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1

Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters  

NASA Technical Reports Server (NTRS)

An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

1990-01-01

2

Surface tension of ZrF4-BaF2-LaF3 glass  

SciTech Connect

A solidified pendant drop technique is presently used in the measurement of surface tension of a 62 mol pct ZrF4, 33 mol pct BaF2, 5 mol pct LaF3 heavy metal-fluoride glass, in keeping with a requirement from a comparison experiment planned for microgravity conditions aboard the Space Shuttle. The surface tension at 550 C is 0.174 + or - 0.005 J/sq m. 9 references.

Bansal, N.P.; Doremus, R.H.

1984-10-01

3

Localization of intrinsic defects in CaF2-BaF2 superlattices  

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

4

BaF2CaF2-YF3-AlF3 Glass Systems for Infrared Transmission  

Microsoft Academic Search

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

Terutoshi Kanamori; Kiyoshi Oikawa; Shuichi Shibata; Toyotaka Manabe

1981-01-01

5

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

NASA Technical Reports Server (NTRS)

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

Deadmore, Daniel L.; Sliney, Harold E.

1987-01-01

6

Annealing effect on ion conduction of nanosized CaF2/BaF2 multilayers  

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

7

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

8

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

SciTech Connect

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

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

2013-12-01

9

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

NASA Astrophysics Data System (ADS)

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

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

1981-05-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

12

Investigation of the superionic behaviour of BaF2 (x mol% LaF3) by Raman and Brillouin scattering and molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

High temperature Raman and Brillouin light scattering experiments have been combined with molecular dynamics simulations to provide a comprehensive study of the superionic state of BaF2 (x mol% LaF3) over a particularly wide range of LaF3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show the usual T-2g symmetry mode at 241 cm(-1) , but for samples with x =20, 30 and 50 the dominant Raman mode is at higher frequencies and of E-g symmetry. The temperature dependence of the Raman line-widths show initial near linear increases followed by substantial increases above temperatures (T-c) at 1200, 850, 800, 975, 950 and 920 K for x =0, 5, 10, 20, 30 and 50. In the Brillouin scattering experiments, the acoustic modes respectively related to elastic constants C-11 and C-44 initially showed a quasi-linear decrease in frequency with increasing temperature. Above the same characteristic values of T-c , where the Raman line-widths show marked increases, there are substantial decreases in the elastic constant C-11 for all samples with x =0 to 50. Only the doped samples showed significant decreases in C-44 at corresponding values of T-c . Molecular dynamics (MD) simulations have been carried out on the same systems. From the calculated mean square displacements, the diffusion coefficients (D) of the mobile fluorine ions were calculated as a function of temperature for each of the samples. Substantial increases in the values of D occur above the respective values of T-c determined in the light scattering experiments. The MD simulations also provide details of the mechanisms of diffusion of the mobile fluorine ions. The results emphasize the role of motional effects as an explanation of the mechanisms responsible and provide a self-consistent explanation of the dominant processes in the superionic phase of doped fluorites.

Rammutla, K. E.; Comins, J. D.; Erasmus, R. M.; Netshisaulu, T. T.; Ngoepe, P. E.; Chadwick, A. V.

13

Enhanced processability of ZrF4-BaF2-LaF3-AlF3-NaF glass in microgravity  

NASA Astrophysics Data System (ADS)

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 ?m in the UV to 7 ?m in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx - Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subject to a heating and quenching test apparatus on the parabolic aircraft, under a controlled 0-g and hyper-g environment and compared with 1-g ground tests. The microgravity duration on board Zero-G Corporation parabolic aircraft is approximately 20 seconds and the hyper-g intervals are approximately 56 seconds. Optical microscopy examination elucidates crystal growth in ZBLAN is suppressed when processed in a microgravity environment. The crystallization temperature, Tx, at which crystals form increased, therefore, significantly broadening the working temperature range for ZBLAN.

Torres, Anthony; Ganley, Jeff; Maji, Arup; Tucker, Dennis; Starodubov, Dmitry

2013-06-01

14

Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass  

NASA Astrophysics Data System (ADS)

Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law ?? dependence in the frequency range 30-300 GHz. Temperature dependence of ?(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation.

Adichtchev, S. V.; Malinovsky, V. K.; Ignatieva, L. N.; Merkulov, E. B.; Surovtsev, N. V.

2014-05-01

15

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

NASA Astrophysics Data System (ADS)

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

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

1982-12-01

16

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

PubMed

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

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

1977-02-01

17

Temperature dependence of the dielectric permittivity of CaF2, BaF2 and Al2O3: application to the prediction of a temperature dependent van der Waals surface interaction exerted onto a neighbouring Cs (8P{3/2}) atom  

E-print Network

The temperature behaviour in the range 22\\degree C to 500\\degree C of the dielectric permittivity in the infrared range is investigated for CaF2, BaF2 and Al2O3 through reflectivity measurements. The dielectric permittivity is retrieved by fitting reflectivity spectra with a model taking into account multiphonon contributions. The results extrapolated from the measurements are applied to predict a temperature-dependent atom-surface van der Waals interaction. We specifically consider as the atom of interest Cs (8P3/2), the most relevant virtual couplings of which, fall in the range of thermal radiation and are located in the vicinity of the reststrahlen band of fluoride materials.

De Silans, Thierry Passerat; Segundo, Pedro Chaves De Souza; Saltiel, Solomon; Gorza, Marie-Pascale; Ducloy, Martial; Bloch, Daniel; Meneses, Domingo De Sousa; Echegut, Patrick; 10.1088/0953-8984/21/25/255902

2009-01-01

18

Ionic conductivity of the phases of five types formed in the BaF2-GdF3 system  

NASA Astrophysics Data System (ADS)

The ionic conductivity has been measured in ceramic phases of five structure types found in the BaF2-GdF3 system: the fluorite type (CaF2), its trigonal and tetragonal distortions, the tysonite type (LaF3), and the orthorhombic ?-YF3 modification. The phases have been obtained by solid-phase synthesis from BaF2 and GdF3 mixtures in hermetic nickel containers at 925, 964, and 1067°C for 108-360 h in a fluorine atmosphere. Their conductivity ? is compared in correlation with the composition and structure type. The highest conductivity values are found for the tysonite Gd1 - y Ba y F3 - y phase (0.10 ? y ? 0.25): (1-2) × 10-3 S/cm at 683 K. The ordered Ba0.60Gd0.40F2.40 and Ba0.57Gd0.43F2.43 phases with fluorite-derived structures and different degrees of order are characterized by the lowest conductivities: i(1.5-3.5 × 10-5) S/cm.

Sorokin, N. I.; Sobolev, B. P.

2012-07-01

19

The spin kinetics of 3He in contact with nanosized crystalline powders LaF3  

NASA Astrophysics Data System (ADS)

The spin kinetics of 3He in contact with nanosized crystalline powders LaF3 has been studied by NMR methods at the temperature 1.5 K. The 3He longitudinal relaxation time increases proportionally to the magnitude of the external magnetic field and the transverse relaxation time does not depend on the magnetic field. Relaxation of the gaseous and liquid 3He in contact with nanosized crystalline powder LaF3 takes place by the 3He adsorbed layer. The nuclear magnetic relaxation of adsorbed 3He layer on the surface of LaF3 nanoparticles is due to the two-dimensional spin-diffusion motion.

Alakshin, E. M.; Gazizulina, A. M.; Gazizulin, R. R.; Klochkov, A. V.; Safin, T. R.; Safiullin, K. R.; Tagirov, M. S.; Zakharov, M. Yu

2014-12-01

20

LaF3 nanoparticles surface modified with tryptophan and their optical properties  

NASA Astrophysics Data System (ADS)

LaF3 nanoparticles were synthesized by the double-jet precipitation technique in presence of tryptophan (Trp). The product was investigated by TEM, IR, absorption, and luminescence spectroscopies. Interaction of Trp with the nanoparticles results in formation of complexes between Trp and La3+ ions on the nanoparticle surface. Surface density of Trp was found as 0.7 molecule nm-2. It is shown that the modifier effects on LaF3 nanoparticle growth and stability of the surface modified LaF3 colloids. Luminescent properties of LaF3 nanoparticles modified with Trp (Trp@LaF3) are investigated. It is determined that Trp@LaF3 and Trp have the same profiles of excitation and photoluminescence spectra. Effects of pH, ionic strength, and Trp concentration on luminescence intensity are studied. At the same Trp amounts in the systems, Trp@LaF3 luminescence intensity is about 6 times less than Trp luminescence intensity. Such products can be used as luminescent labels.

Safronikhin, Anatoly; Ehrlich, Heinrich; Lisichkin, Georgy

2014-10-01

21

Bioconjugations of polyethylenimine-capped LaF3:Ce, Tb nanoparticles with bovine serum albumin and photoluminescent properties.  

PubMed

Water-soluble Ce3+ and Tb3+ co-doped LaF3 nanoparticles with surfaces functionalized by a layer of polyethylenimine (PEI) were synthesized via a facile one-step hydrothermal method. Bovine serum albumin (BSA) protein was conjugated with LaF3:Ce, Tb nanoparticles via free amino groups on the surfaces of the nanocrystals. The final products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet (UV) spectrophotometry, and photoluminescence (PL) spectroscopy. XRD results showed that pure hexagonal phase LaF3:Ce, Tb nanoparticles could be obtained via a PEI assisted hydrothermal process at 180 degrees C for 24 h. The FE-SEM results showed that the morphology of pure LaF3:Ce, Tb nanoparticles was spherical with an average diameter of -20 nm. The UV spectra showed that BSA had been conjugated with LaF3:Ce, Tb nanoparticles. The photoluminescent (PL) properties of LaF3:Ce, Tb nanoparticles were also studied. The strong green emission of Tb3+ in LaF3:Ce, Tb nanoparticles suggests that these nanoparticles may have potential applications for labels in biological imaging and immunoassays. PMID:24734615

Zhang, Wei; Hua, Ruinian; Shao, Wanyue; Zhao, Jun; Na, Liyan

2014-05-01

22

Crystal field of rare earth impurities in LaF3  

NASA Astrophysics Data System (ADS)

The crystal field parameters of 13 trivalent lanthanide ions substituted for La in LaF3 were calculated using the combination of the band structure and Wannier function calculations. Performing an atomic exact diagonalization with thus obtained crystal-field parameters we compute the crystal-field splitting of atomic multiplets. The calculation is compared with the available experimental results and a good agreement is found.

Novák, P.; Kuneš, J.; Knížek, K.

2014-11-01

23

Optical and luminescence characteristics of BaF2 and BaF2:Tm in vacuum UV and UV spectral regions  

NASA Astrophysics Data System (ADS)

The spectral characteristics of BaF2 and BaF2:Tm crystals and ceramics are compared. The vacuum UV (VUV) and UV absorption spectra and excitation spectra of core-valence and exciton luminescence are investigated. The main exciton and electron-hole processes responsible for the structure of recorded spectra are considered.

Rodnyi, P. A.; Khanin, V. M.; Voloshinovskii, A. S.; Striganyuk, G. B.; Garibin, E. A.; Gusev, P. E.; Krutov, M. A.; Demidenko, A. A.

2014-09-01

24

Study on an antiwear and extreme pressure additive of surface coated LaF 3 nanoparticles in liquid paraffin  

Microsoft Academic Search

A LaF3 nanoparticle surface coated by organic compounds containing S and P was synthesized by the chemical surface modification method. The particle size and structure were characterized using a transmission electron microscope (TEM) and electron diffraction (ED), their tribological behaviors were evaluated on a four-ball machine. The results showed that LaF3 nanoparticles as an oil additive can strikingly improve the

Jingfang Zhou; Zhishen Wu; Zhijun Zhang; Weimin Liu; Hongxin Dang

2001-01-01

25

Trigonal LaF3: a novel SRS-active crystal  

NASA Astrophysics Data System (ADS)

Trigonal fluoride LaF3, widely known as a host crystal for Ln3+-lasants, was found to be an attractive many-phonon Raman material and a subject for the investigation of different ?(3)-nonlinear optical effects. We present the manifestation of photon-phonon interactions related to stimulated Raman scattering (SRS) and Raman-induced four-wave mixing (RFWM) processes, initiated by picosecond ex?itation at room temperature. Sesqui-octave-spanning Stokes and anti-Stokes frequency comb generation as well as many-step cascaded and cross-cascaded up-conversion ?(3)-nonlinear processes have been observed. The recorded spectral lines originated by SRS and RFWM are identified and attributed to the three observed SRS-promoting phonon modes. The lower limit of the steady-state Raman gain coefficient for near-IR first Stokes generation was estimated. Moreover, a brief review of known Ln3+?:?LaF3 laser crystals and SRS-active fluorides is given.

Kaminskii, A. A.; Lux, O.; Hanuza, J.; Rhee, H.; Eichler, H. J.; Zhang, J.; Tang, D.; Shen, D.; Yoneda, H.; Shirakawa, A.

2014-12-01

26

Humidity response properties of a potentiometric sensor using LaF3 thin film as the solid electrolyte.  

PubMed

A thin-film type potentiometric sensor has been prepared by the implementation of electro-beam evaporation, rf magnetron sputtering methods, and micromachining processes. Sn film was deposited on n-Si/SiO(2) (400 nm) substrate. A deposited LaF(3) film was applied as solid electrolyte and sputtered Pt film was used as the sensing electrode. The patterns of the Pt and LaF(3) were realized by the micromachining processes. The LaF(3) film was characterized by scanning electron microscopy and energy dispersive x ray. Saturated aqueous solutions were used to achieve controlled humidity environments. When the sensor was exposed to humidity environments, the electromotive force (EMF) of the sensor was examined. It was found that the sensor varies with the relative humidity (RH). The stable response curve was presented and non-Nernst behavior between the average EMF values and RH may be shown. PMID:21895252

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

27

Synthesis and formulation of methotrexate (MTX) conjugated LaF3:Tb(3+)/chitosan nanoparticles for targeted drug delivery applications.  

PubMed

Chitosan functionalized luminescent rare earth doped terbium nanoparticles (LaF3:Tb(3+)/chi NPs) as a drug carrier for methotrexate (MTX) was designed using a simple chemical precipitation method. The synthesized chitosan functionalized nanoparticles were found to be spherical in shape with an average diameter of 10-12nm. They are water soluble and biocompatible, in which the hydroxyl and amino functional groups on its surface are utilized for the bioconjugation of the anticancer drug, the methotrexate. The nature of MTX binding with LaF3:Tb(3+)/chi nanoparticles were examined using X-ray diffraction, zeta potential analyzer and transmission electron microscopy. The other interactions due to complex formation between MTX and LaF3:Tb(3+)/chi NPs were carried out by UV-Visible, steady and excited state fluorescence spectroscopy. The photo-physical characterization revealed that the adsorption and release of MTX from LaF3:Tb(3+)/chi NPs is faster than gold nanoparticles and also confirms that this may be due to weak interaction i.e. the Vander Waals force of attraction between the carboxyl and amino group of drug and nanoparticles. The maximum percentage yield and entrapment efficiency of 85.91±0.71 and 83.82± 0.14 were achieved at a stochiometric ratio of 4:5 of MTX and LaF3:Tb(3+)/chi nanoparticles respectively. In addition, antitumoral activity study reveals that MTX conjugated LaF3:Tb(3+)/chi nanoparticles show higher cytotoxic effect on MCF-7 breast cancer cell lines than that of free MTX. PMID:25661354

Mangaiyarkarasi, Rajendiran; Chinnathambi, Shanmugavel; Aruna, Prakasarao; Ganesan, Singaravelu

2015-02-01

28

Gamma irradiation effect on photoluminescence from functionalized LaF3:Ce nanoparticles  

NASA Astrophysics Data System (ADS)

Oleic acid coated and uncoated LaF3:Ce nano-phosphor particles were synthesized by a co-precipitation method. Nanoparticles were characterized for their structure, organic coating and optical behavior using an X-ray diffraction, a Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption and Photoluminescence spectroscopy. Sizes of nanoparticles were measured from TEM images and were also estimated using the Scherer formula. UV-vis absorption, Photoluminescent and FTIR measurements were done with nanoparticles before and after gamma irradiation up to a dose of 6.19 kGy. The uncoated nanoparticles exhibit emission only at 305 nm when exited with 250 nm. The oleic acid coated nanoparticles exhibit emissions at 308 and 361 nm when exited with 252 nm. Dependence of photo luminescent intensity on gamma dose was studied and the changes were attributed to radiation induced defect traps and also to the breach or damage in the capping material.

Srinivasan, T. K.; Panigrahi, B. S.; Arora, A. K.; Venkatraman, B.; Ponraju, D.

2014-06-01

29

LaF 3:Ce nanocomposite scintillator for gamma-ray detection  

NASA Astrophysics Data System (ADS)

Nanophosphor LaF 3:Ce has been synthesized and incorporated into a matrix to form a nanocomposite scintillator suitable for application to ?-ray detection. Owing to the small nanocrystallite size (sub-10 nm), optical emission from the ? / nanophosphor interaction is only weakly Rayleigh scattered (optical attenuation length exceeds 1 cm for 5-nm crystallites), thus yielding a transparent scintillator. The measured energy resolution is ca. 16% for 137Cs ? rays, which may be improved by utilizing brighter nanophosphors. Synthesis of the nanophosphor is achieved via a solution-precipitation method that is inexpensive, amenable to routine processing, and readily scalable to large volumes. These results demonstrate nanocomposite scintillator proof-of- principle and provide a framework for further research in this nascent field of scintillator research.

McKigney, E. A.; Muenchausen, R. E.; Cooke, D. W.; Del Sesto, R. E.; Gilbertson, R. D.; Bacrania, M. K.; Bennett, B. L.; Jacobsohn, L. G.; McCleskey, T. M.; Ott, K. C.; Sitarz, S. C.; Smith, J. F.; Stange, S.

2007-09-01

30

Refluxing synthesis, photoluminescence and binding ability to deoxyribonucleic acid of water-soluble rare earth ion-doped LaF3 nanoparticles.  

PubMed

Water-soluble rare earth ion (Ce3+, Tb3+)-doped LaF3 nanoparticles with the ability to bind to deoxyribonucleic acid (DNA) were prepared by the refluxing method in a glycerol/water mixture and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and so on. The obtained LaF3:Ce3+, LaF3:Tb3+ and LaF3:Ce3+, Tb3+ nanoparticles are well crystallized with a hexagonal structure and composed of spherical particles with an average size from 11 to 19 nm. The as-prepared samples can be dispersed into water to form a colloidal solution. Under ultraviolet (UV) light irradiation, the emission lines of Tb3+ in the co-doped LaF3:Ce3+, Tb3+ are evidently strengthened compared to those in the single-doped LaF3:Tb3+ nanoparticles, which is due to the energy transfer from Ce3+ to Tb3+ ions in the LaF3:Ce3+, Tb3+ samples. The biological experiment confirms that the water-soluble LaF3:Ce3+, Tb3+ nanoparticles can be bonded to the DNA molecules and emit visible light under UV irradiation. These luminescent nanoparticles could be used similarly to ethidium bromide (EtBr), which has been used extensively as a DNA staining reagent. The advantage that LaF3:Ce3+, Tb3+ nanoparticles have lower toxicity than EtBr makes them a potential reagent instead of EtBr in the DNA staining in biological experiments. PMID:24738421

Wang, Zhenling; Zhang, Yi; Li, Chunyang; Zhang, Xinlei; Chang, Jiazhong; Xie, Jianping; Li, Chengwei

2014-06-01

31

Formation and Luminescence Phenomena of LaF3:Ce3+ Nanoparticles and Lanthanide-Organic Compounds in Dimethyl Sulfoxide  

SciTech Connect

LaF3:Ce3+ doped nanoparticles were synthesized at different temperatures in dimethyl sulfoxide by the chemical reaction of lanthanum nitrate hydrate and cerium nitrate hexahydrate with ammonium fluoride. The formation of Ce3+ doped LaF3 nanoparticles is confirmed by X-ray diffraction and high resolution transmission electron microscopy. An intense emission at around 310 nm from the d - f transition of Ce3+ was observed from the LaF3:Ce3+ powder samples. However, in solution samples, the ultraviolet emission from Ce3+ is mostly absent, but intense luminescence is observed in the visible range from blue to red. The emission wavelength of the solution samples is dependent on the reaction time and temperature. More interestingly, the emission wavelength varies with the excitation wavelength. Most likely, this emission is from the metalorganic compounds of Ce3+ or La3+ and DMSO as similar phenomena are also observed when lanthanum nitrate hydrate or cerium nitrate hexahydrate are heated in DMSO.

Yao, Mingzhen; Joly, Alan G.; Chen, Wei

2010-01-21

32

Colloidal synthesis of BaF2 nanoparticles and their application as fillers in polymer nanocomposites  

NASA Astrophysics Data System (ADS)

Nanoparticles of pure and Eu-doped BaF2 have been prepared through sol-gel colloidal synthesis. In addition, BaF2-filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF2 nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF2 particles with an average diameter of 13.6 nm with a standard deviation of about ±2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu3+ (5D0?7F J ( J=1-4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF2 nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high-voltage applications.

Sathyamurthy, Srivatsan; Tuncer, Enis; More, Karren L.; Gu, Baohua; Sauers, Isidor; Paranthaman, M. Parans

2012-03-01

33

LaF3:Ln mesoporous spheres: controllable synthesis, tunable luminescence and application for dual-modal chemo-/photo-thermal therapy  

NASA Astrophysics Data System (ADS)

In this report, uniform LaF3:Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF3:Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF3:Ln hollow mesoporous spheres (HMSs) and LaF3:Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd3+ ions in LaF3:Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm3+ to Nd3+ ions under 980 nm near-infrared (NIR) irradiation. The LaF3:Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd3+ doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF3:Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging.In this report, uniform LaF3:Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF3:Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF3:Ln hollow mesoporous spheres (HMSs) and LaF3:Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd3+ ions in LaF3:Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm3+ to Nd3+ ions under 980 nm near-infrared (NIR) irradiation. The LaF3:Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd3+ doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF3:Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging. Electronic supplementary information (ESI) available: The SAED pattern of flower-like LaF3:Yb,Er spheres. FT-IR spectra of the La(OH)3:Ln precursor, LaF3:Ln HMSs and LaF3:Ln FMSs. UC emission spectra of the La(OH)3:Yb/Er(Ho/Tm) precursor, LaF3:Yb/Er(Ho/Tm) HMSs, LaF3:Yb/Er(Ho/Tm) FMSs under 980 nm NIR excitation. CIE chromaticity diagram of LaF3:10% Yb/0.5% Tm/x%Nd (x = 0, 1, 2) under 980 nm NIR excitation. CIE chromaticity diagram of LaF3:Yb/Er/Tm/Nd under 980 nm NIR excitation. Infrared thermal images of LaF3:Yb/Er, LaF3:Yb/Er/Tm, and LaF3:Yb/Er/Tm/Nd samples before and after irradiation for 6-8 min under 980 nm laser irradiation with the pump power of 0.6 W cm-2. See DOI: 10.1039/c4nr04336g

Lv, Ruichan; Yang, Guixin; He, Fei; Dai, Yunlu; Gai, Shili; Yang, Piaoping

2014-11-01

34

The luminescence of BaF2 nanoparticles upon high-energy excitation  

NASA Astrophysics Data System (ADS)

The dependence of X-ray excited luminescence intensity on BaF2 nanoparticle size was studied. A sharp decrease of self-trapped exciton luminescence intensity was observed when the nanoparticle size is less than 80 nm. The main mechanism of the luminescence quenching is caused by the escape of electrons from the nanoparticles. Escape of electrons from nanoparticles is confirmed by the considerable increase of luminescence intensity of the polystyrene scintillator with embedded BaF2 nanoparticles comparing with pure polystyrene scintillator.

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

2014-08-01

35

Relaxation of electronic excitations in CaF2 nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

36

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

37

LaF3:Ln mesoporous spheres: controllable synthesis, tunable luminescence and application for dual-modal chemo-/photo-thermal therapy.  

PubMed

In this report, uniform LaF(3):Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF(3):Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF(3):Ln hollow mesoporous spheres (HMSs) and LaF(3):Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd(3+) ions in LaF(3):Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm(3+) to Nd(3+) ions under 980 nm near-infrared (NIR) irradiation. The LaF(3):Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd(3+) doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF(3):Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging. PMID:25359551

Lv, Ruichan; Yang, Guixin; He, Fei; Dai, Yunlu; Gai, Shili; Yang, Piaoping

2014-12-21

38

Time resolved spectra of intrinsic emissions from crystalline BaF2  

NASA Astrophysics Data System (ADS)

The time resolved spectra of intrinsic luminescence at 300 nm and 220 nm in BaF2 crystals following F2p- valence electron and Ba5p++ core electron excitations have been studied. Based on the results the luminescence process related to starting and intensity increase of the emission at 300 nm after stopping excitation has been discussed.

Shi, Chao-shu; Kloiber, Thomas; Zimmerer, Georg

1990-06-01

39

Nd concentration dependence on the optical and scintillation properties of Nd doped BaF 2  

NASA Astrophysics Data System (ADS)

Nd concentration dependence on the scintillation properties of Nd x Ba 1-x F 2+x ( x = 0.001-0.5) crystals were investigated. From X-ray induced emission spectra, the intensity from an intrinsic luminescence of BaF 2 including core-valence luminescence and self-trapped-exciton (STE) emission were decreased with an increase of Nd concentration. Decay times under 241Am ?-ray excitation were evaluated by the Photomultiplier Tube (PMT) Hamamatsu R8778 that was sensitive across the vacuum ultra-violet (VUV) and visible wavelength range. The average decay times indicated that Nd doped BaF 2 with lower Nd concentration has obviously slower decay times than that of samples with higher Nd concentration because the decay time of STE emission was slower than that of the core-valence luminescence in BaF 2 and the emission of 5d-4f transition on Nd 3+. The light yield of fast Nd 3+ 5d-4f luminescence was quite lower than STE emission of BaF 2.

Kawaguchi, Noriaki; Yanagida, Takayuki; Futami, Yoshisuke; Fukuda, Kentaro; Suyama, Toshihisa; Yokota, Yuui; Yoshikawa, Akira; Nikl, Martin

2010-08-01

40

Electron paramagnetic resonance of Gd3+ ions in powders of LaF3:Gd3+ nanocrystals  

NASA Astrophysics Data System (ADS)

The observation of electron paramagnetic resonance of Gd3+ ions in nanosized powders of rare-earth fluorides LaF3:Gd3+ has been reported. The measurements have been performed on a single crystal and micro- and nanosized powders at room temperature. Electron paramagnetic resonance spectra and spin-Hamiltonian parameters of Gd3+ ions have been obtained. A qualitative difference of spectra in nano- and micropowders due to the increase in the spread of the crystal field parameters with the decrease in the particle size has been found. The relationship between the single-crystal domain size and the hydrothermal treatment time has been established.

Gazizulina, A. M.; Alakshin, E. M.; Baibekov, E. I.; Gazizulin, R. R.; Zakharov, M. Yu.; Klochkov, A. V.; Korableva, S. L.; Tagirov, M. S.

2014-04-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

42

VUV luminescence of BaF 2, BaF 2:Nd and BaY 2F 8 crystals under inner-shell excitation  

NASA Astrophysics Data System (ADS)

The VUV luminescence properties of several Ba containing crystals in the temperature range of 10-300 K were investigated using energy- and time-resolved spectroscopy under excitation by XUV photons. The results are compared with those obtained under excitation by photons up to 40 eV. The revealed new emission bands can originate from the radiative recombination of valence electrons with the outermost Ba 2+ 5p core holes and from the radiative transitions of multiply charged Ba ions. The possible inter-atomic cross-relaxation of holes from the fluorine to the barium ion in BaF 2 was revealed as well.

Kirm, Marco; Lushchik, Aleksandr; Lushchik, Cheslav; Makhov, Vladimir; Negodin, Evgeni; Vielhauer, Sebastian; Zimmerer, Georg

2002-06-01

43

Chitosan conjugation: A facile approach to enhance the cell viability of LaF3:Yb,Er upconverting nanotransducers in human breast cancer cells.  

PubMed

In this study, chitosan functionalized LaF3:Yb,Er upconverting nanotransducers (UCNTs) with controlled size and shape have been successfully synthesized by a facile one pot precipitation method. The chitosan encapsulated UCNTs show bright upconversion fluorescence upon excitation with 974nm NIR region. The average crystallite size of UCNTs about 7.6nm was achieved using chitosan mediated synthesis. The FTIR result confirms the chitosan coating over the LaF3:Yb,Er nanoparticles. Due to the surface modification using natural biopolymer chitosan, the as-prepared nanocrystals show excellent biocompatibility even at high dose at 200?g/ml. To the best of our knowledge the presented work is the first report on in vitro analysis of chitosan conjugated LaF3:Yb,Er upconverting nanocrystals in human breast (MCF-7) cancer cells. These nanotransducers can be used as luminescent probes for bioimaging and deep tissue cancer therapeutic applications. PMID:25659702

Gayathri, Sethuraman; Ghosh, Oriparambil Sivaraman Nirmal; Sudhakara, P; Viswanath, Annamraju Kasi

2015-05-01

44

Monodispersed LaF3 nanocrystals: shape-controllable synthesis, excitation-power-dependent multi-color tuning and intense near-infrared upconversion emission  

NASA Astrophysics Data System (ADS)

In this study, monodispersed and high-quality hexagonal phase LaF3 nanocrystals with different shapes and sizes were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared LaF3 nanocrystals were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and analysis of the upconversion spectra. The TEM results reveal that the samples present high uniformity and monodispersity and are self-assembled into a two-dimensional ordered array. Moreover, the shape, size and structure of the nanocrystals can be readily tuned by adjusting the NaF content. With increasing content of NaF, the shape of the LaF3 nanocrystals changed from particle to rod and the size gradually increased. More importantly, high NaF content favors the formation of one-dimensional nanorods. High Y b3+ and Er3+ content is beneficial to synthesizing the hexagonal phase of NaLaF4 nanocrystals. Furthermore, the TEM results show that the shape and size of the LaF3 nanocrystals can also be tuned by doping lanthanide ions, which provides a new route for size and shape control of nanocrystals. In addition, LaF3 nanocrystals co-doped with Y b3+/Tm3+ present efficient near-infrared (NIR)-NIR upconversion luminescence. More importantly, the upconversion luminescent colors can be readily tuned from blue-white to blue by adjusting the excitation power. Therefore, it is expected that these LaF3 nanocrystals with well-controlled shape, size and NIR-NIR upconversion emission have potential applications in biomedical imaging fields.

Rao, Ling; Lu, Wei; Ren, Guozhong; Wang, Haibo; Yi, Zhigao; Liu, Hongrong; Zeng, Songjun

2014-02-01

45

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

Microsoft Academic Search

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

Andrzej Daniluk; Piotr Mazurek; Krzysztof Paprocki; Pawel Mikolajczak

1998-01-01

46

Auger-free luminescence of the BaF 2:Sr, BaF 2:MgF 2 and CsBr:LiBr crystals under excitation of VUV photons and high-energy electrons  

NASA Astrophysics Data System (ADS)

The emission spectrum, the time dependence of the luminescence, the excitation spectrum and the reflectance spectrum have been measured for the pure BaF 2 crystal, the BaF 2:Sr crystals with Sr ++ concentrations of 2 and 5 mol%, the BaF 2:MgF 2 crystal with a mole mixing ratio of 1:2, and the pure CsBr crystal and the CsBr:LiBr crystal with a mole mixing ratio of 1:1. The measurements have been made by using synchrotron orbital radiation and high-energy electrons produced by gamma-rays. It is shown that the BaF 2, the BaF 2:Sr and the BaF 2:MgF 2 crystals have the Auger-free luminescence having decay times around 0.90 ns. The slow and fast luminescence components of the BaF 2 crystal are suppressed by introduction Sr ++ and Mg ++ ions. It is, however, clearly seen that the suppression of the slow component is more effectively occurring than that of the fast component, especially in the BaF 2:MgF 2 crystal. By analyzing the Auger-free luminescence spectrum, it is shown that the valence band widths are 2.7 ± 0.3 eV, 2.7 ± 0.3 eV and 4.2 ± 0.3 eV and the band-gap energies are 11.1 ± 0.3 eV, 11.1 ± 0.4 eV and 11.9 ± 0.4 eV for BaF 2, BaF 2:Sr and BaF 2:MgF 2 crystals, respectively. The introduction of LiBr into CsBr has resulted in a significant enhancement in the luminescence intensity, attaining 40 times larger intensity than that of CsBr crystal at room temperature, due to the suppression of the non-radiative relaxation of the outer-most core holes due to the absorption induced by the Urbach effect. The observations of the increases in the band gap-energy, the exciton energy and the decay time of the CsBr:LiBr crystal compared with those of the CsBr crystal support the argument given in the present study regarding the suppression of the Urbach effect in the CsBr:LiBr crystal. The decay times observed are 0.20 ± 0.05 ns and 0.90 ± 0.06 ns for CsBr and CsBr:LiBr crystals, respectively.

Hamada, Margarida Mizue

1994-03-01

47

Gd 2SiO 5(Ce 3+) and BaF 2 measured electron and photon responses  

NASA Astrophysics Data System (ADS)

Gd 2SiO 5(Ce 3+) (GSO) and BaF 2 electron responses were measured using the Compton Coincidence Technique (CCT). The CCT has previously been used to characterize several scintillators and has proven to be an accurate and reliable technique. The measured GSO electron response was observed to increase by 28% as the electron energy increased from 5 to 445 keV. The measured BaF 2 electron response increased 23% as the electron energy increased from 18 to 436 keV. Both electron responses become linear at higher electron energies (above about 200 keV). These observations made with GSO and BaF 2 in this study are consistent with the general trend reported for previous CCT characterized non-alkali halide scintillators. To validate the GSO and BaF 2 measured electron responses, respective photon responses were calculated and subsequently compared to measured photon response data. MCNP4C together with simplified electron cascade sequences for GSO and BaF 2 were used in these photon responses calculations. Calculated photon responses for both crystals are in good agreement (within 10%) with measured photon responses. This agreement confirms the accuracy of the GSO and BaF 2 measured electron responses.

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

2002-06-01

48

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

PubMed

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

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

2015-02-15

49

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

50

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

51

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

PubMed

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

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

2004-08-15

52

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

NASA Astrophysics Data System (ADS)

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

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

1998-05-01

53

Spectroscopy of single Pr3+ ion in LaF3 crystal at 1.5 K.  

PubMed

Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr(3+) ions in a bulk crystal of LaF3 at 1.5?K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr(3+) was measured at a wing of the spectral line of the (3)H4 ? (3)P0 transition at 627.33?THz (477.89?nm). The spectrum of individual Pr(3+) ions appears on top of the background of 60?cps as isolated peaks with intensities of 20-30?cps and full-width at half-maximum widths of approximately 3?MHz at an excitation intensity of 80?W cm(-2). PMID:25482137

Nakamura, Ippei; Yoshihiro, Tatsuya; Inagawa, Hironori; Fujiyoshi, Satoru; Matsushita, Michio

2014-01-01

54

Spectroscopy of single Pr3+ ion in LaF3 crystal at 1.5 K  

PubMed Central

Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr3+ ions in a bulk crystal of LaF3 at 1.5?K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr3+ was measured at a wing of the spectral line of the 3H4 ? 3P0 transition at 627.33?THz (477.89?nm). The spectrum of individual Pr3+ ions appears on top of the background of 60?cps as isolated peaks with intensities of 20–30?cps and full-width at half-maximum widths of approximately 3?MHz at an excitation intensity of 80?W cm?2. PMID:25482137

Nakamura, Ippei; Yoshihiro, Tatsuya; Inagawa, Hironori; Fujiyoshi, Satoru; Matsushita, Michio

2014-01-01

55

Spectroscopy of single Pr3+ ion in LaF3 crystal at 1.5 K  

NASA Astrophysics Data System (ADS)

Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr3+ ions in a bulk crystal of LaF3 at 1.5 K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr3+ was measured at a wing of the spectral line of the 3H4 --> 3P0 transition at 627.33 THz (477.89 nm). The spectrum of individual Pr3+ ions appears on top of the background of 60 cps as isolated peaks with intensities of 20-30 cps and full-width at half-maximum widths of approximately 3 MHz at an excitation intensity of 80 W cm-2.

Nakamura, Ippei; Yoshihiro, Tatsuya; Inagawa, Hironori; Fujiyoshi, Satoru; Matsushita, Michio

2014-12-01

56

Monodispersed Silica Nanospheres Encapsulating Fe3O4 and LaF3:Eu3+ Nanoparticles for MRI Contrast Agent and Luminescent Imaging  

NASA Astrophysics Data System (ADS)

Bifunctional nanospheres of silica encapsulating Fe3O4 and LaF3:Eu nanoparticles were synthesized in a reverse microemulsion solution. The nanospheres were perfectly monodispersed with a small diameter of 20 nm. The composition of the bifunctional nanospheres was confirmed by powder X-ray diffraction. Their magnetic and luminescent properties were measured at room temperature. The relaxation efficiency and T2-weighted images showed the high-performance for the product as a resonance imaging contrast agent. In addition, a qualitative cell uptake in human cervical cancer HeLa cells demonstrated that the SFLE nanospheres were efficiently up-taken into cytosol. Taken together, these findings suggest that the SiO2/Fe3O4-LaF3:Eu3+ nanospheres are good luminescence probes for bio-imaging.

Tian, Yang; Yu, Binbin; Yang, Hong-Yu; Liao, Ji

2013-02-01

57

Magnetic/upconversion luminescent mesoparticles of Fe3O4@LaF3:Yb3+, Er3+ for dual-modal bioimaging.  

PubMed

Multifunctional magnetic/upconversion luminescent mesoparticles, consisting of a Fe(3)O(4) nanoparticle core and a LaF(3):Yb(3+), Er(3+) nanocrystal shell, have been developed using a facile co-precipitation approach. Owing to their excellent superparamagnetic properties, superior T(2)-enhanced magnetic resonance effect and strong upconversion emissions, the as-formed mesoparticles have great potential in diverse medical diagnostics and biological imaging. PMID:23059635

Zhang, Lu; Wang, Ying-Shuai; Yang, Yang; Zhang, Fan; Dong, Wen-Fei; Zhou, Sheng-Yan; Pei, Wei-Hua; Chen, Hong-Da; Sun, Hong-Bo

2012-11-25

58

Slag Metal Reactions in Binary CaF2-Metal Oxide Welding Fluxes  

E-print Network

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

Eagar, Thomas W.

59

Vacuum ultraviolet Mach-Zehnder interferometer with CaF2 optics  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

60

Influence of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/porous-silicon structure prepared by chemical bath deposition technique  

NASA Astrophysics Data System (ADS)

Effect of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/PS heterojunction has been investigated in this report. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique LaF3 produced as LaCl3 are made to react with hydrofluoric acid on the porous silicon (PS) substrate. This enables direct deposition of LaF3 on the pore walls of the PS leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by energy dispersive of X-ray analysis. The diode ideality factor increases with LaCl3 concentration and decreases with annealing temperature. Therefore, by changing the LaCl3 concentration and annealing temperature quality of the LaF3 layer on PS can be optimized. It was also seen that the Ag/LaF3/PS/Si/Ag structure showed the formation of Schottky diode with a threshold voltage of about 5.5 V. From the experimental results it can be concluded that lanthanum fluorides can be deposited into the pores as well as on the top of PS by the CBD technique, which provides the required passivation for PS. This passivation can enable the PS to be considered as an important material for photonics.

Hafijur Rahman, Md.; Ismail, Abu Bakar Md.

2014-10-01

61

Dependency of built-in potential of LaF3/porous-silicon heterostructure prepared by chemical bath deposition technique on the concentration of LaCl3 and annealing temperature  

NASA Astrophysics Data System (ADS)

Effect of LaCl3 concentration and annealing temperature on the built-in potential of LaF3/PS heterojunction has been investigated in this report. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique LaF3 produced as LaCl3 are made to react with hydrofluoric acid on the porous silicon (PS) substrate. This enables direct deposition of LaF3 on the pore walls of the PS leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by energy dispersive of X-ray analysis. The built-in potential decreases with LaCl3 concentration and increases with annealing temperature. Therefore, by changing the LaCl3 concentration and annealing temperature quality of the LaF3 layer on PS can be optimized. From the experimental results it can be concluded that lanthanum fluorides can be deposited on the PS surface by the CBD technique, which provides the required passivation for PS. This passivation can enable the PS to be considered as an important material for photonics.

Rahman, Md. Hafijur; Ismail, Abu Bakar Md.

2014-12-01

62

Dislocations in YbF3 doped BaF2 crystals  

NASA Astrophysics Data System (ADS)

Three concentrations of YbF3 -doped BaF2 crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (˜10-1 Pa) using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. In order to study the etch pits morphology and the dislocations density the etching method have been used. This method consists in immersing the cleaved sample in 2N HCl at 60°C for 2 minutes. Small etch pits are developed at the emergence points of the dislocations. The etch pits have triangular or hexagonal shapes, depending on the dopant concentration. The dislocations density depends on the dopant concentration.

Cirlan, Florina; Buse, Gabriel; Nicoara, Irina

2014-11-01

63

Self-trapped exciton and core-valence luminescence in BaF2 nanoparticles  

NASA Astrophysics Data System (ADS)

The influence of the BaF2 nanoparticle size on the intensity of the self-trapped exciton luminescence and the radiative core-valence transitions is studied by the luminescence spectroscopy methods using synchrotron radiation. The decrease of the self-trapped exciton emission intensity at energies of exciting photons in the range of optical exciton creation (h? ? Eg) is less sensitive to the reduction of the nanoparticle sizes than in the case of band-to-band excitation, where excitons are formed by the recombination way. The intensity of the core-valence luminescence shows considerably weaker dependence on the nanoparticle sizes in comparison with the intensity of self-trapped exciton luminescence. The revealed regularities are explained by considering the relationship between nanoparticle size and photoelectron or photohole thermalization length as well as the size of electronic excitations.

Vistovskyy, V. V.; Zhyshkovych, A. V.; Chornodolskyy, Ya. M.; Myagkota, O. S.; Gloskovskii, A.; Gektin, A. V.; Vasil'ev, A. N.; Rodnyi, P. A.; Voloshinovskii, A. S.

2013-11-01

64

Nonradiative decay of core excitons in the Auger-free luminescence materials CsCl and BaF2  

NASA Astrophysics Data System (ADS)

The present work has been conducted to understand the decay processes of the Cs-5p and Ba-5p core excitons in CsCl and BaF2, respectively, where the Auger decay process of the Cs-5p and Ba-5p core holes is energetically forbidden. The core-exciton peaks are missing in the excitation spectra for the Auger-free luminescence, which arises from a radiative decay of the valence electrons into these core holes. Resonant enhancement effects of the valence-band photoelectron spectra are observed around 13 eV for CsCl and 17 eV for BaF2. The effects are attributed to the nonradiative decay through the direct-recombination process of an excited electron and the Cs-5p or Ba-5p core hole forming the core exciton. It is also found that the core exciton deforms its surrounding lattice with relaxation energies of about 0.3 eV in CsCl and 0.9 eV in BaF2. The nonradiative direct-recombination probabilities of the core excitons are estimated to be about 32% and 75% for CsCl and BaF2, respectively, by taking account of the lattice relaxation effects.

Kamada, Masao; Itoh, Minoru

2002-05-01

65

Low temperature epitaxy of Ge-Sb-Te films on BaF2 (111) by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition was employed to deposit epitaxial Ge2Sb2Te5-layers on the (111) plane of BaF2 single crystal substrates. X-ray diffraction measurements show a process temperature window for epitaxial growth between 85 °C and 295 °C. No crystalline growth is observed for lower temperatures, whereas higher temperatures lead to strong desorption of the film constituents. The films are of hexagonal structure with lattice parameters consistent with existing models. X-ray pole figure measurements reveal that the films grow with one single out-of-plane crystal orientation, but rotational twin domains are present. The out-of-plane epitaxial relationship is determined to be Ge2Sb2Te5(0001) || BaF2(111), whereas the in-plane relationship is characterized by two directions, i.e., Ge2Sb2Te5 [-12-10] || BaF2[1-10] and Ge2Sb2Te5[1-210] || BaF2[1-10]. Aberration-corrected high-resolution scanning transmission electron microscopy was used to resolve the local atomic structure and confirm the hexagonal structure of the films.

Thelander, E.; Gerlach, J. W.; Ross, U.; Lotnyk, A.; Rauschenbach, B.

2014-12-01

66

Epitaxial growth and characterization of CaF2 on Si  

NASA Astrophysics Data System (ADS)

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

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

1985-07-01

67

Shock Hugoniot and high pressure melting curve for CaF2  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

68

Kapitza limited spin-bath relaxation in CaF2: Ce3+  

Microsoft Academic Search

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

David J. Griffiths; Wen-Hsiung Chen

1979-01-01

69

Void superlattice formation in electron irradiated CaF2: Theoretical analysis  

Microsoft Academic Search

CaF2 is widely adopted as deep-UV window material and thin film optical coating. The void superlattice was observed experimentally under electron irradiation at room temperature. We performed kinetic Monte Carlo (kMC) simulations of the initial stages of the process when short- and intermediate-range order of defects in small Ca colloids and larger interstitial aggregates (F2 gas voids) is created. The

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

2010-01-01

70

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis  

Microsoft Academic Search

CaF2 is widely adopted as deep-UV window material and thin film optical coating. The void superlattice was observed experimentally under electron irradiation at room temperature. We performed kinetic Monte Carlo (kMC) simulations of the initial stages of the process when short- and intermediate-range order of defects in small Ca colloids and larger interstitial aggregates (F2 gas voids) is created. The

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

2010-01-01

71

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

PubMed

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

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

2005-06-29

72

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

PubMed

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

Yu, Shiyong; Zhi, Yunxia; Su, Haiquan

2014-05-01

73

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

Microsoft Academic Search

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

Deng Jianxin; Cao Tongkun; Yang Xuefeng; Liu Jianhua

2006-01-01

74

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

E-print Network

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

Krems, Roman

75

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

78

Cross luminescence of BaF2 crystal: Ab initio calculation  

NASA Astrophysics Data System (ADS)

Using ab initio methods and taking into account the lattice relaxation and polarization caused by the occurrence of the core hole, we have studied theoretically the cross luminescence in barium fluoride crystals in terms of the embedded-cluster approach. Two schemes of modeling of the core hole have been performed—in the form of an additional point charge and in the form of the 5 p state of the barium ion. Calculations have been done both by the Hartree-Fock method and by the density functional method. We have showed that the deformation of the lattice caused by the occurrence of the core hole leads to states localized on fluorine ions of the nearest environment splitting off from the valence band of the BaF2 crystal. The cross-luminescence bands at 5.7, 6.3, and 7.1 eV are caused by transitions from these localized states. We have also showed that the low-energy edge of the cross luminescence is formed by transitions from states that are localized on ions of the second coordination sphere.

Myasnikova, A. S.; Mysovsky, A. S.; Radzhabov, E. A.

2013-03-01

79

Auger-free luminescence due to interatomic transitions of valence electrons into core holes in BaF 2  

NASA Astrophysics Data System (ADS)

The nature of BaF 2 emission is investigated by measuring excitation spectra using synchrotron radiation for the energy range up to 40 eV. Intense emission bands, appearing at 5.6 and 6.4 eV in the Auger-transparent region, are ascribed to a radiative decay of valence electrons into Ba 2+ 5 p core holes. This luminescence process of a new type is discussed.

Itoh, Minoru; Hashimoto, Satoshi; Sakuragi, Shiro; Kubota, Shinzou

1988-02-01

80

Effect of BaF2 on crystal structure and luminescent properties of Sr2SiO4:Eu2+ for light emitting diode lighting.  

PubMed

Divalent europium-activated strontium silicate (Sr2SiO4:Eu2+) phosphors were prepared at relatively low temperature via a conventional solid-state reaction method, in which BaF2 was used as both flux and component. The effect of BaF2 on XRD patterns and luminescent properties of Sr2SiO4:Eu2+ was investigated. BaF2 could enhance the emission intensity and change the wavelength of emission peaks. These phosphors showed yellow to green emission bands with the amounts of BaF2. With a combination of blue LED chip, these phosphors are still more efficient in the amount used than commercial phosphors when they are doped on the chips, indicating that they may become promising phosphor candidates for white LEDs. PMID:23755593

Jeong, Woo Chul; Kim, Chang Hae

2013-03-01

81

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

PubMed

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

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

2008-06-13

82

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

83

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

NASA Astrophysics Data System (ADS)

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

Cho, Byungil; Lyu, Andy; Feldman, Mark

2012-11-01

84

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

85

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

86

Novel CaF2 Nanocomposite with High Strength and Fluoride Ion Release  

PubMed Central

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

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

2010-01-01

87

Facile fabrication and upconversion luminescence enhancement of LaF3:Yb3+/Ln3+@SiO2 (Ln = Er, Tm) nanostructures decorated with Ag nanoparticles.  

PubMed

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF(3):Yb(3+)/Ln(3+)@SiO(2) nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er(3+) and Tm(3+) containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells. PMID:24398901

He, Enjie; Zheng, Hairong; Dong, Jun; Gao, Wei; Han, Qingyan; Li, Junna; Hui, Le; Lu, Ying; Tian, Huani

2014-01-31

88

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

PubMed

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

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

2015-01-14

89

Optimization of BaF2 positron-lifetime spectrometer geometry based on the Geant4 simulations  

NASA Astrophysics Data System (ADS)

Incorrect choice of measuring experimental geometry and energy windows for a positron-lifetime spectrometer with BaF2 scintillators can lead to a significant distortion in a measured spectrum. Contribution of the distorted events for a non-optimal geometry may exceed 50%. It reduces the measured lifetimes of the spectral components and redistributes their intensities. The Geant4 simulation allows to estimate an influence of the measuring geometry on the spectrum distortion and to choose the most appropriate energy windows. The optimal geometry with a lead absorber between detectors suppresses contribution of the distorted coincidences down to 1% providing sufficiently high count rate of true events.

Dubov, L. Yu.; Grafutin, V. I.; Funtikov, Yu. V.; Shtotsky, Yu. V.; Elnikova, L. V.

2014-09-01

90

Melting investigation of the system BaF2 BaO 1/2 Y2O3 CuOx H2O  

NASA Astrophysics Data System (ADS)

In order to understand low-temperature melting during the 'BaF2 process', equilibria in the quaternary Ba, Y, Cu//O, F reciprocal system have been investigated using a compositional model which can be represented as a trigonal prism. This prism is comprised of three tetrahedra: BaF2-Y F3-CuF2-CuOx, BaF2-Y F3-\\case {1}{2} {\\mathrm {Y_{2}O_{3}}} -CuOx, and BaF2-BaO-\\case {1}{2} {\\mathrm {Y_{2}O_{3}}} -CuOx. Systematic differential thermal analysis (DTA) studies of compositions spaced along compositional vectors extending from the fluoride end of the prism to the oxide end gave evidence of low-melting liquids (<600 °C) near the fluorine-rich region in the BaF2-Y F3-CuF2-CuOx tetrahedron. In the intermediate BaF2-Y F3-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx tetrahedron, a low-temperature DTA peak (550-570 °C) was also identified; this has been shown to be due to a reversible phase transformation in crystalline YOF. In the oxide-rich BaF2-BaO-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx tetrahedron, where, in the presence of water vapour, the principal defluorination process is generally thought to occur, the lowest melting temperature observed was 815 °C at pO2 = 20 Pa and pH2O = 2.1 kPa. However, published observations on films undergoing the BaF2 process have suggested the presence of an amorphous phase thought to be a liquid at {\\le } 735\\,^{\\circ }{\\mathrm {C}} . Based on our results, the low-melting liquids reported in the literature do not appear to exist as a stable liquid phase in the BaF2-BaO-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx-H2O system under the conditions of our experiments. Rather, the formation of low-melting liquid in Ba-Y-Cu-O-F films at {\\le } 735\\,^{\\circ }{\\mathrm {C}} may require (a) relatively fluorine-rich compositions, (b) metastable melting, (c) formation of hydroxide- or hydroxyfluoride-based liquids, or (d) some combination thereof.

Wong-Ng, W.; Cook, L. P.; Suh, J.; Levin, I.; Feenstra, R.

2005-04-01

91

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

92

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

PubMed

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

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

2006-01-01

93

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

PubMed

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

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

2004-12-01

94

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

95

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

E-print Network

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

Himpsel, Franz J.

96

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

E-print Network

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

Paris-Sud XI, Université de

97

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

98

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

EPA Science Inventory

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

99

Relaxation and interaction of electronic excitations induced by intense ultra short light pulses in BaF2 scintillator  

NASA Astrophysics Data System (ADS)

Excitation density effects have a pronounced influence on relaxation processes in solids. They come into play in scintillating and dosimetric materials exposed to ionizing radiation or in laser materials operating in intense ultraviolet light fields. The scientific understanding of the underlying process is poor, mainly because most of the studies of light emitting materials under short wavelength excitation have been performed at weak and moderate excitation intensities due to limited availability of powerful light sources. Disembodied data on excitation density effects have been reported for wide-gap dielectrics studied by luminescence spectroscopy, by using such excitation sources as powerful ion beams,1,2pulsed electron beams,2,3 and wide-band hard X-ray synchrotron radiation.4 It is obvious that such non-selective excitation is a good tool for revealing density-related phenomena in these materials in general, but for investigating specific features of relaxation processes in insulators, light sources with well defined parameters are necessary. Since the shortwavelength free electron laser (FEL) technology has been devised by an international consortium at HASYLAB of DESY, resulting in the development of TESLA Test facility (TTF)5 and later in the construction of a dedicated FEL source FLASH in Hamburg,6 more advanced studies became possible. The range of interests towards this light source covers the fields from material science and various other branches of physics to structural biology. The pioneering luminescence study revealed excitation density effects in the decay of Ce3+ 5d-4f luminescence in Y3Al5O12 crystals and luminescence of BaF2 crystals in UV-visible range.7 These results motivated systematic investigations of excitation density effects in wide gap crystals using FEL8,9 and high-harmonic-generated VUV radiation,10 and, at lower energies, femtosecond laser pulses in the UV.11,12 The main goal of the present work is to analyze the same phenomenon in wide-band gap BaF2 crystals, where luminescence centres of different origin (self-trapped excitons and cross-luminescence) are present. Using models developed for explaining the non-linear behaviour of luminescence and exciton-exciton interaction effects causing scintillator non-proportionalities,10,13 simulations of luminescence decay curves are performed. Possible quenching effects in the cross-luminescence decay of BaF2 under XUV excitation have been analyzed by Terekhin et al.14

Kirm, M.; Nagirnyi, V.; Vielhauer, S.; Feldbach, E.

2011-06-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

101

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

PubMed

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

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

2010-06-01

102

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

PubMed

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

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

2005-05-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

105

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

NASA Astrophysics Data System (ADS)

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

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

1990-05-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2000-08-01

107

Transmission and reflection studies of thin films in the vacuum ultraviolet  

NASA Technical Reports Server (NTRS)

Both the transmittance and reflectance of 2 mm thick MgF2 substrates and of thin films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on these substrates were measured for the wavelength range 120 nm to 230 nm. Results for BaF2, LaF2 and MgF2 show promise as being good materials from which interference filters can be made. The software and related hardware needed to take large amounts of data automatically in future measurements of the transmittance and reflectance was developed.

Peterson, Lennart R.

1989-01-01

108

LAMBDA: Large Area Modular BaF2 Detector Array for the measurement of high energy gamma rays  

E-print Network

A large BaF2 detector array along with its dedicated CAMAC electronics and VME based data acquisition system has been designed, constructed and installed successfully at VECC, Kolkata for studying high energy gamma rays (E>8 MeV). The array consists of 162 detector elements. The detectors were fabricated from bare barium fluoride crystals (each measuring 35 cm in length and having cross-sectional area of 3.5 cm X 3.5 cm X 35.0 cm). The basic properties of the detectors (energy resolution, time resolution, efficiency, uniformity, fast to slow ratio etc.) were studied exhaustively. Complete GEANT3 monte carlo simulations were performed to optimize the detector design and also to generate the response function. The detector system has been used successfully to measure high energy photons from 113Sb, formed by bombarding 145 and 160 MeV 20Ne beams on a 93Nb target. The measured experimental spectra are in good agreement with those from a modified version of the statistical model code CASCADE. In this paper, we present the complete description of this detector array along with its in-beam performance.

S. Mukhopadhyay; Srijit Bhattacharya; Deepak Pandit; A. Ray; Surajit Pal; K. Banerjee; S. Kundu; T. K. Rana; S. Bhattacharya; C. Bhattacharya; A. De; S. R. Banerjee

2007-10-11

109

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

NASA Astrophysics Data System (ADS)

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

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

1989-12-01

110

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

111

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

SciTech Connect

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

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

2014-01-01

112

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

E-print Network

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

American Society for Testing and Materials. Philadelphia

2006-01-01

113

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

115

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

NASA Astrophysics Data System (ADS)

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

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

1994-01-01

116

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

Microsoft Academic Search

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

Felix Loske; Michael Reichling; Angelika Kühnle

2011-01-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2007-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

119

The colouration of CaF2 crystals by keV and GeV ions  

NASA Astrophysics Data System (ADS)

CaF2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 nm. This includes the vacuum UV region. For 100 keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10(17) ions cm(2) ) but no colour centres (F, F-2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10(12) ions cm(-2) attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 nm in the VUV and bands at 604 nm and 672 nm in the visible region.

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

120

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

NASA Technical Reports Server (NTRS)

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

Duncan, R. C., Jr.

1972-01-01

121

Structural and magnetic properties of the layered manganese oxychalcogenides (LaO)2Mn2Se2O and (BaF)2Mn2Se2O  

NASA Astrophysics Data System (ADS)

The new layered manganese oxychalcogenides (LaO)2Mn2Se2O and (BaF)2Mn2Se2O, isostructural to (LaO)2Fe2Se2O, were synthesized by solid state reaction method. The single crystals of the former compound were also successfully grown using fusion method. The polycrystalline samples show the semiconducting behavior with the activation energy gaps of about 278 and 416 meV for (LaO)2Mn2Se2O and (BaF)2Mn2Se2O, respectively. The magnetic susceptibility and specific heat indicate an antiferromagnetic (AFM) transition at around 160 ± 1 K for the former compound and 100 ± 1 K for the latter compound. The strong anisotropic magnetic properties below TN of the former compound suggests a long-range canted AFM ordering. A broad maximum of the susceptibility can be observed for the two compounds at high temperatures of 360 and 210 K, respectively, suggesting that strong frustrated magnetic correlation gives rise to low-dimensional AFM or short-range ordering at high temperatures in these rare transition metal oxychalcogenides with an AFM checkerboard spin lattice.

Liu, R. H.; Zhang, J. S.; Cheng, P.; Luo, X. G.; Ying, J. J.; Yan, Y. J.; Zhang, M.; Wang, A. F.; Xiang, Z. J.; Ye, G. J.; Chen, X. H.

2011-05-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

123

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

PubMed

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

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

2014-01-01

124

Intensity Enhancement of Auger-Free Luminescence in BaF2 and CsCl by Acceleration Voltage of Electron-Beam Excitation  

NASA Astrophysics Data System (ADS)

Cathodoluminescence of BaF2 and CsCl has been studied at room temperature by changing the applied acceleration voltage from 2 to 15 kV@. A two-photon emission process takes place in these materials. One is an ordinary interband luminescence (IBL) between the conduction and valence bands. The other is a specific type of luminescence, the so-called Auger-free luminescence (AFL), between the valence and outermost-core bands. It is found that the intensity of AFL enhances with increasing acceleration voltage, compared to that of the IBL@. The present result is important and useful for improving the quantum yield of light-emitting devices.

Yoshida, Hisashi; Hayashi, Masato; Itoh, Minoru

2000-03-01

125

Experimental measurements and GEANT4 simulations for a comparative study of efficiencies of LaBr3:Ce, NaI(Tl), and BaF2  

NASA Astrophysics Data System (ADS)

This paper presents the results of our measurements and detailed simulations using GEANT4 to investigate the performance of LaBr3:Ce detectors. In the first part of the paper we present the results of our experimental studies using cylindrical 1 in.×1 in. LaBr3:Ce scintillator. We have measured the energy and timing resolutions and also the absolute detection efficiencies, both, total detection and photopeak, using known activity sources. The energy dependence of the resolution has been studied using a variety of low energy gamma rays sources. The measured absolute efficiencies have been compared with the simulated values using GEANT4. We have extended our simulations to reproduce the recent measurements (Favalli et al., 2008) [15] of absolute photopeak efficiencies of a 1.5 in.×1.5 in. cylindrical LaBr3:Ce detector up to 5 MeV. The second part of the paper is devoted to a detailed comparative study of the energy dependent absolute efficiencies, both total detection and photopeak, of cylindrical LaBr3, NaI(Tl), and BaF2 scintillators of different sizes for a wide range of gamma rays from 662 keV to 50 MeV. We have also simulated the energy dependent efficiencies for compact assemblies of: (a) LaBr3:Ce and NaI(Tl) and (b) LaBr3:Ce and BaF2 in two different configurations. The efficiencies, so simulated, for these configurations, have been compared with the efficiencies of single scintillators of equivalent volumes. The usefulness of such combined detector assemblies using LaBr3 crystals of available volumes with NaI(Tl)/BaF2 in measurements of high-energy gamma rays (5-50 MeV) is discussed.

Kumar, G. Anil; Mazumdar, I.; Gothe, D. A.

2009-11-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

127

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

NASA Astrophysics Data System (ADS)

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

Loske, Felix; Reichling, Michael; Kühnle, Angelika

2011-08-01

128

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

NASA Astrophysics Data System (ADS)

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

Szenes, G.

2013-02-01

129

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

130

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

NASA Astrophysics Data System (ADS)

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

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

1996-02-01

131

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

Microsoft Academic Search

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

Piotr Mazurek; Andrzej Daniluk; Krzysztof Paprocki

2000-01-01

132

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

Microsoft Academic Search

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

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

2006-01-01

133

10BaF2:NaF, Na3AlF6/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission  

NASA Astrophysics Data System (ADS)

A rare-earth free upconversion luminescent material, 10BaF2:NaF, Na3AlF6, is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light (550 nm—610 nm) into ultraviolet light (290 nm—350 nm), and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF2:NaF, Na3AlF6/TiO2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation (? > 515 nm). The results show that 10BaF2:NaF, Na3AlF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2, their corresponding methanol yields are 179 and 0 ?mol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO2 on 10BaF2:NaF, Na3AlF6/TiO2 is proposed.

Liu, En-Zhou; Fan, Jun; Hu, Xiao-Yun; Hou, Wen-Qian; Dai, Hong-Zhe

2012-04-01

134

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

PubMed Central

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

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

2013-01-01

135

Optimization of single crystals of solid electrolytes with tysonite-type structure (LaF3) for conductivity at 293 K: 2. Nonstoichiometric phases R 1- y M y F3- y ( R = La-Lu, Y; M = Sr, Ba)  

NASA Astrophysics Data System (ADS)

Single crystals of fluorine-conducting solid electrolytes R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y ( R = La-Lu, Y) with a tysonite-type structure (LaF3) have been optimized for room-temperature conductivity ?293 K. The optimization is based on high-temperature measurements of ?( T) in two-component nonstoichiometric phases R 1 - y M y F3 - y ( M = Sr, Ba) as a function of the MF2 content. Optimization for thermal stability is based on studying the phase diagrams of MF2- RF3 systems ( M = Sr, Ba) and the behavior of nonstoichiometric crystals upon heating when measuring temperature dependences ?( T). Single crystals of many studied R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y phases have ?293 K values large enough to use these materials in solid-state electrochemical devices (chemical sensors, fluorine-ion batteries, accumulators, etc.) operating at room temperature.

Sorokin, N. I.; Sobolev, B. P.; Krivandina, E. A.; Zhmurova, Z. I.

2015-01-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

137

Influence of external factors on the self-organization of lead and tin telluride nanostructures on the BaF2(111) surface under conditions close to the thermodynamic equilibrium  

NASA Astrophysics Data System (ADS)

The morphology of PbTe and SnTe nanostructures grown on BaF2(111) substrates from the vapor phase in a vacuum under conditions close to the thermodynamic equilibrium has been investigated using atomic force microscopy. The equilibrium shape of PbTe and SnTe quantum dots and the statistical parameters of arrays of these quantum dots have been studied as a function of the thermodynamic conditions of growth, the crystal lattice mismatch between the materials of the quantum dots and substrate, and elastic properties of these materials. It has been established that, when the BaF2(111) substrate is deformed under external mechanical loading, the self-organization of dislocations on the BaF2(111) surface can result in the formation of a nanoscale ordered strain relief, which can be used for the fabrication of nanostructures. The morphology of this relief depends on the external load and on the temperature at which the substrate is deformed. It has been shown that the deformation effect on the surface of the substrate and light irradiation of the growth zone of nanostructures affect the nucleation of islands and kinetic processes occurring on the surface of the substrate during their growth. Using the influence of external factors on the BaF2(111) surface under certain thermodynamic conditions, it is possible to grow SnTe and PbTe nanostructures with different morphologies: continuous epitaxial layers with a thickness of less than 10 nm, homogeneous arrays of quantum dots with a high lateral density (more than 1011 cm2), quasi-periodic lateral nanostructures (nanowires), "single" and "coupled" quantum dots, and "molecules" of quantum dots.

Bakhtinov, A. P.; Vodop'yanov, V. N.; Ivanov, V. I.; Kovalyuk, Z. D.; Lytvyn, O. S.

2013-01-01

138

Optical properties and electronic structure of CaF2 with the screened-exchange (sX)-LDA-FLAPW approach  

NASA Astrophysics Data System (ADS)

Optical measurements have provided an extremely difficult challenge to existing electronic band structure calculations. Although CaF_2, an important large gap insulator, has been intensively investigated, no parameter-free first-principles calculations have been done due to the well-known failure of LDA in treating excited states. Here, we present results of fully first-principles calculations of the electronic structure and optical properties of CaF2 with the self-consistent screened-exchange LDA (sX-LDA) method(Asahi, Mannstadt and Freeman, PRB 59), 7486 (1999). implemented in the FLAPW approach.(Wimmer, Krakauer, Weinert, Freeman, PRB 24), 864 (1981). The calculated optical energy gap, 11.3 eV, is in very good agreement with experiment (11.8 eV)(Tsujibayashi, Toyoda, Sakuragi, Kamada, Itoh, APL 80), 2883 (2002) and so greatly improves the LDA result (7.3 eV). The optical properties, including the real and imaginary parts of the dielectric function determined ab initio with full matrix elements and no parameters, are in good agreement with experiment. A comparison with the results from LDA calculations (with and without a scissors operator to correct the band gap) is also presented.

Mannstadt, W.; Zhao, Yu-Jun; Kim, Miyoung; Freeman, A. J.

2003-03-01

139

Atomic contrast on a point defect on CaF2(111) imaged by non-contact atomic force microscopy  

NASA Astrophysics Data System (ADS)

A point defect on a cleaved CaF2(111) surface is imaged by non-contact atomic force microscopy in ultrahigh vacuum at room temperature to identify the nature of the point defect. First, atomic contrast formation on the point defect is examined using a negatively and a positively charged tip (i.e. F-- and Ca2+-terminated tips), which are prepared by modifying a Si tip with a CaF2 cluster. Analysis of the two types of atomic contrast imaged by the F-- and Ca2+-terminated tips reveals that the point defect has a positive charge and the positive charge is located on a Ca2+ sublattice. Second, the lateral mobility of the point defect is investigated. We repeated imaging on the point defect by decreasing the tip-sample distance. At the smaller tip-sample distance, the point defect moved laterally to one of six neighbouring sites of the defect when the tip scanned the surface across the point defect. Taking into account (i) the atomic contrast on the point defect by the charged tips with a known terminating ion (i.e. F- or Ca2+) and (ii) the lateral mobility of the point defect, we find a probable simple model of the point defect among six possible candidates.

Fujii, Shintaro; Fujihira, Masamichi

2007-02-01

140

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

141

Characterization of the tribological coating composition 77 wt % CaF2 - 23 wt % Li F fused to IN-750 alloy  

NASA Technical Reports Server (NTRS)

A coating composed of 77 wt % CaF2 - 23 wt % LiF fused on IN-750 nickel-based alloy was studied using SEM, XRD, EDX, and optical microscopic methods. The surfaces examined were the as-fused coating with no subsequent treatment, the coating after ultrasonic cleaning in water, and the uncoated polished and etched metal. It was found that the coating reacts during fusion with Ti and Nb rich inclusions in the alloy. Numerous small rectangular crystallites of Ca(Ti,Nb) oxide are formed beneath an overlay of fused fluoride composition. These crystallines are stubby and appear to be embedded in the metal substrate surface. It is known from previous studies that this coating-alloy system has good tribological properties in extreme conditions, such as liquid fluorine. It has been concluded from the present study that the short firmly embedded crystalline protuberances contribute to the coating adherence and thereby to enhanced coating wear life.

Deadmore, D. L.; Sliney, H. E.

1986-01-01

142

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

143

Estimation Model for Electrical Conductivity of Molten CaF2-Al2O3-CaO Slags Based on Optical Basicity  

NASA Astrophysics Data System (ADS)

Slag properties, such as electrical conductivity, thermal conductivity, density, viscosity, and surface tension, and the prediction of these properties play an important role in melting and metal refining. Optical basicity depends on the electronegativity of the ions of an individual oxide. This feature represents the bonding characteristics, ionization ability, ion size, and consequently the mobility of free ions inside the slag. These properties affect the electrical conductivity of slags. Therefore, in the current study, various slags containing mainly CaF2 and various oxides were prepared. The optical basicity value of each slag was calculated and their electrical conductivities were measured between 1450°C and 1600°C. The relationship between the optical basicity and the measured properties were discussed. It was observed that increasing optical basicity increases the electrical conductivity as well as the temperature. Thus, a new model for predicting electrical conductivity of slags was built between 1450°C and 1600°C depending on optical basicity and temperature.

Birol, Burak; Polat, Gökhan; Saridede, Muhlis Nezihi

2014-12-01

144

On the application of CaF2:Eu and SrF2:Eu phosphors in LED based phototherapy lamp  

NASA Astrophysics Data System (ADS)

In the last few years the interest of scientific community has been increased towards solid state lighting based on LEDs because of their superior advantages over the conventional fluorescent lamps. As the GaN based LEDs are easily available efforts of the researchers are now on making the new phosphors which are excitable in the near UV region (360-400nm) for solid state lighting. This paper reports the photoluminescence characteristics of CaF2:Eu and SrF2:Eu phosphor prepared by wet chemical method. The violet emission of these phosphors with near UV excitation can be useful in making a phototherapy lamp based on LEDs for treating various skin diseases like acne vulgaris and hyperbilirubinemia.

Belsare, P. D.; Moharil, S. V.; Joshi, C. P.; Omanwar, S. K.

2013-06-01

145

Effect of tip polarity on Kelvin probe force microscopy images of thin insulator CaF2 films on Si(111)  

NASA Astrophysics Data System (ADS)

We investigate thin insulating CaF2 films on a Si (111) surface using a combination of noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). Atomic-scale NC-AFM and KPFM images are obtained in different imaging modes by employing two different tip polarities. The KPFM image contrast and the distance-dependent variation of the local contact potential difference (LCPD) give rise to a tip-polarity-dependent contrast inversion. Ca2+ cations had a higher LCPD contrast than F- anions for a positively terminated tip, while the LCPD provided by a negatively charged tip gave a higher contrast for F- anions. Thus, this result implies that it is essential to determine the tip apex polarity to correctly interpret LCPD signals acquired by KPFM.

Yurtsever, Ayhan; Sugimoto, Yoshiaki; Fukumoto, Masaki; Abe, Masayuki; Morita, Seizo

2012-08-01

146

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

147

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

NASA Astrophysics Data System (ADS)

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

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

1993-10-01

148

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

PubMed Central

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

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

2014-01-01

149

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

150

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

NASA Astrophysics Data System (ADS)

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

Yazici, A. Necmeddýn; Haciýbrahýmoðlu, M. Yakup

2001-05-01

151

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

PubMed

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

Atari, N A; Svensson, G K

1986-01-01

152

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

NASA Astrophysics Data System (ADS)

The analytical figures of merit for ultraviolet laser ablation-inductively coupled plasma mass spectrometry (UV-LA-ICP-MS) at 266 nm with respect to the trace element analysis of high-purity, UV-transmitting alkaline earth halides are investigated and discussed. Ablation threshold energy density values and ablation rates for mono- and poly-crystalline CaF 2 samples were determined. Furthermore, Pb-, Rb-, Sr-, Ba- and Yb-specific analysis was performed. For these purposes, a pulsed Nd:YAG laser operated at the fourth harmonic of the fundamental wavelength (?=266 nm) and a double-focusing sector field ICP-MS detector were employed. Depending on the background noise and isotope-specific sensitivity, the detection limits typically varied from 0.7 ng/g for Sr to 7 ng/g in the case of Pb. The concentrations were determined using a glass standard reference material (SRM NIST612). In order to demonstrate the sensitivity of the arrangement described, comparative measurements by means of a commercial ablation system consisting of an ArF excimer laser (?=193 nm) and a quadrupole-type ICP-MS (ICP-QMS) instrument were carried out. The accuracy of both analyses was in good agreement, whereas ablation at 266 nm and detection using sector-field ICP-MS led to a sensitivity that was one order of magnitude above that obtained at 193 nm with ICP-QMS.

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

2002-06-01

153

Investigation of the structure and luminescence properties of CdF2-CaF2 : Eu superlattices on Si(111)  

NASA Astrophysics Data System (ADS)

A complex investigation of CdF2-CaF2 : Eu superlattices with different bilayer thicknesses (2.0-17.5 nm) grown by molecular beam epitaxy on Si(111) has been carried out. The structural perfection of the layers and interfaces of the superlattices have been estimated from the X-ray diffractometry and reflectometry data. The possibility of producing short-period pseudomorphic superlattices with a period of approximately 2 nm has been established. It has been shown that these superlattices are characterized by a larger root-mean-square roughness amplitude of the interfaces as compared to the long-period superlattices. The specific features of cathodoluminescence spectra have been analyzed as a function of the superlattice period. It has been revealed that, with a decrease in the superlattice period, the intrinsic luminescence intensity of fluorides increases in comparison with the intensity of the luminescence associated with the emission of Eu2+ impurity ions; in this case, several Eu3+ luminescence bands appear in the spectrum. The possibilities of electron probe microanalysis for determining the ratio of thicknesses of individual layers in short-period superlattices have been demonstrated.

Valkovskiy, G. A.; Durnev, M. V.; Zamoryanskaya, M. V.; Konnikov, S. G.; Krupin, A. V.; Moroz, A. V.; Sokolov, N. S.; Trofimov, A. N.; Yagovkina, M. A.

2013-07-01

154

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

155

Magnetic anisotropy of cobalt nanoparticle 2D arrays grown on corrugated MnF2(1 1 0) and CaF2(1 1 0) surfaces  

NASA Astrophysics Data System (ADS)

Cobalt nanoparticle 2D arrays with different effective thicknesses of cobalt layer (2 nm < deff < 10 nm) were grown by molecular beam epitaxy on CaF2(1 1 0)/Si(0 0 1) and MnF2(1 1 0)/CaF2(1 1 0)/Si(0 0 1) substrates with corrugated morphology of the surface. Surface morphology analysis showed that for effective thickness of cobalt layer deff = 5 nm the lateral dimensions of cobalt islands are about 5-10 nm and the distances between the islands differs in a half along and across the grooves. In both types of the heterostructures the shape of hysteresis loops measured by LMOKE depend on orientation of in-plane magnetic field relative to the direction of the grooves. The azimuthal dependence of coercive field Hc in Co/CaF2(1 1 0)/Si(0 0 1) structures corresponds to Stoner-Wohlfarth model's predictions, which takes into account the anisotropy of individual particles. In contrast to that, in Co/MnF2(1 1 0)/CaF2(1 1 0)/Si(0 0 1) structures these dependences are analogous to those predicted by the model based on account of magnetic-dipole interaction between particles which are placed in chains (chain-of-spheres-model). Possible explanations of the difference in magnetic anisotropy are suggested.

Baranov, D. A.; Krichevtsov, B. B.; Gastev, S. V.; Banschikov, A. G.; Fedorov, V. V.; Koshmak, K. V.; Suturin, S. M.; Sokolov, N. S.

2013-02-01

156

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

SciTech Connect

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

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

2012-08-01

157

Highly stable persistent spectral hole burning in Eu 3+ ions doped oxy-fluoride glasses of 30CaF 2-10Al 2O 3-60B 2O 3  

NASA Astrophysics Data System (ADS)

High temperature persistent spectral hole burning up to room temperature has been observed in Eu 3+ ions doped oxy-fluoride glasses with a composition of 30CaF 2-10Al 2O 3-60B 2O 3 (mol%) melted in a reducing atmosphere. The hole stability was studied through light-induced hole refilling and temperature cycling experiments. The burned holes survive thermal cycling to 300 K due to a high barrier height of 0.69 eV in the sample.

Liang, Hailian; Hanzawa, Hiromasa; Horikawa, Takashi; Machida, Ken-ichi

2007-08-01

158

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

PubMed

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

Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

2014-07-01

159

Cross sections for He and Ne isotopes in natural Mg, Al, and Si, He isotopes in CaF2, Ar isotopes in natural Ca, and radionuclides in natural Al, Si, Ti, Cr, and stainless steel induced by 12- to 45-MeV protons  

NASA Technical Reports Server (NTRS)

Stacks of thin Mg, Al, Si, Ca, CaF2, Ti, and stainless steel foils were bombarded in twelve irradiations by a variable energy cyclotron. Cross sections are reported for He and Ne in natural Mg, Al, and Si, and for He in CaF2, and for Ar in natural Ca, as determined from mass spectrometer analysis of the inert gases. In addition, cross sections of Na-22 in natural Al and Si, of V-48 in natural Ti, and of Cr-51, Mn-52, and Co-57 in stainless steel are reported. From these were deduced Cr-51 and Mn-52 cross sections in natural Cr.

Walton, J. R.; Heymann, D.; Yaniv, A.; Edgerley, D.; Rowe, M. W.

1976-01-01

160

Role of ionic defects at semiconductor-insulator interfaces: Spectroscopic results on CaF2/InP(001) and SrF2/InP(001) structures  

NASA Astrophysics Data System (ADS)

Epitaxial CaF2 and SrF2 layers were prepared by molecular-beam epitaxy onto clean, (4×2)-reconstructed InP(001) surfaces. The geometric and electronic structures of the layers and the interfaces were investigated by low-energy electron diffraction (LEED), Auger-electron spectroscopy (AES), and x-ray and ultraviolet photoelectron spectroscopies (XPS,UPS). Both fluorides grow at the substrate in a (001) orientation in their bulk cubic structures and form atomically rough, (111)-faceted surfaces as deduced from LEED. The XPS core-level intensity attenuations and the AES depth profiles indicate the formation of sharp interfaces. No interface bonds between InP and overlayer atoms were observed with photoelectron spectroscopy, and the Fermi-level position at the InP surface does not shift after fluoride deposition. The core levels and valence-band maxima of the fluoride overlayers shift to higher binding energies with increasing thickness. Up to 0.5-nm coverage, this is explained by additional screening from the InP substrate. Above 0.5-nm coverage, the shifts are caused by electrostatic-potential differences extending 10 nm away from the interfaces into the fluoride overlayers. The potential differences decrease the binding energies of all electronic levels in the fluoride layers near the interfaces, analogous to a band bending in semiconductors at semiconductor surfaces or semiconductor-metal interfaces. These potential differences are generated by mobile ionic defects in the fluoride layers. A model is presented for this space-charge region caused by ionic point defects in insulating overlayers. Fluoride ions are chemisorbed at the InP surface, thus creating a negative interface charge, which is compensated by excess positively charged fluoride vacancies in the space-charge region. The analogy to space-charge regions in semiconductors due to electronic surface states is discussed. Furthermore, the electronic interface schemes with the band discontinuities, the work functions, and the electron affinities of thick CaF2 and SrF2 overlayers were deduced from the measurements.

Weiss, W.; Wiemhöfer, H. D.; Göpel, W.

1992-04-01

161

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

PubMed

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

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

2014-09-01

162

Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours  

NASA Technical Reports Server (NTRS)

As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.

Whittenberger, J. D.

1992-01-01

163

MMT and Magellan infrared spectrograph B. McLeod, G. Nystrom, H. Bergner, W. Brown, M. Burke, D. Curley, D. Fabricant, G.  

E-print Network

is machined out of Aluminum-6061, diamond-turned, and then post-polished. Separating the slit mask wheel from design. The 520mm focal length collimator has 6 elements, made of CaF2, CaF2, BaF2, ZnSe, Infrasil

164

Influence of strontium on structure, sintering and biodegradation behaviour of CaO-MgO-SrO-SiO2-P2O5-CaF2 glasses  

SciTech Connect

The present study investigates the influence of SrO on structure, apatite forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with composition: mol.% (36.07 – x) CaO – x SrO - 19.24 MgO – 5.61 P2O5 – 38.49 SiO2 – 0.59 CaF2, where x varies between 0 – 10. The detailed structural analysis of glasses has been made by infra red spectroscopy (FTIR) and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h – 7 days. While increasing Sr2+/Ca2+ ratio in glasses did not affect the structure of glasses significantly, their apatite forming ability was decreased considerably. Further, physico-chemical degradation of glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer and the possible implications of ion release profile from glasses in different solutions has been discussed. The addition of strontium in glasses led to a 7-fold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders rendered glass-ceramics (GCs) with varying degree of crystallinity and good flexural strength (98-131 MPa) where the mechanical properties depend on the nature and amount of crystalline phases present in GCs.

Goel, Ashutosh; Rajagopal, Raghu R.; Ferreira, Jose M.

2011-11-01

165

Annealing of electron damage in mid-IR transmitting fluoride glass  

NASA Technical Reports Server (NTRS)

Damage in ZrF4-BaF2-LaF3 glass induced by high-energy electrons was studied by ESR and optical spectroscopy. An optical absorption band at 314 nm in the irradiated glass annealed rapidly above about 50 C, probably by a second-order reaction at room temperature; the ESR lines annealed very slowly at room temperature.

Bansal, Narottam P.; Doremus, Robert H.

1986-01-01

166

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

167

Particle Size Effects on Flow Properties of PS304 Plasma Spray Feedstock Powder Blend  

NASA Technical Reports Server (NTRS)

The effects of BaF2-CaF2 particle size and size distribution on PS304 feedstock powder flowability have been investigated. Angular BaF2-CaF2 eutectic powders were produced by comminution and classified by screening to obtain 38 to 45 microns 45 to 106 microns, 63 to 106 microns, 45 to 53 microns, 63 to 75 microns, and 90 to 106 microns particle size distributions. The fluorides were added incrementally from 0 to 10 wt% to the other powder constituents of the PS304 feedstock: nichrome, chromia, and silver powders. The flow rate of the powder blends decreased linearly with increasing concentration of the fluorides. Flow was degraded with decreasing BaF2-CaF2 particle size and with increasing BaF2-CaF2 particle size distribution. A semiempirical relationship is offered to describe the PS304 powder blend flow behavior. The Hausner Ratio confirmed the funnel flow test results, but was slightly less sensitive to differences in BaF2-CaF2 particle size and size distribution. These findings may have applicability to other powders that do not flow easily, such as ceramic powders.

Stanford, Malcolm K.; DellaCorte, Christopher; Eylon, Daniel

2002-01-01

168

Crystallization of heavy metal fluoride glasses  

NASA Technical Reports Server (NTRS)

The kinetics of crystallization of a number of fluorozirconate glasses were studied using isothermal and dynamic differential scanning calorimetry and X-ray diffraction. The addition of the fluorides LiF, NaF, AlF3, LaF3 to a base glass composition of ZrF4-BaF2 reduced the tendency to crystallize, probably by modifying the viscosity-temperature relation. ZrF4-BaF2-LaF3-AlF3-NaF glass was the most stable against devitrification and perhaps is the best composition for optical fibers with low scattering loss. Some glasses first crystallize out into metastable beta-BaZr2F10 and beta-BaZrF6 phases, which transform into the most stable alpha-phases when heated to higher temperatures. The size of the crystallites was estimated to be about 600 A from X-ray diffraction.

Bansal, Narottam P.; Bruce, Allan J.; Doremus, R. H.; Moynihan, C. T.

1984-01-01

169

Enhanced refractive index without absorption in optical fibers via an indirect incoherent pump field  

NASA Astrophysics Data System (ADS)

We demonstrate a scheme for realizing the refractive index with zero absorption in an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF optical fiber. It is found that the refraction index of the probe laser can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optical-fiber communication.

Ge, Qiang

2014-12-01

170

Growth of YBa 2Cu 3O 7-? on alkaline earth flouride substrates and thin films  

NASA Astrophysics Data System (ADS)

The growth and characterization of YBa 2Cu 3O 7-? (YBCO) thin films grown by laser ablation on MgF 2 (100), CaF 2 (100), SrF 2 (100), and BaF 2 (100) substrates, and on CaF 2 and BaF 2 thin films on LaAlO 3 (100) substrates, are described. High quality superconducting YBCO films could be grown directly only on the BaF 2 substrates and thin films. YBCO films grown directly on MgF 2 or CaF 2 substrates were insulating and showed clear signs of interdiffusion and reaction, as measured by X-ray photoelectron spectroscopy. Superconducting YBCO films could be grown on SrF 2 and CaF 2 substrates and thin films only with an yttria-stabilized zirconia buffer layer and/or with a low YBCO growth temperature, while YBCO grown on MgF 2 yielded insulating films for all growth conditions investigated. The highest quality YBCO films were obtained on BaF 2 substrates ( Tc=87.6 K, ?Tc=0.3 K). These results are discussed in terms of the thermodynamic stability of possible reaction products and the temperature dependence of the ionic mobilities.

Vasquez, R. P.; Foote, M. C.; Hunt, B. D.; Barner, J. B.

1993-03-01

171

Thermal Effects on a Low Cr Modification of PS304 Solid Lubricant Coating  

NASA Technical Reports Server (NTRS)

PS304 is a high temperature composite solid lubricant coating composed of Ni-Cr, Cr2O3, BaF2-CaF2 and Ag. The effect of reducing chromium content on the formation of voids in the Ni-Cr particles after heat treatment in PS304 coating was investigated. Coatings were prepared with Ni-20Cr or Ni-10Cr powder and in various combinations with the other constituents of PS304 (i.e., chromia, silver and eutectic BaF2-CaF2 powders) and deposited on metal substrates by plasma spray. Specimens were exposed to 650 C for 24 hr or 1090 C for 15 hr and then examined for changes in thickness, coating microstructure and adhesion strength. Specimens with Ni-10Cr generally had less thickness increase than specimens with Ni-20Cr, but there was great variance in the data. Reduction of chromium concentration in Ni-Cr powder tended to reduce the appearance of voids in the Ni-Cr phase after heat exposure. The presence of BaF2-CaF2 resulted in a significant increase in coating adhesion strength after heat treatment, while coatings without BaF2-CaF2 had no significant change. Chemical composition analysis suggested that the void formation was due to oxidation of chromium in the Ni-Cr constituent.

Stanford, Malcolm K.; Yanke, Anne M.; DellaCorte, Christopher

2004-01-01

172

Development of infrared sensors using energy transfer/energy upconversion processes: Study of laser excited fluorescence in rare Earth ion doped crystals  

NASA Technical Reports Server (NTRS)

A summary is presented of the spectroscopic study of three systems: LaF3:Ho(3+), LaF3:Er(3+) and CaF2:Nd(3+). When the D levels of Ho(3+) in LaF3 were resonantly excited with a laser beam of 640 nm, upconverted emissions were detected from J (416 nm), F (485 nm), and E (546 nm) levels. Energy upconverted emissions were also observed from F and E levels of Ho(3+) when the material was excited with an 800 nm near infrared laser. When the D levels of Er(3+) in LaF3 were resonantly excited with a laser beam of 637 nm, upconverted emissions were detected from the E (540 nm) and P (320, 400, and 468 nm) levels. Energy upconverted emissions were also observed from F, E, and D levels of Er(3+) when the material was resonantly excited with an 804 nm near infrared laser. When the D levels of Nd(3+) in CaF2 were resonantly excited with a laser beam of 577 nm, upconverted emissions were detected from the L (360 and 382 nm), K (418 nm), and I (432 nm) levels. Very weak upconverted emissions were detected when this system was irradiated with a near infrared laser. The numbers in parentheses are the wavelengths of the emissions.

Nash-Stevenson, S. K.; Reddy, B. R.; Venkateswarlu, P.

1994-01-01

173

The effect of counterface on the tribological performance of a high temperature solid lubricant composite from 25 to 650°C  

Microsoft Academic Search

The effect of counterface selection on the tribological performance of A Ag\\/BaF2?CaF2 containing composite coating are studied. Ceramic (Al2O3) and metal (Inconel X-750) pins are slid against PS300 (a metal bonded chrome oxide coating with Ag and BaF2\\/CaF2 lubricant additives) in a pin-on-disk tribometer at 25, 500 and 650°C.Compared to the ceramic counterface, the metal counterface generally exhibited lower friction

Christopher DellaCorte

1996-01-01

174

High pressure effect on optical properties of cerium ion in fluoroaluminate glass  

Microsoft Academic Search

High pressure effects on optical properties of Ce3+ doped ternary fluoroaluminate (18BaF2·37CaF2·45AlF3) glass have been investigated in terms of ligand field around cerium ion. Five bands due to the 4f–5d transitions were observed in ultraviolet absorption spectra for the glass. A photoluminescence band was observed at around 300 nm under excitation at each band. The photoluminescence band shifted toward smaller

N. Kitamura; K Fukumi; J Nishii; M Makihara; T Sasaki; N Ohno

1999-01-01

175

Improvement in tribological properties of chromium oxide coating at high temperature by solid lubricants  

Microsoft Academic Search

The aim of the investigations was to improve the tribological properties of chromium oxide (Cr203) coating for applications in heat engines at high temperatures. The experimental results show that the solid lubricants CaF2 and BaF2 in composite coatings can reduce and stabilize the friction coefficient, decrease the wear rate, prevent surface damage and improve the load capacity of Cr203 coating

G. H. Liu; F. Robbevalloire; R. Gras; J. Blouet

1993-01-01

176

Diode-pumped regenerative Yb:SrF2 amplifier Sandrine Ricaud1,3,*  

E-print Network

SrF2, SrF2-CaF2, SrF2-BaF2, and YLF," in Advanced Solid-State Photonics, OSA Technical Digest SeriesDiode-pumped regenerative Yb:SrF2 amplifier Sandrine Ricaud1,3,* , Patrick Georges1 , Patrice Camy2 we believe to be the first Yb:SrF2 regenerative femtosecond amplifier. The regenerative amplifier

Boyer, Edmond

177

Mid-infrared supercontinuum generation to 4.5 mum in ZBLAN fluoride fibers by nanosecond diode pumping  

Microsoft Academic Search

A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from ˜0.8 mum to beyond 4.5 mum. The SC has an average power of ˜23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of ˜-20 dBm\\/nm over a large fraction of the spectrum. The

Chenan Xia; Malay Kumar; Ojas P. Kulkarni; Mohammed N. Islam; Fred L. Terry Jr.; Mike J. Freeman; Marcel Poulain; Gwenael Mazé

2006-01-01

178

Effects of Gravity on ZBLAN Glass Crystallization  

NASA Technical Reports Server (NTRS)

The effects of gravity on the crystallization of ZrF4-BaF2-LaF3-AlF3- NaF glasses have been studied utilizing NASA's KC135 and a sounding rocket, Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

Tucker, Dennis S.; Ethridge, Edwin C.; Smith, G. A.; Workman, G.

2003-01-01

179

The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass  

NASA Technical Reports Server (NTRS)

An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

Tucker, Dennis S.; Lapointe, Michael R.; Jia, Zhiyong

2006-01-01

180

Effect of microgravity on crystallization of ZBLAN fibers  

NASA Technical Reports Server (NTRS)

ZrF4-BaF2-LaF3-AIF3-NaF (ZBLAN) optical fiber was flown on board the NASA's KC-135 microgravity aircraft to determine the effects of microgravity on crystal growth in this material. Fiber samples were placed in evacuated quartz ampoules and heated to the crystallization temperature in 0g, 1g, and 2g. The 1g and 2g samples were observed to slump and crystallize. The 0g samples showed no evidence of crystallization.

Tucker, Dennis S.

1994-01-01

181

Effects of Gravity on ZBLAN Glass Crystallization  

NASA Technical Reports Server (NTRS)

The effects of gravity on the crystallization of ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF glasses have been studied using the NASA KC-135 and a sounding rocket. Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

Tucker, Dennis S.; Ethridge, Edwin C.; Smith, Guy A.; Workman, Gary

2004-01-01

182

Note: response characteristics of the sensor based on LaF3 thin film to different humidified gases.  

PubMed

Electromotive force (EMF) transient curves presented that the sensor showed good repeatable response in the humidity environments using ambient atmosphere as the carrier gas at different temperatures. The 90% response time and recovery time were within 40 s and 50 s, respectively. The sensor also presented stable response characteristics in 75.1% RH and 83.6% RH humidity environments using N(2), 5% O(2), and 50% O(2) as the carrier gases, respectively. The EMF always increased with the partial pressure of oxygen in certain relative humidity. However, the ?EMF was decreased with the increase of O(2) content in the carrier gas under the condition of the variation of relative humidity from 75.1% to 83.6%. These phenomena revealed that the sensor was sensitive to water vapor without oxygen in the sample gas and too much water vapor had adverse effect on the response to oxygen. Non-Nernst behavior of the sensor was discussed in detail. PMID:22667667

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde; Guan, Cheng; Zhang, Bike

2012-05-01

183

Red-to-violet and near-infrared-to-green energy upconversion in LaF3:Er(3+)  

NASA Technical Reports Server (NTRS)

When the (sup 4)F(sub 9/2) state was resonantly excited, emission was detected from the higher states (sup 4)S(sub 3/2)((sup 2)H(sub 11/2), (sup 4)G(sub 11/2), and (sup 2)P(sub 3/2) in addition to the resonant emission. Two- and three-photon processes were found to be responsible in populating the (sup 4)S(sub 3/2) and the (sup 2)P(sub 3/2) states, respectively. Energy upconversion efficiencies into the (sup 4)S(sub 3/2) and the (sup 2)P(sub 3/2) states were found to be 7.2 x 10(exp -3) and 1.4 x 10(exp -4), respectively. When the (sup 4)I(sub 9/2) state was resonantly excited we detected green emission from the (sup 4)S(sub 3/2)((sup 2)H(sub 11/2)). The energy upconversion efficiency of this process was found to be 1.4 x 10(exp -3).

Reddy, B. R.; Nash-Stevenson, S. K.

1994-01-01

184

Élimination du bore du silicium par plasma inductif sous champ électrique  

NASA Astrophysics Data System (ADS)

We analyzed purification mechanisms of silicon by inductive plasma with a fluoride slag. The aim is to study boron elimination from doped electronic grade silicon in function of the nature of the slag to obtain a photovoltaic grade silicon. The steady began with the calculation and the comparison of the stability diagram of boron compounds in presence of CaF2, BaF2 and MgF2. This study led us to conclude that BaF2 is the better slag for silicon purification. This has been confirmed by experience. In a second time, we made purifications under electric bias to enhance slag efficiency. We noticed that BaF2 is more sensitive to electric bias than other slags. Nous avons analysé le mécanisme de purification du silicium sous plasma inductif en présence d'un laitier fluoré. L'objectif principal est d'étudier l'élimination du bore du silicium électronique dopé en fonction de la nature du fluorure pour obtenir un silicium de qualité photovoltaïque. L'étude a commencé par l'établissement et la comparaison de diagrammes des composés du bore en présence de CaF2, de MgF2 et de BaF2. Nous avons déduit de cette première étude que BaF2 est le meilleur laitier pour la purification du silicium. Ceci a été corroboré par l'expérience. Nous avons ensuite opéré en présence d'un champ électrique dans le but d'améliorer encore l'efficacité des laitiers. Nous avons constaté que BaF2 est plus sensible au champ électrique que les deux autres laitiers utilisés.

Combes, R.; Morvan, D.; Picard, G.; Amouroux, J.

1993-05-01

185

Identification of hydrogen isotopes with the BaF 2 electromagnetic calorimeter TAPS  

Microsoft Academic Search

The mass spectrum of hydrogen isotope was deduced from the kinetic energy and time-of-flight (TOF) measured with the segmented electromagnetic calorimeter TAPS. The reactions studied were Kr + Ni at 60A MeV and Ar + Ca at 180A MeV. Proper corrections for the energy lost by charged particles in passive absorbers between the target and the scintillator are essential to

T. Matulewicz; L. Aphecetche; Y. Charbonnier; H. Delagrange; F. M. Marqués; G. Martínez; Y. Schutz

1996-01-01

186

BAF(2) POST-DEPOSITION REACTION PROCESS FOR THICK YBCO FILMS.  

SciTech Connect

The basic processes of the so-called BaF{sub 2} process for the formation of YBa{sub 2}Cu{sub 3}O{sub 7}, YBCO, films as well as its advantages over the in situ formation processes are discussed in the previous chapter. The process and the properties of YBCO films by this process were also nicely described in earlier articles by R. Feenstra, et al. Here, we will discuss two pertinent subjects related to fabrication of technologically viable YBCO conductors using this process. These are (1) the growth of thick (>> 1 {micro}m) c-axis-oriented YBCO films and (2) their growth rates. Before the detail discussions of these subjects are given, we first briefly discuss what geometrical structure a YBCO-coated conductor should be. Then, we will provide examples of simple arguments for how thick the YBCO films and how fast their growth rates need to be. Then, the discussions in the following two sections are devoted to: (1) the present understanding of the nucleation and the growth process for YBCO, and why it is so difficult to grow thick c-axis-oriented films (> 3 {micro}m), and (2) our present understanding of the YBCO growth-limiting mechanism and methods to increase the growth rates. The values of critical-current densities J{sub c} in these films are of primary importance for the applications,. and the above two subjects are intimately related to the control of J{sub c} of the films. In general, the lower the temperatures of the YBCO formation are the higher the values of J{sub c} of the films. Thus, the present discussion is limited to those films which are reacted at {approx}735 C. This is the lowest temperature at which c-axis-oriented YBCO films (1-3 {micro}m thick) are comfortably grown. It is also well known that the non-c-axis oriented YBCO platelets are extremely detrimental to the values of J{sub c} such that their effects on J{sub c} dwarf essentially all of other microstructural effects which control J{sub c}. Hence, the discussion given below is mainly focused on how to avoid the growth of these crystallites when the films are thick and/or the growth rates are high.

SUENAGA,M.; SOLOVYOV,V.F.; WU,L.; WIESMANN,H.J.; ZHU,Y.

2001-07-12

187

Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory  

NASA Astrophysics Data System (ADS)

Using periodic density functional theory, we calculate the structure and migration energies of fluorine vacancies and interstitials in the bulk and at the stoichiometric bulk-truncated surface of three alkali-earth fluorides: CaF2 , SrF2 , and BaF2 . We then study the adsorption of water and hydrogen, in both molecular and dissociated form, at the ideal surface, and at neutral and charged vacancies in the surface and subsurface layers. The results demonstrate that in nearly all cases molecular adsorption is strongly favored. For the most probable configurations on the surfaces, we also studied the migration paths and barriers, and found that water is highly mobile on the surface, even when adsorbed at defects. In general, CaF2 and SrF2 show similar behavior with respect to water, while adsorption energies and migration barriers for BaF2 are smaller. Finally, we discuss our results in the context of recent experimental Atomic Force Microscopy studies on CaF2 and compare to calculations on other insulating surfaces.

Foster, A. S.; Trevethan, T.; Shluger, A. L.

2009-09-01

188

Lattice location and annealing studies of Hf implanted CaF 2  

NASA Astrophysics Data System (ADS)

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the <1 1 0> crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with 181Hf( 181Ta) show quadrupole interactions with ? Q1 = 300(3) MHz ( ? = 0.00), ? Q2 = 1285(13) MHz ( ? = 0.43) and ? Q3 = 1035(10) MHz ( ? = 0.00) after annealing up to 1200 K.

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

2009-05-01

189

EPR study of electron bombarded alkali- and alkaline-earth halide crystal surfaces  

NASA Technical Reports Server (NTRS)

An EPR study of electron bombarded LiF, NaCl, KCl, CaF2 and BaF2 polycrystalline surfaces has shown that small metal particles are formed on the surfaces of the crystals. Identification was made from CESR signals. The symmetric line-shape of the signals, even at 77 K, indicated that the particles were less than 0.5 micron in diameter. Signals due to F centers were observed in LiF but not in the other halides. Implications to metal deposition are considered.

Fryburg, G. C.; Lad, R. A.

1975-01-01

190

A multiple pulse zero crossing NMR technique, and its application to F-19 chemical shift measurements in solids  

NASA Technical Reports Server (NTRS)

A simple multiple-pulse 'zero crossing technique' for accurately determining the first moment of a solid-state NMR spectrum is introduced. This technique was applied to obtain the F-19 chemical shift versus pressure curves up to 5 kbar for single crystals of CaF2 (0.29 + or - 0.02 ppm/kbar) and BaF2 (0.62 + or - 0.05 ppm/kbar). Results at ambient temperature and pressure are also reported for a number of other fluorine compounds. Because of its high data rate, this technique is potentially several orders of magnitude more sensitive than similar CW methods.

Burum, D. P.; Elleman, D. D.; Rhim, W.-K.

1978-01-01

191

Ab-initio calculation of formation and migration energies of intrinsic defects in BaF2  

NASA Astrophysics Data System (ADS)

We have performed ab-initio calculations of the formation and migration energies of intrinsic defects (interstitials, vacancies and Frenkel defects) in barium fluoride. The calculations were performed within density-functional theory and the generalized-gradient approximation, employing pseudopotentials and a plane-wave basis set. The results agree reasonably well with available experimental data. They are also compatible with calculations and experimental data on calcium fluoride. We found that Frenkel pairs are composed of pairs of charged defects and that their formation energies are 3.44 eV and 1.88 eV for cation and anion, respectively. The lowest barrier for defect migration was found to correspond to the migration of the anion vacancy along the <100> direction (energy barrier of 0.53 eV), which compares well with the experimental value of 0.59 eV. Cation vacancy migration was instead found to require an energy of at least 2.22 eV along the easiest migration path, <100>.

Nyawere, P. W. O.; Scandolo, S.; Makau, N. W.; Amolo, G. O.

2014-02-01

192

Crystallization And Viscosity Of Heavy Metal Fluoride Glasses  

NASA Astrophysics Data System (ADS)

Shear viscosity data for a glassforming ZrF4-BaF2-LaF3-A1F3 composition covering the range from the highly fluid melt down to the glass transition (10-1 to 1013 P) have been collected from five sources. The viscosity temperature dependence is highly non-Arrhenius and cannot be described by three parameter expressions such as the Fulcher equation. The four parameter Cohen-Grest equation, however, does give a good fit to the data, possibly allowing interpolation in the range of intermediate viscosity important for fiber drawing where data is currently lacking. The viscosity data are compared with crystallization temperatures obtained by DSC during heating and cooling at 10K/min.

Moynihan, C. T.; Mossadegh, R.; Crichton, S. N.; Gupta, P. K.; Drexhage, M. G.

1986-05-01

193

White emission from Tm3+/Tb3+/Eu3+ co-doped fluoride zirconate under ultraviolet excitation  

NASA Astrophysics Data System (ADS)

We synthesize Tm3+/Tb3+/Eu3+ triply-doped ZrF4—BaF2—LaF3—AlF3—NaF (ZBLAN) transparent glass by using a melt-quenching method. Under excitation of 365 nm, the white emission with Commission internationale deL'Eclairage (CIE) coordinates of (0.33, 0.33) is achieved at the Eu3+ concentration of 1.1 mol%. The mechanisms for white emission and the energy transfer process of Tb3+ ? Eu3+ are discussed in terms of the photoluminescence, photoluminescence excitation spectra, and the light emission decay curves. The nature for the Tb3+ ? Eu3+ energy transfer is described with the aid of an energy level diagram.

Sun, Jian; Zhang, Xiao-Song; Yuan, Lin-Lin; Feng, Zhi-Jun; Ling, Zhi; Li, Lan

2014-11-01

194

Fluoride glass starting materials - Characterization and effects of thermal treatment  

NASA Technical Reports Server (NTRS)

The production of heavy metal fluoride (HMF) glasses, and the effects of thermal treatments on the HMF glasses are investigated. ZrF4, BaF2, AlF3, LaF3, and NaF were utilized in the synthesis of zirconium-barium-lanthanum-aluminum-sodium fluoride glass. The purity of these starting materials, in particular ZrF4, is evaluated using XRD analysis. The data reveal that low temperature heating of ZrF4-H2O is effective in removing the water of hydration, but causes the production of ZrF4 and oxyfluorides; however, dehydration followed by sublimation results in the production of monoclinic ZrFe without water or oxyfluoride contaminants.

Chen, William; Dunn, Bruce; Shlichta, Paul; Neilson, George F.; Weinberg, Michael C.

1987-01-01

195

Laser Cooled High-Power Fiber Amplifier  

E-print Network

A theoretical model for laser cooled continuous-wave fiber amplifier is presented. The amplification process takes place in the Tm3+-doped core of the fluoride ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass fiber. The cooling process takes place in the Yb3+:ZBLAN fiber cladding. It is shown that for each value of the pump power and the amplified signal there is a distribution of the concentration of the Tm3+ along the length of the fiber amplifier, which provides its athermal operation. The influence of a small deviation in the value of the amplified signal on the temperature of the fiber with the fixed distribution of the Tm3+ions in the fiber cladding is investigated.

Nemova, Galina

2009-01-01

196

Evaluation of Advanced Solid Lubricant Coatings for Foil Air Bearings Operating at 25 and 500 C  

NASA Technical Reports Server (NTRS)

The tribological properties of one chrome oxide and one chrome carbide based solid lubricant coating were evaluated in a partial-arc foil bearing at 25 and 500 C. Start/stop bearing operation up to 20,000 cycles were run under 10 kPa (1.5 psi) static deadweight load. Bearing friction (torque) was measured during the test. Specimen wear and SEM/EDS surface analyses were conducted after testing to understand and elucidate the tribological characteristics observed. The chrome oxide coating which contains both (Ag) and (BaF2/CaF2) for low and high temperature lubrication, exhibited low friction in sliding against Al2O3 coated foils at 25 and 500 C. The chrome carbide coating, which lacked a low temperature lubricant but contained BaF2/CaF2 as a high temperature lubricant, exhibited high friction at 25 C and low friction at 500 C against both bare and Al2O3 coated superalloy foil surfaces. Post test surface analyses suggest that improved tribological performance is exhibited when a lubricant film from the coating transfers to the foil surface.

DellaCorte, Christopher; Fellenstein, James A.; Benoy, Patricia A.

1998-01-01

197

Tribological and microstructural comparison of HIPped PM212 and PM212/Au self-lubricating composites  

NASA Technical Reports Server (NTRS)

The feasibility of replacing the silver with the volumetric equivalent of gold in the chromium carbide-based self-lubricating composite PM212 (70 wt. percent NiCo-Cr3C2, 15 percent BaF2/CaF2 eutectic) was studied. The new composite, PM212/Au has the following composition: 62 wt. percent NiCo-Cr3C2, 25 percent Au, 13 percent BaF2/CaF2 eutectic. The silver was replaced with gold to minimize the potential reactivity of the composite with possible environmental contaminants such as sulfur. The composites were fabricated by hot isostatic pressing (HIPping) and machined into pin specimens. The pins were slid against nickel-based superalloy disks. Sliding velocities ranged from 0.27 to 10.0 m/s and temperatures from 25 to 900 C. Friction coefficients ranged from 0.25 to 0.40 and wear factors for the pin and disk were typically low 10(exp -5) cu mm/N-m. HIPped PM212 measured fully dense, whereas PM212/Au had 15 percent residual porosity. Examination of the microstructures with optical and scanning electron microscopy revealed the presence of pores in PM212/Au that were not present in PM212. Though the exact reason for the residual porosity in PM212/Au was not determined, it may be due to particle morphology differences between the gold and silver and their effect on powder metallurgy processing.

Bogdanski, Michael S.; Sliney, Harold E.; Dellacorte, Christopher

1992-01-01

198

Tribological and microstructural comparison of HIPped PM212 and PM212/Au self-lubricating composites  

NASA Technical Reports Server (NTRS)

The feasibility of replacing the silver with the volumetric equivalent of gold in the chromium carbide-based self-lubricating composite PM212 (70 wt percent NiCo-Cr3C2, 15 percent BaF2/CaF2 eutectic) was studied. The new composite, PM212/Au has the following composition: 62 wt percent NiCo-Cr3C2, 25 percent Au, 13 percent BaF2/CaF2 eutectic. The silver was replaced with gold to minimize the potential reactivity of the composite with possible environmental contaminants such as sulfur. The composites were fabricated by hot isostatic pressing (HIPping) and machined into pin specimens. The pins were slid against nickel-based superalloy disks. Sliding velocities ranged from 0.27 to 10.0 m/s and temperatures from 25 to 900 C. Frictions coefficients ranged from 0.25 to 0.40 and wear factors for the pin and disk were typically low 10(exp -5) cu mm/N-m. HIPped PM212 measured fully dense, whereas PM212/Au had 15 percent residual porosity. Examination of the microstructures with optical and scanning electron microscopy revealed the presence of pores in PM212/Au that were not present in PM212. Though the exact reason for the residual porosity PM212/Au was not determined, it may be due to practice morphology differences between the gold and silver and their effect on powder metallurgy processing.

Bogdanski, Michael S.; Sliney, Harold E.; Dellacorte, Christopher

1992-01-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

200

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

201

Microwave-assisted rapid synthesis and characterization of CaF2 particles-filled cellulose nanocomposites in ionic liquid.  

PubMed

In this article, we try to compound cellulose/alkali earth metal fluorides (MF2, M=Ca, Mg, Sr, Ba) nanocomposites via microwave-assisted ionic liquid method, wherein cellulose/CaF2 and cellulose/MgF2 were successfully synthesized through this method while cellulose/SrF2 and cellulose/BaF2 could not be synthesized. We focused on the synthesis of cellulose/CaF2 and investigated the influences of the different time and different temperature for the synthesis of cellulose/CaF2 nanocomposites. The influence of different heating methods such as oil-bath heating method was also studied. Ionic liquid ([Bmim][BF4]) was used for dissolving microcrystalline cellulose and providing the source of fluoride ionic and the alkali earth metal nitrate (Ca(NO3)2, Mg(NO3)2, Sr(NO3)2, and Ba(NO3)2) was used as the reaction initiator. They were investigated by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TG), derivative thermogravimetric (DTG), and energy-dispersive X-ray spectra (EDS). The different heating modes have influence on the morphology and property. The different temperature and heating time also have a certain influence on the morphology and crystallinity of calcium fluoride. PMID:25659685

Deng, Fu; Fu, Lian-Hua; Ma, Ming-Guo

2015-05-01

202

Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method.  

PubMed

A periodic electrostatic embedding scheme is presented that uses the periodic fast multipole method. The convergence of properties with increasing cluster size is examined for cluster models of calcium fluoride. Properties investigated are the electron density, the density of states, the electronic excitation of color centers, and energies of defect formation. The embedded cluster method is applied to CeO(2) and oxygen vacancies in bulk CeO(2) as well as on its (111) surface. Employing the PBE0 functional, vacancy formation energies of 3.0 and 3.3 eV have been obtained for the bulk and the (111) surface, respectively. Formation of subsurface defects requires 3.33 eV (singlet open shell). The localization of the electrons left behind on defect formation in Ce 4f states is discussed. Occupied Ce 4f states are well localized on nearest Ce atoms for surface and subsurface vacancies. Localization apart from the vacancy was obtained for bulk. The total CPU time spent on the embedding part did not exceed 30 s on a single CPU even if 8000 basis functions of the cluster are involved. PMID:19425801

Burow, Asbjörn M; Sierka, Marek; Döbler, Jens; Sauer, Joachim

2009-05-01

203

Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method  

NASA Astrophysics Data System (ADS)

A periodic electrostatic embedding scheme is presented that uses the periodic fast multipole method. The convergence of properties with increasing cluster size is examined for cluster models of calcium fluoride. Properties investigated are the electron density, the density of states, the electronic excitation of color centers, and energies of defect formation. The embedded cluster method is applied to CeO2 and oxygen vacancies in bulk CeO2 as well as on its (111) surface. Employing the PBE0 functional, vacancy formation energies of 3.0 and 3.3 eV have been obtained for the bulk and the (111) surface, respectively. Formation of subsurface defects requires 3.33 eV (singlet open shell). The localization of the electrons left behind on defect formation in Ce 4f states is discussed. Occupied Ce 4f states are well localized on nearest Ce atoms for surface and subsurface vacancies. Localization apart from the vacancy was obtained for bulk. The total CPU time spent on the embedding part did not exceed 30 s on a single CPU even if 8000 basis functions of the cluster are involved.

Burow, Asbjörn M.; Sierka, Marek; Döbler, Jens; Sauer, Joachim

2009-05-01

204

The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings  

NASA Technical Reports Server (NTRS)

This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt% NiCr binder, 20 wt% Cr2O3 hardener, and 10 wt% each Ag, and BaF2/CaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc foil bearing. The test load was 10 KPa (1.5 psi) and the bearings were run under start/stop cyclic conditions. The data show good wear performance of the bearing, especially at temperatures above 25 deg. C. Bearing friction was moderate (micron approx. or equal to 0.4) over the entire temperature range. Based upon the results obtained, the PS304 coating has promise for high temperature, oil-free turbomachinery applications.

DellaCorte, Chris

1998-01-01

205

Effects of Humidity On the Flow Characteristics of PS304 Plasma Spray Feedstock Powder Blend  

NASA Technical Reports Server (NTRS)

The effects of environmental humidity on the flow characteristics of PS304 feedstock have been investigated. Angular and spherical BaF2-CaF2 powder was fabricated by comminution and by atomization, respectively. The fluorides were added incrementally to the nichrome, chromia, and silver powders to produce PS304 feedstock. The powders were dried in a vacuum oven and cooled to a Tom temperature under dry nitrogen. The flow of the powder was studied from 2 to 100 percent relative humidity (RH) The results suggest that the feedstock flow is slightly degraded with increasing humidity below 66 percent RH and is more affected above 66 percent RH. There was no flow above 88 percent RH. Narrower particle size distributions of the angular fluorides allowed flow up to 95 percent RH. These results offer guidance that enhances the commercial potential for this material system.

Stanford, Malcolm K.; DellaCorte, Christopher

2002-01-01

206

Fluorescence and phosphorescence of photomultiplier window materials under electron irradiation  

NASA Technical Reports Server (NTRS)

The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation were investigated using a Sr-90/Y-90 beta emitter as the electron source. Spectral emission curves of UV grade, optical grade, and electron-irradiated samples of MGF2 and LiF, CaF2, BaF2, sapphire, fused silica, and UV transmitting glasses were obtained over the spectral range of 200 nm to 650 nm. Fluorescence yields, expressed as the number of counts in a solid angle of 2 pi steradian per 1MeV of incident electron energy deposited, were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively.

Viehmann, W.; Eubanks, A. G.; Bredekamp, J. H.

1974-01-01

207

Tribological Performance of PM300 Solid Lubricant Bushings for High Temperature Applications  

NASA Technical Reports Server (NTRS)

PM300 is a high temperature solid lubricant material produced through conventional powder metallurgy processing. PM300 is a combination of metal binder (NiCr), hardener (Cr2O3) and lubricant (Ag and BaF2/CaF2) phases and is in commercial use in high temperature furnace conveyors. In this paper, the tribological characteristics of PM300 are evaluated using a newly developed bushing test rig in which PM300 bushings are loaded against rotating steel shafts at temperatures from 25 to 650 C. The data shows that friction and wear are low to moderate and that the lubrication performance (friction) improves with increasing temperature. Several alternative PM300 compositions are evaluated which do not contain silver and are targeted at aircraft gas turbine applications in which environmental compatibility of silver is a concern. It is expected that the data resulting from this research will further the commercialization of this technology.

Striebing, Donald R.; Stanford, Malcolm K.; DellaCorte, Christopher; Rossi, Anne M.

2007-01-01

208

The Cryogenic, High-Accuracy, Refraction Measuring System (CHARMS): A New Facility for Cryogenic Infrared through Vacuum Far-Ultraviolet Refractive Index Measurements  

NASA Technical Reports Server (NTRS)

The optical designs of future NASA infrared (IR) missions and instruments, such as the James Webb Space Telescope's (JWST) Near-Mixed Camera (NIRCam), will rely on accurate knowledge of the index of refraction of various IR optical materials at cryogenic temperatures. To meet this need, we have developed a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS). In this paper we discuss the completion of the design and construction of CHARMS as well as the engineering details that constrained the final design and hardware implementation. In addition, we will present our first light, cryogenic, IR index of refraction data for LiF, BaF2, and CaF2, and compare our results to previously published data for these materials.

Frey, Bradley J.; Leviton, Douglas B.

2004-01-01

209

Intervalence charge transfer luminescence: Interplay between anomalous and 5d - 4f emissions in Yb-doped fluorite-type crystals.  

PubMed

In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorite-type crystals associated with Yb(2+)-Yb(3+) mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb(2+)-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb(2+)-Yb(3+) mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4f(14)-1A1g? 4f(13)((2)F7/2)5deg-1T1u absorption in the Yb(2+) part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb(3+) moiety is in the higher 4f(13)((2)F5/2) multiplet. The Yb(2+)-Yb(3+) ? Yb(3+)-Yb(2+) IVCT emission consists of an Yb(2+) 5deg ? Yb(3+) 4f7/2 charge transfer accompanied by a 4f7/2 ? 4f5/2 deexcitation within the Yb(2+) 4f(13) subshell: [(2)F5/25deg,(2)F7/2] ? [(2)F7/2,4f(14)]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the presence of additional 5d-4f emissions in SrCl2 which are absent in SrF2. They also allow to interpret and reproduce recent experiments on transient photoluminescence enhancement in Yb(2+)-doped CaF2 and SrF2, the appearance of Yb(2+) 4f-5d absorption bands in the excitation spectra of the IR Yb(3+) emission in partly reduced CaF2:Yb(3+) samples, and to identify the broadband observed in the excitation spectrum of the so far called anomalous emission of SrF2:Yb(2+) as an IVCT absorption, which corresponds to an Yb(2+) 4f5/2 ? Yb(3+) 4f7/2 electron transfer. PMID:25527954

Barandiarán, Zoila; Seijo, Luis

2014-12-21

210

Effect of group velocity dispersion on supercontinuum generation and filamentation in transparent solids  

NASA Astrophysics Data System (ADS)

We experimentally investigate the spectral extent and spectral profile of the supercontinuum (SC) generated in transparent solids: barium fluoride, calcium fluoride, and fused silica upon irradiation by intense femtosecond-long pulses of 800, 1,380, and 2,200 nm light. These wavelengths correspond to the normal and anomalous group velocity dispersion (GVD) regimes in fused silica calcium fluoride and barium fluoride. We observe an isolated (anti-Stokes) wing on the blue side most prominently in fused silica but also in CaF2. The SC conversion efficiency is measured for the long wavelengths used in our experiments. We also present results on filamentation in BaF2 in the anomalous GVD regime, including visualization of focusing-refocusing events within the crystal; the size of a single filament is also determined. The 15-photon absorption cross section in BaF2 is deduced to be 6.5 × 10-190 cm30 W-15 s-1.

Dharmadhikari, Jayashree A.; Deshpande, Rucha A.; Nath, Arpita; Dota, Krithika; Mathur, Deepak; Dharmadhikari, Aditya K.

2014-10-01

211

A First-Principles Investigation of Core Valence Luminescence in Barium Fluoride  

NASA Astrophysics Data System (ADS)

Rodnyi (P. Rodnyi, Sov. Phys.- Solid State 34, 1078(1992)) showed how the core valence transition (CVL) in a binary compound is determined by the various band parameters associated with the band gap of the material and its valence and core band structures. The most crucial parameter for this process is shown to be ?, which is approximately equal to the ratio of the energy gap between the top of the core band and bottom of the conduction band, and the band gap. We have studied the variation of this band parameter among the alkaline-earth fluorides. Using the band structures from the augmented spherical wave method, the values of ? are found to be 2.79, 2.11 and 1.74 for CaF_2, SrF2 and BaF2 respectively. They are in reasonable agreement with the empirical values reported by Rodnyi^1. The value of ? for BaF2 lies within the limits of 1.34 and 2.00 which is favorable for CVL. A comparison of the band parameters from the ASW method and a cluster approach using the scattered wave X-? method will also be made.

Mishra, K. C.; Johnson, K. H.; Osterloh, I.; Schmidt, P. C.

1997-03-01

212

High T(sub c) thin film superconductors: Preparation, patterning and characterization  

NASA Astrophysics Data System (ADS)

A conventional oil-pumped vacuum system equipped with resistively heated tungsten boat sources was used for evaporation of bismuth- or yttrium-based cuprates for high T(sub c) thin film superconductors. A well-ground mixture with atomic proportions of bismuth, SrF2, CaF2 and copper for bismuth-based material, and of YF3, BaF2 and copper for yttrium-based material, was inserted into the boat and then resistively evaporated onto different substrates such as MgO, ZrO2 and SrTiO3 kept at room temperature. Yttrium-based thin films were found to have a better quality upon reduction of fluorine in the constituents. Thus, films prepared with an yttrium BaF2 and copper mixture show a metallic-like behavior, sharper transition and higher zero-resistance temperature as compared with that of films obtained by using a YF2 constiuent instead of yttrium. Bismuth-based thin films were found to lose bismuth during heat treatment unless the copper constiuent ended the evaporation process and was subsequently fully oxidized at 400 C. Bismuth-based patterned films were easily obtained by using a lift-off photolithographic method. Typical thickness of the films was measured to be about 0.5 micron after heat treatment.

Azoulay, J.

213

Static evaluation of surface coatings for compliant gas bearings in an oxidizing atmosphere to 650 C  

NASA Technical Reports Server (NTRS)

Hard wear-resistant coatings and soft low shear strength coatings were developed for an air-lubricated compliant journal bearing for a future automotive gas turbine engine. The coatings were expected to function in either 540 or 650 C ambient. Soft lubricant coatings were generally limited in temperature. Therefore emphasis was on the hard wear-resistant coatings. The coating materials covered were TiC, B4C, Cr3C2, WC, SiC, CrB2, TiB2, Cr2O3, Al2O3, Si3N4, Tribaloy 800, CaF2, CaF2-BaF2 eutectic, Ni-Co, silver, CdO-graphite and proprietary compounds. The coatings on test coupons were subjected to static oven screening tests. The test consisted of exposure of material samples in an oven for 300 h at the maximum temperature (540 or 650 C) and ten temperature cycles from room temperature to the maximum service temperature. On the basis of the specimen examinations the following coatings were recommended for future wear tests: TiC (sputtered), Cr2O3 (sputtered), Si3N4 (sputtered), CdO and graphite (fused), Kaman DES (a proprietary coating), CrB2 (plasma sprayed), Cr3C2 (detonation gun) and NASA PS-106 (plasma sprayed).

Bhushan, B.; Gray, S.

1978-01-01

214

Thirteen watt all-fiber mid-infrared supercontinuum generation in a single mode ZBLAN fiber pumped by a 2 ?m MOPA system.  

PubMed

All-fiber-integrated mid-infrared (mid-IR) supercontinuum (SC) generation in a single mode ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber with 13 W average output power and a spectrum extending from ?1.9 to 4.3 ?m is reported, which we believe is the highest output power for mid-IR SC generation in ZBLAN fibers. The overall optical conversion efficiency from the 790 nm pump light of the last stage Tm-doped fiber (TDF) amplifier to the total SC output was 20%, and the SC power for wavelengths longer than 2.5 ?m was 6.85 W with a power ratio of 52.69% with respect to the total SC power. The mid-IR SC generation in ZBLAN fiber was pumped by a 2 ?m master oscillator power amplifier (MOPA) system, which is also very appropriate for high power 2-2.5 ?m region SC generation. We also demonstrate high efficiency SC generation in the TDF amplifier with 62.1 W average power, 39.8% optical efficiency, and a spectrum extending from 1.9 to 2.7 ?m. PMID:24686621

Yang, Weiqiang; Zhang, Bin; Xue, Guanghui; Yin, Ke; Hou, Jing

2014-04-01

215

ZBLAN Microgravity Study  

NASA Technical Reports Server (NTRS)

One of the greatest obstacles with the fluorozirconate ZBLAN (ZrF4-BaF2-LaF3-AIF3-NaF) is the problem of devitrification. Fluoride glasses have a narrow working range and the viscosity is a strong function of temperature. Rates of nucleation and growth of crystals in the glass depend on the viscosity, making these glasses unstable and prone to crystallization. The viscosity of ZBLAN at the drawing temperature is low, usually between two to five poise, so it is difficult to obtain fibers from their preform melts without crystallization. The preforms usually contain heterogeneous nuclei which grow into microcrystallites above the glass transition temperature, T(g). Since microcrystallites in an optical fiber cause extrinsic light scattering losses of the optical signal, fiber drawing must be completed in a short time to minimize the generation of light scattering centers. To keep these losses to a minimum and to fabricate low scattering loss fibers and other optical components, this research deals with the possibility of minimizing crystallite formation by removing the gravitational influence of solutal segregation of the ZBLAN elements. This report reviews the early work on the KC-135 aircraft, the development of the ZBLAN Rocket Experiment, preparations at the White Sands Missile Range, analysis of the flight and ground test results, lessons learned and future experimentation.

Workman, Gary L.; Smith, Guy A.; OBrien, Sue; Adcock, Leonard

1995-01-01

216

Commercial Production of Heavy Metal Fluoride Glass Fiber in Space  

NASA Technical Reports Server (NTRS)

International Space Station Alpha (ISSA) will provide a platform not only for materials research but also a possible means to produce products in space which cannot be easily produced on the ground. Some products may even be superior to those now produced in unit gravity due to the lack of gravity induced convection effects. Our research with ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN glass) has shown that gravity does indeed play a major role in the crystallization behavior of this material. At the present time ZBLAN is being produced on earth in fiber optic form for use in surgical lasers and fiber optic lasers among other applications. High attenuation coefficients, however, have kept this material from being used in other applications such as long haul data transmission links. The high attenuation coefficients are due to impurities which can be removed through improved processing techniques and crystals which can only be removed or prevented from forming by processing in a reduced gravity environment.

Tucker, Dennis S.; Workman, Gary L.; Smith, Guy A.

1998-01-01

217

Near-infrared photocatalysts of BiVO4/CaF2:Er3+, Tm3+, Yb3+ with enhanced upconversion properties  

NASA Astrophysics Data System (ADS)

Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO4 (BVO)/CaF2:Er3+, Tm3+, Yb3+ (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi3+ ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO).Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO4 (BVO)/CaF2:Er3+, Tm3+, Yb3+ (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi3+ ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO). Electronic supplementary information (ESI) available: Additional tables and figures. See DOI: 10.1039/c3nr05266d

Huang, Shouqiang; Zhu, Nanwen; Lou, Ziyang; Gu, Lin; Miao, Chen; Yuan, Haiping; Shan, Aidang

2014-01-01

218

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

E-print Network

femtosecond laser A. Lucca, G. Debourg, M. Jacquemet, F. Druon, F. Balembois, and P. Georges Laboratoire. Moncorgé Centre Interdisciplinaire de Recherches sur les Ions et les Lasers, Unité Mixte de Recherche 6637 is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser

Boyer, Edmond

219

Correction of systematic errors in scanning force microscopy images with application to ion track micrographs  

NASA Astrophysics Data System (ADS)

Scanning force microscopy (SFM) is capable of imaging surfaces with resolution on a nanometer scale. This method therefore plays an important role in characterizing radiation-induced defects in solids complementing methods like transmission electron microscopy, small-angle X-ray scattering and optical spectroscopy, to name a few. In particular, the SFM inspection of ionic single-crystals irradiated with energetic heavy ions revealed minute hillocks. The aim to determine the size and shape of these ion tracks as a function of parameters such as energy loss gives rise to critically analyze the interaction between SFM probe tip and sample in order to recognize and take into account systematic errors. Such errors originate especially from the finite size of the sensor tip. This work presents both an uncomplicated model of the SFM imaging process and its experimental verification allowing one to quantify the influence of the tip geometry on the recorded micrographs and correct the resulting data accordingly. For this purpose, a computer program was developed, which is able firstly to determine the tip geometry by means of the known geometry of a calibration standard. Secondly, using this tip geometry, the program reproduces the original sample topography containing the radiation damage structures under study. This is illustrated representatively for artificially generated images and also for a sample micrograph recorded on the surface of U-irradiated CaF 2 to prove the efficiency of the suggested procedures. Afterwards, an existing set of images showing the calibration standard 2D200 (NANOSENSORS) is used to classify the average tip shape. Due to the fact that no large variations in this shape occur, the procedure of imaging the calibration standard for each measurement can be replaced by using this average tip for reconstruction. The article concludes with the elimination of systematic errors in existing data sets of hillock diameters recorded on LiF, CaF 2 and LaF 3 after irradiation with swift heavy ions.

Müller, C.; Voss, K.-O.; Lang, M.; Neumann, R.

2003-12-01

220

Up-conversion emission tuning in triply-doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate glass and glass-ceramics  

NASA Astrophysics Data System (ADS)

New Yb3+, Er3+ and Tm3+ triply doped fluoro-phosphate glasses belonging to the system NaPO3-YF3-BaF2-CaF2 have been prepared by the classical melt-casting technique. Glasses containing up to 10 wt.% of rare-earth ions fluorides have been obtained and characterized by using differential scanning calorimetry (DSC), UV-visible-near-infrared spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and optically homogeneous glass-ceramics have been reproducibly obtained by appropriate heat treatment in view to manage the red, green and blue emissions upon 975 nm laser excitation. According to the applied thermal heat-treatment, a large enhancement of intensity of the up-conversion emission - from 10 to 160 times higher - has been achieved in the glassceramics compared to that of glasses, suggesting incorporation of the rare-earth ions into the crystalline phase. Furthermore, a large range of color rendering has been observed in these materials by controlling the laser excitation power and material crystallization rate. Time-resolved luminescence experiments as well as X-ray diffractometry and scanning electron microscopy techniques have been employed in order to understand and correlate the multicolor emission changes to the crystallization behavior of this material. A progressive phase transformation of the fluorite-type CaF2-based nanocrystals initially generated was observed along with increasing heat-treatment time, thus modifying the rare earth ions spectroscopic features.

Ledemi, Yannick; Trudel, Andrée.-Anne; Rivera, Victor A. G.; Messaddeq, Younes

2014-03-01

221

Structural and transport properties of epitaxial Ba(Fe1?xCox)2As2 thin films on various substrates  

NASA Astrophysics Data System (ADS)

A comprehensive microstructural study was conducted on optimally-doped epitaxial Ba(Fe1?xCox)2As2 thin films grown by pulsed laser deposition on various substrates of a wide range of lattice constants: SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, MgO, CaF2, and BaF2. We found that epitaxial strain directly affects the superconductivity in the film, with the transition temperature decreasing linearly with increasing in-plane lattice constant of the film. However, the strain is not determined by the lattice mismatch between the film and substrate. Instead, the mosaic spread of the grain orientation in the film and the thermal expansion coefficient of the substrate were found to correlate well with the in-plane lattice constant of the film. The result confirms the importance of structural distortions to the superconductivity in the Ba(Fe1?xCox)2As2 films.

Lei, Q. Y.; Golalikhani, M.; Yang, D. Y.; Withanage, W. K.; Rafti, A.; Qiu, J.; Hambe, M.; Bauer, E. D.; Ronning, F.; Jia, Q. X.; Weiss, J. D.; Hellstrom, E. E.; Wang, X. F.; Chen, X. H.; Williams, F.; Yang, Q.; Temple, D.; Xi, X. X.

2014-11-01

222

Friction and Wear Characteristics of a Modified Composite Solid Lubricant Plasma Spray Coating  

NASA Technical Reports Server (NTRS)

LCR304 is a solid lubricant coating composed of Ni-10Cr, Cr2O3, BaF2-CaF2 and Ag and developed for dimensional stability in high temperature air. This coating is a modification of PS304, which differs in that the Ni-Cr constituent contains 20wt% Cr. The tribological characteristics of LCR304 were evaluated by pin-on-disk and foil air bearing rig testing from 25 to 650 C and compared to previous test results with PS304. For both tests, the friction coefficient decreased as temperature increased from 25 to 650 C. Wear generally decreased with increasing temperature for all pin-on-disk tests. LCR304 coated components produced the least wear of Inconel X-750 counterface materials at 427 and 650 C. These results indicate that the LCR304 coating has potential as a replacement for PS304 in, for example, low cycle (minimum wear) applications where dimensional stability is imperative.

Stanford, M. K.; DellaCorte, C.

2004-01-01

223

CONTROL OF LASER RADIATION PARAMETERS: Generation of multiband tunable radiation in TEA CO2 lasers  

NASA Astrophysics Data System (ADS)

A method for generating multiband tunable radiation in TEA CO2 lasers is described. Simultaneous lasing in all four branches of the 1000<-- 0001 and 0200<-- 0001 vibrational — rotational bands of CO2 was achieved. Frequency tuning in each of the bands in multiband lasing was ensured by introduction of selective absorbers (SF6, CF2HCl, CF3I) and/or parallel CaF2 or BaF2 plates into a two-mirror laser cavity. The frequency in a selected band was tuned with the aid of an additional cavity formed by a diffraction grating, a beam-splitting plate inside the main cavity, and one of the laser mirrors. This additional cavity made it possible to control also the energy of a pulse at the resonance frequency and to reduce (by no more than 50 ns) the delay time of this pulse (relative to a discharge-current pulse), compared with the delay times of pulses at other frequencies. The results obtained were used to propose schemes for two-frequency isotopically selective dissociation of molecules inside a nonselective cavity of a TEA CO2 laser (without a diffraction grating).

Makarov, Grigorii N.; Ogurok, D. D.; Petin, A. N.

1997-07-01

224

Composition optimization of chromium carbide based solid lubricant coatings for foil gas bearings at temperatures to 650 C  

NASA Technical Reports Server (NTRS)

A test program to determine the optimum composition of chromium carbide based solid lubricant coatings for compliant gas bearings is described. The friction and wear properties of the coatings are evaluated using a foil gas bearing test apparatus. The various coatings were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized nickel-chromium alloy foils. The test bearings were subjected to repeated start/stop cycles under a 14 kPa (2 psi) bearing unit load. The bearings were tested for 9000 start/stop cycles or until the specimen wear reached a predetermined failure level. In general, the addition of silver and eutectic to the chromium carbide base stock significantly reduced foil wear and increased journal coating wear. The optimum coating composition, PS212 (70 wt% metal bonded Cr3C2, 15 wt% Ag, 15% BaF2/CaF2 eutectic), reduced foil wear by a factor of two and displayed coating wear well within acceptable limits. The load capacity of the bearing using the plasma-sprayed coating prior to and after a run-in period was ascertained and compared to polished Inconel 718 specimens.

Dellacorte, Christopher

1987-01-01

225

Tribological composition optimization of chromium-carbide-based solid lubricant coatings for foil gas bearings at temperatures to 650 C  

NASA Technical Reports Server (NTRS)

The determination of the tribilogically optimum composition of chromium-carbide-based solid lubricant coatings using a foil gas bearing test apparatus is described. The coatings contain a wear resistant chromium carbide `base stock' with the lubricant additives silver and BaF2-CaF2 eutectic. The coating composition is optimized for air-lubricated foil gas bearings at temperatures ranging from 25 to 650 C. The various compositions were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized Ni-Cr alloy foils, and the test bearings were subjected to repeated start-stop cycles under a bearing unit of 14 kPa. Sliding contact between the coated journal and the smooth foil occurs during bearing start-up before lift-off or hydrodynamic lubrication by the air film and during bearing coast-down. The bearings were tested for 9000 start-stop cycles or until specimen reached a predetermined failure level.

Dellacorte, Christopher

1988-01-01

226

High-Temperature Solid Lubricants Developed by NASA Lewis Offer Virtually "Unlimited Life" for Oil-Free Turbomachinery  

NASA Technical Reports Server (NTRS)

The NASA Lewis Research Center is capitalizing on breakthroughs in foil air bearing performance, tribological coatings, and computer analyses to formulate the Oil-free Turbomachinery Program. The program s long-term goal is to develop an innovative, yet practical, oil-free aeropropulsion gas turbine engine that floats on advanced air bearings. This type of engine would operate at higher speeds and temperatures with lower weight and friction than conventional oil-lubricated engines. During startup and shutdown, solid lubricant coatings are required to prevent wear in such engines before the self-generating air-lubrication film develops. NASA s Tribology Branch has created PS304, a chrome-oxide-based plasma spray coating specifically tailored for shafts run against foil bearings. PS304 contains silver and barium fluoride/calcium fluoride eutectic (BaF2/CaF2) lubricant additives that, together, provide lubrication from cold start temperatures to over 650 C, the maximum use temperature for foil bearings. Recent lab tests show that bearings lubricated with PS304 survive over 100 000 start-stop cycles without experiencing any degradation in performance due to wear. The accompanying photograph shows a test bearing after it was run at 650 C. The rubbing process created a "polished" surface that enhances bearing load capacity.

DellaCorte, Christopher; Valco, Mark J.

1999-01-01

227

Fundamentals of dislocation nucleation at nanoindentation  

NASA Astrophysics Data System (ADS)

Microelectronics and micromechanics dominate the development of modern techniques now and in the future. Investigations of the mechanical properties in this field are done favourably by nanoindentation, that means the penetration of the surface to nanometer depths using an indentation device. Indentation of perfect solids at nanometer scale is connected to formation of high local stresses. Using this advantage one can observe besides others the homogenous nucleation of dislocations in locally dislocations-free monocrystals. The mechanical stresses responsible for this process can be estimated in the framework of elastic contact theory from Hertz and Sneddon. Experimental results of the loop nucleation measurements shows a good agreement with the theory of dislocations within the isotropic approach. The Pop-in-effect has been observed in metals (Al, Cu, Ni, W), ionic crystals (CaF2, BaF2) and semiconductors (CdTe, GaAs, GaP, InP, ZnSe). Corresponding dislocations were proved by means of microscopy imaging techniques (transmission electron microscopy TEM, cathodoluminescence imaging CL, and imaging of dislocation-etched surfaces).

Grau, P.; Lorenz, D.; Zeckzer, A.

228

Dual-band antireflection coatings on 3rd Gen lenses  

NASA Astrophysics Data System (ADS)

Use of a dual band FPA necessitates an optical system that is capable of imaging both mid wave infrared (MWIR) and long wave infrared (LWIR) spectral bands simultaneously. Such optical system can have up to 10 lenses, (20 surfaces that require antireflection (AR) coatings) which, if 95% transmitting in each band, will result in overall throughput of just under 60%1. With 99% transmitting in each band, overall throughput would be just over 90%, a relative improvement of 50%. An earlier paper presented dual band antireflection designs, as well as early fabrication attempts on plano Ge, ZnSe, ZnS, AMTIR-1, and CaF2 windows2. This paper presents results of prototype coating fabrication on ZnSe, Ge, and BaF2 lenses that comprise a 7 lens set. The measured performance of the individual elements is used to model overall system performance. The elements were incorporated into an optical assembly and measured overall imager performance is analyzed and presented.

Rahmlow, Thomas D., Jr.; Lazo-Wasem, Jeanne E.; Vizgaitis, Jay N.; Flanagan-Hyde, Justin

2011-06-01

229

Interfacial tension between aluminum and NaCl-KCl-based salt systems  

NASA Astrophysics Data System (ADS)

Aluminum scrap is frequently remelted under a NaCl-KCl based salt flux cover to prevent oxidation, to aid in the stripping of oxide films, and to improve drop coalescence. In this process, the interfacial tension between the aluminum metal and the salt flux plays an important role. However, the measurement of interfacial tensions at high temperature is difficult and prone to errors. Therefore, an interfacial tension model, presented in this article, has been developed. The interfacial tension between aluminum and NaCl-KCl based melts does not change with the addition of chlorides or with variations in the composition of the NaCl-KCl melt. On the other hand, the addition of fluorides decreases the interfacial tension to various extents due to the adsorption of sodium and/or potassium at the interface. Addition of AlF3 is the least effective; additions of LiF, MgF2, CaF2, BaF2, or SrF2 are moderately effective; and additions of NaF or KF are the most effective in lowering the interfacial tension.

Roy, Raja R.; Utigard, Torstein A.

1998-08-01

230

Charge Compensation in RE3+ (RE = Eu, Gd) and M+ (M = Li, Na, K) Co-Doped Alkaline Earth Nanofluorides Obtained by Microwave Reaction with Reactive Ionic Liquids Leading to Improved Optical Properties  

SciTech Connect

Alkaline earth fluorides are extraordinarily promising host matrices for phosphor materials with regard to rare earth doping. In particular, quantum cutting materials, which might considerably enhance the efficiency of mercury-free fluorescent lamps or SC solar cells, are often based on rare earth containing crystalline fluorides such as NaGdF4, GdF3 or LaF3. Substituting most of the precious rare earth ions and simultaneously retaining the efficiency of the phosphor is a major goal. Alkaline earth fluoride nanoparticles doped with trivalent lanthanide ions (which are required for the quantum cutting phenomenon) were prepared via a microwave assisted method in ionic liquids. As doping trivalent ions into a host with divalent cations requires charge compensation, this effect was thoroughly studied by powder X-ray and electron diffraction, luminescence spectroscopy and 23Na, 139La and 19F solid state NMR spectroscopy. Monovalent alkali ions were codoped with the trivalent lanthanide ions to relieve stress and achieve a better crystallinity and higher quantum cutting abilities of the prepared material. 19F-magic angle spinning (MAS)-NMR-spectra, assisted by 19F{23Na} rotational echo double resonance (REDOR) studies, reveal distinct local fluoride environments, the populations of which are discussed in relation to spatial distribution and clustering models. In the co-doped samples, fluoride species having both Na+ and La3+ ions within their coordination sphere can be identified and quantified. This interplay of mono- and trivalent ions in the CaF2 lattice appears to be an efficient charge compensation mechanism that allows for improved performance characteristics of such co-doped phosphor materials.

Lorbeer, C [Ruhr-Universitat Bochum; Behrends, F [Westfalische Wilhelsm-Universitat Munster; Cybinska, J [Ruhr Universitat Bochum; Eckert, H [Westfalische Wilhelsm-Universitat Munster; Mudring, Anja -V [Ames Laboratory

2014-01-01

231

Diopside (CaO-MgO-2SiO2)-fluorapatite (9CaO-3P2O5-CaF2) glass-ceramics: Potential materials for bone tissue engineering  

SciTech Connect

Glass-ceramics in the diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] system are potential candidates for restorative dental and bone implant materials. In the present study, a series of glasses along diopside - fluorapatite binary system have been prepared with varying diopside/fluorapatite ratios for their potential applications in bone tissue engineering. The glasses were obtained from compositions with fluorapatite contents varying between 0-40 wt.%. The sintering ability and crystallization kinetics of as obtained amorphous glasses have been studied through hot-stage microscopy (HSM) and differential thermal analysis (DTA), respectively while crystalline phase evolution in sintered GCs has been followed by X-ray diffraction (XRD) adjoined with Rietveld-R.I.R. technique and scanning electron microscopy (SEM). Further, biodegradation and apatite forming ability of glass-ceramics were investigated by immersion of glass-ceramic discs in simulated body fluid (SBF) solution while chemical degradation and weight loss of glass-ceramics were studied by immersion in Tris-HCl in accordance with standard ISO 10993-14. The addition of fluorapatite (10-25 wt.%) in diopside glass system significantly enhanced the sintering ability of glass-ceramics and improved their apatite forming ability along with their biodegradation behaviour. Moreover, the in vitro cellular responses to glass-ceramics showed good cell viability and significant stimulation of osteoblastic differentiation, suggesting the possible use of the glass-ceramics for bone regeneration.

Kansal, Ishu; Goel, Ashutosh; Tulyaganov, Dilshat U.; Pascual, Maria J.; Lee, Hye-Young; Kim, Hae-Won; Ferreira, Jose M.

2011-08-18

232

Preparation and tribological properties of fluorosilane surface-modified lanthanum trifluoride nanoparticles as additive of fluoro silicone oil  

NASA Astrophysics Data System (ADS)

LaF3 nanoparticles surface-modified with fluorosilane were synthesized by surface modification technology. The size, morphology and phase structure of as-prepared surface-modified LaF3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of surface-modified LaF3 nanoparticles as additive of fluoro silicone oil were evaluated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined with a scanning electron microscope and an X-ray photoelectron spectroscope. Results show that 3-(heptafluoroisopropoxy)propyltriethoxysilane as the modifier is able to improve the dispersibility of LaF3 nanoparticles in fluoro silicone oil. Moreover, when the optimum concentration, 0.08 wt.% of fluorosilane surface-modified LaF3 is added into fluoro silicone oil, as-synthesized fluorosilane surface-modified LaF3 nanoparticles exhibit excellent anti-wear as additive in fluoro silicone oil. The wear scar diameter under the optimum concentration is always smaller than that under the lubrication of fluoro silicone oil alone. Especially, when the load is 500 N, 600 N and 700 N, the wear scar diameter is reduced by 17%, 43% and 42%, respectively. In addition, during the friction process, LaF3 nanoparticles are deposited on the rubbed steel surface to form LaF3 deposition layer which functions jointly with the boundary lubricating film thereby resulting in improved tribological properties.

Hou, Xiao; He, Jie; Yu, Laigui; Li, Zhiwei; Zhang, Zhijun; Zhang, Pingyu

2014-10-01

233

EPR spectra and crystal field of hexamer rare-earth clusters in fluorites  

NASA Astrophysics Data System (ADS)

Disordered fluorite-related solid solutions (AF2)1-x-y (Ln'F3)x (Ln?F3)y , where A=Ca , Sr, Ba; Ln'=Er , Tm, Yb; Ln?=Lu , Y; and x?y=0.001-0.4 , were studied by both optical detection and conventional electron paramagnetic resonance (EPR) techniques. The EPR spectra of paramagnetic rare-earth ions Er3+ , Tm3+ , and Yb3+ in clusters of diamagnetic Y3+ and Lu3+ ions were recorded. It appears that the crystalline electric field at the sites of Ln ions in the clusters is of “nearly” tetragonal symmetry and provides for high values of factors g? , approaching the theoretical limits, and small values of factors g?˜0 in the ground states of the paramagnetic Ln ions. It was assumed that all the clusters of Ln ions in the solid solutions appear to be similar in structure to the hexameric clusters, which are the basic structural units of the homologous series of fluorite-related superstructures (AF2)1-y(LnF3)y with compositions y=5/m , where m is an integer in the range of 13-19. The structure of “symmetric” hexameric clusters in CaF2 , SrF2 , and BaF2 hosts was established by computer simulation. The crystalline electric field and the spectroscopic ground-state parameters for Er3+ , Tm3+ , and Yb3+ ions in the hexameric clusters were calculated and found to be in agreement with the experimental data, being totally different from those known for the “isolated” simple cubic and tetragonal centers in the fluorite crystals.

Kazanskii, S. A.; Ryskin, A. I.; Nikiforov, A. E.; Zaharov, A. Yu.; Ougrumov, M. Yu.; Shakurov, G. S.

2005-07-01

234

The effect of prolonged exposure to 750 C air on the tribological performance of PM212  

NASA Technical Reports Server (NTRS)

The effect of prolonged exposure to 750 C air on the tribological performance and dimensional stability of PM212, a high temperature, self-lubricating composite, is studied. PM212, by weight, contains 70 percent metal-bonded Cr3C2, 15 percent BaF2/CaF2 eutectic, and 15 percent silver. Rub blocks were fabricated from PM212 by cold isostatic pressing followed by sintering. Prior to tribo-testing, the rub blocks were exposed to 750 C air for periods ranging from 100 to 1000 hours. Then, the rub blocks were slid against nickel-based superalloy disks in a double-rub-block tribometer in air under a 66 N load at temperatures from 25 to 750 C with a sliding velocity of 0.36 m/s. Unexposed rub blocks were tested for baseline comparison. Friction coefficients ranged from 0.24 to 0.37 for the unexposed rub blocks and from 0.32 to 0.56 for the exposed ones. Wear for both the composite blocks and superalloy disks was typically in the moderate to low range of 10(exp -5) to 10(exp -6) mm(exp 3)/N-m. Friction and wear data were similar for the rub blocks exposed for 100, 500, and 1000 hours. Prolonged exposure to 750 C air increased friction and wear of the PM212 rub blocks at room temperature, but their triboperformance remained unaffected at higher temperatures, probably due to the formation of lubricious metal oxides. Dimensional stability of the composite was studied by exposing specimens of varying thicknesses for 500 hours in air at 750 C. Block thicknesses were found to increase with increased exposure time until steady state was reached after 100 hours of exposure, probably due to oxidation.

Bemis, Kirk; Bogdanski, Michael S.; Dellacorte, Christopher; Sliney, Harold E.

1994-01-01

235

Visible and Mid-Infrared Supercontinuum Generation and Their Respective Application to Three-Dimensional Imaging and Stand-off Reflection Spectroscopy  

NASA Astrophysics Data System (ADS)

The thesis describes broadband supercontinuum (SC) generation in optical fibers for both the visible and mid-infrared regions of the spectrum, and their respective application to 3D imaging and stand-off reflection spectroscopy. Both SC sources leverage mature telecom technology, and are based on a common all-fiber integrated platform comprising a ˜1.55 mum distributed feedback seed laser diode amplified to high peak powers in two stages of cladding pumped Erbium or Erbium-Ytterbium fiber amplifiers. A visible SC extending from 0.45--1.20 mum with 0.74 W of time-averaged power is demonstrated using a two step process. The output of the Er-Yb power amplifier is frequency doubled to ˜0.78 mum using a periodically poled lithium niobate crystal, followed by non-linear spectral broadening in 2m of high nonlinearity photonic crystal fiber. Numerical simulations based on solving the generalized non-linear Schrodinger equation are also presented to verify the underlying SC generation mechanisms and predict further improvements. The above SC source is used in a Fourier domain line scan interferometer to measure the height and identify shape defects of ˜300 mum high solder balls in a ball grid array. The 3D imaging system has an axial resolution of ˜125 nm, transverse resolution of ˜15 mum, and an angular measurement range between 20 to 60 degrees depending on the sample surface roughness. The mid-infrared SC source is generated by pumping a 9m long ZrE 4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber to obtain a spectrum spanning 0.8--4.3 mum with 3.9 W time-averaged power. The output power is linearly scalable with pump power, but requires optimization of the critical splices and thermal management of the gain fiber and pump diodes to ensure stable high power operation. Finally, an application of the mid-IR SC is demonstrated by measuring the diffuse reflection spectra of solid samples at a stand-off distance of 5 m and 100 ms integration time. The samples can be distinguished using a correlation algorithm based on distinct spectral features in the reflection spectrum. Signal to noise ratio calculations show that the distance is limited by space constraints in our lab and can be extended to ˜150 m.

Kumar, Malay

236

Single mode optical fiber based devices and systems for mid-infrared light generation, communication and metrology  

NASA Astrophysics Data System (ADS)

Fiber-optic systems and devices for broadband mid-infrared light generation, communication and optical metrology are developed in this thesis. Using the nonlinear properties of low mid-infrared loss ZrF4-BaF 2-LaF3-AlF3-NaF (ZBLAN) fiber, a mid-infrared supercontinuum (SC) laser based on a thulium-doped fiber amplifier (TDFA) with spectrum extending from ˜1.9-4.5 microm is demonstrated. A higher efficiency, power-scalable, all-fiber integrated mid-infrared light source is realized capable of generating ˜0.7 W time-average power in wavelengths beyond 3.8 microm. The novelty of the laser lies in its two-step spectral shifting architecture. First, amplified laser diode pulses at 1.55 microm are used to generate a SC extending beyond 2 microm in standard SMF using modulation-instability initiated pulse break-up. A TDFA stage is then used to amplify the ˜2 microm components in the standard SMF continuum. By subsequently coupling the amplified ˜2 microm pulses in to a ZBLAN fiber, an SC with up to ˜2.6 W average power, and ˜9% optical conversion efficiency from the power-amp pump to mid-IR output is demonstrated. The two-step methodology leads to extension in the long wavelength edge of the SC from 4.2 microm to ˜4.5 microm, compared to previously demonstrated systems and ˜2.5 times higher optical efficiency in generating wavelengths beyond 3.8 microm. Numerical simulations are also presented based on solving the generalized non-linear Schrodinger equation to verify and extend experimental results. A broadband surface-normal optical modulator for communication applications with operation demonstrated over 1200--2400 nm is also presented. The modulator uses free-carrier effect in GaAs and mode selectivity of SMF to generate up to ˜43% modulation depth with a maximum operating speed of ˜270 MHz. The broad wavelength range of operation of the modulator can potentially enable higher throughput wavelength-division multiplexed optical network architectures based on broadband light sources. Finally, an optical probe for detection of porosity defects in automotive parts is presented. The probe relies on the spatial coherence properties of SMF output to detect defects as small as ˜50 microm lateral dimensions in bores down to 5 mm diameter. The probe uses a novel two-directional scattering-based non-contact approach to detect and classify defects on surfaces, where human inspection is labor-intensive.

Kulkarni, Ojas P.

237

Mechanisms for the Crystallization of ZBLAN  

NASA Technical Reports Server (NTRS)

The objective of this ground based study is to test the hypothesis that shear thinning (the non-Newtonian response of viscosity to shear rate) is a viable mechanism to explain the observation of enhanced glass formation in numerous low-g experiments. In 1-g, fluid motion results from buoyancy forces and surface tension driven convection. This fluid flow will introduce shear in undercooled liquids in 1-g. In low-g it is known that fluid flows are greatly reduced so that the shear rate in fluids can be extremely low. It is believed that some fluids may have weak structure in the absence of flow. Very small shear rates could cause this structure to collapse in response to shear resulting in a lowering of the viscosity of the fluid. The hypothesis of this research is that: Shear thinning in undercooled liquids decreases the viscosity, increasing the rate of nucleation and crystallization of glass forming melts. Shear in the melt can be reduced in low-g, thus enhancing undercooling and glass formation. The viscosity of a model glass (lithium di-silicate, L2S) often used for crystallization studies has been measured at very low shear rates using a dynamic mechanical thermal analyzer. Our results are consistent with increasing viscosity with a lowering of shear rates. The viscosity of L2S may vary as much as an order of magnitude depending on the shear rate in the temperature region of maximum nucleation and crystal growth. Classical equations for nucleation and crystal growth rates, are inversely related to the viscosity and viscosity to the third power respectively. An order of magnitude variation in viscosity (with shear) at a given temperature would have dramatic effects on glass crystallization Crystallization studies with the heavy metal fluoride glass ZBLAN (ZrF2-BaF2-LaF3-AlF3-NaF) to examine the effect of shear on crystallization are being initiated. Samples are to be melted and quenched under quiescent conditions at different shear rates to determine the effect on crystallization. The results from this study are expected to advance the current scientific understanding of glass formation in low-g and glass crystallization under glass molding conditions and will improve the scientific understanding of technological processes such as fiber pulling, bulk amorphous alloys, and glass fabrication processes.

Ethridge, Edwin C.; Tucker, Dennis S.; Kaukler, William; Antar, Basil

2003-01-01

238

Understanding the role of gravity in the crystallization suppression of ZBLAN glass  

NASA Astrophysics Data System (ADS)

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 ?m in the UV to 7 ?m in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its low loss-capability. Other researchers have shown that microgravity processing leads to suppressed crystal growth in ZBLAN glass, which can lead to lower transmission loss in the desired mid-IR range. However, the mechanism governing crystal growth suppression has not been thoroughly investigated. In the present research multiple ZBLAN samples were subjected to a heating and quenching test apparatus on a parabolic aircraft under controlled ?-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy (transmission and polarized) along with SEM examination elucidates that crystal growth in ZBLAN is suppressed when processed in a microgravity environment. Hence crystallization occurs at a higher temperature in ?-g and the working temperature range at which the fiber can be manufactured has been extended. We postulate that the fundamental process of nano-scale mass transfer (lack of buoyancy driven convection) in the viscous glass is the mechanism responsible for crystal growth suppression in microgravity. Suppressing molecular mobility within the semi-molten glass starves nucleating crystallites and prevents any further growth. A COMSOL Multi-Physics model was developed to show the velocity contours due to convection processes in a 1-g, ?-g, and hyper-g environment. Analytical models show that while suppressing convection is relevant at fiber drawing temperatures (360°C), mass transfer due to diffusion dominates at higher temperatures leading to crystal growth at temperatures ?400°C. ZBLAN fibers are also known for their poor handling ability. Therefore an analysis of the thermal degradation of ZBLAN optical fibers based on fracture mechanics was also conducted. Conditions of crack initiation and stable versus unstable crack growth leading to fiber fracture were analyzed to explain behavior observed from controlled flexure tests of ZBLAN optical fibers exposed to various temperatures.

Torres, Anthony Samuel

239

The Effects of Gravity on the Crystallization Behavior of Heavy Metal Fluoride Glasses  

NASA Technical Reports Server (NTRS)

Heavy metal fluoride glasses are used in such applications as fiber lasers and laser amplifiers. ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is one of the more commonly used heavy metal fluoride glasses. ZBLAN is an infrared transmitter and has a theoretical attenuation coefficient of 0.002 db/km. However, due to impurities and small crystallites this attenuation coefficient has not been achieved to date. ZBLAN is a fragile glass which can lead to rapid crystallization, if the glass is not cooled rapidly to below the glass transition temperature or if the glass is reheated near the crystallization temperature for any period of time. Studies carried on at Marshall Space Flight Center and the University of Alabama in Huntsville since 1993 have shown that heating ZBLAN glass at the crystallization temperature in reduced gravity results in a suppression of crystallization when compared to ZBLAN processed in unit gravity. These studies utilized NASA's KC-135 aircraft and the Conquest sounding rocket. In the first series of experiments, short lengths of ZBLAN fiber were heated to the crystallization temperature in reduced gravity on board the KC- 135 and the Conquest sounding rocket and compared with fibers heated in unit gravity. The fibers processed in reduced gravity showed no evidence of crystallization when studied with x-ray diffraction and scanning electron microscopy. However, the fibers processed in unit gravity were completely crystallized. Subsequent experiments included heating small pieces of ZBLAN glass at the crystallization temperature while viewing with a video camera to follow the crystallization phenomenon. In this experiment crystallization was observed in reduced gravity, however, it was suppressed when compared to heating in unit gravity. In the most recent experiment on board the KC-135, rapid thermal analysis of ZBLAN was performed. A mechanism to explain the observations has been proposed. This mechanism is based on shear thinning whereby, the glass undergoes a reduction in viscosity in the 10(exp 5) - 10(exp 7) poise range, allowing more rapid diffusion and thus crystallization. It is proposed that this mechanism is suppressed in reduced gravity. An experiment is presently being conducted to test this theory. With increased knowledge of ZBLAN behavior in reduced gravity, three low earth orbit tiber drawing facilities have been designed. One would be suitable for use on the International Space Station, another while aboard the Space Shuttle and the third system is a fully automated facility which would operate independently of the ISS or Shuttle in a free float mode. The primary benefits of free floating a facility in LEO includes a higher quality of microgravity and reduced safety concerns since it is not in a manned environment.

Tucker, Dennis S.; Smith, Guy A.

2004-01-01

240

Insulators for Pb(1-x)Sn(x)Te  

NASA Technical Reports Server (NTRS)

Thin films of LaF3 were e-gun and thermally deposited on several substrates. The e-gun deposited films are fluorine deficient, have high ionic conductivities that persist to 77 K, and high effective dielectric constants. The thermally deposited material tends to be closer to stoichiometric, and have higher effective breakdown field strengths. Thermally deposited LaF3 films with resistivities in excess of 10 to the 12th power ohms - cm were deposited on metal coated glass substrates. The LaF3 films were shown to adhere well to PbSnTe, surviving repeated cycles between room temperature and 77 K. The LaF3 films on GaAs were also studied.

Tsuo, Y. H.; Sher, A.

1981-01-01

241

prsente pour obtenir le grade de DOCTEUR DE L'UNIVERSIT LOUIS PASTEUR  

E-print Network

-DRAW software. On top: orthogonal views of a calixarene with selected solvent molecules (left) and biphasic) interface is shown. Bottom: cumulated orthogonal views of a calixarene (left) and a La(F3CSO3)3 salt

Paris-Sud XI, Université de

242

Broadband reflectance coatings for vacuum ultraviolet application  

NASA Technical Reports Server (NTRS)

An experimental investigation has obtained results indicating that neither LaF3 nor LiYF4 are acceptable alternatives to MgF2 as coatings for vacuum-deposited aluminum mirrors from which high UV reflectance down to 1150 A is required. Nevertheless, LaF3 may prove useful in those specialized applications in which the suppression of lower wavelength emissions, such as the 1216-A hydrogen line, is desirable.

Herzig, Howard; Fleetwood, C. M., Jr.; Flint, B. K.

1987-01-01

243

Sensors and Actuators B 49 (1998) 133138 High temperature semiconductor sensor for the detection of  

E-print Network

of fluorine up to 350°C. The use of the structure SiC/SiO2/LaF3/Pt at room temperature leads to results of a single crystal of LaF3 coated with a platinum film to get an all solid state potentiometric device for the determination of fluorine. Drawbacks of this sensor are the high price of the single crystal and the formation

Moritz, Werner

244

Voltammetry with a Fluoride-Selective Electrode with SolidPhase Reference System  

Microsoft Academic Search

Experimental results obtained in a study of the voltammetric response of an all-solid fluoride-selective electrode based on LaF3 (Eu2+ 0.8 mol %), LaF3 (Sr2+ 5 mol %) and CeF3 (Sr2+ 5 mol %) single crystals brought in contact with Ag, Bi, and Sn metal samples are presented. The method of cathodic inversion voltammetry was applied to study the reduction of

M. S. Turaeva; S. A. Kot; O. V. Glumov; I. V. Murin

2001-01-01

245

Reappearance of fine structure as a probe of lifetime broadening mechanisms in the 4f(N) --> 4f(N-1)5d excitation spectra of Tb3+, Er3+, and Tm3+ in CaF2 and LiYF4.  

PubMed

High-energy transitions in the 4f(N) -->4f(N-1)5d excitation spectra of lanthanide ions in host crystals are usually broadened due to the short excited-state lifetimes, whereas low-energy transitions, with longer excited-state lifetimes, may show fine structure. We report the surprising observation that for some materials fine structure is observed not only for the low-energy excitation bands but also for some high-energy transitions. The excited states that display fine structure are those for which the 5d electron is in the lowest crystal-field level but the 4f(N-1) core is in a highly excited state, indicating that the broadening depends only on the energy of the 5d electron and not on the total energy of the 4f(N-1)5d excited state. PMID:11863852

van Pieterson, L; Reid, M F; Meijerink, A

2002-02-11

246

PS300 Tribomaterials Evaluated at 6500C by Bushing Test Rig  

NASA Technical Reports Server (NTRS)

A new facility has been developed to test the tribological behavior (friction and wear) of PS300 solid lubricant bushings at high temperatures. PS300 is a commercially available solid lubricant invented at the NASA Glenn Research Center. It can be prepared as a plasma spray coating or as a free-standing powder metallurgy component, designated PM300. PS300 and PM300 composites are designed to lubricate sliding components at temperatures above the capability of today's best oils, greases, and solid lubricants. One of the primary applications being pursued for PM300 is the development of bushings for use in high-temperature machinery. Examples include inlet guide vane bushings for gas turbines and conveyors, and bearings for industrial furnaces and ovens. Encouraging preliminary field trials indicate that PS300 and PM300 lubricant materials have been commercialized successfully in several industrial applications. However, the lack of laboratory performance data has hindered further commercialization especially for new applications that differ significantly from the established experience base. The purpose of the newly developed bushing test rig will be to determine the performance characteristics of PM300, and other materials, under conditions closely matching intended applications. The data will be used to determine engineering friction and wear rates and to estimate the life expectancy of bushings for new applications. In the new rig, the bushing is loaded against a rotating shaft inside a furnace enclosure (see the preceding photograph). Loads can vary from 5 to 200 N, speeds from 1 to 400 rpm, and temperatures from 25 to 800 C. Furnace temperature, bushing temperature, shaft speed, and torque are monitored during the test, and wear of both the bushing and the shaft is measured after testing is completed. Initially, PM300 bushings will be evaluated and compared with lower temperature, traditional bushing materials like graphite and porous bronze. The baseline PM304 composition is 60 wt% NiCr (a binder), 20 wt% Cr2O3 (a hardener), 10 wt% BaF2/CaF2 (a high-temperature lubricant), and 10 wt% Ag (a low-temperature lubricant). Future research efforts will include determining the effects of load, sliding speed, and temperature on tribological performance and, possibly, tailoring composition for specific applications. We expect that the availability of measured performance data will enhance the market penetration of PM300 technology.

Striebing, Donald R.; DellaCorte, Christopher

2004-01-01

247

Variations of BaSnF4 fast ion conductor with the method of preparation and temperature  

NASA Astrophysics Data System (ADS)

Ionic conductors are solids that have a large number of defects and easy pathways that make it possible for ions to move over long distances in an electric field. In order to be mobile an ion must be small and have a low charge. The fluoride ion is the most mobile anion. The highest performance fluoride ion conductors contain divalent tin, and have a highly layered crystal structure related to the CaF2 fluorite type. BaSnF4 has the ?-PbSnF4 structure, which is a ?2?2 × ?2?2 × ?2 superstructure of the fluorite type, where the tetragonal unit-cell and the value of the a and b parameters being equal to half the diagonals of the (a, b) face of fluorite are due to the loss of the F Bravais lattice, and the Sn Sn Ba Ba order along the c parameter is at the origin of the doubling of the c parameter. The BaSnF4 material was prepared first by Dénès et al. (C. R. Acad. Paris C, 280: 831, 1975), and its superionic properties were characterized by Dénès et al. (Solid State Ion., 13: 213, 1984). It was found to have a conductivity three orders of magnitude higher than that of BaF2, with an ionic conduction rate ?i>0.99. No BaSnF4 was obtained by the aqueous medium, when aqueous solutions of SnF2 and Ba(NO3)2 are mixed together; BaSn2F6 was obtained instead. In a new development of this work, BaSnF4 has been obtained by the wet method for the first time. X-ray powder diffraction showed that the BaSnF4 phase obtained by the wet method varies substantially from one sample to another: (a) signification variations of the c parameter of the tetragonal unit-cell reveals that the interlayer distance is sensitive to the leaching conditions, possibly because some of the leached ions remain in the interlayer spacing; (b) large variations of the crystallite dimensions and, as a result of the two-dimensionality of the structure, a strong crystallite dimension anisotropy are observed, with d?d?, where d? and d? are the crystallite dimensions parallel to the four-fold main axis, and perpendicular to it, respectively, showing that the layers are very thin and the interlayer interactions are very weak. Variable temperature Mossbauer spectroscopy showed an unusual large variation of the quadrupole splitting with temperature. A tentative explanation based on unusually large bond angles has been proposed.

Dénès, Georges; Hantash, Jamil; Muntasar, Abdualhafeed; Oldfield, Philip; Bartlett, Alan

248

[Study on the vacuum ultraviolet transmittance of barium fluoride crystals at different temperature].  

PubMed

Two VUV-grade BaF2 windows with 0.5 mm-thick and 1 mm-thick respectively were selected to study the transmittance variety with the temperature. The results show that the cutoff wavelength of BaF2 crystals will shift towards the long wave with the increase in temperature. In a certain temperature range, BaF2 crystals can depress 130.4 nm radiation well, and also has a high transmittance at 135.6 nm. Compared with the reported method in which SrF2 crystals can be applied to suppress 130.4 nm stray light by heating, BaF2 crystal can inhibit the 130. 4 nm emission line completely, and thus reduce the power consumption of the device at the same time. This indicates that BaF2 crystals can play an important role in the ionosphere optical remote sensing detection. PMID:25208398

Peng, Ru-Yi; Fu, Li-Ping; Tao, Ye

2014-03-01

249

Fluoride-containing bioactive glasses: Fluoride loss during melting and ion release in tris buffer solution  

Microsoft Academic Search

Melt-derived bioactive glasses (SiO2–P2O5–CaO–Na2O–CaF2; CaF2 0 to 17.76mol%) lost fluoride during melting, but nominal and analysed CaF2 contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF2, suggesting that CaF2 impedes absorption of atmospheric water.

Delia S. Brauer; Mohammed Mneimne; Robert G. Hill

2011-01-01

250

The analysis of thermoluminescent glow peaks of CaF : Dy (TLD-200) after -irradiation  

E-print Network

The analysis of thermoluminescent glow peaks of CaF 2 : Dy (TLD-200) after -irradiation of thermoluminescent glow peaks of CaF2 : Dy (TLD-200) after -irradiation A Necmeddin Yazici1,4 , Reuven Chen2 , Semra : Dy, LiF : Mg : Ti(TLD-100) and some other thermoluminescent materials, relatively little work has

Chen, Reuven

251

Titanium dioxide/calcium fluoride nanocrystallite for efficient dye-sensitized solar cell. A strategy of enhancing light harvest  

NASA Astrophysics Data System (ADS)

Enhancement of light harvest for dye excitation is a persistent objective in dye-sensitized solar cell (DSSC). We present here the fabrication of titanium dioxide/calcium fluoride (TiO2/CaF2) photoanodes for efficient DSSC applications. Owing to the interference effect of incident light beams reflected from TiO2/CaF2 and CaF2/electrolyte interfaces, the light intensity and therefore dye excitation have been markedly enhanced. The crystal structure and therefore photovoltaic performance are optimized by adjusting CaF2 dosage. A maximum power conversion efficiency of 7.66% is measured from the DSSC employing TiO2/0.5 wt% CaF2 nanocrystallite in comparison with 6.02% for the solar cell with pristine TiO2 anode.

Wang, Zubin; Tang, Qunwei; He, Benlin; Chen, Xiaoxu; Chen, Haiyan; Yu, Liangmin

2015-02-01

252

Microstructures and properties of superconducting Y-ErBaCuO thin films obtained from disordered Y-ErBaF2Cu films  

NASA Technical Reports Server (NTRS)

The preparation procedure used to obtain superconducting thin films by radio frequency magnetron sputtering of a single mosaic target is described in detail. The single mosaic target is composed of (Y-Er), BaF2, and Cu.

Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Merlo, V.; Messi, R.; Paoluzi, L.; Scopa, L.

1991-01-01

253

Microstructures and properties of superconducting Y-Er-BaCu-O thin films obtained from disordered Y-Er-BaF2-Cu films  

NASA Technical Reports Server (NTRS)

Since the first reports on superconducting thin films obtained by evaporating BaF2, Cu and Y(sup 1), or Yb or Er(sup 2), several others have followed. All these reports describe thin films prepared by means of molecular beam cells or electron guns. Researchers show that films with similar properties can be obtained by radio frequency sputtering of a single mosaic target composed by Y-Er, BaF2 and Cu. Process steps are described.

Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Messi, R.; Paoluzi, L.; Scopa, L.; Tripodi, P.

1990-01-01

254

An in situ spectroscopic study of the local structure of oxyfluoride melts: NMR insights into the speciation in molten LiF-LaF3-Li2O systems.  

PubMed

The local structure of molten LaF3-LiF-Li2O has been investigated by high temperature NMR spectroscopy. The (139)La and (19)F chemical shifts have been measured as a function of temperature and composition. The NMR spectra show that Li2O reacts completely with LaF3 to form a LaOF compound in the solid state below the melting temperature of the sample. LaOF is not completely dissolved in the fluoride melt and solid LaOF is observed in the (19)F spectra for Li2O concentrations above 10 mol%. We discuss the local environment of lanthanum ions in molten LaF3-LiF-Li2O and compare the results to those with the LaF3-LiF-CaO system. The analysis of the temperature and Li2O concentration dependences of the (139)La and (19)F chemical shifts suggests that several kinds of lanthanum oxyfluoride long-lived LaOxFy(3-x-y) units are present in the melt. PMID:24851926

Rollet, Anne-Laure; Matsuura, Haruaki; Bessada, Catherine

2015-01-14

255

The Growth and Characterization of Germanium-Carbon Alloy Thin Films and Solid Phase Equilibria for Metal-Silicon - Ternary Systems: Magnesium, Calcium, Strontium, Barium, Scandium, Yttrium, Lanthanum, Titanium, Zirconium and Hafnium  

NASA Astrophysics Data System (ADS)

Thin films of pure germanium-carbon alloys (Ge _{rm x}C _{rm 1-x} with 0 <=q x <=q 1) have been grown on Si and Al_2O_3 substrates by pulsed laser ablation in a high vacuum chamber. The films were analyzed by x-ray 0-20 diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), conductivity measurements and optical absorption spectroscopy. The analyses of these new materials showed that films of all compositions were amorphous, free of contamination and uniform in composition. By changing the film composition, the optical band gap of these semiconducting films was varied from 0.00 eV to 0.85 eV for x = 0.0 to 1.0 respectively. According to the AES results, the carbon atoms in the Ge-C alloy thin film samples have a bonding structure that is a mixture of sp^2 and sp^3 hybridizations. The presence of the sp^2 C is apparently what causes the bandgap of amorphous Ge-C alloys to decrease with increasing carbon concentration. The solidus portion of the ternary phase diagrams of the type M-Si-O, where M = Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr and Hf have been derived at 298K and 1 atm oxygen partial pressure by investigating the bulk reactions possible in these systems. These phase diagrams, which have been determined by experiments and by calculations using thermodynamic data available, can be used to predict the occurrence of the reaction products or the stability of the phases present at the interfaces between different solid materials. Hence, they provide guides in designing thin film structures and in selecting candidate materials to form chemically stable interfaces. A research effort has been made on the investigation of the growth of diamond thin films from a carbon containing solid-CI_4, using laser ablation technique. The film grown by laser ablation from CI _4 is mainly composed of carbon with very small amount of oxygen and iodine as indicated by x-ray photoelectron spectroscopy data. The Auger electron spectroscopy result shows that the film grown contains a mixture of sp^2 and sp^3 hybridized carbon. By using x-ray powder diffraction and magnetic susceptibility measurements methods, we studied the chemical stability of candidate interlayer materials between YBa _2Cu_3O _7-delta and Si. The results show that CaF_2 reacts with YBCO while BaF_2 is chemically stable with YBCO. LaGaO_3 and Ca _2SiO_4 are chemically stable with Si and more investigations need to be made on the reactivity between Ca_2SiO _4 and YBCO.

Yuan, Haojie

1992-09-01

256

Neutron threshold activation detectors (TAD) for the detection of fissions  

NASA Astrophysics Data System (ADS)

Prompt fission neutrons are one of the strongest signatures of the fission process. Depending on the fission inducing radiation, their average number ranges from 2.5 to 4 neutrons per fission. They are more energetic and abundant, by about 2 orders of magnitude, than the delayed neutrons (?3 vs. ?0.01) that are commonly used as indicators for the presence of fissionable materials. The detection of fission prompt neutrons, however, has to be done in the presence of extremely intense probing radiation that stimulated them. During irradiation, the fission stimulation radiation, X-rays or neutrons, overwhelms the neutron detectors and temporarily incapacitate them. Consequently, by the time the detectors recover from the source radiation, fission prompt neutrons are no longer emitted. In order to measure the prompt fission signatures under these circumstances, special measures are usually taken with the detectors such as heavy shielding with collimation, use of inefficient geometries, high pulse height bias and gamma-neutron separation via pulse-shape discrimination with an appropriate organic scintillator. These attempts to shield the detector from the flash of radiation result in a major loss of sensitivity. It can lead to a complete inability to detect the fission prompt neutrons. In order to overcome the blinding induced background from the source radiation, the detection of prompt fission neutrons needs to occur long after the fission event and after the detector has fully recovered from the source overload. A new approach to achieve this is to detect the delayed activation induced by the fission neutrons. The approach demonstrates a good sensitivity in adverse overload situations (gamma and neutron "flash") where fission prompt neutrons could normally not be detected. The new approach achieves the required temporal separation between the detection of prompt neutrons and the detector overload by the neutron activation of the detector material. The technique, called Threshold Activation Detection (TAD), is to utilize appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation and then measure the radioactively decaying activation products (typically beta and gamma rays) well after the source pulse. The activation material should possess certain properties: a suitable half-life of the order of seconds; an energy threshold below which the numerous source neutrons will not activate it (e.g., 3 MeV); easily detectable activation products (typically >1 MeV beta and gamma rays) and have a usable cross-section for the selected reaction. Ideally the substance would be a part of the scintillator. There are several good material candidates for the TAD, including fluorine, which is a major constituent of available scintillators such as BaF 2, CaF 2 and hydrogen free liquid fluorocarbon. Thus the fluorine activation products, in particular the beta particles, can be measured with a very high efficiency in the detector. The principles, applications and experimental results obtained with the fluorine based TAD are discussed.

Gozani, Tsahi; Stevenson, John; King, Michael J.

2011-10-01

257

Principles of crystallography using Bragg reflection from atomically localized sources  

Microsoft Academic Search

On the basis of the two-beam model for describing element-specific Kikuchi-band effects in X-ray photoelectron diffraction (XPED), we have set up a scheme of Kikuchi-band analysis for determining structure factors and applied the method to the XPED for Ca2p emission from a CaF2 (111) substrate. The three-dimensional potential distribution corresponding to the fluorite structure of the CaF2 crystal was reconstructed

S. Omori; H. Ishii; Y. Nihei

1998-01-01

258

Site controlled metal and semiconductor quantum dots on epitaxial fluoride films  

Microsoft Academic Search

Ga and Al metal dot arrays were formed on epitaxial CaF2 films on Si(111) substrates, where nucleation sites were controlled by two methods: alignment on step edges of CaF2, and local surface modification by focused electron beam exposure. Multitunneling junctions (MTJ) using self-ordering metal dot arrays on the step edges showed Coulomb blockade characteristics at 55K. The electron beam modification

K. Tsutsui; K. Kawasaki; M. Mochizuki; T. Matsubara

1999-01-01

259

PROPRITS MAGNTO-OPTIQUES DE MATRIAUX PARA-, FERRO-ET ANTIFERROMAGNTIQUES CONTENANT L'ION EUROPIUM DIVALENT  

E-print Network

'ION EUROPIUM DIVALENT J. FERR� (*) Laboratoire d'Optique Physique, EPCI (**) 10, rue Vauquelin, 75231 Paris matrices cristallines d'une part (CaF2, KCl), des chalcogénures d'europium EuX, d'autre part (X = O, S, Se) of isolated Eu2+ ions (in CaF2 and KCl) and of europium chalcogenides EuX (X = O, S, Se, Te) are compared

Paris-Sud XI, Université de

260

Fluoride Is Unable to Reduce Dental Erosion from Soft Drinks  

Microsoft Academic Search

The main aim of the present study was to compare the erosive capabilities of some fruit-flavoured drinks, fresh or saturated with CaF2, with their content of acids and with previous results from some carbonated soft drinks. The other aim was to measure and compare the rates of dissolution of CaF2 in some carbonated and non-carbonated drinks and water. Seven commercially

M. J. Larsen; A. Richards

2002-01-01

261

SKYLAB ultraviolet stellar astronomy experiment S019  

Microsoft Academic Search

An objective-prism stellar spectrograph of 15-cm aperture was flown on all three Skylab missions. The wavelength region from 1300 A to 5000 A was covered by a special optical system containing a combination of reflecting telescope optics, a CaF2 objective prism, and an achromatized field-corrector lens system of CaF2 and LiF. Observations of 188 star fields, each covering 4.0 x

F. G. Ocallaghan; K. G. Henize; J. D. Wray

1977-01-01

262

Calcium sulfate as a high temperature solid lubricant  

Microsoft Academic Search

Both composite coatings and layered structures of CaF2 and WS2 were grown via pulsed laser deposition (PLD) on steel substrates and TiN coated steel substrates. Films were found to be lubricious at temperatures up to 500°C. XPS analysis of specimens indicated that the CaF2 and WS2 materials interacted to form CaSO2, among other compounds. CaSO1 was then evaluated as a

P. J. John; S. V. Prasad; A. A. Voevodin; J. S. Zabinski

1998-01-01

263

Nanocrystallization in Fluorochlorozirconate Glass-Ceramics  

PubMed Central

Heat treating fluorochlorozirconate (FCZ) glasses nucleates nanocrystals in the glass matrix, resulting in a nanocomposite glass-ceramic that has optical properties suitable for use as a medical imaging plate. Understanding the way in which the nanocrystal nucleation proceeds is critical to controlling the optical behavior. The nucleation and growth of nanocrystals in FCZ glass-ceramics was investigated with in situ transmission electron microscopy heating experiments. The experiments showed the nucleation and growth of previously unreported BaF2 nanocrystals in addition to the expected BaCl2 nanocrystals. Chemical analysis of the BaF2 nanocrystals shows an association with the optically active dopant previously thought only to interact with BaCl2 nanocrystals. The association of the dopant with BaF2 crystals suggests that it plays a role in the photoluminescent (PL) properties of FCZ glass-ceramics. PMID:24707056

Alvarez, Carlos J.; Liu, Yuzi; Leonard, Russell L.; Johnson, Jacqueline A.; Petford-Long, Amanda K.

2014-01-01

264

Some metal-graphite and metal-ceramic composites for use as high energy brake lining materials  

NASA Technical Reports Server (NTRS)

Materials were studied as candidates for development as potential new aircraft brake lining materials. These families were (1) copper-graphite composites; (2) nickel-graphite composites; (3) copper - rare-earth-oxide (gadolinium oxide (Gd2O3) or lanthanum oxide (La2O3)) composites and copper - rare-earth-oxide (La2O3) - rare-earth-fluoride (lanthanum fluoride (LaF3)) composites; (4) nickel - rare-earth-oxide composites and nickel - rare-earth-oxide - rare-earth-fluoride composites. For comparison purposes, a currently used metal-ceramic composite was also studied. Results showed that the nickel-Gd2O3 and nickel-La2O3-LaF3 composites were comparable or superior in friction and wear performance to the currently used composite and therefore deserve to be considered for further development.

Bill, R. C.

1974-01-01

265

Interaction strength of weakly coupled pairs measured by a two laser spectroscopy technique  

E-print Network

fluorescence from 3Po. On the right, energy levels of interest for Pr3 + : LaF3. The method used for the direct, a direct measurement of the transfer rates between two Pr3 + ions associated as a pair has been reported. - Top : Absorption spectrum around the transition 3H4 -+ 1 D2(2). Bottom : Excitation spectrum of the up-conversion

Paris-Sud XI, Université de

266

Analytica Chimica Acta 437 (2001) 183190 Re-activation of an all solid state oxygen sensor  

E-print Network

Analytica Chimica Acta 437 (2001) 183­190 Re-activation of an all solid state oxygen sensor W/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal can be applied. A heating time as short as 300 ns was sufficient for the re-activation of the sensor

Moritz, Werner

267

Optical and Nuclear Spin Spectroscopy in PRASEODYMIUM(3+):LANTHANUM Fluoride by Optical Pumping  

Microsoft Academic Search

A Stark Modulated Optical Pumping (SMOP) technique was used as a sensitive probe of optical hole-burning to study the effects of nuclear spin interactions in Pr ^{3+}:LaF_3. The results of two experiments are reported. In the first experiment, the SMOP technique is applied for optical detection of the NQR spectrum of the Pr^{3+} optical ground state. Frequency and linewidth variations

Lawrence Leroy Wald

1992-01-01

268

Cascaded Brillouin lasing in monolithic barium fluoride whispering gallery mode resonators  

E-print Network

We report the observation of stimulated Brillouin scattering and lasing at 1550~nm in barium fluoride (BaF$_2$) crystal. Brillouin lasing was achieved with ultra-high quality ($Q$) factor monolithic whispering gallery mode (WGM) mm-size disk resonators. Overmoded resonators were specifically used to provide cavity resonances for both the pump and all Brillouin Stokes waves. Single and multiple Brillouin Stokes radiations with frequency shift ranging from $8.2$ GHz up to $49$ GHz have been generated through cascaded Brillouin lasing. BaF$_2$ resonator-based Brillouin lasing can find potential applications for high-coherence lasers and microwave photonics.

Lin, Guoping; Saleh, Khaldoun; Martinenghi, Romain; Beugnot, Jean-Charles; Sylvestre, Thibaut; Chembo, Yanne K

2015-01-01

269

Cascaded Brillouin lasing in monolithic barium fluoride whispering gallery mode resonators  

NASA Astrophysics Data System (ADS)

We report the observation of stimulated Brillouin scattering and lasing at 1550 nm in barium fluoride (BaF2) crystal. Brillouin lasing was achieved with ultra-high quality (Q) factor monolithic whispering gallery mode mm-size disk resonators. Overmoded resonators were specifically used to provide cavity resonances for both the pump and all Brillouin Stokes waves. Single and multiple Brillouin Stokes radiations with frequency shift ranging from 8.2 GHz up to 49 GHz have been generated through cascaded Brillouin lasing. BaF2 resonator-based Brillouin lasing can find potential applications for high-coherence lasers and microwave photonics.

Lin, Guoping; Diallo, Souleymane; Saleh, Khaldoun; Martinenghi, Romain; Beugnot, Jean-Charles; Sylvestre, Thibaut; Chembo, Yanne K.

2014-12-01

270

Growth of La[sub 0.8]Sr[sub 0.2]CrO[sub 3] thin films from a fluoride sputtering process.  

SciTech Connect

Dense, thin films of La0.8Sr0.2CrO3 were prepared on fully stabilized yttria-stabilized zirconia, sapphire, and polycrystalline substrates using 90 off axis magnetron sputtering from a stoichiometric LaF3/SrF2/Cr composite target in an Ar atmosphere. Dense, intimately mixed films of LaF3/SrF2/Cr were grown at both ambient sputter temperature and at 400 C with the films deposited at higher temperature exhibiting better adhesion to the substrate. Sputtering rates were typically in the range of 1500 to 2000 Angstroms/hr. Subsequent anneal at 800 C in a H2O/Ar atmosphere converted the films to single-phase La0.8Sr0.2CrO3. The room-temperature deposition of LaF3/SrF2/Cr composite, precursor film permitted the patterning of electrodes for high-temperature electrochemical HC/CO gas sensors that operate using a mixed potential response mechanism. Thin films grown on polycrystalline Al2O3 were used to obtain four-point electronic conductivity measurements.

Mukundan, R. (Rangachary); Brown, D. R. (David R.); Garzon, F. H. (Fernando H.); Brosha, E. L. (Eric L.)

2001-01-01

271

On the role of calcium fluoride in the cariostatic mechanism of fluoride.  

PubMed

The literature concerning the formation and stability of CaF2 in the oral environment is reviewed. In early work the CaF2 formed during topical application with fluoride was assumed to be beneficial. It was suggested that it could protect the enamel surface directly or provide free fluoride ions for subsequent incorporation into the hydroxyapatite lattice. However, McCann claimed, in 1968, that CaF2 is soluble in saliva (12-15 mg/l), that it would be rapidly lost in the oral cavity, and that the clinical effect of fluoride was related to formation of firmly bound fluoride only. In this period many authors reported total loss of CaF2 during 24 h after a topical application of fluoride. It has now been shown in several laboratories that calcium fluoride is stable in saliva at neutral pH owing to surface adsorption of HPO2-4 to the crystal surface and formation of a solubility-limiting phase. Extended exposure of saliva can cause formation of a fluorapatite layer on the CaF2 crystals, restricting their dissolution further. Low pH (pH less than 5) causes loss of the solubility-limiting adsorbed HPO2-4 and a slow dissolution of CaF2. The CaF2 crystals may thus serve as pH-controlled reservoirs of fluoride ions on the enamel or in plaque and release fluoride during caries challenges. It is suggested that calcium fluoride is an essential phase explaining important aspects of the mechanism of topically applied fluoride, contrary to what was assumed in the past. PMID:3063053

Rølla, G

1988-12-01

272

A calcium prerinse required to form calcium fluoride in plaque from a sodium fluoride rinse.  

PubMed

The purpose of this study is to determine whether a calcium (Ca) prerinse used before a 228 µg/g (ppm) fluoride (F) rinse would induce the formation of 'calcium fluoride-like' (CaF2-like) deposits in human dental plaque. Sixty minutes after the use of the Ca prerinse/F rinse, plaque samples were collected from 10 volunteers, homogenized, and split into 2 aliquots. The plaque mass from one aliquot was then extracted with a 'plaque-like' solution that extracted all the CaF2-like deposits. The total F in both aliquots was then determined and compared. The results demonstrated that, as in previous studies, the Ca prerinse induced large increases in plaque fluid and total plaque F. However, unlike previous results without the Ca prerinse, 30% of the plaque F deposits were CaF2 or CaF2-like. Given that maintaining an elevated F concentration in the vicinity of a developing lesion may play an important role in the cariostatic effect of this ion, and the potential advantages of CaF2-like deposits as an F source, these results suggest that a Ca prerinse may increase the cariostatic effect of topical agents. PMID:24401761

Vogel, G L; Tenuta, L M A; Schumacher, G E; Chow, L C

2014-01-01

273

Low temperature epitaxial growth of Ge on cube- textured Ni  

SciTech Connect

Quasi- single crystal Ge films were grown on [001]<010> textured Ni substrate at a temperature of 350 oC using an insulating buffer layer of CaF2. A direct deposition of Ge on Ni at 350 oC was shown to alloy with Ni. From x- ray pole figure analysis, it was shown that Ge grew epitaxially with the same orientation as CaF2 and the dispersions in the out- of- plane and in- plane directions were found to be 1.7 0.1o and 6 1o, respectively. In the out- of- plane direction, Ge[111]||CaF2[111]||Ni[001]. In addition, the Ge consisted of four equivalent in- plane oriented domains such that two mutually orthogonal directions: Ge 211 and Ge 011 are parallel to mutually orthogonal directions: Ni 110 and Ni 110 , respectively of the Ni(001) surface. This was shown to be originated from the four equivalent in- plane oriented domains of CaF2 created to minimize the mismatch strain between CaF2 and Ni in those directions.

GIARE, C [Rensselaer Polytechnic Institute (RPI); Palazzo, J [Rensselaer Polytechnic Institute (RPI); Goyal, Amit [ORNL; WANG, G [Rensselaer Polytechnic Institute (RPI); LU, T [Rensselaer Polytechnic Institute (RPI)

2012-01-01

274

Pilot-scale fluoride-containing wastewater treatment by the ballasted flocculation process.  

PubMed

A pilot-scale ballasted flocculation system was used to remove fluoride from one type of industrial wastewater. The system included the formation of calcium fluoride (CaF2) using calcium hydroxide followed by coagulation sedimentation. Calcium fluoride was recycled as nuclei for enhancing CaF2 precipitation and as a ballasting agent for improving fluoride removal and flocculation efficiency. Factors affecting fluoride and turbidity removal efficiencies, including pH in the CaF2-reacting tank and coagulation-mixing tank, sludge recycling ratio, and dosages of FeCl3 and polyacrylamide (PAM), were investigated in the pilot-scale system. The recycled CaF2 precipitates improved CaF2 formation kinetics, enhanced fluoride removal and flocculation performance. Under the optimized condition, the ballast flocculation process reduced fluoride concentration from 288.9 to 10.67 mg/L and the turbidity from 129.6 NTU to below 2.5 NTU. PMID:23823549

Wang, Bin-Yuan; Chen, Zhong-Lin; Zhu, Jia; Shen, Ji-Min; Han, Ying

2013-01-01

275

Simulation of point defects in high-density luminescent crystals: Oxygen in barium fluoride J. M. Vail, E. Emberly, and T. Lu  

E-print Network

Simulation of point defects in high-density luminescent crystals: Oxygen in barium fluoride J. M June 1997; revised manuscript received 25 August 1997 Barium fluoride is an example of a high. INTRODUCTION Barium fluoride, BaF2, is an important representative of a class of high-density luminescent

Pandey, Ravi

276

Rare earths in lead-free oxyfluoride germanate glasses  

NASA Astrophysics Data System (ADS)

Spectroscopic properties of rare earths in lead-free oxyfluoride germanate glasses were studied. The absorption and luminescence spectra of Eu3+, Pr3+ and Er3+ ions were examined as a function of BaF2 concentration and several spectroscopic parameters for rare earths were determined. The ratio of integrated luminescence intensity of the 5D0 ? 7F2 transition to that of the 5D0 ? 7F1 transition of Eu3+ decrease significantly with increasing BaF2 content. The absorption (Er3+) and emission (Pr3+) ‘hypersensitive transitions’ of rare earths are shifted in direction to shorter wavelengths with increasing BaF2 content in glass composition. Emission spectra and their decays corresponding to the main 4I13/2 ? 4I15/2 laser transition of Er3+ were also analyzed. Quite long-lived NIR luminescence of Er3+ is observed for lead-free glass samples with low BaF2 concentration.

Pisarski, Wojciech A.; Pisarska, Joanna; Dorosz, Dominik; Dorosz, Jan

2015-01-01

277

Measurement of the 241Am and the 243Am Neutron Capture Cross Sections at the n_TOF Facility at CERN  

NASA Astrophysics Data System (ADS)

The capture cross sections of 241Am and 243Am were measured at the n_TOF facility at CERN in the epithermal energy range with a BaF2 Total Absorption Calorimeter. A preliminary analysis of the 241Am and a complete analysis of the 243Am measurement, including the data reduction and the resonance analysis, have been performed.

Mendoza, E.; Cano-Ott, D.; Guerrero, C.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Be?vá?, F.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Gunsing, F.; Gurusamy, P.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kivel, N.; Koehler, P.; Kokkoris, M.; Korschinek, G.; Krti?ka, M.; Kroll, J.; Langer, C.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Mastinu, P. F.; Mastromarco, M.; Massimi, C.; Meaze, M.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondelaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Pignatari, M.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Roman, F.; Rubbia, C.; Sarmento, R.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T. J.; Žugec, P.

2014-05-01

278

Solution NMR Structure of the Barrier-to-Autointegration Factor-Emerin Complex*  

E-print Network

DNA (5). Emerin is a member of the LEM (LAP2, Emerin, MAN1) family of nuclear proteins, and its loss-to-autointegration factor BAF binds to the LEM domain (EmLEM ) of the nuclear envelope protein emerin and plays an essential role in the nuclear architecture of metazoan cells. In addition, the BAF2 dimer bridges and compacts

Clore, G. Marius

279

High energy photon emission  

E-print Network

at angles of 90' and 135'. Two 19-element barium fluoride (BaF2) arrays, an array of liquid scintillation fast neutron detectors and plastic scintillation charged-particle veto detectors, together with a silicon-cesium iodide (Si-CsI) telescope and a silicon...

Jabs, Harry

2012-06-07

280

Development of a fast radiation detector based on barium fluoride scintillation crystal.  

PubMed

Barium fluoride (BaF2) is an inorganic scintillation material used for the detection of X?gamma radiation due to its relatively high density, equivalent atomic number, radiation hardness, and high luminescence. BaF2 has a potential capacity to be used in gamma ray timing experiments due to the prompt decay emission components. It is known that the light output from BaF2 has three decay components: two prompt of those at approximately 195 nm and 220 nm with a decay constant around 600-800 ps and a more intense, slow component at approximately 310 nm with a decay constant around 630 ns which hinders fast timing experiments. We report here the development of a fast radiation detector based on a BaF2 scintillation crystal employing a special optical filter device, a multiple reflection multi-path ultraviolet region short-wavelength pass light guides (MRMP-short pass filter) by using selective reflection technique, for which the intensity of the slow component is reduced to less than 1%. The methods used for this study provide a novel way to design radiation detector by utilizing scintillation crystal with several emission bands. PMID:23902059

Han, Hetong; Zhang, Zichuan; Weng, Xiufeng; Liu, Junhong; Guan, Xingyin; Zhang, Kan; Li, Gang

2013-07-01

281

Development of a fast radiation detector based on barium fluoride scintillation crystal  

NASA Astrophysics Data System (ADS)

Barium fluoride (BaF2) is an inorganic scintillation material used for the detection of X/gamma radiation due to its relatively high density, equivalent atomic number, radiation hardness, and high luminescence. BaF2 has a potential capacity to be used in gamma ray timing experiments due to the prompt decay emission components. It is known that the light output from BaF2 has three decay components: two prompt of those at approximately 195 nm and 220 nm with a decay constant around 600-800 ps and a more intense, slow component at approximately 310 nm with a decay constant around 630 ns which hinders fast timing experiments. We report here the development of a fast radiation detector based on a BaF2 scintillation crystal employing a special optical filter device, a multiple reflection multi-path ultraviolet region short-wavelength pass light guides (MRMP-short pass filter) by using selective reflection technique, for which the intensity of the slow component is reduced to less than 1%. The methods used for this study provide a novel way to design radiation detector by utilizing scintillation crystal with several emission bands.

Han, Hetong; Zhang, Zichuan; Weng, Xiufeng; Liu, Junhong; Guan, Xingyin; Zhang, Kan; Li, Gang

2013-07-01

282

Equilibrium : ConcFromKsp (8 Variations)  

NSDL National Science Digital Library

The K sp of BaF 2 is 1.7 x 10 -6 mol/L in water at 25 o C. What is the concentration of barium ions in equilibrium with solid barium fluoride? (Assume that the only relevant reaction is the solubility-product equilibrium.)

283

A computerized glow curve analysis (GCA) method for WinREMS thermoluminescent dosimeter data using MATLAB.  

PubMed

A computerized glow curve analysis (GCA) program for handling of thermoluminescence data originating from WinREMS is presented. The MATLAB program fits the glow peaks using the first-order kinetics model. Tested materials are LiF:Mg,Ti, CaF(2):Dy, CaF(2):Tm, CaF(2):Mn, LiF:Mg,Cu,P, and CaSO(4):Dy, with most having an average figure of merit (FOM) of 1.3% or less, with CaSO(4):Dy 2.2% or less. Output is a list of fit parameters, peak areas, and graphs for each fit, evaluating each glow curve in 1.5 s or less. PMID:21561783

Harvey, John A; Rodrigues, Miesher L; Kearfott, Kimberlee J

2011-09-01

284

Skylab ultraviolet stellar astronomy experiment S019  

NASA Technical Reports Server (NTRS)

An objective-prism stellar spectrograph of 15-cm aperture was flown on all three Skylab missions. The wavelength region from 1300 A to 5000 A was covered by a special optical system containing a combination of reflecting telescope optics, a CaF2 objective prism, and an achromatized field-corrector lens system of CaF2 and LiF. Observations of 188 star fields, each covering 4.0 x 5.0 deg of arc, were conducted at the Skylab antisolar airlock with the aid of an articulated mirror system which allowed acquisition within a 30 by 360 deg band of the sky.

Ocallaghan, F. G.; Henize, K. G.; Wray, J. D.

1977-01-01

285

Growth and characterization of single crystal insulators on silicon  

NASA Technical Reports Server (NTRS)

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

Schowalter, Leo J.; Fathauer, Robert W.

1989-01-01

286

Construction of prototypes of a new class of infrared detectors  

NASA Technical Reports Server (NTRS)

A class of infrared detectors is proposed and experimental results are presented for a prototype device. The material used is LaF3, an ionic conductor with a capacitance that varies exponentially with temperature. The detectivity of a prototype detector is estimated from measured signal voltages and incident power, and a Johnson noise voltage calculated from the measured resistance. For the parameters characterizing this device the estimated detectivity is consistent with a theoretical prediction. The theory further predicts an optimum detectivity for much thinner devices than the prototypes.

Sher, A.

1976-01-01

287

Nanostructured LaF{sub 3}:Ce Quantum Dot Nuclear Radiation Detector  

SciTech Connect

Many radioactive isotopes have low energy X-rays and high energy gamma rays of interest for detection. The goal of the work presented was to demonstrate the possibility of measuring both low-energy X-rays and relatively high-energy gamma rays simultaneously using the nano-structured lanthanum bromide, lanthanum fluoride, or cerium bromide. The key accomplishments of the project was the building and acquisition of the LaF3:Ce nanocomposite detectors. Nanocomposite detectors are sensitive to {gamma}’s as well as n’s and X-rays.

Guss, P., Guise, R., Reed, M., Mukhopadhyay, S., Yuan, D.

2010-11-01

288

Determination of uranium and thorium isotopes in soil samples by coprecipitation  

Microsoft Academic Search

Summary  The paper presents a procedure to prepare soil samples for U and Th isotope measurement by alpha-spectrometry after coprecipitation\\u000a with LaF3. In this procedure the reduction of U(VI) to U(IV) was performed by Zn metal in 4M HCl solution. The recoveries of chemical\\u000a separation equal to eU-chemistry = 78±4% for uranium and eTh-chemistry = 82±4% for thorium. Canberra alpha-spectrometer was

Ngo Quang Huy; Trinh Thi Bich; Nguyen Van Suc

2006-01-01

289

Simultaneous determination of tantalum and hafnium in silicates by neutron activation analysis  

USGS Publications Warehouse

A neutron activation procedure suitable for the routine determination of tantalum and hafnium in silicates is described. The irradiated sample is fused with sodium peroxide and leached, and the insoluble hydroxides are dissolved in dilute hydrofluoric acid-hydrochloric acid. After LaF3 and AgCl scavenges, tantalum and hafnium are separated by anion exchange. Tantalum is obtained radiochemically pure; 233Pa and 95Zr contaminants in the hafnium fraction are resolved by ??-ray spectrometry. The chemical yield of the procedure is detemined after counting by re-irradiation. Values for the 8 U.S. Geological Survey standard rocks are reported. ?? 1968.

Greenland, L.P.

1968-01-01

290

One-pot synthesis of chitosan\\/LaF3 : Eu3+ nanocrystals for bio-applications  

Microsoft Academic Search

Lanthanide-based nanocrystals have shown great potential to be used as\\u000a luminescent materials but their biological applications have been\\u000a limited because most of the nanocrystals synthesized so far are not\\u000a water soluble or biocompatible. We report a very straightforward method\\u000a to synthesize water soluble and biocompatible LaF3 nanocrystals doped\\u000a with Eu3+ via facile co-precipitation with a natural biopolymer,\\u000a chitosan. The nanocrystals

Feng Wang; Yong Zhang; Xianping Fan; Minquan Wang

2006-01-01

291

Lasing properties of new Nd3+-doped tungstate, molybdate, and fluoride materials under selective optical pumping  

Microsoft Academic Search

The purpose of this work was to determine the relative efficiencies of new Nd3+-doped laser active\\/Raman - tungstate, molybdate, and fluoride - materials (SrWO4, PbWO4, BaWO4, SrMoO4, PbMoO4, SrF2, and LaF3) under selective longitudinal optical pumping by the alexandrite (~750nm), or diode (~800nm) laser. Crystals with various length, orientations and active ions concentrations were tested. To optimize the output of

Jan Sulc; Helena Jelínkova; Tolstoban T. Basiev; Maxim E. Doroschenko; Ludmila I. Ivleva; Vyacheslav V. Osiko; Peter G. Zverev

2006-01-01

292

The mechanical properties of fluoride salts at elevated temperatures. [candidate thermal energy storage materials for solar dynamic systems  

NASA Technical Reports Server (NTRS)

The deformation behavior of CaF2 and LiF single crystals compressed in the 111 and the 100 line directions, respectively, are compared with the mechanical properties of polycrystalline LiF-22 (mol pct) CaF2 eutectic mixture in the temperature range 300 to 1275 K for strain rates varying between 7 x 10 to the -7th and 0.2/s. The true stress-strain curves for the single crystals were found to exhibit three stages in an intermediate range of temperatures and strain rates, whereas those for the eutectic showed negative work-hardening rates after a maximum stress. The true stress-strain rate data for CaF2 and LiF-22 CaF2 could be represented by a power-law relation with the strain rate sensitivities lying between 0.05 and 0.2 for both materials. A similar relation was found to be unsatisfactory in the case of LiF.

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

1989-01-01

293

A liquid xenon imaging telescope for 1-30 MeV gamma-ray astrophysics  

Microsoft Academic Search

A study of the primary scintillation light in liquid xenon excited by 241 Am alpha particles and 207 Bi internal conversion electrons are discussed. The time dependence and the intensity of the light at different field strengths have been measured with a specifically designed chamber, equipped with a CaF2 light transmitting window coupled to a UV sensitive PMT. The time

Elena Aprile; Reshmi Mukherjee; Masayo Suzuki

1989-01-01

294

Recycling of an industrial sludge and marine clay as light-weight aggregates  

Microsoft Academic Search

The geographical limitations of Singapore, its restricted natural resources and voluminous municipal and industrial waste streams, make environmental management a major challenge for the island state. In an attempt to find ways to reduce importation of raw materials and the waste sent to landfill, light weight aggregates were produced from marine clay and a CaF2-rich semiconductor industry sludge. Aggregates were

K. Laursen; T. J. White; D. J. F. Cresswell; P. J. Wainwright; J. R. Barton

2006-01-01

295

Observation of whispering gallery modes in the mid-Infrared with a Quantum Cascade Laser: possible applications to nanoliter chemical  

E-print Network

) of a CaF2 ball resonator is demonstrated at 4.5 micron with a pulsed Quantum Cascade laser. A prism in that range, and finally CW QCL sources are still far from as popular as telecom CW diode lasers The schematic of the setup is given in Figure 1. A Quantum Cascade (QC) Distributed Feedback (DFB) pulsed laser

Jensen, Grant J.

296

REGULAR PAPER Deposition Sequence Determines Morphology of C60 and 3,4,9,10-Perylenetetracarboxylic  

E-print Network

,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI of C60 molecules, the PTCDI islands are completely covered by C60. For the opposite deposition order

Kühnle, Angelika

297

Journal of Luminescence 31 & 32 (1984) 251-253 251 North-Holland, Amsterdam  

E-print Network

defeats. These new centers are associated with the cerium ions, and their creation kinetics have been absorption bands. Cerium ions, when doped into a CaF 2 host, have previously been shown to exhibit photochromic properties. 1 These photochromic centers have been ob- - 2+served when the cerium ions have been

Hamilton, Douglas S.

298

Divalent cerium and praseodymium ions in crystals of alkaline-earth fluorides  

NASA Astrophysics Data System (ADS)

We have studied the absorption spectra of radiation-induced divalent cerium and praseodymium ions in crystals of alkaline-earth fluorides. Using ab initio quantum-mechanical methods, we have calculated absorption spectra of divalent praseodymium ions in CaF2 crystals for the first time. The theoretical spectrum agrees rather well with the experimentally registered spectra.

Shendrik, R. Yu.; Myasnikova, A. S.; Egranov, A. V.; Radzhabov, E. A.

2014-05-01

299

Dissociative Binding of Carboxylic Acid Ligand on Nanoceria Surface in Aqueous Solution: A Joint in Situ Spectroscopic Characterization and First-Principles Study  

SciTech Connect

Carboxylic acid is a common ligand anchoring group to functionalize nanoparticle surfaces. Its binding structures and mechanisms as a function of the oxidation states of metal oxide nanoparticle surfaces are not well characterized experimentally. We present an in situ sum frequency generation vibrational spectroscopy (SFG-VS) study on the binding of deuterated acetic acid on ceria nanoparticles in the aqueous solution. In the SFG experiment, ceria nanoparticles were deposited on the flat surface of a CaF2 hemisphere in contact with acetic acid solutions. While the ceria nanoparticle deprotonated the acetic acid, the CaF2 surface could not. Thus, the binding of the deprotonated acetic acid on ceria can be selectively probed. SFG spectra revealed that the binding modes of the carboxylate group depend on the oxidation states of the ceria surfaces. SFG polarization analysis suggested that the bidentate chelating and bridging binding modes co-exist on the reduced ceria surfaces, while the oxidized ceria surfaces are dominated by the bidentate bridging mode. The direct spectroscopic evidence helps to clarify the binding structures and mechanisms on the ceria nanoparticles. Furthermore, the middle-infrared (IR) transparent CaF2 and its chemical inertness make CaF2 and similar substrate materials good candidates for direct SFG-VS measurement of nanoparticle surface reactions and binding chem-istry.

Lu, Zhou; Karakoti, Ajay S.; Velarde Ruiz Esparza, Luis A.; Wang, Weina; Yang, Ping; Thevuthasan, Suntharampillai; Wang, Hongfei

2013-11-21

300

Fluoride Solid Lubricants for Extreme Temperatures and Corrosive Environments  

Microsoft Academic Search

Fluorides of the alkali metals and the alkaline earth metals have an interesting combination of properties that make them promising candidates as solid lubricant materials for use at high temperatures and in corrosive environments. They are chemically inert in strong oxidizing or reducing environments; they are relatively soft and nonabrasive; and some of them, such as CaF2, have planes of

Harold E. Sliney; Thomas N. Strom; Gordon P. Allen

1965-01-01

301

Strength and fluoride release characteristics of a calcium fluoride based dental nanocomposite  

PubMed Central

Secondary caries and restoration fracture remain the two most common problems in restorative dentistry. Release of fluoride ions (F) could be a substantial benefit because F could enrich neighboring enamel or dentin to combat caries. The objective of this study was to incorporate novel CaF2 nanoparticles into dental resin to develop stress-bearing, F-releasing nanocomposite. CaF2 nanoparticles, prepared in our laboratories for the first time, were combined with reinforcing whisker fillers in a resin. Flexural strength (mean ± sd; n = 6) was 110 ± 11 MPa for the composite containing 30% of CaF2 and 35% whiskers by mass. It matched the 108 ± 19 MPa of a stress-bearing, non-releasing commercial composite (Tukey’s at 0.05). The composite containing 20% CaF2 had a cumulative F release of 2.34 ± 0.26 mmol/L at 10 weeks. The initial F release rate was 2 µg/(h·cm2), and the sustained release rate after 10 weeks was 0.29 µg/(h·cm2). These values exceeded the reported releases of traditional and resin-modified glass ionomer materials. In summary, nanocomposites were developed with relatively high strength as well as sustained release of fluoride ions, a combination not available in current materials. These strong and F releasing composites may yield restorations that can reduce the occurrence of both secondary caries and restoration fracture. PMID:18708252

Xu, Hockin H. K.; Moreau, Jennifer; Sun, Limin; Chow, Laurence C.

2008-01-01

302

Composite-Hydroxide-Mediated Approach for the Synthesis of  

E-print Network

such as perovskite, spinel, and garnet have many important properties and applications in science and engineering types, such as perovskites, spinels, monoclinic, corundum, CaF2 structured, tetragonal, and even metal, such as ferroelectricity, ferro- magnetism, colossal magnetoresistance, semiconductors, luminance, and optoelectronics.1

Wang, Zhong L.

303

Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] for long wavelength infrared detection  

E-print Network

The structural, electronic, and optical properties of amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited on Corning glass, Al[subscript 2]O[subscript 3] CdZnTe, SiO[subscript 2]-Si, and CaF2 substrates ...

Zens, Timothy

304

CANDLES Project for the Neutrinoless Double Beta Decay of 48Ca  

NASA Astrophysics Data System (ADS)

CANDLES experiment is the project to search for neutrinoless double beta decay(0v??) of 48Ca by using CaF2 scintillation crystals. The expected performance of the detector for the signal detection and the background rejection method are presented. The current status and future performance of the CANDLES experiment are also described.

Ichimura, Koichi

305

Barium fluoride whispering-gallery-mode disk-resonator with one billion quality-factor  

E-print Network

We demonstrate a monolithic optical whispering gallery mode resonator fabricated with barium fluoride (BaF$_2$) with an ultra-high quality ($Q$) factor above $10^9$ at $1550$ nm, and measured with both the linewidth and cavity-ring-down methods. Vertical scanning optical profilometry shows that the root mean square surface roughness of $2$ nm is achieved for our mm-size disk. To the best of our knowledge, we show for the first time that one billion $Q$-factor is achievable by precision polishing in relatively soft crystals with mohs hardness of ~$3$. We show that complex thermo-optical dynamics can take place in these resonators. Beside usual applications in nonlinear optics and microwave photonics, high energy particle scintillation detection utilizing monolithic BaF$_2$ resonators potentially becomes feasible.

Lin, Guoping; Henriet, Rémi; Jacquot, Maxime; Chembo, Yanne K

2015-01-01

306

Systematic study of doping dependence on linear magnetoresistance in p-PbTe  

NASA Astrophysics Data System (ADS)

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF2 exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ?R/?B is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF2 doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.

Schneider, J. M.; Peres, M. L.; Wiedmann, S.; Zeitler, U.; Chitta, V. A.; Abramof, E.; Rappl, P. H. O.; de Castro, S.; Soares, D. A. W.; Mengui, U. A.; Oliveira, N. F.

2014-10-01

307

Development and Performance Test of Picosecond Pulse X-ray Excited Streak Camera System for Scintillator Characterization  

NASA Astrophysics Data System (ADS)

To observe time and wavelength-resolved scintillation events, picosecond pulse X-ray excited streak camera system is developed. The wavelength range spreads from vacuum ultraviolet (VUV) to near infrared region (110-900 nm) and the instrumental response function is around 80 ps. This work describes the principle of the newly developed instrument and the first performance test using BaF2 single crystal scintillator. Core valence luminescence of BaF2 peaking around 190 and 220 nm is clearly detected by our system, and the decay time turned out to be of 0.7 ns. These results are consistent with literature and confirm that our system properly works.

Yanagida, Takayuki; Fujimoto, Yutaka; Yoshikawa, Akira; Yokota, Yuui; Kamada, Kei; Pejchal, Jan; Chani, Varely; Kawaguchi, Noriaki; Fukuda, Kentaro; Uchiyama, Koro; Mori, Kuniyoshi; Kitano, Ken; Nikl, Martin

2010-05-01

308

High temperature thermodynamic properties of the chromium carbides Cr 7 C 3 and Cr 3 C 2 determined using a galvanic cell technique  

Microsoft Academic Search

The standard free energies of formation of Cr7C3 and Cr3C2 have been obtained from emf measurements on the following galvanic cells with BaF2-BaC2 solid solutions as the electrolyte: Cr,Cr23C6?BaF-BaC2?Cr23C6,Cr7C3 (920 to 1250 K) (A) Cr23C6, Cr7C3 ?BaF2-BaC2?W, WC (900 to 1200 K) (B) WC, W?BaF2-BaC2?Cr3C2, Cr7C3 (973 to 1173 K) (C) Combining the results of this study with a previous

R. G. Coltters; G. R. Belton

1984-01-01

309

Physical and chemical considerations of the role of firmly and loosely bound fluoride in caries prevention.  

PubMed

Historically, there has been considerable debate concerning the roles of loosely bound (calcium fluoride) and firmly bound (fluorapatite) fluoride for caries prevention. Research now shows that fluorapatite (FAP) is a finite reaction product of enamel/apatite fluoridation with or without CaF2 formation, suggesting that CaF2 always be considered as a supplement to, rather than a substitute for, FAP formation. In the presence of low levels of fluoride in the solution phase, the crystallization of hydroxyapatite is enhanced, while the corresponding dissolution is retarded. Fluoride in the bulk FAP or CaF2 solid phase, in contrast, has limited impact on crystal growth or dissolution kinetics. Both FAP and CaF2 can provide F to the solution phase to enhance remineralization and retard demineralization of enamel HAP crystallites. The FAP provides most of this F under low pH conditions, while CaF2 provides F at neutral or lower pH. The reactivity of fluoride on sound and carious enamel differs significantly. Carious enamel acquires more fluoride, acquires it more quickly, and itself acts as a source of retained fluoride in comparison with the more limited reactivity of sound enamel. Overall, the most important question concerning fluoride reactivity relates to its efficiency in enhancing remineralization or retarding demineralization processes. This is influenced not only by the reaction products, e.g., loosely or firmly bound fluoride, but also by the nature of the enamel substrate and frequency of application of the topical fluoridating agent. Inasmuch as the reactivity of bulk HAP is dominated by surface layers of FAP material, the debate over usefulness of various fluoride reaction products solely on a chemical level is no longer critical. Instead, all factors influencing the efficiency of a fluoridating regimen must be considered in the development of improved systems for caries prevention. PMID:2179318

White, D J; Nancollas, G H

1990-02-01

310

Optical coatings on KCl windows for CO2 lasers.  

NASA Astrophysics Data System (ADS)

The surface of polished windows, made from ultratransparent KCl by IRA technique, has been studied by both optical microscopy and spectroscopy during various stages of coatings with a partial reflecting layer of BaF2-ZnSe. It has been found that the adherence of the coating seems to be associated to the presence on the substrate of organic molecules resulting from the diffusion oil.

Medianu, R.; Nistor, S. V.

311

Characteristics of Gd-loaded liquid scintillators BC521 and BC525  

Microsoft Academic Search

Characteristic features of neutron detection properties of the loaded liquid scintillators, i.e., capture time distribution, pulse shape discrimination, and time resolution have been studied for two Gd-loaded liquid scintillators, BC521 and BC525. A new technique to measure the capture time distribution with a small size neutron detector (capacity 7.3l) in combination with BaF2 ?-ray detectors has been demonstrated. The measured

K. Banerjee; S. Kundu; S. Mukhopadhyay; T. K. Rana; S. Bhattacharya; C. Bhattacharya; S. R. Banerjee; T. K. Ghosh; G. Mukherjee; T. Bandyopadhyay; A. Dey; J. K. Meena; P. Mukhopadhyay; D. Gupta; S. Pal; D. Pandit

2007-01-01

312

Development of MBE grown Pb-salt semiconductor lasers for the 8.0 to 15.0 micrometer spectral region  

NASA Technical Reports Server (NTRS)

Diodes lasers are fabricated using multiple source molecular beam expitaxial growth of (PbSn)Te on BaF2 substrates. Methods for crystal growth, crystal transfer, and device fabrication by photolithographic techniques were developed. The lasers operate in the spectra range from 10 microns to 14 microns and at temperatures from 12K to 60K continuous wave and to 95 K pulsed.

Miller, M. D.

1981-01-01

313

Light yield of liquid and solid xenon irradiated with ?-rays  

Microsoft Academic Search

We have measured the absolute light yield of liquid and solid xenon (LXe and SXe respectively) irradiated with ?-rays with energies from 320 keV to 1770 keV. With our method, which consisted of comparing the light yield of LXeSXe with that of BaF2, we found a value of (24±3)×103 photons\\/MeV. This means we estimate the Ws-value to be (42±6) eV.

R. van Sonsbeek; C. W. E. van Eijk; R. W. Hollander

1995-01-01

314

Lattice Relaxation Effect Associated with Core Holes in Ionic Crystals Studied by Time-Resolved Luminescence Spectroscopy  

NASA Astrophysics Data System (ADS)

Auger-decay-free core luminescence in RbF, CsF, CsCl, CsBr and BaF2 has been studied under monochromatic vacuum ultraviolet light excitation using a time-resolved technique. Luminescence spectra associated with core holes are carefully separated from those originating in the valence-band excitation. Based on the spectral shape and energy range of the luminescence bands, a lattice relaxation effect following the core hole creation is discussed.

Matsumoto, Tamao; Kan'no, Ken-ichi; Itoh, Minoru; Ohno, Nobuhito

1996-05-01

315

TDPAC studies of181Hf-labelled transferrin: Comparison between human and rat serum transferrin  

NASA Astrophysics Data System (ADS)

A fast BaF2 TDPAC setup was used to study the binding of181Hf to serum transferrin. Two well-defined binding configurations were observed, which are characterized by high EFGs and large asymetry parameter values. The distribution between these configurations depends essentially on the pH of the serum. Small but significant differences between human and rat serum transferrin can be deduced from the electric quadrupole interaction (QI) parameters.

Appel, H.; Duffield, J.; Taylor, D. M.; Then, G. M.; Thies, W.-G.

1987-04-01

316

Determination of free fatty acids in crude palm oil and refined-bleached-deodorized palm olein using fourier transform infrared spectroscopy  

Microsoft Academic Search

A rapid direct Fourier transform infrared (FTIR) spectroscopic method using a 100 BaF2 transmission cell was developed for the determination of free fatty acid (FFA) in crude palm oil (CPO) and refined-bleached-deodorized\\u000a (RBD) palm olein, covering an analytical range of 3.0–6.5% and 0.07–0.6% FFA, respectively. The samples were prepared by hydrolyzing\\u000a oil with enzyme in an incubator. The optimal calibration

Y. B. Che Man; M. H. Moh; F. R. van de Voort

1999-01-01

317

The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings  

Microsoft Academic Search

This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt. % NiCr binder, 20 wt. % Cr203 hardener, and 10 wt. % each Ag and BaF2ICaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc

Chris Dellacorte

2000-01-01

318

Mid-infrared lead-chlacogenide VECSELs emitting up to above RT at 4–6 um wavelength  

Microsoft Academic Search

The authors describe the first mid-infrared VECSELs (vertical external cavity surface emitting laser) operating up to above room temperature. They employ a resonant design with a one wavelength optical thickness of the active layer (PbSe or PbTe). The structures are grown non-lattice matched on BaF2 or Si substrate by solid state molecular beam epitaxy (MBE).

H. Zogg; M. Rahim; M. Fill; F. Felder; A. Khiar; D. Chappuis

2009-01-01

319

Investigation on photocatalytic degradation of ethyl violet dyestuff using visible light in the presence of ordinary rutile TiO 2 catalyst doped with upconversion luminescence agent  

Microsoft Academic Search

To use solar irradiation or interior lighting efficiently, a new photocatalyst with high catalytic activity in visible light was sought. In this work, an upconversion luminescence agent, 40 CdF2·60 BaF2·1.0 Er2O3, was synthesized and its fluorescent spectrum was determined. It is found that this upconversion luminescence agent can emit five upconversion fluorescent peaks below 387nm under the excitation of 488nm

Jun Wang; Guan Zhang; Zhaohong Zhang; Xiangdong Zhang; Gang Zhao; Fuyu Wen; Zhijun Pan; Ying Li; Peng Zhang; Pingli Kang

2006-01-01

320

Low-temperature electrical-transport properties of single-crystal bismuth films under pressure  

Microsoft Academic Search

We report an investigation of the low-temperature electrical transport properties of bismuth films under applied hydrostatic pressure. Films with their trigonal axis perpendicular to the film plane and thicknesses of 30, 50, and 500 nm were grown by molecular-beam epitaxy on BaF2 substrates. At 500 nm thickness the behavior resembles that of bulk Bi. From the observed Shubnikov-de Haas oscillations

Mei Lu; R. J. Zieve; A. van Hulst; H. M. Jaeger; T. F. Rosenbaum; S. Radelaar

1996-01-01

321

OAK RIDGE NATIONAL LABORATORY U.S. DEPARTMENT OF ENERGY  

E-print Network

), Solution TFA precursor, Pulsed Electron Deposition (PED) of "BaF2-YF3" type precursor, Solution non-type precursor can increase sample inhomogeneity and decrease YBCO growth rate · Buildup of HF within the chamber the gas flow. 1 l/min -2 -1 0 1 2 Width (cm) 0 0.5 -0.5 Height(cm) 3e-6 6 9 12 15 18 21 24 sample gas HF

322

Highly Compressed Two-Dimensional Form of Water at Ambient Conditions  

PubMed Central

The structure of thin-film water on a BaF2(111) surface under ambient conditions was studied using x-ray absorption spectroscopy from ambient to supercooled temperatures at relative humidity up to 95%. No hexagonal ice-like structure was observed in spite of the expected templating effect of the lattice-matched (111) surface. The oxygen K-edge x-ray absorption spectrum of liquid thin-film water on BaF2 exhibits, at all temperatures, a strong resemblance to that of high-density phases for which the observed spectroscopic features correlate linearly with the density. Surprisingly, the highly compressed, high-density thin-film liquid water is found to be stable from ambient (300?K) to supercooled (259?K) temperatures, although a lower-density liquid would be expected at supercooled conditions. Molecular dynamics simulations indicate that the first layer water on BaF2(111) is indeed in a unique local structure that resembles high-density water, with a strongly collapsed second coordination shell. PMID:23323216

Kaya, Sarp; Schlesinger, Daniel; Yamamoto, Susumu; Newberg, John T.; Bluhm, Hendrik; Ogasawara, Hirohito; Kendelewicz, Tom; Brown, Gordon E.; Pettersson, Lars G. M.; Nilsson, Anders

2013-01-01

323

Reactive ion-beam-sputtering of fluoride coatings for the UV/VUV range  

NASA Astrophysics Data System (ADS)

Fluoride coatings produced by thermal evaporation suffer from high scatter losses ageing and cracking due to high tensile stress. These problems impose severe limitations to the production of low loss multilayer coatings for the VUV range. A key position for improved performance is the microstructure of the layers. The aim of our investigations is to improve the microstructure of A1F3- and LaF3-'' films by ionbeamsputtering. Scatter measurements of single layers revealed lower values for lBS than for boat evaporation. Unfortunately sputtered fluoride films nave high absorption losses caused by decomposition of the coating material. By sputtering in reactive atmospheres and annealing we were able to reduce the absorption losses significantly. Antireflective as well as high reflective coatings were produced. Reflection and transmission values were obtained with a VUV-spectrophotometer. Damage tests at the 193 mu ArF laser wavelength were performed at the Laser-Laboratorium Gttingen. Key words: ion-beamsputtering fluoride films UVcoatings VUV-coatings color-center laser damage A]. F3 MgF2 LaF3. 1.

Schink, Harald; Kolbe, Jurgen; Zimmermann, F.; Ristau, Detlev; Welling, Herbert

1991-06-01

324

Photoluminescence of cerium fluoride and cerium-doped lanthanum fluoride nanoparticles and investigation of energy transfer to photosensitizer molecules.  

PubMed

CexLa1-xF3 nanoparticles have been proposed for use in nanoscintillator-photosensitizer systems, where excitation of nanoparticles by ionizing radiation would result in energy transfer to photosensitizer molecules, effectively combining the effects of radiotherapy and photodynamic therapy. Thus far, there have been few experimental investigations of such systems. This study reports novel synthesis methods for water-dispersible Ce0.1La0.9F3/LaF3 and CeF3/LaF3 core/shell nanoparticles and an investigation of energy transfer to photosensitizers. Unbound deuteroporphyrin IX 2,4-disulfonic acid was found to substantially quench the luminescence of large (>10 nm diameter) aminocaproic acid-stabilized nanoparticles at reasonable concentrations and loading amounts: up to 80% quenching at 6% w/w photosensitizer loading. Energy transfer was found to occur primarily through a cascade, with excitation of "regular" site Ce(3+) at 252 nm relayed to photosensitizer molecules at the nanoparticle surface through intermediate "perturbed" Ce(3+) sites. Smaller (<5 nm) citrate-stabilized nanoparticles were coated with the bisphosphonate alendronate, allowing covalent conjugation to chlorin e6 and resulting in static quenching of the nanoparticle luminescence: ?50% at ?0.44% w/w. These results provide insight into energy transfer mechanisms that may prove valuable for optimizing similar systems. PMID:24827162

Cooper, Daniel R; Kudinov, Konstantin; Tyagi, Pooja; Hill, Colin K; Bradforth, Stephen E; Nadeau, Jay L

2014-06-28

325

Microstructural and ionic transport studies of hydrothermally synthesized lanthanum fluoride nanoparticles  

NASA Astrophysics Data System (ADS)

This article presents the structural and transport characteristics of hydrothermally synthesized LaF3 nanoparticles with an average crystallite size of 35nm. The phase formation of the material is confirmed by both X-ray diffraction and transmission electron microscopy techniques. In addition, phase purity of the LaF3 nanoparticles is corroborated by micro-Raman spectroscopy studies. The complex impedance plots at different temperatures reveal that the conductivity is predominantly due to the intrinsic bulk grains and the conductivity relaxation is non-Debye in nature. The frequency variation of conductivity exhibits dispersion at higher frequencies that can be explained with the frame work of Almond-West formalism. The conduction process is controlled by the mobility of the charge carriers and the charge of transport of mobile fluoride ions occur through hopping mechanism. The scaling behavior of both frequency dependence of conductivity and complex impedance plots at different temperatures confirm that the relaxation mechanism of the mobile fluoride ions is independent of temperature.

Patro, L. N.; Kamala Bharathi, K.; Ravi Chandra Raju, N.

2014-12-01

326

Epitaxy of Germanium on Biaxially Textured Germanium and Calcium Fluoride Buffer Layers Through Nanoepitaxy  

NASA Astrophysics Data System (ADS)

The properties of biaxially textured semiconductor films deposited on nanostructured buffer layers with biaxial texture closely approximate the physical properties of single-crystal. This near single-crystal film can serve as substrates and offer significant cost saving benefits in applications such as displays and photovoltaic devices. This thesis provides results of the growth and characterization of Ge films nanoepitaxially deposited onto biaxially textured Ge (homo) and CaF2 (hetero) buffer layers. The film growth method was physical vapor deposition at normal and oblique angles of incidence. The characterization techniques used included atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray pole figure analyses. The Ge films nanoheteroepitaxialy deposited on CaF2 buffer layers were studied as a function of substrate temperature, the CaF2 morphology and orientation ([001] and [110]) to see the influence of these variables on the Ge films. Ge films deposited at 400°C on [001] oriented CaF2 buffer layer with ridge-like features resulted in nearly single-crystal Ge films of [001] orientation with 1.68° +/- 1° in-plane dispersion and a 1:1 main pole to twin pole ratio. Ge films deposited at 400°C onto a [110] oriented CaF2 buffer nanorods layer was found that the [110] Ge film has ˜20° in-plane dispersion but higher 6:1 twin ratio. The increased dispersion (˜20°) was attributed to the large dispersion in the CaF2 buffer layer that resulted from the low vapor incidence angle used during its deposition. The difference in the twin ratio of the Ge films was attributed to the difference in substrate morphology. The [110] oriented CaF2 buffer layer was composed of isolated nanorods while the [001] oriented CaF2 buffer layer had micron long well ordered ridge structures. According to the theory of nanoepitaxy the isolated nanorods in the [110] oriented buffer layer provided more strain relief to the Ge epilayer. This reduced the number of dislocations in the film resulting in a lower relative intensity of the twin poles (or higher main pole to twin pole ratio). The Ge films nanohomoepitaxialy deposited on Ge buffer layers on hydrogen terminated Si(100) were studied as a function of substrate temperature and deposition rate. In both the substrate temperature and deposition rate study the Ge buffer layer deposited at incident angle alpha=87°, temperature T=330°C, and rate=1.6 nm/min had {001}<110> biaxial texture with the lowest in-plane dispersion (0.92° +/- 0.01°) and lowest relative intensity of twin poles (20:1). Ge films deposited on this buffer layer at 400°C had the lowest in-plane dispersion (0.83°), and a twin poles ratio (6:1). Ge films deposited directly on hydrogen terminated Si(100) at 400°C without Ge buffer layer had in-plane dispersion (0.47°) and twin ratio (1:1). The reduction in the relative intensity of the twin poles in the film deposited on the biaxial Ge buffer layer over the film deposited directly on H-Si(001) that has 4.2% Ge to Si lattice mismatch is attributed to the theory of strain relief in nanoepitaxy. The reduced dispersion and improved twin ratio in Ge films deposited on Ge buffer layer as compared to the nanoheteroepitaxial deposition of Ge on the [001] oriented CaF2 buffer layers indicated that the homoepitaxial deposition of Ge films on biaxially textured Ge buffer layers resulted in a better quality Ge film that is nearly single-crystal with twinning.

Snow, Patrick William

327

Possible isotopic fractionation effects in material sputtered from minerals  

NASA Technical Reports Server (NTRS)

A model is presented which predicts isotope fractionation in material sputtered from mineral surfaces. According to the model, the fractionation is a function of the fractional abundances of each isotope, the low-energy collision cross sections and the atomic masses, and the fractionation pattern can be nonlinear. Calculations are illustrated for all sets of isotopes in the minerals perovskite, anorthite, akermanite, enstatite and troilite, and it is found that while O is always positively fractionated, with heavier isotopes sputtered preferentially, heavier elements are generally negatively fractionated. It is noted that the model may be tested by experiments on a system such as CaF2, CaI2, in which the Ca sputtered from CaF2 is predicted to be strongly fractionated in a negative sense and that sputtered from CaI2 is predicted to be strongly fractionated in a positive sense.

Haff, P. K.; Watson, C. C.; Tombrello, T. A.

1981-01-01

328

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

PubMed

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

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

2004-04-01

329

Split-detector computed tomography: a preliminary report.  

PubMed

A split-detector system, consisting of a thin CaF2 scintillator followed by a thick Nal crystal, was installed in an EMI Mark I scanner. Energy discrimination is possible because the CaF2 crystal responds primarily to low-energy photons; dual-energy images can be obtained from only one scan. Calculations and preliminary experiments show that the split-detector separates energies better than the 100-140 kVp method. It was possibel with the split detector to differentiate between two weak solutions of CaCl2 and Kl which had the same computed tomography number (44 H), under normal scanning conditions. PMID:619422

Brooks, R A; Di Chiro, G

1978-01-01

330

Some studies on a solid state sulfur probe for coal gasification systems  

NASA Technical Reports Server (NTRS)

Measurements on the solid electrolyte cell (Ar + H(2) + H(2)S/CaS + CaF(2) + (Pt)//CaF(2)//(Pt) + CaF(2) + CaS/H(2) + H(2)+Ar) show that the emf of the cell is directly related to the difference in sulfur potentials established at the Ar + H(2) + H(2)S/electrode interfaces. The electrodes convert the sulfur potential gradient across the calcium fluoride electrolyte into an equivalent fluorine potential gradient. Response time of the probe varies from approximately 9 hr at 990 K to 2.5 hr at 1225 K. The conversion of calcium sulfide and/or calcium fluoride into calcium oxide is not a problem anticipated in commercial coal gasification systems. Suggestions are presented for improving the cell for such commercial applications.

Jacob, K. T.; Rao, D. B.; Nelson, H. G.

1977-01-01

331

Atomic scale control of hexaphenyl molecules manipulation along functionalized ultra-thin insulating layer on the Si(1?0?0) surface at low temperature (9 K)  

NASA Astrophysics Data System (ADS)

Ultra-thin CaF2 layers are grown on the Si(1?0?0) surface by using a Knudsen cell evaporator. These epitaxial structures are studied with a low temperature (9 K) scanning tunneling microscope and used to electronically decouple hexaphenyl molecules from the Si surface. We show that the ultra-thin CaF2 layers exhibit stripe structures oriented perpendicularly to the silicon dimer rows and have a surface gap of 3.8 eV. The ultra-thin semi-insulating layers are also shown to be functionalized, since 80% of the hexaphenyl molecules adsorbed on these structures self-orients along the stripes. Numerical simulations using time-dependent density functional theory allow comparison of computed orbitals of the hexaphenyl molecule with experimental data. Finally, we show that the hexaphenyl molecules can be manipulated along or across the stripes, enabling the molecules to be arranged precisely on the insulating surface.

Chiaravalloti, Franco; Dujardin, Gérald; Riedel, Damien

2015-02-01

332

System at 1523 K (1250 °C)  

NASA Astrophysics Data System (ADS)

CaO-SiO2-Al2O3-CaF2 is a base system of mold flux for high Al steels. Phase equilibrium in CaO-SiO2-Al2O3-15 mass pct CaF2 system at 1523 K (1250 °C) was investigated using quenching method followed by X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Isothermal section in this system at 1523 K (1250 °C) with Al2O3 being less than 25 mass pct and CaO/SiO2 (mass pct) being between 0.43 and 1.25 was experimentally constructed. The liquidus composition and seven solid-liquid coexistence regions at 1523 K (1250 °C) were determined.

Li, Jiangling; Shu, Qifeng; Chou, Kuochih

2014-10-01

333

Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers  

NASA Astrophysics Data System (ADS)

Metalorganic vapor phase epitaxy has been used for the first time to grow epitaxial GaAs layers on (111) and (100) oriented Si either using CaF 2 or stacked (Ca,Sr)F 2/CaF 2 as a buffer. The GaAs layers show sharp and well resolved electron channeling patterns. The Rutherford backscattering (RBS) ion channeling minimum yield is 5% for (111) orientation and 6% for (100) orientation. The GaAs(111) layers are untwinned. The strain in the GaAs layer has been measured with RBS and X-ray diffraction and it is found that the thermal mismatch-induced strain in the GaAs layer is considerably lower than in similar GaAs films grown without flouride buffer.

Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vèrié, C.

1992-11-01

334

Atomic scale control of hexaphenyl molecules manipulation along functionalized ultra-thin insulating layer on the Si(1?0?0) surface at low temperature (9 K).  

PubMed

Ultra-thin CaF2 layers are grown on the Si(1?0?0) surface by using a Knudsen cell evaporator. These epitaxial structures are studied with a low temperature (9 K) scanning tunneling microscope and used to electronically decouple hexaphenyl molecules from the Si surface. We show that the ultra-thin CaF2 layers exhibit stripe structures oriented perpendicularly to the silicon dimer rows and have a surface gap of 3.8 eV. The ultra-thin semi-insulating layers are also shown to be functionalized, since 80% of the hexaphenyl molecules adsorbed on these structures self-orients along the stripes. Numerical simulations using time-dependent density functional theory allow comparison of computed orbitals of the hexaphenyl molecule with experimental data. Finally, we show that the hexaphenyl molecules can be manipulated along or across the stripes, enabling the molecules to be arranged precisely on the insulating surface. PMID:25414151

Chiaravalloti, Franco; Dujardin, Gérald; Riedel, Damien

2015-02-11

335

Low Radioactivity in CANDLES  

SciTech Connect

CANDLES is the project to search for double beta decay of 48Ca by using CaF2 crystals. Double beta decay of 48Ca has the highest Q value among all nuclei whose double beta decay is energetically allowed. This feature makes the study almost background free and becomes important once the study is limited by the backgrounds. We studied double beta decays of 48Ca by using ELEGANTS VI detector system which features CaF2(Eu) crystals. We gave the best limit on the lifetime of neutrino-less double beta decay of 48Ca although further development is vital to reach the neutrino mass of current interest for which CANDLES is designed. In this article we present how CANDLES can achieve low radioactivity, which is the key for the future double beta decay experiment.

Kishimoto, T.; Ogawa, I.; Hazama, R.; Yoshida, S.; Umehara, S.; Matsuoka, K.; Sakai, H.; Yokoyama, D.; Mukaida, K.; Ichihara, K.; Tatewaki, Y.; Kishimoto, K.; Hirano, Y.; Yanagisawa, A.; Ajimura, S. [Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043 (Japan)

2005-09-08

336

Verification program for a high-precision large cryogenic lens holder  

Microsoft Academic Search

For the Euclid mission a Pre-Development phase is implemented to prove feasibility of individual components of the system. The Near Infrared Spectrometer and Photometer (NISP) of EUCLID requires high precision and large lens holders (Ø170 mm) at cryogenic temperatures (120K - 150K). The four lenses of the optical system are made of different materials: fused silica, CaF2, and LF5G15 that

A. Boesz; F. Grupp; T. Leberle; A. Mottaghibonab; N. Geis; R. Bender

2011-01-01

337

Behavior of nitrogen in a nitrogen-containing chromium-manganese steel during electroslag remelting  

NASA Astrophysics Data System (ADS)

Electroslag remelting of a high-alloyed steel with high contents of nitrogen, chromium, and manganese in an electroslag furnace has been studied. CaF2-MgO-SiO2 slag developed at TsNIITMASh and allowing remelting process at a temperature of 1520-1560°C is used as a flux. It is found that electroslag remelting of high-alloyed steels with a high nitrogen concentration does not change the nitrogen content.

Linchevskii, B. V.; Rigina, L. G.; Takhirov, A. A.

2013-06-01

338

Scintillation properties of SrF2 and SrF2-Ce3+ crystals  

NASA Astrophysics Data System (ADS)

This Letter presents the results of measuring scintillation properties of pure SrF2 crystals and crystals activated by various concentrations of Ce3+ ions. The light yield of these materials is compared to that of the known scintillators NaI-Tl and CaF2-Eu2+. Strontium fluoride crystals activated with Ce3+ ions are found to be characterized by high light yield and to be promising materials for use in scintillation detectors employed for ?-ray well logging.

Shendrik, R. Yu.; Radzhabov, E. A.; Nepomnyashchikh, A. I.

2013-07-01

339

Development of a high-resolution alpha camera  

Microsoft Academic Search

We have developed and tested a high-resolution alpha camera. The alpha camera consists of a thin CaF2(Eu) scintillator, a tapered fiber optics plate (tapered fiber), a position-sensitive photomultiplier tube (PSPMT) and a position calculation circuit. Though this configuration was originally planned as a high-resolution beta camera for direct measurement of positron distribution over brain surface of animals, we found that,

Seiichi Yamamoto; Takao Iida; Iwao Kanno

1997-01-01

340

Supporting Information Exploring Matrix Effects on Photochemistry of  

E-print Network

) using a single stage D (0.25 µm cut point at 9 SLM collection flow), which was modified in the UCI machine shop to accept a 25 mm CaF2 window as the impaction substrate. The flow tube setup is able of the flow tube operation. To prepare the 24-DNP/SOM film for the experiments, a 100 L droplet of 0.01 M 24

Nizkorodov, Sergey

341

Prediction of Mechanical Properties in Submerged Arc Weld Metal of C–Mn Steel  

Microsoft Academic Search

The prediction model has been developed for steel weld metal mechanical properties as a function of flux ingredients such as CaO, MgO, CaF2 and Al2O3 in submerged arc welding carried out at fixed welding parameters. The results of quantitative measurements of mechanical properties on eighteen weld metal samples were utilized for developing the prediction equations of mechanical properties applying statistical

Prasanta Kanjilal; Tapan Kumar Pal; Sujit Kumar Majumdar

2007-01-01

342

Slag-metal equilibrium during submerged arc welding  

Microsoft Academic Search

A thermodynamic model of the equilibria existing between the slag and the weld metal during submerged arc welding is presented.\\u000a As formulated, the model applies only to fused neutral fluxes containing less than 20 pct CaF2, however some results indicate that the model may be useful in more general cases as well. The model is shown to be capable\\u000a of

C. S. Chai; T. W. Eagar

1981-01-01

343

Kosterlitz-Thouless transition for 4He films adsorbed to rough surfaces.  

PubMed

We report the study of adsorption isotherms of 4He on several well characterized rough CaF2 surfaces using a quartz crystal microbalance technique at 1.672 K. The signature of decoupled mass observed on crossing the Kosterlitz-Thouless transition as a function of 4He film thickness decreases and becomes increasingly difficult to identify as the surface roughness is increased. A peak in the dissipation, indicative of the onset of superfluidity, changes little with roughness. PMID:15447205

Luhman, D R; Hallock, R B

2004-08-20

344

Nature and role of loosely bound fluoride in dental caries.  

PubMed

This paper discusses loosely bound fluoride and its role in dental caries and prevention. Loosely bound fluoride (abbr. by Fa) is fluoride adsorbed onto enamel mineral crystallites. Several recent studies indicate that a high total level of fluoride in enamel does not guarantee protection against caries. This leads to the conclusion that a major part of fluoride present in the solid enamel is not active in prevention. The adsorption of Fa to the mineral under acidic conditions is described. Most likely there is a dynamic equilibrium between fluoride in solution and adsorbed Fa at the crystal surface interface. When the crystallite is completely covered by adsorbed Fa, there is a maximum inhibition of dissolution. The rate of dissolution of mineral depends on pH, the actual concentrations of calcium and phosphate in the liquid in contact with the crystallites, and on the fraction of the surface covered by adsorbed fluoride. The fluoride, Fs, localized in the inner part of the crystallites is relatively unimportant. "CaF2-like" material can be formed on and in enamel depending on conditions. The in vivo-formed globular "CaF2-like" material is not pure CaF2 and releases F- ions when dissolving; these ions will also be partly adsorbed as Fa in and on enamel. Presently, the amount and importance of Fa originating from in vivo-formed "CaF2-like" material are not known. The level of fluoride, Fa, necessary for strong inhibition of enamel demineralization in vitro is estimated to correspond to a fluoride concentration, FL, in the liquid phase of 1 ppm or 50 mumol/L fluoride ions.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2179320

Arends, J; Christoffersen, J

1990-02-01

345

Effect of Yb3+ concentration on optical properties of Yb:CaF2 transparent ceramics  

E-print Network

Effect of Yb3+ concentration on optical properties of Yb:CaF2 transparent ceramics Andréas Lyberis Keywords: CaF2 Ytterbium Transparent ceramics Spectroscopy a b s t r a c t In Yb:CaF2, the coordination, and fluorescence lifetime of 0.1, 1, 5, and 10 at% Yb:CaF2 ceramics to determine whether Yb3+ substitutes

346

Epitaxial switchable yttrium-hydride mirrors  

Microsoft Academic Search

By means of x-ray scattering and scanning probe microscopy it is shown that high-quality epitaxial Y films can be deposited on (111)-CaF2 substrates. The films can reversibly be switched from metallic YH2 to transparent insulating YH3-delta. Although hydrogen absorption involves an expansion of the lattice and a symmetry change from hcp to fcc, the epitaxiality of the film remains intact

D. G. Nagengast; J. W. J. Kerssemakers; A. T. M. van Gogh; B. Dam; R. Griessen

1999-01-01

347

Polarization-sensitive optical response of plasmonic metasurfaces  

Microsoft Academic Search

We have fabricated arrays of nanoscale asymmetric cruciform apertures that support localized surface-plasmon polaritons (LSPPs) in the lower mid-infrared. The cruciform apertures were created by focussed ion beam milling into a gold film on a CaF2 substrate. The measured transmission spectra of these arrays show two distinct maxima that correspond to the excitation of LSPPs, the magnitude of which can

Paul G. Thompson; Claudiu G. Biris; Edward J. Osley; Richard M. Osgood Jr.; Nicolae C. Panoiu; Paul A. Warburton

2011-01-01

348

Separation of High Order Harmonics with Fluoride Windows  

SciTech Connect

The lower orders produced in high order harmonic generation can be effciently temporally separated into monochromatic pulses by propagation in a Fluoride window while still preserving their femtosecond pulse duration. We present calculations for MgF2, CaF2, and LiF windows for the third, fifth, and seventh harmonics of 800 nm. We demonstrate the use of this simple and inexpensive technique in a femtosecond pump/probe experiment using the fifth harmonic.

Allison, Tom; van Tilborg, Jeroen; Wright, Travis; Hertlein, Marcus; Falcone, Roger; Belkacem, Ali

2010-08-02

349

PMAS: The Potsdam Multi-Aperture Spectrophotometer. I. Design, Manufacture, and Performance  

Microsoft Academic Search

We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi-Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer optimized to cover the optical wavelength regime of 0.35-1 mum. It is based on the lens array-fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF2 optics, to provide good transmission and high image

Martin M. Roth; Andreas Kelz; Thomas Fechner; Thomas Hahn; Svend-Marian Bauer; Thomas Becker; Petra Böhm; Lise Christensen; Frank Dionies; Jens Paschke; Emil Popow; Dieter Wolter; Jürgen Schmoll; Uwe Laux; Werner Altmann

2005-01-01

350

Electronic structure of hole centers in aluminum doped fluorite crystals  

Microsoft Academic Search

UDC 535.37 A wealth of experimental data are currently available on point defects and processes with their participation in scintillation crystals based on CaF 2 containing rare earth elements (REE). The electronic and spatial structure of a number of hole and electron centers was studied theoretically. The ab initio Hartree-Fock method and the scattered wave method were used to calculate

S. N. Mysovskii

1999-01-01

351

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers  

E-print Network

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers W. K. Liu,a) J The molecular beam epitaxy of InSb/Si structures was accomplished using group IIa fluoride buffer layers. InSb 300 °C and 400 °C, producing In-terminated InSb 111 -A surfaces on CaF2/Si 111 substrates. Reflection

McCann, Patrick

352

On the dissolution\\/reaction of small-grain Bioglass ® 45S5 and F-modified bioactive glasses in artificial saliva (AS)  

Microsoft Academic Search

The reaction of small-grain Bioglass® 45S5 in artificial saliva (AS), to produce a layer of hydroxy-apatite (HA) and\\/or hydroxy-carbonate apatite (HCA), has been studied and compared to the results obtained in a simple buffered solution (TRIS). Some potentially bioactive glasses based on the composition of Bioglass® and containing CaF2 (HCaCaF2 5% and HNaCaF2 5%) have also been studied, in order

Valentina Aina; Luca Bertinetti; Giuseppina Cerrato; Marta Cerruti; Gigliola Lusvardi; Gianluca Malavasi; Claudio Morterra; Linda Tacconi; Ledi Menabue

2011-01-01

353

Fluoride-containing bioactive glasses: Surface reactivity in simulated body fluids solutions  

Microsoft Academic Search

The issue of the contribution of the addition of F to glass bioactivity is not well resolved. This work reports on the surface reactivity in different solutions (DMEM and Tris) for some potentially bioactive glasses based on the composition of 45S5 glass, in which CaF2 is substituted alternately for (part of) CaO and Na2O. The reactivity of F-containing glasses has

G. Lusvardi; G. Malavasi; L. Menabue; V. Aina; C. Morterra

2009-01-01

354

Zeeman Effect in the Absorption Spectra of Trivalent Ytterbium Ions in Different Site Symmetries in Calcium Fluoride  

Microsoft Academic Search

The Zeeman effect has been observed in the optical spectra of Yb3+ ions in different sites in CaF2. All but one of the correlations between ESR and optical spectra, reported by Kirton and McLaughlan, have been checked and confirmed, and the upper-state g values have been determined. Ambiguity in the interpretation of the rhombic spectra has been eliminated, and we

J. Kirton; A. M. White

1969-01-01

355

An investigation of the transfer film characteristics and the tribological behaviors of polyphenylene sulfide composites in sliding against tool steel  

Microsoft Academic Search

The effect of CuS, CuO, CaF2, and ZnF2 fillers in particulate sizes of 200–350 mesh on the friction and wear behavior of polyphenylene sulfide (PPS) was investigated. The filler proportion studied was 35 vol.%. The specimens which were prepared by compression molding were tested for friction and wear in a pin-on-disc configuration using hardened tool steel disc as the counterface.

Laigui Yu; S. Bahadur

1998-01-01

356

Sol-gel synthesis of rare-earth-doped halide optical materials for photonic applications  

NASA Astrophysics Data System (ADS)

Halides have received global attention as potential ultra-low loss optical fiber materials and luminescent sources for all-optical amplification in modern telecommunication systems operating at 1.3 and 1.55 ?m. Unfortunately, conventional processing methods currently have failed in their efforts to produce even near-intrinsic material properties. Based on the well- established notion that sol-gel techniques offer high purity, low processing temperature, and compositionally flexible routes to high quality optics, we examined solution-based approaches to the synthesis of rare-earth- doped halides that provide luminescence in the 1.3 ?m and 1.55 ?m telecommunication windows. Initial studies into metal-organic-derived, ZBLA fluoride glass thin-films proved the spectroscopic performance of dopants was dominated by nonradiative relaxations caused by the presence of remnant carbonaceous species from the precursors. Heat treatments to above the point of glass devitrification did not resolve this problem and dopant emission remained modified by these extrinsic sources of high energy phonons. Inorganic precursors then were studied to circumvent the issues associated with the residual organics. Amorphous and crystalline single-component halide systems were prepared from aqueous solutions of inorganic chloride salts and their luminescence properties at 1.3 and 1.55 ?m studied. Pr3+- and Dy3+- doped LaF3 and LaCl3 powders were prepared that exhibited 1.3 ?m radiative quantum efficiencies of 72 and 78%, respectively, despite chemical analyses that indicated greater than 2% oxide concentrations. The efficiency values represented the highest measured from any halide to-date. Superiority in spectroscopic performance with respect to melt-grown, single-crystal analogs clearly opposed the widely accepted belief that quantum efficiencies are seriously degraded by precursor purity or the presence of oxygen. The results validated our hypothesis that inexpensive, low temperature, aqueous solution-derived materials can possess low-phonon energies. Luminescence was observed at 1.55 ?m from Er3+-doped LaF3 prepared by a single-step, solution-fluorination method. Available emission bandwidths 360% larger than current optical amplifier materials were realized from highly rare-earth-doped LaF3 transparent gels. The aqueous solution synthesis was found to permit rare-earth solid solubility ranges nearly 50 mole % greater than melt-grown equivalents. This compositional metastability was shown to be process-induced and verified our hypothesis that novel compositional flexibility is enabled by solution- based approaches.

Ballato, John Michael

357

Optical and Nuclear Spin Spectroscopy in PRASEODYMIUM(3+):LANTHANUM Fluoride by Optical Pumping  

NASA Astrophysics Data System (ADS)

A Stark Modulated Optical Pumping (SMOP) technique was used as a sensitive probe of optical hole-burning to study the effects of nuclear spin interactions in Pr ^{3+}:LaF_3. The results of two experiments are reported. In the first experiment, the SMOP technique is applied for optical detection of the NQR spectrum of the Pr^{3+} optical ground state. Frequency and linewidth variations of the Pr ^{3+} ground state hyperfine levels for different positions within the main ^3 H_4(Gamma1) -^1D_2(Gamma 1) inhomogeneous optical line and satellite transitions of Pr^{3+}:LaF _3 are observed. A linear increase in the broadening of the Pr^{3+} hyperfine transitions, without a shift of central frequency, is measured as the laser is tuned toward the wings of the inhomogeneous optical transition. The linear variation is attributed to electric quadrupole broadening caused by changes in local density of point defects across the Stark broadened optical transition. The optically detected NQR spectra of the satellite transitions associated with Pr ion pairs are shifted in frequency, and for most satellites are narrower in width than the NQR spectra found in the wings of the main inhomogeneous optical line. In the second experiment, direct evidence for the presence of a spin diffusion barrier or "frozen core" in Pr^{3+}:LaF _3 is observed by examining the cross relaxation between the Pr and F nuclei in a magnetic field chosen so that a pair of the optical ground state Pr^ {3+} hyperfine energy levels matches the F splitting or a multiple of the F splitting. This level crossing condition allows resonant flip-flop interactions with the nearest neighbor frozen core fluorine spins to re-populate Pr^{3+} hyperfine levels emptied by laser hole-burning, and is detected as enhanced absorption of the laser beam. The coupling of core fluorine spins to bulk fluorine spins during Pr-F cross-relaxation is measured by NMR of the bulk fluorine spin magnetization. The rate of cross relaxation between the Pr spins and the bulk F spins measured in this way is at least three to four orders of magnitude slower than that expected in the absence of a spin diffusion barrier. This reduction of coupling indicates nearly complete de-tuning of the frozen core F spins immediately surrounding the Pr^{3+} ion, cutting off resonant coupling with the bulk F spins.

Wald, Lawrence Leroy

358

Mixedness determination of rare earth-doped ceramics  

NASA Astrophysics Data System (ADS)

The lack of chemical uniformity in a powder mixture, such as clustering of a minor component, can lead to deterioration of materials properties. A method to determine powder mixture quality is to correlate the chemical homogeneity of a multi-component mixture with its particle size distribution and mixing method. This is applicable to rare earth-doped ceramics, which require at least 1-2 nm dopant ion spacing to optimize optical properties. Mixedness simulations were conducted for random heterogeneous mixtures of Nd-doped LaF3 mixtures using the Concentric Shell Model of Mixedness (CSMM). Results indicate that when the host to dopant particle size ratio is 100, multi-scale concentration variance is optimized. In order to verify results from the model, experimental methods that probe a mixture at the micro, meso, and macro scales are needed. To directly compare CSMM results experimentally, an image processing method was developed to calculate variance profiles from electron images. An in-lens (IL) secondary electron image is subtracted from the corresponding Everhart-Thornley (ET) secondary electron image in a Field-Emission Scanning Electron Microscope (FESEM) to produce two phases and pores that can be quantified with 50 nm spatial resolution. A macro was developed to quickly analyze multi-scale compositional variance from these images. Results for a 50:50 mixture of NdF3 and LaF3 agree with the computational model. The method has proven to be applicable only for mixtures with major components and specific particle morphologies, but the macro is useful for any type of imaging that produces excellent phase contrast, such as confocal microscopy. Fluorescence spectroscopy was used as an indirect method to confirm computational results for Nd-doped LaF3 mixtures. Fluorescence lifetime can be used as a quantitative method to indirectly measure chemical homogeneity when the limits of electron microscopy have been reached. Fluorescence lifetime represents the compositional fluctuations of a dopant on the nanoscale while accounting for billions of particles in a fast, non-destructive manner. The significance of this study will show how small-scale fluctuations in homogeneity limit the optimization of optical properties, which can be improved by the proper selection of particle size and mixing method.

Czerepinski, Jennifer H.

359

Ablation and plasma emission produced by dual femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Pairs of 80fs, 800nm laser pulses were used to ablate Si, Cu, and CaF2 in air. The spectrally resolved plasma emission was measured as a function of laser fluence and pulse delay. After an initial dip, the fluorescence was found to increase monotonically with pulse delay, reaching a plateau after some tens of picoseconds, depending on the material and fluence. The enhancement ratio (defined as the ratio of the fluorescence produced by the pulse pair to that produced by a single pulse of the same total fluence) reaches a maximum value of 6 and 11 at a fluence of ˜6J /cm2 for Si and Cu, respectively, and declines to a value below 2 at higher fluences. In contrast, the enhancement for CaF2 increases slowly from zero near threshold to a broad maximum value of 2 near 50J /cm2. Using reflectivity and atomic force microscopy measurements as diagnostics, we interpret the Si and Cu behavior in terms of a two phase mechanism, in which the first pulse melts the surface of the crystal and the second pulse ablates the resulting liquid film. A qualitatively different mechanism initiated by multiphoton absorption is involved in CaF2 ablation.

Singha, Sima; Hu, Zhan; Gordon, Robert J.

2008-12-01

360

Laser-induced backside wet etching of fluoride and sapphire using picosecond laser pulses  

NASA Astrophysics Data System (ADS)

Laser-induced backside wet etching (LIBWE) is a promising process for microstructuring of rigid chemical resistant and inert transparent materials. LIBWE with nanosecond laser pulses has been successfully demonstrated in a number of studies. LIBWE in a time scale of femtosecond and picosecond pulse durations has been investigated only in a few studies and just on fused silica. In the present study LIBWE of fluorides (CaF2, MgF2) and sapphire with a mode-locked picosecond ( t p=10 ps) laser at a UV wavelength of ?=355 nm using toluene as absorbing liquid has been demonstrated. The influence of the laser fluence and the pulse number on the etching rate and the achieved surface morphology was investigated. The etching rate grows linearly with the laser fluence in the low and high-fluence ranges with different slopes. The achieved etching rates for CaF2 and for sapphire were in the same range. Contrary to CaF2 and sapphire the etching rates of MgF2 were one magnitude less. For backside etching on sapphire at high fluences smooth surfaces and at low fluences ripples pattern were found, whereas fluoride surfaces showed a trend towards crack formation.

Ehrhardt, M.; Raciukaitis, G.; Gecys, P.; Zimmer, K.

2010-11-01

361

Nanoscintillators for radiation detection  

NASA Astrophysics Data System (ADS)

In the search for faster, more effective methods for detection of and protection against radiological weapons, advances in materials for radiation detection are a critical component of any successful strategy. This work focuses on producing inexpensive, but highly sensitive, nanoparticle alternatives to existing single-crystal installations. Attention is given to particular types of promising inorganic scintillators: LaF3, yttrium-aluminum-garnet (YAG), and SrF2, each one an inorganic host doped with additional elements that encourage luminescent decay and increase effective Z-value. I examine the possible routes to synthesize these compounds, and the difficulties and benefits of each method. After synthesizing these materials, testing was performed to determine comparative performance against each other and commercial solutions, identify structural and compositional characteristics, and explore routes for fixing the scintillators into a detector assembly. The unifying goal is to develop a scintillating material suitable for consistent dosimetry and radio-isotope identification applications.

Hall, Ryan Gregory

362

One-pot synthesis of chitosan/LaF3:Eu3+ nanocrystals for bio-applications  

NASA Astrophysics Data System (ADS)

Lanthanide-based nanocrystals have shown great potential to be used as luminescent materials but their biological applications have been limited because most of the nanocrystals synthesized so far are not water soluble or biocompatible. We report a very straightforward method to synthesize water soluble and biocompatible LaF3 nanocrystals doped with Eu3+ via facile co-precipitation with a natural biopolymer, chitosan. The nanocrystals are very fluorescent and have a small size of about 20 nm. Chitosan is found to cap the nanocrystals during the synthesis process, which renders them water soluble and biocompatible, and provides functional groups such as hydroxyl and amino groups for further attachment of biomolecules. The nanocrystals remain stable in aqueous solution with pH ranging from 2 to 7.4. The nanocrystals are very suitable for use in biological applications, for example, intracellular labelling or measurements, because they are very small in size.

Wang, Feng; Zhang, Yong; Fan, Xianping; Wang, Minquan

2006-03-01

363

Measurement of U-235 Fission Neutron Spectra Using a Multiple Gamma Coincidence Technique  

NASA Astrophysics Data System (ADS)

The Los Alamos Model of Madland and Nix predicts the shape of the fission neutron energy spectrum for incident primary neutrons of different energies. Verifications of the model normally are limited to measurements of the fission neutron spectra for energies higher than that of the primary neutrons because the low-energy spectrum is distorted by the admixture of elastically and inelastically scattered neutrons. This situation can be remedied by using a measuring technique that separates fission from scattering events. One solution consists of using a fissile sample so thin that fission fragments can be observed indicating the occurrence of a fission event. A different approach is considered in this paper. It has been established that a fission event is accompanied by the emission of between seven and eight gamma rays, while in a scattering interaction, between zero and two gammas are emitted, so that a gamma multiplicity detector should supply a datum to distinguish a fission event from a scattering event. We proceed as follows: A subnanosecond pulsed and bunched proton beam from the UML Van de Graaff generates nearly mono-energetic neutrons by irradiating a thin metallic lithium target. The neutrons irradiate a 235U sample. Emerging neutron energies are measured with a time-of-flight spectrometer. A set of four BaF2 detectors is located close to the 235U sample. These detectors together with their electronic components identify five different events for each neutron detected, i.e., whether four, three, two, one, or none of the BaF2 detectors received one (or more) gamma rays. We present work, preliminary to the final measurements, involving feasibility considerations based on gamma-ray coincidence measurements with four BaF2 detectors, and the design of a Fission-Scattering Discriminator under construction.

Ji, Chuncheng; Kegel, G. H. R.; Egan, J. J.; DeSimone, D. J.; Alimeti, A.; Roldan, C. F.; McKittrick, T. M.; Kim, D.-S.; Chen, X.; Tremblay, S. E.

2005-05-01

364

Spectroscopic analysis of Ho3+ transitions in different modifier oxide based lithium-fluoro-borate glasses  

NASA Astrophysics Data System (ADS)

In recent investigations it was observed that the presence of different structural groups in borate glasses was favorable for spectroscopic investigations of rare earth doped borate glasses. Consequent to these observations, the heavy metal fluoride glasses doped with Ho3+ ions received much attention due to their wide transparency in the ultraviolet to infrared region. Keeping these observations in view, the present paper makes an attempt to present spectral investigations of Ho3+ doped lithium-fluoro-borate glasses of the compositions Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. These rare earth doped glasses were synthesized by melt quenching technique and an investigation was carried out to observe the structural (SEM and FT-IR) and optical (absorption and luminescence) properties. The paper also aims at the determination of three phenomenological Judd-Ofelt intensity parameters and special attention was paid to study the emission properties by employing the J-O intensity parameters. The visible emission spectra of Ho3+ ion in different lithium-fluoro-borate glasses were recorded by exciting the samples at 409 nm. The results revealed that among all the glass matrices, cadmium glass matrix have shown higher stimulated emission cross-section, which indicates that this is a good lasing material at this wavelength and highly useful for laser excitation.

Balakrishna, A.; Rajesh, D.; Ratnakaram, Y. C.

2014-10-01

365

Growth Kinetics in Epitaxial Growth  

NASA Astrophysics Data System (ADS)

Growth kinetics in heteroepitaxial growth are related to the nucleation and growth of atomic-height islands during the deposition of a material on a dissimilar substrate. Experimental measurements of the initial morphology of CaF_2 films deposited on Si(111) substrates were performed. These measurements consisted of photoemission spectroscopy and diffraction, which give sub-nanometer scale information averaged over the entire sample, and plan-view transmission electron microscopy, which gives localized information on a scale of several nanometers. These results, combined with others in the literature, revealed four distinct growth morphologies dependent on the deposition rate, substrate temperature and spacing between atomic-height steps on the surface, two of which had not been previously explained. A model based on two extant theories of homoepitaxial growth kinetics was developed to explain the different observed growth morphologies for the heteroepitaxial system CaF_2/Si(111). The first theory deals with whether the initial nucleation will occur at substrate steps or through adatom collisions on flat terraces, while the second deals with the nucleation of subsequent layers as these initial atomic islands increase in size. In extending these theories to heteroepitaxy, very different rates of upper-layer nucleation for the different size islands that nucleated at steps and on terraces are predicted. By applying this theory to CaF_2/Si(111), the diffusion barriers for CaF_2 molecule migration both on the reacted Si-Ca-F interface layer and on subsequent CaF_2 layers was extracted. The four different growth morphologies are explained within a common framework. The theory is quite general, and should apply to most heteroepitaxial systems. These theories were extended to predict a means by which the upper-layer nucleation may be inhibited while the underlying layer is completed. This method involves initiating the growth at conditions favoring many, small islands on atomic terraces, and then completing the growth at conditions inhibiting upper-layer nucleation (lower flux and/or higher temperature). A general formula for either homoepitaxy or heteroepitaxy was developed for the optimal flux and temperature variation during each monolayer to fabricate a flat film in the minimum amount of time.

Hessinger, Uwe

366

Gd 3+ Spin--Phonon Interactions in Rare-Earth Fluoride Crystals  

NASA Astrophysics Data System (ADS)

The X-band EPR study of Gd3+-doped LaF3, La0.9Ce0.1 F3, La0.9Nd0.1F3, LiYF4 and LiY0.9Yb0.1F4 single crystals in the temperature range 4.2--295 K was carried out in order to investigate the Gd3+ spin--phonon interactions. Spin-Hamiltonian parameters are analysed in the light of the superposition model and the rotational invariance theory for phonon-induced contributions to spin-Hamiltonian parameters. The 4f7 electron--phonon interactions can be described by the Debye model. It is suggested, from the rotational invariance mechanism for phonon-induced contributions to spin-Hamiltonian parameters, that the rotational contributions are much smaller than those from the strain. Temperature-induced distortions of the crystal field, as well as these distortions caused by the La3+/Nd3+ and Y3+/ Yb3+ substitutions, influence significantly the 4f7 electron--phonon interactions. The coupling constant K2 of 4f7 electrons to the whole phonon spectrum of the crystal lattice is stronger in the LaF3, La0.9 Ce0.1F43, La0.9Nd0.1F3 with larger temperature-induced distortion of the Gd3+ site symmetry than in LiYF4, LiY0.9Yb0.1F4. Our results are compared with those for Gd3+-doped RbCdF3 and PbF2 single crystals.

Paradowski, M. L.; Misiak, L. E.

2000-09-01

367

Controlling energy transfer between multiple dopants within a single nanoparticle  

PubMed Central

Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF3 nanoparticles doped with Tb3+ and Eu3+ and consisting of up to four layers were synthesized with an outer diameter of ?10 nm. It is found that by varying the thicknesses of an undoped layer between a Tb3+-doped layer and a Eu3+-doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm Tb3+ and 590 nm Eu3+ peaks was tailored from <0.2 to ?2.4 without changing the overall composition of the particles but only by changing the internal structure. Further, the emission spectrum of a blend of singly doped nanoparticles is shown to be equivalent to the spectra of co-doped particles when a core-shell configuration that restricts ET is used. Beyond simply controlling ET, which can be limiting when designing materials for optical applications, this approach can be used to obtain truly engineered spectral features from nanoparticles and composites made from them. Further, it allows for a single excitation source to yield multiple discrete emissions from numerous lanthanide dopants that heretofore would have been quenched in a more conventional active optical material. PMID:18250307

DiMaio, Jeffrey R.; Sabatier, Clément; Kokuoz, Baris; Ballato, John

2008-01-01

368

Measurement of the Neutron Capture Cross Section of the Fissile Isotope 235U with the CERN n_TOF Total Absorption Calorimeter and a Fission Tagging Based on Micromegas Detectors  

NASA Astrophysics Data System (ADS)

Current and future nuclear technologies require more accurate nuclear data on (n,?) cross sections and the ?-ratios of fissile isotopes. Their measurement presents several difficulties, mainly related to the strong fission ?-ray background competing with the weaker ?-ray cascades used as the experimental signature of the (n,?) process. A specific setup was used at the CERN n_TOF facility in 2012 for the measurement of the (n,?) cross section and ?-ratios of fissile isotopes and used for the case of the 235U isotope. The setup consists of a set of micromegas fission detectors surrounding the 235U samples all placed inside a segmented BaF2 Total Absorption Calorimeter.

Balibrea, J.; Mendoza, E.; Cano-Ott, D.; Guerrero, C.; Berthoumieux, E.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Be?vá?, F.; Belloni, F.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Gunsing, F.; Gurusamy, P.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kawano, T.; Kivel, N.; Koehler, P.; Kokkoris, M.; Korschinek, G.; Krti?ka, M.; Kroll, J.; Langer, C.; Lampoudis, C.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Mastinu, P. F.; Mastromarco, M.; Massimi, C.; Meaze, M.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondelaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Pignatari, M.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Roman, F.; Rubbia, C.; Sarmento, R.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Stetcu, I.; Sabaté, M.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T. J.; Žugec, P.

2014-05-01

369

System for measuring temporal profiles of scintillation at high and different linear energy transfers by using pulsed ion beams  

NASA Astrophysics Data System (ADS)

We have developed a system for measuring the temporal profiles of scintillation at high linear energy transfer (LET) by using pulsed ion beams from a cyclotron. The half width at half maximum time resolution was estimated to be 1.5-2.2 ns, which we attributed mainly to the duration of the pulsed ion beam and timing jitter between the trigger signal and the arrival of the ion pulse. The temporal profiles of scintillation of BaF2 at different LETs were successfully observed. These results indicate that the proposed system is a powerful tool for analyzing the LET effects in temporal profiles of scintillation.

Koshimizu, Masanori; Kurashima, Satoshi; Taguchi, Mitsumasa; Iwamatsu, Kazuhiro; Kimura, Atsushi; Asai, Keisuke

2015-01-01

370

Wurtzite-type CdS and CdSe epitaxial layers. 1: Growth and characterization  

NASA Astrophysics Data System (ADS)

CdS and CdSe layers have been grown by hot-wall (-beam) epitaxy on BaF2(111) and GaAs(1'1'1') B substrates. Both CdS and CdSe adopted the wurtzite crystal structure, as found by electron diffraction. For characterization, photoluminescence and reflection spectra were measured at 4.2 K. The luminescence spectra revealed dominant bound-exciton features and a better quality of these hexagonal layers than usually obtained for zinc-blende-type ones.

Grun, M.; Hetterich, M.; Becker, U.; Giessen, H.; Klingshirn, C.

1994-08-01

371

Conversion of Oxyfluoride Based Coated Conductors  

SciTech Connect

Direct measurements of HF pressure in equilibrium with the film during the BaF2 process are sorely needed. It is the HF partial pressure that governs the rate at which the film composition is changing and is, therefore, an important factor in controlling the composition/time trajectory of the film. Establishing the composition/time trajectory of both MOD-derived and e-beam derived films for a given set of conditions is another goal for the project. These studies will provide a fundamental understanding of the ex situ process for producing coated conductors.

Dan Wesolowski

2006-11-01

372

Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET.  

PubMed

This study presents Monte Carlo Simulation (MCS) results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF) PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu(2)SiO(5): Ce in short LSO), Barium Fluoride (BaF(2)) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr(3)) scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF(2) and LaBr(3), although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work) method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom. PMID:20098551

Mondal, Nagendra Nath

2009-10-01

373

Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET  

PubMed Central

This study presents Monte Carlo Simulation (MCS) results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF) PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu2SiO5: Ce in short LSO), Barium Fluoride (BaF2) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr3) scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF2 and LaBr3, although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work) method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom. PMID:20098551

Mondal, Nagendra Nath

2009-01-01

374

Effect of quenching processes on the decay of fast luminescence from barium fluoride excited by VUV synchrotron radiation  

NASA Astrophysics Data System (ADS)

The problem of quenching the luminescence associated with interatomic radiative transitions from the valence band to the deeper lying core level is studied for BaF2, which is known to be the fastest inorganic scintillator. The measurements of excitation spectra and time decay kinetics of the fast fluorescence component (220 nm) for BaF2 crystal excited by photons in the VUV spectral region from 16 to 100 eV are discussed. The quenching process is exhibited in the shortening of this decay and in the decrease of the quantum efficiency. The kinetics is nonexponential for all energies. These effects depend on the excitation photon energy and the angle of light incidence. This behavior is explained by the surface quenching (as has been supposed earlier) and the energy transfer to the excitations produced by the same photon. The relative effect of these processes depends on the excitation energy. For energies below 30 eV the surface quenching dominates, whereas for higher energies the main quenching process is caused by the energy transfer from the core hole to other electronic excitations. The same effect can be observed in other ionic crystals in which the Auger decay of core hole is energetically forbidden.

Terekhin, M. A.; Vasil'ev, A. N.; Kamada, M.; Nakamura, E.; Kubota, S.

1995-08-01

375

A new type of luminescence mechanism in large band-gap insulators: Proposal for fast scintillation materials  

NASA Astrophysics Data System (ADS)

Luminescence components of BaF 2 (180-230 nm), CsF (220-500 nm), CsCl (200-300 nm), CsBr (220-280 nm), and RbF (200-450 nm) have been investigated at room temperature by using synchrotron radiation as a light source. These luminescence components have excitation thresholds at the energy differences from the outermost Ba 2+ 5p, or M +mp ( m = 4 and 5 for M = Rb and Cs, respectively) core state to the conduction band, and are attributeted to the radiative decay of electrons in the X -np halogen valence bands ( n = 2, 3, and 4 for X = F, Cl and Br, respectively) to the outermost-core hole states. Single bunch operation of synchrotron radiation has been used to determine the lifetime of the above luminescence. The measured lifetimes in ns are: BaF 2: 0.88±0.02; CsF: 2.9±0.1; CsCl: 0.88±0.07; CsBr: 0.07±0.03; and RbF: 1.3±0.1 From the above results, it is proposed that insulators having large band-gap energy compared to the energy difference between the valence band and the outermost-core state are candidates for fast scintillation materials, for example, CsCl, CsBr, RbF, KF, BaCl 2, BaBr 2, and BaI 2.

Kubota, Shinzou; Ruan (Gen), Jian-zhi; Itoh, Minoru; Hashimoto, Satoshi; Sakuragi, Shiro

1990-04-01

376

Precipitation of barium flouride microcrystals from electrolytic solutions: The influence of the composition of the precipitating solutions  

NASA Astrophysics Data System (ADS)

The composition, shape and size of the particles obtained by precipitation in aqueous solutions of various barium salts (chloride, nitrate and acetate) with various fluorides (ammonium, sodium and hydrogen) have been studied by X-ray powder diffraction analysis and scanning electron microscopy. From Ba(NO 3) 2 in combination with NH 4F or NaF and from Ba(C 2H 3O 2) 2 in combination with NH 4F, NaF or HF, precipitates of pure cubic-BaF 2 (?-BaF 2) are obtained. The shape and size of ?-BaF 2 particles depend on the combination of the compounds used for the precipitation and their concentrations. It appears that only when (equal volumes of) solutions of Ba(NO 3) 2 (0.125 mol dm -3) or Ba(C 2H 3O 2) 2 (0.125 and 0.150 mol dm -3) and NH 4F (0.250 or 0.300 mol dm -3) are mixed particles are formed as more or less regular cubes with smooth faces. These crystals are suitable to be used in studies of the transport of ions from crystals to the solution and vice versa with the aid of radioactive tracers ("heterogeneous isotopic exchange" studies).

Kolar, Z.; Binsma, J. J. M.; Suboti?, B.

1984-02-01

377

Correlated fluorine diffusion and ionic conduction in the nanocrystalline F(-) solid electrolyte Ba(0.6)La(0.4)F(2.4)-(19)F T1(?) NMR relaxation vs. conductivity measurements.  

PubMed

Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry. PMID:24728404

Preishuber-Pflügl, F; Bottke, P; Pregartner, V; Bitschnau, B; Wilkening, M

2014-05-28

378

Resonant nature of intrinsic defect energy levels in PbTe revealed by infrared photoreflectance spectroscopy  

NASA Astrophysics Data System (ADS)

Step-scan Fourier-transform infrared photoreflectance and modulated photoluminescence spectroscopy were used to characterize the optical transitions of the epitaxial PbTe thin film grown by molecular beam epitaxy on BaF2 (111) substrate in the vicinity of energy gap of lead telluride at 77 K. It is found that the intrinsic defect energy levels in the electronic structure are of resonant nature. The Te-vacancy energy level is located above the conduction band minimum by 29.1 meV. Another defect (VX) energy level situated below valance band maximum by 18.1 meV is also revealed. Whether it is associated with the Pb vacancy is still not clear. It might also be related to the misfit dislocations stemming from the lattice mismatch between PbTe and BaF2 substrate. The experimental results support the theory prediction (N. J. Parada and G. W. Pratt, Jr., Phys. Rev. Lett. 22, 180 (1969), N. J. Parada, Phys. Rev. B 3, 2042 (1971)) and are consistent with the reported Hall experimental results (G. Bauer, H. Burkhard, H. Heinrich, and A. Lopez-Otero, J. Appl. Phys. 47, 1721 (1976)).

Zhang, Bingpo; Cai, Chunfeng; Jin, Shuqiang; Ye, Zhenyu; Wu, Huizhen; Qi, Zhen

2014-07-01

379

Temporal Expression of the Candida albicans Genes CHK1 and CSSK1, Adherence, and Morphogenesis in a Model of Reconstituted Human Esophageal Epithelial Candidiasis  

PubMed Central

We previously demonstrated that genes encoding a putative two-component histidine kinase (CHK1) or a response regulator (CSSK1) are each required for virulence in a murine model of hematogenously disseminated candidiasis and that strains with each gene deleted are also defective in morphogenesis under certain growth conditions. In the present study, the role of these two genes in the adherence to and colonization of reconstituted human esophageal tissue (RHE) is described. We compared strains of Candida albicans with deletions of chk1 (strain CHK21) and cssk1 (strain CSSK21) to wild-type cells (CAF2), as well as strains with CHK1 and CSSK1 reconstituted (strains CHK23 and CSSK23, respectively). Adherence and colonization of RHE were evaluated in periodic acid-Schiff-stained sections, as well as by SEM. We observed that both deletion-containing strains colonized the RHE to a lesser extent than did CAF2 and that the percent germination by both strains was reduced in comparison to that of control strains at 1 h postinfection. Expression of CHK1 or CSSK1 was quantitated by reverse transcription (RT)-PCR from RHE tissues infected with wild-type C. albicans yeast cells. Expression of both CHK1 and CSSK1 increased over the 48-h period following infection of the tissue, although expression of CHK1 was greater than that of CSSK1. By RT-PCR, we have also shown that expression of CHK1 and CSSK1 in the strains with cssk1 and chk1 deleted, respectively, was similar to that of CAF2, indicating that CHK1 and CSSK1 do not regulate each other but probably encode signal proteins of different pathways. Our observations indicate that CHK1 and CSSK1 are each partially required for colonization and conversion to filamentous growth on RHE tissue. PMID:11854244

Li, Dongmei; Bernhardt, Joern; Calderone, Richard

2002-01-01

380

Reaction characteristics of a tooth-bleaching agent containing H2O2 and NaF: in vitro study of crystal structure change in treated hydroxyapatite and chemical states of incorporated fluorine.  

PubMed

This in vitro study was performed to elucidate the reaction mechanism of sodium fluoride (NaF), which is added to tooth-bleaching agents to lessen the adverse effect of hydrogen peroxide (H2O2) on teeth. Both hydroxyapatite (HAP) and dihydrated dicalcium phosphate (DCPD), model substances for dental hard tissues, dissolved easily in a simple H2O2 solution. In the H2O2/NaF solutions, however, fluorine compounds that could not be identified by X-ray diffraction (XRD) due to the smallness of the products were formed on the surface of the HAP. X-ray photoelectron spectroscopy (XPS) studies demonstrated that fluoridated hydroxyapatite (FHAP) was formed on HAP, and that calcium fluoride (CaF2) formation was accelerated by increasing the concentrations of fluorine and H2O2 along with the partial dissolution of HAP. In H2O2/NaF solution, DCPD also transformed easily to FHAP and CaF2, which are favorable to the remineralization process on the tooth surface. Thus, the mechanism of NaF was elucidated, and its use together with H2O2 for tooth bleaching was proved to be effective. Methodologically, the XPS two-dimensional plot made it possible for the first time to directly estimate the ratio of FHAP and CaF2 in the reaction products, in contrast to the conventional wet-analytical method, which is simply based on the difference in solubility of the two components. PMID:15868064

Tanizawa, Y

2005-01-01

381

A transferable representation of the induced multipoles in ionic crystals  

NASA Astrophysics Data System (ADS)

Electronic structure calculations of the induced dipole and quadrupole moments on a fluoride ion at low symmetry sites in a model crystalline environments are described. The results are used to characterize the short range contributions to the induced multipoles on the F- ion that arise from overlap between the wavefunctions of the ions. These are represented by general functions of the positions of the surrounding ions, suitable for use in a computationally tractable simulation model. The present calculations are designed to test the transferability to other classes of materials of this representation which, to date, largely has been deduced from calculations on distorted alkali halide crystals. First, the induced multipoles in mixed crystals of the alkali halides are considered, in order to check that they are predicted reliably by combining the representations deduced for the corresponding pure materials. Second, polarization effects in the alkaline earth fluorides MgF2 and CaF2 in a locally distorted fluorite crystal structure are examined. It is found that the material-specific parameters in the representation are related through simple functions of the ionic radii. This relationship holds between MgF2 and CaF2 in the fluorite structure, but also extends to the alkali fluorides previously studied. In order to illustrate the significance of polarization effects, the polarization model for CaF2 is combined with an ab initio pair potential for the repulsion and dispersion interactions and used in a molecular dynamics simulation. Inclusion of the polarization term improves greatly the calculated phonon frequencies in the crystal.

Domene, Carmen; Fowler, Patrick W.; Wilson, Mark; Madden, Paul A.

2002-12-01

382

A method for the design of two-layer antireflection coatings with stable properties  

NASA Astrophysics Data System (ADS)

A computer program has been written in FORTRAN for calculating optimum values of the refraction index of the layers of two-layer antireflection coatings. The program makes it possible to design antireflection coatings in such a way as to minimize residual reflection at a given wavelength and optimize the stability of the optical characteristics of the coating with respect to inaccuracies in fabrication. The efficiency of the algorithm is demonstrated by calculating the optical characteristics of an antireflection coating on a CaF2 substrate.

Firtsak, Iu. Iu.; Smaga, I. V.; Gleba, A. Iu.; Dovgoshei, N. I.; Migolinets, I. M.; Kurochkina, T. N.

383

Thermal transformation of quaternary compounds in NaF-CaF 2-AlF 3 system  

NASA Astrophysics Data System (ADS)

Details of quaternary compounds formation in the system NaF-CaF 2-AlF 3 are specified. To achieve this aim, the samples of phases NaCaAlF 6 and Na 2Ca 3Al 2F 14 have been obtained by high-temperature solid-phase synthesis. Their thermal behavior when heated up to 800 °C has been studied using the methods of high-temperature X-ray diffraction (XRD) and thermal analysis (TA). The system under consideration can be regarded as a quasibinary section CaF 2-NaAlF 4, where at T=745-750 °C invariant equilibrium is implemented with the phases CaF 2-NaCaAlF 6-Na 2Ca 3Al 2F 14-(liquid melt)-(NaAlF 4). The peculiarity of the equilibrium is NaAlF 4 metastability at normal pressure. Below the equilibrium temperature the quaternary phase Na 2Ca 3Al 2F 14 is stable and NaCaAlF 6 above this temperature. The phase NaCaAlF 6 fixed by rapid quenching from high temperatures and when heated up to 640 °C decomposes, yielding Na 2Ca 3Al 2F 14. Further heating in vacuum at temperature up to 740 °C results in decomposition of Na 2Ca 3Al 2F 14 into CaF 2 and Na 3AlF 6. The expected reverse transformation of Na 2Ca 3Al 2F 14 into NaCaAlF 6 has not been observed under experimental conditions. Transformations in bulk samples reveal direct and reverse transformation of quaternary phases. SynopsisThermal transformation of the quaternary compounds in system (NaF-CaF 2-AlF 3) was investigated using high-temperature X-ray diffraction (XRD) and thermal analysis (TA). In the system the invariant equilibrium is implemented with the phases CaF 2-NaCaAlF 6-Na 2Ca 3Al 2F 14-(liquid melt)-(NaAlF 4) at T=745-750 °C.

Zaitseva, Julia N.; Yakimov, Igor S.; Kirik, Sergei D.

2009-08-01

384

A multistep avalanche chamber with charge-division read-out as a single-photon detector for ring imaging cherenkov counters  

NASA Astrophysics Data System (ADS)

The multiwire proportional chamber is of the multistep type and has 100 mm long stainless-steel anode wires with a pitch of 2 mm. The detector has a CaF 2 window and was filled with an argon-triethylamine gas mixture. A specific detector response of N0=37.9 cm -1 was obtained using 1 m of argon gas as radiator. The resolution of the Cherenkov ring radius was measured to be ?R-=2.3 mm, which implies a Cherenkov angular resolution of ??c / ?c=10.3%. The photon position resolution along the signal wire was found to be ?y?2.3%.

Dulinski, W.; Ekelöf, T.

1983-11-01

385

Analysis of multiple pulse NMR in solids  

NASA Technical Reports Server (NTRS)

The general problems associated with the removal of the effects of dipolar broadening from solid-state NMR spectra are analyzed. The effects of finite pulse width and H sub 1 inhomogeneity are shown to have limited the resolution of previous pulse cycles, and a new eight-pulse cycle designed to minimize these problems is discussed. Spectra for F-19 in CaF2 taken with this cycle are presented which show residual linewidth near 10 Hz. The feasibility of measuring proton chemical shift tensors is discussed.

Rhim, W.-K.; Elleman, D. D.; Vaughan, R. W.

1973-01-01

386

Demonstration of mid-infrared waveguide photonic crystal cavities.  

PubMed

We have demonstrated what we believe to be the first waveguide photonic crystal cavity operating in the mid-infrared. The devices were fabricated from Ge23Sb7S70 chalcogenide glass (ChG) on CaF2 substrates by combing photolithographic patterning and focused ion beam milling. The waveguide-coupled cavities were characterized using a fiber end fire coupling method at 5.2 ?m wavelength, and a loaded quality factor of ~2000 was measured near the critical coupling regime. PMID:23903140

Lin, Hongtao; Li, Lan; Deng, Fei; Ni, Chaoying; Danto, Sylvain; Musgraves, J David; Richardson, Kathleen; Hu, Juejun

2013-08-01

387

Watt-level tunable deep ultraviolet light source by a KBBF prism-coupled device.  

PubMed

We have obtained an average output power as much as 1.2 W at 200 nm by using a 2.71-mm thick KBe2BO3F2 crystal optically contacted by CaF2 and SiO2 prisms on the both sides. Watt-level average-power was generated tunably in the deep ultraviolet region from 185 nm to 200 nm. The average power is the highest, to our knowledge, ever obtained by nonlinear crystals in the wavelength region below 200 nm. PMID:19434203

Kanai, Teruto; Wang, Xiaoyan; Adachi, Shunsuke; Watanabe, Shuntaro; Chen, Chuangtian

2009-05-11

388

Anti-washout carboxymethyl chitosan modified tricalcium silicate bone cement: preparation, mechanical properties and in vitro bioactivity  

Microsoft Academic Search

Anti-washout CaF2 stabilized C3S (F-C3S) bone cement was prepared by adding water-soluble carboxymethyl chitosan (CMCS) to the hydration liquid. The setting time,\\u000a compressive strength and in vitro bioactivity of the CMCS modified F-C3S (CMCS–C3S) pastes were evaluated. The results indicate that CMCS–C3S pastes could be stable in the shaking simulated body fluid (SBF) after immediately mixed. The addition of CMCS

Qing LinXianghui LanYanbao Li; Xianghui Lan; Yanbao Li; Yinhui Yu; Yaru Ni; Chunhua Lu; Zhongzi Xu

2010-01-01

389

Laser-Induced Damage of Calcium Fluoride  

SciTech Connect

As advances continue to be made in laser technology there is an increasing demand for materials that have high thresholds for laser-induced damage. Laser damage occurs when light is absorbed, creating defects in the crystal lattice. These defects can lead to the emission of atoms, ions and molecules from the sample. One specific field where laser damage is of serious concern is semiconductor lithography, which is beginning to use light at a wavelength of 157 nm. CaF2 is a candidate material for use in this new generation of lithography. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanisms for laser damage and the factors that serve to enhance it. In this research, we study various aspects of laser interactions with CaF2, including impurity absorbance and various forms of damage caused by incident laser light. Ultraviolet (UV) laser light at 266 nm with both femtosecond (fs) and nanosecond (ns) pulse widths is used to induce ion and neutral particle emission from cleaved samples of CaF2. The resulting mass spectra show significant differences suggesting that different mechanisms for desorption occur following excitation using the different pulse durations. Following irradiation by ns pulses at 266 nm, multiple single-photon absorption from defect states is likely responsible for ion emission whereas the fs case is driven by a multi-photon absorption process. This idea is further supported by the measurements made of the transmission and reflection of fs laser pulses at 266 nm, the results of which reveal a non-linear absorption process in effect at high incident intensities. In addition, the kinetic energy profiles of desorbed Ca and K contaminant atoms are different indicating that a different mechanism is responsible for their emission as well. Overall, these results show that purity plays a key role in the desorption of atoms from CaF2 when using ns pulses. On the other hand, once the irradiance reaches high levels, like that of the fs case, significant desorption is possible due to multi-photon absorption by the intrinsic material.

Espana, A.; Joly, A.G.; Hess, W.P.; Dickinson, J.T.

2004-01-01

390

Magnetic properties of neptunium and plutonium hydrides  

Microsoft Academic Search

The magnetic susceptibility and magnetization of NpHx and PuHx (2.0<=x<=3.0) compounds have been measured between 4 and 700 K. The susceptibility of the NpHx compounds is weakly temperature dependent and a crystal-field calculation based on the 5f4(Np3+) ground-state configuration was in reasonable agreement with the experimental results for the dihydride (cubic CaF2-type structure). The cubic plutonium dihydride has a susceptibility

A. T. Aldred; G. Cinader; D. J. Lam; L. W. Weber

1979-01-01

391

Microstructure and mechanical properties of hot-pressed Al 2O 3\\/TiC ceramic composites with the additions of solid lubricants  

Microsoft Academic Search

Al2O3\\/TiC ceramic composites with the additions of different solid lubricants such as MoS2, BN, and CaF2 were produced by hot pressing. Effect of the solid lubricants on the microstructure and mechanical properties of this ceramic composite has been studied. No trace of MoS2 was found in the sintered Al2O3\\/TiC\\/MoS2 composite owing to its low melting point and escaping during the

Jianxin Deng; Tongkun Can; Junlong Sun

2005-01-01

392

Radio frequency sputter deposition and properties of calcium fluoride thin films  

NASA Astrophysics Data System (ADS)

Calcium fluoride thin films have been deposited on various substrates by radio frequency sputtering of a hot-pressed CaF2 target in a pure argon plasma using load-locked sputtering equipment. The sputtering power was less than 100 W to avoid crack formation and fracture of the target. As a result, the maximum deposition rate of films was only 2.1 nm/min. The films analyzed by Rutherford backscattering spectroscopy (RBS) were found to be fluorine deficient; depending on the deposition conditions, the content of oxygen atoms incorporated in the films can be as low as the RBS detection limit of 2 at. %. The crystallographic structure of the deposited material was identified to be a CaF2 fluorite phase by x-ray diffraction technique; this phase was preferentially oriented in the (111) direction for films of 0.4-0.5 ?m in thickness. This preferred orientation vanished with increasing film thickness. Films of 2.5 ?m in thickness were slightly (110) oriented. The sputter-deposited CaFx films (with x?1.85) exhibited compressive residual stresses. The apparent Knoop hardness of the films deposited on silicon substrates (harder than CaF2) and measured under a load of 10 and 20 g was about 3500 MPa, i.e., twice the hardness of the bulk CaF2 compound. The surface and cross-section morphology of CaFx films was examined by scanning electron microscopy. These films were resistant to oxidation in air at 500 °C. Tribological characteristics of CaFx films sputter-deposited on cobalt-based alloy disks were determined by pin-on-disk tests. The friction coefficient and wear resistance of these films sliding against Cr-C coated pin specimens in air at 500 °C were found to be encouraging. These films are potential candidates to serve as solid lubricant films for precision components (ball bearings) operating at high temperatures in oxidizing ambient.

Maréchal, N.; Quesnel, E.; Juliet, P.; Pauleau, Y.

1993-10-01

393

Spatially localized measurement of thermal conductivity using a hybrid photothermal technique  

SciTech Connect

A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k=(e2/D)1/2. To generalize this approach, sensitivity analysis was conducted for materials having a range of thermal conductivities. Experimental validation was sought using two substrate materials, SiO2 and CaF2, both coated with thin titanium films. The measured conductivities compare favorably with literature values.

David H Hurley; Marat Khafizov; Zilong Hua; Rory Kennedy; Heng Ban

2012-05-01

394

Passivation of the 157-nm pellicle with nanometer thin films  

NASA Astrophysics Data System (ADS)

The polymeric 157 nm pellicle was passivated on both sides to isolate it from environmental contamination. TAF pellicles were sputter deposited with 5 nm thick films of CaF2, MgF2, Al, Mg, TiN, SiNx, Si, and PTFE, separately. The light transmission and life expectancy of the coated and uncoated pellicles were investigated. The coated pellicles were also analyzed with ESCA for surface structure changes. The coating process changed the pellicle's deterioration mechanism and life expectancy.

Kuo, Yue; Lu, Jiang; Tewg, Jun-Yen; Zimmerman, Paul A.

2003-12-01

395

Characteristics of 355 nm Laser Damage in Bulk Materials  

NASA Astrophysics Data System (ADS)

The laser damage resistances of four crystals (CaF2, MgF2, Al2O3, and SiO2) and fused silica (JGS1) irradiated at 355 nm (8 ns, 300-on-1) are reported. The laser-induced damage threshold is measured using a tripled Nd:YAG laser system. The results obtained from the pure crystals are in accordance with their specific optical, mechanical, and thermal properties. An empirical law based on the Franz—Keldysh effect can interpret the experimental results.

Yu, Zhen-Kun; He, Hong-Bo; Qi, Hong-Ji; Fang, Zhou; Li, Da-Wei

2013-06-01

396

Intergranular fracture of lithium fluoride-22 percent calcium fluoride hypereutectic salt at 800 K  

NASA Technical Reports Server (NTRS)

Substantial strain-hardening was noted during the initial stages of deformation in constant-velocity compression tests conducted on as-cast samples of the LiF-22 mol pct CaF2 hypereutectic salt at 800 K. The deformed specimens exhibited extensive grain-boundary cracking and cavitation, suggesting that such cracking, in conjunction with interfacial sliding, is important for cavity nucleation at grain boundaries and at the LiF-CaF2 interfaces. Cavity growth and interlinkage occur through the preferential failure of the weaker LiF phase.

Raj, Subramanium V.; Whittenberger, J. Daniel

1990-01-01

397

Spatially localized measurement of thermal conductivity using a hybrid photothermal technique  

NASA Astrophysics Data System (ADS)

A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k = (e2/D)1/2. To generalize this approach, sensitivity analysis is conducted for materials having a range of thermal conductivities. Application to nuclear fuel is consider by performing experimental validation using two materials (CaF2 and SiO2) having thermal properties representative of fresh and high burnup nuclear fuel. The measured conductivities compare favorably with literature values.

Hua, Zilong; Ban, Heng; Khafizov, Marat; Schley, Robert; Kennedy, Rory; Hurley, David H.

2012-05-01

398

Atomic force microscope studies of fullerene films - Highly stable C60 fcc (311) free surfaces  

NASA Technical Reports Server (NTRS)

Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.

Snyder, Eric J.; Tong, William M.; Williams, R. S.; Anz, Samir J.; Anderson, Mark S.

1991-01-01

399

Generation of ultrashort 90 µJ deep-ultraviolet pulses by dual broadband frequency doubling with ?-BaB2O4 crystals at 1 kHz  

NASA Astrophysics Data System (ADS)

Fourth-harmonic pulses of a 1 kHz chirped-pulse amplification (CPA) Ti:sapphire laser have been generated by a scheme of dual broadband frequency doubling with two ?-BaB2O4 (BBO) crystals. The pulse energy was 90 µJ with a bandwidth of 2.7 nm (full width at half maximum, FWHM) at a central wavelength of 220 nm. The pulse width was measured to be 45 fs by autocorrelation with the two-photon fluorescence of CaF2, which was much smaller than that (120 fs) obtained by conventional frequency conversion.

Zhou, Chun; Kanai, Teruto; Watanabe, Shuntaro

2015-01-01

400

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

401

Identification of salt-alloy combinations for thermal energy storage applications in advanced solar dynamic power systems  

NASA Technical Reports Server (NTRS)

Thermodynamic calculations based on the available data for flouride salt systems reveal that a number of congruently melting compositions and eutectics exist which have the potential to meet the lightweight, high energy storage requirements imposed for advanced solar dynamic systems operating between about 1000 and 1400 K. Compatibility studies to determine suitable containment alloys to be used with NaF-22CaF2-13MgF2, NaF-32CaF2, and NaF-23MgF2 have been conducted at the eutectic temperature + 25 K for each system. For these three NaF-based eutectics, none of the common, commercially available high temperature alloys appear to offer adequate corrosion resistance for a long lifetime; however mild steel, pure nickel and Nb-1Zr could prove useful. These latter materials suggest the possibility that a strong, corrosion resistant, nonrefractory, elevated temperature alloy based on the Ni-Ni3Nb system could be developed.

Whittenberger, J. D.; Misra, A. K.

1987-01-01

402

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 to 1400 K  

NASA Technical Reports Server (NTRS)

Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

Misra, Ajay K.; Whittenberger, J. Daniel

1987-01-01

403

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K  

NASA Technical Reports Server (NTRS)

Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

Misra, Ajay K.; Whittenberger, J. Daniel

1987-01-01

404

Samarium doped calcium fluoride: A red scintillator and X-ray phosphor  

NASA Astrophysics Data System (ADS)

We report the photoluminescence, X-ray luminescence and scintillation properties of CaF2:Sm2+. Large single crystals of CaF2:Sm2+ were grown by simply slow cooling of the calcium fluorite melt doped with samarium metal. The photoluminescence at room temperature shows a broad red 5d?4f emission band peaked at 725 nm which is well matched to the response of silicon photodetectors, and only a very weak Sm3+ emission is observed. On cooling, the zero phonon lines of the Sm2+ emission can be observed. The lifetime of the broad emission is short at room temperature (46 ns), but temperature dependent, and slows on cooling, reaching a constant value of 1.25 ?s below 180 K. The X-ray luminescence comprises both red Sm2+ and Sm3+ emissions and a blue self-trapped exciton band for low Sm concentrations, but just the broad red emission Sm2+ for highly doped (~1%) samples. The scintillation decay at room temperature shows two components, of 58 ns and 870 ns, in an integrated intensity ratio of 0.7:1 for a 0.1% Sm sample. The light output is around 15,000 photons/MeV when cooled by dry ice, with a scintillation decay time of 1.4 ?s at that temperature. The performance of the material as an X-ray phosphor and scintillator is discussed.

Dixie, Laura Catherine; Edgar, Andrew; Bartle, Colin Murray

2014-07-01

405

High energy resolution bandpass photon detector for inverse photoemission spectroscopy.  

PubMed

We report a bandpass ultraviolet photon detector for inverse photoemission spectroscopy with energy resolution of 82 ± 2 meV. The detector (Sr(0.7)Ca(0.3)F(2)/acetone) consists of Sr(0.7)Ca(0.3)F(2) entrance window with energy transmission cutoff of 9.85 eV and acetone as detection gas with 9.7 eV photoionization threshold. The response function of the detector, measured using synchrotron radiation, has a nearly Gaussian shape. The n = 1 image potential state of Cu(100) and the Fermi edge of silver have been measured to demonstrate the improvement in resolution compared to the CaF(2)/acetone detector. To show the advantage of improved resolution of the Sr(0.7)Ca(0.3)F(2)/acetone detector, the metal to semiconductor transition in Sn has been studied. The pseudogap in the semiconducting phase of Sn could be identified, which is not possible with the CaF(2)/acetone detector because of its worse resolution. PMID:21974594

Maniraj, M; D'Souza, S W; Nayak, J; Rai, Abhishek; Singh, Sanjay; Sekhar, B N Raja; Barman, S R

2011-09-01

406

High energy resolution bandpass photon detector for inverse photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

We report a bandpass ultraviolet photon detector for inverse photoemission spectroscopy with energy resolution of 82 ± 2 meV. The detector (Sr0.7Ca0.3F2/acetone) consists of Sr0.7Ca0.3F2 entrance window with energy transmission cutoff of 9.85 eV and acetone as detection gas with 9.7 eV photoionization threshold. The response function of the detector, measured using synchrotron radiation, has a nearly Gaussian shape. The n = 1 image potential state of Cu(100) and the Fermi edge of silver have been measured to demonstrate the improvement in resolution compared to the CaF2/acetone detector. To show the advantage of improved resolution of the Sr0.7Ca0.3F2/acetone detector, the metal to semiconductor transition in Sn has been studied. The pseudogap in the semiconducting phase of Sn could be identified, which is not possible with the CaF2/acetone detector because of its worse resolution.

Maniraj, M.; D'Souza, S. W.; Nayak, J.; Rai, Abhishek; Singh, Sanjay; Sekhar, B. N. Raja; Barman, S. R.

2011-09-01

407

TL detectors for gamma ray dose measurements in criticality accidents.  

PubMed

Determination of gamma ray dose in mixed neutron+gamma ray fields is still a demanding task. Dosemeters used for gamma ray dosimetry are usually in some extent sensitive to neutrons and their response variations depend on neutron energy i.e., on neutron spectra. Besides, it is necessary to take into account the energy dependence of dosemeter responses to gamma rays. In this work, several types of thermoluminescent detectors (TLD) placed in different holders used for gamma ray dose determination in the mixed fields were examined. Dosemeters were from three different institutions: Ruder Boskovi? Institute (RBI), Croatia, JoZef Stefan Institute (JSI), Slovenia and Autoridad Regulatoria Nuclear (ARN), Argentina. All dosemeters were irradiated during the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002. Three accidental scenarios were reproduced and in each irradiation the dosemeters were exposed placed on the front of phantom and 'free in air'. Following types of TLDs were used: 7LiF (TLD-700), CaF2:Mn and Al2O3:Mg,Y-all from RBI; CaF2:Mn from JSI and 7LiF (TLD-700) from ARN. Reported doses were compared with the reference values as well as with the values obtained from the results of all participants. The results show satisfactory agreement with other dosimetry systems used in the Intercomparison. The influence of different types of holders and applied corrections of dosemeters' readings are discussed. PMID:17369267

Miljani?, Saveta; Zorko, Benjamin; Gregori, Beatriz; Knezevi?, Zeljka

2007-01-01

408

Syntheses, structural characterization, and DPPH radical scavenging activity of cocrystals of caffeine with 1- and 2-naphthoxyacetic acids  

NASA Astrophysics Data System (ADS)

Caffeine:1-naphthoxyacetic acid [(caf)(1-naa)] and caffeine:2-naphthoxyacetic acid [(caf)(2-naa)] cocrystals have been synthesized and single crystals were grown by slow evaporation technique. The structures of the grown crystals were elucidated using single crystal X-ray diffraction analysis. Both the cocrystals belong to the monoclinic crystallographic system with space group P21/c, Z = 4, and ? = ? = 90°, whereas ? = 111.4244(18)° for [(caf)(1-naa)] and ? = 109.281(6)° for [(caf)(2-naa)]. The crystal packing is predominantly stabilized by hydrogen bonding and ?-? stacking interactions. The presence of unionized -COOH functional group in both the cocrystals was identified by FTIR spectral analysis. Thermal behavior and stability of both the cocrystals were studied by TGA/DTA analyses. Solvent-free formation of these cocrystals was confirmed by powder X-ray diffraction analyses. The theoretical energy of cocrystals showed that the formers have higher energy than cocrystals 1 and 2. DPPH radical scavenging activity of cocrystals 1 and 2 is slightly greater than the formers.

Suresh Kumar, G. S.; Seethalakshmi, P. G.; Sumathi, D.; Bhuvanesh, N.; Kumaresan, S.

2013-03-01

409

Efficient burst mode amplifier for ultra-short pulses based on cryogenically cooled Yb³?:CaF?.  

PubMed

We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms are be generated and amplified. They contain 50 to 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps prior to amplification. The amplifier stage is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled up to 915 mJ using a longer pump duration. This corresponds to an efficiency as high as 25% of extracted energy from absorbed pump energy. This is the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier. PMID:24514416

Körner, Jörg; Hein, Joachim; Liebetrau, Hartmut; Seifert, Reinhard; Klöpfel, Diethard; Kahle, Martin; Loeser, Markus; Siebold, Mathias; Schramm, Ulrich; Kaluza, Malte C

2013-11-18

410

Mode-locking operation of quasi-continuous diode pumped TGT-grown Nd,Y-codoped:SrF2 crystal  

NASA Astrophysics Data System (ADS)

Fluoride-type crystals (CaF2, SrF2) doped with neodymium Nd3+ present interesting alternative as a laser active media for the diode-pumped mode-locked laser systems mainly because of their broad emission spectra as well as longer fluorescence lifetime in comparison with well-known materials as Nd:YAG or Nd:YVO4. In comparison with Nd:glass active material, SrF2 and CaF2 have better thermal conductivity. In spite of the thermal conductivity decreases with doping concentration, these crystal might be interesting alternative for the Nd:glass mode-locked laser systems. In this contribution we present the first results of the Nd,Y:SrF2 mode-locked laser diode-pumped at 796nm. Mode-locking operation using SESAM was successfully achieved in the pulsed pumping regime (pulse-duration 1.5 ms, frequency 10 Hz) with the overall average output power of 2.3 mW (corresponding to the power amplitude of 153 mW) in one output beam at the wavelength of ~1055 nm. The actual pulse-duration was 87 ps.

Jelínek, Michal; Kube?ek, Václav; Su, Liangbi; Jiang, Dapeng; Ma, Fengkai; Zhang, Qian; Cao, Yuexin; Xu, Jun

2015-01-01

411

Ellipsometric and optical study of some uncommon insulator films on 3-5 semiconductors  

NASA Technical Reports Server (NTRS)

Optical properties of three types of insulating films that show promise in potential applications in the 3-4 semiconductor technology were evaluated, namely a-C:H, BN and CaF2. The plasma deposited a-C:H shows an amorphous behavior with optical energy gaps of approximately 2 to 2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement, and give a fine-tuned positive confirmation to an existing conjecture on the nature of a-C:H films (1). Ion beam deposited BN films show amorphous behavior with energy gap of 5 eV. These films are nonstoichiometric (B/N approximately 2) and have refractive index, density and/or hardness which are dependent on the deposition conditions. The epitaxially grown CaF2 on GaAs films have optical parameters equal to bulk, but evidence of damage was found in the GaAs at the interface.

Alterovitz, S. A.; Warner, J. D.; Liu, D. C.; Pouch, J. J.

1985-01-01

412

Effect of substrate choice and tissue type on tissue preparation for spectral histopathology by Raman microspectroscopy.  

PubMed

Raman spectroscopy is a non-destructive, non-invasive, rapid and economical technique which has the potential to be an excellent method for the diagnosis of cancer and understanding disease progression through retrospective studies of archived tissue samples. Historically, biobanks are generally comprised of formalin fixed paraffin preserved tissue and as a result these specimens are often used in spectroscopic research. Tissue in this state has to be dewaxed prior to Raman analysis to reduce paraffin contributions in the spectra. However, although the procedures are derived from histopathological clinical practice, the efficacy of the dewaxing procedures that are currently employed is questionable. Ineffective removal of paraffin results in corruption of the spectra and previous experiments have shown that the efficacy can depend on the dewaxing medium and processing time. The aim of this study was to investigate the influence of commonly used spectroscopic substrates (CaF2, Spectrosil quartz and low-E slides) and the influence of different histological tissue types (normal, cancerous and metastatic) on tissue preparation and to assess their use for spectral histopathology. Results show that CaF2 followed by Spectrosil contribute the least to the spectral background. However, both substrates retain paraffin after dewaxing. Low-E substrates, which exhibit the most intense spectral background, do not retain wax and resulting spectra are not affected by paraffin peaks. We also show a disparity in paraffin retention depending upon the histological identity of the tissue with abnormal tissue retaining more paraffin than normal. PMID:24308030

Fullwood, Leanne M; Griffiths, Dave; Ashton, Katherine; Dawson, Timothy; Lea, Robert W; Davis, Charles; Bonnier, Franck; Byrne, Hugh J; Baker, Matthew J

2014-01-21

413

Tribological properties of alumina-boria-silicate fabric from 25 to 850 C  

NASA Technical Reports Server (NTRS)

Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

Dellacorte, Christopher

1988-01-01

414

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.  

PubMed

In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright ?111? streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

2013-08-01

415

Some studies on a solid-state sulfur probe for coal gasification systems  

NASA Technical Reports Server (NTRS)

As a part of a program for the development of a sulfur probe for monitoring the sulfur potential in coal gasification reactors, an investigation was conducted regarding the efficiency of the solid electrolyte cell Ar+H2+H2S/CaS+CaF2+(Pt)//CaF2//Pt)+CaF2+CaS/H2S+H2+Ar. A demonstration is provided of the theory, design, and operation of a solid-state sulfur probe based on CaF2 electrolyte. It was found that the cell responds to changes in sulfur potential in a manner predicted by the Nernst equation. The response time of the cell at 1225 K, after a small change in temperature or gas composition, was 2.5 Hr, while at a lower temperature of 990 K the response time was approximately 9 hr. The cell emf was insensitive to a moderate increase in the flow rate of the test gas and/or the reference gas. The exact factors affecting the slow response time of galvanic cells based on a CaF2 electrolyte have not yet been determined. The rate-limiting steps may be either the kinetics of electrode reactions or the rate of transport through the electrolyte.

Jacob, K. T.; Rao, D. B.; Nelson, H. G.

1978-01-01

416

Identification of salt-alloy combinations for thermal energy storage applications in advanced solar dynamic power systems  

NASA Astrophysics Data System (ADS)

Thermodynamic calculations based on the available data for flouride salt systems reveal that a number of congruently melting compositions and eutectics exist which have the potential to meet the lightweight, high energy storage requirements imposed for advanced solar dynamic systems operating between about 1000 and 1400 K. Compatibility studies to determine suitable containment alloys to be used with NaF-22CaF2-13MgF2, NaF-32CaF2, and NaF-23MgF2 have been conducted at the eutectic temperature + 25 K for each system. For these three NaF-based eutectics, none of the common, commercially available high temperature alloys appear to offer adequate corrosion resistance for a long lifetime; however mild steel, pure nickel and Nb-1Zr could prove useful. These latter materials suggest the possibility that a strong, corrosion resistant, nonrefractory, elevated temperature alloy based on the Ni-Ni3Nb system could be developed.

Whittenberger, J. D.; Misra, A. K.

417

The effects of high ambient radon on thermoluminescence dosimetry readings.  

PubMed

The effect of a high level of ambient (222)Rn gas on thermoluminescence dosemeters (TLDs) is examined. Groups of LiF:Mg,Ti and CaF(2):Dy TLDs were exposed to (222)Rn under controlled environmental conditions over ?7 d using a luminous (226)Ra aircraft dial. LiF:Mg,Ti TLDs were tested bare, and both types were tested mounted in cards used for environmental dosimetry and mounted in cards enclosed in plastic badges. A passive continuous radon monitor was used to measure the (222)Rn level in the small chamber during the experiments. The data were analysed to determine the relationship between the integrated (222)Rn level and the TLD response. Although both LiF:Mg,Ti and CaF(2):Dy TLDs showed a strong response to (222)Rn, the badges prevented measurable radon detection by the TLDs within. The TLDs were not used to directly measure the radon concentration; rather, a correction for its influence was desired. PMID:21177272

Harvey, John A; Kearfott, Kimberlee J

2011-11-01

418

Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach  

NASA Astrophysics Data System (ADS)

We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 ?m carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.

Chiarello, Gian Luca; Nachtegaal, Maarten; Marchionni, Valentina; Quaroni, Luca; Ferri, Davide

2014-07-01

419

Rational design and optimization of plasmonic nanoarrays for surface enhanced infrared spectroscopy  

PubMed Central

We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general framework that allows for the numerical optimization of metamaterial sensor designs in order to maximize the absorbance signal. A critical feature of our method is the explicit compensation for the perturbative effects of the analyte's refractive index which alters the resonance frequency and line-shape of the metamaterial response, thereby leading to spectral distortion in SEIRA signatures. As an example, we leverage our method to optimize the geometry of periodic arrays of plasmonic nanoparticles on both Si and CaF2 substrates. The optimal geometries result in a three-order of magnitude absorbance enhancement compared to an unstructured Au layer, with the CaF2 substrate offering an additional factor of three enhancement in absorbance over a traditional Si substrate. The latter improvement arises from increase of near-field intensity over the Au nanobar surface for the lower index substrate. Finally, we perform sensitivity analysis for our optimized arrays to predict the effects of fabrication imperfections. We find that <20% deviation from the optimized absorbance response is readily achievable over large areas with modern nanofabrication techniques. PMID:22714181

Liberman, Vladimir; Adato, Ronen; Jeys, Thomas H.; Saar, Brian G.; Erramilli, Shyamsunder; Altug, Hatice

2012-01-01

420

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

421

Fluorite solubility equilibria in selected geothermal waters  

USGS Publications Warehouse

Calculation of chemical equilibria in 351 hot springs and surface waters from selected geothermal areas in the western United States indicate that the solubility of the mineral fluorite, CaF2, provides an equilibrium control on dissolved fluoride activity. Waters that are undersaturated have undergone dilution by non-thermal waters as shown by decreased conductivity and temperature values, and only 2% of the samples are supersaturated by more than the expected error. Calculations also demonstrate that simultaneous chemical equilibria between the thermal waters and calcite as well as fluorite minerals exist under a variety of conditions. Testing for fluorite solubility required a critical review of the thermodynamic data for fluorite. By applying multiple regression of a mathematical model to selected published data we have obtained revised estimates of the pK (10,96), ??Gof (-280.08 kcal/mole), ??Hof (-292.59 kcal/mole), S?? (16.39 cal/deg/mole) and CoP (16.16 cal/deg/mole) for CaF2 at 25??C and 1 atm. Association constants and reaction enthalpies for fluoride complexes with boron, calcium and iron are included in this review. The excellent agreement between the computer-based activity products and the revised pK suggests that the chemistry of geothermal waters may also be a guide to evaluating mineral solubility data where major discrepancies are evident. ?? 1977.

Nordstrom, D.K.; Jenne, E.A.

1977-01-01

422

Resistance Switching Memory Characteristics of Si/CaF2/CdF2 Quantum-Well Structures Grown on Metal (CoSi2) Layer  

NASA Astrophysics Data System (ADS)

A novel scheme of resistance switching random access memory (ReRAM) devices fabricated using Si/CaF2/CdF2/CaF2/Si quantum-well structures grown on metal CoSi2 layer formed on a Si substrate has been proposed, and embryonic write/erase memory operation has been demonstrated at room temperature. It has been found that the oxide-mediated epitaxy (OME) technique for forming the CoSi2 layer on Si dramatically improves the stability and reproducibility of the current-voltage (I-V) curve. This technology involves 10-nm-thick Co layer deposition on a protective oxide prepared by boiling in a peroxide-based solution followed by annealing at 550 °C for 30 min for silicidation in ultrahigh vacuum. A switching voltage of lower than 1 V, a peak current density of 32 kA/cm2, and an ON/OFF ratio of 10 have been observed for the sample with the thickness sequence of 0.9/0.9/2.5/0.9/5.0 nm for the respective layers in the Si/CaF2/CdF2/CaF2/Si structure. Results of surface morphology analysis suggest that the grain size of crystal islands with flat surfaces strongly affects the quality of device characteristics.

Denda, Junya; Uryu, Kazuya; Watanabe, Masahiro

2013-04-01

423

High critical currents and flux creep effects in e-gun deposited epitaxially 00L oriented superconducting YBa2Cu3O7-? films  

NASA Astrophysics Data System (ADS)

Thin films of YBa2Cu3O7-? have been made by codeposition of Cu, Y and BaF2 in a UHV system. Annealing in humid oxygen at 835 °C produces high quality single phase preferentially c oriented films. In 1000 Å thin films the transport current density is larger than 106 A/cm2 at 86 K. Even 500 Å films prove to be superconducting above 77 K. Extrapolation to zero field of the magnetization data obtained from torque experiments are consistent with the current transport data. This indicates that the sample is homogeneous and the critical state model can be applied. Both magnetic relaxation measurements and flux creep resistivity in a magnetic field indicate the importance of thermally activated processes.

Dam, B.; Stollman, G. M.; Berghuis, P.; Guo, S. Q.; Flipse, C. F. J.; Lensink, J. G.; Griessen, R. P.

1989-02-01

424

YBa2Cu3O7-? superconducting films prepared by low pressure post-annealing  

NASA Astrophysics Data System (ADS)

YBa2Cu3O7-? precursor films are deposited on 2? LaAlO3 wafer by the co-evaporation technique using Y, BaF2 and Cu as evaporation sources. After deposition, the films are annealed at low-pressure atmosphere with the composition of oxygen and water vapour. Compared with the normal pressure annealing, it is shown that low pressure can greatly improve the superconducting properties of 2? YBCO films with thickness larger than 500 nm, as the microcrack on films surface becomes unobservable the microwave surface resistance is greatly reduced. Furthermore, it is also revealed that the optimal processing window for making high quality superconducting YBCO films through ex-situ process is relatively small, therefore the ambient in annealing furnace is crucial important and should be precisely controlled.

Wang, Lianhong; Liu, Chong; Fan, Jing

2014-12-01

425

Mechanochemical preparation of nanocrystalline BaFCl doped with samarium in the 2+ oxidation state.  

PubMed

We report a facile mechanochemical preparation method for nanocrystalline BaFCl doped with samarium in the 2+ oxidation state by ball milling BaCl2, BaF2, and SmI2 under a nitrogen atmosphere. The resulting phosphors were characterized by powder X-ray diffraction; electron microscopy, X-ray photoelectron spectroscopy; and photoluminescence, photoexcitation, cathodoluminescence, and diffuse reflectance spectroscopy. This is the first report of a direct preparation method of Sm(2+) doped alkaline earth fluorohalides at room temperature and points to a significant potential for the preparation of a wide range of related X-ray storage phosphors containing rare earth ions in divalent and trivalent cationic states by mechanochemical methods. PMID:25113662

Wang, Xiang-lei; Liu, Zhi-qiang; Stevens-Kalceff, Marion A; Riesen, Hans

2014-09-01

426

Annihilation Radiation Gauge for Relative Density and Multiphase Fluid Monitoring  

NASA Astrophysics Data System (ADS)

The knowledge of the multi-phase flow parameters are important for the petroleum industry, specifically during the transport in pipelines and network related to exploitation's wells. Crude oil flow is studied by Monte Carlo simulation and experimentally to determine transient liquid phase in a laboratory system. Relative density and fluid phase time variation is monitored employing a fast nuclear data acquisition setup that includes two large volume BaF2 scintillator detectors coupled to an electronic chain and data display in a LabView® environment. Fluid parameters are determined by the difference in count rate of coincidence pulses. The operational characteristics of the equipment indicate that 2 % deviation in the CCR corresponds to a variation, on average, of 20 % in the fraction of liquid of the multiphase fluid.

Vidal, A.; Viesti, G.; Pino, F.; Barros, H.; Sajo-Bohus, L.

2014-03-01

427

Saturation of the all-optical Kerr effect in solids.  

PubMed

We discuss the influence of the higher-order Kerr effect (HOKE) in wide bandgap solids at extreme intensities below the onset of optically induced damage. Using different theoretical models, we employ multiphoton absorption rates to compute the nonlinear refractive index by a Kramers-Kronig transform. Within this theoretical framework we provide an estimate for the appearance of significant deviations from the standard optical Kerr effect predicting a linear index change with intensity. We discuss the role of the observed saturation behavior in practically relevant situations, including Kerr lens mode-locking and supercontinuum generation in photonic crystal fibers. Furthermore, we present experimental data from a multiwave mixing experiment in BaF2, which can be explained by the appearance of the HOKE. PMID:22555731

Borchers, Bastian; Brée, Carsten; Birkholz, Simon; Demircan, Ayhan; Steinmeyer, Günter

2012-05-01

428

LaCl{sub 3}:Ce scintillator for Gamma ray detection  

SciTech Connect

In this paper, we report on a relatively new cerium doped scintillator - LaCl3 for gamma ray spectroscopy. Crystals of this scintillator have been grown using Bridgman method. This material when doped with 10 percent cerium has high light output ({approx} 50,000 photons/MeV) and fast principal decay time constant ({approx}20 ns). Furthermore, it shows excellent energy resolution for gamma ray detection. For example, energy resolution as low as 3.2 percent (FWHM) has been achieved with 662 keV photons (137Cs source) at room temperature. Also high timing resolution (264 ps - FWHM) has been recorded with LaCl3-PMT and BaF2-PMT detectors operating in coincidence using 511 keV positron annihilation gamma ray pairs. Details of crystal growth, scintillation properties, and variation of these properties with cerium concentration are also reported.

Shah, K.S.; Glodo, J.; Klugerman, M.; Cirignano, L.; Moses, W.W.; Derenzo, S.E.; Weber, M.J.

2002-05-25

429

Optoacoustic measurements of water vapor absorption at selected CO laser wavelengths in the 5-micron region  

NASA Technical Reports Server (NTRS)

Measurements of water vapor absorption were taken with a resonant optoacoustical detector (cylindrical pyrex detector, two BaF2 windows fitted into end plates at slight tilt to suppress Fabry-Perot resonances), for lack of confidence in existing spectral tabular data for the 5-7 micron region, as line shapes in the wing regions of water vapor lines are difficult to characterize. The measurements are required for air pollution studies using a CO laser, to find the differential absorption at the wavelengths in question due to atmospheric constituents other than water vapor. The design and performance of the optoacoustical detector are presented. Effects of absorption by ambient NO are considered, and the fixed-frequency discretely tunable CO laser is found suitable for monitoring urban NO concentrations in a fairly dry climate, using the water vapor absorption data obtained in the study.

Menzies, R. T.; Shumate, M. S.

1976-01-01

430

Bi(111) thin film with insulating interior but metallic surfaces.  

PubMed

The electrical conductance of epitaxial Bi thin films grown on BaF(2)(111) by molecular beam epitaxy has been systematically investigated as a function of both film thickness (4-540 nm) and temperature (5-300 K). Unlike bulk Bi as a prototypical semimetal, the Bi thin films up to 90 nm are found to be insulating in the interior but metallic on the surface. This finding not only has unambiguously resolved the long-standing controversy about the existence of the semimetal-semiconductor transition in Bi thin films but also provided a straightforward interpretation for the perplexing temperature dependence of the resistivity of Bi thin films, which in turn might have some potential applications in spintronics. PMID:23215113

Xiao, Shunhao; Wei, Dahai; Jin, Xiaofeng

2012-10-19

431

Study of the neutron rich sulfure isotope 43S through intermediate energy Coulomb excitation  

NASA Astrophysics Data System (ADS)

The reduced transition probability B(E2: 3/2- 7/2-2) has been measured in 43S using Coulomb excitation at intermediate energy. The nucleus of interest was produced by fragmentation of a 48Ca beam at GANIL. The reaction products were separated in the LISE spectrometer. After Coulomb-excitation of 43S in a 208Pb target, the ? rays emitted inflight were detected by 64 BaF2 detectors of the Ch?teau de Cristal array. The preliminary value deduced for the reduced transition probability B(E2: 3/2-7/2-2) is in agreement with the predictions of the shell model calculations and supports a prolate-spherical shape coexistence in the 43S nucleus.

Calinescu, S.; Cáceres, L.; Grévy, S.; Sohler, D.; Stanoiu, M.; Negoita, F.; Borcea, C.; Borcea, R.; Bowry, M.; Catford, W.; Dombradi, Z.; Franchoo, S.; Gillibert, R.; Thomas, J. C.; Kuti, I.; Lukyanov, S.; Lepailleur, A.; Mrazek, J.; Niikura, M.; Podolyak, Z.; Petrone, C.; Penionzhkevich, Y.; Roger, T.; Rotaru, F.; Sorlin, O.; Stefan, I.; Vajta, Z.; Wilson, E.

2013-02-01

432

High Accuracy, Absolute, Cryogenic Refractive Index Measurements of Infrared Lens Materials for JWST NIRCam using CHARMS  

NASA Technical Reports Server (NTRS)

The current refractive optical design of the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) uses three infrared materials in its lenses: LiF, BaF2, and ZnSe. In order to provide the instrument s optical designers with accurate, heretofore unavailable data for absolute refractive index based on actual cryogenic measurements, two prismatic samples of each material were measured using the cryogenic, high accuracy, refraction measuring system (CHARMS) at NASA GSFC, densely covering the temperature range from 15 to 320 K and wavelength range from 0.4 to 5.6 microns. Measurement methods are discussed and graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient for these three materials are presented along with estimates of uncertainty. Coefficients for second order polynomial fits of measured index to temperature are provided for many wavelengths to allow accurate interpolation of index to other wavelengths and temperatures.

Leviton, Douglas; Frey, Bradley

2005-01-01

433

Comparative Study of Auger-Free Luminescence and Valence-Band Photoemission in Wide-Gap Materials  

NASA Astrophysics Data System (ADS)

The line shape of Auger-free luminescence (AFL), caused by radiative recombination of holes in the outermost-core band with valence electrons, has been studied for CsCl, CsBr and BaF2 in comparison to photoelectron spectra of the valence bands. It is confirmed that the main part of AFL locates on the low-energy side of the valence-band region estimated from the maximum of the outermost-core band in the photoelectron spectra. Furthermore, its low-energy tail extends by approximately 0.5 1.0 eV below the minimum of the valence band. These results clearly indicate that the core hole induces considerable lattice distortion around itself, which is kept well during the radiative transition. The line shape of AFL is favorably explained in terms of an energy-band picture in which the lattice relaxation is taken into account in principle.

Itoh, Minoru; Kamada, Masao

2001-11-01

434

Temperature Dependence of Auger-Free Luminescence in Alkali and Alkaline-Earth Halides  

NASA Astrophysics Data System (ADS)

Auger-free luminescence (AFL) resulting from a radiative transition between theoutermost-core bands and the valence bands in BaF2, RbF, CsF, CsCl and CsBrhas been studied in a wide range of temperatures from 10 to 300 K. The AFLspectra are separated from those originating from the valence-band excitationwith use of time-resolved luminescence spectroscopy. It is found that the decayprofile of AFL in each crystal is essentially the same throughout the spectrum. The remarkable thermal broadening of the linewidth is verified for all systems. This strongly suggests that the core hole generated on a positive ion inducesconsiderable displacement of the surrounding ions within its lifetime. Based onthe present results, the spectral shape of AFL is discussed in terms of acluster model and a two-band model, requiring further development of theinvestigations in theory and experiment.

Itoh, Minoru; Kamada, Masao; Ohno, Nobuhito

1997-08-01

435

Firing condition for entire reactions of fluorides with water vapor in metalorganic deposition method using trifluoroacetate  

NASA Astrophysics Data System (ADS)

To obtain the YBa 2Cu 3O 7- x (YBCO) film on buffered metal tapes, we have to fire films below 800°C and avoid formation of BaF 2 in the films which leads to low Jc by metalorganic deposition using trifluoroacetate method. By estimating each process condition to reaction rate of fluorides with water vapor in precursor, we can established firing profile for YBCO film on buffered metal substrate at 725°C. With the profile, we can successfully obtained YBCO film on CeO 2/YSZ/hastelloy, which has critical current density ( Jc) of 1.72 MA/cm 2 (77 K, 0 T) and thickness of 1860 Å.

Araki, T.; Takahashi, Y.; Yamagiwa, K.; Iijima, Y.; Takeda, K.; Yamada, Y.; Shibata, J.; Hirayama, T.; Hirabayashi, I.

2001-08-01

436

TeV electron measurement with CREST experiment  

NASA Astrophysics Data System (ADS)

CREST, the Cosmic Ray Electron Synchrotron Telescope is a balloon-borne experiment de-signed to measure the spectrum of multi-TeV electrons by the detection of the x-ray synchrotron photons generated in the magnetic field of the Earth. Electrons in the TeV range are expected to reflect the properties of local sources because fluxes from remote locations are suppressed by radiative losses during propagation. Since CREST needs to intersect only a portion of the kilometers-long trail of photons generated by the high-energy electron, the method yields a larger effective area than the physical size of the detector, boosting detection areas. The in-strument is composed of an array of 1024 BaF2 crystals and a set of scintillating veto counters. A long duration balloon flight in Antarctica is currently planned for the 2010-11 season.

Park, Nahee; Anderson, T.; Bower, C.; Coutu, S.; Gennaro, J.; Geske, M.; Muller, D.; Musser, J.; Nutter, S.

437

Count rate performance and deadtime analysis of the new 3D PETRRA PET camera  

NASA Astrophysics Data System (ADS)

We report on the count-rate performance of the unique PETRRA positron camera at activities up to 60MBq. The camera consists of two large area detectors, each comprising a tiled array of 10mm thick BaF2 scintillation crystals interfaced to a multi-step avalanche chamber filled with 4.2mbar of pure TMAE vapor. Preliminary results demonstrate coincident count rates of over 80kcps for a cylindrical (20x20cm3) phantom with 50MBq of F-18 in the field-of-view using a 20ns coincidence time window. Each component of the readout cycle has been characterized in terms of dead-time loss. The camera's dead-time related count loss is well-described by a paralysable model with a dead-time of ~500ns. Other sources of count rate loss are also discussed.

Wells, Kevin; Kakana, Christina; Ott, Robert J.; Flower, M.; Divoli, Antigoni; Meriaux, Sebastian; Bateman, J. E.; Stephenson, R.; Duxbury, D.; Spill, E. J.

2001-12-01

438

Multiphase monitoring by annihilation radiation coincidence mode  

NASA Astrophysics Data System (ADS)

A multiphase monitoring system employing nuclear techniques is reported, which is aimed to provide a rapid - decision tool in oilfield applications. Liquid phase time variation is monitored employing two large volume BaF2 detectors. The radioisotope source of 22Na is a positron emitter, therefore two antiparallel gammas are produced per decay, and phase flow in pipes is related to the count rate of gamma pulses in coincidence providing information on transient liquid phase during transport. Oil, gas, water fraction measurements were performed at a specialized test station assembled in our laboratory to model a wide range of field operating conditions. The time dependence of the mixed substances is monitored with the two most relevant hydrodynamic parameters, the density (type of the fluid) and the flow rate, in a LabView® environment. Performance of the monitoring system; its limitations and the possibility for further improvements are also provided.

Vidal, A.; Viesti, G.; Osorio, C.; Pino, F.; Horvath, A.; Barros, H.; Caldogno, M.; Greaves, E. D.; Sajo-Bohus, L.

2012-02-01

439

Absorption of thin film materials at 10.6 microm.  

PubMed

Absorption indices at a wavelength of 10.6 mum for thin films of As(2)S(3), GeSe, BaF(2), ZnSe, and CdTe were measured by calorimetric techniques with a CO(2) laser. The values obtained, 4.6 x 10(-4), 1.4 x 10(-3), 2.8 x 10(-3), 2.8 x 10(-3), and 5.0 x 10(-3), respectively, were significantly greater than the corresponding values for the bulk materials. This difference was least for the vitreous films, As(2)S(3) and GeSe, which also had a lower absorption than the remaining polycrystalline films. Details are presented of the microstructure of the films as determined by scanning electron microscopy and k-ray diffraction. PMID:20155150

Gibbs, W E; Butterfield, A W

1975-12-01

440

In-beam spectroscopic studies of $^{44}$S nucleus  

E-print Network

The structure of the $^{44}$S nucleus has been studied at GANIL through the one proton knock-out reaction from a $^{45}$Cl secondary beam at 42 A$\\cdot$MeV. The $\\gamma$ rays following the de-excitation of $^{44}$S were detected in flight using the 70 BaF${_2}$ detectors of the Ch\\^{a}teau de Cristal array. An exhaustive $\\gamma\\gamma$-coincidence analysis allowed an unambiguous construction of the level scheme up to an excitation energy of 3301 keV. The existence of the spherical 2$^+_2$ state is confirmed and three new $\\gamma$-ray transitions connecting the prolate deformed 2$^+_1$ level were observed. Comparison of the experimental results to shell model calculations further supports a prolate and spherical shape coexistence with a large mixing of states built on the ground state band in $^{44}$S.

L. Caceres; D. Sohler; S. Grévy; O. Sorlin; Zs. Dombradi; B. Bastin; N. L. Achouri; J. C. Angélique; F. Azaiez; D. Baiborodin; R. Borcea; C. Bourgeois; A. Buta; A. Bürger; R. Chapman; J. C. Dalouzy; Z. Dlouhy; A. Drouard; Z. Elekes; S. Franchoo; L. Gaudefroy; S. Iacob; B. Laurent; M. Lazar; X. Liang; E. Liénard; J. Mrazek; L. Nalpas; F. Negoita; F. Nowacki; N. A. Orr; Y. Penionzhkevich; Zs. Podolyak; F. Pougheon; A. Poves; P. Roussel-Chomaz; M. G. Saint-Laurent; M. Stanoiu; I. Stefan

2012-01-06

441

Measuring TeV Cosmic Ray Electrons in the Earth's Magnetic Field  

NASA Astrophysics Data System (ADS)

Galactic cosmic-ray electrons are thought to be shock accelerated in supernova remnants as evident from observations of non-thermal X-rays and TeV gamma rays. It is expected that above about 1 TeV the local electron spectrum reflects distribution and abundance of nearby acceleration sites. Rates at these energies are low however and current and past electron detectors, typically flown by high altitude balloons, were limited by their short exposure times and small apertures. CREST, a balloon-borne detector array of 1024 BaF2 crystals will measure the intensity and spectrum of multi-TeV electrons by detecting the synchrotron photons emitted from electrons passing through the earth's magnetic field. Thus CREST's acceptance is several times its geometric area providing sensitivity up to about 50 TeV. Following an engineering flight in 2008 CREST will be flown in a circumpolar orbit on an upcoming Antarctic long duration balloon flight.

Schubnell, Michael

2008-03-01

442

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)  

NASA Technical Reports Server (NTRS)

The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

1990-01-01

443

Determination of cell cycle phases in live B16 melanoma cells using IRMS.  

PubMed

The knowledge of cell cycle phase distribution is of paramount importance for understanding cellular behaviour under normal and stressed growth conditions. This task is usually assessed using Flow Cytometry (FC) or immunohistochemistry. Here we report on the use of FTIR microspectroscopy in Microfluidic Devices (MD-IRMS) as an alternative technique for studying cell cycle distribution in live cells. Asynchronous, S- and G0-synchronized B16 mouse melanoma cells were studied by running parallel experiments based on MD-IRMS and FC using Propidium Iodide (PI) staining. MD-IRMS experiments have been done using silicon-modified BaF2 devices, where the thin silicon layer prevents BaF2 dissolution without affecting the transparency of the material and therefore enabling a better assessment of the Phosphate I (PhI) and II (PhII) bands. Hierarchical Cluster Analysis (HCA) of cellular microspectra in the 1300-1000 cm(-1) region pointed out a distribution of cells among clusters, which is in good agreement with FC results among G0/G1, S and G2/M phases. The differentiation is mostly driven by the intensity of PhI and PhII bands. In particular, PhI almost doubles from the G0/G1 to G2/M phase, in agreement with the trend followed by nucleic acids during cellular progression. MD-IRMS is then proposed as a powerful method for the in situ determination of the cell cycle stage of an individual cell, without any labelling or staining, which gives the advantage of possibly monitoring specific cellular responses to several types of stimuli by clearly separating the spectral signatures related to the cellular response from those of cells that are normally progressing. PMID:23662303

Bedolla, Diana E; Kenig, Saša; Mitri, Elisa; Ferraris, Paolo; Marcello, Alessandro; Grenci, Gianluca; Vaccari, Lisa

2013-07-21

444

Lariat ethers with fluoroaryl side-arms: a study of CFmetal cation interaction in the complexes of N-(o-fluoroaryl)azacrown ethers.  

PubMed

New lariat ethers, N-(o-fluorophenyl)aza-15-crown-5 (F-A15C5) and N,N'-bis(o-fluorophenyl)diaza-18-crown-6 (F(2)-A(2)18C6), were prepared by the N-arylation of the corresponding azacrown ethers. The interaction of the ligands with metal cations was studied in solution by (1)H and (19)F NMR (in acetone-d(6)) and UV spectroscopy (MeOH) confirming the formation of complexes of F(2)-A(2)18C6 with K(+), Na(+), Ag(+), Ba(2+), Pb(2+) and of F-A15C5 with Na(+) and giving evidence of CFmetal cation interaction. Cation binding constants (beta, evaluated by UV titration method), demonstrate that F-A15C5 and F(2)-A(2)18C6 form more stable complexes than their fluorine-free analogs. The effect depends on the nature of the metal cation and is at a maximum for hard, singly charged cations (up to 3 logbeta units for K(+) complex of F(2)-A(2)18C6). The X-ray structures of complexes [Pb(F(2)-A(2)18C6)(H(2)O)](ClO(4))(2) () and [Ba(F(2)-A(2)18C6)(ClO(4))(2)] () reveal short Pb-F (2.805 A) and Ba-F (2.965 A) contacts. Complex is centrosymmetric (C(i)), while complex has C(2) symmetry with one-side coordination of o-fluorophenyl groups to Pb(2+). This "one-side" coordination mode of Pb(2+) is indicative of a partial localization of the Pb(2+) lone pair. PMID:19156278

Sazonov, Petr K; Minacheva, Lidiya Kh; Churakov, Andrei V; Sergienko, Vladimir S; Artamkina, Galina A; Oprunenko, Yuri F; Beletskaya, Irina P

2009-02-01

445

Up-conversion visible emission in rare-earth doped fluoride glass waveguides  

NASA Astrophysics Data System (ADS)

The paper presents the visible emissions through frequency up-conversion and energy transfer process in the waveguide rare-earth (RE) codoped with RE/Yb (RE=Er, Pr, Tm), as well as physical properties of fluoride glasses and their fabrication par physical vapor deposition. The RE doping is made by substituting LaF in the base ZLAG glass composition (70%ZrF4-23.5%LaF3-0.5%AlF3-6%GaF3). Under 980-nm excitation, the emissions in planar waveguides of 2 to 3 thickness are found similar to the ones observed in bulk; blue and red emissions for 0.5Pr/xYb codoping and blue emission for 0.75Tm/xYb codoping with x ranging from 1 to 5 mol%. The bulk glass doped with Er/Tm/Yb can generate simultaneously and with high efficiency red-green-blue emissions from single-wave pumping at 980 nm. These preliminary results show that Er/Tm/Yb triply doped ZLA waveguide is a potential material for compact white light sources.

Boulard, Brigitte; Dieudonné, Belto; Gao, Youping; Chiasera, Alessandro; Ferrari, Maurizio

2014-07-01

446

Investigation into Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation Detection  

SciTech Connect

Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and cerium bromide (CeBr3) without requiring the growth of large crystals [1]. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have been seen in photoluminescence from silicon nanocrystals in a densely-packed ensemble [2]. We have fabricated nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.

Guss, P. P., Guise, R., Mukhopadhyay, S., Yuan, D.

2011-07-06

447

Effect of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped in transparent glass-ceramics  

NASA Astrophysics Data System (ADS)

The glass and glass-ceramics samples with composition of 50SiO2-10AlF3-(30-x)BaF2-5TiO2-3.95LaF3- xMnCO3-0.05ErF3-1YbF3 (in mol%, x=0, 0.5, 0.8, 1.0, and 1.2) were prepared using the conventional quenching techniques. The effects of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped transparent glass-ceramics under the changing of heat treatment temperatures and concentrations of Mn2+ ions were investigated. The structural investigation carried out by X-ray diffraction (XRD), and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Mn2+/Er3+/Yb3+ tri-doped was observed in the glass-ceramics. The upconversion mechanism and energy transfer between Mn2+-Yb3+ dimer and Er3+ ions were investigated.

Kim Dan, Ho; Zhou, Dacheng; Wang, Rongfei; Jiao, Qing; Yang, Zhengwen; Song, Zhiguo; Yu, Xue; Qiu, Jianbei

2014-12-01

448

Phosphate-solubilizing potentiality of the microorganisms capable of utilizing aluminium phosphate as a sole phosphate source.  

PubMed

Eight bacteria, each of the genus Bacillus, two actinomycetes, each of the genus Streptomyces, and six fungi, one each of the genus Penicillium and Chaetomium and four of the genus Aspergillus, were isolated on AlPO4-sucrose agar from a typical Indian lateritic soil (Typic Ochragualf). All of them were capable of solubilizing Ca3(PO4)2 to a higher degree than AlPO4. Bacillus subtilis (B-7655), LAB4, Bacillus sp., LAB5, Penicillium sp., LAF2, and Aspergillus spp., LAF3 and LAF4, were solubilizing Ca3(PO4)2 very efficiently, but AlPO4 to a lesser degree. Bacillus spp., LAB1, LAB2, LAB5, LAB6 and LAB7, Chaetomium nigricolor, LAF1, and Aspergillus spp., LAF5 and LAF6, were unable to bring detectable amounts of soluble phosphorus to solution from AlPO4. Except Chaetomium, all the other organisms produced free aliphatic organic acid in detectable amounts. The organic acids produced were oxalic, succinic, citric, and 2-keto gluconic acid. 2-Keto gluconic acid, singly and in combination with succinic or citric acid, accounted for higher solubilization. Amount of free organic acids in the growth medium was not directly correlated with phosphate solubilization. PMID:6845902

Banik, S; Dey, B K

1983-01-01

449

Energies of 4f^N and 4f^N-15d States Relative to Host Bands in Rare-earth-doped Fluorides  

NASA Astrophysics Data System (ADS)

Energies of 4f^N states relative to crystal band states were measured for rare-earth ions in the optical host materials LiYF4, Na0.4Y0.6F2.2, and LaF3 using x-ray photoemission spectroscopy. Spectra were modeled to determine the valence band maximum and 4f^ electron binding energies in each material. These results were combined with 4f^N to 4f^N-15d transition energies to determine 5d binding energies for the lowest levels of excited 4f^N-15d configurations. While 4f^N ground-state energies vary within several eV of the valence band maximum for different rare-earth ions in each host, the lowest 4f^N-15d states have similar energies and are several eV below the bottom of the conduction band. A simple model accurately described 4f^N and 4f^N-15d binding energies across the entire series of rare-earth ions. These results improve the understanding of optical materials for lasers, phosphors, and spectral hole burning applications for optical signal processing and data storage.

Thiel, C. W.; Joubert, M.-F.; Tkachuk, A.

2005-03-01

450

Ultra-broadband amplification through nanotechnology  

NASA Astrophysics Data System (ADS)

As demands for bandwidth continue to increase, telecommunication networks would greatly benefit from the development of broader-band amplifiers. The currently erbium doped fiber amplifiers are limited to amplification of approximately 100 nm bandwidth window. One method to increase the bandwidth of the fiber amplifier would be to incorporate multiple rare earths (REs) into a single fiber which exhibit emissions from ~1000-1800 nm. Unfortunately, energy transfer between rare earth ions typically results in quenching all but selected emissions negating this approach to potential ultra-broadband amplification. It would be ideal if one could take the individual spectra of an ion and place that ion into a host with no regard to other lanthanides that also are present in the host. This problem can be solved by using a composite material that utilizes nanoparticles to constrain different REs to individual particles thereby controlling or preventing energy transfer. In order to control energy transfer, RE doped LaF 3 nanocrystals were grown in an aqueous solution using a core/shell technique to constrain different rare earth into separate particles or shells within a single particle. Using these techniques, we show that energy transfer can be controlled.

DiMaio, Jeffrey R.; Kokuoz, Baris; Ballato, John

2006-10-01

451

Self-organization of three-dimensional nano-void superlattice in electron irradiated calcium fluoride  

NASA Astrophysics Data System (ADS)

To improve the scientific understanding of a spectacular phenomenon observed in electron irradiated calcium fluoride (CaF2), the formation of ordered arrays of nano-voids, three-dimensional nano-void superlattice has been fabricated with high energy electrons and studied with in-situ TEM. Energy transferred from electrons to the atoms in the sample by radiolysis and ballistic processes have been calculated respectively. Unlike the commonly observed randomly distributed defect clusters or precipitates, the voids in these superlattices are extremely uniform in size, about 5 nm in radius, and the lattice parameter of the simple cubic superlattice lies in the range of 15-20 nm. Three void lattice growth/ordering modes have been identified by the in-situ TEM observation. A series of experiments indicates that higher total electron fluence is required at the low temperature for superlattice formation, and the faceted voids forms at the higher temperature with the periodicity starting to disappear at 100°C or higher. Advanced analytical TEM techniques provide solid evidences that these defects are real voids, instead of previously considered Ca colloids. A self-organized ripple pattern is also created on the surface of CaF2 by ion irradiation and characterized using AFM and TEM. The wavelength of the ripple pattern is found to be much larger than the lattice parameter of the void superlattice. The mechanisms responsible for the formation of void superlattice have been discussed. Anisotropic defects diffusion and elastic interactions between voids may explain the self-ordering process. ab initio total energy calculations has been used to determine that the absorption at octahedral sites of displaced F or Ca atoms gives the lowest energy in the irradiated material. The octahedral sites in the crystal are stable sites for Ca interstitial atoms and the interaction between Ca interstitial and CaF2 molecule is strong. Molecular dynamics simulations have been performed to evaluate the Frenkel pair formation energy. Displacement energy and vacancy migration energy along various directions are calculated for both Ca and F, respectively. The anion vacancies have been found to move easily along <100> directions while the cation vacancy has the lowest migration energy along the <110> directions.

Ding, Tianhua

452

-Based Mold Flux and Their Effects on In-Mold Performance during High-Aluminum TRIP Steels Continuous Casting  

NASA Astrophysics Data System (ADS)

Crystallization behaviors of the newly developed lime-alumina-based mold fluxes for high-aluminum transformation induced plasticity (TRIP) steels casting were experimentally studied, and compared with those of lime-silica-based mold fluxes. The effects of mold flux crystallization characteristics on heat transfer and lubrication performance in casting high-Al TRIP steels were also evaluated. The results show that the crystallization temperatures of lime-alumina-based mold fluxes are much lower than those of lime-silica-based mold fluxes. Increasing B2O3 addition suppresses the crystallization of lime-alumina-based mold fluxes, while Na2O exhibits an opposite effect. In continuous cooling of lime-alumina-based mold fluxes with high B2O3 contents and a CaO/Al2O3 ratio of 3.3, faceted cuspidine precipitates first, followed by needle-like CaO·B2O3 or 9CaO·3B2O3·CaF2. In lime-alumina-based mold flux with low B2O3 content (5.4 mass pct) and a CaO/Al2O3 ratio of 1.2, the formation of fine CaF2 takes place first, followed by blocky interconnected CaO·2Al2O3 as the dominant crystalline phase, and rod-like 2CaO·B2O3 precipitates at lower temperature during continuous cooling of the mold flux. In B2O3-free mold flux, blocky interconnected 3CaO·Al2O3 precipitates after CaF2 and 3CaO·2SiO2 formation, and takes up almost the whole crystalline fraction. The casting trials show that the mold heat transfer rate significantly decreases near the meniscus during the continuous casting using lime-alumina-mold fluxes with higher crystallinity, which brings a great reduction of surface depressions on cast slabs. However, excessive crystallinity of mold flux causes poor lubrication between mold and solidifying steel shell, which induces various defects such as drag marks on cast slab. Among the studied mold fluxes, lime-alumina-based mold fluxes with higher B2O3 contents and a CaO/Al2O3 ratio of 3.3 show comparatively improved performance.

Shi, Cheng-Bin; Seo, Myung-Duk; Cho, Jung-Wook; Kim, Seon-Hyo

2014-06-01

453

Ablation of ionic crystals induced by capillary-discharge XUV laser  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

454

Radiation Heat Transfer Modeling Improved for Phase-Change, Thermal Energy Storage Systems  

NASA Technical Reports Server (NTRS)

Spacecraft solar dynamic power systems typically use high-temperature phase-change materials to efficiently store thermal energy for heat engine operation in orbital eclipse periods. Lithium fluoride salts are particularly well suited for this application because of their high heat of fusion, long-term stability, and appropriate melting point. Considerable attention has been focused on the development of thermal energy storage (TES) canisters that employ either pure lithium fluoride (LiF), with a melting point of 1121 K, or eutectic composition lithium-fluoride/calcium-difluoride (LiF-20CaF2), with a 1040 K melting point, as the phase-change material. Primary goals of TES canister development include maximizing the phase-change material melt fraction, minimizing the canister mass per unit of energy storage, and maximizing the phase-change material thermal charge/discharge rates within the limits posed by the container structure.

Kerslake, Thomas W.; Jacqmin, David A.

1998-01-01

455

Orthorhombic structure of cadmium behenate monolayers on the water surface of a Langmuir trough detected by polarization modulation infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was applied to investigate the structure of behenic acid monolayers on the surface of aqueous Cd 2+ sub-phase in a Langmuir trough at the room temperature of 293 K. The PM-IRRAS spectra were recorded at representative points throughout 0.401˜0.100 nm 2 and the surface-pressure area isotherms were recorded during compression to these points. It is found that compressed cadmium behenate (CdB) monolayers possess an orthorhombic unit cell. On the other hand, single monolayers of CdB deposited on CaF 2 substrates at 20 mN m -1 possessed a triclinic parallel packing.

Ren, Yanzhi; Hossain, Md. Mufazzal; Iimura, Ken-ichi; Kato, Teiji

2000-08-01

456

Surface-enhanced Raman scattering-based detection of cancerous renal cells.  

PubMed

Surface-enhanced Raman scattering (SERS) is used for the differentiation of human kidney adenocarcinoma, human kidney carcinoma, and non-cancerous human kidney embryonic cells. Silver nanoparticles (AgNPs) are used as substrate in the experiments. A volume of colloidal suspension containing AgNPs is added onto the cultured cells on a CaF(2) slide, and the slide is dried at the overturned position. A number of SERS spectra acquired from the three different cell lines are statistically analyzed to differentiate the cells. Principal component analysis (PCA) combined with linear discriminate analysis (LDA) was performed to differentiate the three kidney cell types. The LDA, based on PCA, provided for classification among the three cell lines with 88% sensitivity and 84% specificity. This study demonstrates that SERS can be used to identify renal cancers by combining this new sampling method and LDA algorithms. PMID:25014716

Mert, Sevda; Çulha, Mustafa

2014-01-01

457

High field vortex phase diagram of Fe(Se, Te) thin films  

NASA Astrophysics Data System (ADS)

We report on the (H, T) vortex phase diagram up to 35 T of Fe(Se, Te) thin films deposited on CaF2 substrates as determined by resistivity, Nernst effect and critical current measurements. We found the presence of a large region where the vortex is firmly pinned, allowing the adoption of chalcogenides for low temperature but extremely high magnetic field applications. The fact that high critical current density values—larger than 1 MA cm-2 in self-field and liquid helium—are reached together with a very weak dependence on the magnetic field and a complete isotropy, joined with the very high rigidity of the vortex lattice at very high field, makes the Fe(Se, Te) phase very promising for low temperature (?4.2 K) and high field (?25 T) applications.

Bellingeri, E.; Kawale, S.; Caglieris, F.; Braccini, V.; Lamura, G.; Pellegrino, L.; Sala, A.; Putti, M.; Ferdeghini, C.; Jost, A.; Zeitler, U.; Tarantini, C.; Jaroszynski, J.

2014-04-01

458

Surface analysis by laser-induced desorption time-of-flight mass spectrometry  

NASA Astrophysics Data System (ADS)

We have built and tested a laser induced desorption (LID), electron impact ionization, time-of-flight (TOF) mass spectrometer (MS) designed to nondestructively identify and measure adsorbed contaminants on critical surfaces for the microelectronics and optics industries. The LID-TOFMS combines the capability of a TOF mass spectrometer to measure all the desorbed molecules from a single laser shot with an infrared Er:YAG laser (2.94 micron), which is not strongly absorbed by many transparent optical materials but is strongly absorbed by water, the most common adsorbed surface contaminant, to yield surface composition as a function of position on the sample. The LID-TOFMS was calibrated using an oxalic acid film on a polished stainless steel plate, which also contained adsorbed water. Contaminants on CaF2 surfaces measured by LID-TOFMS include water and hydrocarbons. Desorbed molecules decrease with increasing irradiations at a fixed laser fluence, suggesting that the surface is being cleaned.

Allen, Susan D.; Fu, Jinmei; Surapaneni, Yamini; Hopkins, Adam J.; Davis, Phillip

2003-07-01

459

Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study  

SciTech Connect

The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt-Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of < 0,4,4,0 >, < 0,3, 6,0 > and < 0,4,4,2 > with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Xiong, L.H.; Lou, H.B.; Wang, X.D.; Debela, T.T.; Cao, Q.P.; Zhang, D.X.; Wang, S.Y.; Wang, C.Z.; Jiang, J.Z.

2014-04-01

460

Dielectric relaxation in ytterbium- and lead-doped calcium fluoride crystals  

NASA Astrophysics Data System (ADS)

YbF3-doped and 1 mol% PbF2 co-doped CaF2 crystals were grown by vertical Bridgman method using a shaped graphite furnace in vacuum. Dielectric spectra and optical absorption spectra were measured in order to study the influence of Pb2+ ions on the charge compensating defects formation. The influence of Pb2+ ions on the various charge compensating defects depend on the YbF3 concentration. For low YbF3 concentrations the influence is stronger than for concentrations higher than 1 mol% YbF3. Dielectric relaxation in double doped (Yb,Pb):CaF2 crystals in order the study the charge compensating defects formation was not reported before.

Stef, Marius; Nicoara, Irina; Stef, Florica

2013-04-01

461

Optical system design for infrared imaging system of Korea Superconducting Tokamak Advanced Research (KSTAR) device  

NASA Astrophysics Data System (ADS)

The first infrared imaging system, for monitoring the temperature of the inner wall and localized hot spot such as the ICRH antenna was installed on the midplane of the D-port in the Korea Superconducting Tokamak Advanced Research (KSTAR). The cassette system of KSTAR makes a periscope inevitable for infrared imaging system. The periscope is composed of a 3 functional optical lens set (input beam shaper, beam deliverer, output beam shaper). CaF2 was chosen for the material of the lens elements. As an infrared image camera, FLIR/ThermoVision SC6000HS is used. The infrared camera has 640 × 512 pixel resolution and a camera lens set with 25.4 mm of focus length and 50 mm of input pupil. The periscope was designed to have 2.7 m of overall length, 19.07 mm of focal length and 3.81 of f-number.

Oh, S.; Seo, D.; KSTAR Team

2012-02-01

462

Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure  

NASA Astrophysics Data System (ADS)

The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am LIII in neptunium dioxide (NpO2) and americium dioxide (AmO2) with CaF2-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO2 than for NpO2 because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms.

Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

2012-02-01

463

Fundamental research on a cerenkov radiation sensor based on optical glass for detecting beta-rays  

NASA Astrophysics Data System (ADS)

In this study, a Cerenkov radiation sensor for detecting low-energy beta-particles was fabricated using various Cerenkov radiators such as an aerogel and CaF2-, SiO2-, and Al2O3-based optical glasses. Because the Cerenkov threshold energy (CTE) is determined by the refractive index of the Cerenkov radiator, the intensity of Cerenkov radiation varies according to the refractive indices of the Cerenkov radiators. Therefore, we measured the intensities of Cerenkov radiation induced by beta-particles generated from a radioactive isotope as a function of the refractive indices of the Cerenkov radiators. Also, the electron fluxes were calculated for various Cerenkov radiators by using a Monte Carlo N-Particle extended transport code (MCNPX) to determine the relationship between the intensities of the Cerenkov radiation and the electron fluxes.

Kim, Jae Seok; Jang, Kyoung Won; Shin, Sang Hun; Jeon, Dayeong; Hong, Seunghan; Sim, Hyeok In; Kim, Seon Geun; Yoo, Wook Jae; Lee, Bongsoo; Moon, Joo Hyun; Park, Byung Gi

2015-01-01

464

[Dose exposure from analog and digital full mouth radiography and panoramic radiography].  

PubMed

The present study investigated the dose exposition in the head and neck region by use of analog and digital radiographic dental systems. Four radiographic devices were tested: panoramic radiography (analog and digital) and 14-image full-mouth-survey (FMS, analog and digital). Organ doses were measured on a Rando-phantom by use of CaF2-dosimeters according to the IRCP-guidelines and the effective doses calculated. The results were the following: the value of E was lowest in digital FMS (41 microSv) and highest in analog FMS (78 microSv), i.e. dose was reduced by 47% by using a digital device. In panoramic radiography, doses were 17% lower using digital technique (digital 45 microSv vs. analog 54 pSv). Thus, FMS is no longer associated with higher doses than orthopantomography when conventional films are replaced by digital techniques. PMID:15360104

Kiefer, Hanspeter; Lambrecht, J Thomas; Roth, Jakob

2004-01-01