk single crystals are compared. Single crystals are grown by the method of laser-heated pedestal growing with heating by radiation of a CO2 laser (LHPG-method).

  1. Aging and memory effect in magnetoelectric gallium ferrite single crystals

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Mukherjee, Somdutta; Mitra, Chiranjib; Garg, Ashish; Gupta, Rajeev

    2015-02-01

    Here, we present a time and temperature dependent magnetization study to understand the spin dynamics in flux grown single crystals of gallium ferrite (GaFeO3), a known magnetoelectric, ferroelectric and ferrimagnet. Results of the magnetic measurements conducted in the field-cooled (FC) and zero-field-cooled (ZFC) protocols in the heating and cooling cycles were reminiscent of a "memory" effect. Subsequent time dependent magnetic relaxation measurements carried out in ZFC mode at 30 K with an intermittent cooling to 20 K in the presence of a small field show that the magnetization in the final wait period tends to follow its initial state which was present before the cooling break taken at 20 K. These observations provide an unambiguous evidence of single crystal gallium ferrite having a spin glass like phase.

  2. Single crystal electrical resistivity of magnetite under high pressure

    NASA Astrophysics Data System (ADS)

    Muramatsu, Takaki; Helmuth Berger Collaboration; Lev V Gasparov Collaboration; Viktor V. Struzhkin Collaboration; Russell J. Hemley Collaboration

    2015-03-01

    Magnetite (Fe3O4), the oldest known magnetic mineral has the cubic inversed spinel structure at ambient pressure and temperature. It shows a metal to insulator transition (Verway transition) at about 125 K as temperature decreases at ambient pressure. Under high pressure the Verwey transition is suppressed down to 0 K and above 25 GPa magnetite undergoes a structural transformation to high pressure phase. These behaviors have been intensively examined by various experimental means and computational calculations for decades. However only the limited number of the electrical resistivity measurements on single crystal magnetite under pressure have been performed at the moment. We performed high pressure and low temperature experiments by means of the electrical resistivity on single crystal magnetite to examine Verwey transition under pressure and a structural transformation from cubic spinel phase to high pressure phase. We report the results of the temperature dependence of the electrical resistivity in the pressure range from ambient pressure to more than 50 GPa.

  3. Ferromagnetic Ordering in Carbon Nanotubes, Incorporated in Diamond Single Crystals

    E-print Network

    Dmitri Yerchuck; Vyacheslav Stelmakh; Alla Dovlatova; Yauhen Yerchak; Andrey Alexandrov

    2013-06-02

    The physical origin of the mechanism of the formation of ferromagnetic ordering in carbon nanotubes (NTs), produced by high energy ion beam modification of diamond single crystals in $\\langle{110}\\rangle$ and $\\langle{111}\\rangle$ directions has been found. It is concluded from analysis of experimental results on ferromagnetic spin wave resonance observed, that the only $\\pi$-electronic subsystem of given NTs is responsible for the appearance of ferromagnetism. It is determined by asymmetry in spin density distribution in Su-Schrieffer-Heeger (SSH) topological soliton lattice. The formation of SSH topological soliton lattice is considered in the frames of generalized SSH-model of organic conductors, in which $\\pi$-electronic subsystem is represented being to be 1D quantum Fermi liquid. The phenomenon of formation of uncompensated antiferromagnetic ordering coexisting with superconductivity at room temperature in carbon nanotubes, produced by high energy ion beam modification of diamond single crystals in $\\langle{100}\\rangle$ direction is argued.

  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. Challenges for Single-crystal (SX) Crack Cladding

    NASA Astrophysics Data System (ADS)

    Rottwinkel, Boris; Schweitzer, Luiz; Noelke, Christian; Kaierle, Stefan; Wesling, Volker

    The formation of cracks in single-crystal (SX) turbine blades is a common problem for aero-engines. If cracks are located under the tip-area, the blade-repair is not possible. Anew method to repair these cracks is to clad with single-crystal-technology.To reduce the loss of material and working time,notches are used to remove the affected crack zone. The usednotch geometries must be weldable and also permit the material solidification in the same oriented plane as the original microstructure. For that, a thermal gradient has to be introduced in order to guide the grain growth. The process characteristics of laser cladding, such as small local heat input and controlled material supply, make it an efficient process to fill the notch. However, there are challenges to achieve a SX structure without cracks and pores. The unstable energy distribution may result in a polycrystalline structure. Current achievements and further challenges are presented in this paper.

  6. Dynamic gas-inclusion in a single crystal.

    PubMed

    Takamizawa, Satoshi

    2015-06-01

    In solid-state science, most changing phenomena have been mysterious. Furthermore, the changes in chemical composition should be added to mere physical changes to also cover the chemical changes. Here, the first success in characterizing the nature of gas inclusion in a single crystal is reported. The gas inclusion process has been thoroughly investigated by in?situ optical microscopy, single-crystal X-ray diffraction analyses, and gas adsorption measurements. The results demonstrated an inclusion action of a first-order transition behavior induced by a critical concentration on the phase boundary. The transfer of phase boundary and included gas are strongly related. This relationship can generate the dynamic features hidden in the inclusion phenomena, which can lead to the guest capturing and transfer mechanism that can apply to spatiotemporal inclusion applications by using host solids. PMID:25925283

  7. Ultrafast dynamics of excitons in tetracene single crystals

    NASA Astrophysics Data System (ADS)

    Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich

    2014-03-01

    Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states Sn on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.

  8. Ultrafast dynamics of excitons in tetracene single crystals.

    PubMed

    Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich

    2014-03-21

    Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S(n) on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale. PMID:24655187

  9. Ultrafast dynamics of excitons in tetracene single crystals

    SciTech Connect

    Birech, Zephania; Schwoerer, Heinrich, E-mail: heso@sun.ac.za [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa)] [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa); Schwoerer, Markus [Department of Physics, University of Bayreuth, Bayreuth (Germany)] [Department of Physics, University of Bayreuth, Bayreuth (Germany); Schmeiler, Teresa; Pflaum, Jens [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)] [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)

    2014-03-21

    Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S{sub n} on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S{sub 1} on a 40 ps timescale. The high energy Davydov component of the S{sub 1} exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.

  10. 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.

  11. Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa

    NASA Astrophysics Data System (ADS)

    Dorfman, S. M.; Jiang, F.; Mao, Z.; Kubo, A.; Prakapenka, V.; Duffy, T. S.

    2007-12-01

    AX2 compounds include a wide range of oxides and salts of broad interest in geoscience, materials science and chemistry, such as SiO2 and CaF2, and have in common a sequence of phase transitions dependent on ionic size ratio and electronic properties (Leger and Haines, 1997). Shock compression studies have shown that CaF2 transforms to a highly incompressible phase above 1 Mbar along the Hugoniot (Nellis, 2007). In this study we examine phase transitions and equations of state of the alkaline earth fluorides CaF2 and SrF2 to 95 GPa. Angle-dispersive x-ray diffraction experiments were performed on CaF2 and SrF2 samples in laser-heated diamond anvil cells at beamlines X17B3 of the National Synchrotron Light Source and 13-ID-D of the GSECARS sector at the Advanced Photon Source. We confirmed that both materials undergo a phase transition from the cubic fluorite structure to the orthorhombic cotunnite-type structure at pressures less than 10 GPa. Both materials further transform to a hexagonal Ni2In-type structure at 84 and 36 GPa, respectively, following laser heating. This finding is consistent with theoretical calculations and the behavior of the analog compound BaF2 (Leger et al., 1995). For SrF2, the Ni2In-type phase was confirmed by Rietveld refinement. On decompression with heating, we found that Ni2In-type SrF2 passes through an intermediate orthorhombic phase at 28 GPa before returning to cotunnite structure at 22 GPa. This transition appears analogous to the isosymmetric phase transition to the Co2Si-type structure reported in PbF2 by Haines et al. (1998). Unit cell parameters and volumes were determined as a function of pressure for the new phases. We also constrained the equation of state of the cotunnite phase of CaF2 to 82 GPa. Fitting the data to a Birch-Murnaghan equation of state yields a zero-pressure bulk modulus of 97.9 GPa with a pressure derivative of 5.6 for cotunnite-type CaF2. This work represents the first synthesis and characterization of the Ni2In-type phase for these compositions and the first report of Co2Si structure in an alkaline earth fluoride.

  12. Properties of salt-grown uranium single crystals.

    SciTech Connect

    Cooley, J. C. (Jason C.); Hanrahan, R. J. (Robert J.); Hults, W. L. (William L.); Lashley, J. C. (Jason C.); Manley, M. E. (Michael E.); Mielke, C. H. (Charles H.); Smith, J. L. (James L.); Thoma, D. J. (Dan J.); Clark, R. G. (Robert G.); Hamilton, A. R.; O'Brien, J. L. (Jeremy L.); Gay, E. C. (Eddie C.); Lumpkin, N. E.; McPheeters, C. C. (Charles C.); Willit, J.; Schmiedeshoff, G. M. (George M.); Touton, S. (Sharon); Woodfield, B. F. (Brian F.); Lang, B. E. (Brian 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.

  13. Neutron Detectors Based Upon Artificial Single Crystal Diamond

    Microsoft Academic Search

    Maurizio Angelone; Giulio Aielli; Salvatore Almaviva; Roberto Cardarelli; Daniele Lattanzi; Marco Marinelli; Enrico Milani; Giuseppe Prestopino; Mario Pillon; Rinaldo Santonico; Aldo Tucciarone; Claudio Verona; Gianluca Verona-Rinati

    2009-01-01

    This paper reports about state-of-the-art artificial Single Crystal Diamond (SCD) neutron detectors based on a multilayered structure and grown by chemical vapour deposition (CVD) technique. Multilayered SCD detectors covered with a thin layer of 6LiF allow the simultaneous detection of both slow and fast neutrons and can operate in pulse and current mode. These detectors can also be produced with

  14. Stress induced transformations in Beta III Ti alloy single crystals

    Microsoft Academic Search

    J. A. Roberson; S. Fujishiro; V. S. Arunachalam; C. M. Sargent

    1974-01-01

    A combination of X-ray metallographic and transmission electron microscopy techniques have been used to investigate deformation\\u000a modes and deformation products in Beta III Ti alloy single crystals. Crystallographic slip was observed on {110}, {112} and\\u000a {113} planes. Twinning occurred on {ll2}, {332} and {2, 4.8, 4.8} planes. A martensitic transformation of the type proposed\\u000a by Blackburn and Feeney1 took place;

  15. Pockels effect in yttrium aluminum borate single crystals

    Microsoft Academic Search

    A. H. Reshak; A. Majchrowski; W. Imiolek

    2008-01-01

    Experimental measurements of linear electro-optical coefficients are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy at the wavelength of a CW semiconducting GaAlAs laser emitting at 1040 nm. We have found the values of the Pockels coefficients\\u000a to be equal to 0.21 ± 0.06 and 0.56 ± 0.08 pm\\/V for 123 and 222

  16. Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres

    Microsoft Academic Search

    Xiangdong Feng; Dean C. Sayle; Zhong Lin Wang; M. Sharon Paras; Brian Santora; Anthony C. Sutorik; Thi X. T. Sayle; Yi Yang; Yong Ding; Xudong Wang; Yie-Shein Her

    2006-01-01

    Ceria nanoparticles are one of the key abrasive materials for chemical-mechanical planarization of advanced integrated circuits. However, ceria nanoparticles synthesized by existing techniques are irregularly faceted, and they scratch the silicon wafers and increase defect concentrations. We developed an approach for large-scale synthesis of single-crystal ceria nanospheres that can reduce the polishing defects by 80% and increase the silica removal

  17. Constitutive modelling of single crystal and directionally solidified superalloys

    NASA Technical Reports Server (NTRS)

    Walker, Kevin P.; Jordan, Eric H.

    1987-01-01

    Successful attempts were made to model the deformation behavior of nickel base superalloys to be used in gas turbine engines based on both a macroscopic constitutive model and a micromechanical formulation based on crystallographic slip theory. These models were programmed as FORTRAN subroutines, are currently being used to simulate thermomechanical loading predictions expected at the fatigue critical locations on a single crystal turbine blade. Such analyses form a natural precursor to the application of life prediction methods to gas turbine airfoils.

  18. The kinetics of hydrogen diffusion in single crystal orthopyroxene

    Microsoft Academic Search

    Susan Jean Carpenter

    2003-01-01

    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)

  19. Nonpercolative metal-insulator transition in VO2 single crystals

    Microsoft Academic Search

    Bongjin Simon Mun; Kai Chen; Joonseok Yoon; Catherine Dejoie; Nobumichi Tamura; Martin Kunz; Zhi Liu; Michael E. Grass; Sung-Kwan Mo; Changwoo Park; Y. Yvette Lee; Honglyoul Ju

    2011-01-01

    Detailed temperature-dependent transport, optical microscopy, and synchrotron-based polychromatic x-ray microdiffraction measurements have been carried out in the vicinity of the metal-insulator transition (MIT) temperature of VO2 single crystals. The formation and propagation of a real-space phase boundary along the rutile c axis is monitored during the transition. Pure metallic rutile R, as well as insulating monoclinic M1 phases, is observed

  20. Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces

    Microsoft Academic Search

    D. R Mullins; S. H Overbury; D. R Huntley

    1998-01-01

    Valence band photoemission (XPS), valence band electron energy loss spectroscopy (EELS), Ce3d and 4d XPS, O1s XPS and O1s X-ray absorption (XAS) have been investigated for oxidized and sputtered single crystal CeO2 films and for oxidized Ce foil. Features were identified that distinguish between the Ce4+ or Ce3+ oxidation states. Ce4+ was identified by the highest binding energy peaks in

  1. Cascaded fourth-harmonic generation in a single nonlinear crystal

    Microsoft Academic Search

    Rosen Ivanov; Solomon Saltiel

    2005-01-01

    We investigate theoretically the process of phase-matched fourth-harmonic generation in a single quadratic crystal. In the case of a plane-wave fundamental or weak focusing, the results have an analytical form. The optimal focusing position of the fundamental beam depends on the values of the mismatches for each of the two steps of the second-order cascading: doubling of the fundamental frequency

  2. Low temperature strengthening in niobium-hydrogen single crystals

    Microsoft Academic Search

    K. V. Ravi; R. Gibala

    1971-01-01

    The mechanical behavior of high purity niobium and niobium-hydrogen single crystals at temperatures in the range 77? to 380?K\\u000a was investigated. Thermally activated hardening by hydrogen in solution is appreciable at temperatures ?150?K. However, hydride\\u000a precipitation occurs at these temperatures, can be strain-induced during mechanical testing, and accounts for the largest\\u000a part of the decrease in ductility in alloys with

  3. Elastic and Piezoelectric Coefficients of Single-Crystal Barium Titanate

    Microsoft Academic Search

    Don Berlincourt; Hans Jaffe

    1958-01-01

    Mechanical resonance and antiresonance frequencies were measured on barium titanate single-crystal elements maintained under electric dc bias from -50°C to +150°C. A complete set of elastic, piezoelectric, and dielectric constants of the tetragonal modification at 25°C is obtained. The elastic compliances show substantial deviation from cubic symmetry. Measurements in the orthorhombic state show longitudinal compliance four times higher than in

  4. High-temperature creep of forsterite single crystals

    Microsoft Academic Search

    Michel Darot; Yves Gueguen

    1981-01-01

    Creep of forsterite single crystals has been studied with respect to the orientation of the differential stress. Three orientations have been investigated: [110]c, [101]c, and [011]c. Specimens were deformed at high temperature (T?1400°C) and moderate stresses (5 < sigma<110 MPa) in a load creep apparatus at room pressure and under controlled atmosphere. Assuming Assuming, that the creep law has the

  5. Growth of niobium oxide films on single-crystal silicon

    Microsoft Academic Search

    V. A. Logacheva; N. A. Divakova; Yu. A. Tikhonova; E. A. Dolgopolova; A. M. Khoviv

    2007-01-01

    200-nm-thick niobium films grown on single-crystal silicon wafers by magnetron sputtering have been oxidized by annealing\\u000a in flowing oxygen. X-ray diffraction examination revealed the metal-like phase Nb6O in the as-deposited films. Annealing in flowing oxygen for 1 h led to the formation of tetragonal NbO2 at 570 K and hexagonal Nb2O5 at temperatures above 770 K. The grain size and

  6. Internal friction measurement in high purity tungsten single crystal

    NASA Technical Reports Server (NTRS)

    Rieu, G. E.

    1974-01-01

    Internal friction peaks observed after small deformation in high purity tungsten single crystals between liquid helium temperature and 800 K in the frequency range 30-50 KHz, are studied as a function of orientation. An orientation effect is observed in the internal friction spectra due to the creation of internal stresses. The elementary processes related to these peaks are discussed in terms of kink generation and geometric kink motion on screw and edge dislocations in an internal stress field.

  7. Electrical transport properties of CuS single crystals

    Microsoft Academic Search

    A Casaca; E B Lopes; A P Gonçalves; M Almeida

    2012-01-01

    Electrical resistivity, transverse magnetoresistance and thermoelectric power measurements were performed on CuS high quality single crystals in the range 1.2–300 K and under fields of up to 16 T. The zero field resistivity data are well described below 55 K by a quasi-2D model, consistent with a carrier confinement at lower temperatures, before the transition to the superconducting state. The

  8. Dielectric Breakdown of Single-Crystal Strontium Titanate

    Microsoft Academic Search

    Harrison H. Barrett

    1964-01-01

    Measurements of the intrinsic dielectric breakdown strength of single-crystal strontium titanate over a temperature range from ?195° to +100°C and under both pulse and dc conditions are described; dc breakdown at +100°C is thermal in origin. At room temperature and at ?40°C the breakdown strength is independent of duration of applied field and of sample configuration and hence may properly

  9. Hydrogen embrittlement in single- and poly-crystal niobium

    Microsoft Academic Search

    M. M. Farahani; F. Attia; K. Salama

    1981-01-01

    The effects of hydrogen on the yielding and the ductility of niobium have been studied in the temperature range between 373\\u000a and 78 K. Tensile tests were undertaken on single- and poly-crystal specimens containing hydrogen ranging between 30 and 230\\u000a ppm wt. at a strain rate of 1.7 X 10-4 s-1. The fracture surfaces of specimens tested were also examined

  10. Hydrogen embrittlement in single- and poly-crystal niobium

    Microsoft Academic Search

    M. M. Farahani

    1980-01-01

    The effect of dissolved hydrogen on the yielding and the ductility of both poly- and single-crystal niobium was studied in the temperature range between 78 and 373 K. Tensile tests were carried out on niobium specimens containing hydrogen ranging between 30 and 230 ppm wt., at a strain rate of 1.7 x 10 to the -4 power\\/sec. The fracture surfaces

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

    Microsoft Academic Search

    Mingsen Guo; Shuxiang Dong; Bo Ren; Haosu Luo

    2011-01-01

    At the millimeter scale, the motions or force outputs generated by conventional piezoelectric, magnetostrictive, photostrictive, or electromagnetic actuators are very limited. Here, we report a piezoelectric ultrasonic microactuator (size: 1.5 x 1.5 x 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 macroscopic, centimeter-scale linear movement

  12. A study of single crystal zirconia implanted with platinum ions

    Microsoft Academic Search

    D.-Z. Xie; D.-Z. Zhu; D.-X. Cao; Z.-Y. Zhou

    1997-01-01

    Single crystal samples of (100) oriented cubic (yttria stabilized zirconia)(YSZ) were implanted with 105 and 160 keV platinum ions, using a metal vapor vacuum are (MEVVA) high current ion implanter, to nominal doses of 2 × 1016 ions\\/cm2 and 5 × 1016 ions\\/cm2, respectively, at room temperature (RT). The implanted samples were annealed isothermally in air ambient at 850°C and

  13. A study of single crystal zirconia implanted with platinum ions

    Microsoft Academic Search

    Dong-zhu Xie; De-zhang Zhu; De-xin Cao; Zhu-yao Zhou

    1997-01-01

    Single crystal samples of ?1 0 0? oriented cubic (yttria stabilized zirconia) (YSZ) were implanted with 105 and 160 keV platinum ions, using a metal vapor vacuum arc (MEVVA) high current ion implanter, to nominal doses of 2 × 1016ions\\/cm2 and 5 × 1016ions\\/cm2, respectively, at room temperature (RT). The implanted samples were annealed isothermally in air ambient at 850°C

  14. Amplified Ferrimagnetic Echoes in Single Crystal-Polycrystal YIG Composites

    Microsoft Academic Search

    D. E. Kaplan; W. I. Dobrov; G. F. Herrmann

    1972-01-01

    To clarify the conditions for generation of amplified Hahn-type echoes in ferrimagnets, experiments were conducted with composite samples formed by imbedding single crystal YIG wafers at various positions at and near the end of a poly crystalline YIG bar of similar cross section and 4piM value. The poly crystalline component provided the internal field and field gradient needed for echo

  15. Single crystal silicon as a low-temperature structural material

    NASA Astrophysics Data System (ADS)

    Roach, P. R.

    1984-07-01

    In neutron scattering applications, it is frequently desirable to construct a sample container from a material that is strong but has very little neutron absorption of scattering. Single crystal silicon is very good by these criteria but it is difficult to work with because of its brittleness. A technique for gluing silicon was developed that yields high strength joints at low temperatures and allows very compact designs for sample containers.

  16. Shock compression and spallation of single crystal tantalum Sheng-Nian Luo

    E-print Network

    Goddard III, William A.

    Shock compression and spallation of single crystal tantalum Sheng-Nian Luo Citation: AIP Conf. Proc://proceedings.aip.org/about/rights_permissions #12;SHOCK COMPRESSION AND SPALLATION OF SINGLE CRYSTAL TANTALUM Q. An, R. Ravelo, T. C. Germann, W. Z present molecular dynamics simulations of shock-induced plasticity and spall damage in single crystal Ta

  17. NUMERICAL SIMULATIONS OF CRACK TIP STRESS-STRAIN FIELDS IN SINGLE CRYSTAL NICKEL-BASE SUPERALLOYS

    E-print Network

    Paris-Sud XI, Université de

    NUMERICAL SIMULATIONS OF CRACK TIP STRESS-STRAIN FIELDS IN SINGLE CRYSTAL NICKEL-BASE SUPERALLOYS propagation model based on local approach to fracture. 1 INTRODUCTION Single crystal Nickel-base superalloys and turbine performances. In some temperature ranges, single crystal Nickel-base superalloys are prone

  18. A LIFETIME PREDICTION MODEL FOR SINGLE CRYSTAL SUPERALLOYS SUBJECTED TO THERMOMECHANICAL

    E-print Network

    Paris-Sud XI, Université de

    of nickel based single crystal superalloys. These materials are optimized for creep resistance but are proneA LIFETIME PREDICTION MODEL FOR SINGLE CRYSTAL SUPERALLOYS SUBJECTED TO THERMOMECHANICAL CREEP for Single Crystal Superalloys operated at high temperatures and subjected to creep, fatigue and oxidation

  19. 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.

  20. Oxygen tracer diffusion in single-crystal alumina

    NASA Technical Reports Server (NTRS)

    Cawley, James D.; Halloran, John W.; Cooper, Alfred R.

    1991-01-01

    Oxygen tracer diffusion coefficients are determined in single-crystal alumina samples with differing dopant levels using the gas-exchange technique. The diffusion direction is parallel to the c-axis and the ambient PO2 is 1 atm (100,000 Pa) for all experiments except a single run with a low PO2, approximately 10 to the -15th atm (10 to the -10th Pa) produced by a CO/CO2 mixture. The diffusion is insensitive to both impurities and ambient PO2. The insensitivities are discussed in terms of point-defect clustering. Prior tracer studies are compared and discussed.

  1. Large single-crystal monolayer graphene by decomposition of methanol

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Gouri; Adams, Paul M.; Stapleton, Andrew D.; Muller, Heinrich G.; Foran, Brendan J.

    2011-10-01

    We present a novel method for the synthesis of monolayer graphene with large single-crystal domains extending over 10-30 ?m2, produced by the decomposition of methanol on Cu in a single process step, in a flow of pure Ar gas, without H2. Eliminating H2 as a process gas offers increased safety and greatly facilitates fabrication scaling. The graphene grain size and orientation were characterized by selected area electron diffraction in transmission electron microscopy. Based on analyses of effluents from the furnace during the synthesis, a possible mechanism for graphene formation from methanol, involving carbon monoxide as an intermediate, is proposed.

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

    DOEpatents

    Jantzen, Carol M. (Aiken, SC)

    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.

  3. 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.

  4. Biaxially Textured Al Film Growth on CaF2 Nanostructures toward a Method of

    E-print Network

    Wang, Gwo-Ching

    -Crystalline Si Film on Glass Substrates Huafang Li,* Patrick Snow, Ming He, Pei-I Wang,* Gwo-Ching Wang, and Toh consider- able interest in the growth of biaxi- ally crystallographic textured films on glass and flexible textured films can have comparable properties to their single- crystalline counterparts, and (b) the glass

  5. Modeling single-crystal microstructure evolution due to shock loading

    NASA Astrophysics Data System (ADS)

    Lloyd, J. T.; Clayton, J. D.; Austin, R. A.; McDowell, D. L.

    2014-05-01

    An existing high strain rate viscoplastic (HSRVP) model is extended to address single-crystal anisotropic, elastic-plastic material response and is implemented into a steady plastic wave formulation in the weak shock regime. The single-crystal HSRVP model tracks the nucleation, multiplication, annihilation, and trapping of dislocations, as well as thermally activated and phonon drag limited glide kinetics. The steady plastic wave formulation is used to model the elastic-plastic response with respect to a propagating longitudinal wave, and assumes that the magnitudes of quasi-transverse waves are negligible. This steady wave analysis does not require specification of artificial viscosity, which can give rise to spurious dissipative effects. The constitutive model and its numerical implementation are applied to single-crystal pure Al and results are compared with existing experimental data. Dislocation density evolution, lattice reorientation, and macroscopic velocity-time histories are tracked for different initial orientations subjected to varying peak shock pressures. Results suggest that initial material orientation can significantly influence microstructure evolution, which can be captured using the modified Taylor factor.

  6. Hydrogen embrittlement in single- and poly-crystal niobium

    SciTech Connect

    Farahani, M.M.

    1980-01-01

    The effect of dissolved hydrogen on the yielding and the ductility of, both poly- and single-crystal, niobium have been studied in the temperature range between 78 and 373 K. Tensile tests were carried out on niobium specimens containing hydrogen ranging between 30 and 230 ppM wt, at a strain rate of 1.7 x 10/sup -4/ sec/sup -1/. The fracture surfaces of specimens tested were also examined by means of a scanning electron microscope (S.E.M.). These studies were undertaken with the ultimate goal of determining the roles of hydrogen concentration, grain boundaries, and temperature in the embrittlement and fracture process of a representative of group VA metals. The results obtained show that the addition of 30, 80, and 130 ppM wt H has no significant effect on the yield stress of either single- or poly-crystal niobium over the entire range of temperature studied. Addition of 230 ppM wt H to single crystal niobium, however, is found to have a strengthening effect in the temperature range where hydrogen is in solid solution. At lower temperatures, where the hydride phase is to be formed, no increase in the yield stress by hydrogen is observed. The addition of hydrogen strongly influences the temperature dependence of ductility of niobium.

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

    SciTech Connect

    Liu, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Raabe, D. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Roters, F. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Arsenlis, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    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.

  8. 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.

  9. Segregation effects in Fe microalloyed NiAl single crystals

    SciTech Connect

    Vaerst, G.; Loeser, W.; Leonhardt, M.; Oswald, S. [Inst. fur Festkoerper- und Werkstofforschung Dresden (Germany)] [Inst. fur Festkoerper- und Werkstofforschung Dresden (Germany)

    1995-10-15

    The low density, excellent oxidation resistance and high thermal conductivity of the intermetallic phase NiAl compared to conventional nickel-based superalloys make NiAl based materials suitable for gas turbine applications. The lack of room-temperature ductility has been one of the barriers which hamper the technical use of the new material. Recently, a significant enhancement of room temperature tensile ductility up to 6% of soft <110> oriented NiAl single crystalline samples by microalloying with Fe, Ga or Mo was reported, compared with {approximately} 1 to 2% of binary stoichiometric NiAl. Dopant elements can display a rather inhomogeneous distribution along the crystal due to the redistribution of solute during directional solidification. Furthermore, the solute pile-up ahead of the smooth solidification front may lead to a morphological instability and to a transition from the single crystalline to a cellular/dendritic solidification mode. The scope of this paper is, therefore, to investigate the Fe distribution along the directionally solidified NiAl(Fe) crystals and possible transitions in microstructure, in order to reveal limitations for microalloying and to find out appropriate levels of dopant concentration and process parameters for homogeneously microalloyed NiAl single crystals.

  10. Atomic force microscopy of insulin single crystals: direct visualization of molecules and crystal growth.

    PubMed Central

    Yip, C M; Ward, M D

    1996-01-01

    Atomic force microscopy performed on single crystals of three different polymorphs of bovine insulin revealed molecularly smooth (001) layers separated by steps whose heights reflect the dimensions of a single insulin hexamer. Whereas contact mode imaging caused etching that prevented molecular-scale resolution, tapping mode imaging in solution provided molecular-scale contrast that enabled determination of lattice parameters and polymorph identification while simultaneously enabling real-time examination of growth modes and assessment of crystal quality. Crystallization proceeds layer by layer, a process in which the protein molecules assemble homoepitaxially with nearly perfect orientational and translational commensurism. Tapping mode imaging also revealed insulin aggregates attached to the (001) faces, their incorporation into growing terraces, and their role in defect formation. These observations demonstrate that tapping mode imaging is ideal for real-time in situ investigation of the crystallization of soft protein crystals of relatively small proteins such as insulin, which cannot withstand the lateral shear forces exerted by the scanning probe in conventional imaging modes. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 PMID:8842243

  11. A viscoplastic model with application to LiF-22 percent CaF2 hypereutectic salt

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Walker, K. P.

    1990-01-01

    A viscoplastic model for class M (metal-like behavior) materials is presented. One novel feature is its use of internal variables to change the stress exponent of creep (where n is approximately = 5) to that of natural creep (where n = 3), in accordance with experimental observations. Another feature is the introduction of a coupling in the evolution equations of the kinematic and isotropic internal variables, making thermal recovery of the kinematic variable implicit. These features enable the viscoplastic model to reduce to that of steady-state creep in closed form. In addition, the hardening parameters associated with the two internal state variables (one scalar-valued, the other tensor-valued) are considered to be functions of state, instead of being taken as constant-valued. This feature enables each internal variable to represent a much wider spectrum of internal states for the material. The model is applied to a LiF-22 percent CaF2 hypereutectic salt, which is being considered as a thermal energy storage material for space-based solar dynamic power systems.

  12. To PLAnetary Transit or not? An extremely large field of view camera with a CaF2 component tested in thermo-vacuum

    NASA Astrophysics Data System (ADS)

    Bergomi, M.; Magrin, D.; Farinato, J.; Viotto, V.; Ragazzoni, R.; Brunelli, A.; Dima, M.; Christiansen, P.; Ghigo, M.; Laubier, D.; Pasquier, H.; Piazza, D.; Pagano, I.; Piotto, G.; Basile, G.; Catala, C.

    2012-09-01

    Because of its nicely chromatic behavior, Calcium Fluoride (CaF2) is a nice choice for an optical designer as it can easily solve a number of issues, giving the right extra degree of freedom in the optical design tuning. However, switching from tablet screens to real life, the scarcity of information -and sometimes the bad reputation in term of fragility- about this material makes an overall test much more than a "display determination" experiment. We describe the extensive tests performed in ambient temperature and in thermo-vacuum of a prototype, consistent with flight CTEs, of a 200mm class camera envisaged for the PLATO (PLAnetary Transit and Oscillations of Stars) mission. We show how the CaF2 lens uneventfully succeeded to all the tests and handling procedures, and discuss the main results of the very intensive test campaign of the PLATO Telescope Optical Unit prototype.

  13. Design of a single-polarization single-mode photonic crystal fiber double-core coupler

    Microsoft Academic Search

    Jianfeng Li; Kailiang Duan; Yishan Wang; Xiangjie Cao; Yongkang Guo; Xiangdi Lin

    2009-01-01

    A simple single-polarization single-mode (SPSM) photonic crystal fiber (PCF) coupler with two cores is introduced. The full-vector finite-element method (FEM) is applied to analyze the modal interference phenomenon of the even and odd modes of two orthogonal polarizations and the power propagation within the two cores. Meanwhile, the SPSM coupling wavelength range and its corresponding coupling length for different structure

  14. Design of Wideband Single-Polarization Single-Mode Photonic Crystal Fiber

    Microsoft Academic Search

    Fangdi Zhang; Min Zhang; Xiaoyi Liu; Peida Ye

    2007-01-01

    The present paper proposes a novel design for achieving single-polarization single-mode (SPSM) operation in photonic crystal fiber (PCF), using a rectangular-lattice PCF with two lines of three central air holes enlarged. The proposed PCF that is composed entirely of silica material is modeled by a full-vector finite element method with anisotropic perfectly matched layers. The position of the region of

  15. Single-domain-like behavior in a 3-mm natural single crystal of magnetite

    Microsoft Academic Search

    Özden Özdemir; David J. Dunlop

    1998-01-01

    We have observed single-domain (SD) like behavior in a 3-mm natural single crystal of magnetite following low-temperature demagnetization (LTD), which consists of zero-field cycling through the Verwey transition to erase remanence carried by pinned domain walls. We compared stepwise alternating field (AF) and thermal demagnetization curves of 1-mT total thermoremanent magnetization (TRM), 1-mT partial TRM (pTRM) acquired between the Curie

  16. Influence of heat treatments upon the mechanical properties and in vitro bioactivity of ZrO2-toughened MgO-CaO-SiO2-P2O5-CaF2 glass-ceramics.

    PubMed

    Li, Huan-Cai; Wang, Dian-Gang; Meng, Xiang-Guo; Chen, Chuan-Zhong

    2014-09-01

    Zirconia-toughened MgO-CaO-SiO2-P2O5-CaF2 glass-ceramics are prepared using sintering techniques, and a series of heat treatment procedures are designed to obtain a glass-ceramic with improved properties. The crystallization behavior, phase composition, and morphology of the glass-ceramics are characterized. The bending strength, elastic modulus, fracture toughness, and microhardness of the glass-ceramics are investigated, and the effect mechanism of heat treatments upon the mechanical properties is discussed. The bioactivity of glass-ceramics is then evaluated using the in vitro simulated body fluid (SBF) soaking test, and the mechanism whereby apatite forms on the glass-ceramic surfaces in the SBF solution is discussed. The results indicate that the main crystal phase of the G-24 sample undergoing two heat treatment procedures is Ca5(PO4)3F (fluorapatite), and those of the G-2444 sample undergoing four heat treatment procedures are Ca5(PO4)3F and ?-CaSiO3 (?-wollastonite). The heat treatment procedures are found to greatly influence the mechanical properties of the glass-ceramic, and an apatite layer is induced on the glass-ceramic surface after soaking in the SBF solution. PMID:25280855

  17. 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., Jr.; 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?? ?? 0.0013 A??, and c=12.9954 A?? ?? 0.0034 A??) agreed well with the values obtained from the single crystal spheres.

  18. Phosphorus distribution between carbon-saturated iron at 1350 °C and lime-based slags containing Na 2 O and CaF 2

    Microsoft Academic Search

    W. H. Van Niekerk; R. J. Dippenaar

    1998-01-01

    The Corex process is capable of consistently producing hot metal with very low silicon contents (<0.1 pct), and as a consequence,\\u000a its hot metal is ideally suited for the external removal of phosphorus. Various studies have shown that small additions of\\u000a Na2O significantly enhance the ability of lime-based slags to dephosphorize liquid iron. Additions of fluxes (such as CaF2) may

  19. Particle size effect in CaF2:Mn\\/Teflon TLD response at photon energies from 5-1250 keV

    Microsoft Academic Search

    G. A. Carlson; L. Lorence; D. W. Vehar; R. S. Klingler

    1990-01-01

    Thermoluminescent dosimeters (TDLs) fabricated by embedding CaF 2:Mn powder in a Teflon matrix (TTLDs) are sometimes used to monitor dose in silicon-device radiation effects experiments. A potential advantage of TTLDs over other types of TLDs for this application is that their weighted-average mass energy-absorption coefficient is near that of Si. Experimental results are presented which demonstrate that for moderate-energy X-rays,

  20. Influence of CaF2 and Li2O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na2O

    NASA Astrophysics Data System (ADS)

    Park, Hyun Shik; Kim, Hyuk; Sohn, Il

    2011-04-01

    Understanding the viscous behavior of silica-based molten fluxes is essential in maintaining the reliability of steel casting operations and in preventing breakouts. In particular, high concentrations of aluminum in recently developed transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels tend to promote reduction of silica in the mold fluxes that result in the formation of alumina, which in turn increases the viscosity. To counteract this effect, significant amounts of fluidizers such as CaF2 and Li2O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO2-12 wt pct Na2O with various concentrations of CaF2 and Li2O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF2 additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF2 concentrations above this level had a negligible effect on viscosity. Li2O additions up to 2 wt pct were also effective in decreasing the viscosity, but the effect was comparatively negligible above 2 wt pct. Using Fourier transform infrared (FTIR) analysis of as-quenched slag samples, it was concluded that the viscosity was controlled more effectively by changing the larger complex silicate structures of rings and chains than by changing the amounts of simpler dimers and monomers.

  1. Electrodeposition and characterization of Al 2O 3–Cu(Sn), CaF 2–Cu(Sn) and talc–Cu(Sn) electrocomposite coatings

    Microsoft Academic Search

    Y. L Wang; Y. Z Wan; Sh. M Zhao; H. M Tao; X. H Dong

    1998-01-01

    Electrocomposite coatings consisting of Al2O3, CaF2, talc particles and copper–tin alloy were prepared by means of the conventional electrodeposition technique. The effects of cathode current density, particle concentration in the bath and stir rate on the volume percentage of particles Vp in the composite coatings were investigated. It was shown that current density, effective particle concentration in the plating solution

  2. Spectral hole burning of Eu 2+ in MBE-grown superlattices of CaF 2: Eu 2+ CdF 2

    Microsoft Academic Search

    D. M. Boye; Y. Sun; R. S. Meltzer; S. P. Feofilov; N. S. Sokolov; A. Khilko; J. C. Alvarez

    1997-01-01

    Persistent spectral hole burning is observed for the 413 nm 4f7(8S72) ? 4f65d(?8) zero-phonon transition of Eu2+ in MBE-grown superlattices of CaF2:Eu2+CdF2 on Si(111). Possible mechanisms for the trapping of the photoionized electron are discussed in terms of the band offsets of the superlattice layers.

  3. 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.

  4. Strength anomaly in B2 FeAl single crystals

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H. [Oak Ridge National Lab., TN (United States); Matsumoto, N. [Tohoku Univ. (Japan). Graduate School

    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.

  5. Plastic deformation of Ni{sub 3}Nb single crystals

    SciTech Connect

    Hagihara, Kouji; Nakano, Takayoshi; Umakoshi, Yukichi

    1999-07-01

    Temperature dependence of yield stress and operative slip system in Ni{sub 3}Nb single crystals with the D0{sub a} structure was investigated in comparison with that in an analogous L1{sub 2} structure. Compression tests were performed at temperatures between 20 C and 1,200 C for specimens with loading axes perpendicular to (110), (331) and (270). (010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {l{underscore}brace}211{r{underscore}brace}{lt}{bar 1}{bar 0} 7 13{gt} twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 C and 800 C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni{sub 3}Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L1{sub 2}-type compounds.

  6. Electronic properties of graphene-single crystal diamond heterostructures

    SciTech Connect

    Zhao, Fang; Thuong Nguyen, Thuong; Golsharifi, Mohammad; Amakubo, Suguru; Jackman, Richard B., E-mail: r.jackman@ucl.ac.uk [London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London, 17-19 Gordon Street, London WC1H 0AH (United Kingdom); Loh, K. P. [Department of Chemistry, National University of Singapore, 3 Science Drive, Singapore 117543 (Singapore)

    2013-08-07

    Single crystal diamond has been used as a substrate to support single layer graphene grown by chemical vapor deposition methods. It is possible to chemically functionalise the diamond surface, and in the present case H-, F-, O-, and N-group have been purposefully added prior to graphene deposition. The electronic properties of the resultant heterostructures vary strongly; a p-type layer with good mobility and a band gap of ?0.7?eV is created when H-terminated diamond layers are used, whilst a layer with more metallic-like character (high carrier density and low carrier mobility) arises when N(O)-terminations are introduced. Since it is relatively easy to pattern these functional groups on the diamond surface, this suggests that this approach may offer an exciting route to 2D device structures on single layer graphene sheets.

  7. Single crystal growth and mechanical properties of MoSi2 and WSi2

    Microsoft Academic Search

    T. Hirano; M. Nakamura; K. Kimura; Y. Umakoshi

    1991-01-01

    A floating zone (FZ) furnace was modified into a high vacuum type furnace in order to grow high-purity single crystals of MoSi2 and WSi2. The impurity levels of the grown MoSi2 single crystals were very low and the residual resistivity ratio was large, indicating that the grown crystals were of good quality. Compression tests of MoSi2 and WSi2 single crystals

  8. Optical Properties of a Piezoelectric Ta2O5 Single Crystal Film

    Microsoft Academic Search

    Yasuhiko Nakagawa; Isao Morita; Masashi Takahashi; Shoji Kakio

    2007-01-01

    Following the production of a uniaxially oriented Ta2O5 thin film on a single crystal substrate (X-cut LiTaO3) by RF sputtering, a Ta2O5 single-crystal film was created using linear rapid thermal annealing. Then the reflection high-energy electron diffraction (RHEED) pattern and X-ray diffraction pattern of the Ta2O5 single-crystal film were measured to examine its crystallization level. A refractive index tensor was

  9. A measurement of the temperature dependence of the absorption edge of single crystals, using polarized light 

    E-print Network

    Dunham, Robert Latham

    1964-01-01

    ~ ~ ~ ~ ~ . . ~ ~ ~ ~ ~ 24 4 Absorption of Iodine Single Crystals ~ ~ . . ~ ~ . ~ ~ 25 5 Absorption of Cadmium Sulfide Single Crystals ~ ~ 26 INTRODUCTION The objective of this particular research is to determine the absorption edge of single, molecular crystals... in the attempt to determine the absorption edge of the crystal for temperatures varying from SO'K to room temperature Principal drawbacks in the study of iodine are its physical and chemical properties. Its high vapor pressure, even at room temperature...

  10. Crystal structures of carbonates up to Mbar pressures determined by single crystal synchrotron radiation diffraction

    NASA Astrophysics Data System (ADS)

    Merlini, M.

    2013-12-01

    The recent improvements at synchrotron beamlines, currently allow single crystal diffraction experiments at extreme pressures and temperatures [1,2] on very small single crystal domains. We successfully applied such technique to determine the crystal structure adopted by carbonates at mantle pressures. The knowledge of carbon-bearing phases is in fact fundamental for any quantitative modelling of global carbon cycle. The major technical difficulty arises after first order transitions or decomposition reactions, since original crystal (apx. 10x10x5 ?m3) is transformed in much smaller crystalline domains often with random orientation. The use of 3D reciprocal space visualization software and the improved resolution of new generation flat panel detectors, however, allow both identification and integration of each single crystal domain, with suitable accuracy for ab-initio structure solution, performed with direct and charge-flipping methods and successive structure refinements. The results obtained on carbonates, indicate two major crystal-chemistry trends established at high pressures. The CO32- units, planar and parallel in ambient pressure calcite and dolomite structures, becomes non parallel in calcite- and dolomite-II and III phases, allowing more flexibility in the structures with possibility to accommodate strain arising from different cation sizes (Ca and Mg in particular). Dolomite-III is therefore also observed to be thermodynamically stable at lower mantle pressures and temperatures, differently from dolomite, which undergoes decomposition into pure end-members in upper mantle. At higher pressure, towards Mbar (lowermost mantle and D'' region) in agreement with theoretical calculations [3,4] and other experimental results [5], carbon coordination transform into 4-fold CO4 units, with different polymerisation in the structure depending on carbonate composition. The second important crystal chemistry feature detected is related to Fe2+ in Fe-bearing magnesite, which spontaneously oxidises at HP/HT, forming Fe3+ carbonates, Fe3+ oxides and reduced carbon (diamonds). Single crystal diffraction approach allowed full structure determination of these phases, yielding to the discovery of few unpredicted structures, such as Mg2Fe2C4O13 and Fe13O19, which can be well reproduced in different experiments. Mg2Fe2C4O13 carbonate present truncated chain C4O13 groups, and Fe13O19 oxide, whose stoichiometry is intermediate between magnetite and hematite, is a one-layer structure, with features encountered in superconducting materials. The results fully support the ideas of unexpected complexities in the mineralogy of the lowermost mantle, and single crystal technique, once properly optimized in ad-hoc synchrotron beamlines, is fundamental for extracting accurate structural information, otherwise rarely accessible with other experimental techniques. References: [1] Merlini M., Hanfland M. (2013). Single crystal diffraction at Mbar conditions by synchrotron radiation. High Pressure Research, in press. [2] Dubrovinsky et al., (2010). High Pressure Research, 30, 620-633. [3] Arapan et al. (1997). Phys. Rev. Lett., 98, 268501. [4] Oganov et al. (2008) EPSL, 273, 38-47. [5] Boulard et al. (2011) PNAS, 108, 5184-5187.

  11. Quantitative layer analysis of single crystal surfaces by LEIS

    NASA Astrophysics Data System (ADS)

    Beikler, Robert; Taglauer, Edmund

    2002-06-01

    The quantitative interpretation of energy and angle resolved low-energy ion scattering intensity distributions is achieved by comparing the experimental results with those from numerical simulations using the MARLOWE code with extensions for layer selective analysis. The example used is the CuAu(1 0 0) alloy crystal surface. For adequate analysis the potential parameter (i.e. the screening length) has to be calibrated. This is done by using elemental single crystal standards. Anisotropic thermal vibrations are taken into account in correspondence with published Debye temperature values. Neutralization effects are found to be of minor importance for Na + and He + scattering from CuAu. A quantitative analysis of the first and second layer composition of CuAu(1 0 0) as a function of temperature could thus be obtained, the results being in good agreement with theoretical predictions.

  12. Multiband Effects on -FeSe single crystals

    SciTech Connect

    Petrovic C.; Lei, H.; Graf, D.; Hu, R.; Ryu, H.; Choi, E.S.; Tozer, S.W.

    2012-03-01

    We present the upper critical fields {mu}{sub 0}H{sub c2}(T) and Hall effect in {beta}-FeSe single crystals. The {mu}{sub 0}H{sub c2}(T) increases as the temperature is lowered for fields applied parallel and perpendicular to (101), the natural growth facet of the crystal. The {mu}{sub 0}H{sub c2}(T) for both field directions and the anisotropy at low temperature increase under pressure. Hole carriers are dominant at high magnetic fields. However, the contribution of electron-type carriers is significant at low fields and low temperature. Our results show that multiband effects dominate {mu}{sub 0}H{sub c2}(T) and electronic transport in the normal state.

  13. Conoscopic study of strontium-barium niobate single crystals

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Aleksandr; Grechishkin, Rostislav; Malyshkina, Olga; Malyshkin, Yury; Dec, Jan; ?ukasiewicz, Tadeusz; Ivanova, Aleksandra

    2013-12-01

    Optically transparent single crystals of strontium-barium niobate, SrxBa1-xNb2O6, of different compositions (x = 0.26...0.7) were examined with the aid of conoscopic light interference figures. A regular change of the isochrome concentric ring number and diameters consistent with the temperature variation of the value of birefringence is demonstrated by direct observations of polar cuts of optically uniaxial samples. Anomalous violations of the conventional (uniaxial) interference patterns occur occasionaly in some samples being indicative of the existence of biaxial trait in their behaviour even though no voltage is applied. These features may depend on annealing treatments at elevated temperatures. The results of the study show that conoscopic images may serve as a sensitive indicator of the structural state of SBN crystals related to the effects of stress-induced change of optical anisotropy and temperature dependent birefringence parameters.

  14. 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.

  15. The Thermoanalysis of Metal Single Crystals and a New Thermoelectric Effect of Bismuth Crystals Grown in Magnetic Fields

    Microsoft Academic Search

    Alexander Goetz; Maurice F. Hasler

    1930-01-01

    Part I. The Thermoanalysis of Bi Single Crystals Production of crystals.-Crystals of Bi of any desired orientation were grown by the method of Goetz, one half of each normally, the other half within a transversal magnetic field. The orientations, predetermined by a seed crystal, were not affected by this process. Two methods of growth-the continuous and the discontinuous-were used. The

  16. 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.

  17. Bending behavior of a flexible single crystal nanomembrane photonic crystal cavity

    NASA Astrophysics Data System (ADS)

    Xu, Xiaochuan; Subbaraman, Harish; Chen, Ray T.

    2015-02-01

    In this paper, we present experimental and theoretical studies on the bending induced resonance shift of a photonic crystal cavity. The photonic crystal devices are fabricated on a 2cm x 2cm large-area single crystal SiNM which is transferred defect-freely onto a Kapton substrate with an SU-8 bottom cladding. Photonic crystal tapers are implemented at the strip-photonic crystal waveguide interfaces, which lowers the coupling loss and enables operation closer to the band edge. Subwavelength grating (SWG) couplers are employed at the input and output of the device in order to enable device characterization. The device is mounted on the two jaws of a caliper and it can be buckled up and down through sliding one of the jaws. The bending radius at the top of the curvature can be estimated with the length of the specimen and the distance between the two jaws. A minimum bending radius of 5 mm is achieved. Finite element method (FEM) is used to simulate the deformation and the strain of the nanomembrane. The results are used as the input of finite difference time-domain (FDTD) simulation. The analysis shows that the strain sensitivities are 0.673 pm/??, 0.656 pm/??, 0.588 pm/??, and 0.591 pm/??, for longitudinal face-out, longitudinal face-in, transverse face-out, and transverse face-in bending, respectively.

  18. 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. PMID:19375336

  19. Mechanical properties of haynes® alloy 188 after exposure to LiF22CaF 2 , air, and vacuum at 1093 K for periods up to 10,000 hours

    Microsoft Academic Search

    J. D. Whittenberger

    1992-01-01

    As part of a program to provide reassurance that the cobalt- base superalloy Haynes? Alloy 188 can adequately contain a LiF-\\u000a CaF2 eutectic thermal energy storage salt, 4900- and 10,000- hr exposures of Haynes? Alloy 188 to LiF- 22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized\\u000a and the

  20. Growth of High Quality A N Single Crystals and Their Optical Properties

    E-print Network

    Nabben, Reinhard

    Growth of High Quality A N Single Crystals and Their Optical Properties M. strassburgl, J a two-step growth process in a TaN crucible. Crystal defects and the effect of incorporated impurities,2,3]. Hence, the growth and crystal quality opiimhtion of buk AiN crystals is of primary importance

  1. Single crystal NMR studies of high temperature superconductors

    SciTech Connect

    Pennington, C.H.; Durand, D.J.; Zax, D.B.; Slichter, C.P.; Rice, J.P.; Bukowski, E.D.; Ginsberg, D.M.

    1989-01-01

    The authors report Cu NMR studies in the normal state of a single crystal of the T/sub c/ = 90 K superconductor YBa/sub 2/Cu/sub 3/O/sub 7/minus/delta/. The authors have measured the magnetic shift tensor, the electric field gradient tensor, the nuclear spin-lattice relaxation rate tensor, and the time dependence and functional form of the transverse decay. From these data they obtain information about the charge state and magnetic state of the Cu atoms, and the existence and size of the electronic exchange coupling between spins of adjacent Cu atoms. 18 refs., 3 figs., 2 tabs.

  2. Thin single-crystal Ge layers on 2? Si substrates

    NASA Astrophysics Data System (ADS)

    Shengurov, V. G.; Denisov, S. A.; Chalkov, V. Yu.; Buzynin, Yu. N.; Drozdov, M. N.; Buzynin, A. N.; Yunin, P. A.

    2015-01-01

    Conditions for preparing thin homogeneous mirror-smooth Ge layers on 2? Si substrates by hot wire chemical vapor-phase deposition have been determined. Ge layers 200 nm thick have a structure of epitaxial mosaic single crystal with almost completely relaxed elastic stresses. The X-ray diffraction rocking curve half-width is less than 6'. The density of grown-in dislocations in Ge layers is in the range of (3-6) × 105 cm-2, and the rms surface roughness does not exceed 0.8 nm.

  3. Polarization-dependent exciton dynamics in tetracene single crystals.

    PubMed

    Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min

    2014-12-28

    We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors. PMID:25554147

  4. Polarization-dependent exciton dynamics in tetracene single crystals

    E-print Network

    Zhang, Bo; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min

    2014-01-01

    We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.

  5. Polarization-dependent exciton dynamics in tetracene single crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min

    2014-12-01

    We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.

  6. EPR studies of gamma-irradiated taurine single crystals

    NASA Astrophysics Data System (ADS)

    Bulut, A.; Karabulut, B.; Tapramaz, R.; Köksal, F.

    2000-04-01

    An EPR study of gamma-irradiated taurine [C 2H 7NO 3S] single crystal was carried out at room temperature. The EPR spectra were recorded in the three at mutually perpendicular planes. There are two magnetically distinct sites in monoclinic lattice. The principle values of g and hyperfine constants for both sites were calculated. The results have indicated the presence of 32?O -2 and 33?O -2 radicals. The hyperfine values of 33?O -2 radical were used to obtain O-S-O bond angle for both sites.

  7. Characterization of defects in ?-Ga2O3 single crystals

    NASA Astrophysics Data System (ADS)

    Nakai, Katsuhiko; Nagai, Tetsuya; Noami, Kengo; Futagi, Toshiro

    2015-05-01

    We have investigated defects in beta-type gallium oxide (?-Ga2O3) single crystals by X-ray topography, selective etching, and transmission electron microscopy. Two types of defects, namely, dislocations and nanopipes, were found. Dislocations are screw dislocations with Burgers vector parallel to [010]. The majority of them lie on (\\bar{2}01) and (001). Nanopipes are hollow pipes of 0.1 µm diameter and of at least 15 µm length elongated along [010]. No strain field was found around them. From the observation results, we have discussed the formation mechanisms of these defects.

  8. Coherent Josephson phase qubit with a single crystal silicon capacitor

    NASA Astrophysics Data System (ADS)

    Patel, U.; Gao, Y.; Hover, D.; Ribeill, G. J.; Sendelbach, S.; McDermott, R.

    2013-01-01

    We have incorporated a single crystal silicon shunt capacitor into a Josephson phase qubit. The capacitor is derived from a commercial silicon-on-insulator wafer. Bosch reactive ion etching is used to create a suspended silicon membrane; subsequent metallization on both sides is used to form the capacitor. The superior dielectric loss of the crystalline silicon leads to a significant increase in qubit energy relaxation times. T1 times up to 1.6 ?s were measured, more than a factor of two greater than those seen in amorphous phase qubits. The design is readily scalable to larger integrated circuits incorporating multiple qubits and resonators.

  9. Raman Investigations of Rare Earth Arsenate Single Crystals

    SciTech Connect

    Barros, G [Universidade Federal do Ceara, Ceara, Brazil; Santos, C. C. [Universidade Federal do Ceara, Ceara, Brazil; Ayala, A. P. [Universidade Federal do Ceara, Ceara, Brazil; Guedes, I. [Universidade Federal do Ceara, Ceara, Brazil; Boatner, Lynn A [ORNL; Loong, C. K. [Sun Yat-Sen University, Guangzhou, China

    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.

  10. Two-Photon Absorption Spectrum of a Single Crystal Cyanine-like Honghua Hu,

    E-print Network

    Van Stryland, Eric

    Two-Photon Absorption Spectrum of a Single Crystal Cyanine-like Dye Honghua Hu, Dmitry A. Fishman Vegas, New Mexico 87701, United States *S Supporting Information ABSTRACT: The two-photon absorption (2PA) spectrum of an organic single crystal is reported. The crystal is grown by self

  11. Growth of Nd2TiO5 single crystal using optical floating zone technique

    NASA Astrophysics Data System (ADS)

    Murugesan, G.; Nithya, R.; Kalainathan, S.; Ravindran, T. R.

    2015-06-01

    Single crystals of Nd2TiO5 were grown using Optical Floating zone technique in oxygen atmosphere by spontaneous nucleation. Powder X-ray diffraction pattern showed that the grown single crystal is of homogeneous composition. Laue diffraction was recorded in both transmission and backscattering geometries to check the crystal quality. Vibrational properties were analyzed using Raman measurements.

  12. Orientation dependence of plastic deformation in nickel-based single crystal superalloys: Discretecontinuous model simulations

    E-print Network

    Devincre, Benoit

    Orientation dependence of plastic deformation in nickel-based single crystal superalloys: Discrete of single-crystal nickel-based superalloys is simulated. At 1123 K, two uniaxial tensile loading cases crystals of nickel-based superalloys are specifically developed for high-temperature applications [1

  13. Ablation of ionic crystals induced by capillary-discharge XUV laser

    NASA Astrophysics Data System (ADS)

    Pira, Peter; Burian, Tomáš; Vyšín, Ludék; Chalupský, Jaromír; Lan?ok, Ján; Wild, Jan; St?ižík, Michal; Zelinger, Zden?k; Rocca, Jorge J.; Juha, Libor

    2011-06-01

    Single crystals of two fluorides (LiF and CaF2) and a tungstate (PbWO4) were irradiated by nanosecond pulses of 46.9- nm radiation provided by 10-Hz capillary-discharge Ne-like Ar laser (CDL). The damage threshold was determined in LiF using the CDL beam focused by a Sc/Si multilayer-coated spherical mirror. Irradiated samples have been investigated by Nomarski (DIC - Differential Interference Contrast) microscopy and optical (WLI - white light intereferometry) profiler. After an exposure by a certain number of CDL pulses, an ablation rate can be calculated from WLI measured depth of the crater created by the XUV ablation. Potential use of XUV ablation of ionic crystals in pulsed laser deposition (PLD) of thin layers of such a particular material, which is difficult to ablate by conventional UV-Vis- NIR lasers, is discussed in this contribution.

  14. Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal.

    PubMed

    Sudhahar, S; Krishna Kumar, M; Sornamurthy, B M; Mohan Kumar, R

    2014-01-24

    Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. PMID:24184578

  15. Pockels effect in yttrium aluminum borate single crystals

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Majchrowski, A.; Imiolek, W.

    2008-10-01

    Experimental measurements of linear electro-optical coefficients are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy at the wavelength of a CW semiconducting GaAlAs laser emitting at 1040 nm. We have found the values of the Pockels coefficients to be equal to 0.21 ± 0.06 and 0.56 ± 0.08 pm/V for 123 and 222 Pockels components, respectively. Additional measurements performed for the thin-cut samples with the thickness varying within the 100 500 ?m have confirmed the values of the corresponding parameters. We have eliminated a contribution of the piezooptical coefficients as well as for other disturbing factors. We have established that the crystals with a different number of defects do not show any differences, which indicate the principal role of the borate clusters on the observed effects. The temperature changes are very low (due to a low ionic contribution), and do not exceed 5 6%, which indicates the low contribution of the electron-phonon to the Pockels effect. Because the YAB crystals possess a very large photothermal damage (more than 15 GW/cm2) and are only slightly temperature dependent. Hence, they may be proposed as promising materials for high-power laser electro-optic modulators.

  16. Plastic anisotropy in MoSi{sub 2} single crystals

    SciTech Connect

    Mitchell, T.E.; Maloy, S.A.

    1993-05-01

    Single crystals Of MoSi{sub 2} are an order of magnitude stronger when compressed along [001] than along any other orientation. This is because the easy slip systems, <101><100> and <110><111>, have a zero Schmid factor acting on them so that harder slip systems are forced into operation. We find that [001] crystals compressed at 1OOO{degree}C yield by slip on <103><331>. TEM shows that the 1/2<331> dislocations tend to decompose into 1/2<111> and <110> dislocations. This decomposition process apparently inhibits the mobility of 1/2<331> dislocations at higher temperatures and another system, <101><1ll>, becomes operative at 1300{degree}C and above. [021] crystals have been tested for comparison and are found to yield at much lower stresses on the easy systems. In the design of advanced high temperature structural materials based on MOSi{sub 2}, the large plastic anisotropy should be used to advantage.

  17. Hydrogen migration in single crystal and polycrystalline zinc oxide

    NASA Astrophysics Data System (ADS)

    Nickel, N. H.

    2006-05-01

    Hydrogen diffusion in single crystal and polycrystalline zinc oxide was investigated by deuterium diffusion and hydrogen effusion experiments. Deuterium concentration depth profiles were measured as a function of the passivation temperature, while in H effusion experiments the molecular hydrogen flux was measured as a function of the heating rate. The diffusion coefficient exhibits thermally activated behavior and varies between EA=0.17 and 0.37eV . The change of EA is accompanied by a change of the diffusion prefactor by eight orders of magnitude. This indicates that EA is not related to the energetic position of H transport sites or the barrier height between such sites. Using the microscopic diffusion prefactor, the position of the hydrogen chemical potential, ?H , was estimated. With increasing temperature, ?H decreases with a rate of ?0.0013eV/K . At H concentrations of less than 1017cm-3 ?H is pinned. The hydrogen density of states was derived from H effusion data, which is consistent with a diffusion activation of about 1.0eV as was originally reported by Mollwo [Z. Phys. 138, 478 (1954)] and Thomas and Lander [J. Chem. Phys. 25, 1136 (1956)]. Clear evidence for hydrogen deep traps was found in single crystal and polycrystalline ZnO .

  18. 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.

  19. Self-assembled single-crystal silicon circuits on plastic

    PubMed Central

    Stauth, Sean A.; Parviz, Babak A.

    2006-01-01

    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-?m-sized elements. High-yield self-assembly of micrometer-scale functional devices as outlined here provides a powerful approach for production of macroelectronic systems. PMID:16968780

  20. 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.

  1. Tantalum Shear Modulus from Homogenization of Single Crystal Data

    SciTech Connect

    Becker, R

    2007-09-14

    Elastic constants for tantalum single crystals have been calculated by Orlikowski, et al. [1] for a broad range of temperatures and pressures. These moduli can be utilized directly in continuum crystal simulations or dislocation dynamics calculations where the individual grains of the polycrystalline material are explicitly represented. For simulations on a larger size scale, the volume of material represented by the quadrature points of the simulation codes includes many grains, and average moduli are needed. Analytic bounding and averaging schemes exist, but since these do not account for nonuniform stress and strain within the interacting grains, the upper and lower bounds tend to diverge as the crystal anisotropy increases. Local deformation and stress equilibrium accommodate the anisotropic response of the individual grains. One method of including grain interactions in shear modulus averaging calculations is through a highly-descretized finite element model of a polycrystal volume. This virtual test sample (VTS) can be probed to determine the average response of the polycrystal. The desire to obtain isotropic moduli imposes attributes on the VTS. The grains should be equiax and the crystal orientation distribution function should be random. For these simulations, a cube, 300 {micro}m on a side, was discretized with 1 million finite elements on a regular rectangular mesh. The mesh was seeded with 1000 grains generated using a constrained-random placement algorithm, Figure 1. Since the orientations were simply painted in the mesh, the grain boundaries are irregular. The orientation distribution function is shown as pole figure in Figure 2. It has the appearance of being random. Analysis of the simulation results will be used to determine if the randomness of the texture and number of grains are adequate.

  2. 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.

  3. 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.

  4. The Ni and Co substitutions in iron chalcogenide single crystals

    NASA Astrophysics Data System (ADS)

    Bezusyy, V. L.; Gawryluk, D. J.; Malinowski, A.; Berkowski, M.; Cieplak, Marta Z.

    2015-03-01

    We study the ab-plane resistivity and Hall effect in Fe1-yMyTe0.65Se0.35 single crystals with M =Co or Ni, and y up to 0.2. The crystals are grown by Bridgman's method. The low-temperature Hall coefficient RH changes sign to negative for crystals with y exceeding 0.135 (Co) and 0.06 (Ni), consistent with the electron doping induced by these impurities. However, the RH remains positive for all samples at high T, suggesting that remnant hole pockets survive the doping, but the holes become localized at low T in heavily doped crystals. Superconducting transition temperature (Tc) approaches zero for y = 0.14 (Co), and 0.03 (Ni), while the resistivity at the Tc onset is only weakly affected by Co doping, but it increases strongly for the Ni. These results suggest that in case of Co impurity the Tc suppression may be attributed to electron doping. On the other hand, the Ni substitution, in addition to electron doping, induces strong localization effects at small impurity contents. Using two-band conduction model we argue that the localization of electron carriers is responsible for strong superconductivity suppression by Ni impurity. Supported by EC through the FunDMS Advanced Grant of the ERC (FP7 Ideas), by the Polish NCS Grant 2011/01/B/ST3/00462, and by the French-Polish Program PICS 2012. Performed in the laboratories co-financed by NanoFun Project POIG.02.02.00-00-025/09.

  5. 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.

  6. Characterization of pure and urea-doped ?-glycine single crystals grown by solution method

    Microsoft Academic Search

    P. Selvarajan; J. Glorium Arul Raj; S. Perumal

    2009-01-01

    Pure and urea-doped gamma-glycine (?-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in ?-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV–visible transmittance

  7. Synthesis, Growth, Spectral and Optical Properties of Glycinyl Urea Single Crystal

    SciTech Connect

    Shanthi, N. Theresita [Department of Physics, V. V. College of engineering, Thisaiyanvilai-627 657, Tamilnadu (India); Selvarajan, P. [Department of Physics, Aditanar College of Arts and Science, Tiruchendur-628 216, Tamilnadu (India); Rose, A. S. J. Lucia [Department of Physics, St. Mary's College, Thoothukudi-628 001, Tamilnadu (India)

    2011-10-20

    Single crystals of Glycinyl Urea were grown from aqueous solution by slow evaporation technique at room temperature. The cell parameters of the grown crystals were estimated by Single X-ray diffraction studies. The functional groups present in the grown crystals were ascertained using FTIR spectrum analysis. UV-visible transmittance spectrum was recorded to study the optical transparency of the grown crystal. The non-linear optical property has been tested by Kurtz powder technique.

  8. The impact of shell host (NaYF4/CaF2) and shell deposition methods on the up-conversion enhancement in Tb3+, Yb3+ codoped colloidal ?-NaYF4 core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Prorok, Katarzyna; Bednarkiewicz, Artur; Cichy, Bartlomiej; Gnach, Anna; Misiak, Malgorzata; Sobczyk, Marcin; Strek, Wieslaw

    2014-01-01

    Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal ?-NaYF4:Yb3+, Tb3+ doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF4 and CaF2), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF4:Yb3+, Tb3+ core-shell NPs for multi-color emission and spectral multiplexing has been presented.Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal ?-NaYF4:Yb3+, Tb3+ doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF4 and CaF2), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF4:Yb3+, Tb3+ core-shell NPs for multi-color emission and spectral multiplexing has been presented. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05412h

  9. Flux growth and characterizations of NdPO 4 single crystals

    Microsoft Academic Search

    Yongzheng Wang; Jing Li; Jiyang Wang; Shujuan Han; Yongjie Guo

    2010-01-01

    Neodymium phosphate single crystals, NdPO4, have been grown by a flux growth method using Li2CO3-2MoO3 as a flux. The as-grown crystals were characterized by X-ray powder diffraction(XRPD), differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques. The results show that the as-grown crystals were well crystallized. The crystal was stable over the temperature range from 26 to 1200°C in N2.

  10. Studies on synthesis, growth, structural, optical properties of organic 8-hydroxyquinolinium succinate single crystals

    NASA Astrophysics Data System (ADS)

    Thirumurugan, R.; Anitha, K.

    2014-04-01

    8-hydroxyquinolinium succinate (8HQSU), an organic material has been synthesized and single crystals were grown by employing the technique of slow evaporation. The structure of the grown crystal was elucidated by using single crystal X-ray diffraction analysis. 8HQSU crystal belongs to the monoclinic crystallographic system with non-centro symmetric space group of P21. FT-IR spectral investigation has been carried out to identify the various functional groups present in the grown crystal. UV-vis spectral studies reveal that 8HQSU crystals are transparent in the entire visible region and the cut-off wavelength has been found to be 220nm.

  11. Preparation, characterization and magnetic properties of an ordered FeCo single crystal

    E-print Network

    McHenry, Michael E.

    Preparation, characterization and magnetic properties of an ordered FeCo single crystal S.-Y. Chu Laboratory, Washington, DC 20375 Pristine FeCo single crystals with millimeter dimensions were prepared by annealing FeCo ingot samples. The composition and microstructure of a fine polished cylindrical single

  12. Mechanical behavior and microstructure of fatigued aluminium single crystals

    SciTech Connect

    Giese, A. (Technical Univ. Hamburg (Germany)); Estrin, Y. (Univ. of Western Australia, Nedlands (Australia))

    1993-04-01

    For many decades the fatigue behavior of metallic materials has been a subject of intensive studies. Most profoundly investigated are Cu single crystals. A prominent feature of mechanical behavior in cyclically deformed pure Cu, Ni and other fee metals is the occurrence of a plateau in the cyclic stress-strain curve. A characteristic microstructure developing in these metals under cyclic loading exhibits bands of localized strain referred to as persistent slip bands (PSBs). Scarce experimental data on the mechanical response of Al to cyclic loading indicate that at room temperature the behavior of this material differs from that of Cu and Ni. This motivated the present study aiming to obtain more data and to get a better insight into the properties of Al under tension-compression loading. High purity Al single crystals oriented for single slip were tested under cyclic tension-compression conditions at two temperatures (T = 298 K and T = 78 K). For aluminum, the room temperature corresponds to a relatively high homologous temperature of about 0.3. Given the large stacking-fault energy of Al, its fatigue behavior at this temperature can be placed in the category of high-temperature behavior of pure fcc metals. At the liquid nitrogen temperature the dislocation motion tends to become more planar which leads to dislocation structures resembling those found in Cu and other pure fcc metals cyclically deformed at room temperature. A plateau in the cyclic hardening curve associated with the occurrence of the PSBs was found in the fatigued specimens, which is at variance with the cyclic hardening behavior for relatively homogeneous room temperature deformation in tension-compression.

  13. 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.

  14. 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.

  15. High-Temperature Thermoelectric Properties of NaxCoO2-delta Single Crystals

    Microsoft Academic Search

    Kenjiro Fujita; Tadashi Mochida; Kazuo Nakamura

    2001-01-01

    We measure the high-temperature thermoelectric properties of the NaxCoO2-delta single crystal for the first time. The NaxCoO2-delta single crystals are prepared by a flux technique, and the resulting flaky single crystals are very thin on the c-axis. The in-plane electrical resistivity (rho), the thermoelectric power (S) and the in-plane thermal conductivity (kappa) are measured in the range of 300 K

  16. Floating Zone Growth and Scintillation Characteristics of Cerium-Doped Gadolinium Pyrosilicate Single Crystals

    Microsoft Academic Search

    S. Kawamura; J. H. Kaneko; M. Higuchi; T. Yamaguchi; J. Haruna; Y. Yagi; K. Susa; F. Fujita; A. Homma; S. Nishiyama; K. Kurashige; H. Ishibashi; M. Furusaka

    2007-01-01

    Growth of cerium-doped gadolinium pyrosilicate single crystals, which show 2.5 times greater light output for gamma-rays and five times greater light output for alpha-particles than GSO single crystals, is accomplished using the floating zone growth method (FZ method). Although growth of (GPS) single crystal is considered to be difficult because it melts incongruently according to the phase diagram of system,

  17. Synthesis and re-investigation of the elastic properties of single-crystal magnesium silicate perovskite

    Microsoft Academic Search

    Amir Yeganeh-Haeri

    1994-01-01

    Single crystals of MgSiO3 in the perovskite structure have been grown at a peak pressure of 26 GPa and temperature of approximately 1600 K using a 2000 ton uniaxial split-sphere high-pressure apparatus (USSA-2000). The specimens were subsequently utilized to re-investigate the single-crystal elastic properties of this phase at ambient conditions using laser Brillouin spectroscopy. The nine adiabatic single-crystal elastic stiffness

  18. 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 etched independently: one for the substrate and fixed electrode layer, one for the actuator layer, and one for the mirror layer. Subsequently, each of these wafers will be bonded through a thermal fusion process to the others. In an innovative new processing technique, we will employ sacrificial oxide pillars to add temporary support to the otherwise compliant device structures. These pillars will be dissolved after assembly. The result will be a stress-free, single crystal silicon device with broadly expanded design space for geometric parameters such as actuator pitch, mirror diameter, array size, and actuator gap. Consequently, this approach will allow us to make devices with characteristics that are needed for some important NASA applications in space-based coronography, especially where larger array sizes, greater actuator pitch, and better optical surface quality are needed. The significance of this work is that it will provide a technology platform that meets or exceeds the superb optical performance that has been demonstrated in conventional pizezoelectrically actuated DMs, while retaining the advantages in cost, repeatability, and thermal insensitivity that have been demonstrated in the newer generation of MEMS electrostatically actuated DMs. The shift to bonded single-crystal structures will eliminate the single biggest drawback in previously reported NASA-fielded MEMS DM technology: device susceptibility to stress-induced scalloping and print through artifacts resulting from polycrystalline thin film surface micromachining. With single crystal structures bonded at atomic scales, uncorrected surface topography can be controlled to subnanometer levels, enabling the advancement of NASA s next-generation space-based coronagraphs.

  19. Single-Crystal Elasticity of Ettringite at ambient conditions

    NASA Astrophysics Data System (ADS)

    Speziale, S.; Jiang, F.; Mao, Z.; Monteiro, P. J.; Wenk, H.; Duffy, T. S.; Schilling, F.

    2006-12-01

    Ettringite, [Ca6Al2 (SO4)3 (OH)12^{.}26H2O] is a natural trigonal sulfate and one of the most relevant crystalline components of Portland cement. It is both a primary crystalline product during cement paste consolidation and a secondary phase which develops during concrete degradation. Even though the understanding of the mechanical properties of cement paste and of consolidated concrete is a longstanding problem of engineering and materials science, we still have a poor knowledge of the physical properties of ettringite. This makes it difficult to develop quantitative models able to predict the behavior and properties of such a complex multi-component system. We have now determined the single-crystal elastic constants of natural ettringite by Brillouin spectroscopy at ambient conditions. Brillouin scattering was measured along 54 different directions from two 2 mm size platelets of approximate orientation (001) and (100) prepared from a large single crystal of ettringite from South Africa. The six non-zero single-crystal elastic constants of this trigonal mineral are: C11 = 35.1(1) GPa, C12 = 21.9(1) GPa, C13 = 20.0(5) GPa, C14 = 0.6(2) GPa, C_{33 = 55(1) GPa, C44 = 11.0(2) GPa. The Hill average of the aggregate bulk and shear modulus are 27.3(9) GPa and 9.9(1) GPa respectively, more than 35 percent smaller than the moduli of gypsum. Ettringite possesses a large elastic anisotropy, with a difference of 50 percent between the Young's modulus along the stiff c- axis and the a- axis. The rigidity in planes containing the c- axis is 40 percent higher than in the basal plane. The pattern of elastic anisotropy in ettringite is directly connected to its crystallographic structure and to its external morphology. In fact, stiff chains of [Al(OH) 6]^{3-} octahedra alternating with triplets of Ca2+ in eight-fold coordination run parallel to the c- axis. Development of secondary fibrous ettringite elongated parallel to c- axis might play a major role as a mechanism for concrete weakening and deterioration.

  20. CCMR: Growth of Olivine Single Crystals for Point Defect and Transport Investigations

    NSDL National Science Digital Library

    Maier, Mitchell

    2010-08-15

    Using the float-zone technique and an image furnace, single crystals of the olivine compound Mn2SiO4 were grown to be used for defect-related properties analysis. The crystals grown so far are not of high enough quality to perform this analysis on; however, the crystals are well suited for producing oriented seed crystals for later high quality crystal growth. The crystals were grown with the aid of a ceramic afterheater. This type of afterheater proved effective at growing crack-free single crystals, and the use of an afterheater is planned to be implemented for all further growth of high-quality single crystals of Mn2SiO4.

  1. Growth and characterization of isotopically enriched [sup 70]Ge and [sup 74]Ge single crystals

    SciTech Connect

    Itoh, K.

    1992-10-01

    Isotopically enriched [sup 70]Ge and [sup 74]Ge single crystals were successfully gown by a newly developed vertical Bridgman method. The system allows us to reliably grow high purity Ge single crystals of approximately 1 cm[sup 3] volume. To our knowledge, we have grown the first [sup 70]Ge single crystal. The electrically active chemical impurity concentration for both crystals was found to be [approximately]2 [times] cm[sup [minus]3] which is two order of magnitude better that of [sup 74]Ge crystals previously grown by two different groups. Isotopic enrichment of the [sup 70]Ge and the [sup 74]Ge crystals is 96.3% and 96.8%, respectively. The residual chemical impurities present in both crystals were identified as phosphorus, copper, aluminum, and indium. A wide variety of experiments which take advantage of the isotopic purity of our crystals are discussed.

  2. Growth and characterization of isotopically enriched {sup 70}Ge and {sup 74}Ge single crystals

    SciTech Connect

    Itoh, K.

    1992-10-01

    Isotopically enriched {sup 70}Ge and {sup 74}Ge single crystals were successfully gown by a newly developed vertical Bridgman method. The system allows us to reliably grow high purity Ge single crystals of approximately 1 cm{sup 3} volume. To our knowledge, we have grown the first {sup 70}Ge single crystal. The electrically active chemical impurity concentration for both crystals was found to be {approximately}2 {times} cm{sup {minus}3} which is two order of magnitude better that of {sup 74}Ge crystals previously grown by two different groups. Isotopic enrichment of the {sup 70}Ge and the {sup 74}Ge crystals is 96.3% and 96.8%, respectively. The residual chemical impurities present in both crystals were identified as phosphorus, copper, aluminum, and indium. A wide variety of experiments which take advantage of the isotopic purity of our crystals are discussed.

  3. Growth of high quality single-domain single-crystal films of PbTiO3

    Microsoft Academic Search

    Z. Li; C. M. Foster; D. Guo; H. Zhang; G. R. Bai; P. M. Baldo; L. E. Rehn

    1994-01-01

    Single-crystal films of PbTiO3 have been deposited on (100) SrTiO3 substrates by metalorganic chemical vapor deposition. X-ray diffraction spectra and transmission electron microscopy images revealed that the development of 90° domains was directly related to the thickness of the film. Single-domain, single-crystal films were obtained for film thickness less than 150 nm. The minimum yields of the films in ion-channeling

  4. Scaling effect on the operation stability of short-channel organic single-crystal transistors

    NASA Astrophysics Data System (ADS)

    Minari, T.; Miyadera, T.; Tsukagoshi, K.; Hamano, T.; Aoyagi, Y.; Yasuda, R.; Nomoto, K.; Nemoto, T.; Isoda, S.

    2007-08-01

    Organic single-crystal transistors allowed the authors to investigate the essential features of short-channel devices. Rubrene single-crystal transistors with channel lengths of 500 and 100nm exhibited good field-effect characteristics under extremely low operation voltages, although space charge limited current degrades the subthreshold properties of 100nm devices. Furthermore, bias-stress measurements revealed the remarkable stability of organic single-crystal transistors regardless of device size. The bias-stress effect was explained by the trapping of gate-induced charges into localized density of states in the single-crystal channel.

  5. Numerical simulation of the crystallization front inversion in oxide single crystals grown from melt using the Czochralski method

    NASA Astrophysics Data System (ADS)

    Mamedov, V. M.; Yuferev, V. S.

    2008-07-01

    The process of pulling a Czochralski grown oxide single crystal out from melt has been numerically simulated for the first time from the moment of seeding until attaining a stationary growth regime. It is established that the phase boundary inversion at the lateral (shouldering) growth stage is a rather complicated process accompanied by intense oscillations of the crystallization rate. Diagrams illustrating variations of the crystal shape during this process are presented.

  6. Twin nucleation and migration in FeCr single crystals

    SciTech Connect

    Patriarca, L. [Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 34, I-20156 Milano (Italy)] [Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 34, I-20156 Milano (Italy); Abuzaid, Wael [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States)] [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States); Sehitoglu, Huseyin, E-mail: huseyin@illinois.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States)] [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States); Maier, Hans J. [Lehrstuhl fuer Werkstoffkunde (Materials Science), University of Paderborn, 33095 Paderborn (Germany)] [Lehrstuhl fuer Werkstoffkunde (Materials Science), University of Paderborn, 33095 Paderborn (Germany); Chumlyakov, Y. [Physics of Plasticity and Strength of Materials Laboratory, Siberian Physical and Technical Institute, 634050 Tomsk (Russian Federation)] [Physics of Plasticity and Strength of Materials Laboratory, Siberian Physical and Technical Institute, 634050 Tomsk (Russian Federation)

    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.

  7. Evolution of the CaF2:Tm (TLD-300) glow curve as an indicator of beam quality for low-energy photon beams

    NASA Astrophysics Data System (ADS)

    Muñoz, I. D.; Avila, O.; Gamboa-deBuen, I.; Brandan, M. E.

    2015-03-01

    We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6?keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and 60Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1–15.0?mGy and 49.8–373.8?mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029? ± ?0.010 (at 15.2?keV) and 0.821? ± ?0.011 (33.6?keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17?keV effective energy, or 3?keV??m?1 track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique.

  8. Thermal conductivity of U2Ru2Sn single crystal

    NASA Astrophysics Data System (ADS)

    Mucha, J.; Misiorek, H.; Tro?, R.; Coqblin, B.

    2008-02-01

    The thermal conductivity and the Lorenz function have been studied, along the two crystallographic directions a and c in the temperature range of 5-300 K, in a single crystal of the compound U2Ru2Sn, which behaves as a weak Kondo semiconductor with a gap of order 150 K. The observed large anisotropy results from both the considerable difference in the lattice parameters of the tetragonal structure and the difference in the type of thermal conductivity, i.e. crystal and quasi-amorphous ones. The contribution of bipolarons in the thermal conductivity confirms the semiconducting character of this compound. The presented results of the thermal conductivity of a uranium compound, which does not exhibit magnetic order, complete the examinations of the influence of phase transitions on heat transport in the antiferromagnetic UNi0.5Sb2 (Mucha et al 2006 J. Phys.: Condens. Matter. 18 3097) and ferromagnetic UCu2Si2 compounds (Mucha et al 2008 Solid State Commun. at press).

  9. 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.

  10. Growth and spectroscopic properties of Er : YAB single crystals

    NASA Astrophysics Data System (ADS)

    Foldvari, I.; Beregi, E.; Capelletti, R.; Baraldi, A.; Munoz, A.; Sosa, R.

    2003-01-01

    The Er-doped VAB (YAl3(BO3)(4)) is a potential self-frequency-doubling laser material. Single crystals were grown by the top-seeded flux method. The absorption spectra of the infrared Er3+ transitions were monitored in YAB crystals in the 9-300 K temperature range by high-resolution Fourier transform spectroscopy. In the whole spectral range the energy levels and Stark components of 12 transitions were detectable. In this paper the two infrared transitions (from the I-4(15/2) ground state to the I-4(13/2) and I-4(11/2) levels) were analyzed in detail. The low temperature absorption spectra of Er:YAB consist of sharp lines, the number of which corresponds to the theoretical predictions. This suggests that Er3+ ions occupy one specific lattice site (yttrium positions) with negligible aggregation at the higher dopant concentrations investigated (i.e. 0.12 Er atom/YAB mole).

  11. Short-term isothermal annealing of polyethylene single crystals

    NASA Astrophysics Data System (ADS)

    Grubb, David T.; Liu, J. Jui-Hsiang

    1985-10-01

    Polyethylene single-crystal mats 20 ?m thick were heated to the annealing temperatures (120-132 °C) in less than 1 s. The Cornell High Energy Synchrotron Source (CHESS) and a TV detector system were used to obtain wide- and small-angle x-ray scattering patterns from these mats during annealing with a time resolution of 0.3 s. Both whole polymer and a molecular weight fraction showed rapid melting and recrystallization, with a minimum crystallinity at 2-4 s after reaching the annealing temperature. Recrystallization was essentially complete in 60-90 s and most curves could be fitted to the Johnson-Mehl-Avrami equation with exponent n=1. Two-thirds of the material could be molten before there was any loss of the original crystal orientation. The increase in long period was discontinuous at high annealing temperature. The original small-angle long-spacing peak quickly lost intensity as crystallinity fell and a new peak appeared at larger long spacing. This new long spacing increased with time for the whole polymer and was constant for the fractionated material. At lower annealing temperatures the amount melting was small and the small-angle intensity and long period increased continuously.

  12. 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.

  13. 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 ?' particles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the moving boundary and more ?' 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 ?' particles.

  14. 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.

  15. Point defects in irradiated Li3VO4 single crystal

    NASA Astrophysics Data System (ADS)

    Miki, T.; Murata, T.; Ishii, T.; Ebina, Y.; Sakata, S.; Fujii, I.

    1995-03-01

    Radiation-induced defects in a new second harmonic generation material, lithium vanadate single crystal, have been studied by electron paramagnetic resonance (EPR) and optical absorption measurements. EPR detects two intense signals due to intrinsic O- and impurity-associated CO-3 trapped-hole centers at 77 K, but no such signal in the case of trapped-electron centers. The EPR signal of impurity Fe3+ ions is suppressed by 77 K irradiation. Low-temperature irradiation produces three optical absorption bands peaking at 3.14, 2.0, and 1.56 eV. It has been concluded that some of the free electrons produced by irradiation are trapped by Fe3+ ions at low temperatures. After annealing at room temperature all the optical absorption bands disappear, although the EPR signals of CO-3 trapped-hole centers and unidentified electron-type centers at g=1.96 remain stable up to 330 K.

  16. Current-controlled giant magnetoimpedance of iron single crystals

    NASA Astrophysics Data System (ADS)

    Langosch, M.; Gao, H.; Hartmann, U.

    2015-03-01

    Extended magnetoimpedance measurements on iron single crystals(whiskers) with < 100 > growth direction were performed at room temperature as a function of the applied longitudinal magnetic field and of the magnitude of the applied current in the low frequency regime. It is observed that there is a current threshold for inducing a giant magnetoimpedance effect. Calculations based on the standard skin effect formalism permit the determination of the effective circumferential permeability of the whiskers. It is found that the effect has its origin in the circumferential magnetic domain structure of the specimen. For comparison, impedance measurements on an iron wire were performed where no current threshold and continuous increase of the effective circumferential permeability is observed.

  17. Synthesis and growth of GaSe single crystals

    NASA Astrophysics Data System (ADS)

    Zhu, Chongqiang; Lei, Zuotao; Song, Liangcheng; Ma, Tianhui; Yang, Chunhui

    2015-07-01

    One-temperature and two-temperature synthesis methods for GaSe, a nonlinear optical compound, were developed. X-ray diffraction showed that pure ?-GaSe was synthesized. By Vertical Bridgman method using spontaneous nucleation the GaSe single crystals were grown with diameter 20-25 mm and length 40-45 mm and yield ~60%. The rocking curve for the studied GaSe sample was symmetric and its FWHM did not exceed 3?, which corresponds to the dislocation density at the level of 1012-1013 cm-2. SEM showed imperfections of surface of non-etched cleaved GaSe. According the obtained data the absorption coefficient at 1.06 ?m and 2 ?m is ~0.1 cm-1. At 9.3-10.9 ?m for nonpolarized light the calculations give absorption coefficient ~0.1-0.12 cm-1.

  18. Protective CVD Mullite Coatings on Single-Crystal Silicon Substrates

    NASA Astrophysics Data System (ADS)

    Xu, Jiapeng; Erickson, Daniel; Roy, Sudesna; Sarin, Vinod

    2013-04-01

    Silicon has long been the primary material of choice for microelectromechanical systems (MEMS) and integrated circuit (IC) applications. However, it is prone to degradation under severe conditions such as high humidity, high temperature, and corrosive environments. To overcome such extreme conditions and help silicon perform with stability and extended lifetimes, a protection layer is proposed. Mullite (3Al2O3·2SiO2) is a known environmental barrier coating (EBC) material and has been shown to be effective on other Si-based ceramic materials. In this work, dense, high-purity crystalline mullite coatings were deposited onto single-crystal silicon substrates via chemical vapor deposition (CVD). The microstructure, orientation preference, and adhesion of these coatings were investigated. Substrate integrity in relation to the substrate/coating interface by chemical etching and coating stability in a simulated severe environment under corrosive alkali salts were investigated.

  19. Optical properties of reduced lithium niobate single crystals

    NASA Astrophysics Data System (ADS)

    Dhar, Ajay; Mansingh, Abhai

    1990-12-01

    The optical transmission of LiNbO3 single crystals has been measured in the wavelength range 200-900 nm, for different degrees of reduction, to study the effect of reduction on the optical characteristics of LiNbO3 near the fundamental absorption edge. The optical transitions in LiNbO3 were found to be indirect and the band gap decreased with increasing degree of reduction. The band observed at 2.48 eV in the absorption spectrum in heavily reduced samples has been attributed to the formation of polarons, and the theoretical model of Reik and Heese [J. Chem. Solids 28, 581 (1967)] for small polarons is used to correlate the optical and electrical properties.

  20. Single crystal metal wedges for surface acoustic wave propagation

    DOEpatents

    Fisher, Edward S. (Wheaton, IL)

    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.

  1. 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.

  2. 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.

  3. A new, third-generation, single-crystal, casting superalloy

    NASA Astrophysics Data System (ADS)

    Erickson, Gary L.

    1995-04-01

    The CMSX®-10 alloy is a third-generation, single-crystal (SX), nickel-based casting alloy that is characterized by its 6 wt.% rhenium content, relatively high refractory element level (W+Ta + Re+Mo), and low level of chromium employment. Based on published data, the alloy's high-temperature creep-rupture resistance is greater than all other nickel-based alloys (approximately 30 °C better than CMSX-4 and PWA1484). Moreover, the alloy's composition is balanced to provide an attractive blend of SX component castability, heat treatability, impact strength, fatigue strength, and resistance to environmental degradation. Most notably, the alloy provides extremely good bare hot corrosion resistance, despite its novel and relatively low (2-3 wt.%) chromium content.

  4. InPBi Single Crystals Grown by Molecular Beam Epitaxy

    PubMed Central

    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.

    2014-01-01

    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??m which can't be explained by the existing theory. PMID:24965260

  5. Shock compression experiments on Lithium Deuteride single crystals.

    SciTech Connect

    Knudson, Marcus D.; Desjarlais, Michael P.; 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 ~200 - 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 ~900 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.

  6. Single-crystal elastic constants of natural ettringite

    Microsoft Academic Search

    Sergio Speziale; Fuming Jiang; Zhu Mao; Paulo J. M. Monteiro; Hans-Rudolf Wenk; Thomas S. Duffy; Frank R. Schilling

    2008-01-01

    The single-crystal elastic constants of natural ettringite were determined by Brillouin spectroscopy at ambient conditions. The six non-zero elastic constants of this trigonal mineral are: C11=35.1±0.1 GPa, C12=21.9±0.1 GPa, C13=20.0±0.5 GPa, C14=0.6±0.2 GPa, C33=55±1 GPa, C44=11.0±0.2 GPa. The Hill average of the aggregate bulk, shear modulus and the polycrystal Young's modulus and Poisson's ratio are 27.3±0.9 GPa, 9.5±0.8 GPa, 25±2 GPa and 0.34±0.02 respectively. The longitudinal and shear elastic

  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. 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.

  9. Polymorphic single crystal {r_reversible} single crystal transition in K{sub 0.975}Rb{sub 0.025}NO{sub 3}

    SciTech Connect

    Asadov, Yu. G., E-mail: yusifasadov@rambler.ru; Nasirov, E. V. [Azerbaijan National Academy of Sciences, Institute of Physics (Azerbaijan)

    2010-09-15

    Polymorphic transformations in K{sub 0.975}Rb{sub 0.025}NO{sub 3} single crystals have been investigated by optical microscopy and X-ray diffraction. The equilibrium temperature between modifications II and III has been determined. It is established that the crystal growth at II {r_reversible} III polymorphic transitions is accompanied by the formation and growth of daughter-modification nuclei in the matrix crystal.

  10. Tribological properties of spark-plasma-sintered ZrO 2(Y 2O 3)–CaF 2–Ag composites at elevated temperatures

    Microsoft Academic Search

    J. H. Ouyang; S. Sasaki; T. Murakami; K. Umeda

    2005-01-01

    Spark-plasma sintering is employed to synthesize self-lubricating ZrO2(Y2O3) matrix composites with different additives of CaF2 and Ag as solid lubricants by tailoring the composition and by adjusting the sintering temperature. The friction and wear behavior of ZrO2(Y2O3) matrix composites have been investigated in dry sliding against an alumina ball from room temperature to 800°C. The effective self-lubrication at different temperatures

  11. Structure of cleaved (001) USb2 single crystal

    SciTech Connect

    Chen, Shao-ping [Los Alamos National Laboratory; Hawley, Marilyn [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Stockum, Phil B [STANFORD UNIV.; Manoharan, Hari C [STANFORD UNIV

    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, all of which are averaged over when probed in photoemission studies. The quasi two-dimensional USb{sub 2} has a layered tetragonal structure that is easily cleaved and has been extensively studied by a number of different techniques, such as resistivity, Hall effect measurements, photoemission and angle-resolved photoemission spectroscopy, de Haas-van Alphen, neutron diffraction, nuclear magnetic resonance, and U{sup 238} Mossbauer spectroscopy techniques. Here, we provide local information about the surfaces of this interesting compound, which we find to contain a high density of defects.

  12. PROBING STRESS EFFECTS IN SINGLE CRYSTAL ORGANIC TRANSISTORS BY SCANNING KELVIN PROBE MICROSCOPY

    SciTech Connect

    Teague, L.

    2010-06-11

    We report scanning Kelvin probe microscopy (SKPM) of single crystal difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) organic transistors. SKPM provides a direct measurement of the intrinsic charge transport in the crystals independent of contact effects and reveals that degradation of device performance occurs over a time period of minutes as the diF-TESADT crystal becomes charged.

  13. Wall propagation by thermomagnetic writing in MnBi single crystal films

    Microsoft Academic Search

    SHIGEO HONDA; TAKANOBU NOMURA; TETSUZO KUSUDA

    1973-01-01

    When a laser beam is focused to a spot on a MnBi single crystal or a polycrystalline MnBi film, a domain wall is nucleated which propagates from the heated spot by various mechanisms dependent on the direction of magnetization, the process of the crystal growth, and the effect of the adjacent crystal. The mechanism of the propagation can be interpreted

  14. Single-crystal YAG fiber optics for the transmission of high energy laser energy

    E-print Network

    of SC yttrium aluminum garnet, Y3Al5O12 (YAG) fibers from undoped SC source rods using the Laser Heated coefficient is 0.6 cm-1 . The garnet family of crystals is one of the most commonly used oxide crystal hosts of YAG fiber grown has been about 60 cm. Keywords: Infrared fiber optics, single-crystal fibers, oxide

  15. Growth and Characterization of Yttrium Calcium Oxy Borate (YCOB) Single Crystals for Nonlinear Optical Applications

    Microsoft Academic Search

    R. Arun Kumar; M. Senthilkumar; R. Dhanasekaran

    2008-01-01

    The growth of yttrium calcium oxy borate (YCOB) single crystals by the flux technique is reported. Polycrystalline YCOB sample was synthesized and confirmed. Differential thermal analysis was carried out with lithium carbonate flux. The growth of YCOB crystals by flux technique was attempted and several crystals with dimensions of 3×3×5 mm were obtained. Powder XRD analysis confirms the formation of YCOB

  16. Growth of 4-(dimethylamino) benzaldehyde doped triglycine sulphate single crystals and its characterization

    Microsoft Academic Search

    Chitharanjan Rai; K. Sreenivas; S. M. Dharmaprakash

    2009-01-01

    Single crystals of triglycine sulphate (TGS) doped with 1mol% of 4-(dimethylamino) benzaldehyde (DB) have been grown from aqueous solution at ambient temperature by slow evaporation technique. The effect of dopant on the crystal growth and dielectric, pyroelectric and mechanical properties of TGS crystal have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the

  17. Cu(I)-MOF: naked-eye colorimetric sensor for humidity and formaldehyde in single-crystal-to-single-crystal fashion.

    PubMed

    Yu, Yang; Zhang, Xiao-Meng; Ma, Jian-Ping; Liu, Qi-Kui; Wang, Peng; Dong, Yu-Bin

    2014-02-11

    A porous Cu(I)-MOF was constructed from CuI and 1-benzimidazolyl-3,5-bis(4-pyridyl)benzene. This Cu(I)-MOF can be a highly sensitive naked-eye colorimetric sensor to successively detect water and formaldehyde species in a single-crystal-to-single-crystal fashion. Solid-state guest-responsive luminescence is also used to monitor the sensing process. PMID:24352589

  18. Evolution of Magnetism in Single-Crystal Honeycomb Iridates

    NASA Astrophysics Data System (ADS)

    Terzic, Jasminka; Qi, T. F.; Li, L.; Cao, V. S.; Yuan, S. J.; Tovar, M.; Murthy, G.; Kaul, R. K.; Cao, G.

    2014-03-01

    We report the successful synthesis of single-crystals of the layered iridate, (Na1-xLix)2IrO3, 0 <= x <= 0.90, and a thorough study of its structural, magnetic, thermal and transport properties. The new compound allows a controlled interpolation between Na2IrO3andLi2IrO3, while maintaining the novel quantum magnetism of the honeycomb Ir4 + planes. The measured phase diagram demonstrates a suppression of the Neel temperature at an intermediate x indicating that the magnetic order in Na2IrO3andLi2IrO3 are distinct. X-ray data shows that for x =0.70 when the Neel temperature is suppressed the most, the honeycomb structure is least distorted, suggesting at this intermediate doping that the material is closest to the spin liquid that has been sought after in Na2IrO3andLi2IrO3. By analyzing our magnetic data with a single-ion theoretical model we also show that the trigonal splitting, on the Ir4 + ions changes sign from Na2IrO3toLi2IrO3. This work was supported by the US National Science Foundation via grants DMR-0856234, DMR-1265162 and DMR- NSF DMR-1056536 (RKK).

  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. Calcite Single Crystals as Hosts for Atomic-Scale Entrapment and Slow Release of Drugs.

    PubMed

    Magnabosco, Giulia; Giosia, Matteo Di; Polishchuk, Iryna; Weber, Eva; Fermani, Simona; Bottoni, Andrea; Zerbetto, Francesco; Pelicci, Pier Giuseppe; Pokroy, Boaz; Rapino, Stefania; Falini, Giuseppe; Calvaresi, Matteo

    2015-07-01

    Doxorubicin (DOX)/CaCO3 single crystals act as pH responsive drug carrier. A biomimetic approach demonstrates that calcite single crystals are able, during their growth in the presence of doxorubicin, to entrap drug molecules inside their lattice along specific crystallographic directions. Alterations in lattice dimensions and microstructural parameters are determined by means of high-resolution synchrotron powder diffraction measurements. Confocal microscopy confirms that doxorubicin is uniformly embedded in the crystal and is not simply adsorbed on the crystal surface. A slow release of DOX was obtained preferentially in the proximity of the crystals, targeting cancer cells. PMID:26033854

  1. Growth of bulk single crystal of N-acetyl DL-methionine and its spectral characterization

    NASA Astrophysics Data System (ADS)

    Moovendaran, K.; Natarajan, S.

    2015-01-01

    Bulk size single crystal of N-acetyl DL-methionine (C7H13NO3S) (1) was grown using a home-made crystal growth setup (MKN setup). The identity of the grown crystal was confirmed by single crystal X-ray diffraction. The modes of vibrations of the functional groups present were assigned using the infrared (IR) spectrum. UV-vis-NIR spectra showed that the crystals have excellent transparency in the visible and infrared regions. The thermal stability and decomposition of the sample was studied by using thermal analysis (TGA/DTA). Photoluminescence excitation studies showed that the emission occurred at 350 nm for the compound.

  2. Growth of bulk single crystal of N-acetyl DL-methionine and its spectral characterization.

    PubMed

    Moovendaran, K; Natarajan, S

    2015-01-25

    Bulk size single crystal of N-acetyl DL-methionine (C7H13NO3S) (1) was grown using a home-made crystal growth setup (MKN setup). The identity of the grown crystal was confirmed by single crystal X-ray diffraction. The modes of vibrations of the functional groups present were assigned using the infrared (IR) spectrum. UV-vis-NIR spectra showed that the crystals have excellent transparency in the visible and infrared regions. The thermal stability and decomposition of the sample was studied by using thermal analysis (TGA/DTA). Photoluminescence excitation studies showed that the emission occurred at 350 nm for the compound. PMID:25084237

  3. 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

    2015-07-01

    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. PMID:26046376

  4. Growth of CuInTe{sub 2} single crystals by iodine transport and their characterization

    SciTech Connect

    Prabukanthan, P. [Crystal Growth Centre, Anna University, Chennai 600 025 (India); Dhanasekaran, R. [Crystal Growth Centre, Anna University, Chennai 600 025 (India)], E-mail: rdhanasekaran@annauniv.edu

    2008-08-04

    The single crystals with stoichiometry close to 1:1:2 of CuInTe{sub 2} (CIT) have been grown by chemical vapor transport (CVT) technique using iodine as the transporting agent at different growth temperatures. Single crystal X-ray diffraction studies have confirmed the chalcopyrite structure for the grown crystals and the volume of unit cell is found to be the same for the crystals grown at different conditions. Energy dispersive X-ray (EDAX) analysis of CIT single crystals grown shows almost the same stoichiometric compositions. Scanning electron microscope (SEM) analysis reveals kink, step and layer patterns on the surface of CIT single crystals depending on the growth temperatures. The optical absorption spectra of as-grown CIT single crystals grown at different conditions show that they have same band gap energies (1.0405 eV). Raman spectra exhibit a high intensity peak of A{sub 1} mode at 123 cm{sup -1}. Annealed at 473 K in nitrogen atmosphere for 40 h CIT single crystals have higher hole mobility (105.6 cm{sup 2}V{sup -1}s{sup -1}) and hole concentration (23.28 x 10{sup 17} cm{sup -3}) compared with values of hole mobility (63.69 cm{sup 2} V{sup -1} s{sup -1}) and hole concentration (6.99 x 10{sup 15} cm{sup -3}) of the as-grown CIT single crystals.

  5. 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.

  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. PMID:21600840

  7. Electric-field-assisted position and orientation control of organic single crystals.

    PubMed

    Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro

    2014-12-01

    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 [1?10] 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. PMID:25360544

  8. Structural, spectral, optical and dielectric properties of copper and glycine doped LAHCl single crystals

    NASA Astrophysics Data System (ADS)

    Sangeetha, K.; Babu, R. Ramesh; Bhagavannarayana, G.; Ramamurthi, K.

    2011-09-01

    Cu 2+ 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.

  9. Single crystal growth and physical properties of YbPd2Si2

    NASA Astrophysics Data System (ADS)

    Matsumoto, Y.; Hanya, K.; Haga, Y.; Fisk, Z.; Ohara, S.

    2015-03-01

    We report the heat capacity and magnetic properties of single crystals of YbPd2Si2 grown from Sn flux. YbPd2Si2 is a non magnetic heavy fermion compound with electronic specific heat coefficient ? = 95 mJ/mol K2 and Pauli paramagnetic susceptibility ?0 = 0.0115 emu/mol. The density of states of single crystal YbPd2Si2 is approximately half that of polycrystalline YbPd2Si2 while the strength of the Kondo effect in the single crystal is approximately twice that of poly crystal.

  10. Growth and characterization studies on glycine barium dichloride single crystals for NLO applications

    NASA Astrophysics Data System (ADS)

    Prakash, J. Thomas Joseph; Vijayan, N.; Kumararaman, S.

    2008-12-01

    The novel nonlinear optical single crystal of glycine barium chloride has been successfully synthesized by taking the appropriate amount of glycine and barium dichloride and single crystals have been grown by slow evaporation solution growth technique at room temperature. The grown single crystals have been analyzed with XRD, FT-IR, TG/DTA measurements. Its mechanical behavior has been assessed by Vickers Microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV-vis, and found that the crystal is transparent in the region between 250 and 1200 nm.

  11. Growth and characterization studies on glycine barium dichloride single crystals for NLO applications.

    PubMed

    Prakash, J Thomas Joseph; Vijayan, N; Kumararaman, S

    2008-12-15

    The novel nonlinear optical single crystal of glycine barium chloride has been successfully synthesized by taking the appropriate amount of glycine and barium dichloride and single crystals have been grown by slow evaporation solution growth technique at room temperature. The grown single crystals have been analyzed with XRD, FT-IR, TG/DTA measurements. Its mechanical behavior has been assessed by Vickers Microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV-vis, and found that the crystal is transparent in the region between 250 and 1200 nm. PMID:18440858

  12. High-power diode-pumped Er3+ :YAG single-crystal fiber laser

    E-print Network

    Paris-Sud XI, Université de

    applications like remote sensing, free-space communications, range detection, and designation. The opticalHigh-power diode-pumped Er3+ :YAG single-crystal fiber laser Igor Martial,1,2,* Julien Didierjean,2 describe an efficient laser emission from a directly grown Er3+ :YAG single-crystal fiber

  13. Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals

    E-print Network

    Watson, E. Bruce

    Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals X June 2006 Editor: P. Deines Abstract Oxygen diffusion in natural and synthetic single-crystal titanite cold-seal pressure vessels for durations of 1 day to several weeks. Diffusive uptake profiles of 18 O

  14. Rational synthesis of alpha-MnO2 single-crystal nanorods.

    PubMed

    Wang, Xun; Li, Yadong

    2002-04-01

    alpha-MnO2 single-crystal nanorods with diameters 20-80 nm and lengths up to 6 microns have been prepared through a low-temperature liquid-phase comproportionation method, which involves no catalysts or templates and may be adjusted to prepare alpha-MnO2 single-crystal nanorods in large scale. PMID:12119712

  15. EXHAUSTION MECHANISMS IN THE PREYIELD DOMAIN OF NIOBIUM SINGLE CRYSTALS AT LOW TEMPERATURES

    E-print Network

    Paris-Sud XI, Université de

    823 EXHAUSTION MECHANISMS IN THE PREYIELD DOMAIN OF NIOBIUM SINGLE CRYSTALS AT LOW TEMPERATURES A, France (Reçu le 21 février 1975, accepté le 24 avril 1975) Résumé. 2014 Des monocristaux de niobium de. Abstract. 2014 Pure niobium single crystals were tested by tension and by stress-relaxation at stresses

  16. Design and aeroelastic analysis of active twist rotor blades incorporating single crystal macro fiber composite actuators

    Microsoft Academic Search

    Jae-Sang Park; Ji-Hwan Kim

    2008-01-01

    The advanced active twist rotor (AATR) blade incorporating single crystal macro fiber composite (single crystal MFC) actuators is designed and the aeroelastic analysis is performed. The AATR blade is designed based on an existing passive blade and the NASA\\/ARMY\\/MIT active twist rotor (ATR) prototype blade. The AATR blade is designed to satisfy all the requirements and the properties of the

  17. Structural and optical properties of europium doped zirconia single crystals fibers grown by laser floating zone

    Microsoft Academic Search

    M. R. N. Soares; C. Nico; M. Peres; N. Ferreira; A. J. S. Fernandes; T. Monteiro; F. M. Costa

    2011-01-01

    Yttria stabilized zirconia single crystal fibers doped with europium ions were developed envisaging optical applications. The laser floating zone technique was used in order to grow millimetric high quality single crystal fibers. The as-grown fibers are completely transparent and inclusion free, exhibiting a cubic structure. Under ultraviolet (UV) excitation, a broad emission band appears at 551 nm. The europium doped

  18. Analysis of solidification microstructures in Fe-Ni-Cr single-crystal welds

    Microsoft Academic Search

    M. Rappaz; S. A. David; J. M. Vitek; L. A. Boatner

    1990-01-01

    A geometric analysis technique for the evaluation of the microstructures in autogenous single-crystal electron beam welds has been previously developed. In the present work, these analytical methods are further extended, and a general procedure for predicting the solidification microstructure of single-crystal welds with any arbitrary orientation is established. Examples of this general analysis are given for several welding orientations. It

  19. Simultaneous observation of the Barkhausen and magnetoplastic effect in A Ni-single crystal

    Microsoft Academic Search

    B. Röde; F. M. Wagner; P. Deimel; H. Markert

    1978-01-01

    The Barkhausen and magneto-plastic effect in a Ni-single crystal, which was oriented for single slip have been observed in stage II of deformation. Upon loading and unloading the crystal, distinct differences in the shape and instensity of the Barkhausen jump rate versus magnetizing field can be seen. Furthermore it is shown, that there exists a Barkhausen effect during reactivation of

  20. Growth and electrochromic properties of single-crystal V2O5 nanorod arrays

    E-print Network

    Cao, Guozhong

    Growth and electrochromic properties of single-crystal V2O5 nanorod arrays Katsunori Takahashi reports a study on the template-based growth and electrochromic properties of single-crystal vanadium demonstrated significantly enhanced electrochromic properties; both the larger change of transmittance

  1. High-power diode-pumped Q-switched Er3+ :YAG single-crystal fiber

    E-print Network

    Boyer, Edmond

    High-power diode-pumped Q-switched Er3+ :YAG single-crystal fiber laser Igor Martial,1,2,* Julien that is resonantly pumped using a continuous-wave (CW) laser diode at 1532 nm. In a longitudinal pumping, it emits 12+ :YAG single-crystal fiber Q-switched laser. Keywords: Lasers, Solid-state, Diode-pumped, Q

  2. Nanoripples formation in calcite and indium phosphide (InP) single crystals

    Microsoft Academic Search

    Ramakrishna Gunda

    2007-01-01

    In this project we studied the formation of nanoripples in calcite and InP single crystals by continuous scanning using the nanoindenter in the ambient environment and by Argon ion irradiation under ultra high vacuum conditions, respectively. Formation of tip induced nanowear ripples is studied on a freshly cleaved calcite single crystal as a function of scanning frequency and contact load

  3. Carbon monoxide MgO from dispersed solids to single crystals: a review and new advances

    Microsoft Academic Search

    G. Spoto; E. N. Gribov; G. Ricchiardi; A. Damin; D. Scarano; S. Bordiga; C. Lamberti; A. Zecchina

    2004-01-01

    In this review we describe 30 years of research on the surface properties of magnesium oxide, considered as the model prototype oxide of cubic structure. The surface properties of single crystals, thin films and powdered samples (sintered at progressive higher temperatures) are considered and compared, with the aim of demonstrating that the gap between “believed perfect” single crystal surfaces, typical

  4. Effect of fibrous single crystals of mullite on the thermal-shock resistance of alumina

    Microsoft Academic Search

    D. M. Karpinos; V. M. Grosheva; Yu. L. Pilipovskii; E. P. Mikhashchuk

    1973-01-01

    Conclusions A technology was developed for incorporating fibrous single crystal mullite into corundum products. Studies were made of the strength and thermal physical properties of the corundum reinforced with mullite fibers. Judging from the thermal-shock resistance and impact strength, corundum products with additions of fibrous single crystals of mullite are much better than corundum products without the additives.

  5. Asymmetric deformation in fatigue of body-centered-cubic single crystals

    Microsoft Academic Search

    Harmon D. Nine

    1973-01-01

    Asymmetric deformation, the movement of material on single-crystal surfaces in only one crystallographic direction under net zero strain cycle deformation, has been observed in single crystals of iron, niobium, and molybdenum. The effect leads to rapid local deformation and rapid fatigue failure. A dislocation mechanism involving asymmetric slip on {112} and {123} planes and repeated cross slip is proposed to

  6. Growth and characterization of 4-chloro-3-nitrobenzophenone single crystals using vertical Bridgman technique

    SciTech Connect

    Aravinth, K., E-mail: anandcgc@gmail.com; Babu, G. Anandha, E-mail: anandcgc@gmail.com; Ramasamy, P., E-mail: anandcgc@gmail.com [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam -603110, Tamilnadu (India)

    2014-04-24

    4-chloro-3-nitrobenzophenone (4C3N) has been grown by using vertical Bridgman technique. The grown crystal was confirmed by Powder X-ray diffraction analysis. The crystalline perfection of the grown crystal was examined by high-resolution X-ray diffraction study. The fluorescence spectra of grown 4C3N single crystals exhibit emission peak at 575 nm. The micro hardness measurements were used to analyze the mechanical property of the grown crystal.

  7. A Density Model Based on the Modified Quasichemical Model and Applied to the NaF-AlF3-CaF2-Al2O3 Electrolyte

    NASA Astrophysics Data System (ADS)

    Robelin, Christian; Chartrand, Patrice

    2007-12-01

    A theoretical model for the density of multicomponent inorganic liquids based on the modified quasichemical model has been presented in a previous article. In the present article, this model is applied to the NaF-AlF3-CaF2-Al2O3 electrolyte. By introducing in the Gibbs energy of the liquid phase, temperature-dependent molar volume expressions for the pure fluorides and oxides, and pressure-dependent excess parameters for the binary (and sometimes higher-order) interactions, it is possible to reproduce, and eventually predict, the molar volume and the density of the multicomponent liquid phase using standard interpolation methods. All available density data for the NaF-AlF3-CaF2-Al2O3 liquid were collected and critically evaluated, and optimized pressure-dependent model parameters have been found. This new volumetric model can be used with Gibbs energy minimization software, to calculate the molar volume and the density of cryolite-based melts used for the electroreduction of alumina in Hall-Héroult cells.

  8. MgB2 single crystals: high pressure growth and physical properties

    Microsoft Academic Search

    J. Karpinski; M. Angst; J. Jun; S. M. Kazakov; R. Puzniak; A. Wisniewski; J. Roos; H. Keller; A. Perucchi; L. Degiorgi; M. R. Eskildsen; P. Bordet; L. Vinnikov; A. Mironov

    2003-01-01

    Single crystals of MgB2 with a size up to 1.5 x 0.9 x 0.2 mm(3) have been grown with a high pressure cubic anvil technique. The crystal growth process is very peculiar and involves an intermediate nitride, namely MgNB9. Single crystals of BN and MgB2 grow simultaneously by a peritectic decomposition of MgNB9. Magnetic measurements with SQUID magnetometry in fields

  9. The single-crystal elastic constants of cubic (3C) SiC to 1000° C

    Microsoft Academic Search

    Z. Li; R. C. Bradt

    1987-01-01

    Experimental measurements of the polycrystalline elastic moduli of the cubic (3C) beta polytype of SiC at elevated temperatures and the room-temperature single-crystal elastic constants were combined through equations that relate the two to determine the stiffnesses Cij and the compliances Sij to 1000° C. The results demonstrate a general method for estimating the elevated temperature single-crystal constants of cubic crystals

  10. On the anisotropy of dielectric permittivity in single crystal lanthanum aluminate substrates

    Microsoft Academic Search

    Yu. G. Makeev; A. P. Motornenko; N. T. Cherpak; I. P. Babiichuk; M. B. Kosmyna

    2002-01-01

    The dielectric properties of LaAlO3 single crystal plates were studied by microwave techniques in a frequency range from 20 to 28 GHz. The measurements were\\u000a performed using a resonator representing crossed round (cylindrical) and radial evanescent waveguides with the polarization-degenerate\\u000a fundamental oscillation mode. Various single crystal samples, including those obtained from different manufacturers, exhibit\\u000a anisotropy in the (100) crystal plane,

  11. Polarized Raman scattering of multiferroic BiFeO3 single domian crystal and thin film

    Microsoft Academic Search

    R. Palai; H. S. Schmid; R. S. Katiyar

    2008-01-01

    We report the investigation of polarized Raman spectroscopy of multiferroic bismuth ferrite BiFeO3, using a ferroelectric\\/ferroelastic single domain crystal with an as-grown pseudo-cubic (pc) (100)pc surface and (001)pc thin film, grown by pulsed laser deposition. The polarized Raman spectra of the single crystal taken at different crystallographic orientations, agree with the rhombohedral crystal structure with C3v point group, whereas the

  12. Optoelectronic effects in p -CdGeAs 2 single crystals and structures based on them

    Microsoft Academic Search

    B. Kh. Bairamov; I. K. Polushina; Yu. V. Rud; V. Yu. Rud’; P. G. Schunemann; M. C. Ohmer; N. C. Fernelius; G. Irmer; J. Monecke

    1998-01-01

    Spectra of inelastic light scattering by optical phonons in p-CdGeAs2 single crystals were obtained for the first time. The observed clear polarization dependence and the absence of any appreciable\\u000a dependence of the intensity and frequency of the observed lines when the sample is swept in ?300 m steps indicates these\\u000a CdGeAs2 single crystals grown by directional crystallization from a near-stoichiometric

  13. Internal fields in lithium tantalate single crystals Venkatraman Gopalan and Moo! C. Gupta

    E-print Network

    Gopalan, Venkatraman

    -built internal field of 5 KV/nim was measured in Z-cut LiTaO3 single crystals in the direction of the original lies in point defect complexes involving Off ions. Keywords: LiTaO3, LiNbO3, internal field, electric the polarization hysteresis curve for a virgin 0.5 mm thick LiTaO3 single crystal at room temperature. The crystal

  14. Flux growth of yttrium calcium oxy borate (YCOB) single crystals for nonlinear optical applications

    Microsoft Academic Search

    R. Arun Kumar; R. Dhanasekaran

    2009-01-01

    Nonlinear optical single crystals of YCa4O(BO3)3 (YCOB) with good optical quality were grown from boron-tri-oxide flux for the first time. Polycrystalline YCOB samples were synthesized from the solid-state reaction method. Optimum conditions for the growth of YCOB crystals from the flux were determined. Single crystals of YCOB with dimensions 10×5×5mm3 were obtained by the method of ‘slow cooling’. The grown

  15. Radiation detector made of a diamond single crystal grown by a chemical vapor deposition method

    Microsoft Academic Search

    J. H. Kaneko; T. Tanaka; T. Imai; Y. Tanimura; M. Katagiri; T. Nishitani; H. Takeuchi; T. Sawamura; T. Iida

    2003-01-01

    The first investigation of a radiation detector made of a diamond single crystal grown by a chemical vapor deposition (CVD) method was successfully carried out. The diamond single crystal, having a size of 2.0×2.0×0.7mm3, was grown by the CVD method and then applied to the detector. The CVD method was able to reduce nitrogen and boron impurities in diamond crystals

  16. Scintillation Properties of 2-Inch-Diameter (LuAG) Single Crystal

    Microsoft Academic Search

    Kei Kamada; Takayuki Yanagida; Kousuke Tsutsumi; Yoshiyuki Usuki; Mitsuhiro Sato; Hiraku Ogino; Andrey Novoselov; Akira Yoshikawa; Masaaki Kobayashi; Shojiro Sugimoto; Fumio Saito

    2009-01-01

    Pr:LuAG crystals possess interesting properties, such as high density, high light yield, and very fast 5d-4f emission decay time. Recently, we developed a Pr:LuAG single crystal with a diameter of 2 inches for scintillator applications, such as medical imaging. In this study, Pr-doped Lu3Al5O12 (Pr:LuAG) single crystals with a diameter of 2 inches were grown by means of the Czochralski

  17. Growth of semiconductor compound single crystal InSb by floating zone method (M-3)

    NASA Technical Reports Server (NTRS)

    Nakatani, I.

    1993-01-01

    Floating zone methods have potential applications in growing single high-quality semi-conductor crystals. In this method, melts can be sustained without containers and, therefore, are free from contamination from the containers. The main objective of this project is to use the Image Furnace to study a large diameter, (20 mm) single crystal of InSb under microgravity conditions. The behavior of the liquid column is recorded on the VTR tapes and is compared with what is expected theoretically. The single crystal grown in space is characterized by comparing it with single crystals grown on the ground with respect to crystallographic and electronic properties. The goal of this project is to confirm the effects of the microgravity on the single crystals.

  18. The evolution of machining-induced surface of single-crystal FCC copper via nanoindentation

    NASA Astrophysics Data System (ADS)

    Zhang, Lin; Huang, Hu; Zhao, Hongwei; Ma, Zhichao; Yang, Yihan; Hu, Xiaoli

    2013-05-01

    The physical properties of the machining-induced new surface depend on the performance of the initial defect surface and deformed layer in the subsurface of the bulk material. In this paper, three-dimensional molecular dynamics simulations of nanoindentation are preformed on the single-point diamond turning surface of single-crystal copper comparing with that of pristine single-crystal face-centered cubic copper. The simulation results indicate that the nucleation of dislocations in the nanoindentation test on the machining-induced surface and pristine single-crystal copper is different. The dislocation embryos are gradually developed from the sites of homogeneous random nucleation around the indenter in the pristine single-crystal specimen, while the dislocation embryos derived from the vacancy-related defects are distributed in the damage layer of the subsurface beneath the machining-induced surface. The results show that the hardness of the machining-induced surface is softer than that of pristine single-crystal copper. Then, the nanocutting simulations are performed along different crystal orientations on the same crystal surface. It is shown that the crystal orientation directly influences the dislocation formation and distribution of the machining-induced surface. The crystal orientation of nanocutting is further verified to affect both residual defect generations and their propagation directions which are important in assessing the change of mechanical properties, such as hardness and Young's modulus, after nanocutting process.

  19. Small single-crystal silicon cantilevers formed by crystal facets for atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Nakagawa, Kazuhisa; Hashiguchi, Gen; Kawakatsu, Hideki

    2009-09-01

    We have developed a batch fabrication method of small cantilevers formed by crystal facets of single-crystal silicon for improving the sensitivity of atomic force microscopy. In order to realize a small cantilever with a very sharp tip, we have employed KOH anisotropic etching and local oxidation of silicon. We have made two types of small cantilevers, the V-shaped triangular type and the bulk triangular type. The length of each cantilever is 20 ?m. The tip of the V-shaped type is bridged by two wires with thickness of 0.6 ?m. The bulk triangular type has a thickness of 1.5 ?m. The frequency characteristics of the cantilevers vibrated using photothermal excitation were measured by laser Doppler velocimetry. The resonance frequency of the V-shaped type and the bulk triangular type were 687 kHz and 8.42 MHz, and their spring constants are estimated to be 0.7 N/m and 370 N/m, respectively.

  20. 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.

  1. Effect of crystal orientation on conductivity and electron mobility in single-crystal alumina

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The electrical conductivity of high-purity, single-crystal alumina is determined parallel to and perpendicular to the c-axis. The mean conductivity of four samples of each orientation is a factor 3.3 higher parallel to the c-axis than perpendicular to it. The conductivity as a function of temperature is attributed to extrinsic electron conduction at temperatures from 400 to 900 C, and intrinsic semiconduction at temperatures from 900 to 1300 C. In the high-temperature regime, the slope on all eight specimens is 4.7 +/- 0.1 eV. Hence, the thermal bandgap at O K is 9.4 +/- 0.2 eV.

  2. The crystal structure of {pi}-ErBO{sub 3}: New single-crystal data for an old problem

    SciTech Connect

    Pitscheider, Almut [Institut fuer Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universitaet Innsbruck, Innrain 52a, A-6020 Innsbruck (Austria); Kaindl, Reinhard [Institut fuer Mineralogie und Petrographie, Leopold-Franzens-Universitaet Innsbruck, Innrain 52, A-6020 Innsbruck (Austria); Oeckler, Oliver [Department Chemie, Ludwig-Maximilians-Universitaet Muenchen, Butenandtstrasse 5-13, D-81377 Muenchen (Germany); Huppertz, Hubert, E-mail: Hubert.Huppertz@uibk.ac.a [Institut fuer Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universitaet Innsbruck, Innrain 52a, A-6020 Innsbruck (Austria)

    2011-01-15

    Single crystals of the orthoborate {pi}-ErBO{sub 3} were synthesized from Er{sub 2}O{sub 3} and B{sub 2}O{sub 3} under high-pressure/high-temperature conditions of 2 GPa and 800 {sup o}C in a Walker-type multianvil apparatus. The crystal structure was determined on the basis of single-crystal X-ray diffraction data, collected at room temperature. The title compound crystallizes in the monoclinic pseudowollastonite-type structure, space group C2/c, with the lattice parameters a=1128.4(2) pm, b=652.6(2) pm, c=954.0(2) pm, and {beta}=112.8(1){sup o} (R{sub 1}=0.0124 and wR{sub 2}=0.0404 for all data). -- graphical abstract: The first satisfying single-crystal structure determination of {pi}-ErBO{sub 3} sheds light on the extensively discussed structure of {pi}-orthoborates. The application of light pressure during the solid state synthesis yielded in high-quality crystals, due to pressure-induced crystallization. Research highlights: {yields} High-quality single crystals of {pi}-ErBO{sub 3} were prepared via high-pressure-induced crystallization. {yields} At least five different space groups for the rare-earth {pi}-orthoborates are reported. {yields} {pi}-ErBO{sub 3} is isotypic to the pseudowollastonite-type CaSiO{sub 3}. {yields} Remaining ambiguities regarding the structure of the rare-earth {pi}-orthoborates are resolved.

  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 greater amounts of iron. Expressed as Arrhenius relations, hydrogen diffusivities parallel to c, the fastest direction of diffusion, are DEN = 1.63 x 10-5 exp[-161 +/- 17 kJ/mol/RT] m2s-1 for San Carlos enstatite, D OPX 14 = 9.12 x 10-5 exp[-195 +/- 48 kJ/mol/RT] m2s-1 for Sri Lankan orthopyroxene containing the lowest amounts of iron, and D OPX 11 = 91.4 exp[-326 +/- 27 kJ/mol/RT] m2s-1, for Sri Lankan orthopyroxene containing the greatest amounts of iron. The mechanism of hydrogen diffusion in orthopyroxene is believed to be that postulated by Skogby and Rossman (1989), i.e., a coupled redox reaction that incorporates (or releases) hydrogen with a concurrent change in the oxidation state of iron. In all cases, hydrogen diffusivities are approximately 30--100 times lower than those determined for San Carlos olivine and Jaipur diopside (Mackwell and Kohlstedt, 1990 and Woods et al., 2000), and it is concluded that the presence of aluminum is most likely responsible for the difference in behavior as a result of higher binding energies of protons to aluminum than in aluminum free systems. (Abstract shortened by UMI.)

  4. Fluid inclusions and microstructures in experimentally deformed quartz single crystals

    NASA Astrophysics Data System (ADS)

    Thust, A.; Tarantola, A.; Heilbronner, R.; Stünitz, H.

    2009-04-01

    The "H2O-weakening" effect that reduces the strength of quartz dramatically (e.g. Griggs & Blacic 1965) is still not understood. For example, Kronenberg & Tullis (1984) conclude that the weakening effect is pressure dependent while Paterson (1989) infers a glide and recovery control of water. Obviously, the spatial distribution and transport of H2O are important factors (Kronenberg et al. 1986, FitzGerald et al. 1991). We have carried out experiments on milky quartz in a Griggs deformation apparatus. Cylinders (6.5 mm in diameter, 12-13 mm in length) from a milky zone of a natural quartz single crystal have been cored in orientations (1) normal to one of the prism planes and (2) 45? to and 45? to (O+orientation). At 1 GPa confining pressure, 900? C and 10-6s-1, the flow strength is 150 MPa for samples with orientation (1). Further experiments are needed to establish the flow strength for orientation (2). FTIR measurements on double-polished thick sections (200-500 ?m) in the undeformed quartz material yield an average H2O content of approximately 100 H/106Si. The water is heterogeneously distributed in the sample. Direct measurements on fluid inclusions yield a H2O content of more than 25 000 H/106Si. Thus, the H2O in the undeformed material is predominantly present in fluid inclusions of size from tens to hundred microns. Micro-thermometric measurements at low temperature indicate the presence of different salts in the fluid inclusions. The ice melting temperature, between -6.9 and -7.4? C, indicate an average salinity of 10.5 wt% NaCl. After deformation the distribution of H2O is more homogeneous throughout the sample. The majority of the big inclusions have disappeared and very small inclusions of several microns to sub-micron size have formed. FTIR measurements in zones of undulatory extinction and shear bands show an average H2O content of approximately 3000 H/106Si. Moreover, the larger fluid inclusions are characterized by a higher salinity (12 wt%) due to H2O loss into the healed cracks. First observations of deformed samples show abundant deformation lamellae. With higher deformation the lamellae form conjugated zones of high dislocation density and undulatory extinction. Micro cracks are frequently connected to fluid inclusions. Recrystallized grains are rare in deformed samples because of the low strain acquired. In semi-brittle experiments at lower temperature and faster strain rates considerable recrystallization features are visible and clearly connected to initial brittle deformation features. We conclude that fluid inclusion rupture and fast crack healing at high temperatures are necessary for the redistribution of H2O and a prerequisite of ductile deformation. References: Griggs, D.T. & Balcic, J.D. 1965: Quartz: anomalous weakness of synthetic crystals. Science 147, 293-295. FitzGerald, J.D., Boland, J.N., McLaren, A.C., Ord, A., Hobbs, B.E. 1991: Microstructures in water-weakened single crystals of quartz. Journal of Geophysical Research Vol. 96 No. B2, 2139-2155 Kronenberg, A.K. & Tullis, J. 1984: Flow strength of quartz aggregates: grain size and pressure effects due to hydrolytic weakening. Journal of Geophysical Research Vol.89, No. B6, 4281-4297. Kronenberg, A.K., Kirby, S.H., Aines, R.D., Rossman G.R. 1986: Solubility and diffusional uptake of hydrogen in quartz at high water pressures: implication for hydrolytic weakening. Journal of Geophysical Research Vol.91, NO. B12, 12,723-12,744. Paterson, M.S.1989: The interaction of water with quartz and the influence in dislocation flow - an overview. In: S. Karato and M. Toriumi (Editors), Rheology of Solids and of the Earth. Oxford University Press, London, pp. 107-142.

  5. Single Crystal Diffuse X-ray Scattering Using Continuous Rotation

    NASA Astrophysics Data System (ADS)

    Krogstad, Matthew; Chmaissem, Omar; Taddei, Keith; Allred, Jared; Osborn, Raymond; Rosenkranz, Stephan; Wozniak, Justin

    2015-03-01

    Single crystal diffuse scattering provides a measure of the 3D pair distribution function and is thus useful for investigating short-range order in materials. Using very bright synchrotron x-ray sources and fast area detectors, large volumes of reciprocal space can be mapped quickly with a dynamic range large enough to measure both Bragg peaks and the much weaker diffuse scattering. With the appropriate tools for processing and analyzing large data sets (10 to 30GB), this technique can be used to track changes in the defect structures of a material as a function of different parameters, providing a sensitive and efficient method for investigating phenomena associated with disorder. We have been developing methods of measuring diffuse scattering using continuous sample rotations (shutterless mode) at the Advanced Photon Source, and will show data from several systems, including iron pnictides, for a range of temperatures and doping levels. Supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  6. Mechanical deformation of single-crystal ZnO

    NASA Astrophysics Data System (ADS)

    Kucheyev, S. O.; Bradby, J. E.; Williams, J. S.; Jagadish, C.; Swain, M. V.

    2002-02-01

    The deformation behavior of bulk ZnO single crystals is studied by a combination of spherical nanoindentation and atomic force microscopy. Results show that ZnO exhibits plastic deformation for relatively low loads (?4-13 mN with an ˜4.2 ?m radius spherical indenter). Interestingly, the elastic-plastic deformation transition threshold depends on the loading rate, with faster loading resulting, on average, in larger threshold values. Multiple discontinuities (so called "pop-in" events) in force-displacement curves are observed during indentation loading. No discontinuities are observed on unloading. Slip is identified as the major mode of plastic deformation in ZnO, and pop-in events are attributed to the initiation of slip. An analysis of partial load-unload data reveals values of the hardness and Young's modulus of 5.0±0.1 and 111.2±4.7 GPa, respectively, for a plastic penetration depth of 300 nm. Physical processes determining deformation behavior of ZnO are discussed.

  7. A study of single crystal zirconia implanted with platinum ions

    NASA Astrophysics Data System (ADS)

    Xie, Dong-zhu; Zhu, De-zhang; Cao, De-xin; Zhou, Zhu-yao

    1997-11-01

    Single crystal samples of <1 0 0> oriented cubic (yttria stabilized zirconia) (YSZ) were implanted with 105 and 160 keV platinum ions, using a metal vapor vacuum arc (MEVVA) high current ion implanter, to nominal doses of 2 × 10 16ions/cm 2 and 5 × 10 16ions/cm 2, respectively, at room temperature (RT). The implanted samples were annealed isothermally in air ambient at 850°C and 1100°C from 4 to 12 h. Rutherford Backscattering Spectrometry and Channeling (RBS-C) of 2 MeV He ions has been used to study the depth distribution of lattice damage and implant, as well as the annealing behavior. X-ray diffraction (XRD) is employed to analyze the crystallite of implanted platinum. Both as-implanted samples do not show an amorphous phase. The Pt depth profile was almost unchanged for all samples during annealing at 850°C and 1100°C. For the 160 keV implanted sample no loss of Pt was observed after annealing at 1100°C. XRD results provide evidence for the formation of a monoclinic phase of ZrO 2 in the damage region after 1100°C annealing. For all annealed samples, Pt <2 0 0> preferred orientation crystallites were observed by XRD, while the Pt <1 1 1> peak was almost not visible for 850°C annealed samples.

  8. Analysis of ripple formation in single crystal spot welds

    SciTech Connect

    Rappaz, M. [Ecole Polytechnique Federale de Lausanne (Switzerland). Lab de Metallurgie Physique; Corrigan, D.; Boatner, L.A. [Oak Ridge National Lab., TN (United States). Solid State Div.

    1997-10-01

    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 {micro}m) and spacing (typically {approximately} 60 {micro}m) 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.

  9. Pixelated Single-crystal Diamond Detector for fast neutron measurements

    NASA Astrophysics Data System (ADS)

    Rebai, M.; Cazzaniga, C.; Croci, G.; Tardocchi, M.; Perelli Cippo, E.; Calvani, P.; Girolami, M.; Trucchi, D. M.; Grosso, G.; Gorini, G.

    2015-03-01

    Single-crystal Diamond Detectors (SDDs), due to their high radiation hardness, fast response time and small size, are good candidates as fast neutron detectors in those environments where the high neutron flux is an issue, such as spallation neutron sources and the next generation thermonuclear fusion plasmas, i.e. the ITER experiment. Neutron detection in SDDs is based on the collection of electron-hole pairs produced by charged particles generated by neutron interactions with 12C. Recent measurements have demonstrated the SDD capability of measuring the neutron flux with a good energy resolution and at high rates. In this work a novel detector based on a 12-pixels SDD matrix will be presented. Each pixel is equipped with an independent electronic chain: the fast shaping preamplifier coupled to a digitizer is able to combine the high rate capability and the good energy resolution. Two CAEN digitizers are compared and the possibility of performing good energy resolution measurements (<2%) and at high rates (>1 MHz per channel) is described. Each pixel was characterized and calibrated using an 241Am source: the energy resolution was evaluated and gives a mean value of 1.73% at 5.5 MeV. The good energy resolution achieved and its uniformity between pixels are the demonstration of the capability of this novel detector as a spectrometer. This system will be installed during the next Deuterium-Tritium campaign on a collimated vertical line of sight at JET for 14 MeV neutron measurements.

  10. New phenolic N-methylquinolinium single crystals for second-order nonlinear optics

    NASA Astrophysics Data System (ADS)

    Kim, Ji-Soo; Lee, Seung-Heon; Jazbinsek, Mojca; Yun, Hoseop; Kim, Jongtaek; Lee, Yoon Sup; Kim, Jun Wan; Rotermund, Fabian; Kwon, O.-Pil

    2015-07-01

    Highly efficient nonlinear optical quinolinium single crystals are newly designed and synthesized. The quinolinium single crystals consist of a 2-(4-hydroxystyryl)-1-methylquinolinium cation possessing large molecular optical nonlinearity and a 2,4,6-trimethylbenzenesulfonate counter anion. The quinolinium crystals exhibit monoclinic acentric space group P21 symmetry, resulting in large macroscopic nonlinear optical response, which is comparable with those of highly nonlinear optical configurationally locked polyene crystals. Plate-shaped bulk quinolinium crystals with an area of up to 56 mm2 are successfully grown by the solution growth method. Single quinolinium crystals exhibit a large transparency range (550-1600 nm) in the optical region and a relatively low absorption coefficient in the THz region.

  11. Method for the growth of large low-defect single crystals

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor); Neudeck, Philip G. (Inventor); Trunek, Andrew J. (Inventor); Spry, David J. (Inventor)

    2008-01-01

    A method and the benefits resulting from the product thereof are disclosed for the growth of large, low-defect single-crystals of tetrahedrally-bonded crystal materials. The process utilizes a uniquely designed crystal shape whereby the direction of rapid growth is parallel to a preferred crystal direction. By establishing several regions of growth, a large single crystal that is largely defect-free can be grown at high growth rates. This process is particularly suitable for producing products for wide-bandgap semiconductors, such as SiC, GaN, AlN, and diamond. Large low-defect single crystals of these semiconductors enable greatly enhanced performance and reliability for applications involving high power, high voltage, and/or high temperature operating conditions.

  12. Growth and characterization of 100 mm diameter CdZnTe single crystals by the vertical gradient freezing method

    Microsoft Academic Search

    T. Asahi; O. Oda; Y. Taniguchi; A. Koyama

    1996-01-01

    Recent bulk crystal growth of CdTe and Cd1 ? xZnxTe is reviewed from the viewpoint of large diameter single crystal growth. A VGF method based on a multiple-zone furnace has been developed to grow ?111?-oriented 100 mm diameter single crystals. By this method, ?111?-oriented Cd1 ? xZnxTe single crystals can be reproducibly grown. The grown crystals were characterized by the

  13. Molecular-weight-dependent changes in morphology of solution-grown polyethylene single crystals.

    PubMed

    Zhang, Bin; Chen, Jingbo; Baier, Moritz C; Mecking, Stefan; Reiter, Renate; Mülhaupt, Rolf; Reiter, Günter

    2015-01-01

    Polymer single crystals consisting of folded chains are always in a nonequilibrium state, even if they are faceted with a well-defined envelope reflecting the parameters of the crystal unit cell. Heterogeneities like small variations in the degree of chain folding within such crystals are responsible for a rather broad range in melting temperature. Consequently, upon annealing at a given temperature, some parts may be above and some below their respective melting temperatures, inducing a lamellar thickening process, which may vary locally. To emphasize such variations, controlled annealing experiments are performed at comparatively low temperatures and for long times. For single crystals of low-molecular-weight polyethylene, the formation of the well-known "Swiss-cheese"-like morphology with randomly distributed holes of varying sizes within the annealed single crystal is observed. However, for high-molecular-weight polyethylene, a regular pattern appeared upon annealing, characterized by branches of equal width that are oriented perpendicular to the crystal edge. All branches end at the nucleation site. Interestingly, the resulting pattern depends sensitively on both crystallization and annealing conditions. These thermally induced regular patterns within a single crystal are attributed to a stable crystalline framework formed within polyethylene single crystals in the course of growth. PMID:25303218

  14. High aspect-ratio combined poly and single-crystal silicon (HARPSS) MEMS technology

    Microsoft Academic Search

    Farrokh Ayazi; Khalil Najafi

    2000-01-01

    This paper presents a single-wafer high aspect-ratio micromachining technology capable of simultaneously producing tens to hundreds of micrometers thick electrically isolated poly and single-crystal silicon microstructures. High aspect-ratio polysilicon structures are created by refilling hundreds of micrometers deep trenches with polysilicon deposited over a sacrificial oxide layer. Thick single-crystal silicon structures are released from the substrate through the front side

  15. Single crystal silicon as a macro-world structural material : application to compact, lightweight high pressure vessels

    E-print Network

    Garza, Tanya Cruz

    2011-01-01

    Single crystal silicon has promising inherent structural properties which are attractive for weight sensitive applications. Single crystal silicon, however, is a brittle material which makes the usable strength that can ...

  16. Structural, thermal and dielectric properties of cadmium malate single crystal grown in limited diffusion media

    NASA Astrophysics Data System (ADS)

    Lincy, A.; Mahalakshmi, V.; Thomas, J.; Saban, K. V.

    2015-02-01

    Single crystals of cadmium malate trihydrate have been grown by the controlled diffusion of ionic species in hydrosilica gel. Single crystal X-ray diffraction studies show that the crystal belongs to the monoclinic system with space group P21/n. The functional groups elucidated from the FTIR spectrum are in conformity with the information derived from the X- ray diffraction studies. The thermal behaviour of the material has been investigated using TG- DTA techniques. The optical band gap of the material has been estimated using diffuse reflectance spectroscopy. The dielectric constant, dielectric loss and a.c. conductivity of the crystal are studied over wide temperature and frequency ranges.

  17. Orientation evolution of single-crystal superalloys under different solidification interface

    NASA Astrophysics Data System (ADS)

    Yang, Chubin; Liu, Lin; Luo, Ning; Zhang, Jun; Han, Baojun; Liu, Gang; Fu, Hengzhi

    2014-12-01

    The single-crystal superalloys with different deviation angle are prepared by using the liquid metal cooling high-temperature gradient directional solidification furnace, and the orientation evolution of single-crystal superalloys under different solidification interface is studied. The results indicate that the increase of the deviation angle will make the planar interface unstable. With the increase of the solidification rate, the growth direction of the crystal will deviate from the direction of heat flow to the preferred orientation direction. Under the developed dendrite crystal growth, the branches of the dendrite will follow the preferred orientation, nearly free from the effect of the heat flow.

  18. Electrical resistivity measurements on fragile organic single crystals in the diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Adachi, T.; Tanaka, H.; Kobayashi, H.; Miyazaki, T.

    2001-05-01

    A method of sample assembly for four-probe resistivity measurements on fragile organic single crystals using a diamond anvil cell is presented. A procedure to keep insulation between the metal gasket and four leads of thin gold wires bonded to the sample crystal by gold paint is described in detail. The resistivity measurements performed on a single crystal of an organic semiconductor and that of neutral molecules up to 15 GPa and down to 4.2 K showed that this new procedure of four-probe diamond anvil resistivity measurements enables us to obtain sufficiently accurate resistivity data of organic crystals.

  19. Photoinduced Surface Relief Grating Formation for a Single Crystal of 4-Aminoazobenzene

    PubMed Central

    Nakano, Hideyuki

    2010-01-01

    Photoinduced surface relief grating (SRG) formation for a single crystal of 4-aminoazobenzene was investigated. It was found that SRG could be inscribed on the (001) surface of the crystal, which might suggest that the photoinduced SRG formation is a general phenomenon observed for single crystals of azobenzene-based molecules as well as for azobenzene-based amorphous systems. In addition, the dependences of the SRG formation upon the orientation of the sample crystal and upon the polarization of the writing beams were found to be different from those observed for previously reported crystalline systems. PMID:20480021

  20. Interdiffusion behavior between NiAlHf coating and Ni-based single crystal superalloy with different crystal orientations

    NASA Astrophysics Data System (ADS)

    Wang, Ruili; Gong, Xueyuan; Peng, Hui; Ma, Yue; Guo, Hongbo

    2015-01-01

    NiAlHf coatings were deposited onto Ni-based single crystal (SC) superalloy with different crystal orientations by electron beam physical vapor deposition (EB-PVD). The effects of the crystal orientations of the superalloy substrate on inter-diffusion behavior between the substrate and the NiAlHf coating were investigated. Substrate diffusion zone (SDZ) containing needle-like ? phases and interdiffusion zone (IDZ) mainly consisting of the ellipsoidal and rod-like ? phases were formed in the SC alloy after heat-treatment 10 h at 1100 °C. The thickness of secondary reaction zone (SRZ) formed in the SC alloy with (0 1 1) crystal orientation is about 14 ?m after 50 h heat-treatment at 1100 °C, which is relatively thicker than that in the SC alloy with (0 0 1) crystal orientation, whereas the IDZ revealed similar thickness.

  1. A crystal plasticity materials constitutive model for polysynthetically-twinned ?TiAl + ? 2 Ti 3 Al single crystals

    Microsoft Academic Search

    M. Grujicic; S. Batchu

    2001-01-01

    Deformation behavior of polysynthetically-twinned lamellar ?-TiAl + ?2-Ti3Al single crystals has been analyzed using a three-dimensional, isothermal, rate-dependent, large-strain, crystal-plasticity based materials constitutive model. Within the model it is assumed that plastic deformation parallel to the ?-TiAl\\/?2-Ti3Al lamellar boundaries is controlled by the softer ?-TiAl phase while deformation which contains a component normal to these boundaries is dominated by the

  2. Analytical development of single crystal Macro Fiber Composite actuators for active twist rotor blades

    NASA Astrophysics Data System (ADS)

    Park, Jae-Sang; Kim, Ji-Hwan

    2005-08-01

    A Macro Fiber Composite (MFC) is a piezoelectric fiber composite which has an interdigitated electrode, rectangular cross-section and unidirectional polycrystalline piezoceramic (PZT) fibers embedded in the polymer matrix. A MFC actuator has much higher actuation performance and flexibility than a monolithic piezoceramic actuator. Moreover, the single crystal piezoelectric material exhibits much higher induced strain levels, energy density and coupling than those of polycrystalline piezoceramic materials. Thus, the performance of an MFC can be improved by using single crystal piezoelectric fiber instead of polycrystalline piezoceramic fiber. This study investigates the analytical modeling, material properties and actuation performance of an MFC using single crystal piezoelectric material (single crystal MFC). For single crystal MFC, the mechanical properties are calculated by the classical lamination theory, and the uniform fields model (UFM) is adopted to predict piezoelectric strain constants. In addition, the actuation performance of the single crystal MFC with the active twist rotor blade is studied. The material properties and actuation performance of single crystal MFC are compared with those of standard MFC.

  3. Single crystal PMN-PT/epoxy 1-3 composite for energy-harvesting application.

    PubMed

    Ren, Kailiang; Liu, Yiming; Geng, Xuecang; Hofmann, Heath F; Zhang, Qiming M

    2006-03-01

    One key parameter in using electroactive materials to harvest electric energy from mechanical sources is the energy conversion efficiency. Recently, it was shown that, in the relaxor ferroelectric PMN-PT single crystals, a very high longitudinal electromechanical coupling factor (>90%) can be obtained. This paper investigates energy harvesting using 1-3 composites of PMN-PT single crystals in a soft epoxy matrix. It is shown that 1-3 composites enable the single crystals operating in the longitudinal mode to achieve high efficiency for energy harvesting, and the soft-polymer, matrix-supported single-crystal rods maintain high mechanical integrity under different external loads. For comparison, 1-3 composites with piezoceramic PZT also are investigated in energy-harvesting applications, and the results show that the high coupling factor of single crystal PMN-PT 1-3 composites leads to much higher electric energy output for similar mechanical energy input. The harvested energy density of 1-3 composite with single crystal (22.1 mW/cm3 under a stress of 40.4 MPa) is about twice of that harvested with PZT ceramic 1-3 composite (12 mW/cm3 under a stress of 39 MPa). At a higher stress level, the harvested-energy density of 1-3 PMN-PT single crystal composite can reach 96 mW/cm3. PMID:16555772

  4. Mechanical testing of large thallium doped sodium iodide single crystals

    NASA Technical Reports Server (NTRS)

    Lee, H. M.

    1985-01-01

    The findings of mechanical tests performed on five thallium-doped sodium iodide NaI(Tl) crystals are presented. These crystals are all in the shape of circular flat plates, 20.0 in. in diameter an d0.5 in. thick. The test setup, testing procedure, and the test data are presented. Large crystals exhibit a high degree of material plasticity, as well as a much higher strength than previously anticipated, on the order of 500 psi. Also revealed from the testing is the fact that crystal with a large number of grain boundaries developed less plasticity, and therefore less permanent deformation, than those with fewer grain boundaries.

  5. Spectroscopic, dielectric properties and local structure observation by EXAFS for Nd,Y:CaF2 crystal

    NASA Astrophysics Data System (ADS)

    Ma, F. K.; Zhang, Q.; Jiang, D. P.; Su, L. B.; Shao, Y. J.; Wang, J. Y.; Tang, F.; Xu, J.; Solarz, P.; Ryba-Romanowski, W.; Lisiecki, R.; Macalik, B.

    2014-10-01

    Trivalent impurity ions are clustered easily in fluoride crystals. With the addition of Y3+ spectral properties are greatly enhanced. Low temperature absorption and emission spectra are performed to unfold the optical centers in Nd3+,Y3+:CaF2 crystals. The strongest absorption line at around 790?nm belongs to M luminescence quenched centers in 1%Nd3+:CaF2; and at 797?nm to L? centers for a codoped one. For emission spectra 1049.3?nm and 1068.7?nm are attributed to M? and N? non quenched centers; 1054.6?nm to an L? site in a 1%Nd3+,5%Y3+:CaF2 sample. EXAFS spectra, an intuitive approach, are applied to reveal that the first coordination number of Nd3+ increased from 9.2 to 10.7 with the addition of Y3+ ions, and the local lattice expanded.

  6. Study of the microstructure of a Ni(100) single crystal grown by electron beam floating zone melting

    NASA Astrophysics Data System (ADS)

    Alonzo, V.; Berthier, F.; Glebovsky, V. G.; Priester, L.; Semenov, V. N.

    1995-12-01

    The electron beam floating zone melting technique was used to grow oriented single crystals of high-purity nickel. Procedures for the preparation of monocrystalline seeds as well as for the growth of Ni single crystals were developed. Studies of the chemical composition of (100)-oriented single crystals were made. Electrochemical and metallographical methods coupled with microstructural observations by scanning electron microscopy showed the high structural uniformity of the grown single crystals.

  7. Characterization of single crystals and mixed crystals of M(HCOO) 2 · 2urea: M=Mn, Fe, Co, Ni/Mg, Zn, Cd

    NASA Astrophysics Data System (ADS)

    Yamagata, K.; Saito, Y.; Abe, T.; Hashimoto, M.

    1990-12-01

    Growth of single crystals and change of crystal habit with crystal size are reported. Preparation and characterization of Mn-Mg, Mn-Zn, Mn-Cd, Co-Zn and Ni-Zn mixed crystals are described. Preliminary result of structure analysis is discussed.

  8. A 3D MOF showing unprecedented solvent-induced single-crystal-to-single-crystal transformation and excellent CO2 adsorption selectivity at room temperature.

    PubMed

    Qin, Tao; Gong, Jun; Ma, Junhan; Wang, Xin; Wang, Yonghua; Xu, Yan; Shen, Xuan; Zhu, Dunru

    2014-12-28

    A water stable porous 3D metal-organic framework, [Cu3L2(?3-OH)2(?2-H2O)]·2DMA (1, mother crystal, H2L = 2,2'-dinitrobiphenyl-4,4'-dicarboxylic acid, DMA = N,N-dimethylacetamide), shows unprecedented irreversible solvent-induced substitutions of bridging aqua ligands and guest-exchanges in single-crystal-to-single-crystal (SCSC) transformations at room temperature (RT), producing quantitatively three daughter crystals, [Cu3L2(?3-OH)2]·2S (2: 2A, S = acetone; 2B, S = 2-propanol; 2C, S = 2-butanol), which exhibit reversible interconversion by guest-exchanges at RT in SCSC transformations. MOF 1 shows excellent separation selectivity (128) of CO2/N2 at RT and is a better sorbent of micro-solid-phase extraction (?-SPE) than currently known benchmark ZIF-8. PMID:25376240

  9. A finite element characterization of a commercial endlessly single-mode photonic crystal fiber: is it really single mode?

    Microsoft Academic Search

    H.P. Uranus; H. J. W. M. Hoekstra; E. van Groesen

    2007-01-01

    One of interesting properties of photonic crystal fibers (PCFs) is their possibility to be single-moded over a wide wavelength range, down to UV, while still having a reasonably large modal profile. Such properties are attractive for applications like optical sensing, interferometry, and transport of white light. PCFs, which is designed specially for such property are known as the endlessly single-mode

  10. Vibronic spectra of single dibenzoterrylene molecules in anthracene and 2,3-dimethylanthracene crystals

    NASA Astrophysics Data System (ADS)

    Makarewicz, A.; Deperasi?ska, I.; Karpiuk, E.; Nowacki, J.; Kozankiewicz, B.

    2012-05-01

    The vibronic structure of fluorescence excitation spectra of single molecules of dibenzoterrylene (DBT) in anthracene (Ac) and in 2,3-dimethylanthracene (2,3-DMA) crystals were studied at 5 K. The vibronic patterns observed for different single molecules in the same crystal site were explained as fingerprints of the molecular geometry, which according to the ONIOM calculations are strongly dependent on the local insertion cavity. The 'dipolar' disorder encountered in the 2,3-DMA crystals led to a broad frequency distribution of the purely electronic lines of single molecules. The saturation curves for the (0, 0) and vibronic transitions were studied.

  11. Anisotropic constitutive modeling for nickel base single crystal superalloys using a crystallographic approach

    NASA Technical Reports Server (NTRS)

    Stouffer, D. C.; Sheh, M. Y.

    1988-01-01

    A micromechanical model based on crystallographic slip theory was formulated for nickel-base single crystal superalloys. The current equations include both drag stress and back stress state variables to model the local inelastic flow. Specially designed experiments have been conducted to evaluate the effect of back stress in single crystals. The results showed that (1) the back stress is orientation dependent; and (2) the back stress state variable in the inelastic flow equation is necessary for predicting anelastic behavior of the material. The model also demonstrated improved fatigue predictive capability. Model predictions and experimental data are presented for single crystal superalloy Rene N4 at 982 C.

  12. Long range internal stresses in deformed single crystal copper

    NASA Astrophysics Data System (ADS)

    Geantil, Peter T.

    The subject of backstresses or long range internal stresses (LRIS) in plastically deformed crystalline materials has been investigated extensively over the past 40 years. It is currently believed that elevated stresses are present in regions of elevated dislocation density or dislocation heterogeneities in deformed dislocation microstructures. The heterogeneities include dislocation pile-ups, edge dislocation dipole bundles and dislocation dense cell walls in monotonically and cyclically deformed materials. Understanding the magnitude of long range internal stresses (LRIS) is especially important for the understanding of cyclic deformation and monotonic deformation. First, the fundamental theories needed to understand the subject matter are presented. Following this, is a summary of select previous experiments aimed at assessing LRIS. This will then be followed by my results from my experiments and analysis. A number of experiments were performed at the Advanced Photon Source at Argonne National Labs in an effort to measure LRIS within deformed single crystal copper. Measurements were taken from a large number of locations within the dislocation microstructure, both in dislocation dense regions, and regions with low dislocation density. The results from these experiments, as well as additional analysis relating to the nature of the LRIS present, will be discussed. Finally, the question as to the origin of LRIS will be discussed. It's clear that the dislocation microstructure is responsible for the stresses present, but it is unclear as to the configuration of the dislocations within the microstructure (ie. Burgers vector and sign) which causes the LRIS. Theories present possible microstructural configurations which may produce LRIS, and these will be compared to a TEM g · b analysis of the dislocation microstructure. Additionally, dislocation dynamics simulations (DDS) were performed in an effort to model LRIS and the microstructure responsible. These models will be analyzed and the result discussed in detail.

  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. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  15. Method for preparing homogeneous single crystal ternary III-V alloys

    DOEpatents

    Ciszek, Theodore F. (Evergreen, CO)

    1991-01-01

    A method for producing homogeneous, single-crystal III-V ternary alloys of high crystal perfection using a floating crucible system in which the outer crucible holds a ternary alloy of the composition desired to be produced in the crystal and an inner floating crucible having a narrow, melt-passing channel in its bottom wall holds a small quantity of melt of a pseudo-binary liquidus composition that would freeze into the desired crystal composition. The alloy of the floating crucilbe is maintained at a predetermined lower temperature than the alloy of the outer crucible, and a single crystal of the desired homogeneous alloy is pulled out of the floating crucible melt, as melt from the outer crucible flows into a bottom channel of the floating crucible at a rate that corresponds to the rate of growth of the crystal.

  16. Design of single-polarization single-mode photonic crystal fiber at 1.30 and 1.55 ?m

    Microsoft Academic Search

    Jian Ju; Wei Jin; M. Suleyman Demokan

    2006-01-01

    Single-polarization single-mode (SPSM) operation of a highly birefringent (HB) photonic crystal fiber (PCF) is investigated in detail by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs). The cutoff wavelengths of the two linearly polarized principal states can be designed by varying the structure parameters of the PCF. The confinement loss and splice loss to standard single-mode

  17. On the bulk ?-Ga2O3 single crystals grown by the Czochralski method

    NASA Astrophysics Data System (ADS)

    Galazka, Zbigniew; Irmscher, Klaus; Uecker, Reinhard; Bertram, Rainer; Pietsch, Mike; Kwasniewski, Albert; Naumann, Martin; Schulz, Tobias; Schewski, Robert; Klimm, Detlef; Bickermann, Matthias

    2014-10-01

    The growth of bulkx ?-Ga2O3 single crystals by the Czochralski method is reported and discussed in terms of crucial growth conditions and correlated with basic electrical and optical properties of the obtained crystals. ?-Ga2O3 crystals have a tendency to a spiral formation due to free carrier absorption in the near infrared (NIR) wavelength range, which hampers radiative heat transfer through the growing crystal. Moderate or low free electron concentrations (<5×1017 cm-3) lead to cylindrical crystals with a high crystallized fraction (g?0.5). The use of a CO2-containing growth atmosphere provides oxygen partial pressures between 0.8 and 4.4×10-2 bar that is sufficient to obtain cylindrical and semiconducting crystals. Doping with Sn increases the free electron concentration in the crystals to high values (~1019 cm-3) that lead to an immediate spiral formation, while doping with Mg (>6 wt ppm) provides insulating crystals with reduced probability of the spiral formation. The estimated Mg equilibrium segregation coefficient across the liquid-solid interface is 0.10-0.12. Annealing of undoped crystals in an oxidizing atmosphere at temperatures ?1200 °C for 20 h decreases the bulk free electron concentration by about one order of magnitude, while the crystal surface becomes insulating. However, Mg:?-Ga2O3 crystals are insensitive to annealing in both oxygen- and hydrogen-containing atmospheres. The transmittance spectra showed a steep absorption edge at 260 nm and virtually full transparency in the visible and NIR wavelength range for low and moderate free electron concentrations. We also demonstrated the possibility of growing 2 in. diameter ?-Ga2O3 single crystals by the Czochralski method. The good crystal quality is evidenced by rocking curve FWHM values of below 50". We noted that most dislocations propagate parallel to (100) plane. Further, we also provide thermal properties of the crystals as a function of temperature.

  18. A comparison of CaF2:Mn thermoluminescent dosimeter chips to aluminum and silicon x-ray calorimeters in the pulsed Hermes III environment

    NASA Astrophysics Data System (ADS)

    Fehl, D. L.; Sujka, B. R.; Vehar, D. W.; Westfall, R. L.; Lorence, L. J., Jr.; Rice, D. A.; Gilbert, D. W.

    1995-01-01

    Hermes III is a pulsed power, Bremsstrahlung simulator used for radiation-hardness testing of electronics components [19-MeV spectrum, 20-ns pulse duration, and typical doses (silicon) ?100 krad (1 kGy)]. CaF2:Mn thermoluminescent dosimeter chips (TLDs) have been compared to a set of x-ray calorimeters in the Hermes III environment for doses between 10-75 krad. Similar to a design reported by Murray and Attix, this set of detectors included different dosimetric materials (silicon and aluminum) and two independent temperature sensors (thermistors and thermocouples). The electronic recording system was also updated. The average disagreement between TLDs and calorimeters was 1%-3%. Radiation transport calculations, however, suggest a possible bias of 4%-6% (source unknown). With the silicon calorimeter the ac bridge, which measured the resistance of thermistor temperature sensors, was extremely sensitive to EMP.

  19. Estimation Model for Electrical Conductivity of Molten CaF2-Al2O3-CaO Slags Based on Optical Basicity

    NASA Astrophysics Data System (ADS)

    Birol, Burak; Polat, Gökhan; Saridede, Muhlis Nezihi

    2015-02-01

    Slag properties, such as electrical conductivity, thermal conductivity, density, viscosity, and surface tension, and the prediction of these properties play an important role in melting and metal refining. Optical basicity depends on the electronegativity of the ions of an individual oxide. This feature represents the bonding characteristics, ionization ability, ion size, and consequently the mobility of free ions inside the slag. These properties affect the electrical conductivity of slags. Therefore, in the current study, various slags containing mainly CaF2 and various oxides were prepared. The optical basicity value of each slag was calculated and their electrical conductivities were measured between 1450°C and 1600°C. The relationship between the optical basicity and the measured properties were discussed. It was observed that increasing optical basicity increases the electrical conductivity as well as the temperature. Thus, a new model for predicting electrical conductivity of slags was built between 1450°C and 1600°C depending on optical basicity and temperature.

  20. On the application of CaF2:Eu and SrF2:Eu phosphors in LED based phototherapy lamp

    NASA Astrophysics Data System (ADS)

    Belsare, P. D.; Moharil, S. V.; Joshi, C. P.; Omanwar, S. K.

    2013-06-01

    In the last few years the interest of scientific community has been increased towards solid state lighting based on LEDs because of their superior advantages over the conventional fluorescent lamps. As the GaN based LEDs are easily available efforts of the researchers are now on making the new phosphors which are excitable in the near UV region (360-400nm) for solid state lighting. This paper reports the photoluminescence characteristics of CaF2:Eu and SrF2:Eu phosphor prepared by wet chemical method. The violet emission of these phosphors with near UV excitation can be useful in making a phototherapy lamp based on LEDs for treating various skin diseases like acne vulgaris and hyperbilirubinemia.