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Sample records for cubic sic films

  1. 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.

  2. Stress reduction in epitaxial GaN films on Si using cubic SiC as intermediate layers

    NASA Astrophysics Data System (ADS)

    Komiyama, Jun; Abe, Yoshihisa; Suzuki, Shunichi; Nakanishi, Hideo

    2006-08-01

    Stress in the epitaxial films of GaN on Si is reduced by using SiC as intermediate layers. The crystalline films of cubic SiC (0-1μm), thin AlN (50nm), and GaN (1-3μm) were prepared on 3in. (1 1 1) Si substrates—stacked in the order of GaN /AlN/SiC/Si—by metalorganic vapor-phase epitaxy. It is revealed by Raman spectroscopy that the tensile stress in GaN is reduced to half (reduction of about 300MPa) for GaN on Si with SiC intermediate layers compared with GaN on Si without SiC intermediate layers. Because of stress reduction, crack-free GaN on Si with a thickness of 2μm was obtained by using SiC intermediate layers. Cracking was minimized even on thicker GaN on Si (3μm thick) with SiC intermediate layers. The SiC intermediate layers are promising for the realization of nitride based electronic devices on Si.

  3. Ellipsometric study of cubic SiC

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  4. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    PubMed Central

    2011-01-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals. PMID:21762496

  5. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Yong; Chen, Changxin; Li, Jiang-Tao; Yang, Yun; Lin, Zhi-Ming

    2011-07-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  7. 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.

  8. 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.

  9. Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Craciun, V.; Craciun, D.; Socol, G.; Behdad, S.; Boesl, B.; Himcinschi, C.; Makino, H.; Socol, M.; Simeone, D.

    2016-06-01

    The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the Csbnd C bonds and a corresponding decrease of the Sisbnd C bonds in the irradiated area, which could explain the degradation of mechanical properties.

  10. Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition.

    PubMed

    Cheng, Qijin; Xu, S; Long, Jidong; Huang, Shiyong; Guo, Jun

    2007-11-21

    Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500 °C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49 at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6 nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films. PMID:21730481

  11. Low pressure growth of cubic boron nitride films

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P. (Inventor); Shing, Yuh-Han (Inventor)

    1997-01-01

    A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron.

  12. Study of CVD SiC thin film for space mirror

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhan; Zhang, Yumin; Han, Jiecai; He, Xiaodong

    2006-01-01

    The performance of space mirror lied on the properties of the mirror surface material to a great extent. In this paper, the silicon carbide thin film deposited on reaction-bonded silicon carbide (RBSC) space mirror blank was produced by Chemical Vapor Deposition (CVD) process. Some mechanical and physical properties of the SiC thin film were tested because they were important to study ability to work of space mirror. The result of XRD phase analysis indicated that the component of the SiC thin film was β-SiC. The micro hardness of the film was tested. The thickness of SiC thin film was tested using needle touch contour graph. The results showed that the thickness of SiC film was about 20 μm and film was even in the macro scope. The adhesion strength of SiC thin film and RBSC substrate was tested by scratch method and the results showed that was excellent. The residual stress of SiC thin film was tested by X-ray, at the same time; the origin of residual stress and the calculation of thermal stress were discussed. In the room temperature, the residual stress of the SiC film was compressive. After precision grinding, the surface topography and roughness of the SiC thin film was tested by Atomic Force Microscope (AFM). The results showed that the surface of SiC thin film had extremely low surface roughness and high surface form accuracy. The thermal shock resistance of SiC film was fine by tested.

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

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

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

  14. Exciton-polariton state in nanocrystalline SiC films

    NASA Astrophysics Data System (ADS)

    Semenov, А. V.; Lopin, А. V.

    2016-05-01

    We studied the features of optical absorption in the films of nanocrystalline SiC (nc-SiC) obtained on the sapphire substrates by the method of direct ion deposition. The optical absorption spectra of the films with a thickness less than ~500 nm contain a maximum which position and intensity depend on the structure and thickness of the nc-SiC films. The most intense peak at 2.36 eV is observed in the nc-SiC film with predominant 3C-SiC polytype structure and a thickness of 392 nm. Proposed is a resonance absorption model based on excitation of exciton polaritons in a microcavity. In the latter, under the conditions of resonance, there occurs strong interaction between photon modes of light with λph=521 nm and exciton of the 3С polytype with an excitation energy of 2.36 eV that results in the formation of polariton. A mismatch of the frequencies of photon modes of the cavity and exciton explains the dependence of the maximum of the optical absorption on the film thickness.

  15. Effects of Ni doping and structural defects on magnetic properties of annealed SiC films

    NASA Astrophysics Data System (ADS)

    Fu, Yuting; Jin, Xin; Sun, Ning; Li, Chunjing; An, Yukai; Liu, Jiwen

    2016-08-01

    Ni-doped SiC films deposited on Si (100) substrates prepared by RF-magnetron sputtering were discussed in this paper. The results show that with reference to the as-deposited as well as annealing at 800 °C. C atoms were substituted by Ni atoms in the 3Csbnd SiC lattice and Ni-related secondary phase cannot be detected. After annealing at 1200 °C, the crystal quality improved obviously while the majority of Ni atoms form the Ni2Si secondary phase. Temperature dependent on resistivity reveals that the conduction mechanism is dominated by Mott variable range hopping behavior for the Ni-doped SiC films, confirming that the carriers are localized. All the films are ferromagnetic at 300 K and annealing can evidently improve the room-temperature (RT) ferromagnetism. The bound magnetic polarons should be responsible for the RT ferromagnetism of the Ni-doped SiC films.

  16. Ultra-Low-Cost Room Temperature SiC Thin Films

    NASA Technical Reports Server (NTRS)

    Faur, Maria

    1997-01-01

    The research group at CSU has conducted theoretical and experimental research on 'Ultra-Low-Cost Room Temperature SiC Thin Films. The effectiveness of a ultra-low-cost room temperature thin film SiC growth technique on Silicon and Germanium substrates and structures with applications to space solar sells, ThermoPhotoVoltaic (TPV) cells and microelectronic and optoelectronic devices was investigated and the main result of this effort are summarized.

  17. Surface Brillouin scattering of cubic boron nitride films

    NASA Astrophysics Data System (ADS)

    Zinin, P.; Manghnani, M. H.; Zhang, X.; Feldermann, H.; Ronning, C.; Hofsäss, H.

    2002-04-01

    Surface Brillouin scattering has been used to determine the elastic properties of thin hard submicron cubic boron nitride (cBN) films grown on silicon by mass selected ion beam deposition. The elastic properties of the films have been determined by fitting experimental data to theoretical dispersion curves. A Green's function method was used to predict Brillouin scattering spectra of the acoustic excitation at the free surface. Our results demonstrate that the effect of the thin hexagonal boron nitride interlayer located between cBN film and the Si substrate on the velocity of the surface acoustic wave does not exceed 2% for a thin (16 nm) film and is negligible for cBN films thicker than 100 nm. The elastic properties of the cBN films are not softer than those of bulk cBN.

  18. Preparation of superhydrophobic nanodiamond and cubic boron nitride films

    SciTech Connect

    Zhou, Y. B.; Liu, W. M.; Wang, P. F.; Yang, Y.; Ye, Q.; He, B.; Pan, X. J.; Zhang, W. J.; Bello, I.; Lee, S. T.; Zou, Y. S.

    2010-09-27

    Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150 deg. and a sliding angle smaller than 10 deg. were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

  19. ToF-MEIS stopping measurements in thin SiC films

    NASA Astrophysics Data System (ADS)

    Linnarsson, M. K.; Khartsev, S.; Primetzhofer, D.; Possnert, G.; Hallén, A.

    2014-08-01

    Electronic stopping in thin, amorphous, SiC films has been studied by time-of-flight medium energy ion scattering and conventional Rutherford backscattering spectrometry. Amorphous SiC films (8, 21 and 36 nm) were prepared by laser ablation using a single crystalline silicon carbide target. Two kinds of substrate films, one with a lower atomic mass (carbon) and one with higher atomic mass (iridium) compared to silicon has been used. Monte Carlo simulations have been used to evaluate electronic stopping from the shift in energy for the signal scattered from Ir with and without SiC. The two kinds of samples are used to illustrate the strength and challenges for ToF-MEIS compared to conventional RBS.

  20. Time-Domain Thermoreflectance Measurements of Thermal Transport in Amorphous SiC Thin Films

    NASA Astrophysics Data System (ADS)

    Daly, Brian; Hondongwa, Donald; King, Sean

    2010-03-01

    We present ultrafast optical pump-probe measurements of thermal transport in a series of amorphous SiC samples. The samples were grown on Si wafers by plasma enhanced chemical vapor deposition utilizing various combinations of methylsilanes and H2 and He diluent gases. The sample films were well characterized and found to have densities (1.3 -- 2.3 g cm-3) and dielectric constants (4.0 -- 7.2) that spanned a wide range of values. Prior to their measurement, the samples were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser that produced sub-picosecond pulses of a few nJ. The pulses heat the Al coating, causing a transient reflectivity change. As the Al film cools into the SiC film, the reflectivity change can be measured, giving a measure of the thermal effusivity of the SiC film. We then extract values for the thermal conductivity of the SiC films and find that it varies from less than half of the thermal conductivity of amorphous SiO2 for the lower density materials to somewhat larger than amorphous SiO2 for the highest density films.

  1. Conformal Thin Film Packaging for SiC Sensor Circuits in Harsh Environments

    NASA Technical Reports Server (NTRS)

    Scardelletti, Maximilian C.; Karnick, David A.; Ponchak, George E.; Zorman, Christian A.

    2011-01-01

    In this investigation sputtered silicon carbide annealed at 300 C for one hour is used as a conformal thin film package. A RF magnetron sputterer was used to deposit 500 nm silicon carbide films on gold metal structures on alumina wafers. To determine the reliability and resistance to immersion in harsh environments, samples were submerged in gold etchant for 24 hours, in BOE for 24 hours, and in an O2 plasma etch for one hour. The adhesion strength of the thin film was measured by a pull test before and after the chemical immersion, which indicated that the film has an adhesion strength better than 10(exp 8) N/m2; this is similar to the adhesion of the gold layer to the alumina wafer. MIM capacitors are used to determine the dielectric constant, which is dependent on the SiC anneal temperature. Finally, to demonstrate that the SiC, conformal, thin film may be used to package RF circuits and sensors, an LC resonator circuit was fabricated and tested with and without the conformal SiC thin film packaging. The results indicate that the SiC coating adds no appreciable degradation to the circuits RF performance. Index Terms Sputter, silicon carbide, MIM capacitors, LC resonators, gold etchants, BOE, O2 plasma

  2. SiC Nanowire Film Photodetectors: A Promising Candidate Toward High Temperature Photodetectors.

    PubMed

    Chong, Haining; Yang, Huijun; Yang, Weiyou; Zheng, Jinju; Shang, Minghui; Yang, Zuobao; Wei, Guodong; Gao, Fengmei

    2016-04-01

    In this study, UV photodetectors (PDs) based on SiC nanowire films have been successfully prepared by a simple and low-cost drip-coating method followed by sintering at 500 °C. The corresponding electrical characterizations clearly demonstrate that the SiC nanowire based PD devices can be regarded as a promising candidate for UV PDs. The PDs can exhibit the excellent performances of fast, high sensitivity, linearity, and stable response, which can thus achieve on-line monitoring of weak UV light. Furthermore, the SiC nanowire-based PDs enable us to fabricate detectors working under high temperature as high as 150 °C. The high photosensitivity and rapid photoresponse for the PDs can be attributed to the superior single crystalline quality of SiC nanowires and the ohmic contact between the electrodes and nanowires. PMID:27451712

  3. Effects of thermal annealing on photoluminescence of Si+/C+ implanted SiO2 films

    NASA Astrophysics Data System (ADS)

    Chen, Yin-Yu; Chao, Der-Sheng; Tsai, Hsu-Sheng; Liang, Jenq-Horng

    2016-04-01

    The mechanisms of photoluminescence (PL) originating from Si+/C+ implanted SiO2 are still unclear and need to be clarified. Thus, the purpose of this study is to thoroughly investigate the effects of ion implantation and post-annealing temperature on microstructures and PL characteristics of the Si+/C+ implanted SiO2 films. A comparative analysis was also conducted to clarify the different optical properties between the Si+ and Si+/C+ implanted SiO2 films. In this study, thermally-grown SiO2 films on Si substrates were used as the matrix materials. The Si+ ions and C+ ions were separately implanted into the SiO2 films at room temperature. After ion implantation, the post-annealing treatments were carried out using the furnace annealing (FA) method at various temperatures (600-1100 °C) for 1 h in a N2 ambient. The PL characteristics of the implanted SiO2 films were analyzed using a fluorescence spectrophotometer. The results revealed that the distinct PL peaks were observed at approximately 310, 450 and 650 nm in the Si+-implanted SiO2 films, which can be attributed to the defects, the so-called oxygen deficiency centers (ODCs) and non-bridging oxygen hole centers (NBOHCs), in the materials. In contrast to the Si+ ion implantation, the SiO2 films which were sequentially implanted with Si+ and C+ ions and annealed at 1100 °C can emit white light corresponding to the PL peaks located at around 420, 520 and 720 nm, those can be assigned to the Si-C bonding, C-C graphite-like structure (sp2), and Si nanocrystals, respectively. Moreover, a correlation between the optical properties, microstructures, and bonding configurations of the Si+/C+ implanted SiO2 films was also established in this study.

  4. Nanomechanical properties of SiC films grown from C{sub 60} precursors using atomic force microscopy

    SciTech Connect

    Morse, K.; Balooch, M.; Hamza, A.V.; Belak, J.

    1994-12-01

    The mechanical properties of SiC films grown via C{sub 60} precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and modified diamond cantilever AFM tips were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be between 26 and 40 GPa by nanoindentation of the film with the diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of {approximately}300 GPa is estimated for these SiC films. In order to better understand the atomic scale mechanisms that determine the hardness and friction of SiC, we simulated the molecular dynamics of a diamond indenting a crystalline SiC substrate.

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

    SciTech Connect

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

    1999-07-01

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

  6. Quasi-Freestanding multilayer graphene films on the carbon face of SiC

    SciTech Connect

    Siegel, D. A.; Hwang, C. G.; Fedorov, A. V.; Lanzara, A.

    2010-06-30

    The electronic band structure of as-grown and doped graphene grown on the carbon face of SiC is studied by high-resolution angle-resolved photoemission spectroscopy, where we observe both rotations between adjacent layers and AB-stacking. The band structure of quasi-freestanding AB-bilayers is directly compared with bilayer graphene grown on the Si-face of SiC to study the impact of the substrate on the electronic properties of epitaxial graphene. Our results show that the C-face films are nearly freestanding from an electronic point of view, due to the rotations between graphene layers.

  7. Wetting behavior of low-index cubic SiC surfaces.

    PubMed

    Catellani, Alessandra; Cicero, Giancarlo; Galli, Giulia

    2006-01-14

    We report on the interaction of water molecules with polar and nonpolar stoichiometric surfaces of cubic silicon carbide, as described by ab initio molecular dynamics at finite temperature. Our calculations show that, irrespective of coverage, in the gas phase water spontaneously dissociates on both polar Si-terminated (001) and nonpolar (110) surfaces, following similar mechanisms. The specific geometric arrangement of atoms on the outermost surface layer is responsible for water orientation and coordination and thus plays a major role in determining surface reactivity. This is found to be the case also for water on a computer-generated amorphous-SiC surface. In addition, from a macroscopic standpoint, the ability of the two crystalline surfaces with different polarities to induce water dissociation can be related to the similarities of their ionization potentials. PMID:16422626

  8. Characterization Of Superconducting Samples With SIC System For Thin Film Developments: Status And Recent Results

    SciTech Connect

    Phillips, H. Lawrence; Reece, Charles E.; Valente-Feliciano, Anne-Marie; Xiao, Binping; Eremeev, Grigory V.

    2014-02-01

    Within any thin film development program directed towards SRF accelerating structures, there is a need for an RF characterization device that can provide information about RF properties of small samples. The current installation of the RF characterization device at Jefferson Lab is Surface Impedance Characterization (SIC) system. The data acquisition environment for the system has recently been improved to allow for automated measurement, and the system has been routinely used for characterization of bulk Nb, films of Nb on Cu, MgB{sub 2}, NbTiN, Nb{sub 3}Sn films, etc. We present some of the recent results that illustrate present capabilities and limitations of the system.

  9. Growth and interface phase stability of barium hexaferrite films on SiC(0001)

    SciTech Connect

    Lazarov, V. K.; Hasnip, P. J.; Cai, Z.; Ziemer, K. S.; Yoshida, K.

    2011-04-01

    We have studied interface phase stability of the BaFe{sub 12}O{sub 19} (BaM) thin films grown by molecular beam epitaxy on SiC(0001). The films were epitaxially grown with the following crystallographic relation: BaM(0001) parallel SiC(0001) and BaM(11-20) parallel SiC(11-20). High resolution TEM reveals the existence of two interfacial bands with different structure than BaM. The first band close to SiC is SiO{sub x} while the second has spinel structure and chemically corresponds to Fe{sub 3}O{sub 4}. These findings suggest that at initial growth stages Fe{sub 3}O{sub 4} is more favorable than BaM. Density functional theory modeling of the phase stability of BaM compared to Fe{sub 3}O{sub 4} shows that BaM is only stable at high oxygen partial pressures.

  10. Effect of SiC interlayer between Ti6Al4V alloy and hydroxyapatite films.

    PubMed

    Azem, Funda Ak; Birlik, Isil; Braic, Viorel; Toparli, Mustafa; Celik, Erdal; Parau, Anca; Kiss, Adrian; Titorencu, Irina; Vladescu, Alina

    2015-04-01

    Bioactive coatings are frequently used to improve the osseointegration of the metallic implants used in dentistry or orthopaedics. Among different types of bioactive coatings, hydroxyapatite (Ca10(PO4)6(OH)2) is one of the most extensively used due to its chemical similarities to the components of bones and teeth. In this article, production and characterization of hydroxyapatite films deposited on Ti6Al4V alloy prepared by magnetron sputtering were reported. Besides, SiC was deposited on substrate surface to study the interlayer effect. Obtained coatings were annealed at 600 °C for 30 and 120 min in a mixed atmosphere of N2 + H2O vapours with the heating rate of 12 °C min(-1). The effects of SiC interlayer and heat treatment parameters on the structural, mechanical and corrosion properties were investigated. After heat treatment process, the crystalline hydroxyapatite was obtained. Additionally, cell viability tests were performed. The results show that the presence of the SiC interlayer contributes a decrease in surface roughness and improves the mechanical properties and corrosion performance of the hydroxyapatite coatings. Biological properties were not affected by the presence of the SiC interlayer. PMID:25934259

  11. Preparation of films of a highly aligned lipid cubic phase.

    PubMed

    Squires, Adam M; Hallett, James E; Beddoes, Charlotte M; Plivelic, Tomás S; Seddon, Annela M

    2013-02-12

    We demonstrate a method by which we can produce an oriented film of an inverse bicontinuous cubic phase (Q(II)(D)) formed by the lipid monoolein (MO). By starting with the lipid as a disordered precursor (the L(3) phase) in the presence of butanediol, we can obtain a film of the Q(II)(D) phase showing a high degree of in-plane orientation by controlled dilution of the sample under shear within a linear flow cell. We demonstrate that the direction of orientation of the film is different from that found in the oriented bulk material that we have reported previously; therefore, we can now reproducibly form Q(II)(D) samples oriented with either the [110] or the [100] axis aligned in the flow direction depending on the method of preparation. The deposition of MO as a film, via a moving fluid-air interface that leaves a coating of MO in the L(3) phase on the capillary wall, leads to a sample in the [110] orientation. This contrasts with the bulk material that we have previously demonstrated to be oriented in the [100] direction, arising from flow producing an oriented bulk slug of material within the capillary tube. The bulk sample contains significant amounts of residual butanediol, which can be estimated from the lattice parameter of the Q(II)(D) phase obtained. The sample orientation and lattice parameters are determined from synchrotron small-angle X-ray scattering patterns and confirmed by simulations. This has potential applications in the production of template materials and the growth of protein crystals for crystallography as well as deepening our understanding of the mechanisms underlying the behavior of lyotropic liquid-crystal phases. PMID:23347289

  12. Mechanical properties of pulsed laser deposited nanocrystalline SiC films

    NASA Astrophysics Data System (ADS)

    Craciun, D.; Socol, G.; Cristea, D. V.; Stoicanescu, M.; Olah, N.; Balazs, K.; Stefan, N.; Lambers, E.; Craciun, V.

    2015-05-01

    The mechanical properties of nanocrystalline SiC thin films grown on (100) Si at a substrate temperature of 1000 °C under a CH4 atmosphere using the pulsed laser deposition (PLD) technique were investigated. Nanoindentation results showed that films exhibited hardness values around 36 GPa and Young modulus values around 250 GPa. Scratch tests found that films were adherent to the substrate, with critical load values similar to those recorded for other hard coatings deposited on significantly softer Si substrates. Wear tests performed at a temperature of 900 °C showed that films exhibited friction coefficients and wear rates very similar to those measured at room temperature, due to the presence of C-C bonds as evidenced by X-ray photoelectron spectroscopy investigations. These results recommend such coatings for demanding high temperature applications such as nuclear fuel encapsulation.

  13. Enhanced electroactive properties of polyurethane films loaded with carbon-coated SiC nanowires

    NASA Astrophysics Data System (ADS)

    Guiffard, B.; Guyomar, D.; Seveyrat, L.; Chowanek, Y.; Bechelany, M.; Cornu, D.; Miele, P.

    2009-03-01

    Polyurethane-based nanocomposite films were prepared by incorporating carbon-coated SiC nanowires (SiC@C) into the polymer matrix. Electric field-induced strain measurements revealed that a loading of 0.5 wt% SiC@C increased the strain level by a factor of 1.7 at a moderate field strength (6.5 V µm-1). Current-electric field characteristics and the film thickness dependence of strain demonstrated that the improvement of the electromechanical response was linked to a more pronounced space charge effect in the nanocomposite than in the polymer host. DSC measurements revealed that the level of phase mixing in the PU matrix remained unchanged after SiC@C filling; hence, the nano-objects themselves acted as charge traps.

  14. First principles-based multiparadigm, multiscale strategy for simulating complex materials processes with applications to amorphous SiC films

    SciTech Connect

    Naserifar, Saber; Goddard, William A.; Tsotsis, Theodore T.; Sahimi, Muhammad

    2015-05-07

    Progress has recently been made in developing reactive force fields to describe chemical reactions in systems too large for quantum mechanical (QM) methods. In particular, ReaxFF, a force field with parameters that are obtained solely from fitting QM reaction data, has been used to predict structures and properties of many materials. Important applications require, however, determination of the final structures produced by such complex processes as chemical vapor deposition, atomic layer deposition, and formation of ceramic films by pyrolysis of polymers. This requires the force field to properly describe the formation of other products of the process, in addition to yielding the final structure of the material. We describe a strategy for accomplishing this and present an example of its use for forming amorphous SiC films that have a wide variety of applications. Extensive reactive molecular dynamics (MD) simulations have been carried out to simulate the pyrolysis of hydridopolycarbosilane. The reaction products all agree with the experimental data. After removing the reaction products, the system is cooled down to room temperature at which it produces amorphous SiC film, for which the computed radial distribution function, x-ray diffraction pattern, and the equation of state describing the three main SiC polytypes agree with the data and with the QM calculations. Extensive MD simulations have also been carried out to compute other structural properties, as well the effective diffusivities of light gases in the amorphous SiC film.

  15. Theory and practice of SiC growth on Si and its applications to wide-gap semiconductor films

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.

    2014-08-01

    The recent advances in epitaxial SiC films' growth on Si are overviewed. The basic classical methods currently used for SiC films' growth are discussed and their advantages and disadvantages are explored. The basic idea and the theoretical background for a new method of the synthesis of epitaxial SiC films on Si are given. It will be shown that the new method is significantly different from the classical techniques of thin-film growth where the evaporation of the atoms onto the substrate surface is exploited. The new method is based on the substitution of some atoms in the silicon matrix by the carbon atoms to form the molecules of silicon carbide. It will be shown that the following process of SiC nucleation happens gradually without destroying the crystalline structure of the silicon matrix, and the orientation of a grown film is imposed by the original crystalline structure of the silicon matrix (not only by the substrate surface as in conventional methods of film growth). A comparison of the new method with other epitaxy techniques will be given. The new method of solid-phase epitaxy based on the substitution of atoms and on the creation of dilatation dipoles solves one of the major problems in heteroepitaxy. It provides the synthesis of low-defective unstrained epitaxial films with a large difference between the lattice parameters of the film and the substrate without using any additional buffer layers. This method has another unique feature distinguishing it from the classical techniques of SiC films' growth—it allows the growing of SiC films of hexagonal polytypes. A new kind of phase transformation in solids owing to the chemical transformation of one substance into another will be described theoretically and revealed experimentally. This type of phase transformation, and the mechanism of a broad class of heterogeneous chemical reactions between gas and solid phases, will be illustrated by an example of the growth of SiC epitaxial layers due to the

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

    NASA Astrophysics Data System (ADS)

    Addamiano, A.; Sprague, J. A.

    1984-03-01

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

  17. Microstructure investigation of SiC films synthesized from liquid phase in Sm-Co melts

    NASA Astrophysics Data System (ADS)

    Lee, Pei-Ting; Nayak, Pramoda K.; Wang, Sheng-Chang; Sung, James C.; Huang, Jow-Lay

    2011-12-01

    Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure of 10 5 Pa. The synthesis was carried out in a tube furnace through cyclic heating process using methane as a carbon source and Sm-Co mixed powder as a solvent. The growth of SiC from rare earth Sm-based solvent is an innovative approach, and Co can promote the formation of solvent during the growth process. The structural and compositional analyses were carried out using X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and transmission electron microscopy. Results indicated that β-SiC was successfully fabricated on Si (1 1 1) substrate. The heterogeneous nucleation of β-SiC was found to be observed initially at the edge of triangle-shaped sites on Si (1 1 1) surface that formed due to the existence of Co, and then grew and expanded to form β-SiC film. The growth process of SiC via vapour-liquid-solid mechanism was also discussed in this study.

  18. Raman spectroscopy study of SiC thin films prepared by PECVD for solar cell working in hard environment

    NASA Astrophysics Data System (ADS)

    Sasinková, Vlasta; Huran, Jozef; Kleinová, Angela; Boháček, Pavol; Arbet, Juraj; Sekáčova, Mária

    2015-09-01

    Amorphous silicon carbide films were deposited by plasma enhanced chemical vapor deposition (PECVD) technology using SiH4, CH4, H2 and NH3 gas as precursors. The concentration of elements in the films was determined by RBS and ERD analytical method. Chemical compositions were analyzed by FT-IR spectroscopy. Raman spectroscopy study of the SiC films were performed by using a Raman microscope. Irradiation of samples with neutrons to fluencies A(7.9x1014 cm-2), B(5x1015 cm-2) and C(3.4x1016 cm-2) was performed at room temperature. Raman spectroscopy results of SiC films showed decreasing of Raman band feature intensity after neutron irradiation and slightly decreased with increased neutron fluencies. Raman spectra differences between types of films before and after neutron irradiation are discussed. The electrical properties of SiC films were determined by the I-V measurement at 295 K. The measured currents were greater (about two order) after irradiation than the current before irradiation for all samples and rose up with neutron fluencies.

  19. Low energy radiation stability of nano-crystalline cubic Zirconia films

    NASA Astrophysics Data System (ADS)

    Kalita, Parswajit; Ghosh, Santanu; Avasthi, Devesh K.

    2016-07-01

    The radiation stability of nano-crystalline cubic Zirconia films was investigated under 41 keV He ion irradiation. These ions were chosen to simulate alpha particles (produced during fission events) because of the similar electronic energy loss in Zirconia. The ZrO2 films, with an average grain size of 8 nm, were grown on Si (1 0 0) substrates by electron beam assisted thermal evaporation. Although the cubic structure was retained upon irradiation, a slight reduction in crystallinity in the irradiated films was detected as compared to the as-deposited film. No bulk amorphization was however observed for any of the fluences and hence these films are radiation tolerant to alpha particles.

  20. Suppression of UV photoluminescence in sandwich-structured Si/C composite films

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Yuan, C. L.; Liu, R.; Ong, P. P.

    2002-10-01

    Thin films of composite silicon/carbon (Si/C) were prepared by pulsed-laser ablation alternately on C and Si materials on a rotary target, followed by vacuum deposition of the ablated materials on an ultra-clean glass substrate. The film structure consisted of alternate nanolayers of Si nanocrystals and amorphous C, with a fairly sharp demarcation boundary between adjacent layers forming well-defined sandwich structures. At room temperature, this composite nanolayered structure was found to yield much lower photoluminescent (PL) emission in the ultra violet region (300 390 nm) in comparison with that obtained for pure Si or for Si/Al2O3 thin films (see Zhu Y., Wang H. and Ong P. P. J. Phys. D, 33 (2000) 1965, and Zhu Y. and Ong P. P. J. Phys. Condens. Matter, 13 (2001) L1). The suppression mechanism of the UV PL emission appeared to occur in the interfacial surfaces between adjacent crystalline Si and amorphous C layers. It provides a possible way to selectively filter out the usually undesirable UV component of the PL emission from the silicon nanoparticles.

  1. Structural analysis of cubic boron nitride films by ultraviolet Raman spectroscopy

    SciTech Connect

    Leung, K.M.; Li, H.Q.; Zou, Y.S.; Ma, K.L.; Chong, Y.M.; Ye, Q.; Zhang, W.J.; Lee, S.T.; Bello, I.

    2006-06-12

    Cubic boron nitride (BN) films with improved crystallinity are deposited by physical vapor deposition at an extremely low substrate bias (-35 V). The films are characterized by UV Raman in association with Fourier transformed infrared (FTIR) spectroscopy. The influences of bias voltage and film thickness on the characterizations are investigated. UV Raman, in contrast to FTIR, is demonstrated to be a more powerful tool with high sensitivity for quantitative and/or qualitative evaluation of the phase purity and crystallinity, especially as the film thickness increases. Hexagonal BN inclusions (less than 1%), not evident in FTIR, are clearly revealed by UV Raman analysis.

  2. A probabilistic model of the electron transport in films of nanocrystals arranged in a cubic lattice

    NASA Astrophysics Data System (ADS)

    Kriegel, Ilka; Scotognella, Francesco

    2016-08-01

    The fabrication of nanocrystal (NC) films, starting from colloidal dispersion, is a very attractive topic in condensed matter physics community. NC films can be employed for transistors, light emitting diodes, laser, and solar cells. For this reason the understanding of the film conductivity is of major importance. In this paper we describe a probabilistic model that allow to predict the conductivity of the NC films, in this case of a cubic lattice of Lead Selenide NCs. The model is based on the hopping probability between NCs show a comparison with experimental data reported in literature.

  3. Ambient condition laser writing of graphene structures on polycrystalline SiC thin film deposited on Si wafer

    SciTech Connect

    Yue, Naili; Zhang, Yong; Tsu, Raphael

    2013-02-18

    We report laser induced local conversion of polycrystalline SiC thin-films grown on Si wafers into multi-layer graphene, a process compatible with the Si based microelectronic technologies. The conversion can be achieved using a 532 nm CW laser with as little as 10 mW power, yielding {approx}1 {mu}m graphene discs without any mask. The conversion conditions are found to vary with the crystallinity of the film. More interestingly, the internal structure of the graphene disc, probed by Raman imaging, can be tuned with varying the film and illumination parameters, resembling either the fundamental or doughnut mode of a laser beam.

  4. Effects of ambient conditions on the adhesion of cubic boron nitride films on silicon substrates

    SciTech Connect

    Cardinale, G.F.; Howitt, D.G.; Mirkarimi, P.B.; McCarty, K.F.; Klaus, E.J.; Medlin, D.L.

    1994-08-01

    Effect of environmental conditions on cubic boron nitride (cBN) film adhesion to silicon substrates was studied. cBN films were deposited onto (100)-oriented silicon substrates by ion-assisted pulsed laser deposition. Irradiating ions were mixtures of nitrogen with argon, krypton, and xenon. Under room-ambient conditions, the films delaminated in the following time order: N/Xe, N/Kr, and N/Ar. cBN films deposited using N/Xe ion-assisted deposition were exposed to four environmental conditions for several weeks: a 1-mTorr vacuum, high humidity, dry oxygen, and dry nitrogen. Films exposed to the humid environment delaminated whereas those stored under vacuum or in dry gases did not. Films stored in dry nitrogen were removed after nearly two weeks and placed in the high-humidity chamber; these films subsequently delaminated within 14 hours.

  5. Research on the piezoelectric response of cubic and hexagonal boron nitride films

    NASA Astrophysics Data System (ADS)

    Chen, Xi-ming; Sun, Lian-jie; Yang, Bao-he; Guo, Yan; Wu, Xiaoguo

    2012-03-01

    Boron nitride (BN) films for high-frequency surface acoustic wave (SAW) devices are deposited on Ti/Al/Si(111) wafers by radio frequency (RF) magnetron sputtering. The structure of BN films is investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) spectra, and the surface morphology and piezoelectric properties of BN films are characterized by atomic force microscopy (AFM). The results show that when the flow ratio of nitrogen and argon is 2:18, the cubic BN (c-BN) film is deposited with high purity and c-axis orientation, and when the flow ratio of nitrogen and argon is 4:20, the hexagonal BN (h-BN) film is deposited with high c-axis orientation. Both particles are uniform and compact, and the roughnesses are 1.5 nm and 2.29 nm, respectively. The h-BN films have better piezoelectric response and distribution than the c-BN films.

  6. Chemical vapour deposition of undoped and spinel-doped cubic zirconia film using organometallic process

    NASA Astrophysics Data System (ADS)

    Takahashi, Yasutaka; Kawae, Takayuki; Nasu, Mineji

    1986-03-01

    Growth of undoped and spinel-doped ZrO 2 films on glass substrates by the vapour phase decomposition of zirconium t-butoxide (ZTB) was investigated. Undoped tetragonal and monoclinic ZrO 2 films were formed below and above 400°C, respectively. Cubic ZrO 2 films were grown when the ZrO 2 was doped with more than 5 mol% of spinel MgAl 2O 4. Magnesium aluminium isopropoxide MgAl 2 (O-i-Pr) 8 (MAI) was used as the dopant source of the spinel. The cubic films have a higher Vickers hardness than the monoclinic films by about 200-250 kg/mm 2, and are stable up to 800°C, above which they were transformed to the monoclinic phase. This is in contrast to the higher temperature stability of the spinel-doped zirconia powder with spinel content 6 mol% formed by hydrolysis of a isopropanol solution of mixed zirconium n-butoxide and MAI, where the tetragonal form of ZrO 2 was kept unchanged by annealing it up to about 1000°C. The difference is attributed to effect of surface energy control in the tetragonal powders which is absent in the cubic films produced by CVD.

  7. Structure and Luminescence Properties of Eu3+-Doped Cubic Mesoporous Silica Thin Films

    PubMed Central

    2010-01-01

    Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu3+ ions-doped mesoporous silica thin films increases linearly with increasing Eu3+ concentration. PMID:20672132

  8. Cluster-assembled cubic zirconia films with tunable and stable nanoscale morphology against thermal annealing

    NASA Astrophysics Data System (ADS)

    Borghi, F.; Sogne, E.; Lenardi, C.; Podestà, A.; Merlini, M.; Ducati, C.; Milani, P.

    2016-08-01

    Nanostructured zirconium dioxide (zirconia) films are very promising for catalysis and biotechnological applications: a precise control of the interfacial properties of the material at different length scales and, in particular, at the nanoscale, is therefore necessary. Here, we present the characterization of cluster-assembled zirconia films produced by supersonic cluster beam deposition possessing cubic structure at room temperature and controlled nanoscale morphology. We characterized the effect of thermal annealing in reducing and oxidizing conditions on the crystalline structure, grain dimensions, and topography. We highlight the mechanisms of film growth and phase transitions, which determine the observed interfacial morphological properties and their resilience against thermal treatments.

  9. High-quality, faceted cubic boron nitride films grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, W. J.; Jiang, X.; Matsumoto, S.

    2001-12-01

    Thick cubic boron nitride (cBN) films showing clear crystal facets were achieved by chemical vapor deposition. The films show the highest crystallinity of cBN films ever achieved from gas phase. Clear evidence for the growth via a chemical route is obtained. A growth mechanism is suggested, in which fluorine preferentially etches hBN and stabilizes the cBN surface. Ion bombardment of proper energy activates the cBN surface bonded with fluorine so as to enhance the bonding probability of nitrogen-containing species on the F-stabilized B (111) surface.

  10. The synthesis, characterization, and mechanical properties of thick, ultrahard cubic boron nitride films deposited by ion-assisted sputtering

    SciTech Connect

    Mirkarimi, P.B.; Medlin, D.L.; McCarty, K.F.; Dibble, D.C.; Clift, W.M.; Knapp, J.A.; Barbour, J.C.

    1997-08-01

    Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 {mu}m) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60{endash}70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN films are discussed with reference to other ultrahard thin films such as diamond and diamondlike carbon. {copyright} {ital 1997 American Institute of Physics.}

  11. The electrical properties of sulfur-implanted cubic boron nitride thin films

    NASA Astrophysics Data System (ADS)

    Deng, Jin-Xiang; Qin, Yang; Kong, Le; Yang, Xue-Liang; Li, Ting; Zhao, Wei-Ping; Yang, Ping

    2012-04-01

    Cubic boron nitride (c-BN) thin films are deposited on p-type Si wafers using radio frequency (RF) sputtering and then doped by implanting S ions. The implantation energy of the ions is 19 keV, and the implantation dose is between 1015 ions/cm2 and 1016 ions/cm2. The doped c-BN thin films are then annealed at a temperature between 400 °C and 800 °C. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  13. Preparation of cubic boron nitride thin film by the helicon wave plasma enhanced chemical vapor deposition

    SciTech Connect

    Kim, S.; Kim, I.; Kim, K.

    1996-12-01

    Cubic boron nitride ({ital c}-BN) film was deposited on Si(100) substrate using the chemical vapor deposition process assisted by high density plasma of Helicon wave with Borazine (B{sub 3}N{sub 3}H{sub 6}) precursor. It was found that the bombardment of ions with high flux and energy onto the film was necessarily required for synthesizing a {ital c}-BN film. Increasing a negative rf bias on the substrate increased the formation fraction of {ital c}-BN in the film. A nearly pure {ital c}-BN phase was synthesized at the conditions of plasma density in the reactor and rf substrate bias, above 10{sup 11} cm{sup {minus}3} and {minus}350 V, respectively. The phase identification of BN film was carried out by the transmission electron microscopy as well as Fourier transformed infrared spectroscopy. The infrared spectra for {ital c}-BN film synthesized at the rf bias of {minus}350 V appeared at 1093 cm{sup {minus}1} with a strong single peak, which is close to a value for the characteristic vibration mode of bulk {ital c}-BN (1065 cm{sup {minus}1}). The {ital c}-BN in the film was also confirmed and found to be a fine poly-crystalline with the grain sizes ranging from 200 to 400 A. {copyright} {ital 1996 American Institute of Physics.}

  14. Synthesis of cubic boron nitride films with mean ion energies of a few eV

    SciTech Connect

    Teii, Kungen; Yamao, Ryota; Yamamura, Toshifumi; Matsumoto, Seiichiro

    2007-02-01

    The lowest threshold energy of ion bombardment for cubic boron nitride (cBN) film deposition is presented. cBN films are prepared on positively biased Si (100) substrates from boron trifluoride (BF{sub 3}) gas in the high-density source region of an inductively coupled plasma with mean ion impact energies from 45 down to a few eV or less. The great decrease in the threshold ion energy is mainly attributed to specific chemical effects of fluorine as well as high ion-to-boron flux ratios. The results show evidence for the existence of a way to deposit cBN films through quasistatic chemical processes under ultralow-energy ion impact.

  15. Low-temperature synthesis of homogeneous nanocrystalline cubic silicon carbide films

    SciTech Connect

    Cheng Qijin; Xu, S.

    2007-09-01

    Silicon carbide films are fabricated by inductively coupled plasma chemical vapor deposition from feedstock gases silane and methane heavily diluted with hydrogen at a low substrate temperature of 300 deg. C. Fourier transform infrared absorption spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy analyses show that homogeneous nanocrystalline cubic silicon carbide (3C-SiC) films can be synthesized at an appropriate silane fraction X[100%xsilane flow(SCCM)/silane+methane flow(SCCM)] in the gas mixture. The achievement of homogeneous nanocrystalline 3C-SiC films at a low substrate temperature of 300 deg. C is a synergy of a low deposition pressure (22 mTorr), high inductive rf power (2000 W), heavy dilution of feedstock gases silane and methane with hydrogen, and appropriate silane fractions X (X{<=}33%) in the gas mixture employed in our experiments.

  16. Electrochemical properties and applications of nanocrystalline, microcrystalline, and epitaxial cubic silicon carbide films.

    PubMed

    Zhuang, Hao; Yang, Nianjun; Zhang, Lei; Fuchs, Regina; Jiang, Xin

    2015-05-27

    Microstructures of the materials (e.g., crystallinitiy, defects, and composition, etc.) determine their properties, which eventually lead to their diverse applications. In this contribution, the properties, especially the electrochemical properties, of cubic silicon carbide (3C-SiC) films have been engineered by controlling their microstructures. By manipulating the deposition conditions, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are obtained with varied properties. The epitaxial 3C-SiC film presents the lowest double-layer capacitance and the highest reversibility of redox probes, because of its perfect (001) orientation and high phase purity. The highest double-layer capacitance and the lowest reversibility of redox probes have been realized on the nanocrystalline 3C-SiC film. Those are ascribed to its high amount of grain boundaries, amorphous phases and large diversity in its crystal size. Based on their diverse properties, the electrochemical performances of 3C-SiC films are evaluated in two kinds of potential applications, namely an electrochemical capacitor using a nanocrystalline film and an electrochemical dopamine sensor using the epitaxial 3C-SiC film. The nanocrystalline 3C-SiC film shows not only a high double layer capacitance (43-70 μF/cm(2)) but also a long-term stability of its capacitance. The epitaxial 3C-SiC film shows a low detection limit toward dopamine, which is one to 2 orders of magnitude lower than its normal concentration in tissue. Therefore, 3C-SiC film is a novel but designable material for different emerging electrochemical applications such as energy storage, biomedical/chemical sensors, environmental pollutant detectors, and so on. PMID:25939808

  17. CO Oxidation Prefers the Eley-Rideal or Langmuir-Hinshelwood Pathway: Monolayer vs Thin Film of SiC.

    PubMed

    Sinthika, S; Vala, Surya Teja; Kawazoe, Y; Thapa, Ranjit

    2016-03-01

    Using the first-principles approach, we investigated the electronic and chemical properties of wurtzite silicon carbide (2H-SiC) monolayer and thin film structures and substantiated their catalytic activity toward CO oxidation. 2H-SiC monolayer, being planar, is quite stable and has moderate binding with O2, while CO interacts physically; thus, the Eley-Rideal (ER) mechanism prevails over the Langmuir-Hinshelwood (LH) mechanism with an easily cleared activation barrier. Contrarily, 2H-SiC thin film, which exhibits a nonplanar structure, allows moderate binding of both CO and O2 on its surface, thus favoring the LH mechanism over the ER one. Comprehending these results leads to a better understanding of the reaction mechanisms involving structural contrast. Weak overlapping between the 2p(z)(C) and 3p(z)(Si) orbitals of the SiC monolayer system has been found to be the primary reason to revert the active site toward sp(3) hybridization, during interaction with the molecules. In addition, the influences of graphite and Ag(111) substrates on the CO oxidation mechanism were also studied, and it is observed that the ER mechanism is preserved on SiC/G system, while CO oxidation on the SiC/Ag(111) system follows the LH mechanism. The calculated Sabatier activities of the SiC catalysts show that the catalysts are very efficient in catalyzing CO oxidation. PMID:26866799

  18. Semiconducting properties of zinc-doped cubic boron nitride thin films

    SciTech Connect

    Nose, K.; Yoshida, T.

    2007-09-15

    We have examined the electronic properties of zinc-doped cubic boron nitride (cBN) thin films prepared by sputter deposition. The electric conductivity of films deposited in pure Ar increased as the concentration of zinc dopant increased, and hole conduction was identified by the measurement of thermoelectric currents. It was also found that the conductivity increment in such films was accompanied by a linear increase in the B/(B+N) ratio. At the same time, no modification of the composition and the conductivity by incorporated zinc was observed when film growth took place in presence of nitrogen gas. The effect of the excess boron on the conductivity emerged only when films show semi-insulating behavior. These results suggest that Zn substitution for nitrogen causes high electric conductivity of cBN. The electric contact between Ti electrode and semiconducting cBN was examined by the transfer length method, and Ohmic conduction was observed in the Ti/cBN contact. The specific contact resistance was affected by the specific resistance of cBN films, and it was reduced from 10{sup 5} to 100 {omega} cm{sup 2} by increasing the concentration of incorporated Zn.

  19. Role of polytypism and degree of hexagonality on the photoinduced optical second harmonic generation in SiC nanocrystalline films

    NASA Astrophysics Data System (ADS)

    Semenov, A.; Puziko, V.; Skorik, S.; Wojciechowski, A.; Fedorchuk, A. O.; Maciąg, A.

    2015-05-01

    Photoinduced optiсal second harmonic generation was studied in nanocrystalline SiC films prepared by the method of direct ion deposition. For the studies were chosen three types of polytypes (with different degree of hexagonality) - 24R with degree hexagonality G=25, 27R-G=44, 33R with - G=36. The bicolor photoinduced treatment was performed by the wavelengths 1064nm/532 nm by 15 ns YAG:Nd laser. The efficiency of the output SHG was evaluated by ratio of the corresponding signal intensities with respect to the references and by the time delay between the SHG and the fundamental maxima. Explanation of the observed effect is given within a framework of the occurrence of the nano-trapping levels in the film crystalline interfaces.

  20. Molecular dynamics simulation of delamination of a stiff, body-centered-cubic crystalline film from a compliant Si substrate

    NASA Astrophysics Data System (ADS)

    Hale, L. M.; Zhou, X. W.; Zimmerman, J. A.; Moody, N. R.; Ballarini, R.; Gerberich, W. W.

    2009-10-01

    Compliant substrate technology offers an effective approach to grow high-quality multilayered films, of importance to microelectronics and microelectromechanical systems devices. By using a thin, soft substrate to relieve the mismatch strain of an epitaxial film, the critical thickness of misfit dislocation formation in the overlayer is effectively increased. Experiments have indicated that stiff films deposited onto Si substrates can delaminate at the interface. However, the atomic mechanisms of the deformation and the fracture of the films have not been well studied. Here, we have applied molecular dynamics simulations to study the delamination of a stiff body-centered-cubic crystalline film from a compliant Si substrate due to tensile loading. The observed mechanical behavior is shown to be relatively independent of small changes in temperature, loading rate, and system size. Fracture occurs at the interface between the two materials resulting in nearly atomically clean surfaces. Dislocations are seen to nucleate in the body-centered-cubic film prior to delamination. At higher strains, a phase change to a face centered cubic is observed within the body-centered-cubic film, facilitating extensive dislocation growth and interaction. The various defects that form prior to fracture are discussed and related to the mechanical properties of the system.

  1. Nucleation and growth of cubic boron nitride films produced by ion-assisted pulsed laser deposition

    SciTech Connect

    Friedmann, T.A.; Medlin, D.L.; Mirkarimi, P.B.; McCarty, K.F.; Klaus, E.J.; Boehme, D.R.; Johnsen, H.A.; Mills, M.J.; Ottesen, D.K.

    1993-12-31

    We are studying the boron nitride system using a pulsed excimer laser to ablate from hexagonal BN (cBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25--800C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N{sub 2} source gases to produce BN films with a high percentage of sp{sup 3}-bonded cBN. In order to optimize growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp{sup 3}-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30--40 mn. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm{sup {minus}1} and the position decreases with growth time to a constant value of 1085 cm{sup {minus}1}. Since in bulk cBN this IR mode appears at 1065 cm{sup {minus}1}, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.

  2. Cubic AlN thin film formation on quartz substrate by pulse laser deposition

    NASA Astrophysics Data System (ADS)

    Biju, Zheng; Wen, Hu

    2016-06-01

    Cubic AlN thin films were obtained on quartz substrate by pulse laser deposition in a nitrogen reactive atmosphere. A Nd-YAG laser with a wavelength of 1064 nm was used as the laser source. In order to study the influence of the process parameters on the deposited AlN film, the experiments were performed at various technique parameters of laser energy density from 70 to 260 J/cm2, substrate temperature from room temperature to 800 °C and nitrogen pressure from 0.1 to 50 Pa. X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy were applied to characterize the structure and surface morphology of the deposited AlN films. It was found that the structure of AlN films deposited in a vacuum is rocksalt under the condition of substrate temperature 600-800 °C, nitrogen pressure 10-0.1 Pa and a moderate laser energy density (190 J/cm2). The high quality AlN film exhibited good optical property. Project supported by the Yunnan Provincial Natural of Science Foundation of China (No. KKSY201251089).

  3. Surface Chemistry, Microstructure, and Tribological Properties of Cubic Boron Nitride Films

    NASA Technical Reports Server (NTRS)

    Watanabe, Shuichi; Wheeler, Donald R.; Abel, Phillip B.; Street, Kenneth W.; Miyoshi, Kazuhisa; Murakawa, Masao; Miyake, Shojiro

    1998-01-01

    This report deals with the surface chemistry, microstructure, bonding state, morphology, and friction and wear properties of cubic boron nitride (c-BN) films that were synthesized by magnetically enhanced plasma ion plating. Several analytical techniques - x-ray photoelectron spectroscopy, transmission electron microscopy and electron diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, and surface profilometry - were used to characterize the films. Sliding friction experiments using a ball-on-disk configuration were conducted for the c-BN films in sliding contact with 440C stainless-steel balls at room temperature in ultrahigh vacuum (pressure, 10(exp -6), in ambient air, and under water lubrication. Results indicate that the boron-to-nitrogen ratio on the surface of the as-deposited c-BN film is greater than 1 and that not all the boron is present as boron nitride but a small percentage is present as an oxide. Both in air and under water lubrication, the c-BN film in sliding contact with steel showed a low wear rate, whereas a high wear rate was observed in vacuum. In air and under water lubrication, c-BN exhibited wear resistance superior to that of amorphous boron nitride, titanium nitride, and titanium carbide.

  4. Functionalization of cubic boron nitride films with rhodamine B and their fluorescent properties

    SciTech Connect

    Liu, W. M.; Zhang, H. Y.; Wang, P. F.; Ye, Q.; Yang, Y.; He, B.; Bello, I.; Lee, S. T.; Zhang, W. J.

    2011-08-08

    Fluorophore-functionalized cubic boron nitride (cBN) films grown by chemical vapor deposition were achieved by immobilizing rhodamine B isothiocyanate onto their surfaces. To perform the immobilization, the cBN substrates were modified with amino groups by photochemical reaction between hydrogen-terminated cBN surfaces and allylamine. The surface analysis of hydrogen-terminated cBN films surfaces and after functionalization with x-ray photoelectron spectroscopy verified that rhodamine B was indeed attached to the cBN surfaces with covalent bonding. The rhodamine B-functionalized cBN surfaces showed significant variation in fluorescent spectra and confocal imaging upon the treatment in acidic or basic solutions.

  5. Effect of cubic phase evolution on field emission properties of boron nitride island films

    SciTech Connect

    Teii, Kungen; Yamao, Ryota; Matsumoto, Seiichiro

    2009-12-01

    Field emission performance of boron nitride (BN) island films is studied in terms of cubic phase evolution in plasma-enhanced chemical vapor deposition. Fine-grained island films with large surface roughness can be grown for initial sp{sup 2}-bonded BN and subsequent cubic BN (cBN) phases by using low-energy (approx20 eV) ion bombardment. Ultraviolet photoelectron spectroscopy reveals that the electron affinity is as low as 0.3 eV for both sp{sup 2}-bonded BN and cBN phases. The evolution of cBN islands reduces the turn-on field down to around 9 V/mum and increases the current density up to 10{sup -4} A/cm{sup 2}. The emission is facilitated by the larger field enhancement due to the larger roughness and the higher conduction of cBN islands. The potential barrier height is estimated to be about 3.4 eV for emission from the Fermi level, while it is only about 0.3 eV for 'conduction band emission'.

  6. "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.

  7. Influence of sputtering power on structural, mechanical and photoluminescence properties of nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Singh, Narendra; Kaur, Davinder

    2016-05-01

    In the present study, SiC thin films were deposited on Si (100) substrate by magnetron sputtering using a 4N purity commercial SiC target in argon atmosphere. The effect of sputtering RF power (140-170W) on structural, mechanical and photoluminescence properties were systematically studied by X-ray diffraction, field emission scanning electron microscopy, Nanoindentation and Spectrophotometer respectively. X-ray diffraction shows polycrystalline 4H-SiC phase with (105) preferred orientation and an enhancement in crystallite size with increasing power was also observed. The decrement in hardness and Young's modulus with increment in RF power was ascribed to Hall-Petch relation. The maximum hardness and Young's modulus were found to be 32 GPa and 232 GPa respectively. The photoluminescence spectra show peaks at 384 nm (3.22 eV) which corresponds to bandgap of 4H-SiC (phonon assisted band to band recombination) and 416 nm (2.99 eV) may be attributed to defect states and intensity of both peaks decreases as power increases.

  8. Design of Twin Structures in SiC Nanowires

    SciTech Connect

    Yongfeng Zhang; Hanchen Huang

    2012-11-01

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

  9. Low-energy mass-selected ion beam production of fragments produced from hexamethyldisilane for SiC film formation

    NASA Astrophysics Data System (ADS)

    Yoshimura, Satoru; Sugimoto, Satoshi; Kiuchi, Masato

    2016-03-01

    We have proposed an experimental methodology which makes it possible to deposit silicon carbide (SiC) films on Si substrates with a low-energy mass-selected ion beam system using hexamethyldisilane (HMD) as a gas source. In this study, one of the fragment ions produced from HMD, SiCH4+, was mass-selected. The ion energy was approximately 100 eV. Then, the SiCH4+ ions were irradiated to a Si(100) substrate. When the temperature of the Si substrate was set at 800 °C during the ion irradiation, the X-ray diffraction and Raman spectroscopy of the substrate following the completion of ion irradiation experiment demonstrated the occurrence of 3C-SiC deposition.

  10. Cubic-BN-Like Structure of B-C-N Films Synthesized by Plasma Source Ion Nitriding

    NASA Astrophysics Data System (ADS)

    Lei, Ming-kai; Yuan, Li-jiang; Zhang, Zhong-lin; Ma, Teng-cai

    1999-01-01

    Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing them into bulk materials. The ion-plating B-C films were nitrided to synthesize B-C-N films at a nitriding temperature from 300 to 500° C. The x-ray photoelectron spectroscopy and diffuse reflectance Fourier transform infrared spectra analyses showed that the amorphous B-C-N films synthesized at 500° C are composed mainly of cubic-BN-like and hexagonal-BN-like plain microdomains. The higher nitriding temperature contributes to the formation of cubic-BN-like B-C-N structure in the B-C-N films.

  11. Preparation of cubic boron nitride films by radio frequency magnetron sputtering and radio frequency ion plating

    NASA Astrophysics Data System (ADS)

    Ulrich, S.; Scherer, J.; Schwan, J.; Barzen, I.; Jung, K.; Scheib, M.; Ehrhardt, H.

    1996-02-01

    Cubic boron nitride (c-BN) thin films have been deposited by unbalanced rf (13.56 MHz) magnetron sputtering of a hexagonal boron nitride target in a pure argon discharge. Deposition parameters have been 300 W rf target power, 8×10-4 mbar argon pressure, 3.5 cm target substrate distance, and 800 K substrate temperature. Under these conditions the ion current density is 2.25 mA/cm2 and the growth rate is ˜1.1 Å/s. By applying a rf substrate bias the ion plating energy is varied from plasma potential of 37 eV up to 127 eV. The films have been characterized by infrared (IR) and Auger electron spectroscopy (AES), x-ray diffraction (XRD), x-ray reflectivity, elastic recoil detection (ERD), Rutherford backscattering (RBS), nuclear resonance analysis (NRA), and stress measurements. The subplantation model proposed by Lifshitz and Robertson can be applied to the c-BN formation. An energy of about 85±5 eV is found where the stress (25 GPa, 200 nm film thickness) and the c-BN content (≳90%) have a maximum. The grain size of the crystalline c-BN phase was estimated to be in the range of 5 nm. Below an energy of 67±5 eV no c-BN could be detected. An excellent adhesion has been obtained by a special interface treatment.

  12. Hardness and Young's modulus of high-quality cubic boron nitride films grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Philip, J.; Zhang, W. J.; Hess, P.; Matsumoto, S.

    2003-02-01

    The elastic and mechanical properties of high-quality cubic boron nitride (cBN) films with a few microns thickness and submicron grain size grown on silicon substrates by chemical vapor deposition were determined by measuring the dispersion of surface acoustic waves propagating along the surface of the layered system. The values are compared with those obtained with an ultralow load indenter (Triboscope). Specifically, the hardness, Young's modulus and density of the film were measured.

  13. Vertical alignment of liquid crystal through ion beam exposure on oxygen-doped SiC films deposited at room temperature

    SciTech Connect

    Son, Phil Kook; Park, Jeung Hun; Kim, Jae Chang; Yoon, Tae-Hoon; Rho, Soon Joon; Jeon, Back Kyun; Shin, Sung Tae; Kim, Jang Sub; Lim, Soon Kwon

    2007-09-03

    The authors report the vertical alignment of liquid crystal (LC) through the ion beam exposure on amorphous oxygen-doped SiC (SiOC) film surfaces deposited at room temperature. The optical transmittance of these films was similar to that of polyimide layers, but much higher than that of SiO{sub x} films. The light leakage of a LC cell aligned vertically on SiOC films was much lower than those of a LC cell aligned on polyimide layers or other inorganic films. They found that LC molecules align vertically on ion beam treated SiOC film when the roughness of the electrostatic force microscopy (EFM) data is high on the SiOC film surface, while they align homogeneously when the roughness of the EFM data is low.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  15. Consideration of the formation mechanism of an Al2O3-HfO2 eutectic film on a SiC substrate

    NASA Astrophysics Data System (ADS)

    Seya, Kyosuke; Ueno, Shunkichi; Nishimura, Toshiyuki; Jang, Byung-Koog

    2016-01-01

    An Al2O3-HfO2 eutectic EBC film was prepared on a SiC substrate by using the electric furnace heating and the optical zone melting methods. All of Al2O3 phase disappeared during the heating step at a temperature below the melting point, and all of the HfO2 phase reacted with the carbon and boron, which are included in SiC bulk as sintering agents, during the heating step at a temperature below the melting point. The thermal decomposition of the SiC phase, the reduction reaction of Al2O3 phase, the vaporization of the Al2O3 component, the reduction reaction of HfO2 and the formation of the HfC phase occurred at a temperature below the melting point. However, a highly dense HfC phase was formed on the SiC substrate. A rapid heating process becomes possible by using the optical zone melting method. A solidified film that was composed of a highly dense HfC layer as the intermediate layer and the Al2O3-HfO2 eutectic structure layer as the top coat was obtained by using the optical zone melting method.

  16. A study on various fabrication routes for preparing multilayered cubic boron nitride films and sp(3)-like boron nitride films

    NASA Astrophysics Data System (ADS)

    Wong, Sing Fai

    Cubic boron nitride (cBN) has a sp3-bonded structure which leads to excellent mechanical properties. Though cBN-rich films have been successfully fabricated by many techniques, the adhesion of the films is still unsatisfactory due to the high stresses. The maximum sustainable thickness of cBN-rich films with good adhesion is widely reported to be around 200 nm, so many practical applications of cBN coatings are hindered. In this study, we designed a series of deposition schemes in a logical sequence, in order to explore whether stress can be released, or other structural forms of BN with potential applications can be made, and to gain more fundamental understanding on the growth mechanisms of various phases observed in the films. Various fabrication processes were employed according to the following sequence: (1) A single-step process. It was showed that the maximum tolerable thickness of the cBN-rich films prepared by our system (183nm) was compatible with the result in literatures (200nm). (2) A multilayered deposition process. A thick sp2-bonded boron nitride (sP2-BN) buffer layer which was relatively deformable was added, and hence some stresses were released so as to allow a 643nm-thick, 87vol.% cBN-rich layer with acceptable adhesion to grow on top. (3) An advanced multilayer process with subsequent annealing process. A zirconium layer was pre-deposited to remove the soft buffer layer after postannealing. The interface could be strengthened as the zirconium-boride/nitride was formed. (4) Ion assist deposition at unheated condition. Composite BN films containing sp3 nanoclusters embedded in a sp2-BN matrix were fabricated. The IR technique was not sensitive enough to detect spa nanoclusters, but their presence was verified by the results of other measurements. In particular, the sp3 content can be over 30vo1.%, with a hardness 20GPa. The influences of the assist beam energy and substrate temperature on the generation of the sp3 nanoclusters were investigated

  17. Growth of SiC thin films on (100) and (111) silicon by pulsed laser deposition combined with a vacuum annealing process

    SciTech Connect

    Huang, J.; Wang, L.; Wen, J.; Wang, Y.; Lin, C.; Zetterling, C.M.; Oestling, M.

    1999-07-01

    Crystalline 3C-SiC thin films were successfully grown on (100) and (111) Si substrates by using ArF pulsed laser ablation from a SiC ceramic target combined with a vacuum annealing process. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were employed to study the effect of annealing on the structure of thin films deposited at 800 C. It was demonstrated that vacuum annealing could transform the amorphous SiC films into crystalline phase and that the crystallinity was strongly dependent on the annealing temperature. For the samples deposited on (100) and (111) Si, the optimum annealing temperatures were 980 and 920 C, respectively. Scanning electron microscope (SEM) micrographs exhibited different characteristic microstructure for the (100) and (111) Si cases, similar to that observed for the carbonization layer initially formed in chemical vapor deposition of SiC films on Si. This also showed the presence of the epitaxial relationship of 3C-SiC[100]//Si[100] and 3C-SiC[111]//Si[111] in the direction of growth.

  18. Deposition of AlN Thin Films with Cubic Crystal Structures on Silicon Substrates at Room Temperature

    NASA Astrophysics Data System (ADS)

    Ren, Zhong-Min; Lu, Yong-Feng; Goh, Yeow-Whatt; Chong, Tow-Chong; Ng, Mei-Ling; Wang, Jian-Ping; Cheong, Boon-Aik; Liew, Yun-Fook

    2000-05-01

    Cubic AlN thin films were deposited at room temperature by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. The full-width at half maximum (FWHM) of the X-ray diffraction peak in the θ˜ 2θ scan can reach a value of 0.27 degrees. In the Raman spectroscopy measurement, a new peak at 2333 cm-1 originating from cubic AlN polycrystalline was observed. Nitrogen ions not only effectively promote the formation of stable Al-N bonds but also improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed for the thin-film deposition.

  19. Direct deposition of cubic boron nitride films on tungsten carbide-cobalt.

    PubMed

    Teii, Kungen; Matsumoto, Seiichiro

    2012-10-24

    Thick cubic boron nitride (cBN) films in micrometer-scale are deposited on tungsten carbide-cobalt (WC-Co) substrates without adhesion interlayers by inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) using the chemistry of fluorine. The residual film stress is reduced because of very low ion-impact energies (a few eV to ∼25 eV) controlled by the plasma sheath potential. Two types of substrate pretreatment are used successively; the removal of surface Co binder using an acid solution suppresses the catalytic effect of Co and triggers cBN formation, and the surface roughening using mechanical scratching and hydrogen plasma etching increases both the in-depth cBN fraction and deposition rate. The substrate surface condition is evaluated by the wettability of the probe liquids with different polarities and quantified by the apparent surface free energy calculated from the contact angle. The surface roughening enhances the compatibility in energy between the cBN and substrate, which are bridged by the interfacial sp(2)-bonded hexagonal BN buffer layer, and then, the cBN overlayer is nucleated and evolved easier. PMID:22950830

  20. Red, green and blue reflections enabled in an optically tunable self-organized 3D cubic nanostructured thin film.

    PubMed

    Lin, Tsung-Hsien; Li, Yannian; Wang, Chun-Ta; Jau, Hung-Chang; Chen, Chun-Wei; Li, Cheng-Chung; Bisoyi, Hari Krishna; Bunning, Timothy J; Li, Quan

    2013-09-25

    A new light-driven chiral molecular switch doped in a stable blue phase (BP) liquid crystal allows wide optical tunability of three-dimensional cubic nanostructures with a selective reflection wavelength that is reversibly tuned through the visible region. Moreover, unprecedented reversible light-directed red, green, and blue reflections of the self-organized three-dimensional cubic nanostructure in a single film are demonstrated for the first time. Additionally, unusual isothermal photo-stimulated less ordered BP II to more ordered BP I phase transition was observed in the system. PMID:23913627

  1. Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties

    SciTech Connect

    Zhou Hua; Wang Huiqiong; Chen Xiaohang; Zhan Huahan; Kang Junyong; Wu Lijun; Zhu Yimei; Zhang Lihua; Kisslinger, Kim

    2011-10-03

    We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.

  2. Interplay of uniaxial and cubic anisotropy in epitaxial Fe thin films on MgO (001) substrate

    NASA Astrophysics Data System (ADS)

    Mallik, Srijani; Chowdhury, Niru; Bedanta, Subhankar

    2014-09-01

    Epitaxial Fe thin films were grown on annealed MgO(001) substrates at oblique incidence by DC magnetron sputtering. Due to the oblique growth configuration, uniaxial anisotropy was found to be superimposed on the expected four-fold cubic anisotropy. A detailed study of in-plane magnetic hysteresis for Fe on MgO thin films has been performed by Magneto Optic Kerr Effect (MOKE) magnetometer. Both single step and double step loops have been observed depending on the angle between the applied field and easy axis i.e. along ⟨100⟩ direction. Domain images during magnetization reversal were captured by Kerr microscope. Domain images clearly evidence two successive and separate 90° domain wall (DW) nucleation and motion along cubic easy cum uniaxial easy axis and cubic easy cum uniaxial hard axis, respectively. However, along cubic hard axis two 180° domain wall motion dominate the magnetization reversal process. In spite of having four-fold anisotropy it is essential to explain magnetization reversal mechanism in 0°< ϕ < 90° span as uniaxial anisotropy plays a major role in this system. Also it is shown that substrate rotation can suppress the effect of uniaxial anisotropy superimposed on four-fold anisotropy.

  3. Current-direction dependence of the transport properties in single-crystalline face-centered-cubic cobalt films

    SciTech Connect

    Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Ma, D. H.

    2015-07-28

    Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO{sub 3}(001) substrates by molecular beam epitaxy. Transport measurements are conducted in different current directions relative to the crystal axes. We find that the temperature dependent anisotropic magnetoresistance ratio strongly depends on the current direction. However, the anomalous Hall effect shows isotropic behavior independent of the current direction. Our results demonstrate the interplay between the current direction and the crystalline lattice in single-crystalline ferromagnetic films. A phenomenological analysis is presented to interpret the experimental data.

  4. Damage effects from medium-energy ion bombardment during the growth of cubic-boron nitride films

    NASA Astrophysics Data System (ADS)

    Gago, R.; Vinnichenko, M.; Abendroth, B.; Kolitsch, A.; Möller, W.

    2003-09-01

    Cubic-boron nitride (c-BN) films with low stress have been produced by simultaneous 35 keV N+ ion implantation during growth by ion assisted sputtering. The stress release is achieved at the lost of a decrease in the c-BN content. Despite this fact, films with a high c-BN content and relatively large thickness (~0.4 μm) have been produced. The decrease on the c-BN content is discussed in terms of the damage induced by the medium-energy ion implantation.

  5. Current-direction dependence of the transport properties in single-crystalline face-centered-cubic cobalt films

    NASA Astrophysics Data System (ADS)

    Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ma, D. H.; Ding, Z.; Wu, Y. Z.

    2015-07-01

    Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO3(001) substrates by molecular beam epitaxy. Transport measurements are conducted in different current directions relative to the crystal axes. We find that the temperature dependent anisotropic magnetoresistance ratio strongly depends on the current direction. However, the anomalous Hall effect shows isotropic behavior independent of the current direction. Our results demonstrate the interplay between the current direction and the crystalline lattice in single-crystalline ferromagnetic films. A phenomenological analysis is presented to interpret the experimental data.

  6. Tunable in situ growth of porous cubic silicon carbide thin films via methyltrichlorosilane-based chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lien, Wei-Cheng; Ferralis, Nicola; Pisano, Albert P.; Carraro, Carlo; Maboudian, Roya

    2009-09-01

    The growth of cubic silicon carbide films with tunable porosity is demonstrated on Si(100) using a single precursor, methyltrichlorosilane, chemical vapor deposition process in the temperature range of 950-1200 °C. The pore size varies in the range from 250 nm to 2 μm and it is controlled by the growth temperature and the details of hydrogen introduction during substrate heating stage. It is proposed that silicon outdiffusion from substrate combined with hydrogen chloride production and adsorption on the surface at high temperature may be responsible for the porous films thus produced.

  7. Etching characteristics and mechanisms of SiC thin films in inductively-coupled HBr-Ar, N{sub 2}, O{sub 2} plasmas

    SciTech Connect

    Efremov, Alexander; Kang, Sungchil; Kwon, Kwang-Ho; Seok Choi, Won

    2011-11-15

    Etch characteristics and mechanisms of SiC thin films in HBr-Ar, HBr-N{sub 2}, and HBr-O{sub 2} inductively-coupled plasmas were studied using a combination of experimental and modeling methods. The etch rates of SiC thin films were measured as functions of the additive gas fraction in the range of 0-100% for Ar, N{sub 2}, and O{sub 2} at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using Langmuir probe diagnostics and a global (zero-dimensional) plasma model. The good agreement between the behaviors of the SiC etch rate and the H atom flux could suggest that a chemical etch pathway is rather controlled by the gasification of carbon through the CH{sub x} or CH{sub x}Br{sub y} compounds.

  8. The Improvement of Ion Plated Ag and Au Film Adherence to Si3N4 and SiC Surfaces for Increased Tribological Performance

    NASA Technical Reports Server (NTRS)

    Spalvins, Talivaldis

    1998-01-01

    A modified dc-diode plating system, utilizing a metallic screen cage as a cathode and referred as SCREEN CAGE ION PLATING (SCIP), is used to deposit Ag and Au lubricating films on Si3N4 and SiC surfaces. When deposition is performed in Ar or N2, glow discharge, the surface displays poor adhesive strength (less than 5 MPa). A dramatic increase in adhesive strength (less than 80 MPa) is achieved when plating is performed in a reactive 50% 02 + 50% Ar glow discharge. The excited/ionized oxygen species (O2(+)/O(+) in the glow discharge contribute to the oxidation of the Si3N4 or SiC surfaces as determined by X-ray Photoelectron Spectroscopy (XTS) depth profiling. The reactively sputter-oxidized S3N4 or SiC surfaces and the activated-oxidized-metastable Ag or Au species formed in the plasma cooperatively contribute to the increased adherence. As a result, the linear thermal expansion coefficient mismatch at the interface is reduced. These lubricating Ag and Au films under sliding conditions reduce the friction coefficient by a factor of 2-1/2 to 4.

  9. Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

    NASA Astrophysics Data System (ADS)

    Nita, F.; Mastail, C.; Abadias, G.

    2016-02-01

    A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this

  10. Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy

    SciTech Connect

    Casallas-Moreno, Y. L.; Perez-Caro, M.; Gallardo-Hernandez, S.; Ramirez-Lopez, M.; Martinez-Velis, I.; Lopez-Lopez, M.; Escobosa-Echavarria, A.

    2013-06-07

    InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 Degree-Sign C, and different In beam fluxes (BEP{sub In}) ranging from 5.9 Multiplication-Sign 10{sup -7} to 9.7 Multiplication-Sign 10{sup -7} Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 Degree-Sign C by MEE.

  11. The Urbach focus and optical properties of amorphous hydrogenated SiC thin films

    NASA Astrophysics Data System (ADS)

    Guerra, J. A.; Angulo, J. R.; Gomez, S.; Llamoza, J.; Montañez, L. M.; Tejada, A.; Töfflinger, J. A.; Winnacker, A.; Weingärtner, R.

    2016-05-01

    We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.

  12. Chemical vapor deposition of Si:C and Si:C:P films-Evaluation of material quality as a function of C content, carrier gas and doping

    NASA Astrophysics Data System (ADS)

    Dhayalan, Sathish Kumar; Loo, Roger; Hikavyy, Andriy; Rosseel, Erik; Bender, Hugo; Richard, Olivier; Vandervorst, Wilfried

    2015-09-01

    Incorporation of source-drain stressors (S/D) for FinFETs to boost the channel mobility is a promising scaling approach. Typically SiGe:B S/D stressors are used for p FinFETs and Si:C:P S/D stressors for n FinFETs. The deposition of such Si:C:P S/D stressors requires a low thermal budget to freeze the C in substitutional sites and also to avoid problems associated with surface reflow of Si fins. In this work, we report the material properties of Si:C and Si:C:P epitaxial layers grown by chemical vapor deposition, in terms of their defectivity and C incorporation as a function of different process conditions. The undoped Si:C layers were found to be defect free for total C contents below 1%. Above this concentration defects were incorporated and the defect density increased with increasing C content. Abrupt epitaxial breakdown occurred beyond a total C content of 2.3% resulting in amorphous layers. P doping of Si:C layers brought down the resistivity and also thicker Si:C:P films underwent epitaxial breakdown. Additionally, the use of nitrogen instead of hydrogen as carrier gas resulted in an increase of the growth rate and substitutional C incorporation both by a factor of two, while the surface defect density reduced.

  13. Effect of Tilt Angle on the Morphology of SiC Epitaxial Films Grown on Vicinal (0001) SiC Substrates

    NASA Technical Reports Server (NTRS)

    Powell, J. A.; Larkin, D. J.; Abel, P. B.; Zhou, L.; Pirouz, P.

    1996-01-01

    In this study of 4H-SiC and 6H-SiC epitaxial films we found that film morphology was strongly dependent on the tilt angle of the substrate. Large surface steps (up to 25 nm high) due to step bunching were more prevalent at smaller tilt angles. Also, 4H films were more susceptible than 6H to 3C-SiC inclusions during growth. The lateral growth of steps from screw dislocations in low-tilt-angle substrates demonstrated that step bunching on the atomic scale was anisotropic with respect to growth direction for both 4H-SiC and 6H-SiC. A model explaining this behavior is presented. We observed and directly measured the Burgers vector of a 'super' screw dislocation in a 6H-SiC epilayer.

  14. Correlation between stress profiles of cubic boron nitride thin films and the phase sequence revealed from infrared data

    NASA Astrophysics Data System (ADS)

    Klett, A.; Malavé, A.; Freudenstein, R.; Plass, M. F.; Kulisch, W.

    Cubic boron nitride thin films have been ion-beam-assisted deposited on silicon cantilever structures and subsequently back-etched in order to study the stress evolution and finally the growth mechanisms. After each sputtering step, the film stress, the remaining thickness, and the IR data were examined. In this way, the layered sequence of cBN on top of a hBN base layer, influencing the development of the intrinsic film stress, could be studied in detail. The observed stress distribution can be divided into three regions. First, a non-cubic base layer with a constant stress value is formed, followed by a linear increase in the stress after cBN nucleation as a result of the coalescence of cBN nanocrystals. Finally, the stress reaches a second plateau characteristic of the cBN top layer. In addition, the layered sequence was verified by the evolution of the FTIR spectra. Furthermore, the fraction of the sp2-bonded material of the cBN top layer was determined from the IR data. For various deposition conditions, a linear relationship between the stress of the nanocrystalline cBN top layer and the amount of sp3-bonded material was observed. From this, it can be concluded that stress relaxation occurs at the sp2-bonded grain boundary material. No evidence for stress relaxation after cBN nucleation was found.

  15. A Comparison of the Effects of RF Plasma Discharge and Ion Beam Supply on the Growth of Cubic Boron Nitride Films Formed by Laser Physical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kaneda, Kayo; Shibata, Kimihiro

    1994-01-01

    This paper presents a comparison of the effects of RF plasma discharge and ion beam supply on the growth of cubic boron nitride films formed by excimer laser physical vapor deposition (laser PVD). The film structure was analyzed by fourier transformation infrared region (FT-IR) spectroscopy and thin-film X-ray diffraction analysis. The structure of the film deposited with an RF plasma discharge provided between the substrate and target was hexagonal BN. On the other hand, that of the film deposited by irradiating the substrate directly with an ion beam was hexagonal BN (hBN) and cubic BN (cBN). It is thought that direct irradiation of the vapor generated from the target by accelerated ions increased the activation energy of the vapor, with the result that the film structure was changed. Besides irradiating the substrate directly with the ion beam resulted primarily in the etching of hBN while cBN remained.

  16. Orientational relationship between cubic boron nitride and hexagonal boron nitride in a thin film synthesized by ion plating

    NASA Astrophysics Data System (ADS)

    Zhou, Wei-Lie; Ikuhara, Yuichi; Suzuki, Tetsuya

    1995-12-01

    Cubic boron nitride (c-BN) thin films synthesized by the ion-plating method were examined by high-resolution electron microscopy. It was found that the {0002} planes of hexagonal boron nitride (h-BN) at the boundaries of c-BN grains preferred to nucleate almost parallel to {111} planes of c-BN. Cross-sectional observation in the initial stage of growth showed that the c-BN can grow on top of the prismatic planes and the {0001} basal planes of h-BN, keeping the parallelism of the (111)c-BN to (0001)h-BN. A few degrees deviation (˜4°) between h-BN {0002} planes and c-BN {111} planes was frequently found in the film. The nucleation mechanism of c-BN was discussed analogous to that of diamond on graphite.

  17. Determining polytype composition of silicon carbide films by UV ellipsometry

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.

    2016-02-01

    A universal ellipsometric model is proposed that describes the optical properties of silicon carbide (SiC) films grown on Si substrates by the method of atomic substitution due to a chemical reaction between the substrate and gaseous carbon monoxide. According to the proposed three-layer model, Si concentration decreases in a stepwise manner from the substrate to SiC film surface. The ellipsometric curves of SiC/Si(111), SiC/Si(100), and SiC/Si(110) samples grown under otherwise identical conditions have been measured in a 1.35-9.25 eV range using a VUV-VASE (J.A. Woollam Co.) ellipsometer with a rotating analyzer. Processing of the obtained spectra in the framework of the proposed model allowed the polytype composition of SiC films to be determined for the first time. It is established that SiC grown on Si(111) is predominantly cubic, while SiC on Si(110) is predominantly hexagonal (with cubic polytype admixture) and SiC on Si(100) has a mixed polytype composition.

  18. Homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1-x O alloy thin films by pulsed laser deposition technique

    NASA Astrophysics Data System (ADS)

    Hullavarad, S. S.; Hullavarad, N. V.; Pugel, D. E.; Dhar, S.; Takeuchi, I.; Venkatesan, T.; Vispute, R. D.

    2007-08-01

    In this work, we describe the homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1-xO thin films on lattice matched substrates of c-Al2O3, ZnO, MgO and SrTiO3. The crystalline quality, composition and epitaxial nature of the alloy films are obtained by x-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques. The RBS channeling yields are in the range 3-8% for homoepitaxial and hetero-epitaxial thin films. The metal-semiconductor-metal and ultraviolet detectors were fabricated on hexagonal and cubic MgxZn1-xO thin films and the leakage current and UV-visible rejection ratio are correlated with the epitaxial relationship between the film and substrates.

  19. Static and dynamic magnetic properties of cubic Mn-Co-Ga Heusler films

    SciTech Connect

    Demiray, A. S. Iihama, S.; Naganuma, H.; Oogane, M.; Ando, Y.; Kubota, T.; Mizukami, S. Miyazaki, T.

    2014-05-07

    We investigated the static and dynamic magnetic properties of thin films of Mn-Co-Ga Heusler compound. Gilbert damping and exchange stiffness constants of the films were evaluated by using the ferromagnetic resonance technique in the X-band regime (f = 9.4 GHz). By analyzing the experimental spectra, magnetic parameters of the films such as the line width and the Gilbert damping were deduced, and the exchange stiffness constant was estimated from the perpendicular standing spin-wave resonance. The Gilbert damping constant was estimated to be 0.017 in a specific film composition. The exchange stiffness constant showed a linear dependence on the film composition.

  20. Formation of Novel Silicon Nitride with Face-Centered Cubic Crystal Structure in a TaN/Ta/Si(100) Thin Film System

    NASA Astrophysics Data System (ADS)

    Cheng, Wei-Chun; Jou, Shyan-Kay; Chiu, Chuei-Fu

    2005-07-01

    We discovered a new silicon nitride with cubic symmetry formed in the silicon at the Ta/Si interface of the TaN/Ta/Si(100) thin film system when the silicon wafer was annealed at 500 or 600°C. The cubic silicon nitride grew into the silicon crystal in the shape of an inverse pyramid after the annealing process. The boundary planes of the inverse pyramid were the \\{111\\} planes of the silicon crystal. The orientation relationship between the silicon nitride and silicon crystal is cubic to cubic. The lattice constant of the new silicon nitride is a=0.5548 nm and is about 2.2% larger than that of the silicon crystal.

  1. Pure Cubic-Phase Hybrid Iodobismuthates AgBi2 I7 for Thin-Film Photovoltaics.

    PubMed

    Kim, Younghoon; Yang, Zhenyu; Jain, Ankit; Voznyy, Oleksandr; Kim, Gi-Hwan; Liu, Min; Quan, Li Na; García de Arquer, F Pelayo; Comin, Riccardo; Fan, James Z; Sargent, Edward H

    2016-08-01

    Bismuth-based hybrid perovskites are candidates for lead-free and air-stable photovoltaics, but poor surface morphologies and a high band-gap energy have previously limited these hybrid perovskites. A new materials processing strategy to produce enhanced bismuth-based thin-film photovoltaic absorbers by incorporation of monovalent silver cations into iodobismuthates is presented. Solution-processed AgBi2 I7 thin films are prepared by spin-coating silver and bismuth precursors dissolved in n-butylamine and annealing under an N2 atmosphere. X-ray diffraction analysis reveals the pure cubic structure (Fd3m) with lattice parameters of a=b=c=12.223 Å. The resultant AgBi2 I7 thin films exhibit dense and pinhole-free surface morphologies with grains ranging in size from 200-800 nm and a low band gap of 1.87 eV suitable for photovoltaic applications. Initial studies produce solar power conversion efficiencies of 1.22 % and excellent stability over at least 10 days under ambient conditions. PMID:27355567

  2. Surface Transfer Doping of Cubic Boron Nitride Films by MoO3 and Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ).

    PubMed

    He, Bin; Ng, Tsz-Wai; Lo, Ming-Fai; Lee, Chun-Sing; Zhang, Wenjun

    2015-05-13

    Cubic boron nitride (cBN) has strong potential for the applications in high-temperature and high-power electronics and deep ultraviolet devices due to its outstanding combined physical and chemical properties. P-type surface transfer doping of heteroepitaxial cBN films was achieved by employing MoO3 and tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as the surface dopants. The surface conductivities of hydrogenated cBN films increased by 3-6 orders after the deposition of surface dopants. The photoemission spectroscopy (PES) measurements revealed the variation of electronic structures at the interface regions, which suggested that the electron transfer from cBN films to the surface dopants induced hole accumulation at the cBN surface and the increase of surface conductivity. Based on the PES results, the energy level diagrams at MoO3/cBN and F4-TCNQ/cBN interfaces were determined. The achievement provided a potential approach for fabricating cBN-based electronic devices, especially on micrometer and nanometer scales. PMID:25915092

  3. Tricontinuous Cubic Nanostructure and Pore Size Patterning in Mesostructured Silica Films Templated with Glycerol Monooleate

    PubMed Central

    Dunphy, Darren R.; Garcia, Fred L.; Kaehr, Bryan; Khripin, Constantine Y.; Collord, Andrew D.; Baca, Helen K.; Tate, Michael P.; Hillhouse, Hugh W.; Strzalka, Joseph W.; Jiang, Zhang; Wang, Jin; Brinker, C. Jeffrey

    2011-01-01

    The fabrication of nanostructured films possessing tricontinuous minimal surface mesophases with well-defined framework and pore connectivity remains a difficult task. As a new route to these structures, we introduce glycerol monooleate (GMO) as a template for evaporation-induced self-assembly. As deposited, a nanostructured double gyroid phase is formed, as indicated by analysis of grazing-incidence small-angle x-ray scattering data. Removal of GMO by UV/O3 treatment or acid extraction induces a phase change to a nanoporous body-centered structure which we tentatively identify as based on the IW-P surface. To improve film quality, we add a co-surfactant to the GMO in a mass ratio of 1:10; when this co-surfactant is cetyltrimethylammonium bromide, we find an unusually large pore size (8-12 nm) in acid extracted films, while UV/O3 treated films yield pores of only ca. 4 nm. Using this pore size dependence on film processing procedure, we create a simple method for patterning pore size in nanoporous films, demonstrating spatially-defined size-selective molecular adsorption. PMID:21572556

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

    SciTech Connect

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

    1995-11-01

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

  5. Chemically deposited cubic structured CdO thin films: Room temperature

    NASA Astrophysics Data System (ADS)

    Bulakhe, R. N.; Lokhande, C. D.

    2013-06-01

    Cadmium oxide (CdO) thin films have been synthesized using a chemical bath deposition (CBD) method at room temperature. The prepared CdO thin film were annealed and further used for the structural, morphological, UVVIS characterization. The thermo emf study was made with the TEP setup. The structural study showed polycrystalline CdO material. Morphological study reveals the prism like morphology. Optical and thermo emf study showed n-type nature with optical band gap of 2.13 eV.

  6. Thermo-Mechanical Optimization of a Gold Thick-film based SiC Die-attach Assembly using Finite Element Analysis

    NASA Technical Reports Server (NTRS)

    Lin, Shun-Tien; Chen, Liang-Yu

    2002-01-01

    A parametric study of the thermomechanical reliability of a Au thick-film based Sic-die- attach assembly using nonlinear finite element analysis (FEA) was conducted to optimize the die-attach thermo-mechanical performance for operation at temperatures from room temperature to 500 "C. This parametric study centered on material selection, structure design and process control. The die-attach assembly is composed of a 1 mm x 1 mm S i c die attached to a ceramic substrate (either 96% aluminum oxide (A1203) or aluminum nitride (AlN)) with a gold (Au) thick-film attach layer. The effects of die-size, Au attach layer thickness, substrate material, and stress relaxing temperature on the stress/strain distribution and relative fatigue lifetime of the die-attach assembly were numerically analyzed. By comparing the calculated permanent strain in the thick-film attach layer, FEA results indicate that AlN is superior to Al2O3. Thicker Au attach layers and smaller die sizes are recommended to reduce the permanent strain in thick-film die attach layer. Thicker S i c die also reduces the stress near the (top) surface region of the die. A stress relaxing temperature close to the midpoint of the operating temperature range further reduces the maximum stress/strain, thereby improving die-attach thermo-mechanical reliability. These recommendations present guidelines to optimize the thermo-mechanical performance of the die-attach assembly and are valid for a wide range of thermal environments.

  7. Core-shell Si/C nanospheres embedded in bubble sheet-like carbon film with enhanced performance as lithium ion battery anodes.

    PubMed

    Li, Wenyue; Tang, Yongbing; Kang, Wenpei; Zhang, Zhenyu; Yang, Xia; Zhu, Yu; Zhang, Wenjun; Lee, Chun-Sing

    2015-03-18

    Due to its high theoretical capacity and low lithium insertion voltage plateau, silicon has been considered one of the most promising anodes for high energy and high power density lithium ion batteries (LIBs). However, its rapid capacity degradation, mainly caused by huge volume changes during lithium insertion/extraction processes, remains a significant challenge to its practical application. Engineering Si anodes with abundant free spaces and stabilizing them by incorporating carbon materials has been found to be effective to address the above problems. Using sodium chloride (NaCl) as a template, bubble sheet-like carbon film supported core-shell Si/C composites are prepared for the first time by a facile magnesium thermal reduction/glucose carbonization process. The capacity retention achieves up to 93.6% (about 1018 mAh g(-1)) after 200 cycles at 1 A g(-1). The good performance is attributed to synergistic effects of the conductive carbon film and the hollow structure of the core-shell nanospheres, which provide an ideal conductive matrix and buffer spaces for respectively electron transfer and Si expansion during lithiation process. This unique structure decreases the charge transfer resistance and suppresses the cracking/pulverization of Si, leading to the enhanced cycling performance of bubble sheet-like composite. PMID:25346141

  8. Cubic nitride templates

    DOEpatents

    Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

    2013-04-30

    A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

  9. Origin of magnetocrystalline anisotropy oscillations in (001) face-centred-cubic Co thin films and effect of sp d hybridization

    NASA Astrophysics Data System (ADS)

    Cinal, M.

    2003-01-01

    Magnetocrystalline anisotropy (MA) energy of (001) face-centred-cubic Co(N) films is calculated for film thicknesses N = 1-28 in a realistic tight-binding model with and without sp-d orbital hybridization included. The obtained results show that the average MA energy is not largely influenced by the sp-d hybridization. On the other hand, the oscillation pattern is remarkably changed when the sp-d hybridization is included: in this case the MA energy has oscillations with a clear period of 2 atomic layers (AL), similar to the previous ab initio calculations (Szunyogh L, Újfalussy B, Blaas C, Pustugova U, Sommers C and Weinberger P 1997 Phys. Rev. B 56 14036). A careful analysis in k- and N-spaces reveals that the total MA oscillations are a superposition of two oscillatory contributions: one coming from the neighbourhood of the barGamma-point with period close to 2 AL (regardless whether the sp-d hybridization is present or not) and the other originating in the region around the bar M-point. The bar M-point contribution has a larger period and its amplitude is significantly smaller than that of the barGamma-point contribution when the sp-d hybridization is included so that the 2 AL barGamma-point contribution is dominant in this case. The two oscillatory MA contributions are attributed to quantum-well states and the corresponding oscillation periods are related to the extremal radii of the minority-spin bulk Co Fermi surface.

  10. Transparent conducting Si-codoped Al-doped ZnO thin films prepared by magnetron sputtering using Al-doped ZnO powder targets containing SiC

    SciTech Connect

    Nomoto, Jun-ichi; Miyata, Toshihiro; Minami, Tadatsugu

    2009-07-15

    Transparent conducting Al-doped ZnO (AZO) thin films codoped with Si, or Si-codoped AZO (AZO:Si), were prepared by radio-frequency magnetron sputtering using a powder mixture of ZnO, Al{sub 2}O{sub 3}, and SiC as the target; the Si content (Si/[Si+Zn] atomic ratio) was varied from 0 to 1 at. %, but the Al content (Al/[Al+Zn] atomic ratio) was held constant. To investigate the effect of carbon on the electrical properties of AZO:Si thin films prepared using the powder targets containing SiC, the authors also prepared thin films using a mixture of ZnO, Al{sub 2}O{sub 3}, and SiO{sub 2} or SiO powders as the target. They found that when AZO:Si thin films were deposited on glass substrates at about 200 degree sign C, both Al and Si doped into ZnO acted as effective donors and the atomic carbon originating from the sputtered target acted as a reducing agent. As a result, sufficient improvement was obtained in the spatial distribution of resistivity on the substrate surface in AZO:Si thin films prepared with a Si content (Si/[Si+Zn] atomic ratio) of 0.75 at. % using powder targets containing SiC. The improvement in resistivity distribution was mainly attributed to increases in both carrier concentration and Hall mobility at locations on the substrate corresponding to the target erosion region. In addition, the resistivity stability of AZO: Si thin films exposed to air for 30 min at a high temperature was found to improve with increasing Si content.

  11. Chemical vapor deposition (CVD) of cubic silicon carbide. Patent Application

    SciTech Connect

    Addamiano, A.

    1985-07-02

    This invention relates to the growth of cubic silicon carbide crystals. More specifically, this invention relates to the growth of cubic silicon carbide by Chemical Vapor Deposition (CVD). One object of the present invention is to provide a novel method for the production of cubic SiC for high temperature electronic devices. Another object of the present invention is to provide a novel method for the production of highly pure, single crystal cubic SiC that is duplicable. Another object of the present invention is to provide a novel method for the production of large-area single-crystal wafers of cubic SiC. These and other objects of the present invention can be achieved by a method for chemical vapor deposition (CVD) of cubic Silicon Carbide (SiC) comprising the steps of etching silicon substrated having one mechanically polished face; depositing a thin buffer layer of cubic SiC formed by reaction between a heated Si substrate and a H2-C3H8 gas mixuture; and depositing SiC on the buffer layer at high temperature using H2+C3HY+SiH4 mixture.

  12. Changes in characteristics of gadolinium, titanium, and erbium oxide films on the SiC surface under microwave treatment

    SciTech Connect

    Bacherikov, Yu. Yu.; Konakova, R. V.; Milenin, V. V.; Okhrimenko, O. B. Svetlichnyi, A. M.; Polyakov, V. V.

    2008-07-15

    The effect of microwaves on properties of Ti, Gd, and Er oxide films deposited on silicon carbide was studied using optical absorption and photoluminescence methods. The atomic composition of films was analyzed in relation to the microwave treatment time. It was shown that exposure to microwaves results in the appearance of an additional band in the photoluminescence spectra of the structures under study. It was shown that microwave treatment leads to an increase in the sample transmittance, which indicates an improvement in integrated characteristics of structures.

  13. Ion-beam-induced magnetic and structural phase transformation of Ni-stabilized face-centered-cubic Fe films on Cu(100)

    SciTech Connect

    Gloss, Jonas; Shah Zaman, Sameena; Jonner, Jakub; Novotny, Zbynek; Schmid, Michael; Varga, Peter; Urbánek, Michal

    2013-12-23

    Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the transformable region is presented.

  14. Formation of ZrO2 cubic phase microcrystals during crystallization of amorphous films deposited by laser ablation of Zr in an oxygen atmosphere

    NASA Astrophysics Data System (ADS)

    Bagmut, A. G.; Bagmut, I. A.; Reznik, N. A.

    2016-06-01

    The structure and phase transformations during annealing of zirconium dioxide films grown by pulsed laser sputtering of a Zr target in an oxygen atmosphere have been studied by transmission electron microscopy and electron diffraction methods. The conditions of the formation of both amorphous and cubic ZrO2 phases have been determined. The electron beam impact on the amorphous film in vacuum is accompanied by the formation of zirconium dioxide microcrystals with fcc lattice. The average grain size in the crystallized film is ˜0.5 μm. The phase transformation is accompanied by film material densification. The relative change in the density during ZrO2 crystallization is 10.27 ± 2.14%.

  15. Photonic Crystal Cavities in Cubic (3C) Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Radulaski, Marina; Babinec, Thomas; Buckley, Sonia; Rundquist, Armand; Provine, J.; Alassaad, Kassem; Ferro, Gabriel; Vuckovic, Jelena

    2014-03-01

    Silicon carbide (SiC) combines many of the outstanding material properties of other well-known optical and quantum optical materials, including strong optical nonlinearity, high Young's modulus, and a host of optically-active crystalline defects, in a single CMOS-compatible platform. For many applications in classical and quantum information processing, the material properties of the cubic silicon carbide polytype (3C-SiC) in particular are advantageous. We therefore present the design, fabrication, and characterization of high quality factor and small mode volume planar photonic crystal cavities in cubic 3C-SiC thin films (200 nm). We demonstrate cavity resonances across the infrared telecommunications band, with wavelengths from 1.25 - 1.6 μm. Finally, we highlight our progress developing higher Q/V nanobeam cavities, as well as extending this optical cavity platform towards integration with SiC color centers. PECASE Grant ECCS-10 25811, NSF Grant ECS-9731293, Stanford Graduate Fellowship, National Science Graduate Fellowship.

  16. Stoichiometry dependent phase transition in Mn-Co-Ga-based thin films: From cubic in-plane, soft magnetized to tetragonal perpendicular, hard magnetized

    SciTech Connect

    Ouardi, Siham; Fecher, Gerhard H.; Stinshoff, Rolf; Felser, Claudia; Kubota, Takahide; Mizukami, Shigemi; Miyazaki, Terunobu; Ikenaga, Eiji

    2012-12-10

    Epitaxial thin films of Mn{sub 3-x}Co{sub x}Ga were grown on MgO by magnetron co-sputtering with different Co content. Dependent on the Co content tetragonal or cubic structures are obtained. The composition dependence of saturation magnetization M{sub S} and uniaxial magnetic anisotropy K{sub u} in the epitaxial films were investigated. A high magnetic anisotropy K{sub u} of 1.2 MJ m{sup -3} was achieved for the Mn{sub 2.6}Co{sub 0.3}Ga{sub 1.1} film with low magnetic moment of 0.84 {mu}{sub B}. The valence band spectra of the films were investigated mainly by hard x-ray photoelectron spectroscopy. The evidence of sharp states in the cubic case, which are smeared out in the tetragonal case, proof the existence of a van Hove singularity that causes a band Jahn-Teller effect accompanied by a tetragonal distortion. These differences are in well agreement to the ab-initio calculations of the electronic structure.

  17. The competitive growth of cubic domains in Ti(1-x)AlxN films studied by diffraction anomalous near-edge structure spectroscopy.

    PubMed

    Pinot, Y; Tuilier, M-H; Pac, M-J; Rousselot, C; Thiaudière, D

    2015-11-01

    Titanium and aluminium nitride films deposited by magnetron sputtering generally grow as columnar domains made of oriented nanocrystallites with cubic or hexagonal symmetry depending on Al content, which are embedded in more disordered grain boundaries. The substitution of Al atoms for Ti in the cubic lattice of the films improves their resistance to wear and oxidation, allowing their use as protective coatings. Ti K-edge X-ray absorption spectroscopy, which probes both crystallized and more disordered grain boundaries, and X-ray diffraction anomalous fine structure, which is sensitive to short- and long-range order within a given crystallized domain, are carried out on a set of Ti(1-x)AlxN films deposited by magnetron sputtering on Si substrates. Attention is paid to the shape of the pre-edge region, which is sensitive to the symmetry of the site occupied by Ti atoms, either octahedral in face-centred-cubic Ti-rich (TiN, Ti0.54Al0.46N) samples or tetrahedral in hexagonal-close-packed Al-rich (Ti0.32Al0.68N) films. In order to obain information on the titanium environment in the well crystallized areas, subtraction of the smooth part of the energy-dependent structure factor for the Bragg reflections is applied to the pre-edge region of the diffraction anomalous data in order to restore their spectroscopic appearance. A flat pre-edge is related to the typical octahedral environment of Ti atoms for cubic reflections. The difference observed between pre-edge spectra associated with face-centred-cubic 200 and 111 Bragg reflections of Ti0.54Al0.46N is assigned to Ti enrichment of 111 large well ordered domains compared with the more disordered 200 ones. The sharp peak observed in the spectrum recorded from the hexagonal 002 peak of Ti0.32Al0.68N can be regarded as a standard for the pure tetrahedral Ti environment in hexagonal-close-packed nitride. PMID:26524309

  18. Transport Properties of Closely-Packed Carbon Nanotubes Film on SiC Tuned by Si-Doping

    NASA Astrophysics Data System (ADS)

    Norimatsu, Wataru; Maruyama, Takehiro; Yoshida, Kenta; Takase, Koichi; Kusunoki, Michiko

    2012-10-01

    Here, we reveal origins of the planar electrical transport of closely-packed carbon nanotubes (CNTs) and silicon-doped CNTs (Si-CNTs) films. Their electrical resistivities increased with decreasing temperature, but exhibit a plateau below 60 K. This phenomenon can be well described using the simple-two-band model, which is often used to understand the electronic properties of graphite. Cryogenic energy-filtered transmission electron microscopy visualizes Si atoms dispersed finely in CNTs, preserving the structural features of CNTs. These Si atoms induced effective carriers above 150 K, while three-dimensional variable range hopping and weak localization are dominant in their transport below 50 and 10 K, respectively.

  19. Postdeposition annealing induced transition from hexagonal Pr{sub 2}O{sub 3} to cubic PrO{sub 2} films on Si(111)

    SciTech Connect

    Weisemoeller, T.; Bertram, F.; Gevers, S.; Greuling, A.; Deiter, C.; Tobergte, H.; Neumann, M.; Wollschlaeger, J.; Giussani, A.; Schroeder, T.

    2009-06-15

    Films of hexagonal praseodymium sesquioxide (h-Pr{sub 2}O{sub 3}) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 deg. C. The films of the samples annealed at 300 deg. C or more were transformed to PrO{sub 2} with B-oriented Fm3m structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO{sub 2} and PrO{sub 2-d}elta species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO{sub 2}, PrO{sub 2-d}elta has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation.

  20. Phenomenological theory of phase transitions in epitaxial BaxSr1-xTiO3 thin films on (111)-oriented cubic substrates

    NASA Astrophysics Data System (ADS)

    Shirokov, V. B.; Shakhovoy, R. A.; Razumnaya, A. G.; Yuzyuk, Yu. I.

    2015-07-01

    A phenomenological thermodynamic theory of BaxSr1-xTiO3 (BST-x) thin films epitaxially grown on (111)-oriented cubic substrates is developed using the Landau-Devonshire approach. The group-theoretical analysis of the low-symmetry phases was performed taking into account two order parameters: the polarization related to ionic shifts in polar zone-center F1u mode and the out-of-phase rotation of TiO6 octahedra corresponding to the R25 zone-boundary mode in the parent cubic phase P m 3 ¯ m . The eight-order thermodynamic potential for BST-x solid solutions was developed and analyzed. We constructed the "concentration-misfit strain" phase diagram for BST-x thin films at room temperature and found that polar rhombohedral R3m phase with the polarization normal to the substrate is stable for x > 0.72 and negative misfit strains, while ferroelectric monoclinic C2 and Cm phases with in-plane polarization are stable for much smaller x and positive or slightly negative misfit strains. We constructed the "temperature-misfit strain" phase diagrams for several concentrations (x = 1, 0.8, 0.6, 0.4, and 0.2). Systematic changes of the phase transition lines between the paraelectric and ferroelectric phases are discussed. The phase diagrams are useful for practical applications in thin-film engineering.

  1. Synthesis, characterizations and applications of some nanomaterials (TiO2 and SiC nanostructured films, organized CNT structures, ZnO structures and CNT-blood platelet clusters)

    NASA Astrophysics Data System (ADS)

    Srivastava, O. N.; Srivastava, A.; Dash, D.; Singh, D. P.; Yadav, R. M.; Mishra, P. R.; Singh, J.

    2005-10-01

    TiO_{2} nanostructured films have been synthesized by the hydrolysis of Ti[OCH(CH_{3})_{2}]_{4} as the precursor. These films have been utilized for the dissociation of phenol contaminant in water. Free-standing nanostructured film of silicon carbide (SiC) has been synthesized, employing a simple and new route of spray pyrolysis technique utilizing a slurry of Si in hexane. Another study is done on organized carbon nanotube (CNT) structures. These are made in the form of hollow cylinders (50 mm length, 4 mm diameter and 1.5 mm wall thickness). These CNT-based cylinders are made of conventional CNT and bamboo-shaped CNT. The filtrations of heavy hydrocarbons and E. coli bacteria from water have been carried out. In addition to this, ZnO nanostructures have also been studied. Another study concerns CNT-blood platelet clusters.

  2. 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.

  3. Atomistic mechanisms of strain relaxation due to ductile void growth in ultrathin films of face-centered-cubic metals

    NASA Astrophysics Data System (ADS)

    Gungor, M. Rauf; Maroudas, Dimitrios

    2005-06-01

    A comprehensive computational analysis is reported of the atomistic mechanisms of strain relaxation and failure in free-standing Cu thin films under applied biaxial tensile strain for strain levels up to 6%. The analysis focuses on nanometer-scale-thick films with a preexisting void extending across the film thickness and the film plane oriented normal to the [111] crystallographic direction. Our computational study is based on isothermal-isostrain large-scale molecular-dynamics simulations within an embedded-atom-method parametrization for Cu. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Within the considered strain range, after an elastic response at a low strain (<2%), void growth is the major strain relaxation mechanism mediated by the emission of perfect screw dislocation pairs from the void surface and subsequent dislocation propagation; as a result, a plastic zone forms around the void. Plastic deformation is accompanied by the glide motion of the dislocations emitted from the void surface, void surface morphological transitions, formation of a step pattern on the film's surfaces, dislocation jogging, vacancy generation due to gliding jogged dislocations, dislocation-vacancy interactions, vacancy pipe diffusion along dislocation cores, as well as dislocation-dislocation interactions. The increase in film surface roughness with increasing strain eventually leads to nucleation and propagation from the film surfaces of threading dislocation loops, which ultimately break up when they reach the opposite free surface of the thin film.

  4. -SiC Composites

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Ionic Conductivity of Mesostructured Yttria-Stabilized Zirconia Thin Films with Cubic Pore Symmetry—On the Influence of Water on the Surface Oxygen Ion Transport.

    PubMed

    Elm, Matthias T; Hofmann, Jonas D; Suchomski, Christian; Janek, Jürgen; Brezesinski, Torsten

    2015-06-10

    Thermally stable, ordered mesoporous thin films of 8 mol % yttria-stabilized zirconia (YSZ) were prepared by solution-phase coassembly of chloride salt precursors with an amphiphilic diblock copolymer using an evaporation-induced self-assembly process. The resulting material is of high quality and exhibits a well-defined three-dimensional network of pores averaging 24 nm in diameter after annealing at 600 °C for several hours. The wall structure is polycrystalline, with grains in the size range of 7 to 10 nm. Using impedance spectroscopy, the total electrical conductivity was measured between 200 and 500 °C under ambient atmosphere as well as in dry atmosphere for oxygen partial pressures ranging from 1 to 10(-4) bar. Similar to bulk YSZ, a constant ionic conductivity is observed over the whole oxygen partial pressure range investigated. In dry atmosphere, the sol-gel derived films have a much higher conductivity, with different activation energies for low and high temperatures. Overall, the results indicate a strong influence of the surface on the transport properties in cubic fluorite-type YSZ with high surface-to-volume ratio. A qualitative defect model which includes surface effects (annihilation of oxygen vacancies as a result of water adsorption) is proposed to explain the behavior and sensitivity of the conductivity to variations in the surrounding atmosphere. PMID:25984884

  6. Suppression of ferromagnetism and observation of quantum well states in epitaxial thin films of the cubic ruthenate BaRuO3

    NASA Astrophysics Data System (ADS)

    Burganov, Bulat; Paik, Hanjong; Shen, Kyle; Schlom, Darrell

    The pseudocubic perovskite ruthenates ARuO3, where A is alkaline earth metal, are correlated materials where Hund's coupling drives correlations and leads to a low coherence scale, large renormalization, and formation of local moments. The ferromagnetic BaRuO3 has an ideal cubic structure and a larger bandwidth, compared to its GdFeO3-distorted counterparts, CaRuO3 and SrRuO3. In stark contrast to SrRuO3, which is a Fermi liquid below TC, BaRuO3 exhibits critical fluctuations near TC that are enhanced under hydrostatic pressure, which suppresses the Fermi liquid coherence scale and TC and drives a crossover into non-FL regime. Here we use ARPES to characterize the momentum-resolved electronic structure of strained ultrathin BaRuO3 films grown in situ by molecular beam epitaxy. The films on STO (001) are metallic down to 2 u.c. thickness and manifest clearly defined subbands of well-defined quasiparticles which arise due to quantum confinement effects. We observe that the bands are moderately renormalized compared to bare GGA bands and discover that the ferromagnetism can be suppressed in the atomically thin limit. We discuss our results on BaRuO3 in the context of our recent ARPES studies of the other perovskite ruthenates, SrRuO3 and CaRuO3.

  7. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively

    PubMed Central

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-01-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L−1 (cubic SiC NWs) and 5–8000 μmoL L−1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L−1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility. PMID:27109361

  8. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively.

    PubMed

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-01-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50-15000 μmoL L(-1) (cubic SiC NWs) and 5-8000 μmoL L(-1) (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L(-1) respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility. PMID:27109361

  9. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-04-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L‑1 (cubic SiC NWs) and 5–8000 μmoL L‑1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L‑1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility.

  10. SiC Technology

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1998-01-01

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

  11. 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.

  12. Symmetry-broken double fingers and seaweed patterns in thin-film directional solidification of a nonfaceted cubic crystal

    NASA Astrophysics Data System (ADS)

    Akamatsu, Silvère; Faivre, Gabriel; Ihle, Thomas

    1995-05-01

    We present a detailed experimental and numerical investigation of the directional-solidification growth patterns in thin films of the CBr4-8 mol % C2Cl6 alloy, as a function of the orientation of the (fcc) crystal with respect to the solidification setup. Most experiments are performed with single-crystal samples about 10 mm wide and 15 μm thick. The crystal sometimes contains small faceted gas inclusions, the shape of which gives us direct information about the orientation of the crystal. Numerical simulations by a fully dynamical method are carried out with parameters corresponding to the experimental system. We find experimentally that, in crystals with a \\{111\\} plane (nearly) parallel to the plane of the thin film, the growth pattern is nondendritic and unsteady over the explored velocity range (5Vc-50Vc Vc~=1.9 μm s-1 is the cellular threshold velocity). By studying the time evolution of this pattern, we establish that it is essentially similar to the ``seaweed pattern'' characteristic of vanishingly small capillary and kinetic anisotropies of the solid-liquid interface, recently studied numerically [T. Ihle and H. Müller-Krumbhaar, Phys. Rev. E 49, 2972 (1994)]. The building blocks of this pattern are local structures-pairs of symmetry-broken (SB) fingers called ``SB double fingers'' or ``doublons,'' and more complex structures called ``multiplets''-whose lifetime is long but finite. We show experimentally that, in agreement with numerical findings, doublons obey selection rules, but do not have a preferential growth direction. We furthermore find that ``dendritic'' doublons also appear in crystals with a <100> axis close to the pulling direction (thus having a strong two-dimensional anisotropy) above a critical velocity (~=20Vc). The existence and stability of dendritic doublons in directional solidification at high velocity are confirmed by the simulations. Another crystal orientation of interest is that in which two <100> axes are symmetrically

  13. 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.

  14. Structural and chemical analysis of pulsed laser deposited Mg xZn 1- xO hexagonal ( x = 0.15, 0.28) and cubic ( x = 0.85) thin films

    NASA Astrophysics Data System (ADS)

    Hullavarad, S. S.; Hullavarad, N. V.; Pugel, D. E.; Dhar, S.; Venkatesan, T.; Vispute, R. D.

    2008-02-01

    Hexagonal and cubic Mg xZn 1- xO thin films corresponding to optical band gaps of 3.52 eV, 4 eV and 6.42 eV for x = 0.15, 0.28 and 0.85 compositions were grown by pulsed laser deposition technique. The crystalline quality of the films was investigated by X-ray diffraction-rocking curve measurements and indicated a high degree of crystallinity with narrow FWHM's of 0.21°-0.59°. Rutherford back scattering-channeling spectroscopy provides channeling yields of 7-14% indicating the good crystalline quality of the thin films. X-Ray photoelectron spectroscopy measurements clearly indicated different level of oxidation states of Mg and Zn.

  15. 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.

  16. Sputter deposition of SiC coating on silicon wafers

    NASA Technical Reports Server (NTRS)

    Robson, M. T.; Blue, C. A.; Warrier, S. G.; Lin, R. Y.

    1992-01-01

    A study is conducted of the effect of substrate temperature during coating on the properties of coated SiC films on Si wafers, using a scratch test technique. While specimen temperature during coating has little effect on deposition rate, it significantly affects the durability of the coating. Scratch test damage to both film coating and substrate decreased with increasing deposition temperature, perhaps due to the rapid diffusion of the deposited atoms.

  17. 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.

  18. 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.

  19. Atomistic aspects of ductile responses of cubic silicon carbide during nanometric cutting

    PubMed Central

    2011-01-01

    Cubic silicon carbide (SiC) is an extremely hard and brittle material having unique blend of material properties which makes it suitable candidate for microelectromechanical systems and nanoelectromechanical systems applications. Although, SiC can be machined in ductile regime at nanoscale through single-point diamond turning process, the root cause of the ductile response of SiC has not been understood yet which impedes significant exploitation of this ceramic material. In this paper, molecular dynamics simulation has been carried out to investigate the atomistic aspects of ductile response of SiC during nanometric cutting process. Simulation results show that cubic SiC undergoes sp3-sp2 order-disorder transition resulting in the formation of SiC-graphene-like substance with a growth rate dependent on the cutting conditions. The disorder transition of SiC causes the ductile response during its nanometric cutting operations. It was further found out that the continuous abrasive action between the diamond tool and SiC causes simultaneous sp3-sp2 order-disorder transition of diamond tool which results in graphitization of diamond and consequent tool wear. PMID:22078069

  20. 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.

  1. Process for the homoepitaxial growth of single-crystal silicon carbide films on silicon carbide wafers

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor)

    1993-01-01

    The invention is a method for growing homoepitaxial films of SiC on low tilt angle vicinal (0001) SiC wafers. The invention proposes and teaches a new theoretical model for the homoepitaxial growth of SiC films on (0001) SiC substrates. The inventive method consists of preparing the growth surface of SiC wafers slightly off-axis (from less the 0.1 to 6 deg) from the (0001) plane, subjecting the growth surface to a suitable etch, and then growing the homoepitaxial film using conventional SiC growth techniques.

  2. Optical waveguide formed by cubic silicon carbide on sapphire substrates

    NASA Technical Reports Server (NTRS)

    Tang, Xiao; Wongchotigul, Kobchat; Spencer, Michael G.

    1991-01-01

    Optical confinement in beta silicon carbide (beta-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin beta-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. It is believed that this is the first step in validating a silicon carbide optoelectronic technology.

  3. Application of rapid milling technology for fabrication of SiC nanoparticles.

    PubMed

    Kim, Jong-Woong; Shim, Jae-Shik; Kwak, Min-Gi; Hong, Sung-Jei; Cho, Hyun-Min

    2013-09-01

    SiC nanoparticles were successfully fabricated by a high energy ball milling method, so that can be used in the printed electronics to make SiC thin film patterns. Here we utilized the waste of Si sludge for making the SiC nanoparticles. In order to achieve uniform thin film from the nanoparticle ink, fine sized SiC nanoparticles less than 100 nm has to be uniformly dispersed. In this study, we employed the ultra apex milling (UAM) system for particle comminution and dispersion. We investigated the effects of milling parameters, e.g., size of ZrO2 bead and milling time. The size of the SiC particles reached about 103 nm after 4 hours of UAM, when the ZrO2 beads of 50 microm were used. Then SiC ink was formulated with organic solvents and a dispersing agent. A specially designed pattern was printed by an ink-jet printer for evaluating the feasibility of the SiC nanoparticle inks. PMID:24205600

  4. 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.

  5. -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.

  6. Optimizing Graphene Morphology on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Hannon, James

    2009-03-01

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

  7. Piecewise Cubic Interpolation Package

    Energy Science and Technology Software Center (ESTSC)

    1982-04-23

    PCHIP (Piecewise Cubic Interpolation Package) is a set of subroutines for piecewise cubic Hermite interpolation of data. It features software to produce a monotone and "visually pleasing" interpolant to monotone data. Such an interpolant may be more reasonable than a cubic spline if the data contain both 'steep' and 'flat' sections. Interpolation of cumulative probability distribution functions is another application. In PCHIP, all piecewise cubic functions are represented in cubic Hermite form; that is, f(x)more » is determined by its values f(i) and derivatives d(i) at the breakpoints x(i), i=1(1)N. PCHIP contains three routines - PCHIM, PCHIC, and PCHSP to determine derivative values, six routines - CHFEV, PCHFE, CHFDV, PCHFD, PCHID, and PCHIA to evaluate, differentiate, or integrate the resulting cubic Hermite function, and one routine to check for monotonicity. A FORTRAN 77 version and SLATEC version of PCHIP are included.« less

  8. 29 CFR 510.21 - SIC codes.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  9. Evidence for interstellar SiC in the Murray carbonaceous meteorite

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas; Wopenka, Brigitte; Fraundorf, Gail; Ming, Tang; Anders, Edward

    1987-01-01

    Silicon carbide has been identified in two separates from the Murray carbonaceous chondrite that are enriched 20,000-fold in isotopically anomalous neon and xenon. The SiC is present in the form of crystalline grains 0.1-1 micron in size. Cubic and 111-plane-twinned cubic are the most common ordered polytypes observed so far. The anomalous isotopic composition of its carbon, nitrogen, and silicon indicates a presolar origin, probably in the atmospheres of red giants. An additional silicon- and oxygen-rich phase shows large isotropic anomalies in nitrogen and silicon, also associated with a presolar origin.

  10. 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

  11. Design and fabrication of large-scale lightweight SiC space mirror

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhan; Zhang, Yumin; Han, Jiecai; He, Xiaodong; Yao, Wang

    2006-02-01

    Silicon carbide is a new type of optics material developed in recent years because it offered some advantages over other traditional optical substrate materials such as low density, low thermal expansion coefficient, high thermal conductivity, big special heat, big modulus of elasticity and potential cost and schedule. So in this paper, the silicon carbide space mirror was fabricated by both reaction bonded (RB) and chemical vapor deposition (CVD) process. The green body of the space mirror was prepared by silicon carbide powder, carbon powder, dilution and solidified agent using slip casting method. The space mirror blank was prepared by green body and pure silicon powder. They were laid in vacuum sintering furnace and sintered at 1500°C. In this temperature, silicon was melting then infiltrated in SiC green body and reacted with carbon to generate the new SiC, at the same time, bonded original SiC powder, in the end, the nonporous SiC/Si space mirror blank was fabricated. The reaction bonded silicon carbide (RBSiC) was consistent with original SiC powder, new generated SiC and unreacted Si. Because RBSiC was SiC/Si two-phase structure, the hardness difference between SiC and Si made the space mirror difficult to achieve precision optical surface by grinding. So a full density SiC thin film was coated on the surface of space mirror blank with RBSiC by chemical vapor deposition (CVD) process. The raw material was CH3SiCl3. The hydrogen (H2) was catalyst. The deposition temperature was 1300°C. The cooling rate could be controlled. The SiC space mirror was honeycomb open back lightweight structure. The honeycomb cellar could be triangle, rectangle, hexogen and sector. The biggest diameter of SiC space mirror blank which has been fabricated is approach one meter by forgoing process. In order to the forgoing process was feasible, a flat round SiC space mirror with 250mm diameter. The space mirror was composed of a 4mm thick round plane faceplate and hexagonal cellar

  12. Mechanisms of edge-dislocation formation in strained films of zinc blende and diamond cubic semiconductors epitaxially grown on (001)-oriented substrates

    SciTech Connect

    Bolkhovityanov, Yu. B.; Deryabin, A. S.; Gutakovskii, A. K.; Sokolov, L. V.

    2011-06-15

    Ninety degree edge misfit dislocations (MDs) are 'sessile' dislocations; such dislocations, however, were found in large amounts in relaxed films. The commonly accepted formation mechanism of such dislocations is an interaction of two complementary 60 deg. dislocations with appropriate Burger's vectors, for example: a/2[101] + a/2 [011] = a/2 [110]. In the present study, four possible types of interaction were analyzed: (i) random meeting of two complementary MDs; (ii) crossing of two complementary 60 deg. MDs in the vicinity of film-substrate interface in systems grown on substrates misoriented from exact (001) orientation; (iii) formation of edge MDs during cross-slipping of a secondary MD; and (iv) induced nucleation of a secondary complementary 60 deg. MD. Examples of discussed interactions are given. Contrary to the widespread opinion that edge MDs in GeSi and InGaAs films grown by MBE on Si and GaAs substrates predominantly form under elastic strains greater than 2% and at the final stage of plastic relaxation, in the present study, we show that such dislocations may also form at an early stage of plastic relaxation in films with less-than-1% lattice misfit with substrate. A necessary condition for that is a sufficient amount of 60 deg. dislocations available in the system by the moment the strained film starts growing. Dislocations (60 deg. ) can be introduced into the system using a preliminarily grown, partially or fully relaxed buffer layer. This layer serves as a source of threading dislocations for the next growing layer that favor the formation of paired complementary MDs and their 'reagents', edge MDs, at the interface with growing film.

  13. Microstructure of TRISO Coated Particles from the AGR-1 Experiment I: SiC Grain Size and Grain Boundary Character

    SciTech Connect

    Rita Kirchhofer; John D, Hunn; Paul A. Demkowicz; James I. Cole; Brian P. Gorman

    2013-01-01

    Pre-irradiation SiC microstructures in TRISO coated fuel particles from the AGR-1 experiment were quantitatively characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). From EBSD it was determined that only the cubic polymorph of as-deposited SiC was present and the SiC had a high fraction of CSL S3 grain boundaries. Additionally, the local area misorientation (LAM), which is a qualitative measurement of strain in the SiC lattice, was mapped for each fuel variant. The morphology of the SiC / IPyC interfaces were characterized by TEM following site-specific focused ion beam (FIB) specimen preparation. It was determined that the SiC layer had a heavily faulted microstructure typical of CVD deposited SiC and that the average grain diameter increased from the SiC/IPyC interface for all the fuel variants, except V3 that showed a constant grain size across the layer.

  14. SiC Micropipe Sprecta

    NASA Astrophysics Data System (ADS)

    Leff, David; Frasca, Albert

    1997-05-01

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

  15. System for the growth of bulk SiC crystals by modified CVD techniques

    NASA Technical Reports Server (NTRS)

    Steckl, Andrew J.

    1994-01-01

    The goal of this program was the development of a SiC CVD growth of films thick enough to be useful as pseudo-substrates. The cold-walled CVD system was designed, assembled, and tested. Extrapolating from preliminary evaluation of SiC films grown in the system at relatively low temperatures indicates that the growth rate at the final temperatures will be high enough to make our approach practical. Modifications of the system to allow high temperature growth and cleaner growth conditions are in progress. This program was jointly funded by Wright Laboratory, Materials Directorate and NASA LeRC and monitored by NASA.

  16. Moment mapping of body-centered-cubic Fe{sub x}Mn{sub 1−x} alloy films on MgO(001)

    SciTech Connect

    Idzerda, Y. U. Bhatkar, H.; Arenholz, E.

    2015-05-07

    The alloy composition and elemental magnetic moments of bcc single crystal films of compositionally graded Fe{sub x}Mn{sub 1−x} films (20 nm thick films with 0.8 ≤ x ≤ 0.9) grown on MgO(001) are spatially mapped using X-ray absorption spectroscopy and magnetic circular dichroism. Electron diffraction measurements on single composition samples confirmed that the structure of Fe{sub x}Mn{sub 1−x} films remained epitaxial and in the bcc phase from 0.65 ≤ x ≤ 1, but rotated 45° with respect to the MgO(001) surface net. This is beyond the bulk bcc stability limit of x = 0.88. The Fe moment is found to gradually reduce with increasing Mn content with a very abrupt decline at x = 0.85, a slightly higher composition than observed in the bulk. Surprisingly, the Mn exhibits a very small net moment (<0.1 μ{sub B}) at all compositions, suggesting a complex Mn spin structure.

  17. 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.

  18. Growth and oxidization stability of cubic Zr{sub 1−x}Gd{sub x}N solid solution thin films

    SciTech Connect

    Höglund, C.; Alling, B.; Jensen, J.; Hultman, L.; Birch, J.; Hall-Wilton, R.

    2015-05-21

    We report Zr{sub 1−x}Gd{sub x}N thin films deposited by magnetron sputter deposition. We show a solid solubility of the highly neutron absorbing GdN into ZrN along the whole compositional range, which is in excellent agreement with our recent predictions by first-principles calculations. An oxidization study in air shows that Zr{sub 1−x}Gd{sub x}N with x reaching from 1 to close to 0 fully oxidizes, but that the oxidization is slowed down by an increased amount of ZrN or stopped by applying a capping layer of ZrN. The crystalline quality of Zr{sub 0.5}Gd{sub 0.5}N films increases with substrate temperatures increasing from 100 °C to 900 °C.

  19. Epitaxial Growth of beta-Silicon Carbide (SiC) on a Compliant Substrate via Chemical Vapor Deposition (CVD)

    NASA Technical Reports Server (NTRS)

    Mitchell, Sharanda L.

    1996-01-01

    Many lattice defects have been attributed to the lattice mismatch and the difference in the thermal coefficient of expansion between SiC and silicon (Si). Stacking faults, twins and antiphase boundaries are some of the lattice defects found in these SiC films. These defects may be a partial cause of the disappointing performance reported for the prototype devices fabricated from beta-SiC films. The objective of this research is to relieve some of the thermal stress due to lattice mismatch when SiC is epitaxially grown on Si. The compliant substrate is a silicon membrane 2-4 microns thick. The CVD process includes the buffer layer which is grown at 1360 C followed by a very thin epitaxial growth of SiC. Then the temperature is raised to 1500 C for the subsequent growth of SiC. Since silicon melts at 1415 C, the SiC will be grown on molten Silicon which is absorbed by a porous graphite susceptor eliminating the SiC/Si interface. We suspect that this buffer layer will yield less stressed material to help in the epitaxial growth of SiC.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  1. Modified electrodes based on lipidic cubic phases.

    PubMed

    Bilewicz, Renata; Rowiński, Paweł; Rogalska, Ewa

    2005-04-01

    The lipidic cubic phase can be characterized as a curved bilayer forming a three-dimensional, crystallographical, well-ordered structure that is interwoven by aqueous channels. It provides a stable, well-organized environment in which diffusion of both water-soluble and lipid-soluble compounds can take place. Cubic phases based on monoacylglycerols form readily and attract our interest due to their ability to incorporate and stabilize proteins. Their lyotropic and thermotropic phase behaviour has been thoroughly investigated. At hydration over 20%, lipidic cubic phases Ia3d and Pn3m are formed. The latter is stable in the presence of excess water, which is important when the cubic phase is considered as an electrode-modifying material. Due to high viscosity, the cubic phases can be simply smeared over solid substrates such as electrodes and used to host enzymes and synthetic catalysts, leading to new types of catalytically active modified electrodes as shown for the determination of cholesterol, CO(2), or oxygen. The efficiency of transport of small hydrophilic molecules within the film can be determined by voltametry using two types of electrodes: a normal-size electrode working in the linear diffusion regime, and an ultramicroelectrode working under spherical diffusion conditions. This allows determining both the concentration and diffusion coefficient of the electrochemically active probe in the cubic phase. The monoolein-based cubic phase matrices are useful for immobilizing enzymes on the electrode surface (e.g., laccases from Trametes sp. and Rhus vernicifera were employed for monitoring dioxygen). The electronic contact between the electrode and the enzyme was maintained using suitable electroactive probes. PMID:15833697

  2. Accurate monotone cubic interpolation

    NASA Technical Reports Server (NTRS)

    Huynh, Hung T.

    1991-01-01

    Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.

  3. SiC detector damage and characterization for high intensity laser-plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Torrisi, L.; Cannavò, A.

    2016-05-01

    Silicon-Carbide (SiC) detectors are always more extensively employed as diagnostics in laser-generated plasma due to their remarkable properties such as their high band gap, high carrier velocity, high detection efficiency, high radiation resistance and low leakage current at room temperature. SiC detectors, in comparison with Si detectors, have the advantage of being insensitive to visible light, having low reverse current at high temperature and high radiation hardness. A similar energy resolution characterizes the two types of detectors, being 0.8% in Si and 1.0% in SiC, as measured detecting 5.8 MeV alpha particles. Generally, SiC detectors are employed as laser-plasma diagnostics in time-of-flight configuration, permitting the simultaneous detection of photons, electrons and ions based on discrimination of velocity. SiC detectors can be employed in the proportionality regime, because their response is proportional to the radiation energy deposited in the active layer. Using thin absorbers in front of the detectors makes it possible to have further information on the radiation nature, intensity and energy. Surface characterization of SiC before and after prolonged exposure to hot plasma laser generated shows the formation of bulk defects and thin film deposition on the detector surface limiting the device functionality.

  4. Update on SIC-Based Inverter Technology

    SciTech Connect

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

    2009-01-01

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

  5. Interaction Of Water Molecules With SiC(001) Surfaces

    SciTech Connect

    Cicero, G; Catellani, A; Galli, G

    2004-08-10

    We have investigated the interaction of water molecules with the polar Si- and C- terminated surfaces of cubic Silicon Carbide by means of ab initio molecular dynamics simulations at finite temperature. Different water coverages were considered, from {1/4} to a complete monolayer. Irrespective of coverage, we find that water dissociates on the silicon terminated surfaces, leading to important changes in both its structural and electronic properties. On the contrary, the carbon terminated surface remains inert when exposed to water. We propose experiments to reveal the ionic and electronic structure of wet Si-terminated surfaces predicted by our calculations, which at full coverage are notably different from those of hydrated Si(001) substrates. Finally, we discuss the implications of our results for SiC surface functionalization.

  6. In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites

    SciTech Connect

    Cao, J. |

    1996-12-01

    This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1,700 C with 3 wt% Al, 0.6 wt% B, and 2 wt% C additions. These sintering aids also enhanced the {beta}-to-{alpha} (3C-to-4H) phase transformation, which promoted SiC grains to grow into plate-like shapes. Under optimal processing conditions, the microstructure exhibited high-aspect-ratio plate-shaped grains with a thin (< 1 nm) Al-containing amorphous grain boundary film. The mechanical properties of the toughened SiC and the composites were evaluated in comparison with a commercial Hexoloy SiC under identical test conditions. The C-curve behavior was examined using the strength-indentation load relationship and compared with that directly measured using precracked compact tension specimens. The in situ toughened ABC-SiC exhibited much improved flaw tolerance and a significantly rising R-curve behavior. A steady-state toughness in excess of 9 MPam{sup 1/2} was recorded for the ABC-SiC in comparison to a single valued toughness below 3 MPam{sup 1/2} for the Hexoloy. Toughening in the ABC-SiC was mainly attributed to grain bridging and subsequent pullout of the plate-shaped grains. The high toughness ABC-SiC exhibited a bend strength of 650 MPa with a Weibull modulus of 19; in comparison, the commercial SiC showed a bend strength of 400 MPa with a Weibull modulus of 6. Higher fracture toughness was also achieved by the reinforcement of SiC platelets, encapsulated with alumina, yttria, or silica, in a SiC matrix.

  7. Deposition Of Cubic BN On Diamond Interlayers

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P.; Shing, Yuh-Han

    1994-01-01

    Thin films of polycrystalline, pure, cubic boron nitride (c-BN) formed on various substrates, according to proposal, by chemical vapor deposition onto interlayers of polycrystalline diamond. Substrate materials include metals, semiconductors, and insulators. Typical substrates include metal-cutting tools: polycrystalline c-BN coats advantageous for cutting ferrous materials and for use in highly oxidizing environments-applications in which diamond coats tend to dissolve in iron or be oxidized, respectively.

  8. A new approach for fabrications of SiC based photodetectors

    PubMed Central

    Aldalbahi, Ali; Li, Eric; Rivera, Manuel; Velazquez, Rafael; Altalhi, Tariq; Peng, Xiaoyan; Feng, Peter X.

    2016-01-01

    We report on a new approach to quickly synthesize high-quality single crystalline wide band gap silicon carbide (SiC) films for development of high-performance deep ultraviolet (UV) photodetectors. The fabricated SiC based UV photodetectors exhibited high response while maintaining cost-effectiveness and size miniaturization. Focus of the experiments was on studies of electrical and electronic properties, as well as responsivity, response and recovery times, and repeatability of the deep UV photodetectors. Raman scattering spectroscopy and scanning electron microscope (SEM) were used to characterize the SiC materials. Analyses of the SEM data indicated that highly flat SiC thin films have been obtained. Based on the synthesized SiC, deep UV detectors are designed, fabricated, and tested with various UV wavelength lights at different radiation intensities. Temperature effect and bias effect on the photocurrent strength and signal-to-noise ratio, humidity effect on the response time and recovery time of the fabricated detectors have been carefully characterized and discussed. The detectors appear to have a very stable baseline and repeatability. The obtained responsivity is more than 40% higher compared to commercial detectors. The good performance of the photodetectors at operating temperature up to 300 °C remains nearly unchanged. PMID:26988399

  9. A new approach for fabrications of SiC based photodetectors

    NASA Astrophysics Data System (ADS)

    Aldalbahi, Ali; Li, Eric; Rivera, Manuel; Velazquez, Rafael; Altalhi, Tariq; Peng, Xiaoyan; Feng, Peter X.

    2016-03-01

    We report on a new approach to quickly synthesize high-quality single crystalline wide band gap silicon carbide (SiC) films for development of high-performance deep ultraviolet (UV) photodetectors. The fabricated SiC based UV photodetectors exhibited high response while maintaining cost-effectiveness and size miniaturization. Focus of the experiments was on studies of electrical and electronic properties, as well as responsivity, response and recovery times, and repeatability of the deep UV photodetectors. Raman scattering spectroscopy and scanning electron microscope (SEM) were used to characterize the SiC materials. Analyses of the SEM data indicated that highly flat SiC thin films have been obtained. Based on the synthesized SiC, deep UV detectors are designed, fabricated, and tested with various UV wavelength lights at different radiation intensities. Temperature effect and bias effect on the photocurrent strength and signal-to-noise ratio, humidity effect on the response time and recovery time of the fabricated detectors have been carefully characterized and discussed. The detectors appear to have a very stable baseline and repeatability. The obtained responsivity is more than 40% higher compared to commercial detectors. The good performance of the photodetectors at operating temperature up to 300 °C remains nearly unchanged.

  10. A new approach for fabrications of SiC based photodetectors.

    PubMed

    Aldalbahi, Ali; Li, Eric; Rivera, Manuel; Velazquez, Rafael; Altalhi, Tariq; Peng, Xiaoyan; Feng, Peter X

    2016-01-01

    We report on a new approach to quickly synthesize high-quality single crystalline wide band gap silicon carbide (SiC) films for development of high-performance deep ultraviolet (UV) photodetectors. The fabricated SiC based UV photodetectors exhibited high response while maintaining cost-effectiveness and size miniaturization. Focus of the experiments was on studies of electrical and electronic properties, as well as responsivity, response and recovery times, and repeatability of the deep UV photodetectors. Raman scattering spectroscopy and scanning electron microscope (SEM) were used to characterize the SiC materials. Analyses of the SEM data indicated that highly flat SiC thin films have been obtained. Based on the synthesized SiC, deep UV detectors are designed, fabricated, and tested with various UV wavelength lights at different radiation intensities. Temperature effect and bias effect on the photocurrent strength and signal-to-noise ratio, humidity effect on the response time and recovery time of the fabricated detectors have been carefully characterized and discussed. The detectors appear to have a very stable baseline and repeatability. The obtained responsivity is more than 40% higher compared to commercial detectors. The good performance of the photodetectors at operating temperature up to 300 °C remains nearly unchanged. PMID:26988399

  11. CVD of SiC and AlN using cyclic organometallic precursors

    NASA Technical Reports Server (NTRS)

    Interrante, L. V.; Larkin, D. J.; Amato, C.

    1992-01-01

    The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

  12. Atmospheric pressure growth of graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Seyller, Thomas

    2009-03-01

    Graphene, a single monolayer of sp^2-bonded carbon, is a very unique 2-dimensional electron gas system with electronic properties fundamentally different to other 2DEG systems [1]. Several production routes exist for graphene. Among them, the solid-state decomposition of hexagonal silicon carbide (SiC) surfaces [2] is particularly attractive for the development of graphene based electronics [3,4]. The first part of the presentation gives a brief summary of recent studies on the structural and electronic properties of graphene and few-layer graphene grown on SiC(0001) under ultra-high vacuum (UHV) conditions. The second part of the talk is devoted to recent progress in the growth of large domain graphene films on SiC(0001) in Ar atmosphere. It is shown that growth in Ar ambient leads to a significant improvement of the surface morphology and domain size as well as carrier mobility. [4pt] [1] A.H. Castro Neto, et al., Reviews of Modern Physics, in print (arXiv:0709.1163v2); and references therein. [0pt] [2] A. Charrier, et al., J. Appl. Phys. 92 (2002) 2479. [0pt] [3] C. Berger et al., J. Phys. Chem. B 108 (2004) 19912; C. Berger, et al., Science 312 (2006) 1191. [0pt] [4] A.K. Geim and K.S. Novoselov, Nature Mat. 6 (2007) 183.

  13. Reactive sintering of SiC

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  14. Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures

    PubMed Central

    Ou, Yiyu; Zhu, Xiaolong; Jokubavicius, Valdas; Yakimova, Rositza; Mortensen, N. Asger; Syväjärvi, Mikael; Xiao, Sanshui; Ou, Haiyan

    2014-01-01

    We demonstrate a time-efficient and low-cost approach to fabricate Si3N4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si3N4 coating are formed via dry etching and thin film deposition process. By using this method, a significant broadband surface antireflection and a considerable omnidirectional luminescence enhancement are obtained. The experimental observations are then supported by numerical simulations. It is believed that our fabrication method will be well suitable for large-scale production in the future. PMID:24722521

  15. Cubic-normal distribution

    NASA Astrophysics Data System (ADS)

    Peng, Gan Chew; Hin, Pooi Ah; Ho, C. K.

    2015-12-01

    The power-normal distribution given in Yeo and Johnson in year 2000 is a unimodal distribution with wide ranges of skewness and kurtosis. A shortcoming of the power-normal distribution is that the negative and positve parts of the underlying random variable have to be specified by two different expressions of the standard normal random variable. In this paper, we construct a new distribution, called the cubic-normal distribution, via a single polynomial expression in cubic root function. Apart from having the properties which are similar to those of the power-normal distribution, this cubic-normal distribution can be developed into a multivariate version which is more attractive from the theoretical and computational points of view.

  16. Low temperature deposition and characterization of n- and p-type silicon carbide thin films and associated ohmic and Schottky contacts. Annual report, 1 January-31 December 1992

    SciTech Connect

    Davis, R.F.; Nemanich, R.J.; Kern, R.S.; Patterson, R.; Rowland, L.B.

    1992-01-01

    Single-crystal epitaxial films of cubic Beta(3C)-SiC(111) and AlN(0001) have been deposited on alpha(6H)-SiC(OOO1) substrates oriented 3-4 deg towards 1120 at 1050 deg C via gas-source molecular beam epitaxy using disilane (Si2H6), ethylene (C2H4), thermal evaporation of Al and activated N species derived from an ECR plasma. High resolution transmission electron microscopy revealed that the nucleation and growth of the Beta(3C)-SiC regions occurred primarily on terraces between closely spaced steps. Pseudomorphic bilayer structures containing Beta(3C)-SiC and 2H-AlN have been grown under the same conditions for the first time. HREED and cross-sectional HRTEM showed all layers to be monocrystalline. Initial high temperature chemical interdiffusion studies between SiC and AIN show that all components diffuse very slowly across the interface. AHRTEM and SAS are being used to determine the concentration profiles. Thin film solid solutions of AIN and SiC have been deposited using similar techniques and conditions as the individual compounds. Metal contacts of Ti, Pt and Hf deposited at RT on n-type alpha(6H)-SiC(OOO1) exhibit rectifying behavior with ideality factors between 1.01 and 1.09. The Pt and Hf contacts had leakage currents of 5xl0-8 A/cm2 at -10V. Values of barrier heights for all contacts were within a few tenths of 1.0eV which is indicative that the Fermi level is pinned at the SiC surface.... Films, SiC, AlN, Gas source molecular beam epitaxy, Transmission electron microscopy, Chemical interdiffusion, Metal contacts, Ti, Pt, Hf, Ideality factors, Fermi level pinning.

  17. Large-area SiC membrane produced by plasma enhanced chemical vapor deposition at relatively high temperature

    SciTech Connect

    Liu, Yu; Xie, Changqing

    2015-09-15

    Advances in the growth of silicon carbide (SiC) thin films with outstanding thermal and mechanical properties have received considerable attention. However, the fabrication of large-area free-standing SiC membrane still remains a challenge. Here, the authors report a plasma enhanced chemical vapor deposition process at a relatively high temperature to improve the free-standing SiC membrane area. A systematic study on the microstructural, mechanical, and optical properties of hydrogenated polycrystalline silicon carbide (poly-SiC{sub x}:H) thin films deposited at 600 °C with different annealing temperatures has been performed. In the as-deposited state, SiC{sub x}:H thin films show a polycrystalline structure. The crystallinity degree can be further improved with the increase of the postdeposition annealing temperature. The resulting process produced free-standing 2-μm-thick SiC membranes up to 70 mm in diameter with root mean square roughness of 3.384 nm and optical transparency of about 70% at 632.8 nm wavelength. The large-area SiC membranes made out of poly-SiC{sub x}:H thin films deposited at a relatively high temperature can be beneficial for a wide variety of applications, such as x-ray diffractive optical elements, optical and mechanical filtering, lithography mask, lightweight space telescopes, etc.

  18. Molecular Dynamics Modeling of the Thermal Conductivity of Irradiated SiC as a Function of Cascade Overlap

    SciTech Connect

    Crocombette, J.-P.; Dumazer, Guillaume; Hoang, Nguyen Q.; Gao, Fei; Weber, William J.

    2007-01-15

    SiC thermal conductivity is known to decrease under irradiation. To understand this effect, we study the variation of the thermal conductivity of cubic SiC with defect accumulation induced by displacement cascades. We use an empirical potential of the Tersoff type in the framework of non-equilibrium molecular dynamics. The conductivity of SiC is found to decrease with dose, in very good quantitative agreement with low temperature irradiation experiments. The results are analyzed in view of the amorphization states that are created by the cascade accumulation simulations. The calculated conductivity values at lower doses are close to the smallest measured values after high temperature irradiation, indicating that the decrease of the conductivity observed at lower doses is related to the creation of point defects. A subsequent decrease takes place upon further cascade accumulation. It is characteristic of the amorphization of the material and is experimentally observed for low temperature irradiation only.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  20. Electronic and Optical Properties of Nitrogen Doped SiC Nanocrystals: First Principles Study

    NASA Astrophysics Data System (ADS)

    Javan, Masoud Bezi

    2013-05-01

    A typical nitrogen doped spherical SiC nanocrystal with a diameter of 1.2 nm (Si43C44H76) using linear combination atomic orbital (LCAO) in combination with pseudopotential density functional calculation have been studied. Our selected SiC nanocrystal has been modeled taking all the cubic bulk SiC atoms contained within a sphere of a given radius and terminating the surface dangling bonds with hydrogen atoms. We have examined nine possible situations in which nitrogen has a high probability for replacement in the lattice or placed between atoms in the nanocrystal. We have found that the silicone can substitute with a nitrogen atom in each layer as the constructed nanocrystals remain thermodynamically stable. Also the nitrogen atom can be placed between the free atomic spaces as the more thermodynamically stable position of the nitrogen is between the topmost layers. Also the optical absorption and refractive index energy dispersions of the pure and various stable doped SiC nanocrystals were studied.

  1. Ultrafast Optical Measurements of Thermal Conductivity and Sound Velocity of Amorphous SiC

    NASA Astrophysics Data System (ADS)

    Hondongwa, Donald; Olasov, Lauren; Daly, Brian; King, Sean; Bielefeld, Jeff

    2011-03-01

    We present ultrafast optical measurements of longitudinal sound velocity and thermal transport in hydrogenated amorphous carbon (a-SiC:H) films. The films were grown on Si wafers by PECVD using combinations of methylsilanes and H2 and He diluent gases. The films were well characterized and found to have densities (1.0 -- 2.5 g cm-3) and dielectric constants (2.8 -- 7.2) that spanned a wide range of values. Prior to their measurement, the a-SiC:H films were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser. Transient reflectivity changes that are associated with very high frequency sound waves (picosecond ultrasonics) and the cooling rate of the SiC sample (Time Domain Thermorerflectance (TDTR)) were measured. We extract values for the thermal conductivity and sound velocity of the SiC films, and analyze the results in terms of rigidity percolation effects within the SiC layers. This work was supported by NSF award DMR-0906753.

  2. Growth and characterization of cubic and non-cubic Ge nanocrystals

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Pradhan, A.; Mukherjee, S.; Maitra, T.; Nayak, A.; Bhunia, S.

    2016-05-01

    Germanium nanocrystals with tetragonal (ST-12) and diamond like cubic (Ge-I) phases have been selectively grown by controlling the ionization and electrostatic potential of Ge clusters in an ion cluster beam deposition system. Predominantly tetragonal nanocrystals were obtained when grown using neutral clusters. The percentage of cubic phase increased when grown by ionizing the clusters and accelerating them towards substrates by applying electrostatic bias in the range of 1.5 -2.5 kV. Raman spectroscopic measurement showed strong peak at 275 cm-1 and 300 cm-1 for tetragonal and cubic Ge nanocrystals, respectively. TEM measurements showed crystalline lattice fringes of both type of the nanocrystals. The selected area electron diffraction patterns showed (111) and (210) as the dominating lattice planes for tetragonal nanocrystals while the cubic phases had (111), (311) and (331) as the prominent lattice planes. The optical absorption edge redshifted from 1.75 to 1.55 eV as the percentage of the cubic phases increased in the NC composition in the composite film.

  3. Process for the controlled growth of single-crystal films of silicon carbide polytypes on silicon carbide wafers

    NASA Technical Reports Server (NTRS)

    Larkin, David J. (Inventor); Powell, J. Anthony (Inventor)

    1992-01-01

    A method for the controlled growth of single-crystal semiconductor-device-quality films of SiC polytypes on vicinal (0001) SiC wafers with low tilt angles is presented. Both homoepitaxial and heteroepitaxial SiC films can be produced on the same wafer. In particular, 3C-SiC and 6H-SiC films can be produced within selected areas of the same 6H-SiC wafer.

  4. Process for the controlled growth of single-crystal films of silicon carbide polytypes on silicon carbide wafers

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony (Inventor)

    1991-01-01

    This invention is a method for the controlled growth of single-crystal semiconductor device quality films of SiC polytypes on vicinal (0001) SiC wafers with low tilt angles. Both homoepitaxial and heteroepitaxial SiC films can be produced on the same wafer. In particular, 3C-SiC and 6H-SiC films can be produced within selected areas of the same 6H-SiC wafer.

  5. 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.

  6. Absorption and emission of silicon nanocrystals embedded in SiC: Eliminating Fabry-Pérot interference

    SciTech Connect

    Schnabel, M.; Summonte, C.; Canino, M.; Dyakov, S. A.; López-Conesa, L.; Löper, P.; Janz, S.; Wilshaw, P. R.

    2015-01-28

    Silicon nanocrystals embedded in SiC are studied by spectrophotometry and photoluminescence (PL) spectroscopy. Absorptivities are found to be affected by residual Fabry-Pérot interference arising from measurements of reflection and transmission at locations of different film thickness. Multiple computational and experimental methods to avoid these errors in thin film measurements, in general, are discussed. Corrected absorptivity depends on the quantity of Si embedded in the SiC but is independent of the Si crystallinity, indicating a relaxation of the k-conservation criterion for optical transitions in the nanocrystals. Tauc gaps of 1.8–2.0 and 2.12 eV are determined for Si nanoclusters and SiC, respectively. PL spectra exhibit a red-shift of ∼100 nm per nm nominal Si nanocluster diameter, which is in agreement with quantum confinement but revealed to be an artifact entirely due to Fabry-Pérot interference. Several simple experimental methods to diagnose or avoid interference in PL measurements are developed that are applicable to all thin films. Corrected PL is rather weak and invariant with passivation, indicating that non-paramagnetic defects are responsible for rapid non-radiative recombination. They are also responsible for the broad, sub-gap PL of the SiC, and can wholly account for the form of the PL of samples with Si nanoclusters. The PL intensity of samples with Si nanoclusters, however, can only be explained with an increased density of luminescent defects in the SiC due to Si nanoclusters, efficient tunneling of photogenerated carriers from Si nanoclusters to SiC defects, or with emission from a-Si nanoclusters. Films prepared on Si exhibit much weaker PL than the same films prepared on quartz substrates.

  7. Chemically vapor deposited silicon carbide (SiC) for optical applications

    NASA Astrophysics Data System (ADS)

    Pickering, Michael A.; Taylor, Raymond L.; Keeley, Joseph T.; Graves, George A.

    1989-10-01

    Important physical, optical, thermal, and mechanical properties of cubic (beta) silicon carbide produced via a bulk chemical vapor deposition (CVD) process, developed at CVD Incorporated, are presented in this paper. The material's properties make it an ideal candidate material for optical components for lidar mirrors, solar collectors and concentrators, and astronomical telescopes. The CVD process has been scaled to produce large monolithic pieces of bulk SiC, i.e., disks up to 60-cm (24-in.) diameter and plates up to 76-cm (30-in.) long by 46-cm (18-in.) wide with thickness up to 13 mm (0.5 in.).

  8. Ab initio study of electron-phonon coupling in boron-doped SiC

    NASA Astrophysics Data System (ADS)

    Margine, E. R.; Blase, X.

    2008-11-01

    Density functional theory calculations have been used to study the electronic structure, lattice dynamics, and electron-phonon coupling in boron-doped silicon carbide in the cubic phase. Our results provide evidence that the recently discovered superconducting transition in boron-doped silicon carbide can be explained within a standard phonon-mediated mechanism. For the same doping rate, the coupling constant λ in B-doped SiC is very close to that of doped diamond and twice as large as that of B-doped silicon. However, doped silicon carbide differs from its diamond counterpart as most of the electron-phonon coupling originates from low energy vibrational modes.

  9. Comparison of SiC mirror approaches

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  10. SiC nanowires: A photocatalytic nanomaterial

    SciTech Connect

    Zhou Weimin; Yan Lijun; Wang Ying; Zhang Yafei

    2006-07-03

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

  11. Elastic and thermodynamical properties of cubic (3 C) silicon carbide under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Shriya, S.; Varshney, M.; Singh, N.; Khenata, R.

    2015-08-01

    Pressure-dependent first-order phase transition, mechanical, elastic, and thermodynamical properties of cubic zinc blende to rock-salt structures in 3 C silicon carbide (SiC) are presented. An effective interatomic interaction potential for SiC is formulated. The potential for SiC incorporates long-range Coulomb, charge transfer interactions, covalency effect, Hafemeister and Flygare type short-range overlap repulsion extended up to the second-neighbour ions, van der Waals interactions and zero point energy effects. The developed potential including many body non-central forces validates the Cauchy discrepancy successfully to explain the high-pressure structural transition, and associated volume collapse. The 3 C SiC ceramics lattice infers mechanical stiffening, thermal softening, and ductile (brittle) nature from the pressure (temperature) dependent elastic constants behaviour. To our knowledge, these are the first quantitative theoretical predictions of the pressure and temperature dependence of mechanical and thermodynamical properties explicitly the mechanical stiffening, thermally softening, and brittle/ductile nature of 3 C SiC and still awaits experimental confirmations.

  12. 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.

  13. 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.

  14. New biomorphic SiC ceramics coated with bioactive glass for biomedical applications.

    PubMed

    González, P; Serra, J; Liste, S; Chiussi, S; León, B; Pérez-Amor, M; Martínez-Fernández, J; de Arellano-López, A R; Varela-Feria, F M

    2003-11-01

    A new generation of light, tough and high-strength material for medical implants for bone substitutions with a good biological response is presented. The innovative product that fulfills all these requirements is based on biomorphic silicon carbide ceramics coated with a bioactive glass layer. The combination of the excellent mechanical properties and low density of the biomorphic SiC ceramics, used as a base material for implants, with the osteoconducting properties of the bioactive glass materials opens new possibilities for the development of alternative dental and orthopedic implants with enhanced mechanical and biochemical properties that ensures optimum fixation to living tissue. Biomorphic SiC is fabricated by molten-Si infiltration of carbon templates obtained by controlled pyrolysis of wood. Through this process, the microstructure of the final SiC product mimics that of the starting wood, which has been perfected by natural evolution. The basic features of such microstructure are its porosity (ranging from 30% to 70%) and its anisotropy, which resembles the cellular microstructure and the mechanical characteristics of the bone. The SiC ceramics have been successfully coated with a uniform and adherent bioactive glass film by pulsed laser ablation using an excimer ArF laser. The excellent coverage of the SiC rough surface without film spallation or detachment is demonstrated. In order to assess the coating bioactivity, in vitro tests by soaking the samples in simulated body fluid have been carried out. After 72 h, the formation of a dense apatite layer has been observed even in interconnecting pores by SEM and energy dispersive X-ray spectroscopy analysis demonstrating the bioactive response of this product. PMID:14530079

  15. Strong visible electroluminescence from silicon nanocrystals embedded in a silicon carbide film

    SciTech Connect

    Huh, Chul Kim, Tae-Youb; Ahn, Chang-Geun; Kim, Bong Kyu

    2015-05-25

    We report the strong visible light emission from silicon (Si) nanocrystals (NCs) embedded in a Si carbide (SiC) film. Compared to Si NC light-emitting diode (LED) by employing the Si nitride (SiN{sub x}) film as a surrounding matrix, the turn-on voltage of the Si NC LED with the SiC film was significantly decreased by 4 V. This was attributed to a smaller barrier height for injecting the electrons into the Si NCs due to a smaller band gap of SiC film than a SiN{sub x} film. The electroluminescence spectra increases with increasing forward voltage, indicating that the electrons are efficiently injected into the Si NCs in the SiC film. The light output power shows a linear increase with increasing forward voltage. The light emission originated from the Si NCs in a SiC film was quite uniform. The power efficiency of the Si NC LED with the SiC film was 1.56 times larger than that of the Si NC LED with the SiN{sub x} film. The Si NCs in a SiC film show unique advantages and are a promising candidate for application in optical devices.

  16. Packaging Technology Developed for High-Temperature SiC Sensors and Electronics

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Lei, Jih-Fen

    2000-01-01

    A ceramic- and thick-film-materials-based prototype electronic package designed for silicon carbide (SiC) high-temperature sensors and electronics has been successfully tested at 500 C in an oxygen-containing air environment for 500 hours. This package was designed, fabricated, assembled, and electronically evaluated at the NASA Glenn Research Center at Lewis Field with an in-house-fabricated SiC semiconductor test chip. High-temperature electronics and sensors are necessary for harsh-environment space and aeronautical applications, such as space missions to the inner solar system or the emission control electronics and sensors in aeronautical engines. Single-crystal SiC has such excellent physical and chemical material properties that SiC-based semiconductor electronics can operate at temperatures over 600 C, which is significantly higher than the limit for Si-based semiconductor devices. SiC semiconductor chips were recently demonstrated to be operable at temperatures as high as 600 C, but only in the probe station environment because suitable packaging technology for sensors and electronics at temperatures of 500 C and beyond did not exist. Thus, packaging technology for SiC-based sensors and electronics is immediately needed for both application and commercialization of high-temperature SiC sensors and electronics. In response to this need, researchers at Glenn designed, fabricated, and assembled a prototype electronic package for high-temperature electronics, sensors, and microelectromechanical systems (MEMS) using aluminum nitride (AlN) substrate and gold (Au) thick-film materials. This prototype package successfully survived a soak test at 500 C in air for 500 hours. Packaging components tested included thick-film high-temperature metallization, internal wire bonds, external lead bonds, and a SiC diode chip die-attachment. Each test loop, which was composed of thick-film printed wire, wire bond, and lead bond was subjected to a 50-mA direct current for 250

  17. Solute embrittlement of SiC

    NASA Astrophysics Data System (ADS)

    Enrique, Raúl A.; Van der Ven, Anton

    2014-09-01

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

  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. Post-growth thermal oxidation of wurtzite InN thin films into body-center cubic In{sub 2}O{sub 3} for chemical/gas sensing applications

    SciTech Connect

    Liu, H.F.; Yakovlev, N.L.; Chi, D.Z.; Liu, W.

    2014-06-01

    Post-growth thermal oxidations of InN have been studied using high-resolution x-ray diffraction (HRXRD) and secondary ion-mass spectroscopy (SIMS). The InN thin films, having relative high crystal quality, were grown by metal–organic chemical vapor deposition (MOCVD) on c-sapphire substrates using InGaN/GaN buffer layers. HRXRD reveals that oxidation of wurtzite InN into body-center cubic In{sub 2}O{sub 3} occurred at elevated temperatures. A Si{sub 3}N{sub 4} encapsulation improves the crystal quality of In{sub 2}O{sub 3} oxidized by using conventional rapid thermal annealing (RTA) but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profile, using contaminate elements as the ‘interface markers,’ provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. Together with the HRXRD results, we conclude that the crystal quality of the resultant In{sub 2}O{sub 3}/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal dissociation, which can be effectively tuned by cycle-RTA. The obtained In{sub 2}O{sub 3}/InN heterostructures can be fundamental materials for studying high speed chemical/gas sensing devices. - Graphical abstract: Oxidation of h-InN into bcc-In{sub 2}O{sub 3} has been realized at elevated temperatures. A Si{sub 3}N{sub 4} cap improves the crystal quality of In{sub 2}O{sub 3} oxidized by conventional RTA but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profiles provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. The crystal quality of the resultant In{sub 2}O{sub 3}/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal

  20. SiC formation on Si(100) via C 60 precursors

    NASA Astrophysics Data System (ADS)

    De Seta, M.; Tomozeiu, N.; Sanvitto, D.; Evangelisti, F.

    2000-07-01

    The interaction between C 60 molecules and the Si(100) surface and the preparation of silicon-carbide thin films by thermal reaction of C 60 molecules with the Si(100) surface have been investigated using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, reflection high-energy electron diffraction and atomic force microscopy measurements. The effects of annealing temperature and C 60 coverage on the SiC formation will be discussed. It is found that the C 60 molecules bond covalently with silicon, and the number of bonds increase upon increasing the annealing temperature. Annealing at T≥830°C entails the formation of stoichiometric silicon carbide clusters that coalesce to form a continuous SiC layer when the C 60 coverage is greater than one monolayer. Deep pits acting as silicon diffusion channels are present with dimensions that increase with the amounts of C 60. The interaction of C 60 with the SiC surface was also investigated. It is found that a similar covalent interaction is present in the two systems C 60/Si and C 60/SiC.

  1. Examples of conditional SIC-POVMs

    NASA Astrophysics Data System (ADS)

    Ohno, Hiromichi; Petz, Dénes

    2015-10-01

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

  2. 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.

  3. 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.

  4. 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.

  5. S-IC Static Test Stand

    NASA Technical Reports Server (NTRS)

    1977-01-01

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

  6. Stacking faults in SiC nanowires.

    PubMed

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

    2008-07-01

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

  7. 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.

  8. Structural Characterization of Polycrystalline 3C-SiC Films Prepared at High Rates by Atmospheric Pressure Plasma Chemical Vapor Deposition Using Monomethylsilane

    NASA Astrophysics Data System (ADS)

    Kakiuchi, Hiroaki; Ohmi, Hiromasa; Nakamura, Ryota; Aketa, Masatoshi; Yasutake, Kiyoshi

    2006-10-01

    Polycrystalline cubic silicon carbide (3C-SiC) films were deposited at a relatively low temperature of 1070 K on Si(001) substrates by atmospheric pressure plasma chemical vapor deposition. Monomethylsilane (CH3SiH3) was used as the single source. CH4 and SiH4 dual sources were also used to compare deposition characteristics. Under the present deposition conditions, very high deposition rates of more than 3 nm/s were obtained. The structure of the SiC films was evaluated by reflection high-energy electron diffraction, Fourier transform infrared absorption spectroscopy and cross-sectional transmission electron microscopy. In addition, optical emission spectroscopy was employed to study the chemical reactions in the CH4/SiH4 and CH3SiH3 plasmas. The results showed that increasing H2 concentration is essential in forming a high quality 3C-SiC film by enhancing the hydrogen elimination reaction at the film-growing surface. From the optical emission spectra, it was found that atomic hydrogen generated by adding H2 in the plasma increase the amount of principal precursors for the film growth. The utilization of CH3SiH3 also led to a higher concentration of principal precursors in the plasma, enhancing the incorporation of Si-C bonds into the film. As a consequence of simultaneously using a high H2 concentration and the CH3SiH3 single source, the columnar growth of 3C-SiC crystallites was achieved.

  9. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  10. P-V-T equation of state of SiC-3C: implications for primary pressure scale

    NASA Astrophysics Data System (ADS)

    Zhuravlev, Kirill; Goncharov, Alexander F.; Tkachev, Sergey; Dera, Przemyslaw; Prakapenka, Vitali; Geophysical Laboratory, Carnegie InstitutionScience Collaboration

    2014-03-01

    We present a new primary pressure scale based on concomitant measurements of the density and elastic parameters of the single crystal samples of cubic silicon carbide (3C-SiC) under quasi-hydrostatic pressures up to 65 GPa and 773 K. The established pressure scale has precision of 2%-4% up to 65 GPa and will allow more accurate pressure determination in that range than the previously used pressure scales. We also report x-ray diffraction data and Raman spectroscopy on 3C-SiC up to 75 GPa. We determined the P-V-T equation of state (EOS) of 3C-SiC and pressure and temperature dependencies of the zone-center phonons, elastic tensor, and mode Gruneisen parameters. Cubic SiC lattice was found to be stable up to 75 GPa, but there is a tendency for destabilization above 40 GPa, based on softening of a transverse sound velocity. We proposed corrections to the existing ruby and neon pressure scales, and also calibrated cubic SiC as an optical pressure marker using Raman spectroscopy. Presently with University of Hawaii.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Graphene growth on SiC(000-1): optimization of surface preparation and growth conditions

    NASA Astrophysics Data System (ADS)

    Robinson, Zachary R.; Jernigan, Glenn G.; Bussmann, Konrad M.; Nyakiti, Luke O.; Garces, Nelson Y.; Nath, Anindya; Wheeler, Virginia D.; Myers-Ward, Rachael L.; Gaskill, D. K.; Eddy, Charles R.

    2015-09-01

    Graphene growth of high crystal quality and single-layer thickness can be achieved by low pressure sublimation (LPS) on SiC(0001). On SiC(0001), which is the C-terminated polar surface, there has been much less success growing uniform, single-layer films. In this work, a systematic study of surface preparation by hydrogen etching followed by LPS in an argon ambient was performed. Hydrogen etching is an important first step in the graphene growth process because it removes damage caused by polishing the substrate surface. However, for SiC(0001), etching at too high of a temperature or for too long has been found to result in pit formation due to the preferential etching of screw dislocations that intersect the surface. It was found that temperatures above 1450°C in 200mbar of hydrogen result in pitting of the surface, whereas etch temperatures at and below 1450°C can result in atomically at terraces of ~ 1 µm width. Following the hydrogen etch optimization, argon-mediated graphene growth was carried out at several different temperatures. For the growth experiments, pressure and growth time were both fixed. Regardless of growth temperature, all of the films were found to have non-uniform thickness. Further, x-ray photoelectron spectroscopy and low energy electron diffraction measurements reveal that trace amounts of oxygen, which may be present during growth, significantly affects the graphene growth process on this polar surface.

  16. S-IC Test Stand Design Model

    NASA Technical Reports Server (NTRS)

    1962-01-01

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

  17. S-IC Test Stand Design Model

    NASA Technical Reports Server (NTRS)

    1962-01-01

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

  18. Infrared spectra of meteoritic SiC grains

    NASA Astrophysics Data System (ADS)

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

    1999-03-01

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

  19. Synthesis of SiC nanorods from bleached wood pulp

    SciTech Connect

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

    2007-05-01

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

  20. Properties of interfaces between cubic and hexagonal polytypes of silicon carbide

    NASA Astrophysics Data System (ADS)

    Raffy, C.; Furthmüller, J.; Bechstedt, F.

    2002-12-01

    We present ab initio calculations of the properties of two types of interface between the cubic and hexagonal (wurtzite) polytypes of silicon carbide. The results are derived from density-functional calculations within the local-density approximation and the pseudopotential-plane-wave approach. We first study the interface along the (111) plane (corresponding to (0001) in the hexagonal representation) perpendicular to the stacking axis of the bilayers. Then we consider the interface along the (115) plane, which was already identified experimentally as a grain boundary in silicon and germanium. The (115) interfaces are especially interesting, since they may contribute to a quantum wire consisting of an inclusion of cubic SiC in hexagonal SiC. They are made up of five-and seven-membered atom rings and are free of dangling bonds. The cubic and hexagonal grains are tilted with respect to one another by an angle of 38.94°. In both cases of interfaces, the electronic properties are discussed. Whereas the (111) interface induces practically no states in the bulk fundamental gaps, the particular structure of the (115) interface generates a lot of states, resulting in a metallic behaviour.

  1. Silicon threshold displacement energy determined by photoluminescence in electron-irradiated cubic silicon carbide

    SciTech Connect

    Lefevre, Jeremie; Esnouf, Stephane; Petite, Guillaume; Costantini, Jean-Marc

    2009-01-15

    In view of the potential use of silicon carbide (SiC) in the nuclear industry, it is of major interest to understand point defect formation in this material. This work is a contribution to the determination of the silicon threshold displacement energy in the cubic polytype of SiC using electron irradiations with increasing energies from 275 to 680 keV. The photoluminescence signal of the silicon vacancy was related to the number of displacements per atom in the silicon sublattice. This quantity was calculated taking into account the energy loss and angular dispersion of electrons in the target. A best fit of experimental data was obtained for a displacement cross section using a threshold displacement energy of 25 eV along the [100] lattice direction. We checked the relevance of this result by comparing the experimental concentration of silicon single vacancies measured by electron paramagnetic resonance spectroscopy with the theoretical number of displaced silicon atoms.

  2. Multilayer epitaxial graphene grown on the SiC (000- 1) surface; structure and electronic properties

    SciTech Connect

    Sprinkle, M.; Hicks, J.; Tejeda, A.; Taleb-Ibrahimi, A.; Le Fevre, P.; Bertran, F.; Tinkey, H.; Clark, M.C.; Soukiassian, P.; Martinotti, D.; Hass, J.; Conrad, E.H.

    2010-10-22

    We review the progress towards developing epitaxial graphene as a material for carbon electronics. In particular, we discuss improvements in epitaxial graphene growth, interface control and the understanding of multilayer epitaxial graphene's (MEG's) electronic properties. Although graphene grown on both polar faces of SiC will be discussed, our discussions will focus on graphene grown on the (000{bar 1}) C-face of SiC. The unique properties of C-face MEG have become apparent. These films behave electronically like a stack of nearly independent graphene sheets rather than a thin Bernal stacked graphite sample. The origins of multilayer graphene's electronic behaviour are its unique highly ordered stacking of non-Bernal rotated graphene planes. While these rotations do not significantly affect the inter-layer interactions, they do break the stacking symmetry of graphite. It is this broken symmetry that leads to each sheet behaving like isolated graphene planes.

  3. Reactive Plasma Etching of SiC in a Tetrafluoroethane / Oxygen Plasma

    NASA Astrophysics Data System (ADS)

    Galloway, Heather C.; Radican, Kevin P.; Donnelly, David; Koeck, Deborah C.

    2003-03-01

    The etch rate as a function of oxygen concentration was investigated in the RF magnetron plasma etching of SiC with tetrafluoroethane gas. The etch rate and surface roughness was measured with atomic force microscopy, while evidence of polymer deposition was analyzed with FTIR. Etch rates of > 10 nm/sec can be achieved with high selectivity with respect to an aluminum mask, near infinite selectivity with respect to silicon. This has also been found to be compatible with some low-k dielectric films. Tetrafluoroethane is of interest due to its high fluorine content. It is also a nontoxic, ozone friendly gas with a short atmospheric lifetime. The role of oxygen in the etching process will be discussed and this etching process will be compared to other SiC etches that have been previously reported

  4. SiC Sensors in Extreme Environments: Real-time Hydrogen Monitoring for Energy Plant Applications

    NASA Astrophysics Data System (ADS)

    Ghosh, Ruby

    2008-03-01

    Clean, efficient energy production, such as the gasification of coal (syngas), requires physical and chemical sensors for exhaust gas monitoring as well as real-time control of the combustion process. Wide-bandgap semiconducting materials systems can meet the sensing demands in these extreme environments consisting of chemically corrosive gases at high temperature and pressure. We have developed a SiC based micro-sensor for detection of hydrogen containing species with millisecond response at 600 C. The sensor is a Pt-SiO2-SiC device with a dense Pt catalytic sensing film, capable of withstanding months of continuous high temperature operation. The device was characterized in robust sensing module that is compatible with an industrial reactor. We report on the performance of the SiC sensor in a simulated syngas ambient at 370 C containing the common interferants CO2, CH4 and CO [1]. In addition we demonstrate that hours of exposure to >=1000 ppm H2S and 15% water vapor does not degrade the sensor performance. To elucidate the mechanisms responsible for the hydrogen response of the sensor we have modeled the hydrogen adsorptions kinetics at the internal Pt-SiO2 interface, using both the Tempkin and Langmuir isotherms. Under the conditions appropriate for energy plant applications, the response of our sensor is significantly larger than that obtained from ultra-high vacuum electrochemical sensor measurements at high temperatures. We will discuss the role of morphology, at the nano to micro scale, on the enhanced catalytic activity observed for our Pt sensing films in response to a heated hydrogen gas stream at atmospheric pressure. [1] R. Loloee, B. Chorpening, S. Beers & R. Ghosh, Hydrogen monitoring for power plant applications using SiC sensors, Sens. Actuators B:Chem. (2007), doi:10.1016/j.snb.2007.07.118

  5. Corrosion resistance of sintered NdFeB coated with SiC/Al bilayer thin films by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Huang, Yiqin; Li, Heqin; Zuo, Min; Tao, Lei; Wang, Wei; Zhang, Jing; Tang, Qiong; Bai, Peiwen

    2016-07-01

    The poor corrosion resistance of sintered NdFeB imposes a great challenge in industrial applications. In this work, the SiC/Al bilayer thin films with the thickness of 510 nm were deposited on sintered NdFeB by magnetron sputtering to improve the corrosion resistance. A 100 nm Al buffer film was used to reduce the internal stress between SiC and NdFeB and improve the surface roughness of the SiC thin film. The morphologies and structures of SiC/Al bilayer thin films and SiC monolayer film were investigated with FESEM, AFM and X-ray diffraction. The corrosion behaviors of sintered NdFeB coated with SiC monolayer film and SiC/Al bilayer thin films were analyzed by polarization curves. The magnetic properties were measured with an ultra-high coercivity permanent magnet pulse tester. The results show that the surface of SiC/Al bilayer thin films is more compact and uniform than that of SiC monolayer film. The corrosion current densities of SiC/Al bilayer films coated on NdFeB in acid, alkali and salt solutions are much lower than that of SiC monolayer film. The SiC/Al bilayer thin films have little influence to the magnetic properties of NdFeB.

  6. Structure and composition of silicon carbide films synthesized by ion implantation

    NASA Astrophysics Data System (ADS)

    Nussupov, K. Kh.; Beisenkhanov, N. B.; Zharikov, S. K.; Beisembetov, I. K.; Kenzhaliev, B. K.; Akhmetov, T. K.; Seitov, B. Zh.

    2014-11-01

    The mathematical decomposition of the IR absorption spectrum obtained from a Si layer after the C+ ion implantation with an energy of 10 or 40 keV or from a homogeneous SiC0.7 film has demonstrated that fractions of weak elongated Si-C bonds in the amorphous phase, strong shortened Si-C bonds on the surface of small nanocrystals, and tetrahedral Si-C bonds in the crystalline phase (degree of crystallinity) after high-temperature annealing (1250-1400°C) of the layers are equal to 29/29/42, 22/7/71, and 21/31/48%, respectively. A system of SiC2.0, SiO2, SiC0.8, and SiC0.6 layers in the film on the Si substrate has been identified using X-ray reflectometry and the simulation with the Release software. The reflectometry data on fluctuations of the intensity of X-ray reflections in the region of the main maximum have been interpreted in terms of variations in the density over the depth of the layer with a Gaussian distribution of carbon atoms from 2.55 and 2.90 g/cm3 for the SiC0.25 and SiC0.65 layers, respectively, to 3.29 g/cm3 for the SiC1.36 layer.

  7. Tensile strength of SiC fibers

    SciTech Connect

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

    1995-07-01

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

  8. Periodically twinned SiC nanowires.

    PubMed

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

    2008-05-28

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

  9. SiC nanowires synthesized from graphene and silicon vapors

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    PubMed

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

    2016-02-23

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

  11. Direct current conduction in SiC powders

    NASA Astrophysics Data System (ADS)

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

    2001-09-01

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

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

    NASA Technical Reports Server (NTRS)

    1965-01-01

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

  13. Execution of energy efficient detection of hydrogen using Pt/WO x /SiC semiconductor structure

    NASA Astrophysics Data System (ADS)

    Zuev, V. V.; Demin, M. V.; Fominskii, V. Yu.; Romanov, R. I.; Grigor'ev, V. V.; Nevolin, V. N.

    2015-09-01

    It has been shown that, at elevated temperatures (˜350°C), the most distinct response to H2 from the thin film structure Pt/WO x /SiC is achieved at registration of change in voltage for the reverse branch of a current-voltage characteristic. Comparative studies of electric current conduction through the structure and over its surface (with deposited Pt film) have led to the conclusion that a change in properties of the Pt/WO x and WO x /SiC interfaces under action of H2 mostly determines efficiency of response of the structure in the case of "transverse" measuring geometry. In the case of a 2% concentration of H2 in air the voltage shift for the reverse branch at a current of ˜10 μA reached 5 V against 2 V on the forward branch and "planar" geometry of measurements.

  14. Large area supersonic jet epitaxy of AlN, GaN, and SiC on silicon

    SciTech Connect

    Lauhon, L.J.; Ustin, S.A.; Ho, W.

    1997-12-31

    AlN, GaN, and SiC thin films were grown on 100 mm diameter Si(111) and Si(100) substrates using Supersonic Jet Epitaxy (SJE). Precursor gases were seeded in lighter mass carrier gases and free jets were formed using novel slit-jet apertures. The jet design, combined with substrate rotation, allowed for a uniform flux distribution over a large area of a 100 mm wafer at growth pressures of 1--20 mTorr. Triethylaluminum, triethylgallium, and ammonia were used for nitride growth, while disilane, acetylene, and methylsilane were used for SiC growth. The films were characterized by in situ optical reflectivity, x-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE).

  15. Microstructure of GaN epitaxy on SiC using AlN buffer layers

    SciTech Connect

    Ponce, F.A.; Krusor, B.S.; Major, J.S. Jr.; Plano, W.E.; Welch, D.F.

    1995-07-17

    The crystalline structure of GaN epilayers on (0001) SiC substrates has been studied using x-ray diffraction and transmission microscopy. The films were grown by metalorganic chemical vapor deposition, using AlN buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmission electron lattice images show that the AlN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structure of the GaN film away from the substrate consists mostly of threading dislocations with a density of {similar_to}10{sup 9} cm{sup {minus}2}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

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

    NASA Astrophysics Data System (ADS)

    Gorban, Ivan S.; Mishinova, Galina N.

    1998-04-01

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

  17. Effect of van der Waals interactions on the stability of SiC polytypes

    NASA Astrophysics Data System (ADS)

    Kawanishi, Sakiko; Mizoguchi, Teruyasu

    2016-05-01

    Density functional theory calculations with a correction of the long-range dispersion force, namely, the van der Waals (vdW) force, are performed for SiC polytypes. The lattice parameters are in good agreement with those obtained from the experiments. Furthermore, the stability of the polytypes in the experiments, which show 3C-SiC as the most stable, is reproduced by the present calculations. The effects of the vdW force on the electronic structure and the stability of polytypes are discussed. We observe that the vdW interaction is more sensitive to the cubic site than the hexagonal site. Thus, the influence of the vdW force increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC.

  18. Graphene covered SiC powder as advanced photocatalytic material

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  19. 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.

  20. 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.

  1. Si diffusion path for pit-free graphene growth on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Sun, G. F.; Liu, Y.; Rhim, S. H.; Jia, J. F.; Xue, Q. K.; Weinert, M.; Li, L.

    2011-11-01

    Density functional theory calculations reveal that the interfacial 63 × 63 structure [a warped graphene layer with periodic inclusions of pentagon-hexagon-heptagon (H5,6,7) defects] facilitates a Si diffusion path vertically through the interface layer during epitaxial growth of graphene on SiC(0001). The calculated diffusion barrier is 4.7 eV, competitive with Si interstitial diffusion of ˜3.5 eV in SiC [M. Bockstedte , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.68.205201 68, 205201 (2003)]. Scanning tunneling microscopy study shows that, for growth in an Ar background, where Si desorption is suppressed and all diffusion channels contribute, graphene films with reduced pit density can be grown on nominally flat SiC substrates. On the other hand, for Si diffusion-limited growth in ultrahigh vacuum, the Si interstitial diffusion is the energetically favorable path where the step edges serve as the necessary outlet toward Si desorption. The much higher density of step edges on vicinal substrates also facilitates the growth of pit-free graphene.

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

    SciTech Connect

    Henager, Charles H.; Jiang, Weilin

    2014-11-01

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

  3. SIC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION

    SciTech Connect

    Paul K.T. Liu

    2003-12-01

    A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. SiC macro-porous membranes have been successfully fabricated via extrusion of commercially available SiC powder. Also, an SiC hydrogen selective thin film was prepared via our CVD/I technique. This composite membrane demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers and sol-gel techniques. Building upon the positive progress made in the membrane development study, we conducted an optimization study to develop an H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment. In addition, mathematical simulation has been performed to compare the performance of the membrane reactor (MR) vs conventional packed bed reactor for WGS reaction. Our result demonstrates that >99.999% conversion can be accomplished via WGS-MR using the hydrogen selective membrane developed by us. Further, water/CO ratio can be reduced, and >97% hydrogen recovery and <200 ppm CO can be accomplished according to the mathematical simulation. Thus, we believe that the operating economics of WGS can be improved significantly based upon the proposed MR concept. In parallel, gas separations and hydrothermal and long-term-storage stability of the

  4. CVD scaled up for commercial production of bulk SiC

    SciTech Connect

    Not Available

    1993-03-01

    A recent development at Morton International's Advanced Materials group is having a revolutionary impact on the materials world. The firm has successfully scaled production of bulk, cubic ([beta]), chemically vapor deposited (CVD) silicon carbide (SiC) to support commercial requirements. To date, they have produced free standing CVD SiC substrates in sheets up to 60 in. across and over one inch thick. The material can also be grown as smaller near-net-shape parts in many different popular geometries. The parts produced by the process are monolithic. Commercially known as CVD SILICON CARBIDE, the material is single phase, theoretically dense, and 99.999% pure, [beta]-SiC. These characteristics lead to superior product attributes such as high values of hardness, flexural strength, and thermal conductivity. Additionally, the product has demonstrated superior oxidation resistance, and polishability. Several markets have shown an interest in the material including: optics, wear parts, information storage, and electronic packaging. Other applications for the material are emerging on what seems like a daily basis.

  5. Electronic structure of epitaxial graphene layers on SiC: effects of the substrate

    SciTech Connect

    Varchon, F.; Feng, R.; Hass, J.; Li, X.; Nguyen, B. Ngoc; Naud, C.; Mallet, P.; Veuillen, J.-Y.; Berger, C.; Conrad, E.H.; Magaud, L.

    2008-10-17

    A strong substrate-graphite bond is found in the first all-carbon layer by density functional theory calculations and x-ray diffraction for few graphene layers grown epitaxially on SiC. This first layer is devoid of graphene electronic properties and acts as a buffer layer. The graphene nature of the film is recovered by the second carbon layer grown on both the (0001) and (0001{sup -}) 4H-SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. Hence the graphene is doped and a gap opens at the Dirac point after three Bernal stacked carbon layers are formed.

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

    SciTech Connect

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

    1999-11-29

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

  7. Resolution of the SiC problem: astronomical and meteoritic evidence reconciled

    NASA Astrophysics Data System (ADS)

    Speck, A. K.; Hofmeister, A. M.; Barlow, M. J.

    Pre-solar grains of silicon carbide found in meteorites and interpreted as having had an origin around carbon stars from their isotopic composition, have all been found to be of the beta-SiC polytype. Yet to date all fits to the 11.3-microns SiC emission band of carbon stars have been obtained only for alpha-SiC grains. We show that this discrepancy has arisen from inappropriate `KBr corrections' having been made to laboratory spectra of SiC particles dispersed in KBr matrices, this error having propagated through the astronomical literature. We demonstrate that thin film infrared (IR) absorption spectra measured in a diamond anvil cell for both the alpha- and beta-polymorphs of synthetic SiC have positions nearly identical to those obtained previously from finely ground samples in KBr. Hence, it is unnecessary to correct for the presence of a medium if IR spectra of powder dispersions are obtained from dilute, very fine grain sizes. We re-fit a sample of carbon star mid-IR spectra, using laboratory data with no KBr correction applied, and show that beta -SiC grains fit the observations, while alpha-SiC grains do not. The discrepancy between meteoritic and astronomical identifications of the SiC-type is therefore removed. Our results imply that the IR data used by astronomers to identify other dust species should be carefully scrutinized to ensure that the KBr correction factor has not caused other misidentifications of minerals with astronomical dust features.

  8. Using nano hexagonal boron nitride particles and nano cubic silicon carbide particles to improve the thermal conductivity of electrically conductive adhesives

    NASA Astrophysics Data System (ADS)

    Cui, Hui-wang; Li, Dong-sheng; Fan, Qiong

    2013-01-01

    To satisfy the high electrical and thermal conductivity required for the continuous development of electronic products, nano hexagonal boron nitride (BN) particles and nano cubic silicon carbide (SiC) particles were added into electrically conductive adhesives (ECAs) to improve the thermal conductivity. BN and SiC had little negative effect on the electrical conductivity, but improved the thermal conductivity significantly. When their content was 1.5 wt. %, the thermal conductivity at 100°C, 150°C and 200°C was increased by 71% (100°C), 78% (150°C) and 70% (200°C), and 114% (100°C), 110% (150°C) and 98% (200°C) respectively for BN and SiC comparing with those of the ECAs with no thermal conductive fillers. This method is simple, easy to do, and can be used practically in electronic packaging.

  9. Cubic Unit Cell Construction Kit.

    ERIC Educational Resources Information Center

    Mattson, Bruce

    2000-01-01

    Presents instructions for building a simple interactive unit-cell construction kit that allows for the construction of simple, body-centered, and face-centered cubic lattices. The lit is built from inexpensive and readily available materials and can be built in any number of sizes. (WRM)

  10. Cubication of Conservative Nonlinear Oscillators

    ERIC Educational Resources Information Center

    Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada

    2009-01-01

    A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…

  11. Saturn V S-IC Stage LOX Tank

    NASA Technical Reports Server (NTRS)

    1964-01-01

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

  12. Alternate current characteristics of SiC powders

    NASA Astrophysics Data System (ADS)

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

    2001-09-01

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

  13. Cubic Icosahedra? A Problem in Assigning Symmetry

    ERIC Educational Resources Information Center

    Lloyd, D. R.

    2010-01-01

    There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

  14. Solving Cubic Equations by Polynomial Decomposition

    ERIC Educational Resources Information Center

    Kulkarni, Raghavendra G.

    2011-01-01

    Several mathematicians struggled to solve cubic equations, and in 1515 Scipione del Ferro reportedly solved the cubic while participating in a local mathematical contest, but did not bother to publish his method. Then it was Cardano (1539) who first published the solution to the general cubic equation in his book "The Great Art, or, The Rules of…

  15. 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.

  16. 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.

  17. Structure and morphology of c-SiC films obtained by acetylene reaction with Si(111) surface

    NASA Astrophysics Data System (ADS)

    De Crescenzi, M.; Bernardini, R.; Gunnella, R.; Castrucci, P.

    2002-07-01

    In this work we investigated the structure and morphology of silicon carbide films grown under ultra-high-vacuum (UHV) conditions by acetylene (C 2H 2) carbonization of Si(111) surfaces kept at 650 °C. We used several UHV electron techniques to probe the local structural properties of the film and scanning tunneling microscopy (STM) to study its morphology. Our results indicated that C atoms occupy tetrahedral substitutional sites in the Si with a C-Si bond of 1.90±0.03 Å as in a bulk cubic SiC (c-SiC) crystal. X-ray diffraction data confirmed the formation of highly (111) oriented epitaxial crystallites characterized by the c-SiC lattice. STM images showed the formation of ordered, interconnected structures, rather flat at the atomic scale, triangular in shape, characterized by the same orientation and with an average area of 5000 nm 2 and an average height of 10-15 Å. Only a few holes can be detected which may be interpreted as empty spaces left by the patchwork growth of the silicon carbide triangular islands. Therefore, our growth procedure resulted to produce crystalline c-SiC films by using one of the most lowest temperature reported in literature.

  18. Anharmonic phonon decay in cubic GaN

    NASA Astrophysics Data System (ADS)

    Cuscó, R.; Domènech-Amador, N.; Novikov, S.; Foxon, C. T.; Artús, L.

    2015-08-01

    We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found.

  19. Vibrational, elastic, and structural properties of cubic silicon carbide under pressure up to 75 GPa and temperature up to 773K: implication for a primary pressure scale

    NASA Astrophysics Data System (ADS)

    Zhuravlev, K. K.; Goncharov, A.; Prakapenka, V.; Dera, P. K.; Tkachev, S. N.

    2013-12-01

    We present results of concomitant measurements of synchrotron x-ray diffraction, Brillouin, and Raman spectroscopy on the single crystal samples of cubic silicon carbide (3C-SiC) under quasi-hydrostatic pressures up to 68 GPa and temperatures up to 773K, as well as x-ray diffraction and Raman spectroscopy up to 75 GPa. We determined the equation of state (EOS) of 3C-SiC and pressure dependencies of the zone-center phonon, elastic tensor, and mode Gruneisen parameters. Cubic SiC lattice was found to be stable up to 75 GPa, but there is a tendency for destabilization above 40 GPa, based on softening of a transverse sound velocity. By applying the concomitant density and elasticity measurements, we determined the pressure on the SiC sample without referring to any other pressure scale. We proposed corrections to the existing ruby and neon pressure scales and demonstrated the feasibility of using cubic SiC as a pressure calibrant at different temperatures.

  20. 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.

  1. Study of silicon carbide (SiC) polytype heterojunctions

    NASA Astrophysics Data System (ADS)

    Eshun, Ebenezer Emmanuel

    2001-12-01

    The results of a study of the chemical vapor deposition (CVD) growth and characterization of SiC polytype heterojunctions are presented. Device quality alpha-SiC has been grown at 1580°C, with p-type background between 6 x 1014cm-3 and 5 x 1015cm-3. N-type device layers have also been grown using nitrogen as a dopant gas. These materials were characterized by various methods including photoluminescence, atomic force microscopy, scanning electron microscopy, secondary ion mass spectroscopy, reflection high energy electron diffraction, C-V and I-V measurements. The above results along with a pre-growth hydrogen/propane etch study were used as a baseline for developing a growth process for the SiC polytype heterojunctions. High quality heterojunctions have been obtained with almost no polytype inclusions. Characterizations were performed to study the heterojunctions, which included an oxidation study to map polytype inclusions in the layers grown under different conditions resulting in a high (>95%) polytype homogeneity. Transmission electron microscopy (TEM) shows no visible defects and/or columnar growth features, a sign of high quality crystalline films. TEM diffraction patterns obtained are very strong, further indicating high quality 3C-SiC epitaxial layers. X-ray rocking and reciprocal space mapping (RSM) were further used in characterizing the SiC polytype heterojunctions. The FWHM of the x-ray scans are very narrow, between 0.01° and 0.02°, an excellent figure further indicating high quality crystalline 3C-SiC epitaxial layers. Iso-intensity contours from the RSM show very little broadening in o which is due to the mosaic nature of the samples. The o-2theta direction shows almost no broadening implying that there is almost no strain in the material. In addition, the electrical quality of the heterojunctions was obtained by the fabrication and characterization of MESFETs made by growing a 0.6 mum n-type 3C-SiC on a semi-insulating 4H-SiC substrate

  2. Phase stability of cubic pyrochlore rare earth tantalate pinning additives in YBa2Cu3O7- superconductor

    SciTech Connect

    Wee, Sung Hun; Cantoni, Claudia; Zuev, Yuri L; Specht, Eliot D; Goyal, Amit

    2012-01-01

    Phase stability of cubic-pyrochlore-structured RE3TaO7 (RTO, where RE = rare earth elements) pinning additives in YBa2Cu3O7- (YBCO) superconductor and the pinning properties influenced by RTO addition into YBCO films were investigated. RTO completely reacts with YBCO and is converted to cubic-double-perovskite-structured Ba2RETaO6 (BRETO), a more thermodynamically stable tantalate phase within YBCO. In RTO-doped YBCO films, BRETO self-assembled nanocolumnns align along the c-axis of the film and play a major role in the improvement of flux pinning and Jc performance over wide magnetic field and angular ranges.

  3. The equilibrium state in the Si-O-C ternary system during SiC growth by chemical substitution of atoms

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.

    2015-03-01

    The equilibrium state in the silicon-carbon-oxygen (Si-O-C) ternary system has been calculated in the framework of the thermodynamics of chemical reactions. It is established that, in the practically important temperature interval of 1000°C < T < 1400°C, the system initially consisting of crystalline Si and gaseous CO tends toward an equilibrium state comprising a mixture of four solid phases (Si, C, SiC, and SiO2) and vapor mixture (predominantly of SiO, CO, Si, and CO2). Equilibrium partial pressures of all gases in the mixture have been calculated. An optimum regime of SiC film growth from Si by the method of atomic substitution is proposed, whereby only SiC phase is growing while SiO2 and C phases are not formed.

  4. Layer-By Deposition of Silicon Carbide and Characterization of the Resulting Films

    NASA Astrophysics Data System (ADS)

    Sumakeris, Joseph John, Jr.

    1995-01-01

    Silicon carbide is a wide bandgap semiconductor material with great potential for electronic applications. Therefore, heteroepitaxial SiC films on Si substrates have been used in several devices exploiting the capabilities of SiC. However, high SiC growth temperatures complicate device processing, impeding the increased utilization of SiC. Layer-by-layer deposition offers the ability to form SiC films on Si substrates at low temperatures. In addition, the thickness uniformity typical of films deposited by this process would simplify the fabrication of devices employing trench technology. A unique deposition reactor was designed and commissioned in this work. In the reactor, SiC films were deposited on Si substrates in a layer-by-layer fashion using two different methods: a high pressure (~ 1 Torr) and a lower pressure (~ 10^{-2} Torr) process. The resulting films were structurally characterized using the analytical techniques of reflection high energy electron diffraction and high resolution transmission electron microscopy. The lower pressure process was only employed after capping the Si substrates via the higher pressure process because significant out-diffusion of Si from the Si substrate occurred when the low pressure process was performed without first capping the substrate. Very uniform, monocrystalline films were deposited by both processes. Electrical characterization of undoped films revealed an n-type character with approximately 10^ {17} donors cm^{-3 }. SiC films that were doped p-type using Al from triethylaluminum exhibited carrier concentration controllable from ~10 ^{18} to 10^{20 }cm^{-3}. Two batches of trench based heterojunction bipolar transistors were fabricated. None of the wafers in either batch contained operational transistors. This was attributed to an inaccuracy in etching the SiC layer used to form the emitters and an excessively wide base region that permitted injected carriers to recombine before reaching the base -collector junction.

  5. Fabrication of SiC whisker-reinforced SiC ceramics

    SciTech Connect

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

    1992-10-01

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

  6. Growth and electrical characterization of two-dimensional layered MoS{sub 2}/SiC heterojunctions

    SciTech Connect

    Lee, Edwin W.; Nath, Digbijoy N.; Lee, Choong Hee; Arehart, Aaron; Ma, Lu; Wu, Yiying; Rajan, Siddharth

    2014-11-17

    The growth and electrical characterization of the heterojunction formed between two-dimensional (2D) layered p-molybdenum disulfide (MoS{sub 2}) and nitrogen-doped 4H silicon carbide (SiC) are reported. The integration of 2D semiconductors with the conventional three-dimensional (3D) substrates could enable semiconductor heterostructures with unprecedented properties. In this work, direct growth of p-type MoS{sub 2} films on SiC was demonstrated using chemical vapor deposition, and the MoS{sub 2} films were found to be high quality based on x-ray diffraction and Raman spectra. The resulting heterojunction was found to display rectification and current-voltage characteristics consistent with a diode for which forward conduction in the low-bias region is dominated by multi-step recombination tunneling. Capacitance-voltage measurements were used to determine the built-in voltage for the p-MoS{sub 2}/n-SiC heterojunction diode, and we propose an energy band line up for the heterostructure based on these observations. The demonstration of heterogeneous material integration between MoS{sub 2} and SiC enables a promising new class of 2D/3D heterostructures.

  7. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

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

    SciTech Connect

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

    1995-12-31

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

  9. 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.

  10. Quantification Of 4H- To 3C-Polymorphism In Silicon Carbide (SiC) Epilayers And An Investigation Of Recombination-Enhanced Dislocation Motion In SiC By Optical Emission Microscopy (Oem) Techniques

    NASA Technical Reports Server (NTRS)

    Speer, Kevin M.

    2004-01-01

    Environments that impose operational constraints on conventional silicon-(Si) based semiconductor devices frequently appear in military- and space-grade applications. These constraints include high temperature, high power, and high radiation environments. Silicon carbide (SiC), an alternative type of semiconductor material, has received abundant research attention in the past few years, owing to its radiation-hardened properties as well as its capability to withstand high temperatures and power levels. However, the growth and manufacture of SiC devices is still comparatively immature, and there are severe limitations in present crystal growth and device fabrication processes. Among these limitations is a variety of crystal imperfections known as defects. These imperfections can be point defects (e.g., vacancies and interstitials), line defects (e.g., edge and screw dislocations), or planar defects (e.g., stacking faults and double-positioning boundaries). All of these defects have been experimentally shown to be detrimental to the performance of electron devices made from SiC. As such, it is imperative that these defects are significantly reduced in order for SiC devices to become a viable entity in the electronics world. The NASA Glenn High Temperature Integrated Electronics & Sensors Team (HTIES) is working to identify and eliminate these defects in SiC by implementing improved epitaxial crystal growth procedures. HTIES takes two-inch SiC wafers and etches patterns, producing thousands of mesas into each wafer. Crystal growth is then carried out on top of these mesas in an effort to produce films of improved quality-resulting in electron devices that demonstrate superior performance-as well as fabrication processes that are cost-effective, reliable, and reproducible. In this work, further steps are taken to automate HTIES' SiC wafer inspection system. National Instruments LabVIEW image processing and pattern recognition routines are developed that are capable of

  11. SiC formation for a solar cell passivation layer using an RF magnetron co-sputtering system.

    PubMed

    Joung, Yeun-Ho; Kang, Hyun Il; Kim, Jung Hyun; Lee, Hae-Seok; Lee, Jaehyung; Choi, Won Seok

    2012-01-01

    In this paper, we describe a method of amorphous silicon carbide film formation for a solar cell passivation layer. The film was deposited on p-type silicon (100) and glass substrates by an RF magnetron co-sputtering system using a Si target and a C target at a room-temperature condition. Several different SiC [Si1-xCx] film compositions were achieved by controlling the Si target power with a fixed C target power at 150 W. Then, structural, optical, and electrical properties of the Si1-xCx films were studied. The structural properties were investigated by transmission electron microscopy and secondary ion mass spectrometry. The optical properties were achieved by UV-visible spectroscopy and ellipsometry. The performance of Si1-xCx passivation was explored by carrier lifetime measurement. PMID:22221730

  12. 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.

  13. THERMAL CONDUCTIVITY OF SIC AND C FIBERS

    SciTech Connect

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

    2000-09-01

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

  14. Imaging of SiC in metal matrix composites

    SciTech Connect

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

    1992-08-01

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

  15. SSG SiC Optical Systems in Space

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  16. SiC Composite Turbine Vanes

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Verilli, Michael J.

    2006-01-01

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

  17. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  18. Packaging Technologies for 500 C SiC Electronics and Sensors: Challenges in Material Science and Technology

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

    This paper presents ceramic substrates and thick-film metallization based packaging technologies in development for 500C silicon carbide (SiC) electronics and sensors. Prototype high temperature ceramic chip-level packages and printed circuit boards (PCBs) based on ceramic substrates of aluminum oxide (Al2O3) and aluminum nitride (AlN) have been designed and fabricated. These ceramic substrate-based chip-level packages with gold (Au) thick-film metallization have been electrically characterized at temperatures up to 550C. The 96 alumina packaging system composed of chip-level packages and PCBs has been successfully tested with high temperature SiC discrete transistor devices at 500C for over 10,000 hours. In addition to tests in a laboratory environment, a SiC junction field-effect-transistor (JFET) with a packaging system composed of a 96 alumina chip-level package and an alumina printed circuit board was tested on low earth orbit for eighteen months via a NASA International Space Station experiment. In addition to packaging systems for electronics, a spark-plug type sensor package based on this high temperature interconnection system for high temperature SiC capacitive pressure sensors was also developed and tested. In order to further significantly improve the performance of packaging system for higher packaging density, higher operation frequency, power rating, and even higher temperatures, some fundamental material challenges must be addressed. This presentation will discuss previous development and some of the challenges in material science (technology) to improve high temperature dielectrics for packaging applications.

  19. The Band Structure and Bulk Modulus of Cubic (3C) and Hexagonal (2H) Polytypes of Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Mahmood, A.; Sansoresa, L. Enrique

    Silicon carbide (SiC) is a high band-gap semiconductor material, which has very important and interesting characteristics for novel semiconductor applications. We have studied the cubic (3C) and hexagonal (2H) polytypes of this important material. For the band structure calculations of these polytypes, the density functional and total-energy technique have been applied in the generalized gradient approximation, which is the most powerful ab initio quantum-mechanica method. The important energy gaps have been determined and compared with the previous theoretical and experimental results. The density of state, charge density and bulk modulus have also been calculated.

  20. 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.

  1. 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.

  2. 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.

  3. Mechanical Properties of Silicon Carbonitride Thin Films

    NASA Astrophysics Data System (ADS)

    Peng, Xiaofeng; Hu, Xingfang; Wang, Wei; Song, Lixin

    2003-02-01

    Silicon carbonitride thin films were synthesized by reactive rf sputtering a silicon carbide target in nitrogen and argon atmosphere, or sputtering a silicon nitride target in methane and argon atmosphere, respectively. The Nanoindentation technique (Nanoindenter XP system with a continuous stiffness measurement technique) was employed to measure the hardness and elastic modulus of thin films. The effects of sputtering power on the mechanical properties are different for the two SiCN thin films. With increasing sputtering power, the hardness and the elastic modulus decrease for the former but increase for the latter. The tendency is similar to the evolution trend of Si-C bonds in SiCN materials. This reflects that Si-C bonds provide greater hardness for SiCN thin films than Si-N and C-N bonds.

  4. Saturn V S-IC Stage Fuel Tank

    NASA Technical Reports Server (NTRS)

    1964-01-01

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

  5. 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

  6. 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

  7. Near-field radiative heat transfer between metamaterials coated with silicon carbide thin films

    SciTech Connect

    Basu, Soumyadipta Yang, Yue; Wang, Liping

    2015-01-19

    In this letter, we study the near-field radiative heat transfer between two metamaterial substrates coated with silicon carbide (SiC) thin films. It is known that metamaterials can enhance the near-field heat transfer over ordinary materials due to excitation of magnetic plasmons associated with s polarization, while strong surface phonon polariton exists for SiC. By careful tuning of the optical properties of metamaterial, it is possible to excite electrical and magnetic resonances for the metamaterial and surface phonon polaritons for SiC at different spectral regions, resulting in the enhanced heat transfer. The effect of the SiC film thickness at different vacuum gaps is investigated. Results obtained from this study will be beneficial for application of thin film coatings for energy harvesting.

  8. Etching of hexagonal SiC surfaces in chlorine-containing gas media at ambient pressure

    NASA Astrophysics Data System (ADS)

    Zinovev, A. V.; Moore, J. F.; Hryn, J.; Pellin, M. J.

    2006-06-01

    The modification of the silicon carbide (4H-SiC) single-crystal surface in a chlorine-containing gas mixture at high temperature (800-1000 °C) and ambient pressure was investigated. The results of silicon carbide chlorination are found to strongly depend on the hexagonal surface orientation. Due to the thermodynamically more favorable reaction of chlorine with silicon rather than carbon, the C-terminated side (0 0 0 1¯) clearly undergoes considerable changes, resulting in coverage by a black-colored carbon film, whereas the Si-side (0 0 0 1) surprisingly remains visually untouched. With using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS and SEM it is shown that this drastic change in behavior is associated with a different structure of oxicarbide/silicate adlayer formed on the C- and Si-terminated sides of silicon carbide surface during experimental pre-treatment and air exposure. The presence of oxygen bridges connecting the silicate adlayer with the bulk SiC in the case of Si-side inhibits the chlorination reaction and makes this surface strongly resistant to chlorine attack. Only some places on the Si-terminated side demonstrate traces of chlorine etching in the form of hexagonal-shaped voids, which are possibly initiated by distortion of the initial crystalline structure by micropipes. In contrast, a thin carbon layer resulted on the C-terminated side as a consequence of the chlorination process. XPS, ARXPS, SEM and Raman spectroscopy study of created film allows us to argue that it consists mainly of sp2-bonded carbon, mostly in the form of nanoscale graphene sheets. The absence of a protective oxygen bridge between the silicate adlayer and the bulk silicon carbide crystal leads to unlimited growth of carbon film on the SiC(0 0 0 1¯) side.

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

    NASA Technical Reports Server (NTRS)

    Bradt, R. C.

    1984-01-01

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

  10. Optimization, characterization and evaluation of chitosan-tailored cubic nanoparticles of clotrimazole.

    PubMed

    Verma, Purnima; Ahuja, Munish

    2015-02-01

    The present study deals with improvement of the mucoadhesive properties of monoolein based cubic nanoparticles by incorporating chitosan. Chitosan-tailored cubic nanoparticles were prepared by thin film hydration followed by ultrasonication employing clotrimazole as model drug. The effect of Pluronic F127 fraction and concentration of chitosan on particle size and % mucin binding of the formulations was studied using 2-factor, 3-level, central composite experimental design. The concentration of chitosan was found to influence particle size and % mucin binding of cubic nanoparticles while Pluronic F127 fraction influenced only the % mucin binding. Studies indicated 8.33(%w/w) fraction of Pluronic F127 and 0.17 (%w/v) concentration of chitosan as optimum concentration. Finally, the optimized batch was characterized by polarized light microscopy, small-angle X-ray scattering (SAXS) and transmission electron microscopy. The results unveiled incorporation of chitosan did not disrupt the inner cubic structure of nanoparticles. Peak indexing of SAXS data revealed the coexistence of P-type and D-type cubic phases in nanoparticles. Further, comparative evaluation studies showed significantly higher anti-fungal activity of clotrimazole-loaded chitosan-tailored cubic nanoparticles than conventional suspension of clotrimazole against Candida albicans. PMID:25463320

  11. High reflected cubic cavity as long path absorption cell for infrared gas sensing

    NASA Astrophysics Data System (ADS)

    Yu, Jia; Gao, Qiang; Zhang, Zhiguo

    2014-10-01

    One direct and efficient method to improve the sensitivity of infrared gas sensors is to increase the optical path length of gas cells according to Beer-Lambert Law. In this paper, cubic shaped cavities with high reflected inner coating as novel long path absorption cells for infrared gas sensing were developed. The effective optical path length (EOPL) for a single cubic cavity and tandem cubic cavities were investigated based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) measuring oxygen P11 line at 763 nm. The law of EOPL of a diffuse cubic cavity in relation with the reflectivity of the coating, the port fraction and side length of the cavity was obtained. Experimental results manifested an increase of EOPL for tandem diffuse cubic cavities as the decrease of port fraction of the connecting aperture f', and the EOPL equaled to the sum of that of two single cubic cavities at f'<0.01. The EOPL spectra at infrared wavelength range for different inner coatings including high diffuse coatings and high reflected metallic thin film coatings were deduced.

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

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Singh, Mrityunjay

    2004-01-01

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

  13. Monte Carlo study of the hetero-polytypical growth of cubic on hexagonal silicon carbide polytypes

    NASA Astrophysics Data System (ADS)

    Camarda, Massimo

    2012-08-01

    In this article we use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on misoriented hexagonal (4H and 6H) substrates. We analyze the quality of the 3C-SiC film varying the polytype, the miscut angle and the initial surface morphology of the substrate. We find that the use of 6H misoriented (4°-10° off) substrates, with step bunched surfaces, can strongly improve the quality of the cubic epitaxial film whereas the 3C/4H growth is affected by the generation of dislocations, due to the incommensurable periodicity of the 3C (3) and the 4H (4) polytypes. For these reasons, a proper pre-growth treatment of 6H misoriented substrates can be the key for the growth of high quality, twin free, 3C-SiC films.

  14. Analysis of Hard Thin Film Coating

    NASA Technical Reports Server (NTRS)

    Shen, Dashen

    1998-01-01

    MSFC is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using electron cyclotron resonance chemical vapor deposition (ECRCVD) to deposit hard thin film an stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

  15. Analysis of Hard Thin Film Coating

    NASA Technical Reports Server (NTRS)

    Shen, Dashen

    1998-01-01

    Marshall Space Flight Center (MSFC) is interested in developing hard thin film coating for bearings. The wearing of the bearing is an important problem for space flight engine. Hard thin film coating can drastically improve the surface of the bearing and improve the wear-endurance of the bearing. However, many fundamental problems in surface physics, plasma deposition, etc, need further research. The approach is using Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) to deposit hard thin film on stainless steel bearing. The thin films in consideration include SiC, SiN and other materials. An ECRCVD deposition system is being assembled at MSFC.

  16. Magnetotransport of Epitaxial Graphene on Hexagonal SiC Surface Grown with Metal Plate Capping

    NASA Astrophysics Data System (ADS)

    Park, Kibog; Jin, Han Byul; Jung, Sungchul; Kim, Junhyoung; Chae, Dong-Hun; Kim, Wan-Seop; Park, Jaesung

    High quality epitaxial graphene (EG) was grown on a Si-face hexagonal SiC substrate by capping the surface with a metal plate (Molybdenum, Tungsten) during UHV annealing. The growth temperature was ~ 950 degree C, significantly lower than the conventional UHV annealing. The crystallinity of EG film was examined with Raman spectrum measurements. Almost no D-peak and a large narrow 2D-peak ensure that a thin (mono- or bi-layer) EG film was grown with a negligible number of defects. The electrical properties of EG film were also characterized by performing magnetotransport measurements with Hall-bar structures. The carrier type was found to be n-type, the sheet carrier density be (3.6-9.2)x1012 /cm2, and the Hall mobility be ~2100 cm2/Vs. Due to the relatively high carrier density, the Quantum Hall Effect was observed only for high filling factors up to 14 T. However, clear Shubnikov-de-Hass oscillations were observed, indicating that the random carrier scattering due to impurities or defects is minimal in the EG film grown with metal plate capping. Supported by NRF in South Korea (2014M2B2A9031944).

  17. Total displacement functions for SiC

    NASA Astrophysics Data System (ADS)

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

    1997-04-01

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

  18. SPHERICAL INDENTATION OF SiC

    SciTech Connect

    Wereszczak, Andrew A; Johanns, Kurt E

    2007-01-01

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

  19. Formation of cubic boron-nitride by the reactive sputter deposition of boron

    SciTech Connect

    Jankowski, A.F.; Hayes, J.P.; Makowiecki, D.W.; McKeman, M.A.

    1997-03-01

    Boron-nitride films are synthesized by RF magnetron sputtering boron targets where the deposition parameters of gas pressure, flow and composition are varied along with substrate temperature and applied bias. The films are analyzed using Auger electron spectroscopy, transmission electron microscopy, nanoindentation, Raman spectroscopy and x-ray absorption spectroscopy. These techniques provide characterization of film composition, crystalline structure, hardness and chemical bonding, respectively. Reactive, rf-sputtering process parameters are established which lead to the growth of crystalline BN phases. The deposition of stable and adherent boron nitride coatings consisting of the cubic phase requires 400 `C substrate heating and the application of a 300 V negative bias.

  20. Hydrogen monitoring for power plant applications using SiC sensors

    SciTech Connect

    Loloee, R.; Chorpening, B.T.; Beer, S.K.; Ghosh, R.N.

    2008-01-29

    We have developed a high-temperature gas sensing system for the detection of combustion products under harsh conditions, such as an energy plant. The sensor, based on the wide band gap semiconductor silicon carbide (SiC), is a catalytic gate field-effect device (Pt–SiO2–SiC) that can detect hydrogen-containing species in chemically reactive, high-temperature environments. The hydrogen response of the device in an industrially robust module was determined under both laboratory and industrial conditions (1000 sccm of 350 °C gas) from 52 ppm to 50% H2, with the sensor held at 620 °C. From our data we find that the hydrogen adsorption kinetics at the catalyst–oxide interface are well fitted by the linearized Langmuir adsorption isotherm. For hydrogen monitoring in a coal gasification application, we investigated the effect of common interferants on the device response to a 20% H2 gas stream. Within our signal to noise ratio, 40% CO and 5% CH4 had no measurable effect and a 2000 ppm pulse of H2S did not poison the Pt sensing film. We have demonstrated the long-term reliability of our SiC sensor and the robustness of the sensor packaging techniques, as all the data are from a single device, obtained during 5 days of industrial measurements in addition to 480 continuous hours of operation under laboratory conditions.

  1. Structural consequences of hydrogen intercalation of epitaxial graphene on SiC(0001)

    SciTech Connect

    Emery, Jonathan D. E-mail: bedzyk@northwestern.edu; Johns, James E.; McBriarty, Martin E.; Hersam, Mark C.; Wheeler, Virginia H.; Kurt Gaskill, D.; Detlefs, Blanka; Bedzyk, Michael J. E-mail: bedzyk@northwestern.edu

    2014-10-20

    The intercalation of various atomic species, such as hydrogen, to the interface between epitaxial graphene (EG) and its SiC substrate is known to significantly influence the electronic properties of the graphene overlayers. Here, we use high-resolution X-ray reflectivity to investigate the structural consequences of the hydrogen intercalation process used in the formation of quasi-free-standing (QFS) EG/SiC(0001). We confirm that the interfacial layer is converted to a layer structurally indistinguishable from that of the overlying graphene layers. This newly formed graphene layer becomes decoupled from the SiC substrate and, along with the other graphene layers within the film, is vertically displaced by ∼2.1 Å. The number of total carbon layers is conserved during the process, and we observe no other structural changes such as interlayer intercalation or expansion of the graphene d-spacing. These results clarify the under-determined structure of hydrogen intercalated QFS-EG/SiC(0001) and provide a precise model to inform further fundamental and practical understanding of the system.

  2. Band Engineering and Magnetic Doping of Epitaxial Graphene on SiC (0001)

    NASA Astrophysics Data System (ADS)

    Kong, Byoung Don; Jayasekera, Thushari; Kim, Ki Wook; Buongiorno Nardelli, M.

    2010-03-01

    Advances in the epitaxial growth of graphene films on SiC have the potential to open new classes of device applications that may revolutionize the semiconductor roadmap for future decades. However, this progress will require an in-depth understanding and utilization of the electronic processes that take place at the nanoscale, in particular the role of the interface buffer layer, where most of the electronic properties of the system can be controlled. In analogy with the formation of the Schottky barrier in metal-insulator interfaces (the energetic barrier the electrons have to overcome to go from the valence band of the metal to the conduction band of the insulator) here we demonstrate the ability to tune and control the band alignment and the magnetic doping at the heterojunction between graphene and SiC, a fundamental requirement for improving device efficiency and applicability. Using first principles calculations, we will show how the surface electrostatic distribution can be used to tune the valence band offset by introducing surface impurities such as B, Al, N, and P. Similarly, we will demonstrate how the introduction of magnetic impurities in the buffer layer can tune the spintronic behavior of the epitaxial graphene layer. This work was supported, in part, by the NERC/NIST SWAN-NRI and the DARPA/HRL CERA programs.

  3. Hydrogen monitoring for power plant applications using SiC sensors

    SciTech Connect

    Reza Loloee; Benjamin Chorpening; Steve Beer; Ruby N. Ghosha

    2007-08-01

    We have developed a high-temperature gas sensing system for the detection of combustion products under harsh conditions, such as an energy plant. The sensor, based on the wide band gap semiconductor silicon carbide (SiC), is a catalytic gate field-effect device (Pt–SiO2–SiC) that can detect hydrogen-containing species in chemically reactive, high-temperature environments. The hydrogen response of the device in an industrially robust module was determined under both laboratory and industrial conditions (1000 sccm of 350 ◦C gas) from 52 ppm to 50% H2, with the sensor held at 620 ◦C. From our data we find that the hydrogen adsorption kinetics at the catalyst–oxide interface are well fitted by the linearized Langmuir adsorption isotherm. For hydrogen monitoring in a coal gasification application, we investigated the effect of common interferants on the device response to a 20% H2 gas stream. Within our signal to noise ratio, 40% CO and 5% CH4 had no measurable effect and a 2000 ppm pulse of H2S did not poison the Pt sensing film. We have demonstrated the long-term reliability of our SiC sensor and the robustness of the sensor packaging techniques, as all the data are from a single device, obtained during 5 days of industrial measurements in addition to ∼480 continuous hours of operation under laboratory conditions.

  4. Effect of film gradient profile on adhesion strength, residual stress and effective hardness of functionally graded diamond-like carbon films

    NASA Astrophysics Data System (ADS)

    Won, Yoo Jai; Ki, Hyungson

    2014-08-01

    We have studied, for the first time, the effect of continuously-varying film gradient profiles on the adhesion strength, residual stress, and effective film hardness of diamond-like carbon (DLC) films deposited on stainless steel substrates. Precisely graded DLC films with five polynomial profiles (linear, quadratic, cubic, square root and cubic root profiles) were investigated and compared with pure DLC films, and it was shown that by optimizing the film gradient profile the residual stress and adhesion characteristics can be significantly improved but the effective film hardness can be negatively affected.

  5. The effect of Zircaloy-4 substrate surface condition on the adhesion strength and corrosion of SiC coatings

    NASA Astrophysics Data System (ADS)

    Al-Olayyan, Y.; Fuchs, G. E.; Baney, R.; Tulenko, J.

    2005-11-01

    Chemical vapor deposition (CVD) coatings of silicon carbide were deposited on various Zircaloy-4 substrates having different surface preparations to increase the corrosion resistance. The effects of several different surface treatments of the Zircaloy-4 substrate, such as surface roughness, the presence of interlayer, and pickling, on the adhesion and corrosion resistance of the SiC coatings have been evaluated using a scratch test method, electrochemical impedance spectroscopy and scanning electron microscopy. The scratch test was found to be a good tool for qualitative measurement of adhesion strength of thin coating films. Higher adhesion strengths were obtained for a moderate level of substrate roughness and the corrosion resistance of these films was closely related with the adhesion of the film on the substrate, as measured by impedance.

  6. Supersymmetric cubic Galileons have ghosts

    NASA Astrophysics Data System (ADS)

    Koehn, Michael; Lehners, Jean-Luc; Ovrut, Burt A.

    2013-07-01

    Galileons are higher-derivative theories of a real scalar which nevertheless admit second-order equations of motion. They have interesting applications as dark energy models and in early universe cosmology, and have been conjectured to arise as descriptions of brane dynamics in string theory. In the present paper, we study the bosonic sector of globally N=1 supersymmetric extensions of the cubic Galileon Lagrangian in detail. Supersymmetry requires that the Galileon scalar now becomes paired with a second real scalar field. We prove that the presence of this second scalar causes the equations of motion to become higher than second order, thus leading to the appearance of ghosts. We also analyze the energy scales up to which, in an effective field theory description, the ghosts can be tamed.

  7. Thin films for material engineering

    NASA Astrophysics Data System (ADS)

    Wasa, Kiyotaka

    2016-07-01

    Thin films are defined as two-dimensional materials formed by condensing one by one atomic/molecular/ionic species of matter in contrast to bulk three-dimensional sintered ceramics. They are grown through atomic collisional chemical reaction on a substrate surface. Thin film growth processes are fascinating for developing innovative exotic materials. On the basis of my long research on sputtering deposition, this paper firstly describes the kinetic energy effect of sputtered adatoms on thin film growth and discusses on a possibility of room-temperature growth of cubic diamond crystallites and the perovskite thin films of binary compound PbTiO3. Secondly, high-performance sputtered ferroelectric thin films with extraordinary excellent crystallinity compatible with MBE deposited thin films are described in relation to a possible application for thin-film MEMS. Finally, the present thin-film technologies are discussed in terms of a future material science and engineering.

  8. Tribological Analysis of Copper-Coated Graphite Particle-Reinforced A359 Al/5 wt.% SiC Composites

    NASA Astrophysics Data System (ADS)

    Lin, C. B.; Wang, T. C.; Chang, Z. C.; Chu, H. Y.

    2013-01-01

    Copper-coated graphite particles can be mass-produced by the cementation process using simple equipment. Graphite particulates that were coated with electroless copper and 5 wt.% SiC particulates were introduced into an aluminum alloy by compocasting to make A359 Al/5 wt.% SiC(p) composite that contained 2, 4, 6, and 8 wt.% graphite particulate composite. The effects of SiC particles, quantity of graphite particles, normal loading, sliding speed and wear debris on the coefficient of friction, and the wear rate were investigated. The results thus obtained indicate that the wear properties were improved by adding small amounts of SiC and graphite particles into the A359 Al alloy. The coefficient of friction of the A359 Al/5 wt.% SiC(p) composite that contained 6.0 wt.% graphite particulates was reduced to 0.246 and the amount of graphite film that was released on the worn surface increased with the graphite particulate content. The coefficient of friction and the wear rate were insensitive to the variation in the sliding speed and normal loading.

  9. Using a PLD BN/AlN composite as an annealing cap for ion implanted SiC

    NASA Astrophysics Data System (ADS)

    Ruppalt, L. B.; Stafford, S.; Yuan, D.; Jones, K. A.; Ervin, M. H.; Kirchner, K. W.; Zheleva, T. S.; Wood, M. C.; Geil, B. R.; Forsythe, E.; Vispute, R. D.; Venkatesan, T.

    2003-02-01

    A dual BN/AlN capping layer has been developed for annealing implanted SiC up to a temperature of at least 1700 °C. The AlN is used as a protective layer on SiC because it is chemically inert on the material and can be removed selectively with a warm KOH etch, while the BN layer prevents the AlN from evaporating at temperatures above 1600 °C. Prior to etching off the AlN film, the BN film is ion milled off. The BN film appears to be an excellent cap as the hexagonal phases present, hexagonal (hBN) and turbostratic (tBN), are stable to temperatures in excess of 2000 °C. After annealing, the BN forms a tight seal on top of the AlN in a dense epitaxial h-BN phase, with a t-BN layer forming above the hBN. The tBN layer should be able to accommodate strains caused by lattice mismatch and differences in the thermal coefficients of expansion because it, like graphite, forms strong sp 2 bonds in the basal plane, but contains loosely bonded basal planes that easily slip over each other.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  11. Hot corrosion attack and strength degradation of SiC and Si(sub)3N(sub)4

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Fox, Dennis S.; Jacobson, Nathan S.

    1987-01-01

    Thin films of Na2SO4 and Na2CO3 molten salt deposits were used to corrode sintered SiC and Si3N4 at 1000 C. The resulting attack produced pitting and grain boundary etching resulting in strength decreases ranging from 15 to 50 percent. Corrosion pits were the predominant sources of fracture. The degree of strength decrease was found to be roughly correlated with the depth of the pit, as predicted from fracture toughness considerations. Gas evolution and bubble formation were key aspects of pit formation. Many of the observations of furnace exposures held true in a more realistic burner rig test.

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

    PubMed Central

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

    2006-01-01

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

  13. Growth and Features of Epitaxial Graphene on SiC

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  14. Recent Developments in SiC Device Research

    NASA Astrophysics Data System (ADS)

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

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

  15. TRISO coated fuel particles with enhanced SiC properties

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  16. Research on microwave joining of SiC. Final report

    SciTech Connect

    1993-06-30

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

  17. Modification Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1975-01-01

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

  18. 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.

  19. Growth of cubic silicon carbide on oxide using polysilicon as a seed layer for micro-electro-mechanical machine applications

    NASA Astrophysics Data System (ADS)

    Frewin, C. L.; Locke, C.; Wang, J.; Spagnol, P.; Saddow, S. E.

    2009-08-01

    The growth of highly oriented 3C-SiC directly on an oxide release layer, composed of a 20-nm-thick poly-Si seed layer and a 550-nm-thick thermally deposited oxide on a (1 1 1)Si substrate, was investigated as an alternative to using silicon-on-insulator (SOI) substrates for freestanding SiC films for MEMS applications. The resulting SiC film was characterized by X-ray diffraction (XRD) with the X-ray rocking curve of the (1 1 1) diffraction peak displaying a FWHM of 0.115° (414″), which was better than that for 3C-SiC films grown directly on (1 1 1)Si during the same deposition process. However, the XRD peak amplitude for the 3C-SiC film on the poly-Si seed layer was much less than for the (1 1 1)Si control substrate, due to slight in-plane misorientations in the film. Surprisingly, the film was solely composed of (1 1 1) 3C-SiC grains and possessed no 3C-SiC grains oriented along the <3 1 1> and <1 1 0> directions which were the original directions of the poly-Si seed layer. With this new process, MEMS structures such as cantilevers and membranes can be easily released leaving behind high-quality 3C-SiC structures.

  20. Reactive Plasma Etching of SiC in a Tetrafluoroethane / Oxygen Plasma

    NASA Astrophysics Data System (ADS)

    McDonald, James S.; Radican, Kevin; Botello, Eric; Koeck, Deborah C.; Donnelly, David; Geerts, Wilhelmus; Spencer, Gregory; Galloway, Heather C.

    2003-10-01

    Fabrication of waveguides for electrical characterization of dielectric thin films requires a method of etching SiC and SiCN. A method of RF plasma etching was developed to ensure proper ground contact between the substrate and the ground lines. A constant flow of HFC 134a was investigated as compared to various oxygen flow rates, in order to determine the right mixture of HFC 134a and O_2, and the respective etch rate. This presentation will describe the method and techniques that were implemented using a magnetron gun attached to an RF network as a plasma source and a mixture of tetrafluoroethane or HFC 134a and O2 as the process gas.

  1. Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

    NASA Astrophysics Data System (ADS)

    Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven; Weber, William J.

    2015-10-01

    Nano-engineered 3C-SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.

  2. Effect of extreme radiation fluences on parameters of SiC nuclear particle detectors

    SciTech Connect

    Ivanov, A. M. Lebedev, A. A.; Strokan, N. B.

    2006-10-15

    Detectors based on modern CVD-grown films were irradiated with 8 MeV protons at a fluence of 3 x 10{sup 14} cm{sup -2}. The concentration of primary radiation defects was {approx}10{sup 17} cm{sup -3}, which is three orders of magnitude higher than the concentration of the initially present uncompensated donors. The resulting deep compensation of SiC enabled measurements of detector parameters in two modes: under reverse and forward bias. The basic parameters of the detectors degraded by no more than a factor of 1.7, compared with the fluence of 1 x 10{sup 14} cm{sup -2}. However, there appeared a polarization voltage, which indicates that a space charge is accumulated by radiation defects.

  3. Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

    NASA Astrophysics Data System (ADS)

    Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven; Weber, William J.

    2015-10-01

    Nano-engineered 3C-SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.

  4. Anodized Ti3SiC2 As an Anode Material for Li-ion Microbatteries.

    PubMed

    Tesfaye, Alexander T; Mashtalir, Olha; Naguib, Michael; Barsoum, Michel W; Gogotsi, Yury; Djenizian, Thierry

    2016-07-01

    We report on the synthesis of an anode material for Li-ion batteries by anodization of a common MAX phase, Ti3SiC2, in an aqueous electrolyte containing hydrofluoric acid (HF). The anodization led to the formation of a porous film containing anatase, a small quantity of free carbon, and silica. By varying the anodization parameters, various oxide morphologies were produced. The highest areal capacity was achieved by anodization at 60 V in an aqueous electrolyte containing 0.1 v/v HF for 3 h at room temperature. After 140 cycles performed at multiple applied current densities, an areal capacity of 380 μAh·cm(-2) (200 μA·cm(-2)) has been obtained, making this new material, free of additives and binders, a promising candidate as a negative electrode for Li-ion microbatteries. PMID:27282275

  5. Expanding the versatility of silicon carbide thin films and nanowires

    NASA Astrophysics Data System (ADS)

    Luna, Lunet

    Silicon carbide (SiC) based electronics and sensors hold promise for pushing past the limits of current technology to achieve small, durable devices that can function in high-temperature, high-voltage, corrosive, and biological environments. SiC is an ideal material for such conditions due to its high mechanical strength, excellent chemical stability, and its biocompatibility. Consequently, SiC thin films and nanowires have attracted interest in applications such as micro- and nano-electromechanical systems, biological sensors, field emission cathodes, and energy storage devices. However to fully realize SiC in such technologies, the reliability of metal contacts to SiC at high temperatures must be improved and the nanowire growth mechanism must be understood to enable strict control of nanowire crystal structure and orientation. Here, we present a novel metallization scheme, utilizing solid-state graphitization of SiC, to improve the long-term reliability of Pt/Ti contacts to polycrystalline n-type SiC films at high temperature. The metallization scheme includes an alumina protection layer and exhibits low, stable contact resistivity even after long-term (500 hr) testing in air at 450 ºC. We also report the crystal structure and growth mechanism of Ni-assisted silicon carbide nanowires using single-source precursor, methyltrichlorosilane. The effects of growth parameters, such as substrate and temperature, on the structure and morphology of the resulting nanowires will also be presented. Overall, this study provides new insights towards the realization of novel SiC technologies, enabled by advanced electron microscopy techniques located in the user facilities at the Molecular Foundry in Berkeley, California. This work was performed in part at the Molecular Foundry, supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

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

    SciTech Connect

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

    2014-04-01

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

  7. Structural Properties of Liquid SiC during Rapid Solidification

    PubMed Central

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

    2013-01-01

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

  8. Large And Highly Stable Structures Made Of SiC

    NASA Astrophysics Data System (ADS)

    Bougoin, M.; Lavenac, J.

    2012-07-01

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

  9. Aspects of SiC diode assembly using Ag technology

    NASA Astrophysics Data System (ADS)

    Mysliwiec, Marcin; Guziewicz, Marek; Kisiel, Ryszard

    2013-07-01

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

  10. Advanced SiC composites for fusion applications

    SciTech Connect

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

    1995-04-01

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

  11. Synthesis and properties of porous SiC ceramics

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    SciTech Connect

    Appleby, D. M.

    2009-03-10

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

  13. SiC IR emitter design for thermophotovoltaic generators

    NASA Astrophysics Data System (ADS)

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

    1996-02-01

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

  14. Junction barrier Schottky diodes in 6H SiC

    NASA Astrophysics Data System (ADS)

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

    1998-09-01

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

  15. Structural properties of liquid SiC during rapid solidification.

    PubMed

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

    2013-01-01

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

  16. Generalized Vaidya spacetime for cubic gravity

    NASA Astrophysics Data System (ADS)

    Ruan, Shan-Ming

    2016-03-01

    We present a kind of generalized Vaidya solution of a new cubic gravity in five dimensions whose field equations in spherically symmetric spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its spherically symmetric apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally, we present the first law and second law hold in this gravity. Although all the results are analogous to those in Lovelock gravity, we in fact introduce the contribution of a new cubic term in five dimensions where the cubic Lovelock term is just zero.

  17. 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.

  18. Elastic properties of SiC nanoscopic wires

    NASA Astrophysics Data System (ADS)

    Makeev, Maxim; Menon, Madhu; Srivastava, Deepak

    2006-03-01

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

  19. 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.

  20. Spin effects in thermoelectric phenomena in SiC nanoribbons.

    PubMed

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

    2015-01-21

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

  1. Plasma synthesis and characterization of ultrafine SiC

    SciTech Connect

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

    1986-01-01

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

  2. Polyimide nanocomposites based on cubic zirconium tungstate

    NASA Astrophysics Data System (ADS)

    Ramasubramanian Sharma, Gayathri

    2009-12-01

    In this research, cubic zirconium tungstate (ZrW2O8) was used as a filler to reduce the CTE of polyimides (PI), and the effect of ZrW2O8 nanoparticles on the bulk polymer properties was studied. Polyimides are high performance polymers with exceptional thermal stability, and there is a need for PIs with low CTEs for high temperature applications. The nanofiller, cubic ZrW2O8, is well known for its isotropic negative thermal expansion (NTE) over a wide temperature range from -272.7 to 777°C. The preparation of nanocomposites involved the synthesis of ZrW 2O8 nanofiller, engineering the polymer-filler interface using linker groups and optimization of processing strategies to prepare free-standing PI nanocomposite films. A hydrothermal method was used to synthesize ZrW 2O8 nanoparticles. Polyimide-ZrW2O8 interface interaction was enhanced by covalently bonding linker moieties to the surface of ZrW2O8 nanoparticles. Specifically, ZrW 2O8 nanoparticles were functionalized with two different linker groups: (1) a short aliphatic silane, and (2) low molecular weight PI. The surface functionalization was confirmed using X-ray photoelectron spectroscopy and thermal gravimetric analysis (TGA). Reprecipitation blending was used to prepare the freestanding PI-ZrW2O8 nanocomposite films with up to 15 volume% filler loading. SEM images showed the improvements in polymer-filler wetting behavior achieved using interface engineering. SEM images indicated that there was better filler dispersion in the PI matrix using reprecipitation blending, compared to the filler dispersion achieved in the nanocomposites prepared using conventional blending technique. The structure-property relationships in PI-ZrW2O8 nanocomposites were investigated by studying the thermal degradation, glass transition, tensile and thermal expansion properties of the nanocomposites. The properties were studied as a function of filler loading and interface linker groups. Addition of ZrW2O8 nanoparticles did not

  3. Investigation of solution-processed bismuth-niobium-oxide films

    SciTech Connect

    Inoue, Satoshi; Ariga, Tomoki; Matsumoto, Shin; Onoue, Masatoshi; Miyasako, Takaaki; Tokumitsu, Eisuke; Shimoda, Tatsuya; Chinone, Norimichi; Cho, Yasuo

    2014-10-21

    The characteristics of bismuth-niobium-oxide (BNO) films prepared using a solution process were investigated. The BNO film annealed at 550°C involving three phases: an amorphous phase, Bi₃NbO₇ fluorite microcrystals, and Nb-rich cubic pyrochlore microcrystals. The cubic pyrochlore structure, which was the main phase in this film, has not previously been reported in BNO films. The relative dielectric constant of the BNO film was approximately 140, which is much higher than that of a corresponding film prepared using a conventional vacuum sputtering process. Notably, the cubic pyrochlore microcrystals disappeared with increasing annealing temperature and were replaced with triclinic β-BiNbO₄ crystals at 590°C. The relative dielectric constant also decreased with increasing annealing temperature. Therefore, the high relative dielectric constant of the BNO film annealed at 550°C is thought to result from the BNO cubic pyrochlore structure. In addition, the BNO films annealed at 500°C contained approximately 6.5 atm.% carbon, which was lost at approximately 550°C. This result suggests that the carbon in the BNO film played an important role in the formation of the cubic pyrochlore structure.

  4. Very Smooth Ultrananocrystalline Diamond Film Growth by a Novel Pretreatment Technique.

    PubMed

    Park, Jong Cheon; Hwang, Sungu; Kim, Tae Gyu; Kim, Jin Kon; Chun, Ho Hwan; Shin, Sung Chul; Cho, Hyun

    2016-02-01

    Very smooth ultrananocrystalline diamond (UNCD) film growth on SiC substrate was achieved by a novel pretreatment technique consisted of SiC surface texturing and deaggregation of nanodiamond (ND) seed particles. Texturing of SiC surfaces in Ar and SF6/02 plasmas was found to be able to provide normalized roughness values of 0.5-7.0 compared to the untreated surface. SiC surface plasma-textured and seeded with H2 heat-treated ND particles at 600 degrees C showed the highest nucleation density of ~44.2 x 10(11) cm(-2) and a highly uniform coverage of surface with very fine ND seeds. The UNCD film grown with this new pretreatment technique showed a very smooth surface morphology consisted of small and uniformly distributed grains. PMID:27433650

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  6. 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

  7. Atomic scale mobility of the volatile fission products Xe, Kr and I in cubic SiC.

    PubMed

    Cooper, M W D; Kelly, S; Bertolus, M

    2016-06-22

    The migration barriers for the vacancy-assisted migration of fission products in 3C-SiC are reported and analysed in the context of the five frequency model, which enables one to calculate an effective diffusion coefficient from elementary mechanisms. Calculations were carried out using the nudged elastic band method (NEB) with interatomic forces determined from density functional theory (DFT). Justification for treating vacancy-assisted fission product migration as limited to the FCC carbon sublattice is based on the stability of carbon vacancies, unfavourable silicon vacancy formation and the accommodation of fission products on the carbon sublattice. Results show that for most Fermi levels within the band gap the activation energy for I exceeds that of Xe which exceeds that of Kr. Results also indicate that activation energies are higher near the conduction edge, thus, implying that enhanced fission product retention can be achieved through n-type doping of 3C-SiC, which limits the availability of the migration mediating carbon vacancies. PMID:27282287

  8. Electrostatic swelling of bicontinuous cubic lipid phases.

    PubMed

    Tyler, Arwen I I; Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Law, Robert V; Seddon, John M; Brooks, Nicholas J

    2015-04-28

    Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by (a) increasing the bilayer stiffness by adding cholesterol and (b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å. PMID:25790335

  9. The effect of MgO(111) interlayer on the interface phase stability and structure of BaFe12O19/SiC(0001)

    NASA Astrophysics Data System (ADS)

    Lazarov, V. K.; Hasnip, P. J.; Cai, Z.; Yoshida, K.; Ziemer, K. S.

    2012-04-01

    We present a study on the effect of an interlayer of thin MgO(111) film on SiC(0001) on the interface phase stability and structure of the BaFe12O19 (BaM). The 10 nm MgO(111) interlayer followed by the BaM film were grown by molecular beam epitaxy on 6H-SiC. Cross-sectional transmission electron microscopy shows the formation of a magnesium ferrite spinel phase at the interface, and after 25 nm, a well structured BaM film was observed. In addition to the two main phases (Mg-ferrite and BaM), a thin layer of SiOx (2-3 nm) is formed at the SiC interface. In spite of the formation of this amorphous layer, the diffraction studies show that the BaM film is epitaxially grown and it has a single crystal structure. The energy dispersive x-ray analysis from the interface region shows that the MgO layer prevents significant outdiffusion of the Si into the film. Total energy calculations by density functional theory were used to investigate the stability of the various phases and to explain the observed interfacial phases in the studied system.

  10. Top-gated graphene field-effect transistors by low-temperature synthesized SiN x insulator on SiC substrates

    NASA Astrophysics Data System (ADS)

    Ohno, Yasuhide; Kanai, Yasushi; Mori, Yuki; Nagase, Masao; Matsumoto, Kazuhiko

    2016-06-01

    Top-gated devices made from an epitaxial graphene film on a 4H-SiC substrate were fabricated. Atomic force microscopy and Raman spectroscopy results showed that a large-scale highly uniform monolayer graphene film was synthesized on the SiC substrate. A SiN x passivation film was deposited on a SiC graphene device as a top gate insulator by catalytic chemical-vapor deposition (Cat-CVD) below 65 °C. After the top gate electrode was formed on the SiN x film, no leakage current flowed between the gate and source electrodes. The transport characteristics showed clear ambipolar characteristics from 8 to 280 K, and the temperature dependences of the conductance and field-effect mobility of the devices implied that monolayer graphene devices can be successfully fabricated. Moreover, the position of the charge neutrality point after SiN x deposition was around 0 V, indicating p-doping characteristics. These results indicate that SiN x films synthesized by Cat-CVD can be used as gate insulators and that the carrier type may be controlled by adjusting the deposition conditions.

  11. Solitons in yttrium iron garnet thin films with localized gain

    NASA Astrophysics Data System (ADS)

    Pal, Ritu; Loomba, Shally; Kumar, C. N.

    2016-05-01

    We present the exact analytical solutions of cubic-quintic nonlinear Schrödinger equation with localized gain. We have demonstrated that the bright and dark solitons exist for the repulsive cubic and attractive quintic nonlinearity. These solutions have been obtained for those values of parameters which support the formation of solitons in Yttrium iron garnet thin films. Our results may be useful to understand the nonlinear pulse excitations in thin films.

  12. Nano-Engineered Cubic Zirconia for Orthopaedic Implant Applications

    NASA Astrophysics Data System (ADS)

    Namavar, F.; Rubinstein, A.; Sabirianov, R.; Thiele, G.; Sharp, J.; Pokharel, U.; Namavar, R.; Garvin, K.

    2012-02-01

    Osseointegration failure of the prosthesis prevents long-term stability, which contributes to pain, implant loosening, and infection that usually necessitates revision surgery. Cell attachment and spreading in vitro is generally mediated by adhesive proteins such as fibronectin and vitronectin. We designed and produced pure cubic zirconia (ZrO2) ceramic coatings by ion beam assisted deposition (IBAD) with nanostructures comparable to the size of proteins. Our ceramic coatings exhibit high hardness and a zero contact angle with serum. In contrast to Hydroxyapatite (HA), nano-engineered zirconia films possess excellent adhesion to all orthopaedic materials. Adhesion and proliferation experiments were performed with a bona fide mesenchymal stromal cells cell line (OMA-AD). Our experimental results indicated that nano-engineered cubic zirconia is superior in supporting growth, adhesion, and proliferation. We performed a comparative analysis of adsorption energies of the FN fragment using quantum mechanical calculations and Monte Carlo simulation on both types of surfaces: smooth and nanostructured. We have found that the initial FN fragment adsorbs significantly stronger on the nanostructured surface than on the smooth surface.

  13. Role of atomic terraces and steps in the electron transport properties of epitaxial graphene grown on SiC

    NASA Astrophysics Data System (ADS)

    Kuramochi, H.; Odaka, S.; Morita, K.; Tanaka, S.; Miyazaki, H.; Lee, M. V.; Li, S.-L.; Hiura, H.; Tsukagoshi, K.

    2012-03-01

    Thermal decomposition of vicinal SiC substrates with self-organized periodic nanofacets is a promising method to produce large graphene sheets toward the commercial exploitation of graphene's superior electronic properties. The epitaxial graphene films grown on vicinal SiC comprise two distinct regions of terrace and step; and typically exhibit anisotropic electron transport behavior, although limited areas in the graphene film showed ballistic transport. To evaluate the role of terraces and steps in electron transport properties, we compared graphene samples with terrace and step regions grown on 4H-SiC(0001). Arrays of field effect transistors were fabricated on comparable graphene samples with their channels parallel or perpendicular to the nanofacets to identify the source of measured reduced mobility. Minimum conductivity and electron mobility increased with the larger proportional terrace region area; therefore, the terrace region has superior transport properties to step regions. The measured electron mobility in the terrace region, ˜1000 cm2/Vs, is 10 times larger than that in the step region, ˜100 cm2/Vs. We conclusively determine that parasitic effects originate in regions of graphene that grow over step edges in 4H-SiC(0001).

  14. In Situ Study of Fluorine-Functionalized and Tri-Methyl Aluminum Dosed Epitaxial Graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Robinson, Zachary; Wheeler, Virginia; Hernandez, Sandra; Jernigan, Glenn; Myers-Ward, Rachael; Gaskill, D. Kurt; Mowl, Tyler; Ong, Eng Wen; Ventrice, Carl, Jr.; Geisler, Heike; Pletikosic, Ivo; Valla, Tonica; Eddy, Chip, Jr.

    2015-03-01

    Graphene growth in Ar on SiC(0001) results in a single rotational orientation film with single-layer thickness control. For many electronic applications, a gate dielectric, such as Al2O3, must be deposited on top of the graphene. To facilitate this, an atomic layer deposition process was developed to deposit Al2O3 on a fluorine-functionalized graphene surface. The functionalization process was necessary for deposition of the Al2O3. Angle resolved photoelectron spectroscopy and low energy electron diffraction were used to study the functionalized surfaces of bilayer and single layer graphene grown on SiC(0001). It was found that the fluorine had a negligible effect on the electronic structure of the graphene, and upon thermal desorption, caused no damage to the graphene film. Additionally, tri-methyl aluminum was dosed on the graphene in a chamber equipped with in situ XPS. This was performed on both fluorine functionalized and as-grown single layer graphene.

  15. Crystalline islands of semiconductor films

    NASA Astrophysics Data System (ADS)

    Zmievskaya, G. I.; Bondareva, A. L.

    2011-01-01

    Silicon carbide (SiC) nucleation in the form of powder in a discharge plasma and the formation of thin film islands on a Si(100) substrate in the course of gas-phase epitaxy are simulated numerically. Models of plasma-like media and nonequilibrium processes accompanying phase transitions of the first kind (such as condensation and crystallization) in the initial fast (fluctuation) stage are described. The nonstationary evolution of nuclei size distribution functions is modeled by solving kinetic equations in partial derivatives and stochastic Ito-Stratonovich analog equations. This makes it possible to refine the formation mechanisms of microcrystalline state polytypes and calculate the nucleation rate and the initial roughness of a SiC coating.

  16. 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.

  17. Development of SiC Mirror for ASTRO-F

    NASA Astrophysics Data System (ADS)

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

    2000-12-01

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

  18. 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.

  19. Observations of Ag diffusion in ion implanted SiC

    DOE PAGESBeta

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

    2015-03-17

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

  20. 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.

  1. Fission-product SiC reaction in HTGR fuel

    SciTech Connect

    Montgomery, F.

    1981-07-13

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

  2. Metal-oxide-semiconductor characteristics of chemical vapor deposited cubic-SiC

    NASA Astrophysics Data System (ADS)

    Shibahara, K.; Nishino, S.; Matsunami, H.

    1984-11-01

    Thermal oxidation of chemical vapor deposited (CVD) cubic-SiC and fabrication of MOS diodes using a thermal oxide film were carried out. The thermal oxide was found to be SiO2 by Auger electron spectroscopic analysis. Capacitance-voltage curves of MOS diodes measured under the dark condition showed deep depletion characteristics. Inversion characteristics were observed under the illuminated condition for the first time.

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

    SciTech Connect

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

    2015-06-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  5. Electrical transport in three-dimensional cubic Skyrmion crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Xiao; Nagaosa, Naoto

    2015-03-01

    Two-dimensional magnetic Skyrmions have been well confirmed via various experimental techniques in the bulk or on epitaxial thin films. Besides, a topologically nontrivial three-dimensional cubic Skyrmion crystal in the bulk, which is essentially a hedgehog-antihedgehog pair texture predicted theoretically, has also been tentatively observed. Equipped with a sophisticated spectral analysis program, we adopt Matsubara Green's function technique to study electrical transport, especially diagonal conductivity, in such system. We consider conduction electrons interacting with spinwaves via the strong Hund's rule coupling, wherein fluctuation of monopolar emergent electromagnetic field exits within adiabatic approximation. We describe in detail the influence of temperature and Skyrmion number on both dc and ac conductivities. Possible deviation from Fermi liquid behavior will also be discussed.

  6. 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

  7. 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

  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 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.

  9. 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.

  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

    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.

  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. This photo shows the progress of the S-IC test stand as of November 20, 1963.

  13. 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.

  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. Kerosene storage tanks can be seen to the left.

  15. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

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

  16. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1963-01-01

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

  17. 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.

  18. Grain growth and phase stability of nanocrystalline cubic zirconia under ion irradiation

    SciTech Connect

    Zhang, Yanwen; Jiang, Weilin; Wang, Chong M.; Namavar, Fereydoon; Edmondson, Philip D.; Zhu, Zihua; Gao, Fei; Lian, Jie; Weber, William J.

    2010-11-10

    Grain growth, oxygen stoichiometry and phase stability of nanostructurally-stabilized zirconia (NSZ) in pure cubic phase are investigated under 2 MeV Au ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with dose, and follows a power law (n=6) to a saturation value of ~30 nm that decreases with temperature. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that thermal grain growth is not activated and defect-stimulated grain growth is the dominating mechanism. While cubic phase is perfectly retained and no new phases are identified after the high-dose irradiations, reduction of oxygen in the irradiated NSZ films is detected. The ratio of O to Zr decreases from ~2.0 for the as-deposited films to ~1.65 after irradiation to ~35 dpa. Significant increase of oxygen vacancies in nanocrystalline zirconia suggests substantially enhanced oxygen diffusion under ion irradiation, a materials behavior far from equilibrium. The oxygen deficiency may be essential in stabilizing cubic phase to larger grain sizes.

  19. Grain Growth and Phase Stability of Nanocrystalline Cubic Zirconia under Ion Irradiation

    SciTech Connect

    Zhang, Yanwen; Jiang, Weilin; Wang, Chongmin; Namavar, Fereydoon; Edmondson, Philip D.; Zhu, Zihua; Gao, Fei; Lian, Jie; Weber, William J

    2010-01-01

    Grain growth, oxygen stoichiometry and phase stability of nanostructurally-stabilized cubic zirconia (NSZ) are investigated under 2 MeV Au ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with dose, and follows a power law (n=6) to a saturation value of ~30 nm that decreases with temperature. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that the grain growth is not thermally activated and irradiation-induced grain growth is the dominating mechanism. While the cubic structure is retained and no new phases are identified after the high-dose irradiations, oxygen reduction in the irradiated NSZ films is detected. The ratio of O to Zr decreases from ~2.0 for the as-deposited films to ~1.65 after irradiation to ~35 dpa. The loss of oxygen suggests a significant increase of oxygen vacancies in nanocrystalline zirconia under ion irradiation. The oxygen deficiency may be essential in stabilizing the cubic phase to larger grain sizes.

  20. Grain growth and phase stability of nanocrystalline cubic zirconia under ion irradiation

    SciTech Connect

    Zhang Yanwen; Jiang Weilin; Wang Chongmin; Edmondson, Philip D.; Zhu Zihua; Gao Fei; Namavar, Fereydoon; Lian Jie; Weber, William J.

    2010-11-01

    Grain growth, oxygen stoichiometry, and phase stability of nanostructurally stabilized cubic zirconia (NSZ) are investigated under 2 MeV Au-ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with irradiation dose to {approx}30 nm at {approx}35 dpa. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that the grain growth is not thermally activated and irradiation-induced grain growth is the dominating mechanism. While the cubic structure is retained and no new phases are identified after the high-dose irradiations, oxygen reduction in the irradiated NSZ films is detected. The ratio of O to Zr decreases from {approx}2.0 for the as-deposited films to {approx}1.65 after irradiation to {approx}35 dpa. The loss of oxygen suggests a significant increase in oxygen vacancies in nanocrystalline zirconia under ion irradiation. The oxygen deficiency may be essential in stabilizing the cubic phase to larger grain sizes.

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

    SciTech Connect

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

    2004-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  3. Aligned platinum nanowire networks from surface-oriented lipid cubic phase templates

    NASA Astrophysics Data System (ADS)

    Richardson, S. J.; Burton, M. R.; Staniec, P. A.; Nandhakumar, I. S.; Terrill, N. J.; Elliott, J. M.; Squires, A. M.

    2016-01-01

    Mesoporous metal structures featuring a bicontinuous cubic morphology have a wide range of potential applications and novel opto-electronic properties, often orientation-dependent. We describe the production of nanostructured metal films 1-2 microns thick featuring 3D-periodic `single diamond' morphology that show high out-of-plane alignment, with the (111) plane oriented parallel to the substrate. These are produced by electrodeposition of platinum through a lipid cubic phase (QII) template. Further investigation into the mechanism for the orientation revealed the surprising result that the QII template, which is tens of microns thick, is polydomain with no overall orientation. When thicker platinum films are grown, they also show increased orientational disorder. These results suggest that polydomain QII samples display a region of uniaxial orientation at the lipid/substrate interface up to approximately 2.8 +/- 0.3 μm away from the solid surface. Our approach gives previously unavailable information on the arrangement of cubic phases at solid interfaces, which is important for many applications of QII phases. Most significantly, we have produced a previously unreported class of oriented nanomaterial, with potential applications including metamaterials and lithographic masks.Mesoporous metal structures featuring a bicontinuous cubic morphology have a wide range of potential applications and novel opto-electronic properties, often orientation-dependent. We describe the production of nanostructured metal films 1-2 microns thick featuring 3D-periodic `single diamond' morphology that show high out-of-plane alignment, with the (111) plane oriented parallel to the substrate. These are produced by electrodeposition of platinum through a lipid cubic phase (QII) template. Further investigation into the mechanism for the orientation revealed the surprising result that the QII template, which is tens of microns thick, is polydomain with no overall orientation. When thicker

  4. 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

  5. Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3-x through Halide Exchange.

    PubMed

    Hoffman, Jacob B; Schleper, A Lennart; Kamat, Prashant V

    2016-07-13

    All-inorganic cesium lead halide (CsPbX3, X = Br(-), I(-)) perovskites could potentially provide comparable photovoltaic performance with enhanced stability compared to organic-inorganic lead halide species. However, small-bandgap cubic CsPbI3 has been difficult to study due to challenges forming CsPbI3 in the cubic phase. Here, a low-temperature procedure to form cubic CsPbI3 has been developed through a halide exchange reaction using films of sintered CsPbBr3 nanocrystals. The reaction was found to be strongly dependent upon temperature, featuring an Arrhenius relationship. Additionally, film thickness played a significant role in determining internal film structure at intermediate reaction times. Thin films (50 nm) showed only a small distribution of CsPbBrxI3-x species, while thicker films (350 nm) exhibited much broader distributions. Furthermore, internal film structure was ordered, featuring a compositional gradient within film. Transient absorption spectroscopy showed the influence of halide exchange on the excited state of the material. In thicker films, charge carriers were rapidly transferred to iodide-rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge-transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite-based photovoltaics. PMID:27322132

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  7. 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.

  8. Structural forms of cubic BC2N

    SciTech Connect

    Sun, Hong; Jhi, Seung-Hoon; Roundy, David; Cohen, Marvin L.; Louie, Steven G.

    2001-03-01

    Superhard cubic boron-carbonitrides (c-BC2N) are studied with the use of the ab initio pseudopotential density functional method. The total energy, lattice constant, bulk and shear moduli, and electronic band structures as well as the electron density of states are calculated for all the possible c-BC2N structures in an eight-atom zinc-blende-structured cubic unit cell. The results obtained provide a plausible explanation for recent experimental observations as well as a possible path to synthesis of the materials.

  9. Quadratic-Like Dynamics of Cubic Polynomials

    NASA Astrophysics Data System (ADS)

    Blokh, Alexander; Oversteegen, Lex; Ptacek, Ross; Timorin, Vladlen

    2016-02-01

    A small perturbation of a quadratic polynomial f with a non-repelling fixed point gives a polynomial g with an attracting fixed point and a Jordan curve Julia set, on which g acts like angle doubling. However, there are cubic polynomials with a non-repelling fixed point, for which no perturbation results into a polynomial with Jordan curve Julia set. Motivated by the study of the closure of the Cubic Principal Hyperbolic Domain, we describe such polynomials in terms of their quadratic-like restrictions.

  10. Purely cubic action for string field theory

    NASA Technical Reports Server (NTRS)

    Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.

    1986-01-01

    It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

  11. Scanning tunneling microscopy study of the superconducting properties of three-atomic-layer Pb films

    SciTech Connect

    Wang, Yilin; Li, Zhi; Wang, Lili; He, Ke; Ma, Xucun; Chen, Mu; Xue, Qi-Kun

    2013-12-09

    Ultrathin Pb films with a thickness of three monolayers (ML) were prepared on α-√(3)×√(3)Pb/Si(111) (Pb-SIC) substrate by molecular beam epitaxy. Despite significant defect scattering, low temperature scanning tunneling microscopy reveals a high superconducting transition temperature T{sub c} of 6.9 K, compared with the bulk T{sub c} (7.2 K). By applying external magnetic field, magnetic vortices were directly imaged, which demonstrates the robustness of superconductivity. By comparing to nearly free-standing Pb films on graphitized SiC (0001) substrate, we suggest that the higher T{sub c} of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling.

  12. PVD Silicon Carbide as a Thin Film Packaging Technology for Antennas on LCP Substrates for Harsh Environments

    NASA Technical Reports Server (NTRS)

    Scardelletti, Maximilian C.; Stanton, John W.; Ponchak, George E.; Jordan, Jennifer L.; Zorman, Christian A.

    2010-01-01

    This paper describes an effort to develop a thin film packaging technology for microfabricated planar antennas on polymeric substrates based on silicon carbide (SiC) films deposited by physical vapor deposition (PVD). The antennas are coplanar waveguide fed dual frequency folded slot antennas fabricated on liquid crystal polymer (LCP) substrates. The PVD SiC thin films were deposited directly onto the antennas by RF sputtering at room temperature at a chamber pressure of 30 mTorr and a power level of 300 W. The SiC film thickness is 450 nm. The return loss and radiation patterns were measured before and after the SiC-coated antennas were submerged into perchloric acid for 1 hour. No degradation in RF performance or physical integrity of the antenna was observed.

  13. 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).

  14. Interstitial H and H2 in SiC

    NASA Astrophysics Data System (ADS)

    Kaukonen, M.; Fall, C. J.; Lento, J.

    2003-08-01

    The properties of hydrogen in 3C and 4H type silicon carbide (SiC) are studied theoretically at the density functional level. We find that only singly positive or negative charge states of hydrogen are thermodynamically stable in SiC. The transition from the positive to the negative charge state (+/-) is at 0.9 and 1.3 eV above the valence band maximum in 3C and 4H structures, respectively. The diffusion barrier for the proton is 0.5 eV (being, however, anisotropic in 4H). For the negative H- the diffusion barrier is found to be considerably higher, of the order of 3 eV.

  15. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  16. Tga Characteristic and Fabrication of Porous SiC Ceramics

    NASA Astrophysics Data System (ADS)

    Kim, Seong Hoon; Yoon, Han Ki; Kim, Seon Jin; Park, Yi Hyun

    The long-range aim of this research is to develop porous ceramics with high strength, excellent thermal resistance and chemical stability at high temperature in environmental industry. The Cf/SiC was made by hot pressing method with SiC powder whose particle size is 50nm and less on the average also Al2O3, Y2O3 and SiO2 as additive. The carbon fibers of oxidation property are investigated by TGA for finding out decarburization point. As a result, decarburization point selected the specific temperature of TGA curve and the Cf/SiC composites occurred perfectly decarburization at carbon fibers so the clearly porous SiC ceramics were formed many holes of 3-5µm diameters through length direction by its reaction.

  17. 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.

  18. Saturn V S-IC Stage Test Firing

    NASA Technical Reports Server (NTRS)

    1965-01-01

    The Saturn V first stages were test fired at the Mississippi Test Facility and at the Marshall Space Flight Center (MSFC). Five F-1 engines powered the first stage, each developing 1.5 million pounds of thrust. The first stage, known as the S-IC stage, burned over 15 tons of propellant per second during its 2.5 minutes of operation to take the vehicle to a height of about 36 miles and to a speed of about 6,000 miles per hour. The stage was 138 feet long and 33 feet in diameter. This photograph shows the test firing of an F-1 engine at the MSFC's S-IC Static Test Firing Facility.

  19. Oxidation of ZrB2-SiC

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Halbig, Michael C.

    2001-01-01

    In this paper the oxidation behavior of ZrB2-20 vol% SiC is examined. Samples were exposed in stagnant air in a zirconia furnace (Deltech, Inc.) at temperatures of 1327, 1627, and 1927 C for ten ten-minute cycles. Samples were removed from the furnace after one, five, and ten cycles. Oxidized material was characterized by mass change when possible, x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Oxidation kinetics, oxide scale development, and matrix recession were monitored as a function of time and temperature. Oxidation and recession rates of ZrB2 - 20 vol% SiC were adequately modeled by parabolic kinetics. Oxidation rates of this material are rapid, allowing only very short-term application in air or other high oxygen partial pressure environments.

  20. High frequency ultrasonic characterization of sintered SiC

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Generazio, Edward R.; Kiser, James D.

    1987-01-01

    High frequency (60 to 160 MHz) ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90 to 98 percent of theoretical, average grain sizes ranging from 3.0 to 12.0 microns, and average pore sizes ranging from 1.5 to 4.0 microns. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. Attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size.

  1. Toughened Matrix SiC Fiber Reinforced Composites

    NASA Technical Reports Server (NTRS)

    Levine, Stanley R.; Bhatt, Ramakrishna T.; Morscher, Gregory N.; Kiser, James D.

    2005-01-01

    First matrix cracking stress is a critical parameter for application of Sic fiber reinforced composites in highly stressed, environmentally demanding applications such as turbine blades. High matrix fracture toughness is a key property that contributes to high composite fracture stress. Silicon nitride offers reduced matrix elastic modulus, lower coefficient of thermal expansion, and potentially high fracture toughness compared to Sic matrices. All of these factors can be used to advantage to increase matrix fracture stress. As a first model system we are pursuing toughened silicon nitride matrix composites reinforced with SCS-9 fibers. Fabrication is by tape casting the matrix plies and tape lay-up with fiber plies followed by hot pressing at 1800 C. Progress toward this end will be reported.

  2. Liquid water in the domain of cubic crystalline ice Ic

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R.

    1997-01-01

    Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.

  3. 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.

  4. 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.

  5. 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.

  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 photo, depicts the progress of the stand as of January 14, 1963, with its four towers prominently rising.

  7. Thrust Structure of Saturn V S-IC Stage

    NASA Technical Reports Server (NTRS)

    1963-01-01

    This image illustrates technicians working on a full scale engineering mock-up of a Saturn V S-IC stage thrust structure nearing completion at the Manufacturing Engineering Laboratory at Marshall Space Flight Center. The booster, 33 feet in diameter and 138 feet long, was powered by five F-1 engines that provided 7,500,000 pounds of thrust to start the monstrous vehicle on its journey into space.

  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. In this photo, taken June 24, 1963, the four tower legs of the test stand can be seen at their maximum height.

  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 shows the construction progress as of August 5, 1961. Heavy equipment continues to clear the test stand site.

  10. 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.

  11. SiC device development for high temperature sensor applications

    NASA Astrophysics Data System (ADS)

    Shor, J. S.; Goldstein, David; Kurtz, A. D.; Osgood, R. M.

    1992-09-01

    Progress made in the processing and characterization of 3C-SiC for high temperature sensor applications is reviewed. Piezoresistance properties of silicon carbide and the temperature coefficient of resistivity of n-type beta-SiC are presented. In addition, photoelectrical etching and dopant selective etch-stops in SiC and high temperature Ohmic contacts for n-type beta-SiC sensors are discussed.

  12. 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.

  13. 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.

  14. A monotonicity conjecture for real cubic maps

    SciTech Connect

    Dawson, S.P.; Galeeva, R.; Milnor, J.; Tresser, C.

    1993-12-01

    This will be an outline of work in progress. We study the conjecture that the topological entropy of a real cubic map depends ``monotonely`` on its parameters, in the sense that each locus of constant entropy in parameter space is a connected set. This material will be presented in more detail in a later paper.

  15. Sound velocity anisotropy in cubic crystals

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Park, H. Y.

    1983-01-01

    Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.

  16. FTIR spectroscopy of silicon carbide thin films prepared by PECVD technology for solar cell application

    NASA Astrophysics Data System (ADS)

    Kleinová, Angela; Huran, Jozef; Sasinková, Vlasta; Perný, Milan; Å ály, Vladimír.; Packa, Juraj

    2015-09-01

    The plasma CVD reactor with parallel plate electrodes was used for plasma enhanced chemical vapor deposition (PECVD) of two type's silicon carbide thin films on Si substrates. The concentration of elements in the films was determined by RBS and ERD analytical method simultaneously. The chemical compositions of the samples were analyzed by FTIR method. RBS and ERD results showed that the films contain silicon, carbon, hydrogen and small amount of oxygen. FTIR results confirmed the presence of Si-C, Si-H, C-H, and Si-O bonds. From the FTIR spectra the main following vibration frequencies were determined: the band from 2800 to 3000 cm-1 is attributed to stretching vibration of the CHn group in both the sp2 (2880 cm-1) and sp3 (2920 cm-1) configurations. The band at 2100 cm-1 is due to SiHm stretching vibrations. The band at 780 cm-1 can be assigned to Si-C stretching vibration. Main features of FTIR spectra were Gaussian fitted and detailed analyses of chemical bonding in SiC films were performed. Differences between two types of SiC films were discussed with the aim to using these films in the heterojunction solar cell technology.

  17. Stressed-Oxidation Lifetime of Different SiC Fiber, CVI Matrix SiC Minicomposites in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Martinez-Fernandez, Julian

    1998-01-01

    The stressed-oxidation lifetime properties of several minicomposites composed of single fiber tows with a CVI SiC matrix were compared. The minicomposites were made up of Nicalon(Tm) and Hi-Nicalon(Tm) SiC fibers with carbon or BN interphases. Constant load stress-rupture tests were performed between 600 and 13000 C in air for all of the minicomposite systems. Cyclic load testing was performed on the Hi-Nicalon minicomposite systems. The factors controlling the different lifetime behaviors: fiber rupture properties, interphase oxidation, fiber degradation, and fiber-matrix bonding, are discussed in light of different minicomposite constituents. All of the systems were subject to intermediate temperature embrittlement. The Hi-Nicalon fiber, BN interphase system, performed the best for constant load conditions. For cyclic load conditions, both the BN- interphase and C-interphase minicomposites displayed poor, but different failure behavior.

  18. 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.

  19. The electron spin resonance study of heavily nitrogen doped 6H SiC crystals

    SciTech Connect

    Savchenko, D. V.

    2015-01-28

    The magnetic and electronic properties of heavily doped n-type 6H SiC samples with a nitrogen concentration of 10{sup 19} and 4 × 10{sup 19 }cm{sup −3} were studied with electron spin resonance (ESR) at 5–150 K. The observed ESR line with a Dysonian lineshape was attributed to the conduction electrons (CE). The CE ESR (CESR) line was fitted by Lorentzian (insulating phase) (T < 40 K) and by Dysonian lineshape (metallic phase) above 40 K, demonstrating that Mott insulator-metal (IM) transition takes place at ∼40 K, accompanied by significant change in the microwave conductivity. The temperature dependence of CESR linewidth follows the linear Korringa law below 40 K, caused by the coupling of the localized electrons (LE) and CE, and is described by the exponential law above 40 K related to the direct relaxation of the LE magnetic moments via excited levels driven by the exchange interaction of LE with CE. The g-factor of the CESR line (g{sub ‖} = 2.0047(3), g{sub ⊥} = 2.0034(3)) is governed by the coupling of the LE of nitrogen donors at hexagonal and quasi-cubic sites with the CE. The sharp drop in CESR line intensity (25–30 K) was explained by the formation of antiferromagnetic ordering in the spin system close to the IM transition. The second broad ESR line overlapped with CESR signal (5–25 K) was attributed to the exchange line caused by the hopping motion of electrons between occupied and non-occupied positions of the nitrogen donors. Two mechanisms of conduction, hopping and band conduction, were distinguished in the range of T = 10–25 K and T > 50 K, respectively.

  20. Use of Pom Pons to Illustrate Cubic Crystal Structures.

    ERIC Educational Resources Information Center

    Cady, Susan G.

    1997-01-01

    Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

  1. Cubic Polynomials with Rational Roots and Critical Points

    ERIC Educational Resources Information Center

    Gupta, Shiv K.; Szymanski, Waclaw

    2010-01-01

    If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.

  2. 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

  3. SEM analysis of ion implanted SiC

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  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. 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

  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. 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.

  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. 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.

  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. 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

  8. Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

    SciTech Connect

    Soo, Y. L.; Chen, P. J.; Huang, S. H.; Shiu, T. J.; Tsai, T. Y.; Chow, Y. H.; Lin, Y. C.; Weng, S. C.; Chang, S. L.; Wang, G.; Cheung, C. L.; Sabirianov, R. F.; Mei, W. N.; Namavar, F.; Haider, H.; Garvin, K. L.; Lee, J. F.; Lee, H. Y.; Chu, P. P.

    2008-12-01

    Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO{sub 2}) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO{sub 2} nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO{sub 2}. These oxygen vacancies are regarded as the essential stabilizing factor for the nanostructurally stabilized cubic zirconia.

  9. Reaction channels and spectroscopic constants of astrophysical relevant Silicon bearing molecules SiC3H,+ and SiC3H

    NASA Astrophysics Data System (ADS)

    Inostroza Pino, N.; Cardenas, C.; Fuentealba, P.

    2014-10-01

    Reaction channels and spectroscopic properties of a series of silicon-carbon-bearing isomers of SiC3H+ and SiC3H, which are suitable species for astrophysical detection in carbon-rich sources, are calculated with correlated ab initio CCSD(T) and density functional theory methods. We present four isomers of SiC3H+ for which the electronic ground states have closed-shell configurations. For SiC3H, we considered the same structures in order to present a complete study. The global minimum among the SiC3H+ isomers corresponds to the rhomboidal structure with a transannular bond in a 1A1 electronic state (rb3-SiC3H+ C2v X1A1). The next minima correspond to a second rhomboid 1A1 isomer and a linear isomer (X1Σ+) with relative energies 0.86 and 0.93 eV, respectively at the CCSD(T)/cc-pvTZ level of theory. The most stable mono-hydrogenated silicon carbon isomer is linear, followed by two rhomboidal isomers, rb2-SiC3H and rb3-SiC3H (0.23 and 0.31 eV). For each structure, a set of spectroscopic parameters including their equilibrium structures, rotational constants, harmonic frequencies and dipole moment is presented. Furthermore, we discuss plausible formation pathways of SiC3H+ isomers which are classified as charge-exchange, ion-neutral and dissociative recombination reactions. These results show one favourable pathway to produce rb3-SiC3H+ from rb-SiC3-3s. The formation energy of the cation's isomers coming from neutral isomers as linear l1-SiC3H, rb3-SiC3H and rb2-SiC3H plus H+ as reactants (charge-exchange reaction) are 203.8 kcal mol-1 (8.84eV), 175.4 kcal mol-1 (7.60 eV) and 195.2 kcal mol-1 (8.46 eV), which provides us with evidence of the endergonic character of these reactions. As a consequence, it does not seem to be feasible to produce a cation from neutral reactant plus H+ by a charge-exchange reaction that was proposed by UMIST.

  10. Liquid infiltration and pyrolysis of SiC matrix composite materials

    SciTech Connect

    Casadio, S.; Nanneti, C.A.; Donato, A.

    1995-12-01

    SiC matrix composites were prepared by prepregging carbon and Nicalon fibre cloths with polycarbosilane (PCS) solution or nanosized SiC powder dispersion in PCS solution. After consolidation of the stacked cloths and pyrolysis, densification of the matrix was accomplished by multiple infiltration/pyrolysis steps with PCS solution. The pyrolysis behaviour of the SiC nanopowder/PCS matrix material was investigated in comparison to PCS.

  11. 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.

  12. Study on aluminium-based single films.

    PubMed

    Vinod Kumar, G S; García-Moreno, F; Babcsán, N; Brothers, A H; Murty, B S; Banhart, J

    2007-12-28

    In the present paper the authors studied isolated metallic films made from the same material used for making metallic foams, and then characterised their properties. Metal films were made from a liquid aluminium alloy reinforced with ceramic particles of known concentration. Melts without such particles were also investigated. It is shown that stable films could not be made from Al-Si alloy having no particles, and just extremely thin and fragile films could be made from commercially-pure Al. In contrast, aluminium alloys containing particles such as SiC and TiB(2) allowed pulling thin, stable films, which did not rupture. Significant thinning of films was observed when the particle concentration in the melt decreased. By in situ X-ray monitoring of liquid films during pulling, film thickness and drainage effects within the liquid film could be studied. The morphology and microstructure of films was characterised after solidification. Our work shows that the question of how foams are stabilised can be studied using a simplified system such as a film, instead of having to deal with the multitude of different structural elements present in a foam. PMID:18060172

  13. Analysis of material modifications caused by nanosecond pulsed UV laser processing of SiC and GaN

    NASA Astrophysics Data System (ADS)

    Krüger, Olaf; Wernicke, Tim; Würfl, Joachim; Hergenröder, Roland; Tränkle, Günther

    2008-10-01

    The effects of direct UV laser processing on single crystal SiC in ambient air were investigated by cross-sectional transmission electron microscopy, Auger electron spectroscopy, and measurements of the electrical resistance using the transfer length method (TLM). Scanning electron microscopy was applied to study the morphology and dimensions of the laser-treated regions. After laser processing using a nanosecond pulsed solid-state laser the debris consisting of silicon oxide was removed by etching in buffered hydrofluoric acid. A layer of resolidified material remains at the surface indicating the thermal impact of the laser process. The Si/C ratio is significantly disturbed at the surface of the resolidified layer and approaches unity in a depth of several tens of nanometers. A privileged oxidation of carbon leaves elementary resolidified silicon at the surface, where nanocrystalline silicon was detected. Oxygen and nitrogen were detected near the surface down to a depth of some tens of nanometers. A conductive surface film is formed, which is attributed to the thermal impact causing the formation of the silicon-rich surface layer and the incorporation of nitrogen as dopant. No indications for microcrack or defect formation were found beneath the layer of resolidified material.

  14. Unraveling the (3 ×3)-SiC(1 1 1) reconstruction and its role as an interface structure

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    To refine the growth quality of epitaxial graphene on the C-side of SiC and improving the resulting electronic character of these films, it is important to understand the atomic and electronic-structure of the interface. A phase mixture of different surface phases is observed just when surface graphitization first sets in. However, the atomic structure of some of the competing surface phases as well as of the SiC-graphene interface is unknown. We performed a density functional theory study on the C-side of the polar SiC(1 1 1) surface using the all-electron numeric atom-centered basis function code FHI-aims. The formation energy of different reconstructions and model systems for the interface is presented within the thermodynamically allowed range. The surface energies of the known (2 ×2) phase is compared with several structural models of the (3 ×3) phase proposed in the literature. Inorian comparison all the previously suggested (3 ×3) models are higher in energy than the known (2 ×2) phase. We present a new model for the (3 ×3) reconstruction. Its formation energy crosses that of the (2 ×2) phase just at the carbon rich limit of the chemical potential, which explains the observed phase mixture. Present address: AQcomputare GmbH, Business Unit MATcalc, Annabergerstr. 240, 09125 Chemnitz, Germany.

  15. Comment on "Adsorption of hydrogen and hydrocarbon molecules on SiC(001)" by Pollmann et al. (Surf. Sci. Rep. 69 (2014) 55-104)

    NASA Astrophysics Data System (ADS)

    Wimmer, E.; Celasco, E.; Vattuone, L.; Savio, L.; Tejeda, A.; Silly, M.; D'angelo, M.; Sirotti, F.; Rocca, M.; Catellani, A.; Galli, G.; Douillard, L.; Semond, F.; Aristov, V. Yu.; Soukiassian, P.

    2016-02-01

    This comment clarifies two issues related to the (001) surface reconstructions of cubic SiC, namely: (i) The failure of the bridge-bond model for H atoms interacting with the 3C-SiC(001) 3 × 2 reconstruction to explain all the experimental data based on different techniques, while a recent model has reconciled theory and experimental results. This model has not been discussed or even mentioned in the review by Pollmann et al.; and (ii) In their review, two models of the Si-terminated c(4 × 2) 3C-SiC(001) surface reconstruction are presented as equally probable. This is clearly not the case and the reasons are explained in this comment.

  16. 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.

  17. Presolar SiC in chondrites - How variable and how many sources?

    NASA Astrophysics Data System (ADS)

    Alexander, C. M. O'd.

    1993-06-01

    The carbon and silicon isotropic compositions of 246 isotopically anomalous SiC grains measured in low concentration residues are reported. The residues were prepared from nine chondrites, namely, 6 unequilibrated ordinary chondrites (UOCs), Qingzhen (EH3), Leoville (CV3), and Murchison (CM2). Murchison is used as a standard to which all the other meteorites studied are compared. The range of isotopic compositions exhibited by UOC SiC is found to be similar to Murchison, except in Inman. Inman SiC has a distinctly different distribution of its silicon isotopic composition compared to the other meteorites. Residues from Qingzhen and Leoville produce only one anomalous SiC grain each.

  18. 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.

  19. 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.

  20. 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.

  1. Study of deposition of YBa2Cu3O7-x on cubic zirconia

    NASA Technical Reports Server (NTRS)

    Warner, Joseph D.; Meola, Joseph E.; Jenkins, Kimberly A.

    1989-01-01

    Films of YBa2Cu3O7-x were grown on (100) cubic zirconia with 8 percent yttria by laser ablation from sintered targets of YBa2Cu3O7-x. The temperature of the zirconia substrate during growth was varied between 700 and 780 C. The atmosphere during growth was 170 mtorr of O2. The films were subsequently slowly cooled in-situ in 1 atm of O2. The best films were c-axis aligned and had a transition temperature of 87.7 K. The superconducting transition temperature and the X-ray diffraction analysis is reported as a function of the substrate temperature and of the angle between the laser beam and the target's normal.

  2. Tribology and hardness of excimer-laser-processed titanium layers on cubic zirconia

    SciTech Connect

    Zaleski, M.A.; Jervis, T.R. . Dept. of Materials Science and Engineering Los Alamos National Lab., NM ); Mayer, J.W. . Dept. of Materials Science and Engineering)

    1993-02-01

    The authors have examined the wear and friction and surface hardness of excimer-laser-processed Ti layers on cubic zirconia substrates. The film exhibits a complex array of cracking following processing that is related to the crystallographic orientation of the substrate. The friction between the laser-processed layers and both steel and ruby pins is reduced by approximately one-third relative to that of untreated zirconia. In the untreated case, wear is characterized by pin wear and debris, whereas the laser-processed layer wears by film transfer to the pin. The surface hardness of the processed layer is lower than that of both the untreated zirconia and the deposited Ti film. Indentation tests indicate that the surface is brittle following processing.

  3. XPS and STM study of SiC synthesized by acetylene and disilane reaction with the Si(1 0 0)2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Santoni, A.; Frycek, R.; Castrucci, P.; Scarselli, M.; De Crescenzi, M.

    2005-05-01

    The SiC formation on a ordered Si(1 0 0) substrate at low temperatures (980-1180 K) and low total pressures (10 -6 mbar) has been investigated by in situ X-ray photoemission spectroscopy (XPS) and ex situ scanning tunneling microscopy (STM). SiC was grown by chemical vapor deposition (CVD) from C 2H 2 and Si 2H 6 as the precursor gases. At all the temperatures and in presence of both C 2H 2 and Si 2H 6 XPS data showed the formation of sub-stoichiometric Si 1- xC x alloys characterized by excess silicon. By exposing to C 2H 2 only, stoichiometric SiC could be synthesized up to 1080 K. At 1180 K the formation of a Si 1- xC x alloy was observed. STM analysis has pointed out the role of silicon from the gas phase in the growth mechanisms and it has shown that uniform films with low roughness and small nanostructures can be obtained by tuning the acetylene/disilane ratios independently from the temperature selected in the investigated range.

  4. Particles cellulation composite (PCC): Dispersion morphology of SiC particles in Si{sub 3}N{sub 4}/SiC composites

    SciTech Connect

    Yamada, K.; Kamiya, N.

    1995-10-01

    Dispersion morphology of fine SiC particles in Si{sub 3}N{sub 4}/xSiC (x = 0, 10, 20, 30wt%, average size: 0.03 {micro} m) composites was statistically analyzed, and typical properties of the composites such as creep, electric and thermal conductivity were investigated. The dispersion morphology of SiC particles was analyzed by observing the ECR-plasma etched surface of the sintered composites using scanning electron microscopy. SiC particles in Si{sub 3}N{sub 4}/SiC composites were distributed both within Si{sub 3}N{sub 4} grains and on Si{sub 4}N{sub 4} grain boundary, but 90% or more of them was located on the grain boundary. For the composites with 20--30 wt%SiC, the SiC particles on the grain boundary clearly formed a three-dimensional network structure surrounding a few or more Si{sub 3}N{sub 4} crystalline grains. A Si{sub 3}N{sub 4}/SiC composite with a three-dimensional network structure of SiC particles, named particles cellulation composite (PCC), was artificially made by pressing the granulated Si{sub 3}N{sub 4} powder (less than 500 {micro} m diameter) discontinuously coated with SiC particles (average size: 0.4 {micro}m). The creep deformation of PCC was reduced to about 60% of that of the composites with SiC particles randomly dispersed. Electrical and thermal properties were also improved. These results suggest that the formation of three-dimensional network structure by the second phase particles in a composite would considerably improve its mechanical property as well as electrical and thermal properties.

  5. The growth of cubic silicon carbide on a compliant substrate

    NASA Technical Reports Server (NTRS)

    Mitchell, Sharanda; Soward, Ida

    1995-01-01

    Research has shown that silicon carbide grown on silicon and 6H silicon carbide has problems associated with these substrates. This is because silicon and silicon carbide has a 20% lattice mismatch and cubic silicon carbide has not been successfully achieved on 6H silicon carbide. We are investigating the growth of silicon carbide on a compliant substrate in order to grow defect free silicon carbide. This compliant substrate consists of silicon/silicon dioxide with 1200 A of single crystal silicon on the top layer. We are using this compliant substrate because there is a possibility that the silicon dioxide layer and the carbonized layer will allow the silicon lattice to shrink or expand to match the lattice of the silicon carbide. This would improve the electrical properties of the film for the use of device fabrication. When trying to grow silicon carbide, we observed amorphous film. To investigate, we examined the process step by step using RHEED. RHEED data showed that each step was amorphous. We found that just by heating the substrate in the presence of hydrogen it changed the crystal structure. When heated to 1000 C for 2 minutes, RHEED showed that there was an amorphous layer on the surface. We also heated the substrate to 900 C for 2 minutes and RHEED data showed that there was a deterioration of the single crystalline structure. We assumed that the presence of oxygen was coming from the sides of the silicon dioxide layer. Therefore, we evaporated 2500 A of silicon to all four edges of the wafer to try to enclose the oxygen. When heating the evaporated wafer to 900 C the RHEED data showed single crystalline structure however at 1000 C the RHEED data showed deterioration of the single crystalline structure. We conclude that the substrate itself is temperature dependent and that the oxygen was coming from the sides of the silicon dioxide layer. We propose to evaporate more silicon on the edges of the wafer to eliminate the escape of oxygen. this will allow

  6. Reactive ion etching of sputtered silicon carbide and tungsten thin films for device applications

    SciTech Connect

    Pan, W.S.

    1988-01-01

    For high temperature processing and device applications refractory materials, silicon carbide (SiC) and tungsten (W), are considered or evaluated as the basic semiconductor and metallization materials for integrated circuits. In order to pattern fine lines in SiC and W thin films, a selective and anisotropic etching technique is needed. First, materials properties, such as crystallinity, conductivity, refractive index, optical bandgap, etc., of sputtered silicon carbide (SiC) and tungsten (W) thin films have been investigated in conjunction with the rapid thermal annealing (RTA) technique. The RTA temperature dependence of the optical bandgap of SiC thin films has been obtained. High crystallinity W thin of low resistivity films were obtained using by RTA. Reactive ion etching (RIE) of SiC thin films in a variety of fluorinated gas plasmas, such as SF{sub 6}, CBrF{sub 3} and CHF{sub 3} mixed with oxygen has been investigated in depth. The emission spectra and induced DC bias of the RF plasma were monitored to explore the etching mechanisms. A SiC:Si etch ratio higher than unity was obtained for the first time by using CBrF{sub 3}/75%O{sub 2} and CHF{sub 3}/90%O{sub 2} at 200W, 20 sccm, 20mTorr plasma conditions. The best anisotropic profile was observed by using CHF{sub 3} gas in the RIE mode. A typical DC bias, -300V, is concluded from etching experiments to determine the dependence of SiC etch rate and physical reaction under RIE mode. RIE of tungsten (W) thin film was investigated by using the different fluorinated gas plasmas, such as CF{sub 4}, SF{sub 6}, CBrF{sub 3} and CHF{sub 3} mixed with oxygen. We have achieved our goal of selective patterning of tungsten films over SiC, Si, SiO{sub 2}, which required in order to use W in SiC device applications. A very good W:Si and W:SiO{sub 2} selective ratio, 4:1 and 4.8:1, were observed by using CHF{sub 3}/70%O{sub 2} gases under different Plasma conditions.

  7. Nonlinear-optical and structural properties of nanocrystalline silicon carbide films

    SciTech Connect

    Brodyn, M. S.; Volkov, V. I. Lyakhovetskii, V. R.; Rudenko, V. I.; Puzilkov, V. M.; Semenov, A. V.

    2012-02-15

    The aim of this study is to investigate the nonlinearity of refraction in nanostructured silicon carbide films depending on their structural features (synthesis conditions for such films, substrate temperature during their deposition, concentration of the crystalline phase in the film, Si/C ratio of atomic concentrations in the film, and size of SiC nanocrystals formed in the film). The corresponding dependences are obtained, as well as the values of nonlinear-optical third-order susceptibility {chi}{sup (3)}({omega}; {omega}, -{omega}, {omega}) for various silicon polytypes (3C, 21R, and 27R) which exceed the value of {chi}{sup (3)} in bulk silicon carbide single crystals by four orders of magnitude.

  8. 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.

  9. Wavelets based on Hermite cubic splines

    NASA Astrophysics Data System (ADS)

    Cvejnová, Daniela; Černá, Dana; Finěk, Václav

    2016-06-01

    In 2000, W. Dahmen et al. designed biorthogonal multi-wavelets adapted to the interval [0,1] on the basis of Hermite cubic splines. In recent years, several more simple constructions of wavelet bases based on Hermite cubic splines were proposed. We focus here on wavelet bases with respect to which both the mass and stiffness matrices are sparse in the sense that the number of nonzero elements in any column is bounded by a constant. Then, a matrix-vector multiplication in adaptive wavelet methods can be performed exactly with linear complexity for any second order differential equation with constant coefficients. In this contribution, we shortly review these constructions and propose a new wavelet which leads to improved Riesz constants. Wavelets have four vanishing wavelet moments.

  10. Face-Centered-Cubic Nanostructured Polymer Foams

    NASA Astrophysics Data System (ADS)

    Cui, C.; Baughman, R. H.; Liu, L. M.; Zakhidov, A. A.; Khayrullin, I. I.

    1998-03-01

    Beautifully iridescent polymer foams having Fm-3m cubic symmetry and periodicities on the scale of the wavelength of light have been synthesized by the templating of porous synthetic opals. These fabrication processes involve the filling of porous SiO2 opals (with typical cubic lattice parameters of 250 nm) with either polymers or polymer precursors, polymerization of the precursors if necessary, and removal of the fcc array of SiO2 balls to provide an all-polymer structure. The structures of these foams are similar to periodic minimal surfaces, although the Gaussian curvature can have both positive and negative values. Depending upon whether the internal surfaces of the opal are polymer filled or polymer coated, the polymer replica has either one or two sets of independent channels. We fill these channels with semiconductors, metals, or superconductors to provide electronic and optical materials with novel properties dependent on the nanoscale periodicity.

  11. Effect of particle concentration on the structure and tribological properties of submicron particle SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition

    NASA Astrophysics Data System (ADS)

    Gül, H.; Kılıç, F.; Uysal, M.; Aslan, S.; Alp, A.; Akbulut, H.

    2012-03-01

    In the present work, a nickel sulfate bath containing SiC submicron particles between 100 and 1000 nm was used as the plating electrolyte. The aim of this work is to obtain Ni-SiC metal matrix composites (MMCs) reinforced with submicron particles on steel surfaces with high hardness and wear resistance for using in anti-wear applications such as dies, tools and working parts for automobiles and vehicles. The influence of the SiC content in the electrolyte on particle distribution, microhardness and wear resistance of nano-composite coatings was studied. During the electroplating process, the proper stirring speed was also determined for sub-micron SiC deposition with Ni matrix. The Ni films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The depositions were controlled to obtain a specific thickness (between 50 and 200 μm) and volume fraction of the particles in the matrix (between 0.02 and 0.10). The hardness of the coatings was measured to be 280-571 HV depending on the particle volume in the Ni matrix. The tribological behaviors of the electrodeposited SiC nanocomposite coatings sliding against an M50 steel ball (Ø 10 mm) were examined on a tribometer. All the friction and wear tests were performed without lubrication at room temperature and in the ambient air (with a relative humidity of 55-65%). The results showed that the wear resistance of the nanocomposites was approximately 2-2.2 times more than those of unreinforced Ni.

  12. 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.

  13. Method of synthesizing cubic system boron nitride

    SciTech Connect

    Yuzu, S.; Sumiya, H.; Degawa, J.

    1987-10-13

    A method is described for synthetically growing cubic system boron nitride crystals by using boron nitride sources, solvents for dissolving the boron nitride sources, and seed crystals under conditions of ultra-high pressure and high temperature for maintaining the cubic system boron nitride stable. The method comprises the following steps: preparing a synthesizing vessel having at least two chambers, arrayed in order in the synthesizing vessel so as to be heated according to a temperature gradient; placing the solvents having different eutectic temperatures in each chamber with respect to the boron nitride sources according to the temperature gradient; placing the boron nitride source in contact with a portion of each of the solvents heated at a relatively higher temperature and placing at least a seed crystal in a portion of each of the solvents heated at a relatively lower temperature; and growing at least one cubic system boron nitride crystal in each of the solvents in the chambers by heating the synthesizing vessel for establishing the temperature gradient while maintaining conditions of ultra-high pressure and high temperature.

  14. Thermomechanical Behavior of Advanced SiC Fiber Multifilament Tows

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; DiCarlo, James A.

    1997-01-01

    In order to relate single fiber behavior to multiple fiber behavior in composites, fast-fracture tensile strength, creep, and stress-rupture studies were conducted on advanced SiC fiber multifilament tows in the temperature range from 20 to 1400 C in air as well as in inert environments. For conditions of small fiber creep (short times and low temperatures), the tow results of this study confirm the ability of limited single fiber data to model the strength behavior of multiple fibers in a bundle. For conditions of high creep (long times and high temperatures), further studies are needed to explain tow rupture behavior being better than average single fiber behavior.

  15. Construction Progress of the S-IC Test Stand

    NASA Technical Reports Server (NTRS)

    1961-01-01

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

  16. 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.

  17. CONTACT RESISTANCE AT A CVD-SIC/NI INTERFACE

    SciTech Connect

    Youngblood, Gerald E.; Thomsen, Edwin C.

    2011-04-17

    The primary objectives of this task are: (1) to assess the properties and behavior of SiCf/SiC composites made from SiC fibers (with various SiC-type matrices, fiber coatings and architectures) before and after irradiation, and (2) to develop analytic models that describe these properties as a function of temperature and dose as well as composite architecture. In support of the U.S. dual-coolant lead-lithium (DCLL) fusion reactor blanket concept, recent efforts have focused on examining the electrical conductivity properties of SiCf/SiC composites considered for application in FCI-structures.

  18. 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.

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. Thin wetting films from aqueous electrolyte solutions on SiC/Si wafer.

    PubMed

    Diakova, B; Filiatre, C; Platikanov, D; Foissy, A; Kaisheva, M

    2002-02-25

    The stability and rupture of thin wetting films from aqueous NaCl or Na2SO4 solutions of different concentrations on silicon carbide were investigated. The flat surface of SiC was obtained by plasma-enhanced chemical vapor deposition (PE-CVD) on top of a silicon wafer. The microinterferometric method was used for measuring the film thickness with time. The light reflectance was calculated as a function of film thickness for the four-layer system: air/aqueous solution/SiC/Si wafer. The microinterferometric experiments showed that films from aqueous NaCl and Na2SO4 solutions with concentrations up to 0.01 M were stable independent of the pre-treatment of the substrate. The pre-treatment of the SiC surface was crucial for the wetting film stability at electrolyte concentrations greater than 0.01 M. The films were unstable and ruptured if SiC was washed with 5% hydrofluoric acid and concentrated sulfuric acid, while they were stable if washing was in sulfuric acid only, without immersing SiC in HF. The average equilibrium film thickness was determined as a function of electrolyte concentration. Measurements of the electrokinetic potential zeta were performed by electrophores of SiC powder in 0.001 M NaCl. It was shown that silicon carbide surface was negatively charged. The theory of heterocoagulation was used for the interpretation of the results. Besides the DLVO forces, the structural disjoining pressure (both positive and negative) has been included in the analysis. PMID:11908786

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

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

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... codes 20 through 39 to which this part applies. (a) SIC codes. Major group or industry code Exceptions... industry code Exceptions and/or limitations 311—Food Manufacturing Except 311119—Exception is limited to... under SIC 7334, Photocopying and Duplicating Services, (instant printing)); 324—Petroleum and...

  8. The Social Interactive Coding System (SICS): An On-Line, Clinically Relevant Descriptive Tool.

    ERIC Educational Resources Information Center

    Rice, Mabel L.; And Others

    1990-01-01

    The Social Interactive Coding System (SICS) assesses the continuous verbal interactions of preschool children as a function of play areas, addressees, script codes, and play levels. This paper describes the 26 subjects and the setting involved in SICS development, coding definitions and procedures, training procedures, reliability, sample…

  9. Highly flexible, nonflammable and free-standing SiC nanowire paper.

    PubMed

    Chen, Jianjun; Liao, Xin; Wang, Mingming; Liu, Zhaoxiang; Zhang, Judong; Ding, Lijuan; Gao, Li; Li, Ye

    2015-04-14

    Flexible paper-like semiconductor nanowire materials are expected to meet the criteria for some emerging applications, such as components of flexible solar cells, electrical batteries, supercapacitors, nanocomposites, bendable or wearable electronic or optoelectronic components, and so on. As a new generation of wide-bandgap semiconductors and reinforcements in composites, SiC nanowires have advantages in power electronic applications and nanofiber reinforced ceramic composites. Herein, free-standing SiC nanowire paper consisting of ultralong single-crystalline SiC nanowires was prepared through a facile vacuum filtration approach. The ultralong SiC nanowires were synthesized by a sol-gel and carbothermal reduction method. The flexible paper composed of SiC nanowires is ∼100 nm in width and up to several hundreds of micrometers in length. The nanowires are intertwisted with each other to form a three-dimensional network-like structure. SiC nanowire paper exhibits high flexibility and strong mechanical stability. The refractory performance and thermal stability of SiC nanowire paper were also investigated. The paper not only exhibits excellent nonflammability in fire, but also remains well preserved without visible damage when it is heated in an electric oven at a high temperature (1000 °C) for 3 h. With its high flexibility, excellent nonflammability, and high thermal stability, the free-standing SiC nanowire paper may have the potential to improve the ablation resistance of high temperature ceramic composites. PMID:25785912

  10. Silicon Carbide Epitaxial Films Studied by Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Silicon carbide (SiC) holds great potential as an electronic material because of its wide band gap energy, high breakdown electric field, thermal stability, and resistance to radiation damage. Possible aerospace applications of high-temperature, high-power, or high-radiation SiC electronic devices include sensors, control electronics, and power electronics that can operate at temperatures up to 600 C and beyond. Commercially available SiC devices now include blue light-emitting diodes (LED's) and high-voltage diodes for operation up to 350 C, with other devices under development. At present, morphological defects in epitaxially grown SiC films limit their use in device applications. Research geared toward reducing the number of structural inhomogeneities can benefit from an understanding of the type and nature of problems that cause defects. The Atomic Force Microscope (AFM) has proven to be a useful tool in characterizing defects present on the surface of SiC epitaxial films. The in-house High-Temperature Integrated Electronics and Sensors (HTIES) Program at the NASA Lewis Research Center not only extended the dopant concentration range achievable in epitaxial SiC films, but it reduced the concentration of some types of defects. Advanced structural characterization using the AFM was warranted to identify the type and structure of the remaining film defects and morphological inhomogeneities. The AFM can give quantitative information on surface topography down to molecular scales. Acquired, in part, in support of the Advanced High Temperature Engine Materials Technology Program (HITEMP), the AFM had been used previously to detect partial fiber debonding in composite material cross sections. Atomic force microscopy examination of epitaxial SiC film surfaces revealed molecular-scale details of some unwanted surface features. Growth pits propagating from defects in the substrate, and hillocks due, presumably, to existing screw dislocations in the substrates, were

  11. On the impact of the plasma jet energy on the product of plasmadynamic synthesis in the Si-C system

    NASA Astrophysics Data System (ADS)

    Nikitin, D.; Sivkov, A.

    2015-10-01

    Silicon carbide (SiC) nanoparticles can be used for ceramics reinforcement, creation of nanostructured ceramics, microelectromechanical systems. The paper presents the results of plasmadynamic synthesis of silicon carbide nanopowders. This method was realized by the synthesis in an electrodischarge plasma jet generated by a high-current pulsed coaxial magnetoplasma accelerator. Powdered carbon and silicon were used as precursors for the reaction. Four experiments with different energy levels (from 10.0 to 30.0 kJ) were carried out. The synthesized products were analysed by several modern techniques including X-ray diffractometry, scanning and transmission electron microscopy. According to analysis results all the products mainly composed of cubic silicon carbide (b-SiC) with a small amount of unreacted precursors. Silicon carbide particles have a clear crystal structure, a triangular shape and sizes to a few hundred nanometers. Comparison of the results of experiments with different energy levels made it possible to draw conclusions on ways to control product phase composition and dispersion. The silicon carbide content and particles sizes increase with increasing the energy level.

  12. 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)

  13. 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.

  14. Amorphization resistance of nano-engineered SiC under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Imada, Kenta; Ishimaru, Manabu; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven C.; Weber, William J.

    2016-09-01

    Silicon carbide (SiC) with a high-density of planar defects (hereafter, 'nano-engineered SiC') and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. It was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due to the local increase in electronic energy loss that enhanced dynamic recovery.

  15. The Influence of SiC on the Ablation Response of Advanced Refractory Composite Materials

    NASA Technical Reports Server (NTRS)

    Bull, Jeffrey D.; Rasky, Daniel J. (Technical Monitor)

    1994-01-01

    In continuing our studies of advanced refractory composite materials we have recently completed an arc-jet test series of a diverse group of ceramics and ceramic matrix composites. The compositions range from continuous fiber reinforced ceramics to monoliths. Many of these materials contain SiC and one objective of this test series was to identify the influence of SiC oxidation mechanisms on material performance. Hence the arc heater was operated at two conditions; one in which the passive oxidation of SiC would be dominant and the other where the active oxidation of SiC would be dominant. It is shown here that the active oxidation mechanism of SiC does not dominate material performance when it is present at levels equal to or below 20 volume percent.

  16. The first muon beam from a new highly-intense DC muon source, MuSIC

    NASA Astrophysics Data System (ADS)

    Tran, Nam Hoai; MuSIC Collaboration

    2012-09-01

    A new DC muon source, MuSIC, is now under construction at Research Center for Nuclear Physics (RCNP), Osaka University, Japan. The MuSIC adopts a new pion/muon collection system and a curved transport solenoid. These techniques are important in realization of future muon programs such as the muon to electron conversion experiments (COMET/Mu2e), neutrino factories, and muon colliders. The pion capture magnet and a part of the transport solenoid have been built and beam tests were carried out to assess the MuSIC's performance. Muon lifetime measurements and muonic X-ray measurements have been used for estimation of muon yield of the MuSIC. The result indicates that the MuSIC would be one of the most intense DC muon beams in the world.

  17. Mechanical properties of SiC long fibre reinforced copper

    NASA Astrophysics Data System (ADS)

    Brendel, A.; Paffenholz, V.; Köck, Th.; Bolt, H.

    2009-04-01

    SiC fibre reinforced copper is a potential novel heat sink material for the divertor of future fusion reactors to reinforce the zone between plasma facing material (W) and heat sink material (CuCrZr). The metal matrix composite (MMC) should be able to withstand heat loads up to 15 MW/m 2 at operating temperatures of up to 550 °C. SCS6 fibres were coated by magnetron sputtering with a titanium interlayer and the copper matrix was deposited by electroplating. The composite was consolidated by hot-isostatic pressing. The average ultimate tensile strength of composite samples with 20% fibre reinforcement is 640 MPa and for the Young's modulus 162 GPa was determined. The Young's modulus decreases with increasing temperature and reaches 113 GPa at 550 °C. Fracture area analysis after tensile tests show the failure of the SCS 6 fibres at the interface between the two outer carbon layers. Titanium as interlayer led to an improved bonding between the outer carbon coating of the SiC fibres and the copper matrix.

  18. Infrared surface phonon polariton waveguides on SiC Substrate

    NASA Astrophysics Data System (ADS)

    Yang, Yuchen; Manene, Franklin M.; Lail, Brian A.

    2015-08-01

    Surface plasmon polariton (SPP) waveguides harbor many potential applications at visible and near-infrared (NIR) wavelengths. However, dispersive properties of the metal in the waveguide yields weakly coupled and lossy plasmonic modes in the mid and long wave infrared range. This is one of the major reasons for the rise in popularity of surface phonon polariton (SPhP) waveguides in recent research and micro-fabrication pursuit. Silicon carbide (SiC) is a good candidate in SPhP waveguides since it has negative dielectric permittivity in the long-wave infrared (LWIR) spectral region, indicative that coupling to surface phonon polaritons is realizable. Introducing surface phonon polaritons for waveguiding provides good modal confinement and enhanced propagation length. A hybrid waveguide structure at long-wave infrared (LWIR) is demonstrated in which an eigenmode solver approach in Ansys HFSS was applied. The effect of a three layer configuration i.e., silicon wire on a benzocyclobutene (BCB) dielectric slab on SiC, and the effects of varying their dimensions on the modal field distribution and on the propagation length, is presented.

  19. 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.

  20. 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.

  1. 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.

  2. Low dose irradiation performance of SiC interphase SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Snead, L. L.; Osborne, M. C.; Lowden, R. A.; Strizak, J.; Shinavski, R. J.; More, K. L.; Eatherly, W. S.; Bailey, J.; Williams, A. M.

    1998-03-01

    Reduced oxygen Hi-Nicalon™ fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either `porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1×10 25 n m -2 ( E>0.1 MeV) in the temperature range of 260 to 1060°C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber.

  3. Electron affinity of cubic boron nitride terminated with vanadium oxide

    NASA Astrophysics Data System (ADS)

    Yang, Yu; Sun, Tianyin; Shammas, Joseph; Kaur, Manpuneet; Hao, Mei; Nemanich, Robert J.

    2015-10-01

    A thermally stable negative electron affinity (NEA) for a cubic boron nitride (c-BN) surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with in-situ photoelectron spectroscopy. The c-BN films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition employing BF3 and N2 as precursors. Vanadium layers of ˜0.1 and 0.5 nm thickness were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 °C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO2, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B2O3 was detected, showed a positive electron affinity of ˜1.2 eV. The B2O3 evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO2 with the B2O3 layer, a B-O-V layer structure would contribute a dipole between the O and V layers with the positive side facing vacuum. The lower enthalpy of formation for B2O3 is favorable for the formation of the B-O-V layer structure, which provides a thermally stable surface dipole and an NEA surface.

  4. Improved Method of Manufacturing SiC Devices

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.

    2005-01-01

    The phrase, "common-layered architecture for semiconductor silicon carbide" ("CLASSiC") denotes a method of batch fabrication of microelectromechanical and semiconductor devices from bulk silicon carbide. CLASSiC is the latest in a series of related methods developed in recent years in continuing efforts to standardize SiC-fabrication processes. CLASSiC encompasses both institutional and technological innovations that can be exploited separately or in combination to make the manufacture of SiC devices more economical. Examples of such devices are piezoresistive pressure sensors, strain gauges, vibration sensors, and turbulence-intensity sensors for use in harsh environments (e.g., high-temperature, high-pressure, corrosive atmospheres). The institutional innovation is to manufacture devices for different customers (individuals, companies, and/or other entities) simultaneously in the same batch. This innovation is based on utilization of the capability for fabrication, on the same substrate, of multiple SiC devices having different functionalities (see figure). Multiple customers can purchase shares of the area on the same substrate, each customer s share being apportioned according to the customer s production-volume requirement. This makes it possible for multiple customers to share costs in a common foundry, so that the capital equipment cost per customer in the inherently low-volume SiC-product market can be reduced significantly. One of the technological innovations is a five-mask process that is based on an established set of process design rules. The rules provide for standardization of the fabrication process, yet are flexible enough to enable multiple customers to lay out masks for their portions of the SiC substrate to provide for simultaneous batch fabrication of their various devices. In a related prior method, denoted multi-user fabrication in silicon carbide (MUSiC), the fabrication process is based largely on surface micromachining of poly SiC

  5. Cubic silicon carbide and boron nitride as possible primary pressure calibrants for high pressure and temperature scale

    NASA Astrophysics Data System (ADS)

    Zhuravlev, K. K.; Goncharov, A. F.; Tkachev, S. N.; Prakapenka, V.

    2010-12-01

    K. K. Zhuravlev, A. F. Goncharov Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington DC, 20015 V. Prakapenka, S. N. Tkachev CARS, the University of Chicago, Bldg. 434A, Argonne National Laboratory, 9700 S. Cass. Ave., Argonne, IL 60439 Abstract Since its introduction, ruby-based pressure scale (Mao et al., 1986) has been the most commonly used by the high-pressure scientific community. However, it has limited use at elevated temperatures, due to the weakening and broadening of the ruby fluorescence line. The recent developments in the field of high temperature, high pressure physics and geophysics require some alternative pressure scale, which will be capable of measuring pressures at temperatures up to 3000 K. Cubic boron nitride (cBN) was recently (Goncharov et al., 2005) proposed as the possible pressure calibrant. It has been suggested that the simultaneous use of x-ray diffraction to measure density and Brillouin spectroscopy to obtain elastic properties of the crystal can be used to construct the pressure scale independent of any other pressure standards, i.e. cBN can be a primary pressure calibrant. However, the acoustic velocities of cBN are very close to those of diamond and, therefore, are hard to resolve in experiment at high pressures in diamond-anvil cell. Another possible primary pressure calibrant is cubic silicon carbide (SiC-3C). Its density and elastic parameters are quite different from the diamond ones and it is stable over the broad range of temperatures and pressures (up to 1 Mbar). SiC-3C is transparent and allows the use of Brillouin spectroscopy. Additionally, SiC-3C has two strong Raman lines, which can be used for the optical in situ pressure measurements. We report our experimental data on both cBN and SiC-3C and show that they, indeed, can be used in constructing reliable and accurate high-pressure, high-temperature scale. We performed single crystal x-ray diffraction and Brillouin

  6. Electron Confinement Due to Stacking Control of Atomic Layers in SiC Polytypes: Roles of Floating States and Spontaneous Polarization

    NASA Astrophysics Data System (ADS)

    Matsushita, Yu-ichiro; Furuya, Shinnosuke; Oshiyama, Atsushi

    2014-09-01

    We report on first-principles total-energy electronic-structure calculations that clarify the stability and electronic structures of heterocrystalline superlattices consisting of SiC polytypes. The calculated local density of states unequivocally reveals substantial effects of spontaneous polarization in hexagonal polytypes. The polarization in the hexagonal region renders the band lineup slanted in real space along the stacking direction in the superlattice; furthermore, the counterpolarization in the cubic region makes it slanted in the reverse direction. We find that electrons are confined near the interface in the cubic region and that holes are under a negligible band offset. We also find that the slanted band lineup causes a downward (upward) shift of the conduction (valence) band edge and the band gap becomes narrower than that in the bulk polytype, offsetting the band gap increase due to the quantum confinement. The calculated Kohn-Sham orbitals of the conduction band bottoms distribute not at atomic sites but over interstitial channels in the 3C region, thus showing the floating nature common to sp3-bonded materials. It is found that the penetration of the floating states into the hexagonal region further modifies the band gap.

  7. Thermal stability of irradiation-induced point defects in cubic silicon carbide

    SciTech Connect

    Lefevre, Jeremie; Esnouf, Stephane; Petite, Guillaume; Costantini, Jean-Marc

    2009-10-15

    This work aims specifically at studying the evolution of point defects induced by electron irradiation in the cubic polytype of SiC (3C-SiC) at temperatures ranging from 10 to 1450 K by means of photoluminescence (PL) spectroscopy. We identified a first annealing stage between 200 and 245 K, which probably results from migration of interstitials in the carbon sublattice. Moreover, we confirmed the high thermal stability of defect-related PL signals up to about 1100 K and calculated the activation energies associated with their annihilation. Finally, we studied the effect of a high temperature treatment at 1400 K on the D{sub I} center PL intensity in a single-crystal sample irradiated by electrons below the threshold displacement energy of the silicon sublattice. This allows checking the relevance of recent defect models based upon the migration of atoms in the carbon sublattice during the irradiation process. We conclude that the D{sub I} center does not involve the silicon vacancy and could be assigned to an isolated silicon antisite Si{sub C}.

  8. Film Reviews.

    ERIC Educational Resources Information Center

    Lance, Larry M.; Atwater, Lynn

    1987-01-01

    Reviews four Human Sexuality films and videos. These are: "Personal Decisions" (Planned Parenthood Federation of America, 1985); "The Touch Film" (Sterling Production, 1986); "Rethinking Rape" (Film Distribution Center, 1985); "Not A Love Story" (National Film Board of Canada, 1981). (AEM)

  9. History of the ISS/SIC: Antoine Depage, one of the founders of the ISS/SIC.

    PubMed

    Van Hee, R

    2002-10-01

    Antoine Depage, born near Brussels in 1862, was one of the founders and first Secretary General of the Société Internationale de Chirurgie (ISS-SIC). After an excellent medical education at the Free Brussels University, he became professor at the same university at the age of 27. Surgically trained by Prof. Thiriar, he became one of the leading Belgian surgeons at the end of the nineteenth century, and he published more than 100 articles in national and international journals. In 1907 he founded a school for nurses in Brussels, to be directed by Edith Cavell. He also vigorously transformed the organization of the public hospitals in the Belgian capital. During World War I Queen Elisabeth appointed him surgeon-in-chief of the Océan-hospital in De Panne, where more than 50,000 soldiers with wounds, fractures, cerebral trauma, nitrous gas intoxication, and infectious diseases, among other problems were treated. The results he and his team obtained were excellent, and mortality was low. Many surgeons, including Alexis Carrel, as well as distinguished political leaders came to visit him in the hospital barracks. After the war he was honored by many political and scientific organizations, including the Société Internationale de Chirurgie. He served our Society not only as Secretary General from 1902 to 1912 but became President of the 4th Congress of the ISS-SIC in New York. Antoine Depage died after a long illness in 1925. PMID:12205562

  10. Strength and conductivity of unidirectional copper composites reinforced by continuous SiC fibers

    NASA Astrophysics Data System (ADS)

    Kimmig, S.; Allen, I.; You, J. H.

    2013-09-01

    beneficial outcome of the Sigma fiber may be attributed to its smaller radius leading to a larger total interface area for a given fiber content. The fractographic images after tensile rupture and fiber push-out test manifested a solid interfacial bonding via the thin TiC film. The weakest site was identified to be the internal interface between the outer carbon coating and the inner SiC layer. Numerous voids were observed in the plastically ruptured matrix after tensile fracture. The density of the voids was larger at 300 °C than RT. The distributed voids are the evidence of ductile damage affecting the plastic work of the composite.

  11. Theoretical investigation of acoustic wave devices based on different piezoelectric films deposited on silicon carbide

    NASA Astrophysics Data System (ADS)

    Fan, Li; Zhang, Shu-yi; Ge, Huan; Zhang, Hui

    2013-07-01

    Performances of acoustic wave (AW) devices based on silicon carbide (SiC) substrates are theoretically studied, in which two types of piezoelectric films of ZnO and AlN deposited on 4H-SiC and 3C-SiC substrates are adopted. The phase velocities (PV), electromechanical coupling coefficients (ECC), and temperature coefficients of frequency (TCF) for three AW modes (Rayleigh wave, A0 and S0 modes of Lamb wave) often used in AW devices are calculated based on four types of configurations of interdigital transducers (IDTs). It is found that that the ZnO piezoelectric film is proper for the AW device operating in the low-frequency range because a high ECC can be realized using a thin ZnO film. The AlN piezoelectric film is proper for the device operating in the high-frequency range in virtue of the high PV of AlN, which can increase the finger width of the IDT. Generally, in the low-frequency Lamb wave devices using ZnO piezoelectric films with small normalized thicknesses of films to wavelengths hf/λ, thin SiC substrates can increase ECCs but induce high TCFs simultaneously. In the high-frequency device with a large hf/λ, the S0 mode of Lamb wave based on the AlN piezoelectric film deposited on a thick SiC substrate exhibits high performances by simultaneously considering the PV, ECC, and TCF.

  12. Cherenkov and Scintillation Properties of Cubic Zirconium

    NASA Technical Reports Server (NTRS)

    Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.

    2008-01-01

    Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed

  13. Craniofacial reconstruction using rational cubic ball curves.

    PubMed

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R U; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  14. Craniofacial Reconstruction Using Rational Cubic Ball Curves

    PubMed Central

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R. U.; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  15. Study of the crystallographic phase change on copper (I) selenide thin films prepared through chemical bath deposition by varying the pH of the solution

    NASA Astrophysics Data System (ADS)

    Sandoval-Paz, M. G.; Rodríguez, C. A.; Porcile-Saavedra, P. F.; Trejo-Cruz, C.

    2016-07-01

    Copper (I) selenide thin films with orthorhombic and cubic structure were deposited on glass substrates by using the chemical bath deposition technique. The effects of the solution pH on the films growth and subsequently the structural, optical and electrical properties of the films were studied. Films with orthorhombic structure were obtained from baths wherein both metal complex and hydroxide coexist; while films with cubic structure were obtained from baths where the metal hydroxide there is no present. The structural modifications are accompanied by changes in bandgap energy, morphology and electrical resistivity of the films.

  16. Structural, electrical and thermoelectrical analysis of nickel sulphide thin films

    NASA Astrophysics Data System (ADS)

    Chate, P. A.; Sathe, D. J.

    2016-06-01

    A dip method is employed for the deposition of NiS2 thin film at room temperature. Nickel sulphate, succinic acid and thiourea were used as the source materials. The X-ray diffraction analysis shows that the film samples are cubic phase. The specific electrical conductivity of the film was found to be 3.16 × 10-6 (Ω cm)-1. The films show high absorption, and band gap energy value was found to be 1.37 eV. The temperature dependence of an electrical conductivity, thermoelectrical power, carrier density and carrier mobility for NiS2 thin films has been examined.

  17. Probing the electronic properties of graphene on C-face SiC down to single domains by nanoresolved photoelectron spectroscopies

    NASA Astrophysics Data System (ADS)

    Razado-Colambo, I.; Avila, J.; Chen, C.; Nys, J.-P.; Wallart, X.; Asensio, M.-C.; Vignaud, D.

    2015-07-01

    Graphene samples with thicknesses ranging from monolayer to few layer graphene grown on the C-face of SiC by Si flux-assisted molecular beam epitaxy were studied to understand their stacking structure. Particular attention was put on determining the size, thickness, spatial distribution, and orientation relative to the SiC of the graphene domains. A complete electronic characterization of the graphene films down to submicrometer grains was obtained by using synchrotron-based conventional and nanoresolved photoelectron spectroscopies. These measurements were completed with scanning probe techniques like atomic force and scanning tunneling microscopies. By probing exactly the same region of the samples using angular-resolved and core-level photoelectron spectroscopy imaging and point modes, we were able to identify two types of grains constituting the graphene films with radically different thickness, stacking and orientation. The size, distribution, and registry with the substrate for each type of grain were determined. Most interestingly, we have evidenced that multilayer graphene grains with Bernal stacking coexist with areas composed of twisted bilayer graphene grains.

  18. Formation of hexagonal and cubic ice during low-temperature growth

    PubMed Central

    Thürmer, Konrad; Nie, Shu

    2013-01-01

    From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure––that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt(111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the one-molecule-thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than ∼20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice. PMID:23818592

  19. Design of cubic-phase optical elements using subwavelength microstructures.

    PubMed

    Mirotznik, Mark S; van der Gracht, Joseph; Pustai, David; Mathews, Scott

    2008-01-21

    We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, approximately lambda=10.6 microm. Experimental results verify the cubic-phase nature of the element. PMID:18542199

  20. Compositional Heterogeneity in Orgueil SiC: Further Comparisons with Murchison

    NASA Astrophysics Data System (ADS)

    Huss, G. R.; Deloule, E.; Hutcheon, I. D.; Wasserburg, G. J.

    1993-07-01

    Interstellar SiC recovered from primitive chondrites is characterized by large enrichments in ^13C and ^14N, and by Si isotope compositions distinct from solar that define a linear array on a Si 3-isotope plot [1-3]. While most SiC >2 micrometers fit this description, the total population of presolar SiC is not homogeneous. A comparison [4] of C, N, Mg, and Si isotopic characteristic of 2-6 micrometer SiC crystals from Orgueil with Murchison SiC [2,3] found two significant differences: 1) Orgueil SiC do not exhibit the clustering on either an Si 3-isotope plot or on a plot of delta^29Si vs. delta^13C shown by large Murchison SiC, and 2) there were no Orgueil SiC with delta^15N between 0 and -350 per mil. The interpretation of these differences was tempered by the relatively small number of Orgueil SiC that had been measured. We report here new Si and C isotope data for an additional 70 Orgueil SiC grains, making a total of ~110 grains measured to date. We have extended our study to smaller grains, measuring 15 grains less than 2 micrometers. The great majonty (~90%) of Orgueil SiC have roughly similar isotopic compositions and define the main population (Fig. 1). Among the remaining SiC grains, one is extremely enriched in ^28Si (Fig. 1 inset) and extremely depleted in ^13C, like the Murchison 'X' grains [3]. Four grains have delta^13C<0 and Si compositions similar to Murchison 'Y' grains [5]. Two Orgueil SiC ('Z' grains) have delta^29Si ~-75 per mil and delta^30Si ~-34per mil and fall in a previously unoccupied region of Si isotope space. Unlike 'Y' grains, 'Z' grains have delta^13C > 0. Eight Orgueil SiC have extreme enrichments in ^13C (8000 per mil < delta^13C < 3000 per mil); six of the eight lie on the ^28Si-rich end of the Si isotope array (Fig. 1), five with delta^29Si <--4 per mil and the sixth with delta^29Si=13 per mil. The new data reveal a compositional variability among Orgueil SiC larger than ~2 micrometers at least as great as that found for