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1

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

2

The formation of metallic nanoparticles in single crystal CaF2 under 157 nm excimer laser irradiation  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important material for vacuum-ultraviolet optical components. Unfortunately, all metal halides tend to form defects when exposed to energetic particles and laser radiation, and these defects can degrade optical performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser radiation and show that several tens of thousands of pulses at fluences near 1 J/cm2 can color the material. Absorption spectra of the exposed material confirm the formation of metallic calcium nanoparticles similar to those produced by other forms of energetic radiation. The rate of nanoparticle formation depends on the bulk temperature and displays a local maximum near 50 °C. Absorption measurements at 157 nm display a transient absorption component that grows during prolonged irradiation and disappears on time scales of several minutes after irradiation ceases. The implications of these effects in optical components are discussed.

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

2006-03-01

3

Temperature-dependent Urbach tail measurements of CaF2 single crystals  

NASA Astrophysics Data System (ADS)

In the deep ultraviolet spectral range the transmission of high-purity CaF2 was measured using synchrotron radiation. In the vicinity of the band gap below 11.2 eV or for wavelength longer than 90 nm, a scaling behavior of the absorption as a function of photon energy was observed. Temperature-dependent measurements allow one to distinguish two different absorption mechanisms which differ by their ability to couple to phonon excitations. These two types of Urbach tails were analyzed. The origin of the temperature-independent tail is due to defects in the lattice, whereas the temperature-dependent part originates from short-time localization of exciton mode coupling to lattice distortion.

Letz, M.; Gottwald, A.; Richter, M.; Parthier, L.

2009-05-01

4

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

Microsoft Academic Search

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 106Gy and absorption bands centred at about 225, 260, 340, 396 and 580nm are observed. At higher doses, in the case of reactor neutrons

M. Izerrouken; L. Guerbous; A. Meftah

2010-01-01

5

Dependence of luminescence processes and transmission in vacuum-ultraviolet region on surface condition in CaF 2 single crystals  

Microsoft Academic Search

We investigated the effect of the surface condition on luminescence processes in a surface layer of single CaF2 crystals under the excitation by vacuum-ultraviolet (VUV) light (h??13.5 eV). It has been shown that the intensity of the excitonic emission at 4.4 eV in polished crystals essentially decreases with respect to that in freshly cleaved crystals. The decrease at the interband

V. Denks; T Savikhina; V Nagirnyi

2000-01-01

6

Study of haze in artificially grown single crystal CaF2  

NASA Astrophysics Data System (ADS)

The artificially grown calcium fluoride is used as materials of the optics such as the lenses of the illumination optical system and the projection optical system of the lithography equipment that use the sources of light such as excimer lasers. Such calcium fluoride is required high transmittance. However, there are very small scatterers and absorbers inside the crystal and they cause degradation of transmittance. In this study, we examined these defects and clarified the process how they occur. Haze is characteristic optical defect in the artificially grown calcium fluoride. It is thought that haze is an aggregation of very small scatterers and this scatterer is void or calcium oxide crystal. When we irradiate the light into a crystal with much haze, the path of the light looks white. However, we were not able to clarify neither the structure nor components of haze. First, we examined how the scatterers were distributed by an infrared tomography method. The result pointed out that the scatterers were located along sub-grain boundary and dislocation network. We prepared a surface sample for TEM (Transmission Electron Microscopy) with FIB (Focused Ion Beam) from the point where it seemed that the scatterers were located in the dislocation network, and observed it with TEM and analyzed grain boundary region and the grain inside with EDS (Energy Dispersive X-ray Spectroscopy). From the EDS spectrum of the grain boundary region, a very small amount of oxygen was detected, but no oxygen was detected from the grain inside. This suggests that oxygen is located in the grain boundary. From these results, it is suggested that scatterers of haze are made of oxygen voids or calcium oxides crystals.

Azumi, M.

2008-01-01

7

Behaviors of metal-oxide impurities in CaF 2 and BaF 2 single-crystals grown with PbF 2 scavenger by Stockbarger’s method  

Microsoft Academic Search

The concentrations and distribution of trace amounts of metal impurities in CaF2 and BaF2 single-crystals grown from high purity CaF2 and BaF2 raw powders and 14 kinds of trace amounts of metal-oxide impurity additives (metal elements=Li, Na, Mg, Ca, Sr, Ba, Al, Cr, Fe, Ni, Cu, Y, La and Ce) under the addition of 3wt% PbF2 scavenger by the Stockbarger

Tetsuo Yonezawa; Kentaro Matsuo; Jun Nakayama; Yoji Kawamoto

2003-01-01

8

Single-point diamond turning of CaF 2 for nanometric surface  

Microsoft Academic Search

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

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

2004-01-01

9

The mechanism for material removal in ductile mode cutting of CaF2 brittle crystals  

Microsoft Academic Search

Single-crystal calcium fluoride (CaF2) is an indispensable optical material for the deep ultraviolet radiation lithography system. The requirement for extremely high performance using in lithography system can be not satisfied by using conventional polishing because the polishing powder are easy to embed to surface due to its relative softness. In the process of rough finishing of CaF2, ductile cutting of

Haofeng Chen; Yifan Dai; Xiaoqiang Peng; Ziwen Zheng; Chaoliang Guan

2010-01-01

10

Colour centres formation in CaF2 single crystals by gamma-rays and reactor neutrons  

Microsoft Academic Search

The induced colour in single crystals of calcium fluoride irradiated with gamma-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing gamma-rays dose up to 106 Gy and absorption bands centred at about 225, 260, 340, 396 and 580 nm are observed. At higher doses, in the case of

M. Izerrouken; L. Guerbous; A. Meftah

2010-01-01

11

SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: Efficient lasing in diode-pumped Yb3+:CaF2SrF2 solid-solution single crystals  

Microsoft Academic Search

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

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

2007-01-01

12

Behaviors of trace amounts of metal-oxide impurities in CaF 2 crystal grown by Stockbarger's method  

Microsoft Academic Search

The concentrations and distribution of trace amounts of metal impurities in CaF2 crystals grown by the Stockbarger method from CaF2 powder and 14 kinds of metal-oxide additives were examined and compared with CaF2 crystals grown from CaF2 powder and metal-fluoride additives. In the CaF2 crystals grown with metal-oxide additives, the Li, Na, Cr, Fe, Ni, Cu and Pb metal-impurities were

Tetsuo Yonezawa; Jun Nakayama; Kunio Tsukuma; Yoji Kawamoto

2002-01-01

13

U^4+ Ions in CaF2 Crystals  

NASA Astrophysics Data System (ADS)

The structure of U^4+ inclusion sites in CaF2 has been studied for 20 crystals, of dopant concentrations from 0.001 to 0.6 mole%, using electron paramagnetic resonance (EPR), Fourier Transform infra-red (FTIR) Zeeman spectroscopy and optical spectroscopy. These confirm the assignment of green crystals to U^4+ ions footnote R. McLaughlin et al, J Chem Phys. 53, 2031 (1970) rather than the U^2+ assignment of Hargreaves footnote W. A. Hargreaves, Phys Rev. B44, 5293 (1991). Two sites are observed, a trigonal EPR site (consistent with a 1:0:3 arangement) and a tetragonal site with an orbital singlet ground-state. The degree of green coloration depends not only on the concentration of U^4+ ions but also on other factors. Thermal studies and selective spectroscopy are being used to determine which other factors are important.

Choi, J.; Raukas, M.; Happek, U.; Watson, A. M.; Campbell, J. A.

1996-03-01

14

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

15

Creation of nanohillocks on CaF2 surfaces by single slow highly charged ions.  

PubMed

Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 x q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF(2) single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock formation which can be linked to a solid-liquid phase transition. PMID:18643543

El-Said, A S; Heller, R; Meissl, W; Ritter, R; Facsko, S; Lemell, C; Solleder, B; Gebeshuber, I C; Betz, G; Toulemonde, M; Möller, W; Burgdörfer, J; Aumayr, F

2008-06-13

16

Irradiation effects in CaF2: ZnO nanostructed crystals  

NASA Astrophysics Data System (ADS)

Effects of ?, X, and UV radiation were studied in CaF2: ZnO single crystals in which ZnO was embedded as nanoparticles. Absorption measurements of these crystals showed a steep increase below 250nm and a weak absorption peak at about 310nm. After prolonged ? irradiation, additional absorption bands were recorded at 395 and 595nm. The irradiated samples showed during heating several thermoluminescence (TL) peaks. Samples which had been exposed to ?-irradiation at RT and subsequently illuminated at LNT with 390nm light showed during re-heating to RT several TL peaks that are attributed to a process of photo-transferred TL (PTTL). Main photoluminescence (PL) emission bands were recorded at 320 and 340nm with excitation maxima near 250 and 300nm. These emission bands were also observed during X-irradiation as well as additional emission bands near 355 and 400nm. In pre-irradiated samples, a 320nm luminescence band could also be excited by 395nm light and is attributed to a process of photostimulation. The stimulation maxima of the OSL and PTTL in the 390nm region are apparently due to the observed absorption band at 395nm induced by the ?-irradiation. The fact that some of the same emission bands appeared in the XL, PL, TL and OSL of this crystal indicates that the same luminescence centers are involved in these emissions.

Kristianpoller, N.; Chen, Wei; Chen, Reuven; Liu, Yinchu

2010-11-01

17

Sites structure and spectroscopic properties of Yb-doped and Yb, Na-codoped CaF 2 laser crystals  

Microsoft Academic Search

For the first time, the effect of Na+ on crystal structure, valence state of Yb ions, spectroscopic properties of YbF3-doped CaF2 system was systematically studied. Na+ can greatly suppress the deoxidization of Yb3+ to Yb2+. Absorption and emission spectra showed codoping Na+ with different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in CaF2 lattice in

Liangbi Su; Jun Xu; Hongjun Li; Lei Wen; Yueqin Zhu; Zhiwei Zhao; Yongjun Dong; Guoqing Zhou; Jiliang Si

2005-01-01

18

Recording holograms on color centers in CaF2:Na crystals by light with different wavelengths  

NASA Astrophysics Data System (ADS)

The absorption spectra and holographic characteristics of a CaF2:Na crystal sample are measured at different wavelengths within the absorption band of colloidal centers, along with the same characteristics of the samples with holograms after their irradiation by incoherent UV light. Results of the study confirm the diffusion-and-drift mechanism of recording holograms on color centers in ionic crystals.

Shcheulin, A. S.; Angervaks, A. E.; Ryskin, A. I.

2009-12-01

19

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

NASA Astrophysics Data System (ADS)

Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF2:Eu and YAlO3:Ce scintillators to single ions of H+, He+, and O3+ are measured by the corresponding pulse height over a continuous energy range using a time-of-flight-scintillator-photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) can be produced by energetic H+, He+ and O3+ ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of the scintillators to irradiation.

Liu, Peng; Zhang, Yanwen; Xiao, Haiyan; Xiang, Xia; Wang, Xuelin; Weber, William J.

2014-01-01

20

Laser-induced front side etching of CaF2 crystals with KrF excimer laser  

NASA Astrophysics Data System (ADS)

The laser-induced front side etching (LIFE) of amorphous materials like fused silica was manifold studied and the LIFE process was sufficient optimized for the fabrication of well-defined etching trenches with a very low surface roughness. The LIFE process is an indirect laser-induced ablation process, the - for the used laser wavelength - transparent substrate was covered by a highly absorbing material and the absorbing process causes a transfer of the laser energy into the substrate and, finally, to an ablation process of the substrate surface. However, the structuring of crystalline materials like CaF2 is a great challenge for the LIFE process. The properties of CaF2(1 1 1) and CaF2(0 0 1) surfaces etched by KrF excimer laser pulses (pulse duration ?tp = 25 ns, wavelength ? = 248 nm) were analysed by white light interferometry (WLI) as well as scanning electron microscopy (SEM). The surface morphologies of laser etched CaF2 surfaces depend on the laser parameters and on the crystal orientation and are frequently characterized by microcracks and flake spallation. The most probable reasons therefore are laser-induced thermal stress or laser-induced shock waves.

Lorenz, Pierre; Ehrhardt, Martin; Zimmer, Klaus

2013-01-01

21

Influence of Various Impurities on the Optical Properties of YbF3-Doped CaF2 Crystals  

NASA Astrophysics Data System (ADS)

Calcium fluoride crystals doped with YbF3 and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF2. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of the Yb3+ and Yb2+ ions. This means that the developed crystal growth process achieves a good Yb3+ to Yb2+ conversion in the as-grown crystals. The influence of other impurities, such as Na+ or Li+, on the absorption and emission spectrum of YbF3-doped CaF2 was studied. The Li+ and Na+ ions drastically decrease the absorption coefficient of the Yb2+ ions in the UV band and the emission intensity by excitation in 230 nm.

Stef, M.; Pruna, A.; Pecingina-Garjoaba, N.; Nicoara, I.

2007-11-01

22

CaF2:Yb laser ceramics  

NASA Astrophysics Data System (ADS)

CaF2:Yb fluoride laser ceramics, prepared by hot-forming, exhibit the same optical properties as starting single crystals. Slope efficiency of the ?a0.95Yb0.05F2.05 is equal to 35% in the pulsed mode of laser operation. Decrease of ytterbium concentration in CaF2:Yb samples down to 3 mol.% resulted in the essential improvement of ?a0.97Yb0.03F2.03 thermal conductivity from 3.5 to 4.5 W/m K, but slightly decreased (down to 30%) slope efficiency of the samples under both pulsed and CW mode of operation. Alternative hot-pressing synthesis of CaF2:Yb fluoride laser ceramics provided materials with superior mechanical properties (microhardness ? = 3.2 GPa and fracture toughness ?1? = 0.65 ?P? m1/2) in comparison with hot-formed and/or single crystal CaF2:Yb specimens. For the first time, lasing has been observed for the novel aforementioned hot-pressed CaF2:Yb ceramics.

Akchurin, M. Sh.; Basiev, T. T.; Demidenko, A. A.; Doroshenko, M. E.; Fedorov, P. P.; Garibin, E. A.; Gusev, P. E.; Kuznetsov, S. V.; Krutov, M. A.; Mironov, I. A.; Osiko, V. V.; Popov, P. A.

2013-01-01

23

Influence of Various Impurities on the Optical Properties of YbF3-Doped CaF2 Crystals  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF2. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of

M. Stef; A. Pruna; N. Pecingina-Garjoaba; I. Nicoara

2007-01-01

24

Some dielectric and optical properties of PbF2-codoped CaF2:YbF3 crystals  

Microsoft Academic Search

YbF3-doped and PbF2-codoped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The Pb2+ ions modify the characteristic absorption peaks of the Yb2+ ions, but do not influence the Yb3+ ion peaks. The dielectric relaxation gives information about the impurity-defect aggregates. The obtained dielectric spectra show that

M. Stef; G. Buse; A. Pruna; I. Nicoara

2009-01-01

25

The colouration of CaF2 crystals by keV and GeV ions  

Microsoft Academic Search

CaF2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 nm. This includes the vacuum UV region. For 100 keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10(17) ions cm(2) )

A. T. Davidson; A. G. Kozakiewicz; J. D. Comins; T. E. Derry; K. Schwartz; C. Trautmann

2002-01-01

26

Infrared-to-visible upconversion of rare-earth doped glass ceramics containing CaF 2 crystals  

Microsoft Academic Search

Oxy-fluoride glass ceramics containing CaF2 crystals doped with YbF3–LnF3 (Ln=Er, Tm) were prepared by heat-treatment from SiO2–Al2O3–CaO–CaF2 glasses. The upconversion emission spectra of Er3+ and Tm3+ ions in the visible range were measured by 970nm pumping. In the spectrum of the Er doped sample, 540nm upconversion band due to the 4S3\\/2–4I15\\/2 and 660nm band due to the 4F9\\/2–4I15\\/2 were observed.

Yuki Kishi; Setsuhisa Tanabe

2006-01-01

27

Clustering and defect structure of CaF2 crystals doped with YbF3 and ErF3 as determined by 19F nuclear magnetic resonance  

Microsoft Academic Search

19F NMR studies of single crystals of CaF2 doped with 2, 1, and 0.5 mole percent of both ErF3 and YbF3 have been carried out at room temperature. In ErF3-doped crystals, 19F resonances have been identified for lattice fluorides having both one and two Er3+ ions in nearest-neighbor cation sites and for an interstitial fluoride with two Er3+ ions in

R. J. Booth; M. R. Mustafa; B. R. McGarvey

1978-01-01

28

Yb3+-doped CaF2 cubic fluoride crystal: spectroscopic properties, concentration quenching analysis, and laser optimization  

NASA Astrophysics Data System (ADS)

The ytterbium-doped crystals emitting around 1 ?m under laser-diode pumping between 900-980 nm have received an increasing interest in recent years as solid-state laser materials for high power or ultra-fast lasers. In this paper, our main objective is to contribute to Yb3+-doped fluorides mainly on CaF2 cubic host which are characterized by a high value of the thermal conductivity (9.5 W m-1 K-1) as high as YAG. Yb3+-doped CaF2, mono-doped and concentration gradient fibres were grown by both, the laser heated pedestal growth (LHPG) method and by the Czochralski method. Concerning Yb3+ excited state dynamics, the concentration dependence of the 2F5/2 decay time shows a competition between self-trapping and self-quenching processes. Main parameters useful for a theoretical approach of laser potentiality will be given and laser emission under InGaAs laser-diode pumping will be shown.

Boulon, G.; Ito, M.; Guyot, Y.; Goutaudier, C.; Brenier, A.; Jouini, A.; Sato, H.; Fukuda, T.

2007-08-01

29

Judd-Ofelt Analysis of the Er3+ Ions in Double-Doped CaF2:(Er3+,Yb3+) Crystal  

Microsoft Academic Search

The double-doped CaF2:(0.14 mol% ErF3,1.31 mol% YbF3) and CaF2:0.12 mol% ErF3 crystals were grown in our crystal research laboratory using the vertical Bridgman method. The Judd-Ofelt intensity parameters Omega2, Omega4, and Omega6 for f-f transitions of Er3+ ions were determined from the optical absorption spectra using various groups of transitions. Using the J-O parameters the radiative transition probability, oscillator strength,

Gabriel Buse; Eleonora Preda; Marius Stef; Andreea Pruna; Florentina Stef; Irina Nicoara

2009-01-01

30

Some dielectric and optical properties of PbF2-codoped CaF2:YbF3 crystals  

NASA Astrophysics Data System (ADS)

YbF3-doped and PbF2-codoped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The Pb2+ ions modify the characteristic absorption peaks of the Yb2+ ions, but do not influence the Yb3+ ion peaks. The dielectric relaxation gives information about the impurity-defect aggregates. The obtained dielectric spectra show that for our low-YbF3-concentration samples, the main dipole complexes are NN type. The Pb2+ ions do not have an important influence on the dielectric spectra. The activation energy for the dipole reorientation and the relaxation time constant have been determined.

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

2009-07-01

31

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

32

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

33

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

34

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

35

Judd-Ofelt Analysis of the Er3+ Ions in Double-Doped CaF2:(Er3+,Yb3+) Crystal  

NASA Astrophysics Data System (ADS)

The double-doped CaF2:(0.14 mol% ErF3,1.31 mol% YbF3) and CaF2:0.12 mol% ErF3 crystals were grown in our crystal research laboratory using the vertical Bridgman method. The Judd-Ofelt intensity parameters ?2, ?4, and ?6 for f-f transitions of Er3+ ions were determined from the optical absorption spectra using various groups of transitions. Using the J-O parameters the radiative transition probability, oscillator strength, branching ratio and radiative lifetime of Er3+ transitions have been calculated. The radiative transition probability and radiative lifetimes are compared to those of Er3+ transitions in other hosts.

Buse, Gabriel; Preda, Eleonora; Stef, Marius; Pruna, Andreea; Stef, Florentina; Nicoara, Irina

2009-05-01

36

Advances in growth of fiber crystal by the LHPG technique. Application to the optimization of Yb 3+-doped CaF 2 laser crystals  

NASA Astrophysics Data System (ADS)

The laser heated pedestal growth (LHPG) technique is suitable to grow crystalline fibers and has been successfully applied for the general study of a lot of optical materials as laser crystals. Our general approach on the research of diode-pumped Yb 3+-doped host crystals is presented through typical example of CaF 2 fluoride, which is considered among the important laser crystals either for basic or applied reasons. Spectroscopic characterizations were carried out. Especially, Yb 3+ ( 2F 5/2) excited level experimental decay time dependence on Yb 3+ ion concentration is analyzed by using our own approach on the synthesis of a concentration gradient fiber grown in the laboratory. Our main objective is to contribute to have a better understanding of concentration quenching mechanisms not only in laser crystals but more generally in luminescent materials.

Boulon, G.; Ito, M.; Goutaudier, C.; Guyot, Y.

2006-07-01

37

Growth of Doped and Undoped Single Crystal Laser Materials in the System (MF2)x.(YF3)(1-x).  

National Technical Information Service (NTIS)

Laser host materials were grown in the CaF2-YF3 and BaF2-YF3 binaries. Two compositions in the former binary were found to be capable of producing single crystals: 9CaF2.YF3 and CaF2.2.6YF3. The former possessed a fluorite structure and the latter was ind...

J. F. Balascio

1975-01-01

38

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

39

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

40

Radiation defects in CaF2 and SrF2 crystals doped with cadmium or zinc  

NASA Astrophysics Data System (ADS)

The formation of radiation defects in calcium and strontium fluoride single crystals doped with cadmium or zinc has been investigated by luminescence and absorption spectroscopy, as well as by electron spin resonance spectroscopy. It was found that x-irradiation could convert divalent impurity ions located at essentially cubic sites into the univalent state. Three types of Cd+ or Zn+ centers differing by local environment with point symmetries Oh, C3v and C2v are identified in the crystals. The formation of the last two results from the interaction between reduced impurities in the cubic environment and anion vacancies. The latter are intrinsic radiation defects and are not created by x-irradiation in undoped crystals. We also discuss the possible implications of the electric field of the charge impurity defects on separation of the intrinsic radiation defects in these crystals.

Egranov, A. V.; Radzhabov, E. A.; Ivashechkin, V. F.; Semenova, M. A.; Vasil'eva, I. E.

2008-11-01

41

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 authors´ 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

2011-05-01

42

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

43

Temperature and pressure dependence of spectral positions and widths of 5D0 ? 7FJ emission lines from Eu3+ ions in the CaF2 crystal  

NASA Astrophysics Data System (ADS)

The effect of temperature (T) and pressure (P) was studied on the emission zero-phonon lines (ZPLs) corresponding to 5D0 ? 7F0,1,2 electronic transitions in Eu3+ centres of trigonal symmetry in the CaF2 crystal. In the T-range 112-493 K at ambient P, all the lines shift to the blue and broaden. Both effects are explained by the dephasing of electronic transitions due to the Raman scattering of acoustic phonons by impurity ions. The T-shift of the lines is caused not only by the change of the electron-phonon interaction (EPI) in impurity centres, but also by the thermal expansion of the host crystal. In the P-range 0.001-7.3 kbar at room temperature, the width of all lines somewhat decreases, most lines shift to the red, the splitting of 7F1,2 multiplet levels in the crystal field increases, and the energy distance between the 5D0 level and the barycentre of the crystal-field sublevels of 7F0, 7F1 and 7F2 levels decreases. The P-narrowing of the ZPLs can be explained by the P-induced decrease of the EPI coefficient in the framework of the Raman mechanism and also by the decrease in the density of states for acoustic phonons due to the P-induced increase in the Debye T of the crystal. The P-shift of the ZPLs is supposedly caused mainly by changes in the direct interaction of external pressure with impurity centres and not by the P-induced contraction of the host crystal.

Kuznetsov, Anatoli; Laisaar, Arlentin; Kikas, Jaak

2013-11-01

44

Research on the optical spectra, g factors and defect structures for two tetragonal Y2+ centers in the irradiated CaF2: Y crystal  

NASA Astrophysics Data System (ADS)

Based on the defect models that the tetragonal Y2+ (1) center in the irradiated CaF2: Y crystal is due to Y2+ at Ca2+ site associated with a nearest interstitial F- ion along C4 axis and the tetragonal Y2+ (2) center is Y2+ at Ca2+ site where the tetragonal distortion is caused by the static Jahn-Teller effect, the two optical spectral bands and anisotropic g factors for both tetragonal Y2+ centers are calculated. The calculations are made by using two methods based on the cluster approach, one is the complete diagonalization (of energy matrix) method (CDM) and another is the perturbation theory method (PTM). The calculated results for each Y2+ center from CDM and PTM coincide and show reasonable agreement with the experimental values. The calculated isotropic g factor for Y2+ (2) center at higher temperature owing to the dynamical Jahn-Teller effect is also consistent with the observed value. The defect structures (i.e., tetragonal distortion) of the two Y2+ centers are obtained from the calculation. It appears that both theoretical methods can be applied to explain the optical and EPR data, to study the defect model and to determine the defect structures for d1 ions in crystals.

Zheng, Wen-Chen; Mei, Yang; Yang, Yu-Guang; Liu, Hong-Gang

2012-11-01

45

Optical spectroscopy of Yb 2+ ions in YbF 3-doped CaF 2 crystals  

Microsoft Academic Search

Transparent colorless Ca1?xYbx F2+x (x=0.0007–0.016) crystals were grown using the vertical Bridgman technique. In order to obtain efficient Yb3+–Yb2+ conversion in the as-grown crystals, a special procedure has been developed. Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions in the as-grown crystals, with intensities more than 10 times higher than those reported by

Irina Nicoara; Liliana Lighezan; Monica Enculescu; Ionut Enculescu

2008-01-01

46

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

47

Growth of YbF 3-doped CaF 2 crystals and characterization of Yb 3+\\/Yb 2+ conversion  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 and PbF2-, NaF- and LiF-codoped were grown using the vertical Bridgman method. Transparent, high quality, with various high Yb2+ contents in the as-grown crystals has been obtained using a special procedure. The optical absorption spectra reveal the characteristic ultraviolet (UV) absorption bands of the divalent Yb ions. Influence of the codoping with Pb2+, Li+

Irina Nicoara; Marius Stef; Andreea Pruna

2008-01-01

48

Concentration distribution of Yb 2+ and Yb 3+ ions in YbF 3:CaF 2 crystals  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 were grown using the Bridgman technique. The optical absorption spectra reveal the characteristic UV-absorption bands of divalent Ytterbium. The absorption coefficient of divalent Yb is more than ten times higher than that of trivalent Ytterbium. This shows that the developed crystal growth process achieves a good Yb3+–Yb2+ conversion. The concentration distribution of the Yb2+

Irina Nicoara; Nicolae Pecingina-Garjoaba; Octavian Bunoiu

2008-01-01

49

Influence of Li+ and Na+ Ions on the Dielectric Spectra of YbF3 Doped and LiF, NaF Codoped CaF2 Crystals  

Microsoft Academic Search

Various concentrations YbF3 -doped CaF2 and Li- (Na)- codoped crystals were grown using the conventional Bridgman method. The effect of Na+ and Li+ ions on the dielectric spectra was studied. The activation energy and the reciprocal frequency factor have been calculated in order to characterize the observed relaxations. An anomaly of ?1 behavior (not reported before) has been observed which

Andreea Pruna; Marius Stef; Gabriel Buse; Irina Nicoara

2009-01-01

50

Influence of Li+ and Na+ Ions on the Dielectric Spectra of YbF3 Doped and LiF, NaF Codoped CaF2 Crystals  

NASA Astrophysics Data System (ADS)

Various concentrations YbF3 -doped CaF2 and Li- (Na)- codoped crystals were grown using the conventional Bridgman method. The effect of Na+ and Li+ ions on the dielectric spectra was studied. The activation energy and the reciprocal frequency factor have been calculated in order to characterize the observed relaxations. An anomaly of ?1 behavior (not reported before) has been observed which is assigned with a phase transition of the order-disorder type.

Pruna, Andreea; Stef, Marius; Buse, Gabriel; Nicoara, Irina

2009-05-01

51

Thresholds measured with 350-nm pulses at 25 to 100 Hz for bare polished crystals of CaF2 and for silica sol-gel AR coatings on silica substrates  

Microsoft Academic Search

An XeF laser-damage experiment was used to measure damage thresholds for bare polished crystals of CaF2 and porous silica antireflection coatings on fused silica substrates. Damage was induced by applying 1000 350-nm, 25-ns pulses at repetition rates of 25 to 100 Hz to small (typically 0.12 x .03 cm) sites on the surfaces of the sample. Eight samples of fluorescence-free

M. C. Staggs; D. Milam; I. M. Thomas; J. G. Wilder

1986-01-01

52

LET dependence of thermoluminescent efficiency and peak height ratio of CaF 2:Tm  

Microsoft Academic Search

First-order thermoluminescence (TL) kinetics computerized glow curve deconvolution (CGCD) and manual analysis of the composite peak structures have been applied to study the behaviour of glow peaks 3 and 5 in CaF2:Tm (TLD-300, Harshaw-Thermo Fisher Scientific) single crystals after heavy charged particle (HCP) irradiation with respect to Co60 gamma rays for a linear energy transfer (LET) interval from 2.3 to

M. Hajek; T. Berger; R. Bergmann; N. Vana; Y. Uchihori; N. Yasuda; H. Kitamura

2008-01-01

53

Excitonic processes in Li and Na-doped CaF2  

Microsoft Academic Search

The optical properties of nominally pure CaF2 crystals as well as those of pure and Li+ and Na+-doped CaF2 powders are compared. The emission band peaking at 3.85 eV and the excitation band in the region of 10-10.6 eV, observed in CaF2: Li and CaF2: Na powders, are ascribed to the radiative decay of a self-trapped exciton perturbed by an

V. Denks; A. Maaroos; V. Nagirnyi; T. Savikhina; V. Vassiltsenko

1999-01-01

54

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

55

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

56

Conductive nanodots on the surface of irradiated CaF2  

NASA Astrophysics Data System (ADS)

CaF2(111) single crystal surfaces have been irradiated with swift heavy ions under oblique angles resulting in chains of nanosized hillocks. In order to characterize these nanodots with respect to their conductivity we have applied non-contact atomic force microscopy using a magnetic tip. Measurements in UHV as well as under ambient conditions reveal a clearly enhanced electromagnetic interaction between the magnetic tip and the nanodots. The dissipated energy per cycle is comparable to the value found for metals, indicating that the interaction of the ion with the target material leads to the creation of metallic Ca nanodots on the surface.

Roll, Tino; Meier, Marion; Akcöltekin, Sevilay; Klusmann, Miriam; Lebius, Henning; Schleberger, Marika

2008-10-01

57

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

58

Single Crystals  

NASA Astrophysics Data System (ADS)

We have prepared single crystals of type-VIII clathrate Ba8Ga15.9- x In x Sn30.1 for x ? 0.60 by the Sn-flux method. As x is increased from 0 to 0.60, the lattice parameter increases by 0.2%, which is consistent with the larger covalent diameter for In than for Ga. The Seebeck coefficient ?, electrical resistivity ?, and thermal conductivity ? were measured in the temperature range from 300 K to 600 K. For all samples, ? is negative, indicating the dominant charge carriers are electrons. With increasing x from 0 to 0.20, ? and decrease by 50% and 30%, respectively. As a result, the lattice thermal conductivity at 300 K decreases from 0.58 W/Km to 0.41 W/Km, which is ascribed to enhancement of rattling of the guest atoms. It is found that the maximum of the dimensionless figure of merit ZT reaches 1.05 at 540 K for x = 0.20.

Chen, Yuexing; Du, Baoli; Kajisa, Kousuke; Takabatake, Toshiro

2014-06-01

59

Photoionization thresholds of rare-earth impurity ions. EuS :CaF2, CeT :YAG, and SmS :CaF2  

SciTech Connect

The spectral dependence of the photoionization energy of EuS :CaF2, CeT :YAG, and SmS :CaF2 systems have been measured and thresholds experimentally determined and compared with theoretical values calculated from electrostatic models. It is shown that the excited state absorption transitions or the persistent hole burning observed by other authors occur above the threshold energy of photoionization of the impurities and that the states of the crystal which form the bottom of the conduction band may play an important role in the strong probability of these processes. A review of thresholds now known is also given.

Pedrini, C.; Rogemond, F.; McClure, D.S.

1986-02-15

60

Enhanced susceptibility of CaF 2(1 1 1) to adsorption due to ion irradiation  

NASA Astrophysics Data System (ADS)

We have investigated morphological changes of freshly cleaved CaF 2(1 1 1) single crystal surfaces before and after ion irradiation. We show that with or without irradiation the surface undergoes serious changes within minutes after the cleavage if the samples are exposed to ambient conditions. This is most likely due to the adsorption of water and could be avoided only if working under clean ultra-high-vacuum conditions. Ion-induced modifications on this surface seem to act as centers for an increased rate of adsorption so that any quantitative numbers obtained by atomic force microscopy in such experiments have to be treated with caution.

Akcöltekin, S.; Roll, T.; Akcöltekin, E.; Klusmann, M.; Lebius, H.; Schleberger, M.

2009-02-01

61

Characterization of LiF and CaF 2 surfaces using MIES and UPS (HeI)  

Microsoft Academic Search

Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination withab initio calculations (CRYSTAL-code) were applied to study surface and bulk defects in LiF and CaF2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W

D. Ochs; M. Brause; S. Krischok; P. Stracke; W. Maus-Friedrichs; V. Puchin; A. Popov; V. Kempter

1998-01-01

62

Analysis of laser durability of CaF2 for optical lithography  

NASA Astrophysics Data System (ADS)

Photolithography is a key technolgoy for the production of semiconductor devices. It supports the continuing trend towards higher integration density of microelectronic devices. The material used in the optics of lithography tools has to be of extremely high quality to ensure the high demand of the imaging. Due to its properties CaF2 is a material of choice for the application in lithography systems. Because of the compexity of the lithography tools single lenses or lens system modules cannot be replaced. Therefore the lens material has to last the full lifetime of the tool without major degradation. According to the roadmap for next generation of optical lithography tools, like immersion lithography, the requirements of CaF2 for radiation hardness are increasing considerably. We will present a detailed analysis of the key factors influencing the laser hardness covering the complete production chain. Some aspects of the evaluation methods for testing CaF2 laser durability will be presented.

Grabosch, Guenter; Parthier, Lutz; Natura, Ute; Poehl, Karin; Letz, Martin; Muehlig, Christian; Knapp, Konrad

2005-02-01

63

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

64

Site-selective laser spectroscopy of CaF2:Pr3+ and CaF2:Pr3+,R3+ (R3+=Y3+, Gd3+, Nd3+)  

NASA Astrophysics Data System (ADS)

Site-selective laser spectroscopy has been used to investigate the defect structure of a 0.1 mol % Pr3+:CaF2 crystal. Twenty-three distinct sites have been identified from the fluorescence spectra. Only three of the sites were found to be single-ion sites while the rest were assigned to be clusters of two or more ions. The single-ion sites are a C4v site, which dominates the spectrum at 0.1 mol %, a cubic site, and a site of low symmetry. Of the 20 cluster sites identified, two sites undergo intracluster energy transfer at a rate slow enough to be directly observed.

Tissue, Brian M.; Wright, John C.

1987-12-01

65

Single Crystal Membranes  

NASA Technical Reports Server (NTRS)

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

Stormont, R. W.; Morrison, A.

1974-01-01

66

Energy transfer and non-linear optical properties at near ultraviolet wavelengths: rare earth 4f->5d transitions in crystals and glasses. Progress report, June 1, 1985-May 31, 1986. [Ce-doped CaF2 and LiYF4  

SciTech Connect

The project has considered several aspects of how high-fluence, near-ultraviolet laser light modifies the optical properties of cerium-doped crystals. Illumination of CeT :CaF2 at 308 nm leads to a two-photon photoionization and the subsequent creation of photochromic color centers. A one-photon photobleaching of these centers and the finite electron acceptor density leads to a complex but solvable rate equation. The electron acceptors are trivalent cerium ions at quasi-cubic sites, which become divalent following the electron capture. The photo-bleaching involves the photoionization of the divalent cerium ions, with the electron returning to the original tetragonal symmetry site. Thermoluminescence measurements are used to study the thermally activated recombination radiation. Measurements of optical gain and loss in CeT :LiYF4 are presented.

Hamilton, D.S.

1986-01-01

67

Single Crystal Diamond Films.  

National Technical Information Service (NTIS)

Diamond films are important for radiation tolerant devices. However, fabrication of single crystal films has proven to be much more difficult than polycrystalline deposits. A novel deposition process is proposed which can be used to deposit diamond on a s...

S. N. Bunker R. Sahagian

1993-01-01

68

Energy Levels of Ce2+ in CaF2  

Microsoft Academic Search

The absorption spectrum of cerium-doped CaF2 has been observed at several temperatures. When the cerium is reduced to the divalent state at room temperature, the absorption spectrum of Ce2+ is found to be unstable against thermal decay or bleaching by visible light; furthermore, this spectrum is found to comprise one state of a photochromic system. The absorption spectrum of CaF2:

R. C. Alig; Z. J. Kiss; J. P. Brown; D. S. McClure

1969-01-01

69

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

70

Nanostructuring CaF2 surfaces with slow highly charged ions  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

71

Dipole-relaxation parameters for Ce3+-Fint- complexes in CaF2:Ce and CaF2:Ce,Mn  

NASA Astrophysics Data System (ADS)

Dipole-relaxation parameters for Ce3+-Fint- centers (C4v symmetry) in CaF2 are calculated using the method of ionic thermocurrents (ITC). The data indicate concentration-dependent effects if analyzed using the traditional ITC equation, assuming a single value for the reorientation activation energy. This analysis is unable to account for an observed broadening of the ITC peak as more Ce is added to the crystals. However, as has been published for other MF2:R3+ systems, we find that the broadening can be successfully accounted for by adopting a modified ITC equation which allows for a Gaussian distribution of activation energies about a mean value E0 and with a distribution width p. The parameter E0 is found to be independent of dipole content while p is found to increase with increasing dipole concentration. The data are consistent with a perturbation of the dipole-relaxation parameters due to interactions with other defects within the system. However, the strength of the observed effects is difficult to explain by invoking electrostatic dipole-dipole interactions only. Other perturbations, due perhaps to monopole-dipole interactions or elastic interactions, must be taking place. The data indicate that dipole concentrations calculated by ITC will be in error in the presence of such interactions due to a reduction in the mean contribution per dipole to the overall polarization density. For samples in which interaction effects are negligible, we calculate a dipole moment of 3.12×10-29 C m. The data further indicate that that the addition of Mn to the system causes a decrease in the interaction effects via a reduction in the Ce C4v center dipole moment. It appears that the broadening of the ITC curve is sensitive to the defect structure surrounding the dipoles.

Jassemnejad, B.; McKeever, S. W. S.

1987-12-01

72

Hydrothermal synthesis and upconversion properties of CaF2:Er3+/Yb3+ nanocrystals.  

PubMed

A series of rare-earth ions (Er3+ and Yb3+) Co-doped CaF2 upconversion luminescent nanomaterials have been successfully prepared via a facile hydrothermal method using pluronic p123 (p123), pluronic F127 (F127) and sodium citrate as surfactants at 180 degrees C with different reaction time. The crystallographic phase, size and morphology can be controlled by simply tuning the reaction parameters such as the types of surfactants and the reaction time. It is found that reaction time and surfactant play a key role in forming the nanocrystals with different morphologies. X-ray diffraction, field-emission scanning electron microscopy FE-SEM, and photoluminescence spectra were used to characterize the structure, morphology and upconversion luminescence properties of CaF2:Er3+/Yb3+ upconversion nanomaterials, respectively. The experimental results indicate that three monodispersive and highly uniform CaF2:Er3+/Yb3+ nanocrystals with mean size of 200 nm, 3 um, and 700 nm have cubic and sphere shapes, respectively. While the possible mechanisms of upconversion luminescence are analyzed by the diagram of proposed energy transfer mechanisms, the schematic energy level diagrams showing typical upconversion processes for Er3+ also reveals that the as-synthesized CaF2:Er3+/Yb3 nanomaterials may be in the cubic structure with space group Fm-3m, in which Ln3+ cations occupy crystal lattice positions with lower point symmetry, leading to a high upconversion efficiency under the excitation of a 980 nm diode laser. PMID:24734555

Yu, Shiyong; Zhi, Yunxia; Su, Haiquan

2014-05-01

73

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

NASA Astrophysics Data System (ADS)

Rough two-dimensional substrates, such as thermally deposited {CaF}_2 , 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 {CaF}_2 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 {CaF}_2 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 {CaF}_2.

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

2014-05-01

74

Theory of Photochromic Centers in CaF2  

Microsoft Academic Search

On the basis of recent optical and EPR work, it has been suggested that the ionized and thermally stable photochromic centers in CaF2 consist of one and two electrons bound at an anion vacancy adjacent to a trivalent impurity cation. For the ionized center, we have shown that the energy levels and wave functions of the isolated F center are

R. Casanova Alig

1971-01-01

75

Experimental evidence for orientation property of Pb(Zr0.35Ti0.65)O3 by manipulating polar axis angle using CaF2 substrate  

NASA Astrophysics Data System (ADS)

Perfectly oriented (001), (101), and (111) Pb(Zr0.35Ti0.65)O3 (PZT) films were grown on identical (111)CaF2 substrates by metal-organic chemical vapor deposition. These films exclude domains parallel to the surface; therefore, all domains are actively switchable under the electric field between top and bottom electrodes. Saturation polarization values, Psat(001), Psat(101), and Psat(111), for these PZT films were 75, 50, and 43 ?C/cm2, respectively. This orientation dependency was in a good agreement with the theoretical relationship for a tetragonal PZT single crystal, where Psat(001)=Psat(101)/2=Psat(111)/3.

Utsugi, Satoru; Fujisawa, Takashi; Ehara, Yoshitaka; Yamada, Tomoaki; Matsushima, Masaaki; Morioka, Hitoshi; Funakubo, Hiroshi

2010-03-01

76

Bioengineering single crystal growth.  

PubMed

Biomineralization is a "bottom-up" synthesis process that results in the formation of inorganic/organic nanocomposites with unrivaled control over structure, superior mechanical properties, adaptive response, and the capability of self-repair. While de novo design of such highly optimized materials may still be out of reach, engineering of the biosynthetic machinery may offer an alternative route to design advanced materials. Herein, we present an approach using micro-contact-printed lectins for patterning sea urchin embryo primary mesenchyme cells (PMCs) in vitro. We demonstrate not only that PMCs cultured on these substrates show attachment to wheat germ agglutinin and concanavalin A patterns but, more importantly, that the deposition and elongation of calcite spicules occurs cooperatively by multiple cells and in alignment with the printed pattern. This allows us to control the placement and orientation of smooth, cylindrical calcite single crystals where the crystallographic c-direction is parallel to the cylinder axis and the underlying line pattern. PMID:21265521

Wu, Ching-Hsuan; Park, Alexander; Joester, Derk

2011-02-16

77

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

78

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

79

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

80

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

81

Growth of single crystal diamond  

Microsoft Academic Search

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

Murari Regmi

2007-01-01

82

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

83

Aligned single crystal boron nanowires  

Microsoft Academic Search

The well aligned boron nanowires (BNWs) with single crystalline structure were successfully prepared by using nanochannel-Al2O3 as a substrate and a chemical vapor deposition process. The diameter and length of BNWs were around of 40 nm and several micrometers, respectively. The formation of single crystal BNWs has been conceptually interpreted.

Q. Yang; J Sha; J Xu; Y. J Ji; X. Y Ma; J. J Niu; H. Q Hua; D. R Yang

2003-01-01

84

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

85

Radiation induced thermoluminescence in CaF 2:Tm detectors  

NASA Astrophysics Data System (ADS)

The fact that in CaF 2:Tm, thermoluminescence (TL) glow peaks occuring at different temperatures have different sensitivities to low and high LET radiations, has been found useful for the simultaneous and separate determination of fast neutron and gamma ray absorbed doses from therapeutically used neutron beams. The gamma ray and fast neutron responses of the individual glow peaks are found to be additive for separate and successive irradiations. A glow peak at 150° C which has a relatively smaller sensitivity to densely ionizing radiations, exhibit reduced sensitivity to high doses of even low LET radiations ( 60Co gamma rays). On heat treatment, the relative TL responses of 110, 150 and 240°C glow peaks are found to reduce in different proportions. In view of the present study, the various explanations for the difference in LET dependences of the glow peaks have been analysed.

Pradhan, A. S.; Rassow, J.

1987-03-01

86

Design and construction of systems for the single-crystals growth of ternary silver halides, alkali halides, and alkaline earth fluorides, and the dielectric investigation of silver halide  

NASA Astrophysics Data System (ADS)

Large single crystals of several congruently melting and incongruently melting compounds are produced for optics applications. The state diagrams of the quasi-binary silver halide system, are described and verified. The methods for the growth of single crystals from the melt, and from melting solutions, are outlined. The different developed crystal growth apparatus are described. Large single crystals of the congruently melting compounds NaCl, KBr, CsI, MgF2, CaF2, and the incongruently melting compounds RbAg4I5, Rb2AgBr3, AgPb2Br5, Ag3PbI5 are produced. The ionic conductivity of these synthetic ternary silver compounds is measured using a dielectric spectrometer.

Hueben-Riechert, Werner

87

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

88

Electron-surface interaction and metallization of the CaF2 (111)-surface studied by photothermal techniques  

NASA Astrophysics Data System (ADS)

The interaction of low energy electrons with the surface of alkaline-earth halides results in a variety of microscopical physical phenomena commonly described in terms of defect formation and diffusion, surface metallization and desorption of neutral- and charged particles. These processes are accompanied by local changes in the electronic and geometrical structure of bulk and surface and result in a variation of macroscopically measurable parameters like modulated optical reflectance and a deformation of the crystal lattice. In this paper it will be shown that photothermal analysis, that so far has mostly been used for the determination of optical and thermophysical properties of materials, is also capable of measuring defect related nonthermal phenomena apparent during electron irradiation of insulator surfaces. Experiments were performed with an intensity modulated electron beam of typically 1 ?A at 1 keV focused into a spot of 1 mm2 on the (111)-surface of a polished CaF2 single crystal under ultra-high vacuum conditions. Measurements revealed that modulated reflectance is sensitive to changes in optical properties induced by electron irradiation induced defects at low electron dosages. At a dosage level where metallization starts, a dramatic change in the modulated reflectance signal was observed indicating changes in electronic structure due to metal clustering at the surface. The photothermal displacement technique has been utilized to monitor surface deformations induced by electron bombardment. It was found that results cannot be explained by a thermo-elastic expansion model that works well for metal surfaces. Therefore, this technique can be used for the measurement of nonthermal contributions to lattice expansion resulting from volume changes of created defects.

Reichling, Michael

1994-03-01

89

Single Crystal Surfaces  

NASA Astrophysics Data System (ADS)

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

Aguilar-Santillan, Joaquin

2014-06-01

90

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

NASA Astrophysics Data System (ADS)

Tm3+ and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd-Ofelt parameters were calculated based on the absorption spectra, the smaller ?2 and larger ?6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 ?m emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 ?m in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:3H4+Tm3+:3H6-->2Tm3+:3H4, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

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

2010-05-01

91

Adsorption on Single Crystal Planes.  

National Technical Information Service (NTIS)

A working instrument has been developed and tested for measuring work functions of perfect single crystal planes. The longstanding high work function value (6.0 eV) for emission from the (110) plane of tungsten was investigated using the new FN plus energ...

R. D. Young H. E. Clark

1967-01-01

92

Long-range coulomb interaction of electrons of 4 f orbitals in impurity centers Yb3+: KZnF3, CsCaF3, and Sm3+: CaF2  

NASA Astrophysics Data System (ADS)

Expressions for calculating the matrix elements of the Coulomb interaction of f electrons of the isolated ion with an infinite crystal lattice have been obtained. The contribution of this interaction to the parameters of the crystal field in impurity centers Yb3+: KZnF3, CsCaF3, and Sm3+: CaF2 has been calculated.

Anikeenok, O. A.

2013-11-01

93

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

This program investigates the seemingly unusual behavior of single crystal airfoil materials. The fatigue initiation processes in single crystal (SC) materials are significantly more complicated and involved than fatigue initiation and subsequent behavior...

C. Annis

1992-01-01

94

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

This program investigates the seemingly unusual behavior of single crystal airfoil materials. The fatigue initiation processes in single crystal (SC) materials are significantly more complicated and involved than fatigue initiation and subsequent behavior...

D. P. DeLuca C. Annis

1993-01-01

95

Suitability of Glass-Encapsulated CAF2:Mn Thermoluminescent Dosimiters for Environmental Radiation Surviellance.  

National Technical Information Service (NTIS)

The suitability of glass-encapsulated CaF2:Mn thermoluminescent dosimeters for environmental radiation surveillance was investigated. More than two hundred dosimeters were subjected to extensive laboratory and field tests. Various parameters such as accur...

J. E. Partridge S. T. Windham J. L. Lobdell J. A. Oppold

1973-01-01

96

Composition and morphology studies of ultrathin CaF 2 epitaxial films on silicon  

Microsoft Academic Search

Thin CaF2 films with thicknesses between 1 and 100nm were grown on Si(111) at UHV conditions by evaporation from a CaF2 source. The correlation of film composition and growth morphology with the deposition parameters was studied by various techniques such as heavy-ion elastic recoil detection analysis (ERDA), RBS\\/channeling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and auger electron spectroscopy

W. Bohne; J. Rohrich; M. Schmidt; A. Schopke; B. Selle; R. Wurz

2001-01-01

97

High pressure optical studies of rare earth ions in CaF2 and other fluorides  

Microsoft Academic Search

High pressure optical absorption studies have been performed on a series of rare-earth ions Sm2+, Dy2+, Sm2+, and Tm2+ in CaF2, Tm2+ in SrF2, EuF2, and Gd3+ in CaF2. For the first five substances the transitions from the 4fn ground state to the 4fn ? 1 5d configuration shift to lower energy with increasing pressure. This is consistent with the

P. J. Wang; H. G. Drickamer

1973-01-01

98

Single Crystals (M = Fe, Co)  

NASA Astrophysics Data System (ADS)

FeGa3 and related compounds have been subjects of recent investigation for their interesting thermoelectric, electronic, and magnetic behaviors. Here, single crystals of FeGa3- y Ge y were grown by the self-flux technique with effective y = 0, 0.09(1), 0.11(1), and 0.17(1) in order to investigate the evolution of the diamagnetic semiconducting compound FeGa3 into a ferromagnetic metal, which occurs through the electron doping and band structure modifications that result from substitution of Ge for Ga. Heat capacity and magnetization measurements reveal non-Fermi liquid behavior in the vicinity of the transition from a paramagnetic to ferromagnetic ground state, suggesting the presence of a ferromagnetic quantum critical point (FMQCP). We also present the first results of hole doping in this system by the growth of FeGa3- y Zn y single crystals, and electron- and hole doping of the related compound CoGa3 by CoGa3- y Ge y and CoGa3- y Zn y crystal growths, aiming to search for further routes to band structure and charge carrier tuning, thermoelectric optimization, and quantum criticality in this family of compounds. The ability to tune the charge carrier type warrants further investigation of the MGa3 system's thermoelectric properties above room temperature.

Cabrera-Baez, M.; Magnavita, E. Thizay; Ribeiro, Raquel A.; Avila, Marcos A.

2014-06-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

100

Vapor-Deposited Single-Crystal Germanium  

Microsoft Academic Search

Germanium layers have been formed on single-crystal Ge substrates by the thermal decomposition of GeI2. The single-crystal nature of the layers has been established by x-ray and electron diffraction examination and by electrical measurements. The deposition process is described briefly. The crystal growth rate varies with crystal direction, and under certain conditions Ge whiskers appear. The layers as deposited are

Ralph P. Ruth; John C. Marinace; W. C. Dunlap

1960-01-01

101

Performance of Single Crystal Niobium Cavities  

Microsoft Academic Search

We have fabricated and tested a total of six single cell niobium cavities, made from single crystal, high purity niobium. Two of the three cavities of the TESLA shape (1300 MHz) were made from Heraeus niobium by extending a smaller single crystal by rolling and annealing steps; the third cavity was made by spinning from CBMM material. The three other

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

2008-01-01

102

Nanoindentation of gold single crystals  

NASA Astrophysics Data System (ADS)

Nanoindentation is an increasingly used tool to investigate the mechanical properties of very small volumes of material. Gold single crystals were chosen as a model system for surface modification studies, because of the electrochemical advantages and the simple structure of the material. Experiments on these samples displayed a spectrum of residual deformation, with measured hardness values on the same surface differing by over a factor of two. The yield point also exhibited considerable variation, but the depth of penetration was independent of this elastic-plastic transition. The onset of plastic deformation in these tests is observed at stress levels on the order of the theoretical yield strength. There are a limited number of defects in a single crystal specimen of gold, especially on the length scale required to influence nearly every indentation experiment. A test matrix was designed to change the concentrations of possible defects in a sample (dislocations, vacancies, and structural features), by altering some of the surface preparation parameters. The results of these experiments were extremely consistent. Observed trends within the matrix, combined with the observations of reduced hardness and earlier plasticity when compared to the preliminary testing, indicate a decline in the structural continuity of the sample. This is surprising considering the extensive material removal and thermal history of some of these surfaces. There is no indication of a cause for the dramatic inconsistencies in mechanical properties observed in preliminary testing, but a consistent surface enables the study of intentional modifications. Changes in contact area that were undetectable in preliminary results now demonstrate predictable shifts in hardness values. The deposition of a single monolayer of gold oxide raised the average load at yield by a factor of three and increased the hardness by over 26%. Attributing this change to the oxide is corroborated by the reduction of hardness when the oxide is stripped. Similar behavior is observed when a lead monolayer is deposited and tested ex-situ. It is surprising that layers <0.5 nm in thickness would have such a dramatic influence on indentation tests at least 35 nm deep. This indicates that no surface layer can be ignored at this scale. These experiments demonstrate that there is still much to be learned about nanoscale deformation mechanisms.

McCann, Martha Mary

103

Windows for HF/DF chemical lasers - CaF2 or ZnSe  

NASA Astrophysics Data System (ADS)

An investigation of laser-driven phenomena occurring in CaF2 and ZnSe window materials which affect the performance of high energy laser systems at chemical wavelengths is reported. The systems studied comprised an optical cavity, relay tube, beam expander, and output window to the focus. An analysis of the cumulative phaseshifts due to beam defocusing and distortion caused by thermally generated aberrations in the window is performed to determine an expression for the degradation in focal intensity. Optical distortion coefficients are derived for laser beams passing through a solid window, and specifically for polycrystalline CaF2 and ZnSe, along with other elastic, optical, and elastic properties. Performance evaluations are analytically compared for the two materials, and CVD ZnSe windows are found suitable for maximizing peak irradiance, while CaF2 is useful for optimizing energy delivery capabilities of HF/DF lasers.

Klein, C. A.

104

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

105

Fabrication of microlens arrays in CaF2 by ion milling  

NASA Astrophysics Data System (ADS)

Calcium Fluoride microlens arrays have been produced with the help of an ion milling transfer of photoresist lenses which have been fabricated by two different techniques (i) by a melting resist technique and (ii) gray scale lithography. Major technical problems connected with the ion milling transfer of the photoresist lenses in the CaF2 material are surface roughness enhancement and variation of the lens shape. We studied the ion-induced decomposition of CaF2 and the surface roughness equatio in dependence on different milling conditions. For the microlens patter transfer the ratio of etching rates of the photoresist and the CaF2 have been adjusted by gas admixture of nitrogen to the Ar sputtering gas. The angle dependence of the etching rates leads also to a changing of the lens profile. The effect of ion beam induced surface roughness and the accuracy of the transfer process is discussed.

Flamm, Dieter; Schindler, Axel; Harzendorf, Torsten; Kley, Ernst-Bernhard

2000-08-01

106

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

107

Dislocation Distribution in Deformed Copper Single Crystals.  

National Technical Information Service (NTIS)

Observations of dislocation distribution in copper single crystals oriented for single glide and deformed at low temperatures are described. In stage I the dislocation population consists mainly of bundles of long edge dislocations belonging to the primar...

Z. S. Basinski

1964-01-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

109

Femtosecond laser ablation of CaF2: Plasma characterization and thin films deposition  

NASA Astrophysics Data System (ADS)

Nanostructured thin films of CaF2 have been deposited in vacuum by ultra-short pulse laser ablation. The laser-induced plasma, characterized by optical emission spectroscopy and ICCD fast imaging, shows the presence of Ca and F atomic species, neutral and ionized, together with the CaF molecular species. Although continuous blackbody-like emission has not been detected from the plasma, the deposited films, characterized by Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are apparently formed by the coalescence of a large number of nanoparticles composed by stoichiometric CaF2.

De Bonis, A.; Santagata, A.; Galasso, A.; Sansone, M.; Teghil, R.

2014-05-01

110

Confinement stabilises single crystal vaterite rods.  

PubMed

Single-crystals of vaterite, the least-stable anhydrous polymorph of CaCO3, are rare in biogenic and synthetic systems. We here describe the synthesis of high aspect ratio single crystal vaterite rods under additive-free conditions by precipitating CaCO3 within the cylindrical pores of track-etch membranes. PMID:24676457

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

2014-04-01

111

Single crystal growth of actinide compounds  

Microsoft Academic Search

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

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

1985-01-01

112

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

113

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

114

Fabrication of microlens arrays in CaF2 by ion milling  

Microsoft Academic Search

Calcium Fluoride microlens arrays have been produced with the help of an ion milling transfer of photoresist lenses which have been fabricated by two different techniques (i) by a melting resist technique and (ii) gray scale lithography. Major technical problems connected with the ion milling transfer of the photoresist lenses in the CaF2 material are surface roughness enhancement and variation

Dieter Flamm; Axel Schindler; Torsten Harzendorf; Ernst-Bernhard Kley

2000-01-01

115

Spectroscopie et fonctionnement laser de CaF{2}: Yb3+  

NASA Astrophysics Data System (ADS)

CaF{2 }:Yb3+ est un cristal doté de propriétés optiques et thermiques qui en font un matériau de choix pour divers types de fonctionnement laser. Un fonctionnement laser continu accordable entre 1000 et 1060nm et un rendement de conversion de 25% (par rapport au rayonnement de pompage optique incident) ont été déjà obtenus.

Camy, P.; Doualan, J. L.; Petit, V.; Renard, S.; Thuau, M.; Moncorgé, R.

2004-11-01

116

Effect of CaF2 on Interfacial Phenomena of High Alumina Refractories with Al Alloy  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to investigate the interfacial phenomena between Al-alloy and industrial grade high alumina refractories containing varying contents of CaF2 at 1250 °C. Interfacial reaction products and phases formed in the heat-treated refractory samples were characterized using electron probe microanalysis (EPMA) and X-ray diffraction (XRD), respectively, while interfacial phenomena including dynamic wetting behavior were analyzed using the sessile drop technique. Refractories containing less than 5 wt pct CaF2 showed good resistance to reactions with the molten alloy, due to the dominance of corundum, and the presence of anorthite at the interface. However, with a further increase in the additive content, a glassy matrix of anorthite with CaF2 was formed. Formation of this phase significantly increased the intensity of reactions resulting in the buildup of an interfacial layer. The study thus revealed the strong catalytic effect of CaF2 on reactions of high alumina refractories with Al-alloy.

Koshy, Pramod; Gupta, Sushil; Sahajwalla, Veena; Edwards, Phil

2008-08-01

117

Single crystal research — Crystal quality control — Industrial production  

Microsoft Academic Search

A summary is given of the tasks involved in improving crystal quality, their interrelations and the organizational framework\\u000a required for completing them. The possibilities inherent in single crystal research for the development of industrial products\\u000a are demonstrated.

R. Voszka

1985-01-01

118

Seeded Single Crystal Silicon Carbide Growth and Resulting Crystals.  

National Technical Information Service (NTIS)

A method is disclosed for producing a high quality bulk single crystal of silicon carbide in a seeded growth system and in the absence of a solid silicon carbide source, by reducing the separation between a silicon carbide seed crystal and a seed holder u...

D. P. Malta H. M. Hobgood J. R. Jenny M. Brady S. G. Mueller

2005-01-01

119

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

120

Color Centers in Cesium Halide Single Crystals  

Microsoft Academic Search

Color centers have been investigated in the CsCl-type alkali halides. Cesium chloride, bromide, and iodide single crystals were grown from the melt and CsCl crystals also from solution. Coloration was produced by 130-kv x rays, 3.0-Mev electrons, and by electrolysis. In CsI coloration resulted from electrolysis only. The absorption of uncolored and colored crystals has been measured from 0.175 to

Peter Avakian; A. Smakula

1960-01-01

121

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)  

NASA Astrophysics Data System (ADS)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ˜2 × 103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ˜20 nm in the sample.

Nikolaichik, V. I.; Sobolev, B. P.; Zaporozhets, M. A.; Avilov, A. S.

2012-03-01

122

Neutron irradiation effects on YBCO single crystals.  

National Technical Information Service (NTIS)

Fast neutron irradiation of YBCO single crystals has proved to result in significant increases of magnetization hysteresis and consequently an enhancement of critical current densities. In addition, shifts of the irreversibility line have been observed. B...

F. M. Sauerzopf H. P. Wiesinger H. W. Weber G. W. Crabtree

1991-01-01

123

Molybdenum-Reinforced Aluminum Oxide Single Crystals.  

National Technical Information Service (NTIS)

Molybdenum wire-reinforced aluminum oxide single crystals have been fabricated by the heat exchanger method of seeded unidirectional solidification. No interfacial reaction products were observed and cathodoluminescent evaluation indicated a good diffusio...

J. W. McCauley F. Schmid D. J. Viechnicki

1979-01-01

124

Investigation of Growth of Electromagnetic Single Crystals.  

National Technical Information Service (NTIS)

Research was carried out on the growth of single crystals of plain and doped sapphire, ruby, spinel, yttrium oxide, magnesium titanate, yttrium iron garnet, beryl, cerium molybdate, lanthanum molybdate, sodium ferrite, and high melting fluorides. The meth...

C. M. Cobb J. A. Adamski E. B. Wallis

1964-01-01

125

Mechanistic study for heterogeneous product growth in topochemical single-crystal-to-single-crystal transformation  

Microsoft Academic Search

Kinetic evaluation for the solid-state reaction of 1,4-dithiin\\/anthracene mixed single crystal proved the mechanism of the anisotropic heterogeneous propagation during the single-crystal-to-single-crystal transformation. The number of hydrogen bonds in the reactive molecule is directly correlated with the activation energy for the reaction––the ‘chain’ character of solid-state propagation being triggered by the breaking of the C–H?O hydrogen bonds.

Jae Hong Kim; Jae Yun Jaung; Sung Hoon Jeong

2003-01-01

126

Linear analytical theory of a transformation from a single crystal A to another single crystal B  

Microsoft Academic Search

An isothermal phase transformation from a single crystal A to another single crystal B is theoretically investigated along preferred lines (Rosiwal's lines). It is supposed that the nuclei of the B-phase are Poisson distributed within the single crystal A. From these nuclei the B-grains grow instantaneously, equioriented, and in the form of cuboids with three different growth ratesvx,vy andvz. If

G. E. W. Schulze; H.-P. Wilbert

1987-01-01

127

Transition metal complexes with oligopeptides: single crystals and crystal structures.  

PubMed

The coordination chemistry of short chain peptides with transition metals is described in terms of the available crystal structures. Despite their high interest as synthetic models for metalloproteins and as building blocks for molecular materials based on the tuneable properties of oligopeptides, single crystal X-ray diffraction studies are scarce. A perusal of the most relevant results in this field allows us to define the main characteristics of oligopeptide-metal interactions, the fundamental problems for the crystallization of these complexes, and some hints to identify future promising approaches to advance the development of metallopeptide chemistry. PMID:24874062

Lillo, Vanesa; Galán-Mascarós, José Ramón

2014-07-14

128

Performance of Single Crystal Niobium Cavities  

SciTech Connect

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

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

2008-07-01

129

Nanostructures induced by highly charged ions on CaF2 and KBr  

Microsoft Academic Search

Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold

S. Facsko; W. Meissl; R. Heller; R. Wilhelm; A. S. El-Said; G. Kowarik; R. Ritter; F. Aumayr

2009-01-01

130

Persistent spectral hole burning in deuterated CaF2:Tm3+  

Microsoft Academic Search

We report spectral hole burning in the deuteride (D-) modified Tm3+ centers in CaF2, where the hole burning mechanism is known to involve localized displacement of the D- ions. Two main families of Tm3+-D- centers are present; the Li centers yield spectral holes that have been measured to be fully persistent for 48 hours at liquid-helium temperatures, while spectral holes

N. M. Strickland; R. L. Cone; R. M. Macfarlane

1999-01-01

131

The kinetics of CaF 2 metallization induced by low-energy electron irradiation  

Microsoft Academic Search

Results of experimental and theoretical studies on metal colloid growth after irradiation and subsequent heating of CaF2 are presented. Samples at a temperature of 200 K were irradiated in UHV for 30 min with 2.5 keV electrons. After irradiation samples were heated at a rate of about 1 K\\/min and colloid formation was investigated by optical extinction spectroscopy. Colloid radii

M. Huisinga; N. Bouchaala; R. Bennewitz; E. A. Kotomin; M. Reichling; V. N. Kuzovkov; W. von Niessen

1998-01-01

132

Surface colloid evolution during low-energy electron irradiation of CaF 2(111)  

Microsoft Academic Search

The effects of 1 keV electron irradiation (current density typically 40 ?A cm?2) on the surface structure of CaF2 (111) are studied by scanning force microscopy (SFM) to investigate the role of diffusion in the process of electron-induced surface metal colloid formation. Systematic variation of beam voltage, irradiation time, intensity and dosage is investigated in regard to metal formation on

M. Reichling; R. M. Wilson; R. Bennewitz; R. T. Williams; S. Gogoll; E. Stenzel; E. Matthias

1996-01-01

133

Conductivity enhancement of caf 2 by grain boundary activation with lewis acids  

Microsoft Academic Search

CaF2 fine powder and films were treated with the Lewis acids SbF5 and BF3 to create a strong driving force to draw F? ions out of the boundary regions according to L (surface) + FF (boundary) ? LF? (surface) + VF (boundary) (L = SbF5 or BF3). The conductivity results of polycrystalline ceramics treated in this way indicate a significant

Yuria Saito; Joachim Maier

1996-01-01

134

High quality ultrathin Bi2Se3 films on CaF2 and CaF2/Si by molecular beam epitaxy with a radio frequency cracker cell  

NASA Astrophysics Data System (ADS)

We report a method to fabricate high quality Bi2Se3 thin films using molecular beam epitaxy with a radio frequency cracker cell as an atomic selenium source. With Se-to-Bi ratios close to exact stoichiometry, optimal layer-by-layer growth of high quality Bi2Se3 thin films with smooth surfaces has been achieved on CaF2(111) substrates and Si(111) substrates with a thin epitaxial CaF2 buffer layer (CaF2/Si). Transport measurements show a characteristic weak-antilocalization magnetoresistance in all the films, with the emergence of a weak-localization contribution in the ultrathin film limit. Quantum oscillations, attributed to the topological surface states have been observed, including in films grown on CaF2/Si.

Zhang, Li; Hammond, Robert; Dolev, Merav; Liu, Min; Palevski, Alexander; Kapitulnik, Aharon

2012-10-01

135

Sintering of CaF 2 pellets as nuclear fuel analog for surface stability experiments  

NASA Astrophysics Data System (ADS)

To enable a detailed study of the influence of microstructure and surface properties on the stability of spent nuclear fuel, it is necessary to produce analogs that closely resemble nuclear fuel in terms of crystallography and microstructure. One such analog can be obtained by sintering CaF 2 powder. This paper reports the microstructures obtained after sintering CaF 2 powders at temperatures up to 1240 °C. Pellets with microstructure, density and pore structure similar to that of UO 2 spent nuclear fuel pellets were obtained in the temperature range between 900 °C and 1000 °C. When CaF 2 was sintered above 1100 °C the formation of CaO at the grain boundaries caused the disintegration of the pellet due to hydration occurring after sintering. First results from a novel set-up of dissolution experiments show that changes in roughness, dissolution rate and etch pit shape of fluorite surfaces are strongly dependent on the crystallographic orientation of the expose surface. Consequently, the differences observed for each orientation will affect the overall dissolution rate and will lead to uncertainties in the estimation of dissolution rates of spent nuclear fuel.

Godinho, José R. A.; Piazolo, Sandra; Stennett, Martin C.; Hyatt, Neil C.

2011-12-01

136

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

137

Study of electronic sputtering of CaF2 thin films  

NASA Astrophysics Data System (ADS)

In the present work thin films of CaF2 deposited on Si substrate by electron beam evaporation have been investigated for swift heavy ions induced sputtering and surface modifications. Glancing angle X-ray Diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was performed to determine the sputter yield of CaF2 and a decrease in sputter yield has been observed with increase in film thickness. Thermal spike model has been applied to explain this. The confinement of energy in the grains having size smaller than the electron mean free path (?) results in a higher sputtering yield. Atomic force microscopy (AFM) studies of irradiated CaF2 thin films show formation of cracks on film surface at a fluence of 5 × 1012 ions/cm2. Also RBS results confirm the removal of film from the surface and more exposure of substrate with increasing dose of ions.

Pandey, Ratnesh K.; Kumar, Manvendra; Khan, Saif A.; Kumar, Tanuj; Tripathi, Ambuj; Avasthi, D. K.; Pandey, Avinash C.

2014-01-01

138

Oxygen incorporation in rubrene single crystals.  

PubMed

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

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

2014-01-01

139

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

140

Neutron detection with single crystal organic scintillators  

SciTech Connect

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

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

2009-07-15

141

Oxygen Incorporation in Rubrene Single Crystals  

PubMed Central

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

2014-01-01

142

??-SnSb single crystals obtained by the method of inclined front crystallization  

Microsoft Academic Search

?? phase plates of single crystals of SnSb alloy were obtained by using a modification of the horizontal Bridgman method. It was ascertained that during crystallization the single crystals grow in the upper layer of the charge. It was found that the thickness of the single crystal (single crystal layer) and also its relative antimony content, depend on the growth

W. Bogdanowicz; Z. Bojarski

1995-01-01

143

Single-Crystal-to-Single-Crystal Transformations in One Dimensional Ag-Eu Helical System  

SciTech Connect

Single-crystal-to-single-crystal transformation of 1-D 4d-4f coordination polymers have been investigated for the first time. It displays high selectivity for Mg2+ and can be used as magnesium ion-selective luminescent probe. More importantly, we observed the transformation of meso-helical chain to rac-helical chain as a function of temperature.

Cai, Yue-Peng; Zhout, Xiu-Xia; Zhout, Zheng-Yuan; Zhu, Shi-Zheng; Thallapally, Praveen K.; Liu, Jun

2009-07-06

144

Self-diffusion in naphthalene single crystals  

Microsoft Academic Search

Studies of self-diffusion in pure single crystals of naphthalene have been carried out by a sectioning method, using a 14C labelled tracer. The effects of impurity content and pre-annealing upon the diffusion process “were examined. Diffusion coefficients are low compared to those found for other solid systems. In the best available crystals self-diffusion can be described by an equation D

J. N. Sherwood; D. J. White

1967-01-01

145

Single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

146

Czochralski single crystal growth, modeling, and characterization of ilmenite  

Microsoft Academic Search

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

Jayakumar Muthusami

1998-01-01

147

Effect of pressure on the optical absorption of REF centers in Ce and Tb doped CaF2  

Microsoft Academic Search

The effect of pressure to 80 kbar has been measured on the absorption peaks associated with REF centers in Ce and Tb doped CaF2. The results are compared with previous data for Gd doped CaF2. The lowest and highest energy excitations [?(1E) and ?(2E)] are associated with an excited state largely of metal 5d(eg) character. The intermediate peak has predominantly

W. D. Drotning; H. G. Drickamer

1973-01-01

148

Single-Crystal Springs For Accelerometers  

NASA Technical Reports Server (NTRS)

Thermal noise reduced, enabling use of smaller proof masses. Spring-and-mass accelerometers in which springs made of single-crystal material being developed. In spring-and-mass accelerometer, proof mass attached to one end of spring, and acceleration of object at other end of spring measured in terms of deflection of spring, provided frequency spectrum of acceleration lies well below resonant frequency of spring-and-proof-mass system. Use of single-crystal spring materials instead of such polycrystalline spring materials as ordinary metals makes possible to construct highly sensitive accelerometers (including seismometers) with small proof masses.

Vanzandt, Thomas R.; Kaiser, William J.; Kenny, Thomas W.

1995-01-01

149

LETTERS TO THE EDITOR: New crystal lasers utilizing disordered fluoride crystals activated with Nd3+ ions pumped by semiconductor laser radiation  

NASA Astrophysics Data System (ADS)

Diode laser pumping was used to excite for the first time single-mode cw lasing of Nd3+ ions (4F3/2?4I11/2 transition at 300 K) in disordered fluoride crystals (CaF2-YF3, SrF2-GdF3, BaF2-YF3, and BaF2-LaF3).

Kaminski?, A. A.; Verdún, H. R.

1992-02-01

150

Inkjet printing of single-crystal films  

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

151

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

152

CVD-diamond single-crystal growth  

NASA Astrophysics Data System (ADS)

The synthesis of diamond volume crystals is of particular interest due to the material's outstanding physical and mechanical properties. Various techniques are pursued by numerous research groups. In hot-filament CVD (HF-CVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized. These parameters are far beyond growth conditions for HF-CVD diamond coating processes. Extremely low methane content in the feed gas along with high substrate temperatures allows single diamond nuclei of a certain minimum size to grow stable. Crystals up to 100 ?m in diameter were successfully synthesized on ultrasonic pretreated substrates. They were characterized by SEM and Raman spectroscopy. A model for the observed exclusive growth of sufficiently large nuclei is presented. Based on well accepted diamond growth models, an advanced growth theory for the different morphologies and diamond qualities at the {1 0 0} and {1 1 1} faces of the crystals is postulated. The results give bases on which growing processes can be optimized and upscaled in order to evaluate the applicability of the method for single-crystal diamond growth.

Schwarz, S.; Rottmair, C.; Hirmke, J.; Rosiwal, S.; Singer, R. F.

2004-11-01

153

Scientific Review: The Single Crystal Diffractometer RESI  

Microsoft Academic Search

The single crystal diffractometer RESI (REciprocal Space Investigator) provides powerful techniques for structure research using thermal neutrons. With its unique setup of a kappa-goniometer and a neutron sensitive imaging plate, it is very well-suited for recording Bragg data, in particular, on samples with large unit cells, incommensurate structures, phase transitions, or dense patterns of reflections (quasicrystals). It is also designed

Björn Pedersen; Friedrich Frey; Wolfgang Scherer

2007-01-01

154

Multiphonon relaxation in YVO4 single crystals  

Microsoft Academic Search

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

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

2000-01-01

155

Growth and Properties of Hydorxyapatite Single Crystals.  

National Technical Information Service (NTIS)

Four methods were attempted for the growth of large single crystals of hydroxyapatite: hydrothermal synthesis, growth in gels under hydrothermal conditions, growth in aqueous solution at 100C, and growth under conditions where the pH is controlled by the ...

J. F. Kirn H. Leidheiser

1967-01-01

156

Fracture in single crystal NiTi  

Microsoft Academic Search

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

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

2008-01-01

157

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.

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

158

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

PubMed

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

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

159

Single crystal tungsten kinetic energy penetrators  

SciTech Connect

We have explored the terminal ballistic performance of single crystal tungsten as a kinetic energy penetrator. Scientific speculation as to the anticipated penetration performance and nature of the interaction between such a kinetic energy penetrator and semi-infinite and spaced metallic targets has led us to perform laboratory scale experiments and metallographic examinations of post-impact penetrator materials. The single tungsten crystals were ground into kinetic energy penetrators with the [l angle]111[r angle] and [l angle]100[r angle] crystal direction being coincident with the axis of symmetry of the penetrators. The crystals were electro-polished to their final diameter. We, compared the terminal performance at current ordnance speeds of [l angle]111[r angle] single crystal tungsten to 90W-10 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against a spaced steel (triple) target at sixty-five degrees obliquity. We also compared the terminal performance of [l angle]100[r angle] and [l angle]111[r angle] single crystal tungsten with 90W-10 and 98W02 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against monolithic 4340 alloy steel (HRC = 36) at normal impact. We radiographed the penetrators during the interactions with the targets, we recovered portions of the penetrators after the ballistic experiments, and we conducted metallographic examinations of penetrator remnants. From the radiographic records and the metallographic examinations, we drew conclusions pertaining to insights into the terminal interactions of the penetrators with the targets and suggestions as to improved compositions of the cemented tungsten penetrators.

Cline, C.F.; Gogolewski, R.P.

1992-05-01

160

Single crystal tungsten kinetic energy penetrators  

SciTech Connect

We have explored the terminal ballistic performance of single crystal tungsten as a kinetic energy penetrator. Scientific speculation as to the anticipated penetration performance and nature of the interaction between such a kinetic energy penetrator and semi-infinite and spaced metallic targets has led us to perform laboratory scale experiments and metallographic examinations of post-impact penetrator materials. The single tungsten crystals were ground into kinetic energy penetrators with the {l_angle}111{r_angle} and {l_angle}100{r_angle} crystal direction being coincident with the axis of symmetry of the penetrators. The crystals were electro-polished to their final diameter. We, compared the terminal performance at current ordnance speeds of {l_angle}111{r_angle} single crystal tungsten to 90W-10 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against a spaced steel (triple) target at sixty-five degrees obliquity. We also compared the terminal performance of {l_angle}100{r_angle} and {l_angle}111{r_angle} single crystal tungsten with 90W-10 and 98W02 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against monolithic 4340 alloy steel (HRC = 36) at normal impact. We radiographed the penetrators during the interactions with the targets, we recovered portions of the penetrators after the ballistic experiments, and we conducted metallographic examinations of penetrator remnants. From the radiographic records and the metallographic examinations, we drew conclusions pertaining to insights into the terminal interactions of the penetrators with the targets and suggestions as to improved compositions of the cemented tungsten penetrators.

Cline, C.F.; Gogolewski, R.P.

1992-05-01

161

Lattice location and annealing studies of Hf implanted CaF 2  

Microsoft Academic Search

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the ?110? crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of

Thomas Geruschke; Katharina Lorenz; Eduardo Alves; Reiner Vianden

2009-01-01

162

Photoluminescence of C60 Single Crystals  

NASA Astrophysics Data System (ADS)

The photoluminescence (PL) spectra of C60 single crystals grown under double temperature gradient (DTG) and single temperature gradient (STG) techniques were investigated at room temperature. The results show that the PL emission intensity increases first and then decreases with increasing illuminated power density for the C60 single crystals grown by both DTG and STG techniques. Furthermore, one main peak with a shoulder peak can be clearly distinguished at low illumination, while only one main peak without the shoulder peak can be seen at high illumination. The main peak undergoes a continuous blue shift and broadening with the increase of illuminated power density. The difference of PL emission energy at the same illumination density of DTG and STG samples may correlated with the degree of both the orientational disorder of C60 molecule and lattice perfectness. The Laue diffraction patterns show that the DTG sample has stronger strains and poorer crystalline quality than the STG sample.

Li, Chaorong; Wang, Gang; Zhang, Jiaming; Mai, Zhenhong; Zhao, Tienan; Xu, Lu; Xie, Sishen

1995-05-01

163

Neutron Scattering Study of Single Crystal PZT  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

164

Nanostructures induced by highly charged ions on CaF2 and KBr  

NASA Astrophysics Data System (ADS)

Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold the structure size increases linearly with potential energy. The mechanisms for the formation of hillocks and pits are discussed and a first attempt to present a unified microscopic picture is made.

Facsko, S.; Meissl, W.; Heller, R.; Wilhelm, R.; El-Said, A. S.; Kowarik, G.; Ritter, R.; Aumayr, F.

2009-11-01

165

Effect of porosity on impedance of CaF2 ceramic  

NASA Astrophysics Data System (ADS)

Ceramic samples of CaF2 were characterized using impedance spectroscopy to understand the effect of porosity on electrical conductivity upto 150°C. Pellets of cold pressed nano powder as well as those sintered at high temperature and transparent ceramic were investigated. The room temperature conductivity of porous samples (cold pressed and sintered at 700°C) were found to be more than less porous samples (sintered at 1000°C and transparent ceramic). The conductivity was found to increase as the temperature is increased till 100°C and decreases on further increase in temperature. At 150°C transparent ceramic sample shows the maximum conductivity.

Sen, Shashwati; Mittal, Garima; Deshpande, S. K.; Gadkari, S. C.

2013-02-01

166

Microstructure and properties of the composite magnets fabricated with Nd-Fe-B powders coated with CaF2  

NASA Astrophysics Data System (ADS)

Nd-Fe-B powders were coated with CaF2 by three different chemical synthesis methods, named as A: One-step direct precipitation, B: One-step slow dropping, and C: Two-step process. The CaF2-coated Nd-Fe-B powders were hot-pressed and then hot-deformed to fabricate composite magnets. The microstructures, electrical resistivities, and magnetic properties of the Nd-Fe-B composite magnets obtained with different coating methods and parameters were investigated. The results showed that the thickness and continuity of CaF2 coating depended on the coating methods with different Ca(NO3)2 concentrations and coating time. When the Ca(NO3)2 concentration was 2 mol/l, the CaF2 coating synthesized by one-step direct precipitation was a loose and discontinuous film, while the CaF2 coating synthesized by one-step dropping for 30 min was a continuous and dense film, and its thickness reached to 410-450 nm. If the Ca(NO3)2 concentration was further increased to 5.5 mol/l, the thickness of CaF2 reached to 710-900 nm. The electrical resistivities of the composite magnets prepared by one-step slow dropping for 30 min with the Ca(NO3)2 concentrations of 2 and 5.5 mol/l were approximately 680 and 890 ?? cm, which was a 195% and 287% increase, respectively, compared to that of the corresponding magnet prepared with uncoated Nd-Fe-B powders. The coercivities of the composite magnets decreased with increasing thickness of CaF2, while the remanence had only a slight reduction. The composite magnet fabricated by a two-step process achieved both higher maximum energy product ((BH)m = 47.2 MG Oe) and electrical resistivity (847 ?? cm).

Zheng, Liyun; Xin, Honghui; Bi, Wenchao; Zhu, Minggang; Li, Wei; Zhou, Dong

2014-05-01

167

Polar phonons in SO 2 single crystal  

NASA Astrophysics Data System (ADS)

The Raman spectrum of a single SO 2 crystal in various polarization geometries has been measured at 20 K and discussed in terms of LO and TO components of polar crystal modes. Lattice phonons have been assigned on the basis of their behaviour with polarization. Lattice dynamical calculations on both the internal and lattice phonons are in good agreement with experimental data. Using gas-phase transition dipole moments and a dipole—dipole intermolecular potential the angular dispersion of fundamental vibrons has been calculated. For lattice phonons, a combination of atom—atom and electrostatic potential reproduces not only the phonon frequencies but, for polar phonons, also their LO—TO splitting.

Tafi, A.; Procacci, P.; Castellucci, E.; Salvi, P. R.

1991-03-01

168

THERMAL STRESS ANALYSIS OF TETRAGONAL SINGLE CRYSTAL DURING GROWTH PROCESS : PMO SINGLE CRYSTAL  

Microsoft Academic Search

A three-dimensional finite element computer code was developed to deal with thermal stress analyses of tetragonal single crystals during the growth. They have the crystal anisotropy, so three-dimensional analysis is required for calculation of the thermal stress, even though they have axisymmetrical shapes. A tensor transformation technique was used to obtain the components of elastic constant matrix and thermal strain

N. Miyazaki; Y. Matsuura; D. Imahase

169

Defect formation in BAF 2 crystals doped with cadmium  

NASA Astrophysics Data System (ADS)

Defect formation in BaF 2 single crystals doped with cadmium is investigated by optical absorption, electron paramagnetic resonance (EPR) and thermoluminescence. An optical absorption band observed in X-irradiated at 295 K crystals CaF 2 (at 3.8 eV), SrF 2 (at 3.95 eV) and BaF 2 (at 4.08 eV) is assigned to absorption of Cd +-ions. In addition, two type hole centers: pure V k and perturbed V k-centers, are observed in BaF 2-1%CdF 2 crystals X-irradiated at 77 K.

Nepomnyashchikh, A. I.; Radzhabov, E. A.; Egranov, A. V.; Ivashechkin, V. F.; Istomin, A. S.; Kurobori, T.

2005-01-01

170

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

171

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

172

SSME single crystal turbine blade dynamics  

NASA Technical Reports Server (NTRS)

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

Moss, Larry A.; Smith, Todd E.

1987-01-01

173

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

174

Optical properties of some borate single crystals  

NASA Astrophysics Data System (ADS)

This paper describes efforts taken in Institute of Applied Physics and Institute of Electronic Materials Technology to obtain several single crystals from borate family, namely, CsLiB6)10, Ca4GdO(BO3)3, Li2B4O7, (beta) -BaB2O4, and Yal3(BO3)4, pure and doped with several ions. The main goal of this investigation was to develop technology of these new nonlinear optical materials to create possibility of their applications in higher harmonics generators and self- frequency doubling lasers. Depending on such properties of crystallized borate materials as incongruent melting or high temperature phase transitions, Czochralski technique or high temperature solution growth technique were used. The main aspects of crystallization of these materials as well as their optical properties are discussed.

Majchrowski, Andrzej; Lukasiewicz, Tadeusz; Mierczyk, Zygmunt; Malinowski, Michal

2001-08-01

175

Crack growth in single-crystal silicon  

NASA Technical Reports Server (NTRS)

Crack growth in single-crystal silicon at room temperature in air was evaluated by double torsion (DT) load-relaxation method and monitored by acoustic emission (AE) technique. Both DT and AE methods indicated lack of subcritical crack growth in silicon. At the critical stress intensity factor, the crack front was found to be jumping several times in a 'mirror' region and then followed by fast crack growth in a 'hackle' region. Hackle marks were found to be associated with plastic deformation at the tip of the fast moving crack. No dislocation etch pits were found in the 'mirror' region, in which crack growth may result from interatomic bonds broken at the crack tip under stress without any plastic deformation. Acoustic emission appears to be spontaneously generated from both interatomic bonds broken and dislocation generation at the moving crack tip during the crack growth in single-crystal silicon.

Chen, C. P.; Leipold, M. H.

1986-01-01

176

Bridgman growth of paratellurite single crystals  

Microsoft Academic Search

The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120mm long and 25mm in diameter were obtained under a temperature gradient of 10°Ccm?1 and translation rates lower than 0.6mmh?1. The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth

P. Veber; J. Mangin; P. Strimer; P. Delarue; C. Josse; L. Saviot

2004-01-01

177

Crack Growth in Single-Crystal Silicon  

NASA Technical Reports Server (NTRS)

Report describes experiments on crack growth in single-crystal silicon at room temperature in air. Crack growth in (111) cleavage plane of wafers, 50 by 100 by 0.76 mm in dimension, cut from Czochralski singlecrystal silicon studied by double-torsion load-relaxation method and by acoustic-emission measurements. Scanning electron microscopy and X-ray topography also employed. Results aid in design and fabrication of silicon photovoltaic and microelectronic devices.

Chen, C. P.; Leipold, M. H.

1986-01-01

178

Q-1 of forsterite single crystals  

Microsoft Academic Search

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

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

1989-01-01

179

Single crystal cylinder transducers for sonar applications  

NASA Astrophysics Data System (ADS)

A segmented cylinder transducer constructed of single crystal lead magnesium niobate-lead titanate (PMN-PT) has been under development at NUWC and EDO Corporation for several years. The purpose of this development was to provide an extremely compact, high power broadband source. By virtue of their extraordinary material properties, ferroelectric single crystals are the ideal transduction material for developing such compact broadband systems. This presentation shall review the evolution of the transducer design as well as present the results of a successful in-water test conducted at NUWC in October of 2003. It shall be shown that design changes intended to eliminate spurious modes limiting the transducer bandwidth first observed in 2002 were successful, resulting in a transducer with a clean frequency response and an effective coupling factor of 0.85. The measured transducer admittance was in nearly exact agreement with theoretical predictions. The NUWC in-water tests demonstrated that the single crystal cylinder achieved an admittance bandwidth (based on the Stansfield criterion) of over 100%, while the tuned power factor was 0.8 or more over 2.5 octaves of frequency. Additionally, the transducer produced 12 dB higher source levels than a similarly sized PZT transducer. [Work sponsored by DARPA.

Robinson, Harold; Stevens, Gerald; Buffman, Martin; Powers, James

2005-04-01

180

Single crystal diffraction by synchrotron radiation  

SciTech Connect

The tunability and access to short wavelengths in combination with high intensity and the low divergence of the x-ray radiation produced by synchrotron storage rings opens up new and challenging fields for single crystal diffraction. These areas include microcrystal diffraction, studies of time-dependent phenomena, element selective diffraction, studies of materials under extreme conditions, solution of the crystallographic phase problem either by the use of the wavelength dependency of the anomalous scattering or by direct experimental determination of the phases. Single crystal diffraction from proteins and macromolecules using photographic film as a detection medium has already reached considerable maturity, but high-precision data collections using diffractometers at storage rings are still not routine because of the severe requirements for beam stability over extended periods of time. Development work at institutions such as the National Synchrotron Light Source, The Photon Factory, SSRL, CHESS, Hasylab and Daresbury, however, suggest that synchrotron single-crystal diffraction will become an essential part of the research at the synchrotron storage rings in the near future. 9 refs., 2 figs.

Kvick, A.

1988-01-01

181

Fatigue In Single Crystal Nickel Superalloys Technical Progress Report.  

National Technical Information Service (NTIS)

This program investigates the seemingly unusual behavior of single crystal airfoil materials. The fatigue initiation processes in single crystal (SC) materials are significantly more complicated and involved than fatigue initiation and subsequent behavior...

C. Annis

1992-01-01

182

Fatigue In Single Crystal Nickel Superalloys Technical Progress Report.  

National Technical Information Service (NTIS)

This program investigates the seemingly unusual behavior of single crystal airfoil materials. The fatigue initiation processes in single crystal (SC) materials are significantly more complicated and involved than fatigue initiation and subsequent behavior...

C. Annis D. P. DeLuca

1993-01-01

183

Single Crystal Niobium RF Cavity of the TESLA Shape.  

National Technical Information Service (NTIS)

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 gra...

P. Kneisel W. Singer X. Singer

2007-01-01

184

Unidirectional seeded single crystal growth from solution of benzophenone  

Microsoft Academic Search

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

K. Sankaranarayanan; P. Ramasamy

2005-01-01

185

The Fluorescent Response of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) to X-Rays and Low Energy Gamma Rays  

Microsoft Academic Search

The fluorescent response functions of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) have been determined with thin crystals over the energy range from 3.3 keV to 840 keV. A pronounced nonlinear dependence on photon energy has been observed in this region for all four types of crystals investigated. Qualitatively the response functions for NaI(Tl), CsI(Tl) and CsI(Na) are similar down to a

D. W. Aitken; B. L. Beron; G. Yenicay; H. R. Zulliger

1967-01-01

186

Single crystal x-ray diffraction: optical and micro hardness studies on chalcone derivative single crystal  

NASA Astrophysics Data System (ADS)

1-(4-methylphenyl)-3-(4- N, N dimethyl amino phenyl)-2-propen-1-one, a chalcone derivative nonlinear optical material has been synthesized by standard method. FT-IR and NMR spectral studies have been performed to confirm the molecular structure of the synthesized compound. The single crystals up to a dimension of 13 x 9 x 3 mm3 were grown by slow evaporation method. The grown crystals were transparent in the entire visible region and absorbs in the UV-region. The refractive index has been measured using a He-Ne laser. The grown crystals have been subjected to single crystal X-ray diffraction studies to determine the crystal structure and hence the cell parameters of the crystal. From this study it is found that this compound crystallizes in orthorhombic system with a space group P212121 and corresponding lattice parameters are, a = 7.3610(13) Å, b = 11.651(2) Å, c = 17.6490(17) Å. The Kurtz powder second harmonic generation test shows that the compound is a potential candidate for Photonic application. The micro hardness test on these crystals were carried out and the load dependence hardness was observed

Crasta, Vincent; Ravindrachary, V.; Bhajantri, R. F.; Naveen, S.; Shridar, M. A.; Shashidhara Prasad, J.

2005-08-01

187

?'-SnSb single crystals obtained by the method of inclined front crystallization  

NASA Astrophysics Data System (ADS)

?' phase plates of single crystals of SnSb alloy were obtained by using a modification of the horizontal Bridgman method. It was ascertained that during crystallization the single crystals grow in the upper layer of the charge. It was found that the thickness of the single crystal (single crystal layer) and also its relative antimony content, depend on the growth rate and on the angle of inclination of the crystallization front relative to the growth direction. A model proposed for the crystallization process permits the description of these relations obtained. This method for obtaining single crystals, the inclined front crystallization (IFC) method, offers new possibilities for control of chemical composition of plate single crystals of intermetallic phases, by varying the angle of inclination of the crystallization front.

Bogdanowicz, W.; Bojarski, Z.

1995-02-01

188

Large electrostrictive actuation of barium titanate single crystals  

Microsoft Academic Search

An experimental investigation of the electromechanical behavior of single crystals of the ferroelectric perovskite barium titanate is presented. An experimental setup has been designed to investigate large strain actuation in single crystal ferroelectrics subjected to combined electrical and mechanical loading. Experiments have been performed on initially single domain crystals of barium titanate with (100) and (001) orientation at compressive stresses

E. Burcsu; G. Ravichandran; K. Bhattacharya

2004-01-01

189

Dye sensitization of single crystal semiconductor electrodes.  

PubMed

Even though investigations of dye-sensitized nanocrystalline semiconductors in solar cells has dominated research on dye-sensitized semiconductors over the past two decades, single crystal electrodes represent far simpler model systems for studying the sensitization process with a continuing train of studies dating back more than 40 years. Even today single crystal surfaces prove to be more controlled experimental models for the study of dye-sensitized semiconductors than the nanocrystalline substrates. This Account analyzes the scientific advances in the model sensitized single crystal systems that preceded the introduction of nanocrystalline semiconductor electrodes. It then follows the single crystal research to the present, illustrating both their striking simplicity of use and clarity of interpretation relative to nanocrystalline electrodes. Researchers have employed many electrochemical, photochemical, and scanning probe techniques for studying monolayer quantities of sensitizing dyes at specific crystallographic faces of different semiconductors. These methods include photochronocoulometry, electronic spectroscopy, and flash photolysis of dyes at potential-controlled semiconductor electrodes and the use of total internal reflection methods. In addition, we describe the preparation of surfaces of single crystal SnS(2) and TiO(2) electrodes to serve as reproducible model systems for charge separation at dye-sensitized solar cells. This process involves cleaving the SnS(2) electrodes and a photoelectrochemical surface treatment for TiO(2) that produces clean surfaces for sensitization (as verified by AFM) resulting in near unity yields for electron transfer from the molecular excited dyes into the conduction band. In recent experiments with ruthenium complexes at TiO(2) and with carboxylated cyanine dyes, we demonstrate the promise of this simple model for understanding dye-sensitized solar cells. In each of these systems, we can observe and analyze the complex photochemistry in a quantitative manner. Molecules of the well-known N3 ruthenium complex attach to four different crystallographic faces of anatase and rutile TiO(2) at different rates and to a different extent. With carboxylated cyanine dye sensitizers on these surfaces, molecular aggregation on the surface is a function of molecular structure and crystallographic face. In contrast with the N3 sensitizer these organic dyes undergo a photoinduced dimerization and desorption reaction when hydroquinone regenerators are present. With both classes of sensitizers, we demonstrate a new photochronocoulometric technique that quantifies the amount of attached dye on the electrode surface. We have completed initial experiments examining quantum dot sensitization of TiO(2) crystals, which could eventually lead to sensitizers with higher stability and absorption coefficients. Although these single crystal electrode models show promise for providing insights and predictive value in understanding the sensitization process, more sophisticated models will be needed to fully understand the charge transfer from the localized electronic states of the sensitizer to the extended states of the semiconductor. PMID:19924998

Spitler, Mark T; Parkinson, B A

2009-12-21

190

Epitaxial Growth of Ferromagnetic Fe3Si Films on CaF2/Si(111) by Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

Ferromagnetic Fe3Si/CaF2 hybrid structures were epitaxially grown on Si(111) by molecular beam epitaxy. When Si and Fe were directly deposited on the Si substrate, it was difficult to prevent inclusion of FeSi in the grown films. This problem was overcome by forming a CaF2 epitaxial film on Si(111) first, followed by codeposition of Si and Fe to form Fe3Si. Fe3Si films were epitaxially grown on the CaF2 at 400°C. A distinct square-like hysteresis loop was observed at room temperature in the magnetic field dependence of Kerr rotation.

Sunohara, Tsuyoshi; Kobayashi, Ken'ichi; Umada, Masakazu; Yanagihara, Hideto; Kita, Eiji; Akinaga, Hiroyuki; Suemasu, Takashi

2005-05-01

191

Inelastic deformation in shocked sapphire single crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

192

Determinazione dei Parametri Cinetici del Cristallo Termoluminescente CAF2 (TM) (Determination of the Kinetic Parameters of the Thermoluminescent CaF2 (TM) Crystal).  

National Technical Information Service (NTIS)

The kinetic parameters are determined following different procedures, based on the thermoluminescent light emission characteristics curve. The methods include the initial gradient method, the numerical fitting of the glow curve, and the peak shape method....

P. Bernardini C. Bini M. Crisafulli D. Moraldi S. Orlando

1988-01-01

193

Oriented single-crystal-to-single-crystal phase transition with dramatic changes in the dimensions of crystals.  

PubMed

We report here a new polymorph of cocrystal CuQ2-TCNQ that shows an oriented single-crystal-to-single-crystal phase transition along its a-axis at ambient conditions. Upon mechanical stimulation, it converts into another polymorph accompanied by almost doubling its length and halving its thickness. Our crystallographic studies indicate the dramatic changes in crystal dimensions resulted from the prominent changes of molecular stacking patterns. A reasonable mechanism for the phenomenon was proposed on the basis of the structural, microscopic, and thermal analysis. PMID:24372005

Liu, Guangfeng; Liu, Jie; Liu, Yang; Tao, Xutang

2014-01-15

194

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

NASA Astrophysics Data System (ADS)

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

Xu, Weiwei

195

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

196

Metallisation of single crystal diamond radiation detectors  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

197

Fabrication of single-crystal diamond microcomponents  

SciTech Connect

We have combined a technique for the lift-off of thin diamond films from a bulk diamond with a technique for engraving diamond with a focused excimer laser to produce free-standing single-crystal diamond microstructures. One microcomponent that has been produced is a 12 tooth gear [similar to]400 [mu]m in diameter and [similar to]13 [mu]m thick. Other microstructures have also been demonstrated, showing the versatility of this method. This process should be applicable to producing diamond microcomponents down to spatial dimensions (width and thickness) of a few micrometers.

Hunn, J.D.; Withrow, S.P.; White, C.W.; Clausing, R.E.; Heatherly, L. (Oak Ridge National Laboratory, Bldg 5500 MS-6376, Oak Ridge, Tennessee 37831-6376 (United States)); Christensen, C.P. (Potomac Photonics, Lanham, Maryland 20705 (United States))

1994-12-12

198

High power single crystal piezoelectric transformer  

US Patent & Trademark Office Database

A piezoelectric transformer includes a single crystal relaxor ferroelectric element poled along a [0 11] direction and selected from the group consisting of PZN-PT, PMN-PZT, PZN-PT and PMN-PT. The element has two opposed surfaces substantially perpendicular to the [0 11] direction with an input electrode and an output electrode positioned on one surface. The output electrode is isolated from electrical communication with the input electrode. A ground electrode is positioned on the second, opposed surface. Input electrical energy results in piezoelectric change in the element that is mechanically coupled through the element to generate piezoelectric output energy.

2013-03-12

199

Conduction mechanism of single-crystal alumina  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

200

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

201

On the thermoluminescence emission spectra of CaF 2: Tm  

NASA Astrophysics Data System (ADS)

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

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

1991-07-01

202

Correlation between TL and OSL properties of CaF 2:N  

NASA Astrophysics Data System (ADS)

Natural CaF 2 is very well known thermoluminescent (TL) material, since it has been extensively used as a dosimeter. Its basic advantage is the exhibited high TL sensitivity. In the present work, the optically stimulated luminescence (OSL) sensitivity of this material was studied by exposing it to environmental radiation for time intervals of few hours up to a few days, and was found to be very high. By analyzing the TL glow curves and the OSL decay curves into their individual glow-peaks and components respectively, a relation between specific glow-peaks and OSL components was established. An intense thermal transfer effect occurring during optical stimulation at high temperature was observed and an explanation is offered according to existing models.

Polymeris, George S.; Kitis, George; Tsirliganis, Nestor C.

2006-09-01

203

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis  

NASA Astrophysics Data System (ADS)

CaF 2 is widely adopted as deep-UV window material and thin film optical coating. The void superlattice was observed experimentally under electron irradiation at room temperature. We performed kinetic Monte Carlo (kMC) simulations of the initial stages of the process when short- and intermediate-range order of defects in small Ca colloids and larger interstitial aggregates (F 2 gas voids) is created. The kMC model includes fluorine interstitial-vacancy pair creation, defect diffusion, similar defect attraction and dissimilar defect recombination. Special attention is paid to the statistical analysis of the defect aggregate distribution functions under different conditions (dose rate, defect migration and recombination rates). These simulations demonstrate that under certain conditions the dissimilar aggregate recombination is strongly suppressed which stimulates growth of mobile interstitial aggregates that is a precondition for further void ordering into a superlattice.

Kuzovkov, V. N.; Kotomin, E. A.; Merzlyakov, P.; Zvejnieks, G.; Li, K. D.; Ding, T. H.; Wang, L. M.

2010-10-01

204

Single crystals of the fluorite nonstoichiometric phase Eu{0.916/2+}Eu{0.084/3+}F2.084 (conductivity, transmission, and hardness)  

NASA Astrophysics Data System (ADS)

The nonstoichiometric phase EuF2+ x has been obtained via the partial reduction of EuF3 by elementary Si at 900-1100°C. Eu{0.916/2+}Eu{0.084/3+}F2.084 (EuF2.084) single crystals have been grown from melt by the Bridgman method in a fluorinating atmosphere. These crystals belong to the CaF2 structure type (sp. gr. Fm bar 3 m) with the cubic lattice parameter a = 5.8287(2) Å, are transparent in the spectral range of 0.5-11.3 ?m, and have microhardness H ? = 3.12 ± 0.13 GPa and ionic conductivity ? = 1.4 × 10-5 S/cm at 400°C with the ion transport activation energy E a = 1.10 ± 0.05 eV. The physicochemical characteristics of the fluorite phases in the EuF2 - EuF3 systems are similar to those of the phases in the SrF2 - EuF3 and SrF2 - GdF3 systems due to the similar lattice parameters of the EuF2 and SrF2 components. Europium difluoride supplements the list of fluorite components MF2 ( M = Ca, Sr, Ba, Cd, Pb), which are crystal matrices for nonstoichiometric (nanostructured) fluoride materials M 1 - x R x F2 + x ( R are rare earth elements).

Sobolev, B. P.; Turkina, T. M.; Sorokin, N. I.; Karimov, D. N.; Komar'kova, O. N.; Sulyanova, E. A.

2010-07-01

205

Electrochemical Sc 2O 3 single crystal growth  

Microsoft Academic Search

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

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

2004-01-01

206

Growth of Oxalic Acid Single Crystals from Solution: Solvent Effects on Crystal Habit  

Microsoft Academic Search

Single crystals of oxalic acid dihydrate are difficult to grow from pure water solution, but good single crystals of the material may be obtained by growth from mixtures of acetone and water. The solvent markedly affects the crystal habit. Crystals grown in mixtures of acetone and water develop the prismatic habit, while those grown in water alone develop the tabular

John L. Torgesen; John Strassburger

1964-01-01

207

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

208

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.

Barry, Nicolas P. E.; Pitto-Barry, Anais; 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

209

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

210

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

211

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

212

Photoemission Study of CaF2- and SrF2-GaAs(110) Interfaces Formed at Room Temperature.  

National Technical Information Service (NTIS)

Group-II cubic fluorides such as Calcium Fluoride CaF2 and Strontium Fluoride SrF2 are very promising for growing epitaxial insulator-on-semiconductor and semiconductor-on-insulator structures. Interfaces formed by evaporating CaF2 or SrF2 on room-tempera...

A. Kahn

1989-01-01

213

Geometry and Vibrational Spectra of Alkaline-Earth Dihalides, Ii. CaF2, SrF2 and BaF2.  

National Technical Information Service (NTIS)

The infrared spectra of 40CaF2, 44CaF2, 86SrF2, 88SrF2 and BaF2 trapped in solid krypton matrices at 20K are reported. From precise measurements of the shifts of the vibrational modes on isotopic substitution upper and lower limits for the apex angles of ...

V. Calder D. E. Mann K. S. Seshadri M. Allavena D. White

1969-01-01

214

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

215

Pulse shape discrimination with new single crystal organic scintillators  

Microsoft Academic Search

Pulse shape discrimination in organic single crystal and liquid scintillators provides a means of identifying fission energy neutrons with high specificity. We present the results of a broad survey of over one hundred single crystal organic scintillators produced from low-temperature solution growth technique. Each crystal was evaluated for light yield and pulse shape discrimination performance. The pulse shape dependence on

Jason Newby; Natalia Zaitseva; Stephen Payne; Nerine Cherepy; Leslie Carman; Giulia Hull

2009-01-01

216

Growth of strontium tartrate tetrahydrate single crystals in silica gels  

Microsoft Academic Search

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

A. R. Patel; S. K. Arora

1976-01-01

217

Single crystal alumina for dental implants and bone screws.  

PubMed

When ground to a suitable form, flexural strength of single crystal alumina (Al2O3) decreases to as low as one third the strength of the intact crystal. This flexural strength decrease is, however, recovered by chemical etching at a high temperature to eliminate surface defects caused by grinding. By using this strength recovery treatment, various types of single crystal implants with fine structure were able to be designed. Four kinds of single crystal bone screws and single crystal dental implants of screw and anchor type were designed. Flexural strength and impact strength of the implants were measured. PMID:7349666

Kawahara, H; Hirabayashi, M; Shikita, T

1980-09-01

218

Solar cell structure incorporating a novel single crystal silicon material  

DOEpatents

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

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

1983-01-01

219

Mode Gruneisen Parameters for Single Crystal Al2O3.  

National Technical Information Service (NTIS)

Single crystal Al2O3 (sapphire or corundum), crystallizes in the trigonal lattice, point group 3m. Its thermodynamic properties have been extensively investigated over the last years. As the pressure derivatives of its elastic moduli have recently become ...

D. Gerlich

1969-01-01

220

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

221

Hydrogen Annealing Of Single-Crystal Superalloys  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

222

Magnetoplasticity and diffusion in silicon single crystals  

SciTech Connect

The effect of static magnetic fields on the dynamics of surface dislocation segments, as well as the diffusion mobility of a dopant in silicon single crystals, has been analyzed. It has been experimentally found that the preliminary treatment of p-type silicon plates (the dopant is boron with a concentration of 10{sup 16} cm{sup -3}) in the static magnetic field (B = 1 T, a treatment time of 30 min) leads to an increase in the mobility of surface dislocation segments. The characteristic times of observed changes (about 80 h) and the threshold dopant concentration (10{sub 15} cm{sup -3}) below which the magneto-optical effect in silicon is not fixed have been determined. It has been found that diffusion processes in dislocation-free silicon are magnetically sensitive: the phosphorus diffusion depth in p-type silicon that is preliminarily aged in the static magnetic field increases (by approximately 20%) compared to the reference samples.

Skvortsov, A. A., E-mail: SkvortsovAA2009@yandex.ru; Karizin, A. V. [Moscow State Technical University 'MAMI' (Russian Federation)

2012-01-15

223

Constitutive modeling for single crystal superalloys  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

224

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

225

Ultratough CVD single crystal diamond and three dimensional growth thereof  

DOEpatents

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

Hemley, Russell J. (Washington, DC) [Washington, DC; Mao, Ho-kwang (Washington, DC) [Washington, DC; Yan, Chih-shiue (Washington, DC) [Washington, DC

2009-09-29

226

Formation of curved micrometer-sized single crystals.  

PubMed

Crystals in nature often demonstrate curved morphologies rather than classical faceted surfaces. Inspired by biogenic curved single crystals, we demonstrate that gold single crystals exhibiting curved surfaces can be grown with no need of any fabrication steps. These single crystals grow from the confined volume of a droplet of a eutectic composition melt that forms via the dewetting of nanometric thin films. We can control their curvature by controlling the environment in which the process is carried out, including several parameters, such as the contact angle and the curvature of the drops, by changing the surface tension of the liquid drop during crystal growth. Here we present an energetic model that explains this phenomenon and predicts why and under what conditions crystals will be forced to grow with the curvature of the microdroplet even though the energetic state of a curved single crystal is very high. PMID:24694217

Koifman Khristosov, Maria; Kabalah-Amitai, Lee; Burghammer, Manfred; Katsman, Alex; Pokroy, Boaz

2014-05-27

227

Investigation of single crystal silicates for blue tunable lasers  

NASA Astrophysics Data System (ADS)

The single crystal growth of rare earth silicates was investigated for the purpose of tunable laser hosts. Silicates of the type R2SiO5, where R = La, Gd, Y, Lu, were prepared from stoichiometric melts and doped with Ce(3+) activators. Seed crystals were obtained from crystallized melt sections or by growth on an iridium wire. These seeds were utilized in standard Czochralski type growth to obtain larger single crystals. Cathodoluminescence experiments on both powders and single crystals showed wavelength shifts with different rare earth ions. The Gd, Y, and mixed crystals of Gd-Y silicates gave good bright emission with Ce(3+). The emission is broad band and covers the wavelength range of 370 to 525 nm. The peak emission can be centered near 450 to 460 nm by other compositions. Larger single crystals for laser hosts are under development.

Belt, R. F.; Catalano, J. A.

1986-01-01

228

Reversible single-crystal-to-single-crystal photochemical formation and thermal cleavage of a cyclobutane ring.  

PubMed

A [2+2] cycloaddition reaction has been observed in a number of solids. The cyclobutane ring in a photodimerized material can be cleaved into olefins by UV light and heat. The high thermal stability of the metal-organic salt K2SDC (H2SDC = 4,4'-stilbenedicarboxylic acid) has been successfully utilized to investigate the reversible cleavage of a cyclobutane ring. The two polymorphs of K2SDC undergo reversible cyclobutane formation by UV light and cleavage by heat in cycles. Of these, one polymorph retains its single-crystal nature during the reversible processes. Polymorphs are known to show different physical properties and chemical reactivities. This work reveals that the retention of single-crystal nature is strongly associated with the packing of molecules, which is controlled by kinetics and thermodynamics. The photoemissive nature of the products makes this as a promising material for photoswitches and optical data storage devices. PMID:24459072

Kole, Goutam Kumar; Kojima, Tatsuhiro; Kawano, Masaki; Vittal, Jagadese J

2014-02-17

229

Growth of benzophenone single crystals from solution: A novel approach with 100% solute - crystal conversion efficiency  

Microsoft Academic Search

An unidirectional 60mm diameter benzophenone single crystal was successfully grown by utilizing a novel crystal growth method at room temperature. <110> oriented single crystal ingots were grown out of xylene as solvent and by fixing a seed at the bottom of the ampoule. The obtained benzophenone ingots with the sizes of 10mm, 25mm and 60mm diameter evident that ease in

K. Sankaranarayanan; P. Ramasamy

2006-01-01

230

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

231

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

232

Amorphouslike Density of Gap States in Single-Crystal Pentacene  

Microsoft Academic Search

We show that optical and electrical measurements on pentacene single crystals can be used to extract the density of states in the highest occupied molecular orbital lowest unoccupied molecular orbital band gap. It is found that these highly purified crystals possess band tails broader than those typically observed in inorganic amorphous solids. Results on field-effect transistors fabricated from similar crystals

Arthur Ramirez; David Lang; Xiaoliu Chi; Theo Siegrist; Mike Sergent

2004-01-01

233

Responsivity enhancement of mid-infrared PbSe detectors using CaF2 nano-structured antireflective coatings  

NASA Astrophysics Data System (ADS)

The CaF2 nano-structures grown by thermal vapor deposition are presented. Significant responsivity improvement (>200%) of mid-infrared PbSe detectors incorporating a 200 nm nano-structured CaF2 coating was observed. The detector provides a detectivity of 4.2 × 1010 cm · Hz1/2/W at 3.8 ?m, which outperforms all the reported un-cooled PbSe detectors. Structural investigations show that the coating is constructed by tapered-shape nanostructures, which creates a gradient refractive-index profile. Analogy to moth-eye antireflective mechanism, the gradient refractive-index nanostructures play the major roles for this antireflection effect. Some other possible mechanisms that help enhance the device performance are also discussed in the work.

Weng, Binbin; Qiu, Jijun; Yuan, Zijian; Larson, Preston R.; Strout, Gregory W.; Shi, Zhisheng

2014-01-01

234

Microscale Laser Peen Forming of Single Crystal  

SciTech Connect

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

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

2008-01-01

235

Q-1 of forsterite single crystals  

NASA Astrophysics Data System (ADS)

Internal friction ( Q-1) experiments have been performed on synthetic forsterite single crystals in order to investigate the role of temperature, frequency and dislocation density on the Q-1 factor. Data have been obtained for both deformed and undeformed specimens over a frequency range from 10 to 10 -4 Hz at 15, 1000, 1200 and 1400°C. Measurements were done using a torsional pendulum operating in forced oscillations on specimens with dimensions of 20 mm × 5 mm × 1 mm. Samples were maintained in vacuum. Stress amplitudes were 0.1 MPa and strains 10 -6-10 -5. Pre-deformation experiments were creep tests performed at 1600°C and 20 MPa. The amount of strain was 10 -2. Dislocation microstructures were investigated by transmission electron microscopy. At room temperature, undeformed samples show low attenuation with no frequency dependence. At high temperature (1400°C), Q-1 increases up to 5 × 10 -2 for very low frequencies (10 -4 Hz). Deformed specimens show the same trend but there is a more pronounced increase in Q-1 with both frequency and temperature ( Q-1 = 2 × 10 -1, 10 -4 Hz at 1400°C). This high-temperature attenuation is the result of dislocation processes which are probably non-linear in the strain range explored by the present experiments ( ? > 10 -6). Non-linearity appears to be the best explanation for the disagreement between high Q-1 data reported in laboratory and low Q 1 data reported for the upper mantle.

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

1989-06-01

236

Preparation and morphology of pyramidal MFI single-crystal segments.  

PubMed

Single-crystal segments of tetra-n-propylammonium-templated Silicalite-1 and ZSM-5 were prepared by postsynthetic treatment of twinned MFI prisms. Microwave irradiation of the parent crystallites in alkaline solution containing hydrogen peroxide, followed by ultrasound treatment, led to disintegration of the zeolite prisms. The resulting wedge-shaped crystal segments proved to be single crystals of excellent crystallinity as shown by optical and X-ray investigations. The hydroxyl ions, compensating the positive charges of the tetrapropylammonium cations, were located by single-crystal structure refinement in template-containing Silicalite-1 and ZSM-5 but absent from the calcined samples. PMID:17988115

Schmidt, Wolfgang; Wilczok, Ursula; Weidenthaler, Claudia; Medenbach, Olaf; Goddard, Richard; Buth, Gernot; Cepak, Alexander

2007-12-01

237

Fabrication of polypyrrole nano-arrays in lysozyme single crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

238

Shear localization in dynamic deformation of copper single crystals  

Microsoft Academic Search

Dynamic deformation of copper single crystals, especially of fatigued copper single crystals with different orientations, was conducted on a split-Hopkinson pressure bar apparatus. The strain rates were in the range 2 - 9 × 103 s-1. After dynamic deformation, the adiabatic shear bands (ASBs) were examined in a light microscope and SEM. The width and spacing of ASBs formed under

S. X. Li; R. Q. Yang; J. W. Li; Z. F. Zhang

2006-01-01

239

Coefficients of thermal expansion for single crystal piezoelectric fiber composites  

Microsoft Academic Search

Piezoelectric fiber composites were developed to overcome drawbacks of typical monolithic piezoceramic (PZT) actuators. Although piezoelectric fiber composites had many improvements over the monolithic PZT, there are still improvements. Thus, the single crystal piezoelectric fiber composite actuator is proposed. Single crystal piezoelectric materials such as PMN-PT have larger piezoelectric strain constants, higher bandwidth and higher energy density than polycrystalline counterparts.

Jae-Sang Park; Ji-Hwan Kim

2007-01-01

240

Field Emission from Tungsten and Thoriated Tungsten Single Crystals  

Microsoft Academic Search

A reproducible time sequence of different pattern types has been found to appear in electron projector images of field emission from tungsten single crystals when the crystals are kept at temperatures above 1100°K. These pattern types, some of which have been observed before and attributed to migrations of surface tungsten atoms, can best be explained (with a single possible exception)

J. H. Daniel

1942-01-01

241

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

242

Growth and Structure of Single-Crystal Films.  

National Technical Information Service (NTIS)

This research project was concerned with basic research on the growth and structure of single-crystal films of metals obtained by evaporation in ultra-high vaccum onto two types of substrates: mica and metal single-crystal films. The films were prepared i...

E. Grunbaum

1968-01-01

243

Preparation Techniques for Growth of Single Crystals of Nonmetallic Materials.  

National Technical Information Service (NTIS)

The report describes two techniques for growth of highpurity single crystals of nonmetallic materials using r-f induction-heating equipment in a frequency range of 5 to 100 Mc. One technique used for single-crystal growth was the Verneuil method using an ...

E. M. Clausen J. W. Rutter

1964-01-01

244

A Single Crystal Niobium RF Cavity of the TESLA Shape  

Microsoft Academic Search

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

W. Singer; X. Singer; P. Kneisel

2007-01-01

245

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

246

Upconversion white light of Tm 3+\\/Er 3+\\/Yb 3+ tri-doped CaF 2 phosphors  

Microsoft Academic Search

Tm3+\\/Er3+\\/Yb3+ tri-doped CaF2 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 980nm continuous wave diode laser (CW LD 2 W) excitation. As the excitation power density changed in the range of 20–260W\\/cm2, the

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

2008-01-01

247

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

248

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

250

Thermally induced single crystal to single crystal transformation leading to polymorphism  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

251

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

PubMed

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

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

2014-09-15

252

Structural and spectroscopic studies on calcium succinate single crystals  

NASA Astrophysics Data System (ADS)

Calcium succinate crystals have been grown by gel aided solution growth technique. The structure of the crystal is solved by single crystal XRD analysis. The Crystal structure of the title compound is triclinic having space group P(1) Powder XRD studies confirmed the good crystalline nature of the sample. The different functional groups and their assigned vibrations are discussed by FT-IR and FT Raman spectroscopic studies.

Binitha, M. P.; Pradyumnan, P. P.

2014-04-01

253

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

Microsoft Academic Search

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

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

2005-01-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2004-06-01

255

Single-element ultrasonic probe using PZN-PT single crystal  

Microsoft Academic Search

In order to improve the sensitivity and the bandwidth of an ultrasonic probe, the single-element probe using single crystals of the solid solution Pb(Zn1\\/3Nb2\\/3)O3- PbTiO3 (PZN-PT) has been investigated. Single crystals of PZN-PT with 9 mol% PbTiO3 (PZN-PT 91\\/9) single crystals were grown by the self flux method using PbO-based flux. It was confirmed that the single crystal of good

Shiroh Saitoh; Tsuyoshi Kobayashi; Senji Shimanuki; Yohachi Yamashita

1997-01-01

256

Optical and Mechanical Characteristics of PETN Single Crystal  

NASA Astrophysics Data System (ADS)

Pentaerythritol tetranitrate (PETN) is an extensively used crystalline high explosive. A good understanding of the laser- induced chemical decomposition and growth to detonation of PETN is important. This work on PETN single crystals focused primarily on its mechanical and optical properties under laser pulse interaction. Laser pulse (E<2 J, ?= 150 ps, &=tilde; 1.06 ?m) was focused on the single crystal surface to focal point size 80 .. 800 ?m. The goal of this work was to study the early stages of laser-induced explosion decomposition. Crystal response to the laser radiation was determined by the luminescence and conductivity of crystals. Explosion decomposition of PETN single crystals failed to occur within the studied range of initiation energies. Experiments measured the threshold of the optical breakdown for PETN and determined energies when its mechanical destruction begins. Analysis of experiments allowed a new scheme to be proposed for experiments when the laser radiation energy is injected inside the crystal.

Gromov, V. T.

2005-07-01

257

Investigation of single crystal silicates for blue tunable lasers  

NASA Astrophysics Data System (ADS)

The single crystal growth of rare earth silicates was investigated for the purpose of tunable laser hosts. Silicates of the type R2Si05, where R = La, Gd, Y, were prepared from stoichiometric melts and doped with Ce3+ activators. Seed crystals were obtained from crystallized melt sections or by growth on an iridium wire. Cathodoluminescence experiments on both powders and single crystals showed wavelength shifts with different rare earth ions. The Gd, Y, and mixed crystals of Gd-Y silicates gave good bright emission with Ce3+. The emission is broad band and covers the wavelength range of 370 to 525 micron. The peak emission can be centered near 450 to 460 micron by other compositions. Larger single crystals for laser hosts are under development.

Belt, R. F.; Catalano, J. A.

1986-06-01

258

Development of a thermal stress analysis system for anisotropic single crystal growth  

Microsoft Academic Search

We developed a thermal stress analysis system for anisotropic single crystal growth. The analysis system takes account of crystal anisotropy in elastic constants and thermal expansion coefficients and can deal with the thermal stress analyses of five kinds of single crystals, that is, cubic crystal, trigonal crystal, monoclinic crystal, tetragonal crystal and orthorhombic crystal. After calculating thermal stress, we can

N. Miyazaki

2002-01-01

259

Study of single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

260

Hg-1212 and Hg-1223 single crystals: Synthesis and characterisation  

NASA Astrophysics Data System (ADS)

Single crystals of HgBa 2CaCu 2O 6+? (Hg-1212) and HgBa 2Ca 2Cu 3O 8+? (Hg-1223) were grown from the melt at an argon pressure of 10 kbar. Electron microscopy, as well as single crystal X-ray diffraction studies show that the crystals are well ordered. The EDS analysis indicates the presence of a minor amount of other cations replacing Hg, Ba and Ca in the structure. Refined fractional coordinates and thermal parameters are given for a crystal of Hg-1223 type. Magnetic and resistive measurements show a Tc of 133 K for the Hg-1223 phase.

Gatt, R.; Olsson, E.; Morawski, A.; Lada, T.; Paszewin, A.; Bryntse, I.; Grishin, A. M.; Eeltsev, Yu.; Berastegui, P.; Johansson, L.-G.

1997-02-01

261

Growth of Sb-Bi gradient single crystals  

SciTech Connect

The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals.

Kozhemyakin, G. N., E-mail: genakozhemyakin@mail.ru; Lutskiy, D. V. [Dal Eastern Ukraine National University (Ukraine); Rom, M. A.; Mateychenko, P. V. [National Academy of Sciences of Ukraine, Institute for Single Crystals (Ukraine)

2008-12-15

262

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

263

Hard polarized photon emission in single crystals by high energy electrons for planar crystal orientations  

Microsoft Academic Search

The radiation emission spectra of polarized photons emitted from charged particle in single crystals are obtained in the semiclassical theory in Baier-Katkov-Strakhovenko approximation for planar crystal orientation. Optimal crystal orientations for producing unpolarized and polarized photon beams are also found.

S. M. Darbinyan; N. L. Ter-Isaakyan

2002-01-01

264

Hard polarized photon emission in single crystals by high energy electrons for planar crystal orientations  

Microsoft Academic Search

The radiation emission spectra of polarized photons emitted from charged particle in single crystals are obtained in the semiclassical theory in Baier–Katkov–Strakhovenko approximation for planar crystal orientation. Optimal crystal orientations for producing unpolarized and polarized photon beams are also found.

S. M. Darbinyan; N. L. Ter-Isaakyan

2002-01-01

265

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

266

A Single Crystal Niobium RF Cavity of the TESLA Shape  

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

267

Growth of Solid Solution Single Crystals.  

National Technical Information Service (NTIS)

The bulk growth of HgCdTe crystals by modified Bridgman techniques and by quenching anneal recrystallization yields deficient material. The primary complication for growth arises from a pronounced tendency for constitutional supercooling caused by the cha...

A. F. Witt

1981-01-01

268

Barium iodide single-crystal scintillator detectors  

SciTech Connect

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

Cherepy, N

2007-07-30

269

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

270

Single-drop optimization of protein crystallization.  

PubMed

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

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

2012-08-01

271

Epitaxial electrodeposition of freestanding large area single crystal substrates  

SciTech Connect

The authors report on a method for producing freestanding single crystal metal films over large areas using electrodeposition and selective etching. The method can be turned into an inexpensive continuous process for making long ribbons or a large area of single crystal films. Results from a 5x5 mm{sup 2} Ni single crystal film using electron backscattering pattern pole figures and x-ray diffraction demonstrate that the quality of material produced is equivalent to the initial substrate without annealing or polishing.

Shin, Jae Wook; Standley, Adam; Chason, Eric [Brown University, Box D, Providence, Rhode Island 02912 (United States)

2007-06-25

272

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

NASA Technical Reports Server (NTRS)

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

Lal, R. B.

1979-01-01

273

Crystal growth and characterization of La 3Ga 5SiO 14 single crystals  

Microsoft Academic Search

An almost colorless La3Ga5SiO14 (LGS) single crystal with 26 mm in diameter and 25 mm in length was grown by the Czochralski technique. The coloration of the crystal depends on the growth atmosphere. The cutoff wavelength of the colorless LGS crystal is shorter than an annealed crystal and the piezoelectric properties of the former are nearly equal to those of

Zengmei Wang; Duorong Yuan; Lihu Pan; Peilin Zhang; Xiufeng Cheng; Minglei Zhao; Zhengfa Li; Xiulan Duan; Zhenxiang Chen; Shiyi Guo; Dong Xu; Mengkai Lv

2003-01-01

274

Single crystal Processing and magnetic properties of gadolinium nickel  

SciTech Connect

GdNi is a rare earth intermetallic material that exhibits very interesting magnetic properties. Spontaneous magnetostriction occurs in GdNi at T{sub C}, on the order of 8000ppm strain along the c-axis and only until very recently the mechanism causing this giant magnetostriction was not understood. In order to learn more about the electronic and magnetic structure of GdNi, single crystals are required for anisotropic magnetic property measurements. Single crystal processing is quite challenging for GdNi though since the rare-earth transition-metal composition yields a very reactive intermetallic compound. Many crystal growth methods are pursued in this study including crucible free methods, precipitation growths, and specially developed Bridgman crucibles. A plasma-sprayed Gd{sub 2}O{sub 3} W-backed Bridgman crucible was found to be the best means of GdNi single crystal processing. With a source of high-quality single crystals, many magnetization measurements were collected to reveal the magnetic structure of GdNi. Heat capacity and the magnetocaloric effect are also measured on a single crystal sample. The result is a thorough report on high quality single crystal processing and the magnetic properties of GdNi.

Shreve, Andrew John [Ames Laboratory

2012-11-02

275

Performance of Large grain and Single Crystal Niobium Cavities  

Microsoft Academic Search

We have fabricated and tested several single and one multi-cell cavity made from large grain niobium of four different ingots. Two cavities at a frequency of ~ 2.2 GHz were made from single crystal sheets. Large grain material was used for four single cell cavities of the HG â and OC shapes, a 7-cell cavity of the HG â shape

Peter Kneisel; Gianluigi Ciovati; Jacek Sekutowicz

2006-01-01

276

Growth and characterization of ammonium acid phthalate single crystals  

NASA Astrophysics Data System (ADS)

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

Arunkumar, A.; Ramasamy, P.

2013-04-01

277

Twisted Single Crystals of Meta-Aromatic Polyamides  

NASA Astrophysics Data System (ADS)

The morphology of single crystals of the aromatic polyamide poly(metaphenylene isophthalamide) (MPDI or Nomex) was studied by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The single crystals of MPDI were slowly grown from 0.1 weight percent solution. MPDI forms elongated crystals which aggregate together to form highly regular twisted helical bundles. The repeat periods of the helices typically range from 240 nm to 1000 nm and the bundle diameters vary from 36 nm to 120 nm. The angle between the edge of the crystal and the bundle axis varies from 40 to 65 degrees. The regular twisting evidently arises from a bending moment induced by the triclinic symmetry of the MPDI unit cell and the lamellar geometry of the chain-folded single crystal.

Lawrence, D. P.; Martin, D. C.

1996-03-01

278

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

279

On the growth of calcium tartrate tetrahydrate single crystals  

Microsoft Academic Search

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

X. Sahaya Shajan; C. Mahadevan

2004-01-01

280

Large Single Crystal growth of Bi2212 superconducting oxide  

Microsoft Academic Search

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

Genda Gu; Gangyong Xu; John Tranquada

2006-01-01

281

Phase transitions in potassium ammonium dihydrogen phosphate single crystals  

Microsoft Academic Search

An apparatus for growing single crystals from aqueous solution by the slow evaporation method was constructed. Mixed crystals of K1-x(NH 4)xH2PO4 (KADP) with (NH4)H 2PO4 (ADP) fractions of 0.021 and 0.12 were successfully grown. Their composition was determined by means of the x-ray powder diffraction method. This analysis also suggests that those crystals are a mixture of two phases even

Marek Bromberek

2008-01-01

282

Morphology and orientational disorder of C 70 single crystals  

Microsoft Academic Search

C70 single crystals, free from solvent contamination, were grown via vapor phase transport technique. The (0001) face of the C70 crystal was imaged with Atomic Force Microscopy (AFM) under ambient atmosphere. Low-resolution images of a freshly prepared crystal revealed well-ordered faceted regions with multiple terraces extending over a region of several hundred square nanometers. The terraced structure in the images

L. Jiang; J. Li; L. A. Nagahara; N. Kino; K. Kitazawa; T. Iyoda; K. Hashimoto; A. Fujishima

1995-01-01

283

Fluorine K? X-Ray Emission Spectra of MgF2, CaF2, SrF2 and BaF2  

NASA Astrophysics Data System (ADS)

The fluorine K? emission spectra in fluorescence from a series of alkaline-earth fluorides MF2 (M=Mg, Ca, Sr and Ba) are measured with a high-resolution two-crystal vacuum spectrometer. An anomalously low intensity of the K1L1 satellite peak arising from 1s-1(2s2p)-1 initial states is observed for SrF2. The measured emission spectra are presented along with the UPS spectra of the F- 2p valence bands obtained by Poole et al. and the fluorine K absorption-edge spectra by Oizumi et al. By using these spectra, the first peak or shoulder in the fluorine K absorption-edge spectra is identified as being due to a core exciton which is formed below the bottom of the conduction band. The binding energy of the exciton is estimated to be 1.3(± 0.3), 1.1(± 0.2), 1.0(± 0.2) and 1.7(± 0.2) eV for MgF2, CaF2, SrF2 and BaF2, respectively.

Sugiura, Chikara; Konishi, Wataru; Shoji, Shizuko; Kojima, Shinjiro

1990-11-01

284

Zone refining and single crystal growth of cuprous oxide  

Microsoft Academic Search

A method of purification and single crystal growth of cuprous oxide by an R. F. induction heating float zone technique was developed. Ingots of 5\\/1 inches diameter and 6 inches long, with three to six columnar crystals extending the entire length of the rod, were prepared. After etching, these rods can be viewed as red by transmitted visible light. The

ANAND SWAROOP KAKAR

1978-01-01

285

Investigation of Single Crystal Silicates for Blue Tunable Lasers.  

National Technical Information Service (NTIS)

The single crystal growth of rare earth silicates was investigated for the purpose of tunable laser host. Silicates of the type R2SiO5, where R + La, Gd, Y were prepared from stoichiometric melts and doped with Ce+3 activator. Seed crystals were obtained ...

R. F. Belt J. A. Catalano

1986-01-01

286

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

287

Investigation of Single Crystal Silicates for Blue Tunable Lasers.  

National Technical Information Service (NTIS)

The single crystal growth of rare earth silicates was investigated for the purpose of tunable laser hosts. Silicates of the type R2SiO5, where R = La, Gd, Y, Lu, were prepared from stoichiometric melts and doped with Ce(3+) activators. Seed crystals were ...

R. F. Belt J. A. Catalano

1986-01-01

288

RESEARCH NOTES: Directional electric breakdown of KCl single crystals  

Microsoft Academic Search

Controversy exists about whether the discharge channel existing after breakdown in alkali halide crystals marks the path of the electronic instability or results from secondary processes. A fast electro-optical shutter has been used to observe the pre-breakdown light emission from KCl single crystals, and it has been found that the discharge channel does lie in the path of the electronic

R. Cooper; C. T. Elliott

1968-01-01

289

Frequency dependent electro-optic property of SBN single crystal  

NASA Astrophysics Data System (ADS)

In electro-optic (EO) modulator devices ferroelectric crystals of strontium barium niobate (SBN) are attractive due to exceptional high EO coefficients and low half wave voltage. SBN single crystals grown by laser heated pedestal growth are investigated to explore frequency dependent EO property at low frequency and near resonant frequency range. The mechanism of its frequency dependence is discussed briefly.

Huang, Chuanyong; Fu, John; Liu, Hongbo; Liu, Yuexin; Gu, Man; Bhalla, Amar S.; Guo, Ruyan

2005-09-01

290

Heterogeneous deformation resulting from stress gradients in calcite single crystals  

Microsoft Academic Search

The stress gradient calculated from an isotropic elastic approximation does not directly reflect the distribution of permanent deformation in a crystal of the same shape under the same conditions. However, with additional crystallographic constraints, it serves to predict locations where twinning and slip are first activated in a stressed crystal. In this study, thick-walled hollow cylinders were cored from single

Annemarie Meike

1988-01-01

291

Bismuth and aluminum-substituted YIG single-crystal films on modified gadolinium gallium garnet single-crystal substrates  

Microsoft Academic Search

Bismuth- and aluminum-substituted yttrium iron garnet single-crystal films with the nominal composition of Y1.5Bi1.5Fe4.2Al0.8O12 (Bi,Al:YIG) were prepared by spin coating a gel on the (111) plane of (GdCa)3(GaMgZn)5O12 single-crystal garnet plates. Crystallinity of the films varies with temperature and time of heat treatment in air after gel coating. Single-crystal films were obtained at Ta=650 °C for 4 h. The onset

Koji Matsumoto; Satoshi Sasaki; Yasunori Yamanobe; Kazuhiro Yamaguchi; Toshitaka Fujii; Yousuke Asahara

1991-01-01

292

Constitutive Modelling of Single Crystal and Directionally Solidified Superalloys.  

National Technical Information Service (NTIS)

The trend towards improved engine efficiency and durability places increasing demands on materials that operate in the hot section of the gas turbine engine. These demands are being met by new coatings and materials such as single crystal and directionall...

E. H. Jordan K. P. Walker

1986-01-01

293

Single Crystal Growth of Potassium Lithium Niobate for SAW Applications.  

National Technical Information Service (NTIS)

We have successfully demonstrated the growth of good quality, crack-free medium size KLN single crystals using the Czochralski method, with dielectric and piezoelectric properties comparable or superior to the best known bronze composition SBN. However, w...

R. R. Neurgaonkar

1983-01-01

294

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

295

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

296

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 d_{33} 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 d_{33} 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

2013-11-01

297

Deuteron NMR in Formic and Acetic Acid Single Crystals  

Microsoft Academic Search

The deuteron quadrupole coupling constants and asymmetry factors in single crystals of DCOOH and HCOOD are found to be 161± 2 kHz, &eegr;=0.040± 0.025 and 165.1± 2.7 kHz, &eegr;=0.125± 0.030, respectively. These are compared with free molecule and single crystal results of others on the formate group. In addition, attention is called to influence of the X-fragment electronegativity upon the

Guy J. Adriaenssens; John L. Bjorkstam

1972-01-01

298

Shear localization in dynamic deformation of copper single crystals  

Microsoft Academic Search

Dynamic deformation of copper single crystals, especially of fatigued copper single crystals with different orientations, was conducted on a split-Hopkinson pressure bar apparatus. The strain rates were in the range 2???9?×?10?s. After dynamic deformation, the adiabatic shear bands (ASBs) were examined in a light microscope and SEM. The width and spacing of ASBs formed under different strain rates in a

S. X. Li; R. Q. Yang; J. W. Li; Z. F. Zhang

2006-01-01

299

Preparation of Large Area Single-Crystal Cuprous Oxide  

Microsoft Academic Search

Large area single crystals of Cu2O were grown by the process of high temperature annealing. Cu2O was prepared in finely polycrystalline form by the complete oxidation of Cu plate in air at temperatures of 1020°C to 1050°C. Subsequent annealing of the polycrystalline plates at higher temperatures allowed secondary recrystallization to occur. Single-crystal grains having surface areas larger than 1 in.2

Robert S. Toth; Rein Kilkson; Dan Trivich

1960-01-01

300

Electrochemical In 2O 3 single crystal growth  

Microsoft Academic Search

An In2O3 single crystal was successfully grown electrochemically applying the In3+ ion conducting In2(MoO4)3 solid electrolyte. In the In2(MoO4)3 solid electrolyte, only In3+ ion species can migrate in the molybdate solid, and by the DC electrolysis, the In3+ ion species continuously supplied and deposited on the cathodic surface of the electrolyte. Since the single crystal growth can be regulated by

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

2004-01-01

301

Bulk GaN single-crystals growth  

Microsoft Academic Search

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

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

2000-01-01

302

Inhomogeneities in single crystals of cuprate oxide superconductors  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

303

Single Crystal Growth of Photorefractive Sillenites.  

National Technical Information Service (NTIS)

The compounds, crystallized in the cubic form similar to sillenite structure, occur in a number of isomorphs. The well-known representatives of this family are bismuth germanium (BGO) and bismuth silicon oxides (BSo), both of which can be grown from their...

V. V. Volkov Y. F. Kargin V. M. Skorikov

1992-01-01

304

Poly(vinylidene fluoride) single crystals  

Microsoft Academic Search

Information about the structure and properties of bulk poly (vinylidence fluoride) PVF2 has been previously obtained in this laboratory from X-ray diffraction [1], NMR spectra [1], and dielectric constant measurements [2, 3]. Depending on sample preparation, one finds two different types of orthorhomic unit cells (Table 1). Type II appears in samples crystallized from the melt either isothermally or at

K. Sakaoku; A. Peterlin

1967-01-01

305

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

306

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

307

Vortex structure in superconducting iron pnictide single crystals  

NASA Astrophysics Data System (ADS)

The vortex structure in the iron pnictide single crystals Ba1- x K x Fe2As2 and Sr1- x K x Fe2As2 of the 122 type and SmFeAsO1- x F x of the 1111 type has been investigated using the decoration method. In all of the crystals under investigation, no regular vortex lattice has been revealed in the magnetic field range up to 200 Oe. The disordered vortex structure is discussed in view of the vortex pinning in single crystals.

Vinnikov, L. Ya.; Artemova, T. M.; Veshchunov, I. S.; Zhigadlo, N. D.; Karpinski, J.; Popovich, P.; Sun, D. L.; Lin, C. T.; Boris, A. V.

2009-10-01

308

CeSi 2? ? single crystals: growth features and properties  

Microsoft Academic Search

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

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

2004-01-01

309

Optical and photoelectrochemical study of WTe2 single crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

310

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

311

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

NASA Technical Reports Server (NTRS)

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

Vandenberg, Lodewijk

1992-01-01

312

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

313

Raman spectra of deuteriated taurine single crystals  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

314

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

315

Extending the contact regimes to single-crystal indentations  

NASA Astrophysics Data System (ADS)

This article provides a fresh look into the concept of the contact regimes in mechanistic analyses of indentation experiments performed in single crystals. In this context, spherical microindentation experiments in fcc metals are examined through detailed continuum crystal plasticity finite element simulations in order to provide meaning to the onset of fully-plastic and elasto-plastic contact regimes, which are well-known to rule the behavior of polycrystals exhibiting isotropic uniaxial stress-strain curves. Attention is then given to evaluate the applicability of Tabor's hardness relation in ruling fully-plastic single-crystal spherical indentations as well as the extraction of the uniaxial plastic flow properties from a series of microindentation tests performed at different penetrations. A discussion is finally provided on the applicability of self-similarity assumptions to the analysis of single-crystal fully-plastic indentations.

Alcalá, Jorge; Esqué-de los Ojos, Daniel

2011-07-01

316

Light scattering by single ice crystals of cirrus clouds  

NASA Astrophysics Data System (ADS)

In situ measurements of angular scattering intensities (ASIs) related to single ice crystals of cirrus clouds were obtained for the first time with the airborne Polar Nephelometer instrument. These observations were performed in the southern mid-latitudes during the INCA project. The analysis of the data shows that the well marked peaks of the ASIs are undoubtedly attributed to quasi-specular reflections from crystal facets and the refracted rays passed through the ice crystals. Emphasizing that it is not enough to know the shape of the crystal, but also the internal structure is of great importance. Ray tracing simulations reproduce most of the observed ASIs features. The model of surface roughness, which assumes the Weibull statistics, enables to reproduce the quasi-specular external reflection from crystal facets. It follows from the retrievals that the surface of the crystals was deeply rough and the amount of the internal inclusions (air bubbles) was quite high.

Shcherbakov, Valery; Gayet, Jean-François; Jourdan, Olivier; Ström, Johan; Minikin, Andreas

2006-08-01

317

SINGLE CRYSTAL NIOBIUM TUBES FOR PARTICLE COLLIDERS ACCELERATOR CAVITIES  

SciTech Connect

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

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

2013-02-28

318

Precise Magnetic Torque Measurements on Single Crystals of Iron  

Microsoft Academic Search

A rugged balance of sufficiently high sensitivity and a rotating magnet capable of producing a field of over 3000 oersteds are used to make magnetic torque curves. The equations for the torque curve of a single crystal disk of any orientation whatsoever are derived on the assumption that the magnetic anisotropy is adequately described by a single constant. Furthermore, a

L. P. Tarasov; F. Bitter

1937-01-01

319

Optical and Mechanical Characteristics of PETN Single Crystal  

Microsoft Academic Search

Pentaerythritol tetranitrate (PETN) is an extensively used crystalline high explosive. A good understanding of the laser- induced chemical decomposition and growth to detonation of PETN is important. This work on PETN single crystals focused primarily on its mechanical and optical properties under laser pulse interaction. Laser pulse (E<2 J, tau= 150 ps, &=tilde; 1.06 mum) was focused on the single

V. T. Gromov

2005-01-01

320

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

321

Solution-processed, Self-organized Organic Single Crystal Arrays with Controlled Crystal Orientation  

PubMed Central

A facile solution process for the fabrication of organic single crystal semiconductor devices which meets the demand for low-cost and large-area fabrication of high performance electronic devices is demonstrated. In this paper, we develop a bottom-up method which enables direct formation of organic semiconductor single crystals at selected locations with desired orientations. Here oriented growth of one-dimensional organic crystals is achieved by using self-assembly of organic molecules as the driving force to align these crystals in patterned regions. Based upon the self-organized organic single crystals, we fabricate organic field effect transistor arrays which exhibit an average field-effect mobility of 1.1?cm2V?1s?1. This method can be carried out under ambient atmosphere at room temperature, thus particularly promising for production of future plastic electronics.

Kumatani, Akichika; Liu, Chuan; Li, Yun; Darmawan, Peter; Takimiya, Kazuo; Minari, Takeo; Tsukagoshi, Kazuhito

2012-01-01

322

Organic single crystal transistor characteristics of single-crystal phase pentacene grown by ionic liquid-assisted vacuum deposition  

NASA Astrophysics Data System (ADS)

Organic transistor characteristics of single-crystal phase pentacene were investigated. Ionic liquids (ILs) were used as not only a gate dielectric material in the transistors but also a crystallization solvent in vacuum deposition of pentacene. The crystal sizes reached 200 ?m and their surface exhibits a molecularly step-and-terrace structure. There was no sign of IL molecules inside the crystal, and the impurity level of 6,13-pentacenequinone was also reduced. The average value of the field-effect mobility was not so inferior to those for the conventional pentacene single crystals, and the highest value exceeded 5 cm2/Vs, with the on/off current ratio of 104.

Takeyama, Yoko; Ono, Shimpei; Matsumoto, Yuji

2012-08-01

323

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

324

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

325

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

326

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

327

Femtosecond laser pulse excitation of electrons and excitons in CaF2 and SrF2  

NASA Astrophysics Data System (ADS)

Conduction band electrons, valence holes and subsequently self-trapped excitons (STEs) are created in CaF2 and SrF2 by two-photon absorption of 5.9 eV photons. Transient absorption after femtosecond pulse excitation is measured at probe wavelengths of 3.0 eV and 4.4 eV, respectively. Transient absorption of 3.0 eV photons yields a fast initial response in SrF2 due to absorption by conduction band electrons, while in CaF2 we sample the F centre part of the STE at 3.0 eV and determine its formation time constant to be 690 fs. Excitation at 3.0 eV also yields a reduction in STE luminescence sampled nanoseconds after STE creation that is attributed to a forced recombination of the nearest-neighbour defect pair. Probing with 4.4 eV photons yields much weaker absorption but confirms results for 3.0 eV photons. Additionally we observe stronger absorption due to the formation of long living defects.

Lindner, R.; Reichling, M.; Williams, R. T.; Matthias, E.

2001-03-01

328

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

329

Optical and structural properties of chalcone NLO single crystals  

NASA Astrophysics Data System (ADS)

Organic compound (E)-1-(4-methoxyphenyl)-3-(2,3,5-trichlorophenyl)prop-2-en-1-one [MPTCPP] with molecular formula C 16H 11Cl 3O 2 was synthesized using Claisen-Schmidt condensation reaction method. 1H NMR spectra was recorded to identify the various functional groups present in the compound and confirm the chemical structure. The single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum study reveals that the crystal is transparent in the entire visible region and the absorption is observed at 364 nm. The Kurtz powder second harmonic generation (SHG) test shows that the MPTCPP is NLO active and its SHG efficiency is three times that of urea. Single crystal XRD study shows that the compound crystallizes in the monoclinic system with a space group Cc. The corresponding lattice parameters of the crystal are a = 28.215(5) Å, b = 3.9740(4) Å, c = 16.178(3) Å and V = 1503.0(4) Å 3. The micro hardness test was carried out and the work hardening coefficient value ( n) of the crystal was found to be 1.48. This indicates that the crystal is hard and is suitable for device application. The thermal study reveals that the thermal stability of the crystal is good.

Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Manjunath, H. R.; Karegouda, Prakash; Crasta, Vincent; Sridhar, M. A.

2011-11-01

330

''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

331

Double-crystal x-ray diffractometry of single crystals with microdefects  

Microsoft Academic Search

The known method of the `integral' diffuse scattering has been generalized in the Bragg case of x-ray diffraction for crystals, which contain large microdefects commensurable with the extinction length. In the framework of the developed statistical dynamical theory, relatively simple analytical expressions have been derived for coherent and diffuse components of reflectivity of single crystals with randomly distributed microdefects. To

V. B. Molodkin; S. I. Olikhovskii; E. N. Kislovskii; V. P. Krivitsky; E. G. Len; E. V. Pervak; G. E. Ice; B. C. Larson

2001-01-01

332

Structural and thermal characterization of CaO-MgO-SiO2-P2O5-CaF2 glasses  

SciTech Connect

The paper presents the influence of varying CaO/MgO ratio on the structure and thermal properties of CaO-MgO-SiO2-P2O5-CaF2 glasses. A series of eight glass compositions in the glass forming region of diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] - wollastonite (CaSiO3) ternary system have been designed and synthesized by varying diopside/wollastonite ratio in glasses. The as prepared melt-quenched glasses have been characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q2 (Si) species, while phosphorus tends to coordinate in orthophosphate environment in all the investigated glasses. The change in CaO/MgO ratio had an insignificant affect on the structure of glasses. The thermal sintering and crystallization parameters for the studied glasses have been obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass-ceramics have been analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite have crystallized as the main crystalline phases in all the glass-ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. Scanning electron microscopy (SEM) has been used to shed light on the microstructure of glass-ceramics. The possible implications of structure and sintering behaviour of glasses on their bioactivity have been discussed.

Kansal, Ishu; Goel, Ashutosh; Tulyaganov, Dilshat U.; Rajagopal, Raghu R.; Ferreira, Jose M.

2012-08-01

333

Evaluation of granulated BGO, GSO:Ce, YAG:Ce, CaF 2:Eu and ZnS:Ag for alpha\\/beta pulse shape discrimination in a flow-cell radiation detector  

Microsoft Academic Search

Granulated BGO, GSO:Ce, YAG:Ce, and CaF2:Eu; CaF2:Eu coated with a fluorescent polymer, and combinations of coated and uncoated CaF2:Eu with ZnS:Ag were evaluated for their ability to discriminate between alpha and beta particles in a flow-cell radiation detector. The evaluations were based on the analysis of pulse shape spectra. Various granulated scintillators were packed into flow cell detectors that were

T. A DeVol; S. B Chotoo; R. A Fjeld

1999-01-01

334

Enhancing the Mechanical Properties of Single-Crystal CVD Diamond  

SciTech Connect

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

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

2009-01-01

335

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

336

Growth of solid solution single crystals  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

337

Single-crystal structure of a covalent organic framework.  

PubMed

The crystal structure of a new covalent organic framework, termed COF-320, is determined by single-crystal 3D electron diffraction using the rotation electron diffraction (RED) method for data collection. The COF crystals are prepared by an imine condensation of tetra-(4-anilyl)methane and 4,4'-biphenyldialdehyde in 1,4-dioxane at 120 °C to produce a highly porous 9-fold interwoven diamond net. COF-320 exhibits permanent porosity with a Langmuir surface area of 2400 m(2)/g and a methane total uptake of 15.0 wt % (176 cm(3)/cm(3)) at 25 °C and 80 bar. The successful determination of the structure of COF-320 directly from single-crystal samples is an important advance in the development of COF chemistry. PMID:24143961

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

2013-11-01

338

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

339

Single crystal growth of potassium lithium niobate for SAW applications  

NASA Astrophysics Data System (ADS)

The growth of good quality, crack free medium size KLN single crystals using the Czochralski method, with dielectric and piezoelectric properties comparable or superior to the best known bronze composition SBN was demontrated. However, large ( 1 cm diameter) KLN crystals suitable for SAE Surface Acoustic Waves characterization without considerable cracking were not grown. Therefore, in pursuit of alternative bronze compositions with the potential for large crystal growth, work was initiated or, the growth and characterization of PBN and the stuffed bronze BSKNN. Initial characterization work shows both of these materials to be very promising for future SAW device development, and good quality single crystals of BSKNN with 1 cm square cross-section already were successfully grown. The physical properties of PBN and BSKNN also make them of interest for other piezoelectric, electro-optic, and nonlinear optic applications in addition to SAW devices.

Neurgaonkar, R. R.

1982-10-01

340

Isotropic behavior of an anisotropic material: single crystal silicon  

NASA Astrophysics Data System (ADS)

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

McCarter, Douglas R.; Paquin, Roger A.

2013-09-01

341

Dispersion of optical activity of magnesium sulfite hexahydrate single crystals  

NASA Astrophysics Data System (ADS)

The magnesium sulfite hexahydrate (MgSO3.6H2O) crystals are unique because they are the only representative (with sodium periodate) of the crystallographic class C3 (without a center of symmetry). The crystal symmetry suggests presence of nonlinearity, piezo- and pyro-electric properties and gyrotropy as well. Single crystals of MgSO3.6H2O (pure and doped with Ni, Co and Zn) for the time being are grown only by the original method developed in the Laboratory for Crystal growth at the Faculty of Physics in Sofia University. The first results of optical activity of pure MgSO3.6H2O and Zn doped MgSO3.6H2O crystals are described and analyzed in a wide spectral range. The optical activity manifests itself in the direction (0001) as a rotation of the polarization plane.

Dimov, T.; Bunzarov, Zh; Iliev, I.; Petkova, P.; Tzoukrovski, Y.

2010-11-01

342

Indium and nitrogen doping of GaSb single crystals  

NASA Astrophysics Data System (ADS)

GaSb single crystals doped with nitrogen and indium were grown using the Czochralski method without encapsulant in a flowing atmosphere of hydrogen and were studied for etch pit density (EPD) and Hall mobility. It has been found that the dopants had no influence on the average EPD in the GaSb crystals. However, EPD profiles of undoped and In-doped GaSb showed a decrease along the growth direction (from the beginning to the end of the crystals), while the EPD profile of N-doped crystals showed a sharp increase. This behaviour of N-doped crystals can be explained by the development of stresses near the solidification interface, as a result of nitrogen volatilization during growth.

Št?pánek, Bed?ich; Šesták'ová, V?ra

1992-09-01

343

Acquisition of Single Crystal Growth and Characterization Equipment  

Microsoft Academic Search

Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As

M. Brian Maple; Diego A. Zocco

2008-01-01

344

Single Crystal Neutron Diffraction Study of Potassium Cyanide  

Microsoft Academic Search

Neutron diffraction measurements were made on single crystals of KCN to obtain information about the disorder of the CN? ions in the cubic phase. The crystals were obtained by pulling from the melt by a modified Czochralski method. Data were collected on two four-circle diffractometers at room temperature and at 180°K, just above the cubic-orthorhombic phase transition. Structure factors were

D. L. Price; J. M. Rowe; J. J. Rush; E. Prince; D. G. Hinks; S. Susman

1972-01-01

345

Irradiation effects on sodium sulphanilate dihydrate single crystals  

NASA Astrophysics Data System (ADS)

The induced damage in single crystals of Sodium sulphanilate dihydrate (SSDH) irradiated at IUAC, New Delhi with 15 MV Pelletron accelerator with 100 MeV Ag 7+ and 70 MeV Li 3+ ions has been studied by optical measurements, mechanical hardness measurements, Electrical and ERDA measurements. Optical absorption measurements increase with the increase in fluence. The mechanical hardness of the crystal decreases on irradiation. The dielectric constant of SSDH increases on irradiation.

Mythili, P.; Kanagasekaran, T.; Khan, S. A.; Kulriya, P. K.; Kanjilal, D.; Gopalakrishnan, R.

2008-04-01

346

Infrared Optical Properties of Single Crystals of Tellurium  

Microsoft Academic Search

The fundamental optical absorption and photoconductivity of single crystals of tellurium has been investigated. Tellurium crystals exhibit dichroism in the infrared, i.e., the absorption constant depends on the polarization of the incident radiation. At 300°K for radiation polarized perpendicular to the C axis the absorption edge, located by means of an arbitrary criterion, is at 3.82 microns (0.324 ev); for

Joseph J. Loferski

1954-01-01

347

Doubling microsecond single pulses in a KTP crystal  

SciTech Connect

The 90{sup 0} phase-matching SHG is performed for microsecond single pulses from a Nd{sup 3+}:YAP laser in a KTP crystal with the 29% conversion efficiency. The 90{sup 0} phase-matching temperature is 54{sup 0}C. The crystal surface damage threshold measured without and with an antireflection coating was 107{+-}11 and 40{+-}4 J cm{sup -2}, respectively. (nonlinear optical phenomena)

Abrosimov, S A; Kochiev, D G [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Grechin, Sergei G [Scientific-Research Institute of Radioelectronics and Laser Technology at the N.E. Bauman Moscow State Technical University, Moscow (Russian Federation); Maklakova, N Yu; Semenenko, V N [Institute of Mineralogy and Petrography, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

2001-07-31

348

Solution hardening and softening of Nb-Zr single crystals  

Microsoft Academic Search

Single crystals of Nb-Zr solid-solution alloys containing 0.05–2 wt% Zr have been tested in compression at temperatures in the range 4 to 373 K. Stress-strain curves were obtained, and differential tests were made to measure both the strain-rate sensitivity and the thermal stress over the same temperature range. The mechanical data were supplemented by optical microscopy of the crystal surfaces

W. J. Botta; J. W. Christian; G. Taylor

1988-01-01

349

Semiconductor parameters of Bi 2Te 3 single crystal  

Microsoft Academic Search

Single crystals of Bi2Te3 were prepared by a modified Bridgman method. The as-prepared Bi2Te3 was investigated by X-ray diffraction (XRD). Anisotropic phenomena in the layered Bi2Te3 crystal was investigated. The measurements showed that the electrical conductivity, Hall mobility and Seebeck coefficient (TEP) have anisotropic nature. From these measurements type of conduction and several physical parameters such as diffusion coefficients, diffusion

M. M. Nassary; H. T. Shaban; M. S. El-Sadek

2009-01-01

350

Microstructural instability in coated single crystal superalloys  

Microsoft Academic Search

Specimens of CMSX-4 and CMSX-10 alloys have been platinum aluminised to give a single phase (Ni,Pt)Al coating and a two phase PtAl2–(Ni,Pt)Al coating, respectively. Specimens of the coated alloys were exposed in an oxidising environment for 188, 350 and 750h at a temperature of 1100°C. Specimens were then sectioned, polished and examined using scanning electron microscopy (SEM), energy dispersive X-ray

M. Reid; M. J. Pomeroy; J. S. Robinson

2004-01-01

351

Spatial dispersion in CaF2 caused by the vicinity of an excitonic bound state  

Microsoft Academic Search

The microscopic mechanism beyond the optical anisotropy of an ionic crystal which occurs for short wavelengths is investigated. The electron-hole, two particle propagator and its analytical behaviour close to the band edge of the one particle continuum plays a major role for the mechanism of this optical anisotropy. Especially for an ionic crystal the two particle bound state, the exciton,

M. Letza; E. Morsen

352

Spatial dispersion in CaF2 caused by the vicinity of an excitonic bound state  

Microsoft Academic Search

The microscopic mechanism beyond the optical anisotropy of an ionic crystal which occurs for short wavelengths is investigated. The electron-hole, two particle propagator and its analytical behavior close to the band edge of the one particle continuum plays a major role for the mechanism of this optical anisotropy. Especially for an ionic crystal the two particle bound state, the exciton,

Martin Letz; W. Mannstadt; Matthias Brinkmann; Ewald Moersen

2002-01-01

353

High Resolution Technique and Instrument for Measuring Lattice Parameters in Single Crystals.  

National Technical Information Service (NTIS)

A method of measuring the lattice parameter in an unknown single crystal by comparing its diffraction angle to a standard single crystal, on a double-crystal diffractometer is disclosed. The method comprises several steps including mounting the unknown an...

M. Fatemi

1990-01-01

354

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

355

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.

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

2014-01-01

356

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

NASA Technical Reports Server (NTRS)

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

Lundquist, C. A.

1974-01-01

357

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

358

Growth and luminescence properties of GaSb single crystals  

NASA Astrophysics Data System (ADS)

The growth of undoped GaSb single-crystals by the horizontal Bridgman method is analyzed. Photoluminescence measurements are used to determine the usefulness of this method for the production of device quality substrate material. The observed efficient quenching of bound exciton recombination by crystal inhomogeneities and residual stress demonstrated the high crystal quality of the Bridgman grown material. Antisite defect formation is also considered and the following are observed: formation of antimonium vacancies during the solidification process and defect migration causing the formation of double acceptor antisite defect.

Lewandowski, W.; Gajewska, M.; Pastuszka, B.; Bugajski, M.

359

Nucleation kinetics, growth and studies of ?-alanine single crystals  

NASA Astrophysics Data System (ADS)

Solubility and metastable zone width for the re-crystallized salt of ?-alanine was determined. Induction period measurement for the selected supersaturation ratios at room temperature (31 °C) was carried out for supersaturated aqueous solutions of ?-alanine and it is noticed that induction period decreases with increase of supersaturation ratio. The nucleation parameters such as Gibbs free energy change, radius and number of molecules of the critical nucleus, interfacial tension and the nucleation rate have been evaluated by classical nucleation theory. Single crystals of ?-alanine were grown using the optimized nucleation parameters by solution method and grown crystals have been subjected to various studies like XRD studies, FTIR, optical, thermal and SHG studies.

Shanthi, D.; Selvarajan, P.; HemaDurga, K. K.; Lincy Mary Ponmani, S.

2013-06-01

360

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

Microsoft Academic Search

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

Yasuhiko Takahashi; Yoshito Gotoh; Junji Akimoto

2003-01-01

361

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

Microsoft Academic Search

The largest Pb(In1\\/2Nb1\\/2)O3–PbTiO3(PIN-PT) binary system single crystal (about 20mmx10mm×5mm,4.5g) near the morphotropic phase boundary composition with well-developed (100) planes was grown by the flux method using PbO–PbF2–B2O3 flux. The PIN-PT(72\\/28) single crystal was found by simultaneous microdifferential thermal analysis and thermogravimetric analysis to show a peritectic melting at 1283°C with a partial decomposition of the perovskite crystal into a pyrochlore

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

2001-01-01

362

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

363

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

364

Improved growth technology of large MgO single crystals  

NASA Astrophysics Data System (ADS)

An improved growth technology (the arc-fusion method) has been successfully employed to grow large magnesium oxide (MgO) single crystals with an average size of 4-6 cm. Three adjustable graphite electrodes with different electric currents ( I>I>I) are applied, which technology is different from the conventional technology (using a uniform current). In addition, a proper control for the efficient use of different currents reduces the number of bubbles in the growth system, which allows us to obtain optically transparent high-purity MgO single crystals. Our present work shows that control of the temperature-gradient field in the whole process is the key to growing high-purity and large MgO single crystals.

Zhang, Xu; Xue, Dongfeng; Wang, Jiyang; Feng, Xiqi

2006-07-01

365

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

366

Spin and charge transport study in single crystal organic semiconductors  

NASA Astrophysics Data System (ADS)

Spin transport studies in amorphous rubrene films have shown exciting and promising results [1]. A large spin diffusion length in these amorphous films has increased the motivation to perform spin transport study in high purity single crystal rubrene. This will provide the fundamental understanding on the spin transport behavior in OS; not influenced by defects or traps. We will present work on small channel single crystal rubrene FET device with magnetic electrodes. For example, our preliminary studies have show mobility for FET with Co electrode to be 0.014cm^2/V-s. A study on the spin and charge transport properties in single crystals of OS with magnetic electrodes is being done and the results will be reported. The influence of gate voltage and applied magnetic field on the transport properties will be discussed. [1] J.H. Shim et al., PRL 100, 226603 (2008)

Raman, Karthik V.; Mulder, Carlijn L.; Baldo, Marc A.; Moodera, Jagadeesh S.

2009-03-01

367

Solution-phase growth of organic single-crystal arrays  

NASA Astrophysics Data System (ADS)

We have successfully developed a method for directly forming organic single-crystal thin films at designated locations on a substrate by solution-phase growth. An original micropattern, in which small rectangular regions were connected to a large rectangular region, was designed. The small regions and the large region were used as nucleation control regions (NCRs) and a growth control region (GCR), respectively. The key to success was to vary local supersaturation of a solution droplet by making a large difference in solvent evaporation between a NCR and a GCR. We found that the NCR played a very important role in forming a single nucleus and in investigating the possibility of control of the crystal orientation. By using the developed micropattern and controlling the solvent vapor pressure during growth, we fabricated single-crystal arrays of a stable organic semiconductor, 3,9-bis(4-ethylphenyl)-peri-xanthenoxanthene (C2Ph-PXX).

Goto, Osamu; Tomiya, Shigetaka; Murakami, Yosuke; Shinozaki, Akira; Toda, Akira; Kasahara, Jiro; Hobara, Daisuke

2012-10-01

368

Dielectric spectroscopy studies of ZnO single crystal  

NASA Astrophysics Data System (ADS)

Dielectric relaxation and charge transport induced by electron hopping in ZnO single crystal are measured by using a novocontrol broadband dielectric spectrometer. Typical Debye-like dielectric relaxation originating from electronic hopping between electronic traps and conductive band in surface Schottky barrier region is observed for ZnO single crystal-Au electrode system. However, after insulation of ZnO single crystal by heat treatment in rich oxygen atmosphere, dielectric relaxation and alternating current conductance are observed simultaneously in the dielectric spectra, implying that dielectric relaxation and charge transport can be induced simultaneously by electronic hopping at high temperature in an ordered system. The intrinsic correlation between local dielectric relaxation and long range charge transport offers us a new method to explore complicated dielectrics.

Cheng, Peng-Fei; Li, Sheng-Tao; Wang, Hui

2013-10-01

369

Synthesis and properties of erbium oxide single crystals  

SciTech Connect

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

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

1999-04-01

370

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

371

Magnetothermal properties of single crystal dysprosium  

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

372

Crystal growth of alkali metal ion doped potassium niobate fiber single crystals  

NASA Astrophysics Data System (ADS)

Alkali metal (Na, Rb or Cs) ion doped KNbO 3 fiber single crystals are grown using an original pulling down method, to improve their composition change during a crystal growth, by means of co-doping of small ionic size Na and large ionic size Rb or Cs into KNbO 3. In spite of the co-doping, single crystals can be grown with orthorhombic single-phase at room temperature, as well as pure KNbO 3. Their electric properties, such as impedance, are changed depending on the doping ions. Na and Rb co-doped KNbO 3 is promising Pb free ferroelectric and piezoelectric crystals.

Kimura, H.; Tanahashi, R.; Zhao, H. Y.; Maiwa, K.; Cheng, Z. X.; Wang, X. L.

2010-05-01

373

Copper underpotential deposition on Ru quasi-single-crystal films  

Microsoft Academic Search

Ru quasi-single-crystal electrodes, prepared by resistive heating of Ru deposited on Pt single-crystal surfaces in a nitrogen atmosphere, have been used to study copper underpotential deposition (Cu-UPD), Bulk and surface Cu stripping experiments were performed on the low-index Ru\\/Pt(100), Ru\\/Pt(110) and Ru\\/Pt(111) quasi-crystalline film electrodes and also stepped Ru\\/Pt(S)[n(100)×(111)] and Ru\\/Pt(S)[4(111)×(100)] electrodes vicinal to the (100) and (111) planes respectively.

Nicky Bogolowski; Sharon Huxter; Abd-El-Aziz A. Abd-El-Latif; Gary A. Attard; Helmut Baltruschat

2010-01-01

374

Cryogenic motion performances of a piezoelectric single crystal micromotor  

NASA Astrophysics Data System (ADS)

This study investigates the cryogenic performances of a millimeter-size piezoelectric ultrasonic linear micromotor. The piezoelectric vibrator of the micromotor is made of Pb(In1/2Nb1/2)O3 -Pb(Mg1/3Nb2/3)-PbTiO3 single crystal and operated in first-bending wobbling mode. Experiments show that the piezoelectric single crystal micromotor works effectively even at extremely low temperature of -175 °C, although its resonance peaks vary with temperature significantly. This work confirms the feasibility of cryogenic operation of the piezo-micromotor, which is meaningful for aerospace or superconducting microwave application.

Li, Xiaotian; Wu, Yuting; Chen, Zhijiang; Wei, Xiaoyong; Luo, Haosu; Dong, Shuxiang

2014-04-01

375

Apparatus And Method For Producing Single Crystal Metallic Objects  

SciTech Connect

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

376

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

377

Synthesis of Large Single Crystals of LaMnPO  

NASA Astrophysics Data System (ADS)

The compound LaMnPO is isostructural with LaFeAsO, a recently discovered high-temperature superconductor, but optical spectroscopy and transport measurements of this compound have been heretofore limited by small crystal size. Accordingly, crystal syntheses from Sn, Pb and molten salt fluxes (including NaCl/KCl, LiCl/NaCl, KCl, CaCl2, BaCl2/CaCl2 and KCl/CaCl2) were investigated. Fluorine doping was explored; concentrations less than 30 at.% (nominal) had no effect on crystal size; concentrations greater than 40 at.% (nominal) did not yield crystals. Once growth parameters were optimized, the crystals grew in a flat rectangular shape with black luster; their composition was verified with powder and single crystal x-ray diffraction. Successful growths yielded crystals with dimensions up to 3.2 mm by 1 mm by 10 ?m, a significant improvement upon previously reported growths in the literature. These large crystals enabled our group to perform a wide range of experiments that were previously restricted to polycrystalline materials. It may be feasible to extend these methods to the synthesis of similar compounds.

Smith, Greg; Simonson, Jack; Marques, Carlos; Leyva, Victor; Aronson, Meigan

2011-03-01

378

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals  

NASA Astrophysics Data System (ADS)

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV-visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.

Manikandan, M.; Vijaya Prasath, G.; Bhagavannarayan, G.; Vijayan, N.; Mahalingam, T.; Ravi, G.

2012-09-01

379

Crystal growth and spectral studies of nonlinear optical ?-glycine single crystal grown from phosphoric acid  

NASA Astrophysics Data System (ADS)

Single crystals of the organic nonlinear material ?-glycine have been grown in the presence of phosphoric acid by slow-evaporation method. The crystal structure is confirmed by X-ray powder diffraction method. The thermal stability and decomposition of the sample have been studied by thermal analysis. The result shows that the transition temperature, i.e. transition from ?- to ?-glycine is enhanced from 165 °C to 191 °C. The modes of vibrations of different molecular groups present in glycine have been identified by spectral analyses. The transmittance spectrum of ?-glycine crystal shows that the lower UV cut-off wavelength lies at 230 nm. Second harmonic generation (SHG) conversion efficiency has been estimated as 125 mV and the output power by the crystal was 1.3 times that of potassium dihydrogen phosphate (KDP) crystal. The dielectric and microhardness measurements have been carried out on the ?-glycine crystal.

Parimaladevi, R.; Sekar, C.

2010-09-01

380

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

381

Structural and optical properties of a new chalcone single crystal  

NASA Astrophysics Data System (ADS)

A new nonlinear optical material 1-(4-methylthiophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one with molecular formula C17H16O2S was synthesized by using the Claisen-Schmidt condensation reaction method. The Various functional groups present in the compound were identified using recorded FT-IR spectrum. The crystal growth parameters have been studied using solubility test and acetone is found to be a very good solvent for the crystal growth at an ambient temperature. The transparent high quality single crystals up to a size of 26×2×2 mm3 were grown using the slow evaporation solution growth technique. UV-visible study was carried out and the spectrum reveals that the crystal is transparent in the entire visible region and absorptive in the UV region. The refractive index is determined using Brewster's angle method. The optical energy band gap of the material is measured using Tauc's plot and the direct method. The single crystal XRD of MMPP crystal shows the following cell parameters: a=5.9626(2) Å, b=15.3022(6) Å, c=16.0385(7) Å, ?=?=?=90°, volume=1463.37(10) Å3 with a space group of Pna21. The compound MMPP exhibits optical nonlinearity (NLO) and its second order NLO efficiency is 3.15 times to that of urea. The effect of functional groups OCH3 and SCH3 on the non-linearity as well as the structural property of the compound has been discussed. The crystal is thermally stable. High NLO efficiency, good thermal stability, good transparency and ability to grow as a high quality single crystal make this material very attractive for opto-electronic applications.

Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Poojary, Boja

2012-09-01

382

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

383

Tunable Single-Polarization Single-Mode Photonic Crystal Fiber Based on Liquid Infiltrating  

Microsoft Academic Search

We proposed and demonstrated a tunable single-po- larization single-mode photonic crystal fiber (SPSM-PCF) based on selectively infiltrating liquid into air holes of high birefringence photonic crystal fiber (HB-PCF). A full-vector finite-element method (FEM) is used to analyze the SPSM operation range and its tunable characteristics. The starting wavelength of the SPSM operation range can be widely tuned from 2014 to

Xibao Zheng; Yan-Ge Liu; Zhi Wang; Tingting Han; Boyin Tai

2011-01-01

384

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

Microsoft Academic Search

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

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

2004-01-01

385

Relaxor-PT Single crystals: Observations and Developments  

PubMed Central

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

Zhang, Shujun; Shrout, Thomas R.

2011-01-01

386

Growth of Rare Earth-Cobalt Single Crystals  

NASA Astrophysics Data System (ADS)

The next generation of permanent magnet materials appears to be of the rare earth-cobalt type having the general formula R2(Co1-xFex)17. Research on these and related materials requires single crystals for evaluation of fundamental parameters. Two of these, Y2Co17 and Ho2Co17, are the subject of this paper. They are both congruently melting but due to their chemical reactivity and low surface tension are difficult to grow as single crystals. A unique crystal growth method based on thermal-imaging was used and will be briefly described. This technique requires no crucible for Czochralski growth and can operate with any desired atmosphere. Single crystals of both materials have been grown. These crystals are of sufficient size (8 by 30 mm.) for essentially all magnetic measurements. Problems related to their growth are discussed and the growth parameters are given. Results of their evaluation are also presented. They include x-ray, electron microprobe and mass spectrographic evaluation of crystalline perfection and purity.

Field, William G.; Sampson, John L.

1973-01-01

387

Single-point diamond turning of DAST crystals  

NASA Astrophysics Data System (ADS)

Organic nonlinear optical crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate (DAST) can be used for new optical devices such as high frequency electro-optical sampling wavelength conversion, submillimeter wave generation, and terahertz-wave generation. The crystal is soft, brittle and hygroscopic so that it is very difficult to get optical surfaces by using conventional optical polishing process. This paper deals with single-point diamond turning for getting optical surfaces on DAST crystals. Three typical planes on DAST crystals were finished by single-point diamond turning. The quality of single-point diamond turned surface depends upon the crystallographic plane, cutting direction, cutting speed, depth of cut, feed rate, rake angle, nose radius of diamond tool, tool clearance angle, tool wear, lubricant and its supplying method. The turned surface was measured with a Nomarski interference microscope, atomic force microscope, and a three-dimensional optical profiler. By optimizing the machining conditions, 0.33 nm rms surface roughness and 8.7 nm p-v flatness in 1 mm square were obtained on a b-plane of DAST crystal.

Namba, Yoshiharu; Tsukahara, Masahiro; Fushiki, Atsuya; Suizu, Koji; Ito, Hiromasa

2004-01-01

388

Green "planting" nanostructured single crystal silver  

PubMed Central

Design and fabrication of noble metal nanocrystals have attracted much attention due to their wide applications in catalysis, optical detection and biomedicine. However, it still remains a challenge to scale-up the production in a high-quality, low-cost and eco-friendly way. Here we show that single crystalline silver nanobelts grow abundantly on the surface of biomass-derived monolithic activated carbon (MAC), using [Ag(NH3)2]NO3 aqueous solution only. By varying the [Ag(NH3)2]NO3 concentration, silver nanoplates or nanoflowers can also be selectively obtained. The silver growth was illustrated using a galvanic-cell mechanism. The lowering of cell potential via using [Ag(NH3)2]+ precursor, together with the AgCl crystalline seed initiation, and the releasing of OH? in the reaction process, create a stable environment for the self-compensatory growth of silver nanocrystals. Our work revealed the great versatility of a new type of template-directed galvanic-cell reaction for the controlled growth of noble metal nanocrystals.

Zhao, Hong; Wang, Fei; Ning, Yuesheng; Zhao, Binyuan; Yin, Fujun; Lai, Yijian; Zheng, Junwei; Hu, Xiaobin; Fan, Tongxiang; Tang, Jianguo; Zhang, Di; Hu, Keao

2013-01-01

389

Nanowire coupling to photonic crystal nanocavities for single photon sources  

Microsoft Academic Search

We demonstrate highly efficient evanescent coupling via a silica loop-nanowire, to ultra-small (0.5 (lambda\\/n)3 ), InAs\\/InP quantum dot photonic crystal cavities, specifically designed for single photon source applications. This coupling technique enables the tuning of both the Q-factor and the wavelength of the cavity mode independently, which is highly relevant for single photon source applications. First, this allows for the

Christian Grillet; Christelle Monat; Cameron L. Smith; Benjamin J. Eggleton; David J. Moss; Simon Frédérick; Dan Dalacu; Philip J. Poole; Jean Lapointe; Geof Aers; Robin L. Williams

2007-01-01

390

Single-photon frequency conversion in nonlinear crystals  

NASA Astrophysics Data System (ADS)

Frequency conversion of single photons in a nonlinear crystal is theoretically discussed. Losses and noise are included within a Heisenberg-Langevin formalism for the propagating photon field. We calculate the first- and second-order correlation functions of the frequency-converted light when the input is a train of single-photon pulses. This model allows one to identify the requirements on the nonlinear device so that it can be integrated in a quantum network.

Blum, Susanne; Olivares-Rentería, G. A.; Ottaviani, Carlo; Becher, Christoph; Morigi, Giovanna

2013-11-01

391

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

392

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

393

Sodium sulfate heptahydrate I: The growth of single crystals  

NASA Astrophysics Data System (ADS)

Sodium sulfate is one of the most damaging salts for porous building materials. In our quest to increase the durability of civil structures and cultural heritage we need to understand its crystallization behavior. In this paper we investigate the cooling-induced growth of the metastable heptahydrate crystal phase by combining nuclear magnetic resonance, for non-destructive measurement of the concentration, with time-lapse microscopy, to visualize the crystal growth. The growth rate is found to be controlled by interface attachment kinetics. The kinetic growth parameter Gk ranges from 0.001 to 0.007 mm/s for single crystals in a temperature range of 4.8-13 °C.

Derluyn, Hannelore; Saidov, Tamerlan A.; Espinosa-Marzal, Rosa M.; Pel, Leo; Scherer, George W.

2011-08-01

394

Growth of KDP single crystal blocks in defined crystallographic direction  

NASA Astrophysics Data System (ADS)

It has been shown that sectorial and zonary unhomogeneities of the crystal together with changing temperature conditions in the course of its growth are among the main causes of appearance of the structure defectiveness and property unhomogeneities in the volume of crystals grown. The method of rapid growing in the defined crystallographic direction [101] of the large-size KDP and DKDP single crystallites on the plain seed has been developed, which are applicable for production of wide aperture frequency multipliers of laser emission into the second/third harmonics (type II). Usage of such a method of growing allows to increase the coefficient of use of crystal material (KDP up to 40% and DKDP up to 70%) at production of nonlinear laser elements. High quality of the crystals grown has been confirmed by the results of investigation of structural perfection, optical homogeneity and bulk laser damage resistance threshold.

Salo, V. I.; Voronov, A. P.; Tkachenko, V. F.; Babenko, G. N.; Makoveev, A. V.

2011-12-01

395

Strain incompatibility and residual strains in ferroelectric single crystals  

PubMed Central

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

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

2012-01-01

396

Room Temperature Single-Photon Source: Single-Dye Molecule Fluorescence in Liquid Crystal Host  

SciTech Connect

OAK-(B204)We report on new approaches toward an implementation of an efficient, room temperature, deterministically polarized, single-photon source (SPS) on demand-a key hardware element for quantum information and quantum communication. Operation of a room temperature SPS is demonstrated via photon antibunching in the fluorescence from single terrylene-dye molecules embedded in a cholesteric liquid crystal host. Using oxygen-depleted liquid crystal hosts, dye-bleaching was avoided over the course of more than 1 h of continuous 532-nm excitation. Liquid crystal hosts (including liquid crystal oligomers/polymers) permit further increase of the efficiency of the source: (1) by aligning the dye molecules along a direction preferable for the maximum excitation efficiency; (2) by tuning a one-dimensional (1-D) photonic-band-gap microcavity of planar-aligned cholesteric (chiral nematic) liquid crystal layer to the dye fluorescence band.

Lukishova, S.G.; Schmid, A.W.; McNamara, A.J.; Boyd, R.W.; Stroud, C.R.Jr.

2003-12-31

397

Isotopic Mixing in OO'-Dideuterosuccinic Acid Single Crystals  

Microsoft Academic Search

Extensive isotopic mixing in partially deuterated succinic acid single crystals brought about by moderate doses of ionizing radiation point to a radiochemical reaction occurring with very large G value and thus to a free radical chain reaction. The isotopic mixing is evident in the ESR spectrum of the free radicals produced in low concentration and also, remarkably, in the IR

L. G. Ericson; D. R. Cutten

1969-01-01

398

A Study of Single Crystal Fatigue Failure Criteria  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

399

Single Crystals of CeMg3 (TEXUS 7) ESA.  

National Technical Information Service (NTIS)

On Earth, the growth of single crystals of the compound CeMg3 using the vertical Bridgman technique is impeded by the sedimentation of the denser component, cerium, which leads to the formation of the CeMg phase at the bottom of the crucible. By operating...

J. Pierre J. Baruchel M. Schlenker E. Siaud

1991-01-01

400

Low-Cost Single-Crystal Turbine Blades. Volume 2.  

National Technical Information Service (NTIS)

The overall objectives of Project 3 were to develop the exothermic casting process to produce uncooled single-crystal (SC) HP turbine blades in MAR-M 247 and higher strength derivative alloys and to validate the materials process and components through ex...

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

1984-01-01

401

Low-Cost Single-Crystal Turbine Blades, Volume 1.  

National Technical Information Service (NTIS)

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...

T. E. Strangman B. Heath M. Fujii

1983-01-01

402

Anisotropy of Nickel-Base Superalloy Single Crystals.  

National Technical Information Service (NTIS)

The influence of orientation on the tensile and stress rupture behavior of 52 Mar-M247 single crystals was studied. Tensile tests were performed at temperatures between 23 and 1093 C; stress rupture behavior was examined between 760 and 1038 C. The mechan...

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

1980-01-01

403

Neutron spectrometers based on single crystal CVD diamond  

Microsoft Academic Search

A new grade of single crystal CVD diamond has been developed that possesses unprecendented electrical properties [1]. The carrier lifetime in this new material is reported to be > 2 microseconds, a 1000 fold improvement over existing grades of CVD diamond. This could lead to a new generation of electrical devices based on diamond, including radiation sensors. Over the past

Gregory Schmid; Jeffrey Koch; Michael Moran; Richard Lerche; Nobuhiko Izumi; Hye-Sook Park; Thomas Phillips; Robert Turner

2003-01-01

404

Reliability analysis of single crystal NiAl turbine blades  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

405

Electrolytic Growth and Preparations of Transition Metal Compound Single Crystals.  

National Technical Information Service (NTIS)

Single crystals of NbSe2, and WSe2 were grown by a chemical transport technique. The conductivity of NbSe2 which is metallic, varies from 5.5 ohm-cm at 300K to 28 ohm-cm at 100K. It has a superconducting transition temperature at 7K. WSe2 is a p-type semi...

A. Wold

1967-01-01

406

The Growth of Berlinite (AlPO4) Single Crystals.  

National Technical Information Service (NTIS)

Single crystals of the berlinite mineral phase of anhydrous aluminum orthophosphate have been grown for possible surface acoustic wave applications. The desired piezoelectric form of AlPO4 is the alpha-phase which is stable from 130 to 580 C. A seeded hyd...

L. E. Drafall R. F. Belt

1980-01-01

407

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

408

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

409

Creep, plasticity, and fatigue of single crystal superalloy  

Microsoft Academic Search

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

Alexander Staroselsky; Brice N. Cassenti

2011-01-01

410

Single Sideband Quartz Crystal Units for VHF Applications (Metal Enclosures).  

National Technical Information Service (NTIS)

The purpose of this contract is to design, develop and fabricate 4 MHz single sideband quartz crystal units for operation on the fundamental frequency at antiresonance into a load capacitance of 32pf. Improved reliability and frequency-time stability are ...

G. E. Ritter

1966-01-01

411

Ambipolar Electric Double Layer Transistors Using Organic Single Crystals  

Microsoft Academic Search

Among organic devices, ambipolar transistors are very unique device, in which both electrons and holes are equally mobile and we are able to observe light emission through the recombination of them. Progress in the applications of such light-emitting transistors (LETs) based on organic single crystals has provided possibilities in developing organic laser. However, in these LETs, the current density is

Taishi Takenobu; Di Wen; Hidekazu Shimotani; Shimpei Ono; Yoshihiro Iwasa

2011-01-01

412

Ambipolar organic single-crystal transistors based on ion gels.  

PubMed

Ambipolar electric double-layer transistors (EDLTs) using organic single crystals and ion-gel electrolytes are successfully created by optimising the fabrication of gel films. The p- and n-type EDLTs enable us to investigate the HOMO-LUMO gap energy of semiconductors, offering a new method with which to measure it. PMID:22729886

Yomogida, Yohei; Pu, Jiang; Shimotani, Hidekazu; Ono, Shimpei; Hotta, Shu; Iwasa, Yoshihiro; Takenobu, Taishi

2012-08-22

413

MAGNETIZATION IN SINGLE CRYSTALS OF SOME RARE-EARTH ORTHOFERRITES  

Microsoft Academic Search

Single crystals of the rare-earth orthoferrites (MFeOâ) have been ; prepared and their magnetic properties measured from room temperature to 1.3 deg ; K for M = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. (L.T.W.);

R. M. Bozorth; Vivian Kramer; J. P. Remeika

1958-01-01

414

Microwave Resonance Relations in Anisotropic Single Crystal Ferrites  

Microsoft Academic Search

The ferromagnetic resonance relations in magnetically anisotropic single crystal ferrites are reexamined. Detailed analyses are presented for spherical specimens. Generalized nomograms are shown which relate the resonance frequency to static field H, anisotropy parameter K\\/M, and the static field orientation. The nature of the susceptibility tensor is discussed. Below magnetic saturation, multidomain structure is expected. Under these conditions, with H

Joseph Artman

1956-01-01

415

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

416

Unified constitutive model for single crystal deformation behavior with applications  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

417

Vapor Phase Growth of Stannic Oxide Single Crystals.  

National Technical Information Service (NTIS)

Single crystals of stannic oxide, SnO2, of higher purity and with higher Hall mobility than any previously reported have been grown from the vapor using the reaction SnC14 + 2H2 + 02 = SnO2 + 4HCl at 1250C and 10 Torr. The stannic chloride is obtained fro...

C. G. Fanstad A. Linz R. H. Rediker

1969-01-01

418

A Technique for producing Regular Patterns on Single Crystals  

Microsoft Academic Search

TO examine the deformation of single crystals, it is often necessary to have regularly spaced marks or a grid on the surface of the specimen. In particular, the analysis of plastic strains is carried out by investigating the distortion of the grid using the intersections of the lines as reference points. There are several methods for producing a grid, but

G. B. Craig

1963-01-01

419

Dielectric properties of lithium niobate single crystals doped with gadolinium  

NASA Astrophysics Data System (ADS)

In this paper dielectric properties of LiNbO3:Gd single crystals at temperatures ~ 290-490 K at narrow frequency range (0.5-106 Hz) are presented. The influence of growth conditions was also investigated. The anomalies on dielectric plots depend on the development of the micro- and nano-domain structure.

Palatnikov, M. N.; Sidorov, N. V.; Sandler, V. A.; Bormanis, K.; Smeltere, I.

2013-12-01

420

Single-crystal elasticity of hydrous mantle minerals  

Microsoft Academic Search

Elastic properties of minerals are crucial in modeling the velocity structure of Earth's interior, and can be strongly affected by hydration. Measurements on the elasticity of hydrous minerals are essential to help identify hydrogen-rich regions, and understand the behavior of hydrogen in the Earth's deep interior. In this thesis, I used Brillouin scattering to measure the single-crystal elasticity of some

Zhu Mao

2009-01-01

421

Tribological Properties of Sintered Polycrystalline and Single Crystal Silicon Carbide.  

National Technical Information Service (NTIS)

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 i...

D. H. Buckley K. Miyoshi M. inivasan

1982-01-01

422

Mechanical Effects of Electron Irradiation in Iron Single Crystals.  

National Technical Information Service (NTIS)

Electron irradiation (2 MeV, up to 6 x 10 exp 18 e/cm exp 2 ) decreased the yield stress of iron single crystals in the temperature range from 4.2 to 80 exp 0 K. The softening effect was highly dependent on the tensile axis orientation. The temperature an...

M. Meshii A. Sato

1976-01-01

423

Growth and Characterization of Disodium Hydrogen Orthophosphate (DSHP) Single Crystals  

Microsoft Academic Search

Nonlinear optical materials are expected to be active elements for optical communication and optoelectronics. Because of their higher nonlinearity, these materials show the second order nonlinear optical effects. Among the nonlinear phenomena frequency doubling, frequency mixing, and electro-optic modulation are important in the field of optical image storage and optical communications. In the present work, disodium hydrogen orthophosphate single crystals

N. J. John; P. Selvarajan; S. Benita Jeba Silviya; C. K. Mahadevan

2007-01-01

424

Transient Oxidation of Single Crystal NiAl+Zr.  

National Technical Information Service (NTIS)

The 800 C oxidation of oriented single crystals of Zr doped beta-NiAl was studied using transmission electron microscopy. The oxide phases and metal-oxide orientation relationships were determined to characterize the transient stages of oxidation prior to...

J. K. Doychak

1983-01-01

425

Growth of large single crystals of MgO  

SciTech Connect

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

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

1997-06-12

426

Growth of potassium sodium niobate single crystals by solid state crystal growth  

Microsoft Academic Search

Single crystals of (K0.5Na0.5)NbO3 have been grown for the first time by the solid state crystal growth process. A KTaO3 seed crystal was embedded in a matrix of (KxNa1?x)NbO3 powder with a nominal composition of (K0.5Na0.5)NbO3. K4CuNb8O23 was used as a liquid-phase sintering aid. During sintering a single crystal of (K0.5Na0.5)NbO3 grew on the KTaO3 seed. Scanning electron microscopy energy

John G. Fisher; Andreja Bencan; Janez Holc; Marija Kosec; Sophie Vernay; Daniel Rytz

2007-01-01

427

Crystallization and properties of CrSi2 single crystals grown from a tin solution-melt  

NASA Astrophysics Data System (ADS)

Using the solution-melt method combined with the Bridgman method, CrSi2 single-crystal needles and single-crystal tubes are grown at a temperature lower than their melting (crystallization) temperature. Microcrystals thus grown feature an anomalously high thermal emf. The growth of CrSi2 single-crystal tubes is an important step forward in the production of various devices based on high-temperature thermoelectric materials.

Solomkin, F. Yu.; Zaitsev, V. K.; Kartenko, N. F.; Kolosova, A. S.; Orekhov, A. S.; Samunin, A. Yu.; Isachenko, G. N.

2010-01-01

428

Microwave Induced Direct Bonding of Single Crystal Silicon Wafers  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

429

Optical properties of Sulfur doped InP single crystals  

NASA Astrophysics Data System (ADS)

Optical properties of InP:S single crystals were investigated using spectrophotometric measurements in the spectral range of 200–2500 nm. The absorption coefficient and refractive index were calculated. It was found that InP:S crystals exhibit allowed and forbidden direct transitions with energy gaps of 1.578 and 1.528 eV, respectively. Analysis of the refractive index in the normal dispersion region was discussed in terms of the single oscillator model. Some optical dispersion parameters namely: the dispersion energy (Ed), single oscillator energy (Eo), high frequency dielectric constant (??), and lattice dielectric constant (?L) were determined. The volume and the surface energy loss functions (VELF & SELF) were estimated. Also, the real and imaginary parts of the complex conductivity were calculated.

El-Nahass, M. M.; Youssef, S. B.; Ali, H. A. M.

2014-05-01

430

Is the methanation reaction over Ru single crystals structure dependent?  

PubMed

The influence of monoatomic steps and defects on the methanation reaction over ruthenium has been investigated. The experiments are performed on a Ru(0 1 54) ruthenium single crystal, which contains one monoatomic step atom for each 27 terrace atoms. The methanation activity is measured at one bar of hydrogen and CO in a high pressure cell, which enables simultaneous measurements of the local reactivity of the well defined single crystal surface and the global reactivity of the entire crystal and its auxiliary support. By adding sulfur we observe that the measured activity from the well defined stepped front-side of the crystal is poisoned faster than the entire crystal containing more defects. We also observe that additional sputtering of the well-defined front-side increases the reactivity measured on the surface. Based on this, we conclude that the methanation reaction takes place on undercoordinated sites, such as steps and kinks, and that the methanation reaction is extremely structure dependent. Simulations of the flow, temperature, and product distributions in the high pressure cell are furthermore presented as supplementary information. PMID:21258708

Vendelbo, Søren B; Johansson, Martin; Nielsen, Jane H; Chorkendorff, Ib

2011-03-14

431

Growth and characterization of terbium fumarate heptahydrate single crystals  

NASA Astrophysics Data System (ADS)

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

Want, B.; Shah, M. D.

2014-03-01

432

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

NASA Astrophysics Data System (ADS)

A promising WC-Co-Cu-BaF 2/CaF 2 self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC-Co, Cu and BaF 2/CaF 2 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 BaF 2/CaF 2 phase, which not only offered effective solid lubrication, but also acted as bind phases to mend the microstructure and protected WC from decomposition. The optimized specimen contained 10 wt.% Cu and 10 wt.% BaF 2/CaF 2 in a WC-Co matrix, which had excellent frictional and wear performance. The wear mechanism of the self-lubricating wear resistant coating was discussed with the microstructures, compositions and mechanical properties of the composite materials in detail.

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

2010-06-01

433

Single crystal structure analysis of a single Sm2Fe17N3 particle  

NASA Astrophysics Data System (ADS)

We performed single crystal structure analysis of Sm2Fe17N3 using X-ray diffraction. A pick-up system combined with a micromanipulation tool driven by piezoelectric actuators and a microgripper was used. A single Sm2Fe17Nx particle with the diameter of about 20 ?m was picked up, and X-ray diffraction was measured using an X-ray diffractometer at the synchrotron radiation beamline at the Photon Factory, KEK. Single crystal structure analysis of a Sm2Fe17N3 particle was performed and the structure was successfully determined from X-ray diffraction patterns. The space group and the lattice constants were determined to be R-3m (#166) a = b = 8.7206 Å and c = 12.6345 Å, respectively. Atomic positions of Sm and Fe atoms were accurately determined by single crystal structure analysis of only one particle.

Inami, Nobuhito; Takeichi, Yasuo; Ueno, Tetsuro; Saito, Kotaro; Sagayama, Ryoko; Kumai, Reiji; Ono, Kanta

2014-05-01

434

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

Microsoft Academic Search

A novel organic crystal, l-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP), synthesized and grown from aqueous solution, is presented. X-ray single diffraction shows that LAPP belongs to the monoclinic crystallographic system with space group P21. FT-IR and UV\\/vis\\/NIR transmission spectra have been employed to characterize the crystal. The computational calculation based on the density functional theory at the B3LYP\\/6-31G (d, p) level

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

2011-01-01

435

In situ observations of crystal growth of spherical Si single crystals  

NASA Astrophysics Data System (ADS)

Spherical Si single crystals for solar cell substrates have been grown successfully with a yield of almost 100%. Spherical Si multicrystals with diameters of approximately 400 ?m in a teardrop shape were initially fabricated by a dropping method. The as-dropped spherical Si multicrystals were melted into droplets on a silica plate in an oxygen atmosphere, and the Si droplets were then recrystallized to form single crystals by supercooling within a specific temperature range. It was found that the recrystallization process occurred unidirectionally in each Si droplet, and recrystallized spherical Si single crystals free of defects (dislocations and oxidation-induced stacking faults, OSF) were obtained at a supercooling in the range of 12-42 °C. For supercooling ranging from 42 to 87 °C, spherical Si single crystals could still be obtained; however, many defects such as dislocations and OSF were generated. When the supercooling was larger than 87 °C, the crystal growth showed a dendritic growth mode and only multicrystals were obtained.

Huang, Xinming; Uda, Satoshi; Tanabe, Hideyoshi; Kitahara, Nobuyuki; Arimune, Hisao; Hoshikawa, Keigo

2007-09-01

436

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

437

Bulk properties of very large diameter silicon single crystals  

NASA Astrophysics Data System (ADS)

It has been experimentally found that it will be difficult to grow 300 mm or larger diameter crystals with similar quality as for 200 mm or smaller diameter crystals. This phenomenon can be understood within the frame of the Voronkov theory in which the value of the parameter V/ G ( V=pull rate, G=temperature gradient at the growth interface) determines which type of defect forms in the growing crystal. Due to fundamental technological constraints, the pull rate of silicon single crystals has to be reduced as the diameter increases. For crystal diameters beyond 300 mm, the reduction of pull rate is so large, that V/ G( r) ( r=radial position) can probably no longer be kept above the critical value Ccrit=1.34×10 -3 cm 2 K -1 min -1 over the entire crystal volume by the present growth technology. As a result, the defect behavior of the silicon bulk changes. The aggregation of defects is now dominated by excess Si interstitials instead of vacancies and, hence, L-pits (dislocation loops) are observed instead of microvoids. Unless new methods for the suppression of L-pits can be developed, this will seriously challenge the use of polished wafers in very large diameter device manufacturing lines, as L-pits can severely damage the device performance. A promising solution to the defect problem appears to be p+p- epi wafers.

von Ammon, W.; Dornberger, E.; Hansson, P. O.

1999-03-01

438

Growth and electrical properties of mercury indium telluride single crystals  

SciTech Connect

A novel photoelectronic single crystal, mercury indium telluride (MIT), has been successfully grown by using vertical Bridgman method (VB). The crystallinity, thermal and electrical properties of the MIT crystal were investigated. The results of X-ray rocking curve show that the as-grown MIT crystal has good crystal quality with the FWHM on (3 1 1) face of about 173 in. DSC measurement reveals that the Hg element is easy to solely evaporate from the compound when the temperature is higher than 387.9 deg. C in the open system. Hall measurements at room temperature show that the resistivity, carrier density and mobility of the MIT crystal were 4.79 x 10{sup 2} {omega} cm, 2.83 x 10{sup 13} cm{sup -3} and 4.60 x 10{sup 2} cm{sup 2} V{sup -1} s{sup -1}, respectively. The reduction of carrier mobility and the increase of the resistivity are related to the adding of In{sub 2}Te{sub 3} into HgTe, which changes the energy band structure of the crystal.

Wang Linghang [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072 (China)], E-mail: uswlh@yahoo.com.cn; Dong Yangchun; Jie Wanqi [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072 (China)

2007-11-06

439

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

440

Growth and characterization of CePtIn single crystal  

NASA Astrophysics Data System (ADS)

CePtIn crystallizes in a hexagonal ZrNiAl-type structure and exhibits the properties varying between the magnetically ordered state and valence fluctuating state. The competition between RKKY and Kondo interaction in this compound is most significant among the CeTX family. Moreover, the signs of non-Fermi liquid behavior are observed in specific heat and electrical resistivity measurements at low temperatures. Until now all properties have been measured only on polycrystals, often with suspicion of foreign phase in the samples. The preparation of CePtIn single crystal as well as its structure and chemical characterization are presented in detail in this paper.

Klicpera, M.; Pospíšil, J.; Rudajevová, A.; Hoser, A.; Javorský, P.

2014-05-01

441

Electron Paramagnetic Resonance of Yb3+ in Scheelite Single Crystals  

Microsoft Academic Search

The electron paramagnetic resonance spectra of the ground state of trivalent ytterbium have been observed in eight single crystals with scheelite structure at 4.2°K and X band frequencies. The crystals used were CdMoO4, CaWO4, CaMoO4, SrWO4, SrMoO4, PbWO4, PbMoO4, and BaWO4. The tetragonal spectra for Yb171, Yb173, and the even isotopes of ytterbium were best fitted with an axial spin

J. P. Sattler; J. Nemarich

1970-01-01

442

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

443

Small crystals and small coils in variable-temperature single-crystal NMR.  

PubMed

Time savings by a factor of between 20 and 30 in the acquisition of multinuclear single-crystal (SC) NMR spectra have been obtained for submillimeter-size (0.01 to 0.03 mm(3)) single crystals when compared to recent results for (31)P and (87)Rb SC NMR. This gain in sensitivity is achieved by optimizing the filling factor using the smallest possible rf coil (2.0 mm inner diameter) for the specific SC probe design. Furthermore, this small coil is particularly useful for variable-temperature SC NMR studies. A probe design for such studies is presented and demonstrated experimentally. PMID:10648158

Vosegaard, T; Daugaard, P; Hald, E; Jakobsen, H J

2000-02-01

444

Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

445

Photoemission study of CaF2- and SrF2-GaAs(110) interfaces formed at room temperature  

NASA Astrophysics Data System (ADS)

Interfaces formed by evaporating CaF2 or SrF2 on room-temperature GaAs(110) are studied with synchrotron-radiation photoemission spectroscopy. The fluoride films grow uniformly on the GaAs surface. The deposition of CaF2 and SrF2 induces a large initial band bending on p-type GaAs (~0.9 eV) and a small initial band bending on n-type GaAs (~0.25 eV). The valence band is dominated by the F 2p peak which shifts toward high binding energies by ~1.5 eV after the deposition of >=16 Å fluoride. This shift reflects an increase in the valence-band offset between the two materials as the film forms. The final band offsets are estimated at 7.7 and 8.0 eV for CaF2 and SrF2, respectively, and are in qualitative agreement with those expected from the fluoride-Si data. Core-level measurements indicate that no reaction or decomposition of the MF2 molecule takes place at the interface. The F 2s core-level line shape and the increase in the binding-energy separation of F 2s and Ca 3p with increasing coverage suggest the presence of an interface F component. Contrary to the CaF2/Si case, no measurable Ca-substrate bonding effect is observed. The dissociative effect of uv irradiation on the CaF2 film is also investigated.

Mao, D.; Young, K.; Kahn, A.; Zanoni, R.; McKinley, J.; Margaritondo, G.

1989-06-01

446

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

447

Research on VCSEL of single-mode multilayer photonic crystal  

NASA Astrophysics Data System (ADS)

Vertical-Cavity Surface-Emitting Lasers (VCSEL) of single mode have the potential advantage in the domains of optical information network, routing interactions, optical information storage and data transmission for their excellent performance. However, operating on the single-mode model in the whole pumped area is not solved, which impacts the technologies and applications. In this paper, a new research on VCSEL of single mode multilayer photonic crystal is presented. In the structure of photonic crystal, defects in the horizontal direction are provided by the micro-cavity, while the AIR-KTP interface on the top and the KTP-DBR (Distributed Bragg Reflection) interface at the bottom of cavity provide the defects in the vertical direction, which form quantum defects of electron-hole pairs. The PC-VCSEL in the paper has excellent mode-selection characteristics, which can operate continuously at 850nm in single mode. The single-mode suppression ratio (SMSR) of 45dB is obtained in a wide dynamic range. The PC-VCSEL is expected to become a high-power single-mode light in the future.

Li, Wenchao; Liu, Zhengjun; Sha, Xiaopeng

2010-05-01

448

Stress asymmetry of stoichiometric NiAl single crystals  

SciTech Connect

The yield stress properties of stoichiometric NiAl single crystals were investigated in terms of crystal orientation, temperature and the deformation mode. The calculated critical resolved shear stress (CRSS) was a strong function of crystal orientation, temperature and the deformation mode whether tension or compression. The CRSS was, in a wide range of experimental conditions, higher in the sequence of (110)(100), (100)(100) and (hk0)(100) slips. The CRSS in compression was higher particularly at low temperatures than the CRSS in tension. The tension-compression asymmetry on the CRSS was understood qualitatively as being due to the effect of the normal stress on the core structure of a (001) dislocation and a (111) dislocation. It was suggested that a compressive normal stress makes the core configuration more sessile, resulting in the increased stress effectively at low temperatures.

Takasagu, T.; Kishino, J.; Hanada, S. (Tohoku Univ., Sendai (Japan). Inst. for Materials Research)

1993-04-01

449

Nucleation kinetics, growth and studies of ?-alanine single crystals.  

PubMed

Solubility and metastable zone width for the re-crystallized salt of ?-alanine was determined. Induction period measurement for the selected supersaturation ratios at room temperature (31 °C) was carried out for supersaturated aqueous solutions of ?-alanine and it is noticed that induction period decreases with increase of supersaturation ratio. The nucleation parameters such as Gibbs free energy change, radius and number of molecules of the critical nucleus, interfacial tension and the nucleation rate have been evaluated by classical nucleation theory. Single crystals of ?-alanine were grown using the optimized nucleation parameters by solution method and grown crystals have been subjected to various studies like XRD studies, FTIR, optical, thermal and SHG studies. PMID:23548638

Shanthi, D; Selvarajan, P; HemaDurga, K K; Lincy Mary Ponmani, S

2013-06-01

450

Direct observation of aminyl radical intermediate during single-crystal to single-crystal photoinduced Orton rearrangement.  

PubMed

A photoinduced analogue of the thermal Orton rearrangement reaction by which an N-chlorine atom from a side amino group is transferred to a phenyl ring was studied in the solid state. Contrary to the mixture of products obtained in solution, in the N-chloro-N-acetylaminobenzene crystals the photoreaction proceeds with complete preservation of crystallinity, affording selectively and quantitatively the para isomer of chloroacetanilide. Study of the reaction mechanism by in situ steady-state photodiffraction, a combination of photoexcitation by UV light and single-crystal X-ray diffraction analysis, provided evidence for creation of N-acetyl-N-phenylaminyl (AcPhN*) radical as a metastable reaction intermediate. The structure of the aminyl radical produced in 9.2% yield from the major disordered component in the statically 85.6:14.4 disordered crystal was directly observed for the first time. The unprecedented stability of the radical is prescribed to the solid-state cage effect, the reactive center of the radical species being locked away from the reactive target molecules. The creation of the radical and its head-to-tail chain reaction within the undulated hydrogen-bonded ribbons involving the acetyl carbonyl group are employed to explain the high selectivity of the photoinduced single-crystal to single-crystal Orton rearrangement. On the basis of the change of the crystal structure and the physicochemical data, a three-center five-atom mechanism involving homolytic cleavage of the N-Cl bond followed by hydrogen abstraction by the carbonyl group is suggested for the solid-state photoinduced Orton rearrangement. PMID:17696393

Naumov, Pance; Sakurai, Kenji; Tanaka, Masahiko; Hara, Hideyuki

2007-09-01

451

Synthesis of mesoporous zeolite single crystals with cheap porogens  

SciTech Connect

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

Tao Haixiang; Li Changlin; Ren Jiawen [Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237 (China); Wang Yanqin, E-mail: wangyanqin@ecust.edu.cn [Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237 (China); Lu Guanzhong, E-mail: gzhlu@ecust.edu.cn [Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237 (China)

2011-07-15

452

Determining thermodynamic properties of molecular interactions from single crystal studies.  

PubMed

The concept of single crystals of macromolecules as thermodynamic systems is not a common one. However, it should be possible to derive thermodynamic properties from single crystal structures, if the process of crystallization follows thermodynamic rules. We review here an example of how the stabilizing potentials of molecular interactions can be measured from studying the properties of DNA crystals. In this example, we describe an assay based on the four-stranded DNA junction to determine the stabilizing potentials of halogen bonds, a class of electrostatic interactions, analogous to hydrogen bonds, that are becoming increasing recognized as important for conferring specificity in protein-ligand complexes. The system demonstrates how crystallographic studies, when coupled with calorimetric methods, allow the geometries at the atomic level to be directly correlated with the stabilizing energies of molecular interactions. The approach can be generally applied to study the effects of DNA sequence and modifications of the thermodynamic stability of the Holliday junction and, by inference, on recombination and recombination dependent processes. PMID:23933330

Vander Zanden, Crystal M; Carter, Megan; Ho, Pui Shing

2013-11-01

453

Fabrication and characterization of Cr:forsterite single crystal fiber  

NASA Astrophysics Data System (ADS)

Cr:forsterite (Cr:Mg2SiO4) single crystal fibers of diameter less than 100 ?m were made for the first time to our knowledge. This novel fiber material will be used to make fiber light sources such as fiber lasers and broadband light sources for applications in biophotonics and optical communications. Cr:forsterite crystal has a broad emission spectrum ranging from 1.1 to 1.4 ?m that traditional glass fibers or semiconductor light sources cannot offer. And fiber light sources are compact, efficient, maintenance-free and compatible with fiber-optic components potentially leading to new performance and functions. In this work, bulk Cr:forsterite crystal was melted, pulled and re-grown into a long fiber using laser heated pedestal growth (LHPG) technique. Single crystal rhombic structure was preserved and verified by Xray diffractometer. By using electron probe micro-analyzer, change in Cr dopant concentration and distribution profile for various fiber diameters and growth conditions was studied.

Yeh, P. S.; Wang, H. Y.; Huang, K. Y.; Huang, S. L.; Hsu, K. Y.; Jheng, D. Y.

2009-02-01

454

Formation and crystal structure of metallic inclusions in a HPHT as-grown diamond single crystal  

NASA Astrophysics Data System (ADS)

One of the most important characteristics associated with crystal growth technology is the entrapment of inclusions by the growing crystal. Diamond single crystals prepared under high temperature-high pressure (HPHT) usually contain metallic inclusions. In the present paper, metallic inclusions in a diamond grown from a Fe-Ni-C system using the HPHT method have been, for the first time, systematically examined by transmission electron microscopy (TEM). Energy dispersive X-ray spectrometry (EDS) , combined with selected area electron diffraction (SAD) patterns, has been used to identify the chemical composition and crystal structure of the metallic inclusions. The metallic inclusions were found to be composed mainly of cubic ?-(FeNi), face-centered cubic (FeNi)23C6, ortho-rhombic Fe3C and hexagonal Ni3C, which may have been formed through the entrapment of molten catalyst by the growth front or through reaction of the trapped melt with contaminants in the diamond.

Yin, L.-W.; Wang, N.-W.; Zou, Z.-D.; Li, M.-S.; Sun, D.-S.; Zheng, P.-Z.; Yao, Z.-Y.

455

Crystal growth and electrical properties of high-Tc relaxor-PT system single crystals  

Microsoft Academic Search

Single crystals of the xPb(Sc1\\/2Nb1\\/2)O3-yPb(Zn1\\/3Nb2\\/3 O3-zPbTiO3 (PSZNT 100x\\/100y\\/100z) and aPb(In1\\/2Nb1\\/2)O3-bPb(Zn1\\/3Nb2\\/3)O3-cPbTiO3 (PIZNT 100a\\/100b\\/100c) ternary systems. have been synthesized by a flux method using PbO flux. The crystals were grown in a Pt crucible by a mass crystallization, achieved by slow cooling of the 55PbO-45PSZNT 10\\/75\\/15 (mol%) molten solution with 1.5–3°C\\/h from 1,230–1,250°C to 850°C. The resulting crystals are 2–5 mm in

N. Ichinose; Y. Saigo; Y. Hosono; Y. Yamashita

2001-01-01

456

Neutron spectrometers based on single crystal CVD diamond  

NASA Astrophysics Data System (ADS)

A new grade of single crystal CVD diamond has been developed that possesses unprecendented electrical properties [1]. The carrier lifetime in this new material is reported to be > 2 microseconds, a 1000 fold improvement over existing grades of CVD diamond. This could lead to a new generation of electrical devices based on diamond, including radiation sensors. Over the past few months, we have been investigating this new single crystal CVD diamond material as a neutron sensor. We will present our data to date, and also discuss possible spectroscopic applications in both inertial confinement fusion and magnetic confinement fusion. This work was performed at the Lawrence Livermore National Laboratory under the auspices of the United States Dept. of Energy under contract number W-7405-ENG-48. [1] J. Isberg et al, Science 297 (2002)1670

Schmid, Gregory; Koch, Jeffrey; Moran, Michael; Lerche, Richard; Izumi, Nobuhiko; Park, Hye-Sook; Phillips, Thomas; Turner, Robert

2003-10-01

457

High-Quality, Thin-Film Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

458

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

459

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

460

Magnetic anisotropy of NaxCoO2 single crystals  

NASA Astrophysics Data System (ADS)

We report the magnetic properties of single crystals of NaxCoO2 (x=0.42, 0.82, and 0.87). The magnetic susceptibility measurements revealed considerable anisotropy along H?ab and H?c for the as-grown single crystals. It was found that an antiferromagnetic transition with a Neel temperature TN=21 K occurred for the x=0.82 sample, and there was a paramagnetic phase for the x=0.87 sample over a wide temperature range from 2 to 300 K, but the sample with x=0.42 shows a monotonic increase of ? with increasing temperature above ~100 K. In addition, the x=0.82 sample has the largest derived anisotropic g-factor ratio (gab/gc~1.30), whereas the sample with x=0.42 is nearly isotropic (gab/gc~0.96).

Chen, D. P.; Wang, Xiaolin; Lin, C. T.; Dou, S. X.

2008-04-01

461

Positron Annihilation and Electronic Lattice Structure in Insulator Crystals  

Microsoft Academic Search

The dimensions of the electronic lattice structure of the hexagonal quartz crystal and the fcc CaF2 crystal have been measured by resolving characteristic markings on the angular-correlation curves as observed for the two gamma quanta emitted in the annihilation of positrons with electrons in these crystals.

Werner Brandt; Gérard Coussot; Robert Paulin

1969-01-01

462

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

SciTech Connect

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

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

2010-05-15

463

Frictional properties of single crystals HMX, RDX and PETN explosives.  

PubMed

The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations. PMID:20688432

Wu, Y Q; Huang, F L

2010-11-15

464

Temperature dependent polarized Raman spectra of nonaaqualanthanoid (Pr) single crystal.  

PubMed

Polarized Raman spectral changes with respect to temperature were investigated for Pr(BrO3)3.9H2O single crystals. FTIR spectra of hydrated and deuterated analogues were also recorded and analysed. Temperature dependent Raman spectral variation have been explained with the help of the thermograms recorded for the crystal. Factor group analysis could propose the appearance of BrO3 ions at sites corresponding to C3v (4) and D3h (2). Analysis of the vibrational bands at room temperature confirms a distorted C3v symmetry for the BrO3 ion in the crystal. From the vibrations of water molecules, hydrogen bonds of varying strengths have also been identified in the crystal. The appearance upsilon1 mode of BrO3- anion at lower wavenumber region is attributed to the attachment of hydrogen atoms to the BrO3- anion. At high temperatures, structural rearrangement is taking place for both H2O molecule and BrO3 ions leading to the loss of water molecules and structural reorientation of bromate ions causing phase transition of the crystal at the temperature of 447 K. PMID:16332452

Jayasree, R S; Bushiri, M J; John, Annamma; Nayar, V U

2006-05-15

465

Temperature dependent polarized Raman spectra of nonaaqualanthanoid (Pr) single crystal  

NASA Astrophysics Data System (ADS)

Polarized Raman spectral changes with respect to temperature were investigated for Pr(BrO 3) 3·9H 2O single crystals. FTIR spectra of hydrated and deuterated analogues were also recorded and analysed. Temperature dependent Raman spectral variation have been explained with the help of the thermograms recorded for the crystal. Factor group analysis could propose the appearance of BrO 3 ions at sites corresponding to C3v (4) and D3h (2). Analysis of the vibrational bands at room temperature confirms a distorted C3v symmetry for the BrO 3 ion in the crystal. From the vibrations of water molecules, hydrogen bonds of varying strengths have also been identified in the crystal. The appearance ?1 mode of BrO 3- anion at lower wavenumber region is attributed to the attachment of hydrogen atoms to the BrO 3- anion. At high temperatures, structural rearrangement is taking place for both H 2O molecule and BrO 3 ions leading to the loss of water molecules and structural reorientation of bromate ions causing phase transition of the crystal at the temperature of 447 K.

Jayasree, R. S.; Bushiri, M. J.; John, Annamma; Nayar, V. U.

2006-05-01

466

In situ observations of crystal growth of spherical Si single crystals  

Microsoft Academic Search

Spherical Si single crystals for solar cell substrates have been grown successfully with a yield of almost 100%. Spherical Si multicrystals with diameters of approximately 400?m in a teardrop shape were initially fabricated by a dropping method. The as-dropped spherical Si multicrystals were melted into droplets on a silica plate in an oxygen atmosphere, and the Si droplets were then

Xinming Huang; Satoshi Uda; Hideyoshi Tanabe; Nobuyuki Kitahara; Hisao Arimune; Keigo Hoshikawa

2007-01-01

467

The Melting Process of Acetylsalicylic Acid Single Crystals  

Microsoft Academic Search

Crystallisation is generally regarded as a nucleation — growth mechanism of a solid phase and often studied using thermo chemical\\u000a methods. The present work postulates an analogy to melting processes, looking at melting as nucleati