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Sample records for napyivyizolyuyuchomu 6h sic

  1. Ab initio quasiparticle energies in 2H, 4H, and 6H SiC

    NASA Astrophysics Data System (ADS)

    Ummels, R. T. M.; Bobbert, P. A.; van Haeringen, W.

    1998-09-01

    Ab initio quasiparticle energies are calculated for the 2H, 4H, and 6H polytypes of SiC within the GW approximation for the self-energy. The starting point is a calculation within the pseudopotential local-density approximation framework. The calculated fundamental gaps of 3.15, 3.35, and 3.24 eV for 2H, 4H, and 6H SiC, respectively, show very good agreement with experimental data. The energy dependence of the screened interaction is modeled by a plasmon pole model from which the plasmon band structures are obtained.

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

    DOE PAGES

    Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki; ...

    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

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

    SciTech Connect

    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. 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.

  5. Growth of Ba-hexaferrite films on single crystal 6-H SiC

    NASA Astrophysics Data System (ADS)

    Chen, Zhoahui; Yang, Aria; Yoon, S. D.; Ziemer, Katherine; Vittoria, Carmine; Harris, V. G.

    2006-06-01

    Barium hexaferrite films have been processed by pulsed laser deposition on single crystal 6-H silicon carbide substrates. Atomic force microscopy images show hexagonal crystals (˜0.5 μm in diameter) oriented with the c-axis perpendicular to the film plane. X-ray θ-2 θ diffraction measurements indicate a strong (0,0,2n) alignment of crystallites. The magnetization for low-pressure deposition (20 mTorr) is comparable to bulk values (4 πMs˜4320 G). The loop squareness, important for self-bias microwave device applications, increases with oxygen pressure reaching a maximum value of 70%. This marks the first growth of a microwave ferrite on SiC substrates and offers a new approach in the design and development of μ-wave and mm-wave monolithic integrated circuits.

  6. Charge neutrality in epitaxial graphene on 6 H -SiC(0001) via nitrogen intercalation

    NASA Astrophysics Data System (ADS)

    Caffrey, Nuala M.; Armiento, Rickard; Yakimova, Rositsa; Abrikosov, Igor A.

    2015-08-01

    The electronic properties of epitaxial graphene grown on SiC(0001) are known to be impaired relative to those of freestanding graphene. This is due to the formation of a carbon buffer layer between the graphene layers and the substrate, which causes the graphene layers to become strongly n -doped. Charge neutrality can be achieved by completely passivating the dangling bonds of the clean SiC surface using atomic intercalation. So far, only one element, hydrogen, has been identified as a promising candidate. We show, using first-principles density functional calculations, how it can also be accomplished via the growth of a thin layer of silicon nitride on the SiC surface. The subsequently grown graphene layers display the electronic properties associated with charge neutral graphene. We show that the surface energy of this structure is considerably lower than that of others with intercalated atomic nitrogen and determine how its stability depends on the N2 chemical potential.

  7. 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.

  8. 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.

  9. 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.

  10. 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).

  11. 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.

  12. Characterization and formation of NV centers in 3 C , 4 H , and 6 H SiC: An ab initio study

    NASA Astrophysics Data System (ADS)

    Csóré, A.; von Bardeleben, H. J.; Cantin, J. L.; Gali, A.

    2017-08-01

    Fluorescent paramagnetic defects in solids have become attractive systems for quantum information processing in recent years. One of the leading contenders is the negatively charged nitrogen-vacancy (NV) defect in diamond with visible emission, but an alternative solution in a technologically mature host is an immediate quest for many applications in this field. It has been recently found that various polytypes of silicon carbide (SiC), that are standard semiconductors with wafer scale technology, can host a NV defect that could be an alternative qubit candidate with emission in the near infrared region. However, there is much less known about this defect than its counterpart in diamond. The inequivalent sites within a polytype and the polytype variations offer a family of NV defects. However, there is an insufficient knowledge on the magneto-optical properties of these configurations. Here we carry out density functional theory calculations, in order to characterize the numerous forms of NV defects in the most common polytypes of SiC including 3 C , 4 H , and 6 H , and we also provide new experimental data in 4 H SiC. Our calculations mediate the identification of individual NV qubits in SiC polytypes. In addition, we discuss the formation of NV defects in SiC, providing detailed ionization energies of NV defects in SiC, which reveals the critical optical excitation energies for ionizing these qubits in SiC. Our calculations unravel the challenges to produce NV defects in SiC with a desirable spin bath.

  13. Synthesis and Characterization of Indium Compounds with Phosphinothiol Ligands. The Crystal and Molecular Structures of [In{2-(Ph(2)P)C(6)H(4)S}(3)], [In{2-(Ph(2)P)-6-(Me(3)Si)C(6)H(3)S}(2){2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}], and [NMe(4)][In{PhP(C(6)H(4)S-2)(2)}(2)].CH(3)CN.

    PubMed

    Pérez-Lourido, Paulo; Romero, Jaime; García-Vázquez, José Arturo; Sousa, Antonio; Maresca, Kevin; Zubieta, Jon

    1999-03-22

    The electrochemical oxidation of anodic indium metal in an acetonitrile solution of phosphinothiol ligands affords [In{2-(Ph(2)P)C(6)H(4)S}(3)] (1), [In{2-(Ph(2)P)-6-(Me(3)Si)C(6)H(3)S)}(2){2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}] (2), [In{2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}(3)] (3), and [NMe(4)][In{PhP(C(6)H(4)S-2)(2)}(2)].CH(3)CN (4) complexes exhibiting distorted six-coordinate geometries based on {InS(3)P(3)}, {InS(3)P(2)O}, and {InS(4)P(2)} cores, respectively. In all cases, the In-P bond distances are anomalously long, presumably as a consequence of steric crowding. The anion of 4 provides an unusual example of an In(III)-thiolate coordination complex ion. Crystal data: 1, C(54)H(42)InP(3)S(3), monoclinic, P2(1)/c, a = 16.6579(1) Å, b = 12.6628(2) Å, c = 22.5520(3) Å, beta = 96.42(1) degrees, V = 4727.15(1) Å(3), Z = 4, 6176 reflections, R = 0.0579; 2, C(63)H(66)InOP(3)S(3)Si(3), monoclinic, P2(1)/c, a = 11.53090(10) Å, b = 26.2505(3) Å, c = 20.4206(2) Å, beta = 94.0870(10) degrees, V = 6165.43(11) Å(3), Z = 4, 10 699 reflections, R = 0.0621; 4, C(42)H(41)InN(2)P(2)S(4), monoclinic, P2(1), a = 13.0052(2) Å, b = 11.2240(2) Å, c = 14.3070(3) Å, beta = 93.190(1) degrees, V = 2085.16(7) Å(3), Z = 2, 6651 reflections, R = 0.0352.

  14. 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.

  15. 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.

  16. DEFECT SELECTIVE ETCHING OF THICK ALN LAYERS GROWN ON 6H-SIC SEEDS - A TRANSMISSION ELECTRON MICROSCOPY STUDY

    SciTech Connect

    Nyakiti, Luke; Chaudhari, Jharna; Kenik, Edward A; Lu, Peng; Edgar, J H

    2008-01-01

    In the present study, the type and densities of defects in AlN crystals grown on 6H-SiC seeds by the sublimation-recombination method were assessed. The positions of the defects in AlN were first identified by defect selective etching (DSE) in molten NaOH-KOH at 400 C for 2 minutes. Etching produced pits of three different sizes: 1.77 m, 2.35 m , and 2.86 m. The etch pits were either aligned together forming a sub-grain boundary or randomly distributed. The smaller etch pits were either isolated or associated with larger etch pits. After preparing crosssections of the pits by the focused ion beam (FIB) technique, transmission electron microscopy (TEM) was performed to determine which dislocation type (edge, mixed or screw) produced a specific etch pit sizes. Preliminary TEM bright field and dark field study using different zone axes and diffraction vectors indicates an edge dislocation with a Burgers vector 1/3[1120] is associated with the smallest etch pit size.

  17. Temperature dependent behavior of localized and delocalized electrons in nitrogen-doped 6H SiC crystals as studied by electron spin resonance

    SciTech Connect

    Savchenko, D.; Kalabukhova, E.; Shanina, B.; Kiselov, V.; Cichoň, S.; Honolka, J.; Mokhov, E.

    2016-01-28

    We have studied the temperature behavior of the electron spin resonance (ESR) spectra of nitrogen (N) donors in n-type 6H SiC crystals grown by Lely and sublimation sandwich methods (SSM) with donor concentration of 10{sup 17 }cm{sup −3} at T = 60–150 K. A broad signal in the ESR spectrum was observed at T ≥ 80 K with Lorentzian lineshape and g{sub ||} = 2.0043(3), g{sub ⊥} = 2.0030(3), which was previously assigned in the literature to the N donors in the 1s(E) excited state. Based on the analysis of the ESR lineshape, linewidth and g-tensor we attribute this signal to the conduction electrons (CE). The emergence of the CE ESR signal at T > 80 K was explained by the ionization of electrons from the 1s(A{sub 1}) ground and 1s(E) excited states of N donors to the conduction band while the observed reduction of the hyperfine (hf) splitting for the N{sub k1,k2} donors with the temperature increase is attributed to the motional narrowing effect of the hf splitting. The temperature dependence of CE ESR linewidth is described by an exponential law (Orbach process) with the activation energy corresponding to the energy separation between 1s(A{sub 1}) and 1s(E) energy levels for N residing at quasi-cubic sites (N{sub k1,k2}). The theoretical analysis of the temperature dependence of microwave conductivity measured by the contact-free method shows that due to the different position of the Fermi level in two samples the ionization of free electrons occurs from the energy levels of N{sub k1,k2} donors in Lely grown samples and from the energy level of N{sub h} residing at hexagonal position in 6H SiC grown by SSM.

  18. 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.

  19. Growth of high quality 6H-SiC epitaxial films on vicinal (0001) 6H-SiC wafers

    NASA Technical Reports Server (NTRS)

    Powell, J. A.; Larkin, D. J.; Matus, L. G.; Choyke, W. J.; Bradshaw, J. L.

    1990-01-01

    Previously reported growth of SiC films on SiC by chemical vapor deposition (CVD) used alpha-SiC crystal substrates. The CVD growth and evaluation of high quality 6H-SiC films on 6H-SiC wafers cut from large boules grown by the modified-sublimation process is reported. The single-crystal 6H-SiC films were grown on wafers oriented 3 to 4 deg off the (0001) plane toward the 11-20 direction. The films, up to 12 microns thick, had surfaces that were smooth and featureless. The high quality of the films was demonstrated by optical and electron microscopy, and low-temperature photoluminescence.

  20. Growth of high quality 6H-SiC epitaxial films on vicinal (0001) 6H-SiC wafers

    NASA Technical Reports Server (NTRS)

    Powell, J. A.; Larkin, D. J.; Matus, L. G.; Choyke, W. J.; Bradshaw, J. L.

    1990-01-01

    Previously reported growth of SiC films on SiC by chemical vapor deposition (CVD) used alpha-SiC crystal substrates. The CVD growth and evaluation of high quality 6H-SiC films on 6H-SiC wafers cut from large boules grown by the modified-sublimation process is reported. The single-crystal 6H-SiC films were grown on wafers oriented 3 to 4 deg off the (0001) plane toward the 11-20 direction. The films, up to 12 microns thick, had surfaces that were smooth and featureless. The high quality of the films was demonstrated by optical and electron microscopy, and low-temperature photoluminescence.

  1. Fabrication and Characterization of 6H-SiC Switching Devices

    DTIC Science & Technology

    1993-06-01

    ns range at 623 K has been observed in a 6H- SiC pn junction diode[4]. A Pt/6H-SiC Schottky diode has been shown to have 400 V reverse breakdown...6H-SiC Schottky diode switches, and a 75% switching efficiency in p+n 6H-SiC diode switches. A breakdown field of more than 1x106 V /cm is obtained...This could mean a blocking voltage of about 3000 v . A number of successful sic devices has been demonstrated. A high temperature rectifier made

  2. Epitaxial growth of 6H silicon carbide in the temperature range 1320 C to 1390 C

    NASA Technical Reports Server (NTRS)

    Will, H. A.; Powell, J. A.

    1974-01-01

    High-quality epitaxial layers of 6H SiC have been grown on 6H SiC substrates with the grown direction perpendicular to the crystal c-axis. The growth was by chemical vapor deposition from methyltrichlorosilane (CH3SiCl3) in hydrogen at temperatures in the range of 1320 to 1390 C. Epitaxial layers up to 80 microns thick were grown at rates of 0.4 microns/min. Attempts at growth on the (0001) plane of 6H SiC substrates under similar conditions resulted in polycrystalline cubic SiC layers. Optical and X-ray diffraction techniques were used to characterize the grown layers.

  3. Direct observation of porous SiC formed by anodization in HF

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S.; Grimberg, Ilana; Weiss, Ben-Zion; Kurtz, Anthony D.

    1993-01-01

    A process for forming porous SiC from single-crystal SiC wafers has been demonstrated. Porous SiC can be fabricated by anodizing n-type 6H-SiC in HF under UV illumination. TEM reveals pores of sizes 10-30 nm with interpore spacings ranging from roughly 5 to 150 nm. This is the first reported direct observation of porous SiC formation.

  4. 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.

  5. Amorphization of SiC under ion and neutron irradiation

    NASA Astrophysics Data System (ADS)

    Snead, L. L.; Zinkle, S. J.; Hay, J. C.; Osborne, M. C.

    1998-05-01

    This paper presents results on the microstructure and physical properties of SiC amorphized by both ion and neutron irradiation. Specifically, 0.56 MeV Si ions have been implanted in single crystal 6H-SiC from ambient through >200°C and the critical threshold for amorphization was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of the crystalline to amorphous transition region in these materials, elongated pockets of amorphous material oriented parallel to the free surface are observed. Single crystal 6H-SiC and hot pressed and sintered 6H and 3C SiC were neutron irradiated at approximately 70°C to a dose of ˜2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC include a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystallization of the amorphized, single crystal 6H-SiC appears to occur in two stages. In the temperature range of ˜800-1000°C, crystallites nucleate and slowly grow. In the temperature range of 1125-1150°C spontaneous nucleation and rapid growth of crystallites occur. It is further noted that amorphized 6H (alpha) SiC recrystallizes to highly faulted fcc (beta) SiC.

  6. 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.

  7. Identification of 6H-SiC polar faces with pull-off force of atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Gan, Di; Song, Youting; Yang, Junwei; Chen, Hongxiang; Guo, Liwei; Chen, Xiaolong

    2016-12-01

    Distinguishing SiC (0001) Si-face from SiC (000-1) C-face without any damages is extremely important because the two polar faces have different physical and chemical properties which seriously influence the quality of a homoepitaxy or heteroepitaxy thin film on it. Here, a convenient and nondestructive detection method is developed to distinguish the Si-face and C-face of a (0001) oriented SiC wafer by employing a pull-off force measurement using atomic force microscopy. It is found that the pull-off force from a Si-face of 6H-SiC is about two times of that from a C-face, no matter it is a two-face chemical mechanical polishing or etched 6H-SiC wafer. The method developed here is suitable to identify polar faces of materials only if the two polar faces having different surface energy.

  8. Optical characterization of SiC wafers

    SciTech Connect

    Burton, J.C.; Pophristic, M.; Long, F.H.; Ferguson, I.

    1999-07-01

    Raman spectroscopy has been used to investigate wafers of both 4H-SiC and 6H-SiC. The two-phonon Raman spectra from both 4H- and 6H-SiC have been measured and found to be polytype dependent, consistent with changes in the vibrational density of states. They have observed electronic Raman scattering from nitrogen defect levels in both 4H- and 6H-SiC at room temperature. They have found that electronic Raman scattering from the nitrogen defect levels is significantly enhanced with excitation by red or near IR laser light. These results demonstrate that the laser wavelength is a key parameter in the characterization of SiC by Raman scattering. These results suggest that Raman spectroscopy can be used as a noninvasive, in situ diagnostic for SiC wafer production and substrate evaluation. They also present results on time-resolved photoluminescence spectra of n-type SiC wafers.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Impact ionization of nitrogen in 4H- and 6H-SiC

    NASA Astrophysics Data System (ADS)

    Sankin, V. I.; Petrov, A. G.; Kaliteevski, M.

    2013-08-01

    A natural superlattice (NSL) in silicon carbide polytypes induces a miniband structure within the conduction band along the NSL axis C. It was found that the presence of NSL leads to an anisotropy of a nitrogen impurity impact ionization in SiC. For an electric field direction F ∥C, the nitrogen impurity breakdown at temperature 4.2 K has not been observed up to the field 1.6 MV/cm for the polytype 6H-SiC. However, for the polytype 4H-SiC dependence breakdown field on impurity concentration demonstrates its usual behavior, which has also been observed for other semiconductor materials. Therewith, the impurity breakdown at the electric field perpendicular to the axis in 4H- and 6H-SiC demonstrates consistency with traditional conceptions. These results are explained theoretically.

  15. Phonon thermal transport in 2H, 4H and 6H silicon carbide from first principles

    DOE PAGES

    Protik, Nakib Haider; Katre, Ankita; Lindsay, Lucas R.; ...

    2017-06-07

    Here, silicon carbide (SiC) is a wide band gap semiconductor with a variety of industrial applications. Among its many useful properties is its high thermal conductivity, which makes it advantageous for thermal management applications. In this paper we present ab initio calculations of the in-plane and cross-plane thermal conductivities, κin and κout, of three common hexagonal polytypes of SiC: 2H, 4H and 6H. The phonon Boltzmann transport equation is solved iteratively using as input interatomic force constants determined from density functional theory. Both κin and κout decrease with increasing n in nH SiC because of additional low-lying optic phonon branches.more » These optic branches are characterized by low phonon group velocities, and they increase the phase space for phonon-phonon scattering of acoustic modes. Also, for all n, κin is found to be larger than κout in the temperature range considered. At electron concentrations present in experimental samples, scattering of phonons by electrons is shown to be negligible except well below room temperature where it can lead to a significant reduction of the lattice thermal conductivity. This work highlights the power of ab initio approaches in giving quantitative, predictive descriptions of thermal transport in materials. It helps explain the qualitative disagreement that exists among different sets of measured thermal conductivity data and provides information of the relative quality of samples from which measured data was obtained.« less

  16. Embedded SIC-POVMs

    NASA Astrophysics Data System (ADS)

    Dang, Hoan; Blanchfield, Kate; Bengtsson, Ingemar; Appleby, Marcus

    2013-03-01

    Symmetric informationally complete (SIC) sets of quantum states have applications in foundational studies of quantum mechanics, quantum tomography, quantum communication, quantum cryptography, and classical signal processing. However, their existence in every dimension has not been proven, and no general construction has been known. During our study of linear dependencies in Weyl-Heisenberg orbits, we discovered 2-dimensional SICs embedded in a 6-dimensional Hilbert space. This offers a robust construction for 2-dimensional SICs, and may potentially impact the SIC existence problem. In this talk, I will explain how this construction works, and present numerical results for some other dimensions. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada and by the U. S. Office of Naval Research (Grant No. N00014-09-1-0247).

  17. 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.

  18. Charge exchange in C^6+ + H and C^6+ + H2 collisions

    NASA Astrophysics Data System (ADS)

    Guevara-Leon, Nicolais; Saha, Bidhan; Sabin, John R.; Deumens, Erik; Ohrn, N. Y.

    2010-03-01

    In the solar wind, C^6+ ion is one of the most abundant ionic species and its interaction with comets as well as the atmosphere of planets of the solar system produces several interesting phenomena. The charge exchange reaction is one of the most relevant process as it may provide a possible explanation for the X-ray emission from these objects. Electron capture into a highly excited state of C^5+ ion usually generates radiation in the X-ray region of the spectrum. In the present work, charge exchange in C^6+ + H and C^6+ + H2 collisions are investigated theoretically using electron nuclear dynamics (END) [1] at projectile energies below the ionization threshold. For H2 the one- and two- electron charge exchange cross sections are calculated and compared with other theoretical and experimental data. Orientation effects for the collision with the hydrogen molecules will also be discussed at the conference.

  19. Quantum confinement effect in 6H-SiC quantum dots observed via plasmon-exciton coupling-induced defect-luminescence quenching

    NASA Astrophysics Data System (ADS)

    Guo, Xiaoxiao; Zhang, Yumeng; Fan, Baolu; Fan, Jiyang

    2017-03-01

    The quantum confinement effect is one of the crucial physical effects that discriminate a quantum material from its bulk material. It remains a mystery why the 6H-SiC quantum dots (QDs) do not exhibit an obvious quantum confinement effect. We study the photoluminescence of the coupled colloidal system of SiC QDs and Ag nanoparticles. The experimental result in conjunction with the theoretical calculation reveals that there is strong coupling between the localized electron-hole pair in the SiC QD and the localized surface plasmon in the Ag nanoparticle. It results in resonance energy transfer between them and resultant quenching of the blue surface-defect luminescence of the SiC QDs, leading to uncovering of a hidden near-UV emission band. This study shows that this emission band originates from the interband transition of the 6H-SiC QDs and it exhibits a remarkable quantum confinement effect.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

    Neudeck, P. G.; Powell, J. A.; Trunek, A. J.; Spry, D. J.

    2004-01-01

    The off-axis approach to SiC epitaxial growth has not prevented many substrate crystal defects from propagating into SiC epilayers, and does not permit the realization of SiC heteropolytype devices. This paper reviews recent advancements in SiC epitaxial growth that begin to overcome the above shortcomings for arrays of device-sized mesas patterned into on-axis 4H/6HSiC wafers. These on-axis mesa growth techniques have produced 4H/6H-SiC homoepilayers and 3C-SiC heteroepilayers with substantially lower dislocation densities. The results should enable improved homojunction and heterojunction silicon carbide prototype devices.

  2. Sleep inertia during a simulated 6-h on/6-h off fixed split duty schedule.

    PubMed

    Hilditch, Cassie J; Short, Michelle; Van Dongen, Hans P A; Centofanti, Stephanie A; Dorrian, Jillian; Kohler, Mark; Banks, Siobhan

    Sleep inertia is a safety concern for shift workers returning to work soon after waking up. Split duty schedules offer an alternative to longer shift periods, but introduce additional wake-ups and may therefore increase risk of sleep inertia. This study investigated sleep inertia across a split duty schedule. Sixteen participants (age range 21-36 years; 10 females) participated in a 9-day laboratory study with two baseline nights (10 h time in bed, [TIB]), four 24-h periods of a 6-h on/6-h off split duty schedule (5-h TIB in off period; 10-h TIB per 24 h) and two recovery nights. Two complementary rosters were evaluated, with the timing of sleep and wake alternating between the two rosters (2 am/2 pm wake-up roster versus 8 am/8 pm wake-up roster). At 2, 17, 32 and 47 min after scheduled awakening, participants completed an 8-min inertia test bout, which included a 3-min psychomotor vigilance test (PVT-B), a 3-min Digit-Symbol Substitution Task (DSST), the Karolinska Sleepiness Scale (KSS), and the Samn-Perelli Fatigue Scale (SP-Fatigue). Further testing occurred every 2 h during scheduled wakefulness. Performance was consistently degraded and subjective sleepiness/fatigue was consistently increased during the inertia testing period as compared to other testing times. Morning wake-ups (2 am and 8 am) were associated with higher levels of sleep inertia than later wake-ups (2 pm and 8 pm). These results suggest that split duty workers should recognise the potential for sleep inertia after waking, especially during the morning hours.

  3. Chemical reactions of atomic hydrogen at SiC surface and heterogeneous chemiluminescence

    NASA Astrophysics Data System (ADS)

    Styrov, V. V.; Tyutyunnikov, V. I.; Sergeev, O. T.; Oya, Y.; Okuno, K.

    2005-02-01

    In studies of the surface properties of SiC polytypes and chemical reactions of hydrogen atoms at SiC surfaces the surface (chemi)luminescence of SiC has been applied excited in the reaction of hydrogen atoms due to chemical energy released (heterogeneous chemiluminescence, HCL). The bulk photoluminescence (PL) have also been used for comparison with surface HCL. All the samples showed HCL, but only α-SiC (6H, 15R), technologically or specially doped (predominantly by N, B, Al), exhibited PL (λex=365 nm). Cubic polycrystalline β-SiC (or 3C SiC) did not show PL. The general luminescence band of α-SiC (6H, 15R) and B and Al doped SiC (6H) was a broad yellow band with λmax ranged from 620 to 650 nm for PL (110 K). Another less intensive luminescence band is a blue one, which has been observed only at low temperatures for α-SiC (6H,15R) and B and Al doped SiC (6H) in PL spectra and as a shoulder in HCL spectra (λmax=477 nm at 110 K for 15R SiC). The green band near 540 nm was also observed sometimes in PL spectra for α-SiC. The heat of adsorption of hydrogen atoms at polycrystalline β-SiC estimated from HCL data was found to be in the range from 2 to 3 eV.

  4. 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.

  5. 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.

  6. 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.

  7. Surface morphology of 6H-SiC after thermal diffusion

    NASA Astrophysics Data System (ADS)

    Gao, Ying; Soloviev, S. I.; Sudarshan, T. S.

    2002-05-01

    Diffusion of aluminum into 6H-SiC has been carried out in the temperature range of 1800-2100°C. Aluminum carbide (Al4C3) was used for a p-type impurity source; the diffused surface exhibited good stoichiometry and surface morphology. A thin-layer graphite film was developed to protect the wafer surface from deterioration during the high-temperature diffusion process. A high-resolution optical microscope (HROM) and atomic force microscopy (AFM) were employed to evaluate the surface morphology of the diffused samples. The protective graphite layer significantly decreased the surface roughness. X-ray photoelectron spectroscopy (XPS) was used to identify the Si/C ratio near the surface regions. Very little surface graphitization occurred during diffusion. In addition, secondary ion-mass spectroscopy (SIMS) was used to investigate the influence of the thin graphite film on the diffusion properties in SiC. There were no significant differences in doping profiles in the samples with and without the graphite film.

  8. 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.

  9. Study of the interaction of 4H-SiC and 6H-SiC(0001)Si surfaces with atomic nitrogen

    NASA Astrophysics Data System (ADS)

    Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni; Brown, April; Kim, Tong-Ho

    2004-11-01

    The interaction of atomic nitrogen with 4H- and 6H-SiC(0001) Si-face surfaces is investigated. Clean and atomically smooth terraced surfaces obtained by in situ cleaning using atomic hydrogen have been exposed at 200°C and 750°C to atomic nitrogen produced by a rf remote N2 plasma. Spectroscopic ellipsometry is used for real-time monitoring of the kinetics of SiC surface modifications, and determining the thickness and properties of the nitrided layer. Surface potential measurements reveal the band bending of the nitrided SiC surface. An improvement in the heteroepitaxy of GaN on the low-temperature nitrided SiC surface is found.

  10. 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.

  11. Beryllium implantation induced deep levels in 6H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Fung, S.; Beling, C. D.; Gong, M.; Henkel, T.; Tanoue, H.; Kobayashi, N.

    2001-12-01

    Beryllium has been implanted into both n- and p-type 6H-silicon carbide (SiC) with high and low doses. Upon subsequent annealing at 1600°C, Beryllium implantation induced deep levels have been investigated by deep level transient spectroscopy. Five deep level centers labeled as BE1-BE5 were detected from high dose beryllium implantation produced pn junctions. A comparative study of low dose beryllium implanted n-type 6H-SiC sample proved that the BE1-BE3 centers were electron traps located at 0.34, 0.44, and 0.53 eV, respectively below the conduction band edge. At the same time, the BE4 and BE5 centers were found to be hole traps situated at 0.64 and 0.73 eV, respectively, above the valence band edge. In the case of beryllium implanted p-type 6H-SiC, four hole traps labeled as BEP1, BEP2, BEP3, and BEP4 have been observed. The observed levels of the hole traps BEP1 and BEP2 at 0.41 and 0.60 eV, respectively, above the valence band agree well with those from the Hall effect data from material with beryllium acting as doubly charged acceptor. The other hole traps BEP3 and BEP4 at 0.76 and 0.88 eV, above the valence band, respectively, are thought to be due to beryllium implantation induced defects or complexes.

  12. SICs and Algebraic Number Theory

    NASA Astrophysics Data System (ADS)

    Appleby, Marcus; Flammia, Steven; McConnell, Gary; Yard, Jon

    2017-08-01

    We give an overview of some remarkable connections between symmetric informationally complete measurements (SIC-POVMs, or SICs) and algebraic number theory, in particular, a connection with Hilbert's 12th problem. The paper is meant to be intelligible to a physicist who has no prior knowledge of either Galois theory or algebraic number theory.

  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. 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.

  15. Probe-induced native oxide decomposition and localized oxidation on 6H-SiC (0001) surface: an atomic force microscopy investigation.

    PubMed

    Xie, Xian Ning; Chung, Hong Jing; Xu, Hai; Xu, Xin; Sow, Chorng Haur; Wee, Andrew Thye Shen

    2004-06-23

    We report, for the first time, the native oxide decomposition/etching and direct local oxide growth on 6H-SiC (0001) surface induced by atomic force microscopy (AFM). Surface native oxide was decomposed and assembled into protruded lines when the negatively biased AFM tip was scanned over surface areas. The mechanism of decomposition was found to be governed by the Fowler-Nordheim emission current enhanced by the negatively biased AFM tip. Direct oxide growth on the SiC surface was achieved when the AFM tip was immobilized and longer bias duration applied. In particular, the aspect ratio of oxide grown on SiC was found to be several times higher than that on the Si surface. The improved aspect ratio on SiC was attributed to the anisotropic OH(-) diffusion involved in vertical and lateral oxidation along the polar and nonpolar directions such as [0001] and [110] axis in SiC crystal. The electron transport in the above AFM grown oxide on SiC was further investigated by I-V characteristics. The dielectrical strength of AFM oxide against degradation and breakdown under electrical stressing was evaluated.

  16. 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.

  17. 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.

  18. Improvement of high temperature stability of nickel contacts on n-type 6H SiC

    NASA Astrophysics Data System (ADS)

    Roccaforte, F.; La Via, F.; Raineri, V.; Calcagno, L.; Musumeci, P.

    2001-12-01

    The structural and electrical characterisation of nickel contacts on n-type silicon carbide was performed to improve the ohmic behaviour at high temperatures. The formation of nickel silicide (Ni 2Si) was observed after annealing in vacuum of Ni/SiC samples at 600 °C, as well as after rapid thermal annealing (RTA) in N 2 at 700 for 60 s. The carbon was almost uniformly distributed inside the Ni 2Si layer, as monitored by energy dispersion X-ray analysis (EDX). The specific contact resistance ρc was determined by the transmission line method (TLM) for different values of the substrate carrier concentration ND. Ohmic contacts with ρ c=3.9×10 -5 Ω cm 2 were obtained for substrates with N D=7.4×10 18 cm-3 after RTA in N 2 at 950 °C. The optimised contacts maintain their electrical stability even after annealing in N 2 up to 1000 °C.

  19. 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, 26.13 y ± 4.46) participated in a 9-day laboratory study that included two baseline nights (BL, 10h time in bed (TIB), 2200 h-0800 h), 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 0300 h-0800 h and 1500 h-20000 h, or 6-h late: TIB 0900 h-1400 h and 2100 h-0200 h), and two recovery nights (10h TIB per night, 2200 h-0800 h). 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

  20. Mid-ultraviolet pulsed laser micromachining of SiC

    NASA Astrophysics Data System (ADS)

    Qi, Litao; Li, Mingxing; Lin, Haipeng; Hu, Jinping; Tang, Qingju; Liu, Chunsheng

    2014-11-01

    This paper provides an investigation of the ablation behavior of single crystal 4H-SiC and 6H-SiC wafer to improve the manufacturability and high-temperature performance of SiC using laser applications. 266nm pulsed laser micromachining of SiC was investigated. The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, and photomechanical fragmentation, were correlated with the effects of pulse energy. The ablation threshold is obtained with ultraviolet pulsed laser ablation. The results suggested ultraviolet pulsed laser's potential for rapid manufacturing. Excellent quality of machined features with little collateral thermal damage was obtained in the lower pulse energy range. The leading material removal mechanisms under these conditions were discussed.

  1. Surface engineering of SiC via sublimation etching

    NASA Astrophysics Data System (ADS)

    Jokubavicius, Valdas; Yazdi, Gholam R.; Ivanov, Ivan G.; Niu, Yuran; Zakharov, Alexei; Iakimov, Tihomir; Syväjärvi, Mikael; Yakimova, Rositsa

    2016-12-01

    We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10-5 mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.

  2. Luminescence mechanisms in 6H-SiC nanocrystals

    NASA Astrophysics Data System (ADS)

    Botsoa, J.; Bluet, J. M.; Lysenko, V.; Sfaxi, L.; Zakharko, Y.; Marty, O.; Guillot, G.

    2009-10-01

    Experimental conditions allowing consequent selection of a dominating photoluminescence mechanism in 6H-SiC nanocrystals at room temperature are reported. Electrostatic screening of surface states involved in radiative transitions can be efficiently achieved by polar ethanol molecules. This leads to a preponderant radiative channel between the electronic levels corresponding to the impurity atoms (N and Al). This radiative channel is deactivated by centrifugation-induced selection of the smallest colloidal 6H-SiC nanocrystals in which the probability to have both donor and acceptor atoms is negligible. Consequently, for these smallest 6H-SiC nanocrystals with switched off transitions between surface states and impurity levels, quantum-confinement effect can be clearly observed. The formation of energy subbands in the 6H-SiC nanocrystals is then evidenced from photoluminescence excitation and absorption measurements performed on the centrifuged colloidal nanosuspension. A most probable mean diameter of 1.9 nm for these particles is deduced from calculation of energy levels in the effective-mass approximation.

  3. 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.

  4. Ion beam synthesis by tungsten-implantation into 6H-SiC

    SciTech Connect

    Weishart, H.; Schoeneich, J.; Steffen, H.J.; Matz, W.; Skorupa, W.

    1995-12-31

    The authors studied high-dose implantation of tungsten into 6H-silicon carbide in order to synthesize a highly conductive surface layer. Implantation was performed at 200 keV at room temperature. Subsequently, the samples were annealed in two steps at 500 C and 700 C or 950 C, respectively. The influence of dose and annealing temperature on the reaction of W with SiC was investigated. Rutherford Backscattering Spectrometry (RBS), X-Ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) contributed to study structure and composition of the layer as well as chemical states of the elements. During implantation sputtering became significant at a dose exceeding 1.0 {times} 10{sup 17} W{sup +}cm{sup {minus}2}. Formation of tungsten carbide and silicide was observed already in the as-implanted state. An annealing temperature of 950 C was necessary to crystallize tungsten carbide. However, tungsten silicide remained amorphous at this temperature. Therefore, a mixture of polycrystalline tungsten carbide and amorphous tungsten silicide evolved under these conditions. The resistivity of such a layer implanted with 1.0 {times} 10{sup 17} W{sup +} cm{sup {minus}2} and annealed at 950 C is 565 {micro}{Omega}cm.

  5. Ion beam synthesis by tungsten-implantation into 6H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Weishart, H.; Steffen, H. J.; Matz, W.; Voelskow, M.; Skorupa, W.

    1996-05-01

    Synthesis of a highly conductive surface layer on 6H-silicon carbide was achieved by high-dose, room temperature implantation of tungsten at 200 keV. Subsequently, the samples were annealed in two steps, namely at 500°C and 950°C. The influence of both dose and annealing on the reaction of W with SiC was investigated. Rutherford Backscattering Spectrometry (RBS), X-Ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) contributed to study the structure and composition of the layer as well as the chemical states of the elements. During implantation sputtering becomes significant for doses exceeding 1.0 × 10 17 cm -2. Formation of tungsten carbide and silicide is already observed in the as-implanted state. An annealing temperature of 950°C is necessary to crystallize tungsten carbide. However, tungsten silicide remains amorphous at this temperature. Therefore, a mixture of polycrystalline tungsten carbide and amorphous tungsten silicide develops under these conditions. The resistivity of such a layer implanted with 1.0 × 10 17 W +cm -2 and annealed at 950°C is 565 μΩ cm.

  6. Electrical properties of unintentionally doped semi-insulating and conducting 6H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, W. D.; Fang, Z. Q.; Look, D. C.; Smith, S. R.; Smith, H. E.; Khlebnikov, Igor; Khlebnikov, Y. I.; Basceri, C.; Balkas, C.

    2006-08-01

    Temperature dependent Hall effect (TDH), low temperature photoluminescence (LTPL), secondary ion mass spectrometry (SIMS), optical admittance spectroscopy (OAS), and thermally stimulated current (TSC) measurements have been made on 6H-SiC grown by the physical vapor transport technique without intentional doping. n- and p-type as well semi-insulating samples were studied to explore the compensation mechanism in semi-insulating high purity SiC. Nitrogen and boron were found from TDH and SIMS measurements to be the dominant impurities that must be compensated to produce semi-insulating properties. The electrical activation energy of the semi-insulating sample determined from the dependence of the resistivity was 1.0eV. LTPL lines near 1.00 and 1.34eV, identified with the defects designated as UD-1 and UD-3, were observed in all three samples but the intensity of the UD-1 line was almost a factor of 10 more in the n-type sample than in the the p-type sample with that in the semi-insulating sample being intermediate between those two. OAS and TSC experiments confirmed the high purity of this material. The results suggest that the relative concentrations of a dominant deep level and nitrogen and boron impurities can explain the electrical properties in this material.

  7. 6H Silicon Carbide Photoconductive Switches for High Power Applications

    DTIC Science & Technology

    2006-11-01

    6H SILICON CARBIDE PHOTOCONDUCTIVE SWITCHES FOR HIGH POWER APPLICATIONS W. C. Nunnally*, N. Islam, K. Kelkar & C. Fessler Photonics for Radars...PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Photonics for Radars and Optical Systems...switches. Additional work by the UMC Photonics for Radar and Optical Systems (PROS) group has demonstrated that the relatively new material of

  8. Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC

    PubMed Central

    2011-01-01

    Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping. PMID:21801347

  9. 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.

  10. 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.

  11. The investigation of cobalt intercalation underneath epitaxial graphene on 6H-SiC(0 0 0 1)

    NASA Astrophysics Data System (ADS)

    Zhang, Yuxi; Zhang, Hanjie; Cai, Yiliang; Song, Junjie; He, Pimo

    2017-02-01

    The intercalation behaviour of cobalt underneath both epitaxial graphene monolayer and bilayer on 6H-SiC(0001) have been investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). Upon deposition, cobalt atoms prefer to agglomerate into clusters on the epitaxial graphene. After annealing the sample to 850 °C, the intercalation of the adsorbed cobalt atoms into both monolayer and bilayer epitaxial graphene on SiC takes place, as observed by the atomically resolved STM images. Further studies based on DFT modeling and simulated STM images show that, resulting from the interplay between the intercalated cobalt atoms and the carbon layers sandwiching it, the most energetically favourable intercalation sites of cobalt atoms underneath monolayer and bilayer graphene differ. Furthermore, the results show energy barriers of 0.60 eV and 0.41 eV for cobalt penetration through mono-vacancy defects at monolayer and bilayer graphene.

  12. Fe implantation effect in the 6H-SiC semiconductor investigated by Mössbauer spectrometry

    NASA Astrophysics Data System (ADS)

    Diallo, M. L.; Diallo, L.; Fnidiki, A.; Lechevallier, L.; Cuvilly, F.; Blum, I.; Viret, M.; Marteau, M.; Eyidi, D.; Juraszek, J.; Declémy, A.

    2017-08-01

    P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron Mössbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT.

  13. Diffusion of helium in SiC and implications for retention of cosmogenic He

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.; Trappisch, R.; Thomas, J. B.; Chaussende, D.

    2016-11-01

    Diffusion of helium has been characterized in silicon carbide of cubic and hexagonal (4H and 6H) forms. Polished sections of SiC were implanted with 3He at 100 keV at a dose of 1 × 1015/cm2. The implanted SiC samples were sealed under vacuum in silica glass ampoules, and annealed in 1-atm furnaces. 3He distributions following all experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For He diffusion in cubic SiC and 4H hexagonal SiC we obtain the following Arrhenius relations: Dcubic = 1.83 ×10-6 exp (- 254 ± 10kJmol-1 /RT)m2s-1 . D4H = 4.78 ×10-7 exp (- 255 ± 29kJmol-1 /RT)m2s-1 . While He diffusion is considerably slower in SiC than in many silicate phases, He retentivity may be limited under some conditions. For example, helium will be lost from SiC grains over much shorter timescales than potential survival times of SiC presolar grains in the solar nebula. When exposed to impact heating followed by slow cooling, nearly complete loss of He from SiC grains near the site of impact will occur within several hours to a few days. For SiC grains at greater distance from impact sites, He would be better retained, depending on the rapidity of cooling. At tens of km away from a large impactor, where peak T would be ∼800 K, SiC grains would lose about 50% of their He if the grains cooled within a few thousand years, and 5% if they cooled within a few tens of years. At greater distances where heating is more modest (500 K and lower), SiC grains would be quite retentive of He even for cases of very slow cooling. Helium would also be retained in cases of impact heating followed by very rapid cooling. For these short heating pulses, 10 μm diameter SiC grains would retain more than 50% of their He for peak heating temperatures of 2173, 1973 and 1773 K for durations of 3, 10 and 60 s, respectively.

  14. Hydrogen passivation and reactivation of the Al-acceptors in p-type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Samiji, M. E.; Venter, A.; Wagener, M. C.; Leitch, A. W. R.

    2001-10-01

    We report on the passivation by hydrogen and the subsequent thermal reactivation of the acceptors in Al-doped p-type 6H-SiC. Capacitance-voltage measurements revealed that the near-surface free carrier concentration was reduced by at least an order of magnitude after hydrogen plasma treatment. The thermal stability of the Al-H complex in hydrogenated SiC was investigated through a series of isothermal anneals at temperatures ranging from 200 to 275 °C, while applying a reverse bias to a Ru Schottky barrier. Ru was chosen as the Schottky barrier metal for both its permeability to hydrogen as well as its thermal stability. The electric field associated with the applied reverse bias caused the dissociated hydrogen to drift deeper into the material, thereby confirming the positive charge state of atomic H in p-type SiC. The thermal dissociation of the electrically neutral Al-H complex was found to obey first-order kinetics for temperatures above 225 °C with a dissociation energy of (1.51+/-0.12) eV.

  15. 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.

  16. Analysis of the effect of sidewall on the performance of 6H-SiC Schottky barrier source/drain NMOSFETs

    NASA Astrophysics Data System (ADS)

    Tang, Xiao-Yan; Zhang, Yi-Men; Zhang, Yu-Ming; Gao, Jin-Xia

    2004-07-01

    Between source/drain and gate of SiC Schottky barrier source/drain MOSFET (SiC SBSD-MOSFET), there must be a sidewall as isolation. The width of sidewall strongly affects on the device performance. In this paper the effect of sidewall on the performance of 6H-SiC SBSD-NMOSFET is simulated with the 2D simulator MEDICI. The simulated results show that a sidewall with width less than 0.1mum slightly affects the device performance. However, when the width of sidewall exceeds 0.1mum, the conduction does not occur until the drain voltage is high enough and saturation current sharply decreases. The effect of the sidewall on device performance can be reduced by decreasing the doping concentration in the epitaxial layer.

  17. Low energy electron irradiation induced deep level defects in 6H-SiC: the implication for the microstructure of the deep levels E1/E2.

    PubMed

    Chen, X D; Yang, C L; Gong, M; Ge, W K; Fung, S; Beling, C D; Wang, J N; Lui, M K; Ling, C C

    2004-03-26

    N-type 6H-SiC samples irradiated with electrons having energies of E(e)=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E(e)>/=0.3 MeV, deep levels ED1, E(1)/E(2), and E(i) appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E(1)/E(2), as well as ED1 and E(i), involves the displacement of the C atom in the SiC lattice.

  18. Low Energy Electron Irradiation Induced Deep Level Defects in 6H-SiC: The Implication for the Microstructure of the Deep Levels E1/E2

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Yang, C. L.; Gong, M.; Ge, W. K.; Fung, S.; Beling, C. D.; Wang, J. N.; Lui, M. K.; Ling, C. C.

    2004-03-01

    N-type 6H-SiC samples irradiated with electrons having energies of Ee=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2MeV irradiation energy while for Ee≥0.3 MeV, deep levels ED1, E1/E2, and Ei appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E1/E2, as well as ED1 and Ei, involves the displacement of the C atom in the SiC lattice.

  19. Direct growth of few-layer graphene on 6H-SiC and 3C-SiC/Si via propane chemical vapor deposition

    SciTech Connect

    Michon, A.; Vezian, S.; Portail, M.; Ouerghi, A.; Zielinski, M.; Chassagne, T.

    2010-10-25

    We propose to grow graphene on SiC by a direct carbon feeding through propane flow in a chemical vapor deposition reactor. X-ray photoemission and low energy electron diffraction show that propane allows to grow few-layer graphene (FLG) on 6H-SiC(0001). Surprisingly, FLG grown on (0001) face presents a rotational disorder similar to that observed for FLG obtained by annealing on (000-1) face. Thanks to a reduced growth temperature with respect to the classical SiC annealing method, we have also grown FLG/3C-SiC/Si(111) in a single growth sequence. This opens the way for large-scale production of graphene-based devices on silicon substrate.

  20. Isomer Stability of N6C6H6 Cages

    PubMed Central

    Strout, Douglas L.

    2008-01-01

    Recent theoretical studies have identified carbon-nitrogen cages that are potentially stable high energy density materials (HEDM). One such molecule is an N6C6H6 cage in which a six-membered ring of nitrogen is bonded to C3H3 triangles on both sides. This molecule is based on the structure of the most stable N12 cage, with six carbon atoms substituted into the structure. In the current study, several N6C6H6 isomers (including the previously studied cage) are examined by theoretical calculations to determine which is actually the most stable. Stability will be evaluated from two points of view: (1) thermodynamic stability of one isomer versus another, and (2) kinetic stability of each isomer as determined by the energetics of bond breaking. Density functional theory (B3LYP), perturbation theory (MP2 and MP4), and coupled-cluster theory (CCSD(T)) are used in this study, along with the correlation-consistent basis sets of Dunning. Trends in thermodynamic and kinetic stability are discussed. PMID:16737273

  1. Low noise wide bandgap SiC based IMPATT diodes at sub-millimeter wave frequencies and at high temperature

    NASA Astrophysics Data System (ADS)

    Pradhan, J.; Pattanaik, S. R.; Swain, S. K.; Dash, G. N.

    2014-03-01

    We have presented a comparative account of the high frequency prospective as well as noise behaviors of wide-bandgap 4H-SiC and 6H-SiC based on different structures of IMPATT diodes at sub-millimeter-wave frequencies up to 2.18 THz. The computer simulation study establishes the feasibility of the SiC based IMPATT diode as a high power density terahertz source. The most significant feature lies in the noise behavior of the SiC IMPATT diodes. It is noticed that the 6H-SiC DDR diode shows the least noise measure of 26.1 dB as compared to that of other structures. Further, it is noticed that the noise measure of the SiC IMPATT diode is less at a higher operating frequency compared to that at a lower operating frequency.

  2. Technological state of the art of SiC

    NASA Astrophysics Data System (ADS)

    Tyc, Stdphane

    1993-10-01

    In a recent paper [1], Locatelli and Gamal describe the technological state of the art of SiC compared with Si. I would like to bear witness to the rapid advancement of SiC technology by giving a slighty updated account of SiC technology. The boule growth of SiC now achieves diameters up to 60 mm. One of the most problematic standing issues is the presence of micropipes in the wafers with a density of the order of 100 cm^{-2} or more [2]. The doping range available in epilayers is now wider. CAFE Research [3] accepts orders for doping densities from 5 × 10^{15} cm^{-3} to 1 × 10^{19} cm^{-3} in both N and P type. However their state of the art is better (we have received P type with doping 4 × 10^{14} cm^{-3} and N type with doping over 2 × 10^{19} cm^{-3} and they have also delivered [4] N type doping of 5 × 10^{14} cm^{-3}). As for large P dopings, Dmitriev has published [5] dopings over 10^{20} cm^{-3} The specific resistance of contacts on N type layers has also rapidly improved. Kelner has published results of 3 × 10^{-6} Ohm.cm2 with Ni contacts [6]. We have obtained with molybdenum [7] specific resistances of 2 × 10^{-5} Ohm.cm2 on epitaxies doped to 5 × 10^{18} cm^{-3} This value should be rapidly lowered as higher doped layers are used. In sum, I do agree with the authors of [1] that the technology of 6H SiC is rapidly advancing, thanks to breakthroughs in material growth and to a wide ranging renewed interest in this material. The pace may actually be higher than hitherto realized. References: [1] Locatelli and Gamal, J. Phys. III France 3 (1993) 1101. [2] Barret D. L. et al., Tenth Int. Conf. on Crystal Growth, San Diego, CA, USA 16-21 (August 1992). [3] CREE Research Inc., 2810 Meridian Parkway, Durham, NC 27713, USA. [4] Parrish M., private communication. [5] Dmitriev et al., Ext. Abstracts of the Electrochemical Soc. Meeting, 4, 89-2 (1989) 711. [6] Workshop on SiC Material and Devices (Charlottesville, September 10-11 1992) VA 22901. [7] Tyc

  3. 6H-SiC Photoconductive Switches Triggered at Below Bandgap Wavelengths

    DTIC Science & Technology

    2006-05-01

    gap wavelengths of light to trigger the switches. Lateral geometry surface PCSS are limited by surface flashover , surface carrier mobility, and high...Livermore National Laboratory Livermore,CA 94550 Abstract-Semi-insulating Silicon Carbide (SiC) is an attractive material to use to construct high...Previous SiC PCSS work [1,2,3] used high resistivity, low impurity SiC polytypes and focused on lateral geometry surface switches that used above band

  4. 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

  5. Irradiation-induced magnetic ordering in SiC: Experimental results and a density functional study

    SciTech Connect

    He, Xiujie; Zhang, Baoliang; Tan, Jie; Zhao, Mingwen; Liu, Xiangdong; Xia, Huihao; He, Zhoutong; Yang, Xinmei; Zhou, Xingtai

    2013-12-23

    Magnetism of 6H-SiC single crystals implanted with 3 MeV protons is studied both experimentally and theoretically. We found that proton irradiation can induce stable ferromagnetism in 6H-SiC with a Curie temperature above 300 K. There is a dose window available for tuning the magnetization of the samples. The maximum saturation magnetizations (0.17 emu/g) are three orders of magnitude larger than that reported in neutron-irradiated SiC crystals (1 × 10{sup −4} emu/g). First-principles calculations indicate that the ferromagnetism is related to the divacancy-related defects (V{sub Si}V{sub C} + nH, (n = 1–3)) generated under proton irradiation. This offers a promising route for the development of metal-free SiC magnets.

  6. Study of Erosive Wear Behaviour on SIC/SIC Composites

    NASA Astrophysics Data System (ADS)

    Suh, Min-Soo

    In the field of aerospace propulsion system, erosive wear on continuous silicon carbide (SiC) fibre-reinforced SiC (SiC/SiC) composites is of significant issue to achieve high energy efficiency. This paper proposes a crucial factor and a design guideline of SiC/SiC composites for higher erosion performance regarding cost effectiveness. Fabrication and evaluation of impacts and wear on SiC/SiC composites are successfully carried out. Erosive wear behaviours of the CVI and the LPS composites evidently show that the crucial fabrication factor against solid particle erosion (SPE). Erosive wear mechanisms on various SiC/SiC composites are determined based on the analysis of erosive wear behaviour. Designing guideline for the SiC/SiC composites for pursuit of high erosion performance is also proposed as focusing on the followings; volume fraction of matrix, strength of the matrix, bonding strength, and PyC interface.

  7. Hydraulic tests in hole UAe-6h, Amchitka Island, Alaska

    USGS Publications Warehouse

    Ballance, Wilbur C.

    1972-01-01

    Inflatable straddle packers were used to isolate and test 14 intervals ranging from 39 to 258 meters (127 to 846 feet) each in hole UAe-6h. Packer seats were poor in part of the hole because of unstable wall conditions. Thus, some zones had to be tested several times. The static water levels in the intervals tested ranged from about 23 meters (71 feet) below land surface in the upper interval to an estimated 90 meters (295 feet) below land surface in the lower intervals, indicating a decreasing head with depth. The specific capacity of the hole from 85. 0 to 2,133. 6 meters (279 to 7,000 feet) was 1.94 cubic meters per day per meter (0. 11 gallon per minute per foot) of drawdown after the hole had been jetted at an average rate of 327 cubic meters per day (60 gallons per minute) for about 23 hours . Transmissivity computed from the recovery of water level after jetting stopped was 0.60 cubic meter per day per meter (48.3 gallons per day per foot). The relative specific capacities of isolated intervals ranged from 0.004 cubic meter per day per meter (less than 0.001 gallon per minute per foot) of drawdown to 0.430 cubic meter per day per meter (0.024 gallon per minute per foot) of drawdown.

  8. Micro-Raman Measurements and Depth Profiling of SiC

    NASA Astrophysics Data System (ADS)

    Roughani, Bahram; Ramabadran, Uma

    2003-03-01

    Recent progress in growth of high quality 4H- SiC and 6H-SiC polytypes materials may lead to new applications for SiC as high power, high temperature, and high frequency devices that can tolerate harsh environments. Nondestructive techniques that could be used in analyzing various layers of such materials after growth or after exposure to harsh environment could be used in investigation of induced defects or structural damages. We have utilized micro-Raman scattering to investigate the depth profiling of Nitrogen doped 4H-SiC samples. Heavily N-doped 4H-SiC epilayers grown on low doped 4H-SiC substrates were examined. Each SiC sample was placed on micro-positioning translational stage in order to accurately control the focal plane of the laser beam within the sample by adjusting normal distance of the microscope objective with respect to the SiC wafer. We were able to clearly distinguish the epilayer from the SiC substrate. Strong phonon peaks and distinct coupled plasmon-LO phonon modes from the N-doped epilayer were used in this depth profiling analysis. A scattering efficiency model describing the optimal focusing condition for backscattering from a translucent sample was developed. The experimental results of depth profiling and our model for optimal backscattering condition will be presented and discussed.

  9. The Poole-Frenkel effect in 6H-SiC diode characteristics

    SciTech Connect

    Pelaz, L.; Orantes, J.L.; Vincente, J.; Bailon, L.A.; Barbolla, J. . Dept. de Electricidad y Electronica)

    1994-04-01

    The large bandgap of SiC makes the recombination mechanism the main process in determining the forward current in a large range of temperature. The authors have added the Poole-Frenkel effect to the conventional Shockley-Read-Hall (SRH) term of the numerical device simulator MEDICI. This paper shows the influence of this effect on SiC.

  10. Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC.

    PubMed

    Ienaga, Koichiro; Iimori, Takushi; Yaji, Koichiro; Miyamachi, Toshio; Nakashima, Shuhei; Takahashi, Yukio; Fukuma, Kohei; Hayashi, Shingo; Kajiwara, Takashi; Visikovskiy, Anton; Mase, Kazuhiko; Nakatsuji, Kan; Tanaka, Satoru; Komori, Fumio

    2017-06-14

    Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene.

  11. Does the metal-metal sextuple bond exist in the bimetallic sandwich compounds Cr2(C6H6)2, Mo2(C6H6)2, and W2(C6H6)2?†

    NASA Astrophysics Data System (ADS)

    Sun, Zhi; Schaefer, Henry F., III; Xie, Yaoming; Liu, Yongdong; Zhong, Rugang

    2013-09-01

    Although evanescent at best, the bare dimers of the elements Cr, Mo, and W have been identified as possible candidates for the sextuple metal-metal bond. The corresponding dibenzene sandwich compounds Cr2(C6H6)2, Mo2(C6H6)2, and W2(C6H6)2, satisfy the '18-Electron Rule', and might achieve high-order metal-metal bonds and longer lifetimes at the same time. Twenty-two different DFT methods have been used to evaluate this possibility. Based on the present Wiberg bond index and molecular orbital analyses, however, only quadruple metal-metal bonds are predicted for the electronic ground states of Cr2(C6H6)2, Mo2(C6H6)2, and W2(C6H6)2, rather than the sextuple or even quintuple bonds, for both singlet and triplet electronic states. It is possible to force the hypothesised D 6h sextuple bond electron configuration, but the resulting energy is 39 kcal/mol above the D 2h quadruple bond structure for Cr2(C6H6)2. However, the constrained sextuple bond structure for Mo2(C6H6)2 lies 19 kcal/mol above the Mo?Mo singlet. For W2(C6H6)2 the sextuple bond structure is predicted to lie only 3 kcal/mol above the W?W structure. Thus the answer to the question raised in our title is 'almost' for the tungsten-sextuple bond.

  12. Study of defect structures in 6H-SiC a/m-plane pseudofiber crystals grown by hot-wall CVD epitaxy

    SciTech Connect

    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.

    2015-11-25

    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. Lastly, the implication of these results for improving the LTC growth process is addressed.

  13. Study of defect structures in 6H-SiC a/m-plane pseudofiber crystals grown by hot-wall CVD epitaxy

    DOE PAGES

    Goue, Ouloide Y.; Raghothamachar, Balaji; Yang, Yu; ...

    2015-11-25

    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 themore » 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. Lastly, the implication of these results for improving the LTC growth process is addressed.« less

  14. 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.

  15. UHV Growth of Graphene on SiC

    NASA Astrophysics Data System (ADS)

    Campbell, Paul; Jernigan, Glenn; Perkins, Keith; Vanmil, Brenda; Myers-Ward, Rachel; Gaskill, Kurt; Culbertson, James; Robinson, Jeremy; Snow, Eric

    2008-03-01

    We report graphene growth on Si- and C-face semi-insulating 6H SiC in UHV by thermal Si desorption /reconstruction of the remaining C. The SiC was etched in H2 up to 1580 C to smooth the surface. XPS shows the H2-etched surfaces are covered by an oxide which desorbs at 1000 C, resulting in a surface containing excess Si. At 1300 C, the surface becomes stoichiometric in Si and C and a 3 x 3 R30 LEED pattern is observed. At 1350 C, we observe a 63 x 63 R30 LEED pattern develop when graphene has formed, and a 1x1 LEED pattern for graphite films formed at temperatures greater than 1400 C. Graphene layers were grown under a variety of temperatures and conditions and characterized using XPS, LEED, AFM, Raman spectroscopy, and Hall effect. Top-gated FETs were fabricated with a wide range of gate lengths (1-25 microns) and gate widths (2-130 microns), and transistor operation was obtained for both single and multiple graphene layers.

  16. Sporadic SICs and the Normed Division Algebras

    NASA Astrophysics Data System (ADS)

    Stacey, Blake C.

    2017-08-01

    Symmetric informationally complete quantum measurements, or SICs, are mathematically intriguing structures, which in practice have turned out to exhibit even more symmetry than their definition requires. Recently, Zhu classified all the SICs whose symmetry groups act doubly transitively. I show that lattices of integers in the complex numbers, the quaternions and the octonions yield the key parts of these symmetry groups.

  17. Solvent effect on infrared spectra of methyl methacrylate in CCl4/C6H14, CHCl3/C6H14 and C2H5OH/C6H14 binary solvent systems.

    PubMed

    Zheng, Jianping; Liu, Qing; Zhang, Hui; Fang, Danjun

    2004-11-01

    Research of methyl methacrylate (MMA) in three kinds of binary solvent systems (CCl4/C6H14, CHCl3/C6H14 and C2H5OH/C6H14) on the infrared (IR) spectra was reported. Two types of carbonyl stretching vibration bands for MMA in CHCl3/C6H14 or C2H5OH/C6H14 mixtures were found with the changing of the mole fraction of CHCl3 (XCHCl3) or C2H5OH (XC2H5OH). The carbonyl stretching vibration bands at lower frequencies in the above two mixtures were attributed to the formation of hydrogen bonding between MMA and CHCl3 or C2H5OH. While in CCl4/C6H14 mixtures there was only one type of carbonyl stretching vibration band of MMA. Good linear correlations between the frequencies of C=O or C=C stretching vibration band of MMA and XCCl4, XCHCl3 or XC2H5OH were found, respectively. The solute-solvent interactions in the three different binary solvent systems were discussed in detail.

  18. 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.

  19. Direct growth of freestanding GaN on C-face SiC by HVPE.

    PubMed

    Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

    2015-06-02

    In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra.

  20. Direct growth of freestanding GaN on C-face SiC by HVPE

    PubMed Central

    Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

    2015-01-01

    In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra. PMID:26034939

  1. 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.

  2. 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.

  3. F6H8 as an Intraoperative Tool and F6H8/Silicone Oil as a Postoperative Tamponade in Inferior Retinal Detachment with Inferior PVR.

    PubMed

    Tosi, Gian Marco; Marigliani, Davide; Bacci, Tommaso; Romeo, Napoleone; Balestrazzi, Angelo; Martone, Gianluca; Caporossi, Tomaso

    2014-01-01

    Purpose. To evaluate the effectiveness and safety of perfluorohexyloctane (F6H8) for intraoperative flattening of the retina and of F6H8/silicone oil (SO) 1000 cSt as a postoperative tamponade for inferior retinal detachment with inferior proliferative vitreoretinopathy. Methods. This is a retrospective review of 22 patients who underwent pars plana vitrectomy using F6H8 as an intraoperative tool to flatten the retina. At the end of the surgery a direct partial exchange between F6H8 and SO 1000 cSt was performed, tamponing the eye with different ratios of F6H8/SO (70/30, 60/40, 50/50, 40/30, and 30/70). Anatomical and functional results and complications were evaluated over the follow-up period (mean 22.63 months). Results. F6H8 was efficacious for intraoperative flattening of the retina. Twenty-one of the 22 patients achieved a complete retinal reattachment. Postoperative visual acuity (VA) ranged from light perception to 20/70, with 72% of patients obtaining VA better than 20/400. No emulsification/inflammation was observed whatever the ratio of F6H8/SO used. With higher ratios of F6H8/SO (70/30 and 60/40) cloudiness of the tamponade was observed. A transparent mixture was present with all the other ratios. Conclusions. The surgical technique adopted is very simple and safe. The optimal F6H8/SO ratio seems to be between 50/50 and 30/70.

  4. F6H8 as an Intraoperative Tool and F6H8/Silicone Oil as a Postoperative Tamponade in Inferior Retinal Detachment with Inferior PVR

    PubMed Central

    Tosi, Gian Marco; Bacci, Tommaso; Romeo, Napoleone; Balestrazzi, Angelo; Martone, Gianluca; Caporossi, Tomaso

    2014-01-01

    Purpose. To evaluate the effectiveness and safety of perfluorohexyloctane (F6H8) for intraoperative flattening of the retina and of F6H8/silicone oil (SO) 1000 cSt as a postoperative tamponade for inferior retinal detachment with inferior proliferative vitreoretinopathy. Methods. This is a retrospective review of 22 patients who underwent pars plana vitrectomy using F6H8 as an intraoperative tool to flatten the retina. At the end of the surgery a direct partial exchange between F6H8 and SO 1000 cSt was performed, tamponing the eye with different ratios of F6H8/SO (70/30, 60/40, 50/50, 40/30, and 30/70). Anatomical and functional results and complications were evaluated over the follow-up period (mean 22.63 months). Results. F6H8 was efficacious for intraoperative flattening of the retina. Twenty-one of the 22 patients achieved a complete retinal reattachment. Postoperative visual acuity (VA) ranged from light perception to 20/70, with 72% of patients obtaining VA better than 20/400. No emulsification/inflammation was observed whatever the ratio of F6H8/SO used. With higher ratios of F6H8/SO (70/30 and 60/40) cloudiness of the tamponade was observed. A transparent mixture was present with all the other ratios. Conclusions. The surgical technique adopted is very simple and safe. The optimal F6H8/SO ratio seems to be between 50/50 and 30/70. PMID:24672710

  5. 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.

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

    PubMed

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

    2015-01-26

    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).

  7. 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).

  8. Nqrs Data for C6H16I2N4O8 [C6H14N4O2·2(HIO3)] (Subst. No. 0932)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' 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 C6H16I2N4O8 [C6H14N4O2·2(HIO3)] (Subst. No. 0932)

  9. Nqrs Data for C6H16I2N2O8 [C6H14N2O2·2(HIO3)] (Subst. No. 0931)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' 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 C6H16I2N2O8 [C6H14N2O2·2(HIO3)] (Subst. No. 0931)

  10. Nqrs Data for C6H20I6N2O20 [C6H14N2O2·6(HIO3)] (Subst. No. 0939)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' 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 C6H20I6N2O20 [C6H14N2O2·6(HIO3)] (Subst. No. 0939)

  11. Nqrs Data for C6H17I3N2O11 [C6H14N2O2·3(HIO3)] (Subst. No. 0933)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' 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 C6H17I3N2O11 [C6H14N2O2·3(HIO3)] (Subst. No. 0933)

  12. 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.

  13. Thermal expansion of the hexagonal (4H) polytype of SiC

    NASA Technical Reports Server (NTRS)

    Li, Z.; Bradt, R. C.

    1986-01-01

    The principal axial coefficients of thermal expansion, alpha(11) and alpha(33), of the (4H) polytype of hexagonal alpha SiC have been determined by X-ray diffraction measurements in the temperature range 20-1000 C. Alpha(11) and alpha(33), derived from the lattice parameter measurements, were expressed as the second-order polynomials in temperature. Alpha(11) was found to be larger than alpha(33) over the entire temperature range, with a thermal expansion anisotropy factor A increasing from 0.04 at room temperature to 0.11 at 1000 C. The thermal expansion results for the (4H) structure were compared with previously published results for the cubic (3C) and the hexagonal (6H) SiC polytypes.

  14. Why are [P(C6H5)4](+)N3- and [As(C6H5)4](+)N3- ionic salts and Sb(C6H5)4N3 and Bi(C6H5)4N3 covalent solids? A theoretical study provides an unexpected answer.

    PubMed

    Christe, Karl O; Haiges, Ralf; Boatz, Jerry A; Jenkins, H Donald Brooke; Garner, Edward B; Dixon, David A

    2011-04-18

    A recent crystallographic study has shown that, in the solid state, P(C(6)H(5))(4)N(3) and As(C(6)H(5))(4)N(3) have ionic [M(C(6)H(5))(4)](+)N(3)(-)-type structures, whereas Sb(C(6)H(5))(4)N(3) exists as a pentacoordinated covalent solid. Using the results from density functional theory, lattice energy (VBT) calculations, sublimation energy estimates, and Born-Fajans-Haber cycles, it is shown that the maximum coordination numbers of the central atom M, the lattice energies of the ionic solids, and the sublimation energies of the covalent solids have no or little influence on the nature of the solids. Unexpectedly, the main factor determining whether the covalent or ionic structures are energetically favored is the first ionization potential of [M(C(6)H(5))(4)]. The calculations show that at ambient temperature the ionic structure is favored for P(C(6)H(5))(4)N(3) and the covalent structures are favored for Sb(C(6)H(5))(4)N(3) and Bi(C(6)H(5))(4)N(3), while As(C(6)H(5))(4)N(3) presents a borderline case.

  15. Kinetics of oxynitridation of 6H-SiC( 1 1 2¯ 0) and the interface structure analyzed by ion scattering and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Okawa, T.; Fukuyama, R.; Hoshino, Y.; Nishimura, T.; Kido, Y.

    2007-02-01

    Clean and pre-oxidized 6H-SiC( 1 1 2¯ 0) surfaces were annealed in NO at temperatures ranging from 800 to 1000 °C under a pressure of 1 × 10 -3 Torr. The growing surface and interface structures were analyzed in situ by high-resolution medium energy ion scattering (MEIS) and photoelectron spectroscopy using synchrotron-radiation-light. The present result reveals growth of double-layered structure of SiO 2/SiO xN y on SiC for the samples annealed at 1000 °C in NO with and without pre-oxidation in O 2. Oxynitridation takes place only at SiO 2/SiC interfaces. The thickness of growing layers is saturated at ˜0.2 nm of SiO 2 and 0.3-0.4 nm of SiO xN y layers with the elemental compositions unchanged. For the samples pre-oxidized in 18O 2 followed by annealing in N 16O, the exchange reaction between 18O and 16O occurs at the surface and interface. No nitrogen removal was observed by annealing the oxy-nitrided sample in O 2 at 1000 °C and 1 × 10 -3 Torr. We also observed the C 1s, N 1s and Si 2p spectra and identified the N 1s and Si 2p components originating from Si-oxynitride layers.

  16. Experimental characterization and numerical simulation of the electrical properties of nitrogen, aluminum, and boron in 4H/6H-SiC

    SciTech Connect

    Kaindl, W.; Lades, M.; Wachutka, G.; Kaminski, N.; Niemann, E.

    1999-03-01

    Silicon carbide (SiC) receives strong attention for high-power, high-temperature, and high-frequency device applications due to its promising material properties. In order to measure the ionization time constants of dopants in 4H/6H-SiC within a wide range of temperature, nitrogen (N), aluminum (Al), and boron (B) have been characterized using thermal admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS). The temperature extrapolation of the results obtained by AS shows excellent agreement with those obtained by DLTS, yielding the base for an evaluation of incomplete ionization effects in SiC devices within usual operation ranges. The measured data has been analyzed using numerical drift-diffusion simulations based on the method of finite-elements. A numerical investigation of the different freeze-out characteristics of free carriers in p{sup +}n, n{sup +}p, and Schottky diodes shows that unlike in the case of B, the ionization time constant of Al can be exclusively measured in the highly doped region of a p{sup +}n diode.

  17. 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.

  18. Contact formation in SiC devices

    NASA Astrophysics Data System (ADS)

    Pécz, B.

    2001-12-01

    In SiC devices designed for high temperature and high power applications, both ohmic and Schottky contacts are required which are stable at high temperature. The microstructure of contacts is very important to learn. Transmission electron microscopy (TEM) is a powerful method to reveal the microstructure of the contacts. Various contacts to SiC were investigated by TEM in cross-section and are discussed. TiN, Ni and Ni 2Si are ohmic contacts to n-type SiC, while multilayers and WN x contacts are used for Schottky purposes. Magnetron sputtered TiN layers were deposited at 700 °C onto cubic and hexagonal SiC as well. The contacts are ohmic, single crystalline, epitaxial, non-reactive and stable at high temperature. Ni contacts evaporated onto hexagonal SiC and subsequently annealed at 950 °C showed ohmic behavior, but Ni reacted with SiC. The reaction resulted in the formation of nickel silicide together with the formation of high number of voids. Deposition and annealing of Si/Ni multilayer contacts resulted in a void-free Ni 2Si contact layer preserving low contact resistivity. For Schottky purposes, multilayered contacts of Ti/Pt/Au/Ti can be used up to 575 °C, while WN x contacts are rectifying at least up to 800 °C.

  19. 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.

  20. Near-Interface Defects in SiO2/SiC MOS Devices

    NASA Astrophysics Data System (ADS)

    Basile, A. F.; Mooney, P. M.

    2012-02-01

    The implementation of SiO2/SiC MOSFETS for high power applications has been hindered by the high density of near-interface states. We have developed a method to distinguish both the energy and spatial distribution of defect states near insulator-semiconductor interfaces through a comparison of the thermal emission energy extracted from constant capacitance transient spectroscopy (CCDLTS) measurements and the interface Fermi energy (FP). The dependence of FP on trap filling voltage at the CCDLTS peak temperature is determined from temperature-dependent 1MHz C-V curves. Capture by tunneling into oxide traps is detected in 4H- and 6H-SiC capacitors fabricated by oxidation followed by NO-annealing, with the difference in thermal emission energies consistent with the conduction band offsets of the two polytypes at the SiO2/SiC interface. Comparison with results from first principles calculations suggests that the observed oxide traps are CO=CO and interstitial Si [1]. SiC defects having energies close to the SiC conduction band are suggested to be carbon di-interstitial defects, (C2)i, introduced during standard oxidation [1]. Well-known traps introduced in SiC by ion-implantation are observed in 4H-SiC MOS capacitors fabricated by N-implantation followed by standard oxidation, thus validating this new method [2]. *A.F. Basile, et al., J. Appl. Phys. 109, 064514 (2011) *A.F. Basile, et al., J. Appl. Phys. 109, 114505 (2011).

  1. Amorphous and excimer laser annealed SiC films for TFT fabrication

    NASA Astrophysics Data System (ADS)

    García, B.; Estrada, M.; Albertin, K. F.; Carreño, M. N. P.; Pereyra, I.; Resendiz, L.

    2006-02-01

    The characteristics of hydrogenated amorphous silicon carbide films prepared by PECVD and crystallized by KrF UV excimer laser annealing (ELA), for different annealing conditions, are studied to determine particulate size, surface roughness, band gap and resistivity in order to apply them to TFTs fabrication. Raman spectra for ELA SiC films indicate the presence of 6H-SiC polytype together with Si and C crystallites. We also describe the fabrication process to obtain a-Si 1- xC x:H TFTs and ELA TFTs on the same wafer, comparing their output and transfer characteristics.

  2. 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.

  3. 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.

  4. Heat of Mixing and Solution of Hexane C6H14 + C6H18OSi2 Hexamethyldisiloxane (HMSD1111, LB4099_H)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Heat of Mixing and Solution of Hexane C6H14 + C6H18OSi2 Hexamethyldisiloxane (HMSD1111, LB4099_H)' providing data from direct low-pressure calorimetric measurement of molar excess enthalpy at variable mole fraction and constant temperature.

  5. Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1111, LB4819_V0029

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1111, LB4819_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  6. Vapor-Liquid Equilibrium in the Mixture Cyclohexanone C6H10O + C6H12O Cyclohexanol (EVLM1111, LB5657_E)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Vapor-Liquid Equilibrium in the Mixture Cyclohexanone C6H10O + C6H12O Cyclohexanol (EVLM1111, LB5657_E)' providing data from direct measurement of pressure at variable mole fraction in liquid phase and constant temperature.

  7. Heat of Mixing and Solution of Cyclohexanone C6H10O + C6H12O Cyclohexanol (HMSD1121, LB4187_H)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Heat of Mixing and Solution of Cyclohexanone C6H10O + C6H12O Cyclohexanol (HMSD1121, LB4187_H)' providing data from direct calorimetric measurement of molar excess enthalpy at variable mole fraction and constant pressure and temperature.

  8. Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1511, LB4829_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1511, LB4829_V)' providing data from direct measurement of low-pressure thermodynamic speed of sound at variable mole fraction and constant temperature, in the single-phase region(s).

  9. Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1212, LB4824_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Benzene C6H6 + C6H10O Cyclohexanone (VMSD1212, LB4824_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  10. 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.

  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. Knoop Hardness on the (0001) Plane of 4H and 6H SiC Single Crystals Fabricated by Physical Vapor Transport

    DTIC Science & Technology

    2014-05-01

    come off the tips of the 2.94 N indents. In an attempt to alternatively observe differences in each materials response to the indentation process ...CIO LL IMAL HRA MAIL & RECORDS MGMT 1 GOVT PRINTG OFC (PDF) A MALHOTRA 2 RUTGERS UNIVERSITY (PDF) R HABER V DOMNICH 2 JOHNS

  13. Photo Electron Paramagnetic Resonance (Photo EPR) Study of Trapping and Recombination Processes in Semi-Insulating 4H, 6H Sic Crystals Over a Wide Temperature Interval

    DTIC Science & Technology

    2004-07-02

    Proceedings of the ICDS22 (Physica B) accepted. 12. J.S. Blakemore , " Semiconductor Statistics " (Dover Publications, Inc. New York, 1987). STCU...electronic and optical devices. The Institute for Semiconductor Physics, with more than 15 years of experience in semiconductor material analysis, is...levels are among the most important processes in semiconductor physics and technology. An understanding of these processes is essential for device

  14. Characterization of a New Organic-Cation Cyclotetraphosphate: (1,4-HOC 6H 4NH 3) 4P 4O 12· 6H 2O

    NASA Astrophysics Data System (ADS)

    Soumhi, E. H.; Saadoune, I.; Driss, A.; Jouini, T.

    1999-05-01

    The tetra(para-phenolammonium)cyclotetraphosphate hexahydrate, (1,4-HOC6H4NH3)4P4O12· 6H2O (M=864.51 g mol-1), is monoclinicP21/cwith the unit cell parametersa=9.836(2) Å,b=8.591(1) Å,c:22.769(5) Å,β=95.41(2)°. The structure of this compound can be described as a succession of inorganic and organic sheets parallel to the (001) plane. The existence of the OH and NH3groups in positionparato the organic cation leads to the cohesion of the inorganic sheets, forming a three-dimensional network.The IR spectrum of (1,4-HOC6H4NH3)4P4O12· 6H2O is reported and discussed according to the theoretical group analysis. The IR data confirm the atomic arrangement within the structure. The coupled TG-DTA thermal study shows the successive departure of four and two water molecules, confirming the hydrated character of this cyclophosphate.

  15. The interface between benzenes (C6H6;C6H5Cl;2-C6H4OHCl) and amorphous solid water studied with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (HeI and II)

    NASA Astrophysics Data System (ADS)

    Borodin, A.; Höfft, O.; Kahnert, U.; Kempter, V.; Krischok, S.; Abou-Helal, M. O.

    2004-03-01

    Interfaces between films of benzenes (C6H6;C6H5Cl;2-C6H4OHCl) and solid H2O on tungsten substrates were studied between 80 and 200 K with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy [UPS(HeI and II)]. The following cases were studied in detail: (i) Adsorption of the benzenes on solid water in order to simulate their interaction with ice particles, and (ii) deposition of water on benzene films in order to simulate the process of water precipitation. In all cases the prepared interfacial layers were annealed up to 200 K under in situ control of MIES and UPS. The different behavior of the interfaces for the three studied cases is traced back to the different mobilities of the molecules with respect to that of water. The interaction between H2O and the benzenes at the interfaces is discussed on the basis of a qualitative profile for the free energy of that component of the interface which has the larger mobility. Possible implications of the present results for atmospheric physics are briefly mentioned.

  16. 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

  17. Characterization of Liquid Phase Sitered sic and Sic/sic Composite Materials

    NASA Astrophysics Data System (ADS)

    Lee, Moon Hee; Lee, Sang Pill; Hur, Kwan Do

    The characterization of liquid phase sintered(LPS) SiC based materials has been investigated with the analysis of microstructure and flexural strength. Especially, LPS-SiC materials were examined for the variation of test temperature and composition ratios (Al2O3,/Y2O3) of sintering additives. LPS-SiC based materials were fabricated by hot pressing(HP) associated with the liquid phase formation of sintering additives(Al2O3,Y2O3). LPS-SiCf/SiC composites were also fabricated with plane-woven(PW) Tyranno-SA fibers without an interfacial layer. LPS-SiC materials showed a dense morphology with the creation of the secondary phase like YAG. The composition ratio of sintering additives led to the variation of sintered density and flexural strength. The flexural strength of LPS-SiC materials was greatly decreased at the temperature higher than 1000°C. LPS-SiCf/SiC composites represented an average flexural strength of about 260 MPa, accompanying the catastrophic fracture behavior without any full-out phenomena.

  18. 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.

  19. 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:C:Si, SiC:C, 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.

  20. C60 on SiC nanomesh.

    PubMed

    Chen, Wei; Zhang, Hong Liang; Xu, Hai; Tok, Eng Soon; Loh, Kian Ping; Wee, Andrew Thye Shen

    2006-11-02

    A SiC nanomesh is used as a nanotemplate to direct the epitaxy of C60 molecules. The epitaxial growth of C60 molecules on SiC nanomesh at room temperature is investigated by in situ scanning tunneling microscopy, revealing a typical Stranski-Krastanov mode (i.e., for the first one or two monolayers, it is a layer-by-layer growth or 2-D nucleation mode; at higher thicknesses, it changes to island growth or a 3-D nucleation mode). At submonolayer (0.04 and 0.2 ML) coverage, C60 molecules tend to aggregate to form single-layer C60 islands that mainly decorate terrace edges, leaving the uncovered SiC nanomesh almost free of C60 molecules. At 1 ML C60 coverage, a complete wetting layer of hexagonally close-packed C60 molecules forms on top of the SiC nanomesh. At higher coverage from 4.5 ML onward, the C60 stacking adopts a (111) oriented face-centered-cubic (fcc) structure. Strong bright and dim molecular contrasts have been observed on the first layer of C60 molecules, which are proposed to originate from electronic effects in a single-layer C60 island or the different coupling of C60 molecules to SiC nanomesh. These STM molecular contrast patterns completely disappear on the second and all the subsequent C60 layers. It is also found that the nanomesh can be fully recovered by annealing the C60/SiC nanomesh sample at 200 degrees C for 20 min.

  1. SiC for Space Optics

    NASA Astrophysics Data System (ADS)

    Wellman, John

    2012-01-01

    This paper describes SiC mirrors that are large, ultra-lightweight, and actively controlled, for use in space telescopes. "Advanced Hybrid Mirrors” (AHMs) utilize SiC substrates, with embedded solid-state actuators, bonded to Nanolaminate metal foil reflective surfaces. They use replication techniques for high optical quality as well as rapid, low cost manufacturing. AHMs up to 1.35m in size have been made and tested, demonstrating wavefront error to better than the visible diffraction limit. AHMs can be fabricated at production rates after the first unit delivery as fast as 48 day intervals. "Superpolished Si/SiC Active Mirrors” (SSAMs) are similar to AHMs but the SiC mirror substrates have a layer of Si deposited on them to enable direct superpolishing. SSAMs can be much larger, can operate over a wider temperature range, and are better suited to UV astronomy. To make SSAMs larger than 1.8 m, multiple substrates can be joined together, using brazing techniques. Using wavefront sensing and control technology to command the embedded solid-state actuators, final mirror figure will be set after launch. This gives the active SiC mirror the ability to correct nearly any optical error, occurring anywhere in the optical system. As a result, active SiC mirrors can be made to relaxed figure requirements, enabling optical replication, or speeding up polishing, while assuring excellent final performance. Active SiC mirrors will reduce cost, risk and schedule for future astrophysics missions. Their high control authority allows relaxation of fabrication and assembly tolerances from optical to mechanical levels, speeding I & T. They enable rapid system testing to within required performance levels, even in 1 G, lowering mission risk. They are lighter weight and more durable than glass mirrors.

  2. 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.

  3. 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.

  4. SiC MEMS For Harsh Environments

    DTIC Science & Technology

    2003-12-01

    allowed for high g shock loading of a functioning SiC MEMS accelerometer , with published results [1]. 2 2 HIGH TEMPERATURE TESTING OF SiC Measuring...2800 °C, thus capable of being operated in the temperature range of 600-1000 °C [4,5]. The need for the mechanical properties (modulus) of these SiC...VOR-MELT rheometers used for mechanical modulus measurements had a solids fixture, which held both ends of a vertically oriented rectangular cross

  5. 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.

  6. 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.

  7. 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.

  8. Mechanical and electronic properties of SiC nanowires: An ab initio study

    NASA Astrophysics Data System (ADS)

    Oliveira, J. B.; Morbec, J. M.; Miwa, R. H.

    2017-03-01

    Using first-principles calculations, based on the density functional theory, we have investigated the mechanical and electronic properties of hydrogen-passivated 3C-, 2H-, 4H-, and 6H-SiC nanowires (NWs), analyzing the effects of the diameter on these properties. Our results show that the band-gap energies of the nanowires are larger than the corresponding bulk values and decrease with the increasing diameter. All nanowires investigated exhibit direct band gaps, in contrast with the indirect band gaps observed in bulk SiC. The effect of uniaxial stress on the electronic properties of SiC nanowires has also been examined, and our results reveal that the band-gap dependence on the strain is different for each nanowire polytype. In 3C-SiC nanowires, the band gaps increase (decrease) with tensile (compressive) strain. For 4H- and 6H-SiC nanowires, the influence of strain on the band gaps is more pronounced in the thicker wires. Finally, we estimated the band offsets of hypothetical NW homostructures, composed of stacking SiCNW layers with different polytypes.

  9. 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.

  10. Crystal growth of SiC for electronic applications

    NASA Technical Reports Server (NTRS)

    Matus, Lawrence G.; Powell, J. Anthony

    1989-01-01

    The development of SiC as a high temperature semiconductor material is discussed, focusing on the epitaxial growth of single crystal SiC films on inexpensive single crystal silicon wafers. Progress in the improvement of film morphology and the elimination of antiphase disorder is examined. Potential candidate materials for high temperature semiconductor devices are compared and SiC films are evaluated.

  11. 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.

  12. Global reaction route mapping of isomerization pathways of exotic C6H molecular species

    NASA Astrophysics Data System (ADS)

    Vikas, Kaur, Gurpreet

    2013-12-01

    C6H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C6H is explored to search isomers of C6H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C6H. 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 C6H) 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-C6H can readily isomerize to a six-member ring isomer.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Erosion and strength degradation of biomorphic SiC.

    SciTech Connect

    Martinez-Fernandez, J.; de Arellano-Lopez, A. R; Varela-Feria, F. M.; Orlova, T. S.; Goretta, K. C.; Gutierrez-Mora, F.; Chen, N.; Routbort, J. L.; Energy Technology; Univ. de Sevilla; Russian Academy of Sciences

    2004-05-01

    Solid-particle-erosion studies were conducted on biomorphic SiC based on eucalyptus and pine, reaction-bonded (RB) SiC, and hot-pressed (HP) SiC. The erodents were angular SiC abrasives of average diameter 63, 143, or 390 {mu}m and the impact velocity was 100 m s{sup -1}. Impact occurred at normal incidence. Material loss in all targets occurred by brittle fracture. The biomorphic specimens eroded by formation of both lateral and radial cracks and their erosion rates were higher than both conventional SiCs. The RB SiC eroded as a classic brittle material, by formation and propagation of lateral cracks. The HP SiC, the hardest target, was the most erosion resistant. In erosion of the HP SiC, the abrasive particles, especially the largest ones, fragmented upon impact. The resulting dissipation of energy led to relatively low erosion rates. Flexural strength before and after erosion was measured for the biomorphic eucalyptus, RB SiC, and HP SiC. Erosion damage reduced the flexural strengths of all of the specimens. The relative strength reductions were lowest for the biomorphic eucalyptus and highest for the HP SiC. The hot-pressed SiC responded as predicted by accepted models of impact damage in brittle solids. The responses of the biomorphic and reaction-bonded SiC specimens were modeled as if they consisted of only SiC and porosity. This approximation agreed reasonably well with observed degradations of strength.

  19. 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.

  20. Thermal expansion of the hexagonal (6H) polytype of silicon carbide

    NASA Technical Reports Server (NTRS)

    Li, Z.; Bradt, R. C.

    1986-01-01

    X-ray diffraction is presently used to determine the thermal expansion of the hexagonal (6H) polytype of alpha-SiC over the 20-1000 C range. The principal (alpha-11 and alpha-33) axial coefficients of thermal expansion can be expressed by second-order polynomials; the former is noted to be larger than the latter over the entire temperature range, while the thermal expansion anisotropy increases continuously with increasing temperature. The thermal expansion and thermal expansion anisotropy obtained are compared with previously published results for the (6H) polytype, and discussed with respect to the structure.

  1. Defect-induced magnetism in neutron irradiated 6H-SiC single crystals.

    PubMed

    Liu, Yu; Wang, Gang; Wang, Shunchong; Yang, Jianhui; Chen, Liang; Qin, Xiubo; Song, Bo; Wang, Baoyi; Chen, Xiaolong

    2011-02-25

    Defect-induced magnetism is firstly observed in neutron irradiated SiC single crystals. We demonstrated that the intentionally created defects dominated by divacancies (V(Si)V(C)) are responsible for the observed magnetism. First-principles calculations revealed that defect states favor the formation of local moments and the extended tails of defect wave functions make long-range spin couplings possible. Our results confirm the existence of defect-induced magnetism, implying the possibility of tuning the magnetism of wide band-gap semiconductors by defect engineering. © 2011 American Physical Society

  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.

  3. 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}.

  4. Low-temperature transport properties of multigraphene films grown on the SiC surface by sublimation

    SciTech Connect

    Lebedev, A. A. Agrinskaya, N. V.; Lebedev, S. P.; Mynbaeva, M. G.; Petrov, V. N.; Smirnov, A. N.; Strel'chuk, A. M.; Titkov, A. N.; Shamshur, D. V.

    2011-05-15

    Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

  5. 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

  6. 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%.

  7. Pressure induced structural phase transition in SiC

    NASA Astrophysics Data System (ADS)

    Gorai, S.; Bhattacharya, C.; Kondayya, G.

    2017-05-01

    Silicon carbide (SiC) is an excellent ceramic material which exists in several polytypes. In this work, we obtained the structural properties of the ambient Zinc-Blende and high pressure Rock-Salt structures of SiC from density functional theory (DFT). We studied the structural phase transition occurring under compression using Debye Gruneisen theory based on scaled binding energy model. We observed excellent agreement of our predicted 300 K isotherm for SiC with experimental data.

  8. Structural and magnetic properties of irradiated SiC

    SciTech Connect

    Wang, Yutian; Helm, Manfred; Chen, Xuliang; Yang, Zhaorong; Li, Lin; Shalimov, Artem; Prucnal, Slawomir; Munnik, Frans; Skorupa, Wolfgang; Zhou, Shengqiang; Tong, Wei

    2014-05-07

    We present a comprehensive structural characterization of ferromagnetic SiC single crystals induced by Ne ion irradiation. The ferromagnetism has been confirmed by electron spin resonance, and possible transition metal impurities can be excluded to be the origin of the observed ferromagnetism. Using X-ray diffraction and Rutherford backscattering/channeling spectroscopy, we estimate the damage to the crystallinity of SiC, which mutually influences the ferromagnetism in SiC.

  9. 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.

  10. 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.; hide

    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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Deep level defects in sublimation-grown 6H silicon carbide investigated by DLTS and EPR

    NASA Astrophysics Data System (ADS)

    Irmscher, K.; Pintilie, I.; Pintilie, L.; Schulz, D.

    2001-12-01

    6H-SiC bulk single crystals grown by physical vapor transport (PVT) were investigated by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). One of the observed deep level defects was identified as isolated tungsten on Si sites by EPR. The electron spin of {1}/{2} could be explained by W 5+ (5d 1). This is equivalent to the single positive charge state of a double donor when taking into account the Fermi level position in the n-type samples. The interpretation is also consistent with the DLTS detection of a W related deep level which showed a behavior of the capture of electrons and holes that hints at a double donor. In addition a tantalum related deep level is tentatively discussed. W and Ta were incorporated on electrically active sites in 6H-SiC only in low concentrations (2-4×10 14 cm -3) during crystal growth by PVT.

  17. 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.

  18. Early negative ion studies related to C6H- and recent ion spectroscopy

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Kentarou; Fujimori, Ryuji; Ooe, Hiroki; Miyamoto, Yuki

    2015-01-01

    Through a spectral line survey observation with Nobeyama 45-m radio telescope in the 28-50 GHz region toward a late type star IRC+10216, a series of lines of a linear molecule was found in 1995. The rotational constant was determined to be 1376.8641(43) MHz, and the molecule is called B1377. After the detection, various studies related this species were carried out, which are presented in this paper, including Aoki's pioneering prediction and radio searches for NCO-, NCS-, and CCH-, etc. Finally, in 2006, McCarthy et al. succeeded in laboratory detection of the C6H- species by mm wave and FTMW spectroscopy and proved that the C6H- anion is B1377. We also report recent laboratory studies in the following topics:(1) time-resolved Fourier transform (FT) emission and absorption spectroscopy of molecular ions to obtain reaction rate constants, (2) FT infrared absorption spectrum of the H2F+ ion.

  19. FeCl3·6H2O-catalyzed alkenylation of indoles with aldehydes.

    PubMed

    Yang, Qin; Wang, Liandi; Guo, Tenglong; Yu, Zhengkun

    2012-09-21

    FeCl(3)·6H(2)O-catalyzed efficient C3-alkenylation of indoles was realized through the condensation of aldehydes and indole derivatives in the presence of 2 equiv of ethanol at ambient temperature, forming 3-vinylindoles in up to 93% yields. Ethanol promoted formation of the desired products. An obvious solvent effect was observed, and bisindoles were identified as the reaction intermediates.

  20. 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)

  1. Inelastic rate coefficients for collisions of C6H- with H2 and He

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    The recent detection of anions in the interstellar medium has shown that they exist in a variety of astrophysical environments - circumstellar envelopes, cold dense molecular clouds and star-forming regions. Both radiative and collisional processes contribute to molecular excitation and de-excitation in these regions so that the 'local thermodynamic equilibrium' approximation, where collisions cause the gas to behave thermally, is not generally valid. Therefore, along with radiative coefficients, collisional excitation rate coefficients are needed to accurately model the anionic emission from these environments. We focus on the calculation of state-to-state rate coefficients of the C6H- molecule in its ground vibrational state in collisions with para-H2, ortho-H2 and He using new potential energy surfaces. Dynamical calculations for the pure rotational excitation of C6H- were performed for the first 11 rotational levels (up to j1 = 10) using the close-coupling method, while the coupled-states approximation was used to extend the H2 rate coefficients to j1 = 30, where j1 is the angular momentum quantum number of C6H-. State-to-state rate coefficients were obtained for temperatures ranging from 2 to 100 K. The rate coefficients for H2 collisions for Δj1 = -1 transitions are of the order of 10-10 cm3 s-1, a factor of 2 to 3 greater than those of He. Propensity rules are discussed. The collisional excitation rate coefficients produced here impact astrophysical modelling since they are required for obtaining accurate C6H- level populations and line emission for regions that contain anions.

  2. Prolonged 500 C Operation of 6H-SiC JFET Integrated Circuitry

    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.; hide

    2008-01-01

    This paper updates the long-term 500 C electrical testing results from 6H-SiC junction field effect transistors (JFETs) and small integrated circuits that were introduced at ICSCRM-2007. Two packaged JFETs have now been operated in excess of 7000 hours at 500 degC with less than 10% degradation in linear I-V characteristics. Several simple digital and analog demonstration integrated circuits successfully operated for 2000-6500 hours at 500 C before failure.

  3. Solid state and solution study of some phosphoramidate derivatives containing the P(O)NHC(O) bifunctional group: Crystal structures of CCl 2HC(O)NHP(O)(NCH 3(CH 2C 6H 5)) 2, p-ClC 6H 4C(O)NHP(O)(NCH 3(CH 2C 6H 5)) 2, CCl 2HC(O)NHP(O)(N(CH 2C 6H 5) 2) 2 and p-BrC 6H 4C(O)NHP(O)(N(CH 2C 6H 5) 2) 2

    NASA Astrophysics Data System (ADS)

    Dehghanpour, Saeed; Welter, Richard; Barry, Aliou Hamady; Tabasi, Farzaneh

    2010-04-01

    Synthetic methods for several novel phosphoramidate compounds containing the P(O)NHC(O) bifunctional group were developed. These compounds with the general formula R 1C(O)NHP(O)(N(R 2)(CH 2C 6H 5)) 2, where R 1 = CCl 2H, p-ClC 6H 4, p-BrC 6H 4, o-FC 6H 4 and R 2 = hydrogen, methyl, benzyl, were characterized by several spectroscopic methods and analytical techniques. The effects of phosphorus substituents on the rotation rate around the P-N amine bond were also investigated. 1H NMR study of the synthesized compounds demonstrated that the presence of bulky groups attached to the phosphorus center and electron withdrawing groups in the amide moiety lead to large chemical-shift non-equivalence (Δ δH) of diastereotopic methylene protons. The crystal structures of CCl 2HC(O)NHP(O)(NCH 3(CH 2C 6H 5)) 2, p-ClC 6H 4C(O)NHP(O)(NCH 3(CH 2C 6H 5)) 2, CCl 2HC(O)NHP(O)(N(CH 2C 6H 5) 2) 2 and p-BrC 6H 4C(O)NHP(O)(N(CH 2C 6H 5) 2) 2 were determined by X-ray crystallography using single crystals. The coordination around the phosphorus center in these compounds is best described as distorted tetrahedral and the P(O) and C(O) groups are anti with respect to each other. In the compound Br-C 6H 4C(O)NHP(O)(N(CH 2C 6H 5) 2) 2 (with two independent molecules in the unit cell), two conformers are connected to each other via two different N-H⋯O hydrogen bonds forming a non-centrosymmetric dimer. In the crystalline lattice of other compounds, the molecules form centrosymmetric dimers via pairs of same N-H⋯O hydrogen bonds. The structure of CCl 2HC(O)NHP(O)(N(CH 2C 6H 5) 2) 2 reveals an unusual intramolecular interaction between the oxygen of C dbnd O group and amine nitrogen.

  4. Graphitization of the 6H-SiC( 0 0 0 1 ) surface studied by HREELS

    NASA Astrophysics Data System (ADS)

    Angot, T.; Portail, M.; Forbeaux, I.; Layet, J. M.

    2002-04-01

    By using high-resolution electron energy loss spectroscopy (HREELS), we have studied the vibrational properties of the various 6H-SiC(0 0 0 1) reconstructions, from the Si-rich to the graphitized surface. The 6H-SiC(0 0 0 1)-(3×3) exhibits the Fuchs-Kliewer (FK) optical phonons commonly observed on strongly polar materials. The lowering of the energy width of the elastically reflected electrons with increasing primary energies reveals the coupling of FK with the plasmon that derives from the bulk doping level. No particular modification in the HREELS spectra is observed after preparation of the 6H-SiC(0 0 0 1)-(√3×√3) R30° surface. On the (6√3×6√3) R30° reconstructed surface, the FK phonon modes display both a blue shift and an increased damping factor. In the ultra-violet energy region we observed a loss structure at ≈6 eV whose dispersion relation allows to readily conclude on the presence of a pure graphite layer: it almost perfectly match the dispersion relation measured on highly oriented pyrolitic graphite for the so-called `π-plasmon' arising from the electronic excitation of π- π∗ interband transition.

  5. Planar to 3D transition in the B6H(y) anions.

    PubMed

    Olson, J K; Boldyrev, A I

    2013-02-21

    Potential energy surfaces of anionic B(6)H(y) clusters were sampled using the coalescence kick method. We found that the planar to three-dimensional transition occurs in this system when y = 4. This is an important discovery because this transition suggests a major structural change as a function of dehydrogenation for the stoichiometric B(n)H(n)(-) polyhedral boranes. We also found that the B(6)H(3)(-) global minimum structure has an optical isomer. The chemical bonding patterns revealed by the adaptive natural density partitioning (AdNDP) analysis explain the geometric structure of all clusters presented here. From our chemical bonding analysis, we concluded that the 2D-3D transition occurs at B(6)H(4)(-) because the addition of one extra hydrogen atom further destroys the network of the peripheral 2c-2e B-B σ-bonding, making planar structures less stable, and because the distorted octahedral structure provides some occupation of all s- and p-AOs of boron, avoiding the presence of any empty atomic orbitals. Theoretical vertical electron detachment energies (VDEs) were calculated for comparison with future experimental work.

  6. The low frequency dynamics of supercooled LiBr, 6H2O.

    PubMed

    Bove, L; Dreyfus, C; Polian, A; Bonello, B; Malfanti, I; Taschin, A; Torre, R; Pick, R M

    2011-01-21

    We present results of a series of experiments performed on LiBr, 6H(2)0 from room temperature down to 172 K ≈ 1.2T(g). These ultrasound, Brillouin and depolarized light scattering, and transient grating experiments show that, above 215 K, this solution behaves like supercooled water: its zero frequency sound velocity C(0) continuously decreases with decreasing temperature, and the reorientational dynamics of the water molecules can be directly detected at some temperatures of this domain. Conversely, below 215 K, a new regime sets in, where the apparent C(0) is practically temperature independent and where a β, Arrenhius like, relaxation process coexists with the usual, Vogel-Fulcher like, α relaxation process of the supercooled liquid. These results are similar to those recently obtained in LiCl, 6H(2)O. The onset of the new regime is possibly due to an increase of the interaction of the water molecules with a neighboring Li(+) ion when lowering the temperature. We also compare our results with published dielectric data on water solutions of glass forming polyalcohols. Some of them present a low temperature splitting of their relaxation time similar to what is found in LiBr, 6H(2)O.

  7. Photoelectric Properties of Si Doping Superlattice Structure on 6H-SiC(0001).

    PubMed

    Li, Lianbi; Zang, Yuan; Hu, Jichao; Lin, Shenghuang; Chen, Zhiming

    2017-05-25

    The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL) on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001) Si-face by chemical vapor deposition. TEM characterizations of the p/n-Si DSL confirmed the epitaxial growth of the Si films with preferred orientation and the misfit dislocations with a Burgers vector of 1/3 <21-1> at the p-Si/n-Si interface. The device had an obvious rectifying behavior, and the turn-on voltage was about 1.2 V. Under the visible illumination of 0.6 W/cm², the device demonstrated a significant photoelectric response with a photocurrent density of 2.1 mA/cm². Visible light operation of the Si-DSL/6H-SiC heterostructure was realized for the first time.

  8. Al6H18: A baby crystal of γ-AlH3

    NASA Astrophysics Data System (ADS)

    Kiran, B.; Kandalam, Anil K.; Xu, Jing; Ding, Y. H.; Sierka, M.; Bowen, K. H.; Schnöckel, H.

    2012-10-01

    Using global-minima search methods based on the density functional theory calculations of (AlH3)n (n = 1-8) clusters, we show that the growth pattern of alanes for n ≥ 4 is dominated by structures containing hexa-coordinated Al atoms. This is in contrast to the earlier studies where either linear or ring structures of AlH3 were predicted to be the preferred structures in which the Al atoms can have a maximum of five-fold coordination. Our calculations also reveal that the Al6H18 cluster, with its hexa-coordination of the Al atoms, resembles the unit-cell of γ-AlH3, thus Al6H18 is designated as the "baby crystal." The fragmentation energies of the (AlH3)n (n = 2-8) along with the dimerization energies for even n clusters indicate an enhanced stability of the Al6H18 cluster. Both covalent (hybridization) and ionic (charge) contribution to the bonding are the driving factors in stabilizing the isomers containing hexa-coordinated Al atoms.

  9. Al6H18: a baby crystal of γ-AlH3.

    PubMed

    Kiran, B; Kandalam, Anil K; Xu, Jing; Ding, Y H; Sierka, M; Bowen, K H; Schnöckel, H

    2012-10-07

    Using global-minima search methods based on the density functional theory calculations of (AlH(3))(n) (n = 1-8) clusters, we show that the growth pattern of alanes for n ≥ 4 is dominated by structures containing hexa-coordinated Al atoms. This is in contrast to the earlier studies where either linear or ring structures of AlH(3) were predicted to be the preferred structures in which the Al atoms can have a maximum of five-fold coordination. Our calculations also reveal that the Al(6)H(18) cluster, with its hexa-coordination of the Al atoms, resembles the unit-cell of γ-AlH(3), thus Al(6)H(18) is designated as the "baby crystal." The fragmentation energies of the (AlH(3))(n) (n = 2-8) along with the dimerization energies for even n clusters indicate an enhanced stability of the Al(6)H(18) cluster. Both covalent (hybridization) and ionic (charge) contribution to the bonding are the driving factors in stabilizing the isomers containing hexa-coordinated Al atoms.

  10. Photoelectric Properties of Si Doping Superlattice Structure on 6H-SiC(0001)

    PubMed Central

    Li, Lianbi; Zang, Yuan; Hu, Jichao; Lin, Shenghuang; Chen, Zhiming

    2017-01-01

    The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL) on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001) Si-face by chemical vapor deposition. TEM characterizations of the p/n-Si DSL confirmed the epitaxial growth of the Si films with preferred orientation and the misfit dislocations with a Burgers vector of 1/3 <21-1> at the p-Si/n-Si interface. The device had an obvious rectifying behavior, and the turn-on voltage was about 1.2 V. Under the visible illumination of 0.6 W/cm2, the device demonstrated a significant photoelectric response with a photocurrent density of 2.1 mA/cm2. Visible light operation of the Si-DSL/6H-SiC heterostructure was realized for the first time. PMID:28772944

  11. 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.

  12. Epitaxial growth of SiC from Al?Si solution reacting with propane gas

    NASA Astrophysics Data System (ADS)

    Tanaka, A.; Ataka, T.; Ohkura, E.; Katsuno, H.

    2004-09-01

    A new low-temperature LPE technique has been developed. SiC layers were grown on a Si-face of 6H-SiC substrates from Al-Si solution reacting with propane gas at 1000°C. Morphology of the as-grown surface of the layers changed depending on whether the solution was saturated with Si or not. Based on the observation, two growth modes, corresponding to segregation dominance or surface diffusion dominance, were discussed. The use of off-axis substrates made the growth rate increase remarkably. The thickness reached about 10-μm after 8-h growth. PL measurements revealed that the polytype of the grown layers belongs to a hexagonal group.

  13. Localized defects related to the 14N+ ion irradiation-induced magnetism in SiC

    NASA Astrophysics Data System (ADS)

    He, Xiujie; Tan, Jie

    2017-09-01

    The role of localized defects as they pertain to ferromagnetism in SiC, which contains only s and p electrons, is important but unclear. Here, room temperature, macroscopic magnetization is induced and can be tuned in 6H-SiC using 14N+ ion implantation. First-principles density functional theory computation results confirm that 14N+ ion implantation can enhance the ferromagnetic ordering of the local magnetic moments caused by vacancy and substitution defects. The calculated magnetization values in the energetically favored ferromagnetic ordering (1.47-2.93 emu/g for several vacancy and substitution defects) are larger than our experimental values (0.25 emu/g at 5 K and 0.08 emu/g at 300 K), but the result is qualitatively in agreement.

  14. 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.

  15. Reactive Ion Etching of SiC in SF_6/He Plasmas

    NASA Astrophysics Data System (ADS)

    Alapati, Ramakanth; Nordheden, Karen J.

    2003-10-01

    Etch rates of greater than 400 Åmin have been achieved for 6H SiC in a Plasma Therm 790 RIE system using SF_6/He gas mixtures. Both pressure and composition are strong determining factors in optimizing the etch rate. For an rf power of 175 W, the etch rate maximizes at a pressure of 125 mTorr and a composition of 50% SF_6. Microwave measeurements indicate that the addition of helium results in an increase in the average electron density, although significant electron attachment is apparent. The electron density also exhibits a maximum at a pressure of 125 mTorr. Optical emission spectroscopy shows that the addition of helium results in increased emission of F and F_2, and these emissions also exhibit maxima at a pressure of 125 mTorr. The higher electron density and possibility of increased electron temperature, as a result of electron attachment heating, are believed to be responsible for an increase in the dissociation of SF6 which results in an enhanced SiC etch rate.

  16. 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.

  17. Pristine SiC Candidates: Spectral Imaging and Auger Investigations

    NASA Astrophysics Data System (ADS)

    Croat, T. K.; Lebsack, E.; Bernatowicz, T. J.

    2010-03-01

    We describe a new spectral imaging method to locate pristine SiCs (those prepared without acid dissolution) from within Murchison matrix material. We present images,X-ray and Auger electron spectra from pristine SiCs, which show carbonaceous surface coatings.

  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. Three-dimensional crystalline SiC nanowire flowers

    NASA Astrophysics Data System (ADS)

    Ho, Ghim Wei; Weng Wong, Andrew See; Kang, Dae-Joon; Welland, Mark E.

    2004-08-01

    Several techniques have already been developed for synthesizing silicon carbide (SiC) material in the form of nanospheres and nanowires/rods. Here, we report the synthesis of a distinctly different kind of SiC nanostructure in the form of three-dimensional crystalline nanowire-based flower-like structures. Interest in such structures centres around the combination of a simple growth process based on SiC nanowire formation, with a resultant structure having potentially complex mechanical and optical properties, the latter a consequence of the wide band gap of bulk SiC. The synthesis of these SiC nanowire flowers is via a vapour-liquid-solid (VLS) process, on which a detailed study of both the chemical and structural composition has been carried out.

  20. Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

    NASA Astrophysics Data System (ADS)

    Wutimakun, Passapong; Buteprongjit, Chumpol; Morimoto, Jun

    2009-07-01

    Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.

  1. Multidentate aryloxide and oxo-aryloxide complexes of antimony: synthesis and structural characterization of [eta4-N(o-C6H4O)3]Sb(OSMe2), {{[eta3-N(o-C6H4OH)- (o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)2.

    PubMed

    Tanski, Joseph M; Kelly, Bryte V; Parkin, Gerard

    2005-07-21

    Antimony compounds that feature multidentate aryloxide ligands, namely [eta4-N(o-C6H4O)3]Sb(OSMe2), {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2, and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)2 have been synthesized from N(o-C6H4OH)3 and PhN(o-C6H4OH)2 and structurally characterized by X-ray diffraction. While [eta4-N(o-C6H4O)3]Sb(OSMe2) exists as a discrete mononuclear species, the oxo complexes {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(micro3-O)2 are multinuclear. Specifically, the dinuclear fragment {[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)} exists in a dimeric form due to the bridging oxo ligand participating in an intermolecular hydrogen bonding interaction, while the dinuclear fragment {[eta3-PhN(o-C6H4O)2]Sb}2(mu-O) exists in a dimeric form due to the bridging oxo ligand serving as a donor to the antimony of a second fragment. The structures of {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)(2), therefore, indicate that an oxo ligand bridging two Sb(III) centers is sufficiently electron rich to serve as both an effective hydrogen bond acceptor and as a ligand for an additional Sb(III) center.

  2. 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.

  3. 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.

  4. Study of photomodulated reflectance in 6H-SiC single crystals

    SciTech Connect

    Gruzintsev, A. N.

    2013-04-15

    The effect of ultraviolet irradiation of the surface of silicon-carbide (6H-SiC) single crystals on their optical reflectivity in the visible and violet spectral regions is studied. It is shown that the photoreflection-signal intensity is maximal, if the light beam is incident at the Brewster angle and polarized parallel to the plane of incidence. The relative change induced in the refractive index of the surface layers of a crystal (10{sup -3}) upon exposure to nitrogen laser radiation, caused by the generation of nonequilibrium free charge carriers in the conduction band of the material, is established.

  5. 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

  6. 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.

  7. High temperature ohmic and Schottky contacts to N-type 6H-SiC nickel

    NASA Astrophysics Data System (ADS)

    Williams, John R.; Bozack, Michael J.; Isaacs-Smith, Tamara; Luckowski, Eric D.; Meadows, Christopher; Crofton, John; McMullin, Paul G.

    1995-01-01

    We report specific contact resistances measured at elevated temperatures for Ni ohmic contacts to 6H-SiC. The specific contact resistances were measured with the linear transmission line method at both room temperature and at 773 K and yielded values <5×10-6 Ω-cm2 at both temperatures. The trend shows a decreasing contact resistance at higher temperatures. The annealed metal film is a nickel silicide with substantial mixing of C throughout the silicide layer. Also reported are the results of I-V and C-V barrier height measurements for Ni Schottky contacts to 6H-SiC. Current-voltage barrier heights as high as 1.2 eV have been measured, and the contacts show good electrical and physical stability following long-term anneals at 573 K in a vacuum ambient of 10-6 torr. These ohmic and Schottky contacts have been developed by the CCDS in collaboration with the Air Force and the Westinghouse Electric Corporation, and transfer of our contact technology to the Westinghouse Science and Technology is now complete.

  8. 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.

  9. Study of surface exfoliation on 6H-SiC induced by H2+ implantation

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Li, B. S.

    2017-03-01

    The effect of lattice damage generated by the H2+-implantation on exfoliation efficiency in 6H-SiC wafers is investigated. <0001> 6H-SiC wafers were implanted with 134 keV H2+ ions to ion fluences from 1.5×1016 to 5×1016 H2+ cm-2 and subsequently annealed at temperatures from 973 K to 1373 K. The samples were studied by a combination of optical microscopy and transmission electron microscopy. Only after 1373 K annealing for 15 min, blisters and exfoliation occur on the H2+-implanted sample surface. With increasing the implantation fluences from 1.5×1016 to 3.75×1016 H2+ cm-2, the exfoliation mean size decreases, while the exfoliation density increases. For the highest fluence of 5×1016 H2+ cm-2, seldom exfoliations occur on the sample surface. Microstructure analysis shows that exfoliation efficiency is largely controlled by the H2+-implantation-induced lattice damage. The depth of the microcrack is related to the implantation fluence. The effect of implantation fluence on dislocation loops, platelet nucleation and growth is investigated.

  10. Preparation and biodistribution of copper-67-labeled porphyrins and porphyrin-A6H immunoconjugates.

    PubMed

    Bhalgat, M K; Roberts, J C; Mercer-Smith, J A; Knotts, B D; Vessella, R L; Lavallee, D K

    1997-02-01

    The synthetic porphyrins, N-benzyl-5,10,15,20-tetrakis (4-carboxyphenyl) porphine (N-bzHTCPP) and N-4-nitrobenzyl-5-(4-carboxyphenyl)-10,15,20-tris(4-sulfophenyl) porphine (N-bzHCS3P), represent excellent radiocopper chelating agents that may find utility in antibody-mediated diagnosis and/or therapy. N-bzHCS3P was conjugated to an anti-renal cell carcinoma (RCC) antibody, A6H, and labeled with copper-67. 67CuCS3P-A6H was studied for its biodistribution in human RCC xenograft-bearing nude mice, along with the radiolabeled free porphyrins. The porphyrins resulted in tumor:blood ratios in the range of 3 to 4 after 48 h. The radiolabeled antibody achieved a tumor:blood ratio of over 16 after 45 h, indicating accumulation at the desired site. However, unwanted localization also occurred in the liver and spleen, which will have to be rectified before realizing the full potential of this approach.

  11. Experimental study of resonance states in {sup 7}H and {sup 6}H

    SciTech Connect

    Caamano, M.; Mittig, W.; Savajols, H.; Demonchy, C. E.; Jurado, B.; Rejmund, F.; Rejmund, M.; Roussel-Chomaz, P.; Gillibert, A.; Obertelli, A.; Lemmon, R.; Wolski, R.

    2008-10-15

    The {sup 7}H and {sup 6}H nuclear systems were investigated via transfer reactions with a {sup 8}He beam at 15.4A MeV impinging in a {sup 12}C target. The experimental setup allowed a complete reconstruction of the reaction kinematics with the MAYA gas detector, based on the active-target concept, where the carbon atoms of the filling isobutane played also the role of reaction target. The {sup 7}H resonance was observed at 0.57{sub -0.21}{sup +0.42} MeV above the {sup 3}H+4n threshold with a width of 0.09{sub -0.06}{sup +0.94} MeV. The {sup 6}H system was formed at 2.91{sub -0.95}{sup +0.85} MeV with a resonance width of 1.52{sub -0.35}{sup +1.77} MeV. These results show the availability of nuclear structure information well outside the bounding limits, resulting in an extraordinary input to improve the present models and understanding of nuclear matter.

  12. Equilibrium shapes and surface selection of nanostructures in 6H-SiC

    DOE PAGES

    Kondo, Sosuke; Parish, Chad M.; Koyanagi, Takaaki; ...

    2017-04-03

    Here, the equilibrium shape of 6H-SiC nanostructures and their surfaces were studied by analyzing nano-void (~10 nm) shapes, which were introduced in monocrystalline 6H-SiC by high-temperature neutron irradiation, using transmission electron microscopy. The nano-voids were determined to be irregular icosahedrons truncated with six {1¯100}, twelve {1¯103}, one smaller top-basal, and one larger bottom-basal planes, which suggests that {1¯100} and {1¯103} are the next stable surface class after the basal planes. The relatively frequent absence of the {1¯100} surface in the nano-voids indicated that the (1¯103¯) surface type is energetically rather stable. These non-basal surfaces were found not to be atomicallymore » flat due to the creation of nanofacets with half unit-cell height in the c-axis. The {1¯100} and {1¯103} surfaces were classified as two and four face types according to their possible nanofacets and surface termination, respectively. We also discuss the surface energy difference between the (1¯103¯) and (1¯103) face types in relation to the energy balance within the equilibrium, but irregular, polyhedron, in which the (1¯103) surface had double the surface energy of the (1¯103¯) surface (~3900 erg/cm2).« less

  13. 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.

  14. Large-scale growth of well-aligned SiC tower-like nanowire arrays and their field emission properties.

    PubMed

    Wang, Lin; Li, Chengming; Yang, Yang; Chen, Shanliang; Gao, Fengmei; Wei, Guodong; Yang, Weiyou

    2015-01-14

    Fabrication of well-aligned one-dimensional (1D) nanostrucutres is critically important and highly desired since it is the key step to realize the patterned arrays to be used as the display units. In the present work, we report the large-scale and well-aligned growth of n-type SiC nanowire arrays on the 6H-SiC wafer substrates via pyrolysis of polymeric precursors assisted by Au catalysts. The obtained n-type SiC nanowires are highly qualified with sharp tips and numerous sharp corners around the wire bodies, which bring the emitters excellent field emission (FE) performance with low turn-on fields (1.50 V/μm), low threshold fields (2.65 V/μm), and good current emission stabilities (fluctuation <3.8%). The work abilities of the n-type SiC tower-like nanowire arrays under high-temperature harsh environments have been investigated, suggesting that the resultant field emitters could be well serviced up to 500 °C. The temperature-enhanced FE behaviors could be attributed to the reduction of the work function induced by the rise of temperatures and the incorporated N dopants. It is believed that the present well-aligned n-type SiC tower-like nanowire arrays could meet nearly all stringent requirements for an ideal FE emitter with excellent FE properties, making their applications very promising in displays and other electronic nanodevices.

  15. "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.

  16. Thermal expansion of SiC at high pressure-temperature and implications for thermal convection in the deep interiors of carbide exoplanets

    NASA Astrophysics Data System (ADS)

    Nisr, C.; Meng, Y.; MacDowell, A. A.; Yan, J.; Prakapenka, V.; Shim, S.-H.

    2017-01-01

    Recent astrophysical observations have shown that some stars have sufficiently high carbon-to-oxygen ratios and may host planets composed mainly of carbides instead of silicates and oxides. From the low thermal expansion of SiC at 1 bar, it can be inferred that the buoyancy force of thermal anomalies is much lower in the carbide planets than in the silicate planets. However, numerous studies have shown that high pressure in planetary interiors can fundamentally change the physical properties of materials. We have measured the pressure-volume-temperature relations of two SiC polymorphs (3C and 6H) at pressures and temperatures up to 80 GPa and 1900 K and 65 GPa and 1920 K, respectively, in the laser-heated diamond anvil cell combined with synchrotron X-ray diffraction. We found no evidence of dissociations of these phases up to our maximum pressure condition, supporting the stability of SiC to 1900 km depth in Earth-size Si-rich carbide planets. Following the Mie-Grüneisen approach, we fit our data to the Birch-Murnaghan or the Vinet equations of state combined with the Debye approach. We found that the pressure-induced change in the thermal expansion parameter of SiC is much smaller than that of Mg silicate perovskite (bridgmanite). Our new measurements suggest that the thermal buoyancy force may be stronger in the deep interiors of Si-rich carbide exoplanets than in the "Earth-like" silicate planets.

  17. 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.

  18. 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...

  19. 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... 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...

  20. 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...

  1. Fabrication of large aperture SiC brazing mirror

    NASA Astrophysics Data System (ADS)

    Li, Ang; Wang, Peipei; Dong, Huiwen; Wang, Peng

    2016-10-01

    The SiC brazing mirror is the mirror whose blank is made by assembling together smaller SiC pieces with brazing technique. Using such kinds of joining techniques, people can manufacture large and complex SiC assemblies. The key technologies of fabricating and testing SiC brazing flat mirror especially for large aperture were studied. The SiC brazing flat mirror was ground by smart ultrasonic-milling machine, and then it was lapped by the lapping smart robot and measured by Coordinate Measuring Machine (CMM). After the PV of the surface below 4um, we did classic coarse polishing to the surface and studied the shape of the polishing tool which directly effects removal amount distribution. Finally, it was figured by the polishing smart robot and measured by Fizeau interferometer. We also studied the influence of machining path and removal functions of smart robots on the manufacturing results and discussed the use of abrasive in this process. At last, an example for fabricating and measuring a similar SiC brazing flat mirror with the aperture of 600 mm made by Shanghai Institute of Ceramics was given. The mirror blank consists of 6 SiC sectors and the surface was finally processed to a result of the Peak-to-Valley (PV) 150nm and Root Mean Square (RMS) 12nm.

  2. 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.

  3. Outcomes of endovascular treatment for acute large-vessel ischaemic stroke more than 6 h after symptom onset.

    PubMed

    Motyer, R; Kok, H K; Asadi, H; O'Hare, A; Brennan, P; Power, S; Looby, S; Nicholson, P; Williams, D; Murphy, S; Hill, M D; Goyal, M; McManus, J; O'Brien, P; Thornton, J

    2017-09-05

    Benefit from endovascular thrombectomy (EVT) for large-vessel occlusion (LVO) acute ischaemic stroke (AIS) is well demonstrated. Furthermore, emerging evidence supports efficacy in appropriately selected patients treated beyond current recommendations of 6 h. We evaluated clinical outcomes in patients undergoing late EVT at our institution. Retrospective review of prospectively collected clinical database on 355 patients who underwent EVT for LVO AIS. Data collected consisted of patient demographics, radiological findings and outcome details. Outcomes, including 90-day functional status, recanalization, symptomatic intracranial haemorrhage (sICH) and 90-day mortality, for patients undergoing EVT <6 h, >6 h, and >7.3 h, were compared. A total of 355 patients underwent EVT for LVO AIS at our institution during the review period, with 74 (21%) patients treated ≥6 h from symptom onset. Successful recanalization was achieved in 285 (80%) patients, with 228 (81%) achieving a mTICI ≥2b in the <6 h group, and 57 (77%) in the >6 h group (P = 0.429). Ninety-day functional independence (mRS 0-2) was achieved in 162 (46%) patients, with 130 (46%) achieving a mRS of 0-2 in the <6 h group, and 32 (43%) in the >6 h group (P = 0.643). No significant differences were found in rates of sICH or 90-day mortality. No significant differences in functional independence, recanalization rates, sICH or mortality were identified in patients treated with EVT >7.3 h compared to <7.3 h. In appropriately selected patients, EVT >6 h was associated with comparable outcomes to those treated <6 h. These data support a physiological approach to patient selection. © 2017 The Association for the Publication of the Journal of Internal Medicine.

  4. Formation of cobalt disilicide films on (3×3)6H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Platow, W.; Wood, D. K.; Tracy, K. M.; Burnette, J. E.; Nemanich, R. J.; Sayers, D. E.

    2001-03-01

    This paper presents a detailed study of thin Co films grown directly, sequentially, and by codeposition with Si on the (3×3)-R30° surface of 6H-SiC(0001). The structure, chemistry, and morphology of the films were determined using x-ray absorption fine structure, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and atomic force microscopy. For directly deposited Co films (1-8 nm) graphite layers form on top of the film surface during annealing, whereas Co stays mainly unreacted over a temperature range of 300-1000 °C. The formation of CoSi2 is achieved by sequential and codeposition of Co and Si. Films annealed at 550 °C are polycrystalline and further annealing to 650 °C causes no C segregation, but there is islanding of the films. Attempts to improve film morphology and homogeneity including applying a template method and varying growth temperature are also reported.

  5. Upscattering of ultracold neutrons from the polymer [C6H12]n

    NASA Astrophysics Data System (ADS)

    Sharapov, E. I.; Morris, C. L.; Makela, M.; Saunders, A.; Adamek, Evan R.; Broussard, L. J.; Cude-Woods, C. B.; Fellers, Deion E.; Geltenbort, Peter; Hartl, M.; Hasan, S. I.; Hickerson, K. P.; Hogan, G.; Holley, A. T.; Lavelle, C. M.; Liu, Chen-Yu; Mendenhall, M. P.; Ortiz, J.; Pattie, R. W., Jr.; Phillips, D. G., II; Ramsey, J.; Salvat, D. J.; Seestrom, S. J.; Shaw, E.; Sjue, Sky; Sondheim, W. E.; VornDick, B.; Wang, Z.; Womack, T. L.; Young, A. R.; Zeck, B. A.

    2013-12-01

    It is generally accepted that the main cause of ultracold neutron (UCN) losses in storage traps is upscattering to the thermal energy range by hydrogen adsorbed on the surface of the trap walls. However, the data on which this conclusion is based are poor and contradictory. Here we report a measurement, performed at the Los Alamos National Laboratory UCN source, of the average energy of the flux of upscattered neutrons after the interaction of UCN with hydrogen bound in the semicrystalline polymer PMP (trade name TPX), [C6H12]n. Our analysis, performed with the mcnp code which applies the neutron-scattering law to UCN upscattered by bound hydrogen in semicrystalline polyethylene, [C2H4]n, leads us to a flux average energy value of 26±3 meV, in contradiction to previously reported experimental values of 10 to 13 meV and in agreement with the theoretical models of neutron heating implemented in mcnp.

  6. Primary photoluminescence in as-neutron (electron) -irradiated n-type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Zhong, Z. Q.; Wu, D. X.; Gong, M.; Wang, O.; Shi, S. L.; Xu, S. J.; Chen, X. D.; Ling, C. C.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.

    2006-05-01

    Low-temperature photoluminescence spectroscopy has revealed a series of features labeled S1, S2, S3 in n-type 6H-SiC after neutron and electron irradiation. Thermal annealing studies showed that the defects S1, S2, S3 disappeared at 500 °C. However, the well-known D1 center was only detected for annealing temperatures over 700 °C. This experimental observation not only indicated that the defects S1, S2, S3 were a set of primary defects and the D1 center was a kind of secondary defect, but also showed that the D1 center and the E1, E2 observed using deep level transient spectroscopy might not be the same type of defects arising from the same physical origin.

  7. Anomalous behaviors of E1/E2 deep level defects in 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Ling, C. C.; Gong, M.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.

    2005-01-01

    Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E1 and E2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E1/E2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E1/E2. The activation energy and the capture cross section of this defect are EC-0.31eV and σ ˜8×10-14cm2, respectively.

  8. Magnetic properties of the 6H perovskite Ba3Fe2TeO9

    NASA Astrophysics Data System (ADS)

    Tang, Yawei; Paria Sena, Robert; Avdeev, Maxim; Battle, Peter D.; Cadogan, J. M.; Hadermann, Joke; Hunter, Emily C.

    2017-09-01

    A polycrystalline sample of Ba3Fe2TeO9 having the 6H perovskite structure has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. Partial ordering of Fe3+ and Te6+ cations occurs over the six-coordinate sites; the corner-sharing octahedra are predominantly occupied by the former and the face-sharing octahedra by a 1:1 mixture of the two. On cooling through the temperature range 18 < T/K < 295 an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. At 3 K an antiferromagnetic phase and a spin glass coexist.

  9. Bubble formation in oxide scales on SiC

    NASA Technical Reports Server (NTRS)

    Mieskowski, D. M.; Mitchell, T. E.; Heuer, A. H.

    1984-01-01

    The oxidation of alpha-SiC single crystals and sintered alphaand beta-SiC polycrystals has been investigated at elevated temperatures. Bubble formation is commonly observed in oxide scales on polycrystalline SiC, but is rarely found on single-crystal scales; bubbles result from the preferential oxidation of C inclusions, which are abundant in SiC polycrystals. The absence of bubbles on single crystals, in fact, implies that diffusion of the gaseous species formed on oxidation, CO (or possibly SiO), controls the rate of oxidation of SiC.

  10. REVIEW ARTICLE: SiC sensors: a review

    NASA Astrophysics Data System (ADS)

    Wright, N. G.; Horsfall, A. B.

    2007-10-01

    Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

  11. Bubble formation in oxide scales on SiC

    NASA Technical Reports Server (NTRS)

    Mieskowski, D. M.; Mitchell, T. E.; Heuer, A. H.

    1984-01-01

    The oxidation of alpha-SiC single crystals and sintered alphaand beta-SiC polycrystals has been investigated at elevated temperatures. Bubble formation is commonly observed in oxide scales on polycrystalline SiC, but is rarely found on single-crystal scales; bubbles result from the preferential oxidation of C inclusions, which are abundant in SiC polycrystals. The absence of bubbles on single crystals, in fact, implies that diffusion of the gaseous species formed on oxidation, CO (or possibly SiO), controls the rate of oxidation of SiC.

  12. Cast joining between SiC and aluminum

    SciTech Connect

    Sato, Kenji; Kagawa, Yutaka

    1989-10-01

    A simple cast joining process between reaction-bonded SiC and aluminum has been investigated. Processing variables to obtain strong bonding strength were examined. Metallurgical observation showed that an SiC particle/Al-Si alloy composite layer was formed between RB-SiC and solidified aluminum, and Al4C3 was formed between the SiC particle, in the composite layer, and the Al-Si alloy matrix. Formation of Al4C3 and the composite layer was controlled by casting temperature and time, respectively. The bonding strength increased with decreasing of an unjoined area which formed at the joined surface.

  13. Polymer precursors for SiC ceramic materials

    NASA Technical Reports Server (NTRS)

    Litt, Morton H.

    1986-01-01

    Work on precursor polymers to SiC was performed, concentrating on polymers made from decamethyl cyclohexasilyene units. The initial approach was to synthesize mixed diphenyl decamethyl cyclohexasilane, dephenylate, and polymerize. This produced polymers which had yields of up to 50 percent SiC. (Theoretical yield is 75 percent). The present approach is to make the polymer through the intermediate trans-1,4-diphenyl decamethyl cyclohexasilane. This should produce a crystalline polymer and high strength fibers. These will be thermally decomposed to SiC fibers. This requires new chemistry which is currently being studied.

  14. Mechanism and Kinetics of Thermal Decomposition of MgCl2 × 6H2O

    NASA Astrophysics Data System (ADS)

    Huang, Qiong-Zhu; Lu, Gui-Min; Wang, Jin; Yu, Jian-Guo

    2010-10-01

    The reaction mechanism and kinetic behavior of thermal decomposition of MgCl2 × 6H2O were studied by thermal gravimetric analysis. The results showed that the thermal decomposition process of MgCl2 × 6H2O could be divided into six stages. In the first two stages, four crystalline waters were lost. The dehydration and hydrolysis coexisted during the third and fourth stages. The fifth stage corresponded to the evaporation of 0.3 crystalline waters, and one molecular hydrogen chloride was eliminated in the last stage. The kinetic analysis of the thermal decomposition process was performed using the Doyle, Coats-Redfern, and Malek methods. The results suggested that the mechanisms of six stages were two-dimensional phase boundary mechanism, three-dimensional phase boundary mechanism, nucleation and nuclei growth mechanism (Avrami-Erofeev equation n = 3), two-dimensional phase boundary mechanism, three-dimensional diffusion mechanism (cylinder and G-B equation), and nucleation and nuclei growth mechanism (Avrami-Erofeev equation n = 1), respectively. The apparent active energies of six stages were 66.8 kJ × mol-1, 138.0 kJ × mol-1, 77.2 kJ × mol-1, 135.6 kJ × mol-1, 77.4 kJ × mol-1, and 92.2 kJ × mol-1, respectively. The frequency factors were 3.6 × 109 s-1, 8.8 × 1017 s-1, 4.6 × 109 s-1, 3.0 × 1014 s-1, 78.6 s-1, and 1.2 × 103 s-1, respectively.

  15. Short-course postpartum (6-h) magnesium sulfate therapy in severe preeclampsia.

    PubMed

    Anjum, Shaheen; Rajaram, Gade Pramod; Bano, Imam

    2016-05-01

    To assess the efficacy of short-course postpartum (6-h) magnesium sulfate therapy versus 24-h conventional magnesium sulfate therapy in severe preeclampsia. Cases of severe preeclampsia were randomly allocated to group A (n = 76) and group B (n = 43). Group A and group B received magnesium sulfate loading dose (4 g) followed by infusion for 6 and 24 h postpartum (1 gm/h), respectively. Cases in both the groups were monitored closely after the initiation of therapy. t test and Chi-square test were used for data analysis. No occurrence of convulsions was noted in both group A and group B. The mean amount of magnesium sulfate used in the study group was 15.1 ± 5.4 g as against 42.3 ± 7.3 g in controls. The duration of Foley catheterization and monitoring was significantly less in group A (mean 11.3 ± 5.1 and 11.1 ± 4.9 h, respectively) as compared to group B (mean 38.3 ± 7.3 and 38.4 ± 7.2 h, respectively). The mean duration of hospital stay was 2.7 ± 0.7 days in cases delivered vaginally and 7.5 ± 1.6 days in those who underwent cesarean section in group A, while it was 4.04 ± 1.47 and 11.11 ± 3.14 days, respectively, in group B. Short-course, i.e., 6-h, postpartum magnesium sulfate therapy is as effective as conventional 24-h postpartum magnesium sulfate therapy in preventing convulsions in severe preeclampsia.

  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. In situ hole doping of wide-gap semiconductors by dual-target simultaneous laser ablation: GaN and SiC epitaxial films

    NASA Astrophysics Data System (ADS)

    Muto, Hachizo; Asano, Takashi; Wang, Rong-Ping; Kusumori, Takeshi

    2005-10-01

    Apparatus for dual-target simultaneous laser ablation deposition and in situ doping techniques have been developed to achieve p-type doping during epitaxial growth of wide-band-gap semiconductors. The apparatus has two target holders with a target-rotation mechanism and a rotation-axis adjusting mechanism to obtain homogeneously doped films. Mg-doped GaN films have been fabricated on 6H-SiC(0001) and Si(111) substrates in NH3 ambient by simultaneous ablation of GaN and Mg-metal targets using two lasers. Junctions of the films with n-type substrates show a diode curve characteristic of p-n junctions, but not for junction with p-Si, indicating hole doping without further procedures. In situ p-type doping to SiC was also achieved by using SiC and Al4C3 targets.

  18. 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).

  19. Characteristics of Commercial SiC and Synthetic SiC as an Aggregate in Geopolymer Composites

    NASA Astrophysics Data System (ADS)

    Irfanita, R.; Afifah, K. N.; Asrianti; Subaer

    2017-03-01

    This main objective of this study is to investigate the effect silicon carbide (SiC) as an aggregate on the mechanical strength and microstructure of the geopolymer composites. The geopolymers binder were produced by using alkaline activation method of metakaolin and cured at 70oC for 2 hours. In this study commercial and synthetic SiC were used as aggregate to produce composite structure. Synthetic SiC was produced from rice husk ash and coconut shell carbon calcined at 750oC for 2 hours. The addition of SiC in geopolymers paste was varied from 0.25g, 0.50g to 0.75g to form geopolymers composites. The chemical compositions and crystallinity level of SiC and the resulting composites were measured by means of Rigaku MiniFlexII X-Ray Diffraction (XRD). The microstructure of SiC and the composites were examined by using Tescan Vega3SB Scanning Electron Microscopy (SEM). The physical and mechanical properties of the samples were determined based on apparent porosity, bulk density, and three bending flexural strength measurements. The results showed that the commercial and synthetic SiC were effectively produced geopolymers composites with different microstructure, physical and mechanical strength.

  20. High Temperature (250 deg C) SiC Power Module for Military Hybrid Electrical Vehicle Applications

    DTIC Science & Technology

    2011-08-09

    Schottky diodes, SiC JFETs, SiC MOSFETs, and SiC BJTs are now commercially available from multiple companies such as Cree, SemiSouth, Rohm, and...MINI-SYMPOSIUM AUGUST 9-11 DEARBORN, MICHIGAN HIGH TEMPERATURE (250 °C) SIC POWER MODULE FOR MILITARY HYBRID ELECTRICAL VEHICLE APPLICATIONS...performance SiC power modules, HT-2000, for military systems and applications. The HT-2000 series of modules are rated to 1200V, are operational to

  1. Surface and interface characterization of SiC and III-V nitrides

    NASA Astrophysics Data System (ADS)

    King, Sean Wesley

    1997-08-01

    The effects of various wet chemical and chemical vapor processes on the surfaces of (0001) silicon carbide (SiC), aluminum nitride (AlN), and gallium nitride (GaN) were investigated using x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), electron energy loss spectroscopy (EELS), temperature programmed desorption (TPD), and x-ray photoelectron diffraction (XPD). XPS was also used to determine both the (0001) GaN/AlN growth mechanisms as well as the AlN/SiC heterojunction valence band alignment. Scandium nitride (ScN) films were grown on 3C/6H-SiC (0001) substrates by gas source molecular beam epitaxy (GSMBE). Thermally oxidized surfaces of (0001)sbSi 6H-SiC were visually observed to be hydrophilic and terminated with a monolayer coverage of oxygen after oxide removal with HF. A dry cleaning process based on UV/ozone (Osb3) oxidation for carbon removal, followed by HF vapor exposure for oxide removal was demonstrated. Removal of the monolayer coverage of oxygen from (0001)sbSi 6H-SiC surfaces was achieved via chemical vapor cleaning (CVC) in a flux of silane (SiHsb4). Selective removal of silicon from (3 x 3) (0001)sbSi 6H-SiC surfaces by atomic H processes was observed by XPS. Wet chemical processes based on HF (HCl) were found to produce AlN (GaN) surfaces with the lowest oxygen coverages. XPS and AES studies showed fluorine (chlorine) termination of AlN (GaN) surfaces after HF (HCl) wet chemical processes. Desorption of F (Cl) from AlN (GaN) surfaces was not observed to occur until Tsb{sub} > 800sp° C (650sp°C). Annealing GaN surfaces in NHsb3 at 800sp°C was observed to remove both oxygen and carbon below the detection limits of both AES and XPS. Using XPS, it was determined that GaN growth on (0001) AlN by GSMBE occurred via a three dimensional Stranski-Krastonov growth mechanism at Tsb{sub} 800sp°C. A type I heterojunction valence band discontinuity of 1.4 ± 0.3 eV was determined for the (0001

  2. The Number Behind the Simplest SIC-POVM

    NASA Astrophysics Data System (ADS)

    Bengtsson, Ingemar

    2017-08-01

    The simple concept of a SIC poses a very deep problem in algebraic number theory, as soon as the dimension of Hilbert space exceeds three. A detailed description of the simplest possible example is given.

  3. Performance Limiting Defects in SiC Based Transistors

    DTIC Science & Technology

    2006-11-01

    measurements and very sensitive electrically detected magnetic resonance ( EDMR ) measurements to identify performance limiting defects in SiC based metal... EDMR measurements utilize spin- dependent recombination (SDR), a very sensitive electron spin resonance (ESR) technique which allows identification of

  4. Observations of Ag diffusion in ion implanted SiC

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 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. Estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. SiC Protective Coating for Photovoltaic Retinal Prostheses

    PubMed Central

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

    2016-01-01

    Objective To evaluate PECVD SiC 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 subretinally for up to 1 year. Degradation of implants was characterized by optical and scanning electron microscopy. Dissolution rates of SiC, SiNx 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 SiNx dissolved at 18.3±0.3nm/day, while SiO2 grown at high temperature (1000°C) dissolved at 1.04±0.08A/day. SiC films demonstrated the best stability, with no quantifiable change after 112 days. 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 days 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 560nm, as defined by anti-reflective properties and by sufficient coverage to eliminate defects. PMID:27323882

  12. 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

  13. UV-induced SiC nanowire sensors

    NASA Astrophysics Data System (ADS)

    Peng, Gang; Zhou, Yingqiu; He, Yanlan; Yu, Xiaoyan; Zhang, Xue A.; Li, Gong Y.; Haick, Hossam

    2015-02-01

    Ultraviolet (UV)-induced sensors based on a single SiC nanowire (NW) were fabricated and the photoelectric properties including I-V characteristics and time response of the UV sensors were studied. SiC NWs (NWs) were prepared through pyrolyzing a polymer precursor with ferrocene as the catalyst by a CVD route. To elucidate the physical mechanism giving rise to the photoelectrical response in SiC NW sensors, three kinds of contacts between electrodes and SiC NW were prepared, i.e. Schottky contact, p-n junction contact, and Ohmic contact. The photoelectric measurements of the device with Schottky contact indicates the lowest dark current and the largest photocurrent. The results suggest that photocurrent generated at SiC NW-electrode contacts is a result of the photovoltaic effect, in which a built-in electric field accelerates photo generated charge carriers to the electronic contacts. The UV sensors based on SiC NWs could be applied in a harsh environment due to the excellent physical stability and photoelectric properties.

  14. Enterphase Integrity of Neutron Irradiated SiC Composites

    SciTech Connect

    Lara-Curzio, E.; Snead, L.L.

    1999-11-30

    SiC/SiC composites were fabricated from Hi-Nicalon{trademark} fibers with carbon, porous SiC and multilayer SiC interphases. These materials were then irradiated in the High Flux Beam Reactor with fast neutrons at 260 and 900-1060 degrees C to a dose of 1.1X10{sup 25} n/m{sup 2} corresponding to 1.1 displacements per atom (dpa). Results are presented for bend strength of both non-irradiated and irradiated materials. Within the interphases studied the multilayer SiC interphase material showed the least degradation (8-20%) in ultimate bend stress, while porous SiC underwent the greatest degradation ({approximately}35%). The Fiber matrix interphases are studied with TEM for both nonirradiated and irradiated materials. While no irradiation induced microstructural evolution of the interphase was observed, debonding of the interphase from the fiber was observed for all cases. This debonding is attributed to tensile stresses developed at the interface due to densification of the Hi-Nicalon{trademark} fiber. Residual stress analysis of the fiber matrix interface indicates that the irradiation-induced densification of Hi-Nicalon{trademark} and the volumetric expansion of the CVD SiC matrix cause tensile stresses well in excess of those which can be withstood by these, or any other viable SiC composite interphase.

  15. Fabrication of SiC mat by radiation processing

    NASA Astrophysics Data System (ADS)

    Kang, Phil-Hyun; Jeun, Joon-Pyo; Seo, Dong-Kwon; Nho, Young-Chang

    2009-07-01

    Silicon carbide (SiC) exhibits many important properties, such as high intrinsic strength, stiffness, and high temperature stability. Therein, it is considered to be one of the most promising candidates for reinforcement of advanced ceramic matrix composites. The use of preceramic polymers presents the possibility of solving the intricacies involved in obtaining a new generation of ceramic materials. In this study, a radiation processing method was used to fabricate a cured polycarbosilane mat as a preceramic polymer. The polycarbosilane mat was cured by electron beam (e-beam) irradiation up to 10 MGy in an inert gas atmosphere. Next, the e-beam-cured PCS mat, as green fiber, was carbonized to produce the SiC mat. The conversion process of the PCS mat into the SiC mat was investigated by SEM, FT-IR, XRD, and TGA. According to FT-IR analysis, the Si-H peak intensity was observed to decrease as the polymer structure changed from polycarbosilane to SiC. The XRD patterns of SiC showed the diffraction peaks at (1 1 1), (2 2 0), and (3 1 1) which indicated the emergence of β-SiC. TGA curve shows that weight percent of residue of electrospun PCS mat, e-beam-cured PCS mat and pyrolyzed SiC mat up to 1000 °C were 72.5%, 88.3%, and 99.2%, respectively.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Mapping for Iterative MMSE-SIC with Belief Propagation

    NASA Astrophysics Data System (ADS)

    Gounai, Satoshi; Ohtsuki, Tomoaki; Kaneko, Toshinobu

    Multiple-Input Multiple-Output (MIMO) wireless systems offer both high data rates and high capacity. Since different signals are transmitted by different antennas simultaneously, interference occurs between the transmitted signals. Each receive antenna receives all the signals transmitted by each transmit antenna simultaneously. The receiver has to detect each signal from the multiplexed signal. A Minimum Mean Square Error (MMSE) algorithm is used for spatial filtering. MMSE filtering can realize low complexity signal detection, but the signal output by MMSE filtering suffers from interference by the other signals. MMSE-SIC combines MMSE filtering and Soft Interference Cancellation (SIC) with soft replicas and can achieve good Bit Error Rate (BER) performance. If an irregular LDPC code or a turbo code is used, the reliability and BER of the information bits output by the decoder are likely to be higher and better than the parity bits. In MMSE-SIC, bits with poor reliability lower the accuracy of soft replica estimation. When the soft replica is inaccurate, the gain obtained by SIC is small. M-ary Phase Shift Keying (PSK) and M-ary Quadrature Amplitude Modulation (QAM) also achieve high data rates. Larger constellations such as 8PSK and 16QAM transfer more bits per symbol, and the number of bits per symbol impacts the accuracy of SIC. Unfortunately, increasing the number of bits per symbol is likely to lower the accuracy of soft replica estimation. In this paper, we evaluate three mapping schemes for MMSE-SIC with an LDPC code and a turbo code with the goal of effectively increasing the SIC gain. The first scheme is information reliable mapping. In this scheme, information bits are assigned to strongly protected bits. In the second scheme, parity reliable mapping, parity bits are assigned to strongly protected bits. The last one is random mapping. Computer simulations show that in MMSE-SIC with an irregular LDPC code and a turbo code, information reliable mapping

  1. /SiC Composite to Titanium Alloy

    NASA Astrophysics Data System (ADS)

    Hernandez, X.; Jiménez, C.; Mergia, K.; Yialouris, P.; Messoloras, S.; Liedtke, V.; Wilhelmi, C.; Barcena, J.

    2014-08-01

    In view of aerospace applications, an innovative structure for joining a Ti alloy to carbon fiber reinforced silicon carbide has been developed. This is based on the perforation of the CMC material, and this procedure results in six-fold increase of the shear strength of the joint compared to the unprocessed CMC. The joint is manufactured using the active brazing technique and TiCuAg as filler metal. Sound joints without defects are produced and excellent wetting of both the composite ceramic and the metal is observed. The mechanical shear tests show that failure occurs always within the ceramic material and not at the joint. At the CMC/filler, Ti from the filler metal interacts with the SiC matrix to form carbides and silicides. In the middle of the filler region depletion of Ti and formation of Ag and Cu rich regions are observed. At the filler/Ti alloy interface, a layered structure of the filler and Ti alloy metallic elements is formed. For the perforation to have a significant effect on the improvement of the shear strength of the joint appropriate geometry is required.

  2. Detections of Long Carbon Chains CH_{3}CCCCH, C_{6}H, LINEAR-C_{6}H_{2} and C_{7}H in the Low-Mass Star Forming Region L1527

    NASA Astrophysics Data System (ADS)

    Araki, Mitsunori; Takano, Shuro; Sakai, Nami; Yamamoto, Satoshi; Oyama, Takahiro; Kuze, Nobuhiko; Tsukiyama, Koichi

    2017-06-01

    Carbon chains in the warm carbon chain chemistry (WCCC) region has been searched in the 42-44 GHz region by using Green Bank 100 m telescope. Long carbon chains C_{7}H, C_{6}H, CH_{3}CCCCH, and linear-C_{6}H_{2} and cyclic species C_{3}H and C_{3}H_{2}O have been detected in the low-mass star forming region L1527, performing the WCCC. C_{7}H was detected for the first time in molecular clouds. The column density of C_{7}H is derived to be 6.2 × 10^{10} cm^{-2} by using the detected J = 24.5-23.5 and 25.5-24.5 rotational lines. The ^{2}Π_{1/2} electronic state of C_{6}H, locating 21.6 K above the ^{2}Π_{3/2} electronic ground state, and the K_a = 0 line of the para species of linear-C_{6}H_{2} were also detected firstly in molecular clouds. The column densities of the ^{2}Π_{1/2} and ^{2}Π_{3/2} states of C_{6}H in L1527 were derived to be 1.6 × 10^{11} and 1.1 × 10^{12} cm^{-2}, respectively. The total column density of linear-C_{6}H_{2} is obtained to be 1.86 × 10^{11} cm^{-2}. While the abundance ratios of carbon chains in between L1527 and the starless dark cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP) have a trend of decrease by extension of carbon-chain length, column densities of CH_{3}CCCCH and C_{6}H are on the trend. However, the column densities of linear-C_{6}H_{2}, and C_{7}H are as abundant as those of TMC-1 CP in spite of long carbon chain, i.e., they are not on the trend. The abundances of linear-C_{6}H_{2} and C_{7}H show that L1527 is rich for long carbon chains as well as TMC-1 CP.

  3. Insights into Hydrocarbon Chain and Aromatic Ring Formation in the Interstellar Medium: Computational Study of the Isomers of C4H3+ C6H3+ and C6H5+ and Their Formation Pathways

    NASA Astrophysics Data System (ADS)

    Peverati, Roberto; Bera, Partha P.; Lee, Timothy J.; Head-Gordon, Martin

    2016-10-01

    Small hydrocarbons such as acetylene is present in circumstellar envelopes of carbon-rich stars, but the processes that yield larger molecules, and eventually polycyclic aromatic hydrocarbons (PAHs), remain poorly understood. To gain additional insight into the early steps of such processes, electronic structure calculations were performed on the potential energy surfaces of {{{C}}}4{{{{H}}}3}+, {{{C}}}6{{{{H}}}3}+ and {{{C}}}6{{{{H}}}5}+. The results establish reactive pathways from acetylene and its ion to formation of the first aromatic ring. We characterize the stable isomers, their spectroscopic properties, and many of the transition structures that represent barriers to isomerization. The pathways to stabilized {{{C}}}4{{{{H}}}3}+ and {{{C}}}6{{{{H}}}3}+ are most likely to arise from unimolecular decomposition of hot {{{C}}}4{{{{H}}}4}+ and {{{C}}}6{{{{H}}}4}+ by H atom elimination. By contrast, we found an ion-molecule pathway to {{{C}}}6{{{{H}}}5}+ to be very stable to fragmentation and elimination reactions even without collisional stabilization. This aromatic species is a good nucleation center for the growth of larger PAHs in interstellar conditions.

  4. Competitive solvation of K+ by C6H6 and H2O in the K+-(C6H6)n-(H2O)m (n = 1-4; m = 1-6) aggregates

    NASA Astrophysics Data System (ADS)

    Albertí, Margarita; Lago, Noelia Faginas

    2013-04-01

    The competitive solvation of the potassium ion by benzene and water is investigated at molecular level by means of Molecular Dynamics simulations on the K+-(C6H6) n -(H2O) m ( n = 1-4; m = 1-6) ionic aggregates. The preference of K+ to bind C6H6 or H2O is investigated in the range of temperatures in which isomerisation processes are likely by adding water and benzene to the K+-(C6H6) n and K+-(H2O) m aggregates, respectively. Hydrogen bonds and the π-hydrogen bond, in spite of their weakness with respect to the K+- π and K+-H2O interactions, play an important role in stabilising different isomers, thus favouring isomerisation processes. Accordingly with experimental information it has been found that K+ bind preferably C6H6 rather than H2O and that the fragmentation of C6H6 is only observed for aggregates containing four molecules of benzene.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. C6H5NH2 effect on the corrosion inhibition of aluminium in 0.5 M HCl

    NASA Astrophysics Data System (ADS)

    Omotosho, Olugbenga Adeshola; Okeniyi, Joshua Olusegun; Loto, Cleophas Akintoye; Popoola, Abimbola Patricia Idowu; Fademi, Ekundayo Oluwademilade Jacob; Oladipupo, Segun Isaac; Alabi, Ayomide Samuel; Ajibola, Omokolade Bamidele; Emelieze, Alex Nwabunor

    2017-02-01

    In this paper, C6H6NH2 (aniline) effect on the corrosion of aluminium in 0.5 M (i.e. mol/L) HCl medium was studied using gravimetric method by weight loss measurements and electrochemical technique of corrosion potential and potentiodynamic polarization by cyclic voltamery (CV) instrumentation. By these techniques, corrosion rate obtained from aluminium specimens, in 0.5 HCl test-solution having different concentrations of the hydrogen-containing C6H6NH2 chemical, were requisitely analysed. Results showed that the potentiodynamic corrosion rate excellently correlated (R = 98.94%, Nash-Sutcliffe efficiency = 97.89% and ANOVA p-value = 0.0314) with function of the gravimetric corrosion rate and C6H5NH2 concentration. Both experimental and correlated prediction models identified 0.043 mol/L C6H5NH2 with optimal inhibition efficiency performance η = 84.11% by the experimental or η = 81.15% by the predicted models. Fittings of experimental and correlated data showed the data models followed the Langmuir adsorption isotherm from which favourable adsorption and prevalent physisorption were indicated as the C6H5NH2 corrosion-protection on aluminium metal in the 0.5 M HCl medium.

  10. 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.

  11. Terahertz Luminescence and Electrical Characteristics of SiC Structures with Natural Superlattice in Strong Electric Fields

    NASA Astrophysics Data System (ADS)

    Sankin, V. I.; Andrianov, A. V.; Petrov, A. G.; Zakhar'in, A. O.; Nagalyuk, S. S.; Shkrebiy, P. P.

    2017-08-01

    Recently, the intense terahertz electroluminescence from monopolar n++-n--n+ structures of 8H-SiC natural superlattice at helium temperatures due to Bloch oscillations was found out. In the present work, we compare the THz emission and electrical characteristics of monopolar n++-n--n+ and bipolar n++-π-n+ 8H-SiC structures at 7 K. The bipolar n++-π-n+ 8H-SiC structures were analogous to those on which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H, and 8H) at T = 300 K. The obtained results allow one to draw a conclusion about common nature of the negative differential conductivity and THz emission effects in the natural superlattice of SiC caused by Bloch oscillations. These results give the proof of fundamental importance supporting the objectivity of postulates of the F. Bloch - C. Zener - G. N. Wannier theory

  12. 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.

  13. 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.

  14. 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.

  15. Influence of SiC surface polarity on the wettability and reactivity in an Al/SiC system

    NASA Astrophysics Data System (ADS)

    Shen, Ping; Wang, Yi; Ren, Lihua; Li, Shixin; Liu, Yuhua; Jiang, Qichuan

    2015-11-01

    The wetting of (0 0 0 1) 6H-SiC single crystals by molten Al was investigated using a dispensed sessile drop method in a high vacuum at 973-1173 K. The wettability and reactivity in this system are sensitive to the surface polarity of SiC. The interfacial reaction on the Si-terminated surface is rapid. The formation of a continuous Al4C3 product layer at the interface leads to an equilibrium contact angle of 56 ± 1° at 1173 K. In comparison, the interfacial reaction on the C-terminated surface is sluggish. The interface is only partially covered by discrete Al4C3 platelets even after dwelling at 1173 K for 2 h. The final wettability, however, is much better (θF = 41 ± 1°) than that of the Si-terminated surface which was covered by a dense Al4C3 layer, suggesting that the formation of Al4C3 should not always contribute to the wetting in the Al/SiC system. A plausible explanation is that the clean (i.e., deoxidized) C-terminated surface should be well wetted by molten Al in nature, owing to the strong chemical interactions between liquid Al and the surface atoms of the C-terminated SiC. It is likely that the presence of the oxide film at the surface of the molten Al drop or the SiC substrate and the rapid formation of Al4C3, which prevent the establishment of a real Al/SiC interface, conceal the intrinsic wettability of this system.

  16. Improvement on the electrical characteristics of Pd/HfO2/6H-SiC MIS capacitors using post deposition annealing and post metallization annealing

    NASA Astrophysics Data System (ADS)

    Esakky, Papanasam; Kailath, Binsu J.

    2017-08-01

    HfO2 as a gate dielectric enables high electric field operation of SiC MIS structure and as gas sensor HfO2/SiC capacitors offer higher sensitivity than SiO2/SiC capacitors. The issue of higher density of oxygen vacancies and associated higher leakage current necessitates better passivation of HfO2/SiC interface. Effect of post deposition annealing in N2O plasma and post metallization annealing in forming gas on the structural and electrical characteristics of Pd/HfO2/SiC MIS capacitors are reported in this work. N2O plasma annealing suppresses crystallization during high temperature annealing thereby improving the thermal stability and plasma annealing followed by rapid thermal annealing in N2 result in formation of Hf silicate at the HfO2/SiC interface resulting in order of magnitude lower density of interface states and gate leakage current. Post metallization annealing in forming gas for 40 min reduces interface state density by two orders while gate leakage current density is reduced by thrice. Post deposition annealing in N2O plasma and post metallization annealing in forming gas are observed to be effective passivation techniques improving the electrical characteristics of HfO2/SiC capacitors.

  17. 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.

  18. Exfoliation of graphene flake from SiC substrate using hydrogen injection; a first-principle study

    NASA Astrophysics Data System (ADS)

    Lee, Bora; Han, Seungwu; Kim, Yong-Sung

    2009-03-01

    Recently there is an immense interest in studying graphene for investigating its unique electronic properties as well as practical applications to nanoscale devices. Up to now there are two methods to obtain graphene layers. The first one is a mechanical method in which the single graphene sheet is split off the bulk graphite crystals using adhesives. The other method is graphitization of SiC surfaces by annealing at elevated temperatures. Even though the latter approach can provide a graphene layer in a more controlled way, the exfoliation of the graphene layer still poses a big challenge. In this presentation, based on the first-principles results, we propose a novel exfoliation method using hydrogen. As a model system, the 6H-SiC(0001) 4x4 cell is used, which corresponds to the 3x3 graphene cell. We calculate the binding energy of single hydrogen atom in various places; above and below graphene surface and inside the first SiC layer. The binding energies of hydrogen are calculated for different coverages. It is found that at high coverages, the hydrogen atoms prefer to bind below the graphene surface, cutting the graphene-SiC bonds. This means that the graphene can be exfoliated in the hydrogen-rich environment. The detailed analysis including the electronic structures will be presented.

  19. CONDENSED MATTER: STRUCTURE, THERMAL AND MECHANICAL PROPERTIES: SiC based Si/SiC heterojunction and its rectifying characteristics

    NASA Astrophysics Data System (ADS)

    Zhu, Feng; Chen, Zhi-Ming; Li, Lian-Bi; Zhao, Shun-Feng; Lin, Tao

    2009-11-01

    The Si on SiC heterojunction is still poorly understood, although it has a number of potential applications in electronic and optoelectronic devices, for example, light-activated SiC power switches where Si may play the role of an light absorbing layer. This paper reports on Si films heteroepitaxially grown on the Si face of (0001) n-type 6H-SiC substrates and the use of B2H6 as a dopant for p-Si grown at temperatures in a range of 700-950 °C. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) tests have demonstrated that the samples prepared at the temperatures ranged from 850 °C to 900 °C are characterized as monocrystalline silicon. The rocking XRD curves show a well symmetry with FWHM of 0.4339° Omega. Twin crystals and stacking faults observed in the epitaxial layers might be responsible for widening of the rocking curves. Dependence of the crystal structure and surface topography on growth temperature is discussed based on the experimental results. The energy band structure and rectifying characteristics of the Si/SiC heterojunctions are also preliminarily tested.

  20. Optical spectroscopy of ZnSiF6·6H2O:Mn4+ red phosphor

    NASA Astrophysics Data System (ADS)

    Hoshino, Ryosuke; Adachi, Sadao

    2013-12-01

    We report on a method of synthesizing Mn4+-activated ZnSiF6.6H2O hydrate phosphor by the chemical reaction in a Teflon beaker. The structural and optical properties of ZnSiF6.6H2O:Mn4+ are investigated using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, diffuse reflectance measurement, and Raman scattering spectroscopy. The synthesized phosphor exhibits a series of sharp red emission peaks at ˜630 nm, which is characteristic for Mn4+ ions. The luminescent study is focused on the thermal quenching phenomenon above ˜300 K and is found to be caused by thermal decomposition of the ZnSiF6.6H2O host. Degradation in the PL intensity under near-UV light illumination has also been observed to occur in this phosphor.

  1. Nucleation Mechanism of 6H-SiC Polytype Inclusions Inside 15R-SiC Crystals

    SciTech Connect

    Zhang, Y.; Zhang, L.; Chen, H.; Choi, G.; Raghothamachar, B.; Dudley, M.; Edgar, J.H.; Grasza, K.; Tymicki, E.; Su, D.; Zhu, Y.

    2010-06-01

    A model is presented for the nucleation mechanism of 6H-SiC polytype inclusions inside 15R-SiC boules. Inhomogeneous densities of screw dislocations lead to uneven growth rates, resulting in complex step overgrowth processes which can partially suppress the Burgers vector of a 15R 1c screw dislocation through the creation of Frank faults and Frank partial dislocations. Combined with stacking shifts induced by the passage of basal plane partial dislocations, it is shown that the partial Burgers vector suppression can leave behind a residual 6H 1c dislocation, which then acts as a nucleus for reproduction of 6H-SiC structure in the 15R-SiC crystal.

  2. Magneto-optical investigation of MgSO3·6H2O with polarized light

    NASA Astrophysics Data System (ADS)

    Petkova, P.

    2017-10-01

    The crystals of magnesium sulphite hexahydrate (MgSO3·6H2O) belong to point group C3 (no center of symmetry). They possess gyrotropy and nonlinear optical properties. The refractive index no and ne, the angle of Faraday rotation φ(λ), the Verdet constant V(λ), the magneto-optic anomaly factor γ(λ) and the density of oscillators N of MgSO3·6H2O single crystals have been studied in the present work. The investigations were carried out in the spectral range 300 - 800 nm with linear polarized light E ⃗ ⊥ c ̅ , E ⃗ | | c ̅ (c ̅ is the optical axis of MgSO3·6H2O) propagated in the direction (10 1 ̅ 0) .

  3. 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.

  4. 1,1'-Fc(4-C6H4CO2Et)2 and its unusual salt derivative with Z' = 5, catena-[Na+]2[1,1'-Fc(4-C6H4CO2-)2].0.6H2O [1,1'-Fc = (eta5-(C5H4)2Fe].

    PubMed

    Gallagher, John F; Alley, Steven; Brosnan, Marianne; Lough, Alan J

    2010-04-01

    The neutral diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate, Fe[eta(5)-(C(5)H(4))(4-C(6)H(4)CO(2)Et)](2) (I), yields (II) (following base hydrolysis) as the unusual complex salt poly[disodium bis[diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate] 0.6-hydrate] or [Na(+)](2)[Fe{eta(5)-(C(5)H(4))-4-C(6)H(4)CO(2)(-)}(2)].0.6H(2)O with Z' = 5. Compound (I) crystallizes in the triclinic system, space group P1, with two molecules having similar geometry in the asymmetric unit (Z' = 2). The salt complex (II) crystallizes in the orthorhombic system, space group Pbca, with the asymmetric unit comprising poly[decasodium pentakis[diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate] trihydrate] or [Na(+)](10)[Fe{eta(5)-(C(5)H(4))-4-C(6)H(4)CO(2)(-)}(2)](5).3H(2)O. The five independent 1,1'-Fc[(4-C(6)H(4)CO(2))(-)](2) dianions stack in an offset ladder (stepped) arrangement with the ten benzoates mutually oriented cisoid towards and bonded to a central layer comprising the ten Na(+) ions and three water molecules [1,1'-Fc = eta(5)-(C(5)H(4))(2)Fe]. The five dianions differ in the cisoid orientations of their pendant benzoate groups, with four having their -C(6)H(4)- groups mutually oriented at interplanar angles from 0.6 (3) to 3.2 (3) degrees (as pi...pi stacked C(6) rings) and interacting principally with Na(+) ions. The fifth dianion is distorted and opens up to an unprecedented -C(6)H(4)- interplanar angle of 18.6 (3) degrees through bending of the two 4-C(6)H(4)CO(2) groups and with several ionic interactions involving the three water molecules (arranged as one-dimensional zigzag chains in the lattice). Overall packing comprises two-dimensional layers of Na(+) cations coordinated mainly by the carboxylate O atoms, and one-dimensional water chains. The non-polar Fc(C(6)H(4))(2) groups are arranged perpendicular to the layers and mutually interlock through a series of efficient C-H...pi stacking contacts in a herringbone fashion to produce an overall segregation of polar and non

  5. Deposition of hydroxyapatite on SiC nanotubes in simulated body fluid.

    PubMed

    Taguchi, Tomitsugu; Miyazaki, Toshiki; Iikubo, Satoshi; Yamaguchi, Kenji

    2014-01-01

    SiC nanotubes can become candidate reinforcement materials for dental and orthopedic implants due to their light weight and excellent mechanical properties. However, the development of bioactive SiC materials has not been reported. In this study, hydroxyapatites were found on SiC nanotubes treated with NaOH and subsequently HCl solution after soaking in simulated body fluid. On the other hand, hydroxyapatites did not deposit on as-received SiC nanotubes, the SiC nanotubes with NH4OH solution treatment and SiC bulk materials with NaOH and subsequently HCl solution treatment. Therefore, we succeeded in the development of bioactive SiC nanotubes by downsizing SiC materials to nanometer size and treating with NaOH and subsequently HCl solutions for the first time.

  6. Chemical reactivity of SiC fibre-reinforced SiC with beryllium and lithium ceramic breeder materials

    NASA Astrophysics Data System (ADS)

    Kleykamp, H.

    2000-12-01

    SiC fibre-reinforced SiC fabrics (f-SiC/SiC) are considered for structural materials of advanced fusion blanket concepts. Priority tasks are compatibility studies of SiC with Li breeder ceramics and the Be neutron multiplier. Isothermal and anisothermal powder reactions by DTA up to 1220°C were examined between Li 4SiO 4, Li 2ZrO 3 and Li 2TiO 3, respectively, and SiC and SiC/SiO 2 mixtures, respectively. The SiC/SiO 2 mixture simulated the chemical state of Nicalon fibres. Solid state reactions between SiC and Be pellets were studied by capsule experiments. The reaction products Be 2C and Si were observed between the initial phases after annealing at 800°C and 900°C. A parabolic time law with a chemical diffusion coefficient D˜=2.6×10 -15 m 2/s of Be in the products was deduced at 900°C. Additional oxygen released from SiO 2 as a component of the simulated fibres oxidised the reaction products via the gas phase by formation of a Be 2SiO 4 layer. All reactions are kinetically hindered below 700°C.

  7. Thermochemistry and growth mechanism of SiC nanowires

    NASA Astrophysics Data System (ADS)

    Chen, Jianjun; Ding, Lijuan; Xin, Lipeng; Zeng, Fan; Chen, Jun

    2017-09-01

    The chemical reaction thermodynamics and a novel two-stage growth mechanism of SiC nanowires synthesized by carbothermal reduction reactions were investigated based on the Si-C-O systems over a wide temperature range (1050 ≤ T ≤ 2000 K). The carbothermal reduction reaction process involves the fast formation of gaseous SiO and CO crucial intermediates, and the further carbon reduction of SiO to SiC. The relationship between the free energy changes and temperature at different pressures was also discussed. Some fundamental data in the work can help to analyze the thermochemistry of the carbothermal reduction reaction in the Si-C-O system, which is beneficial to optimize the temperature, pressure and the input precursors for controlling the SiC nanowire growth.

  8. Nitrogen Isotopes in SiC: Stellar Nucleosynthesis?

    NASA Astrophysics Data System (ADS)

    Huss, G. R.; Nichols, R. H., Jr.; Wasserburg, G. J.

    1995-09-01

    Nitrogen in presolar SiC varies over a wide range of concentrations and is typically 14N-rich relative to solar N, consistent with 15N being consumed during CNO processing in stellar envelopes [e.g. 1]. Although C is also heavily processed in the envelopes [1], no clear isotopic correlation exists between C and N [e.g. 2], making N-compositions difficult to interpret. Although the same general N features are seen in SiC from many meteorites, clear differences between meteorites have also been observed. In particular, Murchison SiC appears to have systematically higher 15N/14N ratios than Orgueil SiC [2, 3]. Among 15N-poor SiC grains for both meteorites, 15N/14N and 28Si/14N exhibit a positive correlation (Fig. 1). This indicates that a 15N-rich component has been added in roughly constant abundance (relative to Si), affecting the low-N grains most. The slope of the line bounding the field of Murchison SiC data is ~10x greater than that for Orgueil SiC (Fig. 1), implying that Murchison grains carry on average ~10x more of the 15N-rich component. If both meteorites sampled the same presolar SiC reservoir, as indicated by isotope systematics of other elements [3], then the 15N-rich component could not have been acquired at the stellar source or in interstellar space. Spallation in the early solar system can also be excluded. Although the pre-compaction exposure age for Murchison (>= 145 Ma [4]) is considerably longer than the total exposure history of Orgueil (~25 Ma [5]), 15N production rates [6] are 500_2000x too low to explain the data. A more likely scenario is that terrestrial N (15N/14N~0.0037) has been acquired by the grains during sample processing. Measured 15N/14N ratios seldom exceed that of terrestrial N (Fig. 1). A minimum of ~2.5 x 10^-5 atoms of 14N(sub)terr per 28Si atom (0.01%_0.1% of the 14N in a grain) is required to produce the correlation observed for Orgueil; >=10x more is required for Murchison. Systematic differences between SiC grain

  9. 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.

  10. 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.

  11. Selective epitaxial growth of graphene on SiC

    NASA Astrophysics Data System (ADS)

    Camara, N.; Rius, G.; Huntzinger, J.-R.; Tiberj, A.; Mestres, N.; Godignon, P.; Camassel, J.

    2008-09-01

    We present a method of selective epitaxial growth of few layers graphene (FLG) on a "prepatterned" silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with e-beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ˜1582cm-1 in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

  12. Selective epitaxial growth of graphene on SiC

    SciTech Connect

    Camara, N.; Rius, G.; Godignon, P.; Huntzinger, J.-R.; Tiberj, A.; Camassel, J.

    2008-09-22

    We present a method of selective epitaxial growth of few layers graphene (FLG) on a ''prepatterned'' silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with e-beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at {approx}1582 cm{sup -1} in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

  13. 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.

  14. 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.

  15. Characterization of Intrinsic Defects in High-Purity High-Resistivity p-Type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Matsuura, Hideharu; Yanase, Hirokazu; Takahashi, Miyuki

    2008-09-01

    The densities, cross sections, and energy levels of intrinsic defects in high-purity high-resistivity (approximately 106 Ω cm) p-type 6H-SiC are determined using isothermal capacitance transient spectroscopy (ICTS). Five intrinsic defects are detected ranging from 0.76 to 1.35 eV above the valence band. Since the sum of the densities of intrinsic defects detected is the same order of magnitude as the acceptor density in the p-type 6H-SiC, the intrinsic defects are found to decrease the majority-carrier concentration making its resistivity as high as approximately 106 Ω cm.

  16. Growth of improved quality 3C-SiC films on 6H-SiC substrates

    NASA Technical Reports Server (NTRS)

    Powell, J. A.; Matus, L. G.; Choyke, W. J.; Bradshaw, J. L.; Larkin, D. J.

    1990-01-01

    Previously reported chemical vapor deposition of 3C-SiC on 6H-SiC has resulted in films with a high density of double positioning boundaries (DPBs). It is found that growth on as-grow faces of 6H-SiC crystals can yield films that are largely free of DPBs. The (111) 3C-SiC films, up to 12 microns thick, were evaluated by optical and electron microscopy and low-temperature photoluminescence (LTPL). The LTPL spectra of the films were similar to those of high quality Lely-grown 3C-SiC.

  17. Correlation of EBIC and SWBXT Imaged Defects and Epilayer Growth Pits in 6H-SiC Schottky Diodes

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    We show the first direct experimental correlation between the presence of closed core screw dislocations in 6H-SiC epilayers with recombination centers, as well as with some of the small growth pits on the epilayer surface in lightly-doped 6H-SiC Schottky diodes. At every Synchrotron White-Beam X-ray Topography (SWBXT)-identified closed core screw dislocation, an Electron Beam Induced Current (EBIC) image showed a dark spot indicating a recombination center, and Nomarski optical microscope and Atomic Force Microscope (AFM) images showed a corresponding small growth pit with a sharp apex on the surface of the epilayer.

  18. Band alignment of InN/6H-SiC heterojunction determined by x-ray photoelectron spectroscopy

    SciTech Connect

    Jing, Qiang; Wu, Guoguang; Zhang, Yuantao; Gao, Fubin; Cai, Xupu; Zhao, Yang; Li, Wancheng Du, Guotong

    2014-08-11

    The valence band offset (VBO) of InN/6H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be −0.10 ± 0.23 eV and the conduction band offset is deduced to be −2.47 ± 0.23 eV, indicating that the heterojunction has a type-II band alignment. The accurate determination of the valence and conduction band offsets is important for applications and analysis of InN/6H-SiC optoelectronic devices.

  19. Modeling the Thermostructural Stability of Melt-infiltrated Sic/sic Composites

    NASA Technical Reports Server (NTRS)

    DiCarlo, James A.; Bhatt, Ramakrishna T.; McCue, Terry R.

    2003-01-01

    SiC/SiC composites developed by NASA with Sylramic-iBN fibers and melt-infiltrated (MI) SiC-Si matrices have demonstrated 1000-hour rupture life in air at 100 MPa and 1315OC. Recently it has been determined that a major factor controlling the long-term rupture life of these composites is not environment or stress, but an intrinsic microstructural and strength instability caused by a thermally-induced silicon attack of the Sic fibers. The objective of this paper is to present a simple diffusion-based analytical model which predicts well the observed effects of stress-free thermal exposure on the residual tensile strength of Sylramic-iBN/SiC-Si composites. The practical implications of the model for SiC/SiC composites with MI matrices are discussed.

  20. Synthesis of a Bulk Ti4SiC3 MAX Phase by Reduction of TiO2 with SiC.

    PubMed

    Istomin, Pavel; Istomina, Elena; Nadutkin, Aleksandr; Grass, Vladislav; Presniakov, Mikhail

    2016-11-07

    The bulk MAX phase Ti4SiC3 was first synthesized with a yield of 86% by a long-time thermal treatment of TiO2 and SiC powder mixture with a molar ratio of 2:3 at 1600 °C under vacuum conditions. It was found that the appearance of Ti4SiC3 was preceded by the formation of TiC and Ti3SiC2 as a result of the following reactions: (1) combined carbothermic and silicothermic reduction of TiO2 to TiC accompanied by evolution of SiO and CO gases; (2) silicidation of TiC with gaseous SiO, leading to the growth of Ti3SiC2. It was suggested that, apart from TiC and Ti3SiC2 solids, sublimed gaseous species such as Ti, Si, Si2C, SiC2, etc., could take part in the Ti4SiC3 formation that occurred in the next stage. The crystal structure of synthesized Ti4SiC3 was refined by X-ray diffraction Rietveld analysis and confirmed by high-resolution scanning transmission electron microscopy. The measured structural characteristics of bulk Ti4SiC3 are in good agreement with those predicted by ab initio calculations reported in the literature.

  1. On the Band Gap Variation in SiC Polytypes

    NASA Astrophysics Data System (ADS)

    van Haeringen, W.; Bobbert, P. A.; Backes, W. H.

    1997-07-01

    Electronic band gaps of SiC polytypes are reproduced within an interface matching technique of electronic wave functions. Essential features resulting from this treatment are introduced in a one-dimensional model, leading to a transparent description of the electronic band gap variation among polytypes. It is discussed in what sense the polytypes of SiC are exceptional in showing a relatively strong band gap variation, contrary to e.g. polytypes of ZnS and hypothetical polytypes made up from Si, C or AlAs.

  2. 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.

  3. Packaging Technology for SiC High Temperature Electronics

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu; Neudeck, Philip G.; Spry, David J.; Meredith, Roger D.; Nakley, Leah M.; Beheim, Glenn M.; Hunter, Gary W.

    2017-01-01

    High-temperature environment operable sensors and electronics are required for long-term exploration of Venus and distributed control of next generation aeronautical engines. Various silicon carbide (SiC) high temperature sensors, actuators, and electronics have been demonstrated at and above 500 C. A compatible packaging system is essential for long-term testing and application of high temperature electronics and sensors in relevant environments. This talk will discuss a ceramic packaging system developed for high temperature electronics, and related testing results of SiC integrated circuits at 500 C facilitated by this high temperature packaging system, including the most recent progress.

  4. 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.

  5. Study of the K2Ni(SO4)2 • 6H2O-K2Co(SO4)2 • 6H2O-H2O diagram and determination of the conditions for growing K2(Ni,Co)(SO4)2 • 6H2O mixed crystals

    NASA Astrophysics Data System (ADS)

    Zhokhov, A. A.; Masalov, V. M.; Zverkova, I. I.; Emelchenko, G. A.; Manomenova, V. L.; Rudneva, E. B.; Vasilieva, N. A.; Voloshin, A. E.

    2016-11-01

    The phase diagram of the K2Ni(SO4)2 · 6H2O-K2Co(SO4)2 · 6H2O-H2O ternary system is investigated in the temperature range of 30-70°C, and a relationship between the compositions of the equilibrium phases of the K2Co x Ni(1- x)(SO4)2 · 6H2O (KCNSH) solid solution and the growth solution is established. It is shown how the salt compositions of the liquid and solid phases change during crystal growth upon slow cooling of solution. A dependence of the lattice parameters of the KCNSH solid solution on the concentration of isomorphic components is experimentally found.

  6. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... bottling mineral or spring water (previously classified under SIC 5149, Groceries and Related Products, NEC... classified under SIC 2819, Industrial Inorganic chemicals, NEC (recovering sulfur from natural gas..., separating, etc. of minerals in SIC 1499)); 488390Other Support Activities for Water Transportation Limited...

  7. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... bottling mineral or spring water (previously classified under SIC 5149, Groceries and Related Products, NEC... classified under SIC 2819, Industrial Inorganic chemicals, NEC (recovering sulfur from natural gas..., separating, etc. of minerals in SIC 1499)); 488390Other Support Activities for Water Transportation Limited...

  8. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... bottling mineral or spring water (previously classified under SIC 5149, Groceries and Related Products, NEC... classified under SIC 2819, Industrial Inorganic chemicals, NEC (recovering sulfur from natural gas..., separating, etc. of minerals in SIC 1499)); 488390Other Support Activities for Water Transportation Limited...

  9. 40 CFR 372.23 - SIC and NAICS codes to which this Part applies.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... bottling mineral or spring water (previously classified under SIC 5149, Groceries and Related Products, NEC... classified under SIC 2819, Industrial Inorganic chemicals, NEC (recovering sulfur from natural gas..., separating, etc. of minerals in SIC 1499)); 488390Other Support Activities for Water Transportation Limited...

  10. Influence of microstructure on hydrothermal corrosion of chemically vapor processed SiC composite tubes

    NASA Astrophysics Data System (ADS)

    Kim, Daejong; Lee, Ho Jung; Jang, Changheui; Lee, Hyeon-Geun; Park, Ji Yeon; Kim, Weon-Ju

    2017-08-01

    Multi-layered SiC composites consisting of monolithic SiC and a SiCf/SiC composite are one of the accident tolerant fuel cladding concepts in pressurized light water reactors. To evaluate the integrity of the SiC fuel cladding under normal operating conditions of a pressurized light water reactor, the hydrothermal corrosion behavior of multi-layered SiC composite tubes was investigated in the simulated primary water environment of a pressurized water reactor without neutron fluence. The results showed that SiC phases with good crystallinity such as Tyranno SA3 SiC fiber and monolithic SiC deposited at 1200 °C had good corrosion resistance. However, the SiC phase deposited at 1000 °C had less crystallinity and severely dissolved in water, particularly the amorphous SiC phase formed along grain boundaries. Dissolved hydrogen did not play a significant role in improving the hydrothermal corrosion resistance of the CVI-processed SiC phases containing amorphous SiC, resulting in a significant weight loss and reduction of hoop strength of the multi-layered SiC composite tubes after corrosion.

  11. 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

  12. Reaction of 6H-6-oxo-3(5)-halogenoanthra(1,9-cd)isoxazoles with inorganic nucleophiles

    SciTech Connect

    Gornostaev, L.M.; Zeibert, G.F.

    1986-11-20

    The reaction of 6H-6-oxo-3(5)-halogenoanthral(1,9-cd)isoxazoles with sodium azide in DMFA and also the potassium fluoride in acetonitrile in the presence of crown ethers leads to nucleophilic substitution of the halogen by the azide and fluoride ion respectively.

  13. Laboratory submillimeter transition frequencies of Li-7H and Li-6H. [used for abundance investigations in red giant stars

    NASA Technical Reports Server (NTRS)

    Plummer, G. M.; Herbst, E.; De Lucia, F. C.

    1984-01-01

    The fundamental (J = 1 - 0) rotational transition frequencies of Li-7H and Li-6H in their ground (v = 0) vibrational states and of Li-7H in its first excited (v = 1) vibrational state have been measured in the laboratory. Use of these transition frequencies should permit astronomical investigations of LiH abundances in red giant stars of high lithium abundance.

  14. Spectroscopic and thermochemical properties of the c-C6H7 radical: A high-level theoretical study

    NASA Astrophysics Data System (ADS)

    Bargholz, Arne; Oswald, Rainer; Botschwina, Peter

    2013-01-01

    The electronic ground state (tilde X{}^2B_1) of the cyclohexadienyl radical (c-C6H7) has been studied by explicitly correlated coupled cluster theory at the RCCSD(T)-F12x (x = a, b) level, partly in combination with the double-hybrid density functional method B2PLYP. An accurate equilibrium structure has been established and the ground-state rotational constants are predicted to be A0 = 5347.3 MHz, B0 = 5249.7 MHz, and C0 = 2692.5 MHz. The calculated vibrational wavenumbers agree well with the recent p-H2 matrix IR data [M. Bahou, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012), 10.1063/1.3703502] and several predictions have been made. A low value of 6.803 ± 0.005 eV is predicted for the adiabatic ionization energy of c-C6H7. Owing to a moderately large change in the equilibrium structure upon ionization, the first band of the photoelectron spectrum is dominated by the adiabatic peak (100%) and only the peaks corresponding to excitation of the two lowest totally symmetric vibrations (ν12 and ν11) by one vibrational quantum have relative intensities of more than 15%. The C6H6-H dissociation energy is calculated to be D0 = 85.7 kJ mol-1, with an estimated error of ˜2 kJ mol-1.

  15. 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 of...

  16. 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

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Formaldehyde, polymer with... 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...

  17. 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

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Formaldehyde, polymer with... 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...

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

    USDA-ARS?s Scientific Manuscript database

    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...

  19. Time-course of cerebral perfusion and tissue oxygenation in the first 6 h after experimental subarachnoid hemorrhage in rats.

    PubMed

    Westermaier, Thomas; Jauss, Alina; Eriskat, Jörg; Kunze, Ekkehard; Roosen, Klaus

    2009-04-01

    Present knowledge about hemodynamic and metabolic changes after subarachnoid hemorrhage (SAH) originates from neuromonitoring usually starting with aneurysm surgery and animal studies that have been focusing on the first 1 to 3 h after SAH. Most patients, however, are referred to treatment several hours after the insult. We examined the course of hemodynamic parameters, cerebral blood flow, and tissue oxygenation (ptiO2) in the first 6 h after experimental SAH. Sixteen Sprague-Dawley rats were subjected to SAH using the endovascular filament model or served as controls (n=8). Bilateral local cortical blood flow, intracranial pressure, cerebral perfusion pressure, and ptiO2 were followed for 6 h after SAH. After induction of SAH, local cortical blood flow rapidly declined to 22% of baseline and returned to 80% after 6 h. The decline of local cortical blood flow markedly exceeded the decline of cerebral perfusion pressure. ptiO2 declined to 57%, recovered after 2 h, and reached > or =140% of baseline after 6 h. Acute vasoconstriction after SAH is indicated by the marked discrepancy of cerebral perfusion pressure and local cortical blood flow. The excess tissue oxygenation several hours after SAH suggests disturbed oxygen utilization and cerebral metabolic depression. Aside from the sudden increase of intracranial pressure at the time of hemorrhage and delayed cerebral vasospasm, the occurrence of acute vasoconstriction and disturbed oxygen utilization may be additional factors contributing to secondary brain damage after SAH.

  20. Damage Profiles and Ion Distribution in Pt-irradiated SiC

    SciTech Connect

    Xue, Haizhou; Zhang, Yanwen; Zhu, Zihua; Zhang, Weiming; Bae, Dr. In-Tae; Weber, William J

    2012-01-01

    Single crystalline 6H-SiC samples were irradiated at 150 K using 2MeV Pt ions. Local volume swelling is determined by electron energy loss spectroscopy (EELS), a nearly sigmoidal dependence with irradiation dose is observed. The disorder profiles and ion distribution are determined by Rutherford backscattering spectrometry (RBS), transmission electron microscopy and secondary ion mass spectrum. Since the volume swelling reaches 12% over the damage region under high ion fluence, lattice expansion is considered and corrected during the data analysis of RBS spectra to obtain depth profiles. Projectile and damage profiles are estimated by SRIM (Stopping and Range of Ions in Matter). Comparing with the measured profiles, SRIM code significantly overestimates the electronic stopping power for the slow heavy Pt ions, and large derivations are observed in the predicted ion distribution and the damage profiles. Utilizing the reciprocity method that is based on the invariance of the inelastic excitation in ion atom collisions against interchange of projectile and target, much lower electronic stopping 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. Better damage profile and ion range are predicted.

  1. Damage Profiles and Ion Distribution in Pt-irradiated SiC

    SciTech Connect

    Xue, Haizhou; Zhang, Yanwen; Zhu, Zihua; Zhang, Weiming; Bae, In-Tae; Weber, William 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.

  2. The effect of substrate type on SiC nanowire orientation.

    PubMed

    Attolini, Giovanni; Rossi, Francesca; Bosi, Matteo; Watts, Bernard Enrico; Salviati, Giancarlo

    2011-05-01

    beta-SiC nanowires were synthesized on different monocrystalline substrates: Si (001), Si (111), 3C-SiC (001), 4H-SiC (0001), 6H-SiC (0001). The SiC nanowire growth was carried out using a Chemical Vapor Deposition method, with silane and propane diluted in hydrogen (3%) as precursors. The deposition was performed at atmospheric pressure and at 1100 degrees C, after dewetting of the Ni catalyst, which had been previously evaporated onto the substrate, to induce 1D growth according to a VLS process. The crystal structure of the nanowires, as determined by X-ray diffraction and High Resolution Transmission Electron Microscopy, corresponds to 3C-SiC polytype growing along a (111) direction, irrespective of the substrate. The occurrence of (111) stacking faults was observed, partly reduced for samples grown on 3C-SiC substrate. The growth on (111) substrate allowed to achieve a good vertical alignment of the nanowires, as investigated by Scanning Electron Microscopy. High Angle Annular Dark Field imaging and Energy Dispersive X-Ray spectroscopy were performed to study the catalyst particle on top of the wires and showed the formation of a nickel-silicon alloy.

  3. Spectroscopic Ellipsometry, Auger and STM Characterization of Epitaxial Graphene grown on 6H-SiC (0001)

    NASA Astrophysics Data System (ADS)

    Nelson, Florence; Diebold, Alain C.; Sandin, Andreas; Dougherty, Dan; Aspnes, Dave; Rowe, Jack

    2012-02-01

    Graphene grown by the thermal decomposition of SiC has become of interest to the semiconductor industry due to its unique, high-mobility electronic structure. The growth is of a more scalable nature when compared to exfoliated flakes produced from the ``scotch tape'' method. The resulting film rests on a ``buffer layer'' separating the graphene from the underlying substrate, which is thought to consist of a mixture of sp^2 and non-sp^2 bonding due to the sp^3 bonding of the SiC substrate. The mobilities of the graphene layer have previously been shown to differ from that of the interface layer. We investigate the difference in the optical response of the two layers using Spectroscopic Ellipsometry and find a red-shift of the ˜4.5 eV absorbance found in graphene due to the exciton-domianted transition at the M point of the Brilloun Zone. The structural characterization of the films are performed through Auger and STM on substrates which were cleaned by CMP and chemical etching methods prior to the epitaxial growth in UHV.

  4. Synthesis, spectra, and theoretical investigations of the triarylamines based on 6H-indolo[2,3-b]quinoxaline.

    PubMed

    Thomas, K R Justin; Tyagi, Payal

    2010-12-03

    Triarylamines containing a 6H-indolo[2,3-b]quinoxaline core and aromatic units such as phenyl, naphthyl, pyrene, anthracene, or fluorene have been synthesized by employing palladium-catalyzed C-N and C-C coupling reactions and characterized by optical absorption and emission spectra, electrochemical behavior, and thermal studies. Even though the electronic absorption spectra of the compounds were influenced by the nature of the peripheral amines, the emission spectra indicated close similarity for the excited states in these compounds. For the derivatives in which the amines were directly anchored on the 6H-indolo[2,3-b]quinoxaline nucleus, the emission appeared to be dominated by the state localized on the 6H-indolo[2,3-b]quinoxaline chromophore, while in the compounds containing the extended conjugation the fluorescence originated from the polyaromatic linker. The compounds displayed green or yellow emission depending on the nature of the amine segment. All of the dyes displayed one-electron quasi-reversible oxidation couple in the cyclic voltammograms, which is attributable to the oxidation of the peripheral amines at the 6H-indolo[2,3-b]quinoxaline core. An additional one-electron oxidation process observable at the high positive potentials for the compounds 7 and 8 probably arises from the oxidation of the arylthiophene segment. The enhanced thermal stability and relatively higher glass transition temperatures observed for these compounds were attributed to the presence of dipolar 6H-indolo[2,3-b]quinoxaline segment. The origin of the optical spectra and the trends observed therein were rationalized using TDDFT simulations.

  5. Passivation of SiC device surfaces by aluminum oxide

    NASA Astrophysics Data System (ADS)

    Hallén, A.; Usman, M.; Suvanam, S.; Henkel, C.; Martin, D.; Linnarsson, M. K.

    2014-03-01

    A steady improvement in material quality and process technology has made electronic silicon carbide devices commercially available. Both rectifying and switched devices can today be purchased from several vendors. This successful SiC development over the last 25 years can also be utilized for other types of devices, such as light emitting and photovoltaic devices, however, there are still critical problems related to material properties and reliability that need to be addressed. This contribution will focus on surface passivation of SiC devices. This issue is of utmost importance for further development of SiC MOSFETs, which so far has been limited by reliability and low charge carrier surface mobilities. Also bipolar devices, such as BJTs, LEDs, or PV devices will benefit from more efficient and reliable surface passivation techniques in order to maintain long charge carrier lifetimes. Silicon carbide material enables the devices to operate at higher electric fields, higher temperatures and in more radiation dense applications than silicon devices. To be able to utilize the full potential of the SiC material, it is therefore necessary to develop passivation layers that can sustain these more demanding operation conditions. In this presentation it will also be shown that passivation layers of Al2O3 deposited by atomic layer deposition have shown superior radiation hardness properties compared to traditional SiO2-based passivation layers.

  6. 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.

  7. 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.

  8. 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.

  9. Chromium Isotopes in Presolar SiC Grains

    NASA Astrophysics Data System (ADS)

    Savina, M. R.; Levine, J.; Stephan, T.; Dauphas, N.; Davis, A. M.; Knight, K. B.; Pellin, M. J.

    2010-03-01

    The Cr isotopic composition of presolar SiC grains does not account for the anomalies noted in leachates of carbonaceous chondrites, nor does it agree with s-process nucleosynthesis models. It may be reflective of the origin material in the star that produced the grains.

  10. -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.

  11. Observations of Ag diffusion in ion implanted SiC

    DOE PAGES

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; ...

    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

  12. Epitaxial graphene on SiC{0001}: advances and perspectives.

    PubMed

    Norimatsu, Wataru; Kusunoki, Michiko

    2014-02-28

    We review here recent progress on epitaxial graphene grown on a SiC substrate. Epitaxial graphene can be easily grown by heating the SiC single crystal in a high vacuum or in an inert gas atmosphere. The SiC surfaces used for graphene growth contain Si- and C-terminated faces. On the Si-face, homogeneous and clean graphene can be grown with a controlled number of layers, and the carrier mobility reaches as high as several m(2) V s(-1), although this is reduced by the presence of the substrate steps. On the C-face, although the number of layers is not homogeneous, twisted bilayer graphene can be grown, which is expected to be the technique of choice to modify the electronic structure of graphene. From the application point of view, graphene on SiC will be the platform used to fabricate high-speed electronic devices and dense graphene nanoribbon arrays, which will be used to introduce a bandgap.

  13. Validation of the Symptoms of Illness Checklist (SIC) as a tool for health psychology research.

    PubMed

    Stowell, Jeffrey R; Hedges, Dawson W; Ghambaryan, Anna; Key, Colin; Bloch, George J

    2009-01-01

    We developed the Symptoms of Illness Checklist (SIC) to study psychological influences on physical symptoms of illness. A total of 520 participants completed the SIC and, in some samples, the Salient Stressor Impact Questionnaire, Perceived Stress Scale, Daily Hassles and Uplifts Scale, Derogatis Stress Profile, Life Experiences Survey, and the Symptoms CheckList-90-R. The SIC's test-retest, internal reliability, and validity verified by physician ratings, were very good. SIC correlations with diverse stress measures were less inflated than those of other instruments indicating the SIC is a reliable and valid tool to study psychological influences on physical illness.

  14. 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.

  15. 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

  16. 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

  17. PhySIC: a veto supertree method with desirable properties.

    PubMed

    Ranwez, Vincent; Berry, Vincent; Criscuolo, Alexis; Fabre, Pierre-Henri; Guillemot, Sylvain; Scornavacca, Celine; Douzery, Emmanuel J P

    2007-10-01

    This paper focuses on veto supertree methods; i.e., methods that aim at producing a conservative synthesis of the relationships agreed upon by all source trees. We propose desirable properties that a supertree should satisfy in this framework, namely the non-contradiction property (PC) and the induction property (PI). The former requires that the supertree does not contain relationships that contradict one or a combination of the source topologies, whereas the latter requires that all topological information contained in the supertree is present in a source tree or collectively induced by several source trees. We provide simple examples to illustrate their relevance and that allow a comparison with previously advocated properties. We show that these properties can be checked in polynomial time for any given rooted supertree. Moreover, we introduce the PhySIC method (PHYlogenetic Signal with Induction and non-Contradiction). For k input trees spanning a set of n taxa, this method produces a supertree that satisfies the above-mentioned properties in O(kn(3) + n(4)) computing time. The polytomies of the produced supertree are also tagged by labels indicating areas of conflict as well as those with insufficient overlap. As a whole, PhySIC enables the user to quickly summarize consensual information of a set of trees and localize groups of taxa for which the data require consolidation. Lastly, we illustrate the behaviour of PhySIC on primate data sets of various sizes, and propose a supertree covering 95% of all primate extant genera. The PhySIC algorithm is available at http://atgc.lirmm.fr/cgi-bin/PhySIC.

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  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

    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.

  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 photo shows the progress of the S-IC test stand as of October 10, 1963. Kerosene storage tanks can be seen to the left.

  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 photograph taken March 29, 1963, gives a close up look at two of the ever-growing four towers of the S-IC Test Stand.

  11. 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.

  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 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.

  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 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.

  15. Chemical reactivity of CVC and CVD SiC with UO2 at high temperatures

    NASA Astrophysics Data System (ADS)

    Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; Snead, Lance L.

    2015-05-01

    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. However, 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 1500 °C. Furthermore, 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.

  16. On the existence of Si-C double bonded graphene-like layers

    NASA Astrophysics Data System (ADS)

    Huda, Muhammad N.; Yan, Yanfa; Al-Jassim, Mowafak M.

    2009-09-01

    Upon analyzing an earlier experimental study by density-functional theory we have shown that graphene-like SiC layers can exist. We found that, for a particular stacking sequence, Si dbnd C double bond was responsible for the much larger interlayer distances observed in synthesized multi-walled SiC nanotubes. The Si/C ratios in SiC layers determine the extent of interlayer distances and bonding nature. It has been also shown that for some intermediate ratios of Si:C and/or with other stacking sequences, a collapse of SiC layers to tetrahedrally bonded system is possible. We have argued that these synthesized Si dbnd C double-bonded multi-wall silicon-carbide nanotubes may provide a pathway for future realization of SiC graphene-like materials.

  17. LOW ACTIVATION JOINING OF SIC/SIC COMPOSITES FOR FUSION APPLICATIONS: MODELING DUAL-PHASE MICROSTRUCTURES AND DISSIMILAR MATERIAL JOINTS

    SciTech Connect

    Henager, Charles H.; Nguyen, Ba Nghiep; Kurtz, Richard J.; Ferraris, M.; Katoh, Y.

    2016-03-31

    Finite element continuum damage models (FE-CDM) have been developed to simulate and model dual-phase joints and cracked joints for improved analysis of SiC materials in nuclear environments. This report extends the analysis from the last reporting cycle by including results from dual-phase models and from cracked joint models.

  18. Current transport property of n-GaN /n-6H-SiC heterojunction: Influence of interface states

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Fung, S.; Beling, C. D.; Ling, C. C.; Dai, X. Q.; Xie, M. H.

    2005-03-01

    Heterostructures of n-GaN /n-6H-SiC grown by hydride vapor phase epitaxy (HVPE) and molecular-beam epitaxy (MBE) are characterized with the current-voltage (I-V), capacitance-voltage (C-V), and deep level transient spectroscopy (DLTS) techniques. Using different contact configurations, the I -V results reveal a rectifying barrier in the n-GaN /n-6H-SiC heterostructures. When GaN is negatively biased, the current is exponentially proportional to the applied voltage with the built-in barrier being 0.4-1.1eV for the HVPE samples and 0.5eV for the MBE sample. DLTS measurements reveal intense band-like deep level states in the interfacial region of the heterostructure, and the Fermi-level pinning by these deep level defects is invoked to account for the interfacial rectifying barrier of the heterostructures.

  19. Surface birefringence of self-assembly periodic nanostructures induced on 6H-SiC surface by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Song, Juan; Dai, Ye; Tao, Wenjun; Gong, Min; Ma, Guohong; Zhao, Quanzhong; Qiu, Jianrong

    2016-02-01

    In this paper, we report the birefringence effect of surface self-assembly periodic nanostructures induced on 6H-SiC by femtosecond laser irradiation. Birefringence characteristic (e.g. cross-polarized image), measured by cross polarized microscopy, was found to be controlled by both single pulse energy and scanning velocity. Comparing birefringence measurement results of nanostructures and morphology characterization by Scanning electron microscopy, it is shown that ∼200 nm-period deep-subwavelength periodic ripples (DSWR) plays a dominating role in the birefringence effect. Raman spectra show that the change of retardance with pulse energy and scanning velocity is most possibly caused by the thickness variation of DSWR. Finally, a light attenuator based on a single layer of DSWR structure on 6H-SiC surface was constructed and tested by light source of 800 nm to have a tunable attenuating ratio of 69-100%.

  20. FeCl3·6H2O-catalyzed intramolecular allylic amination: synthesis of substituted dihydroquinolines and quinolines.

    PubMed

    Wang, Zhiming; Li, Shen; Yu, Bin; Wu, Haibo; Wang, Yurong; Sun, Xiaoqiang

    2012-10-05

    A facile and efficient method to synthesize 2- or 4-substituted 1,2-dihydroquinolines and quinolines catalyzed by FeCl(3)·6H(2)O (2 mol %) was described. The iron-catalyzed intramolecular allylic amination of 2-aminophenyl-1-en-3-ols proceeded smoothly to afford 13 1,2-dihydroquinoline and 8 quinoline derivatives under mild reaction conditions with good to excellent yields (up to 96%).

  1. Synthesis of benzidine derivatives via FeCl3·6H2O-promoted oxidative coupling of anilines.

    PubMed

    Ling, Xuege; Xiong, Yan; Huang, Ruofeng; Zhang, Xiaohui; Zhang, Shuting; Chen, Changguo

    2013-06-07

    Under open-flask conditions in the presence of commercially available FeCl3·6H2O, N,N-disubstituted anilines can be converted into diversely functionalized benzidines with yields of up to 99%. Oxidative coupling was extended to N-monosubstituted anilines, and the method was applied to the efficient preparation of 6,6'-biquinoline. Mechanistic investigations have also been performed to explain the observed reactivities.

  2. 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).

  3. Low Earth Orbit Space Environment Testing of Extreme Temperature 6H-SiC JFETs on the International Space Station

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Prokop, Norman F.; Greer, Lawrence C., III; Chen, Liang-Yu; Krasowski, Michael J.

    2010-01-01

    This paper reports long-term electrical results from two 6H-SiC junction field effect transistors (JFETs) presently being tested in Low Earth Orbit (LEO) space environment on the outside of the International Space Station (ISS). The JFETs have demonstrated excellent functionality and stability through 4600 hours of LEO space deployment. Observed changes in measured device characteristics tracked changes in measured temperature, consistent with wellknown JFET temperature-dependent device physics.

  4. Cascade synthesis of polyoxygenated 6H,11H-[2]benzopyrano-[4,3-c][1]benzopyran-11-ones.

    PubMed

    Naumov, Mikael I; Sutirin, Sergey A; Shavyrin, Andrey S; Ganina, Olga G; Beletskaya, Irina P; Bourgarel-Rey, Véronique; Combes, Sébastien; Finet, Jean-Pierre; Fedorov, Alexey Yu

    2007-04-27

    2-(methoxymethoxymethyl)aryllead triacetates, obtained in situ from the corresponding arylboronic acids, reacted with 4-hydroxycoumarins, leading to 3-(2-methoxymethoxymethyl)aryl-4-hydroxycoumarin derivatives in good to high yields. These compounds underwent a cascade sequence of reactions, deprotection-halogenation-annulation, to afford polyoxygenated tetracyclic 6H,11H-[2]benzopyrano-[4,3-c] [1]benzopyran-11-ones in good yields. Some compounds showed a moderate cytotoxicity against human epithelial mammary HBL100 cells.

  5. Enhancing the scopolamine production in transgenic plants of Atropa belladonna by overexpressing pmt and h6h genes.

    PubMed

    Wang, Xirong; Chen, Min; Yang, Chunxian; Liu, Xiaoqiang; Zhang, Lei; Lan, Xiaozhong; Tang, Kexuan; Liao, Zhihua

    2011-12-01

    Atropa belladonna is officially deemed as the commercial plant to produce scopolamine in China. In this study we report the simultaneous overexpression of two functional genes involved in biosynthesis of scopolamine, which encode the upstream key enzyme putrescine N-methyltransferase (PMT) and the downstream key enzyme hyoscyamine 6β-hydroxylase (H6H), respectively, in transgenic herbal plants Atropa belladonna. Analysis of gene expression profile indicated that both pmt and h6h were expressed at a higher level in transgenic lines, which would be favorable for biosynthesis of scopolamine. High-performance liquid chromatography result suggested that transgenic lines could produce higher accumulation of scopolamine at different levels compared with wild-type lines. Scopolamine content increased to 7.3-fold in transgenic line D9 compared with control lines. This study not only confirms that co-overexpression of pmt and h6h is an ideal method to improve the biosynthetic capacity of scopolamine but also successfully cultivates the transgenic line D9, which significantly enhanced the scopolamine accumulation. Our research can serve as an alternative choice to provide scopolamine resources for relative industry, which is more competitive than conventional market.

  6. Self-assembly of amphiphilic peptide (AF)6H5K15 derivatives: roles of hydrophilic and hydrophobic residues.

    PubMed

    Thota, Naresh; Jiang, Jianwen

    2014-03-13

    A molecular dynamics simulation study is reported to investigate the roles of hydrophilic and hydrophobic residues in the self-assembly of (AF)6H5K15 peptide derivatives. The peptide, as well as water and counterions, are represented by the MARTINI coarse-grained model. The assembly is observed to follow a three-step process: formation of small clusters, large clusters, and micelles. With increasing length of hydrophilic Lys residues in (AF)6H5Kn (n = 10, 15, 20, and 25), assembly capability is found to be reduced with the formation of smaller micelles or the presence of individual peptide chains. Upon replacing Ala by more hydrophobic Phe in AmFnH5K15 (m + n = 12), larger micelles are formed. With increasing length of hydrophobic Phe residues in FnH5K15 (n = 4, 8, 12, and 16), micelle size increases and the morphology shifts from spherical to fiber-like. The simulation study provides mechanistic insight into the crucial roles of hydrophilicity and hydrophobicity in the assembly of (AF)6H5K15 derivatives; it reveals that assembly capability is reduced by increasing hydrophilicity, whereas increasing hydrophobicity leads to morphology transition.

  7. Generation of gas-phase sodiated arenes such as [(Na3(C6H4)+] from benzene dicarboxylate salts.

    PubMed

    Attygalle, Athula B; Chan, Chang-Ching; Axe, Frank U; Bolgar, Mark

    2010-01-01

    Upon collision-induced activation, gaseous sodium adducts generated by electrospray ionization of disodium salts of 1,2- 1,3-, and 1,4-benzene dicarboxylic acids (m/z 233) undergo an unprecedented expulsion of CO(2) by a rearrangement process to produce an ion of m/z 189 in which all three sodium atoms are retained. When isolated in a collision cell of a tandem-in-space mass spectrometer, and subjected to collision-induced dissociation (CID), only the m/z 189 ions derived from the meta and para isomers underwent a further CO(2) loss to produce a peak at m/z 145 for a sodiated arene of formula (Na(3)C(6)H(4))(+). This previously unreported m/z 145 ion, which is useful to differentiate meta and para benzene dicarboxylates from their ortho isomer, is in fact the sodium adduct of phenelenedisodium. Moreover, the m/z 189 ion from all three isomers readily expelled a sodium radical to produce a peak at m/z 166 for a radical cation [(*C(6)H(4)CO(2)Na(2))(+)], which then eliminated CO(2) to produce a peak at m/z 122 for the distonic cation (*C(6)H(4)Na(2))(+). Copyright 2009 John Wiley & Sons, Ltd.

  8. 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

  9. High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC

    NASA Astrophysics Data System (ADS)

    Liu, Yu-Zhu; Li, Bing-Sheng; Zhang, Li

    2017-05-01

    Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The < 0001> -oriented 6H-SiC wafers are implanted with 15 keV helium ions at a dose of 1 × 10 17 cm -2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473 K for 30 min. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273 K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealing abides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120-135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236 eV. Supported by the National Natural Science Foundation of China under Grant No 11475229.

  10. Evidence from Broadband Rotational Spectroscopy for a Complex Between AgCCH and C6H6

    NASA Astrophysics Data System (ADS)

    Zaleski, Daniel P.; Stephens, Susanna Louise; Walker, Nick; Legon, Anthony

    2014-06-01

    Last year, at the 68th International Symposium of Molecular Spectroscopy, the rotational spectrum of a complex formed between C2H2 and AgCCH was presented. The geometry was found to be T-shaped with the silver atom coordinated to the center of the CC bond in acetylene. Evidence for a new complex formed between AgCCH and C6H6 is now presented in the form of deep-averaged broadband rotational spectra. The spectra are observed only when both C2H2 and C6H6 are present in the gas sample. The relative intensities of the observed spectra are consistent with the naturally-occurring abundance ratio of the isotopes of silver. The shift on substitution of 107Ag for 109Ag implies a silver atom positioned close to the center of mass. The isotopic shifts observed when C2D2 is used as a precursor instead of C2H2 are also consistent with assignment to a complex formed between C6H6 and AgCCH/D. The geometry of the complex is yet to be precisely established.

  11. Deep level defect studies in semi-insulating 4H- and 6H-silicon carbide using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    The objective of this study is to determine the deep vanadium defect levels in semi-insulating 4H- and 6H- silicon carbide using optical admittance spectroscopy. Also infrared spectroscopy and electron paramagnetic resonance spectroscopy are conducted to support the evidence of vanadium donor and acceptor levels obtained from OAS measurements. Vanadium acts as an amphoteric impurity in silicon carbide with a V3+/4+ acceptor level and V4+/5+ donor level. Although the value for the donor level is well established, the V3+/4+ defect level remains controversial. OAS shows that the vanadium donor level is isolated near Ec-1.7 eV, and the vanadium acceptor level is located at Ec-0.75 eV at a cubic site and Ec-0.94 eV at a hexagonal site in 4H-SiC, while the vanadium donor level of 6H-SiC samples is about Ec-1.5 eV. The acceptor levels of 6H-SiC were assigned to Ec-0.67 eV, E c -0.70 eV at two cubic sites, and Ec-0.87 eV at a hexagonal site. IR spectra demonstrated that the signatures of the vanadium V 3+ and V4+ charge states are present in the samples. EPR and photo-induced EPR are used to identify the V3+/4+ and V4+/5+ levels as well as the V3+ and V 4+ charge states. EPR spectra represent both V3+ and V4+ in 4H- and 6H samples consistent with FTIR data. EPR and photo-induced EPR suggest that the va nadium acceptor level is between 0.7 eV and 0.86 eV, while the donor level is near Ec-1.5 eV in 6H-SiC. The donor level of 4H-SiC is located at Ec-1.6 eV. Thus, the data obtained from EPR and FTIR support the assignment of the vanadium defect levels determined by OAS. Vanadium complexes induced by other elements such as titanium, hydrogen, and nitrogen atoms are also observed in OAS spectra and will be discussed in the text.

  12. 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

  13. Total cross sections of electron scattering by C4H8O, C5H10O2, C6H5F, C6H5Cl, C6F5Cl, C6H4(CHO)F and C4H8O2 at 30-5000 eV

    NASA Astrophysics Data System (ADS)

    Shi, D. H.; Liu, Y. F.; Ma, H.; Yu, B. H.; Sun, J. F.; Zhu, Z. L.

    2008-08-01

    Total cross sections for electron scattering by large molecules C4H8O, C5H10O2, C6H5F, C6H5Cl, C6F5Cl, C6H4(CHO)F and C4H8O2 are calculated at the Hartree-Fork level using the modified additivity rule approach. The modified additivity rule approach, which was proposed by Shi et al. [Eur. Phys. J. D 45, 253 (2007); Nucl. Instrum. Meth. B 254, 205 (2007)], takes into consideration that the contributions of the geometric shielding effect vary with the energy of the incident electrons, the target’s molecular dimension and the atomic and electronic numbers of the molecule. The present calculations cover the collision energies ranging from 30 to 5000 eV. The quantitative total cross sections are compared with those obtained by experiments and other theories. Good agreement is obtained even at energies of several tens of eV. It shows that the modified additivity rule approach is applicable to calculate the total cross sections of electron scattering by so large molecules at intermediate and high energies, especially above 100 eV. The total cross sections for electron scattering by the C4H8O2 molecule are predicted although no experimental and theoretical data are available for comparison over the present energy region.

  14. Crystal structure, quantum mechanical study and spectroscopic studies of nitrate and perchlorate salts of 3-chloroaniline, [C6H7ClN]NO3 (I) and [C6H7ClN]ClO4 (II)

    NASA Astrophysics Data System (ADS)

    Bayar, I.; Khedhiri, L.; Jeanneau, E.; Lefebvre, F.; Ben Nasr, C.

    2017-06-01

    Two new organic-inorganic hybrid compounds, 3-chloroanilinium nitrate (I) and 3-chloanilinium perchlorate (II), have been synthesized by an acid/base reaction at room temperature in the presence of 3-chloroaniline as an organic-structure directing agent and their structures were determined by single crystal X-ray diffraction. Compound I, [C6H7ClN]NO3, crystallizes in the orthorhombic space group Pbca with a = 10.4137(16), b = 9.6232(11), c = 16.059(2) Å, V = 1609.3(4) and z = 8. Full-matrix least-squares refinement converged at R = 0.041 and Rw = 0.121. Compound II, [C6H7ClN]ClO4, belongs to the monoclinic system, space group P21/n with the following parameters: a = 10.684(2), b = 7.2667(12), c = 12.229(2) Å, β = 104.27(2)°, V = 920.1(3) and z = 4. The structure was refined to R = 0.054 and Rw = 0.102. Both salts form anionic parallel layers alternating with thick slabs of [C6H7NCl]+ organic molecules. Charge balance is achieved by the protonated amine which interacts with the inorganic framework through hydrogen bonding. Solid-state 13C CP-MAS NMR spectroscopy is in agreement with the X-ray structures. Ab initio calculations allow the partial attribution of carbon signals to the various atoms of the organic groups. Electronic properties such as HOMO and LUMO energies were studied by Quantum mechanical evaluation by using the B3LYP/6-31+G* method.

  15. Astrocyte-Dependent Slow Inward Currents (SICs) Participate in Neuromodulatory Mechanisms in the Pedunculopontine Nucleus (PPN)

    PubMed Central

    Kovács, Adrienn; Pál, Balázs

    2017-01-01

    Slow inward currents (SICs) are known as excitatory events of neurons caused by astrocytic glutamate release and consequential activation of neuronal extrasynaptic NMDA receptors. In the present article we investigate the role of these astrocyte-dependent excitatory events on a cholinergic nucleus of the reticular activating system (RAS), the pedunculopontine nucleus (PPN). It is well known about this and other elements of the RAS, that they do not only give rise to neuromodulatory innervation of several areas, but also targets neuromodulatory actions from other members of the RAS or factors providing the homeostatic drive for sleep. Using slice electrophysiology, optogenetics and morphological reconstruction, we revealed that SICs are present in a population of PPN neurons. The frequency of SICs recorded on PPN neurons was higher when the soma of the given neuron was close to an astrocytic soma. SICs do not appear simultaneously on neighboring neurons, thus it is unlikely that they synchronize neuronal activity in this structure. Occurrence of SICs is regulated by cannabinoid, muscarinic and serotonergic neuromodulatory mechanisms. In most cases, SICs occurred independently from tonic neuronal currents. SICs were affected by different neuromodulatory agents in a rather uniform way: if control SIC activity was low, the applied drugs increased it, but if SIC activity was increased in control, the same drugs lowered it. SICs of PPN neurons possibly represent a mechanism which elicits network-independent spikes on certain PPN neurons; forming an alternative, astrocyte-dependent pathway of neuromodulatory mechanisms. PMID:28203147

  16. 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.

  17. Operating procedure for SiC defect detection: Data support document

    SciTech Connect

    Adams, C.C.; Partain, K.E.

    1989-09-29

    The feasibility of the Hg Intrusion QC method for measuring SiC coating defects for the MHTGR was conducted as a potential improvement for the Burn/Leach (B/L) QC method currently used. The purpose for evaluating the Hg Intrusion QC method as an alternative method was to determine if B/L QC method underestimated SiC coating defects. Some evidence in work conducted earlier, indicated that TRISO-coated fuel particles with low SiC coating defects measured by the B/L QC method showed higher releases of metallic fission products. These data indicated that the SiC coating defect fractions were higher than the B/L measured data indicated. Sample sizes used in the current study were too small to conclusively demonstrate that the B/L QC method under estimate SiC coating defects. However, observations made during this study indicated a need for an additional QC method to the B/L QC method to measure SiC coating defects for the higher quality MHTGR fuels. The B/L QC method is the best method for measuring SiC coating defects with missing SiC layers or broken SiC coatings (gross SiC defects). However, SiC coating defects with microcracks and other SiC defects not detected by the B/L method may contribute to the release of metallic fission products in-service. For these type of SiC coating defects, the Hg Intrusion QC method investigated in this study is feasible, but particle sample size should be increased to a much larger sample size (100,000 particles per test) for the MHTGR. 7 refs., 5 figs., 9 tabs.

  18. Progress of d0 magnetism in SiC

    NASA Astrophysics Data System (ADS)

    Wang, Yutian; Liu, Chenguang; Zhang, Yuming

    2017-03-01

    The properties of defect-induced ferromagnetism ({{{d}}}0 magnetism) in SiC belong to carbon-based material which has been systematically investigated after graphite. In this paper, we reviewed our research progress about {{{d}}}0 magnetism in two aspects, i.e., magnetic source and magnetic coupling mechanism. The {{{V}}}{{Si}} {{{V}}}{{C}} divacancies have been evidenced as the probable source of {{{d}}}0 magnetism in SiC. To trace the ferromagnetic source in microscopic and electronic view, the p electrons of the nearest-neighbor carbon atoms, which are around the {{{V}}}{{Si}} {{{V}}}{{C}} divacancies, are sourced. For magnetic coupling mechanism, a higher divacancy concentration leads to stronger paramagnetic interaction but not stronger ferromagnetic coupling. So the {{{d}}}0 magnetism can probably be explained as a local effect which is incapable of scaling up with the volume.

  19. 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).

  20. Laser synthesis of carbon-rich SiC nanoribbons

    NASA Astrophysics Data System (ADS)

    Salama, I. A.; Quick, N. R.; Kar, A.

    2003-06-01

    A nanosecond pulsed laser direct-write and doping (LDWD) technique is used for the fabrication of carbon-rich silicon carbide nanoribbons heterostructure in a single crystal 4H-SiC wafer. Characterization by high-resolution transmission electron microscope and selected area electron diffraction pattern revealed the presence of nanosize crystalline ribbons with hexagonal graphite structure in the heat-affected zone below the decomposition temperature isotherm in the SiC epilayer. The nanoribbons exist in three layers each being approximately 50-60 nm thick, containing 15-17 individual sheets. The layers are self-aligned on the (0001) plane of the SiC epilayer with their c axis at 87° to the incident laser beam. The LDWD technique permits synthesis of heterostructured nanoribbons in a single step without additional material or catalyst, and effectively eliminates the need for nanostructure handling and transferring processes.

  1. Research on microwave joining of SiC

    SciTech Connect

    1995-12-31

    The objectives of this research project are to identify optimum time-temperature profiles for the microwave joining of silicon carbide and to develop new microwave joining methods that can be applied to accomplish in situ formation of silicon carbide interlayers and to join larger samples required for industrial applications. Work during this reporting period was focused on investigation of the effect of specimen preparation on joining of SiC using polymer precursors to form SiC in situ at the interface. During this period, LANL also completed the evaluation of joints that were made by FMT using four different joining temperatures, as part of an effort to determine optimum joining temperature.

  2. 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.

  3. STM characterization of a graphitized SiC(0001)surface

    NASA Astrophysics Data System (ADS)

    Brar, Victor; Zhang, Yuanbo; Yayon, Yossi; Ohta, Taisuke; McChesney, Jessica; Rotenberg, Eli; Crommie, Mike

    2007-03-01

    The two-dimensional electron gas in a single graphene sheet exhibits unique properties due the cone-shaped electron band structure near the Fermi energy. Recently the growth of a single layer of graphene on SiC(0001) has been demonstrated, opening new possibilities for fabricating large scale graphene-based devices. We have performed scanning tunneling microscopy and spectroscopy of single and bi-layer graphene films on SiC(0001). Atomically resolved topographs and dI/dV maps show clear differences between the single and bi-layer surfaces at different length scales. We have characterized the energy dependence and spatial distribution of the electron local density of states in these single and bi-layer films.

  4. SiC Particle Reinforced Al Matrix Composite by SIMA

    NASA Astrophysics Data System (ADS)

    Aydın, Emirhan; Yuksel, Caglar; Erzi, Eray; Dispinar, Derya

    Strain Induced Melt Activated (SIMA) method is one of the most commonly used techniques for producing near-net-shape parts. The alloy is heated to liquid+solid region and then forged into the die cavity. In this way, homogeneously distributed spherical structure can be obtained. There are no works in the literature on the use of SIMA to produce p/MMC. A cast alloy (A380) and a wrought alloy (A6063) was selected. There different SiC particle size were sieved to be in the range of 50-120 μm. The highest wettability was obtained in 6063 however there was almost no binding in A380. Impact and wear tests were carried to characterise the properties of SiC p/MMC.

  5. The SiC Direct Target Prototype for SPES

    SciTech Connect

    Rizzi, Valentina; Andrighetto, Alberto; Antonucci, C.; Barbui, Marina; Biasetto, Lisa; Carturan, S.; Celona, L.; Cevolani, S.; Chines, Francesco; Cinausero, Marco; Colombo, P.; Cuttone, G.; Di Bernardo, P.; Giacchini, Mauro; Gramegna, Fabiana; Lollo, M.; Maggioni, G.; Manzolaro, Mattia; Meneghetti, G.; Messina, G. Esteban; Petrovich, C.; Piga, L.; Prete, Gianfranco; Re, Maurizio; Rizzo, D.; Stracener, Daniel W; Tonezzer, Michele; Zanonato, P.

    2007-01-01

    A R&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 niA 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. 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.

  7. 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.

  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 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.

  9. 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.

  10. EBSD investigation of SiC for HTR fuel particles

    NASA Astrophysics Data System (ADS)

    Helary, D.; Dugne, O.; Bourrat, X.; Jouneau, P. H.; Cellier, F.

    2006-05-01

    Electron back-scattering diffraction (EBSD) can be successfully performed on SiC coatings for HTR fuel particles. EBSD grain maps obtained from thick and thin unirradiated samples are presented, along with pole figures showing textures and a chart showing the distribution of grain aspect ratios. This information is of great interest, and contributes to improving the process parameters and ensuring the reproducibility of coatings.

  11. 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.

  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 this photo, taken June 24, 1963, the four tower legs of the test stand can be seen at their maximum 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, depicts the progress of the stand as of January 14, 1963, with its four towers prominently rising.

  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. This construction photo depicts the progress of the stand site as of October 8, 1962.

  15. A study of SiC decomposition under laser irradiation

    NASA Astrophysics Data System (ADS)

    Adelmann, B.; Hellmann, R.

    2017-06-01

    In this experimental study we investigate the laser induced thermal decomposition of 4H-Sic under ambient conditions using fiber laser. Using a unique two-color pyrometer setup, we measure the temporal evolution of the temperature in the irradiated zone and determine the decomposition rate for various laser power levels. We find that the temporal evolution of the temperature in the irradiated area exhibits an initial heating phase up to about 1300 K, being characterized by an unaffected SiC surface. Upon an expeditious temperature increase, a decomposition phase follows with temperatures above 1700 K, being accompanied by carbonization of the SiC surface. The decomposed volume depends linearly on the duration of the decomposition phase and increases linearly with laser power. The temperature evaluation of the decomposition speed reveals an Arrhenius-type behavior allowing the calculation of the activation energy for the decomposition under ambient conditions to 613 kJ/mol in the temperature range between 2140 and 2420 K.

  16. 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.

  17. SiC X-ray detectors for harsh environments

    NASA Astrophysics Data System (ADS)

    Lees, J. E.; Barnett, A. M.; Bassford, D. J.; Stevens, R. C.; Horsfall, A. B.

    2011-01-01

    We have characterised a number of SiC Schottky Diodes as soft X-ray photon counting detectors over the temperature range -30°C to +80°C. We present the spectroscopic performance, as measured over the energy range ~ 6 keV-30 keV and correlate the data with measurements of the temperature dependence of the device leakage current. The results show that these detectors can be used for X-ray photon counting spectroscopy over a wide temperature range. Measurement of the radiation tolerance of Semi Transparent SiC Schottky Diodes (STSSD) has shown that these devices can still operate as photon counting X-ray spectrometers after proton irradiation (total dose of 1013 cm-2, 50 MeV). We present measurements on proton irradiated STSSDs that indicate that radiation induced traps, located in the upper half of the bandgap, have reduced the mobility and concentration of charge carriers. X-ray spectra predicted using a Monte Carlo model for SiC diodes are compared with measured spectra.

  18. SYLRAMIC™ SiC fibers for CMC reinforcement

    NASA Astrophysics Data System (ADS)

    Jones, Richard E.; Petrak, Dan; Rabe, Jim; Szweda, Andy

    2000-12-01

    Dow Corning researchers developed SYLRAMIC SiC fiber specifically for use in ceramic-matrix composite (CMC) components for use in turbine engine hot sections where excellent thermal stability, high strength and high thermal conductivity are required. This is a stoichiometric SiC fiber with a high degree of crystallinity, high tensile strength, high tensile modulus and good thermal conductivity. Owing to the small diameter, this textile-grade fiber can be woven into 2-D and 3-D structures for CMC fabrication. These properties are also of high interest to the nuclear community. Some initial studies have shown that SYLRAMIC fiber shows very good dimensional stability in a neutron flux environment, which offers further encouragement. This paper will review the properties of SYLRAMIC SiC fiber and then present the properties of polymer impregnation and pyrolysis (PIP) processed CMC made with this fiber at Dow Corning. While these composites may not be directly applicable to applications of interest to this audience, we believe that the properties shown will give good evidence that the fiber should be suitable for high temperature structural applications in the nuclear arena.

  19. Using SiC for Lightweight EUV Space Optics

    NASA Astrophysics Data System (ADS)

    Martinez-Galarce, Dennis S.; Boerner, P.; De Pontieu, B.; Katz, N.; Title, A.; Soufli, R.; Robinson, J. C.; Baker, S. L.; Gullikson, E. M.

    2009-12-01

    SiC technology is fast becoming a material of choice for space systems. Herein, we present a novel design for an EUV telescope made entirely of SiC - optics and metering structure inclusive - called the High-resolution Lightweight Telescope for the EUV (HiLiTE). HiLiTE is a Cassegrain telescope with multilayer coated SiC optics tuned to operate at 465 Å, and will image Ne VII emission formed in solar transition region plasma at 500,000 K. HiLiTE will have an aperture of 30 cm, angular resolution of 0.2 arc seconds and operate at a cadence of 5 seconds or less, having a mass that is about ¼ that of one of the 20 cm aperture telescopes on the Atmospheric Imaging Assembly (AIA) instrument aboard NASA's Solar Dynamics Observatory (SDO). This new instrument technology thus serves as a path finder to a post-AIA, Explorer-class mission.

  20. Microstructure comparison of transparent and opaque CVD SiC

    SciTech Connect

    Kim, Y.; Zangvil, A.; Goela, J.S.; Taylor, R.L.

    1995-06-01

    Transparent, translucent, and opaque regions of high-purity bulk SiC, produced by CVD, have been characterized for physical properties as well as microstructure and chemical purity to correlate degree of transparency with other material characteristics. A good correlation was obtained between SiC vis-a-vis IR transmission and its microstructure. The transparent material is highly oriented toward the {l_angle}111{r_angle} direction and is characterized by pure, essentially defect-free, cubic {beta}-SiC columnar grains of size 5--10 {micro}m. The translucent material of various colors is mostly cubic in structure but contains large amounts of twins, usually as complex mixtures of several twinning variants and secondary twinning within a single grain. Opaque CVD SiC is randomly oriented, does not exhibit columnar grains, and contains one directional disorder with hexagonal ({alpha}-SiC) symmetry in a majority of grains and high density of dislocations elsewhere.

  1. 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.

  2. 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.

  3. Low-energy SiC2H6+ and SiC3H9+ ion beam productions by the mass-selection of fragments produced from hexamethyldisilane for SiC film formations

    NASA Astrophysics Data System (ADS)

    Yoshimura, Satoru; Sugimoto, Satoshi; Murai, Kensuke; Kiuchi, Masato

    2016-12-01

    We have been attempting to produce low-energy ion beams from fragments produced through the decomposition of hexamethyldisilane (HMD) for silicon carbide (SiC) film formations. We mass-selected SiC2H6+ and SiC3H9+ ions from fragments produced from HMD, and finally produced low-energy SiC2H6+ and SiC3H9+ ion beams. The ion energy was approximately 100 eV. Then, the ion beams were irradiated to Si(100) substrates. The temperature of the Si substrate was 800°C during the ion irradiation. The X-ray diffraction and Raman spectroscopy of the substrates obtained following SiC2H6+ ion irradiation demonstrated the occurrence of 3C-SiC deposition. On the other hand, the film deposited by the irradiation of SiC3H9+ ions included diamond-like carbon in addition to 3C-SiC.

  4. Hypervalent organobismuth(iii) carbonate, chalcogenides and halides with the pendant arm ligands 2-(Me2NCH2)C6H4 and 2,6-(Me2NCH2)2C6H3.

    PubMed

    Breunig, Hans J; Königsmann, Lucia; Lork, Enno; Nema, Mihai; Philipp, Nicky; Silvestru, Cristian; Soran, Albert; Varga, Richard A; Wagner, Roxana

    2008-04-14

    R2BiOH (1) [R = 2-(Me2NCH2)C6H4] and (R2Bi)2O (2) are formed by hydrolysis of R2BiCl with KOH. Single crystals of were obtained by air oxidation of (R2Bi)2. The reaction of R2BiCl and Na2CO3 leads to (R2Bi)2CO3 (3). 3 is also formed by the absorption of CO2 from the air in solutions of 1 or 2 in diethyl ether or toluene. (R2Bi)2S (4) is obtained from R2BiCl and Na2S or from (R2Bi)2 and S8. Exchange reactions between R2BiCl and KBr or NaI give R2BiX [X = Br (5), I (6)]. The reaction of RBiCl2 (7) with Na2S and [W(CO)5(THF)] gives cyclo-(RBiS)2[W(CO)5]2 (8). cyclo-(R'BiS)2 (9) [R' = 2,6-(Me2NCH2)2C6H3] is formed by reaction of R'BiCl2 and Na2S. The structures of were determined by single-crystal X-ray diffraction.

  5. 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.

  6. 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.

  7. Scheduled meal accelerates entrainment to a 6-h phase advance by shifting central and peripheral oscillations in rats.

    PubMed

    Ubaldo-Reyes, L M; Buijs, R M; Escobar, C; Ángeles-Castellanos, M

    2017-08-01

    Travelling across several time zones requires a fast adjustment of the circadian system and the differential adjustment speeds of organs and systems results in what is commonly referred as jet lag. During this transitory state of circadian disruption, individuals feel discomfort, appetite loss, fatigue, disturbed sleep and deficient performance of multiple tasks. We have demonstrated that after a 6-h phase advance of the light-dark cycle (LD) scheduled food in phase with the new night onset can speed up re-entrainment. In this study, we explored the possible mechanisms underlying the fast re-entrainment due to the feeding schedule. We focused on first- and second-order structures that provide metabolic information to the suprachiasmatic nucleus (SCN). We compared (i) control rats without change in LD cycle; (ii) rats exposed to a 6-h phase advance of the LD cycle with food ad libitum; and (iii) rats exposed to the 6-h phase advance combined with food access in phase with the new night. We found an immediate synchronizing effect of food on stomach distention and on c-Fos expression in the nucleus of the solitary tract, arcuate nucleus of the hypothalamus, dorsomedial hypothalamic nucleus and paraventricular nucleus. These observations indicate that in a model of jet lag, scheduled feeding can favour an immediate shift in first- and second-order relays to the SCN and that by keeping feeding schedules coupled to the new night, a fast re-entrainment may be achieved by shifting peripheral and extra-SCN oscillations. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

  8. 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.

  9. Stern-Gerlach experiments of one-dimensional metal-benzene sandwich clusters: Mn(C6H6)m (M = Al, Sc, Ti, and V).

    PubMed

    Miyajima, Ken; Yabushita, Satoshi; Knickelbein, Mark B; Nakajima, Atsushi

    2007-07-11

    A molecular beam of multilayer metal-benzene organometallic clusters Mn(C6H6)m (M = Al, Sc, Ti, and V) was produced by a laser vaporization synthesis method, and their magnetic deflections were measured. Multidecker sandwich clusters of transition-metal atoms and benzene Scn(C6H6)n+1 (n = 1, 2) and Vn(C6H6)n+1 (n = 1-4) possess magnetic moments that increase monotonously with n. The magnetic moments of Al(C6H6), Scn(C6H6)n+1, and Vn(C6H6)n+1 are smaller than that of their spin-only values as a result of intracluster spin relaxation, an effect that depends on the orbital angular momenta and bonding characters of the orbitals containing electron spin. While Ti(C6H6)2 was found to be nonmagnetic, Tin(C6H6)n+1 (n = 2, 3) possess nonzero magnetic moments. The mechanism of ferromagnetic spin ordering in M2(C6H6)3 (M = Sc, Ti, V) is discussed qualitatively in terms of molecular orbital analysis. These sandwich species represent a new class of one-dimensional molecular magnets in which the transition-metal atoms are formally zerovalent.

  10. Comparative calculations of electron transport properties in 6H-SiC using three and five valley models

    NASA Astrophysics Data System (ADS)

    Talha, Nora; Bouazza, Benyounes; Guen Bouazza, Ahlam; Kadoun, Abd-Ed-Daim

    2016-07-01

    Steady-state electron properties are investigated in 6H-SiC at various temperatures, using Monte Carlo simulation where the band structure model is a major part when dealing with high fields. The aim of this work is to optimize the number of valleys involved in the simulation program in order to obtain accurate results while improving the calculation efficiency. For high fields, a five valley model was found to be more accurate than a three valley model and as efficient as the full band method though much less computer time-consuming.

  11. 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.

  12. 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.

  13. AlGaN HEMTs on patterned resistive/conductive SiC templates

    NASA Astrophysics Data System (ADS)

    Prystawko, Pawel; Sarzynski, Marcin; Nowakowska-Siwinska, Anna; Crippa, Danilo; Kruszewski, Piotr; Wojtasiak, Wojciech; Leszczynski, Mike

    2017-04-01

    High performance GaN-based high electron mobility transistors (HEMTs) on SiC require low-miscut ( 0.45°), resistive substrates, which are very expensive. A cost-effective solution is to use resistive SiC template i.e., grow a thick resistive SiC epitaxial layer on cheap, conductive SiC substrate. However, this approach requires much higher miscut (2-8°). In the present work we show a lateral patterning technology capable to locally decrease the high miscut of the resistive SiC template, down to a level acceptable for GaN epitaxy. On such patterned SiC templates we grew smooth AlGaN/GaN structures. The maximum width of flat regions available for device fabrication was nearly 100 μm. In these flat regions AlGaN-based HEMTs were fabricated and characterized.

  14. Effect of oxygen on ion-beam induced synthesis of SiC in silicon

    NASA Astrophysics Data System (ADS)

    Artamonov, V. V.; Valakh, M. Ya.; Klyui, N. I.; Melnik, V. P.; Romanyuk, A. B.; Romanyuk, B. N.; Yuhimchuk, V. A.

    1999-01-01

    The properties of Si-structures with a buried silicon carbide (SiC) layer created by high-dose carbon implantation into Cz-Si or Fz-Si wafers followed by high-temperature annealing were studied by Raman and infrared spectroscopy. The effect of additional oxygen implantation on the peculiarities of SiC layer formation was also studied. It was shown that under the same implantation and post-implantation annealing conditions the buried SiC layer is more effectively formed in Cz-Si or in Si (Cz-or Fz-) subjected to additional oxygen implantation. So we can conclude that oxygen in silicon promotes the SiC layer formation due to SiO x precipitate creation and accommodation of the crystal volume in the region where SiC phase is formed. Carbon segregation and amorphous carbon film formation on SiC grain boundaries were revealed.

  15. Structural and Electronic Evolution from SiC Sheet to Silicene

    NASA Astrophysics Data System (ADS)

    Liu, G.; Wu, M. S.; Ouyang, C. Y.; Xu, B.

    2013-10-01

    The evolution of the structural and electronic properties from SiC sheet to silicene is studied by using first-principles density functional theory. It is found that the planar configurations of the Si-C monolayer systems are basically kept except for the increase of the buckling of the planar structure when the substitution ratio of Si increases. Band gaps of the Si-C monolayer system decrease gradually when the substitution ratio of Si atoms ranges from 0% to 100%. The energy and type of the band gaps are closely related with the substitution ratio of Si atoms and the Si-C order. Further analysis of density of states reveals the orbital contribution of Si and C atoms near the Fermi level. The discussion of the electronic evolution from SiC sheet to silicene would widen the application of the Si-C monolayer systems in the optoelectronic field in the future nanotechnology.

  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. 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.

  17. 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

  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 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

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. [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.

  6. Spin polarization and magnetic characteristics at C6H6/Co2MnSi(001) spinterface

    NASA Astrophysics Data System (ADS)

    Sun, Meifang; Wang, Xiaocha; Mi, Wenbo

    2017-09-01

    Organic materials with mechanical flexibility, low cost, chemical engineering, and long spin lifetime attract considerable attention for building spintronic devices. Here, a C6H6/Co2MnSi(001) spinterface is investigated by first-principles calculations and spin-polarized scanning tunneling microscopy simulations. Several high symmetry adsorption sites are discussed, together with two possible surface terminations of Co2MnSi(001). An inversion of the spin polarization is induced near EF even in the case of an external electric field, indicating that C6H6 can act as a spin filter to exploit the spin injection efficiency in organic spintronic devices. Unlike previous studies on molecule/ferromagnet interfaces, this inversion is closely related to the electronic structure of the atoms in the subsurface layer of Co2MnSi according to the orbital symmetry analysis. Furthermore, the magnetic moment and magnetic anisotropic energy (MAE) in the outermost Co2MnSi layer are studied. Particularly, in the most stable configuration, the sign of MAE is inversed due to hybridization between C p and Co dz2 orbitals, which suggests that a greater modification on MAE can be achieved by the use of a highly chemically reactive organic molecule. These findings improve the study on the engineering of magnetic properties at molecule/ferromagnetic interfaces through a single π-conjugated organic molecule.

  7. Spin polarization and magnetic characteristics at C6H6/Co2MnSi(001) spinterface.

    PubMed

    Sun, Meifang; Wang, Xiaocha; Mi, Wenbo

    2017-09-21

    Organic materials with mechanical flexibility, low cost, chemical engineering, and long spin lifetime attract considerable attention for building spintronic devices. Here, a C6H6/Co2MnSi(001) spinterface is investigated by first-principles calculations and spin-polarized scanning tunneling microscopy simulations. Several high symmetry adsorption sites are discussed, together with two possible surface terminations of Co2MnSi(001). An inversion of the spin polarization is induced near EF even in the case of an external electric field, indicating that C6H6 can act as a spin filter to exploit the spin injection efficiency in organic spintronic devices. Unlike previous studies on molecule/ferromagnet interfaces, this inversion is closely related to the electronic structure of the atoms in the subsurface layer of Co2MnSi according to the orbital symmetry analysis. Furthermore, the magnetic moment and magnetic anisotropic energy (MAE) in the outermost Co2MnSi layer are studied. Particularly, in the most stable configuration, the sign of MAE is inversed due to hybridization between C p and Co dz(2) orbitals, which suggests that a greater modification on MAE can be achieved by the use of a highly chemically reactive organic molecule. These findings improve the study on the engineering of magnetic properties at molecule/ferromagnetic interfaces through a single π-conjugated organic molecule.

  8. 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

  9. Synthesis and biological activity of cocaine analogues. 2. 6H-[2]Benzopyrano[4,3-c]pyridin-6-ones.

    PubMed

    Lazer, E S; Hite, G J; Nieforth, K A; Stratford, E S

    1979-07-01

    1,2,3,4-Tetrahydro-2-methyl-6H-[2]benzopyrano[4,3-c]pyridin-6-one (20) and cis- and trans-1,2,3,4,4a,10b-hexahydro-2-methyl-6H-[2]benzopyrano[4,3-c]pyridin-6-one (3a and 3b) were synthesized. The design of 3b was based on the proposal that the active conformation of cocaine is one in which the phenyl and amino groups are arranged in a manner that will superimpose upon a beta-phenethylamine in a trans-staggered conformation. The compounds were compared with cocaine and tropacocaine for their ability to inhibit uptake of [3H]norepinephrine by rat brain synaptosomal preparations. The test compounds (IC50 = 3.2 X 10(-4) M, 20; 6.5 X 10(-4) M, 3a; and 3.2 X 10(-4) M, 3b; respectively) were considerably weaker than cocaine (IC50 = 5.8 X 10(-7) M) and tropacocaine (IC50 = 5.6 X 10(-6) M). Compound 3b showed selectivity at 1 X 10(-5) M for inhibiting the uptake of norepinephrine (36%). It inhibited dopamine (3%) and serotonin (0%) uptake to a much lesser extent, if at all, at this concentration.

  10. 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.

  11. 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. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  12. [Cloning and expression of the key enzyme hyoscyamine 6 beta-hydroxylase gene (DaH6H) in scopolamine biosynthesis of Datura arborea].

    PubMed

    Qiang, Wei; Hou, Yan-ling; Li, Xiao; Xia, Ke; Liao, Zhi-hua

    2015-10-01

    Hyoscyamine 6 beta-hydroxylase (H6H) is the last rate-limiting enzyme directly catalyzing the formation of scopolamine in tropane alkaloids (TAs) biosynthesis pathway. It is the primary target gene in the genetic modification of TAs metabolic pathway. Full-length cDNA and gDNA sequences of a novel H6H gene were cloned from Datura arborea (DaH6H, GenBank accession numbers for cDNA and gDNA are KR006981 and KR006983, respectively). Nucleotide sequence analysis reveals an open reading frame of 1375 bp encoding 347 amino acids in the cDNA of DaH6H, while the gDNA of DaH6H contains four exons and three introns, with the highest similarity to the gDNA of H6H from D. stramonium. DaH6H also exhibited the most identity of 90.5% with DsH6H in amino acids and harbored conserved 2-oxoglutarate binding motif and two iron binding motifs. The expression level of DaH6H was highest in the mature leaf, followed by the secondary root, and with no expression in the primary root based on qPCR analysis. Its expression was inhibited by MeJA. DaH6H was expressed in E. coli and a 39 kD recombinant protein was detected in SDS-PAGE. Comparison of the contents of scopolamine and hyoscyamine in various TAs-producing plants revealed that D. arborea was one of the rare scopolamine predominant plants. Cloning of DaH6H gene will allow more research in the molecular regulatory mechanism of TAs biosynthesis in distinct plants and provide a new candidate gene for scopolamine metabolic engineering.

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

    NASA Astrophysics Data System (ADS)

    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(SO42-) 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(SeO42-) modes were obtained. Тhe ν3(SO42-) frequency region of the isomorphously isolated SO42- 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(SO42-) 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.

  14. A new approach for transition metal free magnetic SiC: Defect induced magnetism after self-ion implantation

    NASA Astrophysics Data System (ADS)

    Kummari, Venkata Chandra Sekhar

    SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purposes. Among these polytypes 4H-SiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defect-induced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence of low fluence low energy silicon and carbon implantation on the creation of defects in n-type 4H-SiC. The characterization of the defects in these implanted samples was performed using the techniques, RBS-channeling and Raman spectroscopy. We have also utilized these characterization techniques to analyze defects created in much deeper layers of the SiC due to implantation of high energy nitrogen ions. The experimentally determined depths of the Si damage peaks due to low energy (60 keV) Si and C ions with low fluences (< 1015 cm-2) are consistent with the SRIM-2011 simulations. From RBS-C Si sub-lattice measurements for different fluences (1.1x1014 cm-2 to 3.2x1014 cm-2 ) of Si

  15. 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.

  16. Atomic and electronic structure of silicate adlayers on polar hexagonal SiC surfaces

    NASA Astrophysics Data System (ADS)

    Lu, Wenchang; Krüger, Peter; Pollmann, Johannes

    2000-05-01

    Structural and electronic properties of silicate adlayers on (3×3)R30°-reconstructed C-terminated (0001¯) and Si-terminated (0001) surfaces of hexagonal 6H-SiC have been studied using the ab initio pseudopotential supercell method. Two significantly different structural models, previously suggested on the basis of a quantitative low-energy electron diffraction (LEED) analysis for the two adsorbate systems, have been investigated. Both of these models have been considered for both surfaces and the four respective structures have been optimized by total energy minimization calculations. The two structures with the lowest formation energy confirm the interpretation of the LEED data. In addition, they allow us to address the physical origin of the distinctly different reconstruction models for the two surfaces. The electronic structure of these surfaces according to local density approximation calculations is presented and discussed. Both models yield a number of oxygen-induced bound states and resonances within the projected valence band region and a band of localized dangling-bond states within the projected gap. Within the local density approximation, this dangling-bond band turns out to be half-filled in both cases, giving rise to metallic surfaces in contradiction to experiment. Therefore, the systems have also been studied within the framework of the Hubbard model and by employing the local-spin-density approximation. In both cases semiconducting surfaces are obtained in agreement with experiment. The dangling-bond bands resulting within the Hubbard-model calculation, in particular, are in quantitative agreement with most recent angle-resolved photoemission spectroscopy data for a Si2O3 silicate adlayer on SiC(0001¯).

  17. 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.

  18. 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.

  19. 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.

  20. PROPERTIES AND BALLISTIC BEHAVIOR OF PRESSURELESS SINTERED SIC/TIB2 COMPOSITES

    SciTech Connect

    T.M. Lillo; H.S. Chu; B.Merkle; D. Bailey; W.M. Harrison

    2005-01-01

    Pressureless sintering of ceramics for armor applications offers the potential of greatly reduced cost and increased production volume. Previously it was shown that pure SiC could be made by pressureless sintering while achieving a ballistic performance slightly less than commercial SiC made by pressure-assisted densification (PAD). Additions of titanium diboride were made to pin the SiC grain size during pressureless sintering to achieve a final grain size closer to that found in PAD SiC and achieve improved ballistic performance. Silicon carbide/titanium diboride composites of various compositions were blended by various means, consolidated and pressureless sintered to near theoretical density. Additions of TiB2 were <10% by volume and increased the density of the material by less than 3% over that of pure SiC. Variations in the mixing techniques yielded composites with a range of TiB2 particle sizes. TiB2 additions hindered SiC grain growth and the formation of elongated grains during high temperature pressureless sintering. The microstructure of the composites is documented and compared to commercially available SiC material. The SiC/TiB2 composites demonstrated improved ballistic properties in Depth-of-Penetration (DOP) tests over pure, pressureless-sintered SiC material and approach that of SiC made by hot pressing.

  1. SiC Nanoparticles Toughened-SiC/MoSi2-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

    NASA Astrophysics Data System (ADS)

    Abdollahi, Alireza; Ehsani, Naser; Valefi, Zia; Khalifesoltani, Ali

    2017-05-01

    A SiC nanoparticle toughened-SiC/MoSi2-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi2, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi2-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi2-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10-2 g/cm3/h, respectively.

  2. The effect of structural defects in SiC particles on the static & dynamic mechanical response of a 15 volume percent SiC/6061-Al matrix composite

    SciTech Connect

    Vaidya, R.U.; Song, S.G.; Zurek, A.K.; Gray, G.T. III

    1995-09-01

    Static and Dynamic mechanical tests, and microstructural examinations performed on a SiC particle reinforced 6061-Al matrix composite indicated that particle cracking significantly affected the strength, strain hardening, and failure mechanism of the composite. Cracks were observed to nucleate and propagate on stacking faults and interfaces between the various phases within the reinforcing SiC particles. Planar defects were the predominant artifacts seen in the SiC particles. Partial dislocations were also observed bounding the stacking faults within the reinforcement phase.

  3. 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

  4. 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.

  5. Ab initio electronic structure calculations on the benzene dication and other C sub 6 H sub 6 sup 2+ isomers

    SciTech Connect

    Krogh-Jespersen, K. )

    1991-01-16

    High-level ab initio molecular orbital calculations have been carried out on a series of C{sub 6}H{sub 6}{sup 2+} isomers. Optimized geometrical structures have been obtained, and characterized via normal mode and frequency analysis, at the single-determinant Hartree-Fock level with a basis set of split valence plus polarization function quality (HF/6-31G*//6-31G*). Relative energies were derived from calculations including correlation energy corrections at the third-order Moller-Plesset level (MP3/6-31G*//6-31G*) and the zero-point vibrational energy contributions. Both singlet and triplet states were investigated for the benzene dication and only one minimum was located on each potential energy surface.

  6. Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

    SciTech Connect

    Lohrmann, A.; Klein, J. R.; Prawer, S.; McCallum, J. C.; Castelletto, S.; Ohshima, T.; Bosi, M.; Negri, M.; Johnson, B. C.

    2016-01-11

    In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

  7. Solvent effects on infrared spectra of progesterone in CHCl 3/ cyclo-C 6H 12 binary solvent systems

    NASA Astrophysics Data System (ADS)

    Liu, Qing; Wang, Xiao-yan; Zhang, Hui

    2007-01-01

    The infrared spectroscopy studies of the C 3 and C 20 carbonyl stretching vibrations ( υ(C dbnd O)) of progesterone in CHCl 3/ cyclo-C 6H 12 binary solvent systems were undertaken to investigate the solute-solvent interactions. With the mole fraction of CHC1 3 in the binary solvent mixtures increase, three types of C 3 and C 20 carbonyl stretching vibration band of progesterone are observed, respectively. The assignments of υ(C dbnd O) of progesterone are discussed in detail. In the CHCl 3-rich binary solvent systems or pure CHCl 3 solvent, two kinds of solute-solvent hydrogen bonding interactions coexist for C 20 C dbnd O. Comparisons are drawn for the solvent sensitivities of υ(C dbnd O) for acetophenone and 5α-androstan-3,17-dione, respectively.

  8. Growth of fcc(111) Dy multi-height islands on 6H-SiC(0001) graphene.

    PubMed

    Hershberger, M T; Hupalo, M; Thiel, P A; Tringides, M C

    2013-06-05

    Graphene based spintronic devices require an understanding of the growth of magnetic metals. Rare earth metals have large bulk magnetic moments so they are good candidates for such applications, and it is important to identify their growth mode. Dysprosium was deposited on epitaxial graphene, prepared by thermally annealing 6H-SiC(0001). The majority of the grown islands have triangular instead of hexagonal shapes. This is observed both for single layer islands nucleating at the top of incomplete islands and for fully completed multi-height islands. We analyze the island shape distribution and stacking sequence of successively grown islands to deduce that the Dy islands have fcc(111) structure, and that the triangular shapes result from asymmetric barriers to corner crossing.

  9. Positron lifetime studies on 8 MeV electron-irradiated n-type 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Lam, C. H.; Lam, T. W.; Ling, C. C.; Fung, S.; Beling, C. D.; De-Sheng, Hang; Huimin, Weng

    2004-11-01

    The positron lifetime technique was employed to study vacancy-type defects in 8 MeV electron-irradiated n-type 6H silicon carbide. A long-lifetime component having a characteristic lifetime of 223-232 ps was observed in the irradiated sample and was attributed to the VCVSi divacancy. Other positron traps, which dominated at low temperatures, were observed to compete with the VCVSi for trapping positrons. A positron trapping model involving a positron shallow trap, a negatively charged monovacancy and the VCVSi divacancy was found to give a good description of the temperature-dependent positron lifetime data of the 1200 °C annealed sample. The identity of the monovacancy could not be unambiguously determined, but its lifetime was found to be in the range 160-172 ps.

  10. 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.

  11. 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.

  12. Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

    NASA Astrophysics Data System (ADS)

    Lohrmann, A.; Castelletto, S.; Klein, J. R.; Ohshima, T.; Bosi, M.; Negri, M.; Lau, D. W. M.; Gibson, B. C.; Prawer, S.; McCallum, J. C.; Johnson, B. C.

    2016-01-01

    In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

  13. Simulation and Experiment on Surface Morphology and Mechanical Properties Response in Nano-Indentation of 6H-SiC

    NASA Astrophysics Data System (ADS)

    Li, Chen; Zhang, Feihu; Meng, Binbin; Ma, Zhaokai

    2017-03-01

    The nano-indentation test for 6H-SiC is carried out with a Berkovich indenter. The indentation surface morphology is analyzed by SEM, which show that when the maximum load P max is 8 mN, there is only plastic deformation and no cracks on the surface of workpiece after unloading process, and when P max is 10 mN, there is the initiation of crack occurring on the surface of workpiece after unloading process. Based on the strain hardening model, the three-dimensional finite element method of nano-indentation for 6H-SiC is carried out. Simulation results show that in the unloading process the maximum stress and the maximum strain occur in the contact area between the workpiece with the indenter edges, which is consistent with the experimental results. When propagate to the surface from the subsurface, the cracks are subjected to the type I stress and the type II stress due to elastic recovery. After propagating to surface of workpiece, the cracks propagate along a fixed direction because the proportion of type I stress is much larger than that of type II stress. The influence of the cleavage plane on the propagation direction of cracks is obvious. The cracks propagate more easily when the indenter edges are along cleavage plane. The indentation depth and residual depth increase with the increase of P max. While, the elastic recovery rate gradually decreases and tends to be stable with the increase of P max. When P max is <10 mN, the micro-hardness and the elastic modulus increase linearly with the increase of P max. When P max exceeds 10 mN, the micro-hardness decreases with the increase of P max and then gradually tends to be stable, and the elastic modulus increases by power function with the increase of P max and then gradually tends to be stable.

  14. β-FeSi2 films prepared on 6H-SiC substrates by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Hong, Li; Hongbin, Pu; Chunlei, Zheng; Zhiming, Chen

    2015-06-01

    β-FeSi2 thin films have been successfully prepared by magnetron sputtering and post rapid thermal annealing method on 6H-SiC (0001) substrates using a FeSi2 target and a Si target. X-ray diffraction (XRD) and Raman spectroscopy are applied to analyze the formation of β-FeSi2 films. XRD spectra reveal that the amorphous FeSi2 films are transformed to β-FeSi2 phase as the annealing temperature is increased from 500 to 900 °C for 5 min and the optimal annealing temperature is 900 °C. The formation of β-FeSi2 is also confirmed by Raman spectroscopy. Scanning electron microscope (SEM) observations indicate that the film is flat, relatively compact and the interface between β-FeSi2 and 6H-SiC is clear. Atomic force microscope (AFM) measurements demonstrate that the surface roughness confirmed by the root mean square (RMS) of the β-FeSi2 film is 0.87 nm. Near-infrared spectrophotometer observation shows that the absorption coefficient is of the order of 105 cm-1 and the optical band-gap of the β-FeSi2 film is 0.88 eV. The β-FeSi2 film with high crystal quality is fabricated by co-sputtering a FeSi2 target and a Si target for 60 min and annealing at 900 °C for 5 min. Project supported by the National Natural Science Foundation of China (No. 51177134) and the Natural Science Basic Research Plan in Shaanxi Province of China (No. 2015JM6286).

  15. 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.

  16. UV photoemission study of heteroepitaxial AlGaN films grown on 6H-SiC

    NASA Astrophysics Data System (ADS)

    Benjamin, M. C.; Bremser, M. D.; Weeks, T. W.; King, S. W.; Davis, R. F.; Nemanich, R. J.

    1996-09-01

    This study presents results of UV photoemission measurements of the surface and interface properties of heteroepitaxial AlGaN on 6H-SiC. Previous results have demonstrated a negative electron affinity of AlN on 6H-SiC. In this study Al xGa 1- xN alloy films were grown by organometallic vapor phase epitaxy (OMVPE) and doped with silicon. The analytical techniques included UPS, Auger electron spectroscopy, and LEED. All analysis took place in an integrated UHV transfer system which included the analysis techniques, a surface processing chamber and a gas source MBE. The OMVPE alloy samples were transported in air to the surface characterization system while the AlN and GaN investigations were prepared in situ. The surface electronic states were characterized by surface normal UV photoemission to determine whether the electron affinity was positive or negative. Two aspects of the photoemission distinguish a surface that exhibits a NEA: (1) the spectrum exhibits a sharp peak in the low kinetic energy region, and (2) the width of the spectrum is hv - Eg. The in situ prepared AlN samples exhibited the characteristics of a NEA while the GaN and Al 0.13Ga 0.87N samples did not. The Al 0.55Ga 0.45N sample shows a low positive electron affinity. Annealing of the sample to > 400°C resulted in the disappearance of the sharp emission features, and this effect was related to contaminant effects on the surface. The results suggest the potential of nitride based cold cathode electron emitters.

  17. Deep level transient spectroscopy study of particle irradiation induced defects in n-6H-SiC

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Gong, M.; Fung, S.; Beling, C. D.; Ling, C. C.

    2004-03-01

    Neutron and electron irradiation induced deep level defects in n-type 6H-SiC have been investigated using deep level transient spectroscopy (DLTS) combined with annealing experiments. Deep levels ED1, E1/E2, Ei, and Z1/Z2 were observed in n-type 6H-SiC material irradiated with neutron. Thermal annealing studies of these deep levels revealed that ED1 and Ei annealed at a temperature below 350^oC, Z1/Z2 levels annealed out at 900^oC, while the intensity of the E1/E2 peaks increased with annealing temperature, reached a maximum at about 500-750^oC, and finally annealed out at 1400^oC. Upon further annealing at 1600^oC, four deep levels labeled NE1 at EC-0.44eV, NE2 EC-0.53eV, NE3 EC-0.64eV, and NE4 EC-0.68eV are produced. Ionization energies of these levels are similar to E1/E2 and Z1/Z2 respectively, but their capture cross sections are different. Samples were irradiated with electrons with different energies ranging from 0.2MeV to 1.7MeV. No deep level was detected in samples irradiated with 0.2MeV electron and deep levels ED1, E1/E2, and Ei were induced with electron energy larger than 0.3MeV.

  18. Simulation and Experiment on Surface Morphology and Mechanical Properties Response in Nano-Indentation of 6H-SiC

    NASA Astrophysics Data System (ADS)

    Li, Chen; Zhang, Feihu; Meng, Binbin; Ma, Zhaokai

    2017-02-01

    The nano-indentation test for 6H-SiC is carried out with a Berkovich indenter. The indentation surface morphology is analyzed by SEM, which show that when the maximum load P max is 8 mN, there is only plastic deformation and no cracks on the surface of workpiece after unloading process, and when P max is 10 mN, there is the initiation of crack occurring on the surface of workpiece after unloading process. Based on the strain hardening model, the three-dimensional finite element method of nano-indentation for 6H-SiC is carried out. Simulation results show that in the unloading process the maximum stress and the maximum strain occur in the contact area between the workpiece with the indenter edges, which is consistent with the experimental results. When propagate to the surface from the subsurface, the cracks are subjected to the type I stress and the type II stress due to elastic recovery. After propagating to surface of workpiece, the cracks propagate along a fixed direction because the proportion of type I stress is much larger than that of type II stress. The influence of the cleavage plane on the propagation direction of cracks is obvious. The cracks propagate more easily when the indenter edges are along cleavage plane. The indentation depth and residual depth increase with the increase of P max. While, the elastic recovery rate gradually decreases and tends to be stable with the increase of P max. When P max is <10 mN, the micro-hardness and the elastic modulus increase linearly with the increase of P max. When P max exceeds 10 mN, the micro-hardness decreases with the increase of P max and then gradually tends to be stable, and the elastic modulus increases by power function with the increase of P max and then gradually tends to be stable.

  19. Electronic states of the C6H6/Cu{111} system: Energetics, femtosecond dynamics, and adsorption morphology

    NASA Astrophysics Data System (ADS)

    Velic, D.; Hotzel, A.; Wolf, M.; Ertl, G.

    1998-11-01

    Two-photon-photoemission (2PPE) spectroscopy is employed to characterize electronic states of a bilayer C6H6/Cu{111} system at 85 K. The unoccupied benzene π* e2u state is observed with a binding energy of 4.6 eV above the Fermi level. This result agrees with inverse-photoemission (IPE) data and provides a case where the determination of the binding energy is identical for 2PPE and IPE. The π* e2u state is assigned in the 2PPE scheme as a final state which is the first observed final state in 2PPE of adsorbate-surface systems. The dependence of the electron dynamics on the morphology of an incomplete adsorption layer is also investigated. Two (n=1)-like image potential states A and B are observed which presumably originate from two different C6H6 adsorption geometries in the bilayer regime. The two image states A and B are characterized by electron effective masses of 1.1 and 1.9 me, binding energies of 3.30 and 3.45 eV above the Fermi level, and lifetimes of 40 and 20 fs, respectively. The dielectric continuum model and the Kronig-Penney model are employed to simulate the origin of (n=1)-like image states. The work function decreases from 4.9 eV at clean Cu{111} to 4.0 eV at bilayer coverage. The change of the work function and the observation of two image states suggest the redefining of the ratio of the numbers of benzene molecules in the first and the second layers of the bilayer regime to approximately 1:1 instead of 1:2, as previously reported. 2PPE is shown to be sensitive to the changes of morphologies, local work functions, and adsorbate-surface potentials during the layer formation.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  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. 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.

  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, 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.

  7. Formation of SiC by radiative association

    NASA Astrophysics Data System (ADS)

    Andreazza, C. M.; Vichietti, R. M.; Marinho, E. P.

    2009-12-01

    Rate coefficients for radiative association of silicon and carbon atoms to form silicon carbide molecule (SiC) are estimated. The radiative association of Si(3P) and C(3P) atoms mainly occurs through the C3Π state followed by radiative decay to the X3Π state. For the temperature range of 300-14000 K, the rate coefficients slowly increase with temperature and they can be expressed by K(T) = 2.038 × 10-17(T/300)-0.01263 exp(-136.73/T)cm3s-1.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  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 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.

  14. New 10-membered inorganic heterocyclic diphosphanes, PhN(PX)(2)[(-OC(6)H(2)((T)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)] (x = cl, f). Synthesis and transition metal complexes (molybdenum(0), ruthenium(II), palladium(II), and platinum(II)) of heterocyclic diphosphanes. crystal and molecular structures of the chloro derivative, PhN(PCl)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)], and of a molybdenum(0) complex of the fluoro derivative, [Mo(CO)(3)[eta(3)-PhN(PF)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)]-kappa P,kappa P,kappa S

    PubMed

    Balakrishna, M S; Panda, R; Mague, J T

    2001-10-22

    Bis(dichlorophosphino)aniline, PhN(PCl(2))(2), reacts with stoichiometric amounts of 2,2'-thiobis(4,6-di-tert-butylphenol) to afford a 10-membered heterocycle, PhN(PCl)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t))Bu)(2)C(6)H(2)O-)] (1), in high yield. The structure of the heterocycle has been determined by a single-crystal X-ray analysis. The 10-membered heterocycle 1 reacts with SbF(3) to afford the corresponding fluoro derivative 2 in good yield. The compounds 1 and 2 act as tridentate ligands with molybdenum carbonyl derivatives, forming complexes of the type [Mo(CO)(3)[eta(3)-PhN(PX)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)]-kappa P,kappa P,kappa S

  15. 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.

  16. Porous SiC nanowire arrays as stable photocatalyst for water splitting under UV irradiation

    SciTech Connect

    Liu, Hailong; She, Guangwei; Mu, Lixuan; Shi, Wensheng

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Arrays of porous SiC nanowires prepared by a facile in situ carbonizing method. Black-Right-Pointing-Pointer Utilizing the SiC nanowire arrays as photocatalysis for water splitting. Black-Right-Pointing-Pointer Excellent photocatalytic performance under the UV irradiation. Black-Right-Pointing-Pointer Very high stability of the SiC nanowire photocatalyst. -- Abstract: In this study, we report the fabrication and photocatalytic properties of the oriented arrays of SiC nanowires on the Si substrate. The SiC nanowire arrays were prepared by carbonizing the Si nanowire arrays with the graphite powder at 1250 Degree-Sign C. The as-prepared SiC nanowires are highly porous, which endows them with a high surface-to-volume ratio. Considering the large surface areas and the high stability, the porous SiC nanowire arrays were used as photocatalyst for water splitting under UV irradiation. It was found that such porous SiC structure exhibited an enhanced and extremely stable photocatalytic performance.

  17. Iron and Nickel Isotope Measurements on SiC X Grains with CHILI

    NASA Astrophysics Data System (ADS)

    Kodolányi, J.; Stephan, T.; Trappitsch, R.; Hoppe, P.; Pignatari, M.; Davis, A. M.; Pellin, M. J.

    2016-08-01

    New measurements with CHILI on SiC X grains provide more detailed Fe and Ni isotope data than previous NanoSIMS analyses. The new data suggest that Fe-Ni fractionation may occur in supernova ejecta before SiC condensation.

  18. First-principles prediction of stable SiC cage structures and their synthesis pathways

    NASA Astrophysics Data System (ADS)

    Pochet, Pascal; Genovese, Luigi; Caliste, Damien; Rousseau, Ian; Goedecker, Stefan; Deutsch, Thierry

    2010-07-01

    In this paper we use density functional theory calculations to investigate the structure and the stability of different SiC cagelike clusters. In addition to the fullerene family and the mixed four and six membered ring family, we introduce a family based on reconstructed nanotube slices. We propose an alternative synthesis pathway starting from SiC nanotubes.

  19. 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.

  20. Photodissociation dynamics of fluorobenzene (C{sub 6}H{sub 5}F) at 157 and 193 nm: Branching ratios and distributions of kinetic energy

    SciTech Connect

    Lee, S.-H.; Wu, C.-Y.; Yang, S.-K.; Lee, Y.-P.

    2006-10-14

    Following photodissociation of fluorobenzene (C{sub 6}H{sub 5}F) at 193 and 157 nm, we detected the products with fragmentation-translational spectroscopy by utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Between two primary dissociation channels observed upon irradiation at 193 (157) nm, the HF-elimination channel C{sub 6}H{sub 5}F{yields}HF+C{sub 6}H{sub 4} dominates, with a branching ratio of 0.94{+-}0.02 (0.61{+-}0.05) and an average release of kinetic energy of 103 (108) kJ mol{sup -1}; the H-elimination channel C{sub 6}H{sub 5}F{yields}H+C{sub 6}H{sub 4}F has a branching ratio of 0.06{+-}0.02 (0.39{+-}0.05) and an average release of kinetic energy of 18.6 (26.8) kJ mol{sup -1}. Photofragments H, HF, C{sub 6}H{sub 4}, and C{sub 6}H{sub 4}F produced via the one-photon process have nearly isotropic angular distributions. Both the HF-elimination and the H-elimination channels likely proceed via the ground-state electronic surface following internal conversion of C{sub 6}H{sub 5}F; these channels exhibit small fractions of kinetic energy release from the available energy, indicating that the molecular fragments are highly internally excited. We also determined the ionization energy of C{sub 6}H{sub 4}F to be 8.6{+-}0.2 eV.

  1. Reactions of (Cp(CO) sub 2 Fe double bond CHAr) sup + (Ar = p-C sub 6 H sub 4 OMe) with O double bond N-Ar prime (Ar prime = C sub 6 H sub 5 , p-C sub 6 H sub 4 NMe sub 2 ) and PhN double bond NPh

    SciTech Connect

    Peng, Wei-Jun; Gamble, A.S.; Templeton, J.L.; Brookhart, M. )

    1990-02-07

    Organometallic products formed from the reaction of an electrophilic iron carbene complex with nitrosoarenes or azobenzene reflect net insertion of the ArN{double bond}X moiety into the Fe{double bond}CHAr bond. Cp(CO){sub 2}Fe-O-N(Ar{prime}){double bond}CHAr{sup +} and Cp(CO){sub 2}FeN(Ph)-N(Ph){double bond}CHAr{sup +} (Ar = p-C{sub 6}H{sub 4}OMe, Ar{prime} = p-C{sub 6}H{sub 4}NMe{sub 2}) have been isolated and spectroscopically characterized; the crystal structure of Cp(CO){sub 2}Fe-O-N(Ph){double bond}CHAr{sup +} is reported. Exposure of acetone solutions of Cp(CO){sub 2}Fe-O-N(Ar{prime}){double bond}CHAr{sup +} or Cp(CO){sub 2}FeN(Ph)-N(Ph){double bond}char{sup +} to light yields imine products Ar{prime}N{double bond}CHAr or PhN{double bond}CHAr, respectively. There is no evidence to support the formation of the simple stoichiometric iron-containing products of these reactions, the oxo and nitrene complexes Cp(CO){sub 2}Fe{double bond}O{sup +} and Cp(CO){sub 2}Fe{double bond}NPh{sup +}. Hydrolysis of the nitrone complexes Cp(CO){sub 2}Fe-O-N(Ar{prime}){double bond}CHAr{sup +} in aqueous acetone yields aldehyde products Ar{prime}CHO. 30 refs., 1 fig., 4 tabs.

  2. 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)

  3. Synthesis of Freestanding Graphene on SiC by a Rapid-Cooling Technique

    NASA Astrophysics Data System (ADS)

    Bao, Jianfeng; Norimatsu, Wataru; Iwata, Hiroshi; Matsuda, Keita; Ito, Takahiro; Kusunoki, Michiko

    2016-11-01

    Graphene has a negative thermal expansion coefficient; that is, when heated, the graphene lattice shrinks. On the other hand, the substrates typically used for graphene growth, such as silicon carbide, have a positive thermal expansion coefficient. Hence, on cooling graphene on SiC, graphene expands but SiC shrinks. This mismatch will physically break the atomic bonds between graphene and SiC. We have demonstrated that a graphenelike buffer layer on SiC can be converted to a quasifreestanding monolayer graphene by a rapid-cooling treatment. The decoupling of graphene from the SiC substrate was actually effective for reducing the electric carrier scattering due to interfacial phonons. In addition, the rapidly cooled graphene obtained in this way was of high-quality, strain-free, thermally stable, and strongly hole doped. This simple, classical, but quite novel technique for obtaining quasifreestanding graphene could open a new path towards a viable graphene-based semiconductor industry.

  4. 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.

  5. The role of Pd in the transport of Ag in SiC

    NASA Astrophysics Data System (ADS)

    Olivier, E. J.; Neethling, J. H.

    2013-01-01

    This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

  6. Synthesis of Freestanding Graphene on SiC by a Rapid-Cooling Technique.

    PubMed

    Bao, Jianfeng; Norimatsu, Wataru; Iwata, Hiroshi; Matsuda, Keita; Ito, Takahiro; Kusunoki, Michiko

    2016-11-11

    Graphene has a negative thermal expansion coefficient; that is, when heated, the graphene lattice shrinks. On the other hand, the substrates typically used for graphene growth, such as silicon carbide, have a positive thermal expansion coefficient. Hence, on cooling graphene on SiC, graphene expands but SiC shrinks. This mismatch will physically break the atomic bonds between graphene and SiC. We have demonstrated that a graphenelike buffer layer on SiC can be converted to a quasifreestanding monolayer graphene by a rapid-cooling treatment. The decoupling of graphene from the SiC substrate was actually effective for reducing the electric carrier scattering due to interfacial phonons. In addition, the rapidly cooled graphene obtained in this way was of high-quality, strain-free, thermally stable, and strongly hole doped. This simple, classical, but quite novel technique for obtaining quasifreestanding graphene could open a new path towards a viable graphene-based semiconductor industry.

  7. Optimized growth of graphene on SiC: from the dynamic flip mechanism.

    PubMed

    Wang, Dandan; Liu, Lei; Chen, Wei; Chen, Xiaobo; Huang, Han; He, Jun; Feng, Yuan-Ping; Wee, A T S; Shen, D Z

    2015-03-14

    Thermal decomposition of single-crystal SiC is one of the popular methods for growing graphene. However, the mechanism of graphene formation on the SiC surface is poorly understood, and the application of this method is also hampered by its high growth temperature. In this study, based on the ab initio calculations, we propose a vacancy assisted Si-C bond flipping model for the dynamic process of graphene growth on SiC. The fact that the critical stages during growth take place at different energy costs allows us to propose an energetic-beam controlled growth method that not only significantly lowers the growth temperature but also makes it possible to grow high-quality graphene with the desired size and patterns directly on the SiC substrate.

  8. 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.

  9. 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.

  10. 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.

  11. Synthesis and characterization of SiC whiskers

    SciTech Connect

    Wang, L.; Wada, H. ); Allard, L.F. )

    1992-01-01

    SiC whiskers were synthesized by the carbothermal reduction of silica with an addition of halide (3NaF{center dot}AlF{sub 3} or NaF) as an auxiliary bath. The whiskers were {beta} phase (3C) and grew in the (111) direction. Three distinctive morphologies were observed: (1) Type A: thin and straight; (2) Type B: thick and bamboo-like; and (3) Type C: thick, straight, and smooth. Type A whiskers contained a high density of basal plane (111) stacking faults along their entire length, whereas Type B whiskers showed periodic changes between stacking faults and well-defined single crystals. Type C whiskers showed stacking faults on the other {l brace}111{r brace} planes instead of on the basal (111) plane. Silica formed molten fluorosilicate with halide and SiC grew via a vapor-solid reaction mechanism through gaseous SiO. These reactions can be expressed as (SiO{sub 2})+C(s)=SiO(g)+CO(g) and SiO(g)+3CO(g)=SiC(s)+2CO{sub 2}(g). The effects of processing parameters on the morphology and size of the whiskers were examined and the relationship between the morphological development of the whiskers and the stacking fault energy was determined.

  12. Cohort profile: the Social Inequality in Cancer (SIC) cohort study.

    PubMed

    Nordahl, Helene; Hvidtfeldt, Ulla Arthur; Diderichsen, Finn; Rod, Naja Hulvej; Osler, Merete; Frederiksen, Birgitte Lidegaard; Prescott, Eva; Tjønneland, Anne; Lange, Theis; Keiding, Niels; Andersen, Per Kragh; Andersen, Ingelise

    2014-12-01

    The Social Inequality in Cancer (SIC) cohort study was established to determine pathways through which socioeconomic position affects morbidity and mortality, in particular common subtypes of cancer. Data from seven well-established cohort studies from Denmark were pooled. Combining these cohorts provided a unique opportunity to generate a large study population with long follow-up and sufficient statistical power to develop and apply new methods for quantification of the two basic mechanisms underlying social inequalities in cancer-mediation and interaction. The SIC cohort included 83 006 participants aged 20-98 years at baseline. A wide range of behavioural and biological risk factors such as smoking, physical inactivity, alcohol intake, hormone replacement therapy, body mass index, blood pressure and serum cholesterol were assessed by self-administered questionnaires, physical examinations and blood samples. All participants were followed up in nationwide demographic and healthcare registries. For those interested in collaboration, further details can be obtained by contacting the Steering Committee at the Department of Public Health, University of Copenhagen, at inan@sund.ku.dk.

  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. 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.

  15. Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

    DOE PAGES

    Gearba, Raluca I.; Mueller, Kory M.; Veneman, Peter A.; ...

    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

  16. Density functional calculations for a high energy density compound of formula C6H 6-n (NO 2) n.

    PubMed

    Chi, Wei-Jie; Li, Lu-Lin; Li, Bu-Tong; Wu, Hai-Shun

    2012-08-01

    A series of polynitroprismanes, C(6)H(6-n )(NO(2))(n) (n = 1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation (Q) and the theoretical density of the molecule (ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs.

  17. Evolution of Helium Bubbles and Discs in Irradiated 6H-SiC during Post-Implantation Annealing

    PubMed Central

    Shen, Qiang; Zhou, Wei; Ran, Guang; Li, Ruixiang; Feng, Qijie; Li, Ning

    2017-01-01

    The single crystal 6H-SiC with [0001] crystal direction irradiated by 400 keV He+ ions with 1 × 1017 ions/cm2 fluence at 400 °C were annealed at 600, 900, 1200 and 1400 °C for different durations. The evolution of helium bubbles and discs was investigated by transmission electron microscopy. An irradiated layer distributed with fine helium bubbles was formed with a width of ~170 nm after helium ion irradiation. The size of gas bubbles increased with increasing annealing time and temperature and finally reached stable values at a given annealing temperature. According to the relationship between the bubble radii and annealing time, an empirical formula for calculating the bubble radii at the annealing temperature ranged from 600 to 1400 °C was given by fitting the experiment data. Planar bubble clusters (discs) were found to form on (0001) crystal plane at both sides of the bubble layer when the annealing temperature was at the range of 800–1200 °C. The mechanism of bubble growth during post-implantation annealing and the formation of bubble discs were also analyzed and discussed. PMID:28772459

  18. 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.

  19. 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.

  20. Coupled antiferromagnetic spin- 12 chains in green dioptase Cu6[Si6O18]·6H2O

    DOE PAGES

    Podlesnyak, Andrey A; Larry M. Anovitz; Kolesnikov, Alexander I; ...

    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