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Sample records for si crystals measured

  1. Temperature and Field Induced Strain Measurements in Single Crystal Gd5Si2Ge2

    NASA Astrophysics Data System (ADS)

    McCall, S. K.; Nersessian, N.; Carman, G. P.; Pecharsky, V. K.; Schlagel, D. L.; Radousky, H. B.

    2016-06-01

    The first-order magneto-structural transformation that occurs in Gd5Si2Ge2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd5Si2.05Ge1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of -8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of -8500 ppm, +900 ppm and +2300 ppm were measured along the a, b and c axes, respectively. Using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.

  2. Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

    NASA Astrophysics Data System (ADS)

    Azuma, Y.; Barat, P.; Bartl, G.; Bettin, H.; Borys, M.; Busch, I.; Cibik, L.; D'Agostino, G.; Fujii, K.; Fujimoto, H.; Hioki, A.; Krumrey, M.; Kuetgens, U.; Kuramoto, N.; Mana, G.; Massa, E.; Meeß, R.; Mizushima, S.; Narukawa, T.; Nicolaus, A.; Pramann, A.; Rabb, S. A.; Rienitz, O.; Sasso, C.; Stock, M.; Vocke, R. D., Jr.; Waseda, A.; Wundrack, S.; Zakel, S.

    2015-04-01

    New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of NA = 6.022 140 76(12) × 1023 mol-1. The x-ray crystal density method has thus achieved the target relative standard uncertainty of 2.0  ×  10-8 necessary for the realization of the definition of the new kilogram.

  3. Molar-mass measurement of a 28Si-enriched silicon crystal for determination of the Avogadro constant

    NASA Astrophysics Data System (ADS)

    Narukawa, Tomohiro; Hioki, Akiharu; Kuramoto, Naoki; Fujii, Kenichi

    2014-06-01

    The molar mass of a 28Si-enriched crystal was measured at the National Metrology Institute of Japan to determine the Avogadro constant by the x-ray crystal density method as part of the International Avogadro Coordination project. The molar mass was determined by isotope ratio measurements using a multicollector inductively coupled plasma mass spectrometer combined with an isotope dilution technique. The 28Si-enriched crystal was dissolved in tetramethylammonium hydroxide and three different blended solutions were used to correct for mass bias in the measurement. The molar mass of the 28Si-enriched crystal was determined to be 27.976 970 09 g mol-1 with a standard uncertainty of 0.000 000 14 g mol-1. This corresponds to a relative standard uncertainty of 5.2 × 10-9. This result is consistent with measurements reported by the Physikalisch-Technische Bundesanstalt, Germany.

  4. Temperature and field induced strain measurements in single crystal Gd5Si2Ge2

    DOE PAGESBeta

    McCall, S. K.; Nersessian, N.; Carman, G. P.; Pecharsky, V. K.; Schlagel, D. L.; Radousky, H. B.

    2016-03-29

    The first-order magneto-structural transformation that occurs in Gd5Si2Ge2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd5Si2.05Ge1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of –8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of –8500 ppm, +900 ppm and +2300 ppm were measured along the a, b and c axes, respectively. Furthermore,more » using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.« less

  5. Strain distribution in an Si single crystal measured by interference fringes of X-ray mirage diffraction

    PubMed Central

    Jongsukswat, Sukswat; Fukamachi, Tomoe; Ju, Dongying; Negishi, Riichirou; Hirano, Keiichi; Kawamura, Takaaki

    2013-01-01

    In X-ray interference fringes accompanied by mirage diffraction, variations have been observed in the spacing and position of the fringes from a plane-parallel Si single crystal fixed at one end as a function of distance from the incident plane of the X-rays to the free crystal end. The variations can be explained by distortion of the sample crystal due to gravity. From the variations and positions of the fringes, the strain gradient of the crystal has been determined. The distribution of the observed strain agrees with that expected from rod theory except for residual strain. When the distortion is large, the observed strain distribution does not agree with that expected from rod theory. PMID:24068841

  6. Strain distribution in an Si single crystal measured by interference fringes of X-ray mirage diffraction.

    PubMed

    Jongsukswat, Sukswat; Fukamachi, Tomoe; Ju, Dongying; Negishi, Riichirou; Hirano, Keiichi; Kawamura, Takaaki

    2013-10-01

    In X-ray interference fringes accompanied by mirage diffraction, variations have been observed in the spacing and position of the fringes from a plane-parallel Si single crystal fixed at one end as a function of distance from the incident plane of the X-rays to the free crystal end. The variations can be explained by distortion of the sample crystal due to gravity. From the variations and positions of the fringes, the strain gradient of the crystal has been determined. The distribution of the observed strain agrees with that expected from rod theory except for residual strain. When the distortion is large, the observed strain distribution does not agree with that expected from rod theory. PMID:24068841

  7. Lattice compression of Si crystals and crystallographic position of As impurities measured with x-ray standing wave spectroscopy

    SciTech Connect

    Herrera-Gomez, A. |; Rousseau, P.M.; Woicik, J.C.; Kendelewicz, T.; Plummer, J.; Spicer, W.E.

    1999-02-01

    In an earlier letter [Appl. Phys. Lett. {bold 68}, 3090 (1996)] we reported results about heavily arsenic doped silicon crystals, where we unambiguously showed, based on x-ray standing wave spectroscopy (XSW) and other techniques, that electrically deactivated As remains essentially substitutional. In this article we present the analysis methodology that led us to said conclusion, and show how from further analysis it is possible to extract the compression or expansion of thin epitaxial layers. We report the evolution of the compression of highly As doped Si epitaxial layers as deactivation takes place. The XSW measurements required a very small thickness of the doped layer and a perfect registry between the substrate and the surface layer. We found larger values for compression than previously reported, which may be explained by the absence of structural defects on our samples that relax the interface stress. Our results show a saturation on the compression as the electron concentration increases. We also report an estimation of the small displacement from perfect substitutional positions suffered by deactivated As. {copyright} {ital 1999 American Institute of Physics.}

  8. Evaluation of bulk β-FeSi2 crystal as a solar cell semiconductor through the photo-response measurements of Al/n-β-FeSi2 Schottky diodes

    NASA Astrophysics Data System (ADS)

    Fukuzawa, Yasuhiro; Ootsuka, Teruhisa; Nakayama, Yasuhiko; Makita, Yunosuke

    2008-04-01

    β-FeSi2 has many attracting properties as a semiconductor not consisting of toxic chemical elements and is an ideal semiconductor as a thin film solar cell owing to its extremely high optical absorption coefficient. To evaluate β-FeSi2 as a solar cell, photo-response measurement is critically important and useful. Since β-FeSi2 thin films are normally deposited on Si substrates, intrinsic photo-response of β-FeSi2 is usually difficult to be collected due to the strong contribution from Si substrates. We here present the photo-response from bulk β-FeSi2 crystals, expecting that we can eliminate the contributions coming from the Si substrates and the crystallographic defects existing at the β-FeSi2/Si interfaces when we use β-FeSi2 thin films. We prepared bulk specimens by chemical vapor transport method (CVT) in which needle-like and plate-like β-FeSi2 crystals were obtained. We chose the former specimens for the formation of Al/n-β-FeSi2 Schottky contacts to measure their photo-responses. These contacts were found to form Schottky diodes even though there are large series resistances and leakage currents. Under laser light illumination of 1.31 μm through optical fiber, the positive voltage was observed between the Al contact and the In solder glued to the back-surface of β-FeSi2 bulk specimen. Two-dimensional distribution of photo-responses were measured by scanning the above optical fiber with the spot size of 50 μm. The highest photo-response was obtained in the vicinity of Al wire, and was 7.7 mA/W for the as-grown sample, and 31 mA/W for the annealing one, respectively. These observations state that β-FeSi2 holds appropriate optical features to be used as a solar cell.

  9. Influence of Containment on Defects in GeSi Crystals

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Croell, A.; Mazuruk, K.

    2009-01-01

    Crystals grown without being in contact with a container have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. "Detached" or "dewetted" Bridgman growth is similar to regular Bridgman growth in that most of the melt is in contact with the crucible wall, but the crystal is separated from the wall by a small gap, typically of the order of 10(exp -5) m. A small meniscus bridges the gap between the top of the crystal and the wall. Key parameters involved in achieving detached growth are the contact angle between the melt and crucible and the pressure differential across the meniscus. Sessile drop measurements were used to determine the wetting angles of Ge(sub 1-x)Si(sub x) melts on a variety of substrates and found that the highest wetting angles were achieved with pyrolitic boron nitride (pBN). GeSi crystals have been repeatedly grown detached in pBN crucibles but only occasionally in crucibles with lower wetting angles. Experiments have been conducted to assess the effect of pressure differential across the meniscus in sealed crucibles. This was done by adjusting the temperature profile after partial melting of the starting material. In a separate set of experiments, the pressure was controlled by connecting the volume below the meniscus to a regulated gas supply. The experiments were in agreement with calculations which predicted that stable detachment will only occur in crucibles with a low wetting angle over a relatively narrow range of pressure differential. Detached-grown crystals exhibited superior structural quality as evidenced by measurements of etch pit density, synchrotron white beam X-ray topography and double axis X-ray diffraction.

  10. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    NASA Astrophysics Data System (ADS)

    Abrams, K. J.; Hinks, J. A.; Pawley, C. J.; Greaves, G.; van den Berg, J. A.; Eyidi, D.; Ward, M. B.; Donnelly, S. E.

    2012-04-01

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  11. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  12. Laser pulse crystallization and optical properties of Si/SiO2 and Si/Si3N4 multilayer nano-heterostructures

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Arzhannikova, S. A.; Gismatulin, A. A.; Kamaev, G. N.; Antonenko, A. Kh.; Cherkova, S. G.; Cherkov, A. G.; Kochubei, S. A.; Popov, A. A.; Robert, S.; Rinnert, H.; Vergnat, M.

    2013-01-01

    Furnace annealing, cw- and pulse laser treatments were applied for crystallization of amorphous Si nano-layers and Si nanoclusters in SiNx-Si3N4 and Si-SiO2 multilayer nanostructures. The as-deposited and annealed structures were studied using optical methods and electron microscopy techniques. The influence of hydrogen on crystallization and formation of Si nanoclusters was studied. Regimes for pulse laser crystallization of amorphous Si nanoclusters and nanolayers were found. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters and silicon nanostructured films on non-refractory substrates for all-silicon tandem solar cells.

  13. Effect of Crystal Defects on Minority Carrier Diffusion Length in 6H SiC Measured Using the Electron Beam Induced Current Method

    NASA Technical Reports Server (NTRS)

    Tabib-Azar, Massood

    1997-01-01

    We report values of minority carrier diffusion length in n-type 6H SiC measured using a planar Electron Beam Induced Current (EBIC) method. Values of hole diffusion length in defect free regions of n-type 6H SiC, with a doping concentration of 1.7El7 1/cu cm, ranged from 1.46 microns to 0.68 microns. We next introduce a novel variation of the planar method used above. This 'planar mapping' technique measured diffusion length along a linescan creating a map of diffusion length versus position. This map is then overlaid onto the EBIC image of the corresponding linescan, allowing direct visualization of the effect of defects on minority carrier diffusion length. Measurements of the above n-type 6H SiC resulted in values of hole diffusion length ranging from 1.2 micron in defect free regions to below 0.1 gm at the center of large defects. In addition, measurements on p-type 6H SiC resulted in electron diffusion lengths ranging from 1.42 micron to 0.8 micron.

  14. Effect of Pt Doping on Nucleation and Crystallization in Li2O.2SiO2 Glass: Experimental Measurements and Computer Modeling

    NASA Technical Reports Server (NTRS)

    Narayan, K. Lakshmi; Kelton, K. F.; Ray, C. S.

    1996-01-01

    Heterogeneous nucleation and its effects on the crystallization of lithium disilicate glass containing small amounts of Pt are investigated. Measurements of the nucleation frequencies and induction times with and without Pt are shown to be consistent with predictions based on the classical nucleation theory. A realistic computer model for the transformation is presented. Computed differential thermal analysis data (such as crystallization rates as a function of time and temperature) are shown to be in good agreement with experimental results. This modeling provides a new, more quantitative method for analyzing calorimetric data.

  15. Diamond turning of Si and Ge single crystals

    SciTech Connect

    Blake, P.; Scattergood, R.O.

    1988-12-01

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

  16. Mass Spectrometric Investigation of Silicon Extremely Enriched in (28)Si: From (28)SiF4 (Gas Phase IRMS) to (28)Si Crystals (MC-ICP-MS).

    PubMed

    Pramann, Axel; Rienitz, Olaf

    2016-06-01

    A new generation of silicon crystals even further enriched in (28)Si (x((28)Si) > 0.999 98 mol/mol), recently produced by companies and institutes in Russia within the framework of a project initiated by PTB, were investigated with respect to their isotopic composition and molar mass M(Si). A modified isotope dilution mass spectrometric (IDMS) method treating the silicon as the matrix containing a so-called virtual element (VE) existing of the isotopes (29)Si and (30)Si solely and high resolution multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) were applied in combination. This method succeeds also when examining the new materials holding merely trace amounts of (29)Si (x((29)Si) ≈ 5 × 10(-6) mol/mol) and (30)Si (x((30)Si) ≈ 7 × 10(-7) mol/mol) extremely difficult to detect with lowest uncertainty. However, there is a need for validating the enrichment in (28)Si already in the precursor material of the final crystals, silicon tetrafluoride (SiF4) gas prior to crystal production. For that purpose, the isotopic composition of selected SiF4 samples was determined using a multicollector magnetic sector field gas-phase isotope ratio mass spectrometer. Contaminations of SiF4 by natural silicon due to storing and during the isotope ratio mass spectrometry (IRMS) measurements were observed and quantified. The respective MC-ICP-MS measurements of the corresponding crystal samples show-in contrast-several advantages compared to gas phase IRMS. M(Si) of the new crystals were determined to some extent with uncertainties urel(M) < 1 × 10(-9). This study presents a clear dependence of the uncertainty urel(M(Si)) on the degree of enrichment in (28)Si. This leads to a reduction of urel(M(Si)) during the past decade by almost 3 orders of magnitude and thus further reduces the uncertainty of the Avogadro constant NA which is one of the preconditions for the redefinition of the SI unit kilogram. PMID:27173726

  17. Fabrication of nanometer single crystal metallic CoSi2 structures on Si

    NASA Technical Reports Server (NTRS)

    Nieh, Kai-Wei (Inventor); Lin, True-Lon (Inventor); Fathauer, Robert W. (Inventor)

    1991-01-01

    Amorphous Co:Si (1:2 ratio) films are electron gun-evaporated on clean Si(111), such as in a molecular beam epitaxy system. These layers are then crystallized selectively with a focused electron beam to form very small crystalline Co/Si2 regions in an amorphous matrix. Finally, the amorphous regions are etched away selectively using plasma or chemical techniques.

  18. 'Buffer-layer' technique for the growth of single crystal SiC on Si

    NASA Astrophysics Data System (ADS)

    Addamiano, A.; Sprague, J. A.

    1984-03-01

    The nature of the buffer layers needed for the single-crystal deposition of cubic SiC on Si substrates has been studied. The preparation of chemically formed surface layers of SiC on (100) Si wafers is described. The reaction-grown films of SiC were examined by reflection high-energy electron diffraction using an incident electron energy of 200 keV and by SEM using incident electron energies of 20 and 200 keV. It is concluded that the buffer layer obtained at about 1400 C is a stressed monocrystalline layer of cubic SiC whose crystals contain considerable imperfections. The stresses are due to quenching to room temperature because of the large difference between the thermal expansion coefficients of Si and SiC.

  19. Development of SiC Large Tapered Crystal Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Phil

    2010-01-01

    Majority of very large potential benefits of wide band gap semiconductor power electronics have NOT been realized due in large part to high cost and high defect density of commercial wafers. Despite 20 years of development, present SiC wafer growth approach is yet to deliver majority of SiC's inherent performance and cost benefits to power systems. Commercial SiC power devices are significantly de-rated in order to function reliably due to the adverse effects of SiC crystal dislocation defects (thousands per sq cm) in the SiC wafer.

  20. Solid state NMR of SiO 2 nanotube coated ammonium tartrate crystal

    NASA Astrophysics Data System (ADS)

    Lim, A. R.; Schueneman, G. T.; Novak, B. M.

    1999-04-01

    Ammonium tartrate crystal and SiO 2 nanotube coated ammonium tartrate crystal were studied by 13C CP/MAS NMR, and the structure of two samples were verified using the 13C NMR spectrum. The spin-lattice relaxation times for the carbons in the rotating frame, T1 ρ, have been measured as a function of temperature. All relaxation times of the carbons in the two materials undergo slow motions, i.e. motions on the slow side of the T1 ρ minimum. From these relaxation times, we determine the activation energy for the ammonium tartrate crystal and SiO 2 nanotube coated ammonium tartrate crystal, respectively. The activation energies for the SiO 2 nanotube coated ammonium tartrate crystal were found to be generally higher than those of ammonium tartrate crystal. We think that the higher activation energy for the hydrocarbon in the SiO 2 nanotube coated ammonium tartrate crystal is because of the bonding between the oxygen in the SiO 2 nanotube and the hydroxyl group of the ammonium tartrate crystal.

  1. Vertically Conductive Single-Crystal SiC-Based Bragg Reflector Grown on Si Wafer

    PubMed Central

    Massoubre, David; Wang, Li; Hold, Leonie; Fernandes, Alanna; Chai, Jessica; Dimitrijev, Sima; Iacopi, Alan

    2015-01-01

    Single-crystal silicon carbide (SiC) thin-films on silicon (Si) were used for the fabrication and characterization of electrically conductive distributed Bragg reflectors (DBRs) on 100 mm Si wafers. The DBRs, each composed of 3 alternating layers of SiC and Al(Ga)N grown on Si substrates, show high wafer uniformity with a typical maximum reflectance of 54% in the blue spectrum and a stopband (at 80% maximum reflectance) as large as 100 nm. Furthermore, high vertical electrical conduction is also demonstrated resulting to a density of current exceeding 70 A/cm2 above 1.5 V. Such SiC/III-N DBRs with high thermal and electrical conductivities could be used as pseudo-substrate to enhance the efficiency of SiC-based and GaN-based optoelectronic devices on large Si wafers. PMID:26601894

  2. Vertically Conductive Single-Crystal SiC-Based Bragg Reflector Grown on Si Wafer.

    PubMed

    Massoubre, David; Wang, Li; Hold, Leonie; Fernandes, Alanna; Chai, Jessica; Dimitrijev, Sima; Iacopi, Alan

    2015-01-01

    Single-crystal silicon carbide (SiC) thin-films on silicon (Si) were used for the fabrication and characterization of electrically conductive distributed Bragg reflectors (DBRs) on 100 mm Si wafers. The DBRs, each composed of 3 alternating layers of SiC and Al(Ga)N grown on Si substrates, show high wafer uniformity with a typical maximum reflectance of 54% in the blue spectrum and a stopband (at 80% maximum reflectance) as large as 100 nm. Furthermore, high vertical electrical conduction is also demonstrated resulting to a density of current exceeding 70 A/cm(2) above 1.5 V. Such SiC/III-N DBRs with high thermal and electrical conductivities could be used as pseudo-substrate to enhance the efficiency of SiC-based and GaN-based optoelectronic devices on large Si wafers. PMID:26601894

  3. Vertically Conductive Single-Crystal SiC-Based Bragg Reflector Grown on Si Wafer

    NASA Astrophysics Data System (ADS)

    Massoubre, David; Wang, Li; Hold, Leonie; Fernandes, Alanna; Chai, Jessica; Dimitrijev, Sima; Iacopi, Alan

    2015-11-01

    Single-crystal silicon carbide (SiC) thin-films on silicon (Si) were used for the fabrication and characterization of electrically conductive distributed Bragg reflectors (DBRs) on 100 mm Si wafers. The DBRs, each composed of 3 alternating layers of SiC and Al(Ga)N grown on Si substrates, show high wafer uniformity with a typical maximum reflectance of 54% in the blue spectrum and a stopband (at 80% maximum reflectance) as large as 100 nm. Furthermore, high vertical electrical conduction is also demonstrated resulting to a density of current exceeding 70 A/cm2 above 1.5 V. Such SiC/III-N DBRs with high thermal and electrical conductivities could be used as pseudo-substrate to enhance the efficiency of SiC-based and GaN-based optoelectronic devices on large Si wafers.

  4. Synthesis and characterization of Mo 3Si single crystal

    NASA Astrophysics Data System (ADS)

    Rosales, I.

    2008-08-01

    Mo 3Si single crystals were successfully produced using an optical floating zone furnace. Reoriented specimens were obtained from the original crystal with <1 1 1>, <1 1 0> and <1 0 0> orientations. Cracking behavior of the crystals shows an interesting relation regarding their crystal orientation. Fracture toughness values show small orientation dependence. The hardness test shows that the hard plane is the (1 0 0), and the softest plane was the (1 1 0) and not the (1 1 1) as it was expected.

  5. Advanced Si solid phase crystallization for vertical channel in vertical NANDs

    NASA Astrophysics Data System (ADS)

    Lee, Sangsoo; Son, Yong-Hoon; Hwang, Kihyun; Shin, Yoo Gyun; Yoon, Euijoon

    2014-07-01

    The advanced solid phase crystallization (SPC) method using the SiGe/Si bi-layer structure is proposed to obtain high-mobility poly-Si thin-film transistors in next generation vertical NAND (VNAND) devices. During the SPC process, the top SiGe thin film acts as a selective nucleation layer to induce surface nucleation and equiaxial microstructure. Subsequently, this SiGe thin film microstructure is propagated to the underlying Si thin film by epitaxy-like growth. The initial nucleation at the SiGe surface was clearly observed by in situ transmission electron microscopy (TEM) when heating up to 600 °C. The equiaxial microstructures of both SiGe nucleation and Si channel layers were shown in the crystallized bi-layer plan-view TEM measurements. Based on these experimental results, the large-grained and less-defective Si microstructure is expected to form near the channel region of each VNAND cell transistor, which may improve the electrical characteristics.

  6. Advanced Si solid phase crystallization for vertical channel in vertical NANDs

    SciTech Connect

    Lee, Sangsoo; Son, Yong-Hoon; Hwang, Kihyun; Shin, Yoo Gyun; Yoon, Euijoon

    2014-07-01

    The advanced solid phase crystallization (SPC) method using the SiGe/Si bi-layer structure is proposed to obtain high-mobility poly-Si thin-film transistors in next generation vertical NAND (VNAND) devices. During the SPC process, the top SiGe thin film acts as a selective nucleation layer to induce surface nucleation and equiaxial microstructure. Subsequently, this SiGe thin film microstructure is propagated to the underlying Si thin film by epitaxy-like growth. The initial nucleation at the SiGe surface was clearly observed by in situ transmission electron microscopy (TEM) when heating up to 600 °C. The equiaxial microstructures of both SiGe nucleation and Si channel layers were shown in the crystallized bi-layer plan-view TEM measurements. Based on these experimental results, the large-grained and less-defective Si microstructure is expected to form near the channel region of each VNAND cell transistor, which may improve the electrical characteristics.

  7. Measurements, Standards, and the SI.

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 1983

    1983-01-01

    Highlights six papers presented at the Seventh Biennial Conference on Chemical Education (Stillwater, Oklahoma 1982). Topics addressed included history, status, and future of SI units, algebra of SI units, periodic table, new standard-state pressure unit, and suggested new names for mole concept ("numerity" and "chemical amount"). (JN)

  8. Strain relaxation of GaAs/Ge crystals on patterned Si substrates

    SciTech Connect

    Taboada, A. G. Kreiliger, T.; Falub, C. V.; Känel, H. von; Isa, F.; Isella, G.; Salvalaglio, M.; Miglio, L.; Wewior, L.; Fuster, D.; Alén, B.; Niedermann, P.; Neels, A.; Dommann, A.; Mancarella, F.

    2014-01-13

    We report on the mask-less integration of GaAs crystals several microns in size on patterned Si substrates by metal organic vapor phase epitaxy. The lattice parameter mismatch is bridged by first growing 2-μm-tall intermediate Ge mesas on 8-μm-tall Si pillars by low-energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs crystals towards full pyramids exhibiting energetically stable (111) facets with decreasing Si pillar size. The release of the strain induced by the mismatch of thermal expansion coefficients in the GaAs crystals has been studied by X-ray diffraction and photoluminescence measurements. The strain release mechanism is discussed within the framework of linear elasticity theory by Finite Element Method simulations, based on realistic geometries extracted from scanning electron microscopy images.

  9. Tin induced a-Si crystallization in thin films of Si-Sn alloys

    SciTech Connect

    Neimash, V. E-mail: oleks.goushcha@nuportsoft.com; Poroshin, V.; Goushcha, A. O. E-mail: oleks.goushcha@nuportsoft.com; Shepeliavyi, P.; Yukhymchuk, V.; Melnyk, V.; Kuzmich, A.; Makara, V.

    2013-12-07

    Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si{sub 1−x}Sn{sub x}, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si{sub 1−x}Sn{sub x} exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

  10. Shape-controlled crystal growth of Sr3NbGa3Si2O14 and Sr3TaGa3Si2O14 piezoelectric crystals by the micro-pulling-down method.

    PubMed

    Yokota, Yuui; Sato, Masato; Futami, Yoshisuke; Tota, Kazushige; Onodera, Ko; Yanagida, Takayuki; Yoshikawa, Akira

    2012-09-01

    We grew column-shaped Sr(3)NbGa(3)Si(2)O(14) (SNGS) and Sr(3)TaGa(3)Si(2)O(14) (STGS) langasite-type piezoelectric single crystals by the micro-pulling-down (μ-PD) method. 3-mm-diameter SNGS and STGS crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die. According to X-ray rocking curve measurements, the grown crystals had crystallinity equivalent to that of crystals grown by the Czochralski (Cz) method. The crystals were single-phase materials with langasite-type crystal structure. The lattice parameters of the grown crystals were almost consistent with those of crystals grown by the Cz method. PMID:23007751

  11. Studies of relativistic electron scattering at planar alignment in a thin Si crystal

    NASA Astrophysics Data System (ADS)

    Takabayashi, Y.; Pivovarov, Yu. L.; Tukhfatullin, T. A.

    2014-04-01

    Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.

  12. Development of SiC Large Tapered Crystal Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Phil

    2011-01-01

    Research Focus Area: Power Electronics, Temperature Tolerant Devices. Demonstrate initial feasibility of totally new "Large Tapered Crystal" (LTC) process for growing vastly improved large-diameter wide-band gap wafers. Addresses Targets: The goal of this research is to experimentally investigate and demonstrate feasibility of the key unproven LTC growth processes in SiC. Laser-assisted growth of long SiC fiber seeds. Radial epitaxial growth enlargement of seeds into large SiC boules. Uniqueness and Impacts open a new technology path to large-diameter SiC and GaN wafers with 1000-fold defect density improvement at 2-4 fold lower cost. Leapfrog improvement in wide band gap power device capability and cost.

  13. Investigation on cubic boron nitride crystals doped with Si by high temperature thermal diffusion

    NASA Astrophysics Data System (ADS)

    Li, Xinlu; Feng, Shuang; Liu, Xiuhuan; Hou, Lixin; Gao, Yanjun; Wang, Qi; Liu, Nian; Zhang, Hai; Chen, Zhanguo; Zheng, Jie; Jia, Gang

    2014-07-01

    The method of high temperature thermal diffusion was successfully applied for doping Si impurities into cubic boron nitride (cBN) crystals. X-ray photoelectron spectra (XPS) and the current-voltage (I-V) characteristics at different temperatures were respectively used for analyzing the chemical states and the activation energy of Si impurity in cBN. According to the XPS results, Si impurities mainly replace B atoms bonding with the adjacent N atoms and become donors in cBN. Without surface cleaning, there are a lot of C and O contaminations on the surface of cBN, so a small quantity of C-Si and Si-N-O bonds also exist at the surface of cBN. Most Si impurities distribute in the shallow layer underneath the surface of cBN. Based on the electric measurement, Si impurities in cBN usually have the activation energy beyond 0.4 eV, and they can only be slightly ionized at room temperature, therefore the resistivity of Si-doped cBN is still high, and the space charge limited current becomes the main conductive mechanism in cBN. However, the conductivity of Si-doped cBN can rapidly increase with the temperature. In addition, the activation energy and the concentration of Si impurity in cBN can be affected by the temperature and the time of thermal diffusion, which needs to be verified further.

  14. Structural characterization of Lu1.8Y0.2SiO5 crystals

    NASA Astrophysics Data System (ADS)

    Chiriu, Daniele; Faedda, Nicola; Lehmann, Alessandra Geddo; Ricci, Pier Carlo; Anedda, Alberto; Desgreniers, Serge; Fortin, Emery

    2007-08-01

    The structural and vibrational properties of Lu1.8Y0.2SiO5 (LYSO) single crystals were investigated by means of Raman spectroscopy and x-ray diffraction measurements. Unit cell parameters and bond lengths were determined by Rietveld refinement of the collected x-ray diffraction powder spectra. By comparison with the vibrational spectra of the parent compounds Lu2SiO5 and Y2SiO5 and by using polarized Raman measurements, we propose the assignment of the principal vibrational modes of LYSO crystals. The strict connection of Raman spectra of the LYSO solid solution and of the pure lutetium and yttrium crystals, as well as the analysis of the polarized measurements, confirms that LYSO structure adopts the C2/c space group symmetry. The structural analogies of LYSO with the pure compound Lu2SiO5 are further shown by means of high pressure Raman spectroscopy, and the possibility of considering the LYSO crystal analogous to the LSO structure with a tensile stress between 0.25 and 0.80GPa is discussed.

  15. Piezoelectric Ca3NbGa3Si2O14 crystal: crystal growth, piezoelectric and acoustic properties

    NASA Astrophysics Data System (ADS)

    Roshchupkin, Dmitry; Ortega, Luc; Plotitcyna, Olga; Erko, Alexei; Zizak, Ivo; Vadilonga, Simone; Irzhak, Dmitry; Emelin, Evgenii; Buzanov, Oleg; Leitenberger, Wolfram

    2016-08-01

    Ca3NbGa3Si2O14 (CNGS), a five-component crystal of lanthanum-gallium silicate group, was grown by the Czochralski method. The parameters of the elementary unit cell of the crystal were measured by powder diffraction. The independent piezoelectric strain coefficients d{}_{11} and d_{14} were determined by the triple-axis X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves (SAW) were studied by high-resolution X-ray diffraction at BESSY II synchrotron radiation source. The velocity of SAW propagation and power flow angles in the Y-, X- and yxl/{+}36°-cuts of the CNGS crystal were determined from the analysis of the diffraction spectra. The CNGS crystal was found practically isotropic by its acoustic properties.

  16. Crystal structure of laser-induced subsurface modifications in Si

    SciTech Connect

    Verburg, P. C.; Smillie, L. A.; Römer, G. R. B. E.; Haberl, B.; Bradby, J. E.; Williams, J. S.; Huis in ’t Veld, A. J.

    2015-06-04

    Laser-induced subsurface modification of dielectric materials is a well-known technology. Applications include the production of optical components and selective etching. In addition to dielectric materials, the subsurface modification technology can be applied to silicon, by employing near to mid-infrared radiation. An application of subsurface modifications in silicon is laser-induced subsurface separation, which is a method to separate wafers into individual dies. Other applications for which proofs of concept exist are the formation of waveguides and resistivity tuning. However, limited knowledge is available about the crystal structure of subsurface modifications in silicon. In this paper, we investigate the geometry and crystal structure of laser-induced subsurface modifications in monocrystalline silicon wafers. Finally, in addition to the generation of lattice defects, we found that transformations to amorphous silicon and Si-iii/Si-xii occur as a result of the laser irradiation.

  17. Crystal nucleation in Pd-Si alloys. [in containerless environment

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Turnbull, D.

    1982-01-01

    A study of the crystal phase nucleation in undercooled droplets of Pd-Si alloys with composition near the Pd(84.5)Si(15.5) eutectic composition is reported. Molten droplets are released at the top of a drop tube and solidify (to either a crystalline or glassy state) during descent. This provides a containerless (and nearly gravity free) environment so that nucleation due to container walls or vibrations is eliminated. It is found that crystallization, due to homogeneous nucleation, is bypassed in droplets of 1 mm diameter when cooled at 760 K/sec. From this an upper limit of the homogeneous nucleation rate is estimated. Results are compared with a previously published study of nucleation in 0.06 mm to 0.33 mm diameter droplets, which indicated that nucleation results from heterogeneous surface nucleation and that the number of these nuclei is dependent on the atmosphere in the drop tube.

  18. Growth and characterization of large CdSiP 2 single crystals

    NASA Astrophysics Data System (ADS)

    Zawilski, Kevin T.; Schunemann, Peter G.; Pollak, Thomas C.; Zelmon, David E.; Fernelius, Nils C.; Kenneth Hopkins, F.

    2010-04-01

    Large, optically transparent crystals of CdSiP 2 (CSP) have been grown for the first time from a stoichiometric melt. The material is a high temperature analog to ZnGeP 2 with promising characteristics for IR frequency conversion. Crystals are birefringent and are transparent from 0.5 to 9 μm. Polycrystalline charges were successfully synthesized from high purity elemental starting materials by two-temperature vapor transport despite the very high equilibrium vapor pressure (˜22 atm) at the melting point of CdSiP 2 (1133 °C). Single crystals were grown using the horizontal gradient freeze (HGF) technique in high-temperature transparent furnaces. Over the course of several growth runs, the material proved to be prone to cracking and to twinning along (1 1 2) planes. Twinning was eliminated by seeded growth along directions normal to the 112 planar boundaries. Further modifications to growth conditions resulted in high optical quality, crack- and twin-free single crystals 70×25×8 mm 3. The largest CdSiP 2 single crystals previously reported in the literature were grown through either halogen assisted vapor transport or from a molten Sn flux and measured 2×2×0.2 mm 3. The HGF growth of large CdSiP 2 crystals has allowed several bulk properties to be measured for the first time, including the thermal expansion coefficients, thermal conductivity, and wavelength dependent birefringence and dispersion. Measurements of the optical and thermal properties reveal this to be an extremely promising material for 1-, 1.5-, and 2 μm-pumped mid-IR lasers.

  19. Optical hyperpolarization and inductive readout of 31P donor nuclei in natural abundance single crystal 29Si

    NASA Astrophysics Data System (ADS)

    Alexander, Thomas; Haas, Holger; Deshpande, Rahul; Gumann, Patryk; Cory, David

    2016-05-01

    We optically polarize and inductively detect 31P donor nuclei in single crystal silicon at high magnetic fields (6 . 7T). Samples include both natural abundance 29Si and an isotopically purified 28Si sample. We observe dipolar order in the 29Si nuclear spins through a spin-locking measurement. This provides a means of characterizing spin transport in the vicinity of the 31P donors.

  20. Crystallization kinetics and magnetic properties of FeSiCr amorphous alloy powder cores

    NASA Astrophysics Data System (ADS)

    Xu, Hu-ping; Wang, Ru-wu; Wei, Ding; Zeng, Chun

    2015-07-01

    The crystallization kinetics of FeSiCr amorphous alloy, characterized by the crystallization activation energy, Avrami exponent and frequency factor, was studied by non-isothermal differential scanning calorimetric (DSC) measurements. The crystallization activation energy and frequency factor of amorphous alloy calculated from Augis-Bennett model were 476 kJ/mol and 5.5×1018 s-1, respectively. The Avrami exponent n was calculated to be 2.2 from the Johnson-Mehl-Avrami (JMA) equation. Toroid-shaped Fe-base amorphous powder cores were prepared from the commercial FeSiCr amorphous alloy powder and subsequent cold pressing using binder and insulation. The characteristics of FeSiCr amorphous alloy powder and the effects of compaction pressure and insulation content on the magnetic properties, i.e., effective permeability μe, quality factor Q and DC-bias properties of FeSiCr amorphous alloy powder cores, were investigated. The FeSiCr amorphous alloy powder cores exhibit a high value of quality factor and a stable permeability in the frequency range up to 1 MHz, showing superior DC-bias properties with a "percent permeability" of more than 82% at H=100 Oe.

  1. Identifying crystallization- and incorporation-limited regimes during vapor-liquid-solid growth of Si nanowires.

    PubMed

    Pinion, Christopher W; Nenon, David P; Christesen, Joseph D; Cahoon, James F

    2014-06-24

    The vapor-liquid-solid (VLS) mechanism is widely used for the synthesis of semiconductor nanowires (NWs), yet several aspects of the mechanism are not fully understood. Here, we present comprehensive experimental measurements on the growth rate of Au-catalyzed Si NWs over a range of temperatures (365-480 °C), diameters (30-200 nm), and pressures (0.1-1.6 Torr SiH4). We develop a kinetic model of VLS growth that includes (1) Si incorporation into the liquid Au-Si catalyst, (2) Si evaporation from the catalyst surface, and (3) Si crystallization at the catalyst-NW interface. This simple model quantitatively explains growth rate data collected over more than 65 distinct synthetic conditions. Surprisingly, upon increasing the temperature and/or pressure, the analysis reveals an abrupt transition from a diameter-independent growth rate that is limited by incorporation to a diameter-dependent growth rate that is limited by crystallization. The identification of two distinct growth regimes provides insight into the synthetic conditions needed for specific NW-based technologies, and our kinetic model provides a straightforward framework for understanding VLS growth with a range of metal catalysts and semiconductor materials. PMID:24815744

  2. Si-O Bonded Interactions in Silicate Crystals and Molecules: A Comparison

    SciTech Connect

    Gibbs, Gerald V.; Jayatilaka, Dylan; Spackman, M. A.; Cox, David F.; Rosso, Kevin M.

    2006-11-16

    Bond critical point, local kinetic energy density, G(rc), and local potential energy density, V(rc), properties of the electron density distributions, ρ(r), calculated for silicates like quartz and molecules like disiloxane are similar, indicating that the forces that govern the Si-O bonded interactions in crystals are short-ranged and molecular-like. Using the G(rc)/ρ(rc) ratio as a measure of bond character, the ratio increases as the Si-O bond length, the local electronic energy density, H(rc) = G(rc) + V(rc), and the oordination number of the Si atom decrease, and as the value of the electron density at the bond critical point, ρ(rc) and the Laplacian, ∇2ρ(rc), increase. The G(rc)/ρ(rc) and H(rc)/ρ(rc) ratios categorize the bond as observed for other second row atom M-O bonds into nonequivalent classes with the covalent character of each of the M-O bonds increasing with the H(rc)/ρ(rc) ratio. Some workers consider the Si-O bond to be highly ionic and others considered it to be either intermediate or substantially covalent. The character of the bond is examined in terms of the large net atomic basin charges conferred on the Si atoms comprising disiloxane, stishovite, quartz and forsterite, the domains of localized electron density along the Si-O bond vectors and on the reflex side of the Si-O-Si angle together with the close similarity of the Si-O bonded interactions observed for a variety of hydroxyacid silicate molecules and a large number of silicate crystals. The bond critical point and local energy density properties of the electron density distribution indicate that the bond is intermediate in character between Al-O and P-O bonded interations rather than being ionic or covalent.

  3. Magnetic order and crystal structure study of YNi{sub 4}Si-type NdNi{sub 4}Si

    SciTech Connect

    Yao, Jinlei; Isnard, O.; Morozkin, A.V.; Ivanova, T.I.; Koshkid'ko, Yu.S.; Bogdanov, A.E.; Nikitin, S.A.; Suski, W.

    2015-02-15

    Magnetic measurements and neutron powder diffraction investigation of the magnetic structure of the orthorhombic YNi{sub 4}Si-type (space group Cmmm) NdNi{sub 4}Si compound are presented. The magnetocaloric effect of NdNi{sub 4}Si is calculated in terms of the isothermal magnetic entropy change and it reaches the maximum value of –3.3 J/kg K for a field change of 50 kOe near T{sub C}=12 K. Below ∼12 K, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group in a zero magnetic field. At 1.5 K, the neodymium atoms have the magnetic moment of 2.37(5) μ{sub B}. The orthorhombic crystal structure and its thermal evolution are discussed in comparison with the CaCu{sub 5}-type compound. - Graphical abstract: The NdNi{sub 4}Si supplement the series of the orthorhombic derivative of the CaCu{sub 5}-type, namely the YNi{sub 4}Si-type, RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho). Below ∼12 K in a zero applied magnetic field, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group. Compared to the CaCu{sub 5}-type NdNi{sub 4}Si compound, the YNi{sub 4}Si-type counterpart has the relatively high ferromagnetic ordering temperature (9.2 K vs. 12 K), the small magnetocaloric effect (–7.3 J/kg K vs. –3.3 J/kg K for ∆H=50 kOe), and the large magnetic anisotropy at low temperatures. In contrast with CaCu{sub 5}-type NdNi{sub 4}Si, YNi{sub 4}Si-type NdNi{sub 4}Si shows distinct hysteresis loop at 2 K.We suggest that orthorhombic distortion may be used as a prospective route for optimization of permanent magnetic properties in the family of CaCu{sub 5}-type rare earth materials. - Highlights: • Below ∼12 K the YNi{sub 4}Si-type NdNi{sub 4}Si shows a ferromagnetic ordering. • MCE of NdNi{sub 4}Si reaches value of –3.3 J/kg K in 0–50 kOe near Curie point. • NdNi{sub 4}Si exhibits b-axis ferromagnetic order with the Cmm′m magnetic space

  4. Crystal structure of laser-induced subsurface modifications in Si

    DOE PAGESBeta

    Verburg, P. C.; Smillie, L. A.; Römer, G. R. B. E.; Haberl, B.; Bradby, J. E.; Williams, J. S.; Huis in ’t Veld, A. J.

    2015-06-04

    Laser-induced subsurface modification of dielectric materials is a well-known technology. Applications include the production of optical components and selective etching. In addition to dielectric materials, the subsurface modification technology can be applied to silicon, by employing near to mid-infrared radiation. An application of subsurface modifications in silicon is laser-induced subsurface separation, which is a method to separate wafers into individual dies. Other applications for which proofs of concept exist are the formation of waveguides and resistivity tuning. However, limited knowledge is available about the crystal structure of subsurface modifications in silicon. In this paper, we investigate the geometry and crystalmore » structure of laser-induced subsurface modifications in monocrystalline silicon wafers. Finally, in addition to the generation of lattice defects, we found that transformations to amorphous silicon and Si-iii/Si-xii occur as a result of the laser irradiation.« less

  5. Crystal structure of SiB/sub 6/

    SciTech Connect

    Vlasse, M.; Slack, G.A.; Garbauskas, M.; Kasper, J.S.; Viala, J.C.

    1986-06-01

    The accurate and detailed structure of the compound SiB/sub 6/ has been determined by single-crystal X-ray diffraction. The final R value was 6.1% for 4225 reflections. The cell is orthorhombic with space group Pnnm and a = 14.397(7) A, b = 18.318(9) A, c = 9.911(7) A, and from the electron density appears to contain 43 silicon atoms and 238 boron atoms. The structure contains many features found in other structures of boron-rich phases, and obeys the crystal chemistry rules established for them. It contains interconnected icosahedra, icosihexahedra, as well as several isolated boron and silicon atoms. An unusual feature of this structure is the presence of icosihexahedra containing silicon atoms similar to those found previously in BeB/sub 3/.

  6. Si

    NASA Astrophysics Data System (ADS)

    Fiameni, S.; Famengo, A.; Agresti, F.; Boldrini, S.; Battiston, S.; Saleemi, M.; Johnsson, M.; Toprak, M. S.; Fabrizio, M.

    2014-06-01

    Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion in the middle-high temperature range. The detrimental effect of the presence of MgO on the TE properties of Mg2Si based materials is widely known. For this reason, the conditions used for synthesis and sintering were optimized to limit oxygen contamination. The effect of Bi doping on the TE performance of dense Mg2Si materials was also investigated. Synthesis was performed by ball milling in an inert atmosphere starting from commercial Mg2Si powder and Bi powder. The samples were consolidated, by spark plasma sintering, to a density >95%. The morphology, and the composition and crystal structure of samples were characterized by field-emission scanning electronic microscopy and x-ray diffraction, respectively. Moreover, determination of Seebeck coefficients and measurement of electrical and thermal conductivity were performed for all the samples. Mg2Si with 0.1 mol% Bi doping had a ZT value of 0.81, indicative of the potential of this method for fabrication of n-type bulk material with good TE performance.

  7. Single crystal growth and characterization of URu2Si2

    NASA Astrophysics Data System (ADS)

    Haga, Yoshinori; Matsuda, Tatsuma D.; Tateiwa, Naoyuki; Yamamoto, Etsuji; Ōnuki, Yoshichika; Fisk, Zachary

    2014-11-01

    We review recent progress in single crystal growth and study of electronic properties in ?. Czocharalski pulling, using purified uranium metal and subsequent annealing under ultra-high vacuum, is successfully applied to this compound, and it yields the highest residual resistivity ratio. These high-quality single crystals allow us to investigate Fermi surfaces using quantum oscillation and to make detailed transport measurements at low temperature.

  8. GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

    NASA Astrophysics Data System (ADS)

    Taboada, A. G.; MeduÅa, M.; Salvalaglio, M.; Isa, F.; Kreiliger, T.; Falub, C. V.; Barthazy Meier, E.; Müller, E.; Miglio, L.; Isella, G.; von Känel, H.

    2016-02-01

    Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of {111} planes and an apex formed by {137} and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

  9. Orientational bonding of phases accompanying directed crystallization of the eutectic of the system Si-TiSi2

    NASA Astrophysics Data System (ADS)

    Derevyagina, L. S.; Butkevich, L. M.

    1987-09-01

    The characteristic features of structure formation in cast and direct crystallized alloys of the system Si-TiSi2 were studied. It is shown that the predominant orientation of the bonding of the phases in directionally crystallized eutectics (DE) of the system Si-TiSi2, observed at the stage of steady-state growth, already appears on the surface of nucleation, which apparently indicates that the nucleation of the phases in the alloys of this system is of an epitaxial character.

  10. Study of hydrogen states in a-Si:H films, dehydrogenization treatments and influence of hydrogen on nanosecond pulse laser crystallization of a-Si:H

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Galkov, M. S.; Safronova, N. A.; Kamaev, G. N.; Antonenko, A. H.; Kochubey, S. A.

    2014-12-01

    Structures based on hydrogenated amorphous silicon (a-Si:H) films deposited on various substrates (including not refractory ones) are widely applied in giant microelectronics devices, such as flat panel displays based on active matrix thin-film transistors and solar cells. The a-Si:H films produced by plasma enhanced chemical vapor deposition (PECVD) methods, contain up to 40% atoms of hydrogen. The influence of hydrogen on the optical and electrical properties of the films and their degradation is important. Therefore, the development of express and non-destructive methods for control of the hydrogen concentration in thin films continues to be an actual task to date. Previously, from a comparative analysis of infrared (IR) spectroscopy and Raman scattering spectroscopy, the ratios of the integral intensities of Raman peaks due to scattering by vibrations of the Si-H and Si-H2 bonds to the intensity of Raman peak of the Si-Si bonds were experimentally determined. Knowing these ratios, it is possible to measure the hydrogen concentration, moreover, separately in Si-H and Si-H2 states. Proposed quantitative method for determining of the hydrogen concentration from analysis of the Raman spectra is an express, non-destructive method and can be used for "in situ" monitoring of the hydrogen. The aim of this work was to determine the polarization dependence of Raman scattering by stretching vibrations of Si-H bonds and find the form of the corresponding Raman tensors. From analysis of Raman intensities in different polarizations the Raman tensors for Si-H and Si-H2 bonds were determined. The regimes for dehydrogenization of thick (up to 1 micron) a-Si:H films were found. The nanosecond pulse XeCl laser with wavelength of 308 nm and pulse duration of 10 ns was used for pulse crystallization of as-deposited and dehydrogenated films. As it was studied earlier, for a-Si:H films with high hydrogen concentration, the threshold for crystallization is very close to threshold of

  11. Charge transfer of single laser crystallized intrinsic and phosphorus-doped Si-nanocrystals visualized by Kelvin probe force microscopy

    SciTech Connect

    Xu, Jie; Xu, Jun Lu, Peng; Shan, Dan; Li, Wei; Chen, Kunji

    2014-10-07

    Isolated intrinsic and phosphorus doped (P-doped) Si-nanocrystals (Si-NCs) on n- and p-Si substrates are fabricated by excimer laser crystallization techniques. The formation of Si-NCs is confirmed by atomic force microscopy (AFM) and conductive AFM measurements. Kelvin probe force microscopy (KPFM) is then carried out to visualize the trapped charges in a single Si-NC dot which derives from the charge transfer between Si-NCs and Si substrates due to their different Fermi levels. The laser crystallized P-doped Si-NCs have a similar Fermi level around the mid-gap to the intrinsic counterparts, which might be caused by the inactivated impurity atoms or the surface states-related Fermi level pinning. A clear rise of the Fermi level in P-doped Si-NCs is observed after a short time thermal annealing treatment, indicating the activation of dopants in Si-NCs. Moreover, the surface charge quantity can be estimated using a simple parallel plate capacitor model for a quantitative understanding of the KPFM results at the nanoscale.

  12. Plastic anisotropy in MoSi{sub 2} single crystals

    SciTech Connect

    Mitchell, T.E.; Maloy, S.A.

    1993-05-01

    Single crystals Of MoSi{sub 2} are an order of magnitude stronger when compressed along [001] than along any other orientation. This is because the easy slip systems, <101><100> and <110><111>, have a zero Schmid factor acting on them so that harder slip systems are forced into operation. We find that [001] crystals compressed at 1OOO{degree}C yield by slip on <103><331>. TEM shows that the 1/2<331> dislocations tend to decompose into 1/2<111> and <110> dislocations. This decomposition process apparently inhibits the mobility of 1/2<331> dislocations at higher temperatures and another system, <101><1ll>, becomes operative at 1300{degree}C and above. [021] crystals have been tested for comparison and are found to yield at much lower stresses on the easy systems. In the design of advanced high temperature structural materials based on MOSi{sub 2}, the large plastic anisotropy should be used to advantage.

  13. The closo-Si12C12 molecule from cluster to crystal: A theoretical prediction

    NASA Astrophysics Data System (ADS)

    Duan, Xiaofeng F.; Burggraf, Larry W.

    2016-03-01

    The structure of closo-Si12C12 is unique among stable SinCm isomers (n, m > 4) because of its high symmetry, π-π stacking of C6 rings and unsaturated silicon atoms at symmetrical peripheral positions. Dimerization potential surfaces reveal various dimerization reactions that form between two closo-Si12C12 molecules through Si-Si bonds at unsaturated Si atoms. As a result the closo-Si12C12 molecule is capable of polymerization to form stable 1D polymer chains, 2D crystal layers, and 3D crystals. 2D crystal structures formed by side-side polymerization satisfy eight Si valences on each monomer without large distortion of the monomer structure. 3D crystals are formed by stacking 2D structures in the Z direction, preserving registry of C6 rings in monomer moiety.

  14. Calcium aluminate silicate Ca2Al2SiO7 single crystal applicable to piezoelectric sensors at high temperature

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroaki; Hagiwara, Manabu; Noguchi, Hiroaki; Hoshina, Takuya; Takahashi, Tomoko; Kodama, Nobuhiro; Tsurumi, Takaaki

    2013-06-01

    Ca2Al2SiO7 (CAS) bulk single crystals were grown by the Czochralski method. Material constants of the crystal were determined over the driving temperature range of a typical combustion pressure sensor. The electrical resistivity at 800 °C was found to be of the order of 108 Ωcm. We constructed a measurement system for the direct piezoelectric effect at high temperature, and characterized the crystals in a simulated engine cylinder combustion environment. Output charge signal against applied stress was detected at 700 °C. These observations suggest that CAS crystals are superior candidate materials for high temperature for stress sensing.

  15. Investigation of single crystal zircon, (Zr,Pu)SiO4 doped with Pu

    NASA Astrophysics Data System (ADS)

    Hanchar, J. M.; Burakov, B. E.; Anderson, E. B.; Zamoryanskaya, M. V.

    2003-04-01

    Zircon-based ceramics are under consideration as durable waste forms for immobilization of weapons grade plutonium and other actinide elements. Samples of polycrystalline zircon doped with 238Pu and 239Pu have been obtained in previous studies. These materials, however, are difficult to use for precise measurement of the leach-rate of Pu, and to accurately determine the level of Pu doping that can be attained in zircon, (Zr,Pu)SiO_4. Single crystals of 238Pu doped zircon (ranging from 0.3 to 3.5 mm in size) were successfully grown for the first time ever using a Li-Mo flux synthesis method. The incorporation of Pu ranged from 1.9 to 4.7 wt. % el. (with approximately 81 wt.% of 238Pu isotope) based on electron microprobe analysis. The zircon crystals were pinkish-brown when they were crystallized, and then over a period of five months changed to a brown color. After fourteen months the crystals turned to a brown-gray color. The zircon crystals glow in the dark probably from alpha particle induced luminescence. The intensity of the cathodoluminescence (CL) emission in the Pu doped crystals is correlated with the Pu content, and the CL emission showed no change 141 days after the initial CL measurements were made. Single crystal X-ray diffraction results obtained 141 days after synthesis indicate unit cell parameters (in angstroms): a = 6.6267(15), c = 5.9992(10) and a cell volume of 263.41(10). When the zircon crystals were grown, they were free of cracks. Over the course of five months cracks appeared throughout the crystals, and after fourteen months the cracks became much more abundant. The zircon crystals were transparent upon crystallization, and even with numerous cracks throughout the crystals remain transparent. Radiation damage calculations indicate that after only a short period of time, six months, these zircon crystals had already accumulated significant alpha-induced radiation damage (˜2.5 x1014 alpha-decay events per milligram). After five years they

  16. Kinetics of Isothermal Melt Crystallization in CaO-SiO2-CaF2-Based Mold Fluxes

    NASA Astrophysics Data System (ADS)

    Seo, Myung-Duk; Shi, Cheng-Bin; Baek, Ji-Yeon; Cho, Jung-Wook; Kim, Seon-Hyo

    2015-10-01

    A kinetic study for isothermal melt crystallization of CaO-SiO2-CaF2-based mold fluxes with different basicity of 0.94 and 1.34 has been carried out systematically by DSC measurements. The kinetic parameters were determined by Johnson-Mehl-Avrami equation. The average Avrami exponent of cuspidine (3CaO·2SiO2·CaF2) crystallization for mold flux of lower basicity (0.94) is calculated to be 3.1, implying that the crystallization mode is instantaneous nucleation followed by 3-dimensional growth. For the mold flux of higher basicity (1.34), the average Avrami exponent of cuspidine equals to 3.4, strongly suggesting that the growth is still 3 dimensional but the nucleation should be continuous. It was found that the effective crystallization rate constant for both mold fluxes increases as the crystallization temperature decreases, showing that the crystallization rate could be governed by nucleation rate. The negative effective activation energy indicates an anti-Arrhenius behavior for crystallization of the mold fluxes studied. Therefore, it is concluded that the melt crystallization for the commercial mold fluxes will be determined by thermodynamics of nucleation which is relevant to degree of undercooling. The morphology of cuspidine crystals observed by SEM agreeds well with the isothermal crystallization kinetics results.

  17. Evaluation of Stress and Crystal Quality in Si During Shallow Trench Isolation by UV-Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kosemura, Daisuke; Hattori, Maki; Yoshida, Tetsuya; Mizukoshi, Toshikazu; Ogura, Atsushi

    2010-06-01

    Defects and stress gradually accumulate throughout various Si large-scale integration fabrication processes. It is essential to monitor defects and stress carefully to suppress their unintentional introduction. In this study, we measured the stress and crystal quality in shallow trench isolation (STI) samples by ultraviolet (UV)-Raman spectroscopy with an extremely high-resolution wavenumber to evaluate the effect of post-annealing on the recovery of Si crystals. The variations of crystal quality in 200-mm wafers with STI structures gradually decreased after post-annealing for 4 h, 6 h, and 8 h; however, there was no substantial difference in the values of full-width at half-maximum of the Raman spectra. Precise measurements of variations of stress and crystal quality were successfully performed by UV-Raman spectroscopy with a high-resolution wavenumber, which enabled us to evaluate the STI process accurately.

  18. SiPM optical crosstalk amplification due to scintillator crystal: effects on timing performance

    NASA Astrophysics Data System (ADS)

    Gola, Alberto; Ferri, Alessandro; Tarolli, Alessandro; Zorzi, Nicola; Piemonte, Claudio

    2014-07-01

    For a given photon detection efficiency (PDE), the primary, Poisson distributed, dark count rate of the detector (DCR0) is one of the most limiting factors affecting the timing resolution of a silicon photomultiplier (SiPM) in the scintillation light readout. If the effects of DCR0 are removed through a suitable baseline compensation algorithm or by cooling, it is possible to clearly observe another phenomenon that limits the PDE, and thus the timing resolution of the detector. It is caused by the optical crosstalk of the SiPM, which is significantly increased by the presence of the scintillator. In this paper, we describe this phenomenon, which is also easily observed from the reverse I-V curve of the device, and we relate it to the measured coincidence resolving time in 511 keV γ-ray measurements. We discuss its consequences on the SiPM design and, in particular, we observe that there is an optimal cell size, dependent on both SiPM and crystal parameters, that maximizes the PDE in presence of optical crosstalk. Finally, we report on a crosstalk simulator developed to study the phenomenon and we compare the simulation results obtained for different SiPM technologies, featuring different approaches to the reduction of the crosstalk.

  19. SiPM optical crosstalk amplification due to scintillator crystal: effects on timing performance.

    PubMed

    Gola, Alberto; Ferri, Alessandro; Tarolli, Alessandro; Zorzi, Nicola; Piemonte, Claudio

    2014-07-01

    For a given photon detection efficiency (PDE), the primary, Poisson distributed, dark count rate of the detector (DCR0) is one of the most limiting factors affecting the timing resolution of a silicon photomultiplier (SiPM) in the scintillation light readout. If the effects of DCR0 are removed through a suitable baseline compensation algorithm or by cooling, it is possible to clearly observe another phenomenon that limits the PDE, and thus the timing resolution of the detector. It is caused by the optical crosstalk of the SiPM, which is significantly increased by the presence of the scintillator. In this paper, we describe this phenomenon, which is also easily observed from the reverse I-V curve of the device, and we relate it to the measured coincidence resolving time in 511 keV γ-ray measurements. We discuss its consequences on the SiPM design and, in particular, we observe that there is an optimal cell size, dependent on both SiPM and crystal parameters, that maximizes the PDE in presence of optical crosstalk. Finally, we report on a crosstalk simulator developed to study the phenomenon and we compare the simulation results obtained for different SiPM technologies, featuring different approaches to the reduction of the crosstalk. PMID:24922188

  20. Effect of SiO2 on the Crystal Structure Stability of SFC at 1473 K (1200 °C)

    NASA Astrophysics Data System (ADS)

    Ding, Xiang; Guo, Xing-Min; Ma, Chen-Yan; Tang, Kun; Zhao, Yi-Dong

    2015-03-01

    Silico-ferrite of calcium (SFC) is a key intermediate phase in the sintering process of fine iron ores, and SiO2 plays an important role in the formation of SFC. In this work, the crystal structure stability of SFC synthesized at 1473 K (1200 °C) has been determined by X-ray diffraction, field-emission scanning electron microscopy, and X-ray absorption spectra. Synthesis of SFC was carried out under air at 1473 K (1200 °C) by mixing different amounts of SiO2 with Fe2O3 and CaCO3. The results show that the maximum solid solubility of SiO2 in the crystal structure of SFC does not exceed 6.11 wt pct at 1473 K (1200 °C); under these conditions, Fe2O3 begins to appear. The process of Si solution is closely related to the presence of a Ca channel composed of Ca octahedron in the crystal structure of SFC based on the results from the measurements of Ca K-edge X-ray absorption spectra. Si mainly occupies the center positions of the upper and lower tetrahedron adjacent to Ca channel. The length of Ca-Ca bond in Ca channel increases with the increasing of Si content. The crystal structure stability of SFC may be related to the structure of the Ca channel.

  1. Electroactive complex in thermally treated Ge-Si crystals

    SciTech Connect

    Azhdarov, G. Kh.; Zeynalov, Z. M.; Zakhrabekova, Z. M.; Kyazimova, A. I.

    2010-05-15

    It is shown by Hall measurements that quenching complexly doped Ge{sub 1-x}Si{sub x} (0 {<=} x {<=} 0.20) crystals from 1050-1080 K leads to the formation of additional electroactive acceptor centers in them. The activation energy of these centers increases linearly with an increase in the silicon content in the crystal and is described by the relation E{sub k}{sup x} = (52 + 320x) meV. Annealing these crystals at 550-570 K removes the additional acceptor levels. It is established that the most likely model for the additional electroactive centers is a pair composed of substituent copper and aluminum atoms (Cu{sub s}Al{sub s}) or interstitial copper and substituent aluminum atoms (Cu{sub i}Al{sub s}). It is shown that the generation of additional deep acceptor levels must be taken into account when using the method of precise doping of Ge{sub 1-x}Si{sub x} crystals with copper.

  2. Dynamic crystallization during non-isothermal laser treatment of Fe-Si-B metallic glass

    NASA Astrophysics Data System (ADS)

    Joshi, Sameehan S.; Gkriniari, Anna V.; Katakam, Shravana; Dahotre, Narendra B.

    2015-12-01

    Fe-Si-B metallic glass foils were subjected to non-isothermal laser treatment to induce crystallization, and the effect of laser fluence on crystallite size was investigated. Temperature, and corresponding heating and cooling rates generated during laser processing of metallic glass were estimated using multiphysics computational models. Estimation of the onset and arrest temperatures of crystallization was based on the results obtained using the thermal model. Crystallite size was measured with the aid of x-ray diffraction and transmission electron microscopy. The fraction of crystallization was estimated with a differential scanning calorimetry. Crystallite size increased with laser fluence in the initial stages and saturated later within the laser fluence range (0.6-0.9 J mm-2) explored in the current efforts. The fraction of crystallization steadily increased with the increase in laser fluence. Unlike conventional processes, in the present situation the dynamic effects during laser processing dominated the crystallization and growth process. Rapid heating rates during laser processing led to a shift in the onset of crystallization temperature to a higher level. Faster cooling rates prematurely arrested the crystallite growth yielding much finer crystallite sizes.

  3. Morphology and kinetics of crystallization of amorphous V75Si25 thin-alloy films

    NASA Astrophysics Data System (ADS)

    Nava, F.; Weiss, B. Z.; Tu, K. N.; Smith, D. A.; Psaras, P. A.

    1986-10-01

    Electrical and microstructural changes of coevaporated V75Si25 alloy thin films have been studied as a function of temperature from room temperature to 830 °C. In situ resistivity measurements, hot-stage transmission electron microscopy, Rutherford backscattering spectroscopy and the Seeman-Bohlin glancing angle incidence x-ray diffraction technique were applied. Upon heat treatment at a heating rate of 8 °C/min, a sharp decrease in resistivity occurs at ˜670 °C which results from an amorphous to crystalline phase transformation. The crystallized phase was identified as V3Si. The mechanism of transformation is random nucleation at a rapidly decreasing rate and a fast quasi-isotropic growth. The kinetics of crystallization have been studied by utilizing electrical resistivity measurements during isothermal heat treatment. Six different temperatures between 570 °C and 630 °C were adopted. The apparent activation energy (˜3.6 eV) obtained from isothermal measurements was found to be in agreement with that obtained from nonisothermal treatments at varying rates of heating. The distinct change of the Avrami mode parameter from 4 to 2 at a constant value of t/τ during the process of crystallization is not immediately understood.

  4. Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si

    NASA Astrophysics Data System (ADS)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Ferla, G.; Baroetto, F.; Licciardello, A.

    1988-12-01

    The epitaxial crystallization of chemical vapor deposited Si layers on <100> Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350-500 °C. During irradiation the single crystal-amorphous interface velocity was measured in situ by monitoring the reflectivity of He-Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.

  5. Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

    NASA Astrophysics Data System (ADS)

    Shi, Yong-gui; Dai, Pei-yun; Yang, Jian-feng; Jin, Zhi-hao; Liu, Hu-lin

    2012-07-01

    The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically investigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homogeneous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a flat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces between the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with flat growth shapes.

  6. Electron microscopy study of Ni induced crystallization in amorphous Si thin films

    SciTech Connect

    Radnóczi, G. Z.; Battistig, G.; Pécz, B.; Dodony, E.; Vouroutzis, N.; Stoemenos, J.; Frangis, N.; Kovács, A.

    2015-02-17

    The crystallization of amorphous silicon is studied by transmission electron microscopy. The effect of Ni on the crystallization is studied in a wide temperature range heating thinned samples in-situ inside the microscope. Two cases of limited Ni source and unlimited Ni source are studied and compared. NiSi{sub 2} phase started to form at a temperature as low as 250°C in the limited Ni source case. In-situ observation gives a clear view on the crystallization of silicon through small NiSi{sub 2} grain formation. The same phase is observed at the crystallization front in the unlimited Ni source case, where a second region is also observed with large grains of Ni{sub 3}Si{sub 2}. Low temperature experiments show, that long annealing of amorphous silicon at 410 °C already results in large crystallized Si regions due to the Ni induced crystallization.

  7. Single crystal growth of type I Na-Si clathrate by using Na-Sn flux

    NASA Astrophysics Data System (ADS)

    Morito, Haruhiko; Shimoda, Masashi; Yamane, Hisanori

    2016-09-01

    Single crystals of type I Na-Si clathrate, Na8Si46, were synthesized by heating Na, Na4Si4, and Na15Sn4 at 723 K under an Ar gas pressure of 104 Pa for 12 h. The single crystals having {110} habit planes grew up to 1.5 mm in size due to Na evaporation from a Na-Si-Sn melt with a starting compositional molar ratio of Na/Si/Sn=5.75:2:1.

  8. Growth of cubic SiC single crystals by the physical vapor transport technique

    NASA Astrophysics Data System (ADS)

    Semmelroth, K.; Krieger, M.; Pensl, G.; Nagasawa, H.; Püsche, R.; Hundhausen, M.; Ley, L.; Nerding, M.; Strunk, H. P.

    2007-10-01

    Suitable process parameters for the growth of cubic 3C-SiC single crystals via the seeded physical vapor transport (PVT) technique, also known as the modified Lely method, have been determined. Free-standing, 200 μm thick 3C-SiC epilayers with (0 0 1)- or (0 0 1¯)-face grown on undulant Si (0 0 1) as well as 3C-SiC platelets with [1 1 1]- or [1¯ 1¯ 1¯]-orientation grown by thermal decomposition of methyl trichlorosilane in hydrogen were employed as seed crystals. The source material consisted of stoichiometric SiC; in addition, a separate Si source was deposited in the furnace at a temperature of about 1500 °C. The temperature of the seed crystals was kept at about 1900 °C. Stable growth of 3C-SiC bulk material of high crystalline quality was reached on 3C-SiC seed crystals with (0 0 1)-face providing a low density of planar defects and at near-thermal-equilibrium conditions resulting in a reduction of internal stress and as a consequence in avoiding the generation of new extended crystal defects. The growth rate achieved under these conditions was approximately 0.05 mm/h. The nitrogen donor concentration in the grown 3C-SiC crystals was determined to be equal to (2-6)×10 18 cm -3.

  9. Synthesis and crystal growth of Mg2Si by the liquid encapsulated vertical gradient freezing method

    NASA Astrophysics Data System (ADS)

    Nakagawa, Reo; Katsumata, Hiroshi; Hashimoto, Satoshi; Sakuragi, Shiro

    2015-08-01

    The synthesis of Mg2Si bulk crystals was performed by the vertical gradient freezing method using a KCl-MgCl2 eutectic liquid encapsulant. Stoichiometric polycrystalline Mg2Si bulk crystals were successfully grown by changing the composition ratio of starting Mg and Si powders (Mg/Si) from 2.0 to 3.5. A chemical reaction between Mg2Si and the crucible materials was inhibited using encapsulant materials, and the contamination by K or Cl originating from the encapsulant materials was not detected in almost all the samples. However, Mg evaporation could not be prevented completely during the synthesis and crystal growth. The optical band-gap energy of Mg2Si bulk crystals became minimal (0.79 eV) at a Mg/Si ratio of 2.5, at which the maximum electron mobility of 202 cm2·V-1·s-1 was obtained. These results indicate that the composition ratio of Mg/Si = 2.5 for starting Mg and Si powders was optimal for synthesizing Mg2Si bulk crystals with high crystalline quality.

  10. Thermal expansion measurements on Fe substituted URu2Si2

    NASA Astrophysics Data System (ADS)

    Ran, Sheng; Wolowiec, Christian; Jeon, Inho; Pouse, Naveen; Kanchanavatee, Noravee; Huang, Kevin; Maple, M. Brian; Dapron, Tyler; Williamsen, Mark; Snow, David; Martien, Dinesh; Spagna, Stefano

    The search for the order parameter of the hidden order (HO) phase in URu2Si2 has attracted an enormous amount of attention for the past three decades. The small antiferromagnetic moment of only ~0.03 μB/U found in the HO phase is too small to account for the entropy of ~0.2Rln(2) derived from the second order mean field BCS-like specific heat anomaly associated with the HO transition that occurs below To = 17.5 K. A first order transition from the HO phase to a large moment antiferromagnetic (LMAFM) phase occurs under pressure. We have recently demonstrated that tuning URu2Si2B>by substitution of Fe for Ru reproduces the temperature vs applied pressure phase diagram.and offers an opportunity to study the HO and LMAFM phases at atmospheric pressure. Motivated by this observation, we performed thermal expansion measurements on URu2-xFexSi2 single crystals for various values of x in both the HO and LMAFM regions of the phase diagram. Interesting preliminary results have emerged from these studies that shed light on the LMAFM phase and its relationship with the elusive HO phase. Research in UCSD is supported by US DOE BES under Grant No. DE-FG02-04-ER46105 (materials synthesis and characterization) and US NSF under Grant No. DMR-1206553 (low temperature measurements).

  11. Analysis of Basal Plane Bending and Basal Plane Dislocations in 4H-SiC Single Crystals

    NASA Astrophysics Data System (ADS)

    Ohtani, Noboru; Katsuno, Masakazu; Fujimoto, Tatsuo; Nakabayashi, Masashi; Tsuge, Hiroshi; Yashiro, Hirokatsu; Aigo, Takashi; Hirano, Hosei; Hoshino, Taizo; Ohashi, Wataru

    2009-06-01

    4H-SiC single crystals were grown by the physical vapor transport (PVT) growth method under different thermoelastic stress conditions, and the degree of basal plane bending in the crystals was characterized by the peak shift measurement of X-ray rocking curves. The results indicate that the degree of basal plane bending largely depends on the magnitude of the thermoelastic stresses imposed on the crystals during PVT growth. Quantitative analysis of basal plane bending revealed that the density of basal plane dislocations (BPDs) estimated from basal plane bending is much smaller than that obtained from defect-selective etching. It was also found that the BPD density is correlated with the threading screw dislocation (TSD) density in PVT-grown SiC crystals. These aspects of BPDs were discussed in terms of the BPD multiplication process triggered by the intersection of BPDs with a forest of TSDs extending along the c-axis.

  12. Aluminum Nitride-Silicon Carbide Alloy Crystals Grown on SiC Substrates by Sublimation

    SciTech Connect

    Gu, Zheng; Du, L; Edgar, James H.; Payzant, Edward A.; Walker, L. R.; Liu, R.; Engelhard, Mark H.

    2005-12-20

    AlN-SiC alloy crystals, with a thickness greater than 500 m, were grown on 4H- and 6H-SiC substrates from a mixture of AlN and SiC powders by the sublimation-recondensation method at 1860-1990 C. On-axis SiC substrates produced a rough surface covered with hexagonal grains, while 6H- and 4H- off-axis SiC substrates with different miscut angles (8? or 3.68?) formed a relatively smooth surface with terraces and steps. The substrate misorientation ensured that the AlN-SiC alloy crystals grew two dimensionally as identified by scanning electron microscopy (SEM). X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the AlN-SiC alloys had the wurtzite structure. Electron probe microanalysis (EPMA) and x-ray photoelectron spectroscopy (XPS) demonstrated that the resultant alloy crystals had non-stoichiometric ratios of Al:N and Si:C and a uniform composition throughout the alloy crystal from the interface to the surface. The composition ratio of Al:Si of the alloy crystals changed with the growth temperature, and differed from the original source composition, which was consistent with the results predicted by thermodynamic calculation of the solid-vapor distribution of each element. XPS detected the bonding between Si-C, Si-N, Si-O for the Si 2p spectra. The dislocation density decreased with the growth, which was lower than 106 cm-2 at the alloy surface, more than two orders of magnitude lower compared to regions close to the crystal/substrate interface, as determined by TEM.

  13. Oxidation behavior of CVD and single crystal SiC at 1100 C

    SciTech Connect

    Ramberg, C.E.; Spear, K.E.; Tressler, R.E.; Chinone, Yoshiharu

    1995-11-01

    High purity chemical vapor deposition (CVD) silicon carbide fabricated by a commercial process was examined and oxidized at 1,100 C along with high purity single crystal silicon carbide. The freestanding CVD thick films had a highly textured polycrystalline microstructure, with the <111> directions of the crystals parallel to the growth direction. This texturing maintained the polarity of the 43m crystal structure, implying that either the [111] or the [1{und 1}1] direction grew significantly faster during the CVD process. The (111) face of the cubic, CVD-SiC oxidized at the same rate as the (0001) face of the single crystal SiC. The (111) face of the CVD-SiC oxidized at nominally the same rat as the (0001) face of the single crystal SiC.

  14. Truncated tetrahedron seed crystals initiating stereoaligned growth of FeSi nanowires.

    PubMed

    Kim, Si-in; Yoon, Hana; Seo, Kwanyong; Yoo, Youngdong; Lee, Sungyul; Kim, Bongsoo

    2012-10-23

    We have synthesized epitaxially grown freestanding FeSi nanowires (NWs) on an m-Al(2)O(3) substrate by using a catalyst-free chemical vapor transport method. FeSi NW growth is initiated from FeSi nanocrystals, formed on a substrate in a characteristic shape with a specific orientation. Cross-section TEM analysis of seed crystals reveals the crystallographic structure and hidden geometry of the seeds. Close correlation of geometrical shapes and orientations of the observed nanocrystals with those of as-grown NWs indicates that directional growth of NWs is initiated from the epitaxially formed seed crystals. The diameter of NWs can be controlled by adjusting the composition of Si in a Si/C mixture. The epitaxial growth method for FeSi NWs via seed crystals could be employed to heteroepitaxial growth of other compound NWs. PMID:22966939

  15. Low-temperature elastic properties of Sr3NbGa3Si2O14 single crystals

    NASA Astrophysics Data System (ADS)

    Sotnikov, A. V.; Smirnova, E. P.; Schmidt, H.; Weihnacht, M.

    2015-06-01

    The elastic properties of new piezoelectric Sr3NbGa3Si2O14 crystals of the langasite (lanthanum gallium silicate) family have been investigated. The temperature dependences of the elastic constants C 11, C 33, C 66, and C 44 have been measured in a wide temperature range from 300 to 4.2 K. The characteristic parameters of the crystal associated with the Einstein temperature and the Grüneisen parameter have been estimated at cryogenic temperatures. It has been shown that the piezoelectric activity of the crystal remains almost unchanged with a decrease in temperature from 300 to 4.2 K.

  16. Measuring Light Reflectance of BGO Crystal Surfaces

    SciTech Connect

    Janecek, Martin; Moses, William

    2008-07-28

    A scintillating crystal's surface reflectance has to be well understood in order to accurately predict and optimize the crystal?s light collection through Monte Carlo simulations. In this paper, we measure the inner surface reflectance properties for BGO. The measurements include BGO crystals with a mechanically polished surface, rough-cut surface, and chemically etched surface, and with various reflectors attached, both air- coupled and with coupling compound. The measurements are performed with a laser aimed at the center of a hemispherical shaped BGO crystal. The hemispherical shape eliminates any non-perpendicular angles for light entering and exiting the crystal. The reflected light is collected with an array of photodiodes. The laser can be set at an arbitrary angle, and the photodiode array is rotated to fully cover 2? of solid angle. The current produced in the photodiodes is readout with a digital multimeter connected through a multiplexer. The two rows of photodiodes achieve 5-degree by 4-degree resolution, and the current measurement has a dynamic range of 10^5:1. The acquired data was not described by the commonly assumed linear combination of specular and diffuse (Lambertian) distributions, except for a very few surfaces. Surface roughness proved to be the most important parameter when choosing crystal setup. The reflector choice was of less importance and of almost no consequence for rough-cut surfaces. Pure specular reflection distribution for all incidence angles was measured for polished surfaces with VM2000 film, while the most Lambertian distribution for any surface finish was measured for titanium dioxide paint. The distributions acquired in this paper will be used to create more accurate Monte Carlo models for light reflection distribution within BGO crystals.

  17. Improved techniques for growth of large-area single-crystal Si sheets over SiO2 using lateral epitaxy by seeded solidification

    NASA Astrophysics Data System (ADS)

    Tsaur, B.-Y.; Fan, J. C. C.; Geis, M. W.; Silversmith, D. J.; Mountain, R. W.

    1981-10-01

    Continuous single-crystal Si sheets over SiO2 with areas of several square centimeters have been produced from poly-Si films by the LESS technique (lateral epitaxy by seeded solidification). Seeding is achieved either with a narrow stripe opening in a recessed SiO2 layer on a single-crystal Si substrate or with an external single-crystal Si seed. N-channel metal-oxide-semiconductor field-effect transistors (MOSFET's) fabricated in these films exhibit surface electron mobilities as high as 700 sq cm/V s.

  18. Devitrification and delayed crazing of SiO2 on single-crystal silicon and chemically vapor-deposited silicon nitride

    NASA Technical Reports Server (NTRS)

    Choi, Doo Jin; Scott, William D.

    1987-01-01

    The linear growth rate of cristobalite was measured in thin SiO2 films on silicon and chemically vapor-deposited silicon nitride. The presence of trace impurities from alumina furnace tubes greatly increased the crystal growth rate. Under clean conditions, the growth rate was still 1 order-of-magnitude greater than that for internally nucleated crystals in bulk silica. Crystallized films cracked and lifted from the surface after exposure to atmospheric water vapor. The crystallization and subsequent crazing and lifting of protective SiO2 films on silicon nitride should be considered in long-term applications.

  19. Aluminum Nitride-Silicon Carbide Alloy Crystals Grown on SiC Substrates by Sublimation

    SciTech Connect

    Gu, Z; Du, Li; Edgar, J H; Payzant, E Andrew; Walker, Larry R; Liu, R; Engelhard, M H

    2005-01-01

    AlN-SiC alloy crystals, with a thickness greater than 500μm, were grown on 4H- and 6H-SiC substrates from a mixture of AlN and SiC powders by the sublimation-recondensation method at 1860-1990 C. On-axis SiC substrates produced a rough surface covered with hexagonal grains, while 6H- and 4H- off-axis SiC substrates with different miscut angles (8 or 3.68 ) formed a relatively smooth surface with terraces and steps. The substrate misorientation ensured that the AlNSiC alloy crystals grew two dimensionally as identified by scanning electron microscopy (SEM). Xray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the AlN-SiC alloys had the wurtzite structure. Electron probe microanalysis (EPMA) and x-ray photoelectron spectroscopy (XPS) demonstrated that the resultant alloy crystals had non-stoichiometric ratios of Al:N and Si:C and a uniform composition throughout the alloy crystal from the interface to the surface. The composition ratio of Al:Si of the alloy crystals changed with the growth temperature, and differed from the original source composition, which was consistent with the results predicted by thermodynamic calculation of the solid-vapor distribution of each element. XPS detected the bonding between Si-C, Si-N, Si-O for the Si 2p spectra. The dislocation density decreased with the growth, which was lower than 10^6cm-2 at the alloy surface, more than two orders of magnitude lower compared to regions close to the crystal/substrate interface, as determined by TEM.

  20. Plastically deformed region around indentations on Si angle crystal

    NASA Astrophysics Data System (ADS)

    Yoshioka, M.

    1994-12-01

    Expansion of a hemispherical shell by inner pressure has been widely applied for the model of the deformation by an indentation on a flat surface; however, the deformed region is not necessarily spherically symmetric, especially in anisotropic materials such as single crystals. Therefore, whether the spherical model is applicable in an indentation process for objective materials must always be kept in mind. Indentations have been made on the (111) surface of silicon crystal at various temperatures. The three-dimensional shape of the plastically deformed region was experimentally measured by means of an etching technique and its difference from the hemisphere was observed. It was never spherical but much more complicated, similar to a bottle gourd. The slip mechanism, which resulted in the observed shape of the plastic region, is discussed further. The plastic region was analytically obtained also on the assumption that the stress distribution was spherically symmetrical. The result is approximately in accordance with the observed shape. It is therefore concluded that the stress distribution is nearly spherical although the plastic region is far from it. The yield strength of silicon crystals and their temperature dependence were obtained based on the spherical model.

  1. Crystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions.

    PubMed

    Amato, Michele; Kaewmaraya, Thanayut; Zobelli, Alberto; Palummo, Maurizia; Rurali, Riccardo

    2016-09-14

    Recent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Driven by this promising evidence, we use first-principles methods based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of hexagonal-diamond and cubic-diamond Si NWs as well as their homojunctions. We show that hexagonal-diamond NWs are characterized by a more pronounced quantum confinement effect than cubic-diamond NWs. Furthermore, they absorb more light in the visible region with respect to cubic-diamond ones and, for most of the studied diameters, they are direct band gap materials. The study of the homojunctions reveals that the diameter has a crucial effect on the band alignment at the interface. In particular, at small diameters the band-offset is type-I whereas at experimentally relevant sizes the offset turns up to be of type-II. These findings highlight intriguing possibilities to modulate electron and hole separations as well as electronic and optical properties by simply modifying the crystal phase and the size of the junction. PMID:27530077

  2. Liquid crystal quantitative temperature measurement technique

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Wu, Zongshan

    2001-10-01

    Quantitative temperature measurement using wide band thermochromic liquid crystals is an “area” thermal measurement technique. This technique utilizes the feature that liquid crystal changes its reflex light color with variation of temperature and applies an image capturing and processing system to calibrate the characteristic curve of liquid crystal’s color-temperature. Afterwards, the technique uses this curve to measure the distribution of temperature on experimental model. In this paper, firstly, each part of quantitative temperature measurement system using liquid crystal is illustrated and discussed. Then the technique is employed in a long duration hypersonic wind tunnel, and the quantitative result of the heat transfer coefficient along laminar plate is obtained. Additionally, some qualitative results are also given. In the end, comparing the experimental results with reference enthalpy theoretical results, a conclusion of thermal measurement accuracy is drawn.

  3. Measurement of environmental warmth in SI units

    PubMed Central

    Ellis, F. P.; Smith, F. E.; Walters, J. D.

    1972-01-01

    Ellis, F. P., Smith, F. E., and Walters, J. D. (1972).Brit. J. industr. Med.,29, 361-377. Measurement of environmental warmth in SI units. Although `Environmental Warmth and Its Measurement' (Medical Research Council War Memorandum No. 17), written over 25 years ago for the Royal Navy, is still widely used and has not been revised, the validation and amplification of the methods proposed by the late Dr. Thomas Bedford have in the meantime been in hand continuously in the laboratory and in the Fleet under the auspices of the Council's Royal Naval Personnel Research Committee. While it was not considered appropriate by Council to replace or to rewrite the Memorandum at the present time, in view of the recent adoption of the metric system and the units of the International System (SI Units) it was thought that it would be helpful to publish metricated charts corresponding to those which appear in the Supplement to War Memorandum No. 17, together with two additional charts which are the result of work in the post-war years, to provide investigators with simple aids for use in the laboratory or the field and to provide a basis for considering the requirements for further research. PMID:4636658

  4. Characterization of Surface Features in Detached Grown GeSi Crystals

    NASA Technical Reports Server (NTRS)

    Cobb, S. D.; Volz, M. P.; Schweizer, M.; Kaiser, N.; Carpenter, P. K.; Szofran, F. R.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    The growth of detached crystals by the Bridgman technique, in which the growing crystal is not in contact with the crucible wall, has been observed both on earth and in microgravity conditions. At present, the mechanisms contributing to the detachment are not completely understood and until recently detachment has not been reproducibly obtained. It is commonly understood that the main factors that promote the occurrence of detached growth include: high contact angle between the melt and the crucible material, high growth angle, and a pressure difference between the annular gap around the solid below the melt and the volume above the melt along the meniscus. These parameters were varied in Bridgman growth experiments to determine the conditions required to achieve detached growth terrestrially in Ge and GeSi alloys. These experiments are in preparation for experiments on the International Space Station (ISS). The detailed objectives of the flight experiments and a description of the growth methods employed are the subject of another presentation at this Congress. Detached crystals were achieved repeatedly in pyrolytic boron nitride ampoules when a pressure difference was employed. All crystals, except for those grown in fused silica ampoules, were easily removed from their containers; however, this fact alone is not sufficient to infer detached growth. Detachment was verified by comparing profilometer measurements of the radius of the samples with observations of the sample surfaces using optical and electron microscopy. The surfaces of the attached areas of the crystals had the same shape and surface texture as the interior crucible wall. Regions of detached growth contained many unique features and crystal facets could usually be observed. Several of these surface features have been correlated with mechanisms of detachment or free surface growth in general and others to processing events or conditions. These results will be compared with observations of surface

  5. Determination of the Avogadro constant by counting the atoms in a 28Si crystal.

    PubMed

    Andreas, B; Azuma, Y; Bartl, G; Becker, P; Bettin, H; Borys, M; Busch, I; Gray, M; Fuchs, P; Fujii, K; Fujimoto, H; Kessler, E; Krumrey, M; Kuetgens, U; Kuramoto, N; Mana, G; Manson, P; Massa, E; Mizushima, S; Nicolaus, A; Picard, A; Pramann, A; Rienitz, O; Schiel, D; Valkiers, S; Waseda, A

    2011-01-21

    The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA = 6.022,140,78(18) × 10(23) mol(-1), is the most accurate input datum for a new definition of the kilogram. PMID:21405263

  6. Measuring Curved Crystal Performance for a High Resolution, Imaging X-ray Spectrometer

    SciTech Connect

    Michael Haugh and Richard Stewart

    2010-06-07

    This paper describes the design, crystal selection, and crystal testing for a vertical Johann spectrometer operating in the 13 keV range to measure ion Doppler broadening in inertial confinement plasmas. The spectrometer is designed to use thin, curved, mica crystals to achieve a resolving power of E/ΔE>2000. A number of natural mica crystals were screened for flatness and X-ray diffraction width to find samples of sufficient perfection for use in the instrument. Procedures to select and mount high quality mica samples are discussed. A diode-type X-ray source coupled to a dual goniometer arrangement was used to measure the crystal reflectivity curve. A procedure was developed for evaluating the goniometer performance using a set of diffraction grade Si crystals. This goniometer system was invaluable for identifying the best original crystals for further use and developing the techniques to select satisfactory curved crystals for the spectrometer.

  7. Process facilitates photoresist mask alignment on SiC crystals

    NASA Technical Reports Server (NTRS)

    Formigoni, N. P.; Roberts, J. S.

    1967-01-01

    Growth of silicon dioxide on a silicon carbide crystal ensures proper orientation of photoresist masks on the crystals used for semiconductor devices. The crystal is heated in a water vapor-saturated gas to delineate p-n junctions that intersect the crystal surface.

  8. Glass formation and crystallization in high-temperature glass-ceramics and Si3N4

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III

    1991-01-01

    The softening of glassy grain boundaries in ceramic matrix composites and Si3N4 at high temperatures reduces mechanical strength and the upper-use temperature. By crystallizing this glass to a more refractory crystalline phase, a material which performs at higher temperatures may result. Three systems were examined: a cordierite composition with ZrO2 as a nucleating agent; celsian compositions; and yttrium silicate glasses both in bulk and intergranular in Si3N4. For the cordierite compositions, a series of metastable phases was obtained. The crystallization of these compositions was summarized in terms of metastable ternary isothermal sections. Zircon formed at the expense of ZrO2 and spinel. In SiC composites, the transformations were slower. In celsian, two polymorphs were crystallized. One phase, hexacelsian, which always crystallized, even when metastable, had an undesirable volume change. The other phase, celsian, was very difficult to crystallize. In yttrium silicate bulk glasses, similar in composition to the intergranular glass in Si3N4, a number of polymorphs of Y2Si2O7 were crystallized. The conditions under which these polymorphs formed are compared with crystallization in Si3N4.

  9. Glass formation and crystallization in high-temperature glass-ceramics and Si3N4

    NASA Astrophysics Data System (ADS)

    Drummond, Charles H., III

    1991-08-01

    The softening of glassy grain boundaries in ceramic matrix composites and Si3N4 at high temperatures reduces mechanical strength and the upper-use temperature. By crystallizing this glass to a more refractory crystalline phase, a material which performs at higher temperatures may result. Three systems were examined: a cordierite composition with ZrO2 as a nucleating agent; celsian compositions; and yttrium silicate glasses both in bulk and intergranular in Si3N4. For the cordierite compositions, a series of metastable phases was obtained. The crystallization of these compositions was summarized in terms of metastable ternary isothermal sections. Zircon formed at the expense of ZrO2 and spinel. In SiC composites, the transformations were slower. In celsian, two polymorphs were crystallized. One phase, hexacelsian, which always crystallized, even when metastable, had an undesirable volume change. The other phase, celsian, was very difficult to crystallize. In yttrium silicate bulk glasses, similar in composition to the intergranular glass in Si3N4, a number of polymorphs of Y2Si2O7 were crystallized. The conditions under which these polymorphs formed are compared with crystallization in Si3N4.

  10. Precipitates of MnSi cubic phase in tetragonal Mn{sub 4}Si{sub 7} crystal

    SciTech Connect

    Suvorova, E. I. Klechkovskaya, V. V.

    2013-11-15

    Higher manganese silicides (HMSs) exhibit interesting thermoelectric and optoelectronic properties. Development of HMS-based thermoelements and microthermopiles of different designs may meet a number of problems, which can be solved only when the real structure of crystals and thin layers on which they are based is established. We have applied scanning and transmission electron microscopy and electron diffraction to investigate HMS crystals of two types: single crystals grown from melt by the Bridgman method and microislands formed by reactive diffusion during manganese vapor deposition on silicon substrates. The exact phase composition of these materials is established: matrix HMS crystal belonging to tetragonal system (Mn{sub 4}Si{sub 7} composition) and precipitates of cubic manganese monosilicide MnSi. The shape and sizes of precipitates are determined, the crystallographic relationships between the tetragonal and cubic phases are found, and the interface is investigated.

  11. Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

    NASA Astrophysics Data System (ADS)

    Preidel, V.; Amkreutz, D.; Haschke, J.; Wollgarten, M.; Rech, B.; Becker, C.

    2015-06-01

    Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

  12. Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

    SciTech Connect

    Preidel, V. Amkreutz, D.; Haschke, J.; Wollgarten, M.; Rech, B.; Becker, C.

    2015-06-14

    Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

  13. Process dependent morphology of the Si/SiO2 interface measured with scanning tunneling microscopy

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Bell, L. D.; Grunthaner, F. J.; Kaiser, W. J.

    1988-01-01

    A new experimental technique to determine Si/SiO2 interface morphology is described. Thermal oxides of silicon are chemically removed, and the resulting surface topography is measured with scanning tunneling microscopy. Interfaces prepared by oxidation of Si (100) and (111) surfaces, followed by postoxidation anneal (POA) at different temperatures, have been characterized. Correlations between interface structure, chemistry, and electrical characteristics are described.

  14. Fabrication and measurement of quantum dots in double gated, dopantless Si/SiGe heterostructures

    NASA Astrophysics Data System (ADS)

    Ward, Daniel; Mohr, Robert; Prance, Jonathan; Gamble, John; Savage, Don; Lagally, Max; Coppersmith, Susan; Eriksson, Mark

    2012-02-01

    Significant progress has been made towards quantum dot spin qubits in Si/SiGe single and double quantum dots. In the past, these structures have been created by depleting a modulation-doped 2DEG that forms at the Si/SiGe interface. The modulation doping in such devices is believed to be a source of charge noise. Recently, undoped structures have been explored for the formation of both 2DEGs and quantum dots in Si/SiGe. Here we discuss measurements on double gated, dopantless quantum dots in Si/SiGe heterostructures. The devices are based on a new ``island mesa'' design incorporating micro-ohmic contacts. We present transport measurements on a double quantum dot showing a smooth transition from single dot to double dot behavior.

  15. A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited.

    PubMed

    Park, Sanghyun; Lee, Yong Hwan; Wi, Jung-Sub; Oh, Jihun

    2016-07-27

    Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light. PMID:27352938

  16. Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

    SciTech Connect

    Nomura, Masahiro; Kage, Yuta; Müller, David; Moser, Dominik; Paul, Oliver

    2015-06-01

    Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

  17. 35-GHz Measurements of Carbon Dioxide Crystals

    NASA Technical Reports Server (NTRS)

    Foster, J.; Chang, A.; Hall, D.; Tait, A.; Klein, A.

    1998-01-01

    In order to maximize our knowledge of the martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Relatively little attention has been given, thus far, to observing the thermal microwave part of the spectrum. In this experiment, passive microwave radiation emanating from within a 33-cm snowpack was measured with a 35-GHz hand-held radiometer, and in addition to the natural snow measurements, the radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice) crystals. A 1 square meter plate of aluminum sheet metal was positioned beneath the natural snow so that microwave emissions from the underlying soil layers would be minimized. 35 GHz measurements of this plate were made through the 33-cm snowpack. Layers of the snow were removed and measurements were repeated for the diminishing snowpack until the bare plate was in view. Then, 9 cm of CO2 crystals were deposited onto the sheet-metal plate, and as was the case for the natural snow, hand-held measurements were made each time the thickness of the deposit was altered. These CO2 crystals were -0.65 cm in diameter and were cylindrical. The temperature of the dry ice was -76 C, whereas the temperature at the top of the snowpack was -1.9 C (the air temperature was -3 C). Two additional 9-cm increments were placed on top of the existing CO2 crystals, resulting in a total thickness of 27 cm of dry ice. After this series of measurements was made, the CO2 crystals were then placed on top of the snowpack, and as before, measurements were made using the 35-GHz radiometer. As a final part of this experiment, soil particles were spread on top of the dry ice, and once again, microwave measurements were made with the 35-GHz radiometer.

  18. Crystal structure of Si-doped HfO2

    NASA Astrophysics Data System (ADS)

    Zhao, Lili; Nelson, Matthew; Aldridge, Henry; Iamsasri, Thanakorn; Fancher, Chris M.; Forrester, Jennifer S.; Nishida, Toshikazu; Moghaddam, Saeed; Jones, Jacob L.

    2014-01-01

    Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at. %. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution.

  19. Characterization of Surface Features in Detached Grown GeSi Crystals

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    The growth of detached crystals by the Bridgman technique, in which the growing crystal is not in contact with the crucible wall, has been observed both on earth and in microgravity conditions. At present, the mechanisms contributing to the detachment are not completely understood and until recently detachment has not been reproducibly obtained. It is commonly understood that the main factors that promote the occurrence of detached growth include: high contact angle between the melt and the crucible material, high growth angle, and a pressure difference between the annular gap around the solid below the melt and the volume above the melt along the meniscus. These parameters were varied in Bridgman growth experiments to determine the conditions required to achieve detached growth terrestrially in Ge and GeSi alloys. These experiments are in preparation for experiments on the International Space Station (ISS). The detailed objectives of the flight experiments and a description of the growth methods employed are the subject of another presentation at this Conference. Detached crystals were achieved repeatedly in pyrolytic boron nitride ampoules when a pressure difference was employed. All crystals, except for those grown in fused silica ampoules, were easily removed from their containers, however, this fact alone is not sufficient to infer detached growth. Detachment was verified by comparing profilometer measurements of the radius of the samples with observations of the sample surfaces using optical and electron microscopy. The surfaces of the attached areas of the crystals had the same shape and surface texture as the interior crucible wall. Regions of detached growth contained many unique features and crystal facets could usually be observed. Several of these surface features have been correlated with mechanisms of detachment or free-surface growth and others to processing events or conditions.

  20. Measurement of single crystal surface parameters

    NASA Technical Reports Server (NTRS)

    Swanson, L. W.; Bell, A. E.; Strayer, R. W.

    1972-01-01

    The sticking coefficient and thermal desorption spectra of Cs from the (110) plane of W was investigated. A sticking coefficient of unity for the monolayer region was measured for T 250 K. Several distinct binding states were observed in the thermal desorption spectrum. Work function and electron reflection measurements were made on the (110) and (100) crystal faces of Mo. Both LEED and Auger were used to determine the orientation and cleanliness of the crystal surfaces. The work function values obtained for the (110) and (100) planes of Mo were 4.92 and 4.18 eV respectively.

  1. Structural properties of a-Si films and their effect on aluminum induced crystallization

    SciTech Connect

    Tankut, Aydin; Ozkol, Engin; Karaman, Mehmet; Turan, Rasit; Canli, Sedat

    2015-10-15

    In this paper, we report the influence of the structural properties of amorphous silicon (a-Si) on its subsequent crystallization behavior via the aluminum induced crystallization (AIC) method. Two distinct a-Si deposition techniques, electron beam evaporation and plasma enhanced chemical vapor deposition (PECVD), are compared for their effect on the overall AIC kinetics as well as the properties of the final poly-crystalline (poly-Si) silicon film. Raman and FTIR spectroscopy results indicate that the PECVD grown a-Si films has higher intermediate-range order, which is enhanced for increased hydrogen dilution during deposition. With increasing intermediate-range order of the a-Si, the rate of AIC is diminished, leading larger poly-Si grain size.

  2. Inhibition of metal induced crystallization in the system Ag/ZnO/a-Si:H

    SciTech Connect

    Edelman, F.; Brener, R.; Cytermann, C.; Weil, R.; Beneking, C.; Beyer, W.

    1996-12-31

    A systematic investigation has been made on the barrier properties of ZnO layer between n-doped a-Si:H and Ag metallization films in the structures (001)Si/SiO{sub 2}/Ag/ZnO/a-Si:H:P and (001)Si/SiO{sub 2}/a-Si:H:P/ZnO/Ag. Plasma assisted CVD deposition was used to produce a Si:H (2,500 {angstrom} thick) highly P-doped films over thermally oxidized Si-wafers at 190 and 270 C. Transparent conductive ZnO:Al layers, 1,000{angstrom} and 1 {micro}m thickness, and Ag films (1,000{angstrom} thick) were deposited by sputtering. The polycrystalline ZnO layers were textured along the <0001> axis in the as-deposited state. The structures were annealed in vacuum in the temperature range from 300 to 700 C for 1/4 to 16h. X-ray diffraction and transmission electron microscopy studies demonstrated the a-Si:H:P stability against crystallization under ZnO buffer protection up to 700 C (when free a-Si crystallizes itself). The (111) peak position of the Ag reflection was used to show that while the Ag was always strained, the strain was partially relaxed when in contact with the 0.1{micro}m ZnO film, it developed additional strain when in contact with the 1{micro}m ZnO film.

  3. Features of the uniaxial elastic deformation of X-ray-irradiated p-Si crystals

    SciTech Connect

    Pavlyk, B. V.; Lys, R. M. Didyk, R. I.; Shykorjak, J. A.

    2015-05-15

    Changes in the conductivity of p-Si single-crystals irradiated at room temperature during their mechanical compression and stress relief are studied. It is shown that irradiation is accompanied by the generation of point defects in silicon, which play the role of stoppers for dislocation motion. The effect of “radiation memory” in “electronic” silicon crystals is detected.

  4. Si-O Bonded Interactions in Silicate Crystals and Molecules:  A Comparison

    SciTech Connect

    Gibbs, G. V.; Jayatilaka, D.; Spackman, M. A.; Cox, D. F.; Rosso, K. M.

    2006-11-01

    Bond critical point, local kinetic energy density, G(rc), and local potential energy density, V(rc), properties of the electron density distributions, ρ(r), calculated for silicates such as quartz and gas-phase molecules such as disiloxane are similar, indicating that the forces that govern the Si-O bonded interactions in silica are short-ranged and molecular-like. Using the G(rc)/ρ(rc) ratio as a measure of bond character, the ratio increases as the Si-O bond length, the local electronic energy density, H(rc) = G(rc) + V(rc), and the coordination number of the Si atom decrease and as the accumulation of the electron density at the bond critical point, ρ(rc), and the Laplacian, ∇2ρ(rc), increase. The G(rc)/ρ(rc) and H(rc)/ρ(rc) ratios categorize the bonded interaction as observed for other second row atom M-O bonds into discrete categories with the covalent character of each of the M-O bonds increasing with the H(rc)/ρ(rc) ratio. The character of the bond is examined in terms of the large net atomic charges conferred on the Si atoms comprising disiloxane, stishovite, quartz, and forsterite and the domains of localized electron density along the Si-O bond vectors and on the reflex side of the Si-O-Si angle together with the close similarity of the Si-O bonded interactions observed for a variety of hydroxyacid silicate molecules and a large number of silicate crystals. Finally, the bond critical point and local energy density properties of the electron density distribution indicate that the bond is an intermediate interaction between Al-O and P-O bonded interactions rather than being a closed-shell or a shared interaction.

  5. Growth and optical properties of Bi{sub 12}SiO{sub 20} single crystals doped with first row transition metal and aluminum

    SciTech Connect

    Petrova, D.; Gospodinov, M.; Sveshtarov, P.

    1995-10-01

    Bi{sub 12}SiO{sub 20} single crystals co-doped with first row transition metals and aluminum were grown from the melt by the Czochralski technique. Optimal growth conditions for optically homogeneous crystals have been established. Dopant molar concentrations in the crystal were determined and segregation coefficients calculated. Transmission spectra were measured in the 0.38--0.85 {micro}m range. It was established that adding Al to the melt bleached the crystals and blue-shifted the entire transmission spectrum. Doping with Cu produced a strong photochromic effect after daylight exposure, changing the crystal color from yellow to red.

  6. Design, fabrication, and characterization of Si-based ARROW photonic crystal bend waveguides and power splitters.

    PubMed

    Chen, Jian-Hua; Huang, Yang-Tung; Yang, Yu-Lin; Lu, Ming-Feng; Shieh, Jia-Min

    2012-08-20

    Silicon-based (Si-based) photonic crystal waveguide based on antiresonant reflecting optical waveguide (ARROW PCW) structures consisting of 60° bends and Y-branch power splitters were designed and first efficiently fabricated and characterized. The ARROW structure has a relatively large core size suitable for efficient coupling with a single-mode fiber. Simple capsule-shaped topography defects at 60° photonic crystal (PC) bend corners and Y-branch PC power splitters were used for increasing the broadband light transmission. In the preliminary measurements, the propagation losses of the ARROW PC straight waveguides lower than 2 dB/mm with a long length of 1500 μm were achieved. The average bend loss of 60° PC bend waveguides was lower than 3 dB/bend. For the Y-branch PC power splitters, the average power imbalance was lower than 0.6 dB. The results show that our fabricated Si-based ARROW PCWs with 60° bends and Y-branch structures can provide good light transmission and power-splitting ability. PMID:22907016

  7. Crystal structures and magnetic properties of CsAu4Si2 and CeAu2Si2

    SciTech Connect

    Sefat, A.; Palasyuk, A.; Bud'ko, S.; Corbett, J.; Canfield, P.

    2007-12-03

    Single crystals of CeAu{sub 4}Si{sub 2} and CeAu{sub 2}Si{sub 2} have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 C. The single-crystal X-ray refinement result for CeAu{sub 4}Si{sub 2} is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu{sub 2}Si{sub 2}, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu{sub 2}Si{sub 2} is a typical antiferromagnet with T{sub N} = 8.8(1) K and CeAu{sub 4}Si{sub 2} features a ferromagnetic component below T{sub c}=3.3(1) K. Both phases have effective moments close in value to that of free Ce{sup 3+}.

  8. Transient x-ray diffraction used to diagnose shock compressed Si crystals on the Nova laser

    SciTech Connect

    Kalantar, D.H.; Chandler, E.A.; Colvin, J.D.; Lee, R.; Remington, B.A.; Weber, S.V.; Wiley, L.G.; Hauer, A.; Wark, J.S.; Loveridge, A.; Failor, B.H.; Meyers, M.A.; Ravichandran, G.

    1999-01-01

    Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented. {copyright} {ital 1999 American Institute of Physics.}

  9. Scintillation response of Lu1.95Y0.05SiO5:Ce and Y2SiO5:Ce single crystal scintillators

    NASA Astrophysics Data System (ADS)

    Wanarak, C.; Phunpueok, A.; Chewpraditkul, W.

    2012-09-01

    The scintillation response of the new cerium-doped rare-earth scintillator lutetium-yttrium oxyorthosilicate (Lu1.95Y0.05SiO5:Ce, LYSO:Ce) were investigated and compared to those of cerium-doped yttrium oxyorthosilicate (Y2SiO5:Ce, YSO:Ce) crystal. The light yield and energy resolution were measured using photomultiplier tube (PMT) readout. The non-proportionality of the light yield and energy resolution versus γ-ray energy were measured and the intrinsic resolution of the crystals was calculated. For 662 keV γ-rays (137Cs source), LYSO:Ce showed a light yield of 37,400 ± 3700 ph/MeV, which is much higher than that of 26,300 ± 2600 ph/MeV obtained for YSO:Ce. The energy resolution of 6.8 ± 0.2% obtained with YSO:Ce is better than that of 7.7 ± 0.2% obtained with LYSO:Ce, due to its better intrinsic resolution and proportionality in light yield. The photofraction was determined for both crystals and compared with the cross-sections ratio calculated using WinXCom program. The experimental results of the total mass attenuation coefficients for both crystals are in good agreement with the theoretical values, within the experimental uncertainty.

  10. The mechanical properties of single crystal {alpha}-Si{sub 3}N{sub 4}

    SciTech Connect

    Reimanis, I.E.; Suematsu, H.; Petrovic, J.J.; Mitchell, T.E.

    1993-11-01

    The ambient and high temperature mechanical properties of single crystal {alpha}{minus}Si{sub 3}N{sub 4} synthesized by chemical vapor deposition are reported. Crack patterns in the as-grown crystals and around Vicker`s indentations reveal that significant residual stresses develop during growth. Indentation studies indicate that the cleavage is essentially isotropic in {alpha}{minus}Si{sub 3}N{sub 4} at 25 C as well as at 1400 C. Transmission electron microscopy on crystals deformed at high temperatures, confirmed previous observation that high-temperature slip occurs primarily on (1011)[1120] system.

  11. Floating zone crystal growth of selected R2PdSi3 ternary silicides

    SciTech Connect

    Xu, Yiku; Frontzek, Matthias D; Mazilu, Irina; Loeser, W; Behr, G; Buechner, Bernd; Liu, L

    2011-01-01

    Substitution of various rare earths R within the class of R2PdSi3 single crystals with hexagonal AlB2-type crystallographic structure reveals the systematic dependence of anisotropic magnetic properties governed by the interplay of crystal-electric field effects and magnetic two-ion interactions. Here we compare the floating zone (FZ) crystal growth with radiation heating of compounds with R = Tb, Tm, Pr, and Gd. The congruent melting behavior enabled moderate growth velocities of 3 to 5 mmh-1. The preferred growth directions are close to the basal plane of the hexagonal unit cell. The composition of the crystals, except of Tb2PdSi3, is slightly Pd-depleted with respect to the nominal composition 16.7 at.% Pd. Thin precipitates of RSi secondary phases were detected in the crystal matrix. Their phase fraction can be diminished by growth from Pd-rich melt compositions and annealing treatments. The compounds exhibit antiferromagnetic order below the N el temperatures TN: 23.6 K (Tb2PdSi3), 1.8 K (Tm2PdSi3), 2.17 K (Pr2PdSi3) and 22 K (Gd2PdSi3) with different grades of magnetic anisotropy.

  12. Crystal structure of the ternary silicide Gd2Re3Si5

    PubMed Central

    Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

    2014-01-01

    A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta­silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo­octa­hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti­prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re—Re distance of 2.78163 (5) Å and isolated squares with an Re—Re distance of 2.9683 (6) Å. PMID:25552967

  13. Crystal structure of the ternary silicide Gd2Re3Si5.

    PubMed

    Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

    2014-12-01

    A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta-silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo-octa-hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti-prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re-Re distance of 2.78163 (5) Å and isolated squares with an Re-Re distance of 2.9683 (6) Å. PMID:25552967

  14. Infrared response from metallic particles embedded in a single-crystal Si matrix - The layered internal photoemission sensor

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Iannelli, J. M.; Nieh, C. W.; Hashimoto, Shin

    1990-01-01

    Infrared radiation at wavelengths of 1-2 microns has been detected in a new device labeled the layered internal photoemission sensor. The device structure, which is grown by molecular beam epitaxy, incorporates epitaxial CoSi2 particles with dimensions of 10-50 nm. Radiation absorbed by these particles photoexcites carriers into a surrounding single-crystal silicon matrix. A peak quantum efficiency of 1.3 percent is measured, which is approximately six times higher than in planar CoSi2 Schottky diodes with 5-nm silicide thickness.

  15. Measurement of Crystallization Temperature Using Thermography for Thin Film Amorphous Alloy Samples

    NASA Astrophysics Data System (ADS)

    Hata, Seiichi; Aono, Yuko; Sakurai, Junpei; Shimokohbe, Akira

    2009-03-01

    This report describes a new non-contact measurement method for the crystallization temperature (Tx) of a thin film amorphous alloy. The thermal emissivity of the amorphous alloy sample is predicted to be modified when it crystallizes. It was attempted to relate this modification to changes in the apparent temperature by thermography. Thin film amorphous alloys of Pt67Si33 and Pt73Si27 were sputtered onto an Al2O3 substrate and then heated at 20 K/min in vacuum, and the film temperature was monitored by thermography. The Tx indicated by the proposed method coincided with the temperature measured by conventional differential scanning calorimeter within 8 K.

  16. On the Effect of the Film Hydrogen Content and Deposition Type on the Grain Nucleation and Grain Growth During Crystallization of a-Si:H Films: Preprint

    SciTech Connect

    Mahan, A. H.; Ahrenkiel, S. P.; Roy, B.; Schropp, R.E.I.; Li, H.; Ginley, D. S.

    2006-05-01

    We report the effect of the initial film hydrogen content (CH) on the crystallization kinetics, crystallite nucleation rate and grain growth rate when HWCVD and PECVD a-Si:H films are crystallized by annealing at 600 C. For the HWCVD films, both the incubation time and crystallization time decrease, and the full width at half maximum (FWHM) of the XRD (111) peak decreases with decreasing film CH. However, other sources of XRD line broadening exist in such materials in addition to crystallite size, including the density of crystallite defects. To address these issues, TEM measurements have also been performed on a-Si:H films deposited directly onto TEM grids.

  17. Measurement of excited states of Sb impurity in Si by traveling–wave method

    SciTech Connect

    Sun, Yong; Takase, Tsuyoshi; Sakaino, Masamichi; Miyasato, Tatsuro

    2012-07-01

    The ground and excited states of Sb atom in Si, 1s (A{sub 1}), 1s (T{sub 2}), 1s (E), and 2p{sup 0}, were measured by using a traveling-wave method. The Sb-doped Si crystal with donor concentration of 2 × 10{sup 15} cm{sup −3} was placed the distance of 5 μm above a piezoelectric crystal in the fringe field of a surface acoustic wave. The free electrons excited from the bound states of the Sb atom are drifted by the traveling-wave, and thus lose their energy as the Joule heat through lattice and ion scattering processes. A strong temperature-dependent energy loss of the traveling-wave can be observed at temperatures below 200 K. The values of the bound states of the Sb atom can be characterized by using the Arrhenius plot for thermal activation process of the electrons in the bound states. The measurements were carried out at two frequencies of the traveling-wave, 50 MHz and 200 MHz. At the frequency of 50 MHz, the dielectric properties of the Si crystal are governed by dopant polarization but by electronic polarization at 200 MHz. We found that measurement accuracy of the bound states depends mainly on the electron mobility and the dielectric constant of the Si crystal, which are sensitive to the frequency and strength of the traveling-wave as well as electronic polarization properties of the Si crystal.

  18. A novel light trapping concept for liquid phase crystallized poly-Si thin-film solar cells on periodically nanoimprinted glass substrates

    NASA Astrophysics Data System (ADS)

    Preidel, V.; Amkreutz, D.; Sontheimer, T.; Back, F.; Rudigier-Voigt, E.; Rech, B.; Becker, C.

    2013-09-01

    Large grained polycrystalline silicon (poly-Si) absorbers were realized by electron beam induced liquid phase crystallization on 2 μm periodically patterned glass substrates and processed into a-Si:H/poly-Si heterojunction thin-film solar cells. The substrates were structured by nanoimprint lithography using a UV curable hybrid polymer sol-gel resist, resulting in a glassy high-temperature stable micro-structured surface. Structural analysis yielded high quality poly-Si material with grain sizes up to several hundred micrometers. An increase of absorption and an enhancement of the external quantum efficiency in the NIR as a consequence of light trapping due to the micro-structured poly-Si/substrate interface were observed. Up to now, only moderate solar cell parameters, a maximum open-circuit voltage of 413 mV and a short-circuit current density of 8 mA cm-2, were measured being significantly lower to what can be achieved with liquid phase crystallized poly-Si thin-film solar cells on planar glass substrates indicating that the substrate texture has impact on the electrical material quality. By reduction of the SiC interlayer thickness at the micro-structured poly- Si/substrate interface defect-related parasitic absorption was considerably minimized. This encourages the implementation of nanoimprinted tailored substrate textures for light trapping in liquid phase crystallized poly-Si thinfilm solar cells.

  19. Assessment of 4H-SiC epitaxial layers and high resistivity bulk crystals for radiation detectors

    NASA Astrophysics Data System (ADS)

    Mandal, Krishna C.; Muzykov, Peter G.; Chaudhuri, Sandeep K.; Terry, J. R.

    2012-10-01

    We present results of structural, electrical, and defect characterization of 4H-SiC epitaxial layers and bulk crystals and show performance of the radiation detectors fabricated from these materials. The crystal quality was evaluated by x-ray diffraction (XRD) rocking curve measurements, electron beam induced current (EBIC) imaging, and defect delineating etching in conjunction with optical microscopy and scanning electron microscopy (SEM). Studies of the electrically active intrinsic defects and impurities were conducted using thermally stimulated current (TSC) measurements in a wide temperature range of 94 - 750K. The results are correlated with the capability of bulk crystals and epitaxial layers for the detection of α-particles, low to high energy x-rays and gamma rays. High barrier rectifying Schottky diodes have been fabricated and tested. The epitaxial 4H-SiC radiation detectors exhibited low leakage current (< 1 nA) at ~ 200 V operating voltage up to 200 C. The soft x-ray responsivity measurements performed at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab (BNL) showed significantly improved characteristics compared to commercially-available SiC UV photodiode detectors.

  20. A metastable hard magnetic phase in the crystallization process of the Fe75Si11B10Nb3Sn1 alloy

    NASA Astrophysics Data System (ADS)

    Cremaschi, V.; Arcondo, B.; Vázquez, M.; Sirkin, H.

    1999-11-01

    A very interesting characteristic of FeSiB based amorphous alloys is its soft magnetic behavior. Most of these alloys remains soft along the crystallization process up to the nucleation of the iron borides. Examples of this are the widely studied Finemet and the FeSiBSn. In this work the crystallization of Fe76Si11B10Nb3 and Fe75Si11B10Nb3Sn1 is studied by means of X-ray diffraction, Mössbauer spectroscopy and coercive magnetic field measurements after one hour isothermal annealing at different temperatures. In the crystallization process of the latter alloy a hard magnetic phase appeared when the samples were annealed above 773 K. The soft magnetic behavior was recovered after annealing at 873 K. The hyperfine parameters as well as the X-ray diffraction patterns are reported.

  1. Crystallization from high temperature solutions of Si in copper

    DOEpatents

    Ciszek, Theodore F.

    1994-01-01

    A liquid phase epitaxy method for forming thin crystalline layers of device quality silicon having less than 5X10.sup.16 Cu atoms/cc impurity, comprising: preparing a saturated liquid solution melt of Si in Cu at about 16% to about 90% wt. Si at a temperature range of about 800.degree. C. to about 1400.degree. C. in an inert gas; immersing a substrate in the saturated solution melt; supersaturating the solution by lowering the temperature of the saturated solution melt and holding the substrate immersed in the solution melt for a period of time sufficient to cause growing Si to precipitate out of the solution to form a crystalline layer of Si on the substrate; and withdrawing the substrate from the solution.

  2. Measurements of crystal growth kinetics at extreme deviations from equilibrium

    SciTech Connect

    Aziz, M.J.

    1992-07-14

    We have measured solute trapping of several solutes in Al and Ni during rapid solidification. We have also made preliminary measurements of solute trapping of As in Si, trapped 20 atomic percent As in Si, and made a preliminary measurement of the T{sub o} curve in Si-As. 5 figs.

  3. Synthesis, crystal structure, and magnetic properties of novel intermetallic compounds R2Co2SiC (R = Pr, Nd).

    PubMed

    Zhou, Sixuan; Mishra, Trinath; Wang, Man; Shatruk, Michael; Cao, Huibo; Latturner, Susan E

    2014-06-16

    The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) Å, b = 6.094(5) Å, c = 8.903(8) Å (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments. PMID:24898034

  4. Potential for growth of Si-Ge bulk crystals by modified FZ technique

    NASA Astrophysics Data System (ADS)

    Gonik, M. A.

    2014-01-01

    The technique for crucibleless crystal growth of silicon and its alloy with germanium is developed on the basis of the floating zone (FZ) setup equipped with an additional so-called axial heating process (AHP) heater. The heater forms around itself the melt zone being suspended by forces of surface tension between its top surfaces and the growing crystal, as well as between the top surfaces of the AHP heater and the feeding rod. To investigate into the problem of the capillary stability of the pulling process, numerical computations of shaping of the free Si and Ge melt surface during the crystal pulling were performed. The dependences of the crystal radius and the thickness of the melt film on the parameters of the process are analyzed. It is demonstrated that, in the modified FZ method, the thickness of the melt layer between the crystal and the heater can be considerably larger than the capillary constant. A number of Si and Si-Ge crystals with a diameter up to 15 mm are grown. The range of a Si-Ge melt layer, which one could establish as high as possible, was found to be equal to 11-18 mm.

  5. Photonic crystal light emitting diode based on Er and Si nanoclusters co-doped slot waveguide

    SciTech Connect

    Lo Savio, R.; Galli, M.; Liscidini, M.; Andreani, L. C.; Franzò, G.; Iacona, F.; Miritello, M.; Irrera, A.; Sanfilippo, D.; Piana, A.; Priolo, F.

    2014-03-24

    We report on the design, fabrication, and electro-optical characterization of a light emitting device operating at 1.54 μm, whose active layer consists of silicon oxide containing Er-doped Si nanoclusters. A photonic crystal (PhC) is fabricated on the top-electrode to enhance the light extraction in the vertical direction, and thus the external efficiency of the device. This occurs if a photonic mode of the PhC slab is resonant with the Er emission energy, as confirmed by theoretical calculations and experimental analyses. We measure an increase of the extraction efficiency by a factor of 3 with a high directionality of light emission in a narrow vertical cone. External quantum efficiency and power efficiency are among the highest reported for this kind of material. These results are important for the realization of CMOS-compatible efficient light emitters at telecom wavelengths.

  6. Mechanism of the Reduced Thermal Conductivity of Fishbone-Type Si Phononic Crystal Nanostructures

    NASA Astrophysics Data System (ADS)

    Nomura, M.; Maire, J.

    2015-06-01

    The mechanism of the reduced thermal conductivity of fishbone-type phononic crystal (PnC) nanostructures, in which ballistic phonon transport is dominant, was investigated with consideration of both the wave and particle nature of phonons. Phononic band diagrams were calculated for an Si nanowire and a fishbone-type PnC structure with a period of 100 nm, and a clear reduction of the group velocity of phonons, because of a zone-folding effect, was shown. Air-suspended Si nanowires and fishbone-type PnC structures were fabricated by electron beam (EB) lithography, and their thermal conductivities were measured by use of the originally developed micro time-domain thermoreflectance method. The PnC structure had a much lower thermal conductivity. We measured the thermal conductivity of a variety of PnC structures with different fin widths to investigate the mechanism of the reduced thermal conductivity observed. The result indicates that the increase of the phonon traveling distance. as a result of the fins, also results in reduced thermal conductivity.

  7. Mechanism of the Reduced Thermal Conductivity of Fishbone-Type Si Phononic Crystal Nanostructures

    NASA Astrophysics Data System (ADS)

    Nomura, M.; Maire, J.

    2014-09-01

    The mechanism of the reduced thermal conductivity of fishbone-type phononic crystal (PnC) nanostructures, in which ballistic phonon transport is dominant, was investigated with consideration of both the wave and particle nature of phonons. Phononic band diagrams were calculated for an Si nanowire and a fishbone-type PnC structure with a period of 100 nm, and a clear reduction of the group velocity of phonons, because of a zone-folding effect, was shown. Air-suspended Si nanowires and fishbone-type PnC structures were fabricated by electron beam (EB) lithography, and their thermal conductivities were measured by use of the originally developed micro time-domain thermoreflectance method. The PnC structure had a much lower thermal conductivity. We measured the thermal conductivity of a variety of PnC structures with different fin widths to investigate the mechanism of the reduced thermal conductivity observed. The result indicates that the increase of the phonon traveling distance. as a result of the fins, also results in reduced thermal conductivity.

  8. The effect of hydrogen/deuterium introduction on photoluminescence of 3C-SiC crystals

    SciTech Connect

    Lee, B.K.; Steckl, A.J.; Zavada, J.M.; Wilson, R.G.

    1998-12-31

    The effect of the incorporation and annealing of deuterium in 3C-SiC on its photoluminescence is reported. A 3C-SiC crystal has been implanted with 100 kev deuterium and subsequently annealed at temperatures between 1015 C and 1220 C for 1 to 5 minutes. SIMS depth profiles indicate hydrogen is strongly trapped by defects generated through ion bombardment, but a gradual damage repairing occurs during annealing. Photoluminescence was measured with 488 nm Ar laser excitation for sample temperatures from 89 K to 400 K. The PL peak wavelength of 540 nm at room temperature has shifted to 538 nm at 89 K. The peak PL intensity decreases with measurement temperature while its full width at half maximum (FWHM) exhibits an increasing trend. PL data were taken at five annealing stages. The post-implantation peak PL intensity and its integrated area increase initially with annealing temperature and time. After the final annealing at 1218 C for 2 minute, PL intensity and its integrated area exhibit a decrease in level.

  9. Optical filters using Cantor quasi-periodic one dimensional photonic crystal based on Si/SiO2

    NASA Astrophysics Data System (ADS)

    Sahel, S.; Amri, R.; Bouaziz, L.; Gamra, D.; Lejeune, M.; Benlahsen, M.; Zellama, K.; Bouchriha, H.

    2016-09-01

    Quasi-periodic one-dimensional Cantor photonic crystals are elaborated by depositing alternating silicon and silica Si/SiO2 layers by radiofrequency magnetron sputtering technique with cold plasma. Transmittance and reflectance spectra of these quasi crystals exhibit a large photonic band gap in the infrared range at normal incidence which is well reproduced by a theoretical model based on the transfer matrix method. The obtained wide photonic band gap reveals the existence of permitted modes depending on the nature and characteristics of the built in system which can constitute optical windows. This effect can be a good alternative for the design of flexible filters used in many areas of applications such as telecommunication and optoelectronic devices.

  10. The system Ta-V-Si: Crystal structure and phase equilibria

    SciTech Connect

    Khan, A.U.; Broz, P.; Bursik, J.; Grytsiv, A.; Chen, X.-Q.; Giester, G.; Rogl, P.

    2012-03-15

    Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 Degree-Sign C. Three ternary phases were found: {tau}{sub 1}-(Ta,V){sub 5}Si{sub 3} (Mn{sub 5}Si{sub 3}-type), {tau}{sub 2}-Ta(Ta,V,Si){sub 2} (MgZn{sub 2}-type) and {tau}{sub 3}-Ta(Ta,V,Si){sub 2} (MgCu{sub 2}-type). The crystal structure of {tau}{sub 2}-Ta(Ta,V,Si){sub 2} was solved by X-ray single crystal diffraction (space group P6{sub 3}/mmc). Atom order in the crystal structures of {tau}{sub 1}-(Ta,V){sub 5}Si{sub 3} (Mn{sub 5}Si{sub 3} type) and {tau}{sub 3}-Ta(Ta,V,Si){sub 2} was derived from X-ray powder diffraction data. A large homogeneity range was found for {tau}{sub 1}-(Ta{sub x}V{sub 1-x}){sub 5}Si{sub 3} revealing random exchange of Ta and V at a constant Si content. At 1500 Degree-Sign C, the end points of the {tau}{sub 1}-phase solution (0.082{<=}x{<=}0.624) are in equilibrium with the solutions (Ta{sub 1-x}V{sub x}){sub 5}Si{sub 3} (Cr{sub 5}B{sub 3} type, 0{<=}x{<=}0.128) and (Ta{sub x}V{sub 1-x}){sub 5}Si{sub 3} (W{sub 5}Si{sub 3} type, 0{<=}x{<=}0.048). - Graphical abstract: Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 Degree-Sign C. Black-Right-Pointing-Pointer Three ternary phases were found at 1500 Degree-Sign C. Black-Right-Pointing-Pointer At 1500 Degree-Sign C, {tau}{sub 1}-phase has large homogeneity region (0.064{<=}x{<=}0.624).

  11. Studies of an array of PbF2 Cherenkov crystals with large-area SiPM readout

    NASA Astrophysics Data System (ADS)

    Fienberg, A. T.; Alonzi, L. P.; Anastasi, A.; Bjorkquist, R.; Cauz, D.; Fatemi, R.; Ferrari, C.; Fioretti, A.; Frankenthal, A.; Gabbanini, C.; Gibbons, L. K.; Giovanetti, K.; Goadhouse, S. D.; Gohn, W. P.; Gorringe, T. P.; Hertzog, D. W.; Iacovacci, M.; Kammel, P.; Kaspar, J.; Kiburg, B.; Li, L.; Mastroianni, S.; Pauletta, G.; Peterson, D. A.; Počanić, D.; Smith, M. W.; Sweigart, D. A.; Tishchenko, V.; Venanzoni, G.; Van Wechel, T. D.; Wall, K. B.; Winter, P.; Yai, K.

    2015-05-01

    The electromagnetic calorimeter for the new muon (g - 2) experiment at Fermilab will consist of arrays of PbF2 Cherenkov crystals read out by large-area silicon photo-multiplier (SiPM) sensors. We report here on measurements and simulations using 2.0-4.5 GeV electrons with a 28-element prototype array. All data were obtained using fast waveform digitizers to accurately capture signal pulse shapes vs. energy, impact position, angle, and crystal wrapping. The SiPMs were gain matched using a laser-based calibration system, which also provided a stabilization procedure that allowed gain correction to a level of 10-4 per hour. After accounting for longitudinal fluctuation losses, those crystals wrapped in a white, diffusive wrapping exhibited an energy resolution σ/E of (3.4 ± 0.1) % /√{ E / GeV }, while those wrapped in a black, absorptive wrapping had (4.6 ± 0.3) % /√{ E / GeV }. The white-wrapped crystals-having nearly twice the total light collection-display a generally wider and impact-position-dependent pulse shape owing to the dynamics of the light propagation, in comparison to the black-wrapped crystals, which have a narrower pulse shape that is insensitive to impact position.

  12. Metal-induced crystallization of a-Si thin films by nonvacuum treatments

    SciTech Connect

    Kalkan, A.K.; Fonash, S.J.

    1997-11-01

    Thin film polycrystalline Si (poly-Si) is of considerable interest today for microelectronics, flat panel displays, and photovoltaics. Low thermal budget solid-phase crystallization (SPC) of a-Si precursor films was achieved using surface treatments with metal-containing solutions. Two different treatment procedures were demonstrated. With these treatments, one based on a Pd solution and the other on a Ni solution, the SPC time at 600 C was reduced from 18 h to 10 min or less. This approach renders the usual vacuum deposition step used in metal-induced crystallization unnecessary. The authors find that the ultraviolet reflectance and Raman shift signals for the crystallized films are independent of whether the SPC-enhancing metal is applied by vacuum or solution. These characterization results do differ, however, with the metal applied.

  13. Instability of photoinduced optical absorption of Bi12SiO20: Al crystals

    NASA Astrophysics Data System (ADS)

    Panchenko, T. V.; Dyachenko, A. A.; Khmelenko, O. V.

    2015-04-01

    The results of the experimental investigation of the instability of the establishment and relaxation of a photochromic effect in aluminum-doped Bi12SiO20 crystals have been presented. The oscillating and nonmonotonic kinetic dependences of the photoinduced optical absorption have been observed. The absorption oscillations are associated with the competition of the formation and destruction of [AlSiO4]0 photochromic centers.

  14. Ferromagnetism in proton irradiated 4H-SiC single crystal

    SciTech Connect

    Zhou, Ren-Wei; Wang, Hua-Jie; Chen, Wei-Bin; Li, Fei; Liu, Xue-Chao Zhuo, Shi-Yi; Shi, Er-Wei

    2015-04-15

    Room-temperature ferromagnetism is observed in proton irradiated 4H-SiC single crystal. An initial increase in proton dose leads to pronounced ferromagnetism, accompanying with obvious increase in vacancy concentration. Further increase in irradiation dose lowers the saturation magnetization with the decrease in total vacancy defects due to the defects recombination. It is found that divacancies are the mainly defects in proton irradiated 4H-SiC and responsible for the observed ferromagnetism.

  15. Quasi-single-crystal (001) SrTiO{sub 3} templates on Si

    SciTech Connect

    Park, J. W.; Baek, S. H.; Bark, C. W.; Eom, C. B.; Biegalski, M. D.

    2009-08-10

    The integration of multifunctional oxides on semiconductor devices requires the formation of single-crystal-like oxide templates directly on silicon. We report the fabrication of quasi-single-crystal (001) SrTiO{sub 3} templates on (001) Si by annealing 100 nm thick molecular beam epitaxy-grown epitaxial SrTiO{sub 3} films at 900 deg. C. The full width at half maximum of the (002) rocking curve is 0.006 deg., which is much narrower than SrTiO{sub 3} bulk single crystals. An atomically smooth TiO{sub 2}-terminated surface is obtained by buffered-HF etching, which allows us to create functional oxide heterointerfaces on Si. Epitaxial SrRuO{sub 3} thin films grown on the quasi-single-crystal SrTiO{sub 3} template exhibit a superior crystalline quality and surface morphology.

  16. SERS active Ag encapsulated Fe@SiO2 nanorods in electromagnetic wave absorption and crystal violet detection.

    PubMed

    Senapati, Samarpita; Srivastava, Suneel Kumar; Singh, Shiv Brat; Kulkarni, Ajit R

    2014-11-01

    The present work is focused on the preparation of Fe nanorods by the chemical reduction of FeCl3 (aq) using NaBH4 in the presence of glycerol as template followed by annealing of the product at 500°C in the presence of H2 gas flow. Subsequently, its surface has been modified by silica followed by silver nanoparticles to form silica coated Fe (Fe@SiO2) and Ag encapsulated Fe@SiO2 nanostructure employing the Stöber method and silver mirror reaction respectively. XRD pattern of the products confirmed the formation of bcc phase of iron and fcc phase of silver, though silica remained amorphous. FESEM images established the growth of iron nanorods from the annealed product and also formation of silica and silver coating on its surface. The appearance of the characteristics bands in FTIR confirmed the presence of SiO2 on the Fe surface. Magnetic measurements at room temperature indicated the ferromagnetic behavior of as prepared iron nanorods, Fe@SiO2 and silver encapsulated Fe@SiO2 nanostructures. All the samples exhibited strong microwave absorption property in the high frequency range (10GHz), though it is superior for Ag encapsulated Fe@SiO2 (-14.7dB) compared with Fe@SiO2 (-9.7dB) nanostructures of the same thickness. The synthesized Ag encapsulated Fe@SiO2 nanostructure also exhibited the SERS phenomena, which is useful in the detection of the carcinogenic dye crystal violet (CV) upto the concentration of 10(-10)M. All these findings clearly demonstrate that the Ag encapsulated Fe@SiO2 nanostructure could efficiently be used in the environmental remediation. PMID:25262081

  17. Synthesis and crystal structure of cubic Ca16Si17N34.

    PubMed

    Hick, Sandra M; Miller, Mattheu I; Kaner, Richard B; Blair, Richard G

    2012-12-01

    Since the late 1960s, the exact structure of cubic calcium silicon nitride has been a source of debate. This paper offers evidence that the cubic phase CaSiN(2) described in the literature is actually Ca(16)Si(17)N(34). Presented here is a method for synthesizing single crystals of cubic-calcium silicon nitride from calcium nitride and elemental silicon under flowing nitrogen at 1500 °C. The colorless millimeter-sized crystals of Ca(16)Si(17)N(34) with a refractive index (n(25)) = 1.590 were found to be cubic (a = 14.8882 Å) and belong to the space group F43m (216). The synthesis of bulk, powdered cubic-Ca(16)Si(17)N(34) from calcium cyanamide and silicon is also discussed. Ca(16)Si(17)N(34) is a relatively air-stable refractory ceramic. In contrast to the orthorhombic phase of CaSiN(2), in which Ca(2+) sits in octahedral sites, this cubic phase has Ca(2+) in cubic sites that makes it an interesting host for new phosphors and gives rise to unique crystal field splitting. PMID:23157279

  18. Measurements of Local Strain Variation in Si(1-x)Ge(x)/Si Heterostructures

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.; Manion, S. J.; Milliken, S. J.; Pike, W. T.; Fathauer, R. W.

    1995-01-01

    The energy splitting of the conduction-band minimum of Si(1-x), Ge(x), due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si(1-x), Ge(x) structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si(1-x), Ge(x), however, heterogeneity in the strain of the Si(1-x), Ge(x) layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si(1-x)Ge(x) surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.

  19. Numerical simulations of SiGe crystal growth by the traveling liquidus-zone method in a microgravity environment

    NASA Astrophysics Data System (ADS)

    Abe, K.; Sumioka, S.; Sugioka, K.-I.; Kubo, M.; Tsukada, T.; Kinoshita, K.; Arai, Y.; Inatomi, Y.

    2014-09-01

    Recently, a Si1-xGex (approximately x=0.5) crystal has been grown by the traveling liquidus-zone (TLZ) method under microgravity condition in the International Space Station (ISS). In this work, a mathematical model of the TLZ crystal growth has been developed to investigate details of the transport and solidification phenomena occurred during the TLZ growth of SiGe crystals performed in the ISS. Using this model, the experimental Ge concentration distributions in the grown SiGe crystal is explained, and the emissivity variation of the metal cartridge surface due to oxidation during the crystal growth is revealed to strongly affect the Ge concentration distribution in the grown crystal. In addition, a strategy for growing SiGe crystals, which are more homogeneous than those obtained in the current experiment, is proposed on the basis of the numerical results.

  20. 3D position determination in monolithic crystals coupled to SiPMs for PET

    NASA Astrophysics Data System (ADS)

    Etxebeste, Ane; Barrio, John; Muñoz, Enrique; Oliver, Josep F.; Solaz, Carles; Llosá, Gabriela

    2016-05-01

    The interest in using continuous monolithic crystals in positron emission tomography (PET) has grown in the last years. Coupled to silicon photomultipliers (SiPMs), the detector can combine high sensitivity and high resolution, the two main factors to be maximized in a positron emission tomograph. In this work, the position determination capability of a detector comprised of a 12× 12× 10 mm3 LYSO crystal coupled to an 8× 8 -pixel array of SiPMs is evaluated. The 3D interaction position of γ-rays is estimated using an analytical model of the light distribution including reflections on the facets of the crystal. Monte Carlo simulations have been performed to evaluate different crystal reflectors and geometries. The method has been characterized and applied to different cases. Intrinsic resolution obtained with the position estimation method used in this work, applied to experimental data, achieves sub-millimetre resolution values. Average resolution over the detector surface for 5 mm thick crystal is  ∼0.9 mm FWHM and  ∼1.2 mm FWHM for 10 mm thick crystal. Depth of interaction resolution is close to 2 mm FWHM in both cases, while the FWTM is  ∼5.3 mm for 5 mm thick crystal and  ∼9.6 mm for 10 mm thick crystal.

  1. 3D position determination in monolithic crystals coupled to SiPMs for PET.

    PubMed

    Etxebeste, Ane; Barrio, John; Muñoz, Enrique; Oliver, Josep F; Solaz, Carles; Llosá, Gabriela

    2016-05-21

    The interest in using continuous monolithic crystals in positron emission tomography (PET) has grown in the last years. Coupled to silicon photomultipliers (SiPMs), the detector can combine high sensitivity and high resolution, the two main factors to be maximized in a positron emission tomograph. In this work, the position determination capability of a detector comprised of a [Formula: see text] mm(3) LYSO crystal coupled to an [Formula: see text]-pixel array of SiPMs is evaluated. The 3D interaction position of γ-rays is estimated using an analytical model of the light distribution including reflections on the facets of the crystal. Monte Carlo simulations have been performed to evaluate different crystal reflectors and geometries. The method has been characterized and applied to different cases. Intrinsic resolution obtained with the position estimation method used in this work, applied to experimental data, achieves sub-millimetre resolution values. Average resolution over the detector surface for 5 mm thick crystal is  ∼0.9 mm FWHM and  ∼1.2 mm FWHM for 10 mm thick crystal. Depth of interaction resolution is close to 2 mm FWHM in both cases, while the FWTM is  ∼5.3 mm for 5 mm thick crystal and  ∼9.6 mm for 10 mm thick crystal. PMID:27119737

  2. Synthesis and crystal structure of MgB{sub 12}Si{sub 2}-The first ternary compound in the system B/Mg/Si

    SciTech Connect

    Ludwig, Thilo; Hillebrecht, Harald . E-mail: harald.hillebrecht@ac.uni-freiburg.de

    2006-06-15

    We report on the synthesis of MgB{sub 12}Si{sub 2} the first ternary compound in the system B/Mg/Si. Yellow transparent single crystals were yielded from the elements at 1600 deg. C in h-BN crucibles welded in Ta ampoules. MgB{sub 12}Si{sub 2} crystallizes orthorhombic in the space group Pnma with a=10.9797(11)A, b=6.1098(7)A, c=8.3646(12)A and Z=4. The crystal structure is characterized by layers of B{sub 12} icosahedra, connected by isolated Si atoms to a three-dimensional framework. Mg atoms are placed in voids of the framework. Each icosahedron forms 8 B-Si bonds and 4 exohedral B-B bonds. The Si atoms are tetrahedrally coordinated by B atoms of the B{sub 12} icosahedra.

  3. Differential cross sections measurement of 28Si(p,p/γ)28Si and 29Si(p,p/γ)29Si reactions for PIGE applications

    NASA Astrophysics Data System (ADS)

    Jokar, A.; Kakuee, O.; Lamehi-Rachti, M.

    2016-03-01

    Differential cross sections for gamma-ray emission from the 28Si(p,p/γ)28Si (Eγ = 1779 keV) and the 29Si(p,p/γ)29Si (Eγ = 1273 keV) nuclear reactions were measured in the energy range of 2.0-3.2 MeV and 2.0-3.0 MeV, respectively. The thin Si targets were prepared by evaporating natural SiO onto self-supporting Ag films. The gamma-rays and backscattered protons were detected simultaneously. An HPGe detector placed at an angle of 90° with respect to beam direction was employed to collect gamma-rays while an ion implanted Si detector placed at a scattering angle of 165° was used to detect backscattered protons. The great advantage of this work is that differential cross sections were obtained with a procedure irrespective of absolute value of the collected beam charge.

  4. Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices (Invited)

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1999-01-01

    As illustrated by the invited paper at this conference and other works, SiC wafers and epilayers contain a variety of crystallographic imperfections, including micropipes, closed-core screw dislocations, grain boundaries, basal plane dislocations, heteropolytypic inclusions, and surfaces that are often damaged and contain atomically rough features like step bunching and growth pits or hillocks. Present understanding of the operational impact of various crystal imperfections on SiC electrical devices is reviewed, with an emphasis placed on high-field SiC power devices and circuits.

  5. Crystal structures of three intermetallic phases in the Mo-Pt-Si system

    SciTech Connect

    Joubert, J.-M.; Tokaychuk, Ya.; Cerny, R.

    2010-01-15

    The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. All three structures are representative of new structure types. Both the X (MoPt{sub 2}Si{sub 3}, Pmc2{sub 1}, oP12, a=3.48438(6), b=9.1511(2), c=5.48253(8) A) and Y (MoPt{sub 3}Si{sub 4}, Pnma, oP32, a=5.51210(9), b=3.49474(7), c=24.3090(4) A) phases derive from PtSi (FeAs type) structure while the Z phase (ideal composition Mo{sub 32}Pt{sub 20}Si{sub 16}, refined composition Mo{sub 29.9(2)}Pt{sub 21.0(3)}Si{sub 17.1(1)}, Cc, mC68, a=13.8868(3), b=8.0769(2), c=9.6110(2) A, beta=100.898(1){sup o}) present similarities with the group of Frank-Kasper phases. - Graphical abstract: The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. The three structures represent new structure types.

  6. Extreme low thermal conductivity in nanoscale 3D Si phononic crystal with spherical pores.

    PubMed

    Yang, Lina; Yang, Nuo; Li, Baowen

    2014-01-01

    In this work, we propose a nanoscale three-dimensional (3D) Si phononic crystal (PnC) with spherical pores, which can reduce the thermal conductivity of bulk Si by a factor up to 10,000 times at room temperature. Thermal conductivity of Si PnCs depends on the porosity, for example, the thermal conductivity of Si PnCs with porosity 50% is 300 times smaller than that of bulk Si. The phonon participation ratio spectra demonstrate that more phonons are localized as the porosity increases. The thermal conductivity is insensitive to the temperature changes from room temperature to 1100 K. The extreme-low thermal conductivity could lead to a larger value of ZT than unity as the periodic structure affects very little the electric conductivity. PMID:24559126

  7. Anisotropic physical properties of PrRhAl4Si2 single crystal: A non-magnetic singlet ground state compound

    NASA Astrophysics Data System (ADS)

    Maurya, Arvind; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.

    2016-08-01

    We have grown the single crystal of PrRhAl4Si2, which crystallizes in the tetragonal crystal structure. From the low temperature physical property measurements like, magnetic susceptibility, magnetization, heat capacity and electrical resistivity, we found that this compound does not show any magnetic ordering down to 70 mK. Our crystal field calculations on the magnetic susceptibility and specific heat measurements reveal that the 9-fold degenerate (2 J + 1) levels of Pr atom in PrRhAl4Si2 split into 7 levels, with a singlet ground state and a well-separated excited doublet state at 123 K, with a overall level splitting energy of 320 K.

  8. Preferential Crystal Growth of (100)-Oriented BiFeO3 Films on Si Substrate

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Yasui, S.; Funakubo, H.; Uchida, H.

    2011-10-01

    Bi-based perovskite-type oxide materials such as BiFeO3 (BFO) and the related compounds receive much attention and have been developed actively as important candidates for Pb-free ferroelectric / piezoelectric materials instead of toxic Pb-based perovskite oxide materials. Recently, many researches have been reported for thin films of BFO by various film-deposition techniques for actual application of semiconductive devices, microactuators, etc. In this report, we tried preferential crystal growth of BFO films on semiconductive silicon substrates using uniaxial-(100)-oriented LaNiO3 (LNO) buffer layer. BFO films were fabricated via chemical solution deposition (CSD) technique on platinized silicon wafer [(111)Pt/TiO2/(100)Si] and (100)LNO-coated platinized silicon [(100)LNO/(111)Pt/TiO2/(100)Si] substrates. XRD analysis indicated that the films fabricated on (111)Pt/TiO2/(100)Si substrate consisted of randomly-oriented BFO crystal with lower crystallinity and trace amount of the second Bi2Fe4O9 phase. On the other hand, the films on (100)LNO/(111)Pt/TiO2/(100)Si consisted of uniaxial-(100)-oriented BFO crystal with higher crystallinity. The crystallization temperature these films were 450 and 400°C, respectively. These results suggest that the BFO crystal was grown epitaxially on uniaxial oriented (100)LNO plane which also had perovskite-type crystal structure. Consequently, (100)-oriented BFO films were prepared on Si substrate successfully using (100)LNO buffer layer.

  9. Achieving omnidirectional photonic band gap in sputter deposited TiO2/SiO2 one dimensional photonic crystal

    NASA Astrophysics Data System (ADS)

    Jena, S.; Tokas, R. B.; Sarkar, P.; Haque, S. Maidul; Misal, J. S.; Rao, K. D.; Thakur, S.; Sahoo, N. K.

    2015-06-01

    The multilayer structure of TiO2/SiO2 (11 layers) as one dimensional photonic crystal (1D PC) has been designed and then fabricated by using asymmetric bipolar pulse DC magnetron sputtering technique for omnidirectional photonic band gap. The experimentally measured photonic band gap (PBG) in the visible region is well matched with the theoretically calculated band structure (ω vs. k) diagram. The experimentally measured omnidirectional reflection band of 44 nm over the incident angle range of 0°-70° is found almost matching within the theoretically calculated band.

  10. Dopant activation during solid phase crystallization of poly-Si and influence of fluorine and hydrogen

    SciTech Connect

    Kalkan, A.K.; Kingi, R.M.; Fonash, S.J.

    1997-07-01

    Dopant activation for ion implanted solid phase crystallized (SPC) a-Si:H films, deposited by low temperature PECVD, was investigated. The impact of film thickness, the effect of subsequent hydrogenation, and a possible role for fluorine in this process have been studied.

  11. The Formation of Crystal Defects in a Fe-Mn-Si Alloy Under Cyclic Martensitic Transformations.

    PubMed

    Bondar, Vladimir I; Danilchenko, Vitaliy E; Iakovlev, Viktor E

    2016-12-01

    Formation of crystalline defects due to cyclic martensitic transformations (CMT) in the iron-manganese Fe-18 wt.% Mn-2 wt.% Si alloy was investigated using X-ray diffractometry. Conditions for accumulation of fragment sub-boundaries with low-angle misorientations and chaotic stacking faults in crystal lattice of austenite and ε-martensite were analyzed. PMID:26960743

  12. Forced diffusion via electrically induced crystallization for fabricating ZnO–Ti–Si structures

    SciTech Connect

    Chen, Yen-Ting; Hung, Fei-Yi

    2014-11-15

    Highlights: • ZnO–Ti–Si system is very important for the structural design. • The electrically induced crystallization method is useful to diffusion process. • Intermetallic compound characteristics have been presented using electrically induced crystallization. • Interface mechanism about diffusion of TZO–TiSi{sub x}–Si structure is presented. - Abstract: Electrically induced crystallization (EIC) is a recently developed process for material modification. This study is applied to EIC to fabricate ZnO–Ti–Si multi-layer structures of various thicknesses to dope Ti into ZnO thin film and to form TiSi{sub x} intermetallic compound (IMC) in a single step. The IMC layer was confirmed using transmission electron microscopy images. The Ti layer thickness was more than 40 nm, which enhanced electron transmission and decreased the total electrical resistance in the structure. Finally, the diffusion mechanisms of EIC and the annealing process were investigated. This study shows that the EIC process has potential for industrial applications.

  13. Local compositional analysis of magnetic crystal grain and boundary in CoCrPt-SiO2 granular perpendicular recording media

    NASA Astrophysics Data System (ADS)

    Futamoto, Masaaki; Handa, Takahiro; Takahashi, Yoshio

    2010-01-01

    The compositions of magnetic crystal grains and boundaries of a CoCrPt-SiO2 granular perpendicular medium were investigated for plan-view and cross-sectional samples by using a transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The grain boundary composition, which is not easy to measure because of the small width around 1 nm, is estimated from the average composition of magnetic layer and that of crystal grains by considering the grain boundary volume ratio determined by structure observation. The grain boundary is shown to include Si as the major metallic element together with not small amounts of other metallic elements.

  14. Methods for growth of relatively large step-free SiC crystal surfaces

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

    2002-01-01

    A method for growing arrays of large-area device-size films of step-free (i.e., atomically flat) SiC surfaces for semiconductor electronic device applications is disclosed. This method utilizes a lateral growth process that better overcomes the effect of extended defects in the seed crystal substrate that limited the obtainable step-free area achievable by prior art processes. The step-free SiC surface is particularly suited for the heteroepitaxial growth of 3C (cubic) SiC, AlN, and GaN films used for the fabrication of both surface-sensitive devices (i.e., surface channel field effect transistors such as HEMT's and MOSFET's) as well as high-electric field devices (pn diodes and other solid-state power switching devices) that are sensitive to extended crystal defects.

  15. Accidental formation of Gd₄(SiO₄)₂OTe: crystal structure and spectroscopic properties.

    PubMed

    Daszkiewicz, Marek; Gulay, Lubomir D

    2015-07-01

    Designing new functional materials with increasingly complex compositions is of current interest in science and technology. Complex rare-earth-based chalcogenides have specific thermal, electrical, magnetic and optical properties. Tetragadolinium bis[tetraoxidosilicate(IV)] oxide telluride, Gd4(SiO4)2OTe, was obtained accidentally while studying the Gd2Te3-Cu2Te system. The crystal structure was determined by means of single-crystal X-ray diffraction. The compound crystallizes in the space group Pnma. Three symmetry-independent gadolinium sites were determined. The excitation and emission spectra were collected at room temperature and at 10 K. Gd4(SiO4)2OTe appears to be a promising optical material when doped with rare-earth ions. PMID:26146399

  16. Quasi-single-crystal (001) SrTiO3 templates on Si

    SciTech Connect

    Park, Jae Won; Baek, Seung Hyub; Bark, C; Biegalski, Michael D; Eom, Professor Chang-Beom

    2009-01-01

    The integration of high quality multifunctional oxides on semiconductor devices requires single-crystal-like templates directly on silicon that match with thin film heterostructures. We report the fabrication of quasi-single-crystal (001) SrTiO3 templates on (001) Si by annealing MBE-grown epitaxial SrTiO3 films at 900oC in oxygen. The FWHM of (002) SrTiO3 rocking curve is less than 0.006o which is much narrower than SrTiO3 bulk single crystals. Atomically smooth TiO2-terminated surface is obtained by buffered-HF etching, which presents the possibility of creating novel oxide heterointerfaces on Si platform. Epitaxial SrRuO3 films grown on the etched template exhibit a superior crystalline quality to those grown on a untreated template and an atomically smooth surface.

  17. Evolution of the Shape of Detached GeSi Crystals in Microgravity

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    2013-01-01

    A series of GeSi crystal growth experiments are planned to be conducted in the Low Gradient Furnace (LGF) onboard the International Space Station. An objective of these experiments is to understand the mechanisms of detached Bridgman growth, a process in which a gap exists between the growing semiconductor crystal and the crucible wall. Crystals grown without wall contact have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus.

  18. Low Temperature Rhombohedral Single Crystal SiGe Epitaxy on c-plane Sapphire

    NASA Technical Reports Server (NTRS)

    Duzik, Adam J.; Choi, Sang H.

    2016-01-01

    Current best practice in epitaxial growth of rhombohedral SiGe onto (0001) sapphire (Al2O3) substrate surfaces requires extreme conditions to grow a single crystal SiGe film. Previous models described the sapphire surface reconstruction as the overriding factor in rhombohedral epitaxy, requiring a high temperature Al-terminated surface for high quality films. Temperatures in the 850-1100 C range were thought to be necessary to get SiGe to form coherent atomic matching between the (111) SiGe plane and the (0001) sapphire surface. Such fabrication conditions are difficult and uneconomical, hindering widespread application. This work proposes an alternative model that considers the bulk sapphire structure and determines how the SiGe film nucleates and grows. Accounting for thermal expansion effects, calculations using this new model show that both pure Ge and SiGe can form single crystal films in the 450-550 C temperature range. Experimental results confirm these predictions, where x-ray diffraction and atomic force microscopy show the films fabricated at low temperature rival the high temperature films in crystallographic and surface quality. Finally, an explanation is provided for why films of comparable high quality can be produced in either temperature range.

  19. Crystallization Behavior of Amorphous Si3N4 and Particle Size Control of the Crystallized α-Si3N4.

    PubMed

    Chung, Yong-Kwon; Kim, Shin-A; Koo, Jae-Hong; Oh, Hyeon-Cheol; Chi, Eun-Ok; Hahn, Jee-Hyun; Park, Chan

    2016-05-01

    Amorphous silicon nitride powder prepared by low-temperature vapor-phase reaction was heat treated at various temperatures for different periods of time to examine the crystallization behavior. The effects of the heat-treatment temperature and duration on the degree of crystallization were investigated along with the effect of the heat-up rate on the particle size, and its distribution, of the crystallized α-phase silicon nitride powder. A phase transition from amorphous to α-phase occurred at a temperature above 1400 degrees C. The crystallization. process was completed after heat treatment at 1500 degrees C for 3 h or at 1550 degrees C for 1 h. The crystallization process starts at the surface of the amorphous particle: while the outer regions of the particle become crystalline, the inner part remains amorphous. The re-arrangement of the Si and N atoms on the surface of the amorphous particle leads to the formation of hexagonal crystals that are separated from the host amorphous particle. The particle size and size distribution can be controlled by varying the heat-treatment profile (namely, the heat-treatment temperature, heating rate, and heating duration at the specified temperature), which can be used to control the relative extent of the nucleation and growth. The completion of most of the nucleation process by lowering the heat-up rate can be used to achieve a singlet particle size distribution. Bimodal particle size distribution can be achieved by fast heat-up during the crystallization process. PMID:27483939

  20. Preparation and stress evolution of sol-gel SiO2 antireflective coatings for small-size anisotropic lithium triborate crystals

    NASA Astrophysics Data System (ADS)

    Tian, Bingtao; Wang, Xiaodong; Niu, Yanyan; Zhang, Jinlong; Zhang, Qinghua; Zhang, Zhihua; Wu, Guangming; Zhou, Bin; Shen, Jun

    2016-04-01

    Lithium triborate (LiB3O5, LBO) crystal is now one of the most useful nonlinear optical materials for frequency conversion of high power lasers. The use of the crystal, however, has been hampered by the unavailability of antireflective (AR) coatings with high laser damage resistance. In this work, a "point contact" dip-coating method is developed to prepare sol-gel SiO2 AR coatings on small-size LBO crystals. Using this approach, we obtain a homogenous coating surface on an 8 mm×8 mm×3 mm LBO crystal. The stress measurements show that the stresses in sol-gel SiO2 coatings vary with the time of natural drying, which is beyond our expectation. The anisotropic Young's modulus of the LBO crystal and the different evolution tendency of the stress in the different SiO2 coating layers are found to be responsible for the crack of the double-layer AR coatings on anisotropic LBO crystal. Meanwhile, the resulting coatings on LBO crystal achieve a LIDT of over 15 J/cm2 (532 nm, 3ns) and the coated LBO is expected to have a transmittance of over 99% at 800 nm.

  1. MEV ion beam induced epitaxial crystallization of Si0.99C0.01 layers on silicon

    NASA Astrophysics Data System (ADS)

    Rey, S.; Muller, D.; Grob, J. J.; Grob, A.; Stoquert, J. P.

    1997-02-01

    Multiple energy carbon ion implantation was used to form a 150 nm thick uniformly 1 at. %-doped layers in preamorphized silicon. Unlike conventional furnace annealing, inefficient up to 700 °C, a 1.5 MeV 84Kr+ bombardment is shown to induce the crystallization of such layers at temperatures ranging between 400 and 500 °C. RBS-channeling measurements have been used to estimate the crystallization velocity which is in the order of 10 nm per 1015cm-2. After complete recrystallization, the films have been characterized by Fourier Transform Infra-Red spectroscopy showing that the carbon atoms are neither located in substitutional position nor precipitated in SiC clusters. However, the carbon profile, measured by Secondary Ion Mass Spectroscopy is not modified by the process and oblique incidence channeling angular scans demonstrate that the layers are strained.

  2. Numerical design of SiC bulk crystal growth for electronic applications

    SciTech Connect

    Wejrzanowski, T.; Grybczuk, M.; Kurzydlowski, K. J.; Tymicki, E.

    2014-10-06

    Presented study concerns numerical simulation of Physical Vapor Transport (PVT) growth of bulk Silicon Carbide (SiC) crystals. Silicon Carbide is a wide band gap semiconductor, with numerous applications due to its unique properties. Wider application of SiC is limited by high price and insufficient quality of the product. Those problems can be overcame by optimizing SiC production methods. Experimental optimization of SiC production is expensive because it is time consuming and requires large amounts of energy. Numerical modeling allows to learn more about conditions inside the reactor and helps to optimize the process at much lower cost. In this study several simulations of processes with different reactor geometries were presented along with discussion of reactor geometry influence on obtained monocrystal shape and size.

  3. Numerical design of SiC bulk crystal growth for electronic applications

    NASA Astrophysics Data System (ADS)

    Wejrzanowski, T.; Grybczuk, M.; Tymicki, E.; Kurzydlowski, K. J.

    2014-10-01

    Presented study concerns numerical simulation of Physical Vapor Transport (PVT) growth of bulk Silicon Carbide (SiC) crystals. Silicon Carbide is a wide band gap semiconductor, with numerous applications due to its unique properties. Wider application of SiC is limited by high price and insufficient quality of the product. Those problems can be overcame by optimizing SiC production methods. Experimental optimization of SiC production is expensive because it is time consuming and requires large amounts of energy. Numerical modeling allows to learn more about conditions inside the reactor and helps to optimize the process at much lower cost. In this study several simulations of processes with different reactor geometries were presented along with discussion of reactor geometry influence on obtained monocrystal shape and size.

  4. Thomson Scattering Measurements on HIT-SI3

    NASA Astrophysics Data System (ADS)

    Everson, C. J.; Morgan, K. D.; Jarboe, T. R.

    2015-11-01

    A multi-point Thomson Scattering diagnostic has been implemented on HIT-SI3 (Helicity Injected Torus - Steady Inductive 3) to measure electron temperature. The HIT-SI3 experiment is a modification of the original HIT-SI apparatus that uses three injectors instead of two. This modification alters the configuration of magnetic fields and thus the plasma behavior in the device. The scientific aim of HIT-SI3 is to develop a deeper understanding of how injector behavior and interactions influence current drive and plasma performance in the spheromak. The Thomson Scattering system includes a 20 J (1 GW pulse) Ruby laser that provides the incident beam, and collection optics that are installed such that measurements can be taken at four spatial locations in HIT-SI3 plasmas. For each measurement point, a 3-channel polychromator is used to detect the relative level of scattering. These measurements allow for the presence of temperature gradients in the spheromak to be investigated. Preliminary HIT-SI3 temperature data are presented and can be compared to predictions from computational models. Work supported by the D.O.E.

  5. Interfacial push-out measurements of fully-bonded SiC/SiC composites

    SciTech Connect

    Snead, L.L.; Steiner, D. ); Zinkle, S.J. )

    1990-01-01

    The direct measurement of interfacial bond strength and frictional resistance to sliding in a fully-bonded SiC/SiC composite is measured. It is shown that a fiber push-out technique can be utilized for small diameter fibers and very thin composite sections. Results are presented for a 22 micron thick section for which 37 out of 44 Nicalon fibers tested were pushed-out within the maximum nanoindentor load of 120 mN. Fiber interfacial yielding, push-out and sliding resistance were measured for each fiber. The distribution of interfacial strengths is treated as being Weibull in form. 14 refs., 5 figs.

  6. Time of flight measurements based on FPGA and SiPMs for PET-MR

    NASA Astrophysics Data System (ADS)

    Aguilar, Albert; García-Olcina, Raimundo; Martínez, Pedro A.; Martos, Julio; Soret, Jesús; Torres, José; Benlloch, José M.; González, Antonio J.; Sánchez, Filomeno

    2014-01-01

    Coincidence time measurements with SiPMs have shown to be suitable for PET/MR systems. The present study is based on 3×3 mm2 SiPMs, LSO crystals and a conditioning signal electronic circuit. A Constant Fraction Discriminator (CFD) is used to digitalize the signals and a TDC FPGA-implemented is employed for fine time measurements. TDC capability allows processing the arrival of multiple events simultaneously, measuring times under 100 ps. The complete set-up for time measurements results on a resolution of 892±41 ps for a pair of detectors. The details of such implementation are exposed and the trade-offs of each configuration are discussed.

  7. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  8. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1989-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  9. Structural characterization of Lu{sub 1.8}Y{sub 0.2}SiO{sub 5} crystals

    SciTech Connect

    Chiriu, Daniele; Faedda, Nicola; Lehmann, Alessandra Geddo; Ricci, Pier Carlo; Anedda, Alberto; Desgreniers, Serge; Fortin, Emery

    2007-08-01

    The structural and vibrational properties of Lu{sub 1.8}Y{sub 0.2}SiO{sub 5} (LYSO) single crystals were investigated by means of Raman spectroscopy and x-ray diffraction measurements. Unit cell parameters and bond lengths were determined by Rietveld refinement of the collected x-ray diffraction powder spectra. By comparison with the vibrational spectra of the parent compounds Lu{sub 2}SiO{sub 5} and Y{sub 2}SiO{sub 5} and by using polarized Raman measurements, we propose the assignment of the principal vibrational modes of LYSO crystals. The strict connection of Raman spectra of the LYSO solid solution and of the pure lutetium and yttrium crystals, as well as the analysis of the polarized measurements, confirms that LYSO structure adopts the C2/c space group symmetry. The structural analogies of LYSO with the pure compound Lu{sub 2}SiO{sub 5} are further shown by means of high pressure Raman spectroscopy, and the possibility of considering the LYSO crystal analogous to the LSO structure with a tensile stress between 0.25 and 0.80 GPa is discussed.

  10. Fabrication of High-Q Nanobeam Photonic Crystals in Epitaxially Grown 4H-SiC.

    PubMed

    Bracher, David O; Hu, Evelyn L

    2015-09-01

    Silicon carbide (SiC) is an intriguing material due to the presence of spin-active point defects in several polytypes, including 4H-SiC. For many quantum information and sensing applications involving such point defects, it is important to couple their emission to high quality optical cavities. Here we present the fabrication of 1D nanobeam photonic crystal cavities (PCC) in 4H-SiC using a dopant-selective etch to undercut a homoepitaxially grown epilayer of p-type 4H-SiC. These are the first PCCs demonstrated in 4H-SiC and show high quality factors (Q) of up to ∼7000 as well as low modal volumes of <0.5 (λ/n)(3). We take advantage of the high device yield of this fabrication method to characterize hundreds of devices and determine which PCC geometries are optimal. Additionally, we demonstrate two methods to tune the resonant wavelengths of the PCCs over 5 nm without significant degradation of the Q. Lastly, we characterize nanobeam PCCs coupled to luminescence from silicon vacancy point defects (V1, V2) in 4H-SiC. The fundamental modes of two such PCCs are tuned into spectral overlap with the zero phonon line (ZPL) of the V2 center, resulting in an intensity increase of up to 3-fold. These results are important steps on the path to developing 4H-SiC as a platform for quantum information and sensing. PMID:26305122

  11. Thermal Diffusivity Measurement for p-Si and Ag/p-Si by Photoacoustic Technique

    NASA Astrophysics Data System (ADS)

    Hussein, Mohammed Jabbar; Yunus, W. Mahmood Mat; Kamari, Halimah Mohamed; Zakaria, Azmi

    2015-10-01

    Thermal diffusivity (TD) of p-Si and Ag/p-Si samples were measured by photoacoustic technique using open photoacoustic cell (OPC). The samples were annealed by heating them at 960, 1050, 1200, and 1300 °C for 3 h in air. The thermal diffusivity of Ag-coated samples was obtained by fitting the photoacoustic experimental data to the thermally thick equation for Rosencwaig and Gersho (RG) theory. For the single layer samples, the thermal diffusivity can be obtained by fitting as well as by obtaining the critical frequency f c . In this study, the thermal diffusivity of the p-Si samples increased with increasing the annealing temperature. The thermal diffusivity of the Ag/p-Si samples, after reaching the maximum value of about 2.73 cm2/s at a temperature of 1200 °C, decreased due to the silver complete melt in the surface of the silicon.

  12. Crystal nucleation in amorphous (Au/100-y/Cu/y/)77Si9Ge14 alloys

    NASA Technical Reports Server (NTRS)

    Thompson, C. V.; Greer, A. L.; Spaepen, F.

    1983-01-01

    Because, unlike most metallic glasses, melt-spun alloys of the series (Au/100-y/Cu/y/)77Si9Ge14 exhibit well separated glass transition and kinetic crystallization temperatures, crystallization can be studied in the fully relaxed amorphous phase. An isothermal calorimetric analysis of the devitrification kinetics of the amorphous alloy indicates sporadic nucleation and a constant growth rate. It is found for the cases of alloys with y values lower than 25 that the classical theory of homogeneous nucleation is consistent with observations, including transient effects. An analysis of the crystallization kinetics shows that slow crystal growth rates play an important role in glass formation in these alloys. Although the reduced glass transition temperature increases with Cu content, glass formation is more difficult at high Cu contents, perhaps because of a difference in nucleus composition.

  13. Etching studies on lutetium yttrium orthosilicate LuxY2-xSiO5:Ce (LYSO) scintillator crystals

    NASA Astrophysics Data System (ADS)

    Péter, Á.; Berze, N.; Lengyel, K.; Lörincz, E.

    2010-11-01

    Surface dissolution has been investigated on {100}, {010}, {001}, {110} and {101} oriented Lu1.6Y0.4SiO5:Ce crystal samples by using orthophosphoric acid up to 180°C. Depending on the etching temperature and surface orientation smooth or bunched surfaces were produced. In order to study the effect of the etching process on the scintillation properties temperature dependent optical absorption measurements were carried out up to 236°C. It was found that depending on the post-growth history of the sample, etching may influence the scintillation mechanism by modifying the concentration of shallow traps.

  14. Stopped Light at High Storage Efficiency in a Pr3 + :Y2SiO5 Crystal

    NASA Astrophysics Data System (ADS)

    Schraft, Daniel; Hain, Marcel; Lorenz, Nikolaus; Halfmann, Thomas

    2016-02-01

    We demonstrate efficient storage and retrieval of light pulses by electromagnetically induced transparency (EIT) in a Pr3 +:Y2SiO5 crystal. Using a ring-type multipass configuration, we increase the optical depth (OD) of the medium up to a factor of 16 towards OD ≈96 . Combining the large optical depth with optimized conditions for EIT, we reach a light storage efficiency of (76.3 ±3.5 )% . In addition, we perform extended systematic measurements of the storage efficiency versus optical depth, control Rabi frequency, and probe pulse duration. The data confirm the theoretically expected behavior of an EIT-driven solid-state memory.

  15. Detection of high energy muons with sub-20 ps timing resolution using L(Y)SO crystals and SiPM readout

    NASA Astrophysics Data System (ADS)

    Benaglia, A.; Gundacker, S.; Lecoq, P.; Lucchini, M. T.; Para, A.; Pauwels, K.; Auffray, E.

    2016-09-01

    Precise timing capability will be a key aspect of particle detectors at future high energy colliders, as the time information can help in the reconstruction of physics events at the high collision rate expected there. Other than being used in detectors for PET, fast scintillating crystals coupled to compact Silicon Photomultipliers (SiPMs) constitute a versatile system that can be exploited to realize an ad-hoc timing device to be hosted in a larger high energy physics detector. In this paper, we present the timing performance of LYSO:Ce and LSO:Ce codoped 0.4% Ca crystals coupled to SiPMs, as measured with 150 GeV muons at the CERN SPS H2 extraction line. Small crystals, with lengths ranging from 5 mm up to 30 mm and transverse size of 2 × 2mm2 or 3 × 3mm2 , were exposed to a 150 GeV muon beam. SiPMs from two different companies (Hamamatsu and FBK) were used to detect the light produced in the crystals. The best coincidence time resolution value of (14.5 ± 0.5) ps , corresponding to a single-detector time resolution of about 10 ps, is demonstrated for 5 mm long LSO:Ce,Ca crystals coupled to FBK SiPMs, when time walk corrections are applied.

  16. High-resolution thermal expansion measurements of BaCuSi4O10 and BaCuSi2O6

    NASA Astrophysics Data System (ADS)

    Masunaga, Sueli; Rebello, Alwyn; Neumeier, J. J.

    2014-03-01

    BaCuSi4O10 and BaCuSi2O6 were used in many ancient Chinese artifacts as synthetic pigments, and recently named as Han Blue and Han Purple, respectively. Besides being important synthetic pigments of ancient and modern times, these compounds have attracted scientific and technological interest due to their luminescent properties. Moreover, Han Purple is a spin-dimer compound with an interesting phase diagram and a potential solid state device for exploring quantum effects in magnetic field induced Bose-Einstein condensation. In this work, we study BaCuSi2O6 and BaCuSi4O10 single crystals grown by floating zone method and flux growth technique, respectively. The results of thermal expansion, specific heat, and magnetization measurements of these compounds will be presented in detail. This work is supported by CNPq-Brazil under Grant No 237050/2012-9 and National Science Foundation DMR-0907036.

  17. Crystal structure, physical properties and HRTEM investigation of the new oxonitridosilicate EuSi2O2N2.

    PubMed

    Stadler, Florian; Oeckler, Oliver; Höppe, Henning A; Möller, Manfred H; Pöttgen, Rainer; Mosel, Bernd D; Schmidt, Peter; Duppel, Viola; Simon, Arndt; Schnick, Wolfgang

    2006-09-01

    The new layered oxonitridosilicate EuSi(2)O(2)N(2) has been synthesized in a radio-frequency furnace at temperatures of about 1400 degrees C starting from europium(III) oxide (Eu(2)O(3)) and silicon diimide (Si(NH)(2)). The structure of the yellow material has been determined by single-crystal X-ray diffraction analysis (space group P1 (no. 1), a=709.5(1), b=724.6(1), c=725.6(1) pm, alpha=88.69(2), beta=84.77(2), gamma=75.84(2) degrees ,V=360.19(9)x10(6) pm(3), Z=4, R1=0.0631, 4551 independent reflections, 175 parameters). Its anionic Si(2)O(2)N(2) (2-) layers consist of corner-sharing SiON(3) tetrahedra with threefold connecting nitrogen and terminal oxygen atoms. High-resolution transmission electron micrographs indicate both ordered and disordered crystallites as well as twinning. Magnetic susceptibility measurements of EuSi(2)O(2)N(2) exhibit Curie-Weiss behavior above 20 K with an effective magnetic moment of 7.80(5) mu(B) Eu(-1), indicating divalent europium. Antiferromagnetic ordering is detected at 4.5(2) K. EuSi(2)O(2)N(2) shows a field-induced transition with a critical field of 0.50(5) T. The four crystallographically different europium sites cannot be distinguished by (151)Eu Mössbauer spectroscopy. The room-temperature spectrum is fitted by one signal at an isomer shift of delta=-12.3(1) mm s(-1) subject to quadrupole splitting of DeltaE(Q)=-2.3(1) mm s(-1) and an asymmetry parameter of 0.46(3). Luminescence measurements show a narrow emission band with regard to the four crystallographic europium sites with an emission maximum at lambda=575 nm. PMID:16819723

  18. Proposed Route to Thin Film Crystal Si Using Biaxially Textured Foreign Template Layers

    SciTech Connect

    Teplin, C. W.; Ginley, D. S.; van Hest, M.F.A.M.; Perkins, J. D.; Young, D. L.; Stradins, P.; Wang, Q.; Al-Jassim, M.; Iwaniczko, E.; Leenheer, A.; Jones, K. M.; Branz, H. M.

    2005-11-01

    We have developed a new approach to growing photovoltaic-quality crystal silicon (c-Si) films on glass. Other approaches to film c-Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we have developed an approach to align the silicon grains biaxially (both in and out of plane) so that 1) grain boundaries are "low-angle" and have less effect on the electronic properties of the material and 2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass.

  19. Room-temperature light emission from an airbridge double-heterostructure microcavity of Er-doped Si photonic crystal

    NASA Astrophysics Data System (ADS)

    Wang, Yue; An, Jun-ming; Wu, Yuan-da; Hu, Xiong-wei

    2016-01-01

    We experimentally demonstrate an efficient enhancement of luminescence from two-dimensional (2D) hexagonal photonic crystal (PC) airbridge double-heterostructure microcavity with Er-doped silicon (Si) as light emitters on siliconon-insulator (SOI) wafer at room temperature. A single sharp resonant peak at 1 529.6 nm dominates the photoluminescence (PL) spectrum with the pumping power of 12.5 mW. The obvious red shift and the degraded quality factor (Q-factor) of resonant peak appear with the pumping power increasing, and the maximum measured Q-factor of 4 905 is achieved at the pumping power of 1.5 mW. The resonant peak is observed to shift depending on the structural parameters of PC, which indicates a possible method to control the wavelength of enhanced luminescence for Si-based light emitters based on PC microcavity.

  20. Photonic crystals with SiO2-Ag ``post-cap'' nanostructure coatings for surface enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Seok-min; Zhang, Wei; Cunningham, Brian T.

    2008-10-01

    We demonstrate that the resonant near fields of a large-area replica molded photonic crystal (PC) slab can efficiently couple light from a laser to SiO2-Ag "post-cap" nanostructures deposited on the PC surface by a glancing angle evaporation technique for achieving high surface enhanced Raman spectroscopy (SERS) enhancement factor. To examine the feasibility of the PC-SERS substrate, the simulated electric field around individual Ag particles and the measured Raman spectrum of trans-1,2-bis(4pyridyl)ethane on the PC-SERS substrate were compared with those from an ordinary glass substrate coated with the same SiO2-Ag nanostructures.

  1. A LEEM study of bamboo-like growth of Ag crystals on Si(0 0 1) surfaces

    NASA Astrophysics Data System (ADS)

    Li, B. Q.; Swiech, W.; Venables, J. A.; Zuo, J. M.

    2004-10-01

    We report a low-energy electron microscopy study of novel bamboo-like (quasi-one-dimensional) growth during deposition of Ag on Si(0 0 1) surfaces at elevated temperatures. The bamboo crystals, with typical dimensions of 10 μm in length and varied height and width (tens to hundred of nanometers), align primarily along Si[1 1 0] or Si[1 -1 0] orientation. Low-energy electron microscopy imaging further demonstrates that the Ag bamboo crystals are initially stable against annealing, but break into segments upon prolonged annealing at 843 K. Possible growth mechanisms of the bamboo-like crystals are discussed.

  2. Measurements of Protein Crystal Face Growth Rates

    NASA Technical Reports Server (NTRS)

    Gorti, S.

    2014-01-01

    Protein crystal growth rates will be determined for several hyperthermophile proteins.; The growth rates will be assessed using available theoretical models, including kinetic roughening.; If/when kinetic roughening supersaturations are established, determinations of protein crystal quality over a range of supersaturations will also be assessed.; The results of our ground based effort may well address the existence of a correlation between fundamental growth mechanisms and protein crystal quality.

  3. Measurement of Diffraction Properties of Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Selan, Nicholas; Blades, Michael; Joy, Midhun; Gilchrist, James; Rotkin, Slava

    Close-packed, self-assembled arrays of micrometer polystyrene or silica spheres are high quality artificial crystals that generate well-defined diffraction patterns in the visible range. Such crystals are explored as possible substrates for deposition of nanomaterials such as graphene. Quasi-monochromatic visible light diffraction microscopy is used to characterize effective refractive index and crystal structure, specifically grain size, orientation, and lattice parameters. These parameters can be used to monitor deformations of the colloidal crystal lattice during transfer of nanomaterials. NSF ECCS-1509786, N.S. acknowledges RET supplement to NSF ECCS-1202398.

  4. Smart dust: self-assembling, self-orienting photonic crystals of porous Si.

    PubMed

    Link, Jamie R; Sailor, Michael J

    2003-09-16

    Micrometer-sized one-dimensional photonic crystals of porous Si that spontaneously assemble, orient, and sense their local environment are prepared. The photonic crystals are generated by electrochemically etching two discrete porous multilayered dielectric mirrors into Si, one on top of the other. The first mirror is chemically modified by hydrosilylation with dodecene before the etching of the second mirror, which is prepared with an optical reflectivity spectrum that is distinct from the first. The entire film is removed from the substrate, and the second mirror is then selectively modified by mild thermal oxidation. The films are subsequently fractured into small particles by sonication. The chemically asymmetric particles spontaneously align at an organic liquid-water interface, with the hydrophobic side oriented toward the organic phase and the hydrophilic side toward the water. Sensing is accomplished when liquid at the interface infuses into the porous mirrors, inducing predictable shifts in the optical spectra of both mirrors. PMID:12947036

  5. One-step aluminium-assisted crystallization of Ge epitaxy on Si by magnetron sputtering

    SciTech Connect

    Liu, Ziheng Hao, Xiaojing; Ho-Baillie, Anita; Green, Martin A.

    2014-02-03

    In this work, one-step aluminium-assisted crystallization of Ge on Si is achieved via magnetron sputtering by applying an in-situ low temperature (50 °C to 150 °C) heat treatment in between Al and Ge depositions. The effect of heat treatment on film properties and the growth mechanism of Ge epitaxy on Si are studied via X-ray diffraction, Raman and transmission electron microscopy analyses. Compared with the conventional two-step process, the one-step aluminium-assisted crystallization requires much lower thermal budget and results in pure Ge epitaxial layer, which may be suitable for use as a virtual substrate for the fabrication of III-V solar cells.

  6. Crystal structure induced residue formation on 4H-SiC by reactive ion etching

    NASA Astrophysics Data System (ADS)

    Liu, Yi-hong; Sun, Yu-jun; Zhao, Gao-jie; Liao, Li-ming; Wang, Tao; Chen, Zhi-zhan

    2016-06-01

    The (000 1 ¯) C face of 4H-SiC wafer was etched by reactive ion etching in SF6/O2 plasma. The effect of etching parameters, such as work pressure, SF6:O2 ratio and etching time, on the residue formation were systematically investigated. The residue morphologies were observed by scanning electron microscopy and atomic force microscopy, respectively. The residues have spike shape and their facets are defined as { 1 1 ¯ 0 2 ¯ } crystal planes. They are formed at beginning of the etching and no new spikes are generated as prolonging etching time. Both work pressure and SF6:O2 ratio play significant role in the spike formation. The residues can be eliminated completely by increasing the SF6:O2 ratio and work pressure. On the basis of experimental results and of 4H-SiC crystal structure, the spike formation model is proposed.

  7. Magnetostrictive behaviors of Fe-Si(001) single-crystal films under rotating magnetic fields

    NASA Astrophysics Data System (ADS)

    Kawai, Tetsuroh; Aida, Takuya; Ohtake, Mitsuru; Futamoto, Masaaki

    2015-05-01

    Magnetostrictive behaviors under rotating magnetic fields are investigated for bcc(001) single-crystal films of Fe100-x-Six(x = 0, 6, 10 at. %). The magnetostriction observation directions are along bcc[100] and bcc[110] of the films. The magnetostriction waveform varies greatly depending on the observation direction. For the observation along [100], the magnetostriction waveform of all the films is bathtub-like and the amplitude stays at almost constant even when the magnetic field is increased up to the anisotropy field. On the other hand, the waveform along [110] is triangular and the amplitude increases with increasing magnetic field up to the anisotropy field and then saturates. In addition, the waveform of Fe90Si10 film is distorted triangular when the applied magnetic fields are less than its anisotropy field. These magnetostrictive behaviors under rotating magnetic fields are well explained by employing a proposed modified coherent rotation model where the anisotropy field and the magnetization reversal field are determined by using measured magnetization curves. The results show that magnetocrystalline anisotropy plays important role on magnetostrictive behavior under rotating magnetic fields.

  8. Crystallization of ion-beam-synthesized SiC layer by thermal annealing

    NASA Astrophysics Data System (ADS)

    Wu, W.; Chen, D. H.; Cheung, W. Y.; Xu, J. B.; Wong, S. P.; Kwok, R. W. M.; Wilson, I. H.

    Synthesis of β-phase silicon carbide (SiC) layers has been achieved by high-dose carbon ion beam implantation into (100) silicon wafers with two different ion implantation energies, 40 keV and 65 keV. Subsequent furnace annealing was carried out in N2 at temperatures ranging from 600 to 1200 °C for 2 h. Rutherford backscattering spectrometry (RBS) analysis revealed carbon distribution and the formation of an SiC layer. Infrared spectroscopy (IR) exhibited a sharp absorption peak produced by the Si-C bond at 795 cm-1 with full width at half maximum (FWHM) of about 35 cm-1. A layer of crystalline SiC was formed after annealing the as-implanted sample at 1000 °C for 2 h. The influence of annealing temperature on the surface morphology and the dynamics of the crystallization procedure was studied by atomic force microscopy (AFM). A study of grain size and roughness revealed that the morphology of the SiC layer was largely dependent on annealing temperature, and the average grain size increased as the annealing temperature was raised. At about 900 °C, a layer of nanocrystalline SiC was formed on the sample surface, containing columnar grains with a FWHM of tens of nanometers and a height of less than ten nanometers.

  9. Crystallization of Na2O-SiO2 gel and glass

    NASA Technical Reports Server (NTRS)

    Neilson, G. F.; Weinberg, M. C.

    1984-01-01

    The crystallization behavior of a 19 wt pct soda silica gel and gel-derived glass was compared to that of the ordinary glass of the same composition. Both bulk and ground glass samples were utilized. X-ray diffraction measurements were made to identify the crystalline phases and gauge the extent of crystallization. It was found that the gel crystallized in a distinctive manner, while the gel glass behavior was not qualitatively different from that of the ordinary glass.

  10. Shear-Induced Phase Transformation: From Single-Crystal Silicon to Si-IV

    NASA Astrophysics Data System (ADS)

    Zeng, Guosong; Krick, Brandon; Tansu, Nelson

    2015-03-01

    Silicon has been recognized as one of the most important semiconductors in modern electronics industry. Investigations in the past decades have led to observation of more than 12 different polymorphs of silicon. Among these polymorphs, the wurtzite silicon (Si-IV) shows promising application potential. It has been widely accepted that Si-IV is a metastable phase of silicon forming from annealing Si-III at temperature range between 200 C and 600 C. Besides the annealing, the shear stress can also lead to the phase transition from Si-I into Si-IV. It has been confirmed that the mechanism of shear-induced phase transition is different from that observed from hydrostatic pressure-induced phase transition. However, this shear-induced phase transition has not been studied systematically, and further investigations are required to clarify this transition on silicon. In this work, we develop a new method to study the formation of Si-IV. Combining nanoscratching and micro-Raman spectroscopy, shear effect on Si-I to Si-IV phase transformation has been studied qualitatively and quantitatively. A clear evolution of phase transition of silicon has been recorded. The stability of Si-IV has been analyzed by applying an in-situ Raman measurement under various temperature.

  11. From polymer to monomer: cleavage and rearrangement of Si-O-Si bonds after oxidation yielded an ordered cyclic crystallized structure.

    PubMed

    Zuo, Yujing; Gou, Zhiming; Cao, Jinfeng; Yang, Zhou; Lu, Haifeng; Feng, Shengyu

    2015-07-27

    Polymerization reactions are very common in the chemical industry, however, the reaction in which monomers are obtained from polymers is rarely invesitgated. This work reveals for the first time that oxone can break the Si-O-Si bond and induce further rearrangement to yield an ordered cyclic structure. The oxidation of P1, which is obtained by reaction of 2,2'-1,2-ethanediylbis(oxy)bis(ethanethiol) (DBOET) with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (MM(Vi)), with oxone yielded cyclic crystallized sulfone-siloxane dimer (P1-ox) after unexpected cleavage and rearrangement of the Si-O-Si bond. PMID:26186500

  12. Crystal structure and electronic properties of the new compounds, U 6Fe 16Si 7 and its interstitial carbide U 6Fe 16Si 7C

    NASA Astrophysics Data System (ADS)

    Berthebaud, D.; Tougait, O.; Potel, M.; Lopes, E. B.; Gonçalves, A. P.; Noël, H.

    2007-10-01

    The new compounds U6Fe16Si7 and U6Fe16Si7C were prepared by arc-melting and subsequent annealing at 1500 °C. Single-crystal X-ray diffraction showed that they crystallize in the cubic space group Fm3¯m (No. 225), with unit-cell parameters at room temperature a=11.7206(5) Å for U6Fe16Si7 and a=11.7814(2) Å for U6Fe16Si7C. Their crystal structures correspond to ordered variants of the Th6Mn23 type. U6Fe16Si7 adopts the Mg6Cu16Si7 structure type, whereas U6Fe16Si7C crystallizes with a novel "filled" quaternary variant. The inserted carbon is located in octahedral cages formed by six U atoms, with U-U interatomic distances of 3.509(1) Å. Insertion of carbon in the structure of U6Fe16Si7 has a direct influence on the U-Fe and Fe-Fe interatomic distances. The electronic properties of both compounds were investigated by means of DC susceptibility, electrical resistivity and thermopower. U6Fe16Si7 is a Pauli paramagnet. Its electrical resistivity and thermopower point out that it cannot be classified as a simple metal. The magnetic susceptibility of U 6Fe 16Si 7C is best described over the temperature range 100-300 K by using a modified Curie-Weiss law with an effective magnetic moment of 2.3(2) μB/U, a paramagnetic Weiss temperature, θp=57(2) K and a temperature-independent term χ0=0.057(1) emu/mol. Both the electrical resistivity and thermopower reveal metallic behavior.

  13. Diode laser crystallization processes of Si thin-film solar cells on glass

    NASA Astrophysics Data System (ADS)

    Yun, Jae Sung; Ahn, Cha Ho; Jung, Miga; Huang, Jialiang; Kim, Kyung Hun; Varlamov, Sergey; Green, Martin A.

    2014-07-01

    The crystallization of Si thin-film on glass using continuous-wave diode laser is performed. The effect of various processing parameters including laser power density and scanning speed is investigated in respect to microstructure and crystallographic orientation. Optimal laser power as per scanning speed is required in order to completely melt the entire Si film. When scan speed of 15-100 cm/min is used, large linear grains are formed along the laser scan direction. Laser scan speed over 100 cm/min forms relatively smaller grains that are titled away from the scan direction. Two diode model fitting of Suns-Voc results have shown that solar cells crystallized with scan speed over 100 cm/min are limited by grain boundary recombination (n = 2). EBSD micrograph shows that the most dominant misorientation angle is 60°. Also, there were regions containing high density of twin boundaries up to ~1.2 × 10-8/cm2. SiOx capping layer is found to be effective for reducing the required laser power density, as well as changing preferred orientation of the film from ⟨ 110 ⟩ to ⟨ 100 ⟩ in surface normal direction. Cracks are always formed during the crystallization process and found to be reducing solar cell performance significantly.

  14. Characterization of stacked-crystal PET detector designs for measurement of both TOF and DOI

    NASA Astrophysics Data System (ADS)

    Schmall, Jeffrey P.; Surti, Suleman; Karp, Joel S.

    2015-05-01

    A PET detector with good timing resolution and two-level depth-of-interaction (DOI) discrimination can be constructed using a single-ended readout of scintillator stacks of Lanthanum Bromide (LaBr3), with various Cerium dopant concentrations, including pure Cerium Bromide (CeBr3). The stacked crystal geometry creates a unique signal shape for interactions occurring in each layer, which can be used to identify the DOI, while retaining the inherently good timing properties of LaBr3 and CeBr3. In this work, single pixel elements are used to optimize the choice of scintillator, coupling of layers, and type of photodetector, evaluating the performance using a fast, single-channel photomultiplier tube (PMT) and a single 4 × 4 mm2 silicon photomultiplier (SiPM). We also introduce a method to quantify and evaluate the DOI discrimination accuracy. From signal shape measurements using fast waveform sampling, we found that in addition to differences in signal rise times, between crystal layers, there were also differences in the signal fall times. A DOI accuracy of 98% was achieved using our classification method for a stacked crystal pair, consisting of a 15 mm long LaBr3(Ce:20%) crystal on top of a 15 mm long CeBr3 crystal, readout using a PMT. A DOI accuracy of 95% was measured with a stack of two, identical, 12 mm long, CeBr3 crystals. The DOI accuracy of this crystal pair was reduced to 91% when using a SiPM for readout. For the stack of two, 12 mm long, CeBr3 crystals, a coincidence timing resolution (average of timing results from the top and bottom layer) of 199 ps was measured using a PMT, and this was improved to 153 ps when using a SiPM. These results show that with stacked LaBr3/CeBr3 scintillators and fast waveform sampling nearly perfect DOI accuracy can be achieved with excellent timing resolution—timing resolution that is only minimally degraded compared to results from a single CeBr3 crystal of comparable length to the stacked crystals. The

  15. Characterization of stacked-crystal PET detector designs for measurement of both TOF and DOI.

    PubMed

    Schmall, Jeffrey P; Surti, Suleman; Karp, Joel S

    2015-05-01

    A PET detector with good timing resolution and two-level depth-of-interaction (DOI) discrimination can be constructed using a single-ended readout of scintillator stacks of Lanthanum Bromide (LaBr3), with various Cerium dopant concentrations, including pure Cerium Bromide (CeBr3). The stacked crystal geometry creates a unique signal shape for interactions occurring in each layer, which can be used to identify the DOI, while retaining the inherently good timing properties of LaBr3 and CeBr3. In this work, single pixel elements are used to optimize the choice of scintillator, coupling of layers, and type of photodetector, evaluating the performance using a fast, single-channel photomultiplier tube (PMT) and a single 4 × 4 mm(2) silicon photomultiplier (SiPM). We also introduce a method to quantify and evaluate the DOI discrimination accuracy. From signal shape measurements using fast waveform sampling, we found that in addition to differences in signal rise times, between crystal layers, there were also differences in the signal fall times. A DOI accuracy of 98% was achieved using our classification method for a stacked crystal pair, consisting of a 15 mm long LaBr3(Ce:20%) crystal on top of a 15 mm long CeBr3 crystal, readout using a PMT. A DOI accuracy of 95% was measured with a stack of two, identical, 12 mm long, CeBr3 crystals. The DOI accuracy of this crystal pair was reduced to 91% when using a SiPM for readout. For the stack of two, 12 mm long, CeBr3 crystals, a coincidence timing resolution (average of timing results from the top and bottom layer) of 199 ps was measured using a PMT, and this was improved to 153 ps when using a SiPM. These results show that with stacked LaBr3/CeBr3 scintillators and fast waveform sampling nearly perfect DOI accuracy can be achieved with excellent timing resolution-timing resolution that is only minimally degraded compared to results from a single CeBr3 crystal of comparable length to the stacked crystals. The

  16. Characterization of stacked-crystal PET detector designs for measurement of both TOF and DOI

    PubMed Central

    Schmall, Jeffrey P; Surti, Suleman; Karp, Joel S

    2015-01-01

    A PET detector with good timing resolution and two-level depth-of-interaction (DOI) discrimination can be constructed using a single-ended readout of scintillator stacks of Lanthanum Bromide (LaBr3), with various Cerium dopant concentrations, including pure Cerium Bromide (CeBr3). The stacked crystal geometry creates a unique signal shape for interactions occurring in each layer, which can be used to identify the DOI, while retaining the inherently good timing properties of LaBr3 and CeBr3. In this work, single pixel elements are used to optimize the choice of scintillator, coupling of layers, and type of photodetector, evaluating the performance using a fast, single-channel photomultiplier tube (PMT) and a single 4×4 mm2 silicon photomultiplier (SiPM). We also introduce a method to quantify and evaluate the DOI discrimination accuracy. From signal shape measurements using fast waveform sampling, we found that in addition to differences in signal rise times, between crystal layers, there were also differences in the signal fall times. A DOI accuracy of 98% was achieved using our classification method for a stacked crystal pair, consisting of a 15-mm long LaBr3(Ce:20%) crystal on top of a 15-mm long CeBr3 crystal, readout using a PMT. A DOI accuracy of 95% was measured with a stack of two, identical, 12-mm long, CeBr3 crystals. The DOI accuracy of this crystal pair was reduced to 91% when using a SiPM for readout. For the stack of two, 12-mm long, CeBr3 crystals, a coincidence timing resolution (average of timing results from the top and bottom layer) of 199 ps was measured using a PMT, and this was improved to 153 ps when using a SiPM. These results show that with stacked LaBr3/CeBr3 scintillators and fast waveform sampling nearly perfect DOI accuracy can be achieved with excellent timing resolution—timing resolution that is only minimally degraded compared to results from a single CeBr3 crystal of comparable length to the stacked crystals. The interface in the

  17. Mechanism of interactions between CMC binder and Si single crystal facets.

    PubMed

    Vogl, U S; Das, P K; Weber, A Z; Winter, M; Kostecki, R; Lux, S F

    2014-09-01

    Interactions of the active material particles with the binder are crucial in tailoring the properties of composite electrodes used in lithium-ion batteries. The dependency of the protonation degree of the carboxyl group in the carboxymethyl cellulose (CMC) structure on the pH value of the preparation solution was investigated by Fourier transform infrared spectroscopy (FTIR). Three different distinctive chemical states of CMC binder were chosen (protonated, deprotonated, and half-half), and their interactions with different silicon single crystal facets were investigated. The different Si surface orientations display distinct differences of strength of interactions with the CMC binder. The CMC/Si adhesion forces in solution and Si wettability of the silicon are also strongly dependent on the protonation degree of the CMC. This work provides an insight into the nature of these interactions, which determine the electrochemical performance of silicon composite electrodes. PMID:25109709

  18. Crystallization and characterization of Y2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Drummond, C. H., III; Lee, W. E.; Sanders, W. A.; Kiser, J. D.

    1988-01-01

    Glasses in the yttria-silica system with 20-40 mol pct Y2O3 have been subjected to recrystallization studies after melting at 1900-2100 C in W crucibles in 1 and 50 atm N2. The TEM and XRD results obtained indicate the presence of the delta, gamma, gamma-prime, and beta-Y2Si2O7 crystalline phases, depending on melting and quenching conditions. Heat-treatment in air at 1100-1600 C increased the amount of crystallization, and led to the formation of Y2SiO5, cristobalite, and polymorphs of Y2Si2O7. Also investigated were the effects of 5 and 10 wt pct zirconia additions.

  19. Crystallization and characterization of Y2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Lee, William E.; Sanders, W. A.; Kiser, J. D.

    1991-01-01

    Glasses in the yttria-silica system with 20 to 40 mol pct Y2O3 were subjected to recrystallization studies after melting at 1900 to 2100 C in W crucibles in 1 and 50 atm N2. The TEM and XRD results obtained indicate the presence of the delta, gamma, gamma prime, and beta-Y2Si2O7 crystalline phases, depending on melting and quenching conditions. Heat treatment in air at 1100 to 1600 C increased the amount of crystallization, and led to the formation of Y2SiO5, cristabalite, and polymorphs of Y2Si2O7. Also investigated were the effects of 5 and 10 wt pct zirconia additions.

  20. Comparison of the quantum and classical calculations of flux density of (220) channeled positrons in Si crystal

    NASA Astrophysics Data System (ADS)

    Korotchenko, K. B.; Tukhfatullin, TA; Pivovarov, Yu L.; Eikhorn, Yu L.

    2016-07-01

    Simulation of flux-peaking effect of the 255 MeV positrons channeled in (220) Si crystals is performed in the frame of classical and quantum mechanics. Comparison of the results obtained using both approaches shows relatively good agreement.

  1. Searching for the Best Protein Crystals: Synchrotron Based Measurements of Protein Crystal Quality

    NASA Technical Reports Server (NTRS)

    Borgstahl, Gloria; Snell, Edward H.; Bellamy, Henry; Pangborn, Walter; Nelson, Chris; Arvai, Andy; Ohren, Jeff; Pokross, Matt

    1999-01-01

    We are developing X-ray diffraction methods to quantitatively evaluate the quality of protein crystals. The ultimate use for these crystal quality will be to optimize crystal growth and freezing conditions to obtain the best diffraction data. We have combined super fine-phi slicing with highly monochromatic, low divergence synchrotron radiation and the ADSC Quantum 4 CCD detector at the Stanford Synchrotron Radiation laboratory beamline 1.5 to accurately measure crystal mosaicity. Comparisons of microgravity versus earth-grown insulin crystals using these methods will be presented.

  2. Spectral broadening induced by intense ultra-short pulse in 4H–SiC crystals

    NASA Astrophysics Data System (ADS)

    Chun-hua, Xu; Teng-fei, Yan; Gang, Wang; Wen-jun, Wang; Jing-kui, Liang; Xiao-long, Chen

    2016-06-01

    We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H–SiC single crystals. It is demonstrated that the full width at half maximum of output spectrum increases linearly with the light propagation length and the peak power density, reaching a maximum 870 cm‑1 on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm2. Such spectral broadening can be well explained by the self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index. The nonlinear refractive index n 2 is estimated to be 1.88×10‑15 cm2/W. The intensity-dependent refractive index is probably due to both the nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process. Super continuum spectra could arise as crystals are long enough to induce the self-focusing effect. The results show that SiC crystals may find applications in spectral broadening of high power lasers. Project supported by the National High Technology Research and Development Program of China (Grant No. 2014AA041402) and the National Natural Science Foundation of China (Grant Nos. 51272276 and 51322211).

  3. Temperature-controlled coalescence during the growth of Ge crystals on deeply patterned Si substrates

    NASA Astrophysics Data System (ADS)

    Bergamaschini, Roberto; Salvalaglio, Marco; Scaccabarozzi, Andrea; Isa, Fabio; Falub, Claudiu V.; Isella, Giovanni; von Känel, Hans; Montalenti, Francesco; Miglio, Leo

    2016-04-01

    A method for growing suspended Ge films on micron-sized Si pillars in Si(001) is discussed. In [C.V. Falub et al., Science 335 (2012) 1330] vertically aligned three-dimensional Ge crystals, separated by a few tens of nanometers, were obtained by depositing several micrometers of Ge using Low-Energy Plasma-Enhanced Chemical Vapor Deposition. Here a different regime of high growth temperature is exploited in order to induce the merging of the crystals into a connected structure eventually forming a continuous, two-dimensional film. The mechanisms leading to such a behavior are discussed with the aid of an effective model of crystal growth. Both the effects of deposition and curvature-driven surface diffusion are considered to reproduce the main features of coalescence. The key enabling role of high temperature is identified with the activation of the diffusion process on a time scale competitive with the deposition rate. We demonstrate the versatility of the deposition process, which allows to switch between the formation of individual crystals and a continuous suspended film simply by tuning the growth temperature.

  4. Single-crystal structure determination of (Mg,Fe)SiO3 postperovskite.

    PubMed

    Zhang, Li; Meng, Yue; Dera, Przemyslaw; Yang, Wenge; Mao, Wendy L; Mao, Ho-Kwang

    2013-04-16

    Knowledge of the structural properties of mantle phases is critical for understanding the enigmatic seismic features observed in the Earth's lower mantle down to the core-mantle boundary. However, our knowledge of lower mantle phase equilibria at high pressure (P) and temperature (T) conditions has been based on limited information provided by powder X-ray diffraction technique and theoretical calculations. Here, we report the in situ single-crystal structure determination of (Mg,Fe)SiO3 postperovskite (ppv) at high P and after temperature quenching in a diamond anvil cell. Using a newly developed multigrain single-crystal X-ray diffraction analysis technique in a diamond anvil cell, crystallographic orientations of over 100 crystallites were simultaneously determined at high P in a coarse-grained polycrystalline sample containing submicron ppv grains. Conventional single-crystal structural analysis and refinement methods were applied for a few selected ppv crystallites, which demonstrate the feasibility of the in situ study of crystal structures of submicron crystallites in a multiphase polycrystalline sample contained within a high P device. The similarity of structural models for single-crystal Fe-bearing ppv (~10 mol% Fe) and Fe-free ppv from previous theoretical calculations suggests that the Fe content in the mantle has a negligible effect on the crystal structure of the ppv phase. PMID:23576761

  5. Spin measurement in an undoped Si/SiGe double quantum dot incorporating a micromagnet

    NASA Astrophysics Data System (ADS)

    Wu, Xian; Prance, Jonathan; Ward, Daniel; Gamble, John; Savage, Donald; Lagally, Max; Friesen, Mark; Coppersmith, Susan; Eriksson, Mark

    2013-03-01

    We present recent measurements on a double dot formed in an accumulation mode undoped Si/SiGe heterostructure. The double dot incorporates a proximal micromagnet to generate a stable magnetic field difference between the quantum dots. By measuring the ground state and excited state spectrum of this double dot as a function of in-plane magnetic field we identify the (1,1) and (2,0) charge degeneracy point. Using single-shot readout we measure transitions between the (2,0) singlet and the (1,1) triplet states. This method enables the identification of the crossing as a function of detuning between the (1,1) triplet states (both the first and second excited states) and the (2,0) singlet state. We also present data showing that this undoped device has good charge stability and can be measured with high frequency (up to 500MHz) voltage pulses. Now work at Lancaster University

  6. Synthesis and crystal structure of Ba{sub 26}B{sub 12}Si{sub 5}N{sub 27} containing [Si{sub 2}] dumbbells

    SciTech Connect

    Takayuki, Hashimoto; Yamane, Hisanori; Becker, Nils; Dronskowski, Richard

    2015-10-15

    Black, metallic luster, platelet single crystals of Ba{sub 26}B{sub 12}Si{sub 5}N{sub 27} were grown on a BN crucible wall by slowly cooling from 900 °C to 27 °C. X-ray diffraction analysis revealed that Ba{sub 26}B{sub 12}Si{sub 5}N{sub 27} crystallizes in an orthorhombic cell (a=17.6942(4) Å, b=34.1437(6) Å, c=10.0410(2) Å; space group Fdd2). Isolated nitridoborate anionic groups [BN{sub 2}]{sup 3–}, dumbbell-type Zintl polyanions [Si{sub 2}]{sup 2.8–}, and nitride anions N{sup 3–} are included in the structure. The structural formula is represented as (Ba{sup 2+}){sub 26}([BN{sub 2}]{sup 3–}){sub 12}[([Si{sub 2}]{sup 2.8–}){sub 1.25}(N{sup 3–}){sub 2×0.75}]{sub 2}. The [Si{sub 2}]{sup 2.8–} dumbbell with a Si–Si length of 2.177(5) Å has a bond order of 2.6, which is close to the triple bond of Si. - Graphical abstract: Single crystals of Ba{sub 26}B{sub 12}Si{sub 5}N{sub 27} grown by slow cooling from 900 °C have an orthorhombic crystal structure with space group Fdd2, containing nitridoborate anionic groups [BN{sub 2}]{sup 3–}, dumbbell-type Zintl polyanions [Si{sub 2}]{sup 2.8–}, and nitride anions N{sup 3–}. - Highlights: • A novel compound, Ba{sub 26}B{sub 12}Si{sub 5}N{sub 27}, was synthesized by slow cooling from 900 °C. • Single crystal X-ray diffraction clarified a new crystal structure. • Anionic groups [BN{sub 2}]{sup 3–} and dumbbell-type Zintl polyanions [Si{sub 2}]{sup 2.8–} are contained. • The [Si{sub 2}]{sup 2.8–} dumbbell has a bond order of 2.6, which is close to the triple bond.

  7. Improvement and luminescent mechanism of Bi4Si3O12 scintillation crystals by Dy3+ doping

    NASA Astrophysics Data System (ADS)

    Yang, Bobo; Xu, Jiayue; Zhang, Yan; Zeng, Haibo; Tian, Tian; Chu, Yaoqing; Pan, Yubai; Cui, Qingzhi

    2016-01-01

    Bi4Si3O12:Dy (BSO:Dy) crystals have been grown by the modified vertical Bridgeman method and doping effects on light yield have been investigated. Doped with small amount of Dy2O3 (0.05-0.3 mol%), the light yield and energy resolution of BSO crystals were improved significantly. However, high concentrations of Dy2O3 doping resulted in the decrease of light yield. Pulse height measurement under γ-ray irradiation shows that 0.1 mol% Dy2O3 doping can make the relative light yield of BSO from 24.6% to 35.8% of BGO crystal, with fast decay time of ~90 ns. X-ray excited radioluminescence spectra showed Dy doping has an extra emission in the host emission band (Bi3+ emission) and acts as a sensitizer to the Bi luminescent center. These results indicate that BSO:Dy crystal could be one of promising candidates for replacing BGO in some application such as electromagnetic calorimeter and dual readout in nuclear or high energy physics.

  8. Dynamic range measurement and calibration of SiPMs

    NASA Astrophysics Data System (ADS)

    Bretz, T.; Hebbeker, T.; Lauscher, M.; Middendorf, L.; Niggemann, T.; Schumacher, J.; Stephan, M.; Bueno, A.; Navas, S.; Ruiz, A. G.

    2016-03-01

    Photosensors have played and will continue to play an important role in high-energy and Astroparticle cutting-edge experiments. As of today, the most common photon detection device in use is the photomultiplier tube (PMT). However, we are witnessing rapid progress in the field and new devices now show very competitive features when compared to PMTs. Among those state-of-the-art photo detectors, silicon photomultipliers (SiPMs) are a relatively new kind of semiconductor whose potential is presently studied by many laboratories. Their characteristics make them a very attractive candidate for future Astroparticle physics experiments recording fluorescence and Cherenkov light, both in the atmosphere and on the ground. Such applications may require the measurement of the light flux on the sensor for the purpose of energy reconstruction. This is a complex task due to the limited dynamic range of SiPMs and the presence of thermal and correlated noise. In this work we study the response of three SiPM types in terms of delivered charge when exposed to light pulses in a broad range of intensities: from single photon to saturation. The influence of the pulse time duration and the SiPM over-voltage on the response are also quantified. Based on the observed behaviour, a method is presented to reconstruct the real number of photons impinging on the SiPM surface directly from the measured SiPM charge. A special emphasis is placed on the description of the methodology and experimental design used to perform the measurements.

  9. SU-C-201-01: Investigation of the Effects of Scintillator Surface Treatment On Light Output Measurements with SiPM Detectors

    SciTech Connect

    Valenciaga, Y; Prout, D; Chatziioannou, A

    2015-06-15

    Purpose: To examine the effect of different scintillator surface treatments (BGO crystals) on the fraction of scintillation photons that exit the crystal and reach the photodetector (SiPM). Methods: Positron Emission Tomography is based on the detection of light that exits scintillator crystals, after annihilation photons deposit energy inside these crystals. A considerable fraction of the scintillation light gets trapped or absorbed after going through multiple internal reflections on the interfaces surrounding the crystals. BGO scintillator crystals generate considerably less scintillation light than crystals made of LSO and its variants. Therefore, it is crucial that the small amount of light produced by BGO exits towards the light detector. The surface treatment of scintillator crystals is among the factors affecting the ability of scintillation light to reach the detectors. In this study, we analyze the effect of different crystal surface treatments on the fraction of scintillation light that is detected by the solid state photodetector (SiPM), once energy is deposited inside a BGO crystal. Simulations were performed by a Monte Carlo based software named GATE, and validated by measurements from individual BGO crystals coupled to Philips digital-SiPM sensor (DPC-3200). Results: The results showed an increment in light collection of about 4 percent when only the exit face of the BGO crystal, is unpolished; compared to when all the faces are polished. However, leaving several faces unpolished caused a reduction of at least 10 percent of light output when the interaction occurs as far from the exit face of the crystal as possible compared to when it occurs very close to the exit face. Conclusion: This work demonstrates the advantages on light collection from leaving unpolished the exit face of BGO crystals. The configuration with best light output will be used to obtain flood images from BGO crystal arrays coupled to SiPM sensors.

  10. Liquid crystals under the spotlight: light based measurements of electrical and flow properties of liquid crystals

    NASA Astrophysics Data System (ADS)

    Bennett, Thomas P.; Proctor, Matthew B.; Kaczmarek, Malgosia; D'Alessandro, Giampaolo

    2015-09-01

    Optical light modulation in photorefractive liquid crystal cells depends strongly on the relative voltage drop across the photoconductive and liquid crystal layers. This quantity can be estimated using the Voltage Transfer Function, a generalization of the standard cross polarized intensity measurements. Another advantage of this new measurement technique is that we can use it to estimate dynamical parameters of the liquid crystal and of the device, either through simple black-box models or using a full Ericksen-Leslie theory. In this latter case we can obtain estimates of some of the viscosities of the liquid crystal.

  11. Crystal growth, optical properties, and continuous-wave laser operation of Nd3+-doped Lu2SiO5 crystal

    NASA Astrophysics Data System (ADS)

    Li, D. Z.; Xu, X. D.; Zhou, D. H.; Xia, C. T.; Wu, F.; Xu, J.; Cong, Z. H.; Zhang, J.; Tang, D. Y.

    2011-01-01

    High quality Nd3+-doped Lu2SiO5 (Nd:LSO) crystal has been grown by the Czochralski technique. The cell parameters were analyzed with X-ray diffraction (XRD). Room temperature absorption and fluorescence spectra and fluorescence lifetime of the Nd:LSO crystal were measured and analyzed. The Judd-Ofelt intensity parameters Ω2,4,6 were obtained to be 2.59, 4.90, and 5.96×10-20 cm2, respectively. The absorption and emission cross sections and the branching ratios were calculated. The peak emission cross section is 5.8 and 6.6×10-20 cm2 at 1075 and 1079 nm, respectively, with full width at half maximum (FWHM) of 2.8 and 5.1 nm in turn. Pumped by a laser diode, a maximum 2.54 W continuous-wave laser output has been obtained with a slope efficiency of 32%. All the results show that this crystal is a promising laser material.

  12. Study of Electron, Phonon and Crystal Stability Versus Thermoelectric Properties in Mg2X(X = Si, Sn) Compounds and Their Alloys

    NASA Astrophysics Data System (ADS)

    Bourgeois, J.; Tobola, J.; Wiendlocha, B.; Chaput, L.; Zwolenski, P.; Berthebaud, D.; Gascoin, F.; Recour, Q.; Scherrer, H.

    2013-10-01

    We present results of extensive theoretical and experimental investigations of Mg2Si and Mg2Sn and their Mg2Si1-xSnx alloys. Electronic and phonon properties of binary compounds were studied by ab initio calculations. Then, both compounds were synthesized by the solid-state reaction and electrical resistivity and thermopower was measured at high temperature (300-900 K). In both the compounds, the theoretical bandgaps (0.56 eV in Mg2Si and 0.16 eV in Mg2Sn) agree very well with the experimental values (0.6 eV in Mg2Si and 0.17 eV from activation law in Mg2Sn) upon applying the modified Becke-Johnson semilocal exchange potential and including spin-orbit coupling in the calculations. Calculated phonon spectra support crystal stability of both compounds. For Mg2Si, the contributions from Si and Mg are spread over all the spectrum (0-10 THz), whereas in the case of Mg2Sn, a gap opens around 4 THz with Sn and Mg contributions dominating in lower and higher energy range, respectively. The calculated heat capacity at low temperature (0-300 K) fairly agrees with available experimental data. The crystal structure of Mg2Si1-xSnx with x = 0, 0.25, 0.4, 0.75, 1 was studied by X-ray diffraction measurements. The alloy compositions exist in the ranges 0 < x < 0.4 and 0.6 < x < 1 and the obtained samples are almost single phased. Detailed crystal stability study with temperature revealed that all powder samples started to decompose into MgO, Si and Sn at 630 K. For hot pressed bulk materials, the decomposition is much slower than in powder compounds but it still appears. Interestingly, thermoelectric properties measurements performed in Mg2Si1-xSnx show that both electrical resistivity and thermopower curves are repeatable during temperature cycles up to 770 K. On the other hand, temperature-dependent X-ray powder diffraction suggests that these compounds are not stable. Furthermore, electronic structure calculations of almost 40 impurities (s- and p-block, 3d and 4d transition

  13. A review on solar cells from Si-single crystals to porous materials and quantum dots

    PubMed Central

    Badawy, Waheed A.

    2013-01-01

    Solar energy conversion to electricity through photovoltaics or to useful fuel through photoelectrochemical cells was still a main task for research groups and developments sectors. In this article we are reviewing the development of the different generations of solar cells. The fabrication of solar cells has passed through a large number of improvement steps considering the technological and economic aspects. The first generation solar cells were based on Si wafers, mainly single crystals. Permanent researches on cost reduction and improved solar cell efficiency have led to the marketing of solar modules having 12–16% solar conversion efficiency. Application of polycrystalline Si and other forms of Si have reduced the cost but on the expense of the solar conversion efficiency. The second generation solar cells were based on thin film technology. Thin films of amorphous Si, CIS (copper–indium–selenide) and t-Si were employed. Solar conversion efficiencies of about 12% have been achieved with a remarkable cost reduction. The third generation solar cells are based on nano-crystals and nano-porous materials. An advanced photovoltaic cell, originally developed for satellites with solar conversion efficiency of 37.3%, based on concentration of the solar spectrum up to 400 suns was developed. It is based on extremely thin concentration cells. New sensitizer or semiconductor systems are necessary to broaden the photo-response in solar spectrum. Hybrids of solar and conventional devices may provide an interim benefit in seeking economically valuable devices. New quantum dot solar cells based on CdSe–TiO2 architecture have been developed. PMID:25750746

  14. A review on solar cells from Si-single crystals to porous materials and quantum dots.

    PubMed

    Badawy, Waheed A

    2015-03-01

    Solar energy conversion to electricity through photovoltaics or to useful fuel through photoelectrochemical cells was still a main task for research groups and developments sectors. In this article we are reviewing the development of the different generations of solar cells. The fabrication of solar cells has passed through a large number of improvement steps considering the technological and economic aspects. The first generation solar cells were based on Si wafers, mainly single crystals. Permanent researches on cost reduction and improved solar cell efficiency have led to the marketing of solar modules having 12-16% solar conversion efficiency. Application of polycrystalline Si and other forms of Si have reduced the cost but on the expense of the solar conversion efficiency. The second generation solar cells were based on thin film technology. Thin films of amorphous Si, CIS (copper-indium-selenide) and t-Si were employed. Solar conversion efficiencies of about 12% have been achieved with a remarkable cost reduction. The third generation solar cells are based on nano-crystals and nano-porous materials. An advanced photovoltaic cell, originally developed for satellites with solar conversion efficiency of 37.3%, based on concentration of the solar spectrum up to 400 suns was developed. It is based on extremely thin concentration cells. New sensitizer or semiconductor systems are necessary to broaden the photo-response in solar spectrum. Hybrids of solar and conventional devices may provide an interim benefit in seeking economically valuable devices. New quantum dot solar cells based on CdSe-TiO2 architecture have been developed. PMID:25750746

  15. Synthesis, crystal structure and properties of Mg3B36Si9C and related rare earth compounds RE3-xB36Si9C (RE=Y, Gd-Lu)

    NASA Astrophysics Data System (ADS)

    Ludwig, Thilo; Pediaditakis, Alexis; Sagawe, Vanessa; Hillebrecht, Harald

    2013-08-01

    We report on the synthesis and characterisation of Mg3B36Si9C. Black single crystals of hexagonal shape were yielded from the elements at 1600 °C in h-BN crucibles welded in Ta ampoules. The crystal structure (space group R3barm, a=10.0793(13) Å, c=16.372(3) Å, 660 refl., 51 param., R1(F)=0.019; wR2(F2)=0.051) is characterized by a Kagome-net of B12 icosahedra, ethane like Si8-units and disordered SiC-dumbbells. Vibrational spectra show typical features of boron-rich borides and Zintl phases. Mg3B36Si9C is stable against HF/HNO3 and conc. NaOH. The micro-hardness is 17.0 GPa (Vickers) and 14.5 GPa (Knoop), respectively. According to simple electron counting rules Mg3B36Si9C is an electron precise compound. Band structure calculations reveal a band gap of 1.0 eV in agreement to the black colour. Interatomic distances obtained from the refinement of X-ray data are biased and falsified by the disorder of the SiC-dumbbell. The most evident structural parameters were obtained by relaxation calculation. Composition and carbon content were confirmed by WDX measurements. The small but significant carbon content is necessary by structural reasons and frequently caused by contaminations. The rare earth compounds RE3-xB36Si9C (RE=Y, Dy-Lu) are isotypic. Single crystals were grown from a silicon melt and their structures refined. The partial occupation of the RE-sites fits to the requirements of an electron-precise composition. According to the displacement parameters a relaxation should be applied to obtain correct structural parameters.

  16. Syntheses, crystal structures, and electronic properties of Ba8Si2US14 and Ba8SiFeUS14

    NASA Astrophysics Data System (ADS)

    Mesbah, Adel; Prakash, Jai; Lebègue, Sébastien; Stojko, Wojciech; Ibers, James A.

    2015-10-01

    Black single crystals of the new compounds Ba8Si2US14 and Ba8SiFeUS14 have been obtained by high-temperature solid-state methods at 1223 K. These isostructural compounds crystallize in a new structure type in space group C2h3 - C2/m of the monoclinic system. The salt-like structure comprises isolated US6 octahedra and MS4 tetrahedra separated by Ba cations. The US6 octahedra form pseudo-layers that are separated by two other pseudo-layers formed by isolated MS4 tetrahedra. These compounds do not show any short S-S interactions. Ba8Si2US14 charge balances with 8 Ba2+, 2 Si4+, 1 U4+, and 14 S2-; Ba8SiFeUS14 can be charge balanced with 8 Ba2+, 1 Si4+, 1 Fe3+, 1 U5+, and 14 S2-. DFT calculations using the HSE functional indicate that the compounds are semiconductors. The calculated band gaps are 1.2 eV and 1.8 eV for Ba8Si2US14 and Ba8SiFeUS14, respectively.

  17. Ternary rare earth silicides RE2M3Si4 (RE = Sc, Y, Lu; M = Mo, W): crystal structure, coloring and electronic properties.

    PubMed

    Nielsen, Morten B; Xie, Weiwei; Cava, Robert J

    2016-03-01

    The ternary compounds Sc2Mo3Si4, Y2Mo3Si4, Lu2Mo3Si4 and Sc2W3Si4 have been synthesized using arc melting and structurally characterized using single crystal X-ray diffraction. The compounds are isostructural with Gd5Si4 but with coloring (order of the rare earth and transition metals) on the Gd site. In contrast to group 4 and 5 ternaries of the same type, we observe no site mixing between the rare earth and transition metals. The Y compound displays a different, less common coloring from the others and through DFT calculations and investigation of the solid solution between Sc2Mo3Si4 and Y2Mo3Si4 it is shown that the different coloring of the latter is only marginally more stable. The electronic structures of the ternary compounds have been investigated using DFT calculations, yielding densities of states very similar to Gd5Si4. These predict metallic behavior and no magnetism, which is confirmed through resistivity and magnetization measurements. PMID:26817679

  18. Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

    SciTech Connect

    Wen, Guozhi; Zeng, Xiangbin Wen, Xixin; Liao, Wugang

    2014-04-28

    Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

  19. Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

    NASA Astrophysics Data System (ADS)

    Wen, Guozhi; Zeng, Xiangbin; Wen, Xixin; Liao, Wugang

    2014-04-01

    Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

  20. Stability of a Crystal Oscillator, Type Si530, Inside and Beyond its Specified Operating Temperature Range

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Hammoud, Ahmad

    2011-01-01

    Data acquisition and control systems depend on timing signals for proper operation and required accuracy. These clocked signals are typically provided by some form of an oscillator set to produce a repetitive, defined signal at a given frequency. Crystal oscillators are commonly used because they are less expensive, smaller, and more reliable than other types of oscillators. Because of the inherent characteristics of the crystal, the oscillators exhibit excellent frequency stability within the specified range of operational temperature. In some cases, however, some compensation techniques are adopted to further improve the thermal stability of a crystal oscillator. Very limited data exist on the performance and reliability of commercial-off-the-shelf (COTS) crystal oscillators at temperatures beyond the manufacturer's specified operating temperature range. This information is very crucial if any of these parts were to be used in circuits designed for use in space exploration missions where extreme temperature swings and thermal cycling are encountered. This report presents the results of the work obtained on the operation of Silicon Laboratories crystal oscillator, type Si530, under specified and extreme ambient temperatures.

  1. Comprehensive study of Al-induced layer-exchange growth for orientation-controlled Si crystals on SiO{sub 2} substrates

    SciTech Connect

    Kurosawa, Masashi; Sadoh, Taizoh; Miyao, Masanobu

    2014-11-07

    Orientation-controlled crystalline Si films on insulating substrates are strongly required to achieve high-performance thin-film devices for next-generation electronics. We have comprehensively investigated the layer-exchange kinetics of Al-induced crystallization (AIC) in stacked structures, i.e., amorphous-Si/Al-oxide/Al/SiO{sub 2}-substrates, as a function of the air-exposure time of Al surfaces (t{sub air}: 0–24 h) to form Al-oxide interface-layers, the thickness of Al and Si layers (d{sub Al,} d{sub Si}: 50–200 nm), the annealing temperature (450–500 °C), and the annealing time (0–50 h). It has been clarified that longer t{sub air} (>60 min) and/or thinner d{sub Al} and d{sub Si} (<50 nm) lead to the (111) oriented growth; in contrast, shorter t{sub air} (<60 min) and/or thicker d{sub Al} and d{sub Si} (>100 nm) lead to the (100) oriented growth. No correlation between the annealing temperature and the crystal orientation is observed. Detailed analysis reveals that the layer-exchange kinetics are dominated by “supply-limited” processing, i.e., diffusion of Si atoms into Al layers through Al-oxide layer. Based on the growth rate dependent Si concentration profiles in Al layers, and the free-energy of Si at Al-oxide/Al or Al/SiO{sub 2} interfaces, a comprehensive model for layer-exchange growth is proposed. This well explains the experimental results of not only Si-AIC but also another material system such as gold-induced crystallization of Ge. In this way, a growth technique achieving the orientation-controlled Si crystals on insulating substrates is established from both technological and scientific points of view.

  2. Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1999-01-01

    Commercial epilayers are known to contain a variety of crystallographic imperfections. including micropipes, closed core screw dislocations. low-angle boundaries, basal plane dislocations, heteropolytypic inclusions, and non-ideal surface features like step bunching and pits. This paper reviews the limited present understanding of the operational impact of various crystal defects on SiC electrical devices. Aside from micropipes and triangular inclusions whose densities have been shrinking towards manageably small values in recent years, many of these defects appear to have little adverse operational and/or yield impact on SiC-based sensors, high-frequency RF, and signal conditioning electronics. However high-power switching devices used in power management and distribution circuits have historically (in silicon experience) demanded the highest material quality for prolonged safe operation, and are thus more susceptible to operational reliability problems that arise from electrical property nonuniformities likely to occur at extended crystal defects. A particular emphasis is placed on the impact of closed-core screw dislocations on high-power switching devices, because these difficult to observe defects are present in densities of thousands per cm,in commercial SiC epilayers. and their reduction to acceptable levels seems the most problematic at the present time.

  3. Surface characterization and growth mechanism of laminated Ti 3SiC 2 crystals fabricated by hot isostatic pressing

    NASA Astrophysics Data System (ADS)

    Wu, Qiong; Li, Changsheng; Tang, Hua

    2010-09-01

    Laminated Ti 3SiC 2 crystals were prepared by hot isostatic pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1350 °C. The morphology and microstructure of Ti 3SiC 2 crystals were investigated by means of XRD, SEM, and TEM. The high symmetry and crystalline was revealed by high resolution transmission electronic microscope (HRTEM) and selected area electron diffraction (SAED). The growth mechanism of Ti 3SiC 2 crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (0 0 2) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces.

  4. CRYSTALLIZATION EXPERIMENTS OF SiO{sub 2}-RICH AMORPHOUS SILICATE: APPLICATION TO SiO{sub 2}-RICH CIRCUMSTELLAR DUST AND GEMS

    SciTech Connect

    Matsuno, Junya; Tsuchiyama, Akira; Koike, Chiyoe; Chihara, Hiroki; Imai, Yuta; Noguchi, Ryo; Ohi, Shugo

    2012-07-10

    Crystallization experiments of relatively SiO{sub 2}-rich amorphous silicates using the mean chemical composition of the silicate portions in GEMS (glass with embedded metal and sulfide), which is a major component in anhydrous interplanetary dust particles and a primitive material of the early solar system, were performed to understand the presence of crystalline silica around young stars and crystallization in GEMS. Olivine crystallized at {approx}900-1400 K, probably prior to pyroxene. Three different polymorphs of pyroxene, protopyroxene, orthopyroxene, and clinopyroxene, were identified at {>=}1000 K. Cristobalite, which is one of the silica polymorphs, crystallized only at high temperatures ({>=}1500 K). We obtained time-temperature-transformation (TTT) crystallization diagrams. These results suggest that crystallization of a silica polymorph is kinetically difficult in a day or so at {approx}900-1400 K even for the SiO{sub 2}-saturated composition, while the crystallization might be possible after metastable olivine crystallization if duration is long enough. The TTT diagram also indicates that the GEMS cooling timescale was {approx}10{sup 5} s if they condensed at 1000 K as amorphous silicates and annealed during cooling after the condensation.

  5. Extremely large and significantly anisotropic magnetoresistance in ZrSiS single crystals

    NASA Astrophysics Data System (ADS)

    Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Yao, Shu-Hua; Chen, Y. B.; Zhou, Jian; Zhang, Shan-Tao; Lu, Ming-Hui; Chen, Yan-Feng

    2016-06-01

    Recently, the extremely large magnetoresistance (MR) observed in transition metal telluride, like WTe2, attracted much attention because of the potential applications in magnetic sensor. Here, we report the observation of extremely large magnetoresistance as 3.0 × 104% measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (˜1.4 × 104%) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the magnetic sensors.

  6. Hydrogen reduction of wustite single crystals doped with Mg, Mn, Ca, Al, and Si

    NASA Astrophysics Data System (ADS)

    Moukassi, M.; Gougeon, M.; Steinmetz, P.; Dupre, B.; Gleitzer, C.

    1984-06-01

    In order to investigate the reduction mechanism of wustite in the presence of impurities usually met in the ironmaking industry, single crystals have been prepared with Mg, Mn, Ca, Al, and Si as dopants. The amounts of dopant in the lattice is around 4,4,2.5,0.5, and 0.01 mol pct, respectively, at 800 ‡C. For reduction with pure hydrogen, from 600 to 950 ‡C, Ca is the most efficient for accelerating the process at high degrees of reduction (75 pct) Mg and Mn are also active in this respect. Al has only a slowing down effect. Si also slows down the reaction at temperatures between 600 < T < 850 ‡C, but it becomes accelerating at T > 850 ‡C. In the presence of 20 torrs of water vapor in the gas, Mg and Mn are less efficient and unable to prevent the same slowing down of reaction observed with pure wustite at around 850 ‡C and classically called the ‡rate minimum‡. Our interpretation of these results is mainly based upon the observations of microstructures of partly reduced crystals which show a change in the texture of the iron produced which can be correlated with the reduction rate. These observations lead to a possible explanation in terms of the role of inclusions of impurity oxides on the sintering process of the metal, correlated with their ability to dissolve into the wustite lattice. However, this suggestion cannot apply in the case of Si at low temperatures, and this element is therefore supposed to play a role in the stages of reaction associated with the surface of the crystals.

  7. Surface and subsurface cracks characteristics of single crystal SiC wafer in surface machining

    SciTech Connect

    Qiusheng, Y. Senkai, C. Jisheng, P.

    2015-03-30

    Different machining processes were used in the single crystal SiC wafer machining. SEM was used to observe the surface morphology and a cross-sectional cleavages microscopy method was used for subsurface cracks detection. Surface and subsurface cracks characteristics of single crystal SiC wafer in abrasive machining were analysed. The results show that the surface and subsurface cracks system of single crystal SiC wafer in abrasive machining including radial crack, lateral crack and the median crack. In lapping process, material removal is dominated by brittle removal. Lots of chipping pits were found on the lapping surface. With the particle size becomes smaller, the surface roughness and subsurface crack depth decreases. When the particle size was changed to 1.5µm, the surface roughness Ra was reduced to 24.0nm and the maximum subsurface crack was 1.2µm. The efficiency of grinding is higher than lapping. Plastic removal can be achieved by changing the process parameters. Material removal was mostly in brittle fracture when grinding with 325# diamond wheel. Plow scratches and chipping pits were found on the ground surface. The surface roughness Ra was 17.7nm and maximum subsurface crack depth was 5.8 µm. When grinding with 8000# diamond wheel, the material removal was in plastic flow. Plastic scratches were found on the surface. A smooth surface of roughness Ra 2.5nm without any subsurface cracks was obtained. Atomic scale removal was possible in cluster magnetorheological finishing with diamond abrasive size of 0.5 µm. A super smooth surface eventually obtained with a roughness of Ra 0.4nm without any subsurface crack.

  8. Growth and Characterization of Ca2Al2SiO7 Piezoelectric Single Crystals for High-Temperature Sensor Applications

    NASA Astrophysics Data System (ADS)

    Hagiwara, Manabu; Noguchi, Hiroaki; Hoshina, Takuya; Takeda, Hiroaki; Fujihara, Shinobu; Kodama, Nobuhiro; Tsurumi, Takaaki

    2013-09-01

    The electrical properties of a piezoelectric single crystal of calcium aluminate silicate Ca2Al2SiO7 (CAS) were studied at elevated temperatures and its applicability to high-temperature pressure sensors was investigated. The CAS bulk single crystal was grown by the Czochralski method. The piezoelectric d14 and d36 constants were respectively evaluated as 6.04 and 4.04 pC/N by the resonance and antiresonance method. The temperature dependence of the piezoelectric constant was investigated at temperatures up to 500 °C. The electrical resistivity at 800 °C was on the order of 108 Ω.cm along both the crystallographic a- and c-axes. The measurement of direct piezoelectric response at 700 °C demonstrated that the CAS crystal could detect a pseudo-combustion pressure change of an automobile engine. Our observations suggest that CAS crystals are superior candidates for sensing pressure at high temperatures.

  9. Preparation and properties of a novel piezoelectric single-crystal material: Sr{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14}

    SciTech Connect

    Wang Zengmei; Yuan Duorong; Xu Dong; Lue Mengkai; Cheng Xiufeng; Pan Lihu

    2004-06-08

    We have grown a new langasite-type piezoelectric single crystal Sr{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14} (STGS) with dimensions of 15 mm in diameter and 30 mm in length by using the Czochralski technique. The X-ray powder diffraction (XRPD) of single crystal was performed at room temperature. The thermal expansion coefficient perpendicular to Z direction has been measured as 3.2x10{sup -6} K{sup -1} between 343.15 and 493.15 K, and along Z-axis, 9.7x10{sup -6} K{sup -1} between 318.15 and 503.15 K. The specific heat of the crystal has been measured as 0.68 J g{sup -1} K{sup -1} at 468.15 K. The transmittance spectra from 200 to 3200 nm annealed in different atmospheres were measured.

  10. Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

    NASA Astrophysics Data System (ADS)

    Pezzoli, Fabio; Giorgioni, Anna; Gallacher, Kevin; Isa, Fabio; Biagioni, Paolo; Millar, Ross W.; Gatti, Eleonora; Grilli, Emanuele; Bonera, Emiliano; Isella, Giovanni; Paul, Douglas J.; Miglio, Leo

    2016-06-01

    We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in μm-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO2 in passivating the surface of Ge and thus in enhancing the room temperature PL emission.

  11. Basics of luminescent diagnostics of the dislocation structure of SiC crystals

    NASA Astrophysics Data System (ADS)

    Gorban, Ivan S.; Mishinova, Galina N.

    1998-04-01

    The result of the studies of dislocation luminescence in SiC crystals are presented in the report. This semiconductor forms great number of polytypes which differs by periodical alternation of cubic and hexagonal layers in basic planes. High probability of periodic pack infringement caused by very little energy of stacking fault leads to variation of dislocation structures in different glide planes of this crystals. Shockly and Frank partial dislocations are sufficiently important. The dislocation luminescence as growth origin so as dislocations included in result of plastic deformation or high temperature annealing. In this case the spectra of dislocation luminescence are the indicators of processes of phase transitions. The influence of impurities on the dislocation luminescence centers is investigated. The models of structure of dislocation centers and the mechanism of radiative transitions are proposed.

  12. Plastic deformation of Mo(Si,Al){sub 2} single crystals with C40 structure

    SciTech Connect

    Moriwaki, M.; Ito, K.; Inui, H.; Yamaguchi, M.

    1997-12-31

    The deformation behavior of single crystals of Mo(Si,Al){sub 2} with the C40 structure has been studied as a function of crystal orientation and Al content in the temperature range from room temperature to 1,500 C in compression. Plastic flow is possible only above 1,100 C for orientations where slip along <11{bar 2}0> on (0001) is operative and no other slip systems are observed over whole temperature range investigated. The critical resolved shear stress for basal slip decreases rapidly with increasing temperature and the Schmid law is valid. Basal slip appears to occur through a synchroshear mechanism, in which a-dislocations (b = 1/3 <11{bar 2}0>) dissociate into two synchro-partial dislocations with the identical Burgers vector (b = 1/6 <11{bar 2}0>) and each synchro-partial further dissociates into two partials on two adjacent planes.

  13. Effect of SiO2 nanoparticle doping on electro-optical properties of polymer dispersed liquid crystal lens for smart electronic glasses

    NASA Astrophysics Data System (ADS)

    Kim, Eunju; Liu, Yang; Hong, Sung-Jei; Han, Jeong In

    2015-03-01

    In this paper, SiO2 nanoparticle doped polymer dispersed liquid crystal (PDLC) lenses were made from a mixture of prepolymer, E7 liquid crystal and SiO2 nanoparticles by the polymerization induced phase separation (PIPS) process for smart electronic glasses with auto-shading and auto-focusing functions. Electro-optical properties of doped and undoped samples including transmittance, driving voltage, contrast ratio and slope of the linear region of the transmittance-voltage were measured, compared and analyzed. Driving voltage of SiO2 nanoparticle doped PDLC lenses moderately improved. But the slope of linear region, response time and contrast ratio deteriorated, especially the latter two. It can be assumed that these doping effects were due to the mechanistic change from liquid-gel separation to liquid-liquid separation by the fast heterogeneous nucleation rate caused by the increased nucleation at the surface of SiO2 nanoparticles. The marked deteriorations of falling response time and contrast ratio were due to well defined liquid crystal molecules in LC droplets, which induced slow and imperfect random rearrangement of LC molecules at the off state.

  14. Spin measurement in an undoped Si/SiGe double quantum dot incorporating a micromagnet

    NASA Astrophysics Data System (ADS)

    Wu, Xian; Ward, Daniel; Prance, Jonathan; Kim, Dohun; Shi, Zhan; Mohr, Robert; Gamble, John; Savage, Donald; Lagally, Max; Friesen, Mark; Coppersmith, Susan; Eriksson, Mark

    2014-03-01

    We present measurements on a double dot formed in an accumulation-mode undoped Si/SiGe heterostructure. The double dot incorporates a proximal micromagnet to generate a stable magnetic field difference between the quantum dots. The gate design incorporates two layers of gates, and the upper layer of gates is split into five different sections to decrease crosstalk between different gates. A novel pattern of the lower layer gates enhances the tunability of tunnel rates. We will describe our attempts to create a singlet-triplet qubit in this device. This work was supported in part by ARO(W911NF-12-0607), NSF(DMR-1206915), and the United States Department of Defense. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the US Government. Now works at Lancaster University, UK.

  15. Heat capacity and latent heat measurements of CoMnSi using a microcalorimeter.

    PubMed

    Miyoshi, Y; Morrison, K; Moore, J D; Caplin, A D; Cohen, L F

    2008-07-01

    A new method of utilizing a commercial silicon nitride membrane calorimeter to measure the latent heat at a first order phase transition is presented. The method is a direct measurement of the thermoelectric voltage jump induced by the latent heat, in a thermally isolated system ideally suited for single crystal and small microgram samples. We show that when combined with the ac calorimetry technique previously developed, the resultant thermal measurement capabilities are extremely powerful. We demonstrate the applicability of the combined method with measurements on a 100 microm size fragment of CoMnSi exhibiting a sizable magnetocaloric effect near room temperature, and obtain good agreement with previously reported values on bulk samples. PMID:18681727

  16. A direct measurement of the electronic structure of Si nanocrystals and its effect on optoelectronic properties

    SciTech Connect

    Mustafeez, Waqas; Salleo, Alberto; Majumdar, Arka; Vučković, Jelena

    2014-03-14

    Since reports that silicon nanocrystals (Si-NCs) can exhibit direct transition emission, the silicon laser field is at a juncture where the importance of this discovery needs to be evaluated. Most theoretical models predicted a monotonic increase in the bandgap and experimental information currently available on the electronic structure at the Γ valley of these promising materials is circumstantial as it is obtained from emission measurements where competing non-radiative relaxation and recombination processes only provide an incomplete picture of the electronic structure of Si-NCs. Optical absorption, the most immediate probe of the electronic structure beyond the band-edges, showing the evolution of the Γ valley states with nanocrystal size has not been measured. Here, we show such measurements, performed with high dynamic range, allowing us to observe directly the effect of crystal size on the Γ valley splitting far above the band-edges. We show that the splitting is 100 s of meV more pronounced than predicted by pseudo potential calculations and Luttinger-Kohn model. We also show that ultrafast red-shifting emission can be observed in plasma enhanced chemical vapor deposition prepared Si-NCs.

  17. Viscous Fingering and Dendritic Growth of Surface Crystallized Sr2TiSi2O8 Fresnoite

    PubMed Central

    Wisniewski, Wolfgang; Patschger, Marek; Rüssel, Christian

    2013-01-01

    During the quenching of a melt with the composition 2SrO·TiO2·2.75SiO2, cubic SrTiO3- and tetragonal Sr2TiSi2O8-crystals are formed at the surface. Subsequent crystal growth leads to dendritic fresnoite structures which become increasingly finer until the mechanism changes to viscous fingering during further cooling. In the final stages of this initial growth step, the crystal orientations of these dendrites systematically change. Due to a complete absence of bulk nucleation in this system, crystal growth is resumed upon reheating to 970°C and fractal growth with the c-axis tilted by about 45° from the main growth direction is observed. The results are interpreted to confirm the link between viscous fingering and dendritic growth in the case of a true crystallization process. PMID:24356207

  18. Timing performance measurements of Si-PM-based LGSO phoswich detectors

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiichi; Kobayashi, Takahiro; Okumura, Satoshi; Yeom, Jung Yeol

    2016-06-01

    Since the timing resolution was significantly improved using silicon photomultipliers (Si-PMs) combined with fast scintillators, we expect that phoswich detectors will be used in future TOF-PET systems. However, no practical phoswich detector has been proposed for TOF-PET detectors. We conducted timing performance measurements of phoswich detectors comprised of two types of Ce-doped LGSO scintillators with different decay times coupled to Si-PMs and digitized the output signals using a high bandwidth digital oscilloscope. We prepared three types of LGSOs (LGSO-fast, LGSO-standard, and LGSO-slow) with different Ce concentrations. After measuring the decay time, the energy performance, and the timing performance of each LGSO, we conducted pulse shape analysis and timing resolution measurements for two versions of phoswich LGSOs: LGSO-standard/LGSO-fast and LGSO-slow/LGSO-fast combinations. The pulse shape spectra for a 10-mm-long crystal LGSO-slow/LGSO-fast combination showed good separation of the front and back crystals with a peak-to-valley ratio of 2.0. The timing resolutions for the 20-mm-long crystal LGSO-slow/LGSO-fast combination were ~300 ps FWHM. The timing resolutions for the phoswich LGSOs were slightly inferior than that measured with the individual LGSO fast, but the acquired timing resolution for the phoswich configuration, ~300 ps with a LGSO-slow/LGSO-fast combination, is adequate for TOF-PET systems. We conclude that LGSO phoswich detectors are promising for TOF-DOI-PET systems.

  19. In situ synthesis and hydrothermal crystallization of nanoanatase TiO2 -SiO2 coating on aramid fabric (HTiSiAF) for UV protection.

    PubMed

    Deng, Hui; Zhang, Hongda

    2015-10-01

    TiO2 -SiO2 thin film was prepared by sol-gel method and coated on the aramid fabric to prepare functional textiles. The aramid fabric was dipped and withdrawn in TiO2 -SiO2 gel and hydrothermal crystallization at 80(°) C, then its UV protection functionality was evaluated. The crystalline phase and the surface morphology of TiO2 -SiO2 thin film were characterized using SEM, XRD, and AFM respectively. SEM showed hydrothermal crystallization led to a homogeneous dispersion of anatase nonocrystal in TiO2 -SiO2 film, and XRD suggested the mean particle size of the formed anatase TiO2 was less than 30 nm. AFM indicated that hydrothermal treatment enhanced the crystallization of TiO2 . UV protection analysis suggested that the hydrothermally treated coated textile had a better screening property in comparison with TiO2 -SiO2 gel and native aramid fabric. PMID:26303384

  20. Growth of Si spherical crystals and the surface oxidation (M-9)

    NASA Technical Reports Server (NTRS)

    Nishinaga, Tatau

    1993-01-01

    Nearly 90 percent of semiconductor devices are produced with Si single crystals as the starting materials. For instance, the integrated circuits (IC), which are used in almost all electronic equipments such as TV, tape recorders, audio amplifiers, etc., are made after various processings of Si single crystal wafers. In these wafers, the same controlled amounts of impurities are added and the uniformities in their distributions are extremely important. Growth under microgravity makes it possible to eliminate the buoyancy-driven convection in the melt, which is one of the main origins of convections which results in non-uniformity of the impurity. Another source of convection is known as Marangoni convection which is driven on the free surface when a temperature gradient occurs. One of the merits of microgravity experimentation is that the detailed study of this convection becomes possible. Another important advantage of microgravity is that growth of crystals without a crucible is possible. This makes it possible to study melt growth without the strain which is usually introduced on the ground. Nevertheless, we should repeat and analyze many growth experiments in space to get reliable results. However, since in the FMPT, the time for the experiment is limited, we plan to carry out two kinds of very simple and basic experiments as the first step for the semiconductor growth experiment. In the first experiment, we use single crystal Si sphere as the starting material and as shown, this sphere is heated in the furnace at a slightly higher temperature than the melting point. After the melting front moves nearly half way to its center, the temperature is decreased to stop the melting and to start the growth from the seed for which we use the unmelted solid party of the sphere. The sphere is centered by quartz protuberances inside of the quartz crucible. There exists the possibility of temperature fluctuations being introduced when the molten sphere occasionally touches

  1. Simultaneous presence of (Si{sub 3}O{sub 10}){sup 8−} and (Si{sub 2}O{sub 7}){sup 6−} groups in new synthetic mixed sorosilicates: BaY{sub 4}(Si{sub 2}O{sub 7})(Si{sub 3}O{sub 10}) and isotypic compounds, studied by single-crystal X-ray diffraction, Raman spectroscopy and DFT calculations

    SciTech Connect

    Wierzbicka-Wieczorek, Maria; Többens, Daniel M.; Kolitsch, Uwe; Tillmanns, Ekkehart

    2013-11-15

    Three new, isotypic silicate compounds, BaY{sub 4}(Si{sub 2}O{sub 7})(Si{sub 3}O{sub 10}), SrYb{sub 4}(Si{sub 2}O{sub 7})(Si{sub 3}O{sub 10}) and SrSc{sub 4}(Si{sub 2}O{sub 7})(Si{sub 3}O{sub 10}), were synthesized using high-temperature flux growth techniques, and their crystal structures were solved from single-crystal X-ray intensity data: monoclinic, P2{sub 1}/m, with a=5.532(1)/5.469(1)/5.278(1), b=19.734(4)/19.447(4)/19.221(4), c=6.868(1)/6.785(1)/6.562(1) Å, β=106.53(3)/106.20(3)/106.50(3)°, V=718.8(2)/693.0(2)/638.3(2) Å{sup 3}, R(F)=0.0225/0.0204/0.0270, respectively. The topology of the novel structure type contains isolated horseshoe-shaped Si{sub 3}O{sub 10} groups (Si–Si–Si=93.15–95.98°), Si{sub 2}O{sub 7} groups (Si–O{sub bridge}–Si=180°, symmetry-restricted) and edge-sharing M(1)O{sub 6} and M(2)O{sub 6} octahedra. Single-crystal Raman spectra of the title compounds were measured and compared with Raman spectroscopic data of chemically and topologically related disilicates and trisilicates, including BaY{sub 2}(Si{sub 3}O{sub 10}) and SrY{sub 2}(Si{sub 3}O{sub 10}). The band assignments are supported by additional theoretical calculation of Raman vibrations by DFT methods. - Graphical abstract: View of BaY{sub 4}(Si{sub 2}O{sub 7})(Si{sub 3}O{sub 10}) along [100], showing zigzag chains and the tri- and disilicate groups. The unit cell is outlined. Display Omitted - Highlights: • We report a novel interesting crystal structure type for mixed sorosilicates containing Y, Yb, and Sc. • Synthesis of such mixed sorosilicates is possible by a high-temperature flux-growth technique. • Calculation of Raman vibrations by advanced DFT methods allows a considerably improved interpretation of measured Raman spectra.

  2. A high-field magnetization study of a Nd(2)Fe(14)Si(3) single crystal.

    PubMed

    Andreev, A V; Yoshii, S; Kuz'min, M D; de Boer, F R; Kindo, K; Hagiwara, M

    2009-04-01

    Magnetization study of a single crystal of Nd(2)Fe(14)Si(3) (with the rhombohedral Th(2)Zn(17)-type structure) reveals that the compound is a ferromagnet with a spontaneous magnetic moment of 32.3μ(B) per formula unit (at T = 2 K) and a Curie temperature equal to 495 K. The easy-magnetization direction lies close to the b-axis, tilting slightly towards the c-axis. (The b-axis [120] is not a high-symmetry direction in the crystallographic class D(3d).) The observed strong magnetic anisotropy is attributed almost entirely to the Nd sublattice, as concluded from comparison with a Y(2)Fe(14)Si(3) single crystal. A magnetic field applied along the c-axis induces a first-order spin reorientation transition at B(FOMP) = 20 T. In the process of magnetization the Nd and Fe sublattices behave as essentially non-collinear. This is manifest particularly in the downward curvature of the first (pre-FOMP) stage of the magnetization curve. It is proposed to regard this curvature as a validity criterion for the single-sublattice approximation. PMID:21825352

  3. Crystal structure of coesite, a high-pressure form of SiO/sub 2/, at 15 and 298 K from single-crystal neutron and x-ray diffraction data: test of bonding models

    SciTech Connect

    Smyth, J.R.; Smith, J.V.; Artioli, G.; Kvick, A.

    1987-02-12

    The crystal structure of a natural coesite from an eclogite rock fragment in the Roberts Victor kimberlite, South Africa, was determined at 15 K by neutron diffraction (a = 7.1357 (13) A, b = 12.3835 (26) A, c = 7.1859 (11) A, ..beta.. = 120.375 (16)/sup 0/, C2/c), and at approx.298 K by X-ray diffraction. Cell dimensions measured by neutron diffraction at 292 K (7.1464 (9), 12.3796 (19), and 7.1829 (8) A, 120.283 (9)/sup 0/) differed from those determined by X-ray diffraction, probably because of a systematic absorption error for the latter. The strongly anisotropic nature of the thermal expansion is explained qualitatively by the relatively large changes (approx.1%) in the distances between the nonbonded oxygen neighbors and the relatively small changes of Si-O-Si and O-Si-O angles in the compact three-dimensional framework. There is a good, but not perfect, negative correlation between the eight independent Si-O distances and the five independent values for sec theta(Si-O-Si) at 15 K. It is weaker than that for 298 K, and the scatter from a straight-line prediction from molecular-orbital models for small clusters (e.g., H/sub 6/Si/sub 2/O/sub 7/) implies that it is desirably to consider additional forces, including repulsive forces between nonbonded oxygen neighbors. The combined at a for Si-O and Si-O-Si in coesite, quartz, and cristobalite at 10-15 K show less scatter than those for approx.298 K, in accordance with the greater thermal response of framework geometry in the more open structures.

  4. Multiple-layer SOI based on Single-Crystal Si Nanomembrane Transfer

    NASA Astrophysics Data System (ADS)

    Peng, Weina; Roberts, Michelle; Nordberg, Eric; Flack, Frank; Colavita, Paula; Hamers, Robert; Savage, Donald; Lagally, Max; Eriksson, Mark

    2007-03-01

    Silicon-on-insulator (SOI) has many advantages over bulk Si including the reduction of parasitic resistance and increased device speed. Multiple-layer SOI, having more device layers per unit area, enables 3D process integration as well as applications in optics. However, it is impossible to achieve such a system by growth techniques (one can grow only non-crystalline Si on SiO2), and multiple Smart Cut transfers used to create single layer SOI may be prohibitively expensive. We present here a novel method to fabricate such a multiple SOI system using transferred Si nanomembranes^ and subsequent oxidation. The surface roughness and interface quality are examined respectively by AFM and cross-sectional SEM. Low surface roughness (0.176nm) and smooth interfaces are achieved. As an example optical application, we apply the multilayer system to fabricate a Si-based Bragg reflector. The specular reflectivity of one, two, and three-membrane mirrors is measured using FTIR. High specular reflectivity, above 99%, is achieved for three stacked membranes. Comparison of the measured reflectivity with theoretical calculations shows good agreement.

  5. Structural characterization of nanostructures grown by Ni metal induced lateral crystallization of amorphous-Si

    NASA Astrophysics Data System (ADS)

    Radnóczi, G. Z.; Dodony, E.; Battistig, G.; Vouroutzis, N.; Kavouras, P.; Stoemenos, J.; Frangis, N.; Kovács, A.; Pécz, B.

    2016-02-01

    The nickel metal induced lateral crystallization of amorphous silicon is studied by transmission electron microscopy in the range of temperatures from 413 to 521 °C. The structural characteristics of the whiskers grown at 413 °C are compared to the grains grown at 600 °C, where both Metal Induced Lateral Crystallization (MILC) and Solid Phase Crystallization (SPC) are involved. At 413 °C, long whiskers are formed at any crystallographic direction almost free of defects. In contrary, whiskers grown by MILC around 600 °C are crystallized along the ⟨111⟩ directions. These differences are attributed to the low crystallization rate and suppression of the SPC process. The activation energy of the pure MILC was measured in the order of 2 eV. The effect of Ni on the crystallization rate is studied by in-situ heating experiments inside the microscope. The role of contamination that can inhibit MILC is discussed. The cases of MILC process under limited Ni and unlimited Ni source were studied and compared to in-situ annealing experiments. The crystallization rate is strongly influenced by the neighbouring Ni sources; this long-range interaction is attributed to the requirement of a critical Ni concentration in amorphous silicon before the initiation of the MILC process. The long-range interaction can enhance crystallization along a certain direction. The transition from MILC to SPC and the change of the crystallization mode due to the lack of Ni are discussed. The beneficial effect of long annealing at 413 °C is also discussed.

  6. Tunable visible and near-IR emission from sub-10 nm etched single-crystal Si nanopillars.

    PubMed

    Walavalkar, Sameer S; Hofmann, Carrie E; Homyk, Andrew P; Henry, M David; Atwater, Harry A; Scherer, Axel

    2010-11-10

    Visible and near-IR photoluminescence (PL) is reported from sub-10 nm silicon nanopillars. Pillars were plasma etched from single crystal Si wafers and thinned by utilizing strain-induced, self-terminating oxidation of cylindrical structures. PL, lifetime, and transmission electron microscopy were performed to measure the dimensions and emission characteristics of the pillars. The peak PL energy was found to blue shift with narrowing pillar diameter in accordance with a quantum confinement effect. The blue shift was quantified using a tight binding method simulation that incorporated the strain induced by the thermal oxidation process. These pillars show promise as possible complementary metal oxide semiconductor compatible silicon devices in the form of light-emitting diode or laser structures. PMID:20919695

  7. Comparison of modeled and measured performance of a GSO crystal as gamma detector

    NASA Astrophysics Data System (ADS)

    Parno, D. S.; Friend, M.; Mamyan, V.; Benmokhtar, F.; Camsonne, A.; Franklin, G. B.; Paschke, K.; Quinn, B.

    2013-11-01

    We have modeled, tested, and installed a large, cerium-activated Gd2SiO5 crystal scintillator for use as a detector of gamma rays. We present the measured detector response to two types of incident photons: nearly monochromatic photons up to 40 MeV, and photons from a continuous Compton backscattering spectrum up to 200 MeV. Our GEANT4 simulations, developed to determine the analyzing power of the Compton polarimeter in Hall A of Jefferson Lab, reproduce the measured spectra well.

  8. Design and fabrication of Si-based photonic crystal stamps with electron beam lithography (EBL)

    NASA Astrophysics Data System (ADS)

    Jannesary, Reyhaneh; Bergmair, Iris; Zamiri, Saeid; Hingerl, Kurt; Hubbard, Graham; Abbott, Steven; Chen, Qin; Allsopp, Duncan

    2009-05-01

    The quest for mass replication has established technologies like nanoimprinting via hard stamps or PDMS stamps, where the stamps are usually produced via Electron Beam Lithography (EBL) for applications in the microelectronic industry. On the other hand, nanopatterning with self ordered structures1 or via holographic patterns provide the basis for large area imprints for applications for example, antireflection coatings based on biomimetic motheyes2. In this work we report on a technology for enabling the mass replication of custom-designed and e-beam lithographically prepared structures via establishing novel roll to roll nanoimprint processes for pattern transfer into UV curable pre-polymers. The new nano-fabrication technology is based on the concept of Disposal Master Technology (DMT) capable of patterning areas up to 1 x 1 m2 and is suitable for mass volume manufacturing of large area arrays of sub-wavelength photonic elements. As an example to show the potential of the application of the new nanoimprint technologies, we choose the fabrication of a photonic crystal (PhC) structure with integrated light coupling devices for low loss interconnection between PhC lightwave circuits and optical fibre systems. We present two methods for fabrication of nanoimprint lithography stamps in Si substrate. In the first method optimized electron beam lithography (EBL) and lift-off patterning of a 15-nm thick Cr mask, and then the pattern transfer into Si using reacting ion etching (RIE) with SF6 as etch gas. In the first method, we use 200nm of positive resist PMMA 950K for EBL exposure. In this method, resist thickness, exposure dose, development time and parameter for etching have been optimized and a photonic crystal of Si-rods in air was fabricated. In the second method lift-off has not been performed and metal mask has been used as master. The subsequent steps for fabricating the master will be presented in detail.

  9. Critical behavior of the single-crystal helimagnet MnSi

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Menzel, Dirk; Jin, Chiming; Du, Haifeng; Ge, Min; Zhang, Changjin; Pi, Li; Tian, Mingliang; Zhang, Yuheng

    2015-01-01

    The critical behavior of the single-crystal helimagnet MnSi is investigated by means of bulk dc magnetization at the boundary between the conical state and paramagnetic phase. We obtain the critical exponents (β =0.242 ±0.006 ,γ =0.915 ±0.003 , and δ =4.734 ±0.006 ), where the self-consistency and reliability are verified by the Widom scaling law and the scaling equation. The critical exponents of MnSi belong to the universality class of tricritical mean-field theory, which unambiguously indicates a tricritical phenomenon at the boundary between the first-order phase transition and the second-order one induced by the external magnetic field. The tricritical point (TCP) is determined as HTCP≈3200 Oe at the critical temperature, consistent with the previous report [A. Bauer, M. Garst, and C. Pfleiderer, Phys. Rev. Lett. 110, 177207 (2013), 10.1103/PhysRevLett.110.177207]. The critical behavior suggests a long-range magnetic coupling with the exchange distance decaying as J (r ) ≈r-4.3 in MnSi.

  10. History dependence of the magnetic properties of single-crystal Fe1 -xCoxSi

    NASA Astrophysics Data System (ADS)

    Bauer, A.; Garst, M.; Pfleiderer, C.

    2016-06-01

    We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of Fe1 -xCoxSi , 0.20 ≤x ≤0.50 . We determine the magnetic phase diagrams for all major crystallographic directions and cooling histories. After zero-field cooling, the phase diagrams resemble that of the archetypal stoichiometric cubic chiral magnet MnSi. Besides the helical and conical state, we observe a pocket of skyrmion lattice phase just below the helimagnetic ordering temperature. At the phase boundaries between these states evidence for slow dynamics is observed. When the sample is cooled in small magnetic fields, the phase pocket of skyrmion lattice may persist metastably down to the lowest temperatures. Taken together with the large variation in the transition temperatures, transition fields, and helix wavelength as a function of the composition, this hysteresis identifies Fe1 -xCoxSi as an ideal material for future experiments exploring, for instance, the topological unwinding of the skyrmion lattice.

  11. High-performance poly-Si thin film transistors with highly biaxially oriented poly-Si thin films using double line beam continuous-wave laser lateral crystallization

    NASA Astrophysics Data System (ADS)

    Yamano, Masayuki; Kuroki, Shin-Ichiro; Sato, Tadashi; Kotani, Koji

    2014-01-01

    Highly biaxially oriented poly-Si thin films were formed by double-line beam continuous-wave laser lateral crystallization (DLB-CLC). The crystallinities of the DLB-CLC poly-Si thin films were (110), (111), and (211) for the laser scan, transverse, and surface directions, respectively, and an energetically stable Σ3 grain boundary was observed to be dominant. All silicon grains were elongated in the laser scan direction and one-dimensionally very large silicon grains with lengths of more than 100 µm were fabricated. Using these biaxially oriented polycrystalline silicon (poly-Si) films, low-temperature poly-Si TFTs (LTPS-TFTs) were fabricated at low temperatures (≦550 °C) by a metal gate self-aligned process. As a result, a TFT with a high electron field effect mobility of μFE = 450 cm2 V-1 s-1 in a linear region was realized.

  12. Measuring the diffraction properties of an imaging quartz(211) crystal

    NASA Astrophysics Data System (ADS)

    Haugh, M. J.; Jacoby, K. D.; Koch, J. A.; Chen, H.; Hill, K. W.; Schneider, M. B.

    2016-06-01

    A dual goniometer X-ray system was used to measure the reflectivity curve for a spherically bent quartz(211) crystal. An analysis of the dual goniometer instrument response function for the rocking curve width measurement was developed and tested against the actual measurements. The rocking curve was measured at 4510.8 eV using the Ti Kα1 characteristic spectral line. The crystal is the dispersion element for a high resolution spectrometer used for plasma studies. It was expected to have a very narrow rocking curve width. The analysis showed that we could measure the upper bound for the rocking curve width of the Qz(211) crystal. The upper bound was 58 μrad giving a lower bound for the instrument resolving power E/ΔE = 34 000. Greatly improved insight into the dual goniometer operation and its limitations was achieved.

  13. Positron lifetime measurements in chiral nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; Parmar, Devendra S.

    1991-01-01

    Positron lifetimes in the isotropic phases of chiral nematic liquid crystal formulations and their mixtures up to the racemic level were measured. The lifetime spectra for all liquid crystal systems were analyzed into three components. Although the individual spectra in the left- and right-handed components are identical, their racemic mixtures exhibit much larger orthopositronium lifetimes; these larger lifetimes indicate the presence of larger microvoids. This result is consistent with the reportedly higher thermodynamic stability and color play range in the racemic mixtures of chiral nematic liquid crystals.

  14. Irradiation-induced microstructural change in helium-implanted single crystal and nano-engineered SiC

    NASA Astrophysics Data System (ADS)

    Chen, C. H.; Zhang, Y.; Fu, E.; Wang, Y.; Crespillo, M. L.; Liu, C.; Shannon, S.; Weber, W. J.

    2014-10-01

    Microstructural evolution induced by helium implantation and subsequent heavy ion irradiation has been investigated in single crystal and nano-engineered (NE) 3C SiC. Implantation with 65 keV He+ ions was performed at 277 °C, and the helium depth distribution was determined by elastic recoil detection analysis (ERDA). Transmission electron microscopy (TEM) could not resolve the presence of bubbles in any of the helium-implanted single crystal SiC. However, helium platelets and small dislocation loops (∼50 nm in diameter) were observed in the single crystal sample with the highest implantation fluence after 1 h annealing at 700 °C. Following irradiation with 9 MeV Au3+ ions at 700 °C, no bubbles were observed in the helium-implanted single crystal SiC, regardless of helium fluence. For the helium-implanted NE SiC, subsequent irradiation with 9 MeV Au ions to a dose of 10 dpa at 700 °C resulted in the formation and growth of bubbles, and a bimodal helium bubble size distribution was observed at the highest helium concentration (8000 appm) in the NE SiC.

  15. Polarized electronic absorption spectra of Cr2SiO4 single crystals

    NASA Astrophysics Data System (ADS)

    Furche, A.; Langer, K.

    Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000-5000 cm-1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75 Å along [001]. The spectra were scanned at 273 and 120 K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6 μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20 μm and 1 nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35 kbar, above 1440 °C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm-1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10 Dq =10700 cm-1. A relatively intense, sharp band at 18400 cm-1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000 cm-1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr24+, whereas the latter alone would be in conflict with the strong

  16. Structural investigation of the seeding process for physical vapor transport growth of 4H-SiC single crystals

    NASA Astrophysics Data System (ADS)

    Ohtani, Noboru; Ohshige, Chikashi; Katsuno, Masakazu; Fujimoto, Tatsuo; Sato, Shinya; Tsuge, Hiroshi; Ohashi, Wataru; Yano, Takayuki; Matsuhata, Hirofumi; Kitabatake, Makoto

    2014-01-01

    Structural investigation of the seeding process for the physical vapor transport (PVT) growth of 4H-SiC single crystals was conducted by high-resolution x-ray diffraction (HRXRD) and synchrotron x-ray topography. Characteristic lattice plane bending behavior was observed in the near-seed regions of the grown crystals. The bending of the (112¯0) lattice plane was localized near the seed/grown crystal interface, and the (0001) basal plane bent convexly in the growth direction near the interface, indicative of the insertion of extra-half planes pointing toward the growth direction during the seeding process for PVT growth. This study discusses a possible mechanism for the observed lattice plane bending and sheds light on defect formation processes during the PVT growth of 4H-SiC single crystals.

  17. Crystal growth and luminescence properties of Yb2Si2O7 infra-red emission scintillator

    NASA Astrophysics Data System (ADS)

    Horiai, Takahiko; Kurosawa, Shunsuke; Murakami, Rikito; Pejchal, Jan; Yamaji, Akihiro; Shoji, Yasuhiro; Chani, Valery I.; Ohashi, Yuji; Kamada, Kei; Yokota, Yuui; Yoshikawa, Akira

    2016-08-01

    (CexYb1-x)2Si2O7 (x = 0.00, 0.01) single crystals were grown by the micro-pulling-down method to test the possibility of its application as infra-red scintillator for medical imaging. Powder X-ray diffraction analysis indicated that the crystals were single-phase materials. The radioluminescence spectra of the crystals demonstrated presence of two near infra-red emission peaks (at 1010 and 1030 nm). The emission peaks at 420 and 580 nm ascribed to defects were also observed in the crystals. The human body has maximum transmission in wavelength range from 650 to 1200 nm. Therefore, Yb2Si2O7 is expected to be used as efficient infra-red scintillator for medical applications.

  18. Measurements of HB photonic crystal fibers with low temperature sensitivity

    NASA Astrophysics Data System (ADS)

    Makara, Mariusz; Wojcik, Jan; Mergo, Pawel; Klimek, Jacek; Skorupski, Krzysztof; Kopeć, Jarosław

    2008-06-01

    We report on experimental studies of phase and group modal birefringence vs. temperature in two highly birefringent (HB) photonic crystal fibers, in which birefringence is caused by filling factor asymmetry. The sensitivity measurements were carried out at two wavelengths 633 and 834 nm. Our results show that temperature sensitivity in the HB photonic crystal fibers is two orders smaller then in traditional HB fibers. Simultaneously, our results exhibit weak dependence of group modal birefringence on temperature.

  19. Comparison of the Crystallization Behavior of Fe-Si-B-Cu and Fe-Si-B-Cu-Nb-Based Amorphous Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Smith, Casey; Katakam, Shravana; Nag, Soumya; Zhang, Y. R.; Law, J. Y.; Ramanujan, Raju V.; Dahotre, Narendra B.; Banerjee, Rajarshi

    2014-06-01

    The role of the solute elements, copper, and niobium, on the different stages of de-vitrification or crystallization of two amorphous soft magnetic alloys, Fe73.5Si13.5B9Nb3Cu1, also referred to as FINEMET, and a Fe76.5Si13.5B9Cu1 alloy, a model composition without Nb, has been investigated in detail by coupling atom probe tomography and transmission electron microscopy. The effects of copper clustering and niobium pile-up at the propagating interface between the α-Fe3Si nanocrystals and the amorphous matrix, on the nucleation and growth kinetics have been addressed. The results demonstrate that while Cu clustering takes place in both alloys in the early stages, the added presence of Nb in FINEMET severely restricts the diffusivity of solute elements such as Cu, Si, and B. Therefore, the kinetics of solute partitioning and mobility of the nanocrystal/amorphous matrix interface is substantially slower in FINEMET as compared to the Fe76.5Si13.5B9Cu1 alloy. Consequently, the presence of Nb limits the growth rate of the α-Fe3Si nanocrystals in FINEMET and results in the activation of a larger no. of nucleation sites, leading to a substantially more refined microstructure as compared to the Fe76.5Si13.5B9Cu1 alloy.

  20. Hydrogen-plasma-induced Rapid, Low-Temperature Crystallization of μm-thick a-Si:H Films.

    PubMed

    Zhou, H P; Xu, M; Xu, S; Liu, L L; Liu, C X; Kwek, L C; Xu, L X

    2016-01-01

    Being a low-cost, mass-production-compatible route to attain crystalline silicon, post-deposition crystallization of amorphous silicon has received intensive research interest. Here we report a low-temperature (300 °C), rapid (crystallization rate of ~17 nm/min) means of a-Si:H crystallization based on high-density hydrogen plasma. A model integrating the three processes of hydrogen insertion, etching, and diffusion, which jointly determined the hydrogenation depth of the excess hydrogen into the treated micrometer thick a-Si:H, is proposed to elucidate the hydrogenation depth evolution and the crystallization mechanism. The effective temperature deduced from the hydrogen diffusion coefficient is far beyond the substrate temperature of 300 °C, which implies additional driving forces for crystallization, i.e., the chemical annealing/plasma heating and the high plasma sheath electric field. The features of LFICP (low-frequency inductively coupled plasma) and LFICP-grown a-Si:H are also briefly discussed to reveal the underlying mechanism of rapid crystallization at low temperatures. PMID:27600866

  1. Hydrogen-plasma-induced Rapid, Low-Temperature Crystallization of μm-thick a-Si:H Films

    PubMed Central

    Zhou, H. P.; Xu, M.; Xu, S.; Liu, L. L.; Liu, C. X.; Kwek, L. C.; Xu, L. X.

    2016-01-01

    Being a low-cost, mass-production-compatible route to attain crystalline silicon, post-deposition crystallization of amorphous silicon has received intensive research interest. Here we report a low-temperature (300 °C), rapid (crystallization rate of ~17 nm/min) means of a-Si:H crystallization based on high-density hydrogen plasma. A model integrating the three processes of hydrogen insertion, etching, and diffusion, which jointly determined the hydrogenation depth of the excess hydrogen into the treated micrometer thick a-Si:H, is proposed to elucidate the hydrogenation depth evolution and the crystallization mechanism. The effective temperature deduced from the hydrogen diffusion coefficient is far beyond the substrate temperature of 300 °C, which implies additional driving forces for crystallization, i.e., the chemical annealing/plasma heating and the high plasma sheath electric field. The features of LFICP (low-frequency inductively coupled plasma) and LFICP-grown a-Si:H are also briefly discussed to reveal the underlying mechanism of rapid crystallization at low temperatures. PMID:27600866

  2. Oxidation and microstructure evolution of Al-Si coated Ni3Al based single crystal superalloy with high Mo content

    NASA Astrophysics Data System (ADS)

    Tu, Xiaolu; Peng, Hui; Zheng, Lei; Qi, Wenyan; He, Jian; Guo, Hongbo; Gong, Shengkai

    2015-01-01

    A Si modified aluminide (Al-Si) coating was prepared on a Ni3Al based single crystal superalloy with high Mo content by high-activity pack cementation. Cyclic oxidation test at 1150 °C was carried out and the microstructure evolution of the coating was investigated. The results show that the oxidation resistance of the substrate was greatly increased by applying an Al-Si coating. During oxidation, outward diffusion of Mo was effectively blocked due to its high affinity with Si. Besides, a layered structure was formed as a result of the elements inter-diffusion. An obvious degradation of the Al-Si coating was observed after 100 h oxidation. Possible mechanisms related to the oxidation and elements inter-diffusion behaviours were also discussed.

  3. Measurement of ultimate tensile strength and Young modulus in LYSO scintillating crystals

    NASA Astrophysics Data System (ADS)

    Scalise, Lorenzo; Rinaldi, Daniele; Davì, Fabrizio; Paone, Nicola

    2011-10-01

    Scintillating crystals are employed in high energy physics, in medical imaging, diagnostic and security. Two mechanical properties of lutetium-yttrium oxyorthosilicate cerium-doped Lu 2(1- x) Y 2 xSiO 5:Ce with x=0.1 (LYSO) crystals have been measured: the ultimate tensile stress ( σUTS) and the Young elastic modulus ( E). Measurements are made by means of a 4-points loading device and the experimental results account for an elastic-brittle stress-strain relation, which depends heavily on the specimen preparation and the material defects. σUTS along the [0 1 0] tensile direction ranges within 68.14 and 115.61 MPa, which, in the lowest case, is more than twice with respect to those measured for PbWO 4 (PWO), exhibiting a marked difference between the annealed and the not-annealed samples. The mean elastic modulus ( E), along the same direction, is E=1.80×10 11 (±2.15×10 10) N/m 2, with lower dispersion respect to UTS data. This type of analysis and study can be included into quality control procedures of crystals, based on samples taken out of production; such procedures can be established for industrial processing of crystals aimed to the high energy physics (calorimeters) and medical imaging (PET, etc.) applications.

  4. Imaging System For Measuring Macromolecule Crystal Growth Rates in Microgravity

    NASA Technical Reports Server (NTRS)

    Corder, Eric L.; Briscoe, Jeri

    2004-01-01

    In order to determine how macromolecule crystal quality improvement in microgravity is related to crystal growth characteristics, a team of scientists and engineers at NASA's Marshal Space Flight Center (MSFC) developed flight hardware capable of measuring the crystal growth rates of a population of crystals growing under the same conditions. As crystal growth rate is defined as the change or delta in a defined dimension or length (L) of crystal over time, the hardware was named Delta-L. Delta-L consists of three sub assemblies: a fluid unit including a temperature-controlled growth cell, an imaging unit, and a control unit (consisting of a Data Acquisition and Control Unit (DACU), and a thermal control unit). Delta-L will be used in connection with the Glovebox Integrated Microgravity Isolation Technology (g-LIMIT) inside the Microgravity Science Glovebox (MSG), onboard the International Space Station. This paper will describe the Delta-L imaging system. The Delta-L imaging system was designed to locate, resolve, and capture images of up to 10 individual crystals ranging in size from 10 to 500 microns with a point-to-point accuracy of +/- 2.0 microns within a quartz growth cell observation area of 20 mm x 10 mm x 1 mm. The optical imaging system is comprised of a video microscope camera mounted on computer controlled translation stages. The 3-axis translation stages and control units provide crewmembers the ability to search throughout the growth cell observation area for crystals forming in size of approximately 10 microns. Once the crewmember has selected ten crystals of interest, the growth of these crystals is tracked until the size reaches approximately 500 microns. In order to resolve these crystals an optical system with a magnification of 10X was designed. A black and white NTSC camera was utilized with a 20X microscope objective and a 0.5X custom designed relay lens with an inline light to meet the magnification requirement. The design allows a 500 pm

  5. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai; Qi, Tingting; Reed, Evan

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  6. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai B.; Qi, Tingting; Reed, Evan J.

    2016-01-01

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  7. Analysis of rocking curve measurements of LiF flight crystals for the objective crystal spectrometer on SPECTRUM-X-GAMMA

    NASA Astrophysics Data System (ADS)

    Halm, Ingolf; Wiebicke, Hans-Joachim; Geppert, U. R.; Christensen, Finn E.; Abdali, Salim; Schnopper, Herbert W.

    1993-11-01

    The Objective Crystal Spectrometer on the SPECTRUM-X-GAMMA satellite will use three types of natural crystals LiF(220), Si(111), RAP(001), and a multilayer structure providing high-resolution X-ray spectroscopy of Fe, S, O, and C line regions of bright cosmic X-ray sources. 330 - 360 LiF(220) crystals of dimensions approximately 23 X 63 mm(superscript 2) are required to cover one side of a large (1000 X 600 mm(superscript 2)) panel, which is to be mounted in front of one of two high throughput X-ray telescopes. Rocking curves of 441 LiF(220) crystals measured by using an expanded Cu - K(alpha) (subscript 2) beam were analyzed to select the best ones for the flight model. An important parameter is the non-parallelity of the crystal lattice planes with respect to the rear side of the crystals, since it is of the same order of magnitude as the rocking curve width. By lapping the rear side to diminish the non- parallelity and selection the main parameters of the rocking curve averaged over all crystals can be improved at least by a factor of 1.6 both in full width half maximum and peak reflectivity.

  8. Magnetic properties of Cu-flux-grown UCu2Si2 single crystals

    NASA Astrophysics Data System (ADS)

    Tro, R.; Bukowski, Z.

    2006-01-01

    In order to solve a serious problem of understanding the magnetic properties of UCu2Si2, we have grown single crystals of this compound from Cu-flux. Here we focus primarily on the magnetic behavior of this compound. In contrast to some previous polycrystalline and single-crystalline reports on UCu2Si2 no signs of the transition into antiferromagnetic behavior have been observed below T C = 104(1) K. The magnetic properties of this compound are highly anisotropic, with an easy axis of magnetization along the [001] direction. The saturation moment has been determined at 4.2 K to be 1.55 B. In the paramagnetic region the effective moments for the easy and hard directions are both about 3.0μ B. An extensive discussion of the obtained data, compared to those recently published by Fisk et al. and Matsuda et al., also based on single crystalline materials, has been presented. No an antiferromagnetic phase above T C has been detected.

  9. Study of Si-based three-dimensional photonic crystals infiltrated with liquid crystal within a one-dimensional effective model

    NASA Astrophysics Data System (ADS)

    Chang, L.; Liao, C.-Z.; Wu, G. Y.

    2011-07-01

    In this work, we study Si-based three-dimensional photonic crystals infiltrated with liquid crystal (LC), within a one-dimensional effective medium model. Two specific systems of diamond crystal structure compatible with the mature Si technology are considered, namely, (i) diamond-1 which is composed of LC spheres embedded in the Si background, and (ii) diamond-2 which is the inverse of the foregoing structure, with Si spheres immersed in the LC background. For each system, the study is carried out with the LC being in the isotropic/nematic phase. The one-dimensional effective medium model employed in the study is an improved version of the conventional mean field theory (MFT). While retaining partially the typical advantage of MFT, e.g., physical transparency, analytical capability, and computational efficiency, it goes beyond the conventional MFT by taking into account the modulation of dielectric constant in the direction of wave propagation. As such, it improves greatly the poor numerical accuracy inherent in the MFT. We find a partial gap between the 2nd and 3rd bands, with the gap-to-midgap ratio being a few percents. Moreover, the edge of partial gap may be shifted by about 1% (in relative unit) when optical, thermal, or electrical means are applied to alter the phase of LC or rotate the axis of nematic molecules.

  10. Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1989-01-01

    The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by an Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.

  11. Achieving omnidirectional photonic band gap in sputter deposited TiO{sub 2}/SiO{sub 2} one dimensional photonic crystal

    SciTech Connect

    Jena, S. Tokas, R. B.; Sarkar, P.; Thakur, S.; Sahoo, N. K.; Haque, S. Maidul; Misal, J. S.; Rao, K. D.

    2015-06-24

    The multilayer structure of TiO{sub 2}/SiO{sub 2} (11 layers) as one dimensional photonic crystal (1D PC) has been designed and then fabricated by using asymmetric bipolar pulse DC magnetron sputtering technique for omnidirectional photonic band gap. The experimentally measured photonic band gap (PBG) in the visible region is well matched with the theoretically calculated band structure (ω vs. k) diagram. The experimentally measured omnidirectional reflection band of 44 nm over the incident angle range of 0°-70° is found almost matching within the theoretically calculated band.

  12. Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

    NASA Astrophysics Data System (ADS)

    Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

    2007-06-01

    Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

  13. (3+1)-Incommensurately modulated crystal structure of Cs3ScSi6O15.

    PubMed

    Hejny, Clivia; Kahlenberg, Volker; Schmidmair, Daniela; Dabić, Predrag

    2016-02-01

    Single-crystal X-ray diffraction of Cs3ScSi6O15 shows the presence of main reflections and satellite reflections up to the fourth order along the c* direction. The (3+1)-dimensional incommensurately modulated structure was solved in superspace group X3m1(00gamma)0s0 [a = 13.861 (1), c = 6.992 (1) Å, V = 1163.4 (2) Å(3)] with a modulation wavevector q = 0.14153 (2)c*. Refinement of three modulation waves for positional and anisotropic displacement parameter values for all atoms converged to R(obs) values for all, main and satellite reflections of first, second and third order of 0.0200, 0.0166, 0.0181, 0.0214 and 0.0303, respectively. Cs3ScSi6O15 forms a mixed tetrahedral-octahedral framework with prominent six-membered rings of [SiO4]-tetrahedra interconnected by [ScO6]-octahedra. Apart from Sc, all atoms are strongly affected by positional modulation with maximum atomic displacements of up to 0.93 Å causing rigid polyhedral arrangements to perform tilt and twist movements relative to each other, such as a rotation of the Sc-octahedra around the 3-axis by over 38°. Cs has an irregular coordination environment; however, considering distances up to 3.5 Å, the bond-valence sum changes by no more than 0.02 as a function of t and thus overall kept at a level of ca 1.075. PMID:26830802

  14. Behavior of nitrogen in Si crystal during irradiation and post-annealing

    SciTech Connect

    Inoue, Naohisa; Oyama, Hidenori; Watanabe, Kaori; Seki, Hirofumi; Kawamura, Yuichi

    2014-02-21

    Radiation induced complexes in nitrogen (N) -doped silicon crystal was investigated by highly sensitive infrared absorption spectroscopy. The absorption by N{sub 2} pair was reduced by the electron irradiation in FZ crystals. The absorptions appeared on both sides of N{sub 2} line at 766 cm{sup −1}, at about 725 and 778 cm{sup −1}. By the annealing, N{sub 2} lines recovered a little at 600 °C and mostly at 800 °C. The above new absorption lines reduced by the annealing at lower temperatures and other absorption appeared. In CZ silicon, N{sub 2} lines did not change by the irradiation. Dominant absorption in low carbon FZ silicon was that of C-rich type complexes, VO and I{sub n}C{sub i}O{sub im}(n=0–3, m=0,1). Dominant absorption in the irradiated low carbon CZ silicon was that of C-lean type complexes I{sub n}O{sub 2+mi}(n=1, 2, m=0, 1), and the decrease of C-lean type O{sub 2i} and TDD was observed. By the annealing of CZ Si, VO{sub n} (n=2–4) formation and annihilation was observed.

  15. 1H, 13C and 29Si NMR of tetramethylsilane in liquid crystals

    NASA Astrophysics Data System (ADS)

    Hiltunen, Y.; Jokisaari, J.

    1990-12-01

    The 1H, 13C and 29Si NMR spectra of tetramethylsilane (TMS) dissolved in two nematic liquid crystals (LC) and in their three mixtures were recorded. The proton—proton, proton—carbon and proton—silicon dipolar couplings, which arise from molecular deformation in the LC environment, were determined. The results for the 2DHH, 4DHH, 3DCH and 2DSiH couplings show only a small variation as a function of the composition of the LC mixture. On the contrary, the one-bond CH dipolar coupling is markedly solvent dependent: it varies from -6.22 Hz (in ZLI 1167) to +3.63 Hz (in phase IV). The 1DCH coupling of TMS vanishes in a certain mixture of the two liquid crystals; this mixture, however, is not the same as that in which the corresponding coupling of methane was earlier observed to vanish. This different behaviour of TMS and methane may be due to the additional torques which act on the SiC bonds of TMS.

  16. Luminescence of SiO2 and GeO2 crystals with rutile structure. Comparison with α-quartz crystals and relevant glasses (Review Article)

    NASA Astrophysics Data System (ADS)

    Trukhin, A. N.

    2016-07-01

    Luminescence properties of SiO2 in different structural states are compared. Similar comparison is made for GeO2. Rutile and α-quartz structures as well as glassy state of these materials are considered. Main results are that for α-quartz crystals the luminescence of self-trapped exciton is the general phenomenon that is absent in the crystal with rutile structure. In rutile structured SiO2 (stishovite) and GeO2 (argutite) the main luminescence is due to a host material defect existing in as-received (as-grown) samples. The defect luminescence possesses specific two bands, one of which has a slow decay (for SiO2 in the blue and for GeO2, in green range) and another, a fast ultraviolet (UV) band (4.75 eV in SiO2 and at 3 eV in GeO2). In silica and germania glasses, the luminescence of self-trapped exciton coexists with defect luminescence. The latter also contains two bands: one in the visible range and another in the UV range. The defect luminescence of glasses was studied in details during last 60-70 years and is ascribed to oxygen deficient defects. Analogous defect luminescence in the corresponding pure nonirradiated crystals with α-quartz structure is absent. Only irradiation of a α-quartz crystal by energetic electron beam, γ-rays and neutrons provides defect luminescence analogous to glasses and crystals with rutile structure. Therefore, in glassy state the structure containing tetrahedron motifs is responsible for existence of self-trapped excitons and defects in octahedral motifs are responsible for oxygen deficient defects.

  17. Characterization of Si nanostructures using internal quantum efficiency measurements

    SciTech Connect

    ZAIDI,SALEEM H.

    2000-04-01

    Hemispherical reflectance and internal quantum efficiency measurements have been employed to evaluate the response of Si nanostructured surfaces formed by using random and periodic reactive ion etching techniques. Random RIE-textured surfaces have demonstrated solar weighted reflectance of {approx} 3% over 300--1,200-nm spectral range even without the benefit of anti-reflection films. Random RIE-texturing has been found to be applicable over large areas ({approximately} 180 cm{sup 2}) of both single and multicrystalline Si surfaces. Due to the surface contamination and plasma-induced damage, RIE-textured surfaces did not initially provide increased short circuit current as expected from the enhanced absorption. Improved processing combined with wet-chemical damage removal etches resulted in significant improvement in the short circuit current with IQEs comparable to the random, wet-chemically textured surfaces. An interesting feature of the RIE-textured surfaces was their superior performance in the near IR spectral range. The response of RIE-textured periodic surfaces can be broadly classified into three distinct regimes. One-dimensional grating structures with triangular profiles are characterized by exceptionally low, polarization-independent reflective behavior. The reflectance response of such surfaces is similar to a graded-index anti-reflection film. The IQE response from these surfaces is severely degraded in the UV-Visible spectral region due to plasma-induced surface damage. One-dimensional grating structures with rectangular profiles exhibit spectrally selective absorptive behavior with somewhat similar IQE response. The third type of grating structure combines broadband anti-reflection behavior with significant IQE enhancement in 800--1,200-nm spectral region. The hemispherical reflectance of these 2D grating structures is comparable to random RIE-textured surfaces. The IQE enhancement in the long wavelength spectral region can be attributed to

  18. Thermal expansion and elastic anisotropy in single crystal Al2O3 and SiC reinforcements

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Li, Zhuang; Bradt, Richard C.

    1994-01-01

    In single crystal form, SiC and Al2O3 are attractive reinforcing components for high temperature composites. In this study, the axial coefficients of thermal expansion and single crystal elastic constants of SiC and Al2O3 were used to determine their coefficients of thermal expansion and Young's moduli as a function of crystallographic orientation and temperature. SiC and Al2O3 exhibit a strong variation of Young's modulus with orientation; however, their moduli and anisotropies are weak functions of temperature below 1000 C. The coefficients of thermal expansion exhibit significant temperature dependence, and that of the non-cubic Al2O3 is also a function of crystallographic orientation.

  19. Performance of VATA64HDR16 ASIC for medical physics applications based on continuous crystals and SiPMs

    NASA Astrophysics Data System (ADS)

    Barrio, J.; Etxebeste, A.; Lacasta, C.; Muñoz, E.; Oliver, J. F.; Solaz, C.; Llosá, G.

    2015-12-01

    Detectors based on Silicon Photomultipliers (SiPMs) coupled to continuous crystals are being tested in medical physics applications due to their potential high resolution and sensitivity. To cope with the high granularity required for a very good spatial resolution, SiPM matrices with a large amount of elements are needed. To be able to read the information coming from each individual channel, dedicated ASICs are employed. The VATA64HDR16 ASIC is a 64-channel, charge-sensitive amplifier that converts the collected charge into a proportional current or voltage signal. A complete assessment of the suitability of that ASIC for medical physics applications based on continuous crystals and SiPMs has been carried out. The input charge range is linear from 0-2 pC up to 55 pC. The energy resolution obtained at 511 keV is 10% FWHM with a LaBr3 crystal and 16% FWHM with a LYSO crystal. A coincidence timing resolution of 24 ns FWHM is obtained with two LYSO crystals.

  20. Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal

    SciTech Connect

    Valvo, M.; Bongiorno, C.; Giannazzo, F.; Terrasi, A.

    2013-01-21

    Transmission electron microscopy (TEM), atomic force microscopy, and Rutherford backscattering spectrometry (RBS) have been used to investigate the morphology, structure, and composition of self-assembled Ge islands grown on Si (001) substrates by molecular beam epitaxy (MBE) at different temperatures. Increasing the temperature from 550 Degree-Sign C to 700 Degree-Sign C causes progressive size and shape uniformity, accompanied by enhanced Si-Ge intermixing within the islands and their wetting layer. Elemental maps obtained by energy filtered-TEM (EF-TEM) clearly show pronounced Si concentration not only in correspondence of island base perimeters, but also along their curved surface boundaries. This phenomenon is strengthened by an increase of the growth temperature, being practically negligible at 550 Degree-Sign C, while very remarkable already at 650 Degree-Sign C. The resulting island shape is affected, since this localized Si enrichment not only provides strain relief near their highly stressed base perimeters but it also influences the cluster surface energy by effective alloying, so as to form Si-enriched SiGe interfaces. Further increase to 700 Degree-Sign C causes a shape transition where more homogenous Si-Ge concentration profiles are observed. The crucial role played by local 'flattened' alloyed clusters, similar to truncated pyramids with larger bases and enhanced Si enrichment at coherently stressed interfaces, has been further clarified by EF-TEM analysis of a multi-layered Ge/Si structure containing stacked Ge islands grown at 650 Degree-Sign C. Sharp accumulation of Si has been here observed not only in proximity of the uncapped island surface in the topmost layer but also at the buried Ge/Si interfaces and even in the core of such capped Ge islands.

  1. High temperature deformation of Ti[sub 5]Si[sub 3] single crystals with D8[sub 8] structure

    SciTech Connect

    Umakoshi, Y. . Dept. of Materials Science and Engineering); Nakashima, T. )

    1994-06-01

    Silicides with transition metals such as Mo, Nb, W and Ti whose melting temperatures are around or above 2,000 C have been of great interest as the potential candidates for refractory materials operating at more than 1,500 C. Ti[sub 5]Si[sub 3] is also a potential candidate as a refractory material because of its high melting temperature (about 2,130 C), low density (4.32g/cm[sup 3]), high strength and good oxidation resistance at high temperatures. It crystallizes in a hexagonal D8[sub 8] structure. In this paper the orientation and temperature dependence of yield stress of Ti[sub 5]Si[sub 3] single crystals are presented together with the deformation mechanism using these crystals.

  2. Evaluation of the Validity of Crystallization Temperature Measurements Using Thermography with Different Sample Configurations

    NASA Astrophysics Data System (ADS)

    Yuko Aono,; Junpei Sakurai,; Akira Shimokohbe,; Seiichi Hata,

    2010-07-01

    We describe further progress of a previously reported novel crystallization temperature (Tx) measurement method applicable for small sample sizes. The method uses thermography and detects Tx as a change in emissivity of thin film amorphous alloy samples. We applied this method to various sample configurations of Pd-Cu-Si thin film metallic glass (TFMG). The validity of the detected Tx was determined by electrical resistivity monitoring and differential scanning calorimetry (DSC). Crystallization temperature can be detected in all sample configurations; however, it was found that the magnitude of the detected change of emissivity at Tx depended on the sample configuration. This emissivity change was clear in the absence of a higher emissivity material. The results suggest that this method can achieve high-throughput characterization of Tx for integrated small samples such as in a thin film library.

  3. Crystal chemistry of layered carbide, Ti3(Si0.43Ge0.57)C2

    NASA Astrophysics Data System (ADS)

    Yang, Hexiong; Manoun, B.; Downs, R. T.; Ganguly, A.; Barsoum, M. W.

    2006-12-01

    The crystal structure of a layered ternary carbide, Ti3(Si0.43Ge0.57)C2, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P63/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å3. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U11 (=U22) being about three times greater than U33. Compared to Ti3SiC2, the substitution of Ge for Si results in an increase in both A Ti and C Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.

  4. Microstructural evolution on crystallizing the glassy phase in a 6 weight percent Y2O3-Si3N4 ceramic

    NASA Technical Reports Server (NTRS)

    Lee, W. E.; Drummond, C. H., III; Hilmas, G. E.; Kiser, J. D.; Sanders, W. A.

    1988-01-01

    X-ray diffraction and analytical electron microscopy have been used to study the crystallization of the grain-boundary glass in a 6 wt pct Y2O3-Si3N4 ceramic. Upon crystallization, high densities of dislocations formed in the Si3N4 grains and remained after 5 h at temperature. However, prolonged holds at the crystallization temperature effectively annealed out the dislocations. Other features present in the microstructure are characterized.

  5. Crystal Lattice Controlled SiGe Thermoelectric Materials with High Figure of Merit

    NASA Technical Reports Server (NTRS)

    Kim, Hyun-Jung; Park, Yeonjoon; King, Glen C.; Lee, Kunik; Choi, Sang H.

    2010-01-01

    Direct energy conversion between thermal and electrical energy, based on thermoelectric (TE) effect, has the potential to recover waste heat and convert it to provide clean electric power. The energy conversion efficiency is related to the thermoelectric figure of merit ZT expressed as ZT=S(exp 2)(sigma)T/Kappa, T is temperature, S is the Seebeck coefficient, sigma is conductance and Kappa is thermal conductivity. For a lower thermal conductivity Kappa and high power factor (S(exp 2)(sigma)), our current strategy is the development of rhombohedrally strained single crystalline SiGe materials that are highly [111]-oriented twinned. The development of a SiGe "twin lattice structure (TLS)" plays a key role in phonon scattering. The TLS increases the electrical conductivity and decreases thermal conductivity due to phonon scattering at stacking faults generated from the 60 X rotated primary twin structure. To develop high performance materials, the substrate temperature, chamber working pressure, and DC sputtering power are controlled for the aligned growth production of SiGe layer and TLS on a c-plane sapphire. Additionally, a new elevated temperature thermoelectric characterization system, that measures the thermal diffusivity and Seebeck effect nondestructively, was developed. The material properties were characterized at various temperatures and optimized process conditions were experimentally determined. The present paper encompasses the technical discussions toward the development of thermoelectric materials and the measurement techniques.

  6. Crystal structure dependence of antiferromagnetic coupling in Fe/Si multilayers

    SciTech Connect

    Michel, R.P.; Chaiken, A.; Wall, M.A.

    1995-04-01

    Recent reports of temperature dependent antiferromagnetic coupling in Fe/Si multilayers have motivated the generalization of models describing magnetic coupling in metal/metal multilayers to metal/insulator and metal/semiconductor layered systems. Interesting dependence of the magnetic properties on layer thickness and temperature are predicted. We report measurements that show the antiferromagnetic (AF) coupling observed in Fe/Si multilayers is strongly dependent on the crystalline coherence of the silicide interlayer. Electron diffraction images show the silicide interlayer has a CsCl structure. It is not clear at this time whether the interlayer is a poor metallic conductor or a semiconductor so the relevance of generalized coupling theories is unclear.

  7. Crystal measures short-term, large-magnitude forces

    NASA Technical Reports Server (NTRS)

    Pfeiffer, C. G.

    1965-01-01

    By using the magnitude of piezoelectric crystal response to distortion and compression, this device measures transient accelerations and their rate of change. The invention could be used in a servo control system by supplementing the accelerometer and taking over its function when its range was exceeded.

  8. Skin friction measurement with partially exposed polymer dispersed liquid crystals

    NASA Technical Reports Server (NTRS)

    Parmar, D. S.; Holmes, H. K.

    1993-01-01

    Partially exposed polymer dispersed liquid crystal thin film (10-25 microns) deposited on a flat glass substrate has been used for the first time to measure skin friction. Utilizing the shear-stress-induced director reorientation in the partially exposed liquid-crystal droplets, optical transmission under crossed polarization has been measured as a function of the air flow differential pressure. Direct measurement of the skin friction with a skin friction drag balance, under the same aerodynamic conditions, lets us correlate the skin friction with optical transmission. This provides a unique technique for the direct measurement of skin friction from the transmitted light intensity. The results are in excellent agreement with the model suggested in this paper.

  9. Optical properties of self-assembled TiO2-SiO2 double-layered photonic crystals.

    PubMed

    Oh, Yong Taeg; Koo, Bo Ra; Shin, Dong Chan

    2013-01-01

    The optical properties of self-assembled TiO2/SiO2 double-layered photonic crystals were examined using SiO2 and TiO2 nanopowders. The SiO2 and TiO2 nanopowders were fabricated using the well-known Stöber process, and the double-layered structure was self-assembled by an evaporation method. Self-assembled TiO2 thin film was coated at a 1.2 mm thickness by the evaporation process, and 3 atomic layers of the SiO2 layer was coated onto the TiO2 thin film. The relative reflectance peak intensity of the photonic bandgap in the specimen was 13% before thermal treatment. The peak value was increased by sequential heat-treatments and reached the highest value of 21% at 400 degrees C. PMID:23646797

  10. Crystallization of LiAlSiO4 Glass in Hydrothermal Environments at Gigapascal Pressures-Dense Hydrous Aluminosilicates.

    PubMed

    Spektor, Kristina; Fischer, Andreas; Häussermann, Ulrich

    2016-08-15

    High-pressure hydrothermal environments can drastically reduce the kinetic constraints of phase transitions and afford high-pressure modifications of oxides at comparatively low temperatures. Under certain circumstances such environments allow access to kinetically favored phases, including hydrous ones with water incorporated as hydroxyl. We studied the crystallization of glass in the presence of a large excess of water in the pressure range of 0.25-10 GPa and at temperatures from 200 to 600 °C. The p and T quenched samples were analyzed by powder X-ray diffraction, scanning electron microscopy, and IR spectroscopy. At pressures of 0.25-2 GPa metastable zeolite Li-ABW and stable α-eucryptite are obtained at low and high temperatures, respectively, with crystal structures based on tetrahedrally coordinated Al and Si atoms. At 5 GPa a new, hydrous phase of LiAlSiO4, LiAlSiO3(OH)2 = LiAlSiO4·H2O, is produced. Its crystal structure was characterized from single-crystal X-ray diffraction data (space group P21/c, a = 9.547(3) Å, b = 14.461(5) Å, c = 5.062(2) Å, β = 104.36(1)°). The monoclinic structure resembles that of α-spodumene (LiAlSi2O6) and constitutes alternating layers of chains of corner-condensed SiO4 tetrahedra and chains of edge-sharing AlO6 octahedra. OH groups are part of the octahedral Al coordination and extend into channels provided within the SiO4 tetrahedron chain layers. At 10 GPa another hydrous phase of LiAlSiO4 with presently unknown structure is produced. The formation of hydrous forms of LiAlSiO4 shows the potential of hydrothermal environments at gigapascal pressures for creating truly new materials. In this particular case it indicates the possibility of generally accessing pyroxene-type aluminosilicates with crystallographic amounts of hydroxyl incorporated. This could also have implications to geosciences by representing a mechanism of water storage and transport in the depths of the Earth. PMID:27482770

  11. Implanted Si atoms shifting between Ga sites and As sites by thermal stress in conductive-layer GaAs crystals on semi-insulating substrates

    NASA Astrophysics Data System (ADS)

    Saito, Yasuyuki

    1992-04-01

    Large (0.8 V order) discrepancies of threshold voltage Vth between the predicted Vth values by the Lindhard-Scharff-Schio/tt Gaussian approximate calculation and the Vth of the tungsten nitride (WNx) self-alignment (SA) gate GaAs metal-semiconductor field-effect transistors (MESFETs) were observed. These discrepancies were confirmed by the comparison of the Vth of the WNx-SA-gate MESFETs and the Vth of the (N+: high carrier concentration layers self-aligned of source-drain electrodes)-less conventional MESFETs on 2-in.-diam semi-insulating substrates from liquid-encapsulated-Czochralski-technique-grown <100> boules. The discrepancy was also analyzed by the capacitance-voltage (C-V) measurement of large-diameter (440 μm) Schottky diodes which were built into the MESFET arrays. It was found that for obtained SA-process carrier depth profiles (Si, 150 keV, 3×1012 cm-2) the carrier concentration at a depth of 0.25 μm decreased from 5.3×1016 to 2.0×1016 cm-3, but, on the other hand, the peak carrier concentration slightly decreased from 12.8×1016 to 12.4×1016 cm-3. By the calculation for Vth on the basis of the actual C-V carrier depth profiles, it was found that the carrier concentration decrease was comparable to the Vth variation (0.8 V). Furthermore, the Vth variation of the shallow channel implantation (50 keV) was comparable to that of the deep channel implantation (150 keV). As a result of the experiment and analysis, it was found that the large Vth variation for the SA N+ process was caused by reoccupation (Ga sites to As sites) of implanted Si atoms in the channel active-layer crystal by tensile stress formed by the thermal-expansion coefficient difference between chemical-vapor deposition (CVD) phosphosilicate glass (or CVD SiO2) film and (100) GaAs substrate crystal. The Si atom reoccupation quantity was, for the first time, explained by the Si atom compensation ratio equation as a function of the bond length (Si-As and Si-Ga) variation, an equation

  12. Influence of the chemical composition of rapidly quenched amorphous alloys (Ni, Fe, Cr)-B-Si on its crystallization process

    NASA Astrophysics Data System (ADS)

    Elmanov, G.; Dzhumaev, P.; Ivanitskaya, E.; Skrytnyi, V.; Ruslanov, A.

    2016-04-01

    This paper presents results of research of the structure and phase transformations during the multistage crystallization of the metallic glasses with the compositions Ni71,5Cr6,8Fe2,7B11,9Si7,1 and Ni63,4Cr7,4Fe4,3Mn0,8B15,6Si8,5 labeled as AWS BNi-2 according to American Welding Society. Differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX) were used as experimental research methods. The influence of the alloys chemical composition (boron, manganese and iron) on the temperatures and the exothermic heat effects of phase transformations, as well as on the phase composition of alloys at three stages of crystallization was analyzed. We present a thermodynamic explanation of the observed heat effects. It has been shown that manganese has the main influence on the phase transformations temperatures and heat effects in these two alloys. It is also assumed that at the final crystallization stage simultaneously with the formation of phases Ni3B and β1-Ni3Si should occur the nucleation of borides of CrB type with high Cr and low Si content.

  13. From stable divalent to valence-fluctuating behaviour in Eu(Rh(1-x)Ir(x))2Si2 single crystals.

    PubMed

    Seiro, Silvia; Geibel, Christoph

    2011-09-21

    We have succeeded in growing high-quality single crystals of the valence-fluctuating system EuIr(2)Si(2), the divalent Eu system EuRh(2)Si(2) and the substitutional alloy Eu(Rh(1-x)Ir(x))(2)Si(2) across the range 0 < x < 1, which we characterized by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, specific heat, magnetization and resistivity measurements. On increasing x, the divalent Eu ground state subsists up to x = 0.25 with a slight increase in Néel temperature, while for 0.3≤x < 0.7 a sharp hysteretic change in susceptibility and resistivity marks the first-order valence transition. For x≳0.7 the broad feature observed in the physical properties is characteristic of the continuous valence evolution beyond the critical end point of the valence transition line, and the resistivity is reminiscent of Kondo-like behaviour while the Sommerfeld coefficient indicates a mass renormalization of at least a factor of 8. The resulting phase diagram is similar to those reported for polycrystalline Eu(Pd(1-x)Au(x))(2)Si(2) and EuNi(2)(Si(1-x)Ge(x))(2), confirming its generic character for Eu systems, and markedly different to those of homologue Ce and Yb systems, which present a continuous suppression of the antiferromagnetism accompanied by a very smooth evolution of the valence. We discuss these differences and suggest them to be related to the large polarization energy of the Eu half-filled 4f shell. We further argue that the changes in the rare earth valence between RRh(2)Si(2) and RIr(2)Si(2) (R = Ce, Eu, Yb) are governed by a purely electronic effect and not by a volume effect. PMID:21878716

  14. From stable divalent to valence-fluctuating behaviour in Eu(Rh1-xIrx)2Si2 single crystals

    NASA Astrophysics Data System (ADS)

    Seiro, Silvia; Geibel, Christoph

    2011-09-01

    We have succeeded in growing high-quality single crystals of the valence-fluctuating system EuIr2Si2, the divalent Eu system EuRh2Si2 and the substitutional alloy Eu(Rh1-xIrx)2Si2 across the range 0 < x < 1, which we characterized by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, specific heat, magnetization and resistivity measurements. On increasing x, the divalent Eu ground state subsists up to x = 0.25 with a slight increase in Néel temperature, while for 0.3≤x < 0.7 a sharp hysteretic change in susceptibility and resistivity marks the first-order valence transition. For x≳0.7 the broad feature observed in the physical properties is characteristic of the continuous valence evolution beyond the critical end point of the valence transition line, and the resistivity is reminiscent of Kondo-like behaviour while the Sommerfeld coefficient indicates a mass renormalization of at least a factor of 8. The resulting phase diagram is similar to those reported for polycrystalline Eu(Pd1-xAux)2Si2 and EuNi2(Si1-xGex)2, confirming its generic character for Eu systems, and markedly different to those of homologue Ce and Yb systems, which present a continuous suppression of the antiferromagnetism accompanied by a very smooth evolution of the valence. We discuss these differences and suggest them to be related to the large polarization energy of the Eu half-filled 4f shell. We further argue that the changes in the rare earth valence between RRh2Si2 and RIr2Si2 (R = Ce, Eu, Yb) are governed by a purely electronic effect and not by a volume effect.

  15. Determination of struvite crystallization mechanisms in urine using turbidity measurement.

    PubMed

    Triger, Aurélien; Pic, Jean-Stéphane; Cabassud, Corinne

    2012-11-15

    Sanitation improvement in developing countries could be achieved through wastewater treatment processes. Nowadays alternative concepts such as urine separate collection are being developed. These processes would be an efficient way to reduce pollution of wastewater while recovering nutrients, especially phosphorus, which are lost in current wastewater treatment methods. The precipitation of struvite (MgNH(4)PO(4)∙6H(2)O) from urine is an efficient process yielding more than 98% phosphorus recovery with very high reaction rates. The work presented here aims to determine the kinetics and mechanisms of struvite precipitation in order to supply data for the design of efficient urine treatment processes. A methodology coupling the resolution of the population balance equation to turbidity measurement was developed, and batch experiments with synthetic and real urine were performed. The main mechanisms of struvite crystallization were identified as crystal growth and nucleation. A satisfactory approximation of the volumetric crystal size distribution was obtained. The study has shown the low influence on the crystallization process of natural organic matter contained in real urine. It has also highlighted the impact of operational parameters. Mixing conditions can create segregation and attrition which influence the nucleation rate, resulting in a change in crystals number, size, and thus final crystal size distribution (CSD). Moreover urine storage conditions can impact urea hydrolysis and lead to spontaneous struvite precipitation in the stock solution also influencing the final CSD. A few limits of the applied methodology and of the proposed modelling, due to these phenomena and to the turbidity measurement, are also discussed. PMID:22975737

  16. Optimal enhancement in conversion efficiency of crystalline Si solar cells using inverse opal photonic crystals as back reflectors

    NASA Astrophysics Data System (ADS)

    Chaouachi, A.; Chtourou, R.; M'nif, A.; Hamzaoui, A. H.

    2015-04-01

    The effect of using inverse opal photonic crystals as back reflectors on the power conversion efficiency of c-Si solar cells is investigated. The reflection spectra of inverse opal photonic crystals with different diameters of air spheres are simulated using the finite difference time domain (FDTD) method. The reflection peaks are correlated with photonic band gaps present in the photonic band gap diagram. Significant improvement in the optical absorption of the crystalline silicon layer is recorded when inverse opal photonic crystals are considered. Physical mechanisms which may contribute to the enhancement of the light absorption are underlined. With higher short-circuit current enhancement possible, and with no corresponding degradation in open-circuit voltage Voc or the fill factor, the power conversion efficiency is increased significantly when inverse opal photonic crystals are used as back reflectors with optimized diameter of air spheres.

  17. Robust Population Transfer by Stimulated Raman Adiabatic Passage in a Pr{sup 3+}:Y{sub 2}SiO{sub 5} Crystal

    SciTech Connect

    Klein, Jens; Beil, Fabian; Halfmann, Thomas

    2007-09-14

    We report on the experimental implementation of stimulated Raman adiabatic passage (STIRAP) in a Pr{sup 3+}:Y{sub 2}SiO{sub 5} crystal. Our data provide clear and striking proof for nearly complete population inversion between hyperfine levels in the Pr{sup 3+} ions. The transfer efficiency was monitored by absorption spectroscopy. Time-resolved absorption measurements serve to monitor the adiabatic population dynamics during the STIRAP process. Efficient transfer is observed for negative pulse delays (STIRAP), as well as for positive delays. We identify the latter by an alternative adiabatic passage process.

  18. Crystal structures of RPt{sub 3-x}Si{sub 1-y}(R=Y, Tb, Dy, Ho, Er, Tm, Yb) studied by single crystal X-ray diffraction

    SciTech Connect

    Gribanov, Alexander; Grytsiv, Andriy; Rogl, Peter; Seropegin, Yurii; Giester, Gerald

    2009-07-15

    The crystal structures of ternary compounds RPt{sub 3-x}Si{sub 1-y}(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt{sub 3-x}Si{sub 1-y} arises from defects: x{approx}0.20, y{approx}0.14. The crystal structure of RPt{sub 3-x}Si{sub 1-y} can be considered as a packing of four types of building blocks which derive from the CePt{sub 3}B-type unit cell by various degrees of distortion and Pt, Si-defects. - Graphical Abstract: Electron density in RPt{sub 3-x}Si{sub 1-y} at 0, 1/2 , 0.

  19. Magnetic Field Induced Phase Transitions in Gd5(Si1.95Ge2.05)Single Crystal and the Anisotropic Magnetocaloric Effect

    SciTech Connect

    H. Tang; V.K. Pecharsky; A.O. Pecharsky; D.L. Schlagel; T.A. Lograsso; K.A. Gschneidner,jr.

    2004-09-30

    The magnetization measurements using a Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as function of applied field (0-56 kOe) at various temperatures ({approx}5-320 K). The magnetic-field induced phase transformations at temperature above the zero-field critical temperature, i.e. the paramagnetic (PM) {leftrightarrow} ferromagnetic (FM) transitions with application or removal of magnetic field, are found to be temperature dependent and hysteretic. The corresponding critical fields increase with increasing temperature. The magnetic field (H)-temperature (T) phase diagrams have been constructed for the Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with field along the three directions. A small anisotropy has been observed. The magnetocaloric effect (MCE) has been calculated from the isothermal magnetization data, and the observed anisotropy correlates with H-T phase diagrams. The results are discussed in connection with the magnetic-field induced martensitic-like structural transition observed in the Gd{sub 5}(Si{sub 2}Ge{sub 2})-type compounds.

  20. Investigaction of Switching Behavior in a Ferroelectric Liquid Crystal Aligned on Obliquely Deposited SiO Films

    NASA Astrophysics Data System (ADS)

    Yamada, Yuichiro; Yamamoto, Norio; Inoue, Tetsuya; Orihara, Hiroshi; Ishibashi, Yoshihiro

    1989-01-01

    The effect of oblique evaporation of SiO on the chevron structure and the switching behavior in a ferroelectric liquid crystal have been investigated by means of the X-ray diffraction and the stroboscopic micrographs. It is found experimentally that the chevron direction and the domain structure appearing during the switching are determined by the direction of incidence of evaporated SiO. On the basis of the experimental results, it is clarified that the bow and the stern of the boat-shaped domain correspond to {+}2π and {-}2π internal disclinations, respectively. The structure of the zig-zag defect is determined.

  1. The new kilogram definition based on counting the atoms in a 28Si crystal

    NASA Astrophysics Data System (ADS)

    Becker, Peter

    2012-11-01

    The kilogram is the only unit of measure still defined by a physical object. Now, a marathon effort to tie the kilogram to a constant of nature is nearing the finish line. This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, ? , results were larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, ? mol-1 is the most accurate input datum for the kilogram redefinition and differs only by ? from the CODATA 2010 adjusted value. This value is midway between the watt-balance values.

  2. The influence of the energy of photoexcitation in the course of electron irradiation on defect formation in n-Si crystals

    SciTech Connect

    Pagava, T. A. Maisuradze, N. I.

    2009-06-15

    Effect of illumination of n-Si crystals in the course of irradiation with electrons on the nature of radiation defects is studied. The samples irradiated with 2-MeV electrons were subjected to isochronous annealing in the temperature range from 200 to 600 deg. C. After each 20-min cycle of annealing, the electron concentration was measured by the Hall method in the temperature range 77-300 K. It is shown that, if the E centers are excited during irradiation with photons with the energy h{nu} = 0.44 eV (the wavelength {lambda} = 2.8 {mu}m), divacancy phosphorus-containing defects of the PV{sub 2} type are formed in the n-Si crystals, which leads to an increase in the radiation resistance of the crystals under study. If negative vacancies V{sup -} are excited with photons with the energy h{nu} = 0.28 eV ({lambda} = 4.4 {mu}m), the total number of radiation defects increases by a factor of 1.2.

  3. Homo- and heterovalent substitutions in the new clathrates I Si30P16Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x): synthesis, crystal structure, and thermoelectric properties.

    PubMed

    Abramchuk, Nikolay S; Carrillo-Cabrera, Wilder; Veremchuk, Igor; Oeschler, Niels; Olenev, Andrei V; Prots, Yurii; Burkhardt, Ulrich; Dikarev, Evgeny V; Grin, Juri; Shevelkov, Andrei V

    2012-11-01

    The new cationic clathrates I Si(30)P(16)Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x) were synthesized by the standard ampule technique. The Si(30)P(16)Te(8-x)Se(x) (x = 0-2.3) clathrates crystallize in the cubic space group Pm3̅n with the unit cell parameter a ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si(30+x)P(16-x)Te(8-x)Br(x) (x = 1-6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (x = 1-3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group Pm3n to Pm3. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10(-6) to 1.0 × 10(-5) K(-1) in the temperature range of 298-1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of p-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (ZT = 0.1) was achieved for the Br-bearing clathrate Si(32.1(2))P(13.9(2))Te(6.6(2))Br(1.0(1)) at 750 K. PMID:23072375

  4. The crystallization, magnetic and magnetocaloric properties in Fe 76.5-xNb xSi 15.5B 7Au 1 ribbons

    NASA Astrophysics Data System (ADS)

    Hoa, N. Q.; Gam, D. T. H.; Chau, N.; The, N. D.; Yu, S.-C.

    2007-03-01

    Fe 76.5-xNb xSi 15.5B 7Au 1 ribbons ( x=0.0, 1.5, 3.0, 4.5) have been fabricated by rapid quenching technique. The DSC measurements indicated that both first exothermal peak Tp1 (of α-Fe(Si) phase) and second peak Tp2 (of boride phase) as well as crystallization activation energy increase with increasing Nb content substituted, whereas saturation magnetization of samples decreases with x, due to ferromagnetic dilution. Besides, Curie temperature of amorphous phase decreases with x, i.e. Nb stabilizes amorphous structure of ribbons. The investigation of magnetic entropy change of studied samples showed that it may lead to magnetocaloric effect around respective Curie temperature of amorphous phase.

  5. Studies of a-Si:H growth mechanism, using deuterium, by rutherford recoil measurement

    SciTech Connect

    Kuboi, O.; Aratani, M.; Hashimoto, M.; Hayashi, S.; Kohno, I.; Nagai, M.; Nozaki, T.; Yanokura, M.; Yatsurugi, Y.

    1984-05-01

    a-Si:H were grown from silane and disilane by RF glow discharge. Deuterium (D) was used as a tracer in this investigation, in which four gas mixtures (SiH/sub 4/+D/sub 2/, SiD/sub 4/+H/sub 2/, Si/sub 2/H/sub 6/+D/sub 2/, and Si/sub 2/D/sub 6/+H/sub 2/) were employed. a-Si:H so produced were analyzed for H and D by Rutherford recoil measurement to determine whether these elements came from silanes or the dilution gas. When the RF power is low, much larger proportion of hydrogen atoms in silanes than in the dilution gas is found in a-Si:H. On the other hand, at high RF power, an excessive amount of D from the dilution gas, D/sub 2/, appears in a-Si:H.

  6. Czochralski growth of single-crystal gehlenite (Ca 2Al 2SiO 7)

    NASA Astrophysics Data System (ADS)

    Finch, C. B.; Ball, F. L.; Bates, J. B.

    1981-09-01

    Single-crystal boules of gehlenite (Ca 2Al 2SiO 7) were grown from even- and off-stoichiometry melts under differing conditions of oxygen fugacity (ƒ O2). Growth was accomplished by the Czochralski method at 1600°C and 10 5 Pa (1 atm) total pressure, using inductively heated Ir or Pt-20%Rh crucibles. The supra melt gas ambients included air ( ƒ O2 = 0.2 × 10 4Pa), Ar (10 Pa), Ar-50%CO 2-2%H 2 (10 -2 Pa), and Ar-4%H 2-1.5%H 2O (10 -4 Pa). Colorless, transparent material up to 8 mm diam. by 15 mm long was obtained from the evenly stoichiometric melt composition under Ar at growth rates of 1.5 mm/h or less. Growth at rates exceeding 2 mm/h or growth at a high ƒ O2 (e.g., air), led to the formation of bubbles and elongated voids or inclusions, predominantly in the core regions of boules. Optical, X-ray diffraction, and electron-induced X-ray flourescence data are included.

  7. Prediction method of basic domain structure in Fe3%Si(110) single crystal with grooved surface

    SciTech Connect

    Iwata, K.; Fujikura, M.; Arai, S.; Ishiyama, K.

    2014-05-07

    This paper proposes the method to accurately predict the 180° basic domain width (D{sub w}) in demagnetized states of the grooved Fe3%Si(110) single crystal with the tilt angle of [001] out of the sheet surface (β). The evaluation of D{sub w} enables the estimation of the anomalous eddy current losses. In this paper, D{sub w} is optimized to minimize the magnetic Gibbs free energy represented by vector potentials using the finite element method and the conjugate gradient method. The μ*-method is adopted to approximate the magnetization relaxation. The stray field energy generated by the magnetic charges occurring on both grooves cross section and sheet surfaces is considered in our proposed method. The validity of the proposed method was confirmed by comparison with the observed D{sub w}. As a result, we could reveal the β dependence of D{sub w} against the groove depth. Moreover, the theoretical threshold of the domain refinement due to the grooves has been suggested.

  8. Dependence of high-order-harmonic generation on dipole moment in Si O2 crystals

    NASA Astrophysics Data System (ADS)

    Yu, Chao; Zhang, Xirui; Jiang, Shicheng; Cao, Xu; Yuan, Guanglu; Wu, Tong; Bai, Lihua; Lu, Ruifeng

    2016-07-01

    High-order-harmonic generation in α-quartz Si O2 is theoretically investigated under a strong laser field by solving the extended semiconductor Bloch equations. The accurate band structures as well as dipole moments between different bands are obtained from state-of-the-art first-principles calculations. We find that the shapes of k -space-dependent dipole moments play an important role in harmonic generation. The calculated results show that harmonic conversion efficiency is significantly enhanced and the cutoff energy is distinctly increased when the dipole moments change greatly along a valley in the k direction in the solid. Based on that dependence on the dipole moment, we also show that symmetry groups greatly affect the harmonic spectra from the solid materials. Moreover, a two-color synthesized field is used to achieve a supercontinuum harmonic spectrum near the cutoff region, and isolated attosecond pulses can be obtained directly by filtering out the harmonic radiation. We hope the contribution presented in this work provides a useful reference for future studies on laser-crystal interactions.

  9. Crystallization paths in SiO2-Al2O3-CaO system as a genotype of silicate materials

    NASA Astrophysics Data System (ADS)

    Lutsyk, V. I.; Zelenaya, A. E.

    2013-12-01

    The phases trajectories in the fields of primary crystallization of cristobalite (SiO2cr), tridymite (SiO2tr), mullite (3Al2O3-2SiO2) and in a field of liquid immiscibility are analyzed on a basis of computer model for T-x-y diagram of SiO2-Al2O3-CaO system. The concentration fields with unique set of microconstituents and the fields without individual crystallization schemes and microconstituents are revealed.

  10. Precursor routes to quaternary intermetallics: Synthesis, crystal structure, and physical properties of clathrate-II Cs8Na16Al24Si112

    NASA Astrophysics Data System (ADS)

    Wei, Kaya; Dong, Yongkwan; Nolas, George S.

    2016-05-01

    A new quaternary clathrate-II composition, Cs8Na16Al24Si112, was synthesized by kinetically controlled thermal decomposition (KCTD) employing both NaSi and NaAlSi as the precursors and CsCl as a reactive flux. The crystal structure and composition of Cs8Na16Al24Si112 were investigated using both Rietveld refinement and elemental analysis, and the temperature dependent transport properties were investigated. Our results indicate that KCTD with multiple precursors is an effective method for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

  11. Orientational order parameter measurements of discotic liquid crystal

    NASA Astrophysics Data System (ADS)

    Kaur, Supreet; Raina, K. K.; Kumar, S.; Pratibha, R.

    2014-04-01

    The IR dichroism technique is a convenient method which can be used to measure the molecular order parameter corresponding to the IR bands exclusively present in the disc -like molecules in discotic liquid crystal (DLC). To measure orientational order parameter, homeotropic alignment of discotic liquid crystal was attained by slow cooling of sample from isotropic phase on untreated flat CaF2 substrate. The homeotropic alignment thus achieved was found to be thermodynamically stable in the discotic mesophase. IR spectra were recorded at different temperatures for the DLC. The order parameter was calculated by comparing the spectra of discotic phase with that of the isotropic phase. Order parameter has been presented as function of temperature for different significant IR bands present in the DLC.

  12. Orientational order parameter measurements of discotic liquid crystal

    SciTech Connect

    Kaur, Supreet; Raina, K. K.; Kumar, S.; Pratibha, R.

    2014-04-24

    The IR dichroism technique is a convenient method which can be used to measure the molecular order parameter corresponding to the IR bands exclusively present in the disc –like molecules in discotic liquid crystal (DLC). To measure orientational order parameter, homeotropic alignment of discotic liquid crystal was attained by slow cooling of sample from isotropic phase on untreated flat CaF{sub 2} substrate. The homeotropic alignment thus achieved was found to be thermodynamically stable in the discotic mesophase. IR spectra were recorded at different temperatures for the DLC. The order parameter was calculated by comparing the spectra of discotic phase with that of the isotropic phase. Order parameter has been presented as function of temperature for different significant IR bands present in the DLC.

  13. 'Crystal Collimator' Measurement of CESR particle-beam Source Size

    SciTech Connect

    Finkelstein, K.D.; Bazarov, Ivan; White, Jeffrey; Revesz, Peter

    2004-05-12

    We have measured electron and positron beam source size at CHESS when the Cornell Electron Storage Ring (CESR) is run dedicated for the production of synchrotron radiation. Horizontal source size at several beamlines is expected to shrink by a factor of two but synchrotron (visible) light measurements only provide the vertical size. Therefore a 'crystal collimator' using two Bragg reflection in dispersive (+,+) orientation has been built to image the horizontal (vertical) source by passing x-rays parallel to within 5 microradians to an imaging screen and camera. With the 'crystal collimator' we observe rms sizes of 1.2 mm horizontal by 0.28 mm vertical, in good agreement with the 1.27 mm size calculated from lattice functions, and 0.26 mm observed using a synchrotron light interferometer.

  14. Stopping power measurements of He ions in Si and SiC by time-of-flight spectrometry

    SciTech Connect

    Zhang, Yanwen; Jensen, Jens; Possnert, Goran; Grove, David A.; Bae, In-Tae; Weber, William J.

    2007-08-01

    Electronic energy loss is the fundamental mechanism accountable for the response of materials to ions. Helium particles are a product from alpha decay in nuclear waste materials, and helium ions are widely used as projectiles in ion beam analysis. Current work introduces a straightforward approach to determine electronic stopping powers of He ions in Si and SiC over a continuous range of energies. In transmission geometry, the energy loss of He ions in self-supporting stopping foils of Si and SiC is measured using a Time-of-Flight (TOF) set-up. The energy of individual heavy ions prior to impingement on the foil is determined from its TOF data; the exit energy after the stopping foil is essentially measured using the Si detector, for which every channel has been calibrated using TOF data without the stopping foil present. The measured stopping powers demonstrate excellent repeatability of this experimental approach and good reliability as compared with pervious data from the literature and theoretical predictions.

  15. Investigations of 3C-SiC inclusions in 4H-SiC epilayers on 4H-SiC single crystal substrates

    SciTech Connect

    Si, W.; Dudley, M.; Kong, H.S.; Sumakeris, J.; Carter, C. Jr.

    1997-03-01

    Synchrotron white beam x-ray topography (SWBXT) and Nomarski optical microscopy (NOM) have been used to characterize 4H-SiC epilayers and to study the character of triangular inclusions therein. 4H-SiC substrates misoriented by a range of angles from (0001), as well as (1 1{bar 0}0) and (11 2{bar 0}) oriented substrates were used. No evidence was found for the nucleation of 3C-SiC inclusions at superscrew dislocations (along the [0001] axis) in the 4H-SiC substrates. Increasing the off-axis angle of the substrates from 3.5 to 6.5{degree} was found to greatly suppress the formation of the triangular inclusions. In the case of substrates misoriented by 8.0{degree} from (0001) toward [112{bar 0}], the triangular inclusions were virtually eliminated. The crystalline quality of 4H-SiC epilayers grown on the substrates misoriented by 8.0{degree} from (0001) was very good. For the (11{bar 0}0) and (112{bar 0}) samples, there is no indication of 3C-SiC inclusions in the epilayers. Possible formation mechanisms and the morphology of 3C-SiC inclusions are discussed. 17 refs., 13 figs.

  16. Side readout of long scintillation crystal elements with digital SiPM for TOF-DOI PET

    SciTech Connect

    Yeom, Jung Yeol E-mail: cslevin@stanford.edu; Vinke, Ruud; Levin, Craig S. E-mail: cslevin@stanford.edu

    2014-12-15

    Purpose: Side readout of scintillation light from crystal elements in positron emission tomography (PET) is an alternative to conventional end-readout configurations, with the benefit of being able to provide accurate depth-of-interaction (DOI) information and good energy resolution while achieving excellent timing resolution required for time-of-flight PET. This paper explores different readout geometries of scintillation crystal elements with the goal of achieving a detector that simultaneously achieves excellent timing resolution, energy resolution, spatial resolution, and photon sensitivity. Methods: The performance of discrete LYSO scintillation elements of different lengths read out from the end/side with digital silicon photomultipliers (dSiPMs) has been assessed. Results: Compared to 3 × 3 × 20 mm{sup 3} LYSO crystals read out from their ends with a coincidence resolving time (CRT) of 162 ± 6 ps FWHM and saturated energy spectra, a side-readout configuration achieved an excellent CRT of 144 ± 2 ps FWHM after correcting for timing skews within the dSiPM and an energy resolution of 11.8% ± 0.2% without requiring energy saturation correction. Using a maximum likelihood estimation method on individual dSiPM pixel response that corresponds to different 511 keV photon interaction positions, the DOI resolution of this 3 × 3 × 20 mm{sup 3} crystal side-readout configuration was computed to be 0.8 mm FWHM with negligible artifacts at the crystal ends. On the other hand, with smaller 3 × 3 × 5 mm{sup 3} LYSO crystals that can also be tiled/stacked to provide DOI information, a timing resolution of 134 ± 6 ps was attained but produced highly saturated energy spectra. Conclusions: The energy, timing, and DOI resolution information extracted from the side of long scintillation crystal elements coupled to dSiPM have been acquired for the first time. The authors conclude in this proof of concept study that such detector configuration has the potential to enable

  17. Al{sub 4}SiC{sub 4} wurtzite crystal: Structural, optoelectronic, elastic, and piezoelectric properties

    SciTech Connect

    Pedesseau, L. E-mail: jacky.even@insa-rennes.fr; Even, J. E-mail: jacky.even@insa-rennes.fr; Durand, O.; Modreanu, M.; Chaussende, D.; Sarigiannidou, E.; Chaix-Pluchery, O.

    2015-12-01

    New experimental results supported by theoretical analyses are proposed for aluminum silicon carbide (Al{sub 4}SiC{sub 4}). A state of the art implementation of the density functional theory is used to analyze the experimental crystal structure, the Born charges, the elastic properties, and the piezoelectric properties. The Born charge tensor is correlated to the local bonding environment for each atom. The electronic band structure is computed including self-consistent many-body corrections. Al{sub 4}SiC{sub 4} material properties are compared to other wide band gap wurtzite materials. From a comparison between an ellipsometry study of the optical properties and theoretical results, we conclude that the Al{sub 4}SiC{sub 4} material has indirect and direct band gap energies of about 2.5 eV and 3.2 eV, respectively.

  18. Polar nephelometer for light-scattering measurements of ice crystals.

    PubMed

    Barkey, B; Liou, K N

    2001-02-15

    We report on a small, lightweight polar nephelometer for the measurement of the light-scattering properties of cloud particles, specifically designed for use on a balloonborne platform in cirrus cloud conditions. The instrument consists of 33 fiber-optic light guides positioned in a two-dimensional plane from 5 degrees to 175 degrees that direct the scattered light to photodiode detectors-amplifier units. The system uses an onboard computer and data acquisition card to collect and store the measured signals. The instrument's calibration is tested by measurement of light scattered into a two-dimensional plane from small water droplets generated by an ultrasonic humidifier. Excellent comparisons between the measured water-droplet scattering properties and expectations generated by Mie calculation are shown. The measured scattering properties of ice crystals generated in a cold chamber also compare reasonably well with the theoretical results based on calculations from a unified theory of light scattering by ice crystals that use the particle size distribution measured in the chamber. PMID:18033557

  19. High-pressure synthesis and crystal structure of silicon phosphate hydroxide, SiPO{sub 4}(OH)

    SciTech Connect

    Stearns, Linda A. . E-mail: linda.stearns@asu.edu; Groy, Thomas L.; Leinenweber, Kurt

    2005-09-15

    A new high-pressure phase, silicon phosphate hydroxide, was prepared at 8.3+/-0.5GPa and 1000 deg. C in >98% purity. From X-ray diffraction on a pseudo-merohedrally twinned crystal, it was found that SiPO{sub 4}(OH) crystallizes in a monoclinic cell with space group P2{sub 1}/n (No. 14), a=6.8446(11)A,b=6.8683(13)A,c=6.8446(11)A,{beta}=119.77(1){sup o}, and Z=4. The refinement gave a conventional R{sub obs} of 0.0320 and wR{sub obs} of 0.0864 for the overlapped data from both twin components. In the structure, SiO{sub 6} octahedra form chains along [101], with PO{sub 4} tetrahedra alternating along the chain in the b-direction. The parallel chains link up with tetrahedral corners from other chains to form a 3-dimensional network. SiPO{sub 4}(OH) belongs to a structural family that includes HgSeO{sub 4}.H{sub 2}O. It is also related to the SbOPO{sub 4} structure by a small distortion that lowers the symmetry from C2/c in SbOPO{sub 4} to P2{sub 1}/c(P2{sub 1}/n) in SiPO{sub 4}(OH)

  20. Correlated Protein Motion Measurements of Dihydrofolate Reductase Crystals

    NASA Astrophysics Data System (ADS)

    Xu, Mengyang; Niessen, Katherine; Pace, James; Cody, Vivian; Markelz, Andrea

    2014-03-01

    We report the first direct measurements of the long range structural vibrational modes in dihydrofolate reductase (DHFR). DHFR is a universal housekeeping enzyme that catalyzes the reduction of 7,8-dihydrofolate to 5,6,7,8-tetra-hydrofolate, with the aid of coenzyme nicotinamide adenine dinucleotide phosphate (NADPH). This crucial enzymatic role as the target for anti-cancer [methotrexate (MTX)], and other clinically useful drugs, has made DHFR a long-standing target of enzymological studies. The terahertz (THz) frequency range (5-100 cm-1), corresponds to global correlated protein motions. In our lab we have developed Crystal Anisotropy Terahertz Microscopy (CATM), which directly measures these large scale intra-molecular protein vibrations, by removing the relaxational background of the solvent and residue side chain librational motions. We demonstrate narrowband features in the anisotropic absorbance for mouse DHFR with the ligand binding of NADPH and MTX single crystals as well as Escherichia coli DHFR with the ligand binding of NADPH and MTX single crystals. This work is supported by NSF grant MRI2 grant DBI2959989.

  1. Czochralski growth of RE 3Ga 5SiO 14 (RE=La, Pr, Nd) single crystals for the analysis of the influence of rare earth substitution on piezoelectricity

    NASA Astrophysics Data System (ADS)

    Sato, J.; Takeda, H.; Morikoshi, H.; Shimamura, K.; Rudolph, P.; Fukuda, T.

    1998-08-01

    Pr 3Ga 5SiO 14 and Nd 3Ga 5SiO 14 single crystals with constant diameter of 22 mm and lengths up to 145 mm have been grown by the Czochralski method. The phase identification, site occupancy of cations and axial lattice parameter distribution were determined by X-ray analysis. The transmission spectra within the 340-3200 nm wavelength region were measured. The centre of interest are the piezoelectric properties of (2 1¯ 0) and (0 1 0) plates in comparison with former grown La 3Ga 5SiO 14 crystals in order to find out the influence of the rare earth substitution of La 3+ by Pr 3+ and Nd 3+ on the piezoelectric strain constant d11. A decrease of | d11| with increasing atomic number was found giving the hint to the substitution of lanthanum by further elements with larger atomic radii.

  2. Crystal Structure and Magnetic Properties of (Fe,Si,Al)-Based Nanocomposite Magnets Designed for Cryogenic Applications

    NASA Astrophysics Data System (ADS)

    Daniil, Maria; Fonda, Helen M.; Willard, Matthew A.

    2015-06-01

    In this work, we performed a detailed study of the crystallization, crystal structure, and magnetic properties of Fe87- z Si z- x Al x Nb3B9Cu1 nanocrystalline alloys that were designed primarily for low-temperature applications. In addition, their interesting low-temperature [77 K to 300 K (-196 °C to 27 °C)] magnetic properties ( H c and M s) were also investigated. These alloys were produced by annealing their amorphous precursors at 823 K (550 °C). Si and Al substitution do not seem to alter the crystallization procedure and crystal structure of the parent alloy but reduces the lattice parameter, the Curie temperature, and the saturation magnetization. On the other hand, it improves the room temperature coercivity at small amounts ( H c = 0.35 A/m for x = 3.5, z = 19) and changes its temperature dependence. As a result, a remarkably low H c value at 77 K (-196 °C) of 0.45 A/m was observed for x = 6 and z = 23.5.

  3. Measurement of Valley Kondo Effect in a Si/SiGe Quantum Dot

    NASA Astrophysics Data System (ADS)

    Yuan, Mingyun; Yang, Zhen; Tang, Chunyang; Rimberg, A. J.; Joynt, R.; Savage, D. E.; Lagally, M. G.; Eriksson, M. A.

    2013-03-01

    The Kondo effect in Si/SiGe QDs can be enriched by the valley degree of freedom in Si. We have observed resonances showing temperature dependence characteristic of the Kondo effect in two consecutive Coulomb diamonds. These resonances exhibit unusual magnetic field dependence that we interpret as arising from Kondo screening of the valley degree of freedom. In one diamond two Kondo peaks due to screening of the valley index exist at zero magnetic field, revealing a zero-field valley splitting of Δ ~ 0.28 meV. In a non-zero magnetic field the peaks broaden and coalesce due to Zeeman splitting. In the other diamond, a single resonance at zero bias persists without Zeeman splitting for non-zero magnetic field, a phenomenon characteristic of valley non-conservation in tunneling. This research is supported by the NSA and ARO.

  4. Thermal-expansion measurements for Lu5Ir4Si10, Lu5Rh4Si10, Sc5Ir4Si10, and Tm5Ir4Si10: Charge-density-wave effects

    NASA Astrophysics Data System (ADS)

    Swenson, C. A.; Shelton, R. N.; Klavins, P.; Yang, H. D.

    1991-04-01

    Linear-thermal-expansion measurements have determined the small relative length changes (ΔL/L~=-10-4) at the charge-density-wave (CDW) transitions in Lu5Ir4Si10, Lu5Rh4Si10, and Tm5Ir4Si10. Tm5Ir4Si10 shows a second sluggish transition near 18+/-8 K which is comparable in magnitude. Thermal-expansivity measurements show that, for each material, significant changes occur in lattice properties on cooling through the CDW transition. Expansivity data above the low-temperature ordering transitions for these three (Lu5Ir4Si10, Lu5Rh4Si10 superconducting; Tm5Ir4Si10, magnetic) and also for Sc5Ir4Si10 (no CDW, but superconducting) in combination with previous CP results show unusual electronic behavior (large electronic contributions to α for all except Lu5Ir4Si10), a positive lattice expansivity only for Lu5Ir4Si10, and a very large lattice expansivity for Tm5Ir4Si10. The lattice Grüneisen parameters for the superconducting compounds show significant temperature dependence. A comparison of the pressure dependences of the superconducting transition temperatures (dTc/dP) as calculated from the discontinuities in α and CP and as determined in high-pressure experiments suggests a complex Tc(P) behavior. The magnetic contributions to the expansivity of Tm5Ir4Si10 are consistent with different signs for dTc/dP for the 1.9-K ordering transition studied in these experiments and for the 0.86-K transition which has been observed in CP measurements.

  5. Fabrication of FCC-SiO2 colloidal crystals using the vertical convective self-assemble method

    NASA Astrophysics Data System (ADS)

    Castañeda-Uribe, O. A.; Salcedo-Reyes, J. C.; Méndez-Pinzón, H. A.; Pedroza-Rodríguez, A. M.

    2014-05-01

    In order to determine the optimal conditions for the growth of high-quality 250 nm-SiO2 colloidal crystals by the vertical convective self-assemble method, the Design of Experiments (DoE) methodology is applied. The influence of the evaporation temperature, the volume fraction, and the pH of the colloidal suspension is studied by means of an analysis of variance (ANOVA) in a 33 factorial design. Characteristics of the stacking lattice of the resulting colloidal crystals are determined by scanning electron microscopy and angle-resolved transmittance spectroscopy. Quantitative results from the statistical test show that the temperature is the most critical factor influencing the quality of the colloidal crystal, obtaining highly ordered structures with FCC stacking lattice at a growth temperature of 40°C.

  6. Optical absorption of Bi/sub 12/SiO/sub 20/ single crystals doped with chromium or nickel

    SciTech Connect

    Orlov, V.M.; Kolosov, E.E.; Shilova, M.V.

    1986-08-01

    In the present work on Bi/sub 12/SiO/sub 20/ single crystals (BSO) undoped and doped with Cr or Ni, the authors studied the room-temperature optical absorption in the range 0.4-1.2 micrometers during emission of the photochromic effect and determined the impurity level energies due to Cr or Ni. The crystals studied were grown by the Czochralski method. In study of the photochromic effect, the authors used ultraviolet radiation from a mercury lamp and radiation from a He-Ne laser. The optical absorption spectral dependences are shown. It is confirmed that observation of photochromic effect in chromium-doped BSO crystals is encumbered by relaxation of their optical transmission. The extent of optical excitation in these sample depends substantially on the time elapsed after irradiation.

  7. Fabrication of FCC-SiO{sub 2} colloidal crystals using the vertical convective self-assemble method

    SciTech Connect

    Castañeda-Uribe, O. A.; Salcedo-Reyes, J. C.; Méndez-Pinzón, H. A.; Pedroza-Rodríguez, A. M.

    2014-05-15

    In order to determine the optimal conditions for the growth of high-quality 250 nm-SiO{sub 2} colloidal crystals by the vertical convective self-assemble method, the Design of Experiments (DoE) methodology is applied. The influence of the evaporation temperature, the volume fraction, and the pH of the colloidal suspension is studied by means of an analysis of variance (ANOVA) in a 3{sup 3} factorial design. Characteristics of the stacking lattice of the resulting colloidal crystals are determined by scanning electron microscopy and angle-resolved transmittance spectroscopy. Quantitative results from the statistical test show that the temperature is the most critical factor influencing the quality of the colloidal crystal, obtaining highly ordered structures with FCC stacking lattice at a growth temperature of 40°C.

  8. Measurement of probability distributions for internal stresses in dislocated crystals

    SciTech Connect

    Wilkinson, Angus J.; Tarleton, Edmund; Vilalta-Clemente, Arantxa; Collins, David M.; Jiang, Jun; Britton, T. Benjamin

    2014-11-03

    Here, we analyse residual stress distributions obtained from various crystal systems using high resolution electron backscatter diffraction (EBSD) measurements. Histograms showing stress probability distributions exhibit tails extending to very high stress levels. We demonstrate that these extreme stress values are consistent with the functional form that should be expected for dislocated crystals. Analysis initially developed by Groma and co-workers for X-ray line profile analysis and based on the so-called “restricted second moment of the probability distribution” can be used to estimate the total dislocation density. The generality of the results are illustrated by application to three quite different systems, namely, face centred cubic Cu deformed in uniaxial tension, a body centred cubic steel deformed to larger strain by cold rolling, and hexagonal InAlN layers grown on misfitting sapphire and silicon carbide substrates.

  9. Effect of periodic number of [Si/Sb80Te20]x multilayer film on its laser-induced crystallization studied by coherent phonon spectroscopy

    PubMed Central

    2012-01-01

    The periodic number dependence of the femtosecond laser-induced crystallization threshold of [Si(5nm)/Sb80Te20(5nm)]x nanocomposite multilayer films has been investigated by coherent phonon spectroscopy. Coherent optical phonon spectra show that femtosecond laser-irradiated crystallization threshold of the multilayer films relies obviously on the periodic number of the multilayer films and decreases with the increasing periodic number. The mechanism of the periodic number dependence is also studied. Possible mechanisms of reflectivity and thermal conductivity losses as well as the effect of the glass substrate are ruled out, while the remaining superlattice structure effect is ascribed to be responsible for the periodic number dependence. The sheet resistance of multilayer films versus a lattice temperature is measured and shows a similar periodic number dependence with one of the laser irradiation crystallization power threshold. In addition, the periodic number dependence of the crystallization temperature can be fitted well with an experiential formula obtained by considering coupling exchange interactions between adjacent layers in a superlattice. Those results provide us with the evidence to support our viewpoint. Our results show that the periodic number of multilayer films may become another controllable parameter in the design and parameter optimization of multilayer phase change films. PMID:23173850

  10. Crystallization and surface morphology of Au/SiO 2 thin films following furnace and flame annealing

    NASA Astrophysics Data System (ADS)

    De Los Santos, V. Luis; Lee, Dongwook; Seo, Jiwon; Leon, F. Lizbet; Bustamante, D. Angel; Suzuki, Seiichi; Majima, Yutaka; Mitrelias, Thanos; Ionescu, Adrian; Barnes, Crispin H. W.

    2009-10-01

    A crystallization and surface evolution study of Au thin film on SiO 2 substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10 -7 mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO 2 substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO 2 system decreases in the range of 350-400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO 2 surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing

  11. Intrinsic carrier multiplication efficiency in bulk Si crystals evaluated by optical-pump/terahertz-probe spectroscopy

    SciTech Connect

    Yamashita, G.; Nagai, M. E-mail: ashida@mp.es.osaka-u.ac.jp; Ashida, M. E-mail: ashida@mp.es.osaka-u.ac.jp; Matsubara, E.; Kanemitsu, Y.

    2014-12-08

    We estimated the carrier multiplication efficiency in the most common solar-cell material, Si, by using optical-pump/terahertz-probe spectroscopy. Through close analysis of time-resolved data, we extracted the exact number of photoexcited carriers from the sheet carrier density 10 ps after photoexcitation, excluding the influences of spatial diffusion and surface recombination in the time domain. For incident photon energies greater than 4.0 eV, we observed enhanced internal quantum efficiency due to carrier multiplication. The evaluated value of internal quantum efficiency agrees well with the results of photocurrent measurements. This optical method allows us to estimate the carrier multiplication and surface recombination of carriers quantitatively, which are crucial for the design of the solar cells.

  12. Electron density distribution and disordered crystal structure of 15R-SiAlON, SiAl4O2N4

    NASA Astrophysics Data System (ADS)

    Banno, Hiroki; Hanai, Takaaki; Asaka, Toru; Kimoto, Koji; Fukuda, Koichiro

    2014-03-01

    The crystal structure of SiAl4O2N4 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is trigonal with space group R3¯m. The hexagonal unit-cell dimensions (Z=3) are a=0.301332(3) nm, c=4.18616(4) nm and V=0.3291825(5) nm3. The initial structural model was successfully derived by the charge-flipping method and further refined by the Rietveld method. The final structural model showed the positional disordering of one of the three (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp=5.05%, S (=Rwp/Re)=1.21, Rp=3.77%, RB=1.29% and RF=1.01%. The disordered crystal structure was successfully described by overlapping three types of domains with ordered atom arrangements. The distribution of atomic positions in one of the three types of domains can be achieved in the space group R3¯m. The atom arrangements in the other two types of domains are noncentrosymmetrical with the space group R3m. These two structural configurations are related by the pseudo-symmetry inversion.

  13. Crystal structure of Si-doped HfO{sub 2}

    SciTech Connect

    Zhao, Lili; Nelson, Matthew; Fancher, Chris M.; Aldridge, Henry; Iamsasri, Thanakorn; Forrester, Jennifer S.; Jones, Jacob L.; Nishida, Toshikazu; Moghaddam, Saeed

    2014-01-21

    Si-doped HfO{sub 2} was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO{sub 2} was determined as less than 9 at. %. A second phase was identified as Cristobalite (SiO{sub 2}) rather than HfSiO{sub 4}, the latter of which would be expected from existing SiO{sub 2}-HfO{sub 2} phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO{sub 2} shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution.

  14. The systems Sr-Zn-{l_brace}Si,Ge{r_brace}: Phase equilibria and crystal structure of ternary phases

    SciTech Connect

    Romaka, V.V.; Falmbigl, M.; Grytsiv, A.; Rogl, P.

    2012-02-15

    Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of the ternary systems Sr-Zn-Si at 800 Degree-Sign C and Sr-Zn-Ge at 700 Degree-Sign C. In the Sr-Zn-Si system one new ternary compound SrZn{sub 2+x}Si{sub 2-x} (0{<=}x{<=}0.45) with CeAl{sub 2}Ga{sub 2} structure and a statistical mixture of Zn/Si in the 4e site was found. Neither a type-I nor a type-IX clathrate phase was encountered. This system is characterized by formation of two further phases, i.e. SrZn{sub 1-x}Si{sub 1+x} with ZrBeSi-type (0.16{<=}x{<=}0.22) and SrZn{sub 1-x}Si{sub 1+x} with AlB{sub 2}-type (0.35{<=}x{<=}0.65) with a random distribution of Zn/Si atoms in the 2c site. For the Sr-Zn-Ge system, the homogeneity regions of the isotypic phases SrZn{sub 1-x}Ge{sub 1+x} with ZrBeSi-type (0{<=}x{<=}0.17) and AlB{sub 2}-type (0.32{<=}x{<=}0.56), respectively, have been determined. Whereas the germanide SrZn{sub 2+x}Ge{sub 2-x} (CeAl{sub 2}Ga{sub 2}-type) is characterized by a homogeneity region (0{<=}x{<=}0.5), the clathrate type-I phase Sr{sub 8}Zn{sub 8}Ge{sub 38} shows a point composition. - Graphical abstract: Phase equilibria of ternary compounds in the Sr-Zn-Si-system at 800 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Si-system are established at 800 Degree-Sign C. Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Ge-system are established at 700 Degree-Sign C. Black-Right-Pointing-Pointer Crystal structures of the ternary compounds were confirmed by X-ray powder diffraction. Black-Right-Pointing-Pointer All ternary compounds except the clathrate-I in the Ge-system are characterized by a homogeneity region.

  15. Electron density distribution and disordered crystal structure of 15R-SiAlON, SiAl{sub 4}O{sub 2}N{sub 4}

    SciTech Connect

    Banno, Hiroki; Hanai, Takaaki; Asaka, Toru; Kimoto, Koji; Fukuda, Koichiro

    2014-03-15

    The crystal structure of SiAl{sub 4}O{sub 2}N{sub 4} was characterized by laboratory X-ray powder diffraction (CuKα{sub 1}). The title compound is trigonal with space group R3-bar m. The hexagonal unit-cell dimensions (Z=3) are a=0.301332(3) nm, c=4.18616(4) nm and V=0.3291825(5) nm{sup 3}. The initial structural model was successfully derived by the charge-flipping method and further refined by the Rietveld method. The final structural model showed the positional disordering of one of the three (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R{sub wp}=5.05%, S (=R{sub wp}/R{sub e})=1.21, R{sub p}=3.77%, R{sub B}=1.29% and R{sub F}=1.01%. The disordered crystal structure was successfully described by overlapping three types of domains with ordered atom arrangements. The distribution of atomic positions in one of the three types of domains can be achieved in the space group R3-bar m. The atom arrangements in the other two types of domains are noncentrosymmetrical with the space group R3m. These two structural configurations are related by the pseudo-symmetry inversion. -- Graphical abstract: A bird's eye view of electron densities up to 75.3% (0.133 nm{sup −3}) of the maximum on the plane parallel to (110) with the corresponding atomic arrangements of SiAl{sub 4}O{sub 2}N{sub 4}. Highlights: • Crystal structure of SiAl{sub 4}O{sub 2}N{sub 4} is determined by laboratory X-ray powder diffraction. • The atom arrangements are represented by the split-atom model. • The maximum-entropy method-based pattern fitting method is used to confirm the validity of the model. • The disordered structure is described by overlapping three types of domains with ordered atom arrangements.

  16. Crystal structure and electronic properties of the new compounds U{sub 3}Co{sub 12-x}X{sub 4} with X=Si, Ge

    SciTech Connect

    Soude, A.; Tougait, O.; Pasturel, M.; Kaczorowski, D.; Noel, H.

    2010-05-15

    The new compounds U{sub 3}Co{sub 12-x}X{sub 4} with X=Si, Ge were prepared by direct solidification of the corresponding liquid phase, followed by subsequent annealing at 1173 K. Single crystal X-ray diffraction carried out at room temperature showed that they crystallize with the hexagonal space group P6{sub 3}/mmc (no.194) and the unit-cell parameters a=8.130(5), c=8.537(5) A and a=8.256(1), c=8.608(1) A for the silicide and germanide, respectively. Their crystal structure derives from the EuMg{sub 5.2} structure type, and is closely related to the Sc{sub 3}Ni{sub 11}Si{sub 4} and Gd{sub 3}Ru{sub 4-x}Al{sub 12+x} types. For the present compounds, no substitution mechanisms have been observed, the partial occupancy of one Co site results from the presence of vacancies, only. The homogeneity ranges, evaluated by energy dispersive spectroscopy analysis, extend from x=0.0(2) to 0.3(2) and from x=0.0(2) to 1.0(2) for U{sub 3}Co{sub 12-x}Si{sub 4} and U{sub 3}Co{sub 12-x}Ge{sub 4}, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U{sub 3}Co{sub 12-x}X{sub 4} compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior. - Graphical abstract: The crystal structure of the new compounds U{sub 3}Co{sub 12-x}X{sub 4}, X=Si, Ge is a ternary ordered variant of the EuMg{sub 5.2}-type with a site preference for the 4e position.

  17. Prevention of AlN crystal from cracking on SiC substrates by evaporation of the substrates

    NASA Astrophysics Data System (ADS)

    Argunova, T. S.; Gutkin, M. Yu.; Mokhov, E. N.; Kazarova, O. P.; Lim, J.-H.; Shcheglov, M. P.

    2015-12-01

    The problem of prevention of AlN crystal layers from cracking under action of thermoelastic stresses during growth of these layers on SiC substrates has been studied. Calculation of residual thermoelastic stresses in AlN/SiC double-layer system has shown that cracking of the AlN layer during cooling is inevitable until this layer becomes at least 15 times thicker than a substrate. The required ratio of the thicknesses of the layer and the substrate can be reached by growing an AlN layer with simultaneous evaporation of the SiC substrate. Experimentally performed evaporation of SiC substrates in one process with growing AlN single layers on them using the sublimation sandwich method has made it possible to prevent these layers from cracking. Continuous (non-cracked) plates with 0.2-0.8 mm thickness without substrates have been obtained as a result of these experiments. According to X-ray images obtained in synchrotron radiation, they consist of single crystalline AlN of 2H polytype, contain dislocations, but do not contain cracks. The degree of crystallinity of these thin plates, which was estimated by the full widths at half-maximum of rocking curves of X-ray diffraction reflections, corresponds to the degree of crystallinity of thick (3-5 mm) AlN layers grown on nonevaporated SiC substrates.

  18. Energy loss distributions of 7 TeV protons axially channeled in the bent <1 1 0> Si crystal

    NASA Astrophysics Data System (ADS)

    Stojanov, Nace; Petrović, Srdjan

    2016-04-01

    In this article, the energy loss distributions of relativistic protons axially channeled in the bent <1 1 0> Si crystal are studied. The crystal thickness is equal to 1 mm, which corresponds to the reduced crystal thickness, Λ, equal to 1.22, whereas the bending angle, α, was varied from 0 to 30 μrad. The proton energy of 7 TeV was chosen in accordance with the concept of using the bent crystals as a tool for selective deflection of the beam halo particles from the LUA9 experiment at LHC. For the continuum interaction potential of the proton and the crystal the Molière's expression was used and the energy loss of a proton was calculated by applying the trajectory dependent stopping power model. Further, the uncertainness of the scattering angle of the proton caused by its collisions with the electrons of the crystal and the divergence of the proton beam were taken into account. The energy loss distribution of the channeled protons was obtained via the numerical solution of the proton equations of motion in the transverse plane and the computer simulation method. The analysis of the obtained theoretical data shows that the shape of the energy loss distribution strongly depends on the horizontal or vertical direction of the curvature of the crystal. The number of dechanneled protons as a function of the bending angle also strongly depends on the direction of the crystal's curvature. As a result, the dechanneling rates and ranges, obtained from the Gompertz type sigmoidal fitting functions, have different sets of values for different bending orientations. We have also studied the influence of the proton beam divergence on the energy loss distribution of channeled protons.

  19. Li3AlSiO5: the first aluminosilicate as a potential deep-ultraviolet nonlinear optical crystal with the quaternary diamond-like structure.

    PubMed

    Chen, Xinglong; Zhang, Fangfang; Liu, Lili; Lei, Bing-Hua; Dong, Xiaoyu; Yang, Zhihua; Li, Hongyi; Pan, Shilie

    2016-02-14

    Deep-ultraviolet (deep-UV) nonlinear optical (NLO) crystals play a crucial role in modern laser frequency conversion technology. Traditionally, the exploration of deep-UV NLO crystals is mainly focused on borates, while, the use of phosphates recently opened up a novel and promising non-boron pathway for designing new deep-UV NLO crystals. Extending this pathway to aluminosilicates led to the discovery of Li3AlSiO5, the first NLO crystal in this system. It crystallizes in the polar space group Pna21 (no. 33) with a quaternary diamond-like structure composed of LiO4, AlO4 and SiO4 tetrahedral groups. The compound exhibits a deep-UV cut-off edge below 190 nm and is phase matchable with moderate powder second harmonic generation (SHG) intensity (0.8KH2PO4). The band gap calculated using PBE0 is 7.29 eV, indicating that the cut-off edge of the Li3AlSiO5 crystal can be down to 170 nm. In addition, the compound is nonhygroscopic and thermally stable up to ∼1472 K. These results suggest that Li3AlSiO5 is a potential deep-UV NLO crystal. First-principles studies were performed to elucidate the structure-property relationship of Li3AlSiO5. PMID:26788988

  20. Impact of additional Pt and NiSi crystal orientation on channel stress induced by Ni silicide film in metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Mizuo, Mariko; Yamaguchi, Tadashi; Kudo, Shuichi; Hirose, Yukinori; Kimura, Hiroshi; Tsuchimoto, Jun-ichi; Hattori, Nobuyoshi

    2014-01-01

    The impact of additional Pt and Ni monosilicide (NiSi) crystal orientation on channel stress from Ni silicide in metal-oxide-semiconductor field-effect transistors (MOSFETs) has been demonstrated. The channel stress generation mechanism can be explained by the NiSi crystal orientation. In pure Ni silicide films, the channel stress in the p-type substrate is much larger than that in the n-type one, since the NiSi a-axis parallel to the channel direction is strongly aligned on the p-type substrate compared with on the n-type one. On the other hand, in NiPt silicide films, the difference in the channel stress between the p- and n-type substrates is small, because the NiSi crystal orientation on the p-type substrate is similar to that on the n-type one. These results can be explained by the Pt segregation at the interface between the NiSi film and the Si surface. Segregated Pt atoms cause the NiSi b-axis to align normal to the Si(001) surface in the nucleation step owing to the expansion of the NiSi lattice spacing at the NiSi/Si interface. Furthermore, the Pt segregation mechanism is considered to be caused by the grain boundary diffusion in the Ni2Si film during NiSi formation. We confirmed that the grains of Ni2Si on the p-type substrate are smaller than those on the n-type one. The Ni2Si film on the p-type substrate has more grain boundary diffusion paths than that on the n-type one. Therefore, the amount of Pt segregation at the NiSi/Si interface on the p-type substrate is larger than that on the n-type one. Consequently, the number of NiSi grains with the b-axis aligned normal to the Si(001) in the p-type substrate is larger than that in the n-type one. As a result, the channel stress induced by NiPt silicide in PMOS is larger than that in NMOS. According to this mechanism, controlling the Pt concentration at the NiSi/Si interface is one of the key factors for channel stress engineering.

  1. Photothermal method for absorption measurements in anisotropic crystals

    NASA Astrophysics Data System (ADS)

    Stubenvoll, M.; Schäfer, B.; Mann, K.; Novak, O.

    2016-02-01

    A measurement system for quantitative determination of both surface and bulk contributions to the photo-thermal absorption has been extended to anisotropic optical media. It bases upon a highly sensitive Hartmann-Shack wavefront sensor, accomplishing precise on-line monitoring of wavefront deformations of a collimated test beam transmitted perpendicularly through the laser-irradiated side of a cuboid sample. Caused by the temperature dependence of the refractive index as well as thermal expansion, the initially plane wavefront of the test beam is distorted. Sign and magnitude depend on index change and expansion. By comparison with thermal theory, a calibration of the measurement is possible, yielding a quantitative absolute measure of bulk and surface absorption losses from the transient wavefront distortion. Results for KTP and BBO single crystals are presented.

  2. Piconewton force measurement using a nanometric photonic crystal diaphragm.

    PubMed

    Jo, Wonuk; Digonnet, Michel J F

    2014-08-01

    A compact force fiber sensor capable of measuring forces at the piconewton level is reported. It consists of a miniature Fabry-Perot cavity fabricated at the tip a single-mode fiber, in which the external reflector is a compliant photonic-crystal diaphragm that deflects when subjected to a force. In the laboratory environment, this sensor was able to detect a force of only ∼4  pN generated by the radiation pressure of a laser beam. Its measured minimum detectable force (MDF) at 3 kHz was as weak as 1.3  pN/√Hz. In a quiet environment, the measured noise was ∼16 times lower, and the MDF predicted to be ∼76  fN/√Hz. PMID:25078221

  3. Estimation of low-temperature spectra behavior in Nd-doped Sc2SiO5 single crystal.

    PubMed

    Zheng, Lihe; Xu, Jun; Su, Liangbi; Li, Hongjun; Wang, Qingguo; Ryba-Romanowski, Witold; Lisiecki, Radosław; Wu, Feng

    2009-11-15

    High optical quality Nd-doped Sc(2)SiO(5) crystal with size of diameter 27 mm x 60 mm was obtained by Czochralski method. An x-ray diffraction pattern of Nd:SSO crystal confirmed that the as-grown crystal was isostructual with the SSO crystal. Absorption and emission spectra were recorded at 10 K. The Judd-Ofelt theory was applied to obtain standard parameters Omega t(t=2,4,6) and the fitting result of experimental absorption line strengths, which provided the F3/24 radiative lifetime (tau(rad)) of 219 micros and the luminescence branching ratio beta of 0.57 for the (4)F(3/2)-(4)I(9/2) laser transition. The stimulated emission cross section of 1.04 x 10(-19) cm(2) at 1074 nm was calculated using the Füchtbauer-Ladenburg equation. The (4)F(3/2) luminescence lifetimes with 215 micros at 10 K and 198 micros at 300 K were determined from luminescence decay curves, indicating high quantum efficiency in the Nd:SSO crystal. All these results showed that Nd:SSO would be a promising gain media in solid-state lasers. PMID:19927184

  4. The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7.

    PubMed

    Sazonov, Andrew; Hutanu, Vladimir; Meven, Martin; Roth, Georg; Kézsmárki, István; Murakawa, Hiroshi; Tokura, Yoshinori; Náfrádi, Bálint

    2016-02-01

    In the antiferromagnetic ground state, below TN ≃ 5.7 K, Ca2CoSi2O7 exhibits strong magnetoelectric coupling. For a symmetry-consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a prerequisite. Here we report the results of single-crystal neutron diffraction on Ca2CoSi2O7 at temperatures between 10 and 250 K. The low-temperature structure at 10 K was refined assuming twinning in the orthorhombic space group P2(1)2(1)2 with a 3 × 3 × 1 supercell [a = 23.52 (1), b = 23.52 (1), c = 5.030 (3) Å] compared with the high-temperature normal state [tetragonal space group P42(1)m, a = b ≃ 7.86, c ≃ 5.03 Å]. The precise structural parameters of Ca2CoSi2O7 at 10 K are presented and compared with the literature X-ray diffraction results at 130 and 170 K (low-temperature commensurate phase), as well as at ∼ 500 K (high-temperature normal phase). PMID:26830804

  5. The effect of salt on ion adsorption on a SiOx alignment film and reduced conductivity of a liquid crystal host

    NASA Astrophysics Data System (ADS)

    Huang, Yi; Bhowmik, Achintya; Bos, Philip J.

    2012-01-01

    It is shown that the addition of salt to liquid crystal cells, using a SiOx alignment layer, can actually reduce the ion concentration. This seeming contradiction may be explained by the ability of salt to complex with water and to aid the drying of the liquid crystal material. The results show a pathway to purifying liquid crystal devices to the extent needed for low-power low-refresh rate displays for e-book applications.

  6. Active performance of tetrahedral groups to SHG response: theoretical interpretations of Ge/Si-containing borate crystals.

    PubMed

    Li, Linping; Yang, Zhihua; Lei, Bing-Hua; Kong, Qingrong; Lee, Ming-Hsein; Zhang, Bingbing; Pan, Shilie; Zhang, Jun

    2016-02-17

    As potential candidates for deep-UV nonlinear optical (NLO) crystals, borosilicates and borogermanates, which contain NLO-active groups such as B-O, Si-O and Ge-O, have fascinated many scientists. The crystal structures, electronic structures and optical properties of seven borates in different B/R (R = Si, Ge) ratios have been studied using DFT methods. Through the SHG-density, we find that besides the recognized contribution of the π-conjugation configuration of BO3 to second harmonic generation (SHG), the tetrahedra have a non-negligible influence. This is because the non-bonding p orbitals of the bridging oxygen in the tetrahedra are observably closer to the Fermi level than those in BO3, which is observed in the PDOS of Rb4Ge3B6O17 and RbGeB3O7. This conclusion would be very meaningful in the understanding of the relationship between the crystal structure and nonlinear optical properties. PMID:26844983

  7. Electron escape depth variation in thin SiO2 films measured with variable photon energy

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Grunthaner, F. J.; Pianetta, P.; Johansson, L. I.; Lindau, I.

    1984-01-01

    A double crystal monochromator at the Stanford Synchrotron Radiation Laboratory is used to study the Si/SiO2 interface, using photon energies of hv = 1950-3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 A thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100-3600 eV). These differences are attributed to a strained oxide layer near the interface.

  8. Transverse Ultrasound Measurements in 4He Single Crystals

    NASA Astrophysics Data System (ADS)

    Syshchenko, O.; Beamish, J.

    2008-02-01

    Recently, Kim and Chan (Science 305:1941, 2004; Phys. Rev. Lett. 97:115302, 2006) have reported an anomalous decoupling transition of solid 4He in a torsional oscillator measurement, and interpret their results as evidence for non-classical rotational inertia and a possible supersolid phase of 4He. The detailed nature and properties of such a “supersolid” state in 4He are still far from being clear, although there are clues from experiments involving 3He impurities, different sample cell geometries, annealing effects and grain boundary flow. Defects produced during crystal growth or deformation (e.g. dislocations) may affect supersolidity, or even produce it, and they are expected to have significant impact on the elastic properties of the solid. The supersolid fraction could also decouple from the lattice and produce a decrease in the transverse sound speed. We have begun the experiments in this laboratory to study such effects, measuring the velocity and attenuation of transverse ultrasound at 10 MHz in 4He single crystals grown at constant pressure.

  9. Specific features of transmutational doping of {sup 30}Si-enriched silicon crystals with phosphorus: Studies by the method of electron spin resonance

    SciTech Connect

    Baranov, P. G.; Ber, B. Ya.; Godisov, O. N.; Il'in, I. V. Ionov, A. N.; Kaliteevskii, A. K.; Kaliteevskii, M. A.; Lazebnik, I. M.; Safronov, A. Yu.; Pohl, H.-J.; Riemann, H.; Abrosimov, N. V.; Kop'ev, P. S.; Bulanov, A. D.; Gusev, A. V.

    2006-08-15

    Electron spin resonance (ESR) is used to study the neutron transmutation doping of silicon crystals enriched with {sup 30}Si isotope: phosphorus donors and radiation defects produced in the course of transmutational doping are observed. The ESR signals related to the phosphorus uncontrolled impurity in {sup 30}Si before transmutational doping (the P concentration is {approx}10{sup 15} cm{sup -3}) and phosphorus introduced by neutron irradiation with doses {approx}1 x 10{sup 19} cm{sup -2} and {approx}1 x 10{sup 20} cm{sup -2} (the P concentrations are {approx}5 x 10{sup 16} and {approx}7 x 10{sup 17} cm{sup -3}, respectively) are studied. As a result of drastic narrowing of the phosphorus ESR lines in {sup 30}Si, the intensity of lines increased appreciably, which made it possible to measure the phosphorus concentration in the samples with a small volume (down to 10{sup -6} mm{sup -3}). The methods for determining the concentration of P donors from hyperfine structure in the ESR spectra of isolated P atoms, exchange-related pairs, and clusters that consist of three, four, and more P donors are developed. In the region of high concentrations of P donors, in which case the hyperfine structure disappears, the concentration of P donors was estimated from the exchange-narrowed ESR line.

  10. Si1-xGex crystal growth by the floating zone method starting from SPS sintered feed rods - A segregation study

    NASA Astrophysics Data System (ADS)

    Wagner, A. C.; Cröll, A.; Hillebrecht, H.

    2016-08-01

    The availability of suitable feed rods for Si-Ge bulk crystal growth is known to be a limiting factor in floating zone growth and other growth techniques. In this work, three Si-rich SiGe single crystals were crystallized by an optical floating zone technique in a double ellipsoid mirror furnace. The feed rods were prepared by pre-synthesis in the Spark Plasma Sintering (SPS) process starting with powders of different compositions. In a detailed section the preparation method of consolidation by mechanical alloyed powders to feed rods will be given. Results from two growth experiments starting with uniform compositions with 11 at% and 20 at% germanium as well as a zone leveling experiment with a segmented feed rod consisting of a starting zone with 32 at% Ge will be discussed. The latter experiment resulted in a crystal with nearly no axial segregation.

  11. Theoretical investigation of the formation of basal plane stacking faults in heavily nitrogen-doped 4H-SiC crystals

    NASA Astrophysics Data System (ADS)

    Taniguchi, Chisato; Ichimura, Aiko; Ohtani, Noboru; Katsuno, Masakazu; Fujimoto, Tatsuo; Sato, Shinya; Tsuge, Hiroshi; Yano, Takayuki

    2016-04-01

    The formation of basal plane stacking faults in heavily nitrogen-doped 4H-SiC crystals was theoretically investigated. A novel theoretical model based on the so-called quantum well action mechanism was proposed; the model considers several factors, which were overlooked in a previously proposed model, and provides a detailed explanation of the annealing-induced formation of double layer Shockley-type stacking faults in heavily nitrogen-doped 4H-SiC crystals. We further revised the model to consider the carrier distribution in the depletion regions adjacent to the stacking fault and successfully explained the shrinkage of stacking faults during annealing at even higher temperatures. The model also succeeded in accounting for the aluminum co-doping effect in heavily nitrogen-doped 4H-SiC crystals, in that the stacking fault formation is suppressed when aluminum acceptors are co-doped in the crystals.

  12. Simultaneous NO and NO(2) DIAL measurement using BBO crystals.

    PubMed

    Kölsch, H J; Rairoux, P; Wolf, J P; Wöste, L

    1989-06-01

    We report a new differential absorption lidar technique for measuring simultaneously the concentrations of NO and NO(2) in the atmosphere. The technique is based on the correlation of the 450-nm absorption band of NO(2) and 227-nm absorption band of NO by frequency doubling. This performance has been allowed by the advent of a new and highly efficient frequency doubling crystal: the beta-BaB(2)O(4). A test experiment on a NO/NO(2) emitter has been performed, demonstrating the efficiency of the technique. The detection limit is estimated to be ~1 ppm .m for NO(2) and 100 ppb.m for NO. The range of measurement is limited to 1 km, due to the strong UV Rayleigh scattering and O(2) absorption. PMID:20555467

  13. Thermochromic liquid crystal temperature measurements through a borescope imaging system

    NASA Astrophysics Data System (ADS)

    Kodzwa, Paul M.; Elkins, Christopher J.; Mukerji, Debjit; Eaton, John K.

    2007-10-01

    Thermochromic liquid crystals (TLCs) have proven to be a valuable tool for the collection of full-field, high-resolution heat transfer data. This paper presents an extension of previously developed calibration techniques to a simplified transonic linear cascade for a highly cambered turbine blade geometry. This required the introduction of miniature periscopes to image the measurement surfaces. The procedures and equipment used to ensure high-accuracy wide-band TLC measurements are presented. These included a geometry-matched calibration device, mechanisms to accurately position the borescope imaging optics, an algorithm to automatically divide the imaging region into a large number of calibration subregions (termed as cells), and algorithms to correct for geometric and optical image distortions. The cell calibration approach is shown to halve calibration times and dramatically reduce memory requirements when compared to a pixel-by-pixel calibration. The results of an extensive validation study are presented.

  14. Si K Edge Measurements of the ISM with Chandra

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Corrales, Lia; Canizares, C. R.

    2016-01-01

    The Si K edge structure in X-ray spectra of the diffuse ISM is expected to exhibit substructure related to the fact that most absorption is due to silicates in dust. We surveyed high resolution X-ray spectra of a large number of bright low-mass X-ray binaries with column densities significantly larger than 10^22 cm^2. Using the to date unprecedented spectral resolution of the high energy transmission gratings onboard the Chandra X-ray observatory we find complex substructure in the Si K edge. The highest resolved spectra show two edges, one at the expected value for atomic, one at the value for most silicate compounds with the dominant contribution of the latter. There is specific subtructure from silicate optical depth caused by absorption and scattering. Some is also variable and can be attributed to ionized absorption in the vicinity of the X-ray sources.

  15. Electrochemical Characteristics of Cell Cultured Ti-Nb-Zr Alloys After Nano-Crystallized Si-HA Coating.

    PubMed

    Jeong, Yong-Hoon; Choe, Han-Cheol

    2015-01-01

    The aim of this study was to investigate the electrochemical characteristics of nano crystallized Si-HA coating on Ti-Nb-Zr alloy after human osteoblast like (HOB) cell attachment. The Ti-Nb-Zr alloy was manufactured with 35 wt.% of Nb and 10 wt.% of Zr by arc melting furnace to appropriate physical properties as biomaterials. The HA and Si-substituted coatings were prepared by electron-beam physical vapor deposition method with 0.5, 0.8 and 1.2 wt.% of Si contents, and nano aging treatment was performed 500 degrees C for 1 h. The characteristics of coating surface were analyzed by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. To evaluate of cell attachment on cell cultured surface, the potentiodynamic test was performed on the surface using HOB cells. The results showed that the Si-HA coating surface showed higher tendency of cell attachment than that of single HA coating, corrosion resistance value was increased by dense of cell attachment. PMID:26328326

  16. Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals

    DOE PAGESBeta

    Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar

    2016-02-26

    Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materialsmore » as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.« less

  17. Accurate structural study of langasite-family Ca3TaGa3Si2O14 crystal

    NASA Astrophysics Data System (ADS)

    Dudka, A. P.

    2016-03-01

    An accurate X-ray diffraction study of Ca3TaGa3Si2O14 single crystal has been performed using two datasets obtained on a diffractometer equipped with a CCD area detector ( a = 8.1056(2) Å, c = 4.9800(1) Å, sp. gr. P321, Z = 1, R/ wR = 0.486/0.488%). A model structure is determined which is characterized by a high degree of reproducibility of structural parameters. Each site in Ca3TaGa3Si2O14 is occupied by atoms of only one type. Nevertheless, its structural feature is asymmetric disordering of sites of Ca, Ta, Ga, and two out of three oxygen atoms occupying special and general sites. A transition of some part of Ca atoms (~3%) from 3 e sites on the twofold symmetry axis to general 6 g sites is revealed.

  18. Electron-ion recombination of Si IV forming Si III: Storage-ring measurement and multiconfiguration Dirac-Fock calculations

    SciTech Connect

    Schmidt, E. W.; Bernhardt, D.; Mueller, A.; Schippers, S.; Fritzsche, S.; Hoffmann, J.; Jaroshevich, A. S.; Krantz, C.; Lestinsky, M.; Orlov, D. A.; Wolf, A.; Lukic, D.; Savin, D. W.

    2007-09-15

    The electron-ion recombination rate coefficient for Si IV forming Si III was measured at the heavy-ion storage-ring TSR. The experimental electron-ion collision energy range of 0-186 eV encompassed the 2p{sup 6}nln{sup '}l{sup '} dielectronic recombination (DR) resonances associated with 3s{yields}nl core excitations, 2s2p{sup 6}3snln{sup '}l{sup '} resonances associated with 2s{yields}nl (n=3,4) core excitations, and 2p{sup 5}3snln{sup '}l{sup '} resonances associated with 2p{yields}nl (n=3,...,{infinity}) core excitations. The experimental DR results are compared with theoretical calculations using the multiconfiguration Dirac-Fock (MCDF) method for DR via the 3s{yields}3pn{sup '}l{sup '} and 3s{yields}3dn{sup '}l{sup '}(both n{sup '}=3,...,6) and 2p{sup 5}3s3ln{sup '}l{sup '} (n{sup '}=3,4) capture channels. Finally, the experimental and theoretical plasma DR rate coefficients for Si IV forming Si III are derived and compared with previously available results.

  19. BaAl4 derivative phases in the sections {La,Ce}Ni2Si2-{La,Ce}Zn2Si2: phase relations, crystal structures and physical properties.

    PubMed

    Failamani, Fainan; Malik, Zahida; Salamakha, Leonid; Kneidinger, Friedrich; Grytsiv, Andriy; Michor, Herwig; Bauer, Ernst; Giester, Gerald; Rogl, Peter

    2016-03-28

    Phase relations and crystal structures have been evaluated within the sections LaNi2Si2-LaZn2Si2 and CeNi2Si2-CeZn2Si2 at 800 °C using electron microprobe analysis and X-ray powder and single crystal structure analyses. Although the systems La-Zn-Si and Ce-Zn-Si at 800 °C do not reveal compounds such as "LaZn2Si2" or "CeZn2Si2", solid solutions {La,Ce}(Ni1-xZnx)2Si2 exist with the Ni/Zn substitution starting from {La,Ce}Ni2Si2 (ThCr2Si2-type; I4/mmm) up to x = 0.18 for Ce(Ni1-xZnx)2Si2 and x = 0.125 for La(Ni1-xZnx)2Si2. For higher Zn-contents 0.25 ≤ x ≤ 0.55 the solutions adopt the CaBe2Ge2-type (P4/nmm). The investigations are backed by single crystal X-ray diffraction data for Ce(Ni0.61Zn0.39)2Si2 (P4/nmm; a = 0.41022(1) nm, c = 0.98146(4) nm; RF = 0.012) and by Rietveld refinement for La(Ni0.56Zn0.44)2Si2 (P4/nmm; a = 0.41680(6) nm, c = 0.99364(4) nm; RF = 0.043). Interestingly, the Ce-Zn-Si system contains a ternary phase CeZn2(Si1-xZnx)2 of the ThCr2Si2 structure type (0.25 ≤ x ≤ 0.30 at 600 °C), which forms peritectically at T = 695 °C but does not include the composition "CeZn2Si2". The primitive high temperature tetragonal phase with the CaBe2Ge2-type has also been observed for the first time in the Ce-Ni-Si system at CeNi2+xSi2-x, x = 0.33 (single crystal data, P4/nmm; a = 0.40150(2) nm, c = 0.95210(2) nm; RF = 0.0163). Physical properties (from 400 mK to 300 K) including specific heat, electrical resistivity and magnetic susceptibility have been elucidated for Ce(Ni0.61Zn0.39)2Si2 and La(Ni0.56Zn0.44)2Si2. Ce(Ni0.61Zn0.39)2Si2 exhibits a Kondo-type ground state. Low temperature specific heat data of La(Ni0.56Zn0.44)2Si2 suggest a spin fluctuation scenario with an enhanced value of the Sommerfeld constant. PMID:26895373

  20. Time-Domain Thermoreflectance Measurements of Thermal Transport in Amorphous SiC Thin Films

    NASA Astrophysics Data System (ADS)

    Daly, Brian; Hondongwa, Donald; King, Sean

    2010-03-01

    We present ultrafast optical pump-probe measurements of thermal transport in a series of amorphous SiC samples. The samples were grown on Si wafers by plasma enhanced chemical vapor deposition utilizing various combinations of methylsilanes and H2 and He diluent gases. The sample films were well characterized and found to have densities (1.3 -- 2.3 g cm-3) and dielectric constants (4.0 -- 7.2) that spanned a wide range of values. Prior to their measurement, the samples were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser that produced sub-picosecond pulses of a few nJ. The pulses heat the Al coating, causing a transient reflectivity change. As the Al film cools into the SiC film, the reflectivity change can be measured, giving a measure of the thermal effusivity of the SiC film. We then extract values for the thermal conductivity of the SiC films and find that it varies from less than half of the thermal conductivity of amorphous SiO2 for the lower density materials to somewhat larger than amorphous SiO2 for the highest density films.

  1. Simple and quick enhancement of SiC bulk crystal growth using a newly developed crucible material

    NASA Astrophysics Data System (ADS)

    Nakamura, Daisuke

    2016-05-01

    Newly developed highly reliable low-cost TaC-coated graphite materials prepared by a wet ceramic process were applied to SiC sublimation growth. We demonstrated an increased long-duration growth rate and a resultant increase in crystal size by a factor of ∼1.2 (experimental value) after 24 h of growth [and ∼1.5 (extrapolated value) after the optimum duration of 53.1 h] by simply and quickly replacing graphite crucibles with TaC-coated graphite crucibles. Growth with the TaC-coated graphite crucibles reduced source gas leakage and increased the material yield for single crystals because the TaC layers were gas-tight and had a low emissivity.

  2. Crystal structure and electronic properties of the new compounds, U{sub 6}Fe{sub 16}Si{sub 7} and its interstitial carbide U{sub 6}Fe{sub 16}Si{sub 7}C

    SciTech Connect

    Berthebaud, D.; Tougait, O. Potel, M.; Lopes, E.B.; Goncalves, A.P.

    2007-10-15

    The new compounds U6Fe16Si7 and U6Fe16Si7C were prepared by arc-melting and subsequent annealing at 1500 deg. C. Single-crystal X-ray diffraction showed that they crystallize in the cubic space group Fm3-barm (No. 225), with unit-cell parameters at room temperature a=11.7206(5) A for U6Fe16Si7 and a=11.7814(2) A for U6Fe16Si7C. Their crystal structures correspond to ordered variants of the Th6Mn23 type. U6Fe16Si7 adopts the Mg6Cu16Si7 structure type, whereas U6Fe16Si7C crystallizes with a novel 'filled' quaternary variant. The inserted carbon is located in octahedral cages formed by six U atoms, with U-U interatomic distances of 3.509(1) A. Insertion of carbon in the structure of U6Fe16Si7 has a direct influence on the U-Fe and Fe-Fe interatomic distances. The electronic properties of both compounds were investigated by means of DC susceptibility, electrical resistivity and thermopower. U6Fe16Si7 is a Pauli paramagnet. Its electrical resistivity and thermopower point out that it cannot be classified as a simple metal. The magnetic susceptibility of U{sub 6}Fe{sub 16}Si{sub 7}C is best described over the temperature range 100-300 K by using a modified Curie-Weiss law with an effective magnetic moment of 2.3(2) {mu}{sub B}/U, a paramagnetic Weiss temperature, {theta}{sub p}=57(2) K and a temperature-independent term {chi}{sub 0}=0.057(1) emu/mol. Both the electrical resistivity and thermopower reveal metallic behavior. - Graphical abstract: The new compounds U{sub 6}Fe{sub 16}Si{sub 7} and U{sub 6}Fe{sub 16}Si{sub 7}C crystallize with the ternary ordered variant of the Th{sub 6}Mn{sub 23} type, commonly referred as Mg{sub 6}Cu{sub 16}Si7 and with a novel 'filled' variant of this type of structure, respectively.

  3. Crystal structure of (tert-butyl­dimethyl­sil­yl)tri­phenyl­germane, Ph3Ge-SiMe2(t-Bu)

    PubMed Central

    Zaitsev, Kirill V.; Zaitseva, Galina S.; Karlov, Sergey S.; Korlyukov, Alexander A.

    2015-01-01

    In the title compound, Ph3Ge-SiMe2(t-Bu) or C24H30GeSi, the Si and Ge atoms both possess a tetra­hedral coordination environment with C—E—C (E = Si, Ge) angles in the range 104.47 (5)–114.67 (5)°. The mol­ecule adopts an eclipsed conformation, with three torsion angles less than 29.5°. In the crystal, neighbouring mol­ecules are combined to dimers by six T-shaped C—H⋯π inter­actions, forming sixfold phenyl embraces (6PE). PMID:26870472

  4. Rheo-NMR Measurements of Cocoa Butter Crystallized Under

    SciTech Connect

    Mudge, E.; Mazzanti, G

    2009-01-01

    Modifications of a benchtop NMR instrument were made to apply temperature control to a shearing NMR cell. This has enabled the determination in situ of the solid fat content (SFC) of cocoa butter under shearing conditions. The cocoa butter was cooled at 3 C/min to three final temperatures of 17.5, 20.0, and 22.5 C with applied shear rates between 45 and 720 s-1. Polymorphic transitions of the cocoa butter were determined using synchrotron X-ray diffraction with an identical shearing system constructed of Lexan. Sheared samples were shown to have accelerated phase transitions compared to static experiments. In experiments where form V was confirmed to be the dominant polymorph, the final SFC averaged around 50%. However, when other polymorphic forms were formed, a lower SFC was measured because the final temperature was within the melting range of that polymorph and only partial crystallization happened. A shear rate of 720 s-1 delayed phase transitions, likely due to viscous heating of the sample. Pulsed NMR is an invaluable tool for determining the crystalline fraction in hydrogen containing materials, yet its use for fundamental and industrial research on fat or alkanes crystallization under shear has only recently been developed.

  5. Controlled sputtering of AlN (002) and (101) crystal orientations on epitaxial 3C-SiC-on-Si (100) substrate

    NASA Astrophysics Data System (ADS)

    Iqbal, A.; Walker, G.; Iacopi, A.; Mohd-Yasin, F.

    2016-04-01

    Aluminum Nitride (AlN) thin films are successfully deposited on epitaxial 3C-SiC-on-Si (100) substrates using DC magnetron sputterer. The sputtered films are characterized on the following parameters: crystal orientations (Siemens D500 X-Ray diffraction tool), deposition rate (Nanospec AFT 180), surface roughness (Park NX20 Atomic Force Microscopy), refractive index (Rudolph AutoEL IV Ellipsometer), in-plane stress (Tencor Flexus 2320 System) and Raman Spectra (Rennishaw InVia Spectrometer). XRD results demonstrate that the orientation of the AlN thin films can be changed from (002) to (101) by increasing the Nitrogen to Argon ratio from 40% to 80% at the total gas flow of 50 sccm. We are also able to tune the in-plane stress via RF biasing on the substrate. Both controlling abilities enable the applications of these thin films for low cost longitudinal piezoelectric devices and a quasi-shear mode devices using (002) and (101) orientations, respectively.

  6. Photocapacitance and hole drift mobility measurements in hydrogenated amorphous silicon (a-Si:H)

    SciTech Connect

    Nurdjaja, I.; Schiff, E.A.

    1997-07-01

    The authors present measurements of the photocapacitance in hydrogenated amorphous silicon (a-Si:H) Schottky barrier diodes under reverse bias. A calculation relating photocapacitance to hole drift mobility measurements is also presented; the calculation incorporates the prominent dispersion effect for holes in a-Si:H usually attributed to valence bandtail trapping. The calculation accounts quantitatively for the magnitude and voltage-dependence of the photocapacitance.

  7. Two isostructural layered oxohalide compounds containing Mn{sup 2+}, Te{sup 4+} and Si{sup 4+}; crystal structure and magnetic susceptibility

    SciTech Connect

    Zimmermann, Iwan; Kremer, Reinhard K.; Johnsson, Mats

    2014-10-15

    The new compounds Mn{sub 4}(TeO{sub 3})(SiO{sub 4})X{sub 2} (X=Br, Cl) were synthesized by solid state reactions in sealed evacuated silica tubes. The compounds crystallize in the monoclinic space group P2{sub 1}/m with the unit cell parameters a=5.5463(3) Å (5.49434(7) Å), b=6.4893(4) Å (6.44184(9) Å), c=12.8709(7) Å (12.60451(18) Å), β=93.559(5)° (94.1590(12)°) and Z=2 for the respective Br and Cl analogues. Manganese adopts various distorted coordination polyhedra; [MnO{sub 6}] octahedra, [MnO{sub 5}] tetragonal pyramids and [MnO{sub 2}X{sub 2}] tetrahedra. Other building blocks are [SiO{sub 4}] tetrahedra and [TeO{sub 3}] trigonal pyramids. The structure is made up from layers having no net charge that are connected via weak Van der Waal interactions. The layers that are parallel to (1 1 0) consist of two manganese oxide sheets which are separated by [SiO{sub 4}] tetrahedra. On the outer sides of the sheets are the [MnO{sub 2}X{sub 2}] tetrahedra and the [TeO{sub 3}] trigonal pyramids connected so that the halide ions and the stereochemically active lone pairs on the tellurium atoms protrude from the layers. Magnetic susceptibility measurements reveal a Curie law with a Weiss temperature of θ=−153(3) K for temperatures ≥100 K and indicate antiferromagnetic ordering at T{sub N} ∼4 K. Possible structural origins of the large frustration parameter of f=38 are discussed. - Graphical abstract: Table of contents caption. The new compounds Mn{sub 4}(TeO{sub 3})(SiO{sub 4})X{sub 2} (X=Br, Cl) are layered with weak Van der Waal interactions in between the layers. Manganese adopts various distorted coordination polyhedral, other building blocks are [SiO{sub 4}] tetrahedra and [TeO{sub 3}] trigonal pyramids. Magnetic susceptibility measurements indicate antiferromagnetic ordering at low temperatures and a large frustration parameter. - Highlights: • Two new isostructural oxohalide compounds are described. • The compounds are the first examples of

  8. The Influence of Na2O on the Solidification and Crystallization Behavior of CaO-SiO2-Al2O3-Based Mold Flux

    NASA Astrophysics Data System (ADS)

    Gao, Jinxing; Wen, Guanghua; Sun, Qihao; Tang, Ping; Liu, Qiang

    2015-08-01

    The reaction between [Al] and SiO2 sharply increased the Al2O3 and decreased SiO2 contents in mold flux during the continuous casting of high-Al steels. These changes converted original CaO-SiO2-based flux into CaO-SiO2-Al2O3-based flux, promoting the crystallization and deteriorating the mold lubrication. Therefore, study on the solidification and crystallization behavior of CaO-SiO2-Al2O3-based mold flux, with the applicable fluidizers, is of importance. The effect of Na2O, predominantly used as the fluidizer in mold flux, on the solidification and crystallization behavior of CaO-SiO2-Al2O3-based mold flux needs to be investigated. In this study, a CaO-SiO2-Al2O3-based mold flux containing 6.5 wt pct Li2O was designed; the effect of Na2O on the solidification and crystallization behavior of these mold fluxes was investigated using the single hot thermocouple technique (SHTT) and the double hot thermocouple technique (DHTT). Moreover, the slag film obtained by a heat flux simulator was analyzed using X-ray diffraction (XRD). The results indicate that the solid fraction of molten slag (Fs) and the crystalline fraction of solid slag (Fc) in the mold slag films decrease with increasing Na2O content from 0 to 2 wt pct. However, Fs and Fc increased when the Na2O content increased from 2 to 6 wt pct. The critical cooling rates initially decreases and then increases with increasing Na2O content. The XRD analysis results show that LiAlO2 and CaF2 were the basic crystals for all the mold fluxes. Increasing the Na2O content both inhibits the Ca2Al2SiO7 formation and promotes the production of Ca12Al14O33, indicating that the mold lubrication deteriorated because of the high melting-point phase formation of Ca2Al2SiO7 in the CaO-SiO2-Al2O3-based mold flux containing 6.5 wt pct Li2O, without Na2O. The strong crystallization tendency also deteriorated the mold lubrication for the mold flux with a higher Na2O content. Therefore, the addition of Na2O was less than 2 wt pct in

  9. Pixelated Single-crystal Diamond Detector for fast neutron measurements

    NASA Astrophysics Data System (ADS)

    Rebai, M.; Cazzaniga, C.; Croci, G.; Tardocchi, M.; Perelli Cippo, E.; Calvani, P.; Girolami, M.; Trucchi, D. M.; Grosso, G.; Gorini, G.

    2015-03-01

    Single-crystal Diamond Detectors (SDDs), due to their high radiation hardness, fast response time and small size, are good candidates as fast neutron detectors in those environments where the high neutron flux is an issue, such as spallation neutron sources and the next generation thermonuclear fusion plasmas, i.e. the ITER experiment. Neutron detection in SDDs is based on the collection of electron-hole pairs produced by charged particles generated by neutron interactions with 12C. Recent measurements have demonstrated the SDD capability of measuring the neutron flux with a good energy resolution and at high rates. In this work a novel detector based on a 12-pixels SDD matrix will be presented. Each pixel is equipped with an independent electronic chain: the fast shaping preamplifier coupled to a digitizer is able to combine the high rate capability and the good energy resolution. Two CAEN digitizers are compared and the possibility of performing good energy resolution measurements (<2%) and at high rates (>1 MHz per channel) is described. Each pixel was characterized and calibrated using an 241Am source: the energy resolution was evaluated and gives a mean value of 1.73% at 5.5 MeV. The good energy resolution achieved and its uniformity between pixels are the demonstration of the capability of this novel detector as a spectrometer. This system will be installed during the next Deuterium-Tritium campaign on a collimated vertical line of sight at JET for 14 MeV neutron measurements.

  10. High-speed and high-efficiency Si optical modulator with MOS junction, using solid-phase crystallization of polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Fujikata, Junichi; Takahashi, Masashi; Takahashi, Shigeki; Horikawa, Tsuyoshi; Nakamura, Takahiro

    2016-04-01

    We developed a high-speed and high-efficiency MOS-capacitor-type Si optical modulator (Si-MOD) by applying a low optical loss and a low resistivity of a polycrystalline silicon (poly-Si) gate with large grains. To achieve a low resistivity of a poly-Si film, a P-doped poly-Si film based on Si2H6 solid-phase crystallization (SPC) was developed, which showed a comparable resistivity to that of P-doped single-crystal Si. In addition, high-temperature annealing (HTA) after SPC was effective for realizing low optical loss. We designed the optimum Si-MOD structure and demonstrated a very high modulation efficiency of 0.3 V cm, which is very efficient among the Si-MODs developed thus far. High-speed (15 Gbps) operation was achieved with a small footprint of the 200-µm-long phase shifter and a low drive voltage of 1.5 Vpp at a low optical insertion loss of -2.2 dB and 1.55 µm wavelength.

  11. Crystallization from high temperature solutions of Si in Cu/Al solvent

    DOEpatents

    Ciszek, Theodore F.; Wang, Tihu

    1996-01-01

    A liquid phase epitaxy method for forming thin crystalline layers of device quality silicon having less than 3.times.10.sup.16 Cu atoms/cc impurity, comprising: preparing a saturated liquid solution of Si in a Cu/Al solvent at about 20 to about 40 at. % Si at a temperature range of about 850.degree. to about 1100.degree. C. in an inert gas; immersing or partially immersing a substrate in the saturated liquid solution; super saturating the solution by lowering the temperature of the saturated solution; holding the substrate in the saturated solution for a period of time sufficient to cause Si to precipitate out of solution and form a crystalline layer of Si on the substrate; and withdrawing the substrate from the solution.

  12. Crystallization from high temperature solutions of Si in Cu/Al solvent

    DOEpatents

    Ciszek, T.F.; Wang, T.

    1996-08-13

    A liquid phase epitaxy method is disclosed for forming thin crystalline layers of device quality silicon having less than 3{times}10{sup 16} Cu atoms/cc impurity, comprising: preparing a saturated liquid solution of Si in a Cu/Al solvent at about 20 to about 40 at. % Si at a temperature range of about 850 to about 1100 C in an inert gas; immersing or partially immersing a substrate in the saturated liquid solution; super saturating the solution by lowering the temperature of the saturated solution; holding the substrate in the saturated solution for a period of time sufficient to cause Si to precipitate out of solution and form a crystalline layer of Si on the substrate; and withdrawing the substrate from the solution. 3 figs.

  13. Measuring liquid crystal elastic constants with free energy perturbations.

    PubMed

    Joshi, Abhijeet A; Whitmer, Jonathan K; Guzmán, Orlando; Abbott, Nicholas L; de Pablo, Juan J

    2014-02-14

    A first principles method is proposed to calculate the Frank elastic constants of nematic liquid crystals. These include the constants corresponding to standard splay, twist and bend deformations, and an often-ignored surface-like contribution known as saddle-splay. The proposed approach is implemented on the widely studied Gay-Berne (3, 5, 2, 1) model [J. G. Gay and B. J. Berne, J. Chem. Phys., 1981, 74, 3316], and the effects of temperature and system size on the elastic constants are examined in the nematic phase. The results of simulations for splay, twist, and bend elastic constants are consistent with those from previous literature reports. The method is subsequently applied to the saddle-splay elastic constant k24 which is found to exist at the limits of the Ericksen inequalities governing positive definite free energy. Finally, extensions of the method are discussed that present a new paradigm for in silico measurements of elastic constants. PMID:24837037

  14. Si1-x Ge x /Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing.

    PubMed

    Morris, R J H; Hase, T P A; Sanchez, A M; Rowlands, G

    2016-10-01

    The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O2 (+) over an energy range of 0.25-2.5 keV were used to probe the interface between Si0.73Ge0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS. Graphical Abstract ᅟ. PMID:27444703

  15. Si1-x Ge x /Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing

    NASA Astrophysics Data System (ADS)

    Morris, R. J. H.; Hase, T. P. A.; Sanchez, A. M.; Rowlands, G.

    2016-07-01

    The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O2 + over an energy range of 0.25-2.5 keV were used to probe the interface between Si0.73Ge0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS.

  16. Investigation of crystal surface finish and geometry on single LYSO scintillator detector performance for depth-of-interaction measurement with silicon photomultipliers

    NASA Astrophysics Data System (ADS)

    Bircher, Chad; Shao, Yiping

    2012-11-01

    Depth of Interaction (DOI) information can improve quality of reconstructed images acquired from Positron Emission Tomography (PET), especially in high resolution and compact scanners dedicated for breast, brain, or small animal imaging applications. Additionally, clinical scanners with time of flight capability can also benefit from DOI information. One of the most promising methods of determining DOI in a crystal involves reading the signal from two ends of a scintillation crystal, and calculating the signal ratio between the two detectors. This method is known to deliver a better DOI resolution with rough crystals compared to highly polished crystals. However, what is still not well studied is how much of a tradeoff is involved between spatial, energy, temporal, and DOI resolutions as a function of the crystal surface treatment and geometry with the use of Silicon Photomultipliers (SiPM) as the photo detectors. This study investigates the effects of different crystal surface finishes and geometries on energy, timing and DOI resolutions at different crystal depths. The results show that for LYSO scintillators of 1.5×1.5×20 mm3 and 2×2×20 mm3 with their surfaces finished from 0.5 to 30 μm roughness, almost the same energy and coincidence timing resolutions were maintained, around 15% and 2.4 ns, respectively across different crystal depths, while the DOI resolutions were steadily improved from worse than 5 mm to better than 2 mm. They demonstrate that crystal roughness, with proper surface preparing, does not have a significant effect on the energy and coincidence timing resolutions in the crystals examined, and there does not appear to be a tradeoff between improving DOI resolution and degrading other detector performances. These results will be valuable to guide the selection of crystal surface conditions for developing a DOI measurable PET detector with a full array of LYSO scintillators coupled to SiPM arrays.

  17. Investigation of Crystal Surface Finish and Geometry on Single LYSO Scintillator Detector Performance for Depth-of-Interaction Measurement with Silicon Photomultipliers

    PubMed Central

    Bircher, Chad

    2012-01-01

    Depth of Interaction (DOI) information can improve quality of reconstructed images acquired from Positron Emission Tomography (PET), especially in high resolution and compact scanners dedicated for breast, brain, or small animal imaging applications. Additionally, clinical scanners with time of flight capability can also benefit from DOI information. One of the most promising methods of determining DOI in a crystal involves reading the signal from two ends of a scintillation crystal, and calculating the signal ratio between the two detectors. This method is known to deliver a better DOI resolution with rough crystals compared to highly polished crystals. However, what is still not well studied is how much of a tradeoff is involved between spatial, energy, temporal, and DOI resolutions as a function of the crystal surface treatment and geometry with the use of Silicon Photomultipliers (SiPM) as the photo detectors. This study investigates the effects of different crystal surface finishes and geometries on energy, timing and DOI resolutions at different crystal depths. The results show that for LYSO scintillators of 1.5×1.5×20 mm3 and 2×2×20 mm3 with their surfaces finished from 0.5 to 30 micron roughness, almost the same energy and coincidence timing resolutions were maintained, around 15% and 2.4 ns respectively across different crystal depths, while the DOI resolutions were steadily improved from worse than 5 mm to better than 2 mm. They demonstrate that crystal roughness, with proper surface preparing, does not have a significant effect on the energy and coincidence timing resolutions in the crystals examined, and there does not appear to be a tradeoff between improving DOI resolution and degrading other detector performances. These results will be valuable to guide the selection of crystal surface conditions for developing a DOI measurable PET detector with a full array of LYSO scintillators coupled to SiPM arrays. PMID:23087497

  18. On the tensoresistance of n-Ge and n-Si crystals with radiation-induced defects

    SciTech Connect

    Gaidar, G. P.

    2015-09-15

    A variation in the tensoresistance of n-Ge:Sb and n-Si:As crystals as a result of irradiation with γ-ray photons ({sup 60}Co source) at fixed temperatures under conditions of the application of uniaxial elastic stress (0 ≤ X ≤ 1.2 GPa) along the main crystallographic direction is studied. It is found that, in the case of the deformation axis being in an asymmetric position relative to the isoenergetic ellipsoids, there is a maximum for the dependences of the tensoresistance ρ{sub X}/ρ{sub 0} = f(X); an explanation as to the nature of the observed effect is suggested. Tensoresistance is revealed in unirradiated n-Si:As crystals in the case of the deformation axis being in a symmetric position relative to all isoenergetic ellipsoids; the value of the tensoresistance as a result of irradiation with γ-ray photons decreases. It is shown that this effect can be attributed to a variation in the mobility of electrons in the conduction band as a result of an increase in the transverse effective mass and the appearance of new deep-level centers under the effect of irradiation, respectively.

  19. Effects of ultrasonic agitation and surfactant additive on surface roughness of Si (111) crystal plane in alkaline KOH solution.

    PubMed

    Jiao, Qingbin; Tan, Xin; Zhu, Jiwei; Feng, Shulong; Gao, Jianxiang

    2016-07-01

    In the silicon wet etching process, the "pseudo-mask" formed by the hydrogen bubbles generated during the etching process is the reason causing high surface roughness and poor surface quality. Based upon the ultrasonic mechanical effect and wettability enhanced by isopropyl alcohol (IPA), ultrasonic agitation and IPA were used to improve surface quality of Si (111) crystal plane during silicon wet etching process. The surface roughness Rq is smaller than 15nm when using ultrasonic agitation and Rq is smaller than 7nm when using IPA. When the range of IPA concentration (mass fraction, wt%) is 5-20%, the ultrasonic frequency is 100kHz and the ultrasound intensity is 30-50W/L, the surface roughness Rq is smaller than 2nm when combining ultrasonic agitation and IPA. The surface roughness Rq is equal to 1nm when the mass fraction of IPA, ultrasound intensity and the ultrasonic frequency is 20%, 50W and 100kHz respectively. The experimental results indicated that the combination of ultrasonic agitation and IPA could obtain a lower surface roughness of Si (111) crystal plane in silicon wet etching process. PMID:26964944

  20. First measurements of charge carrier density and mobility of in-situ enriched 28Si

    NASA Astrophysics Data System (ADS)

    Ramanayaka, A. N.; Dwyer, K. J.; Kim, Hyun-Soo; Stewart, M. D., Jr.; Pomeroy, J. M.

    Magnetotransport in top gated Hall bar devices is investigated to characterize the electrical properties of in-situ enriched 28Si. Isotopically enriched 28Si is an ideal candidate for quantum information processing devices as the elimination of unpaired nuclear spins improves the fidelity of the quantum information. Using mass filtered ion beam deposition we, in-situ, enrich and deposit epitaxial 28Si, achieving several orders of magnitude better enrichment compared to other techniques. In order to explore the electrical properties and optimize the growth conditions of in-situ enriched 28Si we perform magnetotransport measurements on top gated Hall bar devices at temperatures ranging from 300 K to cryogenic temperatures and at moderate magnetic fields. Here, we report on the charge carrier density and mobility extracted from such experiments, and will be compared among different growth conditions of in-situ enriched 28Si.

  1. Relaxation measurements of the persistent photoconductivity in sulfur-doped a-Si:H

    SciTech Connect

    Quicker, D.; Kakalios, J.

    1996-12-31

    The slow relaxation of the persistent photoconductivity (PPC) effect in sulfur-doped hydrogenated amorphous silicon (a-Si:H) has been measured as a function of temperature and illumination time. The relaxation is found to be thermally activated, with an activation energy which varies with sulfur concentration, while illuminating the film for a longer time leads to a longer relaxation time. A correlation is observed between changes of the photoconductivity during illumination and the magnitude of the PPC effect following illumination. These effects are also observed in compensated a-Si:H, suggesting that the mechanism for the PPC effect is the same in both sulfur-doped a-Si:H and compensated a-Si:H. The presence of donor and compensating acceptor states in sulfur-doped a-Si:H could arise from valence alternation pair sulfur atom defects.

  2. Assessing the quality of x-ray optic surfaces of Si crystals cut by diamond-wire and rotating-blade sawing techniques.

    SciTech Connect

    Wieczorek, M.; Huang, X.; Maj, J.; Conley, R.; Qian, J.; Macrander, A.; Christensen, C.; Hodsden, J.; Khachatryan, R.

    2008-01-01

    The next generation of X-ray diffraction optics will benefit from crystal surfaces with very high quality (extremely flat and strain-free), but knowledge on how to achieve such surfaces and how surface imperfections affect the diffraction properties is sparse in the literature. As a first step to initialize a systematic study on this topic, we evaluate in this paper the surface quality of two Si (111) wafers cut by a diamond-wire saw and a rotating blade saw, respectively. We concentrate on revealing lattice strains induced by the two cutting methods and on strain evolution during three rounds of chemical etching (without polishing). The measurements also provide some important clues as to how surface roughness affects rocking curve widths and other diffraction properties.

  3. Mesoporogen-Free Synthesis of Hierarchically Structured Zeolites with Variable Si/Al Ratios via a Steam-Assisted Crystallization Process.

    PubMed

    He, Xiaoyun; Ge, Tongguang; Hua, Zile; Zhou, Jian; Lv, Jian; Zhou, Jinling; Liu, Zhicheng; Shi, Jianlin

    2016-03-23

    In the absence of additional mesoporous template, hierarchically structured zeolites (HSZs) with variable Si/Al ratios (30-150) have been successfully synthesized via a newly developed steam-assisted crystallization process. The synthesized materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, solid-state nuclear magnetic resonance, and ammonia temperature-programmed desorption. All these results prove that the synthesized materials feature high crystallinity (microporous framework) and auxiliary mesoporous structure. In the model reactions of isopropylbenzene and 1,3,5-triisopropylbenzene cracking, compared to purely microporous ZSM-5 counterparts, here synthesized HSZs exhibited markedly enhanced catalytic performances resulting from their enlarged external surface area and shortened diffusion length in the microporous system. PMID:26928368

  4. Optical, scintillation properties and defect study of Gd2Si2O7:Ce single crystal grown by floating zone method

    NASA Astrophysics Data System (ADS)

    Feng, He; Xu, Wusheng; Ren, Guohao; Yang, Qiuhong; Xie, Jianjun; Xu, Jun; Xu, Jiayue

    2013-02-01

    Single crystal of Gd2Si2O7:Ce (GPS) presenting attractive scintillation performance was grown by the floating zone method. The vacuum ultra-violet (VUV) excitation and emission, ultra-violet (UV) excitation and emission spectra and fluorescent decay time at 77 K and RT were measured and discussed. Relative energy levels of 5d sublevels of Ce3+ in GPS:Ce are detected by the VUV excitation spectrum. The UV emission curve of GPS:1%Ce peaks around 382 nm at 77 K and moves towards longer wavelength direction as temperature increases. Thermally stimulated luminescence (TSL) was employed to investigate the defects in GPS:1%Ce. Energy depths of two traps detected in GPS:1%Ce are 0.64 and 1.00 eV.

  5. Vertical alignment of liquid crystal through ion beam exposure on oxygen-doped SiC films deposited at room temperature

    SciTech Connect

    Son, Phil Kook; Park, Jeung Hun; Kim, Jae Chang; Yoon, Tae-Hoon; Rho, Soon Joon; Jeon, Back Kyun; Shin, Sung Tae; Kim, Jang Sub; Lim, Soon Kwon

    2007-09-03

    The authors report the vertical alignment of liquid crystal (LC) through the ion beam exposure on amorphous oxygen-doped SiC (SiOC) film surfaces deposited at room temperature. The optical transmittance of these films was similar to that of polyimide layers, but much higher than that of SiO{sub x} films. The light leakage of a LC cell aligned vertically on SiOC films was much lower than those of a LC cell aligned on polyimide layers or other inorganic films. They found that LC molecules align vertically on ion beam treated SiOC film when the roughness of the electrostatic force microscopy (EFM) data is high on the SiOC film surface, while they align homogeneously when the roughness of the EFM data is low.

  6. Experimental location of helium atoms in 6H-SiC crystal lattice after implantation and after annealing at 400 °C

    NASA Astrophysics Data System (ADS)

    Linez, F.; Garrido, F.; Erramli, H.; Sauvage, T.; Courtois, B.; Desgardin, P.; Barthe, M.-F.

    2015-04-01

    The question of the helium behavior in silicon carbide has been studied at the atomic scale by numerical simulations, but no experiment has been carried out to assess the results hitherto. This paper describes the first experiments allowing this comparison. 6H-SiC single crystals were implanted with 50-keV He ions at a fluence of 1015 He/cm2 at room temperature. The as-received and as-implanted samples were analyzed by RBS and NRA in channeling mode along the main crystallographic planes and across three main axes. The measurements have shown that a portion of the He is located in the interstitial tetrahedral sites as predicted by the numerical simulations. The same measurements were performed on an implanted sample subsequently annealed at 400 °C under Ar atmosphere. They have shown that the quantity of He detected in interstitial tetrahedral sites TSi and TC has not significantly changed whereas that of He detected in the main crystallographic plane and in the main axis has increased. This increase is likely caused by He atoms migration at 400 °C toward interstitial positions located inside vacancies such as VSi and VSiVC. In parallel a partial recovery of the Si and C sublattices has been observed.

  7. Crystal Phase Transformation in Self-Assembled InAs Nanowire Junctions on Patterned Si Substrates.

    PubMed

    Rieger, Torsten; Rosenbach, Daniel; Vakulov, Daniil; Heedt, Sebastian; Schäpers, Thomas; Grützmacher, Detlev; Lepsa, Mihail Ion

    2016-03-01

    We demonstrate the growth and structural characteristics of InAs nanowire junctions evidencing a transformation of the crystalline structure. The junctions are obtained without the use of catalyst particles. Morphological investigations of the junctions reveal three structures having an L-, T-, and X-shape. The formation mechanisms of these structures have been identified. The NW junctions reveal large sections of zinc blende crystal structure free of extended defects, despite the high stacking fault density obtained in individual InAs nanowires. This segment of zinc blende crystal structure in the junction is associated with a crystal phase transformation involving sets of Shockley partial dislocations; the transformation takes place solely in the crystal phase. A model is developed to demonstrate that only the zinc blende phase with the same orientation as the substrate can result in monocrystalline junctions. The suitability of the junctions to be used in nanoelectronic devices is confirmed by room-temperature electrical experiments. PMID:26881450

  8. Objective Crystal Spectrometer (OXS) on the Spectrum-X-y satellite: crystal calibrations

    NASA Astrophysics Data System (ADS)

    Abdali, Salim; Christensen, Finn E.; Schnopper, Herbert W.; Gerward, Leif; Wiebicke, Hans-Joachim; Halm, Ingolf; Louis, Eric; Voorma, Harm-Jan; Spiller, Eberhard A.; Tarrio, Charles

    1997-10-01

    The four kinds of crystals; RAP(001), Si(111), LiF(220) and the Co/C multilayer on the super polished Si(111) crystals, together make up the objective crystal spectrometer OXS. They cover a wide energy range extending from 0.16 eV to 8 keV. A study of crystal reflectivity and energy resolution including measurements on RAP, LiF and Co/C and a calculation of Si crystals in the respective wavelength bands has been performed and the results are presented.

  9. Growth of single-crystal Al layers on GaAs and Si substrates for microwave superconducting resonators

    NASA Astrophysics Data System (ADS)

    Tournet, J.; Gosselink, D.; Jaikissoon, M.; Miao, G.-X.; Langenberg, D.; Mariantoni, M.; Wasilewski, Zr

    Thin Al layers on dielectrics are essential building blocks of circuits used in the quest for scalable quantum computing systems. While molecular beam epitaxy (MBE) has been shown to produce the highest quality Al layers, further reduction of losses in superconducting resonators fabricated from them is highly desirable. Defects at the Al-substrate interface are likely the key source of losses. Here we report on the optimization of MBE growth of Al layers on GaAs and Si substrates. Si surfaces were prepared by in-situ high temperature substrate annealing. For GaAs, defects typically remaining on the substrate surfaces after oxide desorption were overgrown with GaAs or GaAs/AlAs superlattice buffer layers. Such surface preparation steps were followed by cooling process to below 0°C, precisely controlled to obtain targeted surface reconstructions. Deposition of 110 nm Al layers was done at subzero temperatures and monitored with RHEED at several azimuths simultaneously. The resulting layers were characterized by HRXRD, AFM and Nomarski. Single crystal, near-atomically smooth layers of Al(110) were demonstrated on GaAs(001)-2x4 surface whereas Al(111) of comparable quality was formed on Si(111)-1x1 and 7x7 surfaces.

  10. Crystal structure, characterization and thermoelectric properties of the type-I clathrate Ba 8- ySr yAl 14Si 32 (0.6≤ y≤1.3) prepared by aluminum flux

    NASA Astrophysics Data System (ADS)

    Roudebush, John H.; Toberer, Eric S.; Hope, Håkon; Jeffrey Snyder, G.; Kauzlarich, Susan M.

    2011-05-01

    The title compound was prepared as single crystals using an aluminum flux technique. Single crystal and powder X-ray diffraction indicate that this composition crystallizes in the clathrate type-I structure, space group Pm3¯ n. Electron microprobe characterization indicates the composition to be Ba 8- ySr yAl 14.2(2)Si 31.8(2) (0.77< y<1.3). Single-crystal X-ray diffraction data (90 and 12 K) were refined with the Al content fixed at the microprobe value (12 K data: R1=0.0233, wR2=0.0441) on a crystal of compositions Ba. The Sr atom preferentially occupies the 2 a position; mixed Al/Si occupancy was found on all framework sites. These refinements are consistent with a fully occupied framework and nearly fully occupied cation guest sites as found by microprobe analysis. Temperature dependent electrical resistivity and thermal conductivity have been measured from room temperature to 1200 K on a hot-pressed pellet. Electrical resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity is between 22 and 25 mW/cm K. The sample shows n-type conductivity with a maximum figure of merit, zT of 0.3 at 1200 K. A single parabolic band model predicts a five-fold increase in zT at 800 K if carrier concentration is lowered.

  11. An Introduction to the SI Metric System. Inservice Guide for Teaching Measurement, Kindergarten Through Grade Eight.

    ERIC Educational Resources Information Center

    California State Dept. of Education, Sacramento.

    This handbook was designed to serve as a reference for teacher workshops that: (1) introduce the metric system and help teachers gain confidence with metric measurement, and (2) develop classroom measurement activities. One chapter presents the history and basic features of SI metrics. A second chapter presents a model for the measurement program.…

  12. Hyperchanneling of Ne^10+ ions through the thick <111> Si crystals

    NASA Astrophysics Data System (ADS)

    Borka-Jovanovic, V.; Petrovic, S.; Borka, D.; Neskovic, N.

    2008-07-01

    In this work we investigate the angular distributions of Ne^10+ ions hyperchanneled along the <111> direction in a thick silicon crystals as a function of the reduced crystal thickness. The ion energy is 60 MeV and the reduced crystal thickness, Lambda, is varied from 10 to 21, corresponding to the crystal length from 6.2 to 13.1 mu m. We follow the ion trajectory in the triangular region of the crystal channel determined by the maximum closed equipotential line around the channel axis, where the hyperchanneling occurs. The Henon-Heiles type of the ion-crystal interaction potential is used as the model of the continuum interaction potential obtained assuming the Moliere expression for the ion-atom interaction potential. The angular distributions are generated using the numerical solution of ion's equations of motion in the transverse plane and the computer simulation method. The obtained results show periodicity of the angular distribution, with the period of 0.5. The values of Lambda = 10, 10.5, 11,..., 21, correspond to the beginnings of periodic cycles of the angular distribution. The effect of zero-degree focusing is observed for these values of variable Lambda. Also, one can observe the formation of the symmetrical ridges in the angular distributions around the centre of the scattering angle plane, whose number increases and the average distance between them decreases as the variable Lambda increases.

  13. Dependence of acoustic property on Al substitution for Ca3Ta(Ga1‑ x Al x )3Si2O14 single crystals

    NASA Astrophysics Data System (ADS)

    Ohashi, Yuji; Arakawa, Mototaka; Kudo, Tetsuo; Yokota, Yuui; Shoji, Yasuhiro; Kurosawa, Shunsuke; Kamada, Kei; Kushibiki, Jun-ichi; Yoshikawa, Akira

    2016-07-01

    The acoustic properties of Ca3Ta(Ga1‑ x Al x )3Si2O14 (CTGASx) were experimentally studied as a function of the Al substitution content x in the ranges from x = 0 to 0.50. Five specimens, X-, Y-, Z-, 35°Y-, and 140°Y-cut, were prepared from each crystal of CTGASx (x = 0, 0.25, and 0.50) grown by the Czochralski technique. Longitudinal wave and shear wave velocities for CTGASx linearly increase with Al content for all propagation directions. Dielectric constants and density were measured and then elastic and piezoelectric constants were determined from the measured velocities for each crystal. The results revealed that all of the constants change linearly with Al content. From the relationship, the constants for CTAS (x = 1) were estimated. Calculations of the velocities using the determined constants also suggested that the maximum electromechanical coupling factor k 2 for the slow shear wave mode propagating along the rotated Y-axis direction of CTAS was improved to 4.42% compared with 3.83% for CTGS, owing to the Al substitution effect.

  14. A More Accurate Measurement of the {sup 28}Si Lattice Parameter

    SciTech Connect

    Massa, E. Sasso, C. P.; Mana, G.; Palmisano, C.

    2015-09-15

    In 2011, a discrepancy between the values of the Planck constant measured by counting Si atoms and by comparing mechanical and electrical powers prompted a review, among others, of the measurement of the spacing of {sup 28}Si (220) lattice planes, either to confirm the measured value and its uncertainty or to identify errors. This exercise confirmed the result of the previous measurement and yields the additional value d{sub 220} = 192 014 711.98(34) am having a reduced uncertainty.

  15. Ultrafast Optical Measurements of Thermal Conductivity and Sound Velocity of Amorphous SiC

    NASA Astrophysics Data System (ADS)

    Hondongwa, Donald; Olasov, Lauren; Daly, Brian; King, Sean; Bielefeld, Jeff

    2011-03-01

    We present ultrafast optical measurements of longitudinal sound velocity and thermal transport in hydrogenated amorphous carbon (a-SiC:H) films. The films were grown on Si wafers by PECVD using combinations of methylsilanes and H2 and He diluent gases. The films were well characterized and found to have densities (1.0 -- 2.5 g cm-3) and dielectric constants (2.8 -- 7.2) that spanned a wide range of values. Prior to their measurement, the a-SiC:H films were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser. Transient reflectivity changes that are associated with very high frequency sound waves (picosecond ultrasonics) and the cooling rate of the SiC sample (Time Domain Thermorerflectance (TDTR)) were measured. We extract values for the thermal conductivity and sound velocity of the SiC films, and analyze the results in terms of rigidity percolation effects within the SiC layers. This work was supported by NSF award DMR-0906753.

  16. Measuring the x-ray resolving power of bent potassium acid phthalate diffraction crystals

    SciTech Connect

    Haugh, M. J. Jacoby, K. D.; Wu, M.; Loisel, G. P.

    2014-11-15

    This report presents the results from measuring the X-ray resolving power of a curved potassium acid phthalate (KAP(001)) spectrometer crystal using two independent methods. It is part of a continuing effort to measure the fundamental diffraction properties of bent crystals that are used to study various characteristics of high temperature plasmas. Bent crystals like KAP(001) do not usually have the same diffraction properties as corresponding flat crystals. Models that do exist to calculate the effect of bending the crystal on the diffraction properties have simplifying assumptions and their accuracy limits have not been adequately determined. The type of crystals that we measured is being used in a spectrometer on the Z machine at Sandia National Laboratories in Albuquerque, New Mexico. The first technique for measuring the crystal resolving power measures the X-ray spectral line width of the characteristic lines from several metal anodes. The second method uses a diode X-ray source and a double crystal diffractometer arrangement to measure the reflectivity curve of the KAP(001) crystal. The width of that curve is inversely proportional to the crystal resolving power. The measurement results are analyzed and discussed.

  17. Mid-IR near-perfect absorption with a SiC photonic crystal with angle-controlled polarization selectivity.

    PubMed

    Devarapu, G C R; Foteinopoulou, S

    2012-06-01

    We theoretically investigate mid-IR absorption enhancement with a SiC one-dimensional photonic crystal (PC) microstructure at the frequency regime of the phonon-polariton band gap, where efficient absorption is unattainable in the bulk material. Our study reveals an intricate relationship between absorption efficiency and the energy velocity of light propagation, that is far more complex than hitherto believed. In particular, our findings suggest that absorption peaks away from the photonic-crystal band edge where energy velocity is minimum. While efficient absorption is still associated with a slow-light mode, the latter is faster by at least an order of magnitude in comparison to the bulk material. Moreover, our calculations suggest that absorption becomes optimal when light gradually slow downs as it enters the PC. Relying on this insight, we achieved near-perfect absorption around the phonon-polariton mid-gap frequency with a PC with a suitably terminated end face. We further demonstrate that the near-perfect absorptive property can be tuned with the incident light angle, to be polarization insensitive or polarization selective. We believe our proposed non-metallic paradigm opens up a new route for harnessing infrared absorption with semiconductor and ionic-crystal materials. PMID:22714331

  18. Crystalline and spin chiralities in multiferroics with langasite-type structure and Fe1- x Co x Si crystals

    NASA Astrophysics Data System (ADS)

    Pikin, S. A.; Lyubutin, I. S.; Dudka, A. P.

    2015-09-01

    It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the Néel point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector k z exceeds the magnetic helicoid wave vector by a factor of 2: k z = 2 q z. The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature ( Т U > Т М ), structural displacements may arise in the absence of magnetism at Т М < Т < Т U . In noncentrosymmetric Fe1- x Co x Si crystals (sp. gr. P213), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski-Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

  19. Single-crystal structure and Raman spectroscopy of synthetic titanite analog CaAlSiO4F

    NASA Astrophysics Data System (ADS)

    Krüger, Hannes; Többens, Daniel M.; Tropper, Peter; Haefeker, Udo; Kahlenberg, Volker; Fuchs, Martin R.; Olieric, Vincent; Troitzsch, Ulrike

    2015-10-01

    Synthetic CaAlSiO4F, the Al-F analog of titanite, has been investigated using single-crystal synchrotron diffraction experiments at Beamline X06DA (Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland) and Raman spectroscopy. The presented structural model with 40 parameters was refined against 506 unique reflections to a final R o b s of 0.026 (space group A2/ a, a = 6.9120(11), b = 8.5010(10), c = 6.435(2) Å, β = 114.670(11)°, and Z = 4) and exhibits less distorted coordination polyhedra than earlier models from powder data. Vibrational spectra were calculated in harmonic approximation at the Γ point from fully relaxed energy optimisations of the crystal structure, using 3D-periodic density functional theory with Gaussian basis sets and the software CRYSTAL06. The lattice parameters of the fully relaxed structure were in good agreement with the experimental values, with the calculated values 0.8 ± 0.4 % too large; the monoclinic angle was calculated 0.4° too large. The agreement of the calculated Raman frequencies with the observed ones was very good, with standard deviation ±3 cm-1 and maximum deviations of ±7 cm-1. Furthermore, a detailed discussion of the atomic displacements associated with each Raman mode is given.

  20. Locally measuring the adhesion of InP directly bonded on sub-100 nm patterned Si

    NASA Astrophysics Data System (ADS)

    Pantzas, K.; Le Bourhis, E.; Patriarche, G.; Troadec, D.; Beaudoin, G.; Itawi, A.; Sagnes, I.; Talneau, A.

    2016-03-01

    A nano-scale analogue to the double cantilever experiment that combines instrumented nano-indentation and atomic force microscopy is used to precisely and locally measure the adhesion of InP bonded on sub-100 nm patterned Si using oxide-free or oxide-mediated bonding. Surface-bonding energies of 0.548 and 0.628 J m-2, respectively, are reported. These energies correspond in turn to 51% and 57% of the surface bonding energy measured in unpatterned regions on the same samples, i.e. the proportion of unetched Si surface in the patterned areas. The results show that bonding on patterned surfaces can be as robust as on unpatterned surfaces, provided care is taken with the post-patterning surface preparation process and, therefore, open the path towards innovative designs that include patterns embedded in the Si guiding layer of hybrid III-V/Si photonic integrated circuits.

  1. Locally measuring the adhesion of InP directly bonded on sub-100 nm patterned Si.

    PubMed

    Pantzas, K; Bourhis, E Le; Patriarche, G; Troadec, D; Beaudoin, G; Itawi, A; Sagnes, I; Talneau, A

    2016-03-18

    A nano-scale analogue to the double cantilever experiment that combines instrumented nano-indentation and atomic force microscopy is used to precisely and locally measure the adhesion of InP bonded on sub-100 nm patterned Si using oxide-free or oxide-mediated bonding. Surface-bonding energies of 0.548 and 0.628 J m(-2), respectively, are reported. These energies correspond in turn to 51% and 57% of the surface bonding energy measured in unpatterned regions on the same samples, i.e. the proportion of unetched Si surface in the patterned areas. The results show that bonding on patterned surfaces can be as robust as on unpatterned surfaces, provided care is taken with the post-patterning surface preparation process and, therefore, open the path towards innovative designs that include patterns embedded in the Si guiding layer of hybrid III-V/Si photonic integrated circuits. PMID:26878333

  2. System for the growth of bulk SiC crystals by modified CVD techniques

    NASA Technical Reports Server (NTRS)

    Steckl, Andrew J.

    1994-01-01

    The goal of this program was the development of a SiC CVD growth of films thick enough to be useful as pseudo-substrates. The cold-walled CVD system was designed, assembled, and tested. Extrapolating from preliminary evaluation of SiC films grown in the system at relatively low temperatures indicates that the growth rate at the final temperatures will be high enough to make our approach practical. Modifications of the system to allow high temperature growth and cleaner growth conditions are in progress. This program was jointly funded by Wright Laboratory, Materials Directorate and NASA LeRC and monitored by NASA.

  3. Laser-induced fluorescence measurements and kinetic analysis of Si atom formation in a rotating disk chemical vapor deposition reactor

    SciTech Connect

    Ho, P.; Coltrin, M.E.; Breiland, W.G. )

    1994-10-06

    An extensive set of laser-induced fluorescence (LIF) measurements of Si atoms during the chemical vapor deposition (CVD) of silicon from silane and disilane in a research rotating disk reactor are presented. The experimental results are compared in detail with predictions from a numerical model of CVD from silane and disilane that treats the fluid flow coupled to gas-phase and gas-surface chemistry. The comparisons showed that the unimolecular decomposition of SiH[sub 2] could not account for the observed gas-phase Si atom density profiles. The H[sub 3]SiSiH [leftrightarrow] Si + SiH[sub 4] and H[sub 3]SiSiH + SiH[sub 2] [leftrightarrow] Si + Si[sub 2]H[sub 6] reactions are proposed as the primary Si atom production routes. The model is in good agreement with the measured shapes of the Si atom profiles and the trends in Si atom density with susceptor temperature, pressure, and reactant gas mixture. 33 refs., 12 figs., 3 tabs.

  4. Single crystal growth and heat capacity measurements of triangular lattice R2Pt6Ga15 (R =rare earth)

    NASA Astrophysics Data System (ADS)

    Matsumoto, Y.; Ueda, T.; Ohara, S.

    2016-02-01

    We have succeeded in synthesizing the single crystal of R2Pt6Ga15 (R=La-Nd, Sm- Lu) with hexagonal Sc0.67Fe2Si5-type structure using Ga self flux method. The crystal structure was confirmed by the powder X-ray method. The unit-cell volume V of R2Pt6Ga15 follows the lanthanide concentration except R = Ce, Eu and Yb, indicating that the valences of R = La, Pr, Nd, Sm, Gd-Tm, and Lu ion are trivalent, whereas those of R = Ce, Eu and Yb ion are deviate from trivalent. We have measured the specific heat C(T) of R2Pt6Ga15. It is found that the magnetic order takes place in R2Pt6Ga15 (R=Pr, Nd, Sm-Tm). Moreover, the multiple phase transitions were observed in R2Pt6Ga15 (R = Nd, Eu, Gd and Ho).

  5. Fast, spatially resolved thermometry of Si and GaP crystals using pump-probe two-photon absorption

    NASA Astrophysics Data System (ADS)

    Min, Chang-Ki; Park, Ji Yong; Cahill, David G.; Granick, Steve

    2009-07-01

    Noncontact thermometry with micron-scale lateral spatial resolution and fast time resolution is shown to be enabled by measuring the temperature dependence of two-photon absorption (TPA) on crystalline semiconductors. In the proof-of-concept experiments reported here, for studies of Si, an Er:fiber laser at λ =1.56 μm is split into pump and probe beams; where they overlap, the large TPA signal changes strongly with temperature because the two-photon energy lies between the indirect and direct bandgaps of Si. We show that the TPA coefficient increases by a factor of 2 when the temperature increases from 30 to 300 °C. For studies of GaP, we use instead a Ti:sapphire laser at 790 nm to achieve two-photon excitation above the direct bandgap. In GaP, contributions to the TPA from the dominant direct transition show less temperature dependence than for Si but the additional contribution of the indirect transition gives a similar magnitude as the temperature dependence of TPA on Si. In the current implementation using Si, the spatial resolution of the thermometry is 6×6×50 μm3 and the sensitivity is 0.6 K in a 1 kHz bandwidth.

  6. Crystallography of the NiHfSi Phase in a NiAl (0.5 Hf) Single-Crystal Alloy

    NASA Technical Reports Server (NTRS)

    Garg, A.; Noebe, R. D.; Darolia, R.

    1996-01-01

    Small additions of Hf to conventionally processed NiAl single crystals result in the precipitation of a high density of cuboidal G-phase along with a newly identified silicide phase. Both of these phases form in the presence of Si which is not an intentional alloying addition but is a contaminant resulting from contact with the ceramic shell molds during directional solidification of the single-crystal ingots. The morphology, crystal structure and Orientation Relationship (OR) of the silicide phase in a NiAl (0.5 at.%Hf) single-crystal alloy have been determined using transmission electron microscopy, electron microdiffraction and energy dispersive X-ray spectroscopy. Qualitative elemental analysis and indexing of the electron microdiffraction patterns from the new phase indicate that it is an orthorhombic NiHfSi phase with unit cell parameters, a = 0.639 nm, b = 0.389 nm and c = 0.72 nm, and space group Pnma. The NiHfSi phase forms as thin rectangular plates on NiAl/111/ planes with an OR that is given by NiHfSi(100))(parallel) NiAl(111) and NiHfSi zone axes(010) (parallel) NiAl zone axes (101). Twelve variants of the NiHfSi phase were observed in the alloy and the number of variants and rectangular morphology of NiHfSi plates are consistent with symmetry requirements. Quenching experiments indicate that nucleation of the NiHfSi phase in NiAI(Hf) alloys is aided by the formation of NiAl group of zone axes (111) vacancy loops that form on the NiAl /111/ planes.

  7. Crystallography of the NiHfSi phase in a NiAl(0.5Hf) single-crystal alloy

    SciTech Connect

    Garg, A.; Noebe, R.D.; Darolia, R.

    1996-07-01

    Small additions of Hf to conventionally processed NiAl single crystals result in the precipitation of a high density of cuboidal G-phase along with a newly identified silicide phase. Both of these phases form in the presence of Si which is not an intentional alloying addition but is a contaminant resulting from contact with the ceramic shell molds during directional solidification of the single-crystal ingots. The morphology, crystal structure and orientation relationship (O.R.) of the silicide phase in a NiAl(0.5at.%Hf) single-crystal alloy have been determined using transmission electron microscopy, electron microdiffraction and energy dispersive X-ray spectroscopy. Qualitative elemental analysis and indexing of the electron microdiffraction patterns from the new phase indicate that it is an orthorhombic NiHfSi phase with unit cell parameters, a = 0.639 nm, b = 0.389 nm and c = 0.72 nm, and space group Pnma. The NiHfSi phase forms as thin rectangular plates on {l_brace}111{r_brace}{sub NiAl} planes with an O.R. that is given by (100){sub NiHfSi}{parallel}(111){sub NiAl} and [010]{sub NiHfSi}{parallel}[{bar 1}01]{sub NiAl}. Twelve variants of the NiHfSi phase were observed in the alloy and the number of variants and rectangular morphology of NiHfSi plates are consistent with symmetry requirements. Quenching experiments indicate that nucleation of the NiHfSi phase in NiAl(Hf) alloys is aided by the formation of <111>{sub NiAl} vacancy loops that form on the {l_brace}111{r_brace}{sub NiAl} planes.

  8. Vertical gradient solution growth of N-type Si0.73Ge0.27 bulk crystals with homogeneous composition and its thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Omprakash, M.; Arivanandhan, M.; Sabarinathan, M.; Koyama, T.; Momose, Y.; Ikeda, H.; Tatsuoka, H.; Aswal, D. K.; Bhattacharya, S.; Inatomi, Y.; Hayakawa, Y.

    2016-05-01

    Compositionally homogeneous Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 bulk crystals were grown by a vertical gradient solution growth method. The sandwich sample Si (seed)/Sb-doped Ge/ Si(feed) was set up inside a furnace under a mild temperature gradient 0.57 °C/mm for homogeneous growth. The Si composition was analyzed by electron probe micro- analysis (EPMA). It revealed that the Si composition was homogeneous and the lengths of the Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 bulk crystals were 18.3 and 15.1 mm, respectively. Grain distribution was investigated by electron backscattered diffraction spectrum (EBSD). The Seebeck coefficients (-440 and -426 μV/K) of Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 were higher than the reported value (-211 μV/K) of P-doped (5×1019 cm-3) Si0.8Ge0.2 at room temperature. Thermal conductivity of Ga and Sb-doped SiGe was decreased with temperature due to scattering of phonon at the temperature range between 313 and 913 K. The maximum ZT values of Ga and Sb-doped SiGe were 0.34 and 0.44 at 820 K, respectively. The ZT values of Ga and Sb-doped SiGe were higher (0.07 and 0.13) than the reported value of Ga-doped Si0.81Ge0.19 (0.05) and P-doped (5×1019 cm-3) Si0.8Ge0.2 bulk crystals at room temperature. The improvement in ZT value was caused by a decrease of thermal conductivity which related to a composition of the alloy and doping concentration in the crystal.

  9. Crystal Growth, Structure, and Physical Properties of LnCu[subscript 2](Al,Si)[subscript 5] (Ln = La and Ce)

    SciTech Connect

    Phelan, W. Adam; Kangas, Michael J.; Drake, Brenton L.; Zhao, Liang L.; Wang, Jiakui K.; DiTusa, J.F.; Morosan, Emilia; Chan, Julia Y.

    2012-03-15

    LnCu{sub 2}(Al,Si){sub 5} (Ln = La and Ce) were synthesized and characterized. These compounds adopt the SrAu{sub 2}Ga{sub 5} structure type and crystallize in the tetragonal space group P4/mmm with unit cell dimensions of a {approx} 4.2 {angstrom} and c {approx} 7.9 {angstrom}. Herein, we report the structure as obtained from single crystal X-ray diffraction. Additionally, we report the magnetic susceptibility, magnetization, resistivity, and specific heat capacity data obtained for polycrystalline samples of LnCu{sub 2}(Al,Si){sub 5} (Ln = La and Ce).

  10. Effective refractive index of face-centered-cubic and hexagonal close-packed 250 nm-SiO2 based colloidal crystals

    NASA Astrophysics Data System (ADS)

    Salcedo-Reyes, Juan Carlos

    2012-01-01

    A quantitative kinematic analysis, of the refraction properties of face-centered-cubic and hexagonal close-packed 250 nm-SiO2-based colloidal crystals, was performed using the plane wave expansion method. The angle-dependent effective refractive index, for different frequencies, was calculated taking into account the continuity of the tangential component of the wave vector across the interface and the energy conservation principle as well. The results demonstrate that the unusual optical properties, of the close packed SiO2-based colloidal crystals, depend strongly on the sphere-packing symmetry rather than from the material itself.

  11. Preparation and upconversion emission modification of Yb, Er co-doped Y2SiO5 inverse opal photonic crystals.

    PubMed

    Yan, Dong; Zhu, Jialun; Yang, Zhengwen; Wu, Hangjun; Wang, Rongfei; Qiu, Jianbei; Song, Zhiguo; Zhou, Dacheng; Yang, Yong; Yin, Zhaoyi

    2014-05-01

    Yb, Er co-doped Y2SiO5 inverse opal photonic crystals with three-dimensionally ordered macroporous were fabricated using polystyrene colloidal crystals as the template. Under 980 nm excitation, the effect of the photonic stopband on the upconversion luminescence of Er3+ ions has been investigated in the Y2SiO5:Yb, Er inverse opals. Significant suppression of the green or red UC emissions was detected if the photonic band-gap overlaps with the Er3+ ions emission band. PMID:24734639

  12. Formation of Novel Silicon Nitride with Face-Centered Cubic Crystal Structure in a TaN/Ta/Si(100) Thin Film System

    NASA Astrophysics Data System (ADS)

    Cheng, Wei-Chun; Jou, Shyan-Kay; Chiu, Chuei-Fu

    2005-07-01

    We discovered a new silicon nitride with cubic symmetry formed in the silicon at the Ta/Si interface of the TaN/Ta/Si(100) thin film system when the silicon wafer was annealed at 500 or 600°C. The cubic silicon nitride grew into the silicon crystal in the shape of an inverse pyramid after the annealing process. The boundary planes of the inverse pyramid were the \\{111\\} planes of the silicon crystal. The orientation relationship between the silicon nitride and silicon crystal is cubic to cubic. The lattice constant of the new silicon nitride is a=0.5548 nm and is about 2.2% larger than that of the silicon crystal.

  13. Evaluation of a timing integrated circuit architecture for continuous crystal and SiPM based PET systems

    NASA Astrophysics Data System (ADS)

    Monzo, J. M.; Ros, A.; Herrero-Bosch, V.; Perino, I. V.; Aliaga, R. J.; Gadea-Girones, R.; Colom-Palero, R. J.

    2013-03-01

    Improving timing resolution in positron emission tomography (PET), thus having fine time information of the detected pulses, is important to increase the reconstructed images signal to noise ratio (SNR) [1]. In the present work, an integrated circuit topology for time extraction of the incoming pulses is evaluated. An accurate simulation including the detector physics and the electronics with different configurations has been developed. The selected architecture is intended for a PET system based on a continuous scintillation crystal attached to a SiPM array. The integrated circuit extracts the time stamp from the first few photons generated when the gamma-ray interacts with the scintillator, thus obtaining the best time resolution. To get the time stamp from the detected pulses, a time to digital converter (TDC) array based architecture has been proposed as in [2] or [3]. The TDC input stage uses a current comparator to transform the analog signal into a digital signal. Individually configurable trigger levels allow us to avoid false triggers due to signal noise. Using a TDC per SiPM configuration results in a very area consuming integrated circuit. One solution to this problem is to join several SiPM outputs to one TDC. This reduces the number of TDCs but, on the other hand, the first photons will be more difficult to be detected. For this reason, it is important to simulate how the time resolution is degraded when the number of TDCs is reduced. Following this criteria, the best configuration will be selected considering the trade-off between achievable time resolution and the cost per chip. A simulation is presented that uses Geant4 for simulation of the physics process and, for the electronic blocks, spice and Matlab. The Geant4 stage simulates the gamma-ray interaction with the scintillator, the photon shower generation and the first stages of the SiPM. The electronics simulation includes an electrical model of the SiPM array and all the integrated circuitry

  14. Delta L: An Apparatus for Measuring Macromolecular Crystal Growth Rates in Microgravity

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    In order to determine how macromolecule crystal quality improvement in microgravity is related to crystal growth characteristics, is was necessary to develop new hardware that could measure the crystal growth rates of a population of crystals growing under the same solution conditions. As crystal growth rate is defined as the change or delta in a defined dimension or length (L) of a crystal over time, the hardware was named Delta L. Delta L consists of fluids, optics, and data acquisition, sub-assemblies. Temperature control is provided for the crystal growth chamber. Delta L will be used in connection with the Glovebox Integrated Microgravity Isolation Technology (g-LIMIT) inside the Microgravity Science Glovebox (MSG), onboard the International Space Station (ISS). Delta L prototype hardware has been assembled. This paper will describe an overview of the design of Delta L and present preliminary crystal growth rate data.

  15. Si(Li)-NaI(Tl) detector for direct measurement of plutonium in vivo

    SciTech Connect

    Sherman, I.S.; Strauss, M.G.; Pehl, R.H.

    1983-01-01

    The potential of a Si(Li)-NaI(Tl) detector system for measuring the UL x rays produced in the decay of Pu is discussed. In this paper we describe the conceptual design and expected performance of such a system. The detector can resolve the UL x rays from the NpL x ray thus permitting direct measurement of Pu in the presence of /sup 241/Am. The expected performance of the system was determined from measurements of lung phantoms using a prototype Si detector.

  16. Crystallographic Origin of the Alternate Bright/Dark Contrast in 6H-SiC and other Hexagonal Crystal HREM Images

    NASA Astrophysics Data System (ADS)

    Bow, J. S.; Carpenter, R. W.; Kim, M. J.

    1996-04-01

    Alternating bright/dark anomalous subunitcell contrast in HREM images along or near the close-packed direction of 6H-SiC, Ti5Si3, [alpha]-Ti, and 4H-SiC, all of which are hexagonal, was examined using computer-generated crystal models, HREM image simulations, and digital diffractograms from the corresponding experimental images. The primary variables were crystal tilt and thickness. Crystal model projections showed that the scattering potential was smeared anisotropically within the unit cells by small crystal tilts, which reproduced the experimentally observed anomalous subunit-cell contrast modulations in the corresponding simulations. The effect increased with thickness, but it did not occur in exact zone axis simulations for any crystal thickness. Structural considerations indicated that the contrast resulted from tilt-induced violations of Gjonnes-Moodie dynamical extinctions and excitation of kinematically forbidden reflections in the imaging zone. Digital diffractograms from experimental HREM images confirmed their presence in the imaging zone diffraction patterns. These effects were absent in HREM images from cubic crystals in this material system because the structurally induced requisite kinematically forbidden reflections do not occur in the imaging zone.

  17. Measuring the X-ray Resolving Power of Bent Potassium Acid Phthalate Diffraction Crystals

    SciTech Connect

    Haugh, M. J.; Wu, M.; Jacoby, K. D.; Loisel, G. P.

    2014-11-01

    This report presents the results from measuring the X-ray resolving power of a curved potassium acid phthalate (KAP(001)) spectrometer crystal using two independent methods. It is part of a continuing effort to measure the fundamental diffraction properties of bent crystals that are used to study various characteristics of high temperature plasmas. Bent crystals like KAP(001) do not usually have the same diffraction properties as corresponding flat crystals. Models that do exist to calculate the effect of bending the crystal on the diffraction properties have simplifying assumptions and their accuracy limits have not been adequately determined. The type of crystals that we measured is being used in a spectrometer on the Z machine at Sandia National Laboratories (SNL) in Albuquerque, NM. The first technique for measuring the crystal resolving power measures the X-ray spectral line width of the characteristic lines from several metal anodes. The second method uses a diode X-ray source and a dual goniometer arrangement to measure the reflectivity curve of the KAP(001) crystal. The width of that curve is inversely proportional to the crystal resolving power. The measurement results are analyzed and discussed.

  18. Synthesis and characterization of Gallium-Arsenic compounds containing a four-membered Ga-As-Ga-Cl or Ga-As-Ga-As ring: Crystal structures of (Me3SiCH2)2 GaAs(SiMe3)2 Ga(CH2SiMe3)2 Cl and ((Me3SiCH2)2 GaAs(SiMe3)2)2

    NASA Astrophysics Data System (ADS)

    Wells, Richard L.; Pasterczyk, James W.; McPhail, Andrew T.; Johnson, James D.; Alvanipour, Abbas

    1990-10-01

    The third example of an organogallium four-membered ring compound with arsenic, halogen mixed bridging, Me3SiCH2 2GaAs SiMe3 2Ga CH2SiMe3 2CI, was prepared by the reaction of Me3Si 3As with two equivalents of (Me3SiCH2)2GaCl. X-ray crystallographic analysis showed that the compound contains a nonplanar Ga-As-Ga-C1 ring. The crystals belong to the monoclinic system space group P21/c C52h with four molecules per unit cell of dimensions a 12.476, b 15.832, c22.279 A, Beta 108.87, V 4164(2) A3. The dimer Me3SiCH2 2GaAs SiMe3 22 was prepared by reaction of LiAs SiMe3 2 and Me3SiCH2 2GaCl. Its solid-state dimeric structure was established by single-crystal X-ray analysis.

  19. Property measurements on piezoelectric single crystals and the implications for transducer design

    NASA Astrophysics Data System (ADS)

    Powers, James M.; Viehland, Dwight D.; Ewart, Lynn

    2001-07-01

    Piezoelectric single crystals of lead magnesium niobate in solid solution with lead titanate have generated great interest in the Navy sonar community because of the potential they offer for enhanced transducer performance. Two material properties, in particular, make the piezoelectric single crystals unique; their high 33-mode coupling factor and their low short circuit Young's modulus. Measurements of the large signal electromechanical and mechanical properties on single crystal samples are presented in this paper. These measurements elucidate the behavior of piezoelectric single crystals, including the effect of bias field on the Young's modulus. The ramifications of the measured material properties on transducer design are also discussed.

  20. Far-ultraviolet and visible light scatter measurements for CVD SiC mirrors for SOHO

    NASA Astrophysics Data System (ADS)

    Leviton, Douglas B.; Saha, Timo T.; Gardner, Larry D.

    1998-12-01

    Chemically-vapor-deposited (CVD) silicon carbide (SiC) has become a popular mirror material for spaceborne solar instrumentation for the vacuum ultraviolet wavelength range due to its appreciable broadband reflectance and favorable thermal and opto-mechanical properties. Scatter from surfaces of mirrors operating in this wavelength range can destroy otherwise good image contrast especially for extended targets such as the sun. While valid far ultraviolet (FUV) scatter measurements are entirely non-trivial to conduct and so are rarely performed, visible light scatter measurements are comparatively easy. Unfortunately, it is not straightforward to predict FUV scatter performance based on visible light scatter measurements for mirrors made of CVD SiC. It is hoped that by carrying out scatter measurements in both wavelength regimes for the same CVD SiC mirror, that the ability to make such predictions may be enhanced. Visible light (633 nm) scatter measurements were performed at Goddard Space Flight Center (GSFC) by two different means on CVD SiC telescope mirrors (from the same process and same vendor) for two instruments on the Solar and Heliospheric Observatory (SOHO) - - the Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurement of Emitted Radiation (SUMER). Additionally, extensive FUV scatter measurements were made for SUMER telescope mirrors. In this paper, we correlate the results for those FUV and visible light scatter measurements for this important material.

  1. Measurement of group velocity dispersion in a solid-core photonic crystal fiber filled with a nematic liquid crystal.

    PubMed

    Wahle, Markus; Kitzerow, Heinz

    2014-08-15

    Liquid crystal-filled photonic crystal fibers (PCFs) are promising candidates for electrically tunable integrated photonic devices. In this Letter, we present group velocity measurements on such fibers. A large mode area PCF, LMA8, was infiltrated with the liquid crystal mixture, E7. The measurements were performed with an interferometric setup. The fiber exhibits several spectral transmission windows in the visible wavelength regime that originate from the bandgap guiding mechanism. The dispersion of these windows is very unusual compared to typical fibers. Our measurements show that it can change from -2500 ps km(-1) nm(-1) to +2500 ps km(-1) nm(-1) within a spectral range of only 15 nm. This leads to multiple zero dispersion wavelengths in the visible wavelength range. PMID:25121882

  2. X-ray diffraction on the X-cut of a Ca{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14} single crystal modulated by a surface acoustic wave

    SciTech Connect

    Irzhak, D. Roshchupkin, D.

    2014-06-28

    The result of X-ray diffraction study on a single crystal of the calcium-gallogermanate family Ca{sub 3}TaGa{sub 3}Si{sub 2}O{sub 14} (CTGS) modulated by a surface acoustic wave (SAW) is presented. The power flow angle for SAW propagating along the X{sub 2} axis of the X-cut in CTGS was measured. The rocking curves for the CTGS crystal were recorded at different amplitudes of an input high frequency electric signal on interdigital transducer used to excite a SAW. Based on the data obtained, intensity dependence of diffraction satellites on the amplitude of electric signal exciting a SAW was built. Numerical simulation of the crystal rocking curves and dependence of diffraction satellite intensities on the SAW amplitude enabled the selection of a set of material constants at which the most complete coincidence of experimental and calculated results is observed.

  3. Hydrothermal synthesis and the crystal structure of borate cancrinite (Na,Ca){sub 2}[Na{sub 6}(AlSiO{sub 4}){sub 6}](BO{sub 3}) . 2H{sub 2}O

    SciTech Connect

    Shirinova, A. F. Khrustalev, V. N.; Samedov, H. R.; Chiragov, M. I.

    2006-01-15

    Transparent prismatic single crystals of borate cancrinite (Na,Ca){sub 2}[Na{sub 6}(AlSiO{sub 4}){sub 6}](BO{sub 3}) . 2H{sub 2}O are prepared through hydrothermal crystallization. The parameters of the hexagonal unit cell and intensities of 10806 reflections are measured on an Enraf-Nonius CAD4 automated diffractometer. The compound crystallizes in the hexagonal crystal system with the unit cell parameters a = 12.745(4) A, c = 5.180(2) A, V = 728.6(4) A{sup 3}, and space group P6{sub 3}. The structure is determined by direct methods and refined using the full-matrix least-squares procedure in the anisotropic approximation for the non-hydrogen atoms. The refinement of the structure is performed to the final discrepancy factor R{sub 1} = 0.027 for 2889 unique reflections with I > 2 {sigma} (I). In the structure of the borate cancrinite, the AlO{sub 4} and SiO{sub 4} tetrahedra form a zeolite-like framework in which twelve-membered hexagonal channels are occupied by sodium atoms and BO{sub 3} groups, whereas six-membered channels are filled with sodium and calcium atoms and water molecules. The mean interatomic distances are found to be as follows: (Si-O){sub mean} = 1.614 A and (Al-O){sub mean} = 1.741 A in the AlO{sub 4} and SiO{sub 4} tetrahedra, (Na-O){sub mean} = 2.542 A in the seven-vertex sodium polyhedra, and [(Na,Ca)-O]{sub mean} = 2.589 A in the ditrigonal bipyramids.

  4. Discovery of iron group impurity ion spin states in single crystal Y{sub 2}SiO{sub 5} with strong coupling to whispering gallery photons

    SciTech Connect

    Goryachev, Maxim; Farr, Warrick G.; Carmo Carvalho, Natalia do; Creedon, Daniel L.; Le Floch, Jean-Michel; Probst, Sebastian; Bushev, Pavel; Tobar, Michael E.

    2015-06-08

    Interaction of Whispering Gallery Modes (WGMs) with dilute spin ensembles in solids is an interesting paradigm of Hybrid Quantum Systems potentially beneficial for Quantum Signal Processing applications. Unexpected ion transitions are measured in single crystal Y{sub 2}SiO{sub 5} using WGM spectroscopy with large Zero Field Splittings at 14.7 GHz, 18.4 GHz, and 25.4 GHz, which also feature considerable anisotropy of the g-tensors as well as two inequivalent lattice sites, indicating spins from Iron Group Ion (IGI) impurities. The comparison of undoped and Rare-Earth doped crystals reveal that the IGIs are introduced during co-doping of Eu{sup 3+} or Er{sup 3+} with concentration at much lower levels of order 100 ppb. The strong coupling regime between an ensemble of IGI spins and WGM photons have been demonstrated at 18.4 GHz and near zero field. This approach together with useful optical properties of these ions opens avenues for “spins-in-solids” Quantum Electrodynamics.

  5. Measurement of time resolution of thermoregulated SiPM for time of flight detectors

    NASA Astrophysics Data System (ADS)

    Cavazza, D.; D'Antone, I.; Foschi, E.; Guandalini, C.; Lax, I.; Levi, G.; Quadrani, L.; Sbarra, C.; Zuffa, M.

    2012-11-01

    Silicon Photomultipliers (SiPM) are considered very promising in many application where high timing performances, low cost, hardness to radiation damage and single photon counting are requested. Such applications go from astrophysics, high energy accelerator physics to medical physics. A group of SiPM from Hamamatsu has been tested with a low noise fast amplifier based on a hetero-junction FET, mounted on a proper front end board. A first telescope prototype has been used to test the electronics and results are shown. The SiPM time resolution has been measured to be σ∼30 ps, in agreement with other studies reported in literature. The SiPM gain depends critically on temperature and a thermoelectric module to control the circuit was also studied in order to use the system for space detectors.

  6. Precise control of photoluminescence of silicon-vacancy color centers in homoepitaxial single-crystal diamond: evaluation of efficiency of Si doping from gas phase

    NASA Astrophysics Data System (ADS)

    Ralchenko, Victor; Sedov, Vadim; Saraykin, Vladimir; Bolshakov, Andrey; Zavedeev, Evgeny; Ashkinazi, Evgeny; Khomich, Andrew

    2016-09-01

    Ability to precisely control the Si-related color center abundance in diamond is important for the use of silicon-vacancy (SiV) defects with bright photoluminescence (PL) in quantum information technologies and optical biomarkers. Here, we evaluated the efficiency of Si incorporation in (100) plane of homoepitaxial diamond layers upon in situ doping by adding silane SiH4 in the course of diamond chemical vapor deposition in microwave plasma using CH4-H2 mixtures. Both the Si concentration in the doped samples, as determined by secondary ion mass spectrometry, and PL intensity of SiV centers at 738 nm wavelength, measured at excitation wavelength of 473 nm, demonstrate a linear increase with silane content in feed gas in the range. The incorporation efficiency f, defined as the ratio of Si concentration in diamond to that in gas, f = [Si/C]dia/[Si/C]gas is found to be (1.1 ± 0.5) × 10-3 for the silane concentrations explored, [SiH4/CH4] < 0.7 %; thus, the Si atoms are accommodated in (100) diamond face easier than nitrogen and phosphorus, but more difficult than boron. This finding allows a tailoring of the Si content and photoluminescence intensity of SiV centers in in situ doped CVD diamond.

  7. Genetic algorithm prediction of crystal structure of metastable Si-IX phase

    SciTech Connect

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Yangang; Wang, Cai-Zhuang; Ho, Kai-Ming

    2013-12-14

    We performed genetic algorithm search for the atomic structure of the long Lime unsolved Si-IX phase. We found two new structures with space groups of P4(2)/m and P-4, respectively, which have lattice parameters in excellent agreement with the experimental data. The phonon calculations showed that the P4(2)/m structure exhibits a soft phonon mode, while the P-4 structure is dynamically stable. Our calculation also showed that the P-4 structure is a meta-stable structure in a pressure range from 0 to 40 GPa, The Si-IX phase could be a mixed phase consisting of the P4(2)/m and the P-4 structures. Published by Elsevier Ltd.

  8. Growth of SiC single crystals on patterned seeds by a sublimation method

    NASA Astrophysics Data System (ADS)

    Yang, Xianglong; Chen, Xiufang; Peng, Yan; Xu, Xiangang; Hu, Xiaobo

    2016-04-01

    Growth of 6H-SiC on patterned seeds with the vertical sidewalls composed of {11-20} and {1-100} faces by a sublimation method at 1700-2000 °C was studied. Anisotropy in lateral growth rates was observed, i.e the growth rate towards <11-20> was faster than that along <1-100>. It was found that free lateral growth on mesas was accompanied by a sharp decrease in the density of threading dislocation. The dependence of lateral growth rate on growth conditions such as reactor pressure and growth temperature was investigated. The factors governing the process of lateral growth of 6H-SiC on patterned seeds were discussed.

  9. The measurement of the resonant frequency of quartz crystal units: An ongoing saga

    NASA Astrophysics Data System (ADS)

    Kentley, Eric

    1992-06-01

    The history of practical methods of industrial measurement leading to the present situation is traced. Resonant frequency measurement of a quartz crystal unit has always presented problems due to the fact that a quartz crystal unit is not an absolute frequency determining device. The frequency of oscillation of a quartz crystal unit in an oscillator circuit is a function of the crystal unit and the maintaining oscillator circuit. Since the introduction of zero phase type measurements in a passive network by the I.E.C. in the early 1970's many of these measurement problems have been eliminated or much reduced, but there are still some problem areas. Using the computer aided test methods now available, automatic crystal measurements can be made. These can cause what might be termed computer aided correlation errors due to slightly different measuring procedures and methods of computation.

  10. Kerr-Lens Self-Mode-Locked Laser Characteristics of Yb:Lu2SiO5 Crystal

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Yang, Ji-Min; Wang, Wei-Wei; Zheng, Li-He; Su, Liang-Bi; Xu, Jun

    2011-07-01

    A diode-pumped Kerr-lens self-mode-locked laser is achieved by using Yb: Lu2SiO5(Yb:LSO) crystal without additional components. Under the incident pump power of 14.44 W, a self-mode-locked output power of 2.98 W is obtained in the five-mirror cavity, corresponding to an optical-optical efficiency of 20.6%. Pulses as short as 8.2 ps are realized at 1059 nm, with the corresponding pulse energy and peak power of 28.9 nJ and 3.5 kW, respectively. A pair of SF10 prisms are inserted into the laser cavity to compensate for the group velocity dispersion. The pulse width is compressed to 2.2 ps with an average output power of 1.25 W.

  11. Yb:Lu2SiO5 crystal : characterization of the laser emission along the three dielectric axes

    NASA Astrophysics Data System (ADS)

    Toci, Guido; Pirri, Angela; Beitlerova, Alena; Shoji, Yasuhiro; Yoshikawa, Akira; Hybler, Jiri; Nikl, Martin; Vannini, Matteo

    2015-05-01

    Yb:doped Lu2SiO5 (Lutetium orthosilicate, LSO) is an optically biaxial crystal with laser emission in the range 1000- 1100 nm. It features different absorption and emission spectra for polarization along its three dielectric axes. In this work we have characterized the laser emission properties of Yb:LSO along all the three dielectric axis, evidencing differences that can be exploited in the design of ultrafast laser sources. The material was tested in a longitudinally pumped laser cavity. The laser emission efficiency was found similar along all the three dielectric axes, with slope efficiencies around 90% in most cases. Regarding the tuning range, for the most favourable polarization direction we obtained a continuously tunable emission between 993 and 1088 nm (i. e. 95 nm) peaked at 1040 nm. The tuning curves along the three dielectric axes spanned similar ranges but with relevant differences in the shape.

  12. CW and passively Q-switched laser performance of Nd:Lu2SiO5 crystal

    NASA Astrophysics Data System (ADS)

    Xu, Xiaodong; Di, Juqing; Zhang, Jian; Tang, Dingyuan; Xu, Jun

    2016-01-01

    We demonstrated an efficient and controllable dual-wavelength continuous-wave (CW) laser of Nd:Lu2SiO5 (Nd:LSO) crystal. The maximum output power was 3.02 W at wavelength of 1075 nm and 1079 nm, and with increasing of absorbed pump power, the ratio of 1079 nm laser rose. The slope efficiency of 65.6% and optical-to-optical conversion efficiency of 63.3% were obtained. The passively Q-switched laser properties of Nd:LSO were investigated for the first time. The shortest pulse, maximum pulse energy and peak power were 11.58 ns, 29.05 μJ and 2.34 kW, respectively.

  13. The anisotropy of the basic characteristics of Lamb waves in a (001)-Bi12SiO20 piezoelectric crystal

    NASA Astrophysics Data System (ADS)

    Anisimkin, V. I.

    2016-03-01

    The orientation dependences of the phase velocity, the effective electromechanical coupling coefficient, and the angle between the wave normal and the energy flux vector are numerically calculated for zeroand first-order Lamb waves propagating in the (001) basal plane of a Bi12SiO20 cubic piezoelectric crystal. It is shown that the anisotropies of these modes are different and depend on the plate thickness h and the wavelength λ. For h/λ < 1, the mode anisotropy can exceed the anisotropy of the corresponding characteristics of surface acoustic waves propagating in the same plane; for h/λ > 1, it approximately coincides with the SAW anisotropy for all the characteristics.

  14. Ranges of Channelled keV B Ions in Si Crystals with Impact Parameter Dependent Stopping Power

    NASA Astrophysics Data System (ADS)

    Kabadayi, Önder

    In this study we calculated channelled ion ranges of boron ions by using an impact parameter dependent stopping power model. Impact parameter dependent stopping powers for boron ions penetrating into Si <100> are investigated first for energies from 10 to 150 keV. We assumed that impact parameter dependent stopping powers can be expressed by a modified Oen-Robinson formula [1] (Oen et al. Nucl. Instr. Meth. B132, 647 (1976)). The model is implemented by developing a computer code to solve a differential equation numerically for which mean ion ranges can be obtained. The results are compared with experimental data as well as Crystal-TRIM, SRIM and similar procedures calculating ion ranges in solids. We have found an agreement between our results and literature.

  15. Angular Magnetoresistance and Hall Measurements in New Dirac Material, ZrSiS

    NASA Astrophysics Data System (ADS)

    Ali, Mazhar; Schoop, Leslie; Lotsch, Bettina; Parkin, Stuart

    Dirac and Weyl materials have shot to the forefront of condensed matter research in the last few years. Recently, the square-net material, ZrSiS, was theorized and experimentally shown (via ARPES) to host several highly dispersive Dirac cones, including the first Dirac cone demanded by non-symmorphic symmetry in a Si square net. Here we report the magnetoresistance and Hall Effect measurements in this compound. ZrSiS samples with RRR = 40 were found to have MR values up to 6000% at 2 K, be predominantly p-type with a carrier concentration of ~8 x 1019 cm-3 and mobility ~8500 cm2/Vs. Angular magnetoresistance measurements reveal a peculiar behavior with multiple local maxima, depending on field strength, indicating of a sensitive and sensitive Fermi surface. SdH oscillations analysis confirms Hall and angular magnetoresistance measurements. These results, in the context of the theoretical and ARPES results, will be discussed.

  16. Investigations on the Crystal-Chemical Behavior of Transition-Metal-Bearing Aluminosilicate Garnet Solid Solutions Using 27Al and 29Si NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palke, A. C.; Geiger, C. A.; Stebbins, J. F.

    2015-12-01

    The petrological importance of silicate garnet is derived from the presence of three distinct cation sites of varying size and coordination number. This allows for a wide range of trace, minor, and major element substitutions. However, a full and precise crystal-chemical understanding of the nature of transition metals in garnet is not at hand. Possible mechanisms of various charge-balanced substitutions (e.g. octahedral Ti4+ or tetrahedral Al3+) and the structural state of solid solutions (i.e. short- to long-range ordering) need study. We report on ongoing efforts in these directions using 27Al and 29Si Magic-Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. Early work on synthetic and natural Fe- and Mn-bearing pyrope- and grossular-rich garnets focused on the effect these paramagnetic transition metals have in measuring and interpreting NMR spectra. These results have been expanded with NMR measurements on synthetic pyrope-rich garnets containing other paramagnetic transition metals including Cr3+, V3+, Co2+, and Ni2+ as well as diamagnetic Ti4+. NMR peaks are severely broadened in the presence of even small concentrations of Cr3+, Mn2+, and Fe3+ leading to a loss of spectral resolution. On the other hand, the spectra of garnet containing V3+, Fe2+, Co2+, and Ni2+ have better resolution and show separate paramagnetically shifted NMR peaks. In some cases, crystal-chemical information can be obtained because of the large frequency separations between the NMR peaks that can be assigned to various local atomic configurations around Al and Si. Furthermore, the 27Al NMR spectrum of a synthetic pyrope garnet with about 2% diamagnetic Ti4+ on the octahedral site showed the absence of any tetrahedral Al3+, which rules out the substitution mechanism VITi + IVAl = VIAl + IVSi in the solid solution. Our NMR investigations on garnet are now being made at the exploratory level. We think that NMR spectra of diamagnetic garnet can provide information on a

  17. Synthesis, crystal structure and properties of Mg{sub 3}B{sub 36}Si{sub 9}C and related rare earth compounds RE{sub 3−x}B{sub 36}Si{sub 9}C (RE=Y, Gd–Lu)

    SciTech Connect

    Ludwig, Thilo; Pediaditakis, Alexis; Sagawe, Vanessa; Hillebrecht, Harald

    2013-08-15

    We report on the synthesis and characterisation of Mg{sub 3}B{sub 36}Si{sub 9}C. Black single crystals of hexagonal shape were yielded from the elements at 1600 °C in h-BN crucibles welded in Ta ampoules. The crystal structure (space group R3{sup ¯}m, a=10.0793(13) Å, c=16.372(3) Å, 660 refl., 51 param., R{sub 1}(F)=0.019; wR{sub 2}(F{sup 2})=0.051) is characterized by a Kagome-net of B{sub 12} icosahedra, ethane like Si{sub 8}-units and disordered SiC-dumbbells. Vibrational spectra show typical features of boron-rich borides and Zintl phases. Mg{sub 3}B{sub 36}Si{sub 9}C is stable against HF/HNO{sub 3} and conc. NaOH. The micro-hardness is 17.0 GPa (Vickers) and 14.5 GPa (Knoop), respectively. According to simple electron counting rules Mg{sub 3}B{sub 36}Si{sub 9}C is an electron precise compound. Band structure calculations reveal a band gap of 1.0 eV in agreement to the black colour. Interatomic distances obtained from the refinement of X-ray data are biased and falsified by the disorder of the SiC-dumbbell. The most evident structural parameters were obtained by relaxation calculation. Composition and carbon content were confirmed by WDX measurements. The small but significant carbon content is necessary by structural reasons and frequently caused by contaminations. The rare earth compounds RE{sub 3−x}B{sub 36}Si{sub 9}C (RE=Y, Dy–Lu) are isotypic. Single crystals were grown from a silicon melt and their structures refined. The partial occupation of the RE-sites fits to the requirements of an electron-precise composition. According to the displacement parameters a relaxation should be applied to obtain correct structural parameters. - Graphical abstract: Single crystals of the new boridesilicide Mg{sub 3}B{sub 36}Si{sub 9}C were obtained from the elements in a Si-melt. Besides B{sub 12}-icosahedra and ethan-like Si{sub 8}-units it contains a disordered SiC-dumbbell. Correct distances were obtained by relaxation calculation based on the X-ray data

  18. Crystal structures of (Mg1;#8722;x,Fex)SiO[subscript 3] postperovskite at high pressures

    SciTech Connect

    Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L.; Meng, Yue; Ganesh, P.; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J.

    2012-03-15

    X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg{sub 0.9}Fe{sub 0.1})SiO{sub 3} and (Mg{sub 0.6}Fe{sub 0.4})SiO{sub 3} at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO{sub 3}-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density ({rho} = 6.119(1) g/cm{sup 3}) than the former ({rho} = 5.694(8) g/cm{sup 3}) due to both the larger amount of iron and the smaller ionic radius of Fe{sup 2+} as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe{sup 2+} also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe{sup 2+} in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered.

  19. Crystal structure, characterization and thermoelectric properties of the type-I clathrate Ba{sub 8-y}Sr{sub y}Al{sub 14}Si{sub 32} (0.6{<=}y{<=}1.3) prepared by aluminum flux

    SciTech Connect

    Roudebush, John H.; Toberer, Eric S.; Hope, Hakon; Jeffrey Snyder, G.; Kauzlarich, Susan M.

    2011-05-15

    The title compound was prepared as single crystals using an aluminum flux technique. Single crystal and powder X-ray diffraction indicate that this composition crystallizes in the clathrate type-I structure, space group Pm3-bar n. Electron microprobe characterization indicates the composition to be Ba{sub 8-y}Sr{sub y}Al{sub 14.2(2)}Si{sub 31.8(2)} (0.77crystal X-ray diffraction data (90 and 12 K) were refined with the Al content fixed at the microprobe value (12 K data: R{sub 1}=0.0233, wR{sub 2}=0.0441) on a crystal of compositions Ba. The Sr atom preferentially occupies the 2a position; mixed Al/Si occupancy was found on all framework sites. These refinements are consistent with a fully occupied framework and nearly fully occupied cation guest sites as found by microprobe analysis. Temperature dependent electrical resistivity and thermal conductivity have been measured from room temperature to 1200 K on a hot-pressed pellet. Electrical resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity is between 22 and 25 mW/cm K. The sample shows n-type conductivity with a maximum figure of merit, zT of 0.3 at 1200 K. A single parabolic band model predicts a five-fold increase in zT at 800 K if carrier concentration is lowered. -- Graphical abstract: The inorganic type-I clathrate phase with nominal composition Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} has been prepared by Al flux. Single crystal diffraction at 90 and 12 K reveal that the framework is fully occupied with the cation sites nearly fully occupied. The lattice thermal conductivity is low thereby suggesting further optimization of the carrier concentration will lead to a high zT. Display Omitted Highlights: {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a light element phase ideal for thermoelectric power generation. {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a high melting point cubic

  20. Thermodynamic analysis of binary Fe85B15 to quinary Fe85Si2B8P4Cu1 alloys for primary crystallizations of α-Fe in nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Takeuchi, A.; Zhang, Y.; Takenaka, K.; Makino, A.

    2015-05-01

    Fe-based Fe85B15, Fe84B15Cu1, Fe82Si2B15Cu1, Fe85Si2B12Cu1, and Fe85Si2B8P4Cu1 (NANOMET®) alloys were experimental and computational analyzed to clarify the features of NANOMET that exhibits high saturation magnetic flux density (Bs) nearly 1.9 T and low core loss than conventional nanocrystalline soft magnetic alloys. The X-ray diffraction analysis for ribbon specimens produced experimentally by melt spinning from melts revealed that the samples were almost formed into an amorphous single phase. Then, the as-quenched samples were analyzed with differential scanning calorimeter (DSC) experimentally for exothermic enthalpies of the primary and secondary crystallizations (ΔHx1 and ΔHx2) and their crystallization temperatures (Tx1 and Tx2), respectively. The ratio ΔHx1/ΔHx2 measured by DSC experimentally tended to be extremely high for the Fe85Si2B8P4Cu1 alloy, and this tendency was reproduced by the analysis with commercial software, Thermo-Calc, with database for Fe-based alloys, TCFE7 for Gibbs free energy (G) assessments. The calculations exhibit that a volume fraction (Vf) of α-Fe tends to increase from 0.56 for the Fe85B15 to 0.75 for the Fe85Si2B8P4Cu1 alloy. The computational analysis of the alloys for G of α-Fe and amorphous phases (Gα-Fe and Gamor) shows that a relationship Gα-Fe ˜ Gamor holds for the Fe85Si2B12Cu1, whereas Gα-Fe < Gamor for the Fe85Si2B8P4Cu1 alloy at Tx1 and that an extremely high Vf = 0.75 was achieved for the Fe85Si2B8P4Cu1 alloy by including 2.8 at. % Si and 4.5 at. % P into α-Fe. These computational results indicate that the Fe85Si2B8P4Cu1 alloy barely forms amorphous phase, which, in turn, leads to high Vf and resultant high Bs.

  1. Integrated III-V Photonic Crystal - Si waveguide platform with tailored optomechanical coupling

    NASA Astrophysics Data System (ADS)

    Tsvirkun, Viktor; Surrente, Alessandro; Raineri, Fabrice; Beaudoin, Grégoire; Raj, Rama; Sagnes, Isabelle; Robert-Philip, Isabelle; Braive, Rémy

    2015-11-01

    Optomechanical systems, in which the vibrations of a mechanical resonator are coupled to an electromagnetic radiation, have permitted the investigation of a wealth of novel physical effects. To fully exploit these phenomena in realistic circuits and to achieve different functionalities on a single chip, the integration of optomechanical resonators is mandatory. Here, we propose a novel approach to heterogeneously integrate arrays of two-dimensional photonic crystal defect cavities on top of silicon-on-insulator waveguides. The optomechanical response of these devices is investigated and evidences an optomechanical coupling involving both dispersive and dissipative mechanisms. By controlling the optical coupling between the waveguide and the photonic crystal, we were able to vary and understand the relative strength of these couplings. This scalable platform allows for an unprecedented control on the optomechanical coupling mechanisms, with a potential benefit in cooling experiments, and for the development of multi-element optomechanical circuits in the framework of optomechanically-driven signal-processing applications.

  2. Colors Of Liquid Crystals Used To Measure Surface Shear Stresses

    NASA Technical Reports Server (NTRS)

    Reda, D. C.; Muratore, J. J., Jr.

    1996-01-01

    Developmental method of mapping shear stresses on aerodynamic surfaces involves observation, at multiple viewing angles, of colors of liquid-crystal surface coats illuminated by white light. Report describing method referenced in "Liquid Crystals Indicate Directions Of Surface Shear Stresses" (ARC-13379). Resulting maps of surface shear stresses contain valuable data on magnitudes and directions of skin friction forces associated with surface flows; data used to refine mathematical models of aerodynamics for research and design purposes.

  3. Capillary-force measurement on SiC surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ˜4-14 nm mainly due to sphere morphology, the relative humidity (RH) ˜0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH˜40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.

  4. Capillary-force measurement on SiC surfaces.

    PubMed

    Sedighi, M; Svetovoy, V B; Palasantzas, G

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ∼4-14 nm mainly due to sphere morphology, the relative humidity (RH) ∼0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH∼40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads. PMID:27415337

  5. Depth-of-interaction measurement in a single-layer crystal array with a single-ended readout using digital silicon photomultiplier.

    PubMed

    Lee, Min Sun; Lee, Jae Sung

    2015-08-21

    We present the first experimental evaluation of a depth-of-interaction (DOI) positron emission tomography (PET) detector using a digital silicon photomultiplier (dSiPM). To measure DOI information from a mono-layer array of scintillation crystals with a single-ended readout, our group has previously proposed and developed a new method based on light spread using triangular reflectors. Since this method relies on measurement of the light distribution, dSiPM, which has a fully digital interface, has several merits for our DOI measurement. The DOI PET detector comprised of a dSiPM sensor (DPC-3200-22-44) coupled with a 14   ×   14 array of 2 mm  ×  2 mm  ×  20 mm unpolished LGSO crystals. All crystals were covered with triangular reflectors. To obtain a good performance of the DOI PET detector, several parameters of detector were selected as a preliminary experiment. Detector performance was evaluated with the selected parameters and the optimal experimental setup, and a DOI measurement was conducted by irradiating the crystal block at five DOI positions spaced at intervals of 4 mm. Maximum-likelihood estimation was employed for DOI positioning and the optimal DOI estimation scheme was also investigated in this study. As a result, the DOI PET detector showed clear crystal identification. The energy resolution (full-width at half-maximum (FWHM)) averaged over all depths was 10.21%  ±  0.15% at 511 keV, and time resolution averaged over all depths was 1198.61   ±   39.70 ps FWHM. The average DOI positioning accuracy for all depths was 74.22%  ±  6.77%, which equates to DOI resolution of 4.67 mm. Energy and DOI resolutions were uniform over all crystal positions except for the back parts of the array. Furthermore, additional simulation studies were conducted to verify the results of our DOI measurement method that is combined with dSiPM technology. In conclusion, our continuous DOI PET detector

  6. Depth-of-interaction measurement in a single-layer crystal array with a single-ended readout using digital silicon photomultiplier

    NASA Astrophysics Data System (ADS)

    Lee, Min Sun; Lee, Jae Sung

    2015-08-01

    We present the first experimental evaluation of a depth-of-interaction (DOI) positron emission tomography (PET) detector using a digital silicon photomultiplier (dSiPM). To measure DOI information from a mono-layer array of scintillation crystals with a single-ended readout, our group has previously proposed and developed a new method based on light spread using triangular reflectors. Since this method relies on measurement of the light distribution, dSiPM, which has a fully digital interface, has several merits for our DOI measurement. The DOI PET detector comprised of a dSiPM sensor (DPC-3200-22-44) coupled with a 14   ×   14 array of 2 mm  ×  2 mm  ×  20 mm unpolished LGSO crystals. All crystals were covered with triangular reflectors. To obtain a good performance of the DOI PET detector, several parameters of detector were selected as a preliminary experiment. Detector performance was evaluated with the selected parameters and the optimal experimental setup, and a DOI measurement was conducted by irradiating the crystal block at five DOI positions spaced at intervals of 4 mm. Maximum-likelihood estimation was employed for DOI positioning and the optimal DOI estimation scheme was also investigated in this study. As a result, the DOI PET detector showed clear crystal identification. The energy resolution (full-width at half-maximum (FWHM)) averaged over all depths was 10.21%  ±  0.15% at 511 keV, and time resolution averaged over all depths was 1198.61   ±   39.70 ps FWHM. The average DOI positioning accuracy for all depths was 74.22%  ±  6.77%, which equates to DOI resolution of 4.67 mm. Energy and DOI resolutions were uniform over all crystal positions except for the back parts of the array. Furthermore, additional simulation studies were conducted to verify the results of our DOI measurement method that is combined with dSiPM technology. In conclusion, our continuous DOI PET detector

  7. Defect formation in 4H-SiC single crystal grown on the prismatic seeds

    NASA Astrophysics Data System (ADS)

    Fadeev, A. Yu; Lebedev, A. O.; Tairov, Yu M.

    2014-12-01

    The defect structure of 4H silicon carbide single crystals grown by PVT method on three prismatic seeds (10-10), (11-20) and (8.3.-11.0) is considered. The only defects existing in the grown ingots are stacking faults and basal plane dislocations. The type of stacking fault is studied. The dependence of stacking fault morphology on the seed orientation is analyzed.

  8. Quantum-confined Stark effect measurements in Ge/SiGe quantum-well structures.

    PubMed

    Chaisakul, Papichaya; Marris-Morini, Delphine; Isella, Giovanni; Chrastina, Daniel; Le Roux, Xavier; Gatti, Eleonora; Edmond, Samson; Osmond, Johann; Cassan, Eric; Vivien, Laurent

    2010-09-01

    We investigate the room-temperature quantum-confined Stark effect in Ge/SiGe multiple quantum wells (MQWs) grown by low-energy plasma-enhanced chemical vapor deposition. The active region is embedded in a p-i-n diode, and absorption spectra at different reverse bias voltages are obtained from optical transmission, photocurrent, and differential transmission measurements. The measurements provide accurate values of the fraction of light absorbed per well of the Ge/SiGe MQWs. Both Stark shift and reduction of exciton absorption peak are observed. Differential transmission indicates that there is no thermal contribution to these effects. PMID:20808367

  9. Formation effects and optical absorption of Ag nanocrystals embedded in single crystal SiO2 by implantation

    NASA Astrophysics Data System (ADS)

    Liu, Zhengxin; Li, Hao; Feng, Xiaodong; Ren, Shuguang; Wang, Honghong; Liu, Zhenghui; Lu, Baofu

    1998-08-01

    Ag+ ions of 200 keV were implanted into single crystal SiO2 at room temperature to five different doses: 5×1015, 2.3×1016, 4.5×1016, 5.6×1016, and 6.7×1016/cm2. With increasing dose, the implanted Ag distributions change from usual Gaussian-type profiles to abnormal bimodal profiles with narrow full width at half maximum, which are associated with Ag nanoparticles forming during high dose implantation. The implanted Ag depth profile evolution with dose can be clearly observed during Rutherford backscattering spectroscopy analysis. The nanoparticles form dual-layer structures at high doses: as far as the dose of 6.7×1016/cm2 is concerned, transmission electron microscopy proves that the shallower implanted layer contains noninteracting small Ag nanoparticles with the diameters of about 7 nm; the deeper layer contains a high density of interacting large nanoparticles with the diameters of about 25 nm. High resolution electron microscopy identifies that the nanoparticles are perfect single crystals. Although plasmon resonance frequency of the Ag nanoparticles formed at relatively low dose agrees well with the Mie's theoretical prediction, great redshift due to multipole interactions between high density nanoparticles occurs for high doses, moreover, the magnitude of redshift increases with implanted dose.

  10. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-SiO2, has a density of 3.39 g/cu cm, a thermal expansion coefficient of 6.6 x 10 to the -6th/C, a glass-transition temperature of 910 C, and a dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot-pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass have been studied. CIP'd samples, after appropriate heat treatments, always crystallized out as celsian, whereas presence of 5-10 wt pct of an additive was necessary for formation of celsian in sintered as well as hot-pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot-pressing resulted in fully dense samples.

  11. Investigation of Ca3TaGa3Si2O14 piezoelectric crystals for high temperature sensors

    NASA Astrophysics Data System (ADS)

    Yu, Fapeng; Zhang, Shujun; Zhao, Xian; Yuan, Duorong; Qin, Lifeng; Wang, Qing-ming; Shrout, Thomas R.

    2011-06-01

    The dielectric and electromechanical properties of fully ordered Ca3TaGa3Si2O14 (CTGS) crystals were investigated over the temperature range of -60˜700 °C. The highest electromechanical coupling factor, k26 (18.9%) and piezoelectric coefficient, d26 (-11.5 pC/N) were obtained for (YXl)-25° cuts. The temperature dependent behavior of resonance frequency (fr) was investigated in single-rotated thickness shear mode (TSM) (YXl)θ cuts (θ = -35°˜10°). The turnover temperatures of resonance frequency were found to increase from 20 °C to 330 °C, as the rotation angle θ varied from -22.5° to -35°. Bulk acoustic wave (BAW) resonators based on Y(-30°) monolithic disks with a fundamental frequency ˜2.87 MHz were fabricated, where the in air mechanical quality factor Q was found to be on the order of 24000 and 10000 at 20 °C and 700 °C, respectively. The high coupling k26, high mechanical Q, and high electrical resistivity (16 MΩ.cm) at 700 °C, together with the near zero TCF characteristics at elevated temperatures, demonstrate the potential of CTGS crystals for high temperature sensor applications.

  12. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples.

  13. Epitaxy of Orthorhombic BaSi2 with Preferential In-Plane Crystal Orientation on Si(001): Effects of Vicinal Substrate and Annealing Temperature

    NASA Astrophysics Data System (ADS)

    Toh, Katsuaki; Hara, Kosuke O.; Usami, Noritaka; Saito, Noriyuki; Yoshizawa, Noriko; Toko, Kaoru; Suemasu, Takashi

    2012-09-01

    We attempted to grow orthorhombic BaSi2 epitaxial films having preferential in-plane crystallographic orientation on both exact and vicinal Si(001) substrates with a miscut angle of 2° toward Si[bar 110] by reactive deposition epitaxy (RDE) and subsequent molecular beam epitaxy (MBE). On the vicinal Si(001) substrate, the initial BaSi2 nuclei formed by RDE tended to grow unidirectionally with the [010] direction parallel to Si[110] when the annealing temperature of the Si substrate before the growth was increased from 830 to 1000 °C. Transmission electron microscopy showed that the grain size of the BaSi2 films grown by MBE increased up to approximately 9 µm on the vicinal Si(001) substrate when the substrate annealing temperature was 1000 °C. This is the largest grain size ever obtained for BaSi2. Even in the case of the exact Si(001) substrate, the MBE-grown BaSi2 grains preferentially grew with the [010] direction along Si[110] when the annealing temperature was 1000 °C.

  14. Progress toward thin-film GaAs solar cells using a single-crystal Si substrate with a Ge interlayer

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Zwerdling, S.

    1982-01-01

    Development of a technology for fabricating light-weight, high-efficiency, radiation-resistant solar cells for space applications is reported. The approaches currently adopted are to fabricate shallow homojunction n(+)/p as well as p/n AlGaAs-heteroface GaAs solar cells by organometallic chemical vapor deposition (OM-CVD) on single-crystal Si substrates using in each case, a thin Ge epi-interlayer first grown by CVD. This approach maintains the advantages of the low specific gravity of Si as well as the high efficiency and radiation-resistant properties of the GaAs solar cell which can lead to greatly improved specific power for a solar array. The growth of single-crystal GaAs epilayers on Ge epi-interlayers on Si substrates is investigated. Related solar cell fabrication is reviewed.

  15. Effects of Contact Resistance on Electrical Conductivity Measurements of SiC-Based Materials

    SciTech Connect

    Youngblood, Gerald E.; Thomsen, Edwin C.; Henager, Charles H.

    2012-04-17

    A combination 2/4-probe method was used to measure electrical resistances across a pure, monolithic CVD-SiC disc sample with contact resistance at the SiC/metallic electrode interfaces. By comparison of the almost simultaneous 2/4-probe measurements, the specific contact resistance and its temperature dependence were determined for two types (sputtered gold and porous nickel) electrodes from RT to ~700°C. The specific contact resistance values (Rc) behaved similarly for each type of metallic electrode: Rc >~1000 Ω-cm2 at RT, decreasing continuously to ~1-10 Ω-cm2 at 700°C. The temperature dependence of the inverse Rc indicated thermally activated electrical conduction across the SiC/metallic interface with an apparent activation energy of ~0.3 eV. For the flow channel insert application in a fusion reactor blanket, contact resistance potentially could reduce the transverse electrical conductivity by ~1/2.

  16. Precise half-life measurement of the superallowed {beta}{sup +} emitter {sup 26}Si

    SciTech Connect

    Iacob, V. E.; Hardy, J. C.; Banu, A.; Chen, L.; Golovko, V. V.; Goodwin, J.; Horvat, V.; Nica, N.; Park, H. I.; Trache, L.; Tribble, R. E.

    2010-09-15

    We measured the half-life of the superallowed 0{sup +{yields}}0{sup +} {beta}{sup +} emitter {sup 26}Si to be 2245.3(7) ms. We used pure sources of {sup 26}Si and employed a high-efficiency gas counter, which was sensitive to positrons from both this nuclide and its daughter {sup 26}Al{sup m}. The data were analyzed as a linked parent-daughter decay. To contribute meaningfully to any test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the ft value of a superallowed transition must be determined to a precision of 0.1% or better. With a precision of 0.03%, the present result is more than sufficient to be compatible with that requirement. Only the branching ratio now remains to be measured precisely before a {+-}0.1% ft value can be obtained for the superallowed transition from {sup 26}Si.

  17. Spin alignment and density matrix measurement in sup 28 Si + sup 12 C orbiting reaction

    SciTech Connect

    Ray, A.; Shapira, D.; Halbert, M.L.; Gomez del Campo, J.; Kim, H.J. ); Sullivan, J.P. . Cyclotron Inst.); Shivakumar, B.; Mitchell, J. . Wright Nuclear Structure Lab.)

    1990-01-01

    Gamma-ray angular correlations have been measured for the strongly damped reactions {sup 12}C({sup 28}Si,{sup 12}C){sup 28}Si between {theta}{sub cm} = (120{degree} {minus} 160{degree}) for E{sub cm} = 43.5 and 48 MeV. We find that the density matrices for the {sup 12}C(2{sub 1}{sup +}) and {sup 28}Si states are almost diagonal with respect to the direction of motion of the outgoing particle. The measured density matrices and spin alignments are consistent with the picture of formation of a long-lived dinuclear complex undergoing orbiting, bending and wriggling motions, but not with those obtained from statistical compound nucleus or sticking model calculations. 17 refs., 2 figs., 1 tab.

  18. Measurements of crystal growth kinetics at extreme deviations from equilibrium. Technical progress report, 1 September 1990--31 August 1991

    SciTech Connect

    Aziz, M.J.

    1992-07-14

    We have measured solute trapping of several solutes in Al and Ni during rapid solidification. We have also made preliminary measurements of solute trapping of As in Si, trapped 20 atomic percent As in Si, and made a preliminary measurement of the T{sub o} curve in Si-As. 5 figs.

  19. On the structural-optical properties of Al-containing amorphous Si thin films and the metal-induced crystallization phenomenon

    NASA Astrophysics Data System (ADS)

    Zanatta, A. R.; Kordesch, M. E.

    2014-08-01

    Amorphous (a-)Si-based materials always attracted attention of the scientific community, especially after their use in commercial devices like solar cells and thin film transistors in the 1980s. In addition to their technological importance, the study of a-Si-based materials also present some interesting theoretical-practical challenges. Their crystallization as induced by metal species is one example, which is expected to influence the development of electronic-photovoltaic devices. In fact, the amorphous-to-crystalline transformation of the a-SiAl system has been successfully applied to produce solar cells suggesting that further improvements can be achieved. Stimulated by these facts, this work presents a comprehensive study of the a-SiAl system. The samples, with Al contents in the ˜0-15 at. % range, were made in the form of thin films and were characterized by different spectroscopic techniques. The experimental results indicated that: (a) increasing amounts of Al changed both the atomic structure and the optical properties of the samples; (b) thermal annealing induced the crystallization of the samples at temperatures that depend on the Al concentration; and (c) the crystallization process was also influenced by the annealing duration and the structural disorder of the samples. All of these aspects were addressed in view of the existing models of the a-Si crystallization, which were also discussed to some extent. Finally, the ensemble of experimental results suggest an alternative method to produce cost-effective crystalline Si films with tunable structural-optical properties.

  20. On the structural-optical properties of Al-containing amorphous Si thin films and the metal-induced crystallization phenomenon

    SciTech Connect

    Zanatta, A. R.; Kordesch, M. E.

    2014-08-21

    Amorphous (a-)Si-based materials always attracted attention of the scientific community, especially after their use in commercial devices like solar cells and thin film transistors in the 1980s. In addition to their technological importance, the study of a-Si-based materials also present some interesting theoretical-practical challenges. Their crystallization as induced by metal species is one example, which is expected to influence the development of electronic-photovoltaic devices. In fact, the amorphous-to-crystalline transformation of the a-SiAl system has been successfully applied to produce solar cells suggesting that further improvements can be achieved. Stimulated by these facts, this work presents a comprehensive study of the a-SiAl system. The samples, with Al contents in the ∼0−15 at. % range, were made in the form of thin films and were characterized by different spectroscopic techniques. The experimental results indicated that: (a) increasing amounts of Al changed both the atomic structure and the optical properties of the samples; (b) thermal annealing induced the crystallization of the samples at temperatures that depend on the Al concentration; and (c) the crystallization process was also influenced by the annealing duration and the structural disorder of the samples. All of these aspects were addressed in view of the existing models of the a-Si crystallization, which were also discussed to some extent. Finally, the ensemble of experimental results suggest an alternative method to produce cost-effective crystalline Si films with tunable structural-optical properties.

  1. Focused beam reflectance measurement as a tool for in situ monitoring of the lactose crystallization process.

    PubMed

    Pandalaneni, K; Amamcharla, J K

    2016-07-01

    Lactose accounts for about 75 and 85% of the solids in whey and deproteinized whey, respectively. Production of lactose is usually carried out by a process called crystallization. Several factors including rate of cooling, presence of impurities, and mixing speed influence the crystal size characteristics. To optimize the lactose crystallization process parameters to maximize the lactose yield, it is important to monitor the crystallization process. However, efficient in situ tools to implement at concentrations relevant to the dairy industry are lacking. The objective of the present work was to use a focused beam reflectance measurement (FBRM) system for in situ monitoring of lactose crystallization at supersaturated concentrations (wt/wt) 50, 55, and 60% at 20 and 30°C. The FBRM data were compared with Brix readings collected using a refractometer during isothermal crystallization. Chord length distributions obtained from FBRM in the ranges of <50 µm (fine crystals) and 50 to 300 µm (coarse crystals) were recorded and evaluated in relation to the extent of crystallization and rate constants deduced from the refractometer measurements. Extent of crystallization and rate constants increased with increasing supersaturation concentration and temperature. The measured fine crystal counts from FBRM increased at higher supersaturated concentration and temperature during isothermal crystallization. On the other hand, coarse counts were observed to increase with decreasing supersaturated concentration and temperature. Square weighted chord length distribution obtained from FBRM showed that as concentration increased, a decrease in chord lengths occurred at 20°C and similar observations were made from microscopic images. The robustness of FBRM in understanding isothermal lactose crystallization at various concentrations and temperatures was successfully assessed in the study. PMID:27132102

  2. Influence of the Ca/Si ratio of the C–S–H phase on the interaction with sulfate ions and its impact on the ettringite crystallization pressure

    SciTech Connect

    Kunther, Wolfgang; Lothenbach, Barbara

    2015-03-15

    The effect of the Ca/Si ratio of the calcium–silicate–hydrate (C–S–H) phase on the interaction with sulfate ions is investigated for C–S–H phases (Ca/Si = 0.83, 1.25, 1.50) and mortar samples of blended Portland cements. It is shown that leaching of calcium from C–S–H and portlandite affects the composition of the pore solution and contributes to the developing crystallization pressure of ettringite. Sulfate profiles show that sulfate binding before cracking is similar for different Ca/Si ratios whereas the highest expansion rates are observed for the mortars with the highest Ca/Si ratios. After leaching in sulfate solutions, the C–S–H samples have been characterized by {sup 29}Si MAS NMR, thermogravimetric analysis, and elemental solution analysis. Generally, the exposure to sulfate solutions results in decalcification of the C–S–H, which increases with decreasing Ca/Si ratio. The data are in good agreement with thermodynamic modeling, indicating that equilibrium is almost achieved in the leached systems. Finally, the expansion of mortar samples exposed to sulfate solutions was much less at lower Ca/Si ratios of the cement blends. This reduced expansion can be related to the decrease of the supersaturation of the pore solution with respect to ettringite at lower Ca/Si ratios of the C–S–H and in the absence of portlandite.

  3. BBO crystal component design for ultra-short laser pulse measurement

    NASA Astrophysics Data System (ADS)

    Jia, Yudong; Zhang, Xiaoqing; Zhang, Tianyi; Lu, Lingling

    2014-09-01

    In this paper the mechanism of BBO crystal component for frequency resolved optical gating technique has been researched by mathematical modeling and Simulation. Research shows that thickness of the crystal and the phase matching angle are important parameters affecting the measurement performance. Crystal thickness determines the pulse width limit which this crystal can distinguish; when the phase condition is matched between the fundamental frequency and second-harmonic of light, the SHG efficiency of incident light is highest. According to the calculations, An BBO crystals with 3.5mm thickness, 20.56 degrees phase matching angle is adopted to realize the crystal component for tens to hundreds of femtoseconds pulse width measurement.

  4. A photoelastic measurement system for residual stress analysis in scintillating crystals by conoscopic imaging

    NASA Astrophysics Data System (ADS)

    Montalto, L.; Paone, N.; Scalise, L.; Rinaldi, D.

    2015-06-01

    The assessment of the stress state of scintillating crystals is an important issue for producers as well as users of such materials, because residual stress may arise during growth process. In this paper, a measurement system, based on the use of a photoelastic, conoscopic optical setup, is proposed for the assessment of stress state in scintillating crystals. Local stress values can be measured on the crystal in order to observe their spatial distribution. With the proposed system, it is possible to vary the dimensions of the inspected measurement volume. It has been validated with reference to a known stress state induced in a birefringent crystal sample and it has been tested for the case of loaded and unloaded samples, showing sub-millimetric spatial resolution and stress uncertainty ≤0.25 MPa. The proposed measurement system is a valid method for the inspection of scintillating crystals required by producers and users of such materials.

  5. Transport Measurements on Si Nanostructures with Counted Sb Donors

    NASA Astrophysics Data System (ADS)

    Singh, Meenakshi; Bielejec, Edward; Garratt, Elias; Ten Eyck, Gregory; Bishop, Nathaniel; Wendt, Joel; Luhman, Dwight; Carroll, Malcolm; Lilly, Michael

    2014-03-01

    Donor based spin qubits are a promising platform for quantum computing. Single qubits using timed implant of donors have been demonstrated.1 Extending this to multiple qubits requires precise control over the placement and number of donors. Such control can be achieved by using a combination of low-energy heavy-ion implants (to reduce depth straggle), electron-beam lithography (to define position), focused ion beam (to localize implants to one lithographic site) and counting the number of implants with a single ion detector.2 We report transport measurements on MOS quantum dots implanted with 5, 10 and 20 Sb donors using the approach described above. A donor charge transition is identified by a charge offset in the transport characteristics. Correlation between the number of donors and the charge offsets is studied. These results are necessary first steps towards fabricating donor nanostructures for two qubit interactions. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. The work was supported by Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. 1J. J. Pla et al., Nature 496, 334 (2013) 2J. A. Seamons et al., APL 93, 043124 (2008).

  6. Measurements of Si hybrid CMOS x-ray detector characteristics

    NASA Astrophysics Data System (ADS)

    Bongiorno, Stephen D.; Falcone, Abraham D.; Burrows, David N.; Cook, Robert

    2010-07-01

    The recent development of active pixel sensors as X-Ray focal plane arrays will place them in contention with CCDs on future satellite missions. Penn State University (PSU) is working with Teledyne Imaging Sensors (TIS) to develop X-Ray Hybrid CMOS devices (HCDs), a type of active pixel sensor with fast frame rates, adaptable readout timing and geometry, low power consumption, and inherent radiation hardness. CCDs have been used with great success on the current generation of X-Ray telescopes (e.g. Chandra, XMM, Suzaku, and Swift). However, their bucket-brigade readout architecture, which transfers charge across the chip with discrete component readout electronics, results in clockrate limited readout speeds that cause pileup (saturation) of bright sources and an inherent susceptibility to radiation induced displacement damage that limits mission lifetime. In contrast, HCDs read pixels through the detector substrate with low power, on-chip readout integrated circuits. Faster frame rates, achieved with adaptable readout timing and geometry, will allow the next generation's larger effective area telescopes to observe brighter sources free of pileup. In HCDs, radiation damaged lattice sites affect a single pixel instead of an entire row. The PSU X-ray group is currently testing 4 Teledyne HCDs, with low cross-talk CTIA devices in development. We will report laboratory measurements of HCD readnoise, interpixel-capacitance and its impact on event selection, linearity, and energy resolution as a function of energy.

  7. Integrated X-Ray Reflectivity Measurements for Elliptically Curved PET Crystals

    SciTech Connect

    Haugh, M J; Ross, P W; Regan, P W; Magoon, J; Shoup, M J; Barrios, M A; Emig, J A; Fournier, K B

    2012-04-26

    Spectroscopy provides valuable information about the temperature and density of a compressed pellet in a plasma. Elliptically curved pentaerythritol (PET) crystals are used as components for spectrometers. Their elliptical geometry gives several advantages related to spectral energy range, source focus, and spectral image compression.[1] The crystal curvature increases the spectrometer throughput but at the cost of a loss in resolution. Four different crystals are used in a spectrometer at the National Ignition Facility (NIF) target chamber at Lawrence Livermore National Laboratory (LLNL). Figure 1 shows the arrangement of the elliptical PET crystals in the snout of a NIF target diagnostic shown in Figure 2. The spectrum from the crystals is captured by four image plates located behind the crystals. A typical mandrel, the darkened section, upon which the PET crystal is glued, is shown in Figure 3, which also shows the complete ellipse. There are four elliptical segment types, each having the same major axis but a different minor axis. The crystals are 150 mm long in the diffraction direction and 25.4 mm high. Two crystals of each type were calibrated. The throughput for each spectrometer is determined by the integrated reflectivity of the PET crystal.[1] The goal of this effort was to measure the reflectivity curve of the PET curved crystal at several energies and determine the integrated reflectivity and the curve width as a function of the X-ray spectral energy and location on the ellipse where the beam strikes.

  8. Growth of piezoelectric water-free GeO2 and SiO2-substituted GeO2 single-crystals.

    PubMed

    Lignie, A; Armand, P; Papet, P

    2011-10-01

    Using the slow-cooling method in selected fluxes, we have grown spontaneously nucleated single-crystals of pure GeO(2) and SiO(2)-substituted GeO(2) materials with the α-quartz structure. These piezoelectric materials were obtained in millimeter size as well-faceted, visually colorless, and transparent crystals. Cubic-like or hexagonal prism-like morphology was identified depending on the chemical composition of the single-crystals and on the nature of the flux. Both the silicon substitution rate and the homogeneity of its distribution were estimated by Energy Dispersive X-ray spectroscopy. The cell parameters of the flux-grown GeO(2) and Ge(1-x)Si(x)O(2) (0.038 ≤ x ≤ 0.089) solid-solution were deduced from their X-ray powder diffraction pattern. As expected, the cell volumes decrease as the silicon content substitution increases. A room temperature Infrared spectroscopy study confirms the absence of hydroxyl groups in the as-grown crystals. Unlike what was observed for hydrothermally grown GeO(2) crystals, these flux-grown oxide materials did not present any phase transition before melting as pointed out by a Differential Scanning Calorimetry study. Neither a α-quartz/β-quartz transition as encountered in SiO(2) near 573 °C nor a α-quartz to rutile transformation were detected for these GeO(2) and Ge(1-x)Si(x)O(2) single-crystals. PMID:21875033

  9. Integrated III-V Photonic Crystal--Si waveguide platform with tailored optomechanical coupling.

    PubMed

    Tsvirkun, Viktor; Surrente, Alessandro; Raineri, Fabrice; Beaudoin, Grégoire; Raj, Rama; Sagnes, Isabelle; Robert-Philip, Isabelle; Braive, Rémy

    2015-01-01

    Optomechanical systems, in which the vibrations of a mechanical resonator are coupled to an electromagnetic radiation, have permitted the investigation of a wealth of novel physical effects. To fully exploit these phenomena in realistic circuits and to achieve different functionalities on a single chip, the integration of optomechanical resonators is mandatory. Here, we propose a novel approach to heterogeneously integrate arrays of two-dimensional photonic crystal defect cavities on top of silicon-on-insulator waveguides. The optomechanical response of these devices is investigated and evidences an optomechanical coupling involving both dispersive and dissipative mechanisms. By controlling the optical coupling between the waveguide and the photonic crystal, we were able to vary and understand the relative strength of these couplings. This scalable platform allows for an unprecedented control on the optomechanical coupling mechanisms, with a potential benefit in cooling experiments, and for the development of multi-element optomechanical circuits in the framework of optomechanically-driven signal-processing applications. PMID:26567535

  10. Integrated III-V Photonic CrystalSi waveguide platform with tailored optomechanical coupling

    PubMed Central

    Tsvirkun, Viktor; Surrente, Alessandro; Raineri, Fabrice; Beaudoin, Grégoire; Raj, Rama; Sagnes, Isabelle; Robert-Philip, Isabelle; Braive, Rémy

    2015-01-01

    Optomechanical systems, in which the vibrations of a mechanical resonator are coupled to an electromagnetic radiation, have permitted the investigation of a wealth of novel physical effects. To fully exploit these phenomena in realistic circuits and to achieve different functionalities on a single chip, the integration of optomechanical resonators is mandatory. Here, we propose a novel approach to heterogeneously integrate arrays of two-dimensional photonic crystal defect cavities on top of silicon-on-insulator waveguides. The optomechanical response of these devices is investigated and evidences an optomechanical coupling involving both dispersive and dissipative mechanisms. By controlling the optical coupling between the waveguide and the photonic crystal, we were able to vary and understand the relative strength of these couplings. This scalable platform allows for an unprecedented control on the optomechanical coupling mechanisms, with a potential benefit in cooling experiments, and for the development of multi-element optomechanical circuits in the framework of optomechanically-driven signal-processing applications. PMID:26567535

  11. Crystal chemistry and optical investigations of the Cu{sub 2}Zn(Sn,Si)S{sub 4} series for photovoltaic applications

    SciTech Connect

    Hamdi, Mohamed; Lafond, Alain; Guillot-Deudon, Catherine; Hlel, Faouzi; Gargouri, Mohamed; Jobic, Stéphane

    2014-12-15

    Different compounds in the Cu{sub 2}ZnSnS{sub 4}–Cu{sub 2}ZnSiS{sub 4} system have been prepared via ceramic route and structurally characterized via X-ray diffraction on powders and single crystals. Two solid solutions were identified along the Cu{sub 2}Zn(Sn,Si)S{sub 4} series. Namely, materials with Si-content x=Si/(Sn+Si) lower than 0.5 crystallize with the Cu{sub 2}ZnSnS{sub 4} kesterite structure type while materials with x higher than 0.8 adopt the Cu{sub 2}ZnSiS{sub 4} enargite structure type. In between, a miscibility gap occurs where the Cu{sub 2}ZnSn{sub 0.5}Si{sub 0.5}S{sub 4} and Cu{sub 2}ZnSn{sub 0.2}Si{sub 0.8}S{sub 4} compounds co-exist. The optical bandgap increases continuously with the Si content in the whole series. This opens up the possibility to fine tune the absorption threshold and to adjust it to 1.7 eV for x∼0.5, the optimum value for the top cell of tandem solar devises to achieve high photovoltaic conversion efficiency. - Graphical abstract: Two solid solutions have been pointed out in the Cu{sub 2}Zn(Sn{sub 1−x}Si{sub x})S{sub 4} series with the kesterite and the enargite type structures. - Highlights: • New compounds in Cu{sub 2}Zn(Sn,Si)S{sub 4} series have been prepared. • Two solid solutions Cu{sub 2}ZnSn{sub 1−x}Si{sub x}S{sub 4} were identified for x≤0.5 and x≥0.8. • In the miscibility gap 2 phases co-exist with kesterite and enargite structure types. • The optical bandgap increases continuously with the Si-content in the whole series. • These materials could be envisioned as absorber in thin-film solar cells.

  12. Defects in SiO 2 crystals after neutron irradiations at 20 K and 360 K

    NASA Astrophysics Data System (ADS)

    Nakagawa, M.; Okada, M.; Kawabata, Y.; Atobe, K.; Itoh, H.; Nakanishi, S.

    1994-06-01

    The synthetic silicon dioxide (SiO2), cut parallel (x-plate) or perpendicular (z-plate) to c-axis, are irradiated by reactor neutrons at 360 K (2.8 × 1018 n/cm2) or at 20 K (8.0 × 1016 n/cm2). After neutron irradiation at 360 K, the main absorption peak can be observed at 212 nm (5.84 eV) for z-plate and 217 nm (5.71 eV) for x-plate. After irradiation at 20 K a new band at 250 nm (4.96 eV) can be observed in addition to the band at about 220 nm. The 250 nm band having FWHM ∼ 0.44 eV disappears at 300-340 K. Thermoluminescences are also observed between 80 to 400 K; which show some difference between x-plate and z-plate.

  13. A SiPM-based isotropic-3D PET detector X'tal cube with a three-dimensional array of 1 mm(3) crystals.

    PubMed

    Yamaya, Taiga; Mitsuhashi, Takayuki; Matsumoto, Takahiro; Inadama, Naoko; Nishikido, Fumihiko; Yoshida, Eiji; Murayama, Hideo; Kawai, Hideyuki; Suga, Mikio; Watanabe, Mitsuo

    2011-11-01

    We are developing a novel, general purpose isotropic-3D PET detector X'tal cube which has high spatial resolution in all three dimensions. The research challenge for this detector is implementing effective detection of scintillation photons by covering six faces of a segmented crystal block with silicon photomultipliers (SiPMs). In this paper, we developed the second prototype of the X'tal cube for a proof-of-concept. We aimed at realizing an ultimate detector with 1.0 mm(3) cubic crystals, in contrast to our previous development using 3.0 mm(3) cubic crystals. The crystal block was composed of a 16 × 16 × 16 array of lutetium gadolinium oxyorthosilicate (LGSO) crystals 0.993 × 0.993 × 0.993 mm(3) in size. The crystals were optically glued together without inserting any reflector inside and 96 multi-pixel photon counters (MPPCs, S10931-50P, i.e. six faces each with a 4 × 4 array of MPPCs), each having a sensitive area of 3.0 × 3.0 mm(2), were optically coupled to the surfaces of the crystal block. Almost all 4096 crystals were identified through Anger-type calculation due to the finely adjusted reflector sheets inserted between the crystal block and light guides. The reflector sheets, which formed a belt of 0.5 mm width, were placed to cover half of the crystals of the second rows from the edges in order to improve identification performance of the crystals near the edges. Energy resolution of 12.7% was obtained at 511 keV with almost uniform light output for all crystal segments thanks to the effective detection of the scintillation photons. PMID:21971079

  14. A SiPM-based isotropic-3D PET detector X'tal cube with a three-dimensional array of 1 mm3 crystals

    NASA Astrophysics Data System (ADS)

    Yamaya, Taiga; Mitsuhashi, Takayuki; Matsumoto, Takahiro; Inadama, Naoko; Nishikido, Fumihiko; Yoshida, Eiji; Murayama, Hideo; Kawai, Hideyuki; Suga, Mikio; Watanabe, Mitsuo

    2011-11-01

    We are developing a novel, general purpose isotropic-3D PET detector X'tal cube which has high spatial resolution in all three dimensions. The research challenge for this detector is implementing effective detection of scintillation photons by covering six faces of a segmented crystal block with silicon photomultipliers (SiPMs). In this paper, we developed the second prototype of the X'tal cube for a proof-of-concept. We aimed at realizing an ultimate detector with 1.0 mm3 cubic crystals, in contrast to our previous development using 3.0 mm3 cubic crystals. The crystal block was composed of a 16 × 16 × 16 array of lutetium gadolinium oxyorthosilicate (LGSO) crystals 0.993 × 0.993 × 0.993 mm3 in size. The crystals were optically glued together without inserting any reflector inside and 96 multi-pixel photon counters (MPPCs, S10931-50P, i.e. six faces each with a 4 × 4 array of MPPCs), each having a sensitive area of 3.0 × 3.0 mm2, were optically coupled to the surfaces of the crystal block. Almost all 4096 crystals were identified through Anger-type calculation due to the finely adjusted reflector sheets inserted between the crystal block and light guides. The reflector sheets, which formed a belt of 0.5 mm width, were placed to cover half of the crystals of the second rows from the edges in order to improve identification performance of the crystals near the edges. Energy resolution of 12.7% was obtained at 511 keV with almost uniform light output for all crystal segments thanks to the effective detection of the scintillation photons.

  15. Process Techniques of 15-inch Full-Color High-Resolution Liquid Crystal Displays Addressed by a-Si Thin Film Transistors

    NASA Astrophysics Data System (ADS)

    Fujii, Kenichi; Tanaka, Yasuo; Honda, Kouichi; Tsutsu, Hiroshi; Koseki, Hideo; Hotta, Sadayoshi

    1992-12-01

    A 15 inch-diagonal-size full-color liquid crystal display (LCD) with 1152(× 3)× 900 pixels has been fabricated which enables a portable workstation with improved display performances. The process techniques used for this development are described, with special reference to metallization and dry etching. In multilevel metallization, Cr/Al interconnection is metallurgically undesirable. By contrast, the Cr/Ti/Al metal system provides excellent properties of contact resistivity and thermodynamical stability. Dry etching processes are developed for multilayered insulating films and metallization-related bilayers, namely SiO2/TaOx/SiNx/(i/n+)a-Si and a-Si/Ti, respectively. Fine patterning and easier stepcoverage of subsequently deposited layers are achieved.

  16. Film-Cooling Heat-Transfer Measurements Using Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Hippensteele, Steven A.

    1997-01-01

    The following topics are discussed: (1) The Transient Liquid-Crystal Heat-Transfer Technique; (2) 2-D Film-Cooling Heat-Transfer on an AlliedSignal Vane; and (3) Effects of Tab Vortex Generators on Surface Heat Transfer. Downstream of a Jet in Crossflow.

  17. Crystal chemistry of the G-phases in the {l_brace}Ti, Zr, Hf{r_brace}-Ni-Si systems

    SciTech Connect

    Grytsiv, A.; Chen Xingqiu; Rogl, P. Podloucky, R.; Schmidt, H.; Giester, G.; Pomjakushin, V.

    2007-02-15

    Ternary compounds M{sub 6}Ni{sub 16}Si{sub 7} (M=Ti, Zr, Hf) have been investigated by X-ray powder/single crystal and neutron powder diffraction. Compounds with Zr and Hf crystallize in the ordered Th{sub 6}Mn{sub 23} type (Mg{sub 6}Cu{sub 16}Si{sub 7}-type, space group Fm3-bar m), whereas Ti{sub 6}Ni{sub 16.7}Si{sub 7} contains an additional Ni atom partially occupying the 24e site (M2 site, x=0.4637,0,0; occ.=0.119) inside a Ti octahedron; Ti atoms occupy a split position. Ti{sub 6}Ni{sub 16.7}Si{sub 7} represents a new variant of the filled Th{sub 6}Mn{sub 23} type structure. Ab initio calculations confirm the structural difference: additional Ni atoms favour the 24e site for Ti{sub 6}Ni{sub 16.7}Si{sub 7}, however, for the Zr and Hf-based compounds the unoccupied site renders an energetically lower ground state. Enthalpies of formation of Ti{sub 6}Ni{sub 17}Si{sub 7}, Zr{sub 6}Ni{sub 16}Si{sub 7}, and Hf{sub 6}Ni{sub 16}Si{sub 7} were calculated to be -68.65, -74.78, and -78.59kJ/(mol of atoms), respectively.

  18. Influence of the three dimensionality of the HF electromagnetic field on resistivity variations in Si single crystals during FZ growth

    NASA Astrophysics Data System (ADS)

    Ratnieks, G.; Muiznieks, A.; Buligins, L.; Raming, G.; Mühlbauer, A.; Lüdge, A.; Riemann, H.

    2000-06-01

    Three-dimensional numerical modelling is carried out to analyse the floating zone crystal growth with the needle-eye technique used for the production of high-quality silicon single crystals with large diameters ( ⩾100 mm ). Since the pancake inductor has only one turn, the EM field and the distribution of heat sources and EM forces are only roughly axisymmetric. The non-symmetry together with crystal rotation reflects itself on the hydrodynamic, thermal and dopant concentration fields in the molten zone and causes variations of resistivity in the grown single crystal, which are known as the so-called rotational striations. The non-symmetric high-frequency electromagnetic field of the pancake inductor is calculated by boundary element method. The obtained non-symmetric power distribution on the free melt surface and the corresponding EM forces are used for the coupled calculation of the 3D steady-state hydrodynamic and temperature fields in the molten zone on a body fitted structured 3D grid by a commercial program package with control volume approach. The buoyancy, Marangoni and EM forces are considered. The afterwards calculated corresponding 3D dopant concentration field is used to derive the variations of resistivity in a longitudinal cut of the grown crystal. The results are compared with experimental measurements (photo-scanning method) and with results of 2D transient flow calculations. Rotational striations are found in both 3D-calculated and experimental resistivity distributions and show a qualitative agreement. A Fourier analysis for the resistivity variations is performed and the observed differences are explained by modelling limitations.

  19. In situ Ultrasonic Velocity Measurements Across the Olivine-spinel Transformation in Fe2Si04

    SciTech Connect

    Liu, Q.; Liu, W; Whitaker, M; Wang, L; Li, B

    2010-01-01

    Compressional (P) and shear (S) wave velocities across the olivine-spinel transformation in Fe{sub 2}SiO{sub 4} were investigated in situ using combined synchrotron X-ray diffraction, X-ray imaging, and ultrasonic interferometry up to 5.5 GPa along the 1173 K isotherm. The onset of the spinel to olivine transformation at 4.5 GPa and olivine to spinel transition for Fe{sub 2}SiO{sub 4} at 4.8 GPa was concurrently observed from X-ray diffraction, the amplitude of the ultrasonic signals, the calculated velocities, and the ratio of P and S wave velocities (v{sub P}/v{sub S}). No velocity softening was observed prior to the fayalite to spinel transition. The velocity contrasts across the Fe{sub 2}SiO{sub 4} spinel to fayalite phase transition are derived directly from the measured velocities, which are 13 and 12% for P and S waves, respectively, together with a density contrast of 9.4%. A comparison with literature data indicates that the changes in compressional-wave velocity and density across the olivine-spinel transformation in Fe{sub 2}SiO{sub 4} are comparable to those with different iron concentrations in the (Mg,Fe){sub 2}SiO{sub 4} solid solution, whereas the shear wave velocity contrast decreases slightly with increasing iron concentration.

  20. Compound formation and superconductivity in Au-Si: X-ray absorption measurements on ion-beam-mixed Au-Si films

    SciTech Connect

    Jeon, Y.; Jisrawi, N.; Liang, G.; Lu, F.; Croft, M.; McLean, W.L.; Hart, D.L.; Stoffel, N.G.; Sun, J.Z.; Geballe, T.H.; and others

    1989-03-15

    Multilayered Au-Si thin films have been deposited with the net compositions ''Au/sub 1-//sub x/Si/sub x/,'' x = 0.29, 0.5, and 0.8. After ion-beam mixing these films exhibited superconductivity in the 0.3--1.2 K range despite the nonsuperconducting character of both Au and Si. Near-edge x-ray absorption spectroscopy (XAS) measurements on the Au L/sub 3/ edge in these films indicate that metastable Au-Si compound formation occurs in these ion-mixed materials. Specifically, the XAS measurements indicate changes in Au 5d-orbital occupancy and changes in the local Au structural environment which are both consistent with local compound formation.

  1. Crystal structure of larnite {beta}-Ca{sub 2}SiO{sub 4} and specific features of polymorphic transitions in dicalcium orthosilicate

    SciTech Connect

    Yamnova, N. A. Zubkova, N. V.; Eremin, N. N.; Zadov, A. E.; Gazeev, V. M.

    2011-03-15

    The crystal structure of larnite, a natural analog of synthetic {beta}-Ca{sub 2}SiO{sub 4}, has been determined: a = 5.5051(3) Angstrom-Sign , b = 6.7551(3) Angstrom-Sign , c = 9.3108(5) Angstrom-Sign , {beta} = 94.513(4){sup o}, sp. gr. P2{sub 1}/n, Z = 4, and R{sub 1} = 0.0532 for 1071 reflections with I > 2{sigma} (I). Larnite was found in skarn xenoliths (Lakargi, Kabardino-Balkaria, Russia). The mineral structure is based on a heteropolyhedral glaserite-like framework of interconnected Ca polyhedra and isolated [SiO{sub 4}] tetrahedra. Based on an analysis of the layer-by-layer packing of atoms in the structures of larnite and other Ca{sub 2}SiO{sub 4} polymorphs, the structural features and mechanisms of transitions from high-temperature ({alpha}, {alpha} Prime {sub L}, and {alpha} Prime {sub H}) to low-temperature ({beta} and {gamma}) Ca{sub 2}SiO{sub 4} modifications, as well as their relationship with natural glaserite-like orthosilicates (merwinite Ca{sub 3}Mg[SiO{sub 4}]{sub 2} and bredigite Ca{sub 7}Mg[SiO{sub 4}]{sub 4}), have been considered. The most likely atomic arrangement in hypothetical Ca{sub 2}SiO{sub 4} models has been calculated by the method of atomistic potentials.

  2. Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals

    PubMed Central

    Li, Haifeng; Xiao, Yinguo; Schmitz, Berthold; Persson, Jörg; Schmidt, Wolfgang; Meuffels, Paul; Roth, Georg; Brückel, Thomas

    2012-01-01

    Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around TN the PMRV translates to negative, down to ~−10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices. PMID:23087815

  3. Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals.

    PubMed

    Li, Haifeng; Xiao, Yinguo; Schmitz, Berthold; Persson, Jörg; Schmidt, Wolfgang; Meuffels, Paul; Roth, Georg; Brückel, Thomas

    2012-01-01

    Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around T(N) the PMRV translates to negative, down to ~-10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices. PMID:23087815

  4. Growth conditions, structure, Raman characterization and optical properties of Sm-doped (Lu{sub x}Gd{sub 1-x}){sub 2}SiO{sub 5} single crystals grown by the Czochralski method

    SciTech Connect

    GLowacki, MichaL; Runka, Tomasz; Drozdowski, MirosLaw; Domukhovski, Viktor; Berkowski, Marek

    2012-02-15

    The (Lu{sub x}Gd{sub 0.995-x}Sm{sub 0.005}){sub 2}SiO{sub 5} single crystals with x=0.095, 0.11, 0.15, 0.17, 0.19 0.35 and 0.5 were grown by the Czochralski method. Structural properties were investigated by X-ray diffraction measurements. Unit cell parameters and cell volume were determined by the Rietveld refinement of the collected X-ray powder spectra. The segregation features between Gd and Lu were estimated and analyzed. Vibrational properties of the solid solutions were analyzed on the basis of polarized Raman spectra acquired at 300-875 K temperature range. Absorption and emission spectra of Sm{sup 3+} ion in the crystals with different composition were analyzed in the terms of dopant energy levels, oscillator strengths of transitions and spectral features of luminescence bands in the visible range. Both structural and optical investigations revealed that change of Lu{sup 3+} content in (Lu{sub x}Gd{sub 0.995-x}Sm{sub 0.005}){sub 2}SiO{sub 5} solid solution crystals induces the phase transition from C2/c (Lu{sub 2}SiO{sub 5}) to P2{sub 1}/c (Gd{sub 2}SiO{sub 5}) structure. It was found that the break of LSO to GSO-type structure occurs at 0.15crystals of Sm{sup 3+}-doped (Lu{sub x}Gd{sub 1-x}){sub 2}SiO{sub 5} solid solutions have been grown by Czochralski method and characterized by various techniques. Crystal structure changes from C2/c to P2{sub 1}/c for composition with 0.15crystal structure causes changes in emission spectra. Highlights: Black-Right-Pointing-Pointer The (Lu{sub x}Gd{sub 1-x}){sub 2}SiO{sub 5} crystals are an alternative to LSO and GSO hosts for applications. Black-Right-Pointing-Pointer The break of the P2{sub 1}/c to C2/c structure in (Lu{sub x}Gd{sub 1-x}){sub 2}SiO{sub 5}:Sm occurs for 0.15

  5. Crystal structure of apatite type Ca2.49Nd7.51(SiO4)6O1.75

    PubMed Central

    Le, Thu Hoai; Brooks, Neil R.; Binnemans, Koen; Blanpain, Bart; Guo, Muxing; Van Meervelt, Luc

    2016-01-01

    The title compound, Ca2+xNd8–x(SiO4)6O2–0.5x (x = 0.49), was synthesized at 1873 K and rapidly quenched to room temperature. Its structure has been determined using single-crystal X-ray diffraction and compared with results reported using neutron and X-ray powder diffraction from samples prepared by slow cooling. The single-crystal structure from room temperature data was found to belong to the space group P63/m and has the composition Ca2.49Nd7.51(SiO4)6O1.75 [dicalcium octa­neodymium hexa­kis­(ortho­silicate) dioxide], being isotypic with natural apatite and the previously reported Ca2Nd8(SiO4)6O2 and Ca2.2Nd7.8(SiO4)6O1.9. The solubility limit of calcium in the equilibrium state at 1873 K was found to occur at a composition of Ca2+xNd8–x(SiO4)6O2–0.5x, where x = 0.49. PMID:26958389

  6. Crystal structure of apatite type Ca2.49Nd7.51(SiO4)6O1.75.

    PubMed

    Le, Thu Hoai; Brooks, Neil R; Binnemans, Koen; Blanpain, Bart; Guo, Muxing; Van Meervelt, Luc

    2016-02-01

    The title compound, Ca2+x Nd8-x (SiO4)6O2-0.5x (x = 0.49), was synthesized at 1873 K and rapidly quenched to room temperature. Its structure has been determined using single-crystal X-ray diffraction and compared with results reported using neutron and X-ray powder diffraction from samples prepared by slow cooling. The single-crystal structure from room temperature data was found to belong to the space group P63/m and has the composition Ca2.49Nd7.51(SiO4)6O1.75 [dicalcium octa-neodymium hexa-kis-(ortho-silicate) dioxide], being isotypic with natural apatite and the previously reported Ca2Nd8(SiO4)6O2 and Ca2.2Nd7.8(SiO4)6O1.9. The solubility limit of calcium in the equilibrium state at 1873 K was found to occur at a composition of Ca2+x Nd8-x (SiO4)6O2-0.5x , where x = 0.49. PMID:26958389

  7. Real-time measurements of crystallization processes in viscoelastic polymeric photonic crystals

    NASA Astrophysics Data System (ADS)

    Snoswell, David R. E.; Finlayson, Chris E.; Zhao, Qibin; Baumberg, Jeremy J.

    2015-11-01

    We present a study of the dynamic shear ordering of viscoelastic photonic crystals, based on core-shell polymeric composite particles. Using an adapted shear-cell arrangement, the crystalline ordering of the material under conditions of oscillatory shear is interrogated in real time, through both video imaging and from the optical transmission spectra of the cell. In order to gain a deeper understanding of the macroscopic influences of shear on the crystallization process in this solvent-free system, the development of bulk ordering is studied as a function of the key parameters including duty cycle and shear-strain magnitude. In particular, optimal ordering is observed from a prerandomized sample at shear strains of around 160%, for 1-Hz oscillations. This ordering reaches completion over time scales of order 10 s. These observations suggest significant local strains are needed to drive nanoparticles through energy barriers, and that local creep is needed to break temporal symmetry in such high-viscosity nanoassemblies. Crystal shear-melting effects are also characterized under conditions of constant shear rate. These quantitative experiments aim to stimulate the development of theoretical models which can deal with the strong local particle interactions in this system.

  8. Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy

    NASA Technical Reports Server (NTRS)

    Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

    2014-01-01

    The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the seed crystal. Axial and transverse sections from the as grown crystal samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the seed crystal contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions

  9. A study on dual readout crystal calorimeter for hadron and jet energy measurement at a future lepton collider

    SciTech Connect

    Yeh, G.P.; /Fermilab

    2010-01-01

    Studies of requirements and specifications of crystals are necessary to develop a new generation of crystals for dual readout crystal hadron or total absorption calorimeter. This is a short and basic study of the characteristics and hadron energy measurement of PbWO4 and BGO crystals for scintillation and Cerenkov Dual Readout hadron calorimeter.

  10. Laser cladding of quasi-crystal-forming Al-Cu-Fe-Bi on an Al-Si alloy substrate

    NASA Astrophysics Data System (ADS)

    Biswas, Krishanu; Chattopadhyay, Kamanio; Galun, Rolf; Mordike, Barry L.

    2005-07-01

    We report here the results of an investigation aimed at producing coatings containing phases closely related to the quasi-crystalline phase with dispersions of soft Bi particles using an Al-Cu-Fe-Bi elemental powder mixture on Al-10.5 at. pct Si substrates. A two-step process of cladding followed by remelting is used to fine-tune the alloying, phase distribution, and microstructure. A powder mix of Al64Cu22.3Fe11.7Bi2 has been used to form the clads. The basic reason for choosing Bi lies in the fact that it is immiscible with each of the constituent elements. Therefore, it is expected that Bi will solidify in the form of dispersoids during the rapid solidification. A detailed microstructural analysis has been carried out by using the backscattered imaging mode in a scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructural features are described in terms of layers of different phases. Contrary to our expectation, the quasi-crystalline phase could not form on the Al-Si substrate. The bottom of the clad and remelted layers shows the regrowth of aluminum. The formation of phases such as blocky hexagonal Al-Fe-Si and a ternary eutectic (Al + CuAl2 + Si) have been found in this layer. The middle layer shows the formation of long plate-shaped Al13Fe4 along with hexagonal Al-Fe-Si phase growing at the periphery of the former. The formation of metastable Al-Al6Fe eutectic has also been found in this layer. The top layer, in the case of the as-clad track, shows the presence of plate-shaped Al13Fe4 along with a 1/1 cubic rational approximant of a quasi-crystal. The top layer of the remelted track shows the presence of a significant amount of a 1/1 cubic rational approximant. In addition, the as-clad and remelted microstructures show a fine-scale dispersion of Bi particles of different sizes formed during monotectic solidification. The remelting is found to have a strong effect on the size and distribution of Bi particles. The dry

  11. The electron spin resonance study of heavily nitrogen doped 6H SiC crystals

    SciTech Connect

    Savchenko, D. V.

    2015-01-28

    The magnetic and electronic properties of heavily doped n-type 6H SiC samples with a nitrogen concentration of 10{sup 19} and 4 × 10{sup 19 }cm{sup −3} were studied with electron spin resonance (ESR) at 5–150 K. The observed ESR line with a Dysonian lineshape was attributed to the conduction electrons (CE). The CE ESR (CESR) line was fitted by Lorentzian (insulating phase) (T < 40 K) and by Dysonian lineshape (metallic phase) above 40 K, demonstrating that Mott insulator-metal (IM) transition takes place at ∼40 K, accompanied by significant change in the microwave conductivity. The temperature dependence of CESR linewidth follows the linear Korringa law below 40 K, caused by the coupling of the localized electrons (LE) and CE, and is described by the exponential law above 40 K related to the direct relaxation of the LE magnetic moments via excited levels driven by the exchange interaction of LE with CE. The g-factor of the CESR line (g{sub ‖} = 2.0047(3), g{sub ⊥} = 2.0034(3)) is governed by the coupling of the LE of nitrogen donors at hexagonal and quasi-cubic sites with the CE. The sharp drop in CESR line intensity (25–30 K) was explained by the formation of antiferromagnetic ordering in the spin system close to the IM transition. The second broad ESR line overlapped with CESR signal (5–25 K) was attributed to the exchange line caused by the hopping motion of electrons between occupied and non-occupied positions of the nitrogen donors. Two mechanisms of conduction, hopping and band conduction, were distinguished in the range of T = 10–25 K and T > 50 K, respectively.

  12. Synthesis and crystal structures of RE7Zn(21+x)Si(2-x) [RE = Ce, Pr, and Nd; 0.09 (1) < x < 0.95 (1)].

    PubMed

    Hoos, James; Suen, Nian-Tzu; Bobev, Svilen

    2014-10-01

    The focus of this paper is on the synthesis and crystal structures of three Zn-rich compounds with the general formula RE7Zn(21+x)Si(2-x), where RE = Ce [x = 0.95 (1); heptacerium docosazinc silicon], Pr [x = 0.09 (1); heptapraseodymium henicosazinc disilicon], and Nd [x = 0.53 (1); heptaneodymium docosazinc silicon]. The compounds were obtained by high-temperature reactions, using the respective elements as starting materials. The structures were determined by single-crystal X-ray diffraction. The title compounds crystalize in the orthorhombic space group Pbam (No. 55, Pearson symbol oP60) and are isostructural with about a dozen RE7Zn(21+x)Tt(2-x) (RE = La-Nd; Tt = Ge, Sn, and Pb) compounds previously reported by our group. The results from the present refinements confirm the previously published data on RE7Zn(21+x)Si(2-x) (RE = La and Ce; x ≃ 1.45) [Malik et al. (2013). Intermetallics, 36, 118-126]. Additionally, magnetic susceptibility measurements on the corresponding bulk samples show Curie-Weiss paramagnetic behavior from 5 to 300 K, consistent with RE(3+) ground states and local-moment magnetism due to the core 4f electrons. PMID:25279593

  13. Experimental and Metrological Basis for SI-Traceable Infrared Radiance Measurements From Space

    NASA Astrophysics Data System (ADS)

    Gero, P. J.; Dykema, J. A.; Anderson, J. G.; Leroy, S. S.

    2007-12-01

    In order to establish a climate benchmark record and to be useful in interdecadal climate forecast testing, satellite measurements of high spectral resolution infrared radiance must have uncertainty estimates that can be proven beyond a doubt. An uncertainty in radiance of about 1 part in 1000 is required for climate applications. This can be accomplished by appealing to the best measurement practices of the metrology community. The International System of Units (SI) are linked to fundamental physical properties of matter, and can be realized anywhere in the world without bias. By doing so, one can make an accurate observation to within a specified uncertainty. Achieving SI-traceable radiance measurements from space is a novel requirement, and requires specialized sensor design and a disciplined experimental approach. Infrared remote sensing satellite instruments typically employ blackbody calibration targets, which are tied to the SI through Planck's law and the definition of the Kelvin. The blackbody temperature and emissivity, however, must be determined accurately on- orbit, in order for the blackbody emission scale to be SI-traceable. We outline a methodology of instrument design, pre-flight calibration and on-orbit diagnostics for realizing SI- traceable infrared radiance measurements. This instrument is intended as a component of the Climate Absolute Radiance and Refractivity Earth Observatory (CLARREO), a high priority recommendation of the National Research Council decadal survey. Calibration blackbodies for remote sensing differ from a perfect Planckian blackbody; thus the component uncertainties must be evaluated in order to confer traceability. We have performed traceability experiments in the laboratory to verify blackbody temperature, emissivity and the end-to-end radiance scale. We discuss the design of the Harvard standard blackbody and an intercomparison campaign that will be conducted with the GIFTS blackbody (University of Wisconsin, Madison) and

  14. Calculation of Mass Transfer Coefficients in a Crystal Growth Chamber through Heat Transfer Measurements

    SciTech Connect

    Bell, J H; Hand, L A

    2005-04-21

    The growth rate of a crystal in a supersaturated solution is limited by both reaction kinetics and the local concentration of solute. If the local mass transfer coefficient is too low, concentration of solute at the crystal-solution interface will drop below saturation, leading to a defect in the growing crystal. Here, mass transfer coefficients are calculated for a rotating crystal growing in a supersaturated solution of potassium diphosphate (KDP) in water. Since mass transfer is difficult to measure directly, the heat transfer coefficient of a scale model crystal in water is measured using temperature-sensitive paint (TSP). To the authors' knowledge this is the first use of TSP to measure temperatures in water. The corresponding mass transfer coefficient is then calculated using the Chilton- Colburn analogy. Measurements were made for three crystal sizes at two running conditions each. Running conditions include periodic reversals of rotation direction. Heat transfer coefficients were found to vary significantly both across the crystal faces and over the course of a rotation cycle, but not from one face to another. Mean heat transfer coefficients increased with both crystal size and rotation rate. Computed mass transfer coefficients were broadly in line with expectations from the full-scale crystal growth experiments. Additional experiments show that continuous rotation of the crystal results in about a 30% lower heat transfer compared to rotation with periodic reversals. The continuous rotation case also shows a periodic variation in heat transfer coefficient of about 15%, with a period about 1/20th of the rotation rate.

  15. Magnetic structures of β{sub I}-Li{sub 2}CoSiO{sub 4} and γ{sub 0}-Li{sub 2}MnSiO{sub 4}: Crystal structure type vs. magnetic topology

    SciTech Connect

    Avdeev, Maxim; Mohamed, Zakiah; Ling, Chris D.

    2014-08-15

    The magnetic structure and properties of the candidate lithium-ion battery cathode materials Pbn2{sub 1}(≡Pna2{sub 1}) Li{sub 2}CoSiO{sub 4} and P2{sub 1}/n Li{sub 2}MnSiO{sub 4} have been studied experimentally using low-temperature neutron powder diffraction and magnetometry. Both materials undergo long-range antiferromagnetic ordering, at 14 K and 12 K respectively, due to super–super-exchange mediated by bridging silicate groups. Despite having different crystal structures (wurtzite- vs. “dipolar”-type), Li{sub 2}CoSiO{sub 4} and Li{sub 2}MnSiO{sub 4} have the same topology in terms of magnetic interactions, and adopt collinear magnetic structures of the same type with the propagation vectors (0, 1/2, 1/2) and (1/2, 0, 1/2), respectively. The magnetic moments in the two materials are aligned in parallel and obliquely to the distorted closed-packed layers of oxygen atoms. The experimentally observed values of the ordered magnetic moments, 2.9 μ{sub B} and 4.6 μ{sub B}, are close to those expected for d{sup 7} Co{sup 2+} and d{sup 5} Mn{sup 2+}, respectively. - Graphical abstract: Despite the different crystal structures β{sub I}-Li{sub 2}CoSiO{sub 4} and γ{sub 0}-Li{sub 2}MnSiO{sub 4} have similar magnetic topology and as a result adopt magnetic structure of the same type. - Highlights: • Magnetic structures of Li{sub 2}CoSiO{sub 4} and Li{sub 2}MnSiO{sub 4} were studied for the first time. • Both materials antiferromagnetically order around 12–14 K. • Despite different crystal structure magnetic structures are of the same type. • The fact is attributed to similar topology of magnetic interactions.

  16. Dependences of the Diffraction Efficiency of Photorefractive Holograms on the Sample Thickness and Orientation Angle in a (ī ī 0)-cut Bi12SiO20 Crystal

    NASA Astrophysics Data System (ADS)

    Shepelevich, V. V.; Makarevich, A. V.; Shandarov, S. M.; Ropot, P. I.; Zagorskii, A. E.

    2016-02-01

    We present the results of experimental studies of the dependence of the diffraction efficiency of nonoblique transmission holograms formed in the sample of a (īī0)-cut photorefractive piezoelectric Bi12SiO20 crystal on the sample thickness and orientation angle of the grating vector at two fixed mutually orthogonal orientations of the linear polarization vector of the reading beam. It is shown that only if along with optical activity of the crystal, the electrooptic, inverse piezoelectric, and photoelastic effects are taken into account in the analytical diffraction model, it is possible to carry out satisfactory theoretical interpretation of the experimental data.

  17. Influence of stress in GaN crystals grown by HVPE on MOCVD-GaN/6H-SiC substrate.

    PubMed

    Zhang, Lei; Yu, Jiaoxian; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Shao, Yongliang; Zhang, Haodong; Tian, Yuan

    2014-01-01

    GaN crystals without cracks were successfully grown on a MOCVD-GaN/6H-SiC (MGS) substrate with a low V/III ratio of 20 at initial growth. With a high V/III ratio of 80 at initial growth, opaque GaN polycrystals were obtained. The structural analysis and optical characterization reveal that stress has a great influence on the growth of the epitaxial films. An atomic level model is used to explain these phenomena during crystal growth. It is found that atomic mobility is retarded by compressive stress and enhanced by tensile stress. PMID:24569601

  18. Influence of stress in GaN crystals grown by HVPE on MOCVD-GaN/6H-SiC substrate

    PubMed Central

    Zhang, Lei; Yu, Jiaoxian; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Shao, Yongliang; Zhang, Haodong; Tian, Yuan

    2014-01-01

    GaN crystals without cracks were successfully grown on a MOCVD-GaN/6H-SiC (MGS) substrate with a low V/III ratio of 20 at initial growth. With a high V/III ratio of 80 at initial growth, opaque GaN polycrystals were obtained. The structural analysis and optical characterization reveal that stress has a great influence on the growth of the epitaxial films. An atomic level model is used to explain these phenomena during crystal growth. It is found that atomic mobility is retarded by compressive stress and enhanced by tensile stress. PMID:24569601

  19. A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector

    NASA Astrophysics Data System (ADS)

    Martemianov, M.; Kulikov, V.; Demissie, B. T.; Marinides, Z.; Akondi, C. S.; Annand, J. R. M.; Arends, H. J.; Beck, R.; Borisov, N.; Braghieri, A.; Briscoe, W. J.; Cherepnya, S.; Collicott, C.; Costanza, S.; Downie, E. J.; Dieterle, M.; Ferretti Bondy, M. I.; Fil'kov, L. V.; Garni, S.; Glazier, D. I.; Glowa, D.; Gradl, W.; Gurevich, G.; Hornidge, D.; Huber, G. M.; Kaeser, A.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Krusche, B.; Lazarev, A.; Linturi, J. M.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Manley, D. M.; Martel, P. P.; Middleton, D. G.; Miskimen, R.; Mushkarenkov, A.; Neganov, A.; Neiser, A.; Oberle, M.; Ostrick, M.; Ott, P.; Otte, P. B.; Oussena, B.; Pedroni, P.; Polonski, A.; Prakhov, S.; Ron, G.; Rostomyan, T.; Sarty, A.; Schott, D. M.; Schumann, S.; Sokhoyan, V.; Steffen, O.; Strakovsky, I. I.; Strub, Th.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Usov, Yu. A.; Wagner, S.; Watts, D. P.; Wettig, J.; Werthmüller, D.; Witthauer, L.; Wolfes, M.

    2015-04-01

    We report on a measurement of the neutron detection efficiency in NaI crystals in the Crystal Ball detector obtained from a study of single π0 photoproduction on deuterium using the tagged photon beam at the Mainz Microtron. The results were obtained up to a neutron energy of 400 MeV . They are compared to previous measurements made more than 15 years ago at the pion beam at the BNL AGS.

  20. Automatic liquid crystal thermography for transient heat transfer measurements in hypersonic flow

    NASA Astrophysics Data System (ADS)

    Babinsky, H.; Edwards, J. A.

    1996-08-01

    A technique has been developed to measure surface heat transfer on windtunnel models in hypersonic flow based on the colour response of encapsulated thermochromic liquid crystals. The method supplies results of a superior spatial resolution at experimental uncertainties comparable to traditional methods. The approach is different from other liquid crystal applications in several key areas. It combines the calibration of the liquid crystal coating with the actual mesurement and therefore allows for an efficient experiment. The method is automated in most steps involved. Results are shown for the flow over an axisymmetric compression corner at Mach 5 and compared with surface thermocouple measurements.