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1

Laser induced nanoparticle formation in single crystal CaF2  

Microsoft Academic Search

Single crystal calcium fluoride (CaF2) is a material currently being used for vacuum ultra-violet optical components. However, all metal halides have a strong tendency to form point defects under energetic particle and optical irradiation which can degrade performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser light. This exposure causes absorption in the visible region

L. Cramer; S. C. Langford; J. T. Dickinson

2004-01-01

2

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

3

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

NASA Astrophysics Data System (ADS)

High quality window/plate shaped CaF2 single crystals have developed by vertical Bridgman method of with diameters of 50, 100, and 200 mm and 210 mm width, 200mm length. The CaF2 windows of 30mm diameter obtained from big crystals have evaluated the transmission spectra from 120 nm to 220nm by single beam VUV spectrometer. We could obtain bulk transmission spectra by subtracting surface reflection loss between tow kinds of thickness samples. The results show flat spectra without distinct absorption from 130nm to 220nm. In laser-damage tests with the fourth harmonic (4?) of a Nd:YAG laser below 1NW/cm2 at the CaF2 window, a stable output of 600mW was obtained. ArF laser irradiation of 50mJ/cm2 and 6X104 pulses was tried and the degradation in transmission from 130nm to 220nm not observed. These data show that the radiation hardness of our CaF2 crystals is promising for deep ultra-violet laser applications.

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

2005-02-01

4

Laser induced nanoparticle formation in single crystal CaF2  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is a material currently being used for vacuum ultra-violet optical components. However, all metal halides have a strong tendency to form point defects under energetic particle and optical irradiation which can degrade performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser light. This exposure causes absorption in the visible region due to formations of nanoclusters (colloids) of Ca metal in the bulk. The formation mechanism involves exciton production via two photon absorption. Heating can affect the colloid growth; we have examined the change of transmission at 532 nm vs. temperature during coloring with 157 nm excimer laser light. We find maximum coloration to occur at 50 C. The colloids can also be easily made with exposure to low-energy electrons. The absorption due to colloids can be bleached with subsequent exposure to appropriate laser light. We compare bleaching rates at various wavelengths from 157-1064 nm and find that absorption due to plasmon excitation in the colloids and accompanying heating is the likely bleaching mechanism.

Cramer, L.; Langford, S. C.; Dickinson, J. T.

2004-03-01

5

Laser interactions with embedded Ca metal nanoparticles in single crystal CaF2  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important material for vacuum-ultraviolet optics. Nevertheless, prolonged exposure to energetic radiation can color the material by producing calcium metal nanoparticles. We compare the effectiveness of laser conditioning treatments at wavelengths ranging from the near infrared to the deep ultraviolet in removing this coloration. Treatments at 157, 532, and 1064 nm can significantly reduce the visible coloration due to nanoparticles. In contrast, irradiation at 248 nm has little effect at fluences below the damage threshold for the material employed in this work. We present evidence that the effect of laser irradiation on coloration is principally thermal and is largely confined to the first 50 ns after each laser pulse. We attribute the wavelength dependence of the bleaching process to the wavelength dependence associated with Mie absorption by metal nanoparticles. The consequences of these observations with regard to laser conditioning processes in bulk optical materials are discussed.

Cramer, L. P.; Schubert, B. E.; Petite, P. S.; Langford, S. C.; Dickinson, J. T.

2005-04-01

6

Colour centres formation in CaF 2 single crystals by ?-rays and reactor neutrons  

NASA Astrophysics Data System (ADS)

The induced colour in single crystals of calcium fluoride irradiated with ?-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing ?-rays dose up to 10 6 Gy and absorption bands centred at about 225, 260, 340, 396 and 580 nm are observed. At higher doses, in the case of reactor neutrons irradiation, the absorption spectrum shows a large absorption band centred at about 415 nm and shoulders at 340 nm and 550 nm. This indicates that the absorption bands at 225, 260 and 580 nm are probably saturated at higher doses. Whereas, the band at 396 nm presents both saturation and linearly increasing behaviour. On heating a sample after irradiation, the absorption bands at 225, 260 and 580 nm disappear at 140 °C, and the 396 nm absorption band disappears above 250 °C. Photoluminescence excited with 325 nm photon shows an emission band centred at about 420 nm in the non-irradiated sample. The intensity of such band deceases after irradiation.

Izerrouken, M.; Guerbous, L.; Meftah, A.

2010-09-01

7

SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: Efficient lasing in diode-pumped Yb3+:CaF2-SrF2 solid-solution single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of solid solutions of a high optical quality are grown in the concentration vicinity of the saddle point of the ternary CaF2-SrF2-YbF3 system. Efficient lasing with a small Stokes shift (at 1025 nm) was obtained in 980-nm diode-pumped single crystals. The total lasing efficiency (with respect to the absorbed average pump power) was 59% and the slope efficiency was 83%.

Basiev, T. T.; Vasil'ev, S. V.; Doroshenko, M. E.; Konyushkin, V. A.; Kuznetsov, S. V.; Osiko, V. V.; Fedorov, P. P.

2007-10-01

8

Additive colouring of CaF2:Yb crystals: determination of Yb2+ concentration in CaF2:Yb crystals and ceramics  

NASA Astrophysics Data System (ADS)

When growing CaF2 crystal doped with rare-earth ions, most of these ions are present in a trivalent state. However, due to contact with graphite crucible, a small proportion of a number of ions (Eu, Sm, Yb and Tm) are reduced to a bivalent state. A similar situation takes place during fabrication of CaF2 ceramics doped with rare-earth metals. This fact is of particular importance for laser CaF2:Yb crystals (ceramics), a promising material for short-pulse, high-power, high-energy diode-pumped solid state lasers since the presence of bivalent Yb ions can be a source of thermal losses. To date, there has been no technique to determine Yb2+ concentration in as-grown crystals. The proposed technique is based on a total reduction of Yb3+ ions via the heating of as-grown CaF2 crystals with known concentration of Yb in the reducing atmosphere of metal vapour and determining the cross section of absorption bands of Yb2+ ions. The knowledge of these parameters allows estimation of the Yb2+ content in CaF2:Yb crystals or ceramics by analysing their absorption spectra. Examples of using this technique are given. The technology of CdF2 crystals reduction (an "additive colouring") and features of colouring of crystals doped with rare-earth ions are considered.

Shcheulin, A. S.; Angervaks, A. E.; Semenova, T. S.; Koryakina, L. F.; Petrova, M. A.; Fedorov, P. P.; Reiterov, V. M.; Garibin, E. A.; Ryskin, A. I.

2013-06-01

9

Quadrupole coupling and crystal-field shielding in CaF2:Eu3+:O2- under hydrostatic pressure  

Microsoft Academic Search

The nuclear quadrupole interactions in the 7F0 ground electronic state and the 5D0 excited state of the 151Eu3+ and 153Eu3+ ions have been investigated by optical means. The optically detected nuclear quadrupole resonance, excitation, and luminescence of the Eu3+-O2- C3v symmetry center have been studied at 4.2 K in single crystals of CaF2:Eu:O under hydrostatic pressure up to 7.5 kbar.

Andrzej P. Radlinski; A. J. Silversmith

1986-01-01

10

Growth and spectroscopic characterization of Pb2+:CaF2 crystals  

NASA Astrophysics Data System (ADS)

CaF2 crystals doped with various concentrations of PbF2 (0.4, 0.5, 1 and 2 mol%) were grown in vacuum, in a shaped graphite furnace using the vertical Bridgman method. The optical absorption spectra reveal the four characteristic UV absorption bands (labeled A, B, C and D) of the Pb2+ ions. As the PbF2 concentration increases, the structure of the bands become clearly visible, that is characteristic for the ns 2 ions in various hosts. High intensity emission bands in the near UV spectral region have been observed. The dependence on the Pb2+ concentration of the optical absorption and emission of the Pb2+:CaF2 crystals were not reported before.

Nicoara, I.; Paraschiva, M.; Stef, M.; Stef, F.

2012-08-01

11

Spectroscopic studies of pulsed-laser-induced damage sites in heated CaF2 crystals  

NASA Astrophysics Data System (ADS)

Based upon previous studies of temperature dependent defect state formation in high energy alpha particle irradiated CaF2 analogous temperature dependent effects were expected to occur when heated crystals were exposed to Q- switching emission from a pulsed Nd:YAG laser. It was shown in the (alpha) -irradiation work that optimum clustering of calcium atoms to form colloids would occur at a critical temperature. In recent work irradiation of isothermally heated crystals at fluences on the order of 1 J/cm2 produced both catastrophic mechanical damage to the crystal as well as localized defect states within the lattice. Below 200 degrees C the mechanical damage was severe, as evidenced by extensive fractures radiating from the damage center along the crystal cleavage planes. However, above 200 degrees C, these fracture lines revealed the presence of CaF2 lattice forbidden bands associated with calcium colloids in addition to a blue shift of the principal T2g CaF2 mode frequency. The T2g line shift signifies the presence of compressive stress in the CaF2 lattice induced by the presence of the calcium colloids. Forbidden phonon line intensities varied with Raman probe wavelength, and the associated Raman excitation profile followed the wavelength response of the optical absorption band at 580 nm, which is ascribed to colloid resonance absorption. The presence of colloid was detected at all temperatures, and the extent of colloid formation was found to be only weakly dependent upon the crystal temperature. This lack of sensitivity may be ascribed to highly located heating of the crystal surface during the laser pulse, which could supersede the effect of ambient temperature. Pulsed Raman studies of thin CaF2 section sat laser fluences just below the damage thresholds did indeed indicate temperature excursions within the laser footprint. For samples held at temperatures above 200 degrees C, the color centers were found to absorb more strongly in the 400-500 nm and NIR regions, Probably indicating greater aggregation of F centers in the crystal.

Bozlee, Brian J.; Exarhos, Gregory J.; Teel, Randy W.

1999-04-01

12

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

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

13

The exchange charge model and vibronic interactions for Mn2+ doped in CaF2 crystals  

NASA Astrophysics Data System (ADS)

The aim of this work is to present a crystal field analysis of the [CaF8]6- complex in the static crystal field and vibronic interactions in the dynamic crystal field. The modeling of the crystal field parameters and simulated energy level scheme is presented in the exchange charge model. In this model, the crystal field strength 10?Dq for different impurity-ligand distances near the equilibrium position was obtained. By fitting these values to an exponential law, we found n=7.278, as the exponent power, for the 10?Dq dependence (10?Dq?R-n). The electron-phonon interaction of the bivalent manganese ion doped in CaF2 was studied using the single configuration coordination model. Some physical quantities associated with the normal vibration modes a1g and eg of the [CaF8]6- complex coupled with the electron states of Mn2+ such as the Stokes shift and the Huang-Rhys factors are calculated. The obtained results are discussed and compared with experimental data.

Vaida, M.

2012-05-01

14

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

15

Ultraviolet-infrared femtosecond laser-induced damage in fused silica and CaF2 crystals  

NASA Astrophysics Data System (ADS)

The damage in fused silica and CaF2 crystals induced by wavelength tunable femtosecond lasers is studied. The threshold fluence is observed to increase rapidly with laser wavelength ? in the region of 250-800nm , while it is nearly a constant for 800

Jia, T. Q.; Chen, H. X.; Huang, M.; Zhao, F. L.; Li, X. X.; Xu, S. Z.; Sun, H. Y.; Feng, D. H.; Li, C. B.; Wang, X. F.; Li, R. X.; Xu, Z. Z.; He, X. K.; Kuroda, H.

2006-02-01

16

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

17

X-ray crystal truncation rod scattering from MBE grown (CaF 2-SrF 2)/Si(111) superlattices  

NASA Astrophysics Data System (ADS)

Flouride CaF 2-SrF 2 superlattices (SLs) grown by molecular beam epitaxy have been studied by means of X-ray diffractometry for the first time. The diffraction patterns showed reasonably good crystalline quality of the SLs and a type-B epitaxial relation to the Si(111) substrate. From the analysis of the crystal truncation rod (CTR) profiles, based on the pseudomorphic model, it was obtained that despite the same high temperature (770°C) of formation of the CaF 2/Si(111) interface its structure depended on the growth temperature of the SLs. The shape of the CTR profiles confirmed the existence of the superlattice which consists of one or two monolayer thick SrF 2 layers. Some CaF 2/SrF 2-interface roughness was noticeable.

Harada, J.; Itoh, Y.; Shimura, T.; Takahashi, I.; Alvarez, J. C.; Sokolov, N. S.

1994-01-01

18

Influence of Pb2+ ions on the morphology of etch pits and dislocation density of CaF2:YbF3 crystals  

NASA Astrophysics Data System (ADS)

Various concentrations YbF3 -doped CaF2 and Pb2+ - codoped crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (˜ 10-1 Pa) using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. In order to study the etch pits morphology and the dislocations density we used the chemical etching method. This method consists in immersing the cleaved sample in 4NHCl at 60°C for 5 minutes. Small pits are developed at the emergence points of the dislocations. The etch pits have hexagonal shapes for pure CaF2 crystal and triangular sahpes for doped crystals. The dislocations density depends also on the dopant or on the codopant concentration.

Stef, Marius; Stef, Florica; Buse, Gabriel; Nicoara, Irina

2012-08-01

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

20

Study of Na+ ions influence on the charge compensating defects in CaF2: YbF3 crystals using dielectric relaxation  

NASA Astrophysics Data System (ADS)

YbF3-doped and NaF co-doped calcium fluoride crystals were grown using the Vertical Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (?10-1 Pa) using a shaped graphite furnace. Room temperature absorption spectra and dielectric spectra were measured to study the effect of Na+ ions on the varieties of Yb3+ sites in CaF2 host. The experimental results show that by co-doping with Na+ ions in different Na:Yb ratios we can modulate the type of charge compensating defects of Yb3+ ions in CaF2 lattice. Dielectric relaxation in double doped (Yb, Na):CaF2 crystals-related with the study the charge compensating defects-was not reported before.

Nicoara, I.; Stef, M.

2012-06-01

21

Thermo-optical measurements of ytterbium doped ceramics (Sc2O3, Y203, Lu203, YAG) and crystals (YAG, CaF2) at cryogenic temperatures  

NASA Astrophysics Data System (ADS)

In this paper, we report the measurements of the specific heat, the density and the thermal diffusivity at room and cryogenic temperatures of Ytterbium doped cubic sesquioxides (Sc2O3, Y2O3, Lu2O3) ceramics and of Ytterbium doped crystals (YAG, CaF2). These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers.

Le Garrec, B.; Cardinali, V.; Bourdet, G.

2013-05-01

22

Formation of slab waveguides in eulytine type BGO and CaF2 crystals by implantation of MeV nitrogen ions  

NASA Astrophysics Data System (ADS)

Ion implantation, compared with other waveguide fabrication methods, has some unique advantages. It has proved to be a universal technique for producing waveguides in most optical materials. The authors of the present article reported fabrication of channel and slab waveguides in an Erbium-doped tungsten tellurite glass by implantation of MeV energy N+ ions. The present article reports successful adaptation of the same technique to the fabrication of slab waveguides in eulytine type bismuth germanate (BGO) and CaF2 crystals. This is the first report on successful waveguide fabrication in these materials using 3.5 MeV N+ ions at implanted fluences between 5 × 1015 and 4 × 1016 ions/cm2. Spectroscopic ellipsometric measurements revealed the existence of guiding structures in both materials. M-line spectroscopic measurements indicated guiding effect in the as-implanted BGO up to 1550 nm and up to 980 nm in the as-implanted CaF2. Ion implantation induced the appearance of three peaks in the UV/Vis absorption spectrum of CaF2, that can be attributed to colour centres.

Bányász, I.; Berneschi, S.; Khánh, N. Q.; Lohner, T.; Lengyel, K.; Fried, M.; Péter, Á.; Petrik, P.; Zolnai, Z.; Watterich, A.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.

2012-09-01

23

Ca-induced structural transformation of the single-domain Si(001) surface: CaF2/Si(001)-4° off  

NASA Astrophysics Data System (ADS)

By scanning tunneling microscopy and synchrotron photoemission spectroscopy, it has been found that through CaF2 exposure to the single-domain Si(001)-4° off surface held at 750 °C, Si dimers on Si(001) terraces are replaced preferentially by dissociated Ca atoms while F atoms are desorbed. The resulting 2 × 3 reconstruction saturates the (001) terraces at a coverage between 0.1 and 0.3 monolayers. Additional CaF2 exposure triggers a structural transformation to a stable hill-and-valley structure composed of wider (001)-2 × 3 terraces and compensating facets comprised of (11 17) and (11 13) units, both with a 6 × 1 surface reconstruction. This study demonstrates that the periodic width of the single domain Si(001) surface can be modulated through adsorbing Ca atoms while maintaining one-dimensional symmetry along the DB steps and the semiconducting nature of the surface.

Kim, Hidong; Dugerjav, Otgonbayar; Arvisbaatar, Amarmunkh; Motlak, Moaaed; Seo, Jae M.

2014-05-01

24

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

25

Defect diffusion in CaF2 for optical applications  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important lens material for deep-ultraviolet optics and a key material for 193 nm lithography. The exposure to high radiation densities requires extreme laser-stability of the material, which is to a large part ensured by a high purity level. However, for long exposure times the optical quality of CaF2 is affected by radiation-induced point defects, namely F- and H-centers. The migration and agglomeration of these point defects play an important role in understanding laser-damage processes on a microscopic level. We use ab-initio methods to investigate the stabilization of laser-induced point defects. As stabilization processes involve defect migration, we also focus on diffusion properties of defects. We present results for the diffusion barrier and details of the transition state of the migrating F-center, which shows good agreement with experimental results.

Stephan, Rix; Natura, Ute; Letz, Martin; Parthier, Lutz; Felser, Claudia

2010-03-01

26

Crystal structure and electrical property comparisons of epitaxial Pb(Zr,Ti)O3 thick films grown on (100)CaF2 and (100)SrTiO3 substrates  

NASA Astrophysics Data System (ADS)

Epitaxial Pb(Zr,Ti)O3 (PZT) thick films of 2.0-3.0 ?m thickness were grown at 600 °C on (100)cSrRuO3?(100)SrTiO3 and (100)cSrRuO3?(100)LaNiO3?(100)CaF2 substrates by pulsed-metal organic chemical vapor deposition. All films showed (100) and/or (001) orientations with tetragonal symmetry. It was found that there is an almost linear relationship between the estimated thermal strain from the deposition temperature to the Curie temperature and the volume fraction of (001) orientation in the mixture of (100) and (001) orientations for the films on both substrates. Consequently, the perfectly (001)-oriented, i.e., polar-axis-oriented, PZT thick films were obtained on CaF2 with the Zr/(Zr+Ti) ratio from 0.20 to 0.40. Moreover, the lattice parameter of a- and c-axes and their ratio (c /a) of those polar-axis-oriented films were almost the same as the reported data for the powder, suggesting that the large strain is not remaining in those films. The relative dielectric constant (?r) of the polar-axis-oriented Pb(Zr0.35Ti0.65)O3 thick film on CaF2 was 180 at 1 kHz, which is lower than that of (100)/(001)-oriented thick films on SrTiO3 but almost agrees with the theoretically calculated value for the c-axis of PZT single crystals. Well saturated polarization-electric-field hysteresis loops with a good square shape were observed for the polar-axis-oriented thick films, and the saturation polarization and the coercive field values were 74 ?C/cm2 and 64 kV/cm, respectively. These data clearly show that the electrical properties of the polar-axis-oriented epitaxial thick films are similar to the theoretical predictions for PZT single crystals.

Fujisawa, Takashi; Nakaki, Hiroshi; Ikariyama, Rikyu; Yamada, Tomoaki; Ishikawa, Mutsuo; Morioka, Hitoshi; Funakubo, Hiroshi

2009-03-01

27

Optical properties of CaF2 and Yb3+:CaF2 for laser applications  

NASA Astrophysics Data System (ADS)

Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The author? process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

Stäblein, Jörg; Pöhl, Karin; Weisleder, Andreas; v. d. Gönna, Gordon; Töpfer, Thomas; Hein, Joachim; Siebold, Mathias

2011-06-01

28

Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation  

NASA Astrophysics Data System (ADS)

CaF2 crystals as representatives of the class of ionic nonamorphizable insulators were irradiated with many different swift heavy ions of energy above 0.5 MeV/u providing a broad range of electronic energy losses (Se). Beam-induced modifications were characterized by Channeling Rutherford Backscattering Spectrometry (C-RBS) and x-ray diffraction (XRD), complemented by transmission electron microscopy (TEM). Results from C-RBS give evidence of significant damage appearing above a Se threshold of 5 ± 2 keV/nm. A second critical Se appears around 18 ± 3 keV/nm; below this value the damage as function of ion fluence saturates at 20%, while above this the damage saturation level increases with Se, reaching ˜60% for ions of Se = 30 keV/nm. XRD measurements also show effects indicating two threshold values. Above 5 keV/nm, the widths of the XRD reflection peaks increase due to the formation of nanograins, as seen by TEM, while a significant decrease of the peak areas only occurs above 18 keV/nm. The track radii deduced from C-RBS measurements are in agreement with those extracted from the fluence evolution of the widths of the XRD peaks. Moreover, track radii deduced from the peak area analysis are slightly smaller but in agreement with previous track observations by high resolution electron microscopy. Calculations based on the inelastic thermal spike model suggest that the lower threshold at 5 keV/nm is linked to the quenching of the molten phase, whereas the threshold at 18 keV/nm can be interpreted as quenching of the boiling phase. The results of CaF2 are compared with other nonamorphizable materials such as LiF and UO2.

Toulemonde, M.; Benyagoub, A.; Trautmann, C.; Khalfaoui, N.; Boccanfuso, M.; Dufour, C.; Gourbilleau, F.; Grob, J. J.; Stoquert, J. P.; Costantini, J. M.; Haas, F.; Jacquet, E.; Voss, K.-O.; Meftah, A.

2012-02-01

29

SPECIAL ISSUE DEVOTED TO THE 90TH ANNIVERSARY OF A.M. PROKHOROV: Continuously tunable cw lasing near 2.75 ?m in diode-pumped Er3+ : SrF2 and Er3+ : CaF2 crystals  

NASA Astrophysics Data System (ADS)

CW lasing is obtained in Er3+(5%) : CaF2 and Er3+(5%) : SrF2 crystals near 2.75 ?m with 0.4 and 2 W of output powers, respectively, upon transverse diode laser pumping into the upper 4I11/2 laser level of erbium ions at 980 nm. Continuous tuning of the laser wavelength between 2720 and 2760 nm is realised in the Er3+ : SrF2 crystal.

Basiev, Tasoltan T.; Orlovskii, Yu V.; Polyachenkova, M. V.; Fedorov, Pavel P.; Kuznetsov, S. V.; Konyushkin, V. A.; Osiko, Vyacheslav V.; Alimov, Olimkhon K.; Dergachev, Alexey Yu

2006-07-01

30

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

NASA Technical Reports Server (NTRS)

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

Deadmore, Daniel L.; Sliney, Harold E.

1987-01-01

31

Biaxially-Textured Photovoltaic Film Crystal Silicon on Ion Beam Assisted Deposition CaF2 Seed Layers on Glass  

SciTech Connect

We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF{sub 2} seed layers using ion-beam assisted deposition, then coat the CaF{sub 2} with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF{sub 2} and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.

Groves, J. R.; Li, J. B.; Clemens, B. M.; LaSalvia, V.; Hasoon, F.; Branz, H. M.; Teplin, C. W.

2012-05-01

32

Comment on ``Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation''  

NASA Astrophysics Data System (ADS)

Systematic experiments on irradiation damage in CaF2 were reported in a recent paper [M. Toulemonde , Phys. Rev. BPRBMDO0163-182910.1103/PhysRevB.85.054112 85, 054112 (2012)]. The measurements were performed in a broad range of ion energies and energy deposition and the inelastic thermal spike model was applied for the analysis. Here we demonstrate that contrary to what is stated in the paper, the experimental results do not prove that there is a velocity effect in CaF2 similar to that observed previously in Y3Fe5O12 and other track-forming insulators. We also show that the authors’ results do not support their hypothesis that tracks are formed by quenching of a boiling phase.

Szenes, G.

2013-02-01

33

Radiation Damage in CaF2 and BaF2 Investigated by the Channeling Technique  

Microsoft Academic Search

The radiation damage in single crystals of CaF2 and BaF2 due to room temperature bombardment with 2.0 MeV helium ions has been studied by the channeling technique. Backscattering spectra for the langle111rangle and langle110rangle axial directions were taken after different doses of random irradiation. A slight increase of the aligned yield with radiation dose has been found for both crystals

R. Hellborg; G. Skog

1974-01-01

34

Damage ingrowth and recovery in alpha-irradiated CaF2, SrF2, and BaF2  

Microsoft Academic Search

Single crystals of CaF2, SrF2, and BaF2 were irradiated at room temperature with alpha particles emitted from an effectively semi-infinite PuO2 source to a cumulative dose of 3 × 10 alpha particles\\/m. Although no change in the lattice parameter of CaF2 was observed, the crystals exhibited increasing coloration with dose. The lattice parameters of both SrF2 and BaF2 increased exponentially

W. J. Weber

1983-01-01

35

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

E-print Network

based on an Yb31:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at femtosecond laser A. Lucca, G. Debourg, M. Jacquemet, F. Druon, F. Balembois, and P. Georges Laboratoire. Moncorgé Centre Interdisciplinaire de Recherches sur les Ions et les Lasers, Unité Mixte de Recherche 6637

Boyer, Edmond

36

Behavior Analysis of CaF2 in Magnesia Carbothermic Reduction Process in Vacuum  

NASA Astrophysics Data System (ADS)

Magnesium production by carbothermic reduction of magnesia with CaF2 in vacuum was investigated experimentally by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and thermodynamic analysis. Thermodynamic calculations indicate that magnesium was generated by a carbothermic reduction among MgO-C system, which should be above 1500 K (1227 °C) (50 Pa). According to the carbothermic reduction analysis, the CaF2 does not participate in the carbothermic process. The experimental results demonstrated that the mass loss increased along with increasing CaF2. The percentage was up to 92 pct with 5 pct CaF2.The reduction degree increased with CaF2 more than it without CaF2 obviously. Considering the reduction degree and economic benefit, 5 pct CaF2 was the optimal choice. The purity of metal magnesium reached 95.59 wt pct, which has perfect crystallization and lamellar structure. CaF2 did not participate in magnesia carbothermic reduction in vacuum; instead, it played a catalytic role during the process.

Tian, Yang; Qu, Tao; Yang, Bin; Dai, Yong-Nian; Xu, Bao-Qiang; Geng, Sen

2012-06-01

37

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 BaF 2 and CaF 2 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 BaF 2(111) two-dimensional water layers are formed after accumulation at step edges, CaF 2(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 BaF 2( 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

38

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

39

Radiation Damage in Epitaxial CaF2 Films on Si Substrates by Ar+ Ion Implantation  

NASA Astrophysics Data System (ADS)

Radiation damage in epitaxial CaF2 films on Si substrates produced by 150 keV Ar+ ion implantation has been investigated using Rutherford backscattering and channeling techniques. It has been found that CaF2 films are more stable than Si crystals for ion bombardment and are not amorphized at such a high dose as 6× 1016 cm-2. Recovery of the damage by subsequent thermal annealing has also been investigated.

Ishiwara, Hiroshi; Orihara, Kouzo; Asano, Tanemasa

1983-07-01

40

Analysis of tracks induced by cluster ions in CaF2  

NASA Astrophysics Data System (ADS)

Recent experimental data on latent tracks induced in CaF2 by cluster ions are analyzed applying a thermal spike model. The track evolution can be described by the same equations in radiolysis sensitive CaF2 and in the radiolysis resistant Y3Fe5O12, using similar parameter values. The efficiency of the localized energy deposition g=0.18 for CaF2, which is equal within experimental error to that in Y3Fe5O12 at high ion velocities. This indicates that the damage cross section is not sensitive to the ion velocity in CaF2. The similarities observed in the track evolution in insulating crystals, polymers, semiconductors, and high-Tc superconductors are explained by the Gaussian spatial distribution of the excitation energy with close values of the distribution parameters.

Szenes, G.

2000-06-01

41

Studies of the growth kinetics of CaF 2(1 1 1) by molecular beam methods and atomic force microscopy  

Microsoft Academic Search

The growth kinetics of the (111) surface of CaF2 single crystals is studied by molecular beam methods and atomic force microscopy for temperatures between 1015 and 1099K and saturation ratios up to 354. After passing a transition stage with repeated two-dimensional nucleation, island growth and coalescence of the growing islands the surface develops growth hillocks with closed loop steps of

M. Schick; H. Dabringhaus; K. Wandelt

2005-01-01

42

Determination of the thermo-optic coefficient dn/dT of ytterbium doped ceramics (Sc2O3, Y2O3, Lu2O3, YAG), crystals (YAG, CaF2) and neodymium doped phosphate glass at cryogenic temperature  

NASA Astrophysics Data System (ADS)

In this paper, we report the measurements of the thermal expansion coefficient and the thermo-optic coefficient dn/dT for the ytterbium doped cubic sesquioxides (Sc2O3, Y2O3, Lu2O3) at cryogenic temperature. These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers. Measurements have also been done on YAG ceramic and crystal, CaF2 crystal, and neodymium phosphate glass (Hoya, LHG-8).

Cardinali, V.; Marmois, E.; Le Garrec, B.; Bourdet, G.

2012-04-01

43

Reply to ``Comment on `Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation' ''  

NASA Astrophysics Data System (ADS)

Experimental data presented in our earlier paper [Toulemonde , Phys. Rev. B10.1103/PhysRevB.85.054112 85, 054112 (2012)] indicate that there are two thresholds for damage creation by swift heavy ions in CaF2. Moreover, the comparison of the track sizes observed by transmission electron microscopy and generated by different cluster and monoatomic ion beams supports the occurrence of a velocity effect in this material.

Toulemonde, M.; Benyagoub, A.; Trautmann, C.; Khalfaoui, N.; Boccanfuso, M.; Dufour, C.; Gourbilleau, F.; Grob, J. J.; Stoquert, J. P.; Costantini, J. M.; Haas, F.; Jacquet, E.; Voss, K.-O.; Meftah, A.

2013-02-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

45

Epitaxial growth of Eu doped CaF2 thin film on CaF2 (111)  

NASA Astrophysics Data System (ADS)

Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low temperature solution growth method. The CaF2: Eu films when grown on Si (111) and glass substrate show random orientation having higher degree of surface roughness. As confirmed by the X-ray diffraction and photoluminescence results, Eu (II) ions substitute the Ca sites of CaF2 lattice. Excitation spectrum shows two broad peaks at 282 and 366 nm, which correspond to the allowed transitions of 4f7 to 4f65d1 (eg) and 4f65d1 (t2g) of Eu2+, respectively. Photoluminescence of Eu (II) doped CaF2 films exhibit intense and sharp peak in the blue region of the spectrum.

Ghosh, Manoranjan; Ningthoujam, R. S.; Patra, G. D.; Shinde, Seema; Sen, S.; Bhattacharya, S.; Gadkari, S. C.

2012-06-01

46

Multiple-Quantum NMR Coherence Growth in Single-Crystal and Powdered Calcium Fluoride  

NASA Astrophysics Data System (ADS)

Powdered and oriented single-crystal calcium fluoride (CaF 2) samples were used to determine the orientational dependence of 19F multiple-quantum (MQ) NMR coherence development in the absence of variations in lattice spacing and molecular motion on the experimental time scale. The normalized n-quantum coherence intensities and resultant effective spin-cluster size [ N(?)] of the powdered sample were found to be reproducible and insensitive to the cycle time chosen for the underlying eight-pulse MQ excitation sequence. Oscillations in the time-dependent 0Q and 2Q coherence intensities are seen in the oriented single-crystal samples. However, these oscillations are absent in the powdered CaF 2 sample, indicating damping by its orientational-based dipolar-coupling distribution. However, monotonic growth of the effective number of correlated nuclei, N(?), is still observed. In addition, the applicability of an average product-operator model of coherence growth based on the dimensionality of spin distribution, and previously only applied to powders, is tested for oriented single-crystal CaF 2 samples. The powdered and (100)-oriented single crystal show good agreement with the model, while the growth from the (111) orientation is slightly faster than predicted. This difference most likely arises from the unusual dipole structure of the (111)-oriented crystal, where nearest-neighbor couplings become zero. In addition, the refocused MQ signal intensity ( fMQ) is adversely effected by increasing the number of pulses applied in a fixed MQ preparation time. An empirical prediction of fMQ for samples with a static dipolar field is developed and serves as a basis for predicting the effects of motion on this MQ refocusing fraction. This relationship may also provide some insight into the possibility of extending the MQ technique to study correlations over larger length scales as the relatively rapid decay of fMQ typical limits the present experiment to ˜ 10 Å length scales.

Lathrop, D. A.; Handy, E. S.; Gleason, K. K.

47

Single crystal magnets  

NASA Astrophysics Data System (ADS)

Single crystals of the Fe-Cr-Co alloys without and with 3% Mo were prepared by a recrystallization process. The microstructures and the magnetic properties of <100>, <110>, and <111> single crystals were investigated after the heat treatment in the ridge region of the miscibility gap. The magnetic properties of the Fe-22 Cr-17 Co ridge single crystals were not affected very much by the crystal orientation. However, the Fe-23 Cr-20 Co-3 Mo alloys show the crystal orientation dependence of the magnetic properties. The single crystal alloys are aged in a magnetic field, the direction of which is varied around <100> axes. The magnetic properties are measured parallel to the applied field directions and are summarized in view of deviated angle from a <100> axis. The greater the deviation of the applied field direction from a <100> axis, the poorer are the magnetic properties of the Mo single crystal alloy. The best magnetic properties are achieved with Fe-22 Cr-18.5 Co-3 Mo <100> ridge single crystal as Br=1.58 T (15.8 kG), bHc=72.8 kA/m (910 Oe), and (BH)max=91.2 kJ/m3 (11.4 MGOe), which is the highest energy product reported for the Fe-Cr-Co magnet family.

Ikuta, N.; Okada, M.; Homma, M.; Minowa, T.

1983-09-01

48

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

49

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

50

Paramagnetic hyperfine splitting in the 151Eu Mössbauer spectra of CaF2:Eu2+  

PubMed Central

151Eu Mössbauer spectra in zero magnetic field of highly dilute (0.1 mol%) Eu2+ ions in CaF2 showed an almost temperature-independent asymmetrically split pattern, arising from the paramagnetic hyperfine interaction AS. I in a cubic crystal field with slow electron spin relaxation; in a small external magnetic field B of 0.2 T such that g?BB>A an almost symmetrical pattern was observed. Both the spectra with and without external field are well described using the spin Hamiltonian and previous electron paramagnetic resonance data. A more concentrated (2 mol% Eu2+) sample exhibited a strongly broadened symmetrical resonance line due to an increased Eu-Eu spin relaxation rate; in an external magnetic field of 0.2 T the Mössbauer spectra exhibited further broadening and additional magnetic structures due to the reduced relaxation rate. When a large field of 6 T was applied such that g?BB is much larger than the crystal field splitting, a fully resolved hyperfine pattern was observed at 2.5 K, with an effective field at the Eu nuclei of ?33.7 T; at higher temperatures superimposed patterns originating from excited electronic states were observed in the spectra. The present results on the highly dilute CaF2 : 0.1%Eu2+ sample deliver a straightforward explanation for previous observations of a seemingly large dependence of the Eu2+ isomer shift on europium concentration. PMID:19816547

Selling, J.; Bielemeier, B.; Wortmann, G.; Johnson, J. A.; Alp, E. E.; Chen, T.; Brown, D. E.; Johnson, C. E.; Schweizer, S.

2009-01-01

51

Theory of the Frenkel Debye boundary layer at the (111) surface of pure CaF2  

Microsoft Academic Search

The present paper is concerned with a theoretical study of the properties of the Frenkel Debye boundary layer at the (111) surface of pure (undoped) CaF2, a crystal with anti-Frenkel defects, i.e. with anion vacancies and interstitials. The study is based on theoretical determinations of the adsorption energies of the fluorine ion at the terrace, step and kink sites on

Heinz Dabringhaus; Mikhail F. Butman

2003-01-01

52

Insulating epitaxial films of BaF 2, CaF 2 and Ba xCa 1- xF 2 grown by MBE on InP substrates  

NASA Astrophysics Data System (ADS)

Thin films (? 5000 Å) of BaF 2, CaF 2, and Ba xCa 1- xF 2 have been grown onto InP (001) substrates in a vacuum locked MBE system. Electron diffraction was used to monitor film nucleation and growth at a variety of substrate temperatures. Subsequent ex-situ analysis included X-ray diffraction, electron microscopy and Auger sputter profiling. In addition, capacitance-voltage and current-voltage analyses were performed on MIS sandwich devices formed by evaporating aluminium onto the semiconductor-flouride samples. Deposition of flourides onto room temperature substrates resulted in the growth of smooth, pinhole free, stoichiometric polycrystalline films with little or no preferred orientation. TEM analysis indicates a grain size of the same order as the film thickness (˜ 1000 Å). Deposition of BaF 2 and CaF 2 onto cleaned, well-ordered (001) InP held at temperatures above 200°C resulted in single-crystal, heteroepitaxial growth. In the case of CaF 2, the increase in lattice mismatch on cooling to room temperature resulted in crazing of the epitaxial layer. Film resistivity values around 10 12-10 13? cm and breakdown strengths of 5x10 5V cm -1 have been achieved for both polycrystalline and single-crystal layers. In initial experiments on the growth of Ba xCa 1- xF 2 alloys onto (001) epitaxial films of a single-phase cubic alloy with x ˜ 0.2 were obtained.

Sullivan, P. W.; Farrow, R. F. C.; Jones, G. R.

1982-12-01

53

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

54

Optical detection of electron transfer through interfaces in CaF 2:Eu-CdF 2 SLs  

NASA Astrophysics Data System (ADS)

We present here a further study of unusual features observed in photoluminescence (PL) of Eu 2+ in CaF 2 layers of CaF 2-CdF 2 SLs (SLs) [N.S. Sokolov, S.V.Gastev, A.Yu. Khilko, S.M. Suturin, I.N. Yassievich, J.M. Langer, A. Kozanezcki, Phys.Rev B 59 (1999) R2525]. PL of Eu 2+ in SLs, in contrast to bulk CaF 2:Eu crystals, fades out considerably under continuous UV excitation. This is mainly due to tunneling-assisted photoionization of Eu 2+. We have measured the PL time dependence in uniformly and selectively doped SLs with different periods and compared the results with the calculations in the tunneling model. A careful analysis of PL in selectively doped SLs revealed an additional ionization process suggested to occur in all SLs independent of the Eu ion position. With the account of this process we find that the experimental results are in good agreement with theoretical calculations. We have estimated the values of the main parameters in the tunneling model, which show the best fit with the experiment.

Suturin, S. M.; Basun, S. A.; Gastev, S. V.; Langer, J. M.; Meltzer, R. S.; Sokolov, N. S.

2000-08-01

55

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

56

Preparation of CaF 2 based phosphors by solid state metathesis  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

57

Development of single crystal membranes  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

58

Nanocrystalline CaF 2 particles obtained by high-energy ball milling  

Microsoft Academic Search

Structural changes in mechanically treated CaF2 powders have been studied by X-ray diffraction, transmission electron microscopy, thermal analysis, 19F and 1H MAS Nuclear Magnetic Resonance and Electron Paramagnetic Resonance methods.Applying the same methods, the results could be compared with those of mechanochemically synthesized CaF2 samples, prepared for the first time in this study by high-energy ball milling. The applied methods

G.. Scholz; I. Doerfel; D. Heidemann; M. Feist; R. Stoesser

2006-01-01

59

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: microelectromechanical systems; calorimetry; nanocalorimetry; polyeth- ylene single crystals; melting INTRODUCTION We

Allen, Leslie H.

60

Photon tunnelling microscopy of polyethylene single crystals  

E-print Network

Photon tunnelling microscopy of polyethylene single crystals Mohan Srinivasarao* and Richard S polyethylenesinglecrystals, providing a topographical map ofthe single-crystal surface.Tunnelling increases exponentially:photon tunnellingmicroscopy;single crystals; polyethylene) INTRODUCTION The study of morphology of polymers is an area

Srinivasarao, Mohan

61

Titania single crystals with a curved surface.  

PubMed

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. PMID:25373513

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

2014-01-01

62

Experimental study of the adsorption of lithium fluoride on the (111) surface of CaF 2  

NASA Astrophysics Data System (ADS)

The interaction of molecular beams of the lithium fluoride monomers LiF and dimers Li 2F 2 with the (111) surface of CaF 2 crystals has been studied by the method of desorption transients for crystal temperatures between T=777 and 985 K and for total lithium fluoride fluxes jon=1×10 10-1×10 14 cm -2s -1. The studies show that the monomers are adsorbed at the monatomic steps on the CaF 2 surface. The steps have a limited capacity of the order of 10 12 cm -2 for an adsorption direct at them; further monomers are adsorbed in their immediate neighborhood beside already adsorbed monomers. The adsorption times derived from transient desorption fluxes result as ?0 (s)=1.3 (+9.5, -1.15)×10 -15 exp[(2.70±0.17) eV/ kT] for an adsorption direct at the steps and as ?1 (s)=7.6 (+30, -6.0)×10 -15 exp[(2.44±0.11) eV/ kT] beside them. For the dimers, only a portion ?d, 0.5< ?d( T)<0.85, of the impinging dimer flux reaches the steps, while the remainder desorbs quickly. From ?d( T), the ratio of the mean diffusion length xds on the terrace to the mean step distance, ?, is determined as xds/ ?=(2.9±0.9)×10 -2 exp[(0.5±0.05) eV/2 kT]. With ??8×10 -6 cm as derived from atom force microscopic studies jump distances for the dimers in the order of the lattice constant of CaF 2 are obtained corresponding to a surface diffusion model with jumps between neighboring lattice sites. Dimers at the steps are completely dissociated into monomers. For larger monomer concentrations at the steps also a formation of dimers and their subsequent desorption is observed. By a comparison of experimental desorption transients with a simple theoretical model, the above adsorption times as well as a constant k (cm s -1)=8.0(+42, -6.8) exp[-(1.63±0.16) eV/ kT] describing the formation and desorption of the dimers are determined.

Klumpp, St.; Dabringhaus, H.

1998-11-01

63

Effect of CaF2 addition on optical properties of barium phosphate glasses  

NASA Astrophysics Data System (ADS)

Ternary barium phosphate glasses, (50-X)BaO-XCaF2-50P2O5 have been prepared by adding 0-10 mol% of CaF2 to binary barium phosphate glasses. The amorphous nature of the prepared glasses was confirmed by X-ray diffraction technique. The UV-Visible absorption spectra have been recorded, optical band gap energy Eopt and Urbach energy Etail were determined. Shift in Eopt and Etail with increase in concentration of CaF2 is noted. FTIR analysis was carried out to investigate the short and intermediate-range orders in glasses. Shift of (P-O-P) band to higher wave number with the substitution of BaO with CaF2 shows the shortening of the phosphate chains. Hardness and density of glass samples were measured and correlated with the composition of glasses.

Kumar, N. Manoj; Rao, G. Venkateswara; Akhila, B. E.; Shashikala, H. D.

2014-04-01

64

Growth and optical properties of partially transparent Eu doped CaF2 ceramic  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

65

Growth of single crystal diamond  

NASA Astrophysics Data System (ADS)

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

Regmi, Murari

66

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

67

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

68

Single crystals for welding research  

SciTech Connect

Most welds last for many years, but a few fail after a relatively short time. Knowing the reasons why welds fail is important because cracks in welds can threaten the safety of people in buildings, airplanes, ships, automobiles, and power plants. Bad welds can lead to costly, extended shutdowns of industrial facilities such as petroleum refineries. Thus, research on this very important fabrication technology is critical to the multibillion-dollar welding industry. Research at ORNL and elsewhere strives to determine the structural features that make some welds strong and others weak. The goals are to find cost-effective ways to characterize the structure and strength of a new weld, correctly predict whether it will last a long time, and determine the welding conditions most likely to produce high-quality welds. There is more to welding than meets the eye. The cracks that make welds fail result from the complexities of microstructures formed during welding. Thus weld microstructure is linked to weld properties such as mechanical strength. As the hot weld material cools from a liquid into a solid, the crystalline grains grow at different speeds and in different directions, forming a new microstructure. By using single crystals rather than polycrystalline alloys to study different weld microstructures, scientists at ORNL have developed a way to predict more accurately the microstructures of various welds. The results could guide welders in providing the right conditions (correct welding speed, heat input, and weld thickness) for producing safer, higher-quality, and longer-lasting welds.

David, S.A.; Boatner, L.A.

1991-01-01

69

Method of making single crystal fibers  

NASA Technical Reports Server (NTRS)

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

Westfall, Leonard J. (inventor)

1990-01-01

70

Single Crystal Sapphire Optical Fiber Sensor Instrumentation  

SciTech Connect

The goal of this 30 month program is to develop reliable accurate temperature sensors based on single crystal sapphire materials that can withstand the temperatures and corrosive agents present within the gasifier environment. The research for this reporting period has been segregated into two parallel paths--corrosion resistance measurements for single crystal sapphire fibers and investigation of single crystal sapphire sensor configurations. The ultimate goal of this phase one segment is to design, develop and demonstrate on a laboratory scale a suitable temperature measurement device that can be field tested in phase two of the program.

Anbo Wang; Russell May; Gary R. Pickrell

2000-10-28

71

Electrical Properties of Black Phosphorus Single Crystals  

Microsoft Academic Search

Large single crystals of black phosphorus have been grown under high pressure, and by using the crystals, the Hall measurements have been done in a range from 4.2 K to 550 K. All the undoped samples have exhibited p-type conduction, while we have succeeded in obtaining n-type crystals by doping Te impurity. The effective acceptor concentrations NA-ND of the p-type

Yuichi Akahama; Shoichi Endo; Shin-ichiro Narita

1983-01-01

72

Sublimation Kinetics of Zinc Single Crystals.  

National Technical Information Service (NTIS)

The kinetics of the free surface sublimation of zinc single crystals were investigated using the torsion-Langmuir technique in conjunction with optical and electron microscopes. Sublimation from cleaved surfaces took place in two distinct stages, a stage ...

R. W. Mar

1968-01-01

73

Influence of crystal orientation on ECAP of aluminum single crystals  

Microsoft Academic Search

A single crystal of high purity aluminum, oriented with the {111} slip plane and the ?110? slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and the shear direction, was processed by equal-channel angular pressing (ECAP) through a single pass. This configuration was designated the 20° orientation and the results are compared with earlier data

Yukihide Fukuda; Keiichiro Oh-ishi; Minoru Furukawa; Zenji Horita; Terence G. Langdon

2006-01-01

74

Mechanism of thermoluminescence in CaF2:Eu and CaSO4:Eu phosphors  

Microsoft Academic Search

CaF2:RE and CaSO4:RE are important phosphors. The phosphors corresponding to RE identical to Dy and Tm find applications in thermoluminescence dosimetry using ionizing radiations. Although these phosphors have been in use for several years, the mechanism of thermoluminescence in these phosphors is not well understood. The role of RE ions in emission has been clearly indicated. Two types of model

S. V. Upadeo; T. K. Gundurao; S. V. Moharil

1994-01-01

75

Self-lubrication of sintered ceramic tools with CaF 2 additions in dry cutting  

Microsoft Academic Search

An Al2O3\\/TiC ceramic cutting tool with the additions of CaF2 solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the

Deng Jianxin; Cao Tongkun; Yang Xuefeng; Liu Jianhua

2006-01-01

76

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

77

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

78

Oxygen Incorporation in Rubrene Single Crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

79

Remarkable structural diversity and single-crystal-to-single-crystal transformations in sulfone functionalized lanthanide MOFs  

SciTech Connect

We report the formation of novel open framework lanthanide (La, Ce, Pr and Dy) MOFs using the ligand 4,4{prime}-bibenzoic acid-2,2{prime}-sulfone. In the case of Ce and Pr, an unprecedented single-crystal-to-single-crystal transformation at room temperature was discovered.

Neofotistou, Eleftheria; Malliakas, Christos D.; Trikalitis, Pantelis N. (NWU); (Crete)

2010-04-13

80

Helical Single Crystals Grown in Confined Space  

NASA Astrophysics Data System (ADS)

We report here the formation and growth process of the double-twist PET(R*-9) helical single crystals. It has been observed that the population of helical crystals increases with increasing the thickness of the thin films. In addition to the crystallization temperature effect, the pitch lengths along both the long and short twist axes also change with thin film thickness, which is attributed to the substrate confinement effect on the thin film samples. The early stage of the helical crystals has been studied using solvent washing experiments. It has been found that the morphology is a saddle-like shape. Nucleation starts at the center of the flat-on part, and growth directions include both along the long and short axes of the crystals. Coexistence of the flat-elongated and helical forms will also be discussed.

Li, Christopher; Cheng, Stephen; Zhang, John; Harris, Frank; Chien, Liang-Chy; Lotz, Bernard

2001-03-01

81

Photoluminescence quenching in oligothiophene single crystal  

Microsoft Academic Search

A single crystal of stereo-regularly substituted dihexylsexithiophene (DH6T) was synthesized. The transient photoluminescence decay curve of the crystal was non-exponential as in amorphous polythiophene. This non-exponential decay curve could be successfully described by stretched exponential decay kinetics, which represent the exciton diffusing to the one-dimensionally dispersed quenching centers. The generation of radical species by photoirradiation was confirmed by light-induced ESR

Tadatake Sato; Mamoru Fujitsuka; Motoo Shiro; Kazuyoshi Tanaka

1998-01-01

82

Thermoluminescence, optical absorption and photoluminescence studies on ?-irradiated CaF:Dy:Pb:Na single crystals  

NASA Astrophysics Data System (ADS)

Thermoluminescence (TL) glow, TL emission (TLE), Optical Absorption (OA) and Photoluminescence (PL) studies were made on ?-irradiated CaF 2:Dy:Pb:Na single crystals (Dy-0.005 at%, Pb-0.188 at% and Na-0.007 at%). The TL glow curve (after 206 Gy dose) exhibited three glow peaks around 394, 445 (shoulder) and 536 K. The first peak was found most intense for lower doses (<˜3680 Gy) and beyond this dose the second peak was dominanting. The growth of this peak could be exploited in this system to measure the radiation doses (at least upto ˜8 kGy) as it was at a higher temperature compared to the first peak. The TLE spectra were recorded under each glow peak and found to be the characteristic Dy 3+ emission. The ?-irradiated crystal showed OA bands around 2.06, 3.28, 3.75 (shoulder) and 2.48 eV. The first three bands could be attributed to M Na centre. The thermal bleaching of the OA spectrum was observed. The excitation spectrum for the Dy 3+ emission around 2.15 eV was very broad peaking around 3.55 eV. This consisted of a few overlapping bands originated from different colour centres (CCs) formed after ?-irradiation and M Na was one such centre. The intensiy and shape of the excitation spectrum changed with temperature indicating the decay and conversion of different CCs taking part in the PL process. The probable TL mechanism was suggested for the present system.

Masilla Moses Kennedy, S.

83

First Single-Crystal Mullite Fibers  

NASA Technical Reports Server (NTRS)

Ceramic-matrix composites strengthened by suitable fiber additions are being developed for high-temperature use, particularly for aerospace applications. New oxide-based fibers, such as mullite, are particularly desirable because of their resistance to high-temperature oxidative environments. Mullite is a candidate material in both fiber and matrix form. The primary objective of this work was to determine the growth characteristics of single-crystal mullite fibers produced by the laser-heated floating zone method. Directionally solidified fibers with nominal mullite compositions of 3Al2O3 2SiO2 were grown by the laser-heated floating zone method at the NASA Lewis Research Center. SEM analysis revealed that the single-crystal fibers grown in this study were strongly faceted and that the facets act as critical flaws, limiting fiber strength. The average fiber tensile strength is 1.15 GPa at room temperature. The mullite fibers exhibit superior strength retention (80 percent of their room temperature tensile strength at 1450 C). Examined by transmission electron microscopy, these mullite single crystals are free of dislocations, low-angle boundaries, and voids. In addition, they show a high degree of oxygen vacancy ordering. High-resolution digital images from an optical microscope furnish evidence of the formation of a liquid-liquid miscibility gap during crystal growth. These images represent the first experimental evidence of liquid immiscibility for these compositions and temperatures. Continuing investigation with controlled seeding of mullite single crystals is planned.

1997-01-01

84

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

85

Theory of the Frenkel Debye boundary layer at the (111) surface of pure CaF2  

NASA Astrophysics Data System (ADS)

The present paper is concerned with a theoretical study of the properties of the Frenkel Debye boundary layer at the (111) surface of pure (undoped) CaF2, a crystal with anti-Frenkel defects, i.e. with anion vacancies and interstitials. The study is based on theoretical determinations of the adsorption energies of the fluorine ion at the terrace, step and kink sites on the surface, which are, together with the assumption of experimental step distances and theoretical kink concentrations, necessary pre-requisites for a quantitative description of the surface charge compensating that of the space-charge region. The results show that, for realistic surface conditions, the surface and space charges, and with them the potential between surface and bulk, are reduced considerably compared with those for an unlimited number of accessible surface sites. Nevertheless, on approaching the surface a strong increase in the anion vacancy concentration against that of the bulk still exists, which should lead to an increased ion conductivity in near-surface regions and thin fluorite layers.

Dabringhaus, Heinz; Butman, Mikhail F.

2003-09-01

86

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

87

Single-crystal ruby fiber temperature sensor  

Microsoft Academic Search

Single-crystal ruby fibers with nominal diameters in the range from 80 to 500?m and lengths up to 170mm have been produced using the laser heated miniature pedestal growth technique. These fibers were tested for use as the basis of fiber optic temperature sensors. Characterization of the fiber fluorescence properties and comparison to bulk samples together with their high melting point

H. C Seat; J. H Sharp; Z. Y Zhang; K. T. V. Grattan

2002-01-01

88

Growth of single-crystal gallium nitride  

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

89

Magnetic Properties of Single Crystal Nickel Nanowires  

NASA Astrophysics Data System (ADS)

Toward the goal of understanding magnetism in confined dimensions, we have synthesized Nickel nanowires (NWs) by chemical vapor deposition and characterized their magnetic properties. By tuning chemical vapor deposition synthesis parameters, we can controllably synthesize a variety of morphologically dissimilar Ni products onto untreated amorphous SiO2||Si substrates [1]. These structures include polycrystalline core-shell NWs, single-crystal cubes, in-plane wires, and vertically-oriented single crystal arrays. To probe the magnetic properties of individual NWs, we combined magneto-transport, XPEEM, and magnetic modeling. For polycrystalline NWs, the magnetic properties are dominated by shape anisotropy. However, for single-crystal NWs, there is a competition between the shape anisotropy along the (001) direction and magneto-crystalline anisotropy along the (111) direction. This gives rise to complex magnetic stripe domain patterns along the wires, interesting magneto-transport properties, and novel reversal modes not typically observed in magnetic wires. [4pt] [1] K.T. Chan, J.J. Kan, E.E. Fullerton, et al., "Oriented Growth of Single-Crystal Ni Nanowires onto Amorphous SiO2," Nano Letters, Oct. 2010

Kan, Jimmy; Chan, Keith; Shipton, Erik; Fullerton, Eric

2011-03-01

90

Stress Corrosion cracking of copper single crystals  

Microsoft Academic Search

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 °C. The stress-corrosion fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped, the cracks

K. Sieradzki; R. L. Sabatini; R. C. Newman

1984-01-01

91

Crystal ion slicing of single-crystal magnetic garnet films  

Microsoft Academic Search

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report

M. Levy; R. M. Osgood; A. Kumar; H. Bakhru

1998-01-01

92

Novel CaF2 Nanocomposite with High Strength and Fluoride Ion Release  

PubMed Central

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF2 and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF2 nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF2 content, or with decreasing pH (p < 0.05). F-release rates at 70-84 days were 1.13 µg/(cm2·day) and 0.50 µg/(cm2·day) for nanocomposites containing 30% and 20% nano-CaF2, respectively. They matched the 0.65 µg/(cm2·day) of resin-modified glass ionomer (p > 0.1). The nanocomposites had flexural strengths of 70-120 MPa, after 84-day immersion at pH 4, pH 5.5, and pH 7. These strengths were nearly three-fold that of resin-modified glass ionomer, and matched/exceeded a composite with little F release. In summary, novel CaF2 nanoparticles produced high F release at low filler levels, thereby making room in resin for reinforcement glass. This yielded nanocomposites with high F-release and stress-bearing properties, which may help reduce secondary caries and restoration fracture. PMID:20439933

Xu, H.H.K.; Moreau, J.L.; Sun, L.; Chow, L.C.

2010-01-01

93

Nanocrystalline CaF 2 particles obtained by high-energy ball milling  

NASA Astrophysics Data System (ADS)

Structural changes in mechanically treated CaF 2 powders have been studied by X-ray diffraction, transmission electron microscopy, thermal analysis, 19F and 1H MAS Nuclear Magnetic Resonance and Electron Paramagnetic Resonance methods. Applying the same methods, the results could be compared with those of mechanochemically synthesized CaF 2 samples, prepared for the first time in this study by high-energy ball milling. The applied methods indicate that the mechanically treated samples become, under the applied conditions, nanocrystalline. Unexpectedly, the mechanochemically synthesized samples show the same effects, i.e., nanocrystalline samples were formed. In contrast to many oxide compounds, a weak amorphization takes place only after a strong mechanical impact, and essentially in grain boundaries of spherical particles. Observed effects after the application of mechanical impact like broadening of XRD reflections, broadening of 19F resonances, or the decreasing ability for H rad trapping at ambient temperature, are mainly due to decreasing particle sizes as well as very small structural changes in the bulk of the particles. Surprisingly, the spin relaxation of both nuclear spins ( 19F) and electron spins (H rad ) appears to be the most sensitive tool for the investigation of mechanically and chemically induced changes indicating the increasing surface to bulk ratio with increasing mechanical impact.

Scholz, G.; Dörfel, I.; Heidemann, D.; Feist, M.; Stösser, R.

2006-04-01

94

Experimental Investigation of Orthoenstatite Single Crystal Rheology  

NASA Astrophysics Data System (ADS)

The plasticity of enstatite, upper mantle second most abundant mineral, is still poorly constrained, mostly because of its high-temperature (T) transformation into proto- and clino-enstatite at low pressure (P). Mackwell (1991, GRL, 18, 2027) reports a pioneer study of protoenstatite (Pbcn) single-crystal rheology, but the results do not directly apply to the orthorhombic (Pbca) mantle phase. Ohuchi et al. (2011, Contri. Mineral. Petrol , 161, 961) carried out deformation experiments at P=1.3 GPa on oriented orthoenstatite crystals, investigating the activity of [001](100) and [001](010) dislocation slip systems; they report the first rheological laws for orthoenstatite crystals. However, strain and stress were indirectly constrained in their experiments, which questioned whether steady state conditions of deformation were achieved. Also, data reported for [001](100) slip system were obtained after specimens had transformed by twinning into clinoenstatite. We report here new data from deformation experiments carried out at high T and P ranging from 3.5 to 6.2 GPa on natural Fe-bearing enstatite single crystals, using the Deformation-DIA apparatus (D-DIA) that equipped the X17B2 beamline of the NSLS (NY, USA). The applied stress and specimen strain rates were measured in situ by X-ray diffraction and imaging techniques (e.g., Raterron & Merkel, 2009, J. Sync. Rad., 16, 748; Raterron et al., 2013, Rev. Sci. Instr., 84, 043906). Three specimen orientations were tested: i) with the compression direction along [101]c crystallographic direction, which forms a 45° angle with both [100] and [001] axes, to investigate [001](100) slip-system activity; ii) along [011]c direction to investigate [001](010) system activity; iii) and along enstatite [125] axis, to activate both slip systems together. Crystals were deformed two by two, to compare slip system activities, or against enstatite aggregates or orientated olivine crystals of known rheology for comparison. Run products microstructures were investigated by transmission electron microscopy. Despite a significant hardening with P, enstatite [001](100) slip system is found to be the easiest system at mantle P and T. Furthermore, orthoenstatite crystals exhibit a higher sensitivity to stress than olivine crystals, i.e. a higher n exponent in classical power laws. At the low stress level prevailing in the Earth mantle, enstatite crystals are thus harder than olivine crystals.

fraysse, G.; Girard, J.; Holyoke, C. W.; Raterron, P.

2013-12-01

95

Lightweight optical mirrors formed in single crystal substrate  

NASA Technical Reports Server (NTRS)

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

Bly, Vincent T. (Inventor)

2006-01-01

96

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

97

The Creep of Single Crystals of Aluminum  

NASA Technical Reports Server (NTRS)

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

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

1953-01-01

98

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

99

Single-crystal gallium nitride nanotubes  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

100

Ferromagnetic Resonance of Single-Crystal Gadolinium  

Microsoft Academic Search

Gadolinium metal is a system of relative simplicity as far as exchange interactions and ionic states are concerned. The 8S7?2 state of Gd3+ is consistent with the observed 7?b?atom and the moment contributing f electrons are most likely exchange coupled via conduction electrons. The present work concerns the measurement of the ferromagnetic resonance behavior of a single crystal at frequencies

T. W. Moore; D. S. Rodbell

1964-01-01

101

Amplified spontaneous emission in quaterthiophene single crystals  

Microsoft Academic Search

The authors demonstrate amplified spontaneous emission (ASE) from quaterthiophene single crystals and study its behavior at low temperature. The room temperature photoluminescence exhibits line narrowing (spectral width down to 10 nm) at 553 nm for excitation fluence larger than 1 mJ cm-2. At low temperature (10 K), ASE is observed from two vibronic transitions at 510 nm (0-1) and 553

Marco Polo; Andrea Camposeo; Silvia Tavazzi; Luisa Raimondo; Peter Spearman; Antonio Papagni; Roberto Cingolani; Dario Pisignano

2008-01-01

102

Stress Corrosion cracking of copper single crystals  

Microsoft Academic Search

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied\\u000a potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 ?C. The stress-corrosion\\u000a fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped,\\u000a the cracks

K. Sieradzki; R. L. Sabatini; R. C. Newman

1984-01-01

103

Single crystal diamond detector for radiotherapy  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

104

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

105

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

PubMed

In contrast to the wide number and variety of available synthetic routes to conventional linear polymers, the synthesis of two-dimensional polymers and unambiguous proof of their structure remains a challenge. Two-dimensional polymers-single-layered polymers that form a tiling network in exactly two dimensions-have potential for use in nanoporous membranes and other applications. Here, we report the preparation of a fluorinated hydrocarbon two-dimensional polymer that can be exfoliated into single sheets, and its characterization by high-resolution single-crystal X-ray diffraction analysis. The procedure involves three steps: preorganization in a lamellar crystal of a rigid monomer bearing three photoreactive arms, photopolymerization of the crystalline monomers by [4?+?4] cycloaddition, and isolation of individual two-dimensional polymer sheets. This polymer is a molecularly thin (~1?nm) material that combines precisely defined monodisperse pores of ~9?Å with a high pore density of 3.3?×?10(13) pores?cm(-2). Atomic-resolution single-crystal X-ray structures of the monomer, an intermediate dimer and the final crystalline two-dimensional polymer were obtained and prove the single-crystal-to-single-crystal nature and molecular precision of the two-dimensional photopolymerization. PMID:25143211

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

2014-09-01

106

Chapter III: Catalytic Activation of CO Over Single Crystals  

E-print Network

1 Chapter III: Catalytic Activation of CO Over Single Crystals José A. Rodriguez and D. Wayne Introduction III.2 Methanation of CO on Single Crystal Surfaces III.2.1 CO methanation on clean metal single crystals. III.2.1.1 Monometallic surfaces A. Ni(100) and Ni(111) B. Ru(110) and Ru(001) C. W(110) D. Rh(111

Goodman, Wayne

107

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

108

LiF and CaF2: Dy thermoluminescent dosimeters.  

PubMed

A study has been made of the characteristics of the LiF glow curve as a function of annealing temperature and time. Two annealing methods with different annealing time were studied. The annealing by a hot air stream may anneal quickly. The annealing method affects the shape of the glow curve. If the annealing procedure and the measurement time after irradiation are constant, the fading does not affect the results, except over a long time for uses in personnel dosimetry. For LiF, TLD-600 had a higher sensitivity for 60Co gamma rays than TLD-100 and -700 by a factor of 1.23. For CaF2: Dy, glow curves of unusual shape were obtained, and its relative response was several times greater than that of normal phosphors. PMID:7434378

Tsuda, M; Ohizumi, Y; Mori, T

1980-01-01

109

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

110

Crystal ion slicing of single-crystal magnetic garnet films  

NASA Astrophysics Data System (ADS)

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report here an implementation of epitaxial liftoff in magnetic garnets. Deep ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG (Bi-YIG) epitaxial layers grown on gadolinium gallium garnet (GGG). The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. Ten-micron-thick films have been lifted off from the original GGG substrates by etching in phosphoric acid. Millimeter-size pieces of excellent quality have been transferred to the silicon and gallium arsenide substrates. Study of the magnetic domain structure in the detached epilayers by Faraday contrast shows no changes in film anisotropy. Optical insertion loss measurements are also presented.

Levy, M.; Osgood, R. M.; Kumar, A.; Bakhru, H.

1998-06-01

111

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

112

Design of multifunctional alkali ion doped CaF2 upconversion nanoparticles for simultaneous bioimaging and therapy.  

PubMed

Herein, alkali ion doped CaF2 upconversion nanoparticles (UCNPs) were first reported as a multifunctional theranostic platform for dual-modal imaging and chemotherapy. Interestingly, we found that the alkali ions doping approach could efficiently enhance the upconversion luminescence (UCL) intensity, whereas slightly affect the phase and morphology of the resulting products. In order to further improve the UCL efficacy for bioimaging, a pristine CaF2 shell was grown on the CaF2:Yb, Er core surface to enhance the UCL intensity. After being transferred into hydrophilic UCNPs, these water-soluble UCNPs could be served as contrast agents for in vitro/in vivo UCL imaging and X-ray computed tomography (CT) imaging. Furthermore, the as-prepared UCNPs could also be employed as nano-carriers for drug delivery. Doxorubicin (DOX) can be easily loaded onto the UCNPs and the DOX-loaded UCNPs exhibit a good cell killing ability. Therefore, the multifunctional core-shell CaF2 UCNPs with UCL/CT imaging and drug carrier properties may find extensive applications in simultaneous imaging diagnosis and therapy. PMID:24442070

Yin, Wenyan; Tian, Gan; Ren, Wenlu; Yan, Liang; Jin, Shan; Gu, Zhanjun; Zhou, Liangjun; Li, Juan; Zhao, Yuliang

2014-03-14

113

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...

114

Phase transition in sarcosine phosphite single crystals  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

115

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

116

Single-crystal fiber optics: a review  

NASA Astrophysics Data System (ADS)

Single-crystal (SC) fiber optics have been grown for many years for use as passive fibers for the delivery of IR laser radiation and as active fibers useful as minirod lasers. Most of the early work on SC fiber optics involved the growth of unclad sapphire fibers for the transmission of Er:YAG laser radiation at 2.94 ?m. More recently there has been a renewed interest in rare-earth (RE) doped oxide crystal fibers for use as high power fiber lasers. By analogy with RE doped-bulk laser crystals it is expected that pure YAG and other crystalline SC fibers should be capable of transmitting extremely high laser energies. SC oxide fibers have some distinct advantages over conventional glass fibers including higher thermal conductivity and low stimulated Brillouin scattering (SBS) gain coefficients. The latter can limit the ultimate power output of glass fiber lasers. To date most of the investigators have used the technique of Laser Heated Pedestal Growth (LHPG) to grow unclad SC fibers with diameters ranging from 30 to 350 ?m and in lengths as long as 5 m. The loss for SC sapphire fibers at 2.94 ?m has been measured as low as 0.3 dB/m. In this review we discuss the technique of LHPG, the various SC fiber optics that have been grown for both active and passive applications, and methods that may be used to clad the fibers.

Harrington, James A.

2014-02-01

117

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

118

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

119

Fabrication of crystals from single metal atoms.  

PubMed

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

120

Constitutive modeling for single crystal superalloys  

NASA Technical Reports Server (NTRS)

The inelastic response of single crystal gamma/gamma prime superalloys is quite different from the behavior of polycrystalline nickel base superalloys. Upto a critical temperature the yield stress of single crystal alloys is a function of the material orientation relative to the direction of the applied stress and the material exhibits significant tension/compression asymmetry. This behavior is primarily due to slip on the octahedral slip system. Above the critical temperature there is a sharp drop in the yield stress, cube slip becomes more predominant and the tension/compression asymmetry is reduced. Similar orientation and tension/compression asymmetry is observed in creep and secondary creep above the critical temperature is inferred to occur by octahedral slip. There are two exceptions to this behavior. First, loading near the (111) orientation exhibits cube slip at all temperatures, and; second, loading near the (001) orientation produces only octahedral slip at all temperatures. The constitutive model is based on separating the total global strain into elastic and inelastic components. This model is developed and briefly discussed.

Stouffer, D. C.; Jayaraman, N.; Sheh, M.; Alden, D.

1986-01-01

121

Employing a cylindrical single crystal in gas-surface dynamics  

Microsoft Academic Search

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based

C. Hahn; J. Shan; Y. Liu; O. Berg; A. W. Kleijn; L. B. F. Juurlink

2012-01-01

122

Spatiotemporal growth of faceted and curved single crystals  

PubMed

The spatiotemporal growth of single crystals in a crystalline polymer has been investigated theoretically based on a nonconserved time dependent Ginzburg-Landau equation (known as TDGL model A). In the description of the total free energy, a double-well local free energy density signifying metastability of crystal ordering is combined with a nonlocal free energy term representing an interface gradient. The resulting nonlinear reaction diffusion equation after renormalization possesses a solitary wave property. Two-dimensional numerical calculations were performed to elucidate the faceted single crystal growth including square, rectangular, diamond-shaped, and curved single crystals. A three-dimensional simulation was also undertaken for the emergence of diamond-shaped single crystals in polyethylene. Of particular importance is that the model field parameters can be linked directly to the material parameters of polyethylene single crystals. Simulation with various elements of the interface gradient coefficient tensor captures various topologies of polymer single crystals. PMID:11088211

Kyu; Mehta; Chiu

2000-04-01

123

ORIGINAL PAPER Strength of single-crystal orthopyroxene under lithospheric  

E-print Network

ORIGINAL PAPER Strength of single-crystal orthopyroxene under lithospheric conditions Tomohiro sin- gle crystals was investigated via shear deformation exper- iments under lithospheric conditions under the lithospheric conditions suggesting that orthopyroxene may reduce the strength

124

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

125

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

126

Halide electroadsorption on single crystal surfaces  

SciTech Connect

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied the authors found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocompression). The authors have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, they find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure.

Ocko, B.M. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Wandlowski, T. [Univ. of Ulm (Germany). Dept. of Electrochemistry

1997-07-01

127

Multiphonon relaxation in YVO4 single crystals  

NASA Astrophysics Data System (ADS)

Multiphonon relaxation rates were measured for 13 different energy levels of various rare-earth ions in YVO4 single crystals at 77 K. Dependence of the multiphonon relaxation rate on the energy gap that separates each emitting multiplet from the one lying just below it was investigated over the range from 980 to 5200 cm-1. A significant change in gap dependence was observed for energy gaps smaller than about 2500 cm-1, in agreement with previous observations and with theoretical investigations. An extreme nonradiative transition rate of 1.1×1011 s-1 (?=9 ps), corresponding to a 980 cm-1 energy gap, was deduced from homogeneous absorption linewidth measurements at 1.5 K.

Ermeneux, F. S.; Goutaudier, C.; Moncorgé, R.; Sun, Y.; Cone, R. L.; Zannoni, E.; Cavalli, E.; Bettinelli, M.

2000-02-01

128

Stress- Corrosion cracking of copper single crystals  

NASA Astrophysics Data System (ADS)

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 °C. The stress-corrosion fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped, the cracks apparently stop growing within about 20 /?m. The steps between adjacent flat facets are more energy-absorbing than in a-brass, providing a possible explanation for the importance of dynamic strain. Simultaneous acoustic emission and electrochemical current transients have been measured, and suggest that cracking proceeds by discontinuous cleavage.

Sieradzki, K.; Sabatini, R. L.; Newman, R. C.

1984-10-01

129

Optical emission and energy disposal characterization of the laser ablation process of CaF2, BaF2, and NaCl at 1064 nm  

NASA Astrophysics Data System (ADS)

A method to simultaneously measure the fraction of incident energy spent as absorbed, scattered, and consumed energy by the plasma generated in the ablation process is presented. The results obtained allowed to make an energy balance in the ablation process of halogenated earth alkaline metal crystals (NaCl, BaF2, and CaF2) and to relate the nature of the crystal structure to the absorbed energy. The latter could be determined by monitoring the magnitude of the breakdown induced by the discharge between the plates of a capacitor. Simultaneously, time resolved optical emission spectroscopy was used to analyze the ion emission intensity and as a function of the energy absorbed by the sample. This plot shows the usual sigmoid behavior for the ablation process with the three typical regions, corresponding to the vaporization, screening, and ablation regimes. A heuristic equation has been used to analyze this process in terms of the nature of the crystal structure. From this equation the critical absorbed energy for each of the studied samples could also be determined.

Villagran-Muñiz, M.; Sobral, H.; Rinaldi, C. A.; Cabanillas-Vidosa, I.; Ferrero, J. C.

2008-11-01

130

Synthesis, characteristics and thermoluminescent dosimetry features of ?-irradiated Ce doped CaF2 nanophosphor.  

PubMed

Nanoparticles of cerium doped calcium fluoride (CaF2:Ce) were synthesized for the first time using the hydrothermal method. The formation of nanostructures was confirmed by X-ray diffraction (XRD) patterns, indicating cubic lattice structure for the particles produced. Their shape and size were observed by scanning electron microscopy (SEM). Thermoluminescence characteristics were studied by having the samples irradiated by gamma rays of (60)Co source. The optimum thermal treatment of 400 °C for 30 min was found for the produced nanoparticles. The Tm-Tstop and computerized glow curve deconvolution (CGCD) methods, used to determine the number of component glow peaks and kinetic parameters, indicated seven overlapping glow peaks on the TL glow curve at approximately 394, 411, 425, 445, 556, 594 and 632 K. A linear dose response of up to 2000 Gy, was observed for the prepared nanoparticles. Maximum TL sensitivity was found at 0.4 mol% of Ce impurity. Other TL dosimetry features, including reusability and fading, were also presented and discussed. PMID:23707947

Zahedifar, M; Sadeghi, E; Mozdianfard, M R; Habibi, E

2013-08-01

131

TOPICAL REVIEW: Organic field-effect transistors using single crystals  

Microsoft Academic Search

Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of

Tatsuo Hasegawa; Jun Takeya

2009-01-01

132

Three-dimensional single crystal silicon micromachining  

NASA Astrophysics Data System (ADS)

A monolithic, multiple-level (ML), single-crystal-silicon (SCS) micromachining process called SCREAM3D has been developed. The high-aspect-ratio (HAR) levels are self-aligned and are fabricated from a single substrate by deep etching. Anisotropic reactive ion etching of silicon has been studied in detail and new recipes for the vertical etch and release of HAR ML structures have been developed. The SCREAM3D levels are electrically isolated from the substrate and one another using a novel ML isolation scheme, which requires only a single lithography and metallization step, regardless of the number of levels. Two- and three-level SCREAM3D devices have been fabricated. They demonstrate three device concepts: ML microelectromechanical systems (MEMS), micromachined electron gun arrays (MEGA) and ML actuators for out-of-plane deflection. ML MEMS consist of several suspended levels moving relative to each other. They can be coupled mechanically and/or electrically. One example is a novel clamp-alignment device which uses the relative translation of two initially self-aligned apertures to grip and align an external component (such as an optical fiber) to the wafer. MEGA is a multiple-beam architecture to increase the throughput of electron beam lithography. MEGA is an array of identical electron sources, consisting of silicon field emitters with integrated electrostatic lenses. The parallel operation of a large number (N = 10,000) of sources is required to increase the total current and throughput (60 8"-wafers/hour) of the system while maintaining standard single-beam parameters (10nA, 20MHz exposure rate) and limiting charge-interaction effects. ML actuators have been studied by numerical simulation. All four designs outperform comparable single-level actuators: the generated force is up to five times larger, and the range of motion up to ten times greater. Two of the ML designs operate bi-directionally and one design can be used to form a bi-stable system. Several of the actuators have been integrated with torsional and z-motion-stages and experimentally characterized using laser vibrometry. SCREAM3D extends SCS bulk-micromachining to multiple-level structures. The self-aligned, high-aspect-ratio levels allow the implementation of more efficient device designs and novel ML device concepts. Complex actuators, generating larger forces in reduced chip area, can be fabricated and entire microinstruments can be integrated on a single wafer.

Hofmann, Wolfgang Maximilian Josef

1999-11-01

133

Microstructures and tribological properties of plasma sprayed WC–Co–Cu–BaF 2\\/CaF 2 self-lubricating wear resistant coatings  

Microsoft Academic Search

A promising WC–Co–Cu–BaF2\\/CaF2 self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC–Co, Cu and BaF2\\/CaF2 eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC–Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF2\\/CaF2

Jianhui Yuan; Yingchun Zhu; Heng Ji; Xuebing Zheng; Qichao Ruan; Yaran Niu; Ziwei Liu; Yi Zeng

2010-01-01

134

Intense ultraviolet emission from Tb3+ and Yb3+ codoped glass ceramic containing CaF2 nanocrystals  

NASA Astrophysics Data System (ADS)

A transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramic containing CaF2 nanocrystals was developed. This glass ceramic showed an intense ultraviolet emission at 381nm due to the G65, D35?F67 transitions of Tb3+ ion when excited with a 974nm laser at room temperature. The observed intense ultraviolet emission could be attributed to the change of ligand field of Tb3+ and Yb3+ ions due to the incorporation of some Tb3+ and Yb3+ ions into CaF2 nanocrystals, and the resulting increased branching ratio of the transitions and longer lifetime of D45 level of Tb3+ in the glass ceramic.

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

2007-03-01

135

CaF 2(Eu 2+):LiF – Structural and spectroscopic properties of a new system for neutron detection  

Microsoft Academic Search

A series of composites of CaF2(Eu2+) and LiF with different Ca\\/Li ratios were fabricated via liquid phase consolidation. Luminescent properties of these samples were investigated. Radioluminescence shows the typical Eu2+ blue emission in all the compositions. The energy spectra measured under ? and neutron irradiation indicates that the most promising composition for neutron detection is the eutectic.

Joanna Trojan-Piegza; Jarek Glodo; Vinod Kumar Sarin

2010-01-01

136

Role of Organic Additives in the Sol-Gel Synthesis of Porous CaF 2 Anti-Reflective Coatings  

Microsoft Academic Search

Porous CaF2 anti-reflective coating films were prepared by the sol-gel method. Effects of organic additives on deposition and optical properties of the films were investigated. Amino alcohols (2-aminoethanol, 2-dimethylaminoethanol, and triethanolamine) and alcohols with larger molecular weights (ethyleneglycol, 2-methoxyethanol, cyclohexanol, and 2-(2-n-butoxyethoxy)ethanol) were chosen as the organic additives. Among these additives, cyclohexanol was the most effective to control the surface

Shinobu Fujihara; Yasuhiro Kadota; Toshio Kimura

2002-01-01

137

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

138

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

SciTech Connect

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

2013-12-01

139

P-185 / L. Tan P-185: Single Cell Gap Single Mode Transflective Liquid Crystal Display  

E-print Network

P-185 / L. Tan P-185: Single Cell Gap Single Mode Transflective Liquid Crystal Display with High Kong Abstract A transflective liquid crystal display with single cell gap single mode structure of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong

140

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

141

Investigation on Growth and Surface Analysis of DAST Single Crystals  

SciTech Connect

We have explored the growth of bulk size N, N-dimethylamino-N'-methylstilbazolium p-toluenesulphonate (DAST) using slope nucleation method. The grown crystal was characterized by single crystal X-ray diffraction (XRD), and CHN analyses. The surface morphology of the crystal was analyzed using Scanning electron microscopy (SEM).

Thomas, Tina; Vijay, R. Jerald; Gunaseelan, R.; Sagayaraj, P. [Department of Physics, Loyola College, Chennai - 600 034 (India)

2011-07-15

142

Characterization and growth of magnesium diboride single crystals  

Microsoft Academic Search

Single crystals of magnesium diboride with maximum dimension of 200×200×60?m3 have been successfully grown from copper flux in iron capsules. MgB2 crystallized separately in a system with the composition Mg40Cu40B20, and large single crystals were grown. Crystals grow together in the system with the composition Mg35Cu40B25, and MgB4 is found in this system due to excess B content. MgB2 crystallizes

Z. X. Cheng; X. L. Wang; A. V. Pan; H. L. Liu; S. X. Dou

2004-01-01

143

Fractoemission from cyclotrimethylenetrinitramine (RDX) explosive single crystals  

NASA Astrophysics Data System (ADS)

Production-grade Class D and laboratory-grown cyclotrimethylenetrinitramine (RDX) explosive crystals were fractured in a vacuum (10-5 Pa) while viewed by particle detectors biased to separate positive and negative charge. Fracture was achieved by compressive loading (both production and laboratory crystals) and by three-point bending (laboratory crystals only). ``Cleavage''-type fracture resulted for several crystals subjected to three-point bending and yielded a sharp emission peak followed by rapid decay. Longer and more intense emission was observed for a few crystals broken in flexure which may correspond to more ``energetic'' fracture. Multiple fracture, involving surface frictional grinding, occurred for crystals that were compressed; in this case, relatively intense emission resulted which continued for several minutes after fracturing the crystals. These results are discussed in terms of possible mechanisms.

Dickinson, J. T.; Miles, M. H.; Elban, W. L.; Rosemeier, R. G.

1984-06-01

144

Chemical Solution Routes to Single-Crystal Thin Films  

Microsoft Academic Search

Epitaxial thin films of inorganic single crystals can be grown on single-crystal substrates with a variety of different solution chemistries. This review emphasizes chemical solution deposition, in which a solution is used to deposit a layer of precursor molecules that decompose to low-density, polycrystalline films during heating. Ways to control film cracking during deposition and heat treatment and why many

F. F. Lange

1996-01-01

145

Precipitation of Copper Silicide in Voids in Silicon Single Crystals  

E-print Network

Precipitation of Copper Silicide in Voids in Silicon Single Crystals A thesis presented by Cheng Spaepen Cheng-Yen Wen Precipitation of Copper Silicide in Voids in Silicon Single Crystals Abstract precipitates have filled the open volume. For implementation of this method, precipitation of the Cu silicide

146

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

147

A Multivariant model for single crystal shape memory alloy behavior  

Microsoft Academic Search

A general 3-D multivariant model based on thermodynamics and micromechanics for single crystal shape memory alloy (SMA) behavior is presented. This model is based on the habit plane and transformation directions for the variants of martensite in a given material. From this information, the single crystal behavior of the material to temperature and mechanical loads is derived using the concept

Miinshiou Huang; L. C. Brinson

1998-01-01

148

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

149

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

150

Cleavage oriented iron single crystal fracture toughness  

NASA Astrophysics Data System (ADS)

Fundamental understanding of atomic level mechanisms controlling cleavage fracture in bcc metals, and the corresponding brittle to ductile transition (BDT) has been a long sought, 'grand challenge' of science. This is particularly true for the BDT in Fe, which is among vital elements that underpin our technological civilization. A key obstacle to developing an understanding of the BDT in Fe is the absence of a reliable database on the temperature dependence of toughness in Fe. In ferritic alloys, the micro-arrest toughness of ferrite, Kmu(T), is hypothesized to control macroscopic cleavage. As a surrogate for Kmu(T), special techniques were developed to measure the arrest toughness, Ka(T), for cleavage oriented, Fe single crystals. Further, the mechanisms controlling cleavage and the BDT should be reflected in the loading rate dependence of static-dynamic initiation toughness, K Ic and KId. Thus KIc/d(T) were also measured for K-rate from 10-1 to 104 MPa?m/s. These studies led to the following conclusions: (1) Ka is semi-brittle, increasing from an average of ? 3.5 MPa?m at -196°C to ? 9 MPa?m at 0°C. (2) The (100) Ka are similar in the [010] and [011] and orientations, but cleavage does not occur on (110) planes. (3) The Ka for unalloyed Fe is about 150°C lower than that for Fe-3wt%Si, suggesting that equivalent Ka may occur at equivalent lattice sigmay. (4) Higher K-rate shift K Ic/d(T) curves to higher T. (5) The shifts of the KIc/d(T) and Ka(T) curves can be understood and modeled based on dislocation dynamics concepts for the glide of screw dislocations with a stress (and T) controlled activation energy, Ea, with a maximum value of about ? 0.5 eV. (6) This Ea is consistent with a double kink nucleation mechanism. Etch pit, slip trace and ledge patterns on side, fracture and sectioned surfaces of the crystals were characterized to study dislocation activity associated with cleavage and the BDT. The results showed extensive dislocation activity on {110}<111> and {211}<111> slip systems. Consistent with its semi-brittle nature, there is evidence of significant dislocation glide and multiplication during cleavage, perhaps associated with pre-existing dislocations.

Hribernik, Michael Louis

151

Last advances in Yb3+ doped CaF2 ceramics synthesis  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

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

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

154

Method for harvesting single crystals from a peritectic melt  

DOEpatents

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

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

1996-08-27

155

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

156

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

2011-02-21

157

Carrier recombination-incited substrate vibrations after pulsed UV-laser photolysis of TiO2 thin single-crystal plate and nanoparticle films.  

PubMed

Photo-induced carrier generation and recombination have been regarded as important steps in understanding the photocatalytic reactions on the surfaces of semiconductors such as TiO2. During the investigation of a photocatalytic water-splitting reaction on the surface of semiconductor TiO2 (rutile) single-crystal plate and sintered-nanoparticle (anatase) films coated on a CaF2 plate, a pulsed 355 nm laser was used for band-gap excitation and a continuous-working, mid-infrared laser as the probe to trace the kinetics of the photogenerated electrons. Fast oscillations with periods of 10-50 ?s were observed. We demonstrated experimentally that these oscillations are neither from the nonlinear carrier recombination dynamics nor surface chemical reactions; instead, they are caused by the thermal-induced flexural vibrations initiated by the fast carrier recombination in the light-absorbing area. The observed oscillations can be well accounted for by thermal stress-induced flexural vibrations of the substrates due to rapid charge recombination, and the observed oscillation frequencies match the flexural vibration frequencies predicted by the Kirchhoff-Love thin-plate theory. Light-interference effect caused by the beam reflecting off the surfaces of the substrate and windows, which can amplify the oscillation signals, is also discussed. Several approaches are proposed to minimize or eliminate the interference from the substrate vibration in the transient kinetic measurement when a coherent laser is used as the probe beam. PMID:23643039

Zhu, Ming; Zhu, Gangbei; Weng, Yuxiang

2013-05-01

158

A Single Crystal Niobium RF Cavity of the TESLA Shape  

SciTech Connect

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

Singer, W.; Singer, X.; Kneisel, P. [DESY, Notkestrasse 85, D-22607 Hamburg (Germany); Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

2007-08-09

159

A Single Crystal Niobium RF Cavity of the TESLA Shape  

SciTech Connect

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

W. Singer; X. Singer; P. Kneisel

2007-09-01

160

Dielectric and baric characteristics of TlS single crystal  

NASA Astrophysics Data System (ADS)

The investigation of the frequency dependences of the dielectric coefficients and ac-conductivity of the TlS single crystals made it possible to elucidate the nature of dielectric loss and the charge transfer mechanism. Moreover, we evaluated the density and energy spread of localized states near the Fermi level, the average hopping time and the average hopping length. It was shown that the dc-conductivity of the TlS single crystals can be controlled by varying the hydrostatic pressure. This has opened up possibilities for using TlS single crystals as active elements of pressure detectors.

Mustafaeva, S. N.; Asadov, M. M.; Ismailov, A. A.

2014-11-01

161

The Growth of Large Single Crystals.  

ERIC Educational Resources Information Center

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

Baer, Carl D.

1990-01-01

162

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

PubMed

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

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

2015-01-25

163

Tunability of laser based on Yb-doped hot-pressed CaF2 ceramics  

NASA Astrophysics Data System (ADS)

The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 ?m, NA= 0.22) coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude 10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist diameter ~ 170 ?m). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 ?m, HT @ 0.97 ?m) and curved (r = 150mm) output coupler with a reflectivity of ~ 98% @ 1.01 - 1.09 ?m. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.

Sulc, Jan; Doroshenko, Maxim E.; Jelínková, Helena; Basiev, Tasoltan T.; Konyushkin, Vasilii A.; Osiko, Vyacheslav V.

2012-06-01

164

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

165

X-Ray Study of Polygonization in Copper Single Crystals  

Microsoft Academic Search

Single crystals of electrolytic tough pitch copper and of high purity (99.999%) copper were deformed by bending. The substructure in the as-bent and annealed crystals was studied by means of sensitive x-ray techniques. It was found that regardless of purity, crystals of certain orientations in the as-bent condition do not have sub-boundaries detectable by the methods used. Polygonization took place

C. T. Wei; M. N. Parthasarathi; P. A. Beck

1957-01-01

166

Sensitization of Pr3+ ions by Eu2+ ions in CaF2 thin films deposited by evaporation  

NASA Astrophysics Data System (ADS)

In the present article, we analyse the possibility of sensitizing the 3Pj levels of Pr3+ ion with Eu2+ ion in CaF2 thin film deposited by evaporation. Indeed, the forbidden nature of the 4f-4f transition of Pr3+ ion makes its absorption too weak for thin film applications, while materials doped with the Pr3+-Yb3+ couple are promising candidates for the achievement of efficient down-converter systems and could allow strong reduction of thermalization losses in silicon solar cells.

Guille, A.; Pereira, A.; Bensalah-Ledoux, A.; Moine, B.; Novotný, M.; Bulí?, J.; Fitl, P.; Lan?ok, J.

2013-11-01

167

Synthesis of optically transparent ceramic of CaF2 doped with Mn and Ce for thermoluminescent dosimetry  

NASA Astrophysics Data System (ADS)

Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically transparent ceramics were obtained by vacuum hot-pressing at 1000°C under 20 MPa pressure for 2 h. The duration of pressure and dehydration of the initial powder was found important to achieve the transparency. 50% transparency was observed for a polished disc of 1 mm thickness. SEM micrographs revealed the absence of voids in hot pressed samples. These samples were found to be highly sensitive and linear for TLD and can measure doses from mGy to kGy.

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

2012-06-01

168

Neutrino-less Double Beta Decay of 48Ca studied by CaF2(Eu) Scintillators  

E-print Network

We searched for the neutrino-less double beta decay(0nbb) of 48Ca by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q-value region for the data of 3394 kg days. It gives a lower limit (90% confidence level) of T > 2.7 x 10^22 year for the half life of 0nbb of 48Ca. Combined with our previous data for 1553 kg days, we obtained more stringent limit of T > 5.8 x 10^22 year.

S. Umehara; T. Kishimoto; I. Ogawa; R. Hazama; H. Miyawaki; S. Yoshida; K. Matsuoka; K. Kishimoto; A. Katsuki; H. Sakai; D. Yokoyama; K. Mukaida; S. Tomii; Y. Tatewaki; T. Kobayashi; A. Yanagisawa

2008-10-27

169

Mesoporous silicon photonic crystal microparticles: towards single-cell optical  

E-print Network

Mesoporous silicon photonic crystal microparticles: towards single-cell optical biosensors Bin Guan such as the coupling of antibodies. The surface chemistry remained unchanged after sonication of the PSi to form PSi crystals, with complicated multilayer structures, to be produced. High- quality optical structures

Kilian, Kristopher A.

170

Growth of large single crystals of the orthorhombic paracetamol  

NASA Astrophysics Data System (ADS)

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

Mikhailenko, M. A.

2004-05-01

171

Electrochemistry of transition metal single crystals with well defined surfaces  

Microsoft Academic Search

The effect of extended defects of the surface of metallic single crystals on the electrochemical processes of dissolution and formation of a new phase has been analysed. Theoretical ideas on the rearrangement of a crystal surface (phase transitions of the second kind) during the adsorption of surface-active substances are presented. The reconstruction (faceting) of the surface under the influence of

Gennadii V. Khaldeev; T. A. Syur

1992-01-01

172

Single crystal orientation effects in shock initiation of PETN explosive  

SciTech Connect

Over the past nine years in Los Alamos we have studied shock initiation of detonation in single crystals of PETN explosive. We have demonstrated the effects of point defects and crystal orientation on shock sensitivity. Here we report recent work on orientation effects and anomalous detonation in <110> orientation at 4 GPa. 5 refs.

Dick, J.J.

1988-01-01

173

The Herbertsmithite Hamiltonian: ?SR measurements on single crystals  

E-print Network

We present transverse field muon spin rotation/relaxation measurements on single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find that the spins are more easily polarized when the field is perpendicular ...

Ofer, Oren

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

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

176

Aluminium segregation of TiAl during single crystal growth  

SciTech Connect

{gamma}-TiAl single crystals have been successfully prepared by an induction-heated cold crucible Czochralski technique which offers more flexibility than vertical float zoning. Compositional analysis of the Czochralski grown single crystals indicates a homogeneous composition after initial transition; and the average composition is close to the peritectic composition. However, {gamma}-TiAl single crystals prepared by vertical float zoning show a small aluminium segregation profile along the growth direction; and the average composition of the as-grown crystals is close to that of the starting alloy. Compositional analysis further demonstrated the banded structure with alternative single {gamma}-phase and {alpha}{sub 2} + {gamma} lamellar regions in the vertical float zoned Ti-54 at.% Al.

Bi, Y.J.; Abell, J.S. [Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials] [Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials

1997-09-15

177

High polarization single dipole mode photonic crystal microlaser  

Microsoft Academic Search

A photonic crystal microlaser with elongate lattice was fabricated. Lasing action of single mode, y-dipole mode, was observed. With this mode, a high polarization extinction ratio of 51:1 was obtained.

Wei Chen; Mingxin Xing; Wenjun Zhou; Anjin Liu; Lianghui Chen; Wanhua Zheng

2009-01-01

178

Superconducting Proximity Effect in Single-Crystal Nanowires  

E-print Network

This dissertation describes experimental studies of the superconducting proximity effect in single-crystal Pb, Sn, and Zn nanowires of lengths up to 60 um, with both ends of the nanowires in contact with macroscopic electrodes that are either...

Liu, Haidong

2010-07-14

179

Piezoelectric properties of tetragonal single-domain Mn-doped NBT-6 %BT single crystals  

NASA Astrophysics Data System (ADS)

We report a study of properties of Mn-doped NBT-6 %BT single crystals. We show that tetragonal single-domain states can be stabilized by poling along a [001] direction. For carefully prepared crystals, the piezoelectric coefficient can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit ferroelectric domain structures consistent with tetragonal micron-sized domains, as revealed by optical observation and Raman spectroscopy. The multidomain crystals have lower values, 225 and 130 pC/N for [011] and [111]-oriented crystals, respectively. This trend is commented on from a domain-engineering perspective.

Guennou, Mael; Savinov, Maxim; Drahokoupil, Jan; Luo, Haosu; Hlinka, Jirka

2014-07-01

180

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

181

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

182

Constitutive modeling of creep of single crystal superalloys  

E-print Network

of single crystal nickel based superalloys developed over last few decades. The second and third generation of superalloys are characterized by increasing concentration of Rhenium which improves creep and fatigue resistance. Fourth gener- ation superalloys... of single crystal nickel based superalloys developed over last few decades. The second and third generation of superalloys are characterized by increasing concentration of Rhenium which improves creep and fatigue resistance. Fourth gener- ation superalloys...

Prasad, Sharat Chand

2006-10-30

183

250 W single-crystal fiber Yb:YAG laser.  

PubMed

We demonstrate an Yb:YAG single-crystal fiber laser with 251 W output power in continuous-wave and an optical efficiency of 44%. This performance can be explained by the high overlap between pump and signal beams brought by the pump guiding and by the good thermal management provided by the single-crystal fiber geometry. The oscillator performance with a reflectivity of the output coupler as low as 20% also shows high potential for power amplification. PMID:22825171

Délen, Xavier; Piehler, Stefan; Didierjean, Julien; Aubry, Nicolas; Voss, Andreas; Ahmed, Marwan Abdou; Graf, Thomas; Balembois, Francois; Georges, Patrick

2012-07-15

184

Thermal and dielectric studies of nickel malonate dihydrate single crystals  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

185

Forward diffracted parametric X radiation from a silicon single crystal  

NASA Astrophysics Data System (ADS)

Experiments were performed with the 855 MeV electron beam of the Mainz Microtron MAMI which focused on still open questions in the X-ray emission process upon traversal of ultra relativistic electrons through single crystals. To elucidate the quest of kinematical versus dynamical production of PXR the radiation from silicon single crystal targets, emitted close to the electron direction, has been studied. The observed interference structures show that PXR is produced in a dynamical process.

Backe, H.; Rueda, A.; Lauth, W.; Clawiter, N.; El-Ghazaly, M.; Kunz, P.; Weber, T.

2005-05-01

186

Annealing Effect on Photovoltages of Quartz Single Crystals  

Microsoft Academic Search

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900°C, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994muV at

Lu Tian; Song-Qing Zhao; Kun Zhao

2010-01-01

187

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

188

Single femtosecond laser pulse-single crystal formation of glycine at the solution surface  

NASA Astrophysics Data System (ADS)

We demonstrate femtosecond laser-induced crystallization of glycine from its supersaturated solution depending on laser tunable parameters (pulse energy and repetition rate) and focal position, and examine the crystallization probability, crystal morphology, and crystal polymorph. The generation of cavitation bubble through multiphoton absorption of water depends on input laser pulse energy and repetition rate, which strongly determine morphology and number of the obtained crystals. Significant increase in the crystallization probability is observed by irradiating the femtosecond laser pulses to the air/solution interface, and single pulse-induced single crystal formation is successfully achieved. The crystallization mechanism is discussed in view of inhomogeneous mechanical stress induced by cavitation bubble generation and molecular assembly characteristics of the surface.

Liu, Tsung-Han; Uwada, Takayuki; Sugiyama, Teruki; Usman, Anwar; Hosokawa, Yoichiroh; Masuhara, Hiroshi; Chiang, Ting-Wei; Chen, Chun-Jung

2013-03-01

189

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pr3+ Sm3+, Pd2+, Co2+, Pt4+ and PO43- with L-alanin were grown from aqueous solutions by means of the slow cooling method. Surface morphology, domain structure and P-E hysteresis loops have been investigated. The model of catalyzed growth of {001}and{101}crystal pyramids on the basis of metal-glycine complexes has been suggested. We have found on the basis of experimental results that TGS single crystals doped with Pt4+ and L-alanin are excellent materials for construction of infrared detectors.

Novotny, Jan; Zelinka, J.; Podvalova, Z.

2002-03-01

190

Hydroxyethylammonium maleate (HEAM) single crystal for optical limiting applications  

NASA Astrophysics Data System (ADS)

A novel hydroxyethylammonium maleate single crystal was grown by slow evaporation solution method for the first time. The structure of the title compound is determined by single crystal X-ray diffraction. The linear optical properties were studied using ultraviolet-visible and photoluminescence spectroscopy. The third-order nonlinear optical property of title compound was studied by Z-scan technique to determine its nonlinear absorption and nonlinear refraction. Thermal property was studied by thermogravimetry, differential thermal analysis and differential scanning calorimetric analyses. The mechanical stability of the material was studied by Vickers microhardness tester. Further, etching study was done to examine the defects in the crystal.

Sudharsana, N.; Hamad, S.; Venugopal Rao, S.; Krishnakumar, V.; Nagalakshmi, R.

2014-10-01

191

Growth, Crystal Structure, and Thermopower of Single Crystals of UNi 1.9Sn  

Microsoft Academic Search

We have grown single crystals of UNi1.9(1)Sn from a semi-levitated melt using the Kyropoulos technique. The crystal structure of UNi1.9(1)Sn was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.0336. This compound crystallizes in the cubic MnCu2Al-type structure with the lattice parameter a=6.4633(4) Å. The temperature dependence of the thermoelectric power, different from that observed for

L. Shlyk; J. C. Waerenborgh; M. Almeida

2000-01-01

192

Solution Growth of Rubrene Single Crystals Using Various Organic Solvents  

NASA Astrophysics Data System (ADS)

To fabricate organic field-effect transistors (OFETs) with high carrier mobility, we attempted to grow 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals from solution and to improve their quality. Investigations into solvents in which rubrene was highly soluble proved that its solubility depended on the presence or absence of aromatic rings and chloro groups rather than on the polarity of the solvents. Rubrene crystals were grown from aromatic solvents, specifically from toluene, p-xylene, and aniline solvents, as well as from 1,2-dichloroethane (DCE) solvent. As a result, rubrene single crystals larger than 1 mm were obtained. Powder X-ray diffraction (XRD) analysis showed that the crystals obtained from the p-xylene and toluene solvents were rubrene, and 1H-nuclear magnetic resonance (1H-NMR) measurement proved that the crystals had not incorporated the solvent at the detection level. In addition, atomic force microscopy (AFM) confirmed that the rubrene crystals grown from the p-xylene and aniline solvents had flat faces and that the crystal from the p-xylene solvent had monomolecular steps on parts of the surfaces. Rubrene single crystal OFETs with graphite electrodes and parylene as an insulator showed carrier mobilities of ?0.75 cm2 V-1 s-1.

Matsukawa, Takeshi; Takahashi, Yoshinori; Tokiyama, Tsukasa; Sasai, Kenichi; Murai, Yusuke; Hirota, Nobuhiro; Tominari, Yukihiro; Mino, Norihisa; Yoshimura, Masashi; Abe, Masayuki; Takeya, Junichi; Kitaoka, Yasuo; Mori, Yusuke; Morita, Seizo; Sasaki, Takatomo

2008-12-01

193

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

SciTech Connect

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

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

2010-09-15

194

From composites to solid solutions: modeling of ionic conductivity in the CaF2-BaF2 system.  

PubMed

By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent "dopants" can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state-of-the-art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF(2) lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF(2) phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF(2)-BaF(2) multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge-transfer that occurred at the hetero-interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher-dimensional doping) to homogeneous doping (zero-dimensional doping). PMID:22488848

Zahn, Dirk; Heitjans, Paul; Maier, Joachim

2012-05-14

195

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

196

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

197

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

198

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals  

SciTech Connect

The specific features of photorefractive light scattering in nominally pure stoichiometric (Li/Nb = 1) sin- gle crystals grown from a melt with 58.6 mol % Li{sub 2}O (LiNbO{sub 3}st) and in the stoichiometric single crystals grown from a melt of congruent composition in the presence of K{sub 2}O flux (LiNbO{sub 3}stK{sub 2}O) have been investi- gated. At an excitation power of 30 mW, LiNbO{sub 3}stK{sub 2}O single crystals are found to exhibit a stronger photo- refractive effect than LiNbO{sub 3}st single crystals.

Sidorov, N. V. [Russian Academy of Sciences, Institute of Chemistry and Technology of Rare Earth Elements and Mineral Raw Materials, Kola Scientific Center (Russian Federation); Antonycheva, E. A.; Syui, A. V. [Far Eastern State Transport University (Russian Federation); Palatnikov, M. N., E-mail: palat_mn@chemy.kolasc.net.ru [Russian Academy of Sciences, Institute of Chemistry and Technology of Rare Earth Elements and Mineral Raw Materials, Kola Scientific Center (Russian Federation)

2010-11-15

199

Shock Driven Twinning in Tantalum Single Crystals  

SciTech Connect

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

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

2009-07-20

200

VGF growth of germanium single crystals without crucible contact  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

201

A Study of the Superfluid Transition in $(4) {He} 4 He Films Adsorbed to Rough {CaF}_2$ CaF 2 Over a Large Temperature Range  

NASA Astrophysics Data System (ADS)

Rough two-dimensional substrates, such as thermally deposited , have been shown to modify the experimental signatures of the superfluid transition in adsorbed thin helium films. Previous experiments have investigated a series of increasingly rough surfaces over a limited temperature range and found that the features at the superfluid transition become less defined as substrate roughness is increased. In this work we study the superfluid transition in adsorbed helium films over a wide range of temperatures for a series of substrates. Our results show that as the transition temperature increases the abrupt jump in superfluid density at the transition becomes less distinct. The changing characteristics of the transition on a single substrate with temperature suggest that the reduced observability of the transition on rough substrates cannot be explained entirely by superfluid drag. We discuss several other possible scenarios which may be relevant to the helium films on.

Wadleigh, L. R.; Luhman, D. R.

2014-11-01

202

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

203

Electron paramagnetic resonance of Gd3+ ions in Ca1 - x - y Y x Gd y F2 + x + y crystals  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance of Ca1 - x - y Y x Gd y F2 + x + y single crystals has revealed spectra that are not typical of gadolinium-doped CaF2 crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd3+ ions localized in yttrium clusters. Weak spectra of tetragonal Gd3+ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd3+ ion, have been also detected. These centers are attributed to isolated Gd3+ ions localized near octahedral rare-earth clusters or their associations.

Vazhenin, V. A.; Potapov, A. P.; Fokin, A. V.; Artyomov, M. Yu.

2013-06-01

204

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

205

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

206

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

SciTech Connect

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

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

2003-05-21

207

Inspection of Single Crystal Aerospace Components with Ultrasonic Arrays  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

208

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

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

2014-01-01

209

Photochromism of diarylethene single molecules and single crystals.  

PubMed

Photochromism is characterized as a reversible colour change of a chemical species upon photoirradiation. Although vast numbers of photochromic molecules have been so far synthesized, molecules which exhibit thermally irreversible photochromic reactivity are limited within a few families of compounds. Among the thermally irreversible photochromic molecules, diarylethene derivatives are the most promising candidates for applications to opto-electronic devices because of their fatigue resistance, high sensitivity and rapid response. In this review, characteristic photochromic performances of the derivatives, detection and analysis of the photochromic reactions at a single-molecule level and application of the single-crystalline photochromism to molecular machinery will be described. PMID:20959925

Irie, Masahiro

2010-12-01

210

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

211

Single-atom switching in photonic crystals  

NASA Astrophysics Data System (ADS)

We describe the role of first non-Markovian corrections to resonance fluorescence in photonic crystals, using a perturbative expansion of the Heisenberg equations of motion in powers of the atom-field reservoir coupling strength. Non-Markovian effects arise from the rapid variation of the photonic density of states with frequency. Our method recaptures the physics of the photon-atom bound state in the presence of a full photonic band gap. For the anisotropic three-dimensional photonic band gap, it predicts remarkable features in the resonance fluorescence, such as atomic population inversion and switching behavior in a two-level atom for moderate values of the applied laser field. The magnitude of the switching effect depends sensitively on the external laser intensity and its detuning frequency from the atomic transition. The robustness of this effect against nonradiative decay and dephasing mechanisms is also investigated.

Florescu, Marian; John, Sajeev

2001-09-01

212

Studying the magnetic properties of CoSi single crystals  

SciTech Connect

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

Narozhnyi, V. N., E-mail: narozhnyivn@gmail.com; Krasnorussky, V. N. [Russian Academy of Sciences, Vereshchagin Institute for High Pressure Physics (Russian Federation)

2013-05-15

213

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

214

Textures in Single-Crystal Aluminum Friction Stir Spot Welds  

Microsoft Academic Search

The present article examines the textural features produced during friction stir spot welding of single-crystal aluminum sheet.\\u000a The crystal has the {111} plane perpendicular to the normal direction (ND) of the sheet, and the $$ \\\\left\\\\langle { 1 10} \\\\right\\\\rangle $$ direction parallel to the growth direction (GD). Friction stir spot welding was carried out using a rotation speed of

Toshiya Shibayanagi; Adrian P. Gerlich; Keizo Kashihara; Thomas H. North

2009-01-01

215

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

216

Plane wave simulation of elastic-viscoplastic single crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

217

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

218

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

219

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

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

Elastic constants of single crystal Hastelloy X at elevated temperatures  

SciTech Connect

An acoustic time of flight technique is described in detail for measuring the elastic constants of cubic single crystals that allows for the constants to be determined at elevated temperature. Although the overall technique is not new, various aspects of the present work may prove extremely useful to others interested in finding these values, especially for aerospace materials applications. Elastic constants were determined for the nickel based alloy, Hastelloy X from room temperature to 1,000 C. Accurate elastic constants were needed as part of an effort to predict both polycrystal mechanical properties and the nature of grain induced heterogeneous mechanical response. The increased accuracy of the acoustically determined constants resulted in up to a 15% change in the predicted stresses in individual grains. These results indicate that the use of elastic single crystal constants of pure nickel as an approximation for the constants of gas turbine single crystal alloys, which is often done today, is inaccurate.

Canistraro, H.A. [Univ. of Hartford, CT (United States). Dept. of Mechanical and Audio Engineering Technology; Jordan, E.H.; Shi Shixiang [Univ. of Connecticut, Storrs, CT (United States); Favrow, L.H.; Reed, F.A. [United Technologies Research Center, East Hartford, CT (United States)

1998-07-01

222

Thermoluminescence characteristics of the novel CaF2:Dy nanoparticles prepared by using the hydrothermal method  

NASA Astrophysics Data System (ADS)

Dysprosium doped calcium fluoride (CaF2:Dy) nanoparticles were produced for the first time by using the hydrothermal method. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) patterns were utilized to characterize the synthesized material. The particle size of about 43 nm was evaluated from XRD data and supported by the SEM images. The Tm-Tstop and the computerized glow curve de-convolution (CGCD) methods were employed to determine the number of component glow peaks and kinetic parameters of the synthesized nanoparticles. Thermoluminescence glow curve of this phosphor exhibits six overlapping glow peaks. The optimized concentration of Dy impurity was found at 3 mol%. The prepared nanoparticles exhibit a roughly linear dose response to absorbed dose of 1000 Gy received from 60Co gamma source. This finding recommends this nanomaterial as a good candidate for high dose dosimetry. Other dosimetric features of this novel phosphor are also presented and discussed.

Zahedifar, M.; Sadeghi, E.; Harooni, S.

2012-11-01

223

Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates  

NASA Astrophysics Data System (ADS)

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2(001) substrate. High critical current density values - larger than 1 MA/cm2 in self field and liquid helium - are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through transmission electron microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what was observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction.

Braccini, V.; Kawale, S.; Reich, E.; Bellingeri, E.; Pellegrino, L.; Sala, A.; Putti, M.; Higashikawa, K.; Kiss, T.; Holzapfel, B.; Ferdeghini, C.

2013-10-01

224

Picosecond kinetic confirmation of overlapping Ca cluster and MNa absorption bands in UV grade CaF2  

NASA Astrophysics Data System (ADS)

The ArF laser induced absorption feature between 450 and 700 nm observed in the bulk of mono crystalline calcium fluoride (CaF2) upon prolonged 193 nm irradiation is shown to have two origins: The first band at 530 nm is revealed by a transient femtosecond (fs) laser transparency spectrum and attributed to Ca clusters (colloid). The second band at 600 nm originates from MNa centers as identified by their laser induced fluorescence excitation spectrum, emission wavelength, and fluorescence lifetime. The analysis of the absorption feature by fs pump-probe techniques benefits from the different lifetimes of the transient transparency (excited states of the Ca clusters) and the fluorescing MNa centers of about 5 ps and 22 ns, respectively.

Zeuner, T.; Paa, W.; Triebel, W.; Mühlig, C.; Stafast, H.

2011-09-01

225

Shock wave compression of single-crystal forsterite  

Microsoft Academic Search

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

Ian Jackson; Thomas J. Ahrens

1979-01-01

226

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

227

Imaging linear polarimetry using a single ferroelectric liquid crystal modulator.  

PubMed

In the field of polarimetry, ferroelectric liquid crystal cells are mostly used as bistable polarization rotators suitable to analyze crossed polarizations. This paper shows that, provided such a cell is used at its nominal wavelength and correctly driven, its behavior is close to that of a tunable half-wave plate, and it can be used with much benefit in lightweight imaging polarimetric setups. A partial Stokes polarimeter using a single digital video camera and a single ferroelectric liquid crystal modulator is designed and implemented for linear polarization analysis. Polarization azimuthal angle and degree of linear polarization are available at 150 frames per second with a good accuracy. PMID:20820209

Gendre, Luc; Foulonneau, Alban; Bigué, Laurent

2010-09-01

228

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

229

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

230

perovskite: a single-crystal X-ray diffraction study  

NASA Astrophysics Data System (ADS)

Magnesium silicate perovskite is the predominant phase in the Earth's lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle ( ?) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters ( a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of ? with composition that is independent of the nature of cation substitution (e.g., or substitution mechanism), contrary to previous observations based on unit-cell parameter calculations.

Sinmyo, Ryosuke; Bykova, Elena; McCammon, Catherine; Kupenko, Ilya; Potapkin, Vasily; Dubrovinsky, Leonid

2014-06-01

231

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

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

2001-01-01

232

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

233

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

234

The viscoplastic behavior of Hastelloy-X single crystal  

NASA Technical Reports Server (NTRS)

A viscoplastic constitutive model for simulating the behavior of Hastelloy-X single crystal material was derived based on crystallographic slip theory. To determine the appropriate constitutive model constants and to test the predictions of the model, tests on Hastelloy-X crystals were carried out, including the rate sensitivity, cyclic hardening, nonproportional hardening, relaxation, and strain rate dip tests. It was found necessary to include cube slip in the model in order to correlate the uniaxial behavior of the single crystal, to incorporate the interaction effects in both the hardening and the dynamic recovery evolution equations for the drag stress, and to successfully capture correct strain rate sensitivity under biaxial tension-torsion loading conditions.

Jordan, Eric H.; Shi, Shixiang; Walker, Kevin P.

1993-01-01

235

Characterization of phosphoric acid doped TGS single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) are grown from aqueous solution containing 10-50 mol% of H3PO4. Large sized crystals of dimension (70 mm×40 mm×25 mm) suitable for IR detector applications are obtained with 20 mol% of H3PO4. They exhibit elongated domains, and the domain density is higher than in undoped TGS crystals. FT-IR analysis indicates the presence of both zwitter and glycinium ions in the doped TGSP crystals, which is due to the low incorporation of H3PO4 into the TGS crystal lattice. The dielectric properties TGSP crystals measured in the temperature range 27-65°C and in frequency range 102-105 Hz show a broad transition, and the peak dielectric constant values are reduced with increasing H3PO4 concentration. Hysteresis loops with high coercive fields are observed up to 20 mol% of H3PO4. At a higher concentration, double loops are observed due to the polarization switching inhibition by H3PO4 molecules. Dopant concentration is found to have a marginal influence on the spontaneous polarization of the TGSP crystals.

Saxena, Aparna; Gupta, Vinay; Sreenivas, K.

2004-03-01

236

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

E-print Network

of Materials, University of Oklahoma, Norman, Oklahoma 73019 X. M. Fang and P. J. McCann School of Electrical 110 -oriented epitaxy can be sustained. At the initial growth stage, long strips of CaF2 parallel to result from the combination of favorable energetics in exposing the low-energy 111 facets

McCann, Patrick

237

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

238

Vacancy-Formation Energy and Entropy in Magnesium Single Crystals  

Microsoft Academic Search

Macroscopic thermal dilatation coefficients as well as those of the lattice have been precisely measured along principal crystallographic directions of magnesium single crystals in the temperature range between room temperature and 650°C. The vacancy concentration was thus obtained as a function of temperature and it reached the value of 72×10-5 in the neighborhood of the melting point. An appreciable anisotropy

C. Janot; D. Malléjac; B. George

1970-01-01

239

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

240

Anisotropic continuum damage modeling for single crystals at high temperatures  

Microsoft Academic Search

In single crystals, the process of creep damage is generally anisotropic. Indeed, the damage evolution does not only depend on the loading conditions, but also on the lattice orientation. And the current state of damage has an anisotropic influence on the effective stress state, so that it is represented by a tensorial damage variable. Based on the continuum damage mechanics

Weidong Qi; Albrecht Bertram

1999-01-01

241

Cyclic plasticity of nickel single crystals at elevated temperatures  

Microsoft Academic Search

Single slip oriented nickel crystals have been cyclically deformed at deformation temperatures between 293 K and 900 K until saturation of the stress amplitude. Persistent slip bands (PSBs) with a typical ladder-like dislocation substructure occur at temperatures up to 800 K. At 600 K and 750 K the measured cyclic stress-strain curves (CSSCs) exhibit extended ranges in which the saturation

J. Bretschneider; C. Holste; B. Tippelt

1997-01-01

242

TOPICAL REVIEW: Organic field-effect transistors using single crystals  

NASA Astrophysics Data System (ADS)

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

Hasegawa, Tatsuo; Takeya, Jun

2009-04-01

243

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

244

Anisotropic properties of molybdenum disulfide single crystal in catalysis  

Microsoft Academic Search

When a wafer of molybdenum disulfide single crystal was mounted in a reactor with the basal plane of sulfur exposed and a similar wafer cut into small pieces was mounted in a twin reactor with a large edge surface area of coordinatively unsaturated molybdenum ions exposed, the cut, but not the uncut, catalyst was active for the cis-trans isomerization of

T. Okuhara; K. Tanaka

1978-01-01

245

Birefringence induced by uniaxial stress in cadmium telluride single crystals  

Microsoft Academic Search

The birefringence induced by uniaxial stress in cadmium telluride single crystals was investigated. Static uniaxial compression was applied along the (100), (110), (111) and (112) directions. It was found that n\\/sub \\/\\/\\/-nperpendicular to changes sign near the absorption edge. The position of the inversion point depends on the direction of stress and the direction of light. The components of the

W. Wardzyoski

1970-01-01

246

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

247

The magnetization process in hexagonal ferromagnetic and ferrimagnetic single crystals  

Microsoft Academic Search

Neel's 'theory of phases' is used to study the magnetization process in hexagonal ferromagnetic and ferrimagnetic single-crystal ellipsoids for which the six fold contribution to the magnetocrystalline anisotropy cannot be neglected. Simultaneous equations are presented, the solution of which yields the intensity and orientation of the mean sample magnetization and the various orientations of the saturation magnetization in the domains,

R. R. Birss; D. J. Martin

1975-01-01

248

Polarized superradiance from delocalized exciton transitions in tetracene single crystals  

Microsoft Academic Search

Polarized superradiant emission and exciton delocalization in tetracene single crystals are reported. Polarization-, time-, and temperature-resolved spectroscopies evidence the complete polarization of the zero-phonon line of the intrinsic tetracene emission from both the lower ( F state) and the upper (thermally activated) Davydov excitons. The superradiance of the F emission is substantiated by a nearly linear decrease in the radiative

A. Camposeo; M. Polo; S. Tavazzi; L. Silvestri; P. Spearman; R. Cingolani; D. Pisignano

2010-01-01

249

Single Crystal SiC Microhotplate Conductometric Chemical Sensor Arrays  

Microsoft Academic Search

Microhotplates are miniature (typically ~100µm on a side) micromachined devices with integrated heaters, temperature sensors and film resistance sensors. With their low power consumption, millisecond thermal response times and small size (allowing compact microsensor arrays), microhotplates are versatile chemical sensor platforms (1) and powerful materials deposition and characterization tools (2). When fabricated from single crystal silicon carbide, the mechanical support,

Richard Mlcak; George Whitfield; Harry Tuller

250

Nanoindentation creep of single-crystal tungsten and gallium arsenide  

Microsoft Academic Search

An extensive study of indentation creep on the nanometre scale has been made on single-crystal indium, tungsten and gallium arsenide. We use the force modulation technique which gives a direct measure of contact stiffness and, being insensitive to thermal drift, allows the accurate observation of creep in small indents to be carried out over long time periods: We show that

S. A. Syed Asif; J. B. Pethica

1997-01-01

251

Direct Bonding of LiTaO3 Single Crystals  

Microsoft Academic Search

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

Yoshihiro Tomita; Masato Sugimoto; Kazuo Eda; Tetsuyuki Okano

1994-01-01

252

Elastic constants of single crystal Hastelloy X at elevated temperatures  

Microsoft Academic Search

An acoustic time of flight technique is described in detail for measuring the elastic constants of cubic single crystals that allows for the constants to be determined at elevated temperature. Although the overall technique is not new, various aspects of the present work may prove extremely useful to others interested in finding these values, especially for aerospace materials applications. Elastic

Howard A. Canistraro; Eric H. Jordan; Shi Shixiang; Leroy H. Favrow; Francis A. Reed

1998-01-01

253

Oxidation behavior of single crystal TMS82+ superalloy in air  

Microsoft Academic Search

The oxidation behavior of the single crystal Ni-based superalloy TMS-82+ was studied under cyclic condition at 900 and 1 000 ? for 200 h in air. The oxidation kinetics for the superalloy at both exposure temperatures was explained by the subparabolic relationship. The results show that increasing the exposure temperature from 900 to 1 000 ?, the amounts of ?-Al2O3,

WU Ying; SONG Gui-ming; ZHOU Shao-xiong; T. NARITA

254

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

255

Scalable synthesis of graphene on single crystal Ir(111) films  

NASA Astrophysics Data System (ADS)

We have investigated single crystal Ir(111) films grown heteroepitaxially on Si(111) wafers with yttria-stabilized zirconia (YSZ) buffer layers as possible substrates for an up-scalable synthesis of graphene. Graphene was grown by chemical vapor deposition (CVD) of ethylene. As surface analytical techniques we have used scanning tunneling microscopy (STM), low-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. The mosaic spread of the metal films was below 0.2° similar to or even below that of standard Ir bulk single crystals, and the films were basically twin-free. The film surfaces could be improved by annealing so that they attained the perfection of bulk single crystals. Depending on the CVD conditions a lattice-aligned graphene layer or a film consisting of different rotational domains were obtained. STM data of the non-rotated phase and of the phases rotated by 14° and 19° were acquired. The quality of the graphene was comparable to graphene grown on bulk Ir(111) single crystals.

Zeller, Patrick; Dänhardt, Sebastian; Gsell, Stefan; Schreck, Matthias; Wintterlin, Joost

2012-10-01

256

Novel single-mode and polarization maintaining photonic crystal fiber  

NASA Astrophysics Data System (ADS)

In this paper, we present and propose a novel structure for improved birefringence and single-mode propagation condition photonic crystal fiber (PCF) in a broad range of wavelength. The birefringence of the fundamental mode and single mode property in such a PCF is numerically estimated by employing full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). The simulation results illustrate that we can achieve a high birefringence and perfect single-mode condition by employing silica-filled into one-line elliptical air holes parallel to x-axis and rotated by an angle. Obviously, the proposed PCF is quite useful for optical devices.

Yin, Aihan; Xiong, Lei

2014-11-01

257

Single crystal diamond probes for atomic-force microscopy  

NASA Astrophysics Data System (ADS)

Results obtained in the development and testing of high-strength, chemically inert, and sharply pointed single crystal diamond probes for atomic-force microscopy are presented. The probes were fabricated on the basis of pyramidal diamond single crystals produced by selective oxidation of polycrystalline films grown by chemical vapor deposition. A procedure was developed for attachment of single needles to cantilevers of silicon probes. A transmission electron microscope was used to find that the apical angle of the pyramidal diamond crystallites is about 10° and the radius of curvature of the apex of the diamond crystallite is 2-10 nm. It is shown for the example of two test samples (graphite surface and DNA molecules) that the diamond probes can be effectively used in atomic-force microscopy and make it possible to improve the image quality compared with standard silicon probes.

Tuyakova, F. T.; Obraztsova, E. A.; Klinov, D. V.; Ismagilov, R. R.

2014-07-01

258

Shock wave-induced phase transition in RDX single crystals.  

PubMed

The real-time, molecular-level response of oriented single crystals of hexahydro-1,3,5-trinitro-s-triazine (RDX) to shock compression was examined using Raman spectroscopy. Single crystals of [111], [210], or [100] orientation were shocked under stepwise loading to peak stresses from 3.0 to 5.5 GPa. Two types of measurements were performed: (i) high-resolution Raman spectroscopy to probe the material at peak stress and (ii) time-resolved Raman spectroscopy to monitor the evolution of molecular changes as the shock wave reverberated through the material. The frequency shift of the CH stretching modes under shock loading appeared to be similar for all three crystal orientations below 3.5 GPa. Significant spectral changes were observed in crystals shocked above 4.5 GPa. These changes were similar to those observed in static pressure measurements, indicating the occurrence of the alpha-gamma phase transition in shocked RDX crystals. No apparent orientation dependence in the molecular response of RDX to shock compression up to 5.5 GPa was observed. The phase transition had an incubation time of approximately 100 ns when RDX was shocked to 5.5 GPa peak stress. The observation of the alpha-gamma phase transition under shock wave loading is briefly discussed in connection with the onset of chemical decomposition in shocked RDX. PMID:17718475

Patterson, James E; Dreger, Zbigniew A; Gupta, Yogendra M

2007-09-20

259

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

260

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

261

Heavy ion passive dosimetry with silver halide single crystals  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

262

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

263

Epitaxial growth, structure, and magnetism of epitaxial Ni80Fe20 single-crystal, bicrystal, and quad-crystal films  

E-print Network

Epitaxial growth, structure, and magnetism of epitaxial Ni80Fe20 single-crystal, bicrystal epitaxy MBE growth and structural and magnetic characterizations of high-quality single-crystal, bi the conclusion is made. II. SAMPLE PREPARATION AND MEASUREMENTS The crystal growth was carried out in a MBE

Huang, Jung-Chun

264

Single-crystal Si formed on amorphous substrate at low temperature by nanopatterning and nickel-induced lateral crystallization  

E-print Network

Single-crystal Si formed on amorphous substrate at low temperature by nanopatterning and nickel-induced lateral crystallization Jian Gu and Stephen Y. Chou NanoStructure Laboratory, Department of Electrical, Utah 84020 Received 11 April 2002; accepted for publication 7 June 2002 Single-crystal silicon has been

265

A new material for single crystal modulators: BBO  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

266

Current path simulation of Bi-2212 phase superconducting single crystals  

NASA Astrophysics Data System (ADS)

In the oxide superconductor with layered structure, the superconducting currents flow in the Cu-O 2 plane that is parallel to the a- b axis. The critical current Ic of Bi 2Sr 2CaCu 2O x (Bi-2212) single crystals measured by a four-probe method did not increase linearly with increasing the thickness of the crystal. The saturated Ic value of the crystals was about 2.8 A. The results meant that the current flow in the a- b plane is different from that in c-axis in the oxide superconductor. In the Cu-O 2 planes that are parallel to the a- b plane, the superconducting currents flow in a conventional conduction system, whereas between the Cu-O 2 planes that are perpendicular to the a- b plane, they flow by tunneling mechanism. We assumed the current path in a single crystal, and calculated the Ic by the superconducting current simulation. The results indicated that the superconducting current between the Cu-O 2 planes decreased by 2.5% in every 1 ?m.

Hara, M.; Imao, H.; Matsumoto, K.

2007-10-01

267

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

268

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

269

Flextensional Single Crystal Piezoelectric Actuators for Membrane Deformable Mirrors  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

270

Averaged effective pinning potential in YBCO single crystals near Tc  

NASA Astrophysics Data System (ADS)

The dynamics of magnetic flux trapped in low dc magnetic fields (of the order of the Earth's field) was for the first time studied experimentally in single-crystal YBCO samples with unidirectional twin boundaries in the temperature range near Tc (0.8 < T/Tc < 0.99). Strong pinning in the system of unidirectional planar defects was demonstrated, and a significant deviation from monotonous behavior was established for the averaged effective pinning potential Up(T) for the trapped flux of low density. In order to compare different methods of Jc determination, the field dependences of the magnetization loop width M(H), which are related to the effective pinning and Jc, were obtained, and resistive measurements on microbridges made from the same single crystals were carried out.

Monarkha, V. Yu.; Sivakov, A. G.; Timofeev, V. P.

2014-09-01

271

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

272

Investment casting of NiAl single-crystal alloys  

NASA Astrophysics Data System (ADS)

Significant progress has been made in the understanding of solidification conditions, microstructure evolution, and defect formation during investment casting of NiAl single crystals. The high liquidus temperatures of NiAl alloys result in a larger dendrite arm spacing than is found in superalloy René N5. Because of their higher thermal conductivities, NiAl alloys have higher cooling rates and lower temperature gradients during solidification than René N5. These differences give NiAl alloys a lower tendency to form freckles and a higher tendency to form equiaxed grains. However, with the aid of process modeling, single crystals of various shapes of NiAl alloys have been produced.

Yu, K. O.; Oti, J. A.; Walston, W. S.

1993-05-01

273

Resonant photoemission in single-crystal black phosphorus  

Microsoft Academic Search

Resonant photoemission in single-crystal black phosphorus has been reinvestigated in detail by high-resolution spectroscopy. Partial-yield, valence-band, and constant-initial-state spectra were measured in the 2p core-exciton excitation region. We have confirmed two types of resonances at the 2p core threshold: one is a strong core-exciton-induced resonance with two final valence holes and the other is a weak Fano-type resonance. The Fano-type

M. Taniguchi; J. Ghijsen; R. L. Johnson; S. Suga; Y. Akahama; S. Endo

1989-01-01

274

Deformation of FeAl single crystals at high temperatures  

Microsoft Academic Search

Single crystals of the intermetallic compound FeAl with the CsCl structure have been deformed in compression at temperatures between 470 and 1000 K to study the slip geometry and the dislocation arrangements in this material at high temperatures. At temperatures below 0·44 of the melting temperature, Tm, slip occurs on the {110}?111? systems, while at 0·44Tm, the transitions in the

Y. Umakoshi; M. Yamaguchi

1980-01-01

275

Electrical conductivity of olivine single crystals at high temperature  

Microsoft Academic Search

The electrical conductivity in three single crystal specimens of olivine (fayalite mole %; 7.4, 8.4 and 12.6) is measured along the three crystallographic orientations in the temperature range of 600° to 1200°K. There are two different mechanisms with different activation energy for electrical conduction; presumably the impurity (Fe) conduction is predominant above 800°K and extrinsic conduction is predominant below 800°K.

Yoji Kobayashi; Hiroshi Maruyama

1971-01-01

276

Plastic deformation of nickel single crystals at low temperatures  

Microsoft Academic Search

Single crystals of nickel (purities 99.98% and 99.4%) have been deformed in tension at various temperatures between 4.2°K and 300°K. Shear stress-shear strain relations have been determined as well as the reversible change of flow stress with temperature. The work-hardening parameters obtained are discussed in terms of dislocation theory that has been developed mainly on the basis of data on

Peter Haasen

1958-01-01

277

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

278

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

279

ELECTRICAL CONDUCTION IN SINGLE-CRYSTAL ALUMINUM THIN FILMS  

Microsoft Academic Search

Electrical conduction in thin (400?1500 Å) single-crystal aluminum films vacuum evaporated on NaCl substrates is explained by a simple model and verified by experimental results. The resistivity of the inter-island boundaries is accounted for by considering the film structure as a metal—insulator matrix and calculating its equivalent resistivity. An unambiguous comparison can then be made with the Fuchs—Sondheimer theory of

T. S. Jayadevaiah; Robert E. Kirby

1969-01-01

280

Carrier doping and interlayer coupling in HTSC single crystals  

Microsoft Academic Search

Experimental results of the effect of carrier doping on the irreversibility lines in (La, Sr)2CuO4-delta and Bi2Sr2CaCu2O8+delta single crystals are summarized. As a function of Sr or oxygen contents, systematic and dramatic widening of the irreversible regions in the B - T phase diagram was observed in both systems. The present study suggests the critical importance of carrier concentration which

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

1994-01-01

281

Anisotropy of electronic distribution in a cobalt disilicide single crystal  

NASA Astrophysics Data System (ADS)

An experimental and theoretical analysis of cobalt disilicide Compton profiles is presented. The measurements along [100], [110] and [111] directions of single crystal CoSi 2 are performed with use of synchrotron radiation (59.38 keV). There is a good overall agreement between experimental and theoretical profile anisotropies, obtained from a self consistent linear-muffin-tin-orbitals band structure calculation. The slight difference of observed structures is discussed in terms of d-type bonds.

Bellin, Ch.; Loupias, G.; Manuel, A. A.; Jarlborg, T.; Sakurai, Y.; Tanaka, Y.; Shiotani, N.

1995-11-01

282

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

283

Constitutive modelling of single crystal and directionally solidified superalloys  

NASA Technical Reports Server (NTRS)

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

Walker, Kevin P.; Jordan, Eric H.

1987-01-01

284

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

285

Luminescent properties of CdI2 single crystals  

Microsoft Academic Search

The paper deals with the results of studies in luminescent properties of CdI2 single crystals in natural and polarized light. The existence of several bands of intrinsic emission was established. The emission band of 480 nm is dominant within a temperature range of 200-150 K, whereas that of 550 nm is effective at temperatures below 150 K. Possible reasons for

I. M. Bolesta

1976-01-01

286

Interferometric studies of domain structures in potassium niobate single crystals  

Microsoft Academic Search

Interferometric studies of domain structures in KNbO3 single crystals, grown by using excess of K2CO3 as a flux are reported. The surface deformations produced on the pseudocubic (001) planes by the stable patterns of 90°, 60° and 180° domains have been studied and discussed. If the observed plane is not the plane of the shear, the 90° domains are inclined

K G Deshmukh; S G Ingle

1971-01-01

287

Primary creep in single crystal superalloys: Origins, mechanisms and effects  

Microsoft Academic Search

Creep deformation of the CMSX-4 nickel-base single crystal superalloy is studied in the range 750–850°C. Emphasis is placed on elucidating the factors causing primary creep when the tensile stress is orientated within 20°C of the technologically important ?001? direction. It is demonstrated unambiguously that primary creep occurs only if a threshold stress of approximately 500MPa is exceeded; thereafter the accumulated

C. M. F. Rae; R. C. Reed

2007-01-01

288

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

E-print Network

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

Broholm, Collin Leslie

289

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

290

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

291

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

292

Up-conversion white light of Tm 3+/Er 3+/Yb 3+ tri-doped CaF 2 phosphors  

NASA Astrophysics Data System (ADS)

Tm 3+/Er 3+/Yb 3+ tri-doped CaF 2 phosphors were synthesized using a hydrothermal method. The phosphors were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and up-conversion (UC) emission spectra. After annealing, the phosphors emitted white light under a 980 nm continuous wave diode laser (CW LD 2 W) excitation. As the excitation power density changed in the range of 20-260 W/cm 2, the chromaticity coordinates of the UC light of the phosphor Ca 0.885Tm 0.005Er 0.01Yb 0.1F 2 fell well in the white region of the 1931 CIE diagram. For the proportion of red, green and blue (RGB) in white light is strict, key factors for achieving UC white light, such as host materials, rare earth ions doping concentrations, annealing temperatures, as well as the excitation power densities, were investigated and discussed.

Cao, Chunyan; Qin, Weiping; Zhang, Jisen; Wang, Yan; Wang, Guofeng; Wei, Guodong; Zhu, Peifen; Wang, Lili; Jin, Longzhen

2008-03-01

293

SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION  

SciTech Connect

In this research program, several optical instruments for high temperature measurement based on single crystal sapphire material are introduced and tested for real-time, reliable, long-term monitoring of temperatures for coal gasifier. These are sapphire fiber extrinsic Fabry-Perot interferometric (EFPI) sensor; intensity-measurement based polarimetric sapphire sensor and broadband polarimetric differential interferometric (BPDI) sapphire sensor. Based on current evaluation and analysis of the experimental results, the broadband polarimetric differential interferometric (BPDI) sensor system was chosen for further prototype instrumentation development. This approach is based on the self-calibrating measurement of optical path differences (OPD) in a single-crystal sapphire disk, which is a function of both the temperature dependent birefringence and the temperature dependent dimensional changes. The BPDI sensor system extracts absolute temperature information by absolute measurement of phase delays. By encoding temperature information in optical spectrum instead of optical intensity, this sensor guarantees its relative immunity to optical source power fluctuations and fiber losses, thus providing a high degree of long-term measurement stability which is highly desired in industrial applications. The entire prototype for BPDI system including the single crystal sapphire probe, zirconia prism, alumina extension tube, optical components and signal processing hardware and software have shown excellent performance in the laboratory experiments shown in this report.

A. Wang; G. Pickrell; R. May

2002-09-10

294

Monitoring lidocaine single-crystal dissolution by ultraviolet imaging.  

PubMed

Dissolution critically affects the bioavailability of Biopharmaceutics Classification System class 2 compounds. When unexpected dissolution behaviour occurs, detailed studies using high information content technologies are warranted. In the present study, an evaluation of real-time ultraviolet (UV) imaging for conducting single-crystal dissolution studies was performed. Using lidocaine as a model compound, the aim was to develop a setup capable of monitoring and quantifying the dissolution of lidocaine into a phosphate buffer, pH 7.4, under stagnant conditions. A single crystal of lidocaine was placed in the quartz dissolution cell and UV imaging was performed at 254 nm. Spatially and temporally resolved mapping of lidocaine concentration during the dissolution process was achieved from the recorded images. UV imaging facilitated the monitoring of lidocaine concentrations in the dissolution media adjacent to the single crystals. The concentration maps revealed the effects of natural convection due to density gradients on the dissolution process of lidocaine. UV imaging has great potential for in vitro drug dissolution testing. PMID:21387316

Østergaard, Jesper; Ye, Fengbin; Rantanen, Jukka; Yaghmur, Anan; Larsen, Susan Weng; Larsen, Claus; Jensen, Henrik

2011-08-01

295

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

296

Segregation effects in Fe microalloyed NiAl single crystals  

SciTech Connect

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

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

1995-10-15

297

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 - Keller, D. [Los Alamos National Laboratory

2010-12-23

298

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

299

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

SciTech Connect

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

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

2006-12-01

300

The cadmium oxide-tungsten oxide phase system and growth of cadmium tungstate single crystals  

Microsoft Academic Search

The results of a further study of the cadmium oxide-tungsten oxide phase diagram are presented and the results of attempts to prepare single crystals of cadmium tungstate. The defects encountered in the crystals and attempts to eliminate them are described and the best conditions for growth of high-quality single crystals detailed. The relationship of the defects to the crystal growth

D. S. Robertson; I. M. Young; J. R. Telfer

1979-01-01

301

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

302

Magnetism of powder samples and of single crystals  

NASA Astrophysics Data System (ADS)

The temperature dependence of the magnetic order parameter of NiF2, MnCO3 and K2NiF4 measured on powder samples is compared with data obtained on single crystals. It is found that the dynamic dimensionality of the NiF2 and MnCO3 powder samples is one-dimensional (1D) for all temperatures Tsingle crystals isotropic 3D dynamic symmetry is observed. In order to explain isotropy in the bulk single crystals a dynamic averaging process over all domain orientations has to be postulated. For single crystal material of K2NiF4 a critical exponent of ?=0.14±0.01 has been reported. Our neutron diffraction measurements on powder material yield to a very good approximation mean field critical behaviour indicating isotropic dynamics in the critical range. This unexpected result points to a dynamic averaging process over all differently oriented powder grains. As we have argued earlier, the observed universality in the dynamics of ordered magnets is due to a boson guiding field. Averaging over all powder grains, requests that the mean free path of the field bosons is larger than the size of the grains. Additionally, it must be assumed that the field quanta are able to tunnel across the interface between adjacent grains. In polycrystalline bulk samples of the 2D ferromagnet Rb2CrCl4 and of the 1D antiferromagnet KCuF3 also mean field critical behaviour is identified. As a consequence, a similar averaging process as in the K2NiF4 powder sample can be assumed to average over the mosaic structure of polycrystalline bulk material of Rb2CrCl4 and KCuF3. High quality single crystals of Rb2CrCl4 and of KCuF3 exhibit critical exponent of ?~0.3. Dependence of the critical exponents on the mesoscopic morphology of the sample is considered as a typical indication of a boson controlled dynamics, and may partly explain the surprisingly broad distribution of critical exponent values reported in literature.

Köbler, U.; Hoser, A.

2014-01-01

303

Biaxial constitutive modelling and testing of a single crystal superalloy at elevated temperatures  

NASA Technical Reports Server (NTRS)

A viscoplastic constitutive model for single crystal superalloys is developed from crystallographic slip theory. The model is applied to the tension and torsion deformation behavior of the single crystal superalloy PWA 1480 at 871 C (1600 F). Both octahedral and cube slip behavior are needed to model the deformation behavior of single crystal superalloys at elevated temperature.

Walker, K. P.; Jordan, E. M.

1989-01-01

304

Active Slip Band Separation and the Energetics of Slip in Single Crystals  

E-print Network

Active Slip Band Separation and the Energetics of Slip in Single Crystals to the prediction of stress-strain relations for single crystals and to give precise formulations of experimentally observed connec- tions between hardening of single crystals and separation of active slip

305

Active Slip Band Separation and the Energetics of Slip in Single Crystals  

E-print Network

Active Slip Band Separation and the Energetics of Slip in Single Crystals Luca Deseri David R. Owen­strain relations for single crystals and to give precise formulations of experimentally observed connec­ tions between hardening of single crystals and separation of active slip bands. Non--classical, structured

306

Irradiated cubic single crystal SiC as a high temperature sensor Alex A. Volinsky  

E-print Network

Irradiated cubic single crystal SiC as a high temperature sensor Alex A. Volinsky University to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation was developed a while ago. Single crystal SiC sensor small size (200-500 microns), wide temperature range (150

Volinsky, Alex A.

307

Irradiated Single Crystals for High Temperature Measurements in Space Applications Alex A. Volinsky1  

E-print Network

formation and accumulation in diamond and SiC single crystals, which causes overall lattice expansionIrradiated Single Crystals for High Temperature Measurements in Space Applications Alex A. Volinsky temperature, if the exposure time is known. This paper describes the use of irradiated single crystal high

Volinsky, Alex A.

308

Low-Leakage Superconducting Tunnel Junctions with a Single-Crystal Al2O3 Barrier*  

E-print Network

Low-Leakage Superconducting Tunnel Junctions with a Single-Crystal Al2O3 Barrier* S Oh1,2 , K Cicak Abstract We have developed a two-step growth scheme for single-crystal Al2O3 tunnel barriers. The barriers environment, a morphologically intact single-crystal Al2O3 layer is obtained. Tunnel junctions fabricated from

Martinis, John M.

309

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

310

MICROSCALE LASER PEEN FORMING OF SINGLE CRYSTAL: DYNAMIC DEFORMATION AND ANISOTROPY  

E-print Network

MICROSCALE LASER PEEN FORMING OF SINGLE CRYSTAL: DYNAMIC DEFORMATION AND ANISOTROPY Yajun Fan and anisotropy in micro-scale laser peen forming of aluminum single crystals have been numerically and provide useful insight into the dynamic shock peen-forming process of single crystal. DYNAMIC MODELING

Yao, Y. Lawrence

311

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

312

The effect of CaF2 on thermodynamics of CaO-CaF2-SiO2(-MgO) slags  

NASA Astrophysics Data System (ADS)

To address the role of CaF2 in the CaO-CaF2-SiO2(-MgO) slag system employed for the production of low-pressure rotor steels, the thermodynamic aspects of the slag were investigated by equilibrating it with liquid iron at 1873 K in CaO or MgO crucibles. Presaturation of slag with an oxide block piece of CaO or MgO in a Pt crucible and application of a carbon paste to the outside of an oxide crucible were designed to prevent crucible failure during the slag-metal experiments. The liquidus isotherm and phase boundary of the preceding slag system were investigated using the slag-metal equilibria. Also, the effect of CaF2 on the sulfide capacity and the activity coefficient of Fe t O were of particular interest in controlling the sulfur level and cleanliness of low-pressure rotor steels.

Choi, Chul-Hwan; Jo, Sung-Koo; Kim, Seon-Hyo; Lee, Kwang-Ro; Kim, Jeong-Tae

2004-02-01

313

Pyroelectric properties of phosphoric acid-doped TGS single crystals  

NASA Astrophysics Data System (ADS)

Pyroelectric properties of phosphoric acid (H3PO4)-doped triglycine sulfate (TGSP) single crystals grown from solutions containing 0.1-0.5 mol of H3PO4 have been studied. Incorporation of H3PO4 into the crystal lattice is found to induce an internal bias field (Eb) and is observed through the presence of a sustained polarization and pyroelectricity beyond the transition temperature. The internal bias field has been estimated theoretically by fitting the experimentally measured data on temperature dependence of the pyroelectric coefficient (lgr), dielectric constant (egr') and polarization (P). A high Eb value in the range 9 × 103-15.5 × 104 V m-1 is obtained for crystals grown with 0.1-0.5 mol of H3PO4 in the solution, and a specific concentration of 0.2-0.25 mol of H3PO4 in the solution during crystal growth is found to be optimum for a high figure of merit for detectivity, Fd = 428 µC m-2 K-1.

Saxena, Aparna; Fahim, M.; Gupta, Vinay; Sreenivas, K.

2003-12-01

314

Spectroscopic characterization of YAG and Nd:YAG single crystals  

NASA Astrophysics Data System (ADS)

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

Kosti?, S.; Lazarevi?, Z.; Rom?evi?, M.; Radojevi?, V.; Milutinovi?, A.; Staniši?, G.; Gili?, M.

2014-09-01

315

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

316

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

317

Strain incompatibility and residual strains in ferroelectric single crystals.  

PubMed

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 BaTiO(3) 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

318

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

319

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

NASA Astrophysics Data System (ADS)

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. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.

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

2005-02-01

320

Growth structure investigation of MgF 2 and NdF 3 films grown by molecular beam deposition on CaF 2(111) substrates  

Microsoft Academic Search

The growth structure of MgF2 and NdF3 films grown on polished CaF2(111) substrates deposited by molecular beam deposition has been investigated using transmission electron microscopy (TEM) of microfractographical and surface replications as well as cross-sectional TEM, atomic force microscopy, packing density, and absorption measurements. It has been shown that by taking advantage of ultrahigh vacuum environments and a special stratification

U. Kaiser; M. Adamik; G. Sáfrán; P. B. Barna; S. Laux; W. Richter

1996-01-01

321

An XPS study of the fluorination of carbon anodes in molten NaF–AlF 3 –CaF 2  

Microsoft Academic Search

In the Hall–Héroult process for aluminum production electrolysis takes place in molten cryolite (NaF–AlF3–CaF2) with carbon electrodes. Dewetting of the anode leads to operational instability. A surface energy change due to surface\\u000a fluorocarbon formation during electrolysis is suggested as a contributing factor to diminishing the wettability of the anode.\\u000a In this work the surface composition of graphite anodes after electrolysis

Richard G. Haverkamp

322

Metastable X centers in cadmium telluride single crystals  

NASA Astrophysics Data System (ADS)

A model is proposed for metastable DX centers formed through Jahn-Teller distortion of the crystal lattice of cadmium telluride, i.e., through the displacement of a D Cd residual donor impurity atom (where D is a Group III element of the periodic table) to the region of a nearest neighbor interstice. The configuration-coor-dinate diagram for a V Cd- D i associated defect is constructed with due regard for the tetrahedral and hexagonal positions of interstitial atoms. The Stokes shift, n-type conductivity, location of the Fermi level, specific features of photoluminescence, and some other effects are explained in terms of the configuration-coordinate diagram. The results of experimental investigations of the energy spectrum of DX centers in cadmium telluride single crystals are in agreement with available theoretical data.

Tkachuk, P. N.; Tkachuk, V. I.; Bukivsky, P. N.; Kurik, M. V.

2004-05-01

323

Display projector technology by way of single crystal faceplate technology  

NASA Astrophysics Data System (ADS)

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

Tucker, A.; Kindl, H. J.

1993-09-01

324

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

325

Thermal neutron dosimeter by synthetic single crystal diamond devices.  

PubMed

We report on a new solid state dosimeter based on chemical vapor deposition (CVD) single crystal diamond fabricated at Roma "Tor Vergata" University laboratories. The dosimeter has been specifically designed for direct neutron dose measurements in boron neutron capture therapy (BNCT). The response to thermal neutrons of the proposed diamond dosimeter is directly due to (10)B and, therefore, the dosimeter response is directly proportional to the boron absorbed doses in BNCT. Two single crystal diamond detectors are fabricated in a p-type/intrinsic/metal configuration and are sandwiched together with a boron containing layer in between the metallic contacts (see Fig.1). Neutron irradiations were performed at the Frascati Neutron Generator (FNG) using the 2.5 MeV neutrons produced through the D(d,n)(3)He fusion reaction. Thermal neutrons were then produced by slowing down the 2.5 MeV neutrons using a cylindrical polymethylmethacrylate (PMMA) moderator. The diamond dosimeter was placed in the center of the moderator. The products of (10)B(n,alpha)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed. PMID:19375336

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

2009-07-01

326

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

327

Advanced piezoelectric single crystal based transducers for naval sonar applications  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

328

Dielectric response and magnetoelectric coupling in single crystal gallium ferrite  

NASA Astrophysics Data System (ADS)

Here we report the dielectric response and electric conduction behavior of magnetoelectric gallium ferrite single crystals studied using impedance analysis in time and temperature domain. The material exhibits two distinct relaxation processes: a high frequency bulk response and a low frequency interfacial boundary layer response. Calculated bulk capacitance as a function of temperature showed an anomaly at ferri- to paramagnetic transition temperature (˜ 300 K), suggestive of magneto-dielectric coupling in the material. Interestingly, we also witness an abrupt change in the activation energy at ˜ 220 K, in the vicinity of spin-glass transition temperature in GaFeO3.

Mukherjee, Somdutta; Gupta, Rajeev; Garg, Ashish

2013-05-01

329

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

330

Nanoparticles of Ni in ZnO single crystal matrix  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles were produced in ZnO single crystals using ion implantation of Ni along the [0001] channelling direction of ZnO. The particles were identified by X-ray diffraction and magnetization measurements as a distribution of superparamagnetic nickel nanoparticles having diameters in the range 2 - 3 nm. The depth distribution and size of the particles were determined using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The obtained results agree with magnetization and X-ray diffraction (XRD) data. From the determined depth distribution, the density change of implanted region of the material modified by the implantation procedure was estimated.

Borges, R. P.; Ribeiro, B.; Cruz, M. M.; Godinho, M.; Wahl, U.; da Silva, R. C.; Gonçalves, A. P.; Magén, C.

2013-06-01

331

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

332

Carrier doping and interlayer coupling in HTSC single crystals  

SciTech Connect

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

Kishio, K.; Shimoyama, J.; Kimura, T.; Kotaka, Y.; Kitazawa, K. [Univ. of Tokyo (Japan). Dept. of Applied Chemistry; Yamafuji, K. [Kyushu Univ., Fukuoka (Japan). Dept. of Electronics; Li, Q.; Suenaga, M. [Brookhaven National Lab., Upton, NY (United States). Div. of Materials Science

1994-09-01

333

Single Molecule Studies on Dynamics in Liquid Crystals  

PubMed Central

Single molecule (SM) methods are able to resolve structure related dynamics of guest molecules in liquid crystals (LC). Highly diluted small dye molecules on the one hand explore structure formation and LC dynamics, on the other hand they report about a distortion caused by the guest molecules. The anisotropic structure of LC materials is used to retrieve specific conformation related properties of larger guest molecules like conjugated polymers. This in particular sheds light on organization mechanisms within biological cells, where large molecules are found in nematic LC surroundings. This review gives a short overview related to the application of highly sensitive SM detection schemes in LC. PMID:24077123

Tauber, Daniela; von Borczyskowski, Christian

2013-01-01

334

The sublimation kinetics of GeSe single crystals  

NASA Technical Reports Server (NTRS)

The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by high-temperature mass spectroscopy, quantitative vacuum microbalance techniques, and hot stage optical microscopy. For a mean experimental temperature of 563 K, the activation enthalpy and entropy are found to equal 32.3 kcal/mole and 19.1 eu, respectively. The vaporization coefficient is less than unity for the range of test temperatures, and decreases with increasing temperature. The combined experimental data are correlated by means of a multistep surface adsorption mechanism.

Irene, E. A.; Wiedemeier, H.

1975-01-01

335

Single-crystal indicators of fatigue and plastic deformation damage  

NASA Astrophysics Data System (ADS)

Specially prepared thin single-crystal plates rigidly fastened to the sample surface area are shown to be effective as sensor elements (indicators and detectors) of the deformation damage of multi-phase commercial alloys under fatigue and static loading. It is proposed to estimate the lifetime and the strain of basic material by monitoring the geometric characteristics of band patterns on the detector surface. It is shown that density, direction of deformation bands and fractal dimension of band patterns on surfaces of indicators correlate with the number of cycles, maximum applied stress (fatigue loading) and plastic strain, temperature (static loading).

Gordienko, Y. G.; Zasimchuk, E. E.

1994-09-01

336

Cryogenic Scanning Tunneling Spectroscopy of Superconducting Iron Chalcogenide Single Crystals  

NASA Astrophysics Data System (ADS)

We report scanning tunneling spectroscopy measurements on the iron-based superconductors of the "11" family including Fe1-yTe1-xSex and Fe1-yTe1-xSx. Conductance spectra and atomically-resolved images are obtained on single crystals down to 300 mK. A gap-like structure is observed, showing an asymmetric spectral background, non-trivial spatial variation and temperature dependence. We discuss our data in terms of possible gap anisotropy and doping inhomogeneities, and in relation to other recent spectroscopic measurements on iron-based superconductors.

Wei, J. Y. T.; Fridman, Igor; Yeh, Kuo-Wei; Wu, Maw-Kuen; Hu, Rongwei; Petrovic, C.

2011-03-01

337

Optical properties of Ce:Mn:KLN single crystals  

NASA Astrophysics Data System (ADS)

CeO2 and MnCO3 codoped Potassium Lithium Niobate single crystals were grown by the Czochralski method. It was shown that Ce ions would be precedently substituted for the site of K by the absorption spectra and X-ray diffraction patterns. Otherwise Mn would be substitute for the site of Nb. The response time, exponential gain coefficient and effective carries density was measured by the two beam coupling. The effect of Oxide and reduced treatment on these parameters was researched.

Yang, Chunhui; Chen, Gang; Wang, Biao

2001-10-01

338

Nonlinear microwave switching response of BSCCO single crystals  

SciTech Connect

Measurements of the surface impedance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal with microwave currents flowing along the {cflx c} axis show clear evidence of a step-like nonlinearity. The surface resistance switches between apparently quantized levels for microwave field strength changes < 1 mG. This nonlinear response can arise from the presence of intrinsic Josephson junctions along the {cflx c} axis of these samples driven by the microwave current.

Jacobs, T.; Sridhar, S. [Northeastern Univ., Boston, MA (United States). Dept. of Physics; Willemsen, B.A. [Northeastern Univ., Boston, MA (United States). Dept. of Physics]|[Rome Lab., Hanscom AFB, MA (United States); Li, Qiang [Brookhaven National Lab., Upton, NY (United States); Gu, G.D.; Koshizuka, N. [Superconductivity Research Lab., Tokyo (Japan)

1996-06-01

339

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

340

Preparation of Black Phosphorus Single Crystals by a Completely Closed Bismuth-Flux Method and Their Crystal Morphology  

Microsoft Academic Search

Needle-shaped and film- or plate-shaped black phosphorus single crystals were prepared by an improved bismuth-flux method. The conversion of red phosphorus to white phosphorus and the growth of black phosphorus single crystals from the solution of white phosphorus in liquid bismuth were performed in an evacuated quartz-glass apparatus without breaking the vacuum. Needle crystals measured about 5 mm in length

Mamoru Baba; Fukunori Izumida; Yuji Takeda; Akira Morita

1989-01-01

341

Electronic Properties of CuxTiSe2 Single Crystals  

NASA Astrophysics Data System (ADS)

We investigate the normal state and superconducting properties of 1T-TiSe2 family of single crystals intercalated with different level of copper content. Magnetoresistance and Hall effect data indicate that 1T-TiSe2 is a compensated narrow band-gap semiconductor or semimetal with small number of electron and hole carriers. We compare the influence of copper intercalant and titanium interstiatials on the temperature evolution of charge density waves via resistivity and Hall effect measurements. Our findings indicate that the origin of the charge density waves in 1T-TiSe2 is due to the combination of exciton and Jahn-Teller mechanisms. At higher copper concentrations we investigate the superconducting properties of CuxTiSe2 in overdoped regime and find that the system is a single-gap strongly type-II superconductor with in-plane Ginzburg-Landau parameter reaching 50.

Husanikova, Petra; Fedor, Jan; Derer, Jan; Cambel, Vladimir; Karapetrov, Goran

2013-03-01

342

Ferromagnetism in Single Crystal MoS2  

NASA Astrophysics Data System (ADS)

We report on the magnetic properties of MoS2 flakes measured from room temperature down to 10 K and magnetic fields up to 5 Tesla. Molybdenum disulfide (MoS2) is one of the most stable layered transition metal dichalcogenides, which has a finite band gap and is regarded as a complementary (quasi-) 2D material to graphene. We find that single crystals of MoS2 display ferromagnetism superimposed onto a large temperature-dependent diamagnetism and observe that ferromagnetism persists from 10 K up to room temperature. We attribute the existence of ferromagnetism partly to the presence of zigzag edges in the magnetic ground state at the grain boundaries. Since the magnetic measurements are relatively insensitive to the interlayer coupling, these results are expected to be also valid in the single layer limit.

Saeidi Varnoosfaderani, Sima; Tongay, Sefaattin; Appleton, Bill; Wu, Junqiao; Hebard, Arthur

2013-03-01

343

Axially dependent dielectric relaxation response of natural hydroxyapatite single crystals  

NASA Astrophysics Data System (ADS)

A thermally stimulated depolarization current (TSDC) study of single crystals of natural fluorine-rich hydroxyapatite, polarized with the electric field (Ep) applied parallel and perpendicular to the c axis, has revealed relaxation modes with axially dependent dielectric behavior. The (re)orientation of the OH- ions in the columns and the hydroxyls of the structural H2O molecules give rise to two prominent thermocurrent bands in the temperature range of approx200-340 K. Several weak current bands, below approx200 K, are related to the relaxation of impurity-Ca2+ vacancy (I-V) dipoles. The I-V mechanisms are particularly effective in the case where Epperpendicularc axis and are considered to take place via cation jumps on planes perpendicular to the 0001 crystal axis, at regions near "distorted" Ca(II) triangles (i.e., triangles which include impurity ions and Ca2+ vacancies). The band attributed to rotational relaxation of the OH- ions in the columns shows particular strength when Epperpendicularc axis, and an extensive distribution of relaxation times. The distribution is due to the multiplicity of physicochemical interactions between the OH- ions and their ionic and molecular neighbors (hydrogen bonds with adjacent F-, Cl-, and O2- ions, varying steric hindrances, etc.). The changes induced in the TSDC spectra after annealing processes at selected high temperatures are interpreted based on the gradual loss of structural H2O molecules located in oxygen or calcium vacancies and the resulting local changes in the crystal lattice.

Kalogeras, Ioannis M.; Vassilikou-Dova, Aglaia; Katerinopoulou, Anna

2002-07-01

344

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

345

Microstructural modeling of recrystallization in deformed iron single crystals  

NASA Astrophysics Data System (ADS)

Recrystallization kinetics in a (111)[1bar 10] iron single crystal deformed 70 pet by rolling were characterized experimentally at temperatures between 500°C and 600°C by means of quantitative metallography. A Laplace transform method was applied to the time-dependent global microstructural properties, volume fraction, interface area per unit volume, and the largest intercept-free length (recrystallized grain) to separate nucleation and interface migration effects from the overall recrystallization kinetics. A comprehensive nucleation and growth model was derived from analysis of the microstructural data. The model consisted of the following salient features: (a) nucleation was random and approximately site-saturated with zero incubation time at all temperatures; (b) the recrystallized grains grew three-dimensionally in the shape of prolate spheroids; and (c) interface migration rates were highly anisotropic, the grains growing at an approximately constant rate in one dimension and at a strongly decreasing rate in the other two dimensions. The present findings were compared to a similar earlier study of a deformed iron (111)[bar 1 bar 12] single crystal. The time dependencies of the interface migration rates were rationalized in terms of a deformation-induced, nonuniform distribution of stored energy and an orientation-dependent grain boundary mobility.

Vandermeer, R. A.; Rath, B. B.

1989-10-01

346

Single crystal diamond detectors grown by chemical vapor deposition  

NASA Astrophysics Data System (ADS)

The detection properties of heteropitaxial (polycrystalline, pCVD) and homoepitaxial (single crystal, scCVD) diamond films grown by microwave chemical vapor deposition (CVD) in the Laboratories of Roma "Tor Vergata" University are reported. The pCVD diamond detectors were tested with ?-particles from different sources and 12C ions produced by 15 MV Tandem accelerator at Southern National Laboratories (LNS) in Catania (Italy). pCVDs were also used to monitor 14 MeV neutrons produced by the D-T plasma at Joint European Torus (JET), Culham, U.K. The limit of pCVDs is the poor energy resolution. To overcome this problem, we developed scCVD diamonds using the same reactor parameters that optimized pCVD diamonds. scCVD were grown on a low cost (1 0 0) HPHT single crystal substrate. A detector 110 ?m thick was tested under ?-particles and under 14 MeV neutron irradiation. The charge collection efficiency spectrum measured under irradiation with a triple ?-particle source shows three clearly resolved peaks, with an energy resolution of about 1.1%. The measured spectra under neutron irradiation show a well separated C(n,?0)9Be12 reaction peak with an energy spread of 0.5 MeV for 14.8 MeV neutrons and 0.3 MeV for 14.1 MeV neutrons, which are fully compatible with the energy spread of the incident neutron beams.

Tuvè, C.; Angelone, M.; Bellini, V.; Balducci, A.; Donato, M. G.; Faggio, G.; Marinelli, M.; Messina, G.; Milani, E.; Morgada, M. E.; Pillon, M.; Potenza, R.; Pucella, G.; Russo, G.; Santangelo, S.; Scoccia, M.; Sutera, C.; Tucciarone, A.; Verona-Rinati, G.

2007-01-01

347

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

348

Bithermal fatigue of a nickel-base superalloy single crystal  

NASA Technical Reports Server (NTRS)

The thermomechanical fatigue behavior of a nickel-base superalloy single crystal was investigated using a bithermal test technique. The bithermal fatigue test was used as a simple alternative to the more complex thermomechanical fatigue test. Both in-phase and out-of-phase bithermal tests were performed on (100)-oriented coated and bare Rene N4 single crystals. In out-of-plane bithermal tests, the tensile and compressive halves of the cycle were applied isothermally at 760 and 982 C, respectively, while for the in-phase bithermal tests the temperature-loading sequence was reversed. The bithermal fatigue lives of bare specimens were shorter than the isothermal fatigue lives at either temperature extreme when compared on an inelastic strain basis. Both in-phase and out-of-phase bithermal fatigue life curves converged in the large strain regime and diverged in the small strain regime, out-of-phase resulting in the shortest lives. The coating had no effect on life for specimens cycled in-phase; however, the coating was detrimental for isothermal fatigue at 760 C and for out-of-phase fatigue under large strains.

Verrilli, Michael J.

1988-01-01

349

The fatigue damage behavior of a single crystal superalloy  

NASA Technical Reports Server (NTRS)

The uniaxial fatigue behavior of a single crystal superalloy, PWA 1480, is described. Both monotonic tensile and constant amplitude fatigue tests were conducted at room temperature, in an effort to assess the applicability of polycrystalline-based fatigue life prediction methods to a single crystal superalloy. The observed constant amplitude behavior correlated best using a stress-based life criterion. Nearly all specimens failed at surface or slightly subsurface microporosity; this is thought to be responsible for the unusually large amount of scatter in the test results. An additional term is developed in the stress-life equation for the purpose of accounting for the effect of microporosity on fatigue life. The form chosen is a function of the effective area of the failure-producing microporosity projected on a plane perpendicular to the loading axis, as well as the applied stress. This additional term correlated the data to within factors of two on life. Although speculative, extrapolation of the microporosity relation to zero micropore area indicates that approximately an order of magnitude improvement in fatigue life should result.

Mcgaw, Michael A.

1988-01-01

350

Photoelectrical properties of TlGaSe2 single crystals  

NASA Astrophysics Data System (ADS)

The spectral distribution of photocurrent (PC) of TlGaSe2 single crystals in the range of wavelengths between 500 nm and 700 nm possesses a single maximum at 2.04 eV corresponds to the direct energy band gap of this crystal. The PC is enhanced dramatically by pre-illuminations at low temperatures with band gap light. The temperature dependence of PC of the sample investigated in the temperature range from 80 K to 300 K at constant heating rate shows that the overlapping peaks in the PC spectrum are direct reflection of the Thermally Stimulated Current (TSC) associated with the several trapping levels. The PC response is strongly dependent on the degree of occupancy of traps. The wavelength at the maximum of the PC spectrum is found to be dependent on the wavelength scan direction being up or down. The ferroelectric phase transitions of TlGaSe2 are detected at ˜108 K and ˜118 K in the PC spectrum.

Ozdemir, Selahattin; Bucurgat, Mahmut

2014-07-01

351

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

352

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

353

Anisotropy of magnetic susceptibility in natural olivine single crystals  

NASA Astrophysics Data System (ADS)

flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine's crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3-5 wt % FeO, and along b in samples with 6-10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k', is on the order of 8*10-10 m3/kg for the samples with <1wt % FeO, and ranges from 3.1*10-9 m3/kg to 5.7*10-9 m3/kg for samples with 3-10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p'77 = 7.1 ± 0.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

Biedermann, Andrea R.; Pettke, Thomas; Reusser, Eric; Hirt, Ann M.

2014-07-01

354

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

E-print Network

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

Nabben, Reinhard

355

Growth of Large Single Crystals of Black Phosphorus under High Pressure  

Microsoft Academic Search

A large volume high pressure apparatus has made it possible to grow large single crystals of black phosphorus, P. After converting red P powder into black P under a high pressure of 10 kbar at high temperature, a melt of polycrystalline black P has been gradually solidified to bring about the growth of single crystals. Crystal sizes larger than 5×

Shoichi Endo; Yuichi Akahama; Shin-ichi Terada; Shin-ichiro Narita

1982-01-01

356

Eect of temperature on superdislocation dissociation in CuZnAl 18R single crystals  

E-print Network

Eect of temperature on superdislocation dissociation in Cu±Zn±Al 18R single crystals A. Cunibertia crystals deformed at temperature above room temper- ature is studied by transmission electron microscopy temperature, an eect commonly observed in several LRO intermetallic compounds. 18R single crystals also

Niewczas, Marek

357

250 W single-crystal fiber Yb:YAG laser Xavier Dlen,1,  

E-print Network

-crystal fiber oscillator pumped at 600 W with a fiber coupled laser diode at 940 nm. Furthermore, we discuss250 W single-crystal fiber Yb:YAG laser Xavier Délen,1, * Stefan Piehler,2 Julien Didierjean,3 demonstrate an Yb:YAG single-crystal fiber laser with 251 W output power in continuous-wave and an optical

Paris-Sud XI, Université de

358

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals  

E-print Network

symmetry is in general different from the microscopic symmetry of the crystal when it is not in a single crystal symmetry belongs to the rhombohedral 3m with dipoles formed in 111 family of the parent cubicEffective symmetry and physical properties of twinned perovskite ferroelectric single crystals Jirí

Cao, Wenwu

359

NMR studies of H 2 single crystals. VI. Line shapes in the orientationally ordered phase  

Microsoft Academic Search

We report the first experimental and theoretical study of the NMR lineshape anisotropy in the orientationally ordered cubic phase of H2 single crystals. After a brief review of the orientational phase diagram for ortho-para mixtures, we describe in detail the various cubic crystal structures that are obtained after a transformation from an initial single hcp crystal. We then calculate the

A. B. Harris; S. Washburn; H. Meyer

1983-01-01

360

Single-crystal II-VI on Si single-junction and tandem solar cells  

Microsoft Academic Search

CdTe is one of the leading materials used in solar photovoltaics. However, the maximum reported CdTe cell efficiencies are considerably lower than the theoretically expected efficiencies for the ~1.48 eV CdTe band gap. We report a class of single crystal CdTe-based solar cells grown epitaxially on crystalline Si that show promise for enhancing the efficiency and greatly lowering the cost

M. Carmody; S. Mallick; J. Margetis; R. Kodama; T. Biegala; D. Xu; P. Bechmann; J. W. Garland; S. Sivananthan

2010-01-01

361

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

362

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

363

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

364

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

365

Growth and characterization of organometallic l-alanine cadmium chloride single crystal by slow evaporation technique  

Microsoft Academic Search

Single crystals of l-alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UV–vis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation

K. C. Bright; T. H. Freeda

2010-01-01

366

Growth and characterization of organometallic L-alanine cadmium chloride single crystal by slow evaporation technique  

Microsoft Academic Search

Single crystals of L-alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UV-vis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation

K. C. Bright; T. H. Freeda

2010-01-01

367

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

368

Solidification microstructures in single-crystal stainless steel melt pools  

SciTech Connect

Development of microstructure of stationary melt pools of oriented stainless steel single crystals (70%Fe-15%Ni-15%Cr was analyzed. Stationary melt pools were formed by electron-beam and gas-tungsten-arc heating on (001), (011), and (111) oriented planes of the austenitic, fcc-alloy crystals. Characterization and analysis of resulting microstructure was carried out for each crystallographic plane and welding method. Results showed that crystallography which favors ``easy growth`` along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. These results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.

Sipf, J.B.; Boatner, L.A.; David, S.A.

1994-03-01

369

Scintillation properties of CsI:In single crystals  

NASA Astrophysics Data System (ADS)

Scintillation properties of CsI:In single crystals have been investigated. Scintillation yield of CsI:In measured with the 24 ?s integration time is around 27,000 ph/MeV, reaching the saturation at 0.005 mol% of the activator. However, luminescence yield of CsI:In is close to CsI:Tl scintillation crystals, which is around 60,000 ph/MeV. This difference is explained by the presence of an ultra-long afterglow in CsI:In scintillation pulse. Thermoluminescence studies revealed a stable trap around 240 K that is supposed to be related to millisecond decay components. The best measured energy resolution of (8.5±0.3)% was achieved at 24 ?s peaking time for a CsI sample doped with 0.01 mol% of In. Temperature stability of CsI:In radioluminescence intensity was found to be remarkably high. Its X-ray luminescence yield remains stable up to 600 K, whereafter thermal quenching occurs. The latter property gives CsI:In a potential to be used in well logging applications.

Gridin, S.; Belsky, A.; Moszynski, M.; Syntfeld-Kazuch, A.; Shiran, N.; Gektin, A.

2014-10-01

370

Textures in Single-Crystal Aluminum Friction Stir Spot Welds  

NASA Astrophysics Data System (ADS)

The present article examines the textural features produced during friction stir spot welding of single-crystal aluminum sheet. The crystal has the {111} plane perpendicular to the normal direction (ND) of the sheet, and the left< { 1 10} rightrangle direction parallel to the growth direction (GD). Friction stir spot welding was carried out using a rotation speed of 1500 rpm and a dwell time of 2 seconds, and completed spot welds were characterized using a combination of optical microscopy and electron backscatter diffraction (EBSD). The EBSD measurements indicate there are no significant changes in orientation in locations more than 840 ?m from the stir-zone extremity. The orientation distribution in the thermomechanically-affected zone (TMAZ) region conformed with the {110}?ND orientation within 580 ?m of the stir-zone extremity. In the location immediately adjacent to the stir-zone extremity, there was a deviation from the {110}//ND orientation due to a combination of compressive loading perpendicular to the stir-zone boundary and shear loading in the direction of tool rotation. It is suggested a {111}?ND texture in the stir zone is associated with material flow imposed by the thread on the rotating pin.

Shibayanagi, Toshiya; Gerlich, Adrian P.; Kashihara, Keizo; North, Thomas H.

2009-04-01

371

Redetermination of olivenite from an untwinned single-crystal.  

PubMed

The crystal structure of olivenite, ideally Cu(2)(AsO(4))(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu(2)(As(0.92)P(0.08)O(4)), from Majuba Hill (Nevada, USA). Olivenite is structurally analogous with the important rock-forming mineral andalusite, Al(2)OSiO(4). Its structure consists of chains of edge-sharing, distorted [CuO(4)(OH)(2)] octa-hedra extending parallel to [001]. These chains are cross-linked by isolated AsO(4) tetra-hedra through corner-sharing, forming channels in which dimers of edge-sharing [CuO(4)(OH)] trigonal bipyramids are located. The structure is stabilized by medium to weak O-H?O hydrogen bonds. In contrast to the previous refinements from powder and single crystal X-ray data, all non-H atoms were refined with anisotropic displacement parameters and the H atom was located. PMID:21201567

Li, Chen; Yang, Hexiong; Downs, Robert T

2008-01-01

372

Elastic stability of high coupling ternary single crystals  

NASA Astrophysics Data System (ADS)

A sub-hertz harmonic force was used to investigate the elastic response of ternary (1-y-x)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3 (PIN-PMN-PT) single crystal with compositions (x = 0.30 and x = 0.33) near the Morphotropic Phase Boundary (MPB) under isothermal and zero-field conditions. The observed instability under mechanical compression is attributable to a ferroelectric rhombohedral FR-ferroelectric orthorhombic FO phase transformation. The associated strain is a function of proximity to MPB and is consistent with the prediction of the classical Devonshire theory. Isothermal resonance-antiresonance frequency sweeps versus temperature revealed a non-vertical MPB with (?TRT/?x)<0, where TRT is the rhombohedral-tetragonal transition temperature. These results provide insights into the role of PT content on the stability of PIN-PMN-PT crystals used for electromechanical devices and sound projectors.

Finkel, Peter; Murphy, Colin J.; Stace, Joseph; Bussmann, Konrad; Heitmann, Adam; Amin, Ahmed

2013-05-01

373

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

374

Electronic properties of ?-FeSi2 -- single crystal study  

NASA Astrophysics Data System (ADS)

The discovery of high temperature superconductivity (HTS) in Fe pnictides has simulated a lot of work in field of Fe-based materials. We focus on the tetragonal (high-temperature) form of the iron disilicide, which crystal structure resembles one of the HTS, LiFeAs (Tsc=18 K). Single crystals of ?-FeSi2 with Fe0.83Si2 composition were grown and magnetic, transport and heat capacity studies were performed in consistent way. Magnetic susceptibility of ?-FeSi2 increases in a linear fashion with increasing temperature, as was commonly observed among Fe HTS. In a contrast to superconducting pnictides, where ?(T) ˜ T is associated to antiferromagnetic fluctuations, in ?-FeSi2 this behavior is rather related to the electronic structure of this metal. In Fe-based HTS proximity of the SDW instability seems to be crucial for the emergence of superconducting state -- in ?-FeSi2 the experimental data do not find evidence for any strong electronic correlations. Our LDA and DMFT calculations results find low density of states, supporting weakness of correlations and suggest electronic configuration of Fe close to d^6.

Miiller, Wojciech; Tomczak, Jan; Simonson, Jack; Smith, Greg; Aronson, Meigan

2013-03-01

375

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

376

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

377

Crystal growth and spectroscopic properties of Er3+ ions doped CdF2 single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of Er3+:CdF2 with good optical quality were grown by a Bridgman technique after purification of the starting materials. Absorption and emission spectra are recorded at room temperature. The Judd-Ofelt (JO) analysis was applied to obtain the three phenomenological intensity parameters and the transition strengths. These JO parameters are used to calculate the radiative transition probabilities, the radiation lifetimes and the branching ratios. The results obtained are in good agreement with those of other fluoride laser materials. We also carried out luminescence measurements for red and green emission. The studied host may offer infrared and visible laser emissions.

Djellab, S.; Diaf, M.; Labbaci, K.; Guerbous, L.

2014-04-01

378

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

379

InPBi Single Crystals Grown by Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III-V compound family member for heterostructures. The Bi concentration is found to be 2.4 +/- 0.4% with 94 +/- 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4-2.7 ?m which can't be explained by the existing theory.

Wang, K.; Gu, Y.; Zhou, H. F.; Zhang, L. Y.; Kang, C. Z.; Wu, M. J.; Pan, W. W.; Lu, P. F.; Gong, Q.; Wang, S. M.

2014-06-01

380

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

381

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

382

InPBi Single Crystals Grown by Molecular Beam Epitaxy  

PubMed Central

InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III–V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23?eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4–2.7??m which can't be explained by the existing theory. PMID:24965260

Wang, K.; Gu, Y.; Zhou, H. F.; Zhang, L. Y.; Kang, C. Z.; Wu, M. J.; Pan, W. W.; Lu, P. F.; Gong, Q.; Wang, S. M.

2014-01-01

383

Ultrathin aluminum sample cans for single crystal inelastic neutron scattering  

SciTech Connect

Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to ones measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

Stone, Matthew B [ORNL; Loguillo, Mark [ORNL; Abernathy, Douglas L [ORNL

2011-01-01

384

Radionuclide annular single crystal scintillator camera with rotating collimator  

SciTech Connect

A radionuclide emission tomography camera is described for sensing gamma ray emissions from a source within the field of view consisting of: a fixed, position-sensitive detector means, responsive to the gamma ray emissions and surrounding the field of view for detecting the contact position and the trajectory from which a gamma ray emission originates, the fixed, position-sensitive detector including a single continuous stationary scintillation crystal; rotatable collimator means, disposed between the fixed, position-sensitive detecto means and the field of view, and including at least one array of collimator elements, for restricting and collimating the gamma ray emissions; and means for rotating the collimator means relative to the fixed, position-sensitive detector, for exposing different sections of the position-sensitive detector to the gamma ray emissions in order to view the source from different angles.

Genna, S.; Pang, S.-C.

1986-04-22

385

Ferroelectricity in single crystal InMnO3  

NASA Astrophysics Data System (ADS)

Single crystal synthesis, structure, electric polarization, and heat capacity measurements on hexagonal InMnO3 show that this small R ion in the RMnO3 series is ferroelectric (space group P63cm). Structural analysis of this system reveals a high degree of order within the MnO5 polyhedra but significant distortions in the R-O bond distributions compared to the previously studied materials. Point-charge estimates of the electric polarization yield an electrical polarization of ˜7.8 ?C/cm2, 26% larger than the well-studied YMnO3 system. This system with enhanced room temperature polarization values may serve as a possible replacement for YMnO3 in device applications.

Yu, T.; Gao, P.; Wu, T.; Tyson, T. A.; Lalancette, R.

2013-04-01

386

Electrical conduction in nanodomains in congruent lithium tantalate single crystal  

NASA Astrophysics Data System (ADS)

The electrical current flow behavior was investigated for nanodomains formed in a thin congruent lithium tantalate (LiTaO3) single-crystal plate. When the nanodomains were relatively large, with diameters of about 100 nm, current flow was detected along the domain wall. However, when they were about 40 nm or smaller, the current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. Unlike the case of LiNbO3, optical illumination was not required for current conduction in LiTaO3. A clear temperature dependence of the current was found indicating that the conduction mechanism for nanodomains in LiTaO3 may involve thermally activated carrier hopping.

Cho, Yasuo

2014-01-01

387

Protective CVD Mullite Coatings on Single-Crystal Silicon Substrates  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

388

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

389

Growth and characterization of L-serine formate nonlinear optical single crystal  

NASA Astrophysics Data System (ADS)

A novel organic nonlinear optical single crystal L-Serine Formate (LSF) was successfully grown by solution growth using the slow evaporation technique. The structure of the grown crystal has been determined by single crystal X-ray diffraction analysis. The presence of functional groups in LSF crystal has been identified by FTIR spectrum. The crystal is transparent over entire visible region. The second harmonic generation efficiency of the grown LSF crystal has been obtained by the Kurtz-Perry powder technique. The laser induced surface damage threshold value 6.836 GW/cm2 indicates that this material can be used for high-power laser applications.

Krishnan, P.; Gayathri, K.; Anbalagan, G.

2013-02-01

390

Electrical Conductivity of Hydrous Single Crystal San Carlos Olivine  

NASA Astrophysics Data System (ADS)

The electrical conductivity of anhydrous San Carlos olivine is too low to explain the observed electrical conductivity of Earth's upper mantle. Although the solubility of hydrogen in olivine is relatively low at mantle P and T conditions, it has been estimated that even at concentrations of less than 1000 ppm, electrical conductivity is enhanced by as much as a factor of one hundred, based on a conduction mechanism involving hydrogen diffusion (Karato, Nature 347, 272-273, 1990). In this study we have measured the electrical conductivity of hydrated San Carlos olivine single crystals, oriented along (100), (010) and (001). SCO single crystals were first oriented, machined into 2 mm diameter cylinders, and then sandwiched between layers of a talc+brucite mix in sealed Pt capsules for hydration runs at pressures up to 8 GPa and 1200°C in a multianvil apparatus. Recovered samples were then cut into wafers ranging from 0.2 to 0.6 mm in thickness for subsequent complex impedance measurements to determine electrical conductivity, also carried out at high pressure. For the electrical measurements, temperatures were limited to about 700°C in order to minimize loss of water from the sample. FTIR spectroscopy was used to determine water content of samples both before and after the electrical measurements. Preliminary results indicate that at concentrations of a few hundred ppm water, conductivities are several orders of magnitude higher than for dry olivine. Activation energies decrease with increasing water content, indicating that extrapolation of conductivities to higher temperatures leads to a smaller overall effect. However, based on these results, at upper mantle conditions, the presence of minor amounts of hydrogen in olivine is sufficient to bridge the gap between the conductivity of dry olivine and that of the mantle.

Poe, B.; Romano, C.; Nestola, F.; Rubie, D.

2005-12-01

391

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

392

Method for the preparation of inorganic single crystal and polycrystalline electronic materials  

NASA Technical Reports Server (NTRS)

Large area, semiconductor crystals selected from group 3-5 compounds and alloys are provided for semiconductor device fabrication by the use of a selective etching operation which completely removes the substrate on which the desired crystal was deposited. The substrate, selected from the same group as the single crystal, has a higher solution rate than the epitaxial single crystal which is essentially unaffected by the etching solution. The preparation of gallium phosphide single crystals using a gallium arsenide substrate and a concentrated nitric acid etching solution is described.

Groves, W. O. (inventor)

1969-01-01

393

Melting of polymer single crystals studied by dynamic Monte Carlo simulations  

Microsoft Academic Search

We report dynamic Monte Carlo simulations of lattice polymers melting from a metastable chain-folded lamellar single crystal.\\u000a The single crystal was raised and then melted in an ultrathin film of polymers wetting on a solid substrate, mimicking the\\u000a melting observations made by using Atomic Force Microscopy. We observed that the thickness distribution of the single crystal\\u000a appears quite inhomogeneous and

Y. Ren; A. Ma; J. Li; X. Jiang; Y. Ma; A. Toda; W. Hu

2010-01-01

394

Dielectric response of PMN–0.32PT single crystal and ceramics under dc electric field  

Microsoft Academic Search

The temperature dependences of dielectric properties for [001] PMN–0.32PT single crystal and PMN–0.32PT ceramics under different dc electric field (E) have been investigated. A new monoclinic phase can be induced by electric field with E=1.5–4.0kV\\/cm, while heating, in [001] PMN–0.32PT single crystal. The phase transition process of single crystal is from rhombohedral to monoclinic, then from monoclinic to tetragonal, finally

Zhenrong Li; Zhuo Xu; Zengzhe Xi; Xi Yao

2004-01-01

395

Single-crystal organic field effect transistors with the hole mobility ?8cm2\\/V s  

Microsoft Academic Search

We report on the fabrication and characterization of single-crystal organic p-type field-effect transistors (OFETs) with the field-effect mobility ??8cm2\\/V s, substantially higher than that observed in thin-film OFETs. The single-crystal devices compare favorably with thin-film OFETs not only in this respect: the mobility for the single-crystal devices is nearly independent of the gate voltage and the field effect onset is

V. Podzorov; S. E. Sysoev; E. Loginova; V. M. Pudalov; M. E. Gershenson

2003-01-01

396

High-Temperature Thermoelectric Properties of NaxCoO2-delta Single Crystals  

Microsoft Academic Search

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

Kenjiro Fujita; Tadashi Mochida; Kazuo Nakamura

2001-01-01

397

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

SciTech Connect

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

Itoh, K.

1992-10-01

398

Growth behavior of L-pyrrolidone-2-carboxylic acid (L-PCA) single crystals  

NASA Astrophysics Data System (ADS)

Growth conditions to prepare large single crystals of L-pyrrolidone-2-carboxylic acid (L-PCA), a novel nonlinear optical organic material, have been intensively studied with an attempt for fabrication in optical devices. L-PCA single crystals of good optical quality having dimensions of typically ~ 2.5 × 1.5 ×1.5 cm 3 were grown from aqueous solutions with seed crystals by a slow cooling method. They are chemically stable because molecules are hydrogen bonded to form three-dimensional networks in the crystal state. Further growth conditions to obtain large single crystals in a shorter time have been investigated by considering both mass balance equations and the kinetics for crystal growth. It was found that increasing the cooling rate in the later periods of crystal growth is advantageous for the purpose. The largest crystal was 17.5 g in weight, which was prepared in 6 days.

Kitazawa, Manabu; Takahashi, Mitsuo; Matsuoka, Masakuni

1994-08-01

399

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

SciTech Connect

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

Itoh, K.

1992-10-01

400

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

NSDL National Science Digital Library

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

Maier, Mitchell

2010-08-15

401

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

402

Piezoelectric properties of domain engineered barium titanate single crystals with different volume fractions of domain walls  

PubMed Central

A piezoelectric domain wall model has been developed to analyze the effective piezoelectric properties of domain engineered BaTiO3 (BT) single crystals with different volume fractions of 90° domain walls. The model takes into account the nonuniform deformation in the domain wall region, which can create additional anisotropy to enhanced functional properties of multidomain single crystals. Our theoretical results indicate that a larger volume fraction of domain walls will produce larger effective piezoelectric coefficients. In addition, with the increase in domain wall volume fraction, [011]c poled BT single crystals will have a much larger piezoelectric property enhancement than [111]c poled BT single crystals. PMID:19865498

Xiang, Yang; Zhang, Rui; Cao, Wenwu

2009-01-01

403

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

404

Investigation on crystalline perfection, mechanical, piezoelectric and ferroelectric properties of L-tartaric acid single crystal  

NASA Astrophysics Data System (ADS)

Polar organic nonlinear optical material, L-tartaric acid single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallized in monoclinic system with space group P21. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal quality is good and free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. Piezoelectric d33 co-efficient for the crystal has been examined and its value is 47 pC/N. The ferroelectric behaviour of the crystal was analyzed by polarization-electric field hysteresis loop measurement.

Murugan, G. Senthil; Ramasamy, P.

2014-04-01

405

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

406

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

SciTech Connect

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

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

2010-09-15

407

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

408

Single-crystal elasticity of hydrous wadsleyite by Brillouin scattering  

NASA Astrophysics Data System (ADS)

Wadsleyite (?-Mg2SiO4) is the high-pressure polymorph of olivine that is expected to be a dominant mineral in the transition zone from 410 km to 520 km depth in the mantle. The elasticity of wadsleyite is crucial to constrain the mineralogy of the transition zone. Previous studies show wadsleyite can incorporate variable amounts of water up to 3.3 wt% of water (Kohlstedt et al. 1996; Inoue et al. 1995; Smyth et al. 1987, 1994). The effect of water on the bulk modulus of wadsleyite was studied by x-ray diffraction (Yusa and Inoue, 1997; Smyth et al. 2005) but no constraints on the shear modulus exist. We have measured the single-crystal elastic constants of hydrous wadsleyite with varying water content using Brillouin spectroscopy at ambient conditions. We carried out measurements for samples containing 0.3 wt%, 0.6 wt% and 1.6 wt% water using at least 2 crystal planes for each sample. By computing the aggregate elastic properties, we find that the bulk (K0S) and shear modulus (G0) of hydrous wadsleyite decrease linearly with water content according to the following relations: K0S=169.0-11.8X_W; G0=115.1-12.5X_W; where X_W is the water H2O weight percent. Compared with anhydrous wadsleyite, 1 wt% of water will lead to 7.0% decrease in bulk modulus, 10.9% decrease in shear modulus. Water has a greater effect on the elastic moduli of wadsleyite than that of olivine or ringwoodite. The olivine to wadsleyite phase transition is believed to be the origin of the seismic discontinuity near 410 km. Using these new results, the possible effect of water content on the velocity contrast across the 410-km discontinuity will be examined.

Mao, Z.; Jiang, F.; Jacobsen, S. D.; Smyth, J. R.; Holl, C.; Duffy, T. S.; Frost, D. J.

2006-12-01

409

Fabrication of Single Crystal MgO Capsules  

NASA Technical Reports Server (NTRS)

A method has been developed for machining MgO crystal blocks into forms for containing metallic and silicate liquids at temperatures up to 2,400 C, and pressures up to at least 320 kilobars. Possible custom shapes include tubes, rods, insulators, capsules, and guides. Key differences in this innovative method include drilling along the crystallographic zone axes, use of a vibration minimizing material to secure the workpiece, and constant flushing of material swarf with a cooling medium/lubricant (water). A single crystal MgO block is cut into a section .5 mm thick, 1 cm on a side, using a low-speed saw with a 0.004 blade. The cut is made parallel to the direction of cleavage. The block may be cut to any thickness to achieve the desired length of the piece. To minimize drilling vibrations, the MgO block is mounted on a piece of adhesive putty in a vise. The putty wad cradles the bottom half of the entire block. Diamond coring tools are used to drill the MgO to the desired custom shape, with water used to wet and wash the surface of swarf. Compressed air may also be used to remove swarf during breaks in drilling. The MgO workpiece must be kept cool at all times with water. After all the swarf is rinsed off, the piece is left to dry overnight. If the workpiece is still attached to the base of the MgO block after drilling, it may be cut off by using a diamond cutoff wheel on a rotary hand tool or by using a low-speed saw.

Danielson, Lisa

2012-01-01

410

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

PubMed

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

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

2014-02-11

411

2D superconductivity in single crystals of LSCO  

E-print Network

at relatively high magnetic field, up to 9 Tesla. This could alter the ground state of the system. � We believe laboratory since 2007. Crystal growth technique we use: #12;Crystal growth "technology" 1. Synthesis

Keren, Amit

412

Structure and surface morphology of MnF2 epitaxial layers grown on grooved and ridged CaF2 (1 1 0) surface  

NASA Astrophysics Data System (ADS)

Structural and surface morphology studies of MnF2 epitaxial layers have been performed by x-ray diffraction and atomic force microscopy (AFM). MnF2 layers of different thicknesses (0.12-1.25 µm) were grown by MBE on Si(0 0 1) substrates with the deposited CaF2-buffer layer having a lang1 1 0rang orientation and a grooved and ridged surface. X-ray diffraction patterns in the 10°-60° angular range have been measured. Profiles of diffraction peaks in two directions—parallel and normal to the diffraction vector—as well as the intensity distribution around 2 2 0 reciprocal lattice points were obtained. It was found that the metastable orthorhombic phase of ?-PbO2 type with [1 1 0] growth direction dominates in the films; a much smaller portion of the stable rutile type phase was also detected, though it increases with the film thickness. As follows from the x-ray diffraction data, the films have a mosaic block structure. Parameters of the crystallites were determined using the Williamson-Hall analysis of angular width of the diffraction peaks. It was obtained that the crystallites of the orthorhombic phase have an elongated shape oriented along the direction of the CaF2 ridges. The AFM study confirms a regular distribution of the orthorhombic crystallites and shows the appearance of some irregular shaped crystallites on the top of the thick MnF2 films.

Kyutt, R. N.; Banshchikov, A. G.; Kaveev, A. K.; Sokolov, N. S.; Lomov, A. A.; Ohtake, Y.; Tabuchi, M.; Takeda, Y.

2007-08-01

413

Hydrothermal growth of single crystals of the quantum magnets: Clinoatacamite, paratacamite, and herbertsmithite  

E-print Network

Hydrothermal growth of single crystals of the quantum magnets: Clinoatacamite, paratacamite In this report, we describe crystal growth technology and characterizations of clinoata- camite, paratacamite for growing millimeter-sized crystals of the quantum magnets with formula Cu4-xZnx OH 6Cl2: clinoatacamite x=0

Müller, Peter

414

Observation of defects in single crystal diamond with high resolution x-ray topography  

Microsoft Academic Search

Single crystal diamond is an important optical component at synchrotron facilities, and is one of the best candidates for the optics for the next generation X-ray light source. The imperfections and surface conditions of the synthetic diamond crystals affect their applications. It has been shown that surface etching can improve the FWHM of type IB synthetic diamond crystals having (100)

Yuncheng Zhong

2005-01-01

415

Domain-impurities interaction in KNbO3 single crystals  

Microsoft Academic Search

Impurity segregations and their interactions with domains and dislocations in KNbO3 single crystals have been studied. In the technique used, impurity structures in the bulk are first brought to the surface by removing layers of crystal without stress by methyl alcohol. The domain structure in the crystal remains completely undisturbed in this process. The dislocation pattern is then revealed by

M. B. Mishra; S. G. Ingle

1974-01-01

416

SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION  

SciTech Connect

Accurate measurement of temperature is essential for the safe and efficient operation and control of a wide range of industrial processes. Appropriate techniques and instrumentation are needed depending on the temperature measurement requirements in different industrial processes and working environments. Harsh environments are common in many industrial applications. These harsh environments may involve extreme physical conditions, such as high-temperature, high-pressure, corrosive agents, toxicity, strong electromagnetic interference, and high-energy radiation exposure. Due to these severe environmental conditions, conventional temperature sensors are often difficult to apply. This situation has opened a new but challenging opportunity for the sensor society to provide robust, high-performance, and cost-effective temperature sensors capable of operating in those harsh environments. The focus of this research program has been to develop a temperature measurement system for temperature measurements in the primary and secondary stages of slagging gasifiers. For this application the temperature measurement system must be able to withstand the extremely harsh environment posed by the high temperatures and corrosive agents present in these systems. Real-time, accurate and reliable monitoring of temperature for the coal gasification process is important to realize the full economic potential of these gasification systems. Long life and stability of operation in the high temperature environment is essential for the temperature measurement system to ensure the continuous running of the coal gasification system over the long term. In this high temperature and chemically corrosive environment, rather limited high temperature measurement techniques such as high temperature thermocouples and optical/acoustic pyrometers are available, each with their own limitations. In this research program, five different temperature sensing schemes based on the single crystal sapphire material were thoroughly investigated to determine an optimal approach for on-line, real-time, reliable, long-term monitoring of temperatures inside the coal gasification environment. Among these were a sapphire fiber extrinsic Fabry-Perot interferometric (EFPI) sensor; an intensity-measurement based polarimetric sapphire sensor and a broadband polarimetric differential interferometric (BPDI) sapphire sensor. Based on the current evaluation and analysis of the experimental results, the broadband polarimetric differential interferometric (BPDI) sensor system was chosen for further prototype instrumentation development because of it's superior performance compared to the other systems. This approach is based on the self-calibrating measurement of the optical path length differences in a single-crystal sapphire disk, which is a function of both the temperature dependent birefringence and the temperature dependent dimensional changes.

A. Wang; G. Pickrell; R. May

2002-09-10

417

Water dissolved in olivine: A single-crystal infrared study  

NASA Astrophysics Data System (ADS)

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 groups is composed of three equidistant bands at 3614, 3591, 3567 m-1 and at 3576, 3530, 3485 cm-1 (80 K values). These distinct multiplets are assigned to the OH--compensated octahedral and tetrahedral vacancy defects [OH·V?oct]' and [OH·V'tetr]*, respectively. It is suggested that the reduced effective charge of the tetrahedral, i.e., Si-type, vacancy is due to Si entering a nearby nonideal site for partial charge compensation. The multiplet splitting, 23 and 45 cm-1, is due to the isomorphous substitution of Mg and Fe on the adjacent M1 and M2 positions to which the proton-bearing oxygen is bound. This leads to the combinations (Mg Mg Si), (Mg Fe Si), (Fe Fe Si) and (Mg Mg Mg), (Mg Mg Fe), (Mg Fe Fe) at the octahedral M2 and at the tetrahedral vacancy sites, respectively. An IR signal which would correspond to the fully OH--compensated divalent cation vacancy defect [OH·V?octHO·]* appears to be absent. Instead a weak absorption band is observed in the range of the H-H stretching frequency of molecular H2. By analogy to molecular H2 in MgO and CaO single crystals and in fused silica it is concluded that OH- pairs, associated with this type of defects, undergo a charge transfer conversion into (H2 + O22-). The H2 are loosely bound to the peroxy entities which probably form peroxy bridges between SiO4 tetrahedra, e.g., Si-O-O-Si. Outgassing of H2 would leave excess oxygen behind, shifting the stoichiometry of the olivine in a direction which has never been discussed before.

Freund, Friedemann; Oberheuser, Gert

1986-01-01

418

Growth of single crystals of mercuric iodide on the ground and in space  

SciTech Connect

A short review is given of the methods by which mercuric iodide is prepared and purified to obtain material suitable for the growth of single crystals. Method used in our laboratory to grow single crystals up to 1,000 grams in weight from the vapor is discussed. Effects of gravity on the growth process are described. A crystal growth system suitable for operation in the reduced gravity environment of space has been designed and crystal growth experiments have been performed during the flights of Spacelab 3 (April 1985) and the International Microgravity Laboratory (January 1992). Structural quality and electronic properties of ground-based and space-grown crystals are compared.

van den Berg, L.

1993-06-01

419

Calculation of thermoelastic stresses near the crystallization front for melt-grown single-crystal rods with a circular cross section  

NASA Astrophysics Data System (ADS)

Approximate expressions for the thermoelectric stress tensor components in an isotropic crystal rod of a circular cross section, applicable in the entire crystal including the region near the crystallization front, are obtained. Using the resultant approximate formulas, the stress fields in leucosapphire single crystals are calculated for model temperature fields. It is shown that exactly near the crystallization front, thermoelastic stresses reach maximal values.

Bakholdin, S. I.; Galaktionov, E. V.; Tropp, E. A.

2014-08-01

420

ESTIMATING THE STRENGTH OF SINGLE-ENDED DISLOCATION SOURCES IN MICROMETER-SIZED SINGLE CRYSTALS  

SciTech Connect

A recent study indicated that the behavior of single-ended dislocation sources contributes to the flow strength of micrometer-scale crystals. In this study 3D discrete dislocation dynamics simulations of micrometer-sized volumes are used to calculate the effects of anisotropy of dislocation line tension (increasing Poisson's ratio, {nu}) on the strength of single-ended dislocation sources and, to compare them with the strength of double-ended sources of equal length. This is done by directly modeling their plastic response within a 1 micron cubed FCC Ni single crystal using DDS. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with Poisson ratio ({nu}), exhibiting an increase of about 50% at u = 0.38 (value for Ni) as compared to the value at {nu} = 0. Independent of dislocation line direction, for {nu} greater than 0.20, the strengths of single-ended sources depend upon the sense of the stress applied. The value for {alpha}, in the expression for strength, {tau} = {alpha}(L){micro}b/L is shown to vary from 0.4 to 0.84 depending upon the character of the dislocation and the direction of operation of the source at {nu} corresponding to that of Ni, 0.38 and a length of 933b. By varying the lengths of the sources from 933b to 233b, it was shown that the scaling of the strength of single-ended and double-ended sources with their length both follow a ln(L/b)/(L/b) dependence. Surface image stresses are shown to have little effect on the critical stress of single-ended sources at a length of {approx}250b or greater. The relationship between these findings and a recent statistical model for the hardening of small volumes is also discussed.

Rao, S I; Dimiduk, D M; Tang, M; Parthasarathy, T A; Uchic, M D; Woodward, C

2007-05-03

421

Understanding Molecular Epitaxial Mechanism of the ?-form Crystal and Chain Tilt in the ?-form Single Crystal of Isotactic Polypropylene  

NASA Astrophysics Data System (ADS)

We attempt to investigate how the epitaxial domination of the crystal morphologies takes place in the ?-form of the chain-folded crystals using high molecular weight isotactic polypropylene (i-PP) samples with a controlled number of stereodefects. Two different morphologies were identified via transmission electron and atomic force microscopies (TEM and AFM). One is needle-like and the other is ``flat''. Based on the tilted selected area electron diffraction (SAED) results from TEM, the microscopic formation mechanism of the ``needle'' and ``flat'' morphology was discussed and it revealed that in the ``flat'' ?-form crystal, the initial ?-form single crystal had to have a stem orientation tilted away from the thin film normal within the ac-plane around the b-axis. Elongated ?2-form lath-like single crystals were grown from thin film melt at Tx = 145 ^oC -155 ^oC using commercial sample. SAED experimental results show that the stems in these lath-like single crystals were tilted at an unusual 17^o angle around the b-axis. This 17^o-stem tilt in the ?2-form single crystals favors the (102) fold surface and appears to depend upon both conformational and chain folding constraints.

Cao, Yan; van Horn, Ryan; Zhang, Guoliang; Sun, Hao-Jan; Jeong, Kwang-Un; Auriemma, Finizia; de Rosa, Claudio; Lotz, Bernard; Cheng, Stephen

2012-02-01

422

Organic Single-Crystal Light-Emitting Transistor Coupling with Optical Feedback Resonators  

PubMed Central

Organic light-emitting transistors (OLETs) are of great research interest because they combine the advantage of the active channel of a transistor that can control the luminescence of an in-situ light-emitting diode in the same device. Here we report a novel single-crystal OLET (SCLET) that is coupled with single crystal optical feedback resonators. The combination of single-crystal waveguides with native Fabry-Perot cavities, formed by parallel crystal edges, drastically lowers the threshold energy for spectral narrowing and non-linear intensity enhancement. We apply this structure to SCLETs and demonstrate the first fabrication of a SCLET with the optical feedback resonators. PMID:23248748

Bisri, Satria Zulkarnaen; Sawabe, Kosuke; Imakawa, Masaki; Maruyama, Kenichi; Yamao, Takeshi; Hotta, Shu; Iwasa, Yoshihiro; Takenobu, Taishi

2012-01-01

423

Preparation and Raman Spectrum of Rutile Single Crystals Using Floating Zone Method  

NASA Astrophysics Data System (ADS)

With anatase-type titanium dioxide as the raw materials, the rutile type titanium dioxide single crystal is prepared using the floating zone method. The results of XRD measurement show that the grown crystal is highly crystalline with a rutile structure, which has orientation to the c-axis. The four Raman vibration characteristic peaks (143, 240, 450 and 610 cm-1) at room temperature show that the crystalline structure of the single crystal is a typical rutile phase, meanwhile a new Raman peak at around 690 cm-1 is found. The results of the Raman measurement at various temperatures for the single crystal show that the Raman frequency shifts are different.

Guo, Xing-Yuan; Xu, Da-Peng; Ding, Zhan-Hui; Su, Wen-Hui

2006-06-01

424

Growth rate dispersion of single potassium alum crystals  

NASA Astrophysics Data System (ADS)

The dispersion of growth rates is a lively discussed matter. However, still no acceptable explanation exists for the reason of the phenomenon describing that crystals of the same size growing under the same constant environmental conditions (as supersaturation, temperature and hydrodynamics) might grow with different rates. The individual face-specific growth rates of potassium aluminium alum crystals (diameter 1-3 mm) have been directly determined at different supersaturations ( ? = 0.5-5%). It was found that the order of growth rates of the appearing faces of unhurt and hurt crystals is {111} < {100{ < {110{. Further experiments have shown that face-specific growth rates of unhurt crystals (out of evaporation crystallization) are lower than those of hurt crystals (out of batch crystallization experiments).

Lacmann, Rolf; Tanneberger, Ulrike

1995-01-01

425

Growth of large-diameter ZnTe single crystals by the vertical gradient freezing method  

NASA Astrophysics Data System (ADS)

ZnTe singles crystals (80 mm diameter) were grown by the VGF method without seed crystals. In this method, the high-pressure furnace was used and the melt was encapsulated by B 2O 3 during crystal growth. EPDs of the grown crystals were 5000-10 000 cm -2. The FWHMs of the rocking curve measured by 4-crystal X-ray diffractometry were around 20 arcsec. The crystals grown by the VGF method were of high quality compared with those by other growth methods.

Asahi, T.; Arakawa, A.; Sato, K.

2001-07-01

426

The deformation of AgMg single crystals at high temperatures  

Microsoft Academic Search

Pronounced yield points have been observed in AgMg single crystals which deformed in compression at temperatures above 450 K. The mechanism of the deformation of single crystals of the compound in the presence of the yield point is discussed in terms of atmosphere-dragging-controlled glide.

M. Yamaguchi; Y. Umakoshi

1979-01-01

427

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

E-print Network

P-137 / P. Xu P-137: Photoaligned Transflective Liquid Crystal Display with Single Cell Gap using Transflective liquid crystal display (LCD) with single cell gap consisting optically compensated bend (OCB Chigrinov, and Hoi Sing Kwok Center for Display Research, Department of Electronic and Computer Engineering

428

Mapping of domain structure in Barium Titanate single crystals by synchrotron x-ray topography  

Microsoft Academic Search

Imaging of domains is a key step in understanding the microstructure and hence the properties of ferroelectric single crystals. This understanding is essential for exploiting engineered domain configurations to achieve enhanced performance. In this paper, single crystals of Barium Titanate are observed by reflection topography using unfocussed monochromatic synchrotron X-ray light. A 10 x 10 mm polished surface of an

Prashant R. Potnis; John E. Huber; John P. Sutter; Felix Hofmann; Brian Abbey; Alexander M. Korsunsky

2010-01-01

429

Piezoelectric properties of domain engineered barium titanate single crystals with different volume fractions of domain walls  

E-print Network

Piezoelectric properties of domain engineered barium titanate single crystals with different volume; published online 16 September 2009 A piezoelectric domain wall model has been developed to analyze the effective piezoelectric properties of domain engineered BaTiO3 BT single crystals with different volume

Cao, Wenwu

430

Thiourea:diethyl oxalate(2:1) complex: Single crystal diffraction , Pascal Rousselb  

E-print Network

Thiourea:diethyl oxalate(2:1) complex: Single crystal diffraction at 100k R.Chitraa , Pascal'Ascq Cedex, France Abstract The crystal structure of thiourea:diethyl oxalate at 100k was solved using single of appropriate size and shape [2,3]. One such system studied by us is the thiourea:oxalate ester systems

Paris-Sud XI, Université de

431

Strain localization phenomena under cyclic loading: application to fatigue of single crystals  

Microsoft Academic Search

Kinematic hardening plays an important role in strain localization phenomena under cycling loading. A single crystal constitutive model including non-linear kinematic hardening is presented. Using a heterogeneous distribution of kinematic hardening variable in a single crystal plate, a continuum model for the formation of intrusion\\/extrusion is proposed based on FE simulation. The attention is focused on ratchetting phenomena taking place

S. Flouriot; S. Forest; L. Rémy

2003-01-01

432

Orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals  

E-print Network

extrinsic domain and domain wall contributions. For [011]c poled multi- domain crystals, the intrinsicOrientation dependence of electromechanical properties of relaxor based ferroelectric single of electromechan- ical properties of relaxor based ferroelectric single crystals Pb(Zn1/3Nb2/3)O3­(6­7)%PbTiO3

Cao, Wenwu

433

Amplification of cylindrically polarized laser beams in single crystal fiber amplifiers  

E-print Network

Amplification of cylindrically polarized laser beams in single crystal fiber amplifiers Stefan:YAG single crystal fiber (SCF) amplifiers have recently drawn much attention in the field of amplification excitations of radially and azimuthally polarized Nd3+ :YAG ceramic microchip laser by use of subwavelength

Boyer, Edmond

434

The application of defect maps in the process modeling of single-crystal investment casting  

Microsoft Academic Search

Defect maps, which plot the occurrences of defects on the bases of both temperature gradient and solidification rate, can be used as a performance criterion in process modeling for single-crystal components in order to reduce rejection rates and thereby lower costs. Attention is presently given to the case of defect mapping for single-crystal turbine blade investment castings subjected to grain

John S. Tu; R. K. Foran

1992-01-01

435

Conditions for designing single-mode air-core waveguides in three-dimensional photonic crystals  

E-print Network

in the band diagram.13 Almost any line defect structure in a 3D complete band gap PC behaves as a waveguideConditions for designing single-mode air-core waveguides in three-dimensional photonic crystals that allows the design of single-mode air-core waveguides in three-dimensional photonic crystals

Fan, Shanhui

436

Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals  

E-print Network

Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals X June 2006 Editor: P. Deines Abstract Oxygen diffusion in natural and synthetic single-crystal titanite cold-seal pressure vessels for durations of 1 day to several weeks. Diffusive uptake profiles of 18 O

Watson, E. Bruce

437

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature  

E-print Network

1 Transport properties of low-sanidine single-crystals, glasses and melts at high temperature Maik = 8221 + 9 figures + 5 tables Keywords: laser-flash analysis, high-temperature, thermal diffusivity, viscosity, density, IR spectroscopy, low-sanidine, single-crystal, glass, melt #12;2 Abstract. Thermal

Spera, Frank J.

438

DEVELOPMENT OF PROTECTIVE COATINGS FOR SINGLE CRYSTAL TURBINE BLADES  

SciTech Connect

Turbine blades in coal derived syngas systems are subject to oxidation and corrosion due to high steam temperature and pressure. Thermal barrier coatings (TBCs) are developed to address these problems. The emphasis is on prime-reliant design and a better coating architecture, having high temperature and corrosion resistance properties for turbine blades. In Phase I, UES Inc. proposed to develop, characterize and optimize a prime reliant TBC system, having smooth and defect-free NiCoCrAlY bond layer and a defect free oxide sublayer, using a filtered arc technology. Phase I work demonstrated the deposition of highly dense, smooth and defect free NiCoCrAlY bond coat on a single crystal CMSX-4 substrate and the deposition of alpha-alumina and yttrium aluminum garnet (YAG) sublayer on top of the bond coat. Isothermal and cyclic oxidation test and pre- and post-characterization of these layers, in Phase I work, (with and without top TBC layer of commercial EB PVD YSZ) revealed significant performance enhancement.

Amarendra K. Rai

2006-12-04

439

Piezoelectric anisotropy of KNbO3 single crystal  

SciTech Connect

Orientation dependence of the longitudinal piezoelectric coefficients (d*{sub 33}) of a KNbO{sub 3} single crystal has been investigated as a function of temperature by using the Landau-Ginzburg-Devonshire thermodynamic phenomenological theory. It is shown that the maximum of d*{sub 33} is not always along the polarization direction of the ferroelectric phase. The enhancement of d*{sub 33} d along a nonpolar direction is attributed to the ferroelectric phase transition at which a polarization changes its direction. In the tetragonal phase, the maximum of d*{sub 33}{sup t} for the tetragonal phase at high temperatures is along the tetragonal polar direction and then changes its direction toward the polar direction of the orthorhombic phase when close to the tetragonal-orthorhombic phase transition point. The maximum of d*{sub 33}{sup o} of the orthorhombic phase depends on the competition of both high-temperature and low temperature ferroelectric phase transitions. In the rhombohedral phase, the maximum of d*{sub 33}{sup r} is relatively insensitive to temperature due to the absence of any further phase transitions in the low temperature regime. These results can be generalized to the phase transitions induced by external electric-field, pressure, and composition variations.

Liang, Linyun; Li, Yulan; Hu, Shenyang Y.; Chen, Long-Qing; Lu, Guang-Hong

2010-11-01

440

Flux creep relaxation in single crystal Hg-1201  

NASA Astrophysics Data System (ADS)

Magnetization measurements on a single crystal of the high-Tc cuprate HgBa2CuO4 (Hg-1201) are performed for the two field orientations B||c and B||(a,b). Besides zero-field-cooling (zfc) - field-cooling (fc) and magnetization studies, the flux creep relaxation is determined. The zfc curves exhibit pronounced step-like anomalies in the mixed state above the lower critical field Bc1. They are interpreted as those points in the phase diagram where the penetrating flux fronts meet at the center of the sample. In order to obtain more information about the flux pinning mechanism flux creep relaxation experiments are performed at different temperatures in magnetic fields of 0.15 and 2 T. The resulting supercurrent dependence on the mean activation energy is analysed according to the collective pinning theory which predicts U propto ((j/jc)-? -1). The ?-values for B||c are 0.5 at higher temperatures and 2 at 5 K, and they vary between 1.1 and 1.5 for B||(a,b). The observed behaviour is quite different from that found for powder samples.

Baenitz, M.; Lüders, K.; Bariši?, N.; Cho, Y.; Li, Y.; Yu, G.; Zhao, X.; Greven, M.

2010-06-01

441

Reduction of precursor decay anomaly in single crystal lithium fluoride  

NASA Astrophysics Data System (ADS)

The purpose of this study is to reveal that the precursor decay anomaly in single crystal lithium fluoride is reduced by Sano's decay curve [Y. Sano, J. Appl. Phys. 85, 7616 (1999)], which is much smaller in slope than Asay's decay curve [J. R. Asay, G. R. Fowles, G. E. Duvall, M. H. Miles, and R. F. Tinder, J. Appl. Phys. 43, 2132 (1972)]. To this end, strain, particle, velocity, and stress in a precursor and near the leading edge of the follower changing with time along Sano's decay curve are first analyzed quantitatively. The analysis verified the existence of degenerate contraction waves I and II and a subrarefaction wave R', and the decay process [Y. Sano, J. Appl. Phys. 77, 3746 (1995)] caused in sequence by evolving followers C, I, II, R', Rb. Next, inequalities relating decay rates qualitatively to plastic strain rates at the leading edge of the follower, which are derived using the properties of the followers, are incorporated into the analysis. Calculation results showed that the plastic strain rates were reduced by low decay rates. This indicates that the precursor decay anomaly might be greatly reduced by Sano's decay curve.

Sano, Yukio

2000-08-01

442

Analysis of ripple formation in single crystal spot welds  

SciTech Connect

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

Rappaz, M. [Ecole Polytechnique Federale de Lausanne (Switzerland). Lab de Metallurgie Physique; Corrigan, D.; Boatner, L.A. [Oak Ridge National Lab., TN (United States). Solid State Div.

1997-10-01

443

Hall Effect Measurements in Organic Single-Crystal FETs  

NASA Astrophysics Data System (ADS)

We have observed classical Hall effect in the single-crystal rubrene OFETs [1]. The mobility determined from the Hall measurements (mu&_slash;H) represents intrinsic, i.e. trap independent mobi