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1

Ultra-precision process of CaF2 single crystal  

NASA Astrophysics Data System (ADS)

This paper proposes a new chemical mechanical polishing (CMP) process method for CaF2 single crystal to get ultraprecision surface. The CMP processes are improving polishing pad and using alkaline SiO2 polishing slurry with PH=8, PH=11 two phases to polish, respectively, and the roughness can be 0.181nm Rq (10?m×10?m). The CMP process can't get high surface figure, so we use ion beam figuring (IBF) technology to obtain high surface figure. However, IBF is difficult to improve the CaF2 surface roughness. We optimize IBF process to improve surface figure and keep good surface roughness too. Different IBF incident ion energy from 400ev to 800ev does not affect on the surface roughness obviously but the depth of material removal is reverse. CaF2 single crystal can get high precision surface figure (RMS=2.251nm) and still keep ultra-smooth surface (Rq=0.207nm) by IBF when removal depth is less than 200nm. The researches above provide important information for CaF2 single crystal to realize ultra-precision manufacture.

Yin, Guoju; Li, Shengyi; Xie, Xuhui; Zhou, Lin

2014-08-01

2

Surface modifications of BaF2 and CaF2 single crystals by slow highly charged ions  

NASA Astrophysics Data System (ADS)

Ion-irradiation of solid surfaces is considered as one of the promising and powerful techniques for material nanostructuring. Recently, slow highly charged ions (HCI) have shown their potential in creating surface nanostructures in various solids. Here, we focus on the surface modifications of BaF2 and CaF2 single crystals by HCI. Despite the fact that both materials belong to alkaline-earth fluorides with the same crystalline structure, they exhibit different sensitivity for HCI-induced nanostructure. We discuss similarities and differences for the creation of HCI-induced nanohillocks and etch pits in both materials and their dependence on potential and kinetic energy deposition. Furthermore, we compare the results with modifications induced by swift heavy ions (SHI), in order to reach a better understanding of the mechanisms responsible for the creation of nanostructures in ionic fluoride single crystals.

El-Said, A. S.; Heller, R.; Wilhelm, R. A.; Facsko, S.; Aumayr, F.

2014-08-01

3

Study of the oxygen incorporation during growth of large CaF 2-crystals  

NASA Astrophysics Data System (ADS)

Single crystalline calcium fluoride (CaF 2) is designated as optical material in systems for photolithographic processing of silicon ICs at wavelengths in the deep ultraviolet. The prerequisites for this application are a high transmission and a high resistance with respect to radiation damage under high-intensity laser irradiation. Pure CaF 2 has excellent transmission properties without absorption bands over a wide wavelength range from UV to IR. Selective absorption bands exist in CaF 2 only if the crystal contains impurities. Oxygen is considered as a major impurity in CaF 2. In the present contribution incorporation of oxygen during crystal growth and its influence on the optical properties of CaF 2 is investigated systematically by a specially designed crystal growth facility and processing. A special gas supply system is used to introduce oxygen directly into the CaF 2-melt during crystal growth by a Bridgman-type technique. The concentration of the oxygen in the growth atmosphere and therewith in the crystal was varied over a wide range during growth. The oxygen concentration in the as-grown CaF 2-crystal was determined quantitatively by a special characterization technique called elastic recoil detection (ERD). Concentrations between 5 and 144 ppm were detected. Investigations of the optical properties of the oxygen-doped CaF 2-crystal revealed that the oxygen causes an increase of the absorption in the UV range with a maximum at 197 nm. The relation between the oxygen concentration in the crystal and the absorption coefficient at 197 nm was found to be linear. This calibration relation can now be used in general for the quantitative determination of the oxygen concentration in CaF 2-crystals by absorption measurements at 197 nm. Furthermore, the influence of oxygen on the radiation hardness was examined for X-ray and excimer F 2-laser (157 nm) irradiation.

Molchanov, A.; Friedrich, J.; Wehrhan, G.; Müller, G.

2005-01-01

4

Optical absorption properties and valence states of uranium in CaF 2 crystals grown by TGT  

NASA Astrophysics Data System (ADS)

Calcium fluoride single crystals doped with uranyl nitrate were grown by an improved temperature gradient technique under different conditions. Absorption spectra, energy levels and unit cell parameters were studied to analyze the possible color centers and valence states of uranium ions in as-grown U:CaF 2 crystals. Uranium in U:CaF 2 crystals grown in the presence of PbF 2 as an oxygen scavenger is trivalent. F-centers and other defects related to oxygen, with respective absorption lines at 604 and 526 nm, and impure valence states of uranium ions exist in U 3+:CaF 2 when the molar ratio of PbF 2 to U is less than 25. In the absence of PbF 2, U:CaF 2 crystals are multicolor, consisting of red, cerise, yellow and green volumes from inside to outside where the red part in the core is still U 3+:CaF 2. Mixed valence states of uranium ions exist in the crystal. The valences of uranium ions are inferred to gradually increase from +3 to +6 according to the graded changes of the absorption spectra and unit cell parameters.

Su, Liangbi; Yang, Weiqiao; Xu, Jun; Dong, Yongjun; Zhou, Guoqing

2004-09-01

5

Optical gain in Y2+:CaF2 crystal: potential medium for near-infrared tunable lasers  

NASA Astrophysics Data System (ADS)

Y2+ (4d1 configuration) ion is proposed to be a new laser active optical center. As an example Y2+ in CaF2 crystals demonstrates broad luminescence band with peak at 1146 nm and halfwidth of 2155 cm-1 at room temperature when excited with 532 nm light. It was observed that Y2+ centers in CaF2 are stable under excitation with 532 nm radiation with pumping power density of 233 MW/cm2 from flash-lamp pumped Q-switched Nd3+:YAG laser. Optical gain has been measured in CaF2:Y2+ amplifier at 1150 nm wavelength. It is concluded that Y2+ doped crystals seems to be promising materials for tunable solid-state lasers.

Ter-Mikirtychev, Valerii V.

1998-05-01

6

Investigation of the spin-Hamiltonian parameters for the trigonal U5+ center in CaF2 crystal.  

PubMed

The spin-Hamiltonian parameters (g factor g(//), g(perpendicular) and hyperfine structure constants A(//), A(perpendicular)) of the trigonal U(5+) center in CaF(2) crystal have been calculated from the complete diagonalization (of energy matrix) method (CDM) for 5f(1) ions in trigonal crystal field and under an external magnetic field. In the calculation, the crystal-field parameters are estimated from the superposition model. From the calculations, these spin-Hamiltonian parameters are reasonably explained, and the defect model (i.e., the trigonal U(5+) center is attributed to U(5+) substituting for Ca(2+) in CaF(2) with six F(-) ions replaced by O(2-) and the other two F(-) sites vacant because of charge compensation) given in the previous paper is confirmed. The results are discussed. PMID:20308011

Zheng, Wen-Chen; Liu, Hong-Gang; Yang, Wei-Qing; Su, Ping

2010-06-01

7

Nd3+:CaF2 crystal with controlled photoluminescence spectroscopic properties by codoping Y3+ ions  

NASA Astrophysics Data System (ADS)

High optical quality Nd,Y-codoped CaF2 crystals with diameter 3-inch were obtained by TGT method. Absorption and emission spectra were recorded at 5 K, 12 K, and 300 K respectively. Judd-Ofelt theory was applied to obtain standard parameter ?t (t = 2, 4, 6) and the fitting result of experimental lifetime of Nd3+4F3/2 ? 4I11/2 transition. Broad and flat 1.06 ?m emission spectra of Nd3+ ions were obtained with Y3+-codoping. The largest emission bandwidth of Nd3+4F3/2 ? 4I11/2 transition is up to 28 nm. The results revealed that codoping Y3+ ions in Nd:CaF2 crystal can effectively modulate the spectra properties of Nd3+ ions, in addition to the reduction of fluorescence concentration-quenching.

Wang, Qingguo; Su, Liangbi; Ma, Fengkai; Zhan, Yaoyu; Jiang, Dapeng; Qian, Xiaobo; Wang, Jingya; Zheng, Lihe; Xu, Jun; Ryba-Romanowski, Witold; Solarz, Piotr; Lisiecki, Radoslaw

2013-12-01

8

Spatially selective Er/Yb-doped CaF2 crystal formation by CO2 laser exposure  

NASA Astrophysics Data System (ADS)

We report the glass-ceramic precipitation on the oxyfluoride glass surface by spatially selective annealing with a CO2 laser and a heat gun exposure. X-ray diffraction analysis showed the formation of major CaF2 and miner Ca2SiO4 nanoparticles. We observed ?100 nm nanoparticle aggregation by tunneling electron microscopy and element distribution in glass and crystal phases. Spatial distribution of glass ceramics near the glass surface was probed by confocal fluorescence microscope by using much enhanced emission from the Er ions in the laser-treated area. Strong emissions at 365 nm excitation and visible up-conversion emissions at 980 nm excitation also indicated well incorporation of Er and Yb ions into a crystalline environment.

Kim, Dong-Seon; Lee, Jin-Ho; Lim, Ki-Soo

2014-10-01

9

Nonlinear luminescence response of CaF2:Eu and YAlO3:Ce to single-ion excitation  

SciTech Connect

Pulse-height of CaF2:Eu and YAlO3:Ce scintillators to single H+, He+ and O3+ ions are measured over a continuous energy range using a time-of-flight (TOF) - scintillator - photoelectric multiplier tube (PMT) apparatus. A nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering energy partitioning process. The results show that, in a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) produced by H+, He+ and O3+ ions irradiation, respectively, have significantly different impacts on the response characteristics of these two benchmark scintillators. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of scintillators to irradiation.

Liu, Peng [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Zhang, Yanwen [ORNL] [ORNL; Xiao, Haiyan [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Xiang, Xia [University of Electronic Science and Technology of China (UESTC)] [University of Electronic Science and Technology of China (UESTC); Wang, Xuelin [Shandong University, Jinan, China] [Shandong University, Jinan, China; Weber, William J [ORNL] [ORNL

2014-01-01

10

Transformation of color centers during hologram recording in an additively colored CaF2 crystal  

NASA Astrophysics Data System (ADS)

When holograms are recorded on color centers in calcium fluoride crystals, these centers undergo spatial redistribution in the crystal bulk, which is accompanied by their transformation. The nature of this transformation has been investigated by optical spectroscopy and confocal scanning microscopy. It is shown that, under the recording conditions we used, the degree of center aggregation increases in both minima and maxima of the interference field in which the recording performed. The enhanced aggregation in field minima is caused by the increase in the concentration color centers, while the additional aggregation in maxima is determined by the specific conditions of hologram recording: the wavelength and power density of recording radiation and the crystal temperature.

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

2014-03-01

11

Analysis of single- and double-barrier tunneling diode structures using ultrathin CaF2/CdF2/Si multilayered heterostructures grown on Si  

NASA Astrophysics Data System (ADS)

The current–voltage (I–V) characteristics of single-barrier and double-barrier tunneling diode structures using CaF2/CdF2/Si ultrathin multilayered heterostructures grown on Si substrates have been theoretically analyzed and their material parameters, such as the conduction band discontinuity (?EC) at the heterointerface and effective mass (m*), have been evaluated by fitting simulation with the measured I–V characteristics. ?EC between the ultrathin (1–3 nm) CaF2 and Si layers and m* for CaF2 were found to be 1.5–2.3 eV and 0.3–1.0m0, respectively. A clear thickness dependence of these parameters was observed, and the deviations of m* and ?EC were approximately 30–50%, which probably originated from the thin layer thicknesses in atomic order. Using the estimated values derived from the single-barrier tunneling diodes, m* for CdF2 was also estimated to be 0.36m0 by fitting simulation of double-barrier diodes. These results will contribute to clarifying the design principle of tunneling devices with CaF2 and enhancing quantitative studies on electron transport in atomically thin multilayered heterostructures.

Suda, Keita; Kuwata, Yuya; Watanabe, Masahiro

2015-04-01

12

Ion beam induced damage in CaF2  

Microsoft Academic Search

The change in lattice parameter and the induced damage are studied in single crystal CaF2 bombarded by a 15 MeV Cl ion beam. The lattice parameter change (strain) and the damage for increasing ion beam dose (5 × 1012\\/cm2 to 7 × 1015\\/cm2) is observed via X-ray rocking curve analysis using a double-crystal diffractometer and X-ray reflection topography. The ion

C. R. Wie; T. Vreeland; T. A. Tombrello

1985-01-01

13

Leaky mode suppression in planar optical waveguides written in Er:TeO2-WO3 glass and CaF2 crystal via double energy implantation with MeV N+ ions  

NASA Astrophysics Data System (ADS)

Ion implantation proved to be an universal technique for producing waveguides in most optical materials. Tellurite glasses are good hosts of rare-earth elements for the development of fibre and integrated optical amplifiers and lasers covering all the main telecommunication bands. Er3+-doped tellurite glasses are good candidates for the fabrication of broadband amplifiers in wavelength division multiplexing around 1.55 ?m, as they exhibit large stimulated cross sections and broad emission bandwidth. Calcium fluoride is an excellent optical material, due to its perfect optical characteristics from UV wavelengths up to near IR. It has become a promising laser host material (doped with rare earth elements). Ion implantation was also applied to optical waveguide fabrication in CaF2 and other halide crystals. In the present work first single-energy implantations at 3.5 MeV at various fluences were applied. Waveguide operation up to 1.5 ?m was observed in Er:Te glass, and up to 980 nm in CaF2. Then double-energy implantations at a fixed upper energy of 3.5 MeV and lower energies between 2.5 and 3.2 MeV were performed to suppress leaky modes by increasing barrier width.

Bányász, I.; Zolnai, Z.; Fried, M.; Berneschi, S.; Pelli, S.; Nunzi-Conti, G.

2014-05-01

14

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

E-print Network

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

Boyer, Edmond

15

High-power tunable diode-pumped Yb3+:CaF2 laser  

Microsoft Academic Search

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+-doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as

A. Lucca; M. Jacquemet; F. Druon; F. Balembois; P. Georges; P. Camy; J. L. Doualan; R. Moncorgé

2004-01-01

16

High-power diode-pumped Yb3+:CaF2 femtosecond laser  

Microsoft Academic Search

We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at.% Yb3+-doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W

A. Lucca; G. Debourg; M. Jacquemet; F. Druon; F. Balembois; P. Georges; P. Camy; J. L. Doualan; R. Moncorgé

2004-01-01

17

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

18

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

PubMed

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

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

2014-06-01

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

21

Nanostructuring CaF2 surfaces with slow highly charged ions  

NASA Astrophysics Data System (ADS)

In recent years the potential of slow highly charged ions (HCI) as tools for nanostructuring purposes has received considerable attention and a wide range of material classes, from insulating ionic crystals, polymers and ultrathin films, to semiconducting and conducting substrates have been investigated regarding their response to individual HCI impact. For the majority of investigated materials, however, consistent theoretical modeling to supplement with experimental evidence and to satisfactorily explain the complete physical process from ion approach and impact to the formation of an individual nanostructure is still lacking. CaF2, from both an experimental and theoretical point of view, might be considered the most thoroughly investigated material. Combining results from numerous studies has allowed for the generation of a "phase diagram" for nanostructuring of CaF2 in dependence of ion beam parameters. This paves the way for a first unified picture, as implications from this phase diagram should be applicable to similar materials as well.

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Ritter, R.; Wachter, G.; Facsko, S.; Lemell, C.; Burgdörfer, J.; Aumayr, F.

2014-04-01

22

Single Crystal Membranes  

NASA Technical Reports Server (NTRS)

Single crystal a- and c-axis tubes and ribbons of sodium beta-alumina and sodium magnesium beta-alumina were grown from sodium oxide rich melts. Additional experiments grew ribbon crystals containing sodium magnesium beta, beta double prime, beta triple prime, and beta quadruple prime. A high pressure crystal growth chamber, sodium oxide rich melts, and iridium for all surfaces in contact with the melt were combined with the edge-defined, film-fed growth technique to grow the single crystal beta-alumina tubes and ribbons. The crystals were characterized using metallographic and X-ray diffraction techniques, and wet chemical analysis was used to determine the sodium, magnesium, and aluminum content of the grown crystals.

Stormont, R. W.; Morrison, A.

1974-01-01

23

Gyroid Single Crystal Diffraction  

NASA Astrophysics Data System (ADS)

A “single crystal” of a block copolymer / homopolymer blend with the Gyroid morphology was obtained by slow solvent casting. The block copolymer was an I2S2 star shaped block copolymer, which has two polystyrene arms and two polyisoprene arms connected at a single junction point. The homopolymer was low MW polyisoprene. The sample was studied by SAXS and TEM. SAXS of this sample produced single crystal diffraction patterns of several different zones with as many as 128 diffraction peaks in a single diffraction pattern, and 148 total unique diffraction peaks. Analysis of this data provides the most unambiguous proof to date of the Ia3d symmetry and Gyroid structure.

Yang, L.; Hong, S.; Gido, S. P.; Uhrig, D.; Mays, J. W.

2001-03-01

24

SINGLE CRYSTAL NEUTRON DIFFRACTION.  

SciTech Connect

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.

KOETZLE,T.F.

2001-03-13

25

Room temperature fabrication of dielectric Bragg reflectors composed of a CaF2/ZnS multilayered coating.  

PubMed

We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of ?c = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications. PMID:25510469

Muallem, Merav; Palatnik, Alex; Nessim, Gilbert D; Tischler, Yaakov R

2015-01-14

26

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

27

Dark matter search experiment with CaF2(Eu) scintillator at Kamioka Observatory  

E-print Network

We report recent results of a WIMP dark matter search experiment using 310g of CaF2(Eu) scintillator at Kamioka Observatory. We chose a highly radio-pure crystal, PMTs and radiation shields, so that the background rate decreased considerably. We derived limits on the spin dependent WIMP-proton and WIMP-neutron coupling coefficients, a_p and a_n. The limits excluded a part of the parameter space allowed by the annual modulation observation of the DAMA NaI experiment.

Y. Shimizu; M. Minowa; W. Suganuma; Y. Inoue

2005-10-13

28

A solvent extraction route for CaF2 hollow spheres.  

PubMed

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

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

2010-11-21

29

Elastic Constants of CaF2 at Different Temperature  

NASA Astrophysics Data System (ADS)

A simple and straightforward method for evaluating and predicting elastic constants as a function of temperature is presented on the basis of Murnaghan and Tallon models with first approximation. This theoretical method is used to predict successfully the values of elastic constants C11, C12 and C44 in GPa for CaF2 that are in reasonably good agreement with experimental data.

Sharma, Sheetal; Verma, Ajay Singh; Jindal, V. K.

2011-07-01

30

Temperature dependence of the elastic moduli and damping for polycrystalline LiF-22 pct CaF2 eutectic salt  

NASA Technical Reports Server (NTRS)

Young's and shear moduli and damping were measured for as-cast polycrystalline LiF-(22 mol pct)CaF2 eutectic specimens as a function of temperature using the piezoelectric ultrasonic composite oscillator technique. The shear modulus decreased with increasing temperature from about 40 GPa at 295 K to about 30 GPa at 1000 K, while the Young modulus decreased from about 115 GPa at 295 K to about 35 GPa at 900 K. These values are compared with those derived from the rule of mixtures using elastic moduli data for LiF and CaF2 single crystals. It is shown that, while the shear modulus data agree reasonably well with the predicted trend, there is a large discrepancy between the theoretical calculations and the Young modulus values, where this disagreement increases with increasing temperature.

Wolfenden, A.; Lastrapes, G.; Duggan, M. B.; Raj, S. V.

1991-01-01

31

Comparison of the pinning energy in Fe(Se1-xTex) compound between single crystals and thin films  

NASA Astrophysics Data System (ADS)

Among the families of iron-based superconductors, we investigate flux pinning mechanisms in the Fe(Se1-xTex) compound. We perform magneto-resistance and current-voltage measurements on single-crystals, as well as on several epitaxial thin films grown on different substrates (CaF2, LaAlO3). The activation energy is derived as a function of magnetic field, U(H). The influence of magnetic field orientation on the pinning energy activation mechanism is also studied, leading to the anisotropy analysis which reveals low anisotropy in thin films grown on CaF2 substrate with respect to single crystals and films grown on LaAlO3. Concerning the dominant pinning regime, the exponents of the power law dependence U0(H) ~ H-? have been evaluated, confirm that weak pinning is a general characteristic of this compound. The single exponent feature, generally noticed on thin films grown on SrTiO3 substrate and associated to a strong single vortex regime, has been observed in thin films grown on LaAlO3, only in the parallel configuration. At the end, this overall comparison can be useful to develop a technological material able to compete with high temperature superconductors.

Leo, A.; Guarino, A.; Grimaldi, G.; Nigro, A.; Pace, S.; Bellingeri, E.; Kawale, S.; Ferdeghini, C.; Giannini, E.

2014-05-01

32

Room temperature negative differential resistance of CdF2/CaF2 double-barrier resonant tunneling diode structures grown on Si(100) substrates  

NASA Astrophysics Data System (ADS)

The authors have demonstrated the crystal growth of CaF2/CdF2/CaF2 multilayered heterostructures on Si(100) substrates as double-barrier resonant tunneling diode structures by a low-temperature growth technique. Current-voltage characteristics were investigated and the authors observed negative differential resistance (NDR) characteristics at room temperature. The peak-to-valley current ratio was 2-8, and 13 at maximum, and peak current density was 80-90A /cm2. The quantum-well layer thickness dependence of NDR peak voltages is also discussed on the basis of qualitative analytical model using the Esaki-Tsu formula.

Kanazawa, Tohru; Fujii, Ryo; Wada, Takafumi; Suzuki, Yusuke; Watanabe, Masahiro; Asada, Masahiro

2007-02-01

33

Planar stress relaxation in solid phase epitaxial CaF2 films grown on (111)Si by in situ rapid isothermal processing  

NASA Astrophysics Data System (ADS)

Planar strain in CaF2 films on (111) Si substrate has been measured by an x-ray double-crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are almost free of tensile planar strain, and free from defects as observed by the transmission electron microscope diffraction pattern.

Singh, R.; Kumar, A.; Thakur, R. P. S.; Chou, P.; Chaudhuri, J.; Gondhalekar, V.; Narayan, J.

1990-04-01

34

Single Crystal Silicon Instrument Mirrors  

NASA Technical Reports Server (NTRS)

The goals for the fabrication of single crystal silicon instrument mirrors include the following: 1) Develop a process for fabricating lightweight mirrors from single crystal silicon (SCS); 2) Modest lightweighting: 3X to 4X less than equivalent solid mirror; 3) High surface quality, better than lambda/40 RMS @ 633nm; 4) Significantly less expensive than current technology; and 5) Negligible distortion when cooled to cryogenic temperatures.

Bly, Vince

2007-01-01

35

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

36

A multistep single-crystal-to-single-crystal bromodiacetylene dimerization.  

PubMed

Packing constraints and precise placement of functional groups are the reason that organic molecules in the crystalline state often display unusual physical or chemical properties not observed in solution. Here we report a single-crystal-to-single-crystal dimerization of a bromodiacetylene that involves unusually large atom displacements as well as the cleavage and formation of several bonds. Density functional theory computations support a mechanism in which the dimerization is initiated by a [2 + 1] photocycloaddition favoured by the nature of carbon-carbon short contacts in the crystal structure. The reaction proceeded up to the theoretical degree of conversion without loss of crystallinity, and it was also performed on a preparative scale with good yield. Moreover, it represents the first synthetic pathway to (E)-1,2-dibromo-1,2-diethynylethenes, which could serve as synthetic intermediates for the preparation of molecular carbon scaffolds. Our findings both extend the scope of single-crystal-to-single-crystal reactions and highlight their potential as a synthetic tool for complex transformations. PMID:23511422

Hoheisel, Tobias N; Schrettl, Stephen; Marty, Roman; Todorova, Tanya K; Corminboeuf, Clémence; Sienkiewicz, Andrzej; Scopelliti, Rosario; Schweizer, W Bernd; Frauenrath, Holger

2013-04-01

37

Numerical results on two-body and (two + three)-body lattice dynamics of CaF2, SrF2, and BaF2  

Microsoft Academic Search

Utilizing semiempirical two-body and (two + three)-body force fields, respectively, two distinct sets of shell-model calculations are reported on the crystal dynamics of CaF2, SrF2, and BaF2. The central force computations cover longwave properties, dispersion curves, specific heat, and thermal expansion. Also included are numerical results for mean square amplitudes as calculated conventionally and, in addition, by a new computational

1973-01-01

38

Crystal ball single event display  

SciTech Connect

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

Grosnick, D.; Gibson, A. [Valparaiso Univ., IN (United States). Dept. of Physics and Astronomy; Allgower, C. [Argonne National Lab., IL (United States). High Energy Physics Div.; Alyea, J. [Valparaiso Univ., IN (United States). Dept. of Physics and Astronomy]|[Argonne National Lab., IL (United States). High Energy Physics Div.

1997-10-15

39

Effects of CaF2 vis-a-vis TiO2 as nucleating agent in SiO2-Al2O3-CaO glass-ceramics  

NASA Astrophysics Data System (ADS)

The independent effects of CaF2 and TiO2 on the glass-ceramics based on SiO2-Al2O3-CaO system have been investigated. The crystallization behavior, microstructure, mechanical properties and chemical resistance of the glass-ceramics were studied by Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), FTIR, mechanical and chemical resistance measurements. The CaF2 containing glass ceramics are found to be much superior to that of TiO2 containing glass ceramics on the basis of sintering strength, mechanical and chemical properties.

Mukherjee, Debasis Pradip; Datta, Tanmoy; Das, Sudip Kumar

2013-06-01

40

Photon tunnelling microscopy of polyethylene single crystals  

E-print Network

Photon tunnelling microscopy of polyethylene single crystals Mohan Srinivasarao* and Richard S:photon tunnellingmicroscopy;single crystals; polyethylene) INTRODUCTION The study of morphology of polymers is an area

Srinivasarao, Mohan

41

Nanoscale Calorimetry of Isolated Polyethylene Single Crystals  

E-print Network

Nanoscale Calorimetry of Isolated Polyethylene Single Crystals A. T. KWAN, M. YU. EFREMOV, E. A-film differential scanning calorimetry to investigate the melt- ing of isolated polyethylene single crystals of lamellar single crystals of polyethylene (PE). We obtain thickness, diffraction, and calorimetry data

Allen, Leslie H.

42

Microwave-assisted solvothermal synthesis and upconversion luminescence of CaF2:Yb3+/Er3+ nanocrystals.  

PubMed

Water-dispersible CaF2 and Yb(3+)/Er(3+) codoped CaF2 (CaF2:Yb(3+)/Er(3+)) nanocrystals with different sizes and different Yb(3+) and Er(3+) dopant concentrations were synthesized using ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate as a fluorine source by the rapid microwave-assisted solvothermal method. It was found that the morphology, size and crystallinity of CaF2:Yb(3+)/Er(3+) nanocrystals could be adjusted by using adenosine 5'-triphosphate disodium salt (ATP). Yb(3+) and Er(3+) ions were doped into CaF2 nanocrystals to enable upconversion luminescence emission, and the as-prepared CaF2:Yb(3+)/Er(3+) samples exhibited upconversion luminescence upon excitation at 980 nm. Confocal laser scanning microscopy images showed that the CaF2:Yb(3+)/Er(3+) nanocrystals could be used for efficient labeling of human gastric carcinoma cells. Moreover, in vitro cytotoxicity experiments indicated that the as-prepared CaF2:Yb(3+)/Er(3+) nanocrystals had essentially little cytotoxicity. These results indicate that the as-prepared CaF2:Yb(3+)/Er(3+) nanocrystals are promising for the application as a luminescent label material in biological imaging. PMID:25460687

Zhao, Jing; Zhu, Ying-Jie; Wu, Jin; Chen, Feng

2015-02-15

43

Characterization of electron-beam induced damage structures in natural fluorite, CaF2, by analytical electron microscopy  

NASA Technical Reports Server (NTRS)

This paper describes the damage structure induced in natural CaF2 by the electron beam when using TEM. The observed 10-20 nm periodic features with coherent fringe patterns and the pronounced loss of fluorine found after the TEM exposure of 100-line-oriented and 111-oriented sections of CaF2 provides support for the mechanism of damage by decomposition of CaF2 into 2F and Ca, with the Ca precipitates maintaining a close topotaxial relationship with the parent CaF2.

Blake, D. F.; Freund, Friedemann; Allard, L. F.; Echer, C. J.

1988-01-01

44

Titania single crystals with a curved surface  

NASA Astrophysics Data System (ADS)

Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO2, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface.

Yang, Shuang; Yang, Bing Xing; Wu, Long; Li, Yu Hang; Liu, Porun; Zhao, Huijun; Yu, Yan Yan; Gong, Xue Qing; Yang, Hua Gui

2014-11-01

45

Protein single crystal growth under microgravity  

NASA Astrophysics Data System (ADS)

Crystal growth conditions for proteins under microgravity were investigated with two model compounds (?-galactosidase and lysozyme). The single crystals obtained have been found to be significantly larger than those prepared in the same environment on earth.

Littke, Walter; John, Christina

1986-08-01

46

Growth of high temperature superconducting single crystals  

Microsoft Academic Search

YBa2-xSrxCu3O7-y and YBa2Cu3O7 high-Tc superconducting single crystal up to 2.5×2×1 mm having orthorhombic lattices and transition temperatures of 84 and 94 K, respectively, have been grown. Conductivity anisotropy has been confirmed. The grown single crystals exhibit superconducting properties even without additional thermal treatment.

A. P. Voronov; V. M. Dmitriev; M. B. Kosmyna; S. F. Prokopovich; V. P. Seminozhenko

1988-01-01

47

Ames Lab 101: Single Crystal Growth  

SciTech Connect

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

Schlagel, Deborah

2013-09-27

48

Ultraprecision diamond turning of aluminium single crystals  

Microsoft Academic Search

Ultraprecision diamond turning is an important technology to generate a high surface finish in precision components and optics. In this paper, the diamond turning of aluminium single crystal rods with crystallographic axes normal to , and is analysed. The effect of the crystallographic anisotropy on the machining of these single crystals is investigated in the light of the mechanics of

S. To; W. B. Lee; C. Y. Chan

1997-01-01

49

Single crystal growth of actinide compounds  

Microsoft Academic Search

During recent years, the importance of solid state actinide research has been increasingly recognized. Further progress in actinide solid state physics depends on the availability of pure and perfect single crystals. Actinide compounds have large magnetic anisotropy with anisotropy fields of 8 × 107 A.m-1 or higher. Investigation of the mechanism responsible for such unique behaviour requires large single crystals

J. C. Spirlet; W. Müller; J. van Audenhove

1985-01-01

50

Ames Lab 101: Single Crystal Growth  

ScienceCinema

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

Schlagel, Deborah

2014-06-04

51

Protein Single Crystal Growth under Microgravity  

NASA Astrophysics Data System (ADS)

The preparation of suitably large protein single crystals is essentially the rate-determining step of protein x-ray structure determinations. Attempts to produce single crystals with two model compounds--? -galactosidase and lysozyme--under conditions of microgravity were successful. Crystals formed by salting out from solutions kept free of convection were 27 and 1000 times larger in volume, respectively, than those produced in the same apparatus but exposed to terrestrial gravitation.

Littke, Walter; John, Christina

1984-07-01

52

Defects in the reduced rutile single crystal  

NASA Astrophysics Data System (ADS)

In this paper, the UV-VIS optical absorption spectra of oxidized and reduced rutile single crystals are measured by means of spectrophotometer and two absorption peaks around 430 and 730 nm are found. These spectral data are analyzed by using the crystal field theory. Based on these studies, we suggest that the reduced crystal contain the defect center [Ti 3+-O v], with the oxygen vacancy (O v) on one of the nearest neighbor sites of the central Ti 3+ ion.

Lu, Tie-Cheng; Wu, Shao-Yi; Lin, Li-Bin; Zheng, Wen-Chen

2001-09-01

53

Ultralow-threshold Raman lasing with CaF2 resonators.  

PubMed

We demonstrate efficient Raman lasing with CaF2 whispering-gallery-mode resonators. Continuous-wave emission threshold is shown to be possible below 1 microW with a 5mm cavity, which is to our knowledge orders of magnitude lower than in any other Raman source. Low-threshold lasing is made possible by the ultrahigh optical quality factor of the cavity, of the order of Q=5x10(10). Stokes components of up to the fifth order were observed at a pump power of 160 microW, and up to the eighth order at 1 mW. A lasing threshold of 15 microW was also observed in a 100 microm CaF2 microcavity. Potential applications are discussed. PMID:17186052

Grudinin, Ivan S; Maleki, Lute

2007-01-15

54

Metal( CoSi2)/Insulator( CaF2) Resonant Tunneling Diode  

NASA Astrophysics Data System (ADS)

Negative differential resistance (NDR) of nanometer-thick triple-barrier metal( CoSi2)/insulator( CaF2) resonant tunneling diode (RTD) and the structure dependence of its characteristics are demonstrated. The device consists of metal-insulator (M-I) heterostructures with two metallic ( CoSi2) quantum wells and three insulator ( CaF2) barriers grown on an n-Si(111) substrate. A typical peak-to-valley current ratio (P/V ratio) obtained at 77 K was 2 3 and the largest P/V ratio was 25. A P/V ratio as high as 2 was obtained at 300 K. M-I RTDs with two quantum wells of various thicknesses were fabricated in order to investigate the dependence of resonance voltage on the thickness of the two quantum wells. Reasonable agreement was obtained between theory and experiment for this dependence.

Suemasu, Takashi; Watanabe, Masahiro; Suzuki, Jun; Kohno, Yoshifumi; Asada, Masahiro; Suzuki, Nobuhiro

1994-01-01

55

Magnetic manifestations of thermoluminescence excitation in CaF 2 :Mn (TLD400)  

Microsoft Academic Search

Magnetic susceptibility as a function of temperature (4–250K) and EPR spectra at room temperature were studied for thermoluminescence detectors (TLD) CaF2:Mn with either stored dose information or cleaned dose by annealing. No essential variations of Mn2+ number in detectors were found due to dose storage; however, the exchange interactions between manganese ions are observed as deviations from Curie–Weiss law. These

Mikhail Danilkin; Aleksei Kirillov; Sergei Klimonsky; Vyacheslav Kuznetsov; Aime Lust; Hugo Mändar; Vladimir Nikiforov; Arno Ratas; Aleksandr Ruchkin; Viktor Seeman

2007-01-01

56

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

E-print Network

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

Krems, Roman

57

Cryogenic Temperature-Dependent Refractive Index Measurements of CaF2 and Infrasil 301  

NASA Technical Reports Server (NTRS)

In order to enable high quality lens design using calcium fluoride (CaF2) and Heraeus Infrasil 30 (Infrasil) at cryogenic temperatures, we have measured the absolute refractive index of prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For CaF2, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 25 to 300 K at wavelengths from 0.4 to 5.6 micrometers; for Infrasil we cover temperatures ranging from 35 to 300K and wavelengths from 0.4 to 3.6 micrometers. We investigate the interspecimen variability between measurements of two unrelated samples of CaF2, and we also compare our results for Infrasil to previous measurements fo Corning 7980 fused silica. Finally, we provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures and compare those results to other data found in the literature.

Frey, Bradley J.; Leviton, Douglas B.; Madison, TImothy J.

2007-01-01

58

Intense photoluminescence at 2.7 ?m in transparent Er 3+:CaF2-fluorophosphate glass microcomposite.  

PubMed

Er3+ doped CaF2-fluorophosphate (FP) glass microcomposites were produced by heat-treating the mixture of Er3+:CaF2 precipitate and FP glass powder above the melting temperature of the FP glass. The appearance of CaF2 crystallites in the resulting composites was confirmed by x ray diffraction. Despite the fact that the average diameter of the crystallites was around 10 ?m as revealed by the micromorphology study, a transparent composite was obtained by matching the refractive index of FP glass to that of CaF2. Intense IR fluorescence at around 2.7 ?m was observed in the composite, implying the composite would be a promising candidate for IR lasers and amplifiers. PMID:22089559

Fan, Jintai; Yuan, Xinqiang; Li, Rihong; Dong, Hongxing; Wang, Jun; Zhang, Long

2011-11-15

59

Effect of CaF 2 on densification and properties of hydroxyapatite–zirconia composites for biomedical applications  

Microsoft Academic Search

Hydroxyapatite (HA) composites with zirconia (ZrO2) up to 40vol% were fabricated with the addition of CaF2. The sinterability of the composites was found to be enhanced markedly by the addition of small amounts of CaF2 (<5vol%). Decomposition of HA to ?-TCP was suppressed due to the substitution of F? for OH?, consequently forming fluor-hydroxyapatite (FHA) solid solution. This suppression of

Hae-Won Kim; Yoon-Jung Noha; Young-Hag Koh; Hyoun-Ee Kim; Hyun-Man Kim

2002-01-01

60

Fatigue hardening in niobium single crystals.  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

61

Anisotropic Shock Propagation in Single Crystals  

SciTech Connect

Most single-crystal shock experiments have been performed in high-symmetry directions while the nature of shock propagation in low-symmetry directions remains relatively unstudied. It is well known that small-amplitude, linear acoustic waves propagating in low-symmetry directions can focus and/or form caustics (Wolfe, 1995). In this report we provide evidence for similar focusing behavior in nonlinear (shock) waves propagating in single crystals of silicon and diamond. Using intense lasers, we have driven non-planar (divergent geometry) shock waves through single-crystals of silicon or diamond and into an isotropic backing plate. On recovery of the backing plates we observe a depression showing evidence of anisotropic plastic strain with well-defined crystallographic registration. We observe 4-, 2-, and 3-fold symmetric impressions for [100], [110], and [111] oriented crystals respectively.

Eggert, J; Hicks, D; Celliers, P; Bradley, D; Cox, J; Unites, W; Collins, G; McWilliams, R; Jeanloz, R; Bruygoo, S; Loubeyre, P

2005-05-26

62

2-D electron spin transient nutation spectroscopy of Lanthanoid ion Eu 2+ ( 8 S 7\\/2 ) in a CaF 2 single crystal on the basis of FT-pulsed electron spin resonance spectroscopy: Transition moment spectroscopy  

Microsoft Academic Search

This work demonstrates the usefulness of pulsed electron spin resonance (ESR)-based two-dimensional electron spin transient\\u000a nutation (2-D ESN) spectroscopy for complete assignments of complicated fine-structure hyperfine ESR spectra including hyperfine\\u000a forbidden transitions from electronic and nuclear high-spin systems. The 2-D ESN spectroscopy is termed transition moment\\u000a spectroscopy as spectra are acquired as a function of transition moment instead of transition

H. Matsuoka; K. Sato; D. Shiomi; T. Takui

2003-01-01

63

Performance of Single Crystal Niobium Cavities  

SciTech Connect

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

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

2008-07-01

64

Characterization of zinc selenide single crystals  

NASA Technical Reports Server (NTRS)

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.

Gerhardt, Rosario A.

1996-01-01

65

Development of single crystal filaments. Final report  

SciTech Connect

The program just completed addresses a route to a more efficient longer-lasting electric light bulb filament. All current filaments for light bulbs are metallic in nature. They are subject to embrittlement with age (large grain growth) and relatively high vapor pressures which limits their operating temperature. There is evidence which suggests advantages to using high temperature refractory single crystal fibers as a filament for a light bulb. These refractory materials may include materials such as hafnium or tantalum carbide which have melting points about 500{degrees}C higher than tungsten. Another advantage is that single crystal fibers have a very high degree of crystalline perfection with very few voids and dislocations. Without these imperfections, the atomic mobility at high temperatures is highly restricted. Thus single crystal fibers are very stable at high temperature and will last longer. The efficiencies result from running these single crystal ceramic fiber filaments at higher temperatures and the higher emissivity of the carbide filaments compared to tungsten. The amount of visible light is proportional to the 4the power of the temperature thus a 500{degrees}C higher operating give about a 3-fold increase in radiation in the visible range. The program accomplishments can be summarized as follows: (1) Single crystal fibers of JfC sufficient crystal quality for light bulb filament applications were made. (2) The HfC fiber furnace growth chamber, power control and data collection system was developed for the laboratory scale plant. (3) method for mounting and apparatuses for testing the single crystal fiber filaments were developed and built.

Milewski, J.V.; Shoultz, R.A.; Bourque-McConnell, M.M.

1995-04-01

66

Czochralski single crystal growth, modeling, and characterization of ilmenite  

Microsoft Academic Search

Ilmenite is a wide band gap material, and could be used for electronic applications. Since ilmenite is stoichiometric at its melting point, the single crystals are grown using Czochralski crystal growth method. Earlier research in ilmenite uses ceramic material, and smaller size single crystals. In this research large size single crystals of ilmenite are grown. To grow large size single

Jayakumar Muthusami

1998-01-01

67

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

PubMed Central

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5?MeV) highly charged ions (Xe22+ to Xe30+) as well as swift (kinetic energies between 12 and 58?MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. PMID:25034006

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

2014-01-01

68

Neutron detection with single crystal organic scintillators  

SciTech Connect

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

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

2009-07-15

69

Single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

70

An ultrahigh vacuum single crystal adsorption microcalorimeter  

NASA Astrophysics Data System (ADS)

The design of an ultrahigh vacuum microcalorimeter enabling calorimetric heats of adsorption to be obtained on single crystal surfaces as a detailed function of coverage is discussed. The system comprises a pulsed supersonic molecular beam source, an ultrathin metal single crystal, and remote infrared temperature sensing. Sticking probabilities and coverages are determined pulsewise by the King and Wells method, and heat capacity calibrations are conducted in situ by laser beam pulsing. Results for CO and O2 on Ni{110} demonstrate excellent sensitivity to adsorption of ˜10-13 moles of gas (˜0.01 monolayer). The heat capacity of the calorimeter is 4.2 ?J K-1.

Borroni-Bird, C. E.; King, D. A.

1991-09-01

71

Charge transport in single crystal organic semiconductors  

NASA Astrophysics Data System (ADS)

Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form high-quality single crystals and exhibit large ambipolar mobilities. Nevertheless, a gap remains between the theory-predicted properties and this preliminary result, which itself is another fundamental challenge. This is further addressed by appropriate device optimization, and in particular, contact engineering approach to improve the charge injection efficiencies. The outcome is not only the achievement of new record ambipolar mobilities in one of the derivatives, namely, 4.8 cm2V-1s-1 for holes and 4.2 cm2V-1s-1 for electrons, but also provides a comprehensive and rational pathway towards the realization of high-performance organic semiconductors. Efforts to achieve high mobility in other organic single crystals are also presented. The second challenge is tuning the transition of electronic ground states, i.e., semiconducting, metallic and superconducting, in organic single crystals. Despite an active research area since four decades ago, we aim to employ the electrostatic approach instead of chemical doping for reversible and systematic control of charge densities within the same crystal. The key material in this study is the high-capacitance electrolyte, such as ionic liquids (ILs), whose specific capacitance reaches ~ ?F/cm2, thus allowing accumulation of charge carrier above 1013 cm-2 when novel transport phenomena, such as insulator-metal transition and superconductivity, are likely to occur. This thesis addresses the electrical characterization, device physics and transport physics in electrolyte-gated single crystals, in the device architecture known as the electrical double layer transistor (EDLT). A detailed characterization scheme is first demonstrated for accurate determination of several key parameters, e.g., carrier mobility and charge density, in organic EDLTs. Further studies, combining both experiments and theories, are devoted to understanding the unusual charge density dependent channel conductivity and gate-to-channel capacitance behaviors. In addition, Hall effect and temperature-dependent measurements are employed for more in-depth unders

Xie, Wei

72

Microhardness studies of sulfamic acid single crystal  

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

73

Single crystal articles having reduced anisotropy  

SciTech Connect

This paper describes a method of modifying the nickel base superalloy composition Ni-5Co-10Cr-4W-5Al-1.5Ti-12Ta such that single crystal castings made therefrom have reduced anisotropy. It comprises: adding an effective amount of hafnium to the alloy composition.

Shah, D.M.; Duhl, D.N.

1990-04-10

74

Microstructure and tribological properties of laser clad CaF 2\\/Al 2O 3 self-lubrication wear-resistant ceramic matrix composite coatings  

Microsoft Academic Search

Self-lubrication wear-resistant CaF2\\/Al2O3 ceramic matrix composite coatings were fabricated on substrates of Al2O3 by laser cladding CaF2–Al2O3 mixed powder blends. Compared with laser clad monolithic Al2O3 coatings, the CaF2\\/Al2O3 coating has much superior wear resistance and noticeably lower friction coefficient under dry sliding wear test conditions.

H. M. Wang; Y. L. Yu; S. Q. Li

2002-01-01

75

Facile and controllable synthesis of monodisperse CaF2 and CaF2:Ce3+/Tb3+ hollow spheres as efficient luminescent materials and smart drug carriers.  

PubMed

Highly uniform and well-dispersed CaF(2) hollow spheres with tunable particle size (300-930 nm) have been synthesized by a facile hydrothermal process. Their shells are composed of numerous nanocrystals (about 40 nm in diameter). The morphology and size of the CaF(2) products are strongly dependent on experimental parameters such as reaction time, pH value, and organic additives. The size of the CaF(2) hollow spheres can be controlled from 300 to 930 nm by adjusting the pH value. Nitrogen adsorption-desorption measurements suggest that mesopores (av 24.6 nm) exist in these hollow spheres. In addition, Ce(3+)/Tb(3+)-codoped CaF(2) hollow spheres can be prepared similarly, and show efficient energy transfer from Ce(3+) to Tb(3+) and strong green photoluminescence of Tb(3+) (541 nm, (5)D(4)-->(7)F(5) transition of Tb(3+), the highest quantum efficiency reaches 77%). The monodisperse CaF(2):Ce(3+)/Tb(3+) hollow spheres also have desirable properties as drug carriers. Ibuprofen-loaded CaF(2):Ce(3+)/Tb(3+) samples still show green luminescence of Tb(3+) under UV irradiation, and the emission intensity of Tb(3+) in the drug-carrier system varies with the released amount of ibuprofen, so that drug release can be easily tracked and monitored by means of the change in luminescence intensity. The formation mechanism and luminescent and drug-release properties were studied in detail. PMID:20391571

Zhang, Cuimiao; Li, Chunxia; Peng, Chong; Chai, Ruitao; Huang, Shanshan; Yang, Dongmei; Cheng, Ziyong; Lin, Jun

2010-05-17

76

Transverse acoustic actuation of Ni-Mn-Ga single crystals  

E-print Network

Two methods for the transverse acoustic actuation of {110}-cut Ni-Mn-Ga single crystals are discussed. In this actuation mode, crystals are used that have the {110}- type twinning planes parallel to the base of the crystal. ...

Simon, Jesse Matthew

2007-01-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

78

SSME single-crystal turbine blade dynamics  

NASA Technical Reports Server (NTRS)

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.

Moss, Larry A.

1988-01-01

79

Shock Hugoniot of Single Crystal Copper  

SciTech Connect

The shock Hugoniot of single crystal copper is reported for stresses below 66 GPa. Symmetric impact experiments were used to measure the Hugoniots of three different crystal orientations of copper, [100], [110], [111]. The photonic doppler velocimetry (PDV) diagnostic was adapted into a very high precision time of arrival detector for these experiments. The measured Hugoniots along all three crystal directions were nearly identical to the experimental Hugoniot for polycrystalline Cu. The predicted orientation dependence of the Hugoniot from MD calculations was not observed. At the lowest stresses, the sound speed in Cu was extracted from the PDV data. The measured sound speeds are in agreement with values calculated from the elastic constants for Cu.

Chau, R; Stolken, J; Asoka-Kumar, P; Kumar, M; Holmes, N C

2009-08-28

80

Single crystal growth of SiC and electronic devices  

Microsoft Academic Search

Single crystal growth of silicon carbide (Sic) and application to electronic devices are reviewed. In the crystal growth, bulk and homoepitaxial growth are picked up, and crystal quality and electrical properties are described. For electronic devices, various device processes are argued. Power devices based on Sic are stressed in this review.Bulk single crystals of SiC can be grown by a

Akira Itoh; Hiroyuki Matsunami

1997-01-01

81

Optimizing Scale Adhesion on Single Crystal Superalloys  

NASA Technical Reports Server (NTRS)

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

Smialek, James L.; Pint, Bruce A.

2000-01-01

82

Unidirectional seeded single crystal growth from solution of benzophenone  

Microsoft Academic Search

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means

K. Sankaranarayanan; P. Ramasamy

2005-01-01

83

Single crystal growth of organic photoconductors: phthalocyanine  

Microsoft Academic Search

An effective method of growing single crystals of organic photoconductors such as phthalocyanine in the presence of doping\\u000a impurity such as iodine by vacuum sublimation is discussed in this paper. This method is very useful especially when an organic\\u000a material does not have a melting point but decomposes above a particular temperature. So far, doping has been done by exposing

Francis P Xavier; George J Goldsmith

1996-01-01

84

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

NASA Astrophysics Data System (ADS)

In contrast to the wide number and variety of available synthetic routes to conventional linear polymers, the synthesis of two-dimensional polymers and unambiguous proof of their structure remains a challenge. Two-dimensional polymers—single-layered polymers that form a tiling network in exactly two dimensions—have potential for use in nanoporous membranes and other applications. Here, we report the preparation of a fluorinated hydrocarbon two-dimensional polymer that can be exfoliated into single sheets, and its characterization by high-resolution single-crystal X-ray diffraction analysis. The procedure involves three steps: preorganization in a lamellar crystal of a rigid monomer bearing three photoreactive arms, photopolymerization of the crystalline monomers by [4?+?4] cycloaddition, and isolation of individual two-dimensional polymer sheets. This polymer is a molecularly thin (~1?nm) material that combines precisely defined monodisperse pores of ~9?Å with a high pore density of 3.3?×?1013 pores?cm-2. Atomic-resolution single-crystal X-ray structures of the monomer, an intermediate dimer and the final crystalline two-dimensional polymer were obtained and prove the single-crystal-to-single-crystal nature and molecular precision of the two-dimensional photopolymerization.

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

2014-09-01

85

Formation of the CRS2-CAF2 group II intron splicing complex is mediated by a 22-amino acid motif in the COOH-terminal region of CAF2.  

PubMed

CRS2-associated factors 1 and 2 (CAF1 and CAF2) are closely related proteins that function in concert with chloroplast RNA splicing 2 (CRS2) to promote the splicing of specific sets of group II introns in maize chloroplasts. The CRS2-CAF complexes bind tightly to their cognate group II introns in vivo, with the CAF subunit determining the intron specificity of the complex. In this work we show that the CRS2-CAF complexes are stable in the absence of their intron targets and that CRS2 binds a 22 amino acid motif in the COOH-terminal region of CAF2 that is conserved in CAF1. Yeast two-hybrid assays and co-fractionation studies using recombinant proteins show that this motif is both necessary and sufficient to bind CRS2. The 22-amino acid motif is predicted to form an amphipathic helix whose hydrophobic surface is conserved between CAF1 and CAF2. We propose that this surface binds the hydrophobic patch on the surface of CRS2 previously shown to be necessary for the interaction between CRS2 and CAF2. PMID:16379013

Ostheimer, Gerard J; Rojas, Margarita; Hadjivassiliou, Haralambos; Barkan, Alice

2006-02-24

86

On the thermoluminescence emission spectra of CaF 2: Tm  

NASA Astrophysics Data System (ADS)

Thermoluminescence (TL) emission spectra in the visible and near infrared region of TLD-300 (CaF 2: Tm) commonly used for TL dosimetry were studied at exposures 286 and 7300 R. The TL emission spectra from 300 to 900 nm are observed every 2°C from 50°C to 320°C. Glow peaks appear at 110°C, 145°C, 235°C and 265°C. Emission bands in the spectra were measured at 357, 460, 655 and 805 nm. Discussion is given about a possibility of using the infrared emission band 805 nm as well as the visible emission bands in the routine work of radiation detector dosimetry at a temperature of around 145°C. Further we discuss the change of the integral glow curve for each of these emission bands for the exposure radiation at 286 and 7300 R.

Rasheedy, Mahmoud Said; Nishimura, Fumio; Ichimori, Toshihiro

1991-07-01

87

High-gain amplification in Yb:CaF2 crystals pumped by a high-brightness Yb-doped 976 nm fiber laser  

NASA Astrophysics Data System (ADS)

We report on high single-pass gain in Yb:CaF2 crystal longitudinally pumped with a 40 W high-brightness fiber laser source based on an ytterbium-doped ultra-large core photonic crystal rod-type fiber operating at 976 nm. A single-pass small-signal gain of 3.2 has been achieved in a 6 % Yb-doped 10-mm-long CaF2 crystal at room temperature, outperforming any CW-diode-pumped scheme and paving the way towards very promising innovative lasers and amplifiers schemes merging the Yb-doped solid-state and fiber technologies.

Machinet, G.; Andriukaitis, G.; Sévillano, P.; Lhermite, J.; Descamps, D.; Pugžlys, A.; Baltuška, A.; Cormier, E.

2013-05-01

88

A spontaneous single-crystal-to-single-crystal polymorphic transition involving major packing changes.  

PubMed

4,6-O-Benzylidene-?-d-galactosyl azide crystallizes into two morphologically distinct polymorphs depending on the solvent. While the ? form appeared as thick rods and crystallized in P21 space group (monoclinic) with a single molecule in the asymmetric unit, the ? form appeared as thin fibers and crystallized in P1 space group (triclinic) with six molecules in the asymmetric unit. Both the polymorphs appeared to melt at the same temperature. Differential scanning calorimetry analysis revealed that polymorph ? irreversibly undergoes endothermic transition to polymorph ? much before its melting point, which accounts for their apparently same melting points. Variable temperature powder X-ray diffraction (PXRD) experiments provided additional proof for the polymorphic transition. Single-crystal XRD analyses revealed that ? to ? transition occurs in a single-crystal-to-single-crystal (SCSC) fashion not only under thermal activation but also spontaneously at room temperature. The SCSC nature of this transition is surprising in light of the large structural differences between these polymorphs. Polarized light microscopy experiments not only proved the SCSC nature of the transition but also suggested nucleation and growth mechanism for the transition. PMID:25585170

Krishnan, Baiju P; Sureshan, Kana M

2015-02-01

89

Magnetic circular dichroism of colour centres in CaF2 : Na J. L. Doualan, J. Margerie, F. Martin-Brunetire,  

E-print Network

L-375 Magnetic circular dichroism of colour centres in CaF2 : Na J. L. Doualan, J. Margerie, F. Abstract. - The magnetic circular dichroism (M.C.D.) of several centres in additively coloured CaF2 : Na understood : several centres have been reliably identified by their absorption and fluorescence bands

Boyer, Edmond

90

Growth and characterization of single crystal insulators on silicon  

NASA Technical Reports Server (NTRS)

An overview of the growth and characterization of epitaxial insulators on semiconductors is presented. The potential applications include semiconductor-on-insulator structures, three-dimensional and/or high-density integrated circuits, optoelectronic applications such as integrated waveguides and improved gate insulators. The growth and physical characterization of epitaxial fluorides on semiconductors are discussed. Consideration is also given to the epitaxial overgrowth of epitaxial metal layers with CaF2 as well as to the formation of a novel superlattice of Ca particles in epitaxial CaF2.

Schowalter, Leo J.; Fathauer, Robert W.

1989-01-01

91

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

E-print Network

of this deposition procedure have been described elsewhere [5]. Germanium films were simultaneously deposited by thermal evaporation on unbuffered (bare glass) and CaF2 buffered glass substrates with substrate carried out in a high vacuum chamber with a base pressure of 5 Ã? 10Ã?8 Torr. The substrate to source

Wang, Gwo-Ching

92

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

E-print Network

incidence. The details of this deposition procedure have been described elsewhere [5]. Germanium films were simultaneously deposited by thermal evaporation on unbuffered (bare glass) and CaF2 buffered glass substrates carried out in a high vacuum chamber with a base pressure of 5 Ã? 10Ã?8 Torr. The substrate to source

Wang, Gwo-Ching

93

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

EPA Science Inventory

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

94

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

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

95

Electrochemical Sc 2O 3 single crystal growth  

Microsoft Academic Search

Scandium oxide single crystals were successfully grown electrochemically by applying the Sc3+ ion-conducting Sc2(MoO4)3 solid electrolyte at 1223K. The single crystal growth can be regulated by the electrolysis condition, and the crystal size can be intentionally controlled by adjusting the electrolysis period. Although the single crystal growth of such refractory oxides as Sc2O3 is considerably difficult by the conventional thermal

Toshiyuki Masui; Young Woon Kim; Nobuhito Imanaka; Gin-ya Adachi

2004-01-01

96

Chemical vapor deposition of graphene single crystals.  

PubMed

As a two-dimensional (2D) sp(2)-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and low yields. Recently developed chemical vapor deposition (CVD) techniques have emerged as an important method for the scalable production of large-size and high-quality graphene for various applications. However, CVD-derived graphene is polycrystalline and demonstrates degraded properties induced by grain boundaries. Thus, the next critical step of graphene growth relies on the synthesis of large graphene single crystals. In this Account, we first discuss graphene grain boundaries and their influence on graphene's properties. Mechanical and electrical behaviors of CVD-derived polycrystalline graphene are greatly reduced when compared to that of exfoliated graphene. We then review four representative pathways of pretreating Cu substrates to make millimeter-sized monolayer graphene grains: electrochemical polishing and high-pressure annealing of Cu substrate, adding of additional Cu enclosures, melting and resolidfying Cu substrates, and oxygen-rich Cu substrates. Due to these pretreatments, the nucleation site density on Cu substrates is greatly reduced, resulting in hexagonal-shaped graphene grains that show increased grain domain size and comparable electrical properties as to exfoliated graphene. Also, the properties of graphene can be engineered by its shape, thickness and spatial structure. Thus, we further discuss recently developed methods of making graphene grains with special spatial structures, including snowflakes, six-lobed flowers, pyramids and hexagonal graphene onion rings. The fundamental growth mechanism and practical applications of these well-shaped graphene structures should be interesting topics and deserves more attention in the near future. Following that, recent efforts in fabricating large single-crystal monolayer graphene on other metal substrates, including Ni, Pt, and Ru, are also described. The differences in growth conditions reveal different growth mechanisms on these metals. Another key challenge for graphene growth is to make graphene single crystals on insulating substrates, such as h-BN, SiO2, and ceramic. The recently developed plasma-enhanced CVD method can be used to directly synthesize graphene single crystals on h-BN substrates and is described in this Account as well. To summarize, recent research in synthesizing millimeter-sized monolayer graphene grains with different pretreatments, graphene grain shapes, metal catalysts, and substrates is reviewed. Although great advancements have been achieved in CVD synthesis of graphene single crystals, potential challenges still exist, such as the growth of wafer-sized graphene single crystals to further facilitate the fabrication of graphene-based devices, as well as a deeper understanding of graphene growth mechanisms and growth dynamics in order to make graphene grains with precisely controlled thicknesses and spatial structures. PMID:24527957

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

2014-04-15

97

Growth rate study of canavalin single crystals  

NASA Technical Reports Server (NTRS)

The dependence on supersaturation of the growth rate of single crystals of the protein canavalin is studied. In the supersaturation ranges studied, the rate-limiting step for growth is best described by a screw dislocation mechanism associated with interface attachment kinetics. Using a ln-ln plot, the growth-rate data is found to fit a predictive relationship of the form G = 0.012 x the supersaturation to the 6.66, which, together with the solubility curves, allows the growth rate to be estimated under a variety of conditions.

Demattei, R. C.; Feigelson, R. S.

1989-01-01

98

Triplet exciton dynamics in rubrene single crystals  

NASA Astrophysics Data System (ADS)

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.

Ryasnyanskiy, Aleksandr; Biaggio, Ivan

2011-11-01

99

Metallisation of single crystal diamond radiation detectors  

NASA Astrophysics Data System (ADS)

Properties such as a large band gap, high thermal conductivity and resistance to radiation damage make diamond an extremely attractive candidate for detectors in next generation particle physics experiments. This paper presents our technique for metallisation of a single crystal diamond grown by chemical vapour deposition (CVD) for use as a radiation detector, suitable for operation in places such as the Large Hadron Collider. The front and back side of the diamond are metalised with aluminium and gold on top of titanium respectively, after which the diamond is mounted and read out via a charge sensitive preamplifier. The device is found to collect charge at an efficiency of 97%.

Ong, Lucas; Ganesan, Kumaravelu; Alves, Andrew; Barberio, Elisabetta

2012-10-01

100

Growth of strontium tartrate tetrahydrate single crystals in silica gels  

Microsoft Academic Search

Growth of single crystals of strontium tartrate tetrahydrate by controlled diffusion in silica gels has been narrated. In the field of material science, there is always a keen and competitive race to grow perfect single crystals with sufficient purity and perfection. Successful attempts to larger as well as more perfect crystals of SrTr are described in this paper and thus

A. R. Patel; S. K. Arora

1976-01-01

101

Electron Optical Studies of Barium Titanate Single Crystal Films  

Microsoft Academic Search

Thin single crystal films of barium titanate prepared by chemical thinning of single crystal plates are studied by transmission electron microscopy and electron diffraction. The films as thin as 1000 Å are found to have the same lattice parameters as the bulk crystals, giving no evidence for the existence of the anomalous surface layer proposed by Känzig et al. The

Michiyoshi Tanaka; Goro Honjo

1964-01-01

102

Cutting fluid study for single crystal silicon  

SciTech Connect

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.

Chargin, D.

1998-05-05

103

Fabrication of crystals from single metal atoms  

NASA Astrophysics Data System (ADS)

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15?Å in diameter, within 1?h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium-osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms.

Barry, Nicolas P. E.; Pitto-Barry, Anaïs; Sanchez, Ana M.; Dove, Andrew P.; Procter, Richard J.; Soldevila-Barreda, Joan J.; Kirby, Nigel; Hands-Portman, Ian; Smith, Corinne J.; O'Reilly, Rachel K.; Beanland, Richard; Sadler, Peter J.

2014-05-01

104

Fabrication of crystals from single metal atoms  

PubMed Central

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15?Å in diameter, within 1?h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium–osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms. PMID:24861089

Barry, Nicolas P. E.; Pitto-Barry, Anaïs; Sanchez, Ana M.; Dove, Andrew P.; Procter, Richard J.; Soldevila-Barreda, Joan J.; Kirby, Nigel; Hands-Portman, Ian; Smith, Corinne J.; O’Reilly, Rachel K.; Beanland, Richard; Sadler, Peter J.

2014-01-01

105

Thermodynamic forces in single crystals with dislocations  

NASA Astrophysics Data System (ADS)

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

Van Goethem, Nicolas

2014-06-01

106

Irradiation growth of zirconium single crystals  

NASA Astrophysics Data System (ADS)

Irradiation growth of zirconium single crystals has been studied during neutron irradiation at 353 K and 553 K at fluences up to 2× 10 25 n/m 2. The results may be summarized as follows: (a) there was an expansion parallel to the a-axis and a c-axis contraction; (b) the growth strains were small (~10 -4), (c) growth saturated at fluences less than ~5× 10 24 n/m 2, (d) the growth behaviour was only weakly dependent on temperature for the range studied, (e) there was a calculated volume increase of the same order as the growth strain, and (f) single crystals prepared from stock of iodide and zone-refined purity showed similar growth behaviour at 553 K. The a-axis expansion is attributed to the annihilation of an excess of interstitials at < a>-type dislocations and interstitial loops. The c-axis contraction may be caused by: (1) elastic relaxation around vacancies or small vacancy clusters, (2) non-linear elastic effects at the dislocation cores of small < a>-type loops, or (3) sub-microscopic vacancy loops with < c>-component Burgers vectors. Comparison with data from polycrystalline zirconium confirms that grain boundaries can play an important role in the irradiation growth of zirconium.

Carpenter, G. J. C.; Murgatroyd, R. A.; Rogerson, A.; Watters, J. F.

1981-10-01

107

Solar cell structure incorporating a novel single crystal silicon material  

DOEpatents

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

Pankove, Jacques I. (Princeton, NJ); Wu, Chung P. (Trenton, NJ)

1983-01-01

108

Growing single crystals in silica gel  

NASA Technical Reports Server (NTRS)

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.

Rubin, B.

1970-01-01

109

Experimental dynamic metamorphism of mineral single crystals  

USGS Publications Warehouse

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.

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

1993-01-01

110

Experimental dynamic metamorphism of mineral single crystals  

NASA Astrophysics Data System (ADS)

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 ürtzite ? 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 · nAl 2O 3 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.

Kirby, Stephen H.; Stern, Laura A.

1993-09-01

111

Mechanical properties of single crystal YAg  

SciTech Connect

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

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

2004-08-02

112

Dynamic characteristics of single crystal SSME blades  

NASA Technical Reports Server (NTRS)

The Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) blades are currently manufactured using a directionally solidified (DS) material, MAR-M-246+Hf. However, a necessity to reduce the occurrence of fatigue cracking within the DS blades has lead to an interest in the use of a single crystal (SC) material, PWA-1480. A study was initiated to determine the dynamic characteristics of the HPFTP blades made of SC material and find possible critical engine order excitations. This study examined both the first and second stage drive turbine blades of the HPFTP. The dynamic characterization was done analytically as well as experimentally. The analytical study examined the SC first stage HPFTP blade dynamic characteristics under typical operating conditions. The blades were analyzed using MSC/NASTRAN and a finite element model. Two operating conditions, 27500 RPM and 35000 RPM, were investigated.

Moss, L. A.; Smith, T. E.

1987-01-01

113

Hydrogen Annealing Of Single-Crystal Superalloys  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

114

Thermal debracketing of single crystal sapphire brackets.  

PubMed

Because of their optical clarity, single crystal sapphire brackets provide an esthetic advantage over many other types of orthodontic brackets. However, debonding of these brackets has caused iatrogenic damage to enamel. Thermal debonding has been proposed for use in removing sapphire brackets without causing damage to teeth. This study determined the temperature required at the enamel/resin interface to thermally debond sapphire brackets from etched bovine enamel using 23 different commercially available orthodontic resins and one experimental product. The results indicate a wide range of debonding temperatures for the various resins. As a group, the powder-liquid materials had a statistically lower debonding temperature than the two-paste, the no-mix products, or the light-cured materials, for which the temperatures were all similar. This paper presents relative information a clinician can use in selecting an orthodontic bonding resin to minimize thermal damage to the teeth while debonding sapphire brackets. PMID:1554162

Rueggeberg, F A; Lockwood, P E

1992-01-01

115

Low-cobalt single crystal Rene 150  

NASA Technical Reports Server (NTRS)

The effects of cobalt content on a single crystal version of the advanced, high gamma prime content turbine airfoil alloy Rene 150 were investigated. Cobalt contents under investigation include 12 wt.% (composition level of Rene 150), 6 wt.%, and 0 wt.%. Preliminary test results are presented and compared with the properties of standard DS Rene 150. DTA results indicate that the liquidus goes through a maximum of about 1435 C near 6 wt.% Co. The solidus remains essentially constant at 1390 C with decreasing Co content. The gamma prime solvus appears to go through a minimum of about 1235 C near 6 wt.% Co content. Preliminary as-cast tensile and stress rupture results are presented along with heat treat schedules and future test plans.

Scheuermann, C. M.

1982-01-01

116

Electrical switching in cadmium boracite single crystals  

NASA Astrophysics Data System (ADS)

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed.

Takahashi, T.; Yamada, O.

117

Electrical switching in cadmium boracite single crystals  

NASA Technical Reports Server (NTRS)

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed.

Takahashi, T.; Yamada, O.

1981-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

119

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang,  

E-print Network

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

Kim, Bongsoo

120

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

PubMed

Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca(2+)-binding ability in the C-terminal lobe suggest that the EF-hand Ca(2+)-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface. PMID:25367003

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

2014-12-21

121

Nano-structuring of CaF2 surfaces by slow highly charged ions: simulation and experiment  

NASA Astrophysics Data System (ADS)

The impact of individual slow highly charged ions (HCI) on insulators can create nano-scale surface modifications. We present recent experimental results on nano-hillock and etch pit formation on CaF2, where the appearance of surface modifications is observed only above a threshold projectile potential and kinetic energy depending on the type of damage. A proof-of-principle molecular dynamics simulation offers insights into the early stages of damage formation.

Wachter, G.; Tökési, K.; Betz, G.; Lemell, C.; Burgdörfer, J.; El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Ritter, R.; Aumayr, F.

2014-04-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

123

Radial Diffraction Strength and Elastic Behavior of CaF2 in Low- and High-Pressure Phases  

SciTech Connect

The radial-diffraction lattice behavior of CaF2 was analyzed in its low-pressure (fluorite) and high-pressure phase up to 11.5 GPa using radial x-ray diffraction techniques in the diamond anvil cell. Between 3.5 and 7.1 GPa, fluorite develops a radial-diffraction strength of {approx}0.8 GPa. The corresponding lattice anisotropy of the fluorite phase was measured to be equal to 0.73, in good agreement with previous Brillouin spectroscopy measurements. By 8.8 GPa, CaF2 has undergone a phase transformation to its high-pressure (orthorhombic) phase, with a corresponding volume decrease of 10.4%. By 11.5 GPa, the volume drop between the low-pressure and high-pressure phase has increased to 11.5%. In addition, the high-pressure phase is found to withstand a significantly larger differential stress than the low-pressure fluorite phase, with a large degree of lattice anisotropy. In the maximum stress direction at 8.8 GPa, we observe a time-dependent evolution of the lattice parameters of CaF2, indicating that the high-pressure structure is still undergoing deformation on time scales of hours after the phase boundary has been crossed.

Kavner,A.

2008-01-01

124

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

NASA Astrophysics Data System (ADS)

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

Klein, Claude A.

2005-05-01

125

New Fluorinated Terphenyl Isothiocyanate Liquid Crystal Single Compounds and Mixtures  

E-print Network

New Fluorinated Terphenyl Isothiocyanate Liquid Crystal Single Compounds and Mixtures Amanda Parish fluorinated NCS terphenyl single compounds and mixtures based solely on laterally fluorinated aromatic rigid) alignment interfaces [14]. The high melting temperature can be combated through the lateral fluorination

Wu, Shin-Tson

126

New optical transitions of colour centres in CaF2 : Na+ J. L. Doualan, A. Hamadia, J. Margerie and F. Martin-Brunetire  

E-print Network

a study of their magnetic circular dichroism. We have recently discovered in CaF2 : Na' several other C, or their vibrational satellites, while others are still uni- dentified J. Physique 45 (1984) 1779-1787 NOVEMBRE 1984

Paris-Sud XI, Université de

127

Thermally Triggered Solid-State Single-Crystal-to-Single-Crystal Structural Transformation Accompanies Property Changes.  

PubMed

The 1D complex [(CuL0.5 H2 O)?H2 O]n (1) (H4 L=2,2'-bipyridine-3,3',6,6'-tetracarboxylic acid) undergoes an irreversible thermally triggered single-crystal-to-single-crystal (SCSC) transformation to produce the 3D anhydrous complex [CuL0.5 ]n (2). This SCSC structural transformation was confirmed by single-crystal X-ray diffraction analysis, thermogravimetric (TG) analysis, powder X-ray diffraction (PXRD) patterns, variable-temperature powder X-ray diffraction (VT-PXRD) patterns, and IR spectroscopy. Structural analyses reveal that in complex 2, though the initial 1D chain is still retained as in complex 1, accompanied with the Cu-bound H2 O removed and new O(carboxyl)?Cu bond forming, the coordination geometries around the Cu(II) ions vary from a distorted trigonal bipyramid to a distorted square pyramid. With the drastic structural transition, significant property changes are observed. Magnetic analyses show prominent changes from antiferromagnetism to weak ferromagnetism due to the new formed Cu1-O-C-O-Cu4 bridge. The catalytic results demonstrate that, even though both solid-state materials present high catalytic activity for the synthesis of 2-imidazolines derivatives and can be reused, the activation temperature of complex 1 is higher than that of complex 2. In addition, a possible pathway for the SCSC structural transformations is proposed. PMID:25663637

Li, Quan-Quan; Ren, Chun-Yan; Huang, Yang-Yang; Li, Jian-Li; Liu, Ping; Liu, Bin; Liu, Yang; Wang, Yao-Yu

2015-03-16

128

Single crystal growth and characterization of the nonlinear optical crystal l-arginine hydrofluoride  

Microsoft Academic Search

In this communication, single crystal growth of the nonlinear optical crystal l-arginine hydrofluoride C6H14N4O2. HF (here after abbreviated as LAHF) of dimensions up to 20×15×3mm3 is reported. Crystals have been grown by the temperature lowering method and also by slow evaporation method at constant temperature 30°C from its aqueous solution with pH at 2.2. As-grown single crystals were then characterized

Tanusri Pal; Tanusree Kar

2002-01-01

129

The influence of TiC, CaF 2 and MnS additives on friction and lubrication of sintered high speed steels at elevated temperature  

Microsoft Academic Search

Friction behaviours of sintered high speed steels containing TiC, CaF2 and MnS additives and lubrication mechanisms of these additives have been investigated at sliding conditions at 600°C. Results shown that these additives strongly affected friction behaviours of the sintered high speed steels. Ceramic carbide TiC, as a bonding agent and enhancement phase, bonded the solid lubricant CaF2 and MnS surrounding

Zuomin Liu; T. H. C. Childs

1996-01-01

130

The study of wear characteristics of sintered high speed steels containing CaF 2, MnS and TiC additives at elevated temperature  

Microsoft Academic Search

The wear characteristics of five kinds of sintered high speed steels, which contain MnS, TiC and CaF2 additives, have been investigated at 600°C. The results show that the MnS, TiC and CaF2 additives greatly affect the wear of the steels, and that TiC can improve the wear resistance of the steels. There is also evidence that, at elevated temperature, a

Liu Zuomin; T. H. C Childs

2004-01-01

131

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

DOEpatents

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.

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

1998-01-01

132

Crucibleless crystal growth and Radioluminescence study of calcium tungstate single crystal fiber  

NASA Astrophysics Data System (ADS)

In this article, single phase and high optical quality scheelite calcium tungstate single crystal fibers were grown by using the crucibleless laser heated pedestal growth technique. The as-synthesized calcium tungstate powders used for shaping seed and feed rods were investigated by X-ray diffraction technique. As-grown crystals were studied by Raman spectroscopy and Radioluminescence measurements. The results indicate that in both two cases, calcined powder and single crystal fiber, only the expected scheelite CaWO4 phase was observed. It was verified large homogeneity in the crystal composition, without the presence of secondary phases. The Radioluminescence spectra of the as-grown single crystal fibers are in agreement with that present in Literature for bulk single crystals, presented a single emission band centered at 420 nm when irradiated with ?-rays.

Silva, M. S.; Jesus, L. M.; Barbosa, L. B.; Ardila, D. R.; Andreeta, J. P.; Silva, R. S.

2014-11-01

133

Fast-Response Single Cell Gap Transflective Liquid Crystal Displays  

Microsoft Academic Search

A single cell gap transflective liquid crystal display (TR-LCD) using dual fringing field switching mode is proposed, in which a positive dielectric anisotropy liquid crystal is vertically aligned and driven by fringing fields from both substrates. By optimizing the electrode width and gap of the transmissive and reflective regions, this TR-LCD exhibits a fast response time, high optical efficiency, single

Meizi Jiao; Shin-Tson Wu; Wing-Kit Choi

2009-01-01

134

Mercuric iodide single crystals for nuclear radiation detectors  

Microsoft Academic Search

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

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

1996-01-01

135

Mercuric iodide single crystal for nuclear radiation detectors  

Microsoft Academic Search

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

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

1995-01-01

136

A Quick Method for Determining the Density of Single Crystals.  

ERIC Educational Resources Information Center

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

Roman, Pascual; Gutierrez-Zorrilla, Juan M.

1985-01-01

137

Tensor tomography of residual stresses of hexagonal single crystals  

NASA Astrophysics Data System (ADS)

A method for determining residual stresses in elongated transparent blanks of hexagonal single crystals the optical axis of which is directed along the crystal is proposed. It is assumed that the residual deformation tensor is of thermal character and is characterized by a fictitious temperature. Characteristic parameters of polarized light have been measured by the tomographic method in the plane orthogonal to the single crystal axis.

Puro, A. E.

2014-09-01

138

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

Microsoft Academic Search

Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid–liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds.

R. Hermann; G. Behr; G. Gerbeth; J. Priede; H.-J. Uhlemann; F. Fischer; L. Schultz

2005-01-01

139

Semiconductor single crystal external ring resonator cavity laser and gyroscope  

SciTech Connect

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.

Spitzer, M.P.

1993-08-31

140

Fatigue behavior of a single crystal nickel-base superalloy  

SciTech Connect

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.

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

141

Thermally induced single crystal to single crystal transformation leading to polymorphism.  

PubMed

The robust complex [La(1,10-phen)2(NO3)3] (1,10-phen=1,10-phenanthroline) exhibits thermally induced single crystal to single crystal transformation from one polymorphic phase to another. The complex crystallizes in monoclinic C2/c space group with C2 molecular symmetry at 293K while at 100K it shows P21/c space group with C1 molecular symmetry. Supramolecular investigation shows that at 100K the complex forms 2D achiral sheets whereas at 293K forms two different homochiral 2D sheets. Low temperature DSC analysis indicates that this structural transformation occurs at 246K and also this transformation is reversible in nature. We have shown that thermally induced coherent movement of ligands changes the molecular symmetry of the complex and leads to polymorphism. Photoluminescence property of complex has been studied in both solid state and in methanolic solution at room temperature. The effect of the presence low-lying LUMO orbital of ?-character in the complex is elucidated by theoretical calculation using DFT method. PMID:24813281

Saha, Rajat; Biswas, Susobhan; Dey, Sanjoy Kumar; Sen, Arijit; Roy, Madhusudan; Steele, Ian M; Dey, Kamalendu; Ghosh, Ashutosh; Kumar, Sanjay

2014-09-15

142

Luminescence and scintillation properties of Y 3 A l5 O 12 :Ce single crystals and single-crystal films  

Microsoft Academic Search

Luminescence and scintillation properties of Y3Al5O12:Ce single crystals grown from the melt by the Czochralski and horizontal directed crystallization methods in various gas\\u000a media and Y3Al5O12:Ce single-crystal films grown by liquid-phase epitaxy from a melt solution based on a PbO-B2O3 flux have been comparatively analyzed. The strong dependence of scintillation properties of Y3Al5O12:Ce single crystals on their growth conditions and

Yu. V. Zorenko; V. P. Savchin; V. I. Gorbenko; T. I. Voznyak; T. E. Zorenko; V. M. Puzikov; A. Ya. Dan’ko; S. V. Nizhankovskii

2011-01-01

143

New Configuration of a Transflective Liquid Crystal Display Having a Single Cell Gap and a Single Liquid Crystal Mode  

Microsoft Academic Search

We report on a new tranflective liquid crystal display (LCD) mode having a single cell gap and a single LC mode. For this display mode, a low twisted nematic liquid crystal cell, having the twist angle of 60°, is used for both transmissive and reflective applications. The measured electro-optic characteristics of our transflective cell agree well with numerical simulation results.

Jinyool Kim; Dong-Woo Kim; Chang-Jae Yu; Sin-Doo Lee

2004-01-01

144

Study of single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

145

Crystal Structure of A-amylose: a Revisit from Synchrotron Microdiffraction Analysis of Single Crystals  

E-print Network

1 Crystal Structure of A-amylose: a Revisit from Synchrotron Microdiffraction Analysis of Single;2 Abstract The three-dimensional structure of A-amylose crystals, as a model of the crystal domains of A the resolution of important new fine details. These include a distortion of the amylose double helices resulting

Paris-Sud XI, Université de

146

Hard Polarized Photon Emission in Single Crystals by High Energy Electrons for Planar Crystal Orientations  

E-print Network

The radiation emission spectra of polarized photons emitted from charge particle in single crystal are obtained in semiclassical theory in Baer-Katkov-Strakhovenko approximation for planar crystal orientation. The range of applicability of this approximation is estimated by comparing the results with calculations in exact semiclassical theory. Optimal crystal orientations for producing unpolarized and polarized photon beams are also founded.

S. M. Darbinian; N. L. Ter-Isaakian

1999-09-07

147

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

Microsoft Academic Search

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

Kh. S. Bagdasarov

1987-01-01

148

Method for harvesting single crystals from a peritectic melt  

DOEpatents

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

Todt, Volker R. (Lemont, IL); Sengupta, Suvankar (Columbus, OH); Shi, Donglu (Cincinnati, OH)

1996-01-01

149

Method for harvesting rare earth barium copper oxide single crystals  

DOEpatents

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

Todt, Volker R. (Lemont, IL); Sengupta, Suvankar (Columbus, OH); Shi, Donglu (Cincinnati, OH)

1996-01-01

150

Ion crystal transducer for strong coupling between single ions and single photons  

E-print Network

A new approach for realization of a quantum interface between single photons and single ions in an ion crystal is proposed and analyzed. In our approach the coupling between a single photon and a single ion is enhanced via the collective degrees of freedom of the ion crystal. Applications including single-photon generation, a memory for a quantum repeater, and a deterministic photon-photon, photon-phonon, or photon-ion entangler are discussed.

L. Lamata; D. R. Leibrandt; I. L. Chuang; J. I. Cirac; M. D. Lukin; V. Vuletic; S. F. Yelin

2011-07-11

151

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

PubMed Central

Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp = Jc × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84?GN/m3 at 22.5?T and 4.2?K, the highest value ever reported in any 122 phase. PMID:25467177

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

2014-01-01

152

Ferroelectric polarization reversal in single crystals  

NASA Technical Reports Server (NTRS)

Research on the reversal of polarization in ferroelectric crystals is reviewed. Particular attention is given to observation methods for polarization reversal, BaTiO3 polarization reversal, crystal thickness dependence of polarization reversal, and domain wall movement during polarization reversal in TGS.

Stadler, Henry L.

1992-01-01

153

A Single Crystal Niobium RF Cavity of the TESLA Shape  

NASA Astrophysics Data System (ADS)

A fabrication method for single crystal niobium cavities of the TESLA shape was proposed on the basis of metallographic investigations and electron beam welding tests on niobium single crystals. These tests showed that a cavity can be produced without grain boundaries even in the welding area. An appropriate annealing allows the outgassing of hydrogen and stress relaxation of the material without destruction of the single crystal. A prototype single crystal single cell cavity was build. An accelerating gradient of 37.5 MV/m was reached after approximately 110 ?m of Buffered Chemical Polishing (BCP) and in situ baking at 120°C for 6 hrs with a quality factor exceeding 2×1010 at 1.8 K. The developed fabrication method can be extended to fabrication of multi cell cavities.

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

2007-08-01

154

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

NASA Technical Reports Server (NTRS)

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.

Lal, R. B.

1979-01-01

155

High quality factor single-crystal diamond mechanical resonators  

NASA Astrophysics Data System (ADS)

Single-crystal diamond is a promising material for microelectromechanical systems (MEMs) because of its low mechanical loss, compatibility with extreme environments, and built-in interface to high-quality spin centers. But its use has been limited by challenges in processing and growth. We demonstrate a wafer bonding-based technique to form diamond on insulator, from which we make single-crystal diamond micromechanical resonators with mechanical quality factors as high as 338 000 at room temperature. Variable temperature measurements down to 10 K reveal a nonmonotonic dependence of quality factor on temperature. These resonators enable integration of single-crystal diamond into MEMs technology for classical and quantum applications.

Ovartchaiyapong, P.; Pascal, L. M. A.; Myers, B. A.; Lauria, P.; Bleszynski Jayich, A. C.

2012-10-01

156

Crystal growth and characterization of monometallic NLO single crystals of Cd(IO 3) 2  

Microsoft Academic Search

This work aims to study the growth and physicochemical properties of second-order nonlinear optical active inorganic crystal of cadmium iodate (CDI). Efforts have been made to grow an improved size single crystal of CDI by the slow-cooling technique. The XRD data of CDI are determined by single-crystal XRD analysis. CDI is further characterized by UV–vis–NIR spectroscopy, TGA, dielectric, ac conductivity,

S. M. Ravi Kumar; N. Melikechi; S. Selvakumar; P. Sagayaraj

2009-01-01

157

Single crystal Processing and magnetic properties of gadolinium nickel  

SciTech Connect

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.

Shreve, Andrew John [Ames Laboratory

2012-11-02

158

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

159

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

160

Growth and characterization of organic material 4-dimethylaminobenzaldehyde single crystal  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

161

Growth and characterization of ammonium acid phthalate single crystals  

NASA Astrophysics Data System (ADS)

Ammonium acid phthalate (AAP) has been synthesized and single crystals were grown by slow evaporation solution growth technique. The unit cell parameters were confirmed by single crystal X-ray diffraction analysis and it belongs to orthorhombic system with the space group of Pcab. The high resolution X-ray diffraction studies revealed the crystalline perfection of the grown crystal. The various functional groups of AAP were identified by FT-IR and Raman spectral analyses. Thermal stability of the grown crystals was studied by TGA/DTA. The optical properties of the grown crystals were analyzed by UV-Vis-NIR and photoluminescence spectral studies. The mechanical property of the grown crystal was studied by Vickers microhardness measurement. The growth features of AAP were analyzed by chemical etching.

Arunkumar, A.; Ramasamy, P.

2013-04-01

162

Growing intermetallic single crystals using in situ decanting  

SciTech Connect

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.

Petrovic, Cedomir; Canfield, Paul; Mellen, Jonathan

2012-05-16

163

Large Single Crystal growth of Bi2212 superconducting oxide  

Microsoft Academic Search

A floating zone method was used to study the effects of the growth velocity and starting composition of the feed rod on the crystal growth behaviour of Bi-2212 superconducting materials. It shows that a necessary condition for large single crystal growth is that the solid-liquid interface of a rod maintains a planar interface during crystal growth. The planar solid-liquid interface

Genda Gu; Gangyong Xu; John Tranquada

2006-01-01

164

On the growth of calcium tartrate tetrahydrate single crystals  

Microsoft Academic Search

Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid\\u000a was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals\\u000a was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride.\\u000a The

X. Sahaya Shajan; C. Mahadevan

2004-01-01

165

Designed three-dimensional freestanding single-crystal carbon architectures.  

PubMed

Single-crystal carbon nanomaterials have led to great advances in nanotechnology. The first single-crystal carbon nanomaterial, fullerene, was fabricated in a zero-dimensional form. One-dimensional carbon nanotubes and two-dimensional graphene have since followed and continue to provide further impetus to this field. In this study, we fabricated designed three-dimensional (3D) single-crystal carbon architectures by using silicon carbide templates. For this method, a designed 3D SiC structure was transformed into a 3D freestanding single-crystal carbon structure that retained the original SiC structure by performing a simple single-step thermal process. The SiC structure inside the 3D carbon structure is self-etched, which results in a 3D freestanding carbon structure. The 3D carbon structure is a single crystal with the same hexagonal close-packed structure as graphene. The size of the carbon structures can be controlled from the nanoscale to the microscale, and arrays of these structures can be scaled up to the wafer scale. The 3D freestanding carbon structures were found to be mechanically stable even after repeated loading. The relationship between the reversible mechanical deformation of a carbon structure and its electrical conductance was also investigated. Our method of fabricating designed 3D freestanding single-crystal graphene architectures opens up prospects in the field of single-crystal carbon nanomaterials and paves the way for the development of 3D single-crystal carbon devices. PMID:25329767

Park, Ji-Hoon; Cho, Dae-Hyun; Moon, Youngkwon; Shin, Ha-Chul; Ahn, Sung-Joon; Kwak, Sang Kyu; Shin, Hyeon-Jin; Lee, Changgu; Ahn, Joung Real

2014-11-25

166

Restricted open-shell configuration interaction cluster calculations of the L-edge X-ray absorption study of TiO(2) and CaF(2) solids.  

PubMed

X-ray metal L-edge spectroscopy has proven to be a powerful technique for investigating the electronic structure of transition-metal centers in coordination compounds and extended solid systems. We have recently proposed the Restricted Open-Shell Configuration Interaction Singles (ROCIS) method and its density functional theory variant (DFT/ROCIS) as methods of general applicability for interpreting such spectra. In this work, we apply the ROCIS and DFT/ROCIS methods for the investigation of cluster systems in order to interpret the Ca and Ti L-edge spectra of CaF2 and TiO2 (rutile and anatase), respectively. Cluster models with up to 23 metallic centers are considered together with the hydrogen saturation and embedding techniques to represent the extended ionic and covalent bulk environments of CaF2 and TiO2. The experimentally probed metal coordination environment is discussed in detail. The influence of local as well as nonlocal effects on the intensity mechanism is investigated. In addition, the physical origin of the observed spectral features is qualitatively and quantitatively discussed through decomposition of the dominant relativistic states in terms of leading individual 2p-3d excitations. This contribution serves as an important reference for future applications of ROCIS and DFT/ROCIS methods in the field of metal L-edge spectroscopy in solid-state chemistry. PMID:24871209

Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

2014-07-01

167

Single-drop optimization of protein crystallization  

PubMed Central

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

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

2012-01-01

168

Single-drop optimization of protein crystallization.  

PubMed

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

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

2012-08-01

169

Halide electrodeposition on single-crystal electrodes  

NASA Astrophysics Data System (ADS)

In this dissertation, we investigate in depth by computational and theoretical methods the processes and behavior of submonolayer electrochemical deposition of Br onto single-crystal Ag(100) electrodes. Although this system has little direct industrial application, it provides a test bed for developing theoretical and computational techniques which can be used to study systems of more applied interest. Br electrodeposited onto a Ag(100) substrate at room temperature displays a disordered phase at low electrochemical potentials. At higher electrochemical potentials, the adlayer undergoes a disorder-order phase transition to a c(2 x 2) ordered phase. The phase transition, the equilibrium properties of the adlayer, and the dynamics of the ordering and disordering processes are studied by a variety computational techniques, including static and dynamic lattice-gas models, an off-lattice equilibrium model, and Langevin simulations. Using a two-dimensional lattice-gas approximation for the adlayer, Monte Carlo simulations are used to explore the equilibrium properties of the Br adlayer under different values of the electrochemical potential. The model predicts the existence of low-temperature phases which are not stable at room temperature. The effects of these low-temperature phases on the room-temperature properties of the adlayer are discussed. Starting from the lattice-gas model developed for equilibrium simulations, a dynamic Monte Carlo simulation program is constructed, and the phase-ordering, disordering, and hysteresis behaviors are studied. The phase-ordering process is in the dynamic universality class known as Model A (Lifshitz-Allen-Cahn dynamics), but the disordering behavior is not as easily classified. Dynamic simulations of cyclic-voltammetry experiments show hysteresis due to kinetic limitations associated with the ordering and disordering processes. To further investigate the properties of the adlayer, the lattice-gas approximation was relaxed and replaced by a corrugation-potential approximation. Within this two-dimensional off-lattice model, the equilibrium properties were found to be similar to those of the lattice-gas model. However, the off-lattice model obviously allows calculations of additional quantities, such as the average lateral displacement from the adsorption site. Langevin dynamic simulations of the off-lattice model were also performed to test the validity of the assumptions used in the dynamic Monte Carlo simulations. However, these dynamic simulations were far too computationally intensive to allow off-lattice simulations of the ordering, disordering, and hysteresis behaviors. As a first step towards developing accelerated simulation methods for off-lattice simulations, we construct an advanced dynamic algorithm for continuum spin systems.

Mitchell, Steven James

2001-07-01

170

Brittlestar-Inspired Microlens Arrays Made of Calcite Single Crystals.  

PubMed

Unique concave microlens arrays (MLAs) made of calcite single crystals with tunable crystal orientations can be readily fabricated by template-assisted epitaxial growth in solution without additives under ambient conditions. While the non-birefringent calcite (001) MLA showed excellent imaging performance like brittlestar's microlens arrays, the birefringent calcite (104) MLA exhibited remarkable polarization-dependent optical properties. PMID:25366272

Ye, Xiaozhou; Zhang, Fei; Ma, Yurong; Qi, Limin

2014-11-01

171

Electron-hole fluid in ZnSe single crystals  

NASA Astrophysics Data System (ADS)

Recombination emission and light amplification spectra were obtained for cubic single crystals of ZnSe under intense optical excitation. Experimental results point to the existence of electron-hole plasma droplets in the semiconductor crystals. Electron-hole droplet parameters are examined; reasons for distortions of equilibrium electron and hole concentrations in droplets and of droplet binding energy are discussed.

Baltrameiunas, R.; Kuokshtis, E.

1980-10-01

172

Numerical simulation of single crystal growth by submerged heater method  

Microsoft Academic Search

A novel method of crystal growth which utilizes an axial submerged heater is proposed and numerically simulated. Single crystals should be grown by directional solidification in vertical bottom seeded crucibles. Submerged in the melt, the heater supplies the heat axially downward, enclosing and stratifying a small active portion of the melt.

Aleksandar G. Ostrogorsky

1990-01-01

173

Synthesis and physical characterization of thermoelectric single crystals  

E-print Network

There is much current interest in thermoelectric devices for sustainable energy. This thesis describes a research project on the synthesis and physical characterization of thermoelectric single crystals. 1In?Se?-[delta] ...

Porras Pérez Guerrero, Juan Pablo

2012-01-01

174

On the deformation mechanisms in single crystal Hadfield manganese steels  

SciTech Connect

Austenitic manganese steel, so called Hadfield manganese steel, is frequently used in mining and railroad frog applications requiring excessive deformation and wear resistance. Its work hardening ability is still not completely understood. Previous studies attributed the work-hardening characteristics of this material to dynamic strain aging or an imperfect deformation twin, a so-called pseudotwin. Unfortunately, these previous studies have all focused on polycrystalline Hadfield steels. To properly study the mechanisms of deformation in the absence of grain boundary or texture effects, single crystal specimens are required. The purpose of this work is the following: (1) observe the inelastic stress-strain behavior of Hadfield single crystals in orientations where twinning and slip are individually dominating or when they are competing deformation mechanisms; and (2) determine the microyield points of Hadfield single crystals and use micro-mechanical modeling to predict the stress-strain response of a single crystal undergoing micro-twinning.

Karaman, I.; Sehitoglu, H.; Gall, K. [Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering] [Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering; Chumlyakov, Y.I. [Siberian Physical and Technical Inst., Tomsk (Russian Federation). Physics of Plasticity and Strength of Materials Lab.] [Siberian Physical and Technical Inst., Tomsk (Russian Federation). Physics of Plasticity and Strength of Materials Lab.

1998-02-13

175

Electrical and Optical Properties of Porphyrin Single Crystals  

Microsoft Academic Search

In this work, we investigate the transport and optical properties of single crystal 5,10,15,20-tetrakis (4-N-ethylpyridyl) porphyrin salts, [H2TEPyP·4I]. The electrical conductivity exhibits high anisotropy, in that the conductivity along the stacking column, which is equal to 3.2 × 10?· cm, is three orders of magnitude larger than that perpendicular to the stacking column. The absorption spectra of the single crystals

Y. C. Chen; M. W. Lee; L. L. Li; K. J. Lin

2008-01-01

176

Synthesis and Single-Crystal Growth of Ca  

SciTech Connect

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.

Nakatsuji, Satoru; Maeno, Yoshiteru

2001-01-01

177

Optical characteristics of anisotropic CdP2 single crystals  

NASA Astrophysics Data System (ADS)

The refined results of the specified dispersion of refractive indexes, birefringence, optical activity of anisotropic (beta) -CdP2 single crystals and the components of both the gyration tensor G33 and the optical activity tensor (gamma) 123 in a wide spectral band of polarized light under normal conditions are presented. The influence of temperature and radiation intensity of neodymium and ruby lasers on these characteristics of CdP2 single crystals is studied and analyzed.

Borshch, Volodymyr V.; Gnatyuk, Volodymyr A.; Kovalenko, S. A.; Kuzmenko, M. G.; Yarernko, R. V.

2001-05-01

178

Bulk GaN single-crystals growth  

Microsoft Academic Search

Gallium nitride powder was prepared from gallium and ammonia at temperatures of 1000–1200°C. Parameters of the crystallographic lattice as well as photoluminescence and Raman spectra were determined for the obtained powder. As a result of GaN powder sublimation, GaN single crystals of 3×2×0.2mm were received, at temperatures 1200–1250°C. Single crystals of gallium nitride were also synthesised in a reaction of

Grzegorz Kamler; Janusz Zachara; S?awomir Podsiad?o; Leszek Adamowicz; Wojciech G?bicki

2000-01-01

179

Energy transfer from benzoic acid to lanthanide ions in benzoic acid-functionalized lanthanide-doped CaF 2 nanoparticles  

NASA Astrophysics Data System (ADS)

The preparation of benzoic acid-functionalized CaF 2:Ln 3+ (Ln = Eu or Tb) nanoparticles and their sensitized luminescence are described in this report. First, to achieve sufficient proof for energy transfer from benzoic acid (BA) to lanthanide ions doped in nanoparticles, we employ Eu 3+ as the microscopic probe and investigate the luminescent spectra of benzoic acid-functionalized CaF 2:Eu 3+ (BA-CaF 2:Eu 3+) nanoparticles. Next, to further reveal the difference between sensitized luminescence and common luminescence for Eu 3+ doped in CaF 2 nanoparticles, we study the emission spectra of BA-CaF 2:Eu 3+ nanoparticles excited at 286 nm and 397 nm, respectively. Finally, we analyze and compare the luminescent spectra of BA-CaF 2:Tb 3+ and CaF 2:Ce 3+, Tb 3+ nanoparticles in detail. Our results indicate that both Eu 3+ and Tb 3+ doped in CaF 2 nanoparticles can be efficiently sensitized through benzoic acid.

Wang, Jianshe; Wang, Zongwu; Li, Xia; Wang, Si; Mao, Huadan; Li, Zhongjun

2011-06-01

180

Deformation of as-cast LiF-22 mol pct CaF2 hypereutectic salt between 500 and 1015 K  

NASA Technical Reports Server (NTRS)

Results are presented on compression tests conducted on as-cast LiF-22 mol pct CaF2 hypereutectic specimens at nominal strain rates between 1.8 x 10 to the -6th/sec and 0.25/sec over the temperature range 500-1015 K. In all instances, the stress-strain curves showed broad maxima, with negative strain-hardening rates after the peak stress sigma(max). It was found that, at low temperatures and high stresses, the CaF2 lamellae are rigid while the LiF matrix exhibits extensive transgranular cavitation, while at high temperatures and low stresses the CaF2 lamellae break down and spheroidize while the LiF matrix does not cavitate. It was concluded that the mechanical properties of the as-cast hypereutectic LiF-22 mol pct CaF2 are governed by the rate of deformation of the CaF2 phase. It is suggested that, for thermal energy storage applications, a spheroidal microstructure is more desirable than a lamellar structure.

Raj, S. V.; Whittenberger, J. D.

1990-01-01

181

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

NASA Astrophysics Data System (ADS)

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

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

1989-12-01

182

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

183

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

DOEpatents

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.

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

1998-07-07

184

Differences Between Individual ZSM-5 Crystals in Forming Hollow Single Crystals and Mesopores During Base Leaching.  

PubMed

After base treatment of ZSM-5 crystals below 100?nm in size, TEM shows hollow single crystals with a 10?nm shell. SEM images confirm that the shell is well- preserved even after prolonged treatment. Determination of the Si/Al ratios with AAS and XPS in combination with argon sputtering reveals aluminum zoning of the parent zeolite, and the total pore volume increases in the first two hours of base treatment. In corresponding TEM images, the amount of hollow crystals are observed to increase during the first two hours of base treatment, and intact crystals are visible even after 10?h of leaching; these observations indicate different dissolution rates between individual crystals. TEM of large, commercially available ZSM-5 crystals shows inhomogeneous distribution of mesopores among different crystals, which points to the existence of structural differences between individual crystals. Only tetrahedrally coordinated aluminum is detected with (27) Al MAS NMR after the base leaching of nano-sized ZSM-5. PMID:25720305

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

2015-04-13

185

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

NASA Technical Reports Server (NTRS)

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.

Vandenberg, Lodewijk

1992-01-01

186

Measurement of single crystal surface parameters  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

187

Growth of single crystals by vapor transport  

NASA Technical Reports Server (NTRS)

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

Wiedemeier, H.

1978-01-01

188

Optical and photoelectrochemical study of WTe2 single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of Tungsten Ditelluride (WTe2) having a layered structure grown by chemical vapor transport method using iodine as the transporting agent are studied here. The optical response of these crystals has been obtained by UV-Vis-NIR spectroscopy at room temperature. Results of optical spectra have been analyzed on the basis of three dimensional models. Photoelectrochemical (PEC) characterization of WTe 2 single crystals have been carried out. Photo response measurements were obtained at different intensities of light source to illuminate the photoanode. The effect of intensity in the efficiency of PEC solar cell has been studied. The implications of the results have been discussed.

Desai, P. F.; Patel, D. D.; Bhavsar, D. N.; Jani, A. R.

2013-06-01

189

CeSi 2? ? single crystals: growth features and properties  

Microsoft Academic Search

Single crystals of CeSix (x=1.79–1.85) with an orthorhombic structure have been grown by floating zone methods both with RF induction and optical heating at feed rod compositions CeSiy (y=1.76–1.89). High-perfection single crystals were achieved for a narrow composition interval y=1.81–1.82. A slight axial segregation of Si in the crystal and 2nd phase inclusions of Si (y>1.82) and of CeSi (y<1.80),

D. Souptel; G. Behr; W. Löser; A. Teresiak; S. Drotziger; C. Pfleiderer

2004-01-01

190

Anisotropy of nickel-base superalloy single crystals  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

191

Fatigue Failure Criteria for Single Crystal Nickel Superalloys  

NASA Technical Reports Server (NTRS)

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.

Arakere, Nagaraj K.

1999-01-01

192

Solvent-induced single-crystal-to-single-crystal transformation in multifunctional chiral dysprosium(III) compounds.  

PubMed

Two new enantiomeric ionic chiral dysprosium(III) compounds were designed and synthesized. These compounds show simultaneously the optical activity, ferroelectric effects, nonlinear-optical effects, and slow magnetic relaxation behavior. More interestingly, these compounds exhibit reversible single-crystal-to-single-crystal transformations associated with the release or absorption of solvent molecules. The structure transformations are accompanied by distinct changes in the physical properties. PMID:22862848

Liu, Jian; Zhang, Xiao-Peng; Wu, Tao; Ma, Bin-Bin; Wang, Tian-Wei; Li, Cheng-Hui; Li, Yi-Zhi; You, Xiao-Zeng

2012-08-20

193

Elastic Moduli, Pressure Derivatives, and Temperature Derivatives of Single-Crystal Olivine and Single-Crystal Forsterite  

Microsoft Academic Search

Ultrasonic wave velocities in single-crystal forsteritc (F) and single-crystal olivine (0) have been measured as a function of pressure and of temperature near ambient conditions. Shear and longitudinal velocities were measured in eighteen independent modes, so that each of the nine elastic constants could be calculated by at least two independent equations. The adiabatic stiffness constants c{j (in Mb), their

Mineo Kumazawa; Orson L. Anderson

1969-01-01

194

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

PubMed Central

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

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

2014-01-01

195

Quantum Interference of Electron Wave in Metal (CoSi2)/Insulator (CaF2) Resonant Tunneling Hot Electron Transistor Structure  

NASA Astrophysics Data System (ADS)

We report the observation of multiple negative differential resistance (NDR) in nanometer-thick metal (CoSi2)/insulatro (CaF2) resonant tunneling hot electron transistor (RHET) grown on a silicon substrate. In this transistor, electrons from a resonant tunneling emitter with a 2.2-nm-thick CoSi2 quantum well are transferred to the conduction band of a 4.0-nm-thick CaF2 collector barrier region. Multiple NDR observed here may be attributed to the modulation of the transmission probability of electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers, which is a different mechanism from the resonance in quantum wells previously reported.

Suemasu, Takashi; Kohno, Yoshifumi; Saitoh, Wataru; Suzuki, Nobuhiro; Watanabe, Masahiro; Asada, Masahiro

1994-12-01

196

Negative Differential Resistance of CaF 2/CdF 2 Triple-Barrier Resonant-Tunneling Diode on Si(111) Grown by Partially Ionized Beam Epitaxy  

NASA Astrophysics Data System (ADS)

Room-temperature negative differential resistance (NDR) of triple-barrier cadmium di-fluoride (CdF2)/calcium di-fluoride (CaF2) heterostructure resonant-tunneling diode (RTD) on a Si(111) substrate has been demonstrated. CdF2/CaF2 multilayered heterostructures were grown on a Si(111) substrate using partially ionized beam epitaxy to obtain atomically flat interfaces. The RTD structures, which consist of triple CaF2 energy barriers and double CdF2 quantum wells, were fabricated by electron beam (EB) lithography and dry etching to avoid thermal and chemical damage to the CdF2 layers. In the current-voltage characteristics of the RTD, NDR was clearly observed even at room temperature and the maximum peak-to-valley (P/V) ratio was about 6.

Watanabe, Masahiro; Aoki, Yuichi; Saito, Wataru; Tsuganezawa, Mika

1999-02-01

197

Crystal growth, structural and optical characterization of a semi-organic single crystal for frequency conversionapplications  

NASA Astrophysics Data System (ADS)

Single crystals of semi-organic L-histidine hydrobromide have been grown by slow evaporation technique from a mixture of L-histidine and hydrobromic acid in aqueous solution at ambient temperature. From high-resolution X-ray diffraction analysis, the crystalline perfection of the grown crystal has been studied. Single crystal X-ray diffraction analyses, Nuclear Magnetic Resonance spectral analysis, Thermo-Gravimetry (TG), Differential Thermal Analysis (DTA) and hardness test have been employed to characterize the as-grown crystals. The UV cutoff wavelength of the grown crystal is below 300 nm and has a wide transparency window, which is suitable for second harmonic generation of laser in the blue region. Nonlinear optical characteristics have been studied using Q switched Nd:YAG laser ( ?=1064 nm). The second harmonic generation conversion efficiency of the grown crystals confirms their suitability for frequency conversion applications.

Anandan, P.; Parthipan, G.; Saravanan, T.; Mohan Kumar, R.; Bhagavannarayana, G.; Jayavel, R.

2010-12-01

198

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

NASA Technical Reports Server (NTRS)

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

Arakere, N. K.; Swanson, G.

2002-01-01

199

SINGLE CRYSTAL NIOBIUM TUBES FOR PARTICLE COLLIDERS ACCELERATOR CAVITIES  

SciTech Connect

The objective of this research project is to produce single crystal niobium (Nb) tubes for use as particle accelerator cavities for the Fermi laboratory’s International Linear Collider project. Single crystal Nb tubes may have superior performance compared to a polycrystalline tubes because the absence of grain boundaries may permit the use of higher accelerating voltages. In addition, Nb tubes that are subjected to the high temperature, high vacuum crystallization process are very pure and well annealed. Any impurity with a significantly higher vapor pressure than Nb should be decreased by the relatively long exposure at high temperature to the high vacuum environment. After application of the single crystal process, the surfaces of the Nb tubes are bright and shiny, and the tube resembles an electro polished Nb tube. For these reasons, there is interest in single crystal Nb tubes and in a process that will produce single crystal tubes. To convert a polycrystalline niobium tube into a single crystal, the tube is heated to within a few hundred ?C of the melting temperature of niobium, which is 2477 ?C. RF heating is used to rapidly heat the tube in a narrow zone and after reaching the operating temperature, the hot zone is slowly passed along the length of the tube. For crystallization tests with Nb tubes, the traverse rate was in the range of 1-10 cm per hour. All the crystallization tests in this study were performed in a water-cooled, stainless steel chamber under a vacuum of 5 x10-6 torr or better. In earliest tests of the single crystal growth process, the Nb tubes had an OD of 1.9 cm and a wall thickness of 0.15 mm. With these relatively small Nb tubes, the single crystal process was always successful in producing single crystal tubes. In these early tests, the operating temperature was normally maintained at 2200 ?C, and the traverse rate was 5 cm per hour. In the next test series, the Nb tube size was increased to 3.8 cm OD and the wall thickness was increased 0.18 mm and eventually to 0.21 mm. Again, with these larger tubes, single crystal tubes were usually produced by the crystallization process. The power supply was generally operated at full output during these tests, and the traverse rate was 5 cm per hour. In a few tests, the traverse rate was increased to 10 cm per hour, and at the faster traverse rate, single crystal growth was not achieved. In these tests with a faster traverse rate, it was thought that the tube was not heated to a high enough temperature to achieve single crystal growth. In the next series of tests, the tube OD was unchanged at 3.8 cm and the wall thickness was increased to 0.30 mm. The increased wall thickness made it difficult to reach an operating temperature above 2,000 ?C, and although the single crystal process caused a large increase in the crystal grains, no single crystal tubes were produced. It was assumed that the operating temperature in these tests was not high enough to achieve single crystal growth. In FY 2012, a larger power supply was purchased and installed. With the new power supply, temperatures above the melting point of Nb were easily obtained regardless of the tube thickness. A series of crystallization tests was initiated to determine if indeed the operating temperature of the previous tests was too low to achieve single crystal growth. For these tests, the Nb tube OD remained at 3.8 cm and the wall thickness was 0.30 mm. The first test had an operating temperature of 2,000 ?C. and the operating temperature was increased by 50 ?C increments for each successive test. The final test was very near the Nb melting temperature, and indeed, the Nb tube eventually melted in the center of the tube. These tests showed that higher temperatures did yield larger grain sizes if the traverse rate was held constant at 5 cm per hour, but no single crystal tubes were produced even at the highest operating temperature. In addition, slowing the traverse rate to as low as 1 cm per hour did not yield a single crystal tube regardless of operating temperature. At this time, it

MURPHY, JAMES E [University of Nevada, Reno] [University of Nevada, Reno

2013-02-28

200

Single Crystal Growth of Se-Te Alloys onto Tellurium from the Melts  

Microsoft Academic Search

The method to obtain single crystals of Se-Te alloys is developed. In this method, it is possible to grow a single crystal of an alloy from the melt, using a single crystal of tellurium as a seed for a Bridgmanlike method. The crystal is grown epitaxially onto tellurium. The obtained crystals is homogeneous except the layer of a few mm

Tadashi Shiosaki; Akira Kawabata

1971-01-01

201

THE PALEOMAGNETISM OF SINGLE SILICATE CRYSTALS: RECORDING GEOMAGNETIC FIELD  

E-print Network

THE PALEOMAGNETISM OF SINGLE SILICATE CRYSTALS: RECORDING GEOMAGNETIC FIELD STRENGTH DURING MIXED of the geomagnetic reversal chronology of the last 160 million years are well established. The relationship between of in situ and laboratory-induced alteration. Here we review an alternative approach. Single plagioclase

Jellinek, Mark

202

Raman spectra of deuteriated taurine single crystals  

NASA Astrophysics Data System (ADS)

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.

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

203

Stress-induced single-polarization single-transverse mode photonic crystal fiber with low nonlinearity  

Microsoft Academic Search

We report on the design of a single-polarization single-transverse mode large mode area photonic crystal fiber. By including index-matched stress applying elements in the photonic cladding an ultra-broadband single polarization window is obtained while a large mode field area of ~700 mum is maintained. Based on that design, an Yb-doped double-clad photonic crystal fiber is realized that combines low nonlinearity

T. Schreiber; F. Röser; O. Schmidt; J. Limpert; R. Iliew; F. Lederer; A. Petersson; C. Jacobsen; K. P. Hansen; J. Broeng; A. Tünnermann

2005-01-01

204

Atomic beam scattering from single crystal surfaces  

NASA Astrophysics Data System (ADS)

Application of atom-scattering to a variety of surface problems is expanding rapidly, owing in large part to the extreme surface- sensitivity of this probe. Helium is particularly useful because of its low mass and chemical inertness. Beams with velocity spreads of less than one percent and wavelength of the order of one Angstrom can be formed by nozzle expansion. The scattered flux from a clean, well-ordered crystal surface contains elastic and inelastic, coherent and incoherent, components. The coherent elastic component (i.e., the specular and diffracted beams) contains information about the crystallographic structure of the outer- most atomic layer of the crystal and about the interaction potential between the crystal and the scattered particle. The latter manifests itself in the form of resonances between the incoming free-particle state, and the two-dimensional Bloch states bound in the potential well at the surface. Elastic scattering theory has reached the point where the resonance signatures in the various diffracted beams can be predicted accurately. Crystallographic information resides in the diffracted beam intensities. Theoretical interpretation is less well advanced, though some progress has been made with “hard-wall” models. Experimental studies of reconstructed surfaces and chemisorbed overlayers appear very promising. In inelastic scattering, energy resolution has been achieved by both time-of-flight and diffraction methods. High-resolution studies on alkali halide surfaces have led to experimental determination of Rayleighwave dispersion relations over the full Brillouin zone. Preliminary results have also been obtained on some metals.

Frankl, Daniel R.

205

Crystal rotation in Cu single crystal micropillars: In situ Laue and electron backscatter diffraction  

Microsoft Academic Search

In situ microdiffraction experiments were conducted on focused ion beam machined single crystal Cu pillars oriented for double slip. During deformation, the crystal undergoes lattice rotation on both the primary and critical slip system. In spite of the initial homogeneous microstructure of the Cu pillar, rotation sets in already at yield and is more important at the top of the

R. Maaß; S. van Petegem; D. Grolimund; H. van Swygenhoven; D. Kiener; G. Dehm

2008-01-01

206

Method of making macrocrystalline or single crystal semiconductor material  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

207

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

Microsoft Academic Search

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

Dapeng Chen

2008-01-01

208

Low-cost single-crystal turbine blades, volume 2  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

209

Method for harvesting rare earth barium copper oxide single crystals  

DOEpatents

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.

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

1996-04-02

210

Modelling of Heat Transfer in Single Crystal Growth  

E-print Network

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...

Zhmakin, Alexander I

2014-01-01

211

Single-crystal growth, crystal and electronic structure of NaCoO 2  

Microsoft Academic Search

Single crystals of NaCoO2 have been successfully synthesized for the first time by a flux method at 1323K. A single-crystal X-ray diffraction study confirmed the trigonal R3?m space group and the lattice parameters a=2.8897(15)A?, c=15.609(3)A?. The crystal structure has been refined to the conventional values R=1.9% and wR=2.1% for 309 independent observed reflections. The electron density distribution of NaCoO2 has

Yasuhiko Takahashi; Yoshito Gotoh; Junji Akimoto

2003-01-01

212

Optical properties of tungsten disulfide single crystals doped with gold  

Microsoft Academic Search

Single crystals of WS2 doped with gold have been grown by the chemical vapour transport method using iodine as a transporting agent. X-ray diffraction (XRD) pattern analysis revealed presence of mixed three-layer rhombohedral (3R) and two-layer hexagonal (2H) polytypes for the doped crystals while the undoped one shows only 2H form. Hall measurements indicate that the samples are p-type in

D. O. Dumcenco; H. P. Hsu; Y. S. Huang; C. H. Liang; K. K. Tiong; C. H. Du

2008-01-01

213

Growth and characterization of lithium yttrium borate single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of 0.1% Ce doped Li6Y(BO3)3 have been grown using the Czochralski technique. The photoluminescence study of these crystals shows a broad emission at ˜ 420 nm corresponding to Ce3+ emission from 5d?4f energy levels. The decay profile of this emission shows a fast response of ˜ 28 ns which is highly desirable for detector applications.

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

2014-04-01

214

Orientation effects in nanoindentation of single crystal copper  

Microsoft Academic Search

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

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

2008-01-01

215

Growth and characterization of lithium yttrium borate single crystals  

SciTech Connect

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

Singh, A. K.; Singh, S. G.; Tyagi, M.; Desai, D. G.; Sen, Shashwati [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai- 400085 (India)

2014-04-24

216

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

217

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

NASA Technical Reports Server (NTRS)

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

Lundquist, C. A.

1974-01-01

218

Lithium niobate single-crystal and photo-functional device  

DOEpatents

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.

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

2001-01-01

219

Growth and characterization of 4-methyl benzene sulfonamide single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

220

The Load Capability of Piezoelectric Single Crystal Actuators  

NASA Technical Reports Server (NTRS)

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.

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

2007-01-01

221

The Load Capability of Piezoelectric Single Crystal Actuators  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

222

Synthesis and properties of erbium oxide single crystals  

SciTech Connect

Erbium oxide (Er{sub 2}O{sub 3}, erbia) is a highly stable cubic rare earth oxide with a high melting point of 2,430 C. Because of this, it may have potential applications where high temperature stability and corrosion resistance are required. However, relatively little is known about the properties of this oxide ceramic. The authors have employed a xenon optical floating zone unit with a temperature capability of 3,000 C to grow high quality single crystals of erbia. The conditions for single crystal growth of erbia have been established. The mechanical properties of erbia single crystals have been initially examined using microhardness indentation as a function of temperature.

Petrovic, J.J.; Romero, R.S.; Mendoza, D.; Kukla, A.M.; Hoover, R.C.; McClellan, K.J.

1999-04-01

223

Single Crystal Synthesis and STM Studies of High Temperature Superconductors  

NASA Technical Reports Server (NTRS)

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.

Barrientos, Alfonso

1997-01-01

224

Growth of solid solution single crystals  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

225

Growth of solid solution single crystals  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

226

Anisotropy of nickel-base superalloy single crystals  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

227

Apparatus And Method For Producing Single Crystal Metallic Objects  

DOEpatents

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.

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

228

Two-photon-induced singlet fission in rubrene single crystal  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

229

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

PubMed

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

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

2013-05-14

230

Preparation of single-crystal copper ferrite nanorods and nanodisks  

SciTech Connect

This article, for the first time, reports the preparation of single-crystal copper ferrite nanorods and nanodisks. Using amorphous copper ferrite nanoparticles synthesized by reverse micelle as reaction precursor, single-crystal copper ferrite nanorods were synthesized via hydrothermal method in the presence of surfactant polyethylene glycol (PEG), however, copper ferrite nanodisks were prepared through the same procedures except the surfactant PEG. The resulting nanomaterials have been characterized by powder X-ray diffraction (XRD), selected electron area diffraction (SEAD), and transmission electron microscopy (TEM). The bulk composition of the samples was determined by means of X-ray photoelectron spectroscopy (XPS)

Du Jimin [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China); Liu Zhimin [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China)]. E-mail: liuzm@iccas.ac.cn; Wu Weize [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China); Li Zhonghao [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China); Han Buxing [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China)]. E-mail: hanbx@iccas.ac.cn; Huang Ying [Center for Molecular Sciences, CAS Key Laboratory of Colloid, Interfacial and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No. 2 Beiyijie, Zhongguancun, Beijing 100080 (China)

2005-06-15

231

Single Gap Transflective Liquid Crystal Display with Dual Orientation of Liquid Crystal  

Microsoft Academic Search

We propose a single-cell-gap transflective liquid crystal display (LCD) with dual orientation of LC at an initial state. Owing to hybrid alignment in the reflective region, the effective cell retardation value becomes half of that in the transmissive region where the LCs are homogenously aligned. Consequently, a transflective display driven by a vertical or fringe electric field with a single

Young Jin Lim; Je Hoon Song; Yong Bae Kim; Seung Hee Lee

2004-01-01

232

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The solidification of a solid solution semiconductor, having a wide separation between liquidus and serious has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; mercury cadmium telluride with 80.0 mole percent of HgTe and 84.8 mole percent respectively. These alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed of residual acceleration effects. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system by a previously processed sample, the sample was not received until May 1998, and the preliminary analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. Early results are indicating that the sample may not accomplish the desired objectives. As with the USMP-2 mission, the results of the ground based experiments were compared with the crystal grown in orbit under microgravity conditions. On the earth, it has been demonstrated that the application of the magnetic field leads to a significant reduction in fluid flow, with improved homogeneity of composition. The field strength required to suppress flow increases with diameter of the material. The 8 mm diameter sample used here was less than the upper diameter limit for a ST magnet. The configuration for USMP-4 was changed so that the material was seeded and other processing techniques were also modified. It was decided to examine the effects of a strong magnetic field under the modified configuration and parameters. A further change from USMP-2 was that a different composition of material was grown, namely with 0.152 mole fraction of cadmium telluride rather than the 0.200 of the USMP-2 experiment. The objective was to grow highly homogeneous, low defect density material of a composition at which the conduction band and the valence band of the material impinge against each other. As indicated, the furnace was contaminated during the mission. As a result of solid debris remaining in the furnace bore, the cartridge in this experiment, denoted as SL1-417, was significantly bent during the insertion phase. During translation the cartridge scraped against the plate which isolates the hot and cold zones of the furnace. Thermocouples indicated that a thermal assymetry resulted. The scraping in the slow translation or crystal growth part of the processing was not smooth and it is probable that the jitter was sufficient to give rise to convection in the melt. Early measurements of composition from the surface of the sample have shown that the composition varies in an oscillatory manner.

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

1999-01-01

233

Reflection high-energy electron diffraction study of the molecular beam epitaxial growth of CaF2 on Si(110)  

E-print Network

was carried out in an Intevac modular GEN-II MBE system equipped with a Varian electron gun operated at 9.5 ke electron microscopy SEM data on the mo- lecular beam epitaxial MBE growth of CaF2 on Si 110 . We also

McCann, Patrick

234

pH-responsive drug delivery system based on luminescent CaF(2):Ce(3+)/Tb(3+)-poly(acrylic acid) hybrid microspheres.  

PubMed

In this study, we design a controlled release system based on CaF(2):Ce(3+)/Tb(3+)-poly(acrylic acid) (PAA) composite microspheres, which were fabricated by filling the pH-responsive PAA inside CaF(2):Ce(3+)/Tb(3+) hollow spheres via photopolymerization route. The CaF(2):Ce(3+)/Tb(3+) hollow spheres prepared by hydrothermal route possess mesoporous structure and show strong green fluorescence from Tb(3+) under UV excitation. Doxorubicin hydrochloride (DOX), a widely used anti-cancer drug, was used as a model drug to evaluate the loading and controlled release behaviors of the composite microspheres due to the good biocompatibility of the samples using MTT assay. The composite carriers provide a strongly pH-dependent drug release behavior owing to the intrinsic property of PAA and its interactions with DOX. The endocytosis process of drug-loaded microspheres was observed using confocal laser scanning microscopy (CLSM) and the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carriers was investigated. In addition, the extent of drug release could be monitored by the altering of photoluminescence (PL) intensity of CaF(2):Ce(3+)/Tb(3+). Considering the good biocompatibility, high drug loading content and pH-dependent drug release of the materials, these hybrid luminescent microspheres have potential applications in drug controlled release and disease therapy. PMID:22196902

Dai, Yunlu; Zhang, Cuimiao; Cheng, Ziyong; Ma, Ping'an; Li, Chunxia; Kang, Xiaojiao; Yang, Dongmei; Lin, Jun

2012-03-01

235

CaF2/CdF2 Double-Barrier Resonant Tunneling Diode with High Room-Temperature Peak-to-Valley Ratio  

NASA Astrophysics Data System (ADS)

We have demonstrated room-temperature negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) on the order of 105 using CaF2/CdF2 double-barrier resonant tunneling diode (DBRTD) structures grown on Si(111) substrates. A CdF2 quantum-well layer was grown by molecular-beam epitaxy (MBE) and CaF2 barrier layers were formed by MBE combined with the partially ionized beam technique on an n^+-Si(111) substrate with 0.07^\\circ miscut, in order to reduce the pinhole density of CaF2 barrier layers. The dispersion of the peak current density and bias voltage of the NDR implies that the layer thickness fluctuation of each CaF2 barrier and CdF2 quantum-well layer is suppressed below ±1 unit layer of the (111) atomic plane for DBRTDs with an 18 ?m diameter electrode. The peak and valley currents agreed reasonably with those obtained by theoretical estimation.

Watanabe, Masahiro; Funayama, Toshiyuki; Teraji, Taishi; Sakamaki, Naoto

2000-07-01

236

Room temperature single-photon Source:Single-dye molecule fluorescence in Liquid Crystal host  

Microsoft Academic Search

We report on new approaches toward an implementation of an efficient, room temperature, deterministically polarized, single-photon source (SPS) on demand-a key hardware element for quantum information and quantum communication. Operation of a room temperature SPS is demonstrated via photon antibunching in the fluorescence from single terrylene-dye molecules embedded in a cholesteric liquid crystal host. Using oxygen-depleted liquid crystal hosts, dye-bleaching

Svetlana G. Lukishova; Ansgar W. Schmid; Andrew J. McNamara; Robert W. Boyd; Carlos R. Stroud

2003-01-01

237

Bulk crystal growth and characterization of non-linear optical bisthiourea zinc chloride single crystal by unidirectional growth method  

Microsoft Academic Search

The unidirectional crystal growth method has been employed for the bulk growth of semi-organic non-linear optical bisthiourea zinc chloride single crystal along a-axis with high solute-crystal conversion efficiency. Single crystal X-ray diffraction studies confirm the orthorhombic structure. Optical studies reveal very high transmission of the crystal along the growth axis. Dielectric study shows that the dielectric constant decreases with increase

R. Uthrakumar; C. Vesta; C. Justin Raj; S. Krishnan; S. Jerome Das

2010-01-01

238

Growth and spectroscopic properties of samarium oxalate single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of samarium oxalate decahydrate were synthesized using single diffusion gel technique and the conditions influencing the size, shape and quality were optimized. Highly transparent crystals of size 3×2×1 mm3 with a well defined hexagonal morphology were grown during a time period of two weeks. X ray powder diffraction analysis revealed that the grown crystals crystallize in the monoclinic system with space group P21/c and the proposed chemical formula and linkage of water molecules were confirmed using thermogravimetric analysis. The various functional groups of the oxalate ligand and the water of crystallization were identified by Fourier transform infrared spectroscopy. Spectroscopic investigations such as electric dipole transition probability, magnetic dipole transition probability and branching ratios of all possible transitions from 4G5/2 level of Sm3+ ions were estimated from the absorption spectra using JO theory. The spectroscopic analysis suggested that the crystal has a strong and efficient orange red emission. This is confirmed from the photoluminescence spectrum with a wavelength peak at 595 nm and hence this promising emission can be effectively used for optical amplification.

Vimal, G.; Mani, Kamal P.; Jose, Gijo; Biju, P. R.; Joseph, Cyriac; Unnikrishnan, N. V.; Ittyachen, M. A.

2014-10-01

239

Relaxor-PT Single crystals: Observations and Developments  

PubMed Central

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

Zhang, Shujun; Shrout, Thomas R.

2011-01-01

240

Fretting Stresses in Single Crystal Superalloy Turbine Blade Attachments  

NASA Technical Reports Server (NTRS)

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.

Arakere, Nagaraj K.; Swanson, Gregory

2000-01-01

241

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

NASA Astrophysics Data System (ADS)

Phase transitions and equations of state of the alkaline earth fluorides CaF2 , SrF2 , and BaF2 were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm3¯m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF2 and SrF2 : these materials were observed to transform to a hexagonal (P63/mmc) Ni2In -type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF2 , the Ni2In -type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF2 and SrF2 , the fluorite-cotunnite transition results in a volume decrease of 8-10% , while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni2In -type phase is ˜5% . The percentage increase in the bulk modulus (?K) across the transition is greater when the cation is smaller. While for BaF2 , ?K is 10-30% , ?K values for SrF2 and CaF2 are 45-65% and 20-40% . Although shock data for CaF2 have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.

Dorfman, Susannah M.; Jiang, Fuming; Mao, Zhu; Kubo, Atsushi; Meng, Yue; Prakapenka, Vitali B.; Duffy, Thomas S.

2010-05-01

242

Effect of NiCr Clad BaF2·CaF2 Addition on Wear Performance of Plasma Sprayed Chromium Carbide-Nichrome Coating  

NASA Astrophysics Data System (ADS)

NiCr clad BaF2·CaF2 fluoride eutectic powders were added into chromium carbide-nichrome feedstock to improve the tribological properties of NiCr-Cr3C2 coating, and the structures, mechanical, and ball-on-disk sliding wear performance of the coating were characterized. The results show that NiCr cladding can effectively decrease the density and thermophysical difference between the feedstock components, while alleviate the decarburization and oxidization of the constituent phases, and form the coating with a uniform and dense microstructure. However, the addition of BaF2·CaF2 has a negative effect on mechanical properties of the coating. When the temperature reaches 500 °C, the BaF2·CaF2 eutectic is soften by the heat and smeared by the counterpart, thus the low shear stress lubricating film forms between the contact surface, that improves the tribological properties dramatically. At this temperature, the dominant wear mechanisms also change from splats spallation and abrasive wear at room temperature to plastic deformation and plawing by the counterpart. Within the temperature range from 600 to 800 °C, the friction coefficient, the wear rates of NiCr/Cr3C2-10% BaF2·CaF2 coating and its coupled Si3N4 ball are 20%, 40%, and 75% lower than those of the NiCr/Cr3C2 coating, respectively. The NiCr/Cr3C2-BaF2·CaF2 coating shows superior wear performance to the NiCr/Cr3C2 coating without lubricant additive.

Du, Lingzhong; Huang, Chuanbing; Zhang, Weigang; Zhang, Jingmin; Liu, Wei

2010-03-01

243

Polymer single crystal membrane from liquid/liquid interface  

NASA Astrophysics Data System (ADS)

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.

Wang, Wenda; Li, Christopher

2013-03-01

244

Liquid impact erosion of single-crystal and coated material  

NASA Astrophysics Data System (ADS)

Lithium fluoride in its single-crystal form is an interesting material for investigating the development of fracture by multiple liquid impact owing to its well-characterized crystal structure. The development of fracture during liquid impact is attributed to the extension of short circumferential cracks produced around the loaded area by the passing Rayleigh stress wave after the impact event. The damage threshold of single-crystal lithium fluoride is developed using the multiple-impact jet apparatus (MIJA) as a result of identifying the characteristic fracture annulus associated with liquid impact during a controlled experimental procedure. The observation of damage produced in solids by liquid impact has practical significance in the problems associated with supersonic aircraft flying through rain and in the erosion of turbine blades. The addition of coatings to the surface provides a form of protection at higher speeds but may not completely inhibit damage.

Jackson, M. J.; Telling, R. H.; Field, J. E.

2006-04-01

245

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

Color centers in diamond as single photon emitters, are leading candidates for future quantum devices due to their room temperature operation and photostability. The recently discovered chromium related centers are particularly attractive since they possess narrow bandwidth emission and a very short lifetime. In this paper we investigate the fabrication methodologies to engineer these centers in monolithic diamond. We show that the emitters can be successfully fabricated by ion implantation of chromium in conjunction with oxygen or sulfur. Furthermore, our results indicate that the background nitrogen concentration is an important parameter, which governs the probability of success to generate these centers.

Aharonovich, I; Johnson, B C; McCallum, J C; Prawer, S

2010-01-01

246

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

Color centers in diamond as single photon emitters, are leading candidates for future quantum devices due to their room temperature operation and photostability. The recently discovered chromium related centers are particularly attractive since they possess narrow bandwidth emission and a very short lifetime. In this paper we investigate the fabrication methodologies to engineer these centers in monolithic diamond. We show that the emitters can be successfully fabricated by ion implantation of chromium in conjunction with oxygen or sulfur. Furthermore, our results indicate that the background nitrogen concentration is an important parameter, which governs the probability of success to generate these centers.

I Aharonovich; S Castelletto; B C Johnson; J C McCallum; S Prawer

2010-09-29

247

Field-assisted bonding of single crystal quartz  

Microsoft Academic Search

A technique to produce strong, hermetic bonds between plates of single crystal quartz using a modified field-assisted bonding process is presented. Field-assisted bonding is a technique traditionally used to join glass to metals at temperatures well below normal glass softening temperatures. To promote reactivity between quartz within an electrical field at temperatures well below quartz transformation temperatures, thin films of

Randall D. Watkins; Clinton D. Tuthill; Richard M. Curlee; Dale R. Koehler; Charles F. Joerg

1989-01-01

248

A Study of Single Crystal Fatigue Failure Criteria  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

249

Low temperature magnetic transitions of single crystal HoBi  

SciTech Connect

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

Fente, A. [Universidad Autonoma de Madrid; Suderow, H. [Universidad Autonoma de Madrid; Vieira, S. [Universidad Autonoma de Madrid; Nemes, N. M. [Instituto de Ciencia de Materiales de Madrid; Garcia-Hernandez, M. [Instituto de Ciencia de Materiales de Madrid; Budko, Sergei L. [Ames Laboratory; Canfield, Paul C. [Ames Laboratory

2013-09-04

250

Deformation behaviour of aluminium single crystals in ultraprecision diamond turning  

Microsoft Academic Search

The physical properties of the machined layer of single crystal aluminium after diamond turning were assessed by X-ray diffraction (XRD) to demonstrate the nature and extent of the plastic deformation process that had occurred in the workpiece. In the range of depth of cut investigated, the microstrain was found to vary with the crystallography of the machined surface, whereas the

S. To; W. B. Lee

2001-01-01

251

NANO-SCALE CALORIMETRY OF ISOLATED POLYETHYLENE SINGLE CRYSTALS  

E-print Network

#12;NANO-SCALE CALORIMETRY OF ISOLATED POLYETHYLENE SINGLE CRYSTALS BY ALEX TAN KWAN B.S., Stanford) device, the nanocalorimeter, it was possible to investigate the melting of isolated polyethylene (PE, a simple Ni-foil calorimeter, to measure the heat capacity of a thin polyethylene film to verify

Allen, Leslie H.

252

Low-cost single-crystal turbine blades, volume 1  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

253

Some Debye temperatures from single-crystal elastic constant data  

USGS Publications Warehouse

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

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

1966-01-01

254

Nonlinearities in single-crystal silicon micromechanical resonators  

Microsoft Academic Search

The fundamental performance limit of single-crystal silicon resonators set by device nonlinearities in characterized. Using Leeson's model for near carrier phase noise, the nonlinearity is shown to set the scaling limit in miniaturizing oscillators. A circuit model based on discretization of distributed mass and nonlinear elasticity is introduced to accurately simulate the large amplitude vibrations. Based on published data for

V. Kaajakari; T. Mattila; J. Kiihamaki; H. Kattelus; A. Oja; H. Seppa

2003-01-01

255

Tutorial: Organic Single Crystals 101 Prof. Vitaly Podzorov  

E-print Network

11 Tutorial: Organic Single Crystals 101 Prof. Vitaly Podzorov Institute for Advanced Materials://www.physics.rutgers.edu/~podzorov/index.php http://iamdn.rutgers.edu/ Fall MRS 2012 Nov. 25, 2012 (Boston, MA) Fall MRS-2012 Tutorial (V. Podzorov) #12;22 This tutorial and detailed technical notes can be downloaded from: http

Glashausser, Charles

256

The Electrical Resistivity of FeSn Single Crystals  

Microsoft Academic Search

The electrical resistivity of single crystal FeSn (hex B 35) has been measured for current parallel and perpendicular to the c-axis in the temperature range 4.2-420 K. The critical exponent is determined for I\\/\\/c at the antiferromagnetic ordering temperature TN = 364 K.

Bengt Stenström

1972-01-01

257

Insulating surface layer on single crystal K3C60  

NASA Astrophysics Data System (ADS)

Using angle-dependent photoemission spectra of core and valence levels we show that metallic, single crystal K3C60 is terminated by an insulating or weakly-conducting surface layer. We attribute this to the effects of strong intermolecular correlations combined with the average surface charge state. Several controversies on the electronic structure are thereby resolved.

Schiessling, J.; Kjeldgaard, L.; Käämbre, T.; Marenne, I.; Qian, L.; O'Shea, J. N.; Schnadt, J.; Garnier, M. G.; Nordlund, D.; Nagasono, M.; Glover, C. J.; Rubensson, J.-E.; Mårtensson, N.; Rudolf, P.; Nordgren, J.; Brühwiler, P. A.

2004-10-01

258

High cycle fatigue crack initiation in single crystals and polycrystals  

Microsoft Academic Search

The objective of this research is to analyze the high-cycle fatigue crack initiation in both monocrystalline and polycrystalline ductile metals. Persistent slip bands have been observed in both single crystals and polycrystals in numerous high-cycle fatigue tests. Extrusions and intrusions at the free surface of fatigued specimens are the favorable sites for fatigue crack initiation. In the present study, the

Ningjun Teng

1997-01-01

259

Photo-Induced Magnetic Effects in FZ YIG Single Crystal  

Microsoft Academic Search

Highly pure single crystals of YIG were obtained by an FZ method, and a remarkable photoinduced change in permeability was observed. The permeability of samples held at a temperature of 77K was decreased by more than 90% by illumination. The photoinduced change remained, to some extent, at temperatures up to about 260 K. By annealing at 1100°C (in an oxygen

K. Hisatake; I. Matsubara; K. Maeda; T. Fujihara; I. Sasaki; T. Nakano

1988-01-01

260

Coherence and Polarization Effects in Mössbauer Absorption by Single Crystals  

Microsoft Academic Search

The polarization dependence of the absorption cross section must generally be taken into account in calculating Mössbauer absorption spectra of single crystals which exhibit hyperfine splittings. A method for doing this in an experimentally interesting class of cases is described. In these cases, the incident radiation beam can be divided into two components, each having its own complex index of

R. M. Housley; R. W. Grant; U. Gonser

1969-01-01

261

Unified constitutive model for single crystal deformation behavior with applications  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

262

Ultrasonic characterization of single crystal langatate  

NASA Astrophysics Data System (ADS)

Langatate (LGT), a synthetic piezoelectric crystal with chemical composition La3Ga5.5Ta0.5O14, has recently received significant interest in the sensor and frequency control communities as a possible alternative to quartz owing to its higher piezoelectric coupling, structural stability up to 1400°C and presence of temperature compensated acoustic wave (AW) orientations. With these exciting properties, LGT is expected to find applications in AW sensor, timing, and frequency control. This thesis focuses on the characterization of the acoustic wave material properties of LGT up to 120°C. Such a characterization is critical for the design and fabrication of LGT acoustic wave devices. The elastic and piezoelectric constants were determined through measurements of bulk acoustic wave phase velocities by two independent methods, the pulse echo overlap technique and a combined resonance technique. The extracted constants and temperature coefficients enabled the identification of a range of particularly interesting LGT surface acoustic wave (SAW) orientations with Euler angles (90°, 23°, 118-124°) that exhibits predicted electromechanical coupling up to 0.7% and reduced or zero temperature coefficient of delay (TCD). The consistency of the determined constants and temperature coefficients was established using SAW measurements of seven crystallographic orientations at temperatures ranging up to 120°C. Measured SAW phase velocities and TCDs were found to be in agreement with predictions based on the determined constants. Two of the seven SAW orientations exhibited temperature compensation within 40°C of room temperature, agreeing with predictions. Deposition of SiAlON films on top of LGT SAW devices for surface protection in chemically and mechanically harsh environments was also investigated. SiAlON films deposited by reactive RF magnetron co-sputtering of Al and Si targets were controlled to within a few percent for film thickness and composition. SiAlON thin film clastic constants were extracted using differential SAW delay line methods and were found to be: C11,s = 160 +/- 30 GPa and C44,s = 55 +/- 5 GPa. SiAlON films up to 800 nm in thickness were shown to have no measurable effect on the TCD of LGT SAW delay lines.

Sturtevant, Blake T.

263

Growth of large single crystals of MgO  

SciTech Connect

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.

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

1997-06-12

264

Crystal growth, spectral and laser properties of Nd:LSAT single crystal  

NASA Astrophysics Data System (ADS)

Nd:(La, Sr)(Al, Ta)O3 (Nd:LSAT) crystal was grown by the Czochralski method. The absorption and fluorescence spectra of Nd:LSAT crystal at room temperature were investigated. With a fiber-coupled diode laser as pump source, the continuous-wave (CW) laser action of Nd:LSAT crystal was demonstrated. The result of diode-pumped laser operation of Nd:LSAT crystal single crystal is reported for what is to our knowledge the first time. The maximum output power at 1064 nm was obtained to be 165 mW under the incident pump power of 3 W, with the slope efficiency 10.9%.

Hu, P. C.; Yin, J. G.; Zhao, C. C.; Gong, J.; He, X. M.; Zhang, L. H.; Liang, X. Y.; Hang, Y.

2011-10-01

265

Instability of the single-crystal growth of large-diameter silicon crystals with dislocations  

Microsoft Academic Search

Metallographic, SEM, and X-ray investigations were carried out to elucidate the character and sequence of changes in the growth mechanism and structure of large-diameter (80-150 mm) Czochralski-grown silicon crystals of 111 and 100 line orientations after the termination of growth without dislocations. The single-crystal growth was found to be unstable and to be disrupted by the formation of twins or

N. I. Bletskan; A. N. Buzynin; N. A. Butylkina; Iu. S. Dementev; Iu. M. Litvinov; A. E. Lukianov; V. N. Stepchenkov

1984-01-01

266

Metal insulator semiconductor structure single crystal silicon liquid crystal light valve  

NASA Astrophysics Data System (ADS)

Detailed description of the structure, operation, fabrication, and performance of a fast-response metal- insulator-semiconductor structure single crystal silicon liquid crystal light valve (MIS-Si-LCLV) is given. A 45 degree(s) twisted nematic liquid crystal configuration has been utilized. A MIS-Si-LCLV is demonstrated with a limiting resolution of 40 lp/mm over a 45 mm aperture and contrast ratios of > 50:1, input light sensitivities at (lambda) equals 930 nm ((Delta) (lambda) equals 40 nm) of better than 30 (mu) W/cm2 and response times as fast as 20 ms have been measured.

Gao, JiaoBo; Ye, Ke-fei; Feng, Yue-you

1996-09-01

267

3D numerical simulation of heat transfer during horizontal direct crystallization of corundum single crystals  

NASA Astrophysics Data System (ADS)

This paper describes the numerical simulation of heat transfer in a system for growing corundum single-crystal plates (leucosapphire and ruby) of size 200×200 mm. A mathematical model accounting for the radiative and conductive heat transfer has been developed. Three-dimensional computations have been made with minor simplifications of the furnace geometry. The thermal fields at various positions of the crystal container and the effect of various setup units and their design on the temperature distribution are analyzed. The computed crystallization front shape is compared with the available experimental data. Numerical analysis was used to optimize the hot zone design.

Lukanina, M. A.; Hodosevitch, K. V.; Kalaev, V. V.; Semenov, V. B.; Sytin, V. N.; Raevsky, V. L.

2006-01-01

268

Optimization of the Crystal Surface Temperature Distribution in the Single-Crystal Growth Process by the Czochralski Method  

Microsoft Academic Search

The optimization of the crystal surface temperature distribution is performed for single-crystal growth in the Czochralski process. In the optimization problem, we seek an optimal solution in the sense that the index of crystalline defects is minimized while the single-crystal growth rate is maximized. In the objective function, the von Mises stress is considered a driving force that induces crystalline

Ja Hoon Jeong

2002-01-01

269

Microwave Induced Direct Bonding of Single Crystal Silicon Wafers  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

270

Magnetic heat capacity in lanthanum manganite single crystals  

NASA Astrophysics Data System (ADS)

The heat capacity of single crystal La0.7D0.3MnO3, where D=Ca, Sr, has been measured through the Curie point in fields up to 70 kOe. The magnetic contribution of the Ca sample exhibits a sharp heat capacity peak at TC?218 K in zero field. The peak broadens and decreases in height with increasing field but, unlike an ordinary ferromagnet, the peak shifts substantially in temperature. As a consequence, the heat capacity data cannot be collapsed into a single scaling function. These features indicate that the transition is not an ordinary second-order ferromagnetic transition. Preliminary heat capacity data from the Sr-doped single crystal, with TC?360 K, do not exhibit the same shift in peak position with applied field. We attribute the difference in behavior between Ca- and Sr-doped samples to a change in the nature of the phase transition as TC lowers.

Lin, P.; Chun, S. H.; Salamon, M. B.; Tomioka, Y.; Tokura, Y.

2000-05-01

271

Growth and characterization of terbium fumarate heptahydrate single crystals  

NASA Astrophysics Data System (ADS)

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

Want, B.; Shah, M. D.

2014-03-01

272

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

SciTech Connect

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.

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

273

Crystal morphology characteristics of the domain structure and superconducting properties of 123 single crystals  

Microsoft Academic Search

The characteristics of the domain structure of YBa(2-x)Sr(x)Cu3O(7-delta) single crystals are investigated for x = 0, 0.2, 0.4. and 0.5. A domain structure analysis is also carried out for TmBa(1.5)Sr(0.5)Cu3O(7-delta) single crystals. Various types of domain structure in these materials are identified, and a relationship is established between the domain structure type and the characteristics of the superconducting transition.

A. I. Otko; A. A. Nosenko; O. P. Bal'Va; M. B. Kosmyna; S. F. Prokopovich; A. S. Chernyi

1991-01-01

274

Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

275

Single-crystal CsBr infrared fibers  

NASA Astrophysics Data System (ADS)

A study of the crystal growth, optical losses, and mechanical behavior of single-crystal CsBr infrared fibers is presented. The fibers were grown with a modified pull down technique and showed total losses in the range 2-5 dB/m at 10.6 microns, as well as excess scattering loss from surface imperfections such as growth striations, subgrain boundaries, and flaws. The main absorption loss at the CO2 wavelength is attributed to SO4(2-) ions contained in the raw materials. Because of their yield strength in addition to their flexibility, the (001)-oriented fibers are considered the best mechanically.

Mimura, Y.; Okamura, Y.; Ota, C.

1982-08-01

276

Release melting of shock-loaded single crystal Cu  

NASA Astrophysics Data System (ADS)

We investigate the melting of shock-loaded single crystal Cu during release from solid shock states with molecular dynamics simulations. Cu is subjected to planar shock loading along ?100? with a piston velocity (up) of 2-3 km s-1 into the plastic regime. For up?2.5 km s-1 (above 170 GPa), release melting occurs continuously, and a sustained fully released state (liquid) can be achieved. The shocked crystal may undergo noticeable superheating before release melting. The release path can be regarded as an isentrope regardless of release melting.

Xie, Yun; Han, Li-Bo; An, Qi; Zheng, Lianqing; Luo, Sheng-Nian

2009-03-01

277

Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

278

Fatigue behavior of a single-crystal superalloy  

NASA Technical Reports Server (NTRS)

A single-crystal superalloy, PWA 1480 is under consideration as a replacement material for the turbine blades of the high pressure fuel turbopump (HPFTP) of the space shuttle main engine (SSME). Three separate experimental programs were conducted to characterize the fatigue behavior of this alloy. Fatigue tests were conducted at room temperature (in air) and at 1000 F (in vacuum) on smooth specimens machined from both cast bars and slabs. The data from all of these programs are consolidated to provide a broader characterization of the fatigue behavior of the single crystal PWA 1480. The zero-mean-stress fatigue relationships are expressed in terms of stress range versus cyclic life lines on log-log plots. Characterization of the fatigue behavior of (001) oriented PWA 1480 single crystal under conditions of tensile mean stress was performed by using the unified approach proposed by Heidmann. In this approach the fatigue life is modified by a mean stress parameter so that a single life relationship can be used to represent both zero and tensile mean stress data.

Kalluri, Sreeramesh; Mcgaw, Michael A.

1989-01-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

280

Phase Diagram for Nanostructuring CaF2 Surfaces by Slow Highly Charged Ions  

NASA Astrophysics Data System (ADS)

The impact of individual slow highly charged ions (HCI) on alkaline earth halide and alkali halide surfaces creates nano-scale surface modifications. For different materials and impact energies a wide variety of topographic alterations have been observed, ranging from regularly shaped pits to nanohillocks. We present experimental evidence for the creation of thermodynamically stable defect agglomerations initially hidden after irradiation but becoming visible as pits upon subsequent etching. A well defined threshold separating regions with and without etch-pit formation is found as a function of potential and kinetic energies of the projectile. Combining this novel type of surface defects with the previously identified hillock formation, a phase diagram for HCI induced surface restructuring emerges. The simulation of the energy deposition by the HCI in the crystal provides insight into the early stages of the dynamics of the surface modification and its dependence on the kinetic and potential energies.

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Lemell, C.; Wachter, G.; Burgdörfer, J.; Ritter, R.; Aumayr, F.

2012-09-01

281

Growth of (Na, K, Li)(Nb, Ta)O 3 single crystals by solid state crystal growth  

Microsoft Academic Search

A single crystal of (Na, K, Li)(Nb, Ta)O3 has been grown for the first time by the solid state crystal growth process. A seed crystal of ?001?-oriented KTaO3 was embedded in a matrix of (Na, K, Li)(Nb, Ta)O3 powder, which was then densified by hot-pressing. During annealing of the hot-pressed sample, a single crystal of (Na, K, Li)(Nb, Ta)O3 of

John G. Fisher; Andreja Ben?an; Janez Bernard; Janez Holc; Marija Kosec; Sophie Vernay; Daniel Rytz

2007-01-01

282

Optimization of the parameters affecting the shape and position of crystal–melt interface in YAG single crystal growth  

Microsoft Academic Search

In Czochralski method, the shape of crystal–melt interface and its position play a major role on the quality of single crystals. In the Czochralski crystal growth process having a nearly flat interface, a single crystal with less structural defect, uniform physical properties and homogenous chemical composition is obtained.In the present study, firstly a 2-D fluid flow and solidification model was

Morteza Asadian; S. H. Seyedein; M. R. Aboutalebi; A. Maroosi

2009-01-01

283

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

NASA Astrophysics Data System (ADS)

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

Sankari, R. Siva; Perumal, Rajesh Narayana

2014-04-01

284

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

NASA Technical Reports Server (NTRS)

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.

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

285

Engineering domain configurations for enhanced piezoelectricity in barium titanate single crystals  

E-print Network

Engineering domain configurations for enhanced piezoelectricity in barium titanate single crystals piezoelectric responses of barium titanate single crystals under different crystallographic orientations, and use it to explain the ultrahigh piezoelectric response recently observed in a 270 cut barium titanate

Li, Jiangyu

286

Ultrafast dynamics of excitons in tetracene single crystals  

SciTech Connect

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.

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

287

Constitutive modeling of superalloy single crystals with verification testing  

NASA Technical Reports Server (NTRS)

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.

Jordan, Eric; Walker, Kevin P.

1985-01-01

288

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures  

NASA Technical Reports Server (NTRS)

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.

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

1956-01-01

289

Aging and memory effect in magnetoelectric gallium ferrite single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

290

Ultrafast dynamics of excitons in tetracene single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

291

Ultrafast dynamics of excitons in tetracene single crystals.  

PubMed

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

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

2014-03-21

292

Strontium–barium niobate single crystals, growth and ferroelectric properties  

Microsoft Academic Search

Single crystals of strontium–barium niobate SrxBa1?xNb2O6 (SBN) undoped and doped with Ce or Cr were grown by the Czochralski method. The inductive heating system was used. In order to improve conditions of growth, a crucible-base cooling was introduced. Single crystals of the following nominal compositions have been obtained: Sr0.4Ba0.6Nb2O6, Sr0.5Ba0.5Nb2O6, Sr0.61Ba0.39Nb2O6 (congruent melting) and Sr0.75Ba0.25Nb2O6, designated hereafter as SBN40, SBN50,

T. Lukasiewicz; M. A. Swirkowicz; J. Dec; W. Hofman; W. Szyrski

2008-01-01

293

Challenges for Single-crystal (SX) Crack Cladding  

NASA Astrophysics Data System (ADS)

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.

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

294

High-Quality, Thin-Film Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

Germanium (Ge) has crystallographic characteristics similar to GaAs and compatible with heteroepitaxial growth of GaAs. Further, since efficient heteroface cells already grown on thick Ge single crystals, Ge is excellent substrate candidate for thin-film cells. Required is single-crystal Ge thin film. Method developed for epitaxially growing highquality 10-um Ge thin films on ,100. NaCl substrates by plasma-enhanced chemical-vapor deposition (PECVD) and then separating Ge films by either melt-away or differential-thermal shear stress techniques. Free-standing films used for growth of AlxGa1-xAs/GaAs heteroface cells by similar techniques.

Outlaw, R. A.; Hopson, J., P.

1986-01-01

295

CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes on Si substrates  

NASA Astrophysics Data System (ADS)

CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes have been fabricated by various processes with molecular beam epitaxy in SiO2 windows patterned on Si(111) substrates. Two types of I-V characteristics with negative differential resistance (NDR) were observed in the temperature range from 75 K up to about 200 K. The one is very stable in forward and backward voltage sweeps, and, in contrast to earlier reports, it does not show any hysteresis or trapping effects. Typical diode parameters were: peak voltage Vp = 0.7 V, peak-to-valley current ratio P/V = 1.7 and peak current density Ip = 2 mA cm-2 at 105 K. The second is less stable and the NDR appeared only during forward bias sweeps, possibly due to local trapping effects. But it has larger P/V ratios, the typical parameters being: Vp = 1.2 V,P/V = 5 and Ip = 11 mA cm-2 at 77 K. The observed peak current densities of both NDR types are about five orders of magnitude higher than those reported previously for diodes with the similar structure. We assume that an inhomogeneous Si quantum-well thickness with the current flow localized in small regions of the diode area causes the observed variations in peak voltages, multiple NDR regions, peak spreading and exponentially rising background currents.

Wang, C. R.; Müller, B. H.; Hofmann, K. R.

2003-11-01

296

Properties of salt-grown uranium single crystals.  

SciTech Connect

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.

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

297

Diffusion in single crystals of melilite. I - Oxygen  

Microsoft Academic Search

Oxygen-diffusion coefficients in melilite lattices were estimated by analyzing the structure of O-18 profiles determined in single crystals of gehlenite using SIMS. The lattice diffusion O-coefficients were found to be 2 to 4 orders of magnitude lower than those previously reported by Hayashi and Muehlenbachs (1986) for melilite solid solutions. The reason for these high diffusion rates in melilite solid

Hisayoshi Yurimoto; Masana Morioka; Hiroshi Nagasawa

1989-01-01

298

Evaluation of Gamma-Ray Response of Tm: Single Crystals  

Microsoft Academic Search

Tm3+ doped BaF2 single crystal scintillator has been investigated. Undoped, 0.1, 0.5, and 1% Tm -doped BaF2 are compared in terms of their decay time, light yield, non-proportionality and energy resolution. The fast component of Tm doped BaF2 is characterized by a 5 ~ 6 ns decay time and it can be related to the Tm3+ 5d - 4f VUV

Naoto Abe; Yuui Yokota; Takayuki Yanagida; Noriaki Kawaguchi; Jan Pejchal; Akira Yoshikawa

2010-01-01

299

Electrical resistivity studies of Cr - Ir alloy single crystals  

Microsoft Academic Search

Electrical resistivity has been measured for four Cr - Ir alloy single crystals for concentrations between 0.07 and 0.25 at.% Ir in the temperature range 4 to 1200 K. Well defined magnetic anomalies were observed at the Néel temperature 0953-8984\\/8\\/49\\/035\\/img1 of each alloy as well as at the incommensurate - commensurate (I - C) spin-density-wave (SDW) phase transition temperature of

J. Martynova; H. L. Alberts; P. Smit

1996-01-01

300

The Temperature of a Single Crystal Diamond Tool in Turning  

Microsoft Academic Search

The temperature on the rake face of a single crystal diamond tool in precision turning is investigated experimentally and theoretically. The infrared rays radiated from the contact area between the chip and rake face, and transmitted through the diamond tool, are accepted by a chalcogenide fiber and led to a two-color detector which consists of InSb and HgCdTe detectors. The

Takashi Ueda; Masahiko Sato; Kazuo Nakayama

1998-01-01

301

Single crystal silicon as a low-temperature structural material  

NASA Astrophysics Data System (ADS)

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.

Roach, P. R.

1984-07-01

302

Dislocation generation at surfaces of tin single crystals  

Microsoft Academic Search

Single crystals of 99.999% purityß-tin grown from the melt were shown by X-ray topography to contain dislocations with Burgers vectors of [001] type and of 1\\/2 type. Specimen plates cut roughly parallel to (311) were chemically thinned from 1.25 mm to 100µm thickness and in two cases characteristic dislocation structures were generated at their surfaces. A specimen thinned in concentrated

R. Fiedler; A. R. Lang

1972-01-01

303

Water dissolved in Olivine: A single-crystal infrared study  

Microsoft Academic Search

Polarized infrared spectra of the hydrogen impurities in an olivine single crystal, approximately (Mg0.9Fe0.1)2SiO4, from the Zargabad Island, Red Sea, are reported in the range 4200-3000 cm-1. In the O-H stretching frequency region, two groups of IR absorption bands occur which show the same pleochroism and the same temperature-induced shift between room temperature and 80 K. Each of these IR

Friedemann Freund; Gert Oberheuser

1986-01-01

304

Elastic and Piezoelectric Coefficients of Single-Crystal Barium Titanate  

Microsoft Academic Search

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

Don Berlincourt; Hans Jaffe

1958-01-01

305

Modification of single-crystal sapphire by ion implantation  

Microsoft Academic Search

Some studies have shown that single-crystal sapphire can exhibit a dramatic loss of compressive strength (over 90%) at high temperatures, limiting its use as a shatter-resistant optical window. Other studies have shown that the mechanical behavior of sapphire can be improved by ion implantation, hardening the near-surface region and introducing a compressive stress state, perhaps leading to an increase in

J. D. Demaree; J. K. Hirvonen; S. R. Kirkpatrick; A. R. Kirkpatrick

1997-01-01

306

Pockels effect in yttrium aluminum borate single crystals  

Microsoft Academic Search

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

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

2008-01-01

307

Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces  

Microsoft Academic Search

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

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

1998-01-01

308

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

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.

Jantzen, C.M.

1995-05-09

309

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

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.

Jantzen, Carol M. (Aiken, SC)

1995-01-01

310

Diamond turning of Si and Ge single crystals  

SciTech Connect

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.

Blake, P.; Scattergood, R.O.

1988-12-01

311

Physical properties of CuAlO 2 single crystal  

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

312

Modeling single-crystal microstructure evolution due to shock loading  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

313

Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts  

NASA Technical Reports Server (NTRS)

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.

Arakere, Nagaraj K.

2003-01-01

314

Single crystal plasticity by modeling dislocation density rate behavior  

SciTech Connect

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

Hansen, Benjamin L [Los Alamos National Laboratory; Bronkhorst, Curt [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory; Cerreta, E. K. [Los Alamos National Laboratory; Dennis-Koller, Darcie [Los Alamos National Laboratory

2010-12-23

315

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

316

Suppression of Leakage Current of CdF2/CaF2 Resonant Tunneling Diode Structures Grown on Si(100) Substrates by Nanoarea Local Epitaxy  

NASA Astrophysics Data System (ADS)

CdF2/CaF2 resonant tunneling diode (RTD) structures of 100 nm diameter were fabricated in SiO2 hole arrays formed on Si(100) substrates. RTD structures were grown by molecular beam epitaxy (MBE) in SiO2 hole arrays. After the growth of the initial CaF2 layer at a substrate temperature of 120 °C, in situ annealing at 500 °C was carried out to reduce the density of defects or pinholes in the barrier layer. In the measurement of current-voltage (I-V) characteristics, negative differential resistance (NDR) was clearly demonstrated at room temperature. The peak-to-valley current ratio (PVCR) was 106. The valley current was significantly suppressed. Results obtained here strongly indicates that the RTD structures proposed in this study are promising for high-quality NDR elements compatible with Si LSI technology based on Si(100) substrates.

Kanazawa, Tohru; Morosawa, Atsushi; Fujii, Ryo; Wada, Takafumi; Suzuki, Yusuke; Watanabe, Masahiro; Asada, Masahiro

2007-06-01

317

Acquisition of Single Crystal Growth and Characterization Equipment  

SciTech Connect

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

Maple, M. Brian; Zocco, Diego A.

2008-12-09

318

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

SciTech Connect

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

Sornadurai, D.; Ravindran, T. R.; Paul, V. Thomas; Sastry, V. Sankara [Condensed Matter Physics Division, Materials Science Group, Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu (India); Condensed Matter Physics Division, Materials Science Group (India)

2012-06-05

319

High-power diode-pumped Er3+ :YAG single-crystal fiber laser  

E-print Network

High-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 Er:YAG single-crystal fiber laser. Using an off-axis pumping scheme, CW output powers up to 7.3 W can

Paris-Sud XI, Université de

320

A LIFETIME PREDICTION MODEL FOR SINGLE CRYSTAL SUPERALLOYS SUBJECTED TO THERMOMECHANICAL  

E-print Network

A 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 of nickel based single crystal superalloys. These materials are optimized for creep resistance but are prone

Paris-Sud XI, Université de

321

Operation of multiple 90 switching systems in barium titanate single crystals under electromechanical loading  

E-print Network

Operation of multiple 90° switching systems in barium titanate single crystals under Hysteresis evolution of a 5 5 2 mm3 barium titanate single crystal during a combined electromechanical of barium titanate BaTiO3 single crystals under combined electrical and mechanical loadings was examined

Shu, Yi-Chung

322

Trace element analysis of synthetic mono- and poly-crystalline CaF 2 by ultraviolet laser ablation inductively coupled plasma mass spectrometry at 266 and 193 nm  

Microsoft Academic Search

The analytical figures of merit for ultraviolet laser ablation-inductively coupled plasma mass spectrometry (UV-LA-ICP-MS) at 266 nm with respect to the trace element analysis of high-purity, UV-transmitting alkaline earth halides are investigated and discussed. Ablation threshold energy density values and ablation rates for mono- and poly-crystalline CaF2 samples were determined. Furthermore, Pb-, Rb-, Sr-, Ba- and Yb-specific analysis was performed.

J. Koch; I Feldmann; B Hattendorf; D Günther; U Engel; N Jakubowski; M Bolshov; K Niemax; R Hergenröder

2002-01-01

323

Nanosecond UV laser damage and ablation from fluoride crystals polished by different techniques  

Microsoft Academic Search

Ablation thresholds and damage behavior of cleaved and polished surfaces of CaF2, BaF2, LiF and MgF2 subjected to single-shot irradiation with 248 nm\\/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. For CaF2, standard polishing yields an ablation threshold of typically 20 J\\/cm2. When the surface is polished chemo-mechanically, the threshold can be

M. Reichling; J. Sils; H. Johansen; E. Matthias

1999-01-01

324

Crystal growth and electrical properties of lead indium niobate lead titanate binary single crystal  

NASA Astrophysics Data System (ADS)

The largest Pb(In 1/2Nb 1/2)O 3-PbTiO 3(PIN-PT) binary system single crystal (about 20 mmx10 mm×5 mm, 4.5 g) near the morphotropic phase boundary composition with well-developed (1 0 0) planes was grown by the flux method using PbO-PbF 2-B 2O 3 flux. The PIN-PT(72/28) single crystal was found by simultaneous microdifferential thermal analysis and thermogravimetric analysis to show a peritectic melting at 1283°C with a partial decomposition of the perovskite crystal into a pyrochlore phase, followed by a liquidus point at 1294°C. The electromechanical coupling coefficient in rectangular bar mode, k33'=78%, for phased array ultrasonic transducers was obtained by using the rhombohedral PIN-PT(72/28) single crystal oriented along the [0 0 1] axis. k33'=78% is the highest value reported so far among all the piezoelectric materials with a Tc>250°C and is almost independent of temperature, and even at 200°C decreased only by about 5%. The piezoelectric constant d33=700pC/N was obtained. The relative permittivity ? r decreases after poling. For instance, the ? r value of 2650 before poling, decreases to 1500 after poling.

Yasuda, N.; Ohwa, H.; Kume, M.; Hayashi, K.; Hosono, Y.; Yamashita, Y.

2001-07-01

325

Birefringence measurement of liquid single crystal elastomer swollen with low molecular weight liquid crystal  

NASA Astrophysics Data System (ADS)

We experimentally measured the birefringence of a liquid single crystal elastomer (LSCE) swollen with a low molecular weight liquid crystal (LMWLC), 5CB, by polarizing microscopy as a function of temperature. The optical intensity of swollen LSCE shows significant intensity changes at temperatures TNI, TA and TB that indicates a variety of different transitions. A temperature TNI is known as the apparent nematic-isotropic transition for outside LMWLC, TA and TB are interpreted as the nematic-isotropic transition for LMWLC inside the LSCE and for the swollen LSCE, respectively.

Yusuf, Yusril; Sumisaki, Yusuke; Kai, Shoichi

2003-11-01

326

Hystereses of volume changes in liquid single crystal elastomers swollen with low molecular weight liquid crystal  

NASA Astrophysics Data System (ADS)

The hystereses of volume changes in liquid single crystal elastomers (LSCEs) swollen with a low molecular weight liquid crystal (LMWLC), 5CB, are studied as a function of temperature. The swollen LSCE shows significant hystereses in the volume changes at temperatures TNI and TA during the processes on heating and on cooling, where the temperature TNI is the apparent nematic-isotropic transition for outside LMWLC and TA the nematic-isotropic transition for LMWLC inside the LSCE. No significant hysteresis at TB however can be observed which is the nematic-isotropic phase transition temperature for equilibrium shape of the swollen LSCE (networks).

Yusuf, Yusril; Cladis, P. E.; Brand, Helmut R.; Finkelmann, Heino; Kai, Shoichi

2004-05-01

327

Anisotropic properties of RFe_2Ge2 single crystals  

NASA Astrophysics Data System (ADS)

We have grown RFe_2Ge2 single crystals for R = Y and ten members of the lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The method yields clean, high quality crystal plates as evidenced by residual resistivities and RRR values in the range of 3-12 ?? cm and 20-70 respectively. The crystals are also virtually free of magnetic impurities or secondary phases, allowing the study of the intrinsic anisotropic magnetic behavior of each compound. Characterization was made with X-Ray diffraction, temperature and field dependent magnetization, specific heat and resistivity. Strong anisotropies arising mostly from CEF effects were observed for all magnetic rare earths except Gd. Anti-ferromagnetic ordering occurred at temperatures between 16.5 K (Nd) and 1.25 K (Ho) and for some members there are further well-defined metamagnetic transitions. The calculated effective moments per rare earth atom tend to be larger than the expected values at high temperatures while smaller at low temperatures, probably indicating temperature-dependent contributions of d-band electrons to the magnetic behavior. We acknowledge the help of R. A. Ribeiro and C. Petrovic in the X-Ray diffraction measurements, and K. Myers in the early development and characterization of the crystals. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences.

Avila, M. A.; Bud'Ko, S. L.; Canfield, P. C.

2003-03-01

328

Plastic deformation of Ni{sub 3}Nb single crystals  

SciTech Connect

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.

Hagihara, Kouji; Nakano, Takayoshi; Umakoshi, Yukichi

1999-07-01

329

ESR Study on Irradiated Ascorbic Acid Single Crystal  

SciTech Connect

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.

Tuner, H.; Korkmaz, M. [Hacettepe University, Department of Physics Engineering, Ankara, 06800 (Turkey)

2007-04-23

330

Lithium containing chalcogenide single crystals for neutron detection  

NASA Astrophysics Data System (ADS)

Lithium containing semiconductor-grade chalcogenide single crystals were grown using the vertical Bridgman method. The source material was synthesized from elementary precursors in two steps, (i) preparing the metal alloy LiIn or LiGa, and (ii) reaction with chalcogen - Se or Te. In a number of experiments, enriched 6Li isotope was used for synthesis and growth. The composition and structure of the synthesized materials was verified using powder X-Ray diffraction. The energy band gaps of the crystals were determined using optical absorption measurements. The resistivity of LiInSe2 and LiGaSe2, obtained using current-voltage measurements is on the order of 108-1011 ? cm. Photoconductivity measurement of a yellow LiInSe2 sample showed a peak in the photocurrent around 445 nm. Nuclear radiation detectors were fabricated from single crystal wafers and the responses to alpha particles, neutrons and gammas were measured and presented. It suggests that this material is a promising candidate for neutron detection applications.

Tupitsyn, E.; Bhattacharya, P.; Rowe, E.; Matei, L.; Cui, Y.; Buliga, V.; Groza, M.; Wiggins, B.; Burger, A.; Stowe, A.

2014-05-01

331

Strain incompatibility and residual strains in ferroelectric single crystals  

PubMed Central

Residual strains in ferroelectrics are known to adversely affect the material properties by aggravating crack growth and fatigue degradation. The primary cause for residual strains is strain incompatibility between different microstructural entities. For example, it was shown in polycrystalline ferroelectrics that residual strains are caused due to incompatibility between the electric-field-induced strains in grains with different crystallographic orientations. However, similar characterization of cause-effect in multidomain ferroelectric single crystals is lacking. In this article, we report on the development of plastic residual strains in [111]-oriented domain engineered BaTiO3 single crystals. These internal strains are created due to strain incompatibility across 90° domain walls between the differently oriented domains. The average residual strains over a large crystal volume measured by in situ neutron diffraction is comparable to previous X-ray measurements of localized strains near domain boundaries, but are an order of magnitude lower than electric-field-induced residual strains in polycrystalline ferroelectrics. PMID:23226595

Pramanick, A.; Jones, J. L.; Tutuncu, G.; Ghosh, D.; Stoica, A. D.; An, K.

2012-01-01

332

Strength anomaly in B2 FeAl single crystals  

SciTech Connect

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.

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

1994-12-31

333

Electrical conduction and polarization of calcite single crystals  

NASA Astrophysics Data System (ADS)

The electrical conductivity and polarization properties of calcite single crystals with three orientations, namely, a (00.1) plane perpendicular to the crystallographic c axis (10.0) plane parallel to the crystallographic c axis, and a (10.4) cleavage plane, were studied by both complex impedance and thermally stimulated depolarization current (TSDC) measurements. Conductivities for (00.1)-, (10.0)-, and (10.4)-oriented single calcite crystals at 400-600 °C were 1.16 × 10-7 - 1.05 × 10-5, 7.40 × 10-8 - 4.27 × 10-6, and 4.27 × 10-7 - 2.86 × 10-5 ?-1 m-1, respectively, and the activation energies for conduction were 112, 103, and 101 kJ mol-1, respectively. The TSDC spectra verified the electrical polarizability of calcite crystals. The activation energy for depolarization, estimated from TSDC spectra, of the (00.1)-, (10.0)-, and (10.4)-oriented calcite substrates were 112, 119, and 114 kJ mol-1, respectively. Considering the correlation between the processes of conduction and electric polarization, we proposed the mechanisms of conduction and polarization in calcite on the assumption of oxide ion transport.

Wada, Norio; Horiuchi, Naohiro; Wang, Wei; Hiyama, Tetsuo; Nakamura, Miho; Nagai, Akiko; Yamashita, Kimihiro

2012-10-01

334

Initial testing of a Compact Crystal Positioning System for the TOPAZ Single-Crystal Diffractometer at the Spallation Neutron Source  

Microsoft Academic Search

A precise, versatile, and automated method of orienting a sub-millimeter crystal in a focused neutron beam is required for efficient operation of the TOPAZ Single Crystal Diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory. To fulfill this need, a Compact Crystal Positioning System (CCPS) has been developed in collaboration with Square One Systems Design in Jackson, Wyoming.

Matthew Frost; Christina Hoffmann; Jack Thomison; Mark Overbay; Michael Austin; Peter Carman; Robert Viola; Echo Miller; Lisa Mosier

2010-01-01

335

Initial testing of a Compact Crystal Positioning System for the TOPAZ Single-Crystal Diffractometer at the Spallation Neutron Source  

Microsoft Academic Search

A precise, versatile, and automated method of orienting a sub-millimeter crystal in a focused neutron beam is required for e cient operation of the TOPAZ Single Crystal Di ractometer at the Spallation Neutron Source at Oak Ridge National Laboratory. To ful ll this need, a Compact Crystal Positioning System (CCPS) has been developed in collaboration with Square One Systems Design

Matthew J Frost; Michael D Austin; Robert Viola; Jack Thomison; Peter Carmen; Christina Hoffmann; Echo M Miller; Lisa B Mosier; Mark A Overbay

2009-01-01

336

Electronic properties of graphene-single crystal diamond heterostructures  

SciTech Connect

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.

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

337

Single crystal growth of the spinel-type LiMn 2O 4  

Microsoft Academic Search

Single crystals of the spinel-type LiMn2O4 have been successfully grown by a solvent evaporation flux method at 1173K. The maximum size of the octahedral-shaped single crystal is 0.09×0.09×0.09mm3 along the octahedral edges. The single-crystal X-ray diffraction study confirmed the cubic Fd3?m space group and the lattice parameter of a=8.2483(6)A? of the as-grown single crystal at 297K. The preliminary single-crystal low

Junji Akimoto; Yasuhiko Takahashi; Yoshito Gotoh; Susumu Mizuta

2001-01-01

338

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

NASA Astrophysics Data System (ADS)

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.

Merlini, M.

2013-12-01

339

Preliminary Experiments and Determination of the Thermal Gradient in a 12.7 mm CaF2 Furnace Assembly, Humboldt State University Piston-Cylinder Laboratory  

NASA Astrophysics Data System (ADS)

A 12.7 mm piston-cylinder laboratory has been established at Humboldt State University. A series of double-thermocouple (DTC) experiments were performed to measure the thermal profile of the furnace assembly following the procedures of Pickering et al. (1998, Amer. Min.). Furnace assemblies consist of a 304 stainless base plug, CaF&_{2} sleeve, straight-walled graphite heater tube, crushable MgO inner parts, and lower graphite plug and ring which allow for extrusion of the graphite heater tube during shortening of the sleeve and MgO pieces. Careful measurement of pre- and post-run assembly parts indicate an average 30-35% shortening of the assembly. DTC results show a thermal peak that is displaced \\sim2.0 mm above the center of the effective furnace, defined as the length of inner MgO pieces post-run. This offset is in the same direction (upward, toward base plug), but slightly less than the offset described by Pickering et al. (1998). A secondary measure of the thermal profile using spinel growth via reaction between MgO and Al_{2}O_{3} assembly parts (e.g., Watson et al., 2002, CMP) is underway. A single partial melting experiment was performed at 1.0 GPa and 1330\\degC for 72 hours using intermediate peridotite starting material INT-A in a graphite-lined Pt capsule with vitreous carbon spheres as a melt sink. Phase compositions were determined by electron microprobe and mass balance calculations were made to determine melt fraction and mineral mode. Initial calculations yield glass:olivine:cpx:opx:spinel proportions of: 5.0:54.2:15.9:23.9:1.1. These preliminary results correspond well with previous work performed at the University of Oregon on the same starting material (Schwab and Johnston, 2001). The best match is with a 1315\\degC experiment (INT-A13) in terms of mode (6.9:53.7:13.4:25.0:1.0) and glass composition, indicating that the temperature of this initial experiment may be slightly cooler than the target temperature, however the results of this interlaboratory comparison are still within the \\pm10-15\\deg$C temperature uncertainty of the piston cylinder apparatus. Additional calibration experiments are ongoing.

Schwab, B. E.

2004-12-01

340

Molecular beam epitaxial growth of Eu-doped CaF2 and BaF2 on Si X. M. Fang, T. Chatterjee, and P. J. McCann  

E-print Network

and BaF2 on Si was carried out in an Intevac Modular GEN II MBE system with a back- ground pressure of 10-based technol- ogy. Nd- and Er-doped CaF2 films grown on Si substrates by molecular beam epitaxy MBE have that Eu can be incorporated into epitaxial CaF2 films grown on Si 100 by MBE and that Eu doping as high

McCann, Patrick

341

Polarised IR-microscope spectra of guanidinium hydrogensulphate single crystal.  

PubMed

Polarised IR-microscope spectra of C(NH(2))(3)*HSO(4) small single crystal samples were measured at room temperature. The spectra are discussed on the basis of oriented gas model approximation and group theory. The stretching nuOH vibration of the hydrogen bond with the Ocdots, three dots, centeredO distance of 2.603A gives characteristic broad AB-type absorption in the IR spectra. The changes of intensity of the AB bands in function of polariser angle are described. Detailed assignments for bands derived from stretching and bending modes of sulphate anions and guanidinium cations were performed. The observed intensities of these bands in polarised infrared spectra were correlated with theoretical calculation of directional cosines of selected transition dipole moments for investigated crystal. The vibrational studies seem to be helpful in understanding of physical and chemical properties of described compound and also in design of new complexes with exactly defined behaviors. PMID:16458584

Drozd, M; Baran, J

2006-07-01

342

Crystal oscillators using negative voltage gain, single pole response amplifiers  

NASA Technical Reports Server (NTRS)

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.

Kleinberg, Leonard L. (Inventor)

1989-01-01

343

Stem Cell Labeling using Polyethylenimine Conjugated (?-NaYbF4:Tm3+)/CaF2 Upconversion Nanoparticles  

PubMed Central

We report on a polyethylenimine (PEI) covalently conjugated (?-NaYbF4:Tm3+)/CaF2 upconversion nanoparticle (PEI-UCNP) and its use for labeling rat mesenchymal stem cells (rMSCs). The PEI-UCNPs absorb and emit near-infrared light, allowing for improved in vivo imaging depth over conventional probes. We found that such covalent surface conjugation by PEI results in a much more stable PEI-UCNP suspension in PBS compared to conventional electrostatic layer by layer (LbL) self-assembling coating approach. We systematically examined the effects of nanoparticle dose and exposure time on rat mesenchymal stem cell (rMSC) cytotoxicity. The exocytosis of PEI-UCNPs from labeled rMSCs and the impact of PEI-UCNP uptake on rMSC differentiation was also investigated. Our data show that incubation of 100-µg/mL PEI-UCNPs with rMSCs for 4 h led to efficient labeling of the MSCs, and such a level of PEI-UCNP exposure imposed little cytotoxicity to rMSCs (95% viability). However, extended incubation of PEI-UCNPs at the 100 µg/mL dose for 24 hour resulted in some cytotoxicity to rMSCs (60% viability). PEI-UCNP labeled rMSCs also exhibited normal early proliferation, and the internalized PEI-UCNPs did not leak out to cause unintended labeling of adjacent cells during a 14-day transwell culture experiment. Finally, PEI-UCNP labeled rMSCs were able to undergo osteogenic and adipogenic differentiation upon in vitro induction, although the osteogenesis of labeled rMSCs appeared to be less potent than that of the unlabeled rMSCs. Taken together, PEI-UCNPs are promising agents for stem cell labeling and tracking. PMID:23606911

Zhao, Liang; Kutikov, Artem; Shen, Jie; Duan, Chunying; Song, Jie; Han, Gang

2013-01-01

344

Accelerated damage to blank and antireflectance-coated CaF2 surfaces under 157-nm laser irradiation  

NASA Astrophysics Data System (ADS)

Successful insertion of 157-nm lithography into production requires that materials comprising the optical train meet the lifetime requirements of the industry. At present, no degradation of bulk fluoride materials has been observed for at least up to 109 pulses. However, last year we reported on the surface damage to fluoride materials that appeared after 3-4x109 pulses at moderate fluences of 3-4 mJ/cm2/pulse2. This damage manifested itself as a precipitous transmission drop of up to 50% at 157 nm and was accompanied by the formation of a porous rough surface layer about 0.20 ?m thick. Understanding this surface damage is important for the durability of laser windows and beam delivery optics, and it may also help elucidate fundamental 157-nm photophysics of fluoride surfaces. To understand the underlying phenomena, we have designed and constructed a new accelerated damage test chamber. The chamber utilizes 157-nm light from a lithography-grade laser operating at 1000 Hz. Inside the chamber, light is focused onto the sample to a submillimeter spot size. The chamber allows us to test in-situ transmission of multiple spots on a given sample over a range of fluences up to 140 mJ/cm2/pulse without breaking purge. We have used this chamber to understand the scaling of the damage mechanism for both uncoated and antireflectance (AR) -coated CaF2 samples as a function of laser repetition rate and fluence. Substrate damage appears to be governed by a complex set of mechanisms, both thermal and non-thermal in origin. Preliminary damage studies of AR-coated substrates show that AR-coating related degradation occurs well before the onset of the substrate surface damage.

Liberman, Vladimir; Rothschild, Mordechai; Palmacci, Stephen T.; Efremow, Nikolay N.; Sedlacek, Jan H. C.; Grenville, Andrew

2003-06-01

345

Structures of BaF2-CaF2 heterolayers and their influences on ionic conductivity.  

PubMed

Recently, artificial ion conductors have been prepared by growing epitaxial heterolayers consisting of BaF2-CaF2 using molecular beam epitaxy. The ionic conductivity of these heterolayers shows a strong dependence on the layer thickness [N. Sata, S. Eberman, K. Eberl, and J. Maier, Nature 408, 996 (2000)]. In this paper three such heterolayers with different spacings (sample A: 80 nm, sample B: 10 nm, sample C: 1 nm) are investigated by conventional transmission electron microscopy and high-resolution transmission electron microscopy. The spacings are chosen such that they fall into the three conductivity regimes observed in N. Sata et al. (l > 50 nm; 8 < l < 50 nm; l < 8 nm). In accordance with conductivity studies, the samples with spacings of 10 nm or greater (A,B) are epitaxial and continuous, whereas in the case of extremely small spacing (C) the continuity of the layers is destroyed by formation of a column-like structure. Analytical electron microscopy reveals that, instead of forming multilayers, Ca and Ba separate in different columns in sample C. The structure properties of sample A (large l) are quite ideal: Planar interfaces with regular arrays of misfit dislocations with their Burgers vectors on the interface are observed. In the case of sample B (medium l) the lattice misfit is accommodated, in addition, by wavy interfaces associated with dislocations characterized by a Burgers vector that makes a large angle to the interfaces. The (111) lattice spacing very close to the interfaces is markedly changed due to this novel relaxation mechanism in the multilayer. The influences of the crystallographic defects on the ionic conductivity are also discussed. PMID:15268377

Jin-Phillipp, N Y; Sata, N; Maier, J; Scheu, C; Hahn, K; Kelsch, M; Ruhle, M

2004-02-01

346

Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate.  

PubMed

Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product. PMID:22069168

Kim, Yi-Yeoun; Hetherington, Nicola B J; Noel, Elizabeth H; Kröger, Roland; Charnock, John M; Christenson, Hugo K; Meldrum, Fiona C

2011-12-23

347

Single crystal growth and characterization of binary stoichiometric and Al-rich Ni 3Al  

Microsoft Academic Search

Binary stoichiometric Ni3Al (Ni–25at% Al) single crystals and Al-rich single-crystal-like (Ni–26at% Al, Ni–27at% Al) alloys that do not contain any ternary additions have been successfully grown for the first time, by using the floating zone method. The quality of the crystals was examined by the Laue X-ray back-reflection method and optical microscopy. The stoichiometric single crystals had good crystallinity. The

D. Golberg; M Demura; T Hirano

1998-01-01

348

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

SciTech Connect

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

Prokhorov, I. A., E-mail: igor.prokhorov@mail.ru [Russian Academy of Sciences, Research Center “Space Materials Science”, Shubnikov Institute of Crystallography, Kaluga Branch (Russian Federation); Ralchenko, V. G.; Bolshakov, A. P.; Polskiy, A. V.; Vlasov, A. V. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation); Subbotin, I. A.; Podurets, K. M.; Pashaev, E. M.; Sozontov, E. A. [National Research Centre “Kurchatov Institute” (Russian Federation)

2013-12-15

349

Field emission properties of single crystal chromium disilicide nanowires  

SciTech Connect

The composition, crystal structure, and field emission properties of high-crystallinity chromium disilicide (CrSi{sub 2}) nanowires synthesized by a vapor deposition method have been studied. High resolution transmission electron microscopy, energy dispersive spectroscopy, and selected area electron diffraction studies confirm the single-crystalline structure and composition of the CrSi{sub 2} nanowires. Field emission measurements show that an emission current density of 0.1 {mu}A/cm{sup 2} was obtained at a turn-on electric field intensity of 2.80 V/{mu}m. The maximum emission current measured was 1.86 mA/cm{sup 2} at 3.6 V/{mu}m. The relation between the emission current density and the electric field obtained follows the Fowler-Nordheim equation, with an enhancement coefficient of 1140. The electrical conductivity of single nanowires was measured by using four-point-probe specialized microdevices at different temperatures, and the calculated values are close to those reported in previous studies for highly conductive single crystal bulk CrSi{sub 2}. The thermal tolerance of the nanowires was studied up to a temperature of 1100 Degree-Sign C. The stability of the field emission current, the I-E values, their thermal tolerance, and high electrical conductivity make CrSi{sub 2} nanowires a promising material for field emission applications.

Valentin, L. A.; Carpena-Nunez, J.; Yang, D.; Fonseca, L. F. [Department of Physics, University of Puerto Rico, Rio Piedras Campus, P.O. Box 70377, San Juan, 00931 (Puerto Rico)

2013-01-07

350

Magnetic heat capacity in lanthanum manganite single crystals  

SciTech Connect

The heat capacity of single crystal La{sub 0.7}D{sub 0.3}MnO{sub 3}, where D=Ca, Sr, has been measured through the Curie point in fields up to 70 kOe. The magnetic contribution of the Ca sample exhibits a sharp heat capacity peak at T{sub C}(approx =)218 K in zero field. The peak broadens and decreases in height with increasing field but, unlike an ordinary ferromagnet, the peak shifts substantially in temperature. As a consequence, the heat capacity data cannot be collapsed into a single scaling function. These features indicate that the transition is not an ordinary second-order ferromagnetic transition. Preliminary heat capacity data from the Sr-doped single crystal, with T{sub C}{approx_equal}360 K, do not exhibit the same shift in peak position with applied field. We attribute the difference in behavior between Ca- and Sr-doped samples to a change in the nature of the phase transition as T{sub C} lowers. (c) 2000 American Institute of Physics.

Lin, P. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States); Chun, S. H. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States); Salamon, M. B. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States); Tomioka, Y. [Joint Research Center for Atom Technology, 1-1-4 Higashi, Tsukuba 305-0046, (Japan)] [Joint Research Center for Atom Technology, 1-1-4 Higashi, Tsukuba 305-0046, (Japan); Tokura, Y. [Joint Research Center for Atom Technology, 1-1-4 Higashi, Tsukuba 305-0046, (Japan)] [Joint Research Center for Atom Technology, 1-1-4 Higashi, Tsukuba 305-0046, (Japan)

2000-05-01

351

Experiment MA-028 crystal growth. [low gravity manufacturing of single crystals from Apollo/Soyuz Test Project  

NASA Technical Reports Server (NTRS)

A crystal growth experiment is reported on orbital space flights. The experiment was performed during the Apollo-Soyuz Test Project. The Crystal Growth Experiment assessed a novel process for growing single crystals of insoluble substances by allowing two or more reactant solutions to diffuse toward each other through a region of pure solvent in zero gravity. The experiment was entirely successful and yielded crystals of about the expected size, quality, and number.

Lind, D. M.

1976-01-01

352

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

PubMed

Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, viz., Li(+)inic(-)·S (where S = 0.5 morpholine, 0.5 dioxane, 0.25 n-hexanol, 0.5 N-methylpyrrolidinone, 0.5 N,N-dimethylformamide, 0.5 n-propanol, 0.5 cyclohexanol, 0.5 pyridine, 0.5 t-butanol, 0.5 ethanol, and 0.5 methanol). Three-dimensional Li(+)inic(-) frameworks containing solvent-filled channels are present in all of these except for the MeOH and EtOH solvates. The nondirectional character of the electrostatic interactions between the Li(+) and inic(-) ions bestows an element of "plasticity" upon the framework, manifested in the observation of no less than five different framework structures within the family. Unusual single-crystal-to-single-crystal transformations accompany desolvation of Li(+)inic(-)·S in which the Li(+)inic(-) framework undergoes a major rearrangement (from a structure containing "8484 chains" to one with "6666 chains"). The "before and after" structures are strongly suggestive of the mechanism and the driving force for these solid state framework rearrangements: processes which further demonstrate the "plasticity" of the ionic Li(inic) framework. A solid-state mechanism for these desolvation processes that accounts very satisfactorily for the formation of the channels and for the diverse geometrical/topological aspects of the transformation is proposed. The reverse process allows the regeneration of the solvated 8484 form. When the 6666 Li(+)inic(-) form is immersed in carbon disulfide, a single-crystal-to-single-crystal transformation occurs to generate Li(+)inic(-)·0.25CS2. The hydrate, Li(+)inic(-)·2H2O which consists of discrete Li(inic)·H2O chains obtained by recrystallizing the salt from water, can also be obtained by hydration of the 6666 form. A dense 3D network with the formula, Li(inic) can be obtained in a reversible process by the removal of the water from the hydrated form and also by crystallization from a t-amyl alcohol solution. PMID:24811943

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

2014-05-19

353

Shock response of He bubbles in single crystal Cu  

NASA Astrophysics Data System (ADS)

With large-scale molecular dynamics simulations, we investigate shock response of He nanobubbles in single crystal Cu. For sufficient bubble size or internal pressure, a prismatic dislocation loop may form around a bubble in unshocked Cu. The internal He pressure helps to stabilize the bubble against plastic deformation. However, the prismatic dislocation loops may partially heal but facilitate nucleation of new shear and prismatic dislocation loops. For strong shocks, the internal pressure also impedes internal jetting, while a bubble assists local melting; a high speed jet breaks a He bubble into pieces dispersed among Cu. Near-surface He bubbles may burst and form high velocity ejecta containing atoms and small fragments, while the ejecta velocities do not follow the three-dimensional Maxwell-Boltzmann distributions expected for thermal equilibrium. The biggest fragment size deceases with increasing shock strength. With a decrease in ligament thickness or an increase in He bubble size, the critical shock strength required for bubble bursting decreases, while the velocity range, space extension and average velocity component along the shock direction, increase. Small bubbles are more efficient in mass ejecting. Compared to voids and perfect single crystal Cu, He bubbles have pronounced effects on shock response including bubble/void collapse, Hugoniot elastic limit (HEL), deformation mechanisms, and surface jetting. HEL is the highest for perfect single crystal Cu with the same orientations, followed by He bubbles without pre-existing prismatic dislocation loops, and then voids. Complete void collapse and shear dislocations occur for embedded voids, as opposed to partial collapse, and shear and possibly prismatic dislocations for He bubbles. He bubbles lower the threshhold shock strength for ejecta formation, and increase ejecta velocity and ejected mass.

Li, B.; Wang, L.; E, J. C.; Ma, H. H.; Luo, S. N.

2014-12-01

354

Upconverted fluorescence in Nd3+-doped barium chloride single crystals  

NASA Astrophysics Data System (ADS)

Upon excitation at 796 nm, Nd3+-doped BaCl2 single crystals show several upconverted fluorescence bands in the visible spectral range, with the most intense bands at 530, 590 and 660 nm, in addition to the typical fluorescence bands in the infrared spectral range. The power dependence of the infrared fluorescence and the two-photon upconversion fluorescence intensities as well as the corresponding radiative lifetimes have been investigated. No 'saturation' of the fluorescence intensities was observed upon increasing the excitation power.

Ahrens, B; Miclea, P T; Schweizer, S

2009-03-01

355

EPR studies of gamma-irradiated taurine single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2000-04-01

356

High temperature hardness of bulk single crystal GaN  

SciTech Connect

The hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5 N in the temperature range 20--1,200 C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.

Yonenaga, I.; Hoshi, T.; Usui, A.

2000-07-01

357

Mechanical properties of ZnSe : Cr2+ single crystals  

NASA Astrophysics Data System (ADS)

The microhardness of single-crystal samples of ZnSe: Cr2+ with a chromium concentration in the range from 3.3 × 1017 to 4.0 × 1019 cm-3 has been studied. The microhardness as a function of the load on the indenter on the faces (111), (1bar 10), and (001) of the ZnSe: Cr2+ and ZnSe samples has been measured. It has been established that doping of zinc selenide with chromium leads to a decrease in the anisotropy of the mechanical properties and stabilization of the cubic sphalerite structure.

Fedorenko, O. A.; Zagoruiko, Yu. A.; Kovalenko, N. O.

2012-11-01

358

Constitutive modeling of creep of single crystal superalloys  

E-print Network

[43] on another ?rst generation single crys- tal nickel based superalloy MAR-M 247 at temperature 774 oC showed that crystals having orientations within 25o of the orientation exhibited signi?cantly longer creep lives when their orientations were... closer to the / boundary of the stereographic triangle than to the / boundary. These observations were in accordance with the results for the creep of MAR-M200 ([37, 41]), the only dif- ference being that MAR-M 247 showed best creep...

Prasad, Sharat Chand

2006-10-30

359

Photoconductivity of iodine-doped single crystals of phthalocyanine  

Microsoft Academic Search

Single crystals of metal-free phthalocyanine (H2Pc) and of copper phthalocyanine (CuPc) were grown in the presence of iodine vapour. The presence of iodine enhances the spectral\\u000a dependence of photoconductivity of H2Pc in the visible region but of CuPc in the near-IR region. The dark current is decreased but the photocurrent is increased\\u000a by one order of magnitude in iodine-doped H2Pc

Francis P Xavier; George J Goldsmith

1995-01-01

360

Channeling study of high-Tc superconducting single crystal sublattices  

Microsoft Academic Search

Backscattering of H, 4He, 3He ions, X-ray radiation and the nuclear reactions 16O(4He, 4He)16O, 18O(p, alpha)15N, 16O(3He, 4He)15O, 7Li(p, alpha)4He, etc., in combination with orientation effects have been used to investigate the structure and properties of the single crystals Nd2-xCexCuO4(T'-phase) and La2-xSrxCuO4 (T-phase). The possibility of a selective study of cation and onion sublattices, as well as oxygen O1, O2

N. A. Shakun; A. Yu. Grinchenko; A. S. Deev; V. I. Makarov; V. A. Olejnik; P. A. Svetashov; R. P. Slabospitsky; N. F. Shul'Ga

1992-01-01

361

A macroscopic model for magnetic shape-memory single crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

362

Polarization-dependent exciton dynamics in tetracene single crystals  

E-print Network

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.

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

2014-01-01

363

Polarization-dependent exciton dynamics in tetracene single crystals.  

PubMed

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

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

2014-12-28

364

Polarization-dependent exciton dynamics in tetracene single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

365

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

366

Acoustic and thermal properties of strontium pyroniobate single crystals  

NASA Astrophysics Data System (ADS)

High resolution Brillouin scattering and modulated differential scanning calorimetry (MDSC) experiments were performed to study the acoustic and thermal properties of strontium pyroniobate (Sr2Nb2O7) single crystals. The anomalous temperature dependence of the longitudinal acoustic phonon mode frequency corresponding to c22 elastic stiffness coefficient was observed in the neighbourhood of the normal-incommensurate phase transition temperature Ti (491 K). The specific heat measured by MDSC showed an anomaly around 487+/-2 K. The changes in enthalpy and entropy of the phase transition were estimated as 147 J mol-1 and 0.71 J mol-1 K-1, respectively.

Shabbir, G.; Kojima, S.

2003-04-01

367

Single-crystal elasticity of fayalite to 12 GPa  

Microsoft Academic Search

Single-crystal elastic constants of a natural Fe-rich olivine (Fe0.94Mn0.06)2SiO4 were determined by Brillouin scattering to 12.1 GPa. The aggregate bulk modulus, shear modulus, and their pressure derivatives are KS0 = 136.3 (2) GPa, G0 = 51.2 (2) GPa, (?KS\\/?P)T0 = 4.9 (1), (?G\\/?P)0 = 1.8 (1), and (?2G\\/?P2)0 = ?0.11 (1) GPa?1. The numbers in parentheses are 1? uncertainties on

Sergio Speziale; Thomas S. Duffy; Ross J. Angel

2004-01-01

368

Titanium vacancies in nonstoichiometric TiO2 single crystal  

NASA Astrophysics Data System (ADS)

The semiconducting properties of single-crystal TiO2 and their changes during prolonged oxidation at elevated temperatures and under controlled oxygen activity were monitored using measurements of electrical conductivity and thermo-electric power. Two kinetic regimes were revealed: Regime I - rapid oxidation, associated with the transport of oxygen vacancies, and Regime II - prolonged oxidation, which corresponds to the transport of titanium vacancies. The present data represent the first documented evidence for the formation and transport of titanium vacancies in TiO2. This finding allows the processing of p-type TiO2 without the incorporation of aliovalent foreign ions.

Nowotny, M. K.; Bak, T.; Nowotny, J.; Sorrell, C. C.

2005-09-01

369

Deformation behavior of PZN-6%PT single crystal during nanoindentation  

Microsoft Academic Search

The deformation behavior of [001]- and [011]-cut single crystal solid solution of Pb(Zn1\\/3Nb2\\/3)O3–6% PbTiO3 (PZN–6%PT) in both unpoled and poled states has been investigated by nanoindentation. Nanoindentation experiments reveal that material pile-up and local damage around the indentation impressions are observed at ultra-low loads. These pile-ups and local damage cause a pop-in event (i.e. a sudden increase in displacement at

M. F. Wong; K. Zeng

2008-01-01

370

Single crystal NMR studies of high temperature superconductors  

SciTech Connect

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.

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

1989-01-01

371

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

NASA Astrophysics Data System (ADS)

Knowledge of rheological properties of Earth's materials is essential to understand geological processes. Open questions are the water content and crystallographic orientation dependences of dislocation creep rate, because the dominant slip system changes with increasing water content, which suggest different dislocations have different water content dependence. This project focuses on olivine, which is the most abundant mineral of the upper mantle. It is also considered to be the weakest phase and hence should control the rheology of the upper mantle. Several slip systems were reported for olivine, which are [100](010), [001](010), [001](100) and [100](001), each of which appear under different water content and stress conditions [1]. For this purpose we started to obtain data for 'dry' conditions, providing basic knowledge to understand the effect of water. Variation in dislocation creep rate according to change in physical conditions can be estimated by dislocation recovery experiments [2]. In this technique, deformed crystals are annealed, in which the dislocation density is expected to decrease due to coalescence of two dislocations. Dislocation densities are measured before and after the annealing. Dislocation mobility, which should be directly proportional to the dislocation creep rate, is estimated based on the change in dislocation density and duration of annealing. This technique has significant advantages partly because informations of strain rate and deviatoric stress, which are difficult to measure, are unnecessary, and partly because dislocation annealing is conducted under quasi-hydrostatic conditions, which allows wide ranges of P and T conditions. The first step of the experiments is to deform a single crystal of olivine. For this purpose, we developed an assembly, which deforms a single crystal in simple-shear geometry and prevent breakage, sub-grain formation and recrystallization of the crystal. Olivine single-crystals were placed in the high-pressure assembly so that a particular slip system is activated. The assemblies were compressed to 3 GPa. The shear deformation was conducted at 1600 K. EBSD measurements indicate that the recovered crystals are single crystals and sub-grain formation did not occur in most cases. The second step is to anneal the samples under the same P-T conditions as those of the deformation experiments. Annealing experiments are also performed at ambient pressures at 1600 K. Dislocation density was measured by means of the oxidation decoration technique [3]. The samples were firstly polished and then oxidized at 1200 K for 50 min. The dislocations are preferably oxidized, so that presence of dislocation can be observed using SEM. First Results indicate that the dislocation density decreased by annealing by 1/4 with an annealing period of 10 h for dislocations with b = [001]. References [1] H. Jung and S. I. Karato. Water-induced fabric transitions in olivine. Science, 293(5534):1460-1463, 2001. [2] S. I. Karato, D. C. Rubie, and H. Yan. Dislocation recovery in olivine under deep upper mantle conditions: Implications for creep and diffusion. Journal of Geophysical Research, 98(B6):9761-9768, 1993. [3] D. L. Kohlstedt, C. Goetze, W. B. Durham, and J. V. Sande. New technique for decorating dislocations in olivine. Science, 191(4231):1045-1046, March 1976.

Blaha, Stephan; Katsura, Tomoo

2013-04-01

372

Electrical Properties and Surface Microtopographic Studies of Tungsten Disulfide Single Crystals Grown by CVT Technique  

Microsoft Academic Search

The single crystals of tungsten disulphide (WS2) were grown by chemical vapor transport (CVT) technique, using iodine as the transporting agent. The stoichiometric composition and the crystallographic lattice parameters of the grown crystals were determined by EDAX and X?ray diffraction (XRD) techniques, respectively. The Hall effect measurement and the Seebeck coefficient variation with temperature confirmed that the single crystals were

Sunil Chaki; Ajay Agarwal

2008-01-01

373

P-137 / P. Xu P-137: Photoaligned Transflective Liquid Crystal Display with Single Cell Gap  

E-print Network

Transflective liquid crystal display (LCD) with single cell gap consisting optically compensated bend (OCBP-137 / P. Xu P-137: Photoaligned Transflective Liquid Crystal Display with Single Cell Gap using brightness and high contrast could be obtained. 1. Introduction Recently, transflective liquid crystal

374

DESIGN NOTE: Single-crystal growth by the submerged heater method  

Microsoft Academic Search

A novel method of single-crystal growth from the melt is proposed. Single crystals are grown by directional solidification in vertical bottom-seeded crucibles. The heat is supplied to the melt by an axial submerged heater located close to the growth interface. The crucible is insulated radially. The portion of the melt enclosed between the heater and the growing crystal is thermally

A. G. Ostrogorsky

1990-01-01

375

Germanium–silicon single crystal growth by the axial heat processing (AHP) technique  

Microsoft Academic Search

Bulk Germanium–Silicon single crystal alloys have been grown using a novel crystal growth technique called Axial Heat Processing (AHP). The technique includes an immersed baffle which divides melt into two regions, decreases the melt height, and distributes the heat over the entire growth interface. Two silicon doped germanium single crystals with 12 atomic percent concentration have been grown by the

Aidin Dario; Hasan Ozgen Sicim; Ercan Balikci

2011-01-01

376

Sm^Nd dating of spatially controlled domains of garnet single crystals: a new method of  

E-print Network

Sm^Nd dating of spatially controlled domains of garnet single crystals: a new method of high of the method using the core and bulk ages of garnet single crystals, according to the Sm^Nd decay system exposure of the Salinian terrane, California. We have micro-sampled the garnet crystals over specific

Ganguly, Jibamitra

377

Piezoelectric properties of lithium modified silver niobate perovskite single crystals  

NASA Astrophysics Data System (ADS)

We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1-xLixNbO3. It possesses a rhombohedral structure with high ferroelectric phase transition (Tc=548K for x =0.086) and large spontaneous polarization (Ps˜40?C/cm2 for x =0.062) along the ?111?c direction of pseudocubic perovskite structure for x >0.05-0.06. High quasistatic d33˜210pC/N and low dielectric constant have lead to a very large value of piezoelectric voltage constant g33˜53.9×10-3Vm/N for the ?001?c-cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics.

Fu, Desheng; Endo, Makoto; Taniguchi, Hiroki; Taniyama, Tomoyasu; Koshihara, Shin-ya; Itoh, Mitsuru

2008-04-01

378

Pockels effect in yttrium aluminum borate single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2008-10-01

379

Single-polarization single-mode photonic crystal fiber based on index-matching coupling with a single silica material  

NASA Astrophysics Data System (ADS)

We propose and analyze a novel design of single-polarization single-mode photonic crystal fiber based on index-matching coupling by using a finite-element method. The proposed fiber is designed such that there is a large differential loss between two polarizations of the fundamental mode by reducing two air holes in the cladding region which is composed of hexagonal structured air holes in pure silica. From the numerical analysis it is shown that single-polarization single-mode operation wavelength region can be tuned by adjusting the diameters of two defect air holes. In the proposed design, the spectral region over which the differential loss ratio is larger than 100 can be wider than 150 nm around the wavelength 1.55 or 1.31 ?m. Another novel design that allows simultaneous single-polarization single-mode guidance in two wavelength windows centered at 1.55 and 1.31 ?m is also proposed.

Lee, Sun-Goo; Lim, Sun Do; Lee, Kwanil; Lee, Sang Bae

2011-01-01

380

Ablation of ionic crystals induced by capillary-discharge XUV laser  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

381

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

PubMed

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

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

2014-01-24

382

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

383

Joint Development of a Fourth Generation Single Crystal Superalloy  

NASA Technical Reports Server (NTRS)

A new, fourth generation, single crystal superalloy has been jointly developed by GE Aircraft Engines, Pratt & Whitney, and NASA. The focus of the effort was to develop a turbine airfoil alloy with long-term durability for use in the High Speed Civil Transport. In order to achieve adequate long-time strength improvements at moderate temperatures and retain good microstructural stability, it was necessary to make significant composition changes from 2nd and 3rd generation single crystal superalloys. These included lower chromium levels, higher cobalt and rhenium levels and the inclusion of a new alloying element, ruthenium. It was found that higher Co levels were beneficial to reducing both TCP precipitation and SRZ formation. Ruthenium caused the refractory elements to partition more strongly to the ' phase, which resulted in better overall alloy stability. The final alloy, EPM 102, had significant creep rupture and fatigue improvements over the baseline production alloys and had acceptable microstructural stability. The alloy is currently being engine tested and evaluated for advanced engine applications.

Walston, S.; Cetel, A.; MacKay, R.; OHara, K.; Duhl, D.; Dreshfield, R.

2004-01-01

384

Tribological properties of sintered polycrystalline and single crystal silicon carbide  

NASA Technical Reports Server (NTRS)

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.

Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

1982-01-01

385

Single Crystal Si Passive Optical Components for mm-Astronomy  

NASA Astrophysics Data System (ADS)

Construction of ultrasensitive, cryogenic-focal-planes for mm-radiation detection requires simultaneous maximization of detector quantum efficiency and minimization of stray light effects, e.g., optical ``ghosting''. To achieve this task in the focal plane detector arrays of the Atacama Cosmology Telescope, integration of two technologies are envisioned; (1) an antireflective (AR) coating for reducing ghosting from the reflected component and increasing absorption at the focal plane, and (2) a backside absorber for suppressing reflections of the transmitted component. We propose a novel approach, involving single crystal Si components, to fabricate AR coatings and backside absorbers. AR coatings are made from Si dielectric honeycombs, in which their dielectric constant may be tuned via honeycomb dimension and wall thickness. Backside absorbers consist of AR Si honeycomb coated-resistors, and the resistors consist of P-implanted Si wafers. This approach enables us to circumvent the mechanical complexities arising from thermal expansion effects, because the detector array, back-short, and AR coating are fabricated out of the same material. We also extend the functionality of single crystal Si in the field of mm-radiation detection by fabricating curved, low-loss, broadband waveguides. These waveguides may enable compact structures for applications requiring variable pathlength, e.g., interferometric spectroscopy.

Brown, Ari; Chervenak, James; Chuss, David; Wollack, Edward; Henry, Ross; Moseley, S. Harvey

2006-03-01

386

Self-assembled single-crystal silicon circuits on plastic  

NASA Astrophysics Data System (ADS)

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. macroelectronics | plastic electronics | self-assembly

Stauth, Sean A.; Parviz, Babak A.

2006-09-01

387

Process for Making Single-Domain Magnetite Crystals  

NASA Technical Reports Server (NTRS)

A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

2004-01-01

388

Growth and properties of Lithium Salicylate single crystals  

SciTech Connect

An attractive feature of {sup 6}Li containing fluorescence materials that determines their potential application in radiation detection is the capture reaction with slow ({approx}< 100 keV) neutrons: {sup 6}Li + n = {sup 4}He + {sup 3}H + 4.8MeV. The use of {sup 6}Li-salicylate (LiSal, LiC{sub 6}H{sub 5}O{sub 3}) for thermal neutron detection was previously studied in liquid and polycrystalline scintillators. The studies showed that both liquid and polycrystalline LiSal scintillators could be utilized in pulse shape discrimination (PSD) techniques that enable separation of neutrons from the background gamma radiation. However, it was found that the efficiency of neutron detection using LiSal in liquid solutions was severely limited by its low solubility in commonly used organic solvents like, for example, toluene or xylene. Better results were obtained with neutron detectors containing the compound in its crystalline form, such as pressed pellets, or microscopic-scale (7-14 micron) crystals dispersed in various media. The expectation drown from these studies was that further improvement of pulse height, PSD, and efficiency characteristics could be reached with larger and more transparent LiSal crystals, growth of which has not been reported so far. In this paper, we present the first results on growth and characterization of relatively large, a cm-scale size, single crystals of LiSal with good optical quality. The crystals were grown both from aqueous and anhydrous (methanol) media, mainly for neutron detection studies. However, the results on growth and structural characterization may be interesting for other fields where LiSal, together with other alkali metal salicylates, is used for biological, medical, and chemical (as catalyst) applications.

Zaitseva, N; Newby, J; Hull, G; Saw, C; Carman, L; Cherepy, N; Payne, S

2009-02-13

389

Q-switching with single crystal photo-elastic modulators  

NASA Astrophysics Data System (ADS)

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.

Bammer, F.; Petkovsek, R.

2010-09-01

390

Q-switching with single crystal photo-elastic modulators  

NASA Astrophysics Data System (ADS)

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.

Bammer, F.; Petkovsek, R.

2011-02-01

391

Tantalum Shear Modulus from Homogenization of Single Crystal Data  

SciTech Connect

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.

Becker, R

2007-09-14

392

Polarised IR and Raman spectra of monoglycine nitrate single crystal  

NASA Astrophysics Data System (ADS)

Polarised Raman spectra of the monoglycine (monoglycinium) nitrate (hereafter MGN) single crystal are reported. Additionally, the polarised specular reflection spectra for the (1 0 0) single crystal sample (E|| Y( b) and E|| Z( c)) were measured in the region 3600-80 cm -1. The spectra of the imaginary parts of the refractive indices are computed by the Kramers-Kronig transformation (Opus). The polarised spectra are discussed with respect to the diffraction crystal structure and recent literature data on normal co-ordinate analysis for the glycinium cation ( +NH 3CH 2COOH). The stretching vibrations of the NH3+ groups are explained by considering their hydrogen bonds. The intensity of the Raman bands arising from the stretching vibrations of the CH 2 group are explained assuming that each C sbnd H bond stretches independently. This finding is unusual and suggests that the C(2) sbnd H(5) bond is involved in the hydrogen bonding (improper hydrogen bond). The deformation vibrations of the CH 2 group are explained assuming scissoring, twisting, wagging and rocking type of vibrations. The band at 871 cm -1 exhibits the CC stretching character of the CCN skeleton, whereas the band at ca. 1050 cm -1 shows the ?aCCN character. The stretching ?OH vibrations of the C sbnd O sbnd H⋯O hydrogen bond gives rise to a band at ca. 3087 cm -1, clearly seen in the Y( xx) Z Raman spectrum. Its ?OH mode appears at 896 cm -1. The ?OH vibration is coupled to other vibrations, although the IR band at ca. 1375 (E|| Y) likely arises from this mode. It was impossible to define a character of the glycinium cations deformation vibrations giving rise to the bands observed in between 680 and 490 cm -1, on the basis of their polarisation properties. The polarisation properties of the internal modes of the nitrate ions are discussed.

Baran, Jan A.; Drozd, Marek A.; Ratajczak, Henryk

2010-07-01

393

Lamellar and Bulk Single Crystals Grown in Annealed Films of Vinylidene Fluoride and Trifluoroethylene Copolymers  

NASA Astrophysics Data System (ADS)

Thick lamellar single crystals and large bulk single crystals are found to grow in films of vinylidene fluoride and trifluoroethylene copolymers when they are annealed at temperatures between the Curie point and melting point. The morphologies of these crystals are studied using SEM, TEM, and X-ray diffraction. The lamellar crystals are thick (0.1 ?m) enough to be characterized as extended chain crystals. They are stacked together with their planes perpendicular to the film surface. The bulk single crystals exhibit various crystal habits with the maximum size 12× 10× 10 ?m3. They are developed on the lamellar crystals from which the constituent molecules seem to be supplied. The growth of the crystals is discussed on the basis of the diffusive displacement of the molecules along the chain axis which becomes violent above the Curie temperature.

Ohigashi, Hiroji; Akama, Shuyo; Koga, Keiko

1988-11-01

394

Production of Semiconducting III–V Single Crystals: Current Status and Outlook  

Microsoft Academic Search

The current status of and outlook for the worldwide production of semiconducting III–V single crystals, primarily gallium arsenide, are examined. Particular emphasis is placed on improving production technologies and reaching head positions in the vertical crystallization technology.

A. V. Markov

2003-01-01

395

A preliminary review of organic materials single crystal growth by the Czochralski technique  

NASA Technical Reports Server (NTRS)

The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed.

Penn, B. G.; Shields, A. W.; Frazier, D. O.

1988-01-01

396

Imatinib (Gleevec@) conformations observed in single crystals, protein-Imatinib co-crystals and molecular dynamics: Implications for drug selectivity  

NASA Astrophysics Data System (ADS)

Structure and dynamics of the Leukemia drug, Imatinib, were examined using X-ray crystallography and molecular dynamics studies. Comparison of conformations observed in single crystals with several reported co-crystals of protein-drug complexes suggests existence of two conserved conformations of Imatinib, extended and compact (or folded), corresponding to two binding modes of interaction with the receptor. Furthermore, these conformations are conserved throughout a dynamics simulation. The present study attempts to draw a parallel on conformations and binding patterns of interactions, obtained from small-molecule single-crystal and macromolecule co-crystal studies, and provides structural insights for understanding the high selectivity of this drug molecule.

Golzarroshan, B.; Siddegowda, M. S.; Li, Hong qi; Yathirajan, H. S.; Narayana, B.; Rathore, R. S.

2012-06-01

397

Ductile behaviour in single-point diamond-turning of single-crystal silicon  

Microsoft Academic Search

Single-crystal silicon is usually considered to be extremely brittle and exhibit little ductility in machining. In work reported in the literature during indentation tests, cracks appeared around the impression at loads as small as 5g and the crystallographic direction was found to have a strong influence on the crack initiation and propagation; however, spiral and flake-like swarf were observed in

C. L Chao; K. J Ma; D. S Liu; C. Y Bai; T. L Shy

2002-01-01

398

Regrinding and relapping of single-point, single-crystal diamond turning and boring tools  

SciTech Connect

Single-crystal, single-point diamond tools have been successfully ground and lapped to specific geometries with chip-free cutting edges for producing mirror-like surfaces on nonferrous materials. It was found that the grinding and lapping facility required a special controlled environment and specially constructed grinding and lapping machines. Cleanliness was found to be of utmost importance. Special inspection techniques were used to ensure very accurate and repeatable measurements. Exceptional care is required in handling, grinding, lapping, inspecting, and packaging to prevent cutting edge chippage on the diamond.

Duke, W.L.; Lovell, R.T.

1982-12-01

399

A novel single-polarization single-mode photonic crystal fiber coupler  

NASA Astrophysics Data System (ADS)

A vectorial finite element method is adopted to investigate this novel single-mode single-polarization (SPSM) photonic crystal fiber coupler which has asymmetric dual-core and two lines of enlarged air holes. we demonstrate that the SPSM region of the designed fiber can be more than 250nm wide for a set of optimized air-hole parameters and show that the width of the SPSM region could change slightly by little adjustment of the large inner air holes. The coupling length between the odd and even x-polarization modes are also investigated through fine-tuning the large and small air-hole diameters.

Li, Honglei; Lou, Shuqin; Feng, Suchun; Guo, Tieying; Yao, Lei; Wang, Liwen; Chen, Weiguo; Jian, Shuisheng

2009-08-01

400

An asymmetric dual-core single-polarization single-mode photonic crystal fiber coupler  

NASA Astrophysics Data System (ADS)

A vectorial finite element method (VFEM) is adopted to investigate the novel single-polarization single-mode (SPSM) photonic crystal fiber (PCF) coupler which has asymmetric dual-core and two lines of enlarged air holes. It is demonstrated that the SPSM region of the designed fiber can be more than 250 nm wide with a set of optimized air-hole parameters and the width of the SPSM region could change slightly by fine adjustment of the inner large air holes. The coupling length between the odd and even x-polarization modes is also investigated through fine-tuning the large and small air-hole diameters.

Li, Hong-Lei; Lou, Shu-Qin; Chen, Wei-Guo; Wang, Li-Wen; Jian, Shui-Sheng

2010-07-01

401

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

SciTech Connect

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.

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

402

Single crystal growth and LPE thin film process for RE123 superconducting materials  

Microsoft Academic Search

Fundamentals of solidification processing for high-Tc superconductors (HTSC) and the progress of the crystal pulling and liquid phase epitaxy (LPE) processes were reviewed. RE-123 crystal is solidified by peritectic reaction with diffusion through the liquid. Based on this idea, a modified CZ (SRL-CP) method was developed for continuous single crystal growth. The large Nd123 single crystal, 25×25×25 mm3 in size,

T. Izumi; X. Yao; K. Nomura; K. Kakimoto; M. Egami; A. Hayashi; Y. Shiohara

2000-01-01

403

Single crystal growth and characterization of lanthanum–neodymium oxalate octahydrate  

Microsoft Academic Search

Single crystals of mixed lanthanum–neodymium oxalates are grown by gel diffusion method using agar gel as a medium of growth. The crystals grow in the agar gel with hexagonal morphology having (001), (110) and (010) as habit faces. Single crystal X-ray diffraction results show that the crystals belong to monoclinic system with cell parameters; a=10.344(2)Å, b=9.643(6)Å, c=11.721(2)Å, ?=118.7 (2)° ,

Basharat Want

2011-01-01

404

High Purity Isotopically Enriched 29Si and 30Si Single Crystals: Isotope Separation, Purification, and Growth  

Microsoft Academic Search

We report the successful isotope separation and bulk single crystal growth of 29Si and 30Si stable isotopes. The isotopic enrichments of the 29Si and 30Si single crystals determined by mass spectrometry are 99.23% and 99.74%, respectively. Both crystals have the electrically active net-impurity concentration less than 1015 cm-3. Thanks to the result of this work and the 28Si crystals we

Kohei M. Itoh; Jiro Kato; Masafumi Uemura; Alexey K. Kaliteevskii; Oleg N. Godisov; Grigori G. Devyatych; Andrey D. Bulanov; Anatoli V. Gusev; Igor D. Kovalev; Pyotr G. Sennikov; Hans-J. Pohl; Nikolai V. Abrosimov; Helge Riemann

2003-01-01

405

Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method.

Mahadevan, M.; Ramachandran, K.; Anandan, P.; Arivanandhan, M.; Bhagavannarayana, G.; Hayakawa, Y.

2014-12-01

406

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals.  

PubMed

Single crystals of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of l-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method. PMID:24967545

Mahadevan, M; Ramachandran, K; Anandan, P; Arivanandhan, M; Bhagavannarayana, G; Hayakawa, Y

2014-12-10

407

Synthesis, Microhardness, FT-IR, and Thermal Decomposition of Semiorganic Antimony Thiourea Bromide Monohydrate Single Crystals  

NASA Astrophysics Data System (ADS)

Antimony thiourea bromide monohydrate (ATBM) single crystals were grown by a solution growth technique at room temperature. Microhardness studies on the grown crystal were carried out using the Vickers microhardness tester to estimate the mechanical strength of the crystal. The FT-IR analysis ascertains the presence of a metal-sulphur bond in ATBM crystals. The thermal decomposition of ATBM crystals was investigated by means of thermogravimetric analysis.

Upadhya, K. Mahesha; Udayashankar, N. K.

2012-01-01

408

Floating zone growth and high-temperature hardness of CrB 2 single crystals  

Microsoft Academic Search

Single crystals of CrB2 were prepared by the floating zone method. The crystal quality was improved by controlling the molten zone composition. The crystals preferentially grew normal to the (112?4) plane which has the lowest Vickers hardness, similar to the other refractory boride crystals. On the growth plane, the direction of the a-plane, which longitudinally exists along the crystal rod,

Shigeki Otani; Toshikazu Ohsawa

1999-01-01

409

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

PubMed

We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6?keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and (60)Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1-15.0?mGy and 49.8-373.8?mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029? ± ?0.010 (at 15.2?keV) and 0.821? ± ?0.011 (33.6?keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17?keV effective energy, or 3?keV??m(-1) track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique. PMID:25683355

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

2015-03-21

410

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

411

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

SciTech Connect

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 P2{sub 1}. 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.

Thirumurugan, R., E-mail: singlecrystalxrd@gmail.com; Anitha, K., E-mail: singlecrystalxrd@gmail.com [School of Physics, Madurai Kamaraj University, Madurai-625021 (India)

2014-04-24

412

Single Crystal DMs for Space-Based Observatories  

NASA Astrophysics Data System (ADS)

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.

Bierden, Paul

413

Single-Crystal Elasticity of Ettringite at ambient conditions  

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

414

Comparative study of intrinsic luminescence in undoped transparent ceramic and single crystal garnet scintillators  

NASA Astrophysics Data System (ADS)

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.

Fujimoto, Yutaka; Yanagida, Takayuki; Yagi, Hideki; Yanagidani, Takagimi; Chani, Valery

2014-10-01

415

Investigation of change of the composition and structure of the CaF2/Si films surface at the low-energy bombardment  

NASA Astrophysics Data System (ADS)

The influence of the bombardment by the Ar+, Ba+ and Na+ ions and the subsequent annealing on composition and electron structure of a surface of the CaF2/Si (1 1 1) films is studied. The energy band diagram of the epitaxial nanofilm systems of the Ca-CaF2-Si type is constructed. Optimum regimes of ion implantation and annealing for the production of three-componental nanodimensional structures of the Ca1-XCOXF2 type are determined and parameters of their energy bands are estimated.

Umirzakov, B. E.; Tashmukhamedova, D. A.; Ruzibaeva, M. K.; Djurabekova, F. G.; Danaev, S. B.

2014-05-01

416

Luminescence Properties of ScPO{sub 4} Single Crystals  

SciTech Connect

Flux-grown ScPO{sub 4} single crystals exhibit a number of luminescence bands in their x-ray-excited luminescence spectra - including sharp lines arising from rare-earth elements plus a number of broad bands at 5.6 cV, 4.4 eV, and 3 eV. The band at 5.6 eV was attributed to a self-trapped exciton (STE) [l], and it could be excited at 7 eV and higher energies. This luminescence is strongly polarized (P = 70 %) along the optical axes of the crystal and exhibits a kinetic decay time constant that varies from several ns at room temperature to {approximately}10 {micro}s at 60 K and up to {approximately}1 ms at 10 K. It is assumed that the STE is localized on the SC ions. The band at 3 eV can be excited in the range of the ScPO{sub 4} crystal transparency (decay time = 3 to 4 {micro}s.) This band is attributed to a lead impurity that creates different luminescence centers. At high temperatures, the band at 4.4 eV is dominant in the x-ray-excited TSL and afterglow spectra. Its intensity increases with irradiation time beginning at zero at the initial irradiation time. The 4.4 eV band does not appear in a fast process under a pulsed electron beam, showing that accumulation is necessary for its observation. A sample of ScPO{sub 4} doped with vanadium exhibited a prevalent band at 4.4 eV at T = 480 K.

Boatner, L.A.; Trukhin, A.N.

1999-08-16

417

Twin nucleation and migration in FeCr single crystals  

SciTech Connect

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.

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

418

Single crystal growth of quaternary superconductor YNi 2B 2C by a floating zone method  

Microsoft Academic Search

Single crystals of YNi2B2C have been grown by a floating zone method. Preliminary metallurgical studies indicate that this compound melts incongruently and requires a solution growth technique for obtaining single crystals. We prepared a feed rod of YNi2B2C by arc melting and grew the single crystals in an infrared heating furnace under high purity argon atmosphere by using the traveling

H. Takeya; T. Hirano; K. Kadowaki

1996-01-01

419

Bulk GaN single crystal growth and characterization using various alkali metal flux  

Microsoft Academic Search

Bulk GaN single crystal was grown by the flux growth. Using a flux, the solvent-thermal method for growing bulk GaN single crystal requires lower temperature (?800°C) and pressure (?100atm) than when growing them directly from high-temperature solution. In this study, we investigated the influence of the N2 pressure and flux ratio on the growth of the bulk GaN single crystals

T. I. Shin; H. J. Lee; J. H. Lee; S.-W. Kim; S. J. Suh; D. H. Yoon

2006-01-01

420

Bulk GaN single crystal growth for substrate by solvent-thermal method  

Microsoft Academic Search

We grew bulk GaN single crystals by solvent-thermal method. GaN single crystals were synthesized at 600-800 °C and 6-8 MPa of N2 gas for 200 h. We used 99% pure Na as a flux. The mole fraction of Na \\/ (Na+Ga) were 0.30-0.67. A pyramid GaN single crystal having a size of 1-3 mm grew on the bottom and wall

T. I. Shin; H. J. Lee; K. W. Chung; M. S. Kang; D. H. Yoon

2004-01-01

421

Single crystal growth of copper phthalocyanine using exaltation–evaporation growth method  

Microsoft Academic Search

A new method of growing single crystal for ?-form copper phthalocyanine (CuPc) is presented in this paper. Melted anthracene was used as solvent of CuPc. The method, vaporizing the solvent using an automatic exaltation machine, was employed to grow CuPc single crystals. The needle-like single crystals of CuPc up to 11.6mm in length were obtained by applying this method. The

Wenhai Jiang; Xu Wang; Yuchun Chang; Shukun Yu; Chunyu Ma; Kaiqi Ye; Chuanhui Cheng; Guotong Du

2006-01-01

422

Constitutive modelling of the anisotropic creep behaviour of nickel-base single crystal superalloys  

Microsoft Academic Search

This paper focuses on the modelling of primary, secondary and tertiary creep of nickel-base single crystal superalloys at high temperatures. In particular, we propose an extension of the Cailletaud single crystal plasticity model [Méric L, Poubanne P, Cailletaud G. Single crystal modeling for structural calculations: part I—model presentation. Transactions of the ASME 1991;133:162–170] to include tertiary creep. This is achieved

Ivaylo N. Vladimirov; Stefanie Reese; Gunther Eggeler

2009-01-01

423

Thermal conductivity of 4H-SiC single crystals  

NASA Astrophysics Data System (ADS)

Thermal diffusivity and specific heat of 4H-SiC crystals as a function of temperature are measured, respectively, from room temperature to 600 °C. The thermal conductivity normal to c-axis was calculated from the measured data for both N-type and V-doped semi-insulating (SI) 4H-SiC single crystals. The thermal conductivity of N-type sample normal to c axis is proportional to T-1.26. It is approximately 280 W/mK at the room temperature. For V-doped SI sample, the thermal conductivity is proportional to T-1.256 and it is about 347 W/mK at room temperature, bigger than that of N-type sample. For semiconductor materials, total thermal conductivity is the sum of the contributions of lattice and carrier thermal conductivities. Temperature dependent Raman spectrum showed that the life time of phonons for N-type sample is shorter than that for SI sample. Accordingly thermal conductivity contributions from both lattice and carrier components are relatively small for N-type sample.

Wei, Rusheng; Song, Sheng; Yang, Kun; Cui, Yingxin; Peng, Yan; Chen, Xiufang; Hu, Xiaobo; Xu, Xiangang

2013-02-01

424

Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite  

NASA Technical Reports Server (NTRS)

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.

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

425

Point defects in irradiated Li3VO4 single crystal  

NASA Astrophysics Data System (ADS)

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.

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

1995-03-01

426

Current-controlled giant magnetoimpedance of iron single crystals  

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

427

Analysis of ripple formation in single crystal spot welds  

NASA Technical Reports Server (NTRS)

Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

Rappaz, M.; Corrigan, D.; Boatner, L. A.

1997-01-01

428

Rejecting diffractometer with linear coordinate detector for single crystals  

SciTech Connect

Use of an x-ray beam that is convergent in the specimen and a recording system based on a linear coordinate detector has led to the creation of the ADR-3--a new type of goniometer-free rejecting diffractometer. The deviation of this orientation angle of the surface of a cut from a specified angle is determined by electronic data processing entirely without mechanical movement. The rejector can check the quality of cut treatment and allows the block distribution over the surface of a single crystal to be studied with a localization of 0.2 mm. The test results of the goniometer-free rejecting diffractometer showed its ability to check cut angles under industrial conditions.

Ageev, O.I.; Glazova, L.P.; Goganov, D.A.; Kazanskii, B.V.; Reizis, B.M.

1986-02-01

429

Dislocation nucleation in bcc Ta single crystals studied by nanoindentation  

SciTech Connect

The study of dislocation nucleation in closed-packed metals by nanoindentation has recently attracted much interest. Here, we address the peculiarities of the incipient plasticity in body centered cubic (bcc) metals using low index Ta single-crystals as a model system. The combination of nanoindentation with high-resolution atomic force microscopy provides us with experimental atomic-scale information on the process of dislocation nucleation and multiplication. Our results reveal a unique deformation behavior of bcc Ta at the onset of plasticity which is distinctly different from that of closed-packed metals. Most noticeable, we observe only one rather than a sequence of discontinuities in the load-displacement curves. This and other differences are discussed in context of the characteristic plastic deformation behavior of bcc metals.

Biener, M M; Biener, J; Hodge, A M; Hamza, A V

2007-08-08

430

Field-assisted bonding of single crystal quartz  

NASA Astrophysics Data System (ADS)

A technique to produce strong, hermetic bonds between plates of single crystal quartz using a modified field-assisted bonding process is presented. Field-assisted bonding is a technique traditionally used to join glass to metals at temperatures well below normal glass softening temperatures. To promote reactivity between quartz within an electrical field at temperatures well below quartz transformation temperatures, thin films of silicon metal and glass were vapor deposited onto adjacent quartz plates. Thermal stresses caused by expansion mismatch between the quartz and the films were of concern. These stresses were reduced by determining the minimum film thicknesses capable of yielding sufficient reactivity for bonding. Processing studies were conducted to optimize bond integrity, and bonds were characterized by hermeticity, thermal shock, and mechanical shock. Packages produced under the most ideal conditions were able to survive greater than 1000 psi shock loads.

Watkins, Randall D.; Tuthill, Clinton D.; Curlee, Richard M.; Koehler, Dale R.; Joerg, Charles F.

431

Diffusion in single crystals of melilite. I - Oxygen  

NASA Astrophysics Data System (ADS)

Oxygen-diffusion coefficients in melilite lattices were estimated by analyzing the structure of O-18 profiles determined in single crystals of gehlenite using SIMS. The lattice diffusion O-coefficients were found to be 2 to 4 orders of magnitude lower than those previously reported by Hayashi and Muehlenbachs (1986) for melilite solid solutions. The reason for these high diffusion rates in melilite solid solutions and the heterogeneous distribution of oxygen isotopes in the Allende Ca, Al-rich inclusions (CAIs) was investigated considering the contribution of fast diffusion along dislocations and possible changes in diffusion rate with gehlenite-akermanite ratios in melilite; the oxygen diffusion coefficients along dislocations were calculated by analyzing 'tailing' of the O-diffusion profiles. The results suggest that it is unlikely that the O-isotope differences in the Allende CAI minerals are the result of diffusion processes during a postcrystallization thermal event.

Yurimoto, Hisayoshi; Morioka, Masana; Nagasawa, Hiroshi

1989-09-01

432

Shock compression experiments on Lithium Deuteride single crystals.  

SciTech Connect

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.

Knudson, Marcus D.; Desjarlais, Michael P.; Lemke, Raymond W.

2014-10-01

433

Path to meter class single crystal silicon (SCSi) space optics  

NASA Astrophysics Data System (ADS)

With the global financial crisis affecting funding for space systems development, customers are calling for lower cost systems. Yet, at the same time, these lower cost systems must have increased thermal response to operational environments and load survivability. We submit that single crystal silicon (SCSi) meets both of these requirements. This paper will highlight some key SCSi material properties, discuss the opportunities that led to the development of McCarter processing methods, and present the latest steps in the manufacturing path of McCarter Mirrors using SCSi, GFB (glass frit bonding) and MSF (McCarter super finish), including the concept drawing of a one meter SCSi lightweight mirror, which together sets up the last step toward a lower cost, high performing one meter SCSi space optic.

McCarter, Douglas R.

2012-03-01

434

Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys  

NASA Technical Reports Server (NTRS)

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.

Smialek, James L.

1998-01-01

435

Strain Rate Dependence of a Single Crystal Alloy  

NASA Astrophysics Data System (ADS)

In order to provide data for constitutive modelling, and to better understand mechanisms behind strain rate dependence of metals, characterisation experiments have been performed on the nickel based single crystal alloy CMSX-4. This material has received extensive characterisation in the literature, concentrating on metallurgical aspects as well as creep and fatigue behaviour, giving a good background to the high rate research. The current paper will report data from compression experiments performed at strain rates from 10-3 to 10^3 s-1, and Taylor Impact tests. Data obtained will be evaluated in the light of previous thermo-mechanical characterisation of this alloy, and compared to the high rate response of polycrystalline materials.

Siviour, Clive; Wielewski, Euan; Petrinic, Nik

2009-06-01

436

Ambient Compression-Compression Fatigue Behavior of Magnesium Single Crystal  

NASA Astrophysics Data System (ADS)

A magnesium single crystal sample with a near orientation was tested at room temperature under compression-compression cyclic loading, and the microstructure was characterized to disclose the involved deformation mechanisms. No plastic deformation region appeared on the stress-strain curve during the cyclic loading. The stress-strain curve stabilized at the first cycle, the strain range for each cycle fluctuated slightly around a constant value, and the mean strain for each cycle was in a narrow range from 0.0846 to 0.0863 during the whole test. The ratcheting strain rate decreased exponentially from ~0.0003, and reached a relatively small and stable value of about zero. The observed deformation mechanisms were prismatic slip, compression twinning, and tension twinning. The prismatic dislocation slip roughened the cylindrical sample surface by forming extrusions and intrusions, and small cracks were also observed on the surface.

Li, Qizhen

2014-01-01

437

Interacting superparamagnetic nanoparticles in the Cu-1%Co single crystal  

NASA Astrophysics Data System (ADS)

The results of experimental and theoretical magnetic studies performed for the Cu-1%Co single crystal containing the magnetic Co nanoparticles embedded in the non-magnetic Cu matrix are presented and discussed. The shape of the hysteresis loop measured at room temperature was analysed within the frame of the interacting superparamagnetic particles formalism. The original theoretical model was improved, taking into account the response of each nanoparticle to the mean interaction field. To check the validity of the applied theory, the theoretical magnetization curve was calculated and compared with the experimental data. Additionally, the apparent size distribution of the Co nanoparticles was determined. To obtain the true size distribution of the Co nanoparticles, the scaling procedure including the relation between the interaction field and the characteristic temperature was applied. The result of the scaling was compared with the Co nanoparticles size distribution known from the previous TEM analysis leading to satisfactory agreement between both sets of data.

Czub, J.; Tokarz, W.; Gondek, ?.; Figiel, H.

2013-04-01

438

Super-thin single crystal diamond membrane radiation detectors  

SciTech Connect

We propose to use the non-electronic grade (nitrogen content 5 ppb < [N] < 5 ppm) single crystal (sc) chemical vapour deposited (CVD) diamond as a thin-membrane radiation detector. Using deep Ar/O{sub 2} plasma etching it is possible to produce self-supported few micrometres thick scCVD membranes of a size approaching 7 mm × 7 mm, with a very good surface quality. After metallization and contacting, electrical properties of diamond membrane detectors were probed with 5.486 MeV ?-particles as an ionization source. Despite nitrogen impurity, scCVD membrane detectors exhibit stable operation, charge collection efficiency close to 100%, with homogenous response, and extraordinary dielectric strength up to 30 V/?m.

Pomorski, Michal; Caylar, Benoit; Bergonzo, Philippe [CEA-LIST, Diamond Sensors Laboratory, Gif-sur-Yvette F-91191 (France)] [CEA-LIST, Diamond Sensors Laboratory, Gif-sur-Yvette F-91191 (France)

2013-09-09

439

Single crystal metal wedges for surface acoustic wave propagation  

DOEpatents

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.

Fisher, Edward S. (Wheaton, IL)

1982-01-01

440

Multinuclear NMR relaxometry studies in singly fluorinated liquid crystal  

NASA Astrophysics Data System (ADS)

Nuclear spin-lattice relaxation rate dispersion study of 1H and 19F in the isotropic phase of a singly fluorinated liquid crystal 4?-butoxy-3-fluoro-4-isothiocyantotolane (4OTOLFo) points to their differing relaxation pathways and hence sensitivity to qualitatively different time modulations. In particular fluorine nuclear spins, with strong lattice coupling (larger by two orders) extending to very low frequencies, detect slowly relaxing local structures via the spin-rotation interaction. The field-cycling technique used to carry out these very low frequency measurements, provides for level crossing of the two nuclear species at low enough jump fields, facilitating an additional mechanism of cross-relaxation in the strong coupling limit.

Rajeswari, M.; Molugu, Trivikram R.; Dhara, S.; Venu, K.; Sastry, V. S. S.; Dabrowski, R.

2012-04-01

441

Superconductivity in SrNi2P2 single crystals  

SciTech Connect

Heat capacity, magnetic susceptibility, and resistivity of SrNi{sub 2}P{sub 2} single crystals are presented, illustrating the structural transition at 325 K, and bulk superconductivity at 1.4 K. The magnitude of {Tc}, fits to the heat capacity data, the small upper critical field H{sub c2} = 390 Oe, and {kappa} = 2.1 suggests a conventional fully gapped superconductor. With applied pressure we find that superconductivity persists into the so-called 'collapsed tetragonal' phase, although the transition temperature is monotonically suppressed with increasing pressure. This argues that reduced dimensionality can be a mechanism for increasing the transition temperatures of layered NiP, as well as layered FeAs and NiAs, superconductors.

Ronning, Filip [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Park, Tuscon [Los Alamos National Laboratory; Thompson, Joe D [Los Alamos National Laboratory

2009-01-01

442

Single crystal metal wedges for surface acoustic wave propagation  

DOEpatents

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.

Fisher, E.S.

1980-05-09

443

Process development for single-crystal silicon solar cells  

NASA Astrophysics Data System (ADS)

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.

Bohra, Mihir H.

444

Neodymium-doped graded-index single-crystal fibre lasers  

SciTech Connect

The efficient technology is developed for growing high-quality doped single-crystal fibres by the mini-pedestal method with laser heating. The technology can be used to fabricate high-quality doped single-crystal fibres with a controllable radial gradient of the refractive index. The refractive-index profile in single-crystal fibres is studied experimentally. The efficient operation of a Nd{sup 3+} : YAG single-crystal fibre laser in the waveguide regime was demonstrated upon longitudinal pumping by a laser diode. (special issue devoted to the 90th anniversary of a.m. prokhorov)

Bufetova, G A; Kashin, V V; Nikolaev, D A; Rusanov, S Ya; Seregin, V F; Tsvetkov, V B; Shcherbakov, Ivan A; Yakovlev, A A, E-mail: bufetova@lsk.gpi.r, E-mail: tsvetkov@lsk.gpi.r, E-mail: director@gpi.r [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2006-07-31

445

Electron paramagnetic resonance study of radiation damage in isonipecotic acid single crystal  

NASA Astrophysics Data System (ADS)

The electron spin resonance spectra of the radical produced by gamma-irradiation of a single crystal of isonipecotic acid (piperidine-4-carboxylic acid) were reported, and the structure of the radical was discussed. Isonipecotic acid single crystals were exposed to 60Co-gamma irradiation at room temperature. The irradiated single crystals were investigated by Electron Paramagnetic Resonance (EPR) Spectroscopy between 115 K and 300 K. The spectra were found to be temperature independent. The g values of the radiation damage center observed in isonipecotic acid single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.

Caliskan, Betul; Caliskan, Ali Cengiz; Yerli, Rabia

2014-10-01

446

Studies on the Growth, Spectral, Optical and Thermal Properties of 4-NITROANILINE Picrate Single Crystals  

NASA Astrophysics Data System (ADS)

In this paper, an organic 4-nitroaniline picrate (4NP) single crystal was grown by solution growth method. Single crystal X-ray diffraction study revealed that grown crystal belongs to orthorhombic system with Pbcn space group. The solid state constants such as plasma energy, Penn gap, Fermi energy and polarizability of 4NP crystal were determined theoretically. The functional groups of the grown crystals were confirmed qualitatively from FTIR spectral analysis. The thermal decomposition and melting point of the crystal were determined from thermogravimetric analysis. The optical absorption and cut-off wavelength of the crystal were determined from UV-visible study. The second harmonic generation (SHG) efficiency of the grown crystal was measured by Kurtz-Perry SHG test using Nd:YAG laser. The laser damage threshold value of the grown crystal was estimated by multi-shot method using 1064 nm laser.

Sivakumar, P. K.; Kumar, M. Krishna; Kumar, R. Mohan; Kanagadurai, R.

2013-12-01

447

Crystal growth and neutron scattering studies of single crystal NaFeAs and its Co-doped superconductors  

Microsoft Academic Search

There have been much recent interests in studying FeAs based superconductors. Although there are many families of FeAs-based materials, most work have focused on the BaFe2As2 (122) family of materials because the availability of single crystals of these materials. To expand the single crystal growth capability and compare similarities and differences between different classes of FeAs-based superconductors, we report the

Meng Wang; Chenglin Zhang; Jun Zhao; Miaoyin Wang; Huiqian Luo; Pengcheng Dai

2010-01-01

448

Long-term 193-nm laser irradiation of thin-film-coated CaF2 in the presence of H2O  

NASA Astrophysics Data System (ADS)

The final projection lens element in a 193-nm immersion-based lithographic tool will be in direct contact with water during irradiation. Thus, any lifetime considerations for the lens must include durability data of lens materials and thin films in a water ambient. We have previously shown that uncoated CaF2 is attacked by water in a matter of hours, as manifested by a substantial increase in AFM-measured surface roughness.1 Thus, CaF2 lenses must be protected, possibly by a thin film, and the coatings tested for laser durability in water. To address the above lifetime concerns, we have constructed a marathon laser-irradiation system for testing thin film exposure to water under long-term laser irradiation. Coated substrates are loaded into a custom water cell, made of stainless steel and Teflon parts. Ultrapure water is delivered from a water treatment testbed that includes particle filtration, deionization and degassing stages. In-situ metrology includes 193-nm laser ratiometry, UV spectrophotometry and spectroscopic ellipsometry, all with spatial profiling capabilities. In-situ results are coupled with off-line microscopy, AFM measurements and spatial surface mapping with spectroscopic ellipsometry at multiple incidence angles. A variety of laser-induced changes have been observed, from complete adhesion loss of protective coatings to more subtle changes, such as laser-induced index changes of the thin films or surface roughening. Implications of the study on expected lifetimes of the protective coatings in the system will be discussed.

Liberman, V.; Switkes, M.; Rothschild, M.; Palmacci, S. T.; Sedlacek, J. H. C.; Hardy, D. E.; Grenville, A.

2005-05-01

449

From single crystal surfaces to single atoms: investigating active sites in electrocatalysis  

NASA Astrophysics Data System (ADS)

Electrocatalytic processes will undoubtedly be at the heart of energising future transportation and technology with the added importance of being able to create the necessary fuels required to do so in an environmentally friendly and cost effective manner. For this to be successful two almost mutually exclusive surface properties need to be reconciled, namely producing highly active/reactive surface sites that exhibit long term stability. This article reviews the various approaches which have been undertaken to study the elusive nature of these active sites on metal surfaces which are considered as adatoms or clusters of adatoms with low coordination number. This includes the pioneering studies at extended well defined stepped single crystal surfaces using cyclic voltammetry up to the highly sophisticated in situ electrochemical imaging techniques used to study chemically synthesised nanomaterials. By combining the information attained from single crystal surfaces, individual nanoparticles of defined size and shape, density functional theory calculations and new concepts such as mesoporous multimetallic thin films and single atom electrocatalysts new insights into the design and fabrication of materials with highly active but stable active sites can be achieved. The area of electrocatalysis is therefore not only a fascinating and exciting field in terms of realistic technological and economical benefits but also from the fundamental understanding that can be acquired by studying such an array of interesting materials.

O'Mullane, Anthony P.

2014-03-01

450

Copper(II) carboxylate tetramers formed from an enantiopure ligand containing a ?-stacking supramolecular synthon: single-crystal to single-crystal enantioselective ligand exchange.  

PubMed

An enantiopure ligand built from connecting the ?···? stacking 1,8-naphthalimide supramolecular synthon with L-asparagine, L(asn)(-), forms tetrameric [Cu(4)(L(asn))(8)(py)(MeOH)]. The methanol ligand, located in a chiral pocket, is replaced enantioselectively when exposed to racemic ethyl lactate vapor to yield [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], in a single-crystal to single-crystal gas/solid transformation. PMID:21286624

Reger, Daniel L; Horger, Jacob J; Smith, Mark D

2011-03-14

451

Single-cell-gap transflective liquid-crystal display and the use of photoalignment Lishuang Yao  

E-print Network

Single-cell-gap transflective liquid-crystal display and the use of photoalignment technology Tao Du Lishuang Yao Vladimir G. Chigrinov Hoi-sing Kwok Abstract -- In this paper, transflective liquid-crystal-display liquid-crystal modes are applied to the transmissive and reflective subpixels of the transflective LCD

452

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

SciTech Connect

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.

Teague, L.

2010-06-11

453

Unsteady 3D and analytical analysis of segregation process in FZ Si single crystal growth  

Microsoft Academic Search

D unsteady calculations of velocity, temperature and dopant concentration fields in molten zone in Floating Zone (FZ) Si single crystal growth process are carried out. The recorded fluctuations of physical fields near the crystallization interface are used to estimate the possible fluctuations of crystal growth velocity. An analytical analysis is carried out to estimate the amplitude of concentration oscillations due

K. Lacis; A. Muiznieks; N. Jekabsons; A. Rudevics; G. Ratnieks; B. Nacke

454

A Bayesian Approach to Diameter Estimation in the Diameter Control System of Silicon Single Crystal Growth  

Microsoft Academic Search

In the diameter control system of silicon single crystal growth, the variation of the diameter of the aperture (i.e., a halo with high brightness, which appears at the junction of a solid crystal and a liquid solution) is consistent with the change in the diameter of the growing crystal. Therefore, the diameter of the aperture can be used as a

Ding Liu; Junli Liang

2011-01-01

455

Birefringence of yttrium vanadate single crystals in the middle wavelength infrared  

E-print Network

Birefringence of yttrium vanadate single crystals in the middle wavelength infrared Haitao Luoa Abstract The birefringence of the yttrium vanadate (YVO4) crystals have been measured for the first time of this material for the MWIR polarization applications. Keywords: yttrium vanadate crystal, birefringence

Dereniak, Eustace L.

456

Determination of the crystallographic orientation of a single crystal using resonant ultrasound spectroscopy  

Microsoft Academic Search

Using resonant ultrasound spectroscopy (RUS) we have determined the crystallographic orientation of a tantalum single crystal from a measurement of its mechanical resonance spectrum. This accomplishment is significant not only because it reduces the sample requirements for RUS but also because it is the simplest method for simultaneous determination of a crystal’s elastic constants and microscopic crystallographic orientation.

J. L. Sarrao; S. R. Chen; W. M. Visscher; Ming Lei; U. F. Kocks; A. Migliori

1994-01-01

457

Crystallization and Melting Behavior of Nanopolymeric Particles Containing Single or a Few Chains  

Microsoft Academic Search

Samples of nanopolymeric particles, each containing a single chain or a few chains, were prepared by a freeze-drying method from dilute solutions of isotactic polystyrene (iPS) in benzene. Thermal analysis of the particle samples revealed that the cold crystallization temperature greatly decreases and the crystallization rate remarkably increases as the solution concentration decreases. The increase in crystallization rate can be

HAISHAN BU; FAMING GU; MIN CHEN; LIRONG BAO; JIE CAO

2000-01-01

458

Cross-sectional transmission electron microscopy method and studies of implant damage in single crystal diamond  

E-print Network

crystal diamond D. P. Hickey,a E. Kuryliw, K. Siebein, and K. S. Jones Materials Science and Engineering microscopy TEM studies of single crystal diamond have been reported, most likely due to the time crystal diamond using a focused ion beam and in situ lift-out. The method results in samples approximately

Florida, University of