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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

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

NASA Astrophysics Data System (ADS)

The induced colour in single crystals of calcium fluoride irradiated with ?-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing ?-rays dose up to 106 Gy and absorption bands centred at about 225, 260, 340, 396 and 580 nm are observed. At higher doses, in the case of reactor neutrons irradiation, the absorption spectrum shows a large absorption band centred at about 415 nm and shoulders at 340 nm and 550 nm. This indicates that the absorption bands at 225, 260 and 580 nm are probably saturated at higher doses. Whereas, the band at 396 nm presents both saturation and linearly increasing behaviour. On heating a sample after irradiation, the absorption bands at 225, 260 and 580 nm disappear at 140 C, and the 396 nm absorption band disappears above 250 C. Photoluminescence excited with 325 nm photon shows an emission band centred at about 420 nm in the non-irradiated sample. The intensity of such band deceases after irradiation.

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

2010-09-01

3

Single-point diamond turning of CaF 2 for nanometric surface  

Microsoft Academic Search

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

Jiwang Yan; Junichi Tamaki; Katsuo Syoji; Tsunemoto Kuriyagawa

2004-01-01

4

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

5

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

NASA Astrophysics Data System (ADS)

Single-crystal calcium fluoride (CaF2) is an indispensable optical material for the deep ultraviolet radiation lithography system. The requirement for extremely high performance using in lithography system can be not satisfied by using conventional polishing because the polishing powder are easy to embed to surface due to its relative softness. In the process of rough finishing of CaF2, ductile cutting of CaF2 is considered as a suitable technology instead of tradition polishing to efficiently achieve super-smooth surface without impurity. In this paper, a theoretical and experimental study on the ductile cutting of CaF2 is presented. An energy model for ductile mode cutting of CaF2 is developed, in which the critical undeformed chip thickness can be predicted from the workpiece material characteristics and cutting parameters. The model is verified with experimental results from the micro-grooving of CaF2 on an ultra-precision lathe using a circle diamond crystals tool. The pattern of micro-grooving is inspected using optical microscope, the critical cutting depth of ductile-to-brittle is measured using white-light interferometer. It is shown that the predicted results for the critical undeformed chip thickness corresponding to ductile cutting agree well with the experimental results. Finally, ductile cutting of CaF2 is carried out under the cutting conditions as the maximum undeformed thickness less than the critical undeformed thickness of 233nm obtained above, ductile mode cutting of CaF2 has been achieved a super smooth surface with roughness of 3.50nm (Ra) measured by AFM is obtained.

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

2010-05-01

6

Properties of ultra-large CaF2 crystals for the high NA optics  

NASA Astrophysics Data System (ADS)

CaF2(Calcium fluoride) lens materials are required for the most important component of the ArF laser lithography stepper for the reason of its excellent transparency in DUV region and excellent laser durability as compared with quartz. Last year we reported to succeed in growing both <111> and <100> crystals, which had 210m diameter and 150mm length by the Czochralski (CZ) method with high productivity1). The obtained CaF2 crystal had low stress birefringence by way of the optimized annealing process. Although, for the higher NA system, larger CaF2 single crystals are required for the lens materials having the high quality and high productivity. To meet the above mentioned demands, we made efforts to produce and succeeded the first in the world ultra-large (?300mm over) and high quality CaF2 single crystal by the CZ method with high productivity. The crystal had very low stress birefringence, good transparency in DUV region and good homogeneity. It was also easy to control the orientation of the crystal by the selection of seed crystal.

Hatanaka, Y.; Yanagi, H.; Nawata, T.; Inui, Y.; Mabuchi, T.; Yasumura, K.; Nishijima, E.; Fukuda, T.

2005-05-01

7

Optical properties of a CaF2 crystal  

NASA Astrophysics Data System (ADS)

The electronic structure, the charge-density distribution, and the optical-absorption spectrum of a CaF2 crystal are studied by means of a first-principles local-density calculation. The calculated imaginary part of the dielectric function is in good agreement with experimental measurement up to 27.0 eV. We have also used a simplified self-interaction-correction (SIC) model to address the problem of band-gap underestimation in the local-density calculation. Although some marginal improvement in the optical result has been achieved, there is no strong evidence of unequivocal rectification other than an increment in the band gap. This study shows additional (non-SIC) correction to the conduction-band states of CaF2 may also be necessary.

Gan, Fanqi; Xu, Yong-Nian; Huang, Ming-Zhu; Ching, W. Y.; Harrison, Joseph G.

1992-04-01

8

Nuclear Magnetic Resonance Studies of Pure and Samarium-Doped CAF2 Crystals.  

National Technical Information Service (NTIS)

The spin-lattice relaxation time T1 of Fluorine-19 was measured over a temperature range of 77 to 1300K in natural and synthetic CaF2 crystals and in CaF2 crystals doped with 0.05% Sm, 0.16% Sm, and 1.20% Sm. Most of the data was taken with the magnetic f...

R. J. Lysiak P. P. Mahendroo

1965-01-01

9

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.

2013-03-01

10

Etch pit shapes on {110} surfaces of CaF 2 crystals  

Microsoft Academic Search

{110} surfaces of CaF2 crystals are etched with different concentrations of HCl. It is found that concentrated HCl produces characteristic rectangular\\u000a pyramidal etch pits and 2 volume percent HCl produces boat shaped etch pits. Such variations in the etch pit shapes on {110}\\u000a surfaces of CaF2 crystals with different concentrations of HCl have been explained. Concentrated H2SO4 is found to

G C Jain; L C Jain; T S Murty

1981-01-01

11

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

Microsoft Academic Search

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

Andrzej P. Radlinski; A. J. Silversmith

1986-01-01

12

Additive coloring of CaF2:Sm crystals  

NASA Astrophysics Data System (ADS)

The study of the mechanism of additive coloring of calcium fluoride crystals, both pure and samarium-doped, demonstrates dynamical nature of processes that, in the course of coloring, tend to maintain equilibrium between Sm3+ and Sm2+ ions.

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

2010-06-01

13

Nuclear Spin-Lattice Relaxation in CaF2 Crystals via Paramagnetic Centers  

Microsoft Academic Search

The results of nuclear spin-lattice relaxation-time measurements in the laboratory reference frame (T1) and the rotating reference frame (T1r), made on F19 nuclei in CaF2 crystals doped either with Eu3+, Ce3+, or Mn2+ paramagnetic centers, are reported. From 0.25 to 0.36 of the Debye temperature, values of the correlation time tauc are found from T1r minima for Mn2+ ions. Over

D. Tse; I. J. Lowe

1968-01-01

14

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):5at.% Yb(3+) crystals are quite similar. Yb(2+) absorption bands are observed at 360, 315, 271, 260, 227 and 214nm, 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 540nm luminescence under 357nm 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

2005-06-10

15

Onset of laser ablation in CaF2 crystal under excimer laser irradiation  

Microsoft Academic Search

With the widespread application of excimer lasers for micro- processing, optically transparent materials in the UV region have become more important as optical components. The transparent materials currently available commercially are silica glass and fluoride crystals, CaF2 and MgF2. The resistance of these materials against cumulative irradiation of excimer lasers is required from the viewpoint of application, and it is

Yoshizo Kawaguchi; Aiko Narazaki; Tadatake Sato; Hiroyuki Niino; Akira Yabe

2002-01-01

16

Optical absorption properties and valence states of uranium in CaF2 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:CaF2 crystals. Uranium in U:CaF2 crystals grown in the presence of PbF2 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 U3+:CaF2 when the molar ratio of PbF2 to U is less than 25. In the absence of PbF2, U:CaF2 crystals are multicolor, consisting of red, cerise, yellow and green volumes from inside to outside where the red part in the core is still U3+:CaF2. 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

17

Spectroscopic properties of Er3+ ions in transparent oxyfluoride glass ceramics containing CaF2 nano-crystals  

Microsoft Academic Search

In this paper, the spectroscopic properties of Er3+-doped oxyfluoride glass ceramics containing CaF2 nano-crystals are systematically investigated. X-ray diffraction (XRD) and transmission electron microscope (TEM) experiments confirmed the formation of CaF2 nano-crystals in the glassy matrix. Based on the Judd-Ofelt theory, the intensity parameters Omega2,4,6, spontaneous emission probability, radiative life, radiative quantum efficiency, width of the emission line, stimulated emission

Daqin Chen; Yuansheng Wang; Yunlong Yu; En Ma; Zhongjian Hu

2005-01-01

18

Study of haze in 193nm high dose irradiated CaF2 crystals  

NASA Astrophysics Data System (ADS)

Crystalline calcium fluoride is one of the key materials for 193 nm lithography and is used for laser optics, beam delivery system optics and stepper/scanner optics. Laser damage occurs, when light is absorbed, creating defects in the crystal. Haze is known as a characteristic optical defect after high dose irradiation of CaF2 - an agglomeration of small scattering and absorbing centers. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanism of laser damage, the origin of haze and the factors that serve to prevent it. Stabilized M centers were described as reversible absorbing defects in CaF2, which can be annealed by lamp or laser irradiation. In this study the irreversible defects created by 193 nm laser irradiation were investigated.

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

2009-10-01

19

Onset of laser ablation in CaF2 crystal under excimer laser irradiation  

NASA Astrophysics Data System (ADS)

With the widespread application of excimer lasers for micro- processing, optically transparent materials in the UV region have become more important as optical components. The transparent materials currently available commercially are silica glass and fluoride crystals, CaF2 and MgF2. The resistance of these materials against cumulative irradiation of excimer lasers is required from the viewpoint of application, and it is important to clarify the mechanisms of the optical damage on these materials. In this paper, we report the onset of laser ablation, that is, the initiation of optical breakdown and plume formation, in CaF2 crystal under cumulative irradiation of an ArF excimer laser. When the laser fluence is below the ablation threshold, a blue luminescence due to self-trapped exciton is observed from the whole laser-irradiated region. When the fluence ins increased near the threshold, successive irradiation finally cause a bright, localized luminescence due to the initiation of laser ablation. SEM images of the laser-damaged region show two features: (1) a small bump with pits of the order of 0.1 micrometers formed by UV laser absorption and following local heating, (2) small cracks with triangular fragments caused by mechanisms stress under local heating.

Kawaguchi, Yoshizo; Narazaki, Aiko; Sato, Tadatake; Niino, Hiroyuki; Yabe, Akira

2002-06-01

20

Influence of the Er3+ Ions Concentration on the Structural Deformation in Doped CaF2 Crystals  

NASA Astrophysics Data System (ADS)

Calcium fluoride crystals doped with ErF3 were grown using the Bridgman technique. The dissolved Er ions in CaF2 are trivalent and this leads to the formation of charge-compensating defects. The local compensation, by an interstitial or substitutional F- ion, creates the isolated centers, with various crystal field symmetries of the trivalent erbium ions in the CaF2 host. To study the charge-compensating defects in these crystals we used two methods: the optical absorption spectra and the dielectric spectra.

Nicoara, I.; Munteanu, M.; Stef, M.; Preda, E.; Buse, G.

2010-08-01

21

High quantum fluorescence yield of Er3+ at 1.5 ?m in an Yb3+, Ce3+-codoped CaF2 crystal  

NASA Astrophysics Data System (ADS)

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 ?m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 ? 4I13/2 transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+4I11/2 level. The quaternary-doped CaF2 system shows great potential to achieve high laser performance in the 1.5 ?m region.

Xu, Jun; Su, Liangbi; Li, Hongjun; Zhang, Dan; Wen, Lei; Lin, Hui; Zhao, Guangjun

2007-04-01

22

Convertible holograms in CaF2 crystals with color centers  

NASA Astrophysics Data System (ADS)

When recording hologram in ionic CaF2 crystal with color centers, the center conversion is accompanied with their spatial redistribution. The peculiar diffusion-drift mechanism of the recording is responsible for the extremely high hologram stability to both heating and illumination of the sample with a hologram by non-coherent radiation. However such photo-thermal treatment of the sample results in partial or total transformation of the center type and modification in their space distribution. Thus, keeping the hologram, such treatment influences its character of diffraction response, diffraction efficiency and profile. This work describes the mechanism and the character of these changes. It is shown that photo-thermal treatment can be used for fabrication of thick (up to 10 mm thickness) high stable holograms when reading out both in visible and infrared ranges of the spectrum.

Angervaks, Alexandr E.; Shcheulin, Aleksandr S.; Ryskin, Aleksandr I.

2013-05-01

23

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

NASA Astrophysics Data System (ADS)

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

Vaida, M.

2012-05-01

24

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

Microsoft Academic Search

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 ?F_7\\/2 and excited state ?F_5\\/2 of Yb3+ ions in the three crystals are measured to study the effect of Na+. Experimental

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

2005-01-01

25

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

2010-03-06

26

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

27

Lowest 4f-->5d Transition of Trivalent Rare-Earth Ions in CaF2 Crystals  

Microsoft Academic Search

The lowest 4f-->5d ultraviolet absorption band of eleven (Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) of the fourteen trivalent rare-earth (RE) ions in host CaF2 crystals has been measured. The room temperature absorption cross section [cm2] and half-width [cm-1] of these bands for the first-half series of RE3+ are larger than that of the second-half

Eugene Loh

1966-01-01

28

Ytterbium Clusters in Fluorite CaF2  

NASA Astrophysics Data System (ADS)

The crystal structure of the ytterbium hexameric cluster in CaF2 has been calculated in the framework of the embedded-cluster method within the shell model, in pair potential approximation. The crystal field parameters and scheme of the energy levels for Yb6F36 hexameric cluster were calculated in the exchange charges model. Also, the optical spectra of Yb3+ single center in CaF2 (cubic and tetragonal symmetry) was calculated and discussed.

Nikiforov, Anatoliy E.; Chernyshev, Vladimir A.; Volodin, Vasiliy P.; Avram, Nicolae M.; Avram, Calin N.

2009-05-01

29

Influence of sodium impurities on arf excimer-laser-induced absorption in CaF2 crystals.  

PubMed

The formation of color centers induced by irradiation with ArF excimer lasers in CaF(2) crystals was found to depend strongly on the sodium impurity concentration. Sodium-related color centers were generated by two-photon absorption because the slope of the induced absorption coefficient just after irradiation started was proportional to the square of the laser fluence. The saturation absorption also depended on laser fluence, and a photobleaching induced absorption phenomenon was observed. We concluded that the saturation absorption level was determined by the equilibrium between two-photon excitation and one-photon reverse reaction. PMID:18349970

Komine, N; Sakuma, S; Shiozawa, M; Mizugaki, T; Sato, E

2000-08-01

30

Passively Q-switched Yb(3+) laser with Yb(3+)-doped CaF(2) crystal as saturable absorber.  

PubMed

Passive Q-switching of a diode-pumped Yb:LYSO laser at 1060 nm with a Yb(3+) ions-doped CaF(2) crystal without the excited-state absorption (ESA) was demonstrated. An average output power of 174 mW with pulse duration of 5.6 mus and repetition rate of 27 kHz have been obtained under the unoptimized conditions. And the Q-switching conversion efficiency was as high as 51.7%. PMID:19532474

Su, Liangbi; Zhang, Dan; Li, Hongjun; Du, Juan; Xu, Yi; Liang, Xiaoyan; Zhao, Guangjun; Xu, Jun

2007-03-01

31

Biaxially textured Al film growth on CaF2 nanostructures toward a method of preparing single-crystalline Si film on glass substrates.  

PubMed

We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices. PMID:20839785

Li, Huafang; Snow, Patrick; He, Ming; Wang, Pei-I; Wang, Gwo-Ching; Lu, Toh-Ming

2010-10-26

32

Slip Systems and plastic anisotropy in CaF2  

Microsoft Academic Search

An examination was made of the slip planes activated in high-purity CaF2 single crystals with various orientations deformed by compression between 20 C and 600 C. It was found that 110 was the most difficult and 100 the easiest to activate. These results are compared to results for UO2 and zirconia.

A. Muoz; A. Domnguez-Rodrguez; J. Castaing

1994-01-01

33

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

NASA Astrophysics Data System (ADS)

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

Nicoara, I.; Stef, M.

2012-06-01

34

Trigonal Crystal-Field Energy Levels of Sm(+3) IN CaF2 (Type I).  

National Technical Information Service (NTIS)

Approximate first-order trigonal crystal-field-split energy levels are derived and fitted theoretically for the Sm(3+)-in-CaF2 (Type I) sextet H(7/2), (9/2), (11/2) states of the ground multiplet involved in fluorescence. Crystal-field theory and the Stev...

N. Rabbiner

1968-01-01

35

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

SciTech Connect

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.

Atari, N.A.; Svensson, G.K.

1986-05-01

36

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

Microsoft Academic Search

We developed a new phoswich detector. The detector consists of an inner NE213 organic liquid scintillator and an outer thin CaF2(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

Masashi Takada; Tokushi Shibata; Yoshitomo Uwamino; Takashi Nakamura

1996-01-01

37

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

NASA Astrophysics Data System (ADS)

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

Bnysz, I.; Berneschi, S.; Khnh, N. Q.; Lohner, T.; Lengyel, K.; Fried, M.; Pter, .; Petrik, P.; Zolnai, Z.; Watterich, A.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.

2012-09-01

38

Novel Synthesis of CaF2 Nanocrystals and the Effect of Pyridine Addition on Their Crystal Size  

NASA Astrophysics Data System (ADS)

Various types of calcium fluoride nanocrystals were prepared by the reactions between calcium metal and ammonium fluoride in liquid ammonia. The obtained nanocrystals were observed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), absorption spectroscopy, and fluorescent spectroscopy. The particle size of pure CaF2 nanocrystals was about 14 nm. The addition of pyridine and the selection of the period of pyridine removal gave two particle size ranges, which were 8--10 and 13--15 nm. The nanocrystals were successfully doped with Mn2+ and Eu2+. The optical properties of the nanocrystals were investigated. The results implied that Eu2+ was stable in the CaF2 nanocrystals.

Rungrodnimitchai, Supitcha

2011-01-01

39

Novel Synthesis of CaF2 Nanocrystals and the Effect of Pyridine Addition on Their Crystal Size  

Microsoft Academic Search

Various types of calcium fluoride nanocrystals were prepared by the reactions between calcium metal and ammonium fluoride in liquid ammonia. The obtained nanocrystals were observed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), absorption spectroscopy, and fluorescent spectroscopy. The particle size of pure CaF2 nanocrystals was about 14 nm. The addition of pyridine and the selection of the period

Supitcha Rungrodnimitchai

2011-01-01

40

Defect diffusion in CaF2 for optical applications  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

41

Investigation of the spin-lattice coupling coefficients G11 and G44 for CaF2:V3+ crystal  

NASA Astrophysics Data System (ADS)

In this Letter a uniform and simple method is established to calculate the spin-lattice coupling coefficients G11 and G44 for all dn ions in fourfold or eightfold cubic coordination from the formulas of zero-field splitting in tetragonal and trigonal symmetries. Based on this, the analytic expressions of G11 and G44 for d2 ions in eightfold cubic coordination are given, and as an example, the coefficients G11 and G44 for CaF2:V3+ crystal are calculated by applying the same parameters as those in the calculation within the framework of the exchange-charge model. The calculated results are closer to the experimental values than those calculated from the exchange-charge model.

Zheng, Wen-Chen

1990-05-01

42

The atomic and electronic structure of CaF2 and BaF2 crystals with H centers: a hybrid DFT calculation study.  

PubMed

Using the B3PW method we simulate the ground state of H center systems for CaF(2) and BaF(2) crystals. The energy difference between H centers with different orientations shows that the H center oriented in the [111] direction in alkaline earth fluorides is the most stable. We present the geometric relaxations of the neighboring atoms surrounding the H center. The combination energy of an H center and the formation energy of the related F-H pair in both alkaline earth fluorides are discussed. We also report the electronic structure of the H center systems. The effective charges and spins of the substitutional and interstitial fluorine atoms show that the hole is located at the interstitial fluorine. The band structures are presented. By studying the DOS sketches the constituents of the defect bands are clarified. PMID:21386345

Jia, Ran; Shi, Hongting; Borstel, Gunnar

2010-01-15

43

The use of the green emission in Er(3+)-doped CaF(2) crystals for thermometry application.  

PubMed

We report here the use of the green upconversion emissions originating from the thermally coupled levels (2)H(11/2) and (4)S(3/2) of the Er(3+) ion in CaF(2):Er (0.01at.%) for thermometry application in the range 303-423K. The mechanism responsible for excitation of the green emitting levels is a sequential two-photon absorption process. The fluorescence intensity ratio (FIR) of the green upconversion emissions at wavelengths of about 519 and 551nm is studied as a function of temperature in the range 303-423K using a 634nm tunable dye laser as an excitation source. It is found that the logarithm of the FIR varies linearly with the inverse of temperature. The gap between the two thermally coupled levels (4)S(3/2) and (2)H(11/2) was determined to be about 721cm(-1). This value is in good agreement with that found by spectroscopic investigations. The calibration curve is established, and the temperature is calculated. PMID:21693950

Chouahda, Z; Jouart, J P; Duvaut, T; Diaf, M

2009-05-26

44

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

45

Spin-Hamiltonian parameters for the tetragonal Gd(M)3+-F(i)- centers in CaF(2) and SrF(2) crystals.  

PubMed

The spin-Hamiltonian parameters (g factors g(//), g(?) and zero-field splittings b(2)(0), b(4)(0), b(4)(4), b(6)(0), b(6)(4)) of the tetragonal Gd(M)(3+)-F(i)(-) centers in CaF(2) and SrF(2) crystals at T?1.8K are calculated from the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters used are estimated from the superposition model with the reported defect structural data obtained from the analyses of superhyperfire interaction constants at the same temperature. The calculated results are in reasonable agreement with the experimental values. It appears that the above defect structural data reported in the previous paper are suitable and the diagonalization (of energy matrix) method is effective to the studies of spin-Hamiltonian parameters for 4f(7) ions in crystals. PMID:23298858

Yang, Wei-Qing; Zhang, Ying; Lin, Yuan; Zheng, Wen-Chen

2012-12-20

46

Dependence of the profile of a hologram recorded on color centers in a CaF2 crystal on the type of hologram-forming centers  

NASA Astrophysics Data System (ADS)

A hologram recorded in a CaF2 crystal by modulating the concentration of simple centers ( F, M, R, and N) and highly aggregated (mainly colloidal) color centers has been exposed to incoherent 365-nm light to a dose of about 4000 J/cm2 at a temperature of 80C. As a result of this exposure, the color centers were almost completely transformed into quasi-colloidal centers. The hologram was retained, and its diffraction efficiency increased; the intensity and number of observed diffraction orders increased as well. Analysis of the angular dependences of the diffraction response made it possible to construct a spatial profile of the hologram, which turned out to be much narrower in comparison with the initial-hologram profile; both profiles differ from a sinusoidal one. The hologram's stability to such a large exposure to incoherent light at an elevated temperature is related to the peculiar diffusion-drift mechanism of hologram recording on color centers in ionic crystals.

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

2012-12-01

47

Ionic, electronic and ion-diffusion controlled relaxation processes in CaF2, BaF2 and LiBaF3 crystals  

NASA Astrophysics Data System (ADS)

The ionic, electronic and anion-diffusion controlled thermally stimulated relaxation (TSR) processes at 80-700 K in CaF2 BaF2 and LiBaF3 crystals (X-ray irradiated or non-irradiated) have been investigated by means of ionic conductivity, ionic thermally stimulated (TS) depolarization current (TSDC); as well as current (TSC), luminescence (TSL) and bleaching (TSB) techniques. Above 250-290 K broad and overlapping anion TSDC peaks and correlated TSB stages are detected. The TSB kinetics is initiated and controlled by anion detrapping and interaction with the localized charges, i.e., the anion-diffusion controlled TSR processes take place in fluorides. The TSL and TSC data for LiBaF3 indicate that the lifetime and drift of electrons at 80-250 K is very small because of deep retrapping. The main TSL peaks at 132K, 170K and 220 K are caused by Vk center detrapping and hole-diffusion controlled tunnel recombination within pairs like .

Ziraps, V.; Kulis, P.; Tale, I.; Veispals, A.

48

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

49

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

Microsoft Academic Search

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

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

2004-01-01

50

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

Microsoft Academic Search

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

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

2004-01-01

51

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: A study of resistance of absorbing centres in a Pr2+:CaF2 crystal to high-power laser radiation  

NASA Astrophysics Data System (ADS)

A change in the absorption coefficient of Pr2+:CaF2 crystal in the spectral region from 530 to 1000 nm is found after irradiation by 30-mJ, 20-ns pulses from a repetitively pulsed 1.064-?m neodymium laser with a radiation power density of 500 MW cm-2. After irradiation by 105 pulses, the spectrum of the absorption coefficient variation ?? represents a broad band (~3000 cm-1) centred at 710 nm with the maximum value of ??=1.1 cm-1.

Il'ichev, Nikolai N.; Pashinin, Pavel P.; Gulyamova, E. S.

2001-07-01

52

Mechanochemical synthesis of nonstoichiometric nanocrystals La 1 ? y Ca y F 3 ? y with a tysonite structure and nanoceramic materials from CaF 2 and LaF 3 crystals  

Microsoft Academic Search

The nonstoichiometric phases La1 ? y\\u000a Ca\\u000a y\\u000a F3 ? y\\u000a (y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 1030 nm. It has been shown that the\\u000a compositions of the phases prepared

B. P. Sobolev; I. A. Sviridov; V. I. Fadeeva; S. N. Sulyanov; N. I. Sorokin; Z. I. Zhmurova; I. I. Khodos; A. S. Avilov; M. A. Zaporozhets

2008-01-01

53

Lanthanide doped upconverting colloidal CaF2 nanoparticles prepared by a single-step hydrothermal method: toward efficient materials with near infrared-to-near infrared upconversion emission.  

PubMed

Colloidal Er(3+)/Yb(3+), Tm(3+)/Yb(3+) and Ho(3+)/Yb(3+) doped CaF(2) nanoparticles have been prepared by a one-pot hydrothermal procedure and their upconversion properties have been investigated. PMID:21336370

Pedroni, Marco; Piccinelli, Fabio; Passuello, Tiziana; Giarola, Marco; Mariotto, Gino; Polizzi, Stefano; Bettinelli, Marco; Speghini, Adolfo

2011-02-18

54

Water adsorption on (111) surfaces of BaF2 and CaF2  

NASA Astrophysics Data System (ADS)

Water adsorption on polished (111) surfaces of BaF2 and CaF2 was studied at room temperature under ultrahigh vacuum conditions by optical second-harmonic generation. Above 104 langmuirs, the total second-harmonic yield decreases with increasing exposure. The azimuthal anisotropy is influenced differently on each substrate. Below 104 langmuirs the 3m symmetry of the crystal surface is preserved in both cases, but more pronounced for CaF2. At high doses the symmetry remains for BaF2, but vanishes for CaF2. The results point to pseudomorphous epitaxial growth of water on BaF2 but not on CaF2.

Zink, J. C.; Reif, J.; Matthias, E.

1992-06-01

55

Intrinsic luminescence excitation spectrum and extended x-ray absorption fine structure above the K edge in CaF2  

Microsoft Academic Search

Excitation spectra of the 4.44-eV intrinsic luminescence in a single crystal of CaF2 at liquid-nitrogen temperature was measured using synchrotron radiation in the x-ray region. The intrinsic luminescence at 4.44 eV is due to self-trapped exciton recombination. The intensity of the emitted uv light was measured as a function of the x-ray photon energy from below the calcium K edge

A. Bianconi; D. Jackson; K. Monahan

1978-01-01

56

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF 2(1 1 1) surface  

Microsoft Academic Search

We investigate the formation of nano-sized hillocks on the (111) surface of CaF2 single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solidliquid

A. S. El-Said; W. Meissl; M. C. Simon; J. R. Crespo Lpez-Urrutia; C. Lemell; J. Burgdrfer; I. C. Gebeshuber; Hp. Winter; J. Ullrich; C. Trautmann; M. Toulemonde; F. Aumayr

2007-01-01

57

Single crystal faceplate evaluation  

NASA Astrophysics Data System (ADS)

The Naval Training Systems Center developed single crystal faceplates which held promise for providing a significantly improved life span over conventional power phosphor cathode ray tubes (CRT) while maintaining acceptable resolution and light output characteristics. Single crystal faceplates being evaluated are composed of yttrium aluminum garnet (YAG) with an epitaxial cerium phosphor layer grown on the YAG substrate producing a cathodoluminescent material (CE:YAG). The single crystal nature of these faceplates should allow higher resolution (no phosphor grains) and higher thermal conductivity.

Tucker, A. R.; Kindl, H. J.

1993-10-01

58

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

SciTech Connect

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

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

1986-02-15

59

Tm3+:CaF2 planar waveguides grown by liquid phase epitaxy on CaF2 substrates showing signal enhancement at 1.92 ?m  

NASA Astrophysics Data System (ADS)

We report on relative gain measurements at 1.92 ?m in Tm:CaF2 films grown on pure CaF2 substrates by using Liquid Phase Epitaxy with CaCl2 as a solvent. Electron microscopy and X-ray diffraction measurements show that the Tm3+:CaF2 films are about 5 ?m thick and have a small lattice mismatch with the CaF2 substrate. Room temperature emission spectra of the Tm3+ ions around 1.9 ?m exhibit the same structure as in the bulk crystals and the lifetime of the 3F4 metastable level is found equal to about 12.8 ms. The Tm:CaF2 films are guiding optical waves and exhibit a relative gain of 7% at 1.92 ?m when pumped at 0.765 ?m.

Renard, S.; Camy, P.; Doualan, J. L.; Moncorg, R.; Couchaud, M.; Ferrand, B.

2006-08-01

60

Polarization of CAF2:SM(3+) Fluorescence.  

National Technical Information Service (NTIS)

The particular environments which produce two different types of CaF2:Sm(3+) fluorescence were deduced from study of the polarization of each spectrum. Either trigonal or tetragonal symmetry was observed and attributed to the local charge compensator asso...

T. F. Ewanizky P. J. Caplan J. R. Pastore

1965-01-01

61

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

62

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

63

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

64

Double beta decay study of 48Ca by CaF2 scintillator  

NASA Astrophysics Data System (ADS)

A CaF2 scintillation detector system (ELEGANT VI) is developed to search for neutrinoless double beta decay (0?DBD) of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life, the expected number of background events was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF2 crystals. A new lower limit is obtained to be 1.8 1022 yr at the 90% C.L.

Ogawa, I.; Hazama, R.; Ajimura, S.; Matsuoka, K.; Kudomi, N.; Kume, K.; Ohsumi, H.; Fushimi, K.; Suzuki, N.; Nitta, T.; Miyawaki, H.; Shiomi, S.; Tanaka, Y.; Ishikawa, Y.; Itamura, M.; Kishimoto, K.; Katsuki, A.; Sakai, H.; Yokoyama, D.; Umehara, S.; Tomii, S.; Mukaida, K.; Yoshida, S.; Ejiri, H.; Kishimoto, T.

2003-06-01

65

Single crystal diamond  

US Patent & Trademark Office Database

A single crystal diamond grown by vapor phase synthesis, wherein when one main surface is irradiated with a linearly polarized light considered to be the synthesis of two mutually perpendicular linearly polarized light beams, the phase difference between the two mutually perpendicular linearly polarized light beams exiting another main surface on the opposite side is, at a maximum, not more than 50 nm per 100 .mu.m of crystal thickness over the entire crystal. This single crystal diamond is of a large size and high quality unattainable up to now, and has characteristics that are extremely desirable in semiconductor device substrates and are applied to optical components of which low strain is required.

2009-11-10

66

Single crystals of chitosan.  

PubMed

Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology. PMID:2085494

Cartier, N; Domard, A; Chanzy, H

1990-10-01

67

Fluoride Release from CaF2 and Enamel Demineralization  

Microsoft Academic Search

The anticaries effect of professional fluoride (F) application has been attributed to calcium-fluoride-like deposits (CaF2) formed on enamel, but this has not been clearly demonstrated. We hypothesized that CaF2 formed on plaque-free enamel by F application would reduce enamel demineralization due to the increase of F availability in fluid of subsequently formed plaque. We created distinct levels of CaF2 on

L. M. A. Tenuta; R. V. Cerezetti; A. A. Del Bel Cury; C. P. M. Tabchoury; J. A. Cury

2008-01-01

68

Spectroscopic properties of CaF2:U4+ as a saturable absorber  

Microsoft Academic Search

The spectroscopic properties of crystals of CaF2:U4+ have been examined in light of recent interest expressed for this material as a saturable absorber in the passive Q switching of near infrared solid state lasers. The detailed crystal-field splitting of the energy levels of U4+(5f2 ) is analyzed for the ion in different charge-compensated sites. Identification of the site is based

John B. Gruber; Dhiraj K. Sardar; Larry D. Merkle; Bahram Zandi; Richard Jarman; J. Andrew Hutchinson

2001-01-01

69

Aqueous solution synthesis of CaF2 hollow microspheres via the ostwald ripening process at room temperature.  

PubMed

Nearly monodispersive CaF2 hollow microspheres were synthesized by a facile aqueous solution route from the mixed aqueous solutions of CaCl2, Na2WO4, and NaF at room temperature. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and N2 adsorption-desorption techniques. The CaF2 hollow microspheres have an average diameter of about 1.5 microm and a hollow interior of 0.5 microm. The shell is composed of numerous single-crystalline nanoparticles with diameter of about 20 nm. The morphologies and diameters of the CaF2 products are strongly dependent on the experimental parameters, such as the concentration of the aqueous NaF solution and the reaction temperature. The synthetic experiments indicate that the growth process of CaF2 hollow microspheres involves first the formation of CaWO4 solid microspheres and then the formation of CaF2 solid microspheres through the reaction between CaWO4 and F(-) ions controlled by the difference of the solubility product for CaWO4 and CaF2. Phenomenological elucidation based on TEM observations and XRD patterns of intermediate products at different precipitation stages indicates that the formation mechanism for the CaF2 hollow microspheres is related to the Ostwald ripening mechanism. N2 adsorption-desorption measurement shows that the CaF2 hollow microspheres possess a high Brunauer-Emmett-Teller surface area and porosity properties. The synthetic procedure is straightforward and represents a new example of the Ostwald ripening mechanism for the formation of inorganic hollow structures in an aqueous solution at room temperature. PMID:20356002

Wang, Wen-Shou; Zhen, Liang; Xu, Cheng-Yan; Chen, Jun-Zhou; Shao, Wen-Zhu

2009-04-01

70

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

SciTech Connect

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

Hamilton, D.S.

1986-01-01

71

The Zeeman Spectra of Gd3+ in CaF2 at Cubic Sites.  

National Technical Information Service (NTIS)

The octet S7/2 ground state Gd3+ is split only 0.149/cm by the cubic crystal field in CaF2 and is described at 11.3 kG by the projection quantum number J sub Z referred to the magnetic field axis and behaves like a spin 7/2 system with an isotropic g valu...

J. A. Detrio

1969-01-01

72

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 Grneisen 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

73

Birefringence simulations for annealed ingots of the <001>-and <111>- growth calcium fluoride single crystals with consideration of creep deformation  

NASA Astrophysics Data System (ADS)

We developed an analysis system for simulating birefringence of an annealed ingot of CaF2 single crystal caused by the residual stress after annealing process. The analysis system comprises the heat conduction analysis that provides the temperature distribution during the ingot annealing, the stress analysis to calculate the residual stress after ingot annealing, and the birefringence analysis of an annealed ingot induced by the residual stress. The finite element method was applied to the heat conduction analysis and the stress analysis. In these analyses, the temperature dependence of material properties and the crystal anisotropy were taken into account. In the residual stress calculation, we considered the time-dependent nonlinear deformation behavior of a material called creep. In the birefringence analysis, the distributions of optical path difference were calculated by using average stress method with consideration of the crystal anisotropy. We can perform the birefringence analysis of an ingot of CaF2 single crystal with any growth direction, using this analysis system, and we performed the analyses of the crystals with the <001> and <111> growth directions. From these analyses, we obtained reasonable results of optical path difference in comparison with the experimental results.

Kitamura, Y.; Ogino, H.; Miyazaki, N.; Mabuchi, T.; Nawata, T.

2010-06-01

74

Sensitivity of CaF2 Thermoluminescent Materials to Fast Neutrons,  

National Technical Information Service (NTIS)

The object of the present study is to determine the relative sensitivities of three types of solid CaF2, TL-materials of commercial grade - TLD-200 (CaF2:Dy), TLD-300 (CaF2:TM) and TLD-400 (CaF2:Mn) - under well defined experimental conditions. The TL-res...

J. B. Dielhof A. J. Bos J. Zoetelief J. J. Broerse

1987-01-01

75

CaF2 Formation: Cariostatic Properties and Factors of Enhancing the Effect  

Microsoft Academic Search

CaF2 or a CaF2-like material\\/phosphate-contaminated CaF2 is a major reaction product during topical treatment of dental hard tissues. Recently, evidence has suggested that CaF2 is formed not only on surfaces but also to some extent in the enamel. The minimum concentration of fluoride required for CaF2 formation is not well known and may depend on whether calcium is available from

Bjrn gaard

2001-01-01

76

Fluoride release from CaF2 and enamel demineralization.  

PubMed

The anticaries effect of professional fluoride (F) application has been attributed to calcium-fluoride-like deposits (CaF(2)) formed on enamel, but this has not been clearly demonstrated. We hypothesized that CaF(2) formed on plaque-free enamel by F application would reduce enamel demineralization due to the increase of F availability in fluid of subsequently formed plaque. We created distinct levels of CaF(2) on enamel to evaluate a dose-response effect. Enamel blocks were mounted in contact with a S. mutans test plaque and used in situ by 10 volunteers. F released to the fluid phase of this substrate ("plaque fluid") was measured before a cariogenic challenge. "Plaque fluid" F concentration was highly correlated to the enamel CaF(2) concentration (r = 0.96, p < 0.001) and to consequent enamel demineralization (r = -0.75, p < 0.001). The results suggest that F released to plaque fluid from CaF(2) formed on enamel may play a significant role in the anticaries effect of professionally applied F agents. PMID:18946010

Tenuta, L M A; Cerezetti, R V; Del Bel Cury, A A; Tabchoury, C P M; Cury, J A

2008-11-01

77

Magnetic properties of arrays of cobalt nanoparticles on the CaF2(110)/Si(001) surface  

NASA Astrophysics Data System (ADS)

The Co/CaF2/Si(001) heterostructures with the corrugated (110) surface of the CaF2 buffer layer have been grown by molecular beam epitaxy. The structures are nanoparticle arrays of single-crystal Co, mostly of the cubic fcc modification. The behavior of the magnetic hysteresis loops as a function of the density of coverage of the substrate by cobalt islands, the island size, and the temperature is studied using the magnetooptical technique. At low coverage densities, where the effective cobalt film thickness d eff is less than the critical value d {eff/ c }, the magnetic structure of the films at T = 294 K can be visualized as an ensemble of superparamagnetic, weakly interacting nanoparticles and is characterized by small values of the coercive field H c and the remanent magnetization M rem. A decrease in the temperature leads to a strong increase in H c and M rem, which is associated with the transition of the islands to the blocked state. The blocking temperature of the structures is T b 280 K. The magnetic anisotropy parameter K and the saturation magnetization M s of the islands depend on the growth temperature of cobalt T Co. An increase in the coverage density above the critical thickness d {iff/ c } at T = 294 K brings about a strong increase in H c and M rem and the appearance of a hysteresis loop anisotropy originating from the corrugated structure of the CaF2 buffer layer. The experimental results are compared with the model of an ensemble of noninteracting superparamagnetic particles.

Krichevtsov, B. B.; Gastev, S. V.; Il'Yushchenkov, D. S.; Kaveev, A. K.; Sokolov, N. S.

2009-01-01

78

Growth of Zno Single Crystals.  

National Technical Information Service (NTIS)

Single crystals of ZnO have been grown by subliming both ZnS and ZnSe and reacting them with oxygen in an argon gas flow. Using ZnS as the starting material, both platelet- and prism-type ZnO crystals were grown. Prisms having a cross-sectional area in th...

Y. S. Park D. C. Reynolds

1966-01-01

79

A solvent extraction route for CaF2 hollow spheres.  

PubMed

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

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

2010-09-28

80

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

1991-01-01

81

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

1991-01-01

82

Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor  

NASA Astrophysics Data System (ADS)

CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO4:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn2+ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.

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

2009-02-01

83

Paramagnetic hyperfine splitting in the Eu Mssbauer spectra of CaF(2):Eu.  

PubMed

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

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

2008-06-30

84

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF2(1 1 1) surface  

NASA Astrophysics Data System (ADS)

We investigate the formation of nano-sized hillocks on the (1 1 1) surface of CaF2 single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14 keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid liquid phase transition (melting) on the nanoscale. With increasing potential energy, both the basal diameter and the height of the hillocks increase. The present results reveal a remarkable similarity between the present predominantly potential energy driven process and track formation by the thermal spike of swift (GeV) heavy ions.

El-Said, A. S.; Meissl, W.; Simon, M. C.; Crespo Lpez-Urrutia, J. R.; Lemell, C.; Burgdrfer, J.; Gebeshuber, I. C.; Winter, Hp.; Ullrich, J.; Trautmann, C.; Toulemonde, M.; Aumayr, F.

2007-05-01

85

A model of CaF2 indentation  

NASA Astrophysics Data System (ADS)

A finite element model (FEM) of calcium fluoride (CaF2) with a rate-dependent mesoplastic constitutive formulation was developed and compared with nanoindentation tests. Indentations on the three main crystallographic planes (100), (110), and (111) of (CaF2) were analyzed. Appropriate material parameters were obtained by correlating the FEM results and the corresponding experimental load-displacement curves. The simulations show a value in the range of 74-110 MPa for the initial shear yield strength and a value in the range of 100-180 MPa for the self-hardening modulus. Such estimates can be used to examine the detailed stress distribution induced by the indentation.

Zhang, Q.; Lambropoulos, J. C.

2007-02-01

86

Molecular Dynamics Studies of Superionic Conductor CaF2  

Microsoft Academic Search

In the molecular dynamics study of the superionic conductor CaF2, the ionic soft-core system, of which the pair potential consists of the Coulombic and soft-core potentials, is investigated. The influence of the potential, especially of the softness of the soft-core repulsion, on the distribution of anions and diffusion paths is studied. We also study the dynamics of the diffusion in

Yutaka Kaneko; Akira Ueda

1988-01-01

87

Synthesis and characterization of CaF 2 nanocrystals  

Microsoft Academic Search

Calcium fluoride nanocrystals (CaF2) were synthesized by two different techniques namely co-precipitation and hydrothermal. The synthesized nanocrystals were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared red spectroscopy (FTIR), scanning electron microscopy (SEM), optical absorption and photoluminescence (PL). The crystallite size estimated using Scherer's formula was found to be in the range 3035nm for nanocrystals synthesized by co-precipitation method

C. Pandurangappa; B. N. Lakshminarasappa; B. M. Nagabhushana

2010-01-01

88

Laser-induced damage in SiO 2 and CaF 2 with picosecond and femtosecond laser pulses  

Microsoft Academic Search

Single- and multiple-shot damage thresholds and plasma-emission thresholds for fused silica and CaF2 are reported for 790 nm photons as a function of laser pulse width (190 fs 4.5 ps). The results are compared with single-shot plasma-emission measurements [1] and with multiple-shot damage measurements [2]. Both the damage threshold and the plasma-emission threshold are shown to decrease with decreasing

H. Varel; D. Ashkenasi; A. Rosenfeld; R. Herrmann; F. Noack; E. E. B. Campbell

1996-01-01

89

Search for neutrino-less double beta decay of 48Ca by CaF2 scintillator  

NASA Astrophysics Data System (ADS)

A CaF2 scintillation detector system (ELEGANT VI) has been operating at Oto Cosmo Observatory to study double beta decays of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kgyr data. To derive the lower limit for the half-life of the neutrino-less double beta decay of 48Ca, the expected number of background events in that energy region was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF2 crystals. A new lower limit is obtained to be 1.41022 yr at the 90% C.L. An experimental sensitivity is 5.91021 yr at the 90% C.L.

Ogawa, I.; Hazama, R.; Miyawaki, H.; Shiomi, S.; Suzuki, N.; Ishikawa, Y.; Kunitomi, G.; Tanaka, Y.; Itamura, M.; Matsuoka, K.; Ajimura, S.; Kishimoto, T.; Ejiri, H.; Kudomi, N.; Kume, K.; Ohsumi, H.; Fushimi, K.

2004-01-01

90

Electronic and elastic properties of CaF2 under high pressure from ab initio calculations  

NASA Astrophysics Data System (ADS)

Calcium fluoride CaF2 has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF2 is the fluorite structure (Fm\\bar {3}m ), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni2In-type structure (P63/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the Fm\\bar {3}m and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine pz-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the ch (or ao) direction for the orthorhombic phase is stronger than that in the hexagonal crystal.

Shi, H.; Luo, W.; Johansson, B.; Ahujia, R.

2009-10-01

91

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

C. Annis

1992-01-01

92

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

D. P. DeLuca C. Annis

1991-01-01

93

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

D. P. DeLuca C. Annis

1993-01-01

94

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

D. P. DeLuca C. Ann

1992-01-01

95

Fatigue in Single Crystal Nickel Superalloys.  

National Technical Information Service (NTIS)

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

D. P. DeLuca C. Annis

1994-01-01

96

Thermoluminescence Response of CaF2:Mn, CaF2:Dy and CaSO4:Tm to Protons and Alpha-Particles,  

National Technical Information Service (NTIS)

Proton/gamma and alpha/gamma response ratios have been measured for very fine powders of the thermoluminescent phosphors CaF2:Mn, CaF2:Dy and CaSO4:Tm. This has been done as part of an evaluation of these phosphors for use in a combined neutron/gamma ther...

S. McGowan R. A. Gravelle

1987-01-01

97

Thermoluminescence Response of CaF2:Mn, CaF2:Dy and CaSO4:Tm to Protons and Alpha-Particles,  

National Technical Information Service (NTIS)

Proton/gamma and alpha/gamma response ratios have been measured for very fine powders of the thermoluminescent phosphors CaF2:Mn, CaF2:Dy and CaSO4:Tm. This has been done as Part of an evaluation of these phosphors for use in a combined neutron/gamma ther...

S. McGowan R. A. Gravelle

1987-01-01

98

Tribological investigation of CaF 2 nanocrystals as grease additives  

Microsoft Academic Search

Calcium fluoride (CaF2) nanocrystals with average grain size of 60nm were synthesized via a precipitation method. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM and XRD showed that CaF2 nanocrystals are cubic particles in submicron scale. The tribological properties of the prepared CaF2 nanocrystals as an additive

Libo Wang; Bo Wang; Xiaobo Wang; Weimin Liu

2007-01-01

99

Upconversion luminescence of monodisperse CaF2:Yb(3+)/Er(3+) nanocrystals.  

PubMed

Monodispersed CaF(2):Yb(3+)/Er(3+) nanocrystals have been prepared via a facile wet chemical technology. The upconversion luminescence properties of CaF(2):Yb(3+)/Er(3+) nanocrystals were compared with those of NaYF(4):Yb(3+)/Er(3+) nanocrystals with different phases and particle sizes. The results indicated that CaF(2) is a promising host material for producing desirable upconversion luminescence. PMID:19775118

Wang, Guofeng; Peng, Qing; Li, Yadong

2009-10-14

100

Thermal-mismatch-strain relaxation in epitaxial CaF2, BaF2\\/CaF2, and PbSe\\/BaF2\\/CaF2 layers on Si(111) after many temperature cycles  

Microsoft Academic Search

The thermal mismatch strain in stacks containing PbSe, BaF2, and\\/or CaF2 on Si(111) substrates is relieved by the glide of dislocations in the principal \\\\{100\\\\} glide system. The strain in the BaF2(111) and CaF2(111) buffer layers is relaxed at room temperature regardless of whether they form the top layer in the stack or are overgrown by other layers. PbSe (as

H. Zogg; S. Blunier; A. Fach; C. Maissen; P. Mller; S. Teodoropol; V. Meyer; G. Kostorz; A. Dommann; T. Richmond

1994-01-01

101

Lattice and thermal misfit dislocations in epitaxial CaF2\\/Si(111) and BaF2CaF2\\/Si(111) structures  

Microsoft Academic Search

Atomic force microscopy reveals straight slip steps resulting from dislocation glide in the primary \\\\{100\\\\} glide system in ``low mismatch'' CaF2\\/Si(111) structures. From the height and spacing of the steps, the strain relieved by these misfit dislocations is compatible with the relief of the tensile thermal strain change on cooldown. In ``high mismatch'' BaF2\\/CaF2\\/Si(111) structures, dislocations which relieve the thermal

S. Blunier; H. Zogg; C. Maissen; A. N. Tiwari; R. M. Overney; H. Haefke; P. A. Buffat; G. Kostorz

1992-01-01

102

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 -20C to +55C, 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.; Rmer, K.; Grodzicka, M.; Szcze?niak, T.; Iwanowska, J.; Moszy?ski, M.

2013-06-01

103

MBE Grown Ge Nanostructures on CaF(2)/Si(111).  

National Technical Information Service (NTIS)

Germanium nanocrystals were grown on CaF(2)/Si( 111) by molecular beam epitaxy. Specific features of Ge and CaF(2) growth have been analyzed in this work using electron diffraction and atomic force microscopy Well-pronounced Ge quantum dots were observed ...

L. V. Sokolov M. M. Moisseeva N. S. Sokolov O. P. Pchelyakov

2000-01-01

104

Surface Depletion of InSb by SiO and CaF2.  

National Technical Information Service (NTIS)

Increase in resistance of thin films of InSb with thickness of vacuum-deposited overlays of SiO and CaF2 indicates surface depletion in the semiconductor. Also, the equivalent depletion depth and the net trapped charge are evaluated for the case of a CaF2...

F. C. Luo M. Epstein

1972-01-01

105

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

106

High anion conductivity in a ternary non-equilibrium phase of BaF(2) and CaF(2) with mixed cations.  

PubMed

A highly conductive ternary fluoride with mixed cations is prepared by joint high-energy ball milling of cubic BaF(2) and CaF(2) in the ratio 0.4 : 0.6. The sample produced at room temperature consists of a nanocrystalline, defect-rich mixed (Ba,Ca)F(2) phase with retained cubic symmetry as well as of single-phase CaF(2) particles. The anion conductivity of the mixed phase, which decomposes at higher temperature (770 K) into BaF(2) and CaF(2), exceeds that of single-phase nanocrystalline BaF(2) by two and that of CaF(2) by four orders of magnitude. In turn, these conductivities are each greater by about two orders than those of the respective microcrystalline counterparts. Structural features of the samples are characterized by X-ray diffraction, TEM and (19)F MAS NMR spectroscopy. Static (19)F NMR spectra confirm the unexpectedly high anion conductivity probed by impedance spectroscopy. PMID:19370201

Ruprecht, B; Wilkening, M; Feldhoff, A; Steuernagel, S; Heitjans, P

2009-03-19

107

Ultraprecision diamond turning of aluminium single crystals  

Microsoft Academic Search

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

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

1997-01-01

108

Protein Single Crystal Growth under Microgravity  

NASA Astrophysics Data System (ADS)

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

Littke, Walter; John, Christina

1984-07-01

109

Adhesion of single crystals on modified surfaces in crystallization fouling  

NASA Astrophysics Data System (ADS)

In crystallization fouling it has been observed that during a certain initial phase the fouling is formed by a non-uniform layer consisting of a population of single crystals. These single crystals are frequently formed by inverse soluble salts such as CaCO3. During heterogeneous nucleation and heterogeneous growth an interfacial area between the crystal and the heat transfer surface occurs. The development of this interfacial area is the reason for the adhesion of each single crystal and of all individual crystals, once a uniform layer has been built up. The emerging interfacial area is intrinsic to the heterogeneous nucleation of crystals and can be explained by the thermodynamic principle of the minimum of the Gibbs free energy. In this study CaCO3 crystals were grown heterogeneously on untreated and on modified surfaces inside a flow channel. An untreated stainless steel (AISI 304) surface was used as a reference. Following surface modifications were investigated: enameled and electropolished stainless steel as well as diamond-like-carbon based coatings on stainless steel substrate. The adhesion was measured through a novel measurement technique using a micromanipulator to shear off single crystals from the substrate which was fixed to a spring table inside a SEM.

Mayer, Moriz; Augustin, Wolfgang; Scholl, Stephan

2012-12-01

110

Scintillation Response of CaF2 to H and He over a Continuous Energy Range  

SciTech Connect

Recent demands for new radiation detector materials with improved ?-ray detection performance at room temperature have prompted research efforts on both accelerated material discovery and efficient techniques that can be used to identify material properties relevant to detector performance. New material discovery has been limited due to the difficulties of large crystal growth to completely absorb ??energies; whereas high-quality thin films or small crystals of candidate materials can be readily produced by various modern growth techniques. In this work, an ion-scintillator technique is demonstrated that can be applied to study scintillation properties of thin films and small crystals. The scintillation response of a benchmark scintillator, europium-doped calcium fluoride (CaF2:Eu), to energetic proton and helium ions is studied using the ion-scintillator approach based on a time of flight (TOF) telescope. Excellent energy resolution and fast response of the TOF telescope allow quantitative measurement of light yield, nonlinearity and energy resolution over an energy range from a few tens to a few thousands of keV.

Zhang, Yanwen; Xiang, Xia; Weber, William J.

2008-06-07

111

Characterization of CaF2 surfaces using Adsorption-Desorption Isotherms and Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

We are interested in using rough CaF2 films to study the superfluid transition in two-dimensional helium systems. These experiments require quantitative information regarding the topography of the CaF2 surfaces. The surface roughness of CaF2 films is known to increase with film thickness as has been shown with previous atomic force microscopy (AFM) measurements [1]. We have fabricated a series of CaF2 samples of different film thicknesses and thus different surface roughnesses. These surfaces were studied using AFM and adsorption-desorption isotherm measurements with liquid nitrogen at T=77 K. The isotherm measurements allow us to determine the pore size distribution of each CaF2 film thickness. We find the emergence of hysteretic capillary condensation due to deep pores in the CaF2 as the film thickness increases. The development of these deep pores is also seen in our AFM measurements. Our combined results provide a detailed description of CaF2 surface roughness which can be utilized in the planned superfluid experiment. [1] D.R. Luhman and R.B. Hallock, Phys Rev. E 70, 051606 (2004).

Wadleigh, L. R.; Luhman, D. R.; Bumcrot, P. G.

2012-02-01

112

Photoemission from Germanium Single Crystals.  

National Technical Information Service (NTIS)

Studies of band structure of germanium by using photoemission have been reported recently by Donovan and Spicer and Donovan. Some new experimental results of electronic structures of simple crystal germanium are presented here. Principal results are as fo...

J. Matsuzaki

1970-01-01

113

Single Crystal Sapphire Optical Fiber Sensor Instrumentation  

SciTech Connect

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

Anbo Wang; Russell May; Gary R. Pickrell

2000-10-28

114

Paramagnetic hyperfine splitting in the 151Eu M?ssbauer spectra of CaF2:Eu2+  

PubMed Central

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

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

2009-01-01

115

Eu 2+ ions and CaF 2-containing transparent glass-ceramics  

Microsoft Academic Search

Transparent glass-ceramics have been prepared by heat-treating 45SiO220Al2O310CaO25CaF2 glasses doped with Eu2+ ions (in mol%). The precipitated crystalline phase in the glass-ceramics was CaF2. TEM observation showed the precipitated crystalline phase had a size of 1118nm and dispersed in the amorphous phase without clustering. Fluorescence measurements showed that Eu2+ ions entered into the CaF2 crystalline phase and gave a much

J Fu; J. M Parker; P. S Flower; R. M Brown

2002-01-01

116

EPR study of Ni+ and Ni3+ in x-irradiated CaF2  

NASA Astrophysics Data System (ADS)

EPR measurements of CaF2:Ni crystals before and after room-temperature (RT) x irradiation are reported. Depending on the rare-earth impurity content a small concentration of Ni+ centers is observed in "as-grown" crystals. During RT x irradiation the Ni+ concentration increases. At least two different kinds of Ni+ centers are observed in the EPR spectra. One of them has tetragonal symmetry with g?=2.569 and g?=2.089 and gives a superhyperfine (SHF) structure, due to the interaction with four equivalent flouride ions, which can be resolved at liquid-nitrogen temperature (LNT). The other one has an almost tetragonal symmetry with g factors and SHF structure very close to the former one but the (SHF) structure is resolved at RT. The first Ni+ center is associated with a (NiF4)3- molecular ion with the Ni+ at a distance of about 0.37 from the plane of the fluorine atoms. The other EPR signal is assigned to a similar center with some kind of perturbation. An isotropic EPR signal (g=2.003) with a well-resolved superhyperfine structure due to the interaction with eight equivalent fluorines has been detected in some of the samples after RT x irradiation. The tentative model proposed for the center responsible for this signal is a Ni3+ ion at a Ca2+ substitutional position.

Gonzalez, J. Casas; den Hartog, H. W.; Alcala, R.

1980-05-01

117

Optical Absorption of TNT Single Crystals.  

National Technical Information Service (NTIS)

A method for growing large area, thin, single crystal platelets of TNT is reported. The optical absorption properties of these crystals were studied, and dichroic behavior was observed. The absorption edge is approximately 3.1 eV and is tentatively assign...

A. C. Forsyth D. S. Downs

1973-01-01

118

Single Crystal Diamond Nanomechanical Dome Resonator.  

National Technical Information Service (NTIS)

Superior mechanical and optical properties of single crystal (SC) diamond in combination with a chemically inert and bio-compatible surface enable the design and fabrication of novel nanoscale devices for sensing and signal processing applications. In thi...

B. B. Pate J. Yang J. E. Butler J. W. Baldwin M. K. Zalalutdinov

2008-01-01

119

Single Crystal NMR of High Temperature Superconductors  

Microsoft Academic Search

The author reports Cu NMR studies of the high temperature superconductor YBa_2Cu _3O_{7-delta } (T_{rm c} = 90K) using a 1 mg single crystal. Three types of measurements have been made for both the \\

Charles Holloway Pennington

1989-01-01

120

Computational Techniques in Single Crystal Mossbauer Spectroscopy.  

National Technical Information Service (NTIS)

The report summarizes some computational techniques which can be used to extract the effective field parameters from a given single crystal Mossbauer spectrum. The effective field parameters in this case are the effective electric field gradient and magne...

K. P. Singh G. R. Hoy

1969-01-01

121

Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor  

Microsoft Academic Search

CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

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

2009-01-01

122

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

Microsoft Academic Search

CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

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

2009-01-01

123

The apatite formation ability of CaF2 doping tricalcium silicates in simulated body fluid.  

PubMed

The purpose of this study was to investigate the effects of CaF(2) on the apatite formation ability of tricalcium silicates (Ca(3)SiO(5), C(3)S) and the mechanism of apatite formation on C(3)S pastes. Different amounts of CaF(2) (0, 1, 2 and 3 wt%) were mixed in the raw materials during the synthesis process of C(3)S. The apatite formation ability of the CaF(2) doping C(3)S was examined by soaking the one-day setting pastes in simulated body fluid (SBF). The fluoride concentrations, pH values, structural and morphological variations of the pastes were examined during soaking in SBF. With the addition of CaF(2), the initial crystalline apatite formation time of the pastes was decreased from three days to one day. After soaking for seven days, the thicknesses of apatite layers depositing on the surface of C(3)S doped with 0, 1, 2 and 3 wt% CaF(2) were about 88, 102, 168 and 136 microm, respectively. C(3)S doped with 2 wt% CaF(2) showed the better ability to induce the formation of apatite. Furthermore, the mechanism of the apatite formation of the CaF(2) doping C(3)S pastes may be attributed to the formation and stability of F-substituted apatite determined by x-ray photoelectron spectroscopy (XPS) at the early age. The results indicated that CaF(2) doping C(3)S has better in vitro bioactivity, and may be used to prepare novel bone cement. PMID:19567937

Lin, Qing; Li, Yanbao; Lan, Xianghui; Lu, Chunhua; Chen, Yixin; Xu, Zhongzi

2009-06-30

124

Use of a rapid anneal to improve CaF2:Si (100) epitaxy  

Microsoft Academic Search

Post-anneals of short duration at high temperature are shown to improve significantly the quality of CaF2 films on Si (100). An anneal at 1100 C for 20 s in an Ar ambient reduced ?min, the ratio of backscattered 1.8-MeV 4He+ ions in the aligned to random direction, from 0.26 for an as-grown CaF2 film to 0.03 following the post-anneal. This

Loren Pfeiffer; Julia M. Phillips; T. P. Smith; W. M. Augustyniak; K. W. West

1985-01-01

125

Zero-phonon lines in CaF2 and SrF2  

Microsoft Academic Search

A number of prominent zero-phonon lines have been investigated in additively coloured CaF2 and SrF2 using uniaxial stress. Stark effect and magneto-optical techniques. It is tentatively suggested that a line at 598.8 nm in CaF2 may be a transition of a square planar F4 complex. There is a corresponding centre in SrF2. Other lines investigated appear to be associated with

J. H. Beaumont; A. L. Harmer; W. Hayes; A. R. L. Spray

1972-01-01

126

Synthesis and optical studies of gamma irradiated Eu doped nanocrystalline CaF 2  

Microsoft Academic Search

Europium (Eu) doped Calcium fluoride (CaF2) nanoparticles are synthesized by co-precipitation method and characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Also, optical absorption and photoluminescence (PL) results on gamma irradiated Eu doped CaF2 nanoparticles are presented. The PXRD patterns confirmed the cubic crystallinity of the samples and the particle size is

C. Pandurangappa; B. N. Lakshminarasappa; B. M. Nagabhushana

2011-01-01

127

Phase transition and thermodynamic properties of CaF2 via first principles  

NASA Astrophysics Data System (ADS)

The structural stabilities, phase transitions and thermodynamic properties of CaF2 under high pressure and temperature are investigated by first-principles calculations based on the plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaF2 under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. Our results demonstrate that the sequence of the pressure-induced phase transition of CaF2 is the fluorite structure (Fm3m), PbCl2-type structure (Pnma) and Ni2In-type structure (P63/mmc), and the transition pressures are obtained. The temperature-dependent volume and thermodynamic properties of Fm3m phase CaF2 at 0 GPa are presented. The thermodynamic properties of CaF2 in Fm3m, Pnma and P63/mmc phases at 300 K are predicted using the corrected and uncorrected quasi-harmonic approximation model. The variations of the thermal expansion ? and heat capacity CV with pressure P and temperature T of CaF2 in the three phases are systematically obtained.

Qi, Yuan-Yuan; Cheng, Yan; Liu, Min; Chen, Xiang-Rong; Cai, Ling-Cang

2013-10-01

128

Electronic and elastic properties of CaF(2) under high pressure from abinitio calculations.  

PubMed

Calcium fluoride CaF(2) has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF(2) is the fluorite structure ([Formula: see text]), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni(2)In-type structure (P6(3)/mmc). The two transitions occur at pressures of 8GPa and 105GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the [Formula: see text] and the forepart of Pnma phases. However, on increasing the pressure beyond 60GPa, the gap decreases, which is due to the fluorine p(z)-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the c(h) (or a(o)) direction for the orthorhombic phase is stronger than that in the hexagonal crystal. PMID:21693988

Shi, H; Luo, W; Johansson, B; Ahujia, R

2009-09-23

129

Cutting fluid study for single crystal silicon  

Microsoft Academic Search

An empirical study was conducted to evaluate cutting fluids for Single Point Diamond Turning (SPDT) of single crystal silicon. The pH of distilled waster was adjusted with various additives the examine the effect of pH on cutting operations. Fluids which seemed to promote ductile cutting appeared to increase tool wear as well, an undesirable tradeoff. High Ph sodium hydroxide solutions

Chargin

1998-01-01

130

Piezoelectric anisotropy of orthorhombic ferroelectric single crystals  

NASA Astrophysics Data System (ADS)

In the frame of thermodynamic approach, it is shown that all the admissible values of the d33, d32, and d31 piezoelectric moduli of any orthorhombic (mm2) single crystal in the 3-dimensional (d33, d32, d31) space lie within a restricted area having the form of ellipsoid. The main parameters of this ellipsoid (the aspect ratios and the angles characterizing its orientation) depend only on the elastic constants of the crystal. Using the developed approach, the areas of the allowable values of piezoelectric moduli have been determined for six crystals: single-domain KNbO3 and 0.27Pb(In0.5Nb0.5)O3-0.40Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystals possessing true orthorhombic symmetry and four polydomain macroscopically pseudoorthorhombic crystals--tetragonal BaTiO3 and PbTiO3 crystals with laminate 90 domain structure as well as rhombohedral 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 and 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 crystals, poled along the [011] direction of the prototype cubic cell. Four crystals from this set possess negative values of the longitudinal Poisson's ratio and are thus partially auxetics.

Aleshin, V. I.; Raevski, I. P.

2013-06-01

131

Single crystal fibers for high power lasers  

NASA Astrophysics Data System (ADS)

In this paper, we present our recent results in developing cladded-single crystal fibers for high power single frequency fiber lasers significantly exceeding the capabilities of existing silica fiber based lasers. This fiber laser would not only exploit the advantages of crystals, namely their high temperature stability, high thermal conductivity, superior environmental ruggedness, high propensity for rare earth ion doping and low nonlinearity, but will also provide the benefits from an optical fiber geometry to enable better thermal management thereby enabling the potential for high laser power output in short lengths. Single crystal fiber cores with diameters as small as 35?m have been drawn using high purity rare earth doped ceramic or single crystal feed rods by Laser Heated Pedestal Growth (LHPG) process. The mechanical, optical and morphological properties of these fibers have been characterized. The fibers are very flexible and show good overall uniformity. We also measured the optical loss as well as the non-radiative loss of the doped crystal fibers and the results show that the fibers have excellent optical and morphological quality. The gain coefficient of the crystal fiber matches the low quantum defect laser model and it is a good indication of the high quality of the fibers.

Kim, W.; Florea, C.; Baker, C.; Gibson, D.; Shaw, L. B.; Bowman, S.; O'Connor, S.; Villalobos, G.; Bayya, S.; Aggarwal, I. D.; Sanghera, J. S.

2012-11-01

132

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

133

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

134

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

SciTech Connect

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

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

2009-07-06

135

Electroluminescence Studies in Pyrene Single Crystals  

Microsoft Academic Search

The observation of electroluminescence in pyrene single crystals is reported. Holes and electrons were introduced into the samples by contact injection using CuI and Na-Hg amalgam electrodes as hole and electron injectors, respectively. The radiation-recombination light intensity is found to be directly proportional to the current through the crystal. The yield for light emission is about 2 10 photons

J. Gonzalez Basurto; Z. Burshtein

1975-01-01

136

Single crystal NMR of high temperature superconductors  

Microsoft Academic Search

Cu NMR studies of the high temperature superconductor YBa2Cu3O(7-delta) (T sub c = 90 K) using a 1 mg single crystal is reported. Three types of measurements were made for both the plane and chain Cu crystallographic sites and with the static magnetic field placed successively along each of the three crystal axes a, b, and c: nuclear magnetic resonance

Charles Holloway Pennington

1989-01-01

137

Microscopic analysis of the chemical reaction between Fe(Te, Se) thin films and underlying CaF2  

NASA Astrophysics Data System (ADS)

To understand the chemical reaction at the interface of Fe(Te, Se) and CaF2 materials, we used transmission electron microscopy to analyze five types of Fe(Te, Se) superconducting thin films prepared on different types of substrate: two on a CaF2 substrate, one on a CaF2 substrate with a CaF2 buffer layer, one on a CaF2 substrate with an FeSe buffer layer, and one on a LaAlO3 substrate with a CaF2 buffer layer. Energy-dispersive x-ray spectroscopy analysis revealed a potential interdiffusion between fluorine and selenium that plays a significant role in the variation of the lattice parameters. We conclude that the lattice parameters of the Fe(Te, Se) thin films are primarily determined by the chemical substitution of anions, while the lattice mismatch plays a secondary role.

Ichinose, A.; Nabeshima, F.; Tsukada, I.; Hanawa, M.; Komiya, Seiki; Akiike, T.; Imai, Y.; Maeda, A.

2013-07-01

138

Inkjet printing of single-crystal films.  

PubMed

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 (C(8)-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4?cm(2)?V(-1)?s(-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. PMID:21753752

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

2011-07-13

139

Nano-turning of single crystal silicon  

Microsoft Academic Search

High-quality silicon surfaces have been obtained by single-point diamond turning. After the analysis of the turning mechanism, the relationship between the surface integrity and the turning parameters was studied in detail. Results from the mechanism were compared with turning tests on silicon using a commercially available single-crystal diamond tool with a rake angle of 0. A novel technique was developed

F. Z Fang

1998-01-01

140

Three-dimensional single crystal silicon micromachining  

Microsoft Academic Search

A monolithic, multiple-level (ML), single-crystal-silicon (SCS) micromachining process called SCREAM3D has been developed. The high-aspect-ratio (HAR) levels are self-aligned and are fabricated from a single substrate by deep etching. Anisotropic reactive ion etching of silicon has been studied in detail and new recipes for the vertical etch and release of HAR ML structures have been developed. The SCREAM3D levels are

Wolfgang Maximilian Josef Hofmann

1999-01-01

141

Single Crystal Diffraction by Synchrotron Radiation.  

National Technical Information Service (NTIS)

The tunability and access to short wavelengths in combination with high intensity and the low divergence of the x-ray radiation produced by synchrotron storage rings opens up new and challenging fields for single crystal diffraction. These areas include m...

A. Kvick

1988-01-01

142

Development of single crystal filaments. Final report  

Microsoft Academic Search

The program just completed addresses a route to a more efficient longer-lasting electric light bulb filament. All current filaments for light bulbs are metallic in nature. They are subject to embrittlement with age (large grain growth) and relatively high vapor pressures which limits their operating temperature. There is evidence which suggests advantages to using high temperature refractory single crystal fibers

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

1995-01-01

143

Single crystal tungsten kinetic energy penetrators  

SciTech Connect

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

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

1992-05-01

144

Single crystal tungsten kinetic energy penetrators  

SciTech Connect

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

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

1992-05-01

145

Effect of Bi ion on Eu 2+ ?Eu 3+ conversion in CaF 2 :Eu phosphors for RPL dosimetry  

Microsoft Academic Search

UV photo-excited Eu2+ and Eu3+ luminescence from CaF2:Eu and CaF2:Eu, Bi phosphors were investigated. The effect of gamma exposure followed by temperature effect shows conversion mechanism\\u000a between Eu2+?Eu3+ ion in CaF2:Eu and CaF2:Eu, Bi phosphors which were studied for RPL dosimetry. The photoluminescence and X-ray diffraction characterization are reported\\u000a in this article.

S. J. DhobleI; I. M. Nagpure; N. S. Dhoble; Pablo Molina

146

Single-crystal disk drive miniactuators  

NASA Astrophysics Data System (ADS)

As hard disk drive areal densities increase at a compound annual growth rate (CAGR) of 60%, disk drives must position the head over increasingly small areas while moving more rapidly to reach the desired position. This results in an increase in vibration disturbance. To meet this demand, many hard disk drive manufactures have created prototype dual-stage actuators employing piezoelectric ceramics for the second stage. These are an attractive means of obtaining higher-bandwidth control due to the low inertia and size of the actuator element. As the technology improves, the next limiting factor will be the amount of displacement obtainable with traditional piezoceramic elements. Under the AXIS (Advanced Crystal Integrated System) Consortium program funded by DARPA, the application of PZN-PT single crystal piezoceramic as a second stage disk drive actuator was studied, based on the fact that the single crystal material provides larger stroke than its traditional PZT counterparts. The transverse (d31) strain of PZN-PT single crystal was measured to be about two times larger than that of PZT-5H ceramic. Both materials were integrated into a disk drive system and compared as second stage actuators. The methodologies used and the servo control techniques applied are also discussed in the paper.

Giovanardi, Marco; McKenney, Kevin; Rule, John A.; Yoshikawa, Shoko

2001-08-01

147

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 Schrdinger equation.

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

1998-05-01

148

Synthesis and upconversion luminescence properties of CaF2:Yb3+/Tm3+ microspheres.  

PubMed

CaF2:Yb3+/Tm3+ microspheres were synthesized by using a simple hydrothermal method. Their structures and morphologies were characterized by X-ray diffraction (XRD) and field-effective scanning electron microscopy (FESEM). The microspheres were formed from a large number of nanospheres with almost the same diameter after annealing. The growth mechanism of the microspheres was discussed. Strong ultraviolet (UV) and blue upconversion (UC) emission from the CaF2 microspheres was observed under 980 nm excitation. The enhancement of the UV UC emission was attributed to the size effect of the nanoscale particles. PMID:22413321

Jiang, Tao; Zhao, Dan; Qin, Weiping

2011-11-01

149

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

NASA Astrophysics Data System (ADS)

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

Vural, E. Kafadar; Metin, Bedir; A. Necmeddin, Yaz?c?; Tlin, Gnal

2013-05-01

150

Study of defects in pentacene single crystals  

NASA Astrophysics Data System (ADS)

Our research focuses on the growth of the pentacene single crystals with a high degree of purity, and the investigation of their morphology and physical properties. We are able to reduce the number of traps by two orders of magnitude compared with conventional methods. This is reflected in the value of hole mobility of 35 cm2/Vs at room temperature increasing to 58 cm2/Vs at 225 K. These high mobilities result from a purification of the material, that consists of removal of 6,13-pentacenequinone, as the major impurity, using vacuum sublimation under a temperature gradient. We further study the influence of air exposure on the electronic properties of pentacene single crystals. Our observations show that gases can diffuse reversibly in/out the crystals, and influence the electronic properties. We discern two competing mechanisms that modulate the electronic transport. On the one hand stands the presence of water from ambient air that intercalates into the crystal lattice and forms trapping sites for injected charges. On the other hand, the presence of oxygen increases the hole conduction. The latter effect is enhanced by the presence of visible light.

Jurchescu, Oana D.

2005-03-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

152

Porosity evolution in a creeping single crystal  

NASA Astrophysics Data System (ADS)

Experimental observations on tensile specimens in Srivastava et al (2012 in preparation) indicated that the growth of initially present processing induced voids in a nickel-based single crystal superalloy played a significant role in limiting creep life. Also, creep tests on single crystal superalloy specimens typically show greater creep strain rates and/or reduced creep life for thinner specimens than predicted by current theories. In order to quantify the role of void growth in single crystals in creep loading, we have carried out three-dimensional finite deformation finite element analyses of unit cells containing a single initially spherical void. The materials are characterized by a rate-dependent crystal plasticity constitutive relation accounting for primary and secondary creep. Two types of imposed loading are considered: an applied true stress (force/unit current area) that is time independent; and an applied nominal stress (force/unit initial area) that is time independent. Isothermal conditions are assumed. The evolution of porosity is calculated for various values of stress triaxiality and of the Lode parameter. The evolution of porosity with time is sensitive to whether constant true stress or constant nominal stress loading is applied. However, the evolution of porosity with the overall unit cell strain is insensitive to the mode of loading. At high values of stress triaxiality, the response is essentially independent of the value of the Lode parameter. At sufficiently low values of the stress triaxiality, the porosity evolution depends on the value of the Lode parameter and void collapse can occur. Also, rather large stress concentrations can develop which could play a role in the observed thickness dependence.

Srivastava, A.; Needleman, A.

2012-04-01

153

Single Crystal Metals Encapsulated in Carbon Nanoparticles  

Microsoft Academic Search

Single-domain microcrystals of LaC_2 encapsulated within nanoscale polyhedral carbon particles have been synthesized in a carbon arc. Typical particle sizes are on the order of 20 to 40 nanometers. The stoichiometry and phase of the La-containing crystals have been assigned from characteristic lattice spacings observed by high-resolution transmission electron microscopy and energy dispersive spectroscopy (EDS). EDS spectra show that La

Rodney S. Ruoff; Donald C. Lorents; Bryan Chan; Ripudaman Malhotra; Shekhar Subramoney

1993-01-01

154

The single crystal elastic moduli of neighborite  

Microsoft Academic Search

The adiabatic elastic moduli of a single crystal of Neighborite (NaMgF3perovskite) have been measured at ambient conditions using Brillouin spectroscopy. The adiabatic aggregate (Voight-Reuss-Hill) bulk modulus is K = 75.6 GPa, and shear modulus is = 46.7 GPa. The experimental results show the ratio of linear compressibilities b\\/a = 0.80 for neighborite. These ratios reflect the different amounts of

Yusheng Zhao; Donald J. Weidner

1993-01-01

155

Thermal properties of UO2 single crystal  

NASA Astrophysics Data System (ADS)

For decades UO2 has been the most widely studied actinide oxide because of its technological importance as fuel material for nuclear reactors. Therefore there is a large interest in understanding its thermal, transport and thermodynamic properties. We present recent experimental results for the thermal conductivity and thermal expansion of high quality UO2 single crystal, obtained for different crystallographic directions, and compare with results of molecular dynamics simulations. We will discuss the implications of this study.

Gofryk, K.; Du, S.; Andersson, A. D.; Stanek, C. R.; Schulze, R.; Safarik, D.; Mihaila, B.; Lashley, J. C.; Smith, J. L.

2013-03-01

156

Bridgman growth of paratellurite single crystals  

Microsoft Academic Search

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

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

2004-01-01

157

Single crystal diffraction by synchrotron radiation  

SciTech Connect

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

Kvick, A.

1988-01-01

158

Fatigue In Single Crystal Nickel Superalloys Technical Progress Report.  

National Technical Information Service (NTIS)

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

C. Annis

1992-01-01

159

Analysis of thermoluminescence kinetics of CaF2(Tm) peaks with glow curve deconvolution  

Microsoft Academic Search

The purpose of this study is to achieve detailed information on kinetic parameters of the peaks of a dosimetric material. First and general order kinetic formulas are applied with a computerized deconvolution technique to CaF2(Tm) thermoluminescence glow curves. A comparison is presented between deconvolution kinetic parameters and parameters obtained applying Chen's method.

C. Bacci; P. Bernardini; A. di Domenico; C. Furetta; B. Rispoli

1990-01-01

160

Scanning Force Imaging of Atomic Size Defects on the CaF2\\\\(111\\\\) Surface  

Microsoft Academic Search

Cleaved (111) surfaces on CaF2 were imaged with scanning force microscopy operated in the dynamic mode in ultrahigh vacuum. Imaging the pristine surface reveals an atomic scale contrast with the structure expected for the fluorine terminated surface. We always reproduced the perfect surface periodicity never observing stable defects. However, after exposing the surface to 280 L of oxygen while constantly

M. Reichling; C. Barth

1999-01-01

161

Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers.  

PubMed

Atomistic simulations have shown that the calculated conductivity of nano-polycrystalline BaF2/CaF2 heterolayers is considerably higher than the component bulk materials and we predict that grain-boundary diffusion is the key to fast ionic conductivity in these systems. PMID:12931976

Sayle, Dean C; Doig, James A; Parker, Stephen C; Watson, Graeme W

2003-08-01

162

Electronic shielding by closed shells in CaF2:Yb3+  

Microsoft Academic Search

ENDOR measurements on tetragonal 173Yb3+ sites in CaF2 give a value of (1-gamma?)\\/(1-sigma2) = 75 +\\/- 18, much smaller than theoretical estimates, or previous experimental values. This may indicate sizeable, previously neglected, effects of covalency.

J. M. Baker; W. B. J. Blake

1969-01-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

164

Crystallization and fluorescence properties of Nd 3+-doped transparent oxyfluoride glass ceramics  

Microsoft Academic Search

Nd3+-doped transparent oxyfluoride glass ceramics containing CaF2 were prepared through controlled crystallization of melt-quenched glass. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF2 crystallites with about 13nm in size among the glass matrix after heat-treatment at 650C for 2h. Non-isothermal investigation on CaF2 crystallization kinetics showed that the apparent activation energy Ea and

Daqin Chen; Yuansheng Wang; Yunlong Yu; Zhongjian Hu

2005-01-01

165

Fatigue behavior of a single crystal nickel-base superalloy  

Microsoft Academic Search

While the creep properties of single crystal nickel base superalloys are known to be superior to that of polycrystalline superalloys, the behavior of single crystals in low cycle fatigue (LCF) is less well understood. In this study the low cycle fatigue properties of an experimental single crystal nickel-based superalloy, Rene N4, were examined at 1400 F and 1800 F in

T. P. Gabb; J. Gayda; R. V. Miner

2008-01-01

166

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

167

Optical characterization of organic semiconducting single crystals  

NASA Astrophysics Data System (ADS)

Over the last decade interest in the possibility of "plastic electronics," semi-conducting organic materials that hold the potential for display devices with improved characteristics, has increased. To date, the majority of research has focused on material development and device design. However, if scientists are able to understand the connection between the structural and electronic properties of molecules, they can tailor new compounds with desired physical characteristics. Optical characterization is the first step to understanding the structural properties of materials. This work focuses on characterizing single crystals of two specific molecules: alpha-hexathiophene and 5,6,11,12-tetraphenyl tetracene (rubrene). While there is plenty of information currently available in the literature about alpha-hexathiophene, the resonant Raman experiments I describe in Chapter 3 have uncovered the lowest experimentally-recorded excited electronic levels. I have tentatively identified these states as either a triplet Frenkel exciton or a bound singlet Frenkel exciton. Chapter 4 details how I used Raman, infrared and photoluminescence spectroscopy, as well as computer simulations, to characterize rubrene. Studies of tetracene single crystals helped guide the understanding of the structural and electronic properties of rubrene. Although all molecular crystals have low intermolecular coupling, my analysis showed that rubrene has particularly low coupling, even for a molecular crystal. This result goes against commonly held belief that the best molecules for "plastic electronic" devices should have strong pi-electron overlap. The temperature dependent photoluminescence spectrum clearly reveals emission from free carriers as well as free charge transfer excitons, free Frenkel excitons and deep impurity and defect levels.

Weinberg-Wolf, Jennifer

168

Advanced piezoelectric single crystal based actuators  

Microsoft Academic Search

TRS is developing new actuators based on single crystal piezoelectric materials such as Pb(Zn1\\/3Nb2\\/3)1-xTixO3 (PZN-PT) and Pb(Mg1\\/3Nb2\\/3)x-1TixO3 (PMN-PT) which exhibit very high piezoelectric coefficients (d33 = 1800-2200 pC\\/N) and electromechanical coupling factors (k33 > 0.9), respectively, for a variety of applications, including active vibration damping, active flow control, high precision positioning, ultrasonic motors, deformable mirrors, and adaptive optics. The d32

Xiaoning Jiang; Paul W. Rehrig; Wesley S. Hackenberger; Edward Smith; Shuxiang Dong; Dwight Viehland; Jim Moore Jr.; Brian Patrick

2005-01-01

169

Fabrication of single-crystal diamond microcomponents  

SciTech Connect

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

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

1994-12-12

170

Metallisation of single crystal diamond radiation detectors  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

171

Characterisation of single-crystal mercuric iodide  

NASA Astrophysics Data System (ADS)

The mobility-lifetime product of electrons and holes in single-crystal mercuric iodide for detector applications was measured to be 410-5 and 310-5 cm2/V respectively. The charge carriers were optically induced by a near band gap excitation using a GaP (560nm) light emitting diode. Optical Deep Level Transient Spectrometry measurements of trapping states showed three dominant energy levels at 0.26, 0.8 and 1.4eV. There is little correlation between trapping levels reported in the literature.

Alexiev, D.; Dytlewski, N.; Reinhard, M. I.; Mo, L.

2004-01-01

172

Ultrahigh-quality silicon carbide single crystals  

NASA Astrophysics Data System (ADS)

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 1-10cm-2) and a large density of elementary dislocations (~ 104cm-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.

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

2004-08-01

173

Cutting fluid study for single crystal silicon  

SciTech Connect

An empirical study was conducted to evaluate cutting fluids for Single Point Diamond Turning (SPDT) of single crystal silicon. The pH of distilled waster was adjusted with various additives the examine the effect of pH on cutting operations. Fluids which seemed to promote ductile cutting appeared to increase tool wear as well, an undesirable tradeoff. High Ph sodium hydroxide solutions showed promise for further research, as they yielded the best combination of reduced tool wear and good surface finish in the ductile regime. Negative rake tools were verified to improve the surface finish, but the negative rake tools used in the experiments also showed much higher wear than conventional 0{degree} rake tools. Effects of crystallographic orientation on SPDT, such as star patterns of fracture damage forming near the center of the samples, were observed to decrease with lower feedrates. Silicon chips were observed and photographed, indicative of a ductile materials removal process.

Chargin, D.

1998-05-05

174

Single crystal NMR of high temperature superconductors  

SciTech Connect

Cu NMR studies of the high temperature superconductor YBa2Cu3O(7-delta) (T sub c = 90 K) using a 1 mg single crystal is reported. Three types of measurements were made for both the plane and chain Cu crystallographic sites and with the static magnetic field placed successively along each of the three crystal axes a, b, and c: nuclear magnetic resonance (NMR) lineshapes, spin-lattice relaxation, and transverse relaxation. From these measurements four NMR tensors are deduced: the magnetic shift tensor, the electric field gradient tensor, the spin-lattice relaxation rate tensor, and the transverse relaxation rate tensor. As a preliminary matter, the symmetries of the magnetic shift and electric field gradient tensors were used to assign the two families of NMR lines to their respective crystallographic sites. From an analysis of the electric field gradient tensors it is shown that both the plane and chain Cu have valences Cu(2+), giving a single hold in the Cu atomic d-shell. The spin-lattice relaxation rate and magnetic shift of the plane and chain Cu were analyzed; included were both analyses in which only normal state data were considered, and in which superconducting state measurements of magnetic shifts were considered as well. These analyses show that the plane Cu atom behaves very nearly as a local moment. The chain Cu is probably also in the local moment limit; however, its NMR properties are largely determined by its interaction with oxygen holes in the chain.

Pennington, C.H.

1989-01-01

175

Preparation of ferrite single crystals by new floating zone technique  

Microsoft Academic Search

Single crystals of Ni ferrites and Ni-Zn ferrites having good uniformity were prepared by a new floating zone technique. In the preparation of the Ni-ferrite single crystal the initial molten zone was made from the material having a composition different from that of seed crystal. This made the composition of precipitate from molten zone the same as that of the

T. Akashi; K. Matumi; T. Okada; T. Mizutani

1969-01-01

176

Onset of the optical damage in CaF(2) optics caused by deep-UV lasers.  

PubMed

The exterior sides of calcium fluoride (CaF(2)) outcoupling mirrors are damaged by ArF laser light irradiation with high pulse-energy densities (80 mJ/cm(2)). The damage is generated by a partial alteration of the CaF(2) substrate to calcite. The CaF(2) decomposition is driven by photochemical processes due to the UV light and the presence of water vapor and is supported by elevated temperatures within the laser beam transmitting area. Small filaments act as starting points for the decomposition process, where kerogenous carbon and calcite can occur. PMID:20016623

Bauer, Michael; Bischoff, Martin; Hlsenbusch, Thomas; Matern, Ansgar; Stark, Robert W; Kaiser, Norbert

2009-12-15

177

Ultralow-threshold Raman lasing with CaF2 resonators.  

PubMed

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

Grudinin, Ivan S; Maleki, Lute

2007-01-15

178

Mode Gruneisen Parameters for Single Crystal Al2O3.  

National Technical Information Service (NTIS)

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

D. Gerlich

1969-01-01

179

Experimental dynamic metamorphism of mineral single crystals  

USGS Publications Warehouse

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a-?? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ??? clinoenstatite and w u ??rtzite ??? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO ?? nAl2O3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates. ?? 1993.

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

1993-01-01

180

Windows for HF\\/DF chemical lasers - CaF2 or ZnSe  

Microsoft Academic Search

An investigation of laser-driven phenomena occurring in CaF2 and ZnSe window materials which affect the performance of high energy laser systems at chemical wavelengths is reported. The systems studied comprised an optical cavity, relay tube, beam expander, and output window to the focus. An analysis of the cumulative phaseshifts due to beam defocusing and distortion caused by thermally generated aberrations

C. A. Klein

1981-01-01

181

The measured electron response nonproportionalities of CaF2 , BGO, and LSO  

Microsoft Academic Search

To study the light yield nonproportionality and intrinsic energy resolution of inorganic scintillators, a Compton coincidence technique was previously designed, implemented and benchmarked. This technique provides the ability to accurately measure the electron response of scintillation materials and thus provides an accurate means of studying these characteristics. In this study, the electron responses of two classic scintillators (CaF2(Eu) and Bi4

T. D. Taulbee; B. D. Rooney; W. Mengesha; J. D. Valentine

1997-01-01

182

CaF2 in Enamel Biopsies 6 Weeks and 18 Months after Fluoride Treatment  

Microsoft Academic Search

Fluoride concentrations were studied in enamel biopsies from maxillary central incisors 6 weeks and 18 months after fluoride treatment. In the short-term study biopsies were obtained prior to and after treatment with acidic sodium or ammonium fluoride. The findings showed that large amounts of fluoride were deposited in enamel from NH4F treatment (mean concentration 84,723 ppm), indicating substantial CaF2 formation.

V. Caslavska; P. Gron; R. L. Kent; K. Joshipura; P. F. De Paola

1991-01-01

183

Free-inducation-decay measurements and determination of moments in CaF2  

Microsoft Academic Search

The results of measurements of F19 free-induction-decay (fid) signals in CaF2 are presented. The measurements were performed at 4.2 and 77 K using conventional pulsed-nuclear-magnetic-resonance and zero-time-resolution techniques. The recorded signals spanned four orders of magnitudes and permitted a direct comparison with various theoretical predictions for the asymptotic behavior of the fid signals for long times. A function was constructed,

M. Engelsberg; I. J. Lowe

1974-01-01

184

Effect of CaF2 Content on Rate of Fluoride Release from Filled Resins  

Microsoft Academic Search

Information on the time-dependent release of fluoride from filled resins containing fluoride particles as a function of particle content and solution pH is limited. This study characterized the fluoride ion release from filled resins containing CaF2 particles as a function of filler content and pH. Urethane dimethacrylate and triethylene glycol dimethacrylate resins were used to make filled-resin disks containing 9.09,

K. J. Anusavice; N.-Z. Zhang; C. Shen

2005-01-01

185

Spectroscopy of Yb3+:CaF2 : From isolated centers to clusters  

Microsoft Academic Search

A detailed spectroscopic study of Yb3+:CaF2 is made by using laser selective excitation, low-temperature time-resolved fluorescence, and Raman techniques. Three dominant types of Yb3+ isolated ion centers are identified at very low (0.03at.%) dopant concentration: two of them with cubic and tetragonal symmetries and the third one not clearly identified but likely of trigonal symmetry. Fluorescence decays strongly differ from

V. Petit; P. Camy; J.-L. Doualan; X. Portier; R. Moncorg

2008-01-01

186

Lattice relaxation of highly excited self-trapped excitons in CaF2  

Microsoft Academic Search

We have investigated relaxation in the lattice of CaF2 at 80 K, caused by the electronic excitation of self-trapped excitons. We employed sequential excitation: first an electron pulse to create self-trapped excitons, and second a laser pulse addressed to the electron or the hole. Hole excitation gives rise to stable F centers; these are not generated in significant numbers by

Katsumi Tanimura; Takanori Katoh; Noriaki Itoh

1989-01-01

187

Growth and hydrogenation of epitaxial yttrium switchable mirrors on CaF 2  

Microsoft Academic Search

Rutherford backscattering (RBS) ion channeling measurements and X-ray diffraction experiments are performed to study the epitaxial nature of as-deposited yttrium on CaF2?111? substrates and the effect of hydrogenation on the crystalline quality. The RBS and X-ray results clearly demonstrate the unique epitaxial relation between as-deposited films and the substrate, which is preserved upon loading with hydrogen. X-Ray diffraction reveals: (i)

E. S. Kooij; J. H. Rector; D. G. Nagengast; J. W. J. Kerssemakers; B. Dam; R. Griessen; A. Remhof; H. Zabel

2002-01-01

188

Mechanical properties of single crystal YAg  

SciTech Connect

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

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

2004-08-02

189

Temperature-dependent refractive index of CaF2 and Infrasil 301  

NASA Astrophysics Data System (ADS)

In order to enable high quality lens designs using calcium fluoride (CaF2) and Heraeus Infrasil 301 (Infrasil) for cryogenic operating temperatures, we have measured the absolute refractive index of these two materials as a function of both wavelength and temperature using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center. 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 ?m, while for Infrasil, we cover temperatures ranging from 35 to 300 K and wavelengths from 0.4 to 3.6 ?m. For CaF2, we compare our index measurements to measurements of other investigators. For Infrasil, we compare our measurements to the material manufacturer's data at room temperature and to cryogenic measurements for fused silica from previous investigations including one of our own. Finally, we provide temperature-dependent Sellmeier coefficients based on our measured data to allow accurate interpolation of index to other wavelengths and temperatures.

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

2007-10-01

190

Halide electroadsorption on single crystal surfaces  

SciTech Connect

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

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

1997-07-01

191

Stacking faults in fatigued titanium single crystals  

SciTech Connect

It is generally accepted that the mechanical behavior and interior dislocation substructure of metals and alloys are functions of the stacking fault energies (SFEs). The higher the SFE, the more difficult it is to split a dislocation into two partial dislocations separated by a stacking fault. Whereas materials with high SFE allow easy cross-slip of screw dislocations. Titanium is known to have a high SFE. Even though stacking faults in titanium have been observed experimentally, there is still doubt on them due to the high values of SFE. The purpose of the present study is to obtain further information on stacking faults in fatigued titanium single crystals and to discuss the relation between stacking fault and twinning.

Tan Xiaoli; Gu Haicheng [Xi`an Jiaotong Univ. (China). Research Inst. for Strength of Metals

1995-12-15

192

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

193

High-performance metal-semiconductor-metal InGaN photodetectors using CaF2 as the insulator  

NASA Astrophysics Data System (ADS)

The authors report on the high-performance metal-semiconductor-metal (MSM) photodetectors (PDs) fabricated on high-quality InGaN film by introducing a superwide bandgap calcium fluoride (CaF2) as the insulator. The dark current of the PDs with CaF2 is drastically reduced by six orders of magnitude compared with those without CaF2, resulting in an extremely high discrimination ratio larger than 106 between ultraviolet and visible light. The responsivity at 338 nm is as high as 10.4 A/W biased at 2 V, corresponding to a photocurrent gain around 40. The CaF2 layer behaves as an excellent insulator for the InGaN-based MSM-PDs in dark condition, while it allows the electron injection through the metal/semiconductor interface under ultraviolet illumination, contributing to the photocurrent gain without sacrificing the response time (~ms).

Sang, Liwen; Liao, Meiyong; Koide, Yasuo; Sumiya, Masatomo

2011-03-01

194

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

PubMed

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

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

2011-11-15

195

A GaAsMISFET using an MBE-grown CaF2 gate insulator layer  

Microsoft Academic Search

The CaF2 layer and an undoped GaAs channel layer grown by molecular beam epitaxy (MBE) on a semi-insulating GaAs (100) substrate. The two layers are grown sequentially inside the same MBE chamber to form a clean CaF2-GaAs interface. A self-aligned process using a WSix gate metal is used to fabricate the MISFET. A 1- ?m gate-length FET exhibiting a transconductance

T. Waho; F. Yanagawa

1988-01-01

196

Effect of CaF 2 on densification and properties of hydroxyapatitezirconia composites for biomedical applications  

Microsoft Academic Search

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

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

2002-01-01

197

Simulation of rolling behaviour of cubic oriented al single crystal with crystal plasticity FEM  

Microsoft Academic Search

The crystal plasticity finite element method (CPFEM), which incorporates the crystal plasticity constitutive law into the finite element method, has been used to investigate the rolling processes of the cubic oriented Al single crystal. The developed model has been validated by comparison with the experimental observations. The simulation results have shown that after rolling the crystal predominantly rotates around the

L. Y. Si; C. Lu; N. N. Huynh; A. K. Tieu; X. H. Liu

2008-01-01

198

Ultratough CVD single crystal diamond and three dimensional growth thereof  

DOEpatents

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

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

2009-09-29

199

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

200

Fabrication of polypyrrole nano-arrays in lysozyme single crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

201

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

202

Bonding techniques for single crystal TFT AMLCDs  

NASA Astrophysics Data System (ADS)

Transmissive single crystal AMLCD light valves have recently drawn much attention for application in flat panel displays. The active matrix circuits are fabricated on SIMOX wafers and then transferred to glass. Circuit transfer consists in bonding a CMOS processed SIMOX wafer to a Pyrex glass substrate, thinning the SIMOX wafer and opening the contact pads. The pixel electrodes are made in polysilicon to allow standard CMOS processing. This paper discusses the transparency of the poly electrode and evaluates the potential of anodic bonding and adhesive bonding for circuit transfer. A major challenge for anodic bonding is the protection of the device dielectrics against the high voltages applied during bonding. A test chip was designed to investigate different ways of circumventing breakdown of the dielectrics. A method for adhesive bonding is discussed that assures good uniformity of the thickness of the epoxy layer and avoids the inclusion of air bubbles. It is demonstrated that the epoxies are resistant to the chemicals used for thinning the silicon substrate.

van der Groen, Sonja; Rosmeulen, Maarten; Jansen, Philippe; Deferm, Ludo; Baert, Kris

1996-09-01

203

High pressure synthesis of single crystals of ?-boron  

Microsoft Academic Search

A method of synthesis of single crystals of alfa-boron (?-B) is presented. ?-Boron has been crystallized from a boronplatinum melt at high pressures (611GPa) and high temperatures (12001600C). The method is based on the high-pressure large volume (multi-anvil) press technique. An average size of the as-grown isometric crystals is 6080?m in maximum dimension. A refinement of an accurate crystal structure

Gleb Parakhonskiy; Natalia Dubrovinskaia; Leonid Dubrovinsky; Swastik Mondal; Sander van Smaalen

2011-01-01

204

Anisotropy of Laser-Induced Bulk Damage of Single Crystals  

Microsoft Academic Search

The regularities of laser-induced damage of anisotropic materials, such as LiNbO3 and KDP dielectric single crystals, are experimentally studied. It is revealed that the shape of laser-induced damage in the dielectric crystals depends on the elastic symmetry of crystal and the propagation direction of the laser beam. When the beam propagates along the optic axis of crystals, the figures of

O. Krupych; Ya. Dyachok; I. Smaga; R. Vlokh

2007-01-01

205

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

206

Chemical Solution Routes to Single-Crystal Thin Films  

Microsoft Academic Search

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

F. F. Lange

1996-01-01

207

Investigation of Advanced Processed Single-Crystal Turbine Blade Alloys.  

National Technical Information Service (NTIS)

This investigation studied the influence of thermal processing and microstructure on the mechanical properties of the single-crystal, nickel-based superalloys PWA 1482 and PWA 1484. The objective of the program was to develop an improved single-crystal tu...

B. J. Peters C. M. Biondo D. P. Deluca

1995-01-01

208

Fatigue behavior of a single crystal nickel-base superalloy  

Microsoft Academic Search

Many investigations indicate that high cycle fatigue cracks, in general, initiate at pores, inclusions, and grain boundaries in materials. The fatigue strength limit of a single crystal superalloy increases markedly compared to that of a conventional cast alloy, because the number of pores and inclusions in a single crystal superalloy are less than those of both conventionally cast and directionally

J. H. Zhang; Y. B. Xu; Z. G. Wang; Z. Q. Hu

1995-01-01

209

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

210

Fatigue behavior of a single crystal nickel-base superalloy  

SciTech Connect

Many investigations indicate that high cycle fatigue cracks, in general, initiate at pores, inclusions, and grain boundaries in materials. The fatigue strength limit of a single crystal superalloy increases markedly compared to that of a conventional cast alloy, because the number of pores and inclusions in a single crystal superalloy are less than those of both conventionally cast and directionally solidified superalloys. Also, grain boundaries are eliminated in the single crystal superalloy. The fatigue fracture of a single crystal superalloy usually appears to be brittle. Therefore, it is necessary to study the micro-fracture mechanism. This paper presents an investigation of the fracture characteristics and micro-mechanism of fracture in a single crystal superalloy during high cycle fatigue.

Zhang, J.H.; Xu, Y.B.; Wang, Z.G.; Hu, Z.Q. [Academy of Sciences, Shenyang (China). State Key Lab. for Fatigue and Fracture of Materials

1995-06-15

211

Reshock and release response of aluminum single crystal  

SciTech Connect

Reshock and release experiments were performed on single crystal aluminum along three orientations and on polycrystalline 1050 aluminum with 50 {mu}m grain size at shock stresses of 13 and 21 GPa to investigate the mechanisms for previously observed quasielastic recompression behavior. Particle velocity profiles obtained during reshocking both single crystals and polycrystalline aluminum from initial shock stresses of 13-21 GPa show similar quasielastic recompression behavior. Quasielastic release response is also observed in all single crystals, but the magnitude of the effect is crystal orientation dependent, with [111] and [110] exhibiting more ideal elastic-plastic release for unloading from the shocked state than for the [100] orientation and polycrystalline aluminum. The quasielastic response of 1050 aluminum is intermediate to that of the [100] and [111] orientations. Comparison of the wave profiles obtained for both unloading and reloading of single crystals and polycrystalline 1050 aluminum from shocked states suggests that the observed quasielastic response of polycrystalline aluminum results from the averaging response of single crystals for shock propagation along different orientations, and that the response of 1050 aluminum with large grain boundaries is not significantly different from the results obtained on single crystal aluminum. The yield strength of the single crystals and 1050 aluminum is found to increase with shock stress, which is consistent with previous results [H. Huang and I. R. Asay, J. Appl. Phys. 98, 033524 (2005)].

Huang, H.; Asay, J. R. [Institute for Shock Physics and Department of Physics, Washington State University, Pullman, Washington 99164-2816 (United States)

2007-03-15

212

CaF_2 whispering-gallery-mode-resonator stabilized-narrow-linewidth laser  

NASA Astrophysics Data System (ADS)

A fiber laser is stabilized using a Calcium Fluoride (CaF2) whispering-gallery-mode resonator. It is set up using a semiconductor optical amplifier as a gain medium. The resonator is critically coupled through prisms, and used as a filtering element to suppress the laser linewidth. Using the self-heterodyne beat technique the linewidth is determined to be 13 kHz. This implies an enhancement factor of 10^3 with respect to the passive cavity linewidth. The three-cornered hat method shows a stability of 10^(-11) after 10 \\mu s.

Sprenger, B.; Schwefel, H. G. L.; Lu, Z. H.; Svitlov, S.; Wang, L. J.

2010-08-01

213

CaF2 whispering-gallery-mode-resonator stabilized-narrow-linewidth laser.  

PubMed

A fiber laser is stabilized by introducing a calcium fluoride (CaF(2)) whispering-gallery-mode resonator as a filtering element in a ring cavity. It is set up using a semiconductor optical amplifier as a gain medium. The resonator is critically coupled through prisms, and used as a filtering element to suppress the laser linewidth. A three-cornered-hat method is used and shows a stability of 10(-11) after 10 micros. Using the self-heterodyne beat technique, the linewidth is determined to be 13 kHz. This implies an enhancement factor of 10(3) with respect to the passive cavity linewidth. PMID:20808352

Sprenger, B; Schwefel, H G L; Lu, Z H; Svitlov, S; Wang, L J

2010-09-01

214

Effect of porosity on impedance of CaF2 ceramic  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

215

Neutrino-less double-? decay of Ca48 studied by CaF2(Eu) scintillators  

NASA Astrophysics Data System (ADS)

We searched for the neutrino-less double-? decay(0???) of Ca48 by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q?? value region for the data of 3394 kg day. It gives a lower limit (90% confidence level) of T1/20???>2.71022 year for the half-life of 0??? of Ca48. Combined with our previous data for 1553 kg day [I. Ogawa , Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T1/20???>5.81022 year.

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

2008-11-01

216

Paramagnetic Resonance Spectrum of Manganese in Cubic MgO and CaF2  

Microsoft Academic Search

The paramagnetic resonance spectrum of manganese in cubic MgO and CaF2 has been analyzed at wavelengths of one and three cm. The cubic field splitting in MgO is given by 3a=(+55.9+\\/-0.9)10-4 cm-1. The twofold degenerate level lies lower than the fourfold degenerate level. The hyperfine structure constant is A=(-81.0+\\/-0.2)10-4 cm-1; g=2.0014+\\/-0.0005. The large cubic field splitting and the reduced hyperfine

W. Low

1957-01-01

217

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

2013-03-27

218

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.; Svillano, P.; Lhermite, J.; Descamps, D.; Puglys, A.; Baltuka, A.; Cormier, E.

2013-05-01

219

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

Microsoft Academic Search

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

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

1967-01-01

220

Method for harvesting single crystals from a peritectic melt  

DOEpatents

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

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

1996-08-27

221

Method for harvesting rare earth barium copper oxide single crystals  

DOEpatents

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

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

1996-01-01

222

Method for harvesting single crystals from a peritectic melt  

DOEpatents

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

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

1996-01-01

223

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

Microsoft Academic Search

Self-lubrication wear-resistant CaF2\\/Al2O3 ceramic matrix composite coatings were fabricated on substrates of Al2O3 by laser cladding CaF2Al2O3 mixed powder blends. Compared with laser clad monolithic Al2O3 coatings, the CaF2\\/Al2O3 coating has much superior wear resistance and noticeably lower friction coefficient under dry sliding wear test conditions.

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

2002-01-01

224

Specific ion effects of salt solutions at the CaF2/water interface.  

PubMed

Calcium fluoride is a slightly soluble compound commonly extracted from ores via flotation at elevated pH, where surfactant molecules bind with hydroxylated surface sites. The addition of F-(aq) suppresses surfactant adsorption by replacing these sites. In this paper, we look at the effects of aqueous Cl-, Br-, F-, and SO4(2-) on the water structure at the CaF2/H2O interface at a pH where surface hydroxylation has not yet occurred. Using static and time-resolved vibrational sum-frequency spectroscopy (VSFS), we find that aqueous Cl- and Br- have only electrostatic screening effects on the interface and do not perturb the interfacial water or surface structure. Sulfate, which we find to be strongly attracted to the interface, affects the interfacial water more than Cl- or Br-. This is in contrast to F- ions that directly interact with the surface and alter the water structure and bonding at the CaF2 surface in addition to screening the surface charge. PMID:20423063

Hopkins, Adam J; Schrdle, Simon; Richmond, Geraldine L

2010-07-01

225

Novel CaF(2) nanocomposite with high strength and fluoride ion release.  

PubMed

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF(2) and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF(2) nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF(2) content, or with decreasing pH (p < 0.05). F-release rates at 70-84 days were 1.13 microg/(cm(2) x day) and 0.50 microg/(cm(2) x day) for nanocomposites containing 30% and 20% nano-CaF(2), respectively. They matched the 0.65 microg/(cm(2) x 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 CaF(2) 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

2010-05-03

226

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

227

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

228

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

PubMed

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

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

2010-05-17

229

Epitaxial electrodeposition of freestanding large area single crystal substrates  

SciTech Connect

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

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

2007-06-25

230

Spherical Nb single crystals containerlessly grown by electrostatic levitation  

NASA Astrophysics Data System (ADS)

Spherical Nb (Tm=2750 K) single crystals were grown via containerless electrostatic levitation (ESL). Samples became spherical at melting in levitation and undercooled typically 300-450 K prior to nucleation. As-processed samples were still spherical without any macroscopic shape change by solidification showing a uniform dendritic surface morphology. Crystallographic {111} planes exposed in equilateral triangular shapes on the surface by preferential macroetching and spotty back-reflection Laue patterns confirm the single crystal nature of the ESL-processed Nb samples. No hysteresis in magnetization between zero field and field cooling also implies a clean defect-free condition of the spherical Nb single crystals.

Sung, Y. S.; Takeya, H.; Hirata, K.; Togano, K.

2003-05-01

231

Single crystal Processing and magnetic properties of gadolinium nickel  

SciTech Connect

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

Shreve, Andrew John [Ames Laboratory

2012-11-02

232

Pulse shape discrimination with new single crystal organic scintillators  

NASA Astrophysics Data System (ADS)

Pulse shape discrimination in organic single crystal and liquid scintillators provides a means of identifying fission energy neutrons with high specificity. We present the results of a broad survey of over one hundred single crystal organic scintillators produced from low-temperature solution growth technique. Each crystal was evaluated for light yield and pulse shape discrimination performance. The pulse shape dependence on excitations via a Compton electron from a gamma and a recoil proton from a fast neutron was measured using full waveform digitization. Several groups of compounds were compared in relation to molecular and crystallographic structures, crystal perfection, and the effect of impurities. New prospective materials offering neutron/gamma discrimination comparable or superior to stilbene will be presented. We also report on the growth of large single crystal lithium salicylate and other promising Li compounds which have sensitivity to lower energy neutrons via neutron capture on ^6Li and are separable from other excitations via pulse shape discrimination.

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

2009-10-01

233

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 1200C. 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

234

A new route to grow single-crystal group III-V compound semiconductor nanostructures on non-single-crystal substrates  

Microsoft Academic Search

A new route to grow single-crystal semiconductor nanostructures is reviewed. Unlike conventional epitaxial growth of single-crystal semiconductor films, the proposed route for growing semiconductor nanostructures does not require a single-crystal semiconductor substrate. In the proposed route, instead of using single-crystal semiconductor substrates that are characterized by their long-range atomic order, a non-single-crystal template layer that possesses short-range atomic order prepared

Nobuhiko P. Kobayashi

2007-01-01

235

Linear Compressibilities of Ii-Vi Compound Single Crystals.  

National Technical Information Service (NTIS)

The isothermal linear compressibilities of the II-VI compound single crystals, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, and ZnTe were measured by an optical interferometer. The change in length of the crystals was obtained relative to iron under hydrostatic press...

D. W. Langer R. A. Montalvo

1970-01-01

236

EPR and Optical Absorption Studies of ?-irradiated Pyrene Single Crystals  

Microsoft Academic Search

Pyrene single crystals irradiated with ? rays at room temperature have been investigated by electron paramagnetic resonance and optical absorption experiments. EPR spectra exhibit a triplet characteristic and each line of the triplet shows characteristic features with rotations of the crystals in a magnetic field. From analyses of these spectra the presence of two kinds of hydrogen added pyrene radicals,

Tetsuya Kawakubo

1978-01-01

237

Dislocation Line Direction Determination in Pyrene Single Crystals  

Microsoft Academic Search

A new technique for the unambiguous determination of dislocation line directions in macroscopic single crystals is presented. The technique is based on analysis of the projected directions of the images of the dislocations on synchrotron white beam topographs. Calculation is carried out in a pseudo-cubic axis system which is related to the crystal axis system by a transformation matrix. Final

Ding Yuan; Michael Dudley

1992-01-01

238

Epitaxial Liftoff for Fully Single-Crystal Ferroelectric Thin Films.  

National Technical Information Service (NTIS)

During the period covered by this report we initiated the application of crystal ion slicing to single crystal potassium tantalate and strontium titanate. Transport of ions in matter (TRIM) simulations and ion implantation at 3.8MeV and various dosages we...

R. M. Osgood M. Levy

1999-01-01

239

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

240

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

241

Study of Single Crystals of Metal Solid Solutions.  

National Technical Information Service (NTIS)

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...

J. A. Reising J. P. Doty

1973-01-01

242

Desorption of Oxygen from Virgin CDS Single Crystals.  

National Technical Information Service (NTIS)

Typical desorption data of amu 16 from virgin CdS single crystals is presented for two classes of crystals as determined by their electrical properties. Thermal desorption energies are found in the energy range of 0.87 eV to > with temperatures of maximum...

K. W. Boer R. Schubert C. Wright

1968-01-01

243

Angular Variation of Coercivity in Orthoferrite Single Crystals.  

National Technical Information Service (NTIS)

The coercive force Hc as a function of the angle between the easy axis of magnetization and the external field was studied in orthoferrite single crystals using the vibrating sample technique. (Author)

S. Reich S. Shtrikman D. Treves

1964-01-01

244

Anthracene Fluorescence at Low Temperatures. II. Doped Single Crystals.  

National Technical Information Service (NTIS)

By the addition of dopants to single crystal anthracene it is shown that many of the fluorescence bands additional to exciton emission are due to traces of 2-methylanthracene. Other impurity bands, apparently arising from locally disorientated host molecu...

L. E. Lyons L. J. Warren

1972-01-01

245

Constitutive Modeling of Superalloy Single Crystals with Verification Testing.  

National Technical Information Service (NTIS)

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 e...

E. Jordan K. P. Walker

1985-01-01

246

Planning Study for Preparation of Single Crystal Experiments.  

National Technical Information Service (NTIS)

In order to conceive suitable space experiments with single crystals their properties desired for technical applications must first be considered. By comparing the production possibilities, including their limitations in space and on earth, it is possible...

H. Weiss

1976-01-01

247

Toward, single molecule detection with photonic crystal microcavity biosensors  

Microsoft Academic Search

Time resolved biomolecular binding events were measured using photonic crystal microcavity resonators integrated with microfluidics. The optical field is confined to a volume of 33 times 10-18 liters, which enables monitoring of single binding events

L. W. Mirkarimi; S. Zlatanovic; S. Sigalas; M. A. Bynum; K. Robotti; E. Chow; A. Grot

2006-01-01

248

Aluminium segregation of TiAl during single crystal growth  

SciTech Connect

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

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

1997-09-15

249

Electronic transitions at the CaF2\\/Si(111) interface probed by resonant three-wave mixing spectroscopy  

Microsoft Academic Search

Resonant optical second-harmonic and sum-frequency generation are applied to probe electronic transitions at the Ca-terminated epi- taxial CaF2\\/Si(111) interface. A band gap of 2.4 eV is established for the interface states, a value twice as large as that in bulk Si, but only (1\\/5 of the band gap in CaF2. The experimental three-wave-mixing spectra can be modeled by a two-dimensional

T. F. Heinz; F. J. Himpsel; E. Palange; E. Burstein

1989-01-01

250

Single-crystal piezoceramic actuation for dynamic stall suppression  

Microsoft Academic Search

PZN-8%PT?111? a new single-crystal piezoceramic is explored for its potential to torsionally actuate the existing structure utilizing the induced shear mechanism of piezoceramics. A model of the elastic rotor blade and piezoceramic actuator is developed using the Hamiltons principle and the resulting equations are solved using the finite element method. Numerical results show that the single crystal material is able

D. Thakkar; R. Ganguli

2006-01-01

251

Electron Spin Resonance in an Irradiated Single Crystal of Dimethylglyoxime  

Microsoft Academic Search

The paramagnetic resonance of gamma-irradiated single crystals of dimethylglyoxime has been measured at 23 kMc\\/sec and 9 kMc\\/sec for various orientations of the crystal in the magnetic field. The resonance pattern was found to have a triplet structure caused by coupling to a single N14 nucleus. Both the nuclear coupling and the spectroscopic splitting factor were found to be anisotropic

Ichiro Miyagawa; Walter Gordy

1959-01-01

252

WELDING AND WELD REPAIR OF SINGLE CRYSTAL GAS TURBINE ALLOYS  

Microsoft Academic Search

The cost-effective commercial use of single crystal nickel-based superalloys for land-based turbine engine components such as blades and vanes requires that they can be repair welded to improve as-cast yields or to refurbish worn or failed components after intermediate service intervals. This program addresses this vital need by determining the welding behavior and weldability of single crystal nickel-based superalloys in

J. M. Vitek; S. A. David; S. S. Babu

253

How a silver dendritic mesocrystal converts to a single crystal  

Microsoft Academic Search

In this paper, we demonstrate how a silver dendrite transforms from mesocrystal into single crystal and the stability for a dendritic silver mesocrystal within a Sn\\/AgNO3 galvanic replacement reaction. Our findings provide the direct evidence and visible picture of the transformation from mesocrystal to single crystalline structure and further confirm the particle-mediated crystallization mechanism. At the initial stage of the

Jixiang Fang; Bingjun Ding; Xiaoping Song; Yong Han

2008-01-01

254

Gradient-dependent deformation of two-phase single crystals  

Microsoft Academic Search

In this work, a gradient- and rate-dependent crystallographic formulation is proposed to investigate the macroscopic behaviour of two-phase single crystals. The slip-system-based constitutive formulation relies on strain-gradient concepts to account for the additional strengthening mechanism associated with the deformation gradients within a single crystal with a high volume fraction of dispersed inclusions. The resulting total slip resistance in each active

E. P. Busso; F. T. Meissonnier; N. P. O'Dowd

2000-01-01

255

Synthesis and Single-Crystal Growth of Ca  

SciTech Connect

For the study of the quasi-two-dimensional Mott transition system Ca{sub 2-x}Sr{sub x}RuO{sub 4}, we have succeeded in synthesizing polycrystalline samples and also growing single crystals by a floating-zone method. Details of the preparations for the entire solution range are described. The structural, transport, and magnetic properties of both polycrystalline and single-crystal samples are fully in agreement.

Nakatsuji, Satoru; Maeno, Yoshiteru

2001-01-01

256

Bithermal fatigue of a nickel-base superalloy single crystal  

Microsoft Academic Search

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

Verrilli

1988-01-01

257

Single Crystal Growth of Photorefractive Sillenites.  

National Technical Information Service (NTIS)

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

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

1992-01-01

258

Single-helix crystal in atactic polypropylene  

NASA Astrophysics Data System (ADS)

The conformational arrangement of a locally stereoregular sequence of atactic polypropylene (aPP) was investigated via X-ray diffraction, thermal analysis, and infrared spectroscopy. Since the aPP used was an isotactic-rich sample, the X-ray diffraction pattern showed the typical profile of an ?-iPP (isotactic polypropylene) crystal, indicating that the crystal is constructed from locally stereoregular sequences. Even for a sample with low stereoregularity (meso pentad = 16%), small peaks due to ?-iPP crystals were observed. The melting temperature of aPP was reduced compared with an ?-iPP crystal. This corresponds to a shortening of the lamellar thickness. Helical units from chloroform insoluble and soluble fractions having meso pentads of 0.64 and 0.16, respectively, were composed of 3.5 and 1.2 repeating units, respectively. Such short conformational order was also confirmed by infrared spectroscopy. In general, a conformationally sensitive band is observed over a critical regular sequence (n). For the chloroform soluble fraction, a 977 cm-1 band for n = 5 was observed, but the typical 998 and 841 cm-1 bands for n = 11-12 and 13-15, respectively, were not observed. This signals that the regular conformation consists of 1-2 repeating units. It is concluded that a short conformational order (about 1-2 helical units) can construct the crystalline unit for aPP.

Nakaoki, Takahiko; Fukui, Daisuke

2013-11-01

259

Single Crystal Growth by Laser CVD.  

National Technical Information Service (NTIS)

CO2 gas lasers prove to be a superb heat source for use in various applications. Using the lasers, thin monocrystals with a diameter of less than 1 mm were grown. The processes are discussed for creation of the crystals, including a report on related work...

S. Hayashi

1988-01-01

260

Effect of Stress on CDS Single Crystals.  

National Technical Information Service (NTIS)

The electrical and luminescence properties of CdS crystals, which show the phenomenon of storage, were studied as a function of hydrostatic pressure and uniazial stress. In the excited state, uniaxial stress applied parallel to the c axis resulted in an i...

B. A. Kulp K. A. Gale

1966-01-01

261

Single crystals of single-walled carbon nanotubes formed by self-assembly.  

PubMed

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material. PMID:11292859

Schlittler, R R; Seo, J W; Gimzewski, J K; Durkan, C; Saifullah, M S; Welland, M E

2001-04-05

262

SCREAM I: A single mask, single-crystal silicon, reactive ion etching process for microelectromechanical structures  

Microsoft Academic Search

A single-crystal slhcon, high aspect ratlo, low-temperature process sequence for the fabrlcatlon of suspended rmcroelectromechamcal structures (MEMS) usmg a smgle hthography step and reactwe Ion etching (RIE) IS presented The process IS called SCRJZAM I (single-crystal reactwe etchmg and metalhzatmn) SCREAM I IS a bulk mlcromachmmg process that uses RIE of a s~hcon substrate to fabricate suspended movable smgle-crystal s&on

Kevin A. Shaw; Z. Lisa Zhang; Noel C. MacDonald

1994-01-01

263

Growth of Strontium Titanate Single Crystals from Molten Salts  

Microsoft Academic Search

Single crystals of strontium titanate (SrTiO3) were grown by flux method. The best results were obtained with KF-LiF and KF-K2MoO4 flux systems. Reasonably large single crystals were yielded from the solvent of KF-LiF systems and fine small crystals which were colorless, transparent and flawless were obtained from KF-K2MoO4 systems. The experiments were carried out by slow cooling method, temperature of

Tokuko Sugai; Shuzo Hasegawa; Gisaku Ohara

1968-01-01

264

Hydrothermal growth of carbonate-containing hydroxyapatite single crystals  

Microsoft Academic Search

Single crystals of carbonate-containing hydroxyapatite have been grown hydrothermally by gradually heating with a temperature gradient applied to the vessel, using CaHPO4, H2O and carbon dioxide as dry ice. The optimum conditions to obtain large single crystals are: CaHPO4, 10 g\\/l; final temperature gradient, 33.5C\\/cm; heating rate, 0.005C\\/min; and carbon dioxide, 55 g\\/l. The largest crystal obtained was 12 mm

Atsuo Ito; Satoshi Nakamura; Hideki Aoki; Masaru Akao; Kay Teraoka; Sadao Tsutsumi; Kazuo Onuma; Tetsuya Tateishi

1996-01-01

265

Solution Growth of Rubrene Single Crystals Using Various Organic Solvents  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

266

Spectroscopic Studies of Pulsed-Laser-Induced Damage Sites in Heated CaF2 Crystals  

SciTech Connect

Proceedings contain all papers presented at the 13th Symposium on Optical Materials for High-Powered Lasers, held at the National Institute of Standards and Technology in Boulder, CO, 28 Sept. - 1 Oct. 1998.

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

1999-09-01

267

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

268

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

269

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

270

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals  

SciTech Connect

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

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

2010-11-15

271

Growth and characterization of pure and doped btzs single crystals  

NASA Astrophysics Data System (ADS)

The growth and characterization of pure and doped BTZS single crystals are discussed. In the present study powder X-Ray diffraction data of the grown crystal were recorded using BRUKER D8 Advance powder crystal X-ray diffractometer with 2.2 KW Cu anode ceramic X-ray tube. The various functional groups present in the grown crystals were identified and confirmed by recording the FTIR spectrum using BRUKER IFS-66V spectrophotometer by KBr Pellet Technique in the region 4000 ?? 400 cm The UV - Vis - NIR optical spectra of the crystals were recorded using the VARIAN CARY 5E model spectrophotometer. The degree of dopant inclusion was estimated by using Atomic Absorption Spectroscopy. The SHG efficiencies of the crystals were studied using Nd:YAG Q - switched laser.

Gunasekaran, Sethu; Venkatesan, Padmapriya

2012-05-01

272

Studies of single crystal organic scintillators for neutron detection  

NASA Astrophysics Data System (ADS)

Organic crystal scintillators have long been used for fission energy neutron detection and identification. The gamma/neutron separation techniques, known collectively as pulse shape discrimination (PSD), are based on the relative increase in delayed florescence for neutron excitations in comparison to that of gammas. We have conducted a broad survey of the PSD properties for over one hundred single crystal scintillators produced from solution growth techniques, including Li compounds which have sensitivity to lower energy neutrons via neutron capture on ^6Li. Crystal growth methods utilizing temperature reduction of super-saturated solutions have allowed us to produce large volume (> 100 cm^3) faceted organic crystal scintillators with neutron/gamma PSD comparable or superior to trans-stilbene for a subset of these materials. These results show good progress in overcoming the scalability issues of crystal scintillators for neutron detection. We present a survey of our recent results including mixed crystals of varying stilbene fraction.

Glenn, Andrew; Zaitseva, Natalia; Carman, Leslie; Payne, Stephen; Faust, Michelle; Cherepy, Nerine; Hamel, Sebastien; Newby, Jason

2010-11-01

273

Preparation of bead metal single crystals by electron beam heating  

SciTech Connect

For the fabrication of small metal bead crystals a gas flame is used to melt a wire forming a liquid droplet which solidifies upon cooling into a single crystal metal bead. Due to oxidation under ambient conditions bead crystals can be formed only from noble metals using this method. Here we describe a method how to fabricate bead crystals from a wide variety of metals and metal alloys (Cu, Mo, Ru, Rh, Pd, Ag, Ta, W, Re, Ir, Pt, Au, PtPd, Pd{sub 80}Pt{sub 20}, PtRh, AuAg, and PtIr) by electron beam heating under vacuum conditions. Narrow x-ray diffraction peaks confirm a high crystal quality of the bead crystals.

Voigtlaender, Bert; Linke, Udo; Stollwerk, H.; Brona, J. [Institut fuer Schichten und Grenzflaechen ISG 3 and cni-Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich (Germany); Institut fuer Schichten und Grenzflaechen ISG 3 and cni-Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich, Germany and Institute of Experimental Physics, University of Wroclaw, pl. Maxa Borna 9, PL 50-204 Wroclaw (Poland)

2005-11-15

274

THERMOLUMINESCENCE DOSIMETRY PROPERTIES OF NEW Cu DOPED CaF2 NANOPARTICLES.  

PubMed

Nanoparticles of Cu-doped calcium fluoride were synthesised by using the hydrothermal method. The structure of the prepared nanomaterial was characterised by the X-ray diffraction (XRD) pattern and energy dispersive spectrometer. The particle size of 36 nm was calculated from the XRD data. Its shape and size were also observed by scanning electron microscope. Thermoluminescence (TL) and photoluminescence of the produced phosphor were also considered. The computerised glow curve deconvolution procedure was used to identify the number of glow peaks included in the TL glow curve of the CaF2:Cu nanoparticles. The TL glow curve contains two overlapping glow peaks at ?413 and 451 K. The TL response of this phosphor was studied for different Cu concentrations and the maximum sensitivity was found at 1 mol% of Cu impurity. Other dosimetric characteristics of the synthesised nanophosphor are also presented and discussed. PMID:23765071

Zahedifar, M; Sadeghi, E

2013-06-13

275

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

276

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

2006-05-30

277

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

278

Effect of surface orientation on dissolution rates and topography of CaF2  

NASA Astrophysics Data System (ADS)

This paper reports how during dissolution differences in surface chemistry affect the evolution of topography of CaF2 pellets with a microstructure similar to UO2 spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 h. A NaClO4 (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF2 was used.Measured dissolution rates depend directly on the orientation of the exposed planes. The {1 1 1} is the most stable plane with a dissolution rate of (1.2 0.8) 10-9 mol m-2 s-1, and {1 1 2} the least stable plane with a dissolution rate 33 times faster that {1 1 1}. Surfaces that expose both Ca and F atoms in the same plane dissolve faster. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It is proposed that every surface is characterized by the relative proportions of the three reference planes {1 1 1}, {1 0 0} and {1 1 0}, and by the high energy sites at their interceptions.Based on the different dissolution rates observed we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form while dissolution proceeds leading to an increase of roughness and surface area. This adjustment of the surface suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration when predicting long-term dissolution rates.

Godinho, J. R. A.; Piazolo, S.; Evins, L. Z.

2012-06-01

279

Crystal growth and characterization of L-histidine hydrochloride monohydrate semiorganic nonlinear optical single crystals  

NASA Astrophysics Data System (ADS)

Nearly perfect single crystals of L-histidine hydrochloride monohydrate have been grown from the solution prepared from the mixture of L-histidine and hydrochloric acid using slow evaporation solution growth technique. Single crystal X-ray diffraction analysis, High resolution X-ray diffraction analysis, fourier transform infrared and FT-Raman analyzes were employed for structural characterization. Linear and nonlinear optical properties have been studied by UV-Vis transmission spectrum and Kurtz Perry technique respectively. The refractive index, redox behavior and hardness of the grown crystal have been found by suitable methods. Thermogravimetric, differential thermal analysis were employed to characterize the as-grown crystals. The second harmonic generation conversion efficiency of the grown crystal and other properties show the suitability of the grown crystal for frequency conversion applications.

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

2012-05-01

280

Effect of crystallization conditions on the shape of polymer single crystals: Experimental and theoretical approaches  

NASA Astrophysics Data System (ADS)

A modified system of Mansfield equations with different step propagation rates to the right and left was applied to describe the shape of solution-grown single crystals of long-chain alkanes with asymmetrically curved faces ?ub;110?ub;. Solution of this system of equations and simulation of the shape of single crystals of polyethylene, ?-polyvinylidene fluoride, and polyethylene oxide shows good agreement with the experimental data. Comparison of the simulated shapes and experimental micrographs makes it possible to determine the ratio of the intensity of secondary nucleation to the average propagation rate of the layer as well as the ratio of the rates of lateral steps to the right and left and to calculate the absolute values of the main crystallization parameters when the growth rates of single crystals in certain directions are known. It is shown that the asymmetry of the step propagation rate to the right and left is significant only for crystallization at very small supercoolings.

Shcherbina, M. A.; Chvalun, S. N.; Ungar, G.

2007-07-01

281

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

PubMed

A facile solution process for the fabrication of organic single crystal semiconductor devices which meets the demand for low-cost and large-area fabrication of high performance electronic devices is demonstrated. In this paper, we develop a bottom-up method which enables direct formation of organic semiconductor single crystals at selected locations with desired orientations. Here oriented growth of one-dimensional organic crystals is achieved by using self-assembly of organic molecules as the driving force to align these crystals in patterned regions. Based upon the self-organized organic single crystals, we fabricate organic field effect transistor arrays which exhibit an average field-effect mobility of 1.1?cm(2)V(-1)s(-1). This method can be carried out under ambient atmosphere at room temperature, thus particularly promising for production of future plastic electronics. PMID:22563523

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

2012-05-03

282

Optical Spectroscopy of Single Pentacene Molecules in a Naphthalene Crystal  

Microsoft Academic Search

Dilute mixed molecular crystals of pentacene in naphthalene were prepared by cosublimation of the two compounds. Single pentacene molecules could be detected in the thin platelets by fluorescence excitation spectroscopy. By analyzing the exponential decay of the fluorescence intensity autocorrelation function for a single molecule in the microsecond time regime we could determine the population (k23) and depopulation (k31) rate

Susanne Kummer; Christoph Bruchle; Thomas Basch

1996-01-01

283

Broadband single-polarization guidance in hybrid photonic crystal fibers.  

PubMed

We present hybrid photonic crystal fibers that provide broadband single-polarization guidance based on two different propagation mechanisms, namely, total internal reflection and the photonic bandgap effect. Experimental results demonstrate polarization dependent loss as high as 26.7 dB and the bandwidth of single-polarization behavior over 225 nm. PMID:21263477

Cerqueira S, Arismar; Lona, D G; de Oliveira, I; Hernandez-Figueroa, H E; Fragnito, H L

2011-01-15

284

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

NASA Astrophysics Data System (ADS)

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

Takeyama, Yoko; Ono, Shimpei; Matsumoto, Yuji

2012-08-01

285

Dependence of infrared-to-ultraviolet emission enhancement on Yb3+, Er3+:CaF2 nanoparticle dimension.  

PubMed

In the nanocomplexes with Yb3+, Er(3+)-codoped calcium fluoride (CaF2:Yb3+, Er3+) nanoparticles, the infrared (IR)-to-ultraviolet (UV) upconversion (UC) properties were explored under 980 nm laser diode (LD) excitation. The strong enhancement of UV emission at 407 nm was observed. An UP mechanism of the materials was discussed. PMID:20355611

Zhang, Jisen; Zhang, Liguo; Lv, Shaozhe; Qin, Weiping

2010-03-01

286

Ultrafast time and frequency domain vibrational dynamics of the CaF2\\/H2O interface  

Microsoft Academic Search

The structure of water at the CaF2\\/KOH interface was studied by vibrational sum-frequency-generation (SFG) spectroscopy and ultrafast SFG-Free Induction Decay, suggesting the presence of weakly hydrogen bonded OH at high pH.

Ali Eftekhari-Bafrooei; Satoshi Nihonyanagi; Eric Borguet

2009-01-01

287

Ultrafast time and frequency domain vibrational dynamics of the CaF2/H2O interface  

NASA Astrophysics Data System (ADS)

The structure of water at the CaF2/KOH interface was studied by vibrational sum-frequency-generation (SFG) spectroscopy and ultrafast SFG-Free Induction Decay, suggesting the presence of weakly hydrogen bonded OH at high pH.

Eftekhari-Bafrooei, Ali; Nihonyanagi, Satoshi; Borguet, Eric

288

Morphology and texture evolution of nanostructured CaF2 films on amorphous substrates under oblique incidence flux.  

PubMed

The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200?C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100?C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100?C to [111] at 400?C. In films deposited with an oblique vapour incidence at 100?C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet. PMID:20921590

Gaire, C; Snow, P; Chan, T-L; Yuan, W; Riley, M; Liu, Y; Zhang, S B; Wang, G-C; Lu, T-M

2010-10-05

289

Absorption and Fluorescence of Sm2+ in CaF2, SrF2, and BaF2  

Microsoft Academic Search

The absorption and fluorescence of the Sm2+ ion have been studied for three host lattices, CaF2, SrF2, and BaF2. Measurements of intensity, linewidth, quantum efficiency, and Zeeman splitting are reported. Energy levels belonging to the 4f shell have been identified, and a preliminary analysis of the 4f-->5d transitions is presented.

D. L. Wood; W. Kaiser

1962-01-01

290

Swimming photochromic azobenzene single crystals in triacrylate solution.  

PubMed

Self-motion of a growing single crystal of azobenzene chromophore in triacrylate solution (TA) is investigated in relation to the solid-liquid phase diagram bound by the solidus and liquidus lines. Upon thermal quenching from the isotropic melt to the crystal + liquid gap, various single crystals develop in a manner dependent on concentration and supercooling depth. During the crystal growth, TA solvent is rejected from the growing faceted fronts, enriching with TA in close proximity to the crystal-solution interface. The concentration gradient that formed as the result of TA expulsion induces convective flows in the solution and generates spatial variability of surface tension usually responsible for Marangoni effect. Either or both of these phenomena may have contributed to the observed self-motion including swimming, sinking, and floating of the azobenzene rhomboidal crystal in TA solution. A stationary rhomboidal crystal is also shown to swim upon irradiation with the UV light because of a mechanical torque generated by the trans-cis isomerization. Judging from the sinking or floating behavior of the azobenzene crystal, it may be inferred that the nucleation occurs at the solution-air interface. PMID:20491490

Milam, Kenneth; O'Malley, Garrett; Kim, Namil; Golovaty, Dmitry; Kyu, Thein

2010-06-17

291

Optical and structural properties of chalcone NLO single crystals  

NASA Astrophysics Data System (ADS)

Organic compound (E)-1-(4-methoxyphenyl)-3-(2,3,5-trichlorophenyl)prop-2-en-1-one [MPTCPP] with molecular formula C16H11Cl3O2 was synthesized using Claisen-Schmidt condensation reaction method. 1H NMR spectra was recorded to identify the various functional groups present in the compound and confirm the chemical structure. The single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum study reveals that the crystal is transparent in the entire visible region and the absorption is observed at 364 nm. The Kurtz powder second harmonic generation (SHG) test shows that the MPTCPP is NLO active and its SHG efficiency is three times that of urea. Single crystal XRD study shows that the compound crystallizes in the monoclinic system with a space group Cc. The corresponding lattice parameters of the crystal are a = 28.215(5) , b = 3.9740(4) , c = 16.178(3) and V = 1503.0(4) 3. The micro hardness test was carried out and the work hardening coefficient value (n) of the crystal was found to be 1.48. This indicates that the crystal is hard and is suitable for device application. The thermal study reveals that the thermal stability of the crystal is good.

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

2011-11-01

292

''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

293

Production of Unidirectionally Solidified Columnar Crystal and Single Crystal Superalloy Castings.  

National Technical Information Service (NTIS)

The material selection and casting as well as the properties and heat treatment practices of directionally solidified and single crystal superalloys have been reviewed. The presentation mainly concentrates on the turbine blade castings produced from the n...

J. E. Eklund

1992-01-01

294

Synthesis and Structure Characterization of Forsterite Single Crystal  

NASA Astrophysics Data System (ADS)

Forsterite (Mg2SiO4), the low-pressure polymorph of magnesium orthosilicate, is of great importance in the upper mantle due to its aboundance. Up to now, only powder samples of forsterite can be synthesized due to the difficulty of its crystal growth. Therefore, the exact crystal structure of forsterite is still an open question. The crystal structure of forsterite was firstly studied in 1926 by Brown and Bragg. Numerous experimental investigations have been performed in order to get the structure of the olivine group minerals at ambient conditions and a variety of temperature and pressures by using the advent of the computer, the single crystal diffractometer and the diamond cell. However, there are still considerable uncertaintes regarding the accuracy of its unit-cell parameter values. In this study, we synthesized for the first time high quality single crystals of forsterite using the Quickpress piston-cylinder apparatus. The single crystal of forsterite was synthesized by direct reaction of stoichiometric amounts of MgO and amorphous SiO2 (Alfa Aesar, 99.999%) in the presence of ~10-11 wt% distilled water at 2.0GPa, 1723 K for 12h. A colorless single crystal of Mg2SiO4 with size dimensions 0.160.110.04 mm was selected for single crystal X-ray diffraction analysis. The intensity data were collected with a Rigaku R-AXIS RAPID IP diffractometer by oscillation scans using graphite- monochromated Mo-K?0?6?0?6?7677?0?6?0?6?7699 radiation (?=0.71073 ). Cell refinement and data reduction were accomplished with RAPID AUTO program. The crystal structure was solved by direct methods with the SHELXL crystallographic software package. Single crystal X-ray diffraction analysis shows a crystal structure of orthorhombic space group Pnma (No. 62) with a = 10.2073(11) , b = 5.9863(5) , c = 4.7611(4) and Z = 4. Our new data provides new constraints for theoretical investigations of the physical and chemistry properties and behaviors of forsterite under various pressures.

Wang, C.; Jin, S.; Wang, X.; Liu, X.; Fleet, M. E.; Jin, Z.

2006-12-01

295

Enhancing the Mechanical Properties of Single-Crystal CVD Diamond  

SciTech Connect

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

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

2009-01-01

296

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

297

Molecular dynamics simulation of shock melting of aluminum single crystal  

NASA Astrophysics Data System (ADS)

Molecular dynamics method in conjunction with multi-scale shock technique is employed to study the melting characteristics of aluminum single crystal under dynamic conditions. The simulated results show that a linear relationship exists between the shock wave velocity and particle velocity, in good agreement with the experimental data. Comparing the Lindemann melting curve with the two Hugoniot curves for the solid and liquid phases, the Hugoniot melting is found to begin at 93.6 GPa and end at 140 GPa, which is consistent with the theoretical calculations. The impact of crystal defects on the melting characteristics of aluminum single crystal is also studied, and the results indicate that the pressure and temperature increase slightly for the system experiencing the same dynamic loading due to the crystal defects.

Ju, Yuanyuan; Zhang, Qingming; Gong, Zizheng; Ji, Guangfu; Zhou, Lin

2013-09-01

298

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

299

Doubling microsecond single pulses in a KTP crystal  

SciTech Connect

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

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

2001-07-31

300

Acquisition of Single Crystal Growth and Characterization Equipment  

Microsoft Academic Search

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

M. Brian Maple; Diego A. Zocco

2008-01-01

301

Infrared Optical Properties of Single Crystals of Tellurium  

Microsoft Academic Search

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

Joseph J. Loferski

1954-01-01

302

Thermal properties of single-walled carbon nanotube crystal  

Microsoft Academic Search

In this work, the thermal properties of a single-walled carbon nanotube (SWCNT) crystal are studied. The thermal conductivity of the SWCNT crystal is found to have a linear dependence on temperature in the temperature range from 1.9 K to 100.0 K. In addition, a peak (658 W\\/mK) is found at a temperature of about 100.0 K. The thermal conductivity decreases

Li-Jun Hu; Ji Liu; Zheng Liu; Cai-Yu Qiu; Hai-Qing Zhou; Lian-Feng Sun

2011-01-01

303

Single crystal neutron diffraction study of sodium cyanide  

Microsoft Academic Search

The neutron diffraction pattern of a single crystal of cubic NaCN has been measured at 295K. These data and earlier results for KCN at 180 and 295K have been analyzed in terms of a model which expands the angular distribution of CN? orientations in symmetry-adapted spherical harmonics. From this analysis, the distributions of CN? in these crystals have been derived,

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

1973-01-01

304

Thermal shock cracking of lithium niobate single crystal  

Microsoft Academic Search

The quantitative estimation of failure stress of a lithium niobate (LN) single crystal due to thermal shock was investigated.\\u000a Cylindrical test specimens were used in the thermal shock tests. The thermal stress of an LN test specimen under conditions\\u000a of thermal shock cracking was calculated from a computer program which takes account of the crystal anisotropy, using the\\u000a surface temperature

N. MIYAZAKI; A. HATTORI; H UCHIDA

1997-01-01

305

Single-point diamond turning of DAST crystals  

Microsoft Academic Search

Organic nonlinear optical crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate (DAST) can be used for new optical devices such as high frequency electro-optical sampling wavelength conversion, submillimeter wave generation, and terahertz-wave generation. The crystal is soft, brittle and hygroscopic so that it is very difficult to get optical surfaces by using conventional optical polishing process. This paper deals with single-point diamond turning for getting

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

2004-01-01

306

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

National Technical Information Service (NTIS)

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

M. Fatemi

1990-01-01

307

Crystal growth and characterization of a semiorganic nonlinear optical single crystal of gamma glycine  

NASA Astrophysics Data System (ADS)

Gamma glycine has been successfully synthesized by taking glycine and potassium chloride and single crystals have been grown by solvent evaporation method for the first time. The grown single crystals have been analyzed with XRD, Fourier transform infrared (FTIR), and thermo gravimetric and differential thermal analyses (TG/DTA) measurements. Its mechanical behavior has been assessed by Vickers microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV vis., and found that the crystal is transparent in the region between 240 and 1200 nm. Hence, it may be very much useful for the second harmonic generation (SHG) applications.

Prakash, J. Thomas Joseph; Kumararaman, S.

2008-11-01

308

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

309

Epitaxial Growth of WOx Nanorod on Single Crystal Tungsten Substrate  

NASA Astrophysics Data System (ADS)

Nanorods of substoichiometric tungsten oxide (WOx) were grown on single crystal tungsten substrate. The grown nanorods were investigated with scanning electron micrope and atomic force microscope. WOx nanorods were grown on W(001) in accordance with epitaxial relationship between WO3 crystals and W(001) surface. The results indicate that the WO3 crystals formed at the initial stage act as the nuclei of WOx nanorods. Nanorod growth of certain epitaxial directions can be selectively enhanced by choosing growth methods or choosing suitable crystallographic orientation of substrate surface.

Shingaya, Yoshitaka; Nakayama, Tomonobu

310

Lithium niobate single-crystal and photo-functional device  

SciTech Connect

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

311

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

312

Growth and characterization of single crystal of pentachloropyridine  

NASA Astrophysics Data System (ADS)

Bulk single crystals of pentachloropyridine (PCP) were grown by the Bridgman Stockbarger method. The single crystalline nature of the grown crystals was confirmed using powder X-ray diffraction (XRD) techniques. These were transparent in the 315 2000 nm range. The second harmonic generation (SHG) efficiency of polycrystalline materials using Kurtz powder technique was found to be twice that of the well-known organic nonlinear optical (NLO) material, urea. The mixing behavior of PCP with succinonitrile (SCN) and its effect on SHG and micro-hardness of PCP, along with the physicochemical properties of different compositions of PCP and SCN system were studied in detail. Bulk single crystals of the PCP solid solution containing 0.02 mole fraction of SCN have also been grown using the Bridgman Stockbarger technique.

Rai, R. N.; Varma, K. B. R.

2005-11-01

313

Synthesis and properties of erbium oxide single crystals  

SciTech Connect

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

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

1999-04-01

314

All-glass endless single-mode photonic crystal fibers.  

PubMed

Endless single-mode fibers, which remain single mode over their entire range of guidance, are, to the best of our knowledge, the first reported unique application of photonic crystal fibers. These endless single-mode fibers are made by omitting a single air hole in a periodic array of small air holes in a background silica glass. The feasibility of all-glass endless single-mode photonic crystal fibers where the air holes are replaced by a glass with vanishingly small refractive index contrast relative to silica is first studied theoretically and then demonstrated experimentally. This new all-glass design enables not only ease and consistency of fabrication but also the convenience to be handled and spliced like conventional fibers. PMID:18978880

Dong, Liang; McKay, Hugh A; Fu, Libin

2008-11-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

316

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

317

Electron transport in rubrene single-crystal transistors  

NASA Astrophysics Data System (ADS)

We report a study of impurity effects on the electron transport of rubrene single crystals. A significant improvement of electron carrier mobility up to 0.81 cm2/V s is achieved by performing multiple purifications of single crystals and device aging inside an N2-filled glove box. The hole/electron mobility ratio obtained is in good agreement with the reported theoretical calculation, suggesting that the intrinsic electron transport of organic semiconductors is also exploitable in a manner similar to that of hole transport.

Bisri, Satria Zulkarnaen; Takenobu, Taishi; Takahashi, Tetsuo; Iwasa, Yoshihiro

2010-05-01

318

Advanced piezoelectric single crystal based transducers for naval sonar applications  

Microsoft Academic Search

TRS is developing new transducers based on single crystal piezoelectric materials such as Pb(Mg1\\/3Nb2\\/3)x-1TixO3 (PMN-PT). Single crystal piezoelectrics such as PMN-PT exhibit very high piezoelectric coefficients (d33 ~ 1800 to >2000 pC\\/N) and electromechanical coupling factors (k33 > 0.9), respectively, which may be exploited for improving the performance of broad bandwidth and high frequency sonar. Apart from basic performance, much

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

2005-01-01

319

Energy considerations in crack deflection phenomenon in single crystal silicon  

Microsoft Academic Search

Crack deflection in single-crystal brittle occurs when a crack, propagating on one cleavage plane, chooses, from energy\\u000a considerations, to continue propagating on another cleavage plane. This phenomenon was identified during dynamic crack propagation\\u000a experiments of thin, rectangular [001] single-crystal (SC) silicon specimens subjected to three-point bending (3PB). Specimens\\u000a with long pre-cracks (hence propagating at a low energy and velocity) cleave

Dov Sherman

2006-01-01

320

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

321

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

322

Annealing Effect on Photovoltages of Quartz Single Crystals  

NASA Astrophysics Data System (ADS)

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900C, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994?V at room temperature to 1.551 ?V after treated at 500C, and then increase up to 9.8 ?V after annealed at 900C. The inner mechanism of the present photovoltaic response and surface morphologies is discussed.

Tian, Lu; Zhao, Song-Qing; Zhao, Kun

2010-12-01

323

How a silver dendritic mesocrystal converts to a single crystal  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate how a silver dendrite transforms from mesocrystal into single crystal and the stability for a dendritic silver mesocrystal within a Sn/AgNO3 galvanic replacement reaction. Our findings provide the direct evidence and visible picture of the transformation from mesocrystal to single crystalline structure and further confirm the particle-mediated crystallization mechanism. At the initial stage of the transformation, there is a crystallographic fusion process, dominated by oriented attachment mechanism. Ostwald ripening also plays an important role in forming smooth surface and regular shape of the final nanocrystal.

Fang, Jixiang; Ding, Bingjun; Song, Xiaoping; Han, Yong

2008-04-01

324

How a silver dendritic mesocrystal converts to a single crystal  

SciTech Connect

In this paper, we demonstrate how a silver dendrite transforms from mesocrystal into single crystal and the stability for a dendritic silver mesocrystal within a Sn/AgNO3 galvanic replacement reaction. Our findings provide the direct evidence and visible picture of the transformation from mesocrystal to single crystalline structure and further confirm the particle-mediated crystallization mechanism. At the initial stage of the transformation, there is a crystallographic fusion process, dominated by oriented attachment mechanism. Ostwald ripening also plays an important role in forming smooth surface and regular shape of the final nanocrystal.

Fang, J.; Ding, B.; Song, X.; Han, Y.

2008-05-02

325

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

326

Nanomechanical resonant structures in single-crystal diamond  

NASA Astrophysics Data System (ADS)

With its host of outstanding material properties, single-crystal diamond is an attractive material for nanomechanical systems. Here, the mechanical resonance characteristics of freestanding, single-crystal diamond nanobeams fabricated by an angled-etching methodology are reported. Resonance frequencies displayed evidence of significant compressive stress in doubly clamped diamond nanobeams, while cantilever resonance modes followed the expected inverse-length-squared trend. Q-factors on the order of 104 were recorded in high vacuum. Results presented here represent initial groundwork for future diamond-based nanomechanical systems which may be applied in both classical and quantum applications.

Burek, Michael J.; Ramos, Daniel; Patel, Parth; Frank, Ian W.; Lon?ar, Marko

2013-09-01

327

Preparation of single-crystal copper ferrite nanorods and nanodisks  

SciTech Connect

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

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

2005-06-15

328

Single crystal piezoelectric composite transducers for ultrasound NDE applications  

NASA Astrophysics Data System (ADS)

Single crystal piezoelectric composite transducers including 75 MHz PC-MUT (piezoelectric composite micromachined ultrasound transducers), diced 10 MHz and 15 MHz 1-3 composite transducers were successfully demonstrated with broad bandwidth and high sensitivity. In this paper, the design, fabrication and characterization of composite transducers are reported. C-scan experiments for SiC ceramic samples were performed using these composite transducers as well as some commercial NDE transducers. The results suggest that significant improvements in resolution and penetration depth can be achieved in C-scan NDE imaging using single crystal composite broadband transducers.

Jiang, Xiaoning; Snook, Kevin; Walker, Thomas; Portune, Andrew; Haber, Richard; Geng, Xuecang; Welter, John; Hackenberger, Wesley S.

2008-04-01

329

Structural and optical properties of a new chalcone single crystal  

NASA Astrophysics Data System (ADS)

A new nonlinear optical material 1-(4-methylthiophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one with molecular formula C17H16O2S was synthesized by using the ClaisenSchmidt condensation reaction method. The Various functional groups present in the compound were identified using recorded FT-IR spectrum. The crystal growth parameters have been studied using solubility test and acetone is found to be a very good solvent for the crystal growth at an ambient temperature. The transparent high quality single crystals up to a size of 2622 mm3 were grown using the slow evaporation solution growth technique. UVvisible study was carried out and the spectrum reveals that the crystal is transparent in the entire visible region and absorptive in the UV region. The refractive index is determined using Brewster's angle method. The optical energy band gap of the material is measured using Tauc's plot and the direct method. The single crystal XRD of MMPP crystal shows the following cell parameters: a=5.9626(2) , b=15.3022(6) , c=16.0385(7) , ?=?=?=90, volume=1463.37(10) 3 with a space group of Pna21. The compound MMPP exhibits optical nonlinearity (NLO) and its second order NLO efficiency is 3.15 times to that of urea. The effect of functional groups OCH3 and SCH3 on the non-linearity as well as the structural property of the compound has been discussed. The crystal is thermally stable. High NLO efficiency, good thermal stability, good transparency and ability to grow as a high quality single crystal make this material very attractive for opto-electronic applications.

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

2012-09-01

330

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

Microsoft Academic Search

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

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

2003-01-01

331

Growth and some properties of large praseodymium pentaphosphate single crystals  

SciTech Connect

By means of a high-temperature solution-seeded method, praseodymium pentaphosphate (PrPP) single crystals have been grown directly by using Pr{sub 6}O{sub 11} and H{sub 3}PO{sub 4} as raw materials. The dimension of a PrPP single crystal even reaches as large as 72 {times} 22 {times} 13 mm. Its morphology, XRD, and specific heat data are all determined. In addition, the Raman spectra of PrPP, LaP{sub 5}O{sub 14} (LaPP), and Pr{sub x}La{sub 1-x}P{sub 5}O{sub 14} (PrLaPP) crystal series are also reported in this paper. The phonon soft modes of PrPP crystal corresponding to A{sub g}-B{sub 2g} and B{sub g}-B{sub 3g} have been observed in two geometrical arrangements, Z(YZ)X and Z(XZ)Y, respectively. It is shown that the frequencies, intensities, and peak shapes change evidently with temperature. On the basis of the changes of the soft modes with the temperature, the temperature at which the C{sub 2h}-D{sub 2h} ferroelastic phase transition of PrPP crystal takes place can be deduced. Accordingly, the ferroelastic phase-transition temperature of PrPP crystal is obtained, i.e., 137 {plus minus} 1{degree}C.

Li, Lixia; Wang, Jiyang; Yang, Zhaohe; Jiang, Huizhu; Liu, Yaogang (Shandong Univ., Jinan (China))

1989-09-07

332

Single-point diamond turning of DAST crystals  

NASA Astrophysics Data System (ADS)

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

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

2004-01-01

333

Localization of Deformation in Copper Single Crystals During Explosive Collapse  

Microsoft Academic Search

It is established that high-rate axisymmetric loading of single crystals by the method of explosive collapse of a hollow thick-walled cylinder causes deformation that involves all active close-packed slip systems. The spatial distribution of macroscopic sites of strain localization is determined by the crystallography of the active systems in single-crystalline samples. The established correlation between the observed shear bands in

2003-01-01

334

Single Polarizer Liquid Crystal Display Mode with Fast Response  

Microsoft Academic Search

We propose a single polarizer liquid crystal display (LCD) with a fast response that was designed using a polarization-dependent microlens array fabricated by the planarization of a curved lens surface with a liquid crystalline polymer. The single polarizer LCD is operated by the polarization-dependent focusing properties of a microlens consisting of a circular stop-mask and complementary open mask. Fast response

Young Wook Kim; Jiwon Jeong; Se Hyun Lee; Jae-Hoon Kim; Chang-Jae Yu

2011-01-01

335

Growth and spectroscopic characteristics of Yb:LPS single crystal  

NASA Astrophysics Data System (ADS)

For the first time, a high optical quality Yb3+-doped lutetium pyrosilicate laser crystal Lu2Si2O7 (LPS) was grown by the Czochralski (Cz) method. The segregation coefficient of ytterbium ion in Yb:LPS crystal detected by the inductively coupled plasma atomic emission spectrometer (ICP-AES) method is equal to 0.847. X-ray powder diffraction result confirms the C2/m phase monoclinic space group of the grown crystal and the peaks corresponding to different phases were indexed. The absorption and fluorescence spectra, as well as fluorescence decay lifetime of Yb3+ ion in LPS have been investigated. The absorption and fluorescence cross-sections of the transitions 2F7/2?2F5/2 of Yb3+ ion in LPS crystal have been determined. The advantages of the Yb:LPS crystal including high crystal quality, quasi-four-level laser operating scheme, high absorption cross-sections (1.3310-20 cm2) and particularly broad emission bandwidth (62 nm) indicated that the Yb:LPS crystal seemed to be a promising candidate used as compact, efficient thin chip lasers when LD is pumped at 940 and 980 nm due to its low-symmetry monoclinic structure and single crystallographic site.

Zheng, Lihe; Zhao, Guangjun; Yan, Chengfeng; Yao, Gang; Xu, Xiaodong; Su, Liangbi; Xu, Jun

2007-06-01

336

Growth of hafnium dioxide-based single crystals  

SciTech Connect

This paper considers the induction melting of hafnium dioxide with rare earth oxide mixtures, and studies defects in resulting hafnium dioxide single crystals stabilized by the oxides of scandium, yttrium, neodymium, gadolinium, terbium, erbium, and ytterbium at concentrations between 1 and 33 mole %. Crystallization of solid solutions occurs in the systems HfO/sub 2/Ln/sub 2/O/sub 3/. For the HfO/sub 2/-Er/sub 2/O/sub 3/ system, single crystals grow at 11-33 mole %, for HfO/sub 2/-Tb/sub 2/O/sub 3/ at 10-20 mole % and for HfO/sub 3/Sc/sub 2/O/sub 3/ (Nd/sub 2/O/sub 3/) at 10 mole % rare-earth oxide.

Voronov, V.V.; Lavrishchev, S.V.; Markov, N.I.; Miftyakhetdinova, N.R.; Osiko, V.V.; Tatarintsev, V.M.; Zufarov, M.A.

1986-03-01

337

Low temperature magnetic transitions of single crystal HoBi  

NASA Astrophysics Data System (ADS)

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.; Suderow, H.; Vieira, S.; Nemes, N. M.; Garca-Hernndez, M.; Bud'ko, S. L.; Canfield, P. C.

2013-10-01

338

Studies of the Vaporization Mechanism of Gallium Arsenide Single Crystals  

Microsoft Academic Search

The kinetics of vaporization of gallium arsenide single crystals into vacuum have been investigated using microbalance and mass spectrometric techniques in the temperature range 700900 C. Although gallium arsenide vaporized incongruently to yield liquid gallium and arsenic vapor molecules, initial steady state evaporation rates can be obtained in the temperature range of study. The total evaporation rates and the activation

C. Y. Lou; G. A. Somorjai

1971-01-01

339

Single crystal silicon as a low-temperature structural material  

Microsoft Academic Search

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

P. R. Roach

1984-01-01

340

Ductile-regime turning mechanism of single-crystal silicon  

Microsoft Academic Search

Diamond turning of single-crystal silicon was carried out along all the crystallographic directions on the (001) and (111) planes at depths of cut of 100 nm and 1 ?m, and then the mechanism involved in ductile-regime turning was studied. Pitting damage occurred along certain specific crystallographic orientations. The crystallographic orientation dependence of the surface features also changed with the depth

Takayuki Shibata; Shigeru Fujii; Eiji Makino; Masayuki Ikeda

1996-01-01

341

Mixed valence of Sm on metal single-crystal surfaces  

SciTech Connect

Results of a photoemission study of Sm on a Cu(100) single crystal surface are reported. From the binding energy of the Sm 4f levels it is concluded that the mixed valence of Sm on Cu(100) is of a heterogeneous nature. It is suggested that this conclusion also applies to Al(111) and Al(100).

Andersen, J.N.; Chorkendorff, I.; Onsgaard, J.; Ghijsen, J.; Johnson, R.L.; Grey, F.

1988-03-15

342

Piezoelectric and Elastic Properties of Lithium Niobate Single Crystals  

Microsoft Academic Search

Piezoelectric and elastic constants of lithium niobate single crystal were measured in the temperature range between 20C and 200C. These constants were obtained by measuring the resonant and antiresonant frequencies of the length-extensional mode of bars with various orientations. The measured constants are all of the piezoelectric strain constants and the dielectric constants and a part of the elastic compliances,

Tomoaki Yamada; Nobukazu Niizeki; Hiroo Toyoda

1967-01-01

343

Phase Transition of Excited States of a Pyrene Single Crystal  

Microsoft Academic Search

Luminescence decay time and quantum yield of a pyrene single crystal are observed by a pulse method between 40-300 k. The temperature dependence on the intrinsic life time of emissions shows a peculiar character. The abrupt change of the analyzed intrinsic life time corresponds to the critical temperature of the phase transition. The mechanism of the phase transition is attributed

Masao Tomura; Tadaoki Mitani; Masaaki Tomura

1992-01-01

344

Growth of large single crystals of MgO.  

National Technical Information Service (NTIS)

The progressive identification of new high-technology applications and requirements for MgO single crystals in the commercial realm, as well as in DOE and other government-agency project areas, has resulted in an increased demand and international market ...

L. A. Boatner M. Urbanik

1997-01-01

345

Dielectric parameters of KDP single crystals added with urea  

Microsoft Academic Search

Potassium dihydrogen orthophosphate (KDP) having superior nonlinear optical properties has been exploited for variety of applications. We have grown KDP single crystals added with urea by the slow evaporation method from aqueous solutions. Dielectric measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 313 to 423K by the conventional parallel plate capacitor

S. Goma; C. M. Padma; C. K. Mahadevan

2006-01-01

346

MAGNETIZATION AND ELECTRICAL RESISTIVITY OF GADOLINIUM SINGLE CRYSTALS  

Microsoft Academic Search

The magnetic moment of single-crystal Gd was measured in fields from 0 ; to 18 kOe along the (0001), (1010), and (1120) directions at temperatures from ; 1.4 to 900 deg K. Small anisotropy was observed below the Curie temperature and ; the easy direction of magnetization was found to be a function of temperature. ; The absolute saturation magnetic

H. E. Nigh; S. Legvold; F. H. Spedding

1963-01-01

347

Alloy Design for Nickel-Base Super Alloy Single Crystals.  

National Technical Information Service (NTIS)

The purpose of this study is to develop high creep strength Nickel-base superalloys suitable for single crystal. A computer-aided alloy design system previously developed in NRIM is applied for this purpose. Ten alloys designed contained 5 - 10 Cr, 8 - 19...

T. Yamagata

1984-01-01

348

Anisotropy of Nickel-Base Superalloy Single Crystals.  

National Technical Information Service (NTIS)

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

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

1980-01-01

349

Chromatography in a single metal-organic framework (MOF) crystal.  

PubMed

Millimeter-sized single MOF-5 crystals are used as "chromatographic columns" to effectively separate mixtures of organic dyes. Remarkably, owing to the nanoscopic pore dimensions and the molecular-level interactions between the migrating molecules and the MOF scaffold, the separations occur over a distance of only a few hundred micrometers which is unambiguously confirmed by fluorescence confocal microscopy. PMID:21038922

Han, Shuangbing; Wei, Yanhu; Valente, Cory; Lagzi, Istvn; Gassensmith, Jeremiah J; Coskun, Ali; Stoddart, J Fraser; Grzybowski, Bartosz A

2010-11-01

350

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

351

Grinding of Single-Crystal Silicon Using a Microvibration Device  

Microsoft Academic Search

This paper presents experimental results of grinding of single-crystal silicon using a microvibration device and a diamond grindingwheel. Samples were cut from (100) silicon. The grinding direction was parallel to the [110] direction of (100) silicon. These samples were ground under the same grinding conditions but with different vibration directions, frequencies, and\\/or amplitudes. The surface roughness and the surface texture

Z. W. Zhong; Z. Y. Rui

2005-01-01

352

Ultrabroadband single crystal composite transducers for underwater ultrasound  

Microsoft Academic Search

Through the use of complex piezoelectric structures, it is possible to obtain resonant harmonics not observed in the usual odd- harmonic response of a conventional structure. When combined with inherently broadband components, such as composites made with PMN- PT single crystal material, this permits the realisation of ultrabroadband devices. In the work reported here, results from modelling indicate that a

S. Cochran; M. Parker; P. Marin-Franch

2005-01-01

353

Transient Oxidation of Single Crystal NiAl+Zr.  

National Technical Information Service (NTIS)

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

J. K. Doychak

1983-01-01

354

Dissipation in an ultrathin superconducting single-crystal Pb nanobridge  

Microsoft Academic Search

The transport property of a superconducting Pb nanobridge, which is carved by focus ion beam technique from an atomically flat single-crystal Pb thin film grown on Si(111) substrate, is investigated. Below the superconducting transition temperature TC, the nanobridge exhibits a series of sharp voltage steps as a function of current. The multiple voltage steps are interpreted as a consequence of

Jian Wang; Xu-Cun Ma; Yun Qi; Shuai-Hua Ji; Ying-Shuang Fu; Li Lu; Ai-Zi Jin; Chang-Zhi Gu; X. C. Xie; Ming-Liang Tian; Jin-Feng Jia; Qi-Kun Xue

2009-01-01

355

Magnetic Properties of Lattice Imperfections in Alkali Halide Single Crystals  

Microsoft Academic Search

Using a torque magnetometer, experimental results are reported on some new magnetic properties in high-purity, optical-quality single crystals of lithium fluoride, potassium chloride, and sodium chloride. Since the torque observations are not produced by the gross diamagnetism of these salts, the magnetic centers may be along dislocations because the magnetic susceptibility is observed to possess uniaxial anisotropy. Soft x irradiation

T. W. Adair; E. J. Sharp; C. F. Squire

1966-01-01

356

Deformation behaviour of aluminium single crystals in ultraprecision diamond turning  

Microsoft Academic Search

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

S. To; W. B. Lee

2001-01-01

357

Low-pressure plasma-sprayed ZrO 2CaF 2 composite coating for high temperature tribological applications  

Microsoft Academic Search

The microstructure and tribological behavior of low-pressure plasma-sprayed (LPPS) ZrO2CaF2 composite coatings were studied. Optimum spray parameters were obtained to produce a less porous and strongly adherent ZrO2CaF2 composite through carefully selecting the powder feed rate, primary gas pressure and spraying distance. The as-sprayed composite coating exhibited a typical lamellar structure of ZrO2 and CaF2 constituents, with a lot of

J. H. Ouyang; S. Sasaki; K. Umeda

2001-01-01

358

Growth of large single crystals of MgO  

SciTech Connect

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

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

1997-06-12

359

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

PubMed

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

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

2013-05-02

360

Dose response of CaF2:Tm to charged particles of different LET.  

PubMed

Thermoluminescent dosimeters are well established for performing calibrations in radiotherapy and for monitoring dose to personnel exposed to low linear energy transfer (LET) ionizing radiation. Patients undergoing light ion therapy and astronauts engaged in space flight are, however, exposed to radiation fields consisting of a mix of low- and high-LET charged particles. In this study, glow curves from CaF2:Tm chips were examined after exposure to various electron and ion beams. The annealing and readout procedures for these chips were optimized for these beams. After a 10 min prereadout annealing at 100 degrees C, the optimized glow curve samples the light output between 95 and 335 degrees C with a heating rate of 2 degrees C/s. The ratio of the integral of the glow curve under peaks 4-6 to the integral under peak 3 was approximately 0.9 for electrons, 1.0 for entrance protons, 1.6 for peak protons, and 2.2 for entrance carbon, silicon, and iron ions. The integral light output per unit dose in water for the iron exposures was about half as much as for the electron exposures. The peak-area-ratio can be used to determine a dose response factor for different LET radiations. PMID:19746804

Moyers, M F; Nelson, G A

2009-08-01

361

Electronic states of pyrene single crystal and of its single molecule inserted in a molecular vessel of cyclodextrin  

NASA Astrophysics Data System (ADS)

Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The absorption spectra of the single crystal have been transformed from the reflection spectra between 2.5 and 6.5eV at 2, 77K and room temperature. The dry powder of ?-cyclodextrin including pyrene single molecule were prepared in vacuum to investigate the electronic states of the isolated molecule. The absorption spectra of the single molecule show similar spectra to those of the single crystal. The pyrene molecule keeps its electronic character even in the single crystal.

Takahashi, Nobuaki; Gombojav, Bold; Yoshinari, Takehisa; Nagasaka, Shin-Ichiro; Takahashi, Yoshio; Yamamoto, Aishi; Goto, Takenari; Kasuya, Atsuo

2004-10-01

362

Single crystal-like Si patterns for photonic crystal color filters.  

PubMed

A novel fabrication method for a two-dimensional photonic crystal color filter based on guided mode resonance is proposed. An amorphous silicon layer deposited through the low-temperature plasma enhanced chemical vapor deposition (PECVD) process is patterned into two-dimensional structures using low-cost nanoimprint lithography. It is then effectively crystallized using multi-shot excimer laser annealing at low energy. We have demonstrated analytically and experimentally that single crystal-like silicon patterns on a glass substrate can offer high-efficiency photonic crystal color filters for reflective display applications. The highly crystallized silicon patterning scheme presented here may be very attractive for a variety of devices requiring high carrier mobility and high optical efficiency. PMID:21343641

Cho, Eun-Hyoung; Kim, Hae-Sung; Sohn, Jin-Seung; Moon, Chang-Youl; Park, No-Cheol; Park, Young-Pil

2011-02-22

363

Solid mechanics and material strength studies on the melt growth of bulk single crystals  

Microsoft Academic Search

Microdefects such as dislocations and macrocracking should be controlled during the crystal growth process to obtain high-quality bulk single crystals. Solid mechanics and material strength studies on the single crystals are of importance to solve the problems related to the generation and multiplication of dislocations and the cracking of single crystals. The present paper reviews such research activities that comprise

Noriyuki Miyazaki

2007-01-01

364

Method for Growing Large CdS and ZnS Single Crystals  

Microsoft Academic Search

A new technique for growing single crystals of CdS and ZnS has been devised in which single crystals up to 115 g in weight are obtained. The conversion of sphalerite into wurtzite and vice versa is described. The growth mechanism of the single ZnS crystals is described and compared with that for CdS crystals previously reported.

L. C. Greene; D. C. Reynolds; S. J. Czyzak; W. M. Baker

1958-01-01

365

GROWTH OF SINGLE CRYSTALS OF INCONGRUENTLY MELTING YTTRIUM IRON GARNET BY FLAME FUSION PROCESS  

Microsoft Academic Search

Single crystals of yttrium iron garnet (YFeO) were ; grown using the flame fusion process, even though the compcund is reported to ; melt incongruently. The growth of these single crystals involves a mechanism ; different from that which has been proposed for the growth of single crystals of ; incongruently melting mullite. Crystal boules were grown at varying linear

R. G. Rudness; R. W. Kebler

1960-01-01

366

White light generation in Dy(3+)-doped oxyfluoride glass and transparent glass-ceramics containing CaF2 nanocrystals.  

PubMed

The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram. PMID:21368998

Babu, P; Jang, Kyoung Hyuk; Rao, Ch Srinivasa; Shi, Liang; Jayasankar, C K; Lavn, Vctor; Seo, Hyo Jin

2011-01-31

367

Progressive changes in surface structure and electronic properties on Si(001) surface by CaF2 adsorption  

NASA Astrophysics Data System (ADS)

Ab initio calculations, based on pseudopotentials and density functional theory, have been performed to investigate the atomic geometry and electronic structures of calcium fluoride (CaF2) on the Si(001) surface. We have considered the experimentally observed (21) and (31) reconstructions with different bonding configurations of the CaF2 molecule on the Si(001) surface. Our total energy calculations suggest that the (31) structure is slightly more preferable than the (21). The key structural parameters and electronic surface properties of their most stable structures have been discussed. In contrast to the experimental results, the most stable structures contain an appreciable bonding nature between the surface Si and F atoms, however, no real bonding between Si and Ca atoms is indicated.

Alzahrani, A. Z.; Usanmaz, D.

2011-06-01

368

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

369

Generation of ultrashort 25-?J pulses at 200 nm by dual broadband frequency doubling with a thin KBe2BO3F2 crystal.  

PubMed

Ultrashort pulses with a 25-?J output energy were generated at 200 nm by dual broadband frequency doubling with a thin KBe(2)BO(3)F(2) (KBBF) crystal at 1 kHz as the fourth harmonic of a high power Ti:sapphire laser. The spectrum was broadened to a spectral width of 2.25 nm. The pulse duration of 56 fs was measured by single-shot autocorrelation with two-photon fluorescence from self-trapped excitons in a CaF(2) crystal. PMID:22714434

Zhou, Chun; Kanai, Teruto; Wang, Xiaoyang; Zhu, Yong; Chen, Chuangtian; Watanabe, Shuntaro

2012-06-18

370

Temperature dependence of the elastic moduli and damping for polycrystalline LiF22% CaF 2 eutectic salt  

Microsoft Academic Search

The Young's and shear moduli and damping were measured for as-cast polycrystalline LiF-22 (mol%) CaF2 eutectic specimens as a function of temperature using the piezoelectric ultrasonic composite oscillator technique (PUCOT). The shear modulus decreased with increasing temperature from about 40 GPa at 295 K to about 30 GPa at 1000 K, while the Young's modulus decreased from about 115 GPa

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

1991-01-01

371

Symmetry of spatial-dispersion-induced birefringence and its implications for CaF2 ultraviolet optics  

Microsoft Academic Search

The discovery of a significant spatial-dispersion-induced bire- fringence (intrinsic birefringence) in CaF2 at ultraviolet wavelengths has had a major impact on the design of 157 nm lithography systems, requir- ing complete redesign of the optics to take account of the imaging aber- rations resulting from the birefringence and the accompanying index an- isotropy. This intrinsic birefringence phenomena results from a

John H. Burnett; Zachary H. Levine; Eric L. Shirley; John H. Bruning

2002-01-01

372

Femtosecond time-resolved spectroscopy of the formation of self-trapped excitons in CaF2  

Microsoft Academic Search

Self-trapped excitons (STE's) in CaF2 are formed via two distinct processes after band-gap excitation by femtosecond light pulses at low temperatures; the fast process terminates within a few ps after excitation, and the slow process that follows the former lasts over 20 ps. The fast formation of STE's is associated with the decay of the precursor, which shows a broad

Katsumi Tanimura

2001-01-01

373

Influence of Na-related defects on DUV nonlinear absorption in CaF2: nanosecond versus femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

The influence of Na stabilized F and M centers on the DUV absorption behavior of CaF2 is comparatively studied for nanosecond and femtosecond laser pulses by in-situ transmission and laser induced fluorescence measurements. For 193 nm nanosecond pulses the steady state transmission of ArF laser pulses through CaF2 is measured in dependence on the incident fluence H <= 10 mJ cm-2 pulse-1. The related absorption coefficients ?st(H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients ?eff and ?eff, respectively. The ?eff and ?eff values increase with the Na content of the CaF2 samples as identified by the fluorescence of Na related MNa centers at 740 nm. This relation is simulated by a complex rate equation model describing the ArF laser induced MNa generation and annealing. MNa generation starts with intrinsic 2-photon absorption in CaF2 yielding self-trapped excitons (STE). These pairs of F and H centers can separate upon thermal activation and the F centers combine with FNa to form MNa centers. MNa annealing occurs by its photo dissociation into a pair of F and FNa centers. Comparative transmission measurements with DUV femtosecond pulses are done using the fourth harmonic of a Ti:Safs- laser at 197 nm. The resulting ?eff values virtually show no dependence on the MNa center concentration. Furthermore, the absolute ?eff values are lower by a factor of three compared to those obtained for nanosecond pulses. This is explained by additional two-step absorption for nanosecond pulses after formation of self-trapped excitons (STE).

Mhlig, Ch.; Stafast, H.; Triebel, W.; Zeuner, Th.; Karras, Ch.; Letz, M.

2009-10-01

374

Formation of Eu 2+ and Eu 3+ centers in synthesis of CaF 2 :Eu luminophores  

Microsoft Academic Search

We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+\\/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the\\u000a samples, due to

M. I. Danilkin; A. P. Belousov; S. O. Klimonskii; V. D. Kuznetsov; A. L. Lust; V. N. Nikiforov; L. N. Paama; I. Kh. Pammo; V. O. Seeman

2007-01-01

375

Formation of Eu2+ and Eu3+ centers in synthesis of CaF2:Eu luminophores  

Microsoft Academic Search

We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+\\/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the samples, due to

M. I. Danilkin; A. P. Belousov; S. O. Klimonskii; V. D. Kuznetsov; A. L. Lust; V. N. Nikiforov; L. N. Paama; I. Kh. Pammo; V. O. Seeman

2007-01-01

376

Influence of Na-related defects on ArF laser absorption in CaF2  

NASA Astrophysics Data System (ADS)

ArF laser pulse transmission through commercial high purity CaF2 is determined by measuring the energy of each pulse before and behind the sample up to an incident fluence H of 10 mJ/cm2. The steady state transmission of ArF laser pulses decreases with increasing fluence. The related absorption coefficients ? st( H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients 2.410-4 cm-1? ? eff?16.810-4 cm-1 and 1.710-9 cm W-1? ? eff?9.310-9 cm W-1, respectively. The ? eff and ? eff values increase with the Na content of the CaF2 samples as identified by the fluorescence of Na-related M Na centers at 740 nm. This relation is simulated by a rate equation model describing the ArF laser induced M Na generation in the dark periods between the laser pulses and their annealing during laser irradiation. M Na generation starts with intrinsic 2-photon absorption in CaF2, yielding self-trapped excitons (STE). These pairs of F and H centers move upon thermal activation and the F centers combine with F Na to form M Na centers. M Na annealing occurs by its photo dissociation into a pair of F and F Na centers.

Mhlig, C.; Triebel, W.; Stafast, H.; Letz, M.

2010-05-01

377

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

SciTech Connect

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

Kavner,A.

2008-01-01

378

Dielectric constant measurements on lead azide single crystals  

NASA Astrophysics Data System (ADS)

The dielectric constants of lead azide in single crystal form were measured in the three crystallographic directions and found to be unusually large and highly anisotropic. The dielectric constants are fairly independent of temperature over the range of 100 K to 370 K and of frequency over the range of 100 to 1000 Hz. The dielectric constants of the azides of T1, Na, and K were also measured and compared to published values. Calculations taking into account the crystal structure of lead azide indicate that the observed anistropy arises from polarization of the azide molecules.

Garrett, W. L.; Kemmey, P. J.

1980-09-01

379

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 222 ?m3 cytidine, 600600300 nm3 BaTiO3, and 111 ?m3 silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendellsung method and do not require absorption and extinction corrections.

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

2010-06-01

380

Flux Pinning and Scaling Behavior in La-214 Single Crystal.  

NASA Astrophysics Data System (ADS)

``Fishtails" in magnetic hysteresis loops (M vs. H) were observed in single crystals of La-214. The field at the peak position (H_peak(T)) can be described by a power-law relation. The reduce peak field vs. reduced temperature can be scaled into a single curve for all of La-214, Y-123, and Y-124 single crystals, indicating a similar pinning mechanism. The irreversibility line (H_irr(T)) in La-214 single crystal was measured by both M vs. H and M. vs. T methods. The power-law relation of H_irr(T) has the same functional form as H_peak(T) indicating the ratio of H_irr(T)/H_peak(T) is independent of temperature. * Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. W-7405-ENG-82. The work at University of Chicago is partially supported by the NSF through the Science and Technology Center for Superconductivity under contract No. DMR 91-20000. The work at Argonne is supported by the U. S. DOE, Basic Energy Sciences-Materials Sciences, under Contract No. W-31-109-ENG-38.

Xu, Ming; Finnemore, D. K.; Zhang, K.; Mogilevsky, R.; Hinks, D. J.; Crabtree, G. W.

1996-03-01

381

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

2013-03-04

382

AlSb single-crystal grown by HPBM  

NASA Astrophysics Data System (ADS)

Theoretical prognosis for AlSb places this widegap compound among the best materials for room temperature detectors and spectrometers. However, results experimentally obtained with AlSb are somewhat discouraging showing the necessity for improving the compound quality. The main difficulties connected with single-crystal growth are high reactivity of the melt with crucible material and a high volatility of Sb. In order to counteract the latter obstacle, an attempt was undertaken to synthesize and grow AlSb crystals by HPBM under the inert gas pressure of 40atm. Different crucible materials: aluminum oxide, vitreous carbon, quartz, graphite, beryllium oxide, and zirconium oxide were tested and their comparative analysis was made. The obtained crystals were investigated and some electrophysical properties measured.

Kutny, V. E.; Rybka, A. V.; Abyzov, A. S.; Davydov, L. N.; Komar, V. K.; Rowland, M. S.; Smith, C. F.

2001-02-01

383

Growth and spectral properties of Yb:FAP single crystal  

NASA Astrophysics Data System (ADS)

In this paper, single crystal of ytterbium (Yb) doped Ca5(PO4)3F (FAP) has been grown along the c-axis by using the Czochralski method. The segregation coefficients of Yb3+ in the Yb:FAP crystal has been determined by ICP-AES method. The absorption spectrum, fluorescence spectrum and fluorescence lifetime of the Yb:FAP crystal has been also measured at room temperature. In the absorption spectra, there are two absorption bands at 904 and 982 nm, respectively, which are suitable for InGaAs diode laser pumping. The absorption cross-section (?abs) is 5.117 10-20 cm2 with an FWHM of 4 nm at 982 nm. The emission cross-section (?em) is 3.678 10-20 cm2 at 1042 nm. Favorable values of the absorption cross-section at about 982 nm are promising candidates for laser diode (LD) pumping.

Song, Pingxin; Zhao, Zhiwei; Xu, Xiaodong; Deng, Peizhen; Xu, Jun

2007-01-01

384

Dislocations and Grain Boundaries in Semiconducting Rubrene Single-Crystals  

SciTech Connect

Assessing the fundamental limits of the charge carrier mobilities in organic semiconductors is important for the development of organic electronics. Although devices such as organic field effect transistors (OFETs), organic thin film transistors (OTFTs) and organic light emitting diodes (OLEDs) are already used in commercial applications, a complete understanding of the ultimate limitations of performance and stability in these devices is still lacking at this time. Crucial to the determination of electronic properties in organic semiconductors is the ability to grow ultra-pure, fully ordered molecular crystals for measurements of intrinsic charge transport. Likewise, sensitive tools are needed to evaluate crystalline quality. We present a high-resolution X-ray diffraction and X-ray topography analysis of single-crystals of rubrene that are of the quality being reported to show mobilities as high as amorphous silicon. We show that dislocations and grain boundaries, which may limit charge transfer, are prominent in these crystals.

Chapman,B.; Checco, A.; Pindak, R.; Siegrist, T.; Kloc, C.

2006-01-01

385

Crystal growth and luminescence properties of Cr-doped YAlO3 single crystals  

NASA Astrophysics Data System (ADS)

We have investigated optical and scintillation properties of Cr-doped YAlO3 (Cr:YAP) single crystals with different Cr concentrations. Cr:YAP crystals were grown by the micro-pulling-down (?-PD) method. The grown crystals had a single-phase confirmed by the powder XRD analysis. For all the Cr-doped samples, a peak positioned near 700 nm wavelength dominates the spectra. It can be ascribed to the Cr3+2E?4A2 emission. In X-ray induced radioluminescence spectra, 2E?4A2 emissions were observed. The light output of Cr 0.5%:YAP under X-ray excitation was more than twice as high as the standard CdWO4.

Sugiyama, Makoto; Yanagida, Takayuki; Totsuka, Daisuke; Yokota, Yuui; Futami, Yoshisuke; Fujimoto, Yutaka; Yoshikawa, Akira

2013-01-01

386

Growth and optical property of methyl para hydroxybenzoate sodium dihydrate single crystals  

NASA Astrophysics Data System (ADS)

Methyl parahydroxybenzoate sodium dihydrate (MHBN), a novel semiorganic single crystal has been grown by slow evaporation solution technique (SEST). Single crystal of MHBN with the size of 30 30 10 mm3 has been grown using methanol as a solvent. The crystal structure of MHBN has been confirmed by single crystal X-ray diffraction. The grown crystals were subjected to powder X-ray diffraction studies. The optical transparency was studied using UV-VIS spectrophotometer and it was found that the crystal is having good optical transparency. The mechanical strength of the grown crystal is measured using Vickers microhardness tester. Thermal properties of the MHBN crystals were studied.

Karunagaran, N.; Ramasamy, P.

2013-06-01

387

Mutiple Czochralski growth of silicon crystals from a single crucible  

NASA Astrophysics Data System (ADS)

An apparatus for the Czochralski growth of silicon crystals is presented which is capable of producing multiple ingots from a single crucible. The growth chamber features a refillable crucible with a water-cooled, vacuum-tight isolation valve located between the pull chamber and the growth furnace tank which allows the melt crucible to always be at vacuum or low argon pressure when retrieving crystal or introducing recharge polysilicon feed stock. The grower can thus be recharged to obtain 100 kg of silicon crystal ingots from one crucible, and may accommodate crucibles up to 35 cm in diameter. Evaluation of the impurity contents and I-V characteristics of solar cells fabricated from seven ingots grown from two crucibles reveals a small but consistent decrease in cell efficiency from 10.4% to 9.6% from the first to the fourth ingot made in a single run, which is explained by impurity build-up in the residual melt. The crystal grower thus may offer economic benefits through the extension of crucible lifetime and the reduction of furnace downtime.

Lane, R. L.; Kachare, A. H.

1980-10-01

388

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

2013-08-06

389

The influence of crystal orientations on fatigue life of single crystal cooled turbine blade  

Microsoft Academic Search

A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence

N. X. Hou; W. X. Gou; Z. X. Wen; Z. F. Yue

2008-01-01

390

Comprehensive Investigation of Single Crystal Diamond Deep-Ultraviolet Detectors  

NASA Astrophysics Data System (ADS)

The wide bandgap of diamond, along with its extreme semiconductor properties, offers the promising route for deep-ultraviolet (DUV) detection, especially under solar-blind condition and harsh environments. The ideal photodetector should generally satisfy the 5S requirements such as high sensitivity, high signal-to-noise ratio, high spectral selectivity, high speed, and high stability. In this paper, we comprehensively investigate the DUV detectors fabricated from various kinds of single crystal diamonds such as boron-doped diamond homoepitaxial layer, intrinsic diamond homoepitaxial layers with different thicknesses, and single crystal diamond substrates. The post process such as hydrogen plasma treatment on the performance of the DUV detectors is also examined. The strategies to develop high-performance diamond DUV detectors are provided.

Liao, Meiyong; Sang, Liwen; Teraji, Tokuyuku; Imura, Masataka; Alvarez, Jose; Koide, Yasuo

2012-09-01

391

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

392

Simulation of Sublimation Growth of SiC Single Crystals  

NASA Astrophysics Data System (ADS)

Modelling of sublimation growth of SiC is discussed with the goal to describe the mathematical models necessary to optimize the process and design of the growth system. An analysis of the mechanisms of growth of bulk silicon carbide crystals is performed. Growth conditions which provide stable growth of single SiC crystals without formation of secondary phases are considered. The phase diagram of the formation of extra phases during the sublimation growth of SiC is presented. Modelling of the growth of bulk SiC crystals is considered. Results of modelling the temperature distribution inside the inductively heated system for the growth of bulk SiC crystals are shown. A mechanism of material transport inside the closed Ta container in the absence of an inert gas atmosphere is proposed which is different from that of diffusive or free-molecular transport. First results of the model analysis of chemical processes inside the volume of SiC powder during the sublimation growth are demonstrated. It is shown that the sublimation and re-crystallization of the SiC source is sensitive to the temperature distribution in the source.

Karpov, S. Yu.; Makarov, Yu. N.; Ramm, M. S.

1997-07-01

393

Single crystals of V amylose complexed with glycerol.  

PubMed

Lamellar single crystals of amylose V glycerol were grown at 100 degrees C by evaporating water from solutions of amylose in aqueous glycerol. The crystals which were square, with lateral dimensions of several micrometers, gave sharp electron diffraction patterns presenting an orthorhombic symmetry with a probable space group P2(1)2(1)2(1) and unit cell parameters: a = 1.93 +/- 0.01 nm, b = 1.86 +/- 0.01 nm and c (fiber axis) = 0.83 +/- 0.03 nm. The amylose Vglycerol crystal structure which is isomorphous to that of VDMSO consists of an antiparallel pair of left-handed six-fold amylose helices centered on the two-fold screw axes of the cell and probably separated by glycerol molecules. This packing mode is confirmed by de-solvation experiments where the Vglycerol amylose crystals, annealed in ethanol, could be converted into VH amylose without losing their external appearance. The Vglycerol amylose crystals could be seeded by cellulose microfibrils to yield a shish-kebab structure where the amylose crystalline lamellae grew perpendicular to the microfibril directions. PMID:8852760

Hulleman, S H; Helbert, W; Chanzy, H

1996-02-01

394

Crystal growth of high-quality ZrB 2 single crystals using the floating-zone method  

Microsoft Academic Search

High-quality ZrB2 single crystals with diameters of 13mm and lengths of 45mm were grown from boron-rich molten zones (boron 80mol%), using the RF heated floating-zone method. The (0001) single crystals were also grown using seed crystals. Control of temperature gradients on the growing interfaces was performed by arranging ceramic cylinders around the growing crystals and the feed rods. This made

Kenji Hori; Shinji Inoue; Mineo Isogami

2008-01-01

395

Application of GRID to foreign atom localization in single crystals  

SciTech Connect

The application of GRID (Gamma Ray Induced Doppler broadening) spectroscopy to the localization of foreign atoms in single crystals is demonstrated on erbium in YAP. By the investigation of the Doppler broadened secondary {gamma} line for two crystalline directions, the Er was determined to be localized on the Y site. Conditions for the nuclear parameters of the impurity atoms used for the application of GRID spectroscopy are discussed.

Karmann, A.; Wesch, W.; Weber, B.; Boerner, H.G.; Jentschel, M.

2000-02-01

396

Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces  

Microsoft Academic Search

Valence band photoemission (XPS), valence band electron energy loss spectroscopy (EELS), Ce3d and 4d XPS, O1s XPS and O1s X-ray absorption (XAS) have been investigated for oxidized and sputtered single crystal CeO2 films and for oxidized Ce foil. Features were identified that distinguish between the Ce4+ or Ce3+ oxidation states. Ce4+ was identified by the highest binding energy peaks in

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

1998-01-01

397

Controlled synthesis of gold nanospheres and single crystals in hydrogel  

Microsoft Academic Search

Narrow-dispersed gold nanospheres, regular single-crystal nanoplates and nanobulks were prepared, respectively, by reducing\\u000a HAuCl4 within a hydrogel system under UV irradiation. The formation of gold products with different geometric shape and size was\\u000a found to depend on both the microenvironment of the gel matrix and the initial concentration of HAuCl4. The resultant gold particles were investigated by UVvis spectroscopy, X-ray

Jian Zhang; Baohui Zhao; Linghui Meng; Hongying Wu; Xudong Wang; Chenxi Li

2007-01-01

398

Mechanisms for tertiary creep of single crystal superalloy  

Microsoft Academic Search

During the thermal-mechanical loading of high temperature single crystal turbine components, all three creepstages: primary,\\u000a secondary and tertiary, manifest themselves and, hence, none of them can be neglected. The development of a creep law that\\u000a includes all three stages is especially important in the case of non-homogeneous thermal loading of the component where significant\\u000a stress redistribution and relaxation will result.

Alexander Staroselsky; Brice Cassenti

2008-01-01

399

Fabrication of single crystal PZT thin films on glass substrates  

Microsoft Academic Search

We have successfully transferred heteroepitaxial Pb(Zr,Ti)O3 (PZT) thin films from MgO substrates on to glass substrates. The transferred PZT thin films exhibit single crystal structure with ferroelectric properties similar to the as-grown epitaxial films. The transferring process comprises coating of Cr-metallized surface of epitaxial PZT thin films, pressing and cementing the Cr-metallized surface on to the glass substrates by silicone

Kenichiro Terada; Takaaki Suzuki; Isaku Kanno; Hidetoshi Kotera

2007-01-01

400

High temperature deformation properties of nial single crystals  

Microsoft Academic Search

The high-temperature deformation properties of stoichiometric NiAl single crystals have been studied in the temperature range\\u000a from 850 C and 1200 C. We have established a basic data set for and have explored the high-temperature deformation characteristics\\u000a of this intermetallic compound. The results provide a basis for determining the controlling mechanisms of high-temperature\\u000a deformation. Constant stress tension creep and constant

K. R. Forbes; U. Glatzel; R. Darolia; W. D. Nix

1996-01-01

401

High temperature deformation properties of nial single crystals  

Microsoft Academic Search

The high-temperature deformation properties of stoichiometric NiAl single crystals have been studied in the temperature range from 850 C and 1200 C. We have established a basic data set for and have explored the high-temperature deformation characteristics of this intermetallic compound. The results provide a basis for determining the controlling mechanisms of high-temperature deformation. Constant stress tension creep and constant

K. R. Forbes; U. Glatzel; R. Darolia; W. D. Nix

1996-01-01

402

Acoustic characteristics of FeSe single crystals  

NASA Astrophysics Data System (ADS)

The results of the comprehensive ultrasonic research of high-quality single crystals of FeSe are presented. Absolute values of sound velocities and their temperature dependences were measured; elastic constants and Debye temperature were calculated. The elastic C11-C12 and C11 constants undergo significant softening under the structural tetra-ortho transformation. The significant influence of the superconducting transition on the velocity and attenuation of sound was revealed and the value of the superconducting energy gap was estimated.

Zvyagina, G. A.; Gaydamak, T. N.; Zhekov, K. R.; Bilich, I. V.; Fil, V. D.; Chareev, D. A.; Vasiliev, A. N.

2013-03-01

403

Faraday rotation in single-crystal ytterbium gallium garnet  

Microsoft Academic Search

Faraday rotation (FR) measurements performed on single-crystal ytterbium gallium garnet (YbGG) at 0.6328- and 1.15-?m wavelengths are presented in a magnetic field up to 20 kOe applied along the three main crystallographic directions and in the 6300 K temperature range. At 0.6328 ?m, the FR is proportional to the magnetic field and a strong anisotropy of the Verdet constant (V)

M. Guillot; H. Le Gall; J. Ostorero; M. Artinian; A. Marchand

1987-01-01

404

Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres  

Microsoft Academic Search

Ceria nanoparticles are one of the key abrasive materials for chemical-mechanical planarization of advanced integrated circuits. However, ceria nanoparticles synthesized by existing techniques are irregularly faceted, and they scratch the silicon wafers and increase defect concentrations. We developed an approach for large-scale synthesis of single-crystal ceria nanospheres that can reduce the polishing defects by 80% and increase the silica removal

Xiangdong Feng; Dean C. Sayle; Zhong Lin Wang; M. Sharon Paras; Brian Santora; Anthony C. Sutorik; Thi X. T. Sayle; Yi Yang; Yong Ding; Xudong Wang; Yie-Shein Her

2006-01-01

405

Nonpercolative metal-insulator transition in VO2 single crystals  

Microsoft Academic Search

Detailed temperature-dependent transport, optical microscopy, and synchrotron-based polychromatic x-ray microdiffraction measurements have been carried out in the vicinity of the metal-insulator transition (MIT) temperature of VO2 single crystals. The formation and propagation of a real-space phase boundary along the rutile c axis is monitored during the transition. Pure metallic rutile R, as well as insulating monoclinic M1 phases, is observed

Bongjin Simon Mun; Kai Chen; Joonseok Yoon; Catherine Dejoie; Nobumichi Tamura; Martin Kunz; Zhi Liu; Michael E. Grass; Sung-Kwan Mo; Changwoo Park; Y. Yvette Lee; Honglyoul Ju

2011-01-01

406

Single Crystal Diamond Beam Position Monitors with Radiofrequency Electronic Readout  

Microsoft Academic Search

Over the energy range 5~30 keV a suitably contacted, thin (~100 mum) diamond plate can be operated in situ as a continuous monitor of X-ray beam intensity and position as the diamond absorbs only a small percentage of the incident beam. Single crystal diamond is a completely homogeneous material showing fast (ns), spatially uniform signal response and negligible (

B. Solar; H. Graafsma; J. Morse; M. Salom; G. Potdevin; U. Trunk

2010-01-01

407

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 -50C to +150C. A complete set of elastic, piezoelectric, and dielectric constants of the tetragonal modification at 25C 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

408

Ductile Mode Cuttingof Single-crystal Silicon by Ultrasonic Vibration  

Microsoft Academic Search

Brittle materials have a critical depth of cut between ductile mode and brittle mode In order to increase the critical depth\\u000a of cut, ductile mode cutting of single crystal silicon was realized using ultrasonic vibration. It was clarified that during\\u000a conventional cutting without ultrasonic vibration, the critical depth of cut was dc = 0.15?m. however, during ultrasonic vibration cutting, the

Shigeomi Koshimizu; Jiro Otsuka

409

Synthesis of mesoporous zeolite single crystals with cheap porogens  

Microsoft Academic Search

Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, 27Al magic angle spinning nuclear magnetic resonance (27Al MAS

Haixiang Tao; Changlin Li; Jiawen Ren; Yanqin Wang; Guanzhong Lu

2011-01-01

410

The fatigue of pseudoelastic single crystals of ?-CuAINi  

Microsoft Academic Search

The fatigue life of single crystal ?-CuAINi has been studied on pseudoelastic cyclic loading. In general the fatigue life\\u000a was quite poor with most specimens having less than 3000 cycles to failure. The fatigue life decreased significantly with\\u000a increasing stress level. However, the fatigue failure was due primarily to stress-induced martensite formation, since if the\\u000a stress level on cycling was

L. C. Brown

1979-01-01

411

Anisotropic Linear Compressibilities of MnP Single Crystal  

Microsoft Academic Search

An attempt to measure the linear compressibilities of an MnP single crystal has been made under hydrostatic pressures by means of the paper strain gauge technique, in the range from -70 to 32C including the Curie temperature. Anomalous linear compressibilities are found near the Curie temperature, which are a lambda-type peak along c axis and the lambda-type dips along a

Nobuo Iwata; Tetsuhiko Okamoto

1975-01-01

412

Defects in GaN single crystals and homoepitaxial structures  

Microsoft Academic Search

In this communication crystallographic and chemical inhomogeneities occurring in GaN single crystals, homo-epitaxial layers and quasi-bulk thick epitaxial layers are described. Practical classification of defects as (i) growth-related and (ii) processing-induced is given. On the basis of numerous studies using different examination techniques (DIC and DF optical microscopy, SEM) and methods of revealing (defect-selective etching, PEC etching, X-ray diffraction and

J. L. Weyher; G. Kamler; G. Nowak; J. Borysiuk; B. Lucznik; M. Krysko; I. Grzegory; S. Porowski

2005-01-01

413

The Herbertsmithite Hamiltonian: ?SR measurements on single crystals  

NASA Astrophysics Data System (ADS)

We present transverse field muon spin rotation/relaxation measurements on single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find that the spins are more easily polarized when the field is perpendicular to the kagome plane. We demonstrate that the difference in magnetization between the different directions cannot be accounted for by Dzyaloshinskii-Moriya-type interactions alone and that anisotropic axial interaction is present.

Ofer, Oren; Keren, Amit; Brewer, Jess H.; Han, Tianheng H.; Lee, Young S.

2011-04-01

414

Nonlinear limits for single-crystal silicon microresonators  

Microsoft Academic Search

Nonlinear effects in single-crystal silicon microresonators are analyzed with the focus on mechanical nonlinearities. The bulk acoustic wave (BAW) resonators are shown to have orders-of-magnitude higher energy storage capability than flexural beam resonators. The bifurcation point for the silicon BAW resonators is measured and the maximum vibration amplitude is shown to approach the intrinsic material limit. The importance of nonlinearities

Ville Kaajakari; Tomi Mattila; Aarne Oja; Heikki Sepp

2004-01-01

415

Peculiarities of vibrating Bi 2212 single crystal near Hc1  

Microsoft Academic Search

Vibrating reed experiment with a Bi-based superconducting single crystal were performed for perpendicular orientation of its ab-plane with respect to the applied magnetic field Ba. The temperature behaviour of frequency shift Delta? and damping D(T) of such mechanical oscillator were measured in the applied magnetic field Ba region 400-600 Oe which is close to the first critical value of the

A. V. Drobinin; K. E. Kamentsev; Yu. M. Tsipenyuk

1994-01-01

416

Depressed scattering across grain boundaries in single crystal graphene  

NASA Astrophysics Data System (ADS)

We investigated the electrical and quantum properties of single-crystal graphene (SCG) synthesized by chemical vapor deposition (CVD). Quantum Hall effect and Shubnikov de Hass oscillation, a distinguishing feature of a 2-dimensional electronic material system, were observed during the low temperature transport measurements. Decreased scattering from grain boundaries in SCG was proven through extracting information from weak localization theory. Our results facilitate understanding the electrical properties of SCG grown by CVD and its applications in high speed transistor and quantum devices.

Chen, Jiao; Jin, Zhi; Ma, Peng; Wang, Hong; Wang, Haomin; Shi, Jingyuan; Peng, Songang; Liu, Xinyu; Ye, Tianchun

2012-10-01

417

The dissolution forms of YIG single crystal spheres  

NASA Astrophysics Data System (ADS)

Single crystal spheres of yttrium iron garnet have been dissolved in solvents of H3PO4 and HBr at 140 and 126C, respectively. The final dissolution form was a tetrahexahedron in H3PO4 and an octahedron in HBr. In the latter case the faces were built up of terraces. The observed dissolution forms could be explained using the theory of Lacmann, Franke and Heimann.

Beregi, E.; Sterk, E.; Tanos, F.; Hartmann, E.; Lbr, J.

1983-12-01

418

The Temperature of a Single Crystal Diamond Tool in Turning  

Microsoft Academic Search

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

Takashi Ueda; Masahiko Sato; Kazuo Nakayama

1998-01-01

419

Development of low density single crystal superalloy CMSX-6  

Microsoft Academic Search

Limitations in turbine disc strength capability can, in certain design cases, mandate the use of low density single crystal superalloy turbine blade components. The development of CMSX-6 nickel-base superalloy (density 0.288 lbs\\/cu. in. (7.98 gms.\\/cc)) to meet these design requirements is presented and discussed. Extensive solution treatment studies are shown and enable the high γ\\/γ eutectic content of the as-cast

K. Harris; G. L. Erickson; J. Wortmann; D. Froschhammer

2008-01-01

420

Fatigue strength of a single crystal in the gigacycle regime  

Microsoft Academic Search

The objective of this work is to investigate the fatigue behavior of a single crystal nickel-based superalloy in the gigacycle regime. Testing from 106 to 109 cycles at 593C was performed using an ultrasonic fatigue system operating at 20kHz. Multiple tests were performed at stresses near the fatigue limit to determine the variability in fatigue life in this regime. Endurance

Ryan J. Morrissey; Patrick J. Golden

2007-01-01

421

Superconducting microstrip resonator with yttrium iron garnet single crystals  

Microsoft Academic Search

A magnetically tunable microstrip superconducting resonator using an yttrium-iron-garnet (YIG) single crystal was demonstrated experimentally. Tunability of 200 MHz at a center frequency of 5.3 GHz was observed, and a quality factor of 965 with minimum insertion loss of 19.5 dB was measured for a half-wavelength microstrip line consisting of a YIG-YBCO-MgO composite structure. The dispersion relation of the resonator

Takeshi Fukusako; Makoto Tsutsumi

1997-01-01

422

FERROMAGNETIC RESONANCE LINE WIDTH IN YTTRIUM IRON GARNET SINGLE CRYSTALS  

Microsoft Academic Search

A study of ferromagnetic resonance line width in polished, single-; crystal spheres of yttriunn iron garnet is described. Wave-guide cavity ; perturbation techniques are used with samples 0.013 in. to 0.020 in. in diameter. ; An extremely narrow line width of 520 millioersteds (the full width) is observed ; at 9300 Mc\\/sec along the hard axis STA100!. It is believed

R. C. LeCraw; E. G. Spencer; C. S. Porter

1958-01-01

423

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

424

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

425

Single crystal plasticity by modeling dislocation density rate behavior  

SciTech Connect

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

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

2010-12-23

426

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

SciTech Connect

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

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

2006-12-01

427

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 900C 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

428

Performance of Large grain and Single Crystal Niobium Cavities  

SciTech Connect

We have fabricated and tested several single and one multi-cell cavity made from large grain niobium of four different ingots. Two cavities at a frequency of ~ 2.2 GHz were made from single crystal sheets. Large grain material was used for four single cell cavities of the HG and OC shapes, a 7-cell cavity of the HG shape all resonating at 1500 MHz and an ILC_LL single cell cavity at 1300 MHz. We began to explore also different chemical polishing baths such as a 1:1:1 and a 1:1:2 buffered solution and explored the change of cavity performance as a function of material removal. The results from these preliminary investigations are reported in this contribution.

Kneisel, Peter; Ciovati, Gianluigi; Sekutowicz, Jacek

2006-07-01

429

Effect of organic dopants on ZTS single crystals  

NASA Astrophysics Data System (ADS)

The influence of organic dopants on tristhioureazinc(II)sulphate (ZTS) single crystals from aqueous solutions at 30 C is investigated. The dopants used in the present investigation are disodium salt of ethylenediamminetetraacetic acid (EDTA), benzene and 1,10-phenanthroline (Phen) which are having different structures. Though, all the dopants show better results, prominent influence is observed in case of EDTA dopant with low concentration of 510-3 M L-1 and hence the results pertaining to EDTA dopant are described in detail in the present article. At low concentrations of dopant, an increase in the metastable zone width, leading to an increase in the crystal growth rate is observed. At higher dopant concentration, growth rate decreases. The crystalline perfection of the grown crystals has been evaluated by high-resolution X-ray diffractometry (HRXRD). The diffraction curve (DC) of a typical EDTA-doped as-grown ZTS crystal was observed to contain one additional peak very close to the main peak suggesting the possibility of an epitaxial layer on the surface of the crystal. After removing this layer by lapping followed by chemical etching, the DC was found to contain only a single and very sharp peak showing that the main crystal is having a much better crystalline perfection than that observed for the specimen grown with out using any dopant in the solution. This indicates that the complexation of trace metal ion impurities (present in the solution) with the dopants is responsible for the formation of the layer on the surface of the crystal and prevents the entry of impurities in the growing crystal. The complexation also promotes the growth process leading to a rapid growth with high crystalline quality. Not much variation is observed in FT-IR and XRD of pure and doped ZTS. However, second harmonic generation (SHG) efficiency measurements carried out with different dopants reveal that nonlinear optical (NLO) property is enhanced by EDTA and benzene dopants. However, Phen depresses the NLO efficiency of ZTS.

Meenakshisundaram, Subbiah; Parthiban, S.; Sarathi, N.; Kalavathy, R.; Bhagavannarayana, G.

2006-08-01

430

Growth of Sapphire Single Crystals Transparent Armor by a Modified Verneuil Technique.  

National Technical Information Service (NTIS)

The objective of the process development program was to determine whether it was feasible to produce slab shaped sapphire single crystals by a modified Verneuil technique for transparent armor applications. Seeded single crystals of sapphire were grown wi...

J. S. Haggerty M. Rossetti

1970-01-01

431

Anisotropic Piezocomposite Actuator Incorporating Machined PMN-PT Single Crystal Fibers.  

National Technical Information Service (NTIS)

The design, fabrication, and testing of a flexible, planar, anisotropic piezoelectric composite actuator utilizing machined PMN-32%PT single crystal fibers is presented. The device consists of a layer of rectangular single crystal piezoelectric fibers in ...

W. K. Wilkie D. J. Inman J. M. Lloyd J. W. High

2004-01-01

432

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

Yip, C M; Ward, M D

1996-01-01

433

Computational Modeling of Photonic Crystal Microcavity Single-Photon Emitters  

NASA Astrophysics Data System (ADS)

Conventional cryptography is based on algorithms that are mathematically complex and difficult to solve, such as factoring large numbers. The advent of a quantum computer would render these schemes useless. As scientists work to develop a quantum computer, cryptographers are developing new schemes for unconditionally secure cryptography. Quantum key distribution has emerged as one of the potential replacements of classical cryptography. It relics on the fact that measurement of a quantum bit changes the state of the bit and undetected eavesdropping is impossible. Single polarized photons can be used as the quantum bits, such that a quantum system would in some ways mirror the classical communication scheme. The quantum key distribution system would include components that create, transmit and detect single polarized photons. The focus of this work is on the development of an efficient single-photon source. This source is comprised of a single quantum dot inside of a photonic crystal microcavity. To better understand the physics behind the device, a computational model is developed. The model uses Finite-Difference Time-Domain methods to analyze the electromagnetic field distribution in photonic crystal microcavities. It uses an 8-band k p perturbation theory to compute the energy band structure of the epitaxially grown quantum dots. We discuss a method that combines the results of these two calculations for determining the spontaneous emission lifetime of a quantum dot in bulk material or in a microcavity. The computational models developed in this thesis are used to identify and characterize microcavities for potential use in a single-photon source. The computational tools developed are also used to investigate novel photonic crystal microcavities that incorporate 1D distributed Bragg reflectors for vertical confinement. It is found that the spontaneous emission enhancement in the quasi-3D cavities can be significantly greater than in traditional suspended slab cavities.

Saulnier, Nicole A.

434

Advanced piezoelectric single crystal based transducers for naval sonar applications  

NASA Astrophysics Data System (ADS)

Transducers incorporating single crystal piezoelectric Pb(Mg1/3Nb2/3)x-1TixO3 (PMN-PT) exhibit significant advantages over ceramic piezoelectrics such as PZT, including both high electromechanical coupling (k33 > 90%) and piezoelectric coefficients (d33 > 2000 pC/N). Conventional <001> orientation gives inherently larger bandwidth and output power than PZT ceramics, however, the anisotropy of the crystal also allows for tailoring of the performance by orienting the crystal along different crystallographic axes. This attribute combined with composition refinements can be used to improve thermal or mechanical stability, which is important in high power, high duty cycle sonar applications. By utilizing the "31" resonance mode, the high power performance of PMN-PT can be improved over traditional "33" mode single crystal transducers, due to an improved aspect ratio. Utilizing novel geometries, effective piezoelectric constants of -600 pC/N to -1200 pC/N have been measured. The phase transition point induced by temperature, pre-stress or field is close to that in the "33" mode, and since the prestress is applied perpendicular to the poling direction in "31" mode elements, they exhibit lower loss and can therefore be driven harder. The high power characteristics of tonpilz transducers can also be affected by the composition of the PMN-PT crystal. TRS modified the composition of PMN-PT to improve the thermal stability of the material, while keeping the loss as low as possible. Three dimensional modeling shows that the useable bandwidth of these novel compositions nearly equals that of conventional PMN-PT. A decrease in the source level of up to 6 dB was calculated, which can be compensated for by the higher drive voltages possible.

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

2006-04-01

435

Single-Crystal Studies of Beta - Ag2HgI4.  

National Technical Information Service (NTIS)

The structure and transformation behavior of beta-Ag2HgI4 have been investigated by X-ray diffraction methods using single crystals. It has been verified that a single crystal of the beta-form, stable at room temperature, transforms to a single crystal of...

K. W. Browall J. S. Kasper H. Wiedemeier

1973-01-01

436

Physics of Heavily Implanted Single Crystal Complex Oxides  

NASA Astrophysics Data System (ADS)

Ion implantation is known to result in a significant amount of damage in solid single crystals. In this work a battery of material probes is used to study the effect of a very high-dose He implantation in ferroelectric lithium niobate (LiNbO3) and the implantation-induced formation of defects. In addition, the evolution of these defects with post-implantation annealing is examined. After irradiation, a high concentration of defects is found to collect and create a network of thick prismatic planar defects having typical dimensions of 1.5 microm and 200 nm parallel and perpendicular to the Z axis, respectively. Optical microscopy shows that there is strong temperature dependence for forming the network; the density of these defects reaches a maximum value for an annealing temperature of 250 C. However, annealing to temperatures above 380 C fully eliminates the defects. High-resolution TEM studies indicate that the defects are likely localized twinning and dislocation pileups due to plastic deformation of the lattice to relieve He-implantation-induced stress. During this deformation He accumulates at the twin boundaries. A second type of implantation induced defects is studied using room temperature, high- resolution electron microscopy; this study shows that implanted He in LiNbO3 nucleates and accumulates as bubbles. These He inclusions are at 20 GPa pressure and most probably in the solid phase. In addition, the energetically favored shape of the inclusions in their as-implanted form is spherical and not oblate; this spherical shape is due to the fact their diameter is below a critical radius for balancing the surface and elastics energies as predicted by elastic theory. When annealed, the characteristic length scale of the He inclusions increases, forming faceted bubbles. Annealing also causes the He inclusions to migrate and accumulate into strings due to the preferred {1014}-pyramidal-twinning planes. The ion implantation-induced defects are found to be useful for several microfabrication techniques, in particular we describe the use of these defects for ion slicing of single crystal thin films from bulk crystals and ferroelectric domain patterning by low voltage pulses applied to a scanning force microscope tip. The origin of the rate of anomalously high spatially selective etching of a buried heavily implanted region in complex oxides is found to be closely related to the implantation-induced defects. He+-ion implantation in single-crystal LiNbO3 samples followed by low-temperature anneal and wet etched results in an etch-rate enhancement of 104. This high rate selective etch is crucial for the Crystal Ion Slicing process, a novel technique to fabricate single crystal thin films by slicing them off a bulk crystal. Experiments, using time-resolved optical microscopy and proximal-probe microscopy, show that this enhancement arises from the more rapid etch-solution transport in the thick prismatic planar defect network formed in the implanted region after annealing. Ferroelectric domain patterns are generated in He-implanted single-crystal bulk wafers of LiNbO3 by means of low-voltage pulses applied to a scanning force microscope tip and investigated using piezoresponse force microscopy and selective etching. It is shown that high fluence implantation results in isolation of the near surface region, creating a free-standing-film-like behavior for the layer above the heavily implanted region. At low fluence the implantation damage allows low voltage poling, apparently by vacancy-induced dipole formation. In addition, electrostatic repulsion of the poling-induced buried charges from adjacent domains limits the domain size and depth; this effect results in a uniform domain structures and potentially enables large area nanodomains patterns to be written.

Ofan, Avishai

437

ESR Study on Irradiated Ascorbic Acid Single Crystal  

NASA Astrophysics Data System (ADS)

Food irradiation is a ``cold'' process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. The small temperature increase, absence of residue and effectiveness of treatment of pre-packed food are the main advantages. In food industry, ascorbic acid and its derivatives are frequently used as antioxidant agents. However, irradiation is expected to produces changes in the molecules of food components and of course in the molecules of the agents added as preservation agents such as ascorbic acid. These changes in the molecular structures could cause decreases in the antioxidant actions of these agents. Therefore, the radiation resistance of these agents must be known to determine the amount of radiation dose to be delivered. Electron spin resonance (ESR) is one of the leading methods for identification of intermediates produced after irradiation. ESR spectrum of irradiated solid powder of ascorbic acid is fairly complex and determinations of involved radical species are difficult. In the present work, single crystals of ascorbic acid irradiated by gamma radiation are used to determine molecular structures of radiation induced radicalic species and four radicalic species related in pair with P21 crystal symmetry are found to be responsible from experimental ESR spectrum of gamma irradiated single crystal of ascorbic acid.

Tuner, H.; Korkmaz, M.

2007-04-01

438

Strength anomaly in B2 FeAl single crystals  

SciTech Connect

Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). The orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.

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

1994-12-31

439

ESR Study on Irradiated Ascorbic Acid Single Crystal  

SciTech Connect

Food irradiation is a 'cold' process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. The small temperature increase, absence of residue and effectiveness of treatment of pre-packed food are the main advantages. In food industry, ascorbic acid and its derivatives are frequently used as antioxidant agents. However, irradiation is expected to produces changes in the molecules of food components and of course in the molecules of the agents added as preservation agents such as ascorbic acid. These changes in the molecular structures could cause decreases in the antioxidant actions of these agents. Therefore, the radiation resistance of these agents must be known to determine the amount of radiation dose to be delivered. Electron spin resonance (ESR) is one of the leading methods for identification of intermediates produced after irradiation. ESR spectrum of irradiated solid powder of ascorbic acid is fairly complex and determinations of involved radical species are difficult. In the present work, single crystals of ascorbic acid irradiated by gamma radiation are used to determine molecular structures of radiation induced radicalic species and four radicalic species related in pair with P21 crystal symmetry are found to be responsible from experimental ESR spectrum of gamma irradiated single crystal of ascorbic acid.

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

2007-04-23

440

Search for Superconductivity in Single Crystals of Topological Insulators  

NASA Astrophysics Data System (ADS)

Observation of superconductivity in Cu-intercalated Bi2Se3, and in Bi2Te3 under pressure, open up the possibility of occurrence of superconductivity in other similarly modified structures. Here, we present detailed studies from a comprehensive search for superconductivity in selenides and tellurides of Bismuth and Antimony. High-quality single crystals were intercalated with a number of different elements using both in situ and ex situ techniques, then scanned for a resistive or magnetic transition to superconductivity. With an intent to understand the nature of intercalation in these compounds, we discuss results from our search for superconductivity, together with crystal structure analysis and detailed optical and x-ray photoelectron spectroscopy studies of the cleaved surface.

Guptasarma, Prasenjit; Sen, Somaditya; Dudek, John; Severson, Mary; Bissen, Mark

2012-02-01

441

Elasticity of single-crystal methane hydrate at high pressure  

NASA Astrophysics Data System (ADS)

By using in situ high-pressure Brillouin spectroscopy in a diamond-anvil cell, we have determined the pressure dependence of acoustic velocities, adiabatic elastic moduli, bulk modulus, elastic anisotropy, and Cauchy violation of single-crystal methane hydrate (MH) at pressures up to 0.6 GPa and 296 K. Acoustic velocities show nearly isotropic behaviors with respect to the crystal orientation, and the slight TA-mode softening with pressure implies that the structure of MH is becoming less stable against the shear component under high pressures. Elastic moduli and bulk modulus indicate that MH is slightly more compressible than ice Ih. These results would help to investigate their mechanical and thermodynamical stabilities, and provide important constraints on the icy moons of the outer solar system.

Shimizu, Hiroyasu; Kumazaki, Tatsuya; Kume, Tetsuji; Sasaki, Shigeo

2002-06-01

442

Magnetotransport in Tb2Fe17 single crystals  

NASA Astrophysics Data System (ADS)

We have performed measurements of the Hall effect, electrical resistivity, and magnetization on Tb2Fe17 single crystals in the 5 to 300 K temperature range, and in magnetic fields of up to 5 T. We find that the anomalous Hall effect of this ferromagnet depends strongly on the magnetization direction relative to the crystal axes. The AHE resistivity, measured with an applied magnetic field H perpendicular to the c-axis, is very large and varies linearly with the longitudinal resistivity ?, whereas the AHE resistivity for H along the hard magnetization direction is much smaller and increases as ?2. For the latter configuration, the electrical resistivity shows a sharp decrease at a field-induced first-order magnetization process (FOMP) which is observed in H ~ 2.7 T up to a temperature of 250 K.

Stankiewicz, Jolanta; Skokov, Konstantin P.

2011-07-01

443

Indentation Size Effect and Microhardness Study of ?-Sn Single Crystals  

NASA Astrophysics Data System (ADS)

The load dependence of apparent microhardness of ?-Sn single crystals having different growth directions is investigated. The measurements are performed on (110) planes of these crystals in the load range from 10 to 50 mN. It is found that the degree of the microhardness anisotropy decreases for higher indentation test loads. The examined materials exhibit the behaviour of indentation size effect (ISE), i.e., the apparent hardness increases with decreasing indentation load. Neither Meyer's law nor the proportional specimen resistance (PSR) model can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to modified the PSR model based on the consideration of the effect of machining-induced residually stressed surface on the hardness measurement.

Sahin, O.; Uzun, O.; Kolemen, U.; Duzgun, B.; Ucar, N.

2005-12-01

444

NMR on Single Crystals of Potassium Cyanogen Bromide  

NASA Astrophysics Data System (ADS)

Single crystals of K(CN)_{ rm x}/(Br)_{rm 1-x} enriched in ^{15 }N have been studied by ^{15 }N NMR. Because of the anisotropic chemical shift, the NMR frequency spectrum of the orientational glass state reflects the distribution of cyanide orientations. By studying the spectrum at many orientations of each crystal, the orientational probability distribution function P( Omega) has been determined for x = 0.50 and for x = 0.20. The probability function is largest along the (100) directions, intermediate in the (110) directions, and nearly 0 along the (111) directions. The NMR determined P(Omega) is presented graphically and in terms of the Kubic Harmonic functions. The NMR results are in sharp contrast to molecular dynamics calculations but agree with neutron scattering data for x = 0.53.

Walton, Jeffrey Howard

445

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

446

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

447

CaF2:Tm (TLD300) thermoluminescent response and glow curve induced by gamma-rays and ions  

Microsoft Academic Search

The thermoluminescent response of CaF2:Tm after exposure to 60Co gamma-rays at doses from 0.44 Gy to 8.75 kGy and to low fluences (105 108 cm-2) of 25 and 40 MeV 1H, 75 and 120 MeV 3He, 180, 300 and 480 MeV 12C, 400 MeV 16O and 800 MeV 20Ne ion beams, spanning a LET interval up to about 500

G. Massillon-Jl; I. Gamboa-Debuen; A. E. Buenfil; M. A. Monroy-Rodrguez; M. E. Brandan

2008-01-01

448

CaF 2:Tm (TLD300) thermoluminescent response and glow curve induced by ?-rays and ions  

Microsoft Academic Search

The thermoluminescent response of CaF2:Tm after exposure to 60Co ?-rays at doses from 0.44Gy to 8.75kGy and to low fluences (105?108cm?2) of 25 and 40MeV 1H, 75 and 120MeV 3He, 180, 300 and 480MeV 12C, 400MeV 16O and 800MeV 20Ne ion beams, spanning a LET interval up to about 500keV\\/?m, has been investigated. A careful deconvolution analysis of the glow

G. Massillon-JL; I. Gamboa-deBuen; A. E. Buenfil; M. A. Monroy-Rodrguez; M. E. Brandan

2008-01-01

449

Defect Characterization of High Thermal Conductivity CaF2 Doped AlN Ceramics by Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Calcium fluoride additive was used to produce high thermal conductivity AlN ceramics which has no grain boundary phase. Thermal conductivity of AlN is determined by the point defect, represented as oxygen related defect, within the AlN grain. The defect density characterization of high thermal conductivity CaF2 doped AlN ceramics after heat treatment was conducted by Raman spectroscopy. As measure Raman linewidth broadening, the point defect density variation after heat treatment and corresponding thermal conductivity change was investigated.

Lee, Hyeon-Keun; Kim, Do Kyung

450

Electrical conductivity of NaF-AlF3-CaF2-Al2O3 melts  

NASA Astrophysics Data System (ADS)

The electrical conductivity of NaF-AlF3-Al2O3 melts with a CaF2 concentration of 5 wt % is measured at a continuously varying cell constant when the molar cryolitic ratio CR = [NaF]/[AlF3] changes from 1.2 to 2.0 [1, 2]. The experimental data are used to obtain a regression equation to describe the dependence of the electrical conductivity of the melts under study on CR, the alumina content, and temperature { ?] = f(CR, [Al2O3], T)}.

Bakin, K. B.; Simakova, O. N.; Polyakov, P. V.; Mikhalev, Yu. G.; Simakov, D. A.; Gusev, A. O.

2010-08-01

451

Electronic states of pyrene single crystal and of its single molecule inserted in a molecular vessel of cyclodextrin  

Microsoft Academic Search

Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The absorption spectra of the single crystal have been transformed from the reflection spectra between 2.5 and 6.5eV at 2, 77K and room temperature. The dry powder of ?-cyclodextrin including pyrene single molecule were prepared in vacuum to investigate

Nobuaki Takahashi; Bold Gombojav; Takehisa Yoshinari; Shin-Ichiro Nagasaka; Yoshio Takahashi; Aishi Yamamoto; Takenari Goto; Atsuo Kasuya

2004-01-01

452

The effect of crystal geometry on the formation and crack development in molybdenum single crystals  

NASA Astrophysics Data System (ADS)

The systematic study of the defect structure evolution in single crystal specimens deformed in situ in the high voltage transmission electron microscope (HVTEM) was started around 1977 in the Baikov Metallurgy Institute of the USSR Academy of Sciences. All the experience gathered for the past 30 years has set up the basis for the determination of the way that metals adapt to the different physical factors inside the HVTEM column. In the present work the detailed phenomenology of the generation and propagation process of cracks in single crystals of Mo with different crystallographic orientations as well as the kinetics of opening of primary and secondary cracks and the tip evolution for cracks with different dislocation generation sources is presented.

Tamayo-Meza, Pedro A.; Yermishkin, Viacheslav; Schabes-Retchkiman, Pablo

2010-04-01

453

Advanced piezoelectric single crystal based transducers for naval sonar applications  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

454

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

455

Mechanical properties of ZnSe : Cr2+ single crystals  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

456

Electric detection of ferromagnetic resonance in single crystal iron film  

NASA Astrophysics Data System (ADS)

We report electric detection of ferromagnetic resonance (FMR) in epitaxially grown single crystal iron film through microwave photovoltage generation technique. The experimental results agree well with the established theory about FMR in iron films, showing excellent extendability of such a technique onto different ferromagnets as an effective way to study magnetocrystalline anisotropy and spin excitations. Furthermore, the information about the phase of magnetization precession is implicated in the lineshape of photovoltage, which makes it possible to probe in details into magnetic phase dynamics that is of significance for devising spintronic devices.

Hui, Xiong; Wirthmann, A.; Gui, Y. S.; Tian, Y.; Jin, X. F.; Chen, Z. H.; Shen, S. C.; Hu, C.-M.

2008-12-01

457

Single molecule studies on dynamics in liquid crystals.  

PubMed

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

Tuber, Daniela; von Borczyskowski, Christian

2013-09-26

458

Transient current electric field profiling of single crystal CVD diamond  

NASA Astrophysics Data System (ADS)

The transient current technique (TCT) has been adapted for profiling of the electric field distribution in intrinsic single crystal CVD diamond. It was found that successive hole transits do not appreciably affect the electric field distribution within the sample. Transits of holes can therefore be used to probe the electric field distribution and also the distribution of trapped charge. Electron transits, on the other hand, cause an accumulation of negative charge in the sample. Illumination with blue or green light was shown to lead to accumulation of positive charge. Low concentrations of trapped charge can be detected in diamond using TCT, corresponding to an ionized impurity concentration below N = 1010 cm-3.

Isberg, J.; Gabrysch, M.; Tajani, A.; Twitchen, D. J.

2006-08-01

459

Physical properties of SrSn4 single crystals  

SciTech Connect

We present detailed thermodynamic and transport measurements on single crystals of the recently discovered binary intermetallic superconductor, SrSn{sub 4}. We find this material to be a slightly anisotropic three-dimensional, strongly coupled, possibly multiband, superconductor. Hydrostatic pressure causes a decrease in the superconducting transition temperature at the rate of {approx} -0.068 K kbar{sup -1}. Band structure calculations are consistent with experimental data on the Sommerfeld coefficient and upper superconducting critical field anisotropy, and suggest a complex, multi-sheet Fermi surface formed by four bands.

Lin, Xiao [Iowa State University; Budko, Sergey L [Ames Laboratory and Iowa State University; Samolyuk, German D [ORNL; Torikachvili, Milton S [San Diego State University; Canfield, Paul [Ames Laboratory and Iowa State University

2011-01-01

460

Frost Heave Dynamics at a Single Crystal Interface  

NASA Astrophysics Data System (ADS)

We study flow in a surface-melted layer of a single crystal of ice at a plane solid interface. The flow, which is induced by a temperature gradient in the melted layer, causes the ice to grow normal to the interface. The process is the basis for frost heave in frozen soils. Flow is observed in a limited range of temperatures near the melting point, implying that surface melting is absent below this range. The data are analyzed in terms of a model which allows estimates of the fluid layer thickness. The results are not consistent with interfacial melting due to purely van der Waals forces.

Wilen, L. A.; Dash, J. G.

1995-06-01

461

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

462

Irreversible magnetovolume effect in Nd7Rh3 single crystal  

NASA Astrophysics Data System (ADS)

Magnetovolume effect in Nd7Rh3 single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2 K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.

Tsutaoka, Takanori; Shimomura, Koji; Tanaka, Akira

2011-12-01

463

Raman Investigations of Rare Earth Arsenate Single Crystals  

SciTech Connect

Polarized Raman Spectroscopy was used to investigate the room-temperature phonon characteristics of a series of rare-earth arsenate (REAsO4, RE = Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) single crystals. The Raman data were interpreted in a systematic manner based on the known tetragonal zircon structure of these compounds, and assignments and correlations were made for the observed bands. We found that the wavenumber of the internal modes of the AsO4 tetrahedron increased with increasing atomic number, and for three out of four lattice wavenumbers observed, this tendency was not nearly so marked as in the case of the internal mode wavenumber.

Barros, G [Universidade Federal do Ceara, Ceara, Brazil; Santos, C. C. [Universidade Federal do Ceara, Ceara, Brazil; Ayala, A. P. [Universidade Federal do Ceara, Ceara, Brazil; Guedes, I. [Universidade Federal do Ceara, Ceara, Brazil; Boatner, Lynn A [ORNL; Loong, C. K. [Sun Yat-Sen University, Guangzhou, China

2010-01-01

464

Electrical Resistivities of Nonstoichiometric Cerium Hydride Single Crystals  

Microsoft Academic Search

Electrical resistivities as a function of temperature (?130 to 25C) were determined on single crystals of cerium hydride ranging in composition from CeH1.94&sngbnd;CeH2.85. Measurements were performed in an inert-atmosphere dry box using the four-point probe technique. Cerium hydride exhibited metallic behavior in the range CeH1.9&sngbnd;CeH2.7. However, at a composition of about CeH2.85, a positive temperature coefficient of conductivity indicative of

G. G. Libowitz; J. G. Pack

1969-01-01

465

Single crystal EPR of Mn12-acetate clusters  

NASA Astrophysics Data System (ADS)

We have used electron paramagnetic resonance (EPR) to study the energy level diagram of the Mn12-cluster compound, in the frequency range from 35 to 115 GHz. Our high sensitivity allows the observation of multiple resonances, and their temperature dependence, on high-quality single crystals. The results are in qualitative agreement with the picture of a strong axial anisotropy. Measurements with the field applied parallel and perpendicular to the easy axis reveal significant zero-field splittings and level crossings, as predicted theoretically.

Hill, S.; Perenboom, J. A. A. J.; Stalcup, T.; Dalal, N. S.; Hathaway, T.; Brooks, J. S.

1998-05-01

466

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O 3 films on CaF 2 substrates with transparent (La 0.07Sr 0.93)SnO 3  

Microsoft Academic Search

Epitaxial (La0.07Sr0.93)SnO3 [LSSO] films were deposited on CaF2 substrates by pulse laser deposition. The (100)c orientation of LSSO films was observed only on (110)CaF2, whereas (110)c orientation was found on (111)CaF2 and (100)CaF2. (001) polar axis oriented tetragonal Pb(Zr0.35Ti0.65)O3 films were grown on the fabricated (100)cLSSO?(110)CaF2 by pulsed metal organic chemical vapor deposition. The (001)Pb(Zr0.35Ti0.65)O3?(100)cLSSO?(110)CaF2 stack structure exhibited about 70%

Satoru Utsugi; Yoshitaka Ehara; Hidenori Tanaka; Tomoaki Yamada; Hiroshi Funakubo; Hiroshi Uchida

2010-01-01

467

Photoluminescence properties of MgxZn1-xSe single crystals  

NASA Astrophysics Data System (ADS)

MgxZn1-xSe single crystals were grown by the closed tube sublimation method. The MgxZn1-xSe single crystals crystallized into zincblende and wurtzite structures in the composition ranges of x=0.0-0.1 and x=0.2-0.6, respectively. Blue and violet emissions with LO phonon replica and self-activated emissions in the MgxZn1-xSe single crystals were observed at 10 K.

Park, Sang-An; Song, Ho-Jun; Kim, Wha-Tek; Kim, Hyung-Gon; Jin, Moon-Seog; Kim, Chang-Dae; Yoon, Chang-Sun

1998-03-01

468

The Thermoanalysis of Metal Single Crystals and a New Thermoelectric Effect of Bismuth Crystals Grown in Magnetic Fields  

Microsoft Academic Search

Part I. The Thermoanalysis of Bi Single Crystals Production of crystals.-Crystals of Bi of any desired orientation were grown by the method of Goetz, one half of each normally, the other half within a transversal magnetic field. The orientations, predetermined by a seed crystal, were not affected by this process. Two methods of growth-the continuous and the discontinuous-were used. The

Alexander Goetz; Maurice F. Hasler

1930-01-01

469

Crystal growth, EPR and site-selective laser spectroscopy of Gd 3+-activated LiCaALF 6 single crystals  

Microsoft Academic Search

Ce3+-activated LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) single crystals are the most prospective active media for directly pumped UV solid-state tunable lasers. Due to the geterovalent activation nature of these crystals, crystal spectroscopic properties as well as their laser efficiency strongly depend on the actual crystal growth conditions. In order to establish the growth-related peculiarities of activator center formation in LiCAF,

R. Yu. Abdulsabirov; M. A. Dubinskii; S. L. Korableva; A. K. Naumov; V. V. Semashko; V. G. Stepanov; M. S. Zhuchkov

2001-01-01

470

Experimental deformation of olivine single crystals at lithospheric temperatures  

NASA Astrophysics Data System (ADS)

Rheological properties of mantle minerals and rocks at temperatures (T) appropriate to much of Earth's lithosphere have remained poorly constrained, even though past experimental studies on olivine single crystals and polycrystalline aggregates have quantified the high-temperature creep mechanisms (T > 1200C). Consequently, we have performed deformation experiments on crystals of San Carlos olivine at lower temperatures, from 900 to 1200C, in triaxial compression along the [101]c direction. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at differential stresses of 100 to 500 MPa. Several samples were deformed at constant displacement rate and others at constant load, in order to provide insight into possible effects of work-hardening. Under the deformation conditions investigated, little evidence of work-hardening was observed. The data follow a power-law dependence on stress, as in previous high-temperature deformation studies. The samples were, however, considerably weaker than predicted by the experimentally determined high-temperature constitutive equation for olivine crystals of this orientation from the study of Bai et al. (1991). The mechanical behavior correlates instead with the weaker of the two mechanisms (flow laws) that contribute to the high-temperature constitutive equation. Thus, our experiments demonstrate that published high-temperature constitutive equations overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at lower temperatures than previously inferred.

Demouchy, Sylvie; Schneider, Stephen E.; Mackwell, Stephen J.; Zimmerman, Mark E.; Kohlstedt, David L.

2009-02-01

471

Plastic anisotropy in MoSi{sub 2} single crystals  

SciTech Connect

Single crystals Of MoSi{sub 2} are an order of magnitude stronger when compressed along [001] than along any other orientation. This is because the easy slip systems, <101><100> and <110><111>, have a zero Schmid factor acting on them so that harder slip systems are forced into operation. We find that [001] crystals compressed at 1OOO{degree}C yield by slip on <103><331>. TEM shows that the 1/2<331> dislocations tend to decompose into 1/2<111> and <110> dislocations. This decomposition process apparently inhibits the mobility of 1/2<331> dislocations at higher temperatures and another system, <101><1ll>, becomes operative at 1300{degree}C and above. [021] crystals have been tested for comparison and are found to yield at much lower stresses on the easy systems. In the design of advanced high temperature structural materials based on MOSi{sub 2}, the large plastic anisotropy should be used to advantage.

Mitchell, T.E.; Maloy, S.A.

1993-05-01

472

Synthesis of mesoporous zeolite single crystals with cheap porogens  

NASA Astrophysics Data System (ADS)

Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR), temperature-programmed desorption of ammonia (NH3-TPD) and ultraviolet-visible spectroscopy (UV-vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. 27Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV-vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites.

Tao, Haixiang; Li, Changlin; Ren, Jiawen; Wang, Yanqin; Lu, Guanzhong

2011-07-01

473

Modification of mechanical properties of e-gun evaporated MgF 2 and CaF 2 thin films under ion beam bombardment  

NASA Astrophysics Data System (ADS)

The effect of ion beam assistance on mechanical properties (hardness and adhesion) of MgF 2 and CaF 2 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/mm 2 for CaF 2 and MgF 2 samples, respectively) than unbombarded samples (380 and 300 kg/mm 2 for CaF 2 and MgF 2, respectively). Critical loads (load where the delamination of the coating begins) of 12 and 3 N for bombarded MgF 2 and CaF 2 respectively and 4 and 1 N for unbombarded MgF 2 and CaF 2 samples have been found.

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

1989-12-01

474

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

475

Single crystal integration of an optical interference filter and photodiode  

SciTech Connect

An all-semiconductor, single-crystal, integrated optical detector has been produced for the visible, in which a photodiode and an optical interference filter (high reflector) were integrated in a single growth run by metal-organic chemical vapor deposition. In this structure, the high reflector is both optically and electrically active, being composed of alternating, doped, quarter-wave layers of GaP and GaAs/sub 0.2/P/sub 0.8/. The diode is a p-n junction superlattice composed of much thinner layers of GaP and GaAs/sub 0.35/P/sub 0.65/. The photodiode responds to light from 460 to 600 nm, while the high reflector rejects a narrow 10 nm band centered near 500 nm. The rejection factor is approx.7 db for these prototype devices. The quantum efficiency, linearity, temperature and bias dependence of the spectral response are reported.

Gourley, P.L.; Biefeld, R.M.; Zipperian, T.E.

1986-01-01

476

Thermally reversible single-crystal to single-crystal transformation of mononuclear to dinuclear Zn(ii) complexes by [2+2] cycloaddition reaction.  

PubMed

Two Zn(ii) complexes of trans-4-styrylpyridine ligands undergo [2+2] cycloaddition reaction forming Zn(ii) complex dimers in a single-crystal to single-crystal (SCSC) manner which were thermally reversible. The dimers are presumed to be the stable intermediates in the formation of 1D coordination polymers upon prolonged exposure to UV light. PMID:24022693

Medishetty, Raghavender; Yap, Terence Teck Sheng; Koh, Lip Lin; Vittal, Jagadese J

2013-09-24

477

Solid-state single-crystal-to-single-crystal transformation from a 2D layer to a 3D framework mediated by lattice iodine release.  

PubMed

We describe an exceedingly rare example of solid-state single-crystal-to-single-crystal transformation from a 2D layer to a known 3D framework via lattice iodine release, which involves the formation of a new Cu-O ligand bond and a change in the metal coordination geometry. PMID:22785388

He, Yuan-Chun; Yang, Jin; Yang, Guo-Cheng; Kan, Wei-Qiu; Ma, Jian-Fang

2012-07-02

478

Synthesis, growth and characterization of 4-methyl anilinium phenolsulfonate single crystal  

NASA Astrophysics Data System (ADS)

4-Methyl anilinium phenolsulfonate single crystal has been synthesized and grown by the slow evaporation solution technique at room temperature using methanol as a solvent. The crystal structure of the grown crystal was determined by the single crystal X-ray diffraction method. The various functional groups present in the crystal, and the different types of protons and carbons have been identified by the FT-IR and NMR spectral analyses respectively. Optical properties were determined by UVvisNIR spectroscopic and photoluminescence studies. The thermal and mechanical stabilities of 4-methyl anilinium phenolsulfonate single crystal have been investigated by TGA/DTA and Vickers microhardness measurements respectively.

Jovita, Josephine Viagulamary; Boopathi, Kittusamy; Ramasamy, Perumal; Ramanand, Aroor; Sagayaraj, Pappu

2013-10-01

479

Growth and characterization of large-diameter, lithium-free ZnO single crystals  

NASA Astrophysics Data System (ADS)

Large-diameter, lithium-free ZnO single-crystal substrates of high crystalline quality will enable development and commercialization of high-performance ZnO-based semiconductor devices, such as UV and visible light emitting diodes (LEDs), UV laser diodes and solar-blind UV detectors for variety of applications. We have recently developed a novel crystal growth technique for producing lithium-free ZnO single crystal boules of 1 inch in diameter. We also fabricated ZnO single crystal wafers in sizes up to 1 inch in diameter. Chemical purity, crystalline defects, and electrical resistivity of ZnO single crystals were analyzed. Results from crystal growth and material characterization are presented and discussed. Our research results suggest that the novel crystal growth technique is a viable production technique for producing ZnO single crystals and substrates for semiconductor device applications.

Wang, Shaoping; Kopec, Aneta; Timmerman, Andrew G.

2012-02-01

480

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

481

Experimental and numerical study of the tantalum single crystal spallation  

NASA Astrophysics Data System (ADS)

Using X-microtomography and non equilibrium classical molecular dynamics, we present a study of the elementary processes of spallation of single crystal tantalum. The single crystal is illuminated by a laser pulse which induces the propagation of a strong unsustained shock. The analysed data mainly are number and shape of pores resulting from the tensile inside the material when the incident shock reflects on the opposite face. Experimental pores size distribution exhibits two power laws attributed to the growth and the coalescence stages. The average pore shape is ellipsoid with main axis along the shock axis propagation. This first part is completed by a large scale molecular dynamics simulation mimics at reduced scale the real experiment. After preliminary calculations validating the chosen potential function the formation and shock propagation is detailed. Then we extract from the simulation similar data than in experiment. The pores size distribution shows three power laws identified as the nucleation, the growth and the coalescence stages. The slopes of the two last stages are very similar to the experimental one, confirming the scale invariance of this data as suggested by their analytical form. The general pore shape also is close to the experiment shape but with a different orientation (perpendicular to the shock propagation axis).

Soulard, L.; Bontaz-Carion, J.; Cuq-Lelandais, J. P.

2012-10-01

482

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

PubMed

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

Zahn, Dirk; Heitjans, Paul; Maier, Joachim

2012-04-04

483

Anisotropic Modeling of Shocked Single Crystals with Application to Energetic Materials  

Microsoft Academic Search

A continuum, anisotropic modeling framework has been developed for simulating shock wave propagation in single crystals of arbitrary orientation. Our modeling approach incorporates nonlinear elasticity and crystal plasticity in a thermodynamically consistent tensor formulation. Crystal plasticity is described using a model that considers dislocation motion along specified slip planes. Shear cracking along specified crystal planes is also considered. Numerical simulations,

J. M. Winey

2005-01-01

484

Large CdS single crystals with a high optical strength  

Microsoft Academic Search

Large US single crystals were fabricated by a free growth from the vapour phase in the presence of chemical compounds that bind the excess cadmium and do not enter into the growing crystal. Some parameters of the bulk crystals fabricated by this method and by traditional methods are compared. The crystals grown by the method developed are shown to have

N. V. Klimova; N. E. Korsunskaya; I. V. Markevich; G. S. Pekar; A. F. Singaevsky

1995-01-01

485

High resolution technique and instrument for measuring lattice parameters in single crystals  

US Patent & Trademark Office Database

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