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Sample records for napyivyizolyuyuchomu 6h sic

  1. Junction barrier Schottky diodes in 6H SiC

    NASA Astrophysics Data System (ADS)

    Zetterling, Carl-Mikael; Dahlquist, Fanny; Lundberg, Nils; Östling, Mikael; Rottner, Kurt; Ramberg, Lennart

    1998-09-01

    Junction barrier Schottky (JBS) diodes in 6H SiC have been fabricated and characterised electrically. This device, demonstrated in silicon technology, has the advantage of a low forward voltage drop comparable to that of Schottky diodes, as well as a high blocking voltage and low reverse leakage current of a pn junction. This is especially attractive for wide bandgap materials such as SiC in which pn junctions have a large forward voltage drop. The devices were capable of blocking up to 1100 V with a leakage current density of 0.15 A cm -2, limited by the leakage when the drift region was fully depleted, or breakdown of the SiC material itself. The forward conduction was limited by an on-resistance of 20 mΩ cm 2, resulting in forward voltage drops of 2.6 V at 100 A cm -2.

  2. Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates

    NASA Technical Reports Server (NTRS)

    Steckl, A. J.; Roth, M. D.; Powell, J. A.; Larkin, D. J.

    1993-01-01

    The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic-scale images of the 3C SiC surface have been obtained by STM which confirm the 111 line type orientation of the cubic 3C layer grown on the 0001 plane type surface of the hexagonal 6H substrate. The nearest-neighbor atomic spacing for the 3C layer has been measured to be 3.29 +/- 0.2 A, which is within 7 percent of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to CVD growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 micron.

  3. Aluminum acceptor four particle bound exciton complex in 4H, 6H, and 3C SiC

    NASA Technical Reports Server (NTRS)

    Clemen, L. L.; Devaty, R. P.; Macmillan, M. F.; Yoganathan, M.; Choyke, W. J.; Larkin, D. J.; Powell, J. A.; Edmond, J. A.; Kong, H. S.

    1993-01-01

    Evidence is presented for a four particle acceptor complex in 3C, 6H, and 4H SiC, obtained in low-temperature photoluminescence and cathodoluminescence experiments. The new lines were observed in p-type films lightly doped with aluminum, of 6H, 4H, and 3C SiC grown on the silicon (0001) face of 6H SiC under special conditions. The lines increase in intensity as more aluminum is added during growth. The multiplicity of observed lines is consistent with symmetry-based models similar to those which have been proposed to describe 4A centers in p-type zincblende semiconductors.

  4. Dimensional isotropy of 6H and 3C SiC under neutron irradiation

    NASA Astrophysics Data System (ADS)

    Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki; Terrani, Kurt; Specht, Eliot D.

    2016-04-01

    This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.02-20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstrated equivalent swelling behavior. Moreover the 6H-SiC expanded isotropically. The magnitude of the swelling followed a ∼0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ∼7.8% volume expansion in SiC was observed prior to amorphization. Above ∼0.9 × 1025 n/m2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm3. The as-amorphized density was the same at the 2 × 1025 and 2 × 1026 n/m2 (E > 0.1 MeV) dose levels.

  5. N-VSi-related center in non-irradiated 6H SiC nanostructure

    NASA Astrophysics Data System (ADS)

    Bagraev, Nikolay; Danilovskii, Eduard; Gets, Dmitrii; Kalabukhova, Ekaterina; Klyachkin, Leonid; Malyarenko, Anna; Savchenko, Dariya; Shanina, Bella

    2014-02-01

    We present the first findings of the vacancy-related centers identified by the electron spin resonance (ESR) and electrically-detected (ED) ESR method in the non-irradiated 6H-SiC nanostructure. This planar 6H-SiC nanostructure represents the ultra-narrow p-type quantum well confined by the δ-barriers heavily doped with boron on the surface of the n-type 6H-SiC (0001) wafer. The EDESR method by measuring the only magnetoresistance of the 6H SiC nanostructure under the high frequency generation from the δ-barriers appears to allow the identification of the silicon vacancy centers as well as the triplet center with spin state S=1. The same triplet center that is characterized by the larger value of the zero-field splitting constant D and anisotropic g-factor is revealed by the ESR (X-band) method. The hyperfine (hf) lines in the ESR and EDESR spectra originating from the hf interaction with the 14N nucleus allow us to attribute this triplet center to the N-VSi defect.

  6. Dimensional isotropy of 6H and 3C SiC under neutron irradiation

    DOE PAGESBeta

    Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki; Terrani, Kurt A.; Specht, Eliot D.

    2016-01-16

    This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstrated equivalent swelling behavior.more » Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ~0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ~7.8% volume expansion in SiC was observed prior to amorphization. Above ~0.9 × 1025 n/m2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm3. As a result, the as-amorphized density was the same at the 2 × 1025 and 2 × 1026 n/m2 (E > 0.1 MeV) dose levels.« less

  7. Measured Attenuation of Coplanar Waveguide on 6H, p-type SiC and High Purity Semi-Insulating 4H SiC through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Schwartz, Zachary D.; Alterovitz, Samuel A.; Downey, Alan N.

    2004-01-01

    Wireless sensors for high temperature applications such as oil drilling and mining, automobiles, and jet engine performance monitoring require circuits built on wide bandgap semiconductors. In this paper, the characteristics of microwave transmission lines on 4H-High Purity Semi-Insulating SiC and 6H, p-type SiC is presented as a function of temperature and frequency. It is shown that the attenuation of 6H, p-type substrates is too high for microwave circuits, large leakage current will flow through the substrate, and that unusual attenuation characteristics are due to trapping in the SiC. The 4H-HPSI SiC is shown to have low attenuation and leakage currents over the entire temperature range.

  8. Homoepitaxy of 6H and 4H SiC on nonplanar substrates

    SciTech Connect

    Nordell, N.; Karlsson, S.; Konstantinov, A.O.

    1998-01-01

    Growth by vapor phase epitaxy around stripe mesas and in trenches formed by reactive ion etch on 6H and 4H SiC substrates has been investigated. The mesas were aligned with the low index {l_angle}11{bar 2}0{r_angle} and {l_angle}1{bar 1}00{r_angle} directions, as well as with the high index {l_angle}1,1+{radical}(3),{ovr 2+{radical}(3)},0{r_angle} directions, in order to reveal and study the growth habit. It was found that a low C:Si ratio gave a smooth growth and small differences in growth rate between lattice planes. A larger C:Si ratio gave more faceted growth, both limited by surface kinetics and surface diffusion, and the growth rate was 10{percent} lower in the [1{bar 1}00] direction and 10{percent} higher in the [11{bar 2}0] direction, than on the substrate. Growth on mesas oriented parallel to the substrate off-orientation shows clear step-flow growth, while growth on mesas oriented perpendicular to the off-orientation reveals the singular (0001) plane, where islands are observed, which might indicate Stranski{endash}Krastanov growth. {copyright} {ital 1998 American Institute of Physics.}

  9. 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.

  10. Approaching Truly Freestanding Graphene: The Structure of Hydrogen-Intercalated Graphene on 6 H -SiC (0001 )

    NASA Astrophysics Data System (ADS)

    Sforzini, J.; Nemec, L.; Denig, T.; Stadtmüller, B.; Lee, T.-L.; Kumpf, C.; Soubatch, S.; Starke, U.; Rinke, P.; Blum, V.; Bocquet, F. C.; Tautz, F. S.

    2015-03-01

    We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the (0001) face of 6 H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full (6 √{3 }×6 √{3 } )-R 30 ° unit cell, based on a van der Waals corrected exchange correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments, a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and the lowest known adsorption energy per atom for graphene on any substrate. A structural comparison to other graphenes suggests that hydrogen-intercalated graphene on 6 H -SiC (0001 ) approaches ideal graphene.

  11. N-V{sub Si}-related center in non-irradiated 6H SiC nanostructure

    SciTech Connect

    Bagraev, Nikolay; Danilovskii, Eduard; Gets, Dmitrii; Klyachkin, Leonid; Malyarenko, Anna; Kalabukhova, Ekaterina; Shanina, Bella; Savchenko, Dariya

    2014-02-21

    We present the first findings of the vacancy-related centers identified by the electron spin resonance (ESR) and electrically-detected (ED) ESR method in the non-irradiated 6H-SiC nanostructure. This planar 6H-SiC nanostructure represents the ultra-narrow p-type quantum well confined by the δ-barriers heavily doped with boron on the surface of the n-type 6H-SiC (0001) wafer. The EDESR method by measuring the only magnetoresistance of the 6H SiC nanostructure under the high frequency generation from the δ-barriers appears to allow the identification of the silicon vacancy centers as well as the triplet center with spin state S=1. The same triplet center that is characterized by the larger value of the zero-field splitting constant D and anisotropic g-factor is revealed by the ESR (X-band) method. The hyperfine (hf) lines in the ESR and EDESR spectra originating from the hf interaction with the {sup 14}N nucleus allow us to attribute this triplet center to the N-V{sub Si} defect.

  12. Rb and Cs deposition on epitaxial graphene grown on 6H -SiC(0001)

    NASA Astrophysics Data System (ADS)

    Watcharinyanon, S.; Virojanadara, C.; Johansson, L. I.

    2011-11-01

    Epitaxial graphene grown on the silicon-terminated SiC(0001) is doped by alkali metals deposited on the surface. The synchrotron radiation based photoelectron spectroscopy results presented reveal that Rb and Cs deposited on monolayer graphene samples, grown on the silicon-terminated SiC(0001), gives rise to n-type doping, i.e. electron transfer from the metal to the graphene layer. The Dirac point of the single π-cone is found to shift downwards away from the Fermi level by ca. 1.0 eV after alkali metal depositions. The adsorbed Rb and Cs atoms do initially disrupt the bonds in the graphene layer but after heating the bonds appear to be recreated when the alkali metal coverage start to decrease due to thermal desorption. None of these two alkali metals do intercalate into the graphene and buffer layer after depositing at room temperature or after heating. This is contrary to the case of Li where intercalation occurred directly after deposition.

  13. Nuclear Reaction Analysis of Helium Retention in 6H SiC as a function of irradiation and annealing

    NASA Astrophysics Data System (ADS)

    Bissell, L. J.; Smith, R. J.; Shutthanadan, V.; Adams, E. M.; Thevuthasan, S.; Jiang, W.; Weber, W. J.; Zhang, Y.

    2002-10-01

    Silicon carbide has been proposed as a coating material in nuclear fuel, and silicon carbide composites have been proposed as cladding material in advanced gas-cooled and light water reactors. As such, the effects of irradiation and fission gases on the performance of SiC in the reactor environment are critical in several ways. Since He serves as a fission gas, low-energy He (< 50 keV) will be colliding with coolant gas and outer surface cladding layers. As such, it is important to understand He retention in SiC under advanced reactor operating conditions. We investigated He retention in single crystal 6H SiC as a function of irradiation dose and annealing temperature using nuclear reaction analysis (NRA) via the 3He(D,alpha)1H reaction. Helium ions with 40 keV energy were implanted in the SiC to a depth of ˜360 nm at room temperature under high vacuum conditions. The samples were then transferred to another high vacuum chamber where the NRA was performed using a 1.0 MeV D+ beam. Helium retention was studied as a function of D+ irradiation dose from 5 x 10^(16) to 4 x 10^(18) D+ /cm2, and as a function of annealing temperature ranging from 300 1600 K. No significant helium loss was observed under this dosage range, and only annealing temperatures above 1400 K caused measurable loss of helium. These results will be discussed along with the details associated with the 3He(D,alpha)1H nuclear reaction.

  14. Measurement of N-Type 6H SiC Minority-Carrier Diffusion Lengths by Electron Bombardment of Schottky Barriers

    NASA Technical Reports Server (NTRS)

    Hubbard, S. M.; Tabib-Azar, M.; Balley, S.; Rybickid, G.; Neudeck, P.; Raffaelle, R.

    2004-01-01

    Minority-Carrier diffusion lengths of n-type 6H-SiC were measured using the electron-beam induced current (EBIC) technique. Experimental values of primary beam current, EBIC, and beam voltage were obtained for a variety of SIC samples. This data was used to calculate experimental diode efficiency vs. beam voltage curves. These curves were fit to theoretically calculated efficiency curves, and the diffusion length and metal layer thickness were extracted. The hole diffusion length in n-6H SiC ranged from 0.93 +/- 0.15 microns.

  15. 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.

  16. Electronic Transitions of Jet-cooled SiC2, Si2Cn (n=1-3), Si3Cn (n = 1,2), and SiC6H4 between 250 and 710 nm

    NASA Astrophysics Data System (ADS)

    Steglich, M.; Maier, J. P.

    2015-03-01

    Electronic transitions of the title molecules were measured between 250 and 710 nm using a mass-resolved 1 + 1’ resonant two-photon ionization technique at a resolution of 0.1 nm. Calculations at the B3LYP/aug-cc-pVQZ level of theory support the analyses. Because of their spectral properties, SiC2, linear Si2C2, Si3C, and SiC6H4 are interesting target species for astronomical searches in the visible spectral region. Of special relevance is the Si-C2-Si chain, which features a prominent band at 516.4 nm of a strong transition (f = 0.25). This band and one from SiC6H4 at 445.3 nm were also investigated at higher resolution (0.002 nm).

  17. Theoretical and electron paramagnetic resonance studies of hyperfine interaction in nitrogen doped 4H and 6H SiC

    SciTech Connect

    Szász, K.; Gali, A.

    2014-02-21

    Motivated by recent experimental findings on the hyperfine signal of nitrogen donor (N{sub C}) in 4 H and 6 H SiC, we calculate the hyperfine tensors within the framework of density functional theory. We find that there is negligible hyperfine coupling with {sup 29}Si isotopes when N{sub C} resides at h site both in 4 H and 6 H SiC. We observe measurable hyperfine coupling to a single {sup 29}Si at k site in 4 H SiC and k{sub 1} site in 6 H SiC. Our calculations unravel that such {sup 29}Si hyperfine coupling does not occur at k{sub 2} site in 6 H SiC. Our findings are well corroborated by our new electron paramagnetic resonance studies in nitrogen doped 6 H SiC.

  18. Three-dimensional electron-positron momentum distribution of O3+-irradiated 6H SiC using two positron spectroscopy techniques simultaneously

    NASA Astrophysics Data System (ADS)

    Williams, Christopher; Burggraf, Larry; Adamson, Paul; Petrosky, James

    2011-01-01

    A three-dimensional (3D) positron annihilation spectroscopy system (3DPASS) capable of determining 3D electron-positron (e--e+) momentum densities from measurements of deviations from co-linearity and energies of photons from e--e+ annihilation events was employed to examine the effects of O-atom defects in 6H SiC. Three-dimensional momentum datasets were determined for 6H SiC irradiated with 24 MeV O3+ ions. Angular correlation of annihilation radiation (ACAR) and coincidence Doppler-broadening of annihilation radiation (CDBAR) analyses are presented. In addition, a novel technique is illustrated for analyzing 3D momentum datasets in which the parallel momentum component, p|| (obtained from the CDBAR measurement) is selected for annihilation events that possess a particular perpendicular momentum component, p- observed in the 2D ACAR spectrum.

  19. The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

    NASA Astrophysics Data System (ADS)

    Savchenko, D.; Shanina, B.; Kalabukhova, E.; Pöppl, A.; Lančok, J.; Mokhov, E.

    2016-04-01

    We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation "sandwich method" (SSM) with a donor concentration of about 1017 cm-3 at T = 10-40 K. The donor electrons of the N donors substituting quasi-cubic "k1" and "k2" sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1-1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1-1 for the donor electrons of N substituting hexagonal ("h") site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm-1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed.

  20. Growth of Defect-Free 3C-Sic on 4H- and 6H-SIC Mesas Using Step-Free Surface Heteroepitaxy

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Huang, Xianrong R.; Dudley, Michael

    2002-01-01

    A new growth process, herein named step-free surface heteroepitaxy, has achieved 3C-SiC films completely free of double positioning boundaries and stacking faults on 4H-SiC and 6H-SiC substrate mesas. The process is based upon the initial 2-dimensional nucleation and lateral expansion of a single island of 3C-SiC on a 4H- or 6H-SiC mesa surface that is completely free of bilayer surface steps. Our experimental results indicate that substrate-epilayer in-plane lattice mismatch (Delta/a = 0.0854% for 3C/4H) is at least partially relieved parallel to the interface in the initial bilayers of the heterofilm, producing an at least partially relaxed 3C-SiC film without dislocations that undesirably thread through the thickness of the epilayer. This result should enable realization of improved 3C-SiC devices.

  1. Calculation of positron annihilation characteristics of six main defects in 6 H -SiC and the possibility to distinguish them experimentally

    NASA Astrophysics Data System (ADS)

    Linez, F.; Makkonen, I.; Tuomisto, F.

    2016-07-01

    We have determined positron annihilation characteristics (lifetime and Doppler broadening) in six basic vacancy-type defects of 6 H -SiC and two nitrogen-vacancy complexes using ab initio calculations. The positron characteristics obtained allow us to point out which positron technique in the most adapted to identify a particular defect. They show that the coincidence Doppler broadening technique is the most relevant for observing the silicon vacancy-nitrogen complexes, VSiNC , and carbon vacancy-carbon antisite ones, VCCSi . For the other studied defects, the calculated positron characteristics are found to be too close for the defects to be easily distinguished using a single positron annihilation technique. Then it is required to use complementary techniques, positron annihilation based or other.

  2. Oxidation-Induced Deep Levels in n - and p -Type 4 H - and 6 H -SiC and Their Influence on Carrier Lifetime

    NASA Astrophysics Data System (ADS)

    Booker, I. D.; Abdalla, H.; Hassan, J.; Karhu, R.; Lilja, L.; Janzén, E.; Sveinbjörnsson, E. Ö.

    2016-07-01

    We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4 H -SiC and their 6 H -SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n - and p -type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

  3. Thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap semiconductors SiC, GaN, and ZnO

    SciTech Connect

    Huang, Zheng; Lü, Tie-Yu; Wang, Hui-Qiong; Zheng, Jin-Cheng

    2015-09-15

    We have investigated the thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap(n-type) semiconductors SiC, GaN, and ZnO based on first-principles calculations and Boltzmann transport theory. Our results show that the thermoelectric performance increases from 3C to 6H, 4H, and 2H structures with an increase of hexagonality for SiC. However, for GaN and ZnO, their power factors show a very weak dependence on the polytype. Detailed analysis of the thermoelectric properties with respect to temperature and carrier concentration of 4H-SiC, 2H-GaN, and 2H-ZnO shows that the figure of merit of these three compounds increases with temperature, indicating the promising potential applications of these thermoelectric materials at high temperature. The significant difference of the polytype-dependent thermoelectric properties among SiC, GaN, and ZnO might be related to the competition between covalency and ionicity in these semiconductors. Our calculations may provide a new way to enhance the thermoelectric properties of wide-band-gap semiconductors through atomic structure design, especially hexagonality design for SiC.

  4. Formation of SiC - like layers on Si surface in contact with C6H5CH3 solution by UV laser irradiation

    NASA Astrophysics Data System (ADS)

    Yusupov, M.; Fedorenko, L.; Lytvyn, O.; Yukhimchuk, V.

    2008-09-01

    The review of results of submicron surface layers formation is presented under ultraviolet (UV) N2 - laser (λ = 0.337 μm, tp = 5 ns) ablation of silicon target in liquid environment C6H5CH3. The morphological and deformation state of a near-surface Si layer was investigated by polarization modulation spectroscopy (PMS), atom force microscopy (AFM) and Raman spectra methods before and after irradiation. After irradiation AFM data shows the formation of submicron structures with hexagonal-like type of regularity on Si surface, PMS spectra indicates the increasing of refractive index, Raman spectroscopy reveals the broad band in the range 740-800 cm-1. All that facts allow us to assume the possibility of SiC-like layer formation on silicon monocrystal surface by laser stimulated diffusion of carbon atoms from liquid media. The surface morphology and composition of the irradiated surface varies considerable with the number of laser shots.

  5. 6H-SiC Photoconductive Switches Triggered at Below Bandgap Wavelengths

    SciTech Connect

    Sullivan, J S; Stanley, J R

    2007-02-13

    Semi-insulating silicon carbide (SiC) is an attractive material for application as high voltage, photoconductive semiconductor switches (PCSS) due to its large bandgap, high critical electric field strength, high electron saturation velocity and high thermal conductivity. The critical field strength of 300 MV/m for 6H-SiC makes it particularly attractive for compact, high voltage, fast switching applications. To realize the benefits of the high bulk electric field strength of SiC and diffuse switch current, carriers must be excited throughout the bulk of the photo switch. Photoconducting switches with opposing electrodes were fabricated on ''a'' plane, vanadium compensated, semiinsulating, 6H-SiC substrates. The PCSS devices were switched by optically exciting deep extrinsic levels lying within the 6H-SiC bandgap. The SiC photoswitches were tested up to a bias voltage of 11000 V with a corresponding peak current of 150 A. The 6H-SiC substrates withstood average electric fields up to 27 MV/m. Minimum PCCS dynamic resistances of 2 and 10 {Omega} were obtained with 13 mJ optical pulses at 532 and 1064 nm wavelengths, respectively.

  6. Nitrogen-induced structures in epitaxial graphene on 6H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Sun, Guofeng; Rhim, Sung-Hyon; Qi, Yun; Weinert, Michael; Li, Lian

    2009-03-01

    Nitrogen-induced structures on epitaxial graphene grown on 6H- SiC(0001) are studied by scanning tunneling microscopy (STM) and first-principles calculations. Several defect structures produced by nitrogen incorporation are observed by STM. Calculations of the energetics of nitrogen substitution at various sites neighboring a carbon vacancy indicate that nitrogen prefers to be at the site nearest to the vacancy, consistent with the STM observations.

  7. A new doping method using metalorganics in chemical vapor deposition of 6H-SiC

    NASA Astrophysics Data System (ADS)

    Yoshida, S.; Sakuma, E.; Misawa, S.; Gonda, S.

    1984-01-01

    Aluminum doping was performed using triethylaluminum as the dopant in chemical vapor deposition of 6H-silicon carbide (SiC). Measurements on the electrical and cathodoluminescent properties of the epilayers indicate that the doping concentration of aluminum can be easily controlled by the flow rate of metalorganics. Electroluminescence was also observed for the pn junctions prepared by the successive growth of a nondoped n layer and a p layer doped with aluminum using metalorganics.

  8. Synergistic effects of iodine and silver ions co-implanted in 6H-SiC

    NASA Astrophysics Data System (ADS)

    Kuhudzai, R. J.; Malherbe, J. B.; Hlatshwayo, T. T.; van der Berg, N. G.; Devaraj, A.; Zhu, Z.; Nandasiri, M.

    2015-12-01

    Motivated by the aim of understanding the release of fission products through the SiC coating of fuel kernels in modern high temperature nuclear reactors, a fundamental investigation is conducted to understand the synergistic effects of implanted silver (Ag) and iodine (I) in 6H-SiC. The implantation of the individual species, as well as the co-implantation of 360 keV ions of I and Ag at room temperature in 6H-SiC and their subsequent annealing behaviour has been investigated by Secondary Ion Mass Spectrometry (SIMS), Atom Probe Tomography (APT) and X-ray Photoelectron Spectroscopy (XPS). SIMS and APT measurements indicated the presence of Ag in the co-implanted samples after annealing at 1500 °C for 30 h in sharp contrast to the samples implanted with Ag only. In samples implanted with Ag only, complete loss of the implanted Ag was observed. However, for I only implanted samples, some iodine was retained. APT of annealed co-implanted 6H-SiC showed clear spatial association of Ag and I clusters in SiC, which can be attributed to the observed I assisted retention of Ag after annealing. Such detailed studies will be necessary to identify the fundamental mechanism of fission products migration through SiC coatings.

  9. Synergistic Effects of Iodine and Silver Ions Co-Implanted in 6H-SiC

    SciTech Connect

    Kuhudzai, Remeredzai J.; Malherbe, Johan; Hlatshwayo, T. T.; van der Berg, N. G.; Devaraj, Arun; Zhu, Zihua; Nandasiri, Manjula I.

    2015-10-23

    Motivated by the aim of understanding the release of fission products through the SiC coating of fuel kernels in modern high temperature nuclear reactors, a fundamental investigation is conducted to understand the synergistic effects of implanted silver (Ag) and iodine (I) in 6H-SiC. The implantation of the individual species, as well as the co-implantation of 360 keV ions of I and Ag at room temperature in 6H-SiC and their subsequent annealing behavior has been investigated by Secondary Ion Mass Spectrometry (SIMS), Atom Probe Tomography (APT) and X-ray Photoelectron Spectroscopy (XPS). SIMS and APT measurements indicated the presence of Ag in the co-implanted samples after annealing at 1500 ºC for 30 hours in sharp contrast to the samples implanted with Ag only. In samples implanted with Ag only, complete loss of the implanted Ag was observed. However, for I only implanted samples, some iodine was retained. APT of annealed co-implanted 6H-SiC showed clear spatial association of Ag and I clusters in SiC, which can be attributed to the observed I assisted retention of Ag after annealing. Such detailed studies will be necessary to identify the fundamental mechanism of fission products migration through SiC coatings.

  10. High-voltage 6H-SiC p-n junction diodes

    NASA Technical Reports Server (NTRS)

    Matus, L. G.; Powell, J. A.; Salupo, C. S.

    1991-01-01

    A chemical vapor deposition (CVD) process has been used to produce device structures of n- and p-type 6H-SiC epitaxial layers on commercially produced single-crystal 6H-SiC wafers. Mesa-style p-n junction diodes were successfully fabricated from these device structures using reactive ion etching, oxide passivation, and electrical contact metallization techniques. When tested in air, the 6H-SiC diodes displayed excellent rectification characteristics up to the highest temperature tested, 600 C. To observe avalanche breakdown of the p-n junction diodes, testing under a high-electrical-strength liquid was necessary. The avalanche breakdown voltage was 1000 V representing the highest reverse breakdown voltage to be reported for any CVD-grown SiC diode.

  11. Lattice-matching of Si grown on 6H-SiC(000-1) C-face

    NASA Astrophysics Data System (ADS)

    Li, L. B.; Chen, Z. M.; Xie, L. F.; Yang, C.

    2014-01-01

    Si films with <111> preferred orientation have been prepared on 6H-SiC(000-1) C-face. HRTEM and SAED results indicate that the Si film has epitaxial connection with the 6H-SiC substrate and the parallel-plane relationship of the Si/6H-SiC heterostructure is (111)Si//(000-1)6H-SiC. Using fast Fourier transform and Fourier mask filtering technique, misfit dislocations are clearly observed at the Si/6H-SiC interface, which accommodate the most of lattice mismatch strain. Every four Si (111) lattice planes are registered with five 6H-SiC(000-1) lattice planes along the interface. Based on the 4:5 lattice matching mode, the lattice structure of the Si/6H-SiC interface and its stability were energetically investigated by molecular dynamics simulations. When the Si films grow preferentially along <111> orientation on 6H-SiC(000-1) C-face, the misfit strain in Si layer significantly reduces due to the relaxation of C atoms in SiC layer near the Si/6H-SiC interface, and thus the Si/6H-SiC heterostructure has a stable interface with a small interface formation energy of -14.24 eV.

  12. VIBRATIONALLY EXCITED C{sub 6}H

    SciTech Connect

    Gottlieb, C. A.; McCarthy, M. C.; Thaddeus, P.

    2010-08-15

    Rotational spectra of the linear carbon chain radical C{sub 6}H in two low-lying excited vibrational states were observed both at millimeter wavelengths in a low-pressure glow discharge and at centimeter wavelengths in a supersonic molecular beam. Two series of harmonically related lines with rotational constants within 0.3% of the {sup 2{Pi}} ground state were assigned to the {sup 2{Sigma}} and {sup 2{Delta}} vibronic components of an excited bending vibrational level. Measurements of the intensities of the lines in the glow discharge indicate that the {sup 2{Sigma}} component lies very close to ground, but the {sup 2{Delta}} component is much higher in energy. The standard Hamiltonian for an isolated {sup 2{Delta}} state with five spectroscopic constants reproduces the observed rotational spectrum, but several high-order distortion terms in the spin-rotation interaction are needed to reproduce the spectrum of the {sup 2{Sigma}} component in C{sub 6}H and C{sub 6}D. The derived spectroscopic constants allow astronomers to calculate the rotational spectra of the {sup 2{Sigma}} and {sup 2{Delta}} states up to 260 GHz to within 0.1 km s{sup -1} or better in equivalent radial velocity.

  13. Surface topography in mechanical polishing of 6H-SiC (0001) substrate

    NASA Astrophysics Data System (ADS)

    Yin, Ling; Huang, Han

    2007-12-01

    Silicon carbide (SiC) single crystals have been used as the substrates of a new generation of wide band-gap semiconductors due to their unparalleled combination of high breakdown voltage, extreme temperature tolerance, mobility and radiation hardness. For their applications, the SiC substrates need to be machined with nanometric surface quality as well as high form accuracy. However, the superior properties of the materials render their machinability extremely difficult. In this paper, we report the form error and surface roughness of the 6H-SiC (0001) substrate mechanically polished using 3 μm diamond powders in two different polishing processes. One process was concentrated-load polishing; the other was surface polishing. The polished surfaces were evaluated using white light interferometry and atomic force microscopy (AFM) for assessment of two- and three-dimensional topographies including form error and surface roughness. We found that a large form error was produced on the 6H-SiC (0001) substrate in the concentrated-load polishing. The root-mean-square (RMS) surface roughness of approximately 4 nm was resulted. Surface polishing of the 6H-SiC (0001) substrate remarkably improved form accuracy. The RMS surface roughness of approximately 2.5 nm was obtained.

  14. Oxygen Adsorption on the 6H-SiC(0001) (3x3) Surface

    NASA Astrophysics Data System (ADS)

    Cui, Y.; Li, L.

    2001-03-01

    Silicon carbide (SiC) is an attractive semiconductor for applications requiring a wide bandgap, high temperature/high power and chemical inertness. An investigation of the initial stages of oxidation of SiC, therefore, is important for optimizing the growth of thin, insulating oxide layers in SiC devices. In the present work, scanning tunneling microscopy (STM) has been used to study the initial stages of oxygen adsorption at room temperature on the Si-rich (3x3) surface of 6H-SiC(0001). The (3x3) surface is prepared by a two-step method of etching in hydrogen atmosphere at 1500 ^oC and annealing under Si beam in UHV at 950 ^oC. Upon adsorption of oxygen on the (3x3) surface, only one reaction product has been identified in the STM topographs, which appears as bright sites in the empty-state mode. These bright sites are attributed to the oxygen atoms inserted in one of the Si adatom's back bonds. These results and their implications for oxide growth on SiC will be presented at the meeting.

  15. Three-dimensional positron annihilation momentum measurement technique applied to measure oxygen-atom defects in 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Williams, Christopher S.

    A three-dimensional Positron Annihilation Spectroscopy System (3DPASS) capable to simultaneously measure three-dimensional electron-positron (e--e+) momentum densities measuring photons derived from e--e+ annihilation events was designed and characterized. 3DPASS simultaneously collects a single data set of correlated energies and positions for two coincident annihilation photons using solid-state double-sided strip detectors (DSSD). Positions of photons were determined using an interpolation method which measures a figure-of-merit proportional to the areas of transient charges induced on both charge collection strips directly adjacent to the charge collection strips interacting with the annihilation photons. The subpixel resolution was measured for both double-sided strip detectors (DSSD) and quantified using a new method modeled after a Gaussian point-spread function with a circular aperture. Error associated with location interpolation within an intrinsic pixel in each of the DSSDs, the subpixel resolution, was on the order of +/- 0.20 mm (this represents one-standard deviation). The subpixel resolution achieved was less than one twenty-fifth of the 25-mm2 square area of an intrinsic pixel created by the intersection of the DSSDs' orthogonal charge collection strips. The 2D ACAR and CDBAR response for single-crystal copper and 6H silicon carbide (6H SiC) was compared with results in the literature. Two additional samples of 6H SiC were irradiated with 24 MeV O+ ions, one annealed and one un-annealed, and measured using 3DPASS. Three-dimensional momentum distributions with correlated energies and coincident annihilation photons' positions were presented for all three 6H SiC samples. 3DPASS was used for the first experimental measurement of the structure of oxygen defects in bulk 6H SiC.

  16. Iodine assisted retainment of implanted silver in 6H-SiC at high temperatures

    NASA Astrophysics Data System (ADS)

    Hlatshwayo, T. T.; van der Berg, N. G.; Msimanga, M.; Malherbe, J. B.; Kuhudzai, R. J.

    2014-09-01

    The effect of high temperature thermal annealing on the retainment and diffusion behaviour of iodine (I) and silver (Ag) both individually and co-implanted into 6H-SiC has been investigated using RBS, RBS-C and heavy ion ERDA (Elastic Recoil Detection Analysis). Iodine and silver ions at 360 keV were both individually and co-implanted into 6H-SiC at room temperature to fluences of the order of 1 × 1016 cm-2. RBS analyses of the as-implanted samples indicated that implantation of Ag and of I and co-implantation of 131I and 109Ag at room temperature resulted in complete amorphization of 6H-SiC from the surface to a depth of about 290 nm for the co-implanted samples. Annealing at 1500 °C for 30 h (also with samples annealed at 1700 °C for 5 h) caused diffusion accompanied by some loss of both species at the surface with some iodine remaining in the iodine implanted samples. In the Ag implanted samples, the RBS spectra showed that all the Ag disappeared. SEM images showed different recrystallization behaviour for all three sets of samples, with larger faceted crystals appearing in the SiC samples containing iodine. Heavy Ion ERDA analyses showed that both 109Ag and 131I remained in the co-implanted SiC samples after annealing at 1500 °C for 30 h. Therefore, iodine assisted in the retainment of silver in SiC even at high temperature.

  17. Step Free Surface Heteroepitaxy of 3C-SiC Layers on Patterned 4H/6H-SiC Mesas and Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Spry, David J.

    2003-01-01

    Most SiC devices are implemented in homoepitaxial films grown on 4H/6H-SiC wafers with surfaces 3 degrees to 8 degrees off-axis from the (0001) basal plane. This approach has not prevented many substrate crystal defects from propagating into SiC epilayers, and does not permit the realization of SiC heteropolytype devices. This presentation describes recent advances in SiC epitaxial growth that begun to overcome the above shortcomings for arrays of mesas patterned into on-axis 4H/6H-SiC wafers. First, we demonstrated that atomic-scale surface steps can be completely eliminated from 4H/6H-SiC mesas via on-axis homoepitaxial step-flow growth, forming (0001) basal plane surfaces (up to 0.4 mm x 0.4 mm) for larger than previously thought possible. Step-free surface areas were then extended by growth fo thin lateral cantilevers from the mesa tops. These lateral cantilevers enabled substrate defects to be reduced and relocated in homoepitaxial films in a manner not possible with off-axis SiC growth. Finally, growth of vastly improved 3C-SiC heterofilms was achieved on 4H/6H-SiC mesas using the recently develop step-free surface heteroepitaxy process. These epitaxial growth developments should enable improved homojunction and heterojunction silicon carbide prototype devices.

  18. Imaging of SiC in metal matrix composites

    SciTech Connect

    Radmilovic, V.; O`Keefe, M.A.; Thomas, G.

    1992-08-01

    TEM has advantages over XRD in determining lattice periodicity. This paper reports an attempt in matching a simulation to an experimental image of SiC in an Al-8.5wt%Fe-1.3 wt%V-1.7 wt%Si composite containing 15 wt% SiC particulates, processed by powder metallurgy. The hexagonal allotrope has predominantly the 6H polytype structure; 1/3 of the 15R polytype is also observed. This SiC structure represents the 87R polytype. 6 refs, 2 figs.

  19. Lateral Growth Expansion of 4H/6H-SiC m-plane Pseudo Fiber Crystals by Hot Wall CVD Epitaxy

    NASA Technical Reports Server (NTRS)

    Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Powell, J. A.; Spry, David J.; Raghothamachar, Balaji; Dudley, Michael

    2011-01-01

    Lateral expansion of small mixed polytype 4H/6H-SiC slivers were realized by hot wall chemical vapor deposition (HWCVD). Small slivers cut from m-oriented ..11..00.. SiC boule slices containing regions of 4H and 6H SiC were exposed to HWCVD conditions using standard silane/propane chemistry for a period of up to eight hours. The slivers exhibited approximately 1500 microns (1.5 mm) of total lateral expansion. Initial analysis by synchrotron white beam x-ray topography (SWBXT) confirms, that the lateral growth was homoepitaxial, matching the polytype of the respective underlying region of the seed sliver.

  20. Suppression of Photoanodic Surface Oxidation of n-Type 6H-SiC Electrodes in Aqueous Electrolytes.

    PubMed

    Sachsenhauser, Matthias; Walczak, Karl; Hampel, Paul A; Stutzmann, Martin; Sharp, Ian D; Garrido, Jose A

    2016-02-16

    The photoelectrochemical characterization of silicon carbide (SiC) electrodes is important for enabling a wide range of potential applications for this semiconductor. However, photocorrosion of the SiC surface remains a key challenge, because this process considerably hinders the deployment of this material into functional devices. In this report, we use cyclic voltammetry to investigate the stability of n-type 6H-SiC photoelectrodes in buffered aqueous electrolytes. For measurements in pure Tris buffer, photogenerated holes accumulate at the interface under anodic polarization, resulting in the formation of a porous surface oxide layer. Two possibilities are presented to significantly enhance the stability of the SiC photoelectrodes. In the first approach, redox molecules are added to the buffer solution to kinetically facilitate hole transfer to these molecules, and in the second approach, water oxidation in the electrolyte is induced by depositing a cobalt phosphate catalyst onto the semiconductor surface. Both methods are found to effectively suppress photocorrosion of the SiC electrodes, as confirmed by atomic force microscopy and X-ray photoelectron spectroscopy measurements. The presented study provides straightforward routes to stabilize n-type SiC photoelectrodes in aqueous electrolytes, which is essential for a possible utilization of this material in the fields of photocatalysis and multimodal biosensing. PMID:26795116

  1. Thermal expansion and elastic anisotropies of SiC as related to polytype structure

    NASA Technical Reports Server (NTRS)

    Li, Z.; Bradt, R. C.

    1989-01-01

    The concept of the fraction of hexagonal stacking is used to describe the anisotropic thermal expansion coefficients of polytypes of SiC. The single crystal elastic anisotropy for the SiC polytype structures and the temperature dependencies of the anisotropies are examined. The anisotropic thermoelastic stress index for the 3C and 6H SiC polytypes are illustrated graphically. It is shown that this index is useful for predicting the most desirable crystal growth orientations for SiC whisker incorporation into composite matrices.

  2. Structural variants in attempted hetero-epitaxial growth of B12As2 on 6H-SiC (0001).

    SciTech Connect

    Aselage, Terrence Lee; Michael, Joseph Richard; Emin, David Jacob; Kotula, Paul Gabriel

    2005-03-01

    Boron sub-arsenide, B{sub 12}As{sub 2}, is based on twelve-atom clusters of boron atoms and two-atom As-As chains. By contrast, SiC is a tetrahedrally bonded covalent semiconductor. Despite these fundamental differences, the basal plane hexagonal lattice constant of boron sub-arsenide is twice that of SiC. This coincidence suggests the possibility of heteroepitaxial growth of boron sub-arsenide films on properly aligned SiC. However, there are a variety of incommensurate alignments by which heteroepitaxial growth of B{sub 12}As{sub 2} on (0001) 6H-SiC can occur. In this study, we first used geometrical crystallographic considerations to describe the possible arrangements of B{sub 12}As{sub 2} on (0001) 6H-SiC. We identified four translational and two rotational variants. We then analyzed electron backscattered diffraction and transmission electron microscopy images for evidence of distinct domains of such structural variants. Micron-scale regions with each of the two possible rotational alignments of B{sub 12}As{sub 2} icosahedra with the SiC surface were seen. On a finer length scale (100-300 nm) within these regions, boron-rich boundaries were found, consistent with those between pairs of the four equivalent translational variants associated with a two-to-one lattice match. Boron-carbide reaction layers were also observed at interfaces between SiC and B{sub 12}As{sub 2}.

  3. Blue photoluminescence enhancement in laser-irradiated 6H-SiC at room temperature

    SciTech Connect

    Wu, Yan; Ji, Lingfei Lin, Zhenyuan; Jiang, Yijian; Zhai, Tianrui

    2014-01-27

    Blue photoluminescence (PL) of 6H-SiC irradiated by an ultraviolet laser can be observed at room temperature in dark condition. PL spectra with Gaussian fitting curve of the irradiated SiC show that blue luminescence band (∼440 nm) is more pronounced than other bands. The blue PL enhancement is the combined result of the improved shallow N-donor energy level and the unique surface state with Si nanocrystals and graphene/Si composite due to the effect of photon energy input by the short-wavelength laser irradiation. The study can provide a promising route towards the preparation of well-controlled blue photoluminescence material for light-emitting devices.

  4. Blue photoluminescence enhancement in laser-irradiated 6H-SiC at room temperature

    NASA Astrophysics Data System (ADS)

    Wu, Yan; Ji, Lingfei; Lin, Zhenyuan; Jiang, Yijian; Zhai, Tianrui

    2014-01-01

    Blue photoluminescence (PL) of 6H-SiC irradiated by an ultraviolet laser can be observed at room temperature in dark condition. PL spectra with Gaussian fitting curve of the irradiated SiC show that blue luminescence band (˜440 nm) is more pronounced than other bands. The blue PL enhancement is the combined result of the improved shallow N-donor energy level and the unique surface state with Si nanocrystals and graphene/Si composite due to the effect of photon energy input by the short-wavelength laser irradiation. The study can provide a promising route towards the preparation of well-controlled blue photoluminescence material for light-emitting devices.

  5. Interfacial reactions and surface analysis of W thin film on 6H-SiC

    NASA Astrophysics Data System (ADS)

    Thabethe, T. T.; Hlatshwayo, T. T.; Njoroge, E. G.; Nyawo, T. G.; Ntsoane, T. P.; Malherbe, J. B.

    2016-03-01

    Tungsten (W) thin film was deposited on bulk single crystalline 6H-SiC substrate and annealed in vacuum at temperatures ranging from 700 to 1000 °C for 1 h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectroscopy (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). XRD was used to identify the phases present and to confirm the RBS results. The RBS spectra were simulated using the RUMP software in order to obtain the deposited layer thickness, composition of reaction zone and detect phase formation at the interface. RBS results showed that interaction between W and SiC started at 850 °C. The XRD analysis showed that WC and CW3 were the initial phases formed at 700 and 800 °C. The concentration of the phases was however, too low to be detected by RBS analysis. At temperatures of 900 and 1000 °C, W reacted with the SiC substrate and formed a mixed layer containing a silicide phase (WSi2) and a carbide phase (W2C). The SEM images of the as-deposited samples showed that the W thin film had a uniform surface with small grains. The W layer became heterogeneous during annealing at higher temperatures as the W granules agglomerated into island clusters at temperatures of 800 °C and higher.

  6. Experimental demonstration of mode-selective phonon excitation of 6H-SiC by a mid-infrared laser with anti-Stokes Raman scattering spectroscopy

    SciTech Connect

    Yoshida, Kyohei; Hachiya, Kan; Okumura, Kensuke; Mishima, Kenta; Inukai, Motoharu; Torgasin, Konstantin; Omer, Mohamed; Sonobe, Taro; Zen, Heishun; Negm, Hani; Kii, Toshiteru; Masuda, Kai; Ohgaki, Hideaki

    2013-10-28

    Mode-selective phonon excitation by a mid-infrared laser (MIR-FEL) is demonstrated via anti-Stokes Raman scattering measurements of 6H-silicon carbide (SiC). Irradiation of SiC with MIR-FEL and a Nd-YAG laser at 14 K produced a peak where the Raman shift corresponds to a photon energy of 119 meV (10.4 μm). This phenomenon is induced by mode-selective phonon excitation through the irradiation of MIR-FEL, whose photon energy corresponds to the photon-absorption of a particular phonon mode.

  7. -SiC Composites

    NASA Astrophysics Data System (ADS)

    Chakraborty, Shirshendu; Debnath, Debashish; Mallick, Azizur Rahaman; Das, Probal Kumar

    2014-12-01

    ZrB2-SiC composites were hot pressed at 2473 K (2200 °C) with graded amounts (5 to 20 wt pct) of SiC and the effect of the SiC addition on mechanical properties like hardness, fracture toughness, scratch and wear resistances, and thermal conductivity were studied. Addition of submicron-sized SiC particles in ZrB2 matrices enhanced mechanical properties like hardness (15.6 to 19.1 GPa at 1 kgf), fracture toughness (2 to 3.6 MPa(m)1/2) by second phase dispersion toughening mechanism, and also improved scratch and wear resistances. Thermal conductivity of ZrB2-SiC (5 wt pct) composite was higher [121 to 93 W/m K from 373 K to 1273 K (100 °C to 1000 °C)] and decreased slowly upto 1273 K (1000 °C) in comparison to monolithic ZrB2 providing better resistance to thermal fluctuation of the composite and improved service life in UHTC applications. At higher loading of SiC (15 wt pct and above), increased thermal barrier at the grain boundaries probably reduced the thermal conductivity of the composite.

  8. Magnetic, optical and electrical characterization of SiC doped with scandium during the PVT growth

    NASA Astrophysics Data System (ADS)

    Racka, K.; Avdonin, A.; Sochacki, M.; Tymicki, E.; Grasza, K.; Jakieła, R.; Surma, B.; Dobrowolski, W.

    2015-03-01

    Scandium is introduced into bulk SiC during the physical vapor transport (PVT) growth. SiC crystals grown with different Sc contents (from 0.5 wt% up to 2.5 wt%, added to the SiC source material) are studied. Magnetic properties of SiC doped with scandium during the PVT growth are reported for the first time. The presence of antiferromagnetic interactions between magnetic moments of Sc ions is concluded from the temperature dependence of magnetic susceptibility. Detailed PL spectra of 4H-/6H-SiC:B and 4H-/6H-SiC:Sc crystals are presented. A new energy level of 35-37 meV is found on SiC:Sc samples and its possible assignment to a complex defect, consisting of nitrogen donor and scandium acceptor, is proposed.

  9. Nonuniformities of electrical resistivity in undoped 6H-SiC wafers

    SciTech Connect

    Li, Q.; Polyakov, A.Y.; Skowronski, M.; Sanchez, E.K.; Loboda, M.J.; Fanton, M.A.; Bogart, T.; Gamble, R.D.

    2005-06-01

    Chemical elemental analysis, temperature-dependent Hall measurements, deep-level transient spectroscopy, and contactless resistivity mapping were performed on undoped semi-insulating (SI) and lightly nitrogen-doped conducting 6H-SiC crystals grown by physical vapor transport (PVT). Resistivity maps of commercial semi-insulating SiC wafers revealed resistivity variations across the wafers between one and two orders of magnitude. Two major types of variations were identified. First is the U-shape distribution with low resistivity in the center and high in the periphery of the wafer. The second type had an inverted U-shape distribution. Secondary-ion-mass spectrometry measurements of the distribution of nitrogen concentration along the growth axis and across the wafers sliced from different locations of lightly nitrogen-doped 6H-SiC boules were conducted. The measured nitrogen concentration gradually decreased along the growth direction and from the center to the periphery of the wafers. This change gives rise to the U-like distribution of resistivity in wafers of undoped SI-SiC. The concentrations of deep electron traps exhibited similar dependence. Compensation of nitrogen donors by these traps can result in the inverted U-like distribution of resistivity. Possible reasons for the observed nonuniformities include formation of a (0001) facet in PVT growth coupled with orientation-dependent nitrogen incorporation, systematic changes of the gas phase composition, and increase of the deposition temperature during boule growth.

  10. SiC Technology

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1998-01-01

    Silicon carbide (SiC)-based semiconductor electronic devices and circuits are presently being developed for use in high-temperature, high-power, and/or high-radiation conditions under which conventional semiconductors cannot adequately perform. Silicon carbide's ability to function under such extreme conditions is expected to enable significant improvements to a far-ranging variety of applications and systems. These range from greatly improved high-voltage switching [1- 4] for energy savings in public electric power distribution and electric motor drives to more powerful microwave electronics for radar and communications [5-7] to sensors and controls for cleaner-burning more fuel-efficient jet aircraft and automobile engines. In the particular area of power devices, theoretical appraisals have indicated that SiC power MOSFET's and diode rectifiers would operate over higher voltage and temperature ranges, have superior switching characteristics, and yet have die sizes nearly 20 times smaller than correspondingly rated silicon-based devices [8]. However, these tremendous theoretical advantages have yet to be realized in experimental SiC devices, primarily due to the fact that SiC's relatively immature crystal growth and device fabrication technologies are not yet sufficiently developed to the degree required for reliable incorporation into most electronic systems [9]. This chapter briefly surveys the SiC semiconductor electronics technology. In particular, the differences (both good and bad) between SiC electronics technology and well-known silicon VLSI technology are highlighted. Projected performance benefits of SiC electronics are highlighted for several large-scale applications. Key crystal growth and device-fabrication issues that presently limit the performance and capability of high temperature and/or high power SiC electronics are identified.

  11. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

    2014-03-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

  12. Thermal expansion and thermal expansion anisotropy of SiC polytypes

    NASA Technical Reports Server (NTRS)

    Li, Z.; Bradt, R. C.

    1987-01-01

    The principal axial coefficients of thermal expansion for the (3C), (4H), and (6H) polytypes of SiC are considered to identify the structural role of the stacking layer sequence as it affects the thermal expansion. A general equation based on the fractions of cubic and hexagonal layer stacking is developed that expresses the principal axial thermal expansion coefficients of all of the SiC polytypes. It is then applied to address the thermal expansion anisotropy of the noncubic SiC structures.

  13. Performance of colloidal silica and ceria based slurries on CMP of Si-face 6H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Chen, Guomei; Ni, Zifeng; Xu, Laijun; Li, Qingzhong; Zhao, Yongwu

    2015-12-01

    Colloidal silica and ceria based slurries, both using KMnO4 as an oxidizer, for chemical mechanical polishing (CMP) of Si-face (0 0 0 1) 6H-SiC substrate, were investigated to obtain higher material removal rate (MRR) and ultra-smooth surface. The results indicate that there was a significant difference in the CMP performance of 6H-SiC between silica and ceria based slurries. For the ceria based slurries, a higher MRR was obtained, especially in strong acid KMnO4 environment, and the maximum MRR (1089 nm/h) and a smoother surface with an average roughness Ra of 0.11 nm was achieved using slurries containing 2 wt% colloidal ceria, 0.05 M KMnO4 at pH 2. In contrast, due to the attraction between negative charged silica particles and positive charged SiC surface below pH 5, the maximum MRR of silica based slurry was only 185 nm/h with surface roughness Ra of 0.254 nm using slurries containing 6 wt% colloidal silica, 0.05 M KMnO4 at pH 6. The polishing mechanism was discussed based on the zeta potential measurements of the abrasives and the X-ray photoelectron spectroscopy (XPS) analysis of the polished SiC surfaces.

  14. SiC devices: Physics and numerical simulation

    NASA Astrophysics Data System (ADS)

    Ruff, Martin; Mitlehner, Heinz; Helbig, Reinhard

    1994-06-01

    The important material parameters for 6H silicon carbide (6H-SiC) are extracted from the literature and implemented into the 2-D device simulation programs PISCES and BREAKDOWN and into the 1-D program OSSI Simulations of 6H-SiC p-n junctions show the possibility to operate corresponding devices at temperatures up to 1000 K thanks to their low reverse current densities. Comparison of a 6H-SiC 1200 V p-n(-)-n(+) diode with a corresponding silicon (Si) diode shows the higher switching performance of the 6H-SiC diode, while the forward power loss is somewhat higher than in Si due to the higher built-in voltage of the 6H-SiC p-n junction. This disadvantage can be avoided by a 6H-SiC Schottky diode. The on-resistances of Si, 3C-SiC, and 6H-SiC vertical power MOSFET's are compared by analytical calculations. At room temperature, such SiC MOSFET's can operate up to blocking capabilities of 5000 V with an on-resistance below 0.1 (Omega) sq cm, while Si MOSFET's are limited to below 500 V. This is checked by calculating the characteristics of a 6H-SiC 1200 V MOSFET with PISCES. In the voltage region below 200 V, Si is superior due to its higher mobility and lower threshold voltage. Electric fields in the order of 4 x 10(exp 6) V/cm occur in the gate oxide of the mentioned 6H-SiC MOSFET as well as in a field plate oxide used to passivate its planar junction. To investigate the high frequency performance of SiC devices, a heterobipolartransistor with a 6H-SiC emitter is considered. Base and collector are assumed to be out of 3C-SiC. Frequencies up to 10 GHz with a very high output power are obtained on the basis of analytical considerations.

  15. The effect of split sleep schedules (6h-on/6h-off) on neurobehavioural performance, sleep and sleepiness.

    PubMed

    Short, Michelle A; Centofanti, Stephanie; Hilditch, Cassie; Banks, Siobhan; Lushington, Kurt; Dorrian, Jillian

    2016-05-01

    Shorter, more frequent rosters, such as 6h-on/6h-off split shifts, may offer promise to sleep, subjective sleepiness and performance by limiting shift length and by offering opportunities for all workers to obtain some sleep across the biological night. However, there exists a paucity of studies that have examined these shifts using objective measures of sleep and performance. The present study examined neurobehavioural performance, sleepiness and sleep during 6h-on/6h-off split sleep schedules. Sixteen healthy adults (6 males, 26.13y ± 4.46) participated in a 9-day laboratory study that included two baseline nights (BL, 10h time in bed (TIB), 2200h-0800h), 4 days on one of two types of 6h-on/6h-off split sleep schedules with 5h TIB during each 'off' period (6h early: TIB 0300h-0800h and 1500h-20000h, or 6-h late: TIB 0900h-1400h and 2100h-0200h), and two recovery nights (10h TIB per night, 2200h-0800h). Participants received 10h TIB per 24h in total across both shift schedules. A neurobehavioural test bout was completed every 2 h during wake, which included the Psychomotor Vigilance Task (PVT) and the Karolinska Sleepiness Scale (KSS). Linear mixed effects models were used to assess the effect of day (BL, shift days 1-4), schedule (6h early, 6h late) and trial (numbers 1-6) on PVT lapses (operationalised as the number of reaction times >500 ms), PVT total lapse time, PVT fastest 10% of reaction times and KSS. Analyses were also conducted examining the effect of day and schedule on sleep variables. Overall, PVT lapses and total lapse time did not differ significantly between baseline and shift days, however, peak response speeds were significantly slower on the first shift day when compared to baseline, but only for those in the 6h-late condition. Circadian variations were apparent in performance outcomes, with individuals in the 6h-late condition demonstrated significantly more and longer lapses and slower peak reaction times at the end of their night shift

  16. SEM analysis of ion implanted SiC

    NASA Astrophysics Data System (ADS)

    Malherbe, Johan B.; van der Berg, N. G.; Botha, A. J.; Friedland, E.; Hlatshwayo, T. T.; Kuhudzai, R. J.; Wendler, E.; Wesch, W.; Chakraborty, P.; da Silveira, E. F.

    2013-11-01

    SiC is a material used in two future energy production technologies, firstly as a photovoltaic layer to harness the UV spectrum in high efficient power solar cells, and secondly as a diffusion barrier material for radioactive fission products in the fuel elements of the next generation of nuclear power plants. For both applications, there is an interest in the implantation of reactive and non-reactive ions into SiC and their effects on the properties of the SiC. In this study 360 keV Ag+, I+ and Xe+ ions were separately implanted into 6H-SiC and in polycrystalline SiC at various substrate temperatures. The implanted samples were also annealed in vacuum at temperatures ranging from 900 °C to 1600 °C for various times. In recent years, there had been significant advances in scanning electron microscopy (SEM) with the introduction of an in-lens detector combined with field emission electron guns. This allows defects in solids, such as radiation damage created by the implanted ions, to be detected with SEM. Cross-sectional SEM images of 6H-SiC wafers implanted with 360 keV Ag+ ions at room temperature and at 600 °C and then vacuum annealed at different temperatures revealed the implanted layers and their thicknesses. A similar result is shown of 360 keV I+ ions implanted at 600 °C into 6H-SiC and annealed at 1600 °C. The 6H-SiC is not amorphized but remained crystalline when implanting at 600 °C. There are differences in the microstructure of 6H-SiC implanted with silver at the two temperatures as well as with reactive iodine ions. Voids (bubbles) are created in the implanted layers into which the precipitation of silver and iodine can occur after annealing of the samples. The crystallinity of the substrate via implantation temperature caused differences in the distribution and size of the voids. Implantation of xenon ions in polycrystalline SiC at 350 °C does not amorphize the substrate as is the case with room temperature heavy ion bombardment. Subsequent

  17. Identification and analysis of the human murine putative chromatin structure regulator SUPT6H and Supt6h

    SciTech Connect

    Chiang, Pei-Wen; Wang, SuQing; Hillman, J.

    1996-06-15

    We have isolated and sequenced SUPT6H and Supt6h, the human and murine homologues of the Saccharomyces cerevisiae and Caenorhabditis elegans genes SPT6 (P using 1603 aa = 6.7 e-{sup 95}) and emb-5 (P using 1603 aa = 7.0 e-{sup 288}), respectively. The human and murine SPT6 homologues are virtually identical, as they share >98% identity and >99% similarity at the protein level. The derived amino acid sequences of these two genes predict a 1603-aa protein (human) and a 1726-bp protein (mouse), respectively. There were several known features, including a highly acidic 5{prime}-region, a degenerate SH2 domain, and a leucine zipper. These features are consistent with a nuclear protein that regulates transcription, whose extreme conservation underscores the likely importance of this gene in mammalian development. Expression of human and murine SPT6 homologues was analyzed by Northern blotting, which revealed a 7.0-kb transcript that was expressed constitutively. The SPT6 homologue was mapped to chromosome 17q11.2 in human by somatic cell hybrid analysis and in situ hybridization. These data indicate that SUPT6H and Supt6h are functionally analogous to SPT6 and emb-5 and may therefore regulate transcription through establishment or maintenance of chromatin structure. 23 refs., 3 figs.

  18. ICP Etching of SiC

    SciTech Connect

    Grow, J.M.; Lambers, E.S.; Ostling, M.; Pearton, S.J.; Ren, F.; Shul, R.J.; Wang, J.J.; Zetterling, C.-M.

    1999-02-04

    A number of different plasma chemistries, including NF{sub 3}/O{sub 2}, SF{sub 6}/O{sub 2}, SF{sub 6}/Ar, ICl, IBr, Cl{sub 2}/Ar, BCl{sub 3}/Ar and CH{sub 4}/H{sub 2}/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 {angstrom} cm{sup {minus}1} are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl{sub 2}-based etching does not provide high rates, even though the potential etch products (SiCi{sub 4} and CCl{sub 4}) are volatile. Photoresist masks have poor selectivity over SiC in F{sub 2}-based plasmas under normal conditions, and ITO or Ni are preferred.

  19. 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.

  20. Graphene synthesis on SiC: Reduced graphitization temperature by C-cluster and Ar-ion implantation

    NASA Astrophysics Data System (ADS)

    Zhang, R.; Li, H.; Zhang, Z. D.; Wang, Z. S.; Zhou, S. Y.; Wang, Z.; Li, T. C.; Liu, J. R.; Fu, D. J.

    2015-08-01

    Thermal decomposition of SiC is a promising method for high quality production of wafer-scale graphene layers, when the high decomposition temperature of SiC is substantially reduced. The high decomposition temperature of SiC around 1400 °C is a technical obstacle. In this work, we report on graphene synthesis on 6H-SiC with reduced graphitization temperature via ion implantation. When energetic Ar, C1 and C6-cluster ions implanted into 6H-SiC substrates, some of the Si-C bonds have been broken due to the electronic and nuclear collisions. Owing to the radiation damage induced bond breaking and the implanted C atoms as an additional C source the graphitization temperature was reduced by up to 200 °C.

  1. Microwave annealing of ion implanted 6H-SiC

    SciTech Connect

    Gardner, J.A.; Rao, M.V.; Tian, Y.L.; Holland, O.W.; Kelner, G.; Freitas, J.A. Jr.; Ahmad, I.

    1996-12-31

    Microwave rapid thermal annealing has been utilized to remove the lattice damage caused by nitrogen(N) ion-implantation as well as to activate the dopant in 6H-SiC. Samples were annealed at temperatures as high as 1,400 C, for 10 min. Van der Pauw Hall measurements indicate an implant activation of 36%, which is similar to the value obtained for the conventional furnace annealing at 1,600 C. Good lattice quality restoration was observed in the Rutherford backscattering and photoluminescence spectra.

  2. Microwave annealing of ion implanted 6H-SiC

    SciTech Connect

    Gardner, J.A.; Rao, M.V.; Tian, Y.L.; Holland, O.W.; Kelner, G.; Freitas, J.A. Jr.; Ahmad, I.

    1996-05-01

    Microwave rapid thermal annealing has been utilized to remove the lattice damage caused by nitrogen (N) ion-implantation as well as to activate the dopant in 6H-SiC. Samples were annealed at temperatures as high as 1,400 C, for 10 min. Van der Pauw Hall measurements indicate an implant activation of 36%, which is similar to the value obtained for the conventional furnace annealing at 1,600 C. Good lattice quality restoration was observed in the Rutherford backscattering and photoluminescence spectra.

  3. Low damage, highly anisotropic dry etching of SiC

    SciTech Connect

    Wang, J.J.; Hong, J.; Lambers, E.S.; Pearton, S.J.; Ren, F.; Ostling, M.; Zetterling, C.M.; Grow, J.M.; Shul, R.J.

    1998-03-01

    A parametric study of the etching characteristics of 6H p{sup +} and n{sup +} SiC and thin film SiC{sub 0.5}N{sub 0.5} in Inductively Coupled Plasma NF{sub 3}/O{sub 2} and NF{sub 3}/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF{sub 3} percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide (ITO) masks display relatively good etch selectivity over SiC (maximum of {approximately} 70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF{sub 3}:O{sub 2} conditions.

  4. Stress Analysis of SiC MEMS Using Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ness, Stanley J.; Marciniak, M. A.; Lott, J. A.; Starman, L. A.; Busbee, J. D.; Melzak, J. M.

    2003-03-01

    During the fabrication of Micro-Electro-Mechanical Systems (MEMS), residual stress is often induced in the thin films that are deposited to create these systems. These stresses can cause the device to fail due to buckling, curling, or fracture. Industry is looking for ways to characterize the stress during the deposition of thin films in order to reduce or eliminate device failure. Micro-Raman spectroscopy has been successfully used to characterize poly-Si MEMS devices made with the MUMPS® process. Raman spectroscopy was selected because it is nondestructive, fast and has the potential for in situ stress monitoring. This research attempts to use Raman spectroscopy to analyze the stress in SiC MEMS made with the MUSiC® process. Raman spectroscopy is performed on 1-2-micron-thick SiC thin films deposited on silicon, silicon nitride, and silicon oxide substrates. The most common poly-type of SiC found in thin film MEMS made with the MUSiC® process is 3C-SiC. Research also includes baseline spectra of 6H, 4H, and 15R poly-types of bulk SiC.

  5. High-Field Fast-Risetime Pulse Failures in 4H- and 6H-SiC pn Junction Diodes

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Fazi, Christian

    1996-01-01

    We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3 x 10(exp 17 cm(exp -3)) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.

  6. Oxygen-Atom Defects In 6H Silicon Carbide Implanted Using 24- MeV O3+ Ions Measured Using Three-Dimensional Positron Annihilation Spectroscopy System (3DPASS)

    NASA Astrophysics Data System (ADS)

    Williams, Christopher S.; Duan, Xiaofeng F.; Petrosky, James C.; Burggraf, Larry W.

    2011-06-01

    Three dimensional electron-positron (e--e+) momentum distributions were measured for single crystal 6H silicon carbide (SiC); both virgin and having implanted oxygen-atom defects. 6H SiC samples were irradiated by 24- MeV O3+ ions at 20 particle-nanoamps at the Sandia National Laboratory's Ion Beam Facility. O3+ ions were implanted 10.8 μm deep normal to the (0001) face of one side of the SiC samples. During positron annihilation measurements, the opposite face of the 254.0-μm thick SiC samples was exposed to positrons from a 22Na source. This technique reduced the influence on the momentum measurements of vacancy-type defects resulting from knock-on damage by the O3+ ions. A three-dimensional positron annihilation spectroscopy system (3DPASS) was used to measure e--e+ momentum distributions for virgin and irradiated 6H SiC crystal both before and following annealing. 3DPASS simultaneously measures coincident Doppler-broadening (DBAR) and angular correlation of annihilation radiation (ACAR) spectra. DBAR ratio plots and 2D ACAR spectra are presented. Changes in the momentum anisotropies relative to crystal orientation observed in 2D ACAR spectra for annealed O-implanted SiC agree with the local structure of defect distortion predicted using Surface Integrated Molecular Orbital/Molecular Mechanics (SIMOMM). Oxygen atoms insert between Si and C atoms increasing their separation by 0.9 Å forming a Si-O-C bond angle of ˜150°.

  7. Oxygen-Atom Defects In 6H Silicon Carbide Implanted Using 24- MeV O{sup 3+} Ions Measured Using Three-Dimensional Positron Annihilation Spectroscopy System (3DPASS)

    SciTech Connect

    Williams, Christopher S.; Petrosky, James C.; Burggraf, Larry W.

    2011-06-01

    Three dimensional electron-positron (e{sup -}-e{sup +}) momentum distributions were measured for single crystal 6H silicon carbide (SiC); both virgin and having implanted oxygen-atom defects. 6H SiC samples were irradiated by 24- MeV O{sup 3+} ions at 20 particle-nanoamps at the Sandia National Laboratory's Ion Beam Facility. O{sup 3+} ions were implanted 10.8 {mu}m deep normal to the (0001) face of one side of the SiC samples. During positron annihilation measurements, the opposite face of the 254.0-{mu}m thick SiC samples was exposed to positrons from a {sup 22}Na source. This technique reduced the influence on the momentum measurements of vacancy-type defects resulting from knock-on damage by the O{sup 3+} ions. A three-dimensional positron annihilation spectroscopy system (3DPASS) was used to measure e{sup -}-e{sup +} momentum distributions for virgin and irradiated 6H SiC crystal both before and following annealing. 3DPASS simultaneously measures coincident Doppler-broadening (DBAR) and angular correlation of annihilation radiation (ACAR) spectra. DBAR ratio plots and 2D ACAR spectra are presented. Changes in the momentum anisotropies relative to crystal orientation observed in 2D ACAR spectra for annealed O-implanted SiC agree with the local structure of defect distortion predicted using Surface Integrated Molecular Orbital/Molecular Mechanics (SIMOMM). Oxygen atoms insert between Si and C atoms increasing their separation by 0.9 A forming a Si-O-C bond angle of {approx}150 deg.

  8. The interface analysis of GaN grown on 0° off 6H-SiC with an ultra-thin buffer layer

    NASA Astrophysics Data System (ADS)

    Sun, Zheng; Ohta, Akio; Miyazaki, Seiichi; Nagamatsu, Kentaro; Lee, Hojun; Olsson, Marc; Ye, Zheng; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-01-01

    Previously, we reported a growth method by metalorganic vapor phase epitaxy using a single two-dimensional growth step, resulting in 1.2-µm crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate. Transmission electron microscope and energy dispersive spectrometer analysis of the epitaxial interface to the SiC determined that an ultra-thin AlGaN interlayer had formed measuring around 2-3 nm. We expect our growth technique can be applied to the fabrication of GaN/SiC high frequency and high power devices.

  9. Scanning probe microscopy investigations of the electrical properties of chemical vapor deposited graphene grown on a 6H-SiC substrate.

    PubMed

    Gajewski, Krzysztof; Kopiec, Daniel; Moczała, Magdalena; Piotrowicz, Adam; Zielony, Michał; Wielgoszewski, Grzegorz; Gotszalk, Teodor; Strupiński, Włodek

    2015-01-01

    Sublimated graphene grown on SiC is an attractive material for scientific investigations. Nevertheless the self limiting process on the Si face and its sensitivity to the surface quality of the SiC substrates may be unfavourable for later microelectronic processes. On the other hand, chemical vapor deposited (CVD) graphene does not posses such disadvantages, so further experimental investigation is needed. In this paper CVD grown graphene on 6H-SiC (0001) substrate was investigated using scanning probe microscopy (SPM). Electrical properties of graphene were characterized with the use of: scanning tunnelling microscopy, conductive atomic force microscopy (C-AFM) with locally performed C-AFM current-voltage measurements and Kelvin probe force microscopy (KPFM). Based on the contact potential difference data from the KPFM measurements, the work function of graphene was estimated. We observed conductance variations not only on structural edges, existing surface corrugations or accidental bilayers, but also on a flat graphene surface. PMID:25203361

  10. Trisodium citrate, Na3(C6H5O7)

    PubMed Central

    Rammohan, Alagappa; Kaduk, James A.

    2016-01-01

    The crystal structure of anhydrous tris­odium citrate, Na3(C6H5O7), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT). There are two independent five-coordinate Na+ and one six-coordinate Na+ cations in the asymmetric unit. The [NaO5] and [NaO6] polyhedra share edges and corners to form a three-dimensional framework. There are channels parallel to the a and b axes in which the remainder of the citrate anions reside. The only hydrogen bonds are an intra­molecular one between the hy­droxy group and one of the terminal carboxyl­ate O atoms and an intermolecular one between a methylene group and the hydroxyl O atom. PMID:27308044

  11. Ion implantation induced swelling in 6H-SiC

    SciTech Connect

    Nipoti, R.; Albertazzi, E.; Bianconi, M.; Lotti, R.; Lulli, G.; Cervera, M.; Carnera, A.

    1997-06-01

    Ion implantation induced surface expansion (swelling) of 6H-SiC was investigated through the measurement of the step height between implanted and unimplanted areas. The samples were irradiated at room temperature with 500 keV Al{sup +} ions in the dose range 1.25{times}10{sup 14}{endash}3{times}10{sup 15}ionscm{sup {minus}2}. Swelling was related to dose and the area density of ion-induced damage measured by Rutherford backscattering channeling technique. The observed trend is consistent with the hypothesis that the volume expansion of the ion damaged crystal is proportional to the area density of displaced atoms, plus an additional relaxation occurring at the onset of the crystalline to amorphous transition. {copyright} {ital 1997 American Institute of Physics.}

  12. Fabrication of SiC Blue LEDs Using Off-Oriented Substrates

    NASA Astrophysics Data System (ADS)

    Matsushita, Yasuhiko; Nakata, Toshitake; Uetani, Takahiro; Yamaguchi, Takao; Niina, Tatsuhiko

    1990-02-01

    SiC blue LEDs were fabricated by the dipping technique, using 6H-SiC substrates whose (000\\bar{1})C face varied toward the [11\\bar{2}0] or [10\\bar{1}0] direction. The surface morphology of the epitaxial layers on the off-oriented substrates was a striped pattern perpendicular to the off-axis direction. By using off-oriented substrates, the degradation of SiC blue LEDs can be greatly reduced. High-efficiency blue LEDs (12 mcd at 20 mA) were fabricated by increasing the amount of Al dopant in the n-type layer.

  13. Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC

    NASA Astrophysics Data System (ADS)

    Kuhudzai, R. J.; van der Berg, N. G.; Malherbe, J. B.; Hlatshwayo, T. T.; Theron, C. C.; Buys, A. V.; Botha, A. J.; Wendler, E.; Wesch, W.

    2014-08-01

    The recrystallization and subsequent crystal growth during annealing of amorphous surface layers on 6H-SiC produced by ion implantation is investigated. Amorphous surface layers were produced by ion implantation of 360 keV ions of iodine, silver, xenon, cesium and strontium into single crystalline 6H-silicon carbide samples. The ion fluence for all the implantations were in the order of 1016 cm-2. Vacuum annealing of the damaged silicon carbide samples was then performed. The microstructure of SiC surfaces before and after annealing was investigated using a high resolution field emission scanning electron microscope (SEM). SEM analysis was complimented by Atomic Force Microscopy (AFM). SEM images acquired by an in-lens detector using an accelerating voltage of 2 kV show nano-crystallites developed for all implanted samples after annealing. Larger and more faceted crystallites along with elongated thin crystallites were observed for iodine and xenon implanted 6H-SiC. Crystallites formed on surfaces implanted with strontium and cesium were smaller and less faceted. Strontium, silver and cesium implanted samples also exhibited more cavities on the surface. AFM was used to evaluate the effect of annealing on the surface roughness. For all the amorphous surfaces which were essentially featureless, the root mean square (rms) roughness was approximately 1 nm. The roughness increased to approximately 17 nm for the iodine implanted sample after annealing with the surface roughness below this value for all the other samples. AFM also showed that the largest crystals grew to heights of about 17, 20, 45, 50 and 65 nm for Sr, Cs, Ag, Xe and I implanted samples after annealing at 1200 °C for 5 h respectively. SEM images and AFM analysis suggest that iodine is more effective in promoting crystal growth during the annealing of bombardment-induced amorphous SiC layers than the rest of the ions we implanted. In samples of silicon carbide co-implanted with iodine and silver, few

  14. Site-Competition Epitaxy for N-Type and P-Type Dopant Control in CVD Sic Epilayers

    NASA Technical Reports Server (NTRS)

    Larkin, D. J.

    1995-01-01

    The use of site-competition epitaxy, which is based on intentional variation of the Si/C ratio during epitaxy, has now been reproduced in numerous national and international laboratories. However, previous reports have only considered dopant incorporation control for epitaxy on the Si-face 6H-SiC(OOO1) substrates. Presented in this paper is the extension of this technique for control of phosphorous incorporation and also a comparison of controlled doping on C-face 6H-SiC(OOO1) versus Si-face 6H-SiC(OOO1) substrates for aluminum, boron, nitrogen, and phosphorous.

  15. The status of SiC bulk growth from an industrial point of view

    NASA Astrophysics Data System (ADS)

    Müller, St. G.; Glass, R. C.; Hobgood, H. M.; Tsvetkov, V. F.; Brady, M.; Henshall, D.; Jenny, J. R.; Malta, D.; Carter, C. H.

    2000-04-01

    Silicon-carbide-based device technology as well as the volume production of nitride-based, high brightness blue and green LEDs fabricated on SiC substrates has made tremendous progress within the last several years. The commercial availability of large, high-quality SiC substrates is a key issue for the realization of the full potential of this technology. The current status of SiC bulk sublimation growth for the industrial production of 50 mm diameter 4H and 6H wafers and the quality improvement of 75 mm wafers is reviewed. Results at Cree show a continous reduction of the micropipe density in SiC substrates, demonstrating micropipe free material of a 25 mm diameter and densities as low as 1.1 cm -2 for an entire 50 mm 4H-SiC wafer. We present results of modeling the relevant heat transfer processes during crystal growth and the thermoelastic stress in the growing crystal. The effect on dislocation generation is discussed. The recent interest in SiC for the production of a unique gemstone material (moissanite) additionally increases the demand for high-quality SiC bulk material.

  16. Structural Evolution of SiC Films During Plasma-Assisted Chemical Vapour Deposition

    NASA Astrophysics Data System (ADS)

    Ding, Siye; Yan, Guanchao; Zhu, Xiaodong; Zhou, Haiyang

    2009-04-01

    Evolution of chemical bonding configurations for the films deposited from hexamethyldisiloxane (HMDSO) diluted with H2 during plasma assisted chemical vapour deposition is investigated. In the experiment a small amount of CH4 was added to adjust the plasma environment and modify the structure of the deposited films. The measurements of Raman spectroscopy and X-ray diffraction (XRD) revealed the production of 6H-SiC embedded in the amorphous matrix without the input of CH4. As CH4 was introduced into the deposition reaction, the transition of 6H-SiC to cubic SiC in the films took place, and also the film surfaces changed from a structure of ellipsoids to cauliflower-like shapes. With a further increase of CH4 in the flow ratio, the obtained films varied from Si-C bonding dominant to a sp2/sp3 carbon-rich composition.

  17. Positron diffraction study of SiC(0 0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Kawasuso, A.; Maekawa, M.; Yoshikawa, M.; Ichimiya, A.

    2005-05-01

    Surface structures of 6H SiC(0 0 0 1) after heat treatment in a UHV has been studied using reflection high-energy positron diffraction (RHEPD). After heat treatment at 900 °C, a typical interference effect of positron waves due to Si adatoms appears in the total reflection region of the rocking curve. The further heat treatment at 1100 °C results in surface graphitization. The rocking curve is well reproduced by theoretical calculation assuming the graphite monolayer on SiC substrate. The interlayer distance is fairly large (2.5-3.2 Å), which is comparable to that in the graphite monocrystal suggesting that the weak binding of the graphite monolayer to the SiC surface by the van der Waals force.

  18. Tuning the morphologies of SiC nanowires via the control of growth temperature, and their photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Wu, Renbing; Li, Baosheng; Gao, Mingxia; Chen, Jianjun; Zhu, Qimiao; Pan, Yi

    2008-08-01

    Single crystalline SiC nanowires were synthesized by a catalyst free vapor deposition method using elemental silicon and graphite carbon as the starting materials. The phase, morphology, crystal structure, and defects of the products were characterized by x-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Within a 6 h reaction time, the morphology of the SiC nanowires can be tuned to cylinder, hexagonal prism, or bamboo shape by simply altering the reaction temperature from 1470 °C, 1550 °C to 1630 °C, respectively. The photoluminescence of these differently shaped SiC nanowires was measured and is discussed. Based on the characterization results, the vapor-solid growth mechanisms for the multi-shaped SiC nanowires are proposed by taking into account the possible reactions between intermediate gas phases, the reaction steps, and the surface energy minimization.

  19. Structural and microstructural characterization of III-nitrides on 6H-silicon carbide (0001) substrates

    NASA Astrophysics Data System (ADS)

    Preble, Edward Alfred

    Characterization of nitride films on 6H-SiC (0001) wafers via x-ray, TEM, and AFM was accomplished on standard GAN thin films with AlN or AlGaN buffer layers. TEM sample thinning capability was improved through the use of Nomarski in an optical microscope to gauge the thickness of the sample during preparation. TEM analysis was then completed of Au and Pt films deposited on chemical vapor cleaned GaN with annealed up to 800°C. Chemical reactions were detected in x-ray measurements of the 800°C Pt samples and GaN/metal interface roughening were confirmed by TEM images in both metals. Interface roughening is attributed to the chemical reactions and interfacial stresses greater than the yield stress of the metal created during heat treatments by the difference in the thermal expansion coefficients of the Ga and the metals. The GaN rocking curves were found to track very closely to the values of the underlying substrate and changes in buffer layer growth temperatures were found to change the screw and edge dislocation populations of subsequent GaN layers. GaN grown on 1030°C AlN buffer layers showed the lowest edge dislocation populations when compared against buffers grown in the range of 1010--1220°C, even though the 1220°C AlN was much smoother. AlGaN buffer layers provided more edge dislocation reduction, with a 1090°C Al0.2Ga0.8N layer yielding the best GaN rocking curve values found in this work. GaN films with AlN buffer layers grown on hydrogen etched SiC substrates did not show rocking curve improvement when compared against samples with unetched substrates. The AlN layers showed extremely narrow, substrate limited, on-axis rocking curve values, but it is not clear as to whether additional defects are present that may broaden the off-axis rocking curves, causing the poorer results seen in the GaN films. Reciprocal space maps of uncoalesced, maskless pendeo epitaxy samples revealed that the wing regions are shielded from poor substrate material when

  20. Study of Defect Structures in 6H-SiC a/ m-Plane Pseudofiber Crystals Grown by Hot-Wall CVD Epitaxy

    NASA Astrophysics Data System (ADS)

    Goue, Ouloide Y.; Raghothamachar, Balaji; Yang, Yu; Guo, Jianqiu; Dudley, Michael; Kisslinger, Kim; Trunek, Andrew J.; Neudeck, Philip G.; Spry, David J.; Woodworth, Andrew A.

    2016-04-01

    Structural perfection of silicon carbide (SiC) single crystals is essential to achieve high-performance power devices. A new bulk growth process for SiC proposed by researchers at NASA Glenn Research Center, called large tapered crystal (LTC) growth, based on axial fiber growth followed by lateral expansion, could produce SiC boules with potentially as few as one threading screw dislocation per wafer. In this study, the lateral expansion aspect of LTC growth is addressed through analysis of lateral growth of 6H-SiC a/ m-plane seed crystals by hot-wall chemical vapor deposition. Preliminary synchrotron white-beam x-ray topography (SWBXT) indicates that the as-grown boules match the polytype structure of the underlying seed and have a faceted hexagonal morphology with a strain-free surface marked by steps. SWBXT Laue diffraction patterns of transverse and axial slices of the boules reveal streaks suggesting the existence of stacking faults/polytypes, and this is confirmed by micro-Raman spectroscopy. Transmission x-ray topography of both transverse and axial slices reveals inhomogeneous strains at the seed-epilayer interface and linear features propagating from the seed along the growth direction. Micro-Raman mapping of an axial slice reveals that the seed contains high stacking disorder, while contrast extinction analysis (g· b and g· b× l) of the linear features reveals that these are mostly edge-type basal plane dislocations. Further high-resolution transmission electron microscopy investigation of the seed-homoepilayer interface also reveals nanobands of different SiC polytypes. A model for their formation mechanism is proposed. Finally, the implication of these results for improving the LTC growth process is addressed.

  1. 29 CFR 510.21 - SIC codes.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR... in that census are organized by Standard Industrial Classification (SIC), the statistical... (SIC) code level.” (b) The Standard Industrial Classification (SIC) codes listed in appendix A and...

  2. SiC Micropipe Sprecta

    NASA Astrophysics Data System (ADS)

    Leff, David; Frasca, Albert

    1997-05-01

    This report focuses on the spectral response of 4H SiC PN junction micropipes when reverse and forward biased. Reverse biased 4H SiC PN junctions give a very strong UV line, 385nm (3.22eV), and blue line, 475nm (2.61eV). In the forward bias direction the spectra do not contain the UV, only the blue line, 490nm (2.53eV), with considerably better resolution. For isolating and measuring the micropipe spectra and structure, a sample fixture was fabricated from a power transistor case. In order to activate the micropipes in the SEM, a vacuum feed-thru was made from another power transistor case. The emitter and base leads were used as the vacuum feed-thru and were used to mount a very fine spring for making contact to the 1mm X 1mm PN junction on the SiC chip. In our attempts to study these pipes and their properties, we utilized the SE, BSE, and X-ray detectors on the SEM, a stereo microscope, and a grading monochrometer. From the utilization of this equipment, we found the locations of the micropipes, the forward and reverse bias spectrum, and the possible structural faults in the SiC. Thanks to Dr. Philip Neudeck at LeRC, and Dr. Kenneth Bladh of Wittenberg.

  3. Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H-SiC(0001) surface during scanning tunneling and atomic force microscopy studies

    NASA Astrophysics Data System (ADS)

    Morán Meza, José Antonio; Lubin, Christophe; Thoyer, François; Cousty, Jacques

    2015-06-01

    The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H-SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H-SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15-20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H-SiC(0001).

  4. Thermally stable carbon-related centers in 6H-SiC: Photoluminescence spectra and microscopic models

    SciTech Connect

    Mattausch, Alexander; Bockstedte, Michel; Pankratov, Oleg; Steeds, John W.; Furkert, Suzanne; Hayes, Jonathan M.; Sullivan, Wayne; Wright, Nick G.

    2006-04-15

    Recent ab initio calculations [Mattausch et al., Phys. Rev. B 70, 235211 (2004)] of carbon clusters in SiC reveal a possible connection between the tricarbon antisite (C{sub 3}){sub Si} and the U photoluminescence center in 6H-SiC [Evans et al., Phys. Rev. B 66, 35204 (2002)]. Yet, some of the predicted vibrational modes were not observed experimentally. We report experiments that, indeed, confirm the existence of a low-energy mode for the U center (as well as for the HT3 and HT4 centers with spectral details similar to the U center). We calculated the isotope splitting for the (C{sub 3}){sub Si}-defect and found near-perfect agreement with our data. In addition, we discuss the carbon di-interstitial (C{sub 2}){sub Hex} as a model for the Z and HT5 centers. The isotope splitting is also well reproduced, but the absolute values of the local mode energies show a discrepancy of about 10 meV.

  5. 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.

  6. 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.

  7. The first potential energy surfaces for the C6H--H2 and C6H--He collisional systems and their corresponding inelastic cross sections

    NASA Astrophysics Data System (ADS)

    Walker, Kyle M.; Dumouchel, Fabien; Lique, François; Dawes, Richard

    2016-07-01

    Molecular anions have recently been detected in the interstellar and circumstellar media. Accurate modeling of their abundance requires calculations of collisional data with the most abundant species that are usually He atoms and H2 molecules. In this paper, we focus on the collisional excitation of the first observed molecular anion, C6H-, by He and H2. Theoretical calculations of collisional cross sections rely generally on ab initio interaction potential energy surfaces (PESs). Hence, we present here the first PESs for the C6H--H2 and C6H--He van der Waals systems. The ab initio energy data for the surfaces were computed at the explicitly correlated coupled cluster with single, double, and scaled perturbative triple excitations level of theory. The method of interpolating moving least squares was used to construct 4D and 2D analytical PESs from these data. Both surfaces are characterized by deep wells and large anisotropies. Analytical models of the PESs were used in scattering calculations to obtain cross sections for low-lying rotational transitions. As could have been anticipated, important differences exist between the He and H2 cross sections. Conversely, no significant differences exist between the collisions of C6H- with the two species of H2 (para- and ortho-H2). We expect that these new data will help in accurately determining the abundance of the C6H- anions in space.

  8. Deep Reactive Ion Etching (DRIE) of High Aspect Ratio SiC Microstructures using a Time-Multiplexed Etch-Passivate Process

    NASA Technical Reports Server (NTRS)

    Evans, Laura J.; Beheim, Glenn M.

    2006-01-01

    High aspect ratio silicon carbide (SiC) microstructures are needed for microengines and other harsh environment micro-electro-mechanical systems (MEMS). Previously, deep reactive ion etching (DRIE) of low aspect ratio (AR less than or = 1) deep (greater than 100 micron) trenches in SiC has been reported. However, existing DRIE processes for SiC are not well-suited for definition of high aspect ratio features because such simple etch-only processes provide insufficient control over sidewall roughness and slope. Therefore, we have investigated the use of a time-multiplexed etch-passivate (TMEP) process, which alternates etching with polymer passivation of the etch sidewalls. An optimized TMEP process was used to etch high aspect ratio (AR greater than 5) deep (less than 100 micron) trenches in 6H-SiC. Power MEMS structures (micro turbine blades) in 6H-SiC were also fabricated.

  9. Piezoresistance behaviors of p-type 6H-SiC nanowires.

    PubMed

    Gao, Fengmei; Zheng, Jinju; Wang, Mingfang; Wei, Guodong; Yang, Weiyou

    2011-11-21

    We reported, for the first time, the piezoresistance behaviors of single p-type 6H-SiC nanowires. The results suggest that present p-type 6H-SiC nanowires could be an excellent candidate for the fabrication of robust and reliable stress sensors. PMID:21959148

  10. High-performance surface acoustic wave resonators in the 1 to 3 GHz range using a ScAlN/6H-SiC structure.

    PubMed

    Hashimoto, Ken-ya; Sato, Shuhei; Teshigahara, Akihiko; Nakamura, Takuya; Kano, Kazuhiko

    2013-03-01

    This paper describes application of Sc-doped AlN (ScAlN) to wideband SAW devices in the 1 to 3 GHz range. First, it is shown theoretically that large SAW velocity and electromechanical coupling factor are simultaneously achievable when the ScAlN film is combined with a base substrate with extremely high acoustic wave velocities, such as diamond and SiC. Next, SAW delay lines are fabricated on the ScAlN/6H-SiC structure, and reasonable agreement between the theory and experiment is obtained. Finally, one-port SAW resonators are fabricated on the structure, and it is shown that high-performance is achievable in the 1 to 3 GHz range by use of the structure. PMID:23475930

  11. Deep ultra violet and visible Raman spectroscopy studies of ion implanted 6H-SiC: Recrytallisation behaviour and thermal decomposition/thermal etching of the near surface region

    NASA Astrophysics Data System (ADS)

    Kuhudzai, R. J.; Malherbe, J. B.; van der Berg, N. G.; Hlatshwayo, T. T.; Odutemowo, O.; Prinsloo, L. C.; Buys, A. V.; Erasmus, R.; Wendler, E.

    2015-12-01

    The recystallisation behaviour and thermal decomposition of the near surface amorphised region of 6H-SiC have been investigated by Raman spectroscopy. 360 keV ions of iodine and silver were implanted at room temperature into wafers of 6H-SiC resulting in the amorphisation of the near surface region. Vacuum annealing of the samples was performed at 1200 °C for 5 h and then sequentially from 1200 to 1600 °C in steps of 100 °C for 30 h at each annealing temperature. Raman spectroscopy was performed using two laser wavelength excitation regimes, the 514 nm laser (visible region) and the 244 nm laser (deep ultraviolet region, DUV). Measurements in the visible region for samples annealed at 1200 °C for 5 h showed that the characteristic 6H-SiC peaks, namely, the Transverse Optical (TO) and Longitudinal Optical (LO) are similar to the virgin samples, albeit with lower intensity due to some retained defects upon recystallisation of the SiC surface region. The similarities between the virgin spectra and the annealed sample were due to the deep penetration of the 514 nm laser into 6H-SiC resulting in the signal from the bulk undamaged 6H-SiC contributing to the overall spectra. However, DUV laser excitation, which only probes the near surface region, shows that after annealing the peaks are broader and asymmetrical compared to the virgin samples. DUV Raman spectra of samples annealed at 1600 °C indicate that SiC has completely decomposed and the top surface layer is now covered by a carbon layer. However the deeper penetrating laser in the visible region showed that the extent of decomposition at 1600 °C was greater for the silver implanted samples than for the iodine implanted samples.

  12. Update on SIC-Based Inverter Technology

    SciTech Connect

    Chinthavali, Madhu Sudhan; Zhang, Hui; Tolbert, Leon M; Ozpineci, Burak

    2009-01-01

    This paper presents a study of silicon carbide (SiC) technology which includes device characterization and modeling, inverter simulation, and test results for several prototype inverters. The static and dynamic characteristics of discrete devices and half bridge modules are presented. Test results of a 55 kW hybrid inverter with SiC Schottky diodes and an 18 kW all-SiC inverter using SiC JFETs and Schottky diodes are demonstrated.

  13. Irradiation effects in 6H-SiC induced by neutron and heavy ions: Raman spectroscopy and high-resolution XRD analysis

    NASA Astrophysics Data System (ADS)

    Chen, Xiaofei; Zhou, Wei; Feng, Qijie; Zheng, Jian; Liu, Xiankun; Tang, Bin; Li, Jiangbo; Xue, Jianming; Peng, Shuming

    2016-09-01

    Irradiation effects of neutron and 3 MeV C+, Si+ in 6H-SiC were investigated by Raman spectroscopy and high-resolution XRD. The total disorder values of neutron irradiated SiC agree well with that of samples irradiated by ions at the same doses respectively. On the other hand, high-resolution XRD results shows that the lattice strain rate caused by neutron irradiation is 6.8%/dpa, while it is only 2.6%/dpa and 4.2%/dpa for Si+ and C+ irradiations respectively. Our results illustrate that the total disorder in neutron irradiated SiC can be accurately simulated by MeV Si+ or C+ irradiations at the same dose, but for the lattice strain and strain-related properties like surface hardness, the depth profile of irradiation damages induced by energetic ions must be considered. This research will contribute to a better understanding of the difference in irradiation effects between neutron and heavy ions.

  14. Photoelectrochemical etching of silicon carbide (SiC) and its characterization

    NASA Technical Reports Server (NTRS)

    Collins, D. M.; Harris, G. L.; Wongchotigul, K.

    1995-01-01

    Silicon carbide (SiC) is an attractive semiconductor material for high speed, high density, and high temperature device applications due to its wide bandgap (2.2-3.2 eV), high thermal conductivity, and high breakdown electric field (4 x 10(exp 6) V/cm). An instrumental process in the fabrication of semiconductor devices is the ability to etch in a highly controlled and selective manner for direct patterning techniques. A novel technique in etching using electrochemistry is described. This procedure involves the ultraviolet (UV) lamp-assisted photoelectrochemical etching of n-type 3C- and 6H-SiC to enhance the processing capability of device structures in SiC. While under UV illumination, the samples are anodically biased in an HF based aqueous solution since SiC has photoconductive properties. In order for this method to be effective, the UV light must be able to enhance the production of holes in the SiC during the etching process thus providing larger currents with light from the photocurrents generated than those currents with no light. Otherwise dark methods would be used as in the case of p-type 3C-SiC. Experiments have shown that the I/V characteristics of the SiC-electrolyte interface reveal a minimum etch voltage of 3 V and 4 V for n- and p-type 3C-SiC, respectively. Hence it is possible for etch-stops to occur. Etch rates calculated have been as high as 0.67 micrometer/min for p-type, 1.4 micrometer/min for n-type, and 1.1 micrometer/min for pn layer. On n-type 3C- SiC, an oxide formation is present where after etching a yellowish layer corresponds to a low Si/C ratio and a white layer corresponds to a high Si/C ratio. P-type 3C-SiC shows a grayish layer. Additionally, n-type 6H-SiC shows a brown layer with a minimum etch voltage of 3 V.

  15. SiC field-effect devices operating at high temperature

    NASA Astrophysics Data System (ADS)

    Ghosh, Ruby N.; Tobias, Peter

    2005-04-01

    Field-effect devices based on SiC metal-oxide-semiconductor (MOS) structures are attractive for electronic and sensing applications above 250°C. The MOS device operation in chemically corrosive, high-temperature environments places stringent demands on the stability of the insulating dielectric and the constituent interfaces within the structure. The primary mode of oxide breakdown under these conditions is attributed to electron injection from the substrate. The reliability of n-type SiC MOS devices was investigated by monitoring the gate-leakage current as a function of temperature. We find current densities below 17 nA/cm2 and 3 nA/cm2 at electric field strengths up to 0.6 MV/cm and temperatures of 330°C and 180°C, respectively. These are promising results for high-temperature operation, because the optimum bias point for SiC MOS gas sensors in near midgap, where the field across the oxide is small. Our results are valid for n-type SiC MOS sensors in general and have been observed in both the 4H and 6H polytypes.

  16. The correlation of epitaxial graphene properties and morphology of SiC (0001)

    SciTech Connect

    Guo, Y.; Guo, L. W. E-mail: xlchen@iphy.ac.cn; Huang, J.; Jia, Y. P.; Lin, J. J.; Lu, W.; Li, Z. L.; Yang, R.; Chen, X. L. E-mail: xlchen@iphy.ac.cn

    2014-01-28

    The electronic properties of epitaxial graphene (EG) on SiC (0001) depend sensitively on the surface morphology of SiC substrate. Here, 2–3 layers of graphene were grown on on-axis 6H-SiC with different step densities realized through controlling growth temperature and ambient pressure. We show that epitaxial graphene on SiC (0001) with low step density and straight step edge possesses fewer point defects laying mostly on step edges and higher carrier mobility. A relationship between step density and EG mobility is established. The linear scan of Raman spectra combined with the atomic force microscopy morphology images revealed that the Raman fingerprint peaks are nearly the same on terraces, but shift significantly while cross step edges, suggesting the graphene is not homogeneous in strain and carrier concentration over terraces and step edges of substrates. Thus, control morphology of epitaxial graphene on SiC (0001) is a simple and effective method to pursue optimal route for high quality graphene and will be helpful to prepare wafer sized graphene for device applications.

  17. Fabrication and characterization of ZnO nanorods/p-6H-SiC heterojunction LED by microwave-assisted chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Hassan, J. J.; Mahdi, M. A.; Ramizy, Asmiet; Abu Hassan, H.; Hassan, Z.

    2013-01-01

    High-quality vertically aligned zinc oxide nanorods were successfully grown on p-type 6H-SiC substrate by microwave-assisted chemical bath deposition. The novel seed material poly(vinyl alcohol)-Zn(OH)2 nanocomposites was used to seed the 6H-SiC substrate. X-ray diffraction analysis and field emission scanning electron microscopy showed that the synthesized ZnO nanorods were vertically well aligned in the direction of the (0 0 2) plane of the hexagonal structure. The optical properties were examined by photoluminescence spectroscopy, which showed a high-intensity UV peak compared with visible defect peaks. The current-voltage property proved the good rectifier characteristic of the n-type ZnO nanorod/p-type SiC diode heterojunction. The electroluminescence emission of the heterojunction LED was sufficiently high to be seen with the naked eye, with a broad peak centered at the green part of the visible spectrum.

  18. Reactive sintering of SiC

    NASA Technical Reports Server (NTRS)

    Kim, Y. W.; Lee, J. G.

    1984-01-01

    Investigation of the sintering processes involved in the sintering of SiC revealed a connection between the types and quantities of sintering additives or catalysts and densification, initial shrinkage, and weight loss of the sintered SiC material. By sintering processes, is meant the methods of mass transport, namely solid vapor transport and grain boundary diffusion.

  19. Spin centres in SiC for all-optical nanoscale quantum sensing under ambient conditions

    NASA Astrophysics Data System (ADS)

    Anisimov, A. N.; Babunts, R. A.; Kidalov, S. V.; Mokhov, E. N.; Soltamov, V. A.; Baranov, P. G.

    2016-07-01

    Level anticrossing (LAC) spectroscopy was demonstrated on a family of uniaxially oriented spin colour centres with S = 3/2 in the ground and excited states in hexagonal 4H-, 6H- and rhombic 15R- SiC polytypes. It was shown that these centres exhibit unique characteristics such as optical spin alignment up to the temperatures of 250 ◦C. A sharp variation of the IR photoluminescence intensity in the vicinity of LAC with the record contrast was observed, which can be used for a purely all-optical sensing of the magnetic field and temperature without applying radiofrequency field. A distinctive feature of the LAC signal is weak dependence on the direction of the magnetic field that allows one to monitor the LAC signals in the nonoriented systems, such as powder of SiC nanocrystals.

  20. Coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) and (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2): the effect of alkylating the nitrogen bridge on ligand bridging versus chelating behavior.

    PubMed

    Sekabunga, E J; Smith, Michele L; Webb, T R; Hill, W E

    2002-03-11

    The coordination chemistry of silver(I) with the nitrogen-bridged ligands (C(6)H(5))(2)PN(R)P(C(6)H(5))(2) [R = H (dppa); R = CH(3) (dppma)] has been investigated by (31)P NMR and electrospray mass spectrometry (ESMS). Species observed by (31)P NMR include Ag(2)(mu-dppa)(2+), Ag(2)(mu-dppa)(2)(2+), Ag(2)(mu-dppa)(3)(2+), Ag(2)(mu-dppma)(2+), Ag(2)(mu-dppma)(2)(2+), and Ag(eta(2)-dppma)(2)(+). Species observed by ESMS at low cone voltages were Ag(2)(dppa)(2)(2+), Ag(2)(dppa)(3)(2+), Ag(2)(dppma)(2)(2+), and Ag(dppma)(2)(+). (C(6)H(5))(2)PN(CH(3))P(C(6)H(5))(2) showed a strong tendency to chelate, while (C(6)H(5))(2)PN(H)P(C(6)H(5))(2) preferred to bridge. Differences in the bridging versus chelating behavior of the ligands are assigned to the Thorpe-Ingold effect, where the methyl group on nitrogen sterically interacts with the phenyl groups on phosphorus. The crystal structure of the three-coordinate dinuclear silver(I) complex (Ag(2)[(C(6)H(5))(2)PN(H)P(C(6)H(5))(2)](3))(BF(4))(2) has been determined. Bond distances include Ag-Ag = 2.812(1) A, Ag(1)-P(av) = 2.492(3) A, and Ag(2)-P(av) = 2.509(3) A. The compound crystallizes in the monoclinic space group Cc at 294 K, with a = 18.102(4)(o), Z = 4, V = 7261(3) A(3), R = 0.0503, and R(W) = 0.0670. PMID:11874357

  1. Growth of Si thin film on 6H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Wu, Hsin-Ju; Hoang, M. Tien; Li, Yuntao; First, Phillip N.

    2015-03-01

    Graphene is much studied for its unusual electronic properties. Other carbon group elements such as silicon (Si) and germanium (Ge) also are predicted to have stable 2D phases for which the electronic structure and properties could be still more interesting. Silicon carbide, already an excellent insulating substrate for epitaxial graphene, could potentially play a similar role for silicene. Commonalities in the substrate and processing may lead to the integration of carbon and silicon technologies. Here, we use surface analysis techniques (LEED, AES, STM) to investigate the formation of 2D Si on SiC(0001), under low pressures of silane or silicon. Similar methods allow control of surface graphene growth by compensating Si desorption from SiC. Among several Si-rich reconstructions, we find a single stable hexagonal phase, at a coverage close to twice the Si density predicted for silicene, and with a unit cell consistent with a commensurate layer of silicene or silicane. For a graphitized SiC starting surface, silane is shown to etch graphene, reforming SiC. Work supported in part by NSF (DMR-1106131, DMR-0820382 [MRSEC]).

  2. Global reaction route mapping of isomerization pathways of exotic C{sub 6}H molecular species

    SciTech Connect

    Vikas, E-mail: qlabspu@yahoo.com; Kaur, Gurpreet

    2013-12-14

    C{sub 6}H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C{sub 6}H is explored to search isomers of C{sub 6}H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C{sub 6}H. The reaction route search is performed through global reaction route mapping method, which utilizes an uphill walking technique based on an anharmonic downward distortion following approach to search intermediates and transition states. The computations performed at the CASSCF/aug-cc-pVTZ, CCSD(T)/6-311++G(d,p)//DFT/B3LYP/6-311++G(d,p), and DFT/B3LYP/aug-cc-pVTZ levels of the theory identified 14 isomers (including 8 new isomeric forms of C{sub 6}H) and 28 transition states. Most of the identified isomers are found to have significant multireference character. The kinetic stability and natural bond orbital analysis of the identified isomers is also investigated. The isomeric forms are further characterized using spectral analysis involving rotational constants, vibrational frequencies, and Raman scattering activities as well as analyzing the effect of isotopic substitution of hydrogen on the spectral features. This study proposes that the linear-C{sub 6}H can readily isomerize to a six-member ring isomer.

  3. Direct ab initio study of the C6H6 + CH3/C2H5 = C6H5 + CH4/C2H6 reactions

    NASA Astrophysics Data System (ADS)

    Mai, Tam V.-T.; Ratkiewicz, Artur; Duong, Minh v.; Huynh, Lam K.

    2016-02-01

    A kinetic study of the reactions C6H6 + CH3/C2H5 = C6H5 + CH4/C2H6 was carried out in the temperature range of 300-2500 K using high levels of electronic structure theory, namely, CCSD(T)/CBS//BH&HLYP/cc-pVDZ, and canonical variational transition state theory (CVT) with corrections for small curvature tunneling (SCT) and hindered internal rotation (HIR) treatments. It is found that variational effect is not important and both SCT and HIR corrections noticeably affect the rate constants. Being in good agreement with literature data, the calculated results provide solid basis information for the investigation of the polyaromatic hydrocarbon (PAH) + alkyl radical reaction, an important class in combustion and soot formation.

  4. 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

  5. Moissanite (SiC) from kimberlites: Polytypes, trace elements, inclusions and speculations on origin

    NASA Astrophysics Data System (ADS)

    Shiryaev, A. A.; Griffin, W. L.; Stoyanov, E.

    2011-03-01

    An extensive collection of moissanite (SiC) grains from the Mir, Aikhal and Udachnaya kimberlite pipes of Yakutia has been characterized in terms of structural perfection, defects and the major- and trace-element chemistry of SiC and its included phases. The natural grains are clearly distinct from synthetic SiC produced by various methods. Most of the natural SiC grains are 6H and 15R polytypes. Some of the grains (< 10%) show extremely complex Raman spectra indicating strongly disordered structures. Some grains also show zoning in impurities, C-isotope composition and cathodoluminescence brightness. Inclusions are heterogeneously distributed within the natural SiC; their size varies from a few nanometers to hundreds of microns. The most abundant inclusions in SiC are Si metal and iron silicide (FeSi 2); a Si-C-O phase with stoichiometry close to Si 4(C,O) 7 probably is related to the silicon oxycarbides. FeSi 2 commonly appears to have exsolved from Si metal; in some cases Ti metal then has exsolved from FeSi 2 to form symplectites. Trace elements are strongly concentrated in the inclusions of FeSi 2 and Si 4(C,O) 7. The trace-element patterns of these phases are generally similar in the different kimberlites, but there are some consistent minor differences between localities. The trace-element patterns of FeSi 2 and Si 4(C,O) 7 are strongly enriched in LREE/HREE and are broadly similar to the patterns of kimberlites, carbonatites and some diamond-forming fluids. However, extreme negative anomalies in Eu (and Sm) suggest highly reducing conditions. Yb also shows strong negative anomalies in FeSi 2 from all three localities, and in Si 4(C,O) 7 from Aikhal and Mir, but not in those from Udachnaya. Trace-element chemistry and the nature of the inclusions provide a reliable basis for distinguishing natural and synthetic SiC. Textural and chemical features and the presence of oxidation products (Si 4(C,O) 7 and SiO 2) suggest that moissanite grew at high temperatures

  6. KeV Ion Beam Induced Surface Modification of SiC Hydrogen Sensor

    SciTech Connect

    Muntele, C.I.; Ila, D.; Williams, E.K.; Poker, D.B.; Hensley, D.K.

    1999-11-29

    Silicon carbide, a wide-bandgap semiconductor, is currently used to fabricate an efficient high temperature hydrogen sensor. When a palladium coating is applied on the exposed surface of silicon carbide, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. Rather than applying a palladium film, we have implanted palladium ions into the silicon face of 6H, n-type Sic samples. The implantation energies and fluences, as well as the results obtained by monitoring the current through the sample in the presence of hydrogen are included in this paper.

  7. Fabrication and morphology of porous p-type SiC

    NASA Astrophysics Data System (ADS)

    Shishkin, Y.; Ke, Y.; Devaty, R. P.; Choyke, W. J.

    2005-02-01

    Porous silicon carbide fabricated from p-type 4H and 6H SiC wafers by electrochemical etching in hydrofluoric electrolyte is studied. An investigation of the dependence on wafer polarity reveals that pore formation is favored on the C face while complete dissolution occurs on the Si face. When the etching is done on the C face, the pore wall thickness decreases with increasing current density. The morphology of the front surface of the sample depends on the prior treatment of the workpiece surface. The porosity is estimated based on the analysis of scanning electron microscope images, charge-transfer calculations, and gravimetric analysis.

  8. Evaluation of some basic positron-related characteristics of SiC

    SciTech Connect

    Brauer, G.; Anwand, W.; Nicht, E.; Wagner, N.; Puska, M.J.; Korhonen, T.

    1996-07-01

    First-principles electronic structure and positron-state calculations for perfect and defected 3C- and 6H-SiC polytypes of SiC have been performed. Monovacancies and divacancies have been treated; the influence of lattice position and nitrogen impurities have been considered in the former case. Positron affinities and binding energies have been calculated; trends are discussed, and the results compared with recent atomic superposition method calculations. Experimental determination of the electron and positron work functions of the same 6H-SiC allows an assessment of the accuracy of the present first-principles calculations, and to suggest further improvements. {copyright} {ital 1996 The American Physical Society.}

  9. Refractory Oxide Coatings on Sic Ceramics

    NASA Technical Reports Server (NTRS)

    Lee, Kang N.; Jacobson, Nathan S.; Miller, Robert A.

    1994-01-01

    Silicon carbide with a refractory oxide coating is potentially a very attractive ceramic system. It offers the desirable mechanical and physical properties of SiC and the environmental durability of a refractory oxide. The development of a thermal shock resistant plasma-sprayed mullite coating on SiC is discussed. The durability of the mullite/SiC in oxidizing, reducing, and molten salt environments is discussed. In general, this system exhibits better behavior than uncoated SiC. Areas for further developments are discussed.

  10. Multiphoton ionization studies of clusters of immiscible liquids. II. C6H6- (H2O)n, n=3-8 and (C6H6)2- (H2O)1,2

    NASA Astrophysics Data System (ADS)

    Garrett, Aaron W.; Zwier, Timothy S.

    1992-03-01

    Resonant two-photon ionization (R2PI) time-of-flight mass spectroscopy is used to record S0-S1 spectra of the neutral complexes C6H6-(H2O)n with n=3-8 and (C6H6)2-(H2O)1,2. Due to limitations imposed by the size of these clusters, a number of vibronic level arguments are used to constrain the gross features of the geometries of these clusters. Among the spectral clues provided by the data are the frequency shifts of the transitions, their van der Waals structure, the fragmentation of the photoionized clusters, and the complexation-induced origin intensity and 610 splitting. In the 1:3 cluster, simple arguments are made based on the known structures of the 1:1 and 1:2 clusters which lead to the conclusion that all three water molecules reside on the same side of the benzene ring. Three structures for the 1:3 cluster are proposed which are consistent with the available data. Of these, only one is also consistent with the remarkable similarity of the 1:4 and 1:5 spectra to those of the 1:3 cluster. This structure involves a cyclic water trimer in which one of the water molecules is near the sixfold axis in a π hydrogen-bonded configuration. This structure is then expanded in the 1:4 and 1:5 clusters to incorporate the fourth and fifth water molecules in cyclic structures which place the additional water molecules far from the benzene ring without disturbing the interaction of the other water molecules with the benzene ring. For 1:n clusters with n≥6, subtle and then significant changes are observed in the spectra which indicate changes in the way the water cluster interacts with the benzene ring. This development occurs at precisely the water cluster size which calculations predict that cagelike water cluster structures will begin to compete and eventually be favored over large cyclic structures. Finally, cursory scans of the 2:1 cluster show that this cluster also fragments efficiently upon photoionization by loss of a single water molecule and that it possesses a

  11. High frequency characteristics and modelling of p-type 6H-silicon carbide MOS structures

    NASA Astrophysics Data System (ADS)

    Fernández, J.; Godignon, P.; Berberich, S.; Rebollo, J.; Brezeanu, G.; Millán, J.

    1996-09-01

    This paper presents the high frequency electrical characteristics and modelling of Al/SiO 2/ p-type 6HSiC structures. The oxide was thermally grown under dry conditions. Capacitance and conductance vs bias and frequency measurements have been performed in daylight and exposing the capacitors to u.v. light. The experimental Cm- Vg and Gm- Vg characteristics show hysteresis effects, which are more important when the samples are exposed to 254 nm u.v. light. This behaviour can be explained in terms of interface traps. The MOS structure modelling is based on an interface trap model in which the interface trap levels are considered to be continuously distributed in the SiC bandgap and only charge exchange between interface trap levels and the SiC bands is allowed. From this formulation and from the Gm- f characteristics, the interface state density and the interface trap time constant have been determined.

  12. Bulk Micromachined 6H-SiC High-g Piezoresistive Accelerometer Fabricated and Tested

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.

    2002-01-01

    High-g accelerometers are needed in certain applications, such as in the study and analysis of high-g impact landings and projectiles. Also, these accelerometers must survive the high electromagnetic fields associated with the all-electric vehicle technology needed for aerospace applications. The choice of SiC is largely due to its excellent thermomechanical properties over conventional silicon-based accelerometers, whose material properties inhibit applicability in high electromagnetic radiation and high temperatures (>150 C) unless more complex and sometimes costly packaging schemes are adopted. This work was the outcome of a NASA Glenn Research Center summer internship program, in collaboration with Cornell University and the Munitions Directorate of the U.S. Air Force in Eglin, Florida. It aimed to provide the enabling technology infrastructure (modeling, fabrication, and validation) for the implementation of SiC accelerometers designed specifically for harsh environments.

  13. Monte Carlo Simulation of Electron Transport in 4H- and 6H-SiC

    SciTech Connect

    Sun, C. C.; You, A. H.; Wong, E. K.

    2010-07-07

    The Monte Carlo (MC) simulation of electron transport properties at high electric field region in 4H- and 6H-SiC are presented. This MC model includes two non-parabolic conduction bands. Based on the material parameters, the electron scattering rates included polar optical phonon scattering, optical phonon scattering and acoustic phonon scattering are evaluated. The electron drift velocity, energy and free flight time are simulated as a function of applied electric field at an impurity concentration of 1x10{sup 18} cm{sup 3} in room temperature. The simulated drift velocity with electric field dependencies is in a good agreement with experimental results found in literature. The saturation velocities for both polytypes are close, but the scattering rates are much more pronounced for 6H-SiC. Our simulation model clearly shows complete electron transport properties in 4H- and 6H-SiC.

  14. Comparison of SiC mirror approaches

    NASA Astrophysics Data System (ADS)

    Carrigan, Keith; Riso, Michael; Khatri, Shayna; Douglas, Christopher

    2013-09-01

    Silicon Carbide (SiC) mirrors hold many advantages over traditional optical materials and are increasingly common in optical systems. The wide range of optical applications necessitates different approaches to the manufacturing and finishing of SiC mirrors. Three key advancements have led to this differentiation: 1) manufacturing of CVD clad SiC mirrors in near cost and schedule parity with Zerodur, 2) super-polish of amorphous Silicon claddings, 3) low-roughness polishing results of bare reaction-bonded SiC aspheres. Three approaches which utilize these advancements will be discussed, each with its own strengths and weaknesses for specific applications. The relative schedules and performance of these approaches will also be compared, with Zerodur used as a reference.

  15. SiC nanowires: A photocatalytic nanomaterial

    SciTech Connect

    Zhou Weimin; Yan Lijun; Wang Ying; Zhang Yafei

    2006-07-03

    Single-crystal {beta}-SiC nanowires coated with amorphous SiO{sub 2} were synthesized by a simple thermal evaporation technique. The photocatalytic activity of the SiC nanowires was characterized by measuring the photodegradation rate of acetaldehyde catalyzed by SiC as a function of UV irradiation time. It exhibited excellent photocatalytic activity, leading to the efficient decomposition of acetaldehyde by irradiation with UV light. The progress of the photocatalytic reaction can be monitored by the evolution of one of the products, CO{sub 2}. It has been observed that the as-synthesized SiC nanowires (with the SiO{sub 2} coating) have higher catalytic activity than the HF-etched, oxide-free SiC nanowires.

  16. Study of the effect of doped impurities on polytype stability during PVT growth of SiC using 2D nucleation theory

    NASA Astrophysics Data System (ADS)

    Shiramomo, T.; Gao, B.; Mercier, F.; Nishizawa, S.; Nakano, S.; Kakimoto, K.

    2014-01-01

    The effect of nitrogen and aluminum as doped impurities on the stability of SiC polytypes (C- or Si-face 4H and 6H substrates) formed by physical vapor transport (PVT) was investigated. The stability of the polytypes was analyzed using classical thermodynamic nucleation theory with numerical results obtained from a global model including heat, mass and species transfer in a PVT furnace. The results reveal that the formation of 4H-SiC was more stable than that of 6H-SiC when a grown crystal was doped with nitrogen using C-face 4H- and 6H-SiC as seed crystals. In contrast, formation of 6H-SiC was favored over 4H-SiC when Si-face 4H- and 6H-SiC seed crystals were used. Meanwhile, the formation of 4H-SiC was more stable than that of 6H-SiC when aluminum was the dopant and C- and Si-faces of 6H-SiC were used as seed crystals. Formation of 6H-SiC occurred over that of 4H-SiC in the cases of C- and Si-faces of 4H-SiC as seed crystals.

  17. Development of Sic Gas Sensor Systems

    NASA Technical Reports Server (NTRS)

    Hunter, G. W.; Neudeck, P. G.; Okojie, R. S.; Beheim, G. M.; Thomas, V.; Chen, L.; Lukco, D.; Liu, C. C.; Ward, B.; Makel, D.

    2002-01-01

    Silicon carbide (SiC) based gas sensors have significant potential to address the gas sensing needs of aerospace applications such as emission monitoring, fuel leak detection, and fire detection. However, in order to reach that potential, a range of technical challenges must be overcome. These challenges go beyond the development of the basic sensor itself and include the need for viable enabling technologies to make a complete gas sensor system: electrical contacts, packaging, and transfer of information from the sensor to the outside world. This paper reviews the status at NASA Glenn Research Center of SiC Schottky diode gas sensor development as well as that of enabling technologies supporting SiC gas sensor system implementation. A vision of a complete high temperature microfabricated SiC gas sensor system is proposed. In the long-term, it is believed that improvements in the SiC semiconductor material itself could have a dramatic effect on the performance of SiC gas sensor systems.

  18. Improved Method of Manufacturing SiC Devices

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.

    2005-01-01

    . However, in MUSiC one cannot exploit the superior sensing, thermomechanical, and electrical properties of single-crystal 6H-SiC or 4H-SiC. As a complement to MUSiC, the CLASSiC five-mask process can be utilized to fabricate multiple devices in bulk single-crystal SiC of any polytype. The five-mask process makes fabrication less complex because it eliminates the need for large-area deposition and removal of sacrificial material. Other innovations in CLASSiC pertain to selective etching of indium tin oxide and aluminum in connection with multilayer metallization. One major characteristic of bulk micromachined microelectromechanical devices is the presence of three-dimensional (3D) structures. Any 3D recesses that already exist at a given step in a fabrication process usually make it difficult to apply a planar coat of photoresist for metallization and other subsequent process steps. To overcome this difficulty, the CLASSiC process includes a reversal of part of the conventional flow: Metallization is performed before the recesses are etched.

  19. Silicon vacancy-related centers in non-irradiated 6H-SiC nanostructure

    SciTech Connect

    Bagraev, N. T. Danilovskii, E. Yu.; Gets, D. S.; Kalabukhova, E. N.; Klyachkin, L. E.; Koudryavtsev, A. A.; Malyarenko, A. M.; Mashkov, V. A.; Savchenko, D. V.; Shanina, B. D.

    2015-05-15

    We present the first findings of the silicon vacancy related centers identified in the non-irradiated 6H-SiC nanostructure using the electron spin resonance (ESR) and electrically-detected (ED) ESR technique. This planar 6H-SiC nanostructure represents the ultra-narrow p-type quantum well confined by the δ-barriers heavily doped with boron on the surface of the n-type 6H-SiC(0001) wafer. The new EDESR technique by measuring the only magnetoresistance of the 6H-SiC nanostructure under the high frequency generation from the δ-barriers appears to allow the identification of the isolated silicon vacancy centers as well as the triplet center with spin state S = 1. The same triplet center that is characterized by the large value of the zero-field splitting constant D and anisotropic g-factor is revealed by the ESR (X-band) method. The hyperfine (HF) lines in the ESR and EDESR spectra originating from the HF interaction with the {sup 14}N nucleus seem to attribute this triplet center to the N-V{sub Si} defect.

  20. Stability and isomerization reactions of phenyl cation C6H5+ isomers

    NASA Astrophysics Data System (ADS)

    Shi, Dandan; Yang, Xue; Zhang, Xiaomei; Shan, Shimin; Xu, Haifeng; Yan, Bing

    2016-03-01

    As a key polyatomic molecular cation that plays a pivotal role in growth of the polycyclic aromatic hydrocarbons, phenyl cation C6H5+ exhibits various isomers and isomerization reactions. Investigation on the structure and stability of the isomers as well as the isomerization is important for better understanding the chemical reactions involving C6H5+ cations. In this work, we have performed a theoretical study on the stability and isomerization reactions of C6H5+ isomers at density functional theory B3LYP/6-311G (d, p) level. We have obtained a total of 60 isomers of C6H5+ cations, most of which are reported for the first time. The geometries, vibrational frequencies, thermodynamic properties and stability of 28 out of 60 isomers have been summarized in detail. Different ring-to-ring and ring-to-chain isomerization pathways, which are connected via 28 transition states, have been investigated using the intrinsic reaction coordinate method. The results show that the isomerization reactions occur via hydrogen migration followed by bond-breaking and reconstruction.

  1. 17 CFR 240.6h-1 - Settlement and regulatory halt requirements for security futures products.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Settlement and regulatory halt... § 240.6h-1 Settlement and regulatory halt requirements for security futures products. (a) For the... exchange or national securities association that lists the security. (3) Regulatory halt means a...

  2. 17 CFR 240.6h-1 - Settlement and regulatory halt requirements for security futures products.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Settlement and regulatory halt... § 240.6h-1 Settlement and regulatory halt requirements for security futures products. (a) For the... exchange or national securities association that lists the security. (3) Regulatory halt means a...

  3. 17 CFR 240.6h-1 - Settlement and regulatory halt requirements for security futures products.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Settlement and regulatory halt... § 240.6h-1 Settlement and regulatory halt requirements for security futures products. (a) For the... exchange or national securities association that lists the security. (3) Regulatory halt means a...

  4. 17 CFR 240.6h-1 - Settlement and regulatory halt requirements for security futures products.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Settlement and regulatory halt... § 240.6h-1 Settlement and regulatory halt requirements for security futures products. (a) For the... exchange or national securities association that lists the security. (3) Regulatory halt means a...

  5. 17 CFR 240.6h-1 - Settlement and regulatory halt requirements for security futures products.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Settlement and regulatory halt... § 240.6h-1 Settlement and regulatory halt requirements for security futures products. (a) For the... exchange or national securities association that lists the security. (3) Regulatory halt means a...

  6. Microstructural and superconducting properties of C6H6 added bulk MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Babaoğlu, Meral G.; Safran, Serap; Çiçek, Özlem; Ağıl, Hasan; Ertekin, Ercan; Hossain, Md. Shahriar A.; Yanmaz, Ekrem; Gencer, Ali

    2012-10-01

    The effect of aromatic hydrocarbon (benzene, C6H6) addition on lattice parameters, microstructure, critical temperature (Tc), critical current density (Jc) of bulk MgB2 has been studied. In this work only 2 mol% C6H6 addition was found to be very effective in increasing the Jc values, while resulting in slight reduction of the Tc. Jc values of 2 mol% C6H6 added MgB2 bulks reached to 1.83×106 A/cm2 at 15 K and 0 T. Microstructural analyses suggest that Jc enhancement is associated with the substitution of carbon with boron and which also results in the smaller MgB2 grain size. The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the Tc by carbon addition. We note that our results show the advantages of C6H6 addition include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc of MgB2, compared to un-doped samples.

  7. Biomorphous SiC ceramics prepared from cork oak as precursor

    NASA Astrophysics Data System (ADS)

    Yukhymchuk, V. O.; Kiselov, V. S.; Valakh, M. Ya.; Tryus, M. P.; Skoryk, M. A.; Rozhin, A. G.; Kulinich, S. A.; Belyaev, A. E.

    2016-04-01

    Porous ceramic materials of SiC were synthesized from carbon matrices obtained via pyrolysis of natural cork as precursor. We propose a method for the fabrication of complex-shaped porous ceramic hardware consisting of separate parts prepared from natural cork. It is demonstrated that the thickness of the carbon-matrix walls can be increased through their impregnation with Bakelite phenolic glue solution followed by pyrolysis. This decreases the material's porosity and can be used as a way to modify its mechanical and thermal characteristics. Both the carbon matrices (resulted from the pyrolysis step) and the resultant SiC ceramics are shown to be pseudomorphous to the structure of initial cork. Depending on the synthesis temperature, 3C-SiC, 6H-SiC, or a mixture of these polytypes, could be obtained. By varying the mass ratio of initial carbon and silicon components, stoichiometric SiC or SiC:С:Si, SiC:С, and SiC:Si ceramics could be produced. The structure, as well as chemical and phase composition of the prepared materials were studied by means of Raman spectroscopy and scanning electron microscopy.

  8. The decoupling of epitaxial graphene on SiC by hydrogen intercalation: an ab initio study

    NASA Astrophysics Data System (ADS)

    Nemec, Lydia; Rinke, Patrick; Blum, Volker; Scheffler, Matthias

    2015-03-01

    Large-scale ordered epitaxial graphene can be grown on various substrates, out of which silicon carbide (SiC) is one of the most promising. The exact material properties of graphene depend on the growth conditions and its interaction with the substrate. By hydrogen intercalation of epitaxial graphene on the Si-face of SiC the graphene layer decouples from the substrate forming quasi-free-standing monolayer graphene (QFMLG). We performed an density functional theory study of QFMLG on the polar 6H-SiC(0001) surface based on a van der Waals corrected semi-local exchange-correlation functional using the all-electron numeric atom-centered basis function code FHI-aims. We find an adsorption height in excellent agreement with X-ray standing wave experiments, a very low buckling of the graphene layer, and a very homogeneous electron density at the interface. All these features improve the electronic properties of QFMLG compared to epitaxial graphene. Using the insight gleaned on the Si-face, we present the structure of a hypothetical QFMLG phase on the C-face of SiC. We find that hydrogen intercalation is a promising option to control the SiC-graphene interface.

  9. Hidden Superlattice in Tl2(SC6H4S) and Tl2(SeC6H4Se) Solved from Powder X-ray Diffraction

    SciTech Connect

    K Stone; D Turner; M Singh; T Vaid; P Stephens

    2011-12-31

    The crystal structures of the isostructural title compounds poly[({mu}-benzene-1,4-dithiolato)dithallium], Tl{sub 2}(SC{sub 6}H{sub 4}S), and poly[({mu}-benzene-1,4-diselenolato)dithallium], Tl{sub 2}(SeC{sub 6}H{sub 4}Se), were solved by simulated annealing from high-resolution synchrotron X-ray powder diffraction. Rietveld refinements of an initial structure with one formula unit per triclinic cell gave satisfactory agreement with the data, but led to a structure with impossibly close non-bonded contacts. A disordered model was proposed to alleviate this problem, but an alternative supercell structure leads to slightly improved agreement with the data. The isostructural superlattice structures were confirmed for both compounds through additional data collection, with substantially better counting statistics, which revealed the presence of very weak superlattice peaks not previously seen. Overall, each structure contains Tl-S or Tl-Se two-dimensional networks, connected by phenylene bridges. The sulfur (or selenium) coordination sphere around each thallium is a highly distorted square pyramid or a 'see-saw' shape, depending upon how many Tl-S or Tl-Se interactions are considered to be bonds. In addition, the two compounds contain pairs of Tl{sup I} ions that interact through a closed-shell 'thallophilic' interaction: in the sulfur compound there are two inequivalent pairs of Tl atoms with Tl-Tl distances of 3.49 and 3.58 {angstrom}, while in the selenium compound those Tl-Tl interactions are at 3.54 and 3.63 {angstrom}.

  10. Fully self-consistent calculations of momentum distributions of annihilating electron-positron pairs in SiC

    NASA Astrophysics Data System (ADS)

    Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Barthe, Marie-France; Bertolus, Marjorie

    2016-05-01

    We performed calculations of momentum distributions of annihilating electron-positron pairs in various fully relaxed vacancy defects in SiC. We used self-consistent two-component density functional theory schemes to find the electronic and positronic densities and wave functions in the considered systems. Using the one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) we calculated the line-shape parameters S and W . We emphasize the effect of the experimental resolution and the choice of the integration ranges for the S and W parameters on the distributions of the points corresponding to different defects in the S (W ) plot. We performed calculation for two polytypes of SiC, 3 C , and 6 H and showed that for silicon vacancies and clusters containing this defect there were no significant differences between the Doppler spectra. The results of the Doppler spectra calculations were compared with experimental data obtained for n -type 6 H -SiC samples irradiated with 4-MeV Au ions. We observed a good general agreement between the measured and calculated points.

  11. Cryogenic Performance of Trex SiC Mirror

    NASA Technical Reports Server (NTRS)

    Foss, Colby; Kane, Dave; Bray, Donald; Hadaway, James

    2005-01-01

    Low cost, high performance lightweight Silicon Carbide (Sic) mirrors provide an alternative to Beryllium mirrors. A Trex Enterprises 0.25m diameter lightweight Sic mirror using its patented Chemical Vapor Composites (CVC) technology was evaluated for its optical performance. CVC Sic is chemically pure, thermally stable, and mechanically stiff. CVC technology yields higher growth rate than that of CVD Sic. NASA has funded lightweight optical materials technology development efforts involving Sic mirrors for future space based telescope programs. As part of these efforts, a Trex Sic was measured interferometrically from room temperature to 30 degrees Kelvin. This paper will discuss the test goals, the test instrumentation, test results, and lessons learned.

  12. From nanographene to monolayer graphene on 6H-SiC(0001) substrate

    NASA Astrophysics Data System (ADS)

    Ouerghi, A.; Ridene, M.; Mathieu, C.; Gogneau, N.; Belkhou, R.

    2013-06-01

    Graphene quantum dots, nanoribbons, and nanographene are great promising in various applications owing to the quantum confinement and edge effects. Here we evidence the presence of epitaxial nanographene on SiC. Morphology and electronic structure of the graphene layers have been analyzed by SPELEEM. Using Scanning Tunneling Microscopy, we show that the increase of relative number of clusters carbon enabled the observation of nanographene, the diameter of which was around 20 nm. This nanographene shows a honeycomb structure at atomic level. The local chemical and electronic properties of the sample have been determined by photoelectron spectroscopy using synchrotron radiation.

  13. Tuning Chelation by the Surfactant-Like Peptide A6H Using Predetermined pH Values

    PubMed Central

    2013-01-01

    We examine the self-assembly of a peptide A6H comprising a hexa-alanine sequence A6 with a histidine (H) “head group”, which chelates Zn2+ cations. We study the self-assembly of A6H and binding of Zn2+ ions in ZnCl2 solutions, under acidic and neutral conditions. A6H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A6H in acidic ZnCl2 solutions, the carbonyl oxygen atoms in A6H chelate the Zn2+ ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A6H mixed with water or ZnCl2 solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A6H chelates Zn2+ ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A6H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A6H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A6H determines the internal structure of the self-assembled aggregates independent from changes in chelation. PMID:24369761

  14. Analysis of Ground-State Zero-Field Splitting for Mn2+ in ZnNbOF5·6(H2O) and CoNbOF5·6(H2O)

    NASA Astrophysics Data System (ADS)

    Li, Ju-Fen; Kuang, Xiao-Yu

    2011-06-01

    The electron paramagnetic resonance spectra of trigonal Mn2+ centers in ZnNbOF5·6(H2O) and CoNbOF5·6(H2O) crystals are studied on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field. It is demonstrated that the local lattice structure around a trigonal Mn2+ center has an elongation distortion along the crystalline c3 axis, and when Mn2+ is doped in the ZnNbOF5·6(H2O) and CoNbOF5·6(H2O) crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters for trigonal Mn2+ centers in ZnNbOF5·6(H2O) and CoNbOF5·6(H2O) are determined.

  15. PCl3-C6H6 heterodimers: evidence for Pπ phosphorus bonding at low temperatures.

    PubMed

    Ramanathan, N; Sankaran, K; Sundararajan, K

    2016-07-28

    A phosphorous trichloride (PCl3)-benzene (C6H6) heterodimer was generated in a low temperature N2 matrix and was characterized using infrared spectroscopy. The structure of the heterodimer produced in the matrix isolation experiment was discerned through ab initio computations. Computations disclosed that the experimentally detected dimer is stabilized through strong non-covalent phosphorus bonded Pπ interaction, considered as a class of pnicogen bonding. This experimentally unmapped Pπ interaction so far has been reconnoitered using atoms in molecules and natural bond orbital and energy decomposition analyses. The influence of substitutions on both the PCl3 and C6H6 monomeric units of the heterodimer was subsequently examined to understand the strength of Pπ interaction as a result of these substitutions. PMID:27374927

  16. Si6H12/Polymer Inks for Electrospinning a-Si Nanowire Lithium Ion Battery Anodes

    SciTech Connect

    Schulz, Douglas L.; Hoey, Justin; Smith, Jeremiah; Elangovan, Arumugasamy; Wu, Xiangfa; Akhatov, Iskander; Payne, Scott; Moore, Jayma; Boudjouk, Philip; Pederson, Larry; Xiao, Jie; Zhang, Jiguang

    2010-08-04

    Amorphous silicon nanowires 'a-SiNWs' have been prepared by electrospinning a liquid silane-based precursor. Cyclohexasilane 'Si6H12' was admixed with poly-methyl methacrylate (PMMA) in toluene giving an ink that was electrospun into the Si6H12/PPMA wires with diameters of 50-2000 nm. Raman spectroscopy revealed that thermal treatment at 350 C transforms this deposit into a-SiNWs. These materials were coated with a thin carbon layer and then tested as half-cells where a reasonable plateau in electrochemical cycling was observed after an initial capacity fade. Additionally, porous a-SiNWs were realized when the thermally decomposable binder polypropylene carbonate/polycyclohexene carbonate was used as the polymer carrier.

  17. Photoconductive and photovoltaic response of high-dark-resistivity 6H-SiC devices

    NASA Technical Reports Server (NTRS)

    Cho, Pak S.; Goldhar, Julius; Lee, Chi H.; Saddow, Stephen E.; Neudeck, Philip

    1995-01-01

    The optoelectronic properties of high-resistivity p-type hexagonal silicon carbide (6H-SiC) have been investigated using lateral photoconductive switches. Both photovoltaic and photoconductive effects are reported, measured at 337 nm, which is above the 6H-SiC absorption edge. These photoconductive switches have been fabricated with dark resistances of up to 1 M omega; photoconductive switching efficiencies of more than 80% have been achieved. In addition, these devices displayed a high-speed photovoltaic response to nanosecond laser excitations in the ultraviolet spectral region; in particular, the observed photovoltaic response pulse width can be shorter than the exciting laser pulse width. This subnanosecond photovoltaic response has been modeled and good qualitative agreement with experiment has been obtained.

  18. NQRS Data for F6H12MgO6Si (Subst. No. 2195)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume B 'Substances Containing C10H16 … Zn' of Volume 48 'Nuclear Quadrupole Resonance Spectroscopy Data' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains an extract of Section '3.2 Data tables' of the Chapter '3 Nuclear quadrupole resonance data' providing the NQRS data for F6H12MgO6Si (Subst. No. 2195)

  19. Effect of Ge on SiC film morphology in SiC/Si films grown by MOCVD

    SciTech Connect

    Sarney, W.L.; Salamanca-Riba, L.; Zhou, P.; Spencer, M.G.; Taylor, C.; Sharma, R.P.; Jones, K.A.

    1999-07-01

    SiC/Si films generally contain stacking faults and amorphous regions near the interface. High quality SiC/Si films are especially difficult to obtain since the temperatures usually required to grow high quality SiC are above the Si melting point. The authors added Ge in the form of GeH{sub 2} to the reactant gases to promote two-dimensional CVD growth of SiC films on (111) Si substrates at 1,000 C. The films grown with no Ge are essentially amorphous with very small crystalline regions, whereas those films grown with GeH{sub 2} flow rates of 10 and 15 sccm are polycrystalline with the 3C structure. Increasing the flow rate to 20 sccm improves the crystallinity and induces growth of 6H SiC over an initial 3C layer. This study presents the first observation of spontaneous polytype transformation in SiC grown on Si by MOCVD.

  20. Electronic transitions of C6H4+ isomers: neon matrix and theoretical studies.

    PubMed

    Fulara, Jan; Nagy, Adam; Filipkowski, Karol; Thimmakondu, Venkatesan S; Stanton, John F; Maier, John P

    2013-12-19

    Three open-chain isomers of C6H4(+) and two cyclic ones were detected following mass-selective trapping in 6 K neon matrixes. The open-chain cations 5-hexene-1,3-diyne (CH2═CH-CC-CC-H)(+) and cis- (cis-HCC-CH═CH-CCH)(+) and trans-3-hexene-1,5-diyne (trans-HCC-CH═CH-CCH)(+), possess two absorption systems commencing at 609 and 373, 622 and 385, and 585 and 373 nm, respectively. They are assigned to the 1 (2)A" and 2 (2)A" ← X (2)A", 1(2)A2 and 2 (2)A2 ← X (2)B1, and 1 (2)Bg and 2 (2)B(g) ← X (2)A(u) electronic transitions of these cations. Two overlapping systems are detected at around 420 nm and tentatively assigned to the 1 (2)A" ← X (2)A" electronic transitions of propargyl cyclopropene and 2 (2)B1 ← X (2)A2 of o-benzyne cation structures. The assignment of the electronic transitions is based on theoretical vertical excitation energies calculated with CASPT2 and EOMEE-CCSDT methods for 12 isomers of C6H4(+). These have been carried out at the geometries optimized using several ab initio methods. Adiabatic excitation energies were calculated for the five identified isomers of C6H4(+). PMID:24074188

  1. Density functional study of adenine tetrads with N6-H6...N3 hydrogen bonds.

    PubMed

    Meyer, Michael; Sühnel, Jürgen

    2008-05-01

    The structure and energy of A-tetrads with N6-H6...N3 H-bonds was studied using B3LYP and BH&H density functional theory. The planar A-tetrad with C(4h) symmetry is more stable than the nonplanar structures at C4 and S4 symmetry. This structure corresponds to a local energy minimum. The energies of the structures with N6-H6...N1 and N6-H6...N7 H-bonds studied previously are of similar magnitude. Structures of A-tetrad complexes with sodium and potassium were most stable at S4 symmetry, and similarly, sandwich complexes consisting of two tetrads and a single cation were most stable at S8 symmetry. Relative energies of sandwich complexes with different symmetries obtained with the B3LYP and BH&H methods were quite different. BH&H overestimates the interaction energies between hydrogen-bonded neighbor bases relative to B3LYP. PMID:18380490

  2. Bidimensional intercalation of Ge between SiC(0001) and a heteroepitaxial graphite top layer

    SciTech Connect

    Kubler, L.; Dentel, D.; Bischoff, J.-L.; Derivaz, M.; Aiet-Mansour, K.; Diani, M.

    2005-09-15

    High temperature annealing of 4H- or 6H-SiC(0001) crystals is well known to desorb Si from the surface and to generate a C-rich (6{radical}3x6{radical}3)R30 deg. (6{radical}3) reconstruction explained as a graphite monolayer in heteroepitaxial registry with the substrate. Ge deposition at room temperature and in the monolayer range on this graphitized reconstruction results in Ge islands. Using a number of surface techniques, we follow subsequent Ge morphology evolutions as a function of isochronal post-annealing treatments at increasing temperatures. In a particular temperature window Ge reacts with the substrate by diffusion under the graphite planes and wets the Si-terminated SiC surface. In spite of this bidimensional insertion of a Ge layer, the epitaxial relationship between the SiC substrate and the graphite is maintained as shown by very clear graphite-(1x1) LEED or RHEED patterns. They denote extended and well-ordered graphite planes at the surface of a graphite/Ge/SiC heterostructure. XPS analyses reveal a complete passivation of the intercalated Ge layer against oxidation by the overlying graphite sheets. Moreover, drastic spectroscopic changes on the bulk-SiC Si 2p and C 1s core levels are observed, depending on whether graphite(6{radical}3)/SiC or graphite(1x1)/Ge/SiC terminations are analyzed. In the latter case, the observed core level splitting of the bulk components is interpreted by a significant upward band bending ({approx}1.2 eV) of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300 deg. C, a delayed Ge desorption takes place that allows the graphite sheets to re-form in their initial 6{radical}3 form, i.e., without Ge and with flatter bands.

  3. Vertically conducting deep-ultraviolet light-emitting diodes with interband tunneling junction grown on 6H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Liang, Hongwei; Tao, Pengcheng; Xia, Xiaochuan; Chen, Yuanpeng; Zhang, Kexiong; Liu, Yang; Shen, Rensheng; Luo, Yingmin; Zhang, Yuantao; Du, Guotong

    2016-03-01

    Vertically conducting deep-ultraviolet (DUV) light-emitting diodes (LEDs) with a polarization-induced backward-tunneling junction (PIBTJ) were grown by metal-organic chemical vapor deposition (MOCVD) on 6H-SiC substrates. A self-consistent solution of Poisson-Schrödinger equations combined with polarization-induced theory was applied to simulate the PIBTJ structure, energy band diagrams, and free-carrier concentration distribution. AlN and graded AlxGa1-xN interlayers were introduced between the PIBTJ and multiple quantum well layers to avoid cracking of the n-Al0.5Ga0.5N top layer. At a driving current of 20 mA, an intense DUV emission at ˜288 nm and a weak shoulder at ˜386 nm were observed from the AlGaN top layer side. This demonstrates that the PIBTJ can be used to fabricate vertically conducting DUV LED on SiC substrates.

  4. Low Temperature Ohmic Contact Formation of Ni2Si on N-type 4H-SiC and 6H-SiC

    NASA Technical Reports Server (NTRS)

    Elsamadicy, A. M.; Ila, D.; Zimmerman, R.; Muntele, C.; Evelyn, L.; Muntele, I.; Poker, D. B.; Hensley, D.; Hirvonen, J. K.; Demaree, J. D.; Larkin, David (Technical Monitor)

    2001-01-01

    Nickel Silicide (Ni2Si) is investigated as possible ohmic contact to heavily nitrogen-doped N-type 4H-SiC and 6H-SiC. Nickel Silicide was deposited via electron gun with various thicknesses on both Si and C faces of the SiC substrates. The Ni2Si contacts were formed at room temperature as well as at elevated temperatures (400 to 1000 K). Contact resistivities and I-V characteristics were measured at temperatures between 100 and 700 C. To investigate the electric properties, I-V characteristics were studied and the Transmission Line Method (TLM) was used to determine the specific contact resistance for the samples at each annealing temperature. Both Rutherford Backscattering Spectroscopy (RBS) and Auger Electron Spectroscopy (AES) were used for depth profiling of the Ni2Si, Si, and C. X-ray Photoemission Spectroscopy (XPS) was used to study the chemical structure of the Ni2Si/SiC interface.

  5. Solute embrittlement of SiC

    NASA Astrophysics Data System (ADS)

    Enrique, Raúl A.; Van der Ven, Anton

    2014-09-01

    The energies and stresses associated with the decohesion of β-SiC in the presence of mobile Pd and Ag impurities are studied from first principles. Density functional theory calculations are parameterized with a generalized cohesive zone model and are analyzed within a thermodynamic framework that accounts for realistic boundary conditions in the presence of mobile impurities. We find that Pd impurities will embrittle SiC when Pd is in equilibrium with metallic Pd precipitates. Our thermodynamic analysis predicts that Pd embrittles SiC by substantially reducing the maximum stress of decohesion as a result of a phase transition between decohering planes involving an influx of Pd atoms. The methods presented in this work can be applied to study the thermodynamics of decohesion of SiC in other aggressive environments containing oxygen and water, for example, and yield environment dependent cohesive zone models for use in continuum approaches to study crack propagation and fracture.

  6. Solute embrittlement of SiC

    SciTech Connect

    Enrique, Raúl A.; Van der Ven, Anton

    2014-09-21

    The energies and stresses associated with the decohesion of β-SiC in the presence of mobile Pd and Ag impurities are studied from first principles. Density functional theory calculations are parameterized with a generalized cohesive zone model and are analyzed within a thermodynamic framework that accounts for realistic boundary conditions in the presence of mobile impurities. We find that Pd impurities will embrittle SiC when Pd is in equilibrium with metallic Pd precipitates. Our thermodynamic analysis predicts that Pd embrittles SiC by substantially reducing the maximum stress of decohesion as a result of a phase transition between decohering planes involving an influx of Pd atoms. The methods presented in this work can be applied to study the thermodynamics of decohesion of SiC in other aggressive environments containing oxygen and water, for example, and yield environment dependent cohesive zone models for use in continuum approaches to study crack propagation and fracture.

  7. Dynamics of reactions O((1)D)+C(6)H(6) and C(6)D(6).

    PubMed

    Chen, Hui-Fen; Liang, Chi-Wei; Lin, Jim J; Lee, Yuan-Pern; Ogilvie, J F; Xu, Z F; Lin, M C

    2008-11-01

    The reaction between O((1)D) and C(6)H(6) (or C(6)D(6)) was investigated with crossed-molecular-beam reactive scattering and time-resolved Fourier-transform infrared spectroscopy. From the crossed-molecular-beam experiments, four product channels were identified. The major channel is the formation of three fragments CO+C(5)H(5)+H; the channels for formation of C(5)H(6)+CO and C(6)H(5)O+H from O((1)D)+C(6)H(6) and OD+C(6)D(5) from O((1)D)+C(6)D(6) are minor. The angular distributions for the formation of CO and H indicate a mechanism involving a long-lived collision complex. Rotationally resolved infrared emission spectra of CO (16)H(6) and [CO]/[OD]>2.9 for O((1)D)+C(6)D(6) is consistent with the expectation for an abstraction reaction. The mechanism of the reaction may be understood from considering the energetics of the intermediate species and transition states calculated at the G2M(CC5) level of theory for the O((1)D)+C(6)H(6) reaction. The experimentally observed branching ratios and deuterium isotope effect are consistent with those predicted from calculations. PMID:19045343

  8. Examples of conditional SIC-POVMs

    NASA Astrophysics Data System (ADS)

    Ohno, Hiromichi; Petz, Dénes

    2015-10-01

    The state of a quantum system is a density matrix with several parameters. The concern herein is how to recover the parameters. Several possibilities exist for the optimal recovery method, and we consider some special cases. We assume that a few parameters are known and that the others are to be recovered. The optimal positive-operator-valued measure (POVM) for recovering unknown parameters with an additional condition is called a conditional symmetric informationally complete POVM (SIC-POVM). In this paper, we study the existence or nonexistence of conditional SIC-POVMs. We provide a necessary condition for existence and some examples.

  9. Saturn V S-IC (First) Stage

    NASA Technical Reports Server (NTRS)

    1967-01-01

    This illustration shows a cutaway drawing with callouts of the major components for the S-IC (first) stage of the Saturn V launch vehicle. The S-IC stage is 138 feet long and 33 feet in diameter, producing more than 7,500,000 pounds of thrust through five F-1 engines powered by liquid oxygen and kerosene. Four of the engines are mounted on an outer ring and gimball for control purposes. The fifth engine is rigidly mounted in the center. When ignited, the roar produced by the five engines equals the sound of 8,000,000 hi-fi sets.

  10. Saturn V S-IC (First) Stage

    NASA Technical Reports Server (NTRS)

    1968-01-01

    This is a cutaway view of the Saturn V first stage, known as the S-IC, detailing the five F-1 engines and fuel cells. The S-IC stage is 138 feet long and 33 feet in diameter, producing more than 7,500,000 pounds of thrust through the five F-1 engines that are powered by liquid oxygen and kerosene. Four of the engines are mounted on an outer ring and gimbal for control purposes. The fifth engine is rigidly mounted in the center. When ignited, the roar produced by the five engines equals the sound of 8,000,000 hi-fi sets.

  11. Saturn V S-IC (First) Stage

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This cutaway illustration shows the Saturn V S-IC (first) stage with detailed callouts of the components. The S-IC Stage is 138 feet long and 33 feet in diameter, producing 7,500,000 pounds of thrust through five F-1 engines that are powered by liquid oxygen and kerosene. Four of the engines are mounted on an outer ring and gimbal for control purposes. The fifth engine is rigidly mounted in the center. When ignited, the roar produced by the five engines equals the sound of 8,000,000 hi-fi sets.

  12. S-IC Static Test Stand

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Constructed in 1964, the S-IC Static Test Stand was designed to develop and test the first stage (S-IC) of the Saturn V launch vehicle. In the 1974 the test stand was modified to test the liquid hydrogen tank on the Space Shuttle External Tank. The facility was again modified in 1986 and its name was changed to the Advanced Engine Test Facility. These modifications were made to accommodate the Technology Test Bed engine which is a derivative of the Space Shuttle Main Engine.

  13. Stacking faults in SiC nanowires.

    PubMed

    Wallis, K L; Wieligor, M; Zerda, T W; Stelmakh, S; Gierlotka, S; Palosz, B

    2008-07-01

    SiC nanowires were obtained by a reaction between vapor silicon and multiwall carbon nanotubes, CNT, in vacuum at 1200 degrees C. Raman and IR spectrometry, X-ray diffraction and high resolution transmission electron microscopy, HRTEM, were used to characterize properties of SiC nanowires. Morphology and chemical composition of the nanowires was similar for all samples, but concentration of structural defects varied and depended on the origin of CNT. Stacking faults were characterized by HRTEM and Raman spectroscopy, and both techniques provided complementary results. Raman microscopy allowed studying structural defects inside individual nanowires. A thin layer of amorphous silicon carbide was detected on the surface of nanowires. PMID:19051903

  14. Microwave joining of SiC

    SciTech Connect

    Silberglitt, R.; Ahmad, I.; Tian, Y.L.

    1997-04-01

    The purpose of this work is to optimize the properties of SiC-SiC joints made using microwave energy. The current focus is on identification of the most effective joining methods for scale-up to large tube assemblies, including joining using SiC produced in situ from chemical precursors. During FY 1996, a new microwave applicator was designed, fabricated and tested that provides the capability for vacuum baking of the specimens and insulation and for processing under inert environment. This applicator was used to join continuous fiber-reinforced (CFCC) SiC/SiC composites using a polymer precursor to form a SiC interlayer in situ.

  15. Defect structures and growth mechanisms of boron arsenide epilayers grown on 6H-silicon carbide and 15R-silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Chen, Hui

    B12As2 possesses the extraordinary properties, such as wide bandgap of 3.47eV and unique 'self heal' ability from electron irradiation damage, which make it attractive for the applications in space electronics, high temperature semiconductors and in particular, beta cells, devices capable of producing electrical energy by coupling a radioactive beta emitter to a semiconductor junction. Due to the absence of native substrates, B12As2 has been grown on substrates with compatible structural parameters via chemical vapor deposition. To date, growth on Si with (100), (110) and (111) orientation and (0001) 6H-SiC has been attempted. However, structural variants, including rotational and translational variants, have been observed in the epilayers and are expected to have a detrimental effect on device performance which has severely hindered progress of this material to date. In addition, none of the earlier reports provide a detailed atomic level study of defect structures in the films and growth mechanisms remain obscure. The focus of this thesis is to study defect structures in B12As2 films grown on different SiC substrates using synchrotron x-ray topography, high resolution transmission microscopy as well as other characterization techniques. The goals of the studies are to understand the generations of the defects present in B12As 2 films and their growth mechanisms so as to develop strategies to reduce defect densities and obtain better film quality for future device fabrication. The following detailed studies have been carried out: (1) The microstructures in B12As2 epitaxial layers grown on on-axis c-plane (0001) 6H-SiC substrates were analyzed in detail. Synchrotron white beam X-ray topography (SWBXT) and scanning electron microscopy (SEM) revealed a mosaic structure consisting of a solid solution of twin and matrix epilayer domains. The epitaxial relationship was determined to be (0001)B12As2<112¯0> B12As2||(0001)6H-SiC<112¯0>6H-SiC. B 12As2 twinned domains were

  16. First-principles calculations on atomic and electronic properties of Si(111)/6H-SiC(0001) heterojunction

    NASA Astrophysics Data System (ADS)

    He, Xiao-Min; Chen, Zhi-Ming; Huang, Lei; Li, Lian-Bi

    2015-10-01

    Combining advanced transmission electron microscopy with high-precision first-principles calculations, the properties of Si(111)//6H-SiC(0001) (Si-terminated and C-terminated) heterojunction interface, such as work of adhesion, geometry property, electronic structure and bonding nature, are studied. The experiments have demonstrated that interfacial orientation relationships of Si(111)//6H-SiC(0001) heterojunction are Si[2-1-1]/6H-SiC[101¯0] and Si(111)/6H-SiC(0001). Compared with C-terminated interface, Si-terminated interface has higher adhesion and less relaxation extent.

  17. Si growth at graphene surfaces on 6H-SiC(0001) substrates

    NASA Astrophysics Data System (ADS)

    Sone, Junki; Yamagami, Tsuyoshi; Nakatsuji, Kan; Hirayama, Hiroyuki

    2016-03-01

    We studied the growth of Si at the surface of epitaxial graphene on 6H-SiC(0001). Characteristic flower-like islands with a thickness of 2 to 3 nm nucleated during the growth from 290 to 420 K. The islands became featureless in growth at higher temperatures. The growth was predominantly governed by diffusion-limited aggregation. The diffusion energy was evaluated to be 0.21 eV from the temperature-dependent decrease in the density of the islands.

  18. Multihormonal regulation of thyroglobulin production by the OVNIS 6H thyroid cell line.

    PubMed

    Aouani, A; Hovsépian, S; Fayet, G

    1988-02-01

    The hormonal regulation of thyroglobulin production has been studied using a clone of the ovine thyroid cell line: OVNIS 6H. 3 among the 6 hormones proposed for serum replacement are required for an optimal thyroglobulin production; insulin, hydrocortisone and thyrotropin. Insulin alone stimulates thyroglobulin production. The presence of insulin is also required to observe hydrocortisone and TSH stimulations. Newborn calf serum inhibits thyroglobulin production. The best conditions for optimal thyroglobulin expression and TSH responsiveness are obtained in serum-free medium supplemented with 5 micrograms/ml insulin, 100 nM hydrocortisone and 1 mU/ml TSH. PMID:3286455

  19. Universal Converter Using SiC

    SciTech Connect

    Dallas Marckx; Brian Ratliff; Amit Jain; Matthew Jones

    2007-01-01

    The grantee designed a high power (over 1MW) inverter for use in renewable and distributed energy systems, such as PV cells, fuel cells, variable speed wind turbines, micro turbines, variable speed gensets and various energy storage methods. The inverter uses 10,000V SiC power devices which enable the use of a straight-forward topology for medium voltage (4,160VAC) without the need to cascade devices or topologies as is done in all commercial, 4,160VAC inverters today. The use of medium voltage reduces the current by nearly an order of magnitude in all current carrying components of the energy system, thus reducing size and cost. The use of SiC not only enables medium voltage, but also the use of higher temperatures and switching frequencies, further reducing size and cost. In this project, the grantee addressed several technical issues that stand in the way of success. The two primary issues addressed are the determination of real heat losses in candidate SiC devices at elevated temperature and the development of high temperature packaging for SiC devices.

  20. Passive SiC irradiation temperature monitor

    SciTech Connect

    Youngblood, G.E.

    1996-04-01

    A new, improved passive irradiation temperature monitoring method was examined after an irradiation test at 627{degrees}C. The method is based on the analysis of thermal diffusivity changes during postirradiation annealing of polycrystalline SiC. Based on results from this test, several advantages for using this new method rather than a method based on length or lattice parameter changes are given.

  1. Microwave joining of SiC

    SciTech Connect

    Silberglitt, R.; Ahmad, I.; Black, W.M.

    1995-05-01

    The purpose of this work is to optimize the properties of SiC-SiC joints made using microwave energy. The current focus is on optimization of time-temperature profiles, production of SiC from chemical precursors, and design of new applicators for joining of long tubes.

  2. Synthesis and characterization of SiC and SiC/Si3N4 composite nano powders from waste material.

    PubMed

    Zawrah, M F; Zayed, M A; Ali, Moustafa R K

    2012-08-15

    In the present work, nano silicon carbide has been prepared by pyrolysis of rice-husk ashes as starting materials. Three rice-husk ash samples having different features were used. The first was coarse-grained rice husk ash (fired husk as is), the second was fine rice husk ash (hand-ground), while the third was ball milled one. Effect of ball milling of the starting ashes for 6h on the formation of nano SiC was investigated and compared with those prepared without milling. The particle sizes of the prepared SiC materials were affected by the milling process. The particle sizes of the obtained nano SiC from ball milled staring materials were smaller than those prepared without milling. The pyrolysis conditions, i.e. the temperature and atmosphere were optimized. The optimum firing temperature to obtain well crystalline nano SiC was 1550°C. The effect of pyrolysis atmosphere, i.e. argon, vacuum and nitrogen was also demonstrated. The pyrolysis in argon exhibited lower efficiency on the formation of SiC than vacuum; while the pyrolysis in nitrogen atmosphere led to formation of SiC/Si(3)N(4) nanocomposite. PMID:22673059

  3. Design of Twin Structures in SiC Nanowires

    SciTech Connect

    Yongfeng Zhang; Hanchen Huang

    2012-11-01

    With covalent bonding, SiC has high mechanical strength and a large energy gap in electronic band structure. Nanoscale SiC, in the form of nanowires, has increased mechanical toughness and variable band gaps. Further, introduction of twin boundaries into cubic SiC nanowires can result in improvement in both mechanical and electronic properties. This review presents effects of twin boundaries on properties of cubic SiC nanowires, including mechanical and electronic properties. Further, this review presents recent developments in introducing twin boundaries into cubic SiC nanowires, controllably and uncontrollably.

  4. 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.

  5. 40 CFR 721.5560 - Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz[c...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6-oxide. 721.5560 Section 721... SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.5560 Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz...

  6. 40 CFR 721.5560 - Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz[c...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6-oxide. 721.5560 Section 721... SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.5560 Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz...

  7. 40 CFR 721.5560 - Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz[c...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6-oxide. 721.5560 Section 721... SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.5560 Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz...

  8. 40 CFR 721.5560 - Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz[c...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6-oxide. 721.5560 Section 721... Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6... identified as formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with...

  9. 40 CFR 721.5560 - Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz[c...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6-oxide. 721.5560 Section 721... Formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with 6H-dibenz oxaphosphorin-6... identified as formaldehyde, polymer with (chloromethyl) oxirane and phenol, reaction products with...

  10. S-IC Test Stand Design Model

    NASA Technical Reports Server (NTRS)

    1962-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo is of the S-IC test stand design model created prior to construction.

  11. S-IC Test Stand Design Model

    NASA Technical Reports Server (NTRS)

    1962-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo is of the S-IC test stand design model.

  12. Infrared spectra of meteoritic SiC grains

    NASA Astrophysics Data System (ADS)

    Andersen, A. C.; Jäger, C.; Mutschke, H.; Braatz, A.; Clément, D.; Henning, Th.; Jørgensen, U. G.; Ott, U.

    1999-03-01

    We present here the first infrared spectra of meteoritic SiC grains. The mid-infrared transmission spectra of meteoritic SiC grains isolated from the Murchison meteorite were measured in the wavelength range 2.5-16.5 mu m, in order to make available the optical properties of presolar SiC grains. These grains are most likely stellar condensates with an origin predominately in carbon stars. Measurements were performed on two different extractions of presolar SiC from the Murchison meteorite. The two samples show very different spectral appearance due to different grain size distributions. The spectral feature of the smaller meteoritic SiC grains is a relatively broad absorption band found between the longitudinal and transverse lattice vibration modes around 11.3 mu m, supporting the current interpretation about the presence of SiC grains in carbon stars. In contrast to this, the spectral feature of the large (> 5 mu m) grains has an extinction minimum around 10 mu m. The obtained spectra are compared with commercially available SiC grains and the differences are discussed. This comparison shows that the crystal structure (e.g., beta -SiC versus alpha -SiC) of SiC grains plays a minor role on the optical signature of SiC grains compared to e.g. grain size.

  13. 6H-SiC Transistor Integrated Circuits Demonstrating Prolonged Operation at 500 C

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Chen, Liang-Yu; Chang, Carl W.; Beheim, Glenn M.; Okojie, Robert S.; Evans, Laura J.; Meredith, Roger; Ferrier, Terry; Krasowski, Michael J.; Prokop, Norman F.

    2008-01-01

    The NASA Glenn Research Center is developing very high temperature semiconductor integrated circuits (ICs) for use in the hot sections of aircraft engines and for Venus exploration where ambient temperatures are well above the approximately 300 degrees Centigrade effective limit of silicon-on-insulator IC technology. In order for beneficial technology insertion to occur, such transistor ICs must be capable of prolonged operation in such harsh environments. This paper reports on the fabrication and long-term 500 degrees Centigrade operation of 6H-SiC integrated circuits based on epitaxial 6H-SiC junction field effect transistors (JFETs). Simple analog amplifier and digital logic gate ICs have now demonstrated thousands of hours of continuous 500 degrees Centigrade operation in oxidizing air atmosphere with minimal changes in relevant electrical parameters. Electrical characterization and modeling of transistors and circuits at temperatures from 24 degrees Centigrade to 500 degrees Centigrade is also described. Desired analog and digital IC functionality spanning this temperature range was demonstrated without changing the input signals or power supply voltages.

  14. Synthesis of SiC nanorods from bleached wood pulp

    SciTech Connect

    Shin, Yongsoon; Wang, Chong M.; Samuels, William D.; Exarhos, Gregory J.

    2007-05-01

    Unbleached and bleached soft wood pulps have been used as templates and carbon precursors to produce SiC nanorods. Hydrolyzed tetraethylorthosilicate (TEOS), Silicic acid was infiltrated into the pulps followed by a carbothermal reduction to form SiC nanorods at 1400oC in Ar. Residual carbon formed along with SiC was removed by gasification at 700oC in air. The SiC materials prepared from unbleached pulp were non-uniform SiC with a thick SiO2 coating, while the SiC nanorods prepared from the bleached pulp were uniform and straight with dimensions of 250 nm in diameter and 5.0 mm long. The formation of uniform camelback structure of SiC in the reaction between silica and bleached pulp is attributed to more silica deposited in the amorphous region of cellulose.

  15. Band alignment at organic-inorganic heterojunctions between P3HT and n-type 6H-SiC.

    PubMed

    Dietmueller, Roland; Nesswetter, Helmut; Schoell, Sebastian J; Sharp, Ian D; Stutzmann, Martin

    2011-11-01

    The exact band alignment at organic/inorganic semiconductor heterojunctions is influenced by a variety of properties and is difficult to predict. For organic/inorganic bilayer heterojunctions made of poly(3-hexylthiophene) (P3HT) and n-type 6H-SiC, the band alignment is determined via current-voltage measurements. For this purpose, a model equivalent circuit, combining thermionic emission and space-charge-limited current effects, is proposed which describes the behavior of the heterojunction very well. From the fitting parameters, an interface barrier height of 1.1 eV between the lowest unoccupied molecular orbital (LUMO) of P3HT and the conduction band (CB) of 6H-SiC is determined. In addition, from the maximum open circuit voltage of 6H-SiC/P3HT diodes, a difference of 0.9 eV between the highest occupied molecular orbital (HOMO) of P3HT and the CB of 6H-SiC is deduced. These two values determine the alignment of the energy bands of 6H-SiC relative to the HOMO and LUMO of P3HT. The 6H-SiC/P3HT bilayer heterojunction exhibits an open circuit voltage of ~0.5 V at room temperature, which makes such a materials system a potential candidate for bulk heterojunction hybrid solar cells with 6H-SiC nanoparticles. PMID:21936559

  16. Sodium dipotassium citrate, NaK2C6H5O7.

    PubMed

    Rammohan, Alagappa; Kaduk, James A

    2016-03-01

    The crystal structure of sodium dipotassium citrate, Na(+)·2K(+)·C6H5O7 (3-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The Na(+) and one of the K(+) cations are six-coordinate, with bond-valence sums of 1.13 and 0.92 valence units, respectively, while another crystallographically independent K(+) cation is seven-coordinate with a bond-valence sum of 1.20. The [KO6] and [KO7] polyhedra share edges and corners to form layers perpendicular to the b axis. The distorted [NaO6] octa-hedra share edges to form chains along the a axis. The result is a three-dimensional network. The only O-H⋯O hydrogen bond is an intra-molecular one between the hy-droxy group and a terminal carboxyl-ate group. PMID:27006817

  17. Band gap states of V and Cr in 6H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Achtziger, N.; Grillenberger, J.; Witthuhn, W.

    Band gap states of Ti, V and Cr in n-type 6H-SiC were investigated by radiotracer deep level transient spectroscopy (DLTS). Doping with the radioactive isotopes 48V and 51Cr was done by recoil implantation followed by annealing (1600 K). Repeated DLTS measurements during the elemental transmutation of these isotopes to 48Ti and 51V respectively revealed the corresponding concentration changes of band gap states. Thus, three levels were identified in the band gap: a Cr level at 0.54 eV and two V levels at 0.71 and 0.75 eV below the conduction band edge. There are no deep levels of Ti in the upper part of the band gap.

  18. Rapid thermal annealing of ion implanted 6H-SiC by microwave processing

    SciTech Connect

    Gardner, J.A.; Rao, M.V.; Tian, Y.L.; Holland, O.W.; Roth, E.G.; Chi, P.H.; Ahmad, I.

    1997-03-01

    Rapid thermal processing utilizing microwave energy has been used to anneal N, P, and Al ion-implanted 6H-SiC. The microwaves raise the temperature of the sample at a rate of 200{degree}C/min vs 10{degree}C/min for conventional ceramic furnace annealing. Samples were annealed in the temperature range of 1400-1700{degree}C for 2-10 min. The implanted/annealed samples were characterized using van der Pauw Hall, Rutherford backscattering, and secondary ion mass spectrometry. For a given annealing temperature, the characteristics of the microwave-annealed material are similar to those of conventional furnace anneals despite the difference in cycle time. 19 refs., 7 figs., 3 tabs.

  19. Study of silicon carbide (SiC) polytype heterojunctions

    NASA Astrophysics Data System (ADS)

    Eshun, Ebenezer Emmanuel

    2001-12-01

    . Saturation currents of 8.2 and 18.75 mA were achieved with transconductances of 9.22 and 21.4 mS/mm for two device dimensions with aspect ratios of 24 and 33 respectively. Carrier mobility as high as 700 cm2/V-s has been achieved, which is close to the reported Hall mobilities for 3C-SiC (770 cm2/V-s). The saturation drift velocity obtained (1.9 x 107 cm/s) is also close to theoretical values. By using transmission line model measurements, Ni based ohmic contacts to this material has been calculated to be ˜5 x 10-5 O-cm2, which is two orders of magnitude lower than Ni based ohmic contacts to 6H-SiC at the same doping level.

  20. Electronic and Interfacial Properties of PD/6H-SiC Schottky Diode Gas Sensors

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Bansal, Gaurav; Petit, Jeremy B.; Knight, Dak; Liu, Chung-Chiun; Wu, Qinghai

    1996-01-01

    Pd/SiC Schottky diodes detect hydrogen and hydrocarbons with high sensitivity. Variation of the diode temperature from 100 C to 200 C shows that the diode sensitivity to propylene is temperature dependent. Long-term heat treating at 425 C up to 140 hours is carried out to determine the effect of extended heat treating on the diode properties and gas sensitivity. The heat treating significantly affects the diode's capacitive characteristics, but the diode's current carrying characteristics are much more stable with a large response to hydrogen. Scanning Electron Microscopy and X-ray Spectrometry studies of the Pd surface after the heating show cluster formation and background regions with grain structure observed in both regions. The Pd and Si concentrations vary between grains. Auger Electron Spectroscopy depth profiles revealed that the heat treating promoted interdiffusion and reaction between the Pd and SiC dw broadened the interface region. This work shows that Pd/SiC Schottky diodes have significant potential as high temperature gas sensors, but stabilization of the structure is necessary to insure their repeatability in long-term, high temperature applications.

  1. Structures, molecular orbitals and UV-vis spectra investigations on Br2C6H4: a computational study.

    PubMed

    Wang, Tsang-Hsiu; Hsu, Chen-Shuo; Huang, Wen-Lin; Lo, Yih-Hsing

    2013-11-01

    The dibromobenzenes (1,2-, 1,3- and 1,4-Br2C6H4) have been studied by theoretical methods. The structures of these species are optimized and the structural characteristics are determined by density functional theory (DFT) and the second order Møller-Plesset perturbation theory (MP2) levels. The geometrical structures of Br2C6H4 show a little distortion of benzene ring due to the substitution of highly electronegativity of bromine atoms. The electronegativity of bromine atoms in 1,4-Br2C6H4 is predicted to be more negative than 1,2- and 1,3-Br2C6H4. In addition, dipole moment and frontier molecular orbitals (FMOs) of these Br2C6H4 are performed as well. The 1,4-Br2C6H4 is slightly more reactive than 1,2- and 1,3-Br2C6H4 because of its small HOMO-LUMO energy gap. The simulated UV-vis spectra are investigated by time-dependent density functional theory (TD-DFT) approach, which are in excellent agreement with the available experimental value. Our calculations show that a few of absorption features are between 140nm and 250nm, which is in ultraviolet C range, and the red shift of 1,3- and 1,4-Br2C6H4 are predicted. Moreover, the UV absorption features of these Br2C6H4 in water or methanol are predicted to be more intense than in gas phase due to solvent effect. PMID:23892349

  2. Fast Risetime Reverse Bias Pulse Failures in SiC PN Junction Diodes

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Fazi, Christian; Parsons, James D.

    1996-01-01

    SiC-based high temperature power devices are being developed for aerospace systems which will require high reliability. One behavior crucial to power device reliability. To date, it has necessarily been assumed to date is that the breakdown behavior of SiC pn junctions will be similar to highly reliable silicon-based pn junctions. Challenging this assumption, we report the observation of anomalous unreliable reverse breakdown behavior in moderately doped (2-3 x 10(exp 17) cm(exp -3)) small-area 4H- and 6H-SiC pn junction diodes at temperatures ranging from 298 K (25 C) to 873 K (600 C). We propose a mechanism in which carrier emission from un-ionized dopants and deep level defects leads to this unstable behavior. The fundamental instability mechanism is applicable to all wide bandgap semiconductors whose dopants are significantly un-ionized at typical device operating temperatures.

  3. Theoretical studies of the structure and stability of (Ag(C 6H 6) n+ ( n = 1 and 2)

    NASA Astrophysics Data System (ADS)

    Ma, N. L.; Ng, K. M.; Tsang, C. W.

    1997-10-01

    Ab initio molecular orbital techniques are used to probe the structure and stability of Ag(C 6H 6) + and Ag(C 6H 6) 2+ recently observed in electrospray ionization mass spectra. Of all the Ag(C 6H 6) + structures investigated, the C 6v complex is the most stable. Our calculated first binding energy of benzene to Ag + is in agreement with the experimental value and the second binding enegy of benzene to Ag + is estimated to be 114 (10) kJ mol -1.

  4. Interface-structure of the Si/SiC heterojunction grown on 6H-SiC

    SciTech Connect

    Li, L. B.; Chen, Z. M.; Zang, Y.

    2015-01-07

    The Si/SiC heterojunctions were prepared on 6H-SiC (0001) C-face by low-pressure chemical vapour deposition at 850 ∼ 1050 °C. Transmission electron microscopy and selected area electron diffraction were employed to investigate the interface-structure of Si/SiC heterojunctions. The Si/6H-SiC heterostructure of large lattice-mismatch follows domain matching epitaxy mode, which releases most of the lattice-mismatch strain, and the coherent Si epilayers can be grown on 6H-SiC. Si(1-11)/6H-SiC(0001) heterostructure is obtained at 900 °C, and the in-plane orientation relationship of Si/6H-SiC heterostructure is (1–11)[1-1-2]{sub Si}//(0001)[-2110]{sub 6H-SiC}. The Si(1-11)/6H-SiC(0001) interface has the same 4:5 Si-to-SiC matching mode with a residual lattice-mismatch of 0.26% along both the Si[1-1-2] and Si[110] orientations. When the growth temperature increases up to 1000 °C, the 〈220〉 preferential orientation of the Si film appears. SAED patterns at the Si/6H-SiC interface show that the in-plane orientation relationship is (-220)[001]{sub Si}//(0001)[2-1-10]{sub 6H-SiC}. Along Si[110] orientation, the Si-to-SiC matching mode is still 4:5; along the vertical orientation Si[001], the Si-to-SiC mode change to approximate 1:2 and the residual mismatch is 1.84% correspondingly. The number of the atoms in one matching-period decreases with increasing residual lattice-mismatch in domain matching epitaxy and vice versa. The Si film grows epitaxially but with misfit dislocations at the interface between the Si film and the 6H-SiC substrate. And the misfit dislocation density of the Si(1-11)/6H-SiC(0001) and Si(-220)/6H-SiC(0001) obtained by experimental observations is as low as 0.487 × 10{sup 14 }cm{sup −2} and 1.217 × 10{sup 14 }cm{sup −2}, respectively, which is much smaller than the theoretical calculation results.

  5. Tensile strength of SiC fibers

    SciTech Connect

    Zok, F.W.; Chen, X.; Weber, C.H.

    1995-07-01

    An experimental investigation has been conducted on the effects of gauge length on the tensile strength of SiC fibers. The results show that the overall strength distribution cannot be described solely in terms of the two-parameter Weibull function. The overall distribution is found to be consistent with two concurrent flaw populations, one of them being characteristic of the pristine fibers, and the other characteristic of the additional flaws introduced into the fiber during processing of the composite.

  6. Periodically twinned SiC nanowires.

    PubMed

    Wang, Dong-Hua; Xu, Di; Wang, Qing; Hao, Ya-Juan; Jin, Guo-Qiang; Guo, Xiang-Yun; Tu, K N

    2008-05-28

    Twinning has been recognized to be an important microstructural defect in nanoscale materials. Periodically twinned SiC nanowires were largely synthesized by the carbothermal reduction of a carbonaceous silica xerogel prepared from tetraethoxysilane and biphenyl with iron nitrate as an additive. The twinned β-SiC nanowires, with a hexagonal cross section, a diameter of 50-300 nm and a length of tens to hundreds of micrometers, feature a zigzag arrangement of periodically twinned segments with a rather uniform thickness along the entire growth length. Computer simulation has been used to generate three-dimensional atomic structures of the zigzag columnar twin structure by the stacking of hexagonal discs of {111} planes of SiC. A minimum surface energy and strain energy argument is proposed to explain the formation of periodic twins in the SiC nanowires. The thickness of the periodic twinned segments is found to be linearly proportional to the nanowire diameter, and a constant volume model is proposed to explain the relation. PMID:21730575

  7. Silicon vacancy center in 4 H -SiC: Electronic structure and spin-photon interfaces

    NASA Astrophysics Data System (ADS)

    Soykal, Ö. O.; Dev, Pratibha; Economou, Sophia E.

    2016-02-01

    Defects in silicon carbide are of intense and increasing interest for quantum-based applications due to this material's properties and technological maturity. We calculate the multiparticle symmetry-adapted wave functions of the negatively charged silicon vacancy defect in hexagonal silicon carbide via use of group theory and density functional theory and find the effects of spin-orbit and spin-spin interactions on these states. Although we focused on VSi- in 4 H -SiC because of its unique fine structure due to the odd number of active electrons, our methods can be easily applied to other defect centers of different polytypes, especially to the 6 H -SiC. Based on these results, we identify the mechanism that polarizes the spin under optical drive, obtain the ordering of its dark doublet states, point out a path for electric field or strain sensing, and find the theoretical value of its ground-state zero-field splitting to be 68 MHz, in good agreement with experiment. Moreover, we present two distinct protocols of a spin-photon interface based on this defect. Our results pave the way toward quantum information and quantum metrology applications with silicon carbide.

  8. Gas Sensing Diode Comprising SiC

    NASA Technical Reports Server (NTRS)

    Hunter, Gary William (Inventor)

    2001-01-01

    A diode for sensing hydrogen and hydrocarbons and the process for manufacturing the diode are disclosed. The diode is a Schottky diode which has a palladium chrome contact on the C-face of an n-type 6H Silicon carbide epilayer. The epilayer is grown on the C-face of a 6H silicon carbide substrate. The diode is capable of measuring low concentrations of hydrogen and hydrocarbons at high temperatures, for example, 800 degrees C. The diode is both sensitive and stable at elevated temperatures.

  9. Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum

    NASA Astrophysics Data System (ADS)

    Jokubavicius, Valdas; Sun, Jianwu; Liu, Xinyu; Yazdi, Gholamreza; Ivanov, Ivan. G.; Yakimova, Rositsa; Syväjärvi, Mikael

    2016-08-01

    We demonstrate growth of thick SiC layers (100-200 μm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10-5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 μm/h and 70 μm/h for 6H- and 4H-SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C-SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 μm thick homoepitaxial 6H-SiC layer co-doped with nitrogen and boron in a range of 1018 cm-3 at a growth rate of about 270 μm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer.

  10. Comparative study of 3C-SiC layers sublimation-grown on a 6H-SiC substrate

    SciTech Connect

    Shustov, D. B.; Lebedev, A. A. Lebedev, S. P.; Nelson, D. K.; Sitnikova, A. A.; Zamoryanskaya, M. V.

    2013-09-15

    n-3C-SiC/n-6H-SiC heterostructures grown by vacuum sublimation on CREE commercial 6H-SiC substrates are studied. Transmission electron microscopy (TEM) demonstrated that a transitional layer of varying thickness, composed of a mixture of 3C- and 6H-SiC polytypes, is formed on the substrate. A 3C polytype layer was obtained on the interlayer. Cathodoluminescence study of the surface of the film demonstrated that defects in the form of inclusions of another phase (6H-polytype), stacking faults, and twin boundaries (separating domains of cubic modification, grown in various orientations) are found on the surface and in the surface layer with a thickness on the order of 100 {mu}m. Varying the growth conditions changes the concentration of various types of defects.

  11. SiC nanowires synthesized from graphene and silicon vapors

    NASA Astrophysics Data System (ADS)

    Weichenpei, Luo; Gong-yi, Li; Zengyong, Chu; Tianjiao, Hu; Xiaodong, Li; Xuefei, Zhang

    2016-04-01

    The preparation of silicon carbide (SiC) nanowires is basically important for its potential applications in nanodevices, nanocomposites, etc. In the present work, a simple route was reported to synthesize SiC nanowires by heating commercial graphene with silicon vapors and no catalyst. Characterization by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, electron energy scattering, X-ray diffraction, and Raman dispersive spectrum demonstrates the products are composed of β-SiC crystal. The SiC nanowires have the average diameter of about 50 nm and length of tens of micrometers. The vapor-solid mechanism was employed to interpret the SiC nanowires growth. Gaseous SiO which was produced by the reaction of Si powders with its surface oxidation reacted with the solid graphene to form SiC crystal nuclei. And SiC crystal nuclei would act as active sites for further growing into nanowires.

  12. Ultralight, Strong, Three-Dimensional SiC Structures.

    PubMed

    Chabi, Sakineh; Rocha, Victoria G; García-Tuñón, Esther; Ferraro, Claudio; Saiz, Eduardo; Xia, Yongde; Zhu, Yanqiu

    2016-02-23

    Ultralight and strong three-dimensional (3D) silicon carbide (SiC) structures have been generated by the carbothermal reduction of SiO with a graphene foam (GF). The resulting SiC foams have an average height of 2 mm and density ranging between 9 and 17 mg cm(-3). They are the lightest reported SiC structures. They consist of hollow struts made from ultrathin SiC flakes and long 1D SiC nanowires growing from the trusses, edges, and defect sites between layers. AFM results revealed an average flake thickness of 2-3 nm and lateral size of 2 μm. In-situ compression tests in the scanning electron microscope (SEM) show that, compared with most of the existing lightweight foams, the present 3D SiC exhibited superior compression strengths and significant recovery after compression strains of about 70%. PMID:26580985

  13. Direct current conduction in SiC powders

    NASA Astrophysics Data System (ADS)

    Mârtensson, E.; Gäfvert, U.; Lindefelt, U.

    2001-09-01

    Silicon carbide (SiC) powder is used in nonlinear field grading materials. The composite material, consisting of an insulating polymer matrix filled with the SiC-grains, is usually a percolated system with established conducting paths. In order to explain the properties, the electrical characteristic and conduction mechanisms of the SiC powder itself are of interest. SiC powders have been studied by current-voltage measurements and the influences of grain size and doping have been investigated. The macroscopic current characteristics of green and black SiC powders can be described by the transport mechanisms at the grain contacts, which can be modeled by Schottky-like barriers. The SiC is heavily doped and tunneling by field emission is the dominating conduction mechanism over the major part of the nonlinear voltage range. It is suggested that preavalanche multiplication influences the current at the highest voltages, especially for p-type black SiC.

  14. Investigation of the transition layer in 3C-SiC/6H-SiC heterostructures

    SciTech Connect

    Lebedev, A. A.; Zamorianskaya, M. V.; Davydov, S. Yu.; Kirilenko, D. A.; Lebedev, S. P. Sorokin, L. M.; Shustov, D. B.; Scheglov, M. P.

    2013-11-15

    Transmission electron microscopy and the cathodoluminescence method are used to study the transition region in 3C-SiC/6H-SiC heterostructures. It is shown that this region is, as a rule, constituted by alternating 3C-SiC and 6H-SiC layers with the possible inclusion of other silicon carbide polytypes. An assumption is made that this structure of the transition region can be explained in terms of the model of spinodal decomposition.

  15. Insight into and Computational Studies of the Selective Synthesis of 6H-Dibenzo[b,h]xanthenes.

    PubMed

    Carneiro, Paula F; Pinto, Maria do Carmo F R; Marra, Roberta K F; Campos, Vinícius R; Resende, Jackson Antônio L C; Delarmelina, Maicon; Carneiro, José Walkimar M; Lima, Emerson S; da Silva, Fernando de C; Ferreira, Vitor F

    2016-07-01

    Starting from 2-hydroxy-1,4-naphthoquinone (lawsone), we synthesized eight new 6H-dibenzo[b,h]xanthene derivatives selectively under solvent-free conditions. Spectroscopic investigations confirmed that only the isomer 6H-dibenzo[b,h]xanthene was obtained in all eight cases. Computational studies provide a rationalization for the selective appearance of these isomers having as an intermediate an addition product. PMID:27281677

  16. Long-Term Characterization of 6H-SiC Transistor Integrated Circuit Technology Operating at 500 C

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Chen, Liang-Yu; Chang, Carl W.; Beheim, Glenn M.; Okojie, Robert S.; Evans, Laura J.; Meredith Roger D.; Ferrier, Terry L.; Krasowski, Michael J.; Prokop, Norman F.

    2008-01-01

    NASA has been developing very high temperature semiconductor integrated circuits for use in the hot sections of aircraft engines and for Venus exploration. This paper reports on long-term 500 C electrical operation of prototype 6H-SiC integrated circuits based on epitaxial 6H-SiC junction field effect transistors (JFETs). As of this writing, some devices have surpassed 4000 hours of continuous 500 C electrical operation in oxidizing air atmosphere with minimal change in relevant electrical parameters.

  17. Electrical characterization of 6H crystalline silicon carbide. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Lempner, Stephen E.

    1994-01-01

    Crystalline silicon carbide (SiC) substrates and epilayers, undoped as well as n- and p-doped, have been electrically characterized by performing Hall effect and resistivity measurements (van der Pauw) over the temperature range of approximately 85 K to 650 K (200 K to 500 K for p-type sample). By fitting the measured temperature dependent carrier concentration data to the single activation energy theoretical model: (1) the activation energy for the nitrogen donor ranged from 0.078 eV to 0.101 eV for a doping concentration range of 10(exp 17) cm(exp -3) to 10(exp 18) cm(exp -3) and (2) the activation energy for the aluminum acceptor was 0.252 eV for a doping concentration of 4.6 x 10(exp 18) cm(exp -3). By fitting the measured temperature dependent carrier concentration data to the double activation energy level theoretical model for the nitrogen donor: (1) the activation energy for the hexagonal site was 0.056 eV and 0.093 eV corresponding to doping concentrations of 3.33 x 10 (exp 17) cm(exp -3) and 1.6 x 10(exp 18) cm(exp -3) and (2) the activation energy for the cubic site was 0.113 and 0.126 eV corresponding to doping concentrations of 4.2 x 10(exp 17) cm(exp -3) and 5.4 x 10(exp 18) cm(exp -3).

  18. F-1 Engine Installation to S-IC Stage

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Engineers and technicians at the Marshall Space Flight Center were installing an F-I engine on the Saturn V S-IC (first) stage thrust structure in building 4705. The S-IC (first) stage used five F-1 engines that produced a total thrust of 7,500,000 pounds as each engine produced 1,500,000 pounds of thrust. The S-IC stage lifted the Saturn V vehicle and Apollo spacecraft from the launch pad.

  19. Synthesis, structural characterization and biological activity of fluorinated Schiff-bases of the type [C6H4-1-(OH)-3-(CHdbnd NArF)

    NASA Astrophysics Data System (ADS)

    Avila-Sorrosa, Alcives; Hernández-González, Jorge Ignacio; Reyes-Arellano, Alicia; Toscano, Rubén A.; Reyes-Martínez, Reyna; Roberto Pioquinto-Mendoza, J.; Morales-Morales, David

    2015-04-01

    A series of fluorinated imines of the type [C6H4-1-(OH)-3-(CHdbnd NArF)]; ArFdbnd C6H4-4-F (1), C6H3-2,3-F2 (2), C6H3-3,5-F2 (3), C6H2-2,4,6-F3 (4), C6H4-3-CF3 (5), C6H3-3,5-(CF3)2 (6), were synthesized and fully characterized including single crystal X-ray diffraction analyses of compounds [C6H4-1-(OH)-3-(CHdbnd NC6H4-4-F)] (1), [C6H4-1-(OH)-3-(CHdbnd NC6H3-3,5-F2)] (3), [C6H4-1-(OH)-3-(CHdbnd NC6H4-3-CF3)] (5). Further analyses of these results allowed the identification of the predominant non-covalent interactions and supramolecular arrangements in the solid state. Exploration of the anti-bacterial activity against both gram-positive and gram-negative bacteria showed those compounds including F or CF3 substituents at the meta positions i.e. [C6H4-1-(OH)-3-(CHdbnd NC6H3-3,5-F2)] (3), [C6H4-1-(OH)-3-(CHdbnd NC6H4-3-CF3)] (5), [C6H4-1-(OH)-3-(CHdbnd NC6H3-3,5-(CF3)2)] (6), to be the best when their activity is compared versus ampicillin.

  20. Corrosion pitting of SiC by molten salts

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Smialek, J. L.

    1986-01-01

    The corrosion of SiC by thin films of Na2CO3 and Na2SO4 at 1000 C is characterized by a severe pitting attack of the SiC substrate. A range of different Si and SiC substrates were examined to isolate the factors critical to pitting. Two types of pitting attack are identified: attack at structural discontinuities and a crater-like attack. The crater-like pits are correlated with bubble formation during oxidation of the SiC. It appears that bubbles create unprotected regions, which are susceptible to enhanced attack and, hence, pit formation.

  1. Graphene covered SiC powder as advanced photocatalytic material

    NASA Astrophysics Data System (ADS)

    Zhu, Kaixing; Guo, Liwei; Lin, Jingjing; Hao, Weichang; Shang, Jun; Jia, Yuping; Chen, Lianlian; Jin, Shifeng; Wang, Wenjun; Chen, Xiaolong

    2012-01-01

    Graphene covered SiC powder (GCSP) has been fabricated by well established method of high temperature thermal decomposition of SiC. The structural and photocatalystic characteristics of the prepared GCSP were investigated and compared with that of the pristine SiC powder. Under UV illumination, more than 100% enhancement in photocatalystic activity is achieved in degradation of Rhodamine B (Rh B) by GCSP catalyst than by pristine SiC powder. The possible mechanisms underlining the observed results are discussed. The results suggested that GCSP as a composite of graphene based material has great potential for use as a high performance photocatalyst.

  2. Paralinear Oxidation of CVD SiC in Water Vapor

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Hann, Raiford E., Jr.

    1997-01-01

    The oxidation kinetics of CVD SiC were monitored by thermogravimetric analysis (TGA) in a 50% H2O/50% O2 gas mixture flowing at 4.4 cm/s for temperatures between 1200 and 1400 C. Paralinear weight change kinetics were observed as the water vapor oxidized the SiC and simultaneously volatilized the silica scale. The long-term degradation rate of SiC is determined by the volatility of the silica scale. Rapid SiC surface recession rates were estimated from these data for actual aircraft engine combustor conditions.

  3. SiC Power MOSFET with Improved Gate Dielectric

    SciTech Connect

    Sbrockey, Nick M; Tompa, Gary S; Spencer, Michael G; Chandrashekhar, Chandra MVS

    2010-08-23

    In this STTR program, Structured Materials Industries (SMI), and Cornell University are developing novel gate oxide technology, as a critical enabler for silicon carbide (SiC) devices. SiC is a wide bandgap semiconductor material, with many unique properties. SiC devices are ideally suited for high-power, highvoltage, high-frequency, high-temperature and radiation resistant applications. The DOE has expressed interest in developing SiC devices for use in extreme environments, in high energy physics applications and in power generation. The development of transistors based on the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) structure will be critical to these applications.

  4. Electrical properties of epitaxial 3C- and 6H-SiC p-n junction diodes produced side-by-side on 6H-SiC substrates

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Larkin, David J.; Starr, Jonathan E.; Powell, J. Anthony; Salupo, Carl S.; Matus, Lawrence G.

    1994-01-01

    3C-SiC (beta-SiC) and 6H-SiC p-n junction diodes have been fabricated in regions of both 3C-SiC and 6H-SiC epitaxial layers which were grown side-by-side on low-tilt-angle 6H-SiC substrates via a chemical vapor deposition (CVD) process. Several runs of diodes exhibiting state-of-the-art electrical characteristics were produced, and performance characteristics were measured and compared as a function of doping, temperature, and polytype. The first 3C-SiC diodes which rectify to reverse voltages in excess of 300 V were characterized, representing a six-fold blocking voltage improvement over experimental 3C-SiC diodes produced by previous techniques. When placed under sufficient forward bias, the 3C-SiC diodes emit significantly bright green-yellow light while the 6H-SiC diodes emit in the blue-violet. The 6H-SiC p-n junction diodes represent the first reported high-quality 6H-SiC devices to be grown by CVD on very low-tilt-angle (less than 0.5 deg off the (0001) silicon face) 6H substrates. The reverse leakage current of a 200 micron diameter circular device at 1100 V reverse bias was less than 20 nA at room temperature, and excellent rectification characteristics were demonstrated at the peak characterization temperature of 400 C.

  5. Inelastic X-ray scattering from 6H-SiC

    SciTech Connect

    Macrander, A.T.; Blasdell, B.; Montano, P.A. |; Kao, C.C.

    1995-07-01

    The authors have studied electronic excitations in 6H-SiC using inelastic x-ray scattering. Inelastic scattering spectra were measured at momentum transfers ranging from 0.47 {angstrom}{sup {minus}1} to 2.00 {angstrom}{sup {minus}1} along the c-axis in the hexagonal lattice, i.e. , along [00{center_dot}1], and from 0.67 {angstrom}{sup {minus}1} to 2.00 {angstrom}{sup {minus}1} along the a-axis, i.e., alone, [10{center_dot}0]. Comparison of the two sets of data reveals an orientation dependence of the spectra, except for a characteristic peak at 22--23 eV that occurs for both directions at low Q. This peak has also been observed in electron energy loss spectroscopy studies and is identified as a bulk plasmon. The orientation dependence of the other spectral features is indicative of band structure effects. These data were obtained using a Ge(444) analyzer in a near backscattering geometry.

  6. Sodium dipotassium citrate, NaK2C6H5O7

    PubMed Central

    Rammohan, Alagappa; Kaduk, James A.

    2016-01-01

    The crystal structure of sodium dipotassium citrate, Na+·2K+·C6H5O7 3−, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The Na+ and one of the K+ cations are six-coordinate, with bond-valence sums of 1.13 and 0.92 valence units, respectively, while another crystallographically independent K+ cation is seven-coordinate with a bond-valence sum of 1.20. The [KO6] and [KO7] polyhedra share edges and corners to form layers perpendicular to the b axis. The distorted [NaO6] octa­hedra share edges to form chains along the a axis. The result is a three-dimensional network. The only O—H⋯O hydrogen bond is an intra­molecular one between the hy­droxy group and a terminal carboxyl­ate group. PMID:27006817

  7. Damage Accumulation and Annealing in 6H-SiC Irradiated with Si+

    SciTech Connect

    Jiang, Weilin; Weber, William J.; Thevuthasan, Suntharampillai; McCready, David E.

    1998-10-01

    Damage accumulation and annealing in 6H-silicon carbide (alpha-SiC) single crystals have been studied in situ using 2.0 MeV HeRBS in a <0001>-axial channeling geometry (RBS/C). The damage was induced by 550 keV Si ion implantation (30 degrees off normal) at a temperature of -110 degrees C, and the damage recovery was investigated by subsequent isochromal annealing (20 min) over the temperature range from -110 degrees C to 900 degrees C. At ion fluences below 7.5 X 10 13 Si/cm (0.04 dpa in the damage peak), only point defects appear to be created. Furthermore, the defects on the Si sublattice can be completely recovered by thermal annealing at room temperature (RT), and recovery of defects on the C sublattice is suggested. At higher fluences of 6.6 x 10 15 Si/cm (-90 degrees C), an amorphous layer is created from the surface to a depth of 0.6 mu-m. Because of recovery processes at the buried crystalline-amorphous interface, the apparent thickness of this amorphous layer decreases slightly (<10%) with increasing temperature over the range from -90 degrees C to 600 degrees C.

  8. Rotational spectra and structures of the C6H6-HCN dimer and Ar3-HCN tetramer

    NASA Astrophysics Data System (ADS)

    Gutowsky, H. S.; Arunan, E.; Emilsson, T.; Tschopp, S. L.; Dykstra, C. E.

    1995-09-01

    A comparative study has been made of the rotational properties of C6H6-HCN and Ar3-HCN, observed with the Balle/Flygare pulsed beam, Fourier transform microwave spectrometer. C6H6-HCN is found to be a prolate symmetric top and Ar3-HCN an oblate one, both with the H in the middle. The rotational constants B0, DJ, and DJK of the parent species are 1219.9108(4) MHz, 1.12(3) kHz, and 18.32(8) kHz for C6H6-HCN, and 886.4878(1) MHz, 10.374(2) kHz, and 173.16(1) kHz for Ar3-HCN. Rotational constants are reported for the isotopic species C6H6-H13CN, -HC15N, and 13CC5H6-HC15N, and for Ar3-HC15N and -DCN. Analysis of the 14N hyperfine interaction χ finds its projection on the figure axis to be -4.223(4) MHz in C6H6-HCN and -1.143(2) in Ar3-HCN. They correspond to average projection angles θ between the HCN and figure axes of 15.2° and 45.3°, respectively. A pseudodiatomic analysis of the rotational constants gives the c.m. to c.m. distance to be 3.96 Å in C6H6-HCN and 3.47 Å in Ar3-HCN. While the rotational properties of C6H6-HCN are ``normal,'' those of Ar3-HCN display a long list of ``abnormalities.'' They include a J-dependent χ(14N) similar to that of Ar-HCN; a very large projection angle θ; large centrifugal distortion including higher-order terms in HJ and HJK; splitting of the K=3 transitions into J-dependent doublets; and the ready observation of an excited vibrational state. These behavioral differences are related qualitatively to the interaction surfaces for the two clusters, calculated with the molecular mechanics for clusters (MMC) model, and discussed. The potential minimum for C6H6-HCN is smooth, circular, steep except for a flat bottom, and deep (1762 cm-1). That for Ar3-HCN is tricuspid, with large gullies, and shallow (507 cm-1). In addition to the dispersion forces, the dominant interaction forming C6H6-HCN is between the benzene quadrupole moment and the HCN dipole moment, a strong 4-2 potential. That in Ar3-HCN is polarization of the spherical Ar

  9. Nanocrystalline SiC and Ti3SiC2 Alloys for Reactor Materials: Diffusion of Fission Product Surrogates

    SciTech Connect

    Henager, Charles H.; Jiang, Weilin

    2014-11-01

    MAX phases, such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been suggested in the literature as a possible fuel cladding material. Prior to the application, it is necessary to investigate diffusivities of fission products in the ternary compound at elevated temperatures. This study attempts to obtain relevant data and make an initial assessment for Ti3SiC2. Ion implantation was used to introduce fission product surrogates (Ag and Cs) and a noble metal (Au) in Ti3SiC2, SiC, and a dual-phase nanocomposite of Ti3SiC2/SiC synthesized at PNNL. Thermal annealing and in-situ Rutherford backscattering spectrometry (RBS) were employed to study the diffusivity of the various implanted species in the materials. In-situ RBS study of Ti3SiC2 implanted with Au ions at various temperatures was also performed. The experimental results indicate that the implanted Ag in SiC is immobile up to the highest temperature (1273 K) applied in this study; in contrast, significant out-diffusion of both Ag and Au in MAX phase Ti3SiC2 occurs during ion implantation at 873 K. Cs in Ti3SiC2 is found to diffuse during post-irradiation annealing at 973 K, and noticeable Cs release from the sample is observed. This study may suggest caution in using Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures. Further studies of the related materials are recommended.

  10. Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony

    2004-01-01

    This article describes the initial discovery and development of new approaches to SiC homoepitaxial and heteroepitaxial growth. These approaches are based upon the previously unanticipated ability to effectively supress two-dimensional nucleation of 3C-SiC on large basal plane terraces that form between growth steps when epitaxy is carried out on 4H- and 6H-SiC nearly on-axis substrates. After subdividing the growth surface into mesa regions, pure stepflow homoeptixay with no terrace nucleation was then used to grow all existing surface steps off the edges of screw-dislocation-free mesas, leaving behind perfectly on-axis (0001) basal plane mesa surfaces completely free of atomic-scale steps. Step-free mesa surfaces as large as 0.4 mm x 0.4 mm were experimentally realized, with the yield and size of step-free mesas being initally limited by substrate screw dislocations. Continued epitaxial growth following step-free surface formation leads to the formation of thin lateral cantilevers that extend the step-free surface area from the top edge of the mesa sidewalls. By selecting a proper pre-growth mesa shape and crystallographic orientation, the rate of cantilever growth can be greatly enhanced in a web growth process that has been used to (1) enlarge step-free surface areas and (2) overgrow and laterally relocate micropipes and screw dislocations. A new growth process, named step-free surface heteroepitaxy, has been developed to achieve 3C-SiC films on 4H- and 6H-SiC substrate mesas completely free of double positioning boundary and stacking fault defects. The process is based upon the controlled terrace nucleation and lateral expansion of a single island of 3C-SiC across a step-free mesa surface. Experimental results indicate that substrateepilayer lattice mismatch is at least partially relieved parallel to the interface without dislocations that undesirably thread through the thickness of the epilayer. These results should enable realization of improved SiC

  11. FT-IR study on interactions between medroxyprogesterone acetate and solvent in CHCl3/cyclo-C6H12 and CCl4/cyclo-C6H12 binary solvent systems

    NASA Astrophysics Data System (ADS)

    Shi, Jie-hua; Fan, Chun-hui

    2012-09-01

    The intermolecular interactions between medroxyprogesterone acetate (MPA) and CHCl3 and CCl4 solvent in CHCl3/cyclo-C6H12 and CCl4/cyclo-C6H12 binary solvent systems have been studied by Fourier transform infrared spectroscopy (FT-IR). The experimental results showed that there are hydrogen bonding interactions between oxygen atoms of all carbonyl groups in MPA and hydrogen atom of CHCl3 so as to form 1:3 complex of MPA with CHCl3 and produce three new absorption bands at 1728.9-1736.1, 1712.7-1717.4 and 1661.9-1673.8 cm-1, respectively. And, 1:1 complex of MPA with CCl4 is formed in CCl4/cyclo-C6H12 binary solvent as a result of hydrogen bonding interaction between C3 carbonyl group and empty d-orbital in chlorine atom of CCl4 leading to producing new absorption band at 1673.2-1674.2 cm-1. However, all free carbonyl and associated carbonyl stretching vibrations of MPA in CHCl3/cyclo-C6H12 and CCl4/cyclo-C6H12 binary solvent systems shift to lower wavenumbers with the increasing of volume fraction of CHCl3 and CCl4 in binary solvent systems owing to the dipole-dipole interaction and the dipole-induced dipole interaction between MPA and solvents.

  12. "Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

    NASA Technical Reports Server (NTRS)

    Lu, W. J.; Shi, D. T.; Elshot, K.; Bryant, E.; Lafate, K.; Chen, H.; Burger, A.; Collins, W. E.

    1998-01-01

    Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

  13. Fine Mapping of the Barley Chromosome 6H Net Form Net Blotch Susceptibility Locus

    PubMed Central

    Richards, Jonathan; Chao, Shiaoman; Friesen, Timothy; Brueggeman, Robert

    2016-01-01

    Net form net blotch, caused by the necrotrophic fungal pathogen Pyrenophora teres f. teres, is a destructive foliar disease of barley with the potential to cause significant yield loss in major production regions throughout the world. The complexity of the host–parasite genetic interactions in this pathosystem hinders the deployment of effective resistance in barley cultivars, warranting a deeper understanding of the interactions. Here, we report on the high-resolution mapping of the dominant susceptibility locus near the centromere of chromosome 6H in the barley cultivars Rika and Kombar, which are putatively targeted by necrotrophic effectors from P. teres f. teres isolates 6A and 15A, respectively. Utilization of progeny isolates derived from a cross of P. teres f. teres isolates 6A × 15A harboring single major virulence loci (VK1, VK2, and VR2) allowed for the Mendelization of single inverse gene-for-gene interactions in a high-resolution population consisting of 2976 Rika × Kombar recombinant gametes. Brachypodium distachyon synteny was exploited to develop and saturate the susceptibility region with markers, delimiting it to ∼0.24 cM and a partial physical map was constructed. This genetic and physical characterization further resolved the dominant susceptibility locus, designated Spt1 (susceptibility to P. teres f. teres). The high-resolution mapping and cosegregation of the Spt1.R and Spt1.K gene/s indicates tightly linked genes in repulsion or alleles possibly targeted by different necrotrophic effectors. Newly developed barley genomic resources greatly enhance the efficiency of positional cloning efforts in barley, as demonstrated by the Spt1 fine mapping and physical contig identification reported here. PMID:27172206

  14. Fine Mapping of the Barley Chromosome 6H Net Form Net Blotch Susceptibility Locus.

    PubMed

    Richards, Jonathan; Chao, Shiaoman; Friesen, Timothy; Brueggeman, Robert

    2016-01-01

    Net form net blotch, caused by the necrotrophic fungal pathogen Pyrenophora teres f. teres, is a destructive foliar disease of barley with the potential to cause significant yield loss in major production regions throughout the world. The complexity of the host-parasite genetic interactions in this pathosystem hinders the deployment of effective resistance in barley cultivars, warranting a deeper understanding of the interactions. Here, we report on the high-resolution mapping of the dominant susceptibility locus near the centromere of chromosome 6H in the barley cultivars Rika and Kombar, which are putatively targeted by necrotrophic effectors from P. teres f. teres isolates 6A and 15A, respectively. Utilization of progeny isolates derived from a cross of P. teres f. teres isolates 6A × 15A harboring single major virulence loci (VK1, VK2, and VR2) allowed for the Mendelization of single inverse gene-for-gene interactions in a high-resolution population consisting of 2976 Rika × Kombar recombinant gametes. Brachypodium distachyon synteny was exploited to develop and saturate the susceptibility region with markers, delimiting it to ∼0.24 cM and a partial physical map was constructed. This genetic and physical characterization further resolved the dominant susceptibility locus, designated Spt1 (susceptibility to P. teres f. teres). The high-resolution mapping and cosegregation of the Spt1.R and Spt1.K gene/s indicates tightly linked genes in repulsion or alleles possibly targeted by different necrotrophic effectors. Newly developed barley genomic resources greatly enhance the efficiency of positional cloning efforts in barley, as demonstrated by the Spt1 fine mapping and physical contig identification reported here. PMID:27172206

  15. Conformational Isomerism of trans-[Pt(NH2C6H11)2I2] and the Classical Wernerian Chemistry of [Pt(NH2C6H11)4]X2 (X = Cl, Br, I)1

    PubMed Central

    Johnstone, Timothy C.; Lippard, Stephen J.

    2012-01-01

    X-ray crystallographic analysis of the compound trans-[Pt(NH2C6H11)2I2] revealed the presence of two distinct conformers within one crystal lattice. This compound was studied by variable temperature NMR spectroscopy to investigate the dynamic interconversion between these isomers. The results of this investigation were interpreted using physical (CPK) and computational (molecular mechanics and density functional theory) models. The conversion of the salts [Pt(NH2C6H11)4]X2 into trans-[Pt(NH2C6H11)2X2] (X = Cl, Br, I) was also studied and is discussed here with an emphasis on parallels to the work of Alfred Werner. PMID:23554544

  16. Saturn V S-IC Stage LOX Tank

    NASA Technical Reports Server (NTRS)

    1964-01-01

    This image depicts the Saturn V S-IC (first) stage liquid oxygen (LOX) tank being lowered into the irner tank in a high bay at the Marshall Space Flight Center (MSFC). The S-IC stage utilized five F-1 engines that used liquid oxygen and kerosene as propellant and provided a combined thrust of 7,500,000 pounds.

  17. Alternate current characteristics of SiC powders

    NASA Astrophysics Data System (ADS)

    Mârtensson, E.; Gäfvert, U.; Önneby, C.

    2001-09-01

    Silicon carbide (SiC) powder is used in nonlinear field grading materials. The composite material, consisting of an insulating polymer matrix filled with the SiC grains, is usually a percolated system with established conducting paths. In order to explain the properties, the electrical characteristic of the SiC powder itself is of interest. The ac characteristics of SiC powders have been studied by dielectric response, capacitance-voltage, and ac-pulse measurements. The frequency, electric field, and pressure dependencies have been analyzed for green and black SiC, which have different doping. The ac characteristics of green and black SiC powders are governed by both the barrier regions at the SiC-grain contacts and the surrounding matrix. The nonlinear loss is determined by the conduction current at the contacts. Depending on the doping level of the SiC grains, the capacitance may be controlled by either the nonlinear capacitance of the barrier region or the linear capacitance of the surrounding matrix. Each contact zone may be modeled by a nonlinear resistance in parallel with both a nonlinear and a linear capacitance. The components are considered to be frequency independent. However, in order to explain the macroscopic frequency and field dependencies of the SiC powders, the use of a network of unique contact zones with dissimilar properties is suggested.

  18. Porous silicon carbide (SiC) semiconductor device

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1994-01-01

    A semiconductor device employs at least one layer of semiconducting porous silicon carbide (SiC). The porous SiC layer has a monocrystalline structure wherein the pore sizes, shapes, and spacing are determined by the processing conditions. In one embodiment, the semiconductor device is a p-n junction diode in which a layer of n-type SiC is positioned on a p-type layer of SiC, with the p-type layer positioned on a layer of silicon dioxide. Because of the UV luminescent properties of the semiconducting porous SiC layer, it may also be utilized for other devices such as LEDs and optoelectronic devices.

  19. Processing of sintered alpha SiC

    NASA Technical Reports Server (NTRS)

    Storm, R. S.

    1984-01-01

    Processing methods of sintered alpha SiC for engine applications are developed in a cost effective manner, using a submicron sized powder blended with sintering aids (boron and carbon). The processes for forming a green powder compact, such as dry pressing, cold isostatic pressing and green machining, slip casting, aqueous extrusion, plastic extrusion, and injection molding, are described. Dry pressing is the simplest route to component fabrication, and is carried out at approximately 10,000 psi pressure, while in the cold isostatic method the pressure could go as high as 20,000 psi. Surfactants are added to control settling rates and casting characteristics in the slip casting. The aqueous extrusion process is accomplished by a hydraulic ram forcing the aqueous mixture through a die. The plastic forming processes of extrusion and injection molding offer the potential of greater diversity in shape capacity. The physical properties of sintered alpha SiC (hardness, Young's modulus, shear modulus, and thermal diffusivity) are extensively tested. Corrosion resistance test results of silicon carbide are included.

  20. Synthesis, structural and magnetic characterisation of the fully fluorinated compound 6H-BaFeO{sub 2}F

    SciTech Connect

    Clemens, Oliver; Wright, Adrian J.; Berry, Frank J.; Smith, Ronald I.; Slater, Peter R.

    2013-02-15

    The compound 6H-BaFeO{sub 2}F (P6{sub 3}/mmc) was synthesised by the low temperature fluorination of 6H-BaFeO{sub 3-d} using polyvinylidenedifluoride (PVDF) as a fluorination agent. Structural characterisation by XRD and NPD suggests that the local positions of the oxygen and fluorine atoms vary with no evidence for ordering on the anion sites. This compound shows antiferromagnetic ordering at room temperature with antiparallel alignment of the magnetic moments along the c-axis. The use of PVDF also allows the possibility of tuning the fluorine content in materials of composition 6H-BaFeO{sub 3-d}F{sub y} to any value of 06H-BaFeO{sub 2}F. Highlights: Black-Right-Pointing-Pointer The crystal structure of the hexagonal perovskite phase 6H-BaFeO{sub 2}F. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F and 6H-BaFeO{sub 3-d}F{sub y} were prepared via low temperature fluorination using PVDF. Black-Right-Pointing-Pointer A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. Black-Right-Pointing-Pointer This analysis suggests differences for the local coordination of O{sup 2-} and F{sup -} anions. Black-Right-Pointing-Pointer H-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K. Black-Right-Pointing-Pointer The magnetic moments align parallel to the a-axis.

  1. Immunosuppression Decreases Inflammation and Increases AAV6-hSERCA2a-Mediated SERCA2a Expression

    PubMed Central

    Zhu, Xiaodong; McTiernan, Charles F.; Rajagopalan, Navin; Shah, Hemal; Fischer, David; Toyoda, Yoshiya; Letts, Dustin; Bortinger, Jonathan; Gibson, Gregory; Xiang, Wenyu; McCurry, Kenneth; Mathier, Michael; Glorioso, Joseph C.

    2012-01-01

    Abstract The calcium pump SERCA2a (sarcoplasmic reticulum calcium ATPase 2a), which plays a central role in cardiac contraction, shows decreased expression in heart failure (HF). Increasing SERCA2a expression in HF models improves cardiac function. We used direct cardiac delivery of adeno-associated virus encoding human SERCA2a (AAV6-hSERCA2a) in HF and normal canine models to study safety, efficacy, and the effects of immunosuppression. Tachycardic-paced dogs received left ventricle (LV) wall injection of AAV6-hSERCA2a or solvent. Pacing continued postinjection for 2 or 6 weeks, until euthanasia. Tissue/serum samples were analyzed for hSERCA2a expression (Western blot) and immune responses (histology and AAV6-neutralizing antibodies). Nonpaced dogs received AAV6-hSERCA2a and were analyzed at 12 weeks; a parallel cohort received AAV-hSERCA2a and immunosuppression. AAV-mediated cardiac expression of hSERCA2a peaked at 2 weeks and then declined (to ∼50%; p<0.03, 6 vs. 2 weeks). LV end diastolic and end systolic diameters decreased in 6-week dogs treated with AAV6-hSERCA2a (p<0.05) whereas LV diameters increased in control dogs. Dogs receiving AAV6-hSERCA2a developed neutralizing antibodies (titer ≥1:120) and cardiac cellular infiltration. Immunosuppression dramatically reduced immune responses (reduced inflammation and neutralizing antibody titers <1:20), and maintained hSERCA2a expression. Thus cardiac injection of AAV6-hSERCA2a promotes local hSERCA2a expression and improves cardiac function. However, the hSERCA2a protein level is reduced by host immune responses. Immunosuppression alleviates immune responses and sustains transgene expression, and may be an important adjuvant for clinical gene therapy trials. PMID:22482463

  2. Growth Of Graphitic Polyhedra, SiC Platelets, And Carbon Nanotubes Filled With SiC Nanowires By Laser Ablation

    SciTech Connect

    Kokai, Fumio; Uchiyama, Kunihiro; Chigusa, Hajime; Nozaki, Iori; Noguchi, Eriko; Kameda, Yuto; Koshio, Akira

    2010-10-08

    Three characteristic silicon/carbon nanostructures, i.e., graphitic polyhedral (GP) particles, silicon carbide (SiC) platelets, and carbon nanotubes (CNTs) filled with SiC nanowires, were synthesized by the laser ablation of Si-C targets in the presence of high-pressure Ar gas up to 0.9 MPa. The growth of nanostructures was controlled merely by adjusting the Si content in graphite and the ambient Ar gas pressure. Deposits containing GP particles were purified by heat treatment at 550 deg. C in a pure oxygen atmosphere for 1 h. CNTs filled with SiC nanowires were grown without a catalyst. Unlike previous studies of CNTs filled with metals or compounds, all the CNTs checked by transmission electron microscopy contained SiC nanowires and no unfilled CNTs were produced. We discuss the growth mechanisms of the three nanostructures.

  3. Determination via luminescence spectroscopy and x-ray diffraction of the strain and composition of GaN and Al(x)Ga(1-x)N thin films grown on 6H-SiC(0001) substrates

    NASA Astrophysics Data System (ADS)

    Perry, William George

    1997-12-01

    This dissertation describes the luminescence and x-ray diffraction characterization of GaN and AlxGa1-xN thin films that were deposited on 6H-SiC(0001) substrates. These materials have applications for optoelectronic devices that are operational in the UV to green regions of the spectrum and for high-temperature, high-frequency and high-power microelectronic devices. The primary tools used in this research were photoluminescence and cathodoluminescence spectroscopies and high-resolution x-ray diffraction. Biaxial strains resulting from the mismatches in thermal expansion coefficients and lattice parameters in GaN films grown on AlN buffer layers previously deposited on vicinal and on-axis 6H-SiC(0001) substrates were measured using photoluminescence. A linear relationship between the bound exciton energy (EBX) and the biaxial strain along the c-axis direction was observed. A marked variation in the biaxial strain in GaN films deposited on off- and on-axis SiC was determined. It was attributed to the difference in the density and nature of the microstructural defects that originate at the steps on the SiC surface. The strain in the GaN films was either in tension or compression; whereas, only tensile strains were reported in all previous studies using SiC wafers. This indicated that the lattice mismatch strain in the former films was not fully relieved by defect formation. This result was confirmed by the observation via HRTEM of a 0.9% residual compressive strain at the GaN/AlN interface. Cathodoluminescence was used to determine the optical spectra in AlxGa1-xN films over the entire composition range of x. A bowing parameter of b = 1.65 eV for the bound exciton peak was observed. This bound exciton peak became more localized as the Al mole fraction increased. This was attributed to the increase in the ionization energy (ED) of the donor to which the exciton was bound. The donor-acceptor pair (DAP) band and the so-called 'yellow' emission band that are commonly

  4. Fabrication of SiC whisker-reinforced SiC ceramics

    SciTech Connect

    Miyahara, Kaoru; Watanabe, Takashi; Koga, Shin; Sasa, Tadashi

    1992-10-01

    A fabrication process of SiC whisker-reinforced SiC ceramics consisting of whisker CVD-coating for the control of interfacial bonding, slurry-pressing and HIP consolidation has been developed. Microstructural observation confirmed the incorporation of the interfacial carbon layer in the composites brought about remarkable whisker bridging/pull-out in the fracture. Whisker-bridging was considered to be a predominant toughening mechanism. To optimize the interfacial properties, the effect of coating conditions, i.e., amount of coating and CVD temperature, on the fracture toughness were studied. The effect of whisker diameter on the fracture toughness and anisotropy in the fracture toughness were also investigated. 12 refs.

  5. Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers,Dwight L.; Harder, Bryan J.

    2011-01-01

    The high temperature oxidation of silicon carbide occurs in either a passive or active mode, depending on temperature and oxygen potential. Passive oxidation forms a protective oxide film which limits attack of the SiC:SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g.) Active oxidation forms a volatile oxide and leads to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g). The transition points and rates of active oxidation are a major issue. Previous studies are reviewed and the leading theories of passive/active transitions summarized. Comparisons are made to the active/passive transitions in pure Si, which are relatively well-understood. Critical questions remain about the difference between the active-to-passive transition and passive-to-active transition. For Si, Wagner [2] points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. This suggests a significant oxygen potential difference between these two transitions and our experiments confirm this. For Si, the initial stages of active oxidation are characterized by the formation of SiO(g) and further oxidation to SiO2(s) as micron-sized rods, with a distinctive morphology. SiC shows significant differences. The active-to-passive and the passive-to-active transitions are close. The SiO2 rods only appear as the passive film breaks down. These differences are explained in terms of the reactions at the SiC/SiO2 interface. In order to understand the breakdown of the passive film, pre-oxidation experiments are conducted. These involve forming dense protective scales of 0.5, 1, and 2 microns and then subjecting the samples with these scales to a known active oxidation environment. Microstructural studies show that SiC/SiO2 interfacial reactions lead to a breakdown of the scale with a distinct morphology.

  6. 17 CFR 240.6h-2 - Security future based on note, bond, debenture, or evidence of indebtedness.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Security future based on note... of Exchanges § 240.6h-2 Security future based on note, bond, debenture, or evidence of indebtedness. A security future may be based upon a security that is a note, bond, debenture, or evidence...

  7. Ultrathin oxide interfaces on 6H-SiC formed by plasma hydrogenation: Ultra shallow depth profile study

    NASA Astrophysics Data System (ADS)

    Xie, Xianning; Loh, Kian Ping

    2002-11-01

    Silicon oxide ultrathin films grown on silicon carbide (6H-SiC) by plasma hydrogenation have been studied using ultrashallow depth profiling with time-of-flight secondary ion mass spectrometry. Plasma hydrogenation gives rise to an epitaxial RADICAL:[[RADICAND:[3

  8. Correction: A novel enantioselective synthesis of 6H-dibenzopyran derivatives by combined palladium/norbornene and cinchona alkaloid catalysis.

    PubMed

    Xu, Di; Dai, Li; Catellani, Marta; Motti, Elena; Della Ca', Nicola; Zhou, Zhiming

    2015-02-28

    Correction for 'A novel enantioselective synthesis of 6H-dibenzopyran derivatives by combined palladium/norbornene and cinchona alkaloid catalysis' by Di Xu et al., Org. Biomol. Chem., 2015, DOI: 10.1039/c4ob02551b. PMID:25629771

  9. Identification and transcriptional profile of multiple genes in the posterior kidney of Nile tilapia at 6h post bacterial infections

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To understand the molecular mechanisms involved in response of Nile tilapia (Oreochromis niloticus) to bacterial infection, suppression subtractive cDNA hybridization technique was used to identify upregulated genes in the posterior kidney of Nile tilapia at 6h post infection with Aeromonas hydrophi...

  10. Infrared absorption of gaseous benzoyl radical C6H5CO recorded with a step-scan Fourier-transform spectrometer.

    PubMed

    Lin, Shu-Yu; Lee, Yuan-Pern

    2012-06-21

    A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C(6)H(5)CO. C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm or in reactions of phenyl radical (C(6)H(5)) with CO; C(6)H(5) was produced on photolysis of C(6)H(5)Br at 248 nm. One intense band at 1838 ± 1 cm(-1), one weak band at 1131 ± 3 cm(-1), and two extremely weak bands at 1438 ± 5 and 1590 ± 10 cm(-1) are assigned to the C═O stretching (ν(6)), the C-C stretching mixed with C-H deformation (ν(15)), the out-of-phase C(1)C(2)C(3)/C(5)C(6)C(1) symmetric stretching (ν(10)), and the in-phase C(1)C(2)C(3)/C(4)C(5)C(6) antisymmetric stretching (ν(7)) modes of C(6)H(5)CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C(6)H(5)CO isolated in solid Ar and with values predicted for C(6)H(5)CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm(-1) simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C(6)H(5)C(O)Br, and C(6)H(5)C(O)C(6)H(5) were identified in the C(6)H(5)Br/CO/N(2) experiments; the kinetics involving C(6)H(5)CO and C(6)H(5)C(O)Br are discussed. PMID:22369517

  11. Characterization of multiple SiC and C coatings on SiC fibers for composites

    SciTech Connect

    Paulson, T.E.; Pantano, C.G.; Veitch, L.C.

    1995-12-31

    The timely analysis of materials is crucial as new composites are developed for advanced applications in the aerospace industry. Components of the composites, such as fiber coatings, the interface region between the fiber and the matrix material, and the stability of the fiber coatings and fibers, will influence the final properties of the composite materials. Analyzing non-standard surfaces, i.e. cylindrical vs. flat substrates, in order to properly assess the chemical and microstructural properties of the fibers and coatings is not a trivial task. Sample preparation such as cutting and polishing can destroy valuable information contained at interfaces and within multiple coatings. Existing analytical methods have been investigated where most of the sample preparation has been eliminated. For this study, alternating layers of SiC and C on Textron`s SCS-0 SiC fiber were characterized using Secondary Ion Mass Spectrometry depth profiling (12KeV Cs{sup +} primary beam, negative SIMS mode), Scanning Auger Microscopy and Scanning Electron Microscopy. Several of these fibers were also heat-treated in an oxygen environment at 1200{degrees}C for 1 to 50 hours. SIMS depth profiling and SEM were used to ascertain the oxidative stability of the multi-layer coating on SiC fibers.

  12. Compatibility of SiC and SiC Composites with Molten Lead

    SciTech Connect

    H Tunison

    2006-03-07

    The choice of structural material candidates to contain Lead at 1000 C are limited in number. Silicon carbide composites comprise one choice of possible containment materials. Short term screening studies (120 hours) were undertaken to study the behavior of Silicon Carbide, Silicon Nitride, elemental Silicon and various Silicon Carbide fiber composites focusing mainly on melt infiltrated composites. Isothermal experiments at 1000 C utilized graphite fixtures to contain the Lead and material specimens under a low oxygen partial pressure environment. The corrosion weight loss values (grams/cm{sup 2} Hr) obtained for each of the pure materials showed SiC (monolithic CVD or Hexoloy) to have the best materials compatibility with Lead at this temperature. Increased weight loss values were observed for pure Silicon Nitride and elemental Silicon. For the SiC fiber composite samples those prepared using a SiC matrix material performed better than Si{sub 3}N{sub 4} as a matrix material. Composites prepared using a silicon melt infiltration process showed larger corrosion weight loss values due to the solubility of silicon in lead at these temperatures. When excess silicon was removed from these composite samples the corrosion performance for these material improved. These screening studies were used to guide future long term exposure (both isothermal and non-isothermal) experiments and Silicon Carbide composite fabrication work.

  13. THERMAL CONDUCTIVITY OF SIC AND C FIBERS

    SciTech Connect

    Youngblood, Gerald E.; Senor, David J.; Kowbel, W.; Webb, J.; Kohyama, Akira

    2000-09-01

    Several rod-shaped specimens with uniaxially packed fibers (Hi-Nicalon, Hi-Nicalon Type S, Tyranno SA and Amoco K1100 types) and a pre-ceramic polymer matrix have been fabricated. By using appropriate analytic models, the bare fiber thermal conductivity (Kf) and the interface thermal conductance (h) will be determined as a function of temperature up to 1000?C before and after irradiation for samples cut from these rods. Initial results are: (1) for unirradiated Hi-Nicalon SiC fiber, Kf varied from 4.3 up to 5.9 W/mK for the 27-1000?C range, (2) for unirradiated K1100 graphite fiber, Kf varied from 576 down to 242 W/mK for the 27-1000?C range, and (3) h = 43 W/cm2K at 27?C as a typical fiber/matrix interface conductance.

  14. Ellipsometric study of cubic SiC

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Shoemaker, Neil S.; Powell, J. A.

    1990-01-01

    Variable angle spectroscopic ellipsometry (VASE) was applied to cubic SiC. This technique gives absolute values of the refractive index (n) and the extinction coefficient (k) of a substrate and/or a thin film of unknown material. The samples were grown by chemical vapor deposition (CVD) on p-type silicon. The substrate was aligned either on the (001) axis or 1 degree of (001). Several growth temperatures and growth durations were used. The samples were divided into two groups: (1) thick films of order 10 microns grown near optimal conditions of temperature, flow, and gas ratio; and (2) thin films of order 100 A grown at various temperatures. The ellipsometric results for samples in group 1 were analyzed using a two-phase model (substrate and ambient). Results show that for wavelengths in the visible, the refractive index of these CVD samples is equal to that reported for single crystal cubic SiC, within the experimental error, which is on the order of 1 percent. However, the extinction coefficient has a relatively large value, even above the band gap. The absorption is sample dependent and has a broad peak in the visible. The results for samples in group 2 were analyzed using a three-phase model (substrate, film, and ambient). The dielectric functions of the film, deducted from the measured n and k, were further analyzed using the effective medium approximation. The results show that the films contain 30 to 40 vol. percent amorphous silicon, i.e., silicon with only short-range order.

  15. SSG SiC Optical Systems in Space

    NASA Technical Reports Server (NTRS)

    Robichaud, Joseph; Keys, Andrew S. (Technical Monitor)

    2002-01-01

    Silicon Carbide (SiC) materials provide a number of benefits for space based optical systems. SSG Precision Optronics has extensive experience in the areas of design, fabrication, integration, and test of SiC optical systems. This expertise has been applied to produce a number of SiC-based instruments, including the Miniature Infrared Camera and Spectrometer (MICAS) and Advanced Land Imager (ALI) optical systems which have flown as part of NASA's New Millennium program. Our presentation will provide an overview of SSG's experience in the development of these SiC flight systems.

  16. SiC Composite Turbine Vanes

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Verilli, Michael J.

    2006-01-01

    Turbine inlet guide vanes have been fabricated from composites of silicon carbide fibers in silicon carbide matrices. A unique design for a cloth made from SiC fibers makes it possible to realize the geometric features necessary to form these vanes in the same airfoil shapes as those of prior metal vanes. The fiber component of each of these vanes was made from SiC-fiber cloth coated with boron nitride. The matrix was formed by chemical-vapor infiltration with SiC, then slurry-casting of SiC, followed by melt infiltration with silicon. These SiC/SiC vanes were found to be capable of withstanding temperatures 400 F (222 C) greater than those that can be withstood by nickel-base-superalloy turbine airfoils now in common use in gas turbine engines. The higher temperature capability of SiC/SiC parts is expected to make it possible to use them with significantly less cooling than is used for metallic parts, thereby enabling engines to operate more efficiently while emitting smaller amounts of NOx and CO. The SiC/SiC composite vanes were fabricated in two different configurations. Each vane of one of the configurations has two internal cavities formed by a web between the suction and the pressure sides of the vane. Each vane of the other configuration has no web (see Figure 1). It is difficult to fabricate components having small radii, like those of the trailing edges of these vanes, by use of stiff stoichiometric SiC fibers currently preferred for SiC/SiC composites. To satisfy the severe geometric and structural requirements for these vanes, the aforementioned unique cloth design, denoted by the term Y-cloth, was conceived (see Figure 2). In the regions away from the trailing edge, the Y-cloth features a fiber architecture that had been well characterized and successfully demonstrated in combustor liners. To form a sharp trailing edge (having a radius of 0.3 mm), the cloth was split into two planes during the weaving process. The fiber tows forming the trailing

  17. Microwave joining of SiC ceramics and composites

    SciTech Connect

    Ahmad, I.; Silberglitt, R.; Tian, Y.L.; Katz, J.D.

    1997-04-01

    Potential applications of SiC include components for advanced turbine engines, tube assemblies for radiant burners and petrochemical processing and heat exchangers for high efficiency electric power generation systems. Reliable methods for joining SiC are required in order to cost-effectively fabricate components for these applications from commercially available shapes and sizes. This manuscript reports the results of microwave joining experiments performed using two different types of SiC materials. The first were on reaction bonded SiC, and produced joints with fracture toughness equal to or greater than that of the base material over an extended range of joining temperatures. The second were on continuous fiber-reinforced SiC/SiC composite materials, which were successfully joined with a commercial active brazing alloy, as well as by using a polymer precursor.

  18. Observations of Ag diffusion in ion implanted SiC

    SciTech Connect

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Jerry L. Hunter, Jr.; Giordani, Andrew J.; Allen, Todd R.

    2015-03-17

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500–1625°C, were investigated in this study by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated, including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Lastly, estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.

  19. 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.

  20. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

    Segall, B.; Alterovitz, S. A.; Haugland, E. J.; Matus, L. G.

    1986-01-01

    Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

  1. Saturn V S-IC Stage Fuel Tank

    NASA Technical Reports Server (NTRS)

    1964-01-01

    This image shows the Saturn V S-IC-T stage (S-IC static test article) fuel tank being attached to the thrust structure in the vehicle assembly building at the Marshall Space Flight Center (MSFC). The S-IC stage utilized five F-1 engines that used liquid oxygen and kerosene as propellant and provided a combined thrust of 7,500,000 pounds.

  2. Synthesis of micro-sized interconnected Si-C composites

    DOEpatents

    Wang, Donghai; Yi, Ran; Dai, Fang

    2016-02-23

    Embodiments provide a method of producing micro-sized Si--C composites or doped Si--C and Si alloy-C with interconnected nanoscle Si and C building blocks through converting commercially available SiO.sub.x (0

  3. Electrical Characterization of Defects in SiC Schottky Barriers

    NASA Technical Reports Server (NTRS)

    Schnabel, C. M.; Tabib-Azar, M.; Raffaelle, R. P.; Su, H. B.; Dudley, M.; Neudeck, P. G.; Bailey, S.

    2005-01-01

    We have been investigating the effect of screw dislocation and other structural defects on the electrical properties of SiC. SiC is a wide-bandgap semiconductor that is currently received much attention due to its favorable high temperature behavior and high electric field breakdown strength. Unfortunately, the current state-of-the-art crystal growth and device processing methods produce material with high defect densities, resulting in a limited commercial viability

  4. Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO2

    NASA Astrophysics Data System (ADS)

    Lu, Weifang; Ou, Yiyu; Jokubavicius, Valdas; Fadil, Ahmed; Syväjärvi, Mikael; Petersen, Paul Michael; Ou, Haiyan

    2016-07-01

    Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation.

  5. Epitaxial metallic β-Nb2N films grown by MBE on hexagonal SiC substrates

    NASA Astrophysics Data System (ADS)

    Katzer, D. Scott; Nepal, Neeraj; Meyer, David J.; Downey, Brian P.; Wheeler, Virginia D.; Storm, David F.; Hardy, Matthew T.

    2015-08-01

    RF-plasma MBE was used to epitaxially grow 4- to 100-nm-thick metallic β-Nb2N thin films on hexagonal SiC substrates. When the N/Nb flux ratios are greater than one, the most critical parameter for high-quality β-Nb2N is the substrate temperature. The X-ray characterization of films grown between 775 and 850 °C demonstrates β-Nb2N phase formation. The (0002) and (21\\bar{3}1) X-ray diffraction measurements of a β-Nb2N film grown at 850 °C reveal a 0.68% lattice mismatch to the 6H-SiC substrate. This suggests that β-Nb2N can be used for high-quality metal/semiconductor heterostructures that cannot be fabricated at present.

  6. Study on the machined depth when nanoscratching on 6H-SiC using Berkovich indenter: Modelling and experimental study

    NASA Astrophysics Data System (ADS)

    Zhang, Feihu; Meng, Binbin; Geng, Yanquan; Zhang, Yong

    2016-04-01

    In order to investigate the deformation characteristics and material removing mechanism of the single crystal silicon carbide at the nanoscale, the nanoscratching tests were conducted on the surface of 6H-SiC (0 0 0 1) by using Berkovich indenter. In this paper, a theoretical model for nanoscratching with Berkovich indenter is proposed to reveal the relationship between the applied normal load and the machined depth. The influences of the elastic recovery and the stress distribution of the material are considered in the developed theoretical model. Experimental and theoretical machined depths are compared when scratching in different directions. Results show that the effects of the elastic recovery of the material, the geometry of the tip and the stress distribution of the interface between the tip and sample have large influences on the machined depth which should be considered for this kind of hard brittle material of 6H-SiC.

  7. Approaching truly freestanding graphene: the structure of hydrogen-intercalated graphene on 6H-SiC(0001).

    PubMed

    Sforzini, J; Nemec, L; Denig, T; Stadtmüller, B; Lee, T-L; Kumpf, C; Soubatch, S; Starke, U; Rinke, P; Blum, V; Bocquet, F C; Tautz, F S

    2015-03-13

    We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the (0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full (6√3×6√3)-R30° unit cell, based on a van der Waals corrected exchange correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments, a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and the lowest known adsorption energy per atom for graphene on any substrate. A structural comparison to other graphenes suggests that hydrogen-intercalated graphene on 6H-SiC(0001) approaches ideal graphene. PMID:25815955

  8. Artificial Neural Network Prediction for Thermal Decomposition of Potassium Nitrate (KNO3) and Benzoic Acid (C6H5COOH)

    NASA Astrophysics Data System (ADS)

    Beken, Murat

    The aim of this work is to correlate the results of experimental data by using the differential thermal analysis (DTA) method and predictions of artificial neural networks (ANNs). Thermal decomposition of potassium nitrate (KNO3) and benzoic acid (C6H5COOH) have been analyzed by the simultaneous DTA method. Kinetic parameters (critical points, the change of enthalpy) have been investigated. A computer model, based on multilayer feed-forwarding back-propagation is used for the prediction of critical points, phase transitions of potassium nitrate (KNO3) and benzoic acid (C6H5COOH). As a result of our study, we conclude that the ANN model shows a considerably good result about the prediction of experimental data.

  9. Electrical properties and microstructural characterization of Ni/Ta contacts to n-type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Zhou, Tian-Yu; Liu, Xue-Chao; Huang, Wei; Zhuo, Shi-Yi; Zheng, Yan-Qing; Shi, Er-Wei

    2015-12-01

    A Ni/Ta bilayer is deposited on n-type 6H-SiC and then annealed at different temperatures to form an ohmic contact. The electrical properties are characterized by I-V curve measurement and the specific contact resistance is extracted by the transmission line method. The phase formation and microstructure of the Ni/Ta bilayer are studied after thermal annealing. The crystalline and microstructure properties are analyzed by using glance incident x-ray diffraction (GIXRD), Raman spectroscopy, and transmission electron microscopy. It is found that the transformation from the Schottky to the Ohmic occurs at 1050 °C and the GIXRD results show a distinct phase change from Ta2C to TaC at this temperature. A specific contact resistance of 6.5× 10-5 Ω·cm2 is obtained for sample Ni(80 nm)/Ta(20 nm)/6H-SiC after being annealed at 1050 °C. The formation of the TaC phase is regarded as the main reason for the excellent Ohmic properties of the Ni/Ta contacts to 6H-SiC. Raman and TEM data reveal that the graphite carbon is drastically consumed by the Ta element, which can improve the contact thermal stability. A schematic diagram is proposed to illustrate the microstructural changes of Ni/Ta/6H-SiC when annealed at different temperatures. Project supported by the Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10), the Shanghai Rising-star Program, China (Grant No. 13QA1403800), the Industry-Academic Joint Technological Innovations Fund Project of Jiangsu Province, China (Grant No. BY2011119), and the National High-tech Research and Development Program of China (Grant Nos. 2013AA031603 and 2014AA032602).

  10. Explicitly correlated coupled cluster calculations for the benzenium ion (C6H7(+)) and its complexes with Ne and Ar.

    PubMed

    Botschwina, Peter; Oswald, Rainer

    2011-11-24

    Explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level (Adler, T. B.; Knizia, G.; Werner, H.-J. J. Chem. Phys. 2007, 127, 221106) has been employed in a study of the benzenium ion (C6H7(+)) and its complexes with a neon or an argon atom. The ground-state rotational constants of C6H7(+) are predicted to be A0 = 5445 MHz, B0 = 5313 MHz, and C0 = 2731 MHz. Anharmonic vibrational wavenumbers of this cation were obtained by combination of harmonic CCSD(T*)-F12a values with anharmonic contributions calculated by double-hybrid density functional theory at the B2PLYP-D level. For the complexes of C6H7(+) with Ne or Ar, the lowest energy minimum is of π-bonded structure. The corresponding dissociation energies D0 are estimated to be 160 and 550 cm(-1), respectively. There is no indication of H-bonds to the aromatic or aliphatic hydrogen atoms. Instead, three nonequivalent local energy minima were found for nuclear configurations where the rare-gas atom lies in the ring-plane and approximatly points to the center of one of the six CC bonds. PMID:21981720

  11. 3d electron transitions in Co- and Ni-doped MgSO3·6H2O

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    Absorption spectra of magnesium sulfite hexahydrate (MgSO3·6H2O), doped with Co and Ni, have been studied in the spectral region 1.46-3.1 eV. Investigations have been carried out with linear polarized light E||c, E⊥c (c is the optical axis of MgSO3·6H2O) that propagates in the (1210) direction. The Co structure manifests in the spectral region 2.06-3.1 eV and the Ni structures manifest in the spectral region 1.46-2.26 eV. The peculiarities of the Jahn-Teller effect and spin-orbit interaction with respect to the impurity ions in the crystal lattice of MgSO3·6H2O are analyzed and discussed. The electron transitions in Co2+ and Ni2+ ions are determined for E||c, E⊥c. The crystal field parameter Dq and Racah parameters B and C are also calculated.

  12. Ly6h Regulates Trafficking of Alpha7 Nicotinic Acetylcholine Receptors and Nicotine-Induced Potentiation of Glutamatergic Signaling

    PubMed Central

    Puddifoot, Clare A.; Wu, Meilin; Sung, Rou-Jia

    2015-01-01

    α7 nAChRs are expressed widely throughout the brain, where they are important for synaptic signaling, gene transcription, and plastic changes that regulate sensory processing, cognition, and neural responses to chronic nicotine exposure. However, the mechanisms by which α7 nAChRs are regulated are poorly understood. Here we show that trafficking of α7-subunits is controlled by endogenous membrane-associated prototoxins in the Ly6 family. In particular, we find that Ly6h reduces cell-surface expression and calcium signaling by α7 nAChRs. We detect Ly6h in several rat brain regions, including the hippocampus, where we find it is both necessary and sufficient to limit the magnitude of α7-mediated currents. Consistent with such a regulatory function, knockdown of Ly6h in rat hippocampal pyramidal neurons enhances nicotine-induced potentiation of glutamatergic mEPSC amplitude, which is known to be mediated by α7 signaling. Collectively our data suggest a novel cellular role for Ly6 proteins in regulating nAChRs, which may be relevant to plastic changes in the nervous system including rewiring of glutamatergic circuitry during nicotine addiction. PMID:25716842

  13. Proton Enhancement and Decreased O6+/H at the Heliospheric Current Sheet: Implications for the Origin of Slow Solar Wind

    NASA Astrophysics Data System (ADS)

    Liu, Y. C.-M.; Galvin, A. B.; Popecki, M. A.; Simunac, K. D. C.; Kistler, L.; Farrugia, C.; Lee, M. A.; Klecker, B.; Bochsler, P.; Luhmann, J. L.; Jian, L. K.; Moebius, E.; Wimmer-Schweingruber, R.; Wurz, P.

    2010-03-01

    We investigated the proton enhancement and O6+/H depletion in the vicinity of the heliospheric current sheet (HCS) using data from STEREO/PLASTIC and STEREO/IMPACT. Three HCS crossing events were studied. For the first two events, the proton enhancement and O6+/H depletion are found to lie at one edge of the HCS. The proton density has a steep slope both at the HCS and at the other boundary of the enhancement. In the third event the proton enhancement and O6+/H depletion surround the HCS and last for 8 hours while the density profile is very different from the other two events. Velocity shear is observed at the HCS for the first two events but not for the third. The enhancement of hydrogen and depletion of oxygen at the streamer belt in the solar corona have been reported using UVCS observation. A potential connection with our observations is based on the similar features observed at 1 AU. How the plasma flows out of the streamer belt, and why there are different features in HCS encounters remain open questions for future study.

  14. Ly6h regulates trafficking of alpha7 nicotinic acetylcholine receptors and nicotine-induced potentiation of glutamatergic signaling.

    PubMed

    Puddifoot, Clare A; Wu, Meilin; Sung, Rou-Jia; Joiner, William J

    2015-02-25

    α7 nAChRs are expressed widely throughout the brain, where they are important for synaptic signaling, gene transcription, and plastic changes that regulate sensory processing, cognition, and neural responses to chronic nicotine exposure. However, the mechanisms by which α7 nAChRs are regulated are poorly understood. Here we show that trafficking of α7-subunits is controlled by endogenous membrane-associated prototoxins in the Ly6 family. In particular, we find that Ly6h reduces cell-surface expression and calcium signaling by α7 nAChRs. We detect Ly6h in several rat brain regions, including the hippocampus, where we find it is both necessary and sufficient to limit the magnitude of α7-mediated currents. Consistent with such a regulatory function, knockdown of Ly6h in rat hippocampal pyramidal neurons enhances nicotine-induced potentiation of glutamatergic mEPSC amplitude, which is known to be mediated by α7 signaling. Collectively our data suggest a novel cellular role for Ly6 proteins in regulating nAChRs, which may be relevant to plastic changes in the nervous system including rewiring of glutamatergic circuitry during nicotine addiction. PMID:25716842

  15. The impact resistance of SiC and other mechanical properties of SiC and Si3N4

    NASA Technical Reports Server (NTRS)

    Bradt, R. C.

    1984-01-01

    Studies focused on the impact and mechanical behavior of SiC and Si3N4 at high temperatures are summarized. Instrumented Charpy impact testing is analyzed by a compliance method and related to strength; slow crack growth is related to processing, and creep is discussed. The transient nature of flaw populations during oxidation under load is emphasized for both SiC and Si3N4.

  16. Preflow trimethylaluminum treatment effect on GaN growth on SiC with an ultrathin interlayer

    NASA Astrophysics Data System (ADS)

    Sun, Zheng; Nagamatsu, Kentaro; Olsson, Marc; Song, Peifeng; Deki, Manato; Nitta, Shugo; Honda, Yoshio; Amano, Hiroshi

    2016-05-01

    Previously, we reported a growth method for GaN on SiC by metalorganic vapor phase epitaxy. By using a preflow trimethylaluminum treatment, the poor wetting problem of gallium on the SiC surface was alleviated, resulting in a 1.2-µm-thick crack-free GaN grown on an on-axis 6H-SiC(0001) substrate via an ultrathin AlGaN interlayer. In this study, the impact of the preflow trimethylaluminum treatment time is investigated to understand why a crack-free epilayer was realized. To demonstrate the electrical performance of devices formed by our technique, GaN/SiC vertical Schottky barrier diodes were fabricated and compared with GaN/AlN/SiC and GaN/GaN vertical Schottky barrier diodes. Compared with diodes including a high-resistance AlN interlayer, the series resistance of GaN/SiC Schottky barrier diodes incorporating the ultrathin interlayer with 5 s of TMAl treatment showed a marked reduction from 4.0 × 107 to 2.0 × 10‑1 Ω·cm2. The ultrathin interlayer growth technique is expected to be applied in future GaN/SiC hybrid high-power and high-frequency devices.

  17. Thermomechanical Performance of C and SiC Multilayer, Fiber-Reinforced, CVI SiC Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Singh, Mrityunjay

    2004-01-01

    Hybrid fiber approaches have been attempted in the past to alloy desirable properties of different fiber-types for mechanical properties, thermal stress management, and oxidation resistance. Such an approach has potential for the CrSiC and SiCrSiC composite systems. SiC matrix composites with different stacking sequences of woven C fiber (T300) layers and woven Sic fiber (Hi-NicalonTM) layers were fabricated using the standard CVI process. Delamination occurred to some extent due to thermal mismatch for all of the composites. However, for the composites with a more uniform stacking sequence, minimal delamination occurred, enabling tensile properties to be determined at room temperature and elevated temperatures (stress-rupture in air). Composites were seal-coated with a CVI SiC layer as well as a proprietary C-B-Si (CBS) layer. Definite improvement in rupture behavior was observed in air for composites with increasing SiC fiber content and a CBS layer. The results will be compared to standard C fiber reinforced CVI SiC matrix and Hi-Nicalon reinforced CVI SiC matrix composites.

  18. Total displacement functions for SiC

    NASA Astrophysics Data System (ADS)

    Weber, W. J.; Williford, R. E.; Sickafus, K. E.

    1997-04-01

    Numerical solutions for the displacement functions in SiC are determined from the coupled integro-differential equations governing the total number of type- j atoms displaced in the collision cascade initiated by a primary knock-on atom (PKA) of type- i and energy E. Atomic scattering cross sections based on either the inverse power law screening potentials or the Ziegler, Biersack, and Littmark (ZBL) universal screening potential are used in the calculation of the displacement functions. The electronic stopping powers used in the calculations are either derived from the LSS and Bethe-Bloch theories or generated from the SRIM-96 electronic stopping power data base. The displacement functions determined using LSS/Bethe-Bloch electronic stopping powers are 25 to 100% larger than the displacement functions determined using the electronic stopping powers generated by SRIM-96. The total number of displaced atoms determined numerically for each PKA type, based on ZBL scattering cross sections and SRIM-96 electronic stopping powers, is in excellent agreement, over the entire range of PKA energies (10 eV to 10 MeV), with the total number of displacements determined by full cascade Monte Carlo simulations using the TRIM code in SRIM-96.

  19. SPHERICAL INDENTATION OF SiC

    SciTech Connect

    Wereszczak, Andrew A; Johanns, Kurt E

    2007-01-01

    Instrumented Hertzian indentation testing was performed on several grades of SiCs and the results and preliminary interpretations are presented. The grades included hot-pressed and sintered compositions. One of the hot-pressed grades was additionally subjected to high temperature heat treatment to produce a coarsened grain microstructure to enable the examination of exaggerated grain size on indentation response. Diamond spherical indenters were used in the testing. Indentation load, indentation depth of penetration, and acoustic activity were continually measured during each indentation test. Indentation response and postmortem analysis of induced damage (e.g., ring/cone, radial and median cracking, quasi-plasticity) are compared and qualitatively as a function of grain size. For the case of SiC-N, the instrumented spherical indentation showed that yielding initiated at an average contact stress 12-13 GPa and that there was another event (i.e., a noticeable rate increase in compliance probably associated with extensive ring and radial crack formations) occurring around an estimated average contact stress of 19 GPa.

  20. Mechanistic Aspects of the Holmium-Mediated, Reciprocal Hydrogen/Sulfur Exchange in the Gas Phase: C6 H5 CH3 +CH2 S→C6 H5 CHS+CH4.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-03-18

    The thermal reaction of [Ho(CH2S)](+) with toluene giving rise to [C6H5CHSHo](+) and CH4 has been investigated using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry complemented by density functional theory (DFT) calculations. The high reactivity of [Ho(CH2S)](+) which is in distinct contrast with the non-reactivity of "bare" Ho(+) has its origin in the presence of a carbon-centered radical; the latter initiates hydrogen-atom abstraction from the methyl group of toluene as the first step of a sequence of hydrogen and sulfur transfer mediated by cationic holmium. PMID:26789533

  1. SiC protective coating for photovoltaic retinal prosthesis

    NASA Astrophysics Data System (ADS)

    Lei, Xin; Kane, Sheryl; Cogan, Stuart; Lorach, Henri; Galambos, Ludwig; Huie, Philip; Mathieson, Keith; Kamins, Theodore; Harris, James; Palanker, Daniel

    2016-08-01

    Objective. To evaluate plasma-enhanced, chemically vapor deposited (PECVD) amorphous silicon carbide (α-SiC:H) as a protective coating for retinal prostheses and other implantable devices, and to study their failure mechanisms in vivo. Approach. Retinal prostheses were implanted in rats sub-retinally for up to 1 year. Degradation of implants was characterized by optical and scanning electron microscopy. Dissolution rates of SiC, SiN x and thermal SiO2 were measured in accelerated soaking tests in saline at 87 °C. Defects in SiC films were revealed and analyzed by selectively removing the materials underneath those defects. Main results. At 87 °C SiN x dissolved at 18.3 ± 0.3 nm d‑1, while SiO2 grown at high temperature (1000 °C) dissolved at 0.104 ± 0.008 nm d‑1. SiC films demonstrated the best stability, with no quantifiable change after 112 d. Defects in thin SiC films appeared primarily over complicated topography and rough surfaces. Significance. SiC coatings demonstrating no erosion in accelerated aging test for 112 d at 87 °C, equivalent to about 10 years in vivo, can offer effective protection of the implants. Photovoltaic retinal prostheses with PECVD SiC coatings exhibited effective protection from erosion during the 4 month follow-up in vivo. The optimal thickness of SiC layers is about 560 nm, as defined by anti-reflective properties and by sufficient coverage to eliminate defects.

  2. SiC Homoepitaxy, Etching and Graphene Epitaxial Growth on SiC Substrates Using a Novel Fluorinated Si Precursor Gas (SiF4)

    NASA Astrophysics Data System (ADS)

    Rana, Tawhid; Chandrashekhar, M. V. S.; Daniels, Kevin; Sudarshan, Tangali

    2016-04-01

    Tetrafluorosilane (SiF4 or TFS), a novel precursor gas, has been demonstrated to perform three primary operations of silicon carbide-related processing: SiC etching, SiC epitaxial growth and graphene epitaxial growth. TFS etches SiC substrate vigorously in a H2 ambient by efficient Si removal from the surface, where SiC etch rate is a function of TFS gas concentration. In this SiC etching process, Si is removed by TFS and C is removed by H2. When propane is added to a H2 and TFS gas mixture, etching is halted and high-quality SiC epitaxy takes place in a Si droplet-free condition. TFS's ability to remove Si can also be exploited to grow epitaxial graphene in a controllable manner in an inert (Ar) ambient. Here, TFS enhances graphene growth by selective etching of Si from the SiC surface.

  3. Laser-induced fluorescence of cyclohexadienyl (c-C{sub 6}H{sub 7}) radical in the gas phase

    SciTech Connect

    Imamura, Takashi; Zhang Weijun; Horiuchi, Hiroaki; Hiratsuka, Hiroshi; Kudo, Takako; Obi, Kinichi

    2004-10-08

    A laser-induced fluorescence spectrum was observed in the 500-560 nm region when a mixture of 1,4-cyclohexadiene and oxalyl chloride was photolyzed at 193 nm. The observed excitation spectrum was assigned to the A-tilde {sup 2}A{sub 2}<-X-tilde {sup 2}B{sub 1} transition of the cyclohexadienyl radical c-C{sub 6}H{sub 7}, produced by abstraction of a hydrogen atom from 1,4-cyclohexadiene by Cl atoms. The origin of the A-tilde<-X-tilde transition of c-C{sub 6}H{sub 7} was at 18 207 cm-1. From measurements of the dispersed fluorescence spectra and ab initio calculations, the frequencies of several vibrational modes in both the ground and excited states of c-C{sub 6}H{sub 7} were determined: {nu}{sub 5}(C-H in-plane bend)=1571, {nu}{sub 8}(C-Hin-plane bend)=1174, {nu}{sub 10}(C-C-C in-plane bend)=981, {nu}{sub 12}(C-C-C in-plane bend)=559, {nu}{sub 16}(C-C-C out-of-plane bend)=375, and {nu}{sub 33}(C-C-C in-plane bend)=600 cm{sup -1} for the ground state and {nu}{sub 8}=1118, {nu}{sub 10}=967, {nu}{sub 12}=502, {nu}{sub 16}=172, and {nu}{sub 33}=536 cm{sup -1} for the excited states.

  4. Promoting scopolamine biosynthesis in transgenic Atropa belladonna plants with pmt and h6h overexpression under field conditions.

    PubMed

    Xia, Ke; Liu, Xiaoqiang; Zhang, Qiaozhuo; Qiang, Wei; Guo, Jianjun; Lan, Xiaozhong; Chen, Min; Liao, Zhihua

    2016-09-01

    Atropa belladonna is one of the most important plant sources for producing pharmaceutical tropane alkaloids (TAs). T1 progeny of transgenic A. belladonna, in which putrescine N-methyltransferase (EC. 2.1.1.53) from Nicotiana tabacum (NtPMT) and hyoscyamine 6β-hydroxylase (EC. 1.14.11.14) from Hyoscyamus niger (HnH6H) were overexpressed, were established to investigate TA biosynthesis and distribution in ripe fruits, leaves, stems, primary roots and secondary roots under field conditions. Both NtPMT and HnH6H were detected at the transcriptional level in transgenic plants, whereas they were not detected in wild-type plants. The transgenes did not influence the root-specific expression patterns of endogenous TA biosynthetic genes in A. belladonna. All four endogenous TA biosynthetic genes (AbPMT, AbTRI, AbCYP80F1 and AbH6H) had the highest/exclusive expression levels in secondary roots, suggesting that TAs were mainly synthesized in secondary roots. T1 progeny of transgenic A. belladonna showed an impressive scopolamine-rich chemotype that greatly improved the pharmaceutical value of A. belladonna. The higher efficiency of hyoscyamine conversion was found in aerial than in underground parts. In aerial parts of transgenic plants, hyoscyamine was totally converted to downstream alkaloids, especially scopolamine. Hyoscyamine, anisodamine and scopolamine were detected in underground parts, but scopolamine and anisodamine were more abundant than hyoscyamine. The exclusively higher levels of anisodamine in roots suggested that it might be difficult for its translocation from root to aerial organs. T1 progeny of transgenic A. belladonna, which produces scopolamine at very high levels (2.94-5.13 mg g(-1)) in field conditions, can provide more valuable plant materials for scopolamine production. PMID:27135818

  5. Ft-Ir Measurements of Cold Cross Sections of Benzene (C_6H_6) for Cassini/cirs

    NASA Astrophysics Data System (ADS)

    Sung, Keeyoon; Brown, Linda; Toon, Geoffrey C.

    2014-06-01

    Titan's stratosphere is abundant in hydrocarbons (CxHy) producing highly complicated and crowded features in the spectra of Cassini/CIRS. Among these, benzene (C_6H_6) is the heaviest hydrocarbon ever seen in the Titan and cold planets. For this reason, a series of pure and N_2-broadened C6H6 spectra were recorded in the 640 to 1540 wn region at gas temperatures down to 231 K using a Fourier transform spectrometer (Bruker IFS-125HR) at the Jet Propulsion Laboratory. We report temperature dependent absorption cross sections for three strong fundamental bands (νb{4}, νb{14}, νb{13}). We also derived pseudo-line parameters, which include mean intensities and effective lower state energies on a 0.005 wn frequency grid, obtained by fitting all the laboratory spectra simultaneously. For the pseudoline generation, details can be found in a JPL MK-IV website, http://mark4sun.jpl.nasa.gov/data/spec/Pseudo). The resulting pseudolines of the strong bands reproduce observed cross sections to within ˜3 %. These new results are compared to earlier work, including the C6H6+N2 spectra recorded at PNNL. S. W. Sharpe, et al., Appl Spectrosc 58, 1452-1461 (2004); C. P. Rinsland, et al. JQSRT, 109, 2511-2522 (2008). Research described in this paper was performed at the Jet Propulsion Laboratory and California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration.

  6. Synthesis, structural characterization, electrical properties and antioxidant activity of [p-(NH3)C6H4NH3]3P6O18·6H2O

    NASA Astrophysics Data System (ADS)

    Fezai, Ramzi; Mezni, Ali; Kahlaoui, Messaoud; Rzaigui, Mohamed

    2016-09-01

    Single crystals of a novel organic cyclohexaphosphate, [p-(NH3)C6H4NH3]3P6O18.6H2O, have been prepared in aqueous solution. Its crystal structure can be described by a three-dimensional framework where the P6O186- rings are interconnected by hydrogen bonds to form anionic layers between which organic cations are located. Hydrogen bonding network connecting the different components is given. The thermal stability and spectroscopic properties of this material are given too. Its DC and AC electrical conductivities, modulus analysis and dielectric constants have been investigated. The AC conductivity is found to obey the universal power law. The DC electrical conductivity indicates a semiconductor behavior. The kind of the observed conduction is protonic by translocation. X-rays structural and electrical results are correlated. This compound has also been screened for its antioxidant activity, determined in vitro, using 1,1-diphenyl-2-picrylhydrazyl, reducing power, hydroxyl scavenging ability and ferrous ion chelating (FIC) methods and with ascorbic acid as reference.

  7. Targeted ablation of the Pde6h gene in mice reveals cross-species differences in cone and rod phototransduction protein isoform inventory.

    PubMed

    Brennenstuhl, Christina; Tanimoto, Naoyuki; Burkard, Markus; Wagner, Rebecca; Bolz, Sylvia; Trifunovic, Dragana; Kabagema-Bilan, Clement; Paquet-Durand, Francois; Beck, Susanne C; Huber, Gesine; Seeliger, Mathias W; Ruth, Peter; Wissinger, Bernd; Lukowski, Robert

    2015-04-17

    Phosphodiesterase-6 (PDE6) is a multisubunit enzyme that plays a key role in the visual transduction cascade in rod and cone photoreceptors. Each type of photoreceptor utilizes discrete catalytic and inhibitory PDE6 subunits to fulfill its physiological tasks, i.e. the degradation of cyclic guanosine-3',5'-monophosphate at specifically tuned rates and kinetics. Recently, the human PDE6H gene was identified as a novel locus for autosomal recessive (incomplete) color blindness. However, the three different classes of cones were not affected to the same extent. Short wave cone function was more preserved than middle and long wave cone function indicating that some basic regulation of the PDE6 multisubunit enzyme was maintained albeit by a unknown mechanism. To study normal and disease-related functions of cone Pde6h in vivo, we generated Pde6h knock-out (Pde6h(-/-)) mice. Expression of PDE6H in murine eyes was restricted to both outer segments and synaptic terminals of short and long/middle cone photoreceptors, whereas Pde6h(-/-) retinae remained PDE6H-negative. Combined in vivo assessment of retinal morphology with histomorphological analyses revealed a normal overall integrity of the retinal organization and an unaltered distribution of the different cone photoreceptor subtypes upon Pde6h ablation. In contrast to human patients, our electroretinographic examinations of Pde6h(-/-) mice suggest no defects in cone/rod-driven retinal signaling and therefore preserved visual functions. To this end, we were able to demonstrate the presence of rod PDE6G in cones indicating functional substitution of PDE6. The disparities between human and murine phenotypes caused by mutant Pde6h/PDE6H suggest species-to-species differences in the vulnerability of biochemical and neurosensory pathways of the visual signal transduction system. PMID:25739440

  8. Behavior of Ni2+ cations in aqueous and alcohol solutions of NiCl2 · 6H2O

    NASA Astrophysics Data System (ADS)

    Petkova, P.; Nedkov, V.; Vasilev, P.; Ismailov, I.

    2014-09-01

    We have investigated the optical properties of Ni2+ cations in aqueous and alcohol solutions of NiCl2 · 6H2O at room temperature. We measured the absorption spectra of these two types of solutions in the spectral region 395-795 nm. The Racah’s parameters and the exchange integrals of the aqueous complex [Ni(H2O)6]2+ have been calculated. The parameters Dq, Dt and Ds are also calculated on the basis of our experimental data. The parameters δσ and δπ, connected with the symmetry of the complex, are determined.

  9. Angular correlation of annihilation radiation associated with vacancy defects in electron-irradiated 6H-SiC

    SciTech Connect

    Kawasuso, A.; Chiba, T.; Higuchi, T.

    2005-05-15

    Electron-positron momentum distributions associated with vacancy defects in 6H-SiC after irradiation with 2-MeV electrons and annealing at 1000 deg. C have been studied using angular correlation of annihilation radiation measurements. It was confirmed that the above vacancy defects have dangling bonds along the c axis and the rotational symmetry around it. The first-principles calculation suggested that the vacancy defects are attributable to either carbon-vacancy-carbon-antisite complexes or silicon-vacancy-nitrogen pairs, while isolated carbon vacancies, silicon vacancies, and nearest neighbor divacancies are ruled out.

  10. Infrared and polarized Raman spectra of LiNa 3(MoO 4) 2·6H 2O

    NASA Astrophysics Data System (ADS)

    Isaac, Mary; Nayar, V. U.; Makitova, D. D.; Tkachev, V. V.; Atovmjan, L. O.

    1997-05-01

    The analysis of the infrared and polarized Raman spectra of LiNa 3(MoO 4) 2·6H 2O is reported. The splitting of the nondegenerate symmetric stretching mode in all orientations confirms the presence of two crystallographically independent MoO 42- anions in the crystal. The linear distortion in MoO 4 tetrahedra is found to be greater than the angular distortion. Bands in the stretching region of water indicate the presence of crystallographically different water molecules and hydrogen bonds of varying strengths. The assignments of H 2O bands are confirmed by observing the corresponding bands in the deuterated compounds.

  11. Damage profiles and ion distribution in Pt-irradiated SiC

    NASA Astrophysics Data System (ADS)

    Xue, H. Z.; Zhang, Y.; Zhu, Z.; Zhang, W. M.; Bae, I.-T.; Weber, W. J.

    2012-09-01

    Single crystalline 6H-SiC samples were irradiated at 150 K with 2 MeV Pt ions. The local volume swelling was determined by electron energy loss spectroscopy (EELS), and a nearly sigmoidal dependence on irradiation dose is observed. The disorder profiles and ion distribution were determined by Rutherford backscattering spectrometry (RBS), transmission electron microscopy, and secondary ion mass spectrometry. Since the volume swelling reaches 12% over the damage region at high ion fluence, the effect of lattice expansion is considered and corrected for in the analysis of RBS spectra to obtain depth profiles. Projectile and damage profiles are estimated by SRIM (Stopping and Range of Ions in Matter). When compared with the measured profiles, the SRIM code predictions of ion distribution and the damage profiles are underestimated due to significant overestimation of the electronic stopping power for the slow heavy Pt ions. By utilizing the reciprocity method, which is based on the invariance of the inelastic energy loss in ion-solid collisions against interchange of projectile and target atom, a much lower electronic stopping power is deduced. A simple approach, based on reducing the density of SiC target in SRIM simulation, is proposed to compensate the overestimated SRIM electronic stopping power values, which results in improved agreement between predicted and measured damage profiles and ion ranges.

  12. Saccharomyces cerevisiae Ime2 phosphorylates Sic1 at multiple PXS/T sites but is insufficient to trigger Sic1 degradation

    PubMed Central

    Sedgwick, Chantelle; Rawluk, Matthew; Decesare, James; Raithatha, Sheetal; Wohlschlegel, James; Semchuk, Paul; Ellison, Michael; Yates, John; Stuart, David

    2006-01-01

    The initiation of DNA replication in Saccharomyces cerevisiae depends upon the destruction of the Clb–Cdc28 inhibitor Sic1. In proliferating cells Cln–Cdc28 complexes phosphorylate Sic1, which stimulates binding of Sic1 to SCFCdc4 and triggers its proteosome mediated destruction. During sporulation cyclins are not expressed, yet Sic1 is still destroyed at the G1-/S-phase boundary. The Cdk (cyclin dependent kinase) sites are also required for Sic1 destruction during sporulation. Sic1 that is devoid of Cdk phosphorylation sites displays increased stability and decreased phosphorylation in vivo. In addition, we found that Sic1 was modified by ubiquitin in sporulating cells and that SCFCdc4 was required for this modification. The meiosis-specific kinase Ime2 has been proposed to promote Sic1 destruction by phosphorylating Sic1 in sporulating cells. We found that Ime2 phosphorylates Sic1 at multiple sites in vitro. However, only a subset of these sites corresponds to Cdk sites. The identification of multiple sites phosphorylated by Ime2 has allowed us to propose a motif for phosphorylation by Ime2 (PXS/T) where serine or threonine acts as a phospho-acceptor. Although Ime2 phosphorylates Sic1 at multiple sites in vitro, the modified Sic1 fails to bind to SCFCdc4. In addition, the expression of Ime2 in G1 arrested haploid cells does not promote the destruction of Sic1. These data support a model where Ime2 is necessary but not sufficient to promote Sic1 destruction during sporulation. PMID:16776651

  13. Growth and Features of Epitaxial Graphene on SiC

    NASA Astrophysics Data System (ADS)

    Kusunoki, Michiko; Norimatsu, Wataru; Bao, Jianfeng; Morita, Koichi; Starke, Ulrich

    2015-12-01

    Recent progress of epitaxial graphene on SiC was reviewed, focusing on its growth and structural and electronic features. Homogeneous graphene can be grown on SiC(0001) on a wafer scale, however on SiC(000bar{1}) multilayer but rotationally stacked graphene with monolayer like electronic property grows. HRTEM revealed the formation mechanism and structural features of graphene on the both surfaces. The high structural and electronic quality of the grown graphene is monitored by Raman spectroscopy and magneto-transport characterization. High-resolution ARPES measurements of the electronic dispersion around the bar{text{K}}-point retrieved the ABA and ABC stacked trilayer graphene. The measurements also directly revealed that electronic structures of graphene were manipulated by transfer doping and atomic intercalation. In particular, p- and n-doped regions on a meso-scale and the p-n junctions prepared on SiC via controlling intercalation of Ge exhibited ballistic transport and Klein tunneling, which predicted novel potentials on to epitaxial graphene on SiC.

  14. Recent Developments in SiC Device Research

    NASA Astrophysics Data System (ADS)

    Harris, C. I.; Konstantinov, A. O.

    Silicon Carbide is fast emerging as a mature semiconductor. The unique combination of material properties offered by SiC will allow it to establish itself in applications where the ever dominant Si is approaching the physical (not technical) limits of it's operation. Three key areas will be explored in this paper: (i) High power electronics. SiC devices operating at several kV and capable of MW power handling will revolutionise the way electrical power is transmitted and made use of. Recent progress supported by ABB in Sweden suggests these breakthroughs will begin to play a key role soon after the turn of the century. (ii) High frequency devices made from SiC will also play an increasingly important part in the mobile telecommunication revolution in which we currently live. Northrop Grumman in the USA have demonstrated the transmission of digital TV using SiC based devices. The high power density achieved from such devices make them also suitable for base stations for mobile telephones. (iii) Finally we look at some examples of how SiC is being used to develop new types of sensors that can be used in extreme environments such as high temperatures, high pressures or corrosive environments. Feedback from such sensors is seen as essential to understanding how we effect the world around us and thereby how we can limit pollution.

  15. TRISO coated fuel particles with enhanced SiC properties

    NASA Astrophysics Data System (ADS)

    López-Honorato, E.; Tan, J.; Meadows, P. J.; Marsh, G.; Xiao, P.

    2009-07-01

    The silicon carbide (SiC) layer used for the formation of TRISO coated fuel particles is normally produced at 1500-1650 °C via fluidized bed chemical vapor deposition from methyltrichlorosilane in a hydrogen environment. In this work, we show the deposition of SiC coatings with uniform grain size throughout the coating thickness, as opposed to standard coatings which have larger grain sizes in the outer sections of the coating. Furthermore, the use of argon as the fluidizing gas and propylene as a carbon precursor, in addition to hydrogen and methyltrichlorosilane, allowed the deposition of stoichiometric SiC coatings with refined microstructure at 1400 and 1300 °C. The deposition of SiC at lower deposition temperatures was also advantageous since the reduced heat treatment was not detrimental to the properties of the inner pyrolytic carbon which generally occurs when SiC is deposited at 1500 °C. The use of a chemical vapor deposition coater with four spouts allowed the deposition of uniform and spherical coatings.

  16. Hysteresis in the Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Harder, Bryan J.; Myers, Dwight L.

    2011-01-01

    Si and SiC show both passive oxidation behavior where a protective film of SiO2 forms and active oxidation behavior where a volatile suboxide SiO(g) forms. The active-to-passive and passive-to-active oxidation transitions are explored for both Si and SiC. Si shows a dramatic difference between the P(O2) for the two transitions of 10-4 bar. The active-to-passive transition is controlled by the condition for SiO2/Si equilibrium and the passive-to-active transition is controlled by the decomposition of SiO2. In the case of SiC, the P(O2) for these transitions are much closer. The active-to-passive transition appears to be controlled by the condition for SiO2/SiC equilibrium. The passive-to-active transition appears to be controlled by the interfacial reaction of SiC and SiO2 and subsequent generation of gases at the interface which leads to scale breakdown.

  17. Research on microwave joining of SiC. Final report

    SciTech Connect

    1993-06-30

    Work on microwave joining of sintered SiC has showed that small samples could be jointed using Si interlayer (applied as pressed powder); SEM showed a smooth, homogeneous interlayer 50 {mu}m wide. Objective of this contract is to optimize these joints. Results showed that the interlayer could be reduced to 10-20 {mu}m using an oil-based slurry made from Si powder, and to less than 5 {mu}m by plasma spraying Si on one of the SiC surfaces. Direct joints were made in reaction bonded SiC, using the residual Si. Excellent joints with good mechanical properties were obtained in both small specimens and in small scale tube assemblies like in heat exchanger and radiant burner tubes. In situ reaction synthesis from powders to produce a SiC-TiC-SiC joint was demonstrated, as well feasibility of producing SiC from microwave-assisted decomposition of polymer precursors. Finally, new applicator designs, including a compound adjustable iris and a mitered bend single mode cavity, were demonstrated to provide improved heating of larger and longer specimens. This work provides the foundation for scaleup of microwave joining to SiC components for industrial applications.

  18. Modification Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1975-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was originally designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage. Modifications to the S-IC Test Stand began in 1975 to accommodate space shuttle external tank testing. This photo depicts the continuation of the modification process as of July 14, 1975. The flame deflector originally used to provide water to the 5 F-1 engines of the S-IC stage during testing has been removed.

  19. X-ray fluorescence microtomography of SiC shells

    SciTech Connect

    Ice, G.E.; Chung, J.S.; Nagedolfeizi, M.

    1997-04-01

    TRISCO coated fuel particles contain a small kernel of nuclear fuel encapsulated by alternating layers of C and SiC. The TRISCO coated fuel particle is used in an advanced fuel designed for passive containment of the radioactive isotopes. The SiC layer provides the primary barrier for radioactive elements in the kernel. The effectiveness of this barrier layer under adverse conditions is critical to containment. The authors have begun the study of SiC shells from TRISCO fuel. They are using the fluorescent microprobe beamline 10.3.1. The shells under evaluation include some which have been cycled through a simulated core melt-down. The C buffer layers and nuclear kernels of the coated fuel have been removed by laser drilling through the SiC and then exposing the particle to acid. Elements of interest include Ru, Sb, Cs, Ce and Eu. The radial distribution of these elements in the SiC shells can be attributed to diffusion of elements in the kernel during the melt-down. Other elements in the shells originate during the fabrication of the TRISCO particles.

  20. Group 11 metal chemistry of a tetradentate ligand, phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2.

    PubMed

    Ganesamoorthy, Chelladurai; Balakrishna, Maravanji S; Mague, Joel T

    2009-04-20

    The Cu(I), Ag(I), and Au(I) chemistry of a tetradentate ligand (phenylene-1,4-diaminotetra(phosphonite), p-C(6)H(4)[N{P(OC(6)H(4)OMe-o)(2)}(2)](2) (P(2)NPhiNP(2)) (1)) is described. The flexional conformations in 1 leads to interesting structural variations in transition-metal complexes. The reaction of 1 with 4 equiv of CuX (where X = Br and I) produce the tetranuclear complexes, [{Cu(2)(mu-X)(2)(NCCH(3))(2)}(2)(mu-P(2)NPhiNP(2))] (where X = Br (2) or X = I (3)) in quantitative yield. Treatment of 3 with an excess of pyridine, 2-(piperazin-1-yl)pyrimidine, and pyrazole yielded the tetra-substituted derivatives, [{Cu(2)(mu-I)(2)(L)(2)}(2)(mu-P(2)NPhiNP(2))] (where L = pyridine (4), 2-(piperazin-1-yl)pyrimidine (5), or pyrazole (6)). Similar reactions of 3 with 1,10-phenanthroline (phen) and 2,2'-bipyridine in a 1:2 molar ratio afford the disubstituted derivatives, [(Cu(2)(mu-I))(2)I(2)(phen)(2)(mu-P(2)NPhiNP(2))] (7) and [(Cu(2)(mu-I))(2)I(2)(bipy)(2)(mu-P(2)NPhiNP(2))] (8). The o-methoxyphenoxy substituents on phosphorus in complexes 5 and 7 adopt approximately parallel planar conformations and contain lattice solvents. The reaction of 3 with 1,4-diazabicyclo[2.2.2]octane (DABCO) in a 1:2 molar ratio in a dichloromethane-acetonitrile mixture leads to the formation of an ionic complex [N(CH(2)CH(2))(3)N(+)CH(2)Cl](2)[(Cu(2)(Cl)(I)(2))(2)(NCCH(3))(2)(mu-P(2)NPhiNP(2))](2-) (9), as a result of the chloromethylation of DABCO. Treatment of 1 with 4 equiv of AgClO(4) produces [{Ag(2)(mu-ClO(4))(2))(2)(C(4)H(8)O)(2)}(2)(mu-P(2)NPhiNP(2))] (10). Displacement of perchlorate ions in 10 by PhN{P(OC(6)H(4)OMe-o)(2)}(2) (PNP) or 2,2'-bipyridine yielded [(mu-PNP)(2)Ag(2)(mu-P(2)NPhiNP(2))Ag(2)(mu-PNP)(2)](ClO(4))(4) (11) and [{Ag(2)(bipy)(2)}(2)(mu-P(2)NPhiNP(2))](ClO(4))(4) (12), respectively. The similar reaction of 1 with 2 equiv of AgOTf, in the presence of 4,4'-bipyridine, gave a three-dimensional Ag(I) coordination polymer, [{Ag(2)(C(10)H(8)N(2))(2)(CH(3)CN)(2)}(2)(P(2

  1. Long-Term Observation of Triplex Surgery for Cataract after Phakic 6H Implantation for Super High Myopia

    PubMed Central

    Liu, Xin; Wang, Xiaoying; Lu, Yi; Zheng, Tianyu; Zhou, Xingtao

    2016-01-01

    Purpose. To analyze the safety, effectiveness, and stability of triplex surgery for phakic 6H anterior chamber phakic intraocular lens explantation and phacoemulsification with in-the-bag IOL implantation for super high myopia in long-term observations. Methods. This retrospective case series evaluated 16 eyes of 10 patients who underwent triplex surgery. Best corrected visual acuity (BCVA), endothelial cell density (ECD), and associated adverse events were evaluated. Results. The mean follow-up time after the triplex surgery was 46 ± 14 months. The mean logMAR BCVA was significantly improved after triplex surgery (P = 0.047). One eye developed endophthalmitis five days postoperatively and underwent pars plana vitrectomy (PPV). Five eyes with preoperative severe endothelial cell loss developed corneal decompensation and underwent keratoplasty at a mean time of 9.4 ± 2.6 months after the triplex surgery. One eye had graft failure and underwent a second keratoplasty. The eye developed rhegmatogenous retinal detachment and underwent PPV with silicone oil 18 months later. ECD before the triplex surgery was not significantly different compared with that at last follow-up (P = 0.495) apart from these five eyes. Three eyes (18.8%) developed posterior capsule opacification. Conclusions. Triplex surgery was safe and effective for phakic 6H related complicated cataracts. Early extraction before severe ECD loss is recommended. PMID:27190642

  2. [Synthesis and spectra of transition metals complexes RE3L6(NO3)6(H2O)2].

    PubMed

    Zhao, Qing-shan; Mao, Ju-lin; Zhou, Hui-liang; Hu, Qi-lin; Liu, Wan-yi

    2009-09-01

    Schiff base 4-(p-dimethylaminobenzaldehydeamino)-4H-1,2,4-triazole(L) was synthesized from 4-amino-1,2,4-triazole and p-dimethylaminobenzaldehyde using acetic acid as the catalyst. The solid complexes RE3L6(NO3)6(H2O)2 (RE = Cu, Co, Zn, Cd; x = 3-6) were synthesized with 4-(p-dimethylaminobenzaldehydeamino)-4H-1,2,4-triazole and nitrate of transition metals in ethanol and characterized by elemental analysis, infrared spectroscopy, UV spectrum, and fluorescence spectrum. Experimental results showed that the free ligand is a thermally stable material, and its ethanol solution emitted intense blue fluorescence at the peak wavelength of 416 nm. The absorption band at about 406 nm can be assigned to the intrinsic absorption of C==N. Compared with the fluorescence emission of free ligand in ethanol solution, the emission of the complex of RE3L6 (NO3)6(H2O)2 was red-shifted to 445 nm and narrow in solution. RE(II) was coordinated with N atomy of triazole in 4-(p-dimethylaminobenzaldehydeamino)-4H-1,2,4-triazole. PMID:19950662

  3. Material removal mechanism of 6H-SiC studied by nano-scratching with Berkovich indenter

    NASA Astrophysics Data System (ADS)

    Meng, Binbin; Zhang, Yong; Zhang, Feihu

    2016-03-01

    The aim of this paper was to analyze the deformation characteristics and material removal mechanism of mono-crystal silicon carbide. The nano-scratching tests were conducted on the surface of 6H-SiC (0001) by using Berkovich nano-indenter. In the presence of various characterization techniques, a variety of new achievements have been reached. Phase transformation behavior in the nano-scratching process of mono-crystal silicon carbide (6H-SiC) is revealed by using the transmission electron microscope in this work. Amorphous phase and dislocation activities are found near the surface area under the bottom of the scratch which stands as the major cause triggering the plastic removal of this material, with no other forms of crystalline structure found, by which the plastic removal mechanism of mono-crystal silicon carbide was well identified. With a crack-free surface that had been processed, the chip broke away from the bulk in the form of plastic mode, but the subsurface was covered by cracks with their lengths many times longer than the machined depth. The results of laser Raman indicated that residual amorphous phase exits in the chips under the condition of the plastic removal of this material.

  4. Solid State Reaction and Operational Stability of Ruthenium Schottky Contact-on-6H-SiC Under Argon Annealing

    NASA Astrophysics Data System (ADS)

    Munthali, Kinnock V.; Theron, Chris; Auret, F. Danie; Coelho, Sergio M. M.; Njoroge, Eric

    2015-10-01

    Thin films of ruthenium-on-6-hexagonal silicon carbide (6H-SiC) were analysed by Rutherford backscattering spectroscopy (RBS) at various annealing temperatures. Some thin film samples were also analysed by scanning electron microscope (SEM). RBS analysis indicated minimal element diffusion, and formation of ruthenium oxide after annealing at 500°C. Large-scale diffusion of ruthenium (Ru) was observed to commence at 700°C. The SEM images indicated that the as-deposited Ru was disorderly and amorphous. Annealing of the thin film improved the grain quality of Ru. The fabricated Ru-6H-SiC Schottky barrier diodes (SBD) with nickel ohmic contacts showed excellent rectifying behaviour and linear capacitance-voltage characteristics up to an annealing temperature of 900°C. The SBDs degraded after annealing at 1000°C. The degradation of the SBDs is attributed to the inter-diffusion of Ru and Si at the Schottky-substrate interface.

  5. Vibrational spectra and dispersion analysis of K2Ni(SeO4)2·6H2O Tutton salt single crystal doped with K2Ni(SO4)2·6H2O.

    PubMed

    Ivanovski, Vladimir; Mayerhöfer, Thomas G

    2013-10-01

    Dispersion analysis of the polarized IR reflectance spectra of K2Ni(SeO4)2·6H2O doped with K2Ni(SO4)2·6H2O has been performed. Vibrational parameters like oscillator strength, attenuation constant and frequency of the transversal phonons for the modes of Au symmetry type plus the orientation of the transition dipole moments for the modes of Bu symmetry type in the ac crystal plane have been obtained. The spectra-structure correlation of the H2O stretching vibrations show that bands appearing in the spectra for polarization of the external radiation oriented along the b axis are mainly due to the H2O stretching vibrations of one of the three crystallographically distinct sets of water molecules. The orientation of the transition dipoles of stretching vibrations of the selenate ion differ from the characteristic spectra of the sulfate analog in that no mutually perpendicular transition dipoles are found in the ac crystal plane. Water librational bands masked with the bands of the ν4(SO4(2-)) mode in the sulfate analog have now been unveiled and assigned. The ratio between the oscillator strength and the attenuation constant appears to be a helpful tool in the assignment of the sulfate stretching vibrations and water librations. The vibrational and orientational characteristics of the ν4(SeO4(2-)) modes were obtained. Тhe ν3(SO4(2-)) frequency region of the isomorphously isolated SO4(2-) ion in the K2Ni(SeO4)2·6H2O matrix was investigated in some detail. Contrary to the expected three, four bands can be identified. Three of them were assigned to ν3(SO4(2-)) based on the orientation of the transition dipole moments. On the basis of the IR, but also Raman spectra of the pure and mixed crystals, a discussion of the influence of the potential field and the hydrogen bonds with the change in the volume of the unit cell is given. PMID:23796943

  6. Nanocrystalline SiC and Ti3SiC2 Alloys for Reactor Materials: Thermal and Mechanical Properties

    SciTech Connect

    Henager, Charles H.; Alvine, Kyle J.; Roosendaal, Timothy J.; Shin, Yongsoon; Nguyen, Ba Nghiep; Borlaug, Brennan A.; Jiang, Weilin

    2014-04-01

    SiC-polymers (pure polycarbosilane and polycarbosilane filled with SiC-particles) are being combined with Si and TiC powders to create a new class of polymer-derived ceramics for consideration as advanced nuclear materials in a variety of applications. Compared to pure SiC these materials have increased fracture toughness with only slightly reduced thermal conductivity. Future work with carbon nanotube (CNT) mats will be introduced with the potential to increase the thermal conductivity and the fracture toughness. At present, this report documents the fabrication of a new class of monolithic polymer derived ceramics, SiC + SiC/Ti3SiC2 dual phase materials. The fracture toughness of the dual phase material was measured to be significantly greater than Hexoloy SiC using indentation fracture toughness testing. However, thermal conductivity of the dual phase material was reduced compared to Hexoloy SiC, but was still appreciable, with conductivities in the range of 40 to 60 W/(m K). This report includes synthesis details, optical and scanning electron microscopy images, compositional data, fracture toughness, and thermal conductivity data.

  7. Structural Properties of Liquid SiC during Rapid Solidification

    PubMed Central

    Yan, WanJun; Gao, TingHong; Guo, XiaoTian; Qin, YunXiang; Xie, Quan

    2013-01-01

    The rapid solidification of liquid silicon carbide (SiC) is studied by molecular dynamic simulation using the Tersoff potential. The structural properties of liquid and amorphous SiC are analyzed by the radial distribution function, angular distribution function, coordination number, and visualization technology. Results show that both heteronuclear and homonuclear bonds exist and no atomic segregation occurs during solidification. The bond angles of silicon and carbon atoms are distributed at around 109° and 120°, respectively, and the average coordination number is <4. Threefold carbon atoms and fourfold silicon atoms are linked together by six typical structures and ultimately form a random network of amorphous structure. The simulated results help understand the structural properties of liquid and amorphous SiC, as well as other similar semiconductor alloys. PMID:24288474

  8. Large And Highly Stable Structures Made Of SiC

    NASA Astrophysics Data System (ADS)

    Bougoin, M.; Lavenac, J.

    2012-07-01

    The Boostec® SiC material appears very attractive for manufacturing large space telescopes, thanks to its high specific stiffness and its thermal stability. Its physical properties are perfectly isotropic and it is remarkably more stable than the glass-ceramics in time and also against space radiations. This sintered SiC material has been fully qualified for application at cryogenic temperature. Thanks to its good mechanical strength and toughness, it can be used for making not only the mirrors but also the structure and the focal plane hardware of the optical instruments, thus making “all in SiC” and possibly “athermal” telescopes. The present paper describes the Boostec® SiC properties and then its manufacturing technology. Some examples of the structures of the Multi Spectral Imaging instruments of Sentinel-2 and also the very large Gaia one are further developed.

  9. Aspects of SiC diode assembly using Ag technology

    NASA Astrophysics Data System (ADS)

    Mysliwiec, Marcin; Guziewicz, Marek; Kisiel, Ryszard

    2013-07-01

    The aim of our paper is to consider the possibility of applying pure Ag technology for assembly of SiC Schottky diode into a ceramic package able to work at temperatures up to 350°C. Ag micropowder was used for assembly SiC structure to DBC interposer of the ceramic package. Ag wire bonds as well as flip-chip technology using Ag balls were used as material for interconnection systems. The parameters of I-V characteristics were used as a quality factor to determine the Schottky diode after hermetization into ceramic package as well as after ageing in air at 350°C in comparison with characteristics of bare SiC diode.

  10. Advanced SiC composites for fusion applications

    SciTech Connect

    Snead, L.L.; Schwarz, O.J.

    1995-04-01

    This is a short review of the motivation for and progress in the development of ceramic matrix composites for fusion. Chemically vapor infiltrated silicon carbide (SiC) composites have been fabricated from continuous fibers of either SiC or graphite and tested for strength and thermal conductivity. Of significance is the the Hi-Nicalon{trademark} SiC based fiber composite has superior unirradiated properties as compared to the standard Nicalon grade. Based on previous results on the stability of the Hi-Nicalon fiber, this system should prove more resistant to neutron irradiation. A graphite fiber composite has been fabricated with very good mechnical properties and thermal conductivity an order of magnitude higher than typical SiC/SiC composites.

  11. Synthesis and properties of porous SiC ceramics

    NASA Astrophysics Data System (ADS)

    Kiselov, V. S.; Lytvyn, P. M.; Yukhymchuk, V. O.; Belyaev, A. E.; Vitusevich, S. A.

    2010-05-01

    Porous silicon carbide (SiC) ceramics are produced using carbon matrices derived from natural wood. Such material is especially promising as it is environmentally friendly with attractive physical properties, including a high level of biocompatibility, chemical inertness, and mechanical strength. We have developed a forced impregnation process with further synthesis of SiC using natural wood as well as a variety of industrial carbon materials and compared the properties of these ceramics. The structure and composition of the materials obtained were investigated by Raman scattering spectroscopy. The hardness of the samples was estimated using the Vickers technique. It was shown that the phase composition and mechanical properties of synthesized SiC ceramics can be effectively controlled by the initial Si contents and temperature of the synthesis process. A large variety of options are demonstrated for materials development taking into account an optimal porosity selection for various practical applications.

  12. SIC-POVMS and MUBS: Geometrical Relationships in Prime Dimension

    SciTech Connect

    Appleby, D. M.

    2009-03-10

    The paper concerns Weyl-Heisenberg covariant SIC-POVMs (symmetric informationally complete positive operator valued measures) and full sets of MUBs (mutually unbiased bases) in prime dimension. When represented as vectors in generalized Bloch space a SIC-POVM forms a d{sup 2}-1 dimensional regular simplex (d being the Hilbert space dimension). By contrast, the generalized Bloch vectors representing a full set of MUBs form d+1 mutually orthogonal d-1 dimensional regular simplices. In this paper we show that, in the Weyl-Heisenberg case, there are some simple geometrical relationships between the single SIC-POVM simplex and the d+1 MUB simplices. We go on to give geometrical interpretations of the minimum uncertainty states introduced by Wootters and Sussman, and by Appleby, Dang and Fuchs, and of the fiduciality condition given by Appleby, Dang and Fuchs.

  13. SiC IR emitter design for thermophotovoltaic generators

    NASA Astrophysics Data System (ADS)

    Fraas, Lewis M.; Ferguson, Luke; McCoy, Larry G.; Pernisz, Udo C.

    1996-02-01

    An improved ceramic spine disc burner/emitter for use in a thermophotovoltaic (TPV) generator is described. A columnar infrared (IR) emitter consisting of a stack of silicon carbide (SiC) spine discs provides for both high conductance for the combustion gases and efficient heat transfer from the hot combustion gases to the emitter. Herein, we describe the design, fabrication, and testing of this SiC burner as well as the characterization of the IR spectrum it emits. We note that when the SiC column is surrounded with fused silica heat shields, these heat shields suppress the emitted power beyond 4 microns. Thus, a TPV generator using GaSb photovoltaic cells covered by simple dielectric filters can convert over 30% of the emitted IR radiation to DC electric power.

  14. Structural properties of liquid SiC during rapid solidification.

    PubMed

    Yan, WanJun; Gao, TingHong; Guo, XiaoTian; Qin, YunXiang; Xie, Quan

    2013-01-01

    The rapid solidification of liquid silicon carbide (SiC) is studied by molecular dynamic simulation using the Tersoff potential. The structural properties of liquid and amorphous SiC are analyzed by the radial distribution function, angular distribution function, coordination number, and visualization technology. Results show that both heteronuclear and homonuclear bonds exist and no atomic segregation occurs during solidification. The bond angles of silicon and carbon atoms are distributed at around 109° and 120°, respectively, and the average coordination number is <4. Threefold carbon atoms and fourfold silicon atoms are linked together by six typical structures and ultimately form a random network of amorphous structure. The simulated results help understand the structural properties of liquid and amorphous SiC, as well as other similar semiconductor alloys. PMID:24288474

  15. MD-2 as the target of a novel small molecule, L6H21, in the attenuation of LPS-induced inflammatory response and sepsis

    PubMed Central

    Wang, Yi; Shan, Xiaoou; Chen, Gaozhi; Jiang, Lili; Wang, Zhe; Fang, Qilu; Liu, Xing; Wang, Jingying; Zhang, Yali; Wu, Wencan; Liang, Guang

    2015-01-01

    Background and Purpose Myeloid differentiation 2 (MD-2) recognizes LPS, which is required for TLR4 activation, and represents an attractive therapeutic target for severe inflammatory disorders. We previously found that a chalcone derivative, L6H21, could inhibit LPS-induced overexpression of TNF-α and IL-6 in macrophages. Here, we performed a series of biochemical experiments to investigate whether L6H21 specifically targets MD-2 and inhibits the interaction and signalling transduction of LPS-TLR4/MD-2. Experimental Approach The binding affinity of L6H21 to MD-2 protein was analysed using computer docking, surface plasmon resonance analysis, elisa, fluorescence measurements and flow cytometric analysis. The effects of L6H21 on MAPK and NF-κB signalling were determined using EMSA, fluorescence staining, Western blotting and immunoprecipitation. The anti-inflammatory effects of L6H21 were confirmed using elisa and RT-qPCR in vitro. The anti-inflammatory effects of L6H21 were also evaluated in septic C57BL/6 mice. Key Results Compound L6H21 inserted into the hydrophobic region of the MD-2 pocket, forming hydrogen bonds with Arg90 and Tyr102 in the MD-2 pocket. In vitro, L6H21 subsequently suppressed MAPK phosphorylation, NF-κB activation and cytokine expression in macrophages stimulated by LPS. In vivo, L6H21 pretreatment improved survival, prevented lung injury, decreased serum and hepatic cytokine levels in mice subjected to LPS. In addition, mice with MD-2 gene knockout were universally protected from the effects of LPS-induced septic shock. Conclusions and Implications Overall, this work demonstrated that the new chalcone derivative, L6H21, is a potential candidate for the treatment of sepsis. More importantly, the data confirmed that MD-2 is an important therapeutic target for inflammatory disorders. PMID:26076332

  16. Development of CVD Mullite Coatings for SiC Fibers

    SciTech Connect

    Sarin, V.K.; Varadarajan, S.

    2000-03-15

    A process for depositing CVD mullite coatings on SiC fibers for enhanced oxidation and corrosion, and/or act as an interfacial protective barrier has been developed. Process optimization via systematic investigation of system parameters yielded uniform crystalline mullite coatings on SiC fibers. Structural characterization has allowed for tailoring of coating structure and therefore properties. High temperature oxidation/corrosion testing of the optimized coatings has shown that the coatings remain adherent and protective for extended periods. However, preliminary tests of coated fibers showed considerable degradation in tensile strength.

  17. Elastic properties of SiC nanoscopic wires

    NASA Astrophysics Data System (ADS)

    Makeev, Maxim; Menon, Madhu; Srivastava, Deepak

    2006-03-01

    Mechanical properties of crystalline and amorphous SiC nanowires have been investigated using molecular dynamics simulations with the Tersoff bond-order interatomic potential. The crystalline and a-SiC nanowires of different diameters were studied under tension/compression, torsion, and bending. The bending and torsion rigidities are found to be strongly dependent on the wire size. This is unlike the Young's modulus computed from uniaxial loading curves. Atomistic relaxations effects near the thresholds of structural stability are investigated for the four employed load types. The mechanical properties of crystalline SiC nanowires are compared with a-SiC wires of the same radii.

  18. Saturn V S-IC (First Stage) Structural Arrangement

    NASA Technical Reports Server (NTRS)

    1968-01-01

    This illustration, with callouts, shows the structural arrangement of the major components for the S-IC (first) stage of the Saturn V launch vehicle. The S-IC stage was 138 feet long and 33 feet in diameter, and produced more than 7,500,000 pounds of thrust through five F-1 engines that were powered by liquid oxygen and kerosene. Four of the engines were mounted on an outer ring and gimbal for control purposes. The fifth engine was rigidly mounted in the center. When ignited, the roar produced by the five engines equaled the sound of 8,000,000 hi-fi sets.

  19. Spin effects in thermoelectric phenomena in SiC nanoribbons.

    PubMed

    Zberecki, K; Swirkowicz, R; Wierzbicki, M; Barnaś, J

    2015-01-21

    Using ab initio methods we calculate the thermoelectric and spin thermoelectric properties of zigzag SiC nanoribbons, asymmetrically terminated with hydrogen. Such nanoribbons display a ferromagnetic ground state, with edge magnetic moments oriented in parallel. Both thermopower and spin thermopower have been determined as a function of chemical potential and temperature. To find the thermoelectric efficiency, the total heat conductance has been calculated, i.e. the electronic and phonon contributions. Numerical results for SiC nanoribbons are compared with those for graphene and silicene ones. PMID:25473937

  20. Plasma synthesis and characterization of ultrafine SiC

    SciTech Connect

    Vogt, G.J.; Phillips, D.S.; Taylor, T.N.

    1986-01-01

    Ultrafine SiC powders have been prepared by gas phase synthesis from silane and methane in an argon thermal rf-plasma. Bulk properties of the powders were determined by elemental analysis, x-ray diffractin, helium pycnometry, and BET surface area measurements. The near-surface composition and structure of the particles were examined by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). In addition to free silicon and carbon particles in the powders, free carbon and various silicon/carbon/oxygen species were found on the surface of the SiC particles.

  1. The Commercialization of the SiC Flame Sensor

    NASA Astrophysics Data System (ADS)

    Fedison, Jeffrey B.

    2002-03-01

    The technical and scientific steps required to produce large quantities of SiC flame sensors is described. The technical challenges required to understand, fabricate, test and package SiC photodiodes in 1990 were numerous since SiC device know how was embryonic. A sense of urgency for a timely replacement of the Geiger Muller gas discharge tube soon entered the scene. New dual fuel GE Power Systems gas turbines, which were designed to lean burn either natural gas or oil for low NOx emissions required a much higher sensitivity sensor. Joint work between GE CRD and Cree Research sponsored by the GE Aircraft Engine Division developed the know how for the fabrication of high sensitivity, high yield, reliable SiC photodiodes. Yield issues were uncovered and overcome. The urgency for system insertion required that SiC diode and sensor circuitry development needed to be carried out simultaneously with power plant field tests of laboratory or prototype sensor assemblies. The sensor and reliability specifications were stringent since the sensors installed on power plant turbine combustor walls are subjected to high levels of vibration, elevated temperatures, and high pressures. Furthermore a fast recovery time was required to sense flame out in spite of the fact that the amplifier circuit needed have high gain and high dynamic range. SiC diode technical difficulties were encountered and overcome. The science of hydrocarbon flames will also be described together with the fortunate overlap of the strong OH emission band with the SiC photodiode sensitivity versus wavelength characteristic. The extremely low dark current (<1pA/cm^2) afforded by the wide band gap and the 3eV sensitivity cutoff at 400nm made if possible to produce low amplifier offsets, high sensitivity and high dynamic range along with immunity to black body radiation from combustor walls. Field tests at power plants that had experienced turbine tripping, whenever oil fuel and/or oil with steam injection for

  2. Infrared absorption of C{sub 6}H{sub 5}SO{sub 2} detected with time-resolved Fourier-transform spectroscopy

    SciTech Connect

    Chu, L.-K.; Lee, Y.-P.

    2007-04-07

    C{sub 6}H{sub 5}SO{sub 2} radicals were produced upon irradiation of three flowing mixtures: C{sub 6}H{sub 5}SO{sub 2}Cl in N{sub 2}, C{sub 6}H{sub 5}Cl and SO{sub 2} in CO{sub 2}, and C{sub 6}H{sub 5}Br and SO{sub 2} in CO{sub 2}, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm{sup -1} are assigned to the SO{sub 2}-symmetric and SO{sub 2}-antisymmetric stretching modes, respectively, of C{sub 6}H{sub 5}SO{sub 2}. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C{sub 6}H{sub 5}SO{sub 2} and C{sub 6}H{sub 5}OSO. The vibrational wave numbers and IR intensities of C{sub 6}H{sub 5}SO{sub 2} agree satisfactorily with the observed new features. Rotational contours of IR spectra of C{sub 6}H{sub 5}SO{sub 2} simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO{sub 2}-symmetric stretching band is dominated by a- and c-type rotational structures and the SO{sub 2}-antisymmetric stretching band is dominated by a b-type rotational structure. When C{sub 6}H{sub 5}SO{sub 2}Cl was used as a precursor of C{sub 6}H{sub 5}SO{sub 2}, C{sub 6}H{sub 5}SO{sub 2}Cl was slowly reproduced at the expense of C{sub 6}H{sub 5}SO{sub 2}, indicating that the reaction Cl+C{sub 6}H{sub 5}SO{sub 2} takes place. When C{sub 6}H{sub 5}Br/SO{sub 2}/CO{sub 2} was used as a precursor of C{sub 6}H{sub 5}SO{sub 2}, features at 1186 and 1396 cm{sup -1} ascribable to C{sub 6}H{sub 5}SO{sub 2}Br were observed at a later period due to secondary reaction of C{sub 6}H{sub 5}SO{sub 2} with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.

  3. Infrared absorption of gaseous benzoylperoxy radical C6H5C(O)OO recorded with a step-scan Fourier-transform spectrometer.

    PubMed

    Golec, Barbara; Chen, Jin-Dah; Lee, Yuan-Pern

    2011-12-14

    A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of benzoyl radical, C(6)H(5)CO, with O(2). C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm, or from photolysis of a mixture of benzaldehyde, C(6)H(5)CHO, and Cl(2) at 355 nm. Two intense bands near 1830 and 1226 cm(-1) are assigned to the C=O stretching (ν(6)) and the C-C stretching mixed with C-H deformation (ν(13)) modes, and two weaker bands near 1187 and 1108 cm(-1) are assigned to the ν(14) (C-H deformation) and ν(16) (O-O stretching /C-H deformation) modes of C(6)H(5)C(O)OO, the benzoylperoxy radical. These observed vibrational wave numbers and relative infrared intensities agree with those reported for syn-C(6)H(5)C(O)OO isolated in solid Ar and values predicted for syn-C(6)H(5)C(O)OO with the B3LYP/cc-pVTZ method. The simulated rotational contours of the two intense bands based on rotational parameters predicted with the B3LYP∕cc-pVTZ method fit satisfactorily with experimental results. PMID:22168689

  4. Infrared absorption of gaseous benzoylperoxy radical C6H5C(O)OO recorded with a step-scan Fourier-transform spectrometer

    NASA Astrophysics Data System (ADS)

    Golec, Barbara; Chen, Jin-Dah; Lee, Yuan-Pern

    2011-12-01

    A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of benzoyl radical, C6H5CO, with O2. C6H5CO was produced either from photolysis of acetophenone, C6H5C(O)CH3, at 248 nm, or from photolysis of a mixture of benzaldehyde, C6H5CHO, and Cl2 at 355 nm. Two intense bands near 1830 and 1226 cm-1 are assigned to the C=O stretching (ν6) and the C-C stretching mixed with C-H deformation (ν13) modes, and two weaker bands near 1187 and 1108 cm-1 are assigned to the ν14 (C-H deformation) and ν16 (O-O stretching /C-H deformation) modes of C6H5C(O)OO, the benzoylperoxy radical. These observed vibrational wave numbers and relative infrared intensities agree with those reported for syn-C6H5C(O)OO isolated in solid Ar and values predicted for syn-C6H5C(O)OO with the B3LYP/cc-pVTZ method. The simulated rotational contours of the two intense bands based on rotational parameters predicted with the B3LYP/cc-pVTZ method fit satisfactorily with experimental results.

  5. 6H hexagonal structure of low loss Ba{sub 3}MTiWO{sub 9} (M = Mg, Zn) dielectrics

    SciTech Connect

    Khalyavin, D.D.

    2007-01-18

    The crystal structure of Ba{sub 3}MTiWO{sub 9} (M = Mg, Zn) oxides has been found to be 6H hexagonal, space group P6{sub 3}/mmc, parameters of unit cell: a = 5.7943(1) A, c = 14.1642(1) A and a = 5.7993(1) A, c = 14.1626(1) A for M = Mg and Zn, respectively. The tungsten and titanium atoms are randomly distributed in pairs of face-sharing octahedra separated by octahedral layers containing magnesium or zinc. It was revealed that the structures are well ordered which is believed to result in a low dielectric loss at a microwave frequency reported for these materials.

  6. Disodium hydrogen citrate sesquihydrate, Na2HC6H5O7(H2O)1.5

    PubMed Central

    Rammohan, Alagappa; Sarjeant, Amy A.; Kaduk, James A.

    2016-01-01

    The crystal structure of disodium hydrogen citrate sesquihydrate, 2Na2 +·C6H6O7 2−·1.5H2O, has been solved and refined using laboratory X-ray single-crystal diffraction data, and optimized using density functional techniques. The asymmetric unit contains two independent hydrogen citrate anions, four sodium cations and three water molecules. The coordination polyhedra of the cations (three with a coordination number of six, one with seven) share edges to form isolated 8-rings. The un-ionized terminal carb­oxy­lic acid groups form very strong hydrogen bonds to non-coordinating O atoms, with O⋯O distances of 2.46 Å. PMID:27555936

  7. Internal motion and its pressure dependence in FeSiF6+6/H2O/.

    NASA Technical Reports Server (NTRS)

    Vaughan, R. W.; Nicolaides, G. L.; Elleman, D. D.

    1972-01-01

    Both wideline and pulsed NMR techniques were used to examine the internal motion in FeSiF6+6(H2O). Corrections of second moments for bulk paramagnetic effects were essential. At room temperature and pressure, the fluorine-fluorine contribution to the 19F second moment is 0.38 (plus or minus 0.06) G2, and indicates rapid orientation of the SiF6(--) group. Analysis of the second moment within the transition region allows calculation of an activation volume which is 2.4 (plus or minus 0.4) % of the molar volume. The application of pressure slows the internal motion such that the rigid lattice values of the 19F second moment are obtained above 50 kbar.

  8. Deformation behaviour and 6H-LPSO structure formation at nanoindentation in lamellar high Nb containing TiAl alloy

    NASA Astrophysics Data System (ADS)

    Song, L.; Xu, X. J.; Peng, C.; Wang, Y. L.; Liang, Y. F.; Shang, S. L.; Liu, Z. K.; Lin, J. P.

    2015-02-01

    Microstructure and deformation mechanisms at a nanoindentation in the lamellar colony of high Nb containing TiAl alloy have been studied using the focused ion beam and the transmission electron microscopy. Considerable deformation twins are observed around the nanoindentation, and a strain gradient is generated. A continuous change in the bending angle of the lamellar structure can be derived, and a strain-induced grain refinement process is observed as various active deformations split the γ grains into subgrains. In addition to all possible deformation mechanisms (ordinary dislocation, super-dislocation and deformation twining) activated due to the heavy plastic deformation, a 6-layer hexagonal (6H) long-period stacking ordered structure is identified for the first time near the contact zone and is thought to be closely related to the glide of partial dislocations.

  9. Stable Electrical Operation of 6H-SiC JFETs and ICs for Thousands of Hours at 500 C

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Chen, Liang-Yu; Beheim, Glenn M.; Okojie, Robert S.; Chang, Carl W.; Meredith, Roger D.; Ferrier, Terry L.; Evans, Laura J.; Krasowski, Michael J.; Prokop, Norman F.

    2008-01-01

    The fabrication and testing of the first semiconductor transistors and small-scale integrated circuits (ICs) to achieve up to 3000 h of stable electrical operation at 500 C in air ambient is reported. These devices are based on an epitaxial 6H-SiC junction field-effect transistor process that successfully integrated high temperature ohmic contacts, dielectric passivation, and ceramic packaging. Important device and circuit parameters exhibited less than 10% of change over the course of the 500 C operational testing. These results establish a new technology foundation for realizing durable 500 C ICs for combustion-engine sensing and control, deep-well drilling, and other harsh-environment applications.

  10. Disodium hydrogen citrate sesquihydrate, Na2HC6H5O7(H2O)1.5.

    PubMed

    Rammohan, Alagappa; Sarjeant, Amy A; Kaduk, James A

    2016-07-01

    The crystal structure of disodium hydrogen citrate sesquihydrate, 2Na2 (+)·C6H6O7 (2-)·1.5H2O, has been solved and refined using laboratory X-ray single-crystal diffraction data, and optimized using density functional techniques. The asymmetric unit contains two independent hydrogen citrate anions, four sodium cations and three water molecules. The coordination polyhedra of the cations (three with a coordination number of six, one with seven) share edges to form isolated 8-rings. The un-ionized terminal carb-oxy-lic acid groups form very strong hydrogen bonds to non-coordinating O atoms, with O⋯O distances of 2.46 Å. PMID:27555936

  11. Improved interfacial properties of SiO2 grown on 6H-SiC in diluted NO

    NASA Astrophysics Data System (ADS)

    Lai, P. T.; Xu, J. P.; Li, C. X.; Chan, C. L.

    2005-06-01

    The interface quality and reliability of gate oxides grown on n-/p-type 6H-SiC in diluted NO gas at 1150 °C are investigated. As compared to conventional 100%-NO oxidation, the diluted-NO (50% and 23%) oxidations lead to lower interface-state, border-trap and oxide-charge densities. This is attributed to the fact that carbon-accumulation and carbon-removal rates are closer when oxidation is performed in diluted NO, giving a smoother, less disordered and strained interface. Moreover, less degradation of the diluted-NO samples than 100%-NO samples is observed during high-field stressing (±7 MV/cm), indicating that stronger Si≡N bonds are created near/at the SiC/SiO2 interface for oxide grown in diluted NO ambient.

  12. Surface coating of ZnO nanoparticles onto 6H-SiC(0001): Temperature-dependent rectifying behavior

    NASA Astrophysics Data System (ADS)

    Soylu, Murat

    2016-04-01

    This work reports on the detailed analysis of the temperature-dependent electrical parameters of the ZnO/6H-SiC barrier diodes. The effect of light on the diode current was also examined. It was found that the diode showed low sensitivity to light. No remarkable change in diode characteristics were observed at room temperature. The structure has a high rectification ratio of 1.096×104 at ±2 V with ideality factor of 2.46 at room temperature. The rectification ratio (RR) decreases with increasing temperature, as agree to other heterojunction structures. Some diode parameters such as zero-bias barrier height and ideality factor as temperature-dependent were calculated on the basis of the thermionic emission (TE) theory, by considering a Gaussian distribution (GD).

  13. High power operation of a nitrogen doped, vanadium compensated, 6H-SiC extrinsic photoconductive switch

    SciTech Connect

    Sullivan, J. S.

    2014-04-28

    We report the high power operation of nitrogen doped, vanadium compensated, 6H-SiC, extrinsic photoconductive switches with improved vanadium and nitrogen dopant density. Photoconductive switching tests are performed on 1 mm thick, m-plane, switch substrates at switch voltage and currents up to 17 kV and 1.5 kA, respectively. Sub-ohm minimum switch on resistance is achieved for peak optical intensities ≥35 MW/cm{sup 2} at 532 nm applied to the switch facet. A reduction of greater than nine orders of magnitude is observed in switch material resistivity between dark and illuminated states.

  14. Photoelectron spectroscopy study of AlN films grown on n-type 6H-SiC by MOCVD

    NASA Astrophysics Data System (ADS)

    Liang, F.; Chen, P.; Zhao, D. G.; Jiang, D. S.; Zhao, Z. J.; Liu, Z. S.; Zhu, J. J.; Yang, J.; Liu, W.; He, X. G.; Li, X. J.; Li, X.; Liu, S. T.; Yang, H.; Liu, J. P.; Zhang, L. Q.; Zhang, Y. T.; Du, G. T.

    2016-09-01

    Photoelectron spectroscopy has been employed to analyze the content and chemical states of the elements on the surface of AlN films with different thickness, which are synthesized by metalorganic chemical vapor deposition on the n-type SiC substrates under low pressure. It is found that, besides the carbon and gallium on the AlN surface, the atom percentage of surface oxygen increases from 4.9 to 8.4, and the electron affinity also increases from 0.36 to 0.97 eV, when the thickness of AlN films increase from 50 to 400 nm. Furthermore, accompanying with the high-resolution XPS spectra of the O 1s, it is speculated that surface oxygen may be the major influence on the electron affinity, where the surface oxygen changes the surface chemical states through replacing N to form Al-O bond and Ga-O bond, although there are also a few of Ga and C contaminations in the chemical sate of Ga-O and C-C, respectively.

  15. Fe Isotopic Composition of Presolar SiC Mainstream Grains

    NASA Technical Reports Server (NTRS)

    Tripa, C. E.; Pellin, M. J.; Savina, M. R.; Davis, A. M.; Lewis, R. S.; Clayton, R. N.

    2002-01-01

    Iron isotopic distribution was measured in SiC mainstream grains from the Murchison meteorite by time-of-flight resonance ionization mass spectrometry. All grains exhibit 54Fe depletions of 50 to 200, lower than what are predicted by calculations of s-process nucleosynthesis in AGB stars. Additional information is contained in the original extended abstract.

  16. Development of SiC Mirror for ASTRO-F

    NASA Astrophysics Data System (ADS)

    Kaneda, H.; Onaka, T.; Yamashiro, R.

    2000-12-01

    The development of the light-weight silicon carbide mirrors for the ASTRO-F mission is described in this paper. These mirrors are made of a sandwich-type SiC material, consisting of light porous core and dense CVD (chemical vapor deposition) coat of SiC. The primary mirror has a diameter of 710 mm and weighs only 11 kg. Combined with the secondary mirror of the same type, they form Ritchey-Chretien type telescope (F/6), which is cooled down to 5.8 K. Fabrication of the small-scale test SiC mirror has been successful which shows very little deformation of the figure at liquid-helium temperatures. Another type of the SiC coated mirror has been tested which has the same size as flight model, but of which core is made of graphite. At present, polishing of the flight-model primary mirror is going on. Construction of the flight model telescope system will be finished in 2001.

  17. Saturn V Stage I (S-IC) Overview

    NASA Technical Reports Server (NTRS)

    Interbartolo, Michael

    2009-01-01

    Objectives include: a) Become familiar with the Saturn V Stage I (S-IC) major structural components: Forward Skirt, Oxidizer Tank, Intertank, Fuel Tank, and Thrust Structure. b) Gain a general understanding of the Stage I subsystems: Fuel, Oxidizer, Instrumentation, Flight Control, Environmental Control, Electrical, Control Pressure, and Ordinance.

  18. Observations of Ag diffusion in ion implanted SiC

    DOE PAGESBeta

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Jerry L. Hunter, Jr.; Giordani, Andrew J.; Allen, Todd R.

    2015-03-17

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500–1625°C, were investigated in this study by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated,more » including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Lastly, estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.« less

  19. Towards SiC Surface Functionalization: An Ab Initio Study

    SciTech Connect

    Cicero, G; Catellani, A

    2005-01-28

    We present a microscopic model of the interaction and adsorption mechanism of simple organic molecules on SiC surfaces as obtained from ab initio molecular dynamics simulations. Our results open the way to functionalization of silicon carbide, a leading candidate material for bio-compatible devices.

  20. -SiC nanocomposite coatings synthesized by co-electrodeposition

    NASA Astrophysics Data System (ADS)

    Masoudi, Mehran; Hashim, Mansor; Kamari, Halimah Mohamed

    2014-08-01

    In the present work, Ni-Al2O3, Ni-SiC and novel Ni-Al2O3-SiC metal matrix composite (MMC) coatings were electrodeposited onto pure copper samples using a modified Watt's nickel electroplating bath containing nano alumina and silicon carbide particles with an average particle size of 50 nm. The composition, crystalline structure and surface morphology of the deposits were characterized by X-ray diffractometry (XRD), energy-dispersive X-ray spectroscopy (EDS) and field emission scanning electron microscopy (FESEM). The results indicated that Ni-Al2O3-SiC hybrid composite films with an acceptable homogeneity and granular structure having 9.2 and 7.7 % vol. Al2O3 and SiC nanoparticles, respectively were developed successfully. The nanoparticles incorporated in the nickel layer effectively increased the micro hardness and wear resistance owing to dispersion and grain-refinement strengthening, changing the nickel matrix morphology as well as the texture and preferred grain growth direction from <100> to the close-packed <111>. The oxidation resistance of the Ni-Al2O3-SiC hybrid composite coatings was measured to be approximately 41 % greater than the unreinforced Ni deposit and almost 30 % better than the Ni-Al2O3 composite coatings.

  1. Optimizing Graphene Morphology on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Hannon, James

    2009-03-01

    Many schemes to integrate graphene with microelectronics assume that reliable wafer-scale synthesis processes will be developed. One promising route to wafer-scale synthesis is to form graphene overlayers from the decomposition of SiC at high temperature. We have shown that, even at 1200 C, limited diffusion at the SiC surface leads to pit formation and a non-uniform graphene film thickness [1]. In this talk I will describe our efforts to improve both graphene domain size and thickness uniformity. One way we achieve this is by forming graphene in a background pressure of disilane, which hinders SiC decomposition. Even in rather low Si partial pressures (e.g. 1e-5 Torr), the SiC decomposition temperature can shifted several hundred degrees higher in temperature [2]. Using in situ low-energy electron microscopy (LEEM), we show that this effect can be exploited to form large graphene domains (larger than 10 um) with controlled layer thickness (e.g. 1 ML). Work performed in collaboration with R.M. Tromp. [4pt] [1] J.B. Hannon and R.M. Tromp, Phys. Rev. B77, 241404(R) 2008[0pt] [2] R.M. Tromp and J.B. Hannon, in press.

  2. Fission-product SiC reaction in HTGR fuel

    SciTech Connect

    Montgomery, F.

    1981-07-13

    The primary barrier to release of fission product from any of the fuel types into the primary circuit of the HTGR are the coatings on the fuel particles. Both pyrolytic carbon and silicon carbide coatings are very effective in retaining fission gases under normal operating conditions. One of the possible performance limitations which has been observed in irradiation tests of TRISO fuel is chemical interaction of the SiC layer with fission products. This reaction reduces the thickness of the SiC layer in TRISO particles and can lead to release of fission products from the particles if the SiC layer is completely penetrated. The experimental section of this report describes the results of work at General Atomic concerning the reaction of fission products with silicon carbide. The discussion section describes data obtained by various laboratories and includes (1) a description of the fission products which have been found to react with SiC; (2) a description of the kinetics of silicon carbide thinning caused by fission product reaction during out-of-pile thermal gradient heating and the application of these kinetics to in-pile irradiation; and (3) a comparison of silicon carbide thinning in LEU and HEU fuels.

  3. First principle identification of SiC monolayer as an efficient catalyst for CO oxidation

    SciTech Connect

    Sinthika, S. E-mail: sinthika90@gmail.com; Thapa, Ranjit E-mail: sinthika90@gmail.com; Reddy, C. Prakash

    2015-06-24

    Using density functional theory, we investigated the electronic properties of SiC monolayer and tested its catalytic activity toward CO oxidation. The planar nature of a SiC monolayer is found to stable and is a high band gap semiconductor. CO interacts physically with SiC surface, whereas O{sub 2} is adsorbed with moderate binding. CO oxidation on SiC monolayer prefers the Eley Rideal mechanism over the Langmuir Hinshelwood mechanism, with an easily surmountable activation barrier during CO{sub 2} formation. Overall metal free SiC monolayer can be used as efficient catalyst for CO oxidation.

  4. First principle identification of SiC monolayer as an efficient catalyst for CO oxidation

    NASA Astrophysics Data System (ADS)

    Sinthika, S.; Reddy, C. Prakash; Thapa, Ranjit

    2015-06-01

    Using density functional theory, we investigated the electronic properties of SiC monolayer and tested its catalytic activity toward CO oxidation. The planar nature of a SiC monolayer is found to stable and is a high band gap semiconductor. CO interacts physically with SiC surface, whereas O2 is adsorbed with moderate binding. CO oxidation on SiC monolayer prefers the Eley Rideal mechanism over the Langmuir Hinshelwood mechanism, with an easily surmountable activation barrier during CO2 formation. Overall metal free SiC monolayer can be used as efficient catalyst for CO oxidation.

  5. Fabrication And Evaluation Of Sic/Sic Tubes With Various Fiber Architectures

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; DiCarlo, J. A.; Fox, D. S.

    2003-01-01

    SiC/SiC composites are excellent material candidates for high temperature applications where the performance requirements are high strength, high creep-rupture resistance, high environmental durability, and high thermal conductivity. In the past, the NASA UEET program has demonstrated fabrication of high-performance SiC/SiC flat panels reinforced by Sylramic-iBN SiC fibers. Currently NASA UEET is scaling up this SiC/SiC system by fabrication of more complex shaped components using the same fiber type. This paper reports the effects of various fiber architectures on the processing, mechanical, and durability behavior of small-diameter 0.5" ID SiC/SiC tubes, which are potential sub-elements for leading edges and cooling channels in turbine vanes and blades. Nine different fiber architectures were utilized for construction of seamless tube preforms, from simple 2D jelly-rolling to complex braiding, pin-weaving, filament-winding and 3D orthogonal weaving with approximately 5% fibers in the thru-thickness direction. Using the BN interphase and Sic matrix processing steps established for the flat panels, SiC/SiC tubes were fabricated with wall thicknesses of approximately 60 mils and total fiber fractions of approximately 35%. The "D" split ring tests for hoop tensile properties, micro-structural examinations for relationship between fiber architecture formation and matrix infiltration, and the low-pressure burner rig tests for the high temperature durability under thru-thickness thermal gradient were conducted. The better matrix infiltration and higher hoop strength were achieved using the tri-axial braided and the three-float pin woven SiC/SiC tubes. In general, it needs not only higher hoop direction fibers but also axial direction fibers for the higher hoop strength and the better infiltration, respectively. These results are analyzed to offer general guidelines for selecting fiber pre-form architectures and SiC/SiC processes that maximize tube hoop strength, thru

  6. Improved BN Coatings on SiC Fibers in SiC Matrices

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Bhatt, Ramakrishna; Yun, Hee-Mann; DiCarlo, James A.

    2004-01-01

    Modifications of BN-based coatings that are used as interfacial layers between the fibers and matrices of SiCfiber/SiC-matrix composite materials have been investigated to improve the thermomechanical properties of these materials. Such interfacial coating layers, which are also known as interphases (not to be confused with interphase in the biological sense), contribute to strength and fracture toughness of a fiber/matrix composite material by providing for limited amounts of fiber/matrix debonding and sliding to absorb some of the energy that would otherwise contribute to the propagation of cracks. Heretofore, the debonding and sliding have been of a type called inside debonding because they have taken place predominantly on the inside surfaces of the BN layers that is, at the interfaces between the SiC fibers and the interphases. The modifications cause the debonding and sliding to include more of a type, called outside debonding, that takes place at the outside surfaces of the BN layers that is, at the interfaces between the interphases and the matrix (see figure). One of the expected advantages of outside debonding is that unlike in inside debonding, the interphases would remain on the crack-bridging fibers. The interphases thus remaining should afford additional protection against oxidation at high temperature and should delay undesired fiber/fiber fusion and embrittlement of the composite material. A secondary benefit of outside debonding is that the interphase/matrix interfaces could be made more compliant than are the fiber/interphase interfaces, which necessarily incorporate the roughness of the SiC fibers. By properly engineering BN interphase layers to favor outside debonding, it should be possible, not only to delay embrittlement at intermediate temperatures, but also to reduce the effective interfacial shear strength and increase the failure strain and toughness of the composite material. Two techniques have been proposed and partially experimentally

  7. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the progress of the S-IC test stand as of October 22, 1963. Spherical liquid hydrogen tanks can be seen to the left. Just to the lower front of those are the cylindrical liquid oxygen (LOX) tanks.

  8. Construction Progress of the S-IC Test Stand Towers

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph, taken April 4, 1963, gives a close up look at the ever-growing four towers of the S-IC Test Stand.

  9. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph taken March 29, 1963, gives a close up look at two of the ever-growing four towers of the S-IC Test Stand.

  10. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the progress of the S-IC test stand as of October 10, 1963. Spherical liquid hydrogen tanks can be seen to the left.

  11. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the progress of the S-IC test stand as of November 20, 1963.

  12. Construction Progress of S-IC Test Stand Towers

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph taken April 17, 1963, gives a look at the four tower legs of the S-IC test stand at their completed height.

  13. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the progress of the S-IC test stand as of October 10, 1963. Kerosene storage tanks can be seen to the left.

  14. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph taken February 25, 1963, gives a close up look at two of the ever-growing four towers of the S-IC Test Stand.

  15. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph, taken May 7, 1963, gives a close look at the four concrete tower legs of the S-IC test stand at their completed height.

  16. Construction Progress of the S-IC Test Stand Tower

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photograph, taken from ground level on May 7, 1963, gives a close look at one of the four towers legs of the S-IC test stand nearing its completed height.

  17. Effects of Irradiation and Post-Irradiation Annealing on the Thermal Conductivity/ Diffusivity of Monolithic SIC and SIC/SIC Composites

    SciTech Connect

    Youngblood, Gerald E.; Senor, David J.; Jones, Russell H.

    2004-08-01

    Laser flash thermal diffusivity measurements were made on high-purity monolithic CVD-SiC (impurity concentration <5 wppm) and 2D f-SiC/PyC/ICVI-SiC composite samples (plain weave Hi-Nicalon (Trademark) fabric layers with 0-90 layup made by the isothermal chemical vapor infiltration process and with either a “thick” 1.0 µm or a “thin” 0.11 µm PyC fiber coating) before and after irradiation in the HFIR reactor (250 to 800°C, 4-8 dpa-SiC) and after post-irradiation annealing composite samples to 1200°C. Thermal conductivity in SiC is controlled by phonon transport. Point defects introduced into SiC during neutron irradiation are effective scattering centers for phonons, and as a consequence the thermal conductivity is sharply reduced. For irradiation temperatures below ~800°C, the accumulation of point defects (in SiC mostly single or small clusters of interstitials and isolated vacancies) saturates when the interstitial-vacancy recombination rate equals the defect production rate. For saturation conditions, the relative reduction in the SiC thermal conductivity decreases in a manner similar to its swelling reduction with increasing irradiation temperature. Examination of SiC swelling data at various irradiation temperatures and doses indicates that saturation occurs for ~2 dpa-SiC at 200°C and decreases continuously to ~0.4 dpa-SiC at 800°C. Based on a model that assumes a uniform distribution of the phonon scattering defects, the calculated defect concentration for unirradiated CVD-SiC was less than 1 appm, which is consistent with the manufacturer’s value of <5 wppm impurities. The defect concentrations estimated for the irradiated CVD-SiC samples decreased continuously from ~25,000 to 940 appm as the irradiation temperature increased from 252 to 800°C. The small intrinsic defect concentration in comparison to the rather large extrinsic irradiation-induced defect concentrations illustrates why CVD-SiC makes an ideal irradiation damage monitor.

  18. Influence of defects in SiC (0001) on epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Guo, Yu; Guo, Li-Wei; Lu, Wei; Huang, Jiao; Jia, Yu-Ping; Sun, Wei; Li, Zhi-Lin; Wang, Yi-Fei

    2014-08-01

    Defects in silicon carbide (SiC) substrate are crucial to the properties of the epitaxial graphene (EG) grown on it. Here we report the effect of defects in SiC on the crystalline quality of EGs through comparative studies of the characteristics of the EGs grown on SiC (0001) substrates with different defect densities. It is found that EGs on high quality SiC possess regular steps on the surface of the SiC and there is no discernible D peak in its Raman spectrum. Conversely, the EG on the SiC with a high density of defects has a strong D peak, irregular stepped morphology and poor uniformity in graphene layer numbers. It is the defects in the SiC that are responsible for the irregular stepped morphology and lead to the small domain size in the EG.

  19. Nonlinear thermal lens signal of the (Δυ = 6) C-H vibrational overtone of C6H6 in liquid solutions of n-C6H14 and CCl4

    NASA Astrophysics Data System (ADS)

    Nyaupane, Parashu R.; Diez-y-Riega, Helena; Camejo, David; Manzanares, Carlos E.

    2016-05-01

    The thermal lens technique is applied to vibrational overtone spectroscopy of solutions of benzene. The pump and probe thermal lens technique has been found to be very sensitive for detecting samples of low concentration in transparent solvents. The C-H fifth vibrational (Δ υ = 6) overtone spectrum of benzene is detected at room temperature for compositions per volume in the range (1 to 1 × 10-4) using CCl4 and n-C6H14 as solvents. By detecting the absorption band in a 100-ppm solution, the peak absorption of the signal is approximately (2.2 ± 0.3) × 10-7 cm-1. The parameters that determine the magnitude of the thermal lens signal such as the pump laser power and the thermodynamic properties of the solvent and solute are discussed. A plot of normalized integrated intensity as a function of composition of benzene in solution reveals a nonlinear behavior. The nonlinearity cannot be explained assuming solvent enhancement at low concentrations. A two-color absorption model that includes the simultaneous absorption of the pump and probe lasers explains the enhanced magnitude and the nonlinear behavior of the thermal lens signal for solutions of composition below 0.01.

  20. Dimetallaborane analogues of the octaboranes of the type Cp2M2B6H10: structural variations with changes in the skeletal electron count.

    PubMed

    Brânzanic, Adrian M V; Lupan, Alexandru; King, R Bruce

    2016-05-31

    The structures and energetics of the complete series of hydrogen-rich dimetallaboranes Cp2M2B6H10 and Cp*2M2B6H10 (Cp = η(5)-C5H5; Cp* = η(5)-Me5C5; M = Pd, Pt; Rh, Ir; Ru, Os; Re; Mo, W; Ta), including the experimentally known Cp*2Rh2B6H10 and Cp*2W2B6H10 (Cp* = η(5)-Me5C5), have been investigated by density functional theory. The lowest energy structures of the hyperelectronic Cp2M2B6H10 (M = Pd, Pt; Rh, Ir) systems have central M2B6 frameworks with a hexagonal open face similar to the B8 networks in arachno-B8H14 and nido-B8H12. The two lowest energy structures for Cp2Rh2B6H10 and Cp*2Rh2B6H10, lying within 1 kcal mol(-1) of energy, differ only in the locations of the bridging hydrogen atoms around the hexagonal hole consistent with the experimentally observed fluxionality of the hydrogen atoms in Cp*2Rh2B6H10. Most of the lowest energy Cp2M2B6H10 (M = Ru, Os) structures also have a central M2B6 framework similar to B8H12, typically with such additional features as an additional metal-metal bond or a formal metal-metal double bond. A common motif for the low-energy structures of the hypoelectronic Cp2M2B6H10 (M = Re; Mo, W; Ta) systems, including the experimentally known Cp*2W2B6H10, is a central M2B4 octahedron with its two M2B faces capped by the remaining boron atoms and with four M-B edges bridged by hydrogen atoms. Such structures can also be considered as oblatonido structures derived from the experimentally known 9-vertex oblatocloso Cp*2Re2B7H7 structure by removal of the unique degree 4 vertex atom. PMID:27186632

  1. Targeted Ablation of the Pde6h Gene in Mice Reveals Cross-species Differences in Cone and Rod Phototransduction Protein Isoform Inventory*

    PubMed Central

    Brennenstuhl, Christina; Tanimoto, Naoyuki; Burkard, Markus; Wagner, Rebecca; Bolz, Sylvia; Trifunovic, Dragana; Kabagema-Bilan, Clement; Paquet-Durand, Francois; Beck, Susanne C.; Huber, Gesine; Seeliger, Mathias W.; Ruth, Peter; Wissinger, Bernd; Lukowski, Robert

    2015-01-01

    Phosphodiesterase-6 (PDE6) is a multisubunit enzyme that plays a key role in the visual transduction cascade in rod and cone photoreceptors. Each type of photoreceptor utilizes discrete catalytic and inhibitory PDE6 subunits to fulfill its physiological tasks, i.e. the degradation of cyclic guanosine-3′,5′-monophosphate at specifically tuned rates and kinetics. Recently, the human PDE6H gene was identified as a novel locus for autosomal recessive (incomplete) color blindness. However, the three different classes of cones were not affected to the same extent. Short wave cone function was more preserved than middle and long wave cone function indicating that some basic regulation of the PDE6 multisubunit enzyme was maintained albeit by a unknown mechanism. To study normal and disease-related functions of cone Pde6h in vivo, we generated Pde6h knock-out (Pde6h−/−) mice. Expression of PDE6H in murine eyes was restricted to both outer segments and synaptic terminals of short and long/middle cone photoreceptors, whereas Pde6h−/− retinae remained PDE6H-negative. Combined in vivo assessment of retinal morphology with histomorphological analyses revealed a normal overall integrity of the retinal organization and an unaltered distribution of the different cone photoreceptor subtypes upon Pde6h ablation. In contrast to human patients, our electroretinographic examinations of Pde6h−/− mice suggest no defects in cone/rod-driven retinal signaling and therefore preserved visual functions. To this end, we were able to demonstrate the presence of rod PDE6G in cones indicating functional substitution of PDE6. The disparities between human and murine phenotypes caused by mutant Pde6h/PDE6H suggest species-to-species differences in the vulnerability of biochemical and neurosensory pathways of the visual signal transduction system. PMID:25739440

  2. Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(═O).

    PubMed

    Sebbar, Nadia; Bozzelli, Joseph W; Bockhorn, Henning

    2011-10-27

    Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C(•)═O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical +O2 association reaction are reported along with reaction paths and barriers. Enthalpies, ΔfH298(0), are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C(•)═O radical with O2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol(-1) internal energy; this is significantly more energy than the 21 kcal mol(-1) involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products. PMID:21942384

  3. Oxygen Impurities and Defects in Epitaxial Layer SiC and SiC Wafer Characterized by Room and Low Temperatures FTIR

    NASA Technical Reports Server (NTRS)

    Lu, W. J.; Collins, W. E.; Shi, D. T.; Tung, Y. S.; Larkin, D. J.

    1998-01-01

    SiC as a highly promising semiconducting material has received increasing attention in the last decade. The impurities such as oxygen and hydrogen have a great effect in electronic properties of semiconducting materials. In this study, the FTIR spectra were measured at room temperature (25 C) and low temperature (-70 C) for an n-type SiC substrate, a p-type epitaxial layer SiC, and patterned Ta on a p-type epitaxial layer SiC sample. The oxygen related IR peaks were measured for all three samples at room and low temperatures. The peak at 1105 cm(exp -1) is the result of a substitutional carbon and a interstitial oxygen in SiC. The concentration of the impurity oxygen increases in the SiC epitaxial layer during the CVD and electron beam processes. For the n-type SiC substrate, this peak does not appear. The peak at 905 cm(exp -1) exists in the IR spectra only for two epitaxial layer on p-type SiC substrate samples. This peak is related to oxygen vacancy centers in SiC, which are introduced in the CVD epitaxial growth process. At low temperature, the peak at 1105 cm(exp -1) shifts down and the peak at 905 cm(exp -1) shifts up for the epitaxial layer SiC samples. It can be explained that, at low temperatures, the stress increases due to the distorted bonds. The study shows that FTIR is a very effective method to evaluate low concentration impurities in SiC.

  4. Surface reconstruction and graphene formation on face-to-face 6H-SiC at 2000 ^oC

    NASA Astrophysics Data System (ADS)

    Elmquist, Randolph E.; Real, Mariano; Bush, Brian G.; Shen, Tian; Stiles, Mark D.; Lass, Eric A.

    2012-02-01

    Improved epitaxial graphene films have been widely reported when the sublimation rate of Si is reduced by ambient Ar gas, vapor phase silane, or confined Si vapor. We describe graphene growth on (0001) 6H-SiC samples annealed ``face-to-face'' [1]; in our modified method the separation is limited only by the flatness of the surfaces. After annealing in 100 kPa Ar gas at 2000 ^oC for 300 s, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) show graphene coverage is typically between one and a few layers. Samples without prior hydrogen etching undergo surface reconstruction in the graphitization process, resulting in atomically flat terraces with step bunching. Estimates of the sequestered carbon in the form of graphene are compared to calculated levels due to sublimation and diffusion rates where the sublimated gas is dominated by Si atoms below 2100 ^oC. The 2000 ^oC samples are contrasted against samples processed between 1700 ^oC and 1900 ^oC and transport results on large-scale graphene devices are presented.[4pt] [1] X.Z Yu, C.G. Hwang, C.M. Jozwiak, A. Kohl, A.K. Schmid and A. Lanzara, New synthesis method for the growth of epitaxial graphene, Journal of Electron Spectroscopy and Related Phenomena 184 (2011) 100-106.

  5. Carcass yields and meat quality characteristics of adult emus (Dromaius novaehollandiae) transported for 6h before slaughter.

    PubMed

    Menon, Deepa G; Bennett, Darin C; Uttaro, Bethany; Schaefer, Allan L; Cheng, Kimberly M

    2014-10-01

    The meat quality characteristics of adult emus transported for 6h before slaughter were determined. Forty-two emus were used in two trials, undertaken under warm and cool weather conditions, respectively. Male emus had significantly higher fat yields than females (12.43kg vs 9.5kg, P=0.002). About 38.1% of the emus had no wounds or bruises, 40.5% had bruises, while 21.4% had small wounds after transport. Meat from injured emus had significantly higher pH45. In warm weather, emus experienced significantly higher loss in body weight than that under cool weather. Drip loss in meat after 24h of storage was higher in emus which had greater live weight loss after transport (r=0.66, P<0.0001), confirming the adverse effects of transport stress on meat quality. Nutrient supplementation did not significantly affect processing yield or meat quality characteristics. This study points to the need for optimizing transport conditions of emus to maintain meat quality. PMID:24973774

  6. Study on formation of step bunching on 6H-SiC (0001) surface by kinetic Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Chen, Xuejiang; Su, Juan

    2016-05-01

    The formation and evolution of step bunching during step-flow growth of 6H-SiC (0001) surfaces were studied by three-dimensional kinetic Monte Carlo (KMC) method and compared with the analytic model based on the theory of Burton-Cabera-Frank (BCF). In the KMC model the crystal lattice was represented by a structured mesh which fixed the position of atoms and interatomic bonding. The events considered in the model were adatoms adsorption and diffusion on the terrace, and adatoms attachment, detachment and interlayer transport at the step edges. In addition, effects of Ehrlich-Schwoebel (ES) barriers at downward step edges and incorporation barriers at upwards step edges were also considered. In order to obtain more elaborate information for the behavior of atoms in the crystal surface, silicon and carbon atoms were treated as the minimal diffusing species. KMC simulation results showed that multiple-height steps were formed on the vicinal surface oriented toward [ 1 1 bar 00 ] or [ 11 2 bar 0 ] directions. And then the formation mechanism of the step bunching was analyzed. Finally, to further analyze the formation processes of step bunching, a one-dimensional BCF analytic model with ES and incorporation barriers was used, and then it was solved numerically. In the BCF model, the periodic boundary conditions (PBC) were applied, and the parameters were corresponded to those used in the KMC model. The evolution character of step bunching was consistent with the results obtained by KMC simulation.

  7. The observation of scintillation in a hydrated inorganic compound: CeCl3 6H2O

    SciTech Connect

    Boatner, Lynn A; Neal, John S; Ramey, Joanne Oxendine; Chakoumakos, Bryan C; Custelcean, Radu

    2013-01-01

    We have recently reported the discovery of a new family of rare-earth metal-organic single-crystal scintillators based on Ce3+ as the activator ion. Starting with the CeCl3(CH3OH)4 prototype, this family of scintillators has recently been extended to include complex metal-organic adducts produced by reacting CeCl3 with heavier organics (e.g., isomers of propanol and butanol). Some of these new rare-earth metal-organic materials incorporated waters of hydration in their structures, and the observation of scintillation in these hydrated compounds was an original finding for any solid scintillator. In the present work, we now report what is apparently the initial observation of gamma-ray-excited scintillation in an inorganic hydrated material, namely single-crystal monoclinic CeCl3 6H2O. This observation shows that the mechanisms of the various scintillation energy-transfer processes are not blocked by the presence of waters of hydration in an inorganic material and that the observation of scintillation in other hydrated inorganic compounds is not precluded.

  8. Coupled antiferromagnetic spin-1/2 chains in green dioptase Cu6[Si6O18] .6 H2O

    NASA Astrophysics Data System (ADS)

    Podlesnyak, A.; Anovitz, L. M.; Kolesnikov, A. I.; Matsuda, M.; Prisk, T. R.; Toth, S.; Ehlers, G.

    2016-02-01

    In this paper, we report inelastic neutron scattering measurements of the magnetic excitations of green dioptase Cu6[Si6O18] .6 H2O . The observed spectrum contains two magnetic modes and a prominent spin gap that is consistent with the ordered ground state of Cu moments coupled antiferromagnetically in spiral chains along the c axis and ferromagnetically in a b planes on the hexagonal cell. The data are in excellent agreement with a spin-1/2 Hamiltonian that includes antiferromagnetic nearest-neighbor intrachain coupling Jc=10.6 (1 ) meV, ferromagnetic interchain coupling Ja b=-1.2 (1 ) meV, and exchange anisotropy Δ Jc=0.14 (1 ) meV. We calculated the sublattice magnetization to be strongly reduced, ˜0.39 μB . This appears compatible with a reduced Néel temperature, TN=14.5 K≪Jc , and can be explained by a presence of quantum spin fluctuations.

  9. Characterization and physical modeling of MOS capacitors in epitaxial graphene monolayers and bilayers on 6H-SiC

    NASA Astrophysics Data System (ADS)

    Winters, M.; Sveinbjörnsson, E. Ö.; Melios, C.; Kazakova, O.; Strupiński, W.; Rorsman, N.

    2016-08-01

    Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 ṡ 1012 eV-1 cm-2 is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems.

  10. Effects of 6-h exposure to low relative humidity and low air pressure on body fluid loss and blood viscosity.

    PubMed

    Hashiguchi, N; Takeda, A; Yasuyama, Y; Chishaki, A; Tochihara, Y

    2013-10-01

    The purpose of this study was to investigate the effects of 6-h exposure to low relative humidity (RH) and low air pressure in a simulated air cabin environment on body fluid loss (BFL) and blood viscosity. Fourteen young healthy male subjects were exposed to four conditions, which combined RH (10% RH or 60% RH) and air pressure (NP: sea level or LP: equivalent to an altitude of 2000 m). Subjects remained seated on a chair in the chamber for 6 h. Their diet and water intake were restricted before and during the experiment. Insensible water loss (IWL) in LP10% condition was significantly greater than in NP60% condition; thus, combined 10%RH and LP conditions promoted a greater amount of IWL. The BFL under the LP condition was significantly greater than that under the NP condition. Blood viscosity significantly increased under LP conditions. Increases in red blood cell counts (RBCs) and BFL likely contributed to the increased blood viscosity. These findings suggest that hypobaric-induced hypoxia, similar to the conditions in the air cabin environment, may cause increased blood viscosity and that the combined low humidity and hypobaric hypoxia conditions increase IWL. PMID:23464811

  11. Electron spin resonance spectra and structure of Al(C sub 6 H sub 6 ) hydrocarbon matrices

    SciTech Connect

    Howard, J.A.; Joly, H.A.; Mile, B. )

    1989-10-11

    Reactions of Al atoms with benzene at 77 K in benzene and inert hydrocarbon matrices on a rotating cryostat have been studied by ESR spectroscopy. A monoligand complex, Al(C{sub 6}H{sub 6}), is the only paramagnetic product, and at 4 K the ESR spectrum shows resolvable hyperfine interactions with one aluminum and two equivalent protons and has the following magnetic parameters in adamantane: a{sub x}(Al) = 56 MHz, a{sub y}(Al) = a{sub z}(Al) = 14 MHz, a{sub x}(2H) = a{sub y}(2H) = a{sub y}(2H) = a{sub z}(2H) = 27 MHz, g{sub x} = 2.0010, g{sub y} = 1.9970, and g{sub z} = 2.0060. The spectrum changes with an increase in temperature and at 220 K is more consistent with an interaction with six equivalent protons with parameters a{sub Al} = 9.5 MHz, a{sub H}(6) = 5.3 MHz, and g = 2.0010. Two alternative bonding schemes are discussed.

  12. EPR and ab initio calculation study on the EI4 center in 4H- and 6H-SiC

    SciTech Connect

    Carlsson, P.; Son, N. T.; Janzen, E.; Gali, A.; Isoya, J.; Morishita, N.; Ohshima, T.; Magnusson, B.

    2010-12-15

    We present results from electron paramagnetic resonance (EPR) studies of the EI4 EPR center in 4H- and 6H-SiC. The EPR signal of the EI4 center was found to be drastically enhanced in electron-irradiated high-purity semi-insulating materials after annealing at 700-750 deg. C. Strong EPR signals of the EI4 center with minimal interferences from other radiation-induced defects in irradiated high-purity semi-insulating materials allowed our more detailed study of the hyperfine (hf) structures. An additional large-splitting {sup 29}Si hf structure and {sup 13}C hf lines of the EI4 defect were observed. Comparing the data on the hf interactions and the annealing behavior obtained from EPR experiments and from ab initio supercell calculations of different carbon-vacancy-related complexes, we suggest a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third-neighbor site of the antisite in the neutral charge state, (V{sub C}-C{sub Si}V{sub C}){sup 0}, as a new defect model for the EI4 center.

  13. Pharmacologic Evaluation of Antidepressant Activity and Synthesis of 2-Morpholino-5-phenyl-6H-1,3,4-thiadiazine Hydrobromide.

    PubMed

    Sarapultsev, Alexey P; Chupakhin, Oleg N; Sarapultsev, Petr A; Sidorova, Larisa P; Tseitler, Tatiana A

    2016-01-01

    Substituted thiadiazines exert a reliable therapeutic effect in treating stress, and a schematic description of their ability to influence all aspects of a stress response has been depicted. This study was conducted to pharmacologically evaluate compound L-17, a substituted thiadiazine, (2-morpholino-5-phenyl-6H-1,3,4-thiadiazine, hydrobromide) for possible anti-psychotic/antidepressant activity. Compound L-17 was synthesized by cyclocondensation of α-bromoacetophenone with the original morpholine-4-carbothionic acid hydrazide. Pharmacologic evaluations were conducted using methods described by E.F. Lavretskaya (1985), and in accordance with published guidelines for studying drugs for neuroleptic activity. Compound L-17 was evaluated for various possible mechanisms of action, including its effects on cholinergic system agonists/antagonists, dopaminergic neurotransmission, the adrenergic system, and 5-HT3 serotonin receptors. One or more of these mechanisms may be responsible for the beneficial effects shown by thiadiazine compounds in experiments conducted to evaluate their activity in models of acute stress and acute myocardial infarction. PMID:27213404

  14. X-Ray Photoelectron Spectroscopy Study of the Heating Effects on Pd/6H-SiC Schottky Structure

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Knight, Dak

    1998-01-01

    X-ray photoelectron spectroscopy is used to study the effects of heat treatment on the Pd/6H-SiC Schottky diode structure. After heating the structure at 425 C for 140 h, a very thin surface layer of PdO mixed with SiO(x) formed on the palladium surface of the Schottky structure. Heat treatment promoted interfacial diffusion and reaction which significantly broadened the interfacial region. In the interfacial region, the palladium concentration decreases with depth, and the interfacial products are Pd(x)Si (x = 1,2,3,4). In the high Pd concentration regions, Pd4Si is the major silicide component while gr and Pd2Si are major components in the low Pd concentration region. At the center of the interface, where the total palladium concentration equals that of silicon, the concentrations of palladium associated with various palladium silicides (Pd(x)Si, x= 1,2,3,4) are approximately equal. The surface passivation layer composed of PdO and SiO, may significantly affect the electronic and catalytic properties of the surface of the Schottky diode which plays a major role in gas detection. The electronic properties of the Schottky structure may be dominated by a (Pd+Pd(x)Si)/SiC interface. In order to stabilize the properties of the Schottky structure the surface and interface diffusion and reactions must be controlled.

  15. Pharmacologic Evaluation of Antidepressant Activity and Synthesis of 2-Morpholino-5-phenyl-6H-1,3,4-thiadiazine Hydrobromide

    PubMed Central

    Sarapultsev, Alexey P.; Chupakhin, Oleg N.; Sarapultsev, Petr A.; Sidorova, Larisa P.; Tseitler, Tatiana A.

    2016-01-01

    Substituted thiadiazines exert a reliable therapeutic effect in treating stress, and a schematic description of their ability to influence all aspects of a stress response has been depicted. This study was conducted to pharmacologically evaluate compound L-17, a substituted thiadiazine, (2-morpholino-5-phenyl-6H-1,3,4-thiadiazine, hydrobromide) for possible anti-psychotic/antidepressant activity. Compound L-17 was synthesized by cyclocondensation of α-bromoacetophenone with the original morpholine-4-carbothionic acid hydrazide. Pharmacologic evaluations were conducted using methods described by E.F. Lavretskaya (1985), and in accordance with published guidelines for studying drugs for neuroleptic activity. Compound L-17 was evaluated for various possible mechanisms of action, including its effects on cholinergic system agonists/antagonists, dopaminergic neurotransmission, the adrenergic system, and 5-HT3 serotonin receptors. One or more of these mechanisms may be responsible for the beneficial effects shown by thiadiazine compounds in experiments conducted to evaluate their activity in models of acute stress and acute myocardial infarction. PMID:27213404

  16. Coupled antiferromagnetic spin- 12 chains in green dioptase Cu6[Si6O18]·6H2O

    DOE PAGESBeta

    Podlesnyak, Andrey A; Larry M. Anovitz; Kolesnikov, Alexander I; Matsuda, Masaaki; Prisk, Timothy R; Toth, Sandor; Ehlers, Georg

    2016-02-01

    Inmore » this paper, we report inelastic neutron scattering measurements of the magnetic excitations of green dioptase Cu6[Si6O18]∙6H2O. The observed spectrum contains two magnetic modes and a prominent spin gap that is consistent with the ordered ground state of Cu moments coupled antiferromagnetically in spiral chains along the c axis and ferromagnetically in ab planes on the hexagonal cell. The data are in excellent agreement with a spin- 12Hamiltonian that includes antiferromagnetic nearest-neighbor intrachain coupling Jc=10.6(1) meV, ferromagnetic interchain coupling Jab=₋1.2 (1) meV, and exchange anisotropy ΔJc=0.14(1) meV. We calculated the sublattice magnetization to be strongly reduced, ~0.39μB. This appears compatible with a reduced Néel temperature, TN=14.5K

  17. Pd/CeO2/SiC Chemical Sensors

    NASA Technical Reports Server (NTRS)

    Lu, Weijie; Collins, W. Eugene

    2005-01-01

    The incorporation of nanostructured interfacial layers of CeO2 has been proposed to enhance the performances of Pd/SiC Schottky diodes used to sense hydrogen and hydrocarbons at high temperatures. If successful, this development could prove beneficial in numerous applications in which there are requirements to sense hydrogen and hydrocarbons at high temperatures: examples include monitoring of exhaust gases from engines and detecting fires. Sensitivity and thermal stability are major considerations affecting the development of high-temperature chemical sensors. In the case of a metal/SiC Schottky diode for a number of metals, the SiC becomes more chemically active in the presence of the thin metal film on the SiC surface at high temperature. This increase in chemical reactivity causes changes in chemical composition and structure of the metal/SiC interface. The practical effect of the changes is to alter the electronic and other properties of the device in such a manner as to degrade its performance as a chemical sensor. To delay or prevent these changes, it is necessary to limit operation to a temperature <450 C for these sensor structures. The present proposal to incorporate interfacial CeO2 films is based partly on the observation that nanostructured materials in general have potentially useful electrical properties, including an ability to enhance the transfer of electrons. In particular, nanostructured CeO2, that is CeO2 with nanosized grains, has shown promise for incorporation into hightemperature electronic devices. Nanostructured CeO2 films can be formed on SiC and have been shown to exhibit high thermal stability on SiC, characterized by the ability to withstand temperatures somewhat greater than 700 C for limited times. The exchanges of oxygen between CeO2 and SiC prevent the formation of carbon and other chemical species that are unfavorable for operation of a SiC-based Schottky diode as a chemical sensor. Consequently, it is anticipated that in a Pd

  18. Effects of SiC on Properties of Cu-SiC Metal Matrix Composites

    NASA Astrophysics Data System (ADS)

    Efe, G. Celebi; Altinsoy, I.; Ipek, M.; Zeytin, S.; Bindal, C.

    2011-12-01

    This paper was focused on the effects of particle size and distribution on some properties of the SiC particle reinforced Cu composites. Copper powder produced by cementation method was reinforced with SiC particles having 1 and 30 μm particle size and sintered at 700 °C. SEM studies showed that SiC particles dispersed in copper matrix homogenously. The presence of Cu and SiC components in composites were verified by XRD analysis technique. The relative densities of Cu-SiC composites determined by Archimedes' principle are ranged from 96.2% to 90.9% for SiC with 1 μm particle size, 97.0 to 95.0 for SiC with 30 μm particle size. Measured hardness of sintered compacts varied from 130 to 155 HVN for SiC having 1 μm particle size, 188 to 229 HVN for SiC having 1 μm particle size. Maximum electrical conductivity of test materials was obtained as 80.0% IACS (International annealed copper standard) for SiC with 1 μm particle size and 83.0% IACS for SiC with 30 μm particle size.

  19. Complexes of type C6H7+.L (L = N2 and CO2) studied by explicitly correlated coupled cluster theory

    NASA Astrophysics Data System (ADS)

    Botschwina, Peter; Oswald, Rainer

    2012-05-01

    Complexes of the benzenium ion (C_6 H_7^ +) with N2 or CO2 have been studied by explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level [T. B. Adler et al., J. Chem. Phys. 127, 221106 (2007), 10.1063/1.2817618] and the double-hybrid density functional B2PLYP-D [T. Schwabe and S. Grimme, Phys. Chem. Chem. Phys. 9, 3397 (2007), 10.1039/b704725h]. Improved harmonic vibrational wavenumbers for C_6 H_7^ + have been obtained by CCSD(T*)-F12a calculations with the VTZ-F12 basis set. Combining them with previous B2PLYP-D anharmonic contributions we arrive at anharmonic wavenumbers which are in excellent agreement with recent experimental data from p-H2 matrix isolation IR spectroscopy [M. Bahou et al., J. Chem. Phys. 136, 154304 (2012), 10.1063/1.3703502]. The energetically most favourable conformer of C_6 H_7^ +.N2 shows a π-bonded structure similar to C_6 H_7^ +.Rg (Rg = Ne, Ar) [P. Botschwina and R. Oswald, J. Phys. Chem. A 115, 13664 (2011), 10.1021/jp207905t] with De ≈ 870 cm-1. For C_6 H_7^ +.CO2, a slightly lower energy is calculated for a conformer with the CO2 ligand lying in the ring-plane of the C_6 H_7^ + moiety (De ≈ 1508 cm-1). It may be discriminated from other conformers through a strong band predicted at 1218 cm-1, red-shifted by 21 cm-1 from the corresponding band of free C_6 H_7^ +.

  20. Complexes of type C6H7(+)·L (L = N2 and CO2) studied by explicitly correlated coupled cluster theory.

    PubMed

    Botschwina, Peter; Oswald, Rainer

    2012-05-28

    Complexes of the benzenium ion (C(6)H(7)(+)) with N(2) or CO(2) have been studied by explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level [T. B. Adler et al., J. Chem. Phys. 127, 221106 (2007)] and the double-hybrid density functional B2PLYP-D [T. Schwabe and S. Grimme, Phys. Chem. Chem. Phys. 9, 3397 (2007)]. Improved harmonic vibrational wavenumbers for C(6)H(7)(+) have been obtained by CCSD(T∗)-F12a calculations with the VTZ-F12 basis set. Combining them with previous B2PLYP-D anharmonic contributions we arrive at anharmonic wavenumbers which are in excellent agreement with recent experimental data from p-H(2) matrix isolation IR spectroscopy [M. Bahou et al., J. Chem. Phys. 136, 154304 (2012)]. The energetically most favourable conformer of C(6)H(7)(+)·N(2) shows a π-bonded structure similar to C(6)H(7)(+)·Rg (Rg = Ne, Ar) [P. Botschwina and R. Oswald, J. Phys. Chem. A 115, 13664 (2011)] with D(e) ≈ 870 cm(-1). For C(6)H(7)(+)·CO(2), a slightly lower energy is calculated for a conformer with the CO(2) ligand lying in the ring-plane of the C(6)H(7)(+) moiety (D(e) ≈ 1508 cm(-1)). It may be discriminated from other conformers through a strong band predicted at 1218 cm(-1), red-shifted by 21 cm(-1) from the corresponding band of free C(6)H(7)(+). PMID:22667554

  1. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  2. Interstitial H and H2 in SiC

    NASA Astrophysics Data System (ADS)

    Kaukonen, M.; Fall, C. J.; Lento, J.

    2003-08-01

    The properties of hydrogen in 3C and 4H type silicon carbide (SiC) are studied theoretically at the density functional level. We find that only singly positive or negative charge states of hydrogen are thermodynamically stable in SiC. The transition from the positive to the negative charge state (+/-) is at 0.9 and 1.3 eV above the valence band maximum in 3C and 4H structures, respectively. The diffusion barrier for the proton is 0.5 eV (being, however, anisotropic in 4H). For the negative H- the diffusion barrier is found to be considerably higher, of the order of 3 eV.

  3. Tga Characteristic and Fabrication of Porous SiC Ceramics

    NASA Astrophysics Data System (ADS)

    Kim, Seong Hoon; Yoon, Han Ki; Kim, Seon Jin; Park, Yi Hyun

    The long-range aim of this research is to develop porous ceramics with high strength, excellent thermal resistance and chemical stability at high temperature in environmental industry. The Cf/SiC was made by hot pressing method with SiC powder whose particle size is 50nm and less on the average also Al2O3, Y2O3 and SiO2 as additive. The carbon fibers of oxidation property are investigated by TGA for finding out decarburization point. As a result, decarburization point selected the specific temperature of TGA curve and the Cf/SiC composites occurred perfectly decarburization at carbon fibers so the clearly porous SiC ceramics were formed many holes of 3-5µm diameters through length direction by its reaction.

  4. Molten salt corrosion of SiC: Pitting mechanism

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Smialek, J. L.

    1985-01-01

    Thin films of Na2SO4 and Na2CO3 at 1000 C lead to severe pitting of sintered alpha-SiC. These pits are important as they cause a strength reduction in this material. The growth of product layers is related to pit formation for the Na2CO3 case. The early reaction stages involve repeated oxidation and dissolution to form sodium silicate. This results in severe grain boundary attack. After this a porous silica layer forms between the sodium silicate melt and the SiC. The pores in this layer appear to act as paths for the melt to reach the SiC and create larger pits.

  5. The SiC Direct Target Prototype for SPES

    SciTech Connect

    Rizzi, V.; Andrighetto, A.; Barbui, M.; Carturan, S.; Cinausero, M.; Giacchini, M.; Gramegna, F.; Lollo, M.; Maggioni, G.; Prete, G.; Tonezzer, M.; Antonucci, C.; Cevolani, S.; Petrovich, C.; Biasetto, L.; Colombo, P.; Manzolaro, M.; Meneghetti, M.; Celona, L.; Chines, F.

    2007-10-26

    A R and D study for the realization of a Direct Target is in progress within the SPES project for RIBs production at the Laboratori Nazionali of Legnaro. A proton beam (40 MeV energy, 0.2 mA current) is supposed to impinge directly on a UCx multiple thin disks target, the power released by the proton beam is dissipated mainly through irradiation. A SiC target prototype with a 1:5 scale has been developed and tested. Thermal, mechanical and release calculations have been performed to fully characterize the prototype. An online test has been performed at the HRIBF facility of the Oak Ridge National Laboratory (ORNL), showing that our SiC target can sustain a proton beam current considerably higher than the maximum beam current used with the standard HRIBF target configuration.

  6. Saturn V S-IC Stage Test Firing

    NASA Technical Reports Server (NTRS)

    1965-01-01

    The Saturn V first stages were test fired at the Mississippi Test Facility and at the Marshall Space Flight Center (MSFC). Five F-1 engines powered the first stage, each developing 1.5 million pounds of thrust. The first stage, known as the S-IC stage, burned over 15 tons of propellant per second during its 2.5 minutes of operation to take the vehicle to a height of about 36 miles and to a speed of about 6,000 miles per hour. The stage was 138 feet long and 33 feet in diameter. This photograph shows the test firing of an F-1 engine at the MSFC's S-IC Static Test Firing Facility.

  7. Oxidation of ZrB2-SiC

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Halbig, Michael C.

    2001-01-01

    In this paper the oxidation behavior of ZrB2-20 vol% SiC is examined. Samples were exposed in stagnant air in a zirconia furnace (Deltech, Inc.) at temperatures of 1327, 1627, and 1927 C for ten ten-minute cycles. Samples were removed from the furnace after one, five, and ten cycles. Oxidized material was characterized by mass change when possible, x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Oxidation kinetics, oxide scale development, and matrix recession were monitored as a function of time and temperature. Oxidation and recession rates of ZrB2 - 20 vol% SiC were adequately modeled by parabolic kinetics. Oxidation rates of this material are rapid, allowing only very short-term application in air or other high oxygen partial pressure environments.

  8. High frequency ultrasonic characterization of sintered SiC

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Generazio, Edward R.; Kiser, James D.

    1987-01-01

    High frequency (60 to 160 MHz) ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90 to 98 percent of theoretical, average grain sizes ranging from 3.0 to 12.0 microns, and average pore sizes ranging from 1.5 to 4.0 microns. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. Attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size.

  9. Toughened Matrix SiC Fiber Reinforced Composites

    NASA Technical Reports Server (NTRS)

    Levine, Stanley R.; Bhatt, Ramakrishna T.; Morscher, Gregory N.; Kiser, James D.

    2005-01-01

    First matrix cracking stress is a critical parameter for application of Sic fiber reinforced composites in highly stressed, environmentally demanding applications such as turbine blades. High matrix fracture toughness is a key property that contributes to high composite fracture stress. Silicon nitride offers reduced matrix elastic modulus, lower coefficient of thermal expansion, and potentially high fracture toughness compared to Sic matrices. All of these factors can be used to advantage to increase matrix fracture stress. As a first model system we are pursuing toughened silicon nitride matrix composites reinforced with SCS-9 fibers. Fabrication is by tape casting the matrix plies and tape lay-up with fiber plies followed by hot pressing at 1800 C. Progress toward this end will be reported.

  10. Comparison of aluminum- and boron-implanted vertical 6H-SiC p +n junction diodes

    NASA Astrophysics Data System (ADS)

    Ramungul, N.; Khemka, V.; Tyagi, R.; Chow, T. P.; Ghezzo, M.; Neudeck, P. G.; Kretchmer, J.; Hennessy, W.; Brown, D. M.

    1998-01-01

    The electrical performance of mesa type 6H-SiC p +n junction diodes formed via high temperature implantation of 27Al and 11B has been comparatively studied and analyzed at temperatures up to 400°C using the Shockley model and the space-charge-limited current model. The Al-implanted diodes show better forward current-voltage characteristics with the best ideality factor obtained at 400°C of 1.6 while that for B-implanted diodes is 1.3. The factor that prohibits the forward performance of the Al-implanted diodes appears to be the deep defect center located at 1.2 eV above the valence band while that of B-implanted diodes appears to be the deep boron center called D-center located at 0.7˜0.8 eV above the valence band. On the other hand, B-implanted diodes show a better yield in the reverse direction with at least an order-of-magnitude lower reverse leakage current than that of Al-implanted diodes at all measurement temperatures. Several micropipe microplasmas were plainly visible in the middle of the mesa of the Al-implanted diodes when biased at -250 V but not on boron devices. The forward voltage drop of Al-implanted diodes is tightly distributed at 2.2 V with a forward resistance of 125 Ω while that of B-implanted diodes is broadly distributed with an average value of 2.8 V and nearly 200 times larger forward resistance.

  11. Evolution of strain and mechanical properties upon annealing in He-implanted 6H-SiC

    NASA Astrophysics Data System (ADS)

    Li, B. S.; Wang, Z. G.; Zhang, C. H.; Wei, K. F.; Yao, C. F.; Sun, J. R.; Cui, M. H.; Li, Y. F.; Zhu, H. P.; Du, Y. Y.; Zhu, Y. B.; Pang, L. L.; Song, P.; Wang, J.

    2014-12-01

    The effects of annealing temperature on strain and mechanical property changes of 6H-SiC implanted with helium ions at 600 K to doses of 3 × 1015 cm-2, 1 × 1016 cm-2 and 3 × 1016 cm-2 and at an ion energy of 100 keV were investigated by using high-resolution X-ray diffraction (XRD), nano-indentation and transmission electron microscopy (TEM). Strain increases with increasing displacements per atom (dpa). Strain relaxation in terms of changes in Δd/d exhibited a linear decrease with increasing annealing temperature ranging from 873 K to 1473 K for 30 min in vacuum. The relaxation activation energies of the strains were estimated by Arrhenius law to be in the range of 0.4-0.7 eV. Irradiation-induced hardening was observed via nano-indentation measurements as a function of annealing. The hardness of the highly damaged layer decreased monotonically with increasing annealing temperature for the samples implanted with He ions to doses of 3 × 1015 cm-2 and 1 × 1016 cm-2, and where no helium bubbles were formed in the damaged layer. The hardness of the damaged layer initially decreased and then increased with increasing annealing temperature from 600 K to 1073 K for the sample implanted He ions to a dose of 3 × 1016 cm-2, where numerous helium bubbles were formed in the damaged layer. The TEM results suggest that the growth of helium bubbles emits interstitials upon annealing. These interstitials agglomerate into stacking faults and dislocation loops, which increase the hardness.

  12. Sputter deposition of SiC coating on silicon wafers

    NASA Technical Reports Server (NTRS)

    Robson, M. T.; Blue, C. A.; Warrier, S. G.; Lin, R. Y.

    1992-01-01

    A study is conducted of the effect of substrate temperature during coating on the properties of coated SiC films on Si wafers, using a scratch test technique. While specimen temperature during coating has little effect on deposition rate, it significantly affects the durability of the coating. Scratch test damage to both film coating and substrate decreased with increasing deposition temperature, perhaps due to the rapid diffusion of the deposited atoms.

  13. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo, taken September 5, 1961, shows pumps used for extracting water emerging form a disturbed natural spring that occurred during the excavation of the site. The pumping became a daily ritual and the site is still pumped today.

  14. Bilateral comparison of an IPRT between KRISS and SIC

    NASA Astrophysics Data System (ADS)

    Yang, I.; Sánchez, C. A.

    2013-09-01

    As a follow-up of a memorandum of understanding signed in 2009 between KRISS of Korea and SIC of Colombia, the two national metrology institutes carried out a bilateral comparison of calibration of an industrial platinum resistance thermometer (IPRT). A protocol that was similar to that of APMP.T-S6 has been agreed and followed in the comparison. The method of the calibration at each laboratory was calibration by comparison against calibrated reference thermometers. The nominal temperatures of the comparison were nine temperatures, including the ice point, between -50 °C and 500 °C. One commercially-available IPRT with α ˜ 0.00385 °C-1 that was prepared by KRISS was calibrated by comparison firstly at KRISS, and then at SIC, and finally at KRISS to assess the drift of the artifact during the comparison. At KRISS, an ice-point bath, three liquid baths and a salt bath were used to provide isothermal environment for the comparison. At SIC, an ice-point bath, two liquid baths and a vertical furnace with a metal equalizing block were used. The claimed uncertainty with k=2 of the calibration at KRISS, excluding the longterm instability and hysteresis of the traveling IPRT, was 30 mK, and that at SIC was 120 mK. The capability of the calibration of the two laboratories from -50 °C to 500 °C showed a good agreement within the claimed uncertainty of the calibration. The largest deviation of the two calibration results was 75 mK at 500 °C.

  15. SiC device development for high temperature sensor applications

    NASA Technical Reports Server (NTRS)

    Shor, J. S.; Goldstein, David; Kurtz, A. D.; Osgood, R. M.

    1992-01-01

    Progress made in the processing and characterization of 3C-SiC for high temperature sensor applications is reviewed. Piezoresistance properties of silicon carbide and the temperature coefficient of resistivity of n-type beta-SiC are presented. In addition, photoelectrical etching and dopant selective etch-stops in SiC and high temperature Ohmic contacts for n-type beta-SiC sensors are discussed.

  16. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo, depicts the progress of the stand as of January 14, 1963, with its four towers prominently rising.

  17. Thrust Structure of Saturn V S-IC Stage

    NASA Technical Reports Server (NTRS)

    1963-01-01

    This image illustrates technicians working on a full scale engineering mock-up of a Saturn V S-IC stage thrust structure nearing completion at the Manufacturing Engineering Laboratory at Marshall Space Flight Center. The booster, 33 feet in diameter and 138 feet long, was powered by five F-1 engines that provided 7,500,000 pounds of thrust to start the monstrous vehicle on its journey into space.

  18. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In this photo, taken June 24, 1963, the four tower legs of the test stand can be seen at their maximum height.

  19. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the construction progress as of August 5, 1961. Heavy equipment continues to clear the test stand site.

  20. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1962-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This construction photo depicts the progress of the stand site as of October 8, 1962.

  1. SiC device development for high temperature sensor applications

    NASA Astrophysics Data System (ADS)

    Shor, J. S.; Goldstein, David; Kurtz, A. D.; Osgood, R. M.

    1992-09-01

    Progress made in the processing and characterization of 3C-SiC for high temperature sensor applications is reviewed. Piezoresistance properties of silicon carbide and the temperature coefficient of resistivity of n-type beta-SiC are presented. In addition, photoelectrical etching and dopant selective etch-stops in SiC and high temperature Ohmic contacts for n-type beta-SiC sensors are discussed.

  2. Synchronistic preparation of fibre-like SiC and cubic-ZrO{sub 2}/SiC composite from zircon via carbothermal reduction process

    SciTech Connect

    Xu, Youguo; Liu, Yangai; Huang, Zhaohui; Fang, Minghao; Hu, Xiaozhi; Yin, Li; Huang, Juntong

    2013-01-15

    Graphical abstract: Display Omitted Highlights: ► Zircon carbothermal reduction was carried out in a tailor-made device at high-temperature air atmosphere. ► Fibre-like SiC and cubic-ZrO{sub 2}/SiC composite were obtained synchronically. ► Zirconium and silicon in zircon ore was initial separated. ► [SiO{sub 4}] was mutated to fibre-like SiC, while [ZrO{sub 8}] was transformed to cubic ZrO{sub 2}. ► The SiC were surprisingly enriched in the reducing atmosphere charred coal particles layers by gas–solid reaction. -- Abstract: Fibre-like SiC and cubic-ZrO{sub 2}/SiC composite were prepared respectively from zircon with yttrium oxide addition via carbothermal reduction process at 1600 °C for 4 h in an air atmosphere furnace, where the green samples were immerged in charred coal particles inside a high-temperature enclosed corundum crucible. The reaction products were characterized by XRD, XRF, XPS and SEM. The results indicate that ZrO{sub 2} in the products was mainly existed in the form of cubic phase. The reacted samples mainly contain cubic ZrO{sub 2}, β-SiC and trace amounts of zircon, with the SiC accounting for 14.8 wt%. Furthermore, a large quantity of fibre-like SiC was surprisingly found to concentrate in the charred coal particles layers around the samples. This study obtains fibre-like SiC and cubic-ZrO{sub 2}/SiC composite synchronically from zircon via carbothermal reduction process, which also bring a value-added high-performance application for natural zircon.

  3. The influence of SiC particle size and volume fraction on the thermal conductivity of spark plasma sintered UO2-SiC composites

    NASA Astrophysics Data System (ADS)

    Yeo, Sunghwan; Baney, Ronald; Subhash, Ghatu; Tulenko, James

    2013-11-01

    This study examines the influence of Silicon Carbide (SiC) particle addition on thermal conductivity of UO2-SiC composite pellets. UO2 powder and β-SiC particles of different sizes and of different volume fractions were mechanically mixed and sintered at 1350-1450 °C for 5 min by Spark Plasma Sintering (SPS). The particle size (0.6-55 μm diameter) and volume fraction (5-20%) of SiC were systematically varied to investigate their influence on the resulting UO2-SiC composite pellet microstructure and the thermal properties. It was found that SiC particle size less than 16.9 μm with larger volume fraction is more effective for improving the thermal conductivity of the fuel pellets. Scanning Electron Microscopy examination revealed micro-cracking and interfacial debonding in the composites containing larger size SiC particles (16.9 and 55 μm) which resulted in reduced thermal conductivity. For the UO2-SiC composite pellets containing 1 μm diameter SiC particles, the thermal conductivity increased almost linearly with volume fraction of particles. However, the addition of a larger volume fraction of SiC reduces the amount of heavy metal in the composite pellet and therefore a higher U-235 enrichment is necessary to compensate for the heavy metal loss. The experimental thermal conductivity values of the UO2-SiC composite pellets are in good agreement with the theoretical values based on the available model in the literature.

  4. Research on microwave joining of SiC

    SciTech Connect

    Silberglitt, R.

    1995-07-31

    Results: identification of optimum joining temperature range for reaction bonded Si carbide at 1420-1500 C; demonstration that specimens joined within this range have fracture roughness greater than as-received material; and demonstration of ability to use SiC formed in situ from the decomposition of polycarbosilane as a joining aid for sintered Si carbide. In the latter case, the interlayer material was also shown to fill any pores in the joining specimens near the interlayer. Together with the demonstration of leaktight joints between tube sections of reaction bonded and sintered SiC under the previous contract, these results provide the foundation for scaleup to joining of the larger and longer tubes needed for radiant burner and heat exchanger tube assemblies. The formation of SiC in situ is important because maintaining roundness of these large tubes is a technical challenge for the tube manufacturer, so that formation of a leaktight joint may require some degree of gap filling.

  5. Atmospheric pressure growth of graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Seyller, Thomas

    2009-03-01

    Graphene, a single monolayer of sp^2-bonded carbon, is a very unique 2-dimensional electron gas system with electronic properties fundamentally different to other 2DEG systems [1]. Several production routes exist for graphene. Among them, the solid-state decomposition of hexagonal silicon carbide (SiC) surfaces [2] is particularly attractive for the development of graphene based electronics [3,4]. The first part of the presentation gives a brief summary of recent studies on the structural and electronic properties of graphene and few-layer graphene grown on SiC(0001) under ultra-high vacuum (UHV) conditions. The second part of the talk is devoted to recent progress in the growth of large domain graphene films on SiC(0001) in Ar atmosphere. It is shown that growth in Ar ambient leads to a significant improvement of the surface morphology and domain size as well as carrier mobility. [4pt] [1] A.H. Castro Neto, et al., Reviews of Modern Physics, in print (arXiv:0709.1163v2); and references therein. [0pt] [2] A. Charrier, et al., J. Appl. Phys. 92 (2002) 2479. [0pt] [3] C. Berger et al., J. Phys. Chem. B 108 (2004) 19912; C. Berger, et al., Science 312 (2006) 1191. [0pt] [4] A.K. Geim and K.S. Novoselov, Nature Mat. 6 (2007) 183.

  6. The effect of MgO(111) interlayer on the interface phase stability and structure of BaFe12O19/SiC(0001)

    NASA Astrophysics Data System (ADS)

    Lazarov, V. K.; Hasnip, P. J.; Cai, Z.; Yoshida, K.; Ziemer, K. S.

    2012-04-01

    We present a study on the effect of an interlayer of thin MgO(111) film on SiC(0001) on the interface phase stability and structure of the BaFe12O19 (BaM). The 10 nm MgO(111) interlayer followed by the BaM film were grown by molecular beam epitaxy on 6H-SiC. Cross-sectional transmission electron microscopy shows the formation of a magnesium ferrite spinel phase at the interface, and after 25 nm, a well structured BaM film was observed. In addition to the two main phases (Mg-ferrite and BaM), a thin layer of SiOx (2-3 nm) is formed at the SiC interface. In spite of the formation of this amorphous layer, the diffraction studies show that the BaM film is epitaxially grown and it has a single crystal structure. The energy dispersive x-ray analysis from the interface region shows that the MgO layer prevents significant outdiffusion of the Si into the film. Total energy calculations by density functional theory were used to investigate the stability of the various phases and to explain the observed interfacial phases in the studied system.

  7. Amorphization and dynamic annealing of hexagonal SiC upon heavy-ion irradiation: Effects on swelling and mechanical properties

    NASA Astrophysics Data System (ADS)

    Kerbiriou, Xavier; Costantini, Jean-Marc; Sauzay, Maxime; Sorieul, Stéphanie; Thomé, Lionel; Jagielski, Jacek; Grob, Jean-Jacques

    2009-04-01

    Structural, mechanical, and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are studied by means of Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation, and surface profilometry measurements. 4H- and 6H-SiC single crystals were irradiated with 4 MeV Au2+ and 4 MeV Xe+ ions at room temperature (RT) or 400 °C. Using a Monte Carlo program to simulate the RBS/C spectra (MCCHASY code), we find that Au ion irradiation at RT induces a total silicon sublattice disorder related to full amorphization at a dose of about 0.4 displacement per atom (dpa). A two-step damage process is found on the basis of the disordered fractions deduced from RBS/C data. Complete amorphization cannot be reached upon both Au and Xe ion irradiations at 400 °C up to about 26 dpa because of the dynamic annealing of defects. When complete amorphization is reached at RT, the Young's modulus and Berkovich hardness of irradiated 6H-SiC samples are lower by, respectively, 40% and 45% than those of the virgin crystals. The out-of-plane expansion measured by surface profilometry increases versus irradiation dose and the saturation value measured in the completely amorphous layer (normalized to the ion projected range) is close to 25%. We show that the modifications of the macroscopic properties are mainly due to the amorphization of the material. The macroscopic elasticity constants and dimensional properties are predicted for a composite material made of crystalline matrix containing dispersed amorphous inclusions using simple analytical homogenization models. Voigt's model seems to give the best approximation for disordered fractions larger than 20% in the second step of the damage process.

  8. Amorphization and dynamic annealing of hexagonal SiC upon heavy-ion irradiation: Effects on swelling and mechanical properties

    SciTech Connect

    Kerbiriou, Xavier; Costantini, Jean-Marc; Sauzay, Maxime; Sorieul, Stephanie; Thome, Lionel

    2009-04-01

    Structural, mechanical, and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are studied by means of Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation, and surface profilometry measurements. 4H- and 6H-SiC single crystals were irradiated with 4 MeV Au{sup 2+} and 4 MeV Xe{sup +} ions at room temperature (RT) or 400 deg. C. Using a Monte Carlo program to simulate the RBS/C spectra (MCCHASY code), we find that Au ion irradiation at RT induces a total silicon sublattice disorder related to full amorphization at a dose of about 0.4 displacement per atom (dpa). A two-step damage process is found on the basis of the disordered fractions deduced from RBS/C data. Complete amorphization cannot be reached upon both Au and Xe ion irradiations at 400 deg. C up to about 26 dpa because of the dynamic annealing of defects. When complete amorphization is reached at RT, the Young's modulus and Berkovich hardness of irradiated 6H-SiC samples are lower by, respectively, 40% and 45% than those of the virgin crystals. The out-of-plane expansion measured by surface profilometry increases versus irradiation dose and the saturation value measured in the completely amorphous layer (normalized to the ion projected range) is close to 25%. We show that the modifications of the macroscopic properties are mainly due to the amorphization of the material. The macroscopic elasticity constants and dimensional properties are predicted for a composite material made of crystalline matrix containing dispersed amorphous inclusions using simple analytical homogenization models. Voigt's model seems to give the best approximation for disordered fractions larger than 20% in the second step of the damage process.

  9. Stressed-Oxidation Lifetime of Different SiC Fiber, CVI Matrix SiC Minicomposites in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Martinez-Fernandez, Julian

    1998-01-01

    The stressed-oxidation lifetime properties of several minicomposites composed of single fiber tows with a CVI SiC matrix were compared. The minicomposites were made up of Nicalon(Tm) and Hi-Nicalon(Tm) SiC fibers with carbon or BN interphases. Constant load stress-rupture tests were performed between 600 and 13000 C in air for all of the minicomposite systems. Cyclic load testing was performed on the Hi-Nicalon minicomposite systems. The factors controlling the different lifetime behaviors: fiber rupture properties, interphase oxidation, fiber degradation, and fiber-matrix bonding, are discussed in light of different minicomposite constituents. All of the systems were subject to intermediate temperature embrittlement. The Hi-Nicalon fiber, BN interphase system, performed the best for constant load conditions. For cyclic load conditions, both the BN- interphase and C-interphase minicomposites displayed poor, but different failure behavior.

  10. Fractographic Analysis of HfB2-SiC and ZrB2-SiC Composites

    NASA Technical Reports Server (NTRS)

    Mecholsky, J.J., Jr.; Ellerby, D. T.; Johnson, S. M.; Stackpoole, M. M.; Loehman, R. E.; Arnold, Jim (Technical Monitor)

    2001-01-01

    Hafnium diboride-silicon carbide and zirconium diboride-silicon carbide composites are potential materials for high temperature leading edge applications on reusable launch vehicles. In order to establish material constants necessary for evaluation of in-situ fracture, bars fractured in four point flexure were examined using fractographic principles. The fracture toughness was determined from measurements of the critical crack sizes and the strength values, and the crack branching constants were established to use in forensic fractography of materials for future flight applications. The fracture toughnesses range from about 13 MPam (sup 1/2) at room temperature to about 6 MPam (sup 1/2) at 1400 C for ZrB2-SiC composites and from about 11 MPam (sup 1/2) at room temperature to about 4 MPam (sup 1/2) at 1400 C for HfB2-SiC composites.

  11. SiC Optically Modulated Field-Effect Transistor

    NASA Technical Reports Server (NTRS)

    Tabib-Azar, Massood

    2009-01-01

    An optically modulated field-effect transistor (OFET) based on a silicon carbide junction field-effect transistor (JFET) is under study as, potentially, a prototype of devices that could be useful for detecting ultraviolet light. The SiC OFET is an experimental device that is one of several devices, including commercial and experimental photodiodes, that were initially evaluated as detectors of ultraviolet light from combustion and that could be incorporated into SiC integrated circuits to be designed to function as combustion sensors. The ultraviolet-detection sensitivity of the photodiodes was found to be less than desired, such that it would be necessary to process their outputs using high-gain amplification circuitry. On the other hand, in principle, the function of the OFET could be characterized as a combination of detection and amplification. In effect, its sensitivity could be considerably greater than that of a photodiode, such that the need for amplification external to the photodetector could be reduced or eliminated. The experimental SiC OFET was made by processes similar to JFET-fabrication processes developed at Glenn Research Center. The gate of the OFET is very long, wide, and thin, relative to the gates of typical prior SiC JFETs. Unlike in prior SiC FETs, the gate is almost completely transparent to near-ultraviolet and visible light. More specifically: The OFET includes a p+ gate layer less than 1/4 m thick, through which photons can be transported efficiently to the p+/p body interface. The gate is relatively long and wide (about 0.5 by 0.5 mm), such that holes generated at the body interface form a depletion layer that modulates the conductivity of the channel between the drain and the source. The exact physical mechanism of modulation of conductivity is a subject of continuing research. It is known that injection of minority charge carriers (in this case, holes) at the interface exerts a strong effect on the channel, resulting in amplification

  12. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In addition to the stand itself, related facilities were constructed during this time. Built to the northeast of the stand was a newly constructed Pump House. Its function was to provide water to the stand to prevent melting damage during testing. The water was sprayed through small holes in the stand's 1900 ton flame deflector at the rate of 320,000 gallons per minute. In this photo of the S-IC test stand, taken October 2, 1963, the flame deflector can be seen in the bottom center portion

  13. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In the early stages of excavation, a natural spring was disturbed that caused a water problem which required constant pumping from the site and is even pumped to this day. Behind this reservoir of pumped water is the S-IC test stand boasting its ever-growing four towers as of March 29, 1963.

  14. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In addition to the stand itself, related facilities were constructed during this time. Built northeast of the stand was a newly constructed Pump House. Its function was to provide water to the stand to prevent melting damage during testing. The water was sprayed through small holes in the stand's 1900 ton flame deflector at the rate of 320,000 gallons per minute. In this photo, taken September 5, 1963, the flame deflector is being installed in the S-IC test stand.

  15. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In addition to the stand itself, related facilities were constructed during this time. Built to the northeast of the stand was a newly constructed Pump House. Its function was to provide water to the stand to prevent melting damage during testing. The water was sprayed through small holes in the stand's 1900 ton flame deflector at the rate of 320,000 gallons per minute. In this photo of the S-IC test stand, taken September 25, 1963, the flame deflector can be seen rotated to the outside on

  16. Abnormal difference between the mobilities of left- and right-twisted conformations of C6H12N2 roto-symmetrical molecules at very low temperatures.

    PubMed

    Gabuda, S P; Kozlova, S G

    2015-06-21

    We report an abnormal difference of low-temperature mobility of left-twisted and right-twisted conformations of roto symmetric molecules C6H12N2 (dabco) located in the same positions in crystal Zn2(C8H4O4)2⋅C6H12N2. The difference between (1)H NMR (Nuclear Magnetic Resonance) spin-relaxation data for left-twisted and right-twisted molecules reaches ∼3 × 10(3) times at 8 K and tends to grow at lower temperatures. We argue that taking into account four-component relativistic Dirac wave functions in the vicinity of the nodal plane of dabco molecules and vacuum fluctuations due to virtual particle-antiparticle pairs can explain the changes which C6H12N2 conformations undergo at low temperatures. PMID:26093554

  17. New metal-organic frameworks of [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La, Ce) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O

    SciTech Connect

    Weng Shengfeng; Wang, Yun-Hsin; Lee, Chi-Shen

    2012-04-15

    Two novel materials, [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2), with a metal-organic framework (MOF) were prepared with hydrothermal reactions and characterized with photoluminescence, magnetic susceptibility, thermogravimetric analysis and X-ray powder diffraction in situ. The crystal structures were determined by single-crystal X-ray diffraction. Compound 1 crystallized in triclinic space group P1-bar (No. 2); compound 2 crystallized in monoclinic space group P2{sub 1}/c (No. 14). The structure of 1 is built from a 1D MOF, composed of deprotonated citric ligands of three kinds. Compound 2 contains a 2D MOF structure consisting of citrate and oxalate ligands; the oxalate ligand arose from the decomposition in situ of citric acid in the presence of Cu{sup II} ions. Photoluminescence spectra of compounds 1b and 2 revealed transitions between the 5d{sup 1} excited state and two levels of the 4f{sup 1} ground state ({sup 2}F{sub 5/2} and {sup 2}F{sub 7/2}). Compounds 1b and 2 containing Ce{sup III} ion exhibit a paramagnetic property with weak antiferromagnetic interactions between the two adjacent magnetic centers. - Graphical Abstract: [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2)-with 1D and 2D structures were synthesized and characterized. Highlights: Black-Right-Pointing-Pointer Two MOF - [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2) - with 1D and 2D structures. Black-Right-Pointing-Pointer The adjacent chains of the 1D framework were correlated with each other through an oxalate

  18. Reaction channels and spectroscopic constants of astrophysical relevant Silicon bearing molecules SiC3H,+ and SiC3H

    NASA Astrophysics Data System (ADS)

    Inostroza Pino, N.; Cardenas, C.; Fuentealba, P.

    2014-10-01

    Reaction channels and spectroscopic properties of a series of silicon-carbon-bearing isomers of SiC3H+ and SiC3H, which are suitable species for astrophysical detection in carbon-rich sources, are calculated with correlated ab initio CCSD(T) and density functional theory methods. We present four isomers of SiC3H+ for which the electronic ground states have closed-shell configurations. For SiC3H, we considered the same structures in order to present a complete study. The global minimum among the SiC3H+ isomers corresponds to the rhomboidal structure with a transannular bond in a 1A1 electronic state (rb3-SiC3H+ C2v X1A1). The next minima correspond to a second rhomboid 1A1 isomer and a linear isomer (X1Σ+) with relative energies 0.86 and 0.93 eV, respectively at the CCSD(T)/cc-pvTZ level of theory. The most stable mono-hydrogenated silicon carbon isomer is linear, followed by two rhomboidal isomers, rb2-SiC3H and rb3-SiC3H (0.23 and 0.31 eV). For each structure, a set of spectroscopic parameters including their equilibrium structures, rotational constants, harmonic frequencies and dipole moment is presented. Furthermore, we discuss plausible formation pathways of SiC3H+ isomers which are classified as charge-exchange, ion-neutral and dissociative recombination reactions. These results show one favourable pathway to produce rb3-SiC3H+ from rb-SiC3-3s. The formation energy of the cation's isomers coming from neutral isomers as linear l1-SiC3H, rb3-SiC3H and rb2-SiC3H plus H+ as reactants (charge-exchange reaction) are 203.8 kcal mol-1 (8.84eV), 175.4 kcal mol-1 (7.60 eV) and 195.2 kcal mol-1 (8.46 eV), which provides us with evidence of the endergonic character of these reactions. As a consequence, it does not seem to be feasible to produce a cation from neutral reactant plus H+ by a charge-exchange reaction that was proposed by UMIST.

  19. Liquid infiltration and pyrolysis of SiC matrix composite materials

    SciTech Connect

    Casadio, S.; Nanneti, C.A.; Donato, A.

    1995-12-01

    SiC matrix composites were prepared by prepregging carbon and Nicalon fibre cloths with polycarbosilane (PCS) solution or nanosized SiC powder dispersion in PCS solution. After consolidation of the stacked cloths and pyrolysis, densification of the matrix was accomplished by multiple infiltration/pyrolysis steps with PCS solution. The pyrolysis behaviour of the SiC nanopowder/PCS matrix material was investigated in comparison to PCS.

  20. SiC (SCS-6) Fiber Reinforced-Reaction Formed SiC Matrix Composites: Microstructure and Interfacial Properties

    NASA Technical Reports Server (NTRS)

    Singh, M.; Dickerson, R. M.; Olmstead, Forrest A.; Eldridge, J. I.

    1997-01-01

    Microstructural and interfacial characterization of unidirectional SiC (SCS-6) fiber reinforced-reaction formed SiC (RFSC) composites has been carried out. Silicon-1.7 at.% molybdenum alloy was used as the melt infiltrant, instead of pure silicon, to reduce the activity of silicon in the melt as well as to reduce the amount of free silicon in the matrix. Electron microprobe analysis was used to evaluate the microstructure and phase distribution in these composites. The matrix is SiC with a bi-modal grain-size distribution and small amounts of MoSi2, silicon, and carbon. Fiber push-outs tests on these composites showed that a desirably low interfacial shear strength was achieved. The average debond shear stress at room temperature varied with specimen thickness from 29 to 64 MPa, with higher values observed for thinner specimens. Initial frictional sliding stresses showed little thickness dependence with values generally close to 30 MPa. Push-out test results showed very little change when the test temperature was increased to 800 C from room temperature, indicating an absence of significant residual stresses in the composite.

  1. Mechanism on heavy metals vaporization from municipal solid waste fly ash by MgCl2⋅6H2O.

    PubMed

    Yu, Jie; Sun, Lushi; Ma, Chuan; Qiao, Yu; Xiang, Jun; Hu, Song; Yao, Hong

    2016-03-01

    This work aims to study the mechanism of heavy metals vaporization by MgCl2⋅6H2O. Firstly, the decomposition mechanism of MgCl2⋅6H2O was investigated by thermodynamic equilibrium calculations, XRD and TG. Upon heating, MgCl2⋅6H2O went through the processes of dehydration and hydrolysis simultaneously accompanied by the release of HCl between 150 and 500°C. At temperature higher than 500°C, Mg(OH)Cl gradually release part of HCl. MgCl2⋅6H2O followed the similar processes of decomposition at both oxidative and reductive atmospheres. In oxidative atmosphere, vaporization of Zn and Cu was significantly accelerated by MgCl2⋅6H2O. However, in inert atmosphere, vaporization of Cu was not promoted since copper chloride was only stable in oxidative atmosphere. Under slow heating condition, vaporization of heavy metals were close to that under fast heating condition. This may be partially attributed to that most heavy metals already reacted with HCl forming metal chlorides below 500°C, which can be vaporized at higher temperature. Moreover, the Mg(OH)Cl contributed to release HCl up to 800°C. At such high temperature, the metal chlorides continue to be formed and then vaporized. After treatment, the leaching concentration of heavy metals from treated fly ashes were much lower than that from raw fly ash and met the regulatory limit of leachate. Since a large amount of MgSiO3 were formed during thermal treatment, the fly ash treated with MgCl2⋅6H2O can be used as raw materials for glass-ceramics production. PMID:26748437

  2. Reversible addition of water to the high-hydride-content cluster [Rh6(PiPr3)6H12][BArF4]2. Synthesis and Structure of [Rh6PiPr3)6H11(OH)][BArF4]2.

    PubMed

    Douglas, Thomas M; Brayshaw, Simon K; Raithby, Paul R; Weller, Andrew S

    2008-02-01

    The hydroxyhydrido salt [Rh(6)(P(i)Pr(3))(6)H(11)(OH)][BArF(4)](2) results from the addition of water to [Rh(6)(P(i)Pr(3))(6)H(12)][BArF(4)](2). This reaction is reversible, and the addition of dihydrogen to [Rh(6)(P(i)Pr(3))(6)H(11)(OH)][BArF(4)](2) results in the elimination of water and the regeneration of the hydride cluster. PMID:18181618

  3. High quality SiC microdisk resonators fabricated from monolithic epilayer wafers

    SciTech Connect

    Magyar, Andrew P.; Bracher, David; Lee, Jonathan C.; Hu, Evelyn L.; Aharonovich, Igor

    2014-02-03

    The exquisite mechanical properties of SiC have made it an important industrial material with applications in microelectromechanical devices and high power electronics. Recently, the optical properties of SiC have garnered attention for applications in photonics, quantum information, and spintronics. This work demonstrates the fabrication of microdisks formed from a p-N SiC epilayer material. The microdisk cavities fabricated from the SiC epilayer material exhibit quality factors of as high as 9200 and the approach is easily adaptable to the fabrication of SiC-based photonic crystals and other photonic and optomechanical devices.

  4. Presolar SiC in chondrites - How variable and how many sources?

    NASA Astrophysics Data System (ADS)

    Alexander, C. M. O'd.

    1993-06-01

    The carbon and silicon isotropic compositions of 246 isotopically anomalous SiC grains measured in low concentration residues are reported. The residues were prepared from nine chondrites, namely, 6 unequilibrated ordinary chondrites (UOCs), Qingzhen (EH3), Leoville (CV3), and Murchison (CM2). Murchison is used as a standard to which all the other meteorites studied are compared. The range of isotopic compositions exhibited by UOC SiC is found to be similar to Murchison, except in Inman. Inman SiC has a distinctly different distribution of its silicon isotopic composition compared to the other meteorites. Residues from Qingzhen and Leoville produce only one anomalous SiC grain each.

  5. SiC optics for EUV, UV, and visible space missions

    NASA Astrophysics Data System (ADS)

    Robichaud, Joseph L.

    2003-02-01

    An overview of silicon carbide (SiC) materials is provided, focusing on reaction bonded (RB) SiC and its properties. The Miniature Infrared Camera and Spectrometer (MICAS) and Advanced Land Imager (ALI) SiC space instruments produced by SSGPO and flown under NASA's New Millennium Program are described, and some of the mission requirements associated with UV and extreme UV (EUV) applications are reviewed. Manufacturing options associated with SiC reflectors are reviewed and the optical performance demonstrated with these materials is presented. In order to review the suitability of these materials to UV and EUV missions microroughness and surface scatter results are shown.

  6. Review of data on irradiation creep of monolithic SiC

    SciTech Connect

    Garner, F.A.; Youngblood, G.E.; Hamilton, M.L.

    1996-04-01

    An effort is now underway to design an irradiation creep experiment involving SiC composites to SiC fibers. In order to successfully design such an experiment, it is necessary to review and assess the available data for monolithic SiC to establish the possible bounds of creep behavior for the composite. The data available show that monolithic SiC will indeed creep at a higher rate under irradiation compared to that of thermal creep, and surprisingly, it will do so in a temperature-dependant manner that is typical of metals.

  7. Particles cellulation composite (PCC): Dispersion morphology of SiC particles in Si{sub 3}N{sub 4}/SiC composites

    SciTech Connect

    Yamada, K.; Kamiya, N.

    1995-10-01

    Dispersion morphology of fine SiC particles in Si{sub 3}N{sub 4}/xSiC (x = 0, 10, 20, 30wt%, average size: 0.03 {micro} m) composites was statistically analyzed, and typical properties of the composites such as creep, electric and thermal conductivity were investigated. The dispersion morphology of SiC particles was analyzed by observing the ECR-plasma etched surface of the sintered composites using scanning electron microscopy. SiC particles in Si{sub 3}N{sub 4}/SiC composites were distributed both within Si{sub 3}N{sub 4} grains and on Si{sub 4}N{sub 4} grain boundary, but 90% or more of them was located on the grain boundary. For the composites with 20--30 wt%SiC, the SiC particles on the grain boundary clearly formed a three-dimensional network structure surrounding a few or more Si{sub 3}N{sub 4} crystalline grains. A Si{sub 3}N{sub 4}/SiC composite with a three-dimensional network structure of SiC particles, named particles cellulation composite (PCC), was artificially made by pressing the granulated Si{sub 3}N{sub 4} powder (less than 500 {micro} m diameter) discontinuously coated with SiC particles (average size: 0.4 {micro}m). The creep deformation of PCC was reduced to about 60% of that of the composites with SiC particles randomly dispersed. Electrical and thermal properties were also improved. These results suggest that the formation of three-dimensional network structure by the second phase particles in a composite would considerably improve its mechanical property as well as electrical and thermal properties.

  8. Isolation of 1,4-Li(2)-C(6)H(4) and its reaction with [(Ph(3)P)AuCl].

    PubMed

    Flower, Kevin R; McGown, A T; Miles, Philip J; Pritchard, Robin G; Warren, John E

    2010-04-14

    The difficulty in generating 1,4-Li2-C6H4 utilising the lithium halogen exchange reaction on 1,4-Br2-C6H4, 1,4-I2-C6H4 and 1-Br-4-I-C6H4 is revisited and only on treatment of 1,4-I2-C6H4 with 2 molar equivalents of n-BuLi can 1,4-Li2-C6H4 1 be isolated in excellent yield. Treatment of 1 with two equivalents of [ClAu(PPh3)] gives [1,4-(Ph3PAu)2-C6H4] 2a in excellent yield. Subsequent treatment of 2a with 2.5 molar equivalents of PPh2Me, PPhMe2 or PMe3 affords the PPh3 substituted compounds [1,4-(LAu)2-C6H4] (L = PPh2Me 2b, PPhMe2 2c, PMe3 2d) in essentially quantitative yields. On treatment of 1,4-Br2-C6H4 or 1-Br-4-I-C6H4 with 2 molar equivalents of n-BuLi only mono-lithiation takes place to give 1-Br-4-Li-C6H4 3 as shown through the isolation of essentially 1:1 molar equivalents of Ph2PC6H4-4-Br and Ph2PBu on treatment with 2 molar equivalents of ClPPh2. Treatment of 3, prepared by lithium/iodine exchange on 1-Br-4-I-C6H4, with [ClAu(PPh3)] affords [(Ph3P)Au(C6H4-4-Br)] 4 as expected and in addition [(Ph3P)Au(n-Bu)(C6H4-4-Br)2] 5, indicating the straightforward chloride/aryl exchange at gold may proceed in competition with oxidative addition of the n-BuI, generated in the initial lithium/iodine exchange reaction, to some aurate complex Li[Au(C6H4-4-Br)2] 6 formed in situ followed by reductive elimination of Br-C6H4-4-n-Bu in a manner that mimics lithium diorganocuprate chemistry. All of the gold-containing compounds have been spectroscopically characterised by 1H and 31P-{1H} NMR and in addition compounds 2a-d and 5 by single crystal X-ray diffraction studies. The solid state structures observed for 2a-d are dictated by non-conventional hydrogen bonding and the packing requirements of the phosphine ligands. For 2a and 2b there is no close Au...Au approach, however for 2c and 2d the reduction in the number of phenyl rings allows the formation of Au...Au contacts. For 2c and 2d the extended structures appear to be helical chains with Au...Au contact parameters of 3

  9. Effect of Rare Gas Dilution of SF6 Plasma on RIE Etching Characteristics of SiC

    NASA Astrophysics Data System (ADS)

    Ganguly, J. D.; Bletzinger, B. N.

    1999-10-01

    The etch rates and the anisotropy of etched features of hexagonal 6H-SiC have been measured in a capacitively coupled rf discharge using SF_6+Ar and SF_6+He diluted gas mixtures. These measurements provide evidence for the generic nature of utilizing gas mixtures to modify electrical characteristics of rf discharges to optimize power coupling efficiency, although etch rates and surface morphology do not necessarily scale only with the plasma power coupling efficiency. In spite of the measured lower power deposition with He dilution compared to Ar, He diluted SF6 plasma resulted in 1.5 greater etch rates (up to 300 nm/min) with 50% He dilution, with better anisotropy and surface texture than comparable SF_6+Ar mixtures. Superior SiC etch performance was obtained with He dilution, compared to Ar, over the entire 10% up to 90% range despite lower power coupling efficiency and the notion that Ar^+ ions are expected to enhance ion assisted etch mechanism. The differences in dc self bias and volume plasma E/n leading to the conversion of SF_5^+ ions to SF_3^+ along with Penning ionization of SF6 by metastable He atoms may be responsible for the observed superior etch characteristics.

  10. Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

    DOE PAGESBeta

    Gearba, Raluca I.; Mueller, Kory M.; Veneman, Peter A.; Holliday, Bradley J.; Chan, Calvin K.; Stevenson, Keith J.

    2015-05-09

    Owing to its high conductivity, graphene holds promise as an electrode for energy devices such as batteries and photovoltaics. However, to this end, the work function and doping levels in graphene need to be precisely tuned. One promising route for modifying graphene’s electronic properties is via controlled covalent electrochemical grafting of molecules. We show that by employing diaryliodonium salts instead of the commonly used diazonium salts, spontaneous functionalization is avoided. This then allows for precise tuning of the grafting density. Moreover, by employing bis(4-nitrophenyl)iodonium(III) tetrafluoroborate (DNP) salt calibration curves, the surface functionalization density (coverage) of glassy carbon was controlled usingmore » cyclic voltammetry in varying salt concentrations. These electro-grafting conditions and calibration curves translated directly over to modifying single layer epitaxial graphene substrates (grown on insulating 6H-SiC (0 0 0 1)). In addition to quantifying the functionalization densities using electrochemical methods, samples with low grafting densities were characterized by low-temperature scanning tunneling microscopy (LT-STM). We show that the use of buffer-layer free graphene substrates is required for clear observation of the nitrophenyl modifications. Furthermore, atomically-resolved STM images of single site modifications were obtained, showing no preferential grafting at defect sites or SiC step edges as supposed previously in the literature. Most of the grafts exhibit threefold symmetry, but occasional extended modifications (larger than 4 nm) were observed as well.« less

  11. Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

    SciTech Connect

    Gearba, Raluca I.; Mueller, Kory M.; Veneman, Peter A.; Holliday, Bradley J.; Chan, Calvin K.; Stevenson, Keith J.

    2015-05-09

    Owing to its high conductivity, graphene holds promise as an electrode for energy devices such as batteries and photovoltaics. However, to this end, the work function and doping levels in graphene need to be precisely tuned. One promising route for modifying graphene’s electronic properties is via controlled covalent electrochemical grafting of molecules. We show that by employing diaryliodonium salts instead of the commonly used diazonium salts, spontaneous functionalization is avoided. This then allows for precise tuning of the grafting density. Moreover, by employing bis(4-nitrophenyl)iodonium(III) tetrafluoroborate (DNP) salt calibration curves, the surface functionalization density (coverage) of glassy carbon was controlled using cyclic voltammetry in varying salt concentrations. These electro-grafting conditions and calibration curves translated directly over to modifying single layer epitaxial graphene substrates (grown on insulating 6H-SiC (0 0 0 1)). In addition to quantifying the functionalization densities using electrochemical methods, samples with low grafting densities were characterized by low-temperature scanning tunneling microscopy (LT-STM). We show that the use of buffer-layer free graphene substrates is required for clear observation of the nitrophenyl modifications. Furthermore, atomically-resolved STM images of single site modifications were obtained, showing no preferential grafting at defect sites or SiC step edges as supposed previously in the literature. Most of the grafts exhibit threefold symmetry, but occasional extended modifications (larger than 4 nm) were observed as well.

  12. Active in-core irradiation of SiC JFETs at 300 C in a TRIGA nuclear reactor

    SciTech Connect

    McGarrity, J.; Scozzie, C.; Blackburn, J.; DeLancey, M.

    1996-12-31

    In this paper the authors demonstrate that SiC transistors have the potential to operate in the severe high temperature and radiation environments of commercial and space nuclear power sources. 6H-SiC FETs were exposed to neutron fluxes and gamma dose rates as high as 1.6 {times} 10{sup 12} n/cm{sup 2}/sec and 3.8 {times} 10{sup 4} rad(Si)/sec while they were maintained under bias at both 300 C and room temperature within the core of a TRIGA reactor operated at 200 kW power level. The radiation exposure was continuous and the bias on the devices was interrupted only to record the current-voltage characteristics at various accumulated neutron fluences from 10{sup 13} to 5 {times} 10{sup 15} n/cm{sup 2}. No significant degradation in the device characteristics was observed until the total neutron fluence exceeded 10{sup 15} n/cm{sup 2} for irradiation at 25 C, and no significant changes were observed even at 5 {times} 10{sup 15} n/cm{sup 2} at 300 C.

  13. Hexagonal phase-pure wide band gap ɛ-Ga2O3 films grown on 6H-SiC substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xia, Xiaochuan; Chen, Yuanpeng; Feng, Qiuju; Liang, Hongwei; Tao, Pengcheng; Xu, Mengxiang; Du, Guotong

    2016-05-01

    In this paper, hexagonal structure phase-pure wide-band gap ɛ-Ga2O3 films were grown by metal organic chemical vapor deposition on 6H-SiC substrates. The ɛ-Ga2O3 films with good crystal quality were verified by high-resolution X-ray diffraction. The out-of-plane epitaxial relationship between ɛ-Ga2O3 films and 6H-SiC substrates is confirmed to be ɛ-Ga2O3 (0001)//6H-SiC (0001), and the in-plane epitaxial relationship is also confirmed to be ɛ-Ga2O3 ⟨ 11 2 ¯ 0 ⟩//6H-SiC ⟨ 11 2 ¯ 0 ⟩. The SEM and AFM images show that the ɛ-Ga2O3 films are uniform and flat. The ɛ-Ga2O3 films are thermally stable up to approximately 800 °C and begin to transform into β-phase Ga2O3 at 850 °C. Then, they are completely converted to β-Ga2O3 films under 900 °C. The high-quality ɛ-Ga2O3 films with hexagonal structure have potential application in the optoelectronic field.

  14. Ring-opening polymerization of epoxidized soybean oil catalyzed by the superacid, Fluroantimonic acid hexahydrate (HSbF6-6H2O)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by the super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), in ethyl acetate was conducted. The resulting polymers, SA-RPESO, were characterized using infrared spectroscopy, differential scanning calorimetry, thermogravimetri...

  15. Chromium-induced tropane alkaloid production and H6H gene expression in Atropa belladonna L. (Solanaceae) in vitro-propagated plantlets.

    PubMed

    Vakili, Bahareh; Karimi, Farah; Sharifi, Mozafar; Behmanesh, Mehrdad

    2012-03-01

    Hyoscyamine and scopolamine tropane alkaloids found in several solanaceous plants are anticholinergic drugs. Hyoscyamine 6β-hydroxylase (H6H) catalyzes two consecutive oxidation reactions. The first reaction is the hydroxylation of hyoscyamine to 6β-hydroxyhyoscyamine and the second is epoxidation of 6β-hydroxyhyoscyamine yielding scopolamine that is the final metabolite in the tropane alkaloid biosynthetic pathway. The effects of trivalent chromium as KCr (SO4)(2) on the production of tropane alkaloids and the expression of hyoscyamine 6β-hydroxylase gene (h6h) were studied in micro-propagated Atropa belladonna L. plantlets. The results showed that chromium treatment decreased the growth parameters (weights and lengths of the plantlets) and chlorophyll contents and increased proline contents. Moreover, semiquantitave RT-PCR analysis showed that the transcript level of H6H increased under chromium treatment. This treatment also increased hyoscyamine and scopolamine contents as shown by HPLC analysis. Changes of scopolamine contents correlate with the expression levels of h6h gene under different concentrations of chromium. PMID:22305072

  16. Structures and Spectroscopic Properties Calculated for C_6H_7^+ and its Complexes with Ne, Ar, N_2, or CO_2

    NASA Astrophysics Data System (ADS)

    Botschwina, P.; Oswald, R.

    2012-06-01

    Explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level in conjunction with the double-hybrid density functional B2PLYP-D has been employed in a study of the benzenium ion (C_6H_7^+) and its complexes with simple ligands (L = Ne, Ar, N_2, or CO_2). The ground-state rotational constants of C_6H_7^+ are predicted to be A_0 = 5445 MHz, B_0 = 5313 MHz, and C_0 = 2731 MHz. For the complexes with L = Ne, Ar or N_2, the energetically most favourable structure is of π-bonded type, but for the most strongly bound complex C_6H_7^+ ... CO_2 a conformer with the CO_2 ligand lying in the ring-plane of the C_6H_7^+ moiety is slightly lower in energy. T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys. 127, 221106 (2007) G. Knizia, T. B. Adler, and H.-J. Werner, J. Chem. Phys. 130, 054104 (2009). T. Schwabe and S. Grimme, Phys. Chem. Chem. Phys. 9, 3397 (2007). P. Botschwina and R. Oswald, J. Phys. Chem. A 115, 13664 (2011) P. Botschwina and R. Oswald, J. Chem. Phys. submitted.

  17. Segregation of Incomplete Achromatopsia and Alopecia Due to PDE6H and LPAR6 Variants in a Consanguineous Family from Pakistan.

    PubMed

    Pedurupillay, Christeen Ramane J; Landsend, Erlend Christoffer Sommer; Vigeland, Magnus Dehli; Ansar, Muhammad; Frengen, Eirik; Misceo, Doriana; Strømme, Petter

    2016-01-01

    We report on two brothers with visual impairment, and non-syndromic alopecia in the elder proband. The parents were first-degree Pakistani cousins. Whole exome sequencing of the elder brother and parents, followed by Sanger sequencing of all four family members, led to the identification of the variants responsible for the two phenotypes. One variant was a homozygous nonsense variant in the inhibitory subunit of the cone-specific cGMP phosphodiesterase gene, PDE6H:c.35C>G (p.Ser12*). PDE6H is expressed in the cones of the retina, which are involved in perception of color vision. This is the second report of a homozygous PDE6H:c.35C>G variant causing incomplete achromatopsia (OMIM 610024), thus strongly supporting the hypothesis that loss-of-function variants in PDE6H cause this visual deficiency phenotype. The second variant was a homozygous missense substitution in the lysophosphatidic acid receptor 6, LPAR6:c.188A>T (p.Asp63Val). LPAR6 acts as a G-protein-coupled receptor involved in hair growth. Biallelic loss-of-function variants in LPAR6 cause hypotrichosis type 8 (OMIM 278150), with or without woolly hair, a form of non-syndromic alopecia. Biallelic LPAR6:c.188A>T was previously described in five families from Pakistan. PMID:27472364

  18. Structure activity optimization of 6H-pyrrolo[2,3-e][1,2,4]triazolo[4,3-a]pyrazines as Jak1 kinase inhibitors.

    PubMed

    Friedman, Michael; Frank, Kristine E; Aguirre, Ana; Argiriadi, Maria A; Davis, Heather; Edmunds, Jeremy J; George, Dawn M; George, Jonathan S; Goedken, Eric; Fiamengo, Bryan; Hyland, Deborah; Li, Bin; Murtaza, Anwar; Morytko, Michael; Somal, Gagandeep; Stewart, Kent; Tarcsa, Edit; Van Epps, Stacy; Voss, Jeffrey; Wang, Lu; Woller, Kevin; Wishart, Neil

    2015-10-15

    Previous work investigating tricyclic pyrrolopyrazines as kinase cores led to the discovery that 1-cyclohexyl-6H-pyrrolo[2,3-e][1,2,4]triazolo[4,3-a]pyrazine (12) had Jak inhibitory activity. Herein we describe our initial efforts to develop orally bioavailable analogs of 12 with improved selectivity of Jak1 over Jak2. PMID:26372653

  19. Segregation of Incomplete Achromatopsia and Alopecia Due to PDE6H and LPAR6 Variants in a Consanguineous Family from Pakistan

    PubMed Central

    Pedurupillay, Christeen Ramane J.; Landsend, Erlend Christoffer Sommer; Vigeland, Magnus Dehli; Ansar, Muhammad; Frengen, Eirik; Misceo, Doriana; Strømme, Petter

    2016-01-01

    We report on two brothers with visual impairment, and non-syndromic alopecia in the elder proband. The parents were first-degree Pakistani cousins. Whole exome sequencing of the elder brother and parents, followed by Sanger sequencing of all four family members, led to the identification of the variants responsible for the two phenotypes. One variant was a homozygous nonsense variant in the inhibitory subunit of the cone-specific cGMP phosphodiesterase gene, PDE6H:c.35C>G (p.Ser12*). PDE6H is expressed in the cones of the retina, which are involved in perception of color vision. This is the second report of a homozygous PDE6H:c.35C>G variant causing incomplete achromatopsia (OMIM 610024), thus strongly supporting the hypothesis that loss-of-function variants in PDE6H cause this visual deficiency phenotype. The second variant was a homozygous missense substitution in the lysophosphatidic acid receptor 6, LPAR6:c.188A>T (p.Asp63Val). LPAR6 acts as a G-protein-coupled receptor involved in hair growth. Biallelic loss-of-function variants in LPAR6 cause hypotrichosis type 8 (OMIM 278150), with or without woolly hair, a form of non-syndromic alopecia. Biallelic LPAR6:c.188A>T was previously described in five families from Pakistan. PMID:27472364

  20. Cryptolepine derivative-6h inhibits liver fibrosis in TGF-β1-induced HSC-T6 cells by targeting the Shh pathway.

    PubMed

    He, Ying-Hua; Li, Zeng; Ni, Ming-Ming; Zhang, Xing-Yan; Li, Ming-Fang; Meng, Xiao-Ming; Huang, Cheng; Li, Jun

    2016-09-01

    Liver fibrosis is a worldwide problem with a significant morbidity and mortality. Cryptolepis sanguinolenta (family Periplocaceae) is widely used in West African countries for the treatment of malaria, as well as for some other diseases. However, the role of C. sanguinolenta in hepatic fibrosis is still unknown. It has been reported that Methyl-CpG binding protein 2 (MeCP2) had a high expression in liver fibrosis and played a central role in its pathobiology. Interestingly, we found that a cryptolepine derivative (HZ-6h) could inhibit liver fibrosis by reducing MeCP2 expression, as evidenced by the dramatic downregulation of α-smooth muscle actin (α-SMA) and type I collagen alpha-1 (Col1α1) in protein levels in vitro. Meanwhile, we also found that HZ-6h could reduce the cell viability and promote apoptosis of hepatic stellate cells (HSCs) treated with transforming growth factor beta 1(TGF-β1). Then, we investigated the potential molecular mechanisms and found that HZ-6h blocked Shh signaling in HSC-T6 cells, resulting in the decreased protein expression of Patched-1 (PTCH-1), Sonic hedgehog (Shh), and glioma-associated oncogene homolog 1 (GLI1). In short, these results indicate that HZ-6h inhibits liver fibrosis by downregulating MeCP2 through the Shh pathway in TGF-β1-induced HSC-T6 cells. PMID:27295431

  1. Processing of laser formed SiC powder

    NASA Technical Reports Server (NTRS)

    Haggerty, J. S.; Bowen, H. K.

    1985-01-01

    Superior SiC characteristics can be achieved through the use of ideal constituent powders and careful post-synthesis processing steps. High purity SiC powders of approx. 1000 A uniform diameter, nonagglomerated and spherical were produced. This required major revision of the particle formation and growth model from one based on classical nucleation and growth to one based on collision and coalescence of Si particles followed by their carburization. Dispersions based on pure organic solvents as well as steric stabilization were investigated. Although stable dispersions were formed by both, subsequent part fabrication emphasized the pure solvents since fewer problems with drying and residuals of the high purity particles were anticipated. Test parts were made by the colloidal pressing technique; both liquid filtration and consolidation (rearrangement) stages were modeled. Green densities corresponding to a random close packed structure (approx. 63%) were achieved; this highly perfect structure has a high, uniform coordination number (greater than 11) approaching the quality of an ordered structure without introducing domain boundary effects. After drying, parts were densified at temperatures ranging from 1800 to 2100 C. Optimum densification temperatures will probably be in the 1900 to 2000 C range based on these preliminary results which showed that 2050 C samples had experienced substantial grain growth. Although overfired, the 2050 C samples exhibited excellent mechanical properties. Biaxial tensile strengths up to 714 MPa and Vickers hardness values of 2430 kg/sq mm 2 were both more typical of hot pressed than sintered SiC. Both result from the absence of large defects and the confinement of residual porosity (less than 2.5%) to small diameter, uniformly distributed pores.

  2. Computational Study of the Clustering of a Cyclohexene Autoxidation Product C6H8O7 with Itself and Sulfuric Acid.

    PubMed

    Elm, Jonas; Myllys, Nanna; Hyttinen, Noora; Kurtén, Theo

    2015-07-30

    We investigate the molecular interactions between sulfuric acid and a recently reported C6H8O7 ketodiperoxy acid formed through autoxidation from cyclohexene and ozone. Structurally similar but larger ELVOC (extremely low volatility organic compound) products formed from autoxidation of monoterpenes are believed to play a major role in the formation and early growth of atmospheric aerosol particles. Utilizing density functional theory geometries, with a DLPNO-CCSD(T)/def2-QZVPP single point energy correction, the stepwise Gibbs free energies of formation have been calculated, and the stabilities of the molecular clusters have been evaluated. C6H8O7 interacts weakly with both itself and sulfuric acid, with standard free energies of formation (ΔG at 298 K and 1 atm) around or above 0 kcal/mol. This is due to the presence of strong intramolecular hydrogen bonds in the peroxyacid groups of C6H8O7. These stabilize the isolated molecule with respect to its clusters, and lead to unfavorable interaction energies. The addition of sulfuric acid to clusters containing C6H8O7 is somewhat more favorable, but the formed clusters are still far more likely to evaporate than to grow further in atmospheric conditions. These findings indicate that the O/C ratio cannot exclusively be used as a proxy for volatility in atmospheric new particle formation involving organic compounds. The specific molecular structure, and especially the number of strong hydrogen binding moieties, are equally important. The interaction between the C6H8O7 compound and aqueous phase sulfate ions indicates that ELVOC-type compounds can contribute to aerosol mass by effectively partitioning into the condensed phase. PMID:26154271

  3. Pleiotropy in microdeletion syndromes: Neurologic and spermatogenic abnormalities in mice homozygous for the p{sup 6H} deletion are likely due to dysfunction of a single gene

    SciTech Connect

    Rinchik, E.M.; Carpenter, D.A.; Handel, M.A.

    1995-07-03

    Variability and complexity of phenotypes observed in microdeletion syndromes can be due to deletion of a single gene whose product participates in several aspects of development or can be due to the deletion of a number of tightly linked genes, each adding its own effect to the syndrome. The p{sup 6H} deletion in mouse chromosome 7 presents a good model with which to address this question of multigene vs. single-gene pleiotropy. Mice homozygous for the p{sup 6H} deletion are diluted in pigmentation, are smaller than their littermates, and manifest a nervous jerky-gait phenotype. Male homozygotes are sterile and exhibit profound abnormalities in spermiogenesis. By using N-ethyl-N-nitrosourea (EtNU) mutagenesis and a breeding protocol designed to recover recessive mutations expressed hemizygously opposite a large p-locus deletion, we have generated three noncomplementing mutations that map to the p{sup 6H} deletion. Each of these EtNU-induced mutations has adverse effects on the size, nervous behavior, and progression of spermiogenesis that characterize p{sup 6H} deletion homozygotes. Because etNU is thought to induce primarily intragenic (point) mutations in mouse stem-cell spermatogonia, we propose that the trio of phenotypes (runtiness, nervous jerky gait, and male sterility) expressed in p{sup 6H} deletion homozygotes is the result of deletion of a single highly pleiotropic gene. We also predict that a homologous single locus, quite possibly tightly linked and distal to the D15S12 (P) locus in human chromosome 15q11-q13, may be associated with similar developmental abnormalities in humans. 29 refs., 3 figs., 1 tab.

  4. Thermomechanical Behavior of Advanced SiC Fiber Multifilament Tows

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; DiCarlo, James A.

    1997-01-01

    In order to relate single fiber behavior to multiple fiber behavior in composites, fast-fracture tensile strength, creep, and stress-rupture studies were conducted on advanced SiC fiber multifilament tows in the temperature range from 20 to 1400 C in air as well as in inert environments. For conditions of small fiber creep (short times and low temperatures), the tow results of this study confirm the ability of limited single fiber data to model the strength behavior of multiple fibers in a bundle. For conditions of high creep (long times and high temperatures), further studies are needed to explain tow rupture behavior being better than average single fiber behavior.

  5. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In this photograph taken on August 5th, 1961, a back hoe is nearly submerged in water in the test stand site. During the initial digging, the disturbance of a natural spring contributed to constant water problems during the construction process. It was necessary to pump the water from the site on a daily basis and is still pumped from the site today.

  6. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo shows the construction progress of the test stand as of August 14, 1961. Water gushing in from the disturbance of a natural spring contributed to constant water problems during the construction process. It was necessary to pump water from the site on a daily basis and is still pumped from the site today. The equipment is partially submerged in the water emerging from the spring.

  7. CONTACT RESISTANCE AT A CVD-SIC/NI INTERFACE

    SciTech Connect

    Youngblood, Gerald E.; Thomsen, Edwin C.

    2011-04-17

    The primary objectives of this task are: (1) to assess the properties and behavior of SiCf/SiC composites made from SiC fibers (with various SiC-type matrices, fiber coatings and architectures) before and after irradiation, and (2) to develop analytic models that describe these properties as a function of temperature and dose as well as composite architecture. In support of the U.S. dual-coolant lead-lithium (DCLL) fusion reactor blanket concept, recent efforts have focused on examining the electrical conductivity properties of SiCf/SiC composites considered for application in FCI-structures.

  8. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. This photo, taken September 5, 1961, shows the construction of forms which became the concrete foundation for the massive stand. The lower right hand corner reveals a pump used for extracting water emerging from a disturbed natural spring that occurred during excavation of the site. The pumping became a daily ritual and the site is still pumped today.

  9. Ultra High Temperature (UHT) SiC Fiber (Phase 2)

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Jacobson, Nathan S.; Lizcano, Maricela; Bhatt, Ramakrishna T.

    2015-01-01

    Silicon-carbide fiber-reinforced silicon-carbide ceramic matrix composites (SiCSiC CMC) are emerginglightweight re-usable structural materials not only for hot section components in gas turbine engines, but also for controlsurfaces and leading edges of reusable hypersonic vehicles as well as for nuclear propulsion and reactor components. Ithas been shown that when these CMC are employed in engine hot-section components, the higher the upper usetemperature (UUT) of the SiC fiber, the more performance benefits are accrued, such as higher operating temperatures,reduced component cooling air, reduced fuel consumption, and reduced emissions. The first generation of SiCSiC CMC with a temperature capability of 2200-2400F are on the verge of being introduced into the hot-section components ofcommercial and military gas turbine engines.Today the SiC fiber type currently recognized as the worlds best in terms ofthermo-mechanical performance is the Sylramic-iBN fiber. This fiber was previously developed by the PI at NASA GRC using patented processes to improve the high-cost commercial Sylramic fiber, which in turn was derived from anotherlow-cost low-performance commercial fiber. Although the Sylramic-iBN fiber shows state-of-the art creep and rupture resistance for use temperatures above 2550oF, NASA has shown by fundamental creep studies and model developmentthat its microstructure and creep resistance could theoretically be significantly improved to produce an Ultra HighTemperature (UHT) SiC fiber.This Phase II Seedling Fund effort has been focused on the key objective of effectively repeating the similar processes used for producing the Sylramic-iBN fiber using a design of experiments approach to first understand the cause of the less than optimum Sylramic-iBN microstructure and then attempting to develop processconditions that eliminate or minimize these key microstructural issues. In so doing, it is predicted that that theseadvanced process could result in an UHT SiC

  10. Plastic deformation of alumina reinforced with SiC whiskers

    SciTech Connect

    DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A.; Goretta, K.C.; Routbort, J.L.

    1993-06-01

    Addition of small amounts of stiff reinforcement (SiC whiskers) to a polycrystalline AL{sub 2}O{sub 3} matrix partially inhibits grain boundary sliding because of an increase in threshold stress. When the concentration of whiskers is high enough, a pure diffusional mechanism takes over the control of plastic deformation of the composites. For higher whisker loadings, the materials creep properties depend on a microstructural feature different from the nominal grain size. A tentative correlation of this effective microstructural parameter with the spacing between the whiskers was established through a model.

  11. Construction Progress of S-IC Test Stand Pump House

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In addition to the stand itself, related facilities were constructed during this time. Built to the northeast east was a newly constructed Pump House. Its function was to provide water to the stand to prevent melting damage during testing. The water was sprayed through small holes in the stand's 1900 ton flame deflector at the rate of 320,000 gallons per minute. This photograph of the Pump House area was taken August 13, 1963. The massive round water storage tanks can be seen to the left of

  12. Construction Progress S-IC Test Stand Block House Interior

    NASA Technical Reports Server (NTRS)

    1963-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. In addition to the stand itself, related facilities were constructed during this time. Built directly east of the test stand was the Block House, which served as the control center for the test stand. The two were connected by a narrow access tunnel which housed the cables for the controls. This photograph, taken August 12, 1963, offers a view of the Block House interior.

  13. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1962-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. After a six month delay in construction due to size reconfiguration of the Saturn booster, the site was revisited for modifications in March 1962. The original foundation walls built in the prior year were torn down and re-poured to accommodate the larger boosters. This photo depicts that modification progress as of June 13,1962.

  14. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1962-01-01

    At its founding, the Marshall Space Flight Center (MSFC) inherited the Army's Jupiter and Redstone test stands, but much larger facilities were needed for the giant stages of the Saturn V. From 1960 to 1964, the existing stands were remodeled and a sizable new test area was developed. The new comprehensive test complex for propulsion and structural dynamics was unique within the nation and the free world, and they remain so today because they were constructed with foresight to meet the future as well as on going needs. Construction of the S-IC Static test stand complex began in 1961 in the west test area of MSFC, and was completed in 1964. The S-IC static test stand was designed to develop and test the 138-ft long and 33-ft diameter Saturn V S-IC first stage, or booster stage, weighing in at 280,000 pounds. Required to hold down the brute force of a 7,500,000-pound thrust produced by 5 F-1 engines, the S-IC static test stand was designed and constructed with the strength of hundreds of tons of steel and 12,000,000 pounds of cement, planted down to bedrock 40 feet below ground level. The foundation walls, constructed with concrete and steel, are 4 feet thick. The base structure consists of four towers with 40-foot-thick walls extending upward 144 feet above ground level. The structure was topped by a crane with a 135-foot boom. With the boom in the upright position, the stand was given an overall height of 405 feet, placing it among the highest structures in Alabama at the time. After a 6 month delay in construction due to size reconfiguration of the Saturn booster, the site was revisited for modifications. The original foundation walls built in the prior year had to be torn down and re-poured to accommodate the larger booster. The demolition can be seen in this photograph taken on May 21, 1962.

  15. A comparative study of pi-arene-bridged lanthanum arylamide and aryloxide dimers. Solution behavior, exchange mechanisms, and X-ray crystal structures of La2(NH-2,6-iPr2C6H3)6, La(NH-2,6-iPr2C6H3)3(THF)3, and La(NH-2,6-iPr2C6H3)3(py)2.

    PubMed

    Giesbrecht, Garth R; Gordon, John C; Clark, David L; Hay, P Jeffrey; Scott, Brian L; Tait, C Drew

    2004-05-26

    Reaction of 3 equiv of 2,6-diisopropylaniline with La[N(SiMe(3))(2)](3) produces the dimeric species La(2)(NHAr)(6) (1). X-ray crystallography reveals a centrosymmetric structure, where the dimeric unit is bridged by intermolecular eta(6)-arene interactions of a unique arylamide ligand attached to an adjacent metal center. Exposure of 1 to THF results in formation of the monomeric tris-THF adduct La(NHAr)(3)(THF)(3) (2), which was shown by X-ray crystallography to maintain a fac-octahedral structure in the solid state. (1)H NMR spectroscopy illustrates that the binding of THF to 1 to form 2 is reversible and removal of THF under vacuum regenerates dimeric 1. Addition of pyridine to 1 yields the monomeric bis-pyridine adduct La(NHAr)(3)(py)(2) (3), which exhibits a distorted trigonal-bipyramidal La metal center. Solution (1)H NMR, IR, and Raman spectroscopy indicate that the pi-arene-bridged dimeric structure of 1 is maintained in solution. Variable-temperature (1)H NMR spectroscopic investigations of 1 are consistent with a monomer-dimer equilibrium at elevated temperature. In contrast, variable-temperature (1)H NMR spectroscopic investigations of the aryloxide analogue La(2)(OAr)(6) (4) show that the bridging and terminal aryloxide groups exchange by a mechanism in which the dimeric nature of the compound is retained. Density functional theory (DFT) calculations were carried out on model compounds La(2)(OC(6)H(5))(6), La(2)(NHC(6)H(5))(6), and (C(6)H(5)R)La(XC(6)H(5))(3), where X = O or NH and R = H, OH, or NH(2). The formation of eta(6)-arene interactions is energetically favored over monomeric LaX(3) (X = OPh or NHPh) with the aryloxide pi-arene interaction being stronger than the arylamide pi-arene interaction. Calculation of vibrational frequencies reveals the origin of the observed IR spectral behavior of both La(2)(OC(6)H(5))(6) and La(2)(NHC(6)H(5))(6), with the higher energy nu(C=C) stretch due to terminal ligands and the lower energy stretch associated

  16. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... codes 20 through 39 to which this part applies. (a) SIC codes. Major group or industry code Exceptions... industry code Exceptions and/or limitations 311—Food Manufacturing Except 311119—Exception is limited to... under SIC 7334, Photocopying and Duplicating Services, (instant printing)); 324—Petroleum and...

  17. The Social Interactive Coding System (SICS): An On-Line, Clinically Relevant Descriptive Tool.

    ERIC Educational Resources Information Center

    Rice, Mabel L.; And Others

    1990-01-01

    The Social Interactive Coding System (SICS) assesses the continuous verbal interactions of preschool children as a function of play areas, addressees, script codes, and play levels. This paper describes the 26 subjects and the setting involved in SICS development, coding definitions and procedures, training procedures, reliability, sample…

  18. Highly flexible, nonflammable and free-standing SiC nanowire paper.

    PubMed

    Chen, Jianjun; Liao, Xin; Wang, Mingming; Liu, Zhaoxiang; Zhang, Judong; Ding, Lijuan; Gao, Li; Li, Ye

    2015-04-14

    Flexible paper-like semiconductor nanowire materials are expected to meet the criteria for some emerging applications, such as components of flexible solar cells, electrical batteries, supercapacitors, nanocomposites, bendable or wearable electronic or optoelectronic components, and so on. As a new generation of wide-bandgap semiconductors and reinforcements in composites, SiC nanowires have advantages in power electronic applications and nanofiber reinforced ceramic composites. Herein, free-standing SiC nanowire paper consisting of ultralong single-crystalline SiC nanowires was prepared through a facile vacuum filtration approach. The ultralong SiC nanowires were synthesized by a sol-gel and carbothermal reduction method. The flexible paper composed of SiC nanowires is ∼100 nm in width and up to several hundreds of micrometers in length. The nanowires are intertwisted with each other to form a three-dimensional network-like structure. SiC nanowire paper exhibits high flexibility and strong mechanical stability. The refractory performance and thermal stability of SiC nanowire paper were also investigated. The paper not only exhibits excellent nonflammability in fire, but also remains well preserved without visible damage when it is heated in an electric oven at a high temperature (1000 °C) for 3 h. With its high flexibility, excellent nonflammability, and high thermal stability, the free-standing SiC nanowire paper may have the potential to improve the ablation resistance of high temperature ceramic composites. PMID:25785912

  19. Oxidation of SiC cladding under Loss of Coolant Accident (LOCA) conditions in LWRs

    SciTech Connect

    Lee, Y.; Yue, C.; Arnold, R. P.; McKrell, T. J.; Kazimi, M. S.

    2012-07-01

    An experimental assessment of Silicon Carbide (SiC) cladding oxidation rate in steam under conditions representative of Loss of Coolant Accidents (LOCA) in light water reactors (LWRs) was conducted. SiC oxidation tests were performed with monolithic alpha phase tubular samples in a vertical quartz tube at a steam temperature of 1140 deg. C and steam velocity range of 1 to 10 m/sec, at atmospheric pressure. Linear weight loss of SiC samples due to boundary layer controlled reaction of silica scale (SiO{sub 2} volatilization) was experimentally observed. The weight loss rate increased with increasing steam flow rate. Over the range of test conditions, SiC oxidation rates were shown to be about 3 orders of magnitude lower than the oxidation rates of zircaloy 4. A SiC volatilization correlation for developing laminar flow in a vertical channel is formulated. (authors)

  20. Mechanical and microstructural characterization of Al7075/SiC nanocomposites fabricated by dynamic compaction

    NASA Astrophysics Data System (ADS)

    Atrian, A.; Majzoobi, G. H.; Enayati, M. H.; Bakhtiari, H.

    2014-03-01

    This paper describes the synthesis of Al7075 metal matrix composites reinforced with SiC, and the characterization of their microstructure and mechanical behavior. The mechanically milled Al7075 micron-sized powder and SiC nanoparticles are dynamically compacted using a drop hammer device. This compaction is performed at different temperatures and for various volume fractions of SiC nanoparticles. The relative density is directly related to the compaction temperature rise and indirectly related to the content of SiC nanoparticle reinforcement, respectively. Furthermore, increasing the amount of SiC nanoparticles improves the strength, stiffness, and hardness of the compacted specimens. The increase in hardness and strength may be attributed to the inherent hardness of the nanoparticles, and other phenomena such as thermal mismatch and crack shielding. Nevertheless, clustering of the nanoparticles at aluminum particle boundaries make these regions become a source of concentrated stress, which reduces the load carrying capacity of the compacted nanocomposite.

  1. Amorphization resistance of nano-engineered SiC under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Imada, Kenta; Ishimaru, Manabu; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven C.; Weber, William J.

    2016-09-01

    Silicon carbide (SiC) with a high-density of planar defects (hereafter, 'nano-engineered SiC') and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. It was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due to the local increase in electronic energy loss that enhanced dynamic recovery.

  2. '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.

  3. The Influence of SiC on the Ablation Response of Advanced Refractory Composite Materials

    NASA Technical Reports Server (NTRS)

    Bull, Jeffrey D.; Rasky, Daniel J. (Technical Monitor)

    1994-01-01

    In continuing our studies of advanced refractory composite materials we have recently completed an arc-jet test series of a diverse group of ceramics and ceramic matrix composites. The compositions range from continuous fiber reinforced ceramics to monoliths. Many of these materials contain SiC and one objective of this test series was to identify the influence of SiC oxidation mechanisms on material performance. Hence the arc heater was operated at two conditions; one in which the passive oxidation of SiC would be dominant and the other where the active oxidation of SiC would be dominant. It is shown here that the active oxidation mechanism of SiC does not dominate material performance when it is present at levels equal to or below 20 volume percent.

  4. The first muon beam from a new highly-intense DC muon source, MuSIC

    NASA Astrophysics Data System (ADS)

    Tran, Nam Hoai; MuSIC Collaboration

    2012-09-01

    A new DC muon source, MuSIC, is now under construction at Research Center for Nuclear Physics (RCNP), Osaka University, Japan. The MuSIC adopts a new pion/muon collection system and a curved transport solenoid. These techniques are important in realization of future muon programs such as the muon to electron conversion experiments (COMET/Mu2e), neutrino factories, and muon colliders. The pion capture magnet and a part of the transport solenoid have been built and beam tests were carried out to assess the MuSIC's performance. Muon lifetime measurements and muonic X-ray measurements have been used for estimation of muon yield of the MuSIC. The result indicates that the MuSIC would be one of the most intense DC muon beams in the world.

  5. Mechanical properties of SiC long fibre reinforced copper

    NASA Astrophysics Data System (ADS)

    Brendel, A.; Paffenholz, V.; Köck, Th.; Bolt, H.

    2009-04-01

    SiC fibre reinforced copper is a potential novel heat sink material for the divertor of future fusion reactors to reinforce the zone between plasma facing material (W) and heat sink material (CuCrZr). The metal matrix composite (MMC) should be able to withstand heat loads up to 15 MW/m 2 at operating temperatures of up to 550 °C. SCS6 fibres were coated by magnetron sputtering with a titanium interlayer and the copper matrix was deposited by electroplating. The composite was consolidated by hot-isostatic pressing. The average ultimate tensile strength of composite samples with 20% fibre reinforcement is 640 MPa and for the Young's modulus 162 GPa was determined. The Young's modulus decreases with increasing temperature and reaches 113 GPa at 550 °C. Fracture area analysis after tensile tests show the failure of the SCS 6 fibres at the interface between the two outer carbon layers. Titanium as interlayer led to an improved bonding between the outer carbon coating of the SiC fibres and the copper matrix.

  6. Infrared surface phonon polariton waveguides on SiC Substrate

    NASA Astrophysics Data System (ADS)

    Yang, Yuchen; Manene, Franklin M.; Lail, Brian A.

    2015-08-01

    Surface plasmon polariton (SPP) waveguides harbor many potential applications at visible and near-infrared (NIR) wavelengths. However, dispersive properties of the metal in the waveguide yields weakly coupled and lossy plasmonic modes in the mid and long wave infrared range. This is one of the major reasons for the rise in popularity of surface phonon polariton (SPhP) waveguides in recent research and micro-fabrication pursuit. Silicon carbide (SiC) is a good candidate in SPhP waveguides since it has negative dielectric permittivity in the long-wave infrared (LWIR) spectral region, indicative that coupling to surface phonon polaritons is realizable. Introducing surface phonon polaritons for waveguiding provides good modal confinement and enhanced propagation length. A hybrid waveguide structure at long-wave infrared (LWIR) is demonstrated in which an eigenmode solver approach in Ansys HFSS was applied. The effect of a three layer configuration i.e., silicon wire on a benzocyclobutene (BCB) dielectric slab on SiC, and the effects of varying their dimensions on the modal field distribution and on the propagation length, is presented.

  7. A NEW TYPE OF SIC COMPOSITE FOR FUSION

    SciTech Connect

    Youngblood, Gerald E.; Jones, Russell H.

    2001-04-01

    A new type of SiC composite called Tyrannohex™ is potentially suitable as a fusion reactor structural material. Tyrannohex™ composite plates are made by hot-pressing layups of Tyranno™ SA precursor fibers into various 1D and 2D configurations. The fiber-bonded composite plates contain nearly 100% fiber volume, so take advantage of the outstanding high temperature strength and creep properties of the Tyranno™ SA fiber, a nearly stoichiometric SiC fiber. The hot-pressed plates are dense, strong, rigid, tough, thermally conductive and have high temperature stability. The microstructure and thermal conductivity of a SA-Tyrannohex™ material with a 2D-woven configuration was evaluated prior to irradiation testing. The microstructure contained some small, flat interlaminar pores and intrabundle needle-like pores, and the transverse thermal conductivity was 25 and 21 W/mK at ambient and 1000°C, respectively. These results suggest that careful control of the fiber-bonded interlayers and the fiber architecture are critical to achieve both high thermal conductivity and toughness in Tyrannohex™ type materials.

  8. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-08-01

    A bend stress relaxation (BSR) test is planned to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Baseline 1 hr and 100 hr BSR thermal creep {open_quotes}m{close_quotes} curves have been obtained for five selected advanced SiC fiber types and for standard Nicalon CG fiber. The transition temperature, that temperature where the S-shaped m-curve has a value 0.5, is a measure of fiber creep resistance. In order of decreasing thermal creep resistance, with the 100 hr BSR transition temperature given in parenthesis, the fibers ranked: Sylramic (1261{degrees}C), Nicalon S (1256{degrees}C), annealed Hi Nicalon (1215{degrees}C), Hi Nicalon (1078{degrees}C), Nicalon CG (1003{degrees}C) and Tyranno E (932{degrees}C). The thermal creep for Sylramic, Nicalon S, Hi Nicalon and Nicalon CG fibers in a 5000 hr irradiation creep BSR test is projected from the temperature dependence of the m-curves determined during 1 and 100 hr BSR control tests.

  9. Processing of laser formed SiC powder

    NASA Technical Reports Server (NTRS)

    Haggerty, J. S.; Bowen, H. K.

    1987-01-01

    Processing research was undertaken to demonstrate that superior SiC characteristics could be achieved through the use of ideal constituent powders and careful post-synthesis processing steps. Initial research developed the means to produce approximately 1000 A uniform diameter, nonagglomerated, spherical, high purity SiC powders. Accomplishing this goal required major revision of the particle formation and growth model from one based on classical nucleation and growth to one based on collision and coalescence of Si particles followed by their carburization. Dispersions based on pure organic solvents as well as steric stabilization were investigated. Test parts were made by the colloidal pressing technique; both liquid filtration and consolidation (rearrangement) stages were modeled. Green densities corresponding to a random close packed structure were achieved. After drying, parts were densified at temperatures ranging from 1800 to 2100 C. This research program accomplished all of its major objectives. Superior microstructures and properties were attained by using powders having ideal characteristics and special post-synthesis processing procedures.

  10. Major deep levels with the same microstructures observed in n-type 4H-SiC and 6H-SiC

    SciTech Connect

    Sasaki, S.; Kawahara, K.; Feng, G.; Alfieri, G.; Kimoto, T.

    2011-01-01

    Major deep levels observed in as-grown and irradiated n-type 4H-SiC and 6H-SiC epilayers have been investigated. After low-energy electron irradiation, by which only carbon atoms are displaced, five traps, EH1 (E{sub C}-0.36 eV), Z{sub 1}/Z{sub 2} (E{sub C}-0.65 eV), EH3 (E{sub C}-0.79 eV), EH5 (E{sub C}-1.0 eV), and EH6/7 (E{sub C}-1.48 eV), were detected in 4H-SiC and four traps, E{sub 1}/E{sub 2} (E{sub C}-0.45 eV), RD{sub 5} (E{sub C}-0.57 eV), ES (E{sub C}-0.80 eV), and R (E{sub C}-1.25 eV), were detected in 6H-SiC. The Z{sub 1}/Z{sub 2}, EH6/7 centers in 4H-SiC and the E{sub 1}/E{sub 2}, R centers in 6H-SiC exhibit common features as follows: their generation rates by the e{sup -}-irradiation were almost the same each other, their concentrations were not changed by heat treatments up to 1500 deg. C, and they showed very similar annealing behaviors at elevated temperatures. Furthermore, these defect centers were almost eliminated by thermal oxidation. Taking account of the observed results and the energy positions, the authors suggest that the Z{sub 1}/Z{sub 2} center in 4H-SiC corresponds to the E{sub 1}/E{sub 2} center in 6H-SiC, and the EH6/7 center in 4H-SiC to the R center in 6H-SiC, respectively. Since the concentrations of these four centers are almost the same for as-grown, electron-irradiated, annealed, and oxidized samples, these centers will contain a common intrinsic defect, most likely carbon vacancy. The authors also observed similar correspondence for other thermally unstable traps in 4H-SiC and 6H-SiC.

  11. Low dose irradiation performance of SiC interphase SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Snead, L. L.; Osborne, M. C.; Lowden, R. A.; Strizak, J.; Shinavski, R. J.; More, K. L.; Eatherly, W. S.; Bailey, J.; Williams, A. M.

    1998-03-01

    Reduced oxygen Hi-Nicalon™ fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either `porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1×10 25 n m -2 ( E>0.1 MeV) in the temperature range of 260 to 1060°C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber.

  12. Study of CVD SiC thin film for space mirror

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhan; Zhang, Yumin; Han, Jiecai; He, Xiaodong

    2006-01-01

    The performance of space mirror lied on the properties of the mirror surface material to a great extent. In this paper, the silicon carbide thin film deposited on reaction-bonded silicon carbide (RBSC) space mirror blank was produced by Chemical Vapor Deposition (CVD) process. Some mechanical and physical properties of the SiC thin film were tested because they were important to study ability to work of space mirror. The result of XRD phase analysis indicated that the component of the SiC thin film was β-SiC. The micro hardness of the film was tested. The thickness of SiC thin film was tested using needle touch contour graph. The results showed that the thickness of SiC film was about 20 μm and film was even in the macro scope. The adhesion strength of SiC thin film and RBSC substrate was tested by scratch method and the results showed that was excellent. The residual stress of SiC thin film was tested by X-ray, at the same time; the origin of residual stress and the calculation of thermal stress were discussed. In the room temperature, the residual stress of the SiC film was compressive. After precision grinding, the surface topography and roughness of the SiC thin film was tested by Atomic Force Microscope (AFM). The results showed that the surface of SiC thin film had extremely low surface roughness and high surface form accuracy. The thermal shock resistance of SiC film was fine by tested.

  13. Microstructure characterization of SiC nanowires as reinforcements in composites

    SciTech Connect

    Dong, Ronghua; Yang, Wenshu; Wu, Ping; Hussain, Murid; Xiu, Ziyang; Wu, Gaohui; Wang, Pingping

    2015-05-15

    SiC nanowires have been rarely investigated or explored along their axial direction by transmission electron microscopy (TEM). Here we report the investigation of the cross-section microstructure of SiC nanowires by embedding them into Al matrix. Morphology of SiC nanowires was cylindrical with smooth surface or bamboo shape. Cubic (3C-SiC) and hexagonal structure (2H-SiC) phases were detected by X-ray diffraction (XRD) analysis. High density stacking faults were observed in both the cylindrical and bamboo shaped nanowires which were perpendicular to their axial direction. Selected area electron diffraction (SAED) patterns of the cylindrical and bamboo shaped SiC nanowires both in the perpendicular and parallel direction to the axial direction were equivalent in the structure. After calculation and remodeling, it has been found that the SAED patterns were composed of two sets of diffraction patterns, corresponding to 2H-SiC and 3C-SiC, respectively. Therefore, it could be concluded that the SiC nanowires are composed of a large number of small fragments that are formed by hybrid 3C-SiC and 2H-SiC structures. - Graphical abstract: Display Omitted - Highlights: • Cross-section microstructure of SiC nanowires was observed in Al composite. • Cylindrical with smooth surface or bamboo shape SiC nanowires were found. • The cylindrical and bamboo shaped SiC nanowires were equivalent in structure. • Structure of SiC nanowires was remodeled. • SiC nanowires are composed of hybrid 3C-SiC and 2H-SiC structures.

  14. Characterization of 6H-SiC JFET Integrated Circuits Over A Broad Temperature Range from -150 C to +500 C

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Krasowski, Michael J.; Chen, Liang-Yu; Prokop, Norman F.

    2009-01-01

    The NASA Glenn Research Center has previously reported prolonged stable operation of simple prototype 6H-SiC JFET integrated circuits (logic gates and amplifier stages) for thousands of hours at +500 C. This paper experimentally investigates the ability of these 6H-SiC JFET devices and integrated circuits to also function at cold temperatures expected to arise in some envisioned applications. Prototype logic gate ICs experimentally demonstrated good functionality down to -125 C without changing circuit input voltages. Cascaded operation of gates at cold temperatures was verified by externally wiring gates together to form a 3-stage ring oscillator. While logic gate output voltages exhibited little change across the broad temperature range from -125 C to +500 C, the change in operating frequency and power consumption of these non-optimized logic gates as a function of temperature was much larger and tracked JFET channel conduction properties.

  15. Synthesis, crystal structure and NLO property of a nonmetal pentaborate [C 6H 13N 2][B 5O 6(OH) 4

    NASA Astrophysics Data System (ADS)

    Liu, Huan-Xin; Liang, Yun-Xiao; Jiang, Xiao

    2008-12-01

    A nonmetal pentaborate [C 6H 13N 2][B 5O 6(OH) 4] ( 1) has been synthesized by 1,4-diazabicyclo[2.2.2] octane (DABCO) and boric acid, and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system with space group Cc (no. 9), a=10.205(2) Å, b=14.143(3) Å, c=11.003(2) Å, β=113.97(3)°, V=1451.1(5) Å 3, Z=4. The anionic units, [B 5O 6(OH) 4] -, are interlinked via hydrogen bonding to form a three-dimensional (3D) supramolecular network containing large channels, in which the protonated [C 6H 13N 2] + cations are located. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits SHG efficiency approximately 0.9 times that of potassium dihydrogen phosphate (KDP).

  16. Nonplanar structure of C6H5SCF3 facilitates πσ∗-mediated photodissociation reaction on the S1 state

    NASA Astrophysics Data System (ADS)

    Kim, So-Yeon; Lee, Jeongmook; Kim, Sang Kyu; Choi, Young S.

    2016-08-01

    Vibrational structure of trifluoromethylthiobenzene (C6H5SCF3) on the S1 state has been investigated by resonance-enhanced two-photon ionization spectroscopy and nature of predissociation dynamics is inferred from homogeneously broadened spectral features. As C6H5SCF3 adopts a nonplanar structure in both the S0 and S1 states, the effective adiabatic barrier generated by avoided crossing of optically-bright bound S1 (ππ∗) and dark-repulsive S2 (πσ∗) surfaces along the reaction coordinate is significantly lowered, giving the S1 lifetime of ∼300 fs. This experiment demonstrates that the molecular structure spanned by the reactive flux near the curve-crossing region dictates reaction rate as well as nonadiabatic transition probability.

  17. Characterization of molecular beam epitaxy grown β-Nb2N films and AlN/β-Nb2N heterojunctions on 6H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Nepal, Neeraj; Katzer, D. Scott; Meyer, David J.; Downey, Brian P.; Wheeler, Virginia D.; Storm, David F.; Hardy, Matthew T.

    2016-02-01

    β-Nb2N films and AlN/β-Nb2N heterojunctions were grown by molecular beam epitaxy (MBE) on 6H-SiC. The epitaxial nature and β-Nb2N phase were determined by symmetric and asymmetric high-resolution X-ray diffraction (HRXRD) measurements, and were confirmed by grazing incidence diffraction measurements using synchrotron photons. Measured lattice parameters and the in-plane stress of β-Nb2N on 6H-SiC were c = 5.0194 Å, a = 3.0558 Å, and 0.2 GPa, respectively. The HRXRD, transmission electron microscopy, and Raman spectroscopy revealing epitaxial growth of AlN/β-Nb2N heterojunctions have identical orientations with the substrate, abrupt interfaces, and bi-axial stress of 0.88 GPa, respectively. The current finding opens up possibilities for the next generation of high-power devices that cannot be fabricated at present.

  18. Relative Raman Intensities in C6H6, C6D6, and C6F6: A Comparison of Different Computational Methods

    SciTech Connect

    Williams, Stephen D.; Johnson, Timothy J.; Gibbons, Thomas; Kitchens, Christopher L.

    2007-02-01

    In order to determine which models can best emulate Raman spectra, the accuracy of various computational methods (Hartee-Fock, MP2, CCSD, CAS-SCF, and several types of DFT) for predicting relative intensities in the Raman spectra of C6H6, C6D6, and C6F6 were compared. In particular, the predicted relative intensities for v1 and v2 were compared with relative intensities measured by an FT-Raman spectrometer. While none of these methods excelled at this prediction, Hartee-Fock with a large basis set was most successful for C6H6, and C6D6, while PW91PW91 with the aug-cc-pVTZ basis set was most successful for C6F6.

  19. History of the ISS/SIC: Antoine Depage, one of the founders of the ISS/SIC.

    PubMed

    Van Hee, R

    2002-10-01

    Antoine Depage, born near Brussels in 1862, was one of the founders and first Secretary General of the Société Internationale de Chirurgie (ISS-SIC). After an excellent medical education at the Free Brussels University, he became professor at the same university at the age of 27. Surgically trained by Prof. Thiriar, he became one of the leading Belgian surgeons at the end of the nineteenth century, and he published more than 100 articles in national and international journals. In 1907 he founded a school for nurses in Brussels, to be directed by Edith Cavell. He also vigorously transformed the organization of the public hospitals in the Belgian capital. During World War I Queen Elisabeth appointed him surgeon-in-chief of the Océan-hospital in De Panne, where more than 50,000 soldiers with wounds, fractures, cerebral trauma, nitrous gas intoxication, and infectious diseases, among other problems were treated. The results he and his team obtained were excellent, and mortality was low. Many surgeons, including Alexis Carrel, as well as distinguished political leaders came to visit him in the hospital barracks. After the war he was honored by many political and scientific organizations, including the Société Internationale de Chirurgie. He served our Society not only as Secretary General from 1902 to 1912 but became President of the 4th Congress of the ISS-SIC in New York. Antoine Depage died after a long illness in 1925. PMID:12205562

  20. In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites

    SciTech Connect

    Cao, J. |

    1996-12-01

    This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1,700 C with 3 wt% Al, 0.6 wt% B, and 2 wt% C additions. These sintering aids also enhanced the {beta}-to-{alpha} (3C-to-4H) phase transformation, which promoted SiC grains to grow into plate-like shapes. Under optimal processing conditions, the microstructure exhibited high-aspect-ratio plate-shaped grains with a thin (< 1 nm) Al-containing amorphous grain boundary film. The mechanical properties of the toughened SiC and the composites were evaluated in comparison with a commercial Hexoloy SiC under identical test conditions. The C-curve behavior was examined using the strength-indentation load relationship and compared with that directly measured using precracked compact tension specimens. The in situ toughened ABC-SiC exhibited much improved flaw tolerance and a significantly rising R-curve behavior. A steady-state toughness in excess of 9 MPam{sup 1/2} was recorded for the ABC-SiC in comparison to a single valued toughness below 3 MPam{sup 1/2} for the Hexoloy. Toughening in the ABC-SiC was mainly attributed to grain bridging and subsequent pullout of the plate-shaped grains. The high toughness ABC-SiC exhibited a bend strength of 650 MPa with a Weibull modulus of 19; in comparison, the commercial SiC showed a bend strength of 400 MPa with a Weibull modulus of 6. Higher fracture toughness was also achieved by the reinforcement of SiC platelets, encapsulated with alumina, yttria, or silica, in a SiC matrix.

  1. Distinct lymphocyte antigens 6 (Ly6) family members Ly6D, Ly6E, Ly6K and Ly6H drive tumorigenesis and clinical outcome.

    PubMed

    Luo, Linlin; McGarvey, Peter; Madhavan, Subha; Kumar, Rakesh; Gusev, Yuriy; Upadhyay, Geeta

    2016-03-01

    Stem cell antigen-1 (Sca-1) is used to isolate and characterize tumor initiating cell populations from tumors of various murine models [1]. Sca-1 induced disruption of TGF-β signaling is required in vivo tumorigenesis in breast cancer models [2, 3-5]. The role of human Ly6 gene family is only beginning to be appreciated in recent literature [6-9]. To study the significance of Ly6 gene family members, we have visualized one hundred thirty gene expression omnibus (GEO) dataset using Oncomine (Invitrogen) and Georgetown Database of Cancer (G-DOC). This analysis showed that four different members Ly6D, Ly6E, Ly6H or Ly6K have increased gene expressed in bladder, brain and CNS, breast, colorectal, cervical, ovarian, lung, head and neck, pancreatic and prostate cancer than their normal counter part tissues. Increased expression of Ly6D, Ly6E, Ly6H or Ly6K was observed in sub-set of cancer type. The increased expression of Ly6D, Ly6E, Ly6H and Ly6K was found to be associated with poor outcome in ovarian, colorectal, gastric, breast, lung, bladder or brain and CNS as observed by KM plotter and PROGgeneV2 platform. The remarkable findings of increased expression of Ly6 family members and its positive correlation with poor outcome on patient survival in multiple cancer type indicate that Ly6 family members Ly6D, Ly6E, Ly6K and Ly6H will be an important targets in clinical practice as marker of poor prognosis and for developing novel therapeutics in multiple cancer type. PMID:26862846

  2. Distinct lymphocyte antigens 6 (Ly6) family members Ly6D, Ly6E, Ly6K and Ly6H drive tumorigenesis and clinical outcome

    PubMed Central

    Luo, Linlin; McGarvey, Peter; Madhavan, Subha; Kumar, Rakesh; Gusev, Yuriy; Upadhyay, Geeta

    2016-01-01

    Stem cell antigen-1 (Sca-1) is used to isolate and characterize tumor initiating cell populations from tumors of various murine models [1]. Sca-1 induced disruption of TGF-β signaling is required in vivo tumorigenesis in breast cancer models [2, 3-5]. The role of human Ly6 gene family is only beginning to be appreciated in recent literature [6-9]. To study the significance of Ly6 gene family members, we have visualized one hundred thirty gene expression omnibus (GEO) dataset using Oncomine (Invitrogen) and Georgetown Database of Cancer (G-DOC). This analysis showed that four different members Ly6D, Ly6E, Ly6H or Ly6K have increased gene expressed in bladder, brain and CNS, breast, colorectal, cervical, ovarian, lung, head and neck, pancreatic and prostate cancer than their normal counter part tissues. Increased expression of Ly6D, Ly6E, Ly6H or Ly6K was observed in sub-set of cancer type. The increased expression of Ly6D, Ly6E, Ly6H and Ly6K was found to be associated with poor outcome in ovarian, colorectal, gastric, breast, lung, bladder or brain and CNS as observed by KM plotter and PROGgeneV2 platform. The remarkable findings of increased expression of Ly6 family members and its positive correlation with poor outcome on patient survival in multiple cancer type indicate that Ly6 family members Ly6D, Ly6E, Ly6K and Ly6H will be an important targets in clinical practice as marker of poor prognosis and for developing novel therapeutics in multiple cancer type. PMID:26862846

  3. Draft Genome Sequence of Pseudomonas azotifigens Strain DSM 17556T (6H33bT), a Nitrogen Fixer Strain Isolated from a Compost Pile

    PubMed Central

    Busquets, Antonio; Peña, Arantxa; Gomila, Margarita; Mulet, Magdalena; Mayol, Joan; García-Valdés, Elena; Bennasar, Antonio; Huntemann, Marcel; Han, James; Chen, I-Min; Mavromatis, Konstantinos; Markowitz, Victor; Palaniappan, Krishnaveni; Ivanova, Natalia; Schaumberg, Andrew; Pati, Amrita; Reddy, T. B. K.; Nordberg, Henrik; Woyke, Tanja; Klenk, Hans-Peter; Kyrpides, Nikos

    2013-01-01

    Pseudomonas azotifigens strain 6H33bT is a nitrogen fixer isolated from a hyperthermal compost pile in 2005 by Hatayama and collaborators. Here we report the draft genome, which has an estimated size of 5.0 Mb, exhibits an average G+C content of 66.73%, and is predicted to encode 4,536 protein-coding genes and 100 RNA genes. PMID:24179119

  4. Molybdenum complexes derived from the oxydianiline [(2-NH2C6H4)2O]: synthesis, characterization and ε-caprolactone ROP capability.

    PubMed

    Yang, Wenxue; Zhao, Ke-Qing; Redshaw, Carl; Elsegood, Mark R J

    2015-08-01

    The reaction of Na2MoO4 with 2,2'-oxydianiline (2-aminophenylether), (2-NH2C6H4)2O, LH4, in DME (DME = 1,2-dimethoxyethane) in the presence of Et3N and Me3SiCl afforded either the bis(imido) molybdenum(vi) complex {Mo(L)Cl2(DME)} (), where L = (2-NC6H4)2O, or the molybdenum(v) salt [Mo(L')Cl4][Et3NH] (), where L' = [(2-NH2C6H4)(2-NC6H4)O], depending on the work-up method employed. The same diamine reacted with in situ [Mo(NtBu)2Cl2(DME)] afforded a tetra-nuclear complex [Mo4Cl3(NtBu)3(OSiMe3)(μ4-O)(L)2(L')2]·2MeCN (·2MeCN). The crystal structures of , and ·2MeCN have been determined. The structure of the bis(imido) complex contains two unique molecules paired up via weak π-stacking, whereas the structure of contains a chelating amine/imido ligand, and is made up of discrete units of two cations and two anions which are interacting via H-bonding. The tetra-nuclear structure contains four different types of distorted octahedral molybdenum centre, and a bent Me3SiO group thought to originate from the precursor synthesis. Complexes have been screened for their ability to ring open polymerize (ROP) ε-caprolactone. For and (not ), conversion rates were good (>90%) at high temperatures (100 °C) over 6-24 h, and the polymerization proceeded in a living manner. PMID:26107689

  5. Reduced resuscitation fluid volume for second-degree experimental burns with delayed initiation of vitamin C therapy (beginning 6 h after injury).

    PubMed

    Sakurai, M; Tanaka, H; Matsuda, T; Goya, T; Shimazaki, S; Matsuda, H

    1997-11-01

    We studied the hemodynamic effects of delayed initiation (6 h postburn) of antioxidant therapy with high-dose vitamin C in second-degree thermal injuries. Seventy percent body surface area burns were produced by subxiphoid immersion of 12 guinea pigs into 100 degrees C water for 3 s. The animals were resuscitated with Ringer's lactate solution (R/L) according to the Parkland formula (4 ml/kg/% burn during the first 24 h) from 6 h postburn, after which the resuscitation fluid volume was reduced to 25% of the Parkland formula volume. Animals were divided into two groups. The vitamin C group (n = 6) received R/L to which vitamin C (340 mg/kg/24 h) was added after 6 h postburn. The control group (n = 6) received R/L only. Both groups received identical resuscitation volumes. Heart rates, mean arterial blood pressure, cardiac output, hematocrit level, and water content of burned and unburned tissue were measured before injury and at intervals thereafter. No animals died. There were no significant differences in heart rates or blood pressures between the two groups throughout the 24-h study period. The vitamin C group showed significantly (P < 0.05) lower hematocrits 8 and 24 h postburn, and higher cardiac outputs after 7 h postburn. At 24 h postburn, the burned skin in the vitamin C group had a significantly (P < 0.05) lower water content (73.1 +/- 1.1) than that of the control group (76.0 +/- 0.8). In conclusion, delayed initiation of high-dose vitamin C therapy beginning 6 h postburn with 25% of the Parkland formula volume significantly reduced edema formation in burned tissue, while maintaining stable hemodynamics. PMID:9441788

  6. Structural change induced by thermal annealing of red-light-emitting ZnSnF6 • 6H2O:Mn4+ hexahydrate phosphor

    NASA Astrophysics Data System (ADS)

    Hoshino, Ryosuke; Nakamura, Toshihiro; Adachi, Sadao

    2016-05-01

    Effects of thermal annealing on the red-emitting ZnSnF6 • 6H2O:Mn4+ hexahydrate phosphor properties were investigated using X-ray diffraction measurement (XRD), photoluminescence (PL) analysis, and Raman scattering spectroscopy. Thermal annealing was performed at T a = 50 to 400 °C in air for 1 h. Mn4+-related red emission wavelengths were redshifted about 5 nm after annealing at T a ≥ 200 °C with greatly decreased emission intensities. This change in PL spectral feature was attributed to the dehydration of the hexahydrate phosphor, supported by the XRD and Raman scattering results. The XRD and PL intensity analyses determined thermal decomposition energies of ∼0.3 eV from the ZnSnF6 • 6H2O hexahydrate to anhydrate and of ∼0.9 eV from the ZnSnF6 anhydrate to metallic fluorid/oxide (ZnF2/SnO2). A comparative discussion was given on the PL properties of two different Mn4+-activated phosphors, Ba–IV–F6:Mn4+ anhydrate and Zn–IV–F6 • 6H2O:Mn4+ hexahydrate phosphors with IV = Si, Ge, and Sn.

  7. Vibrational state-selective autodetachment photoelectron spectroscopy from dipole-bound states of cold 2-hydroxyphenoxide: o - HO(C6H4)O-

    NASA Astrophysics Data System (ADS)

    Huang, Dao-Ling; Liu, Hong-Tao; Ning, Chuan-Gang; Wang, Lai-Sheng

    2015-03-01

    We report a photodetachment and high-resolution photoelectron imaging study of cold 2-hydroxyphenoxide anion, o - HO(C6H4)O-, cooled in a cryogenic ion trap. Photodetachment spectroscopy revealed a dipole-bound state (DBS) of the anion, 25 ± 5 cm-1, below the detachment threshold of 18ߙ784 ± 5 cm-1 (2.3289 ± 0.0006 eV ), i.e., the electron affinity of the 2-hydroxyphenoxy radical o - HO(C6H4)Oṡ. Twenty-two vibrational levels of the DBS are observed as resonances in the photodetachment spectrum. By tuning the detachment laser to these DBS vibrational levels, we obtain 22 high-resolution resonant photoelectron spectra, which are highly non-Franck-Condon due to mode-selective autodetachment and the Δv = - 1 propensity rule. Numerous Franck-Condon inactive vibrational modes are observed in the resonant photoelectron spectra, significantly expanding the vibrational information that is available in traditional high-resolution photoelectron spectroscopy. A total of 15 fundamental vibrational frequencies are obtained for the o - HO(C6H4)Oṡ radical from both the photodetachment spectrum and the resonant photoelectron spectra, including six symmetry-forbidden out-of-plane modes as a result of resonant enhancement.

  8. Face-capping μ3-BO in B6(BO)7-: boron oxide analogue of B6H7- with rhombic 4c-2e bonds.

    PubMed

    Guo, Jin-Chang; Lu, Hai-Gang; Zhai, Hua-Jin; Li, Si-Dian

    2013-11-14

    Using the first-principle approaches, we predict a B6(BO)7(-) cluster with a face-capping μ(3)-BO, which is the boron oxide analogue of closo-B6H7(-) with a face-capping μ(3)-H. Detailed topological analysis of electron density clearly reveals the existence of three rhombic 4c-2e bonds around the B/H apex in both C3v B6(BO)7(-) and C3v B6H7(-), which possesses similar electron densities at their bond and ring critical points. The adaptive natural density partitioning (AdNDP) analysis provides a direct and visual picture of the B-B-B-B/H 4c-2e bonds for the first time. Adiabatic and vertical electron detachment energies of the concerned monoanions are calculated to facilitate their future photoelectron spectroscopy measurements and characterizations. The presence of the B6(BO)7(-) and B6H7(-) clusters extends the BO/H isolobal analogy to the whole μ(n)-BO/H series (n = 1, 2, and 3) and enriches the chemistry of boronyl. PMID:24147988

  9. Compositional Heterogeneity in Orgueil SiC: Further Comparisons with Murchison

    NASA Astrophysics Data System (ADS)

    Huss, G. R.; Deloule, E.; Hutcheon, I. D.; Wasserburg, G. J.

    1993-07-01

    Interstellar SiC recovered from primitive chondrites is characterized by large enrichments in ^13C and ^14N, and by Si isotope compositions distinct from solar that define a linear array on a Si 3-isotope plot [1-3]. While most SiC >2 micrometers fit this description, the total population of presolar SiC is not homogeneous. A comparison [4] of C, N, Mg, and Si isotopic characteristic of 2-6 micrometer SiC crystals from Orgueil with Murchison SiC [2,3] found two significant differences: 1) Orgueil SiC do not exhibit the clustering on either an Si 3-isotope plot or on a plot of delta^29Si vs. delta^13C shown by large Murchison SiC, and 2) there were no Orgueil SiC with delta^15N between 0 and -350 per mil. The interpretation of these differences was tempered by the relatively small number of Orgueil SiC that had been measured. We report here new Si and C isotope data for an additional 70 Orgueil SiC grains, making a total of ~110 grains measured to date. We have extended our study to smaller grains, measuring 15 grains less than 2 micrometers. The great majonty (~90%) of Orgueil SiC have roughly similar isotopic compositions and define the main population (Fig. 1). Among the remaining SiC grains, one is extremely enriched in ^28Si (Fig. 1 inset) and extremely depleted in ^13C, like the Murchison 'X' grains [3]. Four grains have delta^13C<0 and Si compositions similar to Murchison 'Y' grains [5]. Two Orgueil SiC ('Z' grains) have delta^29Si ~-75 per mil and delta^30Si ~-34per mil and fall in a previously unoccupied region of Si isotope space. Unlike 'Y' grains, 'Z' grains have delta^13C > 0. Eight Orgueil SiC have extreme enrichments in ^13C (8000 per mil < delta^13C < 3000 per mil); six of the eight lie on the ^28Si-rich end of the Si isotope array (Fig. 1), five with delta^29Si <--4 per mil and the sixth with delta^29Si=13 per mil. The new data reveal a compositional variability among Orgueil SiC larger than ~2 micrometers at least as great as that found for

  10. Hydrogen-bond-directed assemblies of [La(18-crown-6)(H2O)4](BiCl6)·3H2O and [Nd(18-crown-6)(H2O)4](BiCl6)·3.5H2O regulated by different symmetries

    NASA Astrophysics Data System (ADS)

    Zhang, Shi-Yong; Li, Jian; Zeng, Ying; Wen, He-Rui; Du, Zi-Yi

    2016-12-01

    The reactions of La2O3 or Nd2O3 with BiCl3 and 18-crown-6 in the presence of excessive hydrochloric acid afforded two ion-pair compounds, namely [La(18-crown-6)(H2O)4](BiCl6)·3H2O (1) and [Nd(18-crown-6)(H2O)4](BiCl6)·3.5H2O (2). Although these two compounds contain similar building blocks, they exhibit two distinct hydrogen-bonded networks, which are mainly induced by the slightly different geometries of their large-sized cationic [Ln(18-crown-6)(H2O)4]3+ components.

  11. Investigations of the {ReO} core: A '2+2' complex from bidentate and potentially trident ligands: [ReO(η-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η-SC(5)H(4)N)(PPh(3))].

    PubMed

    Chen, Xiaoyuan; Femia, Frank J; Babich, John W; Zubieta, Jon

    2000-08-11

    The reaction of [ReOCl(3)(PPh(3))(2)] with N-(2-hydroxybenzyl)-2-mercaptoaniline (H(3)hbma) (2) and 2-mercaptopyridine in hot CHCl yields [ReO(η(2)-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η(2)-SC(5)H(4)N)(PPh(3))] (3). The structure of 3 consists of distorted octahedral Re(V) monomers. The coordination geometry at the rhenium is defined by a terminal oxo-group, the nitrogen and sulfur donors of the chelating mercaptopyridine, the nitrogen and sulfur donors of a bidentate (Hhbma)(2-) ligand, and the phosphorus of the PPh(3) group. The -C(6)H(4)OH arm of (Hhbma)(2-) is pendant, and the coordinated nitrogen of this ligand is present as a deprotonated amido nitrogen. PMID:21625343

  12. Comparing SiC switching power devices: MOSFET, NPN transistor and GTO thyristor

    NASA Astrophysics Data System (ADS)

    Huang, Alex Q.; Zhang, Bo

    2000-02-01

    This paper for the first time systematically analyzed the operation mechanism of SiC NPN transistors. Theoretical device figure-of-merits for switching power devices based on the conduction loss and switching loss were developed. The on-state loss and the switching loss of 4.5-kV SiC switching power devices (MOSFET, NPN transistor and GTO thyristor) were then compared by using theoretical and numerical calculations. Special emphasis is placed on comparing the total power loss of the devices at a given current density. Theoretical analyses and simulation results show that GTO thyristors have a large switching loss due to the long current tail at turn-off, hence restricting its maximum operation frequency. High voltage SiC MOSFETs have a large on-state power dissipation at high current levels due to the resistive nature of the drift region, restricting their applications at high current densities. SiC NPN transistors have a comparable switching loss as that of SiC MOSFETs, but at the same time, SiC NPN transistors have the lowest on-state loss. This study indicates that SiC NPN transistor is the most attractive switching power device at 4.5 kV.

  13. Near-surface and bulk behavior of Ag in SiC

    SciTech Connect

    Xiao, Haiyan; Zhang, Yanwen; Snead, Lance Lewis; Shutthanandan, Vaithiyalingam; Xue, Haizhou; Weber, William J

    2012-01-01

    The diffusive release of fission products, such as Ag, from TRISO particles at high temperatures has raised concerns regarding safe and economic operation of advanced nuclear reactors. Understanding the mechanisms of Ag diffusion is thus of crucial importance for effective retention of fission products. Two mechanisms, i.e., grain boundary diffusion and vapor or surface diffusion through macroscopic structures such as nano-pores or nano-cracks, remain in debate. In the present work, an integrated computational and experimental study of the near-surface and bulk behavior of Ag in silicon carbide (SiC) has been carried out. The ab initio calculations show that Ag prefers to adsorb on the SiC surface rather than in the bulk, and the mobility of Ag on the surface is high. The energy barrier for Ag desorption from the surface is calculated to be 0.85-1.68 eV, and Ag migration into bulk SiC through equilibrium diffusion process is not favorable. Experimentally, Ag ions are implanted into SiC to produce Ag profiles buried in the bulk and peaked at the surface. High-temperature annealing leads to Ag release from the surface region instead of diffusion into the interior of SiC. It is suggested that surface diffusion through mechanical structural imperfection, such as vapor transport through cracks in SiC coatings, may be a dominating mechanism accounting for Ag release from the SiC in the nuclear reactor.

  14. Additive Manufacturing of SiC Based Ceramics and Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Halbig, Michael Charles; Singh, Mrityunjay

    2015-01-01

    Silicon carbide (SiC) ceramics and SiC fiber reinforcedSiC ceramic matrix composites (SiCSiC CMCs) offer high payoff as replacements for metals in turbine engine applications due to their lighter weight, higher temperature capability, and lower cooling requirements. Additive manufacturing approaches can offer game changing technologies for the quick and low cost fabrication of parts with much greater design freedom and geometric complexity. Four approaches for developing these materials are presented. The first two utilize low cost 3D printers. The first uses pre-ceramic pastes developed as feed materials which are converted to SiC after firing. The second uses wood containing filament to print a carbonaceous preform which is infiltrated with a pre-ceramic polymer and converted to SiC. The other two approaches pursue the AM of CMCs. The first is binder jet SiC powder processing in collaboration with rp+m (Rapid Prototyping+Manufacturing). Processing optimization was pursued through SiC powder blending, infiltration with and without SiC nano powder loading, and integration of nanofibers into the powder bed. The second approach was laminated object manufacturing (LOM) in which fiber prepregs and laminates are cut to shape by a laser and stacked to form the desired part. Scanning electron microscopy was conducted on materials from all approaches with select approaches also characterized with XRD, TGA, and bend testing.

  15. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    PubMed Central

    2011-01-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals. PMID:21762496

  16. Theoretical studies on Si-C bond cleavage in organosilane precursors during polycondensation to organosilica hybrids.

    PubMed

    Shirai, Soichi; Goto, Yasutomo; Mizoshita, Norihiro; Ohashi, Masataka; Tani, Takao; Shimada, Toyoshi; Hyodo, Shi-aki; Inagaki, Shinji

    2010-05-20

    Molecular orbital theory calculations were carried out to predict the occurrence of Si-C bond cleavage in various organosilane precursors during polycondensation to organosilica hybrids under acidic and basic conditions. On the basis of proposed mechanisms for cleavage of the Si-C bonds, the proton affinity (PA) of the carbon atom at the ipso-position and the PA of the carbanion generated after Si-C cleavage were chosen as indices for Si-C bond stability under acidic and basic conditions, respectively. The indices were calculated using a density functional theory (DFT) method for model compounds of organosilane precursors (R-Si(OH)(3)) having organic groups (R) of benzene (Ph), biphenyl (Bp), terphenyl (Tph), naphthalene (Nph), N-methylcarbazole (MCz), and anthracene (Ant). The orders for the predicted stability of the Si-C bond were Ph > Nph > Bp > Ant > Tph > MCz for acidic conditions and Ph > MCz > Bp > Nph > Tph > Ant for basic conditions. These behaviors were primarily in agreement with experimental results where cleavage of the Si-C bonds occurred for Tph (both acidic and basic), MCz (acidic), and Ant (basic). The Si-C bond cleavage of organosilane precursors during polycondensation is qualitatively predicted from these indices based on our theoretical approach. PMID:20429568

  17. Material science and device physics in SiC technology for high-voltage power devices

    NASA Astrophysics Data System (ADS)

    Kimoto, Tsunenobu

    2015-04-01

    Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600-1700 V) SiC Schottky barrier diodes (SBDs) and power metal-oxide-semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

  18. Influence of SiC Particles Distribution and Their Weight Percentage on 7075 Al Alloy

    NASA Astrophysics Data System (ADS)

    Bhushan, Rajesh Kumar; Kumar, Sudhir

    2011-03-01

    The stir casting method was used for fabrication of 7075 aluminum alloy with 10 wt.% SiC particles of size 20-40 μm. The research objective of this paper are to achieve uniform distribution of SiC particles in the 7075 aluminum alloy matrix, characterization, and analysis of mechanical properties of composite formed. Experiments were carried out at stirring speeds of 500, 650, 750 rpm, and stirring period of 10 min. Microstructures of aluminum alloy and composites with 5, 10 wt.% SiC reinforcements were examined. The results reveal that composite produced at stirring speed of 650 rpm and stirring time of 10 min has uniform distribution of SiC particles. XRD and EDAX analysis were carried out for 7075 Al alloy and composite with 10 wt.% SiC reinforcement. No adverse reaction was observed in XRD and EDAX of composite with 10 wt.% SiC reinforcement. Tensile strength and hardness increased by 12.74% and 10.48%, respectively, with the increase in percentage of SiC reinforcement from 5 to 15 wt.%.

  19. SiC nanoparticles as potential carriers for biologically active substances

    NASA Astrophysics Data System (ADS)

    Guevara-Lora, Ibeth; Czosnek, Cezary; Smycz, Aleksandra; Janik, Jerzy F.; Kozik, Andrzej

    2009-01-01

    Silicon carbide SiC thanks to its many advantageous properties has found numerous applications in diverse areas of technology. In this regard, its nanosized forms often with novel properties have been the subject of intense research in recent years. The aim of this study was to investigate the binding of biologically active substances onto SiC nanopowders as a new approach to biomolecule immobilization in terms of their prospective applications in medicine or for biochemical detection. The SiC nanoparticles were prepared by a two-stage aerosol-assisted synthesis from neat hexamethyldisiloxane. The binding of several proteins (bovine serum albumin, high molecular weight kininogen, immunoglobulin G) on SiC particle surfaces was demonstrated at the levels of 1-2 nanograms per mg of SiC. These values were found to significantly increase after suitable chemical modifications of nanoparticle surfaces (by carbodiimide or 3-aminopropyltrietoxysilane treatment). The study of SiC biocompatibility showed a lack of cytotoxicity against macrophages-like cells below the concentration of 1 mg nanoparticles per mL. In summary, we demonstrated the successful immobilization of the selected substances on the SiC nanoparticles. These results including the cytotoxicity study make nano-SiC highly attractive for potential applications in medicine, biotechnology or molecular detection.

  20. Application of rapid milling technology for fabrication of SiC nanoparticles.

    PubMed

    Kim, Jong-Woong; Shim, Jae-Shik; Kwak, Min-Gi; Hong, Sung-Jei; Cho, Hyun-Min

    2013-09-01

    SiC nanoparticles were successfully fabricated by a high energy ball milling method, so that can be used in the printed electronics to make SiC thin film patterns. Here we utilized the waste of Si sludge for making the SiC nanoparticles. In order to achieve uniform thin film from the nanoparticle ink, fine sized SiC nanoparticles less than 100 nm has to be uniformly dispersed. In this study, we employed the ultra apex milling (UAM) system for particle comminution and dispersion. We investigated the effects of milling parameters, e.g., size of ZrO2 bead and milling time. The size of the SiC particles reached about 103 nm after 4 hours of UAM, when the ZrO2 beads of 50 microm were used. Then SiC ink was formulated with organic solvents and a dispersing agent. A specially designed pattern was printed by an ink-jet printer for evaluating the feasibility of the SiC nanoparticle inks. PMID:24205600

  1. Microwave absorbability of unidirectional SiC fiber composites as a function of the constituents’ properties

    NASA Astrophysics Data System (ADS)

    Wan, Guangchao; Jiang, Jianjun; He, Yun; Bie, Shaowei

    2016-06-01

    The electromagnetic properties of unidirectional SiC fibre composites can be efficiently tailored by adjusting the properties of the composite’s constituents making these composites potential microwave absorbers. In this study, the microwave absorbing properties of unidirectional SiC fibre composites were investigated based on the electromagnetic properties of the constituents at frequencies ranging from 8 to 18 GHz. The composite was composed of two types of SiC fibres that individually exhibit relatively high and low electrical conductivity. The matrix together with the low-conductivity SiC fibres were characterized by effective permittivity and conductivity which provided a theoretical calculation of the microwave reflectivity. The theoretical calculation was based on formulas about anisotropic unidirectional composites and was compared to the results obtained from numerical simulations. There was good agreement in the results obtained from both methods. It was found that the intensity of microwave absorption of the composite was dependent primarily on the properties of the high-conductivity SiC fibres. The absorption band appeared to be dependent on the effective permittivity of the matrix and the low-conductivity SiC fibres and the conductivity of the high-conductivity SiC fibres.

  2. Chemical reactivity of CVC and CVD SiC with UO2 at high temperatures

    DOE PAGESBeta

    Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; Snead, Lance L.

    2015-02-11

    Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO2 pellets and evaluated for their potential chemical reaction with UO2. While minor reactivity between chemical-vapor-composited (CVC) SiC and UO2 was observed at comparatively low temperatures of 1100 and 1300 C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity, according to microstructural investigations. But, both CVD and CVC SiCs showed some reaction with UO2 at a higher temperature (1500 C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive than CVD SiC at 1500more » C. Moreover, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi2, and U3Si2 as a result of SiC reaction with UO2.« less

  3. Identifying radiation induced point defect in SiC nanowires: computational modeling

    NASA Astrophysics Data System (ADS)

    Uu, Ming

    SiC nanowires (NWs) are expected to possess higher radiation tolerance compared to their crystalline counterpart due to their efficiency in eliminating point defects generated by the radiations. In this study, we will develop a computational modeling scheme to identify the radiation induced point defects in SiC NWs. A preliminary study on the hexagonal 2H-SiC NWs has demonstrated that the point defects on the surface of the SiC NWs only create local distortions and will not cause the destruction of the entire structure of the SiC NWs. It is also found that the local strain created by the antisite, the C-vacancy, and the Si-interstitial defects induces a few impurity states inside the energy gap, while defects such as the Si-vacancy and C-interstitial defects tend to produce a small tail at the top of the valence band. These observations suggest that the electronic properties of the SiC NWs will not be affected to any great extent by these types of points defects on the surface of the SiC NWs, and therefore the SiC NWs are expected to be tolerant or resistant responding to these types of radiation effect.

  4. The microstructures of SCS-6 and SCS-8 SiC reinforcing fibers

    SciTech Connect

    Sattler, M.L.; Kinney, J.H.; Zywicz, E. ); Alani, R. ); Nichols, M.C. )

    1992-01-01

    The microstructures of SCS-6 and SCS-8 SiC fibers have been examined and analyzed using high resolution transmission electron microscopy (HRTEM), microdiffraction, parallel electron energy loss spectroscopy (PEELS), x-ray diffraction and x-ray spectroscopy. The results of the study confirm findings from earlier studies wherein the microstructure of the fibers have been described as consisting of {beta}-SiC grown upon a monofilament turbostratic carbon core. The present study, however, provides much more detail regarding this microstructure. For example, PEELS spectroscopy and x-ray microscopy indicate that the composition of the SiC varies smoothly from SiC plus free C near the carbon core to SiC at the midradial boundary. The SiC stoichiometry is roughly preserved from the midradial boundary to the exterior interface. HRTEM, microdiffraction, and dark field images provide evidence that the excess carbon is amorphous free carbon which is most likely situated at the grain boundaries of the SiC. The x-ray microscopy results are also consistent with the presence of two phases near the core which consist of SiC and free carbon having density less than graphite (2.25 g/cc). This complex microstructure may explain the recent observations of nonplanar failure in composites fabricated with SCS fibers.

  5. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Yong; Chen, Changxin; Li, Jiang-Tao; Yang, Yun; Lin, Zhi-Ming

    2011-07-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals.

  6. The reaction of N{sub 2}O with phenylium ions C{sub 6}(H,D){sub 5}{sup +}: An integrated experimental and theoretical mechanistic study

    SciTech Connect

    Giordana, Anna; Ghigo, Giovanni; Tonachini, Glauco; Ascenzi, Daniela; Tosi, Paolo; Guella, Graziano

    2009-07-14

    The reaction of N{sub 2}O (known to be an O atom donor under several conditions) with the phenyl cation is studied by experimental and theoretical methods. Phenyl cation (or phenylium), C{sub 6}H{sub 5}{sup +}, and its perdeuterated derivative C{sub 6}D{sub 5}{sup +} are produced either by electron impact or by atmospheric pressure chemical ionization of adequate neutral precursors, and product mass spectra are measured in a guided ion beam tandem mass spectrometer. The ions C{sub 5}(H,D){sub 5}{sup +}, C{sub 6}(H,D){sub 5}O{sup +}, and C{sub 3}(H,D){sub 3}{sup +} are experimentally detected as the most relevant reaction products. In addition, the detection of the adduct (C{sub 6}H{sub 5}{center_dot}N{sub 2}O){sup +}, which is collisionally stabilized in the scattering cell of the mass spectrometer, is reported here for the first time. The reaction pathways, which could bring about the formation of the mentioned ions, are then explored extensively by density functional theory and, for the more promising pathways, by CASPT2/CASSCF calculations. The two reacting species (1) form initially a phenoxydiazonium adduct, C{sub 6}H{sub 5}ON{sub 2}{sup +} (2a), by involving the empty in-plane hybrid C orbital of phenylium. The alternative attack to the ring {pi} system to produce an epoxidic adduct 2c is ruled out on the basis of the energetics. Then, 2a loses N{sub 2} quite easily, thus affording the phenoxyl cation 3. This is only the first of several C{sub 6}H{sub 5}O{sup +} isomers (4-6 and 8-12), which can stem from 3 upon different cleavages and formations of C-C bond and/or H shifts. As regards the formation of C{sub 5}H{sub 5}{sup +}, among several conceivable pathways, a direct CO extrusion from 3 is discarded, while others appear to be viable to different extents, depending on the initial energy of the system. The easiest CO loss is from 4, with formation of the cyclopentadienyl cation 7. Formation of C{sub 3}H{sub 3}{sup +} is generally hindered and its detection

  7. Study of the effects of SiC filler on the internal charging of LDPE in space environment

    NASA Astrophysics Data System (ADS)

    Dong, Lei; Tan, Zhenyu; Tang, Fule

    2015-05-01

    The systematic investigation on the effects of the parameters of SiC filler on the internal charging of low density polyethylene (LDPE) has been performed. The injected current density and the absorbed dose rate in LDPE are calculated by means of the Monte Carlo method based on Geant4 code. Using these obtained quantities and taking into account the high-field conductivity, the electric field distributions in the LDPEs with SiC fillers of the different parameters have been calculated. The following significant results are given. With the increase of SiC filler concentration, the obvious increase of the electric field appears at increasingly small depth in LDPE. At lower SiC filler concentrations, large incident current density leads to large electric field magnitude Emax, but at higher SiC filler concentrations, Emax values under different incident current densities become close to each other. In addition, large particulate size of SiC has a substantial effect on the electric field distributions at high SiC filler concentrations, the contribution of black SiC to the decrease in the electric field is superior to that of green SiC, and the addition of β-form SiC leads to significant low Emax, compared to that by adding α-form SiC.

  8. Effect of grain size on microstructure, properties, and surface roughness of reaction bonded SiC ceramics

    NASA Astrophysics Data System (ADS)

    Aghajanian, Michael; Emmons, Craig; Rummel, Steve; Barber, Paul; Robb, Chris; Hibbard, Doug

    2013-09-01

    Silicon carbide (SiC) based ceramics have received significant study for optical applications due to high specific stiffness, high thermal conductivity, and low coefficient of thermal expansion (CTE). Reaction bonded SiC ceramics, which are composites of SiC and Si, are of particular interest due to large size and complex shape capability. The behavior of these ceramics is very much affected by the grain size of the SiC phase. The present work examines SiC grain sizes ranging from 6 to 50 μm, with the goal of optimizing properties and finishing capability for optical uses. Microstructures are reviewed; physical, mechanical and thermal properties are presented; and post-polishing surface roughness data are provided. In particular, results demonstrate that properties can be tailored by SiC particle size selection, and that measureable enhancement in surface roughness can be achieved by moving to smaller SiC grain size.

  9. Interstellar grains in meteorites. I - Isolation of SiC, graphite, and diamond; size distributions of SiC and graphite. II - SiC and its noble gases

    NASA Astrophysics Data System (ADS)

    Amari, Sachiko; Lewis, Roy S.; Anders, Edward

    1994-01-01

    A new separation procedure is described that permits recovery of grains of interstellar graphite, diamond and SiC from primitive meteorites in greater than 90 percent purity and with yields generally of 70 percent or more. The method relies mainly on a set of progressively more corrosive 'selective solvents' to remove phases one by one, but also includes grain size and density separations. The procedure is applied here to the Murchison C2M meteorite to analyze He, Ne, Ar, Kr, and Xe. The results indicate that the SIC grains are pristine circumstellar condensates from red giant carbon stars representing a range of masses, metallicities, temperatures, and neutron densities. The results suggest that gas-rich SiC grains predate the solar system by at least 130 Ma and possibly up to 2000 Ma.

  10. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  11. Polycrystalline SiC fibers from organosilicon polymers

    NASA Technical Reports Server (NTRS)

    Lipowitz, Jonathan; Rabe, James A.; Zank, Gregg A.

    1991-01-01

    Various organosilicon polymers have been converted into small diameter, fine-grained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to greater than 1600 C. The high pyrolysis temperature densifies the fiber and causes CO evolution which removes nearly all oxygen. An additive prevents the loss of strength normally associated with such treatments. Silicon carbide fibres with up to 2.6 GPa (380 ksi) tensile strength, greater than 420 GPa (greater than 60 Msi) elastic modulus, and 3.1-3.2 mg/cu m density have been prepared via this process. Their microstructure consists of greater than 95 wt pct B-SiC crystallites averaging 30-40 nm diameter, with varying amounts of graphitic carbon between the SiC grains. Under inert conditions, the fibers can be thermally aged at least 12 h/1800 C with minimal change in properties.

  12. Graphene Nanoribbons Anchored to a SiC Substrate

    NASA Astrophysics Data System (ADS)

    Woods, Lilia; Le, Nam

    Due to their exceptional fundamental characteristics graphene nanoribbons play a major role in the development of future nano-technological applications. The high chemical reactivity of the graphene nanoribbon edges can be utilized to create modified materials. Using first principles simulations we explore this possibility to construct patterned systems composed of anchored ribbons of zigzag edges covalently bonded to a SiC substrate. The hybrid edge states are found to possess interesting electronic and magnetic properties, which alter the overall behavior of the entire system as compared to the behavior of the individual components. It is found that the van der Waals interactions are important for the overall stability and structure of the anchored ribbons. Also, spin-polarization effects play a profound role in the electronic structure and associated density of states. The hybrid graphene/SiC zigzag edges are analyzed in terms of their transport characteristics as well.

  13. Interaction Of Water Molecules With SiC(001) Surfaces

    SciTech Connect

    Cicero, G; Catellani, A; Galli, G

    2004-08-10

    We have investigated the interaction of water molecules with the polar Si- and C- terminated surfaces of cubic Silicon Carbide by means of ab initio molecular dynamics simulations at finite temperature. Different water coverages were considered, from {1/4} to a complete monolayer. Irrespective of coverage, we find that water dissociates on the silicon terminated surfaces, leading to important changes in both its structural and electronic properties. On the contrary, the carbon terminated surface remains inert when exposed to water. We propose experiments to reveal the ionic and electronic structure of wet Si-terminated surfaces predicted by our calculations, which at full coverage are notably different from those of hydrated Si(001) substrates. Finally, we discuss the implications of our results for SiC surface functionalization.

  14. Demonstration of SiC Pressure Sensors at 750 C

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.; Lukco, Dorothy; Nguyen, Vu; Savrun, Ender

    2014-01-01

    We report the first demonstration of MEMS-based 4H-SiC piezoresistive pressure sensors tested at 750 C and in the process confirmed the existence of strain sensitivity recovery with increasing temperature above 400 C, eventually achieving near or up to 100% of the room temperature values at 750 C. This strain sensitivity recovery phenomenon in 4H-SiC is uncharacteristic of the well-known monotonic decrease in strain sensitivity with increasing temperature in silicon piezoresistors. For the three sensors tested, the room temperature full-scale output (FSO) at 200 psig ranged between 29 and 36 mV. Although the FSO at 400 C dropped by about 60%, full recovery was achieved at 750 C. This result will allow the operation of SiC pressure sensors at higher temperatures, thereby permitting deeper insertion into the engine combustion chamber to improve the accurate quantification of combustor dynamics.

  15. Graphene nanoribbons anchored to SiC substrates.

    PubMed

    Le, Nam B; Woods, Lilia M

    2016-09-14

    Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties dependent on their width and types of edges. Graphene nanoribbons anchored to substrates is a hybrid system, which offers novel opportunities for property modifications as well as experimental control. Here we present electronic structure calculations of zigzag graphene nanoribbons chemically attached via the edges to the Si or C terminated surfaces of a SiC substrate. The results show that the edge characteristics are rather robust and the properties are essentially determined by the individual nanoribbon. While the localized spin polarization of the graphene nanoribbon edge atoms is not significantly affected by the substrate, secondary energy gaps in the highest conduction and lowest valence region may emerge in the anchored structures. The van der Waals interaction together with the electrostatic interactions due to the polarity of the surface bonds are found to be important for the structure parameters and energy stability. PMID:27392014

  16. Graphene nanoribbons anchored to SiC substrates

    NASA Astrophysics Data System (ADS)

    Le, Nam B.; Woods, Lilia M.

    2016-09-01

    Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties dependent on their width and types of edges. Graphene nanoribbons anchored to substrates is a hybrid system, which offers novel opportunities for property modifications as well as experimental control. Here we present electronic structure calculations of zigzag graphene nanoribbons chemically attached via the edges to the Si or C terminated surfaces of a SiC substrate. The results show that the edge characteristics are rather robust and the properties are essentially determined by the individual nanoribbon. While the localized spin polarization of the graphene nanoribbon edge atoms is not significantly affected by the substrate, secondary energy gaps in the highest conduction and lowest valence region may emerge in the anchored structures. The van der Waals interaction together with the electrostatic interactions due to the polarity of the surface bonds are found to be important for the structure parameters and energy stability.

  17. Saturn V S-IC Stage at Dynamic Test Stand

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Engineers and technicians at the Marshall Space Flight Center placed a Saturn V ground test booster (S-IC-D) into the dynamic test stand. The stand was constructed to test the integrity of the vehicle. Forces were applied to the tail of the vehicle to simulate the engines thrusting, and various other flight factors were fed to the vehicle to test reactions. The Saturn V launch vehicle, with the Apollo spacecraft, was subjected to more than 450 hours of shaking. The photograph shows the 300,000 pound S-IC stage being lifted from its transporter into place inside the 360-foot tall test stand. This dynamic test booster has one dummy F-1 engine and weight simulators are used at the other four engine positions.

  18. Angular Effects on F+ Etching SiC: MD Study

    NASA Astrophysics Data System (ADS)

    Chen, Xu; Tian, Shuping; He, Pingni; Zhao, Chengli; Sun, Weizhong; Zhang, Junyuan; Chen, Feng; Gou, Fujun

    2012-12-01

    Molecular dynamics (MD) simulations were performed to investigate F+ continuously bombarding SiC surfaces with energies of 100 eV at different incident angles at 300 K. The simulated results show that the steady-state uptake of F atoms increases with increasing incident angle. With the steady-state etching established, a Si-C-F reactive layer is formed. It is found that the etching yield of Si is greater than that of C. In the F-containing reaction layer, the SiF species is dominant with incident angles less than 30°. For all incident angles, the CF species is dominant over CF2 and CF3.

  19. Fatigue behavior of SiC reinforced titanium composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Grimes, H. H.

    1979-01-01

    The low cycle axial fatigue properties of 25 and 44 fiber volume percent SiC/Ti(6Al-4V) composites were measured at room temperature and at 650 deg C. The S-N curves for the composites showed no anticipated improvement over bulk matrix behavior at room temperature. Although axial and transverse tensile strength results suggest a degradation in SiC fiber strength during composite fabrication, it appears that the poor fatigue life of the composites was caused by a reduced fatigue resistance of the reinforced Ti(6Al-4V) matrix. The reduced matrix behavior was due, to the presence of flawed and fractured fibers created near the specimen surfaces by preparation techniques and to the large residual tensile stresses that can exist in fiber reinforced matrices. The effects of fatigue testing at high temperature are discussed.

  20. Fatigue behavior of SiC reinforced titanium composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Grimes, H. H.

    1979-01-01

    The low cycle axial fatigue properties of 25 and 44 fiber volume percent SiC/Ti(6Al-4V) composites were measured at room temperature and at 650 C. At room temperature, the S-N curves for the composites showed no anticipated improvement over bulk matrix behavior. Although axial and transverse tensile strength results suggest a degradation in SiC fiber strength during composite fabrication, it appears that the poor fatigue life of the composites was caused by a reduced fatigue resistance of the reinforced Ti(6Al-4V) matrix. Microstructural studies indicate that the reduced matrix behavior was due, in part, to the presence of flawed and fractured fibers created near the specimen surfaces by preparation techniques. Another possible contributing factor is the large residual tensile stresses that can exist in fiber-reinforced matrices. These effects, as well as the effects of fatigue testing at high temperature, are discussed.