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1

Formation and partial recovery of optically induced local dislocations inside CaF2 single crystal.  

PubMed

We reported on the formation of a microstructure (skew cross-shaped pattern) in bulk CaF(2) single crystal, which originates from local dislocations and microcracks around the focal point of a single infrared femtosecond laser beam. Relations between morphology of the microstructure and the laser power as well as the number of laser pulses were discussed. Furthermore, it was observed that the optically induced microstructure could be partially erased by additional irradiation of its neighboring area with femtosecond laser pulses. High-resolution transmission electron microscope (HRTEM) observations confirmed the disappearance of some local dislocations after the additional femtosecond laser irradiation. PMID:19434189

Qian, Bin; Song, Juan; Dong, Guoping; Su, Liangbi; Zhu, Bin; Liu, Xiaofeng; Sun, Shengzhi; Zhang, Qiang; Qiu, Jianrong

2009-05-11

2

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

3

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

4

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

5

Infrared thermooptic coefficient measurement of polycrystalline ZnSe, ZnS, CdTe, CaF(2), and BaF(2), single crystal KCI, and TI-20 glass.  

PubMed

An interferometric technique has been used to determine the thermooptic coefficient (dn/dT) of polycrystalline ZnSe and ZnS at 0.6328 microm, 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CdTe and TI-20 glass at 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CaF(2) and BaF(2) at 0.6328 microm, 1.15 microm, and 3.39 microm, and pure and europium-doped single crystal KCl at 0.6328 microm, 1.15microm, 3.39 microm, and 10.6 microm. The values were obtained over the temperature range of 25-65 degrees C and were calculated using the observed change in optical path of the samples as they were heated. Some difficulties in thermometry were encountered in the standard configuration of sample and thermocouple probe, so measurements were made in an oil bath at the shortest wavelength at which the sample was transparent to provide temperature correction factors for each sample. An empirical dispersion relation for dn/dT has also been found for the semiconductor materials. This dispersion relation is of the form dn/dT = aR(b), where R is defined as lambda(2)/(lambda(2) - lambda(g)(2)), lambda(g) is the short wavelength cutoff associated with the energy gap, and a and b are constants which are different for each material. PMID:20168506

Harris, R J; Johnston, G T; Kepple, G A; Krok, P C; Mukai, H

1977-02-01

6

Optical study of Yb(3+)/Yb(2+) conversion in CaF(2) crystals.  

PubMed

Yb(3+) ions with various site symmetries have been observed in the absorption and emission spectra of Yb(3+):CaF(2) crystals, both ?-irradiated and annealed in hydrogen. The absorption intensity value is found to be much higher for the ?-irradiated crystal and strongly dependent on the gamma dose. The UV absorption spectra of ?-irradiated and H(2)-annealed CaF(2):5 at.% Yb(3+) crystals are quite similar. Yb(2+) absorption bands are observed at 360, 315, 271, 260, 227 and 214 nm, which are called A, B, C, D, F and G bands, respectively. For ?-irradiated CaF(2):30 at.% Yb(3+), an additional band at 234 nm can be seen. It is suggested that only a negligible amount of Yb(3+) ions are converted into Yb(2+) under the ?-irradiation. The presence of Yb(2+) is confirmed by the 565 and 540 nm luminescence under 357 nm excitation. It is also suggested that the excitation in the A, C, D and F absorption bands of Yb(2+) gives rise to photo-ionization of Yb(2+) ions and electrons in the conduction band to form the excited Yb(3+) ions which emit IR Yb(3+) luminescence.The UV absorption and emission spectra obtained for ?-irradiated and H(2)-annealed crystals have different structures. This suggests that different mechanisms are responsible for the creation of Yb(2+) ions. ?-irradiation favours Yb(2+) isolated centres by reduction of Yb(3+) ions located at Ca(2+) lattice sites, whereas annealing in hydrogen favours Yb(2+) centres neighbouring Yb(3+) ions when a Yb(3+) ion pair captures a Compton electron. Also, ?-irradiation does not change the position of Yb(3+) ions converted into Yb(2+) in the CaF(2) lattice. In the case of H(2) annealing, a Yb(3+) ion converted to Yb(2+) is shifted to the Ca(2+) position in the lattice. PMID:21690695

Kaczmarek, S?awomir M; Tsuboi, Taiju; Ito, Masahiko; Boulon, Georges; Leniec, Grzegorz

2005-06-29

7

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

8

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

9

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

PubMed

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

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

2010-06-01

10

Codoping Na+ to modulate the spectroscopy and photoluminescence properties of Yb3+ in CaF2 laser crystal.  

PubMed

Three kinds of Yb3+ - and Na+-codoped CaF2 laser crystal with different Na:Yb ratios of 0, 1.5, and 10 are grown by the temperature gradient technique. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes belonging to the transitions between ground state 2F7/2 and excited state 2F5/2 of Yb3+ ions in the three crystals are measured to study the effect of Na+. Experimental results show that codoping Na+ ions in different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in a CaF2 lattice in a large scope. PMID:15906984

Su, Liangbi; Xu, Jun; Li, Hongjun; Yang, Weiqiao; Zhao, Zhiwei; Si, Jiliang; Dong, Yongjun; Zhou, Guoqing

2005-05-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

12

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

13

The colouration of CaF2 crystals by keV and GeV ions  

NASA Astrophysics Data System (ADS)

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) ) but no colour centres (F, F-2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10(12) ions cm(-2) attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 nm in the VUV and bands at 604 nm and 672 nm in the visible region.

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

14

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

15

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

SciTech Connect

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

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

2014-01-01

16

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

NASA Technical Reports Server (NTRS)

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

Duncan, R. C., Jr.

1972-01-01

17

A high-resolution digital dosimetric system for spatial characterization of radiation fields using a thermoluminescent CaF2:Dy crystal.  

PubMed

A high-resolution digital dosimetric system has been developed for the spatial characterization of radiation fields. The system comprises the following: 0.5-mm-thick, 25-mm-diam CaF2:Dy thermoluminescent crystal; intensified charge coupled device video camera; video cassette recorder; and a computerized image processing subsystem. The optically flat single crystal is used as a radiation imaging device and the subsequent thermally stimulated phosphorescence is viewed by the intensified camera for further processing and analysis. Parameters governing the performance characteristics of the system were measured. A spatial resolution limit of 31 +/- 2 microns (1 sigma) corresponding to 16 +/- 1 line pairs/mm measured at the 4% level of the modulation transfer function has been achieved. The full width at half maximum of the line spread function measured independently by the slit method or derived from the edge response function was found to be 69 +/- 4 microns (1 sigma). The high resolving power, speed of readout, good precision, wide dynamic range, and the large image storage capacity make the system suitable for the digital mapping of the relative distribution of absorbed doses for various small radiation fields and the edges of larger fields. PMID:3724696

Atari, N A; Svensson, G K

1986-01-01

18

A performance study on a phoswich detector consisting of an inner NE213 scintillator and an outer CaF 2(Eu) crystal wall  

NASA Astrophysics Data System (ADS)

We developed a new phoswich detector. The detector consists of an inner NE213 organic liquid scintillator and an outer thin CaF 2(Eu) crystal which are coupled to a photomultiplier. The charged particles produced in the NE213 scintillator by the interaction of radiation with the detector either stop in the NE213 scintillator or pass through both the NE213 scintillator and the outer CaF 2(Eu) crystal. The fast output pulses of a few ns from the NE213 scintillator can easily be separated from the slow output pulses of about 1 ?s from the outer CaF 2(Eu) scintillator. From this difference, the events that the charged particle stops inside NE213 scintillator can be separated out from the events that the charged particle escapes from the inside NE213 detector. The phoswich detector response functions for gamma rays and neutrons measured with the radioactive gamma-ray sources and the neutrons produced by a Be + Cu target bombarded by protons from the cyclotron, and compared with Monte Carlo calculations. It was found that the main characteristics of the NE213 scintillator were not degraded by assembling as a phoswich detector using the CaF 2(Eu) crystal wall. The n-? discrimination property is slightly degraded but neutrons can be separated from gamma rays. Further we used to test the phoswich detector for neutron measurements under the intense charged particles, mainly protons, with considering the possibility of neutron detection in space crafts. It was shown that the phoswich detector is capable of detecting neutrons in the mixed field.

Takada, Masashi; Shibata, Tokushi; Uwamino, Yoshitomo; Nakamura, Takashi

1996-02-01

19

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

20

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

21

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

PubMed

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+ -doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as high as 1.8 was achieved, showing the great potential of Yb3+:CaF2 as an amplifier medium for femtosecond pulses. PMID:15357346

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

2004-08-15

22

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

23

Application of a volume holographic grating in a CaF2 crystal for measuring linear displacements with nanoscale accuracy  

NASA Astrophysics Data System (ADS)

A holographic method for measuring linear displacements based on the use of a highly stable volume scale hologram recorded in an additively colored calcium fluoride crystal with photochromic color centers is proposed and experimentally approved. The essence of this method lies in measuring and analyzing harmonic signals formed during linear displacement of crystal with a volume hologram in an external interference field. A physical model of the formation of harmonic signals in photodetectors when measuring displacements is considered, and a mathematical method for calculating linear displacements by plotting a Lissajous figure is substantiated. A laboratory breadboard of a device for measuring linear displacements in a range of 10 mm, limited by the aperture of crystal with a recorded 8.7-mm-thick hologram, is designed. When using a scale hologram with a period of 2.18 ?m and a 632.8-nm He-Ne laser for reading this hologram, the error in measuring displacements by this method is 9 nm at a resolution of 3 nm.

Shcheulin, A. S.; Angervaks, A. E.; Kupchikov, A. K.; Verkhovskii, E. B.; Ryskin, A. I.

2014-12-01

24

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

SciTech Connect

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

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

2012-05-01

25

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

NASA Astrophysics Data System (ADS)

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

Szenes, G.

2013-02-01

26

Epitaxial growth and characterization of CaF2 on Si  

NASA Astrophysics Data System (ADS)

CaF2 films have been grown epitaxially on (100) and (111) Si substrates by molecular beam epitaxy. These films have been characterized by electron microscopy, reflection high-energy electron diffraction, Rutherford backscattering ion channeling, and back-reflection Laue x-ray diffraction. In addition, chemical etching has been used to reveal dislocations and to delineate cracks. Film cracking appears to be related to crystalline perfection through misfit dislocation mobility. It is possible to grow high quality, (xmin=3.0%) single-crystal films on (111) Si which are free of cracks and atomically flat. However, the high free energy of the (100) surface in an ionic fluorite crystal prevents the growth of comparable CaF2 films on the (100) Si surface.

Schowalter, L. J.; Fathauer, R. W.; Goehner, R. P.; Turner, L. G.; DeBlois, R. W.; Hashimoto, S.; Peng, J.-L.; Gibson, W. M.; Krusius, J. P.

1985-07-01

27

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

29

BaF2CaF2-YF3-AlF3 Glass Systems for Infrared Transmission  

Microsoft Academic Search

Transparent and colorless glass rods have been obtained from the BaF2-CaF2-YF3-AlF3 system, which consists of 15 to 27 mol% BaF2, 13 to 25 mol% CaF2, 6 to 28 mol% YF3 and 37 to 50 mol% AlF3. Certain physical properties for the rods have been measured. Glass transition temperature, crystallization temperature, melting temperature and thermal expansion coefficient for 22BaF2-22CaF2-16YF3-40AlF3 glass are

Terutoshi Kanamori; Kiyoshi Oikawa; Shuichi Shibata; Toyotaka Manabe

1981-01-01

30

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

PubMed

We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at. % Yb3+ -doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W average output power, with a pulse duration of 220 fs, centered at 1049 nm. The laser wavelength could be tuned from 1040 to 1053 nm in the femtosecond regime. Using chirped mirrors for dispersion compensation, the oscillator provided up to 1.74 W of average power, with a pulse duration of 230 fs, corresponding to a pulse energy of 20 nJ and a peak power of 85 kW. PMID:15605499

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

2004-12-01

31

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

32

The microwave characterization of single crystal lithium and calcium fluoride at cryogenic temperatures.  

PubMed

The whispering-gallery mode method is used for very accurate permittivity and dielectric loss measurements of single crystal lithium fluoride (LiF) and calcium fluoride (CaF2) over the temperature range of 4.5 K to 300 K. The absolute uncertainty in the real part of permittivity was estimated to be less than 0.1%, and it was limited principally by uncertainty in dimensions of the samples. Dielectric losses were measured with uncertainties of about 10% limited by the accuracy of Q-factor measurements. The measured materials exhibited dielectric losses between 2-4 x 10(-7) near 5 K. The relative permittivity was evaluated as 6.502 (4.9 K) to 6.844 (296 K) at 17.5 GHz for CaF2 and 8.534 (4.6 K) to 9.063 (300 K) at 13.5 GHz for LiF. PMID:15139539

Hartnett, John G; Fowler, Alison C; Tobar, Michael E; Krupka, Jerzy

2004-04-01

33

Kapitza limited spin-bath relaxation in CaF2: Ce3+  

Microsoft Academic Search

Measurements, at liquid-helium temperature, of the spin-bath relaxation time tau of Ce3+ ions doped into CaF2 reveal the overall return to equilibrium to be limited by the Kapitza resistance of the host crystal. Initial Nonequilibrium within the Ce3+ spin system was produced by superimposing a magnetic field DeltaH upon a steady dc field H0 in a time of the order

David J. Griffiths; Wen-Hsiung Chen

1979-01-01

34

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

35

Shock Hugoniot and high pressure melting curve for CaF2  

NASA Astrophysics Data System (ADS)

CaF2 is an important class of super ionic crystals whose structural properties are of much theoretical and experimental interest at high pressure and temperature. In the present study high pressure melting curve and equations of states (static and dynamics) of B1 phase of CaF2 were investigated. Total energy was calculated by using the DFT based plane-wave pseudopotential (PW-DFT) within the generalized gradient approximation. Nearest-neighbor second-moment tight-binding energy model (TB-SMA) was used for calculating both static and dynamic equations of states. Parameters of the TB-SMA model were determined by the present ab initio pseudopotential calculations. While volume dependence of Grüneisen parameter was used within the Lindemann's criterion to calculate high pressure melting curve. It is found that the present simple TB-SMA scheme is able to mimic shock Hugoniot for such fluorides correctly.

Joshi, R. H.; Patel, A. B.; Bhatt, N. K.; Thakore, B. Y.; Jani, A. R.

2013-06-01

36

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

37

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

38

Arnold Schwarzenegger SINGLE CRYSTAL SILICON  

E-print Network

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

39

Room Temperature Fabrication of Dielectric Bragg Reflectors Composed of a CaF2/ZnS Multilayered Coating.  

PubMed

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

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

2015-01-14

40

Laser spectroscopic measurement of point-defect dynamics in Eu3+:CaF2  

NASA Astrophysics Data System (ADS)

We have developed a site-selective laser method to study the aggregation kinetics of defect sites as a result of heat treatment in EuF3-doped CaF2 crystals. The crystals contain Eu3+ in four dominant defect sites and one minor site that differ in the number of nearby dopant and fluoride interstitial ions. A nonequilibrium site distribution was created by quenching the high-temperature distribution. The kinetics of the reequilibration to a lower-temperature distribution was followed by measuring the absolute concentrations of the defect sites with site-selective laser spectroscopy. The functionality of the temporal changes, the absolute concentrations, and the concentration and temperature dependence of the rate constants have been used to definitively identify the four major sites and to quantitatively describe the entire behavior of the defect distributions. The four sites are identified as an isolated Eu3+; a single-pair site of a Eu3+ ion and a compensating fluoride interstitial; a dimer consisting of two Eu3+ ions, no fluoride vacancies, two displaced fluoride ions, and three fluoride interstitials (2||0||2||31) and a trimer of three Eu3+ ions and four fluoride interstitials (3||0||2||41). It is suggested that the trimer and dimer are related to the hexamer clusters observed with heavier rare-earth dopants and that the hexamers contain extra fluoride interstitials that form a series of clusters with the largest possible cluster being 6||0||32||12. We also determined activation energies of 0.49+/-0.08 eV and 1.5+/-0.4 eV for the formation of the dimer and trimer, respectively. This work presents the first complete microscopic picture for the solid-state defect chemistry of a fluorite material. It is in agreement with recent predictions of hades (Harwell Automatic Defect Examination System) models for fluorite defect centers.

Cirillo-Penn, Kathleen M.; Wright, John C.

1990-05-01

41

Preparation and Single-Crystal Structure Analysis of Ca 2NF  

NASA Astrophysics Data System (ADS)

Single-crystalline samples of Ca2NF were prepared by heating a stoichiometric mixture of Ca metal and CaF2 under N2 to 1000°C, followed by slow cooling from the melt. The resulting Ca2NF crystals were yellow in color, and highly air-sensitive. A single-crystal X-ray diffraction analysis indicated that the compound is isostructural with L-Mg2NF, with tetragonal cell parameters a=4.9018(9) Å and c=10.516(3) Å, Z=4, and space group I41/amd (No. 141). X-ray refinement was carried out by full-matrix least-squares on F2 on all data, to give R1=0.0426 (all data) and wR2=0.0630 for 12 parameters and 101 independent reflections. The final position assignments were analyzed via bond valence sum calculations.

Nicklow, R. A.; Wagner, T. R.; Raymond, C. C.

2001-08-01

42

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

43

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

44

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

45

Deposition Sequence Determines Morphology of C60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111)  

Microsoft Academic Search

The coadsorption of C60 and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI molecules on CaF2(111) yields needle-shaped, molecularly well-ordered crystals. Upon following deposition of C60 molecules, the PTCDI islands are completely covered by C60. For the opposite deposition order, the

Felix Loske; Michael Reichling; Angelika Kühnle

2011-01-01

46

BaF2-CaF2-YF3-AlF3 Glass Systems for Infrared Transmission  

NASA Astrophysics Data System (ADS)

Transparent and colorless glass rods have been obtained from the BaF2-CaF2-YF3-AlF3 system, which consists of 15 to 27 mol% BaF2, 13 to 25 mol% CaF2, 6 to 28 mol% YF3 and 37 to 50 mol% AlF3. Certain physical properties for the rods have been measured. Glass transition temperature, crystallization temperature, melting temperature and thermal expansion coefficient for 22BaF2-22CaF2-16YF3-40AlF3 glass are determined as 430°C, 535°C, 710°C, and 16.5× 10-6/°C for 300-400°C, respectively. The glass is transparent at 0.23-5.2 ?m wavelengths, and shows a refractive index (nD) of about 1.44, density of about 4.0 g/cm3, Knoop hardness of about 360 kg/mm2, and water solubility of about 0.005 g per 100 g cold water. These glass rods have been able to be drawn into trial fibers of a few meters in length.

Kanamori, Terutoshi; Oikawa, Kiyoshi; Shibata, Shuichi; Manabe, Toyotaka

1981-05-01

47

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

48

Relaxation of electronic excitations in CaF2 nanoparticles  

NASA Astrophysics Data System (ADS)

The luminescence properties of CaF2 nanoparticles with various sizes (20-140 nm) are studied upon the excitation by VUV and x-ray quanta in order to reveal the influence of ratio of mean free path and thermalization length of charge carriers and nanoparticle size on the self-trapped exciton luminescence. The luminescence intensity for exciting quantum energies corresponding to optical creation of exciton and to the range of electronic excitation multiplication is not so sensitive to nanoparticle size as for quanta with energy of Eg < h? < 2Eg. The dependences of luminescence intensity on nanoparticle size at the excitation by quanta of various energies are discussed in terms of electron-phonon and electron-electron scattering lengths and energy losses on surface defects.

Vistovskyy, V. V.; Zhyshkovych, A. V.; Mitina, N. E.; Zaichenko, A. S.; Gektin, A. V.; Vasil'ev, A. N.; Voloshinovskii, A. S.

2012-07-01

49

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

50

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

51

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

PubMed

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

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

2013-04-01

52

RHEED intensity oscillations observed during the growth of CaF2 on Si(111)  

Microsoft Academic Search

Analyses of reflection high-energy electron diffraction (RHEED) intensity changes observed during initial stages of heteroepitaxial growth of calcium fluoride (CaF2) on Si(111) are presented. Layers obtained by deposition of CaF2 on a hot (550 °C) substrate demonstrate a high-quality crystallographic structure. The state of the surfaces of growing layers is studied with the in situ combination of RHEED azimuthal plots

Andrzej Daniluk; Piotr Mazurek; Krzysztof Paprocki; Pawel Mikolajczak

1998-01-01

53

Deposition Sequence Determines Morphology of C60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111)  

NASA Astrophysics Data System (ADS)

The coadsorption of C60 and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI molecules on CaF2(111) yields needle-shaped, molecularly well-ordered crystals. Upon following deposition of C60 molecules, the PTCDI islands are completely covered by C60. For the opposite deposition order, the initially grown C60 islands are not covered by PTCDI molecules, instead, most of the PTCDI molecules condense in pure islands, while only few PTCDI molecules nucleate at the edges of previously grown C60 islands. Simultaneous deposition of both molecules results in an intermixed phase with yet another island morphology. The observed fundamental differences in island morphology suggest that different dewetting barriers are involved in the formation process.

Loske, Felix; Reichling, Michael; Kühnle, Angelika

2011-08-01

54

Determination of the Trapping Parameters of Glow Peaks of CAF2:DY(TLD-200) by Using Computer Glov Curve Deconcolution Method  

NASA Astrophysics Data System (ADS)

Computerized glow curve deconvolution method is used to determine the number of peaks, the order of kinetics b, the activation energy Ea,frequency factor s and number of the trapped electrons n0 associated with the glow peaks in single crystal of CaF2:Dy (TLD-200). Glow curve analysis indicate that the glow curve in the temperature region between room temperature and 250 oC can be best described as a superposition of six peaks. First five peaks are described by first-order kinetics and sixth peak general-order kinetic. The number of trapped electrons, activation energies and frequency factor for individual glow peaks are as follows: (Peak 1) 3x1013, 1.27 and 2.13x1017, (Peak 2) 6.3x1013, 1.01 and 9.2x1012, (Peak 3) 3.3x1014, 0.7 and 6.12x107, (Peak 4) 2.4x1014, 1.14 and 3.28x1012, (Peak 5) 1.5x1014, 0.84 and 2.56x108, (Peak 6) 2.4x1014, 0.98 and 1.76x109.

Yazici, A. Necmeddýn; Haciýbrahýmoðlu, M. Yakup

2001-05-01

55

Nanostructured Calcite Single Crystals with Gyroid Morphologies  

E-print Network

Nanostructured Calcite Single Crystals with Gyroid Morphologies By Alexander S. Finnemore, Maik R of which has a complex, sponge-like structure, and yet is a single crystal of calcite.[2] In contrast calcite crystals. Biologically controlled mineralization depends on the interplay between a number

Steiner, Ullrich

56

Interdigitated single crystal piezoelectric actuator  

NASA Astrophysics Data System (ADS)

Piezoelectric actuators are used as critical units or elements of various electromechanical systems. In this paper, we propose a novel piezoelectric actuator cantilever with double interdigitated electrode patterns. We investigate the possibility of both flexural and longitudinal actuation capabilities of the double interdigitated electrode patterns applied on a piezoelectric cantilever structure. This monomorph structure has the interdigitated electrode patterns top and bottom. The structure also uses single-crystal relaxor ferroelectric material. We separately pattern interdigitated electrodes on the top and bottom surfaces of a PMN-PT single crystal cantilever beam. The interdigitated electrode design on a surface of the cantilever beam results in an electric field gradient. This results in a flapping actuation. Previously, we showed that the vertical field component induced by the interdigitated electrode is dominant over the horizontal component under input bias voltage, and generates subsequent contraction of the surface along the axial direction after poling. In this paper, we show that a contraction on the top surface and an elongation on the bottom leads to upward bending motion because of the differential contraction along the thickness induced by the interdigitated electrode pattern. Similarly, an equivalent elongation on the top and bottom surfaces is shown to lead to longitudinal motion in the double interdigitated electrode sample.

Hong, Yong K.; Moon, Kee S.

2005-12-01

57

Titania single crystals with a curved surface  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

58

Growth of ZnSe single crystals  

Microsoft Academic Search

The growth conditions of ZnSe single crystals were investigated by chemical vapor transport (CVT) and physical vapor transport (PVT) methods. The growth temperatures were about 850°C (CVT) and 1100°C (PVT). Single crystals of 18–20mm diameter, 30mm long and orange colored were grown. The homogeneity of crystals was measured. The etch pit density of good crystals is in the range of

C. S Fang; Q. T Gu; J. Q Wei; Q. W Pan; W Shi; J. Y Wang

2000-01-01

59

Microwave-assisted solvothermal synthesis and upconversion luminescence of CaF2:Yb(3+)/Er(3+) nanocrystals.  

PubMed

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

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

2015-02-15

60

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

61

Spectroscopic analysis of Eu doped transparent CaF 2 ceramics at different concentration  

NASA Astrophysics Data System (ADS)

Pure and Eu doped CaF 2 transparent ceramics were prepared for the first time. The samples were subjected to spectroscopic analyses to study the variation of transmission, emission and vibrational properties at various concentrations of Eu ion. Pure CaF 2 shows a good transparency of more than 80% and the Eu doped samples exhibit different absorption peaks corresponding to Eu ion transitions. Emission studies confirm that the divalent Eu ions are dominant at lower concentration whereas trivalent states become dominant as the concentration was increased. Raman measurements show characteristic T 2g phonon band of cubic CaF 2 with spectral shifting and broadening as the dopant concentration was increased. The analyses confirm the major role of interstitial fluorine ion in the spectroscopic properties of the ceramics.

Samuel, P.; Ishizawa, H.; Ezura, Y.; Ueda, Ken Ichi; Babu, S. Moorthy

2011-03-01

62

Localization of intrinsic defects in CaF2-BaF2 superlattices  

NASA Astrophysics Data System (ADS)

We perform first-principles calculations for the formation energies of fluorine self-interstitials (Fi-) and fluorine vacancies (VF+) in CaF2-BaF2 superlattices and in the corresponding bulk compounds. In dislocation-free (strained-layer) superlattices, the calculations show that both the Fi- and the VF+ defects are energetically more stable in the CaF2 layers than in the BaF2 layers. If the misfit stress in the superlattices is released (by dislocations, for instance), our results indicate that charge transfer between layers becomes energetically favorable with Fi- in the CaF2 layers and VF+ in the BaF2 layers. This is consistent with recent experiments.

Kagimura, Ricardo; Chacham, H.; Schmidt, T. M.; Miwa, R. H.

2003-11-01

63

RHEED intensity oscillations observed during the growth of CaF2 on Si(111)  

NASA Astrophysics Data System (ADS)

Analyses of reflection high-energy electron diffraction (RHEED) intensity changes observed during initial stages of heteroepitaxial growth of calcium fluoride (CaF2) on Si(111) are presented. Layers obtained by deposition of CaF2 on a hot (550 °C) substrate demonstrate a high-quality crystallographic structure. The state of the surfaces of growing layers is studied with the in situ combination of RHEED azimuthal plots and rocking curve. The intensity of the reflected beam is calculated by solving the one-dimensional Schrödinger equation.

Daniluk, Andrzej; Mazurek, Piotr; Paprocki, Krzysztof; Miko?ajczak, Pawe?

1998-05-01

64

Optical studies of anthracene single crystals  

Microsoft Academic Search

Recently the polyacene crystals such as pentacene, tetracene and anthracene have attracted great interest both in research and applications. These ultra-pure molecular crystals are very promising materials for FETs, organic photovoltaic diodes, LEDs and lasing. High purity anthracene crystal have been grown by physical vapor transport. High photo luminecense (PL) quantum efficiency(over 20%) was observed in these pure anthracene single

Yuhong Jiang; Matthew Delong; Z. Valy Vardeny

2001-01-01

65

Domain Engineered Relaxor Ferroelectric Single Crystals  

NASA Astrophysics Data System (ADS)

Single crystal relaxor ferroelectric materials exhibit extraordinary electromechanical properties. They are being applied in high performance sensors, actuators, and transducers. Field induced polarization switching and phase transitions of these crystals lead to complex nonlinear behavior. In recent years experimental investigations have been conducted to characterize the polarization switching and phase transition behavior as a function of crystallographic orientation, temperature, electric field, and stress. The results give insight into the mechanism underlying the observed large field hysteretic behavior. This review article describes the observed behavior and presents results of multiscale modeling that predicts the macroscopic behavior from the single domain single crystal behavior and evolution of crystal variants at the microscale.

Liu, T.; Lynch, C. S.

2006-08-01

66

Inkjet printing of single-crystal films  

Microsoft Academic Search

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

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

2011-01-01

67

Method of making single crystal fibers  

NASA Technical Reports Server (NTRS)

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

Westfall, Leonard J. (inventor)

1990-01-01

68

Organic single-crystal complementary inverter  

NASA Astrophysics Data System (ADS)

The authors demonstrate the operation of an organic single-crystal complementary circuit in the form of a simple inverter. The device is constructed from a high mobility p-type organic single-crystal transistor of tetramethylpentacene (TMPC) and a n-type single-crystal transistor of N ,N'-di[2,4-difluorophenyl]-3,4,9,10-perylenetetracarboxylic diimide (PTCDI). Field-effect mobilities of up to 1.0cm2/Vs are reported for TMPC devices, while a mobility of 0.006cm2/Vs is reported for a n-type PTCDI single-crystal device. Considering that organic single-crystal inverters have not yet been explored, they are representative of potential candidates for use in high-performance complementary circuits.

Briseno, Alejandro L.; Tseng, Ricky J.; Li, Sheng-Han; Chu, Chih-Wei; Yang, Yang; Falcao, Eduardo H. L.; Wudl, Fred; Ling, Mang-Mang; Chen, Hong Zheng; Bao, Zhenan; Meng, Hong; Kloc, Christian

2006-11-01

69

Slag Metal Reactions in Binary CaF2-Metal Oxide Welding Fluxes  

E-print Network

) Slag Metal Reactions in Binary CaF2-Metal Oxide Welding Fluxes Some otherwise chemically stable fluxes may decompose into suboxides in the presence of welding arcs, thereby providing higher levels of 0 2 in weld metal than those oxides which do not form suboxides ABSTRACT. The stability of metal

Eagar, Thomas W.

70

Vacuum ultraviolet Mach-Zehnder interferometer with CaF2 optics  

NASA Technical Reports Server (NTRS)

CaF2 beam splitters and compensation and test cell windows have been installed in a VUV Mach-Zehnder interferometer. Results of an evaluation of their performance in the VUV, namely, a measurement of the oscillator strength (f value) of the resonance transition at atomic xenon at 146.9610 nm are reported.

Smith, P. L.; Lombardi, G. G.; Cardon, B. L.; Parkinson, W. H.

1981-01-01

71

Direct comparison of Yb3+:CaF2 and heavily doped Yb3+:YLF as laser media at room temperature.  

PubMed

We report an extensive comparison of the laser performances of diode-pumped Yb(3+):YLF (30% at.) and Yb(3+):CaF(2) (5% at.) crystals, lasing at room-temperature and operating in two different operation mode, i.e. Continuous Wave (CW) and quasi-CW. An in-depth investigation of the crystals behavior by changing the pump power, clearly shows the crystal absorption depends on the lasing conditions. Therefore, we report an unambiguous definition of the slope efficiency calculated taken into account the real measured crystal absorption under laser action. Finally, we present a study of problems related to thermally induced losses which are expected influencing the laser performance. PMID:19907622

Pirri, Angela; Alderighi, Daniele; Toci, Guido; Vannini, Matteo; Nikl, Martin; Sato, Hiroki

2009-09-28

72

Void superlattice formation in electron irradiated CaF2: Theoretical analysis  

Microsoft Academic Search

CaF2 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 (F2 gas voids) is created. The

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

2010-01-01

73

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis  

Microsoft Academic Search

CaF2 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 (F2 gas voids) is created. The

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

2010-01-01

74

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

Microsoft Academic Search

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

Deng Jianxin; Cao Tongkun; Yang Xuefeng; Liu Jianhua

2006-01-01

75

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

E-print Network

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

Krems, Roman

76

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

77

Studies of the Facetting of the Polished (100) Face of CaF2  

NASA Astrophysics Data System (ADS)

The present paper deals with studies of the facetting of the polished (100) surface of CaF2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T = 874 K. Surfaces annealed at T = 974 K exhibit a micro-roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {111} facets. Reflexes from the (100) surface are not seen. After growth of about 660 monolayers of CaF2 at T = 1093 K and a saturation ratio S = 33 from the vapor phase, larger pyramid-like or hip roof-like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {111} facets as proved by their angles of 54.7° with the base (100) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF2 substrate.

Dabringhaus, H.; Schick, M.; Wandelt, K.; Deuster, V.; Kayser, Th.; Klapper, H.

2003-12-01

78

Studies of the facetting of the polished (100) face of CaF 2  

NASA Astrophysics Data System (ADS)

The present paper deals with studies of the facetting of the polished (1 0 0) surface of CaF 2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T=874 K. Surfaces annealed at T=974 K exhibit a micro-roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {1 1 1} facets. Reflexes from the (1 0 0) surface are not seen. After growth of about 660 monolayers of CaF 2 at T=1093 K and a saturation ratio S=33 from the vapor phase, larger pyramid-like or hip roof-like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {1 1 1} facets as proved by their angles of 54.7 o with the base (1 0 0) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF 2 substrate.

Deuster, V.; Schick, M.; Kayser, Th.; Dabringhaus, H.; Klapper, H.; Wandelt, K.

2003-04-01

79

Characterization of zinc selenide single crystals  

NASA Technical Reports Server (NTRS)

ZnSe single crystals of high quality and low impurity levels are desired for use as substrates in optoelectronic devices. This is especially true when the device requires the formation of homoepitaxial layers. While ZnSe is commercially available, it is at present extremely expensive due to the difficulty of growing single crystal boules with low impurity content and the resultant low yields. Many researchers have found it necessary to heat treat the crystals in liquid Zn in order to remove the impurities, lower the resistivity and activate the photoluminescence at room temperature. The physical vapor transport method (PVT) has been successfully used at MSFC to grow many single crystals of II-VI semiconducting materials including ZnSe. The main goal at NASA has been to try to establish the effect of gravity on the growth parameters. To this effect, crystals have been grown vertically upwards or horizontally. Both (111) and (110) oriented ZnSe crystals have been obtained via unseeded PVT growth. Preliminary characterization of the horizontally grown crystals has revealed that Cu is a major impurity and that the low temperature photoluminescence spectra is dominated by the copper peak. The ratio of the copper peak to the free exciton peak is being used to determine variations in composition throughout the crystal. It was the intent of this project to map the copper composition of various crystals via photoluminescence first, then measure their electrical resistivity and capacitance as a function of frequency before proceeding with a heat treatment designed to remove the copper impurities. However, equipment difficulties with the photoluminescence set up, having to establish a procedure for measuring the electrical properties of the as-grown crystals and time limitations made us re-evaluate the project goals. Vertically grown samples designated as ZnSe-25 were chosen to be measured electrically since they were not expected to show as much variation in their composition through their cross-section as the horizontally grown samples.

Gerhardt, Rosario A.

1996-01-01

80

Broadband single-polarization photonic crystal fiber  

Microsoft Academic Search

We demonstrate a single-mode photonic crystal fiber that supports only one polarization state in a 220-nm-broad spectral region centered at 727 nm. The fiber has a mode-field diameter of 15.5 mum and background losses of <15 dB\\/km in the single-polarization region. To our knowledge, these are the broadest bandwidth and the largest mode size yet reported for a single-polarization fiber.

J. R. Folkenberg; M. D. Nielsen; C. Jakobsen

2005-01-01

81

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. 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

82

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

83

Neutron detection with single crystal organic scintillators  

NASA Astrophysics Data System (ADS)

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, Natalia P.; Newby, Jason; Hamel, Sebastien; Carman, Leslie; Faust, Michelle; Lordi, Vincenzo; Cherepy, Nerine J.; Stoeffl, Wolfgang; Payne, Stephen A.

2009-08-01

84

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

85

First Single-Crystal Mullite Fibers  

NASA Technical Reports Server (NTRS)

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

1997-01-01

86

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

87

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

NASA Astrophysics Data System (ADS)

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.

2014-07-01

88

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

89

Surface flatness of polished metal single crystals  

SciTech Connect

The Fizeau interference has been utilized to measure the flatness of a metal single crystal after grinding and polishing by standard techniques. It is postulated that deviations from flatness are due to distortions of flexible abrasive substrates during the grinding step. {copyright} {ital 1996 American Vacuum Society}

Tripa, C.E.; Yates, J.T. Jr. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

1996-07-01

90

MAGNETIC PROPERTIES OF DYSPROSIUM SINGLE CRYSTALS  

Microsoft Academic Search

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

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

1958-01-01

91

Single-crystal ruby fiber temperature sensor  

Microsoft Academic Search

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

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

2002-01-01

92

Laser-induced damage resistance of UV coatings on fused silica and CaF2  

NASA Astrophysics Data System (ADS)

The laser damage resistance (LDR) is a measure of the laser fluence that a coating can withstand without damaging when exposed to a large number of pulses. The LDR of UV coatings has been studied at 266 nm on two common substrate materials. Significantly higher values for the LDR have been measured for the same coating deposited on CaF2 substrate compared to fused silica substrates. Various parameters such as the surface roughness, the absorption and the subsurface damage of these quite different materials were measured in an effort to explain the performance difference. The laser damage morphologies of the coatings were also studied.

Cho, Byungil; Lyu, Andy; Feldman, Mark

2012-11-01

93

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

94

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

95

Shock Hugoniot of Single Crystal Copper  

SciTech Connect

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

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

2009-08-28

96

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

97

SSME single-crystal turbine blade dynamics  

NASA Technical Reports Server (NTRS)

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

Moss, Larry A.

1988-01-01

98

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

99

Adsorption effect in non-reaction wetting: In-Ti on CaF2  

NASA Astrophysics Data System (ADS)

The experiments show that the alloying liquid In with only (0.1-0.5) at% Ti dramatically reduces the equilibrium contact angle ? ? formed by In on the surface of CaF2. The aim of this paper is to clarify whether this practically important and conceptually challenging effect can be explained solely by Ti adsorption at the F-terminated solid-liquid interface without resorting to any other Ti-induced effect. The combination of ab initio calculations and regular solution approximation was proposed for finding the binding energy, ?E Ti of Ti adatom with the interface "CaF2/liquid solutions In-Ti." With thus obtained ?E Ti=1.16 eV, we calculated from the Shishkovsky isotherm the reduction in the solid-liquid interface energy, ?? SL induced by Ti adsorption from liquid In with various Ti concentration, C. It was found that ?? SL( C) dependence demonstrated close inverse correspondence with ? ?( C) and that the theory fitted very well all available experimental data on the concentration and temperature dependence of ?? SL. It was concluded that the Ti adsorption effect is large enough to account for the observed wetting improvement. The proposed multiscale modeling approach to the role of adsorption in wetting can be applied also to other nonreactive systems "liquid metal-ceramics" where the substrate determines the surface density of the adsorption sites for the active element.

Glickman, E.; Fuks, D.; Frage, N.; Barzilai, S.; Froumin, N.

2012-01-01

100

Femtosecond laser-induced subwavelength ripples on Al, Si, CaF2 and CR-39  

NASA Astrophysics Data System (ADS)

The formation of self-organized subwavelength ripples on Al, Si, CaF2 and CR-39 induced by 25 fs laser pulses at central wavelength of 800 nm has been observed under certain experimental conditions. In case of Al subwavelength gratings with periodicities ranging from 20 to 220 nm are reported. For CaF2 the periodicity goes up to 625 nm. In case of Si, nano-gratings have the periodicity of 10-100 nm. The interspacing of these gratings is 60 nm in case of CR-39. These features which are significantly shorter than incident laser wavelength are observed at the irradiation fluence slightly higher than the ablation threshold regardless of the target material. In addition to these nanoripples, classical or microripples with an average spacing of 1-2 ?m have also been registered on irradiated surfaces of Al and Si. These microripples have appeared at fluence higher than that is required for nanoripple-formation. It has been found that the formation of the laser-induced ripples is strongly dependent and quite sensitive to the incident laser fluence and the selection of material.

Bashir, Shazia; Shahid Rafique, M.; Husinsky, Wolfgang

2012-03-01

101

Novel CaF2 Nanocomposite with High Strength and Fluoride Ion Release  

PubMed Central

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

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

2010-01-01

102

Pyroelectroluminescence of barium beta borate single crystals  

Microsoft Academic Search

Investigations were made of the pyroluminescence properties of barium beta borate single crystals. The measurements were made\\u000a at air pressures of 1–10 Pa and temperatures of 80–400 K. Luminescence was observed as isolated flashes over the entire range\\u000a of experimental conditions. It was observed that the light flashes coincided with the pyrocurrent oscillations.

V. T. Adamiv; Ya. V. Burak; M. R. Panasyuk; I. M. Teslyuk

1998-01-01

103

Single crystal silicon micro-actuators  

Microsoft Academic Search

A novel process suitable for fabricating single-crystal silicon microactuators is described. The process utilizes boron-diffused silicon etch stop to define the silicon microstructure thickness and a dry etch process to form narrow and deep trenches, followed by a silicon-to-glass bonding step and subsequent unmasked wafer dissolution. For rotational microactuators, polysilicon trench filling and sacrificial layer patterning are added to define

K. Suzuki

1990-01-01

104

Ionic diffusion in single crystals of vermiculite  

SciTech Connect

Novel guest-host compounds, based on single crystal vermiculite, were synthesized by diffusive techniques through a new hydrogen vermiculite. Single crystals were chosen because of the ease of characterization. An investigation of the ion transport properties of these single crystals was done to determine the mechanism of conductivity including the predominant charge carrier. Measurements of the ionic conductivity using impedance spectroscopy and X-ray lattice parameters of the ion-exchanged samples strongly suggest that the native cations and not protons are the major current carriers. Single crystals of hydrogen vermiculite were synthesized at room temperature by ion exchange from sodium-vermiculite using 1 molar acetic acid for a one week. Subsequent ion exchange with other cations was found to be much enhanced. Thus transition metals were exchanged in about a week in contrast to the need of several months using previous methods. The ionic conductivity of hydrogen vermiculite was measured and shown to be much lower than that of many other monovalent cations in the same host lattice. Its enthalpy of motion is also much lower. These marked differences suggest that protonic species do not play a significant role in charge transport in these layered materials. These materials were characterized by x-ray powder diffraction, thermogravimetric analysis and acid-base titration. Hydrogen-vermiculite was found to react with organic bases, like methylamine, ethylamine, n-butylamine, n-hexylamine, n-octylamine, n-decylamine, aniline, acrylamide, methacrylaminde, urea, 1,10phenanthroline, and 1,1phenanthroline ferrous sulfate complex, to undergo ion exchange with metal cations like sodium, zinc, copper(II) ions and polymerization reactions could be performed in the galleries of the structure like pyrrole and aniline. Its behavior was compared with that of powdered montmorillonite.

Maraqah, H.R.

1993-01-01

105

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

106

Characterization of Defects in PTerphenyl Single Crystals  

Microsoft Academic Search

White Beam Synchrotron X-ray Topography has been used to characterize defects in solution-grown p-terphenyl single crystals. Defects observed include growth dislocations, mechanically introduced dislocations, macroscopic twins, twin lamellae, and dislocations emitted from twin boundaries. Line direction and Burgers Vector analysis of the growth and mechanically introduced dislocations, using projective geometry calculations and g. b analysis, respectively, are presented, along with

Michael Dudley; Rosemarie Disalvo; Shang-Yun Hou; Bruce M. Foxman; William Jones

1992-01-01

107

Flexible single-crystal silicon nanomembrane photonic crystal cavity.  

PubMed

Flexible inorganic electronic devices promise numerous applications, especially in fields that could not be covered satisfactorily by conventional rigid devices. Benefits on a similar scale are also foreseeable for silicon photonic components. However, the difficulty in transferring intricate silicon photonic devices has deterred widespread development. In this paper, we demonstrate a flexible single-crystal silicon nanomembrane photonic crystal microcavity through a bonding and substrate removal approach. The transferred cavity shows a quality factor of 2.2 × 10(4) and could be bent to a curvature of 5 mm radius without deteriorating the performance compared to its counterparts on rigid substrates. A thorough characterization of the device reveals that the resonant wavelength is a linear function of the bending-induced strain. The device also shows a curvature-independent sensitivity to the ambient index variation. PMID:25409282

Xu, Xiaochuan; Subbaraman, Harish; Chakravarty, Swapnajit; Hosseini, Amir; Covey, John; Yu, Yalin; Kwong, David; Zhang, Yang; Lai, Wei-Cheng; Zou, Yi; Lu, Nanshu; Chen, Ray T

2014-12-23

108

A Spontaneous Single-Crystal-to-Single-Crystal Polymorphic Transition Involving Major Packing Changes.  

PubMed

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

Krishnan, Baiju P; Sureshan, Kana M

2015-02-01

109

Guest exchange through single crystal-single crystal transformations in a flexible hydrogen-bonded framework.  

PubMed

A molecular framework based on guanidinium cations and 1,2,4,5-tetra(4-sulfonatophenyl)benzene (TSPB), an aromatic tetrasulfonate with nominal 2-fold and mirror symmetry, exhibits three crystallographically unique one-dimensional channels as a consequence of molecular symmetry and complementary hydrogen bonding between the guanidinium (G) ions and the sulfonate (S) groups of TSPB. Unlike previous GS frameworks, this new topology is sufficiently flexible to permit reversible release and adsorption of guest molecules in large single crystals through a cyclic shrinkage and expansion of the channels with retention of single crystallinity, as verified by single crystal X-ray diffraction. Moreover, the G4TSPB framework permits guest exchange between various guest molecules through SCSCTs as well as exchange discrimination based on the size and character of the three different channels. The exchange of guest molecules during single crystal-single crystal transformations (SCSCT), a rare occurrence for hydrogen-bonded frameworks, is rather fast, with diffusivities of approximately 10(-6) cm(2) s(-1). Rapid diffusion in the two channels having cross sections sufficient to accommodate two guest molecules can be explained by two-way or ring diffusion, most likely vacancy assisted. Surprisingly, rapid guest exchange also is observed in a smaller channel having a cross-section that accommodates only one guest molecule, which can only be explained by guest-assisted single-file unidirectional diffusion. Several single crystals of inclusion compounds can be realized only through guest exchange in the intact framework, suggesting an approach to the synthesis of single crystalline inclusion compounds that otherwise cannot be attained through direct crystallization methods. PMID:25248132

Xiao, Wenchang; Hu, Chunhua; Ward, Michael D

2014-10-01

110

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

111

Growth and characterization of single crystal insulators on silicon  

NASA Technical Reports Server (NTRS)

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

Schowalter, Leo J.; Fathauer, Robert W.

1989-01-01

112

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

113

Intercomparison of dosimetry systems based on CaF2:Mn TL detectors.  

PubMed

The responses of readings by the TL dosimetry system MR200 TL developed in-house and used at JSI and the TOLEDO TL system used at RBI are compared. Ten measurements at different doses ranging from 0.01 mSv to 5 Sv were carried out. A set of 36 dosemeters with three pellets of CaF2:Mn were irradiated in radiation fields of 137Cs and 60Co. Analysis of the measured results shows that at doses below 0.1 Sv, readers' outputs do not differ >5% from each other. At doses >1 Sv, the results obtained by the MR200 reader must be corrected with a known factor. Finally, the reproducibility of the results from the MR200 was tested. PMID:16735564

Zorko, B; Miljani?, S; Veki?, B; Stuhec, M; Gobec, S; Ranogajec-Komor, M

2006-01-01

114

Dynamic dimer formation between superionic fluorines in CaF2  

NASA Astrophysics Data System (ADS)

Recently we have elucidated the formation of the dynamic dimers in the conductor ?-CuI through the analyses of the correlation peaks of the partial pair-distribution functions and the partial angle distribution functions with the first principles molecular dynamics (MD) method.(J. Phys. Soc. Jpn. 81,055603(2012).) The present study investigate the formation of the dynamic dimers and the migration paths of the dimers in the conductor CaF2 with the MD method. The fluorines form the dynamic 32f-8c dimers with the coordinate (x,x,x) x=0.300. These incommensurate dimers allow to decrease the migration barriers of the fluorines.

Saito, Masashi; Tasaka, Tomofumi; Tsumuraya, Kazuo

2013-03-01

115

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

E-print Network

1 Crystal Structure of A-amylose: a Revisit from Synchrotron Microdiffraction Analysis of Single;2 Abstract The three-dimensional structure of A-amylose crystals, as a model of the crystal domains of A-sized single crystals. The resulting datasets allowed a determination of the structure with conventional X

Paris-Sud XI, Université de

116

Chemical vapor deposition of graphene single crystals.  

PubMed

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

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

2014-04-15

117

Annealing effect on ion conduction of nanosized CaF2/BaF2 multilayers  

NASA Astrophysics Data System (ADS)

The transient part of the ion conductivity enhancement in CaF2/BaF2 heterolayers on annealing at elevated temperatures is investigated. It is well established that annealed heterolayers exhibit a strongly increased F- conductivity parallel to the interfaces and a substantial but less strong enhancement perpendicular to the interfaces [N. Sata et al., Nature 408, 946 (2000) and X. X. Guo et al., Appl. Phys. Lett. 91, 103102 (2007)]. This is explained by a F- redistribution from BaF2 to CaF2 as a consequence of contact equilibrium. As to the behavior during annealing, two remarkable features are observed: (i) freshly prepared films show an even higher conductance enhancement if measured in the parallel direction, which decreases on annealing toward the equilibrium situation, while (ii) in the perpendicular direction the conductance variation is very small and of opposite sign. On the basis of the conductivity experiments as a function of temperature, layer-thickness, and anisotropy, in combination with structural investigations by transmission electron microscopy, we conclude that in agreement with earlier experience on composite materials, a high density of unstable defects is formed close to the heterointerfaces during multilayer preparation, which heals off during the temper process. In the final contact equilibrium a regular array of misfit dislocations is left, enabling the epitaxial contact. By assuming that the electroactive unstable microstructural defects are arranged at the heterointerfaces and are charged by fluoride ion trapping, we can explain the experimental features including the space charge overlap using the combined Mott-Schottky and Gouy-Chapman models used previously. The results indicate that the charge density stays approximately constant during the annealing process.

Guo, X. X.; Matei, I.; Jin-Phillipp, N. Y.; van Aken, P. A.; Maier, J.

2009-06-01

118

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

119

Triplet exciton dynamics in rubrene single crystals  

NASA Astrophysics Data System (ADS)

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

Ryasnyanskiy, Aleksandr; Biaggio, Ivan

2011-11-01

120

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

121

Properties of salt-grown uranium single crystals  

Microsoft Academic Search

Recently single crystals of -uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than

J. C. Cooley; R. J. Hanrahan; W. L. Hults; J. C. Lashley; M. E. Manley; C. H. Mielke; J. L. Smith; D. J. Thoma; R. G. Clark; A. R. Hamilton; J. L. OBrien; E. C. Gay; N. E. Lumpkin; C. C. McPheeters; J. Willit; G. M. Schmiedeshoff; S. Touton; B. F. Woodfield; B. E. Lang; Juliana Boerio-Goates

2001-01-01

122

Self-assembled Fe nanowires using organometallic chemical vapor deposition and CaF2 masks on stepped Si,,111...  

E-print Network

Self-assembled Fe nanowires using organometallic chemical vapor deposition and CaF2 masks 30 November 2000 Linear arrays of 3 nm wide Fe stripes with 15 nm spacing are fabricated by self-assembly are self-assembled on a stepped Si 111 surface. Scanning tunneling microscopy is used to investigate

Himpsel, Franz J.

123

Electronic properties of the Fe2+ ion in CaF2 from Mssbauer and far infrared spectroscopy  

E-print Network

997 Electronic properties of the Fe2+ ion in CaF2 from Mössbauer and far infrared spectroscopy J. R studied by Mössbauer spectroscopy in the slow relaxation regime (4.2-14 K). Far infrared experiments have. From both Mössbauer and far infrared results, one can deduce that the average distance between the spin

Paris-Sud XI, Université de

124

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

EPA Science Inventory

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

125

Fabrication of crystals from single metal atoms  

PubMed Central

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

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

2014-01-01

126

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

127

Fabrication of crystals from single metal atoms  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

128

Ultrahigh-quality silicon carbide single crystals.  

PubMed

Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems. PMID:15329716

Nakamura, Daisuke; Gunjishima, Itaru; Yamaguchi, Satoshi; Ito, Tadashi; Okamoto, Atsuto; Kondo, Hiroyuki; Onda, Shoichi; Takatori, Kazumasa

2004-08-26

129

Synthesis and characterization of superconducting single-crystal Sn nanowires  

E-print Network

June 2003 Single-crystal superconducting tin nanowires with diameters of 40­160 nm have been prepared was attributed by the authors to be related to the ``poor crystal structure;'' that is, a lacking of electronSynthesis and characterization of superconducting single-crystal Sn nanowires Mingliang Tian

130

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

131

Piezoelectric single crystals for ultrasonic transducers in biomedical applications.  

PubMed

Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state-of-art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will be addressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN-PT and PIN-PMN-PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single-element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging, and microbeam applications of the single crystal transducers will be discussed. PMID:25386032

Zhou, Qifa; Lam, Kwok Ho; Zheng, Hairong; Qiu, Weibao; Shung, K Kirk

2014-10-01

132

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

133

Growth and characterization of biadmixtured TGS single crystals  

Microsoft Academic Search

Single crystals of triglycine sulfate (TGS) with l-glutamine and l-methionine were grown in aqueous solutions by a slow cooling method. The grown crystals were subjected to single crystal and powder X-ray diffraction studies to identify the morphology and the structure. FTIR and UV–visible spectra reveal the functional group identification and optical property of the grown crystals. The dielectric studies were

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

2009-01-01

134

Growing single crystals in silica gel  

NASA Technical Reports Server (NTRS)

Two types of chemical reactions for crystal growing are discussed. The first is a metathetical reaction to produce calcium tartrate tetrahydrate crystals, the second is a decomplexation reaction to produce cuprous chloride crystals.

Rubin, B.

1970-01-01

135

Ion Crystal Transducer for Strong Coupling between Single Ions and Single Photons  

E-print Network

A new approach for the realization of a quantum interface between single photons and single ions in an ion crystal is proposed and analyzed. In our approach the coupling between a single photon and a single ion is enhanced ...

Lamata, L.

136

Experimental dynamic metamorphism of mineral single crystals  

NASA Astrophysics Data System (ADS)

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a- ? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ? clinoenstatite and w ürtzite ? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO · nAl 2O 3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates.

Kirby, Stephen H.; Stern, Laura A.

1993-09-01

137

Dynamic characteristics of single crystal SSME blades  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

138

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

139

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

140

Vibration-assisted machining of single crystal  

NASA Astrophysics Data System (ADS)

Vibration-assisted machining offers a solution to expanding needs for improved machining, especially where accuracy and precision are of importance, such as in micromachining of single crystals of metals and alloys. Crystallographic anisotropy plays a crucial role in determining on overall response to machining. In this study, we intend to address the matter of ultra-precision machining of material at the micron scale using computational modelling. A hybrid modelling approach is implemented that combines two discrete schemes: smoothed particle hydrodynamics and continuum finite elements. The model is implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine (VUMAT) and used to elucidate the effect of crystallographic anisotropy on a response of face centred cubic (f.c.c.) metals to machining.

Zahedi, S. A.; Roy, A.; Silberschmidt, V. V.

2013-07-01

141

Electrical switching in cadmium boracite single crystals  

NASA Technical Reports Server (NTRS)

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

Takahashi, T.; Yamada, O.

1981-01-01

142

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang,  

E-print Network

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

Kim, Bongsoo

143

Lattice location and annealing studies of Hf implanted CaF 2  

NASA Astrophysics Data System (ADS)

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 <1 1 0> crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with 181Hf( 181Ta) show quadrupole interactions with ? Q1 = 300(3) MHz ( ? = 0.00), ? Q2 = 1285(13) MHz ( ? = 0.43) and ? Q3 = 1035(10) MHz ( ? = 0.00) after annealing up to 1200 K.

Geruschke, Thomas; Lorenz, Katharina; Alves, Eduardo; Vianden, Reiner

2009-05-01

144

Crystallization of single phase (K, Na)clinoptilolite  

Microsoft Academic Search

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of (K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 °C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were

Shigeo Satokawa; Keiji Itabashi

1997-01-01

145

Investigation on Growth and Surface Analysis of DAST Single Crystals  

SciTech Connect

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

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

2011-07-15

146

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

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

148

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

149

Anisotropy of transient photoconductivity in functionalized pentacene single crystals  

E-print Network

to their potential applications in thin film transis- tors, organic light-emitting diodes, solar cells, etc.1 Thin single crystal platelets and polycrystalline thin films are par- ticularly interesting for applicationsAnisotropy of transient photoconductivity in functionalized pentacene single crystals O

Ostroverkhova, Oksana

150

Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires  

E-print Network

Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires Rusen Yang, Yong Ding, and Zhong Lin, deformation-free, single-crystal nanohelixes/nanosprings of piezoelectric ZnO are reported. The nanohelixes observed for carbon nanotubes,1 SiC2 and amorphous silicon carbide.3 The carbon coils are created due

Wang, Zhong L.

151

Precipitation of Copper Silicide in Voids in Silicon Single Crystals  

E-print Network

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

152

The growth technology for 300 mm single crystal silicon  

Microsoft Academic Search

The fabrication technique for 300 mm silicon single crystals and wafers is the central topic of silicon material research recently. The study on the growth technique of 300 mm silicon ingots has been developed in our institute since 1997. The research mainly focuses on the following aspects: (1) process conditions for fabrication of the dislocation-free silicon single crystal; (2) oxygen

H Tu; Q Zhou; G Zhang; J Wang; Q Chang; F Qin; F Fang; Z Wu; G Wan

2001-01-01

153

Single crystal silicon rotary microactuator for hard disk drive  

Microsoft Academic Search

A single crystal silicon rotary microactuator for hard disk drives (HDD) is described in this paper. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio 20:1 directly processed from a single crystal silicon substrate. It consists of a

J. Q. Mou; Y. Lu; J. P. Yang; Q. H. Li

2003-01-01

154

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

155

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

156

Semiconductor single crystal external ring resonator cavity laser and gyroscope  

SciTech Connect

A ring laser is described comprising: a semiconductor single crystal external ring resonator cavity having a plurality of reflecting surfaces defined by the planes of the crystal and establishing a closed optical path; and a discrete laser medium disposed in said semiconductor single crystal external ring resonator cavity for generating coherent light in said cavity, wherein said resonator cavity is decoupled from the laser medium.

Spitzer, M.P.

1993-08-31

157

Hydrothermal synthesis and up-conversion luminescence of Ho3+/Yb3+ co-doped CaF2  

NASA Astrophysics Data System (ADS)

CaF2:Ho3+/Yb3+ nano-particles with intense green up-conversion (UC) luminescence are successfully synthesized via a facile hydrothermal approach by using NH4F as the fluoride source and Na2EDTA as a chelating reagent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and UC emission spectra are used to characterize the structures, shapes, and luminescent properties of the samples. The effects from fluoride sources and chelating reagents on the formations of CaF2 nano-particles are investigated, and the formation process is also deduced. Under the excitation of a 980-nm laser diode, the samples each show a green up-conversion emission centered at 540 nm corresponding to the 5S2/5F4?5I8 transitions of Ho3+. Moreover, the UC mechanisms of Ho3+/Yb3+ co-doped CaF2 nano-particles are also discussed.

Yang, Zheng; Guo, Chong-Feng; Chen, Ye-Qing; Li, Lin; Li, Ting; Jeong, Jung-Hyun

2014-06-01

158

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

159

Advanced single crystal for SSME turbopumps  

NASA Technical Reports Server (NTRS)

The objective of this program was to evaluate the influence of high thermal gradient casting, hot isostatic pressing (HIP) and alternate heat treatments on the microstructure and mechanical properties of a single crystal nickel base superalloy. The alloy chosen for the study was PWA 1480, a well characterized, commercial alloy which had previously been chosen as a candidate for the Space Shuttle Main Engine high pressure turbopump turbine blades. Microstructural characterization evaluated the influence of casting thermal gradient on dendrite arm spacing, casting porosity distribution and alloy homogeneity. Hot isostatic pressing was evaluated as a means of eliminating porosity as a preferred fatigue crack initiation site. The alternate heat treatment was chosen to improve hydrogen environment embrittlement resistance and for potential fatigue life improvement. Mechanical property evaluation was aimed primarily at determining improvements in low cycle and high cycle fatigue life due to the advanced processing methods. Statistically significant numbers of tests were conducted to quantitatively demonstrate life differences. High thermal gradient casting improves as-cast homogeneity, which facilitates solution heat treatment of PWA 1480 and provides a decrease in internal pore size, leading to increases in low cycle and high cycle fatigue lives.

Fritzemeier, L. G.

1989-01-01

160

Single crystal to single crystal transformation and hydrogen-atom transfer upon oxidation of a cerium coordination compound.  

PubMed

Trivalent and tetravalent cerium compounds of the octamethyltetraazaannulene (H2omtaa) ligand have been synthesized. Electrochemical analysis shows a strong thermodynamic preference for the formal cerium(IV) oxidation state. Oxidation of the cerium(III) congener Ce(Homtaa)(omtaa) occurs by hydrogen-atom transfer that includes a single crystal to single crystal transformation upon exposure to an ambient atmosphere. PMID:23534677

Williams, Ursula J; Mahoney, Brian D; Lewis, Andrew J; DeGregorio, Patrick T; Carroll, Patrick J; Schelter, Eric J

2013-04-15

161

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

162

High cycle fatigue crack initiation in single crystals and polycrystals  

NASA Astrophysics Data System (ADS)

The objective of this research is to analyze the high-cycle fatigue crack initiation in both monocrystalline and polycrystalline ductile metals. Persistent slip bands have been observed in both single crystals and polycrystals in numerous high-cycle fatigue tests. Extrusions and intrusions at the free surface of fatigued specimens are the favorable sites for fatigue crack initiation. In the present study, the micromechanic theory of high-cycle fatigue crack initiation, proposed by Lin and Ito, is extended to include the crystal anisotropic effect on the growth of extrusions in polycrystals and to study the high-cycle fatigue deformation in single crystals. Previous studies based on Lin and Ito model mainly concerned the fatigue crack initiation in aluminum and its alloys. The elastic anisotropy of individual crystals is insignificant and was accordingly neglected. However, the anisotropy of the elastic constants of some other metallic crystals, such as titanium and some intermetallic compounds, is not negligible. In this study, the effect of crystal anisotropy is considered by using Eshelby's equivalent inclusion method. The polycrystal of Nisb3Al intermetallic compound is analyzed for studying the effect on fatigue crack initiation. The model of fatigue crack initiation of polycrystals is applied to analyze the fatigue deformation in single crystals. The residual stress field in a single crystal is calculated by using a superposition method. The fatigue deformation of single crystals under the constant plastic strain amplitude control is investigated.

Teng, Ningjun

163

Grooving wear of single-crystal tungsten carbide  

Microsoft Academic Search

The anisotropic nature of tungsten carbide (WC) single crystals has been evaluated in single-tip scratch testing and in multiple-tip abrasion. The single-tip grooves were made with a Vickers diamond indenter and the abrasion tests were performed with diamond and silica grits. All tests were performed on both the prism and basal planes of the WC crystals. A polycrystalline binderless carbide

H Engqvist; S Ederyd; N Axén; S Hogmark

1999-01-01

164

Reversible pressure-induced first-order phase transitions in anion-excess fluorite KY3F10 studied with single-crystal X-ray diffraction  

NASA Astrophysics Data System (ADS)

KY3F10 (Fm3barmZ = 8) has been studied with single-crystal X-ray diffraction to 9.5 GPa in a diamond anvil cell under hydrostatic conditions. At atmospheric pressure, it is an anion-excess 2 × 2 × 2 superstructure of fluorite with two building blocks Y6F36 and Y6F32. In the Y6F36 block, six square YF8 antiprisms share their corners to form an empty F12 cubooctahedron. In the Y6F32 block, six square YF8 antiprisms share their edges to form an empty F8 cube. Upon compression, there occur phase transitions between 5 and 7 GPa due to an instability of the empty F12 cubooctahedra in the 2 × 2 × 2 superstructure. At about 7 GPa, the cubooctahedra collapse completely and all the cations in the new structure (Pm3barm, Z = 1) are surrounded by cubes of the F atoms. The excessive fluorine is located in the F8 cubes. At hydrostatic conditions, all the transformations are reversible. These observations imply that at high pressures the anion-excess fluorite superstructures in general tend to transform to the CaF2 structure.

Grzechnik, Andrzej; Friese, Karen

2014-04-01

165

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

PubMed

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

Zhu, Ming; Zhu, Gangbei; Weng, Yuxiang

2013-05-01

166

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

E-print Network

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

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

2011-02-21

167

Photochemistry of adsorbed molecules. Part XXI. CH 3Br adsorbed on electron-impact- or hydrogen-atom-modified CaF 2(111), at 193 nm  

NASA Astrophysics Data System (ADS)

The photochemistry of CH 3Br adsorbed on CaF 2 has been studied using CaF 2(111) modified by (a) low-energy electron impact and (b) dosing with hydrogen atoms. In each case the temperature-programmed desorption (TPD) behaviour and the photodynamics, i.e. the energy and angular distributions of the photoformed methyl radicals were compared with the same diagnostics applied to unmodified CaF 2(111). Electron irradiation of the CaF 2(111) surface resulted in an increased desorption temperature of the adsorbate, and the emergence of a broadened translational energy photodissociation channel, P( ET'), for CH 3(g), associated in earlier work with photoinduced charge-transfer dissociation of the adsorbate. This suggested the formation of Ca metal clusters by process (a). By contrast, the hydrogen-atom-modified surface exhibited a decreased desorption temperature of the adsorbate and no broadening of P( ET'). The thermal hydrogen atoms may modify the surface by abstracting surface F, forming HF(g). Electron impact and hydrogen atom modification of the CaF 2 changed the angular distributions for the 'directly formed' (fast) CH 3(g) photofragments in a markedly different fashion, indicative of differing structure in the adlayer for CaF 2(111) when modified by processes (a) or (b).

Lee, T. G.; Polanyi, J. C.

2000-08-01

168

Single-crystal gallium nitride nanotubes  

Microsoft Academic Search

Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized

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

2003-01-01

169

Constricted hysteresis loops in Fe and Ni single crystals  

NASA Astrophysics Data System (ADS)

Magnetic hysteresis loops reflect the variety of magnetic domain structures and have been considered to have normal rectangular or leaf-like shapes in standard ferromagnets such as Fe and Ni metals. We report on observations of constricted hysteresis loops in Fe and Ni single crystals with very low defect densities. The constricted loops were observed below T=150 K and in a medium temperature range from 150 to 430 K in Fe and Ni single crystals, respectively. These constricted loops disappear by weak plastic deformation for both single crystals. The origin of constricted hysteresis loops was explained by eddy current effects under less domain wall pinning due to dislocations.

Takahashi, Seiki; Kobayashi, Satoru; Shishido, Toetsu

2010-11-01

170

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

171

Hole mobility in organic single crystals measured by a ``flip-crystal'' field-effect technique  

Microsoft Academic Search

We report on single crystal high mobility organic field-effect transistors prepared on prefabricated substrates using a ``flip-crystal'' approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the field-effect transistors' electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of

C. Goldmann; S. Haas; C. Krellner; K. P. Pernstich; D. J. Gundlach; B. Batlogg

2004-01-01

172

Thermodynamics of mixing of liquids in the system Ca 3(PO 4) 2?CaCl 2?CaF 2?Ca(OH) 2  

NASA Astrophysics Data System (ADS)

Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca 3(PO 4) 2?CaCl 2?CaF 2?Ca(OH) 2. In this model, melt components are expressed as Ca0.5X, where X is hydroxide or a halogen, or as Ca 1.5PO 4. The derived binary interaction parameters ( WG' s) are sufficient to describe deviations from Raoultian behavior for the data. Standard state data are derived for molten Ca(OH) 2 and Ca 3(PO 4) 2, and for the intermediate compounds CaClF, CaClOH, and Ca 2PO 4Cl. Melts in the CaCl 2?CaF 2 system show ideal mixing behavior, while the calcium hydroxide-bearing molten salts form asymmetric regular solutions. The hydroxide-bearing melts show the small positive enthalpies of mixing typical for mixed-anion salts. Similar behavior is measured in simpler molten salt mixtures. The positive deviations from Raoultian behavior are not a mathematical artifact of the model. Data are less extensive for the salt-phosphate systems but cover the essential portions of the systems where salt to phosphate ratios are high. The mixtures of the molten salts and phosphates salts show large negative enthalpy interaction parameters ( WH), as is expected in eutectic systems which mix a high-melting-point crystal with a low-melting-point flux. Adequate reproduction of the data requires that some entropy interaction parameters be negative, although small. This implies the presence of ordering in the melt, which is manifested in more polymerized phosphate liquids and glasses as halogenated and hydroxylated orthophosphate and pyrophosphate species. Results of the model indicate that the quaternary system is a good choice for determination of activity-composition relations for the apatites. Comparison of common sources of standard state thermodynamic data ( ROBIE et al., 1979; JANAF, CHASE et al., 1985; CODATA, GARVIN et al., 1987) shows that the data for the salts are very similar where they are not identical. At temperatures below 900°C in the ternary systems, liquid compositions will be on or near the apatite-crystalline salt cotectics, and dissolve less than 1 mol% Ca 3(PO 4) 2. This makes CaCl 2?CaF 2 mixtures excellent candidates for determination of unambiguous apatite activity-compositional relations. Only the Ca(OH) 2 liquidus is strongly affected by the addition of phosphate, but this effect is closely described by a regular solution model.

Tacker, R. C.; Stormer, J. C., Jr.

1993-10-01

173

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

174

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

175

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

176

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

PubMed

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

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

2015-01-25

177

Growth and characterization of organic material 4-dimethylaminobenzaldehyde single crystal  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

178

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

179

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

180

Designed three-dimensional freestanding single-crystal carbon architectures.  

PubMed

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

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

2014-11-25

181

Growth of Zinc Oxide Single Crystals by Vapor Phase Reaction  

Microsoft Academic Search

ZnO single crystals are grown by vapor phase reaction with ZnI2 source. When the growth region is maintained between 1150°C and 1200°C, crystals grow by oxidation, and between 970°C and 1020°C, by hydrolysis. Crystals are mainly needles 15 mm in length or plates 8 mm2 in area. Patterns suggesting their growth mechanisms are observed in their microphotographs. The present experiments

Masami Hirose

1971-01-01

182

Research on TGS single crystal growth with modulated structure  

NASA Astrophysics Data System (ADS)

The experimental results of TGS crystal growth with modulated structure (periodic laminar of ferroelectric domains) is briefly discussed in this paper. The method used here is to add some DL-alanine additive in the solution of TGS and to apply the electric field during crystal growth, the direction of which is periodically varied. By using this method, TGS single crystals containing a nearly regular and flat periodic laminar structure of ferroelectric domains have been fabricated.

Wang, Wenshan; Qi, Ming

1986-12-01

183

Characterization of phosphoric acid doped TGS single crystals  

Microsoft Academic Search

Single crystals of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) are grown from aqueous solution containing 10–50mol% of H3PO4. Large sized crystals of dimension (70mm×40mm×25mm) suitable for IR detector applications are obtained with 20mol% of H3PO4. They exhibit elongated domains, and the domain density is higher than in undoped TGS crystals. FT-IR analysis indicates the presence of both zwitter and

Aparna Saxena; Vinay Gupta; K. Sreenivas

2004-01-01

184

X-ray topographic examination of large paraffin single crystals  

Microsoft Academic Search

The internal microstructure of large melt-grown paraffin (n-eicosane, C20H42) single crystals was examined by the Lang x-ray diffraction projection topographic technique. Crystal selection was facilitated by use of an electro-optical system which permitted instantaneous display of Laue transmission x-ray diffraction patterns on a television monitor. The crystals were oriented and topographic diffraction planes were selected by the use of a

Robert E. Green; Edward N. Farabaugh; John M. Crissman

1975-01-01

185

Growth and polytypism of single crystals of cadmium bromide  

NASA Astrophysics Data System (ADS)

Single crystals of cadmium bromide have been grown by Bridgman-Stockbarger technique and their polytypism studied by X-ray diffraction. Oscillation photographs obtained from several different regions of the crystals have revealed the occurrence of only the small-period polytype 6R in the crystals. The results have been compared with those reported earlier for the isostructural compounds CdI 2 and PbI 2.

Chaudhary, S. K.; Trigunayat, G. C.

1985-12-01

186

Single-drop optimization of protein crystallization  

PubMed Central

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

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

2012-01-01

187

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

188

Study of single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

The parameters and requirements for growing single crystals of relatively high melting point metals in a zero gravity environment are studied. The crystal growth of metals such as silver, copper, gold, and alloys with a melting point between 900-1100 C is examined.

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

1973-01-01

189

Growth of large single crystals of the orthorhombic paracetamol  

NASA Astrophysics Data System (ADS)

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

Mikhailenko, M. A.

2004-05-01

190

Hertzian Fracture in Single Crystals with the Diamond Structure  

Microsoft Academic Search

Extension of an earlier theory of Hertzian fracture in brittle isotropic materials is here made to include the case of brittle single crystals, with particular reference to crystals having the diamond structure. A detailed description is first given of the inhomogeneous stress field in a flat, elastic specimen loaded normally with a hard sphere. The geometry of cracks growing in

B. R. Lawn

1968-01-01

191

Brittlestar-Inspired Microlens Arrays Made of Calcite Single Crystals.  

PubMed

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

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

2014-11-01

192

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

193

Constitutive modeling of creep of single crystal superalloys  

E-print Network

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

Prasad, Sharat Chand

2006-10-30

194

On the deformation mechanisms in single crystal Hadfield manganese steels  

SciTech Connect

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

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

1998-02-13

195

Growth and properties of shaped single crystals of lithium fluoride  

NASA Astrophysics Data System (ADS)

Shaped single crystals of lithium fluoride have been produced by the Stepanov method using shapers which are wetted and unwetted by the melt. Dislocation structure, porosity, optical properties, ion conductivity, and distribution of magnesium impurities have been studied.

Antonov, P. I.; Krymov, V. M.; Hartmann, E.

1990-07-01

196

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

PubMed Central

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

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

2014-01-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

198

Magnetic properties of Gd doped Y and Sc single crystals  

Microsoft Academic Search

Magnetization measurements on 5 and 15% ScGd single crystals show typical spin glass like behaviour for fields parallel and perpendicular to the c axis of the hexagonal structure. In contrast for1, 2 and 3% Gd doped in Y single crystals there is a cusp in the susceptibility but no irreversibility below the temperature of the cusp. Spin-flop like transitions in

R. Wendler; P. Pureur; A. Fert; K. Baberschke

1984-01-01

199

Melt growth of high purity cadmium bromide single crystals  

NASA Astrophysics Data System (ADS)

The earlier attempts to grow pure single crystals of cadmium bromide by zone-melting have proved difficult due to the very high vapour pressure of the compound. The problem has been successfully overcome now by suitably employing the method of vertical zone-refining, which has helped to reduce the loss of material by evaporation to just 3%. Highly pure single crystals have been grown and results of their preliminary X-ray diffraction analysis have been briefly reported.

Singh, Kulvinder; Trigunayat, G. C.

1989-10-01

200

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

201

Growth of single crystals by vapor transport  

NASA Technical Reports Server (NTRS)

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

Wiedemeier, H.

1978-01-01

202

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

203

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

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

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

2002-03-01

204

Hydroxyethylammonium maleate (HEAM) single crystal for optical limiting applications  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

205

Investigation of localized deformation in NiAl single crystals  

SciTech Connect

Deformation of NiAl single crystals was studied using finite element analysis to investigate the modes of localized deformation. Constitutive parameters and hardening characteristics of the active slip systems were estimated by comparing numerical simulation results with experimental results. Deformation of tensile specimens of NiAl single crystal was simulated when loaded along different crystal orientations to understand the deformation mechanism that results in various localized modes of deformation. In particular, the formation of shear bands and kink bands was studied and the material and geometric characteristics that influence the formation of such localization were investigated.

Kumar, A.V.; Yang, Culho; Seelam, V.B.R. [Univ. of Florida, Gainesville, FL (United States). Dept. of Mechanical Engineering

1998-07-01

206

Fatigue Failure Criteria for Single Crystal Nickel Superalloys  

NASA Technical Reports Server (NTRS)

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine and rocket engine turbopump blades is a pervasive problem. Single crystal turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry and NASA because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the pan geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades is complicated to predict due to the material orthotropy and variations in crystal orientations. A fatigue failure criteria based on the maximum shear stress amplitude [delta t max] on the 30 slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criteria reduces the scatter in uniaxial LCF test data, for four different specimen orientations, for PWA 1484 at 1200 F in air, quite well. A power law curve fit of the failure parameter, delta t max, vs. cycles to failure is presented.

Arakere, Nagaraj K.

1999-01-01

207

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

208

Crystal structure, spectral, thermal and dielectric studies of a new zinc benzoate single crystal  

NASA Astrophysics Data System (ADS)

Single crystals of zinc benzoate with a novel structure were grown in gel media. Sodium metasilicate of gel density 1.04 g/cc at pH 6 was employed to yield transparent single crystals. The crystal structure of the compound was ascertained by single crystal X-ray diffractometry. It was noted that the crystal belongs to monoclinic system with space group P21/c with unit cell parameters a = 10.669(1) Å, b = 12.995(5) Å, c = 19.119(3) Å, and ? = 94.926(3)°. The crystal was seen to possess a linear polymeric structure along b-axis; with no presence of coordinated or lattice water. CHN analysis established the stoichiometric composition of the crystal. The existence of functional groups present in the single crystal system was confirmed by FT-IR studies. The thermal characteristic of the sample was analysed by TGA-DTA techniques, and the sample was found to be thermally stable up to 280 °C. The kinetic and thermodynamic parameters were also determined. UV-Vis spectroscopy corroborated the transparency of the crystal and revealed the optical band gap to be 4 eV. Dielectric studies showed decrease in the dielectric constant of the sample with increase in frequency.

Bijini, B. R.; Prasanna, S.; Deepa, M.; Nair, C. M. K.; Rajendra Babu, K.

2012-11-01

209

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

PubMed

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

Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

2014-07-01

210

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

NASA Astrophysics Data System (ADS)

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

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

1989-12-01

211

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

212

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

NASA Technical Reports Server (NTRS)

High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767

Arakere, N. K.; Swanson, G.

2002-01-01

213

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

214

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

215

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

216

Scintillation Properties of Praseodymium Activated Single Crystals  

Microsoft Academic Search

Scintillation properties of LuAG:Pr grown by Furukawa Co. Ltd., Japan, have been studied. The best crystals display light outputs up to 19000 ph\\/MeV and an energy resolution of 4.6% at 662 keV. The scintillation yield is found to be a function of size and temperature of the sample; it can be enhanced by 40% upon heating to 450 K. Radioluminescence

Winicjusz Drozdowski; Pieter Dorenbos; J. T. M. de Haas; R. Drozdowska; A. Owens; K. Kamada; K. Tsutsumi; Y. Usuki; T. Yanagida; A. Yoshikawa

2008-01-01

217

Standard Practice for Application of CaF2(Mn) Thermoluminescence Dosimeters in Mixed Neutron-Photon Environments  

E-print Network

1.1 This practice describes a procedure for measuring gamma-ray absorbed dose in CaF2(Mn) thermoluminescence dosimeters (TLDs) exposed to mixed neutron-photon environments during irradiation of materials and devices. The practice has broad application, but is primarily intended for use in the radiation-hardness testing of electronics. The practice is applicable to the measurement of absorbed dose from gamma radiation present in fields used for neutron testing. 1.2 This practice describes a procedure for correcting for the neutron response of a CaF2(Mn) TLD. The neutron response may be subtracted from the total response to give the gamma-ray response. In fields with a large neutron contribution to the total response, this procedure may result in large uncertainties. 1.3 More precise experimental techniques may be applied if the uncertainty derived from this practice is larger than the user can accept. These techniques are not discussed here. The references in Section 8 describe some of these techniques. 1.4...

American Society for Testing and Materials. Philadelphia

2006-01-01

218

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

219

''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

220

Crystal Structure, Physical Properties, and Electrochemistry of Copper Substituted LiFePO4 Single Crystals  

E-print Network

indicate that the dark brown color originates from interionic d-d transitions. A part of the lithium ions phosphate, with the olivine structure, has been synthesized hydrothermally as dark-brown single crystals

Ceder, Gerbrand

221

Low-cost single-crystal turbine blades, volume 2  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

222

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

223

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

224

Hydrogen-induced degradation in strontium titanate single crystals  

NASA Astrophysics Data System (ADS)

Hydrogen-induced degradation in strontium titanate single crystals was studied through an electrochemical hydrogen charging process, in which the silver electrodes of the crystals were made a cathode in 0.01 M NaOH solution to evolve hydrogen by electrolysis of water. After the process, the resistance of the crystals was decreased by more than one order of magnitude, the dielectric loss was obviously increased, and the capacitance became more dependent on frequency. It is proposed that atomic hydrogen generated by electrolysis of water diffuses into the crystals and exists as a charged interstitial impurity donating electrons to the conduction band of the crystals. Attention should be paid to this hydrogen-induced degradation when the reliability of perovskite-type ferroelectric devices and components is studied.

Chen, W. P.; Dai, J. Y.; Wang, Y.; Lai-Wah Chan, H.

2005-08-01

225

TGS single crystals doped by Pd(II) ions  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pd(II) were grown from aqueous solutions by means of the slow cooling method. Concentration of the doping compound PdSO 4 in the growth solutions varied from 0.3 to 5 mol%. Morphology, domain structure and P- E hysteresis loops have been investigated. The effect of the dopant on the crystal growth velocity is explained on the basis of the notion of an activated Pd(II)-glycine complex.

Novotný, J.; Prokopová, L.; Mi?ka, Z.

2001-06-01

226

Pyroelectric properties of phosphoric acid-doped TGS single crystals  

Microsoft Academic Search

Pyroelectric properties of phosphoric acid (H3PO4)-doped triglycine sulfate (TGSP) single crystals grown from solutions containing 0.1-0.5 mol of H3PO4 have been studied. Incorporation of H3PO4 into the crystal lattice is found to induce an internal bias field (Eb) and is observed through the presence of a sustained polarization and pyroelectricity beyond the transition temperature. The internal bias field has been

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

2003-01-01

227

Low temperature pyroelectric properties of modified TGS single crystals  

Microsoft Academic Search

Pyroelectric and dielectric properties of three different single crystals in the triglycine sulphate (TGS) family have been studied in the temperature range from 20K to room temperature. These crystals are: (1) unmodified TGS; (2) TGS with L-alanine doping and partial substitution of (PO4) for (SO4), abbreviated as ATGSP; (3) TGS with L-alanine doping and partial substitution of (AsO4) for (SO4)

Zhang Peilin; Zhong Weilie; Fang Changshui; Zhao Huansui; Li Cuiping

1990-01-01

228

Growth and characterization of lithium yttrium borate single crystals  

SciTech Connect

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

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

2014-04-24

229

Orientation effects in nanoindentation of single crystal copper  

Microsoft Academic Search

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

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

2008-01-01

230

Growth Defect Studies in SiC Single Crystals  

Microsoft Academic Search

Growth defects in vapor grown 6H-SiC single crystals have been studied using a combination of techniques, including: synchrotron white beam x-ray topography (SWBXT), conventional optical microscopy, fluorescence microscopy, and epi-fluorescence laser scanning confocal microscopy (LSCM). These studies of crystal sections cut both parallel and perpendicular to the [0001] growth axis focused on growth dislocations of screw character running approximately parallel

Michael Dudley; William M. Vetter

1996-01-01

231

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

232

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

233

Polymer single crystal meets nanoparticle, toward ordered hybrid materials  

NASA Astrophysics Data System (ADS)

Judiciously selected polymer single crystal (PSC) systems can interplay with 1-D and 0-D nanoparticles, forming ordered hybrid structures. In this presentation, I will first focus on patterning PSCs on individual carbon nanotubes (CNT). Using both controlled solution crystallization, thin film crystallization and physical vapor deposition methods, CNTs were periodically decorated with PSCs, resulting in nano hybrid shish-kebab (NHSK) structures. Because the polymer kebabs can be easily removed, these unique NHSKs can serve as templates to fabricate a variety of CNTs-containing hybrid materials with controlled pattering on the CNT surface. Sub-20 nanometer alternating patterning was achieved by using crystalline block copolymers. The mechanism was attributed to the crystallization induced block copolymer phase separation. This pattern was successfully used to template nanoparticles (NP) pattering on CNTs. In the second part of the talk, I will discuss fabricating Janus NPs and patterning these NPs using PSCs. Single crystals of thiol-terminated polyethylene oxide (PEO) were incubated in a gold sol. Au-S bonds were formed between the AuNPs and the PEO single crystal surfaces. The inter-particle spacing was controlled by PEO molecular weights, the incubation time, and the annealing temperatures after incubation. The planar geometry of the PSCs led to Janus NP formation. A series of NP dimers, trimers and tetramers were synthesized. NP nanowires were also fabricated. We anticipate that this observation could lead to controlled synthesis of artificial molecules and NP chains for a variety of optical, electronic, and biomedical applications.

Li, Christopher

2009-03-01

234

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

235

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

236

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

237

Constitutive modelling of single crystal and directionally solidified superalloys  

NASA Technical Reports Server (NTRS)

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 directionally solidified nickel-base superalloys which have greater creep/fatigue resistance at elevated temperatures and reduced susceptibility to grain boundary creep, corrosion and oxidation than conventionally cast alloys. Work carried out as part of a research program aimed at the development of constitutive equations to describe the elevated temperature stress-strain-time behavior of single crystal and directionally solidified turbine blade superalloys is discussed. The program involves both development of suitable constitutive models and their verification through elevated temperature tension-torsion testing of single crystals of PWA 1480.

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

1986-01-01

238

Mechanical properties of hydroxyapatite single crystals from nanoindentation data  

PubMed Central

In this paper we compute elasto-plastic properties of hydroxyapatite single crystals from nanindentation data using a two-step algorithm. In the first step the yield stress is obtained using hardness and Young’s modulus data, followed by the computation of the flow parameters. The computational approach is first validated with data from existing literature. It is observed that hydroxyapatite single crystals exhibit anisotropic mechanical response with a lower yield stress along the [1010] crystallographic direction compared to the [0001] direction. Both work hardening rate and work hardening exponent are found to be higher for indentation along the [0001] crystallographic direction. The stress-strain curves extracted here could be used for developing constitutive models for hydroxyapatite single crystals. PMID:21262492

Zamiri, A.; De, S.

2011-01-01

239

Single-crystal neutron diffraction investigation on crystals belonging to the langasite family: a comparative study.  

PubMed

Crystals of the langasite family are of interest as they are piezoelectric in different devices. The properties of these classes of crystals can be modified within certain limits by isomorphous substitution. Single-crystal neutron diffraction studies were carried out for LGT (La(3)Ga(5.5)Ta(0.5)O(14)), LGST (La(3)Ga(5.25)Ta(0.25)Si(0.5)O(14)) and LGZrT (La(3)Ga(5.25)Ta(0.25)Zr(0.5)O(14)) as the neutron study gives a better average picture of the crystal properties over a macroscopic region of the grown crystal. The effect of small substitutions at various sites on the piezoelectric properties of the crystal was studied. PMID:20841917

Chitra, R; Choudhury, R R

2010-10-01

240

Lead pyrovanadate single crystal as a new SRS material  

SciTech Connect

Lead pyrovanadate Pb{sub 2}V{sub 2}O{sub 7} single crystals of optical quality suitable for laser experiments are obtained. Vibrational modes are identified based on the analysis of the polarised Raman spectra of the single crystals. The main parameters (width at half maximum, peak and integral intensities) of the spectral lines most promising for SRS conversion in this material are estimated. These parameters are compared with the corresponding parameters of the most frequently used lines of known Raman materials: yttrium and gadolinium vanadates, potassium and lead tungstates, and lead molybdate. (active media)

Basiev, Tasoltan T; Voronko, Yu K; Maslov, Vladislav A; Sobol, A A; Shukshin, V E [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2011-02-28

241

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

PubMed

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

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

2013-05-14

242

Two-photon-induced singlet fission in rubrene single crystal  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

243

Apparatus And Method For Producing Single Crystal Metallic Objects  

DOEpatents

A mold is provided for enabling casting of single crystal metallic articles including a part-defining cavity, a sorter passage positioned vertically beneath and in fluid communication with the part-defining cavity, and a seed cavity positioned vertically beneath and in fluid communication with the sorter passage. The sorter passage includes a shape suitable for encouraging a single crystal structure in solidifying molten metal. Additionally, a portion of the mold between the sorter passage and the part-defining cavity includes a notch for facilitating breakage of a cast article proximate the notch during thermal stress build-up, so as to prevent mold breakage or the inclusion of part defects.

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

2006-03-14

244

Growth of single-crystal diamonds in microwave plasma  

NASA Astrophysics Data System (ADS)

A microwave plasma (2.45 GHz) was used for depositing single crystal diamond layers at the deposition rate up to 40 ?m/h in hydrogen-methane mixtures on the substrates from natural and synthetic diamond with the (100) deposition surface and with the size up to 5 × 5 mm. The structure and the defect-impurity composition of the fabricated single crystals with the thickness up to 600 ?m have been investigated using Raman spectroscopy, photoluminescence spectroscopy, cathode luminescence spectroscopy, and electron and optical microscopy. A high quality and purity of the diamond layers deposited from a plasma was confirmed.

Bolshakov, A. P.; Ralchenko, V. G.; Polskiy, A. V.; Konov, V. I.; Ashkinazi, E. E.; Khomich, A. A.; Sharonov, G. V.; Khmelnitsky, R. A.; Zavedeev, E. V.; Khomich, A. V.; Sovyk, D. N.

2012-12-01

245

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

246

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

247

Relaxor-PT single crystals: observations and developments.  

PubMed

Relaxor-PT based ferroelectric single crystals Pb(Zn?/?)Nb(?/?)O?-PbTiO? (PZNT) and Pb(Mg?/?)Nb(?/?)O?-PbTiO? (PMNT) offer high performance with ultra-high electromechanical coupling factors k?? > 0.9 and piezoelectric coefficients d??s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by T(RT)-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T(C), a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these <001>-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective T(C)/T(RT). In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling low-loss crystals with high coupling for high-power applications. PMID:20889397

Zhang, Shujun; Shrout, Thomas

2010-10-01

248

Stroboscopic Picosecond Pulse Radiolysis Using Near-Ultraviolet-Enhanced Femtosecond Continuum Generated by CaF2  

NASA Astrophysics Data System (ADS)

For investigations of ultrafast reactions induced by radiation in the short-wavelength region, a near-ultraviolet-enhanced continuum ranging from ca. 390 to 600 nm was generated by focusing the second-harmonic generation (400 nm) of a femtosecond Ti:sapphire laser into a CaF2 plate and applied to stroboscopic picosecond pulse radiolysis. By utilizing a double-pulse detection scheme, the fluctuation between the signal and reference pulses was improved to 2-12% of the standard deviation. The capability of the system in the wavelength region from 400 to 900 nm is demonstrated by measuring transient photoabsorption spectra in water and in tetrahydrofuran solution of biphenyl, where these spectra are attributed to hydrated electrons and the overlap between biphenyl radical anions and the solvated electrons of tetrahydrofuran, respectively.

Saeki, Akinori; Kozawa, Takahiro; Okamoto, Kazumasa; Tagawa, Seiichi

2007-01-01

249

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

250

A single crystal multiple-wavelength electro-optic modulator  

Microsoft Academic Search

A new multi-wavelength low voltage electro-optic modulator has been constructed using the r41coefficient in a single crystal of ADP. It is intended for use in multi-color laser display and recording systems employing a single source such as a krypton-ion laser. The modulator accepts a coaxial mixed wavelength beam and separates the colors using a set of direct view spectroscopic prisms.

J. Schlafer; V. J. Fowler

1971-01-01

251

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

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

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

2010-09-29

252

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

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

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

2010-01-01

253

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

254

The viscoplastic behavior of Hastelloy-X single crystal  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

255

Ultrasonic characterization of single crystal langatate  

NASA Astrophysics Data System (ADS)

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

Sturtevant, Blake T.

256

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

257

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

258

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

259

Intrinsic electron and hole defects in stabilized zirconia single crystals  

Microsoft Academic Search

Intrinsic defects have been produced in yttria- and calcia-stabilized zirconia (YSZ or CaSZ) single crystals either by x irradiation at 300 and 77 K or by thermochemical reduction at 1370, 1670, and 1870 K. The spectroscopic properties of the defects have been studied by electron paramagnetic resonance (EPR), optical absorption, and photoemission techniques. Their thermal stability and bleaching characteristics have

V. M. Orera; R. I. Merino; Y. Chen; R. Cases; P. J. Alonso

1990-01-01

260

Pyroelectric properties of the modified triglycine sulphate (TGS) single crystals  

Microsoft Academic Search

Several doping substitutions (Li, Mn, D, P, As) in the TGS structure have been studied and the pyroelectric and dielectric properties measured. In the case of TGS single crystals modified by partial substitution of (P04 and (As04) groups for the (S04). higher pyroelectric coefficients and an enhancement of the pyroelectric material figure of merit (p\\/K) > 2 x TGS have

A. S. Bhalla; C. S. Fang; L. E. Cross; Yao Xi

1984-01-01

261

Growth of single crystals of bismuth sulpho iodide in gel  

Microsoft Academic Search

Single crystals of bismuth sulpho iodide have been grown in sodium silicate gel at room temperature by diffusing suitable reactants. In the first batch of experiments 3 to 7 g solution of BiCl3 was diffused into the gel containing 10 to 15% KI. Platelets of dimensions upto 5 mm were obtained in a period of 30 days. When thiourea of

R. Roop Kumar; G. Raman; F. D. Gnanam

1989-01-01

262

High definition TV projection via single crystal faceplate technology  

NASA Astrophysics Data System (ADS)

Single crystal phosphor faceplates are epitaxial phosphors grown on crystalline substrates with the advantages of high light output, resolution, and extended operational life. Single crystal phosphor faceplate industrial technology in the United States is capable of providing a faceplate appropriate to the projection industry of up to four (4) inches in diameter. Projection systems incorporating cathode ray tubes utilizing single crystal phosphor faceplates will produce 1500 lumens of white light with 1000 lines of resolution, non-interlaced. This 1500 lumen projection system will meet all of the currently specified luminance and resolution requirements of Visual Display systems for flight simulators. Significant logistic advantages accrue from the introduction of single crystal phosphor faceplate CRT's. Specifically, the full performance life of a CRT is expected to increase by a factor of five (5); ie, from 2000 to 10,000 hours of operation. There will be attendant reductions in maintenance time, spare CRT requirements, system down time, etc. The increased brightness of the projection system will allow use of lower gain, lower cost simulator screen material. Further, picture performance characteristics will be more balanced across the full simulator.

Kindl, H. J.; St. John, Thomas

1993-03-01

263

Temperature Dependence of Plastic Deformation in White Tin Single Crystals  

Microsoft Academic Search

Tensile experiments have been carried out over a wide range of temperatures on single crystals of high-purity white tin with low dislocation density. From the observations of slip lines it is found that different slip systems are activated for different temperature regions and for different orientations of specimens. By deformation with the (100)[010] slip system the cell structure is formed

Muneo Nagasaka

1989-01-01

264

Studies on Slip in Fe2%V Alloy Single Crystals  

Microsoft Academic Search

In an attempt to measure the critical resolved shear stress for slip of bcc metals, Fe-2%V single crystals were compressed along [110] direction, constraining the side faces, (001) and (00\\\\bar{1}), with a pair of fixed walls. Under these conditions, all slips are geometrically expected to be suppressed, and consequently [100] or [010] slip will be activated. Electron microscope study on

Shin Takeuchi

1969-01-01

265

Low temperature magnetic transitions of single crystal HoBi  

SciTech Connect

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

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

2013-09-04

266

Optical waveguides of single-crystal garnet films  

NASA Astrophysics Data System (ADS)

We report light-wave propagation experiments in single-crystal epitaxially grown garnet films. The discussion includes refractive index and lattice constant considerations for various garnets, and also the use of iron garnet films on gallium garnet substrates as magneto-optical waveguides useful in integrated optics.

Tien, P. K.; Martin, R. J.; Blank, S. L.; Wemple, S. H.; Varnerin, L. J.

1972-09-01

267

Numerical aperture of single-mode photonic crystal fibers  

Microsoft Academic Search

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin ? from the half-divergence angle ? ? tan-1 (?\\/??) with ??2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. (1996), we find

Niels Asger Mortensen; Jacob Riis Folken; Peter M. W. Skovgaard; Jes Broeng

2002-01-01

268

Low-cost single-crystal turbine blades, volume 1  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

269

A model for Large Electrostrictive Actuation in Ferroelectric Single Crystals  

E-print Network

1 A model for Large Electrostrictive Actuation in Ferroelectric Single Crystals D. Shilo1 , E will allow larger strains at lower mechanical loads. Keywords: Ferroelectrics; Actuation; Electromechanical Institute of Technology, Pasadena, CA 91125, USA A new mode of large electrostrictive actuation, based on 90

Bhattacharya, Kaushik

270

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

271

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. PMID:23515002

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

272

X-ray crystal spectroscopy with stationary-state single-crystal utilizing Laue diffraction  

Microsoft Academic Search

A new type of x-ray crystal spectrometry has been designed to characterize a hard x-ray spectrum of each pulse emission from a laser-induced plasma x-ray source. Utilizing the Laue diffraction and a two-dimensional detector, it makes possible the measurement of diffracted monochromatic x rays without any time difference using a single crystal in a stationary state. Thus, a hard x-ray

Kazumasa Honda; Tadayuki Ohchi; Isao Kojima; Shigeki Hayashi

2001-01-01

273

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

274

Ultralarge negative dispersion single-polarization photonic crystal fiber  

NASA Astrophysics Data System (ADS)

The concept of employing a central air hole in the core is exploited to obtain an ultralarge negative dispersion photonic crystal fiber (PCF) over the wavelength range of 1350 to 1650 nm. The results show that the fiber may exhibit an average dispersion well over -500 ps/nm-km with a flattened dispersion profile. It is also found that the fiber shows a high birefringence in the order of 10-2 over the entire wavelength bands of interest. The endlessly single-mode behavior of PCFs is utilized to ensure the single modedness of the proposed fiber. Also, the technique of liquid crystal infiltration is exploited to suppress one of the two orthogonal modes of the fundamental mode. Along with the single-polarization behavior, the fiber shows an even more negative dispersion profile with less dispersion variation.

Islam, Md. Asiful; Alam, M. Shah

2014-09-01

275

Shock wave-induced phase transition in RDX single crystals.  

PubMed

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

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

2007-09-20

276

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

277

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

278

EPR observations of trivalent titanium in orthophosphate single crystals  

SciTech Connect

The ground state spectroscopic properties of the 3d/sup 1/ electronic configuration ion Ti/sup 3 +/ have been investigated using EPR spectroscopy. Trivalent titanium was incorporated as a dilute impurity in single crystals of the tetragonal, zircon-structure hosts ScPO/sub 4/, YPO/sub 4/, and LuPO/sub 4/. The EPR spectrum of Ti/sup 3 +/ was observed in the as-grown orthophosphate crystals, and low temperature irradiations were not required to produce the trivalent state. The EPR results show that Ti/sup 3 +/ occupies a substitutional cation site in the host orthophosphate single crystals. Axial spin-Hamiltonian parameters were determined at 77 K, and these results are compared to those obtained previously for the 4d/sup 1/ and 5d/sup 1/ configuration ions Zr/sup 3 +/ and Hf /sup 3 +/ in the same host crystals. Titanium-doped orthophosphate crystals containing isotopically enriched /sup 47/Ti or /sup 49/Ti were also grown and employed in determinations of the hyperfine parameters. The g-values observed here for Ti/sup 3 +/, and determined previously for Zr/sup 3 +/ and Hf /sup 3 +/ are not accounted for by the published second-order expressions indicating that additional coupling mechanisms are operative.

Abraham, M.M.; Boatner, L.A.; Aronson, M.A.

1986-07-01

279

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

SciTech Connect

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

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

2012-12-15

280

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

281

Single crystal growth and anisotropic crystal-fluid interfacial free energy in soft colloidal systems.  

PubMed

We measure the anisotropy of the crystal-fluid interfacial free energy in soft colloidal systems. A temperature gradient is used to direct crystal nucleation and control the growth of large single crystals in order to achieve well-equilibrated crystal-fluid interfaces. Confocal microscopy is used to follow both the growth process and the equilibrium crystal-fluid interface at the particle scale: heterogeneous crystal nucleation, the advancing interface, and the stationary equilibrium interface. We use the measured growth velocity to determine the chemical potential difference between crystal and fluid phases. Well-equilibrated, large crystal-fluid interfaces are then used to determine the interfacial free energy and its anisotropy directly from thermally excited interface fluctuations. We find that while the measured average interfacial free energy is in good agreement with values found in simulations, the anisotropy is significantly larger than simulation values. Finally, we investigate the effect of impurities on the advancing interface. We determine the critical force needed to overcome impurity particles from the local interface curvature. PMID:21867183

Nguyen, Van Duc; Hu, Zhibing; Schall, Peter

2011-07-01

282

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

283

Single-crystal CsBr infrared fibers  

NASA Astrophysics Data System (ADS)

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

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

1982-08-01

284

Spatial Coherence Preservation By Synthetic Single Diamond Crystals  

SciTech Connect

The degree of spatial coherence after x-ray diffraction by synthetic single diamond crystals was investigated. The coherence preservation was measured by means of the Talbot effect for x-rays at the optics beamline BM5 at the ESRF. The (111)- and (100)- oriented specimens of type Ib and IIa were grown by De Beers. To establish a correlation between the coherence degradation and the surface quality, 3D surface topography was measured with an optical interferometric profiler and an AFM. Likewise, to pinpoint the relationship with crystalline quality, the samples were characterized by means of double crystal x-ray diffractometry with microscopic resolution.

Hoszowska, J.; Freund, A. K.; Guigay, J.-P.; Rommeveaux, A. [European Synchrotron Radiation Facility, 6 Jules Horowitz, F-38043 Grenoble (France)

2004-05-12

285

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

286

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

287

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

NASA Astrophysics Data System (ADS)

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 2×2×2 ?m3 cytidine, 600×600×300 nm3 BaTiO3, and 1×1×1 ?m3 silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendellösung method and do not require absorption and extinction corrections.

Yasuda, Nobuhiro; Fukuyama, Yoshimitsu; Toriumi, Koshiro; Kimura, Shigeru; Takata, Masaki

2010-06-01

288

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

SciTech Connect

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 2x2x2 {mu}m{sup 3} cytidine, 600x600x300 nm{sup 3} BaTiO{sub 3}, and 1x1x1 {mu}m{sup 3} silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendelloesung method and do not require absorption and extinction corrections.

Yasuda, Nobuhiro; Fukuyama, Yoshimitsu; Kimura, Shigeru [Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198 (Japan); Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); Toriumi, Koshiro [Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); University of Hyogo, 3-2-1 Kouto, Kamigori, Ako, Hyogo 678-1297 (Japan); Takata, Masaki [Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198 (Japan); Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5148 (Japan)

2010-06-23

289

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

290

Effect of metallic dopants on potassium acid phthalate (KAP) single crystals  

Microsoft Academic Search

Optically transparent single crystals of Cu2+ and Zn2+ doped potassium acid phthalate (KAP) were grown in aqueous solution by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional groups in the crystal lattice has been determined qualitatively by Fourier transform infrared (FTIR) analysis.

V. Chithambaram; S. Jerome Das; R. Arivudai Nambi; K. Srinivasan; S. Krishnan

2010-01-01

291

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

292

Ultrafast dynamics of excitons in tetracene single crystals  

SciTech Connect

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

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

2014-03-21

293

Constitutive modeling of superalloy single crystals with verification testing  

NASA Technical Reports Server (NTRS)

The goal is the development of constitutive equations to describe the elevated temperature stress-strain behavior of single crystal turbine blade alloys. The program includes both the development of a suitable model and verification of the model through elevated temperature-torsion testing. A constitutive model is derived from postulated constitutive behavior on individual crystallographic slip systems. The behavior of the entire single crystal is then arrived at by summing up the slip on all the operative crystallographic slip systems. This type of formulation has a number of important advantages, including the prediction orientation dependence and the ability to directly represent the constitutive behavior in terms which metallurgists use in describing the micromechanisms. Here, the model is briefly described, followed by the experimental set-up and some experimental findings to date.

Jordan, Eric; Walker, Kevin P.

1985-01-01

294

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

295

Synthesis and characterization of single-crystal strontium hexaboride nanowires.  

PubMed

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm. PMID:18950235

Jash, Panchatapa; Nicholls, Alan W; Ruoff, Rodney S; Trenary, Michael

2008-11-01

296

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

297

A piezoelectric single-crystal ultrasonic microactuator for driving optics.  

PubMed

At the millimeter scale, the motions or force out puts generated by conventional piezoelectric, magnetostrictive, photostrictive, or electromagnetic actuators are very limited. Here, we report a piezoelectric ultrasonic microactuator (size: 1.5 × 1.5 × 5 mm, weight: 0.1 g) made of PIN-PMN-PT single crystal. The actuator converts its high-frequency microscopic displacements (nanometer to micrometer scale) into a macro scopic, centimeter-scale linear movement of a slider via frictional force, resulting in a speed up to 50 mm/s and a very high unit volume direct driving force of 26 mN/mm(3) (which is ~100 times higher than a voice coil motor and ~4 times higher than a piezoceramic ultrasonic motor). This work shows the feasibility of using piezoelectric single-crystal-based ultrasonic microactuator for miniature drive of optics in next-generation mobiles and cameras. PMID:23443709

Guo, Mingsen; Dong, Shuxiang; Ren, Bo; Luo, Haosu

2011-12-01

298

Ultrafast dynamics of excitons in tetracene single crystals.  

PubMed

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

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

2014-03-21

299

Ultrafast dynamics of excitons in tetracene single crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

300

Thermal fatigue of NiAl single crystals  

SciTech Connect

Single crystals of [001]-oriented NiAl single crystals were subjected to thermal fatigue by a method which employs induction heating of disk-shaped specimens heated in an argon atmosphere. Several time-temperature heating and cooling profiles were used to produce different thermal strain histories in specimens cycled between 973 K and 1,473 K. After thermal cycling, pronounced shape changes in the form of diametrical elongations along {l{underscore}angle}100{r{underscore}angle} directions with accompanying increases in thickness at and near the {l{underscore}angle}100{r{underscore}angle} specimen axes were observed. The deformations were analyzed in terms of operative slip systems in tension and compression, ratchetting (cyclic strain accumulation), and the elastic properties of NiAl. The experimental results correlate best with thermal stresses associated with the large elastic anisotropy of NiAl.

Kush, M.T.; Holmes, J.W.; Gibala, R.

1999-07-01

301

Aging and memory effect in magnetoelectric gallium ferrite single crystals  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

302

Engineering domain configurations for enhanced piezoelectricity in barium titanate single crystals  

E-print Network

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

Li, Jiangyu

303

Ultrafast carrier dynamics in pentacene, functionalized pentacene, tetracene, and rubrene single crystals  

E-print Network

photoconduc- tivity in organic single crystals and polycrystalline thin films over picosecond time scales,7 the transient photoconductivity in pentacene, functionalized pentacene, tetracene, and rubrene single crystals charge photogeneration and a peak photoconductive response that increases as the temperature decreases

Ostroverkhova, Oksana

304

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

SciTech Connect

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

Sankari, R. Siva, E-mail: sivasankari.sh@act.edu.in [Department of Physics, Agni College of Technology, Thalambur, Chennai-603103 (India); Perumal, Rajesh Narayana [Department of Physics, SSN College of Engineering, Kalavakkam, Chennai-603110 (India)

2014-04-24

305

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

NASA Technical Reports Server (NTRS)

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

306

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

307

Properties of salt-grown uranium single crystals.  

SciTech Connect

Recently single crystals of {alpha}-uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than those in past work. The resistive signatures of the CDW transitions at 43, 37 and 22 K are obvious to the naked eye. The transition at 22 K exhibits temperature hysteresis that increases with magnetic field. In addition the superconducting transition temperature from resistivity is 820 mK and the critical field is 80 mT. Contrary to earlier work where the Debye temperature ranged from 186 to 218 K, the Debye temperature extracted from the heat capacity is 254 K in good agreement with the predicted value of 250 K. Magnetoresistance, Hall effect and magnetic susceptibility measurements are underway. In time, measurements made on these crystals may help us to understand the origin of superconductivity and its relation to the CDW transitions in pure uranium.

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

2001-01-01

308

Elastic and Piezoelectric Coefficients of Single-Crystal Barium Titanate  

Microsoft Academic Search

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

Don Berlincourt; Hans Jaffe

1958-01-01

309

Growth of Semiconductor Single Crystals from Vapor Phase  

NASA Astrophysics Data System (ADS)

Growth of single crystals from the vapor phase is considered to be an important method to obtain stoichiometric crystalline materials from inexpensive and readily available raw materials. Elements or compounds which are relatively volatile can be grown from vapor phase. Most II-VI, I-III-VI2, and III-N compounds are high-melting-point materials which may be grown as single crystals by careful use of vapor phase. The chemical vapor transport (CVT) method has been widely used as an advantageous method to grow single crystals of different compounds at temperatures lower than their melting points. This method is quite useful for the growth of II-VI and I-III-VI2 compounds, which generally have high melting point and large dissociation pressure at the melting point. In addition, they undergo solid-state phase transition during cooling or heating processes, which makes the growth of these compounds by some other methods, such as from the melt, difficult. In addition, the low growth temperature involved reduces defects produced by thermal strain, pollution from the crucible, and the cost of the growth equipment. II-VI compound semiconductors cover a very broad range of electronic and optical properties due to the large range of their energy gaps. These materials in the form of bulk single crystals or thin films are used in light emitters, detectors, linear and nonlinear optical devices, semiconductor electronics, and other devices. The development of growth technology for II-VI compound semiconductors from the vapor phase with the necessary theoretical background is important. I-III-VI2 chalcopyrite compounds are of technological interest since they show promise for application in areas of visible and infrared light-emitting diodes, infrared detectors, optical parametric oscillators, upconverters, far-infrared generation, and solar energy conversion.

Dhanasekaran, Ramasamy

310

Single crystal silicon as a low-temperature structural material  

NASA Astrophysics Data System (ADS)

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

Roach, P. R.

1984-07-01

311

Low temperature properties of calcia-stabilized zirconia single crystal  

Microsoft Academic Search

We investigated the internal friction, thermal conductivity and heat release for the single crystal of calciastabilized cubic\\u000a zirconia. From the experimental data we determined the values of distribution parameterSNOW coupling constant ? and the temperature\\u000a of the thermal activation of the tunneling systems and compared the results with the theory of the tunneling model and the\\u000a soft potential model. All

S. Abens; K. Topp; S. Sahling; R. O. Pohl

1996-01-01

312

Electrons trapped in single crystals of sucrose: Induced spin densities  

SciTech Connect

Electrons are trapped at intermolecular sites in single crystals of sucrose {ital X} irradiated at 4.2 K. The coupling tensors for the hyperfine couplings between the electron and surrounding protons have been deduced from electron-nuclear double resonance (ENDOR) data. Electron spin densities at nearby hydroxy protons are positive, whereas spin densities at the more remote protons of carbon-bound hydrogen atoms are negative. The origin of these negative spin densities is discussed.

Box, H.C.; Budzinski, E.E.; Freund, H.G. (Biophysics Department, Roswell Park Memorial Institute, Buffalo, New York 14263 (USA))

1990-07-01

313

Numerical aperture of single-mode photonic crystal fibers  

Microsoft Academic Search

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA=sin theta from the half-divergence angle theta ~ tan^{-1}(lambda\\/pi w) with pi w^2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. we find a numerical

N. A. Mortensen; J. R. Folken; P. M. W. Skovgaard; J. Broeng

2002-01-01

314

Occurrence and stability of trivalent zirconium in orthophosphate single crystals  

SciTech Connect

EPR spectroscopy has been used in investigations of the unusual 3+ valence state of zirconium. The EPR spectrum of Zr/sup 3 +/, which was initially observed as a parasitic signal in Fe-doped single crystals of ScPO/sub 4/, was definitively identified by preparing single crystals of ScPO/sub 4/ doped with isotopically enriched (94.6%)/sup 91/Zr. Single crystals of LuPO/sub 4/ and YPO/sub 4/ doped with both naturally abundant and isotopically enriched Zr were also grown and investigated. The EPR spectrum of Zr/sup 3 +/ could be observed at room temperature in the ''as-grown'' single crystals of both ScPO/sub 4/ and LuPO/sub 4/; and, accordingly, the 3+ state is stable at room temperature in these hosts. The spectrum of Zr/sup 3 +/ in the YPO/sub 4/ host could only be observed following a ..gamma.. irradiation at 77 K, and this spectrum decayed rapidly with increasing temperature. Axial spin-Hamiltonian parameters were determined for Zr/sup 3 +/ in all three hosts at a sample temperature of 77 K and at room temperature for the ScPO/sub 4/ and LuPO/sub 4/ hosts. In the case of the latter two hosts, the spin-Hamiltonian parameters were found to exhibit a small temperature dependence. The observed g values were not accounted for by previously published second-order expressions indicating that additional coupling mechanisms are operative.

Abraham, M.M.; Boatner, L.A.; Ramey, J.O.; Rappaz, M.

1984-12-15

315

Sapphire matrix composites reinforced with single crystal YAG phases  

Microsoft Academic Search

An investigation of fabrication technology on eutectic composites consisting of Al2O3 phases and YAG (Y3Al5O12) phases was carried out by applying the unidirectional solidification process. Unidirectionally solidified eutectic composites consisting of sapphire phases and single crystal YAG phases could be fabricated successfully by lowering a Mo crucible at a speed of 5 mm h-1 under a pressure of 10-5 mmHg

Y. Waku; H. Ohtsubo; N. Nakagawa; Y. Kohtoku

1996-01-01

316

Excitonic photoconductivity of 4BCMU polydiacetylene single crystals  

Microsoft Academic Search

Thermal annealing of 4BCMU single crystals increases the transition energy of excitons from 2.0 to 2.3eV and a similar increase is observed for the free carrier gap resolved by electroabsorption spectra. This modification leads to a significant change of the photocurrent threshold which after the transformation shifts to the excitonic absorption edge. Since the exciton binding energy of 0.5eV is

S Möller; G Weiser; C Lapersonne-Meyer

2001-01-01

317

Diamond turning of Si and Ge single crystals  

SciTech Connect

Single-point diamond turning studies have been completed on Si and Ge crystals. A new process model was developed for diamond turning which is based on a critical depth of cut for plastic flow-to-brittle fracture transitions. This concept, when combined with the actual machining geometry for single-point turning, predicts that {open_quotes}ductile{close_quotes} machining is a combined action of plasticity and fracture. Interrupted cutting experiments also provide a meant to directly measure the critical depth parameter for given machining conditions.

Blake, P.; Scattergood, R.O.

1988-12-01

318

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly. 12 figs.

Jantzen, C.M.

1995-05-09

319

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly.

Jantzen, Carol M. (Aiken, SC)

1995-01-01

320

Single particle detection in CMOS compatible photonic crystal nanobeam cavities.  

PubMed

We report the label-free detection of single particles using photonic crystal nanobeam cavities fabricated in silicon-on-insulator platform, and embedded inside microfluidic channels fabricated in poly-dimethylsiloxane (PDMS). Our system operates in the telecommunication wavelength band, thus leveraging the widely available, robust and tunable telecom laser sources. Using this approach, we demonstrated the detection of polystyrene nanoparticles with dimensions down to 12.5nm in radius. Furthermore, binding events of a single streptavidin molecule have been observed. PMID:24514817

Quan, Qimin; Floyd, Daniel L; Burgess, Ian B; Deotare, Parag B; Frank, Ian W; Tang, Sindy K Y; Ilic, Rob; Loncar, Marko

2013-12-30

321

ATMOSPHERIC EFFECTS ON THE PERFORMANCE OF CDZNTE SINGLE CRYSTAL DETECTORS  

SciTech Connect

The production of high-quality ternary single-crystal materials for radiation detectors has progressed over the past 15 years. One of the more common materials being studied is CdZnTe (CZT), which can be grown using several methods to produce detector-grade materials. The work presented herein examines the effects of environmental conditions including temperature and humidity on detector performance [full-width at half-maximum (FWHM)] using the single pixel with guard detector configuration. The effects of electrical probe placement, reproducibility, and aging are also presented.

Washington, A.; Duff, M.; Teague, L.

2010-05-12

322

SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION  

SciTech Connect

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

A. Wang; G. Pickrell; R. May

2002-09-10

323

Segregation effects in Fe microalloyed NiAl single crystals  

SciTech Connect

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

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

1995-10-15

324

Growth and characterization of pure and doped bis thiourea zinc acetate: Semiorganic nonlinear optical single crystals  

Microsoft Academic Search

Metal–organic coordination complex single crystals bis thiourea zinc acetate (BTZA) and Cd2+ doped BTZA have been synthesized and grown successfully by slow-cooling technique from their aqueous solutions. Single crystals of pure and Cd2+ doped BTZA with dimensions of 35×4×2mm3 and 10×5×6mm3, respectively were obtained with well defined morphology. The as grown single crystals are characterized by single crystal XRD studies

M. Lydia Caroline; S. Vasudevan

2009-01-01

325

Acquisition of Single Crystal Growth and Characterization Equipment  

SciTech Connect

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

Maple, M. Brian; Zocco, Diego A.

2008-12-09

326

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

SciTech Connect

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

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

2012-06-05

327

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

E-print Network

NUMERICAL SIMULATIONS OF CRACK TIP STRESS-STRAIN FIELDS IN SINGLE CRYSTAL NICKEL-BASE SUPERALLOYS, FRANCE ABSTRACT This work deals with the finite element analysis of cracks in single crystal Nickel crack in a CT specimen. After a presentation of these crack tip fields in single crystals (Rice [1

Paris-Sud XI, Université de

328

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles  

E-print Network

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles in solution. After template removal, well-defined, calcite single crystals exhibiting a rhombohedral morphology and uniform surface pores are obtained. The surface pore size of the calcite single crystals can

Qi, Limin

329

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky  

E-print Network

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky Department Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa

Volinsky, Alex A.

330

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

E-print Network

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

Volinsky, Alex A.

331

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

E-print Network

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

Martinis, John M.

332

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

PubMed Central

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

Yip, C M; Ward, M D

1996-01-01

333

Pyroelectric properties of phosphoric acid-doped TGS single crystals  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

334

Photorefractive properties of lithium niobate single crystals doped with copper  

NASA Astrophysics Data System (ADS)

Raman scattering with excitation in the ultraviolet, visible, and near infrared and electron paramagnetic resonance are used to study the photorefractive properties of nominally pure, stoichiometric (R = Li/Nb = 1) single crystals of lithium niobate grown from a melt with 58.6 mol% Li2O (LiNbO3stoich), nominally pure crystals with a congruent composition (LiNbO3congr, R = 0.946), and Cu-doped crystals with a congruent composition (LiNbO3:Cu, [Cu] = 0.015 mass%). Optical irradiation is found to cause charge exchange of copper cations, Ca2+ ? Cu, in the LiNbO3:Cu ([Cu] = 0.015 mass%) crystals. Thus, crystalline LiNbO3:Cu ([Cu] = 0.015 mass%) manifests photorefractive properties as a result of charge exchange of copper ions during laser irradiation, in addition to the contribution from intrinsic defects with localized electrons previously observed in LiNbO3stoich and LiNbO3congr.

Sidorov, N. V.; Yanichev, A. A.; Gabain, A. A.; Palatnikov, M. N.; Smirnov, A. N.

2013-05-01

335

Employing a cylindrical single crystal in gas-surface dynamics  

NASA Astrophysics Data System (ADS)

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.

Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W.; Juurlink, Ludo B. F.

2012-03-01

336

Employing a cylindrical single crystal in gas-surface dynamics.  

PubMed

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features. PMID:22443756

Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W; Juurlink, Ludo B F

2012-03-21

337

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

NASA Astrophysics Data System (ADS)

Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.

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

2005-02-01

338

Strain incompatibility and residual strains in ferroelectric single crystals  

PubMed Central

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

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

2012-01-01

339

Electronic properties of graphene-single crystal diamond heterostructures  

SciTech Connect

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

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

2013-08-07

340

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

NASA Astrophysics Data System (ADS)

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 obtain several stress components for evaluation of macro-cracking and crystal quality such as the maximum principal stress, the Mises equivalent stress and stress components acting on the cleavage plane. This analysis system is combined with a pre- and post-processor code MSC/PATRAN to prepare the input data and to visualize the results. As a numerical example obtained from the present system, the results of thermal stress analyses are shown for a lead molybdate (PMO; PbMoO 4) bulk single crystal that belongs to the tetragonal crystal lattice.

Miyazaki, N.

2002-03-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

342

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

NASA Astrophysics Data System (ADS)

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

Merlini, M.

2013-12-01

343

Electronic properties study of CePtIn single crystal  

NASA Astrophysics Data System (ADS)

Heavy fermion CePtIn and CePdIn, together with the isoelectronic valence fluctuator CeNiIn, crystallizing in a hexagonal ZrNiAl-type structure, have attracted the attention of researchers for many years. We present magnetization, specific heat and electrical resistivity data measured on a CePtIn single crystal. The measured data show certain anisotropy of electronic properties, which is discussed in terms of a competition of RKKY and Kondo interactions. No clear trace of magnetic phase transition is observed down to 0.4 K. The specific heat and electrical resistivity data indicate a non-Fermi liquid state at low temperatures, which is discussed with respect to the isostructural CeNi0.4Pd0.6In and CeNi0.6Pd0.4In compounds, showing very similar electronic properties and lattice parameters.

Klicpera, M.; Javorský, P.

2014-03-01

344

Phase transitions in potassium ammonium dihydrogen phosphate single crystals  

NASA Astrophysics Data System (ADS)

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 at room temperature. The details of the structure of the additional phase could not be determined. The dielectric constant epsilon of the mixed crystals as well as pure KH2PO4 (KDP) was measured along the polar axis in the temperature range from 20 K to 300 K. The frequency range of the applied electric field was from 100 Hz to 10 MHz. The data were analyzed by means of the standard Landau theory of phase transitions with coupling terms reflecting the interaction between the electric and elastic degrees of freedom. The temperature dependence of epsilon follows a typical Curie-Weiss behavior in the range of approximately 30 K aboveTc for all crystals studied. The value of the critical temperature decreases with increasing ammonium ion content in agreement with previously published results. The analysis of the frequency dependence of the dielectric susceptibility clearly indicates the existence of two dispersion processes: resonant and relaxational. The former is attributed to the piezoelectric activity of all the crystals studied. The latter is the result of the response of the permanent dipole moments present in ferroelectric crystals to the applied electric field. In the case of mixed crystals the relaxational dispersion is characterized by a distribution of relaxation times. Its mean relaxation time as well as its width increases with decreasing T. This is a typical behavior for mixed crystals for which the two end members of the solid solution in their pure form undergo ferroelectric and antiferroelectric phase transitions, respectively. This behavior is a result of competing long range interactions. New results for the temperature dependence of the CE66 and CE11 elastic constants of the crystals were obtained by means of the Brillouin spectroscopy. In addition to that the soft acoustic mode behaviour was also studied by means of the piezoelectric resonance method. Both of them gave qualitatively similar results which also correlate very well with the dielectric measurements. All major differences could be explained by assuming an inhomogeneous distribution of the ammonium ions in the KDP matrix. The Brillouin results were also analyzed by means of the Landau theory. It approximates very well the temperature dependence of the CE66 elastic constant in the paraelectric phase region for all crystals studied. The measured values of CE66 below Tc are in general lower than those predicted by the model. The greater the NH4 content the bigger the discrepancy. Moreover, the analysis of the temperature dependence of the CE66 elastic constant indicates the existence of a new phase in the mixed materials. Its stability region broadens with increasing NH4 concentration. For the crystal with the highest ammonium concentration studied it coincides with the dielectric plateau region between 70 K and 55 K. At temperatures below the plateau region the K0.88(NH4)0.12H 2PO4 sample scattered the laser light very strongly. This is most likely caused by defects and sample inhomogeneities but annealing the sample for two hours at 400 K does not result in any significant change.

Bromberek, Marek

345

Analysis of RHEED intensities during formations of the CaF 2\\/Si(111) and MgO\\/YSi 2? x \\/Si(100) interface  

Microsoft Academic Search

We have explored the epitaxial growth of two types of insulators on silicon substrate. CaF2 and MgO are able to block silicon diffusion to the growing surface forming stable interfaces type Si–Ca–F and MgO\\/YSi2?x in molecular beam epitaxy (MBE) deposition process. We are able to establish proper condition of epitaxy for this two insulators by controlling nucleation process during formation

Piotr Mazurek; Andrzej Daniluk; Krzysztof Paprocki

2000-01-01

346

Tribological behaviors of hot-pressed Al 2O 3\\/TiC ceramic composites with the additions of CaF 2 solid lubricants  

Microsoft Academic Search

Al2O3\\/TiC ceramic composites with the additions of CaF2 solid lubricants were produced by hot pressing. The effect of the solid lubricant on the microstructure and mechanical properties of the ceramic composite has been studied. The friction coefficient and wear rates were measured using the ring-block method, and the tribological behaviors were discussed in relation to its mechanical properties and microstructure.

Deng Jianxin; Cao Tongkun; Ding Zeliang; Liu Jianhua; Sun Junlong; Zhao Jinlong

2006-01-01

347

Crystal growth and defect crystal structure of CdF2 and nonstoichiometric phases Cd1 - x R x F2 + x ( R = rare earth element or in). 5. Crystal structure of as-grown Cd0.9R0.1F2.1 ( R = La-Nd) single crystals: Nanoclusters of structural defects  

NASA Astrophysics Data System (ADS)

As-grown Cd0.9 R 0.1F2.1 ( R = La-Nd) crystals were assigned to the CaF2 structure type and their structure was determined by X-ray diffraction. A new octacubic cluster of structural defects in Cd0.9 R 0.1F2.1 phases is proposed. The changes in the anionic motif of the Cd0.9 R 0.1F2.1 phase can be explained as a result of the formation of tetrahedral [Cd4 - n R n F26] and inverse octacubic [Cd14 - n R n F68] clusters with, respectively, tetrahedral and cuboctahedral anionic groups as cores. It is established that fluctuations of the La concentration in the cross section of a Cd0.9La0.1F2.1 crystal boule do not exceed 2.7%.

Sul'Yanova, E. A.; Molchanov, V. N.; Sobolev, B. P.

2008-07-01

348

Temperature and frequency dependent dielectric behavior of lead potassium niobate single crystal  

E-print Network

of the pyroelectric current The pyroelectric charge as a function of temperature in BaTiOs single crystal Temperature dependence of the pyroelectric current in Colemanite crystal Real permittivity vs temperature of PKN single crystal at 50Hz, 500Hz, 10KHz, 85KHz... for various potential applications, such as laser modulators, pyroelectric and infrared detectors, SAW device substrate material, optoelectronics device material, and other ferroelectric based devices. Single crystals having TB a The Journal of Applied...

Hossain, Akram

2012-06-07

349

Single crystal silicon capacitors with low microwave loss in the single photon regime  

E-print Network

We have fabricated superconducting microwave resonators in a lumped element geometry using single crystal silicon dielectric parallel plate capacitors with C >2 pF. Aluminum devices with resonant frequencies between 4.0 and 6.5 GHz exhibited an average internal quality factor Q_i of 2 x 10^5 in the single photon excitation regime at T = 20 mK. Attributing all the observed loss to the capacitive element, our measurements correspond to a loss tangent of intrinsic silicon of 5 x 10^-6. This level of loss is an order of magnitude lower than is currently observed in structures incorporating amorphous dielectric materials, thus making single crystal silicon capacitors an attractive, robust route for realizing long-lived quantum circuits.

S. Weber; K. W. Murch; D. H. Slichter; R. Vijay; I. Siddiqi

2011-02-14

350

Field emission properties of single crystal chromium disilicide nanowires  

NASA Astrophysics Data System (ADS)

The composition, crystal structure, and field emission properties of high-crystallinity chromium disilicide (CrSi2) nanowires synthesized by a vapor deposition method have been studied. High resolution transmission electron microscopy, energy dispersive spectroscopy, and selected area electron diffraction studies confirm the single-crystalline structure and composition of the CrSi2 nanowires. Field emission measurements show that an emission current density of 0.1 ?A/cm2 was obtained at a turn-on electric field intensity of 2.80 V/?m. The maximum emission current measured was 1.86 mA/cm2 at 3.6 V/?m. The relation between the emission current density and the electric field obtained follows the Fowler-Nordheim equation, with an enhancement coefficient of 1140. The electrical conductivity of single nanowires was measured by using four-point-probe specialized microdevices at different temperatures, and the calculated values are close to those reported in previous studies for highly conductive single crystal bulk CrSi2. The thermal tolerance of the nanowires was studied up to a temperature of 1100 °C. The stability of the field emission current, the I-E values, their thermal tolerance, and high electrical conductivity make CrSi2 nanowires a promising material for field emission applications.

Valentín, L. A.; Carpena-Nuñez, J.; Yang, D.; Fonseca, L. F.

2013-01-01

351

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

PubMed

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

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

2014-09-01

352

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

NASA Astrophysics Data System (ADS)

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

Prokhorov, I. A.; Ralchenko, V. G.; Bolshakov, A. P.; Polskiy, A. V.; Vlasov, A. V.; Subbotin, I. A.; Podurets, K. M.; Pashaev, E. M.; Sozontov, E. A.

2013-12-01

353

Shock response of He bubbles in single crystal Cu  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

354

Aspects of single crystal and thin film high field electroluminescence  

NASA Astrophysics Data System (ADS)

Electro-optical investigations of unimplanted and ion implanted ZnS and ZnSe direct current electroluminescent (DCEL) devices under reverse bias have enabled advances to be made in understanding some of the physical processes which govern the behavior of such devices. The three types of devices studied were ZnS thin films, ZnS single crystal diodes and ZnSe single crystal diodes. For reasons discussed in the text, greatest stability and uniformity in electroluminescence characteristics were achieved using ion implanted ZnSe single crystals and experiments were predominantly based on such devices. A complicated, but effective, fabrication procedure which involved a multilayer contact structure enabled stable current-voltage characteristics and uniform electroluminescence to be obtained from the ion implanted ZnSe diodes. From the current-voltage characteristics it is clear that the dominant mechanism responsible for the observed current in such devices is the tunnelling of electrons through the Schottky barrier. Analysis of the electroluminescence and cathodoluminescence of ZnSe and ZnS single crystal devices in which both manganese ions and erbium ions have been implanted in the same region and to the same concentration allowed relative cross-sections for impact excitation of the Mn(2+) ions and Er(3+) ions to be calculated. From these calculations it was concluded that the exchange scattering mechanism is responsible for the excitation of Mn(2+) ions. From the applied voltage dependence of the spectral emission intensities of Er(3+) ion transitions in an implanted ZnSe:Er device, the electron energy distribution was shown to be of the Druyvesteyn type. Under certain simplifying assumptions, such an energy distribution can be derived theoretically from the Boltzmann transport equation. Combining theory with experiment shows that the scattering centres which are responsible for the production of a Druyvesteyn distribution have very large impact cross-sections. It is thus concluded that complex molecules, probably involving Er(3+) ions and native lattice defects, are present in these devices.

Swift, Michael Joseph Robert

1989-12-01

355

Aspects of Single Crystal and Thin Film High Field Electroluminescence  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Electro-optical investigations of unimplanted and ion implanted ZnS and ZnSe direct current electroluminescent (DCEL) devices under reverse bias have enabled advances to be made in understanding some of the physical processes which govern the behaviour of such devices. The three types of devices studied were ZnS thin films, ZnS single crystal diodes and ZnSe single crystal diodes. For reasons discussed in the text, greatest stability and uniformity in electroluminescence characteristics were achieved using ion implanted ZnSe single crystals and experiments were predominantly based on such devices. A complicated, but effective, fabrication procedure which involved a multilayer contact structure enabled stable current-voltage characteristics and uniform electroluminescence to be obtained from the ion implanted ZnSe diodes. From the current-voltage characteristics it is clear that the dominant mechanism responsible for the observed current in such devices is the tunnelling of electrons through the Schottky barrier. Analysis of the electroluminescence and cathodoluminescence of ZnSe and ZnS single crystal devices in which both manganese ions and erbium ions have been implanted in the same region and to the same concentration allowed relative cross-sections for impact excitation of the Mn^{2+ } ions and Er^{3+} ions to be calculated. From these calculations it was concluded that the exchange scattering mechanism is responsible for the excitation of Mn^ {2+} ions. From the applied voltage dependence of the spectral emission intensities of Er^{3+} ion transitions in an implanted ZnSe:Er device, the electron energy distribution was shown to be of the Druyvesteyn type. Under certain simplifying assumptions, such an energy distribution can be derived theoretically from the Boltzmann transport equation. Combining theory with experiment shows that the scattering centres which are responsible for the production of a Druyvesteyn distribution have very large impact cross-sections (~ 10^{-12}-10 ^{-13} cm^2). It is thus concluded that complex molecules, probably involving Er^{3+} ions and native lattice defects, are present in these devices.

Swift, Michael Joseph Robert

356

Coherent Josephson phase qubit with a single crystal silicon capacitor  

E-print Network

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

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

2012-10-04

357

EPR studies of gamma-irradiated taurine single crystals  

NASA Astrophysics Data System (ADS)

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

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

2000-04-01

358

Single Molecule Studies on Dynamics in Liquid Crystals  

PubMed Central

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

Täuber, Daniela; von Borczyskowski, Christian

2013-01-01

359

Epitaxial Liftoff for Fully Single Crystal Ferroelectric Thin Films  

NASA Astrophysics Data System (ADS)

High-frequency signal transmission demands in RF and microwave systems, such as electronic phased-array radar and scanning antennas, call for innovative approaches in materials technology. Outstanding issues in such systems are the fabrication of low-loss, highly tunable capacitive elements made of thin-film ferroelecrics. This program used a new epitaxial liftoff technique developed at Columbia University to reduce high-quality, single-crystal films of ferroelectrics such as strontium titanate (ST), potassium tantalate, KTaO3 and potassium tantalate niobate (KTN) for use in microwave devices.

Osgood, Richard M., Jr.; Levy, Miguel; Bakhru, Hassaram; Cross, Eric

2002-08-01

360

Carrier doping and interlayer coupling in HTSC single crystals  

SciTech Connect

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

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

1994-09-01

361

Luminescence of lead thiogallate single crystals doped with cerium ions  

NASA Astrophysics Data System (ADS)

The luminescence of single crystals of lead thiogallate PbGa2S4: Ce3+ has been studied. The observed nonmonotonic temperature dependence of the integrated luminescence intensity of PbGa2S4: Ce3+ has been explained by the energy transfer from the electronic excitations of the matrix to impurity ions and by the temperature quenching of the Ce3+ ion luminescence. The observed structure of the 4 f 05 d 1-4 f 1 (2 F 7/2) band of the Ce3+ ion luminescence indicates the existence, at least, two types of Ce3+ ion centers in PbGa2S4.

Asatryan, G. R.; Badikov, V. V.; Kulinkin, A. B.; Feofilov, S. P.

2015-01-01

362

A macroscopic model for magnetic shape-memory single crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

363

Polarization-dependent exciton dynamics in tetracene single crystals.  

PubMed

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

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

2014-12-28

364

Relaxor-based ferroelectric single crystals for electromechanical actuators  

Microsoft Academic Search

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1\\/3Nb2\\/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1\\/3Nb2\\/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33's) > 2500 pC\\/N and subsequent strain levels up to > 0.6%

Seung Eek Park; Venkata Vedula; Ming Jen Pan; Wesley S. Hackenberger; Patrick Pertsch; Thomas R. Shrout

1998-01-01

365

Relaxor based ferroelectric single crystals for electro-mechanical actuators  

Microsoft Academic Search

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1\\/3Nb2\\/3)O3?PbTiO3 (PZN-PT) and Pb(Mg1\\/3Nb2\\/3)O3?PbTiO3 (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients\\u000a (d33’s ) >2200 pC\\/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed.

S.-E. Park; Thomas R. Shrout

1997-01-01

366

Polarization-dependent exciton dynamics in tetracene single crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

367

Nonlinear microwave switching response of BSCCO single crystals  

SciTech Connect

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

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

1996-06-01

368

Magnetic multi-domain resonance in single crystal ferrite platelets  

NASA Astrophysics Data System (ADS)

We have observed ferromagnetic resonance (FMR) on single crystal platelets of Zn and Co substituted M-type hexagonal ferrites. FMR was observed with both swept field and swept frequency measurements. The results were compared, and agreed well, with calculations of resonance frequencies based on periodic arrays of stripes and bubble domains. In addition to the resonance parameters necessary to describe the results in the magnetically saturated regime, our calculations take into account the wall energy, which results in a field dependence of the domain spacing, which in turn strongly affects the resonances near saturating fields.

Rachford, F. J.; Lubitz, P.; Vittoria, C.

1981-03-01

369

Physical properties of stoichiometric CeN single crystals  

NASA Astrophysics Data System (ADS)

The preparation and definition of stoichiometric large (3-5 mm edge length) single crystals of CeN are described. The band structure is discussed and compared with X-ray-photoemission-spectra (XPS), Bremsstrahlen-isochromat-spectroscopy (BIS) and optical reflectivity. CeN is intermediate valent with partially occupied and empty 4f states near EF. The specific heat is measured until 0.3 K and the ? term exhibits a sharp upturn toward the lowest temperatures. The Debye temperature is evaluated. The magnetic susceptibility is a large Pauli term pointing to a high density of states at EF as expected for a fractionally filled 4f1 state.

Wachter, P.; Zhigadlo, N. D.

370

Coherent Josephson phase qubit with a single crystal silicon capacitor  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

371

Experimental study of the irreversible magnetization in a ? single crystal  

NASA Astrophysics Data System (ADS)

Magnetization cycles and relaxation measurements as a function of temperature and field are reported for a very thin 0953-2048/10/4/004/img9 single crystal (thickness 0953-2048/10/4/004/img10). The fishtail effect was observed between 15 and 26 K at about 400 Oe, at which the relaxation rate was also found to increase rapidly. The observed behaviour is attributed to the field-induced two-dimensional to three-dimensional crossover in the vortex lattice in the presence of bulk pinning and surface barriers which dominate in different regions of the B - T phase diagram.

Fiorani, D.; Rybachuk, V. A.; Testa, A. M.; Kalinov, A. V.; Murashov, V. A.

1997-04-01

372

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

NASA Astrophysics Data System (ADS)

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

Blaha, Stephan; Katsura, Tomoo

2013-04-01

373

Structural, optical, mechanical and dielectric studies of pure and doped L-Prolinium Trichloroacetate single crystals  

NASA Astrophysics Data System (ADS)

In the present work, pure and metal substituted L-Prolinium trichloroacetate (LPTCA) single crystals were grown by slow evaporation method. The grown crystals were subjected to single crystal X-ray diffraction (XRD), powder X-ray diffraction, FTIR, UV-Visible-NIR, hardness, photoluminescence and dielectric studies. The dopant concentration in the crystals was measured by inductively coupled plasma (ICP) analysis. Single crystal X-ray diffraction studies of the pure and metal substituted LPTCA revealed that the grown crystals belong to the trigonal system. Ni2+ and Co2+ doping slightly altered the lattice parameters of LPTCA without affecting the basic structure of the crystal. FTIR spectral analysis confirms the presence of various functional groups in the grown crystals. The mechanical behavior of pure and doped crystals was analyzed by Vickers's microhardness test. The optical transmittance, dielectric and photoluminescence properties of the pure and doped crystals were analyzed.

Renuka, N.; Ramesh Babu, R.; Vijayan, N.; Vasanthakumar, Geetha; Krishna, Anuj; Ramamurthi, K.

2015-02-01

374

Crystal ion slicing of single crystal thin films for optical and electrical applications  

NASA Astrophysics Data System (ADS)

Thin film technologies are the most important element in modern integrated electrical and optical circuits development. Heterogeneous thin film structures make it possible to realize multi-functional highly integrated systems. Recently a new technology called Crystal Ion Slicing (CIS), utilizing ion implantation to slice thin films from single crystal substrates, has been developed at Columbia University. This technique allows the use of existing high quality single crystal wafers to form single-crystal thin films. Thus many materials, which are otherwise very difficult to obtain in thin film form, can now be obtained for thin film device integration. In the course of my thesis work, solutions to three issues of ion-slicing have been considered: applicability of ion-slicing to different materials, integration of sliced thin films, and device fabrication on the sliced thin films. To achieve specific functions, particular material properties are often required. Thus, many thin film technologies have been developed for different materials. In this work, CIS has been applied for wide range of materials such as LiNbO3, YIG, BaTiO3 (BTO), KTaO3 (KTO), and SrTiO3 (STO). CIS processing was adjusted for each material to slice high quality thin films faster. LiNbO3 slicing is well developed and large freestanding films, ˜15 x 15mm, are producible. YIG has been sliced by helium implantation and wet etching. BTO can be sliced by hydrogen implantation and heat treatment. KTO can be sliced by hydrogen implantation and wet etching. Single crystal BaTiO3 thin films have been fabricated for the first time through this work. The second issue considered is the size of ion-sliced films. To fabricate large thin films required for actual devices, a support wafer concept was introduced. Before slicing process, support wafers were bonded to implanted target materials to provide mechanical support for fragile films. The bonded implanted wafer was sliced into a large thin film without damage. This method solved the issue of handling a fragile freestanding thin films. More generally, wafer bonding is important for two applications: fabrication of large films and heterogeneous integration of thin films. Integration of magnetooptical devices on semiconductor platforms was demonstrated by bonding a garnet crystal on a semiconductor surface. Two bonding methods were demonstrated for these purposes; direct wafer bonding and anodic bonding. (Abstract shortened by UMI.)

Izuhara, Tomoyuki

375

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

PubMed Central

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

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

2013-01-01

376

Relaxor-based ferroelectric single crystals for electromechanical actuators  

NASA Astrophysics Data System (ADS)

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33's) > 2500 pC/N and subsequent strain levels up to > 0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, being related to an E-field induced phase transformation. Strain vs. E-field behavior under external stress was also much superior to that of conventional piezoelectric ceramics. High electromechanical coupling (k33) > 90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Park, Seung Eek E.; Vedula, Venkata; Pan, Ming-Jen; Hackenberger, Wesley S.; Pertsch, Patrick; Shrout, Thomas R.

1998-07-01

377

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals  

E-print Network

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals Jirí properties of twinned ferroelectric crystals with perovskite structure were analyzed. The twins or twinbands perovskite structure. When a single fer- roelectric crystal is poled along [001] of the cubic coor- dinates

Cao, Wenwu

378

Growth of single crystal PrFeAsO 1-y and its characterization  

NASA Astrophysics Data System (ADS)

We have successfully grown single crystals of oxygen deficient oxypnictide superconductor PrFeAsO 1-y using high pressure synthesis technique. Typical crystal size is about 600 × 800 × 30 ?m 3, with its T c = 44 K. Their resistivity measurements under magnetic field yield the anisotropic factor ? ? 5, consistent with previous results on smaller single crystals.

Ishikado, M.; Shamoto, S.; Kito, H.; Iyo, A.; Eisaki, H.; Ito, T.; Tomioka, Y.

2009-10-01

379

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

E-print Network

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

Ganguly, Jibamitra

380

Slip systems in NiAl single crystals at 300°K and 77°K  

Microsoft Academic Search

Single crystals of NiAl have been examined by transmission electron microscopy after plastic deformation at 300°K and 77°K. In agreement with earlier work, it is found that single crystals generally slip along ?100?. Further, it is shown that crystals oriented so that there is zero applied stress on the dislocations of b = ?100?, deform by the movement of dislocations

M. H. Loretto; R. J. Wasilewski

1971-01-01

381

Bithermal fatigue of a nickel-base superalloy single crystal  

NASA Technical Reports Server (NTRS)

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

Verrilli, Michael J.

1988-01-01

382

Joint Development of a Fourth Generation Single Crystal Superalloy  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

383

Tribological properties of sintered polycrystalline and single crystal silicon carbide  

NASA Technical Reports Server (NTRS)

Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

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

1982-01-01

384

Process for Making Single-Domain Magnetite Crystals  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

385

Growth and properties of Lithium Salicylate single crystals  

SciTech Connect

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

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

2009-02-13

386

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

387

Crystal growth and composition-property relationship of Ce3Pd20Si6 single crystals  

NASA Astrophysics Data System (ADS)

To elucidate the discrepancies in low-temperature data reported on the quantum critical heavy fermion compound Ce3Pd20Si6 and reveal the compound’s intrinsic properties, single crystals of varying stoichiometry were grown by various techniques—from the melt and from high-temperature solutions using fluxes of various compositions. The resulting stoichiometry of the crystals as well as their physical properties show sizable dependence on the different growth techniques. The Ce content ?Ce varies by more than 3at.% among all grown single crystals. We have revealed a systematic dependence of the residual resistance ratio, the lattice parameter, the (lower) phase-transition temperature TL , and the maximum in the temperature dependent electrical resistivity Tmax with ?Ce . This clarifies the sizable variation in the values of TL reported in the literature. We discuss the physical origin of the observed composition-property relationship in terms of a Kondo lattice picture. We predict that a modest pressure can suppress TL to zero and thus induce a quantum critical point.

Prokofiev, A.; Custers, J.; Kriegisch, M.; Laumann, S.; Müller, M.; Sassik, H.; Svagera, R.; Waas, M.; Neumaier, K.; Strydom, A. M.; Paschen, S.

2009-12-01

388

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

389

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

390

Secondary orientation effects in a single crystal superalloy under mechanical and thermal loads  

NASA Technical Reports Server (NTRS)

The nickel-base single crystal superalloy PWA 1480 is a candidate blading material for the advanced turbopump development program of the SSME. In order to improve thermal fatigue resistance of the turbine blades, the single crystal superalloy PWA 1480 is grown along the low modulus zone axes (001) crystal orientation by a directional solidification process. Since cubic single crystal materials such as PWA 1480 exhibit anisotropic elastic behavior, the stresses developed within the single crystal superalloy due to mechanical and thermal loads are likely to be affected by the exact orientation of the secondary crystallographic direction with respect to the geometry of the turbine blade. The effects of secondary crystal orientation on the elastic response of single crystal PWA 1480 superalloy were investigated.

Kalluri, Sreeramesh; Abdul-Aziz, Ali; Mcgaw, Michael A.

1991-01-01

391

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

SciTech Connect

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

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

2011-10-20

392

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

393

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

SciTech Connect

8-hydroxyquinolinium succinate (8HQSU), an organic material has been synthesized and single crystals were grown by employing the technique of slow evaporation. The structure of the grown crystal was elucidated by using single crystal X-ray diffraction analysis. 8HQSU crystal belongs to the monoclinic crystallographic system with non-centro symmetric space group of P2{sub 1}. FT-IR spectral investigation has been carried out to identify the various functional groups present in the grown crystal. UV–vis spectral studies reveal that 8HQSU crystals are transparent in the entire visible region and the cut-off wavelength has been found to be 220nm.

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

2014-04-24

394

Large molecular dynamics simulations of collision cascades in single-crystal, bi-crystal, and poly-crystal UO 2  

NASA Astrophysics Data System (ADS)

Classical molecular dynamics simulations have been carried out to study the primary damage due to ?-decay self-irradiations in single-, bi-, and poly-crystal UO 2 matrices. In all the cases no amorphization has been found, only the creation of few point defects is observed. However, in all grain boundary systems numerous point defects are created along the interfaces. Furthermore, cascade morphologies depend strongly on the grain boundary structure. For symmetrical tilt grain boundaries with small misorientation angles (lower than 20°) the structure at the grain boundaries is composed of edge dislocations, whereas for higher misorientation angles is formed by Schottky defects. The grain boundary structure in the poly-crystal is found to be highly disordered. For the last two systems, cascades seem stopped by the interfaces unlike those with edge dislocation grain boundaries. These types of interface act like sink which traps moving atoms.

Van Brutzel, L.; Vincent-Aublant, E.; Delaye, J.-M.

2009-09-01

395

Growth of zinc cadmium thiocyanate single crystal for laser diode frequency-doubling  

NASA Astrophysics Data System (ADS)

Zinc cadmium thiocyanate (ZnCd(SCN) 4, ZCTC) crystal is a promising nonlinear optical material as the source of blue-violet light by laser diode frequency-doubling. A series of experiments on the growth of ZCTC crystal are reported in this paper. A larger single crystal, with size 7×7×13 mm 3, was successfully obtained from the NH 4Cl-NH 4SCN-H 2O mixed solvent by using the solvent-evaporation method. The problems in the growth of ZCTC single crystal are discussed and the key to growing large and transparent single ZCTC crystals is proposed.

Jiang, Xue-Ning; Xu, Dong; Yuan, Duorong; Lu, Mengkai; Guo, Shiyi; Zhang, Guanghui; Wang, Xinqiang; Fang, Qi

2001-02-01

396

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

397

Twin nucleation and migration in FeCr single crystals  

SciTech Connect

Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88 MPa, while twinning nucleates at a CRSS of about 191 MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress ( Almost-Equal-To 114-153 MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. - Highlights: Black-Right-Pointing-Pointer Digital image correlation allows to capture slip/twin initiation for bcc FeCr. Black-Right-Pointing-Pointer Crystal orientations from EBSD allow slip/twin system indexing. Black-Right-Pointing-Pointer Nucleation of slip always precedes twinning. Black-Right-Pointing-Pointer Twin growth is sustained with a lower stress than required for nucleation. Black-Right-Pointing-Pointer Twin-slip interactions provide high hardening at the onset of plasticity.

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

2013-01-15

398

High-Temperature Thermoelectric Properties of NaxCoO2-delta Single Crystals  

Microsoft Academic Search

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

Kenjiro Fujita; Tadashi Mochida; Kazuo Nakamura

2001-01-01

399

Surface and bulk diffusion of HDO on ultrathin single-crystal ice multilayers on Ru(001)  

Microsoft Academic Search

The kinetics of HDO surface and bulk diffusion on ultrathin (25-192 BL; 90-700 Å) single-crystal H216O ice multilayers were studied using a combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a single-crystal Ru(001) metal substrate with the basal (001) facet of ice parallel to the Ru(001) surface. HDO

Frank E. Livingston; Galen C. Whipple; Steven M. George

1998-01-01

400

Surface and bulk diffusion of HDO on ultrathin single-crystal ice multilayers on Ru(001)  

Microsoft Academic Search

The kinetics of HDO surface and bulk diffusion on ultrathin (25–192 BL; 90–700 Å) single-crystal H216O ice multilayers were studied using a combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a single-crystal Ru(001) metal substrate with the basal (001) facet of ice parallel to the Ru(001) surface. HDO

Frank E. Livingston; Galen C. Whipple; Steven M. George

1998-01-01

401

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

Microsoft Academic Search

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

Amir Yeganeh-Haeri

1994-01-01

402

Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite  

NASA Technical Reports Server (NTRS)

Ilmenite (FeTiOs) is a wide bandgap semiconductor with an energy gap of 2.58 eV. Ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Single crystal ilmenite has been grown from the melt using the Czochralski method. Growth conditions have a profound effect on the microstructure of the samples. Here we present data from a variety of analytical techniques which indicate that some grown crystals exhibit distinct phase separation during growth. This phase separation is apparent for both post-growth annealed and unannealed samples. Under optical microscopy, there appear two distinct areas forming a matrix with an array of dots on order of 5 pm diameter. While appearing bright in the optical micrograph, atomic force microscope (AFM) shows the dots to be shallow pits on the surface. Magnetic force microscope (MFM) shows the dots to be magnetic. Phase identification via electron microprobe analysis (EMPA) indicates two major phases in the unannealed samples and four in the annealed samples, where the dots appear to be almost pure iron. This is consistent with micrographs taken with a scanning probe microscope used in the magnetic force mode. Samples that do not exhibit the phase separation have little or no discernible magnetic structure detectable by the MFM.

Wilkins, R.; Powell, Kirk St. A.; Loregnard, Kieron R.; Lin, Sy-Chyi; Muthusami, Jayakumar; Zhou, Feng; Pandey, R. K.; Brown, Geoff; Hawley, M. E.

1998-01-01

403

Thermal conductivity of 4H-SiC single crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

404

Redetermination of olivenite from an untwinned single-crystal  

PubMed Central

The crystal structure of olivenite, ideally Cu2(AsO4)(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu2(As0.92P0.08O4), from Majuba Hill (Nevada, USA). Olivenite is structurally analogous with the important rock-forming mineral andalusite, Al2OSiO4. Its structure consists of chains of edge-sharing, distorted [CuO4(OH)2] octa­hedra extending parallel to [001]. These chains are cross-linked by isolated AsO4 tetra­hedra through corner-sharing, forming channels in which dimers of edge-sharing [CuO4(OH)] trigonal bipyramids are located. The structure is stabilized by medium to weak O—H?O hydrogen bonds. In contrast to the previous refinements from powder and single crystal X-ray data, all non-H atoms were refined with anisotropic displacement parameters and the H atom was located. PMID:21201567

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

2008-01-01

405

Scintillation properties of CsI:In single crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

406

Laser Raman study of single crystals of deuterated cadmium fluorosilicate  

NASA Astrophysics Data System (ADS)

A laser Raman study of oriented single crystals of CdSiF 6:6D 2O at room temperature as well as at 10 K in all the six polarization geometries has been made. Also a detailed temperature dependent Raman study from room temperature to 10 K in ( yy) polarization in the region of internal vibrations and lattice modes has been made. Abrupt changes have been observed in frequency shift, line-width and intensity of some of the bands at about 235 K. Some doubly degenerate modes show splitting at the same temperature. From these observations a phase change at about 235 K is inferred for this salt. It has been suggested that when the system is cooled, the lattice contracts and the water molecules lose their reorientational freedom to some extent which might result in the distortion of the [Cd(OD 2) 6] 2+ octahedra triggering a phase transition.

Thakur, Ganesh; Verma, A. L.

1989-01-01

407

Growth and characterization of single crystal refractory oxide fibers  

NASA Astrophysics Data System (ADS)

Single-crystal Nd:YAG, sapphire, and LiNbO3 fibers 30-500 microns in diameter have been produced using the pedestal growth method. It is shown that stable growth is possible with typical diameter reduction ratios of 2-4:1; the laser power necessary to produce a stable melt zone varies from over 20 watts for a 1-mm rod of sapphire to several hundred milliwatts for 100-micron fibers of LiNbO3. The major problem with the current growth system is insufficient control over fiber diameter fluctuations. Fibers produced to date have diameters varying by up to 5 percent. A second-generation growth system is described which is expected to produce fibers with precisely controlled diameters.

Fejer, M.; Byer, R. L.; Feigelson, R.; Kway, W.

1982-12-01

408

Bulk diffusion of niobium in single-crystal titanium dioxide.  

PubMed

The present work reports the tracer diffusion coefficient for (93)Nb in rutile TiO(2) single crystals using secondary ion mass spectrometry (SIMS). The determined tracer diffusion coefficient exhibited the following temperature dependence in air ( p(O2) = 21 kPa) over the range 1073-1573 K: D93(Nb) = (4.7 m2 s(-1))x10(-7+/-0.4) exp ((-244 +/- 9 kJ mol-1)/RT) Through comparison to the self-diffusion of (44)Ti in rutile TiO(2), (93)Nb is interpreted to diffuse via the interstitialcy mechanism. The obtained tracer diffusion data are useful for ensuring compositional control during the processing of Nb-doped TiO(2)-based semiconductors using solid-state reactions between Nb(2)O(5) and TiO(2). PMID:17590035

Sheppard, Leigh R; Atanacio, Armand J; Bak, Tadeusz; Nowotny, Janusz; Prince, Kathryn E

2007-07-19

409

Friction and deformation behavior of single-crystal silicon carbide  

NASA Technical Reports Server (NTRS)

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

Miyoshi, K.; Buckley, D. H.

1977-01-01

410

Thermal conductivity of single crystal and ceramic AlN  

NASA Astrophysics Data System (ADS)

We have applied the Callaway theory and used a detailed account of three-phonon scattering processes to calculate the thermal conductivity of three AlN single crystal samples containing different amounts of oxygen and two AlN ceramic samples with different grain sizes and oxygen contamination levels. The N-drift contribution to the total conductivity has been quantified. The influence on the thermal conductivity of oxygen-related defects, and grain boundaries in ceramic samples, has been investigated. The theoretical results obtained from this work are in good agreement with available experimental data. Our calculations suggest that the "effective" boundary length is greater than the reported grain size for each of the two ceramic samples studied by Watari et al. [J. Mater. Res. 17, 2940 (2002)].

AlShaikhi, A.; Srivastava, G. P.

2008-04-01

411

Analysis of ripple formation in single crystal spot welds  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

412

Ambient Compression-Compression Fatigue Behavior of Magnesium Single Crystal  

NASA Astrophysics Data System (ADS)

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

Li, Qizhen

2014-01-01

413

Single crystal metal wedges for surface acoustic wave propagation  

DOEpatents

An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

Fisher, Edward S. (Wheaton, IL)

1982-01-01

414

Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys  

NASA Technical Reports Server (NTRS)

Single crystal superalloys exhibit excellent cyclic oxidation resistance if their sulfur content is reduced from typical impurity levels of approximately 5 ppmw to below 0.5 ppmw. Excellent alumina scale adhesion was documented for PWA 1480 and PWA 1484 without yttrium additions. Hydrogen annealing produced effective desulfurization of PWA 1480 to less than 0.2 ppmw and was also used to achieve controlled intermediate levels. The direct relationship between cyclic oxidation behavior and sulfur content was shown. An adhesion criterion was proposed based on the total amount of sulfur available for interfacial segregation, e.g., less than or equal to 0.2 ppmw S will maximize adhesion for a 1 mm thick sample. PWA 1484, melt desulfurized to 0.3 ppmw S, also exhibited excellent cyclic oxidation resistance and encouraging TBC lives (10 mils of 8YSZ, plasma sprayed without a bond coat) in 1100 C cyclic oxidation tests.

Smialek, James L.

1998-01-01

415

InPBi Single Crystals Grown by Molecular Beam Epitaxy  

PubMed Central

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

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

2014-01-01

416

A neutron sensor based on synthetic single crystal diamond  

SciTech Connect

We report the first neutron data for a single crystal Chemical Vapor Deposition (CVD) diamond sensor. Results are presented for 2.5, 14.1, and 14.9 MeV incident neutrons. We show that the energy resolution for 14.1 MeV neutrons is at least 2.9% (as limited by the energy spread of the incident neutrons), and perhaps as good as 0.4% (as extrapolated from high resolution {alpha} particle data). This result could be relevant to fusion neutron spectroscopy at machines like the International Thermonuclear Experimental Reactor (ITER). We also show that our sensor has a high neutron linear attenuation coefficient, due to the high atomic density of diamond, and this could lead to applications in fission neutron detection.

Schmid, G J; Koch, J A; Lerche, R A; Moran, M J

2003-10-17

417

Interaction between dislocation and divalent impurity in KBr single crystals  

NASA Astrophysics Data System (ADS)

Interaction between dislocation and divalent impurity has been investigated in KBr single crystals doped with various impurities by strain rate cycling tests under ultrasonic oscillation. The interaction energy between dislocation and impurity-vacancy dipole (I-V dipole) has been obtained by fitting Barnett model to experimental results. The interaction energies between dislocation and I-V dipole were determined to be 0.51, 0.30, 0.23 and 0.36eV for Ba2+, Sr2+, Ca2+ and Mg2+, respectively. The energy increases with increasing ionic radius of divalent impurity except Mg2+. This may be because the I-V dipole is made of a divalent impurity and a nearest vacancy for Ba2+, Sr2+ and Ca2+ but of a divalent one and a next nearest vacancy for Mg2+.

Ohgaku, T.; Matsunaga, T.

2009-07-01

418

Electrical conduction in nanodomains in congruent lithium tantalate single crystal  

SciTech Connect

The electrical current flow behavior was investigated for nanodomains formed in a thin congruent lithium tantalate (LiTaO{sub 3}) single-crystal plate. When the nanodomains were relatively large, with diameters of about 100?nm, current flow was detected along the domain wall. However, when they were about 40?nm or smaller, the current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. Unlike the case of LiNbO{sub 3}, optical illumination was not required for current conduction in LiTaO{sub 3}. A clear temperature dependence of the current was found indicating that the conduction mechanism for nanodomains in LiTaO{sub 3} may involve thermally activated carrier hopping.

Cho, Yasuo [Research Institute of Electrical Communication, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577 (Japan)

2014-01-27

419

Single crystal metal wedges for surface acoustic wave propagation  

DOEpatents

An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

Fisher, E.S.

1980-05-09

420

Shock compression experiments on Lithium Deuteride single crystals.  

SciTech Connect

S hock compression exper iments in the few hundred GPa (multi - Mabr) regime were performed on Lithium Deuteride (LiD) single crystals . This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17 - 32 km/s. Measurements included pressure, density, and temperature between ~200 - 600 GPa along the Principal Hugoniot - the locus of end states achievable through compression by large amplitude shock waves - as well as pressure and density of re - shock states up to ~900 GPa . The experimental measurements are compared with recent density functional theory calculations as well as a new tabular equation of state developed at Los Alamos National Labs.

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

2014-10-01

421

Epitaxial few-layer graphene: towards single crystal growth  

NASA Astrophysics Data System (ADS)

We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

Hibino, H.; Kageshima, H.; Nagase, M.

2010-09-01

422

Ultrathin aluminum sample cans for single crystal inelastic neutron scattering  

NASA Astrophysics Data System (ADS)

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

Stone, M. B.; Loguillo, M. J.; Abernathy, D. L.

2011-05-01

423

Process development for single-crystal silicon solar cells  

NASA Astrophysics Data System (ADS)

Solar energy is a viable, rapidly growing and an important renewable alternative to other sources of energy generation because of its abundant supply and low manufacturing cost. Silicon still remains the major contributor for manufacturing solar cells accounting for 80% of the market share. Of this, single-crystal solar cells account for half of the share. Laboratory cells have demonstrated 25% efficiency; however, commercial cells have efficiencies of 16% - 20% resulting from a focus on implementation processes geared to rapid throughput and low cost, thereby reducing the energy pay-back time. An example would be the use of metal pastes which dissolve the dielectric during the firing process as opposed to lithographically defined contacts. With current trends of single-crystal silicon photovoltaic (PV) module prices down to 0.60/W, almost all other PV technologies are challenged to remain cost competitive. This presents a unique opportunity in revisiting the PV cell fabrication process and incorporating moderately more expensive IC process practices into PV manufacturing. While they may drive the cost toward a 1/W benchmark, there is substantial room to "experiment", leading to higher efficiencies which will help maintain the overall system cost. This work entails a turn-key process designed to provide a platform for rapid evaluation of novel materials and processes. A two-step lithographic process yielding a baseline 11% - 13% efficient cell is described. Results of three studies have shown improvements in solar cell output parameters due to the inclusion of a back-surface field implant, a higher emitter doping and also an additional RCA Clean.

Bohra, Mihir H.

424

Homoepitaxial deposition of boron-doped single crystal diamond  

NASA Astrophysics Data System (ADS)

The boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using a microwave plasma assisted chemical vapor deposition. The optical transmittance of the films was observed to change with the increasing boron content in the film. The effect of boron and nitrogen on the surface morphology of the film has been studied using atomic force microscopy. Use of nitrogen in process gas during boron doping improves the surface topography as well as gives rise to an increase in growth rate of diamond film. However, presence of nitrogen in the process gas significantly lowers the electrical conductivity of the film. Raman spectra showed a few additional bands at the lower wavenumber regions along with the zone center optical phonon mode for doped diamond. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. The sharpening and increase in intensity of the Raman line has been also observed in boron doped diamond film when grown in the presence of nitrogen. Temperature dependent electrical measurement between 90 to 680 K indicates two different conduction mechanisms were responsible for the semiconducting behavior of the film. The observed growth rate for homoepitaxial boron-doped diamond films were in the range of 5-16 microm / hour. Various level of boron doping (1018 to 1020 cm-3) was achieved during this study. The lowest resistivity of one of the boron doped samples at room temperature was calculated to be 0.12 ?cm. The potential of boron-doped single crystal diamond in electronic devices is discussed.

Karna, Sunil Kumar Lal

425

Ablation of ionic crystals induced by capillary-discharge XUV laser  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

426

1ps passively mode-locked laser operation of Na,Yb:CaF2 crystal.  

PubMed

Diode-pumped passively mode-locked laser operation of Yb3+,Na+:CaF2 single crystal has been demonstrated for the first time. By using a SESAM (semiconductor saturable mirror), simultaneous transform-limited 1-ps passively mode-locked pulses, with the repetition rate of 183MHz, were obtained under the self-Q-switched envelope induced by the laser medium. The average output power of 360mW was attained at 1047nm for 3.34W of absorbed power at 976nm, and the corresponding pulse peak power arrived at 27kW, indicating the promising application of Yb3+,Na+ - codoped CaF2 crystals in achieving ultra-short pulses and high pulse peak power. PMID:19498826

Du, Juan; Liang, Xiaoyan; Wang, Yonggang; Su, Liangbi; Feng, Weiwei; Dai, Enwen; Xu, Zhizhan; Xu, Jun

2005-10-01

427

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

SciTech Connect

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

Itoh, K.

1992-10-01

428

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

SciTech Connect

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

Itoh, K.

1992-10-01

429

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

NASA Astrophysics Data System (ADS)

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

Caliskan, Betul; Caliskan, Ali Cengiz; Yerli, Rabia

2014-10-01

430

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

SciTech Connect

Polar organic nonlinear optical material, L-tartaric acid single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallized in monoclinic system with space group P2{sub 1}. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal quality is good and free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. Piezoelectric d{sub 33} co-efficient for the crystal has been examined and its value is 47 pC/N. The ferroelectric behaviour of the crystal was analyzed by polarization-electric field hysteresis loop measurement.

Murugan, G. Senthil, E-mail: nanosen@gmail.com; Ramasamy, P., E-mail: nanosen@gmail.com [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam, Tamilnadu - 603110 (India)

2014-04-24

431

Studies on the Growth, Spectral, Optical and Thermal Properties of 4-NITROANILINE Picrate Single Crystals  

NASA Astrophysics Data System (ADS)

In this paper, an organic 4-nitroaniline picrate (4NP) single crystal was grown by solution growth method. Single crystal X-ray diffraction study revealed that grown crystal belongs to orthorhombic system with Pbcn space group. The solid state constants such as plasma energy, Penn gap, Fermi energy and polarizability of 4NP crystal were determined theoretically. The functional groups of the grown crystals were confirmed qualitatively from FTIR spectral analysis. The thermal decomposition and melting point of the crystal were determined from thermogravimetric analysis. The optical absorption and cut-off wavelength of the crystal were determined from UV-visible study. The second harmonic generation (SHG) efficiency of the grown crystal was measured by Kurtz-Perry SHG test using Nd:YAG laser. The laser damage threshold value of the grown crystal was estimated by multi-shot method using 1064 nm laser.

Sivakumar, P. K.; Kumar, M. Krishna; Kumar, R. Mohan; Kanagadurai, R.

2013-12-01

432

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

NASA Astrophysics Data System (ADS)

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

Murugan, G. Senthil; Ramasamy, P.

2014-04-01

433

Mixed-Ligand MetalOrganic Frameworks with Large Pores: Gas Sorption Properties and Single-Crystal-to-Single-Crystal Transformation on Guest  

E-print Network

-crystal-to-single-crystal transformation on exchange of the DMF guest molecules with hexane to form {[Zn2ACHTUNGTRENNUNG(BPnDC)2ACHTUNGTRENNUNG(dabco)]·6ACHTUNGTRENNUNG(n-hexane)·3H2O}n (2hexane). The X-ray structure of 2hexane reveals

Paik Suh, Myunghyun

434

Single crystal nuclear magnetic resonance in spinning powders  

NASA Astrophysics Data System (ADS)

We present a method for selectively exciting nuclear magnetic resonances (NMRs) from well-defined subsets of crystallites from a powdered sample under magic angle spinning. Magic angle spinning induces a time dependence in the anisotropic interactions, which results in a time variation of the resonance frequencies which is different for different crystallite orientations. The proposed method exploits this by applying selective pulses, which we refer to as XS (for crystallite-selective) pulses, that follow the resonance frequencies of nuclear species within particular crystallites, resulting in the induced flip angle being orientation dependent. By selecting the radiofrequency field to deliver a 180 ? pulse for the target orientation and employing a train of such pulses combined with cogwheel phase cycling, we obtain a high degree of orientational selectivity with the resulting spectrum containing only contributions from orientations close to the target. Typically, this leads to the selection of between 0.1% and 10% of the crystallites, and in extreme cases to the excitation of a single orientation resulting in single crystal spectra of spinning powders. Two formulations of this method are described and demonstrated with experimental examples on [1 - 13C]-alanine and the paramagnetic compound Sm2Sn2O7.

Pell, Andrew J.; Pintacuda, Guido; Emsley, Lyndon

2011-10-01

435

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

436

Theoretical nonlinear response of complex single crystal under multi-axial tensile loading  

E-print Network

The mechanical properties of single crystals are of interest as they represent the behavior of the basic building blocks. Using the density functional theory based ab initio technique we have devised an approach to analyze the behavior of single...

Misra, Anil; Ching, W. Y.

2013-03-19

437

Deterministically Polarized Fluorescence from Single Dye Molecules Aligned in Liquid Crystal Host  

SciTech Connect

We demonstrated for the first time to our konwledge deterministically polarized fluorescence from single dye molecules. Planar aligned nematic liquid crystal hosts provide deterministic alignment of single dye molecules in a preferred direction.

Lukishova, S.G.; Schmid, A.W.; Knox, R.; Freivald, P.; Boyd, R. W.; Stroud, Jr., C. R.; Marshall, K.L.

2005-09-30

438

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

Microsoft Academic Search

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

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

2009-01-01

439

Dielectric and ferroelectric properties of phosphoric acid doped triglycine sulfate single crystals  

Microsoft Academic Search

Single crystals of triglycine sulfate (TGS) grown with 25–50 mol% phosphoric acid dopant in solution were investigated for their dielectric, ferroelectric and mechanical hardness properties. A 25 mol% of H3PO4 in solution yielded crystals with a large area in the ac plane without any seed crystal. The room temperature (300 K) dielectric constant (??) and tan? in the frequency range

Aparna Saxena; Vinay Gupta; K. Sreenivas

2001-01-01

440

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

SciTech Connect

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

Teague, L.

2010-06-11

441

Measurement of optical nonlinear susceptibility of CdS single crystal using a single beam  

NASA Astrophysics Data System (ADS)

We report a measurement of optical nonlinear susceptibility of CdS using Z-scan method. The input laser light irradiating on the CdS single crystal had a wavelength of 514.5 nm and a flux density of 16 kW/cm(sup 2). We estimate a nonlinear susceptibility of chi(sup (3)) = 3.5 x 10(sup - 9) (esu) being in agreement with an anharmonic oscillator model based on excitons. We also found that when a DC electric field was added on the sample of CdS, the nonlinear absorption increased as the applied DC electric field was increased.

Li, Zhengang; Xiong, Guangnan; Zhao, Zhihong; Fan, Xiwu

1994-04-01

442

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

NASA Astrophysics Data System (ADS)

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

Moovendaran, K.; Natarajan, S.

2015-01-01

443

Intrinsic electron and hole defects in stabilized zirconia single crystals  

SciTech Connect

Intrinsic defects have been produced in yttria- and calcia-stabilized zirconia (YSZ or CaSZ) single crystals either by x irradiation at 300 and 77 K or by thermochemical reduction at 1370, 1670, and 1870 K. The spectroscopic properties of the defects have been studied by electron paramagnetic resonance (EPR), optical absorption, and photoemission techniques. Their thermal stability and bleaching characteristics have also been obtained. In the crystals irradiated at 77 K, an orthorhombic EPR signal with {ital g}{sub {ital x}}=2.019{plus minus}0.003, {ital g}{sub {ital y}}=2.012{plus minus}0.003, and {ital g}{sub {ital z}}=2.004{plus minus}0.002 and axes {bold x}{parallel}(110), {bold y}{parallel}({bar 1}12), {bold z}{parallel}(1{bar 1}1), and an absorption band at {lambda}=465 nm have been assigned to a hole trapped at an oxygen adjacent to a Y{sup 3+} or Ca{sup 2+} ion. The trigonal EPR signal with {ital g}{sub {parallel}}=1.989 and {ital g}{sub {perpendicular}}=1.852 and a band at {lambda}=375 nm, which are produced by irradiation and reduction, are associated with electrons trapped at hexacoordinated Zr{sup 3+} ions, whereas the absorption band at about 480 nm appearing in the heavily reduced samples is tentatively assigned to electrons trapped at heptacoordinated Zr{sup 3+} ions. We propose an energy-level diagram for stabilized zirconia that explains the shift of the optical absorption edge, the intrinsic emission, and the bleaching characteristics of the defects.

Orera, V.M.; Merino, R.I. (Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza, Consejo Superior de Investigaciones Cientificas, Facultad de Ciencias, 50009 Zaragoza (Spain)); Chen, Y. (Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN (USA)); Cases, R.; Alonso, P.J. (Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza, Consejo Superior de Investigaciones Cientificas, Facultad de Ciencias, 50009 Zaragoza (Spain))

1990-12-01

444

Growth and characterization of a new organic single crystal: 1-(4-Nitrophenyl) pyrrolidine (4NPY).  

PubMed

A new 1-(4-Nitrophenyl) pyrrolidine single crystal has grown by slow evaporation solution growth technique. The grown crystal have characterized by single crystal X-ray analysis, and it shows that 1-(4-Nitrophenyl) pyrrolidine crystallizes in the orthorhombic space group Pbca, with cell parameters a=10.3270 (5)Å, b=9.9458 (6)Å, c=18.6934 (12)Å, and Z=8. Powder XRD pattern confirmed that grown crystal posses highly crystalline nature. The functional groups have identified by using FTIR spectral analysis. The absorbance and the luminescence spectra of the title compound have analyzed using UV-Visible and PL spectra. The thermo analytical properties of the crystal have studied using TG/DTA spectrum. The mechanical property of the grown crystal has determined using Vickers micro hardness measurement. The grown features of the crystal have analyzed using etching technique. PMID:25523042

Nirosha, M; Kalainathan, S; Aravindan, P G

2015-03-01

445

Fabrication of one-dimensional grating structure on organic single-crystal surface  

NASA Astrophysics Data System (ADS)

Organic single crystals have excellent transport and unique optical properties, which are very advantageous to light-emitting devices. However, it is still difficult to control the emitting color of these devices and we need to establish a novel method to introduce a color-control system into organic single crystals. In this paper, we present an effective approach for the fabrication of submicrometer-scale grating structures on an organic single-crystal surface. Using the UV-nanoimprint lithography and dry-etching methods, one-dimensional grating structures are fabricated on crystal surfaces and, from photoluminescence spectra, we confirmed the color tunability of this novel method.

Maruyama, Kenichi; Li, Jinpeng; Takahashi, Wataru; Hotta, Shu; Takaishi, Shinya; Yamashita, Masahiro; Takenobu, Taishi

2014-02-01

446

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

NASA Astrophysics Data System (ADS)

Cu 2+ and glycine doped L-arginine monohydrochloride monohydrate (LAHCl) single crystals were grown by slow solvent evaporation technique. The grown single crystals were confirmed by X-ray diffraction study and the interaction of dopants with LAHCl molecule was identified in Fourier transform infrared spectra. The crystalline perfection of pure and doped crystals was analyzed by high resolution X-ray diffraction studies. Vickers microhardness and UV-visible spectroscopy were carried out respectively to study the mechanical stability and optical transmittance of pure and doped LAHCl single crystals. He-Ne laser of wavelength 632.8 nm was used to measure refractive index and birefringence of grown crystals. The second harmonic generation efficiency was also measured for pure and doped LAHCl single crystals using Nd:YAG laser.

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

2011-09-01

447

SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION  

SciTech Connect

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

A. Wang; G. Pickrell; R. May

2002-09-10

448

MULTIAXIAL LIFETIME PREDICTIONS OF SINGLE-CRYSTAL SUPERALLOYS: USE OF REFERENCE STRESSES  

Microsoft Academic Search

The high temperature microstructural stability and good thermal-mechanical properties of single crystal superalloys has played a crucial role in the development of these materials for gas turbine blade application. A form of Continuum Damage Mechanics has been successfully developed over a decade or so, to model the anisotropic creep deformation of single crystal superalloys, where in a general formulation the

H. C. Basoalto; M. Ardakani; R. N. Ghosh; M. McLean

2002-01-01

449

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

E-print Network

Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals X June 2006 Editor: P. Deines Abstract Oxygen diffusion in natural and synthetic single-crystal titanite be recognized as responsible for oxygen diffusion. The diffusion profiles showed two segments: a steep one close

Watson, E. Bruce

450

Microhardness of Czochralski-grown single crystals of VB{sub 2}  

SciTech Connect

Single crystals of congruent melting hexagonal VB{sub 2} were grown used a triarc furnace applying the Czochralski technique. Orientation dependent microhardness measurements on a single crystal reveal quasi similar hardness in the crystallographic directions <00.1> and <10.0>, whereas the <10.1> shows slightly lower values.

Bulfon, C.; Sassik, H. [Institut fuer Experimentalphysik, Wien (Austria)] [Institut fuer Experimentalphysik, Wien (Austria); Leithe-Jasper, A.; Rogl, P. [Universitaet Wien (Austria)] [Universitaet Wien (Austria)

1997-10-01

451

Design, fabrication and characterization of single crystal silicon microactuator for hard disk drives  

Microsoft Academic Search

In this paper, a single crystal silicon electrostatic microactuator for hard disk drives' (HDD) dual stage servo systems is presented. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio of 20:1 directly processed from a single crystal silicon

J Q Mou; Y Lu; J P Yang; Q H Li; G X Guo

2004-01-01

452

Optical properties of single-crystal sapphire fibers Rick K. Nubling and James A. Harrington  

E-print Network

Optical properties of single-crystal sapphire fibers Rick K. Nubling and James A. Harrington Single-crystal sapphire fibers have been grown with the laser-heated pedestal-growth method with losses as low as 0.3 dB m of America Key words: Infrared fibers, sapphire fibers, Er:YAG lasers, optical properties. 1. Introduction

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Investigation on the nucleation kinetics of zinc thiourea chloride (ZTC) single crystals  

Microsoft Academic Search

Nucleation parameters such as radius of critical nucleus, critical free energy change and interfacial tension have been investigated for the aqueous solution growth of zinc thiourea chloride (ZTC) single crystals. The formation of ZTC compounds was confirmed by single crystal X-ray diffraction and the functional groups are confirmed by FTIR analysis. Solubility of ZTC has been determined for various temperatures.

R. Rajasekaran; K. V. Rajendiran; R. Mohan Kumar; R. Jayavel; R. Dhanasekaran; P. Ramasamy

2003-01-01

454

Discontinuous surface cracks during stress corrosion cracking of stainless steel single crystal  

E-print Network

Discontinuous surface cracks during stress corrosion cracking of stainless steel single crystal L i n f o Article history: Received 27 March 2011 Accepted 16 June 2011 Available online 23 June 2011 Keywords: A. Stainless steel B. SEM C. Stress corrosion a b s t r a c t Single crystal 321 stainless steel

Volinsky, Alex A.

455

Structural, dielectric and optical properties of N-(2 chlorophenyl)-(1-propanamide) (NCP) single crystals  

Microsoft Academic Search

Good transparent single crystals of N-(2 chlorophenyl)-(1-propanamide) have been grown by slow cooling solution growth technique. From the crystal structure analysis we infer that the crystal belongs to monoclinic system. The grown crystals were subjected to FT-IR and FT-Raman analyses for vibrational assignments, UV–Vis spectral studies for optical transmission and band gap determination, dielectric studies for the study of dependence

P. Srinivasan; T. Kanagasekaran; N. Vijayan; R. Balamurugan; A. R. Charles Sathiya Prakash; P. Kannan; R. Gopalakrishnan; P. Ramasamy

2006-01-01

456

Structural, spectral, thermal, dielectric, mechanical and optical properties of urea l-alanine acetate single crystals  

Microsoft Academic Search

A new organic nonlinear optical crystal, urea l-alanine acetate (ULAA) has been grown by solution growth using slow cooling technique with the vision to improve the properties of the l-alanine crystals. Urea and l-alanine material were mixed in the molar ratio 1:4. Solubility and metastable zone width were determined. Single crystal XRD analyses revealed that the crystal lattice of ULAA

D. Jaikumar; S. Kalainathan; G. Bhagavannarayana

2010-01-01

457

Nucleation of polyvinyl alcohol crystallization by single-walled carbon nanotubes  

Microsoft Academic Search

Non-isothermal crystallization experiments were performed on poly(vinyl alcohol) mixed with single-walled carbon nanotubes. Non-isothermal crystallization experiments showed that nanotubes nucleate crystallinity at weight fractions as low as 0.1%. An Ozawa model was applied to the non-isothermal crystallization data, and this approach confirmed the results deduced from the qualitative examination of the data: there was a clear difference in crystallization kinetics

Olga Probst; Eric M. Moore; Daniel E. Resasco; Brian P. Grady

2004-01-01

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