Sample records for zno single crystal

  1. 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.

  2. Heteroepitaxial growth of Pt\\/Co multilayers on single crystal ZnO

    Microsoft Academic Search

    P. F. Carcia; Z. G. Li; H. W. van Kesteren; M. T. Johnson

    1995-01-01

    We have epitaxially grown Pt\\/Co multilayers by sputtering and vapor-deposition directly on single crystals of ZnO, so that Pt\\/Co (111)¦ZnO (0001) and Pt\\/Co [110]¦[110] ZnO, as characterized by high resolution electron microscopy in sputtered films, and by low energy electron diffraction in evaporated films. These multilayers had very large perpendicular magnetic anisotropy energy, Keff = 2.4 × 107 erg\\/cm3-Co (2.4

  3. Bio-inspired synthesis of ZnO polyhedral single crystals under eggshell membrane direction

    NASA Astrophysics Data System (ADS)

    Su, Huilan; Song, Fang; Dong, Qun; Li, Tuoqi; Zhang, Xin; Zhang, Di

    2011-07-01

    A simple and versatile technique was developed to prepare hierarchical ZnO single crystals by introducing eggshell membrane (ESM) to a bio-inspired approach. Based on the control of nucleation and gestation, ZnO nanocrystallites could grow at three dimensions into polyhedral single crystals through a surface sol-gel process followed by a calcination treatment. Different from traditional wet chemical techniques, our synthetic process depends more on the restrictive or directing functions of the ESM biomacromolecules. The hierarchical ZnO nanostructures doped with polyhedral single crystallites could be desirable for catalysts, photoelectrochemical devices, especially solar cells.

  4. Determination of Na acceptor level in Na+ ion-implanted ZnO single crystal

    NASA Astrophysics Data System (ADS)

    Wang, Zheng; Liu, Huibin; He, Haiping; Huang, Jingyun; Chen, Lingxiang; Ye, Zhizhen

    2015-03-01

    Ion implantation was used to dope Na acceptor into ZnO single crystals. With three mixed implantation energies, uniform depth distribution of Na ion in the surface region (~300 nm) of ZnO bulk crystals is achieved. Via post-implantation annealing, a donor-acceptor pair recombination band is identified in the low-temperature photoluminescence spectra, from which the energy level of Na-related acceptor in single crystalline ZnO is estimated to be 300 meV. A p-n junction based on this ZnO-Na layer shows rectifying characteristics, confirming the p-type conductivity.

  5. Investigation of the Electrophotographic Properties of ZnO Single Crystals.

    PubMed

    Kiess, H

    1969-01-01

    It is shown that ZnO single crystals can be used for electrophotographic processes in the same manner as ZnO layers. This is due to the formation of a Schottky barrier at the surface under glow discharge giving a highly resistive layer that is capable of storing the deposited charge for several hours. The decay of the charge in the dark and the discharge mechanism under illumination and its wavelength dependence have been investigated. The results are analyzed in terms of the theory that was developed for ZnO powder-binder layers. Good agreement is achieved. The physical model developed for ZnO layers appears to apply to ZnO single crystals also. PMID:20076108

  6. Encapsulation of nanoparticles into single-crystal ZnO nanorods and microrods

    PubMed Central

    Notarianni, Marco; Rintoul, Llew; Motta, Nunzio

    2014-01-01

    Summary One-dimensional single crystal incorporating functional nanoparticles of other materials could be an interesting platform for various applications. We studied the encapsulation of nanoparticles into single-crystal ZnO nanorods by exploiting the crystal growth of ZnO in aqueous solution. Two types of nanodiamonds with mean diameters of 10 nm and 40 nm, respectively, and polymer nanobeads with size of 200 nm have been used to study the encapsulation process. It was found that by regrowing these ZnO nanorods with nanoparticles attached to their surfaces, a full encapsulation of nanoparticles into nanorods can be achieved. We demonstrate that our low-temperature aqueous solution growth of ZnO nanorods do not affect or cause degradation of the nanoparticles of either inorganic or organic materials. This new growth method opens the way to a plethora of applications combining the properties of single crystal host and encapsulated nanoparticles. We perform micro-photoluminescence measurement on a single ZnO nanorod containing luminescent nanodiamonds and the spectrum has a different shape from that of naked nanodiamonds, revealing the cavity effect of ZnO nanorod. PMID:24778975

  7. Growth of the 2-in-size bulk ZnO single crystals by the hydrothermal method

    Microsoft Academic Search

    Eriko Ohshima; Hiraku Ogino; Ikuo Niikura; Katsumi Maeda; Mitsuru Sato; Masumi Ito; Tsuguo Fukuda

    2004-01-01

    The hydrothermal method combined with a platinum inner container was applied to grow zinc oxide (ZnO) single crystals. High-purity and transparent single crystals with a large size of 50×50×15mm3 were successfully grown. The higher crystallinity of the hydrothermally grown ZnO crystal compared with the commercial ZnO substrate grown by the chemical vapor transport method was confirmed by X-ray diffraction. The

  8. Ga-doped ZnO single-crystal nanotips grown on fused silica by metalorganic chemical vapor deposition

    E-print Network

    Garfunkel, Eric

    Ga-doped ZnO single-crystal nanotips grown on fused silica by metalorganic chemical vapor 08854-8087 Received 8 April 2003; accepted 29 August 2003 In situ Ga-doped ZnO nanotips were grown, and electrical properties of as-grown ZnO nanotips are investigated. Despite the amorphous nature of fused silica

  9. Heteroepitaxial growth of Pt\\/Co multilayers on single crystal ZnO

    Microsoft Academic Search

    P. F. Carcia; Z. G. Li; H. W. van Kesteren; M. T. Johnson

    1995-01-01

    We have epitaxially grown Pt\\/Co multilayers by sputtering and vapor-deposition directly on single crystals of ZnO, so that Pt\\/Co (111) ||ZnO (0001) and Pt\\/Co [1110]||[110] ZnO, as characterized by high resolution electron microscopy in sputtered films, and by low energy electron diffraction in evaporated films. These multilayers had very large perpendicular magnetic anisotropy energy, Keff = 2.4×107 erg\\/cm3-Co (2.4 MJ\\/m3-Co)

  10. Photoelectrochemical Stability and Alteration Products of n-Type Single-Crystal ZnO Photoanodes

    SciTech Connect

    Paulauskas, Irene E. [University of Tennessee, Knoxville (UTK); Jellison Jr, Gerald Earle [ORNL; Boatner, Lynn A [ORNL; Brown, G. M. [Oak Ridge National Laboratory (ORNL)

    2011-01-01

    The photoelectrochemical stability and surface-alteration characteristics of both doped and undoped n-type ZnO single-crystal photoanode electrodes have been investigated. The single-crystal ZnO photoanode properties were analyzed using current-voltage measurements plus spectral and time-dependent quantum-yield methods. These measurements revealed the presence of a distinct anodic peak and an accompanying cathodic surface degradation process at negative potentials. The features of this peak were found to depend on time as well as the NaOH concentration in the electrolyte, but they were independent of the presence of electrode illumination. Current measurements performed at the peak indicate that charging and discharging effects are apparently taking place at the semiconductor/electrolyte interface. This result is consistent with the significant reactive degradation that takes place on the ZnO single crystal photoanode surface and that ultimately leads to the reduction of the ZnO surface to Zn metal. The resulting Zn-metal reaction products create unusual, dendrite-like, surface alteration structural features that were analyzed using x-ray diffraction, energy-dispersive analysis, and scanning electron microscopy. The ZnO doping methods employed here are also shown to be an effective way of increasing the n-type character of the crystals. Higher doping levels result in smaller depletion widths and lower quantum yields, since the minority carrier diffusion lengths are very short in these materials.

  11. X-ray Characterisation of Zinc Oxide (ZnO) Single Crystal Substrates

    SciTech Connect

    Dhanaraj, G.; Raghothamachar, B; Dudley, M

    2010-01-01

    Single crystal substrates of low defect density are paramount for fully realizing the numerous applications of zinc oxide (ZnO) wide bandgap semiconductors. While ZnO substrates are commercially available from various vendors, very little information is available on the structural properties of these substrates. Therefore, an extensive evaluation of available substrates would serve as a basis for the development of ZnO based devices and technologies. In this study, bulk ZnO single crystal substrates grown by different growth techniques have been characterised using synchrotron white beam X-ray topography and high resolution X-ray diffraction. The substrates exhibit a wide range of dislocation densities from as high as 10{sup 6} cm{sup -2} down to less than 1000 cm{sup -2} depending on the growth technique employed. The authors evaluation reveals that ZnO crystals grown by the hydrothermal technique possess the best structural quality with dislocation densities of 800-1000 cm{sup -2} and rocking curves with a full width half maximum of less than 12 arc seconds.

  12. Gamma-ray irradiation effects on the optical properties of bulk ZnO single crystals

    NASA Astrophysics Data System (ADS)

    Empizo, Melvin John F.; Yamanoi, Kohei; Mori, Kazuyuki; Arita, Ren; Iwano, Keisuke; Takabatake, Masahiro; Fukuda, Kazuhito; Hori, Tatsuhiro; Minami, Yuki; Viet Luong, Mui; Abe, Yuki; Kojima, Sadaoki; Arikawa, Yasunobu; Shimizu, Toshihiko; Sarukura, Nobuhiko; Norimatsu, Takayoshi; Azechi, Hiroshi; Salvador, Arnel A.; Sarmago, Roland V.; Fukuda, Tsuguo

    2015-06-01

    Hydrothermal-grown bulk ZnO single crystals are investigated before and after gamma-ray irradiation. The irradiation does not alter the optical transparency in the visible region. The gamma rays only induce modified near-band-edge UV emission with blue-shifted peaks and shortened response times. From the initial values before irradiation, the peaks shift by 5 to 6 nm, and the response times shorten by 140 to 440 ps. We attribute these observations to the radiation-induced defects on the bulk crystals. Our results nevertheless lead to the realization of short-wavelength ZnO scintillators that can be utilized in high-energy-radiation environments.

  13. Time-dependent mechanical-electrical coupled behavior in single crystal ZnO nanorods

    PubMed Central

    Kim, Yong-Jae; Yun, Tae Gwang; Choi, In-Chul; Kim, Sungwoong; Park, Won Il; Han, Seung Min; Jang, Jae-il

    2015-01-01

    Nanoscale time-dependent mechanical-electrical coupled behavior of single crystal ZnO nanorods was systematically explored, which is essential for accessing the long-term reliability of the ZnO nanorod-based flexible devices. A series of compression creep tests combined with in-situ electrical measurement was performed on vertically-grown single crystal ZnO nanorods. Continuous measurement of the current (I)-voltage (V) curves before, during, after the creep tests revealed that I is non-negligibly increased as a result of the time-dependent deformation. Analysis of the I-V curves based on the thermionic emission-diffusion theory allowed extraction of nanorod resistance, which was shown to decrease as time-dependent deformation. Finally, based on the observations in this study, a simple analytical model for predicting the reduction in nanorod resistance as a function of creep strain that is induced from diffusional mechanisms is proposed, and this model was demonstrated to be in an excellent agreement with the experimental results. PMID:25982962

  14. Time-dependent mechanical-electrical coupled behavior in single crystal ZnO nanorods.

    PubMed

    Kim, Yong-Jae; Yun, Tae Gwang; Choi, In-Chul; Kim, Sungwoong; Park, Won Il; Han, Seung Min; Jang, Jae-il

    2015-01-01

    Nanoscale time-dependent mechanical-electrical coupled behavior of single crystal ZnO nanorods was systematically explored, which is essential for accessing the long-term reliability of the ZnO nanorod-based flexible devices. A series of compression creep tests combined with in-situ electrical measurement was performed on vertically-grown single crystal ZnO nanorods. Continuous measurement of the current (I)-voltage (V) curves before, during, after the creep tests revealed that I is non-negligibly increased as a result of the time-dependent deformation. Analysis of the I-V curves based on the thermionic emission-diffusion theory allowed extraction of nanorod resistance, which was shown to decrease as time-dependent deformation. Finally, based on the observations in this study, a simple analytical model for predicting the reduction in nanorod resistance as a function of creep strain that is induced from diffusional mechanisms is proposed, and this model was demonstrated to be in an excellent agreement with the experimental results. PMID:25982962

  15. Morphological and structural characterization of single-crystal ZnO nanorod arrays on flexible and non-flexible substrates

    PubMed Central

    Farhat, Omar F; Halim, Mohd M; Abdullah, Mat J; Ali, Mohammed K M

    2015-01-01

    Summary We report a facile synthesis of zinc oxide (ZnO) nanorod arrays using an optimized, chemical bath deposition method on glass, PET and Si substrates. The morphological and structural properties of the ZnO nanorod arrays were investigated using various techniques such as field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) measurements, which revealed the formation of dense ZnO nanorods with a single crystal, hexagonal wurtzite structure. The aspect ratio of the single-crystal ZnO nanorods and the growth rate along the (002) direction was found to be sensitive to the substrate type. The lattice constants and the crystallite size of the fabricated ZnO nanorods were calculated based on the XRD data. The obtained results revealed that the increase in the crystallite size is strongly associated with the growth conditions with a minor dependence on the type of substrate. The Raman spectroscopy measurements confirmed the existence of a compressive stress in the fabricated ZnO nanorods. The obtained results illustrated that the growth of high quality, single-crystal ZnO nanorods can be realized by adjusting the synthesis conditions. PMID:25821712

  16. Morphological and structural characterization of single-crystal ZnO nanorod arrays on flexible and non-flexible substrates.

    PubMed

    Farhat, Omar F; Halim, Mohd M; Abdullah, Mat J; Ali, Mohammed K M; Allam, Nageh K

    2015-01-01

    We report a facile synthesis of zinc oxide (ZnO) nanorod arrays using an optimized, chemical bath deposition method on glass, PET and Si substrates. The morphological and structural properties of the ZnO nanorod arrays were investigated using various techniques such as field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) measurements, which revealed the formation of dense ZnO nanorods with a single crystal, hexagonal wurtzite structure. The aspect ratio of the single-crystal ZnO nanorods and the growth rate along the (002) direction was found to be sensitive to the substrate type. The lattice constants and the crystallite size of the fabricated ZnO nanorods were calculated based on the XRD data. The obtained results revealed that the increase in the crystallite size is strongly associated with the growth conditions with a minor dependence on the type of substrate. The Raman spectroscopy measurements confirmed the existence of a compressive stress in the fabricated ZnO nanorods. The obtained results illustrated that the growth of high quality, single-crystal ZnO nanorods can be realized by adjusting the synthesis conditions. PMID:25821712

  17. Coaxial impact-collision ion scattering spectroscopy analysis of ZnO thin films and single crystals

    Microsoft Academic Search

    T. Ohnishi; A. Ohtomo; I. Ohkuboa; M. Kawasaki; M. Yoshimoto; H. Koinuma

    1998-01-01

    Coaxial impact-collision ion scattering spectroscopy (CAICISS) was employed to analyze the surface structure of ZnO single crystals and thin films with various thickness. Epitaxial ZnO films grown on sapphire (?-Al2O3) (0001) by laser molecular beam epitaxy was found to choose the [0001?] growth direction (the (0001?) O face termination) among asymmetric c-axis directions of wurtzite structure by comparing the spectra

  18. Optical signatures of photoinduced Zn vacancies in ZnO single crystal

    SciTech Connect

    Khan, Enamul H., E-mail: enamul-khan@wsu.edu [Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)

    2014-01-07

    193-nm excimer laser interaction with ZnO single-crystal at 0.05–500?KW/cm{sup 2} intensities is investigated under ultra high vacuum conditions by time resolved photoluminescence (PL) spectroscopy. A dominant 3.18?eV PL emission band at 295?K is observed. This band shows unusually long 0.52?±?0.01??s lifetime, indicating a defect mediated emission mechanism. The demonstrated negative thermal quenching for this band confirms its free electron to acceptor type transition. The involved acceptor is attributed to zinc vacancy with ?100?meV shallow acceptor state. This study finds that 193-nm interactions produce Zn vacancies in transient states at 0.05–50?KW/cm{sup 2} excitation intensities and in stable state at 500 KW/cm{sup 2} or above intensities. The transient zinc vacancy production at such low intensities further validates the Frenkel pair creation as mechanism for creating these defects in ZnO single-crystal.

  19. ZnO nanowires array grown on Ga-doped ZnO single crystal for dye-sensitized solar cells

    PubMed Central

    Hu, Qichang; Li, Yafeng; Huang, Feng; Zhang, Zhaojun; Ding, Kai; Wei, Mingdeng; Lin, Zhang

    2015-01-01

    High quality ZnO nanowires arrays were homoepitaxial grown on Ga-doped ZnO single crystal (GZOSC), which have the advantages of high conductivity, high carrier mobility and high thermal stability. When it was employed as a photoanode in the DSSCs, the cell exhibited a 1.44% power-conversion efficiency under the illumination of one sun (AM 1.5G). The performance is superior to our ZnO nanowires/FTO based DSSCs under the same condition. This enhanced performance is mainly attributed to the perfect interface between the ZnO nanowires and the GZOSC substrate that contributes to lower carrier scattering and recombination rates compared with that grown on traditional FTO substrate. PMID:26099568

  20. ZnO nanowires array grown on Ga-doped ZnO single crystal for dye-sensitized solar cells.

    PubMed

    Hu, Qichang; Li, Yafeng; Huang, Feng; Zhang, Zhaojun; Ding, Kai; Wei, Mingdeng; Lin, Zhang

    2015-01-01

    High quality ZnO nanowires arrays were homoepitaxial grown on Ga-doped ZnO single crystal (GZOSC), which have the advantages of high conductivity, high carrier mobility and high thermal stability. When it was employed as a photoanode in the DSSCs, the cell exhibited a 1.44% power-conversion efficiency under the illumination of one sun (AM 1.5G). The performance is superior to our ZnO nanowires/FTO based DSSCs under the same condition. This enhanced performance is mainly attributed to the perfect interface between the ZnO nanowires and the GZOSC substrate that contributes to lower carrier scattering and recombination rates compared with that grown on traditional FTO substrate. PMID:26099568

  1. Glycine adsorption and photo-reaction over ZnO(000?) single crystal

    NASA Astrophysics Data System (ADS)

    Gao, Y. K.; Traeger, F.; Wöll, C.; Idriss, H.

    2014-06-01

    The adsorption and reaction of the amino acid glycine (NH2CH2COOH) are studied experimentally on the polar single crystal surface of zinc oxide, ZnO(000?), by X-ray photoelectron spectroscopy (XPS) under UV light in presence and absence of molecular O2. Deposition at 350 K mainly resulted in a largely deprotonated monolayer (NH2CH2COO-(a) + OH(s); where O is surface oxygen, (a) is for adsorbed and (s) is for surface species) identified by its XPS C1s binding energy at 289.3 eV (COO), 286.7 eV (CH2) and XPS O1s at 531.8 eV (COO). A decrease in the signals of all functional groups of the adsorbed glycine (monitored by their C1s, O1s, and N1s lines) is seen upon UV excitation in the absence and presence of O2 pressures up to 5 × 10- 6 mbar. The photoreaction cross sections extracted from the decrease in the C1s peaks were found to be = 2.6 × 10- 18 (COO(a)) and 1.4 × 10- 18(CH2) cm2. The photoactivity of the ZnO(000?) surface under UHV-conditions is found to be comparable to that seen in direct photolysis of amino acids in solution.

  2. Evaluation of Melt-Grown, ZnO Single Crystals for Use as Alpha-Particle Detectors

    Microsoft Academic Search

    John S. Neal; Nancy C. Giles; Xiaocheng Yang; R. Andrew Wall; K. Burak Ucer; Richard T. Williams; Dariusz J. Wisniewski; Lynn A. Boatner; Varatharajan Rengarajan; Jeff E Nause; Bill Nemeth

    2008-01-01

    As part of an ongoing investigation of the scintillation properties of zinc-oxide-(ZnO)-based scintillators, several melt-grown, ZnO single crystals have been characterized using alpha-particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc., using an oxygen-pressurized melt-growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and lanthanides (Gd,

  3. Double-sided ZnO nanorod arrays on single-crystal Ag holed microdisks with enhanced photocataltytic efficiency

    NASA Astrophysics Data System (ADS)

    Zuo, Yuanhui; Qin, Yao; Jin, Chao; Li, Ying; Shi, Donglu; Wu, Qingsheng; Yang, Jinhu

    2013-05-01

    Novel hierarchical heterostructures of double-sided ZnO nanorod (NR) arrays grown on single-crystal Ag holed microdisks (HMDs) have been prepared through a two-step aqueous strategy including ZnO seed loading and the subsequent heteroepitaxial growth of ZnO NRs on Ag HMDs. By simply adjusting the synthetic parameters, ZnO NRs with variable NR diameters (20-200 nm), lengths (100-1.8 ?m) and unusual shapes (concave, tubular and sharp tips) on Ag HMDs have been realized, which endows the Ag/ZnO heterostructures with versatile morphologies. The novel Ag/ZnO heterostructures consisting of integrated 1D semiconductor/2D metal nanostructured blocks with high specific surface area (SSA) and opened spatial architectures may promise important applications related to photoelectric fields. As expected, in photocatalytic measurements, the typical Ag HMD/ZnO NR heterostructure exhibits superior catalytic activity over other catalysts of bare ZnO NRs, ZnO NR arrays or heterostructured Ag nanowires (NWs)/ZnO NRs. The synergistic effect of the unique Ag HMD/ZnO NR heterostructures contributing to the high catalytic performance has been discussed in detail.Novel hierarchical heterostructures of double-sided ZnO nanorod (NR) arrays grown on single-crystal Ag holed microdisks (HMDs) have been prepared through a two-step aqueous strategy including ZnO seed loading and the subsequent heteroepitaxial growth of ZnO NRs on Ag HMDs. By simply adjusting the synthetic parameters, ZnO NRs with variable NR diameters (20-200 nm), lengths (100-1.8 ?m) and unusual shapes (concave, tubular and sharp tips) on Ag HMDs have been realized, which endows the Ag/ZnO heterostructures with versatile morphologies. The novel Ag/ZnO heterostructures consisting of integrated 1D semiconductor/2D metal nanostructured blocks with high specific surface area (SSA) and opened spatial architectures may promise important applications related to photoelectric fields. As expected, in photocatalytic measurements, the typical Ag HMD/ZnO NR heterostructure exhibits superior catalytic activity over other catalysts of bare ZnO NRs, ZnO NR arrays or heterostructured Ag nanowires (NWs)/ZnO NRs. The synergistic effect of the unique Ag HMD/ZnO NR heterostructures contributing to the high catalytic performance has been discussed in detail. Electronic supplementary information (ESI) available: Synthesis of ZnO seeds (S1), dispersed ZnO NRs (S2) and ordered ZnO NR arrays on ITO substrates (S3) and SEM images of ZnO NR arrays (Fig. S1). See DOI: 10.1039/c3nr34102j

  4. Origin of green luminescence in hydrothermally grown ZnO single crystals

    NASA Astrophysics Data System (ADS)

    ?ížek, J.; Valenta, J.; Hruška, P.; Melikhova, O.; Procházka, I.; Novotný, M.; Bulí?, J.

    2015-06-01

    Combining photoluminescence and positron annihilation studies of hydrothermally grown ZnO crystals with stoichiometry varied by controlled annealing enabled us to clarify the origin of green luminescence. It was found that green luminescence in ZnO has multiple origins and consists of a band at 2.3(1) eV due to recombination of electrons of the conduction band by zinc vacancy acceptors coupled with hydrogen and a band at 2.47(2) eV related to oxygen vacancies. The as-grown ZnO crystals contain zinc vacancies associated with hydrogen and exhibit a green luminescence at 2.3(1) eV. Annealing in Zn vapor removed zinc vacancies and introduced oxygen vacancies. This led to disappearance of the green luminescence band at 2.3(1) eV and appearance of a green emission at higher energy of 2.47(2) eV. Moreover, the color of the crystal was changed from colorless to dark red. In contrast, annealing of the as-grown crystal in Cd vapor did not remove zinc vacancies and did not cause any significant change of green luminescence nor change in coloration.

  5. Low temperature growth of single-crystal ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Boukos, N.; Chandrinou, C.; Stogios, C.; Giannakopoulos, K.; Travlos, A.

    2007-07-01

    ZnO nanorods are grown on large-area glass substrates with a ZnO overlayer by an aqueous solution method at temperatures ranging from 65 °C down to room temperature. The structure and morphology of the nanorods is studied with electron microscopy. They are single crystalline and grow preferentially perpendicular to the substrate. Their aspect ratio can be tailored by modifying the growth parameters. Self-assembly and subsequent selective growth of the nanorods is accomplished in pre-patterned substrates. Room temperature photoluminescence measurements reveal a strong band edge emission at 378 nm, while no defect-related visible emission is detected except for the nanorods grown at RT.

  6. Surface Structure of ZnO Single Crystals Analysed by Ion Scattering Spectroscopy

    Microsoft Academic Search

    Hideyuki Maki; Noboru Ichinose; Shoichi Sekiguchi; Naoki Ohashi; Takaharu Nishihara; Hajime Haneda; Junzo Tanaka

    1999-01-01

    A ZnO crystal of wurtzite-type structure has polar surfaces of (0001) and (000\\\\=1), which are terminated by Zn and O ions, respectively. Observation conducted by atomic force microscopy showed that step\\/terrace structures were formed on the (0001) and (000\\\\=1) surfaces, whose step height was predominantly half of lattice parameter, c0. The ionic arrangement of the surfaces was determined by coaxial

  7. Nitrogen and hydrogen in bulk single-crystal ZnO S.J. Jokela, M.C. Tarun, M.D. McCluskey

    E-print Network

    McCluskey, Matthew

    .elsevier.com/locate/physb Physica B Fig. 1. Schematic diagram of the CVT growth system. Single-crystal ZnO is grown on a seedO as a seed, we obtained bulk single-crystal growth. The N­H bond-stretching mode gives rise to an IR is carefully removed. If a seed crystal is to be used, it must be attached and in good thermal contact

  8. Evaluation of Melt-Grown, ZnO Single Crystals for Use as Alpha-Particle Detectors

    SciTech Connect

    Neal, John S [ORNL; Giles, N. C. [West Virginia University; Yang, Xiaocheng [West Virginia University; Wall, R. Andrew [Wake Forest University, Winston-Salem, NC; Ucer, Burak [Wake Forest University, Winston-Salem, NC; Williams, Richard T. [Wake Forest University, Winston-Salem, NC; Wisniewski, Dariusz J [ORNL; Boatner, Lynn A [ORNL; Rengarajan, Varatharajan [ORNL; Nause, Jeff E [ORNL; Nemeth, Bell [Cermet, Inc., Atlanta

    2008-01-01

    As part of an ongoing investigation of the scintillation properties of zinc-oxide-based scintillators, several melt-grown, ZnO single crystals have been characterized using -particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc. using a pressurized melt growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and Lanthanides (Gd, Er, Tm). The goals of these studies are to better understand the scintillation mechanisms associated with various members of the ZnO scintillator family and to then use this knowledge to improve the radiation detection capabilities of ZnO-based scintillators. One application for which ZnO is particularly well suited as a scintillator is as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic materials, outstanding timing resolution, and high radiation resistance. ZnO(Ga) and ZnO(In) have demonstrated fast (sub-nanosecond) decay times with relatively low light yields, and ZnO(Ga) has been used in a powder form as the associated particle detector for a D-T neutron generator. Four promising candidate materials, ZnO, ZnO:Ga, ZnO:In,Li, and ZnO:Er,Li, were identified in this study. These four samples demonstrated sub-nanosecond decay times and alpha particle excited luminescence comparable to BC-400 fast plastic scintillator. The ZnO:Mg,Ga, ZnO:Gd, and ZnO:Li samples demonstrated appreciable slow (microsecond) decay components that would be incompatible with high-counting-rate applications.

  9. Characteristics of intermediate state related to anti-Stokes luminescence of ZnO single crystals

    SciTech Connect

    Fujii, Katsushi, E-mail: k.fujii@rcast.u-tokyo.ac.jp [Global Solar Plus Initiative, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan); Center for Interdisciplinary Research, Tohoku University, Aramaki aza Aoba 6-3, Aoba-ku, Sendai 980-8578 (Japan); Goto, Takenari [Center for Interdisciplinary Research, Tohoku University, Aramaki aza Aoba 6-3, Aoba-ku, Sendai 980-8578 (Japan); Nakamura Lab., RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Yao, Takafumi [Center for Interdisciplinary Research, Tohoku University, Aramaki aza Aoba 6-3, Aoba-ku, Sendai 980-8578 (Japan); Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2014-06-21

    Anti-Stokes luminescence from ZnO is supposed to be a two-step two-photon absorption process with an intermediate state. The intermediate state is assumed to be a localized state with two different excited and relaxed states. One of the localized states is believed to be the well-known 2.4?eV green luminescence; the other is difficult to observe experimentally. We found an interesting 2.25 eV deep luminescence from ZnO, which has been shown to relate to anti-Stokes luminescence. The 2.25 eV yellow luminescence was observable only below the band gap excitation and through a time-resolved observation after the excitation light was turned off. The intermediate states were found to be a photo-excited donor-acceptor pair and its lattice relaxation state. The characteristics and the role of the intermediate state of ZnO related to the anti-Stokes luminescence are discussed.

  10. Nature of red luminescence band in research-grade ZnO single crystals: A “self-activated” configurational transition

    SciTech Connect

    Chen, Y. N.; Xu, S. J., E-mail: sjxu@hku.hk; Zheng, C. C.; Ning, J. Q.; Ling, F. C. C. [Department of Physics, HKU-Shenzhen Institute of Research and Innovation (HKU-SIRI), HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Anwand, W.; Brauer, G. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, D-01328 Dresden (Germany); Skorupa, W. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, D-01328 Dresden (Germany)

    2014-07-28

    By implanting Zn{sup +} ions into research-grade intentionally undoped ZnO single crystal for facilitating Zn interstitials (Zn{sub i}) and O vacancies (V{sub O}) which is revealed by precise X-Ray diffraction rocking curves, we observe an apparent broad red luminescence band with a nearly perfect Gaussian lineshape. This red luminescence band has the zero phonon line at ?2.4 eV and shows distinctive lattice temperature dependence which is well interpreted with the configurational coordinate model. It also shows a low “kick out” thermal energy and small thermal quenching energy. A “self-activated” optical transition between a shallow donor and the defect center of Zn{sub i}-V{sub O} complex or V{sub Zn}V{sub O} di-vacancies is proposed to be responsible for the red luminescence band. Accompanied with the optical transition, large lattice relaxation simultaneously occurs around the center, as indicated by the generation of multiphonons.

  11. The growth of ZnO crystals from the melt

    E-print Network

    Klimm, D; Schulz, D; Fornari, R

    2008-01-01

    The peculiar properties of zinc oxide (ZnO) make this material interesting for very different applications like light emitting diodes, lasers, and piezoelectric transducers. Most of these applications are based on epitaxial ZnO layers grown on suitable substrates, preferably bulk ZnO. Unfortunately the thermochemical properties of ZnO make the growth of single crystals difficult: the triple point 1975 deg C., 1.06 bar and the high oxygen fugacity at the melting point p_O2 = 0.35 bar lead to the prevailing opinion that ZnO crystals for technical applications can only be grown either by a hydrothermal method or from "cold crucibles" of solid ZnO. Both methods are known to have significant drawbacks. Our thermodynamic calculations and crystal growth experiments show, that in contrast to widely accepted assumptions, ZnO can be molten in metallic crucibles, if an atmosphere with "self adjusting" p_O2 is used. This new result is believed to offer new perspectives for ZnO crystal growth by established standard techn...

  12. Electron-hole recombination on ZnO(0001) single-crystal surface studied by time-resolved soft X-ray photoelectron spectroscopy

    SciTech Connect

    Yukawa, R.; Yamamoto, S.; Ogawa, M.; Yamamoto, Sh.; Fujikawa, K.; Hobara, R.; Matsuda, I., E-mail: imatsuda@issp.u-tokyo.ac.jp [Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581 (Japan); Ozawa, K. [Department of Chemistry and Materials Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan); Emori, M.; Sakama, H. [Department of Physics, Sophia University, Chiyoda-ku, Tokyo 102-8554 (Japan); Kitagawa, S.; Daimon, H. [Nara Institute of Science and Technology (NAIST), Ikoma, Nara 630-0192 (Japan)

    2014-10-13

    Time-resolved soft X-ray photoelectron spectroscopy (PES) experiments were performed with time scales from picoseconds to nanoseconds to trace relaxation of surface photovoltage on the ZnO(0001) single crystal surface in real time. The band diagram of the surface has been obtained numerically using PES data, showing a depletion layer which extends to 1??m. Temporal evolution of the photovoltage effect is well explained by a recombination process of a thermionic model, giving the photoexcited carrier lifetime of about 1 ps at the surface under the flat band condition. This lifetime agrees with a temporal range reported by the previous time-resolved optical experiments.

  13. Characterization of Mn and Fe diffusion into ZnO Films and single crystals for diluted magnetic semiconductor applications

    Microsoft Academic Search

    R. Gateau; D. H. Hill; R. A. Bartynski; P. Wu; Y. Lu

    2006-01-01

    There is growing interesting in the use of transition metal (TM) doped ZnO films as a diluted magnetic semiconductor for room temperature spintronics applications. Various methods of doping have been investigated including ion implantation and co-deposition during the growth process. In essentially all approaches, doping either accompanies, or is followed by, an annealing step intended to achieve a uniform distribution

  14. Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

    Microsoft Academic Search

    Q. Yang; K. Tang; J. Zuo; Y. Qian

    2004-01-01

    Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron

  15. Ferromagnetism in Mn-implanted ZnO:Sn single crystals D. P. Nortona)

    E-print Network

    Hebard, Arthur F.

    Ferromagnetism in Mn-implanted ZnO:Sn single crystals D. P. Nortona) and S. J. Pearton Department 21 November 2002 We have investigated the magnetic properties of Mn-implanted n-type ZnO single should be possible in manganese-doped p-type ZnO, although Mn-doped n-type ZnO should

  16. Photoluminescence properties of a single ZnO microstructure for potential scintillator applications

    NASA Astrophysics Data System (ADS)

    Empizo, Melvin John F.; Fukuda, Kazuhito; Arita, Ren; Minami, Yuki; Yamanoi, Kohei; Shimizu, Toshihiko; Sarukura, Nobuhiko; Vargas, Ray M.; Salvador, Arnel A.; Sarmago, Roland V.

    2014-12-01

    Photoluminescence properties of ZnO microstructures are investigated for potential scintillator applications. Samples are successfully prepared by the carbothermal reduction method. A single free-standing ZnO microribbon exhibits UV and visible emissions which behave differently along the microstructure. Fast UV emission lifetimes of 40 and 150 ps have been observed for the microstructures compared to 440 ps and 2 ns for a bulk crystal. With waveguided emissions and fast lifetimes, the ZnO microstructures have promising applications as future XFEL scintillators.

  17. Single ZnO nanocactus gas sensor formed by etching of ZnO nanorod

    NASA Astrophysics Data System (ADS)

    Ryong Ryu, Sung; Ram, S. D. Gopal; Cho, Hak-Dong; Lee, Dong Jin; Won Kang, Tae; Woo, Yongdeuk

    2015-06-01

    Etching of materials on the nanoscale is a challenging but necessary process in nanomaterials science. Gas sensing using a single ZnO nanocactus (NC), which was prepared by facile isotropic nanoetching of zinc oxide nanorods (NR) grown by chemical vapor deposition (CVD) using an organic photoresist (PR) by a thermochemical reaction, is reported in this work. PR consists of carboxylic acid groups (COOH) and cyclopentanone (C5H8O), which can react with zinc and oxygen atoms, respectively, on the surface of a ZnO NR. The thermochemical reaction is controllable by varying the concentration of PR and reaction time. A gas sensor was fabricated using a single NC. Gas sensing was tested using different gases such as CH4, NH3 and carbon monoxide (CO). It was estimated that the surface area of a ZnO NC in the case of 50% PR was found to increase four-fold. When compared with a single ZnO NR gas sensor, the sensitivity of a ZnO NC was found to increase four-fold. This increase in sensitivity is attributed to the increase in surface area of the ZnO NC. The formed single ZnO NC gas sensor has good stability, response and recovery time.Etching of materials on the nanoscale is a challenging but necessary process in nanomaterials science. Gas sensing using a single ZnO nanocactus (NC), which was prepared by facile isotropic nanoetching of zinc oxide nanorods (NR) grown by chemical vapor deposition (CVD) using an organic photoresist (PR) by a thermochemical reaction, is reported in this work. PR consists of carboxylic acid groups (COOH) and cyclopentanone (C5H8O), which can react with zinc and oxygen atoms, respectively, on the surface of a ZnO NR. The thermochemical reaction is controllable by varying the concentration of PR and reaction time. A gas sensor was fabricated using a single NC. Gas sensing was tested using different gases such as CH4, NH3 and carbon monoxide (CO). It was estimated that the surface area of a ZnO NC in the case of 50% PR was found to increase four-fold. When compared with a single ZnO NR gas sensor, the sensitivity of a ZnO NC was found to increase four-fold. This increase in sensitivity is attributed to the increase in surface area of the ZnO NC. The formed single ZnO NC gas sensor has good stability, response and recovery time. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02387d

  18. Single ZnO nanocactus gas sensor formed by etching of ZnO nanorod.

    PubMed

    Ryong Ryu, Sung; Ram, S D Gopal; Cho, Hak-Dong; Lee, Dong Jin; Won Kang, Tae; Woo, Yongdeuk

    2015-06-18

    Etching of materials on the nanoscale is a challenging but necessary process in nanomaterials science. Gas sensing using a single ZnO nanocactus (NC), which was prepared by facile isotropic nanoetching of zinc oxide nanorods (NR) grown by chemical vapor deposition (CVD) using an organic photoresist (PR) by a thermochemical reaction, is reported in this work. PR consists of carboxylic acid groups (COOH) and cyclopentanone (C5H8O), which can react with zinc and oxygen atoms, respectively, on the surface of a ZnO NR. The thermochemical reaction is controllable by varying the concentration of PR and reaction time. A gas sensor was fabricated using a single NC. Gas sensing was tested using different gases such as CH4, NH3 and carbon monoxide (CO). It was estimated that the surface area of a ZnO NC in the case of 50% PR was found to increase four-fold. When compared with a single ZnO NR gas sensor, the sensitivity of a ZnO NC was found to increase four-fold. This increase in sensitivity is attributed to the increase in surface area of the ZnO NC. The formed single ZnO NC gas sensor has good stability, response and recovery time. PMID:26058431

  19. Crystal phase engineered quantum wells in ZnO nanowires.

    PubMed

    Khranovskyy, V; Glushenkov, Alexey M; Chen, Y; Khalid, A; Zhang, H; Hultman, L; Monemar, B; Yakimova, R

    2013-05-31

    We report the fabrication of quantum wells in ZnO nanowires (NWs) by a crystal phase engineering approach. Basal plane stacking faults (BSFs) in the wurtzite structure can be considered as a minimal segment of zinc blende. Due to the existing band offsets at the wurtzite (WZ)/zinc blende (ZB) material interface, incorporation of a high density of BSFs into ZnO NWs results in type II band alignment. Thus, the BSF structure acts as a quantum well for electrons and a potential barrier for holes in the valence band. We have studied the photoluminescence properties of ZnO NWs containing high concentrations of BSFs in comparison to high-quality ZnO NWs of pure wurtzite structure. It is revealed that BSFs form quantum wells in WZ ZnO nanowires, providing an additional luminescence peak at 3.329 eV at 4 K. The luminescence mechanism is explained as an indirect exciton transition due to the recombination of electrons in the QW conduction band with holes localized near the BSF. The binding energy of electrons is found to be around 100 meV, while the excitons are localized with the binding energy of holes of ?5 meV, due to the coupling of BSFs, which form QW-like structures. PMID:23619281

  20. SINGLE CRYSTAL NEUTRON DIFFRACTION.

    SciTech Connect

    KOETZLE,T.F.

    2001-03-13

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

  1. Potassium acceptor doping of ZnO crystals

    NASA Astrophysics Data System (ADS)

    Parmar, Narendra S.; Corolewski, Caleb D.; McCluskey, Matthew D.; Lynn, K. G.

    2015-05-01

    ZnO bulk single crystals were doped with potassium by diffusion at 950°C. Positron annihilation spectroscopy confirms the filling of zinc vacancies and a different trapping center for positrons. Secondary ion mass spectroscopy measurements show the diffusion of potassium up to 10 ?m with concentration ˜1 × 1016 cm-3. IR measurements show a local vibrational mode (LVM) at 3226 cm-1, at a temperature of 9 K, in a potassium doped sample that was subsequently hydrogenated. The LVM is attributed to an O-H bond-stretching mode adjacent to a potassium acceptor. When deuterium substitutes for hydrogen, a peak is observed at 2378 cm-1. The O-H peak is much broader than the O-D peak, perhaps due to an unusually low vibrational lifetime. The isotopic frequency ratio is similar to values found in other hydrogen complexes. Potassium doping increases the resistivity up to 3 orders of magnitude at room temperature. The doped sample has a donor level at 0.30 eV.

  2. Polarized Raman scattering of single ZnO nanorod

    SciTech Connect

    Yu, J. L., E-mail: jlyu@semi.ac.cn; Lai, Y. F., E-mail: laiyunfeng@gmail.com; Wang, Y. Z.; Cheng, S. Y. [Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou (China); Chen, Y. H. [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)

    2014-01-21

    Polarized Raman scattering measurement on single wurtzite c-plane (001) ZnO nanorod grown by hydrothermal method has been performed at room temperature. The polarization dependence of the intensity of the Raman scattering for the phonon modes A{sub 1}(TO), E{sub 1}(TO), and E{sub 2}{sup high} in the ZnO nanorod are obtained. The deviations of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules are observed, which can be attributed to the structure defects in the ZnO nanorod as confirmed by the comparison of the transmission electron microscopy, photoluminescence spectra as well as the polarization dependent Raman signal of the annealed and unannealed ZnO nanorod. The Raman tensor elements of A{sub 1}(TO) and E{sub 1}(TO) phonon modes normalized to that of the E{sub 2}{sup high} phonon mode are |a/d|=0.32±0.01,?|b/d|=0.49±0.02, and |c/d|=0.23±0.01 for the unannealed ZnO nanorod, and |a/d|=0.33±0.01,?|b/d|=0.45±0.01, and |c/d|=0.20±0.01 for the annealed ZnO nanorod, which shows strong anisotropy compared to that of bulk ZnO epilayer.

  3. Single photon emission from ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Choi, Sumin; Johnson, Brett C.; Castelletto, Stefania; Ton-That, Cuong; Phillips, Matthew R.; Aharonovich, Igor

    2014-06-01

    Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work, we study single photon emission from defect centers in 20 nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640 nm with polarized excitation and emission. The studied emitters showed continuous blinking; however, bleaching can be suppressed using a polymethyl methacrylate coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO.

  4. Single photon emission from ZnO nanoparticles

    SciTech Connect

    Choi, Sumin; Ton-That, Cuong; Phillips, Matthew R.; Aharonovich, Igor, E-mail: igor.aharonovich@uts.edu.au [School of Physics and Advanced Materials, University of Technology Sydney, Ultimo, New South Wales 2007 (Australia); Johnson, Brett C. [Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, Victoria 3010 (Australia); Castelletto, Stefania [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, Victoria 3000 (Australia)

    2014-06-30

    Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work, we study single photon emission from defect centers in 20?nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640?nm with polarized excitation and emission. The studied emitters showed continuous blinking; however, bleaching can be suppressed using a polymethyl methacrylate coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO.

  5. 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

  6. Ultraviolet photoconductive sensor based on single ZnO nanowire

    E-print Network

    Chow, Lee

    contributing to dark current (as a source of noise) is one thousandth of a normal size detector. This allows Waymont Court, S111, Lake Mary, FL 32746, USA 4 Advanced Materials Processing and Analysis Center. The fabrication of an ultraviolet (UV) photoconductive detector based on single ZnO nanowire (100 nm in diameter

  7. Journal of Crystal Growth 286 (2006) 6165 ZnO growth on Si with low-temperature ZnO buffer layers by

    E-print Network

    Yang, Zheng

    2006-01-01

    Journal of Crystal Growth 286 (2006) 61­65 ZnO growth on Si with low-temperature ZnO buffer layers September 2005; accepted 28 September 2005 Communicated by M.S. Goorsky Abstract High-quality ZnO films were grown on Si(1 0 0) substrates with low-temperature (LT) ZnO buffer layers by an electron cyclotron

  8. Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality

    NASA Astrophysics Data System (ADS)

    Hou, Dongchao; Voss, Tobias; Ronning, Carsten; Menzel, Andreas; Zacharias, Margit

    2014-06-01

    The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = INBE/IDLE can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

  9. DOI: 10.1002/adma.200601908 Piezoelectric Gated Diode of a Single ZnO Nanowire**

    E-print Network

    Wang, Zhong L.

    DOI: 10.1002/adma.200601908 Piezoelectric Gated Diode of a Single ZnO Nanowire** By Jr H. He, Cheng potential en- ergy barrier at the junction. ZnO exhibits the most diverse and abundant configurations studies based on ZnO nanostructures have demonstrated nov- el applications due to their semiconducting

  10. Multimode Resistive Switching in Single ZnO Nanoisland System

    PubMed Central

    Qi, Jing; Olmedo, Mario; Zheng, Jian-Guo; Liu, Jianlin

    2013-01-01

    Resistive memory has attracted a great deal of attention as an alternative to contemporary flash memory. Here we demonstrate an interesting phenomenon that multimode resistive switching, i.e. threshold-like, self-rectifying and ordinary bipolar switching, can be observed in one self-assembled single-crystalline ZnO nanoisland with base diameter and height ranging around 30 and 40?nm on Si at different levels of current compliance. Current-voltage characteristics, conductive atomic force microscopy (C-AFM), and piezoresponse force microscopy results show that the threshold-like and self-rectifying types of switching are controlled by the movement of oxygen vacancies in ZnO nanoisland between the C-AFM tip and Si substrate while ordinary bipolar switching is controlled by formation and rupture of conducting nano-filaments. Threshold-like switching leads to a very small switching power density of 1 × 103?W/cm2. PMID:23934276

  11. Fabrication of ZnO crystals by UV-laser annealing on ZnO nanoparticles prepared by laser ablation method

    NASA Astrophysics Data System (ADS)

    Shimogaki, T.; Kawahara, H.; Higashihata, M.; Ikenoue, H.; Nakamura, D.; Nakata, Y.; Okada, T.

    2014-03-01

    Various zinc oxide (ZnO) nanocrystals are expected as new building blocks for optoelectronic devices. Among them, we have studied about fabricating ZnO nanowires using nanoparticle-assisted pulsed laser deposition (NAPLD). Recently, we achieved to fabricate the periodically-aligned ZnO nanowires with a period of from 4 to 5 ?m using interfering four-beams of nanosecond ultraviolet (UV) laser processing. ZnO nanowires with diameters of several dozen nanometers were grown on the ZnO buffer layer prepared by pulsed laser deposition at the low-chamber pressure of 3 Pa. Additionally, crystallization of ZnO nanoparticles collected on a sapphire substrate was achieved by UV-laser annealing. In this method, ZnO nanoparticles were collected at room temperature, then they were laser-annealed with a KrF excimer laser. The particle size increased by instantaneous melting and aggregation of ZnO nanoparticles because of the high absorption efficiency of ZnO in the UV spectral region. It was found that the optical property was improved by UV-laser annealing process. Additionally, their x-ray diffraction peaks of wurtzite ZnO crystals had narrower full width half maximum than those before laser annealing.

  12. A simple method for systematically controlling ZnO crystal size and growth orientation

    SciTech Connect

    Zhang Rong [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States); Kerr, Lei L. [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States)], E-mail: kerrll@muohio.edu

    2007-03-15

    We present a simple, easy and reproducible method to systematically control the dimension and shape evolution of zinc oxide (ZnO) as thin film on glass substrate by chemical bath deposition (CBD). The only varying factor to control crystal transformation is the molar ratio of Cd{sup 2+}/Zn{sup 2+}, R{sub m}, in the initial chemical solution. With the increase of R{sub m}, ZnO crystals transformed from long-and-slim hexagonal rods to fat-and-short hexagonal pyramids, and then to twinning hexagonal dots as observed by scanning electron microscopy (SEM). Film crystallinity was characterized by X-ray diffraction (XRD). Chemical component analysis by energy dispersive spectroscopy (EDS) showed that most cadmium was present in the residual solution instead of the developed film and the precipitate at the bottom of beaker. The mechanism of the cadmium effect, with different initial concentrations, on ZnO crystal transformation was tentatively addressed. We believe that cadmium influences the chelate ligands adsorption onto (0001-bar) plane of ZnO crystals, alters the crystal growth orientation, and thus directs the transformation of the size and shape of ZnO crystals.

  13. Surface-assisted unidirectional orientation of ZnO nanorods hybridized with nematic liquid crystals.

    PubMed

    Kubo, Shoichi; Taguchi, Rei; Hadano, Shingo; Narita, Mamiko; Watanabe, Osamu; Iyoda, Tomokazu; Nakagawa, Masaru

    2014-01-22

    Inorganic semiconductor nanorods are regarded as the primary components of optical and electrical nanoscale devices. In this paper, we demonstrate the unidirectional alignment of monolayered and dispersed ZnO nanorods on a rubbed polyimide alignment layer, which was achieved by a conventional liquid crystal alignment technique. The outermost surfaces of the ZnO nanorods (average diameter 7 nm; length 50 nm) were modified by polymerization initiator moieties, and nematic liquid crystalline (LC) methacrylate polymers were grown by atom transfer radical polymerization. By regulating the densities of the polymerization initiator moieties, we successfully hybridized LC-polymer-grafted ZnO nanorods and small nematic LC molecules. The LC-polymer-modified ZnO nanorods were hierarchically aligned on the substrate via cooperative molecular interactions among the liquid crystal mesogens, which induced molecular orientation on the rubbed polyimide alignment layer. PMID:24299205

  14. Linear and nonlinear optical properties of one-dimensional photonic crystals containing ZnO defects

    Microsoft Academic Search

    Geon Joon Lee; Young Pak Lee; Sung Goo Jung; Chang Kwon Hwangbo; Sunman Kim; Inkyu Park

    2007-01-01

    The linear and nonlinear optical properties of one-dimensional photonic crystals containing ZnO defects were studied by linear absorption spectroscopy and the femtosecond Z-scan technique. Photonic crystals containing ZnO defects, (Ta2O5\\/SiO2)5\\/ZnO\\/(SiO2\\/Ta2O5)5, were prepared using electron-beam deposition and magnetron sputtering. The transmission spectra of these photonic crystals revealed a defect mode resonance and a broad photonic band gap. The observed transmission spectra

  15. Linear and nonlinear optical properties of one-dimensional photonic crystals containing ZnO defects

    Microsoft Academic Search

    Geon Joon Lee; Young Pak Lee; Sung Goo Jung; Chang Kwon Hwangbo; Sunman Kim; Inkyu Park

    2007-01-01

    The linear and nonlinear optical properties of one-dimensional photonic crystals containing ZnO defects were studied by linear absorption spectroscopy and the femtosecond Z-scan technique. Photonic crystals containing ZnO defects, (Ta2O5?SiO2)5?ZnO?(SiO2?Ta2O5)5, were prepared using electron-beam deposition and magnetron sputtering. The transmission spectra of these photonic crystals revealed a defect mode resonance and a broad photonic band gap. The observed transmission spectra

  16. Growth of Single- and Bilayer ZnO on Au(111) and Interaction with Copper

    SciTech Connect

    Deng, Xingyi; Yao, Kun; Sun, Keju; Li, Wei-Xue; Lee, Junseok; Matranga, Christopher

    2013-05-30

    The stoichiometric single- and bi-layer ZnO(0001) have been prepared by reactive deposition of Zn on Au(111) and studied in detail with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Both single- and bi-layer ZnO(0001) adopt a planar, graphite-like structure similar to freestanding ZnO(0001) due to the weak van der Waals interactions dominating their adhesion with the Au(111) substrate. At higher temperature, the single-layer ZnO(0001) converts gradually to bi-layer ZnO(0001) due to the twice stronger interaction between two ZnO layers than the interfacial adhesion of ZnO with Au substrate. It is found that Cu atoms on the surface of bi-layer ZnO(0001) are mobile with a diffusion barrier of 0.31 eV, and likely to agglomerate and form nanosized particles at low coverages; while Cu atoms tend to penetrate a single layer of ZnO(0001) with a barrier of 0.10 eV, resulting in a Cu free surface.

  17. Enhanced ferromagnetism in single crystalline Co-doped ZnO thin films by Al codoping

    Microsoft Academic Search

    Z. L. Lu; W. Miao; W. Q. Zou; M. X. Xu; F. M. Zhang

    2010-01-01

    High-quality (Co, Al)-codoped ZnO single crystalline films have been grown on a-plane sapphire substrates using molecular-beam epitaxy. Al codoping yields the Co-doped ZnO thin films to exhibit metallic conducting behavior with high fee carrier concentration. X-ray absorption studies confirm that nearly all Co ions are in divalent state and actually substituted into the ZnO lattice without formation of any detectable

  18. Growth of ZnO nanolayers inside the capillaries of photonic crystal fibres

    E-print Network

    Konidakis, I; Zito, G; Pissadakis, S

    2013-01-01

    In this study, we describe the formation of ZnO nanolayers inside the air capillaries of a silica photonic crystal fibre (PCF), targeting random laser and organic vapor sensing applications. ZnO nanolayers were developed by infiltrating the capillaries of the silica PCF with Zn-acetate/methanol solutions of various concentrations, followed by annealing treatments. The growth and morphology of the synthesized ZnO nanolayers were characterized by means of scanning electron microscopy (SEM) and found to be affected by the concentration of the Zn-acetate/methanol infiltration solution. For low concentrations, inspection with SEM revealed the formation of 25 and 100-nm-thick ZnO nanolayers across the entire length of the infiltrated capillaries, whereas increasing the Zn-acetate concentration resulted to the formation of randomly placed isolated ZnO nanorods. Room temperature photoluminescence spectra of the ZnO nanolayers inside the PCF were measured and compared with the corresponding spectra reported for ZnO st...

  19. 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.

  20. Effects of interfacial layer structures on crystal structural properties of ZnO films

    SciTech Connect

    Park, J. S.; Minegishi, T.; Lee, S. H.; Im, I. H.; Park, S. H.; Hanada, T.; Goto, T.; Cho, M. W.; Yao, T.; Hong, S. K.; Chang, J. H. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); School of Nanoscience and Technology, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Major of Nano Semiconductor, Korea Maritime University, Youngdo-ku, Pusan 606-791 (Korea, Republic of)

    2008-01-15

    Single crystalline ZnO films were grown on Cr compound buffer layers on (0001) Al{sub 2}O{sub 3} substrates by plasma assisted molecular beam epitaxy. In terms of lattice misfit reduction between ZnO and substrate, the CrN and Cr{sub 2}O{sub 3}/CrN buffers are investigated. The structural and optical qualities of ZnO films suggest the feasibility of Cr compound buffers for high-quality ZnO films growth on (0001) Al{sub 2}O{sub 3} substrates. Moreover, the effects of interfacial structures on selective growth of different polar ZnO films are investigated. Zn-polar ZnO films are grown on the rocksalt CrN buffer and the formation of rhombohedral Cr{sub 2}O{sub 3} results in the growth of O-polar films. The possible mechanism of polarity conversion is proposed. By employing the simple patterning and regrowth procedures, a periodical polarity converted structure in lateral is fabricated. The periodical change of the polarity is clearly confirmed by the polarity sensitive piezo response microscope images and the opposite hysteretic characteristic of the piezo response curves, which are strict evidences for the validity of the polarity controlling method as well as the successful fabrication of the periodical polarity controlled ZnO structure.

  1. Nanorodnanosheet hierarchically structured ZnO crystals on zinc foil as flexible photoanodes for

    E-print Network

    Cao, Guozhong

    Nanorod­nanosheet hierarchically structured ZnO crystals on zinc foil as flexible photoanodes method on zinc foil and used as flexible photoanodes in dye-sensitized solar cells (DSCs). Compared fabrication, ever since a photoanode made of porous titania was reported rst in 1991.1 Much attention had been

  2. Direct Heteroepitaxial Growth of ZnO over GaN Crystal in Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Hamada, Takahiro; Ito, Akihiro; Nagao, Nobuaki; Suzuki, Nobuyasu; Fujii, Eiji; Tsujimura, Ayumu

    2013-04-01

    We report on the structural and electrical properties of ZnO films grown on surface-treated GaN/Al2O3 substrates by chemical bath deposition. X-ray diffraction analysis indicated that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. The ZnO film exhibited n-type conduction with a carrier concentration of 6.9 ×1018 cm-3, an electron mobility of 41 cm2/(V.s), and a resistivity of 2.2 ×10-2 ?.cm. A low specific contact resistivity of 4.3 ×10-3 ?.cm2 was obtained at the ZnO/n-GaN interface. Additionally, the ZnO film exhibited high transparency in the visible and infrared region.

  3. Homoepitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  4. Single and couple doping ZnO nanocrystals characterized by positron techniques

    NASA Astrophysics Data System (ADS)

    Pasang, Tenzin; Namratha, Keerthiraj; Guagliardo, Paul; Byrappa, Kullaiah; Ranganathaiah, Chikkakuntappa; Samarin, S.; Williams, J. F.

    2015-04-01

    Zinc oxide (ZnO) nanocrystals have been synthesized using a mild hydrothermal process using low temperatures and pressures with the advantages of free growth catalyst, low cost and alternative technology. Positron annihilation lifetime spectroscopy and coincidence Doppler broadening (CDB) spectroscopic methods have been used to investigate the roles of single- and co-dopants and native defects of the ZnO nanocrystals controlled by the synthesis process. It is shown that single Ag1+ and Pd2+ dopants occupy interstitial sites of the ZnO lattice and single Ru3+ doping replaces Zn vacancies substitutionally with a significant effect on the CDB momentum ratio curves when compared using ZnO as the reference spectrum. The co-doping of the ZnO lattice with (Sn4+ + Co2+) shows similar CDB ratios as Ru3+ single-doping. Also co-doping with (Ag1+ + Pd2+) or (Ag1+ + W6+) shows significant decreases in the band gap energy up to about 12.6% compared to single doping. The momentum ratio curves, referenced to undoped ZnO, indicate dopants in interstitial and substitutional sites. The presence of transition metal ions interstitially will trap electrons which resist the recombination of electrons and in turn affect the conductivity of the material.

  5. Low-Temperature Heteroepitaxial Growth of Single-Domain V-Doped ZnO Films on c-Face Sapphire

    NASA Astrophysics Data System (ADS)

    Chiba, Hiroshi; Mori, Tatsuya; Kawashima, Tomoyuki; Washio, Katsuyoshi

    2015-05-01

    High-quality single-domain (ZnO[11-20]//Al2O3[10-10]) ZnO heteroepitaxial growth on c-face sapphire [Al2O3(0001)] substrate at low temperature was investigated by vanadium (V) doping at growth temperatures between 150°C and 450°C using radiofrequency (RF) magnetron sputtering. In low-temperature growth at 150°C and 200°C, 30° twisted domains (ZnO[10-10]//Al2O3[10-10]) were eliminated and good in-plane crystal orientation was obtained for V doping of about 2 at.% to 3 at.%. Single domains were grown from the early stage. From the changes of surface morphology and growth rate, it was considered that migration during the growth was enhanced due to the increase of the diffusion energy of adatoms, while random nucleation was suppressed.

  6. Optical injection probing of single ZnO tetrapod lasers

    SciTech Connect

    Szarko, Jodi M.; Song, Jae Kyu; Blackledge, Charles Wesley; Swart, Ingmar; Leone, Stephen R.; Li, Shihong; Zhao, Yiping

    2004-11-23

    The properties of zinc oxide (ZnO) nanotetrapod lasers are characterized by a novel ultrafast two-color pump/stimulated emission probe technique. Single legs of tetrapod species are isolated by a microscope objective, pumped by 267 nm pulses, and subjected to a time-delayed 400 nm optical injection pulse, which permits investigation of the ultrafast carrier dynamics in the nanosize materials. With the optical injection pulse included, a large increase in the stimulated emission at 400 nm occurs, which partially depletes the carriers at this wavelength and competes with the normal 390 nm lasing. At the 390 nm lasing wavelengths, the optical injection causes a decrease in the stimulated emission due to the energetic redistribution of the excited carrier depletion, which occurs considerably within the time scale of the subpicosecond duration of the injection pulse. The effects of the optical injection on the spectral gain are employed to probe the lasing dynamics, which shows that the full width at half maximum of the lasing time is 3 ps.

  7. Growth and field-emission properties of single-crystalline conic ZnO nanotubes

    Microsoft Academic Search

    Ruey-Chi Wang; Chuan-Pu Liu; Jow-Lay Huang; Shu-Jen Chen

    2006-01-01

    Single-crystalline conic ZnO nanotubes were synthesized on Si(001) without catalysts by thermal chemical vapour deposition at 475 °C. The nanotubes grown along the ZnO [0001] direction are sharp open-ended tips consisting of planar defects revealed by transmission electron microscopy and scanning electron microscopy. The nanotubes were formed by self-assembly of numerous six-radiated branches of hexagram nanosheets. The diameters and the

  8. 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

  9. 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

  10. 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.

  11. Imaging and characterization of piezoelectric potential in a single bent ZnO microwire

    SciTech Connect

    Wang, Chiang-Lun; Chen, Jhih-Wei; Chen, Yi-Chun; Wu, Chung-Lin, E-mail: clwuphys@mail.ncku.edu.tw [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Tsai, Shu-Ju [Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan (China); Shiu, Hong-Wei; Chang, Lo-Yueh; Chen, Chia-Hao [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Lin, Kai-Hsiang; Hsu, Hsu-Cheng [Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2014-09-22

    We achieved direct visualization of the piezoelectric potentials in a single bent ZnO microwire (MW) using focused synchrotron radiation (soft x-ray) scanning photoelectron spectro-microscopy. Using radial-line scan across the bent section of ZnO MW, the characteristic core-level shifts were directly related to the spatial distribution of piezoelectric potentials perpendicular to the ZnO polar direction. Using piezoelectric modeling in ZnO, we delineated the band structure distortion and carrier concentration change from tensile to compressed sides by combining the spatial resolved cathodoluminescence characteristics in an individual microwire. This spectro-microscopic technique allows imaging and identification of the electric-mechanical couplings in piezoelectric micro-/nano-wire systems.

  12. Raman Spectroscopy of Co-Doped ZnO Bulk Crystals

    Microsoft Academic Search

    W. Szuszkiewicz; J. F. Morhange; Z. Golacki; A. Lusakowski; M. Schumm; J. Geurts

    2007-01-01

    Low-temperature Raman spectra of a bulk mixed crystal Zn1-xCoxO (x = 0.016) are shown and analyzed. Besides the common modes of the ZnO host lattice, electronic transitions related to the presence of Co2+ ions at the Zn sites are observed. In spite of the low Co concentration the presence of collective excitations corresponding to Co and CoO precipitates is also

  13. ZnO photonic crystal lasers Xiaohua Wua, Alexey Yamilova,b, Xiang Liuc, Shuyou Lic, Vinayak P. Dravidc, Robert P. H.

    E-print Network

    Yamilov, Alexey

    ZnO photonic crystal lasers Xiaohua Wua, Alexey Yamilova,b, Xiang Liuc, Shuyou Lic, Vinayak P with self optimization of laser cavity quality factor has been proposed. Keywords: ZnO, defect mode, Ph feature size for a in plane UV stop band, second, the difficulty in wide band gap materials (e.g., GaN, ZnO

  14. Electrical and optical properties of ZnO bulk crystals with and without lithium grown by the hydrothermal technique

    NASA Astrophysics Data System (ADS)

    Wang, Buguo; Claflin, Bruce; Callahan, Michael; Fang, Z.-.; Look, David

    2014-03-01

    Lithium is usually added into the solution to improve ZnO hydrothermal growth; however, lithium doping affects the properties of the resulting crystals. Optical and electrical properties of hydrothermal ZnO bulk crystals without lithium, have been studied by photoluminescence and Hall-effect measurements. High quality ZnO crystals without lithium were grown in H2O/D2O and in NH3-H2O solutions. The crystals grown from H2O/D2O are conductive with resistivities of 0.6-0.7 ?cm and mobilities of ~ 100 cm2/Vs, while lithium doped ZnO crystals typically have resistivities of ~ 103?-cm and mobilities of ~ 200 cm2/Vs, but can be varied from dozens to 1010 ?-cm depending on lithium concentration. Lithium-free but nitrogen doped crystals grown in NH3-H2O solution have resistivities of 1×100 ?-cm and sometimes show p-type conduction; the resistivity increases to ~ 1×108 ?-cm after annealing at 600° C in air. Lithium and nitrogen co-doped ZnO crystals have resistivities of 108-1012 ?-cm and are semi-insulating after annealling. Electronic irradiation also increases the ZnO resistivity. For lithium-doped samples, a 3.357 eV peak can be seen in the photoluminescence spectra. This is close to the donor-exciton peaks in indium-doped ZnO where 3.3586 eV and 3.357 eV were found on the C+ and C- faces, respectively. More studies are needed to identify lithium-related complexes (defects).

  15. Integration of ZnO Microcrystals with Tailored Dimensions Forming Light

    E-print Network

    Jacobs, Heiko O.

    Integration of ZnO Microcrystals with Tailored Dimensions Forming Light Emitting Diodes and UV approach to produce arrays of ZnO microcrystals for optoelectronic and photovoltaic applications overgrowth producing single crystal disks of ZnO with desired size over 2 in. wafers. The process provides

  16. PHYSICAL REVIEW B 85, 235204 (2012) Optical signatures of nitrogen acceptors in ZnO

    E-print Network

    Nabben, Reinhard

    2012-01-01

    PHYSICAL REVIEW B 85, 235204 (2012) Optical signatures of nitrogen acceptors in ZnO S of nitrogen acceptor-doped ZnO epilayers in the medium and high doping regimes using temperature with ammonia during homoepitaxial growth on ZnO single-crystal substrates with different surface polarities

  17. 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.

  18. Photoresponse from single upright-standing ZnO nanorods explored by photoconductive AFM

    PubMed Central

    Beinik, Igor; Kratzer, Markus; Wachauer, Astrid; Wang, Lin; Piryatinski, Yuri P; Brauer, Gerhard; Chen, Xin Yi; Hsu, Yuk Fan; Djuriši?, Aleksandra B

    2013-01-01

    Summary Background: ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, photoconductive atomic force microscopy (PC-AFM) has been applied to investigate transient photoconductivity and photocurrent spectra of upright-standing ZnO nanorods (NRs). With a view to evaluate the electronic properties of the NRs and to get information on recombination kinetics, we have also performed time-resolved photoluminescence measurements macroscopically. Results: Persistent photoconductivity from single ZnO NRs was observed for about 1800 s and was studied with the help of photocurrent spectroscopy, which was recorded locally. The photocurrent spectra recorded from single ZnO NRs revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV. This value is at least 100 meV lower than the band-gap energy determined from the photoluminescence experiments. Conclusion: The obtained results suggest that the photoresponse in ZnO NRs under ambient conditions originates preferentially from photoexcitation of charge carriers localized at defect states and dominates over the oxygen photodesorption mechanism. Our findings are in agreement with previous theoretical predictions based on density functional theory calculations as well as with earlier experiments carried out at variable oxygen pressure. PMID:23616940

  19. 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...

  20. Picosecond time-resolved photoluminescence of zinc oxide single crystals, films and nanoparticles

    Microsoft Academic Search

    John Henry Wilkinson IV

    2003-01-01

    Zinc oxide (ZnO) is a refractory semiconductor material whose band gap is both wide (3.39 eV) and direct. It is under consideration as a promising material for blue\\/uv semiconducting light emitting diodes (LEDs) and lasers. High purity macroscopic single crystals are available, along with epitaxial films grown by chemical vapor deposition, molecular beam epitaxy or pulsed-laser deposition. The exciton has

  1. Homojunction p-n photodiodes based on As-doped single ZnO nanowire

    SciTech Connect

    Cho, H. D.; Zakirov, A. S.; Yuldashev, Sh. U.; Kang, T. W. [Quantum-Functional Semiconductor Research Center, Dongguk Univ.-Seoul, Seoul 100-715 (Korea, Republic of); Ahn, C. W. [Nano-materials Lab. National Nanofab Center at KAIST, 335 Gwahangno, Daejeon 305-806 (Korea, Republic of); Yeo, Y. K. [Department of Engineering Physics, Air Force Institute of Technology,Wright-Patterson AFB, OH 45433 (United States)

    2013-12-04

    Photovoltaic device was successfully grown solely based on the single ZnO p-n homojunction nanowire. The ZnO nanowire p-n diode consists of an as-grown n-type segment and an in-situ arsenic doped p-type segment. This p-n homojunction acts as a good photovoltaic cell, producing a photocurrent almost 45 times larger than the dark current under reverse-biased condition. Our results demonstrate that present ZnO p-n homojunction nanowire can be used as a self-powered ultraviolet photodetector as well as a photovoltaic cell, which can also be used as an ultralow electrical power source for nano-scale electronic, optoelectronic, and medical devices.

  2. Electrical and photoresponse properties of an intramolecular p-n homojunction in single phosphorus-doped ZnO nanowires.

    PubMed

    Li, Ping-Jian; Liao, Zhi-Min; Zhang, Xin-Zheng; Zhang, Xue-Jin; Zhu, Hui-Chao; Gao, Jing-Yun; Laurent, K; Leprince-Wang, Y; Wang, N; Yu, Da-Peng

    2009-07-01

    The single-crystal n-type and p-type ZnO nanowires (NWs) were synthesized via a chemical vapor deposition method, where phosphorus pentoxide was used as the dopant source. The electrical and photoluminescence studies reveal that phosphorus-doped ZnO NWs (ZnO:P NWs) can be changed from n-type to p-type with increasing P concentration. Furthermore, we report for the first time the formation of an intramolecular p-n homojunction in a single ZnO:P NW. The p-n junction diode has a high on/off current ratio of 2.5 x 10(3) and a low forward turn-on voltage of approximately 1.37 V. Finally, the photoresponse properties of the diode were investigated under UV (325 nm) excitation in air at room temperature. The high photocurrent/dark current ratio (3.2 x 10(4)) reveals that the diode has a potential as extreme sensitive UV photodetectors. PMID:19583279

  3. Exciton recombination dynamics in single ZnO tetrapods

    SciTech Connect

    Fernandes-Silva, Lígia C. [Departamento de Física de Materiales, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Martín, Maria D.; Meulen, Herko P. van der; Calleja, José M.; Viña, Luis [Departamento de Física de Materiales, Universidad Autónoma de Madrid, E-28049 Madrid, Spain and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Klopotowski, Lukasz [Polish Academy of Sciences, Institute of Physics, 02-668 Warsaw (Poland)

    2013-12-04

    We present the optical properties of individual ZnO tetrapods as a function of excitation power and temperature by time-integrated and time-resolved spectroscopy. At 10K, we identify the different excitonic transitions by both their characteristic energy and their excitation power dependence. When we increase the tetrapod temperature we observe that the emission intensity decrease and occur a red shift of the emission energies. Our time-resolved studies confirm the predominance of the radiative recombination at low temperatures (< 45 K). Increasing the temperature opens up the non-radiative channels, which are evidenced by a much faster decay time.

  4. Localized surface plasmon resonance enhanced ultraviolet emission and F-P lasing from single ZnO microflower

    SciTech Connect

    Lin, Yi [State Key Laboratory of Bioelectronics, School of Biological Sciences and Medical Engineering, Southeast University, Nanjing 210096 (China); Display Technology Research Center, School of Electronic Science and Engineering, Southeast University, Nanjing 210096 (China); Li, Jitao; Xu, Chunxiang, E-mail: xcxseu@seu.edu.cn; Fan, Xuemei [State Key Laboratory of Bioelectronics, School of Biological Sciences and Medical Engineering, Southeast University, Nanjing 210096 (China); Wang, Baoping [Display Technology Research Center, School of Electronic Science and Engineering, Southeast University, Nanjing 210096 (China)

    2014-10-06

    In this work, monodispersed ZnO microflowers are fabricated by a vapor phase transport method, and Au nanoparticles (NPs) are directly decorated on the surface of the ZnO microflowers. The micro-photoluminescence of a single ZnO microflower demonstrates that the near band-edge emission is tremendously enhanced while the defect-related emission is completely suppressed after Au decoration. The average enhancement factor reaches up to 65 fold. The enhancement mechanism is assumed to be the electron transfer from excited Au NPs to the ZnO microflower induced by the localized surface plasmon resonance based on the time-resolved photoluminescence. The enhanced F-P lasing from a single ZnO sample is further realized.

  5. ZnO nanowire lasers

    NASA Astrophysics Data System (ADS)

    Vanmaekelbergh, Daniël; van Vugt, Lambert K.

    2011-07-01

    The pathway towards the realization of optical solid-state lasers was gradual and slow. After Einstein's paper on absorption and stimulated emission of light in 1917 it took until 1960 for the first solid state laser device to see the light. Not much later, the first semiconductor laser was demonstrated and lasing in the near UV spectral range from ZnO was reported as early as 1966. The research on the optical properties of ZnO showed a remarkable revival since 1995 with the demonstration of room temperature lasing, which was further enhanced by the first report of lasing by a single nanowire in 2001. Since then, the research focussed increasingly on one-dimensional nanowires of ZnO. We start this review with a brief description of the opto-electronic properties of ZnO that are related to the wurtzite crystal structure. How these properties are modified by the nanowire geometry is discussed in the subsequent sections, in which we present the confined photon and/or polariton modes and how these can be investigated experimentally. Next, we review experimental studies of laser emission from single ZnO nanowires under different experimental conditions. We emphasize the special features resulting from the sub-wavelength dimensions by presenting our results on single ZnO nanowires lying on a substrate. At present, the mechanism of lasing in ZnO (nanowires) is the subject of a strong debate that is considered at the end of this review.

  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. Asymmetry in the excitonic recombinations and impurity incorporation of the two polar faces of homoepitaxially grown ZnO films

    E-print Network

    Nabben, Reinhard

    of homoepitaxially grown ZnO films S. Lautenschlaeger, J. Sann, N. Volbers, and B. K. Meyer Physics Institute, Justus November 2007; revised manuscript received 20 March 2008; published 10 April 2008 Homoepitaxial ZnO layers were grown on O-polar and Zn-polar surfaces of ZnO single crystal substrates by chemical vapor

  8. 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

  9. ZnO field-effect transistors prepared by aqueous solution-growth ZnO crystal thin film

    NASA Astrophysics Data System (ADS)

    Li, Chensha; Li, Yuning; Wu, Yiliang; Ong, Beng S.; Loutfy, Rafik O.

    2007-10-01

    A ZnO thin-film transistor (TFT) with a channel layer formed via aqueous solution-growth at low temperature is demonstrated. This ZnO thin-film semiconductor has a well-controlled crystalline form, exhibiting n-channel, enhancement-mode behavior with a channel mobility as large as 0.56 cm2 V-1 s-1. Low-cost, superior transistor characteristics and low-temperature processing makes ZnO TFT attractive for flexible electronics on temperature sensitive substrates.

  10. A Single Molecule Approach to Defect Studies in ZnO

    NASA Astrophysics Data System (ADS)

    Jungwirth, N. R.; Pai, Y. Y.; Chang, H. S.; Macquarrie, E. R.; Fuchs, G. D.

    2014-03-01

    Single molecule investigations are a powerful tool for understanding molecular systems with inhomogeneous behavior that is either broadened or completely washed out of ensemble measurements. Here we apply single molecule microscopy methods to defects in ZnO. In addition to its status as an emerging optoelectronic material, ZnO hosts point defects which may have useful quantum properties akin to those of nitrogen-vacancy centers in diamond, which are promising as single photon sources and solid-state qubits. We present confocal fluorescence measurements of single defects in ZnO nanoparticles and sputtered films that are selectively excited by sub-bandgap light. The resulting 560-720 nm emission often exhibits two broad spectral peaks separated by approximately 100 meV. Photon correlation measurements yield both antibunching and bunching, indicative of single photon emission from isolated defects with a metastable shelving state. Excited state lifetimes span 1-13 ns and are uncorrelated with doping concentration. We report discrete jumps in the fluorescence intensity between a bright and dark state. The dwell times are exponentially distributed in each state and the average dwell time in the bright (dark) state does (may) depend on the power of the excitation laser.

  11. 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

  12. ZnO nanorods for electronic and photonic device applications

    Microsoft Academic Search

    Gyu-Chul Yi; Jinkyoung Yoo; Sug Woo Jung; Sung Jin An; H. J. Kim; D. W. Kim

    We report on catalyst-free growth of ZnO nanorods and their nano-scale electrical and optical device applications. Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) enables fabrication of size-controlled high purity ZnO single crystal nanorods. Various high quality nanorod heterostructures and quantum structures based on ZnO nanorods were also prepared using the MOVPE method and characterized using scanning electron microscopy, transmission electron microscopy, and

  13. 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 .

  14. Near-room temperature single-domain epitaxy of reactively sputtered ZnO films

    NASA Astrophysics Data System (ADS)

    Chamorro, W.; Horwat, D.; Pigeat, P.; Miska, P.; Migot, S.; Soldera, F.; Boulet, P.; Mücklich, F.

    2013-06-01

    Single-domain epitaxial ZnO films are grown near-room temperature (below 40 °C) on (0?0?0?1)-sapphire using reactive magnetron sputtering of a zinc target in the transition between the metallic and compound sputtering regimes. As the oxygen content in the reactive gas mixture is increased, the in-plane six-fold symmetry of hexagonal wurtzite ZnO, probed by ?-scan measurements, develops. Transmission electron microscopy analyses confirm that single-domain epitaxial layers are formed. This is accompanied by the incorporation of oxygen interstitial defects associated with oxygen over-stoichiometry and by compressive stresses. A model is proposed to explain the observed behaviour based on the transformation of the kinetic energy of fast oxygen particles into the mobility of the adatoms.

  15. Single-crystal CdTe solar cells with Voc greater than 900 mV

    NASA Astrophysics Data System (ADS)

    Duenow, J. N.; Burst, J. M.; Albin, D. S.; Kuciauskas, D.; Johnston, S. W.; Reedy, R. C.; Metzger, W. K.

    2014-08-01

    We fabricated single-crystal CdTe photovoltaic devices in a heterojunction structure with an In-doped CdS window layer and ZnO/Al-doped ZnO front contact. By replacing the polycrystalline absorber layer of a CdTe solar cell with a single crystal, we were able to achieve open-circuit voltage (Voc) as high as 929 mV. Simulations and measurements indicate that increased minority-carrier lifetime and carrier concentration can explain this high Voc. Cu and Na both introduce transient effects in single-crystal CdTe similar to those observed in polycrystalline CdTe, suggesting that Group I dopants pose stability problems that are linked fundamentally to their defect chemistry in CdTe, regardless of the presence of grain boundaries.

  16. Nitrogen doped MgxZn1-xO/ZnO single heterostructure ultraviolet light-emitting diodes on ZnO substrates

    NASA Astrophysics Data System (ADS)

    Nakahara, K.; Akasaka, S.; Yuji, H.; Tamura, K.; Fujii, T.; Nishimoto, Y.; Takamizu, D.; Sasaki, A.; Tanabe, T.; Takasu, H.; Amaike, H.; Onuma, T.; Chichibu, S. F.; Tsukazaki, A.; Ohtomo, A.; Kawasaki, M.

    2010-07-01

    We have grown nitrogen-doped MgxZn1-xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy. As N-sources, we employed NO-plasma or NH3 gas itself. As x increased, optimum growth temperature window for smooth film morphology shifted to higher temperatures, while maintaining high N-concentration (˜1×1019 cm-3). The heterosructures of MgxZn1-xO:N (0.1?x?0.4)/ZnO were fabricated into light emitting diodes of 500-?m-diameter. We observed ultraviolet near-band-edge emission (? ˜382 nm) with an output power of 0.1 ?W for a NO-plasma-doped LED and 70 ?W for a NH3-doped one at a bias current of 30 mA.

  17. 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

  18. 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.

  19. The interaction of 193-nm excimer laser irradiation with single-crystal zinc oxide: Neutral atomic zinc and oxygen emission

    SciTech Connect

    Kahn, E. H. [Washington State University; Langford, S. C. [Washington State University; Dickinson, J. T. [Washington State University; Boatner, Lynn A [ORNL

    2013-01-01

    We report mass-resolved time-of-flight measurements of neutral particles from the surface of single-crystal ZnO during pulsed 193-nm irradiation at laser fluences below the threshold for avalanche breakdown. The major species emitted are atomic Zn and O. We examine the emissions of atomic Zn as a function of laser fluence and laser exposure. Defects at the ZnO surface appear necessary for the detection of these emissions. Our results suggest that the production of defects is necessary to explain intense sustained emissions at higher fluence. Rapid, clean surface etching and high atomic zinc kinetic energies seen at higher laser fluences are also discussed.

  20. 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

  1. 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.

  2. 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.

  3. High-Mobility Field-Effect Transistors Based on Single-Crystalline ZnO Channels

    NASA Astrophysics Data System (ADS)

    Nishii, Junya; Ohtomo, Akira; Ohtani, Keita; Ohno, Hideo; Kawasaki, Masashi

    2005-09-01

    We have fabricated field-effect transistors with single-crystalline ZnO channels consisting of high-quality epitaxial films grown on lattice-matched (0001) ScAlMgO4 substrates by laser molecular-beam epitaxy. Amorphous alumina gate insulators are deposited on the top of the ZnO films using either RF magnetron sputtering or electron-beam evaporation. The field-effect mobility (?FE) of the device prepared by the latter method is as high as 40 cm2\\cdotV-1\\cdots-1, one order of magnitude higher than those typically observed for polycrystalline channel devices. However, hysteresis appears in transfer characteristics. This unfavorable effect is found to be eliminated by the thermal annealing of the entire devices in air. The much larger hysteresis and lower ?FE are observed for the device with sputtered gate insulators. This is presumably due to dense surface states created by ion or electron bombardment during the sputtering.

  4. Single crystalline ZnO nanorods grown by a simple hydrothermal process

    SciTech Connect

    Pei, L.Z., E-mail: lzpei1977@163.com [School of Materials Science and Engineering, Institute of Molecular Engineering and Applied Chemistry, Key Lab of Materials Science and Processing of Anhui Province, Anhui University of Technology, Ma'anshan, Anhui 243002 (China); Zhao, H.S. [School of Materials Science and Engineering, Institute of Molecular Engineering and Applied Chemistry, Key Lab of Materials Science and Processing of Anhui Province, Anhui University of Technology, Ma'anshan, Anhui 243002 (China); Tan, W. [Henkel Huawei Electronics Co. Ltd., Lian'yungang, Jiangsu 222006 (China); Yu, H.Y. [School of Materials Science and Engineering, Institute of Molecular Engineering and Applied Chemistry, Key Lab of Materials Science and Processing of Anhui Province, Anhui University of Technology, Ma'anshan, Anhui 243002 (China); Chen, Y.W. [Department of Materials Science, Fudan University, Shanghai 200433 (China); Zhang Qianfeng [School of Materials Science and Engineering, Institute of Molecular Engineering and Applied Chemistry, Key Lab of Materials Science and Processing of Anhui Province, Anhui University of Technology, Ma'anshan, Anhui 243002 (China)

    2009-09-15

    Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 {mu}m. Raman peak at 437.8 cm{sup -1} displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.

  5. Single ZnO nanowire-PZT optothermal field effect transistors.

    PubMed

    Hsieh, Chun-Yi; Lu, Meng-Lin; Chen, Ju-Ying; Chen, Yung-Ting; Chen, Yang-Fang; Shih, Wan Y; Shih, Wei-Heng

    2012-09-01

    A new type of pyroelectric field effect transistor based on a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT) has been developed. Under infrared (IR) laser illumination, the transconductance of the ZnO NW can be modulated by optothermal gating. The drain current can be increased or decreased by IR illumination depending on the polarization orientation of the Pb(Zr(0.3)Ti(0.7))O(3) (PZT) substrate. Furthermore, by combining the photocurrent behavior in the UV range and the optothermal gating effect in the IR range, the wide spectrum of response of current by light offers a variety of opportunities for nanoscale optoelectronic devices. PMID:22895012

  6. 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

  7. Imaging Single ZnO Vertical Nanowire Laser Cavities using UV-Laser Scanning Confocal Microscopy

    SciTech Connect

    Gargas, D.J.; Toimil-Molares, M.E.; Yang, P.

    2008-11-17

    We report the fabrication and optical characterization of individual ZnO vertical nanowire laser cavities. Dilute nanowire arrays with interwire spacing>10 ?m were produced by a modified chemical vapor transport (CVT) method yielding an ideal platform for single nanowire imaging and spectroscopy. Lasing characteristics of a single vertical nanowire are presented, as well as high-resolution photoluminescence imaging by UV-laser scanning confocal microscopy. In addition, three-dimensional (3D) mapping of the photoluminescence emission performed in both planar and vertical dimensions demonstrates height-selective imaging useful for vertical nanowires and heteronanostructures emerging in the field of optoelectronics and nanophotonics.

  8. Synthesis of PS colloidal crystal templates and ordered ZnO porous thin films by dip-drawing method

    NASA Astrophysics Data System (ADS)

    Liu, Zhifeng; Jin, Zhengguo; Li, Wei; Qiu, Jijun; Zhao, Juan; Liu, Xiaoxin

    2006-05-01

    Polystyrene spheres (PS) were synthesized by an emulsifier-free emulsion polymerization technique and the PS colloidal crystal templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS. Porous ZnO thin films were prepared by filling the ZnO sol into the spaces among the close-packed PS templates and then annealing to remove the PS templates. The effects of ZnO precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed an ordered ZnO porous thin film with designed pore size that depended on the sol concentration and PS size could be obtained. And the shrinkage of pore diameter was about 30-43%. X-ray diffraction (XRD) spectra indicated the thin film was wurtzite structure. The transmittance spectrum showed that optical transmittance decreased with the decrease of wavelength, but kept above 80% optical transmittances beyond the wavelength of 550 nm. Optical band gap of the porous ZnO thin film (fired at 500 °C) was 3.22 eV.

  9. Selective area growth of well-ordered ZnO nanowire arrays with controllable polarity.

    PubMed

    Consonni, Vincent; Sarigiannidou, Eirini; Appert, Estelle; Bocheux, Amandine; Guillemin, Sophie; Donatini, Fabrice; Robin, Ivan-Christophe; Kioseoglou, Joseph; Robaut, Florence

    2014-05-27

    Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices. PMID:24720628

  10. 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

  11. 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.

  12. 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

  13. 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

  14. 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

  15. In-Situ Studies of Photoluminescence Quenching in Single Crystal Quantum Dot Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Shepherd, Douglas; Liang, Yong-Qi; Sambur, Justin; Parkinson, Bruce; Gelfand, Martin; van Orden, Alan

    2011-03-01

    Single crystal quantum dot sensitized solar cells (QDSSC) are a promising photovoltaic system in which collection of multiple charge carriers per photon has recently been reported. Utilizing time-correlated single photon counting we have studied both the fluorescence intensity and fluorescence decay time from CdSe quantum dots coupled to both single crystal Ti O2 and ZnO substrates through short and long chain ligands. We find that for all configurations the fluorescence decay time is quenched compared to unbound quantum dots in solution, while the photovoltaic properties of the system strongly depend on the chain-length of the ligand. These results suggest there exist interactions between either the individual quantum dots or the quantum dots and substrate that may compete with the charge injection process in QDSSCs. Justin B. Sambur, Thomas Novet, B.A. Parkinson, Science 330 (6000) 63-66

  16. 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.

  17. Study of the negative magneto-resistance of single proton-implanted lithium-doped ZnO microwires

    NASA Astrophysics Data System (ADS)

    Lorite, I.; Zandalazini, C.; Esquinazi, P.; Spemann, D.; Friedländer, S.; Pöppl, A.; Michalsky, T.; Grundmann, M.; Vogt, J.; Meijer, J.; Heluani, S. P.; Ohldag, H.; Adeagbo, W. A.; Nayak, S. K.; Hergert, W.; Ernst, A.; Hoffmann, M.

    2015-06-01

    The magneto-transport properties of single proton-implanted ZnO and of Li(7%)-doped ZnO microwires have been studied. The as-grown microwires were highly insulating and not magnetic. After proton implantation the Li(7%) doped ZnO microwires showed a non-monotonous behavior of the negative magneto-resistance (MR) at temperature above 150 K. This is in contrast to the monotonous NMR observed below 50 K for proton-implanted ZnO. The observed difference in the transport properties of the wires is related to the amount of stable Zn vacancies created at the near surface region by the proton implantation and Li doping. The magnetic field dependence of the resistance might be explained by the formation of a magnetic/non-magnetic heterostructure in the wire after proton implantation.

  18. 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.

  19. Effect of complexing agent on hydrothermal growth of ZnO crystals

    NASA Astrophysics Data System (ADS)

    DiLeo, Liliane; Romano, Dana; Schaeffer, Luther; Gersten, Bonnie; Foster, Catherine; Gelabert, Maria C.

    2004-10-01

    In this study, three multidentate ligands—diethylenetriaminepentaacetate (DTPA), ethylenediaminetetraacetate (EDTA) and tetraethylenepentamine (tetren)—were investigated in the hydrothermal growth of crystals of zinc oxide (ZnO). Aqueous solutions containing zinc-ligand complexes and KOH were hydrothermally reacted and the products examined. Reactants were placed in teflon-lined stainless steel autoclaves and heated to a temperature of 200 °C, generating pressures of approximately 15 atm. Optical microscopy and scanning electron microscopy on the resulting products revealed crystals with needle and plate habits, with needle lengths up to approximately 1 mm for EDTA and plate dimensions up to 100 ?m for DTPA. When only complexing agent was varied at high pH, needles were observed for all samples, with EDTA yielding the longest (300 ?m) and tetren yielding the shortest (20 ?m); results were analyzed by considering complex formation constants, qualitative ligand polarity and complex strain. A variable pH study with 2 aminocarboxylic ligands, EDTA and DTPA, yielded mostly needles and dendritic formations for EDTA over the studied pH range (6-14), and plates or needles for DTPA. Results of variable pH products were analyzed by considering concentrations of all zinc-ligand and zinc-hydroxy species as a function of pH.

  20. 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

  1. Substrate Preparations in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.

    2000-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. Annealing-temperature dependence of ZnO substrates was studied. ZnO films grown on sapphire substrates have also been investigated for comparison purposes and the annealing temperature of A1203 substrates is 1000 C. Substrates and films were characterized using photoluminescence (PL) spectrum, x-ray diffraction, atomic force microscope, energy dispersive spectrum, and electric transport measurements. It has been found that the ZnO film properties were different when films were grown on the two polarity surfaces of ZnO substrates and the A1203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of homoepitaxial ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  2. 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.

  3. 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.

  4. ZnO nanodisk based UV detectors with printed electrodes.

    PubMed

    Alenezi, Mohammad R; Alshammari, Abdullah S; Alzanki, Talal H; Jarowski, Peter; Henley, Simon John; Silva, S Ravi P

    2014-04-01

    The fabrication of highly functional materials for practical devices requires a deep understanding of the association between morphological and structural properties and applications. A controlled hydrothermal method to produce single crystal ZnO hexagonal nanodisks, nanorings, and nanoroses using a mixed solution of zinc sulfate (ZnSO4) and hexamethylenetetramine (HMTA) without the need of catalysts, substrates, or templates at low temperature (75 °C) is introduced. Metal-semiconductor-metal (MSM) ultraviolet (UV) detectors were fabricated based on individual and multiple single-crystal zinc oxide (ZnO) hexagonal nanodisks. High quality single crystal individual nanodisk devices were fabricated with inkjet-printed silver electrodes. The detectors fabricated show record photoresponsivity (3300 A/W) and external quantum efficiency (1.2 × 10(4)), which we attribute to the absence of grain boundaries in the single crystal ZnO nanodisk and the polarity of its exposed surface. PMID:24611747

  5. 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

  6. 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.

  7. Elastic-plastic and phase transition of zinc oxide single crystal under shock compression

    NASA Astrophysics Data System (ADS)

    Liu, Xun; Mashimo, Tsutomu; Li, Wei; Zhou, Xianming; Sekine, Toshimori

    2015-03-01

    The Hugoniot data for zinc oxide (ZnO) single crystals were measured up to 80 GPa along both the ? 11 2 ¯ 0 ? (a-axis) and ?0001? (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun and two-stage light gas gun. The Hugoniot-elastic limits of ZnO were determined to be 10.5 and 11.5 GPa along the a- and c-axes, respectively. The wurtzite (B4) to rocksalt (B1) phase transition pressures along the a- and c-axes are 12.3 and 14.4 GPa, respectively. Shock velocity (Us) versus particle velocity (Up) relation of the final phase is given by the following relationship: Us (km/s) = 2.76 + 1.51Up (km/s). Based on the Debye-Grüneisen model and Birch-Murnaghan equation of state (EOS), we discuss the EOS of the B1 phase ZnO. The bulk modulus (K0) and its pressure derivative (K0') are estimated to be K0 = 174 GPa and K0' = 3.9, respectively.

  8. Growth and field-emission properties of single-crystalline conic ZnO nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Ruey-Chi; Liu, Chuan-Pu; Huang, Jow-Lay; Chen, Shu-Jen

    2006-02-01

    Single-crystalline conic ZnO nanotubes were synthesized on Si(001) without catalysts by thermal chemical vapour deposition at 475 °C. The nanotubes grown along the ZnO [0001] direction are sharp open-ended tips consisting of planar defects revealed by transmission electron microscopy and scanning electron microscopy. The nanotubes were formed by self-assembly of numerous six-radiated branches of hexagram nanosheets. The diameters and the wall thicknesses of the nanotubes are in the ranges 30-100 and 15-30 nm, respectively. The lengths and areal densities of the nanotubes are around 0.5 µm and 1-9 × 108 cm-2, respectively. Field-emission measurements on the conic nanotubes show a low turn-on field of 3.5 V µm-1 at 10 µA cm-2. The field-emission properties related to the nanotube density and geometry and the nonlinearity in the Fowler-Nordheim (FN) plot at lower field region are discussed.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Spatial mapping of exciton lifetimes in single ZnO nanowires J. S. Reparaz, G. Callsen, M. R. Wagner, F. Gell, J. R. Morante et al.

    E-print Network

    Nabben, Reinhard

    that ZnO might be a promising candidate for next generation devices such as exciton-polariton lasers.15;APL MATERIALS 1, 012103 (2013) Spatial mapping of exciton lifetimes in single ZnO nanowires J. S semiconductor materials with improved optoelectronic performance has triggered intense research activities

  14. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Lehoczky, S. L.; Harris, M. T.; George, Michael A.; McCarty, P.

    1999-01-01

    As a high temperature semiconductor, ZnO has been used for many applications such as wave-guide, solar cells, and surface acoustic wave devices. Since the ZnO material has an energy gap of 3.3 eV at room temperature and an excitonic binding energy (60 meV) that is possible to make excitonic lasering at room temperature a recent surge of interest is to synthesize ZnO films for electro-optical devices. These applications require films with a smooth surface, good crystal quality, and low defect density. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystals are grown by the hydrothermal method. Substrates are mechanically polished and annealed in air for four hours before deposited films. The annealing temperature-dependence of ZnO substrates is studied. Films are synthesized by the off-axis reactive sputtering deposition. The films have very smooth surface with a roughness crystal substrate. The film quality is determined by measuring the film resistivity, the Hall mobility, carrier densities and the energy band gap. The properties of ZnO films grown of (0001) ZnO and (0001) sapphire substrates will be also compared and discussed in the presentation.

  15. A micro force sensor based on a single ZnO belt coated with chromium film.

    PubMed

    Ren, Xiaoyan; Yang, Xing; Zhou, Zhaoying; Li, Jinming; Liu, Jing

    2010-11-01

    A micro force sensor was fabricated using a single ZnO belt coated with ultra thin Cr film. As a result of the piezoresistive effect of the ultra thin (in nano-scale) Cr film, the bending of the belt led to the change in the resistance of ultra thin Cr film. Based on the mechanics of the materials, the relationship between the deformation and the force was calculated, and a linear relationship between the bending force and the resistance of Cr thin film was deduced at small bending regions. Dielectrophoresis, focused ion beam (FIB) and sputtering were used in the process of the micro force sensor. The experimental results show that the resistance of Cr film is sensitive to the bending force and demonstrate the potential for developing a new class of stable and sensitive nano-sized structures for force sensing. PMID:21137908

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Characterization of the single and double films consisting of Al, Sc-co-doped ZnO\\/Al-doped ZnO and Al-doped ZnO\\/Al, Sc-co-doped ZnO

    Microsoft Academic Search

    Kun-Cheng Peng; Jing-Chie Lin; C. A. Tseng; Sheng-Long Lee

    2008-01-01

    Single and double films consisting of Al, Sc-co-doped ZnO (denoted as S) and Al-doped ZnO (denoted as A) layers were deposited on the Super Twisted Nematic (STN) glass by dc-sputtering on the pure aluminum (99.999%) or Al-0.8 wt.% Sc eutectic alloy target (99.999%) combined with rf-sputtering on the pure zinc oxide (99.99%). The thickness of each layer in the double film

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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).

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Constitutive modeling for single crystal superalloys

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  11. 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.

  12. Green emission in carbon doped ZnO films

    SciTech Connect

    Tseng, L. T.; Yi, J. B., E-mail: jiabao.yi@unsw.edu.au; Zhang, X. Y.; Xing, G. Z.; Luo, X.; Li, S. [School of Materials Science and Engineering, University of New South Wales, Kensington, NSW, 2052 (Australia); Fan, H. M. [School of Chemical Engineering, Northwest University, Xi'an 710069 (China); Herng, T. S.; Ding, J. [Department of Materials Science and Engineering, National University of Singapore, 119260 (Singapore); Ionescu, M. [Australian Nuclear Science and Technology Organization, (ANSTO), New Illawarra Road, Lucas Heights, NSW 2234 (Australia)

    2014-06-15

    The emission behavior of C-doped ZnO films, which were prepared by implantation of carbon into ZnO films, is investigated. Orange/red emission is observed for the films with the thickness of 60–100 nm. However, the film with thickness of 200 nm shows strong green emission. Further investigations by annealing bulk ZnO single crystals under different environments, i.e. Ar, Zn or C vapor, indicated that the complex defects based on Zn interstitials are responsible for the strong green emission. The existence of complex defects was confirmed by electron spin resonance (ESR) and low temperature photoluminescence (PL) measurement.

  13. Heteroepitaxial growth of ZnO thin films by atmospheric pressure CVD method

    Microsoft Academic Search

    Y. Kashiwaba; F Katahira; K Haga; T Sekiguchi; H Watanabe

    2000-01-01

    High-quality ZnO films were successfully prepared by atmospheric pressure CVD using zinc acetylacetonate (Zn(C5H7O2)2) and oxygen as sources. Epitaxial growth was achieved on (011?2)-oriented single-crystal sapphire substrates. The crystal quality of ZnO films was highly dependent on the film thickness, and crystallinity was improved remarkably at thicknesses over 0.32?m. The cathodoluminescence spectra of the films had a strong peak of

  14. Epitaxial growth of znO nanowires over the ZnO thin films deposited on the Si and sapphire substrates.

    PubMed

    Park, No-Kuk; Lee, You Jin; Jung, Ji Young; Lee, Won Guen; Bae, Young Je; Yoon, Suk Hoon; Han, Gi Bo; Ryu, Si Ok; Lee, Tae Jin

    2008-09-01

    Epitaxial growth of ZnO nanowires was carried out using a modified thermal evaporation method with inexpensive experimental setup. ZnO nanowires were synthesized using ZnO thin films. The ZnO thin films were deposited as a buffer layer on silicon and sapphire using an impinging flow reactor (IFR). The IFR system is a modified version of a chemical bath deposition (CBD). Films can be created at low temperature, without any metallic catalysts. The properties of Zinc Oxide films are dependant upon the type of substrate used. The same deposition process with a different substrates yields two films with different properties. The most critical effect on growth of ZnO nanowires were dependent the properties of the buffer layer deposited on the substrate. It was not the type of substrate used. A cost-efficient method for epitaxial growth of single crystal ZnO nanowires is proposed in this work. PMID:19049078

  15. Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films

    Microsoft Academic Search

    Zhong-Lin Lu; Wen-Qin Zou; Ming-Xiang Xu; Feng-Ming Zhang

    2010-01-01

    This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become more conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate

  16. First-principles study on physical properties of a single ZnO monolayer with graphene-like structure

    Microsoft Academic Search

    Z. C. Tu

    2009-01-01

    The elastic, piezoelectric, electronic, and optical properties of a single ZnO monolayer (SZOML) with graphene-like structure are investigated from the first-principles calculations. The phonon dispersion curves contain three acoustic and three optical branches. At $\\\\Gamma$ point, the out-of-plane acoustic mode has an asymptotic behavior $\\\\omega (q)=Bq^2$ with $B=1.385 \\\\times 10^{-7}$ m$^2$\\/s, while two in-plane acoustic modes have sound velocities $2.801$

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. The interaction of 193?nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation

    SciTech Connect

    Khan, Enamul H.; Langford, S. C.; Dickinson, J. T., E-mail: jtd@wsu.edu [Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States); Boatner, L. A. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2014-08-28

    In past studies, we have observed copious emissions of ionic and atomic Zn from single-crystal ZnO accompanying irradiation of single-crystal ZnO with 193-nm excimer laser irradiation at fluences below the onset of optical breakdown. The Zn{sup +} and ground state Zn° are studied using time-of-flight techniques and are mass selected using a quadrupole mass spectrometer. Simultaneously, we have observed emitted particles that are detectable with a Channeltron electron multiplier but cannot be mass selected. It is a reasonable hypothesis that these particles correspond to a neutral atom or molecule in highly excited long lived states. We provide strong evidence that they correspond to high lying Rydberg states of atomic Zn. We propose a production mechanism involving laser excitation via a two photon resonance excitation of Zn°.

  6. 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.

  7. 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

  8. 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.

  9. Competition between second harmonic generation and two-photon-induced luminescence in single, double and multiple ZnO nanorods.

    PubMed

    Dai, Jun; Zeng, Jian-Hua; Lan, Sheng; Wan, Xia; Tie, Shao-Long

    2013-04-22

    The nonlinear optical properties of single, double and multiple ZnO nanorods (NRs) were investigated by using a focused femtosecond (fs) laser beam. The excitation wavelength of the fs laser was intentionally chosen to be 754 nm at which the energy of two photons is slightly larger than that of the exciton ground state but smaller than the bandgap energy of ZnO. Second harmonic generation (SHG) or/and two-photon-induced luminescence (TPL) were observed and their dependences on excitation density were examined. For single ZnO NRs, only SHG was observed even at the highest excitation density we used in the experiments. The situation was changed when the joint point of two ZnO NRs perpendicular to each other was excited. In this case, TPL could be detected at low excitation densities and it increased rapidly with increasing excitation density. At the highest excitation density of ~15 MW/cm(2), the intensity of the TPL became comparable to that of the SHG. For an ensemble of ZnO NRs packed closely, a rapid increase of TPL with a slope of more than 7.0 and a gradual saturation of SHG with a slope of ~0.34 were found at high excitation densities. Consequently, the nonlinear response spectrum was eventually dominated by the TPL at high excitation densities and the SHG appeared to be very weak. We interpret this phenomenon by considering both the difference in electric field distribution and the effect of heat accumulation. It is suggested that the electric field enhancement in double and multiple NRs plays a crucial role in determining the nonlinear response of the NRs. In addition, the reduction in the bandgap energy induced by the heat accumulation effect also leads to the significant change in nonlinear response. This explanation is supported by the calculation of the electric field distribution using the discrete dipole approximation method and the simulation of temperature rise in different ZnO NRs based on the finite element method. PMID:23609708

  10. 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.

  11. 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.

  12. Preparation of single-crystalline ZnO films on ZnO-buffered a-plane sapphire by chemical bath deposition

    Microsoft Academic Search

    Takahiro Hamada; Akihiro Ito; Eiji Fujii; Dewei Chu; Kazumi Kato; Yoshitake Masuda

    2009-01-01

    High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al2O3 (112¯0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 60°C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (?-scans) of the (0002) reflections

  13. 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.

  14. 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.

  15. Heteroepitaxy of ZnO on GaN Templates ) (a), H. Alves (a), D.M. Hofmann (a), B.K. Meyer (a),

    E-print Network

    Nabben, Reinhard

    Heteroepitaxy of ZnO on GaN Templates A. Zeuner1 ) (a), H. Alves (a), D.M. Hofmann (a), B.K. Meyer.1 We report on the growth of ZnO single crystal thin films on GaN templates by vapor phase de- position could not be rea- lised up to now. ZnO and its ternary alloys ZnMgO and ZnCdO have the potential

  16. 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.

  17. 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

  18. 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.

  19. Growing intermetallic single crystals using in situ decanting

    SciTech Connect

    Petrovic, Cedomir; Canfield, Paul; Mellen, Jonathan

    2012-05-16

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

  20. Direct growth of single-walled carbon nanotubes on conducting ZnO films and its field emission properties

    SciTech Connect

    Min, Yo-Sep; Bae, Eun Ju; Kim, Un Jeong; Park, Wanjun; Hwang, Cheol Seong [Materials and Devices Research Center, Samsung Advanced Institute of Technology, Yongin 449-712 (Korea, Republic of); School of Materials Science and Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of)

    2006-09-11

    Despite the necessity of direct growth of single-walled carbon nanotubes (SWNTs) on conducting films for versatility of designing device architectures for nanoelectronics and optoelectronics, most of SWNT growths have been carried out on insulating films or supporting materials such as SiO{sub 2} and Al{sub 2}O{sub 3}. Here, the authors report that conducting ZnO films can be used as both an underlying layer for the SWNT growth and an electrode for device operation. ZnO films with a resistivity in the order of 10{sup -3} {omega} cm were deposited by atomic layer deposition. SWNTs were directly grown on the ZnO film by water plasma chemical vapor deposition. The authors demonstrate field emission properties from the SWNT/ZnO cathode, of which the turn-on electric field for a current density of 10 {mu}A/cm{sup 2} and the field enhancement factor are 1.8 V/{mu}m and 3200, respectively.

  1. 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.

  2. 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.

  3. Aluminum Migration and Intrinsic Defect Interaction in Single-Crystal Zinc Oxide

    NASA Astrophysics Data System (ADS)

    Johansen, K. M.; Vines, L.; Bjørheim, T. S.; Schifano, R.; Svensson, B. G.

    2015-02-01

    Vacancy-mediated migration of Al in single-crystal zinc oxide (ZnO) is investigated using secondary-ion mass spectrometry (SIMS) combined with hybrid density-functional theory (DFT) calculations. A thin film of Al-doped ZnO is deposited by sputtering onto the single-crystal bulk material and heat treated at temperatures in the range of 900 °C - 1300 °C . The migration of Al is found to be Zn-vacancy mediated. In order to elucidate the physical processes involved, an alternative model based on reactive diffusion is developed. The model includes the time evolution of the concentration of Al atoms on the Zn site (AlZn ), Zn vacancies (vZn), and a complex between the two, where the influence of the charge state of vZn on its formation energy is incorporated through the free carrier concentration. The modeling results exhibit close agreement with the experimental data and the AlZnvZn complex is found to diffuse with an activation energy of 2.6 eV and a preexponential factor of 4 ×10-2 cm2 s-1 . The model is supported by the results from hybrid DFT calculations combined with thermodynamical modeling, which also suggest that a complex between AlZn and vZn is promoted in n -doped material. The charge state of this complex is effectively -1 , and it thus acts as a compensating acceptor, limiting full utilization of the shallow AlZn donor. Furthermore, the DFT calculations also predict a high formation energy for both substitutional Al on the O site (AlO ) and interstitial Al (Ali), and are therefore of minor importance for Al migration in ZnO. The close coupling between the hybrid DFT calculations and the developed diffusion model enable benchmarking of the accuracy of several parameters extracted from the DFT calculations. Furthermore, since the diffusion model hinges strongly on defect concentrations, it couples directly to results from measurements by other experimental techniques than those used in this paper and provides an opportunity for independent verification of the estimated values by future studies.

  4. 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.

  5. 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)

  6. 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

  7. 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.

  8. 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...

  9. 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)

  10. 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

  11. 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

  12. 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

  13. 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.

  14. 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,

  15. 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,

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Anisotropy of nickel-base superalloy single crystals

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Photovoltaic effect and charge storage in single ZnO nanowires

    Microsoft Academic Search

    Zhi-Min Liao; Jun Xu; Jing-Min Zhang; Da-Peng Yu

    2008-01-01

    Asymmetric Schottky barriers between ZnO nanowire and metal electrode have been fabricated at the two ends of the nanowire. An obvious photocurrent generated from the device at zero voltage bias can be switched on\\/off with quick response by controlling the light irradiation. Moreover, the device can still afford a current at zero bias after switching off light illumination, which is

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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

  13. Piezotronic-effect enhanced drug metabolism and sensing on a single ZnO nanowire surface with the presence of human cytochrome P450.

    PubMed

    Wang, Ning; Gao, Caizhen; Xue, Fei; Han, Yu; Li, Tao; Cao, Xia; Zhang, Xueji; Zhang, Yue; Wang, Zhong Lin

    2015-03-24

    Cytochromes P450 (CYPs) enzymes are involved in catalyzing the metabolism of various endogenous and exogenous compounds. A rapid analysis of drug metabolism reactions by CYPs is required because they can metabolize 95% of current drugs in drug development and effective therapies. Here, we describe a study of piezotronic-effect enhanced drug metabolism and sensing by utilizing a single ZnO nanowire (ZnO NW) device. Owing to the unique hydrophobic feature of a ZnO NW that provides a desirable "microenvironment" for the immobilization of biomolecules, our device can effectively stimulate the tolbutamide metabolism by decorating a ZnO NW with cytochrome P4502C9/CYPs reductase (CYP2C9/CPR) microsomes. By applying an external compressive strain to the ZnO nanowire, the piezotronic effect, which plays a primary role in tuning the transport behavior of a ZnO NW utilizing the created piezoelectric polarization charges at the local interface, can effectively enhance the performance of the device. A theoretical model is proposed using an energy band diagram to explain the experimental data. This study provides a potential approach to study drug metabolism and trace drug detection based on the piezotronic effect. PMID:25758259

  14. Creation of giant two-dimensional crystal of zinc oxide nanodisk by method of single-particle layer of organo-modified inorganic fine particles.

    PubMed

    Meng, Qi; Honda, Nanami; Uchida, Saki; Hashimoto, Kazuaki; Shibata, Hirobumi; Fujimori, Atsuhiro

    2015-09-01

    In this study, the formation and structure of a single-particle layer of organo-zinc oxide are investigated using surface-pressure-area (?-A) isotherms, out-of-plane X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). Further, techniques for achieving the solubilization of inorganic fine particles in general solvents have been proposed, and a single-particle layer has been formed using such an inorganic solution as a "spreading solution" for an interfacial film. Surface modification of ZnO is performed using a long-chain carboxylic acid. Accordingly, a regular arrangement of ZnO can be easily achieved in order to overcome the relatively weak van der Walls interactions between inorganic materials. A condensed Langmuir monolayer of these particles is also formed. A multiparticle layered structure is constructed by the Langmuir-Blodgett (LB) technique. Out-of-plane XRD measurement results for a single-particle layer of organo-ZnO clearly show a sharp peak at 42Å. This peak is attributed to the distance between ZnO layers. The AFM image of this single-particle layer of organo-ZnO shows a particle assembly with a uniform height of 60nm. These aggregated particles form large two-dimensional crystals. In other words, a regular periodic structure along the c-axis and a condensed single-particle layer had been fabricated using Langmuir and LB techniques. PMID:25978556

  15. 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.

  16. ''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.

  17. 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.

  18. 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.

  19. 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

  20. Infrared dielectric functions and phonon modes of high-quality ZnO films

    Microsoft Academic Search

    N. Ashkenov; B. N. Mbenkum; C. Bundesmann; V. Riede; M. Lorenz; D. Spemann; E. M. Kaidashev; A. Kasic; M. Schubert; M. Grundmann; G. Wagner; H. Neumann; V. Darakchieva; H. Arwin; B. Monemar

    2003-01-01

    Infrared dielectric function spectra and phonon modes of high-quality, single crystalline, and highly resistive wurtzite ZnO films were obtained from infrared (300-1200 cm-1) spectroscopic ellipsometry and Raman scattering studies. The ZnO films were deposited by pulsed-laser deposition on c-plane sapphire substrates and investigated by high-resolution x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering experiments. The crystal structure, phonon modes,

  1. Ultraviolet-light-emitting ZnO nanosheets prepared by a chemical bath deposition method

    Microsoft Academic Search

    Bingqiang Cao; Weiping Cai; Yue Li; Fengqiang Sun; Lide Zhang

    2005-01-01

    Two-dimensional polar-surface-dominated ZnO nanosheets (nanodiscs) with dimensions of several microns and thickness of tens of nanometres were synthesized in bulk quantity at low temperature (~70 °C) by a simple and environmentally benign chemical bath deposition (CBD) method. These ZnO nanosheets are of single-crystal wurtzite structure; they grow along the \\\\langle 01\\\\overline {1} 0 \\\\rangle crystallographic directions within polar {0001} planes.

  2. 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.

  3. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; George, M. A.; McCarty, P.

    1999-01-01

    As a high temperature wide-band-gap (3.3 eV at room temperature) semiconductor, ZnO has been used for many applications such as wave-guides, solar cells, and surface acoustic wave devices, Since ZnO has a 60 meV excitonic binding energy that makes it possible to produce excitonic lasing at room temperature, a recent surge of interest is to synthesize ZnO films for UV/blue/green laser diodes. These applications require films with a smooth surface, good crystal quality, and low defect density. Thus, homoepitaxial film growth is the best choice. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystal substrates grown by the hydrothermal method are mechanically polished and annealed in air for four hours before the films are deposited. The annealing temperature-dependence on ZnO substrate morphology and electrical properties is investigated. Films are synthesized by off-axis reactive sputtering deposition. This produces films that have very smooth surfaces with roughness less than or equal to 5 nm on a 5 microns x 5 microns area. The full width at half maximum of film theta rocking curves measured by the x-ray diffraction is slightly larger than that of the crystal substrate. Films are also characterized by measuring resistivity, optical transmittance, and photoluminescence. The properties of ZnO films grown on (0001) ZnO and (0001) sapphire substrates will also be compared and discussed.

  4. 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...

  5. 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

  6. 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

  7. 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

  8. Low-temperature growth of ZnO nanorods by chemical bath deposition.

    PubMed

    Yi, Sung-Hak; Choi, Seung-Kyu; Jang, Jae-Min; Kim, Jung-A; Jung, Woo-Gwang

    2007-09-15

    Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90-95 degrees C. The ZnO seed precursor was prepared by a sol-gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400-500 nm and a diameter of 25-50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is [0001] (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature. PMID:17570384

  9. 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.

  10. NEXAFS and XMCD studies of single-phase Co doped ZnO thin films

    Microsoft Academic Search

    Abhinav Pratap Singh; Ravi Kumar; P. Thakur; N. B. Brookes; K. H. Chae; W. K. Choi

    2009-01-01

    A study of the electronic structure and magnetic properties of Co doped ZnO thin films synthesized by ion implantation followed by swift heavy ion irradiation is presented using near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) measurements. The spectral features of NEXAFS at the Co L3,2-edge show entirely different features than that of metallic Co clusters

  11. 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.

  12. 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.

  13. Long single ZnO nanowire for logic and memory circuits: NOT, NAND, NOR gate, and SRAM.

    PubMed

    Lee, Young Tack; Ali Raza, Syed Raza; Jeon, Pyo Jin; Ha, Ryong; Choi, Heon-Jin; Im, Seongil

    2013-05-21

    We demonstrate logic and static random access memory (SRAM) circuits using a 100 ?m long and 100 nm thin single ZnO nanowire (NW), which acts as a channel of field-effect transistors (FETs) with Al2O3 dielectrics. NW FETs are thus arrayed in one dimension to consist of NOT, NAND, and NOR gate logic, and SRAM circuits. Two respective top-gate NW FETs with Au and indium-tin-oxide (ITO) were connected to form an inverter, the basic NOT gate component, since the former gate leads to an enhanced mode FET while the latter to depletion mode due to their work function difference. Our inverters showed a high voltage gain of 22 under a 5 V operational voltage, resulting in successful operation of all other devices. We thus conclude that our long single NW approach is quite promising to extend the field of nano-electronics. PMID:23584636

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Lead pyrovanadate single crystal as a new SRS material

    SciTech Connect

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

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. Structure and ferromagnetic properties of Co-doped ZnO powders

    Microsoft Academic Search

    Xingyan Xu; Chuanbao Cao

    2009-01-01

    Single-phase Zn1?xCoxO (x=0.02, 0.04) powders were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO crystallizes in a wurtzite structure. The lattice constants of Co-doped ZnO powders decrease slightly when Co is doped into ZnO. Optical absorption spectra show a decrease in the bandgap with increasing Co content and also give an evidence of the

  7. 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.

  8. Angle-dependent photodegradation over ZnO nanowire arrays on flexible paper substrates

    PubMed Central

    2014-01-01

    In this study, we grew zinc oxide (ZnO) nanowire arrays on paper substrates using a two-step growth strategy. In the first step, we formed single-crystalline ZnO nanoparticles of uniform size distribution (ca. 4 nm) as seeds for the hydrothermal growth of the ZnO nanowire arrays. After spin-coating of these seeds onto paper, we grew ZnO nanowire arrays conformally on these substrates. The crystal structure of a ZnO nanowire revealed that the nanowires were single-crystalline and had grown along the c axis. Further visualization through annular bright field scanning transmission electron microscopy revealed that the hydrothermally grown ZnO nanowires possessed Zn polarity. From photocatalytic activity measurements of the ZnO nanowire (NW) arrays on paper substrate, we extracted rate constants of 0.415, 0.244, 0.195, and 0.08 s-1 for the degradation of methylene blue at incident angles of 0°, 30°, 60°, and 75°, respectively; that is, the photocatalytic activity of these ZnO nanowire arrays was related to the cosine of the incident angle of the UV light. Accordingly, these materials have promising applications in the design of sterilization systems and light-harvesting devices. PMID:25593556

  9. Angle-dependent photodegradation over ZnO nanowire arrays on flexible paper substrates

    NASA Astrophysics Data System (ADS)

    Lu, Ming-Yen; Tseng, Yen-Ti; Chiu, Cheng-Yao

    2014-12-01

    In this study, we grew zinc oxide (ZnO) nanowire arrays on paper substrates using a two-step growth strategy. In the first step, we formed single-crystalline ZnO nanoparticles of uniform size distribution (ca. 4 nm) as seeds for the hydrothermal growth of the ZnO nanowire arrays. After spin-coating of these seeds onto paper, we grew ZnO nanowire arrays conformally on these substrates. The crystal structure of a ZnO nanowire revealed that the nanowires were single-crystalline and had grown along the c axis. Further visualization through annular bright field scanning transmission electron microscopy revealed that the hydrothermally grown ZnO nanowires possessed Zn polarity. From photocatalytic activity measurements of the ZnO nanowire (NW) arrays on paper substrate, we extracted rate constants of 0.415, 0.244, 0.195, and 0.08 s-1 for the degradation of methylene blue at incident angles of 0°, 30°, 60°, and 75°, respectively; that is, the photocatalytic activity of these ZnO nanowire arrays was related to the cosine of the incident angle of the UV light. Accordingly, these materials have promising applications in the design of sterilization systems and light-harvesting devices.

  10. 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

  11. 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.

  12. 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.

  13. Epitaxial properties of ZnO thin films on LaAlO3 substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Jia, C. H.; Wang, S.; Wu, Y. H.; Chen, Y. H.; Sun, X. W.; Zhang, W. F.

    2015-07-01

    Wurtzite ZnO thin films with different epitaxial relationships have been grown on (0 0 1)-, (0 1 1)-, and (1 1 1)LaAlO3 (LAO) single-crystal substrates by pulsed laser deposition. Nonpolar (1 1 2 bar 0)ZnO films with two orthogonal domains were obtained on (0 0 1) LAO, in which the in-plane orientation relationship is demonstrated to be <0 0 0 1>ZnO//<1 1 0>LAO. For ZnO on (0 1 1)- and (1 1 1)LAO substrates, a single-domain epitaxy with c axial orientation is observed, in which the in-plane relationships were <1 1 bar 0 0>ZnO//<0 1 1 bar >LAO irrespective of the substrate orientations. Based on the in-plane orientation relationship, the lattice mismatch has been obtained for these three oriented ZnO/LAO heterointerfaces.

  14. 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.

  15. Ohmic-Rectifying Conversion of Ni Contacts on ZnO and the Possible Determination of ZnO Thin Film Surface Polarity

    PubMed Central

    Saw, Kim Guan; Tneh, Sau Siong; Tan, Gaik Leng; Yam, Fong Kwong; Ng, Sha Shiong; Hassan, Zainuriah

    2014-01-01

    The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x?=?0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films. PMID:24466144

  16. 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.

  17. Role of grain boundaries in ZnO

    NASA Astrophysics Data System (ADS)

    Sato, Yukio; Ikuhara, Yuichi

    2014-03-01

    ZnO is used in a wide variety of applications owing to the electrical properties. Polycrystalline ZnO ceramics have long been used such as varistor, and ZnO films are currently intensively studied for transparent conductor applications. Grain boundary (GB) in ZnO varistor is believed to be the origin of nonlinear current-voltage characteristics, and GB in ZnO films possibly affects the electrical conductivity. It is therefore important to understand the role of ZnO GB on the electrical properties, which should be closely related with the structure in atomic scale. With these viewpoints, we have studied the atomistic structure of ZnO GBs, where the orientation relations of adjacent crystals are well defined. Single GBs studied were obtained by fabricating ZnO bicrystals and the GBs were characterized by scanning transmission electron microscopy (STEM) and theoretical calculations. It is found that coordination number of ions change in ZnO GBs; there are underfold or overfold coordinated ions that are unusual in bulk inside. It is calculated that these atomistic structures alters the electronic structure but would not create deep states in the band gap. On the other hand, when praseodymium (Pr), which is known to be a key dopant element to obtain nonlinear (I-V) characteristics, is added to the GBs, Pr strongly localizes to the GBs and occupies specific atomic sites. Pr facilitates the formation of the acceptorlike defects such as zinc vacancies, which we think that is an important role of Pr on generation of nonlinear (I-V) characteristics. Furthermore, atomic arrangement and localization behavior of Pr are studied for several GBs to obtain fundamental understanding about GB structure formation.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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...

  3. 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.

  4. 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

  5. Synthesis of high surface area ZnO powder by continuous precipitation

    SciTech Connect

    Boz, Ismail, E-mail: ismailb@istanbul.edu.tr [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey)] [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey); Kaluza, Stefan [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)] [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany); Boroglu, Mehtap Safak [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey)] [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey); Muhler, Martin [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)] [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)

    2012-05-15

    Graphical abstract: High surface area ZnO powders are synthesized by a low temperature continuous precipitation under ultrasonication. Urea is used as precipitating agent so that no contamination of ZnO powder emanating from precipitating agent, such as, alkalis, is observed. pH and type of precursor greatly affects the surface area and other properties. In this manuscript, we report a very simple and effective continuous precipitation to synthesize high surface area ZnO powder. Highlights: Black-Right-Pointing-Pointer The synthesis of high surface area ZnO powder was achieved at 90 Degree-Sign C in a continuous precipitation unit. Black-Right-Pointing-Pointer Continuous precipitation unit was ultrasonicated to improve final product homogeneity. Black-Right-Pointing-Pointer Precipitation intermediate, hydrozincite, was led to high surface area ZnO powder. Black-Right-Pointing-Pointer The synthesized ZnO nanoparticles had a rather uniform mesoporous structure. -- Abstract: Synthesis of high surface area ZnO powder was achieved by continuous precipitation using zinc ions and urea at low temperature of 90 Degree-Sign C. The powder precipitated resulted in high-purity single-phase ZnO powder when calcined at 280 Degree-Sign C for 3 h in air. The solution pH and the precipitation duration strongly affected the surface area of the calcined ZnO powder. Detailed structural characterizations demonstrated that the synthesized ZnO powder were single crystalline with wurtzite hexagonal phase. The powdered samples precipitated by homogeneous precipitation crystallized directly to hydrozincite without any intermediate phase formation. The phase structures, morphologies and properties of the final ZnO powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering particle size analysis (DLS), and nitrogen physisorption in order to determine the specific surface area (BET) and the pore size distribution (BJH).

  6. Fabrication of inverted opal ZnO photonic crystals by atomic layer deposition

    E-print Network

    Cao, Hui

    and King et al. have fabricated ZnS photonic crystals with high filling fractions and good luminescence,9 and low-pressure chemical vapor deposition CVD 10,11 see Lopez12 for a recent review as a promising route to fabricate inverted opal structures.15,16 ALD is a modified CVD growth method in which

  7. 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

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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

  16. 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,

  17. 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

  18. 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

  19. 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.

  20. Crystal-field theory of Co2+ in doped ZnO

    Microsoft Academic Search

    R. O. Kuzian; A. M. Daré; P. Sati; R. Hayn

    2006-01-01

    We present a crystal-field theory of transition-metal impurities in semiconductors in a trigonally distorted tetrahedral coordination. We develop a perturbative scheme to treat covalency effects within the weak ligand field case (Coulomb interaction dominates over one-particle splitting) and apply it to ZnO:Co2+ (3d7) . Using the large value of the charge-transfer energy Deltapd compared to the p-d hoppings, we perform

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Copper doping of ZnO crystals by transmutation of {sup 64}Zn to {sup 65}Cu: An electron paramagnetic resonance and gamma spectroscopy study

    SciTech Connect

    Recker, M. C.; McClory, J. W., E-mail: John.McClory@afit.edu; Holston, M. S.; Golden, E. M.; Giles, N. C. [Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio 45433 (United States); Halliburton, L. E. [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States)

    2014-06-28

    Transmutation of {sup 64}Zn to {sup 65}Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5?keV gamma ray from the {sup 65}Zn decay and the positron annihilation peak at 511?keV. Their presence confirmed the successful transmutation of {sup 64}Zn nuclei to {sup 65}Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu{sup 2+} ions (where {sup 63}Cu and {sup 65}Cu hyperfine lines are easily resolved). A spectrum from isolated Cu{sup 2+} (3d{sup 9}) ions acquired after the neutron irradiation showed only hyperfine lines from {sup 65}Cu nuclei. The absence of {sup 63}Cu lines in this Cu{sup 2+} spectrum left no doubt that the observed {sup 65}Cu signals were due to transmuted {sup 65}Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu{sup +}-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu{sup +}-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900?°C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

  9. Strong second harmonic generation in SiC, ZnO, GaN two-dimensional hexagonal crystals from first-principles many-body calculations.

    PubMed

    Attaccalite, C; Nguer, A; Cannuccia, E; Grüning, M

    2015-04-14

    The second harmonic generation (SHG) intensity spectrum of SiC, ZnO, GaN two-dimensional hexagonal crystals is calculated by using a real-time first-principles approach based on Green's function theory [Attaccalite et al., Phys. Rev. B: Condens. Matter Mater. Phys. 2013 88, 235113]. This approach allows one to go beyond the independent particle description used in standard first-principles nonlinear optics calculations by including quasiparticle corrections (by means of the GW approximation), crystal local field effects and excitonic effects. Our results show that the SHG spectra obtained using the latter approach differ significantly from their independent particle counterparts. In particular they show strong excitonic resonances at which the SHG intensity is about two times stronger than within the independent particle approximation. All the systems studied (whose stabilities have been predicted theoretically) are transparent and at the same time exhibit a remarkable SHG intensity in the range of frequencies at which Ti:sapphire and Nd:YAG lasers operate; thus they can be of interest for nanoscale nonlinear frequency conversion devices. Specifically the SHG intensity at 800 nm (1.55 eV) ranges from about 40-80 pm V(-1) in ZnO and GaN to 0.6 nm V(-1) in SiC. The latter value in particular is 1 order of magnitude larger than values in standard nonlinear crystals. PMID:25766901

  10. 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.

  11. Ethyl Cellulose and Cetrimonium Bromide Assisted Synthesis of Mesoporous, Hexagon Shaped ZnO Nanodisks with Exposed ±{0001} Polar Facets for Enhanced Photovoltaic Performance in Quantum Dot Sensitized Solar Cells.

    PubMed

    Chetia, Tridip Ranjan; Ansari, Mohammad Shaad; Qureshi, Mohammad

    2015-06-24

    Hexagon shaped mesoporous zinc oxide nanodisks (ZnO NDs) with exposed ±{0001} polar facets have been synthesized by using ethyl cellulose (EC) and cetrimonium bromide (CTAB) as the capping and structure directing agents. We have characterized ZnO NDs using analytical techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area analysis and proposed a plausible mechanism for the formation of ZnO NDs. EC molecules form a colloidal solution in a 1-butanol:water (3:1) solvent system having a negative zeta potential (? ? -32 mV) value which can inhibit CTAB assisted c-axis growth of ZnO crystal and encourage the formation of ZnO NDs. In the control reactions carried out in presence of only CTAB and only EC, formation of hexagonal ZnO nanorods (NRs) and ZnO nanosheets (NSs) composed of numerous ZnO nanoparticles are observed, respectively. Photovoltaic properties of ZnO NDs as compared to ZnO NRs, ZnO NSs, and conventional ZnO nanoparticles (NPs) are investigated by co-sensitizing with CdS/CdSe quantum dots (QDs). An ?35% increase in power conversion efficiency (PCE, ?) is observed in ZnO NDs (? ? 4.86%) as compared to ZnO NPs (? ? 3.14%) while the values of PCE for ZnO NR and ZnO NS based devices are found to be ?2.52% and ?1.64%, respectively. Enhanced photovoltaic performance of the ZnO NDs based solar cell is attributed to an efficient charge separation and collection, boosted by the exposed ±(0001) facets apart from the single crystalline nature, better light-scattering effects, and high BET surface area for sensitizer particle adsorption. Electrochemical impedance spectroscopy (EIS) analysis further reveals that the charge recombination resistance and photoinduced electron lifetime are substantially higher in the ZnO ND based device than in ZnO NR, ZnO NP, and ZnO NS based devices, which demonstrates a slower electron-hole (e(-)-h(+)) recombination rate and faster charge migration through the single crystalline ZnO NDs. PMID:25966867

  12. Crystal-field theory of Co2+ in doped ZnO

    Microsoft Academic Search

    R. O. Kuzian; A. M. Dare; P. Sati; R. Hayn

    2006-01-01

    We present a crystal field theory of transition metal impurities in\\u000asemiconductors in a trigonally distorted tetrahedral coordination. We develop a\\u000aperturbative scheme to treat covalency effects within the weak ligand field\\u000acase (Coulomb interaction dominates over one-particle splitting) and apply it\\u000ato ZnO:Co$^{2+}$ (3d$^7$). Using the large value of the charge transfer energy\\u000a$\\\\Delta_{pd}$ compared to the $p$-$d$ hoppings,

  13. Photorefractive effects in ZnO nanorod doped liquid crystal cell.

    PubMed

    Guo, Yubing; Chen, Yonghai; Xiang, Ying; Qu, Shengchun; Wang, Zhanguo

    2011-03-10

    In a forced light scattering experiment, after the diffraction efficiency arrives to a stable state, both direct current (DC) voltage and two writing beams are turned off, and then by reapplication of the DC voltage we observed a peak. We provide an explanation based on periodically changed anchoring energy and also discuss the evolution of diffraction efficiency under different grating constants, laser polarization, and the direction of the optical axis of a liquid crystal cell. Experiment results show that photo-introduced charge density is nearly in proportion to the intensity of writing beams. PMID:21394182

  14. 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

  15. Synthesis of ZnO nanowires and their applications as an ultraviolet photodetector.

    PubMed

    Lin, Chih-Cheng; Lin, Wang-Hua; Li, Yuan-Yao

    2009-05-01

    High purity ZnO nanowire arrays were synthesized uniformly on a 1.5 cm x 2 cm tin-doped indium oxide (ITO) glass substrate. The ZnO nanowire arrays were formed with a uniform diameter distribution of 30-50 nm and a length of about 5 microm, synthesized via thermal decomposition of zinc acetate at 300 degrees C in air. Analysis by X-ray diffraction and transmission electron microscopy showed that the ZnO nanowires are of single crystal structure with a preferred growth orientation of [001]. A study of the growth mechanism showed that it is a vapor-solid (VS) growth process. The synthesis of these nanowires begins with the processes of dehydration, vaporization, decomposition, and oxidation of the zinc acetate. Next, the ZnO clusters are deposited to form seeds that give rise to selective epitaxial growth of the ZnO nanowires. Optical analysis of ZnO nanowires was performed by UV-visible and fluorescence spectrophotometry, investigating both the photocurrent characteristics and UV photoresponse of the ZnO nanowire photodetectors. A study of optical properties showed that the as-produced ZnO nanowires have great potential as UV photodetectors/sensors. PMID:19452935

  16. Mechanical properties and crystallization behaviors of nanostructured-Zno/PET in-situ composites.

    PubMed

    Tao, Jie; Wang, Tao; Dong, Xiang; Xiaoqian, Shan

    2006-12-01

    In this paper, the mechanical properties and the crystallization behaviors of nano-ZnO particle reinforced PET (ZnO/PET) composite were investigated in order to verify the possibility of industrial application of ZnO/PET. The addition of nano-ZnO particle (nZnOp) improves the tensile strength and elongation of PET, which reach their maximums at 2 wt% nZnOp addition. The enhancement of tensile properties of ZnO/PET composite indicates the improvement in the crystallinity of PET because of the constancy in molecular weight of PET with and without nZnOp addition. Whereas the impact strength of PET decreases with the nZnO, addition, except the nZnOp addition around 2 wt%, at which the highest value has been achieved among the pure PET and composites. And according to the DSC and XRD results, 2 wt% ZnO/PET composite has the highest crystallinity and among pure PET and composites. Furthermore, by combining both DSC and XRD results, the nZnOp addition was found effective in increasing the crystallinity of PET matrix as well as possibly capable of changing the crystallization form of PET. 2 wt% ZnO/PET composite could be a promising upgrade of PET due to the considerable improvement in mechanical properties. PMID:17256357

  17. 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).

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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°

  3. Photoluminescence of ZnO infiltrated into a three-dimensional photonic crystal

    SciTech Connect

    Gruzintsev, A. N. [Russian Academy of Sciences, Institute of Microelectronic Technology and Ultra-High-Purity Materials (Russian Federation)], E-mail: gran@iptm.ru; Emelchenko, G. A.; Masalov, V. M. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)

    2009-08-15

    The effect of the photonic band gap (stopband) of the photonic crystal, the synthesized SiO{sub 2} opal with embedded zinc oxide, on its luminescence in the violet spectral region is studied. It is shown that the position of the photonic band gap in the luminescence and reflectance spectra of the infiltrated opal depends on the diameter of the constituent nanoglobules, the volume fraction of zinc oxide, and on the signal's acceptance angle. It is found that, for the ZnO-opal nanocomposites, the emission intensity is decreased and the luminescence decay time is increased in the spatial directions, in which the photonic band gap coincides in spectral position with the luminescence peak of zinc oxide. The change in the decay time can be attributed to the change in the local density of photonic states in the photonic band gap.

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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;

  18. 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

  19. 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

  20. 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.

  1. 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)

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. Properties of ZnO single quantum wells in ZnMgO nanocolumns grown on Si (1 1 1)

    NASA Astrophysics Data System (ADS)

    Pietrzyk, M. A.; Stachowicz, M.; Wierzbicka, A.; Reszka, A.; Przezdziecka, E.; Kozanecki, A.

    2015-04-01

    In this paper, we report a method of growing of the catalyst-free self-organized ZnMgO nanocolumns with single quantum well on Si (1 1 1) substrates by plasma-assisted molecular beam epitaxy technique (PA-MBE). The structures were grown without buffer layers. Optical properties of the ZnMgO/ZnO/ZnMgO quantum wells were studied by photo (PL)- and cathodoluminescence (CL) spectroscopy. A detailed analysis of the optical properties has been carried out, including quantum confinement effect and temperature dependence of excitonic emission. The structures reveal intense near band edge emission in PL as well as in CL. Blue shift of excitonic emission from the wells in comparison to bulk ZnO due to the quantum confinement effect is observed. Cross-sectional SEM-CL mapping shows that the ZnO/ZnMgO single quantum wells with different well widths are located in ZnMgO nanocolumns. The crystalline quality of the heterostructure was characterized by X-ray diffraction (XRD). No phase separation in ZnO/ZnMgO quantum structures was found.

  14. Polarity Effects of Substrate Surface in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.; McCarty, P.

    1999-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (0-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films are also deposited on the (000 I) Al203 substrates. It is found that the two polar surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which are strongly inference the epitaxial film growth. The morphology and structure of epitaxial films on the ZnO substrates are different from the film on the Al203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite Surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth using reactive sputtering deposition.

  15. 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

  16. 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

  17. 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

  18. Synthesis of ZnO nanorod–nanosheet composite via facile hydrothermal method and their photocatalytic activities under visible-light irradiation

    SciTech Connect

    Tan, Wai Kian [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan); Abdul Razak, Khairunisak; Lockman, Zainovia [School of Materials and Mineral Resources, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang (Malaysia); Kawamura, Go; Muto, Hiroyuki [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan); Matsuda, Atsunori, E-mail: matsuda@ee.tut.ac.jp [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan)

    2014-03-15

    ZnO composite films consisting of ZnO nanorods and nanosheets were prepared by low-temperature hydrothermal processing at 80 °C on seeded glass substrates. The seed layer was coated on glass substrates by sol–gel dip-coating and pre-heated at 300 °C for 10 min prior to hydrothermal growth. The size of the grain formed after pre-heat treatment was ?40 nm. A preferred orientation seed layer at the c-axis was obtained, which promoted vertical growth of the ZnO nanorod arrays and formation of the ZnO nanosheets. X-ray diffraction patterns and high-resolution transmission electron microscope (HR-TEM) images confirmed that the ZnO nanorods and nanosheets consist of single crystalline and polycrystalline structures, respectively. Room temperature photoluminescence spectra of the ZnO nanorod–nanosheet composite films exhibited band-edge ultraviolet (UV) and visible emission (blue and green) indicating the formation of ZnO crystals with good crystallinity and are supported by Raman scattering results. The formation of one-dimensional (1D) ZnO nanorod arrays and two-dimensional (2D) ZnO nanosheet films using seeded substrates in a single low-temperature hydrothermal step would be beneficial for realization of device applications that utilize substrates with limited temperature stability. The ZnO nanorods and nanosheets composite structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation. -- Graphical abstract: Schematic illustration of ZnO nanorod–nanosheet composite structure formation by hydrothermal at low-temperature of 80 °C against time. Highlights: • Novel simultaneous formation of ZnO nanorods and nanosheets composite structure. • Facile single hydrothermal step formation at low-temperature. • Photoluminescence showed ultraviolet and visible emission. • Feasible application on substrates with low temperature stability. • Improved photocatalytic activity under visible-light irradiation.

  19. 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.

  20. Ultra-fast Microwave Synthesis of ZnO Nanowires and their Dynamic Response Toward Hydrogen Gas

    PubMed Central

    2009-01-01

    Ultra-fast and large-quantity (grams) synthesis of one-dimensional ZnO nanowires has been carried out by a novel microwave-assisted method. High purity Zinc (Zn) metal was used as source material and placed on microwave absorber. The evaporation/oxidation process occurs under exposure to microwave in less than 100 s. Field effect scanning electron microscopy analysis reveals the formation of high aspect-ratio and high density ZnO nanowires with diameter ranging from 70 to 80 nm. Comprehensive structural analysis showed that these ZnO nanowires are single crystal in nature with excellent crystal quality. The gas sensor made of these ZnO nanowires exhibited excellent sensitivity, fast response, and good reproducibility. Furthermore, the method can be extended for the synthesis of other oxide nanowires that will be the building block of future nanoscale devices. PMID:20596440

  1. Effect of solution concentrations on crystal structure, surface topographies and photoluminescence properties of ZnO thin films

    NASA Astrophysics Data System (ADS)

    Lv, Jianguo; Liu, Changlong; Gong, Wanbing; Zi, Zhenfa; Chen, Xiaoshuang; Huang, Kai; Wang, Tao; He, Gang; Song, Xueping; Sun, Zhaoqi

    2012-06-01

    Zinc oxide thin films were deposited on silicon substrates via hydrothermal method. Microstructures, surface topographies and optical properties of ZnO thin films were systematically investigated by X-ray diffraction, atomic force microscopy and fluorescence spectrophotometer. The mean grain size and surface roughness of the thin films decrease first and then increase with increasing the concentration of zinc nitrate hexahydrate. The photoluminescence spectra of ZnO thin films, excited by the 240, 320, 360, 380 and 400 nm excitation wavelength, were investigated in detail. Based on our analysis, it can be noted that mechanisms of the ultraviolet, violet and blue emissions are attributed to the transitions from the localized levels below the conduction band, zinc vacancy, interstitial zinc and extended interstitial zinc levels to the valance band, respectively. Blue-violet emissions of ZnO have great potential in light emitting and biological fluorescence labeling applications.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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...

  9. 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.

  10. A simple route to vertical array of quasi-1D ZnO nanofilms on FTO surfaces: 1D-crystal growth of nanoseeds under ammonia-assisted hydrolysis process

    PubMed Central

    2011-01-01

    A simple method for the synthesis of ZnO nanofilms composed of vertical array of quasi-1D ZnO nanostructures (quasi-NRs) on the surface was demonstrated via a 1D crystal growth of the attached nanoseeds under a rapid hydrolysis process of zinc salts in the presence of ammonia at room temperature. In a typical procedure, by simply controlling the concentration of zinc acetate and ammonia in the reaction, a high density of vertically oriented nanorod-like morphology could be successfully obtained in a relatively short growth period (approximately 4 to 5 min) and at a room-temperature process. The average diameter and the length of the nanostructures are approximately 30 and 110 nm, respectively. The as-prepared quasi-NRs products were pure ZnO phase in nature without the presence of any zinc complexes as confirmed by the XRD characterisation. Room-temperature optical absorption spectroscopy exhibits the presence of two separate excitonic characters inferring that the as-prepared ZnO quasi-NRs are high-crystallinity properties in nature. The mechanism of growth for the ZnO quasi-NRs will be proposed. Due to their simplicity, the method should become a potential alternative for a rapid and cost-effective preparation of high-quality ZnO quasi-NRs nanofilms for use in photovoltaic or photocatalytics applications. PACS: 81.07.Bc; 81.16.-c; 81.07.Gf. PMID:22027275

  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. Recent advances in ZnO materials and devices

    Microsoft Academic Search

    D. C. Look

    2001-01-01

    Wurtzitic ZnO is a wide-bandgap (3.437 eV at 2 K) semiconductor which has many applications, such as piezoelectric transducers, varistors, phosphors, and transparent conducting films. Most of these applications require only polycrystalline material; however, recent successes in producing large-area single crystals have opened up the possibility of producing blue and UV light emitters, and high-temperature, high-power transistors. The main advantages

  17. 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.

  18. 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.

  19. Structural and optical properties of MgO doped ZnO

    SciTech Connect

    Verma, Kavita; Shukla, S.; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore-452001 (India); Varshney, M. [Department of Physics, M. B. Khalsa College, Raj Mohallah, Indore-452002 (India); Asthana, A. [Department of Chemistry, Govt. B. V. T. PG Autonomous College, Durg- 491001 (India)

    2014-04-24

    Samples of ZnO, Zn{sub 0.5}Mg{sub 0.5}O and MgO were prepared by co-precipitation method. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, space group P6{sub 3}mc), MgO crystallizes in cubic Fd3m space group and Zn{sub 0.5}Mg{sub 0.5}O represents mixed nature of ZnO and MgO lattices. Similar features were observed from Raman spectroscopy. The energy band gaps estimated from UV-Vis spectroscopy are found to be 4.21 and 3.42 eV for ZnO and Zn{sub 0.5}Mg{sub 0.5}O samples respectively.

  20. 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

  1. Synthesis, characterization and optical properties of sheet-like ZnO

    SciTech Connect

    Liu, Changzhen [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China)] [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); Meng, Dawei, E-mail: dwmeng@cug.edu.cn [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China) [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Wu, Xiuling [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China) [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Wang, Yongqian; Yu, Xiaohong; Zhang, Zhengjie [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China)] [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); Liu, Xiaoyang [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China)] [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China)

    2011-09-15

    Highlights: {yields} Sheet-like ZnO with regular hexagon shape was synthesized with a two-step method. {yields} Sheet-like ZnO predecessor was synthesized at low temperature in open system. {yields} The diameter and thickness of ZnO sheet can be controlled conveniently. {yields} This low-cost and environmentally benign approach is controllable and reproducible. {yields} Sheet-like ZnO may have potential application in optical and electrical devices. -- Abstract: Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 {sup o}C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. Characteristic properties of Raman scattering and photoluminescence on ZnO crystals doped through phosphorous-ion implantation

    SciTech Connect

    Jeong, T. S.; Yu, J. H.; Mo, H. S.; Kim, T. S.; Lim, K. Y.; Youn, C. J., E-mail: cjyoun@chonbuk.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center (SPRC), Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Hong, K. J. [Department of Physics, Chosun University, Gwangju 501-759 (Korea, Republic of)

    2014-02-07

    P-doped ZnO was fabricated by means of the ion-implantation method. At the Raman measurement, the blue shift of the E{sub 2}{sup high} mode and A{sub 1}(LO) phonon of the inactive mode were observed after the P-ion implantation. It suggested to be caused by the compressive stress. Thus, Hall effect measurement indicates that the acceptor levels exists in P-doped ZnO while still maintaining n-type ZnO. From the X-ray photoelectron spectroscopy, the chemical bond formation of the P2p{sub 3/2} spectrum consisted of 2(P{sub 2}O{sub 5}) molecules. Therefore, the implanted P ions were substituted to the Zn site in ZnO. From the photoluminescence (PL) spectra, P-related PL peaks were observed in the energy ranges of 3.1 and 3.5?eV, and its origin was analyzed at P{sub Zn}-2V{sub Zn} complexes, acting as a shallow acceptor. With increasing temperatures, the neutral-acceptor bound-exciton emission, (A{sup 0}, X), shows a tendency to quench the intensity and extend the emission linewidth. From the relations of the intensity and the linewidth as a function of temperature, the broadening of linewidth was believed to the result that the vibration mode of E{sub 2}{sup high} participates in the broadening process of (A{sup 0}, X) and the change of luminescent intensity was attributed to the partial dissociation of (A{sup 0}, X). Consequently, these facts indicate that the acceptor levels existed in P-doped ZnO layer by the ion implantation.

  16. Enhancing blue luminescence from Ce-doped ZnO nanophosphor by Li doping

    PubMed Central

    2014-01-01

    Undoped ZnO, Ce-doped ZnO, and (Li, Ce)-codoped ZnO nanophosphors were prepared by a sol-gel process. The effects of the additional doping with Li ions on the crystal structure, particle morphology, and luminescence properties of Ce-doped ZnO were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and photoluminescence spectroscopy. The results indicate that the obtained samples are single phase, and a nanorod shaped morphology is observed for (Li, Ce)-codoping. Under excitation with 325 nm light, Ce-doped ZnO phosphors show an ultraviolet emission, a green emission, and a blue emission caused by Zn interstitials. The spectrum of the sample codoped with a proper Li concentration features two additional emissions that can be attributed to the Ce3+ ions. With the increase of the Li doping concentration, the Ce3+ blue luminescence of (Li, Ce)-codoped ZnO is obviously enhanced, which results not only from the increase of the Ce3+ ion concentration itself but also from the energy transfer from the ZnO host material to the Ce3+ ions. This enhancement reaches a maximum at a Li content of 0.02, and then decreases sharply due to the concentration quench. These nanophosphors may promise for application to the visible-light-emitting devices. PACS 78.55.Et; 81.07.Wx; 81.20.Fw PMID:25258604

  17. ZnO deposition on metal substrates: Relating fabrication, morphology, and wettability

    NASA Astrophysics Data System (ADS)

    Beaini, Sara S.; Kronawitter, Coleman X.; Carey, Van P.; Mao, Samuel S.

    2013-05-01

    It is not common practice to deposit thin films on metal substrates, especially copper, which is a common heat exchanger metal and practical engineering material known for its heat transfer properties. While single crystal substrates offer ideal surfaces with uniform structure for compatibility with oxide deposition, metallic surfaces needed for industrial applications exhibit non-idealities that complicate the fabrication of oxide nanostructure arrays. The following study explored different ZnO fabrication techniques to deposit a (super)hydrophobic thin film of ZnO on a metal substrate, specifically copper, in order to explore its feasibility as an enhanced condensing surface. ZnO was selected for its non-toxicity, ability to be made (super)hydrophobic with hierarchical roughness, and its photoinduced hydrophilicity characteristic, which could be utilized to pattern it to have both hydrophobic-hydrophilic regions. We investigated the variation of ZnO's morphology and wetting state, using SEMs and sessile drop contact angle measurements, as a function of different fabrication techniques: sputtering, pulsed laser deposition (PLD), electrodeposition and annealing Zn. We successfully fabricated (super)hydrophobic ZnO on a mirror finish, commercially available copper substrate using the scalable electrodeposition technique. PLD for ZnO deposition did not prove viable, as the ZnO samples on metal substrates were hydrophilic and the process does not lend itself to scalability. The annealed Zn sheets did not exhibit consistent wetting state results.

  18. Preparation of Ag@Ag3PO4@ZnO ternary heterostructures for photocatalytic studies.

    PubMed

    Jin, Chao; Liu, Guanglei; Zu, Lianhai; Qin, Yao; Yang, Jinhu

    2015-09-01

    In this article, we report a novel Ag@Ag3PO4@ZnO ternary heterostructures synthesized through a three-step approach. Firstly, single-crystalline Ag nanorods are fabricated and served as the templates for subsequent Ag3PO4 deposition. Secondly, Ag3PO4 crystals are grown around Ag core nanorods through a solution co-precipitation process, leading to the Ag@Ag3PO4 binary heterostructures. Finally, ZnO nanorod arrays on the surface of the Ag@Ag3PO4 heterostructures are realized via a seeded growth strategy, forming the typical Ag@Ag3PO4@ZnO ternary heterostructures. The photodegradation of rhodamine B under ultraviolet-visible light irradiation indicates that the Ag@Ag3PO4@ZnO ternary heterostructures exhibit much higher activities than pure Ag3PO4 and binary heterostructures of Ag@Ag3PO4. The higher photocatalytic activity of the Ag@Ag3PO4@ZnO composites may be attributed to the effective photogenerated charge separation at heterointerfaces of Ag/Ag3PO4 and Ag3PO4/ZnO, and the rapid electron transport along one-dimensional Ag and ZnO nanorods. PMID:25965430

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Effects of Phonon Coupling and Free Carriers on Band-edge Emission at Room Temperature in n-type ZnO Crystals

    SciTech Connect

    Giles, N. C. [West Virginia University; Xu, Chunchuan [West Virginia University; Callahan, M. J. [Air Force Research Laboratory; Wang, Buguo [Air Force Research Laboratory; Neal, John S [ORNL; Boatner, Lynn A [ORNL

    2006-01-01

    Room-temperature photoluminescence has been studied in n-type bulk ZnO crystals representing three different growth methods and having free-carrier concentrations (n) ranging from 10{sup 13} to 10{sup 18} cm{sup -3}. The near-band-edge emission has both free-exciton and free-exciton-phonon contributions, with the strength of the phonon coupling dependent on sample defect concentrations. Band-gap shrinkage effects are used to explain a decrease in emission energy for the higher n values. Band filling and band nonparabolicity are predicted to be important for n>10{sup 19} cm{sup -3}. At 300 K, in the absence of free carriers, the free-exciton energy is 3.312{+-}0.004 eV.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Schottky barrier height behavior of Pt-Ru alloy contacts on single-crystal n-ZnO

    SciTech Connect

    Nagata, T.; Haemori, M.; Hayakawa, R.; Yoshitake, M.; Chikyow, T. [Advanced Electronic Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Volk, J. [Research Institute for Technical Physics and Materials Science, H-1121 Budapest, Konkoly Thege Miklos ut 29-33 (Hungary); Yamashita, Y. [Advanced Electronic Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Yoshikawa, H.; Ueda, S.; Kobayashi, K. [NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)

    2010-05-15

    We investigated the Schottky barrier height (SBH) behavior of binary alloy Schottky contacts on n-type zinc oxide (n-ZnO) single crystals. Pt-Ru alloy electrodes were deposited on the Zn-polar and O-polar faces of ZnO substrates by combinatorial ion-beam deposition under identical conditions. The crystal structures of the Pt-Ru alloy film changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt-Ru alloy phase diagram with decreasing Pt content. The SBH, determined from current-voltage measurements, decreased with decreasing Pt content, indicating that the SBH behavior also followed the Pt-Ru alloy phase diagram. The alloy electrodes on the Zn-polar face showed better Schottky properties than those on the O-polar face. Hard x-ray photoelectron spectroscopy revealed a difference in the interface oxidization of the Pt-Ru alloy: the interface of the O-polar face and Pt-Ru mixed phase with poor crystallinity had a more oxidized layer than that of the Zn-polar face. As a result of this oxidization, the O-polar face, Pt-Ru mixed, and Ru phases showed poor Schottky properties.

  20. Electromechanical coupling coefficient k15 of polycrystalline ZnO films with the c-axes lie in the substrate plane.

    PubMed

    Yanagitani, Takahiko; Mishima, Natsuki; Matsukawa, Mami; Watanabe, Yoshiaki

    2007-04-01

    The (1120) textured polycrystalline ZnO films with a high shear mode electromechanical coupling coefficient k15 are obtained by sputter deposition. An over-moded resonator, a layered structure of metal electrode film/(1120) textured ZnO piezoelectric film/metal electrode film/silica glass substrate was used to characterize k15 by a resonant spectrum method. The (1120) textured ZnO piezoelectric films with excellent crystallite c-axis alignment showed an electromechanical coupling coefficient k15 of 0.24. This value was 92% of k15 value in single-crystal (k15 = 0.26). PMID:17441579

  1. 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

  2. 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,

  3. 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

  4. 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.

  5. Facile fabrication of hierarchical ZnO microstructures assisted with PAMPSA and enhancement of green emission

    NASA Astrophysics Data System (ADS)

    Huang, Qiang; Cun, Tangxiang; Zuo, Wenbin; Liu, Jianping

    2015-03-01

    We report the fabrication of hierarchically microstructured flower-like ZnO by a facile and single-step procedure involving poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) assisted aqueous chemical method. The shapes and sizes can be controlled just by varying the concentrations of the water-soluble polymer. When a suitable PAMPAS concentration was utilized, uniform well-defined and mono-dispersed chrysanthemum-like ZnO microstructures based on nanorod building blocks were obtained. The formation mechanism of the hierarchical structure was presented. The structured studies using XRD, HRTEM and SAED reveal these ZnO nanorods are composed of a single phase nature with wurtzite structure and grow along with the c-axis. FTIR spectrum indicated the incorporation of a trace of PAMPSA into ZnO crystals. HRTEM, Raman and XPS analyses showed that the hierarchical ZnO microstructures contain high concentration of oxygen vacancies which enable them exhibiting a significant intense deep-level emission centered at green luminescence in its photoluminescence spectra. They also show enhanced photocatalytic efficiency in degradation of methylene blue. It is hoped that the present work may provide a simple method to fabricate ZnO hierarchical microstructures and a positive relationship among polar plane, oxygen vacancy and green emission.

  6. Dynamical nuclear polarization by means of shallow donors in ZnO quantum dots

    NASA Astrophysics Data System (ADS)

    Baranov, Pavel G.; Orlinskii, Sergei B.; de Mello Donega, Celso; Meijerink, Andries; Blok, Hubert; Schmidt, Jan

    2009-12-01

    The almost complete dynamic nuclear polarization (DNP) of nuclear spins has been demonstrated can be achieved in ZnO and AgCl single crystals by saturating the EPR transition of the shallow donor (SD) present in this crystals with using high-frequency (275 and 95 GHz) at low temperatures. DNP effects have also been observed in ZnO quantum dots (QD's) where polarization of 67Zn nuclear spins in ZnO core and of 1H nuclear spins in the Zn(OH) 2 capping layer have been obtained by saturating the EPR transition of the SD present in the ZnO QD's. DNP manifests itself via a shift of the EPR lines of SD in bulk ZnO and AgCl crystals and the creation of a hole and an antihole in the EPR absorption line of the SD in QD's. The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with NMR techniques.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. Energy dissipation channels affecting photoluminescence from resonantly excited Er3+ ions doped in epitaxial ZnO host films

    NASA Astrophysics Data System (ADS)

    Akazawa, Housei; Shinojima, Hiroyuki

    2015-04-01

    We identified prerequisite conditions to obtain intense photoluminescence at 1.54 ?m from Er3+ ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er3+ ions were resonantly excited at a wavelength of 532 nm between energy levels of 4I15/2 and 2H11/2. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er3+ ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er3+ ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er3+ ions were accommodated into ZnO crystals. Optimizing the degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er2O3 crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from Er3+ ions.

  15. 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.

  16. 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).

  17. 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.

  18. 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).

  19. 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.

  20. 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.

  1. 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.

  2. Friction and deformation behavior of single-crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. Vibrational Spectroscopy of NaH Complexes in ZnO NARENDRA S. PARMAR,1,2

    E-print Network

    McCluskey, Matthew

    , acceptor, SIMS Demand for white light-emitting diodes (LEDs),1 high-power solid-state emitters, and lasers-grown cermet ZnO single crystals18 were used in this work. Alkali-metal dis- pensers from SAES Advanced Technology were used as the alkali-metal source. The alkali-metal-gener- ating material is a mixture

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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).

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. 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

  12. ZnO thin films prepared by remote plasma-enhanced CVD method

    Microsoft Academic Search

    K. Haga; M Kamidaira; Y Kashiwaba; T Sekiguchi; H Watanabe

    2000-01-01

    High-quality ZnO films were successfully prepared by a remote plasma-enhanced CVD of Zn(C2H5)2 and carbon dioxide. Plasma excitation in carbon dioxide was critically important to deposit films with good crystallinity. Epitaxial growth could be achieved on (0002) or (011?2) oriented single-crystal sapphire substrates using this simple system. Reflection high-energy electron diffraction and X-ray diffraction patterns show that the ZnO(112?0) plane

  13. Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

    SciTech Connect

    Allen, M. W. [Department of Electrical and Computer Engineering, University of Canterbury, Christchurch 8140 (New Zealand); MacDiarmid Institute for Advanced Materials and Nanotechnology (New Zealand); Zemlyanov, D. Y. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907-2057 (United States); Waterhouse, G. I. N.; Metson, J. B. [Department of Chemistry, University of Auckland, Private Bag 90219, Auckland (New Zealand); MacDiarmid Institute for Advanced Materials and Nanotechnology (New Zealand); Veal, T. D.; McConville, C. F. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Durbin, S. M. [Department of Electrical Engineering and Department of Physics, University at Buffalo, Buffalo, New York 14260 (United States); MacDiarmid Institute for Advanced Materials and Nanotechnology (New Zealand)

    2011-03-07

    Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al K{sub {alpha}} (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. Residual and intentional n-type doping of ZnO thin films grown by metal-organic vapor phase epitaxy on sapphire and ZnO substrates

    NASA Astrophysics Data System (ADS)

    Brochen, Stéphane; Lafossas, Matthieu; Robin, Ivan-Christophe; Ferret, Pierre; Gemain, Frédérique; Pernot, Julien; Feuillet, Guy

    2014-03-01

    ZnO epilayers usually exhibit high n-type residual doping which is one of the reasons behind the difficulties to dope this material p-type. In this work, we aimed at determining the nature of the involved impurities and their potential role as dopant in ZnO thin films grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and ZnO substrates. In both cases, secondary ion mass spectroscopy (SIMS) measurements give evidence for a strong diffusion of impurities from the substrate to the epilayer, especially for silicon and aluminum. In the case of samples grown on sapphire substrates, aluminum follows Fick's diffusion law on a wide growth temperature range (800-1000°C). Thus, the saturation solubility and the diffusion coefficient of aluminum in ZnO single crystals have been determined. Furthermore, the comparison between SIMS impurity and effective dopant concentrations determined by capacitance-voltage measurements highlights, on one hand a substitutional mechanism for aluminum diffusion, and on the other hand that silicon acts as a donor in ZnO and not as an amphoteric impurity. In addition, photoluminescence spectra exhibit excitonic recombinations at the same energy for aluminum and silicon, indicating that silicon behaves as an hydrogenic donor in ZnO. Based on these experimental observations, ZnO thin films with a controlled n-type doping in the 1016-1019cm-3 range have been carried out. These results show that MOVPE growth is fully compatible with the achievement of highly Al-doped n-type thin films, but also with the growth of materials with low residual doping, which is a crucial parameter to address ZnO p-type doping issues.

  3. Superhydrophobic multi-scale ZnO nanostructures fabricated by chemical vapor deposition method.

    PubMed

    Zhou, Ming; Feng, Chengheng; Wu, Chunxia; Ma, Weiwei; Cai, Lan

    2009-07-01

    The ZnO nanostructures were synthesized on Si(100) substrates by chemical vapor deposition (CVD) method. Different Morphologies of ZnO nanostructures, such as nanoparticle film, micro-pillar and micro-nano multi-structure, were obtained with different conditions. The results of XRD and TEM showed the good quality of ZnO crystal growth. Selected area electron diffraction analysis indicates the individual nano-wire is single crystal. The wettability of ZnO was studied by contact angle admeasuring apparatus. We found that the wettability can be changed from hydrophobic to super-hydrophobic when the structure changed from smooth particle film to single micro-pillar, nano-wire and micro-nano multi-scale structure. Compared with the particle film with contact angle (CA) of 90.7 degrees, the CA of single scale microstructure and sparse micro-nano multi-scale structure is 130-140 degrees, 140-150 degrees respectively. But when the surface is dense micro-nano multi-scale structure such as nano-lawn, the CA can reach to 168.2 degrees . The results indicate that microstructure of surface is very important to the surface wettability. The wettability on the micro-nano multi-structure is better than single-scale structure, and that of dense micro-nano multi-structure is better than sparse multi-structure. PMID:19916432

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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